WorldWideScience

Sample records for dynamic species exchange

  1. Exchange frequency in replica exchange molecular dynamics

    Science.gov (United States)

    Sindhikara, Daniel; Meng, Yilin; Roitberg, Adrian E.

    2008-01-01

    The effect of the exchange-attempt frequency on sampling efficiency is studied in replica exchange molecular dynamics (REMD). We show that sampling efficiency increases with increasing exchange-attempt frequency. This conclusion is contrary to a commonly expressed view in REMD. Five peptides (1-21 residues long) are studied with a spectrum of exchange-attempt rates. Convergence rates are gauged by comparing ensemble properties between fixed length test REMD simulations and longer reference simulations. To show the fundamental correlation between exchange frequency and convergence time, a simple model is designed and studied, displaying the same basic behavior of much more complex systems.

  2. Contrasting nuclear and cytoplasmic exchanges between phylogenetically distant oak species (Quercus suber L. and Q. ilex L.) in Southern France: inferring crosses and dynamics.

    Science.gov (United States)

    Mir, C; Jarne, P; Sarda, V; Bonin, A; Lumaret, R

    2009-03-01

    Gene flow is particularly frequent in the genus Quercus (oaks), especially between closely related species. We focus here on Quercus ilex and the cork-producing Quercus suber, which occasionally hybridize although they are phylogenetically markedly separated. Morphological observations were combined with both allozymic and chloroplastic diagnostic markers to characterize hybridization and introgression and to infer their dynamics in two French regions (French Catalonia and Provence), which are separated by several hundred kilometres. Some hybrids were found in both regions, indicating recent hybridization events. As expected from previous studies, most hybrids resulted from female symbol Q. ilex x male symbol Q. suber crosses, but our data showed that the reciprocal cross is also possible. Partial independence between nuclear and chloroplastic introgression was observed in the two species. Nuclear introgression was limited in both species and both regions, with no preferred direction. In Provence, chloroplastic introgression was very rare in both species. Conversely, all Q. suber individuals from French Catalonia were introgressed by Q. ilex chlorotypes. This might be explained by introgression in the Iberian Peninsula antedating the first occurrence of the two species in French Catalonia. We also observed a new chlorotype that was created locally, and was exchanged between the two species. However, the two species still remain genetically differentiated. The dynamics and complexity of exchanges and the factors determining them (including human management of Q. suber) are discussed.

  3. Nonadiabatic exchange dynamics during adiabatic frequency sweeps.

    Science.gov (United States)

    Barbara, Thomas M

    2016-04-01

    A Bloch equation analysis that includes relaxation and exchange effects during an adiabatic frequency swept pulse is presented. For a large class of sweeps, relaxation can be incorporated using simple first order perturbation theory. For anisochronous exchange, new expressions are derived for exchange augmented rotating frame relaxation. For isochronous exchange between sites with distinct relaxation rate constants outside the extreme narrowing limit, simple criteria for adiabatic exchange are derived and demonstrate that frequency sweeps commonly in use may not be adiabatic with regard to exchange unless the exchange rates are much larger than the relaxation rates. Otherwise, accurate assessment of the sensitivity to exchange dynamics will require numerical integration of the rate equations. Examples of this situation are given for experimentally relevant parameters believed to hold for in-vivo tissue. These results are of significance in the study of exchange induced contrast in magnetic resonance imaging.

  4. Dynamics of Non-Classical Interval Exchanges

    CERN Document Server

    Gadre, Vaibhav S

    2009-01-01

    Train tracks with a single vertex are a generalization of interval exchange maps. Here, we consider non-classical interval exchanges: complete train tracks with a single vertex. These can be studied as a dynamical system by considering Rauzy induction in this context. This gives a refinement process on the parameter space similar to Kerckhoff's simplicial systems. We show that the refinement process gives an expansion that has a key dynamical property called uniform distortion. We use uniform distortion to prove normality of the expansion. Consequently we prove an analog of Keane's conjecture: almost every non-classical interval exchange is uniquely ergodic.

  5. Molecular Exchange Dynamics in Block Copolymer Micelles

    Science.gov (United States)

    Bates, Frank; Lu, Jie; Choi, Soohyung; Lodge, Timothy

    2012-02-01

    Poly(styrene-b-ethylene propylene) (PS-PEP) diblock copolymers were mixed with squalane (C30H62) at 1% by weight resulting in the formation of spherical micelles. The structure and dynamics of molecular exchange were characterized by synchrotron small-angle x-ray scattering (SAXS) and time resolved small-angle neutron scattering (TR-SANS), respectively, between 100 C and 160 C. TR-SANS measurements were performed with solutions initially containing deuterium labeled micelle cores and normal cores dispersed in a contrast matched squalane. Monitoring the reduction in scattering intensity as a function of time at various temperatures revealed molecular exchange dynamics highly sensitive to the core molecular weight and molecular weight distribution. Time-temperature superposition of data acquired at different temperatures produced a single master curve for all the mixtures. Experiments conducted with isotopically labeled micelle cores, each formed from two different but relatively mondisperse PS blocks, confirmed a simple dynamical model based on first order kinetics and core Rouse single chain relaxation. These findings demonstrate a dramatic transition to nonergodicity with increasing micelle core molecular weight and confirm the origins of the logarithmic exchange kinetics in such systems.

  6. Wealth distribution of simple exchange models coupled with extremal dynamics

    Science.gov (United States)

    Bagatella-Flores, N.; Rodríguez-Achach, M.; Coronel-Brizio, H. F.; Hernández-Montoya, A. R.

    2015-01-01

    Punctuated Equilibrium (PE) states that after long periods of evolutionary quiescence, species evolution can take place in short time intervals, where sudden differentiation makes new species emerge and some species extinct. In this paper, we introduce and study the effect of punctuated equilibrium on two different asset exchange models: the yard sale model (YS, winner gets a random fraction of a poorer player's wealth) and the theft and fraud model (TF, winner gets a random fraction of the loser's wealth). The resulting wealth distribution is characterized using the Gini index. In order to do this, we consider PE as a perturbation with probability ρ of being applied. We compare the resulting values of the Gini index at different increasing values of ρ in both models. We found that in the case of the TF model, the Gini index reduces as the perturbation ρ increases, not showing dependence with the agents number. While for YS we observe a phase transition which happens around ρc = 0.79. For perturbations ρ increases (an extreme wealth condensation state), whereas for perturbations greater than or equal to ρc the Gini index becomes different to one, avoiding the system reaches this extreme state. We show that both simple exchange models coupled with PE dynamics give more realistic results. In particular for YS, we observe a power low decay of wealth distribution.

  7. Species radiation by DNA replication that systematically exchanges nucleotides?

    Science.gov (United States)

    Seligmann, Hervé

    2014-12-21

    RNA and DNA syntheses share many properties. Therefore, the existence of 'swinger' RNAs, presumed 'orphan' transcripts matching genomic sequences only if transcription systematically exchanged nucleotides, suggests replication producing swinger DNA. Transcripts occur in many short-lived copies, the few cellular DNA molecules are long-lived. Hence pressures for functional swinger DNAs are greater than for swinger RNAs. Protein coding properties of swinger sequences differ from original sequences, suggesting rarity of corresponding swinger DNA. For genes producing structural RNAs, such as tRNAs and rRNAs, three exchanges (AT, CG and AT+CG) conserve self-hybridization properties. All nuclear eukaryote swinger DNA sequences detected in GenBank are for rRNA genes assuming AT+CG exchanges. In brachyuran crabs, 25 species had AT+CG swinger 18S rDNA, all matching the reverse-exchanged version of regular 18S rDNA of a related species. In this taxon, swinger replication of 18S rDNA apparently associated with, or even resulted in species radiation. AT+CG transformation doesn't invert sequence direction, differing from inverted repeats. Swinger repeats (detectable only assuming swinger transformations, AT+CG swinger repeats most frequent) within regular human rRNAs, independently confirm swinger polymerizations for most swinger types. Swinger replication might be an unsuspected molecular mechanism for ultrafast speciation.

  8. Extensions to the Dynamic Aerospace Vehicle Exchange Markup Language

    Science.gov (United States)

    Brian, Geoffrey J.; Jackson, E. Bruce

    2011-01-01

    The Dynamic Aerospace Vehicle Exchange Markup Language (DAVE-ML) is a syntactical language for exchanging flight vehicle dynamic model data. It provides a framework for encoding entire flight vehicle dynamic model data packages for exchange and/or long-term archiving. Version 2.0.1 of DAVE-ML provides much of the functionality envisioned for exchanging aerospace vehicle data; however, it is limited in only supporting scalar time-independent data. Additional functionality is required to support vector and matrix data, abstracting sub-system models, detailing dynamics system models (both discrete and continuous), and defining a dynamic data format (such as time sequenced data) for validation of dynamics system models and vehicle simulation packages. Extensions to DAVE-ML have been proposed to manage data as vectors and n-dimensional matrices, and record dynamic data in a compatible form. These capabilities will improve the clarity of data being exchanged, simplify the naming of parameters, and permit static and dynamic data to be stored using a common syntax within a single file; thereby enhancing the framework provided by DAVE-ML for exchanging entire flight vehicle dynamic simulation models.

  9. Exchange rate movements and export market dynamics: evidence from China

    National Research Council Canada - National Science Library

    Xiaobing Huang

    2017-01-01

    This paper highlights the relationship between foreign exchange rate fluctuations and firms' export market dynamics using a Chinese firm-level production data and a firm-level trade data over the period of 2000-2006...

  10. Dynamics of Surface Exchange Reactions Between Au and Pt for HER and HOR

    DEFF Research Database (Denmark)

    Abrams, Billie; Vesborg, Peter Christian Kjærgaard; Bonde, Jacob Lindner;

    2009-01-01

    Cyclic voltammetric analysis of the Pt-on-Au system for hydrogen evolution and oxidation reactions (HER/HOR) indicates that dynamic surface exchange reactions occur between Pt and Au. HER/HOR activities depend on the dominant surface species present, which is controllable by the potential applied...

  11. Dynamic enhancement of the exchange bias training effect

    Science.gov (United States)

    Sahoo, S.; Polisetty, S.; Binek, Ch.; Berger, A.

    2007-03-01

    Exchange bias in coupled magnetic thin films and its accompanying training effect are fundamental interface phenomena with significant impact in spintronic applications. Both effects are well known in heterosystems of ferro- and antiferromagnetic thin films. Here, we report on the dynamic enhancement of the training effect in an exchange coupled bilayer of soft and hard ferromagnetic materials. Training is referred to as a gradual change of the bias field, which evolves upon cycling the soft layer through consecutive hysteresis loops. Its dynamic enhancement is observed with increasing sweep rate of the applied magnetic field from quasistatic to the fully dynamic range. A dynamically generalized theory based on triggered relaxation is in excellent agreement with the training data. Additionally, we evidence the remarkable universality of our theoretical approach when applying it to the dynamically altered training effect of a conventional exchange bias system involving an antiferromagnetic pinning layer.

  12. Complex dynamical behaviors of daily data series in stock exchange

    Science.gov (United States)

    Wang, Hongchun; Chen, Guanrong; Lü, Jinhu

    2004-12-01

    It is well known that many economic data series show chaotic behaviors. In this Letter, we further investigate the complex dynamical behaviors of the daily data series, including opening quotation, closing quotation, maximum price, minimum price, and total exchange quantum, in Shenzhen stock exchange and Shanghai stock exchange, which are two representative stock exchanges in mainland China. The maximum Lyapunov exponents, correlation dimensions, and frequency spectra are calculated for these time series. Our results indicate that some daily data series of stock exchanges display low-dimensional chaotic behaviors, and some other daily data series do not show any chaotic behavior. Moreover, we introduce a weighted one-rank local-region approach for predicting short-term daily data series of stock exchange.

  13. Information Exchange, Market Transparency and Dynamic Oligopoly

    DEFF Research Database (Denmark)

    Møllgaard, H. Peter; Overgaard, Per Baltzer

    Economic literature often offers conflicting views on the likely efficiency effects of information exchanges, communication between firms, and market transparency. On the one hand, it is argued that increased information dissemination improves firm planning to the benefit of society (including bu...

  14. Dynamic tube/support interaction in heat exchanger tubes

    Energy Technology Data Exchange (ETDEWEB)

    Chen, S.S.

    1991-01-01

    The supports for heat exchanger tubes are usually plates with drilled holes; other types of supports also have been used. To facilitate manufacture and to allow for thermal expansion of the tubes, small clearances are used between tubes and tube supports. The dynamics of tube/support interaction in heat exchangers is fairly complicated. Understanding tube dynamics and its effects is important for heat exchangers. This paper summarizes the current state of the art on this subject and to identify future research needs. Specifically, the following topics are discussed: dynamics of loosely supported tubes, tube/support gap dynamics, tube response in flow, tube damage and wear, design considerations, and future research needs. 55 refs., 1 fig.

  15. Information Exchange, Market Transparency and Dynamic Oligopoly

    DEFF Research Database (Denmark)

    Overgaard, Per Baltzer; Møllgaard, Peter

    2005-01-01

    In the economics literature, various views on the likely (efficiency) effects of information exchange,communication between firms and market transparency present themselves. Often these views oninformation flows are highly conflicting. On the one hand, it is argued that increased informationdisse......In the economics literature, various views on the likely (efficiency) effects of information exchange,communication between firms and market transparency present themselves. Often these views oninformation flows are highly conflicting. On the one hand, it is argued that increased...... potential to the benefit of firms but at the expense of society at large (mainly, potentialcustomers). In this chapter, we try to make sense of these views, with the aim of presenting somesimple lessons for antitrust practice. In addition, the chapter presents some cases, from both sides ofthe Atlantic...

  16. Unified nonequilibrium dynamical theory for exchange bias and training effects

    Institute of Scientific and Technical Information of China (English)

    Zhang Kai-Cheng; Liu Bang-Gui

    2009-01-01

    We have investigated the exchange bias and training effect in the ferromagnetie/antiferromagnetic (FM/AF)heterostructures using a unified Monte Carlo dynamical approach. The magnetization of the uncompensated AF layer is still open after the first field cycling is finished. Our simulated results show obvious shift of hysteresis loops (exchange bias) and cycling dependence of exchange bias (training effect) when the temperature is below 45 K. The exchange bias field decreases with decreasing cooling rate or increasing temperature and the number of the field cycling. Essentially,these two effects can be explained on the basis of the microscopical coexistence of both reversible and irreversible moment reversals of the AF domains. Our simulations are useful to understand the real magnetization dynamics of such magnetic heterostructures.

  17. Information Exchange, Market Transparency and Dynamic Oligopoly

    DEFF Research Database (Denmark)

    Overgaard, Per Baltzer; Møllgaard, Peter

    2005-01-01

    In the economics literature, various views on the likely (efficiency) effects of information exchange,communication between firms and market transparency present themselves. Often these views oninformation flows are highly conflicting. On the one hand, it is argued that increased...... informationdissemination improves firm planning to the benefit of society (including customers) and/or allowspotential customers to make the right decisions given their preferences. On the other hand, theliterature also suggests that increased information dissemination can have significant coordinating orcollusive......, where informational issues have played a significant role....

  18. Information Exchange, Market Transparency and Dynamic Oligopoly

    DEFF Research Database (Denmark)

    Møllgaard, H. Peter; Overgaard, Per Baltzer

    Economic literature often offers conflicting views on the likely efficiency effects of information exchanges, communication between firms, and market transparency. On the one hand, it is argued that increased information dissemination improves firm planning to the benefit of society (including...... buyers) and allows potential buyers to make correct decisions given their preferences. On the other hand, economic literature also shows that increased information dissemination can raise prices through tacit or explicit collusion to the benefit of firms but at the expense of society at large...

  19. Phase transitions and relaxation dynamics of Ising models exchanging particles

    Science.gov (United States)

    Goh, Segun; Fortin, Jean-Yves; Choi, M. Y.

    2017-01-01

    A variety of systems in nature and in society are open and subject to exchanging their constituents with other systems (e.g., environments). For instance, in biological systems, cells collect necessary energy and material by exchange of molecules or ions. Similarly, countries, cities or research institutes evolve as their constituents move in or out. To probe the corresponding particle exchange dynamics in such systems, we consider two Ising models exchanging particles and establish a master equation describing the equilibrium phases as well as the non-equilibrium dynamics of the system. It is found that an additional stable phase emerges as a consequence of the particle exchange process. Furthermore, we formulate the Ginzburg-Landau theory which allows to probe correlation effects. Accordingly, critical slowing down is manifested and the associated dynamic exponent is computed in the linear relaxation regime. In particular, this approach is relevant for investigating the grand canonical description of the system plus environment, with particle exchange and state transitions taken into account explicitly.

  20. Ultrafast 2D-IR and simulation investigations of preferential solvation and cosolvent exchange dynamics.

    Science.gov (United States)

    Dunbar, Josef A; Arthur, Evan J; White, Aaron M; Kubarych, Kevin J

    2015-05-21

    Using a derivative of the vitamin biotin labeled with a transition-metal carbonyl vibrational probe in a series of aqueous N,N-dimethylformamide (DMF) solutions, we observe a striking slowdown in spectral diffusion dynamics with decreased DMF concentration. Equilibrium solvation dynamics, measured with the rapidly acquired spectral diffusion (RASD) technique, a variant of heterodyne-detected photon-echo peak shift experiments, range from 1 ps in neat DMF to ∼3 ps in 0.07 mole fraction DMF/water solution. Molecular dynamics simulations of the biotin-metal carbonyl solute in explicit aqueous DMF solutions show marked preferential solvation by DMF, which becomes more pronounced at lower DMF concentrations. The simulations and the experimental data are consistent with an interpretation where the slowdown in spectral diffusion is due to solvent exchange involving distinct cosolvent species. A simple two-component model reproduces the observed spectral dynamics as well as the DMF concentration dependence, enabling the extraction of the solvent exchange time scale of 8 ps. This time scale corresponds to the diffusive motion of a few Å, consistent with a solvent-exchange mechanism. Unlike most previous studies of solvation dynamics in binary mixtures of polar solvents, our work highlights the ability of vibrational probes to sense solvent exchange as a new, slow component in the spectral diffusion dynamics.

  1. Glucans monomer-exchange dynamics as an open chemical network

    Energy Technology Data Exchange (ETDEWEB)

    Rao, Riccardo, E-mail: riccardo.rao@uni.lu; Esposito, Massimiliano, E-mail: massimiliano.esposito@uni.lu [Complex Systems and Statistical Mechanics, Physics and Materials Science Research Unit, University of Luxembourg, L-1511 Luxembourg (Luxembourg); Lacoste, David [Laboratoire de Physico-Chimie Théorique, UMR CNRS Gulliver 7083, ESPCI - 10 rue Vauquelin, F-75231 Paris (France)

    2015-12-28

    We describe the oligosaccharides-exchange dynamics performed by the so-called D-enzymes on polysaccharides. To mimic physiological conditions, we treat this process as an open chemical network by assuming some of the polymer concentrations fixed (chemostatting). We show that three different long-time behaviors may ensue: equilibrium states, nonequilibrium steady states, and continuous growth states. We dynamically and thermodynamically characterize these states and emphasize the crucial role of conservation laws in identifying the chemostatting conditions inducing them.

  2. Glucans monomer-exchange dynamics as an open chemical network

    CERN Document Server

    Rao, Riccardo; Esposito, Massimiliano

    2015-01-01

    We describe the oligosaccharides-exchange dynamics performed by so-called D-enzymes on polysaccharides. To mimic physiological conditions, we treat this process as an open chemical network by assuming some of the polymer concentrations fixed (chemostatting). We show that three different long-time behaviors may ensue: equilibrium states, nonequilibrium steady states, and continuous growth states. We dynamically and thermodynamically characterize these states and emphasize the crucial role of conservation laws in identifying the chemostatting conditions inducing them.

  3. Ab initio dynamical exchange interactions in frustrated antiferromagnets

    Science.gov (United States)

    Simoni, Jacopo; Stamenova, Maria; Sanvito, Stefano

    2017-08-01

    The ultrafast response to an optical pulse excitation of the spin-spin exchange interaction in transition metal antiferromagnets is studied within the framework of the time-dependent spin-density functional theory. We propose a formulation for the full dynamical exchange interaction, which is nonlocal in space, and it is derived starting from ab initio arguments. Then, we investigate the effect of the laser pulse on the onset of the dynamical process. It is found that we can distinguish two types of excitations, both activated immediately after the action of the laser pulse. While the first one can be associated to a Stoner-like excitation and involves the transfer of spin from one site to another, the second one is related to the ultrafast modification of a Heisenberg-like exchange interaction and can trigger the formation of spin waves in the first few hundred femtoseconds of the time evolution.

  4. Dithioacetal Exchange: A New Reversible Reaction for Dynamic Combinatorial Chemistry.

    Science.gov (United States)

    Orrillo, A Gastón; Escalante, Andrea M; Furlan, Ricardo L E

    2016-05-10

    Reversibility of dithioacetal bond formation is reported under acidic mild conditions. Its utility for dynamic combinatorial chemistry was explored by combining it with orthogonal disulfide exchange. In such a setup, thiols are positioned at the intersection of both chemistries, constituting a connecting node between temporally separated networks.

  5. Combined Steady-State and Dynamic Heat Exchanger Experiment

    Science.gov (United States)

    Luyben, William L.; Tuzla, Kemal; Bader, Paul N.

    2009-01-01

    This paper describes a heat-transfer experiment that combines steady-state analysis and dynamic control. A process-water stream is circulated through two tube-in-shell heat exchangers in series. In the first, the process water is heated by steam. In the second, it is cooled by cooling water. The equipment is pilot-plant size: heat-transfer areas…

  6. Diffusive and Arrestedlike Dynamics in Currency Exchange Markets

    Science.gov (United States)

    Clara-Rahola, J.; Puertas, A. M.; Sánchez-Granero, M. A.; Trinidad-Segovia, J. E.; de las Nieves, F. J.

    2017-02-01

    This work studies the symmetry between colloidal dynamics and the dynamics of the Euro-U.S. dollar currency exchange market (EURUSD). We consider the EURUSD price in the time range between 2001 and 2015, where we find significant qualitative symmetry between fluctuation distributions from this market and the ones belonging to colloidal particles in supercooled or arrested states. In particular, we find that models used for arrested physical systems are suitable for describing the EURUSD fluctuation distributions. Whereas the corresponding mean-squared price displacement (MSPD) to the EURUSD is diffusive for all years, when focusing in selected time frames within a day, we find a two-step MSPD when the New York Stock Exchange market closes, comparable to the dynamics in supercooled systems. This is corroborated by looking at the price correlation functions and non-Gaussian parameters and can be described by the theoretical model. We discuss the origin and implications of this analogy.

  7. Dynamic/Thermochemical Balance Drives Unusual Alkyl/F Exchange Reactions in Siloxides and Analogs.

    Science.gov (United States)

    Correra, Thiago C; Fernandes, André S; Riveros, José M

    2016-03-17

    A recent report has shown that siloxides can undergo an unusual Me/F exchange reaction promoted by NF3 in the gas phase ( Angew. Chem. Int. Ed. 2012, 51, 8632-8635). A more extensive study of this kind of exchange has been carried out using mass spectrometry techniques (FT-ICR), DFT calculations, natural bond orbital (NBO) analysis, and Born-Oppenheimer molecular dynamics simulations (BOMD), using NF3, SO2F2, and CF4 as fluorine donors and evaluating the effect of replacing the Si center by Ge and C. This comprehensive approach shows that NF3 is crucial for the exchange reaction, as SO2F2 forms SO3F(-) via a pentacoordinated channel whereas no reaction is observed for CF4. The uniqueness of NF3 is caused by favorable thermochemical consideration and by dynamic effects that preclude the formation of the ubiquitous Si-F pentacoordinated species. Me3GeO(-) was shown to be as reactive as siloxides toward NF3, whereas C analogs showed no reactions under our experimental conditions. The exchange reaction was also shown to take place for triethylsiloxides. These exchange reactions are examples of reaction systems that avoid the lower energy pathway and are driven by dynamic effects that cannot be explained by the potential energy surface.

  8. Computer simulation of methanol exchange dynamics around cations and anions

    Energy Technology Data Exchange (ETDEWEB)

    Roy, Santanu; Dang, Liem X.

    2016-03-03

    In this paper, we present the first computer simulation of methanol exchange dynamics between the first and second solvation shells around different cations and anions. After water, methanol is the most frequently used solvent for ions. Methanol has different structural and dynamical properties than water, so its ion solvation process is different. To this end, we performed molecular dynamics simulations using polarizable potential models to describe methanol-methanol and ion-methanol interactions. In particular, we computed methanol exchange rates by employing the transition state theory, the Impey-Madden-McDonald method, the reactive flux approach, and the Grote-Hynes theory. We observed that methanol exchange occurs at a nanosecond time scale for Na+ and at a picosecond time scale for other ions. We also observed a trend in which, for like charges, the exchange rate is slower for smaller ions because they are more strongly bound to methanol. This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. The calculations were carried out using computer resources provided by the Office of Basic Energy Sciences.

  9. Laser spectroscopy and dynamics of transient species

    Energy Technology Data Exchange (ETDEWEB)

    Clouthier, D.J. [Univ. of Kentucky, Lexington (United States)

    1993-12-01

    The goal of this program is to study the vibrational and electronic spectra and excited state dynamics of a number of transient sulfur and oxygen species. A variety of supersonic jet techniques, as well as high resolution FT-IR and intracavity dye laser spectroscopy, have been applied to these studies.

  10. Why the long hours? Job demands and social exchange dynamics.

    Science.gov (United States)

    Genin, Emilie; Haines, Victor Y; Pelletier, David; Rousseau, Vincent; Marchand, Alain

    2016-11-22

    This study investigates the determinants of long working hours from the perspectives of the demand-control model [Karasek, 1979] and social exchange theory [Blau, 1964; Goulder, 1960]. These two theoretical perspectives are tested to understand why individuals work longer (or shorter) hours. The hypotheses are tested with a representative sample of 1,604 employed Canadians. In line with Karasek's model, the results support that high job demands are positively associated with longer work hours. The social exchange perspective would predict a positive association between skill discretion and work hours. This hypothesis was supported for individuals with a higher education degree. Finally, the results support a positive association between active jobs and longer work hours. Our research suggests that job demands and social exchange dynamics need to be considered together in the explanation of longer (or shorter) work hours.

  11. Short-run Exchange-Rate Dynamics: Theory and Evidence

    DEFF Research Database (Denmark)

    Carlson, John A.; Dahl, Christian Møller; Osler, Carol L.

    of currency markets, it accurately reflects the constraints and objectives faced by the major participants, and it fits key stylized facts concerning returns and order flow. With respect to macroeconomics, the model is consistent with most of the major puzzles that have emerged under floating rates.......Recent research has revealed a wealth of information about the microeconomics of currency markets and thus the determination of exchange rates at short horizons. This information is valuable to us as scientists since, like evidence of macroeconomic regularities, it can provide critical guidance...... for designing exchange-rate models. This paper presents an optimizing model of short-run exchange-rate dynamics consistent with both the micro evidence and the macro evidence, the first such model of which we are aware. With respect to microeconomics, the model is consistent with the institutional structure...

  12. Dynamics of genome change among Legionella species

    Science.gov (United States)

    Joseph, Sandeep J.; Cox, Daniel; Wolff, Bernard; Morrison, Shatavia S.; Kozak-Muiznieks, Natalia A.; Frace, Michael; Didelot, Xavier; Castillo-Ramirez, Santiago; Winchell, Jonas; Read, Timothy D.; Dean, Deborah

    2016-01-01

    Legionella species inhabit freshwater and soil ecosystems where they parasitize protozoa. L. pneumonphila (LP) serogroup-1 (Lp1) is the major cause of Legionnaires’ Disease (LD), a life-threatening pulmonary infection that can spread systemically. The increased global frequency of LD caused by Lp and non-Lp species underscores the need to expand our knowledge of evolutionary forces underlying disease pathogenesis. Whole genome analyses of 43 strains, including all known Lp serogroups 1–17 and 17 emergent LD-causing Legionella species (of which 33 were sequenced in this study) in addition to 10 publicly available genomes, resolved the strains into four phylogenetic clades along host virulence demarcations. Clade-specific genes were distinct for genetic exchange and signal-transduction, indicating adaptation to specific cellular and/or environmental niches. CRISPR spacer comparisons hinted at larger pools of accessory DNA sequences in Lp than predicted by the pan-genome analyses. While recombination within Lp was frequent and has been reported previously, population structure analysis identified surprisingly few DNA admixture events between species. In summary, diverse Legionella LD–causing species share a conserved core-genome, are genetically isolated from each other, and selectively acquire genes with potential for enhanced virulence. PMID:27633769

  13. A Unified Approach to Dynamic Matching and Barter Exchange

    Science.gov (United States)

    2016-09-01

    knowledge is incomplete: even if a patient and donor are compatible based on the virtual crossmatch (so there is an edge in the input graph), in reality ...and dynamic barter exchange that more accurately reflect reality , prove theoretical statements about the characteristics and behavior of these...interdisciplinary research opportunities. Finally, while an undergraduate, working with Meesh helped me recognize the joy of teaching , and that not all students

  14. Floating Exchange Rate Regime and Changing Dynamics of the Foreign Exchange Market in Turkey

    Directory of Open Access Journals (Sweden)

    Senkan Aldemir

    2011-07-01

    Full Text Available The aim of this study was to determine the changes caused by the implementations of currency basket peg and floating exchange regime on domestic foreign exchange market dynamics through the estimation of weights for the reserve currencies in the currency basket. Elasticity coefficients of Turkish Lira against seven currencies were estimated for two sampling periods (1995:01-1999:07 and 2002:01-2008:01 using generalized vector autoregression method. The study focuses on Turkish economy. The scope of the study represents a quite new field of investigation which is analyzed only to a limited extent in the literature. The main contribution of the study was that the study extended the empirical model which was taken as a basis in the majority of the studies on currency basket and the analyses which estimated using vector autoregression method whose sampling was limited to Asia countries, using generalized impulse response normalization approach. The findings obtained from the first period support the weights of currencies in announced basket of currencies. It was observed that Pound Sterling had a significant weight in domestic foreign exchange market dynamics in the second period.

  15. Challenges in quantifying biosphere-atmosphere exchange of nitrogen species

    DEFF Research Database (Denmark)

    Sutton, M.A.; Nemitz, E.; Erisman, J.W.

    2007-01-01

    Recent research in nitrogen exchange with the atmosphere has separated research communities according to N form. The integrated perspective needed to quantify the net effect of N on greenhouse-gas balance is being addressed by the NitroEurope Integrated Project (NEU). Recent advances have depended...... progress has been made in modelling N fluxes, especially for N2O, NO and bi-directional NH3 exchange. Landscape analysis represents an emerging challenge to address the spatial interactions between farms, fields, ecosystems, catchments and air dispersion/deposition. European up-scaling of N fluxes...

  16. Agent dynamics in kinetic models of wealth exchange

    CERN Document Server

    Chatterjee, Arnab

    2010-01-01

    We study the dynamics of individual agents in some kinetic models of wealth exchange, particularly, the models with savings. For the model with uniform savings, agents perform simple random walks in the `"wealth space". On the other hand, we observe ballistic diffusion in the model with distributed savings. There is an associated skewness in the gain-loss distribution which explains the steady state behavior in such models. We find that in general an agent gains while interacting with an agent with a larger saving propensity.

  17. Dynamic pupillary exchange engages brain regions encoding social salience.

    Science.gov (United States)

    Harrison, Neil A; Gray, Marcus A; Critchley, Hugo D

    2009-01-01

    Covert exchange of autonomic responses may shape social affective behavior, as observed in mirroring of pupillary responses during sadness processing. We examined how, independent of facial emotional expression, dynamic coherence between one's own and another's pupil size modulates regional brain activity. Fourteen subjects viewed pairs of eye stimuli while undergoing fMRI. Using continuous pupillometry biofeedback, the size of the observed pupils was varied, correlating positively or negatively with changes in participants' own pupils. Viewing both static and dynamic stimuli activated right fusiform gyrus. Observing dynamically changing pupils activated STS and amygdala, regions engaged by non-static and salient facial features. Discordance between observed and observer's pupillary changes enhanced activity within bilateral anterior insula, left amygdala and anterior cingulate. In contrast, processing positively correlated pupils enhanced activity within left frontal operculum. Our findings suggest pupillary signals are monitored continuously during social interactions and that incongruent changes activate brain regions involved in tracking motivational salience and attentionally meaningful information. Naturalistically, dynamic coherence in pupillary change follows fluctuations in ambient light. Correspondingly, in social contexts discordant pupil response is likely to reflect divergence of dispositional state. Our data provide empirical evidence for an autonomically mediated extension of forward models of motor control into social interaction.

  18. Challenges in quantifying biosphere-atmosphere exchange of nitrogen species.

    Science.gov (United States)

    Sutton, M A; Nemitz, E; Erisman, J W; Beier, C; Bahl, K Butterbach; Cellier, P; de Vries, W; Cotrufo, F; Skiba, U; Di Marco, C; Jones, S; Laville, P; Soussana, J F; Loubet, B; Twigg, M; Famulari, D; Whitehead, J; Gallagher, M W; Neftel, A; Flechard, C R; Herrmann, B; Calanca, P L; Schjoerring, J K; Daemmgen, U; Horvath, L; Tang, Y S; Emmett, B A; Tietema, A; Peñuelas, J; Kesik, M; Brueggemann, N; Pilegaard, K; Vesala, T; Campbell, C L; Olesen, J E; Dragosits, U; Theobald, M R; Levy, P; Mobbs, D C; Milne, R; Viovy, N; Vuichard, N; Smith, J U; Smith, P; Bergamaschi, P; Fowler, D; Reis, S

    2007-11-01

    Recent research in nitrogen exchange with the atmosphere has separated research communities according to N form. The integrated perspective needed to quantify the net effect of N on greenhouse-gas balance is being addressed by the NitroEurope Integrated Project (NEU). Recent advances have depended on improved methodologies, while ongoing challenges include gas-aerosol interactions, organic nitrogen and N(2) fluxes. The NEU strategy applies a 3-tier Flux Network together with a Manipulation Network of global-change experiments, linked by common protocols to facilitate model application. Substantial progress has been made in modelling N fluxes, especially for N(2)O, NO and bi-directional NH(3) exchange. Landscape analysis represents an emerging challenge to address the spatial interactions between farms, fields, ecosystems, catchments and air dispersion/deposition. European up-scaling of N fluxes is highly uncertain and a key priority is for better data on agricultural practices. Finally, attention is needed to develop N flux verification procedures to assess compliance with international protocols.

  19. Challenges in quantifying biosphere-atmosphere exchange of nitrogen species

    Energy Technology Data Exchange (ETDEWEB)

    Sutton, M.A. [Centre for Ecology and Hydrology (CEH), Edinburgh Research Station, Bush Estate, Penicuik, EH26 0QB (United Kingdom)], E-mail: ms@ceh.ac.uk; Nemitz, E. [Centre for Ecology and Hydrology (CEH), Edinburgh Research Station, Bush Estate, Penicuik, EH26 0QB (United Kingdom); Erisman, J.W. [ECN, Clean Fossil Fuels, PO Box 1, 1755 ZG Petten (Netherlands); Beier, C. [Riso National Laboratory, PO Box 49, DK-4000 Roskilde (Denmark); Bahl, K. Butterbach [Institute of Meteorology and Climate Research, Atmos. Environ. Research (IMK-IFU), Research Centre Karlsruhe GmbH, Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen (Germany); Cellier, P. [INRA Unite Mixte de Recherche, 78850 Thiverval-Grignon (France); Vries, W. de [Alterra, Green World Research, PO Box 47, 6700 AA Wageningen (Netherlands); Cotrufo, F. [Dip. Scienze Ambientali, Seconda Universita degli Studi di Napoli, via Vivaldi 43, 81100 Caserta (Italy); Skiba, U.; Di Marco, C.; Jones, S. [Centre for Ecology and Hydrology (CEH), Edinburgh Research Station, Bush Estate, Penicuik, EH26 0QB (United Kingdom); Laville, P.; Soussana, J.F.; Loubet, B. [INRA Unite Mixte de Recherche, 78850 Thiverval-Grignon (France); Twigg, M.; Famulari, D. [Centre for Ecology and Hydrology (CEH), Edinburgh Research Station, Bush Estate, Penicuik, EH26 0QB (United Kingdom); Whitehead, J.; Gallagher, M.W. [School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester, M13 9PL (United Kingdom); Neftel, A.; Flechard, C.R. [Agroscope FAL Reckenholz, Federal Research Station for Agroecology and Agriculture, PO Box, CH 8046 Zurich (Switzerland)] (and others)

    2007-11-15

    Recent research in nitrogen exchange with the atmosphere has separated research communities according to N form. The integrated perspective needed to quantify the net effect of N on greenhouse-gas balance is being addressed by the NitroEurope Integrated Project (NEU). Recent advances have depended on improved methodologies, while ongoing challenges include gas-aerosol interactions, organic nitrogen and N{sub 2} fluxes. The NEU strategy applies a 3-tier Flux Network together with a Manipulation Network of global-change experiments, linked by common protocols to facilitate model application. Substantial progress has been made in modelling N fluxes, especially for N{sub 2}O, NO and bi-directional NH{sub 3} exchange. Landscape analysis represents an emerging challenge to address the spatial interactions between farms, fields, ecosystems, catchments and air dispersion/deposition. European up-scaling of N fluxes is highly uncertain and a key priority is for better data on agricultural practices. Finally, attention is needed to develop N flux verification procedures to assess compliance with international protocols. - Current N research is separated by form; the challenge is to link N components, scales and issues.

  20. Dynamic Group Diffie-Hellman Key Exchange under standard assumptions

    Energy Technology Data Exchange (ETDEWEB)

    Bresson, Emmanuel; Chevassut, Olivier; Pointcheval, David

    2002-02-14

    Authenticated Diffie-Hellman key exchange allows two principals communicating over a public network, and each holding public-private keys, to agree on a shared secret value. In this paper we study the natural extension of this cryptographic problem to a group of principals. We begin from existing formal security models and refine them to incorporate major missing details (e.g., strong-corruption and concurrent sessions). Within this model we define the execution of a protocol for authenticated dynamic group Diffie-Hellman and show that it is provably secure under the decisional Diffie-Hellman assumption. Our security result holds in the standard model and thus provides better security guarantees than previously published results in the random oracle model.

  1. Leveraged exchange-traded funds price dynamics and options valuation

    CERN Document Server

    Leung, Tim

    2016-01-01

    This book provides an analysis, under both discrete-time and continuous-time frameworks, on the price dynamics of leveraged exchange-traded funds (LETFs), with emphasis on the roles of leverage ratio, realized volatility, investment horizon, and tracking errors. This study provides new insights on the risks associated with LETFs. It also leads to the discussion of new risk management concepts, such as admissible leverage ratios and admissible risk horizon, as well as the mathematical and empirical analyses of several trading strategies, including static portfolios, pairs trading, and stop-loss strategies involving ETFs and LETFs. The final part of the book addresses the pricing of options written on LETFs. Since different LETFs are designed to track the same reference index, these funds and their associated options share very similar sources of randomness. The authors provide a no-arbitrage pricing approach that consistently value options on LETFs with different leverage ratios with stochastic volatility and ...

  2. MODELLING THE WORLD EXCHANGE RATES:DYNAMICS, VOLATILITY AND FORECASTING

    OpenAIRE

    Nwaobi, Godwin

    2008-01-01

    Indeed, the specification of equilibrium in the world economy depends on the exchange rate regime and thus, the early contributions to the postwar literature on exchange rate economics are to a large extent concerened with the role of speculation in foreign exchange markets. However, the world has known several exchange rate systems beginning with the fixed-gold standard, the adjustable-peg system, adjustable-parity system and the flexible exchange rate system. Yet, in 1997, when foreign exch...

  3. Investigating existence of chaos in short and long term dynamics of Moroccan exchange rates

    Science.gov (United States)

    Lahmiri, Salim

    2017-01-01

    This paper proposes a new methodology to investigate presence of chaos in exchange rate time series by combining wavelet transform and Lyapunov exponent estimation. In particular, stationary wavelet transform (SWT) is applied to exchange rate original time series for decomposition purpose. As a result, approximation and details coefficients are extracted. They are used to represent long and short term dynamics of the original exchange rate time series. Then, largest Lyapunov exponent is estimated for each type of dynamics to check for presence of chaos. Our methodology is applied to several Moroccan exchange rate time series. The empirical results show that, in general, the hypothesis of chaotic structure is accepted for currency levels but it is rejected for currency returns on both long and short dynamics. In addition, long and short dynamics exhibit different chaotic patterns in some exchange rate time series. Our approach may be useful to understand chaotic behaviour in original exchange rate time series.

  4. Lability of heavy metal species in aquatic humic substances characterized by ion exchange with cellulose phosphate.

    Science.gov (United States)

    Rocha, J C; Toscano, I A; Burba, P

    1997-01-01

    Labile metal species in aquatic humic substances (HSs) were characterized by ion exchange on cellulose phosphate (CellPhos) by applying an optimized batch procedure. The HSs investigated were pre-extracted from humic-rich waters by ultrafiltration and a resin XAD 8 procedure. The HS-metal species studied were formed by complexation with Cd(II), Ni(II), Cu(II), Mn(II) and Pb(II) as a function of time and the ratio ions to HSs. The kinetics and reaction order of this exchange process were studied. At the beginning ( Pb > Mn > Ni > Cd. The required metal determinations were carried out by atomic absorption spectrometry.

  5. Social organization influences the exchange and species richness of medicinal plants in Amazonian homegardens

    Directory of Open Access Journals (Sweden)

    Isabel Díaz-Reviriego

    2016-03-01

    Full Text Available Medicinal plants provide indigenous and peasant communities worldwide with means to meet their healthcare needs. Homegardens often act as medicine cabinets, providing easily accessible medicinal plants for household needs. Social structure and social exchanges have been proposed as factors influencing the species diversity that people maintain in their homegardens. Here, we assess the association between the exchange of medicinal knowledge and plant material and medicinal plant richness in homegardens. Using Tsimane' Amazonian homegardens as a case study, we explore whether social organization shapes exchanges of medicinal plant knowledge and medicinal plant material. We also use network centrality measures to evaluate people's location and performance in medicinal plant knowledge and plant material exchange networks. Our results suggest that social organization, specifically kinship and gender relations, influences medicinal plant exchange patterns significantly. Homegardens total and medicinal plant species richness are related to gardeners' centrality in the networks, whereby people with greater centrality maintain greater plant richness. Thus, together with agroecological conditions, social relations among gardeners and the culturally specific social structure seem to be important determinants of plant richness in homegardens. Understanding which factors pattern general species diversity in tropical homegardens, and medicinal plant diversity in particular, can help policy makers, health providers, and local communities to understand better how to promote and preserve medicinal plants in situ. Biocultural approaches that are also gender sensitive offer a culturally appropriate means to reduce the global and local loss of both biological and cultural diversity.

  6. Social organization influences the exchange and species richness of medicinal plants in Amazonian homegardens.

    Science.gov (United States)

    2016-03-01

    Medicinal plants provide indigenous and peasant communities worldwide with means to meet their healthcare needs. Homegardens often act as medicine cabinets, providing easily accessible medicinal plants for household needs. Social structure and social exchanges have been proposed as factors influencing the species diversity that people maintain in their homegardens. Here, we assess the association between the exchange of medicinal knowledge and plant material and medicinal plant richness in homegardens. Using Tsimane' Amazonian homegardens as a case study, we explore whether social organization shapes exchanges of medicinal plant knowledge and medicinal plant material. We also use network centrality measures to evaluate people's location and performance in medicinal plant knowledge and plant material exchange networks. Our results suggest that social organization, specifically kinship and gender relations, influences medicinal plant exchange patterns significantly. Homegardens total and medicinal plant species richness are related to gardeners' centrality in the networks, whereby people with greater centrality maintain greater plant richness. Thus, together with agroecological conditions, social relations among gardeners and the culturally specific social structure seem to be important determinants of plant richness in homegardens. Understanding which factors pattern general species diversity in tropical homegardens, and medicinal plant diversity in particular, can help policy makers, health providers, and local communities to understand better how to promote and preserve medicinal plants in situ. Biocultural approaches that are also gender sensitive offer a culturally appropriate means to reduce the global and local loss of both biological and cultural diversity.

  7. Simultaneous Disulfide and Boronic Acid Ester Exchange in Dynamic Combinatorial Libraries

    DEFF Research Database (Denmark)

    Diemer, Sanna L.; Kristensen, Morten; Rasmussen, Brian

    2015-01-01

    Dynamic combinatorial chemistry has emerged as a promising tool for the discovery of complex receptors in supramolecular chemistry. At the heart of dynamic combinatorial chemistry are the reversible reactions that enable the exchange of building blocks between library members in dynamic combinato......Dynamic combinatorial chemistry has emerged as a promising tool for the discovery of complex receptors in supramolecular chemistry. At the heart of dynamic combinatorial chemistry are the reversible reactions that enable the exchange of building blocks between library members in dynamic...... combinatorial libraries (DCLs) ensuring thermodynamic control over the system. If more than one reversible reaction operates in a single dynamic combinatorial library, the complexity of the system increases dramatically, and so does its possible applications. One can imagine two reversible reactions...... that operate simultaneously or two reversible reactions that operate independently. Both these scenarios have advantages and disadvantages. In this contribution, we show how disulfide exchange and boronic ester transesterification can function simultaneous in dynamic combinatorial libraries under appropriate...

  8. Determination of organoarsenic species in marine samples using gradient elution cation exchange HPLC-ICP-MS

    DEFF Research Database (Denmark)

    Sloth, Jens Jørgen; Larsen, Erik Huusfeldt; Julshamn, Kåre

    2003-01-01

    A method for the determination of arsenic species in marine samples using high performance liquid chromatography coupled to inductively coupled mass spectrometry (HPLC-ICP-MS) has been developed. Cation exchange HPLC with gradient elution using pyridine formate as the mobile phase was employed...... the certified limits and low detection limits of 0.002-0.005 mug g(-1) dry mass (as As) for the different arsenic species were obtained. At least 23 different organic arsenic species were detected in a scallop kidney in one analytical run of 25 min duration. The ability of our analytical method to detect...

  9. Atmospheric dust accumulation on native and non-native species: effects on gas exchange parameters.

    Science.gov (United States)

    González, Juan A; Prado, Fernando E; Piacentini, Ruben D

    2014-05-01

    Plants are continuously exposed to atmospheric particulate matter (dust), and their leaves are the main receptors of deposited dust. The objective of this study was to assess the effects of dust deposition on leaf gas exchange parameters of 17 native and non-native tree and shrub species growing in Gran San Miguel de Tucumán in northwestern Argentina. Maximum assimilation rate (), stomatal conductance (), transpiration rate (), internal CO concentration (), and instantaneous water-use efficiency (WUE) were measured in cleaned leaves (CL) and dusted leaves (DL) of different species on November 2010, July 2011, and September 2011. In almost all studied species, gas exchange parameters were significantly affected by dust deposition. Values for , , and of DL were significantly reduced in 11, 12, and 14 species compared with CL. Morphological leaf traits seem to be related to reduction. Indeed, L. and (Mart. ex DC.) Standl. species with pubescent leaves and thick ribs showed the highest reduction percentages. Contrarily, and WUE were increased in DL but were less responsive to dust deposition than other parameters. Increases of and WUE were significant in 5 and 11 species, respectively. Correlation analyses between /, /, and / pairs showed significant positive linear correlations in CL and DL of many studied species, including small and tall plants. These results suggest that leaf stomatal factors and shade-induced effect by accumulated dust are primarily responsible for the observed reductions in photosynthesis rate of DL.

  10. EXCHANGE

    Energy Technology Data Exchange (ETDEWEB)

    Boltz, J.C. (ed.)

    1992-09-01

    EXCHANGE is published monthly by the Idaho National Engineering Laboratory (INEL), a multidisciplinary facility operated for the US Department of Energy (DOE). The purpose of EXCHANGE is to inform computer users about about recent changes and innovations in both the mainframe and personal computer environments and how these changes can affect work being performed at DOE facilities.

  11. Transformations of metal species in ageing humic hydrocolloids studied by competitive ligand and metal exchange.

    Science.gov (United States)

    Burba, Peter; Van den Bergh, Johan

    2004-03-01

    Transformations of metal species (particularly Al, Ca, Fe, Mg, Mn, Zn) in ageing humic hydrocolloids were studied, applying a competitive ligand and metal exchange approach. For this purpose, metal-containing hydrocolloids, freshly collected from humic-rich German bog lake waters (Hohlohsee (HO), Black Forest; Venner Moor (VM), Muensterland; Arnsberger Wald (AW), Northrhine-Westfalia) and conventionally pre-filtered through 0.45 microm membranes, were subjected on-site to an exchange with EDTA and Cu(II) ions, respectively, as a function of time. EDTA complexes gradually formed, metal fractions exchanged by Cu(II) (as well as free Cu(II) concentrations) were operationally discriminated by means of a small time-controlled tangential-flow ultrafiltration unit (nominal cutoff: 1 kDa). Metal and DOM (dissolved organic matter) fractions obtained this way were determined off-site using instrumental methods (AAS, ICP-OES, carbon analyzer). After weeks of storage, the collected hydrocolloids were studied again by this approach. The EDTA availability of colloid-bound metals (particularly Al and Fe) exhibited different ageing trends, dependent on the sample (VM: decrease of Fe availability (98-76%), HO: increase of Fe availability (76-82%)). In contrast, the Cu(II) exchange equilibria of colloid-bound metals revealed merely low availability of Al (16-38%) and Fe (5-11%) towards Cu(II) ions, also dependent on ageing effects. In particular, the conditional copper exchange constants Kex obtained from the exchange between Cu(II) ions and available metal species (such as Ca, Mg, Mn, Zn) exhibited a strong decrease (by a factor of 2-100) during sample storage, indicating considerable non-equilibria complexation of these metal ions in the original bogwaters studied on-site.

  12. Dynamic Relationship between Crude Oil Price, Exchange Rate and ...

    African Journals Online (AJOL)

    DrNneka

    that uses the Granger causality test and generalized variance decomposition analysis ... observed between the Nigerian stock market and crude oil prices and the ... changing oil prices on stock prices and exchange rates an important guide to.

  13. Simultaneous Disulfide and Boronic Acid Ester Exchange in Dynamic Combinatorial Libraries

    DEFF Research Database (Denmark)

    Diemer, Sanna L.; Kristensen, Morten; Rasmussen, Brian

    2015-01-01

    that operate simultaneously or two reversible reactions that operate independently. Both these scenarios have advantages and disadvantages. In this contribution, we show how disulfide exchange and boronic ester transesterification can function simultaneous in dynamic combinatorial libraries under appropriate...

  14. Hamiltonian replica exchange molecular dynamics using soft-core interactions.

    Science.gov (United States)

    Hritz, Jozef; Oostenbrink, Chris

    2008-04-14

    To overcome the problem of insufficient conformational sampling within biomolecular simulations, we have developed a novel Hamiltonian replica exchange molecular dynamics (H-REMD) scheme that uses soft-core interactions between those parts of the system that contribute most to high energy barriers. The advantage of this approach over other H-REMD schemes is the possibility to use a relatively small number of replicas with locally larger differences between the individual Hamiltonians. Because soft-core potentials are almost the same as regular ones at longer distances, most of the interactions between atoms of perturbed parts will only be slightly changed. Rather, the strong repulsion between atoms that are close in space, which in many cases results in high energy barriers, is weakened within higher replicas of our proposed scheme. In addition to the soft-core interactions, we proposed to include multiple replicas using the same Hamiltonian/level of softness. We have tested the new protocol on the GTP and 8-Br-GTP molecules, which are known to have high energy barriers between the anti and syn conformation of the base with respect to the sugar moiety. During two 25 ns MD simulations of both systems the transition from the more stable to the less stable (but still experimentally observed) conformation is not seen at all. Also temperature REMD over 50 replicas for 1 ns did not show any transition at room temperature. On the other hand, more than 20 of such transitions are observed in H-REMD using six replicas (at three different Hamiltonians) during 6.8 ns per replica for GTP and 12 replicas (at six different Hamiltonians) during 8.7 ns per replica for 8-Br-GTP. The large increase in sampling efficiency was obtained from an optimized H-REMD scheme involving soft-core potentials, with multiple simulations using the same level of softness. The optimization of the scheme was performed by fast mimicking [J. Hritz and C. Oostenbrink, J. Chem. Phys. 127, 204104 (2007)].

  15. Seasonal dynamics of CO{sub 2} exchange during primary succession of boreal mires as controlled by phenology of plants

    Energy Technology Data Exchange (ETDEWEB)

    Leppala, M.; Kukko-Oja, K. [Finnish Forest Research Inst., Muhos (Finland); Laine, J. [Finnish Forest Research Inst., Parkano (Finland); Tuittila, E.S. [Helsinki Univ., Helsinki (Finland). Dept. of Forest Ecology, Peatland Ecology Group

    2008-07-01

    Seasonal dynamics in vegetation and carbon dioxide (CO{sub 2}) exchange were studied at 5 small mire basins along a chronosequence from the initial stages of paludification through to the bog stage in the Bay of Bothnia region in Finland. Precipitation and mean temperature during the summer 2004 study season were measured at a nearby meteorological station. Plant community composition was determined by estimating the projection cover of each species. Subplots in each of the study sites were established to count the number of living leaves of all vascular plant species. Sample plots were surrounded by aluminum collars in order to facilitate CO{sub 2} exchange measurements. Infrared gas analyzers were used to measure CO{sub 2} concentrations. Seasonal estimates of CO{sub 2} exchange dynamics were modelled in order to quantify the importance of different functional plant groups during the mire successions. Results of the study showed that seasonal variations in plant phenology and ecosystem respiration decreased in older sites along a mire chronosequence. Photosynthetically effective groups such as sedges and graminoids determined most of the seasonal CO{sub 2} dynamics. The higher level of gross photosynthesis combined with lower ecosystem respiration made the younger successional stages the largest sinks of atmospheric CO{sub 2}. Results suggested that autogenic factors controlled both the level and variation of CO{sub 2} exchange during mire succession. It was concluded that changes in vegetation must be considered when developing dynamic carbon models for mires of different ages, peat depths, and successional stages. 61 refs., 3 tabs., 8 figs.

  16. Contribution of different grass species to plant-atmosphere ammonia exchange in intensively managed grassland

    Science.gov (United States)

    Mattsson, M.; Herrmann, B.; Jones, S.; Neftel, A.; Sutton, M. A.; Schjoerring, J. K.

    2009-01-01

    Species diversity in grasslands usually declines with increasing input of nitrogen from fertilizers or atmospheric deposition. Conversely, species diversity may also impact the build-up of soil and plant nitrogen pools. One important pool is NH3/NH4+ which also can be exchanged between plant leaves and the atmosphere. Limited information is available on how plant-atmosphere ammonia exchange is related to species diversity in grasslands. We have here investigated grass species abundance and different foliar nitrogen pools in 4-year-old intensively managed grassland. Apoplastic pH and NH4+ concentrations of the 8 most abundant species (Lolium perenne, Phleum pratense, Festuca pratensis, Lolium multiflorum, Poa pratensis, Dactylis glomerata, Holcus lanatus, Bromus mollis) were used to calculate stomatal NH3 compensation points. Apoplastic NH4+ concentrations differed considerably among the species, ranging from 13 to 117 μM, with highest values in Festuca pratensis. Also apoplastic pH values varied, from pH 6.0 in Phleum pratense to 6.9 in Dactylis glomerata. The observed differences in apoplastic NH4+ and pH resulted in a large span of predicted values for the stomatal NH3 compensation point which ranged between 0.20 and 6.57 nmol mol-1. Three species (Lolium perenne, Festuca pratensis and Dactylis glomerata) had sufficiently high NH3 compensation point and abundance to contribute to the bi-directional NH3 fluxes recorded over the whole field. The other 5 grass species had NH3 compensation points considerably below the atmospheric NH3 concentration and were thus not likely to contribute to NH3 emission but only to NH3 uptake from the atmosphere. Evaluated across species, leaf bulk-tissue NH4+ concentrations correlated well (r2=0.902) with stomatal NH3 compensation points calculated on the basis of the apoplastic bioassay. This suggests that leaf tissue NH4+ concentrations combined with data for the frequency distribution of the corresponding species can be used for

  17. Effects of Drought and Rewetting on Growth and Gas Exchange of Minor European Broadleaved Tree Species

    Directory of Open Access Journals (Sweden)

    Jörg Kunz

    2016-10-01

    Full Text Available Widespread and economically important European tree species such as Norway spruce, Scots pine, and European beech are projected to be negatively affected by the increasing intensity and frequency of dry and hot conditions in a future climate. Hence, there is an increasing need to investigate the suitability of presumably more drought tolerant species to ensure future ecological stability, biodiversity, and productivity of forests. Based on their distribution patterns and climatic envelopes, the rare, minor broadleaved tree species Sorbus torminalis ((L. CRANTZ, S. domestica (L., Acer campestre (L., and A. platanoides (L. are assumed to be drought tolerant, however, there is only limited experimental basis to support that notion. This study aimed at quantifying growth and gas exchange of seedlings of these species during drought conditions, and their capacity to recover following drought. For that purpose, they were compared to the common companion species Quercus petraea ((MATTUSCHKA LIEBL. and Fagus sylvatica (L.. Here, potted seedlings of these species were exposed to water limitation followed by rewetting cycles in a greenhouse experiment. Photosynthesis and transpiration rates, stomatal conductance as well as root and shoot growth rates indicated a high drought resistance of A. campestre and A. platanoides. Sorbus domestica showed a marked ability to recover after drought stress. Therefore, we conclude that these minor tree species have the potential to enrich forests on drought-prone sites. Results from this pot experiment need to be complemented by field studies, in which the drought response of the species is not influenced by restrictions to root development.

  18. Exchange rate dynamics in crawling-band systems

    OpenAIRE

    José L Torres; M. Isabel Campos

    2007-01-01

    In this note we show that an exchange rate crawling-band system can borrow a portion of those aspects of a target zone that lead to its stabilizing effects on the exchange rate, depending on the relationship between the crawl rate and the drift of the fundamentals process. If the crawl rate is sufficiently high (with respect to the drift), the crawling-band is similar to a free float regime. As the crawl rate decreases, the crawling-band system collapses to a standard target zone.

  19. Capsid structure and dynamics of a human rhinovirus probed by hydrogen exchange mass spectrometry.

    Science.gov (United States)

    Wang, Lintao; Smith, David L

    2005-06-01

    Viral capsids are dynamic protein assemblies surrounding viral genomes. Despite the high-resolution structures determined by X-ray crystallography and cryo-electron microscopy, their in-solution structure and dynamics can be probed by hydrogen exchange. We report here using hydrogen exchange combined with protein enzymatic fragmentation and mass spectrometry to determine the capsid structure and dynamics of a human rhinovirus, HRV14. Capsid proteins (VP1-4) were labeled with deuterium by incubating intact virus in D(2)O buffer at neutral pH. The labeled proteins were digested by immobilized pepsin to give peptides analyzed by capillary reverse-phase HPLC coupled with nano-electrospray mass spectrometry. Deuterium levels incorporated at amide linkages in peptic fragments were measured for different exchange times from 12 sec to 30 h to assess the amide hydrogen exchange rates along each of the four protein backbones. Exchange results generally agree with the crystal structure of VP1-4,with extended, flexible terminal and surface-loop regions in fast exchange and folded helical and sheet structures in slow exchange. In addition, three alpha-helices, one from each of VP1-3, exhibited very slow exchange, indicating high stability of the protomeric interface. The beta-strands at VP3 N terminus also had very slow exchange, suggesting stable pentamer contacts. It was noted, however, that the interface around the fivefold axis had fast and intermediate exchange, indicating relatively more flexibility. Even faster exchange rates were found in the N terminus of VP1 and most segments of VP4, suggesting high flexibilities, which may correspond to their potential roles in virus uncoating.

  20. Laser spectroscopy and dynamics of transient species

    Science.gov (United States)

    Clouthier, D. J.

    1994-02-01

    Work was done on sub-Doppler spectroscopy of thioformaldehyde, electronic spectrum of FS2 radical, FTIR spectra of the transient molecule formyl chloride (HCOCl and DCOCl), and high-resolution FTIR spectra of the nu(sub 9) (CH2 wag) and nu(sub 5) (CSO symm. stretch) bands of sulfine (H2CSO), a transient species formed in pyrolysis of dimethyl sulfoxide and oxidation of thioformaldehyde.

  1. Dynamics of Chain Exchange in Block Copolymer Micelles

    Science.gov (United States)

    Lodge, Timothy

    Block copolymer micelles are rarely at equilibrium. The primary reason is the large number of repeat units in the insoluble block, Ncore, which makes the thermodynamic penalty for extracting a single chain (``unimer exchange'') substantial. As a consequence, the critical micelle concentration (CMC) is rarely accessed experimentally; however, in the proximity of a critical micelle temperature (CMT), equilibration is possible. We have been using time-resolved small angle neutron scattering (TR-SANS) to obtain a detailed picture of the mechanisms and time scales for chain exchange, at or near equilibrium. Our model system is poly(styrene)-block-poly(ethylene-alt-propylene)) (PS-PEP), in the PEP-selective solvent squalane (C30H62) . Equivalent micelles with either normal (hPS) or perdeuterated (dPS) cores are initially mixed in a blend of isotopically substituted squalane, designed to contrast-match a 50:50 hPS:dPS core. Samples are then annealed at a target temperature, and chain exchange is revealed quantitatively by the temporal decay in scattered intensity. The rate of exchange as function of concentration, temperature, Ncore, Ncorona, and chain architecture (diblock versus triblock) will be discussed.

  2. Heterogeneity of agents and exchange rate dynamics: evidence from the EMS

    NARCIS (Netherlands)

    Jong, E. de; Verschoor, W.F.C.; Zwinkels, R.C.J.

    2010-01-01

    We develop and estimate a dynamic heterogeneous agent model for the EMS period. Our empirical results suggest that the existence of heterogeneous interacting agents is indeed a possible explanation for the dynamics of exchange rates during the EMS. We find strong evidence of heterogeneous boundedly

  3. Heterogeneity of Agents and Exchange Rate Dynamics: Evidence from the EMS

    NARCIS (Netherlands)

    Jong, E. de; Verschoor, W.F.C.; Zwinkels, R.C.J.

    2006-01-01

    We develop and estimate a dynamic heterogeneous agent model for the EMS period. Our empirical results suggest that the existence of heterogeneous interacting agents is indeed a possible explanation for the dynamics of exchange rates during the EMS; we find strong evidence in favor of our model using

  4. Random walk theory and exchange rate dynamics in transition economies

    Directory of Open Access Journals (Sweden)

    Gradojević Nikola

    2010-01-01

    Full Text Available This paper investigates the validity of the random walk theory in the Euro-Serbian dinar exchange rate market. We apply Andrew Lo and Archie MacKinlay's (1988 conventional variance ratio test and Jonathan Wright's (2000 non-parametric ranks and signs based variance ratio tests to the daily Euro/Serbian dinar exchange rate returns using the data from January 2005 - December 2008. Both types of variance ratio tests overwhelmingly reject the random walk hypothesis over the data span. To assess the robustness of our findings, we examine the forecasting performance of a non-linear, nonparametric model in the spirit of Francis Diebold and James Nason (1990 and find that it is able to significantly improve upon the random walk model, thus confirming the existence of foreign exchange market imperfections in a small transition economy such as Serbia. In the last part of the paper, we conduct a comparative study on how our results relate to those of other transition economies in the region.

  5. Species Turnover through Time: Colonization and Extinction Dynamics across Metacommunities.

    Science.gov (United States)

    Nuvoloni, Felipe Micali; Feres, Reinaldo José Fazzio; Gilbert, Benjamin

    2016-06-01

    Island biogeography and metacommunity theory often use equilibrium assumptions to predict local diversity, yet nonequilibrium dynamics are common in nature. In nonequilibrium communities, local diversity fluctuates through time as the relative importance of colonization and extinction change. Here, we test the prevalence and causes of nonequilibrium dynamics in metacommunities of mites associated with rubber trees distributed over large spatial (>1,000 km) and temporal (>30-60 generations) scales in Brazil. We measured colonization and extinction rates to test species turnover and nonequilibrium dynamics over a growing season. Mite metacommunities exhibited nonequilibrium dynamics for most months of the year, and these dynamics tracked climatic conditions. Monthly shifts in temperature of more than 1°C resulted in nonequilibrium dynamics, as did mean temperatures outside of two critical ranges. Nonequilibrium dynamics were caused by a change in colonization with temperature change and changes in both colonization and extinction with absolute temperature. Species turnover showed different trends; high relative humidity increased both colonization and extinction rates, increasing turnover but not nonequilibrium dynamics. Our study illustrates that testing nonequilibrium dynamics can provide new insights into the drivers of colonization, extinction, and diversity fluctuations in metacommunities.

  6. THE DYNAMIC RELATIONSHIP BETWEEN STOCK PRICES AND EXCHANGE RATES: EVIDENCE FOR BRAZIL

    OpenAIRE

    Tabak, Benjamin M.

    2006-01-01

    This paper studies the dynamic relationship between stock prices and exchange rates in the Brazilian economy. We use recently developed unit root and cointegration tests, which allow endogenous breaks, to test for a long run relationship between these variables. We performed linear, and nonlinear causality tests after considering both volatility and linear dependence. We found that there is no long run relationship, but there is linear Granger causality from stock prices to exchange rates, in...

  7. Protein structural dynamics at the gas/water interface examined by hydrogen exchange mass spectrometry.

    Science.gov (United States)

    Xiao, Yiming; Konermann, Lars

    2015-08-01

    Gas/water interfaces (such as air bubbles or foam) are detrimental to the stability of proteins, often causing aggregation. This represents a potential problem for industrial processes, for example, the production and handling of protein drugs. Proteins possess surfactant-like properties, resulting in a high affinity for gas/water interfaces. The tendency of previously buried nonpolar residues to maximize contact with the gas phase can cause significant structural distortion. Most earlier studies in this area employed spectroscopic tools that could only provide limited information. Here we use hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for probing the conformational dynamics of the model protein myoglobin (Mb) in the presence of N(2) bubbles. HDX/MS relies on the principle that unfolded and/or highly dynamic regions undergo faster deuteration than tightly folded segments. In bubble-free solution Mb displays EX2 behavior, reflecting the occurrence of short-lived excursions to partially unfolded conformers. A dramatically different behavior is seen in the presence of N(2) bubbles; EX2 dynamics still take place, but in addition the protein shows EX1 behavior. The latter results from interconversion of the native state with conformers that are globally unfolded and long-lived. These unfolded species likely correspond to Mb that is adsorbed to the surface of gas bubbles. N(2) sparging also induces aggregation. To explain the observed behavior we propose a simple model, that is, "semi-unfolded" ↔ "native" ↔ "globally unfolded" → "aggregated". This model quantitatively reproduces the experimentally observed kinetics. To the best of our knowledge, the current study marks the first exploration of surface denaturation phenomena by HDX/MS.

  8. Cluster fusion-fission dynamics in the Singapore stock exchange

    Science.gov (United States)

    Teh, Boon Kin; Cheong, Siew Ann

    2015-10-01

    In this paper, we investigate how the cross-correlations between stocks in the Singapore stock exchange (SGX) evolve over 2008 and 2009 within overlapping one-month time windows. In particular, we examine how these cross-correlations change before, during, and after the Sep-Oct 2008 Lehman Brothers Crisis. To do this, we extend the complete-linkage hierarchical clustering algorithm, to obtain robust clusters of stocks with stronger intracluster correlations, and weaker intercluster correlations. After we identify the robust clusters in all time windows, we visualize how these change in the form of a fusion-fission diagram. Such a diagram depicts graphically how the cluster sizes evolve, the exchange of stocks between clusters, as well as how strongly the clusters mix. From the fusion-fission diagram, we see a giant cluster growing and disintegrating in the SGX, up till the Lehman Brothers Crisis in September 2008 and the market crashes of October 2008. After the Lehman Brothers Crisis, clusters in the SGX remain small for few months before giant clusters emerge once again. In the aftermath of the crisis, we also find strong mixing of component stocks between clusters. As a result, the correlation between initially strongly-correlated pairs of stocks decay exponentially with average life time of about a month. These observations impact strongly how portfolios and trading strategies should be formulated.

  9. Comparison of budburst dynamics between species on altitudinal gradient

    Science.gov (United States)

    Davi, H.; Gillmann, M.; Ibanez, T.

    2009-04-01

    Phenology of plants is a key ecosystem parameter controlling carbon and water fluxes and also acting on the dynamics of communities. This parameter is highly sensitive to the climate and consequently is often used as a proxy of global change. In this paper, we attempt to analyse the dynamics of budburst every week for seven species (Fagus sylvatica L., Acer opalus Mill , Sorbus aria L., Quercus pubescens Willd. Abies alba Mill., Pinus sylvestris L., Pinus nigra Arnold) in two altitudinal gradients, one in a northern slope and one in a southern slope in the Ventoux mountain. The originality of this work is to assess not only the budburst date but to more precisely analyse the dynamics of budburst and its variation with altitude according to the species. Two important results are highlighted. First, the dynamics of budburst changes according to the species. Three distinct patterns can be drawn, a rapid sigmoid increase for the deciduous species, a short sigmoid increase for the pines and an intermediate curve for silver fir. These dynamics can be slowing down for coniferous when frost arises during the budburst. The second topic is the link between budburst and temperature by analysing respectively the year, the altitudinal and the aspect (north and south) effects. In 2007, budburst occurs earlier for Fagus, Acer, and Abies, it does not change for pines and is delayed for Sorbus. Date of beech budburst is the same between north and south in spite of higher temperature in south. The altitude effect on budburst varies greatly according to species and the year with a weak effect on Fagus and a stronger effect for the others species showing a threshold at 1200 m. By analysing the mean of temperatures at each altitude, we conclude that temperature effect acts differently between years or between altitudes. To conclude, we highlighted the complex effect of temperatures on budburst varying between species and situations.

  10. Influence of coupling on thermal forces and dynamic friction in plasmas with multiple ion species

    CERN Document Server

    Kagan, Grigory; Daligault, Jerome

    2016-01-01

    The recently proposed effective potential theory [Phys. Rev. Lett. 110, 235001 (2013)] is used to investigate the influence of coupling on inter-ion-species diffusion and momentum exchange in multi-component plasmas. Thermo-diffusion and the thermal force are found to diminish rapidly as strong coupling onsets. For the same coupling parameters, the dynamic friction coefficient is found to tend to unity. These results provide an impetus for addressing the role of coupling on diffusive processes in inertial confinement fusion experiments.

  11. Simultaneous Disulfide and Boronic Acid Ester Exchange in Dynamic Combinatorial Libraries

    Science.gov (United States)

    Diemer, Sanna L.; Kristensen, Morten; Rasmussen, Brian; Beeren, Sophie R.; Pittelkow, Michael

    2015-01-01

    Dynamic combinatorial chemistry has emerged as a promising tool for the discovery of complex receptors in supramolecular chemistry. At the heart of dynamic combinatorial chemistry are the reversible reactions that enable the exchange of building blocks between library members in dynamic combinatorial libraries (DCLs) ensuring thermodynamic control over the system. If more than one reversible reaction operates in a single dynamic combinatorial library, the complexity of the system increases dramatically, and so does its possible applications. One can imagine two reversible reactions that operate simultaneously or two reversible reactions that operate independently. Both these scenarios have advantages and disadvantages. In this contribution, we show how disulfide exchange and boronic ester transesterification can function simultaneous in dynamic combinatorial libraries under appropriate conditions. We describe the detailed studies necessary to establish suitable reaction conditions and highlight the analytical techniques appropriate to study this type of system. PMID:26378519

  12. Simultaneous Disulfide and Boronic Acid Ester Exchange in Dynamic Combinatorial Libraries

    Directory of Open Access Journals (Sweden)

    Sanna L. Diemer

    2015-09-01

    Full Text Available Dynamic combinatorial chemistry has emerged as a promising tool for the discovery of complex receptors in supramolecular chemistry. At the heart of dynamic combinatorial chemistry are the reversible reactions that enable the exchange of building blocks between library members in dynamic combinatorial libraries (DCLs ensuring thermodynamic control over the system. If more than one reversible reaction operates in a single dynamic combinatorial library, the complexity of the system increases dramatically, and so does its possible applications. One can imagine two reversible reactions that operate simultaneously or two reversible reactions that operate independently. Both these scenarios have advantages and disadvantages. In this contribution, we show how disulfide exchange and boronic ester transesterification can function simultaneous in dynamic combinatorial libraries under appropriate conditions. We describe the detailed studies necessary to establish suitable reaction conditions and highlight the analytical techniques appropriate to study this type of system.

  13. Global attractors and extinction dynamics of cyclically competing species

    Science.gov (United States)

    Rulands, Steffen; Zielinski, Alejandro; Frey, Erwin

    2013-05-01

    Transitions to absorbing states are of fundamental importance in nonequilibrium physics as well as ecology. In ecology, absorbing states correspond to the extinction of species. We here study the spatial population dynamics of three cyclically interacting species. The interaction scheme comprises both direct competition between species as in the cyclic Lotka-Volterra model, and separated selection and reproduction processes as in the May-Leonard model. We show that the dynamic processes leading to the transient maintenance of biodiversity are closely linked to attractors of the nonlinear dynamics for the overall species’ concentrations. The characteristics of these global attractors change qualitatively at certain threshold values of the mobility and depend on the relative strength of the different types of competition between species. They give information about the scaling of extinction times with the system size and thereby the stability of biodiversity. We define an effective free energy as the negative logarithm of the probability to find the system in a specific global state before reaching one of the absorbing states. The global attractors then correspond to minima of this effective energy landscape and determine the most probable values for the species’ global concentrations. As in equilibrium thermodynamics, qualitative changes in the effective free energy landscape indicate and characterize the underlying nonequilibrium phase transitions. We provide the complete phase diagrams for the population dynamics and give a comprehensive analysis of the spatio-temporal dynamics and routes to extinction in the respective phases.

  14. Benchmarking novel approaches for modelling species range dynamics.

    Science.gov (United States)

    Zurell, Damaris; Thuiller, Wilfried; Pagel, Jörn; Cabral, Juliano S; Münkemüller, Tamara; Gravel, Dominique; Dullinger, Stefan; Normand, Signe; Schiffers, Katja H; Moore, Kara A; Zimmermann, Niklaus E

    2016-08-01

    Increasing biodiversity loss due to climate change is one of the most vital challenges of the 21st century. To anticipate and mitigate biodiversity loss, models are needed that reliably project species' range dynamics and extinction risks. Recently, several new approaches to model range dynamics have been developed to supplement correlative species distribution models (SDMs), but applications clearly lag behind model development. Indeed, no comparative analysis has been performed to evaluate their performance. Here, we build on process-based, simulated data for benchmarking five range (dynamic) models of varying complexity including classical SDMs, SDMs coupled with simple dispersal or more complex population dynamic models (SDM hybrids), and a hierarchical Bayesian process-based dynamic range model (DRM). We specifically test the effects of demographic and community processes on model predictive performance. Under current climate, DRMs performed best, although only marginally. Under climate change, predictive performance varied considerably, with no clear winners. Yet, all range dynamic models improved predictions under climate change substantially compared to purely correlative SDMs, and the population dynamic models also predicted reasonable extinction risks for most scenarios. When benchmarking data were simulated with more complex demographic and community processes, simple SDM hybrids including only dispersal often proved most reliable. Finally, we found that structural decisions during model building can have great impact on model accuracy, but prior system knowledge on important processes can reduce these uncertainties considerably. Our results reassure the clear merit in using dynamic approaches for modelling species' response to climate change but also emphasize several needs for further model and data improvement. We propose and discuss perspectives for improving range projections through combination of multiple models and for making these approaches

  15. Separation and determination of arsenic species in water by selective exchange and hybrid resins

    Energy Technology Data Exchange (ETDEWEB)

    Issa, Nureddin Ben [Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, Belgrade (Serbia); Rajakovic-Ognjanovic, Vladana N. [Faculty of Civil Engineering, University of Belgrade, Bulevar Kralja Aleksandra 73, Belgrade (Serbia); Marinkovic, Aleksandar D. [Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, Belgrade (Serbia); Rajakovic, Ljubinka V., E-mail: ljubinka@tmf.bg.ac.rs [Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, Belgrade (Serbia)

    2011-11-07

    Highlights: {yields} A simple and efficient method for separation and determination of arsenic species. {yields} A new hybrid resin HY-AgCl is effective for iAs and oAs analytical separation. {yields} SBAE resin was convenient for the separation of As(III) from As(V) and oAs species. {yields} HY-Fe resin was convenient for the separation of DMAs(V). - Abstract: A simple and efficient method for separation and determination of inorganic arsenic (iAs) and organic arsenic (oAs) in drinking, natural and wastewater was developed. If arsenic is present in water prevailing forms are inorganic acids of As(III) and As(V). oAs can be found in traces as monomethylarsenic acid, MMA(V), and dimethylarsenic acid, DMAs(V). Three types of resins: a strong base anion exchange (SBAE) and two hybrid (HY) resins: HY-Fe and HY-AgCl, based on the activity of hydrated iron oxides and a silver chloride were investigated. It was found that the sorption processes (ion exchange, adsorption and chemisorptions) of arsenic species on SBAE (ion exchange) and HY resins depend on pH values of water. The quantitative separation of molecular and ionic forms of iAs and oAs was achieved by SBAE and pH adjustment, the molecular form of As(III) that exists in the water at pH <8.0 was not bonded with SBAE, which was convenient for direct determination of As(III) concentration in the effluent. HY-Fe resin retained all arsenic species except DMAs(V), which makes possible direct measurements of this specie in the effluent. HY-AgCl resin retained all iAs which was convenient for direct determination of oAs species concentration in the effluent. The selective bonding of arsenic species on three types of resins makes possible the development of the procedure for measuring and calculation of all arsenic species in water. In order to determine capacity of resins the preliminary investigations were performed in batch system and fixed bed flow system. Resin capacities were calculated according to breakthrough

  16. Replica exchange simulations of the three-dimensional Ising spin glass: static and dynamic properties

    Science.gov (United States)

    Yucesoy, Burcu; Machta, Jonathan; Katzgraber, Helmut G.

    2012-02-01

    We present the results of a large-scale numerical study of the equilibrium three-dimensional Ising spin glass with Gaussian disorder. Using replica exchange (parallel tempering) Monte Carlo, we measure various static, as well as dynamical quantities, such as the autocorrelation times and round-trip times for the replica exchange Monte Carlo method. The correlation between static and dynamic observables for 5000 disorder realizations (N <=10^3 spins) down to very low temperatures (T 0.2Tc) is examined. Our results show that autocorrelation times are directly correlated with the roughness of the free energy landscape. We also discuss the size dependence of several static quantities.

  17. Jealousy and Trust: Unexplored Dimensions of Social Exchange Dynamics.

    Science.gov (United States)

    McDonald, Gerald W.; Osmond, Marie Withers

    Little effort has been made to systematically assess the determinants and consequences of marital jealousy which affect marital, familial and extra-familial expectations, interactions and behavior. A preliminary attempt to rectify this omission provides a conceptual/theoretical perspective on jealousy dynamics in marriage. Marital jealousy, a…

  18. Delay driven spatiotemporal chaos in single species population dynamics models.

    Science.gov (United States)

    Jankovic, Masha; Petrovskii, Sergei; Banerjee, Malay

    2016-08-01

    Questions surrounding the prevalence of complex population dynamics form one of the central themes in ecology. Limit cycles and spatiotemporal chaos are examples that have been widely recognised theoretically, although their importance and applicability to natural populations remains debatable. The ecological processes underlying such dynamics are thought to be numerous, though there seems to be consent as to delayed density dependence being one of the main driving forces. Indeed, time delay is a common feature of many ecological systems and can significantly influence population dynamics. In general, time delays may arise from inter- and intra-specific trophic interactions or population structure, however in the context of single species populations they are linked to more intrinsic biological phenomena such as gestation or resource regeneration. In this paper, we consider theoretically the spatiotemporal dynamics of a single species population using two different mathematical formulations. Firstly, we revisit the diffusive logistic equation in which the per capita growth is a function of some specified delayed argument. We then modify the model by incorporating a spatial convolution which results in a biologically more viable integro-differential model. Using the combination of analytical and numerical techniques, we investigate the effect of time delay on pattern formation. In particular, we show that for sufficiently large values of time delay the system's dynamics are indicative to spatiotemporal chaos. The chaotic dynamics arising in the wake of a travelling population front can be preceded by either a plateau corresponding to dynamical stabilisation of the unstable equilibrium or by periodic oscillations.

  19. Modeling and simulation of the dynamic behavior of portable proton exchange membrane fuel cells

    Energy Technology Data Exchange (ETDEWEB)

    Ziegler, C.

    2005-07-01

    In order to analyze the operational behavior, a mathematical model of planar self-breathing fuel cells is developed and validated in Chapter 3 of this thesis. The multicomponent transport of the species is considered as well as the couplings between the transport processes of heat, charge, and mass and the electrochemical reactions. Furthermore, to explain the oxygen mass transport limitation in the porous electrode of the cathode side an agglomerate model for the oxygen reduction reaction is developed. In Chapter 4 the important issue of liquid water generation and transport in PEMFCs is addressed. One of the major tasks when operating this type of fuel cell is avoiding the complete flooding of the PEMFC during operation. A one-dimensional and isothermal model is developed that is based on a coupled system of partial differential equations. The model contains a dynamic and two-phase description of the proton exchange membrane fuel cell. The mass transport in the gas phase and in the liquid phase is considered as well as the phase transition between liquid water and water vapor. The transport of charges and the electrochemical reactions are part of the model. Flooding effects that are caused by liquid water accumulation are described by this model. Moreover, the model contains a time-dependent description of the membrane that accounts for Schroeder's paradox. The model is applied to simulate cyclic voltammograms. Chapter 5 is focused on the dynamic investigation of PEMFC stacks. Understanding the dynamic behavior of fuel cell stacks is important for the operation and control of fuel cell stacks. Using the single cell model of Chapter 3 and the dynamic model of Chapter 4 as basis, a mathematical model of a PEMFC stack is developed. However, due to the complexity of a fuel cell stack, the spatial resolution and dynamic description of the liquid water transport are not accounted for. These restrictions allow for direct comparison between the solution variables of

  20. Forecasting abrupt changes in foreign exchange markets: method using dynamical network marker

    Science.gov (United States)

    Oya, Shunsuke; Aihara, Kazuyuki; Hirata, Yoshito

    2014-11-01

    We apply the idea of dynamical network markers (Chen et al 2012 Sci. Rep. 2 342) to foreign exchange markets so that early warning signals can be provided for any abrupt changes. The dynamical network marker constructed achieves a high odds ratio for forecasting these sudden changes. In addition, we also extend the notion of the dynamical network marker by using recurrence plots so that the notion can be applied to delay coordinates and point processes. Thus, the dynamical network marker is useful in a variety of contexts in science, technology, and society.

  1. Dynamics of a lattice gas system of three species

    Science.gov (United States)

    Wang, Yuanshi; Wu, Hong; Liang, Junhao

    2016-10-01

    This paper considers a mutualism system of three species in which each species provides resource for the next one in a one-directional loop, while there exists spatial competition among them. The system is characterized by a lattice gas model and the cases of obligate mutualisms, obligate-facultative mutualisms and facultative mutualisms are considered. Using dynamical systems theory, it is shown that (i) the mutualisms can lead to coexistence of species; (ii) A weak mutualism or an extremely strong mutualism will result in extinction of species, while even the superior facultative species will be driven into extinction by its over-strong mutualism on the next one; (iii) Initial population density plays a role in the coexistence of species. It is also shown that when there exists weak mutualism, an obligate species can survive by providing more benefit to the next one, and the inferior facultative species will not be driven into extinction if it can strengthen its mutualism on the next species. Moreover, Hopf bifurcation, saddle-node bifurcation and bifurcation of heteroclinic cycles are shown in the system. Projection method is extended to exhibit bistability in the three-dimensional model: when saddle-node bifurcation occurs, stable manifold of the saddle-node point divides intR+3 into two basins of attraction of two equilibria. Furthermore, Lyapunov method is applied to exhibit unstability of heteroclinic cycles. Numerical simulations confirm and extend our results.

  2. Dynamic species distribution models from categorical survey data.

    Science.gov (United States)

    Mieszkowska, Nova; Milligan, Gregg; Burrows, Michael T; Freckleton, Rob; Spencer, Matthew

    2013-11-01

    1. Species distribution models are static models for the distribution of a species, based on Hutchinson's niche concept. They make probabilistic predictions about the distribution of a species, but do not have a temporal interpretation. In contrast, density-structured models based on categorical abundance data make it possible to incorporate population dynamics into species distribution modelling. 2. Using dynamic species distribution models, temporal aspects of a species' distribution can be investigated, including the predictability of future abundance categories and the expected persistence times of local populations, and how these may respond to environmental or anthropogenic drivers. 3. We built density-structured models for two intertidal marine invertebrates, the Lusitanian trochid gastropods Phorcus lineatus and Gibbula umbilicalis, based on 9 years of field data from around the United Kingdom. Abundances were recorded on a categorical scale, and stochastic models for year-to-year changes in abundance category were constructed with winter mean sea surface temperature (SST) and wave fetch (a measure of the exposure of a shore) as explanatory variables. 4. Both species were more likely to be present at sites with high SST, but differed in their responses to wave fetch. Phorcus lineatus had more predictable future abundance and longer expected persistence times than G. umbilicalis. This is consistent with the longer lifespan of P. lineatus. 5. Where data from multiple time points are available, dynamic species distribution models of the kind described here have many applications in population and conservation biology. These include allowing for changes over time when combining historical and contemporary data, and predicting how climate change might alter future abundance conditional on current distributions.

  3. Dynamic Cyclic Thiodepsipeptide Libraries from Thiol-Thioester Exchange

    Science.gov (United States)

    2010-04-01

    the reaction dynamics are discussed. Cyclic peptides have been described as “privileged structures” for drug design because so many natural and...inhibitors, which hold promise for treatment of cancer.4 As drug scaffolds, cyclic peptides are advantageous because they mimic native protein structure...but instead an influence of chirality on the accessibility of the thioester or thiol. We also investigated the effect of positively charged amino

  4. Intention Recognition for Dynamic Role Exchange in Haptic Collaboration

    OpenAIRE

    Küçükyılmaz, Ayşe; Sezgin, Tevfik Metin; Başdoğan, Çağatay

    2013-01-01

    In human-computer collaboration involving haptics, a key issue that remains to be solved is to establish an intuitive communication between the partners. Even though computers are widely used to aid human operators in teleoperation, guidance, and training, because they lack the adaptability, versatility, and awareness of a human, their ability to improve efficiency and effectiveness in dynamic tasks is limited. We suggest that the communication between a human and a computer can be improved i...

  5. Analyzing energy-water exchange dynamics in the Thar desert

    Science.gov (United States)

    Raja, P.; Singh, Nilendu; Srinivas, C. V.; Singhal, Mohit; Chauhan, Pankaj; Singh, Maharaj; Sinha, N. K.

    2017-07-01

    Regions of strong land-atmosphere coupling will be more susceptible to the hydrological impacts in the intensifying hydrological cycle. In this study, micrometeorological experiments were performed to examine the land-atmosphere coupling strength over a heat low region (Thar desert, NW India), known to influence the Indian summer monsoon (ISM). Within the vortex of Thar desert heat low, energy-water exchange and coupling behavior were studied for 4 consecutive years (2011-2014) based on sub-hourly measurements of radiative-convective flux, state parameters and sub-surface thermal profiles using lead-lag analysis between various E-W balance components. Results indicated a strong (0.11-0.35) but variable monsoon season (July-September) land-atmosphere coupling events. Coupling strength declined with time, becomes negative beyond 10-day lag. Evapotranspiration (LE) influences rainfall at the monthly time-scale (20-40 days). Highly correlated monthly rainfall and LE anomalies (r = 0.55, P heating (SH) during March and April are more strongly (r = 0.6-0.7) correlated to ISM rainfall than heating during May or June (r = 0.16-0.36). Analyses show strong and weak couplings among net radiation (Rn)-vapour pressure deficit (VPD), LE-VPD and Rn-LE switching between energy-limited to water-limited conditions. Consistently, +ve and -ve residual energy [(dE) = (Rn - G) - (SH + LE)] were associated with regional wet and dry spells respectively with a lead of 10-40 days. Dew deposition (18.8-37.9 mm) was found an important component in the annual surface water balance. Strong association of variation of LE and rainfall was found during monsoon at local-scale and with regional-scale LE (MERRA 2D) but with a lag which was more prominent at local-scale than at regional-scale. Higher pre-monsoon LE at local-scale as compared to low and monotonous variation in regional-scale LE led to hypothesize that excess energy and water vapour brought through advection caused by pre

  6. Dynamic Linkages between Exchange Rates and Stock Prices: Evidence from Iran and South Korea

    Directory of Open Access Journals (Sweden)

    Akbar Tavakoli

    2013-01-01

    Full Text Available The main purpose of present study is to analyze the relationship between stock and exchange markets in two Asian countries, Iran and South Korea. A monthly time series of stock price and exchange rate are used over the period 2002: 05 - 2012: 03. The data is collected from the Central Bank of each country and WDI. The calculated stock return and real exchange rate change are used in analysis. An econometric multiple generalized autoregressive conditional heteroscedasticity (MGARCH BEKK method and the Rats software are applied to analyze a dynamic relationship between two markets in each country. The estimated results show a bidirectional relationship between two markets in South Korean economy and only a unidirectional relationship from exchange market to stock market in Iranian economy. The persistence of volatility transmission effects of each market on its own is also found in each economy. In the exchange market, this effect is in opposite direction in Iran compared to Korea, whereas in the stock market both effects are positive and almost the same in two economies. The policy implication of finding is clear. The financial policymakers should watch both stock and exchange markets in two economies to prevent the bidirectional volatility effects between two markets in Korea and the unidirectional volatility from the exchange market to sock market in Iran.

  7. Exchange anisotropy and the dynamic phase transition in thin ferromagnetic Heisenberg films.

    Science.gov (United States)

    Jang, Hyunbum; Grimson, Malcolm J; Hall, Carol K

    2003-10-01

    Monte Carlo simulations have been performed to investigate the dependence of the dynamic phase behavior on the bilinear exchange anisotropy of a classical Heisenberg spin system. The system under consideration is a planar thin ferromagnetic film with competing surface fields subject to a pulsed oscillatory external field. The results show that the films exhibit a single discontinuous dynamic phase transition (DPT) as a function of the anisotropy of the bilinear exchange interaction in the Hamiltonian. Furthermore, there is no evidence of stochastic resonance associated with the DPT. These results are in marked contrast to the continuous DPT observed in the same system as a function of temperature and applied field strength for a fixed bilinear exchange anisotropy.

  8. Quantum Dynamics Study on D+OD+ Reaction: Competition between Exchange and Abstraction Channels

    Institute of Scientific and Technical Information of China (English)

    Wen-wu Xu; Pei-yu Zhang; Guo-zhong He

    2013-01-01

    Quantum dynamics for the D+OD+ reaction at the collision energy range of 0.0-1.0 eV was studied on an accurate ab initio potential energy surface.Both of the endothermic abstraction (D+OD+-O++D2) and thermoneutral exchange (D+OD+-D+OD+) channels were investigated from the same set of time-dependent quantum wave packets method under centrifugal sudden approximation.The reaction probability dependence with collision energy,the integral cross sections,and the thermal rate constant of the both channels are calculated.It is found that there is a convex structure in the reaction path of the exchange reaction.The calculated time evolution of the wave packet distribution at J=0 clearly indicates that the convex structure significantly influences the dynamics of the exchange and abstraction channels of title reaction.

  9. Theoretical study of charge exchange dynamics in He$^+$ + NO collisions

    CERN Document Server

    Bene, E

    2014-01-01

    We investigate the charge transfer mechanism in the collisions of helium ions on nitric oxide using a molecular description framework with consideration of the orientation of the projectile toward the target. The anisotropy of the collision process has been analysed in detail in connection with the non-adiabatic interactions around avoided crossings. Potential energy curves, radial and rotational coupling matrix elements have been determined by means of ab initio quantum chemical methods. The collision dynamics is performed in the [1.-25.] keV collision energy range using a semiclassical approach, and the total electron transfer cross sections are analysed with regard to available experimental data.

  10. Genetic Exchange of Multidrug Efflux Pumps among Two Enterobacterial Species with Distinctive Ecological Niches

    Directory of Open Access Journals (Sweden)

    Matthias S. Ullrich

    2009-02-01

    Full Text Available AcrAB-TolC is the major multidrug efflux system in Enterobacteriaceae recognizing structurally unrelated molecules including antibiotics, dyes, and detergents. Additionally, in Escherichia coli it mediates resistance to bile salts. In the plant pathogen Erwinia amylovora AcrAB-TolC is required for virulence and phytoalexin resistance. Exchange analysis of AcrAB-TolC was conducted by complementing mutants of both species defective in acrB or tolC with alleles from either species. The acrB and tolC mutants exhibited increased susceptibility profiles for 24 different antibiotics. All mutants were complemented with acrAB or tolC, respectively, regardless of the taxonomic origin of the alleles. Importantly, complementation of E. amylovora mutants with respective E. coli genes restored virulence on apple plants. It was concluded that AcrAB and TolC of both species could interact and that these interactions did not yield in altered functions despite the divergent ecological niches, to which E. coli and E. amylovora have adopted.

  11. Dynamic modeling of heat exchanger tube-to-support interaction

    Energy Technology Data Exchange (ETDEWEB)

    Azizian, R.; Mureithi, N.W.; Sawadog, T.P.; Pettigrew, M.J. [Ecole Polytechnique, Dept. of Mechanical Engineering, BWC/AECL/NSERC Chair of Fluid-Structure Interaction, Montreal, Quebec (Canada)

    2009-07-01

    Tube arrays in steam generators and heat exchangers operating in two-phase cross-flow are subjected sometimes to strong vibration due mainly to turbulence buffeting and fluidelastic forces. This can lead to tube damage by fatigue or fretting wear. A computer implementation of a fluidelastic instability model is proposed to determine with improved accuracy the fluidelastic forces and hence the critical instability flow velocity. Usually the fluidelastic instability is 'predicted', using the Connors relation with K=3. While the value of K can be determined experimentally to get an accurate prediction of the instability, the Connors relation does not allow good estimation of the fluid forces. Consequently the RMS value of the magnitude of vibration of the tube bundle, necessary to evaluate the work rate and the tube wear is only poorly estimated. The fluidelastic instability analysis presented here is based on the quasi-steady model, originally developed for single phase flow. The fluid forces are expressed in terms of the quasi-static drag and lift force coefficients and their derivatives which are determined experimentally. The forces also depend on the tube displacement and velocity. In the computer code ABAQUS, the fluid forces are provided in the user subroutines VDLOAD or VUEL. A typical simulation of the vibration of a single flexible tube within an array in two phase cross-flow is done in ABAQUS and the results are compared with the experimental measurements for a tube with similar physical properties. For a cantilever tube, in two phase cross-flow of void fraction 60 percent, the numerical critical flow velocity was 2.0 m/s compared to 1.8 m/s obtained experimentally. The relative error was 5 percent compared to 26.6 percent for the Connors relation with K=3. The simulation of the vibration of a typical tube in a steam generator is also presented. The numerical results show good agreement with experimental measurements. (author)

  12. Studying the Early Stages of Protein Aggregation Using Replica Exchange Molecular Dynamics Simulations.

    Science.gov (United States)

    Shea, Joan-Emma; Levine, Zachary A

    2016-01-01

    The simulation of protein aggregation poses several computational challenges due to the disparate time and lengths scales that are involved. This chapter focuses on the use of atomistically detailed simulations to probe the initial steps of aggregation, with an emphasis on the Tau peptide as a model system, run under a replica exchange molecular dynamics protocol.

  13. Dynamic Thermal Model and Temperature Control of Proton Exchange Membrane Fuel Cell Stack

    Institute of Scientific and Technical Information of China (English)

    邵庆龙; 卫东; 曹广益; 朱新坚

    2005-01-01

    A dynamic thermal transfer model of a proton exchange membrane fuel cell (PEMFC) stack is developed based on energy conservation in order to reach better temperature control of PEMFC stack. Considering its uncertain parameters and disturbance, we propose a robust adaptive controller based on backstepping algorithm of Lyaponov function. Numerical simulations indicate the validity of the proposed controller.

  14. A computational fluid dynamics model for designing heat exchangers based on natural convection

    NARCIS (Netherlands)

    Dirkse, M.H.; Loon, van W.K.P.; Walle, van der T.; Speetjens, S.L.; Bot, G.P.A.

    2006-01-01

    A computational fluid dynamics model was created for the design of a natural convection shell-and-tube heat exchanger with baffles. The flow regime proved to be turbulent and this was modelled using the k¿¿ turbulence model. The features of the complex geometry were simplified considerably resulting

  15. Dynamic diversity of synthetic supramolecular polymers in water as revealed by hydrogen/deuterium exchange

    Science.gov (United States)

    Lou, Xianwen; Lafleur, René P. M.; Leenders, Christianus M. A.; Schoenmakers, Sandra M. C.; Matsumoto, Nicholas M.; Baker, Matthew B.; van Dongen, Joost L. J.; Palmans, Anja R. A.; Meijer, E. W.

    2017-05-01

    Numerous self-assembling molecules have been synthesized aiming at mimicking both the structural and dynamic properties found in living systems. Here we show the application of hydrogen/deuterium exchange (HDX) mass spectrometry (MS) to unravel the nanoscale organization and the structural dynamics of synthetic supramolecular polymers in water. We select benzene-1,3,5-tricarboxamide (BTA) derivatives that self-assemble in H2O to illustrate the strength of this technique for supramolecular polymers. The BTA structure has six exchangeable hydrogen atoms and we follow their exchange as a function of time after diluting the H2O solution with a 100-fold excess of D2O. The kinetic H/D exchange profiles reveal that these supramolecular polymers in water are dynamically diverse; a notion that has previously not been observed using other techniques. In addition, we report that small changes in the molecular structure can be used to control the dynamics of synthetic supramolecular polymers in water.

  16. Dynamic Conditional Correlations in International Stock, Bond and Foreign Exchange Markets: Emerging Markets Evidence

    NARCIS (Netherlands)

    M.S. Hakim (Mohamad); M.J. McAleer (Michael)

    2009-01-01

    textabstractThe paper models the dynamic conditional correlations in emerging stock, bond and foreign exchange markets using the DCC model of Engle (2002) and the GARCC model of McAleer et al. (2008). The highly restrictive DCC model suggests that the conditional correlations of the overall returns

  17. Energy exchange via multi-species streaming in laser-driven ion acceleration

    Science.gov (United States)

    King, M.; Gray, R. J.; Powell, H. W.; Capdessus, R.; McKenna, P.

    2017-01-01

    Due to the complex electron dynamics and multiple ion acceleration mechanisms that can take place in the interaction of an ultra-intense laser pulse with a thin foil, it is possible for multiple charged particle populations to overlap in space with varying momentum distributions. In certain scenarios this can drive streaming instabilities such as the relativistic Buneman instability and the ion-ion acoustic instability. The potential for such instabilities to occur are demonstrated using particle-in-cell simulations. It is shown that if a population of ions can be accelerated such that it can propagate through other slowly expanding ion populations, energy exchange can occur via the ion-ion acoustic instability.

  18. Determining habitat quality for species that demonstrate dynamic habitat selection

    Science.gov (United States)

    Beerens, James; Frederick, Peter C; Noonburg, Erik G; Gawlik, Dale E.

    2015-01-01

    Determining habitat quality for wildlife populations requires relating a species' habitat to its survival and reproduction. Within a season, species occurrence and density can be disconnected from measures of habitat quality when resources are highly seasonal, unpredictable over time, and patchy. Here we establish an explicit link among dynamic selection of changing resources, spatio-temporal species distributions, and fitness for predictive abundance and occurrence models that are used for short-term water management and long-term restoration planning. We used the wading bird distribution and evaluation models (WADEM) that estimate (1) daily changes in selection across resource gradients, (2) landscape abundance of flocks and individuals, (3) conspecific foraging aggregation, and (4) resource unit occurrence (at fixed 400 m cells) to quantify habitat quality and its consequences on reproduction for wetland indicator species. We linked maximum annual numbers of nests detected across the study area and nesting success of Great Egrets (Ardea alba), White Ibises (Eudocimus albus), and Wood Storks (Mycteria americana) over a 20-year period to estimated daily dynamics of food resources produced by WADEM over a 7490 km2 area. For all species, increases in predicted species abundance in March and high abundance in April were strongly linked to breeding responses. Great Egret nesting effort and success were higher when birds also showed greater conspecific foraging aggregation. Synthesis and applications: This study provides the first empirical evidence that dynamic habitat selection processes and distributions of wading birds over environmental gradients are linked with reproductive measures over periods of decades. Further, predictor variables at a variety of temporal (daily-multiannual) resolutions and spatial (400 m to regional) scales effectively explained variation in ecological processes that change habitat quality. The process used here allows managers to develop

  19. Invasion dynamics of competing species with stage-structure.

    Science.gov (United States)

    Bewick, Sharon; Wang, Guoqing; Younes, Hannah; Li, Bingtuan; Fagan, William F

    2017-08-03

    The spread of an invasive species often results in a decline and subsequent disappearance of native competitors. Several models, primarily based on spatially explicit Lotka-Volterra competition dynamics, have been developed to understand this phenomenon. In general, the goal of these models is to relate fundamental life history traits, for example dispersal ability and competition strength, to the rate of spread of the invasive species, which is also the rate at which the invasive species displaces its native competitor. Stage-structure is often an important determinant of population dynamics, but it has received little attention within the context of Lotka-Volterra invasion models. For many species, behaviors like dispersal and competition depend on life-stage. To describe the processes of invasion in these species, it is important to understand how behaviors that vary as a function of life-stage can impact spread rate. In this paper, we develop a spatially explicit, stage-structured Lotka-Volterra competition model. By comparing spread speed predictions from this model to spread speed predictions from an analogous single-stage model, we are able to determine when stage-structure is important and how stage-dependent behavior can alter the characteristics of an invasion. Copyright © 2017. Published by Elsevier Ltd.

  20. Relative species abundance of replicator dynamics with sparse interactions

    Science.gov (United States)

    Obuchi, Tomoyuki; Kabashima, Yoshiyuki; Tokita, Kei

    2016-11-01

    A theory of relative species abundance on sparsely-connected networks is presented by investigating the replicator dynamics with symmetric interactions. Sparseness of a network involves difficulty in analyzing the fixed points of the equation, and we avoid this problem by treating large self interaction u, which allows us to construct a perturbative expansion. Based on this perturbation, we find that the nature of the interactions is directly connected to the abundance distribution, and some characteristic behaviors, such as multiple peaks in the abundance distribution and all species coexistence at moderate values of u, are discovered in a wide class of the distribution of the interactions. The all species coexistence collapses at a critical value of u, u c , and this collapsing is regarded as a phase transition. To get more quantitative information, we also construct a non-perturbative theory on random graphs based on techniques of statistical mechanics. The result shows those characteristic behaviors are sustained well even for not large u. For even smaller values of u, extinct species start to appear and the abundance distribution becomes rounded and closer to a standard functional form. Another interesting finding is the non-monotonic behavior of diversity, which quantifies the number of coexisting species, when changing the ratio of mutualistic relations Δ . These results are examined by numerical simulations, which show that our theory is exact for the case without extinct species, but becomes less and less precise as the proportion of extinct species grows.

  1. Dynamic UltraFast 2D EXchange SpectroscopY (UF-EXSY) of hyperpolarized substrates

    Science.gov (United States)

    Leon Swisher, Christine; Koelsch, Bertram; Sukumar, Subramianam; Sriram, Renuka; Santos, Romelyn Delos; Wang, Zhen Jane; Kurhanewicz, John; Vigneron, Daniel; Larson, Peder

    2015-08-01

    In this work, we present a new ultrafast method for acquiring dynamic 2D EXchange SpectroscopY (EXSY) within a single acquisition. This technique reconstructs two-dimensional EXSY spectra from one-dimensional spectra based on the phase accrual during echo times. The Ultrafast-EXSY acquisition overcomes long acquisition times typically needed to acquire 2D NMR data by utilizing sparsity and phase dependence to dramatically undersample in the indirect time dimension. This allows for the acquisition of the 2D spectrum within a single shot. We have validated this method in simulations and hyperpolarized enzyme assay experiments separating the dehydration of pyruvate and lactate-to-pyruvate conversion. In a renal cell carcinoma cell (RCC) line, bidirectional exchange was observed. This new technique revealed decreased conversion of lactate-to-pyruvate with high expression of monocarboxylate transporter 4 (MCT4), known to correlate with aggressive cancer phenotypes. We also showed feasibility of this technique in vivo in a RCC model where bidirectional exchange was observed for pyruvate-lactate, pyruvate-alanine, and pyruvate-hydrate and were resolved in time. Broadly, the technique is well suited to investigate the dynamics of multiple exchange pathways and applicable to hyperpolarized substrates where chemical exchange has shown great promise across a range of disciplines.

  2. Triangleland. I. Classical dynamics with exchange of relative angular momentum

    CERN Document Server

    Anderson, Edward

    2008-01-01

    In Euclidean relational particle mechanics, only relative times, relative angles and relative separations are meaningful. Barbour-Bertotti (1982) theory is of this form and constitutes a recovery of a portion of Newtonian mechanics from relational premises. This is of interest in the absolute versus relative motion debate and also shares a number of features with the geometrodynamical formulation of general relativity, making it suitable for some modelling of the problem of time in quantum gravity. I also study similarity relational particle mechanics (`dynamics of pure shape'), in which only relative times, relative angles and ratios of relative separations are meaningful. This I consider firstly as it is simpler, particularly in 1 and 2 d, for which the configuration space geometry turns out to be well-known, e.g. S^2 for the `triangleland' (3-particle) case considered in detail. Secondly, the similarity model occurs as a submodel within the Euclidean model: that admits a shape-scale split. For harmonic osc...

  3. Dynamics in carbon exchange fluxes for a grazed semi-arid savanna ecosystem in West Africa

    DEFF Research Database (Denmark)

    Tagesson, Torbern; Fensholt, Rasmus; Cropley, Ford;

    2015-01-01

    The main aim of this paper is to study land-atmosphere exchange of carbon dioxide (CO2) for semi-arid savanna ecosystems of the Sahel region and its response to climatic and environmental change. A subsidiary aim is to study and quantify the seasonal dynamics in light use efficiency (ε) being a key...... variable in scaling carbon fluxes from ground observations using earth observation data. The net ecosystem exchange of carbon dioxide (NEE) 2010-2013 was measured using the eddy covariance technique at a grazed semi-arid savanna site in Senegal, West Africa. Night-time NEE was not related to temperature...

  4. The Dynamic Relationship Between Stock Prices and Exchange Rates: Evidence from Four Transition Economies

    OpenAIRE

    Morales, Lucia

    2007-01-01

    This article examines the dynamic relationship between exchange rates and stock prices in four Easter European markets, Czech Republic, Hungary, Poland and Slovakia, using stock price and exchange rate data from these countries, as well as stock prices from the United States, Germany and the United Kingdom. The data set consists of daily data over a 7 year period from 1999 to 2006. Both the long-run and the short-run association between these variables are analyzed. We employed the Johansen c...

  5. Tunneling Dynamics of Two-Species Bose-Einstein Condensates

    Institute of Scientific and Technical Information of China (English)

    YANG Li-Min; YU Zhao-Xian; JIAO Zhi-Yong

    2003-01-01

    We have studied the tunneling dynamics of two-species Bose-Einstein condensates. It is shown that the population difference and the Josephson-like tunneling current between the two condensates exhibit oscillation behaviors and there exists macroscopic quantum self-trapping, which strongly depends on the initial state, interatomic nonlinear self-interaction, interspecies nonlinear interaction, and the total number of atoms in the two condensates.

  6. Relative species abundance of replicator dynamics with sparse interactions

    CERN Document Server

    Obuchi, Tomoyuki; Tokita, Kei

    2016-01-01

    A theory of relative species abundance on sparsely-connected networks is presented by investigating the replicator dynamics with symmetric interactions. Sparseness of a network involves difficulty in analyzing the fixed points of the equation, and we avoid this problem by treating large self interaction $u$, which allows us to construct a perturbative expansion. Based on this perturbation, we find that the nature of the interactions is directly connected to the abundance distribution, and some characteristic behaviors, such as multiple peaks in the abundance distribution and all species coexistence at moderate values of $u$, are discovered in a wide class of the distribution of the interactions. The all species coexistence collapses at a critical value of $u$, $u_c$, and this collapsing is regarded as a phase transition. To get more quantitative information, we also construct a non-perturbative theory on random graphs based on techniques of statistical mechanics. The result shows those characteristic behavior...

  7. Oxytocin receptor dynamics in the brain across development and species.

    Science.gov (United States)

    Vaidyanathan, Radhika; Hammock, Elizabeth A D

    2017-02-01

    Oxytocin (OXT) signaling through the OXT receptor plays a significant role in a variety of physiological processes throughout the lifespan. OXT's effects depend on the tissue distribution of the receptor. This tissue specificity is dynamic and changes across development, and also varies with sex, experience, and species. The purpose of this review is to highlight these themes with examples from several life stages and several species. Important knowledge gaps will also be emphasized. Understanding the effective sites of action for OXT via its receptor will help refine hypotheses about the roles of this important neuropeptide in the experience-dependent development and expression of species-typical social behavior. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 143-157, 2017. © 2016 Wiley Periodicals, Inc.

  8. Dynamics of catalytic resolution of 2-lithio-N-Boc-piperidine by ligand exchange.

    Science.gov (United States)

    Beng, Timothy K; Tyree, William S; Parker, Trent; Su, Chicheung; Williard, Paul G; Gawley, Robert E

    2012-10-10

    The dynamics of the racemization and catalytic and stoichiometric dynamic resolution of 2-lithio-N-Boc-piperidine (7) have been investigated. The kinetic order in tetramethylethylenediamine (TMEDA) for both racemization and resolution of the title compound and the kinetic orders in two resolving ligands have been determined. The catalytic dynamic resolution is second order in TMEDA and 0.5 and 0.265 order in chiral ligands 8 and 10, respectively. The X-ray crystal structure of ligand 10 shows it to be an octamer. Dynamic NMR studies of the resolution process were carried out. Some of the requirements for a successful catalytic dynamic resolution by ligand exchange have been identified.

  9. Population dynamics of species-rich ecosystems: the mixture of matrix population models approach

    DEFF Research Database (Denmark)

    Mortier, Frédéric; Rossi, Vivien; Guillot, Gilles;

    2013-01-01

    Matrix population models are widely used to predict population dynamics, but when applied to species-rich ecosystems with many rare species, the small population sample sizes hinder a good fit of species-specific models. This issue can be overcome by assigning species to groups to increase the size...... species with similar population dynamics....

  10. Anti-inflammatory activity of human IgG4 antibodies by dynamic Fab arm exchange.

    Science.gov (United States)

    van der Neut Kolfschoten, Marijn; Schuurman, Janine; Losen, Mario; Bleeker, Wim K; Martínez-Martínez, Pilar; Vermeulen, Ellen; den Bleker, Tamara H; Wiegman, Luus; Vink, Tom; Aarden, Lucien A; De Baets, Marc H; van de Winkel, Jan G J; Aalberse, Rob C; Parren, Paul W H I

    2007-09-14

    Antibodies play a central role in immunity by forming an interface with the innate immune system and, typically, mediate proinflammatory activity. We describe a novel posttranslational modification that leads to anti-inflammatory activity of antibodies of immunoglobulin G, isotype 4 (IgG4). IgG4 antibodies are dynamic molecules that exchange Fab arms by swapping a heavy chain and attached light chain (half-molecule) with a heavy-light chain pair from another molecule, which results in bispecific antibodies. Mutagenesis studies revealed that the third constant domain is critical for this activity. The impact of IgG4 Fab arm exchange was confirmed in vivo in a rhesus monkey model with experimental autoimmune myasthenia gravis. IgG4 Fab arm exchange is suggested to be an important biological mechanism that provides the basis for the anti-inflammatory activity attributed to IgG4 antibodies.

  11. Real-time observation of cation exchange kinetics and dynamics at the muscovite-water interface

    Science.gov (United States)

    Lee, Sang Soo; Fenter, Paul; Nagy, Kathryn L.; Sturchio, Neil C.

    2017-06-01

    Ion exchange at charged solid-liquid interfaces is central to a broad range of chemical and transport phenomena. Real-time observations of adsorption/desorption at the molecular-scale elucidate exchange reaction pathways. Here we report temporal variation in the distribution of Rb+ species at the muscovite (001)-water interface during exchange with Na+. Time-resolved resonant anomalous X-ray reflectivity measurements at 25 °C reveal that Rb+ desorption occurs over several tens of seconds during which thermodynamically stable inner-sphere Rb+ slowly transforms to a less stable outer-sphere Rb+. In contrast, Rb+ adsorption is about twice as fast, proceeding from Rb+ in the bulk solution to the stable inner-sphere species. The Arrhenius plot of the adsorption/desorption rate constants measured from 9 to 55 °C shows that the pre-exponential factor for desorption is significantly smaller than that for adsorption, indicating that this reduced attempt frequency of cation detachment largely explains the slow cation exchange processes at the interface.

  12. Biomass and leaf-level gas exchange characteristics of three African savanna C4 grass species under optimum growth conditions

    NARCIS (Netherlands)

    Mantlana, K.B.; Veenendaal, E.M.; Arneth, A.; Grispen, V.; Bonyongo, C.M.; Heitkönig, I.M.A.; Lloyd, J.

    2009-01-01

    C4 savanna grass species, Digitaria eriantha, Eragrostis lehmanniana and Panicum repens, were grown under optimum growth conditions with the aim of characterizing their above- and below-ground biomass allocation and the response of their gas exchange to changes in light intensity, CO2 concentration

  13. Ion exchange in alginate gels--dynamic behaviour revealed by electron paramagnetic resonance.

    Science.gov (United States)

    Ionita, Gabriela; Ariciu, Ana Maria; Smith, David K; Chechik, Victor

    2015-12-14

    The formation of alginate gel from low molecular weight alginate and very low molecular weight alginate in the presence of divalent cations was investigated using Electron Paramagnetic Resonance (EPR) spectroscopy. The transition from sol to gel in the presence of divalent cations was monitored by the changes in the dynamics of spin labelled alginate. The immobilisation of the spin labelled alginate in the gel reflects the strength of interaction between the cation and alginate chain. Diffusion experiments showed that both the cation and alginate polyanion in the gel fibres can exchange with molecules in solution. In particular, we showed that dissolved alginate polyanions can replace alginates in the gel fibres, which can hence diffuse through the bulk of the gel. This illustrates the surprisingly highly dynamic nature of these gels and opens up the possibility of preparing multicomponent alginate gels via polyanion exchange process.

  14. Water hexamer: Self-consistent phonons versus reversible scaling versus replica exchange molecular dynamics

    CERN Document Server

    Brown, Sandra E

    2014-01-01

    Classical free energies for the cage and prism isomers of water hexamer computed by the self- consistent phonons (SCP) method and reversible scaling (RS) method are presented for several flexible water potentials. Both methods have been augmented with a rotational correction for improved accuracy when working with clusters. Comparison of the SCP results with the RS results suggests a fairly broad temperature range over which the SCP approximation can be expected to give accurate results for systems of water clusters, and complements a previously reported assessment of SCP. Discrepancies between the SCP and RS results presented here, and recently published replica exchange molecular dynamics (REMD) results bring into question the convergence of the REMD and accompanying replica exchange path integral molecular dynamics results. In addition to the ever-present specter of unconverged results, several possible sources for the discrepancy are explored based on inherent characteristics of the methods used.

  15. Energy exchange analysis in droplet dynamics via the Navier–Stokes–Cahn–Hilliard model

    KAUST Repository

    Espath, L. F. R.

    2016-05-23

    We develop the energy budget equation of the coupled Navier-Stokes-Cahn-Hilliard (NSCH) system. We use the NSCH equations to model the dynamics of liquid droplets in a liquid continuum. Buoyancy effects are accounted for through the Boussinesq assumption. We physically interpret each quantity involved in the energy exchange to gain further insight into the model. Highly resolved simulations involving density-driven flows and the merging of droplets allow us to analyse these energy budgets. In particular, we focus on the energy exchanges when droplets merge, and describe flow features relevant to this phenomenon. By comparing our numerical simulations to analytical predictions and experimental results available in the literature, we conclude that modelling droplet dynamics within the framework of NSCH equations is a sensible approach worthy of further research. © 2016 Cambridge University Press.

  16. Dynamic Simulation of a Proton Exchange Membrane Fuel Cell System For Automotive Applications

    DEFF Research Database (Denmark)

    Rabbani, Raja Abid; Rokni, Masoud

    2012-01-01

    A dynamic model of the PEMFC system is developed to investigate the behaviour and transient response of the fuel cell system for automotive applications. The system accounts for the fuel cell stack with coolant, humidifier, heat exchangers and pumps. Governing equations for fuel cell and humidifier...... sufficient insight for further in-depth analysis of PEMFC and prove to be a basis for efficient control and design methodologies....

  17. Dynamic Conditional Correlations in International Stock, Bond and Foreign Exchange Markets: Emerging Markets Evidence

    OpenAIRE

    2009-01-01

    textabstractThe paper models the dynamic conditional correlations in emerging stock, bond and foreign exchange markets using the DCC model of Engle (2002) and the GARCC model of McAleer et al. (2008). The highly restrictive DCC model suggests that the conditional correlations of the overall returns are constant. In contrast, the GARCC model finds that the conditional correlations between bond-bond markets and between stock-stock markets are relatively constant across developed-emerging market...

  18. Hybrid dynamics in a species group of swallowtail butterflies.

    Science.gov (United States)

    Dupuis, J R; Sperling, F A H

    2016-10-01

    Hybrid zones provide unique natural laboratories for studying mechanisms of evolution. But identification and classification of hybrid individuals (F1, F2, backcross, etc.) can be complicated by real population changes over time as well as by use of different marker types, both of which challenge documentation of hybrid dynamics. Here, we use multiple genetic markers (mitochondrial DNA, microsatellites and genomewide single nucleotide polymorphisms) to re-examine population structure in a hybrid zone between two species of swallowtail butterflies in western Canada, Papilio machaon and P. zelicaon. Our aim was to test whether their hybrid dynamics remain the same as found 30 years ago using morphology and allozymes, and we compared different genetic data sets as well as alternative hybrid identification and classification methods. Overall, we found high differentiation between the two parental species, corroborating previous research from the 1980s. We identified fewer hybrid individuals in the main zone of hybridization in recent years, but this finding depended on the genetic markers considered. Comparison of methods with simulated data sets generated from our data showed that single nucleotide polymorphisms were more powerful than microsatellites for both hybrid identification and classification. Moreover, substantial variation among comparisons underlined the value of multiple markers and methods for documenting evolutionarily dynamic systems.

  19. Gas exchange in Paulownia species growing under different soil moisture conditions in the field.

    Science.gov (United States)

    Llano-Sotelo, J M; Alcaraz-Melendez, L; Castellanos Villegas, A E

    2010-07-01

    In order to evaluate their responses to drought, we determined the photosynthetic activity water potential, stomatal conductance, transpiration, water use efficiency photosynthetic photon flux density and leaf temperature of Paulownia imperialis, P. fortunei and P. elongata in three different soil moisture conditions in the field. Our results showed that P. imperialis had greater photosynthesis (8.86 micromol CO2 m(-2) s(-1)) and instantaneous water use efficiency (0.79 micromol CO2 mmol H2O(-1)) than either P. elongata (8.20 micromol CO2 m(-2) s(-1) and 0.71 micromol CO2 mmol H2O(-1)) or P. fortunei (3.26 micromol CO2 m(-2) s(-1) and 0.07 micromol CO2 mmol H2O(-1)). The rapid growth of Paulownia did not appear to be correlated with photosynthetic rates. Paulownia fortunei showed more transpiration (48.78 mmol H2O m(-2) s(-1)) and stomatal conductance (840 mmol m(-2) s(-1)) than P. imperialis (20 mmol H2O m(-2) s(-1) and 540 mmol m(-2) s(-1)) and P. elongata (20 mmol H2O m(-2) s(-1) and 410 mmol m(-2) s(-1)), which allowed these two Paulownia species to increase their tolerance to low soil moisture, and maintain higher water use efficiency under these conditions. According to our physiological gas exchange field tests, Paulownia imperialis does appear to be capable of successful growth in semiarid zones.

  20. Combining Ballast Water Exchange and Treatment To Maximize Prevention of Species Introductions to Freshwater Ecosystems.

    Science.gov (United States)

    Briski, Elizabeta; Gollasch, Stephan; David, Matej; Linley, R Dallas; Casas-Monroy, Oscar; Rajakaruna, Harshana; Bailey, Sarah A

    2015-08-18

    The most effective way to manage species transfers is to prevent their introduction via vector regulation. Soon, international ships will be required to meet numeric ballast discharge standards using ballast water treatment (BWT) systems, and ballast water exchange (BWE), currently required by several countries, will be phased out. However, there are concerns that BWT systems may not function reliably in fresh and/or turbid water. A land-based evaluation of simulated "BWE plus BWT" versus "BWT alone" demonstrated potential benefits of combining BWE with BWT for protection of freshwater ecosystems. We conducted ship-based testing to compare the efficacy of "BWE plus BWT" versus "BWT alone" on voyages starting with freshwater ballast. We tested the hypotheses that there is an additional effect of "BWE plus BWT" compared to "BWT alone" on the reduction of plankton, and that taxa remaining after "BWE plus BWT" will be marine (low risk for establishment at freshwater recipient ports). Our study found that BWE has significant additional effect on the reduction of plankton, and this effect increases with initial abundance. As per expectations, "BWT alone" tanks contained higher risk freshwater or euryhaline taxa at discharge, while "BWE plus BWT" tanks contained mostly lower risk marine taxa unlikely to survive in recipient freshwater ecosystems.

  1. Influence of dynamic crystallization on exchange-coupled NdFeB nanocrystalline permanent magnets

    Institute of Scientific and Technical Information of China (English)

    ZHANG Ran; LIU Ying; MA Yilong; ZHANG Longfeng; XU Jianchuan; GAO Shengji

    2006-01-01

    Dynamic crystallization was introduced to improve the magnetic properties of NdFeB nanocrystalline permanent magnets by optimizing microstructure. The microstructure was studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It has been determined that, compared with the conventional heat treatment, dynamic crystallization can shorten the crystallization time. Moreover, dynamic crystallization can refine grains, enhance the exchange-coupled interaction among grains, and promote the magnetic properties. As a result, the optimal magnetic properties of Nd10.5(FeCoZr)83.4B6.1(Br=0.685T, Hci =732 kA·m -1 , Hcb =429 kA·m-1 ,( BH )m=75 kJ·m -3 ) are obtained after dynamic crystallization heat treatment at 700 ℃ for 10 min.

  2. Cross-species gene-family fluctuations reveal the dynamics of horizontal transfers.

    Science.gov (United States)

    Grilli, Jacopo; Romano, Mariacristina; Bassetti, Federico; Cosentino Lagomarsino, Marco

    2014-06-01

    Prokaryotes vary their protein repertoire mainly through horizontal transfer and gene loss. To elucidate the links between these processes and the cross-species gene-family statistics, we perform a large-scale data analysis of the cross-species variability of gene-family abundance (the number of members of the family found on a given genome). We find that abundance fluctuations are related to the rate of horizontal transfers. This is rationalized by a minimal theoretical model, which predicts this link. The families that are not captured by the model show abundance profiles that are markedly peaked around a mean value, possibly because of specific abundance selection. Based on these results, we define an abundance variability index that captures a family's evolutionary behavior (and thus some of its relevant functional properties) purely based on its cross-species abundance fluctuations. Analysis and model, combined, show a quantitative link between cross-species family abundance statistics and horizontal transfer dynamics, which can be used to analyze genome 'flux'. Groups of families with different values of the abundance variability index correspond to genome sub-parts having different plasticity in terms of the level of horizontal exchange allowed by natural selection.

  3. On the dynamical behavior of three species food web model

    Energy Technology Data Exchange (ETDEWEB)

    Naji, R.K. [Department of Mathematics, College of Science, University of Baghdad (Iraq)]. E-mail: rknaji@yahoo.com; Balasim, A.T. [Department of Mathematics, College of Science, University of Baghdad (Iraq)]. E-mail: alkhazrejy@yahoo.com

    2007-12-15

    In this paper, a mathematical model consisting of two preys one predator with Beddington-DeAngelis functional response is proposed and analyzed. The local stability analysis of the system is carried out. The necessary and sufficient conditions for the persistence of three species food web model are obtained. For the biologically reasonable range of parameter values, the global dynamics of the system has been investigated numerically. Number of bifurcation diagrams has been obtained; Lyapunov exponents have been computed for different attractor sets. It is observed that the model has different types of attractors including chaos.

  4. Seasonal trends in reduced leaf gas exchange and ozone-induced foliar injury in three ozone sensitive woody plant species

    Energy Technology Data Exchange (ETDEWEB)

    Novak, K. [Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zuercherstrasse 111, 8903 Birmensdorf (Switzerland)]. E-mail: kristopher.novak@wsl.ch; Schaub, M. [Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zuercherstrasse 111, 8903 Birmensdorf (Switzerland); Fuhrer, J. [Swiss Federal Research Station for Agroecology and Agriculture FAL, 8046 Zurich (Switzerland); Skelly, J.M. [Department of Plant Pathology, The Pennsylvania State University, University Park, PA 16802 (United States); Hug, C. [Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zuercherstrasse 111, 8903 Birmensdorf (Switzerland); Landolt, W. [Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zuercherstrasse 111, 8903 Birmensdorf (Switzerland); Bleuler, P. [Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zuercherstrasse 111, 8903 Birmensdorf (Switzerland); Kraeuchi, N. [Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zuercherstrasse 111, 8903 Birmensdorf (Switzerland)

    2005-07-15

    Seasonal trends in leaf gas exchange and ozone-induced visible foliar injury were investigated for three ozone sensitive woody plant species. Seedlings of Populus nigra L., Viburnum lantana L., and Fraxinus excelsior L. were grown in charcoal-filtered chambers, non-filtered chambers and open plots. Injury assessments and leaf gas exchange measurements were conducted from June to October during 2002. All species developed typical ozone-induced foliar injury. For plants exposed to non-filtered air as compared to the charcoal-filtered air, mean net photosynthesis was reduced by 25%, 21%, and 18% and mean stomatal conductance was reduced by 25%, 16%, and 8% for P. nigra, V. lantana, and F. excelsior, respectively. The timing and severity of the reductions in leaf gas exchange were species specific and corresponded to the onset of visible foliar injury. - Reductions in leaf gas exchange corresponded to the onset of ozone-induced visible foliar injury for seedlings exposed to ambient ozone exposures.

  5. A molecular dynamics study of bond exchange reactions in covalent adaptable networks.

    Science.gov (United States)

    Yang, Hua; Yu, Kai; Mu, Xiaoming; Shi, Xinghua; Wei, Yujie; Guo, Yafang; Qi, H Jerry

    2015-08-21

    Covalent adaptable networks are polymers that can alter the arrangement of network connections by bond exchange reactions where an active unit attaches to an existing bond then kicks off its pre-existing peer to form a new bond. When the polymer is stretched, bond exchange reactions lead to stress relaxation and plastic deformation, or the so-called reforming. In addition, two pieces of polymers can be rejoined together without introducing additional monomers or chemicals on the interface, enabling welding and reprocessing. Although covalent adaptable networks have been researched extensively in the past, knowledge about the macromolecular level network alternations is limited. In this study, molecular dynamics simulations are used to investigate the macromolecular details of bond exchange reactions in a recently reported epoxy system. An algorithm for bond exchange reactions is first developed and applied to study a crosslinking network formed by epoxy resin DGEBA with the crosslinking agent tricarballylic acid. The trace of the active units is tracked to show the migration of these units within the network. Network properties, such as the distance between two neighboring crosslink sites, the chain angle, and the initial modulus, are examined after each iteration of the bond exchange reactions to provide detailed information about how material behaviors and macromolecular structure evolve. Stress relaxation simulations are also conducted. It is found that even though bond exchange reactions change the macroscopic shape of the network, microscopic network characteristic features, such as the distance between two neighboring crosslink sites and the chain angle, relax back to the unstretched isotropic state. Comparison with a recent scaling theory also shows good agreement.

  6. The influence of macroeconomic factors to the dynamics of stock exchange in the republic of Kazakhstan

    Directory of Open Access Journals (Sweden)

    Shakizada Uteulievna Niyazbekova

    2016-12-01

    Full Text Available This article describes the influence of macroeconomic factors on Kazakhstan Stock Exchange Market by using data from 2005 to 2014. Engle-Granger cointegration test has shown that stock index is cointegrated with the exchange rate, interest rate, CPI and oil price. Vector error correction model has confirmed that macroeconomic variables and the stock index has a long-term equilibrium relationship. Moreover, empirical results have shown that stock index can be used as a leading indicator of the economic situation in Kazakhstan. Therefore, the authors decided to consider the impact of major macroeconomic indicators to the dynamics of the stock market of the Republic of Kazakhstan. The Engle-Granger cointegration test results show that the following variables such as exchange rate, 10-years long-term bond rate, the consumer price index and the Brent oil price are cointegrated with stock index, which means that there is a long-term relationship between this stock market index and these variables. With the help of econometric models, the authors have found the factors such as the exchange rate, the 10-year long-term bonds rate, the consumer price index and the Brent oil price (these factors have the long-term relationship with stock market index. Changes in the dynamics of the stock market index in Kazakhstan are caused by changes in the dynamics of Central bank's reserves and export. The analysis has shown that the economy of the Republic of Kazakhstan (the index reflects the situation in the real sector of the economy remains dependent on world oil prices, the volume of exports and the rate of the national currency

  7. Hydrogen-deuterium exchange mass spectrometry for investigation of backbone dynamics of oxidized and reduced cytochrome P450cam.

    Science.gov (United States)

    Hamuro, Yoshitomo; Molnar, Kathleen S; Coales, Stephen J; OuYang, Bo; Simorellis, Alana K; Pochapsky, Thomas C

    2008-02-01

    Backbone dynamics of the camphor monoxygenase cytochrome P450(cam) (CYP101) as a function of oxidation/ligation state of the heme iron were investigated via hydrogen/deuterium exchange (H/D exchange) as monitored by mass spectrometry. Main chain amide NH hydrogens can exchange readily with solvent and the rate of this exchange depends upon, among other things, dynamic fluctuations in local structural elements. A fluxional region of the polypeptide will exchange more quickly with solvent than one that is more constrained. In most regions of the enzyme, exchange rates were similar between oxidized high-spin camphor-bound and reduced camphor- and CO-bound CYP101 (CYP-S and CYP-S-CO, respectively). However, in regions of the protein that have previously been implicated in substrate access by structural and molecular dynamics investigations, the reduced enzyme shows significantly slower exchange rates than the oxidized CYP-S. This observation corresponds to increased flexibility of the oxidized enzyme relative to the reduced form. Structural features previously found to be perturbed in CYP-S-CO upon binding of the biologically relevant effector and reductant putidaredoxin (Pdx) as determined by nuclear magnetic resonance are also more protected from exchange in the reduced state. To our knowledge, this study represents the first experimental investigation of backbone dynamics within the P450 family using this methodology.

  8. The plastoquinol-plastoquinone exchange mechanism in photosystem II: insight from molecular dynamics simulations.

    Science.gov (United States)

    Zobnina, Veranika; Lambreva, Maya D; Rea, Giuseppina; Campi, Gaetano; Antonacci, Amina; Scognamiglio, Viviana; Giardi, Maria Teresa; Polticelli, Fabio

    2017-01-01

    In the photosystem II (PSII) of oxygenic photosynthetic organisms, the reaction center (RC) core mediates the light-induced electron transfer leading to water splitting and production of reduced plastoquinone molecules. The reduction of plastoquinone to plastoquinol lowers PSII affinity for the latter and leads to its release. However, little is known about the role of protein dynamics in this process. Here, molecular dynamics simulations of the complete PSII complex embedded in a lipid bilayer have been used to investigate the plastoquinol release mechanism. A distinct dynamic behavior of PSII in the presence of plastoquinol is observed which, coupled to changes in charge distribution and electrostatic interactions, causes disruption of the interactions seen in the PSII-plastoquinone complex and leads to the "squeezing out" of plastoquinol from the binding pocket. Displacement of plastoquinol closes the second water channel, recently described in a 2.9 Å resolution PSII structure (Guskov et al. in Nat Struct Mol Biol 16:334-342, 2009), allowing to rule out the proposed "alternating" mechanism of plastoquinol-plastoquinone exchange, while giving support to the "single-channel" one. The performed simulations indicated a pivotal role of D1-Ser264 in modulating the dynamics of the plastoquinone binding pocket and plastoquinol-plastoquinone exchange via its interaction with D1-His252 residue. The effects of the disruption of this hydrogen bond network on the PSII redox reactions were experimentally assessed in the D1 site-directed mutant Ser264Lys.

  9. Patchiness of ion-exchanged mica revealed by DNA binding dynamics at short length scales

    Science.gov (United States)

    Billingsley, D. J.; Lee, A. J.; Johansson, N. A. B.; Walton, A.; Stanger, L.; Crampton, N.; Bonass, W. A.; Thomson, N. H.

    2014-01-01

    The binding of double-stranded (ds) DNA to mica can be controlled through ion-exchanging the mica with divalent cations. Measurements of the end-to-end distance of linear DNA molecules discriminate whether the binding mechanism occurs through 2D surface equilibration or kinetic trapping. A range of linear dsDNA fragments have been used to investigate length dependences of binding. Mica, ion-exchanged with Ni(II) usually gives rise to kinetically trapped DNA molecules, however, short linear fragments (ion-exchanged mica is heterogeneous, and contains patches or domains, separating different ionic species. These results correlate with imaging of dsDNA under aqueous buffer on Ni(II)-mica and indicate that binding domains are of the order of 100 nm in diameter. Shorter DNA fragments behave intermediate to the two extreme cases of 2D equilibration and kinetic trapping. Increasing the incubation time of Ni(II) on mica, from minutes to hours, brings the conformations of the shorter DNA fragments closer to the theoretical value for kinetic trapping, indicating that long timescale kinetics play a role in ion-exchange. X-ray photoelectron spectroscopy (XPS) was used to confirm that the relative abundance of Ni(II) ions on the mica surface increases with time. These findings can be used to enhance spatial control of binding of DNA to inorganic surfaces with a view to patterning high densities arrays.

  10. General Formalism of Mass Scaling Approach for Replica-Exchange Molecular Dynamics and its Application

    Science.gov (United States)

    Nagai, Tetsuro

    2017-01-01

    Replica-exchange molecular dynamics (REMD) has demonstrated its efficiency by combining trajectories of a wide range of temperatures. As an extension of the method, the author formalizes the mass-manipulating replica-exchange molecular dynamics (MMREMD) method that allows for arbitrary mass scaling with respect to temperature and individual particles. The formalism enables the versatile application of mass-scaling approaches to the REMD method. The key change introduced in the novel formalism is the generalized rules for the velocity and momentum scaling after accepted replica-exchange attempts. As an application of this general formalism, the refinement of the viscosity-REMD (V-REMD) method [P. H. Nguyen, https://doi.org/10.1063/1.3369626" xlink:type="simple">J. Chem. Phys. 132, 144109 (2010)] is presented. Numerical results are provided using a pilot system, demonstrating easier and more optimized applicability of the new version of V-REMD as well as the importance of adherence to the generalized velocity scaling rules. With the new formalism, more sound and efficient simulations will be performed.

  11. Isovector meson-exchange currents in the light-front dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Desplanques, B. [Grenoble-1 Univ., 38 (France). Inst. des Sciences Nucleaires; Karmanov, V.A. [Grenoble-1 Univ., 38 (France). Inst. des Sciences Nucleaires; Mathiot, J.F. [Division de Physique Theorique, Institut de Physique Nucleaire, F-91406 Orsay Cedex (France)

    1995-07-17

    In the light-front dynamics, there is no pair term that plays the role of the dominant isovector pion exchange current. This current gives rise to the large and experimentally observed contribution to the deuteron electrodisintegration cross-section near threshold for pseudo-scalar {pi}NN coupling. We show analytically that in leading 1/m order the amplitude in the light-front dynamics coincides, however, with the one given by the pair term. At high Q{sup 2}, it consists of two equal parts. One comes from extra components of the deuteron and final state relativistic wave functions. The other results from the contact NN{pi}{gamma} interaction which appears in the light-front dynamics. This provides a transparent link between relativistic and non-relativistic approaches. ((orig.)).

  12. Folding of SAM-II riboswitch explored by replica-exchange molecular dynamics simulation.

    Science.gov (United States)

    Xue, Xu; Yongjun, Wang; Zhihong, Li

    2015-01-21

    Riboswitches are cis-acting RNA fragments that function via a conformational transition mechanism when a specific target molecule binds to its binding pocket, representing an inviting new class of biomolecular target for the development of antibiotics. To understand the folding mechanism of SAM-II riboswitch, occurring predominantly in proteobacteria, a 100ns replica-exchange molecular dynamics simulation in explicit solvent is performed. Our results show that this RNA pseudoknot has multiple folding pathways, and various intermediate structures. The resultant riboswitch conformational transition map is well consistent with the recent fluorescence measurement, which confirms the dynamical properties of this pseudoknot. Moreover, a novel transition pathway is predicted. The global folding dynamics is mainly coupled with the helix rather than the loop region. The potential folding pathways of the riboswitch presented here should lead to a deeper understanding of the folding mechanism of the riboswitch, as well as the conformational change of RNA pseudoknot.

  13. Dynamic screening in a two-species asymmetric exclusion process.

    Science.gov (United States)

    Kim, Kyung Hyuk; den Nijs, Marcel

    2007-08-01

    The dynamic scaling properties of the one-dimensional Burgers equation are expected to change with the inclusion of additional conserved degrees of freedom. We study this by means of one-dimensional (1D) driven lattice gas models that conserve both mass and momentum. The most elementary version of this is the Arndt-Heinzel-Rittenberg (AHR) process, which is usually presented as a two-species diffusion process, with particles of opposite charge hopping in opposite directions and with a variable passing probability. From the hydrodynamics perspective this can be viewed as two coupled Burgers equations, with the number of positive and negative momentum quanta individually conserved. We determine the dynamic scaling dimension of the AHR process from the time evolution of the two-point correlation functions, and find numerically that the dynamic critical exponent is consistent with simple Kardar-Parisi-Zhang- (KPZ) type scaling. We establish that this is the result of perfect screening of fluctuations in the stationary state. The two-point correlations decay exponentially in our simulations and in such a manner that in terms of quasiparticles, fluctuations fully screen each other at coarse grained length scales. We prove this screening rigorously using the analytic matrix product structure of the stationary state. The proof suggests the existence of a topological invariant. The process remains in the KPZ universality class but only in the sense of a factorization, as (KPZ)2. The two Burgers equations decouple at large length scales due to the perfect screening.

  14. Effect of tube-support interaction on the dynamic responses of heat exchanger tubes. [LMFBR

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Y.S.; Jendrzejczyk, J.A.; Wambsganss, M.W.

    1977-01-01

    Operating heat exchangers have experienced tube damages due to excessive flow-induced vibration. The relatively small inherent tube-to-baffle hole clearances associated with manufacturing tolerances in heat exchangers affect the tube vibrational characteristics. In attempting a theoretical analysis, questions arise as to the effects of tube-baffle impacting on dynamic responses. Experiments were performed to determine the effects of tube-baffle impacting in vertical/horizontal tube orientation, and in air/water medium on the vibrational characteristics (resonant frequencies, mode shapes, and damping) and displacement response amplitudes of a seven-span tube model. The tube and support conditions were prototypic, and overall length approximately one-third that of a straight tube segment of the steam generator designed for the CRBR. The test results were compared with the analytical results based on the multispan beam with ''knife-edge'' supports.

  15. Simulating the frontal instability of lock-exchange density currents with dissipative particle dynamics

    Science.gov (United States)

    Li, Yanggui; Geng, Xingguo; Wang, Heping; Zhuang, Xin; Ouyang, Jie

    2016-06-01

    The frontal instability of lock-exchange density currents is numerically investigated using dissipative particle dynamics (DPD) at the mesoscopic particle level. For modeling two-phase flow, the “color” repulsion model is adopted to describe binary fluids according to Rothman-Keller method. The present DPD simulation can reproduce the flow phenomena of lock-exchange density currents, including the lobe-and-cleft instability that appears at the head, as well as the formation of coherent billow structures at the interface behind the head due to the growth of Kelvin-Helmholtz instability. Furthermore, through the DPD simulation, some small-scale characteristics can be observed, which are difficult to be captured in macroscopic simulation and experiment.

  16. How Is cis-trans Isomerization Controlled in Dronpa Mutants? A Replica Exchange Molecular Dynamics Study.

    Science.gov (United States)

    Moors, Samuel L C; Michielssens, Servaas; Flors, Cristina; Dedecker, Peter; Hofkens, Johan; Ceulemans, Arnout

    2008-06-01

    The reversibly photoactivatable green fluorescent protein analog Dronpa holds great promise as a marker for various new cellular imaging applications. Using a replica exchange method which combines both Hamiltonian and temperature exchanges, the ground-state dynamics of Dronpa and two mutants with increased switching kinetics, Val157Gly and Met159Thr, were compared. The dominant chromophore state was found to be the cis isomer in all three proteins. The simulation data suggest that both mutations strongly increase the chromophore flexibility and cis-trans isomerization rate. We identify three key amino acids, Val157, Met159, and Phe173, which are able to impede the bottom hula-twist transition path, depending on their position and rotameric state. We believe our insights will help to understand the switching process and provide useful information for the design of new variants with improved fluorescence properties.

  17. Dynamic Regulation of Histone Modifications in Xenopus Oocytes through Histone Exchange

    Science.gov (United States)

    Stewart, M. David; Sommerville, John; Wong, Jiemin

    2006-01-01

    Histone H3 lysine 9 (H3K9) methylation has broad roles in transcriptional repression, gene silencing, maintenance of heterochromatin, and epigenetic inheritance of heterochromatin. Using Xenopus laevis oocytes, we have previously shown that targeting G9a, an H3K9 histone methyltransferase, to chromatin increases H3K9 methylation and consequently represses transcription. Here we report that treatment with trichostatin A induces histone acetylation and is sufficient to activate transcription repressed by G9a, and this activation is accompanied by a reduction in dimethyl H3K9 (H3K9me2). We tested the possibility that the reduction in H3K9me2 was due to the replacement of methylated H3 with unmethylated H3.3. Surprisingly, we found that both free H3 and H3.3 are continually exchanged with chromatin-associated histones. This dynamic exchange of chromatin-associated H3 with free H3/H3.3 was not affected by alterations in transcriptional activity, elongation, acetylation, H3K9 methylation, or DNA replication. In support of this continual histone exchange model, we show that maintenance of H3K9 methylation at a specific site requires the continual presence of an H3K9 histone methyltransferase. Upon dissociation of the methyltransferase, H3K9 methylation decreases. Taken together, our data suggest that chromatin-associated and non-chromatin-associated histones are continually exchanged in the Xenopus oocyte, creating a highly dynamic chromatin environment. PMID:16943430

  18. Ultrafast Study of Dynamic interfacial Exchange Coupling in Ferromagnet/Oxide/Semiconductor Heterostructures

    Science.gov (United States)

    Ou, Yu-Sheng; Chiu, Yi-Hsin; Harmon, Nicholas; Odenthal, Patrick; Sheffield, Matthew; Chilcote, Michael; Kawakami, Roland; Flatté, Michael; Johnston-Halperin, Ezekiel

    Time-resolved Kerr/Faraday rotation (TRKR/TRFR) is employed to study GaAs spin dynamics in the regime of strong and dynamic exchange coupling to an adjacent MgO/Fe layer. This study reveals a dramatic, resonant suppression in the inhomogeneous spin lifetime (T2*) in the GaAs layer. Further investigation of the magnetization dynamics of the neighboring Fe layer, also using TRKR/TRFR, reveals not only the expected Kittel-dispersion but also additional lower frequency modes with very short lifetime (65 ps) that are not easily observed with conventional ferromagnetic resonance (FMR) techniques. These results suggest the intriguing possibility of resonant dynamic spin transfer between the GaAs and Fe spin systems. We discuss the potential for this work to establish GaAs spin dynamics as an efficient detector of spin dissipation and transport in the regime of dynamically-driven spin injection in ferromagnet/semiconductor heterostructures. Center for Emergent Materials; U.S. Department of Energy.

  19. Gas exchange and growth responses to nutrient enrichment in invasive Glyceria maxima and native New Zealand Carex species

    DEFF Research Database (Denmark)

    Sorrell, Brian Keith; Brix, Hans; Fitridge, Isla

    2012-01-01

    We compared photosynthetic gas exchange, the photosynthesis-leaf nitrogen (N) relationship, and growth response to nutrient enrichment in the invasive wetland grass Glyceria maxima (Hartman) Holmburg with two native New Zealand Carex sedges (C. virgata Boott and C. secta Boott), to explore...... the ecophysiological traits contributing to invasive behaviour. The photosynthesis-nitrogen relationship was uniform across all three species, and the maximum light-saturated rate of photosynthesis expressed on a leaf area basis (Amaxa) did not differ significantly between species. However, specific leaf area (SLA...... the sedges, but correlations between leaf N, gas exchange parameters (Amaxa, Amaxm, Rd and gs) and RGR were all highly significant in G. maxima, whereas they were weak or absent in the sedges. Allocation of biomass (root:shoot ratio, leaf mass ratio, root mass ratio), plant N and P content, and allocation...

  20. Dynamic Control of Electric Output Characteristics of Proton Exchange Membrane Fuel Cell System

    Institute of Scientific and Technical Information of China (English)

    刘星则; 朱新坚

    2005-01-01

    This paper discusses dynamic characteristics of proton exchange membrane fuel cell (PEMFC) under rapid fluctuation of power demand. Wavelet neural network is adopted in the identification of the characteristic curve to predict the voltage. The system control scheme of the voltage and power is introduced. The corresponding schemes for voltage and power control are studied. MATLAB is used to simulate the control system. The results reveal that the adopted control schemes can produce expected effects. Corresponding anti-disturbance and robustness simulation are also carried out. The simulation results show that the implemented control schemes have better robustness and adaptability.

  1. Improving dynamic performance of proton-exchange membrane fuel cell system using time delay control

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Young-Bae [Mechanical Engineering Department, Chonnam National University, Gwangju (Korea)

    2010-10-01

    Transient behaviour is a key parameter for the vehicular application of proton-exchange membrane (PEM) fuel cell. The goal of this presentation is to construct better control technology to increase the dynamic performance of a PEM fuel cell. The PEM fuel cell model comprises a compressor, an injection pump, a humidifier, a cooler, inlet and outlet manifolds, and a membrane-electrode assembly. The model includes the dynamic states of current, voltage, relative humidity, stoichiometry of air and hydrogen, cathode and anode pressures, cathode and anode mass flow rates, and power. Anode recirculation is also included with the injection pump, as well as anode purging, for preventing anode flooding. A steady-state, isothermal analytical fuel cell model is constructed to analyze the mass transfer and water transportation in the membrane. In order to prevent the starvation of air and flooding in a PEM fuel cell, time delay control is suggested to regulate the optimum stoichiometry of oxygen and hydrogen, even when there are dynamical fluctuations of the required PEM fuel cell power. To prove the dynamical performance improvement of the present method, feed-forward control and Linear Quadratic Gaussian (LQG) control with a state estimator are compared. Matlab/Simulink simulation is performed to validate the proposed methodology to increase the dynamic performance of a PEM fuel cell system. (author)

  2. Improving dynamic performance of proton-exchange membrane fuel cell system using time delay control

    Science.gov (United States)

    Kim, Young-Bae

    Transient behaviour is a key parameter for the vehicular application of proton-exchange membrane (PEM) fuel cell. The goal of this presentation is to construct better control technology to increase the dynamic performance of a PEM fuel cell. The PEM fuel cell model comprises a compressor, an injection pump, a humidifier, a cooler, inlet and outlet manifolds, and a membrane-electrode assembly. The model includes the dynamic states of current, voltage, relative humidity, stoichiometry of air and hydrogen, cathode and anode pressures, cathode and anode mass flow rates, and power. Anode recirculation is also included with the injection pump, as well as anode purging, for preventing anode flooding. A steady-state, isothermal analytical fuel cell model is constructed to analyze the mass transfer and water transportation in the membrane. In order to prevent the starvation of air and flooding in a PEM fuel cell, time delay control is suggested to regulate the optimum stoichiometry of oxygen and hydrogen, even when there are dynamical fluctuations of the required PEM fuel cell power. To prove the dynamical performance improvement of the present method, feed-forward control and Linear Quadratic Gaussian (LQG) control with a state estimator are compared. Matlab/Simulink simulation is performed to validate the proposed methodology to increase the dynamic performance of a PEM fuel cell system.

  3. A system dynamics evaluation model: implementation of health information exchange for public health reporting.

    Science.gov (United States)

    Merrill, Jacqueline A; Deegan, Michael; Wilson, Rosalind V; Kaushal, Rainu; Fredericks, Kimberly

    2013-06-01

    To evaluate the complex dynamics involved in implementing electronic health information exchange (HIE) for public health reporting at a state health department, and to identify policy implications to inform similar implementations. Qualitative data were collected over 8 months from seven experts at New York State Department of Health who implemented web services and protocols for querying, receipt, and validation of electronic data supplied by regional health information organizations. Extensive project documentation was also collected. During group meetings experts described the implementation process and created reference modes and causal diagrams that the evaluation team used to build a preliminary model. System dynamics modeling techniques were applied iteratively to build causal loop diagrams representing the implementation. The diagrams were validated iteratively by individual experts followed by group review online, and through confirmatory review of documents and artifacts. Three casual loop diagrams captured well-recognized system dynamics: Sliding Goals, Project Rework, and Maturity of Resources. The findings were associated with specific policies that address funding, leadership, ensuring expertise, planning for rework, communication, and timeline management. This evaluation illustrates the value of a qualitative approach to system dynamics modeling. As a tool for strategic thinking on complicated and intense processes, qualitative models can be produced with fewer resources than a full simulation, yet still provide insights that are timely and relevant. System dynamics techniques clarified endogenous and exogenous factors at play in a highly complex technology implementation, which may inform other states engaged in implementing HIE supported by federal Health Information Technology for Economic and Clinical Health (HITECH) legislation.

  4. Photoinduced Dynamics of Neutral, Cationic, and Anionic Species

    DEFF Research Database (Denmark)

    Stephansen, Anne Boutrup

    In contrast to ground state (thermal) chemistry where internal energy is statistically distributed among the molecular degrees of freedom, photo-activation of a reaction entails initial localization of the internal energy in a highly non-statistical manner. The result is often reaction rates fast...... impact on the evolution of the ensuing reaction. The diversity of the processes studied illustrates the versatility of the experimental method as a means to increase knowledge on the complex interplay between structural dynamics and (photo)-reactivity....... than those predicted by statistical models, but also a more critical dependence between molecular structure and (photo)-reactivity. This thesis presents a collection of studies of various types of photoinduced processes in neutral, anionic, or cationic molecular species as introduced below....... The investigations have primarily employed femtosecond time-resolved photoionization or photodetachment techniques. Intersystem crossing (ISC) in neutral organic species is conventionally assumed to be slow due to the spin-forbidden nature of the process; this assumption has been challenged during the past decade...

  5. Cryogenic sample exchange NMR probe for magic angle spinning dynamic nuclear polarization

    Science.gov (United States)

    Barnes, Alexander B.; Mak-Jurkauskas, Melody L.; Matsuki, Yoh; Bajaj, Vikram S.; van der Wel, Patrick C. A.; DeRocher, Ronald; Bryant, Jeffrey; Sirigiri, Jagadishwar R.; Temkin, Richard J.; Lugtenburg, Johan; Herzfeld, Judith; Griffin, Robert G.

    2009-01-01

    We describe a cryogenic sample exchange system that dramatically improves the efficiency of magic angle spinning (MAS) dynamic nuclear polarization (DNP) experiments by reducing the time required to change samples and by improving long-term instrument stability. Changing samples in conventional cryogenic MAS DNP/NMR experiments involves warming the probe to room temperature, detaching all cryogenic, RF, and microwave connections, removing the probe from the magnet, replacing the sample, and reversing all the previous steps, with the entire cycle requiring a few hours. The sample exchange system described here — which relies on an eject pipe attached to the front of the MAS stator and a vacuum jacketed dewar with a bellowed hole — circumvents these procedures. To demonstrate the excellent sensitivity, resolution, and stability achieved with this quadruple resonance sample exchange probe, we have performed high precision distance measurements on the active site of the membrane protein bacteriorhodopsin. We also include a spectrum of the tripeptide N-f-MLF-OH at 100 K which shows 30 Hz linewidths. PMID:19356957

  6. Combining Coarse-Grained Protein Models with Replica-Exchange All-Atom Molecular Dynamics

    CERN Document Server

    Wabik, Jacek; Gront, Dominik; Kouza, Maksim; Kolinski, Andrzej

    2013-01-01

    We describe a combination of all-atom simulations with CABS, a well-established coarse-grained protein modeling tool, into a single multiscale protocol. The simulation method has been tested on the C-terminal beta hairpin of protein G, a model system of protein folding. After reconstructing atomistic details, conformations derived from the CABS simulation were subjected to replica-exchange molecular dynamics simulations with OPLS-AA and AMBER99sb force fields in explicit solvent. Such a combination accelerates system convergence several times in comparison with all-atom simulations starting from the extended chain conformation, demonstrated by the analysis of melting curves, the number of native-like conformations as a function of time and secondary structure propagation. The results strongly suggest that the proposed multiscale method could be an efficient and accurate tool for high-resolution studies of protein folding dynamics in larger systems.

  7. Combining Coarse-Grained Protein Models with Replica-Exchange All-Atom Molecular Dynamics

    Directory of Open Access Journals (Sweden)

    Andrzej Koliński

    2013-05-01

    Full Text Available We describe a combination of all-atom simulations with CABS, a well-established coarse-grained protein modeling tool, into a single multiscale protocol. The simulation method has been tested on the C-terminal beta hairpin of protein G, a model system of protein folding. After reconstructing atomistic details, conformations derived from the CABS simulation were subjected to replica-exchange molecular dynamics simulations with OPLS-AA and AMBER99sb force fields in explicit solvent. Such a combination accelerates system convergence several times in comparison with all-atom simulations starting from the extended chain conformation, demonstrated by the analysis of melting curves, the number of native-like conformations as a function of time and secondary structure propagation. The results strongly suggest that the proposed multiscale method could be an efficient and accurate tool for high-resolution studies of protein folding dynamics in larger systems.

  8. Combining coarse-grained protein models with replica-exchange all-atom molecular dynamics.

    Science.gov (United States)

    Wabik, Jacek; Kmiecik, Sebastian; Gront, Dominik; Kouza, Maksim; Koliński, Andrzej

    2013-05-10

    We describe a combination of all-atom simulations with CABS, a well-established coarse-grained protein modeling tool, into a single multiscale protocol. The simulation method has been tested on the C-terminal beta hairpin of protein G, a model system of protein folding. After reconstructing atomistic details, conformations derived from the CABS simulation were subjected to replica-exchange molecular dynamics simulations with OPLS-AA and AMBER99sb force fields in explicit solvent. Such a combination accelerates system convergence several times in comparison with all-atom simulations starting from the extended chain conformation, demonstrated by the analysis of melting curves, the number of native-like conformations as a function of time and secondary structure propagation. The results strongly suggest that the proposed multiscale method could be an efficient and accurate tool for high-resolution studies of protein folding dynamics in larger systems.

  9. Replica exchange molecular dynamics simulation of cross-fibrillation of IAPP and PrP106-126.

    Science.gov (United States)

    Chua, Khi Pin; Chew, Lock Yue; Mu, Yuguang

    2016-08-01

    Aggregation of proteins into amyloid is the central hallmark of a number of protein diseases. Most studies were carried out on the aggregation between proteins of similar species. However, it was observed that some patients with certain protein disease can easily acquire another unrelated protein disease. As such, it is also important to examine aggregation between proteins of different species. Usually aggregation between proteins of the same species can be attributed to the similarity between their respective amino acid sequences. In this article, we were motivated by an experimental study of aggregation between amylin (Islet Amyloid Polypeptide, IAPP) and prion106-126 (PrP106-126) fragment (JACS, 2013, 135, 13582-9). It was found that the two non-homologous peptides can aggregate quickly to form fibrils in the presence of negatively charged lipid bilayer. We attempted to elucidate the molecular mechanism of the early stage of dimerization of these two peptides through extensive replica exchange molecular dynamics simulations. Conformations consisting of various degrees of β-sheets structures, both intra-chain and inter-chain, were found in the simulations. The conformations of the aggregated complex are very diverse, which suggests that the cross-species fibrils formed between the two proteins are highly polymorphic. The driving forces are mainly hydrophobic interactions, including aromatic-aliphatic interactions. The palindromic region of PrP106-126 and SNNFGAIL region of IAPP were found to play important roles in the interaction. Our study sheds insight into the exciting research of protein cross-fibrillation. Proteins 2016; 84:1134-1146. © 2016 Wiley Periodicals, Inc.

  10. Network impact on persistence in a finite population dynamic diffusion model: application to an emergent seed exchange network.

    Science.gov (United States)

    Barbillon, Pierre; Thomas, Mathieu; Goldringer, Isabelle; Hospital, Frédéric; Robin, Stéphane

    2015-01-21

    Dynamic extinction colonisation models (also called contact processes) are widely studied in epidemiology and in metapopulation theory. Contacts are usually assumed to be possible only through a network of connected patches. This network accounts for a spatial landscape or a social organization of interactions. Thanks to social network literature, heterogeneous networks of contacts can be considered. A major issue is to assess the influence of the network in the dynamic model. Most work with this common purpose uses deterministic models or an approximation of a stochastic Extinction-Colonisation model (sEC) which are relevant only for large networks. When working with a limited size network, the induced stochasticity is essential and has to be taken into account in the conclusions. Here, a rigorous framework is proposed for limited size networks and the limitations of the deterministic approximation are exhibited. This framework allows exact computations when the number of patches is small. Otherwise, simulations are used and enhanced by adapted simulation techniques when necessary. A sensitivity analysis was conducted to compare four main topologies of networks in contrasting settings to determine the role of the network. A challenging case was studied in this context: seed exchange of crop species in the Réseau Semences Paysannes (RSP), an emergent French farmers׳ organisation. A stochastic Extinction-Colonisation model was used to characterize the consequences of substantial changes in terms of RSP׳s social organization on the ability of the system to maintain crop varieties. Copyright © 2014 Elsevier Ltd. All rights reserved.

  11. Modeling the dynamic operation of a small fin plate heat exchanger - parametric analysis

    Science.gov (United States)

    Motyliński, Konrad; Kupecki, Jakub

    2015-09-01

    Given its high efficiency, low emissions and multiple fuelling options, the solid oxide fuel cells (SOFC) offer a promising alternative for stationary power generators, especially while engaged in micro-combined heat and power (μ-CHP) units. Despite the fact that the fuel cells are a key component in such power systems, other auxiliaries of the system can play a critical role and therefore require a significant attention. Since SOFC uses a ceramic material as an electrolyte, the high operating temperature (typically of the order of 700-900 °C) is required to achieve sufficient performance. For that reason both the fuel and the oxidant have to be preheated before entering the SOFC stack. Hot gases exiting the fuel cell stack transport substantial amount of energy which has to be partly recovered for preheating streams entering the stack and for heating purposes. Effective thermal integration of the μ-CHP can be achieved only when proper technical measures are used. The ability of efficiently preheating the streams of oxidant and fuel relies on heat exchangers which are present in all possible configurations of power system with solid oxide fuel cells. In this work a compact, fin plate heat exchanger operating in the high temperature regime was under consideration. Dynamic model was proposed for investigation of its performance under the transitional states of the fuel cell system. Heat exchanger was simulated using commercial modeling software. The model includes key geometrical and functional parameters. The working conditions of the power unit with SOFC vary due to the several factors, such as load changes, heating and cooling procedures of the stack and others. These issues affect parameters of the incoming streams to the heat exchanger. The mathematical model of the heat exchanger is based on a set of equations which are simultaneously solved in the iterative process. It enables to define conditions in the outlets of both the hot and the cold sides

  12. Modeling the dynamic operation of a small fin plate heat exchanger – parametric analysis

    Directory of Open Access Journals (Sweden)

    Motyliński Konrad

    2015-09-01

    Full Text Available Given its high efficiency, low emissions and multiple fuelling options, the solid oxide fuel cells (SOFC offer a promising alternative for stationary power generators, especially while engaged in micro-combined heat and power (μ-CHP units. Despite the fact that the fuel cells are a key component in such power systems, other auxiliaries of the system can play a critical role and therefore require a significant attention. Since SOFC uses a ceramic material as an electrolyte, the high operating temperature (typically of the order of 700–900 °C is required to achieve sufficient performance. For that reason both the fuel and the oxidant have to be preheated before entering the SOFC stack. Hot gases exiting the fuel cell stack transport substantial amount of energy which has to be partly recovered for preheating streams entering the stack and for heating purposes. Effective thermal integration of the μ-CHP can be achieved only when proper technical measures are used. The ability of efficiently preheating the streams of oxidant and fuel relies on heat exchangers which are present in all possible configurations of power system with solid oxide fuel cells. In this work a compact, fin plate heat exchanger operating in the high temperature regime was under consideration. Dynamic model was proposed for investigation of its performance under the transitional states of the fuel cell system. Heat exchanger was simulated using commercial modeling software. The model includes key geometrical and functional parameters. The working conditions of the power unit with SOFC vary due to the several factors, such as load changes, heating and cooling procedures of the stack and others. These issues affect parameters of the incoming streams to the heat exchanger. The mathematical model of the heat exchanger is based on a set of equations which are simultaneously solved in the iterative process. It enables to define conditions in the outlets of both the hot and the

  13. Enhanced conformational sampling of nucleic acids by a new Hamiltonian replica exchange molecular dynamics approach.

    Science.gov (United States)

    Curuksu, Jeremy; Zacharias, Martin

    2009-03-14

    Although molecular dynamics (MD) simulations have been applied frequently to study flexible molecules, the sampling of conformational states separated by barriers is limited due to currently possible simulation time scales. Replica-exchange (Rex)MD simulations that allow for exchanges between simulations performed at different temperatures (T-RexMD) can achieve improved conformational sampling. However, in the case of T-RexMD the computational demand grows rapidly with system size. A Hamiltonian RexMD method that specifically enhances coupled dihedral angle transitions has been developed. The method employs added biasing potentials as replica parameters that destabilize available dihedral substates and was applied to study coupled dihedral transitions in nucleic acid molecules. The biasing potentials can be either fixed at the beginning of the simulation or optimized during an equilibration phase. The method was extensively tested and compared to conventional MD simulations and T-RexMD simulations on an adenine dinucleotide system and on a DNA abasic site. The biasing potential RexMD method showed improved sampling of conformational substates compared to conventional MD simulations similar to T-RexMD simulations but at a fraction of the computational demand. It is well suited to study systematically the fine structure and dynamics of large nucleic acids under realistic conditions including explicit solvent and ions and can be easily extended to other types of molecules.

  14. Dynamics of the Warsaw Stock Exchange index as analysed by the nonhomogeneous fractional relaxation equation

    CERN Document Server

    Kozlowska, M; Kozlowska, Marzena; Kutner, Ryszard

    2006-01-01

    We analyse the dynamics of the Warsaw Stock Exchange index WIG at a daily time horizon before and after its well defined local maxima of the cusp-like shape decorated with oscillations. The rising and falling paths of the index peaks can be described by the Mittag-Leffler function superposed with various types of oscillations. The latter is a solution of our model of index dynamics defined by the nonhomogeneous fractional relaxation equation. This solution is a generalised analog of an exactly solvable model of viscoelastic materials. We found that the Warsaw Stock Exchange can be considered as an intermediate system lying between two complex ones, defined by short and long-time limits of the Mittag-Leffler function; these limits are given by the Kohlraush-Williams-Watts law for the initial times, and the power-law or the Nutting law for asymptotic time. Hence follows the corresponding short- and long-time power-law behaviour (different universality classes) of the time-derivative of the logarithm of WIG whic...

  15. Dynamic occupancy models for analyzing species' range dynamics across large geographic scales

    Science.gov (United States)

    Bled, Florent; Nichols, James D; Altwegg, Res

    2013-01-01

    Large-scale biodiversity data are needed to predict species' responses to global change and to address basic questions in macroecology. While such data are increasingly becoming available, their analysis is challenging because of the typically large heterogeneity in spatial sampling intensity and the need to account for observation processes. Two further challenges are accounting for spatial effects that are not explained by covariates, and drawing inference on dynamics at these large spatial scales. We developed dynamic occupancy models to analyze large-scale atlas data. In addition to occupancy, these models estimate local colonization and persistence probabilities. We accounted for spatial autocorrelation using conditional autoregressive models and autologistic models. We fitted the models to detection/nondetection data collected on a quarter-degree grid across southern Africa during two atlas projects, using the hadeda ibis (Bostrychia hagedash) as an example. The model accurately reproduced the range expansion between the first (SABAP1: 1987–1992) and second (SABAP2: 2007–2012) Southern African Bird Atlas Project into the drier parts of interior South Africa. Grid cells occupied during SABAP1 generally remained occupied, but colonization of unoccupied grid cells was strongly dependent on the number of occupied grid cells in the neighborhood. The detection probability strongly varied across space due to variation in effort, observer identity, seasonality, and unexplained spatial effects. We present a flexible hierarchical approach for analyzing grid-based atlas data using dynamical occupancy models. Our model is similar to a species' distribution model obtained using generalized additive models but has a number of advantages. Our model accounts for the heterogeneous sampling process, spatial correlation, and perhaps most importantly, allows us to examine dynamic aspects of species ranges. PMID:24455124

  16. Cooperation can emerge in prisoner's dilemma from a multi-species predator prey replicator dynamic.

    Science.gov (United States)

    Paulson, Elisabeth; Griffin, Christopher

    2016-08-01

    In this paper we study a generalized variation of the replicator dynamic that involves several species and sub-species that may interact. We show how this dynamic comes about from a specific finite-population model, but also show that one must take into consideration the dynamic nature of the population sizes (and hence proportions) in order to make the model complete. We provide expressions for these population dynamics to produce a kind of multi-replicator dynamic. We then use this replicator dynamic to show that cooperation can emerge as a stable behavior when two species each play prisoner's dilemma as their intra-species game and a form of zero-sum predator prey game as their inter-species game. General necessary and sufficient conditions for cooperation to emerge as stable are provided for a number of game classes. We also showed an example using Hawk-Dove where both species can converge to stable (asymmetric) mixed strategies.

  17. Gas exchange and growth responses to nutrient enrichment in invasive Glyceria maxima and native New Zealand Carex species

    DEFF Research Database (Denmark)

    Sorrell, Brian Keith; Brix, Hans; Fitridge, Isla

    2012-01-01

    the ecophysiological traits contributing to invasive behaviour. The photosynthesis-nitrogen relationship was uniform across all three species, and the maximum light-saturated rate of photosynthesis expressed on a leaf area basis (Amaxa) did not differ significantly between species. However, specific leaf area (SLA....... maxima than the sedges under low nutrient supply supports the importance of nutrient management, especially N, as a strategy to minimise the invasive behaviour of fast-growing herbaceous species in wetlands.......We compared photosynthetic gas exchange, the photosynthesis-leaf nitrogen (N) relationship, and growth response to nutrient enrichment in the invasive wetland grass Glyceria maxima (Hartman) Holmburg with two native New Zealand Carex sedges (C. virgata Boott and C. secta Boott), to explore...

  18. Water exchange and permeability properties of the skin in three species of amphibious sea snakes (Laticauda spp.).

    Science.gov (United States)

    Lillywhite, H B; Menon, J G; Menon, G K; Sheehy, C M; Tu, M C

    2009-06-01

    Evolutionary transitions between different environmental media such as air and water pose special problems with respect to skin permeability because of the dramatic changes in the driving gradients and nature of water exchange processes. Also, during the transitional periods prior to complete adaptation to a new medium, the skin is exposed to two very different sets of environmental conditions. Here, we report new data for transepidermal evaporative water loss (TEWL) and cutaneous resistance to evaporative water loss (R(s)) of sea snakes that are transitional in the sense of being amphibious and semi-terrestrial. We investigated three species of sea kraits (Elapidae: Laticaudinae) that are common to Orchid Island (Lanyu), Taiwan. Generally, R(s) of all three species is lower than that characteristic of terrestrial/xeric species of snakes measured in other taxa. Within Laticauda, R(s) is significantly greater (TEWL lower) in the more terrestrial species and lowest (TEWL highest) in the more aquatic species. Previously reported losses of water from snakes kept in seawater exhibit a reversed trend, with lower rates of loss in the more aquatic species. These data suggest selection for adaptive traits with respect to increasing exposure to the marine environment. Thus, a countergradient of traits is reflected in decreased TEWL in aerial environments and decreased net water efflux in marine environments, acting simultaneously in the three species. The pattern for TEWL correlates with ultrastructural evidence for increased lipogenesis in the stratum corneum of the more terrestrial species. The skin surfaces of all three species are hydrophobic. Species differences in this property possibly explain the pattern for water efflux when these snakes are in seawater, which remains to be investigated.

  19. The long-run dynamic relationship between exchange rate and its attention index: Based on DCCA and TOP method

    Science.gov (United States)

    Wang, Xuan; Guo, Kun; Lu, Xiaolin

    2016-07-01

    The behavior information of financial market plays a more and more important role in modern economic system. The behavior information reflected in INTERNET search data has already been used in short-term prediction for exchange rate, stock market return, house price and so on. However, the long-run relationship between behavior information and financial market fluctuation has not been studied systematically. Further, most traditional statistic methods and econometric models could not catch the dynamic and non-linear relationship. An attention index of CNY/USD exchange rate is constructed based on search data from 360 search engine of China in this paper. Then the DCCA and Thermal Optimal Path methods are used to explore the long-run dynamic relationship between CNY/USD exchange rate and the corresponding attention index. The results show that the significant interdependency exists and the change of exchange rate is 1-2 days lag behind the attention index.

  20. Social organization influences the exchange and species richness of medicinal plants in amazonian homegardens

    NARCIS (Netherlands)

    Díaz-Reviriego, Isabel; González-Segura, Lara; Fernández-Llamazares, Álvaro; Howard, Patricia L.; Molina, José Luis; Reyes-García, Victoria

    2016-01-01

    Medicinal plants provide indigenous and peasant communities worldwide with means to meet their healthcare needs. Homegardens often act as medicine cabinets, providing easily accessible medicinal plants for household needs. Social structure and social exchanges have been proposed as factors influe

  1. SISTER-CHROMATID EXCHANGES IN CULTURED IMMATURE EMBRYOS OF WHEAT SPECIES AND REGENERANTS

    NARCIS (Netherlands)

    PIJNACKER, LP; FERWERDA, MA

    1994-01-01

    Immature embryos of Triticum aestivum (ten cultivars and lines), T. durum, T. dicoccum and T. monococcum were cultured in vitro on MS medium supplemented with 1 or 2 mg/l of 2,4-D and 20 or 30g/l of sucrose for 3 days and processed to score sister chromatid exchanges (SCEs) per chromosome. Media com

  2. Flooding tolerance of Carex species. II. Root gas-exchange capacity

    NARCIS (Netherlands)

    Moog, PR; Bruggemann, W

    1998-01-01

    Root CO2 and O-2 gas exchange were measured in young Carer extensa Good. (flooding sensitive), C. remota L. and C. pseudocyperus L. (both flooding tolerant) plants, precultured either aerobically or anaerobically. Temperature changes form 21 to II degrees C had small effects on root CO2 release from

  3. Dynamics of the outflow and its effect on the hydraulics of two-layer exchange flows in a channel

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    This paper reports that an experimental study is conducted to examine the dynamics of the outflow in two-layer exchange flows in a channel connecting between two water bodies with a small density difference. The experiments reveal the generation of Kelvin-Helmholtz (KH) instabilities within the hydraulically sub-critical flow region of the channel. During maximal exchange, those KH instabilities develops into large-amplitude KH waves as they escape the channel exit into the reservoir. The propagation speed ...

  4. Dynamic Patterns, Parameters, and Climatic Response of CO2 Exchange of Agricultural Crops: Monocotyledons VS. Dicotyledons

    Science.gov (United States)

    Gilmanov, T. G.; Wylie, B. K.; Howard, D. M.

    2012-12-01

    Net CO2 exchange data from long-term flux tower measurements in monocotyledonous (wheat, maize) and dicotyledonous (soybeans, alfalfa, peas, peanuts) crops were partitioned into photosynthesis (P) and respiration (R) using the light-soil temperature-VPD response method. Analysis of the resulting time series of P and R revealed patterns of temporal and phenological dynamics in these plant groups. We established differences in ranges and dynamic patterns of P and R as well as CO2 exchange parameters (quantum yield, photosynthetic capacity, respiration rate, light-use efficiency, curvature of the VPD response). Weekly P and R data combined with remotely sensed 7-day eMODIS NDVI allow identification of the quasi-linear relationships between P, R, and NDVI, as well as estimation of parameters of NDVI response (start of the growing season, duration of the linearity period, slope of NDVI response). While the linear-like patterns occur early in the season, later the flux response to NDVI becomes less pronounced, and for the whole season the flux-NDVI relationship assumes a hysteresis-like pattern. Introduction of VPD and soil moisture limitation as well as phenological controls (growing degree days) leads to more flexible models for P and R in relation to NDVI and on-site drivers. These models allow mapping of the cropland CO2 exchange at regional and larger scales (e.g., the Great Plains). Significant relationships of the crop GPP to the seasonally integrated NDVI were also established, providing an opportunity for mapping of crop productivity using geographically distributed historic NDVI data. On the other hand, long time series (6 to 12 years and longer) of weekly P and R data lead to models of annual photosynthesis and respiration in response to climatic factors that may be used for prognostic purposes. We developed a model of maize GPP on the Great Plains in relation to the sum of temperatures above 5 °C and the hydrologic year precipitation. The model describes 75

  5. Catalysis in a Cage: Condition-Dependent Speciation and Dynamics of Exchanged Cu Cations in SSZ-13 Zeolites.

    Science.gov (United States)

    Paolucci, Christopher; Parekh, Atish A; Khurana, Ishant; Di Iorio, John R; Li, Hui; Albarracin Caballero, Jonatan D; Shih, Arthur J; Anggara, Trunojoyo; Delgass, W Nicholas; Miller, Jeffrey T; Ribeiro, Fabio H; Gounder, Rajamani; Schneider, William F

    2016-05-11

    The relationships among the macroscopic compositional parameters of a Cu-exchanged SSZ-13 zeolite catalyst, the types and numbers of Cu active sites, and activity for the selective catalytic reduction (SCR) of NOx with NH3 are established through experimental interrogation and computational analysis of materials across the catalyst composition space. Density functional theory, stochastic models, and experimental characterizations demonstrate that within the synthesis protocols applied here and across Si:Al ratios, the volumetric density of six-membered-rings (6MR) containing two Al (2Al sites) is consistent with a random Al siting in the SSZ-13 lattice subject to Löwenstein's rule. Further, exchanged Cu(II) ions first populate these 2Al sites before populating remaining unpaired, or 1Al, sites as Cu(II)OH. These sites are distinguished and enumerated ex situ through vibrational and X-ray absorption spectroscopies (XAS) and chemical titrations. In situ and operando XAS follow Cu oxidation state and coordination environment as a function of environmental conditions including low-temperature (473 K) SCR catalysis and are rationalized through first-principles thermodynamics and ab initio molecular dynamics. Experiment and theory together reveal that the Cu sites respond sensitively to exposure conditions, and in particular that Cu species are solvated and mobilized by NH3 under SCR conditions. While Cu sites are spectroscopically and chemically distinct away from these conditions, they exhibit similar turnover rates, apparent activation energies and apparent reaction orders at the SCR conditions, even on zeolite frameworks other than SSZ13.

  6. Plasticity of 150-loop in influenza neuraminidase explored by Hamiltonian replica exchange molecular dynamics simulations.

    Directory of Open Access Journals (Sweden)

    Nanyu Han

    Full Text Available Neuraminidase (NA of influenza is a key target for antiviral inhibitors, and the 150-cavity in group-1 NA provides new insight in treating this disease. However, NA of 2009 pandemic influenza (09N1 was found lacking this cavity in a crystal structure. To address the issue of flexibility of the 150-loop, Hamiltonian replica exchange molecular dynamics simulations were performed on different groups of NAs. Free energy landscape calculated based on the volume of 150-cavity indicates that 09N1 prefers open forms of 150-loop. The turn A (residues 147-150 of the 150-loop is discovered as the most dynamical motif which induces the inter-conversion of this loop among different conformations. In the turn A, the backbone dynamic of residue 149 is highly related with the shape of 150-loop, thus can function as a marker for the conformation of 150-loop. As a contrast, the closed conformation of 150-loop is more energetically favorable in N2, one of group-2 NAs. The D147-H150 salt bridge is found having no correlation with the conformation of 150-loop. Instead the intimate salt bridge interaction between the 150 and 430 loops in N2 variant contributes the stabilizing factor for the closed form of 150-loop. The clustering analysis elaborates the structural plasticity of the loop. This enhanced sampling simulation provides more information in further structural-based drug discovery on influenza virus.

  7. Plasticity of 150-loop in influenza neuraminidase explored by Hamiltonian replica exchange molecular dynamics simulations.

    Science.gov (United States)

    Han, Nanyu; Mu, Yuguang

    2013-01-01

    Neuraminidase (NA) of influenza is a key target for antiviral inhibitors, and the 150-cavity in group-1 NA provides new insight in treating this disease. However, NA of 2009 pandemic influenza (09N1) was found lacking this cavity in a crystal structure. To address the issue of flexibility of the 150-loop, Hamiltonian replica exchange molecular dynamics simulations were performed on different groups of NAs. Free energy landscape calculated based on the volume of 150-cavity indicates that 09N1 prefers open forms of 150-loop. The turn A (residues 147-150) of the 150-loop is discovered as the most dynamical motif which induces the inter-conversion of this loop among different conformations. In the turn A, the backbone dynamic of residue 149 is highly related with the shape of 150-loop, thus can function as a marker for the conformation of 150-loop. As a contrast, the closed conformation of 150-loop is more energetically favorable in N2, one of group-2 NAs. The D147-H150 salt bridge is found having no correlation with the conformation of 150-loop. Instead the intimate salt bridge interaction between the 150 and 430 loops in N2 variant contributes the stabilizing factor for the closed form of 150-loop. The clustering analysis elaborates the structural plasticity of the loop. This enhanced sampling simulation provides more information in further structural-based drug discovery on influenza virus.

  8. Lanthanide paramagnetic probes for NMR spectroscopic studies of fast molecular conformational dynamics and temperature control. Effective six-site proton exchange in 18-crown-6 by exchange spectroscopy.

    Science.gov (United States)

    Babailov, Sergey P

    2012-02-06

    (1)H and (13)C NMR measurements are reported for the CDCl(3) and CD(2)Cl(2) solutions of [La(18-crown-6)(NO(3))(3)] (I), [Pr(18-crown-6) (NO(3))(3)] (II), [Ce(18-crown-6)(NO(3))(3)] (III), and [Nd(18-crown-6)(NO(3))(3)] (IV) complexes. Temperature dependencies of the (1)H NMR spectra of paramagnetic II-IV have been analyzed using the dynamic NMR (DNMR) methods for six-site exchange. Two types of conformational dynamic processes were identified (the first one is conditioned by interconversion of complex enantiomeric forms and pseudorotation of a macrocycle molecule upon the C(2) symmetry axis; the second one is conditioned by macrocycle molecule inversion). Application of exchange spectroscopy (2D-EXSY) of DNMR for investigation of this dynamic system (II-IV) simplifies the assignment of the NMR signals and represents the first experimental study of multisite exchange. In the present work, the methodology of paramagnetic 4f (Ce, Pr, and Nd) probe applications for the study of free-energy, enthalpy, and entropy changes in chemical exchange processes, as well as the advantages of this method in a comparison with DNMR studies of diamagnetic substances, is discussed. In particular, as a result of paramagnetic chemical shifts in 4f complexes, the range of measurable rate constants expands considerably compared to the analogous range in diamagnetic compounds. Coordination compounds investigated in the paper represent new types of thermometric NMR sensors and lanthanide paramagnetic probes for in situ temperature control in solution.

  9. Identifying ligand binding sites and poses using GPU-accelerated Hamiltonian replica exchange molecular dynamics.

    Science.gov (United States)

    Wang, Kai; Chodera, John D; Yang, Yanzhi; Shirts, Michael R

    2013-12-01

    We present a method to identify small molecule ligand binding sites and poses within a given protein crystal structure using GPU-accelerated Hamiltonian replica exchange molecular dynamics simulations. The Hamiltonians used vary from the physical end state of protein interacting with the ligand to an unphysical end state where the ligand does not interact with the protein. As replicas explore the space of Hamiltonians interpolating between these states, the ligand can rapidly escape local minima and explore potential binding sites. Geometric restraints keep the ligands from leaving the vicinity of the protein and an alchemical pathway designed to increase phase space overlap between intermediates ensures good mixing. Because of the rigorous statistical mechanical nature of the Hamiltonian exchange framework, we can also extract binding free energy estimates for all putative binding sites. We present results of this methodology applied to the T4 lysozyme L99A model system for three known ligands and one non-binder as a control, using an implicit solvent. We find that our methodology identifies known crystallographic binding sites consistently and accurately for the small number of ligands considered here and gives free energies consistent with experiment. We are also able to analyze the contribution of individual binding sites to the overall binding affinity. Our methodology points to near term potential applications in early-stage structure-guided drug discovery.

  10. Computing Alchemical Free Energy Differences with Hamiltonian Replica Exchange Molecular Dynamics (H-REMD) Simulations.

    Science.gov (United States)

    Meng, Yilin; Dashti, Danial Sabri; Roitberg, Adrian E

    2011-09-13

    Alchemical free energy calculations play a very important role in the field of molecular modeling. Efforts have been made to improve the accuracy and precision of those calculations. One of the efforts is to employ a Hamiltonian replica exchange molecular dynamics (H-REMD) method to enhance conformational sampling. In this paper, we demonstrated that HREMD method not only improves convergence in alchemical free energy calculations but also can be used to compute free energy differences directly via the Free Energy Perturbation (FEP)algorithm. We show a direct mapping between the H-REMD and the usual FEP equations, which are then used directly to compute free energies. The H-REMD alchemical free energy calculation (Replica exchange Free Energy Perturbation, REFEP) was tested on predicting the pK(a) value of the buried Asp26 in thioredoxin. We compare the results of REFEP with TI and regular FEP simulations. REFEP calculations converged faster than those from TI and regular FEP simulations. The final predicted pK(a) value from the H-REMD simulation was also very accurate, only 0.4 pK(a) unit above the experimental value. Utilizing the REFEP algorithm significantly improves conformational sampling, and this in turn improves the convergence of alchemical free energy simulations.

  11. Computational fluid dynamics simulation of an earth-air heat exchanger for ventilation system

    Science.gov (United States)

    Raczkowski, Andrzej; Suchorab, Zbigniew; Czechowska-Kosacka, Aneta

    2017-07-01

    Directive 2010/31/EU (EPBD Recast) obligates European Union members to improve energetic performance of the buildings. One of the crucial standards of energy-saving buildings are the passive houses, which are characterized by annual maximum space heating below 15 kWh/(m2.a) and the use of the specific primary energy for all domestic applications (also heating, hot water production and electricity) below 120 kWh/(m2.a). To achieve this standard there should be applied the solutions based on ground energy acquisition. One of them is the earth-air heat exchanger (EAHC) for ventilation systems. The article presents numerical simulations conducted by solving partial differential equations for three dimensional heat transfer. For the simulations it was applied Computational Fluid Dynamics (CFD) technique. The efficiency of EAHC was considered under different values of external temperature during the winter period (from -24 to -8 °C). Obtained results prove linear correlation with calculations of EAHC according to standards of the Polish National Energy Conservation Agency (NAPE). The slope of regression between outlet temperatures calculated with CFD model and NAPE standards, equals 0.59 which means, that according the CFD model, the efficiency of the exchanger is lower.

  12. Conformational sampling enhancement of replica exchange molecular dynamics simulations using swarm particle intelligence

    Energy Technology Data Exchange (ETDEWEB)

    Kamberaj, Hiqmet, E-mail: hkamberaj@ibu.edu.mk [Department of Computer Engineering, International Balkan University, Tashko Karadza 11A, Skopje (Macedonia, The Former Yugoslav Republic of)

    2015-09-28

    In this paper, we present a new method based on swarm particle social intelligence for use in replica exchange molecular dynamics simulations. In this method, the replicas (representing the different system configurations) are allowed communicating with each other through the individual and social knowledge, in additional to considering them as a collection of real particles interacting through the Newtonian forces. The new method is based on the modification of the equations of motion in such way that the replicas are driven towards the global energy minimum. The method was tested for the Lennard-Jones clusters of N = 4,  5, and 6 atoms. Our results showed that the new method is more efficient than the conventional replica exchange method under the same practical conditions. In particular, the new method performed better on optimizing the distribution of the replicas among the thermostats with time and, in addition, ergodic convergence is observed to be faster. We also introduce a weighted histogram analysis method allowing analyzing the data from simulations by combining data from all of the replicas and rigorously removing the inserted bias.

  13. Fluid Analysis and Improved Structure of an ATEG Heat Exchanger Based on Computational Fluid Dynamics

    Science.gov (United States)

    Tang, Z. B.; Deng, Y. D.; Su, C. Q.; Yuan, X. H.

    2015-06-01

    In this study, a numerical model has been employed to analyze the internal flow field distribution in a heat exchanger applied for an automotive thermoelectric generator based on computational fluid dynamics. The model simulates the influence of factors relevant to the heat exchanger, including the automotive waste heat mass flow velocity, temperature, internal fins, and back pressure. The result is in good agreement with experimental test data. Sensitivity analysis of the inlet parameters shows that increase of the exhaust velocity, compared with the inlet temperature, makes little contribution (0.1 versus 0.19) to the heat transfer but results in a detrimental back pressure increase (0.69 versus 0.21). A configuration equipped with internal fins is proved to offer better thermal performance compared with that without fins. Finally, based on an attempt to improve the internal flow field, a more rational structure is obtained, offering a more homogeneous temperature distribution, higher average heat transfer coefficient, and lower back pressure.

  14. Characterizing the dynamics of alpha-synuclein oligomers using hydrogen/deuterium exchange monitored by mass spectrometry

    DEFF Research Database (Denmark)

    Mysling, Simon; Betzer, Cristine; Jensen, Poul H;

    2013-01-01

    hydrogen/deuterium exchange monitored by mass spectrometry (HDX-MS), we have analyzed the structural dynamics of soluble αSN oligomers. The analyzed oligomers were metastable, slowly dissociating to monomers over a period of 21 days, after excess monomer had been removed. The C-terminal region of α......-shielded structure. The protected regions were interspersed by two somewhat more dynamic regions (residues 18-38 and 55-70). In the oligomeric state, the isotopic exchange pattern of the region of residues 35-95 of αSN corresponded well with previous nuclear magnetic resonance and electron paramagnetic resonance...

  15. Issues associated with modelling of proton exchange membrane fuel cell by computational fluid dynamics

    Science.gov (United States)

    Bednarek, Tomasz; Tsotridis, Georgios

    2017-03-01

    The objective of the current study is to highlight possible limitations and difficulties associated with Computational Fluid Dynamics in PEM single fuel cell modelling. It is shown that an appropriate convergence methodology should be applied for steady-state solutions, due to inherent numerical instabilities. A single channel fuel cell model has been taken as numerical example. Results are evaluated for quantitative as well qualitative points of view. The contribution to the polarization curve of the different fuel cell components such as bi-polar plates, gas diffusion layers, catalyst layers and membrane was investigated via their effects on the overpotentials. Furthermore, the potential losses corresponding to reaction kinetics, due to ohmic and mas transport limitations and the effect of the exchange current density and open circuit voltage, were also investigated. It is highlighted that the lack of reliable and robust input data is one of the issues for obtaining accurate results.

  16. Horizontal Air-Ground Heat Exchanger Performance and Humidity Simulation by Computational Fluid Dynamic Analysis

    Directory of Open Access Journals (Sweden)

    Paolo Maria Congedo

    2016-11-01

    Full Text Available Improving energy efficiency in buildings and promoting renewables are key objectives of European energy policies. Several technological measures are being developed to enhance the energy performance of buildings. Among these, geothermal systems present a huge potential to reduce energy consumption for mechanical ventilation and cooling, but their behavior depending on varying parameters, boundary and climatic conditions is not fully established. In this paper a horizontal air-ground heat exchanger (HAGHE system is studied by the development of a computational fluid dynamics (CFD model. Summer and winter conditions representative of the Mediterranean climate are analyzed to evaluate operation and thermal performance differences. A particular focus is given to humidity variations as this parameter has a major impact on indoor air quality and comfort. Results show the benefits that HAGHE systems can provide in reducing energy consumption in all seasons, in summer when free-cooling can be implemented avoiding post air treatment using heat pumps.

  17. Intensification of heat exchange in a device for gas-dynamic energy separation

    Science.gov (United States)

    Leontiev, A. I.; Burtsev, S. A.

    2016-11-01

    The operating efficiency of a gas-dynamic energy-separation device is analyzed, and it is shown that it can be improved if we deposit a regular relief on the wall separating the supersonic and subsonic channels. To decrease the total pressure losses on the side of the supersonic channel, shallow spherical dimples (stampings) are deposited, creating spherical ledges in the subsonic channel because of the small thickness of the wall. The calculation technique is modernized, and modeling is carried out, which shows that by introducing intensified heat exchange, it is possible to improve the efficiency of this device by 1.2-1.4 times in air and in natural gas with a simultaneous decrease in the device size by 20-25%.

  18. Replica exchange molecular dynamics optimization of tensor network states for quantum many-body systems.

    Science.gov (United States)

    Liu, Wenyuan; Wang, Chao; Li, Yanbin; Lao, Yuyang; Han, Yongjian; Guo, Guang-Can; Zhao, Yong-Hua; He, Lixin

    2015-03-01

    Tensor network states (TNS) methods combined with the Monte Carlo (MC) technique have been proven a powerful algorithm for simulating quantum many-body systems. However, because the ground state energy is a highly non-linear function of the tensors, it is easy to get stuck in local minima when optimizing the TNS of the simulated physical systems. To overcome this difficulty, we introduce a replica-exchange molecular dynamics optimization algorithm to obtain the TNS ground state, based on the MC sampling technique, by mapping the energy function of the TNS to that of a classical mechanical system. The method is expected to effectively avoid local minima. We make benchmark tests on a 1D Hubbard model based on matrix product states (MPS) and a Heisenberg J1-J2 model on square lattice based on string bond states (SBS). The results show that the optimization method is robust and efficient compared to the existing results.

  19. Exchanges of genomic domains between poliovirus and other cocirculating species C enteroviruses reveal a high degree of plasticity

    Science.gov (United States)

    Bessaud, Maël; Joffret, Marie-Line; Blondel, Bruno; Delpeyroux, Francis

    2016-01-01

    The attenuated Sabin strains contained in the oral poliomyelitis vaccine are genetically unstable, and their circulation in poorly immunized populations can lead to the emergence of pathogenic circulating vaccine-derived polioviruses (cVDPVs). The recombinant nature of most cVDPV genomes and the preferential presence of genomic sequences from certain cocirculating non-polio enteroviruses of species C (EV-Cs) raise questions about the permissiveness of genetic exchanges between EV-Cs and the phenotypic impact of such exchanges. We investigated whether functional constraints limited genetic exchanges between Sabin strains and other EV-Cs. We bypassed the natural recombination events by constructing 29 genomes containing a Sabin 2 capsid-encoding sequence and other sequences from Sabin 2 or from non-polio EV-Cs. Most genomes were functional. All recombinant viruses replicated similarly in vitro, but recombination modulated plaque size and temperature sensitivity. All viruses with a 5′UTR from Sabin 2 were attenuated in mice, whereas almost all viruses with a non-polio 5′UTR caused disease. These data highlight the striking conservation of functional compatibility between different genetic domains of cocirculating EV-Cs. This aspect is only one of the requirements for the generation of recombinant cVDPVs in natural conditions, but it may facilitate the generation of viable intertypic recombinants with diverse phenotypic features, including pathogenicity. PMID:27958320

  20. Physical Non-Contact Communication between Microscopic Aquatic Species: Novel Experimental Evidences for an Interspecies Information Exchange

    Directory of Open Access Journals (Sweden)

    Daniel Fels

    2016-01-01

    Full Text Available Previous experiments on physical non-contact communication within same species gave rise to test for this type of communication also across the species border, which was the aim of the present study. It was found that autotrophic unicellular organisms (Euglena viridis, separated by cuvettes, affected the proliferation rate of heterotrophic unicellular organisms (Paramecium caudatum. Further, the heterotrophic unicellular organism affected also the proliferation rate of a multicellular heterotrophic organism (Rotatoria sp. and vice versa. In the case when populations (of Euglena viridis and Paramecium caudatum were shielded against electromagnetic fields in the optical spectrum from each other, no effects were measured. The results may support the notion that the organisation of ecosystems relies also on the exchange of electromagnetic fields from their constituting biosystems.

  1. Evaluation of enhanced sampling provided by accelerated molecular dynamics with Hamiltonian replica exchange methods.

    Science.gov (United States)

    Roe, Daniel R; Bergonzo, Christina; Cheatham, Thomas E

    2014-04-03

    Many problems studied via molecular dynamics require accurate estimates of various thermodynamic properties, such as the free energies of different states of a system, which in turn requires well-converged sampling of the ensemble of possible structures. Enhanced sampling techniques are often applied to provide faster convergence than is possible with traditional molecular dynamics simulations. Hamiltonian replica exchange molecular dynamics (H-REMD) is a particularly attractive method, as it allows the incorporation of a variety of enhanced sampling techniques through modifications to the various Hamiltonians. In this work, we study the enhanced sampling of the RNA tetranucleotide r(GACC) provided by H-REMD combined with accelerated molecular dynamics (aMD), where a boosting potential is applied to torsions, and compare this to the enhanced sampling provided by H-REMD in which torsion potential barrier heights are scaled down to lower force constants. We show that H-REMD and multidimensional REMD (M-REMD) combined with aMD does indeed enhance sampling for r(GACC), and that the addition of the temperature dimension in the M-REMD simulations is necessary to efficiently sample rare conformations. Interestingly, we find that the rate of convergence can be improved in a single H-REMD dimension by simply increasing the number of replicas from 8 to 24 without increasing the maximum level of bias. The results also indicate that factors beyond replica spacing, such as round trip times and time spent at each replica, must be considered in order to achieve optimal sampling efficiency.

  2. Transient computation fluid dynamics modeling of a single proton exchange membrane fuel cell with serpentine channel

    Science.gov (United States)

    Hu, Guilin; Fan, Jianren

    The proton exchange membrane fuel cell (PEMFC) has become a promising candidate for the power source of electrical vehicles because of its low pollution, low noise and especially fast startup and transient responses at low temperatures. A transient, three-dimensional, non-isothermal and single-phase mathematical model based on computation fluid dynamics has been developed to describe the transient process and the dynamic characteristics of a PEMFC with a serpentine fluid channel. The effects of water phase change and heat transfer, as well as electrochemical kinetics and multicomponent transport on the cell performance are taken into account simultaneously in this comprehensive model. The developed model was employed to simulate a single laboratory-scale PEMFC with an electrode area about 20 cm 2. The dynamic behavior of the characteristic parameters such as reactant concentration, pressure loss, temperature on the membrane surface of cathode side and current density during start-up process were computed and are discussed in detail. Furthermore, transient responses of the fuel cell characteristics during step changes and sinusoidal changes in the stoichiometric flow ratio of the cathode inlet stream, cathode inlet stream humidity and cell voltage are also studied and analyzed and interesting undershoot/overshoot behavior of some variables was found. It was also found that the startup and transient response time of a PEM fuel cell is of the order of a second, which is similar to the simulation results predicted by most models. The result is an important guide for the optimization of PEMFC designs and dynamic operation.

  3. Linking nonstructural carbohydrate dynamics to gas exchange and leaf hydraulic behavior in Pinus edulis and Juniperus monosperma.

    Science.gov (United States)

    Woodruff, David R; Meinzer, Frederick C; Marias, Danielle E; Sevanto, Sanna; Jenkins, Michael W; McDowell, Nate G

    2015-04-01

    Leaf hydraulics, gas exchange and carbon storage in Pinus edulis and Juniperus monosperma, two tree species on opposite ends of the isohydry-anisohydry spectrum, were analyzed to examine relationships between hydraulic function and carbohydrate dynamics. Leaf hydraulic vulnerability, leaf water potential (Ψl ), leaf hydraulic conductance (Kleaf ), photosynthesis (A), stomatal conductance (gs) and nonstructural carbohydrate (NSC) content were analyzed throughout the growing season. Leaf hydraulic vulnerability was significantly lower in the relatively anisohydric J. monosperma than in the more isohydric P. edulis. In P. edulis, Ψl dropped and stayed below 50% loss of leaf hydraulic conductance (P₅₀) early in the day during May, August and around midday in September, leading to sustained reductions in Kleaf . In J. monosperma, Ψl dropped below P₅₀ only during August, resulting in the maintenance of Kleaf during much of the growing season. Mean A and gs during September were significantly lower in P. edulis than in J. monosperma. Foliar total NSC was two to three times greater in J. monosperma than in P. edulis in June, August and September. Consistently lower levels of total NSC in P. edulis suggest that its isohydric strategy pushes it towards the exhaustion of carbon reserves during much of the growing season. No claim to original US Government works New Phytologist © 2014 New Phytologist Trust.

  4. Variation of gas exchange within native plant species of Switzerland and relationships with ozone injury: an open-top experiment.

    Science.gov (United States)

    Zhang, J; Ferdinand, J A; Vanderheyden, D J; Skelly, J M; Innes, J L

    2001-01-01

    Gas exchange and ozone-induced foliar injury were intensively measured during a 6-day period in mid-August 1998 on leaves of Acer pseudoplatanus, Betula pendula, Corylus avellana, Fagus sylvatica, Fraxinus excelsior, Morus nigra, Prunus avium, Prunus serotina, Rhamnus cathartica, and Viburnum lantana at a forest nursery site in Canton Ticino, Switzerland. Plants were grown in four open plots (AA), four open-top chambers receiving carbon-filtered (CF) air, and four receiving non-filtered (NF) air. Significant variation in gas exchange (F > 12.7, P nigra, P. avium, P. serotina, R. cathartica, and V. lantana showed more injury than A. pseudoplatanus, B. pendula, C. avellana, and Fagus sylvatica. Plants grown in CF chambers had significantly higher net photosynthesis (A) and stomatal conductance to water vapor (gwv), and lower foliar injury than plants grown in NF chambers and AA plots; interactions between species and ozone treatments were significant for all variables (F > or = 2.2, P 0.1). Although A and gwv decreased and foliar injury increased with leaf age, the magnitude of these changes was lower for plants grown in CF chambers than for plants grown in NF chambers and AA plots. Neither ozone uptake threshold (r = 0.26, P > 0.20) nor whole-plant injury (r = -0.15, P > 0.41) was significantly correlated with stomatal conductance across these species. It appears that the relationships between stomatal conductance and foliar injury are species-specific and interactions between physiology and environments and leaf biochemical processes must be considered in determining species sensitivity to ambient ozone exposures.

  5. 1H and 23Na MAS NMR spectroscopy of cationic species in CO2 selective alkaline earth metal porous silicoaluminophosphates prepared via liquid and solid state ion exchange

    Science.gov (United States)

    Arévalo-Hidalgo, Ana G.; Dugar, Sneha; Fu, Riqiang; Hernández-Maldonado, Arturo J.

    2012-07-01

    The location of extraframework cations in Sr2+ and Ba2+ ion-exchanged SAPO-34 was estimated by means of 1H and 23Na MAS NMR spectroscopy and spectral deconvolution. Incorporation of the alkaline earth metal cations onto the SAPO framework was achieved via liquid state ion exchange, coupled partial detemplation/solid-state ion exchange, and combination of both techniques. MAS NMR revealed that the level of ion exchange was limited by the presence of protons and sodium cations near hexagonal prisms (site SI), which are relatively difficult to exchange with the alkaline earth metal due to steric and charge repulsion criteria. In addition, the presence of ammonium cations in the supercages facilitated the exchange of otherwise tenacious hydrogen as corroborated by unit cell compositional data as well as enhanced CO2 adsorption at low partial pressures. The extraframework ammonium species were produced from partial detemplation of the structure-directing agent employed for the SAPO-34 synthesis, tetraethylammonium.

  6. Dynamic communities in multichannel data: an application to the foreign exchange market during the 2007-2008 credit crisis.

    Science.gov (United States)

    Fenn, Daniel J; Porter, Mason A; McDonald, Mark; Williams, Stacy; Johnson, Neil F; Jones, Nick S

    2009-09-01

    We study the cluster dynamics of multichannel (multivariate) time series by representing their correlations as time-dependent networks and investigating the evolution of network communities. We employ a node-centric approach that allows us to track the effects of the community evolution on the functional roles of individual nodes without having to track entire communities. As an example, we consider a foreign exchange market network in which each node represents an exchange rate and each edge represents a time-dependent correlation between the rates. We study the period 2005-2008, which includes the recent credit and liquidity crisis. Using community detection, we find that exchange rates that are strongly attached to their community are persistently grouped with the same set of rates, whereas exchange rates that are important for the transfer of information tend to be positioned on the edges of communities. Our analysis successfully uncovers major trading changes that occurred in the market during the credit crisis.

  7. Elastic neutron scattering study of water dynamics in ion-exchanged type-A zeolites.

    Science.gov (United States)

    Corsaro, C; Crupi, V; Longo, F; Majolino, D; Venuti, V; Wanderlingh, U

    2005-12-01

    With the aim to investigate, by means of elastic neutron scattering, the effects produced by the cation substitution on the dynamics of water in zeolites, we measured, using a neutron backscattering spectrometer, the temperature dependence of mean-square atomic displacements [u2] derived from window integrated quasielastic spectra of fully and partially hydrated Na-A and Mg50-A zeolites. The results, collected in the 20-273 K temperature range, reveal that, at low temperature, the [u2] shows a harmonic trend independent of hydration and cation substitution, and, at higher temperatures, the onset of a non-Gaussian dynamics of the elastic intensity. This latter takes place at T approximately 200 K and approximately 150 K for fully and partially hydrated samples, respectively. This behavior has been interpreted in terms of reorientational jumps of H atoms described by two-site processes within an asymmetric double-minimum potential. In spite of its simplicity, the model seems to reproduce the rearrangement of the hydrogen bond network of zeolitic water. The fit results indicate a reduced proton mobility by diminishing the water content and by the induced Na+-->Mg2+ ion exchange, in agreement with previous incoherent quasielastic neutron scattering results at higher temperatures.

  8. Perovskite Quantum Dots Modeled Using ab Initio and Replica Exchange Molecular Dynamics

    KAUST Repository

    Buin, Andrei

    2015-06-18

    © 2015 American Chemical Society. Organometal halide perovskites have recently attracted tremendous attention at both the experimental and theoretical levels. Much of this work has been dedicated to bulk material studies, yet recent experimental work has shown the formation of highly efficient quantum-confined nanocrystals with tunable band edges. Here we investigate perovskite quantum dots from theory, predicting an upper bound of the Bohr radius of 45 Å that agrees well with literature values. When the quantum dots are stoichiometric, they are trap-free and have nearly symmetric contributions to confinement from the valence and conduction bands. We further show that surface-associated conduction bandedge states in perovskite nanocrystals lie below the bulk states, which could explain the difference in Urbach tails between mesoporous and planar perovskite films. In addition to conventional molecular dynamics (MD), we implement an enhanced phase-space sampling algorithm, replica exchange molecular dynamics (REMD). We find that in simulation of methylammonium orientation and global minima, REMD outperforms conventional MD. To the best of our knowledge, this is the first REMD implementation for realistic-sized systems in the realm of DFT calculations.

  9. Influence of Hydration Level on Polymer and Water Dynamics in Alkaline Anion Exchange Fuel Cell Membranes

    Science.gov (United States)

    Tarver, Jacob; Kim, Jenny; Tyagi, Madhu; Soles, Christopher; Tsai, Tsung-Han; Coughlin, Bryan

    2015-03-01

    Triblock copolymers based on poly(chloromethylstyrene)-b-poly(ethylene)-b-poly(chloromethylstyrene) can be quaternized to different extents to yield anion exchange membranes for alkaline fuel cells. In the absence of moisture, these membranes demonstrate bilayer lamellar morphology. Upon high levels of hydration, however, in-situ small angle neutron scattering reveals the emergence of higher-order diffraction peaks. This phenomena has previously been observed in analogous diblock copolymer-based membranes and has been attributed to the induction of a multilayer lamellar morphology in which selective striping of water occurs in the center of the ion-rich domain. By conducting humidity-resolved quasielastic neutron scattering (QENS) measurements using deuterated water, we are able to isolate differences in the pico- to nanosecond timescale dynamics of the hydrogenated membrane upon hydration. QENS measurements in the presence of a hydrogenated water source subsequently permit deconvolution and isolation of the translational and rotational dynamics of water as a function of relative humidity, revealing spatial and temporal changes in polymer and water motion at high levels of hydration.

  10. The dynamics of stock exchange based on the formalism of weak continuous quantum measurement

    Science.gov (United States)

    Melnyk, S.; Tuluzov, I.

    2010-07-01

    The problem of measurement in economic models and the possibility of their quantum-mechanical description are considered. It is revealed that the apparent paradox of such a description is associated with a priori requirement of conformity of the model to all the alternatives of free choice of the observer. The measurement of the state of a trader on a stock exchange is formally defined as his responses to the proposals of sale at a fixed price. It is shown that an analogue of Bell's inequalities for this measurement model is violated at the most general assumptions related to the strategy of the trader and requires a quantum-mechanical description of the dynamics of his condition. In the framework of the theory of weak continuous quantum measurements, the equation of stock price dynamics and the quantum-mechanical generalization of the F. Black and M. Scholes model for pricing options are obtained. The fundamental distinctions between the obtained model and the classical one are discussed.

  11. Ultrafast fluxional exchange dynamics in electrolyte solvation sheath of lithium ion battery

    Science.gov (United States)

    Lee, Kyung-Koo; Park, Kwanghee; Lee, Hochan; Noh, Yohan; Kossowska, Dorota; Kwak, Kyungwon; Cho, Minhaeng

    2017-01-01

    Lithium cation is the charge carrier in lithium-ion battery. Electrolyte solution in lithium-ion battery is usually based on mixed solvents consisting of polar carbonates with different aliphatic chains. Despite various experimental evidences indicating that lithium ion forms a rigid and stable solvation sheath through electrostatic interactions with polar carbonates, both the lithium solvation structure and more importantly fluctuation dynamics and functional role of carbonate solvent molecules have not been fully elucidated yet with femtosecond vibrational spectroscopic methods. Here we investigate the ultrafast carbonate solvent exchange dynamics around lithium ions in electrolyte solutions with coherent two-dimensional infrared spectroscopy and find that the time constants of the formation and dissociation of lithium-ion···carbonate complex in solvation sheaths are on a picosecond timescale. We anticipate that such ultrafast microscopic fluxional processes in lithium-solvent complexes could provide an important clue to understanding macroscopic mobility of lithium cation in lithium-ion battery on a molecular level. PMID:28272396

  12. Temporal stability in forest productivity increases with tree diversity due to asynchrony in species dynamics.

    Science.gov (United States)

    Morin, Xavier; Fahse, Lorenz; de Mazancourt, Claire; Scherer-Lorenzen, Michael; Bugmann, Harald

    2014-12-01

    Theory predicts a positive relationship between biodiversity and stability in ecosystem properties, while diversity is expected to have a negative impact on stability at the species level. We used virtual experiments based on a dynamic simulation model to test for the diversity-stability relationship and its underlying mechanisms in Central European forests. First our results show that variability in productivity between stands differing in species composition decreases as species richness and functional diversity increase. Second we show temporal stability increases with increasing diversity due to compensatory dynamics across species, supporting the biodiversity insurance hypothesis. We demonstrate that this pattern is mainly driven by the asynchrony of species responses to small disturbances rather than to environmental fluctuations, and is only weakly affected by the net biodiversity effect on productivity. Furthermore, our results suggest that compensatory dynamics between species may enhance ecosystem stability through an optimisation of canopy occupancy by coexisting species. © 2014 John Wiley & Sons Ltd/CNRS.

  13. Nutritional stress induces exchange of cell material and energetic coupling between bacterial species.

    Science.gov (United States)

    Benomar, Saida; Ranava, David; Cárdenas, María Luz; Trably, Eric; Rafrafi, Yan; Ducret, Adrien; Hamelin, Jérôme; Lojou, Elisabeth; Steyer, Jean-Philippe; Giudici-Orticoni, Marie-Thérèse

    2015-02-23

    Knowledge of the behaviour of bacterial communities is crucial for understanding biogeochemical cycles and developing environmental biotechnology. Here we demonstrate the formation of an artificial consortium between two anaerobic bacteria, Clostridium acetobutylicum (Gram-positive) and Desulfovibrio vulgaris Hildenborough (Gram-negative, sulfate-reducing) in which physical interactions between the two partners induce emergent properties. Molecular and cellular approaches show that tight cell-cell interactions are associated with an exchange of molecules, including proteins, which allows the growth of one partner (D. vulgaris) in spite of the shortage of nutrients. This physical interaction induces changes in expression of two genes encoding enzymes at the pyruvate crossroads, with concomitant changes in the distribution of metabolic fluxes, and allows a substantial increase in hydrogen production without requiring genetic engineering. The stress induced by the shortage of nutrients of D. vulgaris appears to trigger the interaction.

  14. Dynamics of Human Telomerase Holoenzyme Assembly and Subunit Exchange across the Cell Cycle.

    Science.gov (United States)

    Vogan, Jacob M; Collins, Kathleen

    2015-08-28

    Human telomerase acts on telomeres during the genome synthesis phase of the cell cycle, accompanied by its concentration in Cajal bodies and transient colocalization with telomeres. Whether the regulation of human telomerase holoenzyme assembly contributes to the cell cycle restriction of telomerase function is unknown. We investigated the steady-state levels, assembly, and exchange dynamics of human telomerase subunits with quantitative in vivo cross-linking and other methods. We determined the physical association of telomerase subunits in cells blocked or progressing through the cell cycle as synchronized by multiple protocols. The total level of human telomerase RNA (hTR) was invariant across the cell cycle. In vivo snapshots of telomerase holoenzyme composition established that hTR remains bound to human telomerase reverse transcriptase (hTERT) throughout all phases of the cell cycle, and subunit competition assays suggested that hTERT-hTR interaction is not readily exchangeable. In contrast, the telomerase holoenzyme Cajal body-associated protein, TCAB1, was released from hTR in mitotic cells coincident with TCAB1 delocalization from Cajal bodies. This telomerase holoenzyme disassembly was reversible with cell cycle progression without any change in total TCAB1 protein level. Consistent with differential cell cycle regulation of hTERT-hTR and TCAB1-hTR protein-RNA interactions, overexpression of hTERT or TCAB1 had limited if any influence on hTR assembly of the other subunit. Overall, these findings revealed a cell cycle regulation that disables human telomerase association with telomeres while preserving the co-folded hTERT-hTR ribonucleoprotein catalytic core. Studies here, integrated with previous work, led to a unifying model for telomerase subunit assembly and trafficking in human cells.

  15. Mimicking the action of folding chaperones by Hamiltonian replica-exchange molecular dynamics simulations : Application in the refinement of de novo models

    NARCIS (Netherlands)

    Fan, Hao; Periole, Xavier; Mark, Alan E.

    2012-01-01

    The efficiency of using a variant of Hamiltonian replica-exchange molecular dynamics (Chaperone H-replica-exchange molecular dynamics [CH-REMD]) for the refinement of protein structural models generated de novo is investigated. In CH-REMD, the interaction between the protein and its environment, spe

  16. Population dynamics of Trichoderma species in the rhizosphere of tobacco and four species form China

    Institute of Scientific and Technical Information of China (English)

    YU Ze-fen; ZHANG Ke-qin

    2004-01-01

    @@ To study the effect of tobacco growth on Trichoderma population, we investigated the occurrence of Trichoderma species in the rhizosphere of tobacco plant during the period from transplanting (June) to harvesting (October) and measured relative environmental factors. Eleven species of Trichoderma were isolated, among which T. harzianum, T. viride, T. hamatum, T. atroviride, T.longibrachiatum, T. virens, T. koningii were identified, other four species Ty1, Ty2, Ty3, Ty4are new species. Of the species which occurred at high frequencies, T. harzianum and T. hamatum were most abundant in the July and T. viride in the August. The occurrence of the above three abundant species correlates significantly with the developmental phase of tobacco and correlates apparently with the soil moisture content, but not with the temperature. For the other eight species,no obvious correlation was found between the above factors and them.

  17. Intertypic modular exchanges of genomic segments by homologous recombination at universally conserved segments in human adenovirus species D.

    Science.gov (United States)

    Gonzalez, Gabriel; Koyanagi, Kanako O; Aoki, Koki; Kitaichi, Nobuyoshi; Ohno, Shigeaki; Kaneko, Hisatoshi; Ishida, Susumu; Watanabe, Hidemi

    2014-08-15

    Human adenovirus species D (HAdV-D), which is composed of clinically and epidemiologically important pathogens worldwide, contains more taxonomic "types" than any other species of the genus Mastadenovirus, although the mechanisms accounting for the high level of diversity remain to be disclosed. Recent studies of known and new types of HAdV-D have indicated that intertypic recombination between distant types contributes to the increasing diversity of the species. However, such findings raise the question as to how homologous recombination events occur between diversified types since homologous recombination is suppressed as nucleotide sequences diverge. In order to address this question, we investigated the distribution of the recombination boundaries in comparison with the landscape of intergenomic sequence conservation assessed according to the synonymous substitution rate (dS). The results revealed that specific genomic segments are conserved between even the most distantly related genomes; we call these segments "universally conserved segments" (UCSs). These findings suggest that UCSs facilitate homologous recombination, resulting in intergenomic segmental exchanges of UCS-flanking genomic regions as recombination modules. With the aid of such a mechanism, the haploid genomes of HAdV-Ds may have been reshuffled, resulting in chimeric genomes out of diversified repertoires in the HAdV-D population analogous to the MHC region reshuffled via crossing over in vertebrates. In addition, some HAdVs with chimeric genomes may have had the opportunity to avoid host immune responses thereby causing epidemics. Copyright © 2014 Elsevier B.V. All rights reserved.

  18. Molecular and functional comparisons of the vacuolar Na+/H+ exchangers originated from glycophytic and halophytic species

    Institute of Scientific and Technical Information of China (English)

    Jin-yao LI; Xiao-wei HE; Li XU; Jie ZHOU; Ping WU; Hui-xia SHOU; Fu-chun ZHANG

    2008-01-01

    A novel vacuolar Na+/H+ exchanger, CgNHX1, was cloned from a halophytic species Chenopodium glaucum by using reverse transcriptase-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) technique. Sequence alignment and phylogenetic analysis of 22 NHX genes from GenBank as well as the new CgNHX1 gene indicate that NHX genes shared a great degree of similarity, regardless of their glycophytic or halophytic origin. Expression of the CgNHX1 gene was induced by NaCl and peaked at 400 mmol/L NaCl. Overexpression of NHX1 genes in rice enhanced their tolerance to salt stress.However, there is no significant difference in salt tolerance among the transgenic rice plants overexpressing the NHX1 genes from either glycophytic or halophytic species. The Na+ content of both the wild type (WT) and transgenic plants increased when exposed to 50 and 100 mmol/L NaCl, and the Na+ concentration in transgenic plants was marginally higher than that of WT. Our data demonstrate that the overexpression of the NHX1 gene from either glycophytic or halophytic species resulted in the enhanced tolerance to salt stress at a similar level, suggesting that NHX gene per se might not be the reason accounting for the difference in salt tolerance between glycophytes and halophytes.

  19. Dynamic relationship between Japanese Yen exchange rates and market anxiety: A new perspective based on MF-DCCA

    Science.gov (United States)

    Lu, Xinsheng; Sun, Xinxin; Ge, Jintian

    2017-05-01

    This paper investigates the dynamic relationship between Japanese Yen exchange rates and market anxiety during the period from January 5, 1998 to April 18, 2016. A quantitative technique of multifractal detrended cross-correlation analysis (MF-DCCA) is used to explore the multifractal features of the cross-correlations between USD/JPY, AUD/JPY exchange rates and the market anxiety gauge VIX. The investigation shows that the causal relationship between Japanese Yen exchange rates and VIX are bidirectional in general, and the cross-correlations between the two sets of time series are multifractal. Strong evidence suggests that the cross-correlation exponents tend to exhibit different volatility patterns in response to diverse external shocks such as financial distress and widening in interest rate spread, suggesting that the cross-correlated behavior between Japanese Yen exchange rates and VIX are susceptible to economic uncertainties and risks. In addition, the performances of two market anxiety gauges, the VIX and the TED spread, are compared and the sources of multifractality are also traced. Thus, this paper contributes to the literature by shedding light on the unique driving forces of the Yen exchange rate fluctuations in the international foreign exchange market.

  20. Species active in the selective catalytic reduction of no with iso-butane on iron-exchanged ZSM-5 zeolites

    Directory of Open Access Journals (Sweden)

    M. S. Batista

    2005-09-01

    Full Text Available Fe-ZSM-5 catalysts were prepared by ion exchange in aqueous medium or in the solid state and tested in the catalytic reduction of NO with iso-butane. X-ray powder diffraction (XRD, atomic absorption spectroscopy (AAS, electron paramagnetic resonance spectroscopy (EPR, X-ray absorption spectroscopy (XANES, EXAFS, temperature-programmed reduction by H2 (H2-TPR and Mössbauer spectroscopy (MÖS-S were used for sample characterisation. Irrespective of the method used in catalyst preparation, EPR, XANES and MÖS-S showed Fe atoms in the oxidation state of 3+. MÖS-S and H2-TPR data on Fe-ZSM-5 prepared by ion exchange in the solid state allowed quantification of a lower hematite (Fe2O3 concentration and a higher proportion of Fe cations than samples prepared in an aqueous medium. In all the catalysts studied these Fe cations were the active sites in the reduction of NO to N2 and in the oxidation of iso-butane. It is further suggested that coordination of Fe species is another important aspect to be considered in their behaviour.

  1. Tree species affect cation exchange capacity (CEC) and cation binding properties of organic matter in acid forest soils.

    Science.gov (United States)

    Gruba, Piotr; Mulder, Jan

    2015-04-01

    Soil organic matter (SOM) in forest soil is of major importance for cation binding and acid buffering, but its characteristics may differ among soils under different tree species. We investigated acidity, cation exchange properties and Al bonding to SOM in stands of Scots pine, pedunculate oak, Norway spruce, European beech and common hornbeam in southern Poland. The content of total carbon (Ct) was by far the major contributor to total cation exchange capacity (CECt) even in loamy soils and a strong relationship between Ct and CECt was found. The slope of the regression of CECt to Ct increased in the order hornbeam≈oakacid pH range was smallest for hornbeam and oak, and largest for spruce and pine soils. This was supported by the apparent dissociation constant (pKapp) values of SOM, which were largest in soils under oak. The maximum values of Al saturation were similar between the stands. However, maximum Al bonding to SOM occurred at higher pH values in soils under pine and spruce than under oak. Therefore, at any value in the acid pH range, the SOM in pine soil has less Al complexed and more adsorbed H+ than SOM from oak soils. Such differences in Al and H bonding are not only important for pH buffering and metal solubility controls, but also for stabilization of SOM via saturation of functional groups by Al and H. Copyright © 2015 Elsevier B.V. All rights reserved.

  2. Gas exchange and low temperature resistance in two tropical high mountain tree species from the Venezuelan Andes

    Science.gov (United States)

    Cavieres, Lohengrin A.; Rada, Fermín; Azócar, Aura; García-Núñez, Carlos; Cabrera, Hernán M.

    2000-05-01

    Temperature may determine altitudinal tree distribution in different ways: affecting survival through freezing temperatures or by a negative carbon balance produced by lower photosynthetic rates. We studied gas exchange and supercooling capacity in a timberline and a treeline species ( Podocarpus oleifolius and Espeletia neriifolia, respectively) in order to determine if their altitudinal limits are related to carbon balance, freezing temperature damage, or both. Leaf gas exchange, leaf temperature-net photosynthesis curves and leaf temperature at which ice formation occurred were measured at two sites along an altitudinal gradient. Mean CO 2 assimilation rates for E. neriifolia were 3.4 and 1.3 μmol·m -2·s -1, at 2 400 and 3 200 m, respectively. Mean night respiration was 2.2 and 0.9 μmol·m -2·s -1 for this species at 2 400 and 3 200 m, respectively. Mean assimilation rates for P. oleifolius were 3.8 and 2.2 μmol·m -2·s -1 at 2 550 and 3 200 m, respectively. Night respiration was 0.8 μmol·m -2·s -1 for both altitudes. E. neriifolia showed similar optimum temperatures for photosynthesis at both altitudes, while a decrease was observed in P. oleifolius.E. neriifolia and P. oleifolius presented supercooling capacities of -6.5 and -3.0 °C, respectively. For E. neriifolia, freezing resistance mechanisms are sufficient to reach higher altitudes; however, other environmental factors such as cloudiness may be affecting its carbon balance. P. oleifolius does not reach higher elevations because it does not have the freezing resistance mechanisms.

  3. River temperature processes under contrasting riparian land cover: linking microclimate, heat exchange and water thermal dynamics

    Science.gov (United States)

    Hannah, D. M.; Kantola, K.; Malcolm, I.

    2012-12-01

    River temperature influences strongly growth and survival in salmonid fish, which are often the target of river management strategies. Temperature is controlled by transfers of heat and water to/ from the river system, with land and water management modifying exchanges and consequently thermal regime. In the UK, fisheries managers are promoting riparian forest planting as a climate change adaption measure to reduce water temperature extremes. However, scientific understanding lags behind management and policy needs. Specifically, there is an urgent requirement to determine planting strategies that maximise expected benefits of riparian forest in terms of reduction in maximum water temperature. Scientific knowledge is necessary to underpin conceptual and deterministic models to inform management. To address this research gap, this paper analyses high resolution (15 minute) hydrometeorological data collected over a calendar year in the western Scottish Highlands (Loch Ard) to understand the controls and processes determining river temperature dynamics under open moorland (control), semi-natural woodland and commercial forest. The research programme aims: (1) to characterise spatial and temporal variability in riparian microclimate and stream water temperature regime across forest treatments; (2) to identify the hydrological, climatological and site-specific factors affecting stream temperature; (3) to estimate the energy balance at sites representative of each forest treatment and, thus, yield physical process understanding about dominant heat exchanges driving thermal variability; and (4) to use 1-3 to predict stream temperature sensitivity under different forestry and hydroclimatological scenarios. Results indicated that inter-treatment differences in mean and maximum daily water column temperature were ordered open > semi-natural > commercial during summer, but semi-natural > commercial > open during winter. Minimum water temperature was ordered commercial > semi

  4. Recruitment dynamics mediated by ungulate herbivory can affect species coexistence for tree seedling assemblages

    Directory of Open Access Journals (Sweden)

    Chi-Yu Weng

    2017-08-01

    Full Text Available The best-known mechanism that herbivory affects species coexistence of tree seedlings is negative density-dependency driven by specialist natural enemies. However, in a forest with intense herbivory by non-specialists, what causes a diversifying seedling bank if rare species do not benefit from negative density-dependency in dominant species? We hypothesize that generalist herbivores can cause unevenly distributed species-specific mortality, which mediates recruitment dynamics and therefore affects species coexistence. To answer this question, we conducted a fence-control experiment in a montane cloud forest, Taiwan, and found that herbivorous damages were mainly caused by ungulates, which are generalists. We explored ungulate herbivory effects on recruitment dynamics by censusing tree seedling dynamics for three years. We found that herbivorous damages by ungulates significantly cause seedling death, mostly at their early stage of establishment. The percentage of death caused by herbivory varied among species. In particular, nurse plants and seedling initial height help shade-tolerant species to persist under such intense herbivory. Whereas, deaths caused by other factors occurred more often in older seedlings, with a consistent low percentage among species. We then tested species coexistence maintenance by dynamic modelling under different scenarios of ungulate herbivory. Raising percentages of death by herbivory changes relative species abundances by suppressing light-demanding species and increasing shade-tolerant species. Density-dependent mortality immediately after bursts of recruitments can suppress dominance of abundant species. With ungulate herbivory, fluctuating recruitment further prevent rare species from apparent competition induced by abundant species. Such bio-processes can interact with ungulate herbivory so that long-term coexistence can be facilitated.

  5. Efficient Determination of Relative Entropy Using Combined Temperature and Hamiltonian Replica-Exchange Molecular Dynamics.

    Science.gov (United States)

    Jo, Sunhwan; Chipot, Christophe; Roux, Benoît

    2015-05-12

    The performance and accuracy of different simulation schemes for estimating the entropy inferred from free energy calculations are tested. The results obtained from replica-exchange molecular dynamics (REMD) simulations based on a simplified toy model are compared to exact numerically derived ones to assess accuracy and convergence. It is observed that the error in entropy estimation decreases by at least an order of magnitude and the quantities of interest converge much faster when the simulations are coupled via a temperature REMD algorithm and the trajectories from different temperatures are combined. Simulations with the infinite-swapping method and its variants show some improvement over the traditional nearest-neighbor REMD algorithms, but they are more computationally expensive. To test the methodologies further, the free energy profile for the reversible association of two methane molecules in explicit water was calculated and decomposed into its entropic and enthalpic contributions. Finally, a strategy based on umbrella sampling computations carried out via simultaneous temperature and Hamiltonian REMD simulations is shown to yield the most accurate entropy estimation. The entropy profile between the two methane molecules displays the characteristic signature of a hydrophobic interaction.

  6. Combining Elastic Network Analysis and Molecular Dynamics Simulations by Hamiltonian Replica Exchange.

    Science.gov (United States)

    Zacharias, Martin

    2008-03-01

    Coarse-grained elastic network models (ENM) of proteins can be used efficiently to explore the global mobility of a protein around a reference structure. A new Hamiltonian-replica exchange molecular dynamics (H-RexMD) method has been designed that effectively combines information extracted from an ENM analysis with atomic-resolution MD simulations. The ENM analysis is used to construct a distance-dependent penalty (flooding or biasing) potential that can drive the structure away from its current conformation in directions compatible with the ENM model. Various levels of the penalty or biasing potential are added to the force field description of the MD simulation along the replica coordinate. One replica runs at the original force field. By focusing the penalty potential on the relevant soft degrees of freedom the method avoids the rapid increase of the replica number with increasing system size to cover a desired temperature range in conventional (temperature) RexMD simulations. The application to domain motions in lysozyme of bacteriophage T4 and to peptide folding indicates significantly improved conformational sampling compared to conventional MD simulations.

  7. Replica exchange molecular dynamics study of the truncated amyloid beta (11-40) trimer in solution.

    Science.gov (United States)

    Ngo, Son Tung; Hung, Huynh Minh; Truong, Duc Toan; Nguyen, Minh Tho

    2017-01-18

    Amyloid beta (Aβ) oligomers are neurotoxic compounds that destroy the brain of Alzheimer's disease patients. Recent studies indicated that the trimer is one of the most cytotoxic forms of low molecular weight Aβ oligomers. As there was limited information about the structure of the Aβ trimer, either by experiment or by computation, we determined in this work the structure of the 3Aβ11-40 oligomer for the first time using the temperature replica exchange molecular dynamics simulations in the presence of an explicit solvent. More than 20.0 μs of MD simulations were performed. The probability of the β-content and random coil structure of the solvated trimer amounts to 42 ± 6 and 49 ± 7% which is in good agreement with experiments. Intermolecular interactions in central hydrophobic cores play a key role in stabilizing the oligomer. Intermolecular polar contacts between D23 and residues 24-29 replace the salt bridge D23-K28 to secure the loop region. The hydrophilic region of the N-terminus is maintained by the intermolecular polar crossing contacts H13A-Q15B and H13B-Q15C. The difference in the free energy of binding between the constituting monomers and the others amounts to -36 ± 8 kcal mol(-1). The collision cross section of the representative structures of the trimer was computed to be 1330 ± 47 Å(2), which is in good agreement with previous experiments.

  8. Replica exchange molecular dynamics simulations of coarse-grained proteins in implicit solvent.

    Science.gov (United States)

    Chebaro, Yassmine; Dong, Xiao; Laghaei, Rozita; Derreumaux, Philippe; Mousseau, Normand

    2009-01-08

    Current approaches aimed at determining the free energy surface of all-atom medium-size proteins in explicit solvent are slow and are not sufficient to converge to equilibrium properties. To ensure a proper sampling of the configurational space, it is preferable to use reduced representations such as implicit solvent and/or coarse-grained protein models, which are much lighter computationally. Each model must be verified, however, to ensure that it can recover experimental structures and thermodynamics. Here we test the coarse-grained implicit solvent OPEP model with replica exchange molecular dynamics (REMD) on six peptides ranging in length from 10 to 28 residues: two alanine-based peptides, the second beta-hairpin from protein G, the Trp-cage and zinc-finger motif, and a dimer of a coiled coil peptide. We show that REMD-OPEP recovers the proper thermodynamics of the systems studied, with accurate structural description of the beta-hairpin and Trp-cage peptides (within 1-2 A from experiments). The light computational burden of REMD-OPEP, which enables us to generate many hundred nanoseconds at each temperature and fully assess convergence to equilibrium ensemble, opens the door to the determination of the free energy surface of larger proteins and assemblies.

  9. Custom-tailored adsorbers: A molecular dynamics study on optimal design of ion exchange chromatography material.

    Science.gov (United States)

    Lang, Katharina M H; Kittelmann, Jörg; Pilgram, Florian; Osberghaus, Anna; Hubbuch, Jürgen

    2015-09-25

    The performance of functionalized materials, e.g., ion exchange resins, depends on multiple resin characteristics, such as type of ligand, ligand density, the pore accessibility for a molecule, and backbone characteristics. Therefore, the screening and identification process for optimal resin characteristics for separation is very time and material consuming. Previous studies on the influence of resin characteristics have focused on an experimental approach and to a lesser extent on the mechanistic understanding of the adsorption mechanism. In this in silico study, a previously developed molecular dynamics (MD) tool is used, which simulates any given biomolecule on resins with varying ligand densities. We describe a set of simulations and experiments with four proteins and six resins varying in ligand density, and show that simulations and experiments correlate well in a wide range of ligand density. With this new approach simulations can be used as pre-experimental screening for optimal adsorber characteristics, reducing the actual number of screening experiments, which results in a faster and more knowledge-based development of custom-tailored adsorbers.

  10. Dynamics of Foreign Exchange Networks: A Time-Varying Copula Approach

    Directory of Open Access Journals (Sweden)

    Gang-Jin Wang

    2014-01-01

    Full Text Available Based on a time-varying copula approach and the minimum spanning tree (MST method, we propose a time-varying correlation network-based approach to investigate dynamics of foreign exchange (FX networks. In piratical terms, we choose the daily FX rates of 42 major currencies in the international FX market during the period of 2005–2012 as the empirical data. The empirical results show that (i the distributions of cross-correlation coefficients (distances in the international FX market (network are fat-tailed and negatively skewed; (ii financial crises during the analyzed period have a great effect on the FX network’s topology structure and lead to the US dollar becoming more centered in the MST; (iii the topological measures of the FX network show a large fluctuation and display long-range correlations; (iv the FX network has a long-term memory effect and presents a scale-free behavior in the most of time; and (v a great majority of links between currencies in the international FX market survive from one time to the next, and multistep survive rates of FX networks drop sharply as the time increases.

  11. A methodology for determining the dynamic exchange of resources in nuclear fuel cycle simulation

    Energy Technology Data Exchange (ETDEWEB)

    Gidden, Matthew J., E-mail: gidden@iiasa.ac.at [International Institute for Applied Systems Analysis, Schlossplatz 1, A-2361 Laxenburg (Austria); University of Wisconsin – Madison, Department of Nuclear Engineering and Engineering Physics, Madison, WI 53706 (United States); Wilson, Paul P.H. [University of Wisconsin – Madison, Department of Nuclear Engineering and Engineering Physics, Madison, WI 53706 (United States)

    2016-12-15

    Highlights: • A novel fuel cycle simulation entity interaction mechanism is proposed. • A framework and implementation of the mechanism is described. • New facility outage and regional interaction scenario studies are described and analyzed. - Abstract: Simulation of the nuclear fuel cycle can be performed using a wide range of techniques and methodologies. Past efforts have focused on specific fuel cycles or reactor technologies. The CYCLUS fuel cycle simulator seeks to separate the design of the simulation from the fuel cycle or technologies of interest. In order to support this separation, a robust supply–demand communication and solution framework is required. Accordingly an agent-based supply-chain framework, the Dynamic Resource Exchange (DRE), has been designed implemented in CYCLUS. It supports the communication of complex resources, namely isotopic compositions of nuclear fuel, between fuel cycle facilities and their managers (e.g., institutions and regions). Instances of supply and demand are defined as an optimization problem and solved for each timestep. Importantly, the DRE allows each agent in the simulation to independently indicate preference for specific trading options in order to meet both physics requirements and satisfy constraints imposed by potential socio-political models. To display the variety of possible simulations that the DRE enables, example scenarios are formulated and described. Important features include key fuel-cycle facility outages, introduction of external recycled fuel sources (similar to the current mixed oxide (MOX) fuel fabrication facility in the United States), and nontrivial interactions between fuel cycles existing in different regions.

  12. Experimental and parametric studies of a louvered fin and flat tube compact heat exchanger using computational fluid dynamics

    Directory of Open Access Journals (Sweden)

    P. Karthik

    2015-12-01

    Full Text Available The present study aimed to perform the parametric analysis on thermo-hydraulic performance of a compact heat exchanger using computational fluid dynamics (CFD. The analysis has been carried out at different frontal air velocities by varying the geometrical parameters such as fin pitch, transverse tube pitch, longitudinal tube pitch, louver pitch and louver angle. The air side performance of the heat exchanger has been evaluated by calculating Colburn factor (j and Fanning friction factor (f. The comparison of CFD results with the experimental data exhibited a good agreement and the influence of various geometrical parameters for the selected range of values on the pressure drop, heat transfer coefficient and goodness factor was analyzed. The results obtained from the analysis will be very useful to optimize the louvered fin and flat tube compact heat exchanger for better thermo-hydraulic performance analysis without the need of time consuming and expensive experimentation.

  13. Optimization of the Dynamic Behavior of a Heat Exchanger Subject to Fouling Comparison of Three Optimization Models

    Directory of Open Access Journals (Sweden)

    Michel Feidt

    1999-06-01

    Full Text Available

    This paper proposes a dynamic analysis of fouling of a heat exchanger. The used criteria is mean thermal power exchanged over time. The proposed results are relative to cocurrent configuration and tubular geometry of the heat exchanger, but other cases have been explored (countercurrent, plane geometry. An optimum time is determined, sensitivity analysis of the corresponding value to three cases of flow regimes (constant mass flow rate, constant flow velocity and constant pumping power and various kinetics of fouling has been performed. The time of stop of the installation for cleaning is the main parameter. All the results are proposed in nondimensional form.

    •  This paper was presented at the ECOS’98 Conference in Nancy, June 8-10, 1998

  14. Exchange rate dynamics, structural breaks, and central bank interventions in Colombia

    Directory of Open Access Journals (Sweden)

    Jorge Mario Uribe

    2015-12-01

    Full Text Available We evaluate the effectiveness of the Colombian Central Bank´s interventions in the foreign exchange market during the period 2000 to 2014. We examine the stochastic process that describes the exchange rate, with a focus on the detection of structural breaks or unit roots in the data to determine whether the Central Bank´s interventions were effective. We find that the exchange rate can be described either by a random walk or by a trend-stationary model with multiple breaks. In neither cases do we find any evidence that the exchange rate was affected by the Central Bank interventions.

  15. Elucidation of molecular dynamics of invasive species of rice

    Science.gov (United States)

    Cultivated rice fields are aggressively invaded by weedy rice in the U.S. and worldwide. Weedy rice results in loss of yield and seed contamination. The molecular dynamics of the evolutionary adaptive traits of weedy rice are not fully understood. To understand the molecular basis and identify the i...

  16. Static and dynamic quenching of luminescent species in polymer media.

    Science.gov (United States)

    Hartmann, P; Leiner, M J; Lippitsch, M E

    1994-12-01

    A method developed for quantitative determination of static and dynamic contributions to luminescence quenching is applied to Ru(II) complexes in polymer matrices (silica gel and polystyrene), quenched by oxygen. This method is based on both intensity and lifetime quenching experiments. The curvature of intensity Stern-Volmer plots is related to the results.

  17. Is parasitoid acceptance of different host species dynamic?

    Science.gov (United States)

    Choice of host individuals by parasitoids is dynamic, varying with physiological state and experience. In particular, female parasitoids with high egg loads and low life expectancy are more willing to accept low quality hosts than females with low egg loads and high life expectancy. However, studi...

  18. An enhanced vector-free allele exchange (VFAE) mutagenesis protocol for genome editing in a wide range of bacterial species.

    Science.gov (United States)

    Gomaa, Ahmed E; Zhang, Chen; Yang, Zhimin; Shang, Liguo; Jiang, Shijie; Deng, Zhiping; Zhan, Yuhua; Lu, Wei; Lin, Min; Yan, Yongliang

    2017-12-01

    Vector-free allele exchange (VFAE) is a newly developed protocol for genome editing in Pseudomonas species. Although several parameters have been determined to optimize the procedures for obtaining a stable and high-frequency mutation, numerous false-positive clones still appear on the plate, which increases the difficulty of finding the desired mutants. It has also not been established whether this protocol can be used for genome editing in other bacterial species. In the current study, the protocol was modified to dramatically decrease the occurrence of false-positive colonies using Pseudomonas stutzeri A1501 as a model strain. This improvement was reached by increasing the occurrence of circular-DNA cassettes of the correct size. Furthermore, the enhanced protocol was used to construct mutants in both the gram-negative Escherichia coli BL21 and gram-positive Bacillus subtilis 168 strains. The protocol works well in both strains, yielding ideal results with a low percentage of false-positive colonies. In summary, the enhanced VFAE mutagenesis protocol is a potential tool for use in bacterial genome editing.

  19. Can gas exchange dynamics predict non-structural carbohydrate use under drought stress?

    Science.gov (United States)

    Kannenberg, S.; Phillips, R.

    2016-12-01

    A recent conceptual framework for understanding tree drought responses characterizes species along a continuum from isohydry to anisohydry, with theory predicting that isohydric and anisohydric trees should display different carbon (C) allocation patterns under drought conditions. We tested the hypothesis that the trade-offs inherent in the isohydry-anisohydry framework (i.e., C starvation vs. hydraulic failure) necessitate different allocation patterns to non-structural carbohydrates (NSCs), growth, and respiration. Specifically, we hypothesized that isohydric trees would decrease NSC stores and growth in the face of reduced incoming photoassimilate, whereas anisohydric trees would maintain assimilation, growth, and NSC pools due to decreased demand for stored metabolic C and enhanced osmoregulatory needs. To test this, we subjected saplings of Liriodendron tulipifera (an isohydric tree) and Quercus alba (an anisohydric tree) to a six week drought in the greenhouse, and measured assimilation, leaf water potential (midday and predawn), growth, leaf dark respiration and NSCs (both sugars and starch in aboveground and belowground tissues) in control and droughted plants. Overall, we confirmed that the isohydric and anisohydric species used NSCs differently during drought. In most tissues, both species had similar responses of NSCs to drought: starch NSCs were maintained or decreased while sugar NSCs tended to increase. Stem NSCs were a notable exception, as L. tulipifera decreased total NSC to almost zero while NSCs in Q. alba remained constant. This depletion of stem NSC in L. tulipifera was offset by increases in other tissues, however, resulting in no net change to total NSC during the drought. In contrast, Q. alba increased total NSC. Interestingly, Q. alba also decreased assimilation and growth, indicating a potential trade-off between NSC and biomass allocation. Our results show that NSCs in different tissues may have contrasting uses as storage or

  20. Variation in seed buoyancy of species in wetland ecosystems with different flooding dynamics

    NARCIS (Netherlands)

    van den Broek, T; van Diggelen, R; Bobbink, R

    2005-01-01

    Question: Do species from communities with different flooding dynamics differ in seed buoyancy? Is there a trade-off between seed buoyancy and seed longevity? Methods: Seeds of 55 freshwater wetland species were collected and related to communities along the hydrological gradient, ranging from

  1. Influence of plant species on population dynamics, genotypic diversity and antibiotic production by indigenous Pseudomonas spp

    NARCIS (Netherlands)

    Bergsma-Vlami, M.; Prins, M.E.; Raaijmakers, J.M.

    2005-01-01

    The population dynamics, genotypic diversity and activity of naturally-occurring 2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas spp. was investigated for four plant species (wheat, sugar beet, potato, lily) grown in two different soils. All four plant species tested, except lily and in some

  2. Isobaric Molecular Dynamics Version of the Generalized Replica Exchange Method (gREM): Liquid-Vapor Equilibrium.

    Science.gov (United States)

    Małolepsza, Edyta; Secor, Maxim; Keyes, Tom

    2015-10-22

    A prescription for sampling isobaric generalized ensembles with molecular dynamics is presented and applied to the generalized replica exchange method (gREM), which was designed to simulate first-order phase transitions. The properties of the isobaric gREM ensemble are discussed, and a study is presented for the liquid-vapor equilibrium of the guest molecules given for gas hydrate formation with the mW water model. Phase diagrams, critical parameters, and a law of corresponding states are obtained.

  3. Solution conformation and dynamics of exopolysaccharides from Burkholderia species.

    Science.gov (United States)

    Pol-Fachin, Laercio; Serrato, Rodrigo V; Verli, Hugo

    2010-09-03

    Exopolysaccharides (EPSs) from the Burkholderia genus are proposed to be involved in pathological conditions in humans, such as cystic fibrosis and septicemia, as well as in the stability of soil aggregates. Hence, considering that the conformational and dynamic aspects of such EPSs may influence their biological activity, the current work employs a series of molecular dynamics simulations on di-, oligo-, and polysaccharide fragments of three EPSs, from Burkholderia caribensis, Burkholderia cepacia, and Burkholderia pseudomallei, with previously determined NOE data, to obtain a conformational description of such EPSs at the atomic level. As the obtained results show good agreement with the experimental data, pointing to the adequacy of the employed methodology to accurately describe the dynamics of polysaccharides, the strategy was also employed to predict the conformational behavior of an additional compound, from Burkholderia tropica, for which NOE signals are not available. Taking into account the potential importance of EPSs on the interaction of Burkholderia bacteria with distinct environments, it may be expected that a greater understanding of their structural aspects may contribute to controlling their pathological roles and potential agricultural applications.

  4. Boundary layers at a dynamic interface: Air-sea exchange of heat and mass

    Science.gov (United States)

    Szeri, Andrew J.

    2017-04-01

    Exchange of mass or heat across a turbulent liquid-gas interface is a problem of critical interest, especially in air-sea transfer of natural and anthropogenic gases involved in the study of climate. The goal in this research area is to determine the gas flux from air to sea or vice versa. For sparingly soluble nonreactive gases, this is controlled by liquid phase turbulent velocity fluctuations that act on the thin species concentration boundary layer on the liquid side of the interface. If the fluctuations in surface-normal velocity w' and gas concentration c' are known, then it is possible to determine the turbulent contribution to the gas flux. However, there is no suitable fundamental direct approach in the general case where neither w' nor c' can be easily measured. A new approach is presented to deduce key aspects about the near-surface turbulent motions from measurements that can be taken by an infrared (IR) camera. An equation is derived with inputs being the surface temperature and heat flux, and a solution method developed for the surface-normal strain experienced over time by boundary layers at the interface. Because the thermal and concentration boundary layers experience the same near-surface fluid motions, the solution for the surface-normal strain determines the gas flux or gas transfer velocity. Examples illustrate the approach in the cases of complete surface renewal, partial surface renewal, and insolation. The prospects for use of the approach in flows characterized by sheared interfaces or rapid boundary layer straining are explored.

  5. Effect of the geometric phase on the dynamics of the hydrogen-exchange reaction.

    Science.gov (United States)

    Juanes-Marcos, Juan Carlos; Althorpe, Stuart C; Wrede, Eckart

    2007-01-28

    A recent puzzle in nonadiabatic quantum dynamics is that geometric phase (GP) effects are present in the state-to-state opacity functions of the hydrogen-exchange reaction, but cancel out in the state-to-state integral cross sections (ICSs). Here the authors explain this result by using topology to separate the scattering amplitudes into contributions from Feynman paths that loop in opposite senses around the conical intersection. The clockwise-looping paths pass over one transition state (1-TS) and scatter into positive deflection angles; the counterclockwise-looping paths pass over two transition states (2-TS) and scatter into negative deflection angles. The interference between the 1-TS and 2-TS paths thus integrates to a very small value, which cancels the GP effects in the ICS. Quasiclassical trajectory (QCT) calculations reproduce the scattering of the 1-TS and 2-TS paths into positive and negative deflection angles and show that the 2-TS paths describe a direct insertion mechanism. The inserting atom follows a highly constrained "S-bend" path, which allows it to avoid both the other atoms and the conical intersection and forces the product diatom to scatter into high rotational states. By contrast, the quantum 2-TS paths scatter into a mainly statistical distribution of rotational states, so that the quantum 2-TS total ICS is roughly twice the QCT ICS at 2.3 eV total energy. This suggests that the S-bend constraint is relaxed by tunneling in the quantum system. These findings on H+H(2) suggest that similar cancellations or reductions in GP effects are likely in many other reactions.

  6. Influence of intergranular exchange coupling on the magnetization dynamics of CoCrPt:SiO{sub 2} granular media

    Energy Technology Data Exchange (ETDEWEB)

    Brandt, R.; Schmidt, H. [School of Engineering, University of California-Santa Cruz, 1156 High Street, Santa Cruz, California 95064 (United States); Tibus, S. [Department of Physics, University of Konstanz, D-78457 Konstanz (Germany); Institute of Physics, Chemnitz University of Technology, Reichenhainer Str. 70, 09126 Chemnitz (Germany); Springer, F. [Department of Physics, University of Konstanz, D-78457 Konstanz (Germany); Fassbender, J. [Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, D-01314 Dresden (Germany); Rohrmann, H. [OC Oerlikon Balzers AG, LI-9496 Balzers (Liechtenstein); Albrecht, M. [Institute of Physics, Chemnitz University of Technology, Reichenhainer Str. 70, 09126 Chemnitz (Germany)

    2012-08-01

    We investigate the effect of Co{sup +} irradiation on the magnetization dynamics of CoCrPt:SiO{sub 2} granular media. Increasing irradiation levels reduce the saturation magnetization and effective anisotropy, which decrease the intrinsic magnetization precession frequency. Furthermore, increasing intergranular exchange coupling results in a qualitative change in the behavior of the magnetic material from a collection of individual grains to a homogeneous thin film, as evidenced in both the switching behavior and dynamics. The frequency change cannot be explained by single crystal macrospin modeling, and can only be reproduced by the inclusion of the dipolar effects and anisotropy distribution inherent in a granular medium.

  7. The Effects of Workers’ Remittances on Exchange Rate Volatility and Exports Dynamics -New Evidence from Pakistan

    Directory of Open Access Journals (Sweden)

    Adnan Khurshid

    2017-03-01

    Full Text Available This study examines the impact of remittances on the exchange rate and exports in Pakistan, using the system GMM aproach on annual data series. We carry out a full sample Granger causality test along with the sub-sample rolling window approach using monthly data series to find the causal relationship between remittances (REM and the exchange rate (EXR. The System GMM results reveal that remittances depreciate the exchange rate and have a positive influence on export competitiveness. In addition to this, the remittance inflow appreciates the exchange rate only if it is used for savings and negatively affects competitiveness if it is channeled towards consumption. The change in exchange rate regime from multiple to flexible depreciated the exchange rate while, the global financial crises uplifted the currency rate and negatively affect the exports. The results show the bidirectional causal relationship between remittances and the exchange rate. The outcomes further reveal that the parameters in the VAR model are unstable, which is a clear indication of the presence of structural changes. The rolling window estimation approach with time-varying characteristics finds bi-directional causality between REM and the EXR in the different sub-samples. The results of this study fall in line with the portfolio model proposed by Mussa (1984 which states that the flow of remittances causes appreciation. The sub-sample causality is related to significant economic events, which means the results are not a statistical artifact.

  8. Species dynamics during early secondary forest succession: recruitment, mortality and species turnover.

    NARCIS (Netherlands)

    Breugel, van M.; Bongers, F.J.J.M.; Martínez-Ramos, M.

    2007-01-01

    The "Initial Floristic Composition" hypothesis is applied to secondary tropical rain forest succession in abandoned agricultural fields with light previous land-use and close to seed sources. This hypothesis predicts that both pioneer and shade-tolerant species colonize a site directly after abandon

  9. Long-term successional forest dynamics: species and community responses to climatic variability

    Energy Technology Data Exchange (ETDEWEB)

    Kardol, Paul [ORNL; Todd Jr, Donald E [ORNL; Hanson, Paul J [ORNL; Mulholland, Patrick J [ORNL

    2010-01-01

    Question: Are tree dynamics sensitive to climatic variability, and do tree species differ in their responses to climatic variability? Hence, is vulnerability of forest communities to climatic variability depending on stand composition? Location: Mixed young forest at Walker Branch Watershed near Oak Ridge, East-Tennessee, USA. Methods: Using a long-term data set (1967-2006), we analyzed temporal forest dynamics at the tree and species level, and we analyzed community dynamics for forest stands that different in their initial species composition (i.e., Chestnut Oak, Oak-Hickory, Pine, and Yellow poplar stands). Using summer drought and growing season temperature as defined climate drivers, we evaluated relationships between forest dynamics and climate across levels of organization. Results: Over the 4-decade studied period, forest communities underwent successional change and substantially increased their biomass. Variation in summer drought and growing season temperature contributed to temporal biomass dynamics for some tree species, but not for others. Stand-level responses to climatic variability were shown to be related to responses of specific component species; however, not for Pine stands. Pinus echinata, the dominant species in stands initially identified as Pine stands, decreased over time due to periodical outbreaks of the pine bark beetle (Dendroctonus frontalis). The outbreaks on Walker Branch could not be directly related to climatic conditions. Conclusions: Our results imply that vulnerability of developing forests to predicted climate conditions is stand-type dependent, and hence, is a function of species composition. Autogenic successional processes (or insect outbreaks) were found to prevail over climatic variability in determining long-term forest dynamics for stands dominated by sensitive species, emphasizing the importance of studying interactions between forest succession and climate change.

  10. Quantifying Hyporheic Exchanges in a Large Scale River Reach Using Coupled 3-D Surface and Subsurface Computational Fluid Dynamics Simulations

    Science.gov (United States)

    Bao, J.; Zhou, T.; Huang, M.; Hou, Z.; Perkins, W. A.; Harding, S.; Hammond, G. E.; Ren, H.; Thorne, P. D.; Suffield, S. R.; Zachara, J. M.

    2016-12-01

    Hyporheic exchange between river water and groundwater is an important mechanism for biogeochemical processes, such as carbon and nitrogen cycling, and biodegradation of organic contaminants, in the subsurface interaction zone. The relationship between river flow conditions and hyporheic exchanges therefore is of great interests to hydrologists, biogeochemists, and ecologists. However, quantifying relative influences of hydrostatic and hydrodynamic drivers on hyporheic exchanges is very challenging in large rivers due to accessibility and spatial coverage of measurements, and computational tools available for numerical experiments. In this study, we aim to demonstrate that a high resolution computational fluid dynamics (CFD) model that couples surface and subsurface flow and transport can be used to simulate hyporheic exchanges and the residence time of river water in the hypothetic zone. Base on the assumption that the hyporheic exchange does not affect the surface water flow condition due to its small magnitude compared to the velocity of river water, we developed a one way coupled surface and subsurface water flow model in a commercial CFD software STAR-CCM+, that connects the Reynolds-averaged Navier-Stokes (RANS) equation solver with a realizable two-layer turbulence model, a two-layer all y+ wall treatment, and the volume of fluid (VOF) method for tracking the free water-air interface as well as porous media flow in the subsurface domain. The model is applied to a 7-km long section of the Columbia River and validated against measurements from the acoustic Doppler current profiler (ADCP) in the surface water and hyporheic fluxes derived from a set of temperature profilers installed across the riverbed. The validated model is then employed to systematically investigate how hyporheic exchanges influenced by 1) riverbed properties such as the permeability and thickness of the alluvial layer; 2) surface water hydrodynamics due to channel geomorphological settings

  11. Monitoring the Dynamics of Monomer Exchange Using Electrospray Mass Spectrometry: The Case of the Dimeric Glucosamine-6-Phosphate Synthase

    Science.gov (United States)

    Chevreux, Guillaume; Atmanene, Cédric; Lopez, Philippe; Ouazzani, Jamal; Van Dorsselaer, Alain; Badet, Bernard; Badet-Denisot, Marie-Ange; Sanglier-Cianférani, Sarah

    2011-03-01

    Escherichia coli glucosamine-6-phosphate synthase (GlmS) is a dimeric enzyme from the glutamine-dependent amidotransferases family, which catalyses the conversion of D-fructose-6-phosphate (Fru6P) and glutamine (Gln) into D-glucosamine-6-phosphate (GlcN6P) and glutamate, respectively. Extensive X-ray crystallography investigations have been reported, highlighting the importance of the dimeric association to form the sugar active site as well as significant conformational changes of the protein upon substrate and product binding. In the present work, an approach based on time-resolved noncovalent mass spectrometry has been developed to study the dynamics of GlmS subunit exchange. Using 14N versus 15N labeled proteins, the kinetics of GlmS subunit exchange was monitored with the wild-type enzyme in the presence of different substrates and products as well as with the protein bearing a key amino acid mutation specially designed to weaken the dimer interface. Determination of rate constants of subunit exchange revealed important modifications of the protein dynamics: while glutamine, glutamate, and K603A mutation accelerates subunit exchange, Fru6P and GlcN6P totally prevent it. These results are described in light of the available structural information, providing additional useful data for both the characterization of GlmS catalytic process and the design of new GlmS inhibitors. Finally, time-resolved noncovalent MS can be proposed as an additional biophysical technique for real-time monitoring of protein dynamics.

  12. Dynamics of metal-humate complexation equilibria as revealed by isotope exchange studies - a matter of concentration and time

    Science.gov (United States)

    Lippold, Holger; Eidner, Sascha; Kumke, Michael U.; Lippmann-Pipke, Johanna

    2017-01-01

    Complexation with dissolved humic matter can be crucial in controlling the mobility of toxic or radioactive contaminant metals. For speciation and transport modelling, a dynamic equilibrium process is commonly assumed, where association and dissociation run permanently. This is, however, questionable in view of reported observations of a growing resistance to dissociation over time. In this study, the isotope exchange principle was employed to gain direct insight into the dynamics of the complexation equilibrium, including kinetic inertisation phenomena. Terbium(III), an analogue of trivalent actinides, was used as a representative of higher-valent metals. Isotherms of binding to (flocculated) humic acid, determined by means of 160Tb as a radiotracer, were found to be identical regardless of whether the radioisotope was introduced together with the bulk of stable 159Tb or subsequently after pre-equilibration for up to 3 months. Consequently, there is a permanent exchange of free and humic-bound Tb since all available binding sites are occupied in the plateau region of the isotherm. The existence of a dynamic equilibrium was thus evidenced. There was no indication of an inertisation under these experimental conditions. If the small amount of 160Tb was introduced prior to saturation with 159Tb, the expected partial desorption of 160Tb occurred at much lower rates than observed for the equilibration process in the reverse procedure. In addition, the rates decreased with time of pre-equilibration. Inertisation phenomena are thus confined to the stronger sites of humic molecules (occupied at low metal concentrations). Analysing the time-dependent course of isotope exchange according to first-order kinetics indicated that up to 3 years are needed to attain equilibrium. Since, however, metal-humic interaction remains reversible, exchange of metals between humic carriers and mineral surfaces cannot be neglected on the long time scale to be considered in predictive

  13. Dynamic approaches of mixed species biofilm formation using modern technologies.

    Science.gov (United States)

    Doiron, Kim; Linossier, Isabelle; Fay, Fabienne; Yong, Julius; Abd Wahid, Effendy; Hadjiev, Dimitre; Bourgougnon, Nathalie

    2012-07-01

    Bacteria and diatoms exist in sessile communities and develop as biofilm on all surfaces in aqueous environments. The interaction between these microorganisms in biofilm was investigated with a bacterial genus Pseudoalteromonas sp. (strain 3J6) and two benthic diatoms Amphora coffeaeformis and Cylindrotheca closterium. Each biofilm was grown for 22 days. Images from the confocal microscopy show a difference of adhesion between Pseudoalteromonas 3J6 and diatoms. Indeed, a stronger adhesion is found with C. closterium suggesting cohabitation between Pseudoalteromonas 3J6 and C. closterium compared at an adaptation for bacteria and A. coffeaeformis. The cellular attachment and the growth evolution in biofilm formation depend on each species of diatoms in the biofilm. Behaviour of microalgae in presence of bacteria demonstrates the complexity of the marine biofilm.

  14. Development of gas exchange and ion regulation in two species of air-breathing fish, Betta splendens and Macropodus opercularis.

    Science.gov (United States)

    Huang, Chun-Yen; Lin, Cheng-Huang; Lin, Hui-Chen

    2015-07-01

    Aquatic air-breathing anabantoids, a group of fish species characterized by the presence of a labyrinth organ and some gills, exhibit morphological variations. This study aimed to examine whether unequal gill growth begins during the early stages and described the sequence of the early gill developmental events in Betta splendens and Macropodus opercularis. To determine when the ion regulatory and gas exchange abilities first appear in the gills, mitochondria-rich cells (MRCs) and neuroepithelial cells (NECs) were examined in young B. splendens. To evaluate the relative importance of the gills and the labyrinth organ under different levels of oxygen uptake stress, the levels of carbonic anhydrase II (CAII) and Na(+)/K(+)-ATPase (NKA) protein expressions in 2 gills and the labyrinth organ were examined in M. opercularis. We found that the first 3 gills developed earlier than the 4th gill in both species, an indication that the morphological variation begins early in life. In B. splendens, the MRCs and NECs clearly appeared in the first 3 gills at 4 dph and were first found in the 4th gill until 11 dph. The oxygen-sensing ability of the gills was concordant with the ionoregulatory function. In M. opercularis, the hypoxic group had a significantly higher air-breathing frequency. CAII protein expression was higher in the labyrinth organ in the hypoxic group. The gills exhibited increased NKA protein expression in the hypoxic and restricted groups, respectively. Functional plasticity in CAII and NKA protein expressions was found between the gills and the labyrinth organ in adult M. opercularis.

  15. Dynamic Links between Exchange Rates and Stock Prices in Malaysia: An Asymmetric Cointegration analysis

    National Research Council Canada - National Science Library

    Hamisu Sadi ALI; Umar MUKHTAR; Ganthi Selvi MANIAM

    2015-01-01

    The present article used a monthly data and applied Enders and Siklos (2001) asymmetric cointegration analysis to examine the impact of exchange rates on stock prices in Malaysia for the period of 1999-2014...

  16. A CORBA-based object framework with patient identification translation and dynamic linking. Methods for exchanging patient data.

    Science.gov (United States)

    Wang, C; Ohe, K

    1999-03-01

    Exchanging and integration of patient data across heterogeneous databases and institutional boundaries offers many problems. We focused on two issues: (1) how to identify identical patients between different systems and institutions while lacking universal patient identifiers; and (2) how to link patient data across heterogeneous databases and institutional boundaries. To solve these problems, we created a patient identification (ID) translation model and a dynamic linking method in the Common Object Request Broker Architecture (CORBA) environment. The algorithm for the patient ID translation is based on patient attribute matching plus computer-based human checking; the method for dynamic linking is temporal mapping. By implementing these methods into computer systems with help of the distributed object computing technology, we built a prototype of a CORBA-based object framework in which the patient ID translation and dynamic linking methods were embedded. Our experiments with a Web-based user interface using the object framework and dynamic linking-through the object framework were successful. These methods are important for exchanging and integrating patient data across heterogeneous databases and institutional boundaries.

  17. DYNAMIC PERSPECTIVE ON THE TRIANGLE FOREIGN DIRECT INVESTMENTS – EXCHANGE RATE – CAPITAL MARKET

    OpenAIRE

    2011-01-01

    This paper focuses on the triangular causal relationship between foreign direct investments, exchange rate and capital market at the level of the CEE countries. For this purpose, we use the weight of market capitalization of listed companies into GDP as proxy for the degree corresponding to the stock market development, the variability of the exchange rate as proxy for the macroeconomic environment and weight of foreign direct investments into GDP as a proxy for the country’s capacity to attr...

  18. An Assessment Of The Stock Market And Exchange Rate Dynamics In Industrialized And Emerging Markets

    OpenAIRE

    Beer, F.; F. Hebein

    2011-01-01

    This paper adopts an Exponentional General Autoregressive Conditional Heteroskedasticity (EGARCH) framework to explore the relationship between stock prices and exchange rates for two groups of countries: emerging and developed economies. Results show that some positive significant price spillovers from the foreign exchange market to the stock market exist for Canada, Japan, the U.S and India. Findings also show for the developed countries, there is no persistence of volatility in the stock m...

  19. Impact of Unexpected Events, Shocking News and Rumours on Foreign Exchange Market Dynamics

    CERN Document Server

    McDonald, M; Williams, S; Howison, S; Johnson, N F; Donald, Mark Mc; Suleman, Omer; Williams, Stacy; Howison, Sam; Johnson, Neil F.

    2006-01-01

    We analyze the dynamical response of the world's financial community to various types of unexpected events, including the 9/11 terrorist attacks as they unfolded on a minute-by-minute basis. We find that there are various 'species' of news, characterized by how quickly the news get absorbed, how much meaning and importance is assigned to it by the community, and what subsequent actions are then taken. For example, the response to the unfolding events of 9/11 shows a gradual collective understanding of what was happening, rather than an immediate realization. For news items which are not simple economic statements, and hence whose implications are not immediately obvious, we uncover periods of collective discovery during which collective opinions seem to oscillate in a remarkably synchronized way. In the case of a rumour, our findings also provide a concrete example of contagion in inter-connected communities. Practical applications of this work include the possibility of producing selective newsfeeds for spec...

  20. Structure and thermodynamics of amylin dimer studied by Hamiltonian-temperature replica exchange molecular dynamics simulations.

    Science.gov (United States)

    Laghaei, Rozita; Mousseau, Normand; Wei, Guanghong

    2011-03-31

    The loss of the insulin-producing β-cells in the pancreatic islets of Langerhans, responsible for type-II diabetes, is associated with islet amyloid deposits. The main component of these deposits is the amyloid fibrils formed by the 37-residue human islet amyloid polypeptide (hIAPP also known as amylin). Although the fibrils are well characterized by cross β structure, the structure of the transient oligomers formed in the early stage of aggregation remains elusive. In this study, we apply the Hamiltonian-temperature replica exchange molecular dynamics to characterize the structure and thermodynamics of a full-length hIAPP dimer in both the presence and the absence of the Cys2-Cys7 disulfide bond. We compare these results with those obtained on the monomeric and dimeric forms of rat IAPP (rIAPP) with a disulfide bridge which differ from the hIAPP by 6 amino acids in the C-terminal region, but it is unable to form fibrils. Using a coarse-grained protein force field (OPEP-the Optimized Potential for Efficient peptide structure Prediction) running for a total of 10-28 μs per system studied, we show that sequences sample α-helical structure in the N-terminal region but that the length of this secondary element is shorter and less stable for the chains without the disulfide bridge (residues 5-16 for hIAPP with the bridge vs 10-16 for hIAPP without the bridge). This α-helix is known to be an important transient stage in the formation of oligomers. In the C-terminal, the amyloidogenic region of hIAPP, β-strands are seen for residues 17-26 and 30-35. On the contrary, no significant β-sheet content in the C-terminal is observed for either the monomeric or the dimeric rIAPP. These numerical results are fully consistent with recent experimental findings that the N-terminal residues are not part of the fibril by forming α-helical structure but rather play a significant role in stabilizing the amyloidogenic region available for the fibrillation.

  1. Spin dynamics induced by ultrafast heating with ferromagnetic/antiferromagnetic interfacial exchange in perpendicularly magnetized hard/soft bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Q. L., E-mail: maqinli@gmail.com, E-mail: mizukami@wpi-aimr.tohoku.ac.jp; Miyazaki, T.; Mizukami, S., E-mail: maqinli@gmail.com, E-mail: mizukami@wpi-aimr.tohoku.ac.jp [WPI Advanced Institute for Materials Research, Tohoku University, 2-1-1, Katahira, 980-8577 Sendai (Japan); Iihama, S. [Department of Applied Physics, Tohoku University, 6-6-05 Aza-Aoba, Aramaki, Aoba-ku, Sendai 980-8579 (Japan); Zhang, X. M. [Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819 (China)

    2015-11-30

    The laser-induced spin dynamics of FeCo in perpendicularly magnetized L1{sub 0}-MnGa/FeCo bilayers with ferromagnetic and antiferromagnetic interfacial exchange coupling (IEC) are examined using the time-resolved magneto-optical Kerr effect. We found a precessional phase reversal of the FeCo layer as the IEC changes from ferromagnetic to antiferromagnetic. Moreover, a precession-suspension window was observed when the magnetic field was applied in a certain direction for the bilayer with ferromagnetic IEC. Our observations reveal that the spin dynamics modulation is strongly dependent on the IEC type within the Landau-Lifshitz-Gilbert depiction. The IEC dependence of the precessional phase and amplitude suggests the interesting method for magnetization dynamics modulation.

  2. Dynamic nuclear-polarization studies of paramagnetic species in solution

    Energy Technology Data Exchange (ETDEWEB)

    Glad, W.E.

    1982-07-01

    Dynamic Nuclear Polarization (DNP) was used to measure the electron spin lattice relaxation times, T/sub 1/, of transition metal ions in aqueous solution. Saturation which is induced in the electron spin system is transferred to the solvent proton spins by dipole-dipole interactions. The change in the polarization of the proton spins is much larger than it is in the electron spins. The change in proton polarization is easily measured by proton Nuclear Magnetic Resonance (NMR). In one experimental arrangement the sample solution was continuously flowed through a microwave cavity to the NMR coil. The NMR was observed with a continuous wave NMR spectrometer. In a second arrangement the whole sample tube was moved from within the microwave cavity to the NMR coil in less than 40 ms by a blast of compressed air. The NMR was then observed with a pulse-Fourier-transform spectrometer. With the second arrangement a mean-square microwave magnetic field at the sample of more than 10 G/sup 2/ is obtainable with 14 W of microwave power. Measurements of DNP at 9 GHz were made on aqueous solutions of VO/sup 2 +/, Mn/sup 2 +/, Cr(CN)/sub 6//sup 3 -/, Cu/sup 2 +/ and Cu(ethylenediamine)/sub 2/(H/sub 2/0)/sub 2//sup 2 +/ ions from 3 to 60/sup 0/C. It was also possible to observe DNP on resolved proton resonances from mixed water-acetonitrile solutions of VO/sup 2 +/ and Cr(CN)/sub 6//sup 3 -/ ions.

  3. Analysis of postfire vegetation dynamics of Mediterranean shrub species based on terrestrial and NDVI data.

    Science.gov (United States)

    Hernández-Clemente, Rocío; Cerrillo, R M Navarro; Hernández-Bermejo, J E; Royo, S Escuin; Kasimis, N A

    2009-05-01

    The present study offers an analysis of regeneration patterns and diversity dynamics after a wildfire, which occurred in 1993 and affected about 7000 ha in southern Spain. The aim of the work was to analyze the rule in the succession of shrub species after fire, relating it to the changes registered in the Normalized Difference Vegetation Index (NDVI). Fractional vegetation cover was recorded from permanent plots in 2000 and 2005. NDVI data related to each time were obtained from Landsat images. Both data sets, from fieldwork and remote sensing, were analyzed through statistical and quantitative analyses and then correlated. Results have permitted the description of the change in plant cover and species composition on a global and plot scale. It can be affirmed that, from the seventh to the twelfth year after the fire, the floristic composition within the burned area remained unchanged at a global level. However, on a smaller scale (plot level), the major shrub species, Ulex parviflorus, Rosmarinus officinalis, and Cistus clusii, underwent significant changes. The regeneration dynamics established by these species conditioned plant species composition and, consequently, diversity indexes such as Shannon (H) and Simpson (D). The changes recorded in the NDVI values corresponding to the surveyed plots were highly correlated with those found in the regrowth of the main species. Areas dominated by U. parviflorus in a senile phase were related to a decrease in NDVI values and an increase in the number of species. This result describes the successional dynamics; the dryness of the main colonizer shrub species is allowing the regrowth and re-establishment of other species. Within the study area, NDVI shows sensitivity to postfire plant cover changes and indirectly expresses the diversity dynamics.

  4. Analysis of Postfire Vegetation Dynamics of Mediterranean Shrub Species Based on Terrestrial and NDVI Data

    Science.gov (United States)

    Hernández-Clemente, Rocío; Navarro Cerrillo, R. M.; Hernández-Bermejo, J. E.; Escuin Royo, S.; Kasimis, N. A.

    2009-05-01

    The present study offers an analysis of regeneration patterns and diversity dynamics after a wildfire, which occurred in 1993 and affected about 7000 ha in southern Spain. The aim of the work was to analyze the rule in the succession of shrub species after fire, relating it to the changes registered in the Normalized Difference Vegetation Index (NDVI). Fractional vegetation cover was recorded from permanent plots in 2000 and 2005. NDVI data related to each time were obtained from Landsat images. Both data sets, from fieldwork and remote sensing, were analyzed through statistical and quantitative analyses and then correlated. Results have permitted the description of the change in plant cover and species composition on a global and plot scale. It can be affirmed that, from the seventh to the twelfth year after the fire, the floristic composition within the burned area remained unchanged at a global level. However, on a smaller scale (plot level), the major shrub species, Ulex parviflorus, Rosmarinus officinalis, and Cistus clusii, underwent significant changes. The regeneration dynamics established by these species conditioned plant species composition and, consequently, diversity indexes such as Shannon (H) and Simpson (D). The changes recorded in the NDVI values corresponding to the surveyed plots were highly correlated with those found in the regrowth of the main species. Areas dominated by U. parviflorus in a senile phase were related to a decrease in NDVI values and an increase in the number of species. This result describes the successional dynamics; the dryness of the main colonizer shrub species is allowing the regrowth and re-establishment of other species. Within the study area, NDVI shows sensitivity to postfire plant cover changes and indirectly expresses the diversity dynamics.

  5. Low dynamics, high longevity and persistence of sessile structural species dwelling on Mediterranean coralligenous outcrops.

    Directory of Open Access Journals (Sweden)

    Núria Teixidó

    Full Text Available There is still limited understanding of the processes underlying benthic species dynamics in marine coastal habitats, which are of disproportionate importance in terms of productivity and biodiversity. The life-history traits of long-lived benthic species in these habitats are particularly poorly documented. In this study, we assessed decadal patterns of population dynamics for ten sponge and anthozoan species that play key structural roles in coralligenous outcrops (∼25 m depth in two areas of the NW Mediterranean Sea. This study was based on examination of a unique long-term photographic series, which allowed analysis of population dynamics over extensive spatial and time spans for the very first time. Specifically, 671 individuals were censused annually over periods of 25-, 15-, and 5-years. This long-term study quantitatively revealed a common life-history pattern among the ten studied species, despite the fact they present different growth forms. Low mortality rates (3.4% yr(-1 for all species combined and infrequent recruitment events (mean value of 3.1±0.5 SE recruits yr(-1 provided only a very small fraction of the new colonies required to maintain population sizes. Overall, annual mortality and recruitment rates did not differ significantly among years; however, some species displayed important mortality events and recruitment pulses, indicating variability among species. Based on the growth rates of these 10 species, we projected their longevity and, obtained a mean estimated age of 25-200 years. Finally, the low to moderate turnover rates (mean value 0.80% yr(-1 observed among the coralligenous species were in agreement with their low dynamics and persistence. These results offer solid baseline data and reveal that these habitats are among the most vulnerable to the current increases of anthropogenic disturbances.

  6. Hydrogen-bonding structure and dynamics of aqueous carbonate species from car-parrinello molecular dynamics simulations.

    Science.gov (United States)

    Kumar, P Padma; Kalinichev, Andrey G; Kirkpatrick, R James

    2009-01-22

    A comprehensive Car-Parrinello molecular dynamics (CP-MD) study of aqueous solutions of carbonic acid (H(2)CO(3)), bicarbonate (HCO(3)(-)), carbonate (CO(3)(2-)), and carbon dioxide (CO(2)) provides new quantitative insight into the structural and dynamic aspects of the hydrogen-bonding environments for these important aqueous species and their effects on the structure, H-bonding, and dynamical behavior of the surrounding water molecules. The hydration structures of the different carbonate species depend on their ability to accept and donate H-bonds with H(2)O. The H-bonds donated by the C-O-H sites of the carbonate species to water molecules are generally stronger and longer-lived than those accepted by these sites from water molecules. The structural relaxation among the water molecules is dominated by diffusional (translational) motion of H(2)O, whereas the H-bond reorganization is dominated by the librational motion of the water molecules and the carbonate species. The rates of structural relaxation of the H(2)O molecules and the rates of H-bond reorganization among them are slower in systems containing carbonate species, consistent with previous studies of simple salt solutions. The strengths and lifetimes of H-bonds involving the carbonate species positively correlate with the total negative charge on the species. H-bond donation from H(2)O to CO(2) is weak, but the presence of CO(2) noticeably affects the structure and structural relaxation of the surrounding H-bonding network leading to generally stronger H-bonds and slower relaxation rates, the behavior typical of a hydrophobic solute.

  7. The dynamic effect of exchange-rate volatility on Turkish exports: Parsimonious error-correction model approach

    Directory of Open Access Journals (Sweden)

    Demirhan Erdal

    2015-01-01

    Full Text Available This paper aims to investigate the effect of exchange-rate stability on real export volume in Turkey, using monthly data for the period February 2001 to January 2010. The Johansen multivariate cointegration method and the parsimonious error-correction model are applied to determine long-run and short-run relationships between real export volume and its determinants. In this study, the conditional variance of the GARCH (1, 1 model is taken as a proxy for exchange-rate stability, and generalized impulse-response functions and variance-decomposition analyses are applied to analyze the dynamic effects of variables on real export volume. The empirical findings suggest that exchangerate stability has a significant positive effect on real export volume, both in the short and the long run.

  8. A modelling approach for simulation of water and carbon dioxide exchange between multi-species tropical rain forest and the atmosphere

    DEFF Research Database (Denmark)

    Olchev, A.; Ibrom, Andreas; Ross, T.

    2008-01-01

    An one-dimensional process-based SVAT model (Mixfor-SVAT) was developed to describe energy, water and carbon dioxide exchanges between vegetation canopy and the atmosphere at a local scale. Simulation of the energy, water and CO2 fluxes in Mixfor-SVAT is based on aggregated description......, precipitation rate and global radiation) at some height above a plant canopy within the atmospheric surface layer. For simulation of exchange processes within a multi-specific forest stand Mixfor-SVAT uses both averaged and species specific biophysical parameters of the trees describing their structure (e...

  9. Investigation of the Dynamic Melting Process in a Thermal Energy Storage Unit Using a Helical Coil Heat Exchanger

    Directory of Open Access Journals (Sweden)

    Xun Yang

    2017-08-01

    Full Text Available In this study, the dynamic melting process of the phase change material (PCM in a vertical cylindrical tube-in-tank thermal energy storage (TES unit was investigated through numerical simulations and experimental measurements. To ensure good heat exchange performance, a concentric helical coil was inserted into the TES unit to pipe the heat transfer fluid (HTF. A numerical model using the computational fluid dynamics (CFD approach was developed based on the enthalpy-porosity method to simulate the unsteady melting process including temperature and liquid fraction variations. Temperature measurements using evenly spaced thermocouples were conducted, and the temperature variation at three locations inside the TES unit was recorded. The effects of the HTF inlet parameters were investigated by parametric studies with different temperatures and flow rate values. Reasonably good agreement was achieved between the numerical prediction and the temperature measurement, which confirmed the numerical simulation accuracy. The numerical results showed the significance of buoyancy effect for the dynamic melting process. The system TES performance was very sensitive to the HTF inlet temperature. By contrast, no apparent influences can be found when changing the HTF flow rates. This study provides a comprehensive solution to investigate the heat exchange process of the TES system using PCM.

  10. Linking river management to species conservation using dynamic landscape scale models

    Science.gov (United States)

    Freeman, Mary C.; Buell, Gary R.; Hay, Lauren E.; Hughes, W. Brian; Jacobson, Robert B.; Jones, John W.; Jones, S.A.; LaFontaine, Jacob H.; Odom, Kenneth R.; Peterson, James T.; Riley, Jeffrey W.; Schindler, J. Stephen; Shea, C.; Weaver, J.D.

    2013-01-01

    Efforts to conserve stream and river biota could benefit from tools that allow managers to evaluate landscape-scale changes in species distributions in response to water management decisions. We present a framework and methods for integrating hydrology, geographic context and metapopulation processes to simulate effects of changes in streamflow on fish occupancy dynamics across a landscape of interconnected stream segments. We illustrate this approach using a 482 km2 catchment in the southeastern US supporting 50 or more stream fish species. A spatially distributed, deterministic and physically based hydrologic model is used to simulate daily streamflow for sub-basins composing the catchment. We use geographic data to characterize stream segments with respect to channel size, confinement, position and connectedness within the stream network. Simulated streamflow dynamics are then applied to model fish metapopulation dynamics in stream segments, using hypothesized effects of streamflow magnitude and variability on population processes, conditioned by channel characteristics. The resulting time series simulate spatially explicit, annual changes in species occurrences or assemblage metrics (e.g. species richness) across the catchment as outcomes of management scenarios. Sensitivity analyses using alternative, plausible links between streamflow components and metapopulation processes, or allowing for alternative modes of fish dispersal, demonstrate large effects of ecological uncertainty on model outcomes and highlight needed research and monitoring. Nonetheless, with uncertainties explicitly acknowledged, dynamic, landscape-scale simulations may prove useful for quantitatively comparing river management alternatives with respect to species conservation.

  11. Is It Possible to Replicate the Exchange Rate Volatility Behavior Using Dynamic Strategies?

    Directory of Open Access Journals (Sweden)

    Claudio Henrique Barbedo

    2009-07-01

    Full Text Available The implied volatility is certainly an interesting indicator to help get a sense of the market, because it represents the amount of expected volatility the market is pricing. In over-the-counter exchange rate option, whose trading is volatility oriented, it is the most important variable. This work investigates whether information embedded in this implied volatility market are explained by other traded variables in the Brazilian market. The results show that there are sources of non-negotiable risk that influence this implied volatility. Therefore, exchange rate implied volatility can assist to understand the behavior of the derivatives indexed to dollar.

  12. Effects of Quantum Correction on Dynamical Phase Transition in a Single Species Bosonic Josephson Junction

    Institute of Scientific and Technical Information of China (English)

    TIAN Jing; QIU Hai-Bo

    2013-01-01

    In this paper,by employing Bogliubov backreaction method,we investigate quantum correction effects on dynamical phase transition in a single species bosonic Josephson junction induced by increasing nonlinear interaction.Compared with mean field theory results,we find that the transition point is shifted.The dynamical phase transition is accompanied by a change of the entanglement entropy,which is found to reach a maximum at the transition point of the mean field theory.

  13. Analysis of protein conformation and dynamics by hydrogen/deuterium exchange MS.

    Science.gov (United States)

    Engen, John R

    2009-10-01

    Understanding as much as possible about proteins in the shortest amount of time has long been a goal of hydrogen exchange (HX) MS. Recent technological advances have led to improvements in the technique, but has this goal yet been achieved? (To listen to a podcast about this Feature, please go to the Analytical Chemistry Web site at pubs.acs.org/journal/ancham.).

  14. Dynamics of urokinase receptor interaction with Peptide antagonists studied by amide hydrogen exchange and mass spectrometry

    DEFF Research Database (Denmark)

    Jørgensen, Thomas J D; Gårdsvoll, Henrik; Danø, Keld

    2004-01-01

    Using amide hydrogen exchange combined with electrospray ionization mass spectrometry, we have in this study determined the number of amide hydrogens on several peptides that become solvent-inaccessible as a result of their high-affinity interaction with the urokinase-type plasminogen activator r...

  15. Design of a concentric heat exchanger using computational fluid dynamics as design tool

    NARCIS (Netherlands)

    Oosterhuis, J.P.; Bühler, S.; wilcox, D; Meer, van der T.H.

    2013-01-01

    A concentric gas-to-gas heat exchanger is designed for application as a recuperator in the domestic boiler industry. The recuperator recovers heat from the exhaust gases of a combustion process to preheat the ingoing gaseous fuel mixture resulting in increased fuel efficiency. This applied study sho

  16. The Nonlinear Dynamic Relationship of Exchange Rates: Parametric and Nonparametric Causality testing

    NARCIS (Netherlands)

    Bekiros, S.D.; Diks, C.

    2007-01-01

    The present study investigates the long-term linear and nonlinear causal linkages among six currencies, namely EUR/USD, GBP/USD, USD/JPY, USD/CHF, AUD/USD and USD/CAD. The prime motivation for choosing these exchange rates comes from the fact that they are the most liquid and widely traded, covering

  17. Dynamic Models of Learning That Characterize Parent-Child Exchanges Predict Vocabulary Growth

    Science.gov (United States)

    Ober, David R.; Beekman, John A.

    2016-01-01

    Cumulative vocabulary models for infants and toddlers were developed from models of learning that predict trajectories associated with low, average, and high vocabulary growth rates (14 to 46 months). It was hypothesized that models derived from rates of learning mirror the type of exchanges provided to infants and toddlers by parents and…

  18. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    Energy Technology Data Exchange (ETDEWEB)

    Hall,G.E.; Sears, T.J.

    2009-04-03

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. High-resolution spectroscopy, augmented by theoretical and computational methods, is used to investigate the structure and collision dynamics of chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry. Applications and methods development are equally important experimental components of this work.

  19. Dynamical behavior of a three species food chain model with Beddington-DeAngelis functional response

    Energy Technology Data Exchange (ETDEWEB)

    Naji, Raid Kamel [Department of Mathematics, College of Science, University of Baghdad (Iraq)]. E-mail: rknaji@yahoo.com; Balasim, Alla Tariq [Department of Mathematics, College of Science, University of Baghdad (Iraq)]. E-mail: alkhazrejy@yahoo.com

    2007-06-15

    A three species food chain model with Beddington-DeAngelis functional response is investigated. The local stability analysis is carried out and global behavior is simulated numerically for a biologically feasible choice of parameters. The persistence conditions of a food chain model are established. The bifurcation diagrams are obtained for different parameters of the model after intensive numerical simulations. The results of simulations show that the model could exhibit chaotic dynamics for realistic and biologically feasible parametric values. Finally, the effect of immigration within prey species is investigated. It is observed that adding small amount of constant immigration to prey species stabilize the system.

  20. Climate Variability and Mangrove Cover Dynamics at Species Level in the Sundarbans, Bangladesh

    Directory of Open Access Journals (Sweden)

    Manoj Kumer Ghosh

    2017-05-01

    Full Text Available Mangrove ecosystems are complex in nature. For monitoring the impact of climate variability in this ecosystem, a multidisciplinary approach is a prerequisite. Changes in temperature and rainfall pattern have been suggested as an influential factor responsible for the change in mangrove species composition and spatial distribution. The main aim of this study was to assess the relationship between temperature, rainfall pattern and dynamics of mangrove species in the Sundarbans, Bangladesh, over a 38 year time period from 1977 to 2015. To assess the relationship, a three stage analytical process was employed. Primarily, the trend of temperature and rainfall over the study period were identified using a linear trend model; then, the supervised maximum likelihood classifier technique was employed to classify images recorded by Landsat series and post-classification comparison techniques were used to detect changes at species level. The rate of change of different mangrove species was also estimated in the second stage. Finally, the relationship between temperature, rainfall and the dynamics of mangroves at species level was determined using a simple linear regression model. The results show a significant statistical relationship between temperature, rainfall and the dynamics of mangrove species. The trends of change for Heritiera fomes and Sonneratia apelatala show a strong relationship with temperature and rainfall, while Ceriops decandra shows a weak relationship. In contrast, Excoecaria agallocha and Xylocarpus mekongensis do not show any significant relationship with temperature and rainfall. On the basis of our results, it can be concluded that temperature and rainfall are important climatic factors influencing the dynamics of three major mangrove species viz. H. fomes, S. apelatala and C. decandra in the Sundarbans.

  1. Language evolution and population dynamics in a system of two interacting species

    Science.gov (United States)

    Kosmidis, Kosmas; Halley, John M.; Argyrakis, Panos

    2005-08-01

    We use Monte Carlo simulations and assumptions from evolutionary game theory in order to study the evolution of words and the population dynamics of a system made of two interacting species which initially speak two different languages. The species are characterized by their identity, vocabulary, and have different initial fitness, i.e. reproduction capability. We investigate how different initial fitness affects the vocabulary of the species or the population dynamics by leading to a permanent populational advantage. We further find that the spatial distributions of the species may cause the system to exhibit pattern formation or segregation. We show that an initial fitness advantage, even though very quickly balanced, leads to better spatial arrangement and enhances survival probabilities of the species. In most cases the system will arrive at a final state where both languages coexist. However, in cases where one species greatly outnumbers the other in population and fitness, then only one species survives with its “final” language having a slightly richer vocabulary than its initial language. Thus, our results offer an explanation for the existence and origin of synonyms in spoken languages.

  2. Exchange interaction-driven dynamic nuclear polarization in Mn-doped InGaAs/GaAs quantum dots

    Science.gov (United States)

    Krebs, O.; Baudin, E.; Lemaître, A.

    2016-11-01

    We investigated optical spin orientation and dynamic nuclear polarization (DNP) in individual self-assembled InGaAs/GaAs quantum dots (QDs) doped by a single Mn atom, a magnetic impurity providing a neutral acceptor A0 with an effective spin J =1 . We find that the spin of an electron photocreated in such a quantum dot can be efficiently oriented by a quasiresonant circularly polarized excitation. For the electron spin levels which are made quasidegenerate by a magnetic field compensating the exchange interaction Δe with A0, there is however a full depolarization due the anisotropic part of the exchange. Still, in most studied QDs, the spin polarized photoelectrons give rise to a pronounced DNP which grows with a longitudinal magnetic field until a critical field where it abruptly vanishes. For some QDs, several replica of such DNP sequence are observed at different magnetic fields. This striking behavior is qualitatively discussed as a consequence of different exchange interactions experienced by the electron, driving the DNP rate via the energy cost of electron-nucleus spin flip-flops.

  3. Species-specific dynamic responses of gut bacteria to a mammalian glycan.

    Science.gov (United States)

    Raghavan, Varsha; Groisman, Eduardo A

    2015-05-01

    The mammalian intestine provides nutrients to hundreds of bacterial species. Closely related species often harbor homologous nutrient utilization genes and cocolonize the gut, raising questions regarding the strategies mediating their stable coexistence. Here we reveal that related Bacteroides species that can utilize the mammalian glycan chondroitin sulfate (CS) have diverged in the manner in which they temporally regulate orthologous CS utilization genes. Whereas certain Bacteroides species display a transient surge in CS utilization transcripts upon exposure to CS, other species exhibit sustained activation of these genes. Remarkably, species-specific expression dynamics are retained even when the key players governing a particular response are replaced by those from a species with a dissimilar response. Bacteroides species exhibiting distinct expression behaviors in the presence of CS can be cocultured on CS. However, they vary in their responses to CS availability and to the composition of the bacterial community when CS is the sole carbon source. Our results indicate that diversity resulting from regulation of polysaccharide utilization genes may enable the coexistence of gut bacterial species using a given nutrient. Genes mediating a specific task are typically conserved in related microbes. For instance, gut Bacteroides species harbor orthologous nutrient breakdown genes and may face competition from one another for these nutrients. How, then, does the gut microbial composition maintain such remarkable stability over long durations? We establish that in the case of genes conferring the ability to utilize the nutrient chondroitin sulfate (CS), microbial species vary in how they temporally regulate these genes and exhibit subtle growth differences on the basis of CS availability and community composition. Similarly to how differential regulation of orthologous genes enables related species to access new environments, gut bacteria may regulate the same genes

  4. Modelling static and dynamic behaviour of proton exchange membrane fuel cells on the basis of electro-chemical description

    Science.gov (United States)

    Ceraolo, M.; Miulli, C.; Pozio, A.

    A simplified dynamical model of a fuel cell of the proton exchange membrane (PEM) type, based on physical-chemical knowledge of the phenomena occurring inside the cell has been developed by the authors. The model has been implemented in the MATLAB/SIMULINK environment. Lab tests have been carried out at ENEA's laboratories; and a good agreement has been found between tests and simulations, both in static and dynamic conditions. In a previous study [M. Ceraolo, R. Giglioli, C. Miulli, A. Pozio, in: Proceedings of the 18th International Electric Fuel Cell and Hybrid Vehicle Symposium (EVS18), Berlin, 20-24 October 2001, p. 306] the basic ideas of the model, as well as its experimental validation have been published. In the present paper, the full implementation of the model is reported in detail. Moreover, a procedure for evaluating all the needed numerical parameters is presented.

  5. Low molecular weight oligomers of amyloid peptides display β-barrel conformations: A replica exchange molecular dynamics study in explicit solvent

    Science.gov (United States)

    De Simone, Alfonso; Derreumaux, Philippe

    2010-04-01

    The self-assembly of proteins and peptides into amyloid fibrils is connected to over 40 pathological conditions including neurodegenerative diseases and systemic amyloidosis. Diffusible, low molecular weight protein and peptide oligomers that form in the early steps of aggregation appear to be the harmful cytotoxic species in the molecular etiology of these diseases. So far, the structural characterization of these oligomers has remained elusive owing to their transient and dynamic features. We here address, by means of full atomistic replica exchange molecular dynamics simulations, the energy landscape of heptamers of the amyloidogenic peptide NHVTLSQ from the beta-2 microglobulin protein. The simulations totaling 5 μs show that low molecular weight oligomers in explicit solvent consist of β-barrels in equilibrium with amorphous states and fibril-like assemblies. The results, also accounting for the influence of the pH on the conformational properties, provide a strong evidence of the formation of transient β-barrel assemblies in the early aggregation steps of amyloid-forming systems. Our findings are discussed in terms of oligomers cytotoxicity.

  6. Fish and phytoplankton exhibit contrasting temporal species abundance patterns in a dynamic north temperate lake.

    Directory of Open Access Journals (Sweden)

    Gretchen J A Hansen

    Full Text Available Temporal patterns of species abundance, although less well-studied than spatial patterns, provide valuable insight to the processes governing community assembly. We compared temporal abundance distributions of two communities, phytoplankton and fish, in a north temperate lake. We used both 17 years of observed relative abundance data as well as resampled data from Monte Carlo simulations to account for the possible effects of non-detection of rare species. Similar to what has been found in other communities, phytoplankton and fish species that appeared more frequently were generally more abundant than rare species. However, neither community exhibited two distinct groups of "core" (common occurrence and high abundance and "occasional" (rare occurrence and low abundance species. Both observed and resampled data show that the phytoplankton community was dominated by occasional species appearing in only one year that exhibited large variation in their abundances, while the fish community was dominated by core species occurring in all 17 years at high abundances. We hypothesize that the life-history traits that enable phytoplankton to persist in highly dynamic environments may result in communities dominated by occasional species capable of reaching high abundances when conditions allow. Conversely, longer turnover times and broad environmental tolerances of fish may result in communities dominated by core species structured primarily by competitive interactions.

  7. Inter-species competition-facilitation in stochastic riparian vegetation dynamics.

    Science.gov (United States)

    Tealdi, Stefano; Camporeale, Carlo; Ridolfi, Luca

    2013-02-07

    Riparian vegetation is a highly dynamic community that lives on river banks and which depends to a great extent on the fluvial hydrology. The stochasticity of the discharge and erosion/deposition processes in fact play a key role in determining the distribution of vegetation along a riparian transect. These abiotic processes interact with biotic competition/facilitation mechanisms, such as plant competition for light, water, and nutrients. In this work, we focus on the dynamics of plants characterized by three components: (1) stochastic forcing due to river discharges, (2) competition for resources, and (3) inter-species facilitation due to the interplay between vegetation and fluid dynamics processes. A minimalist stochastic bio-hydrological model is proposed for the dynamics of the biomass of two vegetation species: one species is assumed dominant and slow-growing, the other is subdominant, but fast-growing. The stochastic model is solved analytically and the probability density function of the plant biomasses is obtained as a function of both the hydrologic and biologic parameters. The impact of the competition/facilitation processes on the distribution of vegetation species along the riparian transect is investigated and remarkable effects are observed. Finally, a good qualitative agreement is found between the model results and field data.

  8. Spatial dynamics of plant species in an agricultural landscape in the Netherlands

    NARCIS (Netherlands)

    Geertsema, W.

    2005-01-01

    This study examined the changes in distribution patterns of 13 herbaceous plant species from 1998 to 2000 in ditch banks along the edges of arable fields in the Netherlands. The objective was to test if spatial dynamics could be related to spatial isolation and disturbance of habitat and to the

  9. Capturing the transient species at the electrode-electrolyte interface by in situ dynamic molecular imaging.

    Science.gov (United States)

    Yu, Jiachao; Zhou, Yufan; Hua, Xin; Liu, Songqin; Zhu, Zihua; Yu, Xiao-Ying

    2016-09-21

    In situ time-resolved identification of interfacial transient reaction species were captured using imaging mass spectrometry, leading to the discovery of more complex elementary electrode reactions and providing an unprecedented understanding of the reaction mechanism on the electrode surface and solid-electrolyte interface using dynamic molecular imaging.

  10. Dynamic C and N stocks - key factors controlling the C gas exchange of maize in heterogenous peatland

    Science.gov (United States)

    Pohl, M.; Hoffmann, M.; Hagemann, U.; Giebels, M.; Albiac Borraz, E.; Sommer, M.; Augustin, J.

    2015-05-01

    The drainage and cultivation of fen peatlands create complex small-scale mosaics of soils with extremely variable soil organic carbon (SOC) stocks and groundwater levels (GWLs). To date, the significance of such sites as sources or sinks for greenhouse gases such as CO2 and CH4 is still unclear, especially if the sites are used for cropland. As individual control factors such as GWL fail to account for this complexity, holistic approaches combining gas fluxes with the underlying processes are required to understand the carbon (C) gas exchange of drained fens. It can be assumed that the stocks of SOC and N located above the variable GWL - defined as dynamic C and N stocks - play a key role in the regulation of the plant- and microbially mediated CO2 fluxes in these soils and, inversely, for CH4. To test this assumption, the present study analysed the C gas exchange (gross primary production - GPP; ecosystem respiration - Reco; net ecosystem exchange - NEE; CH4) of maize using manual chambers for 4 years. The study sites were located near Paulinenaue, Germany, where we selected three soil types representing the full gradient of GWL and SOC stocks (0-1 m) of the landscape: (a) Haplic Arenosol (AR; 8 kg C m-2); (b) Mollic Gleysol (GL; 38 kg C m-2); and (c) Hemic Histosol (HS; 87 kg C m-2). Daily GWL data were used to calculate dynamic SOC (SOCdyn) and N (Ndyn) stocks. Average annual NEE differed considerably among sites, ranging from 47 ± 30 g C m-2 yr-1 in AR to -305 ± 123 g C m-2 yr-1 in GL and -127 ± 212 g C m-2 yr-1 in HS. While static SOC and N stocks showed no significant effect on C fluxes, SOCdyn and Ndyn and their interaction with GWL strongly influenced the C gas exchange, particularly NEE and the GPP : Reco ratio. Moreover, based on nonlinear regression analysis, 86% of NEE variability was explained by GWL and SOCdyn. The observed high relevance of dynamic SOC and N stocks in the aerobic zone for plant and soil gas exchange likely originates from the

  11. Dynamic C and N stocks - key factors controlling the C gas exchange of maize in a heterogenous peatland

    Science.gov (United States)

    Pohl, M.; Hoffmann, M.; Hagemann, U.; Giebels, M.; Albiac Borraz, E.; Sommer, M.; Augustin, J.

    2014-11-01

    Drainage and cultivation of fen peatlands creates complex small-scale mosaics of soils with extremely variable soil organic carbon (SOC) stocks and groundwater-level (GWL). To date, it remains unclear if such sites are sources or sinks for greenhouse gases like CO2 and CH4, especially if used for cropland. As individual control factors like GWL fail to account for this complexity, holistic approaches combining gas fluxes with the underlying processes are required to understand the carbon (C) gas exchange of drained fens. It can be assumed that the stocks of SOC and N located above the variable GWL - defined as dynamic C and N stocks - play a key role in the regulation of plant- and microbially mediated C gas fluxes of these soils. To test this assumption, the present study analysed the C gas exchange (gross primary production - GPP, ecosystem respiration - Reco, net ecosystem exchange - NEE, CH4) of maize using manual chambers for four years. The study sites were located near Paulinenaue, Germany. Here we selected three soils, which represent the full gradient in pedogenesis, GWL and SOC stocks (0-1 m) of the fen peatland: (a) Haplic Arenosol (AR; 8 kg C m-2); (b) Mollic Gleysol (GL; 38 kg C m-2); and (c) Hemic Histosol (HS; 87 kg C m-2). Daily GWL data was used to calculate dynamic SOC (SOCdyn) and N (Ndyn) stocks. Average annual NEE differed considerably among sites, ranging from 47 ± 30 g C m-2 a-1 at AR to -305 ± 123 g C m-2 a-1 at GL and -127 ± 212 g C m-2 a-1 at HS. While static SOC and N stocks showed no significant effect on C fluxes, SOCdyn and Ndyn and their interaction with GWL strongly influenced the C gas exchange, particularly NEE and the GPP:Reco ratio. Moreover, based on nonlinear regression analysis, 86% of NEE variability was explained by GWL and SOCdyn. The observed high relevance of dynamic SOC and N stocks in the aerobic zone for plant and soil gas exchange likely originates from the effects of GWL-dependent N availability on C formation and

  12. Measuring dynamics in weakly structured regions of proteins using microfluidics-enabled subsecond H/D exchange mass spectrometry.

    Science.gov (United States)

    Rob, Tamanna; Liuni, Peter; Gill, Preet Kamal; Zhu, Shaolong; Balachandran, Naresh; Berti, Paul J; Wilson, Derek J

    2012-04-17

    This work introduces an integrated microfluidic device for measuring rapid H/D exchange (HDX) in proteins. By monitoring backbone amide HDX on the millisecond to low second time scale, we are able to characterize conformational dynamics in weakly structured regions, such as loops and molten globule-like domains that are inaccessible in conventional HDX experiments. The device accommodates the entire MS-based HDX workflow on a single chip with residence times sufficiently small (ca. 8 s) that back-exchange is negligible (≤5%), even without cooling. Components include an adjustable position capillary mixer providing a variable-time labeling pulse, a static mixer for HDX quenching, a proteolytic microreactor for rapid protein digestion, and on-chip electrospray ionization (ESI). In the present work, we characterize device performance using three model systems, each illustrating a different application of 'time-resolved' HDX. Ubiquitin is used to illustrate a crude, high throughput structural analysis based on a single subsecond HDX time-point. In experiments using cytochrome c, we distinguish dynamic behavior in loops, establishing a link between flexibility and interactions with the heme prosthetic group. Finally, we localize an unusually high 'burst-phase' of HDX in the large tetrameric enzyme DAHP synthase to a 'molten globule-like' region surrounding the active site.

  13. A model of dynamic rewiring and knowledge exchange in R&D networks

    CERN Document Server

    Tomasello, Mario Vincenzo; Schweitzer, Frank

    2015-01-01

    This paper investigates the process of knowledge exchange in inter-firm Research and Development (R&D) alliances by means of an agent-based model. Extant research has pointed out that firms select alliance partners considering both network-related and network-unrelated features (e.g. social capital versus complementary knowledge stocks). In our agent-based model, firms are located in a metric knowledge space. The interaction rules incorporate an exploration phase and a knowledge transfer phase, during which firms search for a new partner and then evaluate whether they can establish a profitable alliance to mutually exchange their knowledge stocks. The model parameters determining the overall system properties are the rate at which alliances form and disappear and the agents' interaction radius. Next, we define a novel indicator of performance, based on the distance traveled by the firms in the knowledge space. Remarkably, we find that - depending on the alliance formation rate and the interaction radius -...

  14. Structual Dynamics and Function of the Na+/H+ Exchanger 1

    DEFF Research Database (Denmark)

    Hendus-Altenburger, Ruth

    Na+/H+ Exchangers (SLC9As) are of pivotal importance in several physiological processes, and their dysfunction is linked to the pathogenesis of several diseases. The Na+/H+ Exchanger 1 (NHE1) is ubiquitously expressed at the plasma membrane. It contains two domains, the transmembrane ion...... structural elements, which are formed upon membrane interaction, were identified.  The importance of intrinsic disorder in regulation of the scaffolding function of NHE1 was characterized for the first time. Three sites in the disordered distal part of the NHE1 regulatory domain were identified to interact......, the molecular structures and mechanisms underlying NHE1 regulation and function are still incompletely understood. In this work, in silico analysis revealed two structured and two intrinsically disordered regions in the regulatory domain. A divide-and-conquer approach was used to identify subdomains...

  15. Chaos and order in stateless societies: Intercommunity exchange as a factor impacting the population dynamical patterns

    Energy Technology Data Exchange (ETDEWEB)

    Medvinsky, Alexander B., E-mail: medvinsky@iteb.ru [Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino 142290, Moscow Region (Russian Federation); Rusakov, Alexey V. [Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino 142290, Moscow Region (Russian Federation)

    2011-06-15

    Highlights: > We model community dynamics in stateless societies. > Intercommunity barter is shown to be a factor impacting the societies dynamics. > Increase in the human population growth rate can lead to appearance of chaos. > Secular and millennial cycles are found to arise as a result of the barter. - Abstract: The once abstract notions of dynamical chaos now appear naturally in various systems [Kaplan D, Glass L. Understanding nonlinear dynamics. New York: Springer; 1995]. As a result, future trajectories of the systems may be difficult to predict. In this paper, we demonstrate the appearance of chaotic dynamics in model human communities, which consist of producers of agricultural product and producers of agricultural equipment. In the case of a solitary community, the horizon of predictability of the human population dynamics is shown to be dependent on both intrinsic instability of the dynamics and the chaotic attractor sizes. Since a separate community is usually a part of a larger commonality, we study the dynamics of social systems consisting of two interacting communities. We show that intercommunity barter can lead to stabilization of the dynamics in one of the communities, which implies persistence of stable equilibrium under changes of the maximum value of the human population growth rate. However, in the neighboring community, the equilibrium turns into a stable limit cycle as the maximum value of the human population growth rate increases. Following an increase in the maximum value of the human population growth rate leads to period-doubling bifurcations resulting in chaotic dynamics. The horizon of predictability of the chaotic oscillations is found to be limited by 5 years. We demonstrate that the intercommunity interaction can lead to the appearance of long-period harmonics in the chaotic time series. The period of the harmonics is of order 100 and 1000 years. Hence the long-period changes in the population size may be considered as an

  16. Dynamic Links between Exchange Rates and Stock Prices in Malaysia: An Asymmetric Cointegration analysis

    OpenAIRE

    ALI, Hamisu Sadi; Umar MUKHTAR; MANIAM, Ganthi Selvi

    2015-01-01

    Abstract. The present article used a monthly data and applied Enders and Siklos (2001) asymmetric cointegration analysis to examine the impact of exchange rates on stock prices in Malaysia for the period of 1999-2014. The result suggests that variables were cointegrated based on Engle-granger two step technique. Moving to threshold auto regressive (TAR) and momentumthreshold auto regressive (M-TAR) the finding reveals that based on the latter variables were asymmetrically cointegrated as null...

  17. Dynamic simulation of accidental closure of intermediate heat exchanger isolation valve in a pool type LMFBR

    Energy Technology Data Exchange (ETDEWEB)

    Natesan, K., E-mail: natesan@igcar.gov.in [Reactor Engineering Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India); Kasinathan, N.; Velusamy, K.; Selvaraj, P.; Chellapandi, P.; Chetal, S.C. [Reactor Engineering Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India)

    2011-04-15

    Research highlights: > Thermal hydraulic analysis closure of sleeve valve in the primary circuit of FBR is discussed. > Numerical modeling of hydraulics in the primary and secondary sodium circuits is presented. > Aspects related to event management are discussed. - Abstract: In a pool type liquid metal cooled fast breeder reactor (LMFBR), core and other internals such as pumps, heat exchangers are immersed in a pool of sodium. Heat exchange from primary sodium circuit (pool) to secondary sodium circuit (loop) is through four intermediate heat exchangers (IHX) immersed in primary sodium pool. Each IHX is provided with a sleeve valve at its primary sodium inlet window for the purpose of isolating the shell side of IHX from the sodium pool. With such a provision, an inadvertent partial or complete closure of a sleeve valve of one of the IHX during normal operation of the reactor has been considered as a design basis event for the reactor. One dimensional transient thermal hydraulic models of the primary and secondary sodium circuits have been developed to study the thermal hydraulic consequences of such an event. The main areas of concern in the plant and the availability of safety parameters for the detection of the event have been evaluated.

  18. Dynamic Links between Exchange Rates and Stock Prices in Malaysia: An Asymmetric Cointegration analysis

    Directory of Open Access Journals (Sweden)

    Hamisu Sadi ALI

    2015-09-01

    Full Text Available Abstract. The present article used a monthly data and applied Enders and Siklos (2001 asymmetric cointegration analysis to examine the impact of exchange rates on stock prices in Malaysia for the period of 1999-2014. The result suggests that variables were cointegrated based on Engle-granger two step technique. Moving to threshold auto regressive (TAR and momentumthreshold auto regressive (M-TAR the finding reveals that based on the latter variables were asymmetrically cointegrated as null hypothesis of no cointegration was rejected at 1% significance level based on Enders and Siklos (2001, while the former shows that variables do not have long-run relationship and the speed of adjustment is symmetric. This signifies that increase in the prices of shares in Malaysian stock market could lead to Malaysian Ringgit appreciation over other major global currencies. The stocks will become more expensive and discourage foreign investors’ participation in the market which inhibits the influx of stable foreign capital into Malaysian financial system. The implication is that regulators should ensure that adequate and efficient policies are put in place in order to keep the Ringgit exchange rates at optimal level so as to enhance the participation of foreign investors and improve market competitiveness.Keywords. Stock prices, Exchange rates, Asymmetric, Cointegration, Malaysia.JEL. F18, F21, F23, O47.

  19. Computer fluid dynamics (CFD) study of a plate heat exchanger working with nanofluids

    Science.gov (United States)

    Stan, Liviu-Constantin; Cǎlimǎnescu, Ioan

    2016-12-01

    The industry fosters many types of heat exchangers such double pipe or plate heat exchangers (HX), but lately the plate HX are gaining the high ground in many applications. Such a plate HX is made out of serial plate modules packed together allowing the warm and cold fluids to pass through and exchange the heat. The paper is demonstrating the functioning of a medium sized plate HX functioning with 10% Al2O3 and water nanofluids flowing in both cold and warm sides of the HX. The influence of the nanofluid properties will be investigated as impact upon the outlet temperature of the fluid leaving the HX. Using the RSM methodology. The main conclusion of this study is that there is a balance between the nanofluids increased conductivity and their increased viscosity. The nanofluids are working well for those applications where the flow is not impeded by narrow fluid passages where the bigger influence of the viscosity is actually worsening the heat transfer conditions instead of increasing it, since the influence of viscosity in that kind of applications is three time bigger. A nanofluid conductivity threshold was also detected over which the nanofluids say with 15$ or 20% alumina content is useless for the overall heat transfer conditions.

  20. Separation of seven arsenic species by ion-pair and ion-exchange high performance liquid chromatography

    DEFF Research Database (Denmark)

    Larsen, Erik Huusfeldt; Hansen, Sven Hedegaard

    1992-01-01

    Arsenite, arsenate, monomethylarsonate, dimethylarsinate, arsenobetaine, arsenocholine and the tetramethylarsonium ion were subjected to ion-exchange and ion-pair reversed phase HPLC. The ion exchange method was superior in selectivity and time of analysis for the arsenic anions. The ammonium ions...... used for the ion-pair method only resulted in separation of some of the anionic arsenic compounds. Flame atomic absorption spectrometry was used for on-line arsenic-specific detection....

  1. Species traits predict assemblage dynamics at ephemeral resource patches created by carrion.

    Science.gov (United States)

    Barton, Philip S; Cunningham, Saul A; Macdonald, Ben C T; McIntyre, Sue; Lindenmayer, David B; Manning, Adrian D

    2013-01-01

    Carrion is an ephemeral and spatially patchy resource that supports a diverse subset of species linked to nutrient cycling and the decomposition process. A number of studies have separately documented changes in the diversity of plants, arthropods and vertebrates at individual carcasses, but there are few studies that have examined how functional traits of different groups of organisms underpin their responses to carrion patches. We used a carrion addition experiment to compare changes in composition and functional traits of insect and plant assemblages at carcasses compared with control sites. We found that significant changes in insect assemblage evenness and heterogeneity was associated with species' dispersal traits, and that plant assemblage responses to subsequent soil nitrogen changes was most apparent among graminoids and exotic species. Beetles at carcasses were twice as large as their counterparts at control sites during the first week of carrion decomposition, and also had higher wing loadings. Plants with high specific leaf area responded faster to the carcass addition, and twice as many species recolonised the centre of carcasses in exotic-dominated grassland compared with carcasses in native-dominated grassland. These results provide an example of how traits of opportunist species enable them to exploit patchy and dynamic resources. This increases our understanding of how carcasses can drive biodiversity dynamics, and has implications for the way carrion might be managed in ecosystems, such as appropriate consideration of spatial and temporal continuity in carrion resources to promote heterogeneity in nutrient cycling and species diversity within landscapes.

  2. Species traits predict assemblage dynamics at ephemeral resource patches created by carrion.

    Directory of Open Access Journals (Sweden)

    Philip S Barton

    Full Text Available Carrion is an ephemeral and spatially patchy resource that supports a diverse subset of species linked to nutrient cycling and the decomposition process. A number of studies have separately documented changes in the diversity of plants, arthropods and vertebrates at individual carcasses, but there are few studies that have examined how functional traits of different groups of organisms underpin their responses to carrion patches. We used a carrion addition experiment to compare changes in composition and functional traits of insect and plant assemblages at carcasses compared with control sites. We found that significant changes in insect assemblage evenness and heterogeneity was associated with species' dispersal traits, and that plant assemblage responses to subsequent soil nitrogen changes was most apparent among graminoids and exotic species. Beetles at carcasses were twice as large as their counterparts at control sites during the first week of carrion decomposition, and also had higher wing loadings. Plants with high specific leaf area responded faster to the carcass addition, and twice as many species recolonised the centre of carcasses in exotic-dominated grassland compared with carcasses in native-dominated grassland. These results provide an example of how traits of opportunist species enable them to exploit patchy and dynamic resources. This increases our understanding of how carcasses can drive biodiversity dynamics, and has implications for the way carrion might be managed in ecosystems, such as appropriate consideration of spatial and temporal continuity in carrion resources to promote heterogeneity in nutrient cycling and species diversity within landscapes.

  3. Genotypic variation in foundation species generates network structure that may drive community dynamics and evolution.

    Science.gov (United States)

    Lau, Matthew K; Keith, Arthur R; Borrett, Stuart R; Shuster, Stephen M; Whitham, Thomas G

    2016-03-01

    Although genetics in a single species is known to impact whole communities, little is known about how genetic variation influences species interaction networks in complex ecosystems. Here, we examine the interactions in a community of arthropod species on replicated genotypes (clones) of a foundation tree species, Populus angustifolia James (narrowleaf cottonwood), in a long-term, common garden experiment using a bipartite "genotype-species" network perspective. We combine this empirical work with a simulation experiment designed to further investigate how variation among individual tree genotypes can impact network structure. Three findings emerged: (1) the empirical "genotype-species network" exhibited significant network structure with modularity being greater than the highly conservative null model; (2) as would be expected given a modular network structure, the empirical network displayed significant positive arthropod co-occurrence patterns; and (3) furthermore, the simulations of "genotype-species" networks displayed variation in network structure, with modularity in particular clearly increasing, as genotypic variation increased. These results support the conclusion that genetic variation in a single species contributes to the structure of ecological interaction networks, which could influence eco-ogical dynamics (e.g., assembly and stability) and evolution in a community context.

  4. The roles of competition and habitat in the dynamics of populations and species distributions.

    Science.gov (United States)

    Yackulic, Charles B; Reid, Janice; Nichols, James D; Hines, James E; Davis, Raymond; Forsman, Eric

    2014-02-01

    The role of competition in structuring biotic communities at fine spatial scales is well known from detailed process-based studies. Our understanding of competition's importance at broader scales is less resolved and mainly based on static species distribution maps. Here, we bridge this gap by examining the joint occupancy dynamics of an invading species (Barred Owl, Strix varia) and a resident species (Northern Spotted Owl, Strix occidentalis caurina) in a 1000-km study area over a 22-year period. Past studies of these competitors have focused on the dynamics of one species at a time, hindering efforts to parse out the roles of habitat and competition and to forecast the future of the resident species. In addition, while these studies accounted for the imperfect detection of the focal species, no multi-season analysis of these species has accounted for the imperfect detection of the secondary species, potentially biasing inference. We analyzed survey data using models that combine the general multistate-multi-season occupancy modeling framework with autologistic modeling, allowing us to account for important aspects of our study system. We found that local extinction probability increases for each species when the other is present; however, the effect of the invader on the resident is greater. Although the species prefer different habitats, these habitats are highly correlated at the patch scale, and the impacts of invader on the resident are greatest in patches that would otherwise be optimal. As a consequence, competition leads to a weaker relationship between habitat and Northern Spotted Owl occupancy. Colonization and extinction rates of the invader are closely related to neighborhood occupancy, and over the first half of the study the availability of colonists limited the rate of population growth. Competition is likely to exclude the resident species, both through its immediate effects on local extinction and by indirectly lowering colonization rates as

  5. Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species

    Energy Technology Data Exchange (ETDEWEB)

    Hall, G.E.

    2011-05-31

    This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

  6. Dynamics of ammonia exchange with cut grassland: strategy and implementation of the GRAMINAE Integrated Experiment

    Directory of Open Access Journals (Sweden)

    M. A. Sutton

    2008-08-01

    Full Text Available A major international experiment on ammonia (NH3 biosphere-atmosphere exchange was conducted over intensively managed grassland at Braunschweig, Germany. The experimental strategy was developed to allow an integrated analysis of different features of NH3 exchange including: a quantification of nearby emissions and advection effects, b estimation of net NH3 fluxes with the canopy by a range of micrometeorological measurements, c analysis of the sources and sinks of NH3 within the plant canopy, including soils and bioassay measurements, d comparison of the effects of grassland management options on NH3 fluxes and e assessment of the interactions of NH3 fluxes with aerosol exchange processes. Additional technical objectives included the inter-comparison of different estimates of sensible and latent heat fluxes, as well as continuous-gradient and Relaxed Eddy Accumulation (REA systems for NH3 fluxes.

    The prior analysis established the spatial and temporal design of the experiment, allowing significant synergy between these objectives. The measurements were made at 7 measurement locations, thereby quantifying horizontal and vertical profiles, and covered three phases: a tall grass canopy prior to cutting (7 days, b short grass after cutting (7 days and c re-growing sward following fertilization with ammonium nitrate (10 days. The sequential management treatments allowed comparison of sources-sinks, advection and aerosol interactions under a wide range of NH3 fluxes.

    This paper describes the experimental strategy and reports the grassland management history, soils, environmental conditions and air chemistry during the experiment, finally summarizing how the results are coordinated in the accompanying series of papers.

  7. Dynamics of ammonia exchange with cut grassland: strategy and implementation of the GRAMINAE Integrated Experiment

    Directory of Open Access Journals (Sweden)

    M. A. Sutton

    2009-03-01

    Full Text Available A major international experiment on ammonia (NH3 biosphere-atmosphere exchange was conducted over intensively managed grassland at Braunschweig, Germany. The experimental strategy was developed to allow an integrated analysis of different features of NH3 exchange including: a quantification of nearby emissions and advection effects, b estimation of net NH3 fluxes with the canopy by a range of micrometeorological measurements, c analysis of the sources and sinks of NH3 within the plant canopy, including soils and bioassay measurements, d comparison of the effects of grassland management options on NH3 fluxes and e assessment of the interactions of NH3 fluxes with aerosol exchange processes. Additional technical objectives included the inter-comparison of different estimates of sensible and latent heat fluxes, as well as continuous-gradient and Relaxed Eddy Accumulation (REA systems for NH3 fluxes.

    The prior analysis established the spatial and temporal design of the experiment, allowing significant synergy between these objectives. The measurements were made at 7 measurement locations, thereby quantifying horizontal and vertical profiles, and covered three phases: a tall grass canopy prior to cutting (7 days, b short grass after cutting (7 days and c re-growing sward following fertilization with ammonium nitrate (10 days. The sequential management treatments allowed comparison of sources-sinks, advection and aerosol interactions under a wide range of NH3 fluxes.

    This paper describes the experimental strategy and reports the grassland management history, soils, environmental conditions and air chemistry during the experiment, finally summarizing how the results are coordinated in the accompanying series of papers.

  8. Factors determining the diurnal dynamics of blooming of chosen plant species

    Directory of Open Access Journals (Sweden)

    Bożena Denisow

    2012-12-01

    Full Text Available The paper attempts to synthesize the determinants which may influence the diurnal rhythm of blooming. Additionally, I tried to explore and bring together topics that concern blooming and have always been considered separately because of their origin in different disciplines. The following species were included: Hydrangea arborescens L. subsp. discolor (Raf., H. paniculata Sieb., Viburnum opulus L., Chaenomeles japonica Lindl., Knautia arvensis L., Adonis vernalis L., Aster saggitifolius Willd., Taraxacum officinale L. Chelidonium majus L. The taxons were observed in Lublin (51008' - 51018' N and 21027' - 21041' E in the years 2001-2007. The blooming of species was determined at least for two vegetation seasons. During observations all flowers developed in one-hour intervals were counted. The diurnal dynamics of blooming differs among species and is modified by different endogenous and exogenous factors. The endogenous determinants of diurnal dynamics of blooming are morphological diversity of flowers (fertility or sterility within species or heterostyly. The different pattern of blooming succour different mechanisms which prevent self-pollination (Chaenomeles japonica Lindl., Knautia arvensis L.. The abiotic factors, such as day length and temperature during the vegetation season, influence the change in the process of diurnal dynamics of blooming (e. g. Taraxacum officinale, Chelidonium majus.

  9. Impacts of land cover data selection and trait parameterisation on dynamic modelling of species' range expansion.

    Directory of Open Access Journals (Sweden)

    Risto K Heikkinen

    Full Text Available Dynamic models for range expansion provide a promising tool for assessing species' capacity to respond to climate change by shifting their ranges to new areas. However, these models include a number of uncertainties which may affect how successfully they can be applied to climate change oriented conservation planning. We used RangeShifter, a novel dynamic and individual-based modelling platform, to study two potential sources of such uncertainties: the selection of land cover data and the parameterization of key life-history traits. As an example, we modelled the range expansion dynamics of two butterfly species, one habitat specialist (Maniola jurtina and one generalist (Issoria lathonia. Our results show that projections of total population size, number of occupied grid cells and the mean maximal latitudinal range shift were all clearly dependent on the choice made between using CORINE land cover data vs. using more detailed grassland data from three alternative national databases. Range expansion was also sensitive to the parameterization of the four considered life-history traits (magnitude and probability of long-distance dispersal events, population growth rate and carrying capacity, with carrying capacity and magnitude of long-distance dispersal showing the strongest effect. Our results highlight the sensitivity of dynamic species population models to the selection of existing land cover data and to uncertainty in the model parameters and indicate that these need to be carefully evaluated before the models are applied to conservation planning.

  10. Hydrogen exchange

    DEFF Research Database (Denmark)

    Jensen, Pernille Foged; Rand, Kasper Dyrberg

    2016-01-01

    Hydrogen exchange (HX) monitored by mass spectrometry (MS) is a powerful analytical method for investigation of protein conformation and dynamics. HX-MS monitors isotopic exchange of hydrogen in protein backbone amides and thus serves as a sensitive method for probing protein conformation...... and dynamics along the entire protein backbone. This chapter describes the exchange of backbone amide hydrogen which is highly quenchable as it is strongly dependent on the pH and temperature. The HX rates of backbone amide hydrogen are sensitive and very useful probes of protein conformation......, as they are distributed along the polypeptide backbone and form the fundamental hydrogen-bonding networks of basic secondary structure. The effect of pressure on HX in unstructured polypeptides (poly-dl-lysine and oxidatively unfolded ribonuclease A) and native folded proteins (lysozyme and ribonuclease A) was evaluated...

  11. The roles of competition and habitat in the dynamics of populations and species distributions

    Science.gov (United States)

    Yackulic, Charles Brandon; Reid, Janice; Nichols, James D.; Hines, James E.; Davis, Raymond; Forsman, Eric

    2014-01-01

    The role of competition in structuring biotic communities at fine spatial scales is well known from detailed process-based studies. Our understanding of competition's importance at broader scales is less resolved and mainly based on static species distribution maps. Here, we bridge this gap by examining the joint occupancy dynamics of an invading (barred owl: Strix varia) and a resident species (Northern spotted owl: Strix occidentalis caurina) in a 1000 km2 study area over a 22 - year period. Past studies of these competitors have focused on the dynamics of one species at a time, hindering efforts to parse out the roles of habitat and competition and to forecast the future of the resident species. In addition, while these studies accounted for the imperfect detection of the focal species, no multiseason analysis of these species has accounted for the imperfect detection of the secondary species, potentially biasing inference. We analyze survey data using models that combine the general multistate-multiseason occupancy modeling framework with autologistic modeling - allowing us to account for important aspects of our study system. We find that local extinction probability increases for each species when the other is present; however, the effect of the invader on the resident is greater. Although the species prefer different habitats, these habitats are highly correlated at the patch scale and the impacts of invader on the resident are greatest in patches that would otherwise be optimal. As a consequence, competition leads to a weaker relationship between habitat and Northern spotted owl occupancy. Colonization and extinction rates of the invader are closely related to neighborhood occupancy, and over the first half of the study the availability of colonists limited the rate of population growth. Competition is likely to exclude the resident species both through its immediate effects on local extinction, and by indirectly lowering colonization rates as Northern

  12. Price dynamics and market power in an agent-based power exchange

    Science.gov (United States)

    Cincotti, Silvano; Guerci, Eric; Raberto, Marco

    2005-05-01

    This paper presents an agent-based model of a power exchange. Supply of electric power is provided by competing generating companies, whereas demand is assumed to be inelastic with respect to price and is constant over time. The transmission network topology is assumed to be a fully connected graph and no transmission constraints are taken into account. The price formation process follows a common scheme for real power exchanges: a clearing house mechanism with uniform price, i.e., with price set equal across all matched buyer-seller pairs. A single class of generating companies is considered, characterized by linear cost function for each technology. Generating companies compete for the sale of electricity through repeated rounds of the uniform auction and determine their supply functions according to production costs. However, an individual reinforcement learning algorithm characterizes generating companies behaviors in order to attain the expected maximum possible profit in each auction round. The paper investigates how the market competitive equilibrium is affected by market microstructure and production costs.

  13. Seasonal dynamics of tick species in an urban park of Rome.

    Science.gov (United States)

    Di Luca, Marco; Toma, Luciano; Bianchi, Riccardo; Quarchioni, Elisa; Marini, Luca; Mancini, Fabiola; Ciervo, Alessandra; Khoury, Cristina

    2013-12-01

    Regular collections were obtained in the Natural Reserve of the Insugherata of Rome during 2011 in order to obtain the tick species composition and the respective seasonal dynamics of the area. A total of 325 ticks was collected in selected sites by means of drag sampling. Among the identified species, Rhipicephalus turanicus was the most abundant (72.3%), followed by Ixodes ricinus (19.7%), Dermacentor marginatus (6.5%), Haemaphysalis punctata (1.2%), and Rhipicephalus bursa (0.3%). R. turanicus occurred mainly in pastures, showing a mono-modal seasonal activity pattern from spring to early summer. Questing I. ricinus were prevalent in woodland from October to May, and the seasonal trend of specimens showed a weak peak in winter. Although adult D. marginatus exhibited seasonal dynamics similar to I. ricinus, with an activity period from October to April, this species occurred in a different environment (pasture) and with considerably lower densities. Haemaphysalis punctata and R. bursa were rare, with an apparent autumn and autumn-winter seasonal activity, respectively. While the species diversity recorded appears as an unequivocal consequence of the natural state of the park, the remarkable R. turanicus density could be a direct effect of the recent introduction of wild boar, as carriers, from the close Veio Park. The presence of the species, a proven vector of various diseases in humans and domestic animals, is discussed in the light of the possible risk of tick-bite exposure of park workers and visitors.

  14. Effects of constant and stepwise changes in temperature on the species abundance dynamics of four cladocera species

    Directory of Open Access Journals (Sweden)

    Verbitsky V. B.

    2011-09-01

    Full Text Available Laboratory experiments with natural zooplankton communities were carried out to study the effects of two contrasting temperature regimes: constant temperature (15, 20, and 25 °C and graded changes in temperature. The graded regime consisted of repeated sustained (three weeks controlled stepwise temperature changes of 5 or 10 °C within 15–25 °C on the population dynamics of four dominant species of lake littoral zooplankton, Daphnia longispina (Müller, 1785, Diaphanosoma brachyurum (Lievin, 1848, Simocephalus vetulus (Müller, 1776 and Chydorus sphaericus (Müller, 1785. The results show that controlled stepwise changes (positive or negative in temperature within the ranges of 15–20, 20–25, and 15–25 °C can exert either stimulating or inhibitory effect (direct or delayed on the development of D. longispina and S. vetulus populations. The development of D. brachyurum and Ch. sphaericus, both more steno-thermophile, was only stimulated by a stable elevated temperature (25 °C. These results support the previously formulated hypothesis that, in determining the ecological temperature optimum of a species within a natural community, it is not enough to define its optimum from constant, cyclic or random temperature fluctuations, but also from unidirectional stepwise changes in temperature. These stepwise changes may also induce prolonged or delayed effects.

  15. Modelling species invasions using thermal and trophic niche dynamics under climate change

    Directory of Open Access Journals (Sweden)

    Simone eLibralato

    2015-05-01

    Full Text Available Changing marine temperatures modify the distributional ranges of natural populations, but the success of invasion of new areas depends on local physical and ecological conditions. We explore the invasion by thermophilic species and their ecosystem effects by simulating a sea surface temperature increase using a trophodynamic model for the northern Adriatic Sea (NAS, in which thermal and trophic niches are explicitly represented for each thermophilic non-indigenous species and native species. The NAS acts as a cul-de-sac for local species, preventing a further poleward migration as a response to temperature rise. In this situation, model results showed that effects of warming and invasion produced complex, non-linear changes on biomasses but never resulted in a complete overturn of a group of native species and/or a bloom of invasive ones. Despite this, the diversity index stabilizes at increased values after simulating invasion, possibly indicating that in such enclosed systems the establishment of invasive species could represent enrichment in ecosystem structure. In addition, the absence of complete species substitution clearly showed the contribution of resident species towards increasing the resilience, i.e. the capability of the system to cope with invasion without changing substantially. Contrasting scenarios highlighted that changes in ecosystem primary production and species adaptation had secondary effects in ecosystem structure, while results for scenarios with different exploitation levels indicated that fishing can destabilize community structure in these change contexts, e.g. reducing community resilience. The results confirmed the importance of an ecological niche approach to analyze possible effects of invasion and highlighted the complexity of dynamics linked to temperature-driven species invasion’, in terms of both the predicted strength of impacts and the direction of biomass change.

  16. Fluid-dynamical description of the gap fluctuations of two trapped fermion species

    Science.gov (United States)

    Capuzzi, P.; Hernández, E. S.; Szybisz, L.

    2010-11-01

    We apply a recent generalisation of the fluid-dynamical scheme developed for two trapped fermion species with pairing interactions to examine the fluctuations of the gap density coupled to the particle transition density at low energy. The dynamical scheme satisfies Kohn's theorem for both the particle density and the pairing gap. We analyse the form of the gap fluctuations in a spherical trap in terms of their multipolarity and the interaction strength, and find that coupling to the particle density produces considerable stiffness of the gap transition density together with compression towards the centre of the trap.

  17. Dynamic structure factor in single- and two-species thermal GBL lattice gas

    Science.gov (United States)

    Dubbeldam, D.; Hoekstra, A. G.; Sloot, P. M. A.

    2000-07-01

    The two-dimensional 19-bits GBL lattice gas model conserves energy in a non-trivial way, allowing temperature, temperature gradients, and heat conduction. We describe the thermodynamics of the model, its equilibrium properties, and confirm the change of sound speed with energy density at fixed density with simulation results. The sound speed, the sound damping, and the thermal diffusivity are extracted from the dynamic structure factor and shown for various energy densities at fixed density. We have extended the 19 bits GBL model with multiple-species (miscible fluid model) and have measured the dynamic structure factor for this two-component thermal lattice gas model.

  18. Tunneling Dynamics of Two-Species Molecular Bose-Einstein Condensates

    Institute of Scientific and Technical Information of China (English)

    CHEN Chang-Yong; GAO Ke-Lin

    2004-01-01

    We study tunneling dynamics of atomic group in two-species molecular Bose-Einstein condensates. It is shown that the tunneling of the atom group depends on not only the tunneling coupling constant between the atomic pair molecular condensate and the three-atomic group molecular condensate, but also the inter-molecular nonlinear interactions and the initial number of atoms in these condensates. It is discovered that besides oscillating tunneling current between the atomic pair molecular condensate and the three-atomic group molecular condensate, the nonlinear atomic group tunneling dynamics sustains a self-maintained population imbalance: a macroscopic quantum self-trapping effect.

  19. Dynamic of population-dynamics in a medically important snail species Lymnaea (Radix Luteola (Lamarck

    Directory of Open Access Journals (Sweden)

    T. K. Misra

    1993-09-01

    Full Text Available The life-cycle parameters of the snail Lymnaea (Radix luteola and the factors influencing the same have been studied under laboratory conditions. Ins each month, from July 1990 to June 1991, a batch of 100 zero-day old individual were considered for studies. The snails of April batch survived for 19.42 days while those in December batch survived for 87.45 days. The May batch individual though survived for 65.67 days gained maximum shell size (15.84 mm in length and body weight (419.87 mg. All individuals of April batch died prior to attainment of sexual maturity. In the remaining 11 batches the snails became sexually mature between 32 and 53 days. At this stage, they were with varying shell lengths, 9.3 mm to 13,11 mm in respect to batches. The reproduction period varied from 1-67 days. An individual laid, on an average, 0,25 (March batch to 443.67 (May batch eggs in its life-span. A batch of such snails would leave 24312, 22520, 720268, 80408, 76067, 418165, 214, 9202, 0, 0, 2459386 and 127894 individuals at the end of 352nd day. Since the environmental conditions were almost similar the 'dynamic' of population dynamics seems to be involved with the 'strain' of the snail individuals of the batches concerned.

  20. Free Energy Perturbation Hamiltonian Replica-Exchange Molecular Dynamics (FEP/H-REMD) for Absolute Ligand Binding Free Energy Calculations.

    Science.gov (United States)

    Jiang, Wei; Roux, Benoît

    2010-07-01

    Free Energy Perturbation with Replica Exchange Molecular Dynamics (FEP/REMD) offers a powerful strategy to improve the convergence of free energy computations. In particular, it has been shown previously that a FEP/REMD scheme allowing random moves within an extended replica ensemble of thermodynamic coupling parameters "lambda" can improve the statistical convergence in calculations of absolute binding free energy of ligands to proteins [J. Chem. Theory Comput. 2009, 5, 2583]. In the present study, FEP/REMD is extended and combined with an accelerated MD simulations method based on Hamiltonian replica-exchange MD (H-REMD) to overcome the additional problems arising from the existence of kinetically trapped conformations within the protein receptor. In the combined strategy, each system with a given thermodynamic coupling factor lambda in the extended ensemble is further coupled with a set of replicas evolving on a biased energy surface with boosting potentials used to accelerate the inter-conversion among different rotameric states of the side chains in the neighborhood of the binding site. Exchanges are allowed to occur alternatively along the axes corresponding to the thermodynamic coupling parameter lambda and the boosting potential, in an extended dual array of coupled lambda- and H-REMD simulations. The method is implemented on the basis of new extensions to the REPDSTR module of the biomolecular simulation program CHARMM. As an illustrative example, the absolute binding free energy of p-xylene to the nonpolar cavity of the L99A mutant of T4 lysozyme was calculated. The tests demonstrate that the dual lambda-REMD and H-REMD simulation scheme greatly accelerates the configurational sampling of the rotameric states of the side chains around the binding pocket, thereby improving the convergence of the FEP computations.

  1. Patterns of structural dynamics in RACK1 protein retained throughout evolution: A hydrogen-deuterium exchange study of three orthologs

    Science.gov (United States)

    Tarnowski, Krzysztof; Fituch, Kinga; Szczepanowski, Roman H; Dadlez, Michal; Kaus-Drobek, Magdalena

    2014-01-01

    RACK1 is a member of the WD repeat family of proteins and is involved in multiple fundamental cellular processes. An intriguing feature of RACK1 is its ability to interact with at least 80 different protein partners. Thus, the structural features enabling such interactomic flexibility are of great interest. Several previous studies of the crystal structures of RACK1 orthologs described its detailed architecture and confirmed predictions that RACK1 adopts a seven-bladed β-propeller fold. However, this did not explain its ability to bind to multiple partners. We performed hydrogen-deuterium (H-D) exchange mass spectrometry on three orthologs of RACK1 (human, yeast, and plant) to obtain insights into the dynamic properties of RACK1 in solution. All three variants retained similar patterns of deuterium uptake, with some pronounced differences that can be attributed to RACK1's divergent biological functions. In all cases, the most rigid structural elements were confined to B-C turns and, to some extent, strands B and C, while the remaining regions retained much flexibility. We also compared the average rate constants for H-D exchange in different regions of RACK1 and found that amide protons in some regions exchanged at least 1000-fold faster than in others. We conclude that its evolutionarily retained structural architecture might have allowed RACK1 to accommodate multiple molecular partners. This was exemplified by our additional analysis of yeast RACK1 dimer, which showed stabilization, as well as destabilization, of several interface regions upon dimer formation. PMID:24591271

  2. Patterns of structural dynamics in RACK1 protein retained throughout evolution: a hydrogen-deuterium exchange study of three orthologs.

    Science.gov (United States)

    Tarnowski, Krzysztof; Fituch, Kinga; Szczepanowski, Roman H; Dadlez, Michal; Kaus-Drobek, Magdalena

    2014-05-01

    RACK1 is a member of the WD repeat family of proteins and is involved in multiple fundamental cellular processes. An intriguing feature of RACK1 is its ability to interact with at least 80 different protein partners. Thus, the structural features enabling such interactomic flexibility are of great interest. Several previous studies of the crystal structures of RACK1 orthologs described its detailed architecture and confirmed predictions that RACK1 adopts a seven-bladed β-propeller fold. However, this did not explain its ability to bind to multiple partners. We performed hydrogen-deuterium (H-D) exchange mass spectrometry on three orthologs of RACK1 (human, yeast, and plant) to obtain insights into the dynamic properties of RACK1 in solution. All three variants retained similar patterns of deuterium uptake, with some pronounced differences that can be attributed to RACK1's divergent biological functions. In all cases, the most rigid structural elements were confined to B-C turns and, to some extent, strands B and C, while the remaining regions retained much flexibility. We also compared the average rate constants for H-D exchange in different regions of RACK1 and found that amide protons in some regions exchanged at least 1000-fold faster than in others. We conclude that its evolutionarily retained structural architecture might have allowed RACK1 to accommodate multiple molecular partners. This was exemplified by our additional analysis of yeast RACK1 dimer, which showed stabilization, as well as destabilization, of several interface regions upon dimer formation.

  3. Recovering kinetics from a simplified protein folding model using replica exchange simulations: a kinetic network and effective stochastic dynamics.

    Science.gov (United States)

    Zheng, Weihua; Andrec, Michael; Gallicchio, Emilio; Levy, Ronald M

    2009-08-27

    We present an approach to recover kinetics from a simplified protein folding model at different temperatures using the combined power of replica exchange (RE), a kinetic network, and effective stochastic dynamics. While RE simulations generate a large set of discrete states with the correct thermodynamics, kinetic information is lost due to the random exchange of temperatures. We show how we can recover the kinetics of a 2D continuous potential with an entropic barrier by using RE-generated discrete states as nodes of a kinetic network. By choosing the neighbors and the microscopic rates between the neighbors appropriately, the correct kinetics of the system can be recovered by running a kinetic simulation on the network. We fine-tune the parameters of the network by comparison with the effective drift velocities and diffusion coefficients of the system determined from short-time stochastic trajectories. One of the advantages of the kinetic network model is that the network can be built on a high-dimensional discretized state space, which can consist of multiple paths not consistent with a single reaction coordinate.

  4. Conformational change upon ligand binding and dynamics of the PDZ domain from leukemia-associated Rho guanine nucleotide exchange factor.

    Science.gov (United States)

    Liu, Jiangxin; Zhang, Jiahai; Yang, Yinshan; Huang, Hongda; Shen, Weiqun; Hu, Qi; Wang, Xingsheng; Wu, Jihui; Shi, Yunyu

    2008-06-01

    Leukemia-associated Rho guanine nucleotide exchange factor (LARG) is a RhoA-specific guanine nucleotide exchange factor (GEF) that can activate RhoA. The PDZ (PSD-95/Disc-large/ZO-1 homology) domain of LARG interacts with membrane receptors, which can relay extracellular signals to RhoA signal transduction pathways. Until now there is no structural and dynamic information about these interactions. Here we report the NMR structures of the LARG PDZ in the apo form and in complex with the plexin-B1 C-terminal octapeptide. Unobservable resonances of the residues in betaB/betaC and betaE/alphaB loops in apo state were observed in the complex state. A distinct region of the binding groove in the LARG PDZ was found to undergo conformational change compared with other PDZs. Analysis of the (15)N relaxation data using reduced spectral density mapping shows that the apo LARG PDZ (especially its ligand-binding groove) is flexible and exhibits internal motions on both picosecond to nanosecond and microsecond to millisecond timescales. Mutagenesis and thermodynamic studies indicate that the conformation of the betaB/betaC and betaE/alphaB loops affects the PDZ-peptide interaction. It is suggested that the conformational flexibility could facilitate the change of structures upon ligand binding.

  5. Weak coordination among petiole, leaf, vein, and gas-exchange traits across 41 Australian angiosperm species and its possible implications

    Science.gov (United States)

    Background and Aims Close coordination between leaf gas exchange and maximal hydraulic supply has been reported across diverse plant life-forms. However, recent reports suggest that this relationship may become weak or break down completely within the angiosperms. Methods To examine this possi...

  6. Control-oriented dynamic fuzzy model and predictive control for proton exchange membrane fuel cell stack

    Institute of Scientific and Technical Information of China (English)

    LI Xi; DENG Zhong-hua; CAO Guang-yi; ZHU Xin-jian; WEI Dong

    2006-01-01

    Proton exchange membrane fuel cell (PEMFC) stack temperature and cathode stoichiometric oxygen are very important control parameters. The performance and lifespan of PEMFC stack are greatly dependent on the parameters. So, in order to improve the performance index, tight control of two parameters within a given range and reducing their fluctuation are indispensable.However, control-oriented models and control strategies are very weak junctures in the PEMFC development. A predictive control algorithm was presented based on their model established by input-output data and operating experiences. It adjusts the operating temperature to 80 ℃. At the same time, the optimized region of stoichiometric oxygen is kept between 1.8-2.2. Furthermore, the control algorithm adjusts the variants quickly to the destination value and makes the fluctuation of the variants the least. According to the test results, compared with traditional fuzzy and PID controllers, the designed controller shows much better performance.

  7. Stereo-dynamics of the exchange reaction Ha+LiHb→LiHa+Hb and its isotopic variants

    Institute of Scientific and Technical Information of China (English)

    Zhai Hong-Sheng; Yin Shu-Hui

    2012-01-01

    The quasi-classical trajectory (QCT) method is used to calculate the stereo-dynamics of the exchange reaction Ha+LiHb→LiHa+Hb and its isotopic variants based on an accurate potential energy surface reported by Prudente et al.[Prudente F V,Marques J M C and Maniero A M 2009 Chem.Phys.Lett.474 18].The reactive probability of the title reaction is computed.The vector correlations and four polarization-dependent generalized differential cross sections (PDDCSs) at different collision energies are presented.The influences of the collision energy and the reagent rotation on the product polarization are studied in the present work.The results indicate that the product rotational angular momentum j' is not only aligned,but also oriented along the direction perpendicular to the scattering plane.The product polarization distributions of the title reaction and its isotopic variants exhibit distinct differences which may arise from different mass combinations.

  8. Solvent exchange in a metal-organic framework single crystal monitored by dynamic in situ X-ray diffraction.

    Science.gov (United States)

    Cox, Jordan M; Walton, Ian M; Bateman, Gage; Benson, Cassidy A; Mitchell, Travis; Sylvester, Eric; Chen, Yu Sheng; Benedict, Jason B

    2017-08-01

    Understanding the processes by which porous solid-state materials adsorb and release guest molecules would represent a significant step towards developing rational design principles for functional porous materials. To elucidate the process of liquid exchange in these materials, dynamic in situ X-ray diffraction techniques have been developed which utilize liquid-phase chemical stimuli. Using these time-resolved diffraction techniques, the ethanol solvation process in a flexible metal-organic framework [Co(AIP)(bpy)0.5(H2O)]·2H2O was examined. The measurements provide important insight into the nature of the chemical transformation in this system including the presence of a previously unreported neat ethanol solvate structure.

  9. Constant pH Molecular Dynamics in Explicit Solvent with Enveloping Distribution Sampling and Hamiltonian Exchange.

    Science.gov (United States)

    Lee, Juyong; Miller, Benjamin T; Damjanović, Ana; Brooks, Bernard R

    2014-07-08

    We present a new computational approach for constant pH simulations in explicit solvent based on the combination of the enveloping distribution sampling (EDS) and Hamiltonian replica exchange (HREX) methods. Unlike constant pH methods based on variable and continuous charge models, our method is based on discrete protonation states. EDS generates a hybrid Hamiltonian of different protonation states. A smoothness parameter s is used to control the heights of energy barriers of the hybrid-state energy landscape. A small s value facilitates state transitions by lowering energy barriers. Replica exchange between EDS potentials with different s values allows us to readily obtain a thermodynamically accurate ensemble of multiple protonation states with frequent state transitions. The analysis is performed with an ensemble obtained from an EDS Hamiltonian without smoothing, s = ∞, which strictly follows the minimum energy surface of the end states. The accuracy and efficiency of this method is tested on aspartic acid, lysine, and glutamic acid, which have two protonation states, a histidine with three states, a four-residue peptide with four states, and snake cardiotoxin with eight states. The pKa values estimated with the EDS-HREX method agree well with the experimental pKa values. The mean absolute errors of small benchmark systems range from 0.03 to 0.17 pKa units, and those of three titratable groups of snake cardiotoxin range from 0.2 to 1.6 pKa units. This study demonstrates that EDS-HREX is a potent theoretical framework, which gives the correct description of multiple protonation states and good calculated pKa values.

  10. Spatial, temporal, and environmental dynamics of a multi-species epinephelid spawning aggregation in Pohnpei, Micronesia

    Science.gov (United States)

    Rhodes, K. L.; Nemeth, R. S.; Kadison, E.; Joseph, E.

    2014-09-01

    Long-term and short-term underwater visual censuses using SCUBA, technical Nitrox, and closed circuit rebreathers (CCR) were carried out in Pohnpei, Micronesia, to define spatial and temporal dynamics within a semi-protected multi-species epinephelid (fish) spawning aggregation (FSA) of brown-marbled grouper, Epinephelus fuscoguttatus, camouflage grouper, Epinephelus polyphekadion, and squaretail coralgrouper, Plectropomus areolatus. Results identified species-specific patterns of habitat use, abundance, residency, and dispersal of FSAs. Fish spawning aggregations formed and dispersed monthly within a 21-160-d period after winter solstice within adjacent yet distinct outer reef habitats. The reproductive season coincided with periods of seasonally low sub-surface seawater temperature. Peaks in density varied among species both within the calendar year and relative to the winter solstice. Significant long-term declines in FSA density were observed for all three species, suggesting population-level fishery-induced impacts, similar to those previously reported for E. polyphekadion. Differences in density estimates were also observed between dive gear, with a threefold difference in densities measured by CCR for E. polyphekadion versus SCUBA that suggest a disturbance effect from exhaled SCUBA bubbles for this species. CCR also allowed surveys to be conducted over a larger area in a single dive, thereby improving the potential to gauge actual abundance and density within FSAs. Based on these findings, a combination of long-term and intensive short-term monitoring strategies is recommended to fully characterize trends in seasonal abundance and habitat use for aggregating species at single or multi-species FSA sites. Inherent variations in the timing and distribution of species within FSA make fine-scale temporal management protocols less effective than blanket protective coverage of these species at (e.g., marine protected areas covering FSAs and adjacent migratory

  11. Dynamics of a three species food chain model with Crowley-Martin type functional response

    Energy Technology Data Exchange (ETDEWEB)

    Upadhyay, Ranjit Kumar [Department of Applied Mathematics, Indian School of Mines University, Dhanbad, Jharkhand 826 004 (India)], E-mail: ranjit_ism@yahoo.com; Naji, Raid Kamel [Department of Mathematics, College of Science, University of Baghdad (Iraq)], E-mail: rknaji@gmail.com

    2009-11-15

    In this paper, a three species food chain model, consisting of a hybrid type of prey-dependent and predator-dependent functional responses, is investigated analytically as well as numerically. The local and global stability analysis is carried out. The persistence conditions are established. Bifurcation diagrams are obtained for biologically feasible parameters. The results show that the system exhibits rich complexity features such as stable, periodic and chaotic dynamics.

  12. Microbial Species Diversity, Community Dynamics, and Metabolite Kinetics of Water Kefir Fermentation

    OpenAIRE

    Laureys, David; De Vuyst, Luc

    2014-01-01

    Water kefir is a sour, alcoholic, and fruity fermented beverage of which the fermentation is started with water kefir grains. These water kefir grains consist of polysaccharide and contain the microorganisms responsible for the water kefir fermentation. In this work, a water kefir fermentation process was followed as a function of time during 192 h to unravel the community dynamics, the species diversity, and the kinetics of substrate consumption and metabolite production. The majority of the...

  13. Human-facilitated metapopulation dynamics in an emerging pest species, Cimex lectularius

    OpenAIRE

    Fountain, T; Duvaux, L; Horsburgh, G.; Reinhardt, K.; Butlin, R. K.

    2014-01-01

    The number and demographic history of colonists can have dramatic consequences for the way in which genetic diversity is distributed and maintained in a metapopulation. The bed bug (Cimex lectularius) is a re-emerging pest species whose close association with humans has led to frequent local extinction and colonization, that is, to metapopulation dynamics. Pest control limits the lifespan of subpopulations, causing frequent local extinctions, and human-facilitated dispersal allows the coloniz...

  14. Dynamical effects of exchange symmetry breaking in mixtures of interacting bosons

    DEFF Research Database (Denmark)

    Tichy, Malte C.; Sherson, Jacob; Mølmer, Klaus

    2012-01-01

    approximates the full counting statistics well also outside the realm of spin-coherent states. The method is extended to general Bose-Hubbard systems and to their classical mean-field limits, which suggests an effective single-species description of multicomponent Bose gases with weakly an...

  15. Efficient Conformational Sampling in Explicit Solvent Using a Hybrid Replica Exchange Molecular Dynamics Method

    Science.gov (United States)

    2011-12-01

    and Biochemistry , U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland §Computational Sciences and Engineering Branch...of motion of a system with constraints: molecular dynamics of n- alkanes . J. Comput. Phys. 1977, 23, 327–341. (29) Feig, M.; Karanicolas, J.; Brooks, C

  16. An Autoethnographic Exchange: Exploring the Dynamics of Selves as Adult Learners and Adult Educators

    Science.gov (United States)

    Plakhotnik, Maria S.; Delgado, Antonio; Seepersad, Rehana

    2015-01-01

    This article explores four former doctoral students' perceptions about their selves as adult learners and adult educators through the use of autoethnography and reflective dialogue. The dynamics between the two selves were explored to identify emerging themes and implications for practice in adult education. The duality of their roles as learners…

  17. Population dynamics of Scirtothrips dorsalis (Thysanoptera: Thripidae) and other thrips species on two ornamental host plant species in Southern Florida.

    Science.gov (United States)

    Mannion, Catharine M; Derksen, Andrew I; Seal, Dakshina R; Osborne, Lance S; Martin, Cliff G

    2014-08-01

    Since its 2005 introduction into the United States, chilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae), has become a problematic pest of agronomic, vegetable, fruit, and ornamental plants. Knowledge of its population dynamics may help managers better monitor and control S. dorsalis. Population estimates were recorded for S. dorsalis and other thrips species on Knock-Out rose (Rosa 'Radrazz') and green buttonwood (Conocarpus erectus L.) from July 2007 to September 2008 in two field plots (one per plant species) in Homestead, FL. Yellow sticky card traps and samples of terminals, flowers, buds, and leaves were collected. S. dorsalis accounted for 95% of all thrips individuals collected from plants and 84% from traps with the remainder including at least 18 other thrips species. More thrips were caught on or flying near rose plants (47,438) than on or near buttonwoods (5,898), and on-plant densities of S. dorsalis appeared higher for rose than for buttonwood. Compared with rose leaves, rose buds, terminals, and flowers each had higher numbers of S. dorsalis, and buds and terminals had higher densities. On each host plant species, S. dorsalis density fluctuated over time with peaks in the late spring, summer, and fall, but populations were consistently low in the late winter and early spring. On roses, increased plant damage ratings correlated with reduced numbers of flowers and buds, reduced mean flower areas, and increased on-plant number and density of S. dorsalis. There were positive correlations over time between S. dorsalis density and plant damage rating for rose flowers (R = 0.78; P = 0.0003) and for buttonwood terminals (R = 0.90; P = 0.0001). Yellow sticky card traps were effective for monitoring S. dorsalis and may be especially useful and economically justified for the most susceptible hosts, but they also work well for less susceptible hosts. A good S. dorsalis scouting program should hence consider trap catches and symptoms such as leaf

  18. Within-host dynamics of multi-species infections: facilitation, competition and virulence.

    Directory of Open Access Journals (Sweden)

    Sandeepa M Eswarappa

    Full Text Available Host individuals are often infected with more than one parasite species (parasites defined broadly, to include viruses and bacteria. Yet, research in infection biology is dominated by studies on single-parasite infections. A focus on single-parasite infections is justified if the interactions among parasites are additive, however increasing evidence points to non-additive interactions being the norm. Here we review this evidence and theoretically explore the implications of non-additive interactions between co-infecting parasites. We use classic Lotka-Volterra two-species competition equations to investigate the within-host dynamical consequences of various mixes of competition and facilitation between a pair of co-infecting species. We then consider the implications of these dynamics for the virulence (damage to host of co-infections and consequent evolution of parasite strategies of exploitation. We find that whereas one-way facilitation poses some increased virulence risk, reciprocal facilitation presents a qualitatively distinct destabilization of within-host dynamics and the greatest risk of severe disease.

  19. Influence of climate drivers on colonization and extinction dynamics of wetland-dependent species

    Science.gov (United States)

    Ray, Andrew M.; Gould, William R.; Hossack, Blake R.; Sepulveda, Adam; Thoma, David P.; Patla, Debra A.; Daley, Rob; Al-Chokhachy, Robert K.

    2016-01-01

    Freshwater wetlands are particularly vulnerable to climate change. Specifically, changes in temperature, precipitation, and evapotranspiration (i.e., climate drivers) are likely to alter flooding regimes of wetlands and affect the vital rates, abundance, and distributions of wetland-dependent species. Amphibians may be among the most climate-sensitive wetland-dependent groups, as many species rely on shallow or intermittently flooded wetland habitats for breeding. Here, we integrated multiple years of high-resolution gridded climate and amphibian monitoring data from Grand Teton and Yellowstone National Parks to explicitly model how variations in climate drivers and habitat conditions affect the occurrence and breeding dynamics (i.e., annual extinction and colonization rates) of amphibians. Our results showed that models incorporating climate drivers outperformed models of amphibian breeding dynamics that were exclusively habitat based. Moreover, climate-driven variation in extinction rates, but not colonization rates, disproportionately influenced amphibian occupancy in monitored wetlands. Long-term monitoring from national parks coupled with high-resolution climate data sets will be crucial to describing population dynamics and characterizing the sensitivity of amphibians and other wetland-dependent species to climate change. Further, long-term monitoring of wetlands in national parks will help reduce uncertainty surrounding wetland resources and strengthen opportunities to make informed, science-based decisions that have far-reaching benefits.

  20. Dynamics of host plant use and species diversity in Polygonia butterflies (Nymphalidae).

    Science.gov (United States)

    Weingartner, E; Wahlberg, N; Nylin, S

    2006-03-01

    The ability of insects to utilize different host plants has been suggested to be a dynamic and transient phase. During or after this phase, species can shift to novel host plants or respecialize on ancestral ones. Expanding the range of host plants might also be a factor leading to higher levels of net speciation rates. In this paper, we have studied the possible importance of host plant range for diversification in the genus Polygonia (Nymphalidae, Nymphalini). We have compared species richness between sistergroups in order to find out if there are any differences in number of species between clades including species that utilize only the ancestral host plants ('urticalean rosids') and their sisterclades with a broader (or in some cases potentially broader) host plant repertoire. Four comparisons could be made, and although these are not all phylogenetically or statistically independent, all showed clades including butterfly species using other or additional host plants than the urticalean rosids to be more species-rich than their sisterclade restricted to the ancestral host plants. These results are consistent with the theory that expansions in host plant range are involved in the process of diversification in butterflies and other phytophagous insects, in line with the general theory that plasticity may drive speciation.

  1. Difference in metapopulation structure and dynamics of two species of coexistent melitaeine butterflies

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    According to investigation on two species of melitaeine butterflies in Yanjiaping Village, Chicheng County, Hebei Province, China, between 1998-2002, together with the use of 1:10000 contour map of the local area, some conclusions are shown by the SPSS and GIS analysis of data obained from GPS: (1) The two species of melitaeine butterflies have different metapopulation structures. M. phoebe is a source-sink metapopulation, while E. aurinia is a classical metapopulation, supporting the analytic result from our former genetic research. (2) The two species of melitaeine butterflies exhibit different trends of population dynamics. M. phoebe source-sink metapopulation is very unsteady, and is always small, thus has a tendency to go extinct gradually. But E. aurinia classical metapopulation is stable, and has maintained a larger population size. Therefore, it stands a better chance of long-term survival. (3) The two species of melitaeine butterflies are significantly related in both patch occupancy and local population size. (4) The effect of isolation is significant on the metapopulations of these two species of melitaeine butterflies, consistent with the classical theories, whereas the effect of patch area is not significant on the metapopulations of these two species of melitaeine butterflies, which is inconsistent with the classical theories. Therefore, other factors, such as habitat quality, should be considered for their influences on metapopulations.

  2. Structure, dynamics, and function of the hammerhead ribozyme in bulk water and at a clay mineral surface from replica exchange molecular dynamics.

    Science.gov (United States)

    Swadling, Jacob B; Wright, David W; Suter, James L; Coveney, Peter V

    2015-03-01

    Compared with proteins, the relationship between structure, dynamics, and function of RNA enzymes (known as ribozymes) is far less well understood, despite the fact that ribozymes are found in many organisms and are often conceived as "molecular fossils" of the first self-replicating molecules to have arisen on Earth. To investigate how ribozymal function is governed by structure and dynamics, we study the full hammerhead ribozyme in bulk water and in an aqueous clay mineral environment by computer simulation using replica-exchange molecular dynamics. Through extensive sampling of the major conformational states of the hammerhead ribozyme, we are able to show that the hammerhead manifests a free-energy landscape reminiscent of that which is well known in proteins, exhibiting a "funnel" topology that guides the ribozyme into its globally most stable conformation. The active-site geometry is found to be closely correlated to the tertiary structure of the ribozyme, thereby reconciling conflicts between previously proposed mechanisms for the self-scission of the hammerhead. The conformational analysis also accounts for the differences reported experimentally in the catalytic activity of the hammerhead ribozyme, which is reduced when interacting with clay minerals as compared with bulk water.

  3. Floral scent of brazilian Passiflora: five species analised by dynamic headspace.

    Science.gov (United States)

    Montero, Daniel A V; Marques, Marcia Ortiz M; Meletti, Laura M M; Kampen, Maria H VAN; Polozzi, Sandra C

    2016-09-01

    This study describes for the first time the chemical composition and olfactive description of floral scent from Brazilian Passiflora (Passiflora edulis Sim, Passiflora alata Curtis, Passiflora cincinnata Mast., Passiflora coccinea Aubl. and Passiflora quadrangularis L.). Five species were grown in greenhouse at the Agronomic Institute (IAC), São Paulo, Brazil. Volatile compounds were collected using dynamic headspace. Analyses of scent composition were performed by gas chromatograph coupled to mass spectrometer. Identification of chemical constituents was conducted through of retention index followed by comparative analysis of mass spectra with specialized databases. The olfactive descriptions of floral scent from each species was evaluated for a professional perfumer. High interspecific diversity was found between chemical compositions of floral scent within Passiflora and different bouquets were observed amount the studied species. Mayor constituents were linalool (P. alata), geraniol (P. quadrangularis), 1,4-dimethoxybenzene (P. edulis), benzaldehyde (P. cincinnata) and 2-methyl-3-pentanone (P. coccinea).

  4. Floral scent of brazilian Passiflora: five species analised by dynamic headspace

    Directory of Open Access Journals (Sweden)

    DANIEL A.V. MONTERO

    2016-01-01

    Full Text Available ABSTRACT This study describes for the first time the chemical composition and olfactive description of floral scent from Brazilian Passiflora (Passiflora edulis Sim, Passiflora alata Curtis, Passiflora cincinnata Mast., Passiflora coccinea Aubl. and Passiflora quadrangularis L.. Five species were grown in greenhouse at the Agronomic Institute (IAC, São Paulo, Brazil. Volatile compounds were collected using dynamic headspace. Analyses of scent composition were performed by gas chromatograph coupled to mass spectrometer. Identification of chemical constituents was conducted through of retention index followed by comparative analysis of mass spectra with specialized databases. The olfactive descriptions of floral scent from each species was evaluated for a professional perfumer. High interspecific diversity was found between chemical compositions of floral scent within Passiflora and different bouquets were observed amount the studied species. Mayor constituents were linalool (P. alata, geraniol (P. quadrangularis, 1,4-dimethoxybenzene (P. edulis, benzaldehyde (P. cincinnata and 2-methyl-3-pentanone (P. coccinea.

  5. Population cycles and species diversity in dynamic Kill-the-Winner model of microbial ecosystems

    Science.gov (United States)

    Maslov, Sergei; Sneppen, Kim

    2017-01-01

    Determinants of species diversity in microbial ecosystems remain poorly understood. Bacteriophages are believed to increase the diversity by the virtue of Kill-the-Winner infection bias preventing the fastest growing organism from taking over the community. Phage-bacterial ecosystems are traditionally described in terms of the static equilibrium state of Lotka-Volterra equations in which bacterial growth is exactly balanced by losses due to phage predation. Here we consider a more dynamic scenario in which phage infections give rise to abrupt and severe collapses of bacterial populations whenever they become sufficiently large. As a consequence, each bacterial population in our model follows cyclic dynamics of exponential growth interrupted by sudden declines. The total population of all species fluctuates around the carrying capacity of the environment, making these cycles cryptic. While a subset of the slowest growing species in our model is always driven towards extinction, in general the overall ecosystem diversity remains high. The number of surviving species is inversely proportional to the variation in their growth rates but increases with the frequency and severity of phage-induced collapses. Thus counter-intuitively we predict that microbial communities exposed to more violent perturbations should have higher diversity.

  6. Mathematical Models of Quasi-Species Theory and Exact Results for the Dynamics.

    Science.gov (United States)

    Saakian, David B; Hu, Chin-Kun

    2016-01-01

    We formulate the Crow-Kimura, discrete-time Eigen model, and continuous-time Eigen model. These models are interrelated and we established an exact mapping between them. We consider the evolutionary dynamics for the single-peak fitness and symmetric smooth fitness. We applied the quantum mechanical methods to find the exact dynamics of the evolution model with a single-peak fitness. For the smooth symmetric fitness landscape, we map exactly the evolution equations into Hamilton-Jacobi equation (HJE). We apply the method to the Crow-Kimura (parallel) and Eigen models. We get simple formulas to calculate the dynamics of the maximum of distribution and the variance. We review the existing mathematical tools of quasi-species theory.

  7. Neutral dynamics with environmental noise: Age-size statistics and species lifetimes

    Science.gov (United States)

    Kessler, David; Suweis, Samir; Formentin, Marco; Shnerb, Nadav M.

    2015-08-01

    Neutral dynamics, where taxa are assumed to be demographically equivalent and their abundance is governed solely by the stochasticity of the underlying birth-death process, has proved itself as an important minimal model that accounts for many empirical datasets in genetics and ecology. However, the restriction of the model to demographic [O (√{N }) ] noise yields relatively slow dynamics that appears to be in conflict with both short-term and long-term characteristics of the observed systems. Here we analyze two of these problems—age-size relationships and species extinction time—in the framework of a neutral theory with both demographic and environmental stochasticity. It turns out that environmentally induced variations of the demographic rates control the long-term dynamics and modify dramatically the predictions of the neutral theory with demographic noise only, yielding much better agreement with empirical data. We consider two prototypes of "zero mean" environmental noise, one which is balanced with regard to the arithmetic abundance, another balanced in the logarithmic (fitness) space, study their species lifetime statistics, and discuss their relevance to realistic models of community dynamics.

  8. Approach combining on-line metal exchange and tangential-flow ultrafiltration for in-situ characterization of metal species in humic hydrocolloids

    Energy Technology Data Exchange (ETDEWEB)

    Goveia, Danielle [UNESP - Universidade Estadual Paulista, Departamento de Engenharia Ambiental, Sorocaba, SP (Brazil); UNESP - Universidade Estadual Paulista, Instituto de Quimica de Araraquara, Araraquara, SP (Brazil); Lobo, Fabiana Aparecida; Fraceto, Leonardo Fernandes; Rosa, Andre Henrique [UNESP - Universidade Estadual Paulista, Departamento de Engenharia Ambiental, Sorocaba, SP (Brazil); Burba, Peter [ISAS - Institute for Analytical Sciences, Dortmund (Germany); Dias Filho, Newton Luiz [UNESP - Universidade Estadual Paulista, Departamento de Fisica e Quimica, Ilha Solteira, SP (Brazil)

    2010-05-15

    This paper deals with the development and optimization of an analytical procedure using ultrafiltration and a flow-injection system, and its application in in-situ experiments to characterize the lability and availability of metal species in humic-rich hydrocolloids. The on-line system consists of a tangential flow ultrafiltration device equipped with a 3-kDa filtration membrane. The concentration of free ions in the filtrate was determined by atomic-absorption spectrometry, assuming that metals not complexed by aquatic humic substances (AHS) were separated from the complexed species (M-AHS) retained by the membrane. For optimization, exchange experiments using Cu(II) solutions and AHS solutions doped with the metal ions Ni(II), Mn(II), Fe(III), Cd(II), and Zn(II) were carried out to characterize the stability of the metal-AHS complexes. The new procedure was then applied in-situ at a tributary of the Ribeira do Iguape river (Iguape, Sao Paulo State, Brazil) and evaluated using the ions Fe(III) and Mn(II), which are considered to be essential constituents of aquatic systems. From the exchange between metal-natural organic matter (M-NOM) and the Cu(II) ions it was concluded that Cu(II) concentrations >485 {mu}g L{sup -1} were necessary to obtain maximum exchange of the complexes Mn-NOM and Fe-NOM, corresponding to 100% Mn and 8% Fe. Moreover, the new analytical procedure is simple and opens up new perspectives for understanding the complexation, transport, stability, and lability of metal species in humic-rich aquatic environments. (orig.)

  9. Approach combining on-line metal exchange and tangential-flow ultrafiltration for in-situ characterization of metal species in humic hydrocolloids.

    Science.gov (United States)

    Goveia, Danielle; Lobo, Fabiana Aparecida; Burba, Peter; Fraceto, Leonardo Fernandes; Dias Filho, Newton Luiz; Rosa, André Henrique

    2010-05-01

    This paper deals with the development and optimization of an analytical procedure using ultrafiltration and a flow-injection system, and its application in in-situ experiments to characterize the lability and availability of metal species in humic-rich hydrocolloids. The on-line system consists of a tangential flow ultrafiltration device equipped with a 3-kDa filtration membrane. The concentration of free ions in the filtrate was determined by atomic-absorption spectrometry, assuming that metals not complexed by aquatic humic substances (AHS) were separated from the complexed species (M-AHS) retained by the membrane. For optimization, exchange experiments using Cu(II) solutions and AHS solutions doped with the metal ions Ni(II), Mn(II), Fe(III), Cd(II), and Zn(II) were carried out to characterize the stability of the metal-AHS complexes. The new procedure was then applied in-situ at a tributary of the Ribeira do Iguape river (Iguape, São Paulo State, Brazil) and evaluated using the ions Fe(III) and Mn(II), which are considered to be essential constituents of aquatic systems. From the exchange between metal-natural organic matter (M-NOM) and the Cu(II) ions it was concluded that Cu(II) concentrations >485 microg L(-1) were necessary to obtain maximum exchange of the complexes Mn-NOM and Fe-NOM, corresponding to 100% Mn and 8% Fe. Moreover, the new analytical procedure is simple and opens up new perspectives for understanding the complexation, transport, stability, and lability of metal species in humic-rich aquatic environments.

  10. Novel Wireless Sensor System for Dynamic Characterization of Borehole Heat Exchangers

    Directory of Open Access Journals (Sweden)

    Raimundo García-Olcina

    2011-07-01

    Full Text Available The design and field test of a novel sensor system based in autonomous wireless sensors to measure the temperature of the heat transfer fluid along a borehole heat exchanger (BHE is presented. The system, by means of two specials valves, inserts and extracts miniaturized wireless sensors inside the pipes of the borehole, which are carried by the thermal fluid. Each sensor is embedded in a small sphere of just 25 mm diameter and 8 gr weight, containing a transceiver, a microcontroller, a temperature sensor and a power supply. A wireless data processing unit transmits to the sensors the acquisition configuration before the measurements, and also downloads the temperature data measured by the sensor along its way through the BHE U-tube. This sensor system is intended to improve the conventional thermal response test (TRT and it allows the collection of information about the thermal characteristics of the geological structure of subsurface and its influence in borehole thermal behaviour, which in turn, facilitates the implementation of TRTs in a more cost-effective and reliable way.

  11. Novel wireless sensor system for dynamic characterization of borehole heat exchangers.

    Science.gov (United States)

    Martos, Julio; Montero, Álvaro; Torres, José; Soret, Jesús; Martínez, Guillermo; García-Olcina, Raimundo

    2011-01-01

    The design and field test of a novel sensor system based in autonomous wireless sensors to measure the temperature of the heat transfer fluid along a borehole heat exchanger (BHE) is presented. The system, by means of two special valves, inserts and extracts miniaturized wireless sensors inside the pipes of the borehole, which are carried by the thermal fluid. Each sensor is embedded in a small sphere of just 25 mm diameter and 8 gr weight, containing a transceiver, a microcontroller, a temperature sensor and a power supply. A wireless data processing unit transmits to the sensors the acquisition configuration before the measurements, and also downloads the temperature data measured by the sensor along its way through the BHE U-tube. This sensor system is intended to improve the conventional thermal response test (TRT) and it allows the collection of information about the thermal characteristics of the geological structure of subsurface and its influence in borehole thermal behaviour, which in turn, facilitates the implementation of TRTs in a more cost-effective and reliable way.

  12. Computational Fluid Dynamic Modeling of Horizontal Air-Ground Heat Exchangers (HAGHE for HVAC Systems

    Directory of Open Access Journals (Sweden)

    Paolo Maria Congedo

    2014-12-01

    Full Text Available In order to satisfy the requirements of Directive 2010/31/EU for Zero Energy Buildings (ZEB, innovative solutions were investigated for building HVAC systems. Horizontal air-ground heat exchangers (HAGHE offer a significant contribution in reducing energy consumption for ventilation, using the thermal energy stored underground, in order to pre-heat or pre-cool the ventilation air, in winter and summer, respectively. This is particularly interesting in applications for industrial, commercial and education buildings where keeping the indoor air quality under control is extremely important. Experimental measurements show that, throughout the year, the outside air temperature fluctuations are mitigated at sufficient ground depth (about 3 m because of the high thermal inertia of the soil, the ground temperature is relatively constant and instead higher than that of the outside air in winter and lower in summer. The study aims to numerically investigate the behavior of HAGHE by varying the air flow rate and soil conductivity in unsteady conditions by using annual weather data of South-East Italy. The analysis shows that, in warm climates, the HAGHE brings a real advantage for only a few hours daily in winter, while it shows significant benefits in the summer for the cooling of ventilation air up to several temperature degrees, already by a short pipe.

  13. Geometric optimization of cross-flow heat exchanger based on dynamic controllability

    Directory of Open Access Journals (Sweden)

    Alotaibi Sorour

    2008-01-01

    Full Text Available The operation of heat exchangers and other thermal equipments in the face of variable loads is usually controlled by manipulating inlet fluid temperatures or mass flow rates, where the controlled variable is usually one of the output temperatures. The aim of this work is to optimize the geometry of a tube with internal flow of water and an external cross-flow of air, based on its controllability characteristics. Controllability is a useful concept both from theoretical and practical perspective since it tells us if a particular output can be controlled by a particular input. This concept can also provide us with information about the easiest operating condition to control a particular output. A transient model of a tube in cross-flow is developed, where an implicit formulation is used for transient numerical solutions. The aspect ratio of the tube is optimized, subject to volume constraints, based on the optimum operation in terms of controllability. The reported optimized aspect ratio, water mass flow rate and controllability are studied for deferent external properties of the tube.

  14. Frequent cytoplasmic exchanges between oak species that are not closely related: Quercus suber and Q. ilex in Morocco.

    Science.gov (United States)

    Belahbib, N; Pemonge, M H; Ouassou, A; Sbay, H; Kremer, A; Petit, R J

    2001-08-01

    Chloroplast (cp) and mitochondrial (mt) DNA variation were studied in 97 populations of cork oak (Quercus suber) in Morocco; in 31 of these populations, holm oak (Quercus ilex), a clearly distinct species, also occurred and was compared with Q. suber. Three cpDNA and one mtDNA primer pairs were used in the survey, each in combination with one restriction enzyme. Six haplotypes belonging to two very divergent lineages were detected; one lineage predominates in each species, and is probably ancestral, as inferred from comparisons with other oak species. In the mixed-species populations, cytoplasmic genomes were frequently shared across species, as indicated by an introgression ratio of 0.63. This index is a new measure of the propensity of species to share locally genetic markers, varying from zero (complete differentiation) to one (no differentiation). By contrast, more closely related deciduous oak species (Q. robur, Q. petraea and Q. pubescens) have introgression ratios varying from 0.82 to 0.97. The introgression events appear to have been more frequent in the direction Q. ilex (female) x Q. suber (male), a finding which seems attributable to the flowering phenology of these two species. This asymmetry may have favoured immigration of Q. suber beyond its main range, in regions already colonized by Q. ilex. There, rare hybridization and further introgression through long distance pollen flow have established populations that are morphologically indistinguishable from Q. suber but that have cytoplasmic genomes originating from the local Q. ilex populations.

  15. Climate, invasive species and land use drive population dynamics of a cold-water specialist

    Science.gov (United States)

    Kovach, Ryan P.; Al-Chokhachy, Robert K.; Whited, Diane C.; Schmetterling, David A.; Dux, Andrew M; Muhlfeld, Clint C.

    2017-01-01

    Climate change is an additional stressor in a complex suite of threats facing freshwater biodiversity, particularly for cold-water fishes. Research addressing the consequences of climate change on cold-water fish has generally focused on temperature limits defining spatial distributions, largely ignoring how climatic variation influences population dynamics in the context of other existing stressors.We used long-term data from 92 populations of bull trout Salvelinus confluentus – one of North America's most cold-adapted fishes – to quantify additive and interactive effects of climate, invasive species and land use on population dynamics (abundance, variability and growth rate).Populations were generally depressed, more variable and declining where spawning and rearing stream habitat was limited, invasive species and land use were prevalent and stream temperatures were highest. Increasing stream temperature acted additively and independently, whereas land use and invasive species had additive and interactive effects (i.e. the impact of one stressor depended on exposure to the other stressor).Most (58%–78%) of the explained variation in population dynamics was attributed to the presence of invasive species, differences in life history and management actions in foraging habitats in rivers, lakes and reservoirs. Although invasive fishes had strong negative effects on populations in foraging habitats, proactive control programmes appeared to effectively temper their negative impact.Synthesis and applications. Long-term demographic data emphasize that climate warming will exacerbate imperilment of cold-water specialists like bull trout, yet other stressors – especially invasive fishes – are immediate threats that can be addressed by proactive management actions. Therefore, climate-adaptation strategies for freshwater biodiversity should consider existing abiotic and biotic stressors, some of which provide potential and realized opportunity for conservation

  16. Hamiltonian replica exchange combined with elastic network analysis to enhance global domain motions in atomistic molecular dynamics simulations.

    Science.gov (United States)

    Ostermeir, Katja; Zacharias, Martin

    2014-12-01

    Coarse-grained elastic network models (ENM) of proteins offer a low-resolution representation of protein dynamics and directions of global mobility. A Hamiltonian-replica exchange molecular dynamics (H-REMD) approach has been developed that combines information extracted from an ENM analysis with atomistic explicit solvent MD simulations. Based on a set of centers representing rigid segments (centroids) of a protein, a distance-dependent biasing potential is constructed by means of an ENM analysis to promote and guide centroid/domain rearrangements. The biasing potentials are added with different magnitude to the force field description of the MD simulation along the replicas with one reference replica under the control of the original force field. The magnitude and the form of the biasing potentials are adapted during the simulation based on the average sampled conformation to reach a near constant biasing in each replica after equilibration. This allows for canonical sampling of conformational states in each replica. The application of the methodology to a two-domain segment of the glycoprotein 130 and to the protein cyanovirin-N indicates significantly enhanced global domain motions and improved conformational sampling compared with conventional MD simulations.

  17. Optical nonlinearity and-ultrafast dynamics of ion exchanged silver nanoparticles embedded in soda-lime silicate glass

    Institute of Scientific and Technical Information of China (English)

    YANG XiuChun; LI ZhiHui; LI WeiJie; XU JingXian; DONG ZhiWei; QIAN ShiXiong

    2008-01-01

    Ag nanoparticles embedded in soda-lime silicate glass were fabricated by ion-exchange and subsequently annealing method. Z-scan technique, femtosecond time-resolved optical Kerr effect (OKE) technique and femtosecond pump-probe experiment were used to investigate the effects of laser wavelength and laser pulse duration as well as annealing temperature on the third-order optical nonlinearity and ultrafast dynamics of the composites. It was found that the third-order susceptibility of Ag nanoparticles composite glass measured by 400 nm pulse source is larger than that measured by 800 nm pulse source due to an enhancement effect of local field near surface plasmon resonance of Ag nanoparticles in silicate glass. The third-order optical nonlinearity measured by ns laser source is about two orders of magnitude larger than that measured from fs pulse. The annealing temperature has an important effect on the third-order optical nonlinearity and ultrafast dynamics of the composites. Third-order nonlinear susceptibility upto 10-10 esu and fast relaxation process up to 0.2 ps have been obtained in Ag nanoparticles doped glass,

  18. Applications of hydrogen deuterium exchange (HDX for the characterization of conformational dynamics in light-activated photoreceptors

    Directory of Open Access Journals (Sweden)

    Robert eLindner

    2015-06-01

    Full Text Available Rational design of optogenetic tools is inherently linked to the understanding of photoreceptor function. Structural analysis of elements involved in signal integration in individual sensor domains provides an initial idea of their mode of operation, but understanding how local structural rearrangements eventually affect signal transmission to output domains requires inclusion of the effector regions in the characterization. However, the dynamic nature of these assemblies renders their structural analysis challenging and therefore a combination of high- and low-resolution techniques is required to appreciate functional aspects of photoreceptors.This review focuses on the potential of Hydrogen-Deuterium exchange coupled to mass spectrometry (HDX-MS for complementing the structural characterization of photoreceptors. In this respect, the ability of HDX-MS to provide information on the conformational dynamics and the possibility to address multiple functionally relevant states in solution render this methodology ideally suitable. We highlight recent examples demonstrating the potential of HDX-MS and discuss how these results can help to improve existing optogenetic systems or guide the design of novel optogenetic tools.

  19. Stochastic description of the dynamics of a random-exchange Heisenberg chain

    Energy Technology Data Exchange (ETDEWEB)

    Vainstein, M.H. [Instituto de Fisica and Nucleo de Supercomputacao e Sistemas Complexos, ICCMP, Universidade de Brasilia, CP 04513, 70919-970 Brasilia, DF (Brazil); Morgado, R. [Instituto de Fisica and Nucleo de Supercomputacao e Sistemas Complexos, ICCMP, Universidade de Brasilia, CP 04513, 70919-970 Brasilia, DF (Brazil); Oliveira, F.A. [Instituto de Fisica and Nucleo de Supercomputacao e Sistemas Complexos, ICCMP, Universidade de Brasilia, CP 04513, 70919-970 Brasilia, DF (Brazil); Moura, F.A.B.F. de [Laboratorio de Fisica Teorica e Computacional, Departamento de Fisica, Universidade Federal de Pernambuco, 50670-901 Recife, PE (Brazil) and Departamento de Fisica, Universidade Federal de Alagoas, 57072-970 Maceio, AL (Brazil)]. E-mail: fidelis@df.ufal.br; Coutinho-Filho, M.D. [Laboratorio de Fisica Teorica e Computacional, Departamento de Fisica, Universidade Federal de Pernambuco, 50670-901 Recife, PE (Brazil)

    2005-05-16

    We study the diffusion process in a Heisenberg chain with correlated spatial disorder, with a power spectrum in the momentum space behaving as k{sup -{beta}}, using a stochastic description. It establishes a direct connection between the fluctuation in the spin-wave density of states and the noise density of states. For continuous ranges of the exponent {beta}, we find superdiffusive and ballistic spin-wave motions. Both diffusion exponents predicted by the stochastic procedure agree with the ones calculated using the Hamiltonian dynamics.

  20. Could beaked whales get the bends? Effect of diving behaviour and physiology on modelled gas exchange for three species: Ziphius cavirostris, Mesoplodon densirostris and Hyperoodon ampullatus.

    Science.gov (United States)

    Hooker, Sascha K; Baird, Robin W; Fahlman, Andreas

    2009-07-31

    A mathematical model, based on current knowledge of gas exchange and physiology of marine mammals, was used to predict blood and tissue tension N2 (P(N2)) using field data from three beaked whale species: northern bottlenose whales, Cuvier's beaked whales, and Blainville's beaked whales. The objective was to determine if physiology (body mass, diving lung volume, dive response) or dive behaviour (dive depth and duration, changes in ascent rate, diel behaviour) would lead to differences in P(N2) levels and thereby decompression sickness (DCS) risk between species. Diving lung volume and extent of the dive response had a large effect on end-dive P(N2). The dive profile had a larger influence on end-dive P(N2) than body mass differences between species. Despite diel changes in dive behaviour, P(N2) levels showed no consistent trend. Model output suggested that all three species live with tissue P(N2) levels that would cause a significant proportion of DCS cases in terrestrial mammals. Cuvier's beaked whale diving behaviour appears to put them at higher risk than the other species, which may explain their prevalence in strandings after the use of mid-frequency sonar.

  1. Dynamic Structure of Mo-O Species in Ag-Mo-P-O Catalyst for Oxidative Dehydrogenation of Propane

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The dynamic structure of Mo-O species in Ag-Mo-P-O catalyst was studied by in situ confocal microprobe laser Raman spectroscopy (LRS) and catalytic test. The results indicate Mo-O species of MoO3 transformed to Mo-O species of AgMoO2PO4 in C3H8/O2/N2 (3/1/4) flow at 773 K. This behavior is closely relative to oxidative dehydrogenation of propane and intrinsic properties of Mo-O species. The Mo-O species of AgMoO2PO4 may be active species for oxidative dehydrogenation of propane.

  2. Dynamic modeling and simulation of air-breathing proton exchange membrane fuel cell

    Energy Technology Data Exchange (ETDEWEB)

    Yalcinoz, T. [Department of Electrical and Computer Engineering, University of South Alabama, Mobile, AL 36688 (United States); Nigde University, Department of Electrical and Electronic Engineering, Nigde 51245 (Turkey); Alam, M.S. [Department of Electrical and Computer Engineering, University of South Alabama, Mobile, AL 36688 (United States)

    2008-07-15

    Small fuel cells have shown excellent potential as alternative energy sources for portable applications. One of the most promising fuel cell technologies for portable applications is air-breathing fuel cells. In this paper, a dynamic model of an air-breathing PEM fuel cell (AB-PEMFC) system is presented. The analytical modeling and simulation of the air-breathing PEM fuel cell system are verified using Matlab, Simulink and SimPowerSystems Blockset. To show the effectiveness of the proposed AB-PEMFC model, two case studies are carried out using the Matlab software package. In the first case study, the dynamic behavior of the proposed AB-PEMFC system is compared with that of a planar air-breathing PEM fuel cell model. In the second case study, the validation of the air-breathing PEM fuel cell-based power source is carried out for the portable application. Test results show that the proposed AB-PEMFC system can be considered as a viable alternative energy sources for portable applications. (author)

  3. Conserved changes in the dynamics of metabolic processes during fruit development and ripening across species.

    Science.gov (United States)

    Klie, Sebastian; Osorio, Sonia; Tohge, Takayuki; Drincovich, María F; Fait, Aaron; Giovannoni, James J; Fernie, Alisdair R; Nikoloski, Zoran

    2014-01-01

    Computational analyses of molecular phenotypes traditionally aim at identifying biochemical components that exhibit differential expression under various scenarios (e.g. environmental and internal perturbations) in a single species. High-throughput metabolomics technologies allow the quantification of (relative) metabolite levels across developmental stages in different tissues, organs, and species. Novel methods for analyzing the resulting multiple data tables could reveal preserved dynamics of metabolic processes across species. The problem we address in this study is 2-fold. (1) We derive a single data table, referred to as a compromise, which captures information common to the investigated set of multiple tables containing data on different fruit development and ripening stages in three climacteric (i.e. peach [Prunus persica] and two tomato [Solanum lycopersicum] cultivars, Ailsa Craig and M82) and two nonclimacteric (i.e. strawberry [Fragaria × ananassa] and pepper [Capsicum chilense]) fruits; in addition, we demonstrate the power of the method to discern similarities and differences between multiple tables by analyzing publicly available metabolomics data from three tomato ripening mutants together with two tomato cultivars. (2) We identify the conserved dynamics of metabolic processes, reflected in the data profiles of the corresponding metabolites that contribute most to the determined compromise. Our analysis is based on an extension to principal component analysis, called STATIS, in combination with pathway overenrichment analysis. Based on publicly available metabolic profiles for the investigated species, we demonstrate that STATIS can be used to identify the metabolic processes whose behavior is similarly affected during fruit development and ripening. These findings ultimately provide insights into the pathways that are essential during fruit development and ripening across species.

  4. Moving Towards Dynamic Ocean Management: How Well Do Modeled Ocean Products Predict Species Distributions?

    Directory of Open Access Journals (Sweden)

    Elizabeth A. Becker

    2016-02-01

    Full Text Available Species distribution models are now widely used in conservation and management to predict suitable habitat for protected marine species. The primary sources of dynamic habitat data have been in situ and remotely sensed oceanic variables (both are considered “measured data”, but now ocean models can provide historical estimates and forecast predictions of relevant habitat variables such as temperature, salinity, and mixed layer depth. To assess the performance of modeled ocean data in species distribution models, we present a case study for cetaceans that compares models based on output from a data assimilative implementation of the Regional Ocean Modeling System (ROMS to those based on measured data. Specifically, we used seven years of cetacean line-transect survey data collected between 1991 and 2009 to develop predictive habitat-based models of cetacean density for 11 species in the California Current Ecosystem. Two different generalized additive models were compared: one built with a full suite of ROMS output and another built with a full suite of measured data. Model performance was assessed using the percentage of explained deviance, root mean squared error (RMSE, observed to predicted density ratios, and visual inspection of predicted and observed distributions. Predicted distribution patterns were similar for models using ROMS output and measured data, and showed good concordance between observed sightings and model predictions. Quantitative measures of predictive ability were also similar between model types, and RMSE values were almost identical. The overall demonstrated success of the ROMS-based models opens new opportunities for dynamic species management and biodiversity monitoring because ROMS output is available in near real time and can be forecast.

  5. Temporal dynamics of deep-sea latitudinal species diversity gradient based on paleoceanographic/micropaleontologic data

    Science.gov (United States)

    Yasuhara, M.; Hunt, G.; Okahashi, H.

    2009-12-01

    Macroecology investigates large-scale ecological phenomena, such as regional-global trends in ecosystem properties and biodiversity, and is used to better understand recent human-induced ecosystem degradation. Paleoceanography investigates physical/chemical parameters, biogeochemical cycles, ocean circulation, and ocean-atmosphere interaction, but rarely includes ecosystem-scale biological processes. Here we adopt a macroecological approach to paleoceanography and present sediment core records of the temporal dynamics of deep-sea species diversity gradients using ostracodes from the equatorial Atlantic Ocean for the past four glacial-interglacial cycles. Results show unexpected instability and high amplitude fluctuations in species diversity in the tropical deep ocean. The results imply that the modern deep-sea latitudinal species diversity gradient is unexpectedly dynamic over short time intervals and collapsed during glacial periods. Unstable tropical diversity requires reconsideration of current ecological hypotheses about the generation and maintenance of biodiversity as they apply to the deep sea, and underscores the potential vulnerability and conservation importance of tropical deep-sea ecosystems.

  6. {sup 1}H and {sup 23}Na MAS NMR spectroscopy of cationic species in CO{sub 2} selective alkaline earth metal porous silicoaluminophosphates prepared via liquid and solid state ion exchange

    Energy Technology Data Exchange (ETDEWEB)

    Arevalo-Hidalgo, Ana G. [Department of Chemical Engineering, University of Puerto Rico-Mayagueez Campus, Mayagueez, PR 00681-9000 (Puerto Rico); Dugar, Sneha; Fu, Riqiang [National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310 (United States); Hernandez-Maldonado, Arturo J., E-mail: arturoj.hernandez@upr.edu [Department of Chemical Engineering, University of Puerto Rico-Mayagueez Campus, Mayagueez, PR 00681-9000 (Puerto Rico)

    2012-07-15

    The location of extraframework cations in Sr{sup 2+} and Ba{sup 2+} ion-exchanged SAPO-34 was estimated by means of {sup 1}H and {sup 23}Na MAS NMR spectroscopy and spectral deconvolution. Incorporation of the alkaline earth metal cations onto the SAPO framework was achieved via liquid state ion exchange, coupled partial detemplation/solid-state ion exchange, and combination of both techniques. MAS NMR revealed that the level of ion exchange was limited by the presence of protons and sodium cations near hexagonal prisms (site SI), which are relatively difficult to exchange with the alkaline earth metal due to steric and charge repulsion criteria. In addition, the presence of ammonium cations in the supercages facilitated the exchange of otherwise tenacious hydrogen as corroborated by unit cell compositional data as well as enhanced CO{sub 2} adsorption at low partial pressures. The extraframework ammonium species were produced from partial detemplation of the structure-directing agent employed for the SAPO-34 synthesis, tetraethylammonium. - Graphical abstract: MAS NMR was used to elucidate the position the cationic species in alkaline earth metal exchanged silicoaluminophosphates. These species played a significant role during the ion exchange process and, therefore, the materials ultimate CO{sub 2} adsorption performance. Highlights: Black-Right-Pointing-Pointer Location of extraframework Sr{sup 2+} or Ba{sup 2+} cations was estimated by means of {sup 1}H and {sup 23}Na MAS NMR. Black-Right-Pointing-Pointer Level of Sr{sup 2+} or Ba{sup 2+} ion exchange was limited by the presence of protons and sodium cations. Black-Right-Pointing-Pointer Presence of ammonium cations in the supercages facilitated the exchange. Black-Right-Pointing-Pointer Sr{sup 2+} and Ba{sup 2+} ion exchanged SAPOs are outstanding CO{sub 2} adsorbents.

  7. Effect of grazing and canopy on Mediterranean ecosystem functioning: Carbon dioxide exchange and the dynamics of carbon and nutrient pools

    Science.gov (United States)

    Mirzaei, Heydar; Tenhunen, John; Hossein, Zaman; Li, Yuelin; Otieno, Dennis

    2010-05-01

    Mediterranean ecosystems occupy less than 5 % of the Earth's surface, yet they contain about 20 % of the world's flora, including important components in grasslands. In this study, important ecosystem functions (CO2 exchange, biomass production and nutrient uptake of the herbaceous layer of a Mediterranean grassland ecosystem) at Herdade da Mitra, in Portugal were studied. The main objectives of this project were, to understand effects of grazing and canopy layer (overstory) on ecosystem functioning respectively. The canopy layer consists of some woody species mainly Quercus ilex and Qu. Suber. Results showed that trees added considerable amounts of nutrients to the soil beneath their canopies, and had the potential to facilitate understory production. Although there was no significant difference in total biomass accumulation between understory and open locations. Analysis of soil N concentration revealed higher soil N under the trees when compared to those in open areas. Although NEE was limited by light intensity in the understory, model projection of GPP showed no difference between the understory and the open locations in their potential assimilatory capacity but depending on the locations (open vs understory), grazing influenced CO2 exchange processes differently. We found no significant differences in GPP between grazed and ungrazed sites in the open locations, while large differences occurred in the understory, with lower NEE in the grazed as compared to the ungrazed locations. Significant differences, however, occurred between the two locations in ecosystem respiration, showing higher respiration in grazed location in the open site while in the understory site respiration was similar in both grazed and ungrazed locations. Foliar N concentration in understory and open sites showed a different pattern, as the ungrazed location in the understory indicated lower values compared to grazed locations, although in the open sites, ungrazed locations exhibited larger

  8. The Dynamics of Exchanges and References among Scientific Texts, and the Autopoiesis of Discursive Knowledge

    CERN Document Server

    Lucio-Arias, Diana

    2009-01-01

    Discursive knowledge emerges as codification in flows of communication. The flows of communication are constrained and enabled by networks of communications as their historical manifestations at each moment of time. New publications modify the existing networks by changing the distributions of attributes and relations in document sets, while the networks are self-referentially updated along trajectories. Codification operates reflexively: the network structures are reconstructed from the perspective of hindsight. Codification along different axes differentiates discursive knowledge into specialties. These intellectual control structures are constructed bottom-up, but feed top-down back upon the production of new knowledge. However, the forward dynamics of diffusion in the development of the communication networks along trajectories differs from the feedback mechanisms of control. Analysis of the development of scientific communication in terms of evolving scientific literatures provides us with a model which ...

  9. Electrical resistivity dynamics beneath a fractured sedimentary bedrock riverbed in response to temperature and groundwater-surface water exchange

    Science.gov (United States)

    Steelman, Colby M.; Kennedy, Celia S.; Capes, Donovan C.; Parker, Beth L.

    2017-06-01

    Bedrock rivers occur where surface water flows along an exposed rock surface. Fractured sedimentary bedrock can exhibit variable groundwater residence times, anisotropic flow paths, and heterogeneity, along with diffusive exchange between fractures and rock matrix. These properties of the rock will affect thermal transients in the riverbed and groundwater-surface water exchange. In this study, surface electrical methods were used as a non-invasive technique to assess the scale and temporal variability of riverbed temperature and groundwater-surface water interaction beneath a sedimentary bedrock riverbed. Conditions were monitored at a semi-daily to semi-weekly interval over a full annual period that included a seasonal freeze-thaw cycle. Surface electromagnetic induction (EMI) and electrical resistivity tomography (ERT) methods captured conditions beneath the riverbed along a pool-riffle sequence of the Eramosa River in Canada. Geophysical datasets were accompanied by continuous measurements of aqueous specific conductance, temperature, and river stage. Time-lapse vertical temperature trolling within a lined borehole adjacent to the river revealed active groundwater flow zones along fracture networks within the upper 10 m of rock. EMI measurements collected during cooler high-flow and warmer low-flow periods identified a spatiotemporal riverbed response that was largely dependent upon riverbed morphology and seasonal groundwater temperature. Time-lapse ERT profiles across the pool and riffle sequence identified seasonal transients within the upper 2 and 3 m of rock, respectively, with spatial variations controlled by riverbed morphology (pool versus riffle) and dominant surficial rock properties (competent versus weathered rock rubble surface). While the pool and riffle both exhibited a dynamic resistivity through seasonal cooling and warming cycles, conditions beneath the pool were more variable, largely due to the formation of river ice during the winter season

  10. The Dynamics of Lateral Gene Transfer in Genus Leishmania - A Route for Adaptation and Species Diversification.

    Science.gov (United States)

    Vikeved, Elisabet; Backlund, Anders; Alsmark, Cecilia

    2016-01-01

    The genome of Leishmania major harbours a comparably high proportion of genes of prokaryote origin, acquired by lateral gene transfer (LGT). Some of these are present in closely related trypanosomatids, while some are detected in Leishmania only. We have evaluated the impact and destiny of LGT in genus Leishmania. To study the dynamics and fate of LGTs we have performed phylogenetic, as well as nucleotide and amino acid composition analyses within orthologous groups of LGTs detected in Leishmania. A set of universal trypanosomatid LGTs was added as a reference group. Both groups of LGTs have, to some extent, ameliorated to resemble the recipient genomes. However, while virtually all of the universal trypanosomatid LGTs are distributed and conserved in the entire genus Leishmania, the LGTs uniquely present in genus Leishmania are more prone to gene loss and display faster rates of evolution. Furthermore, a PCR based approach has been employed to ascertain the presence of a set of twenty LGTs uniquely present in genus Leishmania, and three universal trypanosomatid LGTs, in ten additional strains of Leishmania. Evolutionary rates and predicted expression levels of these LGTs have also been estimated. Ten of the twenty LGTs are distributed and conserved in all species investigated, while the remainder have been subjected to modifications, or undergone pseudogenization, degradation or loss in one or more species. LGTs unique to the genus Leishmania have been acquired after the divergence of Leishmania from the other trypanosomatids, and are evolving faster than their recipient genomes. This implies that LGT in genus Leishmania is a continuous and dynamic process contributing to species differentiation and speciation. This study also highlights the importance of carefully evaluating these dynamic genes, e.g. as LGTs have been suggested as potential drug targets.

  11. Replica exchange Monte Carlo simulations of the ising spin glass: Static and dynamic properties

    Science.gov (United States)

    Yucesoy, Burcu

    Spin glasses have been the subject of intense study and considerable controversy for decades, and the low-temperature phase of short-range spin glasses is still poorly understood. Our main goal is to improve our understanding in this area and find an answer to the following question: Are there only a single pair or a countable infinity of pure states in the low temperature phase of the EA spin glass? To that aim we first start by introducing spin glasses and provide a brief history of their research, then proceed to describe our method of simulation, the parallel tempering Monte Carlo algorithm. Next, we present the results of a large-scale numerical study of the equilibrium three-dimensional Edwards-Anderson Ising spin glass with Gaussian disorder. In order to understand how the parallel tempering algorithm works, we measure various static, as well as dynamical quantities, such as the autocorrelation times and round-trip times for the parallel tempering Monte Carlo method. We examine the correlation between static and dynamic observables for ˜ 5000 disorder realizations and up to 1000 spins down to temperatures at 20% of the critical temperature, and our results show that autocorrelation times are directly correlated with the roughness of the free-energy landscape. In the following chapters, the three- and four-dimensional Edwards-Anderson and mean-field Sherrington-Kirkpatrick Ising spin glasses are studied again via large scale Monte Carlo simulations at low temperatures, deep within the spin glass phase. Performing a careful statistical analysis of several thousand independent disorder realizations and using an observable that detects peaks in the overlap distribution, we show that the Sherrington-Kirkpatrick and Edwards-Anderson models have a distinctly different low-temperature behavior. We arrive to the following conclusion: The structure of the spin-glass overlap distribution for the Edwards-Anderson model suggests that its low-temperature phase has only a

  12. An empirical, hierarchical typology of tree species assemblages for assessing forest dynamics under global change scenarios.

    Science.gov (United States)

    Costanza, Jennifer K; Coulston, John W; Wear, David N

    2017-01-01

    The composition of tree species occurring in a forest is important and can be affected by global change drivers such as climate change. To inform assessment and projection of global change impacts at broad extents, we used hierarchical cluster analysis and over 120,000 recent forest inventory plots to empirically define forest tree assemblages across the U.S., and identified the indicator and dominant species associated with each. Cluster typologies in two levels of a hierarchy of forest assemblages, with 29 and 147 groups respectively, were supported by diagnostic criteria. Groups in these two levels of the hierarchy were labeled based on the top indicator species in each, and ranged widely in size. For example, in the 29-cluster typology, the sugar maple-red maple assemblage contained the largest number of plots (30,068), while the butternut-sweet birch and sourwood-scarlet oak assemblages were both smallest (6 plots each). We provide a case-study demonstration of the utility of the typology for informing forest climate change impact assessment. For five assemblages in the 29-cluster typology, we used existing projections of changes in importance value (IV) for the dominant species under one low and one high climate change scenario to assess impacts to the assemblages. Results ranged widely for each scenario by the end of the century, with each showing an average decrease in IV for dominant species in some assemblages, including the balsam fir-quaking aspen assemblage, and an average increase for others, like the green ash-American elm assemblage. Future work should assess adaptive capacity of these forest assemblages and investigate local population- and community-level dynamics in places where dominant species may be impacted. This typology will be ideal for monitoring, assessing, and projecting changes to forest communities within the emerging framework of macrosystems ecology, which emphasizes hierarchies and broad extents.

  13. Temporal-spatial dynamics in orthoptera in relation to nutrient availability and plant species richness.

    Directory of Open Access Journals (Sweden)

    Rob J J Hendriks

    Full Text Available Nutrient availability in ecosystems has increased dramatically over the last century. Excess reactive nitrogen deposition is known to negatively impact plant communities, e.g. by changing species composition, biomass and vegetation structure. In contrast, little is known on how such impacts propagate to higher trophic levels. To evaluate how nitrogen deposition affects plants and herbivore communities through time, we used extensive databases of spatially explicit historical records of Dutch plant species and Orthoptera (grasshoppers and crickets, a group of animals that are particularly susceptible to changes in the C:N ratio of their resources. We use robust methods that deal with the unstandardized nature of historical databases to test whether nitrogen deposition levels and plant richness changes influence the patterns of richness change of Orthoptera, taking into account Orthoptera species functional traits. Our findings show that effects indeed also propagate to higher trophic levels. Differences in functional traits affected the temporal-spatial dynamics of assemblages of Orthoptera. While nitrogen deposition affected plant diversity, contrary to our expectations, we could not find a strong significant effect of food related traits. However we found that species with low habitat specificity, limited dispersal capacity and egg deposition in the soil were more negativly affected by nitrogen deposition levels. Despite the lack of significant effect of plant richness or food related traits on Orthoptera, the negative effects of nitrogen detected within certain trait groups (e.g. groups with limited disperse ability could be related to subtle changes in plant abundance and plant quality. Our results, however, suggest that the changes in soil conditions (where many Orthoptera species lay their eggs or other habitat changes driven by nitrogen have a stronger influence than food related traits. To fully evaluate the negative effects of nitrogen

  14. Extended Fluid-Dynamics and Collective Motion of Two Trapped Fermion Species with Pairing Interactions

    Science.gov (United States)

    Hernández, E. S.; Capuzzi, P.; Szybisz, L.

    2011-02-01

    We extend our earlier fluid-dynamical description of fermion superfluids incorporating the particle energy flow together with the equation of motion for the internal kinetic energy of the pairs. The formal scheme combines a set of equations similar to those of classical hydrodynamics with the equations of motion for the anomalous density and for its related momentum density and kinetic energy density. This dynamical frame represents a second order truncation of an infinite hierarchy of equations of motion isomorphic to the full time dependent Hartree-Fock-Bogoliubov equations in coordinate representation. We analyze the equilibrium solutions and fluctuations for a homogeneous, unpolarized fermion system of two species, and show that the collective spectrum presents the well-known Anderson-Bogoliubov low energy mode of homogeneous superfluids and a pairing vibration near the gap energy.

  15. Dynamic economic analysis on invasive species management: some policy implications of catchability.

    Science.gov (United States)

    Kotani, Koji; Kakinaka, Makoto; Matsuda, Hiroyuki

    2009-07-01

    The problem of controlling invasive species has emerged as a global issue. In response to invasive species threats, governments often propose eradication. This article challenges the eradication view by studying optimal strategies for controlling invasive species in a simple dynamic model. The analysis mainly focuses on deriving policy implications of catchability in a situation where a series of controlling actions incurs operational costs that derive from the fact that catchability depends on the current stock size of invasive species. We analytically demonstrate that the optimal policy changes drastically, depending on the sensitivity of catchability in response to a change in the stock size, as well as on the initial stock. If the sensitivity of catchability is sufficiently high, the constant escapement policy with some interior target level is optimal. In contrast, if the sensitivity of catchability is sufficiently low, there could exist a threshold of the initial stock which differentiates the optimal action between immediate eradication and giving-up without any control. In the intermediate range, immediate eradication, giving-up without any control, or more complex policies may be optimal. Numerical analysis is employed to present economic intuitions and insights in both analytically tractable and intractable cases.

  16. Particle Currents in a Fluid—Dynamical Description of Two Trapped Fermion Species

    Science.gov (United States)

    Hernández, E. S.; Capuzzi, P.; Szybisz, L.

    2011-02-01

    We apply a recent generalization of the fluid-dynamical scheme of nuclear physics that includes the pair density and current of superfluids, to trace the particle transition currents of an unpolarized fermion system in a harmonic trap. These current fluctuations are driven by the equilibrium density and gap and by the oscillations in the particle densities. We analize the velocity portraits of either species for the lowest multipolar excitations employing different equations of state of the unperturbed fluids, in order to establish the role of the equilibrium gap.

  17. Modified relaxation dynamics and coherent energy exchange in coupled vibration-cavity polaritons

    Science.gov (United States)

    Dunkelberger, A. D.; Spann, B. T.; Fears, K. P.; Simpkins, B. S.; Owrutsky, J. C.

    2016-11-01

    Coupling vibrational transitions to resonant optical modes creates vibrational polaritons shifted from the uncoupled molecular resonances and provides a convenient way to modify the energetics of molecular vibrations. This approach is a viable method to explore controlling chemical reactivity. In this work, we report pump-probe infrared spectroscopy of the cavity-coupled C-O stretching band of W(CO)6 and the direct measurement of the lifetime of a vibration-cavity polariton. The upper polariton relaxes 10 times more quickly than the uncoupled vibrational mode. Tuning the polariton energy changes the polariton transient spectra and relaxation times. We also observe quantum beats, so-called vacuum Rabi oscillations, between the upper and lower vibration-cavity polaritons. In addition to establishing that coupling to an optical cavity modifies the energy-transfer dynamics of the coupled molecules, this work points out the possibility of systematic and predictive modification of the excited-state kinetics of vibration-cavity polariton systems.

  18. Dynamic studies of H-Ras•GTPγS interactions with nucleotide exchange factor Sos reveal a transient ternary complex formation in solution.

    Science.gov (United States)

    Vo, Uybach; Vajpai, Navratna; Embrey, Kevin J; Golovanov, Alexander P

    2016-07-14

    The cycling between GDP- and GTP- bound forms of the Ras protein is partly regulated by the binding of Sos. The structural/dynamic behavior of the complex formed between activated Sos and Ras at the point of the functional cycle where the nucleotide exchange is completed has not been described to date. Here we show that solution NMR spectra of H-Ras∙GTPγS mixed with a functional fragment of Sos (Sos(Cat)) at a 2:1 ratio are consistent with the formation of a rather dynamic assembly. H-Ras∙GTPγS binding was in fast exchange on the NMR timescale and retained a significant degree of molecular tumbling independent of Sos(Cat), while Sos(Cat) also tumbled largely independently of H-Ras. Estimates of apparent molecular weight from both NMR data and SEC-MALS revealed that, at most, only one H-Ras∙GTPγS molecule appears stably bound to Sos. The weak transient interaction between Sos and the second H-Ras∙GTPγS may provide a necessary mechanism for complex dissociation upon the completion of the native GDP → GTP exchange reaction, but also explains measurable GTP → GTP exchange activity of Sos routinely observed in in vitro assays that use fluorescently-labelled analogs of GTP. Overall, the data presents the first dynamic snapshot of Ras functional cycle as controlled by Sos.

  19. Dynamics of ammonia exchange with cut grassland: synthesis of results and conclusions of the GRAMINAE Integrated Experiment

    Science.gov (United States)

    Sutton, M. A.; Nemitz, E.; Milford, C.; Campbell, C.; Erisman, J. W.; Hensen, A.; Cellier, P.; David, M.; Loubet, B.; Personne, E.; Schjoerring, J. K.; Mattsson, M.; Dorsey, J. R.; Gallagher, M. W.; Horvath, L.; Weidinger, T.; Meszaros, R.; Dämmgen, U.; Neftel, A.; Herrmann, B.; Lehman, B. E.; Flechard, C.; Burkhardt, J.

    2009-12-01

    Improved data on biosphere-atmosphere exchange are fundamental to understanding the production and fate of ammonia (NH3) in the atmosphere. The GRAMINAE Integrated Experiment combined novel measurement and modelling approaches to provide the most comprehensive analysis of the interactions to date. Major inter-comparisons of micrometeorological parameters and NH3 flux measurements using the aerodynamic gradient method and relaxed eddy accumulation (REA) were conducted. These showed close agreement, though the REA systems proved insufficiently precise to investigate vertical flux divergence. Grassland management had a large effect on fluxes: emissions increased after grass cutting (-50 to 700 ng m-2 s-1 NH3) and after N-fertilization (0 to 3800 ng m-2 s-1) compared with before the cut (-60 to 40 ng m-2 s-1). Effects of advection and air chemistry were investigated using horizontal NH3 profiles, acid gas and particle flux measurements. Inverse modelling of NH3 emission from an experimental farm agreed closely with inventory estimates, while advection errors were used to correct measured grassland fluxes. Advection effects were caused both by the farm and by emissions from the field, with an inverse dispersion-deposition model providing a reliable new approach to estimate net NH3 fluxes. Effects of aerosol chemistry on net NH3 fluxes were small, while the measurements allowed NH3-induced particle growth rates to be calculated and aerosol fluxes to be corrected. Bioassays estimated the emission potential Γ = [NH4+]/[H+] for different plant pools, with the apoplast having the smallest values (30-1000). The main within-canopy sources of NH3 emission appeared to be leaf litter and the soil surface, with Γ up to 3 million and 300 000, respectively. Cuvette and within-canopy analyses confirmed the role of leaf litter NH3 emission, which, prior to cutting, was mostly recaptured within the canopy. Measured ammonia fluxes were compared with three models: an ecosystem model

  20. Quantum dynamics of {sup 16}O + {sup 36}O{sub 2} and {sup 18}O + {sup 32}O{sub 2} exchange reactions

    Energy Technology Data Exchange (ETDEWEB)

    Rajagopala Rao, T.; Mahapatra, S., E-mail: smsc@uohyd.ernet.in [School of Chemistry, University of Hyderabad, Hyderabad 500 046 (India); Guillon, G. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303, CNRS-Université de Bourgogne, 21078 Dijon Cedex (France); Honvault, P., E-mail: pascal.honvault@univ-fcomte.fr [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303, CNRS-Université de Bourgogne, 21078 Dijon Cedex (France); UFR Sciences et Techniques, Université de Franche-Comté, 25030 Besançon Cedex (France)

    2015-05-07

    We present quantum dynamical investigations of {sup 16}O + {sup 36}O{sub 2} and {sup 18}O + {sup 32}O{sub 2} exchange reactions using a time-independent quantum mechanical method and an accurate global potential energy surface of ozone [Dawes et al., J. Chem. Phys. 135, 081102 (2011)]. Initial state-selected integral cross sections, rate constants, and Boltzmann averaged thermal rate constants are obtained and compared with earlier experimental and theoretical results. The computed thermal rate constants for the oxygen exchange reactions exhibit a negative temperature dependence, as found experimentally. They are in better agreement with the experiments than the previous studies on the same reactions.

  1. Dissecting the effect of RNA aptamer binding on the dynamics of plasminogen activator inhibitor 1 using hydrogen/deuterium exchange mass spectrometry

    DEFF Research Database (Denmark)

    Trelle, Morten B; Dupont, Daniel Miotto; Madsen, Jeppe Buur

    2014-01-01

    , about their effects on protein conformation and dynamics. We have employed hydrogen/deuterium exchange (HDX) mass spectrometry to study the effect of RNA aptamers on the structural flexibility of the serpin plasminogen activator inhibitor-1 (PAI-1). The aptamers have characteristic effects...... of the aptamers to PAI-1 is associated with substantial and widespread protection against deuterium uptake in PAI-1. The aptamers induce protection against exchange with the solvent both in the protein-aptamer interface as well as in other specific areas. Interestingly, the aptamers induce substantial protection...

  2. Seismic dynamic analysis of Heat Exchangers inside of the Auxiliary Buildings in AP1000{sup T}M NPP

    Energy Technology Data Exchange (ETDEWEB)

    Di Fonzo, M.; Aragon, J.; Moraleda, F.; Palazuelos, M.; San vicente, J. L.

    2011-07-01

    Seismic dynamic analysis was carried out for the Heat Exchangers (RNS-HR) located inside of the Auxiliary Building in AP 1000{sup T}M NPP. The main function of the RNS-HX is to provide shutdown reactor cooling. These equipment's are safety-related. So the seismic analysis was done using the methodology for Seismic Category I (SCI) structures. The most important topic is that the RNS-HX shall withstand the effects of the Safe Shutdown Earthquake (SSE) and maintain the specified design functions. for the analysis, two finite element models (FEM) were built in order to investigate the structural response of the couple system of building and equipment. The response spectra method was used. The floor response spectra (FRS) at the slab-wall connection were used as input Lateral seismic restrain was necessary to added in order to achieve the natural frequency of 33 Hz. The global structural response was obtained by means of the modal combination method indicated in the Regulatory Guide 1.92.

  3. Dynamic Na+-H+ Exchanger Regulatory Factor-1 Association and Dissociation Regulate Parathyroid Hormone Receptor Trafficking at Membrane Microdomains*

    Science.gov (United States)

    Ardura, Juan A.; Wang, Bin; Watkins, Simon C.; Vilardaga, Jean-Pierre; Friedman, Peter A.

    2011-01-01

    Na/H exchanger regulatory factor-1 (NHERF1) is a cytoplasmic PDZ (postsynaptic density 95/disc large/zona occludens) protein that assembles macromolecular complexes and determines the localization, trafficking, and signaling of select G protein-coupled receptors and other membrane-delimited proteins. The parathyroid hormone receptor (PTHR), which regulates mineral ion homeostasis and bone turnover, is a G protein-coupled receptor harboring a PDZ-binding motif that enables association with NHERF1 and tethering to the actin cytoskeleton. NHERF1 interactions with the PTHR modify its trafficking and signaling. Here, we characterized by live cell imaging the mechanism whereby NHERF1 coordinates the interactions of multiple proteins, as well as the fate of NHERF1 itself upon receptor activation. Upon PTHR stimulation, NHERF1 rapidly dissociates from the receptor and induces receptor aggregation in long lasting clusters that are enriched with the actin-binding protein ezrin and with clathrin. After NHERF1 dissociates from the PTHR, ezrin then directly interacts with the PTHR to stabilize the PTHR at the cell membrane. Recruitment of β-arrestins to the PTHR is delayed until NHERF1 dissociates from the receptor, which is then trafficked to clathrin for internalization. The ability of NHERF to interact dynamically with the PTHR and cognate adapter proteins regulates receptor trafficking and signaling in a spatially and temporally coordinated manner. PMID:21832055

  4. Dynamic Na+-H+ exchanger regulatory factor-1 association and dissociation regulate parathyroid hormone receptor trafficking at membrane microdomains.

    Science.gov (United States)

    Ardura, Juan A; Wang, Bin; Watkins, Simon C; Vilardaga, Jean-Pierre; Friedman, Peter A

    2011-10-07

    Na/H exchanger regulatory factor-1 (NHERF1) is a cytoplasmic PDZ (postsynaptic density 95/disc large/zona occludens) protein that assembles macromolecular complexes and determines the localization, trafficking, and signaling of select G protein-coupled receptors and other membrane-delimited proteins. The parathyroid hormone receptor (PTHR), which regulates mineral ion homeostasis and bone turnover, is a G protein-coupled receptor harboring a PDZ-binding motif that enables association with NHERF1 and tethering to the actin cytoskeleton. NHERF1 interactions with the PTHR modify its trafficking and signaling. Here, we characterized by live cell imaging the mechanism whereby NHERF1 coordinates the interactions of multiple proteins, as well as the fate of NHERF1 itself upon receptor activation. Upon PTHR stimulation, NHERF1 rapidly dissociates from the receptor and induces receptor aggregation in long lasting clusters that are enriched with the actin-binding protein ezrin and with clathrin. After NHERF1 dissociates from the PTHR, ezrin then directly interacts with the PTHR to stabilize the PTHR at the cell membrane. Recruitment of β-arrestins to the PTHR is delayed until NHERF1 dissociates from the receptor, which is then trafficked to clathrin for internalization. The ability of NHERF to interact dynamically with the PTHR and cognate adapter proteins regulates receptor trafficking and signaling in a spatially and temporally coordinated manner.

  5. Membrane insertion of fusion peptides from Ebola and Marburg viruses studied by replica-exchange molecular dynamics simulations.

    Science.gov (United States)

    Olson, Mark A; Lee, Michael S; Yeh, In-Chul

    2017-01-28

    This work presents replica-exchange molecular dynamics simulations of inserting a 16-residue Ebola virus fusion peptide into a membrane bilayer. A computational approach is applied for modeling the peptide at the explicit all-atom level and the membrane-aqueous bilayer by a generalized Born continuum model with a smoothed switching function (GBSW). We provide an assessment of the model calculations in terms of three metrics: (1) the ability to reproduce the NMR structure of the peptide determined in the presence of SDS micelles and comparable structural data on other fusion peptides; (2) determination of the effects of the mutation Trp-8 to Ala and sequence discrimination of the homologous Marburg virus; and (3) calculation of potentials of mean force for estimating the partitioning free energy and their comparison to predictions from the Wimley-White interfacial hydrophobicity scale. We found the GBSW implicit membrane model to produce results of limited accuracy in conformational properties of the peptide when compared to the NMR structure, yet the model resolution is sufficient to determine the effect of sequence differentiation on peptide-membrane integration. © 2016 Wiley Periodicals, Inc.

  6. Similarity measure and topology evolution of foreign exchange markets using dynamic time warping method: Evidence from minimal spanning tree

    Science.gov (United States)

    Wang, Gang-Jin; Xie, Chi; Han, Feng; Sun, Bo

    2012-08-01

    In this study, we employ a dynamic time warping method to study the topology of similarity networks among 35 major currencies in international foreign exchange (FX) markets, measured by the minimal spanning tree (MST) approach, which is expected to overcome the synchronous restriction of the Pearson correlation coefficient. In the empirical process, firstly, we subdivide the analysis period from June 2005 to May 2011 into three sub-periods: before, during, and after the US sub-prime crisis. Secondly, we choose NZD (New Zealand dollar) as the numeraire and then, analyze the topology evolution of FX markets in terms of the structure changes of MSTs during the above periods. We also present the hierarchical tree associated with the MST to study the currency clusters in each sub-period. Our results confirm that USD and EUR are the predominant world currencies. But USD gradually loses the most central position while EUR acts as a stable center in the MST passing through the crisis. Furthermore, an interesting finding is that, after the crisis, SGD (Singapore dollar) becomes a new center currency for the network.

  7. Quantifying humpback whale song sequences to understand the dynamics of song exchange at the ocean basin scale.

    Science.gov (United States)

    Garland, Ellen C; Noad, Michael J; Goldizen, Anne W; Lilley, Matthew S; Rekdahl, Melinda L; Garrigue, Claire; Constantine, Rochelle; Daeschler Hauser, Nan; Poole, M Michael; Robbins, Jooke

    2013-01-01

    Humpback whales have a continually evolving vocal sexual display, or "song," that appears to undergo both evolutionary and "revolutionary" change. All males within a population adhere to the current content and arrangement of the song. Populations within an ocean basin share similarities in their songs; this sharing is complex as multiple variations of the song (song types) may be present within a region at any one time. To quantitatively investigate the similarity of song types, songs were compared at both the individual singer and population level using the Levenshtein distance technique and cluster analysis. The highly stereotyped sequences of themes from the songs of 211 individuals from populations within the western and central South Pacific region from 1998 through 2008 were grouped together based on the percentage of song similarity, and compared to qualitatively assigned song types. The analysis produced clusters of highly similar songs that agreed with previous qualitative assignments. Each cluster contained songs from multiple populations and years, confirming the eastward spread of song types and their progressive evolution through the study region. Quantifying song similarity and exchange will assist in understanding broader song dynamics and contribute to the use of vocal displays as population identifiers.

  8. Macroevolutionary dynamics and historical biogeography of primate diversification inferred from a species supermatrix.

    Directory of Open Access Journals (Sweden)

    Mark S Springer

    Full Text Available Phylogenetic relationships, divergence times, and patterns of biogeographic descent among primate species are both complex and contentious. Here, we generate a robust molecular phylogeny for 70 primate genera and 367 primate species based on a concatenation of 69 nuclear gene segments and ten mitochondrial gene sequences, most of which were extracted from GenBank. Relaxed clock analyses of divergence times with 14 fossil-calibrated nodes suggest that living Primates last shared a common ancestor 71-63 Ma, and that divergences within both Strepsirrhini and Haplorhini are entirely post-Cretaceous. These results are consistent with the hypothesis that the Cretaceous-Paleogene mass extinction of non-avian dinosaurs played an important role in the diversification of placental mammals. Previous queries into primate historical biogeography have suggested Africa, Asia, Europe, or North America as the ancestral area of crown primates, but were based on methods that were coopted from phylogeny reconstruction. By contrast, we analyzed our molecular phylogeny with two methods that were developed explicitly for ancestral area reconstruction, and find support for the hypothesis that the most recent common ancestor of living Primates resided in Asia. Analyses of primate macroevolutionary dynamics provide support for a diversification rate increase in the late Miocene, possibly in response to elevated global mean temperatures, and are consistent with the fossil record. By contrast, diversification analyses failed to detect evidence for rate-shift changes near the Eocene-Oligocene boundary even though the fossil record provides clear evidence for a major turnover event ("Grande Coupure" at this time. Our results highlight the power and limitations of inferring diversification dynamics from molecular phylogenies, as well as the sensitivity of diversification analyses to different species concepts.

  9. Dynamics of novel forests of Castilla elastica in Puerto Rico: from species to ecosystems.

    Science.gov (United States)

    Fonseca da Silva, Jéssica

    2015-08-01

    Novel forests (NFs)-forests that contain a combination of introduced and native species-are a consequence of intense anthropogenic disturbances and the natural resilience of disturbed ecosystems. The extent to which NFs have similar forest function as comparable native secondary forests is a matter of debate in the scientific community. Little is known about the performance of individual species in those forests. This study focuses on the functional attributes of Castilla elastica NFs in Puerto Rico and on the differences between introduced and native species growing side by side in these forests. Rates of processes measured here were later compared with data from literature about NSFs. I hypothesize that juvenile plants of C. elastica in NFs have higher survival rate than those of native species and that C. elastica trees have faster biomass fluxes than native trees. To test the hypotheses, I measured survival rates of juvenile plants and tree growth and characterized the aboveground litter fluxes and storage. Although juvenile plants of native species displayed higher survival rates than those of C. elastica (53% vs. 28%), the latter was dominant in the understory (96%). Stand biomass growth rate was 2.0 ± 0.4 (average ± one standard deviation) Mg·ha(-1)·year(-1) for the whole forest, and Guarea guidonia, a native species, exhibited the highest tree growth. Total litter fall was 9.6 ± 0.5 Mg·ha(-1)·year(-1), and mean litter standing stock was 4.4 ± 0.1 Mg·ha(-1). Castilla elastica litter fall decomposed twice as fast as that of native species (5.8 ± 1.1 vs. 3.03 ± 1 k·year(-1)). Literature comparisons show that the present NFs differ in some rates of processes from NSFs. This study brings unique and detailed supporting data about the ecological dynamics under mature novel forest stands. Further comprehensive studies about NFs are important to strengthen the body of knowledge about the wide range of variation of emerging tropical ecosystems. Due to the

  10. Population dynamics of two diplectanid species (Monogenea) parasitising sparid hosts (Sparidae).

    Science.gov (United States)

    Emre, Yilmaz; Emre, Nesrin; Aydogdu, Ali; Bušelić, Ivana; Smales, Lesley R; Mladineo, Ivona

    2015-03-01

    Economically important sparid fish species, gilthead (Sparus aurata) and white seabream (Diplodus sargus) (Sparidae) are frequently parasitised by diplectanid monogeneans, known to induce severe losses in farming conditions. We have analysed population dynamic of two diplectanid species, Lamellodiscus echeneis and Lamellodiscus ignoratus (Monogenea: Diplectanidae) collected from two bream species in the Beymelek Lagoon (southwest coast of Turkey), comparing it between different host variables (fish size, age and sex) in order to have insight in parasites' ecology, important for managing parasitosis in the intensive aquaculture system. In seabream (N = 127), L. echeneis prevalence was 46.5 % (exact 95 % confidence limits 38.90-54.14), mean abundance 5.64 (bootstrap 95 % confidence limits 4.20-7.65) and mean intensity 12.14 (bootstrap 95 % confidence limits 9.49-15.59). In white seabream (N = 102), L. ignoratus prevalence was 24.5 % (exact 95 % confidence limits 16.53-34.03), mean abundance 1.73 (bootstrap 95 % confidence limits 0.98-3.21) and mean intensity 7.04 (bootstrap 95 % confidence limits 4.60-11.40). Parasites' parameters differed only between seasons in both hosts and between age categories in gilthead, but not in white seabream.

  11. Flight dynamics of some Lepidoptera species of sugar beet and possibilities their control (Transylvania-Romania

    Directory of Open Access Journals (Sweden)

    Muresanu Felicia

    2006-01-01

    Full Text Available In this paper, the authors present the obtained results regarding the flight dynamics of some Lepidoptera species in sugar beet crops in Transylvania (the central part of Romania. In order to limit the appearance of mentioned pests to the economic threshold, Trichogramma spp. were obtained in laboratory conditions at ARDS Turda and SBRDS Brasov. The experiments were conducted in production areas on 0,5 ha minimum for each variant. The variants included four Trichogramma species: T. dendrolimi, T. evanescens, T. maidis, T. buesi that were manually released three times: the first release, 10.000 individuals/ha, the second, 120.000 individuals/ha and the third, 150.000 individuals/ha. The first release was performed at the beginning of the Lepidoptera flight, the second at the maximum flight and the third 5 days after the second. The efficiency of T. maidis was between 75-90%, of T. evanescens, it was between 73-88%, of T. dendrolimi, it was between 85-92% and of T. buesi 79-82%. Among the Trichogramma species utilized, T. dendrolimi and T. evanescens were very efficient in the reduction of mentioned pests. Root production was significantly higher compared to the untreated variant, 4,0-4,7 t/ha more were recorded after the application of biological treatments with T. evanescens and T. dendrolimi.

  12. A Bayesian integrated population dynamics model to analyze data for protected species

    Directory of Open Access Journals (Sweden)

    Hoyle, S. D.

    2004-06-01

    Full Text Available Managing wildlife-human interactions demands reliable information about the likely consequences of management actions. This requirement is a general one, whatever the taxonomic group. We describe a method for estimating population dynamics and decision analysis that is generally applicable, extremely flexible, uses data efficiently, and gives answers in a useful format. Our case study involves bycatch of a protected species, the Northeastern Offshore Spotted Dolphin (Stenella attenuata, in the tuna fishery of the eastern Pacific Ocean. Informed decision-making requires quantitative analyses taking all relevant information into account, assessing how bycatch affects these species and how regulations affect the fisheries, and describing the uncertainty in analyses. Bayesian analysis is an ideal framework for delivering information on uncertainty to the decision-making process. It also allows information from other populations or species or expert judgment to be included in the analysis, if appropriate. Integrated analysis attempts to include all relevant data for a population into one analysis by combining analyses, sharing parameters, and simultaneously estimating all parameters, using a combined objective function. It ensures that model assumptions and parameter estimates are consistent throughout the analysis, that uncertainty is propagated through the analysis, and that the correlations among parameters are preserved. Perhaps the most important aspect of integrated analysis is the way it both enables and forces consideration of the system as a whole, so that inconsistencies can be observed and resolved.

  13. Microbial species diversity, community dynamics, and metabolite kinetics of water kefir fermentation.

    Science.gov (United States)

    Laureys, David; De Vuyst, Luc

    2014-04-01

    Water kefir is a sour, alcoholic, and fruity fermented beverage of which the fermentation is started with water kefir grains. These water kefir grains consist of polysaccharide and contain the microorganisms responsible for the water kefir fermentation. In this work, a water kefir fermentation process was followed as a function of time during 192 h to unravel the community dynamics, the species diversity, and the kinetics of substrate consumption and metabolite production. The majority of the water kefir ecosystem was found to be present on the water kefir grains. The most important microbial species present were Lactobacillus casei/paracasei, Lactobacillus harbinensis, Lactobacillus hilgardii, Bifidobacterium psychraerophilum/crudilactis, Saccharomyces cerevisiae, and Dekkera bruxellensis. The microbial species diversities in the water kefir liquor and on the water kefir grains were similar and remained stable during the whole fermentation process. The major substrate, sucrose, was completely converted after 24 h of fermentation, which coincided with the production of the major part of the water kefir grain polysaccharide. The main metabolites of the fermentation were ethanol and lactic acid. Glycerol, acetic acid, and mannitol were produced in low concentrations. The major part of these metabolites was produced during the first 72 h of fermentation, during which the pH decreased from 4.26 to 3.45. The most prevalent volatile aroma compounds were ethyl acetate, isoamyl acetate, ethyl hexanoate, ethyl octanoate, and ethyl decanoate, which might be of significance with respect to the aroma of the end product.

  14. Microbial Species Diversity, Community Dynamics, and Metabolite Kinetics of Water Kefir Fermentation

    Science.gov (United States)

    Laureys, David

    2014-01-01

    Water kefir is a sour, alcoholic, and fruity fermented beverage of which the fermentation is started with water kefir grains. These water kefir grains consist of polysaccharide and contain the microorganisms responsible for the water kefir fermentation. In this work, a water kefir fermentation process was followed as a function of time during 192 h to unravel the community dynamics, the species diversity, and the kinetics of substrate consumption and metabolite production. The majority of the water kefir ecosystem was found to be present on the water kefir grains. The most important microbial species present were Lactobacillus casei/paracasei, Lactobacillus harbinensis, Lactobacillus hilgardii, Bifidobacterium psychraerophilum/crudilactis, Saccharomyces cerevisiae, and Dekkera bruxellensis. The microbial species diversities in the water kefir liquor and on the water kefir grains were similar and remained stable during the whole fermentation process. The major substrate, sucrose, was completely converted after 24 h of fermentation, which coincided with the production of the major part of the water kefir grain polysaccharide. The main metabolites of the fermentation were ethanol and lactic acid. Glycerol, acetic acid, and mannitol were produced in low concentrations. The major part of these metabolites was produced during the first 72 h of fermentation, during which the pH decreased from 4.26 to 3.45. The most prevalent volatile aroma compounds were ethyl acetate, isoamyl acetate, ethyl hexanoate, ethyl octanoate, and ethyl decanoate, which might be of significance with respect to the aroma of the end product. PMID:24532061

  15. T dependence of vibrational dynamics of water in ion-exchanged zeolites A: a detailed Fourier transform infrared attenuated total reflection study.

    Science.gov (United States)

    Crupi, Vincenza; Longo, Francesca; Majolino, Domenico; Venuti, Valentina

    2005-10-15

    In order to explore the influence of cation substitution on the vibrational dynamics of water molecules in zeolites, the evolution of structural properties of the O-H stretching band of water in fully hydrated Na-A and Mg-exchanged A zeolites has been studied, for different percentages of induced ion exchange, by Fourier transform infrared attenuated total reflection spectroscopy as a function of temperature. The differences revealed in the O-H stretching band shapes have been accounted by fitting the spectra as a sum of four components, corresponding to water molecules exhibiting different types of hydrogen bonding. The dependencies of the relative intensities, peak wave numbers, and bandwidths of the resolved components on temperature and Mg2+ content have been discussed. Evidence of the "structure-maker" role played by a zeolitic surface on physisorbed water, systematically enhanced by increasing the percentage of induced ion exchange, is given in the whole explored temperature range.

  16. Dynamics of CO2-exchange and C-budgets due to soil erosion: Insights from a 4 years observation period

    Science.gov (United States)

    Hoffmann, Mathias; Albiac Borraz, Elisa; Garcia Alba, Juana; Augustin, Jürgen; Sommer, Michael

    2015-04-01

    Agriculture in the hummocky ground moraine landscape of NE-Germany is characterized by an increase in energy crop cultivation, like maize or sorghum. Both enhance lateral C fluxes by erosion and induce feedbacks on C dynamics of agroecosystems as a result of reduced wintertime plant cover and vigorous crop growth during summer. However, the actual impact of these phenomena on the CO2-sink/-source function of agricultural landscapes, is still not clear. Therefore, the interdisciplinary project "CarboZALF" was established in Dedelow/Prenzlau (NE-Germany) in 2009. Within the field experiment CarboZALF-D, CO2 fluxes for the soil-plant systems were monitored, covering typical landscape relevant soil states in respect to erosion and deposition, like Calcic Cutanic Luvisol and Endogleyic Colluvic Regosol. Automated chamber systems, each consisting of four transparent chambers (2.5 m height, basal area 2.25 m2), were placed along gradients at both measurement sites. Monitored CO2 fluxes were gap-filled on a high-temporal resolution by modelling ecosystem respiration (Reco), gross primary productivity (GPP) and net ecosystem exchange (NEE) based on parallel and continuous measurements of the CO2 exchange, soil and air temperatures as well as photosynthetic active radiation (PAR). Gap-filling was e.g. needed in case of chamber malfunctions and abrupt disturbances by farming practice. The monitored crop rotation was corn-winter wheat (2 a), sorghum-winter triticale and alfalfa (1.5 a). In our presentation we would like to show insights from a 4 years observation period, with prounounced differences between the eroded and the colluvial soil: The Endogleyic Colluvic Regosol showed higher flux rates for Reco, GPP and NEE compared to the Calcic Cutanic Luvisol. Site-specific NEE and C-balances were positively related to soil C-stocks as well as biomass production, and generated a minor C-sink in case of the Calcic Cutanic Luvisol and a highly variable C-source in case of the

  17. Electrical resistivity dynamics beneath a fractured sedimentary bedrock riverbed in response to temperature and groundwater–surface water exchange

    Directory of Open Access Journals (Sweden)

    C. M. Steelman

    2017-06-01

    Full Text Available Bedrock rivers occur where surface water flows along an exposed rock surface. Fractured sedimentary bedrock can exhibit variable groundwater residence times, anisotropic flow paths, and heterogeneity, along with diffusive exchange between fractures and rock matrix. These properties of the rock will affect thermal transients in the riverbed and groundwater–surface water exchange. In this study, surface electrical methods were used as a non-invasive technique to assess the scale and temporal variability of riverbed temperature and groundwater–surface water interaction beneath a sedimentary bedrock riverbed. Conditions were monitored at a semi-daily to semi-weekly interval over a full annual period that included a seasonal freeze–thaw cycle. Surface electromagnetic induction (EMI and electrical resistivity tomography (ERT methods captured conditions beneath the riverbed along a pool–riffle sequence of the Eramosa River in Canada. Geophysical datasets were accompanied by continuous measurements of aqueous specific conductance, temperature, and river stage. Time-lapse vertical temperature trolling within a lined borehole adjacent to the river revealed active groundwater flow zones along fracture networks within the upper 10 m of rock. EMI measurements collected during cooler high-flow and warmer low-flow periods identified a spatiotemporal riverbed response that was largely dependent upon riverbed morphology and seasonal groundwater temperature. Time-lapse ERT profiles across the pool and riffle sequence identified seasonal transients within the upper 2 and 3 m of rock, respectively, with spatial variations controlled by riverbed morphology (pool versus riffle and dominant surficial rock properties (competent versus weathered rock rubble surface. While the pool and riffle both exhibited a dynamic resistivity through seasonal cooling and warming cycles, conditions beneath the pool were more variable, largely due to the formation of river

  18. Dynamics of leaf gas exchange, xylem and phloem transport, water potential and carbohydrate concentration in a realistic 3-D model tree crown.

    Science.gov (United States)

    Nikinmaa, Eero; Sievänen, Risto; Hölttä, Teemu

    2014-09-01

    Tree models simulate productivity using general gas exchange responses and structural relationships, but they rarely check whether leaf gas exchange and resulting water and assimilate transport and driving pressure gradients remain within acceptable physical boundaries. This study presents an implementation of the cohesion-tension theory of xylem transport and the Münch hypothesis of phloem transport in a realistic 3-D tree structure and assesses the gas exchange and transport dynamics. A mechanistic model of xylem and phloem transport was used, together with a tested leaf assimilation and transpiration model in a realistic tree architecture to simulate leaf gas exchange and water and carbohydrate transport within an 8-year-old Scots pine tree. The model solved the dynamics of the amounts of water and sucrose solute in the xylem, cambium and phloem using a fine-grained mesh with a system of coupled ordinary differential equations. The simulations predicted the observed patterns of pressure gradients and sugar concentration. Diurnal variation of environmental conditions influenced tree-level gradients in turgor pressure and sugar concentration, which are important drivers of carbon allocation. The results and between-shoot variation were sensitive to structural and functional parameters such as tree-level scaling of conduit size and phloem unloading. Linking whole-tree-level water and assimilate transport, gas exchange and sink activity opens a new avenue for plant studies, as features that are difficult to measure can be studied dynamically with the model. Tree-level responses to local and external conditions can be tested, thus making the approach described here a good test-bench for studies of whole-tree physiology.

  19. The Role of Explicitly Modeling Bryophytes in Simulating Carbon Exchange and Permafrost Dynamics of an Arctic Coastal Tundra at Barrow, Alaska

    Science.gov (United States)

    Yuan, F.; Thornton, P. E.; McGuire, A. D.; Oechel, W. C.; Yang, B.; Tweedie, C. E.; Rogers, A.; Norby, R. J.

    2013-12-01

    Bryophyte cover is greater than 50% in many Arctic tundra ecosystems. In regions of the Arctic where shrubs are expanding it is expected that bryophyte cover will be substantially reduced. Such a loss in cover could influence the hydrological, biogeochemical, and permafrost dynamics of Arctic tundra ecosystems. The explicit representation of bryophyte physiological and biophysical processes in large-scale ecological and land surface models is rare, and we hypothesize that the representation of bryophytes has consequences for estimates of the exchange of water, energy, and carbon by these models. This study explicitly represents the effects of bryophyte function and structure on the exchange of carbon (e.g., summer photosynthesis effects) and energy (e.g., summer insulation effects) with the atmosphere in the Community Land Model (CLM-CN). The modified model was evaluated for its ability to simulate C exchange, soil temperature, and soil moisture since the 1970s at Barrow, Alaska through comparison with data from AmeriFlux sites, USDA Soil Climate Networks observation sites at Barrow, and other sources. We also compare the outputs of the CLM-CN simulations with those of the recently developed Dynamical Organic Soil coupled Terrestrial Ecosystem Model (DOS-TEM). Overall, our evaluation indicates that bryophytes are important contributors to land-atmospheric C exchanges in Arctic tundra and that they play an important role to permafrost thermal and hydrological processes which are critical to permafrost stability. Our next step in this study is to examine the climate system effects of explicitly representing bryophyte dynamics in the land surface model. Key Words: Bryophytes, Arctic coastal tundra, Vegetation composition, Net Ecosystem Exchange, Permafrost, Land Surface Model, Terrestrial Ecosystem Model

  20. Dynamic Circulation and Genetic Exchange of a Shrew-borne Hantavirus, Imjin virus, in the Republic of Korea

    Science.gov (United States)

    Lee, Seung-Ho; Kim, Won-Keun; No, Jin Sun; Kim, Jeong-Ah; Kim, Jin Il; Gu, Se Hun; Kim, Heung-Chul; Klein, Terry A.; Park, Man-Seong; Song, Jin-Won

    2017-01-01

    Hantaviruses (family Bunyaviridae) are enveloped negative-sense tripartite RNA viruses. The natural hosts of hantaviruses include rodents, shrews, moles, and bats. Imjin virus (MJNV) is a shrew-borne hantavirus identified from the Ussuri white-toothed shrews (Crocidura lasiura) in the Republic of Korea (ROK) and China. We have isolated MJNV and determined its prevalence and molecular diversity in Gyeonggi province, ROK. However, the distribution and phylogeography of MJNV in other regions of ROK remain unknown. A total of 96 C. lasiura were captured from Gangwon and Gyeonggi provinces, ROK, during 2011–2014. Among them, four (4.2%) shrews were positive for anti-MJNV IgG and MJNV RNA was detected from nine (9.4%), respectively. Based on the prevalence of MJNV RNA, the preponderance of infected shrews was male and adult, consistent with the gender- and weight-specific prevalence of hantaviruses in other species. We monitored the viral load of MJNV RNA in various tissues of shrews, which would reflect the dynamic infectious status and circulation of MJNV in nature. Our phylogeographic and genomic characterization of MJNV suggested natural occurrences of recombination and reassortment in the virus population. Thus, these findings provide significant insights into the epidemiology, phylogeographic diversity, and dynamic circulation and evolution of shrew-borne hantaviruses. PMID:28295052

  1. Flow-Induced New Channels of Energy Exchange in Multi-Scale Plasma Dynamics – Revisiting Perturbative Hybrid Kinetic-MHD Theory

    Science.gov (United States)

    Shiraishi, Junya; Miyato, Naoaki; Matsunaga, Go

    2016-01-01

    It is found that new channels of energy exchange between macro- and microscopic dynamics exist in plasmas. They are induced by macroscopic plasma flow. This finding is based on the kinetic-magnetohydrodynamic (MHD) theory, which analyses interaction between macroscopic (MHD-scale) motion and microscopic (particle-scale) dynamics. The kinetic-MHD theory is extended to include effects of macroscopic plasma flow self-consistently. The extension is realised by generalising an energy exchange term due to wave-particle resonance, denoted by δ WK. The first extension is generalisation of the particle’s Lagrangian, and the second one stems from modification to the particle distribution function due to flow. These extensions lead to a generalised expression of δ WK, which affects the MHD stability of plasmas. PMID:27160346

  2. Temperature dynamic models of heat exchanger for photosensitive material coating and drying processes; Kanko zairyo tofu kanso process ni okeru kucho system no ondo doteki model

    Energy Technology Data Exchange (ETDEWEB)

    Kido, K.; Sato, N.; Shimoji, M. [Konica Co. Ltd., Tokyo (Japan); Nakanishi, E. [Kobe University, Kobe (Japan). Faculty of Engineering

    1996-01-20

    Nonlinear and linear temperature dynamic models of a heat exchanger were investigated for air conditioning control of coating and drying processes for photosensitive materials. The nonlinear model was derived from heat balance based on the assumption of lumped parameter system that the heat exchanger is divided into small parts in the direction of flow (divided cell model). In each part, the temperature of the heating fluid, heated fluid and heat transfer tube with fin are assumed to be uniform. Parameters involved in this model were estimated from experimental data of the step response characteristics of temperature. The linear model is obtained by linearizing this nonlinear model. It was confirmed that the dynamic behavior of temperature can be successfully expressed by both nonlinear and linear models. Both models are considered to be utilizable for process analysis and control system design of the air conditioning system under consideration. 1 ref., 13 figs., 2 tabs.

  3. Tuning Exchange Anisotropy of Exchange-Biased System

    Institute of Scientific and Technical Information of China (English)

    XU Yan; HU Jing-Guo; R.L.Stamps

    2008-01-01

    Exchange anisotropy in FM/AFM bilayers has given a lot of static magnetization properties such as enhanced coercivity and magnetization loop shifts.These phenomena are primarily from the effective anisotropies intro-duced into a ferromagnet by exchange coupling with a strongly anisotropic antiferromagnet.These effective anisotropies can also be used to explain the dynamic consequences of exchange-biased bilayers.In this article,the dynamic con-sequences such as exchange-induced susceptibility,exchange-induced permeability,and the corresponding domain wall characteristics in the exchange-biased structures of ferromagnet/antiferromagnetl/antiferromagnet2 are studied.The results show that the second antiferromagnetic layer can largely affect the dynamic consequences of exchange-biased bilayers.Especially in the ease of critical temperature,the effects become more obvious.Practically,the exchange anisotropy of biased bilayer system can be tuned by exchange coupling with the second antiferromagnetic layer.

  4. Dynamic model of counter flow air to air heat exchanger for comfort ventilation with condensation and frost formation

    DEFF Research Database (Denmark)

    Nielsen, Toke Rammer; Rose, Jørgen; Kragh, Jesper

    2009-01-01

    In cold climates heat recovery in the ventilation system is essential to reduce heating energy demand. Condensation and freezing occur often in efficient heat exchangers used in cold climates. To develop efficient heat exchangers and defrosting strategies for cold climates, heat and mass transfer...

  5. Molecular dynamical studies of the dissociation of a diatomic molecular crystal. I. Energy exchange in rapid exothermic reactions

    Science.gov (United States)

    Tsai, D. H.; Trevino, S. F.

    1983-08-01

    We discuss the results of a study of the exothermic dissociation of a model diatomic molecular crystal. Our main purpose is to investigate the dynamics of energy transport and energy sharing in this system during the dissociation process. The crystal was prepared in a metastable molecular form, in thermal equilibrium at a low initial temperature and pressure. When we heated the system to a higher temperature, at constant volume, we observed thermally initiated dissociations which progressed rapidly to completion. During the dissociation process, we found that the sharing of the potential energy released by the metastable molecules with the rest of the system, and the sharing of the kinetic energy of the dissociated fragments with the kinetic energy of the molecules in the translational degrees of freedom, were rather efficient. But the intra- and intermolecular exchange of the kinetic energy among the various degrees of freedom, viz., translation-rotation, translation-vibration, and rotation-vibration was inefficient. Dissociation would occur in one of the regions of high local kinetic energy density, after a molecule in that region had acquired sufficient vibrational energy to break apart, and when the ``caging'' effect was favorable to allow the molecule to dissociate. From such a reaction site, and there may be others, the reaction would spread to a neighboring site, and continue this way until all the molecules became dissociated. The induction time showed an approximately logarithmic dependence on the inverse of the temperature of the system after heating. But during the process of rapid dissociation, both the potential energy and the kinetic energy of the system underwent rapid changes, and thermal equilibrium was not reached until the end of the process.

  6. Dynamics of domain walls with lines in rare-earth orthoferrites in magnetic and electric fields with exchange relaxation processes taken into account

    Science.gov (United States)

    Ekomasov, E. G.

    2003-08-01

    The influence of exchange relaxation on the dynamics of domain walls with a "fine structure" in rare-earth orthoferrites in the presence of external magnetic and electric fields is investigated. A system of differential equations is obtained which describe the dynamics of a domain wall with a solitary line. The dependence of the steady-state velocity of the domain wall and line on the values of the relaxation parameters and on the components of the magnetic and electric fields is found. The results are compared with the known experimental results.

  7. The dynamics of the plankton for the second summer of carp polyculture with phytoplankton consumer species

    Directory of Open Access Journals (Sweden)

    Corina GHEORGHE

    2010-08-01

    Full Text Available The biologic processes in water are strictly dependent on physical-chemical factors. By maintaining the balances of the environmental factors, it can ensures the micro and macro fauna development with direct implication on breeding and developing the fishy material.The aim of this article was to monitor and register the plankton dynamics in six rearing ponds for the polyculture of carp (Cyprinus carpio with Asian complex species: silver carp (H. molitrix, grass carp (Ct. idella and bighead carp (A. nobilis. The experiment took place in six ponds of C.C.D.P. Nucet, during a period of 120 days.At the end of the experiment one determined that the evolution of both phytoplankton and zooplankton was in a close correlation with both the variation of physical-chemical factors as well as with thetechnology of the fishy material in these ponds.

  8. Studies of ground-state dynamics in isolated species by ionization-detected stimulated Raman techniques

    Energy Technology Data Exchange (ETDEWEB)

    Felker, P.M. [Univ. of California, Los Angeles (United States)

    1993-12-01

    First, the author aims to develop methods of nonlinear Raman spectroscopy for application in studies of sparse samples. Second, the author wishes to apply such methods to structural and dynamical studies of species (molecules, complexes, and clusters) in supersonic molecular beams. In the past year, the author has made progress in several areas. The first pertains to the application of mass-selective ionization-detected stimulated Raman spectroscopies (IDSRS) to the size-specific vibrational spectroscopy of solute-solvent{sub n} clusters. The second involves the application of IDSRS methods to studies of jet-cooled benzene clusters. The third pertains to the use of IDSRS methods in the study of intermolecular vibrational transitions in van der Waals complexes.

  9. Fluid-dynamical scheme for equilibrium properties of two trapped fermion species with pairing interactions

    Science.gov (United States)

    Capuzzi, P.; Hernández, E. S.; Szybisz, L.

    2008-10-01

    We present a generalization of the fluid-dynamical scheme developed for nuclear physics to the case of two trapped fermion species with pairing interactions. To establish a macroscopic description of the mass and momentum conservation laws, we adopt a generalization of the usual Thomas-Fermi approach that includes the pairing energy. We analyze the equilibrium density and gap profiles for an equal population mixture of harmonically trapped Li6 atoms for different choices of the local equation of state. We examine slight departures from equilibrium within our formulation, finding that density oscillations can propagate as first sound coupled to pairing vibrations, that in a homogeneous fermion system exhibit a Bogoliubov-like quasiparticle spectrum. In this case, the dispersion relation for the coupled modes displays a rich scenario of stable, unstable, and damped regimes.

  10. Dynamics of ammonia exchange with cut grassland: synthesis of results and conclusions of the GRAMINAE Integrated Experiment

    Directory of Open Access Journals (Sweden)

    M. A. Sutton

    2009-01-01

    Full Text Available Improved data on biosphere-atmosphere exchange are fundamental to understanding the production and fate of ammonia (NH3 in the atmosphere. The GRAMINAE Integrated Experiment combined novel measurement and modelling approaches to provide the most comprehensive analysis of the interactions to date. Major inter-comparisons of micrometeorological parameters and NH3 flux measurements using the aerodynamic gradient method and relaxed eddy accumulation (REA were conducted. These showed close agreement, though the REA systems proved insufficiently precise to investigate vertical flux divergence. Grassland management had a large effect on fluxes: Emissions increased after grass cutting (−50 to 700 ng m−2 s−1 NH3 and after N-fertilization (0 to 3800 ng m−2 s compared with before the cut (−60 to 40 ng m−2 s.

    Effects of advection and air chemistry were investigated using horizontal NH3 profiles, acid gas and particle flux measurements. Inverse modelling of NH3 emission from an experimental farm agreed closely with inventory estimates, while advection errors were used to correct measured grassland fluxes. Advection effects were caused both by the farm and by emissions from the field, with an inverse dispersion-deposition model providing a reliable new approach to estimate net NH3 fluxes. Effects of aerosol chemistry on net NH3 fluxes were small, while the measurements allowed NH3-induced particle growth rates to be calculated and aerosol fluxes to be corrected.

    Bioassays estimated the emission potential Γ=[NH4+]/[H+] for different plant pools, with the apoplast having the smallest values (30–1000. The main sources of NH3 emission appeared to be leaf litter and the soil surface, with Γ up to 3 million and 300 000

  11. Structure and Dynamics of NBD1 from CFTR Characterized Using Crystallography and Hydrogen/Deuterium Exchange Mass Spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, H.A.; Wang, C.; Zhao, X.; Hamuro, Y.; Conners, K.; Kearins, M.C.; Lu, F.; Sauder, J.M.; Molnar, K.S.; Coales, S.J.; Maloney, P.C.; Guggino, W.B.; Wetmore, D.R.; Weber, P.C.; Hunt, J.F. (SGX); (ExSAR); (Cystic); (JHU-MED); (Columbia)

    2012-04-30

    The {Delta}F508 mutation in nucleotide-binding domain 1 (NBD1) of the cystic fibrosis transmembrane conductance regulator (CFTR) is the predominant cause of cystic fibrosis. Previous biophysical studies on human F508 and {Delta}F508 domains showed only local structural changes restricted to residues 509-511 and only minor differences in folding rate and stability. These results were remarkable because {Delta}F508 was widely assumed to perturb domain folding based on the fact that it prevents trafficking of CFTR out of the endoplasmic reticulum. However, the previously reported crystal structures did not come from matched F508 and {Delta}F508 constructs, and the {Delta}F508 structure contained additional mutations that were required to obtain sufficient protein solubility. In this article, we present additional biophysical studies of NBD1 designed to address these ambiguities. Mass spectral measurements of backbone amide {sup 1}H/{sup 2}H exchange rates in matched F508 and {Delta}F508 constructs reveal that {Delta}F508 increases backbone dynamics at residues 509-511 and the adjacent protein segments but not elsewhere in NBD1. These measurements also confirm a high level of flexibility in the protein segments exhibiting variable conformations in the crystal structures. We additionally present crystal structures of a broader set of human NBD1 constructs, including one harboring the native F508 residue and others harboring the {Delta}F508 mutation in the presence of fewer and different solubilizing mutations. The only consistent conformational difference is observed at residues 509-511. The side chain of residue V510 in this loop is mostly buried in all non-{Delta}F508 structures but completely solvent exposed in all {Delta}F508 structures. These results reinforce the importance of the perturbation {Delta}F508 causes in the surface topography of NBD1 in a region likely to mediate contact with the transmembrane domains of CFTR. However, they also suggest that increased

  12. Structure and dynamics of NBD1 from CFTR characterized using crystallography and hydrogen/deuterium exchange mass spectrometry.

    Science.gov (United States)

    Lewis, H A; Wang, C; Zhao, X; Hamuro, Y; Conners, K; Kearins, M C; Lu, F; Sauder, J M; Molnar, K S; Coales, S J; Maloney, P C; Guggino, W B; Wetmore, D R; Weber, P C; Hunt, J F

    2010-02-19

    The DeltaF508 mutation in nucleotide-binding domain 1 (NBD1) of the cystic fibrosis transmembrane conductance regulator (CFTR) is the predominant cause of cystic fibrosis. Previous biophysical studies on human F508 and DeltaF508 domains showed only local structural changes restricted to residues 509-511 and only minor differences in folding rate and stability. These results were remarkable because DeltaF508 was widely assumed to perturb domain folding based on the fact that it prevents trafficking of CFTR out of the endoplasmic reticulum. However, the previously reported crystal structures did not come from matched F508 and DeltaF508 constructs, and the DeltaF508 structure contained additional mutations that were required to obtain sufficient protein solubility. In this article, we present additional biophysical studies of NBD1 designed to address these ambiguities. Mass spectral measurements of backbone amide (1)H/(2)H exchange rates in matched F508 and DeltaF508 constructs reveal that DeltaF508 increases backbone dynamics at residues 509-511 and the adjacent protein segments but not elsewhere in NBD1. These measurements also confirm a high level of flexibility in the protein segments exhibiting variable conformations in the crystal structures. We additionally present crystal structures of a broader set of human NBD1 constructs, including one harboring the native F508 residue and others harboring the DeltaF508 mutation in the presence of fewer and different solubilizing mutations. The only consistent conformational difference is observed at residues 509-511. The side chain of residue V510 in this loop is mostly buried in all non-DeltaF508 structures but completely solvent exposed in all DeltaF508 structures. These results reinforce the importance of the perturbation DeltaF508 causes in the surface topography of NBD1 in a region likely to mediate contact with the transmembrane domains of CFTR. However, they also suggest that increased exposure of the 509-511 loop

  13. The effect of flooding on the exchange of the volatile C2-compounds ethanol, acetaldehyde and acetic acid between leaves of Amazonian floodplain tree species and the atmosphere

    Science.gov (United States)

    Rottenberger, S.; Kleiss, B.; Kuhn, U.; Wolf, A.; Piedade, M. T. F.; Junk, W.; Kesselmeier, J.

    2008-08-01

    The effect of root inundation on the leaf emissions of ethanol, acetaldehyde and acetic acid in relation to assimilation and transpiration was investigated with 2 3 years old tree seedlings of four Amazonian floodplain species by applying dynamic cuvette systems under greenhouse conditions. Emissions were monitored over a period of several days of inundation using a combination of Proton Transfer Reaction Mass Spectrometry (PTR-MS) and conventional techniques (HPLC, ion chromatography). Under non-flooded conditions, none of the species exhibited measurable emissions of any of the compounds, but rather low deposition of acetaldehyde and acetic acid was observed instead. Tree species specific variations in deposition velocities were largely due to variations in stomatal conductance. Flooding of the roots resulted in leaf emissions of ethanol and acetaldehyde by all species, while emissions of acetic acid were only observed from the species exhibiting the highest ethanol and acetaldehyde emission rates. All three compounds showed a similar diurnal emission profile, each displaying an emission burst in the morning, followed by a decline in the evening. This concurrent behavior supports the conclusion, that all three compounds emitted by the leaves are derived from ethanol produced in the roots by alcoholic fermentation, transported to the leaves with the transpiration stream and finally partly converted to acetaldehyde and acetic acid by enzymatic processes. Co-emissions and peaking in the early morning suggest that root ethanol, after transportation with the transpiration stream to the leaves and enzymatic oxidation to acetaldehyde and acetate, is the metabolic precursor for all compounds emitted, though we can not totally exclude other production pathways. Emission rates substantially varied among tree species, with maxima differing by up to two orders of magnitude (25 1700 nmol m-2 min-1 for ethanol and 5 500 nmol m-2 min-1 for acetaldehyde). Acetic acid emissions

  14. Dynamics of ammonia exchange with cut grassland: synthesis of results and conclusions of the GRAMINAE Integrated Experiment

    Directory of Open Access Journals (Sweden)

    M. A. Sutton

    2009-12-01

    Full Text Available Improved data on biosphere-atmosphere exchange are fundamental to understanding the production and fate of ammonia (NH3 in the atmosphere. The GRAMINAE Integrated Experiment combined novel measurement and modelling approaches to provide the most comprehensive analysis of the interactions to date. Major inter-comparisons of micrometeorological parameters and NH3 flux measurements using the aerodynamic gradient method and relaxed eddy accumulation (REA were conducted. These showed close agreement, though the REA systems proved insufficiently precise to investigate vertical flux divergence. Grassland management had a large effect on fluxes: emissions increased after grass cutting (−50 to 700 ng m−2 s−1 NH3 and after N-fertilization (0 to 3800 ng m−2 s−1 compared with before the cut (−60 to 40 ng m−2 s−1.

    Effects of advection and air chemistry were investigated using horizontal NH3 profiles, acid gas and particle flux measurements. Inverse modelling of NH3 emission from an experimental farm agreed closely with inventory estimates, while advection errors were used to correct measured grassland fluxes. Advection effects were caused both by the farm and by emissions from the field, with an inverse dispersion-deposition model providing a reliable new approach to estimate net NH3 fluxes. Effects of aerosol chemistry on net NH3 fluxes were small, while the measurements allowed NH3-induced particle growth rates to be calculated and aerosol fluxes to be corrected.

    Bioassays estimated the emission potential Γ = [NH4+]/[H+] for different plant pools, with the apoplast having the smallest values (30–1000. The main within-canopy sources of NH3 emission appeared to be leaf litter and the soil surface, with Γ up to 3 million and

  15. The Ecuadorian Artisanal Fishery for Large Pelagics: Species Composition and Spatio-Temporal Dynamics.

    Science.gov (United States)

    Martínez-Ortiz, Jimmy; Aires-da-Silva, Alexandre M; Lennert-Cody, Cleridy E; Maunder, Mark N

    2015-01-01

    The artisanal fisheries of Ecuador operate within one of the most dynamic and productive marine ecosystems of the world. This study investigates the catch composition of the Ecuadorian artisanal fishery for large pelagic fishes, including aspects of its spatio-temporal dynamics. The analyses of this study are based on the most extensive dataset available to date for this fishery: a total of 106,963 trip-landing inspection records collected at its five principal ports during 2008 ‒ 2012. Ecuadorian artisanal fisheries remove a substantial amount of biomass from the upper trophic-level predatory fish community of the eastern tropical Pacific Ocean. It is estimated that at least 135 thousand metric tons (mt) (about 15.5 million fish) were landed in the five principal ports during the study period. The great novelty of Ecuadorian artisanal fisheries is the "oceanic-artisanal" fleet component, which consists of mother-ship (nodriza) boats with their towed fiber-glass skiffs (fibras) operating with pelagic longlines. This fleet has fully expanded into oceanic waters as far offshore as 100°W, west of the Galapagos Archipelago. It is estimated that nodriza operations produce as much as 80% of the total catches of the artisanal fishery. The remainder is produced by independent fibras operating in inshore waters with pelagic longlines and/or surface gillnets. A multivariate regression tree analysis was used to investigate spatio-environmental effects on the nodriza fleet (n = 6,821 trips). The catch species composition of the nodriza fleet is strongly influenced by the northwesterly circulation of the Humboldt Current along the coast of Peru and its associated cold waters masses. The target species and longline gear-type used by nodrizas change seasonally with the incursion of cool waters (Coryphaena hippurus) dominates the catches. However, in warmer waters, the fishery changes to tuna-billfish-shark longline gear and the catch composition becomes much more diverse.

  16. Gas exchange, growth, and chemical parameters in a native Atlantic forest tree species in polluted areas of Cubatão, Brazil.

    Science.gov (United States)

    Moraes, R M; Delitti, W B C; Moraes, J A P V

    2003-03-01

    The Atlantic forest species near the industrial complex of Cubatão, Brazil have been subjected to heavy air pollution for decades. In this study, we used some physiological parameters (gas exchange, growth and chemical contents) to biomonitor the effects of air pollution on Tibouchina pulchra, one of the most common tree species in this forest. Under standardized conditions, saplings were exposed to the environment from April to July and from July to September of 1998, at three different sites in the vicinity of the industrial complex: the Valley of Pilões River (VP), the control area; the Valley of Mogi River (VM), near fertilizer, metallurgical, and cement industries sustaining high concentrations of fluorides, N and S oxides, and particulate materials; and Caminho do Mar (CM), near petrochemical industries under N and S oxides, photooxidants, and organic compounds. Plants exposed to CM and VM conditions presented visible injuries, reductions in net photosynthesis, growth parameters, and ascorbate concentrations, and increased F, N, and S foliar concentrations. These results indicate that the environmental conditions around these industries are still harmful to plants.

  17. Population dynamics, distribution, and species diversity of fruit flies on cucurbits in Kashmir Valley, India.

    Science.gov (United States)

    Ganie, S A; Khan, Z H; Ahangar, R A; Bhat, H A; Hussain, Barkat

    2013-01-01

    Given the economic importance of cucurbits and the losses incurred by fruit fly infestation, the population dynamics of fruit flies in cucurbit crops and the influence of abiotic parameters, such as temperature, relative humidity, rainfall, and total sunshine hours per day on the fruit fly population were studied. The study was carried out at six locations; in district Srinagar the locations were Batmaloo, Shalimar, and Dal, while in district Budgam the locations were Chadoora, Narkara, and Bugam (Jammu and Kashmir, India). Various cucurbit crops, such as cucumber, bottle gourd, ridge gourd and bitter gourd, were selected for the study. With regard to locations, mean fruit fly population was highest (6.09, 4.55, 3.87, and 3.60 flies/trap/week) at Batamaloo and Chadoora (4.73, 3.93, 2.73, and 2.73 flies/trap/week) on cucumber, bottle gourd, ridge gourd, and bitter gourd, respectively. The population of fruit flies was significantly correlated with the minimum and maximum temperature. The maximum species diversity of fruit flies was 0.511, recorded in Chadoora. Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae) was the most predominant species in both Srinagar and Budgam, followed by B. dorsalis (Hendel) and B. tau (Walker), while B. scutellaris (Bezzi) was found only in Chadoora. Results of the present investigation may be utilized in developing a sustainable pest management strategy in the agroecological system.

  18. Synthesis of Formamide and Related Organic Species in the Interstellar Medium via Chemical Dynamics Simulations

    Science.gov (United States)

    Spezia, Riccardo; Jeanvoine, Yannick; Hase, William L.; Song, Kihyung; Largo, Antonio

    2016-08-01

    We show, by means of direct dynamics simulations, how it is possible to define possible reactants and mechanisms leading to the formation of formamide in the interstellar medium. In particular, different ion-molecule reactions in the gas phase were considered: NH3OH+, NH2OH{}2+, H2COH+, and NH4 + for the ions and NH2OH, H2CO, and NH3 for the partner neutrals. These calculations were combined with high level ab initio calculations to investigate possible further evolution of the products observed. In particular, for formamide, we propose that the NH2OH{}2+ + H2CO reaction can produce an isomer, NH2OCH{}2+, that, after dissociative recombination, can produce neutral formamide, which was observed in space. The direct dynamics do not pre-impose any reaction pathways and in other reactions, we did not observe the formation of formamide or any possible precursor. On the other hand, we obtained other interesting reactions, like the formation of NH2CH{}2+. Finally, some radiative association processes are proposed. All of the results obtained are discussed in light of the species observed in radioastronomy.

  19. Incongruent range dynamics between co-occurring Asian temperate tree species facilitated by life history traits.

    Science.gov (United States)

    Zhao, Yun-Peng; Yan, Xiao-Ling; Muir, Graham; Dai, Qiong-Yan; Koch, Marcus A; Fu, Cheng-Xin

    2016-04-01

    Postglacial expansion to former range limits varies substantially among species of temperate deciduous forests in eastern Asia. Isolation hypotheses (with or without gene flow) have been proposed to explain this variance, but they ignore detailed population dynamics spanning geological time and neglect the role of life history traits. Using population genetics to uncover these dynamics across their Asian range, we infer processes that formed the disjunct distributions of Ginkgo biloba and the co-occurring Cercidiphyllum japonicum (published data). Phylogenetic, coalescent, and comparative data suggest that Ginkgo population structure is regional, dichotomous (to west-east refugia), and formed ˜51 kya, resulting from random genetic drift during the last glaciation. This split is far younger than the north-south population structure of Cercidiphyllum (~1.89 Mya). Significant (recent) unidirectional gene flow has not homogenized the two Ginkgo refugia, despite 2Nm > 1. Prior to this split, gene flow was potentially higher, resulting in conflicting support for a priori hypotheses that view isolation as an explanation for the variation in postglacial range limits. Isolation hypotheses (with or without gene flow) are thus not necessarily mutually exclusive due to temporal variation of gene flow and genetic drift. In comparison with Cercidiphyllum, the restricted range of Ginkgo has been facilitated by uncompetitive life history traits associated with seed ecology, highlighting the importance of both demography and lifetime reproductive success when interpreting range shifts.

  20. Human-facilitated metapopulation dynamics in an emerging pest species, Cimex lectularius.

    Science.gov (United States)

    Fountain, Toby; Duvaux, Ludovic; Horsburgh, Gavin; Reinhardt, Klaus; Butlin, Roger K

    2014-03-01

    The number and demographic history of colonists can have dramatic consequences for the way in which genetic diversity is distributed and maintained in a metapopulation. The bed bug (Cimex lectularius) is a re-emerging pest species whose close association with humans has led to frequent local extinction and colonization, that is, to metapopulation dynamics. Pest control limits the lifespan of subpopulations, causing frequent local extinctions, and human-facilitated dispersal allows the colonization of empty patches. Founder events often result in drastic reductions in diversity and an increased influence of genetic drift. Coupled with restricted migration, this can lead to rapid population differentiation. We therefore predicted strong population structuring. Here, using 21 newly characterized microsatellite markers and approximate Bayesian computation (ABC), we investigate simplified versions of two classical models of metapopulation dynamics, in a coalescent framework, to estimate the number and genetic composition of founders in the common bed bug. We found very limited diversity within infestations but high degrees of structuring across the city of London, with extreme levels of genetic differentiation between infestations (FST  = 0.59). ABC results suggest a common origin of all founders of a given subpopulation and that the numbers of colonists were low, implying that even a single mated female is enough to found a new infestation successfully. These patterns of colonization are close to the predictions of the propagule pool model, where all founders originate from the same parental infestation. These results show that aspects of metapopulation dynamics can be captured in simple models and provide insights that are valuable for the future targeted control of bed bug infestations.

  1. 129I and its species in the East China Sea: level, distribution, sources and tracing water masses exchange and movement

    Science.gov (United States)

    Liu, Dan; Hou, Xiaolin; Du, Jinzhou; Zhang, Luyuan; Zhou, Weijian

    2016-11-01

    Anthropogenic 129I as a long-lived radioisotope of iodine has been considered as an ideal oceanographic tracer due to its high residence time and conservative property in the ocean. Surface water samples collected from the East China Sea (ECS) in August 2013 were analyzed for 129I, 127I and their inorganic chemical species in the first time. The measured 129I/127I ratio is 1-3 orders of magnitude higher than the pre-nuclear level, indicating its dominantly anthropogenic sources. Relatively high 129I levels were observed in the Yangtze River and its estuary, as well as in the southern Yellow Sea, and 129I level in seawater declines towards the ECS shelf. In the open sea, 129I and 127I in surface water exists mainly as iodate, while in Yangtze River estuary and some locations, iodide is dominated. The results indicate that the Fukushima nuclear accident has no detectable effects in the ECS until August 2013. The obtained results are used for investigation of interaction of various water masses and water circulation in the ECS, as well as the marine environment in this region. Meanwhile this work provides essential data for evaluation of the possible influence of the increasing NPPs along the coast of the ECS in the future.

  2. The importance of incorporating functional habitats into conservation planning for highly mobile species in dynamic systems.

    Science.gov (United States)

    Webb, Matthew H; Terauds, Aleks; Tulloch, Ayesha; Bell, Phil; Stojanovic, Dejan; Heinsohn, Robert

    2017-10-01

    The distribution of mobile species in dynamic systems can vary greatly over time and space. Estimating their population size and geographic range can be problematic and affect the accuracy of conservation assessments. Scarce data on mobile species and the resources they need can also limit the type of analytical approaches available to derive such estimates. We quantified change in availability and use of key ecological resources required for breeding for a critically endangered nomadic habitat specialist, the Swift Parrot (Lathamus discolor). We compared estimates of occupied habitat derived from dynamic presence-background (i.e., presence-only data) climatic models with estimates derived from dynamic occupancy models that included a direct measure of food availability. We then compared estimates that incorporate fine-resolution spatial data on the availability of key ecological resources (i.e., functional habitats) with more common approaches that focus on broader climatic suitability or vegetation cover (due to the absence of fine-resolution data). The occupancy models produced significantly (P < 0.001) smaller (up to an order of magnitude) and more spatially discrete estimates of the total occupied area than climate-based models. The spatial location and extent of the total area occupied with the occupancy models was highly variable between years (131 and 1498 km(2) ). Estimates accounting for the area of functional habitats were significantly smaller (2-58% [SD 16]) than estimates based only on the total area occupied. An increase or decrease in the area of one functional habitat (foraging or nesting) did not necessarily correspond to an increase or decrease in the other. Thus, an increase in the extent of occupied area may not equate to improved habitat quality or function. We argue these patterns are typical for mobile resource specialists but often go unnoticed because of limited data over relevant spatial and temporal scales and lack of spatial data on the

  3. Phylogenetic fields through time: temporal dynamics of geographical co-occurrence and phylogenetic structure within species ranges.

    Science.gov (United States)

    Villalobos, Fabricio; Carotenuto, Francesco; Raia, Pasquale; Diniz-Filho, José Alexandre F

    2016-04-05

    Species co-occur with different sets of other species across their geographical distribution, which can be either closely or distantly related. Such co-occurrence patterns and their phylogenetic structure within individual species ranges represent what we call the species phylogenetic fields (PFs). These PFs allow investigation of the role of historical processes--speciation, extinction and dispersal--in shaping species co-occurrence patterns, in both extinct and extant species. Here, we investigate PFs of large mammalian species during the last 3 Myr, and how these correlate with trends in diversification rates. Using the fossil record, we evaluate species' distributional and co-occurrence patterns along with their phylogenetic structure. We apply a novel Bayesian framework on fossil occurrences to estimate diversification rates through time. Our findings highlight the effect of evolutionary processes and past climatic changes on species' distributions and co-occurrences. From the Late Pliocene to the Recent, mammal species seem to have responded in an individualistic manner to climate changes and diversification dynamics, co-occurring with different sets of species from different lineages across their geographical ranges. These findings stress the difficulty of forecasting potential effects of future climate changes on biodiversity.

  4. Differences in plant cover and species composition of semiarid grassland communities of Central Mexico and its effects on net ecosystem exchange

    Directory of Open Access Journals (Sweden)

    J. Delgado-Balbuena

    2012-12-01

    Full Text Available Changes in land use across the semiarid grasslands of Northern Mexico have driven a decline of plant cover and alteration of plant species composition. A number of different plant communities have resulted from these changes, however, their implications on the carbon cycle and regional carbon balance are still poorly understood. Here, we examined the effects of plant cover loss and changes in species composition on net ecosystem CO2 exchange (NEE and their biotic and abiotic controls. Five typical plant community types were examined in the semiarid grassland by encasing the entire above-ground ecosystem using the geodesic dome method. Sites included an oat crop (crop, a moderately grazed grassland (moderate grazing, a 28 yr-old grazing exclosure (exclosure, an overgrazed site with low perennial grass cover (overgrazed, and an overgrazed site presenting shrub encroachment (shrub encroachment. For natural vegetation, rates of daytime NEE for sites with a high plant cover (exclosure and moderate grazing were similar (P>0.05 as compared to sites with low plant cover (overgrazed and shrub encroachment. However, night time NEE (carbon loss was more than double (P<0.05 for sites with high plant cover compared to sites with low cover, resulting into slight C sinks for the low plant cover sites and neutral or sources for the high plant cover sites on an annual basis. Differences in plant cover and its associated biomass defined the sensitivity to environmental controls. Thus, daytime NEE in low plant cover sites reached light compensation points at lower PPFD values than those from high plant cover sites. Differences in species composition did not influence NEE rates even though there were transient or permanent changes in C3 vs. C4 functional groups.

  5. Dynamics in Thermotoga neapolitana adenylate kinase: 15N relaxation and hydrogen-deuterium exchange studies of a hyperthermophilic enzyme highly active at 30 degrees C.

    Science.gov (United States)

    Krishnamurthy, Harini; Munro, Kim; Yan, Honggao; Vieille, Claire

    2009-03-31

    Backbone conformational dynamics of Thermotoga neapolitana adenylate kinase in the free form (TNAK) and inhibitor-bound form (TNAK*Ap5A) were investigated at 30 degrees C using (15)N NMR relaxation measurements and NMR monitored hydrogen-deuterium exchange. With kinetic parameters identical to those of Escherichia coli AK (ECAK) at 30 degrees C, TNAK is a unique hyperthermophilic enzyme. These catalytic properties make TNAK an interesting and novel model to study the interplay between protein rigidity, stability, and activity. Comparison of fast time scale dynamics (picosecond to nanosecond) in the open and closed states of TNAK and ECAK at 30 degrees C reveals a uniformly higher rigidity across all domains of TNAK. Within this framework of a rigid TNAK structure, several residues located in the AMP-binding domain and in the core-lid hinge regions display high picosecond to nanosecond time scale flexibility. Together with the recent comparison of ECAK dynamics with those of hyperthermophilic Aquifex aeolicus AK (AAAK), our results provide strong evidence for the role of picosecond to nanosecond time scale fluctuations in both stability and activity. In the slow time scales, TNAK's increased rigidity is not uniform but localized in the AMP-binding and lid domains. The core domain amides of ECAK and TNAK in the open and closed states show comparable protection against exchange. Significantly, the hinges framing the lid domain show similar exchange data in ECAK and TNAK open and closed forms. Our NMR relaxation and hydrogen-deuterium exchange studies therefore suggest that TNAK maintains high activity at 30 degrees C by localizing flexibility to the hinge regions that are key to facilitating conformational changes.

  6. Co-ordination of growth, gas exchange and hydraulics define the carbon safety margin in tree species with contrasting drought strategies.

    Science.gov (United States)

    Mitchell, P J; O'Grady, A P; Tissue, D T; Worledge, D; Pinkard, E A

    2014-05-01

    Gas exchange, growth, water transport and carbon (C) metabolism diminish during drought according to their respective sensitivities to declining water status. The timing of this sequence of declining physiological functions may determine how water and C relations compromise plant survival. In this paper, we test the hypothesis that the degree of asynchrony between declining C supply (photosynthesis) and C demand (growth and respiration) determines the rate and magnitude of changes in whole-plant non-structural carbohydrates (NSC) during drought. Two complementary experiments using two tree species (Eucalyptus globulus Labill. and Pinus radiata D. Don) with contrasting drought response strategies were performed to (i) assess changes in radial stem growth, transpiration, leaf water potential and gas exchange in response to chronic drought, and (ii) evaluate the concomitant impacts of these drought responses on the temporal patterns of NSC during terminal drought. The three distinct phases of water stress were delineated by thresholds of growth cessation and stomatal closure that defined the 'carbon safety margin' (i.e., the difference between leaf water potential when growth is zero and leaf water potential when net photosynthesis is zero). A wider C safety margin in E. globulus was defined by an earlier cessation of growth relative to photosynthesis that reduced the demand for NSC while maintaining C acquisition. By contrast, the narrower C safety margin in P. radiata was characterized by a synchronous decline in growth and photosynthesis, whereby growth continued under a declining supply of NSC from photosynthesis. The narrower C safety margin in P. radiata was associated with declines in starch concentrations after ∼ 90 days of chronic drought and significant depletion of starch in all organs at mortality. The observed divergence in the sensitivity of drought responses is indicative of a potential trade-off between maintaining hydraulic safety and adequate C

  7. SCREENING OF CONTENT AND DYNAMIC OF ACCUMULATION OF POLYPHENOLS IN SOME BASIDIOMYCETES SPECIES

    Directory of Open Access Journals (Sweden)

    A. K. Veligodska

    2015-11-01

    Full Text Available The aim of the study was to investigate the total content of polyphenolic substances in Basidiomycetes carpophores from 50 species, of which 27 belong to the order Polyporales and 23 to the order Agaricales. Introduced 23 strains of 8 species of Basidiomycetes. Methods. Gathered wild carpophores dried and crushed to a particle size of 0,1 till 0,01 mm and searching strains were cultured in Erlenmeyyers flasks by surface method on standard glucose-peptone culture medium. Determination of total content of polyphenolic compounds was carried out in ethanol extracts of mycological material by a modified method of Folin-Chokalteu. Completely dry biomass of carpophores and mycelium was determined gravimetrically. Results. There was identified the species of polyporal fungi Ganoderma applanatum, Ganoderma lucidum, Laetiporus sulphureus and Fomes fomentarius and types of agarical mushrooms Stropharia rugosoannulata, Agrocybe cylindracea, Tricholoma flavovirens, Flammulina velutipes, Pleurotus ostreatus and Fistulina hepatica high in polyphenolic compounds. It was determined the content of polyphenols ranging from more than 60 mg / g completely dry biomass. For introduced strains established dynamics of growth and accumulation of polyphenolic compounds in the mycelium and culture filtrate during fermentation on glucose-peptone medium. All cultures reach a maximum accumulation of biomass on the 12th day of growth. Shizophyllum commune Sc-1101 and 10 and F. velutipes F-202 have been identified as the most productive strains. The lowest accumulation of absolutely dry biomass was recorded for strain P. ostreatus P-192 and strain F. fomentarius Ff-09. Cultures have investigated individual value growth such as biomass accumulation in the applied cultivation conditions, which probably reflects the suitability of the medium for their growth and genotypic characteristics. Strains are overwhelmingly able to accumulate polyphenolic compounds in both mycelium and

  8. SCREENING OF CONTENT AND DYNAMIC OF ACCUMULATION OF POLYPHENOLS IN SOME BASIDIOMYCETES SPECIES

    Directory of Open Access Journals (Sweden)

    Veligodska A. K.

    2015-12-01

    Full Text Available The aim of the study was to investigate the total content of polyphenolic substances in Basidiomycetes carpophores from 50 species, of which 27 belong to the order Polyporales and 23 to the order Agaricales. Introduced 23 strains of 8 species of Basidiomycetes. Methods. Gathered wild carpophores dried and crushed to a particle size of 0,1 till 0,01 mm and searching strains were cultured in Erlenmeyyers flasks by surface method on standard glucose-peptone culture medium. Determination of total content of polyphenolic compounds was carried out in ethanol extracts of mycological material by a modified method of Folin-Chokalteu. Completely dry biomass of carpophores and mycelium was determined gravimetrically. Results. There was identified the species of polyporal fungi Ganoderma applanatum, Ganoderma lucidum, Laetiporus sulphureus and Fomes fomentarius and types of agarical mushrooms Stropharia rugosoannulata, Agrocybe cylindracea, Tricholoma flavovirens, Flammulina velutipes, Pleurotus ostreatus and Fistulina hepatica high in polyphenolic compounds. It was determined the content of polyphenols ranging from more than 60 mg / g completely dry biomass. For introduced strains established dynamics of growth and accumulation of polyphenolic compounds in the mycelium and culture filtrate during fermentation on glucose-peptone medium. All cultures reach a maximum accumulation of biomass on the 12th day of growth. Shizophyllum commune Sc-1101 and 10 and F. velutipes F-202 have been identified as the most productive strains. The lowest accumulation of absolutely dry biomass was recorded for strain P. ostreatus P-192 and strain F. fomentarius Ff-09. Cultures have investigated individual value growth such as biomass accumulation in the applied cultivation conditions, which probably reflects the suitability of the medium for their growth and genotypic characteristics. Strains are overwhelmingly able to accumulate polyphenolic compounds in both mycelium and

  9. The Ecuadorian Artisanal Fishery for Large Pelagics: Species Composition and Spatio-Temporal Dynamics.

    Directory of Open Access Journals (Sweden)

    Jimmy Martínez-Ortiz

    Full Text Available The artisanal fisheries of Ecuador operate within one of the most dynamic and productive marine ecosystems of the world. This study investigates the catch composition of the Ecuadorian artisanal fishery for large pelagic fishes, including aspects of its spatio-temporal dynamics. The analyses of this study are based on the most extensive dataset available to date for this fishery: a total of 106,963 trip-landing inspection records collected at its five principal ports during 2008 ‒ 2012. Ecuadorian artisanal fisheries remove a substantial amount of biomass from the upper trophic-level predatory fish community of the eastern tropical Pacific Ocean. It is estimated that at least 135 thousand metric tons (mt (about 15.5 million fish were landed in the five principal ports during the study period. The great novelty of Ecuadorian artisanal fisheries is the "oceanic-artisanal" fleet component, which consists of mother-ship (nodriza boats with their towed fiber-glass skiffs (fibras operating with pelagic longlines. This fleet has fully expanded into oceanic waters as far offshore as 100°W, west of the Galapagos Archipelago. It is estimated that nodriza operations produce as much as 80% of the total catches of the artisanal fishery. The remainder is produced by independent fibras operating in inshore waters with pelagic longlines and/or surface gillnets. A multivariate regression tree analysis was used to investigate spatio-environmental effects on the nodriza fleet (n = 6,821 trips. The catch species composition of the nodriza fleet is strongly influenced by the northwesterly circulation of the Humboldt Current along the coast of Peru and its associated cold waters masses. The target species and longline gear-type used by nodrizas change seasonally with the incursion of cool waters (< 25°C from the south and offshore. During this season, dolphinfish (Coryphaena hippurus dominates the catches. However, in warmer waters, the fishery changes to tuna

  10. The Ecuadorian Artisanal Fishery for Large Pelagics: Species Composition and Spatio-Temporal Dynamics

    Science.gov (United States)

    Martínez-Ortiz, Jimmy; Aires-da-Silva, Alexandre M.; Lennert-Cody, Cleridy E.; Maunder, Mark N.

    2015-01-01

    The artisanal fisheries of Ecuador operate within one of the most dynamic and productive marine ecosystems of the world. This study investigates the catch composition of the Ecuadorian artisanal fishery for large pelagic fishes, including aspects of its spatio-temporal dynamics. The analyses of this study are based on the most extensive dataset available to date for this fishery: a total of 106,963 trip-landing inspection records collected at its five principal ports during 2008 ‒ 2012. Ecuadorian artisanal fisheries remove a substantial amount of biomass from the upper trophic-level predatory fish community of the eastern tropical Pacific Ocean. It is estimated that at least 135 thousand metric tons (mt) (about 15.5 million fish) were landed in the five principal ports during the study period. The great novelty of Ecuadorian artisanal fisheries is the “oceanic-artisanal” fleet component, which consists of mother-ship (nodriza) boats with their towed fiber-glass skiffs (fibras) operating with pelagic longlines. This fleet has fully expanded into oceanic waters as far offshore as 100°W, west of the Galapagos Archipelago. It is estimated that nodriza operations produce as much as 80% of the total catches of the artisanal fishery. The remainder is produced by independent fibras operating in inshore waters with pelagic longlines and/or surface gillnets. A multivariate regression tree analysis was used to investigate spatio-environmental effects on the nodriza fleet (n = 6,821 trips). The catch species composition of the nodriza fleet is strongly influenced by the northwesterly circulation of the Humboldt Current along the coast of Peru and its associated cold waters masses. The target species and longline gear-type used by nodrizas change seasonally with the incursion of cool waters (< 25°C) from the south and offshore. During this season, dolphinfish (Coryphaena hippurus) dominates the catches. However, in warmer waters, the fishery changes to tuna

  11. Operculina from the northwestern Pacific (Sesoko Island, Japan) Species Differentiation, Population Dynamics, Growth and Development

    Science.gov (United States)

    Woeger, Julia; Eder, Wolfgang; Kinoshita, Shunichi; Briguglio, Antonino; Hohenegger, Johann

    2017-04-01

    During the last decades larger benthic foraminifera have gained importance as indicator species and are used in a variety of applications, from ecological monitoring, studying the effects of ocean acidification, or reconstructing paleoenvironments. They significantly contribute to the carbonate budget of costal areas and are invaluable tools in biostratigraphy. Even before their advancement as bioindicators, laboratory experiments have been conducted to investigate the effects of various ecological parameters on community composition, biology of single species, or investigating the effects of salinity and temperature on stable isotope composition of the foraminiferal test, to name only a few. The natural laboratory approach (continuous sampling over a period of more than one year) was conducted at the island of Sesoko (Okinawa, Japan). in combination with µ-CT scanning was used to reveal population dynamics of 3 different morphotypes of Operculina. The clarification of reproductive cycles as well as generation and size abundances were used to calculate natural growth models. Best fit was achieved using Bertalanffy and Michaelis-Menten functions. Exponential-, logistic-, generalized logistic-, Gompertz-function yielded weaker fits, when compared by coefficient of determination as well as Akaike Information criterion. The resulting growth curves and inferred growth rates were in turn used to evaluate the quality of a laboratory cultivation experiment carried out simultaneously over a period of 15 months. Culturing parameters such as temperature, light intensities, salinity and pH and light-dark duration were continuously adapted to measurements in the field. The average investigation time in culture was 77days. 13 Individuals lived more than 200 days, 3 reproduced asexually and one sexually. 14% of 186 Individuals were lost, while 22% could not be kept alive for more than one month. Growth curves also represent an instrumental source of information for the various

  12. Dynamic control of osmolality and ionic composition of the xylem sap in two mangrove species.

    Science.gov (United States)

    López-Portillo, Jorge; Ewers, Frank W; Méndez-Alonzo, Rodrigo; Paredes López, Claudia L; Angeles, Guillermo; Alarcón Jiménez, Ana Luisa; Lara-Domínguez, Ana Laura; Torres Barrera, María Del Carmen

    2014-06-01

    • Premise of the study: Xylem sap osmolality and salinity is a critical unresolved issue in plant function with impacts on transport efficiency, pressure gradients, and living cell turgor pressure, especially for halophytes such as mangrove trees.• Methods: We collected successive xylem vessel sap samples from stems and shoots of Avicennia germinans and Laguncularia racemosa using vacuum and pressure extraction and measured their osmolality. Following a series of extractions with the pressure chamber, we depressurized the shoot and pressurized again after various equilibration periods (minutes to hours) to test for dynamic control of osmolality. Transpiration and final sap osmolality were measured in shoots perfused with deionized water or different seawater dilutions.• Key results: For both species, the sap osmolality values of consecutive samples collected by vacuum extraction were stable and matched those of the initial samples extracted with the pressure chamber. Further extraction of samples with the pressure chamber decreased sap osmolality, suggesting reverse osmosis occurred. However, sap osmolalities increased when longer equilibration periods after sap extraction were allowed. Analysis of expressed sap with HPLC indicated a 1:1 relation between measured osmolality and the osmolality of the inorganic ions in the sap (mainly Na(+), K(+), and Cl(-)), suggesting no contamination by organic compounds. In stems perfused with deionized water, the sap osmolality increased to mimic the native sap osmolality.• Conclusions: Xylem sap osmolality and ionic contents are dynamically adjusted by mangroves and may help modulate turgor pressure, hydraulic conductivity, and water potential, thus being important for mangrove physiology, survival, and distribution. © 2014 Botanical Society of America, Inc.

  13. Carbon dynamics in aboveground biomass of co-dominant plant species: related rather to leaf life span than to species

    Science.gov (United States)

    Ostler, Ulrike; Schleip, Inga; Lattanzi, Fernando A.; Schnyder, Hans

    2016-04-01

    This study investigates the role of individual organisms in whole ecosystem carbon (C) fluxes. It is currently unknown if different plant community members share the same or different kinetics of C pools in aboveground biomass, thereby adding (or not) variability to the first steps in ecosystem C cycling. We assessed the residence times in metabolic and non-metabolic (or structural) C pools and the allocation pattern of assimilated C in aboveground plant parts of four co-existing, co-dominant species from different functional groups in a temperate grassland community. For this purpose continuous, 14-16 day long 13CO2/12CO2-labeling experiments were performed in Sept. 2006, May 2007 and Sept. 2007, and the tracer kinetics were analysed with compartmental modeling. In all experimental periods, the species shared vastly similar residence times in metabolic C (5-8 d). In contrast, the residence times in non-metabolic C ranged from 20 to 58 d (except one outlier) and the fraction of fixed C allocated to the non-metabolic pool from 7 to 45%. These variations in non-metabolic C kinetics were not systematically associated with species or experimental periods, but exhibited close relationships with (independent estimates of) leaf life span, particularly in the grasses. This adds new meaning to leaf life span as a functional trait in the leaf and plant economics spectrum and its implication for C cycle studies in grassland and also forest systems. As the four co-dominant species accounted for ~80% of total community shoot biomass, we should also expect that the observed similarities in pool kinetics and allocation will scale up to similar relationships at the community level.

  14. Population dynamics of the species Plantago major L. and Poa annua L. in a replacement series experiment

    Directory of Open Access Journals (Sweden)

    Mijović A.

    2009-01-01

    Full Text Available Population dynamics of the species Plantago major L. and Poa annua L., typical representatives of ruderal vegetation, was analyzed in a replacement series experiment. The analyzed species were sown in an area with meadow vegetation, where the vegetation present had been previously removed by a total herbicide and additionally by hoeing. The objective of the experiment was to monitor growth dynamics and the effect of intra- and inter-specific interaction of the species Plantago major and Poa annua in conditions of different sowing densities and proportions. The effects of intra- and inter-specific interference and the density-dependent responses were assessed on the basis of several parameters (natality, mortality, age structure, and measures of ontogenetic changes. Based on the study results, it can be concluded that the responses of the species in the experiment were different, which is explained by different adaptive mechanisms, i.e., strategies, in the specific environmental conditions. An effect of the density dependent response was present in both species in the replacement series experiment. The response was amplified by water deficit caused by intensive evapora­tion of the bare soil. No effect of inter-specific interference was observed at the given densities of the study species on the sample plots. An effect of intra-specific interference of the species Plantago major and Poa annua was observed in the guise of a density-negative response of the rate of ontogenetic changes and fecundity.

  15. Interactions of elevated CO{sub 2} and drought stress in gas exchange and water-use efficiency in three temperate deciduous tree species

    Energy Technology Data Exchange (ETDEWEB)

    Liang, N.; Maruyama, K.; Huang, Y. [Niigata University, Niigata (Japan). Graduate School of Science and Technology

    1995-12-31

    The effect of CO{sub 2} increase on gas exchange and water-use efficiency (WUE) in three temperate deciduous species (Fagus crenata, Ginkgo biloba and Alnus firma) under gradually-developing drought-stress was assessed. Seedlings were grown within transparent open-top cabinets and maintained for 4 months at mean CO{sub 2} concentrations of either 350(ambient; C-350) or 700{mu}mol mol{sup -1} (elevated; C-700) and combined with five water regimes (leaf water potential, Psi{sub w}, higher than -0.3 (well-watered), -0.5 and -0.8 (moderate drought), -1.0 and fewer than -1.2 MPa (serious drought-stress)). Increase in CO{sub 2} concentration induced a 60% average increase in net photosynthetic rate (P-N) under well-watered conditions. The effect of C-700 became more pronounced with drought stress established, with an 80% average increase in P-N at Psi{sub w}, as low as -0.8 MPa; leaf conductance to water vapour transfer (g{sub s}) and transpiration rate (E), however, were significantly decreased. Consequently, WUE increased under drought, through drought stress affected potential E sooner than potential P-N. The interaction of CO{sub 2} x drought stress on WUE was significant in that P-N was stimulated while E in C-700 enriched plants resembled that of C-350 plants under drought. Hence if a doubling of atmospheric CO{sub 2} concentration occurs by the mid 21st century, then greater P-N in F. crenata, G. biloba and A. firma may be expected and the drought susceptibility of these species will be substantially enhanced.

  16. Temporal dynamics of arthropods on six tree species in dry woodlands on the Caribbean Island of Puerto Rico

    Science.gov (United States)

    W. Beltran; Joseph Wunderle Jr.

    2014-01-01

    The seasonal dynamics of foliage arthropod populations are poorly studied in tropical dry forests despite the importance of these studies for understanding arthropod population responses to environmental change.We monitored the abundance, temporal distributions, and body size of arthropods in five naturalized alien and one native tree species to characterize arthropod...

  17. Characterization of mu s-ms dynamics of proteins using a combined analysis of N-15 NMR relaxation and chemical shift: Conformational exchange in plastocyanin induced by histidine protonations

    DEFF Research Database (Denmark)

    Hass, M. A. S.; Thuesen, Marianne Hallberg; Christensen, Hans Erik Mølager

    2004-01-01

    An approach is presented that allows a detailed, quantitative characterization of conformational exchange processes in proteins on the mus-ms time scale. The approach relies on a combined analysis of NMR relaxation rates and chemical shift changes and requires that the chemical shift...... of the exchanging species can be determined independently of the relaxation rates. The applicability of the approach is demonstrated by a detailed analysis of the conformational exchange processes previously observed in the reduced form of the blue copper protein, plastocyanin from the cyanobacteria Anabaena...... quantitatively by the correlation between the R-ex terms and the corresponding chemical shift differences of the exchanging species. By this approach, the R-ex terms of N-15 nuclei belonging to contiguous regions in the protein could be assigned to the same exchange process. Furthermore, the analysis...

  18. Strategy Dependent Swimming Dynamics Change among a Predatory Algae Species with Different Strains

    Science.gov (United States)

    Katz, Joseph; Sheng, Jian; Malkiel, Edwin; Adolf, Jason; Place, Allen

    2008-11-01

    Digital holographic microscopic cinematography is used for measuring the 3D, time resolved, swimming behavior of toxic and non-toxic strains the marine dinoflagellate Karlodinium veneficum. We focus on the response of predators of the same species, but with different predation strategy, to the presence of prey, Storeatula major. Experiments are performed in a 3x3 mm cuvette, at densities extending to 100,000 cells/ml. Holograms are recorded at 60fps and at 20X magnification. In each case, we simultaneously track 200-500 cells in the 3mm deep sample, at a spatial resolution of 0.4x0.4x2 μm. We show that responses are largely dependent on the predation strategy. K. veneficum 2064, a toxic mixotroph, slows down and decreases the helix radius and clusters around the prey. Conversely, MD5, a non-toxic, autotrophic-like strain is completely oblivious to prey. Strain 1974, which is toxic and twice as motile, shows heterotrophic-like responses with characteristics of an active hunter. Also, on going spectral analysis of the 3-D motion provides quantitative insight on the swimming dynamics of microorganisms.

  19. Capturing the transient species at the electrode-electrolyte interface by in situ dynamic molecular imaging

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Jiachao; Zhou, Yufan; Hua, Xin; Liu, Songqin; Zhu, Zihua; Yu, Xiao-Ying

    2016-09-01

    The electrochemical interface between the solid electrode and liquid electrolyte has long been studied because of its importance in electrical energy storage, material synthesis, catalysis, and energy conversions.1 However, such interfaces are complex and extremely difficult to observe directly and are poorly under-stood due to lack of true in situ tools.2 Although electrochemical techniques have been widely used to investigate such interfaces, they are based on macroscopic models or current changes that could not provide direct ionic and molecular information of the interfacial structure. Many in situ and ex situ spectroscopy and microscopy techniques have been used to study the solid–liquid (s–l) interface.3,4 In situ TEM in sealed liquid cells has notably become a popular choice to provide structural information of s–l at the atomic level.5,6 However, real-time spatial mapping of the ionic and molecular intermediate species at the dynamic inter-face still remains a key challenge.

  20. Quantification of the effect of water exchange in dynamic contrast MRI perfusion measurements in the brain and heart

    DEFF Research Database (Denmark)

    Larsson, H B; Rosenbaum, S; Fritz-Hansen, T

    2001-01-01

    Measurement of myocardial and brain perfusion when using exogenous contrast agents (CAs) such as gadolinium-DTPA (Gd-DTPA) and MRI is affected by the diffusion of water between compartments. This water exchange may have an impact on signal enhancement, or, equivalently, on the longitudinal......(i)) by using a realistic simulation. These results were verified by in vivo studies of the heart and brain in humans. The conclusion is that water exchange between the vascular and extravascular extracellular space has no effect on K(i) estimation in the myocardium when a normal dose of Gd-DTPA is used. Water...... exchange can have a significant effect on perfusion estimation (F) in the brain when using Gd-DTPA, where it acts as an intravascular contrast agent....

  1. Carbon and Nitrogen dynamics in forest soils depending on light conditions and tree species

    Science.gov (United States)

    Veselinovic, Bojana; Hager, Herbert

    2013-04-01

    Climate change mitigation actions under the Kyoto Protocol apply among other decreases of CO2-emissions and/or increases of carbon (C) stocks. As soils represent the second biggest C-reservoir on Earth, an exact estimation of the stocks and reliable knowledge on C-dynamics in forest soils is of high importance. Anyhow, here, the accurate GHG-accounting, emission reductions and increase in C stocks is hampered due to lack of reliable data and solid statistical methods for the factors which influence C-sequestration in and its release from these systems. In spite of good progress in the scientific research, these factors are numerous and diverse in their interactions. This work focuses on influence of the economically relevant tree species - Picea abies, Fagus sylvatica and Quercus spp. - and light conditions on forest floor and mineral soil C and N dynamics in forest soils. Spruce monocultures have been widely used management practices in central European forests during the past century. Such stands are in lower altitudes and on heavy and water logged soils unstable and prone to disturbances, especially to windthrows. We hypothesize that windthrow areas loose C & N and that the establishment of the previous nutrient stocks is, if at all, only possible to be reached over the longer periods of time. We research also how the increased OM depletion affects the change of C & N stocks in forest floor vs. mineral soil. Conversion of such secondary spruce monocultures to site adequate beech and oak forests may enable higher stocks allocated predominantly as stable organic carbon and as plant available nitrogen. For this purpose sites at 300-700 m altitude with planosols were chosen in the region of the Northern Alpine Foothills. A false chronosequence approach was used in order to evaluate the impacts of the tree species and change in light conditions on dynamic of C & N in the forest floor and mineral soil, over the period 0-100 (for oak 120 y.) years. The C- and N

  2. The effect of flooding on the exchange of the volatile C2-compounds ethanol, acetaldehyde and acetic acid between leaves of Amazonian floodplain tree species and the atmosphere

    Directory of Open Access Journals (Sweden)

    W. Junk

    2008-08-01

    Full Text Available The effect of root inundation on the leaf emissions of ethanol, acetaldehyde and acetic acid in relation to assimilation and transpiration was investigated with 2–3 years old tree seedlings of four Amazonian floodplain species by applying dynamic cuvette systems under greenhouse conditions. Emissions were monitored over a period of several days of inundation using a combination of Proton Transfer Reaction Mass Spectrometry (PTR-MS and conventional techniques (HPLC, ion chromatography. Under non-flooded conditions, none of the species exhibited measurable emissions of any of the compounds, but rather low deposition of acetaldehyde and acetic acid was observed instead. Tree species specific variations in deposition velocities were largely due to variations in stomatal conductance. Flooding of the roots resulted in leaf emissions of ethanol and acetaldehyde by all species, while emissions of acetic acid were only observed from the species exhibiting the highest ethanol and acetaldehyde emission rates. All three compounds showed a similar diurnal emission profile, each displaying an emission burst in the morning, followed by a decline in the evening. This concurrent behavior supports the conclusion, that all three compounds emitted by the leaves are derived from ethanol produced in the roots by alcoholic fermentation, transported to the leaves with the transpiration stream and finally partly converted to acetaldehyde and acetic acid by enzymatic processes. Co-emissions and peaking in the early morning suggest that root ethanol, after transportation with the transpiration stream to the leaves and enzymatic oxidation to acetaldehyde and acetate, is the metabolic precursor for all compounds emitted, though we can not totally exclude other production pathways. Emission rates substantially varied among tree species, with maxima differing by up to two orders of magnitude (25–1700 nmol m−2 min−1 for ethanol and 5–500 nmol m−2 min−1 for

  3. Occupancy dynamics in a tropical bird community: unexpectedly high forest use by birds classified as non-forest species

    Science.gov (United States)

    Ruiz-Gutierrez, Viviana; Zipkin, Elise F.; Dhondt, Andre A.

    2010-01-01

    1. Worldwide loss of biodiversity necessitates a clear understanding of the factors driving population declines as well as informed predictions about which species and populations are at greatest risk. The biggest threat to the long-term persistence of populations is the reduction and changes in configuration of their natural habitat. 2. Inconsistencies have been noted in the responses of populations to the combined effects of habitat loss and fragmentation. These have been widely attributed to the effects of the matrix habitats in which remnant focal habitats are typically embedded. 3. We quantified the potential effects of the inter-patch matrix by estimating occupancy and colonization of forest and surrounding non-forest matrix (NF). We estimated species-specific parameters using a dynamic, multi-species hierarchical model on a bird community in southwestern Costa Rica. 4. Overall, we found higher probabilities of occupancy and colonization of forest relative to the NF across bird species, including those previously categorized as open habitat generalists not needing forest to persist. Forest dependency was a poor predictor of occupancy dynamics in our study region, largely predicting occupancy and colonization of only non-forest habitats. 5. Our results indicate that the protection of remnant forest habitats is key for the long-term persistence of all members of the bird community in this fragmented landscape, including species typically associated with open, non-forest habitats. 6.Synthesis and applications. We identified 39 bird species of conservation concern defined by having high estimates of forest occupancy, and low estimates of occupancy and colonization of non-forest. These species survive in forest but are unlikely to venture out into open, non-forested habitats, therefore, they are vulnerable to the effects of habitat loss and fragmentation. Our hierarchical community-level model can be used to estimate species-specific occupancy dynamics for focal

  4. Dynamic habitat selection by two wading bird species with divergent foraging strategies in a seasonally fluctuating wetland

    Science.gov (United States)

    Beerens, J.M.; Gawlik, D.E.; Herring, G.; Cook, Mark I.

    2011-01-01

    Seasonal and annual variation in food availability during the breeding season plays an influential role in the population dynamics of many avian species. In highly dynamic ecosystems like wetlands, finding and exploiting food resources requires a flexible behavioral response that may produce different population trends that vary with a species' foraging strategy. We quantified dynamic foraging-habitat selection by breeding and radiotagged White Ibises (Eudocimus albus) and Great Egrets (Ardea alba) in the Florida Everglades, where fluctuation in food resources is pronounced because of seasonal drying and flooding. The White Ibis is a tactile "searcher" species in population decline that specializes on highly concentrated prey, whereas the Great Egret, in a growing population, is a visual "exploiter" species that requires lower prey concentrations. In a year with high food availability, resource-selection functions for both species included variables that changed over multiannual time scales and were associated with increased prey production. In a year with low food availability, resource-selection functions included short-term variables that concentrated prey (e.g., water recession rates and reversals in drying pattern), which suggests an adaptive response to poor foraging conditions. In both years, the White Ibis was more restricted in its use of habitats than the Great Egret. Real-time species-habitat suitability models were developed to monitor and assess the daily availability and quality of spatially explicit habitat resources for both species. The models, evaluated through hindcasting using independent observations, demonstrated that habitat use of the more specialized White Ibis was more accurately predicted than that of the more generalist Great Egret. ?? The American Ornithologists' Union, 2011.

  5. Solvent Dynamical Effects in Electron Transfer: Electrochemical-Exchange Kinetics of Sesquibicyclic Hydrazines as a Probe of Coupled Vibrational Activation

    Science.gov (United States)

    1992-10-01

    Wisconsin group shows that a significantly better correlation of the solvent-dependent kinetics are obtained with the Kosower Z parameter than with the...log kh1 for 1+/0 self exchange in nine solvents, including three alcohols, correlates linearly with the Kosower Z or the closely related E?(30

  6. Research on Economics and Management%Extension of Mundell-Fleming Model and RMB Exchange Rate Dynamics

    Institute of Scientific and Technical Information of China (English)

    赵志君; 李睿

    2016-01-01

    本文回顾了关于人民币汇率的几次大讨论,揭示了国际收支失衡背后的国际货币体系因素。针对蒙代尔-弗莱明模型不适合分析人民币汇率和国际收支失衡的现象,本文将蒙代尔-弗莱明模型扩展成一个两国模型,发现汇率与利率和收入之间存在的非线性关系能为国际收支和汇率长期失衡提供一种理论解释,大国应该采取浮动汇率制并有必要加强宏观政策协调。本文还用向量误差修正模型估计了人民币名义有效汇率和对美元汇率,发现当前两种汇率都处于高估状态,在未来一段时间人民币汇率有向下调整的压力。%This paper reviews several controversies over RMB exchange rates,and reveals the international monetary system background of persistent imbalances of international payments.In connection with that the situation that Mundell-Fleming model,designed for a single small economy under Bretton Woods System,is no longer relevant to analysing RMB exchange rate and imbalances of international payment,this paper extends Mundell-Fleming model to the one that includes two big countries,and finds that there is a nonlinear relationship among exchange rates,interest rates and income of two countries,which can provide another theoretical explanation for the deviation of exchange rate from its baseline and imbalances of international payment.Moreover,the paper believes that it is necessary to adopt flexible exchange rate regime and strengthen coordination of macroeconomic policies between big countries.Using the VEC model,this paper estimates both RMB nominal effective exchange rate and RMB-USD exchange rate,finding that both are currently overvalued and may experience depreciation for some time in the future.

  7. Uncovering the microscopic mechanism of strand exchange during RecA mediated homologous recombination using all-atom molecular dynamics simulations

    Science.gov (United States)

    Shankla, Manish; Yoo, Jejoong; Aksimentiev, Aleksei

    2012-02-01

    Homologous recombination (HR) is a key step during the repair process of double-stranded DNA (dsDNA) breakage. RecA is a protein that mediates HR in bacteria. RecA monomers polymerize on a single-stranded DNA (ssDNA) separated from the broken dsDNA to form a helical filament, thus allowing strand exchange to occur. Recent crystal structures depict each RecA monomer in contact with three contiguous nucleotides called DNA triplets. Surprisingly, the conformation of each triplet is similar to that of a triplet in B-form DNA. However, in the filament the neighboring triplets are separated by loops of the RecA proteins. Single molecule experiments demonstrated that strand exchange propagation occurs in 3 base-pair increments. However, the temporal resolution of the experiments was insufficient to determine the exact molecular mechanism of the triplet propagation. Using all-atom molecular dynamics simulations, we investigated the effect of both the RecA protein and the conformation of the bound ssDNA fragment on the stability of the duplex DNA intermediate formed during the strand-exchange process. Specifically, we report simulations of force-induced unzipping of duplex DNA in the presence and absence of the RecA filament that explored the effect of the triplet ladder conformation.

  8. Seasonal Dynamics of Phlebotomine Sand Fly Species Proven Vectors of Mediterranean Leishmaniasis Caused by Leishmania infantum.

    Directory of Open Access Journals (Sweden)

    Bulent Alten

    2016-02-01

    Full Text Available The recent geographical expansion of phlebotomine vectors of Leishmania infantum in the Mediterranean subregion has been attributed to ongoing climate changes. At these latitudes, the activity of sand flies is typically seasonal; because seasonal phenomena are also sensitive to general variations in climate, current phenological data sets can provide a baseline for continuing investigations on sand fly population dynamics that may impact on future scenarios of leishmaniasis transmission. With this aim, in 2011-2013 a consortium of partners from eight Mediterranean countries carried out entomological investigations in sites where L. infantum transmission was recently reported.A common protocol for sand fly collection included monthly captures by CDC light traps, complemented by sticky traps in most of the sites. Collections were replicated for more than one season in order to reduce the effects of local weather events. In each site, the trapping effort was left unchanged throughout the survey to legitimate inter-seasonal comparisons. Data from 99,000 collected specimens were analyzed, resulting in the description of seasonal dynamics of 56,000 sand flies belonging to L. infantum vector species throughout a wide geographical area, namely P. perniciosus (Portugal, Spain and Italy, P. ariasi (France, P. neglectus (Greece, P. tobbi (Cyprus and Turkey, P. balcanicus and P. kandelakii (Georgia. Time of sand fly appearance/disappearance in collections differed between sites, and seasonal densities showed variations in each site. Significant correlations were found between latitude/mean annual temperature of sites and i the first month of sand fly appearance, that ranged from early April to the first half of June; ii the type of density trend, varying from a single peak in July/August to multiple peaks increasing in magnitude from May through September. A 3-modal trend, recorded for P. tobbi in Cyprus, represents a novel finding for a L. infantum vector

  9. Seasonal Dynamics of Phlebotomine Sand Fly Species Proven Vectors of Mediterranean Leishmaniasis Caused by Leishmania infantum

    Science.gov (United States)

    Alten, Bulent; Maia, Carla; Afonso, Maria Odete; Campino, Lenea; Jiménez, Maribel; González, Estela; Molina, Ricardo; Bañuls, Anne Laure; Prudhomme, Jorian; Vergnes, Baptiste; Toty, Celine; Cassan, Cécile; Rahola, Nil; Thierry, Magali; Sereno, Denis; Bongiorno, Gioia; Bianchi, Riccardo; Khoury, Cristina; Tsirigotakis, Nikolaos; Dokianakis, Emmanouil; Antoniou, Maria; Christodoulou, Vasiliki; Mazeris, Apostolos; Karakus, Mehmet; Ozbel, Yusuf; Arserim, Suha K.; Erisoz Kasap, Ozge; Gunay, Filiz; Oguz, Gizem; Kaynas, Sinan; Tsertsvadze, Nikoloz; Tskhvaradze, Lamzira; Gramiccia, Marina; Volf, Petr; Gradoni, Luigi

    2016-01-01

    Background The recent geographical expansion of phlebotomine vectors of Leishmania infantum in the Mediterranean subregion has been attributed to ongoing climate changes. At these latitudes, the activity of sand flies is typically seasonal; because seasonal phenomena are also sensitive to general variations in climate, current phenological data sets can provide a baseline for continuing investigations on sand fly population dynamics that may impact on future scenarios of leishmaniasis transmission. With this aim, in 2011–2013 a consortium of partners from eight Mediterranean countries carried out entomological investigations in sites where L. infantum transmission was recently reported. Methods/Principal Findings A common protocol for sand fly collection included monthly captures by CDC light traps, complemented by sticky traps in most of the sites. Collections were replicated for more than one season in order to reduce the effects of local weather events. In each site, the trapping effort was left unchanged throughout the survey to legitimate inter-seasonal comparisons. Data from 99,000 collected specimens were analyzed, resulting in the description of seasonal dynamics of 56,000 sand flies belonging to L. infantum vector species throughout a wide geographical area, namely P. perniciosus (Portugal, Spain and Italy), P. ariasi (France), P. neglectus (Greece), P. tobbi (Cyprus and Turkey), P. balcanicus and P. kandelakii (Georgia). Time of sand fly appearance/disappearance in collections differed between sites, and seasonal densities showed variations in each site. Significant correlations were found between latitude/mean annual temperature of sites and i) the first month of sand fly appearance, that ranged from early April to the first half of June; ii) the type of density trend, varying from a single peak in July/August to multiple peaks increasing in magnitude from May through September. A 3-modal trend, recorded for P. tobbi in Cyprus, represents a novel

  10. Microbial species diversity, community dynamics, and metabolite kinetics of water kefir fermentation

    National Research Council Canada - National Science Library

    Laureys, David; De Vuyst, Luc

    2014-01-01

    .... The most important microbial species present were Lactobacillus casei/paracasei, Lactobacillus harbinensis, Lactobacillus hilgardii, Bifidobacterium psychraerophilum/crudilactis, Saccharomyces...

  11. The dynamic chamber method: trace gas exchange fluxes (NO, NO2, O3 between plants and the atmosphere in the laboratory and in the field

    Directory of Open Access Journals (Sweden)

    F. X. Meixner

    2012-05-01

    Full Text Available We describe a dynamic chamber system to determine reactive trace gas exchange fluxes between plants and the atmosphere under laboratory and, with small modifications, also under field conditions. The system allows measurements of the flux density of the reactive NO-NO2-O3 triad and additionally of the non-reactive trace gases CO2 and H2O. The chambers are made of transparent and chemically inert wall material and do not disturb plant physiology. For NO2 detection we used a highly NO2 specific blue light converter coupled to chemiluminescence detection of the photolysis product, NO. Exchange flux densities derived from dynamic chamber measurements are based on very small concentration differences of NO2 (NO, O3 between inlet and outlet of the chamber. High accuracy and precision measurements are therefore required, and high instrument sensitivity (limit of detection and the statistical significance of concentration differences are important for the determination of corresponding exchange flux densities, compensation point concentrations, and deposition velocities. The determination of NO2 concentrations at sub-ppb levels (2 analyzer with a lower detection limit (3σ-definition of 0.3 ppb or better. Deposition velocities and compensation point concentrations were determined by bi-variate weighted linear least-squares fitting regression analysis of the trace gas concentrations, measured at the inlet and outlet of the chamber. Performances of the dynamic chamber system and data analysis are demonstrated by studies of Picea abies L. (Norway Spruce under field and laboratory conditions. Our laboratory data show that the quality selection criterion based on the use of only significant NO2 concentration differences has a considerable impact on the resulting compensation point concentrations yielding values closer to zero. The results of field experiments demonstrate the need to consider photo-chemical reactions of NO, NO2, and O3 inside the chamber for

  12. Effects of pressure, temperature and atomic exchanges on phase separation dynamics in Au/Ni(111) surface alloy: Kinetic Monte Carlo study

    Energy Technology Data Exchange (ETDEWEB)

    Zvejnieks, G. [Institute for Solid State Physics, University of Latvia, Kengaraga 8, LV-1063 Riga (Latvia); Ibenskas, A., E-mail: ibenskas@pfi.lt [Center for Physical Sciences and Technology, Semiconductor Physics Institute, Gostauto 11, LT-01108 Vilnius (Lithuania); Tornau, E.E. [Center for Physical Sciences and Technology, Semiconductor Physics Institute, Gostauto 11, LT-01108 Vilnius (Lithuania)

    2015-11-15

    Instability of the Au/Ni(111) surface alloy is studied in different CO gas pressure, p, and temperature limits using kinetic Monte Carlo simulations. We analyze the reaction front dynamics and formation of Au clusters using the model which takes into account surface adatom pair and three-body interactions, CO adsorption and desorption, catalytic carbonyl formation reaction, Au and Ni adatom diffusion and their concerted exchange. Variation of interaction parameters allows us to identify three possible reaction front propagation limits with different pressure dependencies: (i) slow channel-like flow in agreement with experimental data [1] (step flow rate, R, increases with p), (ii) intermediate regime (weak p–dependence), and (iii) fast homogeneous flow (R decreases with p). We find that only Au–Ni exchange, contrary to both Ni–CO and Au–CO exchanges, significantly reduces the number of screened Ni atoms inside the Au clusters and stimulates the occurrence of Ni-free Au clusters. The size of Au islands depends on both pressure and temperature. At a fixed temperature it decreases with pressure due to an increased step flow rate. In the high temperature limit, despite the step flow rate exponential increase with temperature, the cluster size increases due to an enhanced Au mobility. - Highlights: • Kinetic Monte Carlo study of Au–Ni surface alloy instability to CO pressure and temperature. • Three reaction front propagation regimes. • In channel-like regime, the step flow rate increases with CO pressure as in experiment. • Ni-free Au islands are obtained when Au-Ni adatom exchange mechanism is considered. • The size of Au islands decreases with pressure and increases with temperature.

  13. The Constant Parameter Output of Heat Exchangers During Dynamic Processes%换热器动态过程中的定常输出

    Institute of Scientific and Technical Information of China (English)

    汤盛; 李科群

    2012-01-01

    为了使换热器在动态过程中保持目标出口参数的恒定,从整体系统考虑建立了换热器动态过程的数学模型,采用I.aplace变换及其逆变换推导了换热器出口温度响应的分析解,并在一个或者多个进口参数阶跃变化的情况下,推导了两股流换热器和多股流换热器的调节方法.结果表明:在动态过程中,通过对换热器进口参数的调节可以精确地控制换热器出口参数,保证换热器的稳定和安全运行.%To keep the target output parameters of various heat exchangers constant during dynamic proces- ses, a mathematical model has been set up from an integral standpoint, with which analytical solutions of the outlet temperature responses were calculated by using Laplace and inverse Laplace transform, while an adjustment method deduced for target output parameters of two- and multi stream heat exchangers with step changes of one or more inlet parameters. Results show that the output parameters of heat exchanger can be accurately controlled by adjusting the inlet parameters, so as to secure the operation stability and safety of heat exchangers.

  14. Fine-scale population dynamics in a marine fish species inferred from dynamic state-space models.

    Science.gov (United States)

    Rogers, Lauren A; Storvik, Geir O; Knutsen, Halvor; Olsen, Esben M; Stenseth, Nils C

    2017-07-01

    Identifying the spatial scale of population structuring is critical for the conservation of natural populations and for drawing accurate ecological inferences. However, population studies often use spatially aggregated data to draw inferences about population trends and drivers, potentially masking ecologically relevant population sub-structure and dynamics. The goals of this study were to investigate how population dynamics models with and without spatial structure affect inferences on population trends and the identification of intrinsic drivers of population dynamics (e.g. density dependence). Specifically, we developed dynamic, age-structured, state-space models to test different hypotheses regarding the spatial structure of a population complex of coastal Atlantic cod (Gadus morhua). Data were from a 93-year survey of juvenile (age 0 and 1) cod sampled along >200 km of the Norwegian Skagerrak coast. We compared two models: one which assumes all sampled cod belong to one larger population, and a second which assumes that each fjord contains a unique population with locally determined dynamics. Using the best supported model, we then reconstructed the historical spatial and temporal dynamics of Skagerrak coastal cod. Cross-validation showed that the spatially structured model with local dynamics had better predictive ability. Furthermore, posterior predictive checks showed that a model which assumes one homogeneous population failed to capture the spatial correlation pattern present in the survey data. The spatially structured model indicated that population trends differed markedly among fjords, as did estimates of population parameters including density-dependent survival. Recent biomass was estimated to be at a near-record low all along the coast, but the finer scale model indicated that the decline occurred at different times in different regions. Warm temperatures were associated with poor recruitment, but local changes in habitat and fishing pressure may

  15. A Hamiltonian replica exchange molecular dynamics (MD) method for the study of folding, based on the analysis of the stabilization determinants of proteins.

    Science.gov (United States)

    Meli, Massimiliano; Colombo, Giorgio

    2013-06-06

    Herein, we present a novel Hamiltonian replica exchange protocol for classical molecular dynamics simulations of protein folding/unfolding. The scheme starts from the analysis of the energy-networks responsible for the stabilization of the folded conformation, by means of the energy-decomposition approach. In this framework, the compact energetic map of the native state is generated by a preliminary short molecular dynamics (MD) simulation of the protein in explicit solvent. This map is simplified by means of an eigenvalue decomposition. The highest components of the eigenvector associated with the lowest eigenvalue indicate which sites, named "hot spots", are likely to be responsible for the stability and correct folding of the protein. In the Hamiltonian replica exchange protocol, we use modified force-field parameters to treat the interparticle non-bonded potentials of the hot spots within the protein and between protein and solvent atoms, leaving unperturbed those relative to all other residues, as well as solvent-solvent interactions. We show that it is possible to reversibly simulate the folding/unfolding behavior of two test proteins, namely Villin HeadPiece HP35 (35 residues) and Protein A (62 residues), using a limited number of replicas. We next discuss possible implications for the study of folding mechanisms via all atom simulations.

  16. A Hamiltonian Replica Exchange Molecular Dynamics (MD Method for the Study of Folding, Based on the Analysis of the Stabilization Determinants of Proteins

    Directory of Open Access Journals (Sweden)

    Massimiliano Meli

    2013-06-01

    Full Text Available Herein, we present a novel Hamiltonian replica exchange protocol for classical molecular dynamics simulations of protein folding/unfolding. The scheme starts from the analysis of the energy-networks responsible for the stabilization of the folded conformation, by means of the energy-decomposition approach. In this framework, the compact energetic map of the native state is generated by a preliminary short molecular dynamics (MD simulation of the protein in explicit solvent. This map is simplified by means of an eigenvalue decomposition. The highest components of the eigenvector associated with the lowest eigenvalue indicate which sites, named “hot spots”, are likely to be responsible for the stability and correct folding of the protein. In the Hamiltonian replica exchange protocol, we use modified force-field parameters to treat the interparticle non-bonded potentials of the hot spots within the protein and between protein and solvent atoms, leaving unperturbed those relative to all other residues, as well as solvent-solvent interactions. We show that it is possible to reversibly simulate the folding/unfolding behavior of two test proteins, namely Villin HeadPiece HP35 (35 residues and Protein A (62 residues, using a limited number of replicas. We next discuss possible implications for the study of folding mechanisms via all atom simulations.

  17. Scaling up of Carbon Exchange Dynamics from AmeriFlux Sites to a Super-Region in the Eastern United States

    Energy Technology Data Exchange (ETDEWEB)

    Hans Peter Schmid; Craig Wayson

    2009-05-05

    The primary objective of this project was to evaluate carbon exchange dynamics across a region of North America between the Great Plains and the East Coast. This region contains about 40 active carbon cycle research (AmeriFlux) sites in a variety of climatic and landuse settings, from upland forest to urban development. The core research involved a scaling strategy that uses measured fluxes of CO{sub 2}, energy, water, and other biophysical and biometric parameters to train and calibrate surface-vegetation-atmosphere models, in conjunction with satellite (MODIS) derived drivers. To achieve matching of measured and modeled fluxes, the ecosystem parameters of the models will be adjusted to the dynamically variable flux-tower footprints following Schmid (1997). High-resolution vegetation index variations around the flux sites have been derived from Landsat data for this purpose. The calibrated models are being used in conjunction with MODIS data, atmospheric re-analysis data, and digital land-cover databases to derive ecosystem exchange fluxes over the study domain.

  18. Dynamics of Gas Exchange through the Fractal Architecture of the Human Lung, Modeled as an Exactly Solvable Hierarchical Tree

    Science.gov (United States)

    Mayo, Michael; Pfeifer, Peter; Gheorghiu, Stefan

    2008-03-01

    The acinar airways lie at the periphery of the human lung and are responsible for the transfer of oxygen from air to the blood during respiration. This transfer occurs by the diffusion-reaction of oxygen over the irregular surface of the alveolar membranes lining the acinar airways. We present an exactly solvable diffusion-reaction model on a hierarchically branched tree, allowing a quantitative prediction of the oxygen current over the entire system of acinar airways responsible for the gas exchange. We discuss the effect of diffusional screening, which is strongly coupled to oxygen transport in the human lung. We show that the oxygen current is insensitive to a loss of permeability of the alveolar membranes over a wide range of permeabilities, similar to a ``constant-current source'' in an electric network. Such fault tolerance has been observed in other treatments of the gas exchange in the lung and is obtained here as a fully analytical result.

  19. Seasonal dynamics, age structure and reproduction of four Carabus species (Coleoptera: Carabidae) living in forested landscapes in Hungary

    DEFF Research Database (Denmark)

    Kádár, Ferenc; Fazekas, Judit P.; Sárospataki, Miklós;

    2015-01-01

    Seasonal dynamics and reproductive phenological parameters of four Carabus species (C. convexus, C. coriaceus, C. germarii and C. hortensis) common in Hungary were studied by pitfall trapping and dissection. Beetles were collected in an abandoned apple orchard and in the bordering oak forest near...... Budapest (Central Hungary), in 1988–1991. The sex ratio was male-dominated, but this was significant only for C. coriaceus. The catch of C. germarii adults showed relatively short activity period with unimodal curve, but activity was longer and bimodal for the other three species. Adults of C. germarii...

  20. The invasive species Ulex europaeus (Fabaceae) shows high dynamism in a fragmented landscape of south-central Chile.

    Science.gov (United States)

    Altamirano, Adison; Cely, Jenny Paola; Etter, Andrés; Miranda, Alejandro; Fuentes-Ramirez, Andres; Acevedo, Patricio; Salas, Christian; Vargas, Rodrigo

    2016-08-01

    Ulex europaeus (gorse) is an invasive shrub deemed as one of the most invasive species in the world. U. europaeus is widely distributed in the south-central area of Chile, which is considered a world hotspot for biodiversity conservation. In addition to its negative effects on the biodiversity of natural ecosystems, U. europaeus is one of the most severe pests for agriculture and forestry. Despite its importance as an invasive species, U. europaeus has been little studied. Although information exists on the potential distribution of the species, the interaction of the invasion process with the spatial dynamic of the landscape and the landscape-scale factors that control the presence or absence of the species is still lacking. We studied the spatial and temporal dynamics of the landscape and how these relate to U. europaeus invasion in south-central Chile. We used supervised classification of satellite images to determine the spatial distribution of the species and other land covers for the years 1986 and 2003, analysing the transitions between the different land covers. We used logistic regression for modelling the increase, decrease and permanence of U. europaeus invasion considering landscape variables. Results showed that the species covers only around 1 % of the study area and showed a 42 % reduction in area for the studied period. However, U. europaeus was the cover type which presented the greatest dynamism in the landscape. We found a strong relationship between changes in land cover and the invasion process, especially connected with forest plantations of exotic species, which promotes the displacement of U. europaeus. The model of gorse cover increase presented the best performance, and the most important predictors were distance to seed source and landscape complexity index. Our model predicted high spread potential of U. europaeus in areas of high conservation value. We conclude that proper management for this invasive species must take into account

  1. Thermochemistry and Dynamics of Reactive Species: Nitrogen-rich Compounds, Metals and SiC Clusters in Free and Solvated Environment

    Science.gov (United States)

    2005-10-31

    of Reactive Species : Nitrogen-rich F49620-02-1-0371 Compounds, Metals and SiC clusters in Free and Solvated Environments Sb. GRANT NUMBER 5c. PROGRAM...F49620-02-1-0371 Thermochemistry and Dynamics of Reactive Species : Nitrogen-rich Compounds, Metals, and SiC clusters in Free and Solvated Environments...research program remain the same as before: obtaining fundamental thermochemical and dynamical data on reactive species Status of Effort This report

  2. Effective carrying capacity and analytical solution of a particular case of the Richards-like two-species population dynamics model

    Science.gov (United States)

    Cabella, Brenno Caetano Troca; Ribeiro, Fabiano; Martinez, Alexandre Souto

    2012-02-01

    We consider a generalized two-species population dynamic model and analytically solve it for the amensalism and commensalism ecological interactions. These two-species models can be simplified to a one-species model with a time dependent extrinsic growth factor. With a one-species model with an effective carrying capacity one is able to retrieve the steady state solutions of the previous one-species model. The equivalence obtained between the effective carrying capacity and the extrinsic growth factor is complete only for a particular case, the Gompertz model. Here we unveil important aspects of sigmoid growth curves, which are relevant to growth processes and population dynamics.

  3. A high-throughput detection method for invasive fruit fly (Diptera: Tephritidae) species based on microfluidic dynamic array.

    Science.gov (United States)

    Jiang, Fan; Fu, Wei; Clarke, Anthony R; Schutze, Mark Kurt; Susanto, Agus; Zhu, Shuifang; Li, Zhihong

    2016-11-01

    Invasive species can be detrimental to a nation's ecology, economy and human health. Rapid and accurate diagnostics are critical to limit the establishment and spread of exotic organisms. The increasing rate of biological invasions relative to the taxonomic expertise available generates a demand for high-throughput, DNA-based diagnostics methods for identification. We designed species-specific qPCR primer and probe combinations for 27 economically important tephritidae species in six genera (Anastrepha, Bactrocera, Carpomya, Ceratitis, Dacus and Rhagoletis) based on 935 COI DNA barcode haplotypes from 181 fruit fly species publically available in BOLD, and then tested the specificity for each primer pair and probe through qPCR of 35 of those species. We then developed a standardization reaction system for detecting the 27 target species based on a microfluidic dynamic array and also applied the method to identify unknown immature samples from port interceptions and field monitoring. This method led to a specific and simultaneous detection for all 27 species in 7.5 h, using only 0.2 μL of reaction system in each reaction chamber. The approach successfully discriminated among species within complexes that had genetic similarities of up to 98.48%, while it also identified all immature samples consistent with the subsequent results of morphological examination of adults which were reared from larvae of cohorts from the same samples. We present an accurate, rapid and high-throughput innovative approach for detecting fruit flies of quarantine concern. This is a new method which has broad potential to be one of international standards for plant quarantine and invasive species detection. © 2016 John Wiley & Sons Ltd.

  4. The seabird paradox: dispersal, genetic structure and population dynamics in a highly mobile, but philopatric albatross species.

    Science.gov (United States)

    Milot, Emmanuel; Weimerskirch, Henri; Bernatchez, Louis

    2008-04-01

    The philopatric behaviour of albatrosses has intrigued biologists due to the high mobility of these seabirds. It is unknown how albatrosses maintain a system of fragmented populations without frequent dispersal movements, in spite of the long-term temporal heterogeneity in resource distribution at sea. We used both genetic (amplified fragment length polymorphism) and capture-mark-recapture (CMR) data to identify explicitly which among several models of population dynamics best applies to the wandering albatross (Diomedea exulans) and to test for migration-drift equilibrium. We previously documented an extremely low genetic diversity in this species. Here, we show that populations exhibit little genetic differentiation across the species' range (Theta(B) albatross. Yet, our data suggest that several other factors including ongoing gene flow, recurrent long-distance dispersal and source-sink dynamics have contributed to different extent in shaping the genetic signature observed in this species. Our results show that an absence of genetic structuring may in itself reveal little about the true population dynamics in seabirds, but can provide insights into important processes when a comparison with other information, such as demographic data, is possible.

  5. Dynamical Decomposition of Multifractal Time Series as Fractal Evolution and Long-Term Cycles: Applications to Foreign Currency Exchange Market

    Science.gov (United States)

    Turiel, A.; Perez-Vicente, C.

    The application of the multifractal formalism to the study of some time series with scale invariant evolution has given rise to a rich framework of models and processing tools for the analysis of these signals. The formalism has been successfully exploited in different ways and with different goals: to obtain the effective variables governing the evolution of the series, to predict its future evolution, to estimate in which regime the series are, etc. In this paper, we discuss on the capabilities of a new, powerful processing tool, namely the computation of dynamical sources. With the aid of the source field, we will separate the fast, chaotic dynamics defined by the multifractal structure from a new, so-far unknown slow dynamics which concerns long cycles in the series. We discuss the results on the perspective of detection of sharp dynamic changes and forecasting.

  6. Effects of glacier runoff and wind on surface layer dynamics and Atlantic Water exchange in Kongsfjorden, Svalbard; a model study

    Science.gov (United States)

    Sundfjord, A.; Albretsen, J.; Kasajima, Y.; Skogseth, R.; Kohler, J.; Nuth, C.; Skarðhamar, J.; Cottier, F.; Nilsen, F.; Asplin, L.; Gerland, S.; Torsvik, T.

    2017-03-01

    A high resolution numerical ocean circulation model has been used to investigate exchange mechanisms and transport of thermal energy towards the inner part of Kongsfjorden, Svalbard; a location where tidewater glaciers expose large calving fronts to the ocean water and sea ice has been a regular winter feature until recently. Comparison of model simulations against a large set of observational data shows that the model captures the main features of seasonality and geographical distribution of hydrography. The model is able to simulate inflow of Atlantic Water although the timing, strength and depth of inflow events are not always the same in the model as in mooring records. The model shows water entering via the shelf consistently penetrating deep into the fjord, and volume transport toward the interior parts are large even under winter conditions. Heat transports are smaller in winter than in summer due to generally lower winter temperatures. Results indicate that glacial freshwater discharge in the surface layer is not a necessary factor for driving sub-surface exchange; rather, along-fjord winds stand out as important for the circulation and hence water exchange in the inner part of the fjord. The combination of inflow of Atlantic Water from the outer shelf into the central part of the fjord, and further transport of mixed water masses with intermediate heat content toward the inner part, constitutes a significant transfer of thermal energy from the outer shelf and deep into the fjord. The potential for glacier front melting is larger in summer than in winter as heat transports are larger this time of year, while even modest heat transports in the upper part of the water column may influence the sea ice cover in winter.

  7. Structure and water exchange dynamics of hydrated oxo halo ions in aqueous solution using QMCF MD simulation, large angle X-ray scattering and EXAFS

    Science.gov (United States)

    Eklund, Lars; Hofer, Tomas S.

    2014-01-01

    Theoretical ab initio quantum mechanical charge field molecular dynamics (QMCF MD) has been applied in conjunction with experimental large angle X-ray scattering (LAXS) and EXAFS measurements to study structure and dynamics of the hydrated oxo chloro anions chlorite, ClO2−, chlorate, ClO3−, and perchlorate, ClO4−. In addition, the structures of the hydrated hypochlorite, ClO−, bromate, BrO3−, iodate, IO3− and metaperiodate, IO4−, ions have been determined in aqueous solution by means of LAXS. The structures of the bromate, metaperiodate, and orthoperiodate, H2IO63−, ions have been determined by EXAFS as solid sodium salts and in aqueous solution as well. The results show clearly that the only form of periodate present in aqueous solution is metaperiodate. The Cl-O bond distances in the hydrated oxo chloro anions as determined by LAXS and obtained in the QMCF MD simulations are in excellent agreement, being 0.01–0.02 Å longer than in solid anhydrous salts due to hydration through hydrogen bonding to water molecules. The oxo halo anions, all with unit negative charge, have low charge density making them typical structure breakers, thus the hydrogen bonds formed to the hydrating water molecules are weaker and more short-lived than those between water molecules in pure water. The water exchange mechanism of the oxo chloro anions resembles those of the oxo sulfur anions with a direct exchange at the oxygen atoms for perchlorate and sulfate. The water exchange rate for the perchlorate ion is significantly faster, τ0.5=1.4 ps, compared to the hydrated sulfate ion and pure water, τ0.5=2.6 and 1.7 ps, respectively. The angular radial distribution functions show that the chlorate and sulfite ions have a more complex water exchange mechanism. As the chlorite and chlorate ions are more weakly hydrated than the sulfite ion the spatial occupancy is less well-defined and it is not possible to follow any well-defined migration pattern as it is difficult to

  8. The dynamic chamber method: trace gas exchange fluxes (NO, NO2, O3) between plants and the atmosphere in the laboratory and in the field

    Science.gov (United States)

    Breuninger, C.; Oswald, R.; Kesselmeier, J.; Meixner, F. X.

    2012-05-01

    We describe a dynamic chamber system to determine reactive trace gas exchange fluxes between plants and the atmosphere under laboratory and, with small modifications, also under field conditions. The system allows measurements of the flux density of the reactive NO-NO2-O3 triad and additionally of the non-reactive trace gases CO2 and H2O. The chambers are made of transparent and chemically inert wall material and do not disturb plant physiology. For NO2 detection we used a highly NO2 specific blue light converter coupled to chemiluminescence detection of the photolysis product, NO. Exchange flux densities derived from dynamic chamber measurements are based on very small concentration differences of NO2 (NO, O3) between inlet and outlet of the chamber. High accuracy and precision measurements are therefore required, and high instrument sensitivity (limit of detection) and the statistical significance of concentration differences are important for the determination of corresponding exchange flux densities, compensation point concentrations, and deposition velocities. The determination of NO2 concentrations at sub-ppb levels (data analysis are demonstrated by studies of Picea abies L. (Norway Spruce) under field and laboratory conditions. Our laboratory data show that the quality selection criterion based on the use of only significant NO2 concentration differences has a considerable impact on the resulting compensation point concentrations yielding values closer to zero. The results of field experiments demonstrate the need to consider photo-chemical reactions of NO, NO2, and O3 inside the chamber for the correct determination of the exchange flux densities, deposition velocities, as well as compensation point concentrations. Under our field conditions NO2 deposition velocities would have been overestimated up to 80%, if NO2 photolysis has not been considered. We also quantified the photolysis component for some previous NO2 flux measurements. Neglecting photo

  9. Vegetation development following stream/river restoration: more natural fluvial dynamics and morphology, return of aquatic and riparian plant species?

    Science.gov (United States)

    Soons, M. B.

    2012-04-01

    After centuries of human interventions in stream/river dynamics and morphology aimed at optimizing landscapes for agricultural and industrial purposes, new insights have inspired water managers to try and combine stream and river ecosystem functions with the conservation of biodiversity. Around the world, aquatic and riparian species have declined strongly due to pollution, destruction and fragmentation of their habitat, so that biodiversity conservation initiatives primarily focus on habitat restoration. In the past decades many stream and river restoration projects have been carried out and often hydrological dynamics and morphology have been restored to a more natural state. However, the successful restoration of aquatic and riparian habitats very often failed to result in restoration of their biodiversity. This lack of success from a biodiversity conservation perspective is usually attributed to 'dispersal limitation', meaning that the habitat may be restored, but species fail to reach the site and re-colonize it. Especially re-colonization by aquatic and riparian plant species is important, as such species function as ecosystem engineers: their presence alters fluvial dynamics and morphology, generates additional habitat heterogeneity and provides habitat and food for animal species. Following minor disturbances, re-colonization is often possible through locally remaining populations, by seeds in the seed bank or by surviving plant fragments. However, following major disturbances, colonization and establishment from other source populations are necessary. This usually occurs through dispersal of seeds (and in more aquatic species also by dispersal of vegetative fragments) into the restored wetland area. As dispersal occurs predominantly over short distances and source populations of aquatic and riparian species may be lacking in the surroundings, dispersal may be a limiting factor in the development of aquatic and riparian vegetation at a restored site. But

  10. Studies on cambial activity: advances and challenges in the knowledge of growth dynamics of Brazilian woody species

    Directory of Open Access Journals (Sweden)

    CÁTIA H. CALLADO

    2014-03-01

    Full Text Available The lack of specific research on the sequence of events that determine plant growth from meristem until wood formation represents a gap in the knowledge of growth dynamics in woody species. In this work, we surveyed published studies concerning cambial activity of Brazilian native species aiming at allowing the comparison of applied methods and obtained results. The annual cambial seasonality was observed in all the investigated species. Nevertheless, we found high heterogeneity in the used methodologies. As a result from this analysis, our opinion points to the need for standardizing sampling protocols and for discussing the suitability of experimental designs. This will help to define with greater precision the factors that determine the radial growth in the different tropical ecosystems.

  11. Species-specific flight styles of flies are reflected in the response dynamics of a homologue motion sensitive neuron

    Directory of Open Access Journals (Sweden)

    Bart eGeurten

    2012-03-01

    Full Text Available Hoverflies and blowflies have distinctly different flight styles. Yet, both species have been shown to structure their flight behaviour in a way that facilitates extraction of 3D information from the image flow on the retina (optic flow. Neuronal candidates to analyse the optic flow are the tangential cells in the third optical ganglion – the lobula complex. These neurons are directionally selective and integrate the optic flow over large parts of the visual field. Homologue tangential cells in hoverflies and blowflies have a similar morphology. Because blowflies and hoverflies have similar neuronal layout but distinctly different flight behaviours, they are an ideal substrate to pinpoint potential neuronal adaptations to the different flight styles.In this article we describe the relationship between locomotion behaviour and motion vision on three different levels:1.We compare the different flight styles based on the categorisation of flight behaviour into prototypical movements.2.We measure the species specific dynamics of the optic flow under naturalistic flight conditions. We found the translational optic flow of both species to be very different.3.We describe possible adaptations of a homologue motion sensitive neuron. We stimulate this cell in blowflies (Calliphora and hoverflies (Eristalis with naturalistic optic flow generated by both species during free flight. The characterized hoverfly tangential cell responds faster to transient changes in the optic flow than its blowfly homologue. It is discussed whether and how the different dynamical response properties aid optic flow analysis.

  12. Empirical phylogenies and species abundance distributions are consistent with pre-equilibrium dynamics of neutral community models with gene flow

    KAUST Repository

    Bonnet-Lebrun, Anne-Sophie

    2017-03-17

    Community characteristics reflect past ecological and evolutionary dynamics. Here, we investigate whether it is possible to obtain realistically shaped modelled communities - i.e., with phylogenetic trees and species abundance distributions shaped similarly to typical empirical bird and mammal communities - from neutral community models. To test the effect of gene flow, we contrasted two spatially explicit individual-based neutral models: one with protracted speciation, delayed by gene flow, and one with point mutation speciation, unaffected by gene flow. The former produced more realistic communities (shape of phylogenetic tree and species-abundance distribution), consistent with gene flow being a key process in macro-evolutionary dynamics. Earlier models struggled to capture the empirically observed branching tempo in phylogenetic trees, as measured by the gamma statistic. We show that the low gamma values typical of empirical trees can be obtained in models with protracted speciation, in pre-equilibrium communities developing from an initially abundant and widespread species. This was even more so in communities sampled incompletely, particularly if the unknown species are the youngest. Overall, our results demonstrate that the characteristics of empirical communities that we have studied can, to a large extent, be explained through a purely neutral model under pre-equilibrium conditions. This article is protected by copyright. All rights reserved.

  13. Large-scale synchrony of gap dynamics and the distribution of understory tree species in maple-beech forests.

    Science.gov (United States)

    Gravel, Dominique; Beaudet, Marilou; Messier, Christian

    2010-01-01

    Large-scale synchronous variations in community dynamics are well documented for a vast array of organisms, but are considerably less understood for forest trees. Because of temporal variations in canopy gap dynamics, forest communities-even old-growth ones-are never at equilibrium at the stand scale. This paucity of equilibrium may also be true at the regional scale. Our objectives were to determine (1) if nonequilibrium dynamics caused by temporal variations in the formation of canopy gaps are regionally synchronized, and (2) if spatiotemporal variations in canopy gap formation affect the relative abundance of tree species in the understory. We examined these questions by analyzing variations in the suppression and release history of Acer saccharum Marsh. and Fagus grandifolia Ehrh. from 481 growth series of understory saplings taken from 34 mature stands. We observed that (1) the proportion of stems in release as a function of time exhibited a U-shaped pattern over the last 35 years, with the lowest levels occurring during 1975-1985, and that (2) the response to this in terms of species composition was that A. saccharum became more abundant at sites that had the highest proportion of stems in release during 1975-1985. We concluded that the understory dynamics, typically thought of as a stand-scale process, may be regionally synchronized.

  14. Species-specific earthworm population responses in relation to flooding dynamics in a Dutch floodplain soil

    NARCIS (Netherlands)

    Zorn, M.I.; Gestel, van C.A.M.; Eijsackers, H.J.P.

    2005-01-01

    Earthworms dominate the animal biomass in moist floodplain soils. They are known to survive long periods in aerated water, but little is known about earthworm population dynamics in floodplain systems with changing inundation frequencies. This study determined earthworm population dynamics in a floo

  15. Evolutionary dynamics of microsatellite distribution in plants: insight from the comparison of sequenced brassica, Arabidopsis and other angiosperm species.

    Directory of Open Access Journals (Sweden)

    Jiaqin Shi

    Full Text Available Despite their ubiquity and functional importance, microsatellites have been largely ignored in comparative genomics, mostly due to the lack of genomic information. In the current study, microsatellite distribution was characterized and compared in the whole genomes and both the coding and non-coding DNA sequences of the sequenced Brassica, Arabidopsis and other angiosperm species to investigate their evolutionary dynamics in plants. The variation in the microsatellite frequencies of these angiosperm species was much smaller than those for their microsatellite numbers and genome sizes, suggesting that microsatellite frequency may be relatively stable in plants. The microsatellite frequencies of these angiosperm species were significantly negatively correlated with both their genome sizes and transposable elements contents. The pattern of microsatellite distribution may differ according to the different genomic regions (such as coding and non-coding sequences. The observed differences in many important microsatellite characteristics (especially the distribution with respect to motif length, type and repeat number of these angiosperm species were generally accordant with their phylogenetic distance, which suggested that the evolutionary dynamics of microsatellite distribution may be generally consistent with plant divergence/evolution. Importantly, by comparing these microsatellite characteristics (especially the distribution with respect to motif type the angiosperm species (aside from a few species all clustered into two obviously different groups that were largely represented by monocots and dicots, suggesting a complex and generally dichotomous evolutionary pattern of microsatellite distribution in angiosperms. Polyploidy may lead to a slight increase in microsatellite frequency in the coding sequences and a significant decrease in microsatellite frequency in the whole genome/non-coding sequences, but have little effect on the microsatellite

  16. Remote-Sensed Monitoring of Dominant Plant Species Distribution and Dynamics at Jiuduansha Wetland in Shanghai, China

    Directory of Open Access Journals (Sweden)

    Wenpeng Lin

    2015-08-01

    Full Text Available Spartina alterniflora is one of the most hazardous invasive plant species in China. Monitoring the changes in dominant plant species can help identify the invasion mechanisms of S. alterniflora, thereby providing scientific guidelines on managing or controlling the spreading of this invasive species at Jiuduansha Wetland in Shanghai, China. However, because of the complex terrain and the inaccessibility of tidal wetlands, it is very difficult to conduct field experiments on a large scale in this wetland. Hence, remote sensing plays an important role in monitoring the dynamics of plant species and its distribution on both spatial and temporal scales. In this study, based on multi-spectral and high resolution (<10 m remote sensing images and field observational data, we analyzed spectral characteristics of four dominant plant species at different green-up phenophases. Based on the difference in spectral characteristics, a decision tree classification was built for identifying the distribution of these plant species. The results indicated that the overall classification accuracy for plant species was 87.17%, and the Kappa Coefficient was 0.81, implying that our classification method could effectively identify the four plant species. We found that the area of Phragmites australi showed an increasing trend from 1997 to 2004 and from 2004 to 2012, with an annual spreading rate of 33.77% and 31.92%, respectively. The area of Scirpus mariqueter displayed an increasing trend from 1997 to 2004 (12.16% per year and a decreasing trend from 2004 to 2012 (−7.05% per year. S. alterniflora has the biggest area (3302.20 ha as compared to other species, accounting for 51% of total vegetated area at the study region in 2012. It showed an increasing trend from 1997 to 2004 and from 2004 to 2012, with an annual spreading rate of 130.63% and 28.11%, respectively. As a result, the native species P. australi was surrounded and the habitats of S. mariqueter were

  17. Hydrological exchanges and Organic Matter dynamics in highly vulnerable tidal wetland ecosystems at the land-ocean interface

    Science.gov (United States)

    Tzortziou, M.; Neale, P.; Megonigal, P.; Loughner, C.

    2014-12-01

    Occupying a critical interface between the land and the sea, tidal wetlands are amongst the most ecologically valuable and economically important ecosystems on Earth, but also especially vulnerable to human pressures and climate change. These rich in biodiversity and highly productive ecosystems are hot spots of biogeochemical transformations, consistently exchanging Organic Matter with adjacent estuarine waters through tidal flushing. Here we discuss new results on the amount and directions of biogeochemical exchanges at the tidal wetland-estuary interface. Detailed microbial and photochemical degradation experiments and high resolution bio-optical observations in tidal freshwater and salt marsh systems of the Eastern US coast provide insights on the quality and fate of the organic compounds exported from tidal marshes and their influence on near-shore biological processes, biogeochemical cycles and optical variability. Impacts of anthropogenic activities and resulting air-pollution are also discussed. High resolution model runs were performed using the Community Multi-scale Air Quality (CMAQ) model, to examine atmospheric composition along the shoreline where processes such as sea and bay breeze circulations often favor the accumulation and air-deposition of atmospheric pollutants, impacting biogeochemical processes in sensitive tidal wetland ecosystems.

  18. Soft mode characteristics of up-up-down-down spin chains: The role of exchange interactions on lattice dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Y. J. [School of Physics and Electronic Engineering, Jiangsu Second Normal University, Nanjing 210013 (China); Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Gao, Y. J.; Ge, C. N [School of Physics and Electronic Engineering, Jiangsu Second Normal University, Nanjing 210013 (China); Guo, Y. Y. [College of Electronic Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210003 (China); Yan, Z. B.; Liu, J.-M., E-mail: liujm@nju.edu.cn [Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China)

    2015-05-07

    In this work, the dynamics of a diatomic chain is investigated with ↑↑↓↓ spin order in which the dispersion relation characterizes the effect of magnetic interactions on the lattice dynamics. The optical or acoustic mode softening in the center or boundary of the Brillouin zone can be observed, indicating the transitions of ferroelectric state, antiferromagnetic state, or ferroelastic state. The coexistence of the multiferroic orders related to the ↑↑↓↓ spin order represents a type of intrinsic multiferroic with strong ferroelectric order and different microscopic mechanisms.

  19. Fluid dynamics simulation of highly loaded anion-exchange chromatography of Np(IV) based on adsorption isotherm determined by {sup 237+239}Np

    Energy Technology Data Exchange (ETDEWEB)

    Yamamura, T. [Institute for Materials Research, Tohoku University, Sendai, Miyagi 980-8577 (Japan)], E-mail: yamamura@imr.tohoku.ac.jp; Mitsugashira, T. [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Shiokawa, Y. [Institute for Materials Research, Tohoku University, Sendai, Miyagi 980-8577 (Japan); Aoki, D.; Homma, Y. [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan)

    2007-10-11

    In order to investigate the optimum condition for anion-exchange chromatography for purification and recovery of actinide(IV) constituting transuranium elements, a convective-diffusion equation model treating mass balance and Langmuir-type kinetics in porous system, which was developed for thorium(IV) by us, was applied to neptunium(IV). Absorption isotherm of neptunium(IV) to anion-exchange (MSA-1) resin was carried out by using {sup 237+239}Np in 6N HNO{sub 3} media and hereby parameters of the Langmuir-type kinetics were determined as k{sub 0} = 2.5 x 10{sup 3} and s{sub max} = 1.0. Accompanied with the fluid dynamics parameters already determined for the column system used for {sup 227+232}Th, elution curves of neptunium(IV) at highly loaded condition were estimated by the numerical calculation. According to the result, the loading of more than 10% of resin capacity leads to rapid breakthrough and severe tailing of neptunium which lowers purity and yield in the purification procedure. This numerical calculation will serve as a valuable measure to figure out column operation conditions for purification and recovery of transuranium elements.

  20. Nitrous oxide and methane dynamics in a coral reef lagoon driven by pore water exchange: Insights from automated high-frequency observations

    Science.gov (United States)

    O'Reilly, Chiara; Santos, Isaac R.; Cyronak, Tyler; McMahon, Ashly; Maher, Damien T.

    2015-04-01

    Automated cavity ring down spectroscopy was used to make continuous measurements of dissolved methane, nitrous oxide, and carbon dioxide in a coral reef lagoon for 2 weeks (Heron Island, Great Barrier Reef). Radon (222Rn) was used to trace the influence of tidally driven pore water exchange on greenhouse gas dynamics. Clear tidal variation was observed for CH4, which correlated to 222Rn in lagoon waters. N2O correlated to 222Rn during the day only, which appears to be a response to coupled nitrification-denitrification in oxic sediments, fueled by nitrate derived from bird guano. The lagoon was a net source of CH4 and N2O to the atmosphere and a sink for atmospheric CO2. The estimated pore water-derived CH4 and N2O fluxes were 3.2-fold and 24.0-fold greater than the fluxes to the atmosphere. Overall, pore water and/or groundwater exchange were the only important sources of CH4 and major controls of N2O in the coral reef lagoon.

  1. Spatio-temporal competition dynamics of larch species in North Central Siberia

    OpenAIRE

    2016-01-01

    In North Central Siberia larch trees dominate huge parts of the prevailing light-coniferous taiga. In this unique ecosystem, permafrost limits the soil layer that thaws in summer and hence the supply of nutrients and water available for plants. Two larch species dominate the forest and build the tree line: Siberian larch (Larix sibirica LEDEB.) and Dahurian larch (Larix gmelinii (RUPr.) RUPR.). In changing climatic conditions, the distribution areas of both species will shift and overlap more...

  2. Dynamics of Long-lived Foundation Species: The History of Quercus in Southern Scandinavia

    OpenAIRE

    Foster, David Russell; Lindbladh, Matts

    2010-01-01

    (1) The long-term history of Quercus in southern Scandinavia has received little attention despite its important role in modern conservation. In this study the 4000-year dynamics of Quercus, its habitat and other important taxa were analysed with pollen data from 25 small hollows and 6 regional sites across southern Scandinavia. The aim was to provide a context for understanding the species’ current status and managing its future dynamics. (2) The results indicate that Quercus is much less ab...

  3. Solvent exchange in a metal–organic framework single crystal monitored by dynamic in situ X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Cox, Jordan M.; Walton, Ian M.; Bateman, Gage; Benson, Cassidy A.; Mitchell, Travis; Sylvester, Eric; Chen, Yu-Sheng; Benedict, Jason B.

    2017-07-25

    Understanding the processes by which porous solid-state materials adsorb and release guest molecules would represent a significant step towards developing rational design principles for functional porous materials. To elucidate the process of liquid exchange in these materials, dynamicin situX-ray diffraction techniques have been developed which utilize liquid-phase chemical stimuli. Using these time-resolved diffraction techniques, the ethanol solvation process in a flexible metal–organic framework [Co(AIP)(bpy)0.5(H2O)]·2H2O was examined. The measurements provide important insight into the nature of the chemical transformation in this system including the presence of a previously unreported neat ethanol solvate structure.

  4. Communication: Rigorous quantum dynamics of O + O2 exchange reactions on an ab initio potential energy surface substantiate the negative temperature dependence of rate coefficients.

    Science.gov (United States)

    Li, Yaqin; Sun, Zhigang; Jiang, Bin; Xie, Daiqian; Dawes, Richard; Guo, Hua

    2014-08-28

    The kinetics and dynamics of several O + O2 isotope exchange reactions have been investigated on a recently determined accurate global O3 potential energy surface using a time-dependent wave packet method. The agreement between calculated and measured rate coefficients is significantly improved over previous work. More importantly, the experimentally observed negative temperature dependence of the rate coefficients is for the first time rigorously reproduced theoretically. This negative temperature dependence can be attributed to the absence in the new potential energy surface of a submerged "reef" structure, which was present in all previous potential energy surfaces. In addition, contributions of rotational excited states of the diatomic reactant further accentuate the negative temperature dependence.

  5. Mimicking the action of folding chaperones by Hamiltonian replica-exchange molecular dynamics simulations: application in the refinement of de novo models.

    Science.gov (United States)

    Fan, Hao; Periole, Xavier; Mark, Alan E

    2012-07-01

    The efficiency of using a variant of Hamiltonian replica-exchange molecular dynamics (Chaperone H-replica-exchange molecular dynamics [CH-REMD]) for the refinement of protein structural models generated de novo is investigated. In CH-REMD, the interaction between the protein and its environment, specifically, the electrostatic interaction between the protein and the solvating water, is varied leading to cycles of partial unfolding and refolding mimicking some aspects of folding chaperones. In 10 of the 15 cases examined, the CH-REMD approach sampled structures in which the root-mean-square deviation (RMSD) of secondary structure elements (SSE-RMSD) with respect to the experimental structure was more than 1.0 Å lower than the initial de novo model. In 14 of the 15 cases, the improvement was more than 0.5 Å. The ability of three different statistical potentials to identify near-native conformations was also examined. Little correlation between the SSE-RMSD of the sampled structures with respect to the experimental structure and any of the scoring functions tested was found. The most effective scoring function tested was the DFIRE potential. Using the DFIRE potential, the SSE-RMSD of the best scoring structures was on average 0.3 Å lower than the initial model. Overall the work demonstrates that targeted enhanced-sampling techniques such as CH-REMD can lead to the systematic refinement of protein structural models generated de novo but that improved potentials for the identification of near-native structures are still needed.

  6. Calculation and Analysis of Dynamic Parameter Modeling for Heat Exchangers%换热器动态参数模型的建立与计算分析

    Institute of Scientific and Technical Information of China (English)

    孙斌; 周妍

    2013-01-01

    利用分布集中参数法建立了换热器(蒸发器和冷凝器)的动态参数模型,膨胀阀和压缩机采用稳态方程的形式作为动态模型的可移动边界,从而使模型方程封闭可解.模型针对水源热泵机组内的蒸发器和冷凝器在模拟工况下进行计算.求解基于MATLAB的偏微分方程组,利用PDEPE函数,输入初值函数、边界条件和问题描述函数,分别得出机组运行过程中换热器内制冷剂的温度、压力和换热系数随换热管长度的变化曲线.%With distributed and lumped parameter method,a dynamic parameter model for the heat exchanger (evaporator and condenser) was established,in which,both expanding valve and compressor which adopting steady state equation were taken as the dynamic model' s moving boundary to make the model equation closed and solved.This model for evaporator and condenser of the water source heat pump units in the simulation conditions were calculated.Based on MATLAB partial differential equation method,the PDEPE function,was used to input initial value function,boundary conditions and problem description function so that the changing curve of refrigerant' s temperature,pressure and heat transfer coefficient can be calculated,which changing with the heat exchange tube's length.

  7. Permafrost dynamics structure species compositions of oribatid mite (Acari: Oribatida communities in sub-Arctic palsa mires

    Directory of Open Access Journals (Sweden)

    Inkeri Markkula

    2014-10-01

    Full Text Available Palsa mires are sub-Arctic peatland complexes, vulnerable ecosystems with patches of permafrost. Permafrost thawing in palsa mires occurs throughout Fennoscandia, probably due to local climatic warming. In palsa mires, permafrost thaw alters hydrological conditions, vegetation structure and microhabitat composition with unknown consequences for invertebrate fauna. This study's objectives were to examine the role of microhabitat heterogeneity and the effects of permafrost dynamics and thaw on oribatid mite communities in palsa mires. Oribatid mites were sampled in two palsa mires in Finland and Norway. Three different types of microhabitats were examined: graminoid-dominated wet sites, herb-dominated small hummocks and evergreen shrub-dominated permafrost-underlain palsa hummocks. The results indicate that permafrost dynamics are an important factor structuring oribatid mite communities in palsa mires. The community composition of oribatid mites differed remarkably among microhabitats. Six species were significantly more abundant in permafrost-underlain microhabitats in relation to non-permafrost microhabitats. None of the species identified occurred exclusively in permafrost-underlain microhabitats. Findings suggest that permafrost thaw may not have an impact on species diversity but may alter community composition of oribatid mites in palsa mire ecosystems.

  8. Temporal dynamics of demersal chondrichthyan species in the central western Mediterranean

    Directory of Open Access Journals (Sweden)

    Antonello Mulas

    2015-11-01

    Full Text Available The rapid expansion of fisheries and globalized trade are emerging as the principal drivers of coastal and ocean threat. Considering the important role of Chondrichthyes as predators at the top of food chain in marine ecosystems, knowledge on their biology remains scarce in the Mediterranean. In this regard, our objective is to give information on their spatial distribution, abundance and population structure. Data were collected for 25 demersal species, including batoid species, sharks and holocephalans from 1994 to 2013 during scientific bottom trawl surveys (MEDITS project carried out around the Sardinian seas. The total frequency of occurrence (f%, the Biomass Index (BI, kg/km2, and the Density Index (DI, N/km2 were estimated for the continental shelf (10-200 m, slope (200-800 m, and overall (10-800 m depth strata. Size trends were also calculated for the most abundant species considering all depth strata. The correlation among MEDITS figures (f%, BI, DI, size structure and years were assessed by species computing the Pearson linear coefficient. From f% and abundance indexes investigation, only the small spotted catshark Scyliorhinus canicula and the thornback ray Raja clavata were ubiquitous in all strata investigated, instead, all the other species showed a preferential distribution for the shelf or the slope. In general, the temporal trends of BI and DI were stable or positive for both macro-strata, except for the longnose spurdog Squalus blainville which seemed to show a statistically significant decreasing trend. All analyzed species displayed temporal stable trends in size structure analysis, apart from Raja brachyura and Dipturus oxyrinchus that showed a statistically significant increase. Despite the time series analysis revealed stable or positive trends, it appears clear the need of urgent management measures to protect the demersal chondrichthyan species extending the monitoring over time and implementing the data collected by

  9. Different conformational dynamics of β-arrestin1 and β-arrestin2 analyzed by hydrogen/deuterium exchange mass spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Yun, Youngjoo; Kim, Dong Kyun [School of Pharmacy, Sungkyunkwan University, Suwon (Korea, Republic of); Seo, Min-Duk [College of Pharmacy & Department of Molecular Science and Technology, Ajou University, Suwon (Korea, Republic of); Kim, Kyeong-Man [College of Pharmacy, Chonnam National University, Gwang-Ju (Korea, Republic of); Chung, Ka Young, E-mail: kychung2@skku.edu [School of Pharmacy, Sungkyunkwan University, Suwon (Korea, Republic of)

    2015-01-30

    Highlights: • The conformational dynamics of β-arrestin1 or β-arrestin2 were analyzed by HDX-MS. • β-Strands II through IV were more dynamic in β-arrestin2 than in β-arrestin1. • The middle loop was less dynamic in β-arrestin2 than in β-arrestin1. • Upon pre-activation by the R169E mutation, β-arrestins became more dynamic. • Pre-activation affected a wider region of β-arrestin1 compared to β-arrestin2. - Abstract: Arrestins have important roles in G protein-coupled receptor (GPCR) signaling including desensitization of GPCRs and G protein-independent signaling. There have been four arrestins identified: arrestin1, arrestin2 (e.g. β-arrestin1), arrestin3 (e.g. β-arrestin2), and arrestin4. β-Arrestin1 and β-arrestin2 are ubiquitously expressed and regulate a broad range of GPCRs, while arrestin1 and arrestin4 are expressed in the visual system. Although the functions of β-arrestin1 and β-arrestin2 widely overlap, β-arrestin2 has broader receptor selectivity, and a few studies have suggested that β-arrestin1 and β-arrestin2 have distinct cellular functions. Here, we compared the conformational dynamics of β-arrestin1 and β-arrestin2 by hydrogen/deuterium exchange mass spectrometry (HDX-MS). We also used the R169E mutant as a pre-activation model system. HDX-MS data revealed that β-strands II through IV were more dynamic in β-arrestin2 in the basal state, while the middle loop was more dynamic in β-arrestin1. With pre-activation, both β-arrestin1 and β-arrestin2 became more flexible, but broader regions of β-arrestin1 became flexible compared to β-arrestin2. The conformational differences between β-arrestin1 and β-arrestin2 in both the basal and pre-activated states might determine their different receptor selectivities and different cellular functions.

  10. Population dynamics of mosquito species in a West Nile virus endemic area in Madagascar.

    Science.gov (United States)

    Tantely, Luciano Michaël; Cêtre-Sossah, Catherine; Rakotondranaivo, Tsiriniaina; Cardinale, Eric; Boyer, Sébastien

    2017-01-01

    Human and animal serological surveys suggest that West Nile virus (WNV) circulation is widely distributed in Madagascar. However, there are no reported West Nile fever outbreaks or epizootics in the country and only one fatal human case has been reported to date. Currently there is very limited information on the maintenance and the transmission of WNV in Madagascar and particularly on the mosquito species involved in transmission cycles. In 2014, we initiated a study to investigate mosquito species composition, relative abundance, and trophic behavior in Mitsinjo District close to Lake Kinkony, a WNV endemic area in north-western Madagascar. We collected a total of 2519 adult mosquitoes belonging to 21 different species. The most abundant species was Aedeomyia (Aedeomyia) madagascarica Brunhes, Boussès & da Cunha Ramos, which made up 83% of all the mosquitoes collected. Mosquito abundance was associated with proximity to the lake (Morafeno and Ankelimitondrotra). Additionally, a correlation was observed between the lake-side biotope and the abundance of mosquito vectors in Morafeno. WNV RNA was detected in one pool of Ae. madagascarica and one pool of Anopheles (Cellia) pauliani Grjebine, suggesting that these two species may be involved in the maintenance and/or transmission of WNV in Madagascar. © L.M. Tantely et al., published by EDP Sciences, 2017.

  11. Species and Media Effects on Soil Carbon Dynamics in the Landscape

    Science.gov (United States)

    Marble, S. Christopher; Prior, Stephen A.; Runion, G. Brett; Torbert, H. Allen; Gilliam, Charles H.; Fain, Glenn B.; Sibley, Jeff L.; Knight, Patricia R.

    2016-05-01

    Three woody shrub species [cleyera (Ternstroemia gymnanthera Thunb. ‘Conthery’), Indian hawthorn (Rhaphiolepis indica L.) and loropetalum (Loropetalum chinensis Oliv.‘Ruby’)] were container-grown for one growing season in 2008 using either pinebark (industry standard), clean chip residual or WholeTree (derived by-products from the forestry industry) as potting substrates and then transplanted into the landscape in 2008. An Automated Carbon Efflux System was used to continually monitor soil CO2 efflux from December 2010 through November 2011 in each species and substrate combination. Changes in soil carbon (C) levels as a result of potting substrate were assessed through soil sampling in 2009 and 2011 and plant biomass was determined at study conclusion. Results showed that soil CO2-C efflux was similar among all species and substrates, with few main effects of species or substrate observed throughout the study. Soil analysis showed that plots with pinebark contained higher levels of soil C in both 2009 and 2011, suggesting that pinebark decomposes slower than clean chip residual or WholeTree and consequently has greater C storage potential than the two alternative substrates. Results showed a net C gain for all species and substrate combinations; however, plants grown in pinebark had greater C sequestration potential.

  12. Dynamics and genetics of a disease-driven species decline to near extinction: lessons for conservation

    Science.gov (United States)

    Hudson, M. A.; Young, R. P.; D’Urban Jackson, J.; Orozco-terWengel, P.; Martin, L.; James, A.; Sulton, M.; Garcia, G.; Griffiths, R. A.; Thomas, R.; Magin, C.; Bruford, M. W.; Cunningham, A. A.

    2016-01-01

    Amphibian chytridiomycosis has caused precipitous declines in hundreds of species worldwide. By tracking mountain chicken (Leptodactylus fallax) populations before, during and after the emergence of chytridiomycosis, we quantified the real-time species level impacts of this disease. We report a range-wide species decline amongst the fastest ever recorded, with a loss of over 85% of the population in fewer than 18 months on Dominica and near extinction on Montserrat. Genetic diversity declined in the wild, but emergency measures to establish a captive assurance population captured a representative sample of genetic diversity from Montserrat. If the Convention on Biological Diversity’s targets are to be met, it is important to evaluate the reasons why they appear consistently unattainable. The emergence of chytridiomycosis in the mountain chicken was predictable, but the decline could not be prevented. There is an urgent need to build mitigation capacity where amphibians are at risk from chytridiomycosis. PMID:27485994

  13. Genesis of chromatin and transcription dynamics in the origin of species.

    Science.gov (United States)

    Koster, Maria J E; Snel, Berend; Timmers, H Th Marc

    2015-05-07

    Histone proteins compact and stabilize the genomes of Eukarya and Archaea. By forming nucleosome(-like) structures they restrict access of DNA-binding transcription regulators to cis-regulatory DNA elements. Dynamic competition between histones and transcription factors is facilitated by different classes of proteins including ATP-dependent remodeling enzymes that control assembly, access, and editing of chromatin. Here, we summarize the knowledge on dynamics underlying transcriptional regulation across the domains of life with a focus on ATP-dependent enzymes in chromatin structure or in TATA-binding protein activity. These insights suggest directions for future studies on the evolution of transcription regulation and chromatin dynamics. Copyright © 2015 Elsevier Inc. All rights reserved.

  14. Tunneling Dynamics of Two-Species Bose-Einstein Condensates with Feshbach Resonances

    Institute of Scientific and Technical Information of China (English)

    CHENChanu-Yonu

    2003-01-01

    We investigate tunneling dynamics of atomic group consisting of three atoms in Bose-Einstein condensates with Feshbach resonance. It is shown that the tunneling of the atom group depends not only on the inter-atomic nonlinear interactions and the initial number of atoms in these condensates, but also on the tunneling coupling between the atomic condensate and the three-atomic molecular condensate. It is found that besides oscillating tunneling current between the atomic condensate and the molecular condensate, the nonlinear atomic group tunneling dynamics sustains a self-maintained population imbalance: a macroscopic quantum self-trapping effect. The influence of de-coherence caused by non-condensate atoms on the tunneling dynamics is studied. It is indicated that de-coherence suppresses the atomic group tunneling.

  15. Tunneling Dynamics of Two-Species Bose-Einstein Condensates with Feshbach Resonances

    Institute of Scientific and Technical Information of China (English)

    CHEN Chang-Yong

    2003-01-01

    We investigate tunneling dynamics of atomic group consisting of three atoms in Bose-Einstein condensateswith Feshbach resonance. It is shown that the tunneling of the atom group depends not only on the inter-atomicnonlinear interactions and the initial number of atoms in these condensates, but also on the tunneling coupling betweenthe atomic condensate and the three-atomic molecular condensate. It is found that besides oscillating tunneling currentbetween the atomic condensate and the molecular condensate, the nonlinear atomic group tunneling dynamics sustains aself-maintained population imbalance: a macroscopic quantum self-trapping effect. The influence of de-coherence causedby non-condensate atoms on the tunneling dynamics is studied. It is indicated that de-coherence suppresses the atomicgroup tunneling.

  16. Molecular identification and population dynamics of two species of Pemphigus (Homoptera: Pemphidae) on cabbage

    Institute of Scientific and Technical Information of China (English)

    Naiqi Chen; Tong-Xian Liu; Mamoudou Sétamou; J. Victor French; Eliezer S. Louzada

    2009-01-01

    The poplar petiole gall aphid, Pemphiguspopulitransversus Riley, has been one of the major pests on cruciferous vegetable in the Rio Grande Valley (LRGV) of Texas since the late 1940s. It normally migrates from poplar trees to cruciferous vegetables in the fall, and migrates back to the trees in early spring of the coming year. Some root-feeding aphids were found on cruciferous vegetables in late spring and early summer in 1998 and the following years. Those aphids have been identified as Pemphigus obesinymphae Moran. This discovery completely changed the current knowledge about the root-feeding aphids on cruciferous vegetables in the LRGV. Due to their small size, morphological and feeding similarities between P. populitransversus and P. obesinymphae, their identification and distinction are difficult. In this study, random amplification ofpolymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) were used to distinguish these two species over a period of time when the two species occurred together, or separately, in cabbage fields. The two species occurred on cabbage at different times of the year, and overlapped from October to June. From May to October, both species migrated to their primary hosts. The apterous aphids found on cabbage in winter contained mainly P. obesinymphae, whereas in early spring more apterous P. populitransversus were recovered. The root-feeding aphids would feed on cabbage plants as long as this host was available even during the hot, dry summer in the LRGV, although their populations were generally low. Both RAPD and AFLP techniques were efficient in discriminating the two species that showed obviously genetic variability. These molecular techniques confirmed the existence of the two aphid species in apterous samples collected from the soil in cabbage fields in the LRGV, and the results performed by RAPD were confirmed by AFLP. Furthermore, the results suggest that RAPD technique was a better choice despite its

  17. Сhanges of species diversity of aquatic assemblages as a dynamic process

    Directory of Open Access Journals (Sweden)

    V. G. Tereshchenko

    2008-10-01

    Full Text Available Analysis of long-term dynamics of the fish assemblage diversity of 70 large lakes and reservoirs of Russia and other countries of CIS shows, that the response of the community to the increase of load consists of two phases. Under the weak loads the population waves amplitude increases. With intensifying influence the structural and functional features of the fish community changes. It causes the consideration of the biodiversity dynamics as a complex stochastic process. Simple comparative analysis of the biodiversity indices in different spans can result in erroneous conclusions.

  18. Influence of moisture regime and tree species composition on nitrogen cycling dynamics in hardwood forests of Mammoth Cave National Park, Kentucky, USA

    National Research Council Canada - National Science Library

    Fabio, Eric S; Arthur, Mary A; Rhoades, Charles C

    2009-01-01

    .... Seasonal monitoring of N cycling dynamics was carried out for 2 years in deciduous forest stands that differed in soil moisture status and geologic substrate, and thus, in tree species composition...

  19. Hierarchical demographic approaches for assessing invasion dynamics of non-indigenous species: An example using northern snakehead (Channa argus)

    Science.gov (United States)

    Jiao, Y.; Lapointe, N.W.R.; Angermeier, P.L.; Murphy, B.R.

    2009-01-01

    Models of species' demographic features are commonly used to understand population dynamics and inform management tactics. Hierarchical demographic models are ideal for the assessment of non-indigenous species because our knowledge of non-indigenous populations is usually limited, data on demographic traits often come from a species' native range, these traits vary among populations, and traits are likely to vary considerably over time as species adapt to new environments. Hierarchical models readily incorporate this spatiotemporal variation in species' demographic traits by representing demographic parameters as multi-level hierarchies. As is done for traditional non-hierarchical matrix models, sensitivity and elasticity analyses are used to evaluate the contributions of different life stages and parameters to estimates of population growth rate. We applied a hierarchical model to northern snakehead (Channa argus), a fish currently invading the eastern United States. We used a Monte Carlo approach to simulate uncertainties in the sensitivity and elasticity analyses and to project future population persistence under selected management tactics. We gathered key biological information on northern snakehead natural mortality, maturity and recruitment in its native Asian environment. We compared the model performance with and without hierarchy of parameters. Our results suggest that ignoring the hierarchy of parameters in demographic models may result in poor estimates of population size and growth and may lead to erroneous management advice. In our case, the hierarchy used multi-level distributions to simulate the heterogeneity of demographic parameters across different locations or situations. The probability that the northern snakehead population will increase and harm the native fauna is considerable. Our elasticity and prognostic analyses showed that intensive control efforts immediately prior to spawning and/or juvenile-dispersal periods would be more effective

  20. Population dynamics and spatial distribution of microbial species in multispecies biofilms under the action of direct electric current

    Institute of Scientific and Technical Information of China (English)

    CAO Hongbin; LI Xingang; WU Jinchuan; ZHONG Fangli; ZHANG Yi

    2003-01-01

    The metabolism, population dynamics and spatial distribution of nitrifying bacteria and heterotrophs in biofilms under the action of direct electric current were investigated by using the micro-slicing technique. The nitrification rate of nitrifying bacteria was severely inhibited by a current over 10 Am-2 at lower C/N ratios. Compared to heterotrophs, the nitrifying bacteria in the surface biofilms were severely inhibited, resulting in a significant decrease in bacterial density. An increase in current density narrowed the less current-sensitive inner biofilm region, and in addition the density of NO2-oxidizers decreased more significantly than that of NH4-oxidizers in the surface biofilms probably due to electrochemical reactions at the anode. However, the effect of current on both the population dynamics and the spatial distribution of the microbial species was less significant at larger C/N ratios.

  1. Impact assessment of non-indigenous jellyfish species on the estuarine community dynamic: A model of medusa phase

    Science.gov (United States)

    Muha, Teja Petra; Teodósio, Maria Alexandra; Ben-Hamadou, Radhouan

    2017-03-01

    Non-indigenous jellyfish species (NIJS) Blackforida virginica have recently been introduced to the Guadiana Estuary. A modelling approach was used for the assessment of the species-specific impact on the native community, during the medusa phase. The novel interactions between NIJS and the native community are assessed through biomass variation including hydrodynamic and climatic variables. Sensitivity analysis shows that both native species, as well as NIJS highly depend on the water discharge regime, nutrient contribution and the amount of detritus production. Abiotic factors such as the Northern Atlantic Oscillation, water discharge, nutrient load and detritus production are the most influential factors for the dynamics of the estuarine ecosystem demonstrated by the model. Low water discharge and low nutrient retention rate appear to be the most favourable conditions for B. virginica. The species is a non-selective predator able to integrate into the system effectively and has caused a decrease in the biomass of other organisms in the estuarine ecosystem throughout the summer after dam removal. The B. virginica significant impact can be evaluated only when the jellyfish detritus food pathway is involved. The B. virginica predatory impact potential, as well as food preference, appears to be the most influential factors for the overall biomass variation. On the contrary, winter freshwater pulses reduce the survival rate of jellyfish polyps which results in a decrease of medusa during summer. The model presents a strong ecohydrology movement where the fluctuation of organism biomass strongly depends on the hydrological conditions including the amount of nutrient load.

  2. Emergent dynamics of fairness in the spatial coevolution of proposer and responder species in the ultimatum game.

    Science.gov (United States)

    Suzuki, Reiji; Okamoto, Tomoko; Arita, Takaya

    2015-01-01

    While spatially local interactions are ubiquitous between coevolving species sharing recourses (e.g., plant-insect interactions), their effects on such coevolution processes of strategies involving the share of a resource are still not clearly understood. We construct a two-dimensional spatial model of the coevolution of the proposer and responder species in the ultimatum game (UG), in which a pair of proposer and responder individuals at each site plays the UG. We investigate the effects of the locality of interactions and the intensity of selection on the emergence of fairness between these species. We show that the lower intensity of selection favors fair strategies in general, and there are no significant differences in the evolution of fairness between the cases with local and global interactions when the intensity of selection is low. However, as the intensity of selection becomes higher, the spatially local interactions contribute to the evolution of fairer strategies more than the global interactions, even though fair strategies become more difficult to evolve. This positive effect of spatial interactions is expected to be due to the mutual benefit of fairness for both proposer and responder species in future generations, which brings about a dynamic evolution process of fairness.

  3. Regeneration dynamics of dominant tree species along an altitudinal gradient in moist temperate valley slopes of the Garhwal Himalaya

    Institute of Scientific and Technical Information of China (English)

    Sumeet Gairola; C.M.Sharma; S.K.Ghildiyal; Sarvesh Suyal

    2012-01-01

    The present study was undertaken in moist temperate forest of Mandal-Chopta area in the Garhwal region of Uttarakhand,India.The aim of the present study was to understand the regeneration dynamics of the dominant tree species along an altitudinal gradient in naturally regenerating,restricted access forest.The overall regeneration status was fairly high in the study area.Most of the native canopy and undercanopy dominants had frequent reproduction and expanding populations,which suggests the stability of forest structure/composition and further expansion of dominant species.The overall regeneration of trees in the forest had a greater contribution of middle and understorey species.Because of infrequent reproduction and declining populations of some of the dominant native species viz.,Abies pindrow,Alnus nepalensis and Betula alnoides,structural/compositional changes in the future are expected in respective forests dominated by them.Abies pindrow and Taxus baccata need immediate attention by forest managers for their survival in the area.Seedlings were found to be more prone to competition from herb and shrubs than saplings.

  4. Long term dynamic of real exchange rate, trade liberalization and financial integration: The case of south-east Mediterranean countries

    Directory of Open Access Journals (Sweden)

    Amor Hadj Thouraya

    2009-01-01

    Full Text Available The purpose of this paper is to estimate the effects of the trade liberalization and of the international financial integration on the long-term behavior of Real Exchange Rate (RER for the South East Mediterranean countries. So the following question: how does the new trade and financial context affect the Equilibrium RER? We refer to the econometric technique of time series analysis, (the unit root tests of Dickey-Fuller (1979 and we apply the cointegration test of Engle and Granger (1987 of single equation for six South East Mediterranean countries (Algeria, Egypt, Lebanon, Morocco, Tunisia and Turkey over the period of 1979-2004. Our estimates suggest that, for the six countries, long-term RER behavior depends essentially on economic specificity of each country and in particular on their degree of financial integration and trade opening. Our results also show that the evolution of the RER misalignment during our sample period, seem to be for some countries persistant and recurrent, but with decrease.

  5. Hybridising Medicine: Illness, Healing and the Dynamics of Reciprocal Exchange on the Upper Guinea Coast (West Africa)

    Science.gov (United States)

    Havik, Philip J.

    2016-01-01

    The present article s