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Sample records for range density dependent

  1. Evolution of density-dependent movement during experimental range expansions.

    Science.gov (United States)

    Fronhofer, E A; Gut, S; Altermatt, F

    2017-12-01

    Range expansions and biological invasions are prime examples of transient processes that are likely impacted by rapid evolutionary changes. As a spatial process, range expansions are driven by dispersal and movement behaviour. Although it is widely accepted that dispersal and movement may be context-dependent, for instance density-dependent, and best represented by reaction norms, the evolution of density-dependent movement during range expansions has received little experimental attention. We therefore tested current theory predicting the evolution of increased movement at low densities at range margins using highly replicated and controlled range expansion experiments across multiple genotypes of the protist model system Tetrahymena thermophila. Although rare, we found evolutionary changes during range expansions even in the absence of initial standing genetic variation. Range expansions led to the evolution of negatively density-dependent movement at range margins. In addition, we report the evolution of increased intrastrain competitive ability and concurrently decreased population growth rates in range cores. Our findings highlight the importance of understanding movement and dispersal as evolving reaction norms and plastic life-history traits of central relevance for range expansions, biological invasions and the dynamics of spatially structured systems in general. © 2017 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2017 European Society For Evolutionary Biology.

  2. Multi-configuration time-dependent density-functional theory based on range separation

    DEFF Research Database (Denmark)

    Fromager, E.; Knecht, S.; Jensen, Hans Jørgen Aagaard

    2013-01-01

    Multi-configuration range-separated density-functional theory is extended to the time-dependent regime. An exact variational formulation is derived. The approximation, which consists in combining a long-range Multi-Configuration- Self-Consistent Field (MCSCF) treatment with an adiabatic short......-range density-functional (DFT) description, is then considered. The resulting time-dependent multi-configuration short-range DFT (TD-MC-srDFT) model is applied to the calculation of singlet excitation energies in H, Be, and ferrocene, considering both short-range local density (srLDA) and generalized gradient...

  3. Density-dependent home-range size revealed by spatially explicit capture–recapture

    Science.gov (United States)

    Efford, M.G.; Dawson, Deanna K.; Jhala, Y.V.; Qureshi, Q.

    2016-01-01

    The size of animal home ranges often varies inversely with population density among populations of a species. This fact has implications for population monitoring using spatially explicit capture–recapture (SECR) models, in which both the scale of home-range movements σ and population density D usually appear as parameters, and both may vary among populations. It will often be appropriate to model a structural relationship between population-specific values of these parameters, rather than to assume independence. We suggest re-parameterizing the SECR model using kp = σp √Dp, where kp relates to the degree of overlap between home ranges and the subscript p distinguishes populations. We observe that kp is often nearly constant for populations spanning a range of densities. This justifies fitting a model in which the separate kp are replaced by the single parameter k and σp is a density-dependent derived parameter. Continuous density-dependent spatial variation in σ may also be modelled, using a scaled non-Euclidean distance between detectors and the locations of animals. We illustrate these methods with data from automatic photography of tigers (Panthera tigris) across India, in which the variation is among populations, from mist-netting of ovenbirds (Seiurus aurocapilla) in Maryland, USA, in which the variation is within a single population over time, and from live-trapping of brushtail possums (Trichosurus vulpecula) in New Zealand, modelling spatial variation within one population. Possible applications and limitations of the methods are discussed. A model in which kp is constant, while density varies, provides a parsimonious null model for SECR. The parameter k of the null model is a concise summary of the empirical relationship between home-range size and density that is useful in comparative studies. We expect deviations from this model, particularly the dependence of kp on covariates, to be biologically interesting.

  4. Multi-configuration time-dependent density-functional theory based on range separation

    CERN Document Server

    Fromager, Emmanuel; Jensen, Hans Jørgen Aa

    2012-01-01

    Multi-configuration range-separated density-functional theory is extended to the time-dependent regime. An exact variational formulation is derived. The approximation, which consists in combining a long-range Multi-Configuration-Self-Consistent Field (MCSCF) treatment with an adiabatic short-range density-functional (DFT) description, is then considered. The resulting time-dependent multi-configuration short-range DFT (TD-MC-srDFT) model is applied to the calculation of singlet excitation energies in H2, Be and ferrocene, considering both short-range local density (srLDA) and generalized gradient (srGGA) approximations. In contrast to regular TD-DFT, TD-MC-srDFT can describe double excitations. As expected, when modeling long-range interactions with the MCSCF model instead of the adiabatic Buijse-Baerends density-matrix functional as recently proposed by Pernal [K. Pernal, J. Chem. Phys. 136, 184105 (2012)], the description of both the 1^1D doubly-excited state in Be and the 1^1\\Sigma^+_u state in the stretch...

  5. Combining Density Functional Theory and Green's Function Theory: Range-Separated, Nonlocal, Dynamic, and Orbital-Dependent Hybrid Functional.

    Science.gov (United States)

    Kananenka, Alexei A; Zgid, Dominika

    2017-11-14

    We present a rigorous framework which combines single-particle Green's function theory with density functional theory based on a separation of electron-electron interactions into short- and long-range components. Short-range contribution to the total energy and exchange-correlation potential is provided by a density functional approximation, while the long-range contribution is calculated using an explicit many-body Green's function method. Such a hybrid results in a nonlocal, dynamic, and orbital-dependent exchange-correlation functional of a single-particle Green's function. In particular, we present a range-separated hybrid functional called srSVWN5-lrGF2 which combines the local-density approximation and the second-order Green's function theory. We illustrate that similarly to density functional approximations, the new functional is weakly basis-set dependent. Furthermore, it offers an improved description of the short-range dynamic correlation. The many-body contribution to the functional mitigates the many-electron self-interaction error present in many density functional approximations and provides a better description of molecular properties. Additionally, we illustrate that the new functional can be used to scale down the self-energy and, therefore, introduce an additional sparsity to the self-energy matrix that in the future can be exploited in calculations for large molecules or periodic systems.

  6. Range-separated time-dependent density-functional theory with a frequency-dependent second-order Bethe-Salpeter correlation kernel

    CERN Document Server

    Rebolini, Elisa

    2015-01-01

    We present a range-separated linear-response time-dependent density-functional theory (TDDFT) which combines a density-functional approximation for the short-range response kernel and a frequency-dependent second-order Bethe-Salpeter approximation for the long-range response kernel. This approach goes beyond the adiabatic approximation usually used in linear-response TDDFT and aims at improving the accuracy of calculations of electronic excitation energies of molecular systems. A detailed derivation of the frequency-dependent second-order Bethe-Salpeter correlation kernel is given using many-body Green-function theory. Preliminary tests of this range-separated TDDFT method are presented for the calculation of excitation energies of four small molecules: N2, CO2, H2CO, and C2H4. The results suggest that the addition of the long-range second-order Bethe-Salpeter correlation kernel overall slightly improves the excitation energies.

  7. Why Density Dependent Propulsion?

    Science.gov (United States)

    Robertson, Glen A.

    2011-01-01

    In 2004 Khoury and Weltman produced a density dependent cosmology theory they call the Chameleon, as at its nature, it is hidden within known physics. The Chameleon theory has implications to dark matter/energy with universe acceleration properties, which implies a new force mechanism with ties to the far and local density environment. In this paper, the Chameleon Density Model is discussed in terms of propulsion toward new propellant-less engineering methods.

  8. Density dependent neurodynamics.

    Science.gov (United States)

    Halnes, Geir; Liljenström, Hans; Arhem, Peter

    2007-01-01

    The dynamics of a neural network depends on density parameters at (at least) two different levels: the subcellular density of ion channels in single neurons, and the density of cells and synapses at a network level. For the Frankenhaeuser-Huxley (FH) neural model, the density of sodium (Na) and potassium (K) channels determines the behaviour of a single neuron when exposed to an external stimulus. The features of the onset of single neuron oscillations vary qualitatively among different regions in the channel density plane. At a network level, the density of neurons is reflected in the global connectivity. We study the relation between the two density levels in a network of oscillatory FH neurons, by qualitatively distinguishing between three regions, where the mean network activity is (1) spiking, (2) oscillating with enveloped frequencies, and (3) bursting, respectively. We demonstrate that the global activity can be shifted between regions by changing either the density of ion channels at the subcellular level, or the connectivity at the network level, suggesting that different underlying mechanisms can explain similar global phenomena. Finally, we model a possible effect of anaesthesia by blocking specific inhibitory ion channels.

  9. Assessment of charge-transfer excitations with time-dependent, range-separated density functional theory based on long-range MP2 and multiconfigurational self- consistent field wave functions

    DEFF Research Database (Denmark)

    Hedegård, Erik D.; Jensen, Hans Jørgen Aagaard; Knecht, Stefan

    2013-01-01

    Charge transfer excitations can be described within Time-Dependent Density Functional Theory (TD-DFT), not only by means of the Coulomb Attenuated Method (CAM) but also with a combination of wave function theory and TD-DFT based on range separation. The latter approach enables a rigorous formulat......Charge transfer excitations can be described within Time-Dependent Density Functional Theory (TD-DFT), not only by means of the Coulomb Attenuated Method (CAM) but also with a combination of wave function theory and TD-DFT based on range separation. The latter approach enables a rigorous...... formulation of multi-determinantal TD-DFT schemes where excitation classes, which are absent in conventional TD-DFT spectra (like for example double excitations), can be addressed. This paper investigates the combination of both the long-range Multi-Configuration Self-Consistent Field (MCSCF) and Second Order...... Polarization Propagator Approximation (SOPPA) ansätze with a short-range DFT (srDFT) description. We find that the combinations of SOPPA or MCSCF with TD-DFT yield better results than could be expected from the pure wave function schemes. For the Time-Dependent MCSCF short-range DFT ansatz (TD...

  10. Challenging Adiabatic Time-dependent Density Functional Theory with a Hubbard Dimer: The Case of Time-Resolved Long-Range Charge Transfer

    CERN Document Server

    Fuks, Johanna I

    2014-01-01

    We explore an asymmetric two-fermion Hubbard dimer to test the accuracy of the adiabatic approximation of time-dependent density functional theory in modelling time-resolved charge transfer. We show that the model shares essential features of a ground state long-range molecule in real-space, and by applying a resonant field we show that the model also reproduces essential traits of the CT dynamics. The simplicity of the model allows us to propagate with an "adiabatically-exact" approximation, i.e. one that uses the exact ground-state exchange-correlation functional, and compare with the exact propagation. This allows us to study the impact of the time-dependent charge-transfer step feature in the exact correlation potential of real molecules on the resulting dynamics. Tuning the parameters of the dimer allows a study both of charge-transfer between open-shell fragments and between closed-shell fragments. We find that the adiabatically-exact functional is unable to properly transfer charge, even in situations ...

  11. Density-dependent electron scattering in photoexcited GaAs

    DEFF Research Database (Denmark)

    Mics, Zoltán; D'’Angio, Andrea; Jensen, Søren A.

    2013-01-01

    —In a series of systematic optical pump - terahertz probe experiments we study the density-dependent electron scattering rate in photoexcited GaAs in a large range of carrier densities. The electron scattering time decreases by as much as a factor of 4, from 320 to 60 fs, as the electron density...

  12. Density dependence in North American ducks

    Directory of Open Access Journals (Sweden)

    Jamieson, L. E.

    2004-06-01

    Full Text Available The existence or otherwise of density dependence within a population can have important implications for the management of that population. Here, we use estimates of abundance obtained from annual aerial counts on the major breeding grounds of a variety of North American duck species and use a state space model to separate the observation and ecological system processes. This state space approach allows us to impose a density dependence structure upon the true underlying population rather than on the estimates and we demonstrate the improved robustness of this procedure for detecting density dependence in the population. We adopt a Bayesian approach to model fitting, using Markov chain Monte Carlo (MCMC methods and use a reversible jump MCMC scheme to calculate posterior model probabilities which assign probabilities to the presence of density dependence within the population, for example. We show how these probabilities can be used either to discriminate between models or to provide model-averaged predictions which fully account for both parameter and model uncertainty.

  13. and density-dependent quark mass model

    Indian Academy of Sciences (India)

    659–668. Radial oscillations of magnetized proto strange stars in temperature- and density-dependent quark mass model. V K GUPTA£, ASHA GUPTA, ..... D58, 083001 (1998). [13] O G Benvenuto and G Lugones, Mon. Not. R. Astron. Soc. 304, L25 (1999). [14] V K Gupta, Asha Gupta, S Singh and J D Anand, Int. J. Mod.

  14. Implications of density-dependent population growth for frequency and density-dependent selection

    Energy Technology Data Exchange (ETDEWEB)

    Smouse, P.E.

    1976-01-01

    The relationship between density-dependent population growth and frequency- and density-dependent selection was investigated. For the haploid asexual case, Malthusian growth leads to constant birth and death rates and constant fitness values. A more general Lotka-Volterrra formulation leads to both density- and frequency-dependent selection. The more general formulation is necessary but not sufficient for polymorphic coexistence in asexual forms. For the diploid sexual case, Malthusian growth leads to frequency-dependent population trajectories, but the basic birth and death rates are constant. A density-dependent model, analogous to the Lotka-Volterra model of the asexual case, leads to both frequency- and density-dependent fitness values and selection differentials. If selective differentials are solely reproductive in origin, whether density dependent or independent, Hardy-Weinberg frequencies characterize the polymorphic equilibrium, when it exists. This is not the case when selection differentials involve survival components, whether density dependent or independent. It is shown that heterosis is not necessary to achieve stable polymorphism and that the polymorphic condition can be maintained by certain types of intergenotypic competition as well.

  15. Density dependence of clutch size: habitat heterogeneity or individual adjustment?

    NARCIS (Netherlands)

    Both, C.

    1998-01-01

    1. Two hypotheses have been proposed to explain density- dependent patterns in reproduction. The habitat heterogeneity hypothesis (HHH) explains density-dependent reproduction at the population level from poorer quality territories in heterogeneous environments only being occupied at high densities.

  16. Stochastic processes and long range dependence

    CERN Document Server

    Samorodnitsky, Gennady

    2016-01-01

    This monograph is a gateway for researchers and graduate students to explore the profound, yet subtle, world of long-range dependence (also known as long memory). The text is organized around the probabilistic properties of stationary processes that are important for determining the presence or absence of long memory. The first few chapters serve as an overview of the general theory of stochastic processes which gives the reader sufficient background, language, and models for the subsequent discussion of long memory. The later chapters devoted to long memory begin with an introduction to the subject along with a brief history of its development, followed by a presentation of what is currently the best known approach, applicable to stationary processes with a finite second moment. The book concludes with a chapter devoted to the author’s own, less standard, point of view of long memory as a phase transition, and even includes some novel results. Most of the material in the book has not previously been publis...

  17. Epidemiological reference ranges for low-density lipoprotein ...

    African Journals Online (AJOL)

    Although there is widespread acceptance that total cholesterol (TC) value reference ranges should be based on epidemiological rather than statistical considerations, the epidemiological action limits for Iow-density lipoprotein cholesterol (LDL-C) are still incomplete and only statistical reference ranges for apolipoprotein B ...

  18. Density-dependent nest predation in waterfowl: the relative importance of nest density versus nest dispersion.

    Science.gov (United States)

    Ringelman, Kevin M; Eadie, John M; Ackerman, Joshua T

    2012-07-01

    When nest predation levels are very high or very low, the absolute range of observable nest success is constrained (a floor/ceiling effect), and it may be more difficult to detect density-dependent nest predation. Density-dependent nest predation may be more detectable in years with moderate predation rates, simply because there can be a greater absolute difference in nest success between sites. To test this, we replicated a predation experiment 10 years after the original study, using both natural and artificial nests, comparing a year when overall rates of nest predation were high (2000) to a year with moderate nest predation (2010). We found no evidence for density-dependent predation on artificial nests in either year, indicating that nest predation is not density-dependent at the spatial scale of our experimental replicates (1-ha patches). Using nearest-neighbor distances as a measure of nest dispersion, we also found little evidence for "dispersion-dependent" predation on artificial nests. However, when we tested for dispersion-dependent predation using natural nests, we found that nest survival increased with shorter nearest-neighbor distances, and that neighboring nests were more likely to share the same nest fate than non-adjacent nests. Thus, at small spatial scales, density-dependence appears to operate in the opposite direction as predicted: closer nearest neighbors are more likely to be successful. We suggest that local nest dispersion, rather than larger-scale measures of nest density per se, may play a more important role in density-dependent nest predation.

  19. Low larval densities in northern populations reinforce range expansion by a Mediterranean damselfly

    DEFF Research Database (Denmark)

    Therry, Lieven; Swaegers, Janne; Dinh, Khuong Van

    2016-01-01

    towards the very edge of the expansion front has been neglected. Density effects may, however, have a profound direct impact on traits involved in range expansion and influence range dynamics. 2. In this study, we contrast the effects of high conspecific larval density typical for established populations...... and low larval density typical for newly founded populations at the edge of the expansion front on a set of larval traits that may affect the range dynamics in the poleward moving damselfly Coenagrion scitulum. We therefore ran an outdoor mesocosm experiment with a low- and high-density treatment close...... in voltinism) at low conspecific density will translate in increased population growth rates. Furthermore, nutritional advantages at low conspecific density may increase investment in dispersal ability. Together, these direct and delayed density-dependent effects that gradually increase towards the expansion...

  20. Density of biogas digestate depending on temperature and composition.

    Science.gov (United States)

    Gerber, Mandy; Schneider, Nico

    2015-09-01

    Density is one of the most important physical properties of biogas digestate to ensure an optimal dimensioning and a precise design of biogas plant components like stirring devices, pumps and heat exchangers. In this study the density of biogas digestates with different compositions was measured using pycnometers at ambient pressure in a temperature range from 293.15 to 313.15K. The biogas digestates were taken from semi-continuous experiments, in which the marine microalga Nannochloropsis salina, corn silage and a mixture of both were used as feedstocks. The results show an increase of density with increasing total solid content and a decrease with increasing temperature. Three equations to calculate the density of biogas digestate were set up depending on temperature as well as on the total solid content, organic composition and elemental composition, respectively. All correlations show a relative deviation below 1% compared to experimental data. Copyright © 2015. Published by Elsevier Ltd.

  1. Saturating interactions in /sup 4/He with density dependence

    Energy Technology Data Exchange (ETDEWEB)

    Bloom, S.D.; Resler, D.A.; Moszkowski, S.A.

    1989-05-03

    With the advent of larger and faster computers, as well as modern shell model codes, nuclear structure calculations for the light nuclei (A<16) which include full 2/bar h/..omega.. model spaces are quite feasible. However, there can be serious problems in the mixing of 2/bar h/..omega.. and higher excitations into the low-lying spectra if the effective interaction is non-saturating. Furthermore, effective interactions which are both saturating and density dependent have not generally been used in previous nuclear structure calculations. Therefore, we have undertaken studies of /sup 4/He using two-body potential interactions which incorporate both saturation and density-dependence. Encouraging initial results in remedying the mixing of 0 and 2/bar h/..omega.. excitations have been obtained. We have also considered the effects of our interaction on the /sup 4/He compressibility and the centroid of the breathing mode strength. First indications are that a saturating effective interaction, with a short-range density dependent part and a long-range density independent part, comes close to matching crude predictions for the compressibility of /sup 4/He. 11 refs., 6 tabs.

  2. Wildlife disease elimination and density dependence

    KAUST Repository

    Potapov, A.

    2012-05-16

    Disease control by managers is a crucial response to emerging wildlife epidemics, yet the means of control may be limited by the method of disease transmission. In particular, it is widely held that population reduction, while effective for controlling diseases that are subject to density-dependent (DD) transmission, is ineffective for controlling diseases that are subject to frequency-dependent (FD) transmission. We investigate control for horizontally transmitted diseases with FD transmission where the control is via culling or harvest that is non-selective with respect to infection and the population can compensate through DD recruitment or survival. Using a mathematical model, we show that culling or harvesting can eradicate the disease, even when transmission dynamics are FD. Eradication can be achieved under FD transmission when DD birth or recruitment induces compensatory growth of new, healthy individuals, which has the net effect of reducing disease prevalence by dilution. We also show that if harvest is used simultaneously with vaccination, and there is high enough transmission coefficient, application of both controls may be less efficient than vaccination alone. We illustrate the effects of these control approaches on disease prevalence for chronic wasting disease in deer where the disease is transmitted directly among deer and through the environment.

  3. A mechanistic analysis of density dependence in algal population dynamics

    Directory of Open Access Journals (Sweden)

    Adrian eBorlestean

    2015-04-01

    Full Text Available Population density regulation is a fundamental principle in ecology, but the specific process underlying functional expression of density dependence remains to be fully elucidated. One view contends that patterns of density dependence are largely fixed across a species irrespective of environmental conditions, whereas another is that the strength and expression of density dependence are fundamentally variable depending on the nature of exogenous or endogenous constraints acting on the population. We conducted a study investigating the expression of density dependence in Chlamydomonas spp. grown under a gradient from low to high nutrient density. We predicted that the relationship between per capita growth rate (pgr and population density would vary from concave up to concave down as nutrient density became less limiting and populations experienced weaker density regulation. Contrary to prediction, we found that the relationship between pgr and density became increasingly concave-up as nutrient levels increased. We also found that variation in pgr increased, and pgr levels reached higher maxima in nutrient-limited environments. Most likely, these results are attributable to population growth suppression in environments with high intraspecific competition due to limited nutrient resources. Our results suggest that density regulation is strongly variable depending on exogenous and endogenous processes acting on the population, implying that expression of density dependence depends extensively on local conditions. Additional experimental work should reveal the mechanisms influencing how the expression of density dependence varies across populations through space and time.

  4. Joint product numerical range and geometry of reduced density matrices

    Science.gov (United States)

    Chen, Jianxin; Guo, Cheng; Ji, Zhengfeng; Poon, Yiu-Tung; Yu, Nengkun; Zeng, Bei; Zhou, Jie

    2017-02-01

    The reduced density matrices of a many-body quantum system form a convex set, whose three-dimensional projection Θ is convex in R3. The boundary ∂Θ of Θ may exhibit nontrivial geometry, in particular ruled surfaces. Two physical mechanisms are known for the origins of ruled surfaces: symmetry breaking and gapless. In this work, we study the emergence of ruled surfaces for systems with local Hamiltonians in infinite spatial dimension, where the reduced density matrices are known to be separable as a consequence of the quantum de Finetti's theorem. This allows us to identify the reduced density matrix geometry with joint product numerical range Π of the Hamiltonian interaction terms. We focus on the case where the interaction terms have certain structures, such that a ruled surface emerges naturally when taking a convex hull of Π. We show that, a ruled surface on ∂Θ sitting in Π has a gapless origin, otherwise it has a symmetry breaking origin. As an example, we demonstrate that a famous ruled surface, known as the oloid, is a possible shape of Θ, with two boundary pieces of symmetry breaking origin separated by two gapless lines.

  5. Density-dependent growth in invasive Lionfish (Pterois volitans.

    Directory of Open Access Journals (Sweden)

    Cassandra E Benkwitt

    Full Text Available Direct demographic density dependence is necessary for population regulation and is a central concept in ecology, yet has not been studied in many invasive species, including any invasive marine fish. The red lionfish (Pterois volitans is an invasive predatory marine fish that is undergoing exponential population growth throughout the tropical western Atlantic. Invasive lionfish threaten coral-reef ecosystems, but there is currently no evidence of any natural population control. Therefore, a manipulative field experiment was conducted to test for density dependence in lionfish. Juvenile lionfish densities were adjusted on small reefs and several demographic rates (growth, recruitment, immigration, and loss were measured throughout an 8-week period. Invasive lionfish exhibited direct density dependence in individual growth rates, as lionfish grew slower at higher densities throughout the study. Individual growth in length declined linearly with increasing lionfish density, while growth in mass declined exponentially with increasing density. There was no evidence, however, for density dependence in recruitment, immigration, or loss (mortality plus emigration of invasive lionfish. The observed density-dependent growth rates may have implications for which native species are susceptible to lionfish predation, as the size and type of prey that lionfish consume is directly related to their body size. The absence of density-dependent loss, however, contrasts with many native coral-reef fish species and suggests that for the foreseeable future manual removals may be the only effective local control of this invasion.

  6. Density dependence in demography and dispersal generates fluctuating invasion speeds.

    Science.gov (United States)

    Sullivan, Lauren L; Li, Bingtuan; Miller, Tom E X; Neubert, Michael G; Shaw, Allison K

    2017-05-09

    Density dependence plays an important role in population regulation and is known to generate temporal fluctuations in population density. However, the ways in which density dependence affects spatial population processes, such as species invasions, are less understood. Although classical ecological theory suggests that invasions should advance at a constant speed, empirical work is illuminating the highly variable nature of biological invasions, which often exhibit nonconstant spreading speeds, even in simple, controlled settings. Here, we explore endogenous density dependence as a mechanism for inducing variability in biological invasions with a set of population models that incorporate density dependence in demographic and dispersal parameters. We show that density dependence in demography at low population densities-i.e., an Allee effect-combined with spatiotemporal variability in population density behind the invasion front can produce fluctuations in spreading speed. The density fluctuations behind the front can arise from either overcompensatory population growth or density-dependent dispersal, both of which are common in nature. Our results show that simple rules can generate complex spread dynamics and highlight a source of variability in biological invasions that may aid in ecological forecasting.

  7. Density-dependent feedbacks can mask environmental drivers of populations

    DEFF Research Database (Denmark)

    Dahlgren, Johan Petter

    I present some results from studies identifying environmental drivers of vital rates and population dynamics when controlling for intraspecific density statistically or experimentally, show that density dependence can be strong even in populations of slow-growing species in stressful habitats......, and argue that controlling for density will often be necessary for identifying spatial variation in environmental drivers of demographic patterns in plants....

  8. Prevalence and strength of density-dependent tree recruitment

    Science.gov (United States)

    Kai Zhu; Christopher W. Woodall; Joao V.D. Monteiro; James S. Clark

    2015-01-01

    Density dependence could maintain diversity in forests, but studies continue to disagree on its role. Part of the disagreement results from the fact that different studies have evaluated different responses (survival, recruitment, or growth) of different stages (seeds, seedlings, or adults) to different inputs (density of seedlings, density or distance to adults). Most...

  9. Experimental evidence for density dependence of reproduction in great tits

    NARCIS (Netherlands)

    Both, Christiaan

    1998-01-01

    1.  Density dependence of avian reproduction has often been analysed using correlations between annual mean reproductive output and population density. Experiments are necessary to prove that density is the cause of the observed patterns, but so far, three out of four experimental studies do not

  10. Experimental evidence for density dependence of reproduction in great tits

    NARCIS (Netherlands)

    Both, C.

    1998-01-01

    1. Density dependence of avian reproduction has often been analysed using correlations between annual mean reproductive output and population density. Experiments are necessary to prove that density is the cause of the observed patterns, but so far, three out of four experimental studies do not

  11. Density dependence of clutch size : habitat heterogeneity or individual adjustment?

    NARCIS (Netherlands)

    Both, Christiaan

    1998-01-01

    1.   Two hypotheses have been proposed to explain density-dependent patterns in reproduction. The habitat heterogeneity hypothesis (HHH) explains density-dependent reproduction at the population level from poorer quality territories in hetero geneous environments only being occupied at high

  12. Development and application of a density dependent matrix ...

    Science.gov (United States)

    Ranging along the Atlantic coast from US Florida to the Maritime Provinces of Canada, the Atlantic killifish (Fundulus heteroclitus) is an important and well-studied model organism for understanding the effects of pollutants and other stressors in estuarine and marine ecosystems. Matrix population models are useful tools for ecological risk assessment because they integrate effects across the life cycle, provide a linkage between endpoints observed in the individual and ecological risk to the population as a whole, and project outcomes for many generations in the future. We developed a density dependent matrix population model for Atlantic killifish by modifying a model developed for fathead minnow (Pimephales promelas) that has proved to be extremely useful, e.g. to incorporate data from laboratory studies and project effects of endocrine disrupting chemicals. We developed a size-structured model (as opposed to one that is based upon developmental stages or age class structure) so that we could readily incorporate output from a Dynamic Energy Budget (DEB) model, currently under development. Due to a lack of sufficient data to accurately define killifish responses to density dependence, we tested a number of scenarios realistic for other fish species in order to demonstrate the outcome of including this ecologically important factor. We applied the model using published data for killifish exposed to dioxin-like compounds, and compared our results to those using

  13. The Ionization Constant of Water over Wide Ranges of Temperature and Density

    Science.gov (United States)

    Bandura, Andrei V.; Lvov, Serguei N.

    2006-03-01

    A semitheoretical approach for the ionization constant of water, KW, is used to fit the available experimental data over wide ranges of density and temperature. Statistical thermodynamics is employed to formulate a number of contributions to the standard state chemical potential of the ionic hydration process. A sorption model is developed for calculating the inner-shell term, which accounts for the ion-water interactions in the immediate ion vicinity. A new analytical expression is derived using the Bragg-Williams approximation that reproduces the dependence of a mean ion solvation number on the solvent chemical potential. The proposed model was found to be correct at the zero-density limit. The final formulation has a simple analytical form, includes seven adjustable parameters, and provides good fitting of the collected KW data, within experimental uncertainties, for a temperature range of 0-800 °C and densities of 0-1.2 g cm-3.

  14. Density-dependent growth in invasive Lionfish (Pterois volitans)

    National Research Council Canada - National Science Library

    Benkwitt, Cassandra E

    2013-01-01

    Direct demographic density dependence is necessary for population regulation and is a central concept in ecology, yet has not been studied in many invasive species, including any invasive marine fish. The red lionfish (Pterois volitans...

  15. Evolution of complex density-dependent dispersal strategies.

    Science.gov (United States)

    Parvinen, Kalle; Seppänen, Anne; Nagy, John D

    2012-11-01

    The question of how dispersal behavior is adaptive and how it responds to changes in selection pressure is more relevant than ever, as anthropogenic habitat alteration and climate change accelerate around the world. In metapopulation models where local populations are large, and thus local population size is measured in densities, density-dependent dispersal is expected to evolve to a single-threshold strategy, in which individuals stay in patches with local population density smaller than a threshold value and move immediately away from patches with local population density larger than the threshold. Fragmentation tends to convert continuous populations into metapopulations and also to decrease local population sizes. Therefore we analyze a metapopulation model, where each patch can support only a relatively small local population and thus experience demographic stochasticity. We investigated the evolution of density-dependent dispersal, emigration and immigration, in two scenarios: adult and natal dispersal. We show that density-dependent emigration can also evolve to a nonmonotone, "triple-threshold" strategy. This interesting phenomenon results from an interplay between the direct and indirect benefits of dispersal and the costs of dispersal. We also found that, compared to juveniles, dispersing adults may benefit more from density-dependent vs. density-independent dispersal strategies.

  16. Field dependence of critical current density in flat superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Kondo, Ryuji [Faculty of Engineering, Oita University, 700 Dannoharu Oita (Japan); Fukami, Takeshi [Department of Materials Science and Engineering, Himeji Institute of Technology, Himeji (Japan); Tamegai, Tsuyoshi, E-mail: ryuji-kondo@susi.oita-u.ac.j [Department of Applied Physics, University of Tokyo, Tokyo (Japan)

    2009-03-01

    Surface field of a thin superconductor YBa{sub 2}Cu{sub 3}O{sub 7-delta} in mixed state is measured by a Hall probe array. To reproduce the measured field profiles, shielding current distributions are determined by numerical iterative calculations without supposing any models for field dependence of critical current density J{sub c} (B). Utilizing the estimated local current density and local magnetic field for x - y coordinates, a field variation of current density is plotted. Though any model for J{sub c} (B) is not used for numerical calculations, the field variation roughly shows a dependence like Kim model.

  17. Density-dependence as a size-independent regulatory mechanism

    NARCIS (Netherlands)

    De Vladar, H.P.

    2006-01-01

    The growth function of populations is central in biomathematics. The main dogma is the existence of density-dependence mechanisms, which can be modelled with distinct functional forms that depend on the size of the Population. One important class of regulatory functions is the theta-logistic, which

  18. Time-Dependent (Current) Density Functional Theory for Periodic Systems

    NARCIS (Netherlands)

    Kootstra, F.; Boeij, P.L. de; Leeuwen, R. van; Snijders, J.G.

    2002-01-01

    In this article we review time-dependent density functional theory for calculating the static and frequency-dependent dielectric function ε(ω) of nonmetallic crystals. We show that a real-space description becomes feasible for solids by using a combination of a lattice-periodic (microscopic) scalar

  19. Impact of density-dependent symmetry energy and Coulomb ...

    Indian Academy of Sciences (India)

    Research Articles Volume 82 Issue 3 March 2014 pp 515-527 ... In this paper, we study the time evolution, impact parameter, and excitation energy dependence of IMF production for the different forms of density-dependent symmetry ... School of Physics and Material Science, Thapar University, Patiala 147 004, India ...

  20. Evaluating the impact of a wide range of vegetation densities on river channel pattern

    Science.gov (United States)

    Pattison, Ian; Roucou, Ron

    2016-04-01

    Braided rivers are very dynamic systems which have complex controls over their planform and flow dynamics. Vegetation is one variable which influences channel geometry and pattern, through its effect on local flow hydraulics and the process continuum of sediment erosion-transport-deposition. Furthermore, where in the braided floodplain stable vegetation develops depends on the temporal sequencing of the river discharge i.e. floods. Understanding the effect of vegetation in these highly dynamic systems has multiple consequences for human activity and floodplain management. This paper focusses on the specific role of vegetation density in controlling braided river form and processes. Previous research in this field has been contradictory; with Gran and Paola (2001) finding that increasing vegetation density decreased the number of active channels. In contrast, Coulthard (2005] observed that as vegetation become denser there was an increase in the number of channels. This was hypothesized to be caused by flow separation around vegetation and the development of bars immediately downstream of the plant. This paper reports the results from a set of experiments in a 4m by 1m flume, where discharge, slope and sediment size were kept constant. Artificial grass was used to represent vegetation with a density ranging from 50 plants/m2 to 400 plants/m2. Digital photographs, using a GoPro camera with a fish eye lens, were taken from ~1m above the flume at an interval of 30 seconds during the 3 hour experiment. The experiments showed that as the vegetation density increased from 50 to 150 plants/m2, the number of channel bars developing doubled from 12 to 24. At vegetation densities greater than 150 plants/m2 there was a decline in the number of bars created to a minimum of 8 bars for a density of 400 plants/m2. We attribute these patterns to the effect that the vegetation has on flow hydraulics, sediment transport processes and the spatial patterns of erosion and deposition. We

  1. Experimental evidence that density dependence strongly influences plant invasions through fragmented landscapes.

    Science.gov (United States)

    Williams, Jennifer L; Levine, Jonathan M

    2018-01-20

    Populations of range expanding species encounter patches of both favorable and unfavorable habitat as they spread across landscapes. Theory shows that increasing patchiness slows the spread of populations modeled with continuously varying population density when dispersal is not influence by the environment or individual behavior. However, as is found in uniformly favorable landscapes, spread remains driven by fecundity and dispersal from low density individuals at the invasion front. In contrast, when modeled populations are composed of discrete individuals, patchiness causes populations to build up to high density before dispersing past unsuitable habitat, introducing an important influence of density dependence on spread velocity. To test the hypothesized interaction between habitat patchiness and density dependence, we simultaneously manipulated these factors in a greenhouse system of annual plants spreading through replicated experimental landscapes. We found that increasing the size of gaps and amplifying the strength of density dependence both slowed spread velocity, but contrary to predictions, the effect of amplified density dependence was similar across all landscape types. Our results demonstrate that the discrete nature of individuals in spreading populations has a strong influence on how both landscape patchiness and density dependence influence spread through demographic and dispersal stochasticity. Both finiteness and landscape structure should be critical components to theoretical predictions of future spread for range expanding native species or invasive species colonizing new habitat. © 2018 by the Ecological Society of America.

  2. Joint product numerical range and geometry of reduced density matrices

    OpenAIRE

    Chen, Jianxin; Guo, Cheng; Ji, Zhengfeng; Poon, Yiu-Tung; Yu, Nengkun; Zeng, Bei; Zhou, Jie

    2016-01-01

    The reduced density matrices of a many-body quantum system form a convex set, whose three-dimensional projection $\\Theta$ is convex in $\\mathbb{R}^3$. The boundary $\\partial\\Theta$ of $\\Theta$ may exhibit nontrivial geometry, in particular ruled surfaces. Two physical mechanisms are known for the origins of ruled surfaces: symmetry breaking and gapless. In this work, we study the emergence of ruled surfaces for systems with local Hamiltonians in infinite spatial dimension, where the reduced d...

  3. Parametrization of the average ionization and radiative cooling rates of carbon plasmas in a wide range of density and temperature

    OpenAIRE

    Gil de la Fe, Juan Miguel; Rodriguez Perez, Rafael; Florido, Ricardo; Garcia Rubiano, Jesus; Mendoza, M. A.; Nuez, A. de la; Espinosa, G.; Martel Escobar, Carlos; Mínguez Torres, Emilio

    2013-01-01

    In this work we present an analysis of the influence of the thermodynamic regime on the monochromatic emissivity, the radiative power loss and the radiative cooling rate for optically thin carbon plasmas over a wide range of electron temperature and density assuming steady state situations. Furthermore, we propose analytical expressions depending on the electron density and temperature for the average ionization and cooling rate based on polynomial fittings which are valid for the whole range...

  4. Charge transfer in time-dependent density functional theory

    Science.gov (United States)

    Maitra, Neepa T.

    2017-10-01

    Charge transfer plays a crucial role in many processes of interest in physics, chemistry, and bio-chemistry. In many applications the size of the systems involved calls for time-dependent density functional theory (TDDFT) to be used in their computational modeling, due to its unprecedented balance between accuracy and efficiency. However, although exact in principle, in practise approximations must be made for the exchange-correlation functional in this theory, and the standard functional approximations perform poorly for excitations which have a long-range charge-transfer component. Intense progress has been made in developing more sophisticated functionals for this problem, which we review. We point out an essential difference between the properties of the exchange-correlation kernel needed for an accurate description of charge-transfer between open-shell fragments and between closed-shell fragments. We then turn to charge-transfer dynamics, which, in contrast to the excitation problem, is a highly non-equilibrium, non-perturbative, process involving a transfer of one full electron in space. This turns out to be a much more challenging problem for TDDFT functionals. We describe dynamical step and peak features in the exact functional evolving over time, that are missing in the functionals currently used. The latter underestimate the amount of charge transferred and manifest a spurious shift in the charge transfer resonance position. We discuss some explicit examples.

  5. Comment on "Conspecific negative density dependence and forest diversity".

    Science.gov (United States)

    Dickie, Ian A; Hurst, Jennifer M; Bellingham, Peter J

    2012-10-26

    Johnson and colleagues (Reports, 18 May 2012, p. 904) claim that conspecific negative density dependence is a pervasive mechanism driving forest diversity, especially for rare tree species. We show that their results are due to a statistical bias in their analysis caused by the exclusion of joint absences.

  6. Bulk viscosity of strange quark matter in density dependent quark ...

    Indian Academy of Sciences (India)

    Abstract. We have studied the bulk viscosity of strange quark matter in the density dependent quark mass model (DDQM) and compared results with calculations done earlier in the MIT bag model where u, d masses were neglected and first order interactions were taken into account. We find that at low temperatures and ...

  7. Impact of density-dependent symmetry energy and Coulomb ...

    Indian Academy of Sciences (India)

    2014-03-07

    Mar 7, 2014 ... exhausted by the pygmy dipole resonance in 68Ni+132Sn, are useful for the investigation of neutron radii and the observables which can shed light on the density dependence of symmetry energy [10,11]. The collective flow [9], pygmy dipole resonance, and neutron skin thickness [4,11] are suggested to ...

  8. Density-dependent changes in reproductive parameters and ...

    African Journals Online (AJOL)

    Biological parameters did not vary in or out of phase with time-series of sea surface temperature in the southern Benguela, weakening the hypothesis of environmentally mediated changes in these parameters and hence providing support for the hypothesis of a direct density-dependent response by sardine. Keywords: ...

  9. Density-dependent compensatory growth in brown trout (Salmo trutta) in nature.

    Science.gov (United States)

    Sundström, L Fredrik; Kaspersson, Rasmus; Näslund, Joacim; Johnsson, Jörgen I

    2013-01-01

    Density-dependence is a major ecological mechanism that is known to limit individual growth. To examine if compensatory growth (unusually rapid growth following a period of imposed slow growth) in nature is density-dependent, one-year-old brown trout (Salmo trutta L.) were first starved in the laboratory, and then released back into their natural stream, either at natural or at experimentally increased population density. The experimental trout were captured three times over a one-year period. We found no differences in growth, within the first month after release (May-June), between the starved fish and the control group (i.e. no evidence of compensation). During the summer however (July-September), the starved fish grew more than the control group (i.e. compensation), and the starved fish released into the stream at a higher density, grew less than those released at a natural density, both in terms of weight and length (i.e. density-dependent compensation). Over the winter (October-April), there were no effects of either starvation or density on weight and length growth. After the winter, starved fish released at either density had caught up with control fish in body size, but recapture rates (proxy for survival) did not indicate any costs of compensation. Our results suggest that compensatory growth in nature can be density-dependent. Thus, this is the first study to demonstrate the presence of ecological restrictions on the compensatory growth response in free-ranging animals.

  10. Energy and centrality dependence of rapidity densities at RHIC energies.

    Science.gov (United States)

    Wang, X N; Gyulassy, M

    2001-04-16

    The energy and centrality dependence of the charged multiplicity per participant nucleon is shown to be able to differentiate between final state saturation and fixed scale perturbative QCD models of initial entropy production in high-energy heavy-ion collisions. The energy dependence is shown to test the nuclear enhancement of the minijet component of the initial conditions, while the centrality dependence provides a key test of whether gluon saturation is reached at RHIC energies. The HIJING model predicts that the rapidity density per participant increases with centrality, while the saturation model prediction is essentially independent of centrality.

  11. Stochasticity and determinism: how density-independent and density-dependent processes affect population variability.

    Science.gov (United States)

    Ohlberger, Jan; Rogers, Lauren A; Stenseth, Nils Chr

    2014-01-01

    A persistent debate in population ecology concerns the relative importance of environmental stochasticity and density dependence in determining variability in adult year-class strength, which contributes to future reproduction as well as potential yield in exploited populations. Apart from the strength of the processes, the timing of density regulation may affect how stochastic variation, for instance through climate, translates into changes in adult abundance. In this study, we develop a life-cycle model for the population dynamics of a large marine fish population, Northeast Arctic cod, to disentangle the effects of density-independent and density-dependent processes on early life-stages, and to quantify the strength of compensatory density dependence in the population. The model incorporates information from scientific surveys and commercial harvest, and dynamically links multiple effects of intrinsic and extrinsic factors on all life-stages, from eggs to spawners. Using a state-space approach we account for observation error and stochasticity in the population dynamics. Our findings highlight the importance of density-dependent survival in juveniles, indicating that this period of the life cycle largely determines the compensatory capacity of the population. Density regulation at the juvenile life-stage dampens the impact of stochastic processes operating earlier in life such as environmental impacts on the production of eggs and climate-dependent survival of larvae. The timing of stochastic versus regulatory processes thus plays a crucial role in determining variability in adult abundance. Quantifying the contribution of environmental stochasticity and compensatory mechanisms in determining population abundance is essential for assessing population responses to climate change and exploitation by humans.

  12. Energy dependence with the number of particles: Density and reduced density matrices functionals

    Science.gov (United States)

    Miranda-Quintana, Ramón A.; Bochicchio, Roberto C.

    2014-02-01

    The energy of a physical domain within a molecular system considered as a quantum open system is analyzed as a functional of the electron distribution dependence with the number of particles. Our attention is focused upon the constrained-search functionals of the electron density, the 1- and 2-reduced density matrices (1-, 2-RDMs) for grand-canonical states. It is shown that functionals of the 2-RDM depend on the number of particles if the ground state energy is not a convex function of them.

  13. Density-dependent vulnerability of forest ecosystems to drought

    Science.gov (United States)

    Bottero, Alessandra; D'Amato, Anthony W.; Palik, Brian J.; Bradford, John B.; Fraver, Shawn; Battaglia, Mike A.; Asherin, Lance A.

    2017-01-01

    1. Climate models predict increasing drought intensity and frequency for many regions, which may have negative consequences for tree recruitment, growth and mortality, as well as forest ecosystem services. Furthermore, practical strategies for minimizing vulnerability to drought are limited. Tree population density, a metric of tree abundance in a given area, is a primary driver of competitive intensity among trees, which influences tree growth and mortality. Manipulating tree population density may be a mechanism for moderating drought-induced stress and growth reductions, although the relationship between tree population density and tree drought vulnerability remains poorly quantified, especially across climatic gradients.2. In this study, we examined three long-term forest ecosystem experiments in two widely distributed North American pine species, ponderosa pine Pinus ponderosa (Lawson & C. Lawson) and red pine Pinus resinosa (Aiton), to better elucidate the relationship between tree population density, growth and drought. These experiments span a broad latitude and aridity range and include tree population density treatments that have been purposefully maintained for several decades. We investigated how tree population density influenced resistance (growth during drought) and resilience (growth after drought compared to pre-drought growth) of stand-level growth during and after documented drought events.3. Our results show that relative tree population density was negatively related to drought resistance and resilience, indicating that trees growing at lower densities were less vulnerable to drought. This result was apparent in all three forest ecosystems, and was consistent across species, stand age and drought intensity.4. Synthesis and applications. Our results highlighted that managing pine forest ecosystems at low tree population density represents a promising adaptive strategy for reducing the adverse impacts of drought on forest growth in coming decades

  14. Outdoor stocking density in free-range laying hens: radio-frequency identification of impacts on range use.

    Science.gov (United States)

    Campbell, D L M; Hinch, G N; Dyall, T R; Warin, L; Little, B A; Lee, C

    2017-01-01

    The number and size of free-range laying hen (Gallus gallus domesticus) production systems are increasing within Australia in response to consumer demand for perceived improvement in hen welfare. However, variation in outdoor stocking density has generated consumer dissatisfaction leading to the development of a national information standard on free-range egg labelling by the Australian Consumer Affairs Ministers. The current Australian Model Code of Practice for Domestic Poultry states a guideline of 1500 hens/ha, but no maximum density is set. Radio-frequency identification (RFID) tracking technology was used to measure daily range usage by individual ISA Brown hens housed in six small flocks (150 hens/flock - 50% of hens tagged), each with access to one of three outdoor stocking density treatments (two replicates per treatment: 2000, 10 000, 20 000 hens/ha), from 22 to 26, 27 to 31 and 32 to 36 weeks of age. There was some variation in range usage across the sampling periods and by weeks 32 to 36 individual hens from the lowest stocking density on average used the range for longer each day (Paccessed the range with 2% of tagged hens in each treatment never venturing outdoors and a large proportion that accessed the range daily (2000 hens/ha: 80.5%; 10 000 hens/ha: 66.5%; 20 000 hens/ha: 71.4%). On average, 38% to 48% of hens were seen on the range simultaneously and used all available areas of all ranges. These results of experimental-sized flocks have implications for determining optimal outdoor stocking densities for commercial free-range laying hens but further research would be needed to determine the effects of increased range usage on hen welfare.

  15. Energy dependence of polymer gels in the orthovoltage energy range

    Directory of Open Access Journals (Sweden)

    Yvonne Roed

    2014-03-01

    Full Text Available Purpose: Ortho-voltage energies are often used for treatment of patients’ superficial lesions, and also for small- animal irradiations. Polymer-Gel dosimeters such as MAGAT (Methacrylic acid Gel and THPC are finding increasing use for 3-dimensional verification of radiation doses in a given treatment geometry. For mega-voltage beams, energy dependence of MAGAT has been quoted as nearly energy-independent. In the kilo-voltage range, there is hardly any literature to shade light on its energy dependence.Methods: MAGAT was used to measure depth-dose for 250 kVp beam. Comparison with ion-chamber data showed a discrepancy increasing significantly with depth. An over-response as much as 25% was observed at a depth of 6 cm.Results and Conclusion: Investigation concluded that 6 cm water in the beam resulted in a half-value-layer (HVL change from 1.05 to 1.32 mm Cu. This amounts to an effective-energy change from 81.3 to 89.5 keV. Response measurements of MAGAT at these two energies explained the observed discrepancy in depth-dose measurements. Dose-calibration curves of MAGAT for (i 250 kVp beam, and (ii 250 kVp beam through 6 cm of water column are presented showing significant energy dependence.-------------------Cite this article as: Roed Y, Tailor R, Pinksy L, Ibbott G. Energy dependence of polymer gels in the orthovoltage energy range. Int J Cancer Ther Oncol 2014; 2(2:020232. DOI: 10.14319/ijcto.0202.32 

  16. Long-range dependence and sea level forecasting

    CERN Document Server

    Ercan, Ali; Abbasov, Rovshan K

    2013-01-01

    This study shows that the Caspian Sea level time series possess long range dependence even after removing linear trends, based on analyses of the Hurst statistic, the sample autocorrelation functions, and the periodogram of the series. Forecasting performance of ARMA, ARIMA, ARFIMA and Trend Line-ARFIMA (TL-ARFIMA) combination models are investigated. The forecast confidence bands and the forecast updating methodology, provided for ARIMA models in the literature, are modified for the ARFIMA models. Sample autocorrelation functions are utilized to estimate the differencing lengths of the ARFIMA

  17. Modelling interactions of toxicants and density dependence in wildlife populations

    Science.gov (United States)

    Schipper, Aafke M.; Hendriks, Harrie W.M.; Kauffman, Matthew J.; Hendriks, A. Jan; Huijbregts, Mark A.J.

    2013-01-01

    1. A major challenge in the conservation of threatened and endangered species is to predict population decline and design appropriate recovery measures. However, anthropogenic impacts on wildlife populations are notoriously difficult to predict due to potentially nonlinear responses and interactions with natural ecological processes like density dependence. 2. Here, we incorporated both density dependence and anthropogenic stressors in a stage-based matrix population model and parameterized it for a density-dependent population of peregrine falcons Falco peregrinus exposed to two anthropogenic toxicants [dichlorodiphenyldichloroethylene (DDE) and polybrominated diphenyl ethers (PBDEs)]. Log-logistic exposure–response relationships were used to translate toxicant concentrations in peregrine falcon eggs to effects on fecundity. Density dependence was modelled as the probability of a nonbreeding bird acquiring a breeding territory as a function of the current number of breeders. 3. The equilibrium size of the population, as represented by the number of breeders, responded nonlinearly to increasing toxicant concentrations, showing a gradual decrease followed by a relatively steep decline. Initially, toxicant-induced reductions in population size were mitigated by an alleviation of the density limitation, that is, an increasing probability of territory acquisition. Once population density was no longer limiting, the toxicant impacts were no longer buffered by an increasing proportion of nonbreeders shifting to the breeding stage, resulting in a strong decrease in the equilibrium number of breeders. 4. Median critical exposure concentrations, that is, median toxicant concentrations in eggs corresponding with an equilibrium population size of zero, were 33 and 46 μg g−1 fresh weight for DDE and PBDEs, respectively. 5. Synthesis and applications. Our modelling results showed that particular life stages of a density-limited population may be relatively insensitive to

  18. Density-Dependent Phase Polyphenism in Nonmodel Locusts: A Minireview

    Directory of Open Access Journals (Sweden)

    Hojun Song

    2011-01-01

    Full Text Available Although the specific mechanisms of locust phase transformation are wellunderstood for model locust species such as the desert locust Schistocerca gregaria and the migratory locust Locusta migratoria, the expressions of density-dependent phase polyphenism in other nonmodel locust species are not wellknown. The present paper is an attempt to review and synthesize what we know about these nonmodel locusts. Based on all available data, I find that locust phase polyphenism is expressed in many different ways in different locust species and identify a pattern that locust species often belong to large taxonomic groups which contain mostly nonswarming grasshopper species. Although locust phase polyphenism has evolved multiple times within Acrididae, I argue that its evolution should be studied from a phylogenetic perspective because I find similar density-dependent phenotypic plasticity among closely related species. Finally, I emphasize the importance of comparative analyses in understanding the evolution of locust phase and propose a phylogeny-based research framework.

  19. Angular momentum dependence of the nuclear level density parameter

    Directory of Open Access Journals (Sweden)

    Gohil M.

    2014-03-01

    Full Text Available Neutron evaporation spectra alongwith γ-multiplicity has been measured from the 185Re* compound nucleus at the excitation energies ~27 and 37 MeV. Statistical model analysis of the experimental data has been carried out to extract the value of the inverse level density parameter k at different angular momentum regions (J corresponding to different γ-multiplicity. It is observed that, for the present system the value of k remains almost constant for different J. The present results on the angular momentum dependence of the nuclear level density (NLD parameter ã (=A/k, for nuclei with A ~180 is quite different from our earlier measurements in case of light and medium mass systems. The present analysis provides useful information to understand the angular momentum dependence of NLD at different nuclear mass regions.

  20. Time dependent density matrix theory and effective interaction

    Energy Technology Data Exchange (ETDEWEB)

    Tohyama, Mitsuru [Kyorin Univ., Mitaka, Tokyo (Japan). School of Medicine

    1998-07-01

    A correlated ground state of {sup 16}O and an E2 giant resonance built on it are calculated using an extended version of the time-dependent Hartree-Fock theory called the time-dependent density-matrix theory (TDDM). The Skyrme force is used in the calculation of both a mean field and two-body correlations. It is found that TDDM gives reasonable ground-state correlations and a large spreading width of the E2 giant resonance when single-particle states in the continuum are treated appropriately. (author)

  1. Density regulation in Northeast Atlantic fish populations: Density dependence is stronger in recruitment than in somatic growth.

    Science.gov (United States)

    Zimmermann, Fabian; Ricard, Daniel; Heino, Mikko

    2018-01-30

    Population regulation is a central concept in ecology, yet in many cases its presence and the underlying mechanisms are difficult to demonstrate. The current paradigm maintains that marine fish populations are predominantly regulated by density-dependent recruitment. While it is known that density-dependent somatic growth can be present too, its general importance remains unknown and most practical applications neglect it. This study aimed to close this gap by for the first time quantifying and comparing density dependence in growth and recruitment over a large set of fish populations. We fitted density-dependent models to time-series data on population size, recruitment and age-specific weight from commercially exploited fish populations in the Northeast Atlantic Ocean and the Baltic Sea. Data were standardized to enable a direct comparison within and among populations, and estimated parameters were used to quantify the impact of density regulation on population biomass. Statistically significant density dependence in recruitment was detected in a large proportion of populations (70%), whereas for density dependence in somatic growth the prevalence of density dependence depended heavily on the method (26% and 69%). Despite age-dependent variability, the density dependence in recruitment was consistently stronger among age groups and between alternative approaches that use weight-at-age or weight increments to assess growth. Estimates of density-dependent reduction in biomass underlined these results: 97% of populations with statistically significant parameters for growth and recruitment showed a larger impact of density-dependent recruitment on population biomass. The results reaffirm the importance of density-dependent recruitment in marine fishes, yet they also show that density dependence in somatic growth is not uncommon. Furthermore, the results are important from an applied perspective because density dependence in somatic growth affects productivity and

  2. Time-dependent density functional theory for quantum transport.

    Science.gov (United States)

    Zheng, Xiao; Chen, GuanHua; Mo, Yan; Koo, SiuKong; Tian, Heng; Yam, ChiYung; Yan, YiJing

    2010-09-21

    Based on our earlier works [X. Zheng et al., Phys. Rev. B 75, 195127 (2007); J. S. Jin et al., J. Chem. Phys. 128, 234703 (2008)], we propose a rigorous and numerically convenient approach to simulate time-dependent quantum transport from first-principles. The proposed approach combines time-dependent density functional theory with quantum dissipation theory, and results in a useful tool for studying transient dynamics of electronic systems. Within the proposed exact theoretical framework, we construct a number of practical schemes for simulating realistic systems such as nanoscopic electronic devices. Computational cost of each scheme is analyzed, with the expected level of accuracy discussed. As a demonstration, a simulation based on the adiabatic wide-band limit approximation scheme is carried out to characterize the transient current response of a carbon nanotube based electronic device under time-dependent external voltages.

  3. Influence of density-dependent competition on foraging and migratory behavior of a subtropical colonial seabird.

    Science.gov (United States)

    Lamb, Juliet S; Satgé, Yvan G; Jodice, Patrick G R

    2017-08-01

    Density-dependent competition for food resources influences both foraging ecology and reproduction in a variety of animals. The relationship between colony size, local prey depletion, and reproductive output in colonial central-place foragers has been extensively studied in seabirds; however, most studies have focused on effects of intraspecific competition during the breeding season, while little is known about whether density-dependent resource depletion influences individual migratory behavior outside the breeding season. Using breeding colony size as a surrogate for intraspecific resource competition, we tested for effects of colony size on breeding home range, nestling health, and migratory patterns of a nearshore colonial seabird, the brown pelican (Pelecanus occidentalis), originating from seven breeding colonies of varying sizes in the subtropical northern Gulf of Mexico. We found evidence for density-dependent effects on foraging behavior during the breeding season, as individual foraging areas increased linearly with the number of breeding pairs per colony. Contrary to our predictions, however, nestlings from more numerous colonies with larger foraging ranges did not experience either decreased condition or increased stress. During nonbreeding, individuals from larger colonies were more likely to migrate, and traveled longer distances, than individuals from smaller colonies, indicating that the influence of density-dependent effects on distribution persists into the nonbreeding period. We also found significant effects of individual physical condition, particularly body size, on migratory behavior, which in combination with colony size suggesting that dominant individuals remain closer to breeding sites during winter. We conclude that density-dependent competition may be an important driver of both the extent of foraging ranges and the degree of migration exhibited by brown pelicans. However, the effects of density-dependent competition on breeding

  4. Evidence for density dependence in foraging and migratory behavior of a subtropical nearshore seabird

    Science.gov (United States)

    Lamb, Juliet S.; Satgé, Yvan G.; Jodice, Patrick

    2017-01-01

    Density-dependent competition for food resources influences both foraging ecology and reproduction in a variety of animals. The relationship between colony size, local prey depletion, and reproductive output in colonial central-place foragers has been extensively studied in seabirds; however, most studies have focused on effects of intraspecific competition during the breeding season, while little is known about whether density-dependent resource depletion influences individual migratory behavior outside the breeding season. Using breeding colony size as a surrogate for intraspecific resource competition, we tested for effects of colony size on breeding home range, nestling health, and migratory patterns of a nearshore colonial seabird, the brown pelican (Pelecanus occidentalis), originating from seven breeding colonies of varying sizes in the subtropical northern Gulf of Mexico. We found evidence for density-dependent effects on foraging behavior during the breeding season, as individual foraging areas increased linearly with the number of breeding pairs per colony. Contrary to our predictions, however, nestlings from more numerous colonies with larger foraging ranges did not experience either decreased condition or increased stress. During nonbreeding, individuals from larger colonies were more likely to migrate, and traveled longer distances, than individuals from smaller colonies, indicating that the influence of density-dependent effects on distribution persists into the nonbreeding period. We also found significant effects of individual physical condition, particularly body size, on migratory behavior, which in combination with colony size suggesting that dominant individuals remain closer to breeding sites during winter. We conclude that density-dependent competition may be an important driver of both the extent of foraging ranges and the degree of migration exhibited by brown pelicans. However, the effects of density-dependent competition on breeding

  5. Modelling density-dependent resistance in insect-pathogen interactions.

    Science.gov (United States)

    White, K A; Wilson, K

    1999-10-01

    We consider a mathematical model for a host-pathogen interaction where the host population is split into two categories: those susceptible to disease and those resistant to disease. Since the model was motivated by studies on insect populations, we consider a discrete-time model to reflect the discrete generations which are common among insect species. Whether an individual is born susceptible or resistant to disease depends on the local population levels at the start of each generation. In particular, we are interested in the case where the fraction of resistant individuals in the population increases as the total population increases. This may be seen as a positive feedback mechanism since disease is the only population control imposed upon the system. Moreover, it reflects recent experimental observations from noctuid moth-baculovirus interactions that pathogen resistance may increase with larval density. We find that the inclusion of a resistant class can stabilise unstable host-pathogen interactions but there is greatest regulation when the fraction born resistant is density independent. Nonetheless, inclusion of density dependence can still allow intrinsically unstable host-pathogen dynamics to be stabilised provided that this effect is sufficiently small. Moreover, inclusion of density-dependent resistance to disease allows the system to give rise to bistable dynamics in which the final outcome is dictated by the initial conditions for the model system. This has implications for the management of agricultural pests using biocontrol agents-in particular, it is suggested that the propensity for density-dependent resistance be determined prior to such a biocontrol attempt in order to be sure that this will result in the prevention of pest outbreaks, rather than their facilitation. Finally we consider how the cost of resistance to disease affects model outcomes and discover that when there is no cost to resistance, the model predicts stable periodic outbreaks of

  6. Whitebark pine, population density, and home-range size of grizzly bears in the greater yellowstone ecosystem.

    Directory of Open Access Journals (Sweden)

    Daniel D Bjornlie

    Full Text Available Changes in life history traits of species can be an important indicator of potential factors influencing populations. For grizzly bears (Ursus arctos in the Greater Yellowstone Ecosystem (GYE, recent decline of whitebark pine (WBP; Pinus albicaulis, an important fall food resource, has been paired with a slowing of population growth following two decades of robust population increase. These observations have raised questions whether resource decline or density-dependent processes may be associated with changes in population growth. Distinguishing these effects based on changes in demographic rates can be difficult. However, unlike the parallel demographic responses expected from both decreasing food availability and increasing population density, we hypothesized opposing behavioral responses of grizzly bears with regard to changes in home-range size. We used the dynamic changes in food resources and population density of grizzly bears as a natural experiment to examine hypotheses regarding these potentially competing influences on grizzly bear home-range size. We found that home-range size did not increase during the period of whitebark pine decline and was not related to proportion of whitebark pine in home ranges. However, female home-range size was negatively associated with an index of population density. Our data indicate that home-range size of grizzly bears in the GYE is not associated with availability of WBP, and, for female grizzly bears, increasing population density may constrain home-range size.

  7. Whitebark pine, population density, and home-range size of grizzly bears in the greater yellowstone ecosystem.

    Science.gov (United States)

    Bjornlie, Daniel D; Van Manen, Frank T; Ebinger, Michael R; Haroldson, Mark A; Thompson, Daniel J; Costello, Cecily M

    2014-01-01

    Changes in life history traits of species can be an important indicator of potential factors influencing populations. For grizzly bears (Ursus arctos) in the Greater Yellowstone Ecosystem (GYE), recent decline of whitebark pine (WBP; Pinus albicaulis), an important fall food resource, has been paired with a slowing of population growth following two decades of robust population increase. These observations have raised questions whether resource decline or density-dependent processes may be associated with changes in population growth. Distinguishing these effects based on changes in demographic rates can be difficult. However, unlike the parallel demographic responses expected from both decreasing food availability and increasing population density, we hypothesized opposing behavioral responses of grizzly bears with regard to changes in home-range size. We used the dynamic changes in food resources and population density of grizzly bears as a natural experiment to examine hypotheses regarding these potentially competing influences on grizzly bear home-range size. We found that home-range size did not increase during the period of whitebark pine decline and was not related to proportion of whitebark pine in home ranges. However, female home-range size was negatively associated with an index of population density. Our data indicate that home-range size of grizzly bears in the GYE is not associated with availability of WBP, and, for female grizzly bears, increasing population density may constrain home-range size.

  8. Density dependence, whitebark pine, and vital rates of grizzly bears

    Science.gov (United States)

    van Manen, Frank T.; Haroldson, Mark A.; Bjornlie, Daniel D; Ebinger, Michael R.; Thompson, Daniel J.; Costello, Cecily M; White, Gary C.

    2016-01-01

    Understanding factors influencing changes in population trajectory is important for effective wildlife management, particularly for populations of conservation concern. Annual population growth of the grizzly bear (Ursus arctos) population in the Greater Yellowstone Ecosystem, USA has slowed from 4.2–7.6% during 1983–2001 to 0.3–2.2% during 2002–2011. Substantial changes in availability of a key food source and bear population density have occurred. Whitebark pine (Pinus albicaulis), the seeds of which are a valuable but variable fall food for grizzly bears, has experienced substantial mortality primarily due to a mountain pine beetle (Dendroctonus ponderosae) outbreak that started in the early 2000s. Positive growth rates of grizzly bears have resulted in populations reaching high densities in some areas and have contributed to continued range expansion. We tested research hypotheses to examine if changes in vital rates detected during the past decade were more associated with whitebark pine decline or, alternatively, increasing grizzly bear density. We focused our assessment on known-fate data to estimate survival of cubs-of-the-year (cubs), yearlings, and independent bears (≥2 yrs), and reproductive transition of females from having no offspring to having cubs. We used spatially and temporally explicit indices for grizzly bear density and whitebark pine mortality as individual covariates. Models indicated moderate support for an increase in survival of independent male bears over 1983–2012, whereas independent female survival did not change. Cub survival, yearling survival, and reproductive transition from no offspring to cubs all changed during the 30-year study period, with lower rates evident during the last 10–15 years. Cub survival and reproductive transition were negatively associated with an index of grizzly bear density, indicating greater declines where bear densities were higher. Our analyses did not support a similar relationship for the

  9. Time-dependent density-functional theory concepts and applications

    CERN Document Server

    Ullrich, Carsten A

    2011-01-01

    Time-dependent density-functional theory (TDDFT) describes the quantum dynamics of interacting electronic many-body systems formally exactly and in a practical and efficient manner. TDDFT has become the leading method for calculating excitation energies and optical properties of large molecules, with accuracies that rival traditional wave-function based methods, but at a fraction of the computational cost.This book is the first graduate-level text on the concepts and applications of TDDFT, including many examples and exercises, and extensive coverage of the literature. The book begins with a s

  10. Limits for density dependent time inhomogeneous Markov processes.

    Science.gov (United States)

    Smith, Andrew G

    2015-10-01

    A new functional law of large numbers to approximate a time inhomogeneous Markov process that is only density dependent in the limit as an index parameter goes to infinity is developed. This extends previous results by other authors to a broader class of Markov processes while relaxing some of the conditions required for those results to hold. This result is applied to a stochastic metapopulation model that accounts for spatial structure as well as within patch dynamics with the novel addition of time dependent dynamics. The resulting nonautonomous differential equation is analysed to provide conditions for extinction and persistence for a number of examples. This condition shows that the migration of a species will positively impact the reproduction in less populated areas while negatively impacting densely populated areas. Crown Copyright © 2015. Published by Elsevier Inc. All rights reserved.

  11. Outdoor stocking density in free-range laying hens: effects on behaviour and welfare.

    Science.gov (United States)

    Campbell, D L M; Hinch, G N; Downing, J A; Lee, C

    2017-06-01

    Free-range laying hen systems are increasing within Australia and research is needed to determine optimal outdoor stocking densities. Six small (n=150 hens) experimental flocks of ISA Brown laying hens were housed with access to ranges simulating one of three outdoor stocking densities with two pen replicates per density: 2000 hens/ha, 10 000 hens/ha or 20 000 hens/ha. Birds were provided daily range access from 21 to 36 weeks of age and the range usage of 50% of hens was tracked using radio-frequency identification technology. Throughout the study, basic external health assessments following a modified version of the Welfare Quality® protocol showed most birds were in visibly good condition (although keel damage was increasingly present with age) with few differences between stocking densities. Toenail length at 36 weeks of age was negatively correlated with hours spent ranging for all pens of birds (all r⩾-0.23, P⩽0.04). At 23 weeks of age, there were no differences between outdoor stocking densities in albumen corticosterone concentrations (P=0.44). At 35 weeks of age, density effects were significant (Pdensity showed the highest albumen corticosterone concentrations, although eggs from hens in the 10 000 hens/ha density showed the lowest concentrations (Pdensities showed the least foraging on the range but the most resting outdoors, with hens from the 20 000 hens/ha densities showing the least amount of resting outdoors (all Pdensities (P=0.08). For each of the health and behavioural measures there were differences between pen replicates within stocking densities. These data show outdoor stocking density has some effects on hen welfare, and it appears that consideration of both individual and group-level behaviour is necessary when developing optimal stocking density guidelines and free-range system management practices.

  12. Density of wild prey modulates lynx kill rates on free-ranging domestic sheep.

    Directory of Open Access Journals (Sweden)

    John Odden

    Full Text Available Understanding the factors shaping the dynamics of carnivore-livestock conflicts is vital to facilitate large carnivore conservation in multi-use landscapes. We investigated how the density of their main wild prey, roe deer Capreolus capreolus, modulates individual Eurasian lynx Lynx lynx kill rates on free-ranging domestic sheep Ovis aries across a range of sheep and roe deer densities. Lynx kill rates on free-ranging domestic sheep were collected in south-eastern Norway from 1995 to 2011 along a gradient of different livestock and wild prey densities using VHF and GPS telemetry. We used zero-inflated negative binomial (ZINB models including lynx sex, sheep density and an index of roe deer density as explanatory variables to model observed kill rates on sheep, and ranked the models based on their AICc values. The model including the effects of lynx sex and sheep density in the zero-inflation model and the effect of lynx sex and roe deer density in the negative binomial part received most support. Irrespective of sheep density and sex, we found the lowest sheep kill rates in areas with high densities of roe deer. As roe deer density decreased, males killed sheep at higher rates, and this pattern held for both high and low sheep densities. Similarly, females killed sheep at higher rates in areas with high densities of sheep and low densities of roe deer. However, when sheep densities were low females rarely killed sheep irrespective of roe deer density. Our quantification of depredation rates can be the first step towards establishing fairer compensation systems based on more accurate and area specific estimation of losses. This study demonstrates how we can use ecological theory to predict where losses of sheep will be greatest, and can be used to identify areas where mitigation measures are most likely to be needed.

  13. Density of wild prey modulates lynx kill rates on free-ranging domestic sheep.

    Science.gov (United States)

    Odden, John; Nilsen, Erlend B; Linnell, John D C

    2013-01-01

    Understanding the factors shaping the dynamics of carnivore-livestock conflicts is vital to facilitate large carnivore conservation in multi-use landscapes. We investigated how the density of their main wild prey, roe deer Capreolus capreolus, modulates individual Eurasian lynx Lynx lynx kill rates on free-ranging domestic sheep Ovis aries across a range of sheep and roe deer densities. Lynx kill rates on free-ranging domestic sheep were collected in south-eastern Norway from 1995 to 2011 along a gradient of different livestock and wild prey densities using VHF and GPS telemetry. We used zero-inflated negative binomial (ZINB) models including lynx sex, sheep density and an index of roe deer density as explanatory variables to model observed kill rates on sheep, and ranked the models based on their AICc values. The model including the effects of lynx sex and sheep density in the zero-inflation model and the effect of lynx sex and roe deer density in the negative binomial part received most support. Irrespective of sheep density and sex, we found the lowest sheep kill rates in areas with high densities of roe deer. As roe deer density decreased, males killed sheep at higher rates, and this pattern held for both high and low sheep densities. Similarly, females killed sheep at higher rates in areas with high densities of sheep and low densities of roe deer. However, when sheep densities were low females rarely killed sheep irrespective of roe deer density. Our quantification of depredation rates can be the first step towards establishing fairer compensation systems based on more accurate and area specific estimation of losses. This study demonstrates how we can use ecological theory to predict where losses of sheep will be greatest, and can be used to identify areas where mitigation measures are most likely to be needed.

  14. Experimental Examination of Intraspecific Density-Dependent Competition during the Breeding Period in Monarch Butterflies (Danaus plexippus)

    Science.gov (United States)

    Flockhart, D. T. Tyler; Martin, Tara G.; Norris, D. Ryan

    2012-01-01

    A central goal of population ecology is to identify the factors that regulate population growth. Monarch butterflies (Danaus plexippus) in eastern North America re-colonize the breeding range over several generations that result in population densities that vary across space and time during the breeding season. We used laboratory experiments to measure the strength of density-dependent intraspecific competition on egg laying rate and larval survival and then applied our results to density estimates of wild monarch populations to model the strength of density dependence during the breeding season. Egg laying rates did not change with density but larvae at high densities were smaller, had lower survival, and weighed less as adults compared to lower densities. Using mean larval densities from field surveys resulted in conservative estimates of density-dependent population reduction that varied between breeding regions and different phases of the breeding season. Our results suggest the highest levels of population reduction due to density-dependent intraspecific competition occur early in the breeding season in the southern portion of the breeding range. However, we also found that the strength of density dependence could be almost five times higher depending on how many life-stages were used as part of field estimates. Our study is the first to link experimental results of a density-dependent reduction in vital rates to observed monarch densities in the wild and show that the effects of density dependent competition in monarchs varies across space and time, providing valuable information for developing robust, year-round population models in this migratory organism. PMID:22984614

  15. Experimental examination of intraspecific density-dependent competition during the breeding period in monarch butterflies (Danaus plexippus.

    Directory of Open Access Journals (Sweden)

    D T Tyler Flockhart

    Full Text Available A central goal of population ecology is to identify the factors that regulate population growth. Monarch butterflies (Danaus plexippus in eastern North America re-colonize the breeding range over several generations that result in population densities that vary across space and time during the breeding season. We used laboratory experiments to measure the strength of density-dependent intraspecific competition on egg laying rate and larval survival and then applied our results to density estimates of wild monarch populations to model the strength of density dependence during the breeding season. Egg laying rates did not change with density but larvae at high densities were smaller, had lower survival, and weighed less as adults compared to lower densities. Using mean larval densities from field surveys resulted in conservative estimates of density-dependent population reduction that varied between breeding regions and different phases of the breeding season. Our results suggest the highest levels of population reduction due to density-dependent intraspecific competition occur early in the breeding season in the southern portion of the breeding range. However, we also found that the strength of density dependence could be almost five times higher depending on how many life-stages were used as part of field estimates. Our study is the first to link experimental results of a density-dependent reduction in vital rates to observed monarch densities in the wild and show that the effects of density dependent competition in monarchs varies across space and time, providing valuable information for developing robust, year-round population models in this migratory organism.

  16. Record length requirement of long-range dependent teletraffic

    Science.gov (United States)

    Li, Ming

    2017-04-01

    This article contributes the highlights mainly in two folds. On the one hand, it presents a formula to compute the upper bound of the variance of the correlation periodogram measurement of teletraffic (traffic for short) with long-range dependence (LRD) for a given record length T and a given value of the Hurst parameter H (Theorems 1 and 2). On the other hand, it proposes two formulas for the computation of the variance upper bound of the correlation periodogram measurement of traffic of fractional Gaussian noise (fGn) type and the generalized Cauchy (GC) type, respectively (Corollaries 1 and 2). They may constitute a reference guideline of record length requirement of traffic with LRD. In addition, record length requirement for the correlation periodogram measurement of traffic with either the Schuster type or the Bartlett one is studied and the present results about it show that both types of periodograms may be used for the correlation measurement of traffic with a pre-desired variance bound of correlation estimation. Moreover, real traffic in the Internet Archive by the Special Interest Group on Data Communication under the Association for Computing Machinery of US (ACM SIGCOMM) is analyzed in the case study in this topic.

  17. Insect herbivores, density dependence, and the performance of the perennial herb Solanum carolinense.

    Science.gov (United States)

    Underwood, Nora; Halpern, Stacey L

    2012-05-01

    How insect herbivores affect plant performance is of central importance to basic and applied ecology. A full understanding of herbivore effects on plant performance requires understanding interactions (if any) of herbivore effects with plant density and size because these interactions will be critical for determining how herbivores influence plant population size. However, few studies have considered these interactions, particularly over a wide enough range of densities to detect nonlinear effects. Here we ask whether plant density and herbivores influence plant performance linearly or nonlinearly, how plant density affects herbivore damage, and how herbivores alter density dependence in transitions between plant size classes. In a large field experiment, we manipulated the density of the herbaceous perennial plant Solanum carolinense and herbivore presence in a fully crossed design. We measured plant size, sexual reproduction, and damage to plants in two consecutive years, and asexual reproduction of new stems in the second year, allowing us to characterize both plant performance and rates of transition between plant size classes across years. We found nonlinear effects of plant density on damage. Damage by herbivores and plant density both influenced sexual and asexual reproduction of S. carolinense; these effects were mostly mediated via effects on plant size. Importantly, we found that herbivores altered the pattern of linear density dependence in some transition rates (including survival and asexual reproduction) between plant size classes. These results suggest that understanding the ecological or evolutionary effects of herbivores on plant populations requires consideration of plant density and plant size, because feedbacks between density, herbivores, and plant size may complicate longer-term dynamics.

  18. Progress in Time-Dependent Density-Functional Theory

    CERN Document Server

    Casida, M E

    2011-01-01

    The classic density-functional theory (DFT) formalism introduced by Hohenberg, Kohn, and Sham in the mid-1960s, is based upon the idea that the complicated N-electron wavefunction can be replaced with the mathematically simpler 1-electron charge density in electronic struc- ture calculations of the ground stationary state. As such, ordinary DFT is neither able to treat time-dependent (TD) problems nor describe excited electronic states. In 1984, Runge and Gross proved a theorem making TD-DFT formally exact. Information about electronic excited states may be obtained from this theory through the linear response (LR) theory formalism. Begin- ning in the mid-1990s, LR-TD-DFT became increasingly popular for calculating absorption and other spectra of medium- and large-sized molecules. Its ease of use and relatively good accuracy has now brought LR-TD-DFT to the forefront for this type of application. As the number and the diversity of applications of TD-DFT has grown, so too has grown our understanding of the str...

  19. Density dependence triggers runaway selection of reduced senescence.

    Directory of Open Access Journals (Sweden)

    Robert M Seymour

    2007-12-01

    Full Text Available In the presence of exogenous mortality risks, future reproduction by an individual is worth less than present reproduction to its fitness. Senescent aging thus results inevitably from transferring net fertility into younger ages. Some long-lived organisms appear to defy theory, however, presenting negligible senescence (e.g., hydra and extended lifespans (e.g., Bristlecone Pine. Here, we investigate the possibility that the onset of vitality loss can be delayed indefinitely, even accepting the abundant evidence that reproduction is intrinsically costly to survival. For an environment with constant hazard, we establish that natural selection itself contributes to increasing density-dependent recruitment losses. We then develop a generalized model of accelerating vitality loss for analyzing fitness optima as a tradeoff between compression and spread in the age profile of net fertility. Across a realistic spectrum of senescent age profiles, density regulation of recruitment can trigger runaway selection for ever-reducing senescence. This novel prediction applies without requirement for special life-history characteristics such as indeterminate somatic growth or increasing fecundity with age. The evolution of nonsenescence from senescence is robust to the presence of exogenous adult mortality, which tends instead to increase the age-independent component of vitality loss. We simulate examples of runaway selection leading to negligible senescence and even intrinsic immortality.

  20. Density-functional perturbation theory goes time-dependent

    Directory of Open Access Journals (Sweden)

    Gebauer, Ralph

    2008-05-01

    Full Text Available The scope of time-dependent density-functional theory (TDDFT is limited to the lowest portion of the spectrum of rather small systems (a few tens of atoms at most. In the static regime, density-functional perturbation theory (DFPT allows one to calculate response functions of systems as large as currently dealt with in ground-state simulations. In this paper we present an effective way of combining DFPT with TDDFT. The dynamical polarizability is first expressed as an off-diagonal matrix element of the resolvent of the Kohn-Sham Liouvillian super-operator. A DFPT representation of response functions allows one to avoid the calculation of unoccupied Kohn-Sham orbitals. The resolvent of the Liouvillian is finally conveniently evaluated using a newly developed non-symmetric Lanczos technique, which allows for the calculation of the entire spectrum with a single Lanczos recursion chain. Each step of the chain essentially requires twice as many operations as a single step of the iterative diagonalization of the unperturbed Kohn-Sham Hamiltonian or, for that matter, as a single time step of a Car-Parrinello molecular dynamics run. The method will be illustrated with a few case molecular applications.

  1. High density, multi-range analog output Versa Module Europa board for control system applications

    Science.gov (United States)

    Singh, Kundan; Das, Ajit Lal

    2014-01-01

    A new VMEDAC64, 12-bit 64 channel digital-to-analog converter, a Versa Module Europa (VME) module, features 64 analog voltage outputs with user selectable multiple ranges, has been developed for control system applications at Inter University Accelerator Centre. The FPGA (Field Programmable Gate Array) is the module's core, i.e., it implements the DAC control logic and complexity of VMEbus slave interface logic. The VMEbus slave interface and DAC control logic are completely designed and implemented on a single FPGA chip to achieve high density of 64 channels in a single width VME module and will reduce the module count in the control system applications, and hence will reduce the power consumption and cost of overall system. One of our early design goals was to develop the VME interface such that it can be easily integrated with the peripheral devices and satisfy the timing specifications of VME standard. The modular design of this module reduces the amount of time required to develop other custom modules for control system. The VME slave interface is written as a single component inside FPGA which will be used as a basic building block for any VMEbus interface project. The module offers multiple output voltage ranges depending upon the requirement. The output voltage range can be reduced or expanded by writing range selection bits in the control register. The module has programmable refresh rate and by default hold capacitors in the sample and hold circuit for each channel are charged periodically every 7.040 ms (i.e., update frequency 284 Hz). Each channel has software controlled output switch which disconnects analog output from the field. The modularity in the firmware design on FPGA makes the debugging very easy. On-board DC/DC converters are incorporated for isolated power supply for the analog section of the board.

  2. Time-dependent probability density function in cubic stochastic processes

    Science.gov (United States)

    Kim, Eun-jin; Hollerbach, Rainer

    2016-11-01

    We report time-dependent probability density functions (PDFs) for a nonlinear stochastic process with a cubic force using analytical and computational studies. Analytically, a transition probability is formulated by using a path integral and is computed by the saddle-point solution (instanton method) and a new nonlinear transformation of time. The predicted PDF p (x ,t ) in general involves a time integral, and useful PDFs with explicit dependence on x and t are presented in certain limits (e.g., in the short and long time limits). Numerical simulations of the Fokker-Planck equation provide exact time evolution of the PDFs and confirm analytical predictions in the limit of weak noise. In particular, we show that transient PDFs behave drastically differently from the stationary PDFs in regard to the asymmetry (skewness) and kurtosis. Specifically, while stationary PDFs are symmetric with the kurtosis smaller than 3, transient PDFs are skewed with the kurtosis larger than 3; transient PDFs are much broader than stationary PDFs. We elucidate the effect of nonlinear interaction on the strong fluctuations and intermittency in the relaxation process.

  3. Home range and density of three sympatric felids in the Southern Atlantic Forest, Brazil.

    Science.gov (United States)

    Kasper, C B; Schneider, A; Oliveira, T G

    2016-02-01

    Home range and minimal population densities of Southern tiger cat (Leopardus guttulus), margay (Lepardus wiedii) and jaguarundi (Puma yagouaroundi) were estimated between 2005 and 2006 in Taquari Valley, near the southern edge of the Atlantic Rainforest in Brazil. Home range data were collected by conventional radio telemetry (VHF) locations in a highly fragmented landscape. The average home range size, calculated using 95% kernel density estimates, was 16.01 km2 for Southern tiger cat, 21.85 km2 for margay and 51.45 km2 for jaguarundi. Telemetry data were used to obtain minimal density estimates of 0.08 Southern tiger cats / km2, and 0.04 jaguarundi / km2. The density estimates arise from areas where ocelot (Leopardus pardalis) and other larger-bodied carnivores were locally extinct, and they suggest a specific type of mesopredator release known as the ocelot effect, which is likely enabling the increase in smaller felid populations in this area.

  4. Native birds and alien insects: spatial density dependence in songbird predation of invading oak gallwasps.

    Directory of Open Access Journals (Sweden)

    Karsten Schönrogge

    Full Text Available Revealing the interactions between alien species and native communities is central to understanding the ecological consequences of range expansion. Much has been learned through study of the communities developing around invading herbivorous insects. Much less, however, is known about the significance of such aliens for native vertebrate predators for which invaders may represent a novel food source. We quantified spatial patterns in native bird predation of invading gall-inducing Andricus wasps associated with introduced Turkey oak (Quercus cerris at eight sites across the UK. These gallwasps are available at high density before the emergence of caterpillars that are the principle spring food of native insectivorous birds. Native birds showed positive spatial density dependence in gall attack rates at two sites in southern England, foraging most extensively on trees with highest gall densities. In a subsequent study at one of these sites, positive spatial density dependence persisted through four of five sequential week-long periods of data collection. Both patterns imply that invading galls are a significant resource for at least some native bird populations. Density dependence was strongest in southern UK bird populations that have had longest exposure to the invading gallwasps. We hypothesise that this pattern results from the time taken for native bird populations to learn how to exploit this novel resource.

  5. Latitudinal Density Dependence of Magnetic Field Lines Inferred from Polar Plasma Wave Data

    Science.gov (United States)

    Goldstein, J.; Denton, R. E.; Hudson, M. K.; Miftakhova, E. G.; Menietti, J. D.; Gallagher, D. L.

    2000-01-01

    Using observations of the electron density, n(sub e), based on measurement of the upper hybrid resonance frequency by the Polar spacecraft Plasma Wave Instrument, we have examined the radial density dependence along field lines in the outer plasmasphere and the near plasmatrough. Sampled L values range from 2.5 to 6.6. Our technique depends on the fact that Polar crosses particular L values at two different points with different radial distance R. In our plasmaspheric data set (n(sub e) > 100/cm3), we find that on average n(sub e) is flat along field lines from the equator up to the latitudes sampled by Polar (R approximately equal to or > 2.0). In the plasmatrough data set (n(sub e) < 100/cm-3), there is on average a mild radial dependence n(sub e) varies as R(exp -1.7).

  6. Lengthscale-Dependent Solvation and Density Fluctuations in n-Octane.

    Science.gov (United States)

    Wu, Eugene; Garde, Shekhar

    2015-07-23

    Much attention has been focused on the solvation and density fluctuations in water over the past decade. These studies have brought to light interesting physical features of solvation in condensed media, especially the dependence of solvation on the solute lengthscale, which may be general to many fluids. Here, we focus on the lengthscale-dependent solvation and density fluctuations in n-octane, a simple organic liquid. Using extensive molecular simulations, we show a crossover in the solvation of solvophobic solutes with increasing size in n-octane, with the specifics of the crossover depending on the shape of the solute. Large lengthscale solvation, which is dominated by interface formation, emerges over subnanoscopic lengthscales. The crossover in n-octane occurs at smaller lengthscales than that in water. We connect the lengthscale of crossover to the range of attractive interactions in the fluid. The onset of the crossover is accompanied by the emergence of non-Gaussian tails in density fluctuations in solute shaped observation volumes. Simulations over a range of temperatures highlight a corresponding thermodynamic crossover in solvation. Qualitative similarities between lengthscale-dependent solvation in water, n-octane, and Lennard-Jones fluids highlight the generality of the underlying physics of solvation.

  7. Effective-range dependence of two-dimensional Fermi gases

    Science.gov (United States)

    Schonenberg, L. M.; Verpoort, P. C.; Conduit, G. J.

    2017-08-01

    The Feshbach resonance provides precise control over the scattering length and effective range of interactions between ultracold atoms. We propose the ultratransferable pseudopotential to model effective interaction ranges -1.5 ≤kF2Reff2≤0 , where Reff is the effective range and kF is the Fermi wave vector, describing narrow to broad Feshbach resonances. We develop a mean-field treatment and exploit the pseudopotential to perform a variational and diffusion Monte Carlo study of the ground state of the two-dimensional Fermi gas, reporting on the ground-state energy, contact, condensate fraction, momentum distribution, and pair-correlation functions as a function of the effective interaction range across the BEC-BCS crossover. The limit kF2Reff2→-∞ is a gas of bosons with zero binding energy, whereas ln(kFa )→-∞ corresponds to noninteracting bosons with infinite binding energy.

  8. Experimental evidence for density-dependent reproduction in a cooperatively breeding passerine

    NARCIS (Netherlands)

    Brouwer, Lyanne; Tinbergen, Joost M.; Both, Christiaan; Bristol, Rachel; Richardson, David S.; Komdeur, Jan; Sauer, J.R.

    Temporal variation in survival, fecundity, and dispersal rates is associated with density-dependent and density-independent processes. Stable natural populations are expected to be regulated by density-dependent factors. However, detecting this by investigating natural variation in density is

  9. Alternative separation of exchange and correlation energies in range-separated density-functional perturbation theory

    DEFF Research Database (Denmark)

    Cornaton, Y.; Stoyanova, A.; Jensen, Hans Jørgen Aagaard

    2013-01-01

    An alternative separation of short-range exchange and correlation energies is used in the framework of second-order range-separated density-functional perturbation theory. This alternative separation was initially proposed by Toulouse and relies on a long-range-interacting wave function instead...... of the noninteracting Kohn-Sham one. When second-order corrections to the density are neglected, the energy expression reduces to a range-separated double-hybrid (RSDH) type of functional, RSDHf, where "f" stands for "full-range integrals" as the regular full-range interaction appears explicitly in the energy...... on the potential energy curves in the equilibrium region, improving the accuracy of binding energies and equilibrium bond distances when second-order perturbation theory is appropriate....

  10. Surface properties of liquid mercury: a comparison of density-dependent and density-independent force fields

    OpenAIRE

    Iakovlev, A.; Bedrov, D; Müller, M

    2014-01-01

    Motivated by an experimental interest we investigate by the means of atomistic Molecular Dynamics simulation the ability of density-independent, empiric density-dependent, and recently proposed embedded-atom force fields for liquid mercury to predict the surface tension of the free surface of liquid mercury at the temperature of 293~K. The effect of the density dependence of the studied models on the liquid-vapor coexistence and surface tension is discussed in detail. In view of computational...

  11. Widespread density-dependent seedling mortality promotes species coexistence in a highly diverse Amazonian rain forest.

    Science.gov (United States)

    Metz, Margaret R; Sousa, Wayne P; Valencia, Renato

    2010-12-01

    Negative density-dependent mortality can promote species coexistence through a spacing mechanism that prevents species from becoming too locally abundant. Negative density-dependent seedling mortality can be caused by interactions among seedlings or between seedlings and neighboring adults if the density of neighbors affects the strength of competition or facilitates the attack of natural enemies. We investigated the effects of seedling and adult neighborhoods on the survival of newly recruited seedlings for multiple cohorts of known age from 163 species in Yasuni National Park, Ecuador, an ever-wet, hyper-diverse lowland Amazonian rain forest. At local scales, we found a strong negative impact on first-year survival of conspecific seedling densities and adult abundance in multiple neighborhood sizes and a beneficial effect of a local tree neighborhood that is distantly related to the focal seedling. Once seedlings have survived their first year, they also benefit from a more phylogenetically dispersed seedling neighborhood. Across species, we did not find evidence that rare species have an advantage relative to more common species, or a community compensatory trend. These results suggest that the local biotic neighborhood is a strong influence on early seedling survival for species that range widely in their abundance and life history. These patterns in seedling survival demonstrate the role of density-dependent seedling dynamics in promoting and maintaining diversity in understory seedling assemblages. The assemblage-wide impacts of species abundance distributions may multiply with repeated cycles of recruitment and density-dependent seedling mortality and impact forest diversity or the abundance of individual species over longer time scales.

  12. Effective-range dependence of resonant Fermi gases

    Science.gov (United States)

    Schonenberg, L. M.; Conduit, G. J.

    2017-01-01

    A Fermi gas of cold atoms allows precise control over the dimensionless effective range, kFReff , of the Feshbach resonance. Our pseudopotential formalism allows us to create smooth potentials with effective range, -2 ≤kFReff≤2 , which we use for a variational and diffusion Monte Carlo study of the ground state of a unitary Fermi gas. We report values for the universal constants of ξ =0.388 (1 ) and ζ =0.087 (1 ) , and compute the condensate fraction, momentum distribution, and pair correlations functions. Finally, we show that a gas with kFReff≳1.9 is thermodynamically unstable.

  13. Bracket bond strength dependence on light power density.

    Science.gov (United States)

    Staudt, Christine Bettina; Krejci, Ivo; Mavropoulos, Anestis

    2006-08-01

    In order to reduce curing time for bracket bonding with light-cured composites, manufacturers increase the power density (PD) of light sources. The present study aims at investigating the relationship between PD and shear bond strength (SBS) at short exposure time. Stainless steel brackets were bonded to bovine incisors using light-cured adhesive. Six groups of 20 incisors each were exposed to 4s of halogen light with different PD increasing from 500 to 3000 mW/cm(2) in steps of 500 mW/cm(2). Two more groups were exposed to a PD of 3000 mW/cm(2) for 6s (n=15) and 8s (n=19), thus simulating non-available PD of 4500 and 6000 mW/cm(2) for 4s. A halogen lamp with a PD of 1000 mW/cm(2) was used for 40s in the control group (n=15). After storage for 24h at 37 degrees C in water, SBS and adhesive remnant index (ARI) were recorded. SBS was significantly different among groups (ANOVA, pbracket/adhesive interface. Our findings show the SBS dependence on PD, and thus provide a valuable tool for the development of light-curing systems. An exponential model suggests that SBS enters a region of saturation and cannot be improved significantly by further increasing PD.

  14. Dissecting the roles of local packing density and longer-range effects in protein sequence evolution

    CERN Document Server

    Shahmoradi, Amir

    2015-01-01

    What are the structural determinants of protein sequence evolution? A number of site-specific structural characteristics have been proposed, most of which are broadly related to either the density of contacts or the solvent accessibility of individual residues. Most importantly, there has been disagreement in the literature over the relative importance of solvent accessibility and local packing density for explaining site-specific sequence variability in proteins. We show here that this discussion has been confounded by the definition of local packing density. The most commonly used measures of local packing, such as the contact number and the weighted contact number, represent by definition the combined effects of local packing density and longer-range effects. As an alternative, we here propose a truly local measure of packing density around a single residue, based on the Voronoi cell volume. We show that the Voronoi cell volume, when calculated relative to the geometric center of amino-acid side chains, be...

  15. Are populations of European earwigs, Forficula auricularia, density dependent?

    DEFF Research Database (Denmark)

    Moerkens, R.; Leirs, H; Peusens, G.

    2009-01-01

    and various apple aphid species. Earwigs therefore play an important role in integrated pest management in fruit orchards and are essential in organic top fruit cultures. However, earwig populations are very unstable, showing large between-year variation in densities, which limits their practical use...... also observed a yearly population crash at the time of moulting into adults. This population decrease was correlated with earwig numbers at peak density. The crash occurred at lower earwig densities in apple orchards than in pear orchards. Six possible regulating mechanisms for this density......, hereby increasing population densities in the orchards....

  16. Postcatastrophe population dynamics and density dependence of an endemic island duck

    Science.gov (United States)

    Seavy, N.E.; Reynolds, M.H.; Link, W.A.; Hatfield, J.S.

    2009-01-01

    Laysan ducks (Anas laysanensis) are restricted to approximately 9 km2 in the Northwestern Hawaiian Islands, USA. To evaluate the importance of density dependence for Laysan ducks, we conducted a Bayesian analysis to estimate the parameters of a Gompertz model and the magnitude of process variation and observation error based on the fluctuations in Laysan duck abundance on Laysan Island from 1994 to 2007. This model described a stationary distribution for the population at carrying capacity that fluctuates around a long-term mean of 456 ducks and is between 316 to 636 ducks 95% of the time. This range of expected variability can be used to identify changes in population size that warn of catastrophic events. Density-dependent population dynamics may explain the recovery of Laysan duck from catastrophic declines and allow managers to identify population monitoring thresholds.

  17. Application of ferrofluid density separation to particles in the micrometer-size range

    Energy Technology Data Exchange (ETDEWEB)

    Strebin, R.S. Jr.; Johnson, J.W.; Robertson, D.M.

    1976-02-01

    A device designed and described by AVCO* as a ''Ferrofluid Density Separator''/sup (1)/ develops an apparent fluid density from nominally 2 to 20 g/cm/sup 3/ dependent on the magnitude of an imposed magnetic field gradient. The ferrofluid retains other normal properties of a liquid. One of these devices and a concentration series of ferrofluids were obtained in order to determine the practicality of separating groups of micrometer-size particles into density fractions. Such separations would be of enormous value in the study of various particle burdens because particles of interest are almost always diluted with overwhelming amounts of other particles. The results of a study of separations of micrometer-size particles with the ferrofluid density separator are presented.

  18. Density-dependent growth of the polychaete Diopatra aciculata

    Directory of Open Access Journals (Sweden)

    Milada Safarik

    2006-12-01

    Full Text Available Effects of intraspecific density on growth of the tube-building polychaete Diopatra aciculata (Onuphidae were examined over a three-month period within a marine worm aquaculture facility. Three polychaete densities (500, 1000 and 2000 worms/m2 were represented within triplicate 0.30 m2 boxes containing late juvenile D. aciculata, sandy sediment and recirculating seawater. Daily food ration per worm was held constant across all density levels. Total length, weight and number of segments were recorded for 20 polychaetes randomly removed from each of nine treatment boxes at weeks 1, 7 and 14. Mean daily growth was higher during weeks 1-7 than during weeks 7-14 for all growth variables at each density level. Polychaetes at the highest density level exhibited lower rates of growth and more broken and/or regenerating posterior segments than those at low density. High D. aciculata density was also associated with reduced dissolved oxygen concentrations and high polychaete mortality (20%. At medium polychaete density (1000/m2, D. aciculata exhibited low levels of apparent stress and high biomass return per unit area, both of which are important considerations in the aquaculture rearing of this species. We suggest that further studies focus on age- and size-related factors contributing to density effects on polychaete growth.

  19. Density-dependent growth and metamorphosis in the larval bronze ...

    Indian Academy of Sciences (India)

    The tadpoles were raised as siblings or in groups of non-siblings at increasing density levels, viz. 15, 30, 60 and 120/5 l water. With an increase in density level from 15 to 120 tadpoles/5 l water, duration of the larval stage increased and fewer individuals metamorphosed irrespective of whether they belonged to sibling or ...

  20. Density-dependent diffusion in the periodic Lorentz gas

    CERN Document Server

    Klages, R; Dellago, Chr.

    1999-01-01

    We study the deterministic diffusion coefficient of the two-dimensional periodic Lorentz gas as a function of the density of scatterers. Results obtained from computer simulations are compared to the analytical approximation of Machta and Zwanzig [Phys.Rev.Lett. 50, 1959 (1983)] showing that their argument is only correct in the limit of high densities. We discuss how the Machta-Zwanzig argument, which is based on treating diffusion as a Markovian hopping process on a lattice, can be corrected systematically by including microscopic correlations. We furthermore show that, on a fine scale, the diffusion coefficient is a non-trivial function of the density. We finally argue that, on a coarse scale and for lower densities, the diffusion coefficient exhibits a Boltzmann-like behavior, whereas for very high densities it crosses over to a regime which can be understood qualitatively by the Machta-Zwanzig approximation.

  1. Density dependence drives habitat production and survivorship of Acropora cervicornis used for restoration on a Caribbean coral reef

    Directory of Open Access Journals (Sweden)

    Mark C Ladd

    2016-12-01

    Full Text Available AbstractCoral restoration is gaining traction as a viable strategy to help restore degraded reefs. While the nascent field of coral restoration has rapidly progressed in the past decade, significant knowledge gaps remain regarding the drivers of restoration success that may impede our ability to effectively restore coral reef communities. Here, we conducted a field experiment to investigate the influence of coral density on the growth, habitat production, and survival of corals outplanted for restoration. We used nursery-raised colonies of Acropora cervicornis to experimentally establish populations of corals with either 3, 6, 12, or 24 corals within 4m2 plots, generating a gradient of coral densities ranging from 0.75 corals m-2 to 12 corals m-2. After 13 months we found that density had a significant effect on the growth, habitat production, and survivorship of restored corals. We found that coral survivorship increased as colony density decreased. Importantly, the signal of density dependent effects was context dependent. Our data suggest that positive density dependent effects influenced habitat production at densities of 3 corals m-2, but further increases in density resulted in negative density dependent effects with decreasing growth and survivorship of corals. These findings highlight the importance of density dependence for coral restoration planning and demonstrate the need to evaluate the influence of density for other coral species used for restoration. Further work focused on the mechanisms causing density dependence such as increased herbivory, rapid disease transmission, or altered predation rates are important next steps to advance our ability to effectively restore coral reefs.

  2. RANGE AND DENSITY OF ALIEN FISH IN WESTERN STREAMS AND RIVERS, US

    Science.gov (United States)

    Alien fish have become increasingly prevalent in Western U.S. waters. The EPA Environmental Monitoring and Assessment Program's Western Pilot (12 western states), which is based upon a probabilistic design, provides an opportunity to make inferences about the range and density of...

  3. Evidence of Long Range Dependence and Self-similarity in Urban Traffic Systems

    Energy Technology Data Exchange (ETDEWEB)

    Thakur, Gautam S [ORNL; Helmy, Ahmed [University of Florida, Gainesville; Hui, Pan [Hong Kong University of Science & Technology

    2015-01-01

    Transportation simulation technologies should accurately model traffic demand, distribution, and assignment parame- ters for urban environment simulation. These three param- eters significantly impact transportation engineering bench- mark process, are also critical in realizing realistic traffic modeling situations. In this paper, we model and charac- terize traffic density distribution of thousands of locations around the world. The traffic densities are generated from millions of images collected over several years and processed using computer vision techniques. The resulting traffic den- sity distribution time series are then analyzed. It is found using the goodness-of-fit test that the traffic density dis- tributions follows heavy-tail models such as Log-gamma, Log-logistic, and Weibull in over 90% of analyzed locations. Moreover, a heavy-tail gives rise to long-range dependence and self-similarity, which we studied by estimating the Hurst exponent (H). Our analysis based on seven different Hurst estimators strongly indicate that the traffic distribution pat- terns are stochastically self-similar (0.5 H 1.0). We believe this is an important finding that will influence the design and development of the next generation traffic simu- lation techniques and also aid in accurately modeling traffic engineering of urban systems. In addition, it shall provide a much needed input for the development of smart cities.

  4. Time-dependent quantum fluid density functional theory of hydrogen ...

    Indian Academy of Sciences (India)

    WINTEC

    GNLSE) of motion was earlier derived in our laboratory by combining density functional theory and quantum fluid dynamics in three- dimensional space. In continuation of the work reported previously, the GNLSE is applied to provide addi-.

  5. Age-specific density-dependent survival in Mediterranean Gulls Larus melanocephalus

    NARCIS (Netherlands)

    te Marvelde, Luc; Meininger, Peter L.; Flamant, Renaud; Dingemanse, Niels J.

    2009-01-01

    Survival and reproductive rates often decrease with increasing population density. Such negative density dependence reflects a changing net balance between the benefits and costs of presence of others with increasing density. When densities are low, however, survival and reproductive rates might

  6. Intensity of space use reveals conditional sex-specific effects of prey and conspecific density on home range size.

    Science.gov (United States)

    Aronsson, Malin; Low, Matthew; López-Bao, José V; Persson, Jens; Odden, John; Linnell, John D C; Andrén, Henrik

    2016-05-01

    Home range (HR) size variation is often linked to resource abundance, with sex differences expected to relate to sex-specific fitness consequences. However, studies generally fail to disentangle the effects of the two main drivers of HR size variation, food and conspecific density, and rarely consider how their relative influence change over spatiotemporal scales. We used location data from 77 Eurasian lynx (Lynx lynx) from a 16-year Scandinavian study to examine HR sizes variation relative to prey and conspecific density at different spatiotemporal scales. By varying the isopleth parameter (intensity of use) defining the HR, we show that sex-specific effects were conditional on the spatial scale considered. Males had larger HRs than females in all seasons. Females' total HR size declined as prey and conspecific density increased, whereas males' total HR was only affected by conspecific density. However, as the intensity of use within the HR increased (from 90% to 50% isopleth), the relationship between prey density and area showed opposing patterns for females and males; for females, the prey density effect was reduced, while for males, prey became increasingly important. Thus, prey influenced the size of key regions within male HRs, despite total HR size being independent of prey density. Males reduced their HR size during the mating season, likely to remain close to individual females in estrous. Females reduced their HR size postreproduction probably because of movement constrains imposed by dependent young. Our findings highlight the importance of simultaneously considering resources and intraspecific interactions as HR size determinants. We show that sex-specific demands influence the importance of prey and conspecific density on space use at different spatiotemporal scales. Thus, unless a gradient of space use intensity is examined, factors not related to total HR size might be disregarded despite their importance in determining size of key regions within

  7. Analysis of density-dependent binding of glycans by lectins using carbohydrate microarrays.

    Science.gov (United States)

    Tian, Xizhe; Pai, Jaeyoung; Shin, Injae

    2012-09-01

    To investigate the density-dependent binding of glycans by lectins using carbohydrate microarrays, a number of C-terminal hydrazide-conjugated neoglycopeptides with various valences and different spatial arrangements of the sugar ligands were prepared on a solid support. The synthetic strategy includes (1) assembly of alkyne-linked peptides possessing C-terminal hydrazide on a solid support, (2) coupling of azide-linked, unprotected sugars to the alkyne-linked peptides on the solid support utilizing click chemistry, and (3) release of the neoglycopeptides from the solid support. By using this synthetic methodology, sixty five neoglycopeptides with a valency ranging from 1 to 4 and different spatial arrangements of the carbohydrate ligands were generated. Carbohydrate microarrays were constructed by immobilizing the prepared neoglycopeptides on epoxide-derivatized glass slides and were used to analyze the density-dependent binding of glycans by lectins. The results of binding property determinations show that lectin binding is highly dependent on the surface glycan density. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Home range and density of three sympatric felids in the Southern Atlantic Forest, Brazil

    Directory of Open Access Journals (Sweden)

    C. B. Kasper

    Full Text Available Abstract Home range and minimal population densities of Southern tiger cat (Leopardus guttulus, margay (Lepardus wiedii and jaguarundi (Puma yagouaroundi were estimated between 2005 and 2006 in Taquari Valley, near the southern edge of the Atlantic Rainforest in Brazil. Home range data were collected by conventional radio telemetry (VHF locations in a highly fragmented landscape. The average home range size, calculated using 95% kernel density estimates, was 16.01 km2 for Southern tiger cat, 21.85 km2 for margay and 51.45 km2 for jaguarundi. Telemetry data were used to obtain minimal density estimates of 0.08 Southern tiger cats / km2, and 0.04 jaguarundi / km2. The density estimates arise from areas where ocelot (Leopardus pardalis and other larger-bodied carnivores were locally extinct, and they suggest a specific type of mesopredator release known as the ocelot effect, which is likely enabling the increase in smaller felid populations in this area.

  9. Long-term persistence, density dependence and effects of climate change on rosyside dace (Cyprinidae)

    Science.gov (United States)

    Gary D. Grossman; Gary Sundin; Robert E. Ratajczak

    2016-01-01

    SummaryWe used long-term population data for rosyside dace (Clinostomus funduloides), a numerically dominant member of a stochastically organised fish assemblage, to evaluate the relative importance of density-dependent and density-independent processes to population...

  10. Pressure dependence of the charge-density-wave gap in rare-earth tritellurides.

    Science.gov (United States)

    Sacchetti, A; Arcangeletti, E; Perucchi, A; Baldassarre, L; Postorino, P; Lupi, S; Ru, N; Fisher, I R; Degiorgi, L

    2007-01-12

    We investigate the pressure dependence of the optical properties of CeTe3, which exhibits an incommensurate charge-density-wave (CDW) state already at 300 K. Our data are collected in the midinfrared spectral range at room temperature and at pressures between 0 and 9 GPa. The energy for the single particle excitation across the CDW gap decreases upon increasing the applied pressure, similarly to the chemical pressure by rare-earth substitution. The broadening of the bands upon lattice compression removes the perfect nesting condition of the Fermi surface and therefore diminishes the impact of the CDW transition on the electronic properties of RTe3.

  11. Pressure Dependence of the Charge-Density-Wave Gap in Rare-Earth Tri-Tellurides

    Energy Technology Data Exchange (ETDEWEB)

    Sacchetti, A.; /Zurich, ETH; Arcangeletti, E.; Perucchi, A.; Baldassarre, L.; Postorino, P.; Lupi, S.; /Rome U.; Ru, N.; Fisher, I.R.; /Stanford U., Geballe Lab.; Degiorgi, L.; /Zurich, ETH

    2009-12-14

    We investigate the pressure dependence of the optical properties of CeTe{sub 3}, which exhibits an incommensurate charge-density-wave (CDW) state already at 300 K. Our data are collected in the mid-infrared spectral range at room temperature and at pressures between 0 and 9 GPa. The energy for the single particle excitation across the CDW gap decreases upon increasing the applied pressure, similarly to the chemical pressure by rare-earth substitution. The broadening of the bands upon lattice compression removes the perfect nesting condition of the Fermi surface and therefore diminishes the impact of the CDW transition on the electronic properties of RTe{sub 3}.

  12. Quark mass density- and temperature- dependent model for bulk strange quark matter

    OpenAIRE

    al, Yun Zhang et.

    2002-01-01

    It is shown that the quark mass density-dependent model can not be used to explain the process of the quark deconfinement phase transition because the quark confinement is permanent in this model. A quark mass density- and temperature-dependent model in which the quark confinement is impermanent has been suggested. We argue that the vacuum energy density B is a function of temperature. The dynamical and thermodynamical properties of bulk strange quark matter for quark mass density- and temper...

  13. Density dependence of relaxation dynamics in glass formers, and ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 129; Issue 7 ... We employ density-temperature scaling, analyzed in recent studies, to address the question. ... Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru 560 064, India; TIFR Center for Interdisciplinary Sciences, 21 Brundavan Colony, ...

  14. Density dependence of relaxation dynamics in glass formers, and ...

    Indian Academy of Sciences (India)

    Anshul D S Parmar

    Within the framework of the Adam-Gibbs relation, by employing density temperature scaling for the analysis, we find that softer particles make more fragile glasses, as deduced from dynamical quantities, which is found to be consistent with the Adam-Gibbs fragility. Keywords. Glass; fragility; supercooled liquids etc. 1.

  15. Bracket bond strength dependence on light power density

    OpenAIRE

    Staudt, Christine Bettina; Krejci, Ivo; Mavropoulos, Anestis

    2006-01-01

    In order to reduce curing time for bracket bonding with light-cured composites, manufacturers increase the power density (PD) of light sources. The present study aims at investigating the relationship between PD and shear bond strength (SBS) at short exposure time.

  16. Mountain lions: preliminary findings on home-range use and density, central Sierra Nevada

    Science.gov (United States)

    Donald L. Neal; George N. Steger; Ronald C. Bertram

    1987-01-01

    Between August 1983 and December 1985, 19 mountain lions were captured, radio equipped, and monitored daily within a portion of the North Kings deer herd range on the west slope of the central Sierra Nevada in California. The density of adult mountain lions was estimated to be one per 33.3 km²; that of adults and kittens together was estimated to be one per 20...

  17. Self-consistent many-body perturbation theory in range-separated density-functional theory

    DEFF Research Database (Denmark)

    Fromager, Emmanuel; Jensen, Hans Jørgen Aagaard

    2008-01-01

    In many cases, density-functional theory (DFT) with current standard approximate functionals offers a relatively accurate and computationally cheap description of the short-range dynamic electron correlation effects. However, in general, standard DFT does not treat the dispersion interaction...... effects adequately which, on the other hand, can be described by many-body perturbation theory MBPT. It is therefore of interest to develop a hybrid model which combines the best of both the MBPT and DFT approaches. This can be achieved by splitting the two-electron interaction into long-range and short...

  18. The nest site lottery: how selectively neutral density dependent growth suppression induces frequency dependent selection.

    Science.gov (United States)

    Argasinski, K; Broom, M

    2013-12-01

    Modern developments in population dynamics emphasize the role of the turnover of individuals. In the new approaches stable population size is a dynamic equilibrium between different mortality and fecundity factors instead of an arbitrary fixed carrying capacity. The latest replicator dynamics models assume that regulation of the population size acts through feedback driven by density dependent juvenile mortality. Here, we consider a simplified model to extract the properties of this approach. We show that at the stable population size, the structure of the frequency dependent evolutionary game emerges. Turnover of individuals induces a lottery mechanism where for each nest site released by a dead adult individual a single newborn is drawn from the pool of newborn candidates. This frequency dependent selection leads towards the strategy maximizing the number of newborns per adult death. However, multiple strategies can maximize this value. Among them, the strategy with the greatest mortality (which implies the greatest instantaneous growth rate) is selected. This result is important for the discussion about universal fitness measures and which parameters are maximized by natural selection. This is related to the fitness measures R0 and r, because the number of newborns per single dead individual equals the lifetime production of newborn R0 in models without aging. We thus have a two-stage procedure, instead of a single fitness measure, which is a combination of R0 and r. According to the nest site lottery mechanism, at stable population size, selection favors strategies with the greatest r, i.e. those with the highest turnover, from those with the greatest R0. Copyright © 2013 Elsevier Inc. All rights reserved.

  19. Resampling method for applying density-dependent habitat selection theory to wildlife surveys.

    Science.gov (United States)

    Tardy, Olivia; Massé, Ariane; Pelletier, Fanie; Fortin, Daniel

    2015-01-01

    Isodar theory can be used to evaluate fitness consequences of density-dependent habitat selection by animals. A typical habitat isodar is a regression curve plotting competitor densities in two adjacent habitats when individual fitness is equal. Despite the increasing use of habitat isodars, their application remains largely limited to areas composed of pairs of adjacent habitats that are defined a priori. We developed a resampling method that uses data from wildlife surveys to build isodars in heterogeneous landscapes without having to predefine habitat types. The method consists in randomly placing blocks over the survey area and dividing those blocks in two adjacent sub-blocks of the same size. Animal abundance is then estimated within the two sub-blocks. This process is done 100 times. Different functional forms of isodars can be investigated by relating animal abundance and differences in habitat features between sub-blocks. We applied this method to abundance data of raccoons and striped skunks, two of the main hosts of rabies virus in North America. Habitat selection by raccoons and striped skunks depended on both conspecific abundance and the difference in landscape composition and structure between sub-blocks. When conspecific abundance was low, raccoons and striped skunks favored areas with relatively high proportions of forests and anthropogenic features, respectively. Under high conspecific abundance, however, both species preferred areas with rather large corn-forest edge densities and corn field proportions. Based on random sampling techniques, we provide a robust method that is applicable to a broad range of species, including medium- to large-sized mammals with high mobility. The method is sufficiently flexible to incorporate multiple environmental covariates that can reflect key requirements of the focal species. We thus illustrate how isodar theory can be used with wildlife surveys to assess density-dependent habitat selection over large

  20. Effect of deformation and orientation on spin orbit density dependent nuclear potential

    Science.gov (United States)

    Mittal, Rajni; Kumar, Raj; Sharma, Manoj K.

    2017-11-01

    Role of deformation and orientation is investigated on spin-orbit density dependent part VJ of nuclear potential (VN=VP+VJ) obtained within semi-classical Thomas Fermi approach of Skyrme energy density formalism. Calculations are performed for 24-54Si+30Si reactions, with spherical target 30Si and projectiles 24-54Si having prolate and oblate shapes. The quadrupole deformation β2 is varying within range of 0.023 ≤ β2 ≤0.531 for prolate and -0.242 ≤ β2 ≤ -0.592 for oblate projectiles. The spin-orbit dependent potential gets influenced significantly with inclusion of deformation and orientation effect. The spin-orbit barrier and position gets significantly influenced by both the sign and magnitude of β2-deformation. Si-nuclei with β220. The possible role of spin-orbit potential on barrier characteristics such as barrier height, barrier curvature and on the fusion pocket is also probed. In reference to prolate and oblate systems, the angular dependence of spin-orbit potential is further studied on fusion cross-sections.

  1. Density-dependence of functional spiking networks in vitro

    Energy Technology Data Exchange (ETDEWEB)

    Ham, Michael I [Los Alamos National Laboratory; Gintautuas, Vadas [Los Alamos National Laboratory; Rodriguez, Marko A [Los Alamos National Laboratory; Bettencourt, Luis M A [Los Alamos National Laboratory; Bennett, Ryan [UNIV OF NORTH TEXAS; Santa Maria, Cara L [UNIV OF NORTH TEXAS

    2008-01-01

    During development, the mammalian brain differentiates into specialized regions with unique functional abilities. While many factors contribute to this functional specialization, we explore the effect neuronal density can have on neuronal interactions. Two types of networks, dense (50,000 neurons and glia support cells) and sparse (12,000 neurons and glia support cells), are studied. A competitive first response model is applied to construct activation graphs that represent pairwise neuronal interactions. By observing the evolution of these graphs during development in vitro we observe that dense networks form activation connections earlier than sparse networks, and that link-!llltropy analysis of the resulting dense activation graphs reveals that balanced directional connections dominate. Information theoretic measures reveal in addition that early functional information interactions (of order 3) are synergetic in both dense and sparse networks. However, during development in vitro, such interactions become redundant in dense, but not sparse networks. Large values of activation graph link-entropy correlate strongly with redundant ensembles observed in the dense networks. Results demonstrate differences between dense and sparse networks in terms of informational groups, pairwise relationships, and activation graphs. These differences suggest that variations in cell density may result in different functional specialization of nervous system tissue also in vivo.

  2. Density dependence in an age-structured population of great tits: identifying the critical age classes

    NARCIS (Netherlands)

    Gamelon, M.; Grotan, V.; Engen, S.; Bjørkvoll, E.; Visser, M.E.; Sæther, Bernt-Erik

    2016-01-01

    Classical approaches for the analyses of density dependence assume that all the individuals in a population equally respond and equally contribute to density dependence. However, in age-structured populations, individuals of different ages may differ in their responses to changes in population size

  3. Estimation of density-dependent mortality of juvenile bivalves in the Wadden Sea

    NARCIS (Netherlands)

    Andresen, H.; Strasser, M.; van der Meer, J.

    2014-01-01

    We investigated density-dependent mortality within the early months of life of the bivalves Macoma balthica (Baltic tellin) and Cerastoderma edule (common cockle) in the Wadden Sea. Mortality is thought to be density-dependent in juvenile bivalves, because there is no proportional relationship

  4. Estimation of Density-Dependent Mortality of Juvenile Bivalves in the Wadden Sea

    NARCIS (Netherlands)

    Andresen, H.; Strasser, M.; van der Meer, J.

    2014-01-01

    We investigated density-dependent mortality within the early months of life of the bivalves Macoma balthica (Baltic tellin) and Cerastoderma edule (common cockle) in the Wadden Sea. Mortality is thought to be density-dependent in juvenile bivalves, because there is no proportional relationship

  5. Seasonal variation in density dependence in age-specific survival of a long-distance migrant

    NARCIS (Netherlands)

    Lok, Tamar; Overdijk, Otto; Tinbergen, Joost M.; Piersma, Theunis; Valone, T.J.

    2013-01-01

    Density dependence in vital rates is key to population regulation. Rather than being constant, the strength of density dependence may vary throughout the year, but empirical evidence is limited. Based on 22 years of data of color-banded birds from a recovering population of Eurasian Spoonbills

  6. The temperature dependence of intermediate range oxygen-oxygen correlations in liquid water.

    Science.gov (United States)

    Schlesinger, Daniel; Wikfeldt, K Thor; Skinner, Lawrie B; Benmore, Chris J; Nilsson, Anders; Pettersson, Lars G M

    2016-08-28

    We analyze the recent temperature dependent oxygen-oxygen pair-distribution functions from experimental high-precision x-ray diffraction data of bulk water by Skinner et al. [J. Chem. Phys. 141, 214507 (2014)] with particular focus on the intermediate range where small, but significant, correlations are found out to 17 Å. The second peak in the pair-distribution function at 4.5 Å is connected to tetrahedral coordination and was shown by Skinner et al. to change behavior with temperature below the temperature of minimum isothermal compressibility. Here we show that this is associated also with a peak growing at 11 Å which strongly indicates a collective character of fluctuations leading to the enhanced compressibility at lower temperatures. We note that the peak at ∼13.2 Å exhibits a temperature dependence similar to that of the density with a maximum close to 277 K or 4 °C. We analyze simulations of the TIP4P/2005 water model in the same manner and find excellent agreement between simulations and experiment albeit with a temperature shift of ∼20 K.

  7. Effective size of density-dependent two-sex populations: the effect of mating systems.

    Science.gov (United States)

    Myhre, A M; Engen, S; SAEther, B-E

    2017-08-01

    Density dependence in vital rates is a key feature affecting temporal fluctuations of natural populations. This has important implications for the rate of random genetic drift. Mating systems also greatly affect effective population sizes, but knowledge of how mating system and density regulation interact to affect random genetic drift is poor. Using theoretical models and simulations, we compare N e in short-lived, density-dependent animal populations with different mating systems. We study the impact of a fluctuating, density-dependent sex ratio and consider both a stable and a fluctuating environment. We find a negative relationship between annual N e /N and adult population size N due to density dependence, suggesting that loss of genetic variation is reduced at small densities. The magnitude of this decrease was affected by mating system and life history. A male-biased, density-dependent sex ratio reduces the rate of genetic drift compared to an equal, density-independent sex ratio, but a stochastic change towards male bias reduces the N e /N ratio. Environmental stochasticity amplifies temporal fluctuations in population size and is thus vital to consider in estimation of effective population sizes over longer time periods. Our results on the reduced loss of genetic variation at small densities, particularly in polygamous populations, indicate that density regulation may facilitate adaptive evolution at small population sizes. © 2017 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2017 European Society For Evolutionary Biology.

  8. A better understanding of long-range temporal dependence of traffic flow time series

    Science.gov (United States)

    Feng, Shuo; Wang, Xingmin; Sun, Haowei; Zhang, Yi; Li, Li

    2018-02-01

    Long-range temporal dependence is an important research perspective for modelling of traffic flow time series. Various methods have been proposed to depict the long-range temporal dependence, including autocorrelation function analysis, spectral analysis and fractal analysis. However, few researches have studied the daily temporal dependence (i.e. the similarity between different daily traffic flow time series), which can help us better understand the long-range temporal dependence, such as the origin of crossover phenomenon. Moreover, considering both types of dependence contributes to establishing more accurate model and depicting the properties of traffic flow time series. In this paper, we study the properties of daily temporal dependence by simple average method and Principal Component Analysis (PCA) based method. Meanwhile, we also study the long-range temporal dependence by Detrended Fluctuation Analysis (DFA) and Multifractal Detrended Fluctuation Analysis (MFDFA). The results show that both the daily and long-range temporal dependence exert considerable influence on the traffic flow series. The DFA results reveal that the daily temporal dependence creates crossover phenomenon when estimating the Hurst exponent which depicts the long-range temporal dependence. Furthermore, through the comparison of the DFA test, PCA-based method turns out to be a better method to extract the daily temporal dependence especially when the difference between days is significant.

  9. Density and current profiles in Uq (A2(1)) zero range process

    Science.gov (United States)

    Kuniba, A.; Mangazeev, V. V.

    2017-09-01

    The stochastic R matrix for Uq (An(1)) introduced recently gives rise to an integrable zero range process of n classes of particles in one dimension. For n = 2 we investigate how finitely many first class particles fixed as defects influence the grand canonical ensemble of the second class particles. By using the matrix product stationary probabilities involving infinite products of q-bosons, exact formulas are derived for the local density and current of the second class particles in the large volume limit.

  10. Aberrant long-range functional connectivity density in generalized tonic-clonic seizures.

    Science.gov (United States)

    Zhu, Ling; Li, Yibo; Wang, Yifeng; Li, Rong; Zhang, Zhiqiang; Lu, Guangming; Chen, Huafu

    2016-06-01

    Studies in generalized tonic-clonic seizures (GTCS) have reported both structural and functional alterations in the brain. However, changes in spontaneous neuronal functional organization in GTCS remain largely unknown.In this study, 70 patients with idiopathic generalized epilepsy characterized by tonic-clonic seizures and 70 age- and sex-matched healthy controls were recruited. Here, functional connectivity density (FCD) mapping, an ultrafast data-driven method based on functional magnetic resonance imaging (fMRI), was applied for the first time to investigate the changes of spontaneous functional brain activity caused by epilepsy.The results showed significantly decreased long-range FCD in the middle and inferior temporal, prefrontal, and inferior parietal cortices as well as increased long-range FCD in the cerebellum anterior lobe and sensorimotor areas. Negative correlation between duration of disease and reduced long-range FCD was found. In addition, most regions with reduced long-range FCD showed decreased resting-state functional connectivity (rsFC) within default mode network.Negative correlation between duration of disease and long-range FCD may reflect an adverse consequence eventually from original. Furthermore, the observed FCD and rsFC alterations have been speculated to be associated with the social-cognitive impairments as well as motor control. Our study provided novel evidences to look into neuro-pathophysiological mechanisms underlying GTCS.

  11. Density and Phonon-Stiffness Anomalies of Water and Ice in the Full Temperature Range.

    Science.gov (United States)

    Sun, Chang Q; Zhang, Xi; Fu, Xiaojian; Zheng, Weitao; Kuo, Jer-Lai; Zhou, Yichun; Shen, Zexiang; Zhou, Ji

    2013-10-03

    The specific-heat difference between the O:H van der Waals bond and the H-O polar-covalent bond and the Coulomb repulsion between electron pairs on adjacent oxygen atoms determine the angle-length-stiffness relaxation dynamics of the hydrogen bond (O:H-O), which is responsible for the density and phonon-stiffness oscillation of water ice over the full temperature range. Cooling shortens and stiffens the part of relatively lower specific-heat, and meanwhile lengthens and softens the other part of the O:H-O bond via repulsion. Length contraction/elongation of a specific part always stiffens/softens its corresponding phonon. In the liquid and in the solid phase, the O:H bond contracts more than the H-O elongates, hence, an O:H-O cooling contraction and the seemingly "regular" process of cooling densification take place. During freezing, the H-O contracts less than the O:H elongates, leading to an O:H-O elongation and volume expansion. At extremely low temperatures, the O:H-O angle stretching lowers the density slightly as the O:H and the H-O lengths change insignificantly. In ice, the O-O distance is longer than it is in water, resulting in a lower density, so that ice floats.

  12. Benchmarks for electronically excited states: Time-dependent density functional theory and density functional theory based multireference configuration interaction

    DEFF Research Database (Denmark)

    Silva-Junior, Mario R.; Schreiber, Marko; Sauer, Stephan P. A.

    2008-01-01

    Time-dependent density functional theory (TD-DFT) and DFT-based multireference configuration interaction (DFT/MRCI) calculations are reported for a recently proposed benchmark set of 28 medium-sized organic molecules. Vertical excitation energies, oscillator strengths, and excited-state dipole...

  13. Temperature dependence of Henry's law constant in an extended temperature range.

    Science.gov (United States)

    Görgényi, Miklós; Dewulf, Jo; Van Langenhove, Herman

    2002-08-01

    The Henry's law constants H for chloroform, 1,1-dichloroethane, 1,2-dichloropropane, trichloroethene, chlorobenzene, benzene and toluene were determined by the EPICS-SPME technique (equilibrium partitioning in closed systems--solid phase microextraction) in the temperature range 275-343 K. The curvature observed in the ln H vs. 1/T plot was due to the temperature dependence of the change in enthalpy delta H0 during the transfer of 1 mol solute from the aqueous solution to the gas phase. The nonlinearity of the plot was explained by means of a thermodynamic model which involves the temperature dependence of delta H0 of the compounds and the thermal expansion of water in the three-parameter equation ln (H rho TT) = A2/T + BTB + C2, where rho T is the density of water at temperature T, TB = ln(T/298) + (298-T)/T, A2 = -delta H298(0)/R, delta H298(0) is the delta H0 value at 298 K, B = delta Cp0/R, and C2 is a constant. delta Cp0 is the molar heat capacity change in volatilization from the aqueous solution. A statistical comparison of the two models demonstrates the superiority of the three-parameter equation over the two-parameter one ln H vs. 1/T). The new, three-parameter equation allows a more accurate description of the temperature dependence of H, and of the solubility of volatile organic compounds in water at higher temperatures.

  14. Density dependence of spin relaxation in GaAs quantum well at room temperature

    Science.gov (United States)

    Teng, L. H.; Zhang, P.; Lai, T. S.; Wu, M. W.

    2008-10-01

    Carrier density dependence of electron spin relaxation in an intrinsic GaAs quantum well is investigated at room temperature using time-resolved circularly polarized pump-probe spectroscopy. It is revealed that the spin relaxation time first increases with density in the relatively low-density regime where the linear D'yakonov-Perel' spin-orbit coupling terms are dominant, and then tends to decrease when the density is large and the cubic D'yakonov-Perel' spin-orbit coupling terms become important. These features are in good agreement with theoretical predictions on density dependence of spin relaxation by Lüet al. (Phys. Rev. B, 73 (2006) 125314). A fully microscopic calculation based on numerically solving the kinetic spin Bloch equations with both the D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms included, reproduces the density dependence of spin relaxation very well.

  15. Cosmological Constraints from the Redshift Dependence of the Alcock-Paczynski Test: Galaxy Density Gradient Field

    Science.gov (United States)

    Li, Xiao-Dong; Park, Changbom; Forero-Romero, J. E.; Kim, Juhan

    2014-12-01

    We propose a method based on the redshift dependence of the Alcock-Paczynski (AP) test to measure the expansion history of the universe. It uses the isotropy of the galaxy density gradient field to constrain cosmological parameters. If the density parameter Ω m or the dark energy equation of state w are incorrectly chosen, the gradient field appears to be anisotropic with the degree of anisotropy varying with redshift. We use this effect to constrain the cosmological parameters governing the expansion history of the universe. Although redshift-space distortions (RSD) induced by galaxy peculiar velocities also produce anisotropies in the gradient field, these effects are close to uniform in magnitude over a large range of redshift. This makes the redshift variation of the gradient field anisotropy relatively insensitive to the RSD. By testing the method on mock surveys drawn from the Horizon Run 3 cosmological N-body simulations, we demonstrate that the cosmological parameters can be estimated without bias. Our method is complementary to the baryon acoustic oscillation or topology methods as it depends on DAH , the product of the angular diameter distance and the Hubble parameter.

  16. Cosmological constraints from the redshift dependence of the Alcock-Paczynski test: galaxy density gradient field

    Energy Technology Data Exchange (ETDEWEB)

    Li, Xiao-Dong; Park, Changbom [School of Physics, Korea Institute for Advanced Study, 85 Heogiro, Dongdaemun-gu, Seoul 130-722 (Korea, Republic of); Forero-Romero, J. E. [Departamento de Física, Universidad de los Andes, Cra. 1 No. 18A-10, Edificio Ip, Bogotá (Colombia); Kim, Juhan, E-mail: xiaodongli@kias.re.kr, E-mail: cbp@kias.re.kr, E-mail: je.forero@uniandes.edu.co, E-mail: kjhan@kias.re.kr [Center for Advanced Computation, Korea Institute for Advanced Study, 85 Hoegi-ro, Dongdaemun-gu, Seoul 130-722 (Korea, Republic of)

    2014-12-01

    We propose a method based on the redshift dependence of the Alcock-Paczynski (AP) test to measure the expansion history of the universe. It uses the isotropy of the galaxy density gradient field to constrain cosmological parameters. If the density parameter Ω {sub m} or the dark energy equation of state w are incorrectly chosen, the gradient field appears to be anisotropic with the degree of anisotropy varying with redshift. We use this effect to constrain the cosmological parameters governing the expansion history of the universe. Although redshift-space distortions (RSD) induced by galaxy peculiar velocities also produce anisotropies in the gradient field, these effects are close to uniform in magnitude over a large range of redshift. This makes the redshift variation of the gradient field anisotropy relatively insensitive to the RSD. By testing the method on mock surveys drawn from the Horizon Run 3 cosmological N-body simulations, we demonstrate that the cosmological parameters can be estimated without bias. Our method is complementary to the baryon acoustic oscillation or topology methods as it depends on D{sub AH} , the product of the angular diameter distance and the Hubble parameter.

  17. A unified dislocation density-dependent physical-based constitutive model for cold metal forming

    Science.gov (United States)

    Schacht, K.; Motaman, A. H.; Prahl, U.; Bleck, W.

    2017-10-01

    Dislocation-density-dependent physical-based constitutive models of metal plasticity while are computationally efficient and history-dependent, can accurately account for varying process parameters such as strain, strain rate and temperature; different loading modes such as continuous deformation, creep and relaxation; microscopic metallurgical processes; and varying chemical composition within an alloy family. Since these models are founded on essential phenomena dominating the deformation, they have a larger range of usability and validity. Also, they are suitable for manufacturing chain simulations since they can efficiently compute the cumulative effect of the various manufacturing processes by following the material state through the entire manufacturing chain and also interpass periods and give a realistic prediction of the material behavior and final product properties. In the physical-based constitutive model of cold metal plasticity introduced in this study, physical processes influencing cold and warm plastic deformation in polycrystalline metals are described using physical/metallurgical internal variables such as dislocation density and effective grain size. The evolution of these internal variables are calculated using adequate equations that describe the physical processes dominating the material behavior during cold plastic deformation. For validation, the model is numerically implemented in general implicit isotropic elasto-viscoplasticity algorithm as a user-defined material subroutine (UMAT) in ABAQUS/Standard and used for finite element simulation of upsetting tests and a complete cold forging cycle of case hardenable MnCr steel family.

  18. Disentangling density-dependent dynamics using full annual cycle models and Bayesian model weight updating

    Science.gov (United States)

    Robinson, Orin J.; McGowan, Conor P.; Devers, Patrick K.

    2017-01-01

    Density dependence regulates populations of many species across all taxonomic groups. Understanding density dependence is vital for predicting the effects of climate, habitat loss and/or management actions on wild populations. Migratory species likely experience seasonal changes in the relative influence of density dependence on population processes such as survival and recruitment throughout the annual cycle. These effects must be accounted for when characterizing migratory populations via population models.To evaluate effects of density on seasonal survival and recruitment of a migratory species, we used an existing full annual cycle model framework for American black ducks Anas rubripes, and tested different density effects (including no effects) on survival and recruitment. We then used a Bayesian model weight updating routine to determine which population model best fit observed breeding population survey data between 1990 and 2014.The models that best fit the survey data suggested that survival and recruitment were affected by density dependence and that density effects were stronger on adult survival during the breeding season than during the non-breeding season.Analysis also suggests that regulation of survival and recruitment by density varied over time. Our results showed that different characterizations of density regulations changed every 8–12 years (three times in the 25-year period) for our population.Synthesis and applications. Using a full annual cycle, modelling framework and model weighting routine will be helpful in evaluating density dependence for migratory species in both the short and long term. We used this method to disentangle the seasonal effects of density on the continental American black duck population which will allow managers to better evaluate the effects of habitat loss and potential habitat management actions throughout the annual cycle. The method here may allow researchers to hone in on the proper form and/or strength of

  19. Estimation of density-dependent mortality of juvenile bivalves in the Wadden Sea.

    Directory of Open Access Journals (Sweden)

    Henrike Andresen

    Full Text Available We investigated density-dependent mortality within the early months of life of the bivalves Macoma balthica (Baltic tellin and Cerastoderma edule (common cockle in the Wadden Sea. Mortality is thought to be density-dependent in juvenile bivalves, because there is no proportional relationship between the size of the reproductive adult stocks and the numbers of recruits for both species. It is not known however, when exactly density dependence in the pre-recruitment phase occurs and how prevalent it is. The magnitude of recruitment determines year class strength in bivalves. Thus, understanding pre-recruit mortality will improve the understanding of population dynamics. We analyzed count data from three years of temporal sampling during the first months after bivalve settlement at ten transects in the Sylt-Rømø-Bay in the northern German Wadden Sea. Analyses of density dependence are sensitive to bias through measurement error. Measurement error was estimated by bootstrapping, and residual deviances were adjusted by adding process error. With simulations the effect of these two types of error on the estimate of the density-dependent mortality coefficient was investigated. In three out of eight time intervals density dependence was detected for M. balthica, and in zero out of six time intervals for C. edule. Biological or environmental stochastic processes dominated over density dependence at the investigated scale.

  20. Analyzing Density Operator in Thermal State for Complicated Time-Dependent Optical Systems

    Directory of Open Access Journals (Sweden)

    Jeong Ryeol Choi

    2014-01-01

    Full Text Available Density operator of oscillatory optical systems with time-dependent parameters is analyzed. In this case, a system is described by a time-dependent Hamiltonian. Invariant operator theory is introduced in order to describe time-varying behavior of the system. Due to the time dependence of parameters, the frequency of oscillation, so-called a modified frequency of the system, is somewhat different from the natural frequency. In general, density operator of a time-dependent optical system is represented in terms of the modified frequency. We showed how to determine density operator of complicated time-dependent optical systems in thermal state. Usually, density operator description of quantum states is more general than the one described in terms of the state vector.

  1. Implementation and benchmark of a long-range corrected functional in the density functional based tight-binding method

    Energy Technology Data Exchange (ETDEWEB)

    Lutsker, V.; Niehaus, T. A., E-mail: thomas.niehaus@physik.uni-regensburg.de [Department of Theoretical Physics, University of Regensburg, 93040 Regensburg (Germany); Aradi, B. [BCCMS, University of Bremen, 28359 Bremen (Germany)

    2015-11-14

    Bridging the gap between first principles methods and empirical schemes, the density functional based tight-binding method (DFTB) has become a versatile tool in predictive atomistic simulations over the past years. One of the major restrictions of this method is the limitation to local or gradient corrected exchange-correlation functionals. This excludes the important class of hybrid or long-range corrected functionals, which are advantageous in thermochemistry, as well as in the computation of vibrational, photoelectron, and optical spectra. The present work provides a detailed account of the implementation of DFTB for a long-range corrected functional in generalized Kohn-Sham theory. We apply the method to a set of organic molecules and compare ionization potentials and electron affinities with the original DFTB method and higher level theory. The new scheme cures the significant overpolarization in electric fields found for local DFTB, which parallels the functional dependence in first principles density functional theory (DFT). At the same time, the computational savings with respect to full DFT calculations are not compromised as evidenced by numerical benchmark data.

  2. Density-dependent electron scattering in photoexcited GaAs in strongly diffusive regime

    DEFF Research Database (Denmark)

    Mics, Zoltán; D’Angio, Andrea; Jensen, Søren A.

    2013-01-01

    In a series of systematic optical pump–terahertz probe experiments, we study the density-dependent electron scattering rate in photoexcited GaAs in the regime of strong carrier diffusion. The terahertz frequency-resolved transient sheet conductivity spectra are perfectly described by the Drude...... model, directly yielding the electron scattering rates. A diffusion model is applied to determine the spatial extent of the photoexcited electron-hole gas at each moment after photoexcitation, yielding the time-dependent electron density, and hence the density-dependent electron scattering time. We find...

  3. High velocity proton collision with liquid lithium: a time dependent density functional theory study.

    Science.gov (United States)

    Bi, Gang; Kang, Jun; Wang, Lin-Wang

    2017-03-29

    Liquid lithium is often used as a coating material in fusion reaction chambers, where it is under constant bombardment from high speed neutrons and protons. However, numerous fundamental questions are unanswered, for example whether a single proton impact can cause Li atom sputtering, and what is the electron excitation energy profile after a collision particularly for extremely high energy projectiles. Herein, we use a real-time dependent density functional method to study these questions for proton energies in the range of 30 eV to 1 MeV. The calculated stopping power agrees well with experiment, and it is found that the stopping power cannot be described by the single electron exciting spectrum based on the adiabatic eigen energies, and Li atom sputtering is not observed within our simulation time.

  4. Time-dependent spin-density-functional-theory description of He+-He collisions

    Science.gov (United States)

    Baxter, Matthew; Kirchner, Tom; Engel, Eberhard

    2017-09-01

    Theoretical total cross-section results for all ionization and capture processes in the He+-He collision system are presented in the approximate impact energy range of 10-1000 keV/amu. Calculations were performed within the framework of time-dependent spin-density functional theory. The Krieger-Li-Iafrate approximation was used to determine an accurate exchange-correlation potential in the exchange-only limit. The results of two models, one where electron translation factors in the orbitals used to calculate the potential are ignored and another where partial electron translation factors are included, are compared with available experimental data as well as a selection of previous theoretical calculations.

  5. A numerical shallow-water model for gravity currents for a wide range of density differences

    Science.gov (United States)

    Shimizu, Hiroyuki A.; Koyaguchi, Takehiro; Suzuki, Yujiro J.

    2017-12-01

    Gravity currents with various contrasting densities play a role in mass transport in a number of geophysical situations. The ratio of the density of the current, ρ c, to the density of the ambient fluid, ρ a, can vary between 100 and 103. In this paper, we present a numerical method of simulating gravity currents for a wide range of ρ c/ ρ a using a shallow-water model. In the model, the effects of varying ρ c/ ρ a are taken into account via the front condition (i.e., factors describing the balance between the driving pressure and the ambient resistance pressure at the flow front). Previously, two types of numerical models have been proposed to solve the front condition. These are referred to here as the Boundary Condition (BC) model and the Artificial Bed (AB) model. The front condition is calculated as a boundary condition at each time step in the BC model, whereas it is calculated by setting a thin artificial bed ahead of the front in the AB model. We assessed the BC and AB models by comparing their numerical results with the analytical results for a simple case of homogeneous currents. The results from the BC model agree well with the analytical results when ρ c/ ρ a≲102, but the model tends to overestimate the speed of the front position when ρ c/ρ a≳102. In contrast, the AB model generates good approximations of the analytical results for ρ c/ρ a≳ 102, given a sufficiently small artificial bed thickness, but fails to reproduce the analytical results when ρ c/ ρ a≲102. Therefore, we propose a numerical method in which the BC model is used for currents with ρ c/ ρ a≲102 and the AB model is used for currents with ρ c/ρ a≳ 102.

  6. A minimal model for excitons within time-dependent density-functional theory.

    Science.gov (United States)

    Yang, Zeng-hui; Li, Yonghui; Ullrich, Carsten A

    2012-07-07

    The accurate description of the optical spectra of insulators and semiconductors remains an important challenge for time-dependent density-functional theory (TDDFT). Evidence has been given in the literature that TDDFT can produce bound as well as continuum excitons for specific systems, but there are still many unresolved basic questions concerning the role of dynamical exchange and correlation (xc). In particular, the roles of the long spatial range and the frequency dependence of the xc kernel f(xc) for excitonic binding are still not very well explored. We present a minimal model for excitons in TDDFT, consisting of two bands from a one-dimensional (1D) Kronig-Penney model and simple approximate xc kernels, providing an easily accessible model system for studying excitonic effects in TDDFT. For the 1D model system, it is found that adiabatic xc kernels can produce at most two bound excitons, confirming that the long spatial range of f(xc) is not a necessary condition. It is shown how the Wannier model, featuring an effective electron-hole interaction, emerges from TDDFT. The collective, many-body nature of excitons is explicitly demonstrated.

  7. Density-dependent microbial turnover improves soil carbon model predictions of long-term litter manipulations

    Science.gov (United States)

    Georgiou, Katerina; Abramoff, Rose; Harte, John; Riley, William; Torn, Margaret

    2017-04-01

    Climatic, atmospheric, and land-use changes all have the potential to alter soil microbial activity via abiotic effects on soil or mediated by changes in plant inputs. Recently, many promising microbial models of soil organic carbon (SOC) decomposition have been proposed to advance understanding and prediction of climate and carbon (C) feedbacks. Most of these models, however, exhibit unrealistic oscillatory behavior and SOC insensitivity to long-term changes in C inputs. Here we diagnose the sources of instability in four models that span the range of complexity of these recent microbial models, by sequentially adding complexity to a simple model to include microbial physiology, a mineral sorption isotherm, and enzyme dynamics. We propose a formulation that introduces density-dependence of microbial turnover, which acts to limit population sizes and reduce oscillations. We compare these models to results from 24 long-term C-input field manipulations, including the Detritus Input and Removal Treatment (DIRT) experiments, to show that there are clear metrics that can be used to distinguish and validate the inherent dynamics of each model structure. We find that widely used first-order models and microbial models without density-dependence cannot readily capture the range of long-term responses observed across the DIRT experiments as a direct consequence of their model structures. The proposed formulation improves predictions of long-term C-input changes, and implies greater SOC storage associated with CO2-fertilization-driven increases in C inputs over the coming century compared to common microbial models. Finally, we discuss our findings in the context of improving microbial model behavior for inclusion in Earth System Models.

  8. Investigation of Multiconfigurational Short-Range Density Functional Theory for Electronic Excitations in Organic Molecules

    DEFF Research Database (Denmark)

    Hubert, Mickaël; Hedegård, Erik D.; Jensen, Hans Jørgen Aa

    2016-01-01

    -srDFT for a selected benchmark set of electronic excitations of organic molecules, covering the most common types of organic chromophores. This investigation confirms the expectation that the MC-srDFT method is accurate for a broad range of excitations and comparable to accurate wave function methods such as CASPT2......Computational methods that can accurately and effectively predict all types of electronic excitations for any molecular system are missing in the toolbox of the computational chemist. Although various Kohn-Sham density-functional methods (KS-DFT) fulfill this aim in some cases, they become...... and double excitations have been promising, it is nevertheless important that the accuracy of MC-srDFT is at least comparable to the best KS-DFT methods also for organic molecules that are typically of single-reference character. In this paper we therefore systematically investigate the performance of MC...

  9. High-density native-range species affects the invasive plant Chromolaena odorata more strongly than species from its invasive range.

    Science.gov (United States)

    Zheng, Yulong; Liao, Zhiyong

    2017-11-22

    Invasive plant species often form dense mono-dominant stands in areas they have invaded, while having only sparse distribution in their native ranges, and the reasons behind this phenomenon are a key point of research in invasive species biology. Differences in species composition between native and invasive ranges may contribute to the difference in distribution status. In this study, we found that the high-density condition had a more negative effect on C. odorata than the low-density condition when co-grown with neighbor plants from its native range in Mexico, while this pattern was not in evidence when it was grown with neighbors from its invasive range in China. Different competitive ability and coevolutionary history with C. odorata between native-range neighbors and invasive-range neighbors may lead to the inconsistent patterns.

  10. Evolvement law of a macroscopic traffic model accounting for density-dependent relaxation time

    Science.gov (United States)

    Wang, Yu-Qing; Chu, Xing-Jian; Zhou, Chao-Fan; Jia, Bin; Lin, Sen; Wu, Zi-Han; Zhu, Hua-Bing; Gao, Zi-You

    2017-11-01

    In this paper, a modified macroscopic traffic flow model is presented. The term of the density-dependent relaxation time is introduced here. The relation between the relaxation time and the density in traffic flow is presented quantitatively. Besides, a factor R depicting varied properties of traffic flow in different traffic states is also introduced in the formulation of the model. Furthermore, the evolvement law of traffic flow with distinctly initial density distribution and boundary perturbations is emphasized.

  11. Explaining density-dependent regulation in earthworm populations using life-history analysis

    NARCIS (Netherlands)

    Kammenga, J.E.; Spurgeon, D.J.; Svendsen, C.; Weeks, J.M.

    2003-01-01

    At present there is little knowledge about how density regulates population growth rate and to what extent this is determined by life-history patterns. We compared density dependent population consequences in the Nicholsonian sense based oil experimental observations and life-history modeling for

  12. An experimental field study of delayed density dependence in natural populations of Aedes albopictus.

    Directory of Open Access Journals (Sweden)

    Rachael K Walsh

    Full Text Available Aedes albopictus, a species known to transmit dengue and chikungunya viruses, is primarily a container-inhabiting mosquito. The potential for pathogen transmission by Ae. albopictus has increased our need to understand its ecology and population dynamics. Two parameters that we know little about are the impact of direct density-dependence and delayed density-dependence in the larval stage. The present study uses a manipulative experimental design, under field conditions, to understand the impact of delayed density dependence in a natural population of Ae. albopictus in Raleigh, North Carolina. Twenty liter buckets, divided in half prior to experimentation, placed in the field accumulated rainwater and detritus, providing oviposition and larval production sites for natural populations of Ae. albopictus. Two treatments, a larvae present and larvae absent treatment, were produced in each bucket. After five weeks all larvae were removed from both treatments and the buckets were covered with fine mesh cloth. Equal numbers of first instars were added to both treatments in every bucket. Pupae were collected daily and adults were frozen as they emerged. We found a significant impact of delayed density-dependence on larval survival, development time and adult body size in containers with high larval densities. Our results indicate that delayed density-dependence will have negative impacts on the mosquito population when larval densities are high enough to deplete accessible nutrients faster than the rate of natural food accumulation.

  13. Density Dependence and Growth Rate: Evolutionary Effects on Resistance Development to Bt (Bacillus thuringiensis).

    Science.gov (United States)

    Martinez, Jeannette C; Caprio, Michael A; Friedenberg, Nicholas A

    2018-02-09

    It has long been recognized that pest population dynamics can affect the durability of a pesticide, but dose remains the primary component of insect resistance management (IRM). For transgenic pesticidal traits such as Bt (Bacillus thuringiensis Berliner (Bacillales: Bacillaceae)), dose (measured as the mortality of susceptibles caused by a toxin) is a relatively fixed characteristic and often falls below the standard definition of high dose. Hence, it is important to understand how pest population dynamics modify durability and what targets they present for IRM. We used a deterministic model of a generic arthropod pest to examine how timing and strength of density dependence interacted with population growth rate and Bt mortality to affect time to resistance. As in previous studies, durability typically reached a minimum at intermediate doses. However, high population growth rates could eliminate benefits of high dose. The timing of density dependence had a more subtle effect. If density dependence operated simultaneously with Bt mortality, durability was insensitive to its strengths. However, if density dependence was driven by postselection densities, decreasing its strength could increase durability. The strength of density dependence could affect durability of both single traits and pyramids, but its influence depended on the timing of density dependence and size of the refuge. Our findings suggest the utility of a broader definition of high dose, one that incorporates population-dynamic context. That maximum growth rates and timing and strength of interactions causing density dependent mortality can all affect durability, also highlights the need for ecologically integrated approaches to IRM research. © The Author(s) 2017. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  14. System Estimation of Panel Data Models under Long-Range Dependence

    DEFF Research Database (Denmark)

    Ergemen, Yunus Emre

    A general dynamic panel data model is considered that incorporates individual and interactive fixed effects allowing for contemporaneous correlation in model innovations. The model accommodates general stationary or nonstationary long-range dependence through interactive fixed effects and innovat...

  15. Kernel density estimators of home range: smoothing and the autocorrelation red herring.

    Science.gov (United States)

    Fieberg, John

    2007-04-01

    Two oft-cited drawbacks of kernel density estimators (KDEs) of home range are their sensitivity to the choice of smoothing parameter(s) and their need for independent data. Several simulation studies have been conducted to compare the performance of objective, data-based methods of choosing optimal smoothing parameters in the context of home range and utilization distribution (UD) estimation. Lost in this discussion of choice of smoothing parameters is the general role of smoothing in data analysis, namely, that smoothing serves to increase precision at the cost of increased bias. A primary goal of this paper is to illustrate this bias-variance trade-off by applying KDEs to sampled locations from simulated movement paths. These simulations will also be used to explore the role of autocorrelation in estimating UDs. Autocorrelation can be reduced (1) by increasing study duration (for a fixed sample size) or (2) by decreasing the sampling rate. While the first option will often be reasonable, for a fixed study duration higher sampling rates should always result in improved estimates of space use. Further, KDEs with typical data-based methods of choosing smoothing parameters should provide competitive estimates of space use for fixed study periods unless autocorrelation substantially alters the optimal level of smoothing.

  16. Improving Delay-Range-Dependent Stability Condition for Systems with Interval Time-Varying Delay

    Directory of Open Access Journals (Sweden)

    Wei Qian

    2013-01-01

    Full Text Available This paper discusses the delay-range-dependent stability for systems with interval time-varying delay. Through defining the new Lyapunov-Krasovskii functional and estimating the derivative of the LKF by introducing new vectors, using free matrices and reciprocally convex approach, the new delay-range-dependent stability conditions are obtained. Two well-known examples are given to illustrate the less conservatism of the proposed theoretical results.

  17. A parameterization of momentum roughness length and displacement height for a wide range of canopy densities

    Directory of Open Access Journals (Sweden)

    A. Verhoef

    1997-01-01

    Full Text Available Values of the momentum roughness length, z0, and displacement height, d, derived from wind profiles and momentum flux measurements, are selected from the literature for a variety of sparse canopies. These include savannah, tiger-bush and several row crops. A quality assessment of these data, conducted using criteria such as available fetch, height of wind speed measurement and homogeneity of the experimental site, reduced the initial total of fourteen sites to eight. These datapoints, combined with values carried forward from earlier studies on the parameterization of z0 and d, led to a maximum number of 16 and 24 datapoints available for d and z0, respectively. The data are compared with estimates of roughness length and displacement height as predicted from a detailed drag partition model, R92 (Raupach, 1992, and a simplified version of this model, R94 (Raupach, 1994. A key parameter in these models is the roughness density or frontal area index, λ. Both the comprehensive and the simplified model give accurate predictions of measured z0 and d values, but the optimal model coefficients are significantly different from the ones originally proposed in R92 and R94. The original model coefficients are based predominantly on measured aerodynamic parameters of relatively closed canopies and they were fitted `by eye'. In this paper, best-fit coefficients are found from a least squares minimization using the z0 and d values of selected good-quality data for sparse canopies and for the added, mainly closed canopies. According to a statistical analysis, based on the coefficient of determination (r2, the number of observations and the number of fitted model coefficients, the simplified model, R94, is deemed to be the most appropriate for future z0 and d predictions. A CR value of 0.35 and a cd1 value of about 20 are found to be appropriate for a large range of canopies varying in density from closed to very sparse. In this case, 99% of the total variance

  18. Parents benefit from eating offspring: density-dependent egg survivorship compensates for filial cannibalism.

    Science.gov (United States)

    Klug, Hope; Lindström, Kai; St Mary, Colette M

    2006-10-01

    Why should animals knowingly consume their own young? It is difficult to imagine many circumstances in which eating one's own young (i.e., filial cannibalism) actually increases an individual's fitness; however, filial cannibalism commonly co-occurs with parental care in fishes. The evolutionary significance of filial cannibalism remains unclear. The most commonly accepted explanation is that filial cannibalism is a mechanism by which caring males gain energy or nutrients that they reinvest into future reproduction, thereby increasing net reproductive success. There is mixed support for this hypothesis and, at best, it can only explain filial cannibalism in some species. A recent alternative hypothesis suggests that filial cannibalism improves the survivorship of remaining eggs by increasing oxygen availability, and thus increases current reproductive success. This theory has received little attention as of yet. We evaluated the hypothesis of oxygen-mediated filial cannibalism in the sand goby by examining the effect of oxygen and egg density on the occurrence of filial cannibalism, evaluating the effects of partial clutch cannibalism on the survivorship of remaining eggs, and comparing potential costs and benefits of filial cannibalism related to the net number of eggs surviving. Indeed, we found that oxygen level and egg density affected the occurrence of cannibalism and that simulated partial clutch cannibalism improved survivorship of the remaining eggs. Additionally, because increased egg survivorship, stemming from partial egg removal, compensated for the cost of cannibalism (i.e., number of eggs removed) at a range of cannibalism levels, filial cannibalism potentially results in no net losses in reproductive success. However, oxygen did not affect egg survivorship. Thus, we suggest a more general hypothesis of filial cannibalism mediated by density-dependent egg survivorship.

  19. A novel nuclear dependence of nucleon–nucleon short-range correlations

    Energy Technology Data Exchange (ETDEWEB)

    Dai, Hongkai [College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China); Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Wang, Rong, E-mail: rwang@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China); Lanzhou University, Lanzhou 730000 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Huang, Yin [Lanzhou University, Lanzhou 730000 (China); Chen, Xurong [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000 (China)

    2017-06-10

    A linear correlation is found between the magnitude of nucleon–nucleon short-range correlations and the nuclear binding energy per nucleon with pairing energy removed. By using this relation, the strengths of nucleon–nucleon short-range correlations of some unmeasured nuclei are predicted. Discussions on nucleon–nucleon pairing energy and nucleon–nucleon short-range correlations are made. The found nuclear dependence of nucleon–nucleon short-range correlations may shed some lights on the short-range structure of nucleus.

  20. Calculation of the density of solutions (sunflower oil + n-hexane) over a wide range of temperatures and pressure

    Science.gov (United States)

    Safarov, M. M.; Abdukhamidova, Z.

    1995-09-01

    We present the results from an experimental investigation of the density of the sunflower oil system as a function of the mass concentration of n-hexane in the ranges of temperatures T=290 520 K and pressures P=0.101 98.1 MPa. A method of hydrostatic weighing was used to measure the density of the solutions under study.

  1. Global cold curve. New representation for zero-temperature isotherm in whole density range

    CERN Document Server

    Iosilevskiy, Igor

    2014-01-01

    Non-standard representation for so-called "cold curve" of matter (i.e. isotherm $T = 0$) is proposed as Global Cold Curve (GCC). The main point is that chemical potential of substance, $\\mu$, plays role of ruling parameter in basic GCC-dependence of internal energy under compression, $U = U(\\mu)$, in contrast to the standard form $U = U(\\rho)$. This substitution changes radically low-density ("gaseous") part of GCC. Namely: ($i$) - physically meaningless part of standard cold curve $(U(\\rho)$ at $T \\rightarrow 0)$ disappears totally from new version of GCC. This deleted part corresponded to absolutely thermodynamically unstable states in standard representation $U(\\rho)$; ($ii$) - new gaseous branch of cold curve, $U = U(\\mu)$, comes in GCC. It describes in simple, schematic way thermodynamics of whole gas-like plasma in low-temperature limit (Iosilevskiy: arXiv:0902.3708) as combination of all ionization and dissociation processes available for equilibrium plasma at finite temperature. This gaseous branch co...

  2. Density-dependent coral recruitment displays divergent responses during distinct early life-history stages.

    Science.gov (United States)

    Doropoulos, Christopher; Evensen, Nicolas R; Gómez-Lemos, Luis A; Babcock, Russell C

    2017-05-01

    Population growth involves demographic bottlenecks that regulate recruitment success during various early life-history stages. The success of each early life-history stage can vary in response to population density, interacting with intrinsic (e.g. behavioural) and environmental (e.g. competition, predation) factors. Here, we used the common reef-building coral Acropora millepora to investigate how density-dependence influences larval survival and settlement in laboratory experiments that isolated intrinsic effects, and post-settlement survival in a field experiment that examined interactions with environmental factors. Larval survival was exceptionally high (greater than 80%) and density-independent from 2.5 to 12 days following spawning. By contrast, there was a weak positive effect of larval density on settlement, driven by gregarious behaviour at the highest density. When larval supply was saturated, settlement was three times higher in crevices compared with exposed microhabitats, but a negative relationship between settler density and post-settlement survival in crevices and density-independent survival on exposed surfaces resulted in similar recruit densities just one month following settlement. Moreover, a negative relationship was found between turf algae and settler survival in crevices, whereas gregarious settlement improved settler survival on exposed surfaces. Overall, our findings reveal divergent responses by coral larvae and newly settled recruits to density-dependent regulation, mediated by intrinsic and environmental interactions.

  3. Density-dependent seedling mortality varies with light availability and species abundance in wet and dry Hawaiian forests

    Science.gov (United States)

    Faith Inman-Narahari; Rebecca Ostertag; Stephen P. Hubbell; Christian P. Giardina; Susan Cordell; Lawren Sack; Andrew MacDougall

    2016-01-01

    Conspecific density may contribute to patterns of species assembly through negative density dependence (NDD) as predicted by the Janzen-Connell hypothesis, or through facilitation (positive density dependence; PDD). Conspecific density effects are expected to be more negative in darker and wetter environments due to higher pathogen abundance and...

  4. Combined effects of climate, predation, and density dependence on Greater and Lesser Scaup population dynamics.

    Science.gov (United States)

    Ross, Beth E; Hooten, Mevin B; DeVink, Jean-Michel; Koons, David N

    2015-09-01

    An understanding of species relationships is critical in the management and conservation of populations facing climate change, yet few studies address how climate alters species interactions and other population drivers. We use a long-term, broad-scale data set of relative abundance to examine the influence of climate, predators, and density dependence on the population dynamics of declining scaup (Aythya) species within the core of their breeding range. The state-space modeling approach we use applies to a wide range of wildlife species, especially populations monitored over broad spatiotemporal extents. Using this approach, we found that immediate snow cover extent in the preceding winter and spring had the strongest effects, with increases in mean snow cover extent having a positive effect on the local surveyed abundance of scaup. The direct effects of mesopredator abundance on scaup population dynamics were weaker, but the results still indicated a potentil interactive process between climate and food web dynamics (mesopredators, alternative prey, and scaup). By considering climate variables and other potential effects on population dynamics, and using a rigorous estimation framework, we provide insight into complex ecological processes for guiding. conservation and policy actions aimed at mitigating and reversing the decline of scaup.

  5. Density-dependent intraspecific aggression regulates survival in northern Yellowstone wolves (Canis lupus).

    Science.gov (United States)

    Cubaynes, Sarah; MacNulty, Daniel R; Stahler, Daniel R; Quimby, Kira A; Smith, Douglas W; Coulson, Tim

    2014-11-01

    Understanding the population dynamics of top-predators is essential to assess their impact on ecosystems and to guide their management. Key to this understanding is identifying the mechanisms regulating vital rates. Determining the influence of density on survival is necessary to understand the extent to which human-caused mortality is compensatory or additive. In wolves (Canis lupus), empirical evidence for density-dependent survival is lacking. Dispersal is considered the principal way in which wolves adjust their numbers to prey supply or compensate for human exploitation. However, studies to date have primarily focused on exploited wolf populations, in which density-dependent mechanisms are likely weak due to artificially low wolf densities. Using 13 years of data on 280 collared wolves in Yellowstone National Park, we assessed the effect of wolf density, prey abundance and population structure, as well as winter severity, on age-specific survival in two areas (prey-rich vs. prey-poor) of the national park. We further analysed cause-specific mortality and explored the factors driving intraspecific aggression in the prey-rich northern area of the park. Overall, survival rates decreased during the study. In northern Yellowstone, density dependence regulated adult survival through an increase in intraspecific aggression, independent of prey availability. In the interior of the park, adult survival was less variable and density-independent, despite reduced prey availability. There was no effect of prey population structure in northern Yellowstone, or of winter severity in either area. Survival was similar among yearlings and adults, but lower for adults older than 6 years. Our results indicate that density-dependent intraspecific aggression is a major driver of adult wolf survival in northern Yellowstone, suggesting intrinsic density-dependent mechanisms have the potential to regulate wolf populations at high ungulate densities. When low prey availability or high

  6. Dependence with air density of the response of the PTW SourceCheck ionization chamber for low energy brachytherapy sources.

    Science.gov (United States)

    Tornero-López, Ana M; Guirado, Damián; Perez-Calatayud, Jose; Ruiz-Arrebola, Samuel; Simancas, Fernando; Gazdic-Santic, Maja; Lallena, Antonio M

    2013-12-01

    Air-communicating well ionization chambers are commonly used to assess air kerma strength of sources used in brachytherapy. The signal produced is supposed to be proportional to the air density within the chamber and, therefore, a density-independent air kerma strength is obtained when the measurement is corrected to standard atmospheric conditions using the usual temperature and pressure correction factor. Nevertheless, when assessing low energy sources, the ionization chambers may not fulfill that condition and a residual density dependence still remains after correction. In this work, the authors examined the behavior of the PTW 34051 SourceCheck ionization chamber when measuring the air kerma strength of (125)I seeds. Four different SourceCheck chambers were analyzed. With each one of them, two series of measurements of the air kerma strength for (125)I selectSeed(TM) brachytherapy sources were performed inside a pressure chamber and varying the pressure in a range from 747 to 1040 hPa (560 to 780 mm Hg). The temperature and relative humidity were kept basically constant. An analogous experiment was performed by taking measurements at different altitudes above sea level. Contrary to other well-known ionization chambers, like the HDR1000 PLUS, in which the temperature-pressure correction factor overcorrects the measurements, in the SourceCheck ionization chamber they are undercorrected. At a typical atmospheric situation of 933 hPa (700 mm Hg) and 20 °C, this undercorrection turns out to be 1.5%. Corrected measurements show a residual linear dependence on the density and, as a consequence, an additional density dependent correction must be applied. The slope of this residual linear density dependence is different for each SourceCheck chamber investigated. The results obtained by taking measurements at different altitudes are compatible with those obtained with the pressure chamber. Variations of the altitude and changes in the weather conditions may produce

  7. Dependence of various SOL widths on plasma current and density in NSTX H-mode plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Ahn, J; Maingi, R; Boedo, J; Soukhanovskii, V A

    2009-02-12

    The dependence of various SOL widths on the line-averaged density ({ovr n}{sub e}) and plasma current (l{sub p}) for the quiescent H-mode plasmas with Type-V ELMs in the National Spherical Torus Experiment (NSTX) was investigated. It is found that the heat flux SOL width ({lambda}{sub q}), measured by the IR camera, is virtually insensitive to {ovr n}{sub e} and has a strong negative dependence on l{sub p}. This insensitivity of {lambda}{sub q} to {ovr n}{sub e} is consistent with the scaling law from JET H-mode plasmas that shows a very weak dependence on the upstream density. The electron temperature, ion saturation current density, electron density, and electron pressure decay lengths ({lambda}{sub Te}, {lambda}{sub jsat}, {lambda}{sub ne}, and {lambda}{sub pe}, respectively) measured by the probe showed that {lambda}{sub Te} and {lambda}{sub jsat} have strong negative dependence on l{sub p}, whereas {lambda}{sub ne} and {lambda}{sub pe} revealed only a little or no dependence. The dependence of {lambda}{sub Te} on l{sub p} is consistent with the scaling law in the literature while {lambda}{sub ne} and {lambda}{sub pe} dependence shows a different trend.

  8. Density dependence of hydrogen bonding and the translational-orientational structural order in supercritical water: a molecular dynamics study.

    Science.gov (United States)

    Ma, Haibo; Ma, Jing

    2011-08-07

    Molecular dynamics simulation have been performed with a wide range of densities along a near critical isotherm of supercritical water (SCW) in order to study the density dependence of the structure order and hydrogen bonding (HB). It is revealed that the translational structure order is nearly invariant while the orientational tetrahedral structure order is very sensitive to the bulk density under supercritical conditions. Meanwhile, some energetically unfavorable intermediate water dimer structures are found to appear under supercritical conditions due to the reduced energy difference and the enhanced energy fluctuation. As a consequence, a general geometrical criterion or the inclusion of a energy-based criterion instead of currently widely adopted pure r(OH)-based geometric criterion is suggested to be used in the HB statistics under supercritical conditions. It is found that the average HB number per H(2)O molecule (n(HB)) reduces with the decreasing SCW bulk density although a given pair of H(2)O molecules are shown to have a stronger ability to form a hydrogen bond under lower SCW bulk densities. Accordingly, the orientational tetrahedral structure order q decreases with the reducing bulk density under supercritical conditions. However, when the fluid is dilute with ρ ≤ 0.19ρ(c) (ρ(c) = 0.322 g/cm(3)), the energy fluctuation increases sharply and the short-range order is destroyed, signifying the supercritical fluid (SCF)-gas state transition. Accordingly, the orientational tetrahedral structure order q gets reversal around ρ = 0.19ρ(c) and approaches zero under very dilute conditions. The sensitivity of the orientational order to the density implies the microscopic origin of the significant dependence of SCF's physicochemical properties on the pressure.

  9. Cell density dependence of Microcystis aeruginosa responses to copper algaecide concentrations: Implications for microcystin-LR release.

    Science.gov (United States)

    Kinley, Ciera M; Iwinski, Kyla J; Hendrikse, Maas; Geer, Tyler D; Rodgers, John H

    2017-11-01

    Along with mechanistic models, predictions of exposure-response relationships for copper are often derived from laboratory toxicity experiments with standardized experimental exposures and conditions. For predictions of copper toxicity to algae, cell density is a critical factor often overlooked. For pulse exposures of copper-based algaecides in aquatic systems, cell density can significantly influence copper sorbed by the algal population, and consequent responses. A cyanobacterium, Microcystis aeruginosa, was exposed to a copper-based algaecide over a range of cell densities to model the density-dependence of exposures, and effects on microcystin-LR (MC-LR) release. Copper exposure concentrations were arrayed to result in a gradient of MC-LR release, and masses of copper sorbed to algal populations were measured following exposures. While copper exposure concentrations eliciting comparable MC-LR release ranged an order of magnitude (24-h EC50s 0.03-0.3mg Cu/L) among cell densities of 10 6 through 10 7 cells/mL, copper doses (mg Cu/mg algae) were similar (24-h EC50s 0.005-0.006mg Cu/mg algae). Comparisons of MC-LR release as a function of copper exposure concentrations and doses provided a metric of the density dependence of algal responses in the context of copper-based algaecide applications. Combined with estimates of other site-specific factors (e.g. water characteristics) and fate processes (e.g. dilution and dispersion, sorption to organic matter and sediments), measuring exposure-response relationships for specific cell densities can refine predictions for in situ exposures and algal responses. These measurements can in turn decrease the likelihood of amending unnecessary copper concentrations to aquatic systems, and minimize risks for non-target aquatic organisms. Copyright © 2017 Elsevier Inc. All rights reserved.

  10. Density dependence and population differentiation of genetic architecture in Impatiens capensis in natural environments.

    Science.gov (United States)

    Donohue, K; Pyle, E H; Messiqua, D; Heschel, M S; Schmitt, J

    2000-12-01

    We identified environment-dependent constraints on the evolution of plasticity to density under natural conditions in two natural populations of Impatiens capensis. We also examined the expression of population divergence in genetic variance-covariance matrices in these natural environments. Inbred lines, originally collected from a sunny site with high seedling densities and a woodland site with low seedling densities, were planted in both original sites at natural high densities and at low density. Morphological and life-history characters were measured. More genetic variation for plastic responses to density was expressed in the sun site than in the woodland site, so the evolutionary potential of plasticity was greater in the sun site. Strong genetic correlations between the same character expressed at different densities and correlations among different characters could constrain the evolution of plasticity in both sites. Genetically based trade-offs in meristem allocation to vegetative growth and reproduction were apparent only in the high-resource environment with no overhead canopy and no intraspecific competition. Therefore, genetic constraints on the evolution of plasticity depended on the site and density in which plants were grown, and correlated responses to selection on plastic characters are also expected to differ between sites and densities. Population differentiation in genetic variance-covariance matrices was detected, but matrix structural differences, as opposed to proportional differences, were detected between populations only in the sun site at natural high density. Thus, population divergence in genetic architecture can occur rapidly and on a fine spatial scale, but the expression of such divergence may depend on the environment.

  11. Density dependence of the symmetry energy from neutron skin thickness in finite nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Vinas, X.; Centelles, M. [Universitat de Barcelona, Departament d' Estructura i Constituents de la Materia and Institut de Ciencies del Cosmos, Facultat de Fisica, Barcelona (Spain); Roca-Maza, X. [Universita degli Studi di Milano (Italy); INFN, Dipartamento di Fisica, Milano (Italy); Warda, M. [Uniwersytet Marii Curie-Sklodowskiej ul. Radziszewskiego 10, Katedra Fizyki Teoretycznej, Lublin (Poland)

    2014-02-15

    The density dependence of the symmetry energy around saturation density, characterized by the slope parameter L, is studied using information provided by the neutron skin thickness in finite nuclei. An estimate for L is obtained from experimental data on neutron skins extracted from antiprotonic atoms. We also discuss the ability of parity-violating elastic electron scattering to obtain information on the neutron skin thickness in {sup 208}Pb and to constrain the density dependence of the nuclear symmetry energy. The size and shape of the neutron density distribution of {sup 208}Pb predicted by mean-field models is briefly addressed. We conclude with a comparative overview of the L values predicted by several existing determinations. (orig.)

  12. Robustness of Estimators of Long-Range Dependence and Self-Similarity under non-Gaussianity

    CERN Document Server

    Franzke, Christian L E; Watkins, Nicholas W; Gramacy, Robert B; Hughes, Cecilia

    2011-01-01

    Long-range dependence and non-Gaussianity are ubiquitous in many natural systems like ecosystems, biological systems and climate. However, it is not always appreciated that both phenomena usually occur together in natural systems and that the superposition of both phenomena constitute the self-similarity of a system. These features, which are common in complex systems, impact the attribution of trends and the occurrence and clustering of extremes. The risk assessment of systems with these properties will lead to different outcomes (e.g. return periods) than the more common assumption of independence of extremes. Two paradigmatic models are discussed which can simultaneously account for long-range dependence and non-Gaussianity: Autoregressive Fractional Integrated Moving Average (ARFIMA) and Linear Fractional Stable Motion (LFSM). Statistical properties of estimators for long-range dependence and self-similarity are critically assessed. It is found that the most popular estimators are not robust. In particula...

  13. Fractality Evidence and Long-Range Dependence on Capital Markets: a Hurst Exponent Evaluation

    Science.gov (United States)

    Oprean, Camelia; Tănăsescu, Cristina

    2014-07-01

    Since the existence of market memory could implicate the rejection of the efficient market hypothesis, the aim of this paper is to find any evidence that selected emergent capital markets (eight European and BRIC markets, namely Hungary, Romania, Estonia, Czech Republic, Brazil, Russia, India and China) evince long-range dependence or the random walk hypothesis. In this paper, the Hurst exponent as calculated by R/S fractal analysis and Detrended Fluctuation Analysis is our measure of long-range dependence in the series. The results reinforce our previous findings and suggest that if stock returns present long-range dependence, the random walk hypothesis is not valid anymore and neither is the market efficiency hypothesis.

  14. Density-dependent selection on mate search and evolution of Allee effects.

    Science.gov (United States)

    Berec, Luděk; Kramer, Andrew M; Bernhauerová, Veronika; Drake, John M

    2018-01-01

    Sexually reproducing organisms require males and females to find each other. Increased difficulty of females finding mates as male density declines is the most frequently reported mechanism of Allee effects in animals. Evolving more effective mate search may alleviate Allee effects, but may depend on density regimes a population experiences. In particular, high-density populations may evolve mechanisms that induce Allee effects which become detrimental when populations are reduced and maintained at a low density. We develop an individual-based, eco-genetic model to study how mating systems and fitness trade-offs interact with changes in population density to drive evolution of the rate at which males or females search for mates. Finite mate search rate triggers Allee effects in our model and we explore how these Allee effects respond to such evolution. We allow a population to adapt to several population density regimes and examine whether high-density populations are likely to reverse adaptations attained at low densities. We find density-dependent selection in most of scenarios, leading to search rates that result in lower Allee thresholds in populations kept at lower densities. This mainly occurs when fecundity costs are imposed on mate search, and provides an explanation for why Allee effects are often observed in anthropogenically rare species. Optimizing selection, where the attained trait value minimizes the Allee threshold independent of population density, depended on the trade-off between search and survival, combined with monogamy when females were searching. Other scenarios led to runaway selection on the mate search rate, including evolutionary suicide. Trade-offs involved in mate search may thus be crucial to determining how density influences the evolution of Allee effects. Previous studies did not examine evolution of a trait related to the strength of Allee effects under density variation. We emphasize the crucial role that mating systems, fitness

  15. Cosmological constraints from the redshift dependence of the Alcock-Paczynski test: galaxy density gradient field

    OpenAIRE

    Li, Xiao-Dong; Park, Changbom; Forero-Romero, Jaime E.; Kim, Juhan

    2014-01-01

    We propose a method based on the redshift dependence of the Alcock-Paczynski (AP) test to measure the expansion history of the Universe. It uses the isotropy of the galaxy density gradient field to constrain cosmological parameters. If the density parameter $\\Omega_m$ or the dark energy equation of state $w$ are incorrectly chosen, the gradient field appears to be anisotropic with the degree of anisotropy varying with redshift. We use this effect to constrain the cosmological parameters gover...

  16. Anatomy of a population cycle: the role of density dependence and demographic variability on numerical instability and periodicity.

    Science.gov (United States)

    Row, Jeffrey R; Wilson, Paul J; Murray, Dennis L

    2014-07-01

    Determining the causes of cyclic fluctuations in population size is a central tenet in population ecology and provides insights into population regulatory mechanisms. We have a firm understanding of how direct and delayed density dependence affects population stability and cyclic dynamics, but there remains considerable uncertainty in the specific processes contributing to demographic variability and consequent change in cyclic propensity. Spatiotemporal variability in cyclic propensity, including recent attenuation or loss of cyclicity among several temperate populations and the implications of habitat fragmentation and climate change on this pattern, highlights the heightened need to understand processes underlying cyclic variation. Because these stressors can differentially impact survival and productivity and thereby impose variable time delays in density dependence, there is a specific need to elucidate how demographic vital rates interact with the type and action of density dependence to contribute to population stability and cyclic variation. Here, we address this knowledge gap by comparing the stability of time series derived from general and species-specific (Canada lynx: Lynx canadensis; small rodents: Microtus, Lemmus and Clethrionomys spp.) matrix population models, which vary in their demographic rates and the direct action of density dependence. Our results reveal that density dependence acting exclusively on survival as opposed to productivity is destabilizing, suggesting that a shift in the action of population regulation toward reproductive output may decrease cyclic propensity and cycle amplitude. This result was the same whether delayed density dependence was pulsatile and acted on a single time period (e.g. t-1, t-2 or t-3) vs. more constant by affecting a successive range of years (e.g. t-1,…, t-3). Consistent with our general models, reductions in reproductive potential in both the lynx and small rodent systems led to notably large drops in

  17. Stochastic seasonality and nonlinear density-dependent factors regulate population size in an African rodent

    DEFF Research Database (Denmark)

    Leirs, Herwig; Steneth, Nils Chr.; Nichols, James D.

    1997-01-01

    Ecology has long been troubled by the controversy over how populations are regulated(1,2). Some ecologists focus on the role of environmental effects, whereas others argue that density-dependent feedback mechanisms are central(3-6). The relative importance of both processes is still hotly debated......, but clear examples of both processes acting in the same population are rare(7,8). Key-factor analysis (regression of population changes on possible causal factors) and time-series analysis are often used to investigate the presence of density dependence, but such approaches may be biased and provide...... that they do not affect all demographic rates in the same way. We have incorporated the obtained estimates of demographic rates in a population dynamics model and show that the observed dynamics are affected by stabilizing nonlinear density-dependent components coupled with strong deterministic and stochastic...

  18. Density-dependent gastroretentive microparticles motion in human gastric emptying studied using computer simulation.

    Science.gov (United States)

    Hao, Shilei; Wang, Bochu; Wang, Yazhou

    2015-04-05

    Density-dependent gastroretentive drug delivery systems have been used to prolong the gastric retention time of drugs since the 1960s. The design of density-dependent gastroretentive dosage forms, however, usually focuses on specific parameters rather than combines with the fluid dynamics of dosage form in the gastric emptying. Therefore, the purpose of the present study was to develop a 2-D model of multiple-phase flows for the simulation of gastric emptying and gastroretentive microparticles motion, and the influence of microparticle density, microparticle viscosity, and gastric juice viscosity on the gastric retention were studied. The recirculating flows, formed in the gastric emptying, could mix the conventional-density microparticles and transport them to the pylorus. However, the low-density microparticles remained floating on the surface of gastric juice, while the high-density microparticles could sink and deposit in the bottom of the stomach. The remaining integral area of microparticles was higher than 90% after 18.33min of simulation when the density of microparticles was lower than 550kg/m(3) or higher than 2500kg/m(3), which was higher compared to conventional-density microparticles (67.05%). These results are in good agreement with experimental data previously reported. In addition, the viscosity of microparticle and gastric juice also influenced the remaining integral area of gastroretentive microparticles. This study shows that the multiple-phase computational fluid dynamics models could provide detailed insights into the fluid dynamics of density-dependent gastroretentive microparticles in gastric emptying, which offers a powerful tool to further understand the mechanism of gastric retention for gastroretentive dosage forms and study the influence of different parameters on their ability for gastric retention. Copyright © 2015 Elsevier B.V. All rights reserved.

  19. Delay-range-dependent chaos synchronization approach under varying time-lags and delayed nonlinear coupling.

    Science.gov (United States)

    Zaheer, Muhammad Hamad; Rehan, Muhammad; Mustafa, Ghulam; Ashraf, Muhammad

    2014-11-01

    This paper proposes a novel state feedback delay-range-dependent control approach for chaos synchronization in coupled nonlinear time-delay systems. The coupling between two systems is esteemed to be nonlinear subject to time-lags. Time-varying nature of both the intrinsic and the coupling delays is incorporated to broad scope of the present study for a better-quality synchronization controller synthesis. Lyapunov-Krasovskii (LK) functional is employed to derive delay-range-dependent conditions that can be solved by means of the conventional linear matrix inequality (LMI)-tools. The resultant control approach for chaos synchronization of the master-slave time-delay systems considers non-zero lower bound of the intrinsic as well as the coupling time-delays. Further, the delay-dependent synchronization condition has been established as a special case of the proposed LK functional treatment. Furthermore, a delay-range-dependent condition, independent of the delay-rate, has been provided to address the situation when upper bound of the delay-derivative is unknown. A robust state feedback control methodology is formulated for synchronization of the time-delay chaotic networks against the L2 norm bounded perturbations by minimizing the L2 gain from the disturbance to the synchronization error. Numerical simulation results are provided for the time-delay chaotic networks to show effectiveness of the proposed delay-range-dependent chaos synchronization methodologies. Copyright © 2014 ISA. Published by Elsevier Ltd. All rights reserved.

  20. Bayesian inference on the effect of density dependence and weather on a guanaco population from Chile.

    Directory of Open Access Journals (Sweden)

    María Zubillaga

    Full Text Available Understanding the mechanisms that drive population dynamics is fundamental for management of wild populations. The guanaco (Lama guanicoe is one of two wild camelid species in South America. We evaluated the effects of density dependence and weather variables on population regulation based on a time series of 36 years of population sampling of guanacos in Tierra del Fuego, Chile. The population density varied between 2.7 and 30.7 guanaco/km2, with an apparent monotonic growth during the first 25 years; however, in the last 10 years the population has shown large fluctuations, suggesting that it might have reached its carrying capacity. We used a Bayesian state-space framework and model selection to determine the effect of density and environmental variables on guanaco population dynamics. Our results show that the population is under density dependent regulation and that it is currently fluctuating around an average carrying capacity of 45,000 guanacos. We also found a significant positive effect of previous winter temperature while sheep density has a strong negative effect on the guanaco population growth. We conclude that there are significant density dependent processes and that climate as well as competition with domestic species have important effects determining the population size of guanacos, with important implications for management and conservation.

  1. Egg production and egg quality in free-range laying hens housed at different outdoor stocking densities.

    Science.gov (United States)

    Campbell, D L M; Lee, C; Hinch, G N; Roberts, J R

    2017-09-01

    Free-range laying hen systems are increasing in number within Australia. Variation in outdoor stocking densities has led to development of a national information standard on free-range egg labeling, including setting a maximum density of 10,000 hens per hectare. However, there are few data on the impacts of differing outdoor densities on production and egg quality. ISA Brown hens in small (150 hens) flocks were housed in identical indoor pens, each with access (from 21 weeks) to different sized ranges simulating one of three outdoor stocking densities (2 replicates each: 2,000 hens/hectare (ha), 10,000 hens/ha, 20,000 hens/ha). Hen-day production was tracked from 21 through 35 weeks with eggs visually graded daily for external deformities. All eggs laid on one day were weighed each week. Eggs were collected from each pen at 25, 30, and 36 weeks and analyzed for egg quality. There were no effects of outdoor stocking density on average hen-day percentage production (P = 0.67), egg weight (P = 0.09), percentages of deformed eggs (P = 0.30), shell reflectivity (P = 0.74), shell breaking strength (P = 0.07), shell deformation (P = 0.83), or shell thickness (P = 0.24). Eggs from hens in the highest density had the highest percentage shell weight (P = 0.004) and eggs from the lowest density had the highest yolk color score (P < 0.001). The amount of cuticle present did not differ between densities (P = 0.95) but some aspects of shell colors (P ≤ 0.01) and location of protoporphyrin IX (P = 0.046) varied. Hen age affected the majority of measurements. Stocking density differences may be related to hen diet as previous radio-frequency identification tracking of individual hens in these flocks showed birds used the range for longer in the lowest density and the least in the highest density, including depleting the range of vegetation sooner in the smaller ranges. An additional study assessing the relationship between individual hen range use, nutrition, and egg

  2. Constraints on spin-dependent short-range interactions using gravitational quantum levels of ultracold neutrons

    CERN Document Server

    Baeßler, S; Pignol, G; Protasov, K V; Voronin, A Yu

    2009-01-01

    In this paper, we discuss a possibility to improve constraints on spin-dependent short-range interactions in the range of 1 - 200 micrometer significantly. For such interactions, our constraints are without competition at the moment. They were obtained through the observation of gravitationally bound states of ultracold neutrons. We are going to improve these constraints by about three orders of magnitude in a dedicated experiment with polarized neutrons using the next-generation spectrometer GRANIT.

  3. Ionic strength-dependent changes in tentacular ion exchangers with variable ligand density. II. Functional properties.

    Science.gov (United States)

    Bhambure, Rahul; Angelo, James M; Gillespie, Christopher M; Phillips, Michael; Graalfs, Heiner; Lenhoff, Abraham M

    2017-07-14

    The effect of ligand density was studied on protein adsorption and transport behavior in tentacular cation-exchange sorbents at different ionic strengths. Results were obtained for lysozyme, lactoferrin and a monoclonal antibody (mAb) in order to examine the effects of protein size and charge. The combination of ligand density and ionic strength results in extensive variability of the static and dynamic binding capacities, transport rate and binding affinity of the proteins. Uptake and elution experiments were performed to quantify the transport behavior of selected proteins, specifically to estimate intraparticle protein diffusivities. The observed trend of decreasing uptake diffusivities with an increase in ligand density was correlated to structural properties of the ligand-density variants, particularly the accessible porosity. Increasing the ionic strength of the equilibration buffer led to enhanced mass transfer during uptake, independent of the transport model used, and specifically for larger proteins like lactoferrin and mAb, the most significant effects were evident in the sorbent of the highest ligand density. For lysozyme, higher ligand density leads to higher static and dynamic binding capacities whereas for lactoferrin and the mAb, the binding capacity is a complex function of accessible porosity due to ionic strength-dependent changes. Ligand density has a less pronounced effect on the elution rate, presumably due to ionic strength-dependent changes in the pore architecture of the sorbents. Copyright © 2017 Elsevier B.V. All rights reserved.

  4. Size dependent electronic properties of silicon quantum dots-An analysis with hybrid, screened hybrid and local density functional theory

    Science.gov (United States)

    Gabay, D.; Wang, X.; Lomakin, V.; Boag, A.; Jain, M.; Natan, A.

    2017-12-01

    We use an efficient projection scheme for the Fock operator to analyze the size dependence of silicon quantum dots (QDs) electronic properties. We compare the behavior of hybrid, screened hybrid and local density functionals as a function of the dot size up to ∼800 silicon atoms and volume of up to ∼20 nm3. This allows comparing the calculations of hybrid and screened hybrid functionals to experimental results over a wide range of QD sizes. We demonstrate the size dependent behavior of the band gap, density of states, ionization potential and HOMO level shift after ionization. We also demonstrate how the use of Graphical Processing Units (GPUs) can further accelerate such calculations.

  5. Optical Absorption in Molecular Crystals from Time-Dependent Density Functional Theory

    Science.gov (United States)

    2017-04-23

    from time-dependent density functional theory 5a.  CONTRACT NUMBER 5b.  GRANT NUMBER FA9550-15-1-0290 5c.  PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S...AFRL-AFOSR-UK-TR-2017-0030 Optical absorption in molecular crystals from time-dependent density functional theory Leeor Kronik WEIZMANN INSTITUTE OF...does not display a currently valid OMB control number . PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION. 1. REPORT DATE (DD-MM-YYYY)      23

  6. A metamaterial having a frequency dependent elasticity tensor and a zero effective mass density

    Energy Technology Data Exchange (ETDEWEB)

    Milton, Graeme [Department of Mathematics, University of Utah, Salt Lake City, UT 84112 (United States); Seppecher, Pierre [Institut de Mathematiques de Toulon, Universite du Sud Toulon-Var, BP 132, 83957 La Garde Cedex (France)

    2012-07-15

    Within the context of linear elasticity we show that a two-terminal network of springs and masses, can respond exactly the same as a normal spring, but with a frequency dependent spring constant. A network of such springs can have a frequency dependent effective elasticity tensor but zero effective mass density. The internal masses influence the elasticity tensor, but do not contribute to the effective mass density. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  7. Analytic Expressions for the Gravity Gradient Tensor of 3D Prisms with Depth-Dependent Density

    Science.gov (United States)

    Jiang, Li; Liu, Jie; Zhang, Jianzhong; Feng, Zhibing

    2017-12-01

    Variable-density sources have been paid more attention in gravity modeling. We conduct the computation of gravity gradient tensor of given mass sources with variable density in this paper. 3D rectangular prisms, as simple building blocks, can be used to approximate well 3D irregular-shaped sources. A polynomial function of depth can represent flexibly the complicated density variations in each prism. Hence, we derive the analytic expressions in closed form for computing all components of the gravity gradient tensor due to a 3D right rectangular prism with an arbitrary-order polynomial density function of depth. The singularity of the expressions is analyzed. The singular points distribute at the corners of the prism or on some of the lines through the edges of the prism in the lower semi-space containing the prism. The expressions are validated, and their numerical stability is also evaluated through numerical tests. The numerical examples with variable-density prism and basin models show that the expressions within their range of numerical stability are superior in computational accuracy and efficiency to the common solution that sums up the effects of a collection of uniform subprisms, and provide an effective method for computing gravity gradient tensor of 3D irregular-shaped sources with complicated density variation. In addition, the tensor computed with variable density is different in magnitude from that with constant density. It demonstrates the importance of the gravity gradient tensor modeling with variable density.

  8. Density-dependent light-assisted tunneling in fermionic optical lattices

    Science.gov (United States)

    Xu, Wenchao; Morong, William; Demarco, Brian

    2016-05-01

    Many recent theoretical proposals have discussed the possibility to realize density-dependent tunneling in optical lattices via external periodic driving. These methods enable the simulation of novel many-body quantum phases. Here we present experimental progress on realizing density-dependent tunneling for ultracold 40K atoms trapped in a cubic optical lattice via stimulated Raman transitions. After preparing a spin-polarized gas in the Mott insulator regime of the Hubbard model, a pair of Raman beams is applied to flip the spin of atoms. The Raman beams also introduce an effective density-dependent tunneling that can be tuned by the Raman frequency difference and Rabi rate. The Mott gap inferred from measurements of the fraction of atoms transferred between spin states as the Raman frequency difference is adjusted matches the prediction based on a tight-binding model. We also observe the interaction-dependent tunneling by measuring the fraction of doubly-occupied sites created by the Raman driving. This method allows the engineering of density-dependent tunneling and effective nearest-neighbor interactions in fermionic optical lattices. The authors acknowledge funding from the National Science Foundation (Grant No. PHY15-05468) and the Army Research Office (Grant No. W911NF-12-1-0462).

  9. Density-dependent natal dispersal patterns in a leopard population recovering from over-harvest.

    Directory of Open Access Journals (Sweden)

    Julien Fattebert

    Full Text Available Natal dispersal enables population connectivity, gene flow and metapopulation dynamics. In polygynous mammals, dispersal is typically male-biased. Classically, the 'mate competition', 'resource competition' and 'resident fitness' hypotheses predict density-dependent dispersal patterns, while the 'inbreeding avoidance' hypothesis posits density-independent dispersal. In a leopard (Panthera pardus population recovering from over-harvest, we investigated the effect of sex, population density and prey biomass, on age of natal dispersal, distance dispersed, probability of emigration and dispersal success. Over an 11-year period, we tracked 35 subadult leopards using VHF and GPS telemetry. Subadult leopards initiated dispersal at 13.6 ± 0.4 months. Age at commencement of dispersal was positively density-dependent. Although males (11.0 ± 2.5 km generally dispersed further than females (2.7 ± 0.4 km, some males exhibited opportunistic philopatry when the population was below capacity. All 13 females were philopatric, while 12 of 22 males emigrated. Male dispersal distance and emigration probability followed a quadratic relationship with population density, whereas female dispersal distance was inversely density-dependent. Eight of 12 known-fate females and 5 of 12 known-fate male leopards were successful in settling. Dispersal success did not vary with population density, prey biomass, and for males, neither between dispersal strategies (philopatry vs. emigration. Females formed matrilineal kin clusters, supporting the resident fitness hypothesis. Conversely, mate competition appeared the main driver for male leopard dispersal. We demonstrate that dispersal patterns changed over time, i.e. as the leopard population density increased. We conclude that conservation interventions that facilitated local demographic recovery in the study area also restored dispersal patterns disrupted by unsustainable harvesting, and that this indirectly improved

  10. Functional framework and hardware platform for dependability study in short range wireless embedded systems

    NARCIS (Netherlands)

    Senouci, B.; Annema, Anne J.; Bentum, Marinus Jan; Kerkhoff, Hans G.

    2011-01-01

    A new direction in short-range wireless applications has appeared in the form of high-speed data communication devices for distances of a few meters. Behind these embedded applications, a complex Hardware/Software architecture is built. Dependability is one of the major challenges in these systems.

  11. Analytic model utilizing the complex ABCD method for range dependency of a monostatic coherent lidar

    DEFF Research Database (Denmark)

    Olesen, Anders Sig; Pedersen, Anders Tegtmeier; Hanson, Steen Grüner

    2014-01-01

    In this work, we present an analytic model for analyzing the range and frequency dependency of a monostatic coherent lidar measuring velocities of a diffuse target. The model of the signal power spectrum includes both the contribution from the optical system as well as the contribution from the t...

  12. Thickness dependent charge transfer states and dark carriers density in vacuum deposited small molecule organic photocell

    Science.gov (United States)

    Shekhar, Himanshu; Tzabari, Lior; Solomeshch, Olga; Tessler, Nir

    2016-10-01

    We have investigated the influence of the active layer thickness on the balance of the internal mechanisms affecting the efficiency of copper phthalocyanine - fullerene (C60) based vacuum deposited bulk heterojunction organic photocell. We fabricated a range of devices for which we varied the thickness of the active layer from 40 to 120 nm and assessed their performance using optical and electrical characterization techniques. As reported previously for phthalocyanine:C60, the performance of the device is highly dependent on the active layer thickness and of all the thicknesses we tried, the 40 nm thin active layer device showed the best solar cell characteristic parameters. Using the transfer matrix based optical model, which includes interference effects, we calculated the optical power absorbed in the active layers for the entire absorption band, and we found that this cannot explain the trend with thickness. Measurement of the cell quantum efficiency as a function of light intensity showed that the relative weight of the device internal processes changes when going from 40 nm to 120 nm thick active layer. Electrical modeling of the device, which takes different internal processes into account, allowed to quantify the changes in the processes affecting the generation - recombination balance. Sub gap external quantum efficiency and morphological analysis of the surface of the films agree with the model's result. We found that as the thickness grows the density of charge transfer states and of dark carriers goes up and the uniformity in the vertical direction is reduced.

  13. Density dependence of the "symmetry energy" in the lattice gas model

    OpenAIRE

    Su, Q. M.; Ma, Y. G.(Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China); Tian, W. D.; Fang, D. Q.(Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China); Cai, X.Z.; Wang, K.

    2007-01-01

    Isoscaling behavior of the statistical emission fragments from the equilibrated sources with $Z$ = 30 and $N$ = 30, 33, 36 and 39, resepectively, is investigated in the framework of isospin dependent lattice gas model. The dependences of isoscaling parameters $\\alpha$ on source isospin asymmetry, temperature and freeze-out density are studied and the "symmetry energy" is deduced from isoscaling parameters. Results show that "symmetry energy" $C_{sym}$ is insensitive to the change of temperatu...

  14. Equations for O2 and CO2 solubilities in saline and plasma: combining temperature and density dependences.

    Science.gov (United States)

    Christmas, Kevin M; Bassingthwaighte, James B

    2017-05-01

    Solubilities of respiratory gasses in water, saline, and plasma decrease with rising temperatures and solute concentrations. Henry's Law, C = α·P, states that the equilibrium concentration of a dissolved gas is solubility times partial pressure. Solubilities in the water of a solution depend on temperature and the content of other solutes. Blood temperatures may differ more than 20°C between skin and heart, and an erythrocyte will undergo that range as blood circulates. The concentrations of O2 and CO2 are the driving forces for diffusion, exchanges, and for reactions. We provide an equation for O2 and CO2 solubilities, α, that allows for continuous changes in temperature, T, and solution density, ρ, in dynamically changing states:[Formula: see text]This two-exponential expression with a density scalar γ, and a density exponent β, accounts for solubility changes due to density changes of an aqueous solution. It fits experimental data on solubilities in water, saline, and plasma over temperatures from 20 to 40°C, and for plasma densities, ρsol up to 1.020 g/ml with ~0.3% error. The amounts of additional bound O2 (to Hb) and CO2 (bicarbonate and carbamino) depend on the concentrations in the local water space and the reaction parameters. During exercise, solubility changes are large; both ρsol and T change rapidly with spatial position and with time. In exercise hemoconcentration plasma, ρsol exceeds 1.02, whereas T may range over 20°C. The six parameters for O2 and the six for CO2 are constants, so solubilities are calculable continuously as T and ρsol change.NEW & NOTEWORTHY Solubilities for oxygen and carbon dioxide are dependent on the density of the solution, on temperature, and on the partial pressure. We provide a brief equation suitable for hand calculators or mathematical modeling, accounting for these factors over a wide range of temperatures and solution densities for use in rapidly changing conditions, such as extreme exercise or osmotic

  15. Autonomic imbalance induced breakdown of long-range dependence in healthy heart rate.

    Science.gov (United States)

    Aoyagi, N; Struzik, Z R; Kiyono, K; Yamamoto, Y

    2007-01-01

    The investigation of the relation between the long-range correlation property of heart rate and autonomic balance. An investigation of the fractal scaling properties of heart rate variability was carried out by using detrended fluctuation analysis (DFA). Eleven healthy subjects were examined for two consecutive days, which included usual daily activity, strenuous prolonged experimental exercise, and sleep. We also considered two patient groups with autonomic dysfunction characterized by selective sympathetic and parasympathetic dominance. Robust long-range dependence in heart rate is observed only in the state of usual daily activity, characterized by normal heart rate typical of balanced autonomic sympathetic and parasympathetic regulation. This confirms the previously postulated behavioral independence of heart rate regulation, but reveals that the occurrence of 1/f, long-range dependence is restricted to only the state of autonomic balance. Both the sympathetic dominant high heart rate state, realized during strenuous experimental exercise, and the parasympathetic dominant low heart rate state, prevalent in (deep) sleep, are characterized by uncorrelated, near white-noise-like scaling, lacking long-range dependence. Remarkably, the breakdown of the long-range correlations observed in healthy heart rate in the states of sympathetic and parasympathetic dominance is in stark contrast to the increased correlations which have previously been observed in neurogenic parasympathetic and sympathetic dominance in patients suffering from primary autonomic failure and congestive heart failure, respectively. Our findings further reveal the diagnostic capabilities of heart rate dynamics, by differentiating physiological healthy states from pathology.

  16. Density dependence of avian clutch size in resident and migrant species : is there a constraint on the predictability of competitor density?

    NARCIS (Netherlands)

    Both, C

    The presence of density dependence of clutch size is tested in 57 long-term population studies of 10 passerine bird species. In about half of the studies of tit species Parus spp. density dependence of clutch size was found, while none was found in studies of two flycatcher species Ficedula spp. One

  17. Density dependence of avian clutch size in resident and migrant species: is there a constraint on the predictability of competitor density?

    NARCIS (Netherlands)

    Both, C.

    2000-01-01

    The presence of density dependence of clutch size is tested in 57 long-term population studies of 10 passerine bird species. In about half of the studies of tit species Parus spp. density dependence of clutch size was found, while none was found in studies of two flycatcher species Ficedula spp. One

  18. Stable renal function in insulin-dependent diabetes mellitus 10 years after nephrotic range proteinuria.

    Science.gov (United States)

    Gault, M H; Fernandez, D

    1996-01-01

    It has been considered unlikely that patients with insulin-dependent diabetes and diabetic nephropathy with nephrotic range proteinuria can substantially reduce proteinuria and continue for many years without further loss of renal function. We present a patient who had the diagnosis of insulin-dependent diabetes made at age 15, had his first of 6 laser treatments for proliferative and hemorrhagic retinopathy at age 27 and was found to have nephrotic range proteinuria and edema with hypertension at age 29, when results of a renal biopsy were typical of diabetic nephropathy. Ten years later, with the last 5.5 years on ACE inhibitors, proteinuria has been neprotic range is very rare in reports, if not unique.

  19. Collective motion of self-propelled particles with density-dependent switching effect

    Science.gov (United States)

    Chen, Qiu-shi; Ma, Yu-qiang

    2016-05-01

    We study the effect of density-dependent angular response on large scale collective motion, that particles are more likely to switch their moving direction within lower local density region. We show that the presence of density-dependent angular response leads to three typical phases: polar liquid, micro-phase separation and disordered gas states. In our model, the transition between micro-phase separation and disordered gas is discontinuous. Giant number fluctuation is observed in polar liquid phase with statistically homogeneous order. In the micro-phase separation parameter space, high order and high density bands dominate the dynamics. We also compare our results with Vicsek model and show that the density-dependent directional switching response can stabilize the band state to very low noise condition. This band stripe could recruit almost all the particles in the system, which greatly enhances the coherence of the system. Our results could be helpful for understanding extremely coherent motion in nature and also would have practical implications for designing novel self-organization pattern.

  20. Two-electron Rabi oscillations in real-time time-dependent density-functional theory.

    Science.gov (United States)

    Habenicht, Bradley F; Tani, Noriyuki P; Provorse, Makenzie R; Isborn, Christine M

    2014-11-14

    We investigate the Rabi oscillations of electrons excited by an applied electric field in several simple molecular systems using time-dependent configuration interaction (TDCI) and real-time time-dependent density-functional theory (RT-TDDFT) dynamics. While the TDCI simulations exhibit the expected single-electron Rabi oscillations at a single resonant electric field frequency, Rabi oscillations in the RT-TDDFT simulations are a two-electron process. The existence of two-electron Rabi oscillations is determined both by full population inversion between field-free molecular orbitals and the behavior of the instantaneous dipole moment during the simulations. Furthermore, the Rabi oscillations in RT-TDDFT are subject to an intensity threshold of the electric field, below which Rabi oscillations do not occur and above which the two-electron Rabi oscillations occur at a broad range of frequencies. It is also shown that at field intensities near the threshold intensity, the field frequency predicted to induce Rabi oscillations by linear response TDDFT only produces detuned Rabi oscillations. Instead, the field frequency that yields the full two-electron population inversion and Rabi oscillation behavior is shown to be the average of single-electron transition frequencies from the ground S0 state and the doubly-excited S2 state. The behavior of the two-electron Rabi oscillations is rationalized via two possible models. The first model is a multi-photon process that results from the electric field interacting with the three level system such that three level Rabi oscillations may occur. The second model suggests that the mean-field nature of RT-TDDFT induces paired electron propagation.

  1. Density-dependent role of an invasive marsh grass, Phragmites australis, on ecosystem service provision.

    Directory of Open Access Journals (Sweden)

    Seth J Theuerkauf

    Full Text Available Invasive species can positively, neutrally, or negatively affect the provision of ecosystem services. The direction and magnitude of this effect can be a function of the invaders' density and the service(s of interest. We assessed the density-dependent effect of an invasive marsh grass, Phragmites australis, on three ecosystem services (plant diversity and community structure, shoreline stabilization, and carbon storage in two oligohaline marshes within the North Carolina Coastal Reserve and National Estuarine Research Reserve System (NCNERR, USA. Plant species richness was equivalent among low, medium and high Phragmites density plots, and overall plant community composition did not vary significantly by Phragmites density. Shoreline change was most negative (landward retreat where Phragmites density was highest (-0.40 ± 0.19 m yr-1 vs. -0.31 ± 0.10 for low density Phragmites in the high energy marsh of Kitty Hawk Woods Reserve and most positive (soundward advance where Phragmites density was highest (0.19 ± 0.05 m yr-1 vs. 0.12 ± 0.07 for low density Phragmites in the lower energy marsh of Currituck Banks Reserve, although there was no significant effect of Phragmites density on shoreline change. In Currituck Banks, mean soil carbon content was approximately equivalent in cores extracted from low and high Phragmites density plots (23.23 ± 2.0 kg C m-3 vs. 22.81 ± 3.8. In Kitty Hawk Woods, mean soil carbon content was greater in low Phragmites density plots (36.63 ± 10.22 kg C m-3 than those with medium (13.99 ± 1.23 kg C m-3 or high density (21.61 ± 4.53 kg C m-3, but differences were not significant. These findings suggest an overall neutral density-dependent effect of Phragmites on three ecosystem services within two oligohaline marshes in different environmental settings within a protected reserve system. Moreover, the conceptual framework of this study can broadly inform an ecosystem services-based approach to invasive species

  2. Balancing food and density-dependence in the spatial distribution of an interference-prone forager

    NARCIS (Netherlands)

    Dokter, Adriaan M.; Loon, van E.E.; Rappoldt, Cornelis; Oosterbeek, Kees; Baptist, Martin J.; Bouten, Willem; Ens, Bruno J.

    2017-01-01

    Foraging distributions are thought to be density-dependent, because animals not only select for a high availability and quality of resources, but also avoid conspecific interference. Since these processes are confounded, their relative importance in shaping foraging distributions remains poorly

  3. Density-dependent energy use contributes to the self-thinning relationship of cohorts.

    Science.gov (United States)

    Smith, James A; Baumgartner, Lee J; Suthers, Iain M; Fielder, D Stewart; Taylor, Matthew D

    2013-03-01

    In resource-limited populations, an increase in average body size can occur only with a decline in abundance. This is known as self-thinning, and the decline in abundance in food-limited populations is considered proportional to the scaling of metabolism with body mass. This popular hypothesis may be inaccurate, because self-thinning populations can also experience density-dependent competition, which could alter their energy use beyond the predictions of metabolic scaling. This study tested whether density-dependent competition has an energetic role in self-thinning, by manipulating the abundance of the fish Macquaria novemaculeata and tank size to partition the effects of competition from metabolic scaling. We found that self-thinning can be density dependent and that changes in intraspecific competition may be more influential than metabolic scaling on self-thinning relationships. The energetic mechanism we propose is that density-dependent competition causes variation in the allocation of energy to growth, which alters the energetic efficiency of self-thinning cohorts. The implication is that food-limited cohorts and populations with competitive strategies that encourage fast-growing individuals will have less body mass at equilibrium and higher mortality rates. This finding sheds light on the processes structuring populations and can be used to explain inconsistencies in the mass-abundance scaling of assemblages and communities (the energetic-equivalence rule).

  4. The Heated Laminar Vertical Jet in a Liquid with Power-law Temperature Dependence of Density

    OpenAIRE

    Sharifulin, V. A.

    2009-01-01

    The analytical solution of heated laminar vertical jet in a liquid with power-law temperature dependence of density was obtained in the skin-layer approximation for certain values of Prandtl number. Cases of point and linear sources were considered.

  5. Time-dependent current-density-functional theory for the metallic response of solids

    NARCIS (Netherlands)

    Romaniello, P; de Boeij, PL

    We extend the formulation of time-dependent current-density-functional theory for the linear response properties of dielectric and semi-metallic solids [Kootstra , J. Chem. Phys. 112, 6517 (2000)] to treat metals as well. To achieve this, the Kohn-Sham response functions have to include both

  6. A spatial interpretation of the density dependence model in industrial demography

    NARCIS (Netherlands)

    van Wissen, L

    2004-01-01

    In this paper the density dependence model, which was developed in organizational ecology, is compared to the economic-geographical notion of agglomeration economies. There is a basic resemblance: both involve some form of positive feedback between size of the population and growth. The paper

  7. Demonstrating the Temperature Dependence of Density via Construction of a Galilean Thermometer

    Science.gov (United States)

    Priest, Marie A.; Padgett, Lea W.; Padgett, Clifford W.

    2011-01-01

    A method for the construction of a Galilean thermometer out of common chemistry glassware is described. Students in a first-semester physical chemistry (thermodynamics) class can construct the Galilean thermometer as an investigation of the thermal expansivity of liquids and the temperature dependence of density. This is an excellent first…

  8. Gold Nanowires : A Time-Dependent Density Functional Assessment of Plasmonic Behavior

    NARCIS (Netherlands)

    Piccini, GiovanniMaria; Havenith, Remco W. A.; Broer, Ria; Stener, Mauro

    2013-01-01

    The surface plasmon resonance has been theoretically investigated in gold nanowires by means of time-dependent density functional theory. Linear chains of Au atoms and nanowires with the structure of the fcc bulk gold grown along the <110 > and <111 > directions have been considered. The effects of

  9. Nonequilibrium green functions in time-dependent current-density-functional theory

    NARCIS (Netherlands)

    Bonitz, M; Semkat, D

    2003-01-01

    We give an overview of the underlying concepts of time-dependent current-density functional theory (TDCDFT). We show how the basic equations of TDCDFT can be elegantly derived using the time contour method of nonequilibrium Green function theory. We further demonstrate how the formalism can be used

  10. Density dependence of the symmetry energy from neutron skin thickness in finite nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Vinas, X.; Centelles, M.; Roca-Maza, X.; Warda, M. [Departament d' Estructura i Conastituents de la Materia and Institut de Ciencies del Cosmos, Facultat de Fisica, Universitat de Barcelona, Marti i Franques 1, 08028, Barcelona (Spain); Instituto Nazionale di Fisica Nucleare, Sezione di Milano , Via Celoria 16, I-20133 Milano (Italy); Katedra Fizyki Teoretycznej, Uniwersytet Marii Curie-Skodowskiej ul. Radziszewskiego 10, 20-031 Lublin (Poland)

    2012-10-20

    The density dependence of the symmetry energy, characterized by the parameter L, is studied using information provided by the neutron skin thickness in finite nuclei. An estimate of L is obtained from experimental data of antiprotonic atoms. We also discuss the ability of parity violating electron scatering to obtain information about the neutron skin thickness in {sup 208}Pb.

  11. Variation in the strength of inbreeding depression across environments: effects of stress and density dependence.

    Science.gov (United States)

    Yun, Li; Agrawal, Aneil F

    2014-12-01

    In what types of environments should we expect to find strong inbreeding depression? Previous studies indicate that inbreeding depression, δ, is positively correlated with the stressfulness of the environment in which it is measured. However, it remains unclear why stress, per se, should increase δ. To our knowledge, only "competitive stress" has a logical connection to δ. Through competition for resources, better quality (outbred) individuals make the environment worse for lower quality (inbred) individuals, accentuating the differences between them. For this reason, we expect inbreeding depression to be stronger in environments where the fitness of individuals is more sensitive to the presence of conspecifics (i.e., where fitness is more density dependent). Indeed, some studies suggest a role for competition within environments, but this idea has not been tested in the context of understanding variation in δ across environments. Using Drosophila melanogaster, we estimated δ for viability in 22 different environments. These environments were simultaneously characterized for (1) stressfulness and (2) density dependence. Although stress and density dependence are moderately correlated with each other, inbreeding depression is much more strongly correlated with density dependence. These results suggest that mean selection across the genome is stronger in environments where competition is intense, rather than in environments that are stressful for other reasons. © 2014 The Author(s). Evolution © 2014 The Society for the Study of Evolution.

  12. Relativistic Adiabatic Time-Dependent Density Functional Theory Using Hybrid Functionals and Noncollinear Spin Magnetization

    DEFF Research Database (Denmark)

    Bast, Radovan; Jensen, Hans Jørgen Aagaard; Saue, Trond

    2009-01-01

    We report an implementation of adiabatic time-dependent density functional theory based on the 4-component relativistic Dirac-Coulomb Hamiltonian and a closed-shell reference. The implementation includes noncollinear spin magnetization and full derivatives of functionals, including hybrid general...

  13. BONE-DENSITY IN NON-INSULIN-DEPENDENT DIABETES-MELLITUS - THE ROTTERDAM STUDY

    NARCIS (Netherlands)

    VANDAELE, PLA; STOLK, RP; BURGER, H; ALGRA, D; GROBBEE, DE; HOFMAN, A; BIRKENHAGER, JC; POLS, HAP

    1995-01-01

    Objective: To investigate the relation between noninsulin-dependent diabetes mellitus and bone mineral density at the lumbar spine and hip. Design: Population-based study with a cross-sectional survey, Setting: A district of Rotterdam, the Netherlands. Participants: 5931 residents (2481 men, 3450

  14. The Keldysh formalism applied to time-dependent current-density-functional theory

    NARCIS (Netherlands)

    Gidopoulos, NI; Wilson, S

    2003-01-01

    In this work we demonstrate how to derive the Kohn-Sham equations of time-dependent current-density functional theory from a generating action functional defined on a Keldysh time contour. These Kohn-Sham equations contain an exchange-correlation contribution to the vector potential. For this

  15. Density dependence and stochastic variation in a newly established population of a small songbird

    NARCIS (Netherlands)

    Sæther, Bernt-Erik; Engen, Steinar; Lande, Russell; Both, Christiaan; Visser, Marcel E.

    2002-01-01

    Models describing fluctuations in population size should include both density dependence and stochastic effects. We examine the relative contribution of variation in parameters of the expected dynamics as well as demographic and environmental stochasticity to fluctuations in a population of a small

  16. Application of the density dependent hadron field theory to neutron star matter

    NARCIS (Netherlands)

    Hofmann, F.; Keil, C. M.; Lenske, H.

    2001-01-01

    Published in: Phys. Rev., C 64 (2001) 025804 citations recorded in [Science Citation Index] Abstract: The density dependent hadron field (DDRH) theory, previously applied to isospin nuclei and hypernuclei is used to describe $beta$-stable matter and neutron stars under consideration of the complete

  17. Mixed time-dependent density-functional theory/classical photodynamics study of oxirane photochemistry

    NARCIS (Netherlands)

    Tapavicza, Enrico; Tavernelli, Ivano; Rothlisberger, Ursula; Filippi, Claudia; Casida, Mark E.

    2008-01-01

    We present a mixed time-dependent density-functional theory (TDDFT)/classical trajectory surface hopping (SH) study of the photochemical ring opening in oxirane. Previous preparatory work limited to the symmetric CC ring-opening pathways of oxirane concluded that the Tamm-Dancoff approximation (TDA)

  18. Dependence of critical current density on crystalline direction in thin YBCO films

    DEFF Research Database (Denmark)

    Paturi, P.; Peurla, M.; Raittila, J.

    2005-01-01

    The dependence of critical current density (J(c)) on the angle between the current direction and the (100) direction in the ab-plane of thin YBCO films deposited on (001)-SrTiO3 from natiocrystalline and microcrystalline targets is studied using magneto-optical microscopy. In the films made from...

  19. Plant diversity increases with the strength of negative density dependence at the global scale

    Science.gov (United States)

    Joseph A. LaManna; Scott A. Mangan; Alfonso Alonso; Norman A. Bourg; Warren Y. Brockelman; Sarayudh Bunyavejchewin; Li-Wan Chang; Jyh-Min Chiang; George B. Chuyong; Keith Clay; Richard Condit; Susan Cordell; Stuart J. Davies; Tucker J. Furniss; Christian P. Giardina; I. A. U. Nimal Gunatilleke; C. V. Savitri Gunatilleke; Fangliang He; Robert W. Howe; Stephen P. Hubbell; Chang-Fu Hsieh; Faith M. Inman-Narahari; David Janík; Daniel J. Johnson; David Kenfack; Lisa Korte; Kamil Král; Andrew J. Larson; James A. Lutz; Sean M. McMahon; William J. McShea; Hervé R. Memiaghe; Anuttara Nathalang; Vojtech Novotny; Perry S. Ong; David A. Orwig; Rebecca Ostertag; Geoffrey G. Parker; Richard P. Phillips; Lawren Sack; I-Fang Sun; J. Sebastián Tello; Duncan W. Thomas; Benjamin L. Turner; Dilys M. Vela Díaz; Tomáš Vrška; George D. Weiblen; Amy Wolf; Sandra Yap; Jonathan A. Myers

    2017-01-01

    Theory predicts that higher biodiversity in the tropics is maintained by specialized interactions among plants and their natural enemies that result in conspecific negative density dependence (CNDD). By using more than 3000 species and nearly 2.4 million trees across 24 forest plots worldwide, we show that global patterns in tree species diversity reflect not only...

  20. Spatially heterogeneous dynamics investigated via a time-dependent four-point density correlation function

    DEFF Research Database (Denmark)

    Lacevic, N.; Starr, F. W.; Schrøder, Thomas

    2003-01-01

    correlation function g4(r,t) and corresponding "structure factor" S4(q,t) which measure the spatial correlations between the local liquid density at two points in space, each at two different times, and so are sensitive to dynamical heterogeneity. We study g4(r,t) and S4(q,t) via molecular dynamics......Relaxation in supercooled liquids above their glass transition and below the onset temperature of "slow" dynamics involves the correlated motion of neighboring particles. This correlated motion results in the appearance of spatially heterogeneous dynamics or "dynamical heterogeneity." Traditional...... two-point time-dependent density correlation functions, while providing information about the transient "caging" of particles on cooling, are unable to provide sufficiently detailed information about correlated motion and dynamical heterogeneity. Here, we study a four-point, time-dependent density...

  1. Time-dependent density functional theory for many-electron systems interacting with cavity photons.

    Science.gov (United States)

    Tokatly, I V

    2013-06-07

    Time-dependent (current) density functional theory for many-electron systems strongly coupled to quantized electromagnetic modes of a microcavity is proposed. It is shown that the electron-photon wave function is a unique functional of the electronic (current) density and the expectation values of photonic coordinates. The Kohn-Sham system is constructed, which allows us to calculate the above basic variables by solving self-consistent equations for noninteracting particles. We suggest possible approximations for the exchange-correlation potentials and discuss implications of this approach for the theory of open quantum systems. In particular we show that it naturally leads to time-dependent density functional theory for systems coupled to the Caldeira-Leggett bath.

  2. Ionic strength-dependent changes in tentacular ion exchangers with variable ligand density. I. Structural properties.

    Science.gov (United States)

    Bhambure, Rahul; Gillespie, Christopher M; Phillips, Michael; Graalfs, Heiner; Lenhoff, Abraham M

    2016-09-09

    The ligand density critically affects the performance of ion-exchange resins in such measures as the adsorption capacity and transport characteristics. However, for tentacular and other polymer-modified exchangers, the mechanistic basis of the effect of ligand density on performance is not yet fully understood. In this study we map the ionic strength-dependent structural changes in tentacular cation exchangers with variable ligand densities as the basis for subsequent investigation of effects on functional properties. Inverse size-exclusion chromatography (ISEC), scanning electron microscopy (SEM) and small-angle x-ray scattering (SAXS) were used to assess the effect of ionic strength on the pore size and intraparticle architecture of resin variants with different ligand densities. Comparison of ISEC and cryo-SEM results shows a considerable reduction in average pore size with increasing ligand density; these methods also confirm an increase of average pore size at higher ionic strengths. SAXS analysis of ionic strength-dependent conformational changes in the grafted polyelectrolyte layer shows a characteristic ionomer peak at values of the scattering vector q (0.1-0.2Å(-1)) that depend on the ligand density and the ionic strength of the solution. This peak attribution reflects nanoscale changes in the structure of the grafted polyelectrolyte chains that can in turn be responsible for observed pore-size changes in the resins. Finally, salt breakthrough experiments confirm a stronger Donnan exclusion effect on pore accessibility for small ions in the high ligand density variant. Copyright © 2016 Elsevier B.V. All rights reserved.

  3. Is contextual-potentiated eating dependent on caloric density of food?

    Directory of Open Access Journals (Sweden)

    Fernando Fernández-Aranda

    2009-01-01

    Full Text Available One experiment tested whether a specific context could elicit eating in rats as a result of Pavlovian conditioning and whether this effect depended on the caloric density of food. Thirty two deprived rats experienced two contexts. They had access to food in context A, but no food was available in context B. During conditioning, half of the animals received high density caloric food (HD groups whereas the other half, low density caloric food (LD groups. Then, half of the rats in each type of food group was tested in context A and the other half in context B. The results demonstrated an effect of context conditioning only in HD groups. These findings suggest the relevance of both contextual conditioning and caloric density of food in eating behaviour. Implications for the aetiology of binge eating will be discussed.

  4. Density Dependence of Particle Transport in ECH Plasmas of the TJ-II Stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Vargas, V. I.; Lopez-Bruna, D.; Guasp, J.; Herranz, J.; Estrada, T.; Medina, F.; Ochando, M.A.; Velasco, J.L.; Reynolds, J.M.; Ferreira, J.A.; Tafalla, D.; Castejon, F.; Salas, A.

    2009-05-21

    We present the experimental dependence of particle transport on average density in electron cyclotron heated (ECH) hydrogen plasmas of the TJ-II stellarator. The results are based on: (I) electron density and temperature data from Thomson Scattering and reflectometry diagnostics; (II) a transport model that reproduces the particle density profiles in steady state; and (III) Eirene, a code for neutrals transport that calculates the particle source in the plasma from the particle confinement time and the appropriate geometry of the machine/plasma. After estimating an effective particle diffusivity and the particle confinement time, a threshold density separating qualitatively and quantitatively different plasma transport regimes is found. The poor confinement times found below the threshold are coincident with the presence of ECH-induced fast electron losses and a positive radial electric field all over the plasma. (Author) 40 refs.

  5. The role of relativity in the optical response of gold within the time-dependent current-density-functional theory.

    Science.gov (United States)

    Romaniello, P; de Boeij, P L

    2005-04-22

    We included relativistic effects in the formulation of the time-dependent current-density-functional theory for the calculation of linear response properties of metals [P. Romaniello and P. L. de Boeij, Phys. Rev. B (to be published)]. We treat the dominant scalar-relativistic effects using the zeroth-order regular approximation in the ground-state density-functional theory calculations, as well as in the time-dependent response calculations. The results for the dielectric function of gold calculated in the spectral range of 0-10 eV are compared with experimental data reported in literature and recent ellipsometric measurements. As well known, relativistic effects strongly influence the color of gold. We find that the onset of interband transitions is shifted from around 3.5 eV, obtained in a nonrelativistic calculation, to around 1.9 eV when relativity is included. With the inclusion of the scalar-relativistic effects there is an overall improvement of both real and imaginary parts of the dielectric function over the nonrelativistic ones. Nevertheless some important features in the absorption spectrum are not well reproduced, but can be explained in terms of spin-orbit coupling effects. The remaining deviations are attributed to the underestimation of the interband gap (5d-6sp band gap) in the local-density approximation and to the use of the adiabatic local-density approximation in the response calculation.

  6. Progression of Plasmodium berghei through Anopheles stephensi is density-dependent.

    Directory of Open Access Journals (Sweden)

    Robert E Sinden

    2007-12-01

    Full Text Available It is well documented that the density of Plasmodium in its vertebrate host modulates the physiological response induced; this in turn regulates parasite survival and transmission. It is less clear that parasite density in the mosquito regulates survival and transmission of this important pathogen. Numerous studies have described conversion rates of Plasmodium from one life stage to the next within the mosquito, yet few have considered that these rates might vary with parasite density. Here we establish infections with defined numbers of the rodent malaria parasite Plasmodium berghei to examine how parasite density at each stage of development (gametocytes; ookinetes; oocysts and sporozoites influences development to the ensuing stage in Anopheles stephensi, and thus the delivery of infectious sporozoites to the vertebrate host. We show that every developmental transition exhibits strong density dependence, with numbers of the ensuing stages saturating at high density. We further show that when fed ookinetes at very low densities, oocyst development is facilitated by increasing ookinete number (i.e., the efficiency of ookinete-oocyst transformation follows a sigmoid relationship. We discuss how observations on this model system generate important hypotheses for the understanding of malaria biology, and how these might guide the rational analysis of interventions against the transmission of the malaria parasites of humans by their diverse vector species.

  7. Positive density-dependent growth supports costs sharing hypothesis and population density sensing in a manipulative parasite.

    Science.gov (United States)

    Gopko, Mikhail; Mikheev, Victor N; Taskinen, Jouni

    2017-09-01

    Parasites manipulate their hosts' phenotype to increase their own fitness. Like any evolutionary adaptation, parasitic manipulations should be costly. Though it is difficult to measure costs of the manipulation directly, they can be evaluated using an indirect approach. For instance, theory suggests that as the parasite infrapopulation grows, the investment of individual parasites in host manipulation decreases, because of cost sharing. Another assumption is that in environments where manipulation does not pay off for the parasite, it can decrease its investment in the manipulation to save resources. We experimentally infected rainbow trout Oncorhynchus mykiss with the immature larvae of the trematode Diplostomum pseudospathaceum, to test these assumptions. Immature D. pseudospathaceum metacercariae are known for their ability to manipulate the behaviour of their host enhancing its anti-predator defenses to avoid concomitant predation. We found that the growth rate of individual parasites in rainbow trout increased with the infrapopulation size (positive density-dependence) suggesting cost sharing. Moreover, parasites adjusted their growth to the intensity of infection within the eye lens where they were localized suggesting population density sensing. Results of this study support the hypothesis that macroparasites can adjust their growth rate and manipulation investment according to cost sharing level and infrapopulation size.

  8. Wave-vector dependence of spin and density multipole excitations in quantum dots

    Science.gov (United States)

    Barranco, Manuel; Colletti, Leonardo; Lipparini, Enrico; Emperador, Agustí; Pi, Martí; Serra, Llorenç

    2000-03-01

    We have employed time-dependent local-spin density-functional theory to analyze the multipole spin and charge density excitations in GaAs-AlxGa1-xAs quantum dots. The on-plane transferred momentum degree of freedom has been taken into account, and the wave-vector dependence of the excitations is discussed. In agreement with previous experiments, we have found that the energies of these modes do not depend on the transferred wave vector, although their intensities do. Comparison with a recent resonant Raman scattering experiment [C. Schüller et al., Phys. Rev. Lett. 80, 2673 (1998)] is made. This allows us to identify the angular momentum of several of the observed modes as well as to reproduce their energies.

  9. Shape of the liquid-vapor coexistence curve for temperature and density dependent effective interactions.

    Science.gov (United States)

    Amokrane, S; Bouaskarne, M

    2002-05-01

    The asymmetry of the coexistence curve that is observed in several micellar systems is discussed in relation with the dependence of the effective interaction on temperature and density. Standard results for the diameter of the coexistence curve in the van der Waals theory are generalized so as to deal with this combined dependence. The qualitative trends so deduced are assessed by comparison with coexistence curves of Yukawa fluids computed with integral equation theories. The role of the variables used to plot the coexistence curve and the nonlinear behavior of its diameter beyond the critical region are discussed in relation with the decrease of the interaction strength with density. The possibility of using the asymmetry of the coexistence curve as an indicator of the state dependence of the effective interaction is finally discussed.

  10. Short-Range Correlations and Their Implications for Isospin-Dependent Modification of Nuclear Quark Distributions

    Energy Technology Data Exchange (ETDEWEB)

    Arrington, John

    2016-03-25

    The past decade has provided a much clearer picture of the structure of highmomentum components in nucleons, associated with hard, short-distance interactions between pairs of nucleons. Recent Jefferson Lab data on light nuclei suggest a connection between these so-called ’short-range correlations’ and the modification of the quark structure of nucleons in the nuclear environment. In light of this discovery that the detailed nuclear structure is important in describing the nuclear quark distributions, we examine the potential impact of the isospin-dependent structure of nuclei to see at what level this might yield flavor-dependent effects in nuclear quark distributions.

  11. Do sex-specific densities affect local survival of free-ranging great tits?

    NARCIS (Netherlands)

    Michler, Stephanie P. M.; Nicolaus, Marion; Ubels, Richard; van der Velde, Marco; Both, Christiaan; Tinbergen, Joost M.; Komdeur, Jan

    2011-01-01

    Competition within sexes is expected when resources are sex specific, whereas competition between sexes can occur when similar resources are exploited. Local population density and sex ratio will determine the amount of sex-specific interactions and thus the potential degree of sex-specific

  12. Unveiling the nature of post-linear response Z-vector method for time-dependent density functional theory

    Science.gov (United States)

    Pastore, Mariachiara; Assfeld, Xavier; Mosconi, Edoardo; Monari, Antonio; Etienne, Thibaud

    2017-07-01

    We report a theoretical study on the analysis of the relaxed one-particle difference density matrix characterizing the passage from the ground to the excited state of a molecular system, as obtained from time-dependent density functional theory. In particular, this work aims at using the physics contained in the so-called Z-vector, which differentiates between unrelaxed and relaxed difference density matrices to analyze excited states' nature. For this purpose, we introduce novel quantum-mechanical quantities, based on the detachment/attachment methodology, for analysing the Z-vector transformation for different molecules and density functional theory functionals. A derivation pathway of these novel descriptors is reported, involving a numerical integration to be performed in the Euclidean space on the density functions. This topological analysis is then applied to two sets of chromophores, and the correlation between the level of theory and the behavior of our descriptors is properly rationalized. In particular, the effect of range-separation on the relaxation amplitude is discussed. The relaxation term is finally shown to be system-specific (for a given level of theory) and independent of the number of electrons (i.e., the relaxation amplitude is not simply the result of a collective phenomenon).

  13. Density dependence of the stress relaxation function of a simple fluid

    NARCIS (Netherlands)

    Hartkamp, Remco; Daivis, P.J.; Todd, B.D.

    2013-01-01

    We present accurate molecular dynamics calculations of the shear stress relaxation modulus of a simple atomic fluid over a wide range of densities. The high accuracy of the data enables us to study changes in the functional form of the shear relaxation modulus, and the properties that are derived

  14. Density dependence of SOL power width in ASDEX upgrade L-Mode

    Directory of Open Access Journals (Sweden)

    B. Sieglin

    2017-08-01

    A recent study [4] with an open divertor configuration found an asymmetry of the power fall-off length between inner and outer target with a smaller power fall-off length λq,i on the inner divertor target. Measurements with a closed divertor configuration find a similar asymmetry for low recycling divertor conditions. It is found, in the experiment, that the in/out asymmetry λq,i/λq,o is strongly increasing with increasing density. Most notably the heat flux density at the inner divertor target is reducing with increasing λq,i whilst the total power onto each divertor target stays constant. It is found that λq,o exhibits no significant density dependence for hydrogen and deuterium but increases with about the square root of the electron density for helium. The difference between H,D and He could be due to the different recycling behaviour in the divertor. These findings may help current modelling attempts to parametrize the density dependence of the widening of the power channel and thus allow for detailed comparison to both divertor effects like recycling or increased upstream SOL cross field transport.

  15. Detection of density-dependent effects on caribou numbers from a series of census data

    Directory of Open Access Journals (Sweden)

    Francois Messier

    1991-10-01

    Full Text Available The main objective of this paper is to review and discuss the applicability of statistical procedures for the detection of density dependence based on a series of annual or multi-annual censuses. Regression models for which the statistic value under the null hypothesis of density independence is set a priori (slope = 0 or 1, generate spurious indications of density dependence. These tests are inappropriate because low sample sizes, high variance, and sampling error consistently bias the slope when applied to a finite number of population estimates. Two distribution-free tests are reviewed for which the rejection region for the hypothesis of density independence is derived intrinsically from the data through a computer-assisted permutation process. The "randomization test" gives the best results as the presence of a pronounced trend in the sequence of population estimates does not affect test results. The other non-parametric test, the "permutation test", gives reliable results only if the population fluctuates around a long-term equilibrium density. Both procedures are applied to three sets of data (Pukaskwa herd, Avalon herd, and a hypothetical example that represent quite divergent population trajectories over time.

  16. Anopheles mortality is both age- and Plasmodium-density dependent: implications for malaria transmission.

    Science.gov (United States)

    Dawes, Emma J; Churcher, Thomas S; Zhuang, Shijie; Sinden, Robert E; Basáñez, María-Gloria

    2009-10-12

    Daily mortality is an important determinant of a vector's ability to transmit pathogens. Original simplifying assumptions in malaria transmission models presume vector mortality is independent of age, infection status and parasite load. Previous studies illustrate conflicting evidence as to the importance of Plasmodium-induced vector mortality, but very few studies to date have considered the effect of infection density on mosquito survival. A series of three experiments were conducted, each consisting of four cages of 400-1,000 Anopheles stephensi mosquitoes fed on blood infected with different Plasmodium berghei ookinete densities per microlitre of blood. Twice daily the numbers of dead mosquitoes in each group were recorded, and on alternate days a sample of live mosquitoes from each group were dissected to determine parasite density in both midgut and salivary glands. Survival analyses indicate that mosquito mortality is both age- and infection intensity-dependent. Mosquitoes experienced an initially high, partly feeding-associated, mortality rate, which declined to a minimum before increasing with mosquito age and parasite intake. As a result, the life expectancy of a mosquito is shown to be dependent on both insect age and the density of Plasmodium infection. These results contribute to understanding in greater detail the processes that influence sporogony in the mosquito, indicate the impact that parasite density could have on malaria transmission dynamics, and have implications for the design, development, and evaluation of transmission-blocking strategies.

  17. Anopheles mortality is both age- and Plasmodium-density dependent: implications for malaria transmission

    Directory of Open Access Journals (Sweden)

    Sinden Robert E

    2009-10-01

    Full Text Available Abstract Background Daily mortality is an important determinant of a vector's ability to transmit pathogens. Original simplifying assumptions in malaria transmission models presume vector mortality is independent of age, infection status and parasite load. Previous studies illustrate conflicting evidence as to the importance of Plasmodium-induced vector mortality, but very few studies to date have considered the effect of infection density on mosquito survival. Methods A series of three experiments were conducted, each consisting of four cages of 400-1,000 Anopheles stephensi mosquitoes fed on blood infected with different Plasmodium berghei ookinete densities per microlitre of blood. Twice daily the numbers of dead mosquitoes in each group were recorded, and on alternate days a sample of live mosquitoes from each group were dissected to determine parasite density in both midgut and salivary glands. Results Survival analyses indicate that mosquito mortality is both age- and infection intensity-dependent. Mosquitoes experienced an initially high, partly feeding-associated, mortality rate, which declined to a minimum before increasing with mosquito age and parasite intake. As a result, the life expectancy of a mosquito is shown to be dependent on both insect age and the density of Plasmodium infection. Conclusion These results contribute to understanding in greater detail the processes that influence sporogony in the mosquito, indicate the impact that parasite density could have on malaria transmission dynamics, and have implications for the design, development, and evaluation of transmission-blocking strategies.

  18. Quorum sensing and density-dependent dispersal in an aquatic model system.

    Directory of Open Access Journals (Sweden)

    Simon Fellous

    Full Text Available Many organisms use cues to decide whether to disperse or not, especially those related to the composition of their environment. Dispersal hence sometimes depends on population density, which can be important for the dynamics and evolution of sub-divided populations. But very little is known about the factors that organisms use to inform their dispersal decision. We investigated the cues underlying density-dependent dispersal in inter-connected microcosms of the freshwater protozoan Paramecium caudatum. In two experiments, we manipulated (i the number of cells per microcosm and (ii the origin of their culture medium (supernatant from high- or low-density populations. We found a negative relationship between population density and rates of dispersal, suggesting the use of physical cues. There was no significant effect of culture medium origin on dispersal and thus no support for chemical cues usage. These results suggest that the perception of density - and as a result, the decision to disperse - in this organism can be based on physical factors. This type of quorum sensing may be an adaptation optimizing small scale monitoring of the environment and swarm formation in open water.

  19. A consumer-resource approach to the density-dependent population dynamics of mutualism.

    Science.gov (United States)

    Holland, J Nathaniel; DeAngelis, Donald L

    2010-05-01

    Like predation and competition, mutualism is now recognized as a consumer-resource (C-R) interaction, including, in particular, bi-directional (e.g., coral, plant-mycorrhizae) and uni-directional (e.g., ant-plant defense, plant-pollinator) C-R mutualisms. Here, we develop general theory for the density-dependent population dynamics of mutualism based on the C-R mechanism of interspecific interaction. To test the influence of C-R interactions on the dynamics and stability of bi- and uni-directional C-R mutualisms, we developed simple models that link consumer functional response of one mutualistic species with the resources supplied by another. Phase-plane analyses show that the ecological dynamics of C-R mutualisms are stable in general. Most transient behavior leads to an equilibrium of mutualistic coexistence, at which both species densities are greater than in the absence of interactions. However, due to the basic nature of C-R interactions, certain density-dependent conditions can lead to C-R dynamics characteristic of predator-prey interactions, in which one species overexploits and causes the other to go extinct. Consistent with empirical phenomena, these results suggest that the C-R interaction can provide a broad mechanism for understanding density-dependent population dynamics of mutualism. By unifying predation, competition, and mutualism under the common ecological framework of consumer-resource theory, we may also gain a better understanding of the universal features of interspecific interactions in general.

  20. A Holling Type II Pest and Natural Enemy Model with Density Dependent IPM Strategy

    Directory of Open Access Journals (Sweden)

    Xia Wang

    2017-01-01

    Full Text Available Resource limitations and density dependent releasing of natural enemies during the pest control and integrated pest management will undoubtedly result in nonlinear impulsive control. In order to investigate the effects of those nonlinear control strategies on the successful pest control, we have proposed a pest-natural enemy system concerning integrated pest management with density dependent instant killing rate and releasing rate. In particular, the releasing rate depicts how the number of natural enemy populations released was guided by their current density at the fixed moment. The threshold condition which ensures the existence and global stability of pest-free periodic solution has been discussed first, and the effects of key parameters on the threshold condition reveal that reducing the pulse period does not always benefit pest control; that is, frequent releasing of natural enemies may not be beneficial to the eradication of pests when the density dependent releasing method has been implemented. Moreover, the forward and backward bifurcations could occur once the pest-free periodic solution becomes unstable, and the system could exist with very complex dynamics. All those results confirm that the control actions should be carefully designed once the nonlinear impulsive control measures have been taken for pest management.

  1. A consumer-resource approach to the density-dependent population dynamics of mutualism

    Science.gov (United States)

    Holland, J. Nathaniel; DeAngelis, Donald L.

    2010-01-01

    Like predation and competition, mutualism is now recognized as a consumer resource (C-R) interaction, including, in particular, bi-directional (e.g., coral, plant- mycorrhizae) and uni-directional (e.g., ant-plant defense, plant-pollinator) C-R mutualisms. Here, we develop general theory for the density-dependent population dynamics of mutualism based on the C-R mechanism of interspecific interaction. To test the influence of C-R interactions on the dynamics and stability of bi- and uni-directional C-R mutualisms, we developed simple models that link consumer functional response of one mutualistic species with the resources supplied by another. Phase-plane analyses show that the ecological dynamics of C-R mutualisms are stable in general. Most transient behavior leads to an equilibrium of mutualistic coexistence, at which both species densities are greater than in the absence of interactions. However, due to the basic nature of C-R interactions, certain density-dependent conditions can lead to C-R dynamics characteristic of predator-prey interactions, in which one species overexploits and causes the other to go extinct. Consistent with empirical phenomena, these results suggest that the C-R interaction can provide a broad mechanism for understanding density-dependent population dynamics of mutualism. By unifying predation, competition, and mutualism under the common ecological framework of consumer-resource theory, we may also gain a better understanding of the universal features of interspecific interactions in general.

  2. Intraspecific and interspecific competition induces density-dependent habitat niche shifts in an endangered steppe bird.

    Science.gov (United States)

    Tarjuelo, Rocío; Morales, Manuel B; Arroyo, Beatriz; Mañosa, Santiago; Bota, Gerard; Casas, Fabián; Traba, Juan

    2017-11-01

    Interspecific competition is a dominant force in animal communities that induces niche shifts in ecological and evolutionary time. If competition occurs, niche expansion can be expected when the competitor disappears because resources previously inaccessible due to competitive constraints can then be exploited (i.e., ecological release). Here, we aimed to determine the potential effects of interspecific competition between the little bustard (Tetrax tetrax) and the great bustard (Otis tarda) using a multidimensional niche approach with habitat distribution data. We explored whether the degree of niche overlap between the species was a density-dependent function of interspecific competition. We then looked for evidences of ecological release by comparing measures of niche breadth and position of the little bustard between allopatric and sympatric situations. Furthermore, we evaluated whether niche shifts could depend not only on the presence of great bustard but also on the density of little and great bustards. The habitat niches of these bustard species partially overlapped when co-occurring, but we found no relationship between degree of overlap and great bustard density. In the presence of the competitor, little bustard's niche was displaced toward increased use of the species' primary habitat. Little bustard's niche breadth decreased proportionally with great bustard density in sympatric sites, in consistence with theory. Overall, our results suggest that density-dependent variation in little bustard's niche is the outcome of interspecific competition with the great bustard. The use of computational tools like kernel density estimators to obtain multidimensional niches should bring novel insights on how species' ecological niches behave under the effects of interspecific competition in ecological communities.

  3. Common long-range dependence in a panel of hourly Nord Pool electricity prices and loads

    DEFF Research Database (Denmark)

    Ergemen, Yunus Emre; Haldrup, Niels; Rodríguez-Caballero, Carlos Vladimir

    Equilibrium electricity spot prices and loads are often determined simultaneously in a day-ahead auction market for each hour of the subsequent day. Hence daily observations of hourly prices take the form of a periodic panel rather than a time series of hourly observations. We consider novel panel...... data approaches to analyse the time series and the cross-sectional dependence of hourly Nord Pool electricity spot prices and loads for the period 2000-2013. Hourly electricity prices and loads data are characterized by strong serial long-range dependence in the time series dimension in addition...... of the underlying production technology and because the demand is more volatile than the supply, equilibrium prices and loads are argued to identify the periodic power supply curve. The estimated supply elasticities are estimated from fractionally co-integrated relations and range between 0.5 and 1...

  4. Hot-electron-assisted femtochemistry at surfaces: A time-dependent density functional theory approach

    DEFF Research Database (Denmark)

    Gavnholt, Jeppe; Rubio, Angel; Olsen, Thomas

    2009-01-01

    Using time-evolution time-dependent density functional theory (TDDFT) within the adiabatic local-density approximation, we study the interactions between single electrons and molecular resonances at surfaces. Our system is a nitrogen molecule adsorbed on a ruthenium surface. The surface is modeled...... at two levels of approximation, first as a simple external potential and later as a 20-atom cluster. We perform a number of calculations on an electron hitting the adsorbed molecule from inside the surface and establish a picture, where the resonance is being probed by the hot electron. This enables us...

  5. The dependence of ZnO photoluminescence efficiency on excitation conditions and defect densities

    Energy Technology Data Exchange (ETDEWEB)

    Simmons, Jay G.; Liu, Jie [Department of Chemistry, Duke University, Durham, North Carolina 27708 (United States); Foreman, John V. [U.S. Army Aviation and Missile Research, Development, and Engineering Center, Redstone Arsenal, Alabama 35898 (United States); Everitt, Henry O., E-mail: everitt@phy.duke.edu [U.S. Army Aviation and Missile Research, Development, and Engineering Center, Redstone Arsenal, Alabama 35898 (United States); Department of Physics, Duke University, Durham, North Carolina 27708 (United States)

    2013-11-11

    The quantum efficiencies of both the band edge and deep-level defect emission from annealed ZnO powders were measured as a function of excitation fluence and wavelength from a tunable sub-picosecond source. A simple model of excitonic decay reproduces the observed excitation dependence of rate constants and associated trap densities for all radiative and nonradiative processes. The analysis explores how phosphor performance deteriorates as excitation fluence and energy increase, provides an all-optical approach for estimating the number density of defects responsible for deep-level emission, and yields new insights for designing efficient ZnO-based phosphors.

  6. Modeling carrier density dependent charge transport in semiconducting carbon nanotube networks

    Science.gov (United States)

    Schießl, Stefan P.; de Vries, Xander; Rother, Marcel; Massé, Andrea; Brohmann, Maximilian; Bobbert, Peter A.; Zaumseil, Jana

    2017-09-01

    Charge transport in a network of only semiconducting single-walled carbon nanotubes is modeled as a random-resistor network of tube-tube junctions. Solving Kirchhoff's current law with a numerical solver and taking into account the one-dimensional density of states of the nanotubes enables the evaluation of carrier density dependent charge transport properties such as network mobility, local power dissipation, and current distribution. The model allows us to simulate and investigate mixed networks that contain semiconducting nanotubes with different diameters, and thus different band gaps and conduction band edge energies. The obtained results are in good agreement with available experimental data.

  7. Changes in home range sizes and population densities of carnivore species along the natural to urban habitat gradient

    Czech Academy of Sciences Publication Activity Database

    Šálek, Martin; Drahníková, L.; Tkadlec, Emil

    2015-01-01

    Roč. 45, č. 1 (2015), s. 1-14 ISSN 0305-1838 Institutional support: RVO:68081766 Keywords : Carnivores * home range size * natural–urban gradient * population density * review Subject RIV: EG - Zoology Impact factor: 4.116, year: 2015

  8. Density dependence governs when population responses to multiple stressors are magnified or mitigated.

    Science.gov (United States)

    Hodgson, Emma E; Essington, Timothy E; Halpern, Benjamin S

    2017-10-01

    Population endangerment typically arises from multiple, potentially interacting anthropogenic stressors. Extensive research has investigated the consequences of multiple stressors on organisms, frequently focusing on individual life stages. Less is known about population-level consequences of exposure to multiple stressors, especially when exposure varies through life. We provide the first theoretical basis for identifying species at risk of magnified effects from multiple stressors across life history. By applying a population modeling framework, we reveal conditions under which population responses from stressors applied to distinct life stages are either magnified (synergistic) or mitigated. We find that magnification or mitigation critically depends on the shape of density dependence, but not the life stage in which it occurs. Stressors are always magnified when density dependence is linear or concave, and magnified or mitigated when it is convex. Using Bayesian numerical methods, we estimated the shape of density dependence for eight species across diverse taxa, finding support for all three shapes. © 2017 by the Ecological Society of America.

  9. Density-dependent effects of ants on selection for bumble bee pollination in Polemonium viscosum.

    Science.gov (United States)

    Galen, Candace; Geib, Jennifer C

    2007-05-01

    Mutualisms are commonly exploited by cheater species that usurp rewards without providing reciprocal benefits. Yet most studies of selection between mutualist partners ignore interactions with third species and consequently overlook the impact of cheaters on evolution in the mutualism. Here, we explicitly investigate how the abundance of nectar-thieving ants (cheaters) influences selection in a pollination mutualism between bumble bees and the alpine skypilot, Polemonium viscosum. As suggested in past work with this species, bumble bees accounted for most of the seed production (78% +/- 6% [mean +/- SE]) in our high tundra study population and, in the absence of ants, exerted strong selection for large flowers. We tested for indirect effects of ant abundance on seed set through bumble bee pollination services (pollen delivery and pollen export) and a direct effect through flower damage. Ants reduced seed set per flower by 20% via flower damage. As ant density increased within experimental patches, the rate of flower damage rose, but pollen delivery and export did not vary significantly, showing that indirect effects of increased cheater abundance on pollinator service are negligible in this system. To address how ants affect selection for plant participation in the pollination mutualism we tested the impact of ant abundance on selection for bumble bee-mediated pollination. Results show that the impact of ants on fitness (seed set) accruing under bumble bee pollination is density dependent in P. viscosum. Selection for bumble bee pollination declined with increasing ant abundance in experimental patches, as predicted if cheaters constrain fitness returns of mutualist partner services. We also examined how ant abundance influences selection on flower size, a key component of plant investment in bumble bee pollination. We predicted that direct effects of ants would constrain bumble bee selection for large flowers. However, selection on flower size was significantly

  10. Density-Dependent Spacing Behaviour and Activity Budget in Pregnant, Domestic Goats (Capra hircus).

    Science.gov (United States)

    Vas, Judit; Andersen, Inger Lise

    2015-01-01

    Very little is known about the spacing behaviour in social groups of domestic goats (Capra hircus) in the farm environment. In this experiment, we studied interindividual distances, movement patterns and activity budgets in pregnant goats housed at three different densities. Norwegian dairy goats were kept in stable social groups of six animals throughout pregnancy at 1, 2 or 3 m2 per individual and their spacing behaviours (i.e., distance travelled, nearest and furthest neighbour distance) and activity budgets (e.g., resting, feeding, social activities) were monitored. Observations were made in the first, second and last thirds of pregnancy in the mornings, at noon and in the afternoons of each of these phases (4.5 hours per observation period). The findings show that goats held at animal densities of 2 and 3 m2 moved longer distances when they had more space per animal and kept larger nearest and furthest neighbour distances when compared to the 1 m2 per animal density. Less feeding activity was observed at the high animal density compared to the medium and low density treatments. The phase of gestation also had an impact on almost all behavioural variables. Closer to parturition, animals moved further distances and the increase in nearest and furthest neighbour distance was more pronounced at the lower animal densities. During the last period of gestation, goats spent less time feeding and more on resting, social behaviours and engaging in other various activities. Our data suggest that more space per goat is needed for goats closer to parturition than in the early gestation phase. We concluded that in goats spacing behaviour is density-dependent and changes with stages of pregnancy and activities. Finally, the lower density allowed animals to express individual preferences regarding spacing behaviour which is important in ensuring good welfare in a farming situation.

  11. Density-Dependent Spacing Behaviour and Activity Budget in Pregnant, Domestic Goats (Capra hircus.

    Directory of Open Access Journals (Sweden)

    Judit Vas

    Full Text Available Very little is known about the spacing behaviour in social groups of domestic goats (Capra hircus in the farm environment. In this experiment, we studied interindividual distances, movement patterns and activity budgets in pregnant goats housed at three different densities. Norwegian dairy goats were kept in stable social groups of six animals throughout pregnancy at 1, 2 or 3 m2 per individual and their spacing behaviours (i.e., distance travelled, nearest and furthest neighbour distance and activity budgets (e.g., resting, feeding, social activities were monitored. Observations were made in the first, second and last thirds of pregnancy in the mornings, at noon and in the afternoons of each of these phases (4.5 hours per observation period. The findings show that goats held at animal densities of 2 and 3 m2 moved longer distances when they had more space per animal and kept larger nearest and furthest neighbour distances when compared to the 1 m2 per animal density. Less feeding activity was observed at the high animal density compared to the medium and low density treatments. The phase of gestation also had an impact on almost all behavioural variables. Closer to parturition, animals moved further distances and the increase in nearest and furthest neighbour distance was more pronounced at the lower animal densities. During the last period of gestation, goats spent less time feeding and more on resting, social behaviours and engaging in other various activities. Our data suggest that more space per goat is needed for goats closer to parturition than in the early gestation phase. We concluded that in goats spacing behaviour is density-dependent and changes with stages of pregnancy and activities. Finally, the lower density allowed animals to express individual preferences regarding spacing behaviour which is important in ensuring good welfare in a farming situation.

  12. Time-dependent density-functional-theory investigation of the collisions of protons and α particles with uracil and adenine

    Science.gov (United States)

    Covington, Cody; Hartig, Kara; Russakoff, Arthur; Kulpins, Ryan; Varga, Kálmán

    2017-05-01

    Time-dependent density-functional theory was employed to study the effects of proton and α -particle radiation on uracil and adenine. This method has the advantage of treating nuclear motion and electronic motion simultaneously, allowing for the study of electronic excitation, charge transfer, ionization, and nuclear motion. Particle energies were surveyed in the range of 15-500 keV for protons and 100-2000 keV for α particles in conjunction with impact points both on and off carbon bonds in order to investigate the electron and nuclear dynamics of irradiated molecules and the form and quantity of transferred energy. The stopping power, energy transferred, and ionization were found, and the relationship between incident particle energy and electron density of the target molecule was characterized for proton and α -particle radiation incident on adenine and uracil.

  13. Laboratory Calibration of Density-Dependent Lines in the EUV and Soft X-Ray Regions

    Energy Technology Data Exchange (ETDEWEB)

    Lepson, J K; Beiersdorfer, P; Gu, M F; Desai, P

    2010-12-09

    We analyzed spectral data of Fe XXII and Ar XIV from laboratory sources in which the electron density varies by several orders of magnitude to help benchmark density-sensitive emission lines useful for astrophysics and to test the atomic models underlying the diagnostic line ratios. We found excellent agreement for Fe XXII, but poorer agreement for Ar XIV. A number of astrophysically important emission lines are sensitive to electron density in the EUV and soft X-ray regions. Lines from Fe XXII, for example, have been used in recent years as diagnostics of stellar coronae, such as the active variable AB Dor, Capella, and EX Hya (Sanz-Forcada et al. 2003, Mewe et al. 2001, Mauche et al. 2003). Here we report spectral data of Fe XXII and Ar XIV from laboratory sources in which the electron density is known from either K-shell density diagnostics (for electron beam ion traps) or from non-spectroscopic means (tokamaks), ranging from 5 x 10{sup 10} cm{sup -3} to 5 x 10{sup 14} cm{sup -3}. These measurements were used to test the atomic data underlying the density diagnostic line ratios, complementing earlier work (Chen et al. 2004).

  14. Time-dependent local spin density approximation study of Luttinger liquids

    Science.gov (United States)

    Lipparini, E.; Zobele, G.

    2011-08-01

    We perform a time-dependent local spin density approximation (TDLSDA) study of one-dimensional Fermions with a contact interaction. We show that the simple TDLSDA approximation provides an exact description for density and spin density modes and conductance G in one-dimensional quantum wires, by establishing a general equivalence between TDSLDA and Tomonaga-Luttinger model for the elementary excitation spectra in one-dimensional Fermi systems. The role of interaction effects is carefully analyzed especially in relation to the problem of the universality of the result G=2e2/h for the conductance of one-dimensional systems. Finally our results are in good agreement with the available experimental data on the one-dimensional plasmon dispersion, and conductance in GaAs quantum wires.

  15. Asymmetric nuclear matter studied by time-dependent local isospin density approximation

    Science.gov (United States)

    Lipparini, Enrico; Pederiva, Francesco

    2013-08-01

    The dynamic response of asymmetric nuclear matter is studied by means of a time-dependent local isospin density approximation (TDLIDA) approach. Calculations are based on a local density energy functional derived by an auxiliary field diffusion Monte Carlo (AFDMC) calculation of bulk nuclear matter. Three types of excited states emerge: collective states, a continuum of quasiparticle-quasihole excitations and unstable solutions. These states are analyzed and discussed for different values of the nuclear density ρ and isospin asymmetry ξ=(N-Z)/A. An analytical expression of the compressibility as a function of ρ and ξ is derived which shows explicitly an instability of the neutron matter around ρ≃0.09 fm-3 when a small fraction of protons are added to the system.

  16. Two-component hybrid time-dependent density functional theory within the Tamm-Dancoff approximation

    Energy Technology Data Exchange (ETDEWEB)

    Kühn, Michael [Institut für Physikalische Chemie, Karlsruher Institut für Technologie, Kaiserstraße 12, 76131 Karlsruhe (Germany); Weigend, Florian, E-mail: florian.weigend@kit.edu [Institut für Physikalische Chemie, Karlsruher Institut für Technologie, Kaiserstraße 12, 76131 Karlsruhe (Germany); Institut für Nanotechnologie, Karlsruher Institut für Technologie, Postfach 3640, 76021 Karlsruhe (Germany)

    2015-01-21

    We report the implementation of a two-component variant of time-dependent density functional theory (TDDFT) for hybrid functionals that accounts for spin-orbit effects within the Tamm-Dancoff approximation (TDA) for closed-shell systems. The influence of the admixture of Hartree-Fock exchange on excitation energies is investigated for several atoms and diatomic molecules by comparison to numbers for pure density functionals obtained previously [M. Kühn and F. Weigend, J. Chem. Theory Comput. 9, 5341 (2013)]. It is further related to changes upon switching to the local density approximation or using the full TDDFT formalism instead of TDA. Efficiency is demonstrated for a comparably large system, Ir(ppy){sub 3} (61 atoms, 1501 basis functions, lowest 10 excited states), which is a prototype molecule for organic light-emitting diodes, due to its “spin-forbidden” triplet-singlet transition.

  17. On the universality of the long-/short-range separation in multiconfigurational density-functional theory

    DEFF Research Database (Denmark)

    Fromager, Emmanuel; Toulouse, Julien; Jensen, Hans Jørgen Aagaard

    2007-01-01

    ) adequately which, on the other hand, can be described in wave-function theory (WFT), for example, with a multiconfigurational self-consistent field (MCSCF) model. It is therefore of high interest to develop a hybrid model which combines the best of both WFT and DFT approaches. The merge of WFT and DFT can......In many cases, the dynamic correlation can be calculated quite accurately and at a fairly low computational cost in Kohn-Sham density-functional theory (KS-DFT), using current standard approximate functionals. However, in general, KS-DFT does not treat static correlation effects (near degeneracy...

  18. Warm asymmetric quark matter and protoquark stars within the confined isospin-density-dependent mass model

    Science.gov (United States)

    Chu, Peng-Cheng; Chen, Lie-Wen

    2017-11-01

    We extend the confined isospin-density-dependent mass (CIDDM) model to include temperature dependence of the equivalent mass for quarks. Within the CIDDM model, we study the equation of state for β -equilibrium quark matter, quark symmetry energy, quark symmetry free energy, and the properties of quark stars at finite temperatures. We find that including the temperature dependence of the equivalent mass can significantly influence the properties of the strange quark matter as well as the quark symmetry energy, the quark symmetry free energy, and the maximum mass of quark stars at finite temperatures. The mass-radius relations for different stages of the protoquark stars (PQSs) along the star evolution are analyzed. Our results indicate that the heating (cooling) process for PQSs will increase (decrease) the maximum mass within the CIDDM model by including temperature dependence of the equivalent mass for quarks.

  19. Early onset alcohol dependence with high density of family history is not "male limited".

    Science.gov (United States)

    Magnusson, Asa; Göransson, Mona; Heilig, Markus

    2010-03-01

    Based on classical adoption studies, early onset type II alcoholism was originally described as "male limited." We examined the possible expression of this subtype in present day alcohol-dependent women. Detailed systematic assessment was obtained from 200 treatment-seeking alcohol-dependent women and 189 healthy population controls. Women fulfilling type II alcoholism criteria had higher alcoholism severity as measured by The Alcohol Use Disorders Identification Test and markedly higher use of illicit drugs. Both alcoholism subtypes scored higher than normal on anxiety and impulsivity traits, but type II women scored markedly higher on aggression subscales than either of the other groups. Importantly, density of family history was markedly higher in type II women, suggesting a higher heritability. Despite its original description as male limited, early onset alcoholism with high density of family history is likely to be a valid construct in women. Its recognition has important implications for diagnosis, treatment, and research. Published by Elsevier Inc.

  20. Magnetic circular dichroism in real-time time-dependent density functional theory

    CERN Document Server

    Lee, K -M; Bertsch, G F

    2010-01-01

    We apply the adiabatic time-dependent density functional theory to magnetic ci the real-space, real-time computational method. The standard formulas for the MCD response and its A and B terms are derived from the observables in the time-dependent wave function. We find the real time method is well suited for calculating the overall spectrum, particularly at higher excitation energies where individual excited states are numerous and overlapping. The MCD sum rules are derived and interpreted in the real-time formalism; we find that they are very useful for normalization purposes and assessing the accuracy of the theory. The method is applied to MCD spectrum of C-60 using the adiabatic energy functional from the local density approximation. The theory correctly predicts the signs of the A and B terms for the lowest allowed excitations. However, the magnitudes of the terms only show qualitative agreement with experiment.

  1. Disentangling the effects of climate, density dependence, and harvest on an iconic large herbivore's population dynamics

    DEFF Research Database (Denmark)

    Koons, David; Colchero, Fernando; Hersey, Kent

    2015-01-01

    Understanding the relative effects of climate, harvest, and density dependence on population dynamics is critical for guiding sound population management, especially for ungulates in arid and semi-arid environments experiencing climate change. To address these issues for bison in southern Utah, we...... than precipitation and other temperature-related variables (model weight > 3 times more than that for other climate variables). Although we hypothesized that harvest is the primary driving force of bison population dynamics in southern Utah, our elasticity analysis indicated that changes in early...... spring temperature could have a greater ‘relative effect’ on equilibrium abundance than either harvest or the strength of density dependence. Our findings highlight the utility of incorporating elasticity analyses into state-space population models, and the need to include climatic processes in wildlife...

  2. Estimating the density of honeybee colonies across their natural range to fill the gap in pollinator decline censuses.

    Science.gov (United States)

    Jaffé, Rodolfo; Dietemann, Vincent; Allsopp, Mike H; Costa, Cecilia; Crewe, Robin M; Dall'olio, Raffaele; DE LA Rúa, Pilar; El-Niweiri, Mogbel A A; Fries, Ingemar; Kezic, Nikola; Meusel, Michael S; Paxton, Robert J; Shaibi, Taher; Stolle, Eckart; Moritz, Robin F A

    2010-04-01

    Although pollinator declines are a global biodiversity threat, the demography of the western honeybee (Apis mellifera) has not been considered by conservationists because it is biased by the activity of beekeepers. To fill this gap in pollinator decline censuses and to provide a broad picture of the current status of honeybees across their natural range, we used microsatellite genetic markers to estimate colony densities and genetic diversity at different locations in Europe, Africa, and central Asia that had different patterns of land use. Genetic diversity and colony densities were highest in South Africa and lowest in Northern Europe and were correlated with mean annual temperature. Confounding factors not related to climate, however, are also likely to influence genetic diversity and colony densities in honeybee populations. Land use showed a significantly negative influence over genetic diversity and the density of honeybee colonies over all sampling locations. In Europe honeybees sampled in nature reserves had genetic diversity and colony densities similar to those sampled in agricultural landscapes, which suggests that the former are not wild but may have come from managed hives. Other results also support this idea: putative wild bees were rare in our European samples, and the mean estimated density of honeybee colonies on the continent closely resembled the reported mean number of managed hives. Current densities of European honeybee populations are in the same range as those found in the adverse climatic conditions of the Kalahari and Saharan deserts, which suggests that beekeeping activities do not compensate for the loss of wild colonies. Our findings highlight the importance of reconsidering the conservation status of honeybees in Europe and of regarding beekeeping not only as a profitable business for producing honey, but also as an essential component of biodiversity conservation.

  3. Tilted Magnetic Levitation Enables Measurement of the Complete Range of Densities of Materials with Low Magnetic Permeability.

    Science.gov (United States)

    Nemiroski, Alex; Soh, Siowling; Kwok, Sen Wai; Yu, Hai-Dong; Whitesides, George M

    2016-02-03

    Magnetic levitation (MagLev) of diamagnetic or weakly paramagnetic materials suspended in a paramagnetic solution in a magnetic field gradient provides a simple method to measure the density of small samples of solids or liquids. One major limitation of this method, thus far, has been an inability to measure or manipulate materials outside of a narrow range of densities (0.8 g/cm(3) levitated magnetically. Tilting the MagLev device relative to the gravitational vector enables the magnetic force to be decreased (relative to the magnetic force) along the axis of measurement. This approach enables many practical measurements over the entire range of densities observed in matter at ambient conditions-from air bubbles (ρ ≈ 0) to osmium and iridium (ρ ≈ 23 g/cm(3)). The ability to levitate, simultaneously, objects with a broad range of different densities provides an operationally simple method that may find application to forensic science (e.g., for identifying the composition of miscellaneous objects or powders), industrial manufacturing (e.g., for quality control of parts), or resource-limited settings (e.g., for identifying and separating small particles of metals and alloys).

  4. Parton densities in quantum chromodynamics. Gauge invariance, path-dependence, and Wilson lines

    Energy Technology Data Exchange (ETDEWEB)

    Cherednikov, Igor O. [Antwerpen Univ. (Belgium). Dept. Fysica; Veken, Frederik F. van der [CERN, Geneva (Switzerland)

    2017-05-01

    The purpose of this book is to give a systematic pedagogical exposition of the quantitative analysis of Wilson lines and gauge-invariant correlation functions in quantum chromodynamics. Using techniques from the previous volume (Wilson Lines in Quantum Field Theory, 2014), an ab initio methodology is developed and practical tools for its implementation are presented. Emphasis is put on the implications of gauge invariance and path-dependence properties of transverse-momentum dependent parton density functions. The latter are associated with the QCD factorization approach to semi-inclusive hadronic processes, studied at currently operating and planned experimental facilities.

  5. Formation of collective excitations in quasi-one dimensional metallic nanostructures: size and density dependance

    OpenAIRE

    Cassidy, Amy; Grigorenko, Ilya; Haas, Stephan

    2008-01-01

    We investigate theoretically the formation of collective excitations in atomic scale quasi-one dimensional metallic nanostructures. The response of the system is calculated within the linear response theory and random phase approximation. For uniform nanostructures a transition from quantum single particle excitations to classical plasmon scaling is observed, depending on the system length and electron density. We find crucial differences in the scaling behavior for quasi-one dimensional and ...

  6. Time-dependent density-functional theory in the projector augmented-wave method

    DEFF Research Database (Denmark)

    Walter, Michael; Häkkinen, Hannu; Lehtovaara, Lauri

    2008-01-01

    We present the implementation of the time-dependent density-functional theory both in linear-response and in time-propagation formalisms using the projector augmented-wave method in real-space grids. The two technically very different methods are compared in the linear-response regime where we...... surfaces for a set of atoms and molecules with the linear-response method and by calculating nonlinear emission spectra using the time-propagation method....

  7. Optical properties of Al nanostructures from time dependent density functional theory

    KAUST Repository

    Mokkath, Junais Habeeb

    2016-04-05

    The optical properties of Al nanostructures are investigated by means of time dependent density functional theory, considering chains of varying length and ladders/stripes of varying aspect ratio. The absorption spectra show redshifting for increasing length and aspect ratio. For the chains the absorption is dominated by HOMO → LUMO transitions, whereas ladders and stripes reveal more complex spectra of plasmonic nature above a specific aspect ratio.

  8. Evolution of stochastic demography with life history tradeoffs in density-dependent age-structured populations.

    Science.gov (United States)

    Lande, Russell; Engen, Steinar; Sæther, Bernt-Erik

    2017-10-31

    We analyze the stochastic demography and evolution of a density-dependent age- (or stage-) structured population in a fluctuating environment. A positive linear combination of age classes (e.g., weighted by body mass) is assumed to act as the single variable of population size, [Formula: see text], exerting density dependence on age-specific vital rates through an increasing function of population size. The environment fluctuates in a stationary distribution with no autocorrelation. We show by analysis and simulation of age structure, under assumptions often met by vertebrate populations, that the stochastic dynamics of population size can be accurately approximated by a univariate model governed by three key demographic parameters: the intrinsic rate of increase and carrying capacity in the average environment, [Formula: see text] and [Formula: see text], and the environmental variance in population growth rate, [Formula: see text] Allowing these parameters to be genetically variable and to evolve, but assuming that a fourth parameter, [Formula: see text], measuring the nonlinearity of density dependence, remains constant, the expected evolution maximizes [Formula: see text] This shows that the magnitude of environmental stochasticity governs the classical trade-off between selection for higher [Formula: see text] versus higher [Formula: see text] However, selection also acts to decrease [Formula: see text], so the simple life-history trade-off between [Formula: see text]- and [Formula: see text]-selection may be obscured by additional trade-offs between them and [Formula: see text] Under the classical logistic model of population growth with linear density dependence ([Formula: see text]), life-history evolution in a fluctuating environment tends to maximize the average population size. Published under the PNAS license.

  9. The importance of spatial models for estimating the strength of density dependence

    DEFF Research Database (Denmark)

    Thorson, James T.; Skaug, Hans J.; Kristensen, Kasper

    2014-01-01

    the California Coast. In this case, the nonspatial model estimates implausible oscillatory dynamics on an annual time scale, while the spatial model estimates strong autocorrelation and is supported by model selection tools. We conclude by discussing the importance of improved data archiving techniques, so...... that spatial models can be used to re-examine classic questions regarding the presence and strength of density dependence in wild populations Read More: http://www.esajournals.org/doi/abs/10.1890/14-0739.1...

  10. The temperature dependence of the BK channel activity - kinetics, thermodynamics, and long-range correlations.

    Science.gov (United States)

    Wawrzkiewicz-Jałowiecka, Agata; Dworakowska, Beata; Grzywna, Zbigniew J

    2017-10-01

    Large-conductance, voltage dependent, Ca2+-activated potassium channels (BK) are transmembrane proteins that regulate many biological processes by controlling potassium flow across cell membranes. Here, we investigate to what extent temperature (in the range of 17-37°C with ΔT=5°C step) is a regulating parameter of kinetic properties of the channel gating and memory effect in the series of dwell-time series of subsequent channel's states, at membrane depolarization and hyperpolarization. The obtained results indicate that temperature affects strongly the BK channels' gating, but, counterintuitively, it exerts no effect on the long-range correlations, as measured by the Hurst coefficient. Quantitative differences between dependencies of appropriate channel's characteristics on temperature are evident for different regimes of voltage. Examining the characteristics of BK channel activity as a function of temperature allows to estimate the net activation energy (Eact) and changes of thermodynamic parameters (ΔH, ΔS, ΔG) by channel opening. Larger Eact corresponds to the channel activity at membrane hyperpolarization. The analysis of entropy and enthalpy changes of closed to open channel's transition suggest the entropy-driven nature of the increase of open state probability during voltage activation and supports the hypothesis about the voltage-dependent geometry of the channel vestibule. Copyright © 2017 Elsevier B.V. All rights reserved.

  11. A long range dependent model with nonlinear innovations for simulating daily river flows

    Directory of Open Access Journals (Sweden)

    P. Elek

    2004-01-01

    Full Text Available We present the analysis aimed at the estimation of flood risks of Tisza River in Hungary on the basis of daily river discharge data registered in the last 100 years. The deseasonalised series has skewed and leptokurtic distribution and various methods suggest that it possesses substantial long memory. This motivates the attempt to fit a fractional ARIMA model with non-Gaussian innovations as a first step. Synthetic streamflow series can then be generated from the bootstrapped innovations. However, there remains a significant difference between the empirical and the synthetic density functions as well as the quantiles. This brings attention to the fact that the innovations are not independent, both their squares and absolute values are autocorrelated. Furthermore, the innovations display non-seasonal periods of high and low variances. This behaviour is characteristic to generalised autoregressive conditional heteroscedastic (GARCH models. However, when innovations are simulated as GARCH processes, the quantiles and extremes of the discharge series are heavily overestimated. Therefore we suggest to fit a smooth transition GARCH-process to the innovations. In a standard GARCH model the dependence of the variance on the lagged innovation is quadratic whereas in our proposed model it is a bounded function. While preserving long memory and eliminating the correlation from both the generating noise and from its square, the new model is superior to the previously mentioned ones in approximating the probability density, the high quantiles and the extremal behaviour of the empirical river flows.

  12. Temperature- and density-dependent transport regimes in a h-BN/bilayer graphene/h-BN heterostructure

    Science.gov (United States)

    Cobaleda, C.; Pezzini, S.; Diez, E.; Bellani, V.

    2014-03-01

    We report on multiterminal electrical transport measurements performed on a bilayer graphene sheet enclosed by two hexagonal boron nitride flakes. We characterize the temperature dependence of electrical resistivity from 300 mK to 50 K, varying the carrier densities with a back gate. The resistivity curves clearly show a temperature-independent crossing point at density n =nc≈2.5×1011 cm-2 for both positive and negative carriers, separating two distinct regions with dρ /dT0, respectively. Our analysis rules out the possibility of a zero-T quantum phase transition, revealing instead the onset of robust ballistic transport for n >nc, while the T dependence close to the neutrality point is the one expected from the parabolic energy-momentum relation. At low temperature (T ≪10 K), the data are compatible with transport via variable range hopping mediated by localized impurity sites, with a characteristic exponent 1/3 that is renormalized to 1/2 by Coulomb interaction in the high-density regime.

  13. Cell density-dependent differential proliferation of neural stem cells on omnidirectional nanopore-arrayed surface.

    Science.gov (United States)

    Cha, Kyoung Je; Kong, Sun-Young; Lee, Ji Soo; Kim, Hyung Woo; Shin, Jae-Yeon; La, Moonwoo; Han, Byung Woo; Kim, Dong Sung; Kim, Hyun-Jung

    2017-10-12

    Recently, the importance of surface nanotopography in the determination of stem cell fate and behavior has been revealed. In the current study, we generated polystyrene cell-culture dishes with an omnidirectional nanopore arrayed surface (ONAS) (diameter: 200 nm, depth: 500 nm, center-to-center distance: 500 nm) and investigated the effects of nanotopography on rat neural stem cells (NSCs). NSCs cultured on ONAS proliferated better than those on the flat surface when cell density was low and showed less spontaneous differentiation during proliferation in the presence of mitogens. Interestingly, NSCs cultured on ONAS at clonal density demonstrated a propensity to generate neurospheres, whereas those on the flat surface migrated out, proliferated as individuals, and spread out to attach to the surface. However, the differential patterns of proliferation were cell density-dependent since the distinct phenomena were lost when cell density was increased. ONAS modulated cytoskeletal reorganization and inhibited formation of focal adhesion, which is generally observed in NSCs grown on flat surfaces. ONAS appeared to reinforce NSC-NSC interaction, restricted individual cell migration and prohibited NSC attachment to the nanopore surface. These data demonstrate that ONAS maintains NSCs as undifferentiated while retaining multipotency and is a better topography for culturing low density NSCs.

  14. Plant host range of Verticillium longisporum and microsclerotia density in Swedisch soils

    NARCIS (Netherlands)

    Johansson, A.; Goud, J.C.; Dixelius, C.

    2006-01-01

    Verticillium longisporum is a soil-borne fungal pathogen causing vascular wilt of Brassica crops. This study was conducted to enhance our knowledge on the host range of V. longisporum. Seven crop species (barley, oat, oilseed rape, pea, red clover, sugar beet and wheat) and five weed species (barren

  15. A novel approach for assessing density and range-wide abundance of prairie dogs

    Science.gov (United States)

    Aaron N. Facka; Paulette L. Ford; Gary W. Roemer

    2008-01-01

    Habitat loss, introduced disease, and government-sponsored eradication programs have caused population declines in all 5 species of prairie dogs. Black-tailed prairie dogs (Cynomys ludovicianus) currently occupy only about 2% of an extensive geographic range (160 million hectares) and were recently considered for listing under the United States...

  16. Influence of excitation power density on temperature dependencies of NaYF4: Yb, Er nanoparticles luminescence spectra

    Science.gov (United States)

    Ustalkov, Sergey O.; Kozlova, Ekaterina A.; Savenko, Olga A.; Mohammed, Ammar H. M.; Kochubey, Vyacheslav I.; Skaptsov, Alexander A.

    2017-03-01

    Upconversion nanoparticles are good candidates for nanothermometry. The wavelength of the excitation and luminescence lie in optical window. The influence of the excitation power density on the luminescence temperature dependences is studded. Ratio of luminescence intensities linearly depends on temperature.

  17. The isovector nuclear density and improved description of cluster decay half-lives using isospin-dependent NN interaction

    Science.gov (United States)

    Ismail, M.; Adel, A.

    2017-12-01

    The sensitivity of cluster-decay half-life time to the isospin effect of the nucleon–nucleon (NN) interaction and the neutron-skin thickness is explored in the framework of the Wentzel–Kramers–Brillouin approximation. Within the generalized double-folding model, the cluster-daughter potential is calculated in terms of the isoscalar and isovector parts using the explicit proton and neutron density distributions. Realistic density-dependent Michigan-three-Yukawa (CDM3Y1 and CDM3Y6) NN interactions with the finite-range exchange NN force are considered in the present work. The calculated cluster-decay half-lives including the isospin effect and the differences between neutron and proton density distributions are found to be in somewhat better agreement with the experimental data as compared without these effects. This may indicate the necessity of considering the isospin effect and the neutron–proton differences of the density distributions in cluster-decay, especially for extremely neutron-rich nuclei. Predictions of cluster decay half-lives from possible cluster emitters are presented which may be helpful for future experiments. The present study could be a significant step forward in improving the description of cluster decay half-lives.

  18. Density of states of two-dimensional systems with long-range logarithmic interactions

    Energy Technology Data Exchange (ETDEWEB)

    Somoza, Andrés M.; Ortuño, Miguel; Baturina, Tatyana I.; Vinokur, Valerii M.

    2015-08-03

    We investigate a single-particle density of states (DOS) in strongly disordered two- dimensional high dielectric permittivity systems with logarithmic Coulomb interaction between particles. We derive self-consistent DOS at zero temperature and show that it is appreciably suppressed as compared to the DOS expected from the Efros-Shklovskii approach.We carry out zero- and finite-temperature Monte Carlo numerical studies of the DOS and find the perfect agreement between the numerical and analytical results at zero temperature, observing, in particular, a hardening of the Coulomb gap with the increasing electrostatic screening length. At finite temperatures, we reveal a striking scaling of the DOS as a function of energy normalized to the temperature of the system.

  19. Whitebark Pine, Population Density, and Home-Range Size of Grizzly Bears in the Greater Yellowstone Ecosystem

    OpenAIRE

    Bjornlie, Daniel D; van Manen, Frank T.; Ebinger, Michael R.; Haroldson, Mark A; Thompson, Daniel J.; Cecily M Costello

    2014-01-01

    Changes in life history traits of species can be an important indicator of potential factors influencing populations. For grizzly bears (Ursus arctos) in the Greater Yellowstone Ecosystem (GYE), recent decline of whitebark pine (WBP; Pinus albicaulis), an important fall food resource, has been paired with a slowing of population growth following two decades of robust population increase. These observations have raised questions whether resource decline or density-dependent processes may be as...

  20. Extended density-dependent mortality in mature conifer forests: causes and implications for ecosystem management.

    Science.gov (United States)

    Gendreau-Berthiaume, Benoit; Macdonald, S Ellen; Stadt, J John

    2016-07-01

    Understanding processes driving mortality in forests is important for comprehension of natural stand dynamics and for informing natural disturbance-based ecosystem management. There has been considerable study of mortality in forests during the self-thinning phase but we know much less about processes driving mortality in stands at later successional stages. We addressed this through study of five 1-ha spatially explicit permanent plots in mature (111-186 yr old in 2012) Pinus contorta stands in the Canadian Rocky Mountains using data from repeated measurements over a 45-yr period, dendrochronological information, and point pattern analysis. We tested the hypothesis that these stands had completed the self-thinning/density-dependent mortality stage of succession. Contrary to our expectations, the self-thinning phase can persist for more than 140 yr following stand establishment. Our findings suggest this was attributable to prolonged post-fire establishment periods due to surface fires in three of the plots while in the other two plots moist conditions and slow growth most likely delayed the onset of competition. Several pieces of evidence indicated the importance of density-dependent mortality in these stands over the study period: (1) The diameter distribution of individuals changed from initially right-skewed toward normality as a result of mortality of smaller-diameter stems. (2) Individuals of lower canopy positions were proportionally more affected by mortality. (3) When compared to the pre-mortality pattern, surviving stems in all stands had an increasingly uniform spatial distribution. In two of the plots, recent windthrow and/or ingrowth initially hindered our ability to detect density-dependent mortality but our dendrochronological sampling and permanent plot data allowed us to untangle the different processes at play; in doing so we demonstrate for the first time how density-independent processes can mask underlying density-dependent mortality

  1. Scale-dependent habitat use by a large free-ranging predator, the Mediterranean fin whale

    Science.gov (United States)

    Cotté, Cédric; Guinet, Christophe; Taupier-Letage, Isabelle; Mate, Bruce; Petiau, Estelle

    2009-05-01

    Since the heterogeneity of oceanographic conditions drives abundance, distribution, and availability of prey, it is essential to understand how foraging predators interact with their dynamic environment at various spatial and temporal scales. We examined the spatio-temporal relationships between oceanographic features and abundance of fin whales ( Balaenoptera physalus), the largest free-ranging predator in the Western Mediterranean Sea (WM), through two independent approaches. First, spatial modeling was used to estimate whale density, using waiting distance (the distance between detections) for fin whales along ferry routes across the WM, in relation to remotely sensed oceanographic parameters. At a large scale (basin and year), fin whales exhibited fidelity to the northern WM with a summer-aggregated and winter-dispersed pattern. At mesoscale (20-100 km), whales were found in colder, saltier (from an on-board system) and dynamic areas defined by steep altimetric and temperature gradients. Second, using an independent fin whale satellite tracking dataset, we showed that tracked whales were effectively preferentially located in favorable habitats, i.e. in areas of high predicted densities as identified by our previous model using oceanographic data contemporaneous to the tracking period. We suggest that the large-scale fidelity corresponds to temporally and spatially predictable habitat of whale favorite prey, the northern krill ( Meganyctiphanes norvegica), while mesoscale relationships are likely to identify areas of high prey concentration and availability.

  2. Generalized Efficient Inference on Factor Models with Long-Range Dependence

    DEFF Research Database (Denmark)

    Ergemen, Yunus Emre

    . Short-memory dynamics are allowed in the common factor structure and possibly heteroskedastic error term. In the estimation, a generalized version of the principal components (PC) approach is proposed to achieve efficiency. Asymptotics for efficient common factor and factor loading as well as long......A dynamic factor model is considered that contains stochastic time trends allowing for stationary and nonstationary long-range dependence. The model nests standard I(0) and I(1) behaviour smoothly in common factors and residuals, removing the necessity of a priori unit-root and stationarity testing...

  3. Trade-off between toxicity and signal detection orchestrated by frequency- and density-dependent genes.

    Directory of Open Access Journals (Sweden)

    Laury Arthaud

    Full Text Available Behaviors in insects are partly highly efficient Bayesian processes that fulfill exploratory tasks ending with the colonization of new ecological niches. The foraging (for gene in Drosophila encodes a cGMP-dependent protein kinase (PKG. It has been extensively described as a frequency-dependent gene and its transcripts are differentially expressed between individuals, reflecting the population density context. Some for transcripts, when expressed in a population at high density for many generations, concomitantly trigger strong dispersive behavior associated with foraging activity. Moreover, genotype-by-environment interaction (GEI analysis has highlighted a dormant role of for in energetic metabolism in a food deprivation context. In our current report, we show that alleles of for encoding different cGMP-dependent kinase isoforms influence the oxidation of aldehyde groups of aromatic molecules emitted by plants via Aldh-III and a phosphorylatable adaptor. The enhanced efficiency of oxidation of aldehyde odorants into carboxyl groups by the action of for lessens their action and toxicity, which should facilitate exploration and guidance in a complex odor environment. Our present data provide evidence that optimal foraging performance requires the fast metabolism of volatile compounds emitted by plants to avoid neurosensory saturation and that the frequency-dependent genes that trigger dispersion influence these processes.

  4. Dependability of the Exemplary Technical System for Assumed Functions of Defect Density

    Directory of Open Access Journals (Sweden)

    Stępień Sławomir

    2016-12-01

    Full Text Available The analysis of structural dependability of technical system, especially determining the change in dependability over time, requires knowledge on density function or the understanding of cumulative distribution function of components belonging to the structure. Based on previously registered data concerning component defect, it is relatively easy to establish the average uptime of component as well as the standard deviation for this time. However, defining distribution shape gives rise to some difficulties. Usually, we do not have the sufficient number of data at our disposal to verify the hypothesis regarding the distribution shape. Due to this fact, it is a common practice, depending on the case under consideration, to apply the function of defect density. However, the question arises: Does the incorrect determination of types of distributions of components leads to the big error of estimation results of dependability and system durability? This article will not respond to this question in whole, but one will conduct a comparison of calculation results for a few cases. The calculations were conducted for the exemplary technical system.

  5. Survival Kinetics of Starving Bacteria Is Biphasic and Density-Dependent

    Science.gov (United States)

    Phaiboun, Andy; Zhang, Yiming; Park, Boryung; Kim, Minsu

    2015-01-01

    In the lifecycle of microorganisms, prolonged starvation is prevalent and sustaining life during starvation periods is a vital task. In the literature, it is commonly assumed that survival kinetics of starving microbes follows exponential decay. This assumption, however, has not been rigorously tested. Currently, it is not clear under what circumstances this assumption is true. Also, it is not known when such survival kinetics deviates from exponential decay and if it deviates, what underlying mechanisms for the deviation are. Here, to address these issues, we quantitatively characterized dynamics of survival and death of starving E. coli cells. The results show that the assumption – starving cells die exponentially – is true only at high cell density. At low density, starving cells persevere for extended periods of time, before dying rapidly exponentially. Detailed analyses show intriguing quantitative characteristics of the density-dependent and biphasic survival kinetics, including that the period of the perseverance is inversely proportional to cell density. These characteristics further lead us to identification of key underlying processes relevant for the perseverance of starving cells. Then, using mathematical modeling, we show how these processes contribute to the density-dependent and biphasic survival kinetics observed. Importantly, our model reveals a thrifty strategy employed by bacteria, by which upon sensing impending depletion of a substrate, the limiting substrate is conserved and utilized later during starvation to delay cell death. These findings advance quantitative understanding of survival of microbes in oligotrophic environments and facilitate quantitative analysis and prediction of microbial dynamics in nature. Furthermore, they prompt revision of previous models used to analyze and predict population dynamics of microbes. PMID:25838110

  6. Dependence of superconducting layer thickness on critical current density of IBAD/CVD-processed YBCO coated conductors

    Energy Technology Data Exchange (ETDEWEB)

    Himeki, K.; Kiuchi, M.; Otabe, E.S. [Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, 680-4 Kawazu, Iizuka, Fukuoka 820-8502 (Japan); Matsushita, T., E-mail: matusita@cse.kyutech.ac.j [Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, 680-4 Kawazu, Iizuka, Fukuoka 820-8502 (Japan); Shikimachi, K.; Watanabe, T.; Kashima, N.; Nagaya, S. [Chubu Electric Power Co., Inc., 20-1, Kitasekiyama, Ohdaka-cho, Midori-ku, Nagoya 459-8522 (Japan); Yamada, Y.; Shiohara, Y. [Superconductivity Research Laboratory, 1-10-13 Shinonome, Koto-ku, Tokyo 135-0062 (Japan)

    2009-10-15

    The thickness dependence of the critical current characteristics was investigated for YBa{sub 2}Cu{sub 3}O{sub 7-d}elta (YBCO) coated conductors fabricated by Ion Beam Assist Deposition (IBAD)/Chemical Vapor Deposition (CVD) method in the range of 0.18-0.90 mum to find out the optimum thickness for various applications. The transport and magnetization critical current densities were estimated using the electric field criterion of E{sub c} = 1.0 x 10{sup -4} V/m and E{sub c} = 1.0 x 10{sup -9} V/m, respectively. The critical current density decreased with increase thickness in the low magnetic field region in the both electric field region because of the structural degradation of superconducting layer. This decreasing rate was lower than in Pulsed Laser Deposition (PLD)-processed YBCO coated conductors. It is found that the thickness dependence of irreversibility field B{sub i} differed between the low and normal electric field region. In the low electric field region, B{sub i} increased with increasing thickness. On the other hand, B{sub i} is almost independent of the thickness in the normal electric field region. The thickness dependence of B{sub i} was also superior to that of PLD-processed YBCO coated conductors.

  7. The influence of vegetation cover on debris-flow density during an extreme rainfall in the northern Colorado Front Range

    Science.gov (United States)

    Rengers, Francis; McGuire, Luke; Coe, Jeffrey A.; Kean, Jason W.; Baum, Rex L.; Staley, Dennis M.; Godt, Jonathan W.

    2016-01-01

    We explored regional influences on debris-flow initiation throughout the Colorado Front Range (Colorado, USA) by exploiting a unique data set of more than 1100 debris flows that initiated during a 5 day rainstorm in 2013. Using geospatial data, we examined the influence of rain, hillslope angle, hillslope aspect, and vegetation density on debris-flow initiation. In particular we used a greenness index to differentiate areas of high tree density from grass and bare soil. The data demonstrated an overwhelming propensity for debris-flow initiation on south-facing hillslopes. However, when the debris-flow density was analyzed with respect to total rainfall and greenness we found that most debris flows occurred in areas of high rainfall and low tree density, regardless of hillslope aspect. These results indicate that present-day tree density exerts a stronger influence on debris-flow initiation locations than aspect-driven variations in soil and bedrock properties that developed over longer time scales.

  8. Dynamical phase transitions in long-range Hamiltonian systems and Tsallis distributions with a time-dependent index.

    Science.gov (United States)

    Campa, Alessandro; Chavanis, Pierre-Henri; Giansanti, Andrea; Morelli, Gianluca

    2008-10-01

    We study dynamical phase transitions in systems with long-range interactions, using the Hamiltonian mean field model as a simple example. These systems generically undergo a violent relaxation to a quasistationary state (QSS) before relaxing towards Boltzmann equilibrium. In the collisional regime, the out-of-equilibrium one-particle distribution function (DF) is a quasistationary solution of the Vlasov equation, slowly evolving in time due to finite- N effects. For subcritical energy densities, we exhibit cases where the DF is well fitted by a Tsallis q distribution with an index q(t) slowly decreasing in time from q approximately = 3 (semiellipse) to q=1 (Boltzmann). When the index q(t) reaches an energy-dependent critical value q_(crit) , the nonmagnetized (homogeneous) phase becomes Vlasov unstable and a dynamical phase transition is triggered, leading to a magnetized (inhomogeneous) state. While Tsallis distributions play an important role in our study, we explain this dynamical phase transition by using only conventional statistical mechanics. For supercritical energy densities, we report the existence of a magnetized QSS with a very long lifetime.

  9. Stocking density affects the growth performance of broilers in a sex-dependent fashion.

    Science.gov (United States)

    Zuowei, S; Yan, L; Yuan, L; Jiao, H; Song, Z; Guo, Y; Lin, H

    2011-07-01

    The effects of stocking density, sex, and dietary ME concentration on live performance, footpad burns, and leg weakness of broilers were investigated. A total of 876 male and 1,020 female 1-d-old chicks were placed in 24 pens to simulate final stocking density treatments of 26 kg (LSD; 10 males or 12 females/m(2)) and 42 kg (HSD; 16 males or 18 females/m(2)) of BW/m(2) floor space. Two series of experimental diets with a 150 kcal/kg difference in ME concentration (2,800, 2,900, and 3,000 or 2,950, 3,050, and 3,150 kcal of ME/kg) were compared in a 3-phase feeding program. The HSD treatment significantly decreased BW gain and feed conversion ratio (FCR). The HSD chickens consumed less feed by 35 d of age; thereafter, the reverse was true. Male chickens had significantly higher feed intake (FI), BW gain, and FCR compared with females. A significant interaction was found of stocking density and age for FI, BW gain, and FCR. Compared with LSD treatment, HSD broilers had a higher FI and a lower FCR from 36 to 42 d of age. Stocking density, sex, and age had a significant interaction for BW gain and FCR. Female broilers had worse BW gain and FCR when stocked at high density from 36 to 42 d of age. Stocking density had no significant influence on breast, thigh, or abdominal fat yield. Female broilers had significantly higher breast yield and abdominal fat. Male broilers and HSD treatment had high footpad burn and gait scores. A low ME diet increased footpad burn score but had no effect on gait score. The result indicated that stocking density had a more severe effect on the growth of male broilers before 35 d of age. Female broilers need more space than males at similar BW per square meter near marketing age. The incidence and severity of leg weakness are associated with sex, diet, and stocking density. This result suggests that the deteriorated effect of high stocking density is sex and age dependent.

  10. Density-dependent reduction and induction of milkweed cardenolides by a sucking insect herbivore.

    Science.gov (United States)

    Martel, John W; Malcolm, Stephen B

    2004-03-01

    The effect of aphid population size on host-plant chemical defense expression and the effect of plant defense on aphid population dynamics were investigated in a milkweed-specialist herbivore system. Density effects of the aposematic oleander aphid, Aphis nerii, on cardenolide expression were measured in two milkweed species, Asclepias curassavica and A. incarnata. These plants vary in constitutive chemical investment with high mean cardenolide concentration in A. curassavica and low to zero in A. incarnata. The second objective was to determine whether cardenolide expression in these two host plants impacts mean A. nerii colony biomass (mg) and density. Cardenolide concentration (microgram/g) of A. curassavica in both aphid-treated leaves and opposite, herbivore-free leaves decreased initially in comparison with aphid-free controls, and then increased significantly with A. nerii density. Thus, A. curassavica responds to aphid herbivory initially with density-dependent phytochemical reduction, followed by induction of cardenolides to concentrations above aphid-free controls. In addition, mean cardenolide concentration of aphid-treated leaves was significantly higher than that of opposite, herbivore-free leaves. Therefore, A. curassavica induction is strongest in herbivore-damage tissue. Conversely, A. incarnata exhibited no such chemical response to aphid herbivory. Furthermore, neither host plant responded chemically to herbivore feeding duration time (days) or to the interaction between herbivore initial density and feeding duration time. There were also no significant differences in mean colony biomass or population density of A. nerii reared on high cardenolide (A. curassavica) and low cardenolide (A. incarnata) hosts.

  11. Assessment of oscillator strengths with multiconfigurational short-range density functional theory for electronic excitations in organic molecules

    DEFF Research Database (Denmark)

    Hedegård, Erik Donovan

    2017-01-01

    considered the large collection of organic molecules whose excited states were investigated with a range of electronic structure methods by Thiel et al. As a by-product of our calculations of oscillator strengths, we also obtain electronic excitation energies, which enable us to compare the performance......We have in a series of recent papers investigated electronic excited states with a hybrid between a complete active space self-consistent field (CASSCF) wave function and density functional theory (DFT). This method has been dubbed the CAS short-range DFT method (CAS–srDFT). The previous papers...

  12. A finite range pairing force for density functional theory in superfluid nuclei

    Science.gov (United States)

    Tian, Y.; Ma, Z. Y.; Ring, P.

    2009-06-01

    The problem of pairing in the S10 channel of finite nuclei is revisited. In nuclear matter forces of separable form can be adjusted to the bare nuclear force, to any phenomenological pairing interaction such as the Gogny force or to exact solutions of the gap equation. In finite nuclei, because of translational invariance, such forces are no longer separable. Using well-known techniques of Talmi and Moshinsky we expand the matrix elements in a series of separable terms, which converges quickly preserving translational invariance and finite range. In this way the complicated problem of a cut-off at large momenta or energies inherent in other separable or zero range pairing forces is avoided. Applications in the framework of the relativistic Hartree-Bogoliubov approach show that the pairing properties are depicted on almost the same footing as by the original pairing interaction not only in nuclear matter, but also in finite nuclei. This simple separable force can be easily applied for the investigation of pairing properties in nuclei far from stability as well as for further investigations going beyond mean field theory.

  13. Long Range Dependence Prognostics for Bearing Vibration Intensity Chaotic Time Series

    Directory of Open Access Journals (Sweden)

    Qing Li

    2016-01-01

    Full Text Available According to the chaotic features and typical fractional order characteristics of the bearing vibration intensity time series, a forecasting approach based on long range dependence (LRD is proposed. In order to reveal the internal chaotic properties, vibration intensity time series are reconstructed based on chaos theory in phase-space, the delay time is computed with C-C method and the optimal embedding dimension and saturated correlation dimension are calculated via the Grassberger–Procaccia (G-P method, respectively, so that the chaotic characteristics of vibration intensity time series can be jointly determined by the largest Lyapunov exponent and phase plane trajectory of vibration intensity time series, meanwhile, the largest Lyapunov exponent is calculated by the Wolf method and phase plane trajectory is illustrated using Duffing-Holmes Oscillator (DHO. The Hurst exponent and long range dependence prediction method are proposed to verify the typical fractional order features and improve the prediction accuracy of bearing vibration intensity time series, respectively. Experience shows that the vibration intensity time series have chaotic properties and the LRD prediction method is better than the other prediction methods (largest Lyapunov, auto regressive moving average (ARMA and BP neural network (BPNN model in prediction accuracy and prediction performance, which provides a new approach for running tendency predictions for rotating machinery and provide some guidance value to the engineering practice.

  14. Predator effects on reef fish settlement depend on predator origin and recruit density.

    Science.gov (United States)

    Benkwitt, Cassandra E

    2017-04-01

    During major life-history transitions, animals often experience high mortality rates due to predation, making predator avoidance particularly advantageous during these times. There is mixed evidence from a limited number of studies, however, regarding how predator presence influences settlement of coral-reef fishes and it is unknown how other potentially mediating factors, including predator origin (native vs. nonnative) or interactions among conspecific recruits, mediate the non-consumptive effects of predators on reef fish settlement. During a field experiment in the Caribbean, approximately 52% fewer mahogany snapper (Lutjanus mahogoni) recruited to reefs with a native predator (graysby grouper, Cephalopholis cruentata) than to predator-free control reefs and reefs with an invasive predator (red lionfish, Pterois volitans) regardless of predator diet. These results suggest that snapper recruits do not recognize nonnative lionfish as a threat. However, these effects depended on the density of conspecific recruits, with evidence that competition may limit the response of snapper to even native predators at the highest recruit densities. In contrast, there was no effect of predator presence or conspecific density on the recruitment of bicolor damselfish (Stegastes partitus). These context-dependent responses of coral-reef fishes to predators during settlement may influence individual survival and shape subsequent population and community dynamics. © 2017 by the Ecological Society of America.

  15. Experimental evidence for density-dependent responses to mortality of snake-necked turtles.

    Science.gov (United States)

    Fordham, Damien A; Georges, Arthur; Brook, Barry W

    2009-03-01

    Density-dependent compensation has rarely been demonstrated in long-lived vertebrates in highly variable environments, such as the wet-dry tropics, where complex factors impact on vital rates. We used an experimental manipulation of population density in six replicated wild populations of the northern snake-necked turtle (Chelodina rugosa). We show that this species can rebound rapidly following reductions in density, and so is resilient to harvest and predation by pigs. Remarkably, in some populations, turtle abundance took as little as 1 year to recover from a strong negative perturbation (>50% experimental population reduction) in adult density. This was achieved through an increase in hatchling recruitment and survival into larger size classes. Our manipulative experiments, viewed concomitantly with previous experimental and correlative research, challenge the general perceptions that freshwater turtles universally are highly susceptible to any form of off-take and that high sub-adult and adult survival is crucial for achieving long-term population stability in freshwater turtles generally. In the case of C. rugosa, such generalities would produce overly cautious prescriptions for sustainable management.

  16. Vertical distribution of zooplankton: density dependence and evidence for an ideal free distribution with costs

    Directory of Open Access Journals (Sweden)

    Lampert Winfried

    2005-04-01

    Full Text Available Abstract Background In lakes with a deep-water algal maximum, herbivorous zooplankton are faced with a trade-off between high temperature but low food availability in the surface layers and low temperature but sufficient food in deep layers. It has been suggested that zooplankton (Daphnia faced with this trade-off distribute vertically according to an "Ideal Free Distribution (IFD with Costs". An experiment has been designed to test the density (competition dependence of the vertical distribution as this is a basic assumption of IFD theory. Results Experiments were performed in large, indoor mesocosms (Plankton Towers with a temperature gradient of 10°C and a deep-water algal maximum established below the thermocline. As expected, Daphnia aggregated at the interface between the two different habitats when their density was low. The distribution spread asymmetrically towards the algal maximum when the density increased until 80 % of the population dwelled in the cool, food-rich layers at high densities. Small individuals stayed higher in the water column than large ones, which conformed with the model for unequal competitors. Conclusion The Daphnia distribution mimics the predictions of an IFD with costs model. This concept is useful for the analysis of zooplankton distributions under a large suite of environmental conditions shaping habitat suitability. Fish predation causing diel vertical migrations can be incorporated as additional costs. This is important as the vertical location of grazing zooplankton in a lake affects phytoplankton production and species composition, i.e. ecosystem function.

  17. Quantum electrodynamical time-dependent density functional theory for many-electron systems on a lattice

    Science.gov (United States)

    Farzanehpour, Mehdi; Tokatly, Ilya; Nano-Bio Spectroscopy Group; ETSF Scientific Development Centre Team

    2015-03-01

    We present a rigorous formulation of the time-dependent density functional theory for interacting lattice electrons strongly coupled to cavity photons. We start with an example of one particle on a Hubbard dimer coupled to a single photonic mode, which is equivalent to the single mode spin-boson model or the quantum Rabi model. For this system we prove that the electron-photon wave function is a unique functional of the electronic density and the expectation value of the photonic coordinate, provided the initial state and the density satisfy a set of well defined conditions. Then we generalize the formalism to many interacting electrons on a lattice coupled to multiple photonic modes and prove the general mapping theorem. We also show that for a system evolving from the ground state of a lattice Hamiltonian any density with a continuous second time derivative is locally v-representable. Spanish Ministry of Economy and Competitiveness (Grant No. FIS2013-46159-C3-1-P), Grupos Consolidados UPV/EHU del Gobierno Vasco (Grant No. IT578-13), COST Actions CM1204 (XLIC) and MP1306 (EUSpec).

  18. Earthquake simulations with time-dependent nucleation and long-range interactions

    Directory of Open Access Journals (Sweden)

    J. H. Dieterich

    1995-01-01

    Full Text Available A model for rapid simulation of earthquake sequences is introduced which incorporates long-range elastic interactions among fault elements and time-dependent earthquake nucleation inferred from experimentally derived rate- and state-dependent fault constitutive properties. The model consists of a planar two-dimensional fault surface which is periodic in both the x- and y-directions. Elastic interactions among fault elements are represented by an array of elastic dislocations. Approximate solutions for earthquake nucleation and dynamics of earthquake slip are introduced which permit computations to proceed in steps that are determined by the transitions from one sliding state to the next. The transition-driven time stepping and avoidance of systems of simultaneous equations permit rapid simulation of large sequences of earthquake events on computers of modest capacity, while preserving characteristics of the nucleation and rupture propagation processes evident in more detailed models. Earthquakes simulated with this model reproduce many of the observed spatial and temporal characteristics of clustering phenomena including foreshock and aftershock sequences. Clustering arises because the time dependence of the nucleation process is highly sensitive to stress perturbations caused by nearby earthquakes. Rate of earthquake activity following a prior earthquake decays according to Omori's aftershock decay law and falls off with distance.

  19. Synthesizing mechanisms of density dependence in reef fishes: behavior, habitat configuration, and observational scale.

    Science.gov (United States)

    White, J Wilson; Samhouri, Jameal F; Stier, Adrian C; Wormald, Clare L; Hamilton, Scott L; Sandin, Stuart A

    2010-07-01

    Coral and rocky reef fish populations are widely used as model systems for the experimental exploration of density-dependent vital rates, but patterns of density-dependent mortality in these systems are not yet fully understood. In particular, the paradigm for strong, directly density-dependent (DDD) postsettlement mortality stands in contrast to recent evidence for inversely density-dependent (IDD) mortality. We review the processes responsible for DDD and IDD per capita mortality in reef fishes, noting that the pattern observed depends on predator and prey behavior, the spatial configuration of the reef habitat, and the spatial and temporal scales of observation. Specifically, predators tend to produce DDD prey mortality at their characteristic spatial scale of foraging, but prey mortality is IDD at smaller spatial scales due to attack-abatement effects (e.g., risk dilution). As a result, DDD mortality may be more common than IDD mortality on patch reefs, which tend to constrain predator foraging to the same scale as prey aggregation, eliminating attack-abatement effects. Additionally, adjacent groups of prey on continuous reefs may share a subset of refuges, increasing per capita refuge availability and relaxing DDD mortality relative to prey on patch reefs, where the patch edge could prevent such refuge sharing. These hypotheses lead to a synthetic framework to predict expected mortality patterns for a variety of scenarios. For nonsocial, nonaggregating species and species that aggregate in order to take advantage of spatially clumped refuges, IDD mortality is possible but likely superseded by DDD refuge competition, especially on patch reefs. By contrast, for species that aggregate socially, mortality should be IDD at the scale of individual aggregations but DDD at larger scales. The results of nearly all prior reef fish studies fit within this framework, although additional work is needed to test many of the predicted outcomes. This synthesis reconciles some

  20. Time-dependent density functional theory study on direction-dependent electron and hole transfer processes in molecular systems.

    Science.gov (United States)

    Partovi-Azar, Pouya; Kaghazchi, Payam

    2017-04-15

    We report on real-time time-dependent density functional theory calculations on direction-dependent electron and hole transfer processes in molecular systems. As a model system, we focus on α-sulfur. It is shown that time scale of the electron transfer process from a negatively charged S8 molecule to a neighboring neutral monomer is comparable to that of a strong infrared-active molecular vibrations of the dimer with one negatively charged monomer. This results in a strong coupling between the electrons and the nuclei motion which eventually leads to S8 ring opening before the electron transfer process is completed. The open-ring structure is found to be stable. The similar infrared-active peak in the case of hole transfer, however, is shown to be very weak and hence no significant scattering by the nuclei is possible. The presented approach to study the charge transfer processes in sulfur has direct applications in the increasingly growing research field of charge transport in molecular systems. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  1. Energy and centrality dependences of charged multiplicity density in relativistic nuclear collisions

    CERN Document Server

    Sá Ben-Hao; Tai, A; Zhou Dai Mei; Sa, Ben-Hao; Tai, An; Zhou, Dai-Mei

    2001-01-01

    Using a hadron and string cascade model, JPCIAE, the energy and centrality dependences of charged particle pseudorapidity density in relativistic nuclear collisions were studied. Within the framework of this model, both the relativistic $p+\\bar p$ experimental data and the PHOBOS and PHENIX $Au+Au$ data at $\\sqrt s_{nn}$=130 GeV could be reproduced fairly well without retuning the model parameters. The predictions for full RHIC energy $Au+Au$ collisions and for $Pb+Pb$ collisions at the ALICE energy were given. Participant nucleon distributions were calculated based on different methods. It was found that the number of participant nucleons, $$, is not a well defined variable both experimentally and theoretically. Therefore, it is inappropriate to use charged particle pseudorapidity density per participant pair as a function of $$ for distinguishing various theoretical models.

  2. Time-Dependent Density Functional Theory for Open Systems and Its Applications.

    Science.gov (United States)

    Chen, Shuguang; Kwok, YanHo; Chen, GuanHua

    2018-02-20

    Photovoltaic devices, electrochemical cells, catalysis processes, light emitting diodes, scanning tunneling microscopes, molecular electronics, and related devices have one thing in common: open quantum systems where energy and matter are not conserved. Traditionally quantum chemistry is confined to isolated and closed systems, while quantum dissipation theory studies open quantum systems. The key quantity in quantum dissipation theory is the reduced system density matrix. As the reduced system density matrix is an O(M! × M!) matrix, where M is the number of the particles of the system of interest, quantum dissipation theory can only be employed to simulate systems of a few particles or degrees of freedom. It is thus important to combine quantum chemistry and quantum dissipation theory so that realistic open quantum systems can be simulated from first-principles. We have developed a first-principles method to simulate the dynamics of open electronic systems, the time-dependent density functional theory for open systems (TDDFT-OS). Instead of the reduced system density matrix, the key quantity is the reduced single-electron density matrix, which is an N × N matrix where N is the number of the atomic bases of the system of interest. As the dimension of the key quantity is drastically reduced, the TDDFT-OS can thus be used to simulate the dynamics of realistic open electronic systems and efficient numerical algorithms have been developed. As an application, we apply the method to study how quantum interference develops in a molecular transistor in time domain. We include electron-phonon interaction in our simulation and show that quantum interference in the given system is robust against nuclear vibration not only in the steady state but also in the transient dynamics. As another application, by combining TDDFT-OS with Ehrenfest dynamics, we study current-induced dissociation of water molecules under scanning tunneling microscopy and follow its time dependent

  3. Noise-amplitude dependence of the invariant density for noisy, fully chaotic one-dimensional maps

    Science.gov (United States)

    Seshadri, S.; Balakrishnan, V.; Lakshmibala, S.

    1999-07-01

    We present some analytic, nonperturbative results for the invariant density ρ(x) for noisy one-dimensional maps at fully developed chaos. Under periodic boundary conditions, the Fourier expansion method is used to show precisely how noise makes ρ(x) absolutely continuous and smooths it out. Simple solvable models are used to illustrate the explicit dependence of ρ(x) on the amplitude η of the noise distribution, all the way from the case of zero noise (η-->0) to the completely noise-dominated limit (η=1).

  4. Density-Dependent Conformable Space-time Fractional Diffusion-Reaction Equation and Its Exact Solutions

    Science.gov (United States)

    Hosseini, Kamyar; Mayeli, Peyman; Bekir, Ahmet; Guner, Ozkan

    2018-01-01

    In this article, a special type of fractional differential equations (FDEs) named the density-dependent conformable fractional diffusion-reaction (DDCFDR) equation is studied. Aforementioned equation has a significant role in the modelling of some phenomena arising in the applied science. The well-organized methods, including the \\exp (-φ (\\varepsilon )) -expansion and modified Kudryashov methods are exerted to generate the exact solutions of this equation such that some of the solutions are new and have been reported for the first time. Results illustrate that both methods have a great performance in handling the DDCFDR equation.

  5. lambda. and. sigma. single-particle potentials with density-dependent effective interactions

    Energy Technology Data Exchange (ETDEWEB)

    Kohno, Michio

    1987-07-01

    Single-particle potentials experienced by the ..lambda.. and ..sigma.. in nuclei are calculated in a parameter-free way, using a microscopic density-dependent effective hyperon-nucleon interaction. The mean field becomes non-local because of the Majorana exchange character of the effective force. For the ..lambda.., single particle spectra are similar to those obtained from a standard Woods-Saxon potential, while the r.m.s. radii are systematically larger due to non-locality effects. For the ..sigma.., the calculated potential is much weaker. No bound p-state is predicted in light ..sigma.. hypernuclear systems.

  6. On the calculation of Δ for electronic excitations in time-dependent density-functional theory

    Science.gov (United States)

    Myneni, Hemanadhan; Casida, Mark E.

    2017-04-01

    Excited states are often treated within the context of time-dependent (TD) density-functional theory (DFT), making it important to be able to assign the excited spin-state symmetry. While there is universal agreement on how Δ , the difference between for ground and excited states, should be calculated in a wave-function-like formalism such as the Tamm-Dancoff approximation (TDA), confusion persists as to how to determine the spin-state symmetry of excited states in TD-DFT. We try to clarify the origins of this confusion by examining various possibilities for the parameters (σ1 ,σ2) in the formula

  7. Dependence of the structural parameters and properties of low density polyethylene on the synthesis conditions

    Directory of Open Access Journals (Sweden)

    MILOVAN R. JANKOVIC

    1999-10-01

    Full Text Available In a previous publicaitons from the authors' laboratotry a method was developed to predict the structure and properties of low density polyethylene (PE-LD that could be obtained over a very wide range of polymerization conditions. The method was proved using experimental data from the literature. However, some shortcomings of the method were noticed. The aim of this work was to overcome the shortcomings and to enable the better manipulation of experimental data using a computer. A computer program has been developed to establish the mathematical relationships between ethylene entropy and the structural parameters and density of Pe-LD. All available experimental data (more than 300 experimental points have elaborated and confirmed our mathematical models and our theoretical predictions.

  8. Testing and validation of high density resequencing microarray for broad range biothreat agents detection.

    Directory of Open Access Journals (Sweden)

    Tomasz A Leski

    Full Text Available Rapid and effective detection and identification of emerging microbiological threats and potential biowarfare agents is very challenging when using traditional culture-based methods. Contemporary molecular techniques, relying upon reverse transcription and/or polymerase chain reaction (RT-PCR/PCR provide a rapid and effective alternative, however, such assays are generally designed and optimized to detect only a limited number of targets, and seldom are capable of differentiation among variants of detected targets. To meet these challenges, we have designed a broad-range resequencing pathogen microarray (RPM for detection of tropical and emerging infectious agents (TEI including biothreat agents: RPM-TEI v 1.0 (RPM-TEI. The scope of the RPM-TEI assay enables detection and differential identification of 84 types of pathogens and 13 toxin genes, including most of the class A, B and C select agents as defined by the Centers for Disease Control and Prevention (CDC, Atlanta, GA. Due to the high risks associated with handling these particular target pathogens, the sensitivity validation of the RPM-TEI has been performed using an innovative approach, in which synthetic DNA fragments are used as templates for testing the assay's limit of detection (LOD. Assay specificity and sensitivity was subsequently confirmed by testing with full-length genomic nucleic acids of selected agents. The LOD for a majority of the agents detected by RPM-TEI was determined to be at least 10(4 copies per test. Our results also show that the RPM-TEI assay not only detects and identifies agents, but is also able to differentiate near neighbors of the same agent types, such as closely related strains of filoviruses of the Ebola Zaire group, or the Machupo and Lassa arenaviruses. Furthermore, each RPM-TEI assay results in specimen-specific agent gene sequence information that can be used to assess pathogenicity, mutations, and virulence markers, results that are not generally

  9. Interaction Models for Common Long-Range Dependence in Asset Prices Volatility

    Science.gov (United States)

    Teyssière, G.

    We consider a class of microeconomic models with interacting agents which replicate the main properties of asset prices time series: non-linearities in levels and common degree of long-memory in the volatilities and co-volatilities of multivariate time series. For these models, long-range dependence in asset price volatility is the consequence of swings in opinions and herding behavior of market participants, which generate switches in the heteroskedastic structure of asset prices. Thus, the observed long-memory in asset prices volatility might be the outcome of a change-point in the conditional variance process, a conclusion supported by a wavelet anaysis of the volatility series. This explains why volatility processes share only the properties of the second moments of long-memory processes, but not the properties of the first moments.

  10. Redshift space correlations and scale-dependent stochastic biasing of density peaks

    Science.gov (United States)

    Desjacques, Vincent; Sheth, Ravi K.

    2010-01-01

    We calculate the redshift space correlation function and the power spectrum of density peaks of a Gaussian random field. Our derivation, which is valid on linear scales k≲0.1hMpc-1, is based on the peak biasing relation given by Desjacques [Phys. Rev. DPRVDAQ1550-7998, 78, 103503 (2008)10.1103/PhysRevD.78.103503]. In linear theory, the redshift space power spectrum is Ppks(k,μ)=exp⁡(-f2σvel2k2μ2)[bpk(k)+bvel(k)fμ2]2Pδ(k), where μ is the angle with respect to the line of sight, σvel is the one-dimensional velocity dispersion, f is the growth rate, and bpk(k) and bvel(k) are k-dependent linear spatial and velocity bias factors. For peaks, the value of σvel depends upon the functional form of bvel. When the k dependence is absent from the square brackets and bvel is set to unity, the resulting expression is assumed to describe models where the bias is linear and deterministic, but the velocities are unbiased. The peak model is remarkable because it has unbiased velocities in this same sense—peak motions are driven by dark matter flows—but, in order to achieve this, bvel must be k dependent. We speculate that this is true in general: k dependence of the spatial bias will lead to k dependence of bvel even if the biased tracers flow with the dark matter. Because of the k dependence of the linear bias parameters, standard manipulations applied to the peak model will lead to k-dependent estimates of the growth factor that could erroneously be interpreted as a signature of modified dark energy or gravity. We use the Fisher formalism to show that the constraint on the growth rate f is degraded by a factor of 2 if one allows for a k-dependent velocity bias of the peak type. Our analysis also demonstrates that the Gaussian smoothing term is part and parcel of linear theory. We discuss a simple estimate of nonlinear evolution and illustrate the effect of the peak bias on the redshift space multipoles. For k≲0.1hMpc-1, the peak bias is deterministic but k

  11. Coupling Real-Time Time-Dependent Density Functional Theory with Polarizable Force Field.

    Science.gov (United States)

    Donati, Greta; Wildman, Andrew; Caprasecca, Stefano; Lingerfelt, David B; Lipparini, Filippo; Mennucci, Benedetta; Li, Xiaosong

    2017-11-02

    Real-time time-dependent density functional theory (RT-TDDFT) is a powerful tool for obtaining spectroscopic observables and understanding complex, time-dependent properties. Currently, performing RT-TDDFT calculations on large, fully quantum mechanical systems is not computationally feasible. Previously, polarizable mixed quantum mechanical and molecular mechanical (QM/MMPol) models have been successful in providing accurate, yet efficient, approximations to a fully quantum mechanical system. Here we develop a coupling scheme between induced dipole based QM/MMPol and RT-TDDFT. Our approach is validated by comparing calculated spectra with both real-time and linear-response TDDFT calculations. The model developed within provides an accurate method for performing RT-TDDFT calculations on extended systems while accounting for mutual polarization between the quantum mechanical and molecular mechanical regions.

  12. Giant quadrupole resonances in time-dependent density-matrix theory

    CERN Document Server

    Tohyama, M

    1999-01-01

    Damping of an isoscalar giant quadrupole resonance (GQR) in sup 4 sup 0 Ca is studied using an extended version of the time-dependent Hartree--Fock theory known as the time-dependent density-matrix theory (TDDM). The Skyrme III force is used as an effective interaction for the calculation of both a mean-field potential and a two-body correlation function, and a correlated state is used as the ground state on which GQR is built. It is found that the calculated strength of GQR is split into a major component and a minor component. The spreading width of the major component is found small as compared with experimental data. A double giant quadrupole resonance (DGQR) is also studied in TDDM, and it is found that DGQR given in TDDM has properties of the double phonon state of GQR calculated in the random phase approximation.

  13. Accurate high-harmonic spectra from time-dependent two-particle reduced density matrix theory

    CERN Document Server

    Lackner, Fabian; Sato, Takeshi; Ishikawa, Kenichi L; Burgdörfer, Joachim

    2016-01-01

    The accurate description of the non-linear response of many-electron systems to strong-laser fields remains a major challenge. Methods that bypass the unfavorable exponential scaling with particle number are required to address larger systems. In this paper we present a fully three-dimensional implementation of the time-dependent two-particle reduced density matrix (TD-2RDM) method for many-electron atoms. We benchmark this approach by a comparison with multi-configurational time-dependent Hartree-Fock (MCTDHF) results for the harmonic spectra of beryllium and neon. We show that the TD-2RDM is very well-suited to describe the non-linear atomic response and to reveal the influence of electron-correlation effects.

  14. Electric Double Layer electrostatics of spherical polyelectrolyte brushes with pH-dependent charge density

    Science.gov (United States)

    Li, Hao; Chen, Guang; Sinha, Shayandev; Das, Siddhartha; Soft Matter, Interfaces,; Energy Laboratory (Smiel) Team

    Understanding the electric double layer (EDL) electrostatics of spherical polyelectrolyte (PE) brushes, which are spherical particles grafted with PE layers, is essential for appropriate use of PE-grfated micro-nanoparticles for targeted drug delivery, oil recovery, water harvesting, emulsion stabilization, emulsion breaking, etc. Here we elucidate the EDL electrostatics of spherical PE brushes for the case where the PE exhibits pH-dependent charge density. This pH-dependence necessitates the consideration of explicit hydrogen ion concentration, which in turn dictates the distribution of monomers along the length of the grafted PE. This monomer distribution is shown to be a function of the nature of the sphere (metallic or a charged or uncharged dielectric or a liquid-filled sphere). All the calculations are performed for the case where the PE electrostatics can be decoupled from the PE elastic and excluded volume effects. Initial predictions are also provided for the case where such decoupling is not possible.

  15. A discontinuous functional for linear response time-dependent density functional theory: the exact-exchange kernel and approximate forms

    CERN Document Server

    Hellgren, M

    2013-01-01

    We present a detailed study of the exact-exchange (EXX) kernel of time-dependent density functional theory with an emphasis on its discontinuity at integer particle numbers. It was recently found that this exact property leads to sharp peaks and step features in the kernel that diverge in the dissociation limit of diatomic systems [Hellgren and Gross, Phys. Rev. A, 022514 (2012)]. To further analyze the discontinuity of the kernel we here make use of two different approximations to the EXX kernel: the PGG approximation and a common energy denominator approximation (CEDA). It is demonstrated that whereas the PGG approximation neglects the discontinuity the CEDA includes it explicitly. By studying model molecular systems it is shown that the so-called field counter-acting effect in the density functional description of molecular chains can be viewed in terms of the discontinuity of the static kernel. The role of the frequency dependence is also investigated, highlighting its importance for long-range charge tra...

  16. IMPLEMENTATION OF ZOOM-DEPENDENT CAMERA CALIBRATION IN CLOSE-RANGE PHOTOGRAMMETRY

    Directory of Open Access Journals (Sweden)

    C. S. Fraser

    2012-07-01

    Full Text Available The application of consumer-grade cameras for photogrammetric measurement has traditionally been subject to the requirement that imagery is recorded at fixed zoom and focus settings. The camera is then metrically calibrated, usually via self-calibration, for the lens setting employed. This requirement arises since camera parameters, and especially principal distance and lens distortion coefficients, vary significantly with zoom/focus setting. A recently developed process, titled zoom-dependent (Z-D calibration, removes the necessity for the zoom setting to be fixed during the image capture process. Implementation of Z-D calibration requires that the camera be pre-calibrated at four or more focal settings within the zoom range, nominally at shortest and longest focal lengths, and at two mid-zoom settings. This requirement, coupled with issues of data management in carrying different focal settings for potentially every image within a bundle adjustment, has largely accounted for the reason that Z-D calibration has not previously been implemented within COTS software for close-range photogrammetry. The objective of this paper is to describe the practical implementation of Z-D calibration within software, along with its associated workflow, and to discuss issues that impact upon the accuracy, reliability and appropriateness of the technique. Experimental testing is used to highlight the merits and shortcomings of ZD calibration.

  17. Context-dependent JPEG backward-compatible high-dynamic range image compression

    Science.gov (United States)

    Korshunov, Pavel; Ebrahimi, Touradj

    2013-10-01

    High-dynamic range (HDR) imaging is expected, together with ultrahigh definition and high-frame rate video, to become a technology that may change photo, TV, and film industries. Many cameras and displays capable of capturing and rendering both HDR images and video are already available in the market. The popularity and full-public adoption of HDR content is, however, hindered by the lack of standards in evaluation of quality, file formats, and compression, as well as large legacy base of low-dynamic range (LDR) displays that are unable to render HDR. To facilitate the wide spread of HDR usage, the backward compatibility of HDR with commonly used legacy technologies for storage, rendering, and compression of video and images are necessary. Although many tone-mapping algorithms are developed for generating viewable LDR content from HDR, there is no consensus of which algorithm to use and under which conditions. We, via a series of subjective evaluations, demonstrate the dependency of the perceptual quality of the tone-mapped LDR images on the context: environmental factors, display parameters, and image content itself. Based on the results of subjective tests, it proposes to extend JPEG file format, the most popular image format, in a backward compatible manner to deal with HDR images also. An architecture to achieve such backward compatibility with JPEG is proposed. A simple implementation of lossy compression demonstrates the efficiency of the proposed architecture compared with the state-of-the-art HDR image compression.

  18. Coherent reverberation model based on adiabatic normal mode theory in a range dependent shallow water environment

    Science.gov (United States)

    Li, Zhenglin; Zhang, Renhe; Li, Fenghua

    2010-09-01

    Ocean reverberation in shallow water is often the predominant background interference in active sonar applications. It is still an open problem in underwater acoustics. In recent years, an oscillation phenomenon of the reverberation intensity, due to the interference of the normal modes, has been observed in many experiments. A coherent reverberation theory has been developed and used to explain this oscillation phenomenon [F. Li et al., Journal of Sound and Vibration, 252(3), 457-468, 2002]. However, the published coherent reverberation theory is for the range independent environment. Following the derivations by F. Li and Ellis [D. D. Ellis, J. Acoust. Soc. Am., 97(5), 2804-2814, 1995], a general reverberation model based on the adiabatic normal mode theory in a range dependent shallow water environment is presented. From this theory the coherent or incoherent reverberation field caused by sediment inhomogeneity and surface roughness can be predicted. Observations of reverberation from the 2001 Asian Sea International Acoustic Experiment (ASIAEX) in the East China Sea are used to test the model. Model/data comparison shows that the coherent reverberation model can predict the experimental oscillation phenomenon of reverberation intensity and the vertical correlation of reverberation very well.

  19. NEUTRON-PROTON EFFECTIVE RANGE PARAMETERS AND ZERO-ENERGY SHAPE DEPENDENCE.

    Energy Technology Data Exchange (ETDEWEB)

    HACKENBURG, R.W.

    2005-06-01

    A completely model-independent effective range theory fit to available, unpolarized, np scattering data below 3 MeV determines the zero-energy free proton cross section {sigma}{sub 0} = 20.4287 {+-} 0.0078 b, the singlet apparent effective range r{sub s} = 2.754 {+-} 0.018{sub stat} {+-} 0.056{sub syst} fm, and improves the error slightly on the parahydrogen coherent scattering length, a{sub c} = -3.7406 {+-} 0.0010 fm. The triplet and singlet scattering lengths and the triplet mixed effective range are calculated to be a{sub t} = 5.4114 {+-} 0.0015 fm, a{sub s} = -23.7153 {+-} 0.0043 fm, and {rho}{sub t}(0,-{epsilon}{sub t}) = 1.7468 {+-} 0.0019 fm. The model-independent analysis also determines the zero-energy effective ranges by treating them as separate fit parameters without the constraint from the deuteron binding energy {epsilon}{sub t}. These are determined to be {rho}{sub t}(0,0) = 1.705 {+-} 0.023 fm and {rho}{sub s}(0,0) = 2.665 {+-} 0.056 fm. This determination of {rho}{sub t}(0,0) and {rho}{sub s}(0,0) is most sensitive to the sparse data between about 20 and 600 keV, where the correlation between the determined values of {rho}{sub t}(0,0) and {rho}{sub s}(0,0) is at a minimum. This correlation is responsible for the large systematic error in r{sub s}. More precise data in this range are needed. The present data do not event determine (with confidence) that {rho}{sub t}(0,0) {ne} {rho}{sub t}(0, -{epsilon}{sub t}), referred to here as ''zero-energy shape dependence''. The widely used measurement of {sigma}{sub 0} = 20.491 {+-} 0.014 b from W. Dilg, Phys. Rev. C 11, 103 (1975), is argued to be in error.

  20. Time-dependent density functional theory for ion diffusion in electrochemical systems.

    Science.gov (United States)

    Jiang, Jian; Cao, Dapeng; Jiang, De-en; Wu, Jianzhong

    2014-07-16

    We introduce a generic form of time-dependent density functional theory (TDDFT) to describe ion diffusion in electrochemical systems to account for steric effects and electrostatic correlations neglected in the Poisson-Nernst-Planck equations. An efficient numerical algorithm is proposed to analyze the charging kinetics of electric double layers in model electrochemical systems that consist of spherical ions in a dielectric continuum confined between two planar electrodes. By comparing the theoretical predictions from TDDFT and conventional electrokinetic methods for constant-voltage charging of the model electrochemical cells, we demonstrate that thermodynamic non-ideality plays a pivotal role in electrodiffusion even at relatively low electrolyte concentrations, and this effect cannot be captured by the lattice-gas model for the excluded volume effects. In particular, TDDFT predicts 'wave-like' variation of the ionic density profiles that has not been identified in previous investigations. At conditions where there are no significant correlations between electric double layers from opposite electrodes, the charging kinetics follows an exponential behavior with a linear dependence of the relaxation time on the cell thickness in excellent agreement with the equivalent circuit model. However, the conventional electrokinetic model breaks down when the electrodes are at small separation, in particular for systems with low ionic strength or high charging voltage. We also find that ionic screening retards the charging kinetics at low salt concentrations, but has the opposite effect at large salt concentrations.

  1. Kinetic modeling of rhamnolipid production by Pseudomonas aeruginosa PAO1 including cell density-dependent regulation.

    Science.gov (United States)

    Henkel, Marius; Schmidberger, Anke; Vogelbacher, Markus; Kühnert, Christian; Beuker, Janina; Bernard, Thomas; Schwartz, Thomas; Syldatk, Christoph; Hausmann, Rudolf

    2014-08-01

    The production of rhamnolipid biosurfactants by Pseudomonas aeruginosa is under complex control of a quorum sensing-dependent regulatory network. Due to a lack of understanding of the kinetics applicable to the process and relevant interrelations of variables, current processes for rhamnolipid production are based on heuristic approaches. To systematically establish a knowledge-based process for rhamnolipid production, a deeper understanding of the time-course and coupling of process variables is required. By combining reaction kinetics, stoichiometry, and experimental data, a process model for rhamnolipid production with P. aeruginosa PAO1 on sunflower oil was developed as a system of coupled ordinary differential equations (ODEs). In addition, cell density-based quorum sensing dynamics were included in the model. The model comprises a total of 36 parameters, 14 of which are yield coefficients and 7 of which are substrate affinity and inhibition constants. Of all 36 parameters, 30 were derived from dedicated experimental results, literature, and databases and 6 of them were used as fitting parameters. The model is able to describe data on biomass growth, substrates, and products obtained from a reference batch process and other validation scenarios. The model presented describes the time-course and interrelation of biomass, relevant substrates, and products on a process level while including a kinetic representation of cell density-dependent regulatory mechanisms.

  2. Herbivore-specific, density-dependent induction of plant volatiles: honest or "cry wolf" signals?

    Directory of Open Access Journals (Sweden)

    Kaori Shiojiri

    Full Text Available Plants release volatile chemicals upon attack by herbivorous arthropods. They do so commonly in a dose-dependent manner: the more herbivores, the more volatiles released. The volatiles attract predatory arthropods and the amount determines the probability of predator response. We show that seedlings of a cabbage variety (Brassica oleracea var. capitata, cv Shikidori also show such a response to the density of cabbage white (Pieris rapae larvae and attract more (naive parasitoids (Cotesia glomerata when there are more herbivores on the plant. However, when attacked by diamondback moth (Plutella xylostella larvae, seedlings of the same variety (cv Shikidori release volatiles, the total amount of which is high and constant and thus independent of caterpillar density, and naive parasitoids (Cotesia vestalis of diamondback moth larvae fail to discriminate herbivore-rich from herbivore-poor plants. In contrast, seedlings of another cabbage variety of B. oleracea (var. acephala: kale respond in a dose-dependent manner to the density of diamondback moth larvae and attract more parasitoids when there are more herbivores. Assuming these responses of the cabbage cultivars reflect behaviour of at least some genotypes of wild plants, we provide arguments why the behaviour of kale (B. oleracea var acephala is best interpreted as an honest signaling strategy and that of cabbage cv Shikidori (B. oleracea var capitata as a "cry wolf" signaling strategy, implying a conflict of interest between the plant and the enemies of its herbivores: the plant profits from being visited by the herbivore's enemies, but the latter would be better off by visiting other plants with more herbivores. If so, evolutionary theory on alarm signaling predicts consequences of major interest to students of plant protection, tritrophic systems and communication alike.

  3. Correlated electron dynamics and memory in time-dependent density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Thiele, Mark

    2009-07-28

    Time-dependent density functional theory (TDDFT) is an exact reformulation of the time-dependent many-electron Schroedinger equation, where the problem of many interacting electrons is mapped onto the Kohn-Sham system of noninteracting particles which reproduces the exact electronic density. In the Kohn-Sham system all non-classical many-body effects are incorporated in the exchange-correlation potential which is in general unknown and needs to be approximated. It is the goal of this thesis to investigate the connection between memory effects and correlated electron dynamics in strong and weak fields. To this end one-dimensional two-electron singlet systems are studied. At the same time these systems include the onedimensional helium atom model, which is an established system to investigate the crucial effects of correlated electron dynamics in external fields. The studies presented in this thesis show that memory effects are negligible for typical strong field processes. Here the approximation of the spatial nonlocality is of primary importance. For the photoabsorption spectra on the other hand the neglect of memory effects leads to qualitative and quantitative errors, which are shown to be connected to transitions of double excitation character. To develop a better understanding of the conditions under which memory effects become important quantum fluid dynamics has been found to be especially suitable. It represents a further exact reformulation of the quantum mechanic many-body problem which is based on hydrodynamic quantities such as density and velocity. Memory effects are shown to be important whenever the velocity field develops strong gradients and dissipative effects contribute. (orig.)

  4. Dependence of galaxy stellar populations on density at z=0.3--1.5

    Science.gov (United States)

    McKenzie, Eric Howie

    I investigate the evolution of galaxy clustering and dependence on environment by comparing galaxies' spatial correlation lengths with their photometrically- determined spectral energy distribution (SED) types. This complements work on the density-morphology relation and expands our understanding of galaxy evolution at high redshifts (z FLAMINGOS Extragalactic Survey (FLAMEX), extending the techniques developed in the SPICES survey to examine the density-SED relation and its redshift dependence for a much larger sample. The results indicate that the density-SED relation is already established by z = 1.5, with no substantive evolution between that epoch to the present, and that the relation is in place prior to cluster assembly. I also investigate how clustering differs for extremely red objects (EROs) versus non-ERO galaxies and for L > L* versus L > .6L* galaxies, and I compare the spatial correlation lengths for specific clusters to the cluster detection significance. Finally, I present a separate project on the dissipation rates of open star clusters within our own galaxy. Studying the age distribution of the complete sample of 997 clusters for which age values are available, I propose that clusters are disrupted by at least three different mechanisms acting on different timescales: a long-term mechanism that produces a cluster half-life of 354 ± 13 million years, a medium-term mechanism with a cluster half-life of 105 ± 30 million years, and a short-term mechanism with a cluster half-life of 5.0 ± .8 million years. I also estimate that 220 ± 70 clusters are formed per ten million years within our current limits of observation.

  5. Free-ranging domestic cats (Felis catus) on public lands: estimating density, activity, and diet in the Florida Keys

    Science.gov (United States)

    Cove, Michael V.; Gardner, Beth; Simons, Theodore R.; Kays, Roland; O'Connell, Allan F.

    2017-01-01

    Feral and free-ranging domestic cats (Felis catus) can have strong negative effects on small mammals and birds, particularly in island ecosystems. We deployed camera traps to study free-ranging cats in national wildlife refuges and state parks on Big Pine Key and Key Largo in the Florida Keys, USA, and used spatial capture–recapture models to estimate cat abundance, movement, and activities. We also used stable isotope analyses to examine the diet of cats captured on public lands. Top population models separated cats based on differences in movement and detection with three and two latent groups on Big Pine Key and Key Largo, respectively. We hypothesize that these latent groups represent feral, semi-feral, and indoor/outdoor house cats based on the estimated movement parameters of each group. Estimated cat densities and activity varied between the two islands, with relatively high densities (~4 cats/km2) exhibiting crepuscular diel patterns on Big Pine Key and lower densities (~1 cat/km2) exhibiting nocturnal diel patterns on Key Largo. These differences are most likely related to the higher proportion of house cats on Big Pine relative to Key Largo. Carbon and nitrogen isotope ratios from hair samples of free-ranging cats (n = 43) provided estimates of the proportion of wild and anthropogenic foods in cat diets. At the population level, cats on both islands consumed mostly anthropogenic foods (>80% of the diet), but eight individuals were effective predators of wildlife (>50% of the diet). We provide evidence that cat groups within a population move different distances, exhibit different activity patterns, and that individuals consume wildlife at different rates, which all have implications for managing this invasive predator.

  6. High energy storage density over a broad temperature range in sodium bismuth titanate-based lead-free ceramics.

    Science.gov (United States)

    Yang, Haibo; Yan, Fei; Lin, Ying; Wang, Tong; Wang, Fen

    2017-08-18

    A series of (1-x)Bi0.48La0.02Na0.48Li0.02Ti0.98Zr0.02O3-xNa0.73Bi0.09NbO3 ((1-x)LLBNTZ-xNBN) (x = 0-0.14) ceramics were designed and fabricated using the conventional solid-state sintering method. The phase structure, microstructure, dielectric, ferroelectric and energy storage properties of the ceramics were systematically investigated. The results indicate that the addition of Na0.73Bi0.09NbO3 (NBN) could decrease the remnant polarization (P r ) and improve the temperature stability of dielectric constant obviously. The working temperature range satisfying TCC 150 °C ≤±15% of this work spans over 400 °C with the compositions of x ≥ 0.06. The maximum energy storage density can be obtained for the sample with x = 0.10 at room temperature, with an energy storage density of 2.04 J/cm(3) at 178 kV/cm. In addition, the (1-x)LLBNTZ-xNBN ceramics exhibit excellent energy storage properties over a wide temperature range from room temperature to 90 °C. The values of energy storage density and energy storage efficiency is 0.91 J/cm(3) and 79.51%, respectively, for the 0.90LLBNTZ-0.10NBN ceramic at the condition of 100 kV/cm and 90 °C. It can be concluded that the (1-x)LLBNTZ-xNBN ceramics are promising lead-free candidate materials for energy storage devices over a broad temperature range.

  7. Warming and nitrogen affect size structuring and density dependence in a host–parasitoid food web

    Science.gov (United States)

    de Sassi, Claudio; Staniczenko, Phillip P. A.; Tylianakis, Jason M.

    2012-01-01

    Body size is a major factor constraining the trophic structure and functioning of ecological communities. Food webs are known to respond to changes in basal resource abundance, and climate change can initiate compounding bottom-up effects on food-web structure through altered resource availability and quality. However, the effects of climate and co-occurring global changes, such as nitrogen deposition, on the density and size relationships between resources and consumers are unknown, particularly in host–parasitoid food webs, where size structuring is less apparent. We use a Bayesian modelling approach to explore the role of consumer and resource density and body size on host–parasitoid food webs assembled from a field experiment with factorial warming and nitrogen treatments. We show that the treatments increased resource (host) availability and quality (size), leading to measureable changes in parasitoid feeding behaviour. Parasitoids interacted less evenly within their host range and increasingly focused on abundant and high-quality (i.e. larger) hosts. In summary, we present evidence that climate-mediated bottom-up effects can significantly alter food-web structure through both density- and trait-mediated effects. PMID:23007092

  8. Age-dependent differences in brain tissue microstructure assessed with neurite orientation dispersion and density imaging.

    Science.gov (United States)

    Merluzzi, Andrew P; Dean, Douglas C; Adluru, Nagesh; Suryawanshi, Gaurav S; Okonkwo, Ozioma C; Oh, Jennifer M; Hermann, Bruce P; Sager, Mark A; Asthana, Sanjay; Zhang, Hui; Johnson, Sterling C; Alexander, Andrew L; Bendlin, Barbara B

    2016-07-01

    Human aging is accompanied by progressive changes in executive function and memory, but the biological mechanisms underlying these phenomena are not fully understood. Using neurite orientation dispersion and density imaging, we sought to examine the relationship between age, cellular microstructure, and neuropsychological scores in 116 late middle-aged, cognitively asymptomatic participants. Results revealed widespread increases in the volume fraction of isotropic diffusion and localized decreases in neurite density in frontal white matter regions with increasing age. In addition, several of these microstructural alterations were associated with poorer performance on tests of memory and executive function. These results suggest that neurite orientation dispersion and density imaging is capable of measuring age-related brain changes and the neural correlates of poorer performance on tests of cognitive functioning, largely in accordance with published histological findings and brain-imaging studies of people of this age range. Ultimately, this study sheds light on the processes underlying normal brain development in adulthood, knowledge that is critical for differentiating healthy aging from changes associated with dementia. Copyright © 2016 Elsevier Inc. All rights reserved.

  9. Numerical implementation of time-dependent density functional theory for extended systems in extreme environments

    Energy Technology Data Exchange (ETDEWEB)

    Baczewski, Andrew David; Shulenburger, Luke; Desjarlais, Michael Paul; Magyar, Rudolph J.

    2014-02-01

    In recent years, DFT-MD has been shown to be a useful computational tool for exploring the properties of WDM. These calculations achieve excellent agreement with shock compression experiments, which probe the thermodynamic parameters of the Hugoniot state. New X-ray Thomson Scattering diagnostics promise to deliver independent measurements of electronic density and temperature, as well as structural information in shocked systems. However, they require the development of new levels of theory for computing the associated observables within a DFT framework. The experimentally observable x-ray scattering cross section is related to the electronic density-density response function, which is obtainable using TDDFT - a formally exact extension of conventional DFT that describes electron dynamics and excited states. In order to develop a capability for modeling XRTS data and, more generally, to establish a predictive capability for rst principles simulations of matter in extreme conditions, real-time TDDFT with Ehrenfest dynamics has been implemented in an existing PAW code for DFT-MD calculations. The purpose of this report is to record implementation details and benchmarks as the project advances from software development to delivering novel scienti c results. Results range from tests that establish the accuracy, e ciency, and scalability of our implementation, to calculations that are veri ed against accepted results in the literature. Aside from the primary XRTS goal, we identify other more general areas where this new capability will be useful, including stopping power calculations and electron-ion equilibration.

  10. Quantifying the range of cross-correlated fluctuations using a q- L dependent AHXA coefficient

    Science.gov (United States)

    Wang, Fang; Wang, Lin; Chen, Yuming

    2018-03-01

    Recently, based on analogous height cross-correlation analysis (AHXA), a cross-correlation coefficient ρ×(L) has been proposed to quantify the levels of cross-correlation on different temporal scales for bivariate series. A limitation of this coefficient is that it cannot capture the full information of cross-correlations on amplitude of fluctuations. In fact, it only detects the cross-correlation at a specific order fluctuation, which might neglect some important information inherited from other order fluctuations. To overcome this disadvantage, in this work, based on the scaling of the qth order covariance and time delay L, we define a two-parameter dependent cross-correlation coefficient ρq(L) to detect and quantify the range and level of cross-correlations. This new version of ρq(L) coefficient leads to the formation of a ρq(L) surface, which not only is able to quantify the level of cross-correlations, but also allows us to identify the range of fluctuation amplitudes that are correlated in two given signals. Applications to the classical ARFIMA models and the binomial multifractal series illustrate the feasibility of this new coefficient ρq(L) . In addition, a statistical test is proposed to quantify the existence of cross-correlations between two given series. Applying our method to the real life empirical data from the 1999-2000 California electricity market, we find that the California power crisis in 2000 destroys the cross-correlation between the price and the load series but does not affect the correlation of the load series during and before the crisis.

  11. Inflammation triggers emergency granulopoiesis through a density-dependent feedback mechanism.

    Directory of Open Access Journals (Sweden)

    Derek W Cain

    Full Text Available Normally, neutrophil pools are maintained by homeostatic mechanisms that require the transcription factor C/EBPα. Inflammation, however, induces neutrophilia through a distinct pathway of "emergency" granulopoiesis that is dependent on C/EBPβ. Here, we show in mice that alum triggers emergency granulopoiesis through the IL-1RI-dependent induction of G-CSF. G-CSF/G-CSF-R neutralization impairs proliferative responses of hematopoietic stem and progenitor cells (HSPC to alum, but also abrogates the acute mobilization of BM neutrophils, raising the possibility that HSPC responses to inflammation are an indirect result of the exhaustion of BM neutrophil stores. The induction of neutropenia, via depletion with Gr-1 mAb or myeloid-specific ablation of Mcl-1, elicits G-CSF via an IL-1RI-independent pathway, stimulating granulopoietic responses indistinguishable from those induced by adjuvant. Notably, C/EBPβ, thought to be necessary for enhanced generative capacity of BM, is dispensable for increased proliferation of HSPC to alum or neutropenia, but plays a role in terminal neutrophil differentiation during granulopoietic recovery. We conclude that alum elicits a transient increase in G-CSF production via IL-1RI for the mobilization of BM neutrophils, but density-dependent feedback sustains G-CSF for accelerated granulopoiesis.

  12. Dynamics of a recovering Arctic bird population: the importance of climate, density dependence, and site quality

    Science.gov (United States)

    Bruggeman, Jason E.; Swem, Ted; Andersen, David E.; Kennedy, Patricia L.; Nigro, Debora A.

    2015-01-01

    Intrinsic and extrinsic factors affect vital rates and population-level processes, and understanding these factors is paramount to devising successful management plans for wildlife species. For example, birds time migration in response, in part, to local and broadscale climate fluctuations to initiate breeding upon arrival to nesting territories, and prolonged inclement weather early in the breeding season can inhibit egg-laying and reduce productivity. Also, density-dependent regulation occurs in raptor populations, as territory size is related to resource availability. Arctic Peregrine Falcons (Falco peregrinus tundrius; hereafter Arctic peregrine) have a limited and northern breeding distribution, including the Colville River Special Area (CRSA) in the National Petroleum Reserve–Alaska, USA. We quantified influences of climate, topography, nest productivity, prey habitat, density dependence, and interspecific competition affecting Arctic peregrines in the CRSA by applying the Dail-Madsen model to estimate abundance and vital rates of adults on nesting cliffs from 1981 through 2002. Arctic peregrine abundance increased throughout the 1980s, which spanned the population's recovery from DDT-induced reproductive failure, until exhibiting a stationary trend in the 1990s. Apparent survival rate (i.e., emigration; death) was negatively correlated with the number of adult Arctic peregrines on the cliff the previous year, suggesting effects of density-dependent population regulation. Apparent survival and arrival rates (i.e., immigration; recruitment) were higher during years with earlier snowmelt and milder winters, and apparent survival was positively correlated with nesting season maximum daily temperature. Arrival rate was positively correlated with average Arctic peregrine productivity along a cliff segment from the previous year and initial abundance was positively correlated with cliff height. Higher cliffs with documented higher productivity (presumably

  13. Impact of spin-orbit density dependent potential in heavy ion reactions forming Se nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Rajni; Sharma, Ishita; Sharma, Manoj K. [Thapar University, School of Physics and Materials Science, Patiala (India); Jain, Deepika [Mata Gujri College, Department of Physics, Fatehgarh Sahib (India)

    2017-10-15

    The Skyrme energy density formalism is employed to explore the effect of spin-orbit interaction potential by considering a two nucleon transfer process via various entrance channels such as {sup 23}Na + {sup 49}V, {sup 25}Mg + {sup 47}Ti, {sup 27}Al + {sup 45}Sc, {sup 29}Si + {sup 43}Ca and {sup 31}P + {sup 41}K, all forming the same compound system {sup 72}Se*, using both spherical as well as quadrupole deformed (β{sub 2}) nuclei. For spherical nuclei, the spin-orbit density part V{sub J} of nuclear potential remains unaffected with the transfer of two nucleons from the target to the projectile, however, show notable variation in magnitude after inclusion of deformation effects. Likewise, deformations play an important role in the spin-orbit density independent part V{sub P}, as the fusion pocket start appears, which otherwise diminish for the spherical nuclei. Further, the effect of an increase in the N/Z ratio of Se is explored on V{sub J} as well as V{sub P} and results are compared with transfer channels. In addition to this, the role of double spin-orbit parameters (W{sub 0} and W{sub 0}{sup '}) with relative contribution of the isoscalar and isovector parts of spin-orbit strength is explored in view of SkI2, SkI3 and SkI4 Skyrme forces. Beside this, the decay path of {sup 72}Se* nucleus formed in {sup 27}Al + {sup 45}Sc reaction is investigated within the framework of dynamical cluster decay model (DCM), where the nuclear proximity potential is obtained by both Skyrme energy density formalism (SEDF) and proximity pocket formula. The fusion hindrance in the {sup 27}Al + {sup 45}Sc reaction is also addressed via the barrier lowering parameter ΔV{sub B}. Finally, the contribution of spin-orbit density dependent interaction potential is estimated for the {sup 27}Al + {sup 45}Sc reaction using single (W{sub 0} or W{sub 0}{sup '}) and double spin-orbit parameters (W{sub 0} and W{sub 0}{sup '}). (orig.)

  14. Temperature dependence of electron density and electron-electron interactions in monolayer epitaxial graphene grown on SiC

    Science.gov (United States)

    Liu, Chieh-Wen; Chuang, Chiashain; Yang, Yanfei; Elmquist, Randolph E.; Ho, Yi-Ju; Lee, Hsin-Yen; Liang, Chi-Te

    2017-06-01

    We report carrier density measurements and electron-electron (e-e) interactions in monolayer epitaxial graphene grown on SiC. The temperature (T)-independent carrier density determined from the Shubnikov-de Haas (SdH) oscillations clearly demonstrates that the observed logarithmic temperature dependence of the Hall slope in our system must be due to e-e interactions. Since the electron density determined from conventional SdH measurements does not depend on e-e interactions based on Kohn’s theorem, SdH experiments appear to be more reliable compared with the classical Hall effect when one studies the T dependence of the carrier density in the low T regime. On the other hand, the logarithmic T dependence of the Hall slope δR xy /δB can be used to probe e-e interactions even when the conventional conductivity method is not applicable due to strong electron-phonon scattering.

  15. Strongly angle-dependent magnetoresistance in Weyl semimetals with long-range disorder

    Science.gov (United States)

    Behrends, Jan; Bardarson, Jens H.

    2017-08-01

    The chiral anomaly in Weyl semimetals states that the left- and right-handed Weyl fermions, constituting the low energy description, are not individually conserved, resulting, for example, in a negative magnetoresistance in such materials. Recent experiments see strong indications of such an anomalous resistance response; however, with a response that at strong fields is more sharply peaked for parallel magnetic and electric fields than expected from simple theoretical considerations. Here, we uncover a mechanism, arising from the interplay between the angle-dependent Landau-level structure and long-range scalar disorder, that has the same phenomenology. In particular, we analytically show, and numerically confirm, that the internode scattering time decreases exponentially with the angle between the magnetic field and the Weyl node separation in the large field limit, while it is insensitive to this angle at weak magnetic fields. Since, in the simplest approximation, the internode scattering time is proportional to the anomaly-related conductivity, this feature may be related to the experimental observations of a sharply peaked magnetoresistance.

  16. Long-range dependence in returns and volatility of global gold market amid financial crises

    Science.gov (United States)

    Omane-Adjepong, Maurice; Boako, Gideon

    2017-04-01

    Using sampled historical daily gold market data from 07-03-1985 to 06-01-2015, and building on a related work by Bentes (2016), this paper examines the presence of long-range dependence (LRD) in the world's gold market returns and volatility, accounting for structural breaks. The sampled gold market data was divided into subsamples based on four global crises: the September 1992 collapse of the European Exchange Rate Mechanism (ERM), the Asian financial crisis of mid-1997, the Subprime meltdown of 2007, and the recent European sovereign debt crisis, which hit the world's market with varying effects. LRD test was carried-out on the full-sample and subsample periods using three semiparametric methods-before and after adjusting for structural breaks. The results show insignificant evidence of LRD in gold returns. However, very diminutive evidence is found for periods characterized by financial/economic shocks, with no significant detections for post-shock periods. Collectively, this is indicative that the gold market is less speculative, and hence could be somehow less risky for hedging and portfolio diversification.

  17. Effects of dispersal, shrubs, and density-dependent morality on seed and seedling distributions in temperate forests

    Science.gov (United States)

    Janneke Hille Ris Lambers; James S. Clark

    2003-01-01

    Processes limiting recruitment of trees may have large impacts on forest dynamics. In this paper, we determined the effects of dispersal, shrubs (Rhododendron maximum), and density-dependent mortality on seed and seedling distributions of Southern Appalachian trees. We quantified the spatial distribution of seed rain, seed bank densities, first-year...

  18. Inelastic collisions and density-dependent excitation suppression in a 87Sr optical lattice clock

    Science.gov (United States)

    Bishof, M.; Martin, M. J.; Swallows, M. D.; Benko, C.; Lin, Y.; Quéméner, G.; Rey, A. M.; Ye, J.

    2011-11-01

    We observe two-body loss of 3P0 87Sr atoms trapped in a one-dimensional optical lattice. We measure loss rate coefficients for atomic samples between 1 and 6 μK that are prepared either in a single nuclear-spin sublevel or with equal populations in two sublevels. The measured temperature and nuclear-spin preparation dependence of rate coefficients agree well with calculations and reveal that rate coefficients for distinguishable atoms are only slightly enhanced over those of indistinguishable atoms. We further observe a suppression of excitation and losses during interrogation of the 1S0-3P0 transition as density increases and Rabi frequency decreases, which suggests the presence of strong interactions in our dynamically driven many-body system.

  19. Inelastic collisions and density-dependent excitation suppression in a {sup 87}Sr optical lattice clock

    Energy Technology Data Exchange (ETDEWEB)

    Bishof, M.; Martin, M. J.; Swallows, M. D.; Benko, C.; Lin, Y.; Quemener, G.; Rey, A. M.; Ye, J. [JILA, NIST and University of Colorado, Boulder, Colorado 80309-0440 (United States); Department of Physics, University of Colorado, Boulder, Colorado 80309-0390 (United States)

    2011-11-15

    We observe two-body loss of {sup 3} P{sub 0} {sup 87}Sr atoms trapped in a one-dimensional optical lattice. We measure loss rate coefficients for atomic samples between 1 and 6 {mu}K that are prepared either in a single nuclear-spin sublevel or with equal populations in two sublevels. The measured temperature and nuclear-spin preparation dependence of rate coefficients agree well with calculations and reveal that rate coefficients for distinguishable atoms are only slightly enhanced over those of indistinguishable atoms. We further observe a suppression of excitation and losses during interrogation of the {sup 1} S{sub 0}-{sup 3} P{sub 0} transition as density increases and Rabi frequency decreases, which suggests the presence of strong interactions in our dynamically driven many-body system.

  20. Self-consistent RPA and the time-dependent density matrix approach

    Energy Technology Data Exchange (ETDEWEB)

    Schuck, P. [Institut de Physique Nucleaire, Orsay (France); CNRS et Universite Joseph Fourier, Laboratoire de Physique et Modelisation des Milieux Condenses, Grenoble (France); Tohyama, M. [Kyorin University School of Medicine, Mitaka, Tokyo (Japan)

    2016-10-15

    The time-dependent density matrix (TDDM) or BBGKY (Bogoliubov, Born, Green, Kirkwood, Yvon) approach is decoupled and closed at the three-body level in finding a natural representation of the latter in terms of a quadratic form of two-body correlation functions. In the small amplitude limit an extended RPA coupled to an also extended second RPA is obtained. Since including two-body correlations means that the ground state cannot be a Hartree-Fock state, naturally the corresponding RPA is upgraded to Self-Consistent RPA (SCRPA) which was introduced independently earlier and which is built on a correlated ground state. SCRPA conserves all the properties of standard RPA. Applications to the exactly solvable Lipkin and the 1D Hubbard models show good performances of SCRPA and TDDM. (orig.)

  1. Plant diversity increases with the strength of negative density dependence at the global scale

    Science.gov (United States)

    LaManna, Joseph A.; Mangan, Scott A.; Alonso, Alfonso; Bourg, Norman; Brockelman, Warren Y.; Bunyavejchewin, Sarayudh; Chang, Li-Wan; Chiang, Jyh-Min; Chuyong, George B.; Clay, Keith; Condit, Richard; Cordell, Susan; Davies, Stuart J.; Furniss, Tucker J.; Giardina, Christian P.; Gunatilleke, I.A.U. Nimal; Gunatilleke, C.V. Savitri; He, Fangliang; Howe, Robert W.; Hubbell, Stephen P.; Hsieh, Chang-Fu; Inman-Narahari, Faith M.; Janik, David; Johnson, Daniel J.; Kenfack, David; Korte, Lisa; Kral, Kamil; Larson, Andrew J.; Lutz, James A.; McMahon, Sean M.; McShea, William J.; Memiaghe, Herve R.; Nathalang, Anuttara; Novotny, Vojtech; Ong, Perry S.; Orwig, David A.; Ostertag, Rebecca; Parker, Geoffrey G.; Phillips, Richard P.; Sack, Lawren; Sun, I-Fang; Tello, J. Sebastian; Thomas, Duncan W.; Turner, Benjamin L.; Vela Diaz, Dilys M.; Vrska, Tomas; Weiblen, George D.; Wolf, Amy; Yap, Sandra; Myers, Jonathan A.

    2017-01-01

    Theory predicts that higher biodiversity in the tropics is maintained by specialized interactions among plants and their natural enemies that result in conspecific negative density dependence (CNDD). By using more than 3000 species and nearly 2.4 million trees across 24 forest plots worldwide, we show that global patterns in tree species diversity reflect not only stronger CNDD at tropical versus temperate latitudes but also a latitudinal shift in the relationship between CNDD and species abundance. CNDD was stronger for rare species at tropical versus temperate latitudes, potentially causing the persistence of greater numbers of rare species in the tropics. Our study reveals fundamental differences in the nature of local-scale biotic interactions that contribute to the maintenance of species diversity across temperate and tropical communities.

  2. Optical conductivity of magnetized warm dense matter using time-dependent density functional theory

    Science.gov (United States)

    Jensen, Daniel; Baczewski, Andrew; Cangi, Attila; Hansen, Stephanie

    2017-10-01

    In magnetized liner inertial fusion (MagLIF), matter is subjected to 10-30 T magnetic fields that are then flux compressed to strengths greater than 1 kT. The determination of transport properties in such extreme fields and the warm dense regime are of vital importance to experimental design. We show how time-dependent density functional theory (TDDFT) can be used to extract optical conductivities in and beyond the linear response regime. Building on work studying scalar linear perturbations to warm dense matter, we present the necessary theoretical modifications as well as some preliminary results. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy's National Nuclear S.

  3. Time-dependent quantum many-body systems. Linear response, electronic transport, and reduced density matrices

    Energy Technology Data Exchange (ETDEWEB)

    Appel, H.

    2007-05-15

    In part I of this work we present a double-pole approximation (DPA) to the response equations of time-dependent density functional theory (TDDFT). The double-pole approximation provides an exact description of systems with two strongly coupled excitations which are isolated from the rest of the spectrum. In contrast to the traditional single-pole approximation of TDDFT the DPA also yields corrections to the Kohn-Sham oscillator strengths. We also demonstrate how to invert the double-pole solution which allows us to predict matrix elements of the exchange-correlation kernel f{sub xc} from experimental input. We attempt some first steps towards a time-dependent generalization of reduced density matrix functional theory (RDMFT). In part II we derive equations of motion for natural orbitals and occupation numbers. Using the equation of motion for the occupation numbers we show that an adiabatic extension of presently known ground-state functionals of static RDMFT always leads to occupation numbers which are constant in time. From the stationary conditions of the equations of motion for the N-body correlations (correlated parts of the N-body matrices) we derive a new class of ground-state functionals which can be used in static RDMFT. Applications are presented for a one-dimensional model system where the time-dependent many-body Schroedinger equation can be propagated numerically. We use optimal control theory to find optimized laser pulses for transitions in a model for atomic Helium. From the numerically exact correlated wavefunction we extract the exact time evolution of natural orbitals and occupation numbers for (i) laser-driven Helium and (ii) electron-ion scattering. Part III of this work considers time-dependent quantum transport within TDDFT. We present an algorithm for the calculation of extended eigenstates of single-particle Hamiltonians which is especially tailored to a finite-difference discretization of the Schroedinger equation. We consider the

  4. Systematic measurements of opacity dependence on temperature, density, and atomic number at stellar interior conditions

    Science.gov (United States)

    Nagayama, Taisuke

    2017-10-01

    Model predictions for iron opacity are notably different from measurements performed at matter conditions similar to the boundary between the solar radiation and convection zones. The calculated iron opacities have narrower spectral lines, weaker quasi-continuum at short wavelength, and deeper opacity windows than the measurements. If correct, these measurements help resolve a decade old problem in solar physics. A key question is therefore: What is responsible for the model-data discrepancy? The answer is complex because the experiments are challenging and opacity theories depend on multiple entangled physical processes such as the influence of completeness and accuracy of atomic states, line broadening, contributions from myriad transitions from excited states, and multi-photon absorption processes. To help determine the cause of this discrepancy, a systematic study of opacity variation with temperature, density, and atomic number is underway. Measurements of chromium, iron, and nickel opacities have been performed at two different temperatures and densities. The collection of measured opacities provides constraints on hypotheses to explain the discrepancy. We will discuss implications of measured opacities, experimental errors, and possible opacity model refinements. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.

  5. Groucho-mediated repression may result from a histone deacetylase-dependent increase in nucleosome density.

    Directory of Open Access Journals (Sweden)

    Clint J Winkler

    2010-04-01

    Full Text Available Groucho (Gro is a Drosophila melanogaster transcriptional corepressor that directly interacts with the histone deacetylase Rpd3. Although previous studies suggest that this interaction is required for repression of Gro-responsive reporters in cultured cells, the in vivo significance of this interaction and the mechanism by which it leads to repression remain largely unexplored. In this study, we show that Gro is partially dependent on Rpd3 for repression, supporting the idea that Rpd3-mediated repression is one mode of Gro-mediated repression. We demonstrate that Gro colocalizes with Rpd3 to the chromatin of a target gene and that this is accompanied by the deacetylation of specific lysines within the N-terminal tails of histones H3 and H4. Gro overexpression leads to wing patterning defects and ectopic repression in the wing disc of transcription directed by the vestigial quadrant enhancer. These effects are reversed by the histone deacetylase inhibitors TSA and HC-Toxin and by the reduction of Rpd3 gene dosage. Furthermore, repression of the vestigial quadrant enhancer is accompanied by a Gro-mediated increase in nucleosome density, an effect that is reversed by histone deacetylase inhibitors. We propose a model in which Gro-mediated histone deacetylation results in increased nucleosome density leading to transcriptional repression.

  6. Groucho-mediated repression may result from a histone deacetylase-dependent increase in nucleosome density.

    Science.gov (United States)

    Winkler, Clint J; Ponce, Alberto; Courey, Albert J

    2010-04-13

    Groucho (Gro) is a Drosophila melanogaster transcriptional corepressor that directly interacts with the histone deacetylase Rpd3. Although previous studies suggest that this interaction is required for repression of Gro-responsive reporters in cultured cells, the in vivo significance of this interaction and the mechanism by which it leads to repression remain largely unexplored. In this study, we show that Gro is partially dependent on Rpd3 for repression, supporting the idea that Rpd3-mediated repression is one mode of Gro-mediated repression. We demonstrate that Gro colocalizes with Rpd3 to the chromatin of a target gene and that this is accompanied by the deacetylation of specific lysines within the N-terminal tails of histones H3 and H4. Gro overexpression leads to wing patterning defects and ectopic repression in the wing disc of transcription directed by the vestigial quadrant enhancer. These effects are reversed by the histone deacetylase inhibitors TSA and HC-Toxin and by the reduction of Rpd3 gene dosage. Furthermore, repression of the vestigial quadrant enhancer is accompanied by a Gro-mediated increase in nucleosome density, an effect that is reversed by histone deacetylase inhibitors. We propose a model in which Gro-mediated histone deacetylation results in increased nucleosome density leading to transcriptional repression.

  7. Farmers’ spatial behaviour, demographic density dependence and the spread of Neolithic agriculture in Central Europe

    Directory of Open Access Journals (Sweden)

    Serge Svizzero

    2015-12-01

    Full Text Available Since the early 1970s, the demic diffusion model is the cornerstone of the migrationist approach of the European neolithization. It considers the latter as a slow, gradual and unintentionally process. During the last decade its relevance has been challenged by the observed variability of the spread, such as the extreme one exhibited by the LBK expansion in Central Europe. To account for it, migration - which is usually explained by exogenous push-pull factors - must rather be viewed as the result of farmers’ spatial behaviour. We adopt this approach and highlight the influence on farmers’ location choice of agglomeration effects and Allee effect in settled areas, an influence which also leads to define migration endogenously. Both effects – which find support in archaeological records - exhibit demographic density dependence and help to explain an observed but counter-intuitive result. Indeed, a high demographic density is associated with a slower rate of expansion of farming; this may result from strong agglomeration and Allee effects which hinder – or even stop - the migratory spread of agriculture. Farmers’ cooperation with indigenous populations are leading to acculturation of the latter and therefore may reduce the influence of both effects, fostering farmers’ migration.

  8. Density-dependent effective baryon–baryon interaction from chiral three-baryon forces

    Energy Technology Data Exchange (ETDEWEB)

    Petschauer, Stefan, E-mail: stefan.petschauer@ph.tum.de [Physik Department, Technische Universität München, D-85747 Garching (Germany); Haidenbauer, Johann [Institute for Advanced Simulation, Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich, D-52425 Jülich (Germany); Kaiser, Norbert [Physik Department, Technische Universität München, D-85747 Garching (Germany); Meißner, Ulf-G. [Institute for Advanced Simulation, Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich, D-52425 Jülich (Germany); Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, D-53115 Bonn (Germany); Bethe Center for Theoretical Physics, Universität Bonn, D-53115 Bonn (Germany); Weise, Wolfram [Physik Department, Technische Universität München, D-85747 Garching (Germany)

    2017-01-15

    A density-dependent effective potential for the baryon–baryon interaction in the presence of the (hyper)nuclear medium is constructed, based on the leading (irreducible) three-baryon forces derived within SU(3) chiral effective field theory. We evaluate the contributions from three classes: contact terms, one-pion exchange and two-pion exchange. In the strangeness-zero sector we recover the known result for the in-medium nucleon–nucleon interaction. Explicit expressions for the ΛN in-medium potential in (asymmetric) nuclear matter are presented. Our results are suitable for implementation into calculations of (hyper)nuclear matter. In order to estimate the low-energy constants of the leading three-baryon forces we introduce the decuplet baryons as explicit degrees of freedom and construct the relevant terms in the minimal non-relativistic Lagrangian. With these, the constants are estimated through decuplet saturation. Utilizing this approximation we provide numerical results for the effect of the three-body force in symmetric nuclear matter and pure neutron matter on the ΛN interaction. A moderate repulsion that increases with density is found in comparison to the free ΛN interaction.

  9. Performance of Tamm-Dancoff approximation on nonadiabatic couplings by time-dependent density functional theory

    Science.gov (United States)

    Hu, Chunping; Sugino, Osamu; Watanabe, Kazuyuki

    2014-02-01

    The Tamm-Dancoff approximation (TDA), widely used in physics to decouple excitations and de-excitations, is well known to be good for the calculation of excitation energies but not for oscillator strengths. In particular, the sum rule is violated in the latter case. The same concern arises within the TDA in the calculation of nonadiabatic couplings (NACs) by time-dependent density functional theory (TDDFT), due to the similarities in the TDDFT formulations of NACs and oscillator strengths [C. Hu, H. Hirai, and O. Sugino, J. Chem. Phys. 127, 064103 (2007)]. In this study, we present a systematic evaluation of the performance of TDDFT/TDA for the calculation of NACs. In the cases we considered, including a variety of systems possessing Jahn-Teller and Renner-Teller intersections, as well as an example with accidental conical intersections, it is found that the TDDFT/TDA performs better than the full TDDFT, contrary to the conjecture that the TDA might cause the NAC results to deteriorate and violate the sum rule. The surprisingly good performance of the TDA for NACs is probably because the TDA can partially compensate for the local-density-approximation error and give better excitation energies in the vicinity of intersections of potential energy surfaces. Our study also shows that it is important to use the TDA based on the rigorous full-TDDFT formulation of NACs, instead of using it based on an alternative approximate formulation.

  10. Transgenerational effects modulate density-dependent prophylactic resistance to viral infection in a lepidopteran pest.

    Science.gov (United States)

    Wilson, Kenneth; Graham, Robert I

    2015-03-01

    There is an increasing appreciation of the importance of transgenerational effects on offspring fitness, including in relation to immune function and disease resistance. Here, we assess the impact of parental rearing density on offspring resistance to viral challenge in an insect species expressing density-dependent prophylaxis (DDP); i.e. the adaptive increase in resistance or tolerance to pathogen infection in response to crowding. We quantified survival rates in larvae of the cotton leafworm (Spodoptera littoralis) from either gregarious- or solitary-reared parents following challenge with the baculovirus S. littoralis nucleopolyhedrovirus. Larvae from both the parental and offspring generations exhibited DDP, with gregarious-reared larvae having higher survival rates post-challenge than solitary-reared larvae. Within each of these categories, however, survival following infection was lower in those larvae from gregarious-reared parents than those from solitary-reared, consistent with a transgenerational cost of DDP immune upregulation. This observation demonstrates that crowding influences lepidopteran disease resistance over multiple generations, with potential implications for the dynamics of host-pathogen interactions. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  11. Modelling density-dependent flow and solute transport at the Lake Tutchewop saline disposal complex, Victoria

    Science.gov (United States)

    Simmons, Craig T.; Narayan, Kumar A.

    1998-05-01

    Intercepted saline groundwaters and drainage effluent from irrigation are commonly stored in both natural and artificial saline disposal basins throughout the Murray-Darling Basin of Australia. Their continued use as wastewater evaporation sites requires an understanding of existing groundwater dynamics. The useful of individual basins, their sustainability and possible environmental impacts remain largely unknown. In this work, the movement of salt to the underlying groundwater system from Lake Tutchewop, a saline disposal complex in north-central Victoria, was modelled in cross-section. Due to the salinity contrast between the hypersaline basin waters and the regional groundwater, it was necessary to simulate density-dependent flow behaviour. Under certain conditions, these density-stratified systems may become unstable leading to the onset of convective behaviour, which greatly increases the movement of salt from the basin to the groundwater system. Modelled concentration profiles in the aquifer system and calculated seepage rates from the basin show that Lake Tutchewop is stable under its present operating regime. The downward movement of salt is mainly controlled by diffusion and dispersion. The calibrated model was used to assess the impact of several management scenarios using time-dependent boundary conditions for lake salinity and water levels. The influence of heterogeneous basin linings on ensuing salt flux rates is examined, and results show that increased solute transport will occur under such conditions. A sensitivity analysis performed on governing variables showed that salt fluxes were most sensitive to lake salinity levels. A solute Rayleigh number defined in terms of basin salinity and hydrogeologic parameters is seen to be an effective tool for predicting the long term behaviour of such saline disposal basins. The models and concepts developed in this work may find application in the design and management of saline disposal complexes.

  12. Spin and density longitudinal response of quantum dots in the time-dependent local-spin-density approximation

    Science.gov (United States)

    Serra, Ll.; Barranco, M.; Emperador, A.; Pi, M.; Lipparini, E.

    1999-06-01

    The longitudinal dipole response of a quantum dot has been calculated in the far-infrared regime using local-spin-density-functional theory. We have studied the coupling between the collective spin and density modes as a function of the magnetic field. We have found that the spin dipole mode and single-particle excitations have a sizable overlap, and that the magnetoplasmon modes can be excited by the dipole spin operator if the dot is spin polarized. The frequency of the dipole spin edge mode presents an oscillation which is clearly filling factor (ν) related. We have found that the spin dipole mode is especially soft for even-ν values. Results for selected numbers of electrons and confining potentials are discussed.

  13. Overpotential-induced lability of the electronic overlap factor in long-range electrochemical electron transfer: charge and distance dependence

    DEFF Research Database (Denmark)

    Kornyshev, A. A.; Kuznetsov, A. M.; Nielsen, Jens Ulrik

    2000-01-01

    Long-distance electrochemical electron transfer exhibits approximately exponential dependence on the electron transfer distance. On the basis of a jellium model of the metal surface we show that the slope of the logarithm of the current vs. the transfer distance also depends strongly...... on the electrode charge. The slope is smaller the more negative the charge density due to enhanced extension of the surface electronic density profile on the solution side, and thereby better electronic overlap with the reacting molecule. The effect is sensitive to the bulk electron density of the metal...... and the localization of the electronic state at the molecular reactant site. Effects similar to these have been observed experimentally and could be common for electronically light metals....

  14. Time-dependent density-functional theory in massively parallel computer architectures: the octopus project

    Science.gov (United States)

    Andrade, Xavier; Alberdi-Rodriguez, Joseba; Strubbe, David A.; Oliveira, Micael J. T.; Nogueira, Fernando; Castro, Alberto; Muguerza, Javier; Arruabarrena, Agustin; Louie, Steven G.; Aspuru-Guzik, Alán; Rubio, Angel; Marques, Miguel A. L.

    2012-06-01

    Octopus is a general-purpose density-functional theory (DFT) code, with a particular emphasis on the time-dependent version of DFT (TDDFT). In this paper we present the ongoing efforts to achieve the parallelization of octopus. We focus on the real-time variant of TDDFT, where the time-dependent Kohn-Sham equations are directly propagated in time. This approach has great potential for execution in massively parallel systems such as modern supercomputers with thousands of processors and graphics processing units (GPUs). For harvesting the potential of conventional supercomputers, the main strategy is a multi-level parallelization scheme that combines the inherent scalability of real-time TDDFT with a real-space grid domain-partitioning approach. A scalable Poisson solver is critical for the efficiency of this scheme. For GPUs, we show how using blocks of Kohn-Sham states provides the required level of data parallelism and that this strategy is also applicable for code optimization on standard processors. Our results show that real-time TDDFT, as implemented in octopus, can be the method of choice for studying the excited states of large molecular systems in modern parallel architectures.

  15. Layer- and substrate-dependent charge density wave criticality in 1T-TiSe2

    Science.gov (United States)

    Kolekar, Sadhu; Bonilla, Manuel; Ma, Yujing; Coy Diaz, Horacio; Batzill, Matthias

    2018-01-01

    TiSe2 exhibits an unconventional charge density wave (CDW) that has been associated with an excitonic insulator transition. Here we investigate how the CDW transition is changed for single to few layers compared to bulk TiSe2. TiSe2 grown by molecular beam epitaxy on HOPG- or MoS2-substrates is characterized by variable temperature scanning tunneling microscopy and spectroscopy. We show that the CDW state persists for the monolayer but the transition temperature T CDW is significantly increased compared to the bulk. Furthermore, T CDW is strongly dependent on the substrate material. Within the model of an excitonic insulator phase for TiSe2, the substrate dependence may be associated with variations of the excitonic binding energies by the dielectric properties of the substrate. Interestingly, for single layer TiSe2 on HOPG we also observe peaks in the tunneling spectra below 50 K, which are tentatively assigned to coherence peaks of an excitonic condensate. The peaks are observed below T CDW of ~230 K, suggesting that an excitonic insulator induced CDW can exist without a phase coherent state.

  16. Dependence of rate of physical erosion on orientation and density in mineralised tissues.

    Science.gov (United States)

    Boyde, A

    1984-01-01

    Bone, dentine and enamel samples were treated with a gas-propelled jet of an abrasive, NaHCO3, which is physically much softer than any of these tissues in their fully mineralised condition. It was nevertheless found that they are all eroded by this treatment, which can therefore be used as a new kind of qualitative test of physical properties relating to wear resistance. General correlations were found between both degree of mineralisation and between structure orientation and erosion rate, surface-parallel-feature zones being worn more rapidly. Bone domains with surface-parallel collagen were eroded faster than those with perpendicular lamellae even if they were more densely mineralised. Rates of dentine wear depended on both density and tubule orientation, with peritubular zones and better mineralised incremental layers being more resistant. Enamel tufts wear more rapidly than the surrounding well mineralised regions. Enamel diazones wear less than parazones (areas with surface parallel prisms). At the prism scale, enamel is removed more rapidly near prism boundary discontinuities and in tubular enamel, at tubule walls. As regards the common orientation dependent effects seen in these three tissues, a cohesive explanation would be that structure discontinuities can be better exploited in a wear process if they allow cleavage from the surface; which tendency will increase with parallelism to the surface.

  17. Oxidized low-density lipoproteins upregulate proline oxidase to initiate ROS-dependent autophagy.

    Science.gov (United States)

    Zabirnyk, Olga; Liu, Wei; Khalil, Shadi; Sharma, Anit; Phang, James M

    2010-03-01

    Epidemiological studies showed that high levels of oxidized low-density lipoproteins (oxLDLs) are associated with increased cancer risk. We examined the direct effect of physiologic concentrations oxLDL on cancer cells. OxLDLs were cytotoxic and activate both apoptosis and autophagy. OxLDLs have ligands for peroxisome proliferator-activated receptor gamma and upregulated proline oxidase (POX) through this nuclear receptor. We identified 7-ketocholesterol (7KC) as a main component responsible for the latter. To elucidate the role of POX in oxLDL-mediated cytotoxicity, we knocked down POX via small interfering RNA and found that this (i) further reduced viability of cancer cells treated with oxLDL; (ii) decreased oxLDL-associated reactive oxygen species generation; (iii) decreased autophagy measured via beclin-1 protein level and light-chain 3 protein (LC3)-I into LC3-II conversion. Using POX-expressing cell model, we established that single POX overexpression was sufficient to activate autophagy. Thus, it led to autophagosomes accumulation and increased conversion of LC3-I into LC3-II. Moreover, beclin-1 gene expression was directly dependent on POX catalytic activity, namely the generation of POX-dependent superoxide. We conclude that POX is critical in the cellular response to the noxious effects of oxLDL by activating protective autophagy.

  18. Demographic models reveal the shape of density dependence for a specialist insect herbivore on variable host plants.

    Science.gov (United States)

    Miller, Tom E X

    2007-07-01

    1. It is widely accepted that density-dependent processes play an important role in most natural populations. However, persistent challenges in our understanding of density-dependent population dynamics include evaluating the shape of the relationship between density and demographic rates (linear, concave, convex), and identifying extrinsic factors that can mediate this relationship. 2. I studied the population dynamics of the cactus bug Narnia pallidicornis on host plants (Opuntia imbricata) that varied naturally in relative reproductive effort (RRE, the proportion of meristems allocated to reproduction), an important plant quality trait. I manipulated per-plant cactus bug densities, quantified subsequent dynamics, and fit stage-structured models to the experimental data to ask if and how density influences demographic parameters. 3. In the field experiment, I found that populations with variable starting densities quickly converged upon similar growth trajectories. In the model-fitting analyses, the data strongly supported a model that defined the juvenile cactus bug retention parameter (joint probability of surviving and not dispersing) as a nonlinear decreasing function of density. The estimated shape of this relationship shifted from concave to convex with increasing host-plant RRE. 4. The results demonstrate that host-plant traits are critical sources of variation in the strength and shape of density dependence in insects, and highlight the utility of integrated experimental-theoretical approaches for identifying processes underlying patterns of change in natural populations.

  19. Decadal declines in avian herbivore reproduction: density-dependent nutrition and phenological mismatch in the Arctic

    Science.gov (United States)

    Ross, Megan V.; Alisaukas, Ray T.; Douglas, David C.; Kellett, Dana K.

    2017-01-01

    A full understanding of population dynamics depends not only on estimation of mechanistic contributions of recruitment and survival, but also knowledge about the ecological processes that drive each of these vital rates. The process of recruitment in particular may be protracted over several years, and can depend on numerous ecological complexities until sexually mature adulthood is attained. We addressed long-term declines (23 breeding seasons, 1992–2014) in the per capita production of young by both Ross's Geese (Chen rossii) and Lesser Snow Geese (Chen caerulescens caerulescens) nesting at Karrak Lake in Canada's central Arctic. During this period, there was a contemporaneous increase from 0.4 to 1.1 million adults nesting at this colony. We evaluated whether (1) density-dependent nutritional deficiencies of pre-breeding females or (2) phenological mismatch between peak gosling hatch and peak forage quality, inferred from NDVI on the brood-rearing areas, may have been behind decadal declines in the per capita production of goslings. We found that, in years when pre-breeding females arrived to the nesting grounds with diminished nutrient reserves, the proportional composition of young during brood-rearing was reduced for both species. Furthermore, increased mismatch between peak gosling hatch and peak forage quality contributed additively to further declines in gosling production, in addition to declines caused by delayed nesting with associated subsequent negative effects on clutch size and nest success. The degree of mismatch increased over the course of our study because of advanced vegetation phenology without a corresponding advance in Goose nesting phenology. Vegetation phenology was significantly earlier in years with warm surface air temperatures measured in spring (i.e., 25 May–30 June). We suggest that both increased phenological mismatch and reduced nutritional condition of arriving females were behind declines in population-level recruitment

  20. Time-dependent probability density functions and information geometry in stochastic logistic and Gompertz models

    Science.gov (United States)

    Tenkès, Lucille-Marie; Hollerbach, Rainer; Kim, Eun-jin

    2017-12-01

    A probabilistic description is essential for understanding growth processes in non-stationary states. In this paper, we compute time-dependent probability density functions (PDFs) in order to investigate stochastic logistic and Gompertz models, which are two of the most popular growth models. We consider different types of short-correlated multiplicative and additive noise sources and compare the time-dependent PDFs in the two models, elucidating the effects of the additive and multiplicative noises on the form of PDFs. We demonstrate an interesting transition from a unimodal to a bimodal PDF as the multiplicative noise increases for a fixed value of the additive noise. A much weaker (leaky) attractor in the Gompertz model leads to a significant (singular) growth of the population of a very small size. We point out the limitation of using stationary PDFs, mean value and variance in understanding statistical properties of the growth in non-stationary states, highlighting the importance of time-dependent PDFs. We further compare these two models from the perspective of information change that occurs during the growth process. Specifically, we define an infinitesimal distance at any time by comparing two PDFs at times infinitesimally apart and sum these distances in time. The total distance along the trajectory quantifies the total number of different states that the system undergoes in time, and is called the information length. We show that the time-evolution of the two models become more similar when measured in units of the information length and point out the merit of using the information length in unifying and understanding the dynamic evolution of different growth processes.

  1. Density dependence of the entropy and the solvation shell structure in supercritical water via molecular dynamics simulation.

    Science.gov (United States)

    Ma, Haibo

    2012-06-07

    We perform molecular dynamics simulations of supercritical water (SCW) with a wide range of densities along a near critical isotherm using the simple point charge extended (SPC/E) pair potential in order to study the entropy and the solvation shell structure around a central water molecule. It is shown that both the translational and orientational two-particle correlation entropy terms can serve as the metrics of the translational-orientational structural orders in water and it is revealed that the translational structural order is very sensitive to the density variation in the gas-like and liquid-like region, while the orientational structural order is much more dependent upon compression in the medium-density SCW region. The comparison of the magnitudes of the full thermodynamic excess entropy and two-particle correlation entropy confirms the recent findings that the many-body terms other than two-body ones also present significant and non-neglectable contributions to the full excess entropy for the highly anomalous fluids like water. The analysis of entropy terms as a function of intermolecular distance and the orientational distribution functions as well as the three-dimensional spatial distribution functions indicate that the structural order occurs only in a much more diffused first solvation shell due to the elongated hydrogen bonds under supercritical conditions. It is revealed that no obvious second or higher neighbor shells occur in SCW, in contrast with the feature of normal liquid water that the anomalous decrease of translational order upon compression occurs mainly in the second shell.

  2. Roles of density-dependent growth and life history evolution in accounting for fisheries-induced trait changes.

    Science.gov (United States)

    Eikeset, Anne Maria; Dunlop, Erin S; Heino, Mikko; Storvik, Geir; Stenseth, Nils C; Dieckmann, Ulf

    2016-12-27

    The relative roles of density dependence and life history evolution in contributing to rapid fisheries-induced trait changes remain debated. In the 1930s, northeast Arctic cod (Gadus morhua), currently the world's largest cod stock, experienced a shift from a traditional spawning-ground fishery to an industrial trawl fishery with elevated exploitation in the stock's feeding grounds. Since then, age and length at maturation have declined dramatically, a trend paralleled in other exploited stocks worldwide. These trends can be explained by demographic truncation of the population's age structure, phenotypic plasticity in maturation arising through density-dependent growth, fisheries-induced evolution favoring faster-growing or earlier-maturing fish, or a combination of these processes. Here, we use a multitrait eco-evolutionary model to assess the capacity of these processes to reproduce 74 y of historical data on age and length at maturation in northeast Arctic cod, while mimicking the stock's historical harvesting regime. Our results show that model predictions critically depend on the assumed density dependence of growth: when this is weak, life history evolution might be necessary to prevent stock collapse, whereas when a stronger density dependence estimated from recent data is used, the role of evolution in explaining fisheries-induced trait changes is diminished. Our integrative analysis of density-dependent growth, multitrait evolution, and stock-specific time series data underscores the importance of jointly considering evolutionary and ecological processes, enabling a more comprehensive perspective on empirically observed stock dynamics than previous studies could provide.

  3. The extended Thomas Fermi kinetic energy density functional with position-dependent effective mass in one dimension

    Science.gov (United States)

    Bencheikh, K.; Berkane, K.; Bouizane, S.

    2004-11-01

    The point canonical transformations map the Schrödinger equation with constant mass to a wave equation with a position-dependent effective mass. Using such a technique we derive, for a one-dimensional inhomogeneous system of noninteracting fermions with density ρ(x) and spatially dependent effective mass distribution m(x), the semiclassical kinetic energy density functional τ(ρ) in the so-called extended Thomas-Fermi model up to order planck2. For a given position-dependent mass, we compare numerically the total semiclassical kinetic energy with its exact quantum mechanical counterpart. The qualitative agreement is excellent.

  4. Pressure dependence of the optical properties of the charge-density-wave compound LaTe2

    Energy Technology Data Exchange (ETDEWEB)

    Lavagnini, M.; Sacchetti, A.; Degiorgi, L.; /Zurich, ETH; Arcangeletti, E.; Baldassarre, L.; Postorino, P.; Lupi, S.; /Rome U.; Perucchi, A.; /INFM, Trieste; Shin, K.Y.; Fisher, I.R.; /Stanford U., Geballe Lab.

    2009-12-14

    We report the pressure dependence of the optical response of LaTe{sub 2}, which is deep in the charge-density-wave (CDW) ground state even at 300 K. The reflectivity spectrum is collected in the mid-infrared spectral range at room temperature and at pressures between 0 and 7 GPa. We extract the energy scale due to the single particle excitation across the CDW gap and the Drude weight. We establish that the gap decreases upon compressing the lattice, while the Drude weight increases. This signals a reduction in the quality of nesting upon applying pressure, therefore inducing a lesser impact of the CDW condensate on the electronic properties of LaTe{sub 2}. The consequent suppression of the CDW gap leads to a release of additional charge carriers, manifested by the shift of weight from the gap feature into the metallic component of the optical response. On the contrary, the power-law behavior, seen in the optical conductivity at energies above the gap excitation and indicating a weakly interacting limit within the Tomonaga-Luttinger liquid scenario, seems to be only moderately dependent on pressure.

  5. Correction of stress-depended changes of glucoproteid platelet receptors activity by electromagnetic radiation of terahertz range

    Directory of Open Access Journals (Sweden)

    V.F. Kirichuk

    2010-09-01

    Full Text Available The research goal is correction of stress-depended changes of glucoproteid (Gp platelet receptors activity by electromagnetic radiation of terahertz range. Influence of electromagnetic waves of terahertz range at the frequency of molecular spectrum of radiation and absorption of nitrogen oxide on lectin-induced platelet aggregation of white rats in the stressed condition was investigated

  6. Doping dependence of the charge-density-wave order in HgBa2CuO4+δ

    Science.gov (United States)

    Yu, Biqiong

    Following the original discovery of short-range charge-density-wave (CDW) order in the orthorhombic double-layer cuprate YBa2Cu3O6+δ (YBCO) below optimal doping, resonant X-ray scattering measurements have revealed that the simple tetragonal single-layer compound HgBa2CuO4+δ (Hg1201; Tc = 71 K) exhibits short-range CDW order as well. Here we report on the doping dependence of the CDW order in Hg1201 and contrast our results with the extensive data available for YBCO. Work done in collaboration with: W. Tabis, G. Yu, M.J. Veit, N. BarisŬić, M.K. Chan, C.J. Dorow, X. Zhao, M. Greven (University of Minnesota); M. Bluschke, E. Weschke (BESSY, Berlin); T. Kolodziej, I. Bialo, A. Kozlowski (AGH, Krakow); M. Hepting, H. Gretarsson, M. Le Tacon, M. Minola, B. Keimer (MPI, Stuttgart); Ronny Sutarto (CLS, Saskatoon); Y. Li (PKU, Beijing); L. Braicovich, G. Dellea, G. Ghiringhelli (CNR-SPIN, Milano); A. Kreyssig, M. Ramazanoglu, A.I. Goldman (Iowa State University and Ames Lab); T. Schmitt (PSI, Switzerland). We acknowledge the support from US Department of Energy, Office of Basic Energy Sciences.

  7. Analysis of self-consistency effects in range-separated density-functional theory with Møller-Plesset perturbation theory

    DEFF Research Database (Denmark)

    Fromager, Emmanuel; Jensen, Hans Jørgen Aagaard

    2011-01-01

    -cluster theories, self-consistency effects are introduced in the density functional part, which for an exact solution requires iterations. They are generally assumed to be small but no detailed study has been performed so far. Here, the authors analyze self-consistency when using Møller-Plesset-type (MP......Range-separated density-functional theory combines wave function theory for the long-range part of the two-electron interaction with density-functional theory for the short-range part. When describing the long-range interaction with non-variational methods, such as perturbation or coupled......) perturbation theory for the long range interaction. The lowest-order self-consistency corrections to the wave function and the energy, that enter the perturbation expansions at the second and fourth order, respectively, are both expressed in terms of the one-electron reduced density matrix. The computational...

  8. Lianas escape self-thinning: Experimental evidence of positive density dependence in temperate lianas Celastrus orbiculatus and C. scandens

    Science.gov (United States)

    Leicht-Young, S. A.; Latimer, A.M.; Silander, J.A.

    2011-01-01

    The neighborhood density of plants strongly affects their growth, reproduction, and survival. In most cases, high density increases competition and negatively affects a focal plant in predictable ways, leading to the self-thinning law. There are, however, situations in which high densities of plants facilitate focal plant performance, resulting in positive density dependence. Despite their importance in forest gap dynamics and distinctive growth form, there have been very few studies of the effect of density on lianas or vines. We grew an invasive (Celastrus orbiculatus) and a native (Celastrus scandens) liana species together in three different density treatments, while also manipulating the light and support availability. We found that across treatment conditions, C. orbiculatus always out-performed C. scandens, showing greater relative growth rate in height and diameter, greater biomass and higher survival. Both species responded similarly to the density treatments: with plants in high density not showing a decrease in relative height growth rate compared to medium density. Aboveground biomass for C. scandens was not affected by density, while for C. orbiculatus, the most massive plants were growing in medium density without support. More surprisingly, survival analysis indicated that the two species both had significantly lower mortality rates in the highest density treatment; this trend held true across the other treatments of light and supports. More generally, this study demonstrates that these lianas can escape the consequences of high density and thus the self-thinning law that affects self-supporting plants. This suggests a broader hypothesis about lianas in general: their greater flexibility in allocating growth resources allows them to grow taller and thinner without collapsing and thereby potentially escape shading and mortality even at high densities.

  9. Wide Dynamic Range Multiband Infrared Radiometer for In-Fire Measurements of Wildland Fire Radiant Flux Density

    Science.gov (United States)

    Kremens, R.; Dickinson, M. B.; Hardy, C.; Skowronski, N.; Ellicott, E. A.; Schroeder, W.

    2016-12-01

    We have developed a wide dynamic range (24-bit) data acquisition system for collection of radiant flux density (FRFD) data from wildland fires. The data collection subsystem was designed as an Arduino `shield' and incorporates a 24-bit analog-to-digital converter, precision voltage reference, real time clock, microSD card interface, audible annuciator and interface for various digital communication interfaces (RS232, I2C, SPI, etc.). The complete radiometer system consists of our custom-designed `shield', a commercially available Arduino MEGA computer circuit board and a thermopile sensor -amplifier daughter board. Software design and development is greatly assisted by the availability of a library of public-domain, user-implemented software. The daughter board houses a 5-band radiometer using thermopiles designed for this experiment (Dexter Research Corp., Dexter, MI) to allow determination of the total FRFD from the fire (using a wide band thermopile with a KRS-5 window, 0.1 - 30 um), the FRFD as would be received by an orbital asset like MODIS (3.95 um center wavelength (CWL) and 10.95 CWL, corresponding to MODIS bands 21/22 and 31, respectively) and wider bandpass (0.1-5.5 um and 8-14 um) corresponding to the FRFD recorded by `MWIR' and `LWIR' imaging systems. We required a very wide dynamic range system in order to be able to record the flux density from `cold' ground before the fire, through the `hot' flaming combustion stage, to the `cool' phase after passage of the fire front. The recording dynamic range required (with reasonable resolution at the lowest temperatures) is on the order of 106, which is not currently available in commercial instrumentation at a price point, size or feature set that is suitable for wildland fire investigations. The entire unit, along with rechargeable battery power supply is housed in a fireproof aluminum chassis box, which is then mounted on a mast at a height of 5 - 7 m above the fireground floor. We will report initial

  10. Sapling growth rates reveal conspecific negative density dependence in a temperate forest.

    Science.gov (United States)

    Ramage, Benjamin S; Johnson, Daniel J; Gonzalez-Akre, Erika; McShea, William J; Anderson-Teixeira, Kristina J; Bourg, Norman A; Clay, Keith

    2017-10-01

    Local tree species diversity is maintained in part by conspecific negative density dependence (CNDD). This pervasive mechanism occurs in a variety of forms and ecosystems, but research to date has been heavily skewed toward tree seedling survival in tropical forests. To evaluate CNDD more broadly, we investigated how sapling growth rates were affected by conspecific adult neighbors in a fully mapped 25.6 ha temperate deciduous forest. We examined growth rates as a function of the local adult tree neighborhood (via spatial autoregressive modeling) and compared the spatial positioning of faster-growing and slower-growing saplings with respect to adult conspecific and heterospecific trees (via bivariate point pattern analysis). In addition, to determine whether CNDD-driven variation in growth rates leaves a corresponding spatial signal, we extended our point pattern analysis to a static, growth-independent comparison of saplings and the next larger size class. We found that negative conspecific effects on sapling growth were most prevalent. Five of the nine species that were sufficiently abundant for analysis exhibited CNDD, while only one species showed evidence of a positive conspecific effect, and one or two species, depending on the analysis, displayed heterospecific effects. There was general agreement between the autoregressive models and the point pattern analyses based on sapling growth rates, but point pattern analyses based on single-point-in-time size classes yielded results that differed markedly from the other two approaches. Our work adds to the growing body of evidence that CNDD is an important force in temperate forests, and demonstrates that this process extends to sapling growth rates. Further, our findings indicate that point pattern analyses based solely on size classes may fail to detect the process of interest (e.g., neighborhood-driven variation in growth rates), in part due to the confounding of tree size and age.

  11. Extension of biomass estimates to pre-assessment periods using density dependent surplus production approach

    Science.gov (United States)

    Horbowy, Jan

    2017-01-01

    Biomass reconstructions to pre-assessment periods for commercially important and exploitable fish species are important tools for understanding long-term processes and fluctuation on stock and ecosystem level. For some stocks only fisheries statistics and fishery dependent data are available, for periods before surveys were conducted. The methods for the backward extension of the analytical assessment of biomass for years for which only total catch volumes are available were developed and tested in this paper. Two of the approaches developed apply the concept of the surplus production rate (SPR), which is shown to be stock density dependent if stock dynamics is governed by classical stock-production models. The other approach used a modified form of the Schaefer production model that allows for backward biomass estimation. The performance of the methods was tested on the Arctic cod and North Sea herring stocks, for which analytical biomass estimates extend back to the late 1940s. Next, the methods were applied to extend biomass estimates of the North-east Atlantic mackerel from the 1970s (analytical biomass estimates available) to the 1950s, for which only total catch volumes were available. For comparison with other methods which employs a constant SPR estimated as an average of the observed values, was also applied. The analyses showed that the performance of the methods is stock and data specific; the methods that work well for one stock may fail for the others. The constant SPR method is not recommended in those cases when the SPR is relatively high and the catch volumes in the reconstructed period are low. PMID:29131850

  12. High current density PQQ-dependent alcohol and aldehyde dehydrogenase bioanodes.

    Science.gov (United States)

    Aquino Neto, Sidney; Hickey, David P; Milton, Ross D; De Andrade, Adalgisa R; Minteer, Shelley D

    2015-10-15

    In this paper, we explore the bioelectrooxidation of ethanol using pyrroloquinoline quinone (PQQ)-dependent alcohol and aldehyde dehydrogenase (ADH and AldDH) enzymes for biofuel cell applications. The bioanode architectures were designed with both direct electron transfer (DET) and mediated electron transfer (MET) mechanisms employing high surface area materials such as multi-walled carbon nanotubes (MWCNTs) and MWCNT-decorated gold nanoparticles, along with different immobilization techniques. Three different polymeric matrices were tested (tetrabutyl ammonium bromide (TBAB)-modified Nafion; octyl-modified linear polyethyleneimine (C8-LPEI); and cellulose) in the DET studies. The modified Nafion membrane provided the best electrical communication between enzymes and the electrode surface, with catalytic currents as high as 16.8 ± 2.1 µA cm(-2). Then, a series of ferrocene redox polymers were evaluated for MET. The redox polymer 1,1'-dimethylferrocene-modified linear polyethyleneimine (FcMe2-C3-LPEI) provided the best electrochemical response. Using this polymer, the electrochemical assays conducted in the presence of MWCNTs and MWCNTs-Au indicated a Jmax of 781 ± 59 µA cm(-2) and 925 ± 68 µA cm(-2), respectively. Overall, from the results obtained here, DET using the PQQ-dependent ADH and AldDH still lacks high current density, while the bioanodes that operate via MET employing ferrocene-modified LPEI redox polymers show efficient energy conversion capability in ethanol/air biofuel cells. Copyright © 2015 Elsevier B.V. All rights reserved.

  13. Pair correlation functions and the wavevector-dependent surface tension in a simple density functional treatment of the liquid-vapour interface.

    Science.gov (United States)

    Parry, A O; Rascón, C; Willis, G; Evans, R

    2014-09-03

    We study the density-density correlation function G(r, r') in the interfacial region of a fluid (or Ising-like magnet) with short-ranged interactions using square gradient density functional theory. Adopting a simple double parabola approximation for the bulk free-energy density, we first show that the parallel Fourier transform G(z, z'; q) and local structure factor S(z; q) separate into bulk and excess contributions. We attempt to account for both contributions by deriving an interfacial Hamiltonian, characterised by a wavevector dependent surface tension σ(q), and then reconstructing density correlations from correlations in the interface position. We show that the standard crossing criterion identification of the interface, as a surface of fixed density (or magnetization), does not explain the separation of G(z, z'; q) and the form of the excess contribution. We propose an alternative definition of the interface position based on the properties of correlations between points that 'float' with the surface and show that this describes the full q and z dependence of the excess contributions to both G and S. However, neither the 'crossing-criterion' nor the new 'floating interface' definition of σ(q) are quantities directly measurable from the total structure factor S(tot)(q) which contains additional q dependence arising from the non-local relation between fluctuations in the interfacial position and local density. Since it is the total structure factor that is measured experimentally or in simulations, our results have repercussions for earlier attempts to extract and interpret σ(q).

  14. Efficient block preconditioned eigensolvers for linear response time-dependent density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Vecharynski, Eugene; Brabec, Jiri; Shao, Meiyue; Govind, Niranjan; Yang, Chao

    2017-12-01

    We present two efficient iterative algorithms for solving the linear response eigen- value problem arising from the time dependent density functional theory. Although the matrix to be diagonalized is nonsymmetric, it has a special structure that can be exploited to save both memory and floating point operations. In particular, the nonsymmetric eigenvalue problem can be transformed into a product eigenvalue problem that is self-adjoint with respect to a K-inner product. This product eigenvalue problem can be solved efficiently by a modified Davidson algorithm and a modified locally optimal block preconditioned conjugate gradient (LOBPCG) algorithm that make use of the K-inner product. The solution of the product eigenvalue problem yields one component of the eigenvector associated with the original eigenvalue problem. However, the other component of the eigenvector can be easily recovered in a postprocessing procedure. Therefore, the algorithms we present here are more efficient than existing algorithms that try to approximate both components of the eigenvectors simultaneously. The efficiency of the new algorithms is demonstrated by numerical examples.

  15. Spatial and temporal features of density-dependent contaminant transport: experimental investigation and numerical modeling.

    Science.gov (United States)

    Zoia, Andrea; Latrille, Christelle; Beccantini, Alberto; Cartadale, Alain

    2009-10-13

    We investigate the spatial and temporal features of variable-density contaminant plumes migration in porous materials. Our analysis is supported by novel experimental results concerning concentration profiles inside a vertical column setup that has been conceived at CEA to this aim. The experimental method relies on X-ray spectrometry, which allows determining solute profiles as a function of time at several positions along the column. The salient outcomes of the measurements are elucidated, with focus on miscible fluids in homogeneous saturated media. The role of the injected solution molarity is evidenced. As molarity increases, the solutes plume transport progressively deviates from the usual Fickian behavior, and pollutants distribution becomes skewed in the direction dictated by gravity. By resorting to a finite elements approach, we numerically solve the nonlinear equations that rule the pollutants migration: a good agreement is found between the simulated profiles and the experimental data. At high molarity, a strong dependence on initial conditions is found. Finally, we qualitatively explore the (unstable) interfacial dynamics between the dense contaminant plume and the lighter resident fluid that saturates the column, and detail its evolution for finite-duration contaminant injections.

  16. Determining excitation-energy transfer times and mechanisms from stochastic time-dependent density functional theory.

    Science.gov (United States)

    Hofmann-Mees, D; Appel, H; Di Ventra, M; Kümmel, S

    2013-11-21

    We developed an approach for calculating excitation-energy transfer times in supermolecular arrangements based on stochastic time-dependent density functional theory (STDDFT). The combination of real-time propagation and the stochastic Schrödinger equation with a Kohn-Sham Hamiltonian allows for simulating how an excitation spreads through an assembly of molecular systems. The influence that approximations, such as the dipole-dipole coupling approximation of Förster theory, have on energy-transfer times can be checked explicitly. As a first application of our approach we investigate a light-harvesting-inspired model ring system, calculating the time it takes for an excitation to travel from one side of the ring to the opposite side under ideal and perturbed conditions. Among other things we find that completely removing a molecule from the ring may inhibit energy transfer less than having an energetically detuned molecule in the ring. In addition, Förster's dipole coupling approximation may noticeably overestimate excitation-energy transfer efficiency.

  17. Time dependentdensity functional theory characterization of organic dyes for dye-sensitized solar cells

    KAUST Repository

    Hilal, Rifaat

    2017-06-19

    We aim at providing better insight into the parameters that govern the intramolecular charge transfer (ICT) and photo-injection processes in dyes for dye-sensitised solar cells (DSSC). Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations are utilized to study the geometry, electronic structure, electrostatic potential (ESP) and absorption spectrum, for a representative donor-π bridge-acceptor (D–π–A) dye for DSSC. The coplanar geometry of the dye (D1) facilitates strong conjugation and considerable delocalization originating the π CT interaction from donor to acceptor orbitals and the hyper-conjugative interactions involving Rydberg states. A model simulating the adsorption of the dye on the TiO surface is utilized to estimate binding energies. The effect of fluorine substituents in the π-spacer on the quantum efficiency of DSSCs was investigated. Gibb’s free energy values, redox potentials, excited state lifetime, non-linear optical properties (NLO) and driving forces for D1 and its fluorinated derivatives were computed.

  18. Time-dependent density functional theory calculations of the solvatochromism of some azo sulfonamide fluorochromes.

    Science.gov (United States)

    Krawczyk, Przemysław

    2015-05-01

    The absorption and emission spectra of three azo sulfonamide compounds in different solvents were investigated theoretically by using response functions combined with density functional theory (DFT), while the solvent effect on the structure and the electronic transitions was determined using the integral equation formalism for the polarizable continuum model (IEF-PCM). The results show that the applied different exchange-correlation functionals can reproduce the experimental values well. DFT calculations of the title compounds showed that the H-bond formed between the solute and solvent molecules is one of the major causes of the reversible solvatochromism observed in measured spectra. This is due to a better stabilization of the neutral form than the zwitterionic form in the polar protic solvents, which is characteristic of the hypsochromic shift. On the other hand, the molecules considered exhibit a monotonic behavior regarding the polarity of the low-lying excited state (Δμg-CT) as a function of the solvent polarity. This dependence occurs in the case of the positive solvatochromism and confirms the thesis regarding the H-bond solute-solvent interactions. Theoretically determined values of the two-photon cross section revealed that the (σOF(2)) shows similar trends with changes in λabs, in contrast to values. In conclusion, the results demonstrate that the investigated molecules can be used successfully as fluorochromes in bioimaging.

  19. Efficient block preconditioned eigensolvers for linear response time-dependent density functional theory

    Science.gov (United States)

    Vecharynski, Eugene; Brabec, Jiri; Shao, Meiyue; Govind, Niranjan; Yang, Chao

    2017-12-01

    We present two efficient iterative algorithms for solving the linear response eigenvalue problem arising from the time dependent density functional theory. Although the matrix to be diagonalized is nonsymmetric, it has a special structure that can be exploited to save both memory and floating point operations. In particular, the nonsymmetric eigenvalue problem can be transformed into an eigenvalue problem that involves the product of two matrices M and K. We show that, because MK is self-adjoint with respect to the inner product induced by the matrix K, this product eigenvalue problem can be solved efficiently by a modified Davidson algorithm and a modified locally optimal block preconditioned conjugate gradient (LOBPCG) algorithm that make use of the K-inner product. The solution of the product eigenvalue problem yields one component of the eigenvector associated with the original eigenvalue problem. We show that the other component of the eigenvector can be easily recovered in an inexpensive postprocessing procedure. As a result, the algorithms we present here become more efficient than existing methods that try to approximate both components of the eigenvectors simultaneously. In particular, our numerical experiments demonstrate that the new algorithms presented here consistently outperform the existing state-of-the-art Davidson type solvers by a factor of two in both solution time and storage.

  20. Altered Long- and Short-Range Functional Connectivity in Patients with Betel Quid Dependence: A Resting-State Functional MRI Study

    Directory of Open Access Journals (Sweden)

    Tao Liu

    2016-12-01

    Full Text Available Objective: Addiction is a chronic relapsing brain disease. Brain structural abnormalities may constitute an abnormal neural network that underlies the risk of drug dependence. We hypothesized that individuals with Betel Quid Dependence (BQD have functional connectivity alterations that can be described by long- and short-range functional connectivity density(FCD maps. Methods: We tested this hypothesis using functional magnetic resonance imaging (fMRI data from subjects of the Han ethnic group in Hainan, China. Here, we examined BQD individuals (n = 33 and age-, sex-, and education-matched healthy controls (HCs (n = 32 in a rs-fMRI study to observe FCD alterations associated with the severity of BQD. Results: Compared with HCs, long-range FCD was decreased in the right anterior cingulate cortex (ACC and increased in the left cerebellum posterior lobe (CPL and bilateral inferior parietal lobule (IPL in the BQD group. Short-range FCD was reduced in the right ACC and left dorsolateral prefrontal cortex (dlPFC, and increased in the left CPL. The short-range FCD alteration in the right ACC displayed a negative correlation with the Betel Quid Dependence Scale (BQDS (r=-0.432, P=0.012, and the long-range FCD alteration of left IPL showed a positive correlation with the duration of BQD(r=0.519, P=0.002 in BQD individuals. Conclusions: fMRI revealed differences in long- and short- range FCD in BQD individuals, and these alterations might be due to BQ chewing, BQ dependency, or risk factors for developing BQD.

  1. Adult trees cause density-dependent mortality in conspecific seedlings by regulating the frequency of pathogenic soil fungi.

    Science.gov (United States)

    Liang, Minxia; Liu, Xubing; Gilbert, Gregory S; Zheng, Yi; Luo, Shan; Huang, Fengmin; Yu, Shixiao

    2016-12-01

    Negative density-dependent seedling mortality has been widely detected in tropical, subtropical and temperate forests, with soil pathogens as a major driver. Here we investigated how host density affects the composition of soil pathogen communities and consequently influences the strength of plant-soil feedbacks. In field censuses of six 1-ha permanent plots, we found that survival was much lower for newly germinated seedlings that were surrounded by more conspecific adults. The relative abundance of pathogenic fungi in soil increased with increasing conspecific tree density for five of nine tree species; more soil pathogens accumulated around roots where adult tree density was higher, and this greater pathogen frequency was associated with lower seedling survival. Our findings show how tree density influences populations of soil pathogens, which creates plant-soil feedbacks that contribute to community-level and population-level compensatory trends in seedling survival. © 2016 John Wiley & Sons Ltd/CNRS.

  2. Bone density and neuromuscular function in older competitive athletes depend on running distance.

    Science.gov (United States)

    Gast, U; Belavý, D L; Armbrecht, G; Kusy, K; Lexy, H; Rawer, R; Rittweger, J; Winwood, K; Zieliński, J; Felsenberg, D

    2013-07-01

    Individuals who are involved in explosive sport types, such as 100-m sprints and long jump, have greater bone density, leg muscle size, jumping height and grip strength than individuals involved in long-distance running. The purpose of this study is to examine the relationship between different types of physical activity with bone, lean mass and neuromuscular performance in older individuals. We examined short- (n = 50), middle- (n = 19) and long-distance (n = 109) athletes at the 15th European Masters Championships in Poznań, Poland. Dual X-ray absorptiometry was used to measure areal bone mineral density (aBMD) and lean tissue mass. Maximal countermovement jump, multiple one-leg hopping and maximal grip force tests were performed. Short-distance athletes showed significantly higher aBMD at the legs, hip, lumbar spine and trunk compared to long-distance athletes (p ≤ 0.0012). Countermovement jump performance, hop force, grip force, leg lean mass and arm lean mass were greater in short-distance athletes (p ≤ 0.027). A similar pattern was seen in middle-distance athletes who typically showed higher aBMD and better neuromuscular performance than long-distance athletes, but lower in magnitude than short-distance athletes. In all athletes, aBMD was the same or higher than the expected age-adjusted population mean at the lumbar spine, hip and whole body. This effect was greater in the short- and middle-distance athletes. The stepwise relation between short-, middle- and long-distance athletes on bone suggests that the higher-impact loading protocols in short-distance disciplines are more effective in promoting aBMD. The regional effect on bone, with the differences between the groups being most marked at load-bearing regions (legs, hip, spine and trunk) rather than non-load-bearing regions, is further evidence in support of the idea that bone adaptation to exercise is dependent upon the local loading environment, rather than as part of a

  3. Symmetry energy of the nucleus in the relativistic Thomas-Fermi approach with density-dependent parameters

    Science.gov (United States)

    Haddad, S.

    2017-11-01

    The symmetry energy of a nucleus is determined in a local density approximation and integrating over the entire density distribution of the nucleus, calculated utilizing the relativistic density-dependent Thomas-Fermi approach. The symmetry energy is found to decrease with increasing neutron excess in the nucleus. The isovector coupling channel reduces the symmetry energy, and this effect increases with increased neutron excess. The isovector coupling channel increases the symmetry energy integral in ^{40}Ca and reduces it in ^{48}Ca, and the interplay between the isovector and the isoscalar channels of the nuclear force explains this isotope effect.

  4. Correction of a phase dependent error in a time-of-flight range sensor

    Science.gov (United States)

    Seiter, Johannes; Hofbauer, Michael; Davidovic, Milos; Zimmermann, Horst

    2013-04-01

    Time-of-Flight (TOF) 3D cameras determine the distance information by means of a propagation delay measurement. The delay value is acquired by correlating the sent and received continuous wave signals in discrete phase delay steps. To reduce the measurement time as well as the resources required for signal processing, the number of phase steps can be decreased. However, such a change results in the arising of a crucial systematic distance dependent distance error. In the present publication we investigate this phase dependent error systematically by means of a fiber based measurement setup. Furthermore, the phase shift is varied with an electrical delay line device rather than by moving an object in front of the camera. This procedure allows investigating the above mentioned phase dependent error isolated from other error sources, as, e.g., the amplitude dependent error. In other publications this error is corrected by means of a look-up table stored in a memory device. In our paper we demonstrate an analytical correction method that dramatically minimizes the demanded memory size. For four phase steps, this approach reduces the error dramatically by 89.4 % to 13.5 mm at a modulation frequency of 12.5 MHz. For 20.0 MHz, a reduction of 86.8 % to 11.5 mm could be achieved.

  5. Prediction of the concentration dependence of the surface tension and density of salt solutions: atomistic simulations using Drude oscillator polarizable and nonpolarizable models.

    Science.gov (United States)

    Neyt, Jean-Claude; Wender, Aurélie; Lachet, Véronique; Ghoufi, Aziz; Malfreyt, Patrice

    2013-07-28

    Molecular simulations using Drude oscillator polarizable and nonpolarizable models for water and ions are carried out to predict the dependence of the surface tension on salt concentration. The polarizable water and ion models are based only on the classical Drude oscillators. The temperature dependence of the surface tension of water is examined for different water models. The dependence of salt densities on salt concentration is investigated through the nonpolarizable and Drude oscillator polarizable models. Finally, the reproduction of the surface tension of salt solution over a large range of concentrations is analyzed through a number of combinations between ions and water force fields. The structure of the interface is then discussed as a function of polarization effects. We establish here the inability of the Drude oscillator polarizable force fields to reproduce the salt concentration dependence of surface tension of NaCl aqueous solutions.

  6. The density of knobs on Plasmodium falciparum-infected erythrocytes depends on developmental age and varies among isolates

    DEFF Research Database (Denmark)

    Quadt, Katharina A; Barfod, Lea; Andersen, Daniel

    2012-01-01

    . Therefore, the aim of this study was to provide detailed information on isolate- and time-dependent differences in knob size and density. METHODOLOGY/PRINCIPAL FINDINGS: We used atomic force microscopy to characterize knobs on the surface of P. falciparum-infected erythrocytes. Fourteen ex vivo isolates......-IE surface depends on time since invasion, but is also determined by the infecting isolate in a time-independent manner. This is the first study to quantitatively evaluate knob densities and dimensions on different P. falciparum isolates, to examine ex vivo isolates from humans, and to compare ex vivo...

  7. Prison construction and guarding behaviour by European honeybees is dependent on inmate small hive beetle density.

    Science.gov (United States)

    Ellis, J D; Hepburn, H R; Ellis, A M; Elzen, P J

    2003-08-01

    Increasing small hive beetle (Aethina tumida Murray) density changes prison construction and guarding behaviour in European honeybees (Apis mellifera L.). These changes include more guard bees per imprisoned beetle and the construction of more beetle prisons at the higher beetle density. Despite this, the number of beetles per prison (inmate density) did not change. Beetles solicited food more actively at the higher density and at night. In response, guard bees increased their aggressive behaviour towards beetle prisoners but did not feed beetles more at the higher density. Only 5% of all beetles were found among the combs at the low density but this percentage increased five-fold at the higher one. Successful comb infiltration (and thus reproduction) by beetles is a possible explanation for the significant damage beetles cause to European honeybee colonies in the USA.

  8. Truncation scheme of time-dependent density-matrix approach II

    Energy Technology Data Exchange (ETDEWEB)

    Tohyama, Mitsuru [Kyorin University School of Medicine, Mitaka, Tokyo (Japan); Schuck, Peter [Institut de Physique Nucleaire, IN2P3-CNRS, Universite Paris-Sud, Orsay (France); Laboratoire de Physique et de Modelisation des Milieux Condenses, CNRS et Universite Joseph Fourier, Grenoble (France)

    2017-09-15

    A truncation scheme of the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy for reduced density matrices, where a three-body density matrix is approximated by two-body density matrices, is improved to take into account a normalization effect. The truncation scheme is tested for the Lipkin model. It is shown that the obtained results are in good agreement with the exact solutions. (orig.)

  9. Novel genes identified in a high-density genome wide association study for nicotine dependence

    National Research Council Canada - National Science Library

    Bierut, Laura Jean; Madden, Pamela A.F; Breslau, Naomi; Johnson, Eric O; Hatsukami, Dorothy; Pomerleau, Ovide F; Swan, Gary E; Rutter, Joni; Bertelsen, Sarah; Fox, Louis; Fugman, Douglas; Goate, Alison M; Hinrichs, Anthony L; Konvicka, Karel; Martin, Nicholas G; Montgomery, Grant W; Saccone, Nancy L; Saccone, Scott F; Wang, Jen C; Chase, Gary A; Rice, John P; Ballinger, Dennis G

    .... To identify novel genes for which natural variation contributes to the development of nicotine dependence, we performed a comprehensive genome wide association study using nicotine dependent smokers...

  10. A resprouter herb reduces negative density-dependent effects among neighboring seeders after fire

    Science.gov (United States)

    Raventós, José; Wiegand, Thorsten; Maestre, Fernando T.; de Luis, Martín

    2012-01-01

    Plant communities are often composed of species belonging to different functional groups, but relatively few studies to date have explicitly linked their spatial structure to the outcome of the interaction among them. We investigated if mortality of seeder species during their establishment after fire is influenced by the proximity of the resprouter herb Brachypodium retusum. The study was conducted in a Mediterranean shrubland (00°39' W; 38°43' N), 40 km northwest of Alicante (Spain) with Ulex parviflorus, Cistus albidus, Helianthemum marifolium, and Ononis fruticosa as dominant obligate seeder species and a herbaceous layer is dominated by the resprouter B. retusum. We followed the fate of mapped seedlings and the biomass of B. retusum one, two, three and nine years after an experimental fire. We used point pattern analyses to evaluate the spatial pattern of mortality of seeder species at these years in relation to the biomass of B. retusum. We hypothesize that B. retusum may initially have a positive impact on seeder survival. We implemented this hypothesis as a point process model that maintains the overall number of dead seeder plants, but seeder survival varied proportionally to the biomass of B. retusum in its neighborhood. We then contrasted this hypothesis with a previous analysis based on a random mortality hypothesis. Our data were consistent with the hypothesis that proximity of B. retusum reduced the mortality of seeder plants at their establishment phase (i.e., 2 yrs after fire). However, we found no evidence that B. retusum influenced seeder mortality when plants grow to maturity. We also found that, under the more stressful conditions (fire + erosion scenario), B. retusum had a lower impact on the performance of seeder species. Our results suggest that B. retusum may reduce negative density-dependent effects among neighboring seeder plants during the first years after fire.

  11. Sensitivity of physiological emotional measures to odors depends on the product and the pleasantness ranges used

    Directory of Open Access Journals (Sweden)

    Aline Marie Pichon

    2015-12-01

    Full Text Available Emotions are characterized by synchronized changes in several components of an organism. Among them, physiological variations provide energy support for the expression of approach/avoid action tendencies induced by relevant stimuli, while self-reported subjective pleasantness feelings integrate all other emotional components and are plastic.Consequently, emotional responses evoked by odors should be highly differentiated when they are linked to different functions of olfaction (e.g., avoiding environmental hazards. As this differentiation has been observed for contrasted odors (very pleasant or unpleasant, we questioned whether subjective and physiological emotional response indicators could still disentangle subtle affective variations when no clear functional distinction is made (mildly pleasant or unpleasant fragrances. Here, we compared the sensitivity of behavioral and physiological (respiration, skin conductance, facial electromyography (EMG, and heart rate indicators in differentiating odor-elicited emotions in two situations: when a wide range of odor families was presented (e.g., fruity, animal, covering different functional meanings; or in response to a restricted range of products in one particular family (fragrances. Results show clear differences in physiological indicators to odors that display a wide range of reported pleasantness, but these differences almost entirely vanish when fragrances are used even though their subjective pleasantness still differed. Taken together, these results provide valuable information concerning the ability of classic verbal and psychophysiological measures to investigate subtle differences in emotional reactions to a restricted range of similar olfactory stimuli.

  12. Evidence of long range dependence in Asian equity markets: the role of liquidity and market restrictions

    Science.gov (United States)

    Cajueiro, Daniel O.; Tabak, Benjamin M.

    2004-11-01

    In this paper, the efficient market hypothesis is tested for China, Hong Kong and Singapore by means of the long memory dependence approach. We find evidence suggesting that Hong Kong is the most efficient market followed by Chinese A type shares and Singapore and finally by Chinese B type shares, which suggests that liquidity and capital restrictions may play a role in explaining results of market efficiency tests.

  13. The role of landscape features and density dependence in growth and fledging rates of Piping Plovers in North Dakota, USA

    Science.gov (United States)

    Anteau, Michael J.; Wiltermuth, Mark T.; Sherfy, Mark H.; Shaffer, Terry L.; Pearse, Aaron T.

    2014-01-01

    For species with precocial young, survival from hatching to fledging is a key factor influencing recruitment. Furthermore, growth rates of precocial chicks are an indicator of forage quality and habitat suitability of brood-rearing areas. We examined how growth and fledging rates of Piping Plover (Charadrius melodus) chicks were influenced by landscape features, such as hatchling density (hatchlings per hectare of remotely sensed habitat [H ha-1]), island vs. mainland, and wind fetch (exposure to waves) at 2-km segments (n ¼ 15) of Lake Sakakawea, North Dakota, during 2007–2008. Hatchling growth was comparable with published estimates for other habitats. Models for fledging rate (fledged young per segment) assuming density dependence had more support (wi ¼ 96%) than those assuming density independence (wi ¼ 4%). Density-dependent processes appeared to influence fledging rate only at densities .5 H ha-1, which occurred in 19% of the segments we sampled. When areas with densities .5 H ha-1 were excluded, density-dependence and density-independence models were equally supported (wi ¼ 52% and 48%, respectively). Fledging rate declined as the wind fetch of a segment increased. Fledging rate on mainland shorelines was 4.3 times greater than that on islands. Previous work has indicated that plovers prefer islands for nesting, but our results suggest that this preference is not optimal and could lead to an ecological trap for chicks. While other researchers have found nesting-habitat requirements to be gravelly areas on exposed beaches without fine-grain substrates, our results suggest that chicks fledge at lower rates in these habitats. Thus, breeding plovers likely require complexes of these nesting habitats along with protected areas with fine, nutrient-rich substrate for foraging by hatchlings.

  14. Simulation of Field Dependence of Critical Current Densities of Bulk High Tc Superconducting Materials regarding Thermally Activated Flux Motion

    Science.gov (United States)

    Santosh, M.; Naik, S. Pavan Kumar; Koblischka, M. R.

    2017-07-01

    In the upcoming generation, bulk high temperature superconductors (HTS) will play a crucial and a promising role in numerous industrial applications ranging from Maglev trains to magnetic resonance imaging, etc. Especially, the bulk HTS as permanent magnets are suitable due to the fact that they can trap magnetic fields being several orders of magnitude higher than those of the best hard ferromagnets. The bulk HTS LREBa2Cu3O7-δ (LREBCO or LRE-123, LRE: Y, Gd, etc.,) materials could obtain very powerful compact superconducting super-magnets, which can be operated at the cheaper liquid nitrogen temperature or below due to higher critical temperatures (i.e., ∼90 K). As a result, the new advanced technology can be utilized in a more attractive manner for a variety of technological and medical applications which have the capacity to revolutionize the field. An understanding of the magnetic field dependence of the critical current density (J c(H)) is important to develop better adapted materials. To achieve this goal, a variety of Jc (H) behaviours of bulk LREBCO samples were modelled regarding thermally activated flux motion. In essence, the Jc (H) curves follows a certain criterion where an exponential model is applied. However, to fit the complete Jc (H) curve of the LRE-123 samples an unique model is necessary to explain the behavior at low and high fields. The modelling of the various superconducting materials could be understood in terms of the pinning mechanisms.

  15. Examining real-time time-dependent density functional theory nonequilibrium simulations for the calculation of electronic stopping power

    Science.gov (United States)

    Yost, Dillon C.; Yao, Yi; Kanai, Yosuke

    2017-09-01

    In ion irradiation processes, electronic stopping power describes the energy transfer rate from the irradiating ion to the target material's electrons. Due to the scarcity and significant uncertainties in experimental electronic stopping power data for materials beyond simple solids, there has been growing interest in the use of first-principles theory for calculating electronic stopping power. In recent years, advances in high-performance computing have opened the door to fully first-principles nonequilibrium simulations based on real-time time-dependent density functional theory (RT-TDDFT). While it has been demonstrated that the RT-TDDFT approach is capable of predicting electronic stopping power for a wide range of condensed matter systems, there has yet to be an exhaustive examination of the physical and numerical approximations involved and their effects on the calculated stopping power. We discuss the results of such a study for crystalline silicon with protons as irradiating ions. We examine the influences of key approximations in RT-TDDFT nonequilibrium simulations on the calculated electronic stopping power, including approximations related to basis sets, finite size effects, exchange-correlation approximation, pseudopotentials, and more. Finally, we propose a simple and efficient correction scheme to account for the contribution from core-electron excitations to the stopping power, as it was found to be significant for large proton velocities.

  16. Bone mineral density, osteocalcin, and bone-specific alkaline phosphatase in patients with insulin-dependent diabetes mellitus.

    Science.gov (United States)

    Lumachi, Franco; Camozzi, Valentina; Tombolan, Valeria; Luisetto, Giovanni

    2009-09-01

    The aims of this study were to evaluate the prevalence of osteopenia and the relationships between osteocalcin (OC), bone alkaline phosphatase (bALP), and bone mineral density (BMD) in patients with insulin-dependent diabetes mellitus (IDDM). A group of 18 patients (median age 47, range 36-51) with uncomplicated IDDM (Group A) were matched by sex, age, and body mass index with 21 healthy control volunteers (Group B). All subjects underwent osteodensitometry with measurement of BMD at the lumbar spine and femoral neck. Osteopenia was present in 11 (61.1%) and 2 (9.5%) of Group A and B patients (P= 0.01), respectively. Both OC (28.4 +/- 16.4 versus 41.2 +/- 14.6 ng/mL; P= 0.005) and bALP (51.3 +/- 11.8 versus 61.7 +/- 10.6 U/L; P= 0.006) serum levels were significantly lower in patients with IDDM. BMD did not correlate with either OC or bALP. In conclusion, osteopenia is common among patients with IDDM, but the relationship between bone formation markers and BMD is still unclear.

  17. Tailored pump-probe transient spectroscopy with time-dependent density-functional theory: controlling absorption spectra

    Science.gov (United States)

    Walkenhorst, Jessica; De Giovannini, Umberto; Castro, Alberto; Rubio, Angel

    2016-05-01

    Recent advances in laser technology allow us to follow electronic motion at its natural time-scale with ultra-fast time resolution, leading the way towards attosecond physics experiments of extreme precision. In this work, we assess the use of tailored pumps in order to enhance (or reduce) some given features of the probe absorption (for example, absorption in the visible range of otherwise transparent samples). This type of manipulation of the system response could be helpful for its full characterization, since it would allow us to visualize transitions that are dark when using unshaped pulses. In order to investigate these possibilities, we perform first a theoretical analysis of the non-equilibrium response function in this context, aided by one simple numerical model of the hydrogen atom. Then, we proceed to investigate the feasibility of using time-dependent density-functional theory as a means to implement, theoretically, this absorption-optimization idea, for more complex atoms or molecules. We conclude that the proposed idea could in principle be brought to the laboratory: tailored pump pulses can excite systems into light-absorbing states. However, we also highlight the severe numerical and theoretical difficulties posed by the problem: large-scale non-equilibrium quantum dynamics are cumbersome, even with TDDFT, and the shortcomings of state-of-the-art TDDFT functionals may still be serious for these out-of-equilibrium situations.

  18. Wilderness experience quality: Effects of use density depend on how experience is conceived

    Science.gov (United States)

    David N. Cole; Troy E. Hall

    2012-01-01

    Different conceptions of experience and experience quality can explain ambiguous relationships among use density, crowding, experience and experience quality. We employed multiple methods to quantify experiential dimensions at a popular lake in the Alpine Lakes Wilderness, WA. Comparing weekdays to weekends, when use density is typically four times as high, we assessed...

  19. Lithology- versus base level-dependent morphogenesis of the Hausruck - Kobernaußerwald range

    Science.gov (United States)

    Baumann, Sebastian; Robl, Jörg; Salcher, Bernhard; Prasicek, Günther; Keil, Melanie

    2016-04-01

    The Hausruck - Kobernaußerwald range has the highest relief in the Northern Molasse Basin in front of the Eastern Alps. The highest peaks of the range exceed an elevation of 800 m and are characterized by a local relief of about 400 m relative to the adjacent lowlands. The Hausruck - Kobernaußerwald range has never been glaciated and erosion is solely driven by fluvial incision and corresponding hillslope processes since the inversion of the Molasse Basin. Landslides are frequently observed at hillslopes in the Hausruck domain in the west but are completely missing in the Kobernaußerwald domain in the east. Recent tectonic activity like faulting has not been reported for that region and the stratigraphic record shows no evidence for tectonically induced discontinuities. The morphological expression of the western Kobernaußerwald and the eastern Hausruck apparently differ in their degree of erosional landscape decay with a gently incised western and deeply incised eastern domain. These domains correspond with two different lithological units of the Upper Freshwater Molasse: The simultaneously deposited western Kobernaußerwald Formation (Kobernaußerwald domain) and the eastern Ampfelwang Formation (Hausruck domain) are interpreted as sedimentary deposits of a fluvial fan in proximal and distal position, respectively, and show fining of the sedimentary record from west to east. The stratigraphic highest unit of the study region, the Hausruck Fm., consists of well consolidated fluvial gravels uniformly covering the hill tops of both domains. We used a high resolution LiDAR digital elevation model and performed a series of morphometric analyses to investigate the effects of different base levels and contrasting lithology on the topographic evolution of the Hausruck - Kobernaußerwald range. The analysis of longitudinal river profiles reveals that all channels independent from base level, bed rock and overall morphological expression are well graded with steep

  20. Local environment and density-dependent feedbacks determine population growth in a forest herb

    DEFF Research Database (Denmark)

    Dahlgren, Johan Petter; Östergård, Hannah; Ehrlén, Johan

    2014-01-01

    Linking spatial variation in environmental factors to variation in demographic rates is essential for a mechanistic understanding of the dynamics of populations. However, we still know relatively little about such links, partly because feedbacks via intraspecific density make them difficult...... to observe in natural populations. We conducted a detailed field study and investigated simultaneous effects of environmental factors and the intraspecific density of individuals on the demography of the herb Lathyrus vernus. In regression models of vital rates we identified effects associated with spring...... shade on survival and growth, while density was negatively correlated with these vital rates. Density was also negatively correlated with average individual size in the study plots, which is consistent with self-thinning. In addition, average plant sizes were larger than predicted by density in plots...

  1. Roles of density-dependent growth and life history evolution in accounting for fisheries-induced trait changes

    Science.gov (United States)

    Eikeset, Anne Maria; Dunlop, Erin S.; Heino, Mikko; Storvik, Geir; Stenseth, Nils C.; Dieckmann, Ulf

    2016-01-01

    The relative roles of density dependence and life history evolution in contributing to rapid fisheries-induced trait changes remain debated. In the 1930s, northeast Arctic cod (Gadus morhua), currently the world’s largest cod stock, experienced a shift from a traditional spawning-ground fishery to an industrial trawl fishery with elevated exploitation in the stock’s feeding grounds. Since then, age and length at maturation have declined dramatically, a trend paralleled in other exploited stocks worldwide. These trends can be explained by demographic truncation of the population’s age structure, phenotypic plasticity in maturation arising through density-dependent growth, fisheries-induced evolution favoring faster-growing or earlier-maturing fish, or a combination of these processes. Here, we use a multitrait eco-evolutionary model to assess the capacity of these processes to reproduce 74 y of historical data on age and length at maturation in northeast Arctic cod, while mimicking the stock’s historical harvesting regime. Our results show that model predictions critically depend on the assumed density dependence of growth: when this is weak, life history evolution might be necessary to prevent stock collapse, whereas when a stronger density dependence estimated from recent data is used, the role of evolution in explaining fisheries-induced trait changes is diminished. Our integrative analysis of density-dependent growth, multitrait evolution, and stock-specific time series data underscores the importance of jointly considering evolutionary and ecological processes, enabling a more comprehensive perspective on empirically observed stock dynamics than previous studies could provide. PMID:27940913

  2. Effects of density dependent larval competition on the life history traits of Aedes aegypti and Aedes albopictus (Diptera: Culicidae

    Directory of Open Access Journals (Sweden)

    Sampa Banerjee

    2017-06-01

    Full Text Available Consequences of larval competition at the population level provide explanation for the differences in relative abundance of Aedes aegypti and Aedes albopictus in different geographical regions. The outcome of competition is assessed through the estimates of the life history traits as a response to varying density and resource available for larval development. In the present study, variations in the life history traits due to density-dependent intra- and inter- specific competition involving A. aegypti and A. albopictus were assessed following the minimalist model. The instar-I larvae (0-day old F2 generation of both Aedes species were reared to the adult stages using the initial rearing density of 1, 2, 4 and 6 (individuals/10ml in multiple replicates. The age at pupation, pupal weight, adult weight and adult wing length of the individuals were considered as the response variables and surrogates of estimating the competitive interactions. Density dependent variations in the competitive interactions were evident for both the mosquitoes with reference to the selected life history traits. In A. aegypti, the life history traits varied with the levels of competition, which was not observed for A. albopictus. Although the density levels considered in the present instance were lower than in earlier studies, the observations were similar, with A. albopictus being competitively superior. It appears that irrespective of the density levels, interspecific competition affects A. aegypti and thus may bear population level consequences and overall abundance in the areas where both species are present.

  3. Evidence of adaptive divergence in plasticity: density- and site-dependent selection on shade-avoidance responses in Impatiens capensis.

    Science.gov (United States)

    Donohue, K; Messiqua, D; Pyle, E H; Heschel, M S; Schmitt, J

    2000-12-01

    We investigated the conditions under which plastic responses to density are adaptive in natural populations of Impatiens capensis and determined whether plasticity has evolved differently in different selective environments. Previous studies showed that a population that evolved in a sunny site exhibited greater plasticity in response to density than did a population that evolved in a woodland site. Using replicate inbred lines in a reciprocal transplant that included a density manipulation, we asked whether such population differentiation was consistent with the hypothesis of adaptive divergence. We hypothesized that plasticity would be more strongly favored in the sunny site than in the woodland site; consequently, we predicted that selection would be more strongly density dependent in the sunny site, favoring the phenotype that was expressed at each density. Selection on internode length and flowering date was consistent with the hypothesis of adaptive divergence in plasticity. Few costs or benefits of plasticity were detected independently from the expressed phenotype, so plasticity was selected primarily through selection on the phenotype. Correlations between phenotypes and their plasticity varied with the environment and would cause indirect selection on plasticity to be environment dependent. We showed that an appropriate plastic response even to a rare environment can greatly increase genotypic fitness when that environment is favorable. Selection on the measured characters contributed to local adaptation and fully accounted for fitness differences between populations in all treatments except the woodland site at natural density.

  4. Extending the range and physical accuracy of coarse-grained models: Order parameter dependent interactions

    Science.gov (United States)

    Wagner, Jacob W.; Dannenhoffer-Lafage, Thomas; Jin, Jaehyeok; Voth, Gregory A.

    2017-07-01

    Order parameters (i.e., collective variables) are often used to describe the behavior of systems as they capture different features of the free energy surface. Yet, most coarse-grained (CG) models only employ two- or three-body non-bonded interactions between the CG particles. In situations where these interactions are insufficient for the CG model to reproduce the structural distributions of the underlying fine-grained (FG) model, additional interactions must be included. In this paper, we introduce an approach to expand the basis sets available in the multiscale coarse-graining (MS-CG) methodology by including order parameters. Then, we investigate the ability of an additive local order parameter (e.g., density) and an additive global order parameter (i.e., distance from a hard wall) to improve the description of CG models in interfacial systems. Specifically, we study methanol liquid-vapor coexistence, acetonitrile liquid-vapor coexistence, and acetonitrile liquid confined by hard-wall plates, all using single site CG models. We find that the use of order parameters dramatically improves the reproduction of structural properties of interfacial CG systems relative to the FG reference as compared with pairwise CG interactions alone.

  5. Data from: Balancing food and density-dependence in the spatial distribution of an interference-prone forager

    NARCIS (Netherlands)

    Dokter, Adriaan M.; Loon, E.E.; Rappoldt, Cornelis; Oosterbeek, Kees; Baptist, M.J.; Bouten, Willem; Ens, Bruno J.

    2017-01-01

    Foraging distributions are thought to be density-dependent, because animals not only select for a high availability and quality of resources, but also avoid conspecific interference. Since these processes are confounded, their relative importance in shaping foraging distributions remains poorly

  6. The role of relativity in the optical response of gold within the time-dependent current-density-functional theory

    NARCIS (Netherlands)

    Romaniello, P; de Boeij, PL

    2005-01-01

    We included relativistic effects in the formulation of the time-dependent current-density-functional theory for the calculation of linear response properties of metals [P. Romaniello and P. L. de Boeij, Phys. Rev. B (to be published)]. We treat the dominant scalar-relativistic effects using the

  7. Bone tissue stiffness in the mandibular condyle is dependent on the direction and density of the cancellous structure.

    NARCIS (Netherlands)

    Eijden, T.M. van; Ruijven, L.J. van; Giesen, E.B.W.

    2004-01-01

    Variation in the apparent stiffness of cancellous bone is generally ascribed to variation in cancellous structure and density, while the bone tissue stiffness is assumed to be constant. The purpose of the present study was to examine whether the bone tissue stiffness is dependent on the direction

  8. Relativistic mean field theory with density dependent coupling constants for nuclear matter and finite nuclei with large charge asymmetry

    Energy Technology Data Exchange (ETDEWEB)

    Typel, S.; Wolter, H.H. [Sektion Physik, Univ. Muenchen, Garching (Germany)

    1998-06-01

    Nuclear matter and ground state properties for (proton and neutron) semi-closed shell nuclei are described in relativistic mean field theory with coupling constants which depend on the vector density. The parametrization of the density dependence for {sigma}-, {omega}- and {rho}-mesons is obtained by fitting to properties of nuclear matter and some finite nuclei. The equation of state for symmetric and asymmetric nuclear matter is discussed. Finite nuclei are described in Hartree approximation, including a charge and an improved center-of-mass correction. Pairing is considered in the BCS approximation. Special attention is directed to the predictions for properties at the neutron and proton driplines, e.g. for separation energies, spin-orbit splittings and density distributions. (orig.)

  9. Density-dependent reproductive and vegetative allocation in the aquatic plant Pistia stratiotes (Araceae

    Directory of Open Access Journals (Sweden)

    Flávia Freitas Coelho

    2005-09-01

    Full Text Available Pistia stratiotes is an aquatic macrophyte that grows in temporary-ponds in the southern Pantanal, Brazil. It reproduces both sexually and asexually and is usually observed forming dense mats on the water surface, a condition favored by the plant’s vegetative reproduction coupled with an ability for rapid growth. In this study we examined the effect of densely crowded conditions on the production of reproductive and vegetative structures. In addition, we verified whether there is a trade-off between clonal growth and investment in sexual reproductive structures, and whether there is an allocation pattern with plant size. Individual plant biomass and the number of the rosettes producing sexual reproductive structures and vegetative growth structures both increased with density. Increase in plant size resulted in increased proportional allocation to sexual reproductive structures and vegetative growth structures. Allocation of biomass to reproduction did not occur at the expense of clonal growth. Thus, the density response appears as a increase of rosettes producing sexual reproductive structures and vegetative growth structures. Therefore, long leaves and stolons may be adaptive under densely crowded conditions where competition for light is intense. An important aspect in the study of trade-offs is the size-dependency of the allocation patterns .Usually, larger plants produce more biomass. Therefore, larger plants can allocate more biomass to both vegetative and sexual reproduction than smaller plants and thus show a positive correlation between both traits rather than the expected negative one. Rev. Biol. Trop. 53(3-4: 369-376. Epub 2005 Oct 3.Pistias strariotes es una macrófita acuática que crece en charcas estacionales en el Pantanal sureño de Brasil. Se reproduce tanto sexual como asexualmente y se obsrva generalmente que forma densas parches sobre la superficie del agua, una condicion que favorecida por la reproduccion vegetativa de la

  10. Large range localized surface plasmon resonance of Ag nanoparticles films dependent of surface morphology

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Lijuan; Yan, Yaning; Xu, Leilei; Ma, Rongrong; Jiang, Fengxian; Xu, Xiaohong, E-mail: xuxh@dns.sxnu.edu.cn

    2016-03-30

    Graphical abstract: - Highlights: • Large range tuned localized surface plasmon resonance of Ag nanoparticles films. • The noble metal Ag has the strongest localized surface plasmon resonance and low optical loss. Besides, it is the cheaper than other noble metal. • The nanoparticles films fabricated using physical methods have the stronger interaction with substrates than chemical methods, which are not easy exfoliation. - Abstract: Noble metal nanoparticles (NPs) have received enormous attention since it displays uniquely optical and electronic properties. In this work, we study localized surface plasmon resonances (LSPR) at different thicknesses and substrate temperatures of Ag NPs films grown by Laser Molecule Beam Epitaxy (LMBE). The LSPR wavelength can be largely tuned in the visible light range of 470 nm to 770 nm. The surface morphology is characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The average size of Ag NPs increased with the thickness increased which leading to the LSPR band broaden and wavelength red-shift. As the substrate temperature is increased from RT to 200 °C, the Ag NPs size distribution becomes homogeneous and particle shape changes from oblate spheroid to sphere, the LSPR band displays sharp, blue-shift and significantly symmetric. Obviously, the morphology of Ag NPs films is important for tuning absorption position. We obtain the cubic crystal structure of Ag NPs with a (1 1 1) main diffraction peak from the X-ray diffraction (XRD) spectra. The high resolution TEM (HR-TEM) and selected area electron diffraction (SAED) prove that Ag NPs is polycrystal structure. The Ag NPs films with large range absorption in visible light region can composite with semiconductor to apply in various optical or photoelectric devices.

  11. Seed yield and protein content in sunflower depending on stand density

    Directory of Open Access Journals (Sweden)

    Balalić Igor M.

    2016-01-01

    Full Text Available The aim of this research was to investigate the effect of stand density on seed yield and protein content in sunflower hybrids. The field experiment was carried out at Rimski Šančevi location. Six NS sunflower hybrids were examined. Five hybrids are confectionery (NS Goliat, NS Slatki, NS Gricko, Vranac and Cepko, and one is used for bird food (NS-H-6485. The trial was arranged as randomized complete block design (RCBD with four replications. Sowing was done with six different densities (from 20,000 to 70,000 plants per hectare, with an increment of 10,000 plants per hectare. Analysis of variance (ANOVA showed that the effect of hybrid, stand density and hybrid × stand density interation were highly significant for seed yield and protein content. The highest seed yield, on the basis of average for all densities, was found in NS-H-6485 (4.77 t ha-1 and in NS Gricko (4.43 t ha-1. Average seed yield of hybrids significantly increased up to 50,000 plants per ha-1, when it reached the value of 4.50 t ha-1, and then decreased. Significantly higher protein content, taking into account all stand densities, showed hybrid Cepko (16.94%. Protein content, above the overall average value, was achieved in hybrid Vranac (16.11%. The high­est protein content in the average for all six hybrids was at the lowest stand density (20,000 plants per ha-1, and then decreased up to higher densities. The results showed that stand density had significant effect on seed yield and protein content in sunflower hybrids. [Projekat Ministarstva nauke Republike Srbije, br. TR31025: The development of new cultivars and improving the technology of producing oil plant species for different purposes

  12. Quantum electrodynamical time-dependent density-functional theory for many-electron systems on a lattice

    Science.gov (United States)

    Farzanehpour, M.; Tokatly, I. V.

    2014-11-01

    We present a rigorous formulation of the time-dependent density-functional theory for interacting lattice electrons strongly coupled to cavity photons. We start with an example of one particle on a Hubbard dimer coupled to a single photonic mode, which is equivalent to the single mode spin-boson model or the quantum Rabi model. For this system we prove that the electron-photon wave function is a unique functional of the electronic density and the expectation value of the photonic coordinate, provided the initial state and the density satisfy a set of well defined conditions. Then we generalize the formalism to many interacting electrons on a lattice coupled to multiple photonic modes and prove the general mapping theorem. We also show that for a system evolving from the ground state of a lattice Hamiltonian any density with a continuous second time derivative is locally v representable.

  13. Density-dependence and within-host competition in a semelparous parasite of leaf-cutting ants

    DEFF Research Database (Denmark)

    Hughes, William; Petersen, Klaus; Ugelvig, Line

    2004-01-01

    BACKGROUND:Parasite heterogeneity and within-host competition are thought to be important factors influencing the dynamics of host-parasite relationships. Yet, while there have been many theoretical investigations of how these factors may act, empirical data is more limited. We investigated...... the effects of parasite density and heterogeneity on parasite virulence and fitness using four strains of the entomopathogenic fungus, Metarhizium anisopliae var. anisopliae, and its leaf-cutting ant host Acromyrmex echinatior as the model system.RESULTS:The relationship between parasite density and infection...... was sigmoidal, with there being an invasion threshold for an infection to occur (an Allee effect). Although spore production was positively density-dependent, parasite fitness decreased with increasing parasite density, indicating within-host scramble competition. The dynamics differed little between the four...

  14. Selective excavation of decalcified dentin using a mid-infrared tunable nanosecond pulsed laser: wavelength dependency in the 6 μm wavelength range

    Science.gov (United States)

    Ishii, Katsunori; Saiki, Masayuki; Yoshikawa, Kazushi; Yasuo, Kenzo; Yamamoto, Kazuyo; Awazu, Kunio

    2011-07-01

    Selective caries treatment has been anticipated as an essential application of dentistry. In clinic, some lasers have already realized the optical drilling of dental hard tissue. However, conventional lasers lack the selectivity, and still depend on the dentist's ability. Based on the absorption property of carious dentin, 6 μm wavelength range shows specific absorptions and promising characteristics for excavation. The objective of this study is to develop a selective excavation of carious dentin by using the laser ablation with 6 μm wavelength range. A mid-infrared tunable pulsed laser was obtained by difference-frequency generation technique. The wavelength was tuned around the absorption bands called amide 1 and amide 2. In the wavelength range from 5.75 to 6.60 μm, the difference of ablation depth between demineralized and normal dentin was observed. The wavelength at 6.02 μm and the average power density of 15 W/cm2, demineralized dentin was removed selectively with less-invasive effect on normal dentin. The wavelength at 6.42 μm required the increase of average power density, but also showed the possibility of selective ablation. This study provided a valuable insight into a wavelength choice for a novel dental laser device under development for minimal intervention dentistry.

  15. Spatio-temporal dependence of the signaling response in immune-receptor trafficking networks regulated by cell density: a theoretical model.

    Directory of Open Access Journals (Sweden)

    Pilar García-Peñarrubia

    Full Text Available Cell signaling processes involve receptor trafficking through highly connected networks of interacting components. The binding of surface receptors to their specific ligands is a key factor for the control and triggering of signaling pathways. In most experimental systems, ligand concentration and cell density vary within a wide range of values. Dependence of the signal response on cell density is related with the extracellular volume available per cell. This dependence has previously been studied using non-spatial models which assume that signaling components are well mixed and uniformly distributed in a single compartment. In this paper, a mathematical model that shows the influence exerted by cell density on the spatio-temporal evolution of ligands, cell surface receptors, and intracellular signaling molecules is developed. To this end, partial differential equations were used to model ligand and receptor trafficking dynamics through the different domains of the whole system. This enabled us to analyze several interesting features involved with these systems, namely: a how the perturbation caused by the signaling response propagates through the system; b receptor internalization dynamics and how cell density affects the robustness of dose-response curves upon variation of the binding affinity; and c that enhanced correlations between ligand input and system response are obtained under conditions that result in larger perturbations of the equilibrium ligand + surface receptor [Please see text] ligand - receptor complex. Finally, the results are compared with those obtained by considering that the above components are well mixed in a single compartment.

  16. Density-dependent adaptive resistance allows swimming bacteria to colonize an antibiotic gradient

    NARCIS (Netherlands)

    Hol, F.J.H.; Hubert, A.W.R.; Dekker, C.; Keymer Vergara, J.E.

    2016-01-01

    During antibiotic treatment, antibiotic concentration gradients develop. Little is know regarding the effects of antibiotic gradients on populations of nonresistant bacteria. Using a microfluidic device, we show that high-density motile Escherichia coli populations composed of nonresistant

  17. Densities and volume properties of (water + tert-butanol) over the temperature range of (274.15 to 348.15) K at pressure of 0.1 MPa

    Energy Technology Data Exchange (ETDEWEB)

    Egorov, Gennadiy I., E-mail: gie@isc-ras.r [Laboratory of Structure and Dynamics of Molecular and Ion-Molecular Solutions, Institute of Solution Chemistry, Russian Academy of Sciences, 1 Akademicheskaya Street, 153045 Ivanovo (Russian Federation); Makarov, Dmitriy M. [Laboratory of Structure and Dynamics of Molecular and Ion-Molecular Solutions, Institute of Solution Chemistry, Russian Academy of Sciences, 1 Akademicheskaya Street, 153045 Ivanovo (Russian Federation)

    2011-03-15

    The densities of {l_brace}water (1) + tert-butanol (2){r_brace} binary mixture were measured over the temperature range (274.15 to 348.15) K at atmospheric pressure using 'Anton Paar' digital vibrating-tube densimeter. Density measurements were carried out over the whole concentration range at (308.15 to 348.15) K. The following volume parameters were calculated: excess molar volumes and thermal isobaric expansivities of the mixture, partial molar volumes and partial molar thermal isobaric expansivities of the components. Concentration dependences of excess molar volumes were fitted with Redlich-Kister equation. The results of partial molar volume calculations using four equations were compared. It was established that for low alcohol concentrations at T {<=} 208 K the inflection points at x{sub 2} {approx} 0.02 were observed at concentration dependences of specific volume. The concentration dependences of partial molar volumes of both water and tert-butanol had extremes at low alcohol content. The temperature dependence of partial molar volumes of water had some inversion at x{sub 2} {approx} 0.65. The temperature dependence of partial molar volumes of tert-butanol at infinite dilution had minimum at {approx}288 K. It was discovered that concentration dependences of thermal isobaric expansivities of the mixture at small alcohol content and low temperatures passed through minimum.

  18. Dependence of simulations of long range transport on meteorology, model and dust size

    Science.gov (United States)

    Mahowald, N. M.; Albani, S.; Smith, M.; Losno, R.; Marticorena, B.; Ridley, D. A.; Heald, C. L.; Qu, Z.

    2015-12-01

    Mineral aerosols interact with radiation directly, as well as modifying climate, and provide important micronutrients to ocean and land ecosystems. Mineral aerosols are transported long distances from the source regions to remote regions, but the rates at which this occurs can be difficult to deduce from either observations or models. Here we consider interactions between the details of the simulation of dust size and long-range transport. In addition, we compare simulations of dust using multiple reanalysis datasets, as well as different model basis to understand how robust the mean, seasonality and interannual variability are in models. Models can provide insight into how long observations are required in order to characterize the atmospheric concentration and deposition to remote regions.

  19. Communication: Anomalous temperature dependence of the intermediate range order in phosphonium ionic liquids

    Energy Technology Data Exchange (ETDEWEB)

    Hettige, Jeevapani J.; Kashyap, Hemant K.; Margulis, Claudio J., E-mail: claudio-margulis@uiowa.edu [Department of Chemistry, University of Iowa, Iowa City, Iowa 52242 (United States)

    2014-03-21

    In a recent article by the Castner and Margulis groups [Faraday Discuss. 154, 133 (2012)], we described in detail the structure of the tetradecyltrihexylphosphonium bis(trifluoromethylsulfonyl)-amide ionic liquid as a function of temperature using X-ray scattering, and theoretical partitions of the computationally derived structure function. Interestingly, and as opposed to the case in most other ionic-liquids, the first sharp diffraction peak or prepeak appears to increase in intensity as temperature is increased. This phenomenon is counter intuitive as one would expect that intermediate range order fades as temperature increases. This Communication shows that a loss of hydrophobic tail organization at higher temperatures is counterbalanced by better organization of polar components giving rise to the increase in intensity of the prepeak.

  20. Dependence of intermittent density fluctuations on collisionality in TJ-K

    Energy Technology Data Exchange (ETDEWEB)

    Reuther, Kyle; Garland, Stephen; Ramisch, Mirko [Institut fuer Grenzflaechenverfahrenstechnikund Plasmatechnologie, Universitaet Stuttgart (Germany); Manz, Peter [Physik-Department E28, Technische Universitaet Muenchen, Garching (Germany)

    2016-07-01

    Particle and heat transport losses due to edge turbulence are well known phenomena commonly seen in toroidal magnetic confinement devices. Furthermore in the scrape-off layer (SOL), turbulent density fluctuations are often observed to be intermittent and dominate particle transport to the vessel walls. In the adiabatic limit (small collisionality), of the two-field Hasegawa-Wakatani model, simulated turbulent density fluctuations are observed to couple to potential fluctuations and exhibit Gaussian behavior. However, in the hydrodynamic limit (large collisionality) the density and potential decouple. As a result, the density becomes passively advected, evolves towards the vorticity, and exhibits intermittent behavior. The relationship between collisionality and intermittency is investigated experimentally at the stellarator TJ-K. To vary the plasma collisionality, which is related to electron density and temperature, parameters such as gas type, neutral gas pressure, magnetic field, and heating power are varied. Radial profiles of plasma density, temperature, floating potential, and vorticity are recorded via a scanning 7-tip Langmuir probe array. First results are presented.

  1. Constraints on rapidity-dependent initial conditions from charged-particle pseudorapidity densities and two-particle correlations

    Science.gov (United States)

    Ke, Weiyao; Moreland, J. Scott; Bernhard, Jonah E.; Bass, Steffen A.

    2017-10-01

    We study the initial three-dimensional spatial configuration of the quark-gluon plasma (QGP) produced in relativistic heavy-ion collisions using centrality and pseudorapidity-dependent measurements of the medium's charged particle density and two-particle correlations. A cumulant-generating function is first used to parametrize the rapidity dependence of local entropy deposition and extend arbitrary boost-invariant initial conditions to nonzero beam rapidities. The model is then compared to p +Pb and Pb + Pb charged-particle pseudorapidity densities and two-particle pseudorapidity correlations and systematically optimized using Bayesian parameter estimation to extract high-probability initial condition parameters. The optimized initial conditions are then compared to a number of experimental observables including the pseudorapidity-dependent anisotropic flows, event-plane decorrelations, and flow correlations. We find that the form of the initial local longitudinal entropy profile is well constrained by these experimental measurements.

  2. Incident particle range dependence of radiation damage in a power bipolar junction transistor

    Science.gov (United States)

    Liu, Chao-Ming; Li, Xing-Ji; Geng, Hong-Bin; Rui, Er-Ming; Guo, Li-Xin; Yang, Jian-Qun

    2012-10-01

    The characteristic degradations in silicon NPN bipolar junction transistors (BJTs) of type 3DD155 are examined under the irradiations of 25-MeV carbon (C), 40-MeV silicon (Si), and 40-MeV chlorine (Cl) ions respectively. Different electrical parameters are measured in-situ during the exposure of heavy ions. The experimental data shows that the changes in the reciprocal of the gain variation (Δ(1/β)) of 3DD155 transistors irradiated respectively by 25-MeV C, 40-MeV Si, and 40-MeV Cl ions each present a nonlinear behaviour at a low fluence and a linear response at a high fluence. The Δ(1/β) of 3DD155 BJT irradiated by 25-MeV C ions is greatest at a given fluence, a little smaller when the device is irradiated by 40-MeV Si ions, and smallest in the case of the 40-MeV Cl ions irradiation. The measured and calculated results clearly show that the range of heavy ions in the base region of BJT affects the level of radiation damage.

  3. Metabolomic unveiling of a diverse range of green tea (Camellia sinensis) metabolites dependent on geography.

    Science.gov (United States)

    Lee, Jang-Eun; Lee, Bum-Jin; Chung, Jin-Oh; Kim, Hak-Nam; Kim, Eun-Hee; Jung, Sungheuk; Lee, Hyosang; Lee, Sang-Jun; Hong, Young-Shick

    2015-05-01

    Numerous factors such as geographical origin, cultivar, climate, cultural practices, and manufacturing processes influence the chemical compositions of tea, in the same way as growing conditions and grape variety affect wine quality. However, the relationships between these factors and tea chemical compositions are not well understood. In this study, a new approach for non-targeted or global analysis, i.e., metabolomics, which is highly reproducible and statistically effective in analysing a diverse range of compounds, was used to better understand the metabolome of Camellia sinensis and determine the influence of environmental factors, including geography, climate, and cultural practices, on tea-making. We found a strong correlation between environmental factors and the metabolome of green, white, and oolong teas from China, Japan, and South Korea. In particular, multivariate statistical analysis revealed strong inter-country and inter-city relationships in the levels of theanine and catechin derivatives found in green and white teas. This information might be useful for assessing tea quality or producing distinct tea products across different locations, and highlights simultaneous identification of diverse tea metabolites through an NMR-based metabolomics approach. Copyright © 2014 Elsevier Ltd. All rights reserved.

  4. Simple illustrations of range-dependence and 3-D effects by normal-mode sound propagation modelling

    CERN Document Server

    Ivansson, Sven

    2016-01-01

    As is well known, the sound-speed profile has significant effects on underwater acoustic sound propagation. These effects can be quantified by normal-mode models, for example. The basic case is a laterally homogeneous medium, for which the sound speed and the density depend on depth only and not on horizontal position. Effects of horizontal medium-parameter variation can be quantified by coupled-mode models, with coupling between mode expansions for laterally homogeneous parts of the medium. In the present paper, these effects are illustrated for media with a particularly simple horizontal parameter variation such that mode shapes do not vary with horizontal position. The modal wavenumbers depend on horizontal position, however. At a vertical interface between regions with laterally homogeneous medium parameters, each mode is reflected as well as transmitted. For the media considered, reflection and transmission coefficients can be computed separately for each mode without mode coupling, and this is done recu...

  5. Non-linear density-dependent effects of an intertidal ecosystem engineer.

    Science.gov (United States)

    Harley, Christopher D G; O'Riley, Jaclyn L

    2011-06-01

    Ecosystem engineering is an important process in a variety of ecosystems. However, the relationship between engineer density and engineering impact remains poorly understood. We used experiments and a mathematical model to examine the role of engineer density in a rocky intertidal community in northern California. In this system, the whelk Nucella ostrina preys on barnacles (Balanus glandula and Chthamalus dalli), leaving empty barnacle tests as a resource (favorable microhabitat) for other species. Field experiments demonstrated that N. ostrina predation increased the availability of empty tests of both barnacle species, reduced the density of the competitively dominant B. glandula, and indirectly increased the density of the competitively inferior C. dalli. Empty barnacle tests altered microhabitat humidity, but not temperature, and presumably provided a refuge from wave action. The herbivorous snail Littorina plena was positively associated with empty test availability in both observational comparisons and experimental manipulations of empty test availability, and L. plena density was elevated in areas with foraging N. ostrina. To explore the effects of variation in N. ostrina predation, we constructed a demographic matrix model for barnacles in which we varied predation intensity. The model predicted that number of available empty tests increases with predation intensity to a point, but declines when predation pressure was strong enough to severely reduce adult barnacle densities. The modeled number of available empty tests therefore peaked at an intermediate level of N. ostrina predation. Non-linear relationships between engineer density and engineer impact may be a generally important attribute of systems in which engineers influence the population dynamics of the species that they manipulate.

  6. Time-Local Equation for the Exact Optimized Effective Potential in Time-Dependent Density Functional Theory

    Science.gov (United States)

    Liao, Sheng-Lun; Ho, Tak-San; Rabitz, Herschel; Chu, Shih-I.

    2017-06-01

    A long-standing challenge in the time-dependent density functional theory is to efficiently solve the exact time-dependent optimized effective potential (TDOEP) integral equation derived from orbital-dependent functionals, especially for the study of nonadiabatic dynamics in time-dependent external fields. In this Letter, we formulate a completely equivalent time-local TDOEP equation that admits a unique real-time solution in terms of time-dependent Kohn-Sham and effective memory orbitals. The time-local formulation is numerically implemented, with the incorporation of exponential memory loss to address the unaccounted for correlation component in the exact-exchange-only functional, to enable the study of the many-electron dynamics of a one-dimensional hydrogen chain. It is shown that the long time behavior of the electric dipole converges correctly and the zero-force theorem is fulfilled in the current implementation.

  7. Charge Transfer Enhancement in the D-π-A Type Porphyrin Dyes: A Density Functional Theory (DFT and Time-Dependent Density Functional Theory (TD-DFT Study

    Directory of Open Access Journals (Sweden)

    Guo-Jun Kang

    2016-11-01

    Full Text Available The electronic geometries and optical properties of two D-π-A type zinc porphyrin dyes (NCH3-YD2 and TPhe-YD were systematically investigated by density functional theory (DFT and time-dependent density functional theory (TD-DFT to reveal the origin of significantly altered charge transfer enhancement by changing the electron donor of the famous porphyrin-based sensitizer YD2-o-C8. The molecular geometries and photophysical properties of dyes before and after binding to the TiO2 cluster were fully investigated. From the analyses of natural bond orbital (NBO, extended charge decomposition analysis (ECDA, and electron density variations (Δρ between the excited state and ground state, it was found that the introduction of N(CH32 and 1,1,2-triphenylethene groups enhanced the intramolecular charge-transfer (ICT character compared to YD2-o-C8. The absorption wavelength and transition possess character were significantly influenced by N(CH32 and 1,1,2-triphenylethene groups. NCH3-YD2 with N(CH32 groups in the donor part is an effective way to improve the interactions between the dyes and TiO2 surface, light having efficiency (LHE, and free energy change (ΔGinject, which is expected to be an efficient dye for use in dye-sensitized solar cells (DSSCs.

  8. Density-dependent adaptive resistance allows swimming bacteria to colonize an antibiotic gradient.

    Science.gov (United States)

    Hol, Felix J H; Hubert, Bert; Dekker, Cees; Keymer, Juan E

    2016-01-01

    During antibiotic treatment, antibiotic concentration gradients develop. Little is know regarding the effects of antibiotic gradients on populations of nonresistant bacteria. Using a microfluidic device, we show that high-density motile Escherichia coli populations composed of nonresistant bacteria can, unexpectedly, colonize environments where a lethal concentration of the antibiotic kanamycin is present. Colonizing bacteria establish an adaptively resistant population, which remains viable for over 24 h while exposed to the antibiotic. Quantitative analysis of multiple colonization events shows that collectively swimming bacteria need to exceed a critical population density in order to successfully colonize the antibiotic landscape. After colonization, bacteria are not dormant but show both growth and swimming motility under antibiotic stress. Our results highlight the importance of motility and population density in facilitating adaptive resistance, and indicate that adaptive resistance may be a first step to the emergence of genetically encoded resistance in landscapes of antibiotic gradients.

  9. Time dependent human hip joint lubrication for periodic motion with stochastic asymmetric density function.

    Science.gov (United States)

    Wierzcholski, Krzysztof

    2014-01-01

    The present paper is concerned with the calculation of the human hip joint parameters for periodic, stochastic unsteady, motion with asymmetric probability density function for gap height. The asymmetric density function indicates that the stochastic probabilities of gap height decreasing are different in comparison with the probabilities of the gap height increasing. The models of asymmetric density functions are considered on the grounds of experimental observations. Some methods are proposed for calculation of pressure distributions and load carrying capacities for unsteady stochastic conditions in a super thin layer of biological synovial fluid inside the slide biobearing gap limited by a spherical bone acetabulum. Numerical calculations are performed in Mathcad 12 Professional Program, by using the method of finite differences. This method assures stability of numerical solutions of partial differential equations and gives proper values of pressure and load carrying capacity forces occurring in human hip joints.

  10. Withdrawal of corticosteroids in inflammatory bowel disease patients after dependency periods ranging from 2 to 45 years: a proposed method.

    LENUS (Irish Health Repository)

    Murphy, S J

    2012-02-01

    BACKGROUND: Even in the biologic era, corticosteroid dependency in IBD patients is common and causes a lot of morbidity, but methods of withdrawal are not well described. AIM: To assess the effectiveness of a corticosteroid withdrawal method. METHODS: Twelve patients (10 men, 2 women; 6 ulcerative colitis, 6 Crohn\\'s disease), median age 53.5 years (range 29-75) were included. IBD patients with quiescent disease refractory to conventional weaning were transitioned to oral dexamethasone, educated about symptoms of the corticosteroid withdrawal syndrome (CWS) and weaned under the supervision of an endocrinologist. When patients failed to wean despite a slow weaning pace and their IBD remaining quiescent, low dose synthetic ACTH stimulation testing was performed to assess for adrenal insufficiency. Multivariate analysis was performed to assess predictors of a slow wean. RESULTS: Median durations for disease and corticosteroid dependency were 21 (range 3-45) and 14 (range 2-45) years respectively. Ten patients (83%) were successfully weaned after a median follow-up from final wean of 38 months (range 5-73). Disease flares occurred in two patients, CWS in five and ACTH testing was performed in 10. Multivariate analysis showed that longer duration of corticosteroid use appeared to be associated with a slower wean (P = 0.056). CONCLUSIONS: Corticosteroid withdrawal using this protocol had a high success rate and durable effect and was effective in patients with long-standing (up to 45 years) dependency. As symptoms of CWS mimic symptoms of IBD disease flares, gastroenterologists may have difficulty distinguishing them, which may be a contributory factor to the frequency of corticosteroid dependency in IBD patients.

  11. The Potential Energy Density in Transverse String Waves Depends Critically on Longitudinal Motion

    Science.gov (United States)

    Rowland, David R.

    2011-01-01

    The question of the correct formula for the potential energy density in transverse waves on a taut string continues to attract attention (e.g. Burko 2010 "Eur. J. Phys." 31 L71), and at least three different formulae can be found in the literature, with the classic text by Morse and Feshbach ("Methods of Theoretical Physics" pp 126-127) stating…

  12. Bayesian inference on the effect of density dependence and weather on a guanaco population from Chile

    DEFF Research Database (Denmark)

    Zubillaga, Maria; Skewes, Oscar; Soto, Nicolás

    2014-01-01

    on a time series of 36 years of population sampling of guanacos in Tierra del Fuego, Chile. The population density varied between 2.7 and 30.7 guanaco/km², with an apparent monotonic growth during the first 25 years; however, in the last 10 years the population has shown large fluctuations, suggesting...

  13. Age dependent mineral density in the bones of inhabitants of Karelia

    Directory of Open Access Journals (Sweden)

    I. G. Pashkova

    2013-01-01

    Full Text Available Analysis of the age changes of mineral density in the lumbar vertebrae was carried out in 929 people (740 women and 189 men at the age of 20 to 87 years, living in Karelia. Bone mineral density was evaluated by dual xray absorptiometry. In the women and in the men the spine bone mineralization peak was seen at the age of 22. The peak mineral density values were 5 % lower in the men and 1.6 % in the women in comparison with the data of the densitometer base. Considerable decrease of the bone mineral density in the vertebrae in the women began at the age of 41–45 years, and in the men – at the age of 51–55 years. Demineralization of the vertebrae in 75 year old women was 20 %, in the men it was 11.1 %, and in 81–87 year old women – 25.2 %.

  14. Yields of ZP sweet maize hybrids in dependence on sowing densities

    Directory of Open Access Journals (Sweden)

    Srdić Jelena

    2008-01-01

    Full Text Available Sweet maize differs from maize of standard grain quality by many important traits that affect the ear appearance, and especially by traits controlling taste. The ear appearance trait encompasses the kernel row number, configuration, row pattern (direction and arrangement, seed set, kernel width and depth, ear shape and size. The quality of immature kernels is controlled by genes by which sweet maize differs from common maize. In order to obtain high-ranking and high-quality yields, it is necessary to provide the most suitable cropping practices for sweet maize hybrids developed at the Maize Research Institute, Zemun Polje. The adequate sowing density is one of more important elements of correct cropping practices. The objective of the present study was to determine the effect of four sowing densities in four ZP sweet maize hybrids of different FAO maturity groups on ear qualitative traits and yields obtained on chernozem type of soil in Zemun Polje. The observed traits of sweet maize (ear length, kernel row number, number of kernels per row, yield and shelling percentage significantly varied over years. The higher sowing density was the higher yield of sweet maize was, hence the highest ear yield of 9.67 t ha-1 , on the average for all four hybrids, was recorded at the highest sowing density of 70,000 plants ha-1. The highest yield was detected in the hybrid ZP 424su. The highest shelling percentage (67.81% was found in the hybrid ZP 521su at the sowing density of 60,000 plants ha-1. Generally, it can be stated that sweet maize hybrids of a shorter growing season (FAO 400 could be cultivated up to 70,000 plants ha-1, while those of a longer growing season (FAO 500 could be grown up to 60,000 plants ha-1. In such a way, the most favorable parameters of yields and the highest yields can be obtained.

  15. In situ characterization of ZnTe epilayer irradiation via time-resolved and power-density-dependent Raman spectroscopy

    Science.gov (United States)

    Wiedemeier, V.; Berth, G.; Zrenner, A.; Larramendi, E. M.; Woggon, U.; Lischka, K.; Schikora, D.

    2011-10-01

    Laser irradiation damage in ZnTe epilayers was analyzed in situ by power-density-dependent and time-resolved micro-Raman spectroscopy. Damage by ablation or compound decomposition on the sample surface was revealed by the decrease of the ZnTe-nLO mode intensity with the increase of laser power density. The appearance of the peaks associated with the stronger crystalline-tellurium modes, tellurium aggregates and second-order Raman scattering at room temperature μ-Raman spectra was observed for higher power densities than 4.4 × 105 W cm-2. The Raman signal time transients of ZnTe-nLO and crystalline-tellurium modes reveal an exponential evolution of the laser irradiation damage and a fast formation of crystalline tellurium aggregates on the layer surface.

  16. Approximating the nonlinear density dependence of electron transport coefficients and scattering rates across the gas–liquid interface

    Science.gov (United States)

    Garland, N. A.; Boyle, G. J.; Cocks, D. G.; White, R. D.

    2018-02-01

    This study reviews the neutral density dependence of electron transport in gases and liquids and develops a method to determine the nonlinear medium density dependence of electron transport coefficients and scattering rates required for modeling transport in the vicinity of gas–liquid interfaces. The method has its foundations in Blanc’s law for gas-mixtures and adapts the theory of Garland et al (2017 Plasma Sources Sci. Technol. 26) to extract electron transport data across the gas–liquid transition region using known data from the gas and liquid phases only. The method is systematically benchmarked against multi-term Boltzmann equation solutions for Percus–Yevick model liquids. Application to atomic liquids highlights the utility and accuracy of the derived method.

  17. Linear interpolation method in ensemble Kohn-Sham and range-separated density-functional approximations for excited states

    DEFF Research Database (Denmark)

    Senjean, Bruno; Knecht, Stefan; Jensen, Hans Jørgen Aa

    2015-01-01

    Gross-Oliveira-Kohn density-functional theory (GOK-DFT) for ensembles is, in principle, very attractive but has been hard to use in practice. A practical model based on GOK-DFT for the calculation of electronic excitation energies is discussed. The model relies on two modifications of GOK-DFT: us...

  18. Time-dependent density-functional theory simulation for electron-ion dynamics in molecules under intense laser pulses.

    Science.gov (United States)

    Kawashita, Y; Nakatsukasa, T; Yabana, K

    2009-02-11

    We have developed a simulation method to describe three-dimensional dynamics of electrons and ions in a molecule based on the time-dependent density-functional theory. We solve the time-dependent Kohn-Sham equation for electrons employing the real-space and real-time method, while the ion dynamics are described in classical mechanics by the Ehrenfest method. For an efficient calculation in massively parallel computers, the code is parallelized dividing the spatial grid points. We apply the method to the Coulomb explosion of the H(2)S molecule under an intense and ultrashort laser pulse and investigate the mechanism of the process.

  19. Angular dependence of critical current density and magnetoresistance of sputtered high-T{sub c}-films

    Energy Technology Data Exchange (ETDEWEB)

    Geerkens, A.; Frenck, H.J.; Ewert, S. [Technical Univ. of Cottbus (Germany)] [and others

    1994-12-31

    The angular dependence of the critical current density and the magnetoresistance of high-T{sub c}-films in high and low magnetic fields and for different temperatures were measured to investigate the flux pinning and the superconducting properties. A comparison of the results for the different superconductors shows their increasing dependence on the angle {Theta} between the magnetic field and the c-axis of the film due to the anisotropy of the chosen superconductor. Furthermore the influence of the current direction to the {Theta}-rotation plane is discussed.

  20. A Room to Grow: The Residential Density-dependence of Childbearing in Europe and the United States

    Directory of Open Access Journals (Sweden)

    Nathanael Lauster

    2010-01-01

    Full Text Available I argue that cultural processes linked to the demographic transition produce new density-dependent fertility dynamics. In particular, childbearing becomes dependent upon residential roominess. This relationship is culturally specific, and I argue that the cultural nature of this relationship means that professional and managerial classes are likely to be particularly influenced by residential roominess, while immigrants are less likely to be influenced. I test hypotheses linking residential roominess to the presence of an “own infant” in the household using census data from the Austria, Greece, Portugal, Spain, and the United States. Roominess predicts fertility in all countries, but to differing degrees.

  1. Survival of diurnally sub periodic Wuchereria bancrofti in Downsiomyia nivea (Diptera: Culicidae: a density dependent factor from Andaman & Nicobar Islands

    Directory of Open Access Journals (Sweden)

    A N Shriram

    2014-01-01

    Full Text Available Background & objectives: In India, diurnally sub periodic Wuchereria bancrofti transmitted by Downsiomyia nivea is prevalent only in the Nicobar district of Andaman and Nicobar Islands. The ongoing LF elimination programme aims at transmission interruption by bringing down the microfilarie (mf load in the community, which has implication on the parasite load in mosquito vector. Therefore, understanding density dependent constraints on transmission assumes significance from control perspective. The present study was undertaken in Teressa Island to understand the density dependent parasite mortality and survival probability of the parasite Do. nivea. Methods: The entomological data collected from Teressa Island, endemic for the diurnally sub periodic form of W. bancrofti were used to examine the parasite loss and its survival up to infectivity. Patterns of parasite distribution in Do. nivea were examined. Results: Distribution patterns of microfilariae were found to be over dispersed in Do. nivea. The later stages of the parasite in the vector were randomly distributed. Distribution pattern of various filarial larval stages suggested that the loss of parasites occurred as development progressed and was maximal between the first and second stages. Further, both the prevalence of infection and the degree of parasite aggregation in the vector population have fallen significantly with development of parasite stage. Interpretation & conclusions: Results indicate the operation of parasite density dependent mortality of vectors or parasite loss or combination of both. The present study with Aedes transmitted filariasis conducted before launching LF elimination programme in the study area indicates a comparable level of parasite regulation in the vector which has similar implications on the transmission threshold. Thus, the consideration of Aedes with Culex in deriving the critical level of antigen positive for making decisions on cessation of mass drug

  2. Visualizing the mechanism that determines the critical current density in polycrystalline superconductors using time-dependent Ginzburg-Landau theory.

    OpenAIRE

    Carty, G. J.; Hampshire, D. P.

    2008-01-01

    In polycrystalline superconducting materials optimized for high critical current density (JC) in high magnetic fields, the mechanism that determines JC has long remained uncertain because of the complicated manner in which the fluxon-fluxon and fluxon-microstructure forces combine. In this work, the time-dependent Ginzburg-Landau equations are used to produce visualizations of fluxons at JC that show the disorder in the pinned part of the flux-line lattice and the motion of those fluxons alon...

  3. Demographics and practices of semi-intensive free-range farming systems in Australia with an outdoor stocking density of ≤1500 hens/hectare.

    Directory of Open Access Journals (Sweden)

    Mini Singh

    Full Text Available Baseline information on demographics and practices on semi-intensive free-range egg farms with an outdoor stocking density of ≤1500 hens/hectare in Australia is presented. Free-range egg production is changing the structure of the egg industry in Australia and a broad variety and tiers of free-range systems have emerged due to lack of concrete legislative standards on outdoor stocking densities in the past. Information was extracted from a pre-existing online free-range poultry survey dataset, consisting of a total of 79 questions related to nutrition, pasture management, welfare and health, animal housing, environmental impact and economics. Forty-one free-range egg farms, with an outdoor stocking density of ≤1500 hens/hectare, were identified in the dataset from all major Australian states. Two types of semi-intensive free-range housing systems were documented: mobile (modified caravan/trailer housing (56%, and fixed sheds (44%. Seventy-two percent of respondents reported >75% of the hens in the flock used the outdoor range. All respondents reported ingestion of range components by hens in the form of vegetation, insects, stones and grit. Up to 10% mortality was reported by 40% respondents with predation (34%, cannibalism (29%, heat stress (24% and grass impaction (19.5% as major causes. Biosecurity on farms was sub-optimal with 8 of the 10 actions implemented by <50% respondents. Customer demand, consumer sentiment and welfare were the major factors for farmers moving into free-range egg production. This study resulted in identification of current practices and key challenges on semi-intensive free-range egg farms. Applied research and communication of results to farmers is highly recommended to ensure optimum health and welfare of free-range laying hens and sustained egg production.

  4. Results of Current Density Distribution Mapping in PEM Fuel Cells Dependent on Operation Parameters

    Directory of Open Access Journals (Sweden)

    Zbigniew A. Styczynski

    2013-07-01

    Full Text Available This paper presents in situ measurements of a newly developed current density measurement system for proton exchange membrane fuel cells (PEMFC. While the functional principle and technical evaluation of the measurement system were presented in a previous paper, this paper analyzes the influence of various operation parameters, including multiple start-stop operation, at the anode, cathode and cooling locations on the distribution and long-term development of the current density. The system was operated for 500 h over two years with long periods of inactivity between measurements. The measurement results are evaluated and provide additional information on how to optimize the operation modes of fuel cells, including the start and stop of such systems as well as the water balance.

  5. Quantum computing without wavefunctions: time-dependent density functional theory for universal quantum computation.

    Science.gov (United States)

    Tempel, David G; Aspuru-Guzik, Alán

    2012-01-01

    We prove that the theorems of TDDFT can be extended to a class of qubit Hamiltonians that are universal for quantum computation. The theorems of TDDFT applied to universal Hamiltonians imply that single-qubit expectation values can be used as the basic variables in quantum computation and information theory, rather than wavefunctions. From a practical standpoint this opens the possibility of approximating observables of interest in quantum computations directly in terms of single-qubit quantities (i.e. as density functionals). Additionally, we also demonstrate that TDDFT provides an exact prescription for simulating universal Hamiltonians with other universal Hamiltonians that have different, and possibly easier-to-realize two-qubit interactions. This establishes the foundations of TDDFT for quantum computation and opens the possibility of developing density functionals for use in quantum algorithms.

  6. Dislocation density dependent electroabsorption in epitaxial lateral overgrown InGaN/GaN quantum structures.

    Science.gov (United States)

    Sari, Emre; Jang, Lee Woon; Baek, Jong Hyeob; Lee, In Hwan; Sun, Xiao Wei; Demir, Hilmi Volkan

    2013-01-14

    We study electroabsorption (EA) behavior of InGaN/GaN quantum structures grown using epitaxial lateral overgrowth (ELOG) in correlation with their dislocation density levels and in comparison to steady state and time-resolved photoluminescence measurements. The results reveal that ELOG structures with decreasing mask stripe widths exhibit stronger EA performance, with a maximum EA enhancement factor of 4.8 compared to the reference without ELOG. The analyses show that the EA performance follows similar trends with decreasing dislocation density as the essential parameters of the photoluminescence spectra (peak position, width and intensity) together with the photoluminescence lifetimes. While keeping the growth window widths constant, compared to photoluminescence behavior, however, EA surprisingly exhibits the largest performance variation, making EA the most sensitive to the mask stripe widths.

  7. Effect of glycaemic control, metformin and gliclazide on platelet density and aggregability in recently diagnosed type 2 (non-insulin-dependent) diabetic patients.

    Science.gov (United States)

    Collier, A; Watson, H H; Patrick, A W; Ludlam, C A; Clarke, B F

    1989-01-01

    Platelet density profiles, intraplatelet nucleotides, intraplatelet beta thromboglobulin (beta TG), plasma beta TG levels, intraplatelet cyclic AMP (cAMP) levels, platelet release reaction, platelet thromboxane (TX)B2 production and plasma fibrinogen levels were investigated in 24 newly diagnosed, non-insulin-dependent diabetic patients and 12 comparable controls. These variables were measured at diagnosis, after a 3-6 week dietary run-in period, and again after 6 months on treatment with either metformin or gliclazide therapy. With dietary restriction of refined carbohydrate and oral hypoglycaemic therapy, there was a reduction in platelet density (p less than 0.05), intraplatelet nucleotides (p less than 0.001), intraplatelet beta TG (p less than 0.001), plasma beta TG (p less than 0.001) and there was an increase in intraplatelet cAMP levels (p less than 0.05). Although these platelet variables returned towards normal, only the platelet density mean returned to within the normal range. There was no significant change in the platelet TXB2 production and plasma fibrinogen levels with treatment. Metformin and gliclazide were equally effective in the glycaemic control of non-insulin-dependent diabetes, and there was no difference between the platelet variables measured in the two groups. We would therefore suggest that improvement of glycaemic control, rather than any specific effect of the oral hypoglycaemic agent employed, is the most important factor in returning these parameters towards normality.

  8. The energy dependence of the lateral dose response functions of detectors with various densities in photon-beam dosimetry.

    Science.gov (United States)

    Looe, Hui Khee; Harder, Dietrich; Poppe, Björn

    2017-02-07

    The lateral dose response function is a general characteristic of the volume effect of a detector used for photon dosimetry in a water phantom. It serves as the convolution kernel transforming the true absorbed dose to water profile, which would be produced within the undisturbed water phantom, into the detector-measured signal profile. The shape of the lateral dose response function characterizes (i) the volume averaging attributable to the detector's size and (ii) the disturbance of the secondary electron field associated with the deviation of the electron density of the detector material from the surrounding water. In previous work, the characteristic dependence of the shape of the lateral dose response function upon the electron density of the detector material was studied for 6 MV photons by Monte Carlo simulation of a wall-less voxel-sized detector (Looe et al 2015 Phys. Med. Biol. 60 6585-07). This study is here continued for 60Co gamma rays and 15 MV photons in comparison with 6 MV photons. It is found (1) that throughout these photon spectra the shapes of the lateral dose response functions are retaining their characteristic dependence on the detector's electron density, and (2) that their energy-dependent changes are only moderate. This appears as a practical advantage because the lateral dose response function can then be treated as practically invariant across a clinical photon beam in spite of the known changes of the photon spectrum with increasing distance from the beam axis.

  9. Bone density and neuromuscular function in older competitive athletes depend on running distance

    OpenAIRE

    Gast, Ulf; Belavy, Daniel; Armbrecht, Gabriele; Kusy, Krzysztof; Lexy, H; Rawer, R; Rittweger, Jörn; Winwood, Keith; Zielinski, Jacek; Felsenberg, Dieter

    2013-01-01

    Summary Individuals who are involved in explosive sport types, such as 100-m sprints and long jump, have greater bone density, leg muscle size, jumping height and grip strength than individuals involved in long-distance running. Introduction The purpose of this study is to examine the relationship between different types of physical activity with bone, lean mass and neuromuscular performance in older individuals. Methods We examined short- (n050), middle- (n019) and lo...

  10. Oxidized low-density lipoproteins upregulate proline oxidase to initiate ROS-dependent autophagy

    OpenAIRE

    Zabirnyk, Olga; Liu, Wei; Khalil, Shadi; Sharma, Anit; Phang, James M.

    2009-01-01

    Epidemiological studies showed that high levels of oxidized low-density lipoproteins (oxLDLs) are associated with increased cancer risk. We examined the direct effect of physiologic concentrations oxLDL on cancer cells. OxLDLs were cytotoxic and activate both apoptosis and autophagy. OxLDLs have ligands for peroxisome proliferator-activated receptor gamma and upregulated proline oxidase (POX) through this nuclear receptor. We identified 7-ketocholesterol (7KC) as a main component responsible ...

  11. Responsivity Dependent Anodization Current Density of Nanoporous Silicon Based MSM Photodetector

    Directory of Open Access Journals (Sweden)

    Batool Eneaze B. Al-Jumaili

    2016-01-01

    Full Text Available Achieving a cheap and ultrafast metal-semiconductor-metal (MSM photodetector (PD for very high-speed communications is ever-demanding. We report the influence of anodization current density variation on the response of nanoporous silicon (NPSi based MSM PD with platinum (Pt contact electrodes. Such NPSi samples are grown from n-type Si (100 wafer using photoelectrochemical etching with three different anodization current densities. FESEM images of as-prepared samples revealed the existence of discrete pores with spherical and square-like shapes. XRD pattern displayed the growth of nanocrystals with (311 lattice orientation. The nanocrystallite sizes obtained using Scherrer formula are found to be between 20.8 nm and 28.6 nm. The observed rectifying behavior in the I-V characteristics is ascribed to the Pt/PSi/n-Si Schottky barrier formation, where the barrier height at the Pt/PSi interface is estimated to be 0.69 eV. Furthermore, this Pt/PSi/Pt MSM PD achieved maximum responsivity of 0.17 A/W and quantum efficiency as much as 39.3%. The photoresponse of this NPSi based MSM PD demonstrated excellent repeatability, fast response, and enhanced saturation current with increasing anodization current density.

  12. Density dependence of electron-spin polarization and relaxation in intrinsic GaAs at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Teng, L H; Chen, K; Wen, J H; Lin, W Z; Lai, T S, E-mail: stslts@mail.sysu.edu.c [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Zhongshan (Sen Yat-Sen) University, Guangzhou, Guangdong 510275 (China)

    2009-07-07

    Time-resolved circularly polarized pump-probe spectroscopy is used to study the carrier-density dependence of the electron-spin polarization and spin relaxation dynamics in bulk intrinsic GaAs near the bottom of the conduction band. The experimental result shows that the initial degree of the electron-spin polarization is less than 0.5, and both the initial degree of spin polarization and the spin relaxation time decrease with increasing carrier densities. The simulation calculation shows that the band-gap renormalization effect has a significant influence on the initial degree of spin polarization, but it is not the physical origin of the decrease in the electron-spin polarization. Contrarily, the initial degree of spin polarization can be greatly enhanced by the band-gap renormalization effect for carrier densities above 3.5 x 10{sup 17} cm{sup -3}. In intrinsic GaAs, both the D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms play an important role. The Bir-Aronov-Pikus mechanism becomes stronger with the increase in the carrier density, and becomes dominant at high carrier density.

  13. Density dependence of electron-spin polarization and relaxation in intrinsic GaAs at room temperature

    Science.gov (United States)

    Teng, L. H.; Chen, K.; Wen, J. H.; Lin, W. Z.; Lai, T. S.

    2009-07-01

    Time-resolved circularly polarized pump-probe spectroscopy is used to study the carrier-density dependence of the electron-spin polarization and spin relaxation dynamics in bulk intrinsic GaAs near the bottom of the conduction band. The experimental result shows that the initial degree of the electron-spin polarization is less than 0.5, and both the initial degree of spin polarization and the spin relaxation time decrease with increasing carrier densities. The simulation calculation shows that the band-gap renormalization effect has a significant influence on the initial degree of spin polarization, but it is not the physical origin of the decrease in the electron-spin polarization. Contrarily, the initial degree of spin polarization can be greatly enhanced by the band-gap renormalization effect for carrier densities above 3.5 × 1017 cm-3. In intrinsic GaAs, both the D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms play an important role. The Bir-Aronov-Pikus mechanism becomes stronger with the increase in the carrier density, and becomes dominant at high carrier density.

  14. Demographics and practices of semi-intensive free-range farming systems in Australia with an outdoor stocking density of ≤1500 hens/hectare.

    Science.gov (United States)

    Singh, Mini; Ruhnke, Isabelle; de Koning, Carolyn; Drake, Kelly; Skerman, Alan G; Hinch, Geoff N; Glatz, Philip C

    2017-01-01

    Baseline information on demographics and practices on semi-intensive free-range egg farms with an outdoor stocking density of ≤1500 hens/hectare in Australia is presented. Free-range egg production is changing the structure of the egg industry in Australia and a broad variety and tiers of free-range systems have emerged due to lack of concrete legislative standards on outdoor stocking densities in the past. Information was extracted from a pre-existing online free-range poultry survey dataset, consisting of a total of 79 questions related to nutrition, pasture management, welfare and health, animal housing, environmental impact and economics. Forty-one free-range egg farms, with an outdoor stocking density of ≤1500 hens/hectare, were identified in the dataset from all major Australian states. Two types of semi-intensive free-range housing systems were documented: mobile (modified caravan/trailer) housing (56%), and fixed sheds (44%). Seventy-two percent of respondents reported >75% of the hens in the flock used the outdoor range. All respondents reported ingestion of range components by hens in the form of vegetation, insects, stones and grit. Up to 10% mortality was reported by 40% respondents with predation (34%), cannibalism (29%), heat stress (24%) and grass impaction (19.5%) as major causes. Biosecurity on farms was sub-optimal with 8 of the 10 actions implemented by intensive free-range egg farms. Applied research and communication of results to farmers is highly recommended to ensure optimum health and welfare of free-range laying hens and sustained egg production.

  15. Reconstructing the galaxy density field with photometric redshifts - II. Environment-dependent galaxy evolution since z ≃ 3

    Science.gov (United States)

    Malavasi, Nicola; Pozzetti, Lucia; Cucciati, Olga; Bardelli, Sandro; Ilbert, Olivier; Cimatti, Andrea

    2017-09-01

    Although extensively investigated, the role of the environment in galaxy formation is still not well understood. In this context, the galaxy stellar mass function (GSMF) is a powerful tool to understand how environment relates to galaxy mass assembly and the quenching of star formation. In this work, we make use of the high-precision photometric redshifts of the UltraVISTA Survey to study the GSMF in different environments up to z ˜ 3, on physical scales from 0.3 to 2 Mpc, down to masses of M ˜ 1010 M⊙. We witness the appearance of environmental signatures for both quiescent and star-forming galaxies. We find that the shape of the GSMF of quiescent galaxies is different in high- and low-density environments up to z ˜ 2 with the high-mass end (M ≳ 1011 M⊙) being enhanced in high-density environments. On the contrary, for star-forming galaxies, a difference between the GSMF in high- and low-density environments is present for masses M ≲ 1011 M⊙. Star-forming galaxies in this mass range appear to be more frequent in low-density environments up to z 2. Our results, in terms of general trends in the shape of the GSMF, are in agreement with a scenario in which galaxies are quenched when they enter hot gas-dominated massive haloes that are preferentially in high-density environments.

  16. Prey-predator dynamics in rotifers: density-dependent consequences of spatial heterogeneity due to surface attachment.

    Science.gov (United States)

    Vadstein, Olav; Olsen, Lasse M; Andersen, Tom

    2012-08-01

    Classical models of prey-predator interactions assume that per capita prey consumption is dependent on prey density alone and that prey consumption (functional response) and consumer proliferation (numerical response) operate on the same timescales and without time lags. Several modifications have been proposed for resolving this timescale discrepancy, including variants where the functional response depends on both prey and predator densities. A microcosm system with the rotifer Brachionus 'Nevada' feeding on the prasinophyte Tetraselmis sp. showed significant (P rotifers, which can result in a predator-dependent functional response. We also show that partitioning between the attached and free-swimming habitats was fast compared to the timescale of the numerical response. When attached to surfaces, rotifers maximized net energy gain by avoiding the high cost of swimming and by increased food capture due to reduced viscous drag. A mathematical model with prey-dependent functional response and wall-attached and free-swimming fractions of the population describes our data adequately. We discuss the implications of this finding for extrapolating microcosm experiments to systems with other surface-to-volume ratios, and to what extent our findings may apply to other popular model organisms for prey-predator interaction.

  17. Long-Range van der Waals Correction to a Semilocal Density Functional: The Tail Need Not Wag the Dog

    Science.gov (United States)

    Perdew, John P.

    The SCAN (strongly constrained and appropriately normed) meta-generalized gradient approximation satisfies all 17 exact constraints that a semilocal functional can. Without being fitted to any bonded system, it correctly describes most kinds of bonding, including intermediate-range van der Waals (vdW) interaction. It can be supplemented [3.4] with a long-range vdW correction such as D3 or rVV10, which have the flexibility to exclude any intermediate-range contribution. Accurate results are found for free molecules, for molecules weakly bound to metal surfaces, and for interlayer binding energies of layered materials. Despite being a pair-interaction model, the rVV10 correction to SCAN also gives a random-phase-approximation-like long-range contribution to the binding energy curve for graphene on a nickel surface. Supported by DOE BES and NSF DMR.

  18. A Quantitative Analysis of Light-Driven Charge Transfer Processes Using Voronoi Partitioning of Time Dependent DFT-Derived Electron Densities

    NARCIS (Netherlands)

    Rombouts, J.A.; Ehlers, A.W.; Lammertsma, K.

    2017-01-01

    An analytical method is presented that provides quantitative insight into light-driven electron density rearrangement using the output of standard time-dependent density functional theory (TD-DFT) computations on molecular compounds. Using final and initial electron densities for photochemical

  19. A density-dependent switch drives stochastic clustering and polarization of signaling molecules.

    Directory of Open Access Journals (Sweden)

    Alexandra Jilkine

    2011-11-01

    Full Text Available Positive feedback plays a key role in the ability of signaling molecules to form highly localized clusters in the membrane or cytosol of cells. Such clustering can occur in the absence of localizing mechanisms such as pre-existing spatial cues, diffusional barriers, or molecular cross-linking. What prevents positive feedback from amplifying inevitable biological noise when an un-clustered "off" state is desired? And, what limits the spread of clusters when an "on" state is desired? Here, we show that a minimal positive feedback circuit provides the general principle for both suppressing and amplifying noise: below a critical density of signaling molecules, clustering switches off; above this threshold, highly localized clusters are recurrently generated. Clustering occurs only in the stochastic regime, suggesting that finite sizes of molecular populations cannot be ignored in signal transduction networks. The emergence of a dominant cluster for finite numbers of molecules is partly a phenomenon of random sampling, analogous to the fixation or loss of neutral mutations in finite populations. We refer to our model as the "neutral drift polarity model." Regulating the density of signaling molecules provides a simple mechanism for a positive feedback circuit to robustly switch between clustered and un-clustered states. The intrinsic ability of positive feedback both to create and suppress clustering is a general mechanism that could operate within diverse biological networks to create dynamic spatial organization.

  20. Monte Carlo study of voxel S factor dependence on tissue density and atomic composition

    Energy Technology Data Exchange (ETDEWEB)

    Amato, Ernesto, E-mail: eamato@unime.it [University of Messina, Department of Biomedical Sciences and of Morphologic and Functional Imaging, Section of Radiological Sciences, via Consolare Valeria, 1, I-98125 Messina (Italy); Italiano, Antonio [INFN – Istituto Nazionale di Fisica Nucleare, Gruppo Collegato di Messina (Italy); Baldari, Sergio [University of Messina, Department of Biomedical Sciences and of Morphologic and Functional Imaging, Section of Radiological Sciences, via Consolare Valeria, 1, I-98125 Messina (Italy)

    2013-11-21

    Voxel dosimetry is a common approach to the internal dosimetry of non-uniform activity distributions in nuclear medicine therapies with radiopharmaceuticals and in the estimation of the radiation hazard due to internal contamination of radionuclides. Aim of the present work is to extend our analytical approach for the calculation of voxel S factors to materials different from the soft tissue. We used a Monte Carlo simulation in GEANT4 of a voxelized region of each material in which the source of monoenergetic electrons or photons was uniformly distributed within the central voxel, and the energy deposition was scored over the surrounding 11×11×11 voxels. Voxel S factors were obtained for the following standard ICRP materials: Adipose tissue, Bone cortical, Brain, Lung, Muscle skeletal and Tissue soft with 1 g cm{sup −3} density. Moreover, we considered the standard ICRU materials: Bone compact and Muscle striated. Voxel S factors were represented as a function of the “normalized radius”, defined as the ratio between the source–target voxel distance and the voxel side. We found that voxel S factors and related analytical fit functions are mainly affected by the tissue density, while the material composition gives only a slight contribution to the difference between data series, which is negligible for practical purposes. Our results can help in broadening the dosimetric three-dimensional approach based on voxel S factors to other tissues where diagnostic and therapeutic radionuclides can be taken up and radiation can propagate.

  1. Mechanics, hydrodynamics and energetics of blue whale lunge feeding: efficiency dependence on krill density.

    Science.gov (United States)

    Goldbogen, J A; Calambokidis, J; Oleson, E; Potvin, J; Pyenson, N D; Schorr, G; Shadwick, R E

    2011-01-01

    Lunge feeding by rorqual whales (Balaenopteridae) is associated with a high energetic cost that decreases diving capacity, thereby limiting access to dense prey patches at depth. Despite this cost, rorquals exhibit high rates of lipid deposition and extremely large maximum body size. To address this paradox, we integrated kinematic data from digital tags with unsteady hydrodynamic models to estimate the energy budget for lunges and foraging dives of blue whales (Balaenoptera musculus), the largest rorqual and living mammal. Our analysis suggests that, despite the large amount of mechanical work required to lunge feed, a large amount of prey and, therefore, energy is obtained during engulfment. Furthermore, we suggest that foraging efficiency for blue whales is significantly higher than for other marine mammals by nearly an order of magnitude, but only if lunges target extremely high densities of krill. The high predicted efficiency is attributed to the enhanced engulfment capacity, rapid filter rate and low mass-specific metabolic rate associated with large body size in blue whales. These results highlight the importance of high prey density, regardless of prey patch depth, for efficient bulk filter feeding in baleen whales and may explain some diel changes in foraging behavior in rorqual whales.

  2. A Density-Dependent Switch Drives Stochastic Clustering and Polarization of Signaling Molecules

    Science.gov (United States)

    Jilkine, Alexandra; Angenent, Sigurd B.; Wu, Lani F.; Altschuler, Steven J.

    2011-01-01

    Positive feedback plays a key role in the ability of signaling molecules to form highly localized clusters in the membrane or cytosol of cells. Such clustering can occur in the absence of localizing mechanisms such as pre-existing spatial cues, diffusional barriers, or molecular cross-linking. What prevents positive feedback from amplifying inevitable biological noise when an un-clustered “off” state is desired? And, what limits the spread of clusters when an “on” state is desired? Here, we show that a minimal positive feedback circuit provides the general principle for both suppressing and amplifying noise: below a critical density of signaling molecules, clustering switches off; above this threshold, highly localized clusters are recurrently generated. Clustering occurs only in the stochastic regime, suggesting that finite sizes of molecular populations cannot be ignored in signal transduction networks. The emergence of a dominant cluster for finite numbers of molecules is partly a phenomenon of random sampling, analogous to the fixation or loss of neutral mutations in finite populations. We refer to our model as the “neutral drift polarity model.” Regulating the density of signaling molecules provides a simple mechanism for a positive feedback circuit to robustly switch between clustered and un-clustered states. The intrinsic ability of positive feedback both to create and suppress clustering is a general mechanism that could operate within diverse biological networks to create dynamic spatial organization. PMID:22102805

  3. Pressure-Dependent Electronic and Transport Properties of Bulk Platinum Oxide by Density Functional Theory

    Science.gov (United States)

    Kansara, Shivam; Gupta, Sanjeev K.; Sonvane, Yogesh; Nekrasov, Kirill A.; Kichigina, Natalia V.

    2018-02-01

    The structural, electronic, and vibrational properties of bulk platinum oxide (PtO) at compressive pressures in the interval from 0 GPa to 35 GPa are investigated using the density functional theory. The calculated electronic band structure of PtO shows poor metallicity at very low density of states on the Fermi level. However, the hybrid pseudopotential calculation yielded 0.78 eV and 1.30 eV direct band and indirect gap, respectively. Importantly, our results predict that PtO has a direct band gap within the framework of HSE06, and it prefers equally zero magnetic order at different pressures. In the Raman spectra, peaks are slightly shifted towards higher frequency with the decrease in pressure. We have also calculated the thermoelectric properties, namely the electronic thermal conductivity and electrical conductivity, with respect to temperature and thermodynamic properties such as entropy, specific heat at constant volume, enthalpy and Gibbs free energy with respect to pressure. The result shows that PtO is a promising candidate for use as a catalyst, in sensors, as a photo-cathode in water electrolysis, for thermal decomposition of inorganic salt and fuel cells.

  4. Pressure-Dependent Electronic and Transport Properties of Bulk Platinum Oxide by Density Functional Theory

    Science.gov (United States)

    Kansara, Shivam; Gupta, Sanjeev K.; Sonvane, Yogesh; Nekrasov, Kirill A.; Kichigina, Natalia V.

    2017-11-01

    The structural, electronic, and vibrational properties of bulk platinum oxide (PtO) at compressive pressures in the interval from 0 GPa to 35 GPa are investigated using the density functional theory. The calculated electronic band structure of PtO shows poor metallicity at very low density of states on the Fermi level. However, the hybrid pseudopotential calculation yielded 0.78 eV and 1.30 eV direct band and indirect gap, respectively. Importantly, our results predict that PtO has a direct band gap within the framework of HSE06, and it prefers equally zero magnetic order at different pressures. In the Raman spectra, peaks are slightly shifted towards higher frequency with the decrease in pressure. We have also calculated the thermoelectric properties, namely the electronic thermal conductivity and electrical conductivity, with respect to temperature and thermodynamic properties such as entropy, specific heat at constant volume, enthalpy and Gibbs free energy with respect to pressure. The result shows that PtO is a promising candidate for use as a catalyst, in sensors, as a photo-cathode in water electrolysis, for thermal decomposition of inorganic salt and fuel cells.

  5. Aspect-dependent soil saturation and insight into debris-flow initiation during extreme rainfall in the Colorado Front Range

    Science.gov (United States)

    Ebel, Brian A.; Rengers, Francis K.; Tucker, Gregory E.

    2015-01-01

    Hydrologic processes during extreme rainfall events are poorly characterized because of the rarity of measurements. Improved understanding of hydrologic controls on natural hazards is needed because of the potential for substantial risk during extreme precipitation events. We present field measurements of the degree of soil saturation and estimates of available soil-water storage during the September 2013 Colorado extreme rainfall event at burned (wildfire in 2010) and unburned hillslopes with north- and south-facing slope aspects. Soil saturation was more strongly correlated with slope aspect than with recent fire history; south-facing hillslopes became fully saturated while north-facing hillslopes did not. Our results suggest multiple explanations for why aspect-dependent hydrologic controls favor saturation development on south-facing slopes, causing reductions in effective stress and triggering of slope failures during extreme rainfall. Aspect-dependent hydrologic behavior may result from (1) a larger gravel and stone fraction, and hence lower soil-water storage capacity, on south-facing slopes, and (2) lower weathered-bedrock permeability on south-facing slopes, because of lower tree density and associated deep roots penetrating bedrock as well as less intense weathering, inhibiting soil drainage.

  6. Density, abundance, survival, and ranging patterns of common bottlenose dolphins (Tursiops truncatus) in Mississippi Sound following the Deepwater Horizon oil spill.

    Science.gov (United States)

    Mullin, Keith D; McDonald, Trent; Wells, Randall S; Balmer, Brian C; Speakman, Todd; Sinclair, Carrie; Zolman, Eric S; Hornsby, Fawn; McBride, Shauna M; Wilkinson, Krystan A; Schwacke, Lori H

    2017-01-01

    After the Deepwater Horizon (DWH) oil spill began in April 2010, studies were initiated on northern Gulf of Mexico common bottlenose dolphins (Tursiops truncatus) in Mississippi Sound (MSS) to determine density, abundance, and survival, during and after the oil spill, and to compare these results to previous research in this region. Seasonal boat-based photo-identification surveys (2010-2012) were conducted in a section of MSS to estimate dolphin density and survival, and satellite-linked telemetry (2013) was used to determine ranging patterns. Telemetry suggested two different ranging patterns in MSS: (1) inshore waters with seasonal movements into mid-MSS, and (2) around the barrier islands exclusively. Based upon these data, dolphin density was estimated in two strata (Inshore and Island) using a spatially-explicit robust-design capture-recapture model. Inshore and Island density varied between 0.77-1.61 dolphins km-2 ([Formula: see text] = 1.42, 95% CI: 1.28-1.53) and 3.32-5.74 dolphins km-2 ([Formula: see text] = 4.43, 95% CI: 2.70-5.63), respectively. The estimated annual survival rate for dolphins with distinctive fins was very low in the year following the spill, 0.73 (95% CI: 0.67-0.78), and consistent with the occurrence of a large scale cetacean unusual mortality event that was in part attributed to the DWH oil spill. Fluctuations in density were not as large or seasonally consistent as previously reported. Total abundance for MSS extrapolated from density results ranged from 4,610 in July 2011 to 3,046 in January 2012 ([Formula: see text] = 3,469, 95% CI: 3,113-3,725).

  7. Density, abundance, survival, and ranging patterns of common bottlenose dolphins (Tursiops truncatus in Mississippi Sound following the Deepwater Horizon oil spill.

    Directory of Open Access Journals (Sweden)

    Keith D Mullin

    Full Text Available After the Deepwater Horizon (DWH oil spill began in April 2010, studies were initiated on northern Gulf of Mexico common bottlenose dolphins (Tursiops truncatus in Mississippi Sound (MSS to determine density, abundance, and survival, during and after the oil spill, and to compare these results to previous research in this region. Seasonal boat-based photo-identification surveys (2010-2012 were conducted in a section of MSS to estimate dolphin density and survival, and satellite-linked telemetry (2013 was used to determine ranging patterns. Telemetry suggested two different ranging patterns in MSS: (1 inshore waters with seasonal movements into mid-MSS, and (2 around the barrier islands exclusively. Based upon these data, dolphin density was estimated in two strata (Inshore and Island using a spatially-explicit robust-design capture-recapture model. Inshore and Island density varied between 0.77-1.61 dolphins km-2 ([Formula: see text] = 1.42, 95% CI: 1.28-1.53 and 3.32-5.74 dolphins km-2 ([Formula: see text] = 4.43, 95% CI: 2.70-5.63, respectively. The estimated annual survival rate for dolphins with distinctive fins was very low in the year following the spill, 0.73 (95% CI: 0.67-0.78, and consistent with the occurrence of a large scale cetacean unusual mortality event that was in part attributed to the DWH oil spill. Fluctuations in density were not as large or seasonally consistent as previously reported. Total abundance for MSS extrapolated from density results ranged from 4,610 in July 2011 to 3,046 in January 2012 ([Formula: see text] = 3,469, 95% CI: 3,113-3,725.

  8. Density, abundance, survival, and ranging patterns of common bottlenose dolphins (Tursiops truncatus) in Mississippi Sound following the Deepwater Horizon oil spill

    Science.gov (United States)

    Mullin, Keith D.; Wells, Randall S.; Balmer, Brian C.; Speakman, Todd; Sinclair, Carrie; Zolman, Eric S.; Hornsby, Fawn; McBride, Shauna M.; Wilkinson, Krystan A.; Schwacke, Lori H.

    2017-01-01

    After the Deepwater Horizon (DWH) oil spill began in April 2010, studies were initiated on northern Gulf of Mexico common bottlenose dolphins (Tursiops truncatus) in Mississippi Sound (MSS) to determine density, abundance, and survival, during and after the oil spill, and to compare these results to previous research in this region. Seasonal boat-based photo-identification surveys (2010–2012) were conducted in a section of MSS to estimate dolphin density and survival, and satellite-linked telemetry (2013) was used to determine ranging patterns. Telemetry suggested two different ranging patterns in MSS: (1) inshore waters with seasonal movements into mid-MSS, and (2) around the barrier islands exclusively. Based upon these data, dolphin density was estimated in two strata (Inshore and Island) using a spatially-explicit robust-design capture-recapture model. Inshore and Island density varied between 0.77–1.61 dolphins km−2 (x¯ = 1.42, 95% CI: 1.28–1.53) and 3.32–5.74 dolphins km−2 (x¯ = 4.43, 95% CI: 2.70–5.63), respectively. The estimated annual survival rate for dolphins with distinctive fins was very low in the year following the spill, 0.73 (95% CI: 0.67–0.78), and consistent with the occurrence of a large scale cetacean unusual mortality event that was in part attributed to the DWH oil spill. Fluctuations in density were not as large or seasonally consistent as previously reported. Total abundance for MSS extrapolated from density results ranged from 4,610 in July 2011 to 3,046 in January 2012 (x¯ = 3,469, 95% CI: 3,113–3,725). PMID:29053728

  9. Development and application of a density dependent matrix population model for Atlantic killifish (Fundulus heteroclitus)

    Science.gov (United States)

    Ranging along the Atlantic coast from US Florida to the Maritime Provinces of Canada, the Atlantic killifish (Fundulus heteroclitus) is an important and well-studied model organism for understanding the effects of pollutants and other stressors in estuarine and marine ecosystems....

  10. Density-dependence and within-host competition in a semelparous parasite of leaf-cutting ants

    Directory of Open Access Journals (Sweden)

    Thomsen Lene

    2004-11-01

    Full Text Available Abstract Background Parasite heterogeneity and within-host competition are thought to be important factors influencing the dynamics of host-parasite relationships. Yet, while there have been many theoretical investigations of how these factors may act, empirical data is more limited. We investigated the effects of parasite density and heterogeneity on parasite virulence and fitness using four strains of the entomopathogenic fungus, Metarhizium anisopliae var. anisopliae, and its leaf-cutting ant host Acromyrmex echinatior as the model system. Results The relationship between parasite density and infection was sigmoidal, with there being an invasion threshold for an infection to occur (an Allee effect. Although spore production was positively density-dependent, parasite fitness decreased with increasing parasite density, indicating within-host scramble competition. The dynamics differed little between the four strains tested. In mixed infections of three strains the infection-growth dynamics were unaffected by parasite heterogeneity. Conclusions The strength of within-host competition makes dispersal the best strategy for the parasite. Parasite heterogeneity may not have effected virulence or the infection dynamics either because the most virulent strain outcompeted the others, or because the interaction involved scramble competition that was impervious to parasite heterogeneity. The dynamics observed may be common for virulent parasites, such as Metarhizium, that produce aggregated transmission stages. Such parasites make useful models for investigating infection dynamics and the impact of parasite competition.

  11. Density-dependent effects on growth, body size, and clutch size in Black Brant

    Science.gov (United States)

    Sedinger, James S.; Lindberg, Mark S.; Person, Brian T.; Eichholz, Michael W.; Herzog, Mark P.; Flint, Paul L.

    1998-01-01

    We documented gosling size in late summer, adult body size, and clutch size of known-age Black Brant (Branta bernicla nigricans) females nesting on the Tutakoke River colony between 1986 and 1995. During this period, the colony increased from 1,100 to >5,000 nesting pairs. Gosling mass at 30 days of age declined from 764 ± SE of 13 g and 723 ± 15 g for males and females, respectively, in the 1986 cohort, to 665 ± 18 g and 579 ± 18 g in the 1994 cohort. Gosling size was directly negatively correlated with number of Black Brant broods. We detected no trend in adult body size for individuals from these cohorts; in fact, adults from the 1992 and 1994 cohorts had the largest overall masses. Clutch size increased with age from 3.4 eggs for 2-year-old females to 4.4 eggs for 5-year-old females. Clutch size declined during the study by 0.20 (3-year-old females) to 0.45 (2-year-old females) eggs. Clutch size did not decline between the 1986 and 1990 cohorts for females that were >5 years old. Our results for clutch size and gosling size are similar to those recorded for Lesser Snow Geese (Chen caerulescens caerulescens). Our failure to detect a trend in adult body size, however, differs from the response of other geese to increasing population density. We interpret this difference in effects of density on adult size between Black Brant and other geese as an indication of stronger selection against the smallest individuals in Black Brant relative to other species of geese.

  12. Implications of late-in-life density-dependent growth for fishery size-at-entry leading to maximum sustainable yield

    DEFF Research Database (Denmark)

    van Gemert, Rob; Andersen, Ken Haste

    2018-01-01

    Currently applied fisheries models and stock assessments rely on the assumption that density-dependent regulation only affects processes early in life, as described by stock–recruitment relationships. However, many fish stocks also experience density-dependent processes late in life......, such as density-dependent adult growth. Theoretical studies have found that, for stocks which experience strong late-in-life density dependence, maximum sustainable yield (MSY) is obtained with a small fishery size-at-entry that also targets juveniles. This goes against common fisheries advice, which dictates...... that primarily adults should be fished. This study aims to examine whether the strength of density-dependent growth in actual fish stocks is sufficiently strong to reduce optimal fishery size-at-entry to below size-at-maturity. A size-structured model is fitted to three stocks that have shown indications of late-in-life...

  13. Non-covalent interactions and thermochemistry using XDM-corrected hybrid and range-separated hybrid density functionals.

    Science.gov (United States)

    Otero-de-la-Roza, A; Johnson, Erin R

    2013-05-28

    The exchange-hole dipole-moment model (XDM) for dispersion is combined with a collection of semilocal, hybrid, and range-separated hybrid functionals. The resulting XDM-corrected functionals are tested against standard benchmarks for non-covalent interactions at and away from equilibrium, conformer ranking in water clusters, thermochemistry, and kinetics. We show that functionals with the correct -1∕r tail of the exchange potential yield superior accuracy for weak interactions. Thus, balancing long-range exchange with dispersion interactions in XDM is essential in the correct description of dimers with significant non-dispersion contributions to binding. With the exception of the noble gases, the performance of PW86PBE-XDM is improved upon at the semilocal (BLYP), hybrid (B3LYP), and range-separated hybrid (LC-ωPBE) levels. Based on its excellent performance, we propose LC-ωPBE-XDM as an accurate functional for hard and soft matter.

  14. A short-range gradient-corrected spin density functional in combination with long-range coupled-cluster methods: Application to alkali-metal rare-gas dimers

    Energy Technology Data Exchange (ETDEWEB)

    Goll, Erich [Institut fuer Theoretische Chemie, Universitaet Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart (Germany)], E-mail: goll@theochem.uni-stuttgart.de; Werner, Hans-Joachim [Institut fuer Theoretische Chemie, Universitaet Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart (Germany); Stoll, Hermann [Institut fuer Theoretische Chemie, Universitaet Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart (Germany); Leininger, Thierry [Laboratoire de Physique Quantique, UMR 5626 du CNRS, Universite Paul Sabatier, 118 Route de Narbonne, F-31062 Toulouse Cedex 04 (France); Gori-Giorgi, Paola [Laboratoire de Chimie Theorique, CNRS UMR7616, Universite Pierre et Marie Curie, 4 Place Jussieu, F-75252 Paris (France); Savin, Andreas [Laboratoire de Chimie Theorique, CNRS UMR7616, Universite Pierre et Marie Curie, 4 Place Jussieu, F-75252 Paris (France)

    2006-10-26

    We extend our recently published short-range gradient-corrected density functional from the closed-shell to Open-shell case, combine it with long-range coupled-cluster methods (CCSD, CCSD(T)), and apply it to the weakly bound alkali-metal rare-gas dimers AmRg (Am = Li-Cs; Rg = Ne-Xe). The results are shown to be superior, with medium-size basis sets, to pure DFT and pure coupled-cluster calculations.

  15. Collision dynamics of H+ + N2 at low energies based on time-dependent density-functional theory

    Science.gov (United States)

    Yu, W.; Zhang, Y.; Zhang, F. S.; Hutton, R.; Zou, Y.; Gao, C.-Z.; Wei, B.

    2018-02-01

    Using time-dependent density-functional theory at the level of local density approximation augmented by a self-interaction correction and coupled non-adiabatically to molecular dynamics, we study, from a theoretical perspective, scattering dynamics of the proton in collisions with the N2 molecule at 30 eV. Nine different collision configurations are employed to analyze the proton energy loss spectra, electron depletion, scattering angles and self-interaction effects. Our results agree qualitatively with the experimental data and previous theoretical calculations. The discrepancies are ascribed to the limitation of the theoretical models in use. We find that self-interaction effects can significantly influence the electron capture and the excited diatomic vibrational motion, which is in consistent with other calculations. In addition, it is found that the molecular structure can be readily retrieved from the proton energy loss spectra due to a significant momentum transfer in head-on collisions.

  16. Physiology and growth of redwood and Douglas-fir planted after variable density retention outside redwood’s range

    Science.gov (United States)

    Lucy Kerhoulas; Nicholas Kerhoulas; Wade Polda; John-Pascal Berrill

    2017-01-01

    Reforestation following timber harvests is an important topic throughout the coast redwood (Sequoia sempervirens (D. Don) Endl.) range. Furthermore, as drought-induced mortality spreads across many of California’s forests, it is important to understand how physiology and stand structure influence reforestation success. Finally, as climate...

  17. Scale dependence of multiplier distributions for particle concentration, enstrophy, and dissipation in the inertial range of homogeneous turbulence

    Science.gov (United States)

    Hartlep, Thomas; Cuzzi, Jeffrey N.; Weston, Brian

    2017-03-01

    Turbulent flows preferentially concentrate inertial particles depending on their stopping time or Stokes number, which can lead to significant spatial variations in the particle concentration. Cascade models are one way to describe this process in statistical terms. Here, we use a direct numerical simulation (DNS) dataset of homogeneous, isotropic turbulence to determine probability distribution functions (PDFs) for cascade multipliers, which determine the ratio by which a property is partitioned into subvolumes as an eddy is envisioned to decay into smaller eddies. We present a technique for correcting effects of small particle numbers in the statistics. We determine multiplier PDFs for particle number, flow dissipation, and enstrophy, all of which are shown to be scale dependent. However, the particle multiplier PDFs collapse when scaled with an appropriately defined local Stokes number. As anticipated from earlier works, dissipation and enstrophy multiplier PDFs reach an asymptote for sufficiently small spatial scales. From the DNS measurements, we derive a cascade model that is used it to make predictions for the radial distribution function (RDF) for arbitrarily high Reynolds numbers, Re, finding good agreement with the asymptotic, infinite Re inertial range theory of Zaichik and Alipchenkov [New J. Phys. 11, 103018 (2009), 10.1088/1367-2630/11/10/103018]. We discuss implications of these results for the statistical modeling of the turbulent clustering process in the inertial range for high Reynolds numbers inaccessible to numerical simulations.

  18. New insights on the rarity of the vulnerable Cinereous Warbling-finch (Aves, Emberizidae based on density, home range, and habitat selection

    Directory of Open Access Journals (Sweden)

    F Marques-Santos

    Full Text Available The Cinereous Warbling-finch Poospiza cinerea (Emberizidae is a Neotropical grassland bird considered rare, with population declining due to habitat loss and classified as vulnerable. However, the species conspicuously remains in several degraded areas, suggesting that it may be favored by these environments. Studies which focus on this species were inexistent until 2012, making questionable any statement about its threaten status. Here we analyzed population density, home range, and habitat selection of two groups of P. cinerea at independent sites that differ in human impact levels. Density was estimated by counting and mapping birds. Kernel density and minimum convex polygon were used to estimate home ranges. Habitat selection was inferred from use and availability of every habitat identified within the home range boundaries. One group positively selected urban tree vegetation, despite the availability of natural habitats in its home range. Based on a review on the literature and our findings, we assume that it is unlikely that P. cinerea is rare owing to habitat degradation, as previously thought. Nevertheless, this species was always recorded around native Cerrado vegetation and thus habitat modification may still threaten this species at some level. It is suggested that this species might be a woodland edge species, but future studies are necessary to confirm this assumption.

  19. Calculation of the Effect of Random Superfluid Density on the Temperature Dependence of the Penetration Depth

    Energy Technology Data Exchange (ETDEWEB)

    Lippman, Thomas; Moler, Kathryn A.

    2012-07-20

    Microscopic variations in composition or structure can lead to nanoscale inhomogeneity in superconducting properties such as the magnetic penetration depth, but measurements of these properties are usually made on longer length scales. We solve a generalized London equation with a non-uniform penetration depth {lambda}(r), obtaining an approximate solution for the disorder-averaged Meissner screening. We find that the effective penetration depth is different from the average penetration depth and is sensitive to the details of the disorder. These results indicate the need for caution when interpreting measurements of the penetration depth and its temperature dependence in systems which may be inhomogeneous.

  20. Yeast silent mating type loci form heterochromatic clusters through silencer protein-dependent long-range interactions.

    Directory of Open Access Journals (Sweden)

    Adriana Miele

    2009-05-01

    Full Text Available The organization of eukaryotic genomes is characterized by the presence of distinct euchromatic and heterochromatic sub-nuclear compartments. In Saccharomyces cerevisiae heterochromatic loci, including telomeres and silent mating type loci, form clusters at the nuclear periphery. We have employed live cell 3-D imaging and chromosome conformation capture (3C to determine the contribution of nuclear positioning and heterochromatic factors in mediating associations of the silent mating type loci. We identify specific long-range interactions between HML and HMR that are dependent upon silencing proteins Sir2p, Sir3p, and Sir4p as well as Sir1p and Esc2p, two proteins involved in establishment of silencing. Although clustering of these loci frequently occurs near the nuclear periphery, colocalization can occur equally at more internal positions and is not affected in strains deleted for membrane anchoring proteins yKu70p and Esc1p. In addition, appropriate nucleosome assembly plays a role, as deletion of ASF1 or combined disruption of the CAF-1 and HIR complexes abolishes the HML-HMR interaction. Further, silencer proteins are required for clustering, but complete loss of clustering in asf1 and esc2 mutants had only minor effects on silencing. Our results indicate that formation of heterochromatic clusters depends on correctly assembled heterochromatin at the silent loci and, in addition, identify an Asf1p-, Esc2p-, and Sir1p-dependent step in heterochromatin formation that is not essential for gene silencing but is required for long-range interactions.

  1. Social Sustainability Issues and Older Adults’ Dependence on Automobiles in Low-Density Environments

    Directory of Open Access Journals (Sweden)

    Hitomi Nakanishi

    2015-06-01

    Full Text Available An implicit assumption underlying government strategies to achieve a more sustainable urban transportation system is that all automobile users will be encouraged or persuaded to use more “green” transportation: public transportation, walking and cycling. Little consideration has been given as to how sustainable transportation policies and programmess might impact on different age groups in society, including those retired or semi-retired, despite the fact that an unprecedented number of older drivers will be on the highways in the next few decades. There is limited literature on the contextual factors behind their continued reliance on automobiles, their actual driving behavior (e.g., route choice and time of day to drive framed within the context of social sustainability. This paper introduces the elements of transportation and social sustainability then conducts a comprehensive international literature review focusing on older drivers, their travel choices and associated social sustainability issues. It describes a case study, low-density city and presents empirical evidence, from two surveys conducted in Canberra, Australia. The paper concludes with future research directions that address these issues associated with sustainable transportation.

  2. The potential energy density in transverse string waves depends critically on longitudinal motion

    Energy Technology Data Exchange (ETDEWEB)

    Rowland, David R, E-mail: d.rowland@uq.edu.au [Student Services, University of Queensland, Brisbane QLD 4072 (Australia)

    2011-11-15

    The question of the correct formula for the potential energy density in transverse waves on a taut string continues to attract attention (e.g. Burko 2010 Eur. J. Phys. 31 L71), and at least three different formulae can be found in the literature, with the classic text by Morse and Feshbach (Methods of Theoretical Physics pp 126-127) stating that the formula is inherently ambiguous. The purpose of this paper is to demonstrate that neither the standard expression nor the alternative proposed by Burko can be considered to be physically consistent, and that to obtain a formula free of physical inconsistencies and which also removes the ambiguity of Morse and Feshbach, the longitudinal motion of elements of the string needs to be taken into account, even though such motion can be neglected when deriving the linear transverse wave equation. Two derivations of the correct formula are sketched, one proceeding from a consideration of the amount of energy required to stretch a small segment of string when longitudinal displacements are considered, and the other from the full wave equation. The limits of the validity of the derived formulae are also discussed in detail.

  3. Dependence of rapeseed quality and yield on density, variety and year of production

    Directory of Open Access Journals (Sweden)

    Vujaković Milka

    2015-01-01

    Full Text Available Rapeseed is an important industrial plant in the world. In Vojvodina region of Serbia it is grown on well aerated and deep soils. Most often it is sown with the distance between the rows of 25 cm, and 5-6 cm within the row. The trial with three winter rapeseed genotypes (Banaćanka, Slavica and NS-H-2 was set up at Rimski Šančevi (Vojvodina during growing seasons of 2009/2010 and 2010/2011. Seed was sown with inter row spacing of 25 cm, and spacing within the rows of 5 cm, 8 cm, 10 cm and 16 cm. The following parameters were tested upon harvesting: seed germination, 1000 seed weight, test weight, seed yield, oil content and total protein in seed. No effect of planting density was observed on rapeseed seed quality produced in 2009/10 and 2010/11, which should be kept in mind when determining the quantity of seed required for sowing.

  4. Site-specific and time-dependent activation of the endocannabinoid system after transection of long-range projections.

    Directory of Open Access Journals (Sweden)

    Sonja Kallendrusch

    Full Text Available BACKGROUND: After focal neuronal injury the endocannabinioid system becomes activated and protects or harms neurons depending on cannabinoid derivates and receptor subtypes. Endocannabinoids (eCBs play a central role in controlling local responses and influencing neural plasticity and survival. However, little is known about the functional relevance of eCBs in long-range projection damage as observed in stroke or spinal cord injury (SCI. METHODS: In rat organotypic entorhino-hippocampal slice cultures (OHSC as a relevant and suitable model for investigating projection fibers in the CNS we performed perforant pathway transection (PPT and subsequently analyzed the spatial and temporal dynamics of eCB levels. This approach allows proper distinction of responses in originating neurons (entorhinal cortex, areas of deafferentiation/anterograde axonal degeneration (dentate gyrus and putative changes in more distant but synaptically connected subfields (cornu ammonis (CA 1 region. RESULTS: Using LC-MS/MS, we measured a strong increase in arachidonoylethanolamide (AEA, oleoylethanolamide (OEA and palmitoylethanolamide (PEA levels in the denervation zone (dentate gyrus 24 hours post lesion (hpl, whereas entorhinal cortex and CA1 region exhibited little if any changes. NAPE-PLD, responsible for biosynthesis of eCBs, was increased early, whereas FAAH, a catabolizing enzyme, was up-regulated 48hpl. CONCLUSION: Neuronal damage as assessed by transection of long-range projections apparently provides a strong time-dependent and area-confined signal for de novo synthesis of eCB, presumably to restrict neuronal damage. The present data underlines the importance of activation of the eCB system in CNS pathologies and identifies a novel site-specific intrinsic regulation of eCBs after long-range projection damage.

  5. Identification of the density dependent coefficient in an inverse reaction-diffusion problem from a single boundary data

    Directory of Open Access Journals (Sweden)

    Ramazan Tinaztepe

    2014-01-01

    Full Text Available This study is devoted to the numerical solution of an inverse coefficient problem for a density dependent nonlinear reaction-diffusion equation. The method is based on approximating the unknown coefficient by polynomials. An optimal idea for solving the inverse problem is to minimize an error functional between the output data and the additional data. For this purpose, we find a polynomial of degree n that minimizes the error functional; i.e, n-th degree polynomial approximation of the unknown coefficient for the desired n.

  6. Visualizing the mechanism that determines the critical current density in polycrystalline superconductors using time-dependent Ginzburg-Landau theory

    Science.gov (United States)

    Carty, George J.; Hampshire, Damian P.

    2008-05-01

    In polycrystalline superconducting materials optimized for high critical current density (JC) in high magnetic fields, the mechanism that determines JC has long remained uncertain because of the complicated manner in which the fluxon-fluxon and fluxon-microstructure forces combine. In this work, the time-dependent Ginzburg-Landau equations are used to produce visualizations of fluxons at JC that show the disorder in the pinned part of the flux-line lattice and the motion of those fluxons along grain boundaries that cause dissipation. Calculated values of JC are consistent with experimental data.

  7. Electron-Ion Dynamics with Time-Dependent Density Functional Theory: Towards Predictive Solar Cell Modeling: Final Technical Report

    Energy Technology Data Exchange (ETDEWEB)

    Maitra, Neepa [Hunter College City University of New York, New York, NY (United States)

    2016-07-14

    This project investigates the accuracy of currently-used functionals in time-dependent density functional theory, which is today routinely used to predict and design materials and computationally model processes in solar energy conversion. The rigorously-based electron-ion dynamics method developed here sheds light on traditional methods and overcomes challenges those methods have. The fundamental research undertaken here is important for building reliable and practical methods for materials discovery. The ultimate goal is to use these tools for the computational design of new materials for solar cell devices of high efficiency.

  8. Density-dependent benefits in ant-hemipteran mutualism? The case of the ghost ant Tapinoma melanocephalum (Hymenoptera: Formicidae) and the invasive mealybug Phenacoccus solenopsis (Hemiptera: Pseudococcidae).

    Science.gov (United States)

    Zhou, Aiming; Kuang, Beiqing; Gao, Yingrui; Liang, Guangwen

    2015-01-01

    Although density-dependent benefits to hemipterans from ant tending have been measured many times, few studies have focused on integrated effects such as interactions between ant tending, natural enemy density, and hemipteran density. In this study, we tested whether the invasive mealybug Phenacoccus solenopsis is affected by tending by ghost ants (Tapinoma melanocephalum), the presence of parasitoids, mealybug density, parasitoid density and interactions among these factors. Our results showed that mealybug colony growth rate and percentage parasitism were significantly affected by ant tending, parasitoid presence, and initial mealybug density separately. However, there were no interactions among the independent factors. There were also no significant interactions between ant tending and parasitoid density on either mealybug colony growth rate or percentage parasitism. Mealybug colony growth rate showed a negative linear relationship with initial mealybug density but a positive linear relationship with the level of ant tending. These results suggest that benefits to mealybugs are density-independent and are affected by ant tending level.

  9. Gonadal steroid–dependent effects on bone turnover and bone mineral density in men

    Science.gov (United States)

    Finkelstein, Joel S.; Lee, Hang; Leder, Benjamin Z.; Goldstein, David W.; Hahn, Christopher W.; Hirsch, Sarah C.; Linker, Alex; Perros, Nicholas; Servais, Andrew B.; Taylor, Alexander P.; Webb, Matthew L.; Youngner, Jonathan M.; Yu, Elaine W.

    2016-01-01

    BACKGROUND. Severe gonadal steroid deficiency induces bone loss in adult men; however, the specific roles of androgen and estrogen deficiency in hypogonadal bone loss are unclear. Additionally, the threshold levels of testosterone and estradiol that initiate bone loss are uncertain. METHODS. One hundred ninety-eight healthy men, ages 20–50, received goserelin acetate, which suppresses endogenous gonadal steroid production, and were randomized to treatment with 0, 1.25, 2.5, 5, or 10 grams of testosterone gel daily for 16 weeks. An additional cohort of 202 men was randomized to receive these treatments plus anastrozole, which suppresses conversion of androgens to estrogens. Thirty-seven men served as controls and received placebos for goserelin and testosterone. Changes in bone turnover markers, bone mineral density (BMD) by dual-energy x-ray absorptiometry (DXA), and BMD by quantitative computed tomography (QCT) were assessed in all men. Bone microarchitecture was assessed in 100 men. RESULTS. As testosterone dosage decreased, the percent change in C-telopeptide increased. These increases were considerably greater when aromatization of testosterone to estradiol was also suppressed, suggesting effects of both testosterone and estradiol deficiency. Decreases in DXA BMD were observed when aromatization was suppressed but were modest in most groups. QCT spine BMD fell substantially in all testosterone-dose groups in which aromatization was also suppressed, and this decline was independent of testosterone dose. Estradiol deficiency disrupted cortical microarchitecture at peripheral sites. Estradiol levels above 10 pg/ml and testosterone levels above 200 ng/dl were generally sufficient to prevent increases in bone resorption and decreases in BMD in men. CONCLUSIONS. Estrogens primarily regulate bone homeostasis in adult men, and testosterone and estradiol levels must decline substantially to impact the skeleton. TRIAL REGISTRATION. ClinicalTrials.gov, NCT00114114

  10. Gonadal steroid-dependent effects on bone turnover and bone mineral density in men.

    Science.gov (United States)

    Finkelstein, Joel S; Lee, Hang; Leder, Benjamin Z; Burnett-Bowie, Sherri-Ann M; Goldstein, David W; Hahn, Christopher W; Hirsch, Sarah C; Linker, Alex; Perros, Nicholas; Servais, Andrew B; Taylor, Alexander P; Webb, Matthew L; Youngner, Jonathan M; Yu, Elaine W

    2016-03-01

    Severe gonadal steroid deficiency induces bone loss in adult men; however, the specific roles of androgen and estrogen deficiency in hypogonadal bone loss are unclear. Additionally, the threshold levels of testosterone and estradiol that initiate bone loss are uncertain. One hundred ninety-eight healthy men, ages 20-50, received goserelin acetate, which suppresses endogenous gonadal steroid production, and were randomized to treatment with 0, 1.25, 2.5, 5, or 10 grams of testosterone gel daily for 16 weeks. An additional cohort of 202 men was randomized to receive these treatments plus anastrozole, which suppresses conversion of androgens to estrogens. Thirty-seven men served as controls and received placebos for goserelin and testosterone. Changes in bone turnover markers, bone mineral density (BMD) by dual-energy x-ray absorptiometry (DXA), and BMD by quantitative computed tomography (QCT) were assessed in all men. Bone microarchitecture was assessed in 100 men. As testosterone dosage decreased, the percent change in C-telopeptide increased. These increases were considerably greater when aromatization of testosterone to estradiol was also suppressed, suggesting effects of both testosterone and estradiol deficiency. Decreases in DXA BMD were observed when aromatization was suppressed but were modest in most groups. QCT spine BMD fell substantially in all testosterone-dose groups in which aromatization was also suppressed, and this decline was independent of testosterone dose. Estradiol deficiency disrupted cortical microarchitecture at peripheral sites. Estradiol levels above 10 pg/ml and testosterone levels above 200 ng/dl were generally sufficient to prevent increases in bone resorption and decreases in BMD in men. Estrogens primarily regulate bone homeostasis in adult men, and testosterone and estradiol levels must decline substantially to impact the skeleton. ClinicalTrials.gov, NCT00114114. AbbVie Inc., AstraZeneca Pharmaceuticals LP, NIH.

  11. Centrality dependence of the pseudorapidity density distribution for charged particles in Pb–Pb collisions at sNN=5.02 TeV

    Directory of Open Access Journals (Sweden)

    J. Adam

    2017-09-01

    Full Text Available We present the charged-particle pseudorapidity density in Pb–Pb collisions at sNN=5.02 TeV in centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from −3.5 to 5, which is sufficient for reliable estimates of the total number of charged particles produced in the collisions. For the most central (0–5% collisions we find 21400±1300, while for the most peripheral (80–90% we find 230±38. This corresponds to an increase of (27±4% over the results at sNN=2.76 TeV previously reported by ALICE. The energy dependence of the total number of charged particles produced in heavy-ion collisions is found to obey a modified power-law like behaviour. The charged-particle pseudorapidity density of the most central collisions is compared to model calculations — none of which fully describes the measured distribution. We also present an estimate of the rapidity density of charged particles. The width of that distribution is found to exhibit a remarkable proportionality to the beam rapidity, independent of the collision energy from the top SPS to LHC energies.

  12. Density Functional Study of the Carbon Dependence of the Structural, Mechanic, Thermodynamic, and Dynamic Properties of SiC Alloys

    Science.gov (United States)

    Langueur, H.; Kassali, K.

    2017-03-01

    Using a density functional scheme, for the first time the carbon dependence on the structural, dynamic, thermodynamic, and dynamic properties of Si_{1-x}Cx alloys (x=0.0 to 1.0 in steps of 0.125) has been investigated. The structural properties of these materials, in particular, the composition dependence of the lattice parameter and bulk modulus, are in excellent agreement with experimental data and follow a quadratic law in ( x). A nonlinear relationship is found between the elastic constants C_{11}, C_{12}, and C_{44} and the carbon concentration ( x). The behavior of the acoustical and optical phonon frequencies at high-symmetry points Γ, X, and L is predicted. Through the quasi-harmonic Debye model, in which the photonic effects are taken into account, the Debye temperature, the heat capacity, the Helmholtz free energy, the internal energy, and the entropy are determined for the Si_{1-x}C_{x } compounds.

  13. Thermodynamic Properties of Low-Density {}^{132}Xe Gas in the Temperature Range 165-275 K

    Science.gov (United States)

    Akour, Abdulrahman

    2018-01-01

    The method of static fluctuation approximation was used to calculate selected thermodynamic properties (internal energy, entropy, energy capacity, and pressure) for xenon in a particularly low-temperature range (165-270 K) under different conditions. This integrated microscopic study started from an initial basic assumption as the main input. The basic assumption in this method was to replace the local field operator with its mean value, then numerically solve a closed set of nonlinear equations using an iterative method, considering the Hartree-Fock B2-type dispersion potential as the most appropriate potential for xenon. The results are in very good agreement with those of an ideal gas.

  14. Charge-Transfer in Time-Dependent Density Functional Theory: Insights from the Asymmetric Hubbard Dimer

    CERN Document Server

    Fuks, J I

    2013-01-01

    We show that an asymmetric two-fermion two-site Hubbard model illustrates the essential features of long-range charge-transfer dynamics in a real-space molecule. We apply a resonant field that transfers one fermion from one site to the other. Via constrained search we find the exact ground-state exchange-correlation functional, and use it to propagate the Kohn-Sham system, giving the first "adiabatically-exact" calculation of time-resolved charge-transfer. This propagation fails to properly transfer charge. We analyze why by comparing the exact and adiabatically-exact potentials and discuss the role of the derivative discontinuity. The implication for real-space molecules is that even the best possible adiabatic approximation, despite capturing non-local step features relevant to dissociation and charge-transfer excitations, cannot capture fully time-resolved charge-transfer dynamics.

  15. Density dependence of the 5 micron infrared spectrum of NH3

    Science.gov (United States)

    Chapados, Camille; Bjoraker, Gordon L.; Birnbaum, George

    1990-01-01

    Measurements of dilute mixtures of NH3 in H2 were made in the window region 1900-2100/cm of the NH3 spectrum to determine is behavior with increasing pressure of H2. The spectra of pure H2, pure NH3, and mixtures of the two, in the total pressure range from 2.38 to 8.17 atm at 309 K, were obtained with a 975-cm white-cell. Synthetic spectra were calculated using precise line strengths, line positions, and a Lorentz profile. The experimental and calculated spectra are in reasonably good agreement, except that the former is super-imposed on a rather flat background not given by the calculation. A possible mechanism for this background is suggested.

  16. Hypoxic areas, density-dependence and food limitation drive the body condition of a heavily exploited marine fish predator

    DEFF Research Database (Denmark)

    Casini, Michele; Käll, Filip; Hansson, Martin

    2016-01-01

    Investigating the factors regulating fish condition is crucial in ecology and the management of exploited fish populations. The body condition of cod (Gadus morhua) in the Baltic Sea has dramatically decreased during the past two decades, with large implications for the fishery relying on this re......Investigating the factors regulating fish condition is crucial in ecology and the management of exploited fish populations. The body condition of cod (Gadus morhua) in the Baltic Sea has dramatically decreased during the past two decades, with large implications for the fishery relying...... shift that occurred in the Baltic Sea in the early 1990s. The changes in cod condition related to feeding opportunities, driven either by density-dependence or food limitation, along the whole period investigated and to the fivefold increase in the extent of hypoxic areas in the most recent 20 years...... and density-dependent processes. These results furnish novel insights into the population dynamics of Baltic Sea cod that can aid the management of this currently threatened population....

  17. Density-Dependent Formulation of Dispersion-Repulsion Interactions in Hybrid Multiscale Quantum/Molecular Mechanics (QM/MM) Models.

    Science.gov (United States)

    Curutchet, Carles; Cupellini, Lorenzo; Kongsted, Jacob; Corni, Stefano; Frediani, Luca; Steindal, Arnfinn Hykkerud; Guido, Ciro A; Scalmani, Giovanni; Mennucci, Benedetta

    2018-02-22

    Mixed multiscale quantum/molecular mechanics (QM/MM) models are widely used to explore the structure, reactivity, and electronic properties of complex chemical systems. Whereas such models typically include electrostatics and potentially polarization in so-called electrostatic and polarizable embedding approaches, respectively, nonelectrostatic dispersion and repulsion interactions are instead commonly described through classical potentials despite their quantum mechanical origin. Here we present an extension of the Tkatchenko-Scheffler semiempirical van der Waals (vdW TS ) scheme aimed at describing dispersion and repulsion interactions between quantum and classical regions within a QM/MM polarizable embedding framework. Starting from the vdW TS expression, we define a dispersion and a repulsion term, both of them density-dependent and consistently based on a Lennard-Jones-like potential. We explore transferable atom type-based parametrization strategies for the MM parameters, based on either vdW TS calculations performed on isolated fragments or on a direct estimation of the parameters from atomic polarizabilities taken from a polarizable force field. We investigate the performance of the implementation by computing self-consistent interaction energies for the S22 benchmark set, designed to represent typical noncovalent interactions in biological systems, in both equilibrium and out-of-equilibrium geometries. Overall, our results suggest that the present implementation is a promising strategy to include dispersion and repulsion in multiscale QM/MM models incorporating their explicit dependence on the electronic density.

  18. Polarization Dependent Bulk-sensitive Valence Band Photoemission Spectroscopy and Density Functional Theory Calculations: Part I. 3d Transition Metals

    Science.gov (United States)

    Ueda, Shigenori; Hamada, Ikutaro

    2017-12-01

    The X-ray polarization dependent valence band HAXPES spectra of 3d transition metals (TMs) of Ti-Zn were measured to investigate the orbital resolved electronic structures by utilizing that the fact the photoionization cross-section of the atomic orbitals strongly depends on the experimental geometry. We have calculated the HAXPES spectra, which correspond to the cross-section weighted densities of states (CSW-DOSs), where the DOSs were obtained by the density functional theory calculations, and we have determined the relative photoionization cross-sections of the 4s and 4p orbitals to the 3d orbital in the 3d TMs. The experimentally obtained bulk-sensitive 3d and 4s DOSs were good agreement with the calculated DOSs in Ti, V, Cr, and Cu. In contrast, the deviations between the experimental and calculated 3d DOSs for Mn, Fe, Co, Ni were found, suggesting that the electron correlation plays an important role in the electronic structures for these materials.

  19. Cell-density-dependent regulation of expression and glycosylation of dopachrome tautomerase/tyrosinase-related protein-2.

    Science.gov (United States)

    Hornyak, T J; Hayes, D J; Ziff, E B

    2000-07-01

    The expression of the dopachrome tautomerase gene (Dct) and its protein product, tyrosinase-related protein-2, was studied in the cultured, phorbol-ester-dependent murine melanocyte cell line melan-a. Increased cell density was found to stimulate Dct expression both in cells stably transfected with a Dct promoter-lacZ construct and endogenously in nontransfected cells. Increased Dct expression under these conditions corresponds to increased tyrosinase-related protein-2 production. Tyrosinase-related protein-2 was found to exist in two distinct glycoforms with different endoglycosidase sensitivities. Density-dependent expression of tyrosinase-related protein-2 was independent of time of cell growth, cell proliferation, and soluble factors, implying that cell-cell contact is the important determinant governing increased Dct expression under these conditions. Tyrp1 gene expression and tyrosinase-related protein-1 production were also induced under similar conditions. The results show that cell-cell contact between melanocytes induces a coordinated response at both transcriptional and nontranscriptional levels that induces production of the tyrosinase-related proteins that have a significant role in melanization.

  20. Generalized folding model for elastic and inelastic nucleus-nucleus scattering using realistic density dependent nucleon-nucleon interaction

    CERN Document Server

    Khoa, D T

    2000-01-01

    A generalized double-folding model for elastic and inelastic nucleus-nucleus scattering is presented. It is designed to accommodate effective nucleon-nucleon (NN) interactions that depend upon the density of nuclear matter in which the two nucleons are immersed. A recently parametrized density dependent M3Y interaction, based on the G-matrix elements of the Paris NN potential, has been used in the present folding calculation. The effects of knock-on exchange of the interacting nucleon pair are included in an accurate local approximation. Examples of the application of this model to study the refractive elastic and inelastic scattering data of sup 1 sup 2 C+ sup 1 sup 2 C and alpha+ sup 5 sup 8 sup , sup 6 sup 0 Ni systems are presented. A detailed comparison of the use of deformed optical potential (DP) and microscopic folded potential in the analysis of inelastic scattering has shown that the use of DP fails to reproduce the inelastic sup 1 sup 2 C+ sup 1 sup 2 C scattering data measured over a wide angular ...