WorldWideScience

Sample records for chemical evolution modeller

  1. A chemical evolution model for galaxy clusters

    OpenAIRE

    Portinari, L.; A. Moretti(Fermilab, Batavia, IL, USA); Chiosi, C.

    2001-01-01

    We develop a toy-model for the chemical evolution of the intracluster medium, polluted by the galactic winds from elliptical galaxies. The model follows the "galaxy formation history" of cluster galaxies, constrained by the observed luminosity function.

  2. Chemical Evolution models of Local Group galaxies

    CERN Document Server

    Tosi, M P

    2003-01-01

    Status quo and perspectives of standard chemical evolution models of Local Group galaxies are summarized, discussing what we have learnt from them, what we know we have not learnt yet, and what I think we will learn in the near future. It is described how Galactic chemical evolution models have helped showing that: i) stringent constraints on primordial nucleosynthesis can be derived from the observed Galactic abundances of the light elements, ii) the Milky Way has been accreting external gas from early epochs to the present time, iii) the vast majority of Galactic halo stars have formed quite rapidly at early epochs. Chemical evolution models for the closest dwarf galaxies, although still uncertain so far, are expected to become extremely reliable in the nearest future, thanks to the quality of new generation photometric and spectroscopic data which are currently being acquired.

  3. Uncertainties in Galactic Chemical Evolution Models

    Science.gov (United States)

    Côté, Benoit; Ritter, Christian; O’Shea, Brian W.; Herwig, Falk; Pignatari, Marco; Jones, Samuel; Fryer, Chris L.

    2016-06-01

    We use a simple one-zone galactic chemical evolution model to quantify the uncertainties generated by the input parameters in numerical predictions for a galaxy with properties similar to those of the Milky Way. We compiled several studies from the literature to gather the current constraints for our simulations regarding the typical value and uncertainty of the following seven basic parameters: the lower and upper mass limits of the stellar initial mass function (IMF), the slope of the high-mass end of the stellar IMF, the slope of the delay-time distribution function of Type Ia supernovae (SNe Ia), the number of SNe Ia per M ⊙ formed, the total stellar mass formed, and the final mass of gas. We derived a probability distribution function to express the range of likely values for every parameter, which were then included in a Monte Carlo code to run several hundred simulations with randomly selected input parameters. This approach enables us to analyze the predicted chemical evolution of 16 elements in a statistical manner by identifying the most probable solutions, along with their 68% and 95% confidence levels. Our results show that the overall uncertainties are shaped by several input parameters that individually contribute at different metallicities, and thus at different galactic ages. The level of uncertainty then depends on the metallicity and is different from one element to another. Among the seven input parameters considered in this work, the slope of the IMF and the number of SNe Ia are currently the two main sources of uncertainty. The thicknesses of the uncertainty bands bounded by the 68% and 95% confidence levels are generally within 0.3 and 0.6 dex, respectively. When looking at the evolution of individual elements as a function of galactic age instead of metallicity, those same thicknesses range from 0.1 to 0.6 dex for the 68% confidence levels and from 0.3 to 1.0 dex for the 95% confidence levels. The uncertainty in our chemical evolution model

  4. The Impact of Modeling Assumptions in Galactic Chemical Evolution Models

    CERN Document Server

    Côté, Benoit; Ritter, Christian; Herwig, Falk; Venn, Kim A

    2016-01-01

    We use the OMEGA galactic chemical evolution code to investigate how the assumptions used for the treatment of galactic inflows and outflows impact numerical predictions. The goal is to determine how our capacity to reproduce the chemical evolution trends of a galaxy is affected by the choice of implementation used to include those physical processes. In pursuit of this goal, we experiment with three different prescriptions for galactic inflows and outflows and use OMEGA within a Markov Chain Monte Carlo code to recover the set of input parameters that best reproduces the chemical evolution of nine elements in the dwarf spheroidal galaxy Sculptor. Despite their different degrees of intended physical realism, we found that all three prescriptions can reproduce in an almost identical way the stellar abundance trends observed in Sculptor. While the three models have the same capacity to fit the data, the best values recovered for the parameters controlling the number of Type Ia supernovae and the strength of gal...

  5. Hydrogeochemical modeling of groundwater chemical environmental evolution in Hebei Plain

    Institute of Scientific and Technical Information of China (English)

    郭永海; 沈照理; 钟佐燊

    1997-01-01

    Using the hydrogeochemical modeling method, the groundwater chemical environmental problems of the Hebei Plain which involve increasing of hardness and total dissolved solids in piedmont area and mixing of saline water with fresh water in middle-eastern area are studied. The water-rock interactions and mass transfer along a ground-water flow path and in mixing processes are calculated. Thus the evolution mechanisms of the groundwater chemical environment are brought to light.

  6. A Chemical Evolution Model for the Fornax Dwarf Spheroidal Galaxy

    Directory of Open Access Journals (Sweden)

    Yuan Zhen

    2016-01-01

    Full Text Available Fornax is the brightest Milky Way (MW dwarf spheroidal galaxy and its star formation history (SFH has been derived from observations. We estimate the time evolution of its gas mass and net inflow and outflow rates from the SFH usinga simple star formation law that relates the star formation rate to the gas mass. We present a chemical evolution model on a 2D mass grid with supernovae (SNe as sources of metal enrichment. We find that a key parameter controlling the enrichment is the mass Mx of the gas to mix with the ejecta from each SN. The choice of Mx depends on the evolution of SN remnants and on the global gas dynamics. It differs between the two types of SNe involved and between the periods before and after Fornax became an MW satellite at time t = tsat. Our results indicate that due to the global gas outflow at t > tsat, part of the ejecta from each SN may directly escape from Fornax. Sample results from our model are presented and compared with data.

  7. A Chemical Evolution Model for the Fornax Dwarf Spheroidal Galaxy

    CERN Document Server

    Yuan, Zhen; Jing, Y P

    2015-01-01

    Fornax is the brightest Milky Way (MW) dwarf spheroidal galaxy and its star formation history (SFH) has been derived from observations. We estimate the time evolution of its gas mass and net inflow and outflow rates from the SFH using a simple star formation law that relates the star formation rate to the gas mass. We present a chemical evolution model on a 2D mass grid with supernovae (SNe) as sources of metal enrichment. We find that a key parameter controlling the enrichment is the mass M_x of the gas to mix with the ejecta from each SN. The choice of M_x depends on the evolution of SN remnants and on the global gas dynamics. It differs between the two types of SNe involved and between the periods before and after Fornax became an MW satellite at time t = t_sat . Our results indicate that due to the global gas outflow at t > t_sat , part of the ejecta from each SN may directly escape from Fornax. Sample results from our model are presented and compared with data.

  8. Chemical Evolution Models of Local dSph Galaxies

    CERN Document Server

    Carigi, L; Gilmore, G; Carigi, Leticia; Hernandez, Xavier; Gilmore, Gerard

    2002-01-01

    We calculate chemical evolution models for 4 dwarf spheroidal satellites of the Milky Way (Carina, Ursa Minor, Leo I and Leo II) for which reliable non-parametric star formation histories have been derived. In this way, the independently obtained star formation histories are used to constrain the evolution of the systems we are treating. This allows us to obtain robust inferences on the history of such crucial parameters of galactic evolution as gas infall, gas outflows and global metallicities for these systems. We can then trace the metallicity and abundance ratios of the stars formed, the gas present at any time within the systems and the details of gas ejection, of relevance to enrichment of the galaxies environment. We find that galaxies showing one single burst of star formation (Ursa Minor and Leo II) require a dark halo slightly larger that the current estimates for their tidal radii, or the presence of a metal rich selective wind, which might carry away much of the energy output of their supernovae b...

  9. Modeling the chemical evolution of nitrogen oxides near roadways

    Science.gov (United States)

    Wang, Yan Jason; DenBleyker, Allison; McDonald-Buller, Elena; Allen, David; Zhang, K. Max

    2011-01-01

    The chemical evolution of nitrogen dioxide (NO 2) and nitrogen monoxide (NO) in the vicinity of roadways is numerically investigated using a computational fluid dynamics model, CFD-VIT-RIT and a Gaussian-based model, CALINE4. CFD-VIT-RIT couples a standard k- ɛ turbulence model for turbulent mixing and the Finite-Rate model for chemical reactions. CALINE4 employs a discrete parcel method, assuming that chemical reactions are independent of the dilution process. The modeling results are compared to the field measurement data collected near two roadways in Austin, Texas, State Highway 71 (SH-71) and Farm to Market Road 973 (FM-973), under parallel and perpendicular wind conditions during the summer of 2007. In addition to ozone (O 3), other oxidants and reactive species including hydroperoxyl radical (HO 2), organic peroxyl radical (RO 2), formaldehyde (HCHO) and acetaldehyde (CH 3CHO) are considered in the transformation from NO to NO 2. CFD-VIT-RIT is shown to be capable of predicting both NO x and NO 2 profiles downwind. CALINE4 is able to capture the NO x profiles, but underpredicts NO 2 concentrations under high wind velocity. Our study suggests that the initial NO 2/NO x ratios have to be carefully selected based on traffic conditions in order to assess NO 2 concentrations near roadways. The commonly assumed NO 2/NO x ratio by volume of 5% may not be suitable for most roadways, especially those with a high fraction of heavy-duty truck traffic. In addition, high O 3 concentrations and high traffic volumes would lead to the peak NO 2 concentration occurring near roadways with elevated concentrations persistent over a long distance downwind.

  10. Chemical evolution of galaxies

    CERN Document Server

    Matteucci, Francesca

    2012-01-01

    The term “chemical evolution of galaxies” refers to the evolution of abundances of chemical species in galaxies, which is due to nuclear processes occurring in stars and to gas flows into and out of galaxies. This book deals with the chemical evolution of galaxies of all morphological types (ellipticals, spirals and irregulars) and stresses the importance of the star formation histories in determining the properties of stellar populations in different galaxies. The topic is approached in a didactical and logical manner via galaxy evolution models which are compared with observational results obtained in the last two decades: The reader is given an introduction to the concept of chemical abundances and learns about the main stellar populations in our Galaxy as well as about the classification of galaxy types and their main observables. In the core of the book, the construction and solution of chemical evolution models are discussed in detail, followed by descriptions and interpretations of observations of ...

  11. Modelling the chemical evolution in galaxies with KROME

    CERN Document Server

    Bovino, Stefano; Capelo, Pedro R; Schleicher, Dominik R G; Banerjee, R

    2015-01-01

    In this paper we present and test chemical models for three-dimensional hydrodynamical simulations of galaxy evolution. The microphysics is modelled by employing the public chemistry package KROME and the chemical networks have been tested to work in a wide range of densities and temperatures. We describe a simple H/He network following the formation of H2, and a more sophisticated network which includes metals. Photochemistry, thermal processes, and different prescriptions for the H2 catalysis on dust are presented and tested within a simple one-zone framework. We explore the effect of changing some of the key parameters such as metallicity, radiation and non-equilibrium versus equilibrium metal cooling approximations on the transition between the different gas phases. We find that employing an accurate treatment of the dust-related processes induces a faster HI-H2 transition. In addition, we show when the equilibrium assumption for metal cooling holds, and how a non-equilibrium approach affects the thermal ...

  12. Modelling the spectro-photometric and chemical evolution of Low Surface Brightness spiral galaxies

    OpenAIRE

    Hoek, L. B. van den; de Blok, W J G

    1995-01-01

    We investigate the star formation history and chemical evolution of Low Surface Brightness (LSB) spiral galaxies by means of their observed spectro-photometric and chemical properties. We present preliminary results for Johnson-Cousins UBVRI magnitudes and stellar [O/H] abundance ratios using a galactic chemical evolution model incorporating a detailed metallicity dependent set of stellar input data covering all relevant stages of stellar evolution. Comparison of our model results with observ...

  13. A Physically Based Coupled Chemical and Physical Weathering Model for Simulating Soilscape Evolution

    Science.gov (United States)

    Willgoose, G. R.; Welivitiya, D.; Hancock, G. R.

    2015-12-01

    A critical missing link in existing landscape evolution models is a dynamic soil evolution models where soils co-evolve with the landform. Work by the authors over the last decade has demonstrated a computationally manageable model for soil profile evolution (soilscape evolution) based on physical weathering. For chemical weathering it is clear that full geochemistry models such as CrunchFlow and PHREEQC are too computationally intensive to be couplable to existing soilscape and landscape evolution models. This paper presents a simplification of CrunchFlow chemistry and physics that makes the task feasible, and generalises it for hillslope geomorphology applications. Results from this simplified model will be compared with field data for soil pedogenesis. Other researchers have previously proposed a number of very simple weathering functions (e.g. exponential, humped, reverse exponential) as conceptual models of the in-profile weathering process. The paper will show that all of these functions are possible for specific combinations of in-soil environmental, geochemical and geologic conditions, and the presentation will outline the key variables controlling which of these conceptual models can be realistic models of in-profile processes and under what conditions. The presentation will finish by discussing the coupling of this model with a physical weathering model, and will show sample results from our SSSPAM soilscape evolution model to illustrate the implications of including chemical weathering in the soilscape evolution model.

  14. Modelling the chemical evolution of star forming filaments

    Science.gov (United States)

    Seifried, D.; Walch, S.

    2016-05-01

    We present simulations of star forming filaments incorporating - to our knowledge - the largest chemical network used to date on-the-fly in a 3D-MHD simulation. The network contains 37 chemical species and about 300 selected reaction rates. For this we use the newly developed package KROME (Grassi et al. [4]). Our results demonstrate the feasibility of using such a complex chemical network in 3D-MHD simulations on modern supercomputers. We perform simulations with different strengths of the interstellar radiation field and the cosmic ray ionisation rate and find chemical and physical results in accordance with observations and other recent numerical work.

  15. Modelling the chemical evolution of star forming filaments

    CERN Document Server

    Seifried, D

    2015-01-01

    We present simulations of star forming filaments incorporating - to our knowledge - the largest chemical network used to date on-the-fly in a 3D-MHD simulation. The network contains 37 chemical species and about 300 selected reaction rates. For this we use the newly developed package KROME (Grassi et al. 2014). Our results demonstrate the feasibility of using such a complex chemical network in 3D-MHD simulations on modern supercomputers. We perform simulations with different strengths of the interstellar radiation field and the cosmic ray ionisation rate and find chemical and physical results in accordance with observations and other recent numerical work.

  16. Modelling the chemical evolution of molecular clouds as a function of metallicity

    CERN Document Server

    Penteado, Em M; Rocha-Pinto, H J

    2014-01-01

    The Galaxy is in continuous elemental evolution. Since new elements produced by dying stars are delivered to the interstellar medium, the formation of new enerations of stars and planetary systems is influenced by this metal enrichment. We aim to study the role of the metallicity on the gas phase chemistry of the interstellar medium. Using a system of coupled-ordinary differential equations to model the chemical reactions, we simulate the evolution of the abundance of molecules in the gas phase for different initial interstellar elemental compositions. These varying initial elemental compositions consider the change in the "elemental abundances" predicted by a self-consistent model of the elemental evolution of the Galaxy. As far as we are aware, this is the first attempt to combine elemental evolution of the Galaxy and chemical evolution of molecular clouds. The metallicity was found to have a strong effect on the overall gas phase composition. With decreasing metallicity, the number of long carbon chains wa...

  17. Towards an improved modeling of chemical weathering in the SoilGen soil evolution model

    Science.gov (United States)

    Opolot, Emmanuel; Finke, Peter

    2014-05-01

    As the need for soil information particularly in the fields of agriculture, land evaluation, hydrology, biogeochemistry and climate change keeps increasing, models for soil evolution are increasingly becoming valuable tools to provide such soil information. Although still limited, such models are progressively being developed. The SoilGen model is one of such models with capabilities to provide soil information such as soil texture, pH, base saturation, organic carbon, CEC, etc over multi-millennia time scale. SoilGen is a mechanistic water flow driven pedogenetic model describing soil forming processes such as carbon cycling, clay migration, decalcification, bioturbation, physical weathering and chemical weathering. The model has been calibrated and confronted with field measurements in a number of case studies, giving plausible results. Discrepancies between measured and simulated soil properties as concluded from case studies have been mainly attributed to (i) the simple chemical weathering system (ii) poor estimates of initial data inputs such as bulk density and element fluxes, and (iii) incorrect values of variables that describe boundary conditions such as precipitation and potential evapotranspiration. This study focuses on extending the chemical weathering system, such that it can deal with a more heterogeneous composition of primary minerals and includes more elements such as Fe and Si. We propose and discuss here an extended description of chemical weathering in the model that is based on more primary minerals, taking into account the role of the specific area of these minerals, and the effect of physical weathering on these specific areas over time. In the initial stage, the proposed chemical weathering mechanism is also implemented in PHREEQC (a widely applied geochemical code with capabilities to simulate equilibrium reactions involving water and minerals, surface complexes and ion exchangers, etc.) to facilitate comparison with the model results

  18. Chemical evolution of spiral galaxies: models with star formation proportional to molecular hydrogen

    OpenAIRE

    Tosi, M.; Angeles I. Díaz

    1990-01-01

    This is an electronic version of an article published in Monthly Notices of the Royal Astronomical Society. Tosi, M., Díaz, A.I. Chemical evolution of spiral galaxies: models with star formation proportional to molecular hydrogen. Monthly Notices of the Royal Astronomical Society 246 (1990): 616-623

  19. Lighting up stars in chemical evolution models: the CMD of Sculptor

    Science.gov (United States)

    Vincenzo, F.; Matteucci, F.; de Boer, T. J. L.; Cignoni, M.; Tosi, M.

    2016-08-01

    We present a novel approach to draw the synthetic colour-magnitude diagram (CMD) of galaxies, which can provide - in principle - a deeper insight in the interpretation and understanding of current observations. In particular, we `light up' the stars of chemical evolution models, according to their initial mass, metallicity and age, to eventually understand how the assumed underlying galaxy formation and evolution scenario affects the final configuration of the synthetic CMD. In this way, we obtain a new set of observational constraints for chemical evolution models beyond the usual photospheric chemical abundances. The strength of our method resides in the very fine grid of metallicities and ages of the assumed data base of stellar isochrones. In this work, we apply our photochemical model to reproduce the observed CMD of the Sculptor dSph and find that we can reproduce the main features of the observed CMD. The main discrepancies are found at fainter magnitudes in the main sequence turn-off and sub-giant branch, where the observed CMD extends towards bluer colours than the synthetic one; we suggest that this is a signature of metal-poor stellar populations in the data, which cannot be captured by our assumed one-zone chemical evolution model.

  20. Chemical evolution of galaxies

    International Nuclear Information System (INIS)

    Initial conditions are probably set by results of Big Bang nucleosynthesis (BBNS) without intervening complications affecting the composition of visible matter so that extrapolation of observed abundances to BBNS products seems fairly secure. Primordial helium and deuterium abundances deduced in this way place upper and lower limits on baryonic density implying that both baryonic and non-baryonic dark matter exist and predicting no more than 3 neutrino flavours as recently confirmed in accelerator experiments. The validity of simple galactic chemical evolution models assumed in extrapolating back to the Big Bang is examined in the light of the frequency distribution of iron or oxygen abundances in the Galactic halo, bulge and disk. (orig.)

  1. Towards an Integrated Model of Earth's Thermo-Chemical Evolution and Plate Tectonics

    Science.gov (United States)

    Tackley, P. J.; Xie, S.

    2001-05-01

    It has long been a challenge for geodynamicists, who have typically modeled homogeneous mantles, to explain the geochemical evidence for the existence of several distinct chemical reservoirs, in terms of a dynamically and chemically self-consistent model. While the mixing behavior of generalized tracers has received much attention in the modeling community, a recent trend has been towards mantle convection models that track the evolution of specific chemical species, both major and minor, and can thus be related to geochemical observations. However, obtaining realistic chemical evolution in such models is dependent on their having a reasonable representation of plate tectonic behavior since the recycling of oceanic crust and complementary depleted residuum is a key process in Earth that other terrestrial planets may lack. In general, this has required inserting plate motions by hand in models. In recent years, however, we have learned how to perform numerical simulations of mantle convection in which plate tectonic behavior is introduced self-consistently through plastic yielding of the lithosphere. In this presentation, models of mantle convection that combine a treatment of geochemical evolution with self-consistently generated plate tectonics, will be presented. Preliminary results indicate that the system can self-consistently evolve regions which have a HIMU-like signature as well as regions with a high He3/He4 ratio.

  2. Introduction to Galactic Chemical Evolution

    CERN Document Server

    Matteucci, Francesca

    2016-01-01

    In this lecture I will introduce the concept of galactic chemical evolution, namely the study of how and where the chemical elements formed and how they were distributed in the stars and gas in galaxies. The main ingredients to build models of galactic chemical evolution will be described. They include: initial conditions, star formation history, stellar nucleosynthesis and gas flows in and out of galaxies. Then some simple analytical models and their solutions will be discussed together with the main criticisms associated to them. The yield per stellar generation will be defined and the hypothesis of instantaneous recycling approximation will be critically discussed. Detailed numerical models of chemical evolution of galaxies of different morphological type, able to follow the time evolution of the abundances of single elements, will be discussed and their predictions will be compared to observational data. The comparisons will include stellar abundances as well as interstellar medium ones, measured in galax...

  3. Chemical evolution and life

    Directory of Open Access Journals (Sweden)

    Malaterre Christophe

    2015-01-01

    Full Text Available In research on the origins of life, the concept of “chemical evolution” aims at explaining the transition from non-living matter to living matter. There is however strong disagreement when it comes to defining this concept more precisely, and in particular with reference to a chemical form of Darwinian evolution: for some, chemical evolution is nothing but Darwinian evolution applied to chemical systems before life appeared; yet, for others, it is the type of evolution that happened before natural selection took place, the latter being the birthmark of living systems. In this contribution, I review the arguments defended by each side and show how both views presuppose a dichotomous definition of “life”.

  4. Lighting up stars in chemical evolution models: the CMD of Sculptor

    CERN Document Server

    Vincenzo, Fiorenzo; de Boer, Thomas J L; Cignoni, Michele; Tosi, Monica

    2016-01-01

    We present a novel approach to draw the synthetic color-magnitude diagram of galaxies, which can provide - in principle - a deeper insight in the interpretation and understanding of current observations. In particular, we `light up' the stars of chemical evolution models, according to their initial mass, metallicity and age, to eventually understand how the assumed underlying galaxy formation and evolution scenario affects the final configuration of the synthetic CMD. In this way, we obtain a new set of observational constraints for chemical evolution models beyond the usual photospheric chemical abundances. The strength of our method resides in the very fine grid of metallicities and ages of the assumed database of stellar isochrones. In this work, we apply our photo-chemical model to reproduce the observed CMD of the Sculptor dSph and find that we can reproduce the main features of the observed CMD. The main discrepancies are found at fainter magnitudes in the main sequence turn-off and sub-giant branch, wh...

  5. The mineralogic evolution of the Martian surface through time: Implications from chemical reaction path modeling studies

    Science.gov (United States)

    Plumlee, G. S.; Ridley, W. I.; Debraal, J. D.; Reed, M. H.

    1993-01-01

    Chemical reaction path calculations were used to model the minerals that might have formed at or near the Martian surface as a result of volcano or meteorite impact driven hydrothermal systems; weathering at the Martian surface during an early warm, wet climate; and near-zero or sub-zero C brine-regolith reactions in the current cold climate. Although the chemical reaction path calculations carried out do not define the exact mineralogical evolution of the Martian surface over time, they do place valuable geochemical constraints on the types of minerals that formed from an aqueous phase under various surficial and geochemically complex conditions.

  6. A new galactic chemical evolution model with dust: results for dwarf irregular galaxies and DLA systems

    CERN Document Server

    Gioannini, Lorenzo; Vladilo, Giovanni; Calura, Francesco

    2016-01-01

    We present a galactic chemical evolution model which adopts updated prescriptions for all the main processes governing the dust cycle. We follow in detail the evolution of the abundances of several chemical species (C, O, S, Si, Fe and Zn) in the gas and dust of a typical dwarf irregular galaxy. The dwarf irregular galaxy is assumed to evolve with a low but continuous level of star formation and experience galactic winds triggered by supernova explosions. We predict the evolution of the gas to dust ratio in such a galaxy and discuss critically the main processes involving dust, such as dust production by AGB stars and Type II SNe, destruction and accretion (gas condensation in clouds). We then apply our model to Damped Lyman-Alpha systems which are believed to be dwarf irregulars, as witnessed by their abundance patterns. Our main conclusions are: i) we can reproduce the observed gas to dust ratio in dwarf galaxies. ii) We find that the process of dust accretion plays a fundamental role in the evolution of du...

  7. A new galactic chemical evolution model with dust: results for dwarf irregular galaxies and DLA systems

    Science.gov (United States)

    Gioannini, L.; Matteucci, F.; Vladilo, G.; Calura, F.

    2016-09-01

    We present a galactic chemical evolution model which adopts updated prescriptions for all the main processes governing the dust cycle. We follow in detail the evolution of the abundances of several chemical species (C, O, S, Si, Fe and Zn) in the gas and dust of a typical dwarf irregular galaxy. The dwarf irregular galaxy is assumed to evolve with a low but continuous level of star formation and experience galactic winds triggered by supernova explosions. We predict the evolution of the gas to dust ratio in such a galaxy and discuss critically the main processes involving dust, such as dust production by AGB stars and Type II SNe, destruction and accretion (gas condensation in clouds). We then apply our model to Damped Lyman-α systems which are believed to be dwarf irregulars, as witnessed by their abundance patterns. Our main conclusions are: i) we can reproduce the observed gas to dust ratio in dwarf galaxies. ii) We find that the process of dust accretion plays a fundamental role in the evolution of dust and in certain cases it becomes the dominant process in the dust cycle. On the other hand, dust destruction seems to be a negligible process in irregulars. iii) Concerning Damped Lyman-α systems, we show that the observed gas-phase abundances of silicon, normalized to volatile elements (zinc and sulfur), are in agreement with our model. iv) The abundances of iron and silicon in DLA systems suggest that the two elements undergo a different history of dust formation and evolution. Our work casts light on the nature of iron-rich dust: the observed depletion pattern of iron is well reproduced only when an additional source of iron dust is considered. Here we explore the possibility of a contribution from Type Ia SNe as well as an efficient accretion of iron nano-particles.

  8. Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models

    CERN Document Server

    Andrews, Brett H; Schönrich, Ralph; Johnson, Jennifer A

    2016-01-01

    Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the IMF, the SNIa delay time distribution, stellar yields, and mixing of stellar populations. Using flexCE, a new, flexible one-zone chemical evolution code, we investigate the effects of individual parameters and the trade-offs between them. Two of the most important parameters are the SFE and outflow mass-loading parameter, which shift the knee in [O/Fe]-[Fe/H] and the equilibrium abundances, respectively. One-zone models with simple star formation histories follow narrow tracks in [O/Fe]-[Fe/H] that do not match the observed bimodality in this plane. A mix of one-zone models with variations in their inflow timescales and outflow mass-loading parameters, as motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the high- and low-alpha sequences b...

  9. Evolution of chemical abundances in Seyfert galaxies

    OpenAIRE

    Ballero, S. K.; Matteucci, F; Ciotti, L.; Calura, F; P. Padovani

    2007-01-01

    We computed the chemical evolution of spiral bulges hosting Seyfert nuclei, based on updated chemical and spectro-photometrical evolution models for the bulge of our Galaxy, made predictions about other quantities measured in Seyferts, and modeled the photometry of local bulges. The chemical evolution model contains detailed calculations of the Galactic potential and of the feedback from the central supermassive black hole, and the spectro-photometric model covers a wide range of stellar ages...

  10. A simple multistage closed-(box+reservoir model of chemical evolution

    Directory of Open Access Journals (Sweden)

    Caimmi R.

    2011-01-01

    Full Text Available Simple closed-box (CB models of chemical evolution are extended on two respects, namely (i simple closed-(box+reservoir (CBR models allowing gas outflow from the box into the reservoir (Hartwick 1976 or gas inflow into the box from the reservoir (Caimmi 2007 with rate proportional to the star formation rate, and (ii simple multistage closed-(box+reservoir (MCBR models allowing different stages of evolution characterized by different inflow or outflow rates. The theoretical differential oxygen abundance distribution (TDOD predicted by the model maintains close to a continuous broken straight line. An application is made where a fictitious sample is built up from two distinct samples of halo stars and taken as representative of the inner Galactic halo. The related empirical differential oxygen abundance distribution (EDOD is represented, to an acceptable extent, as a continuous broken line for two viable [O/H]-[Fe/H] empirical relations. The slopes and the intercepts of the regression lines are determined, and then used as input parameters to MCBR models. Within the errors (-+σ, regression line slopes correspond to a large inflow during the earlier stage of evolution and to low or moderate outflow during the subsequent stages. A possible inner halo - outer (metal-poor bulge connection is also briefly discussed. Quantitative results cannot be considered for applications to the inner Galactic halo, unless selection effects and disk contamination are removed from halo samples, and discrepancies between different oxygen abundance determination methods are explained.

  11. Evolution of Autocatalytic Sets in Computational Models of Chemical Reaction Networks

    Science.gov (United States)

    Hordijk, Wim

    2016-06-01

    Several computational models of chemical reaction networks have been presented in the literature in the past, showing the appearance and (potential) evolution of autocatalytic sets. However, the notion of autocatalytic sets has been defined differently in different modeling contexts, each one having some shortcoming or limitation. Here, we review four such models and definitions, and then formally describe and analyze them in the context of a mathematical framework for studying autocatalytic sets known as RAF theory. The main results are that: (1) RAF theory can capture the various previous definitions of autocatalytic sets and is therefore more complete and general, (2) the formal framework can be used to efficiently detect and analyze autocatalytic sets in all of these different computational models, (3) autocatalytic (RAF) sets are indeed likely to appear and evolve in such models, and (4) this could have important implications for a possible metabolism-first scenario for the origin of life.

  12. Beverton-Holt discrete pest management models with pulsed chemical control and evolution of pesticide resistance

    Science.gov (United States)

    Liang, Juhua; Tang, Sanyi; Cheke, Robert A.

    2016-07-01

    Pest resistance to pesticides is usually managed by switching between different types of pesticides. The optimal switching time, which depends on the dynamics of the pest population and on the evolution of the pesticide resistance, is critical. Here we address how the dynamic complexity of the pest population, the development of resistance and the spraying frequency of pulsed chemical control affect optimal switching strategies given different control aims. To do this, we developed novel discrete pest population growth models with both impulsive chemical control and the evolution of pesticide resistance. Strong and weak threshold conditions which guarantee the extinction of the pest population, based on the threshold values of the analytical formula for the optimal switching time, were derived. Further, we addressed switching strategies in the light of chosen economic injury levels. Moreover, the effects of the complex dynamical behaviour of the pest population on the pesticide switching times were also studied. The pesticide application period, the evolution of pesticide resistance and the dynamic complexity of the pest population may result in complex outbreak patterns, with consequent effects on the pesticide switching strategies.

  13. Introduction to Galactic Chemical Evolution

    Science.gov (United States)

    Matteucci, Francesca

    2016-04-01

    In this lecture I will introduce the concept of galactic chemical evolution, namely the study of how and where the chemical elements formed and how they were distributed in the stars and gas in galaxies. The main ingredients to build models of galactic chemical evolution will be described. They include: initial conditions, star formation history, stellar nucleosynthesis and gas flows in and out of galaxies. Then some simple analytical models and their solutions will be discussed together with the main criticisms associated to them. The yield per stellar generation will be defined and the hypothesis of instantaneous recycling approximation will be critically discussed. Detailed numerical models of chemical evolution of galaxies of different morphological type, able to follow the time evolution of the abundances of single elements, will be discussed and their predictions will be compared to observational data. The comparisons will include stellar abundances as well as interstellar medium ones, measured in galaxies. I will show how, from these comparisons, one can derive important constraints on stellar nucleosynthesis and galaxy formation mechanisms. Most of the concepts described in this lecture can be found in the monograph by Matteucci (2012).

  14. Extremely Metal-Poor Stars and a Hierarchical Chemical Evolution Model

    CERN Document Server

    Komiya, Yutaka

    2011-01-01

    Early phases of the chemical evolution and formation history of extremely metal poor (EMP) stars are investigated using hierarchical galaxy formation models. We build a merger tree of the Galaxy according to the extended Press-Schechter theory. We follow the chemical evolution along the tree, and compare the model results to the metallicity distribution function (MDF) and abundance ratio distribution of the Milky Way halo. We adopt three different initial mass functions (IMFs). In a previous studies, we argue that typical mass of EMP stars should be high-mass(~10Msun) based on studies of binary origin carbon-rich EMP stars. In this study, we show that only the high-mass IMF can explain a observed small number of EMP stars. For relative element abundances, the high-mass IMF and the Salpeter IMF predict similar distributions. We also investigate dependence on nucleosynthetic yields of supernovae (SNe). The theoretical SN yields by Kobayashi et al.(2006) and Chieffi & Limonge (2004) show reasonable agreement...

  15. A NEW CHEMICAL EVOLUTION MODEL FOR DWARF SPHEROIDAL GALAXIES BASED ON OBSERVED LONG STAR FORMATION HISTORIES

    International Nuclear Information System (INIS)

    We present a new chemical evolution model for dwarf spheroidal galaxies (dSphs) in the local universe. Our main aim is to explain both their observed star formation histories and metallicity distribution functions simultaneously. Applying our new model for the four local dSphs, that is, Fornax, Sculptor, Leo II, and Sextans, we find that our new model reproduces the observed chemical properties of the dSphs consistently. Our results show that the dSphs have evolved with both a low star formation efficiency and a large gas outflow efficiency compared with the Milky Way, as suggested by previous works. Comparing the observed [α/Fe]-[Fe/H] relation of the dSphs with the model predictions, we find that our model favors a longer onset time of Type Ia supernovae (i.e., 0.5 Gyr) than that suggested in previous studies (i.e., 0.1 Gyr). We discuss the origin of this discrepancy in detail

  16. A NEW CHEMICAL EVOLUTION MODEL FOR DWARF SPHEROIDAL GALAXIES BASED ON OBSERVED LONG STAR FORMATION HISTORIES

    Energy Technology Data Exchange (ETDEWEB)

    Homma, Hidetomo; Murayama, Takashi [Astronomical Institute, Tohoku University, Aoba-ku, Sendai 980-8578 (Japan); Kobayashi, Masakazu A. R.; Taniguchi, Yoshiaki, E-mail: hide@astr.tohoku.ac.jp [Research Center for Space and Cosmic Evolution, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577 (Japan)

    2015-02-01

    We present a new chemical evolution model for dwarf spheroidal galaxies (dSphs) in the local universe. Our main aim is to explain both their observed star formation histories and metallicity distribution functions simultaneously. Applying our new model for the four local dSphs, that is, Fornax, Sculptor, Leo II, and Sextans, we find that our new model reproduces the observed chemical properties of the dSphs consistently. Our results show that the dSphs have evolved with both a low star formation efficiency and a large gas outflow efficiency compared with the Milky Way, as suggested by previous works. Comparing the observed [α/Fe]-[Fe/H] relation of the dSphs with the model predictions, we find that our model favors a longer onset time of Type Ia supernovae (i.e., 0.5 Gyr) than that suggested in previous studies (i.e., 0.1 Gyr). We discuss the origin of this discrepancy in detail.

  17. Galactic Chemical Evolution

    CERN Document Server

    Gibson, B K; Renda, A; Kawata, D; Lee, H; Gibson, Brad K.; Fenner, Yeshe; Renda, Agostino; Kawata, Daisuke; Lee, Hyun-chul

    2003-01-01

    The primary present-day observables upon which theories of galaxy evolution are based are a system's morphology, dynamics, colour, and chemistry. Individually, each provides an important constraint to any given model; in concert, the four represent a fundamental (intractable) boundary condition for chemodynamical simulations. We review the current state-of-the-art semi-analytical and chemodynamical models for the Milky Way, emphasising the strengths and weaknesses of both approaches.

  18. Chemical Evolution of the Galaxy

    OpenAIRE

    Tosi, M.

    1994-01-01

    Standard models for the chemical evolution of the Galaxy are reviewed with particular emphasis on the history of the abundance gradients in the disk. The effects on the disk structure and metallicity of gas accretion are discussed, showing that a significant fraction of the current disk mass has been accreted in the last Gyrs and that the chemical abundances of the infalling gas can be non primordial but should not exceed 0.3 Z(sun). The distributions with time and with galactocentric distanc...

  19. Modeling the chemical evolution of a collapsing prestellar core in two spatial dimensions

    CERN Document Server

    van Weeren, R J; Hogerheijde, M R

    2009-01-01

    The physical conditions in a collapsing cloud can be traced by observations of molecular lines. To correctly interpret these observations the abundance distributions of the observed species need to be derived. The chemistry in a collapsing molecular cloud is not in a steady state as the density and temperature evolve. We therefore need to follow chemical reactions, both in the gas phase and on dust grains, as well as gas-grain interactions, to predict the abundance distributions. Our aim is to model the abundances of molecules, in the gas phase and on grain mantles in the form of ice, from prestellar core collapse to disk formation. We use a 2-dimensional hydrodynamical simulation as a physical model from which we take the density, temperature, and the flow of the gas. Trace particles, moving along with the gas, are used to follow the chemistry during prestellar core collapse and disk formation. The evolution of the abundances and the composition of ices on grain mantles were compared to observations. We also...

  20. Chemical Evolution in Omega Centauri

    OpenAIRE

    Smith, Verne V.

    2003-01-01

    The globular cluster Omega Centauri displays evidence of a complex star formation history and peculiar internal chemical evolution, setting it apart from essentially all other globular clusters of the Milky Way. In this review we discuss the nature of the chemical evolution that has occurred within Omega Cen and attempt to construct a simple scenario to explain its chemistry.

  1. The galactic habitable zone of the Milky Way and M31 from chemical evolution models with gas radial flows

    CERN Document Server

    Spitoni, E; Sozzetti, A

    2014-01-01

    The galactic habitable zone is defined as the region with sufficient abundance of heavy elements to form planetary systems in which Earth-like planets could be born and might be capable of sustaining life, after surviving to close supernova explosion events. Galactic chemical evolution models can be useful for studying the galactic habitable zones in different systems. We apply detailed chemical evolution models including radial gas flows to study the galactic habitable zones in our Galaxy and M31. We compare the results to the relative galactic habitable zones found with "classical" (independent ring) models, where no gas inflows were included. For both the Milky Way and Andromeda, the main effect of the gas radial inflows is to enhance the number of stars hosting a habitable planet with respect to the "classical" model results, in the region of maximum probability for this occurrence, relative to the classical model results. These results are obtained by taking into account the supernova destruction process...

  2. Chemical Evolution of Dwarf Irregular Galaxies chemodynamical models and the effect of gas infall

    CERN Document Server

    Hensler, G; Köppen, J; Hensler, Gerhard; Rieschick, Andreas; K"oppen, Joachim

    1999-01-01

    Because of their low gravitational energies dwarf galaxies are greatly exposed to energetical influences by the interstellar medium, like e.g. stellar radiation, winds or explosions, or by their environment. While the metallicity depletion in dwarf galaxies can be explained in general by supernova-driven galactic winds, the reason for their low N/O ratios at low O abundance is not yet completely understood. Stellar yields enrich the different gas phases with elements that are characteristic for their stellar progenitors. Gas-phase transitions are necessary for a mixing of elements, but depend sensitively on the thermal and dynamical state of the interstellar medium. Models of chemical evolution start usually with a high N/O ratio at low O abundance according to a metal enrichment by ancient stellar populations with traditional yields, but can only reproduce the N/O-O peculiarity by the stepwise element release and mostly by the application of multiple starbursts in order to account also for a selective elemen...

  3. Beverton-Holt discrete pest management models with pulsed chemical control and evolution of pesticide resistance

    OpenAIRE

    Liang, Juhua; Tang, Sanyi; Cheke, Robert

    2016-01-01

    Pest resistance to pesticides is usually managed by switching between different types of pesticides. The optimal switching time, which depends on the dynamics of the pest population and on the evolution of the pesticide resistance, is critical. Here we address how the dynamic complexity of the pest population, the development of resistance and the spraying frequency of pulsed chemical control affect optimal switching strategies given different control aims. To do this, we developed novel disc...

  4. Mercury's thermo-chemical evolution from numerical models constrained by Messenger observations

    Science.gov (United States)

    Tosi, N.; Breuer, D.; Plesa, A. C.; Wagner, F.; Laneuville, M.

    2012-04-01

    The Messenger spacecraft, in orbit around Mercury for almost one year, has been delivering a great deal of new information that is changing dramatically our understanding of the solar system's innermost planet. Tracking data of the Radio Science experiment yielded improved estimates of the first coefficients of the gravity field that permit to determine the normalized polar moment of inertia of the planet (C/MR2) and the ratio of the moment of inertia of the mantle to that of the whole planet (Cm/C). These two parameters provide a strong constraint on the internal mass distribution and, in particular, on the core mass fraction. With C/MR2 = 0.353 and Cm/C = 0.452 [1], interior structure models predict a core radius as large as 2000 km [2], leaving room for a silicate mantle shell with a thickness of only ~ 400 km, a value significantly smaller than that of 600 km usually assumed in parametrized [3] as well as in numerical models of Mercury's mantle dynamics and evolution [4]. Furthermore, the Gamma-Ray Spectrometer measured the surface abundance of radioactive elements, revealing, besides uranium and thorium, the presence of potassium. The latter, being moderately volatile, rules out traditional formation scenarios from highly refractory materials, favoring instead a composition not much dissimilar from a chondritic model. Considering a 400 km thick mantle, we carry out a large series of 2D and 3D numerical simulations of the thermo-chemical evolution of Mercury's mantle. We model in a self-consistent way the formation of crust through partial melting using Lagrangian tracers to account for the partitioning of radioactive heat sources between mantle and crust and variations of thermal conductivity. Assuming the relative surface abundance of radiogenic elements observed by Messenger to be representative of the bulk mantle composition, we attempt at constraining the degree to which uranium, thorium and potassium are concentrated in the silicate mantle through a broad

  5. Laboratory photochemical formation of peptides in presence of meteorites as a model of chemical evolution process

    Science.gov (United States)

    Gontareva, N. B.; Kuzicheva, E. A.

    2001-08-01

    To have a better understanding of the processes leading to the origin, evolution and distribution of life on Earth and elsewhere we have performed experiments on the prebiotic synthesis of peptides. In this paper we took glycine+phenylalanine dry films exposed to short ultraviolet irradiation because solar UV is known as a driving force of organic chemical evolution. It seems very important to evaluate the possible influence of meteorites on solid phase synthesis of peptides. Dipeptides and tripeptides were identified by means of HPLC technique. Total yield of peptides synthesized follows certain sequences: yield in presence of Murchison meteorite > yield in presence of Allende meteorite > yield in the absence of mineral beds. It has been stated that in average the presence of mineral dust at the exposure of dry films increased total product yield roughly by two times. Photolysis of initial aminoacids was also studied. Our results coincided with those obtained for peptide synthesis in presence of lunar soil.

  6. Concrete Chemical Evolution

    Energy Technology Data Exchange (ETDEWEB)

    D.H. Tang

    1998-07-31

    The objectives of this analysis are to discuss and evaluate testing results that were performed for the M&O by the Pennsylvania State University (PSU) to evaluate the potential long-term evolution of organic admixtures in cementitious materials at elevated temperatures. The testing was designed to help provide a basis for a determination by the Performance Assessment group (PA) of the long-term acceptability and longevity of cementitious materials for repository use. The main purpose of the testing was to assess the evolution of gases (especially CO{sub 2}) from hydrated cement paste at elevated temperatures and to determine the impact on alkalinity, i.e., the pH value of cement paste pore solution. This information in turn can be used as scoping information to determine if further tests of this nature are needed to support PA. As part of this discussion and evaluation of the PSU results, an assessment of alkalinity in a ''cementitious repository'' and an evaluation of organic materials are presented.

  7. Chemical Evolution in Hierarchical Clustering Scenarios

    OpenAIRE

    Tissera, Patricia B.; Scannapieco, Cecilia

    2003-01-01

    We present first results of an implementation of chemical evolution in a cosmological hydrodynamical code, focusing the analysis on the effects of cooling baryons according to their metallicity. We found that simulations with primordial cooling can underestimate the star formation rate from $z < 3$ and by up to $\\approx 20 %$. We constructed simulated spectra by combining the star formation and chemical history of galactic systems with spectra synthesis models and assess the impact of chemica...

  8. The Chemical Evolution of the Milky Way

    CERN Document Server

    Tosi, M P

    1999-01-01

    The field of chemical evolution modeling of the Galaxy is experiencing in the last years a phase of high activity and important achievements. There are, however, several open questions which still need to be answered. In this review I summarize what have been the most important achievements and what are some of the most urgent questions to be answered.

  9. Modeling the chemical evolution of Omega Centauri using three-dimensional hydrodynamical simulations

    CERN Document Server

    Marcolini, A; D'Ercole, A; Gibson, B K; Ferraro, F R

    2007-01-01

    We present a hydrodynamical and chemical model for the globular cluster Omega Cen, under the assumption that it is the remnant of an ancient dwarf spheroidal galaxy (dSph), the bulk of which was disrupted and accreted by our Galaxy ~10 Gyr ago. We highlight the very different roles played by Type II and Type Ia supernovae (SNe) in the chemical enrichment of the inner regions of the putative parent dSph. While the SNe II pollute the interstellar medium rather uniformly, the SNe Ia ejecta may remain confined inside dense pockets of gas as long as succesive SNe II explosions spread them out. Stars forming in such pockets have lower alpha-to-iron ratios than the stars forming elsewhere. Owing to the inhomogeneous pollution by SNe Ia, the metal distribution of the stars in the central region differs substantially from that of the main population of the dwarf galaxy, and resembles that observed in Omega Cen. This inhomogeneous mixing is also responsible for a radial segregation of iron-rich stars with depleted [alp...

  10. Galactic chemical evolution hydrogen through zinc

    CERN Document Server

    Timmes, F X; Timmes, F X; Woosley, S E

    1994-01-01

    Using the output from a grid of 60 Type II supernova models (Woosley \\& Weaver 1994) of varying mass (11 \\ltaprx M/M\\sun \\ltaprx 40) and metallicity (0, 10^{-4}, 0.01, 0.1, and 1 Z\\sol), the chemical evolution of 76 stable isotopes, from hydrogen to zinc, is calculated. The chemical evolution calculation employs a simple dynamical model for the Galaxy (infall with a 4 billion year e-folding time scale onto a exponential disk and 1/r^2 bulge), and standard evolution parameters, such as a Salpeter initial mass function and a quadratic Schmidt star formation rate. The theoretical results are compared in detail with observed stellar abundances in stars with metallicities in the range -3.0 \\ltaprx [Fe/H] \\ltaprx 0.0 dex. While our discussion focuses on the solar neighborhood where there are the most observations, the supernovae rates, an intrinsically Galactic quantity, are also discussed.

  11. Chemical evolution of the early Martian hydrosphere

    Science.gov (United States)

    Schaefer, M. W.

    1990-01-01

    The chemical evolution of the early Martian hydrosphere is discussed. The early Martian ocean can be modeled as a body of relatively pure water in equilibrium with a dense carbon dioxide atmosphere. The chemical weathering of lavas, pyroclastic deposits, and impact melt sheets would have the effect of neutralizing the acidity of the juvenile water. As calcium and other cations are added to the water by chemical weathering, they are quickly removed by the precipitation of calcium carbonate and other minerals, forming a deposit of limestone beneath the surface of the ocean. As the atmospheric carbon dioxide pressure and the temperature decrease, the Martian ocean would be completely frozen. Given the scenario for the chemical evolution of the northern lowland plains of Mars, it should be possible to draw a few conclusions about the expected mineralogy and geomorphology of this regions.

  12. Evolution of chemical abundances in Seyfert galaxies

    CERN Document Server

    Ballero, S K; Ciotti, L; Calura, F; Padovani, P

    2007-01-01

    We computed the chemical evolution of spiral bulges hosting Seyfert nuclei, based on updated chemical and spectro-photometrical evolution models for the bulge of our Galaxy, made predictions about other quantities measured in Seyferts, and modeled the photometry of local bulges. The chemical evolution model contains detailed calculations of the Galactic potential and of the feedback from the central supermassive black hole, and the spectro-photometric model covers a wide range of stellar ages and metallicities. We followed the evolution of bulges in the mass range 10^9 - 10^{11} Msun by scaling the star formation efficiency and the bulge scalelength as in the inverse-wind scenario for elliptical galaxies, and considering an Eddington limited accretion onto the central supermassive black hole. We successfully reproduced the observed black hole-host bulge mass relation. The observed nuclear bolometric luminosity is reproduced only at high redshift or for the most massive bulges; in the other cases, at z = 0 a r...

  13. Stochastic processes, galactic star formation, and chemical evolution. Effects of accretion, stripping, and collisions in multiphase multi-zone models

    CERN Document Server

    Valle, G D; Galli, D

    2005-01-01

    This paper reports simulations allowing for stochastic accretion and mass loss within closed and open systems modeled using a previously developed multi-population, multi-zone (halo, thick disk, thin disk) treatment. The star formation rate is computed as a function of time directly from the model equations and all chemical evolution is followed without instantaneous recycling. Several types of simulations are presented here: (1) a closed system with bursty mass loss from the halo to the thick disk, and from the thick to the thin disk, in separate events to the thin disk; (2) open systems with random environmental (extragalactic) accretion, e.g. by infall of high velocity clouds directly to the thin disk; (3) schematic open system single and multiple collision events and intracluster stripping. For the open models, the mass of the Galaxy has been explicitly tracked with time. We present the evolution of the star formation rate, metallicity histories, and concentrate on the light elements. We find a wide range...

  14. Structure and evolution of collapse sinkholes: Combined interpretation from physico-chemical modelling and geophysical field work

    Science.gov (United States)

    Kaufmann, Georg; Romanov, Douchko

    2016-09-01

    In karst rocks (limestone, anhydrite, gypsum, etc.), water flowing through fissures and bedding partings can enlarge voids either by physical or chemical dissolution. Within a geologically short period of time, the increase in void space creates a large secondary porosity typical for soluble rocks, which is responsible for preferential flow through the karst rock, often through cave systems with passages reaching the meter-scale and more. This large-scale voids in the sub-surface can initiate collapse of the overburden, either through wall or roof breakdown, and the initial void created by dissolution can migrate upwards and finally cause a surface collapse and create a collapse sinkhole. While the dissolution part of this evolution is in the order of 10,000-100,000 years, the final mechanical collapse can occur on time scales of days. We have studied a typical collapse sinkhole site in the southern Harz Mountains in Germany, with anhydrite (partly converted to gypsum) as soluble rock in the sub-surface. We discuss geophysical measurements (gravity, electrical resistivity tomography, self potential, magnetics) from the location to identify the local collapse sinkhole signal and the possibility to separate the collapse sinkhole signal from the broader geological signal of the study site. We model the initiation of sub-surface voids with our numerical tool KARSTAQUIFER, a 3D karst evolution model describing flow and dissolution in karst rocks. We apply this numerical model to predict collapse sinkholes in a locality in the Harz Mountains.

  15. Chemical Evolution of the Juvenile Universe

    CERN Document Server

    Wasserburg, G J

    2009-01-01

    Only massive stars contribute to the chemical evolution of the juvenile universe corresponding to [Fe/H]-0.32. Recent observations show that there are stars with [Sr/Fe]<-2 and [Fe/H]<-3. This proves that the two-component model is not correct and that a third component is necessary to explain the observations. This leads to a simple three-component model including low-mass and normal SNe II and hypernovae (HNe), which gives a good description of essentially all the data for stars with [Fe/H]<-1.5. We conclude that HNe are more important than normal SNe II in the chemical evolution of the low-A elements, in sharp distinction to earlier models. (Abridged)

  16. Characterizing the local population of star-forming and passive galaxies with analytical models of chemical evolution

    CERN Document Server

    Spitoni, E; Matteucci, F

    2016-01-01

    Analytical models of chemical evolution, including inflow and outflow of gas, are important tools to study how the metal content in galaxies evolves as a function of time. In this work, we present new analytical solutions for the evolution of the gas mass, total mass and metallicity of a galactic system, when a decaying exponential infall rate of gas and galactic winds are assumed. We apply our model to characterize a sample of local star-forming and passive galaxies from the Sloan Digital Sky Survey data, with the aim of reproducing their observed mass-metallicity relation; in this way, we can derive how the two populations of star-forming and passive galaxies differ in their particular distribution of ages, formation time scales, infall masses and mass loading factors. We find that the local passive galaxies are on average older and assembled on shorter typical time-scales than the local star-forming ones; on the other hand, the larger mass star-forming galaxies show generally older ages and longer typical ...

  17. Models of disk chemical evolution focusing the pure dynamical radial mixing

    Directory of Open Access Journals (Sweden)

    Re Fiorentin P.

    2012-02-01

    Full Text Available We performed N-body simulations to study the dynamical evolution of a stellar disk inside a Dark Matter (DM halo. Our results evidence how a standard -radially decreasing- metallicity gradient produces a negative vϕ vs. [Fe/H] correlation, similar to that shown by the thin disk stars, while an inverse radial gradient generates a positive rotation-metallicity correlation, as that observed in the old thick population.

  18. Chemical Evolution of Groundwater Near a Sinkhole Lake, Northern Florida: 2. Chemical Patterns, Mass Transfer Modeling, and Rates of Mass Transfer Reactions

    Science.gov (United States)

    Katz, Brian G.; Plummer, L. Niel; Busenberg, Eurybiades; Revesz, Kinga M.; Jones, Blair F.; Lee, Terrie M.

    1995-06-01

    Chemical patterns along evolutionary groundwater flow paths in silicate and carbonate aquifers were interpreted using solute tracers, carbon and sulfur isotopes, and mass balance reaction modeling for a complex hydrologic system involving groundwater inflow to and outflow from a sinkhole lake in northern Florida. Rates of dominant reactions along defined flow paths were estimated from modeled mass transfer and ages obtained from CFC-modeled recharge dates. Groundwater upgradient from Lake Barco remains oxic as it moves downward, reacting with silicate minerals in a system open to carbon dioxide (CO2), producing only small increases in dissolved species. Beneath and downgradient of Lake Barco the oxic groundwater mixes with lake water leakage in a highly reducing, silicate-carbonate mineral environment. A mixing model, developed for anoxic groundwater downgradient from the lake, accounted for the observed chemical and isotopic composition by combining different proportions of lake water leakage and infiltrating meteoric water. The evolution of major ion chemistry and the 13C isotopic composition of dissolved carbon species in groundwater downgradient from the lake can be explained by the aerobic oxidation of organic matter in the lake, anaerobic microbial oxidation of organic carbon, and incongruent dissolution of smectite minerals to kaolinite. The dominant process for the generation of methane was by the CO2 reduction pathway based on the isotopic composition of hydrogen (δ2H(CH4) = -186 to -234‰) and carbon (δ13C(CH4) = -65.7 to -72.3‰). Rates of microbial metabolism of organic matter, estimated from the mass transfer reaction models, ranged from 0.0047 to 0.039 mmol L-1 yr-1 for groundwater downgradient from the lake.

  19. Abundance Ratios in Stars vs. Hot Gas in Elliptical Galaxies: the Chemical Evolution Modeller Point of View

    CERN Document Server

    Pipino, A

    2009-01-01

    I will present predictions from chemical evolution model aimed at a self-consistent study of both optical (i.e. stellar) and X-ray (i.e.gas) properties of present-day elliptical galaxies. Detailed cooling and heating processes in the interstellar medium (ISM) are taken into and allow a reliable modelling of the SN-driven galactic wind. SNe Ia activity, in fact, may power a galactic wind lasting for a considerable amount of the galactic lifetime, even in the case for which the efficiency of energy transfer into the ISM per SN Ia event is less than unity. The model simultaneously reproduces the mass-metallicity, the colour-magnitude, the L_X - L_B and the L_X - T relations, as well as the observed trend of the [Mg/Fe] ratio as a function of sigma, by adopting the prescriptions of Pipino & Matteucci (2004) for the gas infall and star formation timescales. The "iron discrepancy", namely the too high predicted iron abundance in X-ray haloes of ellipticals compared to observations, can be solved by taking into ...

  20. Chemical evolution during the process of proto-star formation by considering a two dimensional hydrodynamic model

    CERN Document Server

    Das, Ankan; Chakrabarti, Sandip K; Chakrabarti, Sonali

    2013-01-01

    Chemical composition of a molecular cloud is highly sensitive to the physical properties of the cloud. In order to obtain the chemical composition around a star forming region, we carry out a two dimensional hydrodynamical simulation of the collapsing phase of a proto-star. A total variation diminishing scheme (TVD) is used to solve the set of equations governing hydrodynamics. This hydrodynamic code is capable of mimicking evolution of the physical properties during the formation of a proto-star. We couple our reasonably large gas-grain chemical network to study the chemical evolution during the collapsing phase of a proto-star. To have a realistic estimate of the abundances of bio-molecules in the interstellar medium, we include the recently calculated rate coefficients for the formation of several interstellar bio-molecules into our gas phase network. Chemical evolution is studied in detail by keeping grain at the constant temperature throughout the simulation as well as by using the temperature variation ...

  1. Chemical Evolution of Blue Compact Galaxies

    Institute of Scientific and Technical Information of China (English)

    Fei Shi; Xu Kong; Fu-Zhen Cheng

    2006-01-01

    Based on a sample of 72 Blue Compact Galaxies (BCGs) observed with the 2.16 m telescope of the National Astronomical Observatories, Chinese Academy of Sciences (NAOC) and about 4000 strong emission line galaxies from the Sloan Digital Sky Survey,we analyzed their chemical evolution history using the revised chemical evolution model of Larsen et al. Our sample covers a much larger metallicity range (7.2<12+log(O/H) <9.0). We found that, in order to reproduce the observed abundance pattern and gas fraction over the whole metallicity range, a relatively continuous star formation history is needed for high metallicity galaxies, while assuming a series of instantaneous bursts with long quiescent periods (some Gyrs) for low metallicity galaxies. Model calculations also show that only the closed-box model is capable of reproducing the observational data over the whole metallicity range. Models that consider the ordinary winds and/or inflow can only fit the observations in the low metallicity range, and a model with enriched wind cannot fit the data in the whole metallicity range. This implies that the current adopted simple wind and inflow models are not applicable to massive galaxies, where the underlying physics of galactic winds or inflow could be more complicated.

  2. Equilibrium and Sudden Events in Chemical Evolution

    CERN Document Server

    Weinberg, David H; Freudenburg, Jenna

    2016-01-01

    We present new analytic solutions for one-zone (fully mixed) chemical evolution models and explore their implications. In contrast to existing analytic models, we incorporate a realistic delay time distribution for Type Ia supernovae (SNIa) and can therefore track the separate evolution of $\\alpha$-elements produced by core collapse supernovae (CCSNe) and iron peak elements synthesized in both CCSNe and SNIa. In generic cases, $\\alpha$ and iron abundances evolve to an equilibrium at which element production is balanced by metal consumption and gas dilution, instead of continuing to increase over time. The equilibrium absolute abundances depend principally on supernova yields and the outflow mass loading parameter $\\eta$, while the equilibrium abundance ratio [$\\alpha$/Fe] depends mainly on yields and secondarily on star formation history. A stellar population can be metal-poor either because it has not yet evolved to equilibrium or because high outflow efficiency makes the equilibrium abundance itself low. Sy...

  3. Multiphase chemical evolution in elliptical galaxies

    CERN Document Server

    Fujita, Y; Okoshi, K

    1996-01-01

    The recent {\\em ASCA} results show that the iron abundance of the X-ray gas of elliptical galaxies is less than the solar abundance (Z_{\\sun}). The observed low iron abundance is inconsistent with the predictions of the previous chemical evolution models. In order to solve this problem, we present a simple model of chemical evolution for elliptical galaxies after the galactic wind period under the assumption that the gases ejected from stars do not mix with the circumferential gas. The ejected gas components evolve separately according to their birth time and origin. We have investigated their evolution qualitatively. The gas components originated from supernova remnant shells cool and drop out of the hot gas faster than the other components because of their high density and metal abundance. As a result, supernovae cannot heat the whole gas of the elliptical galaxies effectively, in contrary to the previous results. If the metal abundance of mass-loss gas is not uniform, the mass-loss gas with higher abundanc...

  4. The Chemical Evolution of the Universe

    Science.gov (United States)

    Baker, A. C.; Mathlin, G. P.; Churches, D. K.; Edmunds, M. G.

    2000-12-01

    We have constructed a simple, robust model of the chemical evolution of galaxies from high to low redshift, and applied it to published observations of damped Lyman-alpha quasar absorption line systems (DLAs). The elementary 'monolithic collapse' model assumes quiescent star formation and isolated galaxies (no interactions, mergers or gas flows). These calculations appear in Mathlin, Baker, Churches and Edmunds (2000) (astro-ph/0009226, MNRAS in press), where we also consider the influence of dust and chemical gradients in the galaxies, and hence explore the selection effects in quasar surveys. We fit individual DLA systems to predict observable properties of the absorbing galaxies, and also indicate the expected redshift behaviour of chemical element ratios involving nucleosynthetic time delays. Many DLA absorber galaxies are rather faint and close to the quasar line-of-sight, requiring at least eight-metre class telescopes, and adaptive optics to be detected even in the near-IR. Despite its simplicity, our elementary model gives a good account of the distribution and evolution of the metallicity and column density of DLAs, and of the evolution of the global star formation rate and gas density below redshifts z ~ 3. However, from the comparison of our model with observations, star formation rates at higher redshifts (z > 3) are clearly enhanced in the real Universe. Galaxy interactions and mergers, and gas flows very probably play a major role. We are now engaged in a 'two pronged' attack on the questions raised in Mathlin et al. (2000). As part of the QuickStart Gemini North observations programme, we are acquiring deep, high spatial resolution Hopuka'a/QUIRC K band observations of DLA quasars studied by Mathlin et al. (2000). We are also incorporating merger-induced starburst activity into our chemical evolution models. I will present our latest results from Gemini North, and their interpretation in our revised theoretical framework. Research funded by the UK

  5. Dynamical and chemical evolution of NGC1569

    CERN Document Server

    Recchi, S; Angeretti, L; Matteucci, F

    2005-01-01

    Blue Compact Dwarf and Dwarf Irregular galaxies are generally believed to be unevolved objects, due to their blue colors, compact appearance and large gas fractions. Many of these objects show an ongoing intense burst of star formation or have experienced it in the recent past. By means of 2-D hydrodynamical simulations, coupled with detailed chemical yields originating from SNeII, SNeIa, and intermediate-mass stars, we study the dynamical and chemical evolution of model galaxies with structural parameters similar to NGC1569, a prototypical starburst galaxy. A burst of star formation with short duration is not able to account for the chemical and morphological properties of this galaxy. The best way to reproduce the chemical composition of this object is by assuming long-lasting episodes of star formation and a more recent burst, separated from the previous episodes by a short quiescent period. The last burst of star formation, in most of the explored cases, does not affect the chemical composition of the gal...

  6. Chemical evolution in hierarchical scenarios

    Directory of Open Access Journals (Sweden)

    Tissera P.B.

    2012-02-01

    Full Text Available We studied the chemical properties of Milky-Way mass galaxies. We found common global chemical patterns with particularities which reflect their different assembly histories in a hierarchical scenario. We carried out a comprehensively analysis of the dynamical components (central spheroid, disc, inner and outer haloes and their chemical properties.

  7. Chemical evolution and the origin of life

    Science.gov (United States)

    Oro, J.

    1983-01-01

    A review is presented of recent advances made in the understanding of the formation of carbon compounds in the universe and the occurrence of processes of chemical evolution. Topics discussed include the principle of evolutionary continuity, evolution as a fundamental principle of the physical universe, the nuclear synthesis of biogenic elements, organic cosmochemistry and interstellar molecules, the solar nebula and the solar system in chemical evolution, the giant planets and Titan in chemical evolution, and comets and their interaction with the earth. Also examined are carbonaceous chondrites, environment of the primitive earth, energy sources available on the primitive earth, the synthesis of biochemical monomers and oligomers, the abiotic transcription of nucleotides, unified prebiotic and enzymatic mechanisms, phospholipids and membranes, and protobiological evolution.

  8. The impact of chemical evolution on the observable properties of stellar populations

    CERN Document Server

    Tosi, M P

    2000-01-01

    The major effects of the chemical evolution of galaxies on the characteristics of their stellar populations are reviewed. A few examples of how the observed stellar properties derived from colour--magnitude diagrams can constrain chemical evolution models are given.

  9. Simulating emission and chemical evolution of coarse sea-salt particles in the Community Multiscale Air Quality (CMAQ) model

    Science.gov (United States)

    Kelly, J. T.; Bhave, P. V.; Nolte, C. G.; Shankar, U.; Foley, K. M.

    2010-04-01

    Chemical processing of sea-salt particles in coastal environments significantly impacts concentrations of particle components and gas-phase species and has implications for human exposure to particulate matter and nitrogen deposition to sensitive ecosystems. Emission of sea-salt particles from the coastal surf zone is known to be elevated compared to that from the open ocean. Despite the importance of sea-salt emissions and chemical processing, the US EPA's Community Multiscale Air Quality (CMAQ) model has traditionally treated coarse sea-salt particles as chemically inert and has not accounted for enhanced surf-zone emissions. In this article, updates to CMAQ are described that enhance sea-salt emissions from the coastal surf zone and allow dynamic transfer of HNO3, H2SO4, HCl, and NH3 between coarse particles and the gas phase. Predictions of updated CMAQ models and the previous release version, CMAQv4.6, are evaluated using observations from three coastal sites during the Bay Regional Atmospheric Chemistry Experiment (BRACE) in Tampa, FL in May 2002. Model updates improve predictions of NO3-, SO42-, NH4+, Na+, and Cl- concentrations at these sites with only a 8% increase in run time. In particular, the chemically interactive coarse particle mode dramatically improves predictions of nitrate concentration and size distributions as well as the fraction of total nitrate in the particle phase. Also, the surf-zone emission parameterization improves predictions of total sodium and chloride concentration. Results of a separate study indicate that the model updates reduce the mean absolute error of nitrate predictions at coastal CASTNET and SEARCH sites in the eastern US. Although the new model features improve performance relative to CMAQv4.6, some persistent differences exist between observations and predictions. Modeled sodium concentration is biased low and causes under-prediction of coarse particle nitrate. Also, CMAQ over-predicts geometric mean diameter and

  10. On Multiobjective Evolution Model

    OpenAIRE

    Ahmed, E; Elettreby, M. F.

    2004-01-01

    Self-Organized Criticality (SOC) phenomena could have a significant effect on the dynamics of ecosystems. The Bak-Sneppen (BS) model is a simple and robust model of biological evolution that exhibits punctuated equilibrium behavior. Here we will introduce random version of BS model. Also we generalize the single objective BS model to a multiobjective one.

  11. On Multiobjective Evolution Model

    Science.gov (United States)

    Ahmed, E.; Elettreby, M. F.

    Self-Organized Criticality (SOC) phenomena could have a significant effect on the dynamics of ecosystems. The Bak-Sneppen (BS) model is a simple and robust model of biological evolution that exhibits punctuated equilibrium behavior. Here, we will introduce random version of BS model. We also generalize the single objective BS model to a multiobjective one.

  12. Chemically homogeneous evolution in massive binaries

    CERN Document Server

    de Mink, S E; Langer, N; Pols, O R

    2010-01-01

    Rotation can have severe consequences for the evolution of massive stars. It is now considered as one of the main parameters, alongside mass and metallicity that determine the final fate of single stars. In massive, fast rotating stars mixing processes induced by rotation may be so efficient that helium produced in the center is mixed throughout the envelope. Such stars evolve almost chemically homogeneously. At low metallicity they remain blue and compact, while they gradually evolve into Wolf-Rayet stars and possibly into progenitors of long gamma-ray bursts. In binaries this type of evolution may occur because of (I) tides in very close binaries, as a result of (II) spin up by mass transfer, as result of (III) a merger of the two stars and (IV) when one of the components in the binary was born with a very high initial rotation rate. As these stars stay compact, the evolutionary channels are very different from what classical binary evolutionary models predict. In this contribution we discuss examples of ne...

  13. Radiation-induced chemical evolution of biomolecules

    International Nuclear Information System (INIS)

    Chemical evolution in glycilglycine (Gly2) films irradiated with 146 nm vacuum ultraviolet light was studied. It is found that quantum efficiency of chemical evolution from Gly2 to glycilglycilglycine (Gly3) is smaller than that to glycilglycilglycilglycine (Gly4) due to the multiple step of reaction. Furthermore, we have carried out measurement of soft X-ray natural circular dichroism spectra for serine and alanine films in the energy region of oxygen 1s transition and we report the splitting of 1s→π* transitions.

  14. Synthetic photometry for M and K giants and stellar evolution: hydrostatic dust-free model atmospheres and chemical abundances

    Science.gov (United States)

    Aringer, B.; Girardi, L.; Nowotny, W.; Marigo, P.; Bressan, A.

    2016-04-01

    Based on a grid of hydrostatic spherical COMARCS models for cool stars, we have calculated observable properties of these objects, which will be mainly used in combination with stellar evolution tracks and population synthesis tools. The high-resolution opacity sampling and low-resolution convolved spectra as well as bolometric corrections for a large number of filter systems are made electronically available. We exploit those data to study the effect of mass, C/O ratio and nitrogen abundance on the photometry of K and M giants. Depending on effective temperature, surface gravity and the chosen wavelength ranges, variations of the investigated parameters cause very weak to moderate and, in the case of C/O values close to 1, even strong shifts of the colours. For the usage with stellar evolution calculations, they will be treated as correction factors applied to the results of an interpolation in the main quantities. When we compare the synthetic photometry to observed relations and to data from the Galactic bulge, we find in general a good agreement. Deviations appear for the coolest giants showing pulsations, mass-loss and dust shells, which cannot be described by hydrostatic models.

  15. Synthetic photometry for M and K giants and stellar evolution: hydrostatic dust-free model atmospheres and chemical abundances

    CERN Document Server

    Aringer, Bernhard; Nowotny, Walter; Marigo, Paola; Bressan, Alessandro

    2016-01-01

    Based on a grid of hydrostatic spherical COMARCS models for cool stars we have calculated observable properties of these objects, which will be mainly used in combination with stellar evolution tracks and population synthesis tools. The high resolution opacity sampling and low resolution convolved spectra as well as bolometric corrections for a large number of filter systems are made electronically available. We exploit those data to study the effect of mass, C/O ratio and nitrogen abundance on the photometry of K and M giants. Depending on effective temperature, surface gravity and the chosen wavelength ranges variations of the investigated parameters cause very weak to moderate and, in the case of C/O values close to one, even strong shifts of the colours. For the usage with stellar evolution calculations they will be treated as correction factors applied to the results of an interpolation in the main quantities. When we compare the synthetic photometry to observed relations and to data from the Galactic Bu...

  16. The Chemical Evolution of Dynamically Hot Galaxies

    Directory of Open Access Journals (Sweden)

    Michael G. Richer

    2001-01-01

    Full Text Available We investigate the chemical properties of M32, the bulges of M31 and the Milky Way, and the dwarf spheroidal galaxies NGC 205, NGC 185, Sagittarius, and Fornax using oxygen abundances for their planetary nebulae. Our principal result is that the mean stellar oxygen abundances correlate very well with thei r mean velocity dispersions, implying that the balance between energy input from type II supernovae and the gravitational potential controls chemical evolution in bulges, ellipticals, and dwarf spheroidals. It appears that chemical evolution ceases once supernovae have injected sufficient energy that a galacti c wind develops. All of the galaxies follow a single relation between oxygen abundance and luminosity, but the dwarf spheroidals have systematically higher [O/Fe] ratios than the other galaxies. Consequently, dynamically hot galaxies do not share a common star formation history nor need to a common chemical evolution, despite attaining similar mean stellar oxygen abundances when formin g similar masses. The oxygen abundances support previous indications that stars in higher luminosity ellipticals and bulges were formed on a shorter time scale than their counterparts in less luminous systems.

  17. Close Pairs as Probes of the Galaxy's Chemical Evolution

    CERN Document Server

    Vanbeveren, D; Vanbeveren, Dany; Donder, Erwin De

    2006-01-01

    Understanding the galaxy in which we live is one of the great intellectual challenges facing modern science. With the advent of high quality observational data, the chemical evolution modeling of our galaxy has been the subject of numerous studies in the last years. However, all these studies have one missing element which is the evolution of close binaries. Reason: their evolution is very complex and single stars only perhaps can do the job. (Un)Fortunately at present we know that a significant fraction of the observed intermediate mass and massive stars are members of a binary or multiple system and that certain objects can only be formed through binary evolution. Therefore galactic studies that do not account for close binaries may be far from realistic. We implemented a detailed binary population in a galactic chemical evolutionary model. Notice that this is not something simple like replacing chemical yields. Here we discuss three topics: the effect of binaries on the evolution of 14N, the evolution of t...

  18. Contrasting the chemical evolution of the Milky Way and Andromeda galaxies

    OpenAIRE

    Renda, Agostino; Kawata, Daisuke; Fenner, Yeshe; Gibson, Brad K.

    2004-01-01

    The chemical evolution history of a galaxy hides clues about how it formed and has been changing through time. We have studied the chemical evolution history of the Milky Way (MW) and Andromeda (M31) to find which are common features in the chemical evolution of disc galaxies as well as which are galaxy-dependent. We use a semi-analytic multi-zone chemical evolution model. Such models have succeeded in explaining the mean trends of the observed chemical properties in these two Local Group spi...

  19. Evolution of Business Models

    OpenAIRE

    Antero, Michelle C.; Hedman, Jonas; Henningsson, Stefan

    2013-01-01

    The ERP industry has undergone dramatic changes over the past decades due to changing market demands, thereby creating new challenges and opportunities, which have to be managed by ERP vendors. This paper inquires into the necessary evolution of business models in a technology-intensive industry (e.g., develop new offerings, engage in partnerships, and the utilize new sales channels). This paper draws from strategy process perspective to develop an evolutionary business model (EBM...

  20. Evolution of the habitable zone of low-mass stars. Detailed stellar models and analytical relationships for different masses and chemical compositions

    CERN Document Server

    Valle, G; Moroni, P G Prada; Degl'Innocenti, S

    2014-01-01

    We study the temporal evolution of the habitable zone (HZ) of low-mass stars - only due to stellar evolution - and evaluate the related uncertainties. These uncertainties are then compared with those due to the adoption of different climate models. We computed stellar evolutionary tracks from the pre-main sequence phase to the helium flash at the red-giant branch tip for stars with masses in the range [0.70 - 1.10] Msun, metallicity Z in the range [0.005 - 0.04], and various initial helium contents. We evaluated several characteristics of the HZ, such as the distance from the host star at which the habitability is longest, the duration of this habitability, the width of the zone for which the habitability lasts one half of the maximum, and the boundaries of the continuously habitable zone (CHZ) for which the habitability lasts at least 4 Gyr. We developed analytical models, accurate to the percent level or lower, which allowed to obtain these characteristics in dependence on the mass and the chemical composit...

  1. Evolution of associative learning in chemical networks.

    Directory of Open Access Journals (Sweden)

    Simon McGregor

    Full Text Available Organisms that can learn about their environment and modify their behaviour appropriately during their lifetime are more likely to survive and reproduce than organisms that do not. While associative learning - the ability to detect correlated features of the environment - has been studied extensively in nervous systems, where the underlying mechanisms are reasonably well understood, mechanisms within single cells that could allow associative learning have received little attention. Here, using in silico evolution of chemical networks, we show that there exists a diversity of remarkably simple and plausible chemical solutions to the associative learning problem, the simplest of which uses only one core chemical reaction. We then asked to what extent a linear combination of chemical concentrations in the network could approximate the ideal Bayesian posterior of an environment given the stimulus history so far? This Bayesian analysis revealed the 'memory traces' of the chemical network. The implication of this paper is that there is little reason to believe that a lack of suitable phenotypic variation would prevent associative learning from evolving in cell signalling, metabolic, gene regulatory, or a mixture of these networks in cells.

  2. Thermal and Chemical Evolution of Collapsing Filaments

    Energy Technology Data Exchange (ETDEWEB)

    Gray, William J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Scannapieco, Evan [Arizona State Univ., Mesa, AZ (United States). School of Earth and Space Exploration

    2013-01-15

    Intergalactic filaments form the foundation of the cosmic web that connect galaxies together, and provide an important reservoir of gas for galaxy growth and accretion. Here we present very high resolution two-dimensional simulations of the thermal and chemical evolution of such filaments, making use of a 32 species chemistry network that tracks the evolution of key molecules formed from hydrogen, oxygen, and carbon. We study the evolution of filaments over a wide range of parameters including the initial density, initial temperature, strength of the dissociating UV background, and metallicity. In low-redshift, Z ≈ 0.1Z filaments, the evolution is determined completely by the initial cooling time. If this is sufficiently short, the center of the filament always collapses to form dense, cold core containing a substantial fraction of molecules. In high-redshift, Z = 10-3Z filaments, the collapse proceeds much more slowly. This is due mostly to the lower initial temperatures, which leads to a much more modest increase in density before the atomic cooling limit is reached, making subsequent molecular cooling much less efficient. Finally, we study how the gravitational potential from a nearby dwarf galaxy affects the collapse of the filament and compare this to NGC 5253, a nearby starbusting dwarf galaxy thought to be fueled by the accretion of filament gas. In contrast to our fiducial case, a substantial density peak forms at the center of the potential. This peak evolves faster than the rest of the filament due to the increased rate at which chemical species form and cooling occur. We find that we achieve similar accretion rates as NGC 5253 but our two-dimensional simulations do not recover the formation of the giant molecular clouds that are seen in radio observations.

  3. Chemical Properties of Starburst Galaxies Near and Far: Clues to Galaxy Evolution

    OpenAIRE

    Contini, T.; Treyer, M. -A.; Mouhcine, M.; Sullivan, M.; Ellis, R. S.,

    2001-01-01

    The determination of chemical abundances in star-forming galaxies and the study of their evolution on cosmological timescales are powerful tools for understanding galaxy formation and evolution. This contribution presents the latest results in this domain. We show that detailed studies of chemical abundances in UV-selected, HII and starburst nucleus galaxies, together with the development of new chemical evolution models, put strong constraints on the evolutionary stage of these objects in te...

  4. Evolution of Business Models

    DEFF Research Database (Denmark)

    Antero, Michelle C.; Hedman, Jonas; Henningsson, Stefan

    2013-01-01

    The ERP industry has undergone dramatic changes over the past decades due to changing market demands, thereby creating new challenges and opportunities, which have to be managed by ERP vendors. This paper inquires into the necessary evolution of business models in a technology-intensive industry (e.......g., develop new offerings, engage in partnerships, and the utilize new sales channels). This paper draws from strategy process perspective to develop an evolutionary business model (EBM) framework that explains the components and processes involved. The framework is then applied to a longitudinal case study...... of SAP to explain how its success in a technology-intensive industry hinges on its ability to reconfigure its business model. The paper contributes to the extant literature on business models in two ways: first, by identifying and explaining the need for an evolutionary perspective; and second...

  5. Oparin's coacervates as an important milestone in chemical evolution

    Science.gov (United States)

    Kolb, Vera M.

    2015-09-01

    Although Oparin's coacervate model for the origin of life by chemical evolution is almost 100 years old, it is still valid. However, the structure of his originally proposed coacervate is not considered prebiotic, based on some recent developments in prebiotic chemistry. We have remedied this deficiency of the Oparin's model, by substituting his coacervate with a prebiotically feasible one. Oparin's coacervates are aqueous structures, but have a boundary with the rest of the aqueous medium. They exhibit properties of self-replication, and provide a path to a primitive metabolism, via chemical competition and thus a primitive selection. Thus, coacervates are good models for proto-cells. We review here some salient points of Oparin's model and address also some philosophical views on the beginning of natural selection in primitive chemical systems.

  6. A two-dimensional model of chemical vapor infiltration with radio-frequency heating and spatio-temporal evolution of a pulsed chlorine plasma

    Science.gov (United States)

    Midha, Vikas

    The first part of this work focused on modeling radio- frequency assisted chemical vapor infiltration (CVI) for the fabrication of fiber-reinforced composite materials. CVI involves diffusion and chemical reaction of precursor gases in a fibrous preform to deposit solid material within the pores. A two-dimensional finite-element model was developed which included the solution of Maxwell's equations for electromagnetic fields, transport equations for multicomponent gas diffusion and chemical kinetics for the deposition of solid material. Simulation results showed that densification of long cylindrical preforms initially occurred radially around the central zone and then axially towards the ends of the preform. This densification pattern resulted in significant entrapment of porosity at the center of the preform and required a relatively long time for completion. Comparison of results with reported experimental data showed agreement of important trends which could not be predicted by existing one-dimensional models. Based on the geometry of the preform, novel schemes for improved radio-frequency assisted CVI were proposed which resulted in complete densification and reduced overall processing time significantly compared to conventional isothermal processes. The second part of this work focused on modeling of high- density, low-pressure chlorine discharges used for the fabrication of sub-micron devices in the semiconductor industry. Recent experiments showed that pulsing of input power can lead to significant improvement in the etching characteristics of electronegative gas discharges. A one- dimensional model was developed which captured the transition of an electron-ion plasma in the active glow to a negative-ion dominated or ion-ion plasma in the afterglow phase of a pulse. The spatial evolution of the negative-ion density showed formation of self-sharpening fronts during the active glow and subsequent back- propagation of the fronts during the afterglow. In the

  7. Chemical Models of Collapsing Envelopes

    CERN Document Server

    Bergin, E A

    1999-01-01

    We discuss recent models of chemical evolution in the developing and collapsing protostellar envelopes associated with low-mass star formation. In particular, the effects of depletion of gas-phase molecules onto grain surfaces is considered. We show that during the middle to late evolutionary stages, prior to the formation of a protostar, various species selectively deplete from the gas phase. The principal pattern of selective depletions is the depletion of sulfur-bearing molecules relative to nitrogen-bearing species: NH3 and N2H+. This pattern is shown to be insensitive to the details of the dynamics and marginally sensitive to whether the grain mantle is dominated by polar or non-polar molecules. Based on these results we suggest that molecular ions are good tracers of collapsing envelopes. The effects of coupling chemistry and dynamics on the resulting physical evolution are also examined. Particular attention is paid to comparisons between models and observations.

  8. The chemical, mechanical, and hydrological evolution of weathering granitoid

    Science.gov (United States)

    Goodfellow, Bradley W.; Hilley, George E.; Webb, Samuel M.; Sklar, Leonard S.; Moon, Seulgi; Olson, Christopher A.

    2016-08-01

    Surprisingly few studies connect the chemical, mechanical, and hydrological evolution of rock as it weathers to saprolite and soil. We assess this coevolution in granodiorite from Monterey Peninsula, California, by measuring changes in bulk chemistry, mineralogy, volumetric strain, the oxidation state of Fe in biotite crystals, tensile strength, abrasion rate, connected porosity, and hydraulic conductivity in samples covering a range of weathering grades. We identify the oxidative dissolution of biotite as the key chemical reaction because of the volumetric expansion that accompanies formation of altered biotite and precipitation of ferrihydrite. We show how the associated accumulation of elastic strain produces an energy density that is sufficient to support rock fracturing over length scales equivalent to constituent crystals. The resulting intragranular and intergranular cracking profoundly reduces tensile strength and increases the abrasion rate, connected porosity, and hydraulic conductivity of the rock matrix. These changes increase the rate of plagioclase weathering, and ultimately the rock disintegrates into grus and clay. Major changes in rock properties can occur with only minor element leaching, and the threshold behavior of weathering that arises from the coevolution of chemical, hydrological, and mechanical properties may be difficult to capture using simplified weathering models that fail to incorporate these properties. Our results, which combine the mechanical and hydrological evolution of weathering rock with more common measurements of chemical changes, should help to more accurately model the effects of, and mechanical and hydrological feedbacks upon, chemical weathering of rock.

  9. Dictyostelium discoideum, a lower eukaryote model for the study of DNA repair: Implications for the role of DNA-damaging chemicals in the evolution of repair proficient cells

    Science.gov (United States)

    Deering, R. A.

    1994-10-01

    The evolution of the ability of living cells to cope with stress is crucial for the maintenance of their genetic integrity. Yet low levels of mutation must remain to allow adaptation to environmental changes. The cellular slime mold D. discoideum is a good system for studying molecular aspects of the repair of lethal and mutagenic damage to DNA by radiation and chemicals. The wild-type strains of this soil microorganism are extremely resistant to DNA damaging agents. In nature the amoeboid cells in their replicative stage feed on soil bacteria and are exposed to numerous DNA-damaging chemicals produced by various soil microorganisms. It is probable that the evolution of repair systems in this organism and perhaps in others is a consequence of the necessity to cope with chemical damage which also confers resistance to radiation.

  10. The Gaia-ESO Survey: Separating disk chemical substructures with cluster models. Evidence of a separate evolution in the metal-poor thin disk

    Science.gov (United States)

    Rojas-Arriagada, A.; Recio-Blanco, A.; de Laverny, P.; Schultheis, M.; Guiglion, G.; Mikolaitis, Š.; Kordopatis, G.; Hill, V.; Gilmore, G.; Randich, S.; Alfaro, E. J.; Bensby, T.; Koposov, S. E.; Costado, M. T.; Franciosini, E.; Hourihane, A.; Jofré, P.; Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Worley, C. C.; Zaggia, S.; Chiappini, C.

    2016-02-01

    Context. Recent spectroscopic surveys have begun to explore the Galactic disk system on the basis of large data samples, with spatial distributions sampling regions well outside the solar neighborhood. In this way, they provide valuable information for testing spatial and temporal variations of disk structure kinematics and chemical evolution. Aims: The main purposes of this study are to demonstrate the usefulness of a rigorous mathematical approach to separate substructures of a stellar sample in the abundance-metallicity plane, and provide new evidence with which to characterize the nature of the metal-poor end of the thin disk sequence. Methods: We used a Gaussian mixture model algorithm to separate in the [Mg/Fe] vs. [Fe/H] plane a clean disk star subsample (essentially at RGC -0.25 dex) highlight a change in the slope at solar metallicity. This holds true at different radial regions of the Milky Way. The distribution of Galactocentric radial distances of the metal-poor part of the thin disk ([Fe/H] levels might be due to their origin from gas pre-enriched by outflows from the thick disk or the inner halo. The smooth trends of their properties (their spatial distribution with respect to the plane, in particular) with [Fe/H] and [Mg/Fe] suggested by the data indicates a quiet dynamical evolution, with no relevant merger events. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council.

  11. JINA-NuGrid Galactic Chemical Evolution Pipeline

    CERN Document Server

    Côté, Benoit; Herwig, Falk; O'Shea, Brian W; Pignatari, Marco; Silvia, Devin; Jones, Samuel; Fryer, Chris L

    2016-01-01

    Galactic chemical evolution is a topic that involves nuclear physics, stellar evolution, galaxy evolution, observation, and cosmology. Continuous communication and feedback between these fields is a key component in improving our understanding of how galaxies form and how elements are created and recycled in galaxies and intergalactic space. In this proceedings, we present the current state of the JINA-NuGrid chemical evolution pipeline. It is designed to probe the impact of nuclear astrophysics uncertainties on galactic chemical evolution, to improve our knowledges regarding the origin of the elements in a cosmological context, and to create the required interdisciplinary connections.

  12. The role of OH in the chemical evolution of protoplanetary disks : II. Gas-rich environments

    NARCIS (Netherlands)

    Chaparro-Molano, German; Kamp, I.

    2012-01-01

    Context. We present a method for including gas extinction of cosmic-ray-generated UV photons in chemical models of the midplane of protoplanetary disks, focusing on its implications on ice formation and chemical evolution. Aims. Our goal is to improve on chemical models by treating cosmic rays, the

  13. Chemical models of interstellar gas-grain processes. II - The effect of grain-catalysed methane on gas phase evolution

    Science.gov (United States)

    Brown, Paul D.; Charnley, S. B.

    1991-01-01

    The effects on gas phase chemistry which result from the continuous desorption of methane molecules from grain surfaces are studied. Significant and sustained enhancements in the abundances of several complex hydrocarbon molecules are found, in good agreement with their observed values in TMC-1. The overall agreement is, however, just as good for the case of zero CH4 desorption efficiency. It is thus impossible to determine from the models whether or not the grain-surface production of methane is responsible for the observed abundances of some hydrocarbon molecules.

  14. The Chemical Evolution of Titan's Atmosphere

    Science.gov (United States)

    Kaiser, Ralf I.

    2010-11-01

    Astrochemistry or Astrochemical Dynamics presents a newly emerging, interdisciplinary and innovative field comprising scientists in chemistry, physics, biology, astronomy, and planetary chemistry. The prime directive of Astrochemical Dynamics is to understand the origin and chemical evolution of the interstellar medium and of our Solar System. Here, the arrival of the Cassini-Huygens probe at Saturn's moon Titan - the only Solar System body besides Earth and Venus with a solid surface and thick atmosphere - in 2004 opened up a new chapter in the history of Solar System exploration. Titan's most prominent optically visible features are the aerosol-based haze layers, which give Titan its orange-brownish color. However, the underlying chemical processes, which initiate the haze formation, have been the least understood to date. This talk reviews recent laboratory studies on the role of polyacetylenes (polyynes) and (hetero)aromatic molecules like the phenyl radical, benzene, and pyridine in the formation of Titan's organic haze layers utilizing crossed molecular beam experiments. Those investigations provide key concepts on the formation mechanisms of unsaturated hydrocarbon molecules - in particular polyynes and aromatic compounds - together with their hydrogen deficient precursors from the "bottom up" in the atmosphere of Saturn's moon Titan. A brief outline to future research directions tackling also the heterogeneous chemistry on Titan and in hydrocarbon-rich atmospheres in the outer Solar System in general will also be presented.

  15. From the CMD of Omega Centauri and (super-)AGB stellar models to a Galactic plane passage gas purging chemical evolution scenario

    CERN Document Server

    Herwig, Falk; Navarro, Julio F; Ferguson, Jason; Paxton, Bill

    2012-01-01

    [Abbreviated] We have investigated the color-magnitude diagram of Omega Centauri and find that the blue main sequence (bMS) can be reproduced only by models that have a of helium abundance in the range Y=0.35-$0.40. To explain the faint subgiant branch of the reddest stars ("MS-a/RG-a" sequence), isochrones for the observed metallicity ([Fe/H]\\approx0.7) appear to require both a high age (~13Gyr) and enhanced CNO abundances ([CNO/Fe]\\approx0.9$). Y~0.35 must also be assumed in order to counteract the effects of high CNO on turnoff colors, and thereby to obtain a good fit to the relatively blue turnoff of this stellar population. This suggest a short chemical evolution period of time (=6.8M_sun, M_He,core>=1.245M_sun) predict too large N-enhancements, which limits their role in contributing to the extreme populations. We show quantitatively that highly He- and N-enriched AGB ejecta have particularly efficient cooling properties. Based on these results and on the reconstruction of the orbit of Omega Cen with re...

  16. Chemical evolution of A- and B-type stars in open clusters: observed abundances vs. diffusion models. Am stars in the Praesepe cluster

    Science.gov (United States)

    Fossati, L.; Bagnulo, S.; Monier, R.; Khan, S. A.; Kochukhov, O.; Landstreet, J. D.; Wade, G. A.; Weiss, W. W.

    2008-04-01

    We have decided to address the problem of how abundances and peculiarities change during main sequence evolution. We have setup a program to measure the atmospheric abundance patterns from tens of A-type star members of clusters of different ages, and compare the results with theory predictions. In this paper we present the overall project and we focus on the results obtained for a sample of Am stars of the Praesepe cluster (log t= 8.85 ± 0.15; González-García et al., 2006). We have obtained spectra for eight Am stars, two normal A-type stars and one blue straggler, that are probable members of the Praesepe cluster. For all of these stars we have determined fundamental parameters and photospheric abundances for a large number of chemical elements. For seven stars we also obtained spectra in circular polarisation and applied the LSD technique to measure the mean longitudinal magnetic field. We have found good agreement between abundance predictions of diffusion models and measured abundances, except for Na and S. Li appears to be overabundant in three stars of our sample. No magnetic field was detected in any of the analysed stars.

  17. The Chemical Evolution of Heavy Elements in Globular Clusters

    Science.gov (United States)

    Shingles, Luke J.; Karakas, Amanda I.; Hirschi, Raphael

    2014-01-01

    We present preliminary results from a chemical evolution model that tracks the composition of heavy elements beyond iron in a globular cluster. The heavy elements can be used as tracers of the nucleosynthetic events that defined the formation and evolution of star clusters in the early Universe. In particular, the chemical evolution model focuses on the hypothesis that rapidly-rotating massive stars produced the heavy elements via the slow neutron-capture process and seeded the proto-cluster while the stars we see today were still forming. We compare our model with heavy element abundances in M4 and M5, and M22. Our results are strongly dependent on the highly uncertain rate of the 17O(α,γ)21Ne reaction, which determines the strength of 16O as a neutron poison. We find that the [Pb/Ba] ratio is too low to match the empirical value, which might suggest that a contribution from AGB stars is required.

  18. Modeling chemical kinetics graphically

    NARCIS (Netherlands)

    A. Heck

    2012-01-01

    In literature on chemistry education it has often been suggested that students, at high school level and beyond, can benefit in their studies of chemical kinetics from computer supported activities. Use of system dynamics modeling software is one of the suggested quantitative approaches that could h

  19. Modeling in Chemical Engineering

    Directory of Open Access Journals (Sweden)

    Jaap van Brakel

    2000-10-01

    Full Text Available Models underlying the use of similarity considerations, dimensionless numbers, and dimensional analysis in chemical engineering are discussed. Special attention is given to the many levels at which models and ceteris paribus conditions play a role and to the modeling of initial and boundary conditions. It is shown that both the laws or dimensionless number correlations and the systems to which they apply are models. More generally, no matter which model or description one picks out, what is being modeled is itself a model of something else. Instead of saying that the artifact S models the given B, it is therefore better to say that S and B jointly make up B and S.

  20. Chemical evolution and nature of Damped Lyman-Alpha systems

    CERN Document Server

    Calura, F; Vladilo, G

    2003-01-01

    We study the nature of Damped Lyman -Alpha systems (DLAs) by means of a comparison between observed abundances and models of chemical evolution of galaxies of different morphological type. In particular, we compare for the first time the abundance ratios as functions of metallicity and redshift with dust-corrected data. We have developed detailed models following the evolution of several chemical elements (H, D, He, C, N, O, Ne, Mg, Si, S, Fe, Ni and Zn) for elliptical, spiral and irregular galaxies. Each of the models is calibrated to reproduce the main features of a massive elliptical, the Milky Way and the LMC, respectively. In addition, we run some models also for dwarf irregular starburst galaxies. All the models share the same uptodate nucleosynthesis prescriptions but differ in their star formation histories. The role of SNe of different type (II, Ia) is studied in each galaxy model together with detailed and up to date nucleosynthesis prescriptions. Our main conclusions are: 1) when dust depletion is ...

  1. From chemical reactions to evolution: Emergence of species

    Science.gov (United States)

    Carletti, T.; Fanelli, D.

    2007-01-01

    The Chemoton model constitutes a minimalistic description of a protocell unit. The original formulation assumes three coupled chemical networks, representing a proto-metabolism, a template duplication and the membrane growth. An improved version is here proposed that explicitly incorporates the effects of the volume changes, due to the membrane growth. A stochastic mechanism is also introduced that mimics a stochastic source of error in the template duplication process. Numerical simulations are performed to monitor the time evolution of a family of protocells, under the chemoton hypothesis. An open-ended Darwinian evolution under the pressure of the environment is reproduced thus allowing to conclude that differentiation into species is an emergent property of the model.

  2. TESTING THE ROLE OF SNe Ia FOR GALACTIC CHEMICAL EVOLUTION OF p-NUCLEI WITH TWO-DIMENSIONAL MODELS AND WITH s-PROCESS SEEDS AT DIFFERENT METALLICITIES

    International Nuclear Information System (INIS)

    The bulk of p isotopes is created in the ''gamma processes'' mainly by sequences of photodisintegrations and beta decays in explosive conditions in Type Ia supernovae (SNIa) or in core collapse supernovae (ccSN). The contribution of different stellar sources to the observed distribution of p-nuclei in the solar system is still under debate. We explore single degenerate Type Ia supernovae in the framework of two-dimensional SNIa delayed-detonation explosion models. Travaglio et al. discussed the sensitivity of p-nuclei production to different SNIa models, i.e., delayed detonations of different strength, deflagrations, and the dependence on selected s-process seed distributions. Here we present a detailed study of p-process nucleosynthesis occurring in SNIa with s-process seeds at different metallicities. Based on the delayed-detonation model DDT-a of TRV11, we analyze the dependence of p-nucleosynthesis on the s-seed distribution obtained from different strengths of the 13C pocket. We also demonstrate that 208Pb seed alone changes the p-nuclei production considerably. The heavy-s seeds (140 ≤A < 208) contribute with about 30%-40% to the total light-p nuclei production up to 132Ba (with the exception of 94Mo and 130Ba, to which the heavy-s seeds contribute with about 15% only). Using a Galactic chemical evolution code from Travaglio et al., we study the contribution of SNIa to the solar stable p-nuclei. We find that explosions of Chandrasekhar-mass single degenerate systems produce a large amount of p-nuclei in our Galaxy, both in the range of light (A ≤ 120) and heavy p-nuclei, at almost flat average production factors (within a factor of about three). We discussed in details p-isotopes such as 94Mo with a behavior diverging from the average, which we attribute to uncertainties in the nuclear data or in SNIa modeling. Li et al. find that about 70% of all SNeIa are normal events. If these are explained in the framework of explosions of

  3. Sixth Symposium on Chemical Evolution and the Origin and Evolution of Life

    Science.gov (United States)

    Acevedo, Sara (Editor); DeVincenzi, Donald L. (Editor); Chang, Sherwood (Editor)

    1998-01-01

    The 6th Symposium on Chemical Evolution and the Origin and Evolution of Life was convened at NASA Ames Research Center, November 17-20, 1997. This Symposium is convened every three years under the auspices of NASA's Exobiology Program Office. All Principal Investigators funded by this Program present their most recent research accomplishments at the Symposium. Scientific papers were presented in the following areas: cosmic evolution of the biogenic elements, prebiotic evolution (both planetary and chemical), evolution of early organisms and evolution of organisms in extreme environments, solar system exploration, and star and planet formation. The Symposium was attended by over 200 scientists from NASA centers and Universities nationwide.

  4. Dynamical and chemical evolution of the thin disc

    Science.gov (United States)

    Just, A.; Rybizki, J.

    2016-09-01

    Our detailed analytic local disc model (JJ-model) quantifies the interrelation between kinematic properties (e.g. velocity dispersions and asymmetric drift), spatial parameters (scale-lengths and vertical density profiles), and properties of stellar sub-populations (age and abundance distributions). Any consistent radial extension of the disc evolution model should predict specific features in the different distribution functions and in their correlations. Large spectroscopic surveys (SEGUE, RAVE, APOGEE, Gaia-ESO) allow significant constraints on the long-term evolution of the thin disc. We discuss the qualitative difference of correlations (like the α-enhancement as function of metallicity) and distribution functions (e.g. in [Mg/H] or [Fe/H]) for the construction of a disc model. In the framework of the JJ-model we build a local chemical enrichment model and show that significant vertical gradients for main sequence and red clump stars are expected in the thin disc. A Jeans analysis of the asymmetric drift provides a link to the radial structure of the disc. The derived metallicity-dependent radial scale-lengths can be combined in the future with the abundance distributions at different Galactocentric distances to construct full disc models. We expect to be able to constrain possible scenarios of inside-out growth of the thin disc and to characterise those populations, which require significant radial migration.

  5. TMDs: Evolution, modeling, precision

    Directory of Open Access Journals (Sweden)

    D’Alesio Umberto

    2015-01-01

    Full Text Available The factorization theorem for qT spectra in Drell-Yan processes, boson production and semi-inclusive deep inelastic scattering allows for the determination of the non-perturbative parts of transverse momentum dependent parton distribution functions. Here we discuss the fit of Drell-Yan and Z-production data using the transverse momentum dependent formalism and the resummation of the evolution kernel. We find a good theoretical stability of the results and a final χ2/points ≲ 1. We show how the fixing of the non-perturbative pieces of the evolution can be used to make predictions at present and future colliders.

  6. TMDs: Evolution, modeling, precision

    CERN Document Server

    D'Alesio, Umberto; Melis, Stefano; Scimemi, Ignazio

    2014-01-01

    The factorization theorem for $q_T$ spectra in Drell-Yan processes, boson production and semi-inclusive deep inelastic scattering allows for the determination of the non-perturbative parts of transverse momentum dependent parton distribution functions. Here we discuss the fit of Drell-Yan and $Z$-production data using the transverse momentum dependent formalism and the resummation of the evolution kernel. We find a good theoretical stability of the results and a final $\\chi^2/{\\rm points}\\lesssim 1$. We show how the fixing of the non-perturbative pieces of the evolution can be used to make predictions at present and future colliders.

  7. Dynamical and chemical evolution of the thin disc

    CERN Document Server

    Just, Andreas

    2015-01-01

    Our detailed analytic local disc model (JJ-model) quantifies the interrelation between kinematic properties (e.g. velocity dispersions and asymmetric drift), spatial parameters (scale-lengths and vertical density profiles), and properties of stellar sub-populations (age and abundance distributions). Any consistent radial extension of the disc evolution model should predict specific features in the different distribution functions and in their correlations. Large spectroscopic surveys (SEGUE, RAVE, APOGEE, Gaia-ESO) allow significant constraints on the long-term evolution of the thin disc. We discuss the qualitative difference of correlations (like the alpha-enhancement as function of metallicity) and distribution functions (e.g. in [Mg/H] or [Fe/H]) for the construction of a disc model. In the framework of the JJ-model we build a local chemical enrichment model and show that significant vertical gradients for main sequence and red clump stars are expected in the thin disc. A Jeans analysis of the asymmetric d...

  8. Planetary nebulae and the chemical evolution of the Magellanic Clouds

    CERN Document Server

    Maciel, W J; Idiart, T E P

    2009-01-01

    The determination of accurate chemical abundances of planetary nebulae (PN) in different galaxies allows us to obtain important constraints of chemical evolution models for these systems. We have a long term program to derive abundances in the galaxies of the Local Group, particularly the Large and Small Magellanic Clouds. In this work, we present our new results on these objects and discuss their implications in view of recent abundance determinations the literature. In particular, we obtain distance-independent correlations involving He, N, O, Ne, S, and Ar, and compare the results with data from our own Galaxy and other galaxies in the Local Group. As a result of our observational program, we have a large database of PN in the Galaxy and the Magellanic Clouds, so that we can obtain reliable constraints to the nucleosynthesis processes in the progenitor stars in galaxies of different metallicities.

  9. Chemical evolution of the Earth: Equilibrium or disequilibrium process?

    Science.gov (United States)

    Sato, M.

    1985-01-01

    To explain the apparent chemical incompatibility of the Earth's core and mantle or the disequilibrium process, various core forming mechanisms have been proposed, i.e., rapid disequilibrium sinking of molten iron, an oxidized core or protocore materials, and meteorite contamination of the upper mantle after separation from the core. Adopting concepts used in steady state thermodynamics, a method is devised for evaluating how elements should distribute stable in the Earth's interior for the present gradients of temperature, pressure, and gravitational acceleration. Thermochemical modeling gives useful insights into the nature of chemical evolution of the Earth without overly speculative assumptions. Further work must be done to reconcile siderophile elements, rare gases, and possible light elements in the outer core.

  10. Galactic chemical evolution: Carbon through Zinc

    CERN Document Server

    Kobayashi, C; Nomoto, K; Tominaga, N; Ohkubo, T

    2006-01-01

    We calculate the evolution of heavy element abundances from C to Zn in the solar neighborhood adopting our new nucleosynthesis yields. Our yields are calculated for wide ranges of metallicity (Z=0-Z_\\odot) and the explosion energy (normal supernovae and hypernovae), based on the light curve and spectra fitting of individual supernovae. The elemental abundance ratios are in good agreement with observations. Among the alpha-elements, O, Mg, Si, S, and Ca show a plateau at [Fe/H] < -1, while Ti is underabundant overall. The observed abundance of Zn ([Zn/Fe] ~ 0) can be explained only by the high energy explosion models, which requires a large contribution of hypernovae. The observed decrease in the odd-Z elements (Na, Al, and Cu) toward low [Fe/H] is reproduced by the metallicity effect on nucleosynthesis. The iron-peak elements (Cr, Mn, Co, and Ni) are consistent with the observed mean values at -2.5 < [Fe/H] < -1$, and the observed trend at the lower metallicity can be explained by the energy effect. ...

  11. Chemical kinetics modeling

    Energy Technology Data Exchange (ETDEWEB)

    Westbrook, C.K.; Pitz, W.J. [Lawrence Livermore National Laboratory, CA (United States)

    1993-12-01

    This project emphasizes numerical modeling of chemical kinetics of combustion, including applications in both practical combustion systems and in controlled laboratory experiments. Elementary reaction rate parameters are combined into mechanisms which then describe the overall reaction of the fuels being studied. Detailed sensitivity analyses are used to identify those reaction rates and product species distributions to which the results are most sensitive and therefore warrant the greatest attention from other experimental and theoretical research programs. Experimental data from a variety of environments are combined together to validate the reaction mechanisms, including results from laminar flames, shock tubes, flow systems, detonations, and even internal combustion engines.

  12. Chemical effects of ionizing radiation and sonic energy in the context of chemical evolution

    International Nuclear Information System (INIS)

    Ionizing radiation and sonic energy are considered as sources for chemical evolution processes. These sources have still a modest place in the interdisciplinary approach for the prebiological synthesis of organic compounds. Studies in Radiation Chemistry and Sonochemistry can provide a deeper insight into the chemical processes that may have importance for prebiotic chemistry. The present work concerns the analysis of some chemical reactions induced by ionizing radiation or cavitation in aqueous media that may be relevant to chemical evolution studies. (author)

  13. A simple and general method for solving detailed chemical evolution with delayed production of iron and other chemical elements

    CERN Document Server

    Vincenzo, Fiorenzo; Spitoni, Emanuele

    2016-01-01

    In this Letter, we present a new theoretical method for solving the chemical evolution of galaxies, by assuming the instantaneous recycling approximation for chemical elements restored by massive stars and the Delay Time Distribution formalism for the delayed chemical enrichment by Type Ia Supernovae. The galaxy gas mass assembly history, together with the assumed stellar yields and initial mass function, represent the starting point of this method. We derive a very simple and general equation which closely relates the Laplace transforms of the galaxy gas accretion and star formation history, which can be used to simplify the problem of retrieving these quantities in most of current galaxy evolution models. We find that - once the galaxy star formation history has been reconstructed from our assumptions - the differential equation for the evolution of the chemical element $X$ can be suitably solved with classical methods. We apply our model to reproduce the $[\\text{O/Fe}]$ and $[\\text{Si/Fe}]$ vs. $[\\text{Fe/...

  14. Chemical evolution of two-component galaxies. II

    International Nuclear Information System (INIS)

    In order to confirm and refine the results obtained in a previous paper the chemical evolution of two-component (spheroid + disk) galaxies is derived rejecting the instantaneous recycling approximation, by means of numerical computations, accounting for (i) the collapse phase of the gas, assumed to be uniform in density and composition, and (ii) a birth-rate stellar function. Computations are performed relatively to the solar neighbourhood and to model galaxies which closely resemble the real morphological sequence: in both cases, numerical results are compared with analytical ones. The numerical models of this paper constitute a first-order approximation, while higher order approximations could be made by rejecting the hypothesis of uniform density and composition, and making use of detailed dynamical models. (Auth.)

  15. Shallow nitrogen ion implantation: Evolution of chemical state and defect structure in titanium

    Science.gov (United States)

    Manojkumar, P. A.; Chirayath, V. A.; Balamurugan, A. K.; Krishna, Nanda Gopala; Ilango, S.; Kamruddin, M.; Amarendra, G.; Tyagi, A. K.; Raj, Baldev

    2016-09-01

    Evolution of chemical states and defect structure in titanium during low energy nitrogen ion implantation by Plasma Immersion Ion Implantation (PIII) process is studied. The underlying process of chemical state evolution is investigated using secondary ion mass spectrometry and X-ray photoelectron spectroscopy. The implantation induced defect structure evolution as a function of dose is elucidated using variable energy positron annihilation Doppler broadening spectroscopy (PAS) and the results were corroborated with chemical state. Formation of 3 layers of defect state was modeled to fit PAS results.

  16. Conference on chemical evolution and the origin of life

    International Nuclear Information System (INIS)

    This report contains 19 summaries of papers presented at the Conference on Chemical Evolution and the Origin of Life held at the International Centre for Theoretical Physics. A separate indexing is provided for each summary

  17. On the transition period from chemical to biological evolution

    International Nuclear Information System (INIS)

    We discuss the consequences of the hypothesis that biological evolution was contemporary with an important event in chemical evolution, namely, the induction of a small chiral bias by the electroweak neutral interaction, amplified by the Salam enhancement factor, which we discuss in terms of familiar crystallographic terms. (author). 18 refs, 3 tabs

  18. Cycles and the qualitative evolution of chemical systems.

    Directory of Open Access Journals (Sweden)

    Peter Kreyssig

    Full Text Available Cycles are abundant in most kinds of networks, especially in biological ones. Here, we investigate their role in the evolution of a chemical reaction system from one self-sustaining composition of molecular species to another and their influence on the stability of these compositions. While it is accepted that, from a topological standpoint, they enhance network robustness, the consequence of cycles to the dynamics are not well understood. In a former study, we developed a necessary criterion for the existence of a fixed point, which is purely based on topological properties of the network. The structures of interest we identified were a generalization of closed autocatalytic sets, called chemical organizations. Here, we show that the existence of these chemical organizations and therefore steady states is linked to the existence of cycles. Importantly, we provide a criterion for a qualitative transition, namely a transition from one self-sustaining set of molecular species to another via the introduction of a cycle. Because results purely based on topology do not yield sufficient conditions for dynamic properties, e.g. stability, other tools must be employed, such as analysis via ordinary differential equations. Hence, we study a special case, namely a particular type of reflexive autocatalytic network. Applications for this can be found in nature, and we give a detailed account of the mitotic spindle assembly and spindle position checkpoints. From our analysis, we conclude that the positive feedback provided by these networks' cycles ensures the existence of a stable positive fixed point. Additionally, we use a genome-scale network model of the Escherichia coli sugar metabolism to illustrate our findings. In summary, our results suggest that the qualitative evolution of chemical systems requires the addition and elimination of cycles.

  19. Calculating Chemical Evolution on the Web

    Science.gov (United States)

    Meyer, B. S.; Denny, J. E.; Clayton, D. D.

    2001-01-01

    We have constructed an interactive web site that may be of interest to cosmochemists seeking to understand the evolution of isotopes in the Galaxy. The URL is http://photon.phys.clemson.edu/gce.html. Additional information is contained in the original extended abstract.

  20. ABC model and floral evolution

    Institute of Scientific and Technical Information of China (English)

    LI Guisheng; MENG Zheng; KONG Hongzhi; CHEN Zhiduan; LU Anming

    2003-01-01

    The paper introduces the classical ABC model of floral development and thereafter ABCD, ABCDE and quartet models, and presents achievements in the studies on floral evolution such as the improved understanding on the relationship of reproductive organs between gnetophytes and angiosperms, new results in perianth evolution and identified homology of floral organs between dicots and monocots. The evo-devo studies on plant taxa at different evolutionary levels are useful to better understanding the homology of floral organs, and to clarifying the mysteries of the origin and subsequent diversification of flowers.

  1. CMS Computing Model Evolution

    CERN Document Server

    Grandi, Claudio; Colling, D; Fisk, I; Girone, M

    2014-01-01

    The CMS Computing Model was developed and documented in 2004. Since then the model has evolved to be more flexible and to take advantage of new techniques, but many of the original concepts remain and are in active use. In this presentation we will discuss the changes planned for the restart of the LHC program in 2015. We will discuss the changes planning in the use and definition of the computing tiers, that were defined with the MONARC project. We will present how we intend to use new services and infrastructure to provide more efficient and transparent access to the data. We will discuss the computing plans to make better use of the computing capacity by scheduling more of the processor nodes, making better use of the disk storage, and more intelligent use of the networking.

  2. Reduction of chemical reaction models

    Science.gov (United States)

    Frenklach, Michael

    1991-01-01

    An attempt is made to reconcile the different terminologies pertaining to reduction of chemical reaction models. The approaches considered include global modeling, response modeling, detailed reduction, chemical lumping, and statistical lumping. The advantages and drawbacks of each of these methods are pointed out.

  3. Massive star evolution in close binaries. Conditions for homogeneous chemical evolution

    Science.gov (United States)

    Song, H. F.; Meynet, G.; Maeder, A.; Ekström, S.; Eggenberger, P.

    2016-01-01

    Aims: We investigate the impact of tidal interactions, before any mass transfer, on various properties of the stellar models. We study the conditions for obtaining homogeneous evolution triggered by tidal interactions, and for avoiding any Roche lobe overflow (RLOF) during the main-sequence phase. By homogeneous evolution, we mean stars evolving with a nearly uniform chemical composition from the centre to the surface. Methods: We consider the case of rotating stars computed with a strong core-envelope coupling mediated by an interior magnetic field. Models with initial masses between 15 and 60 M⊙, for metallicities between 0.002 and 0.014 and with initial rotation equal to 30% and 66% the critical rotation on the zero age main sequence, are computed for single stars and for stars in close binary systems. We consider close binary systems with initial orbital periods equal to 1.4, 1.6, and 1.8 days and a mass ratio equal to 3/2. Results: In models without any tidal interaction (single stars and wide binaries), homogeneous evolution in solid body rotating models is obtained when two conditions are realised: the initial rotation must be high enough, and the loss of angular momentum by stellar winds should be modest. This last point favours metal-poor fast rotating stars. In models with tidal interactions, homogeneous evolution is obtained when rotation imposed by synchronisation is high enough (typically a time-averaged surface velocities during the main-sequence phase above 250 km s-1), whatever the mass losses. We present plots that indicate for which masses of the primary and for which initial periods the conditions for the homogenous evolution and avoidance of the RLOF are met, for various initial metallicities and rotations. In close binaries, mixing is stronger at higher than at lower metallicities. Homogeneous evolution is thus favoured at higher metallicities. RLOF avoidance is favoured at lower metallicities because stars with less metals remain more

  4. Chemical Evolution of Irregular and Blue Compact Galaxies

    OpenAIRE

    L. Carigi; Colin, P.; Peimbert, M.; Sarmiento, A

    1994-01-01

    We discuss the chemical evolution of metal poor galaxies and conclude that their oxygen deficiency is not due to: the production of black holes by massive stars or a varying slope of the Initial Mass Function, IMF, at the high-mass end. A varying IMF at the low-mass end alone or in combination with: (a) an outflow of oxygen-rich material, (b) an outflow of well-mixed material, and (c) the presence of dark matter that does not participate in the chemical evolution process, is needed to explain...

  5. Stellar Abundance and Galactic Chemical Evolution through LAMOST Spectroscopic Survey

    Institute of Scientific and Technical Information of China (English)

    Gang Zhao; Yu-Qin Chen; Jian-RongShi; Yan-Chun Liang; Jin-Liang Hou; Li Chen; Hua-Wei Zhang; Ai-Gen Li

    2006-01-01

    A project of a spectroscopic survey of Galactic structure and evolution with a Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) is presented. The spectroscopic survey consists of two observational modes for various targets in our Galaxy. One is a major survey of the Milky Way aimed at a systematic study of the stellar abundance and Galactic chemical evolution through low resolution (R=1000 - 2000) spectroscopy.Another is a follow-up observation with medium resolution (R=10000) spectrographs aimed at detailed studies of the selected stars with different chemical composition, kinematicsand dynamics.

  6. Toward a novel high-resolution modeling approach for the study of chemical evolution of pollutant plumes during long-range transport

    Science.gov (United States)

    Real, E.; Pisso, I.; Law, K. S.; Legras, B.; Bousserez, N.; Schlager, H.; Roiger, A.; Attié, J. L.

    2010-06-01

    This paper presents results from a new method, ZooM-CiTTy, that aims to accurately reproduce filamentation observed in profiles of chemically active species in the free troposphere. Lagrangian tracer reconstructions of aircraft measurements across pollutant plumes including a stochastic representation of mixing are coupled with photochemical trajectory simulations, initialized with global model fields. The results provide a high-resolution simulation of trace gases along the flight track together with a detailed picture about the multiple air mass origins influencing chemical composition in the region where plume measurements were taken. This paper builds on results from Pisso et al. (2009) for the dynamic part of the model (the stochastic tracer reconstructions) and focuses on reconstruction of reactive species like O3. The model is evaluated for a case of long-range transport of a forest fire plume from Alaska to Europe. Simulated trace species are compared with measurements made in the plume by the DLR Falcon aircraft flying over Europe, and the role of photochemistry in governing the chemical composition across the plume is evaluated. It is shown that the model reproduces well O3 and NOy concentrations and O3 production per CO in the plumes as well as gradients at plume edges. In particular, because ZooM-CiTTy represents the contribution of several air masses to a measurement at a particular location, the model can reproduce so-called mixing lines between air masses. Results show that photochemistry and mixing contributions vary in different parts of the plume and that resulting trace gas correlations are a combination of these different mixtures. One limitation of the method is the fact that mixing between air masses is only performed at the end of the trajectories. Errors on simulated O3 reconstruction from this formulation are evaluated. These errors seems to be negligible in this case (in the free troposphere, far from emission region) because strong

  7. Chemical Evolution in Hierarchical Models of Cosmic Structure II: The Formation of the Milky Way Stellar Halo and the Distribution of the Oldest Stars

    CERN Document Server

    Tumlinson, Jason

    2009-01-01

    This paper presents theoretical star formation and chemical enrichment histories for the stellar halo of the Milky Way based on new chemodynamical modeling. The goal of this study is to assess the extent to which metal-poor stars in the halo reflect the star formation conditions that occurred in halo progenitor galaxies at high redshift, before and during the epoch of reionization. Simple prescriptions that translate dark-matter halo mass into baryonic gas budgets and star formation histories yield models that resemble the observed Milky Way halo in its total stellar mass, metallicity distribution, and the luminosity function and chemical enrichment of dwarf satellite galaxies. These model halos in turn allow an exploration of how the populations of interest for probing the epoch of reionization are distributed in physical and phase space, and of how they are related to lower-redshift populations of the same metallicity. The fraction of stars dating from before a particular time or redshift depends strongly o...

  8. The Chemical Evolution of Globular Clusters - II. Metals and Fluorine

    CERN Document Server

    Sanchez-Blazquez, Patricia; Gibson, Brad K; Karakas, Amanda I; Pilkington, Kate; Calura, Francesco

    2011-01-01

    In the first paper in this series, we proposed a new framework in which to model the chemical evolution of globular clusters. This model, is predicated upon the assumption that clusters form within an interstellar medium enriched locally by the ejecta of a single Type Ia supernova and varying numbers of asymptotic giant branch stars, superimposed on an ambient medium pre-enriched by low-metallicity Type II supernovae. Paper I was concerned with the application of this model to the observed abundances of several reactive elements and so-called non-metals for three classical intermediate-metallicity clusters, with the hallmark of the work being the successful recovery of many of their well-known elemental and isotopic abundance anomalies. Here, we expand upon our initial analysis by (a) applying the model to a much broader range of metallicities (from the factor of three explored in Paper I, to now, a factor of ~50; i.e., essentially, the full range of Galactic globular cluster abundances, and (b) incorporating...

  9. The isotopic and chemical evolution of planets: Mars as a missing link

    Science.gov (United States)

    Depaolo, D. J.

    1988-01-01

    The study of planetary bodies has advanced to a stage where it is possible to contemplate general models for the chemical and physical evolution of planetary interiors, which might be referred to as UMPES (Unified Models of Planetary Evolution and Structure). UMPES would be able to predict the internal evolution and structure of a planet given certain input parameters such as mass, distance from the sun, and a time scale for accretion. Such models are highly dependent on natural observations because the basic material properties of planetary interiors, and the processes that take place during the evolution of planets are imperfectly understood. The idea of UMPES was particularly unrealistic when the only information available was from the earth. However, advances have been made in the understanding of the general aspects of planetary evolution now that there is geochemical and petrological data available for the moon and for meteorites.

  10. Star Formation History and Chemical Evolution of the Sextans Dwarf Spheroidal Galaxy

    OpenAIRE

    Lee, Myung Gyoon; Yuk, In-Soo; Park, Hong Soo; Harris, Jason; Zaritsky, Dennis

    2009-01-01

    We present the star formation history and chemical evolution of the Sextans dSph dwarf galaxy as a function of galactocentric distance. We derive these from the $VI$ photometry of stars in the $42' \\times 28'$ field using the SMART model developed by Yuk & Lee (2007, ApJ, 668, 876) and adopting a closed-box model for chemical evolution. For the adopted age of Sextans 15 Gyr, we find that $>$84% of the stars formed prior to 11 Gyr ago, significant star formation extends from 15 to 11 Gyr ago (...

  11. The age of the Galactic disk - Inflow, chemical evolution, astration, and radioactivity

    Science.gov (United States)

    Clayton, Donald D.

    1989-01-01

    Theoretical models of Galactic evolution and observational data on the age of the Galaxy are compared, with a focus on recent results. Topics addressed include the infall of material and its effects on the age-metallicity relation, the distribution of metallicity, the present gas fraction and metallicity, and the age spectrum of interstellar nuclei; the chemical evolution of the solar neighborhood; the key results of nuclear cosmochronology; and astration effects on Galactic age. It is found that both nuclear cosmochronology and detailed stellar and Galactic evolution models tend to support an age of 12-16 Gyr.

  12. Chemical evolution of giant molecular clouds in simulations of galaxies

    Science.gov (United States)

    Richings, Alexander J.; Schaye, Joop

    2016-08-01

    We present an analysis of giant molecular clouds (GMCs) within hydrodynamic simulations of isolated, low-mass (M* ˜ 109 M⊙) disc galaxies. We study the evolution of molecular abundances and the implications for CO emission and the XCO conversion factor in individual clouds. We define clouds either as regions above a density threshold n_{H, min} = 10 {cm}^{-3}, or using an observationally motivated CO intensity threshold of 0.25 {K} {km} {s}^{-1}. Our simulations include a non-equilibrium chemical model with 157 species, including 20 molecules. We also investigate the effects of resolution and pressure floors (i.e. Jeans limiters). We find cloud lifetimes up to ≈ 40 Myr, with a median of 13 Myr, in agreement with observations. At one-tenth solar metallicity, young clouds ( ≲ 10-15 Myr) are underabundant in H2 and CO compared to chemical equilibrium, by factors of ≈3 and one to two orders of magnitude, respectively. At solar metallicity, GMCs reach chemical equilibrium faster (within ≈ 1 Myr). We also compute CO emission from individual clouds. The mean CO intensity, ICO, is strongly suppressed at low dust extinction, Av, and possibly saturates towards high Av, in agreement with observations. The ICO-Av relation shifts towards higher Av for higher metallicities and, to a lesser extent, for stronger UV radiation. At one-tenth solar metallicity, CO emission is weaker in young clouds ( ≲ 10-15 Myr), consistent with the underabundance of CO. Consequently, XCO decreases by an order of magnitude from 0 to 15 Myr, albeit with a large scatter.

  13. Losing track of the time: the chemical clock of prestellar core evolution in hydrodynamic simulation

    Science.gov (United States)

    Szucs, L.; Glover, S.; Caselli, P.

    2016-05-01

    The ortho:para ratio of H2D+ is a proposed observational indicator of prestellar core ages, and thus a possible tool to determine the typical star formation time scale. The conversion of the measured ratio to an age estimate requires modelling of the chemical evolution. Such models usually consider static, one zone models of physical conditions. The relevant chemical time scales, however, are comparable to the dynamic time scale, therefore the history of gas might affect the ratio. To investigate the significance of gas dynamics and history on the spin-state ratio, we analyse prestellar cores formed in various environment in a hydrodynamic simulation. The fully time dependent, spatially resolved chemical evolution of the cores are computed using a state-of-art ortho:para and deuteration chemical network. The true ages are compared to the once indicated by the ortho:para ratio.

  14. Magnesium isotopes as a probe of the Milky Way chemical evolution

    OpenAIRE

    Thygesen, Anders Overaa

    2015-01-01

    The study of elemental abundance ratios from spectroscopy of stars has for a long time been used to investigate the structure and the chemical evolution history of the Milky Way. However, even with the ever-increasing number of stars with detailed abundances, many details about the Milky Way evolution are still not understood. While elemental abundance measurements already provide a lot of information, nucleosynthesis models predict not only bulk abundances of an element, but also its isotopi...

  15. Stellar Populations and Chemical Evolution of Late--Type Dwarf Galaxies

    CERN Document Server

    Tosi, M P

    2001-01-01

    Some aspects of the chemical evolution of late-type dwarf galaxies are reviewed, together with their implications on three issues of cosmological relevance: similarity to primeval galaxies, derivation of the primordial helium abundance, contribution to the excess of faint blue galaxies. A more detailed approach to model their evolution is suggested. The importance of deriving the star formation history in these systems by studying their resolved stellar populations is emphasized.

  16. Galactic chemical evolution of heavy elements from Barium to Europium

    CERN Document Server

    Travaglio, C; Gallino, R; Busso, M; Ferrini, F; Straniero, O

    1999-01-01

    We follow the chemical evolution of the Galaxy for elements from Ba to Eu, using an evolutionary model suitable to reproduce a large set of Galactic (local and non local) and extragalactic constraints. Input stellar yields for neutron-rich nuclei have been separated into their s-process and r-process components. The production of s-process elements in thermally pulsing asymptotic giant branch stars of low mass proceeds from the combined operation of two neutron sources: the dominant reaction 13C(alpha,n)16O, which releases neutrons in radiative conditions during the interpulse phase, and the reaction 22Ne(alpha,n)25Mg, marginally activated during thermal instabilities. The resulting s-process distribution is strongly dependent on the stellar metallicity. For the standard model discussed in this paper, it shows a sharp production of the Ba-peak elements around Z = Z_sun/4. Concerning the r-process yields, we assume that the production of r-nuclei is a primary process occurring in stars near the lowest mass lim...

  17. Reconstructing the cosmic evolution of the chemical elements

    CERN Document Server

    Frebel, Anna

    2014-01-01

    The chemical elements are created in nuclear fusion processes in the hot and dense cores of stars. The energy generated through nucleosynthesis allows stars to shine for billions of years. When these stars explode as massive supernovae, the newly made elements are expelled, chemically enriching the surrounding regions. Subsequent generations of stars are formed from gas that is slightly more element enriched than that from which previous stars formed. This chemical evolution can be traced back to its beginning soon after the Big Bang by studying the oldest and most metal-poor stars still observable in the Milky Way today. Through chemical analysis, they provide the only available tool for gaining information about the nature of the short-lived first stars and their supernova explosions more than thirteen billion years ago. These events set in motion the transformation of the pristine universe into a rich cosmos of chemically diverse planets, stars, and galaxies.

  18. The New Model of Chemical Evolution of r-process Elements Based on The Hierarchical Galaxy Formation I: Ba and Eu

    CERN Document Server

    Komiya, Yutaka; Suda, Takuma; Fujimoto, Masayuki Y

    2014-01-01

    We investigate the chemical enrichment of r-process elements in the early evolutionary stages of the Milky Way halo within the framework of hierarchical galaxy formation using a semi-analytic merger tree. In this paper, we focus on heavy r-process elements, Ba and Eu, of extremely metal-poor (EMP) stars and give constraints on their astronomical sites. Our models take into account changes of the surface abundances of EMP stars by the accretion of interstellar matter (ISM). We also consider metal-enrichment of intergalactic medium (IGM) by galactic winds and the resultant pre-enrichment of proto-galaxies. The trend and scatter of the observed r-process abundances are well reproduced by our hierarchical model with $\\sim 10\\%$ of core-collapse supernovae in low-mass end ($\\sim 10M_{\\odot}$) as a dominant r-process source and the star formation efficiency of $\\sim 10^{-10} \\hbox{yr}^{-1}$. For neutron star mergers as an r-process source, their coalescence timescale has to be $ \\sim 10^7$yrs, and the event rates $...

  19. The fast debris evolution model

    Science.gov (United States)

    Lewis, H. G.; Swinerd, G. G.; Newland, R. J.; Saunders, A.

    2009-09-01

    The 'particles-in-a-box' (PIB) model introduced by Talent [Talent, D.L. Analytic model for orbital debris environmental management. J. Spacecraft Rocket, 29 (4), 508-513, 1992.] removed the need for computer-intensive Monte Carlo simulation to predict the gross characteristics of an evolving debris environment. The PIB model was described using a differential equation that allows the stability of the low Earth orbit (LEO) environment to be tested by a straightforward analysis of the equation's coefficients. As part of an ongoing research effort to investigate more efficient approaches to evolutionary modelling and to develop a suite of educational tools, a new PIB model has been developed. The model, entitled Fast Debris Evolution (FADE), employs a first-order differential equation to describe the rate at which new objects ⩾10 cm are added and removed from the environment. Whilst Talent [Talent, D.L. Analytic model for orbital debris environmental management. J. Spacecraft Rocket, 29 (4), 508-513, 1992.] based the collision theory for the PIB approach on collisions between gas particles and adopted specific values for the parameters of the model from a number of references, the form and coefficients of the FADE model equations can be inferred from the outputs of future projections produced by high-fidelity models, such as the DAMAGE model. The FADE model has been implemented as a client-side, web-based service using JavaScript embedded within a HTML document. Due to the simple nature of the algorithm, FADE can deliver the results of future projections immediately in a graphical format, with complete user-control over key simulation parameters. Historical and future projections for the ⩾10 cm LEO debris environment under a variety of different scenarios are possible, including business as usual, no future launches, post-mission disposal and remediation. A selection of results is presented with comparisons with predictions made using the DAMAGE environment model

  20. Modeling of turbulent chemical reaction

    Science.gov (United States)

    Chen, J.-Y.

    1995-01-01

    Viewgraphs are presented on modeling turbulent reacting flows, regimes of turbulent combustion, regimes of premixed and regimes of non-premixed turbulent combustion, chemical closure models, flamelet model, conditional moment closure (CMC), NO(x) emissions from turbulent H2 jet flames, probability density function (PDF), departures from chemical equilibrium, mixing models for PDF methods, comparison of predicted and measured H2O mass fractions in turbulent nonpremixed jet flames, experimental evidence of preferential diffusion in turbulent jet flames, and computation of turbulent reacting flows.

  1. CHEMICAL EVOLUTION AND THE GALACTIC HABITABLE ZONE OF M31

    Directory of Open Access Journals (Sweden)

    Leticia Carigi

    2013-01-01

    Full Text Available We have computed the Galactic Habitable Zones (GHZs of the Andromeda galaxy (M31 based on the probability of terrestrial planet formation, which depends on the metallicity (Z of the interstellar medium, and the number of stars formed per unit surface area. The GHZ was obtained from a chemical evolution model built to reproduce a metallicity gradient in the galactic disk, [O/H](r=−0.015 dex kpc−1 × r(kpc + 0.44 dex. If we assume that Earth-like planets form with a probability law that follows the Z distribution shown by stars with detected planets, the most probable GHZ per pc2 is located between 3 and 7 kpc for planets with ages between 6 and 7 Gyr. However, the highest number of stars with habitable planets is located in a ring between 12 and 14 kpc with a mean age of 7 Gyr. 11% and 6.5% of the all formed stars in M31 may have planets capable of hosting basic and complex life, respectively.

  2. The chemical evolution in the early phases of massive star formation I

    CERN Document Server

    Gerner, T; Semenov, D; Linz, H; Vasyunina, T; Bihr, S; Shirley, Y L; Henning, Th

    2014-01-01

    Understanding the chemical evolution of young (high-mass) star-forming regions is a central topic in star formation research. Chemistry is employed as a unique tool 1) to investigate the underlying physical processes and 2) to characterize the evolution of the chemical composition. We observed a sample of 59 high-mass star-forming regions at different evolutionary stages varying from the early starless phase of infrared dark clouds to high-mass protostellar objects to hot molecular cores and, finally, ultra-compact HII regions at 1mm and 3mm with the IRAM 30m telescope. We determined their large-scale chemical abundances and found that the chemical composition evolves along with the evolutionary stages. On average, the molecular abundances increase with time. We modeled the chemical evolution, using a 1D physical model where density and temperature vary from stage to stage coupled with an advanced gas-grain chemical model and derived the best-fit chi^2 values of all relevant parameters. A satisfying overall a...

  3. Chemical Evolution of the Galactic Disk and Bulge

    OpenAIRE

    Wyse, Rosemary F. G.

    1994-01-01

    Invited Review at IAU Symp 164 on Stellar Populations. The Milky Way Galaxy offers a unique opportunity for testing theories of galaxy formation and evolution. The study of the spatial distribution, kinematics and chemical abundances of stars in the Milky Way Galaxy allows one to address specific questions pertinent to this meeting such as When was the Galaxy assembled? Is this an ongoing process? What was the merging history of the Milky Way?

  4. Inhomogeneous Chemical Evolution of the Galaxy in the Solar Neighbourhood

    Indian Academy of Sciences (India)

    S. Sahijpal

    2013-12-01

    -body numerical simulations of an inhomogeneous Galactic Chemical Evolution (GCE) of the solar neighbourhood with a high temporal resolution are presented. The solar annular ring is divided into distinct spatial grids of area ∼ 1–2 kpc2. Each grid evolves distinctly in terms of star formation and nucleosynthetic yields from numerous generations of stars. The evolution of the galaxy is simulated by considering discrete episodes of star formation. Subsequent to the evolution of the simulated stars within each grid the stellar nucleosynthetic yields are homogenized within the grid rather than the traditionally adopted criteria of homogenizing over the entire solar annular ring. This provides a natural mechanism of generating heterogeneities in the elemental abundance distribution of stars. A complex chemical evolutionary history is inferred that registers episodes of time-dependent contributions from SN II+Ib/c with respect to SN Ia. It was observed that heterogeneities can remerge even after episodes of large scale homogenizations on scales larger than the grid size. However, a comparison of the deduced heterogeneities with the observed scatter in the elemental abundances of the dwarf stars suggest only a partial match, specifically, for [Fe/H] > -0.5. The deduced heterogeneities in the case of carbon, oxygen, magnesium, silicon, sulphur, calcium and titanium can explain the observed heterogeneities for [Fe/H] < -0.5. It may not be possible to explain the entire observed spread exclusively on the basis of the inhomogeneous GCE.

  5. The Evolution Model of Intelligent Matter

    Directory of Open Access Journals (Sweden)

    Bazaluk Oleg

    2014-03-01

    Full Text Available The article deals with the evolution model of reasonable matter (noogenesis, discovering the planetary and cosmic scale of the mind development. The author considers a historiography of this problem field, a contribution of scientific community to the development of basic provisions - noogenesis. According to the author, the evolution model of reasonable matter consists of three interdependent and mutually complementary models: 1. Models of continuous and nonlinear complication of structures of reasonable matter (neuro-evolution; 2. Models of continuous and nonlinear complication of types of interacting (or shown functions structures of the system of reasonable matter. 3. Models of continuous and nonlinear complication of the surroundings of reasonable matter (socio-cultural evolution. All these models include the author's understanding and corresponding arguments. In conclusion the author compares models of living and reasonable matter (biological evolution and noogenesis

  6. A paradigm-based evolution of chemical engineering

    Institute of Scientific and Technical Information of China (English)

    Alexandru Woinaroschy

    2016-01-01

    A short presentation of chemical engineering evolution, as guided by its paradigms, is exposed. The first paradigm–unit operations–has emerged as a necessity of systematization due to the explosion of chemical industrial applica-tions at the end of 19th century. The birth in the late 1950s of the second paradigm–transport phenomena–was the consequence of the need for a deep, scientific knowledge of the phenomena that explain what happens inside of unit operations. In the second part of 20th century, the importance of chemical product properties and qualities has become essential y in the market fights. Accordingly, it was required with additional and even new fundamen-tal approaches, and product engineering was recognized as the third paradigm. Nowadays chemical industry, as a huge materials and energy consumer, and with a strong ecological impact, couldn't remain outside of sustainability requirements. The basics of the fourth paradigm–sustainable chemical engineering–are now formulated.

  7. Simple models of evolution and extinction

    CERN Document Server

    Newman, M E J

    1999-01-01

    This article gives a brief introduction to the mathematical modeling of large-scale biological evolution and extinction. We give three examples of simple models in this field: the coevolutionary avalanche model of Bak and Sneppen, the environmental stress model of Newman, and the increasing fitness model of Sibani, Schmidt, and Alstrom. We describe the features of real evolution which these models are intended to explain and compare the results of simulations against data drawn from the fossil record.

  8. Simple models of evolution and extinction

    OpenAIRE

    Newman, M. E. J.

    1999-01-01

    This article gives a brief introduction to the mathematical modeling of large-scale biological evolution and extinction. We give three examples of simple models in this field: the coevolutionary avalanche model of Bak and Sneppen, the environmental stress model of Newman, and the increasing fitness model of Sibani, Schmidt, and Alstrom. We describe the features of real evolution which these models are intended to explain and compare the results of simulations against data drawn from the fossi...

  9. Tabletop imaging of structural evolutions in chemical reactions

    CERN Document Server

    Ibrahim, Heide; Beaulieu, Samuel; Schmidt, Bruno E; Thiré, Nicolas; Bisson, Éric; Hebeisen, Christoph T; Wanie, Vincent; Giguére, Mathieu; Kieffer, Jean-Claude; Sanderson, Joseph; Schuurman, Michael S; Légaré, François

    2014-01-01

    The introduction of femto-chemistry has made it a primary goal to follow the nuclear and electronic evolution of a molecule in time and space as it undergoes a chemical reaction. Using Coulomb Explosion Imaging we have shot the first high-resolution molecular movie of a to and fro isomerization process in the acetylene cation. So far, this kind of phenomenon could only be observed using VUV light from a Free Electron Laser [Phys. Rev. Lett. 105, 263002 (2010)]. Here we show that 266 nm ultrashort laser pulses are capable of initiating rich dynamics through multiphoton ionization. With our generally applicable tabletop approach that can be used for other small organic molecules, we have investigated two basic chemical reactions simultaneously: proton migration and C=C bond-breaking, triggered by multiphoton ionization. The experimental results are in excellent agreement with the timescales and relaxation pathways predicted by new and definitively quantitative ab initio trajectory simulations.

  10. The nature of chemical innovation: new enzymes by evolution.

    Science.gov (United States)

    Arnold, Frances H

    2015-11-01

    I describe how we direct the evolution of non-natural enzyme activities, using chemical intuition and information on structure and mechanism to guide us to the most promising reaction/enzyme systems. With synthetic reagents to generate new reactive intermediates and just a few amino acid substitutions to tune the active site, a cytochrome P450 can catalyze a variety of carbene and nitrene transfer reactions. The cyclopropanation, N-H insertion, C-H amination, sulfimidation, and aziridination reactions now demonstrated are all well known in chemical catalysis but have no counterparts in nature. The new enzymes are fully genetically encoded, assemble and function inside of cells, and can be optimized for different substrates, activities, and selectivities. We are learning how to use nature's innovation mechanisms to marry some of the synthetic chemists' favorite transformations with the exquisite selectivity and tunability of enzymes.

  11. An Evolution Model of Space Debris Environment

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Various types of models including engineering models andevolution models have been developed to understand space debris environment since 1960s. Evolution model, consisting of a set of supporting models such as Launch Model, Breakup Model and Atmosphere Model, can reliably predicts the evolution of space debris environment. Of these supporting models, Breakup Model is employed to describe the distribution of debris and debris cloud during a explosion or collision case which is one of the main factors affecting the amount of total space debris. An analytical orbit debris environment model referred to as the “Particles-In-Boxes" model has been introduced. By regarding the orbit debris as the freedom particles running in the huge volume, the sources and sinks mechanism is established. Then the PIB model is expanded to the case of multiple-species in multiple-tier system. Combined with breakup model, the evolution of orbit debris environment is predicted.

  12. The gas-ice chemical interplay during cloud evolution

    CERN Document Server

    Hocuk, S

    2014-01-01

    During the evolution of diffuse clouds to molecular clouds, gas-phase molecules freeze out on surfaces of small dust particles to form ices. On dust surfaces, water is the main constituent of the icy mantle in which a complex chemistry is taking place. We aim to study the formation pathways and the composition of the ices throughout the evolution of diffuse clouds. For this purpose, we use time-dependent rate equations to calculate the molecular abundances in both gas phase and on solid surfaces (onto dust grains). We fully consider the gas-dust interplay by including the details of freeze-out, chemical and thermal desorption, as well as the most important photo-processes on grain surfaces. The difference in binding energies of chemical species on bare and icy surfaces is also incorporated into our equations. Using the numerical code FLASH, we perform a hydrodynamical simulation of a gravitationally bound diffuse cloud and follow its contraction. We find that while the dust grains are still bare, water format...

  13. The chemical evolution of self-gravitating primordial disks

    CERN Document Server

    Schleicher, Dominik R G; Latif, Muhammad A; Ferrara, Andrea; Grassi, Tommaso

    2016-01-01

    Numerical simulations show the formation of self-gravitating primordial disks during the assembly of the first structures in the Universe, in particular during the formation of Pop. III and supermassive stars. Their subsequent evolution is expected to be crucial to determine the mass scale of the first cosmological objects, which depends on the temperature of the gas and the dominant cooling mechanism. Here, we derive a one-zone framework to explore the chemical evolution of such disks and show that viscous heating leads to the collisional dissociation of an initially molecular gas. The effect is relevant on scales of 10 AU (1000 AU) for a central mass of 10 M_solar (10^4 M_solar) at an accretion rate of 0.1 M_solar/yr, and provides a substantial heat input to stabilize the disk. If the gas is initially atomic, it remains atomic during the further evolution, and the effect of viscous heating is less significant. The additional thermal support is particularly relevant for the formation of very massive objects,...

  14. The Evolution Model of Intelligent Matter

    OpenAIRE

    Bazaluk Oleg

    2014-01-01

    The article deals with the evolution model of reasonable matter (noogenesis), discovering the planetary and cosmic scale of the mind development. The author considers a historiography of this problem field, a contribution of scientific community to the development of basic provisions - noogenesis. According to the author, the evolution model of reasonable matter consists of three interdependent and mutually complementary models: 1. Models of continuous and nonlinear complication of structu...

  15. Chemical kinetics and combustion modeling

    Energy Technology Data Exchange (ETDEWEB)

    Miller, J.A. [Sandia National Laboratories, Livermore, CA (United States)

    1993-12-01

    The goal of this program is to gain qualitative insight into how pollutants are formed in combustion systems and to develop quantitative mathematical models to predict their formation rates. The approach is an integrated one, combining low-pressure flame experiments, chemical kinetics modeling, theory, and kinetics experiments to gain as clear a picture as possible of the process in question. These efforts are focused on problems involved with the nitrogen chemistry of combustion systems and on the formation of soot and PAH in flames.

  16. Bacterial Evolution and Bak-Sneppen Model

    OpenAIRE

    Bose, Indrani; Chaudhuri, Indranath

    2002-01-01

    Recently, Lenski et al [Elena,Lenski,Travisano] have carried out several experiments on bacterial evolution. Their findings support the theory of punctuated equilibrium in biological evolution. They have further quantified the relative contributions of adaptation, chance and history to bacterial evolution. In this paper, we show that a modified $M$-trait Bak-Sneppen model can explain many of the experimental results in a qualitative manner.

  17. The Chemical Evolution of the Atmospheres and Oceans

    Science.gov (United States)

    Arthur, Michael A.

    Having devoured Holland's earlier book on the modern state of ocean and atmosphere chemical reservoirs, The Chemistry of the Atmosphere and Oceans (Wiley-Interscience, New York, 1978), and having read several of the stimulating papers that derived from his work on the promised companion volume, concerned with the history of atmospheric and ocean chemistry, I eagerly anticipated publication of The Chemical Evolution of the Atmosphere and Oceans. It has been published, and I am not disappointed, nor will the education of any graduate student or practing professional in the earth or ocean sciences be complete without thorough study of this long-awaited book. There is nothing else that resembles it in subject matter, comprehensiveness, and thoughtful and objective analysis of data and of old and new ideas in the field.Holland has devoted space and consideration in his book to the different episodes in atmospheric and ocean chemical history of the earth roughly in proportion to the relative duration of each episode. This, of course, means that the treatment of the relatively data-rich Phanerozoic interval is more terse than the sections on the Precambrian. Yet Holland handles the paucity of data for the Precambrian with flair and appropriate conjecture. In fact, it is in this part of the book that his impressive intellect shines.

  18. Testing the role of SNe Ia for Galactic chemical evolution of p-nuclei with 2D models and with s-process seeds at different metallicities

    CERN Document Server

    Travaglio, C; Rauscher, T; Ropeke, F K; Hillebrandt, W

    2014-01-01

    The bulk of p isotopes is created in the 'gamma processes' mainly by sequences of photodisintegrations and beta decays in explosive conditions in Type Ia supernovae (SNIa) or in core collapse supernovae (ccSN). The contribution of different stellar sources to the observed distribution of p-nuclei in the Solar System is still under debate. We explore single degenerate Type Ia supernovae in the framework of two-dimensional SNIa delayed-detonation explosion models. Travaglio et al. (2011, TRV11) discussed the sensitivity of p-nuclei production to different SNIa models, i.e. delayed detonations of different strength, deflagrations, and the dependence on selected s-process seed distributions. Here we present a detailed study of p-process nucleosynthesis occuring in SNIa with s-process seeds at different metallicities. Based on the delayed-detonation model DDT-a of TRV11, we analyze the dependence of p-nucleosynthesis on the s-seed distribution obtained from different strengths of the 13C-pocket. Using a Galactic c...

  19. Chemical modeling of waste sludges

    Energy Technology Data Exchange (ETDEWEB)

    Weber, C.F.; Beahm, E.C.

    1996-10-01

    The processing of waste from underground storage tanks at the Oak Ridge National Laboratory (ORNL) and other facilities will require an understanding of the chemical interactions of the waste with process chemicals. Two aspects of sludge treatment should be well delineated and predictable: (1) the distribution of chemical species between aqueous solutions and solids, and (2) potential problems due to chemical interactions that could result in process difficulties or safety concerns. It is likely that the treatment of waste tank sludge will begin with washing, followed by basic or acidic leaching. The dissolved materials will be in a solution that has a high ionic strength where activity coefficients are far from unity. Activity coefficients are needed in order to calculate solubilities. Several techniques are available for calculating these values, and each technique has its advantages and disadvantages. The techniques adopted and described here is the Pitzer method. Like any of the methods, prudent use of this approach requires that it be applied within concentration ranges where the experimental data were fit, and its use in large systems should be preceded by evaluating subsystems. While much attention must be given to the development of activity coefficients, other factors such as coprecipitation of species and Ostwald ripening must also be considered when one aims to interpret results of sludge tests or to predict results of treatment strategies. An understanding of sludge treatment processes begins with the sludge tests themselves and proceeds to a general interpretation with the aid of modeling. One could stop with only data from the sludge tests, in which case the table of data would become an implicit model. However, this would be a perilous approach in situations where processing difficulties could be costly or result in concerns for the environment or health and safety.

  20. SYNTHETIC AGB EVOLUTION .1. A NEW MODEL

    NARCIS (Netherlands)

    GROENEWEGEN, MAT; DEJONG, T

    1993-01-01

    We have constructed a model to calculate in a synthetic way the evolution of stars on the asymptotic giant branch (AGB). The evolution is started at the first thermal pulse (TP) and is terminated when the envelope mass has been lost due to mass loss or when the core mass reaches the Chandrasekhar ma

  1. Time Evolution of Thermo-Mechanically and Chemically Coupled Magma Chambers

    Science.gov (United States)

    Ozimek, C.; Karlstrom, L.; Erickson, B. A.

    2015-12-01

    Complexity in the volcanic eruption cycle reflects time variation both of magma inputs to the crustal plumbing system and of crustal melt storage zones (magma chambers). These data include timing and volumes of eruptions, as well as erupted compositions. Thus models must take into account the coupled nature of physical attributes. Here we combine a thermo-mechanical model for magma chamber growth and pressurization with a chemical model for evolving chamber compositions, in the limit of rapid mixing, to study controls on eruption cycles and compositions through time. We solve for the mechanical evolution of a 1D magma chamber containing melt, crystals and bubbles, in a thermally evolving and viscoelastic crust. This pressure and temperature evolution constrains the input values of a chemical box model (Lee et al., 2013) that accounts for recharge, eruption, assimilation and fractional crystallization (REAFC) within the chamber. We plan to study the influence of melt supply, input composition, and chamber depth eruptive fluxes and compositions. Ultimately we will explore multiple chambers coupled by elastic-walled dikes. We expect that this framework will facilitate self-consistent inversion of long-term eruptive histories in terms of magma transport physics. Lee, C.-T. A., Lee, T.-C., Wu, C.-T., 2013. Modeling the compositional evolution of recharging, evacuating, and fractionating (REFC) magma chambers: Implications for differentiationof arc magmas. Geochemica Cosmochimica Acta, http://dx.doi.org/10.1016/j.gca.2013.08.009.

  2. Markov Model Applied to Gene Evolution

    Institute of Scientific and Technical Information of China (English)

    季星来; 孙之荣

    2001-01-01

    The study of nucleotide substitution is very important both to our understanding of gene evolution and to reliable estimation of phylogenetic relationships. In this paper nucleotide substitution is assumed to be random and the Markov model is applied to the study of the evolution of genes. Then a non-linear optimization approach is proposed for estimating substitution in real sequences. This substitution is called the "Nucleotide State Transfer Matrix". One of the most important conclusions from this work is that gene sequence evolution conforms to the Markov process. Also, some theoretical evidences for random evolution are given from energy analysis of DNA replication.

  3. Structure Model of Urban Traffic System Evolution

    Institute of Scientific and Technical Information of China (English)

    JIANG Ke-jin; ZHANG Dian-ye

    2008-01-01

    A structure model of urban traffic system evolution is built based on the analysis of the factors influencing the system evolution and the hierarchy between the factors. Then the influencing degrees of the factors are quantificationally analyzed by DEMATE (decision making trial and evaluation laboratory). The analysis results indicate that the traffic mode structure which achieves the highest central degree is the dominant influencing factor of the urban traffic system evolution, and that economy development and the traffic poficy axe the second important factors that also affect the traffic mode structures. Furthermore, physical geography is a basic restriction to the urban traffic system evolution.

  4. Cosmic chemical evolution with intermediate mass pop III stars

    International Nuclear Information System (INIS)

    We explore the consequences of an early population of intermediate mass stars (IMS) in the 2 – 8 Msun range on cosmic chemical evolution. We discuss the implications of this population as it pertains to several cosmological and astrophysical observables. Some very metal-poor galactic stars show large enhancements of carbon, typical of the C-rich ejecta of IMS; moreover, halo star carbon and oxygen abundances show a scatter, which imply a wide range of star-formation and nucleosynthetic histories contributed to the first generations of stars. Also, recent analyses of the He abundance in metal-poor extragalactic H II regions suggest an elevated primitive abundance of Helium, Yp ≅ 0.256 by mass, higher than the predicted result from big bang nucleosynthesis assuming the baryon density determined by WMAP, Yp ≅ 0.249. This offset suggests a prompt initial enrichment of He in early metal-poor structures, and IMS Pop III stars are again good candidates. We also discuss the effect of these Pop III stars on global cosmic evolution for example the reionization of the Universe. We conclude that if IMS are to be associated with some Population III stars, their relevance is limited to low mass structures involving a little fraction of the total baryon content of the Universe typical at redshift 10 [1].

  5. Galactic chemical abundance evolution in the solar neighborhood up to the Iron peak

    CERN Document Server

    Alibes, A; Canal, R; Alibes, Andreu; Labay, Javier; Canal, Ramon

    2000-01-01

    We have developed a detailed standard chemical evolution model to study the evolution of all the chemical elements up to the iron peak in the solar vicinity. We consider that the Galaxy was formed through two episodes of exponentially decreasing infall, out of extragalactic gas. In a first infall episode, with a duration of $\\sim$ 1 Gyr, the halo and the thick disk were assembled out of primordial gas, while the thin disk formed in a second episode of infall of slightly enriched extragalactic gas, with much longer timescale. The model nicely reproduces the main observational constraints of the solar neighborhood, and the calculated elemental abundances at the time of the solar birth are in excellent agreement with the solar abundances. By the inclusion of metallicity dependent yields for the whole range of stellar masses we follow the evolution of 76 isotopes of all the chemical elements between hydrogen and zinc. Those results are confronted with a large and recent body of observational data, and we discuss ...

  6. Chemical evolution of protoplanetary disks - the effects of viscous accretion, turbulent mixing and disk winds

    CERN Document Server

    Heinzeller, Dominikus; Walsh, Catherine; Millar, Tom J

    2011-01-01

    We calculate the chemical evolution of protoplanetary disks considering radial viscous accretion, vertical turbulent mixing and vertical disk winds. We study the effects on the disk chemical structure when different models for the formation of molecular hydrogen on dust grains are adopted. Our gas-phase chemistry is extracted from the UMIST Database for Astrochemistry (Rate06) to which we have added detailed gas-grain interactions. We use our chemical model results to generate synthetic near- and mid-infrared LTE line emission spectra and compare these with recent Spitzer observations. Our results show that if H2 formation on warm grains is taken into consideration, the H2O and OH abundances in the disk surface increase significantly. We find the radial accretion flow strongly influences the molecular abundances, with those in the cold midplane layers particularly affected. On the other hand, we show that diffusive turbulent mixing affects the disk chemistry in the warm molecular layers, influencing the line ...

  7. CNEM: Cluster Based Network Evolution Model

    Directory of Open Access Journals (Sweden)

    Sarwat Nizamani

    2015-01-01

    Full Text Available This paper presents a network evolution model, which is based on the clustering approach. The proposed approach depicts the network evolution, which demonstrates the network formation from individual nodes to fully evolved network. An agglomerative hierarchical clustering method is applied for the evolution of network. In the paper, we present three case studies which show the evolution of the networks from the scratch. These case studies include: terrorist network of 9/11 incidents, terrorist network of WMD (Weapons Mass Destruction plot against France and a network of tweets discussing a topic. The network of 9/11 is also used for evaluation, using other social network analysis methods which show that the clusters created using the proposed model of network evolution are of good quality, thus the proposed method can be used by law enforcement agencies in order to further investigate the criminal networks

  8. The effects of a Variable IMF on the Chemical Evolution of the Galaxy

    CERN Document Server

    Chiappini, C; Chiappini, Cristina; Matteucci, Francesca

    2000-01-01

    In this work we explore the effects of adopting an initial mass function (IMF) variable in time on the chemical evolution of the Galaxy. In order to do that we adopt a chemical evolution model which assumes two main infall episodes for the formation of the Galaxy. We study the effects on such a model of different IMFs. First, we use a theoretical one based on the statistical description of the density field arising from random motions in the gas. This IMF is a function of time as it depends on physical conditions of the site of star formation. We also investigate the behaviour of the model predictions using other variable IMFs, parameterized as a function of metallicity. Our results show that the theoretical IMF when applied to our model depends on time but such time variation is important only in the early phases of the Galactic evolution, when the IMF is biased towards massive stars. We also show that the use of an IMF which is a stronger function of time does not lead to a good agreement with the observati...

  9. On a Nonlinear Model in Adiabatic Evolutions

    Science.gov (United States)

    Sun, Jie; Lu, Song-Feng

    2016-08-01

    In this paper, we study a kind of nonlinear model of adiabatic evolution in quantum search problem. As will be seen here, for this problem, there always exists a possibility that this nonlinear model can successfully solve the problem, while the linear model can not. Also in the same setting, when the overlap between the initial state and the final stare is sufficiently large, a simple linear adiabatic evolution can achieve O(1) time efficiency, but infinite time complexity for the nonlinear model of adiabatic evolution is needed. This tells us, it is not always a wise choice to use nonlinear interpolations in adiabatic algorithms. Sometimes, simple linear adiabatic evolutions may be sufficient for using. Supported by the National Natural Science Foundation of China under Grant Nos. 61402188 and 61173050. The first author also gratefully acknowledges the support from the China Postdoctoral Science Foundation under Grant No. 2014M552041

  10. An algebraic model of software evolution

    OpenAIRE

    Keller, Benjamin J.d

    1990-01-01

    A model of the software evolution process, called the Abstraction Refinement Model, is described which builds on the algebraic influence of the Laws of Programming and the transformational Draco Paradigm. The result is an algebraic structure consisting of the states of the software product (system descriptions) ordered by a relation of relative correctness with transformations defined between the system descriptions. This structure is interpreted as the software evolution space, ...

  11. Chemical Evolution of Mn in Three Dwarf Spheroidal Galaxies

    Indian Academy of Sciences (India)

    Men-Quan Liu; Jie Zhang

    2014-09-01

    Based on an improved model, more reasonable nucleosyn-thesis and explosion rate of SNeIa and CCSNe, we studied Mn evolution for three local dwarf spheroidal galaxies (dSphs), considering the detailed SNe yield and explosion rates for different types of progenitors. The results can explain the main observation ofMn abundance for tens stars in those dSphs, and give some constraints to the nucleosynthesis and explosion ratio of different types of supernovae and Star Formation Rates (SFR) in those dSphs.

  12. Second Symposium on Chemical Evolution and the Origin of Life

    Science.gov (United States)

    Devincenzi, D. L. (Editor); model. (Editor)

    1986-01-01

    Recent findings by NASA Exobiology investigators are reported. Scientific papers are presented in the following areas: cosmic evolution of biogenic compounds, prebiotic evolution (planetary and molecular), early evolution of life (biological and geochemical), evolution of advanced life, solar system exploration, and the Search for Extraterrestrial Intelligence (SETI).

  13. Second Symposium on Chemical Evolution and the Origin of Life

    Energy Technology Data Exchange (ETDEWEB)

    Devincenzi, D.L.; Dufour, P.A.

    1986-05-01

    Recent findings by NASA Exobiology investigators are reported. Scientific papers are presented in the following areas: cosmic evolution of biogenic compounds, prebiotic evolution (planetary and molecular), early evolution of life (biological and geochemical), evolution of advanced life, solar system exploration, and the Search for Extraterrestrial Intelligence (SETI).

  14. The role of OH in the chemical evolution of protoplanetary disks II. Gas-rich environments

    CERN Document Server

    Molano, Germán Chaparro

    2012-01-01

    Context. We present a method for including gas extinction of cosmic-ray-generated UV photons in chemical models of the midplane of protoplanetary disks, focusing on its implications on ice formation and chemical evolution. Aims. Our goal is to improve on chemical models by treating cosmic rays, the main source of ionization in the midplane of the disk, in a way that is consistent with current knowledge of the gas and grain environment present in those regions. We trace the effects of cosmic rays by identifying the main chemical reaction channels and also the main contributors to the gas opacity to cosmic-ray-induced UV photons. This information is crucial in implementing gas opacities for cosmic-ray-induced reactions in full 2D protoplanetary disk models. Methods. We considered time-dependent chemical models within the range 1-10 AU in the midplane of a T Tauri disk. The extinction of cosmic-ray-induced UV photons by gaseous species was included in the calculation of photorates at each timestep. We integrated...

  15. Cyril Ponnamperuma Memorial. Trieste conference on chemical evolution, 4: Physics of the origin and evolution of life. Summaries

    International Nuclear Information System (INIS)

    The document includes 19 summaries of papers presented at the Trieste Conference on Chemical Evolution, 4: Physics of the Origin and Evolution of Life (Cyril Ponnamperuma Memorial), Miramare, Trieste, 4-8 September 1995. The abstracts have been indexed individually. 3 refs, 1 fig

  16. Chemical modeling of exoplanet atmospheres

    CERN Document Server

    Venot, Olivia

    2014-01-01

    The past twenty years have revealed the diversity of planets that exist in the Universe. It turned out that most of exoplanets are different from the planets of our Solar System and thus, everything about them needs to be explored. Thanks to current observational technologies, we are able to determine some information about the atmospheric composition, the thermal structure and the dynamics of these exoplanets, but many questions remain still unanswered. To improve our knowledge about exoplanetary systems, more accurate observations are needed and that is why the Exoplanet Characterisation Observatory (EChO) is an essential space mission. Thanks to its large spectral coverage and high spectral resolution, EChO will provide exoplanetary spectra with an unprecedented accuracy, allowing to improve our understanding of exoplanets. In this work, we review what has been done to date concerning the chemical modeling of exoplanet atmospheres and what are the main characteristics of warm exoplanet atmospheres, which a...

  17. Engineered Barrier System: Physical and Chemical Environment Model

    International Nuclear Information System (INIS)

    The conceptual and predictive models documented in this Engineered Barrier System: Physical and Chemical Environment Model report describe the evolution of the physical and chemical conditions within the waste emplacement drifts of the repository. The modeling approaches and model output data will be used in the total system performance assessment (TSPA-LA) to assess the performance of the engineered barrier system and the waste form. These models evaluate the range of potential water compositions within the emplacement drifts, resulting from the interaction of introduced materials and minerals in dust with water seeping into the drifts and with aqueous solutions forming by deliquescence of dust (as influenced by atmospheric conditions), and from thermal-hydrological-chemical (THC) processes in the drift. These models also consider the uncertainty and variability in water chemistry inside the drift and the compositions of introduced materials within the drift. This report develops and documents a set of process- and abstraction-level models that constitute the engineered barrier system: physical and chemical environment model. Where possible, these models use information directly from other process model reports as input, which promotes integration among process models used for total system performance assessment. Specific tasks and activities of modeling the physical and chemical environment are included in the technical work plan ''Technical Work Plan for: In-Drift Geochemistry Modeling'' (BSC 2004 [DIRS 166519]). As described in the technical work plan, the development of this report is coordinated with the development of other engineered barrier system analysis model reports

  18. Trends in Substitution Models of Molecular Evolution

    Directory of Open Access Journals (Sweden)

    Miguel eArenas

    2015-10-01

    Full Text Available Substitution models of evolution describe the process of genetic variation through fixed mutations and constitute the basis of the evolutionary analysis at the molecular level. Almost forty years after the development of first substitution models, highly sophisticated and data-specific substitution models continue emerging with the aim of better mimicking real evolutionary processes. Here I describe current trends in substitution models of DNA, codon and amino acid sequence evolution, including advantages and pitfalls of the most popular models. The perspective concludes that despite the large number of currently available substitution models, further research is required for more realistic modeling, especially for DNA coding and amino acid data. Additionally, the development of more accurate complex models should be coupled with new implementations and improvements of methods and frameworks for substitution model selection and downstream evolutionary analysis.

  19. Protoplanetary Disk Structure With Grain Evolution: the ANDES Model

    CERN Document Server

    Akimkin, V; Wiebe, D; Semenov, D; Pavlyuchenkov, Ya; Vasyunin, A; Birnstiel, T; Henning, Th

    2013-01-01

    We present a self-consistent model of a protoplanetary disk: 'ANDES' ('AccretioN disk with Dust Evolution and Sedimentation'). ANDES is based on a flexible and extendable modular structure that includes 1) a 1+1D frequency-dependent continuum radiative transfer module, 2) a module to calculate the chemical evolution using an extended gas-grain network with UV/X-ray-driven processes surface reactions, 3) a module to calculate the gas thermal energy balance, and 4) a 1+1D module that simulates dust grain evolution. For the first time, grain evolution and time-dependent molecular chemistry are included in a protoplanetary disk model. We find that grain growth and sedimentation of large grains to the disk midplane lead to a dust-depleted atmosphere. Consequently, dust and gas temperatures become higher in the inner disk (R 50 AU), in comparison with the disk model with pristine dust. The response of disk chemical structure to the dust growth and sedimentation is twofold. First, due to higher transparency a partl...

  20. Extragalactic Planetary Nebulae: tracers of the chemical evolution of nearby galaxies

    OpenAIRE

    Magrini, Laura; Stanghellini, Letizia; Goncalves, Denise R.

    2011-01-01

    The study of the chemical composition of Planetary Nebulae in external galaxies is of paramount importance in the fields of stellar evolution and of the chemical enrichment history of galaxies. In the last years a number of spectroscopic studies with 6-8m-class telescopes have been devoted to this subject improving our knowledge of, among other, the time-evolution of the radial metallicity gradient in disk galaxies, the chemical evolution of dwarf galaxies, and the stellar evolution at low me...

  1. Chemical evolution of giant molecular clouds in simulations of galaxies

    CERN Document Server

    Richings, Alexander J

    2016-01-01

    We present an analysis of Giant Molecular Clouds (GMCs) identified in hydrodynamic simulations of isolated, low-mass (M* ~ 10^9 M_sol) disc galaxies, with a particular focus on the evolution of molecular abundances and the implications for CO emission and the X_CO conversion factor in individual clouds. We define clouds either as regions above a density threshold n_H,min = 10 cm^-3, or using an observationally motivated velocity-integrated CO line intensity threshold of 0.25 K km s^-1. Our simulations include a non-equilibrium treatment for the chemistry of 157 species, including 20 molecules. We use a suite of runs to carefully investigate the effects of numerical resolution and pressure floors (i.e. Jeans mass limiters). We find cloud lifetimes up to ~40 Myr, with a median of 13 Myr, in agreement with observations. At ten per cent solar metallicity, young clouds (<10-15 Myr) tend to be underabundant in H2 and CO compared to chemical equilibrium, by factors of ~3 and 1-2 orders of magnitude, respectively....

  2. The Galactic Habitable Zone I. Galactic Chemical Evolution

    CERN Document Server

    González, G; Ward, P; Gonzalez, Guillermo; Brownlee, Donald; Ward, Peter

    2001-01-01

    We propose the concept of a "Galactic Habitable Zone" (GHZ). Analogous to the Circumstellar Habitable Zone (CHZ), the GHZ is that region in the Milky Way where an Earth-like planet can retain liquid water on its surface and provide a long-term habitat for animal-like aerobic life. In this paper we examine the dependence of the GHZ on Galactic chemical evolution. The single most important factor is likely the dependence of terrestrial planet mass on the metallicity of its birth cloud. We estimate, very approximately, that a metallicity at least half that of the Sun is required to build a habitable terrestrial planet. The mass of a terrestrial planet has important consequences for interior heat loss, volatile inventory, and loss of atmosphere. A key issue is the production of planets that sustain plate tectonics, a critical recycling process that provides feedback to stabilize atmospheric temperatures on planets with oceans and atmospheres. Due to the more recent decline from the early intense star formation ac...

  3. Radiolysis and Thermolysis of Cytosine: Importance in Chemical Evolution

    Directory of Open Access Journals (Sweden)

    J. Cruz-Castañeda

    2016-08-01

    Full Text Available An important aspect of chemical evolution is the study of the stability of organic molecules with biological significance in primitive conditions, especially in the presence of constant energy sources. An example of sets of biologically important organic compounds is nitrogenous bases. The presence of these compounds in prebiotic environments is very important in forming more complex systems, such as nucleic acids, in which nitrogenous bases are an essential component. The aim of the present work is to study the stability of cytosine, a pyrimidine base, in high-radiation fields or at high temperature and to evaluate its recovery. Our results show that the cytosine (1x10-4 M aqueous solution, oxygen-free decomposed completely at a dose of 22 kGy, and 25% recovery was obtained with a dose of 7.4 kGy. The analysis of irradiated samples was followed by HPLC, HPLC-mass spectrometry and UV-VIS spectroscopy. The main product in both thermolysis and radiolysis was uracil, formed via a deamination reaction. Uracil is another nitrogenous base with biological significance.

  4. Chemical evolution of volatile organic compounds in the outflow of the Mexico City Metropolitan area

    Directory of Open Access Journals (Sweden)

    E. C. Apel

    2010-03-01

    Full Text Available The volatile organic compound (VOC distribution in the Mexico City Metropolitan Area (MCMA and its evolution as it is uplifted and transported out of the MCMA basin was studied during the 2006 MILAGRO/MIRAGE-Mex field campaign. The results show that in the morning hours in the city center, the VOC distribution is dominated by non-methane hydrocarbons (NMHCs but with a substantial contribution from oxygenated volatile organic compounds (OVOCs, predominantly from primary emissions. Alkanes account for a large part of the NMHC distribution in terms of mixing ratios. In terms of reactivity, NMHCs also dominate overall, especially in the morning hours. However, in the afternoon, as the boundary layer lifts and air is mixed and aged within the basin, the distribution changes as secondary products are formed. The WRF-Chem (Weather Research and Forecasting with Chemistry model and MOZART (Model for Ozone and Related chemical Tracers were able to approximate the observed MCMA daytime patterns and absolute values of the VOC OH reactivity. The MOZART model is also in agreement with observations showing that NMHCs dominate the reactivity distribution except in the afternoon hours. The WRF-Chem and MOZART models showed higher reactivity than the experimental data during the nighttime cycle, perhaps indicating problems with the modeled nighttime boundary layer height.

    A northeast transport event was studied in which air originating in the MCMA was intercepted aloft with the Department of Energy (DOE G1 on 18 March and downwind with the National Center for Atmospheric Research (NCAR C130 one day later on 19 March. A number of identical species measured aboard each aircraft gave insight into the chemical evolution of the plume as it aged and was transported as far as 1000 km downwind; ozone was shown to be photochemically produced in the plume. The WRF-Chem and MOZART models were used to examine the spatial extent and temporal evolution of the plume

  5. Modeling Concept Evolution: A Historical Perspective

    Science.gov (United States)

    Rizzolo, Flavio; Velegrakis, Yannis; Mylopoulos, John; Bykau, Siarhei

    The world is changing, and so must the data that describes its history. Not surprisingly, considerable research effort has been spent in Databases along this direction, covering topics such as temporal models and schema evolution. A topic that has not received much attention, however, is that of concept evolution. For example, Germany (instance-level concept) has evolved several times in the last century as it went through different governance structures, then split into two national entities that eventually joined again. Likewise, a caterpillar is transformed into a butterfly, while a mother becomes two (maternally-related) entities. As well, the concept of Whale (a class-level concept) changed over the past two centuries thanks to scientific discoveries that led to a better understanding of what the concept entails. In this work, we present a formal framework for modeling, querying and managing such evolution. In particular, we describe how to model the evolution of a concept, and how this modeling can be used to answer historical queries of the form "How has concept X evolved over period Y". Our proposal extends an RDF-like model with temporal features and evolution operators. Then we provide a query language that exploits these extensions and supports historical queries.

  6. Modeling the evolution of galactic magnetic fields

    International Nuclear Information System (INIS)

    An analytic model for evolution of galactic magnetic fields in hierarchical galaxy formation frameworks is introduced. Its major innovative components include explicit and detailed treatment of the physics of merger events, mass gains and losses, gravitational energy sources and delays associated with formation of large-scale magnetic fields. This paper describes the model, its implementation, and core results obtained by its means

  7. Mathematical Modeling of Chemical Stoichiometry

    Science.gov (United States)

    Croteau, Joshua; Fox, William P.; Varazo, Kristofoland

    2007-01-01

    In beginning chemistry classes, students are taught a variety of techniques for balancing chemical equations. The most common method is inspection. This paper addresses using a system of linear mathematical equations to solve for the stoichiometric coefficients. Many linear algebra books carry the standard balancing of chemical equations as an…

  8. Mathematical models of ecology and evolution

    DEFF Research Database (Denmark)

    Zhang, Lai

    2012-01-01

    dynamics but as a trade-o promotes species survival by shortening juvenile delay between birth and the onset of reproduction. Paper II compares the size-spectrum and food-web representations of communities using two traits (body size and habitat location) based unstructured population model of Lotka......) based size-structured population model, that is, interference in foraging, maintenance, survival, and recruitment. Their impacts on the ecology and evolution of size-structured populations and communities are explored. Ecologically, interference aects population demographic properties either negatively...... interference mechanisms, survival interference is more likely to produce large communities with complex trophic patterns through gradual evolution and successive speciation...

  9. A stochastic model of evolution

    CERN Document Server

    Guiol, Herve; Schinazi, Rinaldo B

    2009-01-01

    We propose an alternative to the Bak-Sneppen model for species survival. In our model the number of species is random. Births and deaths occur with constant probabilities and it is only the species with lowest fitness which is removed. We show that there is a sharp phase transition when the birth probability is larger than the death probability. The set of species with fitness higher than a certain critical value approach an uniform distribution. On the other hand the species with fitness less than the critical disappear after a finite (random) time.

  10. FAME: Face Association through Model Evolution

    OpenAIRE

    Golge, Eren; Duygulu, Pinar

    2014-01-01

    We attack the problem of learning face models for public faces from weakly-labelled images collected from web through querying a name. The data is very noisy even after face detection, with several irrelevant faces corresponding to other people. We propose a novel method, Face Association through Model Evolution (FAME), that is able to prune the data in an iterative way, for the face models associated to a name to evolve. The idea is based on capturing discriminativeness and representativenes...

  11. A simple and general method for solving detailed chemical evolution with delayed production of iron and other chemical elements

    OpenAIRE

    Vincenzo, Fiorenzo; Matteucci, Francesca; Spitoni, Emanuele

    2016-01-01

    In this Letter, we present a new theoretical method for solving the chemical evolution of galaxies, by assuming the instantaneous recycling approximation for chemical elements restored by massive stars and the Delay Time Distribution formalism for the delayed chemical enrichment by Type Ia Supernovae. The galaxy gas mass assembly history, together with the assumed stellar yields and initial mass function, represent the starting point of this method. We derive a very simple and general equatio...

  12. Chemical reactor modeling multiphase reactive flows

    CERN Document Server

    Jakobsen, Hugo A

    2014-01-01

    Chemical Reactor Modeling closes the gap between Chemical Reaction Engineering and Fluid Mechanics.  The second edition consists of two volumes: Volume 1: Fundamentals. Volume 2: Chemical Engineering Applications In volume 1 most of the fundamental theory is presented. A few numerical model simulation application examples are given to elucidate the link between theory and applications. In volume 2 the chemical reactor equipment to be modeled are described. Several engineering models are introduced and discussed. A survey of the frequently used numerical methods, algorithms and schemes is provided. A few practical engineering applications of the modeling tools are presented and discussed. The working principles of several experimental techniques employed in order to get data for model validation are outlined. The monograph is based on lectures regularly taught in the fourth and fifth years graduate courses in transport phenomena and chemical reactor modeling, and in a post graduate course in modern reactor m...

  13. Modeling Microscopic Chemical Sensors in Capillaries

    CERN Document Server

    Hogg, Tad

    2008-01-01

    Nanotechnology-based microscopic robots could provide accurate in vivo measurement of chemicals in the bloodstream for detailed biological research and as an aid to medical treatment. Quantitative performance estimates of such devices require models of how chemicals in the blood diffuse to the devices. This paper models microscopic robots and red blood cells (erythrocytes) in capillaries using realistic distorted cell shapes. The models evaluate two sensing scenarios: robots moving with the cells past a chemical source on the vessel wall, and robots attached to the wall for longer-term chemical monitoring. Using axial symmetric geometry with realistic flow speeds and diffusion coefficients, we compare detection performance with a simpler model that does not include the cells. The average chemical absorption is quantitatively similar in both models, indicating the simpler model is an adequate design guide to sensor performance in capillaries. However, determining the variation in forces and absorption as cells...

  14. Chemical evolution of volatile organic compounds in the outflow of the Mexico City Metropolitan area

    Energy Technology Data Exchange (ETDEWEB)

    Apel, E.; Springston, S.; Karl, T.; Emmons, L.; Flocke, F.; Hills, A. J.; Madronich, S.; Lee-Taylor, J.; Fried, A.; Weibring, P.; Walega, J.; Richter, D., Tie, X.; Mauldin, L.; Campos, T.; Sive, B.; Kleinman, L.; Springston, S., Zaveri, R.; deGouw, J.; Zheng, J.; Zhang, R.; Rudolph, J.; Junkermann, W.; Riemer, D. D.

    2009-11-01

    The volatile organic compound (VOC) distribution in the Mexico City Metropolitan Area (MCMA) and its evolution as it is uplifted and transported out of the MCMA basin was studied during the 2006 MILAGRO/MIRAGE-Mex field campaign. The results show that in the morning hours in the city center, the VOC distribution is dominated by non-methane hydrocarbons (NMHCs) but with a substantial contribution from oxygenated volatile organic compounds (OVOCs), predominantly from primary emissions. Alkanes account for a large part of the NMHC distribution in terms of mixing ratios. In terms of reactivity, NMHCs also dominate overall, especially in the morning hours. However, in the afternoon, as the boundary layer lifts and air is mixed and aged within the basin, the distribution changes as secondary products are formed. The WRF-Chem (Weather Research and Forecasting with Chemistry) model and MOZART (Model for Ozone and Related chemical Tracers) were able to reproduce the general features of the daytime cycle of the VOC OH reactivity distribution showing that NMHCs dominate the distribution except in the afternoon hours and that the VOC OH reactivity peaks in the early morning due to high morning emissions from the city into a shallow boundary layer. The WRF-Chem and MOZART models showed higher reactivity than the experimental data during the nighttime cycle, perhaps indicating problems with the modeled nighttime boundary layer height. In addition, a plume was studied in which air was advected out of the MCMA and intercepted downwind with the DOE G1 on 18 March and the NCAR C130 one day later on 19 March. A number of identical species measured aboard each aircraft gave insight into the chemical evolution of the plume as it aged and was transported as far as 1000 km downwind. Ozone and many OVOCs were photochemically produced in the plume. The WRF-Chem and MOZART models were used to examine the spatial and temporal extent of the 19 March plume and to help interpret the OH

  15. Chemical evolution of volatile organic compounds in the outflow of the Mexico City Metropolitan area

    Directory of Open Access Journals (Sweden)

    W. Junkermann

    2009-11-01

    Full Text Available The volatile organic compound (VOC distribution in the Mexico City Metropolitan Area (MCMA and its evolution as it is uplifted and transported out of the MCMA basin was studied during the 2006 MILAGRO/MIRAGE-Mex field campaign. The results show that in the morning hours in the city center, the VOC distribution is dominated by non-methane hydrocarbons (NMHCs but with a substantial contribution from oxygenated volatile organic compounds (OVOCs, predominantly from primary emissions. Alkanes account for a large part of the NMHC distribution in terms of mixing ratios. In terms of reactivity, NMHCs also dominate overall, especially in the morning hours. However, in the afternoon, as the boundary layer lifts and air is mixed and aged within the basin, the distribution changes as secondary products are formed. The WRF-Chem (Weather Research and Forecasting with Chemistry model and MOZART (Model for Ozone and Related chemical Tracers were able to reproduce the general features of the daytime cycle of the VOC OH reactivity distribution showing that NMHCs dominate the distribution except in the afternoon hours and that the VOC OH reactivity peaks in the early morning due to high morning emissions from the city into a shallow boundary layer. The WRF-Chem and MOZART models showed higher reactivity than the experimental data during the nighttime cycle, perhaps indicating problems with the modeled nighttime boundary layer height. In addition, a plume was studied in which air was advected out of the MCMA and intercepted downwind with the DOE G1 on 18~March and the NCAR C130 one day later on 19~March. A number of identical species measured aboard each aircraft gave insight into the chemical evolution of the plume as it aged and was transported as far as 1000 km downwind. Ozone and many OVOCs were photochemically produced in the plume. The WRF-Chem and MOZART models were used to examine the spatial and temporal extent of the 19~March plume and to help interpret

  16. Chemical evolution of volatile organic compounds in the outflow of the Mexico City Metropolitan area

    Energy Technology Data Exchange (ETDEWEB)

    Apel, Eric; Emmons, L.; Karl, Thomas G.; Flocke, Frank M.; Hills, A. J.; Madronich, Sasha; Lee-Taylor, J.; Fried, Alan; Weibring, P.; Walega, J.; Richter, Dirk; Tie, X.; Mauldin, L.; Campos, Teresa; Weinheimer, Andrew J.; Knapp, David; Sive, B.; Kleinman, Lawrence I.; Springston, S.; Zaveri, Rahul A.; Ortega, John V.; Voss, Paul B.; Blake, D. R.; Baker, Angela K.; Warneke, Carsten; Welsh-Bon, Daniel; de Gouw, Joost A.; Zheng, J.; Zhang, Renyi; Rudolph, Jochen; Junkermann, W.; Riemer, D.

    2010-01-01

    The volatile organic compound (VOC) distribution in the Mexico City Metropolitan Area (MCMA) and its evolution as it is uplifted and transported out of the MCMA basin was studied during the 2006 MILAGRO/MIRAGE-Mex field campaign. The results show that in the morning hours in the city center, the VOC distribution is dominated by non-methane hydrocarbons (NMHCs) but with a substantial contribution from oxygenated volatile organic compounds (OVOCs), predominantly from primary emissions. Alkanes account for a large part of the NMHC distribution in terms of mixing ratios. In terms of reactivity, NMHCs also dominate overall, especially in the morning hours. However, in the afternoon, as the boundary layer lifts and air is mixed and aged within the basin, the distribution changes as secondary products are formed. The WRF-Chem (Weather Research and Forecasting with Chemistry) model and MOZART (Model for Ozone and Related chemical Tracers) were able to reproduce the general features of the daytime cycle of the VOC OH reactivity distribution showing that NMHCs dominate the distribution except in the afternoon hours and that the VOC OH reactivity peaks in the early morning due to high morning emissions from the city into a shallow boundary layer. The WRF-Chem and MOZART models showed higher reactivity than the experimental data during the nighttime cycle, perhaps indicating problems with the modeled nighttime boundary layer height. In addition, a plume was studied in which air was advected out of the MCMA and intercepted downwind with the DOE G1 on March 18 and the NCAR C130 one day later on March 19. A number of identical species measured aboard each aircraft gave insight into the chemical evolution of the plume as it aged and was transported as far as 1000 km downwind. Ozone and many OVOCs were photochemically produced in the plume. The WRF-Chem and MOZART models were used to examine the spatial and temporal extent of the March 19 plume and to help interpret the OH

  17. Modeling of microstructural evolution under irradiation

    International Nuclear Information System (INIS)

    Microstructural evolution under irradiation is an extremely complex phenomenon involving numerous interacting mechanisms which alter both the microstructure and microchemistry of structural alloys. Predictive procedures which correlate primary irradiation and material variables to microstructural response are needed to extrapolate from the imperfect data base, which will be available, to fusion reactor conditions. Clearly, a marriage between models and experiments is needed. Specific steps to achieving such a marriage in the form of composite correlation model analysis are outlined and some preliminary results presented. The strongly correlated nature of microstructural evolution is emphasized and it is suggested that rate theory models, resting on the principle of material balances and focusing on coupled point defect-microchemical segregation processes, may be a practical approach to correlation model development. (orig.)

  18. A Simple Model for the Evolution of Evolution

    CERN Document Server

    Fussy, S; Schwabl, H; Fussy, Siegfried; Groessing, Gerhard; Schwabl, Herbert

    1997-01-01

    A simple model of macroevolution is proposed exhibiting both the property of punctuated equilibrium and the dynamics of potentialities for different species to evolve towards increasingly higher complexity. It is based on the phenomenon of "fractal evolution" which has been shown to constitute a fundamental property of nonlinear discretized systems with one memory- or random-based feedback loop. The latter involves a basic "cognitive" function of each species given by the power of distinction of states within some predefined resolution. The introduction of a realistic background noise limiting the range of the feedback operation yields a pattern signature in fitness space with a distribution of temporal boost/mutation distances according to a randomized devil's staircase function. Introducing a further level in the hierarchy of the system's rules, the possibility of an adaptive evolutionary change of the resolution itself is implemented, thereby providing a time-dependent measure of the species' cognitive abi...

  19. Chemical evolution and the galactic habitable zone of M31 (the Andromeda Galaxy)

    CERN Document Server

    Carigi, L; Garcia-Rojas, J

    2012-01-01

    We have computed the Galactic Habitable Zones (GHZs) of the Andromeda galaxy (M31) based mainly, but not exclusively, on the probability of terrestrial planet formation, which depends on the metallicity (Z) of the interstellar medium. The GHZ was therefore obtained from a chemical evolution model built to reproduce a precise metallicity gradient in the galactic disk, [O/H](r) $ = -0.015 \\pm 0.003 dex kpc^{-1} x r(kpc) + 0.44 \\pm 0.04 dex $. This gradient is the most probable when intrinsic scatter is present in the observational data. The chemical evolution model predicted a higher star formation history in both the halo and disk components of M31 and a less efficient inside-out galactic formation, compared to those of the Milky Way. If we assumed that Earth-like planets form with a probability law that follows the Z distribution shown by stars with detected planets, the most probable GHZ with basic life is located between 6 and 17 kpc on planets with ages between 4.5 and 1 Gy, and the most probable GHZ with ...

  20. Global Models of Planet Formation and Evolution

    CERN Document Server

    Mordasini, C; Dittkrist, K -M; Jin, S; Alibert, Y

    2014-01-01

    Despite the increase in observational data on exoplanets, the processes that lead to the formation of planets are still not well understood. But thanks to the high number of known exoplanets, it is now possible to look at them as a population that puts statistical constraints on theoretical models. A method that uses these constraints is planetary population synthesis. Its key element is a global model of planet formation and evolution that directly predicts observable planetary properties based on properties of the natal protoplanetary disk. To do so, global models build on many specialized models that address one specific physical process. We thoroughly review the physics of the sub-models included in global formation models. The sub-models can be classified as models describing the protoplanetary disk (gas and solids), the (proto)planet (solid core, gaseous envelope, and atmosphere), and finally the interactions (migration and N-body interaction). We compare the approaches in different global models and id...

  1. A model for evolution and extinction

    CERN Document Server

    Roberts, B W; Roberts, Bruce W

    1995-01-01

    We present a model for evolution and extinction in large ecosystems. The model incorporates the effects of interactions between species and the influences of abiotic environmental factors. We study the properties of the model by approximate analytic solution and also by numerical simulation, and use it to make predictions about the distribution of extinctions and species lifetimes that we would expect to see in real ecosystems. It should be possible to test these predictions against the fossil record. The model indicates that a possible mechanism for mass extinction is the coincidence of a large coevolutionary avalanche in the ecosystem with a severe environmental disturbance.

  2. Fourth Symposium on Chemical Evolution and the Origin and Evolution of Life

    Science.gov (United States)

    Wharton, Robert A., Jr. (Editor); Andersen, Dale T. (Editor); Bzik, Sara E. (Editor); Rummel, John D. (Editor)

    1991-01-01

    This symposium was held at the NASA Ames Research Center, Moffett Field, California, July 24-27, 1990. The NASA exobiology investigators reported their recent research findings. Scientific papers were presented in the following areas: cosmic evolution of biogenic compounds, prebiotic evolution (planetary and molecular), early evolution of life (biological and geochemical), evolution of advanced life, solar system exploration, and the Search for Extraterrestrial Intelligence (SETI).

  3. Modeling Network Evolution Using Graph Motifs

    CERN Document Server

    Conway, Drew

    2011-01-01

    Network structures are extremely important to the study of political science. Much of the data in its subfields are naturally represented as networks. This includes trade, diplomatic and conflict relationships. The social structure of several organization is also of interest to many researchers, such as the affiliations of legislators or the relationships among terrorist. A key aspect of studying social networks is understanding the evolutionary dynamics and the mechanism by which these structures grow and change over time. While current methods are well suited to describe static features of networks, they are less capable of specifying models of change and simulating network evolution. In the following paper I present a new method for modeling network growth and evolution. This method relies on graph motifs to generate simulated network data with particular structural characteristic. This technique departs notably from current methods both in form and function. Rather than a closed-form model, or stochastic ...

  4. Computational modelling of evolution: ecosystems and language

    CERN Document Server

    Lipowski, Adam

    2008-01-01

    Recently, computational modelling became a very important research tool that enables us to study problems that for decades evaded scientific analysis. Evolutionary systems are certainly examples of such problems: they are composed of many units that might reproduce, diffuse, mutate, die, or in some cases for example communicate. These processes might be of some adaptive value, they influence each other and occur on various time scales. That is why such systems are so difficult to study. In this paper we briefly review some computational approaches, as well as our contributions, to the evolution of ecosystems and language. We start from Lotka-Volterra equations and the modelling of simple two-species prey-predator systems. Such systems are canonical example for studying oscillatory behaviour in competitive populations. Then we describe various approaches to study long-term evolution of multi-species ecosystems. We emphasize the need to use models that take into account both ecological and evolutionary processe...

  5. Modelling the sulphur chemistry evolution in Orion KL

    CERN Document Server

    Esplugues, G B; Goicoechea, J R; Cernicharo, J

    2014-01-01

    We study the sulphur chemistry evolution in the Orion KL along the gas and grain phases of the cloud. We investigate the processes that dominate the sulphur chemistry and to determine how physical and chemical parameters, such as the final star mass and the initial elemental abundances, influence the evolution of the hot core and of the surrounding outflows and shocked gas (the plateau). We independently modelled the chemistry evolution of both components using the time-dependent gas-grain model UCL_CHEM and considering two different phase calculations. Phase I starts with the collapsing cloud and the depletion of atoms and molecules onto grain surfaces. Phase II starts when a central protostar is formed and the evaporation from grains takes place. We show how the gas density, the gas depletion efficiency, the initial sulphur abundance, the shocked gas temperature and the different chemical paths on the grains leading to different reservoirs of sulphur on the mantles affect sulphur-bearing molecules at differ...

  6. Coulombic Models in Chemical Bonding.

    Science.gov (United States)

    Sacks, Lawrence J.

    1986-01-01

    Compares the coulumbic point charge model for hydrogen chloride with the valence bond model. It is not possible to assign either a nonpolar or ionic canonical form of the valence bond model, while the covalent-ionic bond distribution does conform to the point charge model. (JM)

  7. The origin of nitrogen and the chemical evolution of spiral galaxies

    OpenAIRE

    Angeles I. Díaz; Tosi, M.

    1986-01-01

    This is an electronic version of an article published in Astronomy and Astrophysics. Diaz, A.I. and M. Tosi. The origin of nitrogen and the chemical evolution of spiral galaxies. Astronomy and Astrophysics 158 (1986): 60-66

  8. Chemodynamical Modelling of Galaxy Formation and Evolution

    CERN Document Server

    Berczik, P; Theis, C; Spurzem, R; Theis, Ch.

    2002-01-01

    We present our recently developed 3-dimensional chemodynamical code for galaxy evolution. This code follows the evolution of different galactic components like stars, dark matter and different components of the interstellar medium (ISM), i.e. a diffuse gaseous phase and the molecular clouds. Stars and dark matter are treated as collisionless N-body systems. The ISM is numerically described by a smoothed particle hydrodynamics (SPH) approach for the diffuse gas and a sticky particle scheme for the molecular clouds. Additionally, the galactic components are coupled by several phase transitions like star formation, stellar death or condensation and evaporation processes within the ISM. As an example we show the dynamical and chemical evolution of a star forming dwarf galaxy with a total baryonic mass of $2 \\cdot 10^9 M_\\odot$. After a moderate collapse phase the stars and the molecular clouds follow an exponential radial distribution, whereas the diffuse gas shows a central depression as a result of stellar feed...

  9. Chemical equilibrium modeling of detonation

    Energy Technology Data Exchange (ETDEWEB)

    Fried, Laurence E. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Bastea, Sorin [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2010-05-19

    Energetic materials are unique for having a strong exothermic reactivity, which has made them desirable for both military and commercial applications. Energetic materials are commonly divided into high explosives, propellants, and pyrotechnics. We will focus on high explosive (HE) materials here, although there is a great deal of commonality between the classes of energetic materials. Furthermore the history of HE materials is long, their condensed-phase chemical properties are poorly understood.

  10. Engineered Barrier System: Physical and Chemical Environment Model

    Energy Technology Data Exchange (ETDEWEB)

    D. M. Jolley; R. Jarek; P. Mariner

    2004-02-09

    The conceptual and predictive models documented in this Engineered Barrier System: Physical and Chemical Environment Model report describe the evolution of the physical and chemical conditions within the waste emplacement drifts of the repository. The modeling approaches and model output data will be used in the total system performance assessment (TSPA-LA) to assess the performance of the engineered barrier system and the waste form. These models evaluate the range of potential water compositions within the emplacement drifts, resulting from the interaction of introduced materials and minerals in dust with water seeping into the drifts and with aqueous solutions forming by deliquescence of dust (as influenced by atmospheric conditions), and from thermal-hydrological-chemical (THC) processes in the drift. These models also consider the uncertainty and variability in water chemistry inside the drift and the compositions of introduced materials within the drift. This report develops and documents a set of process- and abstraction-level models that constitute the engineered barrier system: physical and chemical environment model. Where possible, these models use information directly from other process model reports as input, which promotes integration among process models used for total system performance assessment. Specific tasks and activities of modeling the physical and chemical environment are included in the technical work plan ''Technical Work Plan for: In-Drift Geochemistry Modeling'' (BSC 2004 [DIRS 166519]). As described in the technical work plan, the development of this report is coordinated with the development of other engineered barrier system analysis model reports.

  11. Comparison of skid resistance evolution models

    OpenAIRE

    Cerezo, Véronique; Do, Minh Tan; Kane, Malal

    2012-01-01

    This paper presents results of a research aiming at modeling the evolution of road surface skid resistance using statistical and phenomenological approaches. Data are provided by a database composed of measurements collected on French roads during ten years: skid resistance values (Sideway Force Coefficient measured by SCRIM machine), macrotexture values (Mean Profile Depth), road geometry, traffic and age. Principal component analyses determine the connection between relevant factors. Analys...

  12. Microstructural and continuum evolution modeling of sintering.

    Energy Technology Data Exchange (ETDEWEB)

    Braginsky, Michael V.; Olevsky, Eugene A. (San Diego State University, San Diego, CA); Johnson, D. Lynn (Northwest University, Evanston, IL); Tikare, Veena; Garino, Terry J.; Arguello, Jose Guadalupe, Jr.

    2003-12-01

    All ceramics and powder metals, including the ceramics components that Sandia uses in critical weapons components such as PZT voltage bars and current stacks, multi-layer ceramic MET's, ahmindmolybdenum & alumina cermets, and ZnO varistors, are manufactured by sintering. Sintering is a critical, possibly the most important, processing step during manufacturing of ceramics. The microstructural evolution, the macroscopic shrinkage, and shape distortions during sintering will control the engineering performance of the resulting ceramic component. Yet, modeling and prediction of sintering behavior is in its infancy, lagging far behind the other manufacturing models, such as powder synthesis and powder compaction models, and behind models that predict engineering properties and reliability. In this project, we developed a model that was capable of simulating microstructural evolution during sintering, providing constitutive equations for macroscale simulation of shrinkage and distortion during sintering. And we developed macroscale sintering simulation capability in JAS3D. The mesoscale model can simulate microstructural evolution in a complex powder compact of hundreds or even thousands of particles of arbitrary shape and size by 1. curvature-driven grain growth, 2. pore migration and coalescence by surface diffusion, 3. vacancy formation, grain boundary diffusion and annihilation. This model was validated by comparing predictions of the simulation to analytical predictions for simple geometries. The model was then used to simulate sintering in complex powder compacts. Sintering stress and materials viscous module were obtained from the simulations. These constitutive equations were then used by macroscopic simulations for simulating shrinkage and shape changes in FEM simulations. The continuum theory of sintering embodied in the constitutive description of Skorohod and Olevsky was combined with results from microstructure evolution simulations to model shrinkage

  13. Minimal model for genome evolution and growth

    CERN Document Server

    Hsieh, L C; Ji, F M; Lee, H C

    2002-01-01

    Textual analysis of typical microbial genomes reveals that they have the statistical characteristics of a DNA sequence of a much shorter length. This peculiar property supports an evolutionary model in which a genome evolves by random mutation but primarily grows by random segmental self-copying. That genomes grew mostly by self-copying is consistent with the observation that repeat sequences in all genomes are widespread and intragenomic and intergenomic homologous genes are preponderance across all life forms. The model predicates the coexistence of the two competing modes of evolution: the gradual changes of classical Darwinism and the stochastic spurts envisioned in ``punctuated equilibrium''.

  14. Brand Equity Evolution: a System Dynamics Model

    Directory of Open Access Journals (Sweden)

    Edson Crescitelli

    2009-04-01

    Full Text Available One of the greatest challenges in brand management lies in monitoring brand equity over time. This paper aimsto present a simulation model able to represent this evolution. The model was drawn on brand equity concepts developed by Aaker and Joachimsthaler (2000, using the system dynamics methodology. The use ofcomputational dynamic models aims to create new sources of information able to sensitize academics and managers alike to the dynamic implications of their brand management. As a result, an easily implementable model was generated, capable of executing continuous scenario simulations by surveying casual relations among the variables that explain brand equity. Moreover, the existence of a number of system modeling tools will allow extensive application of the concepts used in this study in practical situations, both in professional and educational settings

  15. Chemical Kinetic Modeling of Advanced Transportation Fuels

    Energy Technology Data Exchange (ETDEWEB)

    PItz, W J; Westbrook, C K; Herbinet, O

    2009-01-20

    Development of detailed chemical kinetic models for advanced petroleum-based and nonpetroleum based fuels is a difficult challenge because of the hundreds to thousands of different components in these fuels and because some of these fuels contain components that have not been considered in the past. It is important to develop detailed chemical kinetic models for these fuels since the models can be put into engine simulation codes used for optimizing engine design for maximum efficiency and minimal pollutant emissions. For example, these chemistry-enabled engine codes can be used to optimize combustion chamber shape and fuel injection timing. They also allow insight into how the composition of advanced petroleum-based and non-petroleum based fuels affect engine performance characteristics. Additionally, chemical kinetic models can be used separately to interpret important in-cylinder experimental data and gain insight into advanced engine combustion processes such as HCCI and lean burn engines. The objectives are: (1) Develop detailed chemical kinetic reaction models for components of advanced petroleum-based and non-petroleum based fuels. These fuels models include components from vegetable-oil-derived biodiesel, oil-sand derived fuel, alcohol fuels and other advanced bio-based and alternative fuels. (2) Develop detailed chemical kinetic reaction models for mixtures of non-petroleum and petroleum-based components to represent real fuels and lead to efficient reduced combustion models needed for engine modeling codes. (3) Characterize the role of fuel composition on efficiency and pollutant emissions from practical automotive engines.

  16. Optimal evolution models for quantum tomography

    International Nuclear Information System (INIS)

    The research presented in this article concerns the stroboscopic approach to quantum tomography, which is an area of science where quantum physics and linear algebra overlap. In this article we introduce the algebraic structure of the parametric-dependent quantum channels for 2-level and 3-level systems such that the generator of evolution corresponding with the Kraus operators has no degenerate eigenvalues. In such cases the index of cyclicity of the generator is equal to 1, which physically means that there exists one observable the measurement of which performed a sufficient number of times at distinct instants provides enough data to reconstruct the initial density matrix and, consequently, the trajectory of the state. The necessary conditions for the parameters and relations between them are introduced. The results presented in this paper seem to have considerable potential applications in experiments due to the fact that one can perform quantum tomography by conducting only one kind of measurement. Therefore, the analyzed evolution models can be considered optimal in the context of quantum tomography. Finally, we introduce some remarks concerning optimal evolution models in the case of n-dimensional Hilbert space. (paper)

  17. Optimal evolution models for quantum tomography

    Science.gov (United States)

    Czerwiński, Artur

    2016-02-01

    The research presented in this article concerns the stroboscopic approach to quantum tomography, which is an area of science where quantum physics and linear algebra overlap. In this article we introduce the algebraic structure of the parametric-dependent quantum channels for 2-level and 3-level systems such that the generator of evolution corresponding with the Kraus operators has no degenerate eigenvalues. In such cases the index of cyclicity of the generator is equal to 1, which physically means that there exists one observable the measurement of which performed a sufficient number of times at distinct instants provides enough data to reconstruct the initial density matrix and, consequently, the trajectory of the state. The necessary conditions for the parameters and relations between them are introduced. The results presented in this paper seem to have considerable potential applications in experiments due to the fact that one can perform quantum tomography by conducting only one kind of measurement. Therefore, the analyzed evolution models can be considered optimal in the context of quantum tomography. Finally, we introduce some remarks concerning optimal evolution models in the case of n-dimensional Hilbert space.

  18. Biomass torrefaction: modeling of volatile and solid product evolution kinetics.

    Science.gov (United States)

    Bates, Richard B; Ghoniem, Ahmed F

    2012-11-01

    The aim of this work is the development of a kinetics model for the evolution of the volatile and solid product composition during torrefaction conditions between 200 and 300°C. Coupled to an existing two step solid mass loss kinetics mechanism, this model describes the volatile release kinetics in terms of a set of identifiable chemical components, permitting the solid product composition to be estimated by mass conservation. Results show that most of the volatiles released during the first stage include highly oxygenated species such as water, acetic acid, and carbon dioxide, while volatiles released during the second step are composed primarily of lactic acid, methanol, and acetic acid. This kinetics model will be used in the development of a model to describe reaction energy balance and heat release dynamics.

  19. Geochemical modelling study on the age and evolution of the groundwater at the Romuvaara site

    Energy Technology Data Exchange (ETDEWEB)

    Pitkaenen, P.; Vuorinen, U.; Leino-Forsman, H. [Technical Research Centre of Finland, Espoo (Finland); Snellman, M. [Imatran Voima Oy, Helsinki (Finland)

    1996-09-01

    The objective of the study was to interpret the processes and factors which control the hydrogeochemistry (e.g. pH and redox conditions) in the radioactive waste disposal environment. A model of the hydrogeochemical evolution and the chemical flowpaths in different parts of the bedrock at the Romuvaara (in Finland) site has been created. The significance of chemical reactions along different flowpaths is calculated. Furthermore, the consistency of the hydrogeochemical model and the hydrogeological model is examined. (107 refs.).

  20. Geochemical modelling study on the age and evolution of the groundwater at the Romuvaara site

    International Nuclear Information System (INIS)

    The objective of the study was to interpret the processes and factors which control the hydrogeochemistry (e.g. pH and redox conditions) in the radioactive waste disposal environment. A model of the hydrogeochemical evolution and the chemical flowpaths in different parts of the bedrock at the Romuvaara (in Finland) site has been created. The significance of chemical reactions along different flowpaths is calculated. Furthermore, the consistency of the hydrogeochemical model and the hydrogeological model is examined. (107 refs.)

  1. Statistics of Certain Models of Evolution

    CERN Document Server

    Standish, R K

    1999-01-01

    In a recent paper, Newman surveys the literature on power law spectra in evolution, self-organised criticality and presents a model of his own to arrive at a conclusion that self-organised criticality is not necessary for evolution. Not only did he miss a key model (Ecolab) that has a clear self-organised critical mechanism, but also Newman's model exhibits the same mechanism that gives rise to power law behaviour as does Ecolab. I would argue that this mechanism should be described as self-organised critical. In this paper, I have also implemented Newman's model using the Ecolab software, removing the restriction that the number of species remains constant. It turns out that the requirement of constant species number is non-trivial, leading to a global coupling between species that is similar in effect to the species interactions seen in Ecolab. In fact, the model must self-organise to a state where the long time average of speciations balances that of the extinctions, otherwise the system either collapses o...

  2. Testing spherical evolution for modelling void abundances

    Science.gov (United States)

    Achitouv, Ixandra; Neyrinck, Mark; Paranjape, Aseem

    2015-08-01

    We compare analytical predictions of void volume functions to those measured from N-body simulations, detecting voids with the ZOBOV void finder. We push to very small, non-linear voids, below few Mpc radius, by considering the unsampled dark matter density field. We also study the case where voids are identified using haloes. We develop analytical formula for the void abundance of both the excursion set approach and the peaks formalism. These formulas are valid for random walks smoothed with a top-hat filter in real space, with a large class of realistic barrier models. We test the extent to which the spherical evolution approximation, which forms the basis of the analytical predictions, models the highly aspherical voids that occur in the cosmic web, and are found by a watershed-based algorithm such as ZOBOV. We show that the volume function returned by ZOBOV is quite sensitive to the choice of treatment of subvoids, a fact that has not been appreciated previously. For reasonable choices of subvoid exclusion, we find that the Lagrangian density δv of the ZOBOV voids - which is predicted to be a constant δv ≈ -2.7 in the spherical evolution model - is different from the predicted value, showing substantial scatter and scale dependence. This result applies to voids identified at z = 0 with effective radius between 1 and 10 h-1 Mpc. Our analytical approximations are flexible enough to give a good description of the resulting volume function; however, this happens for choices of parameter values that are different from those suggested by the spherical evolution assumption. We conclude that analytical models for voids must move away from the spherical approximation in order to be applied successfully to observations, and we discuss some possible ways forward.

  3. Galactic Chemical Evolution and the Oxygen Isotopic Composition of the Solar System

    CERN Document Server

    Nittler, Larry R

    2012-01-01

    We review current observational and theoretical constraints on the Galactic chemical evolution (GCE) of oxygen isotopes in order to explore whether GCE plays a role in explaining the lower 17O/18O ratio of the Sun, relative to the present-day interstellar medium, or the existence of distinct 16O-rich and 16O-poor reservoirs in the Solar System. Although the production of both 17O and 18O are related to the metallicity of progenitor stars, 17O is most likely produced in stars that evolve on longer timescales than those that produce 18O. Therefore the 17O/18O ratio need not have remained constant over time, contrary to preconceptions and the simplest models of GCE. An apparent linear, slope-one correlation between delta17O and delta18O in the ISM need not necessarily reflect an O isotopic gradient, and any slope-one galactocentric gradient need not correspond to evolution in time. Instead, increasing 17O/18O is consistent both with observational data from molecular clouds and with modeling of the compositions o...

  4. Prebiotic coordination chemistry: The potential role of transition-metal complexes in the chemical evolution

    Science.gov (United States)

    Beck, M.

    1979-01-01

    In approaching the extremely involved and complex problem of the origin of life, consideration of the coordination chemistry appeared not only as a possibility but as a necessity. The first model experiments appear to be promising because of prebiotic-type synthesis by means of transition-metal complexes. It is especially significant that in some instances various types of vitally important substances (nucleic bases, amino acids) are formed simultaneously. There is ground to hope that systematic studies in this field will clarify the role of transition-metal complexes in the organizatorial phase of chemical evolution. It is obvious that researchers working in the fields of the chemistry of cyano and carbonyl complexes, and of the catalytic effect of transition-metal complexes are best suited to study these aspects of the attractive and interesting problem of the origin of life.

  5. Chemical communication: a jewel sheds light on signal evolution.

    Science.gov (United States)

    Lassance, Jean-Marc; Löfstedt, Christer

    2013-05-01

    When others show sexy tails or sing elaborate songs, many animals use the language of chemistry to attract potential mates. A study provides insights into the evolutionary conundrum of how new chemical signals can evolve in an established communication system. PMID:23660353

  6. Chemical Evolution and the Galactic Habitable Zone of M31

    NARCIS (Netherlands)

    Carigi, Leticia; Garcia-Rojas, Jorge; Meneses-Goytia, Sofia

    2013-01-01

    We have computed the Galactic Habitable Zones (GHZs) of the Andromeda galaxy (M31) based on the probability of terrestrial planet formation, which depends on the metallicity (Z) of the interstellar medium, and the number of stars formed per unit surface area. The GHZ was obtained from a chemical evo

  7. Influence of Population III stars on cosmic chemical evolution

    OpenAIRE

    Rollinde, E.; Vangioni, E.; Maurin, D.; Olive, K. A.; Daigne, F.; Silk, J.; Vincent, F.

    2008-01-01

    New observations from the Hubble ultra deep field suggest that the star formation rate at z>7 drops off faster than previously thought. Using a newly determined star formation rate for the normal mode of Population II/I stars (PopII/I), including this new constraint, we compute the Thomson scattering optical depth and find a result that is marginally consistent with WMAP5 results. We also reconsider the role of Population III stars (PopIII) in light of cosmological and stellar evolution const...

  8. Testing spherical evolution for modelling void abundances

    CERN Document Server

    Achitouv, Ixandra; Paranjape, Aseem

    2013-01-01

    We compute analytical predictions for the volume function of voids based on the excursion set approach and the peaks formalism for random walks smoothed with a top-hat filter in real space and a large class of realistic barrier models. We test our prediction by comparing with voids identified in the dark matter density field in N-body simulations using the ZOBOV void finder. This tests the extent to which the spherical evolution approximation, which forms the basis of the analytical predictions, models the highly aspherical voids that occur in the cosmic web, and are found by a watershed-based algorithm such as ZOBOV. We show that the volume function returned by ZOBOV is quite sensitive to the choice of treatment of sub-voids, a fact that has not been appreciated previously. For reasonable choices of sub-void exclusion, we find that the Lagrangian density deltav of the ZOBOV voids -- which is predicted to be a constant deltav=-2.7 in the spherical evolution model -- is quite different from the predicted value...

  9. Culinary evolution models for Indian cuisines

    CERN Document Server

    Jain, Anupam

    2015-01-01

    Culinary systems, the practice of preparing a refined combination of ingredients that is palatable as well as socially acceptable, are examples of complex dynamical systems. They evolve over time and are affected by a large number of factors. Modeling the dynamic nature of evolution of regional cuisines may provide us a quantitative basis and exhibit underlying processes that have driven them into the present day status. This is especially important given that the potential culinary space is practically infinite because of possible number of ingredient combinations as recipes. Such studies also provide a means to compare and contrast cuisines and to unearth their therapeutic value. Herein we provide rigorous analysis of modeling eight diverse Indian regional cuisines, while also highlighting their uniqueness, and a comparison among those models at the level of flavor compounds which opens up molecular level studies associating them especially with non-communicable diseases such as diabetes.

  10. Late stages of the evolution of A-type stars on the main sequence: comparison between observed chemical abundances and diffusion models for 8 Am stars of the Praesepe cluster

    CERN Document Server

    Fossati, L; Monier, R; Khan, S A; Kochukhov, O; Landstreet, J; Wade, G; Weiss, W

    2007-01-01

    Aims. We aim to provide observational constraints on diffusion models that predict peculiar chemical abundances in the atmospheres of Am stars. We also intend to check if chemical peculiarities and slow rotation can be explained by the presence of a weak magnetic field. Methods. We have obtained high resolution, high signal-to-noise ratio spectra of eight previously-classified Am stars, two normal A-type stars and one Blue Straggler, considered to be members of the Praesepe cluster. For all of these stars we have determined fundamental parameters and photospheric abundances for a large number of chemical elements, with a higher precision than was ever obtained before for this cluster. For seven of these stars we also obtained spectra in circular polarization and applied the LSD technique to constrain the longitudinal magnetic field. Results. No magnetic field was detected in any of the analysed stars. HD 73666, a Blue Straggler previously considered as an Ap (Si) star, turns out to have the abundances of a no...

  11. Mathematical modeling a chemical engineer's perspective

    CERN Document Server

    Rutherford, Aris

    1999-01-01

    Mathematical modeling is the art and craft of building a system of equations that is both sufficiently complex to do justice to physical reality and sufficiently simple to give real insight into the situation. Mathematical Modeling: A Chemical Engineer's Perspective provides an elementary introduction to the craft by one of the century's most distinguished practitioners.Though the book is written from a chemical engineering viewpoint, the principles and pitfalls are common to all mathematical modeling of physical systems. Seventeen of the author's frequently cited papers are reprinted to illus

  12. The Chemical and Dynamical Evolution of Isolated Dwarf Galaxies

    OpenAIRE

    Pilkington, K.; Gibson, B. K.; Calura, F; Stinson, G.S.; Brook, C. B.; Brooks, A.

    2011-01-01

    Using a suite of simulations (Governato et al. 2010) which successfully produce bulgeless (dwarf) disk galaxies, we provide an analysis of their associated cold interstellar media (ISM) and stellar chemical abundance patterns. A preliminary comparison with observations is undertaken, in order to assess whether the properties of the cold gas and chemistry of the stellar components are recovered successfully. To this end, we have extracted the radial and vertical gas density profiles, neutral h...

  13. Chemical Evolution in the Interstellar Medium: From Astrochemistry to Astrobiology

    Science.gov (United States)

    Allamandola, Louis J.

    2009-01-01

    Great strides have been made in our understanding of interstellar material thanks to advances in infrared astronomy and laboratory astrophysics. Ionized polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by earlier astrochemical standards, are widespread and very abundant throughout much of the Universe. In cold molecular clouds, the birthplace of planets and stars, interstellar molecules freeze onto dust and ice particles forming mixed molecular ices dominated by simple species such as water, methanol, ammonia, and carbon monoxide. Within these clouds, and especially in the vicinity of star and planet forming regions, these ices and PAHs are processed by ultraviolet light and cosmic rays forming hundreds of far more complex species, some of biogenic interest. Eventually, these are delivered to primordial planets by comets and meteorites. Astrochemical evolution, highlights of this field from a chemist's perspective, and the astronomer's infrared toolbox will be reviewed.

  14. Nematode model systems in evolution and development.

    Science.gov (United States)

    Sommer, Ralf J; Bumbarger, Daniel J

    2012-01-01

    The free-living nematode Caenorhabditis elegans is one of the most important model organisms in all areas of modern biology. Using the knowledge about C. elegans as a baseline, nematodes are now intensively studied in evolution and development. Evolutionary developmental biology or for short, 'evo-devo' has been developed as a new research discipline during the last two decades to investigate how changes in developmental processes and mechanisms result in the modification of morphological structures and phenotypic novelty. In this article, we review the concepts that make nematode evo-devo a successful approach to evolutionary biology. We introduce selected model systems for nematode evo-devo and provide a detailed discussion of four selected case studies. The most striking finding of nematode evo-devo is the magnitude of developmental variation in the context of a conserved body plan. Detailed investigation of early embryogenesis, gonad formation, vulva development, and sex determination revealed that molecular mechanisms evolve rapidly, often in the context of a conserved body plan. These studies highlight the importance of developmental systems drift and neutrality in evolution. PMID:23801489

  15. Change-centric Model for Web Service Evolution

    OpenAIRE

    Zuo, Wei; Aïcha-Nabila, Benharkat; Amghar, Youssef

    2014-01-01

    International audience; —Web service is subject to frequent changes during its lifecycle. Web service evolution is a widely discussed topic. Many related problems have also been generated from Web service evolution such as Web service adaptation, Web service versioning and Web service change management. To treat with these issues efficiently, a complete evolution model for Web service should be built. In this paper, we introduce our change-centric model for Web service evolution and how we us...

  16. Genealogies in simple models of evolution

    International Nuclear Information System (INIS)

    We review the statistical properties of the genealogies of a few models of evolution. In the asexual case, selection leads to coalescence times which grow logarithmically with the size of the population, in contrast with the linear growth of the neutral case. Moreover for a whole class of models, the statistics of the genealogies are those of the Bolthausen–Sznitman coalescent rather than the Kingman coalescent in the neutral case. For sexual reproduction in the neutral case, the time to reach the first common ancestors for the whole population and the time for all individuals to have all their ancestors in common are also logarithmic in the population size, as predicted by Chang in 1999. We discuss how these times are modified by introducing selection in a simple way. (paper)

  17. Recent advances in chemical evolution and the origins of life

    Science.gov (United States)

    Oro, John; Lazcano, Antonio

    1992-01-01

    Consideration is given to the ideas of Oparin and Haldane who independently suggested more than 60 years ago that the first forms of life were anaerobic, heterotrophic bacteria that emerged as the result of a long period of chemical abiotic synthesis of organic compounds. It is suggested that at least some requirements for life are met in the Galaxy due to the cosmic abundance of carbon, nitrogen, oxygen, and other biogenic elements; the existence of extraterrestrial organic compounds; and the processes of stellar and interstellar planetary formation.

  18. Radiative transfer modeling of surface chemical deposits

    Science.gov (United States)

    Reichardt, Thomas A.; Kulp, Thomas J.

    2016-05-01

    Remote detection of a surface-bound chemical relies on the recognition of a pattern, or "signature," that is distinct from the background. Such signatures are a function of a chemical's fundamental optical properties, but also depend upon its specific morphology. Importantly, the same chemical can exhibit vastly different signatures depending on the size of particles composing the deposit. We present a parameterized model to account for such morphological effects on surface-deposited chemical signatures. This model leverages computational tools developed within the planetary and atmospheric science communities, beginning with T-matrix and ray-tracing approaches for evaluating the scattering and extinction properties of individual particles based on their size and shape, and the complex refractive index of the material itself. These individual-particle properties then serve as input to the Ambartsumian invariant imbedding solution for the reflectance of a particulate surface composed of these particles. The inputs to the model include parameters associated with a functionalized form of the particle size distribution (PSD) as well as parameters associated with the particle packing density and surface roughness. The model is numerically inverted via Sandia's Dakota package, optimizing agreement between modeled and measured reflectance spectra, which we demonstrate on data acquired on five size-selected silica powders over the 4-16 μm wavelength range. Agreements between modeled and measured reflectance spectra are assessed, while the optimized PSDs resulting from the spectral fitting are then compared to PSD data acquired from independent particle size measurements.

  19. Evolution of species from Darwin theory: A simple model

    Science.gov (United States)

    Moret, M. A.; Pereira, H. B. B.; Monteiro, S. L.; Galeão, A. C.

    2012-04-01

    Evolution of species is a complex phenomenon. Some theoretical models take into account evolution of species, like the Bak-Sneppen model that obtain punctuated equilibrium from self-organized criticality and the Penna model for biological aging that consists in a bit-string model subjected to aging, reproduction and death. In this work we propose a simple model to study different scenarios used to simulate the evolution of species. This model is based on Darwin's ideas of evolution. The present findings show that punctuated equilibria and stasis seem to be obtained directly from the mutation, selection of parents and the genetic crossover, and are very close to the fossil data analysis.

  20. Coupling Landform Evolution and Soil Pedogenesis - Initial Results From the SSSPAM5D Model

    Science.gov (United States)

    Willgoose, G. R.; Welivitiya, W. D. D. P.; Hancock, G. R.; Cohen, S.

    2015-12-01

    Evolution of soil on a dynamic landform is a crucial next step in landscape evolution modelling. Some attempts have been taken such as MILESD by Vanwalleghem et al. to develop a first model which is capable of simultaneously evolving both the soil profile and the landform. In previous work we have presented physically based models for soil pedogenesis, mARM and SSSPAM. In this study we present the results of coupling a landform evolution model with our SSSPAM5D soil pedogenesis model. In previous work the SSSPAM5D soil evolution model was used to identify trends of the soil profile evolution on a static landform. Two pedogenetic processes, namely (1) armouring due to erosion, and (2) physical and chemical weathering were used in those simulations to evolve the soil profile. By incorporating elevation changes (due to erosion and deposition) we have advanced the SSSPAM5D modelling framework into the realm of landscape evolution. Simulations have been run using elevation and soil grading data of the engineered landform (spoil heap) at the Ranger Uranium Mine, Northern Territory, Australia. The results obtained for the coupled landform-soil evolution simulations predict the erosion of high slope areas, development of rudimentary channel networks in the landform and deposition of sediments in lowland areas, and qualitatively consistent with landform evolution models on their own. Examination of the soil profile characteristics revealed that hill crests are weathering dominated and tend to develop a thick soil layer. The steeper hillslopes at the edge of the landform are erosion dominated with shallow soils while the foot slopes are deposition dominated with thick soil layers. The simulation results of our coupled landform and soil evolution model provide qualitatively correct and timely characterization of the soil evolution on a dynamic landscape. Finally we will compare the characteristics of erosion and deposition predicted by the coupled landform-soil SSSPAM

  1. Geologic and chemical evolution of volcan tepetiltic, Nayarit, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Deremer, L.A.; Nelson, S.A.

    1985-01-01

    Volcan Tepetiltic is located in the northwestern segment of the Mexican Volcanic Belt, about 40 km SW of the city of Tepic. The structure is a calc-alkaline stratovolcano composed primarily of andesite and dacite lava flows topped by an elliptical caldera measuring approximately 5 by 2.5 km. At least two cycles of andesite volcanism followed by rapid differentiation into volumetrically subordinate dacite flows and dikes built the majority of the complex. The second pulse of andesitic lavas were more basic than the first and appear to have been the result of reinjection of mafic magma into the shallow andesitic magma chamber. This was closely followed by the emplacement of two rhyolite domes and associated ash deposits on the eastern flank of the volcano. Finally, two small hornblende andesite domes were erupted on the floor of the caldera, and a lake formed in the northeastern corner of the caldera. Cinder cones on the flanks of the volcano have erupted alkaline lavas of mugearitic affinity. These are chemically unrelated to the calc-alkaline lavas erupted from Tepetiltic itself. The latest activity of Tepetiltic was the emplacement of a crystal rich rhyolite domes on the southern flank, which has blocked stream drainages to form a coulee lake. This last event has occurred within the last several thousand years. The rocks erupted from Tepetiltic form a chemically continuous suite which could have been derived through crystal fractionation of andesitic magma. No basic parental magmas, however, have erupted throughout the area.

  2. Merging binary black holes formed through chemically homogeneous evolution in short-period stellar binaries

    Science.gov (United States)

    Mandel, Ilya; de Mink, Selma E.

    2016-05-01

    We explore a newly proposed channel to create binary black holes of stellar origin. This scenario applies to massive, tight binaries where mixing induced by rotation and tides transports the products of hydrogen burning throughout the stellar envelopes. This slowly enriches the entire star with helium, preventing the build-up of an internal chemical gradient. The stars remain compact as they evolve nearly chemically homogeneously, eventually forming two black holes, which we estimate typically merge 4-11 Gyr after formation. Like other proposed channels, this evolutionary pathway suffers from significant theoretical uncertainties, but could be constrained in the near future by data from advanced ground-based gravitational-wave detectors. We perform Monte Carlo simulations of the expected merger rate over cosmic time to explore the implications and uncertainties. Our default model for this channel yields a local binary black hole merger rate of about 10 Gpc-3 yr-1 at redshift z = 0, peaking at twice this rate at z = 0.5. This means that this channel is competitive, in terms of expected rates, with the conventional formation scenarios that involve a common-envelope phase during isolated binary evolution or dynamical interaction in a dense cluster. The events from this channel may be distinguished by the preference for nearly equal-mass components and high masses, with typical total masses between 50 and 110 M⊙. Unlike the conventional isolated binary evolution scenario that involves shrinkage of the orbit during a common-envelope phase, short time delays are unlikely for this channel, implying that we do not expect mergers at high redshift.

  3. On the Galactic chemical evolution of sulphur. Sulphur abundances from the [S i] 1082 nm line in giants

    CERN Document Server

    Matrozis, E; Dupree, A K

    2013-01-01

    Context. The Galactic chemical evolution of sulphur is still under debate. At low metallicities some studies find no correlation between [S/Fe] and [Fe/H], others find [S/Fe] increasing towards lower metallicities, and still others find a combination of the two. Each scenario has different implications for the Galactic chemical evolution of sulphur. Aims. To contribute to the discussion on the Galactic chemical evolution of sulphur by deriving sulphur abundances from non-LTE insensitive spectral diagnostics in Disk and Halo stars with homogeneously determined stellar parameters. Methods. We derive Teff from photometric colours, logg from stellar isochrones and Bayesian estimation, and [Fe/H] and [S/Fe] from spectrum synthesis. We derive [S/Fe] from the [S i] 1082 nm line in 39 mostly cool and metal-poor giants, using 1D LTE MARCS model atmospheres to model our high-resolution NIR spectra obtained with the VLT, NOT and Gemini South telescopes. Results. We derive homogeneous stellar parameters for 29 stars. Our...

  4. Modelling Organisational Evolution and Change - a Complex Systems Modelling Perspective

    OpenAIRE

    Strathern, M.

    2008-01-01

    The cumulative output of these papers emphasise that modelling organisational evolution and change from a complex systems perspective makes a significant contribution to organisational studies and brings new insight and understandings both to theory and practice. It is also true that the studies and modelling presented in these papers has pushed forward the boundaries of complex systems science, again both in theory and practice. The papers have made new findings and underst...

  5. Modeling Co-evolution of Speech and Biology.

    Science.gov (United States)

    de Boer, Bart

    2016-04-01

    Two computer simulations are investigated that model interaction of cultural evolution of language and biological evolution of adaptations to language. Both are agent-based models in which a population of agents imitates each other using realistic vowels. The agents evolve under selective pressure for good imitation. In one model, the evolution of the vocal tract is modeled; in the other, a cognitive mechanism for perceiving speech accurately is modeled. In both cases, biological adaptations to using and learning speech evolve, even though the system of speech sounds itself changes at a more rapid time scale than biological evolution. However, the fact that the available acoustic space is used maximally (a self-organized result of cultural evolution) is constant, and therefore biological evolution does have a stable target. This work shows that when cultural and biological traits are continuous, their co-evolution may lead to cognitive adaptations that are strong enough to detect empirically.

  6. THE GALACTIC STRUCTURE AND CHEMICAL EVOLUTION TRACED BY THE POPULATION OF PLANETARY NEBULAE

    International Nuclear Information System (INIS)

    Planetary nebulae (PNe) derive from the evolution of ∼1-8 Msun mass stars, corresponding to a wide range of progenitor ages, and thus are essential probes of the chemical evolution of galaxies, and indispensable to constrain the results from chemical models. We use an extended and homogeneous data set of Galactic PNe to study the metallicity gradients and the Galactic structure and evolution. The most up-to-date abundances, distances (calibrated with Magellanic Cloud PNe), and other parameters have been employed, together with a novel homogeneous morphological classification, to characterize the different PN populations. We confirm that morphological classes have a strong correlation with Peimbert's type PN, and also with their distribution on the Galactic landscape. We studied the α-element distribution within the Galactic disk, and found that the best selected disk population (i.e., excluding bulge and halo component), together with the most reliable PN distance scale yields to a radial oxygen gradient of Δlog(O/H)/ΔRG = -0.023 ± 0.006 dex kpc-1 for the whole disk sample, and of Δlog(O/H)/ΔRG = -0.035 ± 0.024, -0.023 ± 0.005, and -0.011 ± 0.013 dex kpc-1, respectively for Type I, II, and III PNe, i.e., for high-, intermediate-, and low-mass progenitors. Neon gradients for the same PN types confirm the trend. Accurate statistical analysis shows moderately high uncertainties in the slopes, but also confirms the trend of steeper gradient for PNe with more massive progenitors, indicating a possible steepening with time of the Galactic disk metallicity gradient for what the α-elements are concerned. We found that the metallicity gradients are almost independent on the distance scale model used, as long as these scales are equally well calibrated with the Magellanic Clouds. The PN metallicity gradients presented here are consistent with the local metallicity distribution; furthermore, oxygen gradients determined with young and intermediate age PNe show good

  7. The 1st Symposium on Chemical Evolution and the Origin and Evolution of Life

    Science.gov (United States)

    Devincenzi, D. L. (Editor); Pleasant, L. G. (Editor)

    1982-01-01

    This symposium provided an opportunity for all NASA Exobiology principal investigators to present their most recent research in a scientific meeting forum. Papers were presented in the following exobiology areas: extraterrestrial chemistry primitive earth, information transfer, solar system exploration, planetary protection, geological record, and early biological evolution.

  8. Chemical Kinetic Modeling of 2-Methylhexane Combustion

    KAUST Repository

    Mohamed, Samah Y.

    2015-03-30

    Accurate chemical kinetic combustion models of lightly branched alkanes (e.g., 2-methylalkanes) are important for investigating the combustion behavior of diesel, gasoline, and aviation fuels. Improving the fidelity of existing kinetic models is a necessity, as new experiments and advanced theories show inaccuracy in certain portions of the models. This study focuses on updating thermodynamic data and kinetic model for a gasoline surrogate fuel, 2-methylhexane, with recently published group values and rate rules. These update provides a better agreement with rapid compression machine measurements of ignition delay time, while also strengthening the fundamental basis of the model.

  9. CYANAMIDE: A POSSIBLE KEY COMPOUND IN CHEMICAL EVOLUTION

    Energy Technology Data Exchange (ETDEWEB)

    Steinman, Gary; Lemmon, Richard M.; Calvin, Melvin

    1964-05-01

    The prebiotic synthesis of phosphorus-containing compounds--such as nucleotides and polynucleotides--would require both a geologically plausible source of the element and pathways for its incorporation into chemical systems on the primitive Earth. The mineral apatite, which is the only significant source of phosphate on Earth, has long been thought to be problematical in this respect due to its low solubility and reactivity. However, in the last decade or so, at least two pathways have been demonstrated which would circumvent these perceived problems. In addition, recent results would seem to suggest an additional, extraterrestrial source of reactive phosphorus. It appears that the 'phosphorus problem' is no longer the stumbling block which it was once thought to be.

  10. Modelling stratospheric chemistry in a global three-dimensional chemical transport model

    Energy Technology Data Exchange (ETDEWEB)

    Rummukainen, M. [Finnish Meteorological Inst., Sodankylae (Finland). Sodankylae Observatory

    1995-12-31

    Numerical modelling of atmospheric chemistry aims to increase the understanding of the characteristics, the behavior and the evolution of atmospheric composition. These topics are of utmost importance in the study of climate change. The multitude of gases and particulates making up the atmosphere and the complicated interactions between them affect radiation transfer, atmospheric dynamics, and the impacts of anthropogenic and natural emissions. Chemical processes are fundamental factors in global warming, ozone depletion and atmospheric pollution problems in general. Much of the prevailing work on modelling stratospheric chemistry has so far been done with 1- and 2-dimensional models. Carrying an extensive chemistry parameterisation in a model with high spatial and temporal resolution is computationally heavy. Today, computers are becoming powerful enough to allow going over to 3-dimensional models. In order to concentrate on the chemistry, many Chemical Transport Models (CTM) are still run off-line, i.e. with precalculated and archived meteorology and radiation. In chemistry simulations, the archived values drive the model forward in time, without interacting with the chemical evolution. This is an approach that has been adopted in stratospheric chemistry modelling studies at the Finnish Meteorological Institute. In collaboration with the University of Oslo, a development project was initiated in 1993 to prepare a stratospheric chemistry parameterisation, fit for global 3-dimensional modelling. This article presents the parameterisation approach. Selected results are shown from basic photochemical simulations

  11. The Migrating Embryo Model for Disk Evolution

    CERN Document Server

    Basu, Shantanu

    2012-01-01

    A new view of disk evolution is emerging from self-consistent numerical simulation modeling of the formation of circumstellar disks from the direct collapse of prestellar cloud cores. This has implications for many aspects of star and planet formation, including the growth of dust and high-temperature processing of materials. A defining result is that the early evolution of a disk is crucially affected by the continuing mass loading from the core envelope, and is driven into recurrent phases of gravitational instability. Nonlinear spiral arms formed during these episodes fragment to form gaseous clumps in the disk. These clumps generally migrate inward due to gravitational torques arising from their interaction with a trailing spiral arm. Occasionally, a clump can open up a gap in the disk and settle into a stable orbit, revealing a direct pathway to the formation of companion stars, brown dwarfs, or giant planets. At other times, when multiple clumps are present, a low mass clump may even be ejected from the...

  12. In-Space Chemical Propulsion System Model

    Science.gov (United States)

    Byers, David C.; Woodcock, Gordon; Benfield, Michael P. J.

    2004-01-01

    Multiple, new technologies for chemical systems are becoming available and include high temperature rockets, very light propellant tanks and structures, new bipropellant and monopropellant options, lower mass propellant control components, and zero boil off subsystems. Such technologies offer promise of increasing the performance of in-space chemical propulsion for energetic space missions. A mass model for pressure-fed, Earth and space-storable, advanced chemical propulsion systems (ACPS) was developed in support of the NASA MSFC In-Space Propulsion Program. Data from flight systems and studies defined baseline system architectures and subsystems and analyses were formulated for parametric scaling relationships for all ACPS subsystem. The paper will first provide summary descriptions of the approaches used for the systems and the subsystems and then present selected analyses to illustrate use of the model for missions with characteristics of current interest.

  13. Modeling texture evolution during recrystallization in aluminum

    International Nuclear Information System (INIS)

    The main aim of this work was to develop a model with predictive capability for microstructural evolution during recrystallization and to identify factors that exert the greatest effect on the development of texture. To achieve this aim, geometric and crystallographic observations from two orthogonal sections through a polycrystal were used as input to the computer simulations, to create a statistically representative three-dimensional model. Assignment of orientations to the grains was performed so as to optimize agreement between the orientation and misorientation distributions of assigned and observed orientations. The microstructures thus created were allowed to evolve using a Monte Carlo simulation. As a demonstration of the model the effects of anisotropy, both in energy and in mobility, stored energy and oriented nucleation (ON) on overall texture development were studied. The results were analyzed with reference to the various established competing theories of ON and oriented growth. The results suggested that all of ON, mobility anisotropy, stored energy and energy anisotropy (listed in order of their relative importance) influence texture development. It was also determined that comparison of simulated and measured textures throughout the recrystallization process is a more severe test of a model than the typical comparison of textures only at the end of the process

  14. The dynamics of a coupled soilscape-landscape evolution model

    Science.gov (United States)

    Welivitiya, Dimuth; Willgoose, Garry; Hancock, Greg

    2016-04-01

    In this study we present results obtained from a landform evolution model coupled with SSSPAM5D soilscape evolution model. This presentation will show a number of computer animations with this coupled model using a range of widely accepted soil profile weathering models, and erosion/armouring models. The animations clearly show that subtle changes in process can result in dramatic changes in long-term equilibrium hillslope and soilscape form. We will discuss the reasons for these differences, arguing from the various mathematical and physical assumptions modelled, and infer how observed hillslope form may provide identifiable (and perhaps quantifiable) landform and soilscape signatures of landscape and soilscape process, and in particular the coupling between the landscape and the soilscape. Specifically we have simulated soilscapes using 3 depth dependent weathering functions: 1) Exponential, 2) Humped and 3) Reversed exponential. The Exponential weathering function simulates physical weathering due to thermal effects, and the weathering rate exponentially decreases with depth. The Humped function simulates chemical and/or physical weathering with moisture feedbacks, where the highest weathering rate is at a finite depth below the surface and exponentially declines with depth. The Reversed exponential function simulates chemical weathering, and the highest weathering rate is at the soil-saprolite interface and exponentially decreases both above and below the interface. Both the Humped and Reversed exponential functions can be used as approximations to chemical weathering as they can be derived analytically by solving widely accepted geochemical weathering equations. The Humped function can arise where the weathering fluid is introduced at the top of the soil profile (e.g. rainfall equilibrated with carbon dioxide in the atmosphere), while the Reversed exponential can be derived when carbon dioxide is generated within the profile (e.g. by biodegradation of soil

  15. Modelling Chemical Reasoning to Predict Reactions

    CERN Document Server

    Segler, Marwin H S

    2016-01-01

    The ability to reason beyond established knowledge allows Organic Chemists to solve synthetic problems and to invent novel transformations. Here, we propose a model which mimics chemical reasoning and formalises reaction prediction as finding missing links in a knowledge graph. We have constructed a knowledge graph containing 14.4 million molecules and 8.2 million binary reactions, which represents the bulk of all chemical reactions ever published in the scientific literature. Our model outperforms a rule-based expert system in the reaction prediction task for 180,000 randomly selected binary reactions. We show that our data-driven model generalises even beyond known reaction types, and is thus capable of effectively (re-) discovering novel transformations (even including transition-metal catalysed reactions). Our model enables computers to infer hypotheses about reactivity and reactions by only considering the intrinsic local structure of the graph, and because each single reaction prediction is typically ac...

  16. Using chemical organization theory for model checking

    OpenAIRE

    Kaleta, Christoph; Richter, Stephan; Dittrich, Peter

    2009-01-01

    Motivation: The increasing number and complexity of biomodels makes automatic procedures for checking the models' properties and quality necessary. Approaches like elementary mode analysis, flux balance analysis, deficiency analysis and chemical organization theory (OT) require only the stoichiometric structure of the reaction network for derivation of valuable information. In formalisms like Systems Biology Markup Language (SBML), however, information about the stoichiometric coefficients re...

  17. Chemical and Hydrodynamical Models of Cometary Comae

    Science.gov (United States)

    Charnley, Steven

    2012-01-01

    Multi-fluid modelling of the outflowing gases which sublimate from cometary nuclei as they approach the Sun is necessary for understanding the important physical and chemical processes occurring in this complex plasma. Coma chemistry models can be employed to interpret observational data and to ultimately determine chemical composition and structure of the nuclear ices and dust. We describe a combined chemical and hydrodynamical model [1] in which differential equations for the chemical abundances and the energy balance are solved as a function of distance from the cometary nucleus. The presence of negative ions (anions) in cometary comae is known from Giotto mass spectrometry of 1P/Halley. The anions O(-), OH(-), C(-), CH(-) and CN(-) have been detected, as well as unidentified anions with masses 22-65 and 85-110 amu [2]. Organic molecular anions such as C4H(-) and C6H(-) are known to have a significant impact on the charge balance of interstellar clouds and circumstellar envelopes and have been shown to act as catalysts for the gas-phase synthesis of larger hydrocarbon molecules in the ISM, but their importance in cometary comae has not yet been fully explored. We present details of new models for the chemistry of cometary comae that include atomic and molecular anions and calculate the impact of these anions on the coma physics and chemistry af the coma.

  18. Evolution and chemical and dynamical effects of high-mass stars

    CERN Document Server

    Meynet, Georges; Georgy, Cyril; Pignatari, Marco; Hirschi, Raphael; Ekstrom, Sylvia; Maeder, Andre

    2008-01-01

    We review general characteristics of massive stars, present the main observable constraints that stellar models should reproduce. We discuss the impact of massive star nucleosynthesis on the early phases of the chemical evolution of the Milky Way (MW). We show that rotating models can account for the important primary nitrogen production needed at low metallicity. Interestingly such rotating models can also better account for other features as the variation with the metallicity of the C/O ratio. Damped Lyman Alpha (DLA) systems present similar characteristics as the halo of the MW for what concern the N/O and C/O ratios. Although in DLAs, the star formation history might be quite different from that of the halo, in these systems also, rotating stars (both massive and intermediate) probably play an important role for explaining these features. The production of primary nitrogen is accompanied by an overproduction of other elements as $^{13}$C, $^{22}$Ne and s-process elements. We show also how the observed var...

  19. Modeling heterogeneous chemical processes on aerosol surface

    Institute of Scientific and Technical Information of China (English)

    Junjun Deng; Tijian Wang; Li Liu; Fei Jiang

    2010-01-01

    To explore the possible impact of heterogeneous chemical processes on atmospheric trace components,a coupled box model including gas-phase chemical processes,aerosol thermodynamic equilibrium processes,and heterogeneous chemical processes on the surface of dust,black carbon(BC)and sea salt is set up to simulate the effects of heterogeneous chemistry on the aerosol surface,and analyze the primary factors affecting the heterogeneous processes.Results indicate that heterogeneous chemical processes on the aerosol surface in the atmosphere will affect the concentrations of trace gases such as H2O2,HO2,O3,NO2,NO3,HNO3 and SO2,and aerosols such as SO42-,NO3-and NH4+.Sensitivity tests suggest that the magnitude of the impact of heterogeneous processes strongly depends on aerosol concentration and the surface uptake coefficients used in the box model.However,the impact of temperature on heterogeneous chemical processes is considerably less.The"renoxification"of HNO3 will affect the components of the troposphere such as nitrogen oxide and ozone.

  20. A model for the evolution of nucleotide polymerase directionality.

    Directory of Open Access Journals (Sweden)

    Joshua Ballanco

    Full Text Available BACKGROUND: In all known living organisms, every enzyme that synthesizes nucleic acid polymers does so by adding nucleotide 5′-triphosphates to the 3′-hydroxyl group of the growing chain. This results in the well known 5'→3' directionality of all DNA and RNA Polymerases. The lack of any alternative mechanism, e.g. addition in a 3'→5' direction, may indicate a very early founder effect in the evolution of life, or it may be the result of a selective pressure against such an alternative. METHODOLOGY/PRINCIPAL FINDINGS: In an attempt to determine whether the lack of an alternative polymerase directionality is the result of a founder effect or evolutionary selection, we have constructed a basic model of early polymerase evolution. This model is informed by the essential chemical properties of the nucleotide polymerization reaction. With this model, we are able to simulate the growth of organisms with polymerases that synthesize either 5'→3' or 3'→5' in isolation or in competition with each other. CONCLUSIONS/SIGNIFICANCE: We have found that a competition between organisms with 5'→3' polymerases and 3'→5' polymerases only results in a evolutionarily stable strategy under certain conditions. Furthermore, we have found that mutations lead to a much clearer delineation between conditions that lead to a stable coexistence of these populations and conditions which ultimately lead to success for the 5'→3' form. In addition to presenting a plausible explanation for the uniqueness of enzymatic polymerization reactions, we hope these results also provide an example of how whole organism evolution can be understood based on molecular details.

  1. Features in chemical kinetics. I. Signatures of self-emerging dimensional reduction from a general format of the evolution law

    Science.gov (United States)

    Nicolini, Paolo; Frezzato, Diego

    2013-06-01

    Simplification of chemical kinetics description through dimensional reduction is particularly important to achieve an accurate numerical treatment of complex reacting systems, especially when stiff kinetics are considered and a comprehensive picture of the evolving system is required. To this aim several tools have been proposed in the past decades, such as sensitivity analysis, lumping approaches, and exploitation of time scales separation. In addition, there are methods based on the existence of the so-called slow manifolds, which are hyper-surfaces of lower dimension than the one of the whole phase-space and in whose neighborhood the slow evolution occurs after an initial fast transient. On the other hand, all tools contain to some extent a degree of subjectivity which seems to be irremovable. With reference to macroscopic and spatially homogeneous reacting systems under isothermal conditions, in this work we shall adopt a phenomenological approach to let self-emerge the dimensional reduction from the mathematical structure of the evolution law. By transforming the original system of polynomial differential equations, which describes the chemical evolution, into a universal quadratic format, and making a direct inspection of the high-order time-derivatives of the new dynamic variables, we then formulate a conjecture which leads to the concept of an "attractiveness" region in the phase-space where a well-defined state-dependent rate function ω has the simple evolution dot{ω }= - ω ^2 along any trajectory up to the stationary state. This constitutes, by itself, a drastic dimensional reduction from a system of N-dimensional equations (being N the number of chemical species) to a one-dimensional and universal evolution law for such a characteristic rate. Step-by-step numerical inspections on model kinetic schemes are presented. In the companion paper [P. Nicolini and D. Frezzato, J. Chem. Phys. 138, 234102 (2013)], 10.1063/1.4809593 this outcome will be naturally

  2. The dynamical and chemical evolution of dwarf spheroidal galaxies with GEAR

    Science.gov (United States)

    Revaz, Y.; Jablonka, P.

    2012-02-01

    We present the fully parallel chemo-dynamical Tree/SPH code GEAR, which allows us to perform high resolution simulations with detailed chemical diagnostics. Starting from the public version of Gadget-2, we included the complex treatment of the baryon physics: gas cooling, star formation law, chemical evolution, and supernova feedback. We qualified the performances of GEAR in the case of dwarf spheroidal galaxies (dSphs) galaxies. Our code GEAR conserves the total energy budget of the systems to better than 5% over 14 Gyr and provides an excellent convergence of the results with numerical resolution. We showed that models of dSphs in a static Euclidean space, where the expansion of the universe is neglected are valid. In addition, we tackled some existing open questions in the field, such as the stellar mass fraction of dSphs and its link to the predicted dark matter halo mass function, the effect of supernova feedback, the spatial distribution of the stellar populations, and the origin of the diversity in star formation histories and chemical abundance patterns. Strong supernova-driven winds seem incompatible with the observed metallicities and luminosities. Despite newly formed stars being preferentially found in the galaxy central parts, turbulent motions in the gas can quickly erase any metallicity gradient. The diversity in properties of dSph are related to a range of total masses, as well as a range of dispersion in the central densities, which is also seen in the halos emerging from a ΛCDM cosmogony. Appendices A and B are available in electronic form at http://www.aanda.org

  3. The search for life's origins: Progress and future directions in planetary biology and chemical evolution

    Science.gov (United States)

    1990-01-01

    The current state is reviewed of the study of chemical evolution and planetary biology and the probable future is discussed of the field, at least for the near term. To this end, the report lists the goals and objectives of future research and makes detailed, comprehensive recommendations for accomplishing them, emphasizing those issues that were inadequately discussed in earlier Space Studies Board reports.

  4. Impact of solar system exploration on theories of chemical evolution and the origin of life

    Science.gov (United States)

    Devincenzi, D. L.

    1983-01-01

    The impact of solar system exploration on theories regarding chemical evolution and the origin of life is examined in detail. Major findings from missions to Mercury, Venus, the moon, Mars, Jupiter, Saturn, and Titan are reviewed and implications for prebiotic chemistry are discussed. Among the major conclusions are: prebiotic chemistry is widespread throughout the solar system and universe; chemical evolution and the origin of life are intimately associated with the origin and evolution of the solar system; the rate, direction, and extent of prebiotic chemistry is highly dependent upon planetary characteristics; and continued exploration will increase understanding of how life originated on earth and allow better estimates of the likelihood of similar processes occurring elsewhere.

  5. Modeling Temporal Evolution and Multiscale Structure in Networks

    DEFF Research Database (Denmark)

    Herlau, Tue; Mørup, Morten; Schmidt, Mikkel Nørgaard

    2013-01-01

    -point model to account for the temporal evolution of each vertex. We demonstrate that our model is able to infer time-varying multiscale structure in synthetic as well as three real world time-evolving complex networks. Our modeling of the temporal evolution of hierarchies brings new insights...

  6. About evolution of alive orgamisms in conditions of radioactive and chemical stress (biophysical aspect)

    International Nuclear Information System (INIS)

    The problems of evolution of living organisms in conditions of radioactive and chemical stress are considered. Tendencies of development of the world community are evidence of global anthropogenic influence increase on biosphere, which is caused by many components, the main of them being radiation contamination and chemical pollution. The possible mechanisms of new species appearance are discussed on molecular level taking into account mutagenic factors caused by radiation and chemical stress. The quantum field hypothesis on the basis of Landau-Ginzburg equation of molecular mechanisms of mutations connected with new species appearance is presented.(A.A.D.)

  7. THERMAL AND CHEMICAL EVOLUTIONS OF GALAXY CLUSTERS OBSERVED WITH SUZAKU

    Directory of Open Access Journals (Sweden)

    Kosuke Sato

    2013-12-01

    Full Text Available We studied the properties of the intracluster medium (ICM of galaxy clusters to outer regions observed with Suzaku. The observed temperature dropped by about ~30% from the central region to the virial radius of the clusters. The derived entropy profile agreed with the expectation from simulations within r500, while the entropy profile in r > r500 indicated a flatter slope than the simulations. This would suggest that the cluster outskirts were out of hydrostatic equilibrium. As for the metallicity, we studied the metal abundances from O to Fe up to ~0.5 times the virial radius of galaxy groups and clusters. Comparing the results with supernova nucleosynthesis models, the number ratio of type II to Ia supernovae is estimated to be ~3.5. We also calculated not only Fe, but also O and Mg mass-to-light ratios (MLRs with K-band luminosity. The MLRs in the clusters had a similar feature.

  8. Can Galactic chemical evolution explain the oxygen isotopic variations in the Solar System?

    CERN Document Server

    Lugaro, Maria; Ireland, Trevor R; Maddison, Sarah T

    2012-01-01

    A number of objects in primitive meteorites have oxygen isotopic compositions that place them on a distinct, mass-independent fractionation line with a slope of one on a three-isotope plot. The most popular model for describing how this fractionation arose assumes that CO self-shielding produced 16O-rich CO and 16O-poor H2O, where the H2O subsequently combined with interstellar dust to form relatively 16O-poor solids within the Solar Nebula. Another model for creating the different reservoirs of 16O-rich gas and 16O-poor solids suggests that these reservoirs were produced by Galactic chemical evolution (GCE) if the Solar System dust component was somewhat younger than the gas component and both components were lying on the line of slope one in the O three-isotope plot. We argue that GCE is not the cause of mass-independent fractionation of the oxygen isotopes in the Solar System. The GCE scenario is in contradiction with observations of the 18O/17O ratios in nearby molecular clouds and young stellar objects. ...

  9. Modeling Dynamic Evolution of Online Friendship Network

    Institute of Scientific and Technical Information of China (English)

    吴联仁; 闫强

    2012-01-01

    In this paper,we study the dynamic evolution of friendship network in SNS (Social Networking Site).Our analysis suggests that an individual joining a community depends not only on the number of friends he or she has within the community,but also on the friendship network generated by those friends.In addition,we propose a model which is based on two processes:first,connecting nearest neighbors;second,strength driven attachment mechanism.The model reflects two facts:first,in the social network it is a universal phenomenon that two nodes are connected when they have at least one common neighbor;second,new nodes connect more likely to nodes which have larger weights and interactions,a phenomenon called strength driven attachment (also called weight driven attachment).From the simulation results,we find that degree distribution P(k),strength distribution P(s),and degree-strength correlation are all consistent with empirical data.

  10. Chemical evolution and the origin of life: cumulative keyword subject index 1970-1986

    Science.gov (United States)

    Roy, A. C.; Powers, J. V.; Rummel, J. D. (Principal Investigator)

    1990-01-01

    This cumulative subject index encompasses the subject indexes of the bibliographies on Chemical Evolution and the Origin of Life that were first published in 1970 and have continued through publication of the 1986 bibliography supplement. Early bibliographies focused on experimental and theoretical material dealing directly with the concepts of chemical evolution and the origin of life, excluding the broader areas of exobiology, biological evolution, and geochemistry. In recent years, these broader subject areas have also been incorporated as they appear in literature searches relating to chemical evolution and the origin of life, although direct attempts have not been made to compile all of the citations in these broad areas. The keyword subject indexes have also undergone an analogous change in scope. Compilers of earlier bibliographies used the most specific term available in producing the subject index. Compilers of recent bibliographies have used a number of broad terms relating to the overall subject content of each citation and specific terms where appropriate. The subject indexes of these 17 bibliographies have, in general, been cumulatively compiled exactly as they originally appeared. However, some changes have been made in an attempt to correct errors, combine terms, and provide more meaningful terms.

  11. Modeling evolution using the probability of fixation: history and implications.

    Science.gov (United States)

    McCandlish, David M; Stoltzfus, Arlin

    2014-09-01

    Many models of evolution calculate the rate of evolution by multiplying the rate at which new mutations originate within a population by a probability of fixation. Here we review the historical origins, contemporary applications, and evolutionary implications of these "origin-fixation" models, which are widely used in evolutionary genetics, molecular evolution, and phylogenetics. Origin-fixation models were first introduced in 1969, in association with an emerging view of "molecular" evolution. Early origin-fixation models were used to calculate an instantaneous rate of evolution across a large number of independently evolving loci; in the 1980s and 1990s, a second wave of origin-fixation models emerged to address a sequence of fixation events at a single locus. Although origin fixation models have been applied to a broad array of problems in contemporary evolutionary research, their rise in popularity has not been accompanied by an increased appreciation of their restrictive assumptions or their distinctive implications. We argue that origin-fixation models constitute a coherent theory of mutation-limited evolution that contrasts sharply with theories of evolution that rely on the presence of standing genetic variation. A major unsolved question in evolutionary biology is the degree to which these models provide an accurate approximation of evolution in natural populations.

  12. Modeling the evolution of infrared galaxies: A Parametric backwards evolution model

    CERN Document Server

    Béthermin, Matthieu; Lagache, Guilaine; Borgne, Damien Le; Pénin, Aurélie

    2010-01-01

    We aim at modeling the infrared galaxy evolution in an as simple as possible way and reproduce statistical properties among which the number counts between 15 microns and 1.1 mm, the luminosity functions, and the redshift distributions. We then aim at using this model to interpret the recent observations (Spitzer, Akari, BLAST, LABOCA, AzTEC, SPT and Herschel), and make predictions for future experiments like CCAT or SPICA. This model uses an evolution in density and luminosity of the luminosity function with two breaks at redshift ~0.9 and 2 and contains the two populations of the Lagache et al. (2004) model: normal and starburst galaxies. We also take into account the effect of the strong lensing of high-redshift sub-millimeter galaxies. It has 13 free parameters and 8 additional calibration parameters. We fit the parameters to the IRAS, Spitzer, Herschel and AzTEC measurements with a Monte-Carlo Markov chain. The model ajusted on deep counts at key wavelengths reproduces the counts from the mid-infrared to...

  13. Irradiated solutions of citric acid in the context of chemical evolution

    International Nuclear Information System (INIS)

    The radiolysis of citric acid in an aqueous solution and its connection with chemical evolution has been investigated. The importance of this compound which, probably had a double role during the evolutive period, first as a precursor in the synthesis of some pyrimidines and second as metabolic intermediary in the carboxilic acids cycle. The decomposition of the citric acid, the identification of the products obtained from the radiolysis and the distributions of these products were investigated with relation to the different doses used. (author) 9 refs.; 1 fig

  14. Chemical spots and their dynamical evolution on HgMn stars

    CERN Document Server

    Korhonen, Heidi; Briquet, Maryline; Gonzalez, Federico; Savanov, Igor

    2010-01-01

    Our recent studies of late B-type stars with HgMn peculiarity revealed for the first time the presence of fast dynamical evolution of chemical spots on their surfaces. These observations suggest a hitherto unknown physical process operating in the stars with radiative outer envelopes. Furthermore, we have also discovered existence of magnetic fields on these stars that have up to now been thought to be non-magnetic. Here we will discuss the dynamical spot evolution on HD 11753 and our new results on magnetic fields on AR Aur.

  15. Models of Protocellular Structure, Function and Evolution

    Science.gov (United States)

    New, Michael H.; Pohorille, Andrew; Szostak, Jack W.; Keefe, Tony; Lanyi, Janos K.

    2001-01-01

    In the absence of any record of protocells, the most direct way to test our understanding of the origin of cellular life is to construct laboratory models that capture important features of protocellular systems. Such efforts are currently underway in a collaborative project between NASA-Ames, Harvard Medical School and University of California. They are accompanied by computational studies aimed at explaining self-organization of simple molecules into ordered structures. The centerpiece of this project is a method for the in vitro evolution of protein enzymes toward arbitrary catalytic targets. A similar approach has already been developed for nucleic acids in which a small number of functional molecules are selected from a large, random population of candidates. The selected molecules are next vastly multiplied using the polymerase chain reaction. A mutagenic approach, in which the sequences of selected molecules are randomly altered, can yield further improvements in performance or alterations of specificities. Unfortunately, the catalytic potential of nucleic acids is rather limited. Proteins are more catalytically capable but cannot be directly amplified. In the new technique, this problem is circumvented by covalently linking each protein of the initial, diverse, pool to the RNA sequence that codes for it. Then, selection is performed on the proteins, but the nucleic acids are replicated. Additional information is contained in the original extended abstract.

  16. Models of protocellular structures, functions and evolution

    Science.gov (United States)

    Pohorille, Andrew; New, Michael H.; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    The central step in the origin of life was the emergence of organized structures from organic molecules available on the early earth. These predecessors to modern cells, called 'proto-cells,' were simple, membrane bounded structures able to maintain themselves, grow, divide, and evolve. Since there is no fossil record of these earliest of life forms, it is a scientific challenge to discover plausible mechanisms for how these entities formed and functioned. To meet this challenge, it is essential to create laboratory models of protocells that capture the main attributes associated with living systems, while remaining consistent with known, or inferred, protobiological conditions. This report provides an overview of a project which has focused on protocellular metabolism and the coupling of metabolism to energy transduction. We have assumed that the emergence of systems endowed with genomes and capable of Darwinian evolution was preceded by a pre-genomic phase, in which protocells functioned and evolved using mostly proteins, without self-replicating nucleic acids such as RNA.

  17. Exploring Contextual Models in Chemical Patent Search

    Science.gov (United States)

    Urbain, Jay; Frieder, Ophir

    We explore the development of probabilistic retrieval models for integrating term statistics with entity search using multiple levels of document context to improve the performance of chemical patent search. A distributed indexing model was developed to enable efficient named entity search and aggregation of term statistics at multiple levels of patent structure including individual words, sentences, claims, descriptions, abstracts, and titles. The system can be scaled to an arbitrary number of compute instances in a cloud computing environment to support concurrent indexing and query processing operations on large patent collections.

  18. Integrating Geochemical and Geodynamic Numerical Models of Mantle Evolution and Plate Tectonics

    Science.gov (United States)

    Tackley, P. J.; Xie, S.

    2001-12-01

    The thermal and chemical evolution of Earth's mantle and plates are inextricably coupled by the plate tectonic - mantle convective system. Convection causes chemical differentiation, recycling and mixing, while chemical variations affect the convection through physical properties such as density and viscosity which depend on composition. It is now possible to construct numerical mantle convection models that track the thermo-chemical evolution of major and minor elements, and which can be used to test prospective models and hypotheses regarding Earth's chemical and thermal evolution. Model thermal and chemical structures can be compared to results from seismic tomography, while geochemical signatures (e.g., trace element ratios) can be compared to geochemical observations. The presented, two-dimensional model combines a simplified 2-component major element model with tracking of the most important trace elements, using a tracer method. Melting is self-consistently treated using a solidus, with melt placed on the surface as crust. Partitioning of trace elements occurs between melt and residue. Decaying heat-producing elements and secular cooling of the mantle and core provide the driving heat sources. Pseudo-plastic yielding of the lithosphere gives a first-order approximation of plate tectonics, and also allows planets with a rigid lid or intermittent plate tectonics to be modeled simply by increasing the yield strength. Preliminary models with an initially homogeneous mantle show that regions with a HIMU-like signature can be generated by crustal recycling, and regions with high 3He/4He ratios can be generated by residuum recycling. Outgassing of Argon is within the observed range. Models with initially layered mantles will also be investigated. In future it will be important to include a more realistic bulk compositional model that allows continental crust as well as oceanic crust to form, and to extend the model to three dimensions since toroidal flow may alter

  19. Modeling rocky coastline evolution and equilibrium

    Science.gov (United States)

    Limber, P. W.; Murray, A. B.

    2010-12-01

    Many of the world’s rocky coastlines exhibit planform roughness in the form of alternating headlands and embayments. Along cliffed coasts, it is often assumed that headlands consist of rock that is more resistant to wave attack than in neighboring bays, because of either structural or lithologic variations. Bays would then retreat landward faster than headlands, creating the undulating planform profiles characteristic of a rocky coastal landscape. While the interplay between alongshore rock strength and nearshore wave energy is, in some circumstances, a fundamental control on coastline shape, beach sediment is also important. Laboratory experiments and field observations have shown that beach sediment, in small volumes, can act as an abrasive tool to encourage sea cliff retreat. In large volumes, though, sediment discourages wave attack on the cliff face, acting as a protective barrier. This nonlinearity suggests a means for headland persistence, even without alongshore variations in rock strength: bare-rock headlands could retreat more slowly than, or at the same rate as, neighboring sediment-filled embayments because of alongshore variations in the availability of beach sediment. Accordingly, nearshore sediment dynamics (i.e. sediment production from sea cliff retreat and alongshore sediment transport) could promote the development of autogenic planform geometry. To explore these ideas, we present numerical and analytical modeling of large-scale (> one kilometer) and long-term (millennial-scale) planform rocky coastline evolution, in which sediment is supplied by both sea cliff erosion and coastal rivers and is distributed by alongshore sediment transport. We also compare model predictions with real landscapes. Previously, our modeling exercises focused on a basic rocky coastline configuration where lithologically-homogeneous sea cliffs supplied all beach sediment and maintained a constant alongshore height. Results showed that 1) an equilibrium alongshore

  20. Scaling Theory and Modeling of DNA Evolution

    Science.gov (United States)

    Buldyrev, Sergey V.

    1998-03-01

    We present evidence supporting the possibility that the nucleotide sequence in noncoding DNA is power-law correlated. We do not find such long-range correlation in the coding regions of the gene, so we build a ``coding sequence finder'' to locate the coding regions of an unknown DNA sequence. We also propose a different coding sequence finding algorithm, based on the concept of mutual information(I. Große, S. V. Buldyrev, H. Herzel, H. E. Stanley, (preprint).). We describe our recent work on quantification of DNA patchiness, using long-range correlation measures (G. M. Viswanathan, S. V. Buldyrev, S. Havlin, and H. E. Stanley, Biophysical Journal 72), 866-875 (1997).. We also present our recent study of the simple repeat length distributions. We find that the distributions of some simple repeats in noncoding DNA have long power-law tails, while in coding DNA all simple repeat distributions decay exponentially. (N. V. Dokholyan, S. V. Buldyrev, S. Havlin, and H. E. Stanley, Phys. Rev. Lett (in press).) We discuss several models based on insertion-deletion and mutation-duplication mechanisms that relate long-range correlations in non-coding DNA to DNA evolution. Specifically, we relate long-range correlations in non-coding DNA to simple repeat expansion, and propose an evolutionary model that reproduces the power law distribution of simple repeat lengths. We argue that the absence of long-range correlations in protein coding sequences is related to their highly conserved primary structure which is necessary to insure protein folding.

  1. Quantitative Modeling of Landscape Evolution, Treatise on Geomorphology

    NARCIS (Netherlands)

    Temme, A.J.A.M.; Schoorl, J.M.; Claessens, L.F.G.; Veldkamp, A.; Shroder, F.S.

    2013-01-01

    This chapter reviews quantitative modeling of landscape evolution – which means that not just model studies but also modeling concepts are discussed. Quantitative modeling is contrasted with conceptual or physical modeling, and four categories of model studies are presented. Procedural studies focus

  2. A chemical model for the interstellar medium in galaxies

    Science.gov (United States)

    Bovino, S.; Grassi, T.; Capelo, Pedro R.; Schleicher, D. R. G.; Banerjee, R.

    2016-05-01

    Aims: We present and test chemical models for three-dimensional hydrodynamical simulations of galaxies. We explore the effect of changing key parameters such as metallicity, radiation, and non-equilibrium versus equilibrium metal cooling approximations on the transition between the gas phases in the interstellar medium. Methods: The microphysics was modelled by employing the public chemistry package KROME, and the chemical networks were tested to work in a wide range of densities and temperatures. We describe a simple H/He network following the formation of H2 and a more sophisticated network that includes metals. Photochemistry, thermal processes, and different prescriptions for the H2 catalysis on dust are presented and tested within a one-zone framework. The resulting network is made publicly available on the KROME webpage. Results: We find that employing an accurate treatment of the dust-related processes induces a faster HI-H2 transition. In addition, we show when the equilibrium assumption for metal cooling holds and how a non-equilibrium approach affects the thermal evolution of the gas and the HII-HI transition. Conclusions: These models can be employed in any hydrodynamical code via an interface to KROME and can be applied to different problems including isolated galaxies, cosmological simulations of galaxy formation and evolution, supernova explosions in molecular clouds, and the modelling of star-forming regions. The metal network can be used for a comparison with observational data of CII 158 μm emission both for high-redshift and for local galaxies.

  3. Recent Advances in Shell Evolution with Shell-Model Calculations

    CERN Document Server

    Utsuno, Yutaka; Tsunoda, Yusuke; Shimizu, Noritaka; Honma, Michio; Togashi, Tomoaki; Mizusaki, Takahiro

    2014-01-01

    Shell evolution in exotic nuclei is investigated with large-scale shell-model calculations. After presenting that the central and tensor forces produce distinctive ways of shell evolution, we show several recent results: (i) evolution of single-particle-like levels in antimony and cupper isotopes, (ii) shape coexistence in nickel isotopes understood in terms of configuration-dependent shell structure, and (iii) prediction of the evolution of the recently established $N=34$ magic number towards smaller proton numbers. In any case, large-scale shell-model calculations play indispensable roles in describing the interplay between single-particle character and correlation.

  4. Dynamics of surface evolution in semiconductor thin films grown from a chemical bath.

    Science.gov (United States)

    Gupta, Indu; Mohanty, Bhaskar Chandra

    2016-01-01

    Dynamics of surface evolution in CdS thin films grown by chemical bath deposition technique has been studied from time sequence of atomic force micrographs. Detailed scaling analysis of surface fluctuation in real and Fourier space yielded characteristic exponents αloc = 0.78 ± 0.07, α = 2.20 ± 0.08, αs = 1.49 ± 0.22, β = 0.86 ± 0.05 and βloc = 0.43 ± 0.10, which are very different from those predicted by the local growth models and are not related to any known universality classes. The observed anomalous scaling pattern, characterized by power law scaling dependence of interface width on deposition time differently at local and global scale, with rapid roughening of the growth front has been discussed to arise as a consequence of a nonlocal effect in the form of diffusional instability. PMID:27615367

  5. Ultrafaint dwarfs—star formation and chemical evolution in the smallest galaxies

    International Nuclear Information System (INIS)

    In earlier work, we showed that a dark matter halo with a virial mass of 107 M ☉ can retain a major part of its baryons in the face of the pre-ionization phase and supernova (SN) explosion from a 25 M ☉ star. Here, we expand on the results of that work, investigating the star formation and chemical evolution of the system beyond the first SN. In a galaxy with a mass M vir = 107 M ☉, sufficient gas is retained by the potential for a second period of star formation to occur. The impact of a central explosion is found to be much stronger than that of an off-center explosion both in blowing out the gas and in enriching it, as in the off-center case most of the SN energy and metals escape into the intergalactic medium. We model the star formation and metallicity, given the assumption that stars form for 100, 200, 400, and 600 Myr, and discuss the results in the context of recent observations of very low-mass galaxies. We show that we can account for most features of the observed relationship between [α/Fe] and [Fe/H] in ultra-faint dwarf galaxies with the assumption that the systems formed at a low mass, rather than being remnants of much larger systems.

  6. Ultrafaint dwarfs—star formation and chemical evolution in the smallest galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Webster, David; Bland-Hawthorn, Joss [Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia); Sutherland, Ralph, E-mail: d.webster@physics.usyd.edu.au [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston, ACT 2611 (Australia)

    2014-11-20

    In earlier work, we showed that a dark matter halo with a virial mass of 10{sup 7} M {sub ☉} can retain a major part of its baryons in the face of the pre-ionization phase and supernova (SN) explosion from a 25 M {sub ☉} star. Here, we expand on the results of that work, investigating the star formation and chemical evolution of the system beyond the first SN. In a galaxy with a mass M {sub vir} = 10{sup 7} M {sub ☉}, sufficient gas is retained by the potential for a second period of star formation to occur. The impact of a central explosion is found to be much stronger than that of an off-center explosion both in blowing out the gas and in enriching it, as in the off-center case most of the SN energy and metals escape into the intergalactic medium. We model the star formation and metallicity, given the assumption that stars form for 100, 200, 400, and 600 Myr, and discuss the results in the context of recent observations of very low-mass galaxies. We show that we can account for most features of the observed relationship between [α/Fe] and [Fe/H] in ultra-faint dwarf galaxies with the assumption that the systems formed at a low mass, rather than being remnants of much larger systems.

  7. Early Star Formation, Nucleosynthesis, and Chemical Evolution in Proto-Galactic Clouds

    CERN Document Server

    Saleh, L; Mathews, G J

    2006-01-01

    We present numerical simulations to describe the nucleosynthesis and evolution of pre-Galactic clouds in a model which is motivated by cold dark matter simulations of hierarchical galaxy formation. We adopt a SN-induced star-formation mechanism and follow the chemical enrichment and energy input by Type II and Type Ia SNe. We utilize metallicity-dependent yields and include finite stellar lifetimes. We derive the metallicity distribution functions, the age-metallicity relation, and relative elemental abundances for a number of alpha- and Fe-group elements. We find that the dispersion of the metallicity distribution function of the outer halo is reproduced by contributions from clouds with different initial conditions. Clouds with initial masses greater than that of present globular clusters are found to survive the first 0.1 Gyr, suggesting that such systems may have contributed to the formation of the first stars, and could have been self-enriched. More massive clouds are only stable when one assumes an init...

  8. New trajectory driven aerosol and chemical process model: chemical and aerosol Lagrangian model (CALM)

    OpenAIRE

    Tunved, P.; D. G. Partridge; Korhonen, H.

    2010-01-01

    A new Chemical and Aerosol Lagrangian Model (CALM) have been developed and tested. The model incorporates all central aerosol dynamical processes, from nucleation, condensation, coagulation and deposition to cloud formation and in-cloud processing. The model is tested and evaluated against observations performed at the SMEAR II station located at Hyytiälä (61°51' N, 24°17' E) over a time period of two years, 2000–2001. The model shows good agreement with measurements thro...

  9. An Appreciative Model of Schumpeterian Evolution

    OpenAIRE

    Pol, Eduardo-Fernandez

    2007-01-01

    Schumpeter persistently sought to reconcile innovation with general equilibrium to explain economic evolution. In essence, he was interested in innovatory discontinuities that upset equilibrium and generate a transitional dynamics converging to a different state of technology. There are two central approaches to the analysis of economic evolution which revolve around the Schumpeterian vision: the evolutionary approach as originated in the landmark book by Nelson and Winter An Evolutionary The...

  10. The Chemical Evolution of Narrow Emission Line Galaxies: the Key to their Formation Processes

    CERN Document Server

    Torres-Papaqui, J P; Ortega-Minakata, R A

    2011-01-01

    Using the largest sample of narrow emission line galaxies available so far, we show that their spectral characteristics are correlated with different physical parameters, like the chemical abundances, the morphologies, the masses of the bulge and the mean stellar age of the stellar populations of the host galaxies. It suggests that the spectral variations observed in standard spectroscopic diagnostic diagrams are not due solely to variations of ionization parameters or structures but reflect also the chemical evolution of the galaxies, which in turn can be explained by different galaxy formation processes.

  11. The chemical evolution of a travertine-depositing stream: geochemical processes and mass transfer reactions

    Science.gov (United States)

    Lorah, M.M.; Herman, J.S.

    1988-01-01

    Focuses on quantiatively defining the chemical changes occurring in Falling Spring Creek, a travertine-depositing stream located in Alleghany County, Virgina. The processes of CO2 outgassing and calcite precipitation or dissolution control the chemical evolution of the stream. Physical evidence for calcite precipitation exists in the travertine deposits which are first observed immediately above the waterfall and extend for at least 1.0 km below the falls. Net calcite precipitation occurs at all times of the year but is greatest during low-flow conditions in the summer and early fall. -from Authors

  12. Dynamic landscapes: a model of context and contingency in evolution.

    Science.gov (United States)

    Foster, David V; Rorick, Mary M; Gesell, Tanja; Feeney, Laura M; Foster, Jacob G

    2013-10-01

    Although the basic mechanics of evolution have been understood since Darwin, debate continues over whether macroevolutionary phenomena are driven by the fitness structure of genotype space or by ecological interaction. In this paper we propose a simple model capturing key features of fitness-landscape and ecological models of evolution. Our model describes evolutionary dynamics in a high-dimensional, structured genotype space with interspecies interaction. We find promising qualitative similarity with the empirical facts about macroevolution, including broadly distributed extinction sizes and realistic exploration of the genotype space. The abstraction of our model permits numerous applications beyond macroevolution, including protein and RNA evolution.

  13. Chemical evolution of groundwater in a drainage basin of Holocene age, east-central Alberta, Canada

    Science.gov (United States)

    Wallick, E. I.

    1981-12-01

    Chemical evolution of groundwater in a small drainage basin of glacial origin (10,250 yr. B.P., based on radiocarbon age dating of gyttja from a closed saline lake in the basin) was studied in order to understand the generation of salts in surface-mined areas on the interior plains of Alberta. The basin was considered to be a natural analogue of a surface-disturbed area because of the large volumes of rock that had been redistributed by glaciers with the resulting change in topography and drainage. The distributions of hydraulic head, total dissolved solids (TDS), and environmental isotopes essentially reflect the superimposition of groundwater flow systems associated with the post-glacial topography upon a regional bedrock flow system of older but undertermined age. In the glacial drift aquifers and aquitards (sands and till), the groundwater composition was typically Ca-Mg-bicarbonate type at depths less than 30 m, but at depths of 30-100 m, the composition was Na-bicarbonate-sulfate type. In the deeper bedrock aquifers (> 100 m), Nabicarbonate-sulfate and Na-bicarbonate-chloride types were present. TDS was as low as 400 mg/l in the shallow drift aquifer, generally constant at ˜1000 mg/l in the deep drift and shallow bedrock aquifer, and over 1700 mg/l in the deep bedrock aquifer system. Chemical evolution of groundwater in the area appears to be dominated by two depth zones having different types of water-rock interaction. In the shallow drift zone, the dissolution of soil CO 2 in infiltrating groundwater, oxidation of organic carbon, sulfur and pyrite result in the formation of carbonic and sulfuric acids that attack carbonate and silicate minerals. On the basis of X-ray diffraction analysis, these minerals were calcite, dolomite, plagioclase feldspar, and smectite clays. However, in the deep regional bedrock aquifer, conditions are reducing (presence of methane), groundwater is alkaline (pH 8.6-10.3), and the Na-bicarbonate-chloride composition of groundwater

  14. Bacterial Evolution and the Bak-Sneppen Model

    Science.gov (United States)

    Bose, Indrani; Chaudhuri, Indranath

    Recently, Lenski et al.1-3 have carried out several experiments on bacterial evolution. Their findings support the theory of punctuated equilibrium in biological evolution. They have further quantified the relative contributions of adaptation, chance and history to bacterial evolution. In this paper, we show that a modified M-trait Bak-Sneppen model can explain many of the experimental results in a qualitative manner.

  15. Bacterial evolution and the Bak-Sneppen model

    OpenAIRE

    Bose, Indrani; Chaudhuri, Indranath

    2001-01-01

    Recently, Lenski et al \\cite{Elena,Lenski,Travisano} have carried out several experiments on bacterial evolution. Their findings support the theory of punctuated equilibrium in biological evolution. They have further quantified the relative contributions of adaptation, chance and history to bacterial evolution. In this Brief Report, we show that a modified M-trait Bak-Sneppen model can explain many of the experimental results in a qualitative manner.

  16. Galactic evolution. I - Single-zone models. [encompassing stellar evolution and gas-star dynamic theories

    Science.gov (United States)

    Thuan, T. X.; Hart, M. H.; Ostriker, J. P.

    1975-01-01

    The two basic approaches of physical theory required to calculate the evolution of a galactic system are considered, taking into account stellar evolution theory and the dynamics of a gas-star system. Attention is given to intrinsic (stellar) physics, extrinsic (dynamical) physics, and computations concerning the fractionation of an initial mass of gas into stars. The characteristics of a 'standard' model and its variants are discussed along with the results obtained with the aid of these models.

  17. Self-organized Critical Model Of Biological Evolution

    OpenAIRE

    Chau, H. F.; Mak, L; Kwok, P. K.

    1994-01-01

    A punctuated equilibrium model of biological evolution with relative fitness between different species being the fundamental driving force of evolution is introduced. Mutation is modeled as a fitness updating cellular automaton process where the change in fitness after mutation follows a Gaussian distribution with mean $x>0$ and standard deviation $\\sigma$. Scaling behaviors are observed in our numerical simulation, indicating that the model is self-organized critical. Besides, the numerical ...

  18. Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft mission: Design, execution, and first results

    Science.gov (United States)

    Jacob, Daniel J.; Crawford, James H.; Kleb, Mary M.; Connors, Vickie S.; Bendura, Richard J.; Raper, James L.; Sachse, Glen W.; Gille, John C.; Emmons, Louisa; Heald, Colette L.

    2003-10-01

    The NASA Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft mission was conducted in February-April 2001 over the NW Pacific (1) to characterize the Asian chemical outflow and relate it quantitatively to its sources and (2) to determine its chemical evolution. It used two aircraft, a DC-8 and a P-3B, operating out of Hong Kong and Yokota Air Force Base (near Tokyo), with secondary sites in Hawaii, Wake Island, Guam, Okinawa, and Midway. The aircraft carried instrumentation for measurements of long-lived greenhouse gases, ozone and its precursors, aerosols and their precursors, related species, and chemical tracers. Five chemical transport models (CTMs) were used for chemical forecasting. Customized bottom-up emission inventories for East Asia were generated prior to the mission to support chemical forecasting and to serve as a priori for evaluation with the aircraft data. Validation flights were conducted for the Measurements Of Pollution In The Troposphere (MOPITT) satellite instrument and revealed little bias (6 ± 2%) in the MOPITT measurements of CO columns. A major event of transpacific Asian pollution was characterized through combined analysis of TRACE-P and MOPITT data. The TRACE-P observations showed that cold fronts sweeping across East Asia and the associated warm conveyor belts (WCBs) are the dominant pathway for Asian outflow to the Pacific in spring. The WCBs lift both anthropogenic and biomass burning (SE Asia) effluents to the free troposphere, resulting in complex chemical signatures. The TRACE-P data are in general consistent with a priori emission inventories, lending confidence in our ability to quantify Asian emissions from socioeconomic data and emission factors. However, the residential combustion source in rural China was found to be much larger than the a priori, and there were also unexplained chemical enhancements (HCN, CH3Cl, OCS, alkylnitrates) in Chinese urban plumes. The Asian source of CCl4 was found to be much

  19. Transport and Chemical Evolution over the Pacific (TRACE-P)Aircraft Mission: Design, Execution, and First Results

    Science.gov (United States)

    Jacob, Daniel J.; Crawford, James H.; Kleb, Mary M.; Connors, Vickie S.; Bendura, Richard J.; Raper, James L.; Sachse, Glen W.; Gille, John C.; Emmons, Louisa; Heald, Colette L.

    2003-01-01

    The NASA Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft mission was conducted in February-April 2001 over the NW Pacific (1) to characterize the Asian chemical outflow and relate it quantitatively to its sources and (2) to determine its chemical evolution. It used two aircraft, a DC-8 and a P-3B, operating out of Hong Kong and Yokota Air Force Base (near Tokyo), with secondary sites in Hawaii, Wake Island, Guam, Okinawa, and Midway. The aircraft carried instrumentation for measurements of long-lived greenhouse gases, ozone and its precursors, aerosols and their precursors, related species, and chemical tracers. Five chemical transport models (CTMs) were used for chemical forecasting. Customized bottom-up emission inventories for East Asia were generated prior to the mission to support chemical forecasting and to serve as a priori for evaluation with the aircraft data. Validation flights were conducted for the Measurements Of Pollution In The Troposphere (MOPITT) satellite instrument and revealed little bias (6 plus or minus 2%) in the MOPITT measurements of CO columns. A major event of transpacific Asian pollution was characterized through combined analysis of TRACE-P and MOPITT data. The TRACE-P observations showed that cold fronts sweeping across East Asia and the associated warm conveyor belts (WCBs) are the dominant pathway for Asian outflow to the Pacific in spring. The WCBs lift both anthropogenic and biomass burning (SE Asia) effluents to the free troposphere, resulting in complex chemical signatures. The TRACE-P data are in general consistent with a priori emission inventories, lending confidence in our ability to quantify Asian emissions from socioeconomic data and emission factors. However, the residential combustion source in rural China was found to be much larger than the a priori, and there were also unexplained chemical enhancements (HCN, CH3Cl, OCS, alkylnitrates) in Chinese urban plumes. The Asian source of CCl4 was found to

  20. Chemical Evolution in Sersic 159-03 Observed with Xmm-Newton

    Energy Technology Data Exchange (ETDEWEB)

    de Plaa, Jelle; Werner, N.; Bykov, A.M.; Kaastra, J.S.; Mendez, M.; Vink, J.; Bleeker, J.A.M.; Bonamente, M.; Peterson, J.R.; /SRON, Utrecht /Utrecht, Astron. Inst.

    2006-03-10

    Using a new long X-ray observation of the cluster of galaxies Sersic 159-03 with XMM-Newton, we derive radial temperature and abundance profiles using single- and multi-temperature models. The fits to the EPIC and RGS spectra prefer multi-temperature models especially in the core. The radial profiles of oxygen and iron measured with EPIC/RGS and the line profiles in RGS suggest that there is a dip in the O/Fe ratio in the centre of the cluster compared to its immediate surroundings. A possible explanation for the large scale metallicity distribution is that SNIa and SNII products are released in the ICM through ram-pressure stripping of in-falling galaxies. This causes a peaked metallicity distribution. In addition, SNIa in the central cD galaxy enrich mainly the centre of the cluster with iron. This excess of SNIa products is consistent with the low O/Fe ratio we detect in the centre of the cluster. We fit the abundances we obtain with yields from SNIa, SNII and Population-III stars to derive the clusters chemical evolution. We find that the measured abundance pattern does not require a Population-III star contribution. The relative contribution of the number of SNIa with respect to the total number of SNe which enrich the ICM is about 25-50%. Furthermore, we discuss the possible presence of a non-thermal component in the EPIC spectra. A potential source of this non-thermal emission can be inverse-Compton scattering between Cosmic Microwave Background (CMB) photons and relativistic electrons, which are accelerated in bow shocks associated with ram-pressure stripping of in-falling galaxies.

  1. CAN GALACTIC CHEMICAL EVOLUTION EXPLAIN THE OXYGEN ISOTOPIC VARIATIONS IN THE SOLAR SYSTEM?

    Energy Technology Data Exchange (ETDEWEB)

    Lugaro, Maria [Monash Centre for Astrophysics (MoCA), Building 28, Monash University, Clayton, VIC 3800 (Australia); Liffman, Kurt [CSIRO/MSE, P.O. Box 56, Highett, VIC 3190 (Australia); Ireland, Trevor R. [Planetary Science Institute and Research School of Earth Sciences, Australian National University, Canberra, ACT 0200 (Australia); Maddison, Sarah T., E-mail: maria.lugaro@monash.edu [Centre for Astrophysics and Supercomputing, Swinburne University, H39, P.O. Box 218, Hawthorn, VIC 3122 (Australia)

    2012-11-01

    A number of objects in primitive meteorites have oxygen isotopic compositions that place them on a distinct, mass-independent fractionation line with a slope of one on a three-isotope plot. The most popular model for describing how this fractionation arose assumes that CO self-shielding produced {sup 16}O-rich CO and {sup 16}O-poor H{sub 2}O, where the H{sub 2}O subsequently combined with interstellar dust to form relatively {sup 16}O-poor solids within the solar nebula. Another model for creating the different reservoirs of {sup 16}O-rich gas and {sup 16}O-poor solids suggests that these reservoirs were produced by Galactic chemical evolution (GCE) if the solar system dust component was somewhat younger than the gas component and both components were lying on the line of slope one in the O three-isotope plot. We argue that GCE is not the cause of mass-independent fractionation of the oxygen isotopes in the solar system. The GCE scenario is in contradiction with observations of the {sup 18}O/{sup 17}O ratios in nearby molecular clouds and young stellar objects. It is very unlikely for GCE to produce a line of slope one when considering the effect of incomplete mixing of stellar ejecta in the interstellar medium. Furthermore, the assumption that the solar system dust was younger than the gas requires unusual timescales or the existence of an important stardust component that is not theoretically expected to occur nor has been identified to date.

  2. Island Model based Differential Evolution Algorithm for Neural Network Training

    Directory of Open Access Journals (Sweden)

    Htet Thazin Tike Thein

    Full Text Available There exist many approaches to training neural network. In this system, training for feed forward neural network is introduced by using island model based differential evolution. Differential Evolution (DE has been used to determine optimal value for ANN ...

  3. Computer models of vocal tract evolution: an overview and critique

    NARCIS (Netherlands)

    B. de Boer; W. T. Fitch

    2010-01-01

    Human speech has been investigated with computer models since the invention of digital computers, and models of the evolution of speech first appeared in the late 1960s and early 1970s. Speech science and computer models have a long shared history because speech is a physical signal and can be model

  4. The Statistical Evolution of Multiple Generations of Oxidation Products in the Photochemical Aging of Chemically Reduced Organic Aerosol

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, Kevin R.; Smith, Jared D.; Kessler, Sean; Kroll, Jesse H.

    2011-10-03

    The heterogeneous reaction of hydroxyl radicals (OH) with squalane and bis(2-ethylhexyl) sebacate (BES) particles are used as model systems to examine how distributions of reactionproducts evolve during the oxidation of chemically reduced organic aerosol. A kinetic model of multigenerational chemistry, which is compared to previously measured (squalane) and new(BES) experimental data, reveals that it is the statistical mixtures of different generations of oxidation products that control the average particle mass and elemental composition during thereaction. The model suggests that more highly oxidized reaction products, although initially formed with low probability, play a large role in the production of gas phase reaction products.In general, these results highlight the importance of considering atmospheric oxidation as a statistical process, further suggesting that the underlying distribution of molecules could playimportant roles in aerosol formation as well as in the evolution of key physicochemical properties such as volatility and hygroscopicity.

  5. Chemical Pollution and Evolution of Massive Starbursts: Cleaning up the Environment in Star-Forming Galaxies

    Science.gov (United States)

    Kobulnicky, C.

    1996-12-01

    I present the results of a research program seeking to characterize the impact of massive star-clusters on the chemical and dynamical evolution of metal-poor, irregular and blue compact galaxies. The evolution of high mass stars is thought to contribute the bulk of heavy element enrichment in the interstellar medium, especially alpha -process elements like O, Si, etc. Yet, in actively star-forming galaxies, localized chemical inhomogeneities are seldom observed. Spatially-resolved optical and ultraviolet spectroscopy from the Hubble Space Telescope and ground-based observatories is used to search for chemical enrichment in the vicinity of young star clusters in nearby galaxies. VLA aperture synthesis maps are used to examine the neutral hydrogen content, dynamics, and local environment of the sample galaxies. Despite the spread in evolutionary state of the starbursts determined by the EW of Balmer emission lines and the radio continuum spectral index, few instances of localized enrichment are found. In light of these data, the ``instantaneous enrichment'' scenario for extragalactic HII regions appears less probable than one which operates on long timescales and global spatial scales. The results are consistent with the idea that starburst driven winds expel freshly synthesized metals in a hot 10(6) K phase into the halos of galaxies where they cool, condense into globules, and mix homogeneously with the rest of the galaxy on long (dynamical) timescales. The C/O and N/O ratios of the galaxies are used as new tools for measuring the recent star formation history. Implications for chemical evolution of galaxies both locally and cosmologically are developed.

  6. Modelling the evolution and diversity of cumulative culture

    OpenAIRE

    Enquist, Magnus; Ghirlanda, Stefano; Eriksson, Kimmo

    2011-01-01

    Previous work on mathematical models of cultural evolution has mainly focused on the diffusion of simple cultural elements. However, a characteristic feature of human cultural evolution is the seemingly limitless appearance of new and increasingly complex cultural elements. Here, we develop a general modelling framework to study such cumulative processes, in which we assume that the appearance and disappearance of cultural elements are stochastic events that depend on the current state of cul...

  7. BAK-SNEPPEN MODELS FOR THE EVOLUTION OF STRUCTURED KNOWLEDGE

    OpenAIRE

    Piccinini, Livio Clemente; Chang, Ting Fa Margherita; Lepellere, Maria Antonietta; Taverna, Mario; Tubaro, Giovanni

    2016-01-01

    Scientific knowledge is subject to a twin evolution, since its development towards novelty creates disconnections and inconsistencies, while the need of structure requires order and method so that transmission and comprehension can be ensured. Models of biological evolution can help to understand many social and economical phenomena where the search for optimality is hindered by voluntary or random competition. Bak-Sneppen is one of the most significant models because it balances at best expl...

  8. An Inherited Efficiencies Model of Non-Genomic Evolution

    Science.gov (United States)

    New, Michael H.; Pohorille, Andrew

    1999-01-01

    A model for the evolution of biological systems in the absence of a nucleic acid-like genome is proposed and applied to model the earliest living organisms -- protocells composed of membrane encapsulated peptides. Assuming that the peptides can make and break bonds between amino acids, and bonds in non-functional peptides are more likely to be destroyed than in functional peptides, it is demonstrated that the catalytic capabilities of the system as a whole can increase. This increase is defined to be non-genomic evolution. The relationship between the proposed mechanism for evolution and recent experiments on self-replicating peptides is discussed.

  9. Synthetic clusters of massive stars to test stellar evolution models

    CERN Document Server

    Georgy, Cyril

    2015-01-01

    During the last few years, the Geneva stellar evolution group has released new grids of stellar models, including the effect of rotation and with updated physical inputs (Ekstr\\"om et al. 2012; Georgy et al. 2013a,b). To ease the comparison between the outputs of the stellar evolution computations and the observations, a dedicated tool was developed: the Syclist toolbox (Georgy et al. 2014). It allows to compute interpolated stellar models, isochrones, synthetic clusters, and to simulate the time-evolution of stellar populations.

  10. Evolution of the stratospheric temperature and chemical composition over one Titanian year

    Energy Technology Data Exchange (ETDEWEB)

    Coustenis, Athena; Bampasidis, G.; Vinatier, S. [Laboratoire d' Etudes Spatiales et d' Instrumentation en Astrophysique (LESIA), Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, 5, place Jules Janssen, F-92195 Meudon Cedex (France); Achterberg, R. K.; Jennings, D. E.; Nixon, C. A.; Flasar, F. M.; Carlson, R. C.; Romani, P. N.; Guandique, E. A. [NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Lavvas, P. [GSMA, Université Reims Champagne-Ardenne, F-51687 Reims Cedex 2 (France); Teanby, N. A. [School of Earth Sciences, University of Bristol, Bristol BS8 1RJ (United Kingdom); Orton, G. [MS 183-501, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Stamogiorgos, S., E-mail: athena.coustenis@obspm.fr [Faculty of Physics, National and Kapodistrian University of Athens, Panepistimioupolis, GR 15783 Zographos, Athens (Greece)

    2013-12-20

    Since the Voyager 1 (V1) flyby in 1980, Titan's exploration from space and the ground has been ongoing for more than a full revolution of Saturn around the Sun (one Titanian year or 29.5 Earth years had elapsed in 2010 May). In this study, we search for temporal variations affecting Titan's atmospheric thermal and chemical structure within that year. We process Cassini/CIRS data taken during the Titan flybys from 2006-2013 and find a rather uneventful equatorial evolution. Conversely, at northern latitudes, we found enhanced abundances around the period of the northern spring equinox in mid-2009, which subsequently decreased (from 2010 to 2012), returning to values similar to those found in the V1 epoch, one Titanian year before. In the southern latitudes, since 2012, we see a trend for an increase of several trace gases (C{sub 4}H{sub 2}, C{sub 3}H{sub 4}, and HCN), indicative of a seasonal atmospheric reversal setting in. When we compare the CIRS 2010 and the 1980 V1/IRIS spectra (reanalyzed here), we find limited inter-annual variations. A return to the 1980 stratospheric temperatures and abundances is generally achieved from 50°N to 50°S, indicative of the solar radiation being the dominating energy source at 10 AU, as for the Earth, as predicted by general circulation and photochemical models. Exceptions concern the most complex hydrocarbons (C{sub 4}H{sub 2} and C{sub 3}H{sub 4}). We also consider data from ground-based and Earth-orbiting observatories (such as from the Infrared Space Observatory, revisited here) and discuss possible atmospheric composition trends during a Titanian year.

  11. Hydro-chemical study of the evolution of interstellar pre-biotic molecules during the collapse of molecular clouds

    Institute of Scientific and Technical Information of China (English)

    Liton Majumdar; Ankan Das; Sandip K. Chakrabarti; Sonali Chakrabarti

    2012-01-01

    One of the stumbling blocks for studying the evolution of interstellar molecules is the lack of adequate knowledge about the rate coefficients of various reactions which take place in the interstellar medium and molecular clouds.Some theoretical models of rate coefficients do exist in the literature for computing abundances of complex pre-biotic molecules.So far these have been used to study the abundances of these molecules in space.However,in order to obtain more accurate final compositions in these media,we have calculated the rate coefficients for the formation of some of the most important interstellar pre-biotic molecules by using quantum chemical theory.We use these rates inside our hydro-chemical model to examine the chemical evolution and final abundances of pre-biotic species during the collapsing phase of a proto-star.We find that a significant amount of various pre-biotic molecules could be produced during the collapse phase of a proto-star.We thoroughly study the formation of these molecules via successive neutral-neutral and radical-radical/radicalmolecular reactions.We present the time evolution of the chemical species with an emphasis on how the production of these molecules varies with the depth of a cloud.We compare the formation of adenine in interstellar space using our rate-coefficients and using those obtained from existing theoretical models.Formation routes of the pre-biotic molecules are found to be highly dependent on the abundances of the reactive species and the rate coefficients involved in the reactions.The presence of grains strongly affects the abundances of the gas phase species.We also carry out a comparative study between different pathways available for the synthesis of adenine,alanine,glycine and other molecules considered in our network.Despite the huge abundances of the neutral reactive species,production of adenine is found to be strongly dominated by the radical-radical/radical-molecular reaction pathways.If all the

  12. Hydro-chemical study of the evolution of interstellar pre-biotic molecules during the collapse of molecular clouds

    International Nuclear Information System (INIS)

    One of the stumbling blocks for studying the evolution of interstellar molecules is the lack of adequate knowledge about the rate coefficients of various reactions which take place in the interstellar medium and molecular clouds. Some theoretical models of rate coefficients do exist in the literature for computing abundances of complex pre-biotic molecules. So far these have been used to study the abundances of these molecules in space. However, in order to obtain more accurate final compositions in these media, we have calculated the rate coefficients for the formation of some of the most important interstellar pre-biotic molecules by using quantum chemical theory. We use these rates inside our hydro-chemical model to examine the chemical evolution and final abundances of pre-biotic species during the collapsing phase of a proto-star. We find that a significant amount of various pre-biotic molecules could be produced during the collapse phase of a proto-star. We thoroughly study the formation of these molecules via successive neutral-neutral and radical-radical/radical-molecular reactions. We present the time evolution of the chemical species with an emphasis on how the production of these molecules varies with the depth of a cloud. We compare the formation of adenine in interstellar space using our rate-coefficients and using those obtained from existing theoretical models. Formation routes of the pre-biotic molecules are found to be highly dependent on the abundances of the reactive species and the rate coefficients involved in the reactions. The presence of grains strongly affects the abundances of the gas phase species. We also carry out a comparative study between different pathways available for the synthesis of adenine, alanine, glycine and other molecules considered in our network. Despite the huge abundances of the neutral reactive species, production of adenine is found to be strongly dominated by the radical-radical/radical-molecular reaction pathways

  13. A framework for modeling human evolution.

    Science.gov (United States)

    Gintis, Herbert

    2016-01-01

    Culture-led gene-culture coevolution is a framework within which substantive explanations of human evolution must be located. It is not itself an explanation. Explanations depend on such concrete historical evolutionary factors such as the control of fire, collective child-rearing, lethal weapon technology, altruistic cooperation and punishment, and the mastery of complex collaboration protocols leading to an effective division of social labor. PMID:27561218

  14. New trajectory-driven aerosol and chemical process model Chemical and Aerosol Lagrangian Model (CALM)

    OpenAIRE

    Tunved, P.; D. G. Partridge; Korhonen, H.

    2010-01-01

    A new Chemical and Aerosol Lagrangian Model (CALM) has been developed and tested. The model incorporates all central aerosol dynamical processes, from nucleation, condensation, coagulation and deposition to cloud formation and in-cloud processing. The model is tested and evaluated against observations performed at the SMEAR II station located at Hyytiälä (61° 51' N, 24° 17' E) over a time period of two years, 2000–2001. The model shows good agreement with measurements throughout mos...

  15. Conference on chemical evolution and the origin of life: Self-organization of the macromolecules of life

    International Nuclear Information System (INIS)

    The formation of biomolecules was a necessary step in the evolution of life on earth. This interdisciplinary conference emphasized the role of replication in processes of self-organization of biological macromolecules. The present document contains abstracts of the 26 contributions to the conference on chemical evolution. The individual contributions have been indexed separately for the database

  16. Construction Method of Supernetwork Evolution Model

    Institute of Scientific and Technical Information of China (English)

    LIU; Qiang; FANG; Jin-qing; LI; Yong

    2013-01-01

    Real networks often have small-world and scale-free characteristics.Based on BA and WS model,we proposed the following construction method for TLSEM(Fig.1).Three layers are BA model(TBA),three layers are SW model(TSW),the first and third layers are BA model,the middle layer is SW model(BA-SW),the first and third layers are SW model,and the middle layer is BA model(SW-BA).The

  17. Temporal evolution of the chemical structure during the pattern transfer by ion-beam sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Ha, N.-B.; Jeong, S.; Yu, S.; Ihm, H.-I.; Kim, J.-S.

    2015-01-01

    Highlights: • Chemical analyses of the individual nano structures simultaneously with the investigation of their morphological evolution were performed. • Degradation of the transferred pattern starts before the overlayer is fully removed. • The chemical analysis reveals the severe reduction of the sputter yield of the material forming the overlayer near the interface due to the compound formation, requesting caution in the practice of the pattern transfer. - Abstract: Ru films patterned by ion-beam sputtering (IBS) serve as sacrificial masks for the transfer of the patterns to Si(1 0 0) and metallic glass substrates by continued IBS. Under the same sputter condition, however, both bare substrates remain featureless. Chemical analyses of the individual nano structures simultaneously with the investigation of their morphological evolution reveal that the pattern transfer, despite its apparent success, suffers from premature degradation before the mask is fully removed by IBS. Moreover, the residue of the mask or Ru atoms stubbornly remains near the surface, resulting in unintended doping or alloying of both patterned substrates.

  18. Planet signatures and effect of the chemical evolution of the Galactic thin-disk stars

    CERN Document Server

    Spina, Lorenzo; Ramírez, Ivan

    2016-01-01

    Context: Studies based on high-precision abundance determinations revealed that chemical patterns of solar twins are characterised by the correlation between the differential abundances relative to the Sun and the condensation temperatures (Tc) of the elements. It has been suggested that the origin of this relation is related to the chemical evolution of the Galactic disk, but other processes, associated with the presence of planets around stars, might also be involved. Aims: We analyse HIRES spectra of 14 solar twins and the Sun to provide new insights on the mechanisms that can determine the relation between [X/H] and Tc. Methods: Our spectroscopic analysis produced stellar parameters (Teff, log g, [Fe/H], and $\\xi$), ages, masses, and abundances of 22 elements (C, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, and Ba). We used these determinations to place new constraints on the chemical evolution of the Galactic disk and to verify whether this process alone can explain the diff...

  19. A kinetic model for chemical neurotransmission

    Science.gov (United States)

    Ramirez-Santiago, Guillermo; Martinez-Valencia, Alejandro; Fernandez de Miguel, Francisco

    Recent experimental observations in presynaptic terminals at the neuromuscular junction indicate that there are stereotyped patterns of cooperativeness in the fusion of adjacent vesicles. That is, a vesicle in hemifusion process appears on the side of a fused vesicle and which is followed by another vesicle in a priming state while the next one is in a docking state. In this talk we present a kinetic model for this morphological pattern in which each vesicle state previous to the exocytosis is represented by a kinetic state. This chain states kinetic model can be analyzed by means of a Master equation whose solution is simulated with the stochastic Gillespie algorithm. With this approach we have reproduced the responses to the basal release in the absence of stimulation evoked by the electrical activity and the phenomena of facilitation and depression of neuromuscular synapses. This model offers new perspectives to understand the underlying phenomena in chemical neurotransmission based on molecular interactions that result in the cooperativity between vesicles during neurotransmitter release. DGAPA Grants IN118410 and IN200914 and Conacyt Grant 130031.

  20. Surfactant-controlled damage evolution during chemical mechanical planarization of nanoporous films

    International Nuclear Information System (INIS)

    The integration of nanoporous organosilicate thin films involving chemical mechanical planarization (CMP) is a significant challenge due the evolution of defects in the films during CMP in the form of cracking and delamination. This study shows that small changes in CMP electrolyte chemistry and surfactant additions can have dramatic effects on crack growth rates in the films. Crack growth rates were sensitive to the type of electrolyte and decreased in the presence of electrolytes that caused crack tip blunting. Growth rates were also sensitive to nonionic surfactant additions where molecular structure and weight were demonstrated to be important variables. An optimized blend of surfactants and electrolytes can significantly retard defect evolution due to molecular bridging. Surfactant self-assembly and resulting molecular bridging were characterized by in situ atomic force microscopy and used to quantify the molecular bridging observed.

  1. Chemically induced skin carcinogenesis: Updates in experimental models (Review).

    Science.gov (United States)

    Neagu, Monica; Caruntu, Constantin; Constantin, Carolina; Boda, Daniel; Zurac, Sabina; Spandidos, Demetrios A; Tsatsakis, Aristidis M

    2016-05-01

    Skin cancer is one of the most common malignancies affecting humans worldwide, and its incidence is rapidly increasing. The study of skin carcinogenesis is of major interest for both scientific research and clinical practice and the use of in vivo systems may facilitate the investigation of early alterations in the skin and of the mechanisms involved, and may also lead to the development of novel therapeutic strategies for skin cancer. This review outlines several aspects regarding the skin toxicity testing domain in mouse models of chemically induced skin carcinogenesis. There are important strain differences in view of the histological type, development and clinical evolution of the skin tumor, differences reported decades ago and confirmed by our hands‑on experience. Using mouse models in preclinical testing is important due to the fact that, at the molecular level, common mechanisms with human cutaneous tumorigenesis are depicted. These animal models resemble human skin cancer development, in that genetic changes caused by carcinogens and pro‑inflammatory cytokines, and simultaneous inflammation sustained by pro‑inflammatory cytokines and chemokines favor tumor progression. Drugs and environmental conditions can be tested using these animal models. keeping in mind the differences between human and rodent skin physiology. PMID:26986013

  2. Experimental evolution in silico: a custom-designed mathematical model for virulence evolution of Bacillus thuringiensis.

    Science.gov (United States)

    Strauß, Jakob Friedrich; Crain, Philip; Schulenburg, Hinrich; Telschow, Arndt

    2016-08-01

    Most mathematical models on the evolution of virulence are based on epidemiological models that assume parasite transmission follows the mass action principle. In experimental evolution, however, mass action is often violated due to controlled infection protocols. This "theory-experiment mismatch" raises the question whether there is a need for new mathematical models to accommodate the particular characteristics of experimental evolution. Here, we explore the experimental evolution model system of Bacillus thuringiensis as a parasite and Caenorhabditis elegans as a host. Recent experimental studies with strict control of parasite transmission revealed that one-sided adaptation of B. thuringiensis with non-evolving hosts selects for intermediate or no virulence, sometimes coupled with parasite extinction. In contrast, host-parasite coevolution selects for high virulence and for hosts with strong resistance against B. thuringiensis. In order to explain the empirical results, we propose a new mathematical model that mimics the basic experimental set-up. The key assumptions are: (i) controlled parasite transmission (no mass action), (ii) discrete host generations, and (iii) context-dependent cost of toxin production. Our model analysis revealed the same basic trends as found in the experiments. Especially, we could show that resistant hosts select for highly virulent bacterial strains. Moreover, we found (i) that the evolved level of virulence is independent of the initial level of virulence, and (ii) that the average amount of bacteria ingested significantly affects the evolution of virulence with fewer bacteria ingested selecting for highly virulent strains. These predictions can be tested in future experiments. This study highlights the usefulness of custom-designed mathematical models in the analysis and interpretation of empirical results from experimental evolution.

  3. Chemical cleaning specification: few tube test model

    International Nuclear Information System (INIS)

    The specification is for the waterside chemical cleaning of the 2 1/4 Cr - 1 Mo steel steam generator tubes. It describes the reagents and conditions for post-chemical cleaning passivation of the evaporator tubes

  4. The Gaia-ESO Survey: Sodium and aluminium abundances in giants and dwarfs. Implications for stellar and Galactic chemical evolution

    Science.gov (United States)

    Smiljanic, R.; Romano, D.; Bragaglia, A.; Donati, P.; Magrini, L.; Friel, E.; Jacobson, H.; Randich, S.; Ventura, P.; Lind, K.; Bergemann, M.; Nordlander, T.; Morel, T.; Pancino, E.; Tautvaišienė, G.; Adibekyan, V.; Tosi, M.; Vallenari, A.; Gilmore, G.; Bensby, T.; François, P.; Koposov, S.; Lanzafame, A. C.; Recio-Blanco, A.; Bayo, A.; Carraro, G.; Casey, A. R.; Costado, M. T.; Franciosini, E.; Heiter, U.; Hill, V.; Hourihane, A.; Jofré, P.; Lardo, C.; de Laverny, P.; Lewis, J.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Sbordone, L.; Sousa, S. G.; Worley, C. C.; Zaggia, S.

    2016-05-01

    Context. Stellar evolution models predict that internal mixing should cause some sodium overabundance at the surface of red giants more massive than ~1.5-2.0 M⊙. The surface aluminium abundance should not be affected. Nevertheless, observational results disagree about the presence and/or the degree of Na and Al overabundances. In addition, Galactic chemical evolution models adopting different stellar yields lead to very different predictions for the behavior of [Na/Fe] and [Al/Fe] versus [Fe/H]. Overall, the observed trends of these abundances with metallicity are not well reproduced. Aims: We readdress both issues, using new Na and Al abundances determined within the Gaia-ESO Survey. Our aim is to obtain better observational constraints on the behavior of these elements using two samples: i) more than 600 dwarfs of the solar neighborhood and of open clusters and ii) low- and intermediate-mass clump giants in six open clusters. Methods: Abundances were determined using high-resolution UVES spectra. The individual Na abundances were corrected for nonlocal thermodynamic equilibrium effects. For the Al abundances, the order of magnitude of the corrections was estimated for a few representative cases. For giants, the abundance trends with stellar mass are compared to stellar evolution models. For dwarfs, the abundance trends with metallicity and age are compared to detailed chemical evolution models. Results: Abundances of Na in stars with mass below ~2.0 M⊙, and of Al in stars below ~3.0 M⊙, seem to be unaffected by internal mixing processes. For more massive stars, the Na overabundance increases with stellar mass. This trend agrees well with predictions of stellar evolutionary models. For Al, our only cluster with giants more massive than 3.0 M⊙, NGC 6705, is Al enriched. However, this might be related to the environment where the cluster was formed. Chemical evolution models that well fit the observed [Na/Fe] vs. [Fe/H] trend in solar neighborhood dwarfs

  5. Hydro-chemical evolution of groundwater and mixing between aquifers: a statistical approach based on major ions

    Science.gov (United States)

    Sun, Linhua; Gui, Herong

    2015-03-01

    Geochemical analysis is a useful tool in hydrogeological assessment, particularly in constructing a conceptual model of a hydrogeological system. In this study, major ion concentrations of 53 groundwater samples from the coal-bearing aquifer in the Qidong coal mine, northern Anhui Province of China have been processed by statistical analysis for understanding either hydro-chemical characteristics or hydrological evolution, which will be useful for the safety of coal mining. The results suggest that most of the samples are Na-SO4 and Na-HCO3 types, and their hydro-chemical compositions are mainly controlled by dissolution of more soluble minerals (e.g. calcite) and weathering of silicate minerals (e.g. plagioclase). Two groups of samples have been subdivided by quantile and scatter plots of factor scores, one is related to different degrees of water-rock interactions and another is related to groundwater mixing. Moreover, four end members have been identified and the mixing calculation suggests that the groundwater samples affected by mixing have 20-100 % contribution from the loose layer aquifer (LA), and therefore, groundwater from the LA in the coal mine should be taken seriously during coal mining. The study demonstrated that statistical analysis is useful for connecting the hydrochemistry of groundwater with hydrological evolution of the aquifer.

  6. Contribution of Neutron Star Mergers to the r-Process Chemical Evolution in the Hierarchical Galaxy Formation

    Science.gov (United States)

    Komiya, Yutaka; Shigeyama, Toshikazu

    2016-10-01

    The main astronomical source of r-process elements has not yet been identified. One plausible site is neutron star mergers (NSMs), but from the perspective of the Galactic chemical evolution, it has been pointed out that NSMs cannot reproduce the observed r-process abundance distribution of metal-poor stars at [{Fe}/{{H}}]\\lt -3. Recently, Tsujimoto & Shigeyama pointed out that NSM ejecta can spread into a much larger volume than ejecta from a supernova. We re-examine the enrichment of r-process elements by NSMs considering this difference in propagation using the chemical evolution model under the hierarchical galaxy formation. The observed r-process enhanced stars around [{Fe}/{{H}}]∼ -3 are reproduced if the star formation efficiency is lower for low-mass galaxies under a realistic delay-time distribution for NSMs. We show that a significant fraction of NSM ejecta escape from its host proto-galaxy to pollute intergalactic matter and other proto-galaxies. The propagation of r-process elements over proto-galaxies changes the abundance distribution at [{Fe}/{{H}}]\\lt -3 and obtains distribution compatible with observations of the Milky Way halo stars. In particular, the pre-enrichment of intergalactic medium explains the observed scarcity of extremely metal-poor stars without Ba and abundance distribution of r-process elements at [{Fe}/{{H}}]≲ -3.5.

  7. Contribution of Neutron Star Mergers to the R-process Chemical Evolution in the Hierarchical Galaxy Formation

    CERN Document Server

    Komiya, Yutaka

    2016-01-01

    The main astronomical source of r-process elements has not yet been identified. One plausible site is neutron star mergers (NSMs), but from perspective of the Galactic chemical evolution, it has been pointed out that NSMs cannot reproduce the observed r-process abundance distribution of metal-poor stars at [Fe/H] $< -3$. Recently, Tsujimoto & Shigeyama (2014) pointed out that NSM ejecta can spread into much larger volume than ejecta from a supernova. We re-examine the enrichment of r-process elements by NSMs considering this difference in propagation using the chemical evolution model under the hierarchical galaxy formation. The observed r-process enhanced stars around [Fe/H] $\\sim -3$ are reproduced if the star formation efficiency is lower for low-mass galaxies under a realistic delay time distribution for NSMs. We show that a significant fraction of NSM ejecta escape from its host proto-galaxy to pollute intergalactic matter and other proto-galaxies. The propagation of r-process elements over proto-...

  8. Early time evolution of negative ion clouds and electron density depletions produced during electron attachment chemical release experiments

    Science.gov (United States)

    Scales, W. A.; Bernhardt, P. A.; Ganguli, G.

    1994-01-01

    Two-dimensional electrostatic particle-in-cell simulations are used to study the early time evolution of electron depletions and negative ion clouds produced during electron attachment chemical releases in the ionosphere. The simulation model considers the evolution in the plane perpendicular to the magnetic field and a three-species plasma that contains electrons, positive ions, and also heavy negative ions that result as a by-product of the electron attachment reaction. The early time evolution (less than the negative ion cyclotron period) of the system shows that a negative charge surplus initially develops outside of the depletion boundary as the heavy negative ions move across the boundary. The electrons are initially restricted from moving into the depletion due to the magnetic field. An inhomogenous electric field develops across the boundary layer due to this charge separation. A highly sheared electron flow velocity develops in the depletion boundary due to E x B and Delta-N x B drifts that result from electron density gradients and this inhomogenous electric field. Structure eventually develops in the depletion boundary layer due to low-frequency electrostatic waves that have growth times shorter than the negative ion cyclotron period. It is proposed that these waves are most likely produced by the electron-ion hybrid instability that results from sufficiently large shears in the electron flow velocity.

  9. A mesoscale chemical transport model (MEDIUM) nested in a global chemical transport model (MEDIANTE)

    Energy Technology Data Exchange (ETDEWEB)

    Claveau, J.; Ramaroson, R. [Office National d`Etudes et de Recherches Aerospatiales (ONERA), 92 - Chatillon (France)

    1997-12-31

    The lower stratosphere and upper troposphere (UT-LS) are frequently subject to mesoscale or local scale exchange of air masses occurring along discontinuities. This exchange (e.g. downward) can constitute one of the most important source of ozone from the stratosphere down to the middle troposphere where strong mixing dilutes the air mass and competing the non-linear chemistry. The distribution of the chemical species in the troposphere and the lower stratosphere depends upon various source emissions, e.g. from polluted boundary layer or from aircraft emissions. Global models, as well as chemical transport models describe the climatological state of the atmosphere and are not able to describe correctly the stratosphere and troposphere exchange. Mesoscale models go further in the description of smaller scales and can reasonably include a rather detailed chemistry. They can be used to assess the budget of NO{sub x} from aircraft emissions in a mesoscale domain. (author) 4 refs.

  10. Modelin the Transport and Chemical Evolution of Onshore and Offshore Emissions and Their Impact on Local and Regional Air Quality Using a Variable-Grid-Resolution Air Quality Model

    Energy Technology Data Exchange (ETDEWEB)

    Adel Hanna

    2008-10-16

    The overall objective of this research project was to develop an innovative modeling technique to adequately model the offshore/onshore transport of pollutants. The variable-grid modeling approach that was developed alleviates many of the shortcomings of the traditionally used nested regular-grid modeling approach, in particular related to biases near boundaries and the excessive computational requirements when using nested grids. The Gulf of Mexico region contiguous to the Houston-Galveston area and southern Louisiana was chosen as a test bed for the variable-grid modeling approach. In addition to the onshore high pollution emissions from various sources in those areas, emissions from on-shore and off-shore oil and gas exploration and production are additional sources of air pollution. We identified case studies for which to perform meteorological and air quality model simulations. Our approach included developing and evaluating the meteorological, emissions, and chemistry-transport modeling components for the variable-grid applications, with special focus on the geographic areas where the finest grid resolution was used. We evaluated the performance of two atmospheric boundary layer (ABL) schemes, and identified the best-performing scheme for simulating mesoscale circulations for different grid resolutions. Use of a newly developed surface data assimilation scheme resulted in improved meteorological model simulations. We also successfully ingested satellite-derived sea surface temperatures (SSTs) into the meteorological model simulations, leading to further improvements in simulated wind, temperature, and moisture fields. These improved meteorological fields were important for variable-grid simulations, especially related to capturing the land-sea breeze circulations that are critical for modeling offshore/onshore transport of pollutants in the Gulf region. We developed SMOKE-VGR, the variable-grid version of the SMOKE emissions processing model, and tested and

  11. Stellar Evolution Models of Young Stars: Progress and Limitations

    CERN Document Server

    Feiden, Gregory A

    2015-01-01

    Stellar evolution models are a cornerstone of young star astrophysics, which necessitates that they yield accurate and reliable predictions of stellar properties. Here, I review the current performance of stellar evolution models against young astrophysical benchmarks and highlight recent progress incorporating non-standard physics, such as magnetic field and starspots, to explain observed deficiencies. While addition of these physical processes leads to improved agreement between models and observations, there are several fundamental limitations in our understanding about how these physical processes operate. These limitations inhibit our ability to form a coherent picture of the essential physics needed to accurately compute young stellar models, but provide rich avenues for further exploration.

  12. The first Step of Evolution from the View Point of chemical Catalysis

    Science.gov (United States)

    Parmon, V.; Snytnikov, V.

    A kinetic analysis of the steady state replication of molecules Xi due to consumption a "food" R via simple autocatalytic processes likekiktiR + Xi2Xi ,XiP,k -i and its more complicated analogs demonstrates inevitability of arising an irreversible and thus progressive evolution of autocatalyst molecules Xi , if only the autocatalysts can undergo a chemical mutation and the concentration of "food" R can fall below a critical valueRcri = k ti / k t . The natural selection of simple autocatalysts mimics a protolife and occurs in only one direction toward minimizing the value of Rcri which is improved through the mutation. The driving force of this selection is the long-term existence of a deficiency in "food" R. No doubt, this ability of simple autocatalytic systems to an irreversible progressive evolution is a total analogy of the existence of a primitive biological memory. This evidences in the possibility of starting a progressive prebiotic evolution even in the absence of special evolution information carriers like RNA or DNA molecules. One of the most plausible candidates for the first protolife autocatalytic reaction is the well-known "formosa" reaction of autocatalytic polymerization of formaldehyde into a variety of C3 -C6 monosaccharides in water solution catalyzed by the dissolved omnipresent calcium cations. Note, that formaldehyde was also a typical constituent of the Protoearth atmosphere. Mutation of saccharides is very easy and can be exemplified by any chemical modification of saccharide molecules, e.g., by nitrogen- or phosphate-containing derivatives, with the formation and progressive selection of initial biological building blocks. One may expect that the natural selection in abiogenous formosa systems could serve as a trigger of evolution mechanism. Also, formosa systems themselves may be a real precursor of appearance of the first and most primitive, but operating RNA molecules that resulted later in the first biological systems. Thus, the RNA or

  13. Chemical leasing business models: a contribution to the effective risk management of chemical substances.

    Science.gov (United States)

    Ohl, Cornelia; Moser, Frank

    2007-08-01

    Chemicals indisputably contribute greatly to the well-being of modern societies. Apart from such benefits, however, chemicals often pose serious threats to human health and the environment when improperly handled. Therefore, the European Commission has proposed a regulatory framework for the Registration, Evaluation and Authorization of Chemicals (REACH) that requires companies using chemicals to gather pertinent information on the properties of these substances. In this article, we argue that the crucial aspect of this information management may be the honesty and accuracy of the transfer of relevant knowledge from the producer of a chemical to its user. This may be particularly true if the application of potentially hazardous chemicals is not part of the user's core competency. Against this background, we maintain that the traditional sales concept provides no incentives for transferring this knowledge. The reason is that increased user knowledge of a chemical's properties may raise the efficiency of its application. That is, excessive and unnecessary usage will be eliminated. This, in turn, would lower the amount of chemicals sold and in competitive markets directly decrease profits of the producer. Through the introduction of chemical leasing business models, we attempt to present a strategy to overcome the incentive structure of classical sales models, which is counterproductive for the transfer of knowledge. By introducing two models (a Model A that differs least and a Model B that differs most from traditional sales concepts), we demonstrate that chemical leasing business models are capable of accomplishing the goal of Registration, Evaluation and Authorization of Chemicals: to effectively manage the risk of chemicals by reducing the total quantity of chemicals used, either by a transfer of applicable knowledge from the lessor to the lessee (Model A) or by efficient application of the chemical by the lessor him/herself (Model B).

  14. Topological evolution of virtual social networks by modeling social activities

    Science.gov (United States)

    Sun, Xin; Dong, Junyu; Tang, Ruichun; Xu, Mantao; Qi, Lin; Cai, Yang

    2015-09-01

    With the development of Internet and wireless communication, virtual social networks are becoming increasingly important in the formation of nowadays' social communities. Topological evolution model is foundational and critical for social network related researches. Up to present most of the related research experiments are carried out on artificial networks, however, a study of incorporating the actual social activities into the network topology model is ignored. This paper first formalizes two mathematical abstract concepts of hobbies search and friend recommendation to model the social actions people exhibit. Then a social activities based topology evolution simulation model is developed to satisfy some well-known properties that have been discovered in real-world social networks. Empirical results show that the proposed topology evolution model has embraced several key network topological properties of concern, which can be envisioned as signatures of real social networks.

  15. Hierarchical Model for the Evolution of Cloud Complexes

    CERN Document Server

    Sánchez, N; Sanchez, Nestor; Parravano, Antonio

    1999-01-01

    The structure of cloud complexes appears to be well described by a "tree structure" representation when the image is partitioned into "clouds". In this representation, the parent-child relationships are assigned according to containment. Based on this picture, a hierarchical model for the evolution of Cloud Complexes, including star formation, is constructed, that follows the mass evolution of each sub-structure by computing its mass exchange (evaporation or condensation) with its parent and children, which depends on the radiation density at the interphase. For the set of parameters used as a reference model, the system produces IMFs with a maximum at too high mass (~2 M_sun) and the characteristic times for evolution seem too long. We show that these properties can be improved by adjusting model parameters. However, the emphasis here is to illustrate some general properties of this nonlinear model for the star formation process. Notwithstanding the simplifications involved, the model reveals an essential fe...

  16. Influence of chemical disorder on energy dissipation and defect evolution in concentrated solid solution alloys

    Science.gov (United States)

    Zhang, Yanwen; Stocks, G. Malcolm; Jin, Ke; Lu, Chenyang; Bei, Hongbin; Sales, Brian C.; Wang, Lumin; Béland, Laurent K.; Stoller, Roger E.; Samolyuk, German D.; Caro, Magdalena; Caro, Alfredo; Weber, William J.

    2015-10-01

    A grand challenge in materials research is to understand complex electronic correlation and non-equilibrium atomic interactions, and how such intrinsic properties and dynamic processes affect energy transfer and defect evolution in irradiated materials. Here we report that chemical disorder, with an increasing number of principal elements and/or altered concentrations of specific elements, in single-phase concentrated solid solution alloys can lead to substantial reduction in electron mean free path and orders of magnitude decrease in electrical and thermal conductivity. The subsequently slow energy dissipation affects defect dynamics at the early stages, and consequentially may result in less deleterious defects. Suppressed damage accumulation with increasing chemical disorder from pure nickel to binary and to more complex quaternary solid solutions is observed. Understanding and controlling energy dissipation and defect dynamics by altering alloy complexity may pave the way for new design principles of radiation-tolerant structural alloys for energy applications.

  17. Chemical Kinetic Modeling of Biofuel Combustion

    Science.gov (United States)

    Sarathy, Subram Maniam

    Bioalcohols, such as bioethanol and biobutanol, are suitable replacements for gasoline, while biodiesel can replace petroleum diesel. Improving biofuel engine performance requires understanding its fundamental combustion properties and the pathways of combustion. This study's contribution is experimentally validated chemical kinetic combustion mechanisms for biobutanol and biodiesel. Fundamental combustion data and chemical kinetic mechanisms are presented and discussed to improve our understanding of biofuel combustion. The net environmental impact of biobutanol (i.e., n-butanol) has not been studied extensively, so this study first assesses the sustainability of n-butanol derived from corn. The results indicate that technical advances in fuel production are required before commercializing biobutanol. The primary contribution of this research is new experimental data and a novel chemical kinetic mechanism for n-butanol combustion. The results indicate that under the given experimental conditions, n-butanol is consumed primarily via abstraction of hydrogen atoms to produce fuel radical molecules, which subsequently decompose to smaller hydrocarbon and oxygenated species. The hydroxyl moiety in n-butanol results in the direct production of the oxygenated species such as butanal, acetaldehyde, and formaldehyde. The formation of these compounds sequesters carbon from forming soot precursors, but they may introduce other adverse environmental and health effects. Biodiesel is a mixture of long chain fatty acid methyl esters derived from fats and oils. This research study presents high quality experimental data for one large fatty acid methyl ester, methyl decanoate, and models its combustion using an improved skeletal mechanism. The results indicate that methyl decanoate is consumed via abstraction of hydrogen atoms to produce fuel radicals, which ultimately lead to the production of alkenes. The ester moiety in methyl decanoate leads to the formation of low molecular

  18. Present state and chemical evolution of the atmospheres of Titan, Triton, and Pluto

    International Nuclear Information System (INIS)

    An evaluation is made of the current understanding of the atmospheres of Titan, Triton, and Pluto, as well as of theoretical models for their origin and evolution. All three atmospheres contain methane, while Titan, and probably Triton, have nitrogen. The primary driver in the evolution of the Titan atmosphere has been the irreversible photolysis of methane. If a surface reservoir of liquid methane exists to resupply the atmosphere, it is subject to enrichment in ethane due to the long-term photolysis of methane. The key issue in the origin and early evolution of Titan's atmosphere is the source of molecular nitrogen; two schemes for the conversion of ammonia to nitrogen have been considered

  19. Coupled thermo-hydro-chemical models of swelling bentonites

    Science.gov (United States)

    Samper, Javier; Mon, Alba; Zheng, Liange; Montenegro, Luis; Naves, Acacia; Pisani, Bruno

    2014-05-01

    The disposal of radioactive waste in deep geological repositories is based on the multibarrier concept of retention of the waste by a combination of engineered and geological barriers. The engineered barrier system (EBS) includes the solid conditioned waste-form, the waste container, the buffer made of materials such as clay, grout or crushed rock that separate the waste package from the host rock and the tunnel linings and supports. The geological barrier supports the engineered system and provides stability over the long term during which time radioactive decay reduces the levels of radioactivity. The strong interplays among thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes during the hydration, thermal and solute transport stages of the engineered barrier system (EBS) of a radioactive waste repository call for coupled THMC models for the metallic overpack, the unsaturated compacted bentonite and the concrete liner. Conceptual and numerical coupled THMC models of the EBS have been developed, which have been implemented in INVERSE-FADES-CORE. Chemical reactions are coupled to the hydrodynamic processes through chemical osmosis (C-H coupling) while bentonite swelling affects solute transport via changes in bentonite porosity changes (M-H coupling). Here we present THMC models of heating and hydration laboratory experiments performed by CIEMAT (Madrid, Spain) on compacted FEBEX bentonite and numerical models for the long-term evolution of the EBS for 1 Ma. The changes in porosity caused by swelling are more important than those produced by the chemical reactions during the early evolution of the EBS (t < 100 years). For longer times, however, the changes in porosity induced by the dissolution/precipitation reactions are more relevant due to: 1) The effect of iron mineral phases (corrosion products) released by the corrosion of the carbon steel canister; and 2) The hyper alkaline plume produced by the concrete liner. Numerical results show that

  20. Molybdenum and technetium cycle in the environment. Physical chemical evolution and mobility in soils and plants

    International Nuclear Information System (INIS)

    Molybdenum 99 and technetium 99 from liquid discharges of base nuclear installations (reactors, reprocessing plants, UF6 treatment, etc.) can reach the environment via irrigation waters and atmospheric deposits. The contribution to the soil by irrigation results in a physical-chemical transformation, the results of which, in the case of technetium 99, could be volatilization via microbes. The changes in the physical-chemical forms of technetium in different soils reveals the preponderant effect of the initial amount deposited. The determination of the rate of technetium and molybdenum assimilation shows a certain similarity in behaviour; yet the localization of these isotopes is not the same. The transfer of molybdenum and technetium via the root system is different in its intensity; this is mainly due to different physical-chemical forms. Finally, each isotope has an optimum assimilation threshold and a toxicity threshold. The study of the physical-chemical evolution and the mobility in the soil-plant-water table system of these two isotopes shows a new aspect with respect to certain transfer channels to the human being

  1. Multiobjective optimization of an extremal evolution model

    International Nuclear Information System (INIS)

    We propose a two-dimensional model for a co-evolving ecosystem that generalizes the extremal coupled map lattice model. The model takes into account the concept of multiobjective optimization. We find that the system self-organizes into a critical state. The distributions of the distances between subsequent mutations as well as the distribution of avalanches sizes follow power law. (author)

  2. Analysis of the chemical evolution of the Galactic disk via dynamical simulations of the open cluster system

    OpenAIRE

    Tecce, T. E.; Pellizza, L. J.; Piatti, A. E.

    2006-01-01

    For several decades now, open clusters have been used to study the structure and chemical evolution of the disk of our Galaxy. Due to the fact that their ages and metallicities can be determined with relatively good precision, and since they can be observed even at great distances, they are excellent tracers of the variations in the abundance of heavy chemical elements with age and position in the Galactic disk. In the present work we analyze the star formation history and the chemical evolut...

  3. Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft mission: Design, execution, and first results

    OpenAIRE

    Jacob, Daniel James; Crawford, James; Kleb, Mary; Connors, VIckie; Bendura, Richard; Raper, James; Sachse, Glen; Gille, John; Emmons, Louisa; Heald, Colette

    2003-01-01

    The NASA Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft mission was conducted in February–April 2001 over the NW Pacific (1) to characterize the Asian chemical outflow and relate it quantitatively to its sources and (2) to determine its chemical evolution. It used two aircraft, a DC-8 and a P-3B, operating out of Hong Kong and Yokota Air Force Base (near Tokyo), with secondary sites in Hawaii, Wake Island, Guam, Okinawa, and Midway. The aircraft carried instrumentation f...

  4. A last updating evolution model for online social networks

    Science.gov (United States)

    Bu, Zhan; Xia, Zhengyou; Wang, Jiandong; Zhang, Chengcui

    2013-05-01

    As information technology has advanced, people are turning to electronic media more frequently for communication, and social relationships are increasingly found on online channels. However, there is very limited knowledge about the actual evolution of the online social networks. In this paper, we propose and study a novel evolution network model with the new concept of “last updating time”, which exists in many real-life online social networks. The last updating evolution network model can maintain the robustness of scale-free networks and can improve the network reliance against intentional attacks. What is more, we also found that it has the “small-world effect”, which is the inherent property of most social networks. Simulation experiment based on this model show that the results and the real-life data are consistent, which means that our model is valid.

  5. Chemical Mechanism Solvers in Air Quality Models

    OpenAIRE

    Linford, John C.; Adrian Sandu; Rolf Sander; Hong Zhang

    2011-01-01

    The solution of chemical kinetics is one of the most computationally intensive tasks in atmospheric chemical transport simulations. Due to the stiff nature of the system, implicit time stepping algorithms which repeatedly solve linear systems of equations are necessary. This paper reviews the issues and challenges associated with the construction of efficient chemical solvers, discusses several families of algorithms, presents strategies for increasing computational efficiency, and gives insi...

  6. Comment on "Avalanche dynamics in evolution, growth and depinning models"

    CERN Document Server

    Dahlbom, M; Dahlbom, Mats; Irback, Anders

    1996-01-01

    In a recent paper Paczuski, Maslov and Bak present a comprehensive theory of avalanche dynamics in models of growth, interface depinning and evolution. One of their main results is the so-called gamma equation, which is claimed to be exact. In this note it is shown that this equation requires a numerical correction factor in order to become exact. The exactness is needed when using the equation to determine the exponent \\gamma. The correct equation is tested against numerical results for the Bak-Sneppen evolution model and two closely related models, and it turns out that it improves the description of data in a statistically significant way.

  7. Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries.

    Science.gov (United States)

    Lin, Feng; Markus, Isaac M; Nordlund, Dennis; Weng, Tsu-Chien; Asta, Mark D; Xin, Huolin L; Doeff, Marca M

    2014-01-01

    The present study sheds light on the long-standing challenges associated with high-voltage operation of LiNi(x)Mn(x)Co(1-2x)O2 cathode materials for lithium-ion batteries. Using correlated ensemble-averaged high-throughput X-ray absorption spectroscopy and spatially resolved electron microscopy and spectroscopy, here we report structural reconstruction (formation of a surface reduced layer, to transition) and chemical evolution (formation of a surface reaction layer) at the surface of LiNi(x)Mn(x)Co(1-2x)O2 particles. These are primarily responsible for the prevailing capacity fading and impedance buildup under high-voltage cycling conditions, as well as the first-cycle coulombic inefficiency. It was found that the surface reconstruction exhibits a strong anisotropic characteristic, which predominantly occurs along lithium diffusion channels. Furthermore, the surface reaction layer is composed of lithium fluoride embedded in a complex organic matrix. This work sets a refined example for the study of surface reconstruction and chemical evolution in battery materials using combined diagnostic tools at complementary length scales. PMID:24670975

  8. Surface reconstruction and chemical evolution of stoichiometric layered cathode materials for lithium-ion batteries.

    Science.gov (United States)

    Lin, Feng; Markus, Isaac M; Nordlund, Dennis; Weng, Tsu-Chien; Asta, Mark D; Xin, Huolin L; Doeff, Marca M

    2014-03-27

    The present study sheds light on the long-standing challenges associated with high-voltage operation of LiNi(x)Mn(x)Co(1-2x)O2 cathode materials for lithium-ion batteries. Using correlated ensemble-averaged high-throughput X-ray absorption spectroscopy and spatially resolved electron microscopy and spectroscopy, here we report structural reconstruction (formation of a surface reduced layer, to transition) and chemical evolution (formation of a surface reaction layer) at the surface of LiNi(x)Mn(x)Co(1-2x)O2 particles. These are primarily responsible for the prevailing capacity fading and impedance buildup under high-voltage cycling conditions, as well as the first-cycle coulombic inefficiency. It was found that the surface reconstruction exhibits a strong anisotropic characteristic, which predominantly occurs along lithium diffusion channels. Furthermore, the surface reaction layer is composed of lithium fluoride embedded in a complex organic matrix. This work sets a refined example for the study of surface reconstruction and chemical evolution in battery materials using combined diagnostic tools at complementary length scales.

  9. ASTRO-H White Paper - Chemical Evolution in High-z Universe

    CERN Document Server

    Tashiro, M S; Ohno, M; Sameshima, H; Seta, H; Ueno, H; Nakagawa, T; Tamura, T; Paerels, F; Kawai, N

    2014-01-01

    In this paper, we demonstrate ASTRO-H's capability to measure the chemical evolution in the high-z (z <~ 3) universe by observing X-ray afterglows of gamma-ray bursts (GRBs) and distant Blazars. Utilizing these sources as background light sources, the excellent energy resolution of ASTRO-H/SXS allows us to detect emission and absorption features from heavy elements in the circumstellar material in the host galaxies, from the intergalactic medium (IGM) and in the ejecta of GRB explosions. In particular, we can constrain the existence of the warm-hot intergalactic material (WHIM), thought to contain most of the baryons at redshift of z < ~3, with a typical exposure of one day for a follow-up observation of a GRB afterglow or 300 ks exposure for several distant Blazars. In addition to the chemical evolution study, the combination of the SGD, HXI, SXI and SXS will measure, for the first time, the temporal behavior of the spectral continuum of GRB afterglows and Blazars over a broad energy range and short ti...

  10. Chemical evolution at the coasts of active volcanic islands in a primordial salty ocean

    Science.gov (United States)

    Strasdeit, H.; Fox, S.

    2008-09-01

    formula (CaCl2)3(Hala)2 · 6H2O. The coordination has a significant influence on the thermal behavior of the amino acids. It prevents them from subliming and forces them to undergo chemical reactions when heated. In fact, the hot-volcanic-coast scenario comprises not only the formation of solid sea salt-amino acid mixtures but also their subsequent exposure to higher temperatures. Chemical evolution I: from amino acids to pyrroles On heating to 350 °C in a slow stream of nitrogen gas, the solid salt-amino acid mixtures described above produced several methylated and ethylated pyrroles 1 (amino acid = rac-alanine, rac-valine, α-aminoisobutyric acid and rac-isovaline, respectively; see Fig. 1). The quantitative importance of this reaction in a prebiotic environment can be estimated as follows. During a volcanic eruption, more than 108 m3 of lava can enter the sea and evaporate the same volume of seawater [4]. Assuming that (i) the amino acid concentration in the upper ocean layer was 0.3 mmol/L [9], and (ii) only 10 mol-% of the amino acids formed pyrroles, we calculate from our experimental chemical yield that ca. 103 kg of pyrroles could have been formed in a single volcanic eruption. Thus, over long periods of time, large amounts of alkylpyrroles may have accumulated. Alkylpyrroles are thermally quite stable and easily evaporate at higher temperatures. Therefore they must have escaped from the very hot places of their formation and condensed at cooler ones. Chemical evolution II: oligomerization of pyrroles Another interesting aspect of the hot-volcanic-coast scenario is the formation of hydrogen chloride (HCl) when lava flows into the ocean and decomposes the sea salt component MgCl2 · 6H2O [4]. It is known that HCl catalyzes the reaction between pyrrole and aldehydes, for example formaldehyde, in water. Formaldehyde is regarded as a prebiotic molecule [10]. We therefore studied the reaction of kryptopyrrole 2 with formaldehyde in HCl-containing artificial seawater

  11. Prediction of long-term chemical evolution of a low-pH cement designed for underground radioactive waste repositories

    International Nuclear Information System (INIS)

    Low-pH cements, also referred as low-alkalinity cements, are binders with a pore solution pH ≤ 11. They can be designed by replacing significant amounts of Portland cement (OPC) (>40%) by silica fume, which can be associated in some cases to low-CaO fly ash and/or ground granulated blast furnace slag to decrease the heat output during hydration by dilution of OPC and improve the mechanical strength of the final material. With the prospect of using these materials in a geological repository, it is of main importance to estimate their long-term properties and the influence of external and internal factors (chemical composition of the binder, storage temperature) on their characteristics. For this purpose, a three-way original approach was adopted. First, the hydration of low-pH cements was accelerated by milling cement slurries with zirconia beads. Secondly, the low-pH cement pastes were mimicked from mixtures of appropriate highly reactive oxides (lime, silica, calcium aluminate and calcium sulphate) in diluted suspensions. Thirdly, thermodynamic modelling was carried out to predict the mineral assemblage and composition of the solution at equilibrium, starting from the composition of the initial low-pH cement studied. Comparing the different results showed that this three-way approach is suitable to understand and predict the long-term chemical evolution of the cements since the final states obtained in all cases were equivalent. This method was then used to investigate the influence of temperature in the range 20-80 C on the chemical evolution of a low-pH cement. (authors)

  12. Contamination weeping: A chemical ion exchange model

    International Nuclear Information System (INIS)

    Experiments have been conducted to determine the applicability of a chemical ion-exchange model to characterize the problem of nuclear fuel transportation cask contamination and release (''weeping''). Surface charge characteristics of Cr2O3 and stainless steel (304) powders have been measured to determine the potential for ion exchange at metal oxide -- aqueous interfaces. The solubility of pool contaminant Co and Cs electrolytes at varying pH and the adsorption characteristics of these ions on Cr2O3 and stainless steel powders in aqueous slurries have been studied. Experiments show that Co ions do reversibly adsorb on these powder surfaces and, more specifically, that adsorption occurs in the nominal pH range (pH = 4--6) of a boric acid-moderated spent fuel pool. Desorption has been demonstrated to occur at pH ≤ 3. Cs ions also have been shown to have an affinity for these surfaces although the reversibility of Cs+ bonding by H+ ion exchange has not been fully demonstrated. These results have significant implications for effective decontamination and coating processes used on nuclear fuel transportation casks. 9 refs., 5 figs., 1 tab

  13. The Evolution of Galaxy Clustering in Hierarchical Models

    OpenAIRE

    Cole, Shaun; Benson, Andrew; Baugh, Carlton,; Lacey, Cedric; Frenk, Carlos

    1999-01-01

    The main ingredients of recent semi-analytic models of galaxy formation are summarised. We present predictions for the galaxy clustering properties of a well specified LCDM model whose parameters are constrained by observed local galaxy properties. We present preliminary predictions for evolution of clustering that can be probed with deep pencil beam surveys.

  14. The chemical transport model Oslo CTM3

    Directory of Open Access Journals (Sweden)

    O. A. Søvde

    2012-06-01

    Full Text Available We present here the global chemical transport model Oslo CTM3, an update of the Oslo CTM2. The update comprises a faster transport scheme, an improved wet scavenging scheme for large scale rain, updated photolysis rates and a new lightning parameterization. Oslo CTM3 is better parallelized and allows for stable, large time steps for advection, enabling more complex or high resolution simulations. Thorough comparisons between the Oslo CTM3, Oslo CTM2 and measurements are performed, and in general the Oslo CTM3 is found to reproduce measurements well. Inclusion of tropospheric sulfur chemistry and nitrate aerosols in CTM3 is shown to be important to reproduce tropospheric O3, OH and the CH4 lifetime well. Using the same meteorology to drive the two models, shows that some features related to transport are better resolved by the CTM3, such as polar cap transport, while features like transport close to the vortex edge are resolved better in the Oslo CTM2 due to its required shorter transport time step. The longer transport time steps in CTM3 result in larger errors e.g. near the jets, and when necessary, this can be remedied by using a shorter time step. An additional, more accurate and time consuming, treatment of polar cap transport is presented, however, both perform acceptably. A new treatment of the horizontal distribution of lightning is presented and found to compare well with measurements. Vertical distributions of lighting are updated, and tested against the old vertical distribution. The new profiles are found to produce more NOx in the tropical middle troposphere, and less at the surface and at high altitudes.

  15. Modelling evolution in a spatial continuum

    Science.gov (United States)

    Barton, N. H.; Etheridge, A. M.; Véber, A.

    2013-01-01

    We survey a class of models for spatially structured populations which we have called spatial Λ-Fleming-Viot processes. They arise from a flexible framework for modelling in which the key innovation is that random genetic drift is driven by a Poisson point process of spatial 'events'. We demonstrate how this overcomes some of the obstructions to modelling populations which evolve in two-(and higher-) dimensional spatial continua, how its predictions match phenomena observed in data and how it fits with classical models. Finally we outline some directions for future research.

  16. Modeling deuterium fractionation in cold and warm molecular environments with large chemical networks

    CERN Document Server

    Albertsson, T; Henning, Th

    2013-01-01

    Observations of deuterated species have long proven essential to probe properties and thermal history of various astrophysical environments. We present an elaborated chemical model that includes tens of thousands of reactions with multi-deuterated species, both gas-phase and surface, in which the most recent information on deuterium chemistry is implemented. A detailed study of the chemical evolution under wide range of temperatures and densities typical of cold molecular cores, warm protostellar envelopes, and hot cores/corinos is performed. We consider two cases of initial abundances, with 1) mainly atomic composition and all deuterium locked in HD, and 2) molecular abundances accumulated at 1 Myr of the evolution of a cold prestellar core. We indicate deuterated species that are particularly sensitive to temperature gradients and initial chemical composition. Many multiply-deuterated species produced at 10 K by exothermic ion-molecule chemistry retain large abundances even when temperature rises above 100 ...

  17. The Gaia-ESO Survey: Sodium and aluminium abundances in giants and dwarfs - Implications for stellar and Galactic chemical evolution

    CERN Document Server

    Smiljanic, R; Bragaglia, A; Donati, P; Magrini, L; Friel, E; Jacobson, H; Randich, S; Ventura, P; Lind, K; Bergemann, M; Nordlander, T; Morel, T; Pancino, E; Tautvaisiene, G; Adibekyan, V; Tosi, M; Vallenari, A; Gilmore, G; Bensby, T; Francois, P; Koposov, S; Lanzafame, A C; Recio-Blanco, A; Bayo, A; Carraro, G; Casey, A R; Costado, M T; Franciosini, E; Heiter, U; Hill, V; Hourihane, A; Jofre, P; Lardo, C; de Laverny, P; Lewis, J; Monaco, L; Morbidelli, L; Sacco, G G; Sbordone, L; Sousa, S G; Worley, C C; Zaggia, S

    2016-01-01

    Stellar evolution models predict that internal mixing should cause some sodium overabundance at the surface of red giants more massive than ~ 1.5--2.0 Msun. The surface aluminium abundance should not be affected. Nevertheless, observational results disagree about the presence and/or the degree of the Na and Al overabundances. In addition, Galactic chemical evolution models adopting different stellar yields lead to quite different predictions for the behavior of [Na/Fe] and [Al/Fe] versus [Fe/H]. Overall, the observed trends of these abundances with metallicity are not well reproduced. We readdress both issues, using new Na and Al abundances determined within the Gaia-ESO Survey, using two samples: i) more than 600 dwarfs of the solar neighborhood and of open clusters and ii) low- and intermediate-mass clump giants in six open clusters. Abundances of Na in giants with mass below ~2.0 Msun, and of Al in giants below ~3.0 Msun, seem to be unaffected by internal mixing processes. For more massive giants, the Na o...

  18. Modeling Electric Double-Layers Including Chemical Reaction Effects

    DEFF Research Database (Denmark)

    Paz-Garcia, Juan Manuel; Johannesson, Björn; Ottosen, Lisbeth M.;

    2014-01-01

    A physicochemical and numerical model for the transient formation of an electric double-layer between an electrolyte and a chemically-active flat surface is presented, based on a finite elements integration of the nonlinear Nernst-Planck-Poisson model including chemical reactions. The model works...

  19. Modeling release of chemicals from multilayer materials into food

    Directory of Open Access Journals (Sweden)

    Huang Xiu-Ling

    2016-01-01

    Full Text Available The migration of chemicals from materials into food is predictable by various mathematical models. In this article, a general mathematical model is developed to quantify the release of chemicals through multilayer packaging films based on Fick's diffusion. The model is solved numerically to elucidate the effects of different diffusivity values of different layers, distribution of chemical between two adjacent layers and between material and food, mass transfer at the interface of material and food on the migration process.

  20. Modeling the connection between development and evolution: Preliminary report

    Energy Technology Data Exchange (ETDEWEB)

    Mjolsness, E.; Reinitz, J. [Yale Univ., New Haven, CT (United States); Garrett, C.D. [Washington Univ., Seattle, WA (United States). Dept. of Computer Science; Sharp, D.H. [Los Alamos National Lab., NM (United States)

    1993-07-29

    In this paper we outline a model which incorporates development processes into an evolutionary frame work. The model consists of three sectors describing development, genetics, and the selective environment. The formulation of models governing each sector uses dynamical grammars to describe processes in which state variables evolve in a quantitative fashion, and the number and type of participating biological entities can change. This program has previously been elaborated for development. Its extension to the other sectors of the model is discussed here and forms the basis for further approximations. A specific implementation of these ideas is described for an idealized model of the evolution of a multicellular organism. While this model doe not describe an actual biological system, it illustrates the interplay of development and evolution. Preliminary results of numerical simulations of this idealized model are presented.

  1. Chemical, physical, and optical evolution of biomass burning aerosols: a case study

    Directory of Open Access Journals (Sweden)

    G. Adler

    2010-10-01

    Full Text Available In-situ chemical composition measurements of ambient aerosols have been used for characterizing the evolution of submicron aerosols from a large anthropogenic biomass burning (BB event in Israel. A high resolution Time of Flight Aerosol Mass Spectrometer (Hi-RES-TOF-AMS was used to follow the chemical evolution of BB aerosols during a night-long, extensive nationwide wood burning event and during the following day. While extensive BB is not common in this region, burning of agricultural waste is a common practice. The aging process of the BB aerosols was followed through their chemical, physical and optical properties. Mass spectrometric analysis of the aerosol organic component showed that aerosol aging is characterized by shifting from less oxidized fresh BB aerosols to more oxidized aerosols. Evidence for aerosol aging during the day following the BB event was indicated by an increase in the organic mass, its oxidation state, the total aerosol concentration, and a shift in the modal particle diameter. The effective broadband refractive index (EBRI was derived using a white light optical particle counter (WELAS. The average EBRI for a mixed population of aerosols dominated by open fires was m=1.53(±0.03+0.07i(±0.03, during the smoldering phase of the fires we found the EBRI to be m=1.54(±0.01+0.04i(±0.01 compared to m=1.49(±0.01+0.02i(±0.01 of the aged aerosols during the following day. This change indicates a decrease in the overall aerosol absorption and scattering. Elevated levels of particulate Polycyclic Aromatic Hydrocarbons (PAHs were detected during the entire event, which suggest possible implications for human health during such extensive event.

  2. Evolution of chemical composition of fogwater in winter in Chengdu, China

    Institute of Scientific and Technical Information of China (English)

    Hongling Yin; Zhixiang Ye; Yingchun Yang; Wei Yuan; Changyan Qiu; Huawei Yuan; Min Wang

    2013-01-01

    Two sampling sites representing the urban and suburban area of Chengdu,China were sampled and analyzed for selected chemicals to characterize the evolution of the chemical composition of fogwater.A trend of total organic carbon (TOC) > total nitrogen (TN) >total inorganic carbon (TIC) was observed for both sites.Variation of inorganic ions indicated that inorganic pollutants were not accumulated in the fog.Concentrations of n-alkanes (Cll-C37) at the urban site ranged from 7.58 to 27.75 ng/mL while at the suburban site concentrations were 2.57-21.55 ng/mL.The highest concentration of n-alkanes was observed in the mature period of fog (393.12 ng/mL) which was more than ten times that in the fog formation period (27.83 ng/mL) and the fog dissipation period (14.87 ng/mL).Concentrations ofΣ15PAHs were in the range of 7.27-38.52 ng/mL at the urban site and 2.59-22.69 ng/mL at the suburban site.Contents of PAHs in the mature period of fog (27.15 ng/mL) > fog dissipation period (11.59 ng/mL) > fog formation period (6.42 ng/mL).Concentrations of dicarboxylic acids (C5-C9) ranged from 10.92 to 40.78 ng/mL,with glutaric acid (C5) as the dominant dicarboxylic acid.These data provide strong indications of the accumulation of certain organic chemicals of environmental concern in fog and fog water,and provide additional insights about processes in urban and suburban air acting on organic chemicals with similar physical chemical properties.

  3. Evolution of metastasis revealed by mutational landscapes of chemically induced skin cancers | Office of Cancer Genomics

    Science.gov (United States)

    Human tumors show a high level of genetic heterogeneity, but the processes that influence the timing and route of metastatic dissemination of the subclones are unknown. Here we have used whole-exome sequencing of 103 matched benign, malignant and metastatic skin tumors from genetically heterogeneous mice to demonstrate that most metastases disseminate synchronously from the primary tumor, supporting parallel rather than linear evolution as the predominant model of metastasis.

  4. Evolution of the Dynamic Symptoms Model.

    Science.gov (United States)

    Brant, Jeannine M; Dudley, William N; Beck, Susan; Miaskowski, Christine

    2016-09-01

    Theories and conceptual models can be thought of as broad nets that attempt to rationalize, explain, and master a phenomenon within clinical nursing and interdisciplinary care. They can be used to guide a review of the literature and to formulate and organize research variables and relationships. Gaps in the literature can be identified and opportunities for additional research revealed (Fawcett, 2005). A variety of symptom models or theories exist, including the Theory of Symptom Management (Dodd et al., 2001), Theory of Unpleasant Symptoms (Lenz, Pugh, Milligan, Gift, & Suppe, 1997), Symptoms Experience Model (Armstrong, 2003), and Symptom Experiences in Time Theory (Henly, Kallas, Klatt, & Swenson, 2003). Most recently, the National Institute of Nursing Research identified a new National Institutes of Health Symptom Science Model to guide symptom science research (Cashion & Grady, 2015).
. PMID:27541557

  5. Marine and terrestrial herbivores display convergent chemical ecology despite 400 million years of independent evolution.

    Science.gov (United States)

    Rasher, Douglas B; Stout, E Paige; Engel, Sebastian; Shearer, Tonya L; Kubanek, Julia; Hay, Mark E

    2015-09-29

    Chemical cues regulate key ecological interactions in marine and terrestrial ecosystems. They are particularly important in terrestrial plant-herbivore interactions, where they mediate both herbivore foraging and plant defense. Although well described for terrestrial interactions, the identity and ecological importance of herbivore foraging cues in marine ecosystems remain unknown. Here we show that the specialist gastropod Elysia tuca hunts its seaweed prey, Halimeda incrassata, by tracking 4-hydroxybenzoic acid to find vegetative prey and the defensive metabolite halimedatetraacetate to find reproductive prey. Foraging cues were predicted to be polar compounds but instead were nonpolar secondary metabolites similar to those used by specialist terrestrial insects. Tracking halimedatetraacetate enables Elysia to increase in abundance by 12- to 18-fold on reproductive Halimeda, despite reproduction in Halimeda being rare and lasting for only ∼36 h. Elysia swarm to reproductive Halimeda where they consume the alga's gametes, which are resource rich but are chemically defended from most consumers. Elysia sequester functional chloroplasts and halimedatetraacetate from Halimeda to become photosynthetic and chemically defended. Feeding by Elysia suppresses the growth of vegetative Halimeda by ∼50%. Halimeda responds by dropping branches occupied by Elysia, apparently to prevent fungal infection associated with Elysia feeding. Elysia is remarkably similar to some terrestrial insects, not only in its hunting strategy, but also its feeding method, defense tactics, and effects on prey behavior and performance. Such striking parallels indicate that specialist herbivores in marine and terrestrial systems can evolve convergent ecological strategies despite 400 million years of independent evolution in vastly different habitats.

  6. The Composition of the Sagittarius Dwarf Spheroidal Galaxy and Implications for Nucleosynthesis and Chemical Evolution

    CERN Document Server

    McWilliam, A; William, Andrew Mc; Smecker-Hane, Tammy A.

    2004-01-01

    We outline the results of a study of the chemical composition of 14 stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph). For the Sgr dSph stars with [Fe/H]>-1 the abundances are highly unusual, showing a striking enhancement in heavy s-process elements, increasing with [Fe/H], deficiencies of the alpha- elements (O, Si, Ca, and Ti), deficiencies of Al and Na, and deficiencies of the iron-peak elements Mn and Cu. Our abundances suggest that the composition of the metal-rich Sgr dSph stars is dominated by the ejecta of an old, metal-poor population, including products of AGB stars and type Ia supernovae (SN). We suggest two scenarios to explain the observations: Prolonged chemical evolution in a galaxy experiencing significant mass-loss, and chemical enrichment with episodic bursts of star formation. The Galactic globular cluster Omega Cen, and the Fornax dwarf galaxy show similar abundance patterns, which suggests that those systems evolved similar to the Sgr dSph.

  7. Development of a numerical 2-dimensional beach evolution model

    DEFF Research Database (Denmark)

    Baykal, Cüneyt

    2014-01-01

    This paper presents the description of a 2-dimensional numerical model constructed for the simulation of beach evolution under the action of wind waves only over the arbitrary land and sea topographies around existing coastal structures and formations. The developed beach evolution numerical mode...... groin, and a series of offshore breakwaters. The numerical model gave results in agreement with the measurements both qualitatively and quantitatively and reflected the physical concepts well for the selected conceptual cases.......This paper presents the description of a 2-dimensional numerical model constructed for the simulation of beach evolution under the action of wind waves only over the arbitrary land and sea topographies around existing coastal structures and formations. The developed beach evolution numerical model...... is composed of 4 submodels: a nearshore spectral wave transformation model based on an energy balance equation including random wave breaking and diffraction terms to compute the nearshore wave characteristics, a nearshore wave-induced circulation model based on the nonlinear shallow water equations...

  8. Continuous "in vitro" Evolution of a Ribozyme Ligase: A Model Experiment for the Evolution of a Biomolecule

    Science.gov (United States)

    Ledbetter, Michael P.; Hwang, Tony W.; Stovall, Gwendolyn M.; Ellington, Andrew D.

    2013-01-01

    Evolution is a defining criterion of life and is central to understanding biological systems. However, the timescale of evolutionary shifts in phenotype limits most classroom evolution experiments to simple probability simulations. "In vitro" directed evolution (IVDE) frequently serves as a model system for the study of Darwinian…

  9. Avalanche dynamics in evolution, growth, and depinning models

    CERN Document Server

    Paczuski, M; Bak, P

    1995-01-01

    The dynamics of complex systems in nature often occurs in terms of punctuations, or avalanches, rather than following a smooth, gradual path. A comprehensive theory of avalanche dynamics in models of growth, interface depinning, and evolution is presented. Specifically, we include the Bak-Sneppen evolution model, the Sneppen interface depinning model, the Zaitsev flux creep model, invasion percolation, and several other depinning models into a unified treatment encompassing a large class of far from equilibrium processes. The formation of fractal structures, the appearance of 1/f noise, diffusion with anomalous Hurst exponents, Levy flights, and punctuated equilibria can all be related to the same underlying avalanche dynamics. This dynamics can be represented as a fractal in d spatial plus one temporal dimension. We develop a scaling theory that relates many of the critical exponents in this broad category of extremal models, representing different universality classes, to two basic exponents characterizing ...

  10. Neutral evolution: A null model for language dynamics

    CERN Document Server

    Blythe, R A

    2011-01-01

    We review the task of aligning simple models for language dynamics with relevant empirical data, motivated by the fact that this is rarely attempted in practice despite an abundance of abstract models. We propose that one way to meet this challenge is through the careful construction of null models. We argue in particular that rejection of a null model must have important consequences for theories about language dynamics if modelling is truly to be worthwhile. Our main claim is that the stochastic process of neutral evolution (also known as genetic drift or random copying) is a viable null model for language dynamics. We survey empirical evidence in favour and against neutral evolution as a mechanism behind historical language changes, highlighting the theoretical implications in each case.

  11. Chemical Leasing business models and corporate social responsibility.

    Science.gov (United States)

    Moser, Frank; Jakl, Thomas; Joas, Reihard; Dondi, Francesco

    2014-11-01

    Chemical Leasing is a service-oriented business model that shifts the focus from increasing sales volume of chemicals towards a value-added approach. Recent pilot projects have shown the economic benefits of introducing Chemical Leasing business models in a broad range of sectors. A decade after its introduction, the promotion of Chemical Leasing is still predominantly done by the public sector and international organizations. We show in this paper that awareness-raising activities to disseminate information on this innovative business model mainly focus on the economic benefits. We argue that selling Chemical Leasing business models solely on the grounds of economic and ecological considerations falls short of branding it as a corporate social responsibility initiative, which, for this paper, is defined as a stakeholder-oriented concept that extends beyond the organization's boundaries and is driven by an ethical understanding of the organization's responsibility for the impact of its business activities. For the analysis of Chemical Leasing business models, we introduce two case studies from the water purification and metal degreasing fields, focusing on employees and local communities as two specific stakeholder groups of the company introducing Chemical Leasing. The paper seeks to demonstrate that Chemical Leasing business models can be branded as a corporate social responsibility initiative by outlining the vast potential of Chemical Leasing to improve occupational health and safety and to strengthen the ability of companies to protect the environment from the adverse effects of the chemicals they apply.

  12. Chemical Leasing business models and corporate social responsibility.

    Science.gov (United States)

    Moser, Frank; Jakl, Thomas; Joas, Reihard; Dondi, Francesco

    2014-11-01

    Chemical Leasing is a service-oriented business model that shifts the focus from increasing sales volume of chemicals towards a value-added approach. Recent pilot projects have shown the economic benefits of introducing Chemical Leasing business models in a broad range of sectors. A decade after its introduction, the promotion of Chemical Leasing is still predominantly done by the public sector and international organizations. We show in this paper that awareness-raising activities to disseminate information on this innovative business model mainly focus on the economic benefits. We argue that selling Chemical Leasing business models solely on the grounds of economic and ecological considerations falls short of branding it as a corporate social responsibility initiative, which, for this paper, is defined as a stakeholder-oriented concept that extends beyond the organization's boundaries and is driven by an ethical understanding of the organization's responsibility for the impact of its business activities. For the analysis of Chemical Leasing business models, we introduce two case studies from the water purification and metal degreasing fields, focusing on employees and local communities as two specific stakeholder groups of the company introducing Chemical Leasing. The paper seeks to demonstrate that Chemical Leasing business models can be branded as a corporate social responsibility initiative by outlining the vast potential of Chemical Leasing to improve occupational health and safety and to strengthen the ability of companies to protect the environment from the adverse effects of the chemicals they apply. PMID:24943884

  13. A chemical model of meteoric ablation

    Directory of Open Access Journals (Sweden)

    T. Vondrak

    2008-12-01

    Full Text Available Most of the extraterrestrial dust entering the Earth's atmosphere ablates to produce metal vapours, which have significant effects on the aeronomy of the upper mesosphere and lower thermosphere. A new Chemical Ablation Model (CAMOD is described which treats the physics and chemistry of ablation, by including the following processes: sputtering by inelastic collisions with air molecules before the meteoroid melts; evaporation of atoms and oxides from the molten particle; diffusion-controlled migration of the volatile constituents (Na and K through the molten particle; and impact ionization of the ablated fragments by hyperthermal collisions with air molecules. Evaporation is based on thermodynamic equilibrium in the molten meteoroid (treated as a melt of metal oxides, and between the particle and surrounding vapour phase. The loss rate of each element is then determined assuming Langmuir evaporation. CAMOD successfully predicts the meteor head echo appearance heights, observed from incoherent scatter radars, over a wide range of meteoroid velocities. The model also confirms that differential ablation explains common-volume lidar observations of K, Ca and Ca+ in fresh meteor trails. CAMOD is then used to calculate the injection rates into the atmosphere of a variety of elements as a function of altitude, integrated over the meteoroid mass and velocity distributions. The most abundant elements (Fe, Mg and Si have peak injection rates around 85 km, with Na and K about 8 km higher. The more refractory element Ca ablates around 82 km with a Na:Ca ratio of 4:1, which does therefore not explain the depletion of atomic Ca to Na, by more than 2 orders of magnitude, in the upper mesosphere. Diffusion of the most volatile elements (Na and K does not appear to be rate-limiting except in the fastest meteoroids. Non-thermal sputtering causes ~35% mass loss from the fastest (~60–70 km s−1 and smallest (10−17–10

  14. A chemical model of meteoric ablation

    Directory of Open Access Journals (Sweden)

    T. Vondrak

    2008-07-01

    Full Text Available Most of the extraterrestrial dust entering the Earth's atmosphere ablates to produce metal vapours, which have significant effects on the aeronomy of the upper mesosphere and lower thermosphere. A new Chemical Ablation Model (CAMOD is described which treats the physics and chemistry of ablation, by including the following processes: sputtering by inelastic collisions with air molecules before the meteoroid melts; evaporation of atoms and oxides from the molten particle; diffusion-controlled migration of the volatile constituents (Na and K through the molten particle; and impact ionization of the ablated fragments by hyperthermal collisions with air molecules. Evaporation is based on thermodynamic equilibrium in the molten meteoroid (treated as a melt of metal oxides, and between the particle and surrounding vapour phase. The loss rate of each element is then determined assuming Langmuir evaporation. CAMOD successfully predicts the meteor head echo appearance heights, observed from incoherent scatter radars, over a wide range of meteoroid velocities. The model also confirms that differential ablation explains common-volume lidar observations of K, Ca and Ca+ in fresh meteor trails. CAMOD is then used to calculate the injection rates into the atmosphere of a variety of elements as a function of altitude, integrated over the meteoroid mass and velocity distributions. The most abundant elements (Fe, Mg and Si have peak injection rates around 85 km, with Na and K about 8 km higher. The more refractory element Ca ablates around 82 km with a Na:Ca ratio of 4:1, which does therefore not explain the depletion of atomic Ca to Na, by more than 2 orders of magnitude, in the upper mesosphere. Diffusion of the most volatile elements (Na and K does not appear to be rate-limiting except in the fastest meteoroids. Non-thermal sputtering causes ~35% mass loss from the fastest (~60–70 km s−1 and smallest (10−17–10

  15. MATHEMATICAL MODELS FOR MICROSTRUCTURE EVOLUTION IN THE SEAMLESS TUBE ROLLING

    OpenAIRE

    Ricardo Nolasco de Carvalho; Marcelo Almeida Cunha Ferreira; Dagoberto Brandão Santos; Ronaldo Antônio Neves Marques Barbosa

    2013-01-01

    The goal of this work is to present recent developments on mathematical modeling for microstructure evolution in different steel types, applied to a continuous rolling of seamless tubes. The development of these models depends on careful characterization of the thermomechanical cycle and/on correct selection and adjustment of equations which describes the several metallurgical phenomena involved on this process. The adjustments of these models are done using the results obtained i...

  16. Modeling microstructural evolution of multiple texture components during recrystallization

    DEFF Research Database (Denmark)

    Vandermeer, R.A.; Juul Jensen, D.

    1994-01-01

    using stereological point and lineal measurements of microstructural properties in combination with EBSP analysis for orientation determinations. The potential of the models to describe the observed recrystallization behavior of heavily cold-rolled commercial aluminum was demonstrated. A successful MPM......Models were formulated in an effort to characterize recrystallization in materials with multiple texture components. The models are based on a microstructural path methodology (MPM). Experimentally the microstructural evolution of conmmercial aluminum during recrystallization was characterized...

  17. Uranus evolution models with simple thermal boundary layers

    OpenAIRE

    Nettelmann, N.; Wang, K.; Fortney, J. J.; Hamel, S; Yellamilli, S.; Bethkenhagen, M.; Redmer, R.

    2016-01-01

    The strikingly low luminosity of Uranus (Teff ~ Teq) constitutes a long-standing challenge to our understanding of Ice Giant planets. Here we present the first Uranus structure and evolution models that are constructed to agree with both the observed low luminosity and the gravity field data. Our models make use of modern ab initio equations of state at high pressures for the icy components water, methane, and ammonia. Proceeding step by step, we confirm that adiabatic models yield cooling ti...

  18. Uranus evolution models with simple thermal boundary layers

    Science.gov (United States)

    Nettelmann, Nadine; Redmer, Ronald; Fortney, Jonathan J.; Hamel, Sebastien; Bethkenhagen, Mandy

    2016-04-01

    The strikingly low luminosity of Uranus imposes a long-standing challenge to our understanding of Ice Giant planets. Similar to the Earth, Uranus appears to evolve in equilibrium with the solar incident flux (Teq). Here we present the first Uranus structure and evolution models that are constructed to agree with both the observed low luminosity and the gravity field data. Our models make use of modern ab initio equations of state at high pressures for the icy components water, methane, and ammonia. We argue that the transition between the ice/rock-rich interior and the H/He-rich outer envelope should be stably stratified. Therefore, we introduce a simple thermal boundary layer (TBL) and adjust it to reproduce the luminosity. Due to this TBL, the deep interior of the Uranus models are up to a factor 3 warmer than adiabatic models, necessitating the presence of rocks there with a possible I:R of 1 x solar. Furthermore, we also allow for an equilibrium evolution (Teff ~ Teq) that begun prior to the present day, which would therefore no longer constitute a "special time" in Uranus' evolution. Once Teff ~ Teq happens, a shallow, subadiabatic zone in the atmosphere begins to develop. Its depth is adjusted to meet the luminosity constraint. This work provides a simple foundation for future Ice Giant structure and evolution models, that can be improved by properly treating the heat and particle fluxes in the diffusive zones.

  19. Evolution of linear perturbations in spherically symmetric dust models

    CERN Document Server

    February, Sean; Clarkson, Chris; Pollney, Denis

    2013-01-01

    We present a new numerical code to solve the master equations describing the evolution of linear perturbations in a spherically symmetric but inhomogeneous background. This code can be used to simulate several configurations of physical interest, such as relativistic corrections to structure formation, the lensing of gravitational waves and the evolution of perturbations in a cosmological void model. This paper focuses on the latter problem, i.e. structure formation in a Hubble scale void in the linear regime. This is considerably more complicated than linear perturbations of a homogeneous and isotropic background because the inhomogeneous background leads to coupling between density perturbations and rotational modes of the spacetime geometry, as well as gravitational waves. Previous analyses of this problem ignored this coupling in the hope that the approximation does not affect the overall dynamics of structure formation in such models. We show that for a giga-parsec void, the evolution of the density cont...

  20. A new model for discrete character evolution.

    Science.gov (United States)

    Grafen, A; Ridley, M

    1997-01-01

    The paper provides an explicit justification for the principle that a uniform taxon should contribute only one datapoint in comparative analyses with discrete variables. The justification is that phylogenetic patterns in variables unincluded in the proposed test vitiate the assumption of independence, both at the level of species and at the level of branch segments. The consequence is that a uniform taxon cannot safely be counted as more than one datapoint. The arguments use a branching discrete Markov process in continuous time, with the new feature that the tested variables are only a subset of the evolving characters. This model is proposed as a useful criterion for measuring the merit of proposed tests, and illustrates the necessity for models in evaluating comparative methods. PMID:9039396

  1. Ovarian Cancer Pathogenesis: A Model in Evolution

    Directory of Open Access Journals (Sweden)

    Alison M. Karst

    2010-01-01

    Full Text Available Ovarian cancer is a deadly disease for which there is no effective means of early detection. Ovarian carcinomas comprise a diverse group of neoplasms, exhibiting a wide range of morphological characteristics, clinical manifestations, genetic alterations, and tumor behaviors. This high degree of heterogeneity presents a major clinical challenge in both diagnosing and treating ovarian cancer. Furthermore, the early events leading to ovarian carcinoma development are poorly understood, thus complicating efforts to develop screening modalities for this disease. Here, we provide an overview of the current models of ovarian cancer pathogenesis, highlighting recent findings implicating the fallopian tube fimbria as a possible site of origin of ovarian carcinomas. The ovarian cancer model will continue to evolve as we learn more about the genetics and etiology of this disease.

  2. A Baseline Model of Industry Evolution

    OpenAIRE

    Winter, Sidney G.; Yuri M. Kaniovski; Dosi, Giovanni

    1997-01-01

    The paper analyses some general dynamic properties of industries characterized by heterogeneous firms and continuing stochastic entry. After a brief critical assessment of some significant drawbacks of recent contributions to modeling of stochastic industrial dynamics, we propose a novel analytical apparatus able to derive some generic properties of the underlying competition process combining persistent technological heterogeneity, differential growth of individual firms and turnover. The ba...

  3. Minimal model for genome evolution and growth

    OpenAIRE

    Hsieh, L. C.; Luo, L. F.; Ji, F. M.; Lee, H C

    2002-01-01

    Textual analysis of typical microbial genomes reveals that they have the statistical characteristics of a DNA sequence of a much shorter length. This peculiar property supports an evolutionary model in which a genome evolves by random mutation but primarily grows by random segmental self-copying. That genomes grew mostly by self-copying is consistent with the observation that repeat sequences in all genomes are widespread and intragenomic and intergenomic homologous genes are preponderance ac...

  4. Development of regionalized multimedia chemical fate models for China

    OpenAIRE

    Zhu, Ying

    2016-01-01

    To balance the economic development with environmental safety and human health, China has released chemicals management legislation for which chemical prioritization and risk assessment are key issues. To support these ambitions two versions of an environmental fate and behaviour model SESAMe (Sino Evaluative Simplebox-MAMI models), have been developed with different resolutions and structures in this thesis. SESAMe is applied to hypothetical chemicals to investigate the influence of environm...

  5. Models of the Protocellular Structures, Functions and Evolution

    Science.gov (United States)

    Pohorille, Andrew; New, Michael; Keefe, Anthony; Szostak, Jack W.; Lanyi, Janos F.; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    In the absence of extinct or extant record of protocells, the most direct way to test our understanding of the origin of cellular life is to construct laboratory models that capture important features of protocellular systems. Such efforts are currently underway in a collaborative project between NASA-Ames, Harvard medical School and University of California. They are accompanied by computational studies aimed at explaining self-organization of simple molecules into ordered structures. The centerpiece of this project is a method for the in vitro evolution of protein enzymes toward arbitrary catalytic targets. A similar approach has already been developed for nucleic acids: First, a very large population of candidate molecules is generated using a random synthetic approach. Next, the small numbers of molecules that can accomplish the desired task are selected. These molecules are next vastly multiplied using the polymerase chain reaction. A mutagenic approach, in which the sequences of selected molecules are randomly altered, can yield further improvements in performance or alterations of specificities. Unfortunately, the catalytic potential of nucleic acids is rather limited. Proteins are more catalytically capable but cannot be directly amplified. In the new technique, this problem is circumvented by covalently linking each protein of the initial, diverse, pool to the RNA sequence that codes for it. Then, selection is performed on the proteins, but the nucleic acids are replicated. To date, we have obtained "a proof of concept" by evolving simple, novel proteins capable of selectively binding adenosine tri-phosphate (ATP). Our next goal is to create an enzyme that can phosphorylate amino acids and another to catalyze the formation of peptide bonds in the absence of nucleic acid templates. This latter reaction does not take place in contemporary cells. once developed, these enzymes will be encapsulated in liposomes so that they will function in a simulated cellular

  6. Beyond the pseudo-time-dependent approach: chemical models of dense core precursors

    OpenAIRE

    Hassel, G. E.; Herbst, E.; Bergin, E. A.

    2010-01-01

    Context: Chemical models of dense cloud cores often utilize the so-called pseudo-time-dependent approximation, in which the physical conditions are held fixed and uniform as the chemistry occurs. In this approximation, the initial abundances chosen, which are totally atomic in nature except for molecular hydrogen, are artificial. A more detailed approach to the chemistry of dense cold cores should include the physical evolution during their early stages of formation. Aims: Our major goal is t...

  7. Voltammetry as a Model for Teaching Chemical Instrumentation.

    Science.gov (United States)

    Gunasingham, H.; Ang, K. P.

    1985-01-01

    Voltammetry is used as a model for teaching chemical instrumentation to chemistry undergraduates at the National University of Singapore. Lists six criteria used to select a successful teaching model and shows how voltammetry satisfies each criterion. (JN)

  8. Radiation-induced chemical evolution of glycine to (Gly)2, (Gly)3, and (Gly)4

    International Nuclear Information System (INIS)

    Recently amino acids were detected from some meteorites. Since these amino acids were found after hydrolysis, some oligopeptides were possibly formed in space. A simulation experiment of chemical evolution from Glycine (Gly) to Glycylglycine ((Gly)2) was reported by Kaneko et al. In this work, we irradiated (Gly)2 with 8 eV vacuum ultraviolet photons or with 530 eV soft X-ray photons and examined absolute values of quantum yield of radiation-induced chemical evolution from Gly2 to Glycylglycylglycine ((Gly)3) and Glycylglycylglycylglycine ((Gly)4). Thin films of (Gly)2 were prepared on quartz plate or CuBe plate with a vacuum evaporation technique. These samples were irradiated by 8 eV photons from a Xe2* excimer lamp or by 530 eV soft X-ray photons at SPring-8 Synchrotron Radiation Facility. Irradiated samples were analyzed with a high performance liquid chromatography HPLC. Decomposition of (Gly)2 and production of Gly, (Gly)3 and (Gly)4 were observed. Quantum yield Y was defined to be N = Y N0, where N is the number of produced or decomposed molecule, and N0 is the number of (Gly)2 molecules excited by photons. Obtained results by 8 eV irradiation were summarized in Table 1. The similar magnitude of decomposition of (Gly)2 may show that yield of the primary breaking reaction upon photo-excitation is of similar magnitude. It should be noted that (Gly)3 and (Gly)4 was produced by irradiation with the yield of 10-4 without any catalysis. For soft X-ray irradiation, yield of Gly was tentatively determined to be about 40. This largervalue than that for 8 eV irradiation may originate from large energy of incident soft X-ray photons just like a result reported by Simakov et al. We will discuss in detail at the conference. (authors)

  9. Evolution of limestone fracture permeability under coupled thermal, hydrologi-cal, mechanical, and chemical conditions

    Institute of Scientific and Technical Information of China (English)

    李凤滨; 盛金昌; 詹美礼; 徐力猛; 吴强; 贾春兰

    2014-01-01

    The effect of temperature on the rock fracture permeability is a very important factor in the prediction of the permeability of enhanced geothermal systems and in reservoir engineering. In this study, the flow-through experiments were conducted on a single limestone fracture at different temperatures of 25oC, 40oC and 60oC, and with differential pressures of 0.3 MPa and 0.4 MPa. The experimental results suggest a complex temporal evolution of the fracture aperture. The aperture increases considerably with increasing temperature and reduces gradually to a steady value at a stable temperature. The results of three short-term experiments (QT-1, QT-2, QT-3) indicate an exponential relationship between the permeability and the temperature change ratio (DT/T ) , which provides a further evidence that the rising temperature increases the aperture. It is shown that the changing temperature has its influence on two possible accounts:the chemical dissolution and the pressure dissolution. These two processes have opposite impacts on the fracture permeability. The chemical dissolution increases the permeability with a rising temperature while the pressure disso-lution reduces the permeability with a stable temperature. These make a very complex picture of the permeability evolution. Our results show that the fracture permeability reduces 39.2%when the temperature increases by 15oC (during the 25oC-40 C interval) and 42.6% when the temperature increases by 20oC (during the 40oC-60oC interval). It can be concluded that the permeability decreases to a greater extent for larger increases in temperature.

  10. Partial melting in one-plate planets: Implications for thermo-chemical and atmospheric evolution

    Science.gov (United States)

    Plesa, A.-C.; Breuer, D.

    2014-08-01

    In the present work, we investigate the influence of partial melting on mantle dynamics, crustal formation, and volcanic outgassing of a one-plate planet using a 2D mantle convection code. When melt is extracted to form crust, the mantle material left behind is more buoyant than its parent material and depleted in radioactive heat sources. The extracted heat-producing elements are then enriched in the crust, which also has an insulating effect due to its lower thermal conductivity compared to the mantle. In addition, partial melting can influence the mantle rheology through the dehydration (water depletion) of the mantle material by volcanic outgassing. As a consequence, the viscosity of water-depleted regions increases more than two orders of magnitude compared to water-saturated rocks resulting in slower cooling rates. The most important parameter influencing the thermo-chemical evolution is the assumed density difference between the primitive and the depleted mantle material (i.e., between peridotite and harzburgite). With small or negligible values of compositional buoyancy, crustal formation including crustal delamination is very efficient, also resulting in efficient processing and degassing of the mantle. The convecting mantle below the stagnant lid depletes continuously with time. In contrast, with increasing compositional buoyancy, crustal formation and mantle degassing are strongly suppressed although partial melting is substantially prolonged in the thermal evolution. The crust shows strong lateral variations in thickness, and crustal delamination is reduced and occurs only locally. Furthermore, two to four different mantle reservoirs can form depending on the initial temperature distribution. Two of these reservoirs can be sustained during the entire evolution - a scenario possibly valid for Mars as it may explain the isotope characteristic of the Martian meteorites.

  11. Evolution models for mass transportation problems

    CERN Document Server

    Buttazzo, Giuseppe

    2012-01-01

    We present a survey on several mass transportation problems, in which a given mass dynamically moves from an initial configuration to a final one. The approach we consider is the one introduced by Benamou and Brenier in [5], where a suitable cost functional $F(\\rho,v)$, depending on the density $\\rho$ and on the velocity $v$ (which fulfill the continuity equation), has to be minimized. Acting on the functional $F$ various forms of mass transportation problems can be modeled, as for instance those presenting congestion effects, occurring in traffic simulations and in crowd motions, or concentration effects, which give rise to branched structures.

  12. Chemical evolution in the early phases of massive star formation II: Deuteration

    CERN Document Server

    Gerner, Th; Beuther, H; Semenov, D; Linz, H; Abertsson, T; Henning, Th

    2015-01-01

    The chemical evolution in high-mass star-forming regions is still poorly constrained. Studying the evolution of deuterated molecules allows to differentiate between subsequent stages of high-mass star formation regions due to the strong temperature dependence of deuterium isotopic fractionation. We observed a sample of 59 sources including 19 infrared dark clouds, 20 high-mass protostellar objects, 11 hot molecular cores and 9 ultra-compact HII regions in the (3-2) transitions of the four deuterated molecules, DCN, DNC, DCO+ and N2D+ as well as their non-deuterated counterpart. The overall detection fraction of DCN, DNC and DCO+ is high and exceeds 50% for most of the stages. N2D+ was only detected in a few infrared dark clouds and high-mass protostellar objects. It can be related to problems in the bandpass at the frequency of the transition and to low abundances in the more evolved, warmer stages. We find median D/H ratios of ~0.02 for DCN, ~0.005 for DNC, ~0.0025 for DCO+ and ~0.02 for N2D+. While the D/H ...

  13. Modelling the Evolution of Social Structure

    Science.gov (United States)

    Sutcliffe, A. G.; Dunbar, R. I. M.; Wang, D.

    2016-01-01

    Although simple social structures are more common in animal societies, some taxa (mainly mammals) have complex, multi-level social systems, in which the levels reflect differential association. We develop a simulation model to explore the conditions under which multi-level social systems of this kind evolve. Our model focuses on the evolutionary trade-offs between foraging and social interaction, and explores the impact of alternative strategies for distributing social interaction, with fitness criteria for wellbeing, alliance formation, risk, stress and access to food resources that reward social strategies differentially. The results suggest that multi-level social structures characterised by a few strong relationships, more medium ties and large numbers of weak ties emerge only in a small part of the overall fitness landscape, namely where there are significant fitness benefits from wellbeing and alliance formation and there are high levels of social interaction. In contrast, ‘favour-the-few’ strategies are more competitive under a wide range of fitness conditions, including those producing homogeneous, single-level societies of the kind found in many birds and mammals. The simulations suggest that the development of complex, multi-level social structures of the kind found in many primates (including humans) depends on a capacity for high investment in social time, preferential social interaction strategies, high mortality risk and/or differential reproduction. These conditions are characteristic of only a few mammalian taxa. PMID:27427758

  14. Modelling the Evolution of Social Structure.

    Directory of Open Access Journals (Sweden)

    A G Sutcliffe

    Full Text Available Although simple social structures are more common in animal societies, some taxa (mainly mammals have complex, multi-level social systems, in which the levels reflect differential association. We develop a simulation model to explore the conditions under which multi-level social systems of this kind evolve. Our model focuses on the evolutionary trade-offs between foraging and social interaction, and explores the impact of alternative strategies for distributing social interaction, with fitness criteria for wellbeing, alliance formation, risk, stress and access to food resources that reward social strategies differentially. The results suggest that multi-level social structures characterised by a few strong relationships, more medium ties and large numbers of weak ties emerge only in a small part of the overall fitness landscape, namely where there are significant fitness benefits from wellbeing and alliance formation and there are high levels of social interaction. In contrast, 'favour-the-few' strategies are more competitive under a wide range of fitness conditions, including those producing homogeneous, single-level societies of the kind found in many birds and mammals. The simulations suggest that the development of complex, multi-level social structures of the kind found in many primates (including humans depends on a capacity for high investment in social time, preferential social interaction strategies, high mortality risk and/or differential reproduction. These conditions are characteristic of only a few mammalian taxa.

  15. Evolution: Ocean Models Reveal Life in Deep Seas.

    Science.gov (United States)

    Eizaguirre, Christophe

    2016-09-26

    Even though the deep sea represents the largest area in the world, evolution of species from those environments remains largely unstudied. A series of recent papers indicate that combining molecular tools with biophysical models can help us resolve some of these deep mysteries.

  16. Theoretical models of stadial-evolutive development of civilizations

    OpenAIRE

    Grčić Mirko

    2005-01-01

    Civilizations, like all geographical systems, are dependant on the regularities of geographical process. Geographical process - it is the process of genesis, evolution and fading of geosystems. Different authors' points of view differ considering the movement forces of this process. The comparative analysis of Gumilev's, Toynbee's and Sorokin's theoretical models of civilizations development is represented in this article.

  17. Overdeepening development in a glacial landscape evolution model with quarrying

    DEFF Research Database (Denmark)

    Ugelvig, Sofie Vej; Egholm, D.L.; Iverson, Neal R.;

    In glacial landscape evolution models, subglacial erosion rates are often related to basal sliding or ice discharge by a power-law. This relation can be justified when considering bed abrasion, where rock debris transported in the basal ice drives erosion. However, the relation is not well...

  18. Modeling river dune evolution using a parameterization of flow separation

    NARCIS (Netherlands)

    Paarlberg, Andries J.; Dohmen-Janssen, C. Marjolein; Hulscher, Susanne J.M.H.; Termes, Paul

    2009-01-01

    This paper presents an idealized morphodynamic model to predict river dune evolution. The flow field is solved in a vertical plane assuming hydrostatic pressure conditions. The sediment transport is computed using a Meyer-Peter–Müller type of equation, including gravitational bed slope effects and a

  19. Evolution: Ocean Models Reveal Life in Deep Seas.

    Science.gov (United States)

    Eizaguirre, Christophe

    2016-09-26

    Even though the deep sea represents the largest area in the world, evolution of species from those environments remains largely unstudied. A series of recent papers indicate that combining molecular tools with biophysical models can help us resolve some of these deep mysteries. PMID:27676306

  20. Suggested model for prebiotic evolution: the use of chaos.

    OpenAIRE

    Anderson, P W

    1983-01-01

    I elaborate on an earlier model for prebiotic evolution by adding a selection function depending randomly on base-pair correlations along the replicating RNA chains. By analogy with the equilibrium statistics of spin glass, this should give a wide variety of metastable "species" that can mutate or combine symbiotically.

  1. Modeling microstructural evolution of multiple texture components during recrystallization

    Energy Technology Data Exchange (ETDEWEB)

    Vandermeer, R.A. (Naval Research Lab., Washington, DC (United States)); Jensen, D.J. (Risoe National Lab., Roskilde (Denmark). Materials Dept.)

    1994-07-01

    Models were formulated in an effort to characterize recrystallization in materials with multiple texture components. The models are based on a microstructural path methodology (MPM). Experimentally the microstructural evolution of commercial aluminum during recrystallization was characterized using stereological point and lineal measurements of microstructural properties in combination with EBSP analysis for orientation determinations. The potential of the models to describe the observed recrystallization behavior of heavily cold-rolled commercial aluminum was demonstrated. A successful MPM model was reduced which, for each texture component -- random, rolling and cube orientations, was quantitatively consistent with the measured microstructural properties. Nucleation and growth rates were deduced for each texture component using the model.

  2. Evolution and physics in comparative protein structure modeling.

    Science.gov (United States)

    Fiser, András; Feig, Michael; Brooks, Charles L; Sali, Andrej

    2002-06-01

    From a physical perspective, the native structure of a protein is a consequence of physical forces acting on the protein and solvent atoms during the folding process. From a biological perspective, the native structure of proteins is a result of evolution over millions of years. Correspondingly, there are two types of protein structure prediction methods, de novo prediction and comparative modeling. We review comparative protein structure modeling and discuss the incorporation of physical considerations into the modeling process. A good starting point for achieving this aim is provided by comparative modeling by satisfaction of spatial restraints. Incorporation of physical considerations is illustrated by an inclusion of solvation effects into the modeling of loops.

  3. Modeling language evolution: Aromanian, an endangered language in Greece

    Science.gov (United States)

    Bakalis, Evangelos; Galani, Alexandra

    2012-10-01

    Time evolution of the relative density of speakers of an endangered language, Aromanian, which is spoken by a bilingual community in North-Western Greece, is approached theoretically by means of a two-state model and a three-state model. The same prestige and volatility parameters are used in these two models. Furthermore, a culture parameter and a second exponent are introduced in the three-state model. The parameters of each model are fitted to the current status of Aromanian, on the basis of field evidence collected by us, and the first findings about the risk of the language’s extinction are presented.

  4. Property Modelling for Applications in Chemical Product and Process Design

    DEFF Research Database (Denmark)

    Gani, Rafiqul

    is missing, the atom connectivity based model is employed to predict the missing group interaction. In this way, a wide application range of the property modeling tool is ensured. Based on the property models, targeted computer-aided techniques have been developed for design and analysis of organic chemicals......, polymers, mixtures as well as separation processes. The presentation will highlight the framework (ICAS software) for property modeling, the property models and issues such as prediction accuracy, flexibility, maintenance and updating of the database. Also, application issues related to the use of property......Physical-chemical properties of pure chemicals and their mixtures play an important role in the design of chemicals based products and the processes that manufacture them. Although, the use of experimental data in design and analysis of chemicals based products and their processes is desirable...

  5. Fate modelling of chemical compounds with incomplete data sets

    DEFF Research Database (Denmark)

    Birkved, Morten; Heijungs, Reinout

    2011-01-01

    and other indicators. ERA typically addresses one specific chemical, but in an LCIA, the number of chemicals encountered may be quite high, up to hundreds or thousands. This study explores the development of meta-models, which are supposed to reflect the “true”multi-media fate and exposure model......, and to provide simplified proxies for the more complicated “real”model relationships. In the presented study two approaches for the reduction of the data demand associated with characterization of chemical emissions in USEtoxTM are tested: The first approach yields a simplified set of mode of entry specific meta-models......Impact assessment of chemical compounds in Life Cycle Impact Assessment (LCIA) and Environmental Risk Assessment (ERA) requires a vast amount of data on the properties of the chemical compounds being assessed. These data are used in multi-media fate and exposure models, to calculate risk levels...

  6. The puzzle of the Krebs citric acid cycle: assembling the pieces of chemically feasible reactions, and opportunism in the design of metabolic pathways during evolution.

    Science.gov (United States)

    Meléndez-Hevia, E; Waddell, T G; Cascante, M

    1996-09-01

    The evolutionary origin of the Krebs citric acid cycle has been for a long time a model case in the understanding of the origin and evolution of metabolic pathways: How can the emergence of such a complex pathway be explained? A number of speculative studies have been carried out that have reached the conclusion that the Krebs cycle evolved from pathways for amino acid biosynthesis, but many important questions remain open: Why and how did the full pathway emerge from there? Are other alternative routes for the same purpose possible? Are they better or worse? Have they had any opportunity to be developed in cellular metabolism evolution? We have analyzed the Krebs cycle as a problem of chemical design to oxidize acetate yielding reduction equivalents to the respiratory chain to make ATP. Our analysis demonstrates that although there are several different chemical solutions to this problem, the design of this metabolic pathway as it occurs in living cells is the best chemical solution: It has the least possible number of steps and it also has the greatest ATP yielding. Study of the evolutionary possibilities of each one-taking the available material to build new pathways-demonstrates that the emergence of the Krebs cycle has been a typical case of opportunism in molecular evolution. Our analysis proves, therefore, that the role of opportunism in evolution has converted a problem of several possible chemical solutions into a single-solution problem, with the actual Krebs cycle demonstrated to be the best possible chemical design. Our results also allow us to derive the rules under which metabolic pathways emerged during the origin of life.

  7. THE METALLICITY DISTRIBUTION FUNCTIONS OF SEGUE G AND K DWARFS: CONSTRAINTS FOR DISK CHEMICAL EVOLUTION AND FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Schlesinger, Katharine J. [Research School of Astronomy and Astrophysics, Australian National University, Weston, ACT 2611 (Australia); Johnson, Jennifer A.; Schoenrich, Ralph [Department of Astronomy, The Ohio State University, 140 W 18th Avenue, Columbus, OH 43210 (United States); Rockosi, Constance M. [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Lee, Young Sun [Tombaugh Fellow, Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States); Morrison, Heather L.; Harding, Paul [Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106 (United States); Allende Prieto, Carlos [Instituto de Astrofisica de Canarias, E-38205 La Laguna, Tenerife (Spain); Beers, Timothy C. [Department of Physics and Astronomy and JINA (Joint Institute for Nuclear Astrophysics), Michigan State University, East Lansing, MI 48824 (United States); Yanny, Brian [Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510 (United States); Schneider, Donald P. [Department of Astronomy and Astrophysics, Penn State University, 408A Davey Laboratory, University Park, PA 16802 (United States); Chiappini, Cristina; Da Costa, Luiz N.; Maia, Marcio A. G.; Rocha-Pinto, Helio; Santiago, Basilio X. [Laboratorio Interinstitucional de e-Astronomia (LIneA), Rua Gal. Jose Cristino 77, 20921-400 Rio de Janeiro (Brazil); Minchev, Ivan [Leibniz-Institut fuer Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany)

    2012-12-20

    We present the metallicity distribution function (MDF) for 24,270 G and 16,847 K dwarfs at distances from 0.2 to 2.3 kpc from the Galactic plane, based on spectroscopy from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. This stellar sample is significantly larger in both number and volume than previous spectroscopic analyses, which were limited to the solar vicinity, making it ideal for comparison with local volume-limited samples and Galactic models. For the first time, we have corrected the MDF for the various observational biases introduced by the SEGUE target-selection strategy. SEGUE is particularly notable for its sample of K dwarfs, which are too faint to examine spectroscopically far from the solar neighborhood. The MDF of both spectral types becomes more metal-poor with increasing |Z|, which reflects the transition from a sample with small [{alpha}/Fe] values at small heights to one with enhanced [{alpha}/Fe] above 1 kpc. Comparison of our SEGUE distributions to those of two different Milky Way models reveals that both are more metal-rich than our observed distributions at all heights above the plane. Our unbiased observations of G and K dwarfs provide valuable constraints over the |Z|-height range of the Milky Way disk for chemical and dynamical Galaxy evolution models, previously only calibrated to the solar neighborhood, with particular utility for thin- and thick-disk formation models.

  8. Digital Forensic Investigation Models, an Evolution study

    Directory of Open Access Journals (Sweden)

    Khuram Mushtaque

    2015-10-01

    Full Text Available In business today, one of the most important segments that enable any business to get competitive advantage over others is appropriate, effective adaptation of Information Technology into business and then managing and governing it on their will. To govern IT organizations need to identify value of acquiring services of forensic firms to compete cyber criminals. Digital forensic firms follow different mechanisms to perform investigation. Time by time forensic firms are facilitated with different models for investigation containing phases for different purposes of the entire process. Along with forensic firms, enterprises also need to build a secure and supportive platform to make successful investigation process possible. We have underlined different elements of organizations in Pakistan; need to be addressed to provide support to forensic firms.

  9. Diagnostics and future evolution analysis of the two parametric models

    CERN Document Server

    Yang, Guang; Meng, Xinhe

    2016-01-01

    In this paper, we apply three diagnostics including $Om$, Statefinder hierarchy and the growth rate of perturbations into discriminating the two parametric models for the effective pressure with the $\\Lambda$CDM model. By using the $Om$ diagnostic, we find that both the model 1 and the model 2 can be hardly distinguished from each other as well as the $\\Lambda$CDM model in terms of 68\\% confidence level. As a supplement, by using the Statefinder hierarchy diagnostics and the growth rate of perturbations, we discover that not only can our two parametric models be well distinguished from $\\Lambda$CDM model, but also, by comparing with $Om$ diagnostic, the model 1 and the model 2 can be distinguished better from each other. In addition, we also explore the fate of universe evolution of our two models by means of the rip analysis.

  10. Evolution of spherical domain walls in solitonic symmetron models

    CERN Document Server

    Peyravi, Marzieh; Lobo, Francisco S N

    2016-01-01

    In this work, inspired by the symmetron model, we analyse the evolution of spherical domain walls by considering specific potentials that ensure symmetry breaking and the occurrence of degenerate vacua that are necessary for the formation of domain walls. By considering a simple analytical model of spherical domain wall collapse, in vacuum, it is shown that this model fits the more accurate numerical results very well until full collapse, after which oscillations and scalar radiation take place. Furthermore, we explore the effect of a central non-relativistic matter lump on the evolution of a spherical domain wall and show that the central lump can prevent the full collapse and annihilation of the domain wall bubble, due to the repulsion between the domain wall and matter over-density within the adopted symmetron inspired model.

  11. Evolution of stalk/spore ratio in a social amoeba: cell-to-cell interaction via a signaling chemical shaped by cheating risk.

    Science.gov (United States)

    Uchinomiya, Kouki; Iwasa, Yoh

    2013-11-01

    The social amoeba (or cellular slime mold) is a model system for cell cooperation. When food is depleted in the environment, cells aggregate together. Some of these cells become stalks, raising spores to aid in their dispersal. Differentiation-inducing factor-1 (DIF-1) is a signaling chemical produced by prespore cells and decomposed by prestalk cells. It affects the rate of switching between prestalk and prespore cells, thereby achieving a stable stalk/spore ratio. In this study we analyzed the evolution of the stalk/spore ratio. Strains may differ in the production and decomposition rates of the signaling chemical, and in the sensitivity of cells to switch in response to the signaling chemical exposure. When two strains with the same stalk/spore ratio within their own fruiting body are combined into a single fruiting body, one strain may develop into prespores to a greater degree than the other. Direct evolutionary simulations and quantitative genetic dynamics demonstrate that if a fruiting body is always formed by a single strain, the cells evolve to produce less signaling chemical and become more sensitive to the signaling chemical due to the cost of producing the chemical. In contrast, if a fruiting body is formed by multiple strains, the cells evolve to become less sensitive to the signaling chemical and produce more signaling chemical in order to reduce the risk of being exploited. In contrast, the stalk-spore ratio is less likely to be affected by small cheating risk.

  12. Evolution of stalk/spore ratio in a social amoeba: cell-to-cell interaction via a signaling chemical shaped by cheating risk.

    Science.gov (United States)

    Uchinomiya, Kouki; Iwasa, Yoh

    2013-11-01

    The social amoeba (or cellular slime mold) is a model system for cell cooperation. When food is depleted in the environment, cells aggregate together. Some of these cells become stalks, raising spores to aid in their dispersal. Differentiation-inducing factor-1 (DIF-1) is a signaling chemical produced by prespore cells and decomposed by prestalk cells. It affects the rate of switching between prestalk and prespore cells, thereby achieving a stable stalk/spore ratio. In this study we analyzed the evolution of the stalk/spore ratio. Strains may differ in the production and decomposition rates of the signaling chemical, and in the sensitivity of cells to switch in response to the signaling chemical exposure. When two strains with the same stalk/spore ratio within their own fruiting body are combined into a single fruiting body, one strain may develop into prespores to a greater degree than the other. Direct evolutionary simulations and quantitative genetic dynamics demonstrate that if a fruiting body is always formed by a single strain, the cells evolve to produce less signaling chemical and become more sensitive to the signaling chemical due to the cost of producing the chemical. In contrast, if a fruiting body is formed by multiple strains, the cells evolve to become less sensitive to the signaling chemical and produce more signaling chemical in order to reduce the risk of being exploited. In contrast, the stalk-spore ratio is less likely to be affected by small cheating risk. PMID:23911583

  13. A grand model for chemical product design

    DEFF Research Database (Denmark)

    Fung, Ka Y.; Ng, Ka M.; Zhang, Lei;

    2016-01-01

    Chemical engineering has been expanding its focus from primarily business-to-business products (B2B) to business-to-consumer (B2C) products. The production of B2B products generally emphasizes on process design and optimization, whereas the production of B2C products focuses on product quality, i...

  14. Modelling Human Exposure to Chemicals in Food

    NARCIS (Netherlands)

    Slob W

    1993-01-01

    Exposure to foodborne chemicals is often estimated using the average consumption pattern in the human population. To protect the human population instead of the average individual, however, interindividual variability in consumption behaviour must be taken into account. This report shows how food

  15. A Solvable Model of Species Body Mass Evolution

    CERN Document Server

    Clauset, Aaron

    2008-01-01

    We present a quantitative model for the biological evolution of species body masses within large groups of related species, e.g., terrestrial mammals, in which body mass M evolves according to branching (speciating) multiplicative diffusion and an extinction probability that increases logarithmically with mass. We describe this evolution in terms of a convection-diffusion-reaction equation for ln M. The steady-state behavior is in good agreement with empirical data on recent terrestrial mammals, and the time-dependent behavior also agrees with data on extinct mammal species between 95 - 50 million years ago.

  16. Natural Models for Evolution on Networks

    CERN Document Server

    Mertzios, George B; Raptopoulos, Christoforos; Spirakis, Paul G

    2011-01-01

    Evolutionary dynamics have been traditionally studied in the context of homogeneous populations, mainly described my the Moran process. Recently, this approach has been generalized in \\cite{LHN} by arranging individuals on the nodes of a network. Undirected networks seem to have a smoother behavior than directed ones, and thus it is more challenging to find suppressors/amplifiers of selection. In this paper we present the first class of undirected graphs which act as suppressors of selection, by achieving a fixation probability that is at most one half of that of the complete graph, as the number of vertices increases. Moreover, we provide some generic upper and lower bounds for the fixation probability of general undirected graphs. As our main contribution, we introduce the natural alternative of the model proposed in \\cite{LHN}, where all individuals interact simultaneously and the result is a compromise between aggressive and non-aggressive individuals. That is, the behavior of the individuals in our new m...

  17. Chemical and Phase Evolution of Amorphous Molybdenum Sulfide Catalysts for Electrochemical Hydrogen Production.

    Science.gov (United States)

    Lee, Sang Chul; Benck, Jesse D; Tsai, Charlie; Park, Joonsuk; Koh, Ai Leen; Abild-Pedersen, Frank; Jaramillo, Thomas F; Sinclair, Robert

    2016-01-26

    Amorphous MoSx is a highly active, earth-abundant catalyst for the electrochemical hydrogen evolution reaction. Previous studies have revealed that this material initially has a composition of MoS3, but after electrochemical activation, the surface is reduced to form an active phase resembling MoS2 in composition and chemical state. However, structural changes in the MoSx catalyst and the mechanism of the activation process remain poorly understood. In this study, we employ transmission electron microscopy (TEM) to image amorphous MoSx catalysts activated under two hydrogen-rich conditions: ex situ in an electrochemical cell and in situ in an environmental TEM. For the first time, we directly observe the formation of crystalline domains in the MoSx catalyst after both activation procedures as well as spatially localized changes in the chemical state detected via electron energy loss spectroscopy. Using density functional theory calculations, we investigate the mechanisms for this phase transformation and find that the presence of hydrogen is critical for enabling the restructuring process. Our results suggest that the surface of the amorphous MoSx catalyst is dynamic: while the initial catalyst activation forms the primary active surface of amorphous MoS2, continued transformation to the crystalline phase during electrochemical operation could contribute to catalyst deactivation. These results have important implications for the application of this highly active electrocatalyst for sustainable H2 generation. PMID:26624225

  18. Life in the light: nucleic acid photoproperties as a legacy of chemical evolution.

    Science.gov (United States)

    Beckstead, Ashley A; Zhang, Yuyuan; de Vries, Mattanjah S; Kohler, Bern

    2016-09-21

    Photophysical investigations of the canonical nucleobases that make up DNA and RNA during the past 15 years have revealed that excited states formed by the absorption of UV radiation decay with subpicosecond lifetimes (i.e., blocks is an elegant solution to the threat of photochemical damage. Ultrafast excited-state deactivation strongly supports the hypothesis that UV radiation played a major role in shaping molecular inventories on the early Earth before the emergence of life and the subsequent development of a protective ozone shield. Here, we review the general physical and chemical principles that underlie the photostability, or "UV hardiness", of modern nucleic acids and discuss the possible implications of these findings for prebiotic chemical evolution. In RNA and DNA strands, much longer-lived excited states are observed, which at first glance appear to increase the risk of photochemistry. It is proposed that the dramatically different photoproperties that emerge from assemblies of photostable building blocks may explain the transition from a world of molecular survival to a world in which energy-rich excited electronic states were eventually tamed for biological purposes such as energy transduction, signaling, and repair of the genetic machinery. PMID:27539809

  19. Damage evolution assessment and modeling for CBN grinding wheel wear

    OpenAIRE

    YU, TIANYU; Bastawros, Ashraf F; Chandra, Abhijit

    2014-01-01

    The wear rate of a grinding wheel directly affects the workpiece surface integrity and tolerances. This paper summarizes a combined experimental-modeling framework for life expectancy of an electroplated Cubic Boron Nitride (CBN) grinding wheel, typically utilized in nickel-based superalloy grinding. The article presents an experimental framework to facilitate the formulation of a micromechanics based modeling framework. The presented study investigates the topological evolution of the grindi...

  20. Simple model of self-organized biological evolution

    Energy Technology Data Exchange (ETDEWEB)

    de Boer, J.; Derrida, B.; Flyvbjerg, H.; Jackson, A.D.; Wettig, T. (Department of Physics, State University of New York at Stony Brook, Stony Brook, New York 11794-3800 (United States) The Isaac Newton Institute for Mathematical Sciences, 20 Clarkson Road, Cambridge, CB4 0EH (United Kingdom) Laboratoire de Physique Statistique, Ecole Normale Superieure, 24 rue Lhomond, F-75005 Paris (France) Service de Physique Theorique, Centre de Etudes Nucleaires de Saclay, F-91191, Gif-Sur-Yvette (France) CONNECT, The Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen (Denmark))

    1994-08-08

    We give an exact solution of a recently proposed self-organized critical model of biological evolution. We show that the model has a power law distribution of durations of coevolutionary avalanches'' with a mean field exponent 3/2. We also calculate analytically the finite size effects which cut off this power law at times of the order of the system size.

  1. Landscape evolution models: A review of their fundamental equations

    Science.gov (United States)

    Chen, Alex; Darbon, Jérôme; Morel, Jean-Michel

    2014-08-01

    This paper reviews the main physical laws proposed in landscape evolution models (LEMs). It discusses first the main partial differential equations involved in these models and their variants. These equations govern water runoff, stream incision, regolith-bedrock interaction, hillslope evolution, and sedimentation. A synthesis of existing LEMs is proposed. It proposes three models with growing complexity and with a growing number of components: two-equation models with only two components, governing water and bedrock evolution; three-equation models with three components where water, bedrock, and sediment interact; and finally models with four equations and four interacting components, namely water, bedrock, suspended sediment, and regolith. This analysis is not a mere compilation of existing LEMs. It attempts at giving the simplest and most general physically consistent set of equations, coping with all requirements stated in LEMs and LEM software. Three issues are in particular addressed and hopefully resolved. The first one is a correct formulation of the water transport equation down slopes. A general formulation for this equation is proposed, coping not only with the simplest form computing the drainage area but also with a sound energy dissipation argument associated with the Saint-Venant shallow water equations. The second issue arises from the coexistence of two competing modes, namely the detachment-limited erosion mode on hillslopes, and the transport-limited sediment transport on river beds. The third issue (linked to the second) is the fact that no conservation law is available for material in these two modes. A simple solution proposed to resolve these issues is the introduction, as suggested by several authors, of an additional variable for suspended sediment load in water. With only three variables and three equations, the above-mentioned contradictions seem to be eliminated. Several numerical experiments on real digital elevation models (DEMs

  2. Phase field modeling of microstructure evolution in nuclear materials

    International Nuclear Information System (INIS)

    The paper presents two examples of phase field modeling of microstructure evolution of materials used in nuclear power industry. In the first example, an elasto-plastic phase field model was developed to predict hydrogen diffusion, hydride precipitation and fracture in zirconium at crack and notch tips. In the second example, some preliminary results of our current research on void lattice formation in irradiated materials will be given

  3. EVOC: A Computer Model of the Evolution of Culture

    OpenAIRE

    Gabora, Liane

    2013-01-01

    EVOC is a computer model of the EVOlution of Culture. It consists of neural network based agents that invent ideas for actions, and imitate neighbors' actions. EVOC replicates using a different fitness function the results obtained with an earlier model (MAV), including (1) an increase in mean fitness of actions, and (2) an increase and then decrease in the diversity of actions. Diversity of actions is positively correlated with number of needs, population size and density, and with the erosi...

  4. Deep mantle heat flow and thermal evolution of the Earth's core based on thermo-chemical mantle convection

    Science.gov (United States)

    Nakagawa, T.; Tackley, P.; Buffett, B.

    2004-12-01

    A coupled core-mantle evolution model that combines the global heat balance in the core with a fully-dynamical thermo-chemical mantle convection [Nakagawa and Tackley, 2004 published in EPSL] is used to investigate the deep mantle heat flow that is required to sustain the magnetic field generated by the geodynamo process. Effects of a radioactive heat source due to potassium in the core are also included in the global heat balance in the Earth??s core. Two important parameters are checked in this study; (1) density variation between depleted hartzbergite and basaltic material (0 to 3 percent) and (2) concentration of radioactive potassium in the core alloy (0ppm to 400ppm). The parameter set that most closely satisfies the criteria of size of the inner core (1220km at present time) is around 2 percent of density difference in a convecting mantle and 200ppm of radioactive heat source in the core. The concentration of potassium in the core is consistent with the geochemical approach [Murthy et al., 2003] but smaller than other successful thermal evolution models [Labrosse, 2003; Nimmo et al., 2004]. Heat flow through the core-mantle boundary and the contribution of radioactive heat sources in the core are consistent with theoretical estimates [e.g. Buffett, 2002] and geochemical constraints [Gessmann and Wood, 2002]. The power available to the geodynamo, based on the predicted heat flow through the core-mantle boundary, is approximately four times greater than the value predicted by numerical models of the geodynamo [Christensen and Kutzner, 2004] but closer to theoretical estimates [e.g. Buffett, 2002].

  5. Interaction of Tryptophane and Phenylalanine with Cadmium and Molybdenum Ferrocyanides and Its Implications in Chemical Evolution and Origins of Life.

    Science.gov (United States)

    Tewari, Brij

    2016-07-01

    Insoluble metal hexacyanoferrate(II) complexes could have concentrated biomonomers from dilute prebiotic soup during course of chemical evolution and origin of life or primitive earth. In the light of above hypothesis, adsorption of tryptophane and phenylalanine was studied on cadmium and molybdenum ferrocyanides at neutral pH (7.0 ± 0.01) and at a temperature of 30 ± 1º C. Interaction of amino acids with metal ferrocyanides are found to be maximum at neutral pH. Neutral pH is chosen for the adsorption studies because most of the reactions in biological systems taken place at neutral pH range. Adsorption trend follow Langmuir isotherm model. The Langmuir constants b and Qo were calculated at neutral pH, tryptophane was found to more adsorbed than phenylalanine on both metal ferrocyanides studied. Molybdenum ferrocyanides studied. Molybdenum ferrocyanides was found to have more uptake capacity for both adsorbates than cadmium ferrocyanides. The present study suggests that metal ferrocyanides might have played a role in the stabilization of biomolecules through their surface activity during course of chemical solution and origins of life on primitive earth.

  6. Mitosis: spindle evolution and the matrix model.

    Science.gov (United States)

    Pickett-Heaps, Jeremy; Forer, Art

    2009-03-01

    Current spindle models explain "anaphase A" (movement of chromosomes to the poles) in terms of a motility system based solely on microtubules (MTs) and that functions in a manner unique to mitosis. We find both these propositions unlikely. An evolutionary perspective suggests that when the spindle evolved, it should have come to share not only components (e.g., microtubules) of the interphase cell but also the primitive motility systems available, including those using actin and myosin. Other systems also came to be involved in the additional types of motility that now accompany mitosis in extant spindles. The resultant functional redundancy built reliability into this critical and complex process. Such multiple mechanisms are also confusing to those who seek to understand how chromosomes move. Narrowing this commentary down to just anaphase A, we argue that the spindle matrix participates with MTs in anaphase A and that this matrix may contain actin and myosin. The diatom spindle illustrates how such a system could function. This matrix may be motile and work in association with the MT cytoskeleton, as it does with the actin cytoskeleton during cell ruffling and amoeboid movement. Instead of pulling the chromosome polewards, the kinetochore fibre's role might be to slow polewards movement to allow correct chromosome attachment to the spindle. Perhaps the earliest eukaryotic cell was a cytoplast organised around a radial MT cytoskeleton. For cell division, it separated into two cytoplasts via a spindle of overlapping MTs. Cytokinesis was actin-based cleavage. As chromosomes evolved into individual entities, their interaction with the dividing cytoplast developed into attachment of the kinetochore to radial (cytoplast) MTs. We believe it most likely that cytoplasmic motility systems participated in these events. PMID:19255823

  7. A dynamical evolution model on the black-hole horizon

    Energy Technology Data Exchange (ETDEWEB)

    Zhu Jianyang [Department of Physics, Beijing Normal University, Beijing 100875 (China); CCAST (World Laboratory), Box 8730, Beijing 100080 (China)

    2005-07-07

    This paper demonstrates a dynamical evolution model of the black-hole (BH) horizon. The result indicates that a kinetic area-cell model of the BH horizon can model the evolution of the BH due to the Hawking radiation, and this area-cell system can be considered as an interacting geometrical particle system. Thus, the evolution turns into a problem of statistical physics. In the present work, this problem is treated in the framework of non-equilibrium statistics. It is proposed that each area cell possesses energy like a microscopic black hole and has gravitational interaction with the other area cells. We consider both a non-interaction ideal system and a system with small nearest-neighbour interactions, and obtain an analytic expression of the expected value of the horizon area of a dynamical BH. We find that, after a long enough evolution, a dynamical BH with the Hawking radiation can be in equilibrium with a finite-temperature radiation field. However, we also find that the system has a critical point, and when the temperature of the radiation field surrounding the BH approaches the critical temperature of the BH, a critical slowing-down phenomenon occurs.

  8. Physico-chemical evolution of low-pH cements: influence of the temperature and the retention mechanism of alkalis

    International Nuclear Information System (INIS)

    Because of their high alkalinity, Portland cement (OPC)-based materials may have deleterious effects in an underground waste repository. A solution would be to use low-alkalinity cements (also referred as low-pH cements) generating interstitial solutions with a reduced pH (11 instead of 13.5 for OPC), and thus showing an improved chemical compatibility with the repository environment. In this work, the investigated formulations were based on binary (OPC / silica fume) or ternary (OPC / silica fume / slag or fly ash) blends, with high substitution levels of CEM I (from 30% to 80%). This research project met two main objectives: (i) study the chemical evolution of low-pH cements at 50 C or 80 C, since such temperatures could be encountered in certain zones of the waste repositories, and (ii) determine the mechanisms of alkali retention by hydrated low-pH cements. (i) Investigation of low-pH cement pastes with ongoing hydration over one year showed that increasing the temperature from 20 C to 80 C accelerated cement hydration and favoured the depletion of portlandite. A lengthening of the C-A-S-H silicate chains was also detected by 27Al and 29Si NMR analyses. Besides, ettringite precipitated at 20 C, but was destabilised at higher temperature. The released sulphates were partly adsorbed on the C-A-S-H and dissolved in the interstitial solution. The pH of this solution was reduced from 1.7 to 2.2 units depending on the formulations. The soluble fractions of alkalis did not significantly change with temperature. Among the five investigated blends, ternary binder T1 (37.5% CEM I, 32.5% silica fume, 30% fly ash) was the only one giving a pore solution pH lower than 11 at 20, 50 and 80 C (curing time of 6 months and 1 year). Its long-term evolution was simulated by model systems reproducing its chemical composition with reactive oxides. At equilibrium, the hydrate assemblage comprised C-A-S-H (Ca/Si and Al/Si ratios of 0.75 and 0.15 respectively), amorphous silica and

  9. Modeling evolution and immune system by cellular automata

    Energy Technology Data Exchange (ETDEWEB)

    Bezzi, M. [Scuola Internazionale Superiore di Studi Avanzati, Trieste (Italy); Istituto Nazionale di Fisica della Materia, Florence (Italy)

    2001-07-01

    In this review the behavior of two different biological systems is investigated using cellular automata. Starting from this spatially extended approach it is also tried, in some cases, to reduce the complexity of the system introducing mean-field approximation, and solving (or trying to solve) these simplified systems. It is discussed the biological meaning of the results, the comparison with experimental data (if available) and the different features between spatially extended and mean-field versions. The biological systems considered in this review are the following: Darwinian evolution in simple ecosystems and immune system response. In the first section the main features of molecular evolution are introduced, giving a short survey of genetics for physicists and discussing some models for prebiotic systems and simple ecosystems. It is also introduced a cellular automaton model for studying a set of evolving individuals in a general fitness landscape, considering also the effects of co-evolution. In particular the process of species formation (speciation) is described in sect. 5. The second part deals with immune system modeling. The biological features of immune response are discussed, as well as it is introduced the concept of shape space and of idiotypic network. More detailed reviews which deal with immune system models (mainly focused on idiotypic network models) can be found. Other themes here discussed: the applications of CA to immune system modeling, two complex cellular automata for humoral and cellular immune response. Finally, it is discussed the biological data and the general conclusions are drawn in the last section.

  10. Modeling evolution and immune system by cellular automata

    International Nuclear Information System (INIS)

    In this review the behavior of two different biological systems is investigated using cellular automata. Starting from this spatially extended approach it is also tried, in some cases, to reduce the complexity of the system introducing mean-field approximation, and solving (or trying to solve) these simplified systems. It is discussed the biological meaning of the results, the comparison with experimental data (if available) and the different features between spatially extended and mean-field versions. The biological systems considered in this review are the following: Darwinian evolution in simple ecosystems and immune system response. In the first section the main features of molecular evolution are introduced, giving a short survey of genetics for physicists and discussing some models for prebiotic systems and simple ecosystems. It is also introduced a cellular automaton model for studying a set of evolving individuals in a general fitness landscape, considering also the effects of co-evolution. In particular the process of species formation (speciation) is described in sect. 5. The second part deals with immune system modeling. The biological features of immune response are discussed, as well as it is introduced the concept of shape space and of idiotypic network. More detailed reviews which deal with immune system models (mainly focused on idiotypic network models) can be found. Other themes here discussed: the applications of CA to immune system modeling, two complex cellular automata for humoral and cellular immune response. Finally, it is discussed the biological data and the general conclusions are drawn in the last section

  11. Stochastic evolutions of dynamic traffic flow modeling and applications

    CERN Document Server

    Chen, Xiqun (Michael); Shi, Qixin

    2015-01-01

    This book reveals the underlying mechanisms of complexity and stochastic evolutions of traffic flows. Using Eulerian and Lagrangian measurements, the authors propose lognormal headway/spacing/velocity distributions and subsequently develop a Markov car-following model to describe drivers’ random choices concerning headways/spacings, putting forward a stochastic fundamental diagram model for wide scattering flow-density points. In the context of highway onramp bottlenecks, the authors present a traffic flow breakdown probability model and spatial-temporal queuing model to improve the stability and reliability of road traffic flows. This book is intended for researchers and graduate students in the fields of transportation engineering and civil engineering.

  12. Setting the volatile composition of (exo)planet-building material. Does chemical evolution in disk midplanes matter?

    CERN Document Server

    Eistrup, Christian; van Dishoeck, Ewine F

    2016-01-01

    [Abridged] Chemical evolution in the protoplanetary disk midplane can modify the composition of ices and gases. We have investigated if and how chemical evolution affects the abundances and distributions of key volatile species in the midplane of a protoplanetary disk in the 0.2-30 AU range. A full chemical network including gas-phase, gas-grain interactions and grain-surface chemistry is used to evolve chemistry in time, for 1 Myr. Great diversity is observed in the relative abundance ratios of the main considered species: H2O, CO, CO2, CH4, O2, NH3 and N2. The choice of ionisation level, the choice of initial abundances, as well as the extent of chemical reaction types included are all factors that affect the chemical evolution. The only exception is the inheritance scenario with a low ionisation level, which results in negligible changes compared with the initial abundances, regardless of whether grain-surface chemistry is included. The chemical processing changes the C/O ratios for gas and ice significant...

  13. Detailed Chemical Kinetic Modeling of Cyclohexane Oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Silke, E J; Pitz, W J; Westbrook, C K; Ribaucour, M

    2006-11-10

    A detailed chemical kinetic mechanism has been developed and used to study the oxidation of cyclohexane at both low and high temperatures. Reaction rate constant rules are developed for the low temperature combustion of cyclohexane. These rules can be used for in chemical kinetic mechanisms for other cycloalkanes. Since cyclohexane produces only one type of cyclohexyl radical, much of the low temperature chemistry of cyclohexane is described in terms of one potential energy diagram showing the reaction of cyclohexyl radical + O{sub 2} through five, six and seven membered ring transition states. The direct elimination of cyclohexene and HO{sub 2} from RO{sub 2} is included in the treatment using a modified rate constant of Cavallotti et al. Published and unpublished data from the Lille rapid compression machine, as well as jet-stirred reactor data are used to validate the mechanism. The effect of heat loss is included in the simulations, an improvement on previous studies on cyclohexane. Calculations indicated that the production of 1,2-epoxycyclohexane observed in the experiments can not be simulated based on the current understanding of low temperature chemistry. Possible 'alternative' H-atom isomerizations leading to different products from the parent O{sub 2}QOOH radical were included in the low temperature chemical kinetic mechanism and were found to play a significant role.

  14. Cosmic star formation, gamma-ray burst rate at high redshift and cosmic chemical evolution

    International Nuclear Information System (INIS)

    Recent optical observations and Gamma-ray burst rate determinations have led to significant progress in establishing the star formation rate (SFR) at high redshift. The SFR in turn is used to predict the ionization history of the Universe (using last results from CMB WMAP mission), the cosmic chemical abundances, and supernova rates. These predictions are done using a hierarchical model for structure formation (Press and Schechter). (author)

  15. Microeconomic co-evolution model for financial technical analysis signals

    CERN Document Server

    Rotundo, G

    2006-01-01

    Technical analysis (TA) has been used for a long time before the availability of more sophisticated instruments for financial forecasting in order to suggest decisions on the basis of the occurrence of data patterns. Many mathematical and statistical tools for quantitative analysis of financial markets have experienced a fast and wide growth and have the power for overcoming classical technical analysis methods. This paper aims to give a measure of the reliability of some information used in TA by exploring the probability of their occurrence within a particular $microeconomic$ agent based model of markets, i.e., the co-evolution Bak-Sneppen model originally invented for describing species population evolutions. After having proved the practical interest of such a model in describing financial index so called avalanches, in the prebursting bubble time rise, the attention focuses on the occurrence of trend line detection crossing of meaningful barriers, those that give rise to some usual technical analysis str...

  16. Review of permeability evolution model for fractured porous media

    Institute of Scientific and Technical Information of China (English)

    Jianjun Ma

    2015-01-01

    The ability to capture permeability of fractured porous media plays a significant role in several engi-neering applications, including reservoir, mining, petroleum and geotechnical engineering. In order to solve fluid flow and coupled flow-deformation problems encountered in these engineering applications, both empirical and theoretical models had been proposed in the past few decades. Some of them are simple but still work in certain circumstances;others are complex but also need some modifications to be applicable. Thus, the understanding of state-of-the-art permeability evolution model would help researchers and engineers solve engineering problems through an appropriate approach. This paper summarizes permeability evolution models proposed by earlier and recent researchers with emphasis on their characteristics and limitations.

  17. Differential Evolution algorithm applied to FSW model calibration

    Science.gov (United States)

    Idagawa, H. S.; Santos, T. F. A.; Ramirez, A. J.

    2014-03-01

    Friction Stir Welding (FSW) is a solid state welding process that can be modelled using a Computational Fluid Dynamics (CFD) approach. These models use adjustable parameters to control the heat transfer and the heat input to the weld. These parameters are used to calibrate the model and they are generally determined using the conventional trial and error approach. Since this method is not very efficient, we used the Differential Evolution (DE) algorithm to successfully determine these parameters. In order to improve the success rate and to reduce the computational cost of the method, this work studied different characteristics of the DE algorithm, such as the evolution strategy, the objective function, the mutation scaling factor and the crossover rate. The DE algorithm was tested using a friction stir weld performed on a UNS S32205 Duplex Stainless Steel.

  18. Parameter Estimates in Differential Equation Models for Chemical Kinetics

    Science.gov (United States)

    Winkel, Brian

    2011-01-01

    We discuss the need for devoting time in differential equations courses to modelling and the completion of the modelling process with efforts to estimate the parameters in the models using data. We estimate the parameters present in several differential equation models of chemical reactions of order n, where n = 0, 1, 2, and apply more general…

  19. Learning of Chemical Equilibrium through Modelling-Based Teaching

    Science.gov (United States)

    Maia, Poliana Flavia; Justi, Rosaria

    2009-01-01

    This paper presents and discusses students' learning process of chemical equilibrium from a modelling-based approach developed from the use of the "Model of Modelling" diagram. The investigation was conducted in a regular classroom (students 14-15 years old) and aimed at discussing how modelling-based teaching can contribute to students learning…

  20. A Coupled Multiscale Model of Texture Evolution and Plastic Anisotropy

    Science.gov (United States)

    Gawad, J.; Van Bael, A.; Yerra, S. K.; Samaey, G.; Van Houtte, P.; Roose, D.

    2010-06-01

    In this paper we present a multiscale model of a plastic deformation process in which the anisotropy of plastic properties is related to the evolution of the crystallographic texture. The model spans several length scales from the macroscopic deformation of the workpiece to the microscale interactions between individual grains in a polycrystalline material. The macroscopic behaviour of the material is described by means of a Finite Element (FE) model. Plastic anisotropy is taken into account in a constitutive law, based on the concept of a plastic potential in strain rate space. The coefficients of a sixth-order Facet equation are determined using the Taylor theory, provided that the current crystallographic texture at a given FE integration point is known. Texture evolution in the FE integration points is predicted by an ALAMEL micromechanical model. Mutual interactions between coarse and fine scale are inherent in the physics of the deformation process. These dependencies are taken into account by full bidirectional coupling in the model. Therefore, the plastic deformation influences the crystallographic texture and the evolution of the texture induces anisotropy of the macroscopic deformation. The presented approach enables an adaptive texture and yield surface update scheme with respect to the local plastic deformation in the FE integration points. Additionally, the computational cost related to the updates of the constitutive law is reduced by application of parallel computing techniques. Suitability of on-demand computing for this computational problem is discussed. The parallelisation strategy addresses both distributed memory and shared memory architectures. The cup drawing process has been simulated using the multiscale model outlined above. The discussion of results includes the analysis of the planar anisotropy in the cup and the influence of complex deformation path on texture development. Evolution of texture at selected material points is assessed as

  1. Uranus evolution models with simple thermal boundary layers

    Science.gov (United States)

    Nettelmann, N.; Wang, K.; Fortney, J. J.; Hamel, S.; Yellamilli, S.; Bethkenhagen, M.; Redmer, R.

    2016-09-01

    The strikingly low luminosity of Uranus (Teff ≃ Teq) constitutes a long-standing challenge to our understanding of Ice Giant planets. Here we present the first Uranus structure and evolution models that are constructed to agree with both the observed low luminosity and the gravity field data. Our models make use of modern ab initio equations of state at high pressures for the icy components water, methane, and ammonia. Proceeding step by step, we confirm that adiabatic models yield cooling times that are too long, even when uncertainties in the ice:rock ratio (I:R) are taken into account. We then argue that the transition between the ice/rock-rich interior and the H/He-rich outer envelope should be stably stratified. Therefore, we introduce a simple thermal boundary and adjust it to reproduce the low luminosity. Due to this thermal boundary, the deep interior of the Uranus models are up to 2-3 warmer than adiabatic models, necessitating the presence of rocks in the deep interior with a possible I:R of 1 × solar. Finally, we allow for an equilibrium evolution (Teff ≃ Teq) that begun prior to the present day, which would therefore no longer require the current era to be a "special time" in Uranus' evolution. In this scenario, the thermal boundary leads to more rapid cooling of the outer envelope. When Teff ≃ Teq is reached, a shallow, subadiabatic zone in the atmosphere begins to develop. Its depth is adjusted to meet the luminosity constraint. This work provides a simple foundation for future Ice Giant structure and evolution models, that can be improved by properly treating the heat and particle fluxes in the diffusive zones.

  2. Multi-Model approach to reconstruct the Mediterranean Freshwater Evolution

    Science.gov (United States)

    Simon, Dirk; Marzocchi, Alice; Flecker, Rachel; Lunt, Dan; Hilgen, Frits; Meijer, Paul

    2016-04-01

    Today the Mediterranean Sea is isolated from the global ocean by the Strait of Gibraltar. This restricted nature causes the Mediterranean basin to react more sensitively to climatic and tectonic related phenomena than the global ocean. Not just eustatic sea-level and regional river run-off, but also gateway tectonics and connectivity between sub-basins are leaving an enhanced fingerprint in its geological record. To understand its evolution, it is crucial to understand how these different effects are coupled. The Miocene-Pliocene sedimentary record of the Mediterranean shows alternations in composition and colour and has been astronomically tuned. Around the Miocene-Pliocene Boundary the most extreme changes occur in the Mediterranean Sea. About 6% of the salt in the global ocean deposited in the Mediterranean Region, forming an approximately 2 km thick salt layer, which is still present today. This extreme event is named the Messinian Salinity Crisis (MSC, 5.97-5.33 Ma). The gateway and climate evolution is not well constrained for this time, which makes it difficult to distinguish which of the above mentioned drivers might have triggered the MSC. We, therefore, decided to tackle this problem via a multi-model approach: (1) We calculate the Mediterranean freshwater evolution via 30 atmosphere-ocean-vegetation simulations (using HadCM3L), to which we fitted to a function, using a regression model. This allows us to directly relate the orbital curves to evaporation, precipitation and run off. The resulting freshwater evolution can be directly correlated to other sedimentary and proxy records in the late Miocene. (2) By feeding the new freshwater evolution curve into a box/budget model we can predict the salinity and strontium evolution of the Mediterranean for a certain Atlantic-Mediterranean gateway. (3) By comparing these results to the known salinity thresholds of gypsum and halite saturation of sea water, but also to the late Miocene Mediterranean strontium

  3. New trajectory-driven aerosol and chemical process model Chemical and Aerosol Lagrangian Model (CALM

    Directory of Open Access Journals (Sweden)

    P. Tunved

    2010-11-01

    Full Text Available A new Chemical and Aerosol Lagrangian Model (CALM has been developed and tested. The model incorporates all central aerosol dynamical processes, from nucleation, condensation, coagulation and deposition to cloud formation and in-cloud processing. The model is tested and evaluated against observations performed at the SMEAR II station located at Hyytiälä (61° 51' N, 24° 17' E over a time period of two years, 2000–2001. The model shows good agreement with measurements throughout most of the year, but fails in reproducing the aerosol properties during the winter season, resulting in poor agreement between model and measurements especially during December–January. Nevertheless, through the rest of the year both trends and magnitude of modal concentrations show good agreement with observation, as do the monthly average size distribution properties. The model is also shown to capture individual nucleation events to a certain degree. This indicates that nucleation largely is controlled by the availability of nucleating material (as prescribed by the [H2SO4], availability of condensing material (in this model 15% of primary reactions of monoterpenes (MT are assumed to produce low volatile species and the properties of the size distribution (more specifically, the condensation sink. This is further demonstrated by the fact that the model captures the annual trend in nuclei mode concentration. The model is also used, alongside sensitivity tests, to examine which processes dominate the aerosol size distribution physical properties. It is shown, in agreement with previous studies, that nucleation governs the number concentration during transport from clean areas. It is also shown that primary number emissions almost exclusively govern the CN concentration when air from Central Europe is advected north over Scandinavia. We also show that biogenic emissions have a large influence on the amount of potential CCN observed

  4. New trajectory driven aerosol and chemical process model: chemical and aerosol Lagrangian model (CALM

    Directory of Open Access Journals (Sweden)

    P. Tunved

    2010-06-01

    Full Text Available A new Chemical and Aerosol Lagrangian Model (CALM have been developed and tested. The model incorporates all central aerosol dynamical processes, from nucleation, condensation, coagulation and deposition to cloud formation and in-cloud processing. The model is tested and evaluated against observations performed at the SMEAR II station located at Hyytiälä (61°51' N, 24°17' E over a time period of two years, 2000–2001. The model shows good agreement with measurements throughout most of the year, but fails in reproducing the aerosol properties during the winter season, resulting in poor agreement between model and measurements especially during December–January. Nevertheless, through the rest of the year both trends and magnitude of modal concentrations show good agreement with observation, as do the monthly average size distribution properties. The model is also shown to capture individual nucleation events to a certain degree. This indicates that nucleation largely is controlled by the availability of nucleating material (as prescribed by the [H2SO4], availability of condensing material (in this model 15% of primary reactions of monoterpenes (MT are assumed to produce low volatile species and the properties of the size distribution (more specifically, the condensation sink. This is further demonstrated by the fact that the model captures the annual trend in nuclei mode concentration. The model is also used, alongside sensitivity tests, to examine which processes dominate the aerosol size distribution physical properties. It is shown, in agreement with previous studies, that nucleation governs the number concentration while transport from clean areas takes place. It is also shown that primary number emissions almost exclusively govern the CN concentration when air from Central Europe is advected north over Scandinavia. We also show that biogenic emissions have a large influence on the amount of potential CCN observed

  5. Chemically induced intestinal damage models in zebrafish larvae.

    Science.gov (United States)

    Oehlers, Stefan H; Flores, Maria Vega; Hall, Christopher J; Okuda, Kazuhide S; Sison, John Oliver; Crosier, Kathryn E; Crosier, Philip S

    2013-06-01

    Several intestinal damage models have been developed using zebrafish, with the aim of recapitulating aspects of human inflammatory bowel disease (IBD). These experimentally induced inflammation models have utilized immersion exposure to an array of colitogenic agents (including live bacteria, bacterial products, and chemicals) to induce varying severity of inflammation. This technical report describes methods used to generate two chemically induced intestinal damage models using either dextran sodium sulfate (DSS) or trinitrobenzene sulfonic acid (TNBS). Methods to monitor intestinal damage and inflammatory processes, and chemical-genetic methods to manipulate the host response to injury are also described.

  6. Last interglacial temperature evolution – a model inter-comparison

    Directory of Open Access Journals (Sweden)

    H. Renssen

    2012-09-01

    Full Text Available There is a growing number of proxy-based reconstructions detailing the climatic changes during the Last Interglacial period. This period is of special interest because large parts of the globe were characterized by a warmer-than-present-day climate, making this period an interesting test bed for climate models in the light of projected global warming. However, mainly because synchronizing the different records is difficult, there is no consensus on a global picture of Last Interglacial temperature changes. Here we present the first model inter-comparison of transient simulations covering the Last Interglacial period. By comparing the different simulations we aim at investigating the robustness of the simulated surface air temperature evolution. The model inter-comparison shows a robust Northern Hemisphere July temperature evolution characterized by a maximum between 130–122 ka BP with temperatures 0.4 to 6.8 K above pre-industrial values. This temperature evolution is in line with the changes in June insolation and greenhouse-gas concentrations. For the evolution of July temperatures in the Southern Hemisphere, the picture emerging from the inter-comparison is less clear. However, it does show that including greenhouse-gas concentration changes is critical. The simulations that include this forcing show an early, 128 ka BP July temperature anomaly maximum of 0.5 to 2.6 K. The robustness of simulated January temperatures is large in the Southern Hemisphere and the mid-latitudes of the Northern Hemisphere. In these latitudes maximum January temperature anomalies of respectively −2.5 to 2 K and 0 to 2 K are simulated for the period after 118 ka BP. The inter-comparison is inconclusive on the evolution of January temperatures in the high-latitudes of the Northern Hemisphere. Further investigation of regional anomalous patterns and inter-model differences indicate that in specific regions, feedbacks within the climate system are important for the

  7. Evolution of metastasis revealed by mutational landscapes of chemically induced skin cancers

    Science.gov (United States)

    McCreery, Melissa Q; Halliwill, Kyle D; Chin, Douglas; Delrosario, Reyno; Hirst, Gillian; Vuong, Peter; Jen, Kuang-Yu; Hewinson, James; Adams, David J; Balmain, Allan

    2016-01-01

    Human tumors show a high level of genetic heterogeneity, but the processes that influence the timing and route of metastatic dissemination of the subclones are unknown. Here we have used whole-exome sequencing of 103 matched benign, malignant and metastatic skin tumors from genetically heterogeneous mice to demonstrate that most metastases disseminate synchronously from the primary tumor, supporting parallel rather than linear evolution as the predominant model of metastasis. Shared mutations between primary carcinomas and their matched metastases have the distinct A-to-T signature of the initiating carcinogen dimethylbenzanthracene, but non-shared mutations are primarily G-to-T, a signature associated with oxidative stress. The existence of carcinomas that either did or did not metastasize in the same host animal suggests that there are tumor-intrinsic factors that influence metastatic seeding. We also demonstrate the importance of germline polymorphisms in determining allele-specific mutations, and we identify somatic genetic alterations that are specifically related to initiation of carcinogenesis by Hras or Kras mutations. Mouse tumors that mimic the genetic heterogeneity of human cancers can aid our understanding of the clonal evolution of metastasis and provide a realistic model for the testing of novel therapies. PMID:26523969

  8. Thinking Developmentally: The Next Evolution in Models of Health.

    Science.gov (United States)

    Garner, Andrew S

    2016-09-01

    As the basic sciences that inform conceptions of human health advance, so must the models that are used to frame additional research, to teach the next generation of providers, and to inform health policy. This article briefly reviews the evolution from a biomedical model to a biopsychosocial (BPS) model and to an ecobiodevelopmental (EBD) model. Like the BPS model, the EBD model reaffirms the biological significance of psychosocial features within the patient's ecology, but it does so at the molecular and cellular levels. More importantly, the EBD model adds the dimension of time, forcing providers to "think developmentally" and to acknowledge the considerable biological and psychological consequences of previous experiences. For the health care system to move from a reactive "sick care" system to a proactive "well care" system, all providers must begin thinking developmentally by acknowledging the dynamic but cumulative dance between nature and nurture that drives development, behavior, and health, not only in childhood, but across the lifespan. PMID:27429356

  9. A Chemical Properties Simulator to Support Integrated Environmental Modeling (proceeding)

    Science.gov (United States)

    Users of Integrated Environmental Modeling (IEM) systems are responsible for defining individual chemicals and their properties, a process that is time-consuming at best and overwhelming at worst, especially for new chemicals with new structures. A software tool is needed to allo...

  10. Upper Secondary Teachers' Knowledge for Teaching Chemical Bonding Models

    Science.gov (United States)

    Bergqvist, Anna; Drechsler, Michal; Chang Rundgren, Shu-Nu

    2016-01-01

    Researchers have shown a growing interest in science teachers' professional knowledge in recent decades. The article focuses on how chemistry teachers impart chemical bonding, one of the most important topics covered in upper secondary school chemistry courses. Chemical bonding is primarily taught using models, which are key for understanding…

  11. THEORETICAL CHEMICAL ENGINEERING - Modeling and Simulation by Christo Boyadjiev

    Directory of Open Access Journals (Sweden)

    Simeon Oka

    2010-01-01

    Full Text Available Book Title: THEORETICAL CHEMICAL ENGINEERING - Modeling and Simulation Author(s: Christo Boyadjiev Institute of Chemical Engineering, Bulgarian Academy of Science, Sofia Publisher: Springer, 2010 ISBN: 978-3-642-10777-1 Review by: Prof. Simeon Oka, Ph. D., Scientific advisor - retired

  12. Hints on halo evolution in SFDM models with galaxy observations

    CERN Document Server

    Gonzalez-Morales, Alma X; Urena-Lopez, L Arturo; Valenzuela, Octavio

    2012-01-01

    A massive, self-interacting scalar field has been considered as a possible candidate for the dark matter in the universe. We present an observational constraint to the model arising from strong lensing observations in galaxies. The result points to a discrepancy in the properties of scalar field dark matter halos for dwarf and lens galaxies, mainly because halo parameters are directly related to physical quantities in the model. This is an important indication that it becomes necessary to have a better understanding of halo evolution in scalar field dark matter models, where the presence of baryons can play an important role.

  13. Interaction Strength and a Generalized Bak-Sneppen Evolution Model

    Institute of Scientific and Technical Information of China (English)

    李炜; 蔡勖

    2002-01-01

    The Bak-Sneppen evolution model is generalized in terms of a new concept and quantity: interaction strength.Based on a quantitative definition, the interaction strength describes the strength of the interaction between thenearest-neighbour individuals in the model Self-organized criticality is observed for the generalized model withten different values of interaction strength. The gap equation governing the self-organization is derived. It is alsofound that the self-organized threshold depends on the value of the interaction strength.

  14. Interaction Strength and a Generalized Bak-Sneppen Evolution Model

    Science.gov (United States)

    Li, Wei; Cai, Xu

    2002-10-01

    The Bak-Sneppen evolution model is generalized in terms of a new concept and quantity: interaction strength. Based on a quantitative definition, the interaction strength describes the strength of the interaction between the nearest-neighbour individuals in the model. Self-organized criticality is observed for the generalized model with ten different values of interaction strength. The gap equation governing the self-organization is derived. It is also found that the self-organized threshold depends on the value of the interaction strength.

  15. Interaction strength and a generalized Bak-Sneppen evolution model

    CERN Document Server

    Li Wei

    2002-01-01

    The Bak-Sneppen evolution model is generalized in terms of a new concept and quantity: interaction strength. Based on a quantitative definition, the interaction strength describes the strength of the interaction between the nearest-neighbour individuals in the model. Self-organized criticality is observed for the generalized model with ten different values of interaction strength. The gap equation governing the self-organization is derived. It is also found that the self-organized threshold depends on the value of the interaction strength

  16. Harmony search algorithm with differential evolution based control parameter co-evolution and its application in chemical process dynamic optimization

    Institute of Scientific and Technical Information of China (English)

    范勤勤; 王循华; 颜学峰

    2015-01-01

    A modified harmony search algorithm with co-evolutional control parameters (DEHS), applied through differential evolution optimization, is proposed. In DEHS, two control parameters, i.e., harmony memory considering rate and pitch adjusting rate, are encoded as a symbiotic individual of an original individual (i.e., harmony vector). Harmony search operators are applied to evolving the original population. DE is applied to co-evolving the symbiotic population based on feedback information from the original population. Thus, with the evolution of the original population in DEHS, the symbiotic population is dynamically and self-adaptively adjusted, and real-time optimum control parameters are obtained. The proposed DEHS algorithm has been applied to various benchmark functions and two typical dynamic optimization problems. The experimental results show that the performance of the proposed algorithm is better than that of other HS variants. Satisfactory results are obtained in the application.

  17. A coupled physical-biological-chemical model for the Indian Ocean

    Indian Academy of Sciences (India)

    P S Swathi; M K Sharada; K S Yajnik

    2000-12-01

    A coupled physical-biological-chemical model has been developed at C-MMACS. for studying the time- variation of primary productivity and air-sea carbon-dioxide exchange in the Indian Ocean. The physical model is based on the Modular Ocean Model, Version 2 (MOM2) and the biological model describes the nonlinear dynamics of a 7-component marine ecosystem. The chemical model includes dynamical equation for the evolution of dissolved inorganic carbon and total alkalinity. The interaction between the biological and chemical model is through the Redfield ratio. The partial pressure of carbon dioxide pCO2 of the surface layer is obtained from the chemical equilibrium equations of Peng et al 1987. Transfer coefficients for air-sea exchange of CO2 are computed dynamically based on the wind speeds. The coupled model reproduces the high productivity observed in the Arabian Sea off the Somali and Omani coasts during the Southwest (SW) monsoon. The entire Arabian Sea is an outgassing region for CO2 in spite of high productivity with transfer rates as high as 80 m-mol C/m2/day during SW monsoon near the Somali Coast on account of strong winds.

  18. Phylogenetic ANOVA: The Expression Variance and Evolution Model for Quantitative Trait Evolution.

    Science.gov (United States)

    Rohlfs, Rori V; Nielsen, Rasmus

    2015-09-01

    A number of methods have been developed for modeling the evolution of a quantitative trait on a phylogeny. These methods have received renewed interest in the context of genome-wide studies of gene expression, in which the expression levels of many genes can be modeled as quantitative traits. We here develop a new method for joint analyses of quantitative traits within- and between species, the Expression Variance and Evolution (EVE) model. The model parameterizes the ratio of population to evolutionary expression variance, facilitating a wide variety of analyses, including a test for lineage-specific shifts in expression level, and a phylogenetic ANOVA that can detect genes with increased or decreased ratios of expression divergence to diversity, analogous to the famous Hudson Kreitman Aguadé (HKA) test used to detect selection at the DNA level. We use simulations to explore the properties of these tests under a variety of circumstances and show that the phylogenetic ANOVA is more accurate than the standard ANOVA (no accounting for phylogeny) sometimes used in transcriptomics. We then apply the EVE model to a mammalian phylogeny of 15 species typed for expression levels in liver tissue. We identify genes with high expression divergence between species as candidates for expression level adaptation, and genes with high expression diversity within species as candidates for expression level conservation and/or plasticity. Using the test for lineage-specific expression shifts, we identify several candidate genes for expression level adaptation on the catarrhine and human lineages, including genes putatively related to dietary changes in humans. We compare these results to those reported previously using a model which ignores expression variance within species, uncovering important differences in performance. We demonstrate the necessity for a phylogenetic model in comparative expression studies and show the utility of the EVE model to detect expression divergence

  19. Sr isotope evolution during chemical weathering of granites -- impact of relative weathering rates of minerals

    Institute of Scientific and Technical Information of China (English)

    MA; Yingjun

    2001-01-01

    [1]Ma, Y. J., Liu, C. Q., Geochemistry of strontium isotopes in the crust weathering system, Acta Mineralogica Sinica (in Chinese), 1998, 18(3): 350.[2]Ma, Y. J., Liu, C. Q., Using strontium isotopes to trace nutrient element circulation and hydrochemical evolution within an ecosystem, Advance in Earth Sciences (in Chinese), 1999, 14 (4): 377.[3]Brantley, S. L., Chesley, J. T., Stillings, L. L., Isotopic ratios and release rates of strontium from weathering feldspars, Geochim. Cosmochim. Acta, 1998, 62(9): 1493.[4]Blum, J. D., Erel, Y., A silicate weathering mechanism linking increases in marine 87Sr/86Sr with global glaciation, Nature, 1995, 373: 415.[5]Blum, J. D., Erel, Y., Rb-Sr isotope systematics of granitic soil chronosequence: The importance of biotite weathering, Geochim. Cosmochim. Acta, 1997, 61(15): 3193.[6]Bullen, T., Krabbenhoft, D., Kendall, C., Kinetic and mineralogic controls on the evolution of groundwater chemistry and 87Sr/86Sr in a sandy silicate aquifer, northern Wisconsin, USA, Geochim. Cosmochim. Acta, 1996, 60: 1807.[7]Bullen, T., White, A., Blum, A. et al., Chemical weathering of a soil chronosequence on granitoid alluvium: Ⅱminer-alogic and isotopic constraints on the behavior of strontium, Geochim. Cosmochim. Acta, 1997, 61: 291.[8]Blum, J. D., Erel, Y., Brown, K., 87Sr/86Sr ratios of Sierra Nevada stream waters: Implications for relative mineral weath-ering rates, Geochim. Cosmochim. Acta, 1993, 57: 5019.[9]Ma Yingjun, Trace element and strontium isotope geochemistry during chemical weathering, Ph. D. Dissertation, 1999, Institute of Geochemistry, Chinese Academy of Sciences.[10]Nesbitt, H. W., Markovics, G., Price, R. C., Chemical processes affecting alkalis and alkaline earths during continental weathering, Geochim. Cosmochim. Acta, 1980, 44: 1659.[11]Clauer, N., Strontium and argon isotopes in naturally weathered biotites, muscovites and feldspars, Chem. Geol., 1981, 31: 325.[12

  20. Extension of association models to complex chemicals

    DEFF Research Database (Denmark)

    Avlund, Ane Søgaard

    Summary of “Extension of association models to complex chemicals”. Ph.D. thesis by Ane Søgaard Avlund The subject of this thesis is application of SAFT type equations of state (EoS). Accurate and predictive thermodynamic models are important in many industries including the petroleum industry. Th...

  1. Merging binary black holes formed through chemically homogeneous evolution in short-period stellar binaries

    CERN Document Server

    Mandel, Ilya

    2016-01-01

    We explore a newly proposed channel to create binary black holes of stellar origin. This scenario applies to massive, tight binaries where mixing induced by rotation and tides transports the products of hydrogen burning throughout the stellar envelopes. This slowly enriches the entire star with helium, preventing the build-up of an internal chemical gradient. The stars remain compact as they evolve nearly chemically homogeneously, eventually forming two black holes, which, we estimate, typically merge 4 to 11 Gyr after formation. Like other proposed channels, this evolutionary pathway suffers from significant theoretical uncertainties, but could be constrained in the near future by data from advanced ground-based gravitational-wave detectors. We perform Monte Carlo simulations of the expected merger rate over cosmic time to explore the implications and uncertainties. Our default model for this channel yields a local binary black hole merger rate of about $10$ Gpc$^{-3}$ yr$^{-1}$ at redshift $z=0$, peaking at...

  2. Long range anti-ferromagnetic spin model for prebiotic evolution

    Energy Technology Data Exchange (ETDEWEB)

    Nokura, Kazuo [Shonan Institute of Technology, Fujisawa 251-8511 (Japan)

    2003-11-28

    I propose and discuss a fitness function for one-dimensional binary monomer sequences of macromolecules for prebiotic evolution. The fitness function is defined by the free energy of polymers in the high temperature random coil phase. With repulsive interactions among the same kind of monomers, the free energy in the high temperature limit becomes the energy function of the one-dimensional long range anti-ferromagnetic spin model, which is shown to have a dynamical phase transition and glassy states.

  3. Evolution of migration rate in a spatially realistic metapopulation model.

    OpenAIRE

    Heino,-M; Hanski,-I

    2001-01-01

    We use an individual-based, spatially realistic metapopulation model to study the evolution of migration rate. We first explore the consequences of habitat change in hypothetical patch networks on a regular lattice. If the primary consequence of habitat change is an increase in local extinction risk as a result of decreased local population sizes, migration rate increases. A nonmonotonic response, with migration rate decreasing at high extinction rate, was obtained only by assuming very frequ...

  4. Evolution of Migration Rate in a Spatially Realistic Metapopulation Model.

    OpenAIRE

    Heino, M.; Hanski, I.

    2000-01-01

    We use an individual-based, spatially realistic metapopulation model to study the evolution of migration rate. We first explore the evolutionary consequences of habitat change in hypothetical patch networks on a regular lattice. If the primary consequence of habitat change is an increase in local extinction risk due to decreased local population sizes, migration rate increases. A non-monotonic response, with migration rate decreasing at high extinction rate, was obtained only by assuming very...

  5. Modeling the Microstructural Evolution during Hot Deformation of Microalloyed Steels

    OpenAIRE

    Bäcke, Linda

    2009-01-01

      This thesis contains the development of a physically-based model describing the microstructural evolution during hot deformation of microalloyed steels. The work is mainly focused on the recrystallization kinetics. During hot rolling, the repeated deformation and recrystallization provides progressively refined recrystallized grains. Also, recrystallization enables the material to be deformed more easily and knowledge of the recrystallization kinetics is important in order to predict the re...

  6. Long range anti-ferromagnetic spin model for prebiotic evolution

    International Nuclear Information System (INIS)

    I propose and discuss a fitness function for one-dimensional binary monomer sequences of macromolecules for prebiotic evolution. The fitness function is defined by the free energy of polymers in the high temperature random coil phase. With repulsive interactions among the same kind of monomers, the free energy in the high temperature limit becomes the energy function of the one-dimensional long range anti-ferromagnetic spin model, which is shown to have a dynamical phase transition and glassy states

  7. A quantitative model for integrating landscape evolution and soil formation

    Science.gov (United States)

    Vanwalleghem, T.; Stockmann, U.; Minasny, B.; McBratney, Alex B.

    2013-06-01

    evolution is closely related to soil formation. Quantitative modeling of the dynamics of soils and landscapes should therefore be integrated. This paper presents a model, named Model for Integrated Landscape Evolution and Soil Development (MILESD), which describes the interaction between pedogenetic and geomorphic processes. This mechanistic model includes the most significant soil formation processes, ranging from weathering to clay translocation, and combines these with the lateral redistribution of soil particles through erosion and deposition. The model is spatially explicit and simulates the vertical variation in soil horizon depth as well as basic soil properties such as texture and organic matter content. In addition, sediment export and its properties are recorded. This model is applied to a 6.25 km2 area in the Werrikimbe National Park, Australia, simulating soil development over a period of 60,000 years. Comparison with field observations shows how the model accurately predicts trends in total soil thickness along a catena. Soil texture and bulk density are predicted reasonably well, with errors of the order of 10%, however, field observations show a much higher organic carbon content than predicted. At the landscape scale, different scenarios with varying erosion intensity result only in small changes of landscape-averaged soil thickness, while the response of the total organic carbon stored in the system is higher. Rates of sediment export show a highly nonlinear response to soil development stage and the presence of a threshold, corresponding to the depletion of the soil reservoir, beyond which sediment export drops significantly.

  8. Spin Glass Models of Syntax and Language Evolution

    CERN Document Server

    Siva, Karthik; Marcolli, Matilde

    2015-01-01

    Using the SSWL database of syntactic parameters of world languages, and the MIT Media Lab data on language interactions, we construct a spin glass model of language evolution. We treat binary syntactic parameters as spin states, with languages as vertices of a graph, and assigned interaction energies along the edges. We study a rough model of syntax evolution, under the assumption that a strong interaction energy tends to cause parameters to align, as in the case of ferromagnetic materials. We also study how the spin glass model needs to be modified to account for entailment relations between syntactic parameters. This modification leads naturally to a generalization of Potts models with external magnetic field, which consists of a coupling at the vertices of an Ising model and a Potts model with q=3, that have the same edge interactions. We describe the results of simulations of the dynamics of these models, in different temperature and energy regimes. We discuss the linguistic interpretation of the paramete...

  9. Towards consensus in chemical characterization modeling for LCA:

    DEFF Research Database (Denmark)

    Rosenbaum, Ralf; Hauschild, Michael Zwicky; Bachmann, Till;

    2006-01-01

    components are and if there can be a consensus model built from them, leading towards recommended practice in chemical characterization for LCIA. The models were selected in an open process inviting all models identified to be capable of characterizing a chemical in terms of environmental fate, human...... exposure, human toxicity and ecotoxicity. The invitation was accepted by the developers of CalTOX, IMPACT 2002, USES-LCA, EDIP, WATSON, and EcoSense. A consistent chemical test set comprising 66 organic (generic, amphiphilic and dissociating) and inorganic (metals, salts) compounds was selected...... representing a wide range of substance property combinations. All compared models showed correlation for human health endpoints for generic organics, with high variations on individual chemicals, typically with high Kow. For the other organics and inorganics, less agreement was observed. Influential processes...

  10. Dynamical Models Explaining Social Balance and Evolution of Cooperation

    CERN Document Server

    Traag, V A; De Leenheer, P

    2013-01-01

    In social networks with positive and negative links the dominant theory of explaining its structure is that of social balance. The theory states that a network is balanced if its triads are balanced. Such a balanced network can be split into (at most) two opposing factions with positive links within a faction and negative links between them. Although inherently dynamical, the theory has long remained static, with a focus on finding such partitions. Recently however, a dynamical model was introduced which was shown to converge to a socially balanced state for certain symmetric initial conditions. Here we show this does not hold for general (non-symmetric) initial conditions. We propose an alternative model and show that it does converge to a socially balanced state generically. Moreover, in a basic model of evolution of cooperation of indirect reciprocity, the alternative model has an evolutionary advantage compared to the earlier model. The principal difference between the two models can be understood in term...

  11. NONLINEAR MODEL PREDICTIVE CONTROL OF CHEMICAL PROCESSES

    Directory of Open Access Journals (Sweden)

    SILVA R. G.

    1999-01-01

    Full Text Available A new algorithm for model predictive control is presented. The algorithm utilizes a simultaneous solution and optimization strategy to solve the model's differential equations. The equations are discretized by equidistant collocation, and along with the algebraic model equations are included as constraints in a nonlinear programming (NLP problem. This algorithm is compared with the algorithm that uses orthogonal collocation on finite elements. The equidistant collocation algorithm results in simpler equations, providing a decrease in computation time for the control moves. Simulation results are presented and show a satisfactory performance of this algorithm.

  12. Models for the directed evolution of bacterial allelopathy: bacteriophage lysins

    Directory of Open Access Journals (Sweden)

    James J. Bull

    2015-04-01

    Full Text Available Microbes produce a variety of compounds that are used to kill or suppress other species. Traditional antibiotics have their origins in these natural products, as do many types of compounds being pursued today in the quest for new antibacterial drugs. When a potential toxin can be encoded by and exported from a species that is not harmed, the opportunity exists to use directed evolution to improve the toxin’s ability to kill other species—allelopathy. In contrast to the typical application of directed evolution, this case requires the co-culture of at least two species or strains, a host that is unharmed by the toxin plus the intended target of the toxin. We develop mathematical and computational models of this directed evolution process. Two contexts are considered, one with the toxin encoded on a plasmid and the other with the toxin encoded in a phage. The plasmid system appears to be more promising than the phage system. Crucial to both designs is the ability to co-culture two species/strains (host and target such that the host is greatly outgrown by the target species except when the target species is killed. The results suggest that, if these initial conditions can be satisfied, directed evolution is feasible for the plasmid-based system. Screening with a plasmid-based system may also enable rapid improvement of a toxin.

  13. Observation and modeling of the evolution of Texas power plant plumes

    OpenAIRE

    Zhou, W.; Cohan, D. S.; R. W. Pinder; Neuman, J.A.; J. S. Holloway; J. Peischl; Ryerson, T. B.; Nowak, J. B.; Flocke, F.; Zheng, W. G.

    2012-01-01

    During the second Texas Air Quality Study 2006 (TexAQS II), a full range of pollutants was measured by aircraft in eastern Texas during successive transects of power plant plumes (PPPs). A regional photochemical model is applied to simulate the physical and chemical evolution of the plumes. The observations reveal that SO2 and NOy were rapidly removed from PPPs on a cloudy day but not on the cloud-free days, indicating efficient aqueous processing...

  14. Thermodynamically consistent model calibration in chemical kinetics

    Directory of Open Access Journals (Sweden)

    Goutsias John

    2011-05-01

    Full Text Available Abstract Background The dynamics of biochemical reaction systems are constrained by the fundamental laws of thermodynamics, which impose well-defined relationships among the reaction rate constants characterizing these systems. Constructing biochemical reaction systems from experimental observations often leads to parameter values that do not satisfy the necessary thermodynamic constraints. This can result in models that are not physically realizable and may lead to inaccurate, or even erroneous, descriptions of cellular function. Results We introduce a thermodynamically consistent model calibration (TCMC method that can be effectively used to provide thermodynamically feasible values for the parameters of an open biochemical reaction system. The proposed method formulates the model calibration problem as a constrained optimization problem that takes thermodynamic constraints (and, if desired, additional non-thermodynamic constraints into account. By calculating thermodynamically feasible values for the kinetic parameters of a well-known model of the EGF/ERK signaling cascade, we demonstrate the qualitative and quantitative significance of imposing thermodynamic constraints on these parameters and the effectiveness of our method for accomplishing this important task. MATLAB software, using the Systems Biology Toolbox 2.1, can be accessed from http://www.cis.jhu.edu/~goutsias/CSS lab/software.html. An SBML file containing the thermodynamically feasible EGF/ERK signaling cascade model can be found in the BioModels database. Conclusions TCMC is a simple and flexible method for obtaining physically plausible values for the kinetic parameters of open biochemical reaction systems. It can be effectively used to recalculate a thermodynamically consistent set of parameter values for existing thermodynamically infeasible biochemical reaction models of cellular function as well as to estimate thermodynamically feasible values for the parameters of new

  15. Potts Flux Tube Model at Nonzero Chemical Potential

    CERN Document Server

    Condella, J; Condella, Jac; Tar, Carleton De

    2000-01-01

    We model the deconfinement phase transition in quantum chromodynamics at nonzero baryon number density and large quark mass by extending the flux tube model (three-state, three-dimensional Potts model) to nonzero chemical potential. In a direct numerical simulation we confirm mean-field-theory predictions that the deconfinement transition does not occur in a baryon-rich environment.

  16. Organics Produced by Irradiation of Frozen and Liquid HCN Solutions: Implications for Chemical Evolution Studies

    Science.gov (United States)

    Colín-García, M.; Negrón-Mendoza, A.; Ramos-Bernal, S.

    2009-04-01

    Hydrogen cyanide (HCN), an important precursor of organic compounds, is widely present in extraterrestrial environments. HCN is also readily synthesized in prebiotic simulation experiments. To gain insight into the radiation chemistry of one of the most important and highly versatile constituents of cometary ices, we examined the behavior of over-irradiated frozen and liquid HCN solutions under ionizing radiation. The samples were exposed to gamma radiation at a dose range from 0 up to 419 kGy. Ultraviolet spectroscopy and gas chromatography were used to follow the process. The analyses confirmed that gamma-ray irradiation of liquid HCN solutions generates several organic products. Many of them are essential to life; we verified the presence of carboxylic acids (some of them members of the Krebs cycle) as well as free amino acids and urea. These are the first studies to reveal the presence of these compounds in experiments performed at low temperatures and bulk irradiation. Organic material was produced even at low temperatures and low radiation doses. This work strongly supports the presumption that, as a parent molecule, HCN played a central essential role in the process of chemical evolution on early Earth, comets, and other extraterrestrial environments.

  17. Structural and morphological evolution of gallium nitride nanorods grown by chemical beam epitaxy

    International Nuclear Information System (INIS)

    The morphological and structural evolution is presented for GaN nanorods grown by chemical beam epitaxy on (0001) Al2O3 substrates. Their structural and optical properties are investigated by x-ray diffraction, scanning and transmission electron microscopy, and temperature-dependent photoluminescence measurements. While increasing the growth temperature and the flow rate of radio-frequency nitrogen radical, the three-dimensional growth mode will be enhanced to form one-dimensional nanostructures. The high density of well-aligned nanorods with a diameter of 30-50 nm formed uniformly over the entire sapphire substrate. The x-ray diffraction patterns and transmission electron microscopic images indicate that the self-assembled GaN nanorods are a pure single crystal and preferentially oriented in the c-axis direction. Particularly, the ''S-shape'' behavior with localization of ∼10 meV observed in the temperature-dependent photoluminescence might be ascribed to the fluctuation in crystallographic defects and composition.

  18. Microstructure and chemical bond evolution of diamond-like carbon films machined by femtosecond laser

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jing; Wang, Chunhui [Science and Technology on Thermostructure Composite Materials Laboratory, Northwestern Polytechnical University, Xi’an 710072 (China); Liu, Yongsheng, E-mail: yongshengliu@nwpu.edu.cn [Science and Technology on Thermostructure Composite Materials Laboratory, Northwestern Polytechnical University, Xi’an 710072 (China); Cheng, Laifei [Science and Technology on Thermostructure Composite Materials Laboratory, Northwestern Polytechnical University, Xi’an 710072 (China); Li, Weinan [State Key Laboratory of Transient Optics and Photonics, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 10068 (China); Zhang, Qing [Science and Technology on Thermostructure Composite Materials Laboratory, Northwestern Polytechnical University, Xi’an 710072 (China); Yang, Xiaojun [State Key Laboratory of Transient Optics and Photonics, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 10068 (China)

    2015-06-15

    Highlights: • The machining depth was essentially proportional to the laser power. • The well patterned microgrooves and ripple structures with nanoparticles were formed distinctly in the channels. And the number of nanoparticles increased with the processing power as well. • It revealed a conversion from amorphous carbon to nanocrystalline graphite after laser treated with increasing laser power. • It showed that a great decrease of sp{sup 3}/sp{sup 2} after laser treatment. - Abstract: Femtosecond laser is of great interest for machining high melting point and hardness materials such as diamond-like carbon, SiC ceramic, et al. In present work, the microstructural and chemical bond evolution of diamond-like carbon films were investigated using electron microscopy and spectroscopy techniques after machined by diverse femtosecond laser power in air. The results showed the machining depth was essentially proportional to the laser power. The well patterned microgrooves and ripple structures with nanoparticles were formed distinctly in the channels. Considering the D and G Raman band parameters on the laser irradiation, it revealed a conversion from amorphous carbon to nanocrystalline graphite after laser treated with increasing laser power. X-ray photoelectron spectroscopy analysis showed a great decrease of sp{sup 3}/sp{sup 2} after laser treatment.

  19. Microstructure and chemical bond evolution of diamond-like carbon films machined by femtosecond laser

    International Nuclear Information System (INIS)

    Highlights: • The machining depth was essentially proportional to the laser power. • The well patterned microgrooves and ripple structures with nanoparticles were formed distinctly in the channels. And the number of nanoparticles increased with the processing power as well. • It revealed a conversion from amorphous carbon to nanocrystalline graphite after laser treated with increasing laser power. • It showed that a great decrease of sp3/sp2 after laser treatment. - Abstract: Femtosecond laser is of great interest for machining high melting point and hardness materials such as diamond-like carbon, SiC ceramic, et al. In present work, the microstructural and chemical bond evolution of diamond-like carbon films were investigated using electron microscopy and spectroscopy techniques after machined by diverse femtosecond laser power in air. The results showed the machining depth was essentially proportional to the laser power. The well patterned microgrooves and ripple structures with nanoparticles were formed distinctly in the channels. Considering the D and G Raman band parameters on the laser irradiation, it revealed a conversion from amorphous carbon to nanocrystalline graphite after laser treated with increasing laser power. X-ray photoelectron spectroscopy analysis showed a great decrease of sp3/sp2 after laser treatment

  20. Bimodal chemical evolution of the Galactic disk and the Barium abundance of Cepheids

    CERN Document Server

    Lepine, Jacques R D; Barros, Douglas A; Junqueira, Thiago C; Scarano, Sergio

    2013-01-01

    In order to understand the Barium abundance distribution in the Galactic disk based on Cepheids, one must first be aware of important effects of the corotation resonance, situated a little beyond the solar orbit. The thin disk of the Galaxy is divided in two regions that are separated by a barrier situated at that radius. Since the gas cannot get across that barrier, the chemical evolution is independent on the two sides of it. The barrier is caused by the opposite directions of flows of gas, on the two sides, in addition to a Cassini-like ring void of HI (caused itself by the flows). A step in the metallicity gradient developed at corotation, due to the difference in the average star formation rate on the two sides, and to this lack of communication between them. In connection with this, a proof that the spiral arms of our Galaxy are long-lived (a few billion years) is the existence of this step. When one studies the abundance gradients by means of stars which span a range of ages, like the Cepheids, one has...

  1. Chemical Evolution in High-Mass Star-Forming Regions: Results from the MALT90 Survey

    CERN Document Server

    Hoq, Sadia; Foster, Jonathan B; Sanhueza, Patricio; Guzman, Andres; Whitaker, J Scott; Claysmith, Christopher; Rathborne, Jill M; Vasyunina, Tatiana; Vasyunin, Anton

    2013-01-01

    The chemical changes of high-mass star-forming regions provide a potential method for classifying their evolutionary stages and, ultimately, ages. In this study, we search for correlations between molecular abundances and the evolutionary stages of dense molecular clumps associated with high-mass star formation. We use the molecular line maps from Year 1 of the Millimetre Astronomy Legacy Team 90 GHz (MALT90) Survey. The survey mapped several hundred individual star-forming clumps chosen from the ATLASGAL survey to span the complete range of evolution, from prestellar to protostellar to H II regions. The evolutionary stage of each clump is classified using the Spitzer GLIMPSE/MIPSGAL mid-IR surveys. Where possible, we determine the dust temperatures and H2 column densities for each clump from Herschel Hi-GAL continuum data. From MALT90 data, we measure the integrated intensities of the N2H+, HCO+, HCN and HNC (1-0) lines, and derive the column densities and abundances of N2H+ and HCO+. The Herschel dust tempe...

  2. Evolution of microbiological and physico-chemical quality of pasteurized milk

    Directory of Open Access Journals (Sweden)

    Natalia Gonzaga

    2015-11-01

    Full Text Available Milk quality is defined, among other parameters, by a reduced number of spoilage microorganisms, low somatic cell count and the absence of pathogens and chemical waste. Several studies conducted in different regions of the country have emphasized the high percentage of samples not complying with the standard. The purpose of this study was to evaluate the evolution of microbiological and physicochemical quality of pasteurized milk produced in the State of Paraná over 7 years. A total of 457 samples of pasteurized milk were analyzed, 104 samples in 2008, 269 samples in 2011 and 84 samples in 2014. The samples were subjected to physicochemical analysis of cryoscopy and enzyme search for alkaline phosphatase and peroxidase. Regarding microbiological tests, coliform counts were performed at 30°C and 45°C and count plate pattern. In the laboratory, physicochemical analysis were performed according to the Normative 68 and microbiological as normative instruction 62, both of the Brazilian Ministry of Agriculture, Livestock and Food Supply. The results showed that over the years the microbiological quality of milk decreased, with an increase of non-standard samples. For enzymes alkaline phosphatase, peroxidase, the pasteurization temperature has been observed over time and the overheating of the milk was more frequent in 2011. Fraud by addition of water in milk has either decreased or become more sophisticated, making its detection difficult.

  3. The Influence of Environment on the Chemical Evolution in Low-mass Galaxies

    CERN Document Server

    Liu, Yiqing; Peng, Eric

    2016-01-01

    The mean alpha-to-iron abundance ratio ([$\\alpha$/Fe]) of galaxies is sensitive to the chemical evolution processes at early time, and it is an indicator of star formation timescale ($\\tau_{{\\rm SF}}$). Although the physical reason remains ambiguous, there is a tight relation between [$\\alpha$/Fe] and stellar velocity dispersion ($\\sigma$) among massive early-type galaxies (ETGs). However, no work has shown convincing results as to how this relation behaves at low masses. We assemble 15 data sets from the literature and build a large sample that includes 192 nearby low-mass ($18<\\sigma<80$~\\kms) ETGs. We find that the [$\\alpha$/Fe]-$\\sigma$ relation generally holds for low-mass ETGs, except in extreme environments. Specifically, in normal galaxy cluster environments, the [$\\alpha$/Fe]-$\\sigma$ relation and its intrinsic scatter are, within uncertainties, similar for low-mass and high-mass ETGs. However, in the most massive relaxed galaxy cluster in our sample, the zero point of the relation is higher an...

  4. Probing the early chemical evolution of the Sculptor dSph with purely old stellar tracers

    CERN Document Server

    Martínez-Vázquez, C E; Gallart, C; Bono, G; Bernard, E J; Stetson, P B; Ferraro, I; Walker, A R; Dall'Ora, M; Fiorentino, G; Iannicola, G

    2016-01-01

    We present the metallicity distribution of a sample of 471 RR Lyrae (RRL) stars in the Sculptor dSph, obtained from the $I$-band Period-Luminosity relation. It is the first time that the early chemical evolution of a dwarf galaxy is characterized in such a detailed and quantitative way, using photometric data alone. We find a broad metallicity distribution (FWHM=0.8 dex) that is peaked at [Fe/H]$\\simeq$-1.90 dex, in excellent agreement with literature values obtained from spectroscopic data. Moreover, we are able to directly trace the metallicity gradient out to a radius of $\\sim$55 arcmin. We find that in the outer regions (r$>\\sim$32 arcmin) the slope of the metallicity gradient from the RRLs (-0.025 dex arcmin$^{-1}$) is comparable to the literature values based on red giant (RG) stars. However, in the central part of Sculptor we do not observe the latter gradients. This suggests that there is a more metal-rich and/or younger population in Sculptor that does not produce RRLs. This scenario is strengthened ...

  5. Probing the early chemical evolution of the Sculptor dSph with purely old stellar tracers

    Science.gov (United States)

    Martínez-Vázquez, C. E.; Monelli, M.; Gallart, C.; Bono, G.; Bernard, E. J.; Stetson, P. B.; Ferraro, I.; Walker, A. R.; Dall'Ora, M.; Fiorentino, G.; Iannicola, G.

    2016-09-01

    We present the metallicity distribution of a sample of 471 RR Lyrae (RRL) stars in the Sculptor dSph, obtained from the I-band period-luminosity relation. It is the first time that the early chemical evolution of a dwarf galaxy is characterized in such a detailed and quantitative way, using photometric data alone. We find a broad metallicity distribution (full width at half-maximum equals to 0.8 dex) that is peaked at [Fe/H] ≃ -1.90 dex, in excellent agreement with literature values obtained from spectroscopic data. Moreover, we are able to directly trace the metallicity gradient out to a radius of ˜55 arcmin. We find that in the outer regions (r > ˜32 arcmin) the slope of the metallicity gradient from the RRLs (-0.025 dex arcmin-1) is comparable to the literature values based on red giant (RG) stars. However, in the central part of Sculptor, we do not observe the latter gradients. This suggests that there is a more metal-rich and/or younger population in Sculptor that does not produce RRLs. This scenario is strengthened by the observation of a metal-rich peak in the metallicity distribution of RG stars by other authors, which is not present in the metallicity distribution of the RRLs within the same central area.

  6. Evolution of spectral behavior and chemical composition in the tree canopy of a dehesa ecosystem

    Directory of Open Access Journals (Sweden)

    R. González-Cascón

    2016-06-01

    Full Text Available In the context of the BIOSPEC and FLUXPEC projects (http://www.lineas.cchs.csic.es/fluxpec/, spectral and biophysical variables measurements at leaf level have been conducted in the tree canopy of a holm oak dehesa (Quercus ilex ecosystem during four vegetative periods. Measurements of bi-conical reflectance factor of intact leaf (ASD Fieldspec 3® spectroradiometer, specific leaf mass (SLM, leaf water content (LWC, nutrient (N, P, K, Ca, Mg, Mn, Fe, and Zn and chlorophyll concentration were performed. The spectral measurements have been related with the biophysical variables by stepwise and partial least squares regression analyses. These analyses allowed to identify the spectral bands and regions that best explain the evolution of the biophysical variables and to estimate the nutrient contents during the leaf maturation process. Statistically significant estimates of the majority of the variables studied were obtained. Wavelengths that had the highest contributions explaining the chemical composition of the forest canopy were located in spectral regions of the red edge, the green visible region, and the shortwave infrared.

  7. Golden jubilee year of Stanley Miller experiment and chemical evolution and origin of life

    Science.gov (United States)

    Chakrabarti, Sandip K.

    2013-06-01

    I give a brief review of how some of the major players in the subject approached the problem of the origin of pre-biotic molecules on Earth. For paucity of space, I will start with the developments starting with Stanley Miller's experiment on abiotic synthesis of amino acids till the most recent work on numerical simulation of hydro-chemical processes of collapsing clouds and the evolution of complex bio-molecules. We are evidently far away from actually solving the problem of origin of life. What is clear, however, is that the formation of complex amino acids in interstellar region is indeed possible, independently, in many star forming regions inside protostellar disks. Possibly, the delivery of these important ingredients to the earth was done by comets and meteorites. Finally, I conclude that since only a small part of the universe is involved for a relatively short time to create the present life-form, far more complex and possibly 'super-civilized' systems are possible in this universe, and could even be present elsewhere.

  8. A self-organized model for network evolution. Coupling network evolution and extremal dynamics

    Science.gov (United States)

    Caldarelli, G.; Capocci, A.; Garlaschelli, D.

    2008-08-01

    Here we provide a detailed analysis, along with some extensions and additonal investigations, of a recently proposed [1] self-organized model for the evolution of complex networks. Vertices of the network are characterized by a fitness variable evolving through an extremal dynamics process, as in the Bak-Sneppen [2] model representing a prototype of Self-Organized Criticality. The network topology is in turn shaped by the fitness variable itself, as in the fitness network model [3]. The system self-organizes to a nontrivial state, characterized by a power-law decay of dynamical and topological quantities above a critical threshold. The interplay between topology and dynamics in the system is the key ingredient leading to an unexpected behaviour of these quantities.

  9. Chemical Kinetic Models for HCCI and Diesel Combustion

    Energy Technology Data Exchange (ETDEWEB)

    Pitz, W J; Westbrook, C K; Mehl, M; Sarathy, S M

    2010-11-15

    Predictive engine simulation models are needed to make rapid progress towards DOE's goals of increasing combustion engine efficiency and reducing pollutant emissions. These engine simulation models require chemical kinetic submodels to allow the prediction of the effect of fuel composition on engine performance and emissions. Chemical kinetic models for conventional and next-generation transportation fuels need to be developed so that engine simulation tools can predict fuel effects. The objectives are to: (1) Develop detailed chemical kinetic models for fuel components used in surrogate fuels for diesel and HCCI engines; (2) Develop surrogate fuel models to represent real fuels and model low temperature combustion strategies in HCCI and diesel engines that lead to low emissions and high efficiency; and (3) Characterize the role of fuel composition on low temperature combustion modes of advanced combustion engines.

  10. Models of evolution of gas and abundances in dwarf irregular galaxies

    CERN Document Server

    Gavilan, M; Díaz, A I

    2009-01-01

    We have developed a grid of chemical evolution models applied to dwarf isolated galaxies, using \\cite{gav05} yields. The input data enclose different star formation efficiencies, galaxy mass and collapse time values. The result is a wide collection of solutions that vary from objects with low metallicity and great amount of gas, to those with little gas and high metallicity. No environmental effects like tidal or galactic winds have been treated, so these objects are expected to be close to field dwarf galaxies, more than cluster ones. We have studied the time evolution of the abundance of oxygen and nitrogen and the amount of gas, related to their star formation history, as well as the possibility of gas losses by SN winds.

  11. Introducing Graduate Students to the Chemical Information Landscape: The Ongoing Evolution of a Graduate-Level Chemical Information Course

    Science.gov (United States)

    Currano, Judith N.

    2016-01-01

    The University of Pennsylvania's doctoral chemistry curriculum has included a required course in chemical information since 1995. Twenty years later, the course has evolved from a loosely associated series of workshops on information resources to a holistic examination of the chemical literature and its place in the general research process. The…

  12. Understanding the evolution of learning by explicitly modeling learning mechanisms

    Institute of Scientific and Technical Information of China (English)

    Michal ARBILLY

    2015-01-01

    Models of the evolution of learning often assume that learning leads to the best solution to any task,and disregard the details of the learning and decision-making process along with its potential pitfalls.These models therefore do not explain instances in the animal behavior literature in which learning leads to maladaptive behaviors.In recent years a growing number of theoretical studies use explicit models of learning mechanisms,offering a fresh perspective on the issue by revealing the dynamics of information acquisition and biases arising from it.These models have pointed out possible learning rules and their adaptive value,and shown that the value of learning may crucially depend on such factors as the layout of the physical environment to be leamed,the structure of the payoffs offered by different alternatives,the risk of failure,characteristics of the learner and social interactions.This review considers the merits of explicit modeling in studying the evolution of learning,describes the kinds of results that can only be obtained from this modeling approach,and outlines directions for future research [Current Zoology 61 (2):341-349,2015].

  13. SIGNUM: A Matlab, TIN-based landscape evolution model

    Science.gov (United States)

    Refice, A.; Giachetta, E.; Capolongo, D.

    2012-08-01

    Several numerical landscape evolution models (LEMs) have been developed to date, and many are available as open source codes. Most are written in efficient programming languages such as Fortran or C, but often require additional code efforts to plug in to more user-friendly data analysis and/or visualization tools to ease interpretation and scientific insight. In this paper, we present an effort to port a common core of accepted physical principles governing landscape evolution directly into a high-level language and data analysis environment such as Matlab. SIGNUM (acronym for Simple Integrated Geomorphological Numerical Model) is an independent and self-contained Matlab, TIN-based landscape evolution model, built to simulate topography development at various space and time scales. SIGNUM is presently capable of simulating hillslope processes such as linear and nonlinear diffusion, fluvial incision into bedrock, spatially varying surface uplift which can be used to simulate changes in base level, thrust and faulting, as well as effects of climate changes. Although based on accepted and well-known processes and algorithms in its present version, it is built with a modular structure, which allows to easily modify and upgrade the simulated physical processes to suite virtually any user needs. The code is conceived as an open-source project, and is thus an ideal tool for both research and didactic purposes, thanks to the high-level nature of the Matlab environment and its popularity among the scientific community. In this paper the simulation code is presented together with some simple examples of surface evolution, and guidelines for development of new modules and algorithms are proposed.

  14. An exploratory numerical model of rocky shore profile evolution

    Science.gov (United States)

    Matsumoto, Hironori; Dickson, Mark E.; Kench, Paul S.

    2016-09-01

    Rocky shores occur along much of the world's coastline and include a wide range of coastal morphologies, such as intertidal shore platforms. Considerable research effort has been placed on trying to understand developmental processes on rocky shores, but progress has been forestalled because these landscapes develop slowly and preserve little evidence of evolution through time. This paper presents a new exploratory numerical model developed to study long-term shore profile evolution on rock coasts. The model purposely considers only a limited number of processes, each represented in a highly abstracted way. Despite these simplifications, the model exhibits a large range of emergent shore profile shapes. This behavior is enabled both by broader spatial representation of the driving erosion forces and the flexibility provided by a grid discretization scheme. Initial model testing shows the development of varied rocky profile geometries, ranging from steep plunging cliffs, cliffs with narrow benches, and cliffs with a variety of shore platform shapes. Most of the model geometries are similar to those observed in the field, and model behavior is robust and internally consistent across a relatively large parameter space. This paper provides a detailed description of the new model and its subsequent testing. Emphasis is placed on comparison of model results with published field observations in which morphometric relationships are described between shore platform gradient and tidal range, and platform elevation and platform width. The model adequately simulates these morphometric relationships, while retaining its ability to simulate a wide range of profile shapes. The simplicity of process representations, and the limited number of processes implemented, means that model outputs can be interpreted reasonably easily. Hence, an opportunity is now provided, following the testing described in this paper, to use the model to systematically investigate the broader controlling

  15. Systems evolution: the conceptual framework and a formal model

    OpenAIRE

    S. Gao

    1992-01-01

    This research addresses to some of the fundamental problems in systems science.T he aim of this study is to: (1) provide a general conceptual framework for systems evolution; (2) develop a formal model for evolving systems based on dynamical systems theory; (3) analyse the evolving behaviour of various systems by using the formal model so far developed. First of all, it is argued that a system, which can be recognized by an observer as a system, is characterised by some emergent properties at...

  16. Evolution of Interacting Viscous Dark Energy Model in Einstein Cosmology

    Institute of Scientific and Technical Information of China (English)

    CHEN Ju-Hua; ZHOU Sheng; WANG Yong-Jiu

    2011-01-01

    We investigate the evolution of the viscous dark energy (DE) interacting with the dark matter (DM) in the Einstein cosmology model. By using the linearizing theory of the dynamical system, we find that, in our model,there exists a stable late time scaling solution which corresponds to the accelerating universe. We also find the unstable solution under some appropriate parameters. In order to alleviate the coincidence problem, some authors considered the effect of quantum correction due to the conform anomaly and the interacting dark energy with the dark matter. However, if we take into account the bulk viscosity of the cosmic fluid, the coincidence problem will be softened just like the interacting dark energy cosmology model. That is to say, both the non-perfect fluid model and the interacting the dark energy cosmic model can alleviate or soften the singularity of the universe.%@@ We investigate the evolution of the viscous dark energy (DE) interacting with the dark matter (DM) in the Einstein cosmology model.By using the linearizing theory of the dynamical system, we find that, in our model, there exists a stable late time scaling solution which corresponds to the accelerating universe.We also find the unstable solution under some appropriate parameters.In order to alleviate the coincidence problem, some authors considered the effect of quantum correction due to the conform anomaly and the interacting dark energy with the dark matter.However, if we take into account the bulk viscosity of the cosmic fluid, the coincidence problem will be softened just like the interacting dark energy cosmology model.That is to say, both the non-perfect fluid model and the interacting the dark energy cosmic model can alleviate or soften the singularity of the universe.

  17. Chemical kinetics with electrical and gas dynamics modelization for NOx removal in an air corona discharge

    International Nuclear Information System (INIS)

    A non-stationary reactive gas dynamics model in a mono-dimensional geometry, including radial mass diffusion, gas temperature variation and chemical kinetics, is developed in this paper. The aim is to analyse the spatio-temporal evolution of the main neutral species involved in a corona discharge used for NO pollution control in polluted air at atmospheric pressure and ambient temperature. The present reactive gas dynamics model takes into account 16 neutral chemical species (including certain metastable species) reacting following 110 selected chemical reactions. The initial concentration of each neutral species is obtained from a 1.5D electrical discharge model. The gas temperature variations are due to direct Joule heating during the discharge phase, and also result from the delayed heating due to the relaxation of the vibrational energy into a random thermal energy during the post-discharge phase. The simulation conditions are those of an existing experimental setup (anode voltage of 10 kV in the case of a point to plane geometry with an interelectrode distance of 10 mm). The obtained results show that the diffusion phenomena and the gas temperature rise affect quite well the gas reactivity and the neutral species evolution. This allows us to better understand the different reaction processes and transport phenomena affecting the NO concentration magnitude inside the discharge channel. (author)

  18. Free Energy Transduction in a Chemical Motor Model

    CERN Document Server

    Baker, J E

    2003-01-01

    Motor enzymes catalyze chemical reactions, like the hydrolysis of ATP, and in the process they also perform work. Recent studies indicate that motor enzymes perform work with specific intermediate steps in their catalyzed reactions, challenging the classic view (in Brownian motor models) that work can only be performed within biochemical states. An alternative class of models (chemical motor models) has emerged in which motors perform work with biochemical transitions, but many of these models lack a solid physicochemical foundation. In this paper, I develop a self consistent framework for chemical motor models. This novel framework accommodates multiple pathways for free energy transfer, predicts rich behaviors from the simplest multi motor systems, and provides important new insights into muscle and motor function.

  19. Evolution of the dipole geomagnetic field. Observations and models

    Science.gov (United States)

    Reshetnyak, M. Yu.; Pavlov, V. E.

    2016-01-01

    The works on paleomagnetic observations of the dipole geomagnetic field, its variations, and reversals in the last 3.5 billion years have been reviewed. It was noted that characteristic field variations are related to the evolution of the convection processes in the liquid core due to the effect of magnetic convection and solid core growth. Works on the geochemistry and energy budget of the Earth's core, the effect of the solid core on convection and the generation of the magnetic field, dynamo models are also considered. We consider how core growth affects the magnetic dipole generation and variations, as well as the possibility of magnetic field generation up to the appearance of the solid core. We also pay attention to the fact that not only the magnetic field but also its configuration and time variations, which are caused by the convection evolution in the core on geological timescales, are important factors for the biosphere.

  20. Last interglacial temperature evolution – a model inter-comparison

    Directory of Open Access Journals (Sweden)

    P. Bakker

    2013-03-01

    Full Text Available There is a growing number of proxy-based reconstructions detailing the climatic changes that occurred during the last interglacial period (LIG. This period is of special interest, because large parts of the globe were characterized by a warmer-than-present-day climate, making this period an interesting test bed for climate models in light of projected global warming. However, mainly because synchronizing the different palaeoclimatic records is difficult, there is no consensus on a global picture of LIG temperature changes. Here we present the first model inter-comparison of transient simulations covering the LIG period. By comparing the different simulations, we aim at investigating the common signal in the LIG temperature evolution, investigating the main driving forces behind it and at listing the climate feedbacks which cause the most apparent inter-model differences. The model inter-comparison shows a robust Northern Hemisphere July temperature evolution characterized by a maximum between 130–125 ka BP with temperatures 0.3 to 5.3 K above present day. A Southern Hemisphere July temperature maximum, −1.3 to 2.5 K at around 128 ka BP, is only found when changes in the greenhouse gas concentrations are included. The robustness of simulated January temperatures is large in the Southern Hemisphere and the mid-latitudes of the Northern Hemisphere. For these regions maximum January temperature anomalies of respectively −1 to 1.2 K and −0.8 to 2.1 K are simulated for the period after 121 ka BP. In both hemispheres these temperature maxima are in line with the maximum in local summer insolation. In a number of specific regions, a common temperature evolution is not found amongst the models. We show that this is related to feedbacks within the climate system which largely determine the simulated LIG temperature evolution in these regions. Firstly, in the Arctic region, changes in the summer sea-ice cover control the evolution of LIG winter