Science.gov

Sample records for chemical equilibrium models

  1. Chemical equilibrium modeling of detonation

    SciTech Connect

    Fried, Laurence E.; Bastea, Sorin

    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.

  2. Learning of Chemical Equilibrium through Modelling-Based Teaching

    ERIC Educational Resources Information Center

    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…

  3. Learning of Chemical Equilibrium through Modelling-Based Teaching

    ERIC Educational Resources Information Center

    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…

  4. Dynamic Processes of Conceptual Change: Analysis of Constructing Mental Models of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Chiu, Mei-Hung; Chou, Chin-Cheng; Liu, Chia-Ju

    2002-01-01

    Investigates students' mental models of chemical equilibrium using dynamic science assessments. Reports that students at various levels have misconceptions about chemical equilibrium. Involves 10th grade students (n=30) in the study doing a series of hands-on chemical experiments. Focuses on the process of constructing mental models, dynamic…

  5. Dynamic Processes of Conceptual Change: Analysis of Constructing Mental Models of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Chiu, Mei-Hung; Chou, Chin-Cheng; Liu, Chia-Ju

    2002-01-01

    Investigates students' mental models of chemical equilibrium using dynamic science assessments. Reports that students at various levels have misconceptions about chemical equilibrium. Involves 10th grade students (n=30) in the study doing a series of hands-on chemical experiments. Focuses on the process of constructing mental models, dynamic…

  6. Computing Equilibrium Chemical Compositions

    NASA Technical Reports Server (NTRS)

    Mcbride, Bonnie J.; Gordon, Sanford

    1995-01-01

    Chemical Equilibrium With Transport Properties, 1993 (CET93) computer program provides data on chemical-equilibrium compositions. Aids calculation of thermodynamic properties of chemical systems. Information essential in design and analysis of such equipment as compressors, turbines, nozzles, engines, shock tubes, heat exchangers, and chemical-processing equipment. CET93/PC is version of CET93 specifically designed to run within 640K memory limit of MS-DOS operating system. CET93/PC written in FORTRAN.

  7. Computing Equilibrium Chemical Compositions

    NASA Technical Reports Server (NTRS)

    Mcbride, Bonnie J.; Gordon, Sanford

    1995-01-01

    Chemical Equilibrium With Transport Properties, 1993 (CET93) computer program provides data on chemical-equilibrium compositions. Aids calculation of thermodynamic properties of chemical systems. Information essential in design and analysis of such equipment as compressors, turbines, nozzles, engines, shock tubes, heat exchangers, and chemical-processing equipment. CET93/PC is version of CET93 specifically designed to run within 640K memory limit of MS-DOS operating system. CET93/PC written in FORTRAN.

  8. Dynamic processes of conceptual change: Analysis of constructing mental models of chemical equilibrium

    NASA Astrophysics Data System (ADS)

    Chiu, Mei-Hung; Chou, Chin-Cheng; Liu, Chia-Ju

    2002-10-01

    The purpose of this study was to investigate students' mental models of chemical equilibrium using dynamic science assessments. Research in chemical education has shown that students at various levels have misconceptions about chemical equilibrium. According to Chi's theory of conceptual change, the concept of chemical equilibrium has constraint-based features (e.g., random, simultaneous, uniform activities) that might prevent students from deeply understanding the nature of the concept of chemical equilibrium. In this study, we examined how students learned and constructed their mental models of chemical equilibrium in a cognitive apprenticeship context. Thirty 10th-grade students participated in the study: 10 in a control group and 20 in a treatment group. Both groups were presented with a series of hands-on chemical experiments. The students in the treatment group were instructed based on the main features of cognitive apprenticeship (CA), such as coaching, modeling, scaffolding, articulation, reflection, and exploration. However, the students in the control group (non-CA group) learned from the tutor without explicit CA support. The results revealed that the CA group significantly outperformed the non-CA group. The students in the CA group were capable of constructing the mental models of chemical equilibrium - including dynamic, random activities of molecules and interactions between molecules in the microworld - whereas the students in the non-CA group failed to construct similar correct mental models of chemical equilibrium. The study focuses on the process of constructing mental models, on dynamic changes, and on the actions of students (such as self-monitoring/self-correction) who are learning the concept of chemical equilibrium. Also, we discuss the implications for science education.

  9. Exploring the Use of Multiple Analogical Models when Teaching and Learning Chemical Equilibrium

    ERIC Educational Resources Information Center

    Harrison, Allan G.; De Jong, Onno

    2005-01-01

    This study describes the multiple analogical models used to introduce and teach Grade 12 chemical equilibrium. We examine the teacher's reasons for using models, explain each model's development during the lessons, and analyze the understandings students derived from the models. A case study approach was used and the data were drawn from the…

  10. Exploring the Use of Multiple Analogical Models when Teaching and Learning Chemical Equilibrium

    ERIC Educational Resources Information Center

    Harrison, Allan G.; De Jong, Onno

    2005-01-01

    This study describes the multiple analogical models used to introduce and teach Grade 12 chemical equilibrium. We examine the teacher's reasons for using models, explain each model's development during the lessons, and analyze the understandings students derived from the models. A case study approach was used and the data were drawn from the…

  11. A Review of Equation of State Models, Chemical Equilibrium Calculations and CERV Code Requirements for SHS Detonation Modelling

    DTIC Science & Technology

    2009-10-01

    Beattie - Bridgeman Virial expansion The above equations are suitable for moderate pressures and are usually based on either empirical constants...CR 2010-013 October 2009 A Review of Equation of State Models, Chemical Equilibrium Calculations and CERV Code Requirements for SHS Detonation...Defence R&D Canada. A Review of Equation of State Models, Chemical Equilibrium Calculations and CERV Code Requirements for SHS Detonation

  12. Chemical Principles Revisited: Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Mickey, Charles D.

    1980-01-01

    Describes: (1) Law of Mass Action; (2) equilibrium constant and ideal behavior; (3) general form of the equilibrium constant; (4) forward and reverse reactions; (5) factors influencing equilibrium; (6) Le Chatelier's principle; (7) effects of temperature, changing concentration, and pressure on equilibrium; and (8) catalysts and equilibrium. (JN)

  13. Evaluation of the equilibrium calculations within acidification models: the effect of uncertainty in measured chemical components

    SciTech Connect

    Schecher, W.D.; Driscoll, C.T.

    1988-04-01

    There is much concern over the effects of acidic deposition on soils and draining waters. To better understand the processes regulating the acidification of surface waters, computer models have been developed which utilize equilibrium calculations to predict the concentration of chemical parameters such as pH, acid neutralizing capacity, dissolved inorganic carbon, Al and SO/sub 4//sup 2 -/. A simple chemical equilibrium model (ALCHEMI) was used to evaluate the effect of uncertainty in the measurement of chemical constituents on thermodynamic calculations. For calculations where pH was not allowed to vary, uncertainty in Al speciation was small and largely due to imprecision in the measurement of total F and pH. When calculations were made from electroneutrality based on measured constituents, most of the uncertainty associated with the values of output parameters was due to imprecision in the determination of SO/sub 4//sup 2 -/.

  14. Molecular finite-size effects in stochastic models of equilibrium chemical systems.

    PubMed

    Cianci, Claudia; Smith, Stephen; Grima, Ramon

    2016-02-28

    The reaction-diffusion master equation (RDME) is a standard modelling approach for understanding stochastic and spatial chemical kinetics. An inherent assumption is that molecules are point-like. Here, we introduce the excluded volume reaction-diffusion master equation (vRDME) which takes into account volume exclusion effects on stochastic kinetics due to a finite molecular radius. We obtain an exact closed form solution of the RDME and of the vRDME for a general chemical system in equilibrium conditions. The difference between the two solutions increases with the ratio of molecular diameter to the compartment length scale. We show that an increase in the fraction of excluded space can (i) lead to deviations from the classical inverse square root law for the noise-strength, (ii) flip the skewness of the probability distribution from right to left-skewed, (iii) shift the equilibrium of bimolecular reactions so that more product molecules are formed, and (iv) strongly modulate the Fano factors and coefficients of variation. These volume exclusion effects are found to be particularly pronounced for chemical species not involved in chemical conservation laws. Finally, we show that statistics obtained using the vRDME are in good agreement with those obtained from Brownian dynamics with excluded volume interactions.

  15. General multi-group macroscopic modeling for thermo-chemical non-equilibrium gas mixtures

    NASA Astrophysics Data System (ADS)

    Liu, Yen; Panesi, Marco; Sahai, Amal; Vinokur, Marcel

    2015-04-01

    This paper opens a new door to macroscopic modeling for thermal and chemical non-equilibrium. In a game-changing approach, we discard conventional theories and practices stemming from the separation of internal energy modes and the Landau-Teller relaxation equation. Instead, we solve the fundamental microscopic equations in their moment forms but seek only optimum representations for the microscopic state distribution function that provides converged and time accurate solutions for certain macroscopic quantities at all times. The modeling makes no ad hoc assumptions or simplifications at the microscopic level and includes all possible collisional and radiative processes; it therefore retains all non-equilibrium fluid physics. We formulate the thermal and chemical non-equilibrium macroscopic equations and rate coefficients in a coupled and unified fashion for gases undergoing completely general transitions. All collisional partners can have internal structures and can change their internal energy states after transitions. The model is based on the reconstruction of the state distribution function. The internal energy space is subdivided into multiple groups in order to better describe non-equilibrium state distributions. The logarithm of the distribution function in each group is expressed as a power series in internal energy based on the maximum entropy principle. The method of weighted residuals is applied to the microscopic equations to obtain macroscopic moment equations and rate coefficients succinctly to any order. The model's accuracy depends only on the assumed expression of the state distribution function and the number of groups used and can be self-checked for accuracy and convergence. We show that the macroscopic internal energy transfer, similar to mass and momentum transfers, occurs through nonlinear collisional processes and is not a simple relaxation process described by, e.g., the Landau-Teller equation. Unlike the classical vibrational energy

  16. General multi-group macroscopic modeling for thermo-chemical non-equilibrium gas mixtures.

    PubMed

    Liu, Yen; Panesi, Marco; Sahai, Amal; Vinokur, Marcel

    2015-04-07

    This paper opens a new door to macroscopic modeling for thermal and chemical non-equilibrium. In a game-changing approach, we discard conventional theories and practices stemming from the separation of internal energy modes and the Landau-Teller relaxation equation. Instead, we solve the fundamental microscopic equations in their moment forms but seek only optimum representations for the microscopic state distribution function that provides converged and time accurate solutions for certain macroscopic quantities at all times. The modeling makes no ad hoc assumptions or simplifications at the microscopic level and includes all possible collisional and radiative processes; it therefore retains all non-equilibrium fluid physics. We formulate the thermal and chemical non-equilibrium macroscopic equations and rate coefficients in a coupled and unified fashion for gases undergoing completely general transitions. All collisional partners can have internal structures and can change their internal energy states after transitions. The model is based on the reconstruction of the state distribution function. The internal energy space is subdivided into multiple groups in order to better describe non-equilibrium state distributions. The logarithm of the distribution function in each group is expressed as a power series in internal energy based on the maximum entropy principle. The method of weighted residuals is applied to the microscopic equations to obtain macroscopic moment equations and rate coefficients succinctly to any order. The model's accuracy depends only on the assumed expression of the state distribution function and the number of groups used and can be self-checked for accuracy and convergence. We show that the macroscopic internal energy transfer, similar to mass and momentum transfers, occurs through nonlinear collisional processes and is not a simple relaxation process described by, e.g., the Landau-Teller equation. Unlike the classical vibrational energy

  17. General multi-group macroscopic modeling for thermo-chemical non-equilibrium gas mixtures

    SciTech Connect

    Liu, Yen Vinokur, Marcel; Panesi, Marco; Sahai, Amal

    2015-04-07

    This paper opens a new door to macroscopic modeling for thermal and chemical non-equilibrium. In a game-changing approach, we discard conventional theories and practices stemming from the separation of internal energy modes and the Landau-Teller relaxation equation. Instead, we solve the fundamental microscopic equations in their moment forms but seek only optimum representations for the microscopic state distribution function that provides converged and time accurate solutions for certain macroscopic quantities at all times. The modeling makes no ad hoc assumptions or simplifications at the microscopic level and includes all possible collisional and radiative processes; it therefore retains all non-equilibrium fluid physics. We formulate the thermal and chemical non-equilibrium macroscopic equations and rate coefficients in a coupled and unified fashion for gases undergoing completely general transitions. All collisional partners can have internal structures and can change their internal energy states after transitions. The model is based on the reconstruction of the state distribution function. The internal energy space is subdivided into multiple groups in order to better describe non-equilibrium state distributions. The logarithm of the distribution function in each group is expressed as a power series in internal energy based on the maximum entropy principle. The method of weighted residuals is applied to the microscopic equations to obtain macroscopic moment equations and rate coefficients succinctly to any order. The model’s accuracy depends only on the assumed expression of the state distribution function and the number of groups used and can be self-checked for accuracy and convergence. We show that the macroscopic internal energy transfer, similar to mass and momentum transfers, occurs through nonlinear collisional processes and is not a simple relaxation process described by, e.g., the Landau-Teller equation. Unlike the classical vibrational energy

  18. Chemical Equilibrium Modeling of Hanford Waste Tank Processing: Applications of Fundamental Science

    SciTech Connect

    Felmy, Andrew R.; Wang, Zheming; Dixon, David A.; Hess, Nancy J.

    2004-05-01

    The development of computational models based upon fundamental science is one means of quantitatively transferring the results of scientific investigations to practical application by engineers in laboratory and field situations. This manuscript describes one example of such efforts, specifically the development and application of chemical equilibrium models to different waste management issues at the U.S. Department of Energy (DOE) Hanford Site. The development of the chemical models is described with an emphasis on the fundamental science investigations that have been undertaken in model development followed by examples of different waste management applications. The waste management issues include the leaching of waste slurries to selective remove non-hazardous components and the separation of Sr90 and transuranics from the waste supernatants. The fundamental science contributions include: molecular simulations of the energetics of different molecular clusters to assist in determining the species present in solution, advanced synchrotron research to determine the chemical form of precipitates, and laser based spectroscopic studies of solutions and solids.

  19. Chemical equilibrium modeling of organic acids, pH, aluminum, and iron in Swedish surface waters.

    PubMed

    Sjöstedt, Carin S; Gustafsson, Jon Petter; Köhler, Stephan J

    2010-11-15

    A consistent chemical equilibrium model that calculates pH from charge balance constraints and aluminum and iron speciation in the presence of natural organic matter is presented. The model requires input data for total aluminum, iron, organic carbon, fluoride, sulfate, and charge balance ANC. The model is calibrated to pH measurements (n = 322) by adjusting the fraction of active organic matter only, which results in an error of pH prediction on average below 0.2 pH units. The small systematic discrepancy between the analytical results for the monomeric aluminum fractionation and the model results is corrected for separately for two different fractionation techniques (n = 499) and validated on a large number (n = 3419) of geographically widely spread samples all over Sweden. The resulting average error for inorganic monomeric aluminum is around 1 µM. In its present form the model is the first internally consistent modeling approach for Sweden and may now be used as a tool for environmental quality management. Soil gibbsite with a log *Ks of 8.29 at 25°C together with a pH dependent loading function that uses molar Al/C ratios describes the amount of aluminum in solution in the presence of organic matter if the pH is roughly above 6.0.

  20. Developing Problem-Solving Skills in Chemical Equilibrium--A Constructive Model.

    ERIC Educational Resources Information Center

    Chiu, Mei-Hung

    The purpose of this study is to analyze the perceived thought processes of several students as they learn, and then attempt to solve problems about chemical equilibrium. Four tenth grade students in Taipei, Taiwan, were audiotaped as they individually attempted to solve problems. The problems were such that they required more than mere recall or…

  1. Evaluation of trace metals bioavailability in Japanese river waters using DGT and a chemical equilibrium model.

    PubMed

    Han, Shuping; Naito, Wataru; Hanai, Yoshimichi; Masunaga, Shigeki

    2013-09-15

    To develop efficient and effective methods of assessing and managing the risk posed by metals to aquatic life, it is important to determine the effects of water chemistry on the bioavailability of metals in surface water. In this study, we employed the diffusive gradients in thin-films (DGT) to determine the bioavailability of metals (Ni, Cu, Zn, and Pb) in Japanese water systems. The DGT results were compared with a chemical equilibrium model (WHAM 7.0) calculation to examine its robustness and utility to predict dynamic metal speciation. The DGT measurements showed that biologically available fractions of metals in the rivers impacted by mine drainage and metal industries were relatively high compared with those in urban rivers. Comparison between the DGT results and the model calculation indicated good agreement for Zn. The model calculation concentrations for Ni and Cu were higher than the DGT concentrations at most sites. As for Pb, the model calculation depended on whether the precipitated iron(III) hydroxide or precipitated aluminum(III) hydroxide was assumed to have an active surface. Our results suggest that the use of WHAM 7.0 combined with the DGT method can predict bioavailable concentrations of most metals (except for Pb) with reasonable accuracy.

  2. Computer program to solve two-dimensional shock-wave interference problems with an equilibrium chemically reacting air model

    NASA Technical Reports Server (NTRS)

    Glass, Christopher E.

    1990-01-01

    The computer program EASI, an acronym for Equilibrium Air Shock Interference, was developed to calculate the inviscid flowfield, the maximum surface pressure, and the maximum heat flux produced by six shock wave interference patterns on a 2-D, cylindrical configuration. Thermodynamic properties of the inviscid flowfield are determined using either an 11-specie, 7-reaction equilibrium chemically reacting air model or a calorically perfect air model. The inviscid flowfield is solved using the integral form of the conservation equations. Surface heating calculations at the impingement point for the equilibrium chemically reacting air model use variable transport properties and specific heat. However, for the calorically perfect air model, heating rate calculations use a constant Prandtl number. Sample calculations of the six shock wave interference patterns, a listing of the computer program, and flowcharts of the programming logic are included.

  3. Simulations for Teaching Chemical Equilibrium

    NASA Astrophysics Data System (ADS)

    Huddle, Penelope A.; White, Margaret Dawn; Rogers, Fiona

    2000-07-01

    This paper outlines a systematic approach to teaching chemical equilibrium using simulation experiments that address most known alternate conceptions in the topic. Graphs drawn using the data from the simulations are identical to those obtained using real experimental data for reactions that go to equilibrium. This allows easy mapping of the analogy to the target. The requirements for the simulations are simple and inexpensive, making them accessible to even the poorest schools. The simulations can be adapted for all levels, from pupils who are first encountering equilibrium through students in tertiary education to qualified teachers who have experienced difficulty in teaching the topic. The simulations were piloted on four very different audiences. Minor modifications were then made before the Equilibrium Games as reported in this paper were tested on three groups of subjects: a Grade 12 class, college students, and university Chemistry I students. Marked improvements in understanding of the concept were shown in two of the three sets of subjects.

  4. Three model space experiments on chemical reactions. [Gibbs adsorption, equilibrium shift and electrodeposition

    NASA Technical Reports Server (NTRS)

    Grodzka, P.; Facemire, B.

    1977-01-01

    Three investigations conducted aboard Skylab IV and Apollo-Soyuz involved phenomena that are of interest to the biochemistry community. The formaldehyde clock reaction and the equilibrium shift reaction experiments conducted aboard Apollo Soyuz demonstrate the effect of low-g foams or air/liquid dispersions on reaction rate and chemical equilibrium. The electrodeposition reaction experiment conducted aboard Skylab IV demonstrate the effect of a low-g environment on an electrochemical displacement reaction. The implications of the three space experiments for various applications are considered.

  5. Basis invariant description of chemical equilibrium with implications for a recent axionic leptogenesis model

    NASA Astrophysics Data System (ADS)

    Shi, Bowen; Raby, Stuart

    2015-10-01

    We provide a systematic treatment of chemical equilibrium in the presence of a specific type of time dependent background. The type of time dependent background we consider appears, for example, in recently proposed axion/Majoron leptogenesis models [A. Kusenko, K. Schmitz, and T. T. Yanagida, Phys. Rev. Lett. 115, 011302 (2015) and M. Ibe and K. Kaneta, Phys. Rev. D 92, 035019 (2015)]. In describing the chemical equilibrium we use quantities which are invariant under redefinition of fermion phases (we refer to this redefinition as a change of basis for short In this paper, change of basis does not mean change of Lorentz frame. All calculations in this paper are performed in the center-of-momentum frame of the thermal plasma, i.e. the Lorentz frame in which the average momentum of particles is zero.), and therefore it is a basis invariant treatment. The change of the anomaly terms due to the change of the path integral measure [K. Fujikawa, Phys. Rev. Lett. 42, 1195 (1979) and K. Fujikawa, Phys. Rev. D 29, 285 (1984)] under a basis change is taken into account. We find it is useful to go back and forth between different bases, and there are insights which can be more easily obtained in one basis rather than another. A toy model is provided to illustrate the ideas. For the axion leptogenesis model [A. Kusenko, K. Schmitz, and T. T. Yanagida, Phys. Rev. Lett. 115, 011302 (2015)], our result suggests that at T >1013 GeV , when sphaleron processes decouple and ΓB +L≪H <ΓL (where H is the Hubble parameter at temperature T and ΓL is the Δ L =2 lepton number violating interaction rate), the amount of B -L created is controlled by the smallness of the sphaleron interaction rate, ΓB +L. Therefore it is not as efficient as described. In addition, we notice an interesting modification of gauge boson dispersion relations at subleading order.

  6. A reaction-based paradigm to model reactive chemical transport in groundwater with general kinetic and equilibrium reactions.

    PubMed

    Zhang, Fan; Yeh, Gour-Tsyh; Parker, Jack C; Brooks, Scott C; Pace, Molly N; Kim, Young-Jin; Jardine, Philip M; Watson, David B

    2007-06-16

    This paper presents a reaction-based water quality transport model in subsurface flow systems. Transport of chemical species with a variety of chemical and physical processes is mathematically described by M partial differential equations (PDEs). Decomposition via Gauss-Jordan column reduction of the reaction network transforms M species reactive transport equations into two sets of equations: a set of thermodynamic equilibrium equations representing N(E) equilibrium reactions and a set of reactive transport equations of M-N(E) kinetic-variables involving no equilibrium reactions (a kinetic-variable is a linear combination of species). The elimination of equilibrium reactions from reactive transport equations allows robust and efficient numerical integration. The model solves the PDEs of kinetic-variables rather than individual chemical species, which reduces the number of reactive transport equations and simplifies the reaction terms in the equations. A variety of numerical methods are investigated for solving the coupled transport and reaction equations. Simulation comparisons with exact solutions were performed to verify numerical accuracy and assess the effectiveness of various numerical strategies to deal with different application circumstances. Two validation examples involving simulations of uranium transport in soil columns are presented to evaluate the ability of the model to simulate reactive transport with complex reaction networks involving both kinetic and equilibrium reactions.

  7. A reaction-based paradigm to model reactive chemical transport in groundwater with general kinetic and equilibrium reactions

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; Yeh, Gour-Tsyh; Parker, Jack C.; Brooks, Scott C.; Pace, Molly N.; Kim, Young-Jin; Jardine, Philip M.; Watson, David B.

    2007-06-01

    This paper presents a reaction-based water quality transport model in subsurface flow systems. Transport of chemical species with a variety of chemical and physical processes is mathematically described by M partial differential equations (PDEs). Decomposition via Gauss-Jordan column reduction of the reaction network transforms M species reactive transport equations into two sets of equations: a set of thermodynamic equilibrium equations representing NE equilibrium reactions and a set of reactive transport equations of M- NE kinetic-variables involving no equilibrium reactions (a kinetic-variable is a linear combination of species). The elimination of equilibrium reactions from reactive transport equations allows robust and efficient numerical integration. The model solves the PDEs of kinetic-variables rather than individual chemical species, which reduces the number of reactive transport equations and simplifies the reaction terms in the equations. A variety of numerical methods are investigated for solving the coupled transport and reaction equations. Simulation comparisons with exact solutions were performed to verify numerical accuracy and assess the effectiveness of various numerical strategies to deal with different application circumstances. Two validation examples involving simulations of uranium transport in soil columns are presented to evaluate the ability of the model to simulate reactive transport with complex reaction networks involving both kinetic and equilibrium reactions.

  8. Atomistic-level non-equilibrium model for chemically reactive systems based on steepest-entropy-ascent quantum thermodynamics

    NASA Astrophysics Data System (ADS)

    Li, Guanchen; Al-Abbasi, Omar; von Spakovsky, Michael R.

    2014-10-01

    This paper outlines an atomistic-level framework for modeling the non-equilibrium behavior of chemically reactive systems. The framework called steepest- entropy-ascent quantum thermodynamics (SEA-QT) is based on the paradigm of intrinsic quantum thermodynamic (IQT), which is a theory that unifies quantum mechanics and thermodynamics into a single discipline with wide applications to the study of non-equilibrium phenomena at the atomistic level. SEA-QT is a novel approach for describing the state of chemically reactive systems as well as the kinetic and dynamic features of the reaction process without any assumptions of near-equilibrium states or weak-interactions with a reservoir or bath. Entropy generation is the basis of the dissipation which takes place internal to the system and is, thus, the driving force of the chemical reaction(s). The SEA-QT non-equilibrium model is able to provide detailed information during the reaction process, providing a picture of the changes occurring in key thermodynamic properties (e.g., the instantaneous species concentrations, entropy and entropy generation, reaction coordinate, chemical affinities, reaction rate, etc). As an illustration, the SEA-QT framework is applied to an atomistic-level chemically reactive system governed by the reaction mechanism F + H2 leftrightarrow FH + H.

  9. Competitive adsorption of metal cations onto two gram positive bacteria: testing the chemical equilibrium model

    NASA Astrophysics Data System (ADS)

    Fowle, David A.; Fein, Jeremy B.

    1999-10-01

    In order to test the ability of a surface complexation approach to account for metal-bacteria interactions in near surface fluid-rock systems, we have conducted experiments that measure the extent of adsorption in mixed metal, mixed bacteria systems. This study tests the surface complexation approach by comparing estimated extents of adsorption based on surface complexation modeling to those we observed in the experimental systems. The batch adsorption experiments involved Ca, Cd, Cu, and Pb adsorption onto the surfaces of 2 g positive bacteria: Bacillus subtilis and Bacillus licheniformis. Three types of experiments were performed: 1. Single metal (Ca, Cu, Pb) adsorption onto a mixture of B. licheniformis and B. subtilis; 2. mixed metal (Cd, Cu, and Pb; Ca and Cd) adsorption onto either B. subtilis or B. licheniformis; and 3. mixed or single metal adsorption onto B. subtilis and B. licheniformis. %Independent of the experimental results, and based on the site specific stability constants for Ca, Cd, Cu, and Pb interactions with the carboxyl and phosphate sites on B. licheniformis and B. subtilis determined by Fein et al. (1997), by Daughney et al. (1998) and in this study, we estimate the extent of adsorption that is expected in the above experimental systems. Competitive cation adsorption experiments in both single and double bacteria systems exhibit little adsorption at pH values less than 4. With increasing pH above 4.0, the extent of Ca, Cu, Pb and Cd adsorption also increases due to the increased deprotonation of bacterial surface functional groups. In all cases studied, the estimated adsorption behavior is in excellent agreement with the observations, with only slight differences that were within the uncertainties of the estimation and experimental procedures. Therefore, the results indicate that the use of chemical equilibrium modeling of aqueous metal adsorption onto bacterial surfaces yields accurate predictions of the distribution of metals in complex

  10. Microscopic Simulation and Macroscopic Modeling for Thermal and Chemical Non-Equilibrium

    NASA Technical Reports Server (NTRS)

    Liu, Yen; Panesi, Marco; Vinokur, Marcel; Clarke, Peter

    2013-01-01

    This paper deals with the accurate microscopic simulation and macroscopic modeling of extreme non-equilibrium phenomena, such as encountered during hypersonic entry into a planetary atmosphere. The state-to-state microscopic equations involving internal excitation, de-excitation, dissociation, and recombination of nitrogen molecules due to collisions with nitrogen atoms are solved time-accurately. Strategies to increase the numerical efficiency are discussed. The problem is then modeled using a few macroscopic variables. The model is based on reconstructions of the state distribution function using the maximum entropy principle. The internal energy space is subdivided into multiple groups in order to better describe the non-equilibrium gases. The method of weighted residuals is applied to the microscopic equations to obtain macroscopic moment equations and rate coefficients. The modeling is completely physics-based, and its accuracy depends only on the assumed expression of the state distribution function and the number of groups used. The model makes no assumption at the microscopic level, and all possible collisional and radiative processes are allowed. The model is applicable to both atoms and molecules and their ions. Several limiting cases are presented to show that the model recovers the classical twotemperature models if all states are in one group and the model reduces to the microscopic equations if each group contains only one state. Numerical examples and model validations are carried out for both the uniform and linear distributions. Results show that the original over nine thousand microscopic equations can be reduced to 2 macroscopic equations using 1 to 5 groups with excellent agreement. The computer time is decreased from 18 hours to less than 1 second.

  11. Chemical Principles Revisited: Using the Equilibrium Concept.

    ERIC Educational Resources Information Center

    Mickey, Charles D., Ed.

    1981-01-01

    Discusses the concept of equilibrium in chemical systems, particularly in relation to predicting the position of equilibrium, predicting spontaneity of a reaction, quantitative applications of the equilibrium constant, heterogeneous equilibrium, determination of the solubility product constant, common-ion effect, and dissolution of precipitates.…

  12. A chemical model for generating the sources of mare basalts - Combined equilibrium and fractional crystallization of the lunar magmasphere

    NASA Technical Reports Server (NTRS)

    Snyder, Gregory A.; Taylor, Lawrence A.; Neal, Clive R.

    1992-01-01

    A chemical model for simulating the sources of the lunar mare basalts was developed by considering a modified mafic cumulate source formed during the combined equilibrium and fractional crystallization of a lunar magma ocean (LMO). The parameters which influence the initial LMO and its subsequent crystallization are examined, and both trace and major elements are modeled. It is shown that major elements tightly constrain the composition of mare basalt sources and the pathways to their creation. The ability of this LMO model to generate viable mare basalt source regions was tested through a case study involving the high-Ti basalts.

  13. An ab initio chemical reaction model for the direct simulation Monte Carlo study of non-equilibrium nitrogen flows

    NASA Astrophysics Data System (ADS)

    Mankodi, T. K.; Bhandarkar, U. V.; Puranik, B. P.

    2017-08-01

    A new ab initio based chemical model for a Direct Simulation Monte Carlo (DSMC) study suitable for simulating rarefied flows with a high degree of non-equilibrium is presented. To this end, Collision Induced Dissociation (CID) cross sections for N2+N2→N2+2 N are calculated and published using a global complete active space self-consistent field-complete active space second order perturbation theory N4 potential energy surface and quasi-classical trajectory algorithm for high energy collisions (up to 30 eV). CID cross sections are calculated for only a selected set of ro-vibrational combinations of the two nitrogen molecules, and a fitting scheme based on spectroscopic weights is presented to interpolate the CID cross section for all possible ro-vibrational combinations. The new chemical model is validated by calculating equilibrium reaction rate coefficients that can be compared well with existing shock tube and computational results. High-enthalpy hypersonic nitrogen flows around a cylinder in the transition flow regime are simulated using DSMC to compare the predictions of the current ab initio based chemical model with the prevailing phenomenological model (the total collision energy model). The differences in the predictions are discussed.

  14. An ab initio chemical reaction model for the direct simulation Monte Carlo study of non-equilibrium nitrogen flows.

    PubMed

    Mankodi, T K; Bhandarkar, U V; Puranik, B P

    2017-08-28

    A new ab initio based chemical model for a Direct Simulation Monte Carlo (DSMC) study suitable for simulating rarefied flows with a high degree of non-equilibrium is presented. To this end, Collision Induced Dissociation (CID) cross sections for N2+N2→N2+2N are calculated and published using a global complete active space self-consistent field-complete active space second order perturbation theory N4 potential energy surface and quasi-classical trajectory algorithm for high energy collisions (up to 30 eV). CID cross sections are calculated for only a selected set of ro-vibrational combinations of the two nitrogen molecules, and a fitting scheme based on spectroscopic weights is presented to interpolate the CID cross section for all possible ro-vibrational combinations. The new chemical model is validated by calculating equilibrium reaction rate coefficients that can be compared well with existing shock tube and computational results. High-enthalpy hypersonic nitrogen flows around a cylinder in the transition flow regime are simulated using DSMC to compare the predictions of the current ab initio based chemical model with the prevailing phenomenological model (the total collision energy model). The differences in the predictions are discussed.

  15. Metals sorption from aqueous solutions by Kluyveromyces marxianus: process optimization, equilibrium modeling and chemical characterization.

    PubMed

    Pal, Rama; Tewari, Saumyata; Rai, Jai P N

    2009-10-01

    The dead Kluyveromyces marxianus biomass, a fermentation industry waste, was used to explore its sorption potential for lead, mercury, arsenic, cobalt, and cadmium as a function of pH, biosorbent dosage, contact time, agitation speed, and initial metal concentration. The equilibrium data fitted the Langmuir model better for cobalt and cadmium, but Freundlich isotherm for all metals tested. At equilibrium, the maximum uptake capacity (Qmax) was highest for lead followed by mercury, arsenic, cobalt, and cadmium. The RL values ranged between 0-1, indicating favorable sorption of all test metals by the biosorbent. The maximum Kf value of Pb showed its efficient removal from the solution. However, multi-metal analysis depicted that sorption of all metals decreased except Pb. The potentiometric titration of biosorbent revealed the presence of functional groups viz. amines, carboxylic acids, phosphates, and sulfhydryl group involved in heavy metal sorption. The extent of contribution of functional groups and lipids to biosorption was in the order: carboxylic>lipids>amines>phosphates. Blocking of sulfhydryl group did not have any significant effect on metal sorption.

  16. Stochastic dynamics and non-equilibrium thermodynamics of a bistable chemical system: the Schlögl model revisited.

    PubMed

    Vellela, Melissa; Qian, Hong

    2009-10-06

    Schlögl's model is the canonical example of a chemical reaction system that exhibits bistability. Because the biological examples of bistability and switching behaviour are increasingly numerous, this paper presents an integrated deterministic, stochastic and thermodynamic analysis of the model. After a brief review of the deterministic and stochastic modelling frameworks, the concepts of chemical and mathematical detailed balances are discussed and non-equilibrium conditions are shown to be necessary for bistability. Thermodynamic quantities such as the flux, chemical potential and entropy production rate are defined and compared across the two models. In the bistable region, the stochastic model exhibits an exchange of the global stability between the two stable states under changes in the pump parameters and volume size. The stochastic entropy production rate shows a sharp transition that mirrors this exchange. A new hybrid model that includes continuous diffusion and discrete jumps is suggested to deal with the multiscale dynamics of the bistable system. Accurate approximations of the exponentially small eigenvalue associated with the time scale of this switching and the full time-dependent solution are calculated using Matlab. A breakdown of previously known asymptotic approximations on small volume scales is observed through comparison with these and Monte Carlo results. Finally, in the appendix section is an illustration of how the diffusion approximation of the chemical master equation can fail to represent correctly the mesoscopically interesting steady-state behaviour of the system.

  17. Parameterization of the non-local thermodynamic equilibrium source function with chemical production by an equivalent two-level model

    NASA Astrophysics Data System (ADS)

    Zhu, Xun

    2003-07-01

    The classic two-level or equivalent two-level model that includes only the statistical equilibrium of radiative and thermal processes of excitation and quenching between two vibrational energy levels is extended by adding chemical production to the rate equations. The modifications to the non-local thermodynamic equilibrium source function and cooling rate are parameterized by ϕc, which characterizes the ratio of chemical production to collisional quenching. For applications of broadband emission of O3 at 9.6 μm, the non-LTE effect of chemical production on the cooling rate and limb emission is proportional to the ratio of O to O3. For a typical [O]/[O3], the maximum enhancements of limb radiance and cooling rate are about 15% 30% and 0.03 0.05 K day-1, respectively, both occurring near the mesopause regions. This suggests that the broadband limb radiance above ˜80 km is sensitive to O3 density but not sensitive to the direct cooling rate along the line-of-sight, which makes O3 retrieval feasible but the direct cooling rate retrieval difficult by using the O3 9.6 μm band limb emission.

  18. Exploring Chemical Equilibrium in Hot Jovians

    NASA Astrophysics Data System (ADS)

    Blumenthal, Sarah; Harrington, Joseph; Mandell, Avi; Hébrard, Eric; Venot, Olivia; Cubillos, Patricio; Blecic, Jasmina; Challener, Ryan

    2016-01-01

    It has been established that equilibrium chemistry is usually achieved deep in the atmosphere of hot Jovians where timescales are short (Line and Yung 2013). Thus, equilibrium chemistry has been used as a starting point (setting initial conditions) for evaluating disequilibrium processes. We explore parameters of setting these initial conditions including departures from solar metallicity, the number of species allowed in a system, the types of species allowed in a system, and different thermodynamic libraries in an attempt to create a standard for evaluating equilibrium chemistry. NASA's open source code Chemical Equilibrium and Applications (CEA) is used to calculate model planet abundances by varying the metallicity, in the pressure regime 0.1 to 1 bar. These results are compared to a variety of exoplanets(Teq between 600 and 2100K) qualitatively by color maps of the dayside with different temperature redistributions. Additionally, CEA (with an up-dated thermodynamic library) is compared with the thermochemical model presented in Venotet al. (2012) for HD 209458b and HD 189733b. This same analysis is then applied to the cooler planet HD 97658b. Spectra are generated and we compare both models' outputs using the open source codetransit (https://github.com/exosports/transit) using the opacities of 15 molecules. We make the updated CEA thermodyanamic library and supporting Python scripts to do the CEA analyses available open source. Thiswork was supported by NASA Planetary Atmospheres grant NNX12AI69G.

  19. Using a chemical equilibrium model to predict amendments required to precipitate phosphorus as struvite in liquid swine manure.

    PubMed

    Celen, Ipek; Buchanan, John R; Burns, Robert T; Robinson, R Bruce; Raman, D Raj

    2007-04-01

    Precipitation of phosphate minerals from liquid swine manure is an established means of reducing the orthophosphate (OP) concentration. This project investigated the usefulness of a chemical equilibrium model, Visual Minteq, for prescribing the amendments needed to maximize struvite precipitation from liquid swine manure and thus reduce the OP phosphorus concentration. The actual concentrations of Mg(2+), Ca(2+), K(+), OP, NH(4)(+), alkalinity and pH from a liquid swine manure system were used as inputs to the model. The model was modified to remove species with extremely low formation rates, because they would not significantly precipitate in the reaction occurring in a short retention-time process such as those envisioned for swine manure struvite-formation reactors. Using the model's output, a series of 19-L reactors were used to verify the results. Verification results demonstrated that Visual Minteq can be used to pre-determine the concentration of amendments required to maximize struvite recovery.

  20. Chemical Equilibrium And Transport (CET)

    NASA Technical Reports Server (NTRS)

    Mcbride, B. J.

    1991-01-01

    Powerful, machine-independent program calculates theoretical thermodynamic properties of chemical systems. Aids in design of compressors, turbines, engines, heat exchangers, and chemical processing equipment.

  1. Chemical Equilibrium And Transport (CET)

    NASA Technical Reports Server (NTRS)

    Mcbride, B. J.

    1991-01-01

    Powerful, machine-independent program calculates theoretical thermodynamic properties of chemical systems. Aids in design of compressors, turbines, engines, heat exchangers, and chemical processing equipment.

  2. Equilibrium and Sudden Events in Chemical Evolution

    NASA Astrophysics Data System (ADS)

    Weinberg, David H.; Andrews, Brett H.; Freudenburg, Jenna

    2017-03-01

    We present new analytic solutions for one-zone (fully mixed) chemical evolution models that incorporate a realistic delay time distribution for Type Ia supernovae (SNe Ia) and can therefore track the separate evolution of α-elements produced by core collapse supernovae (CCSNe) and iron peak elements synthesized in both CCSNe and SNe Ia. Our solutions allow constant, exponential, or linear–exponential ({{te}}-t/{τ {sfh}}) star formation histories, or combinations thereof. In generic cases, α 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 η, while the equilibrium abundance ratio [α /{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. Systems with ongoing gas accretion develop metallicity distribution functions (MDFs) that are sharply peaked, while “gas starved” systems with rapidly declining star formation, such as the conventional “closed box” model, have broadly peaked MDFs. A burst of star formation that consumes a significant fraction of a system’s available gas and retains its metals can temporarily boost [α /{Fe}] by 0.1–0.3 dex, a possible origin for rare, α-enhanced stars with intermediate age and/or high metallicity. Other sudden transitions in system properties can produce surprising behavior, including backward evolution of a stellar population from high to low metallicity.

  3. Computing Properties Of Chemical Mixtures At Equilibrium

    NASA Technical Reports Server (NTRS)

    Mcbride, B. J.; Gordon, S.

    1995-01-01

    Scientists and engineers need data on chemical equilibrium compositions to calculate theoretical thermodynamic properties of chemical systems. Information essential in design and analysis of such equipment as compressors, turbines, nozzles, engines, shock tubes, heat exchangers, and chemical-processing equipment. CET93 is general program that calculates chemical equilibrium compositions and properties of mixtures for any chemical system for which thermodynamic data are available. Includes thermodynamic data for more than 1,300 gaseous and condensed species and thermal-transport data for 151 gases. Written in FORTRAN 77.

  4. Computing Properties Of Chemical Mixtures At Equilibrium

    NASA Technical Reports Server (NTRS)

    Mcbride, B. J.; Gordon, S.

    1995-01-01

    Scientists and engineers need data on chemical equilibrium compositions to calculate theoretical thermodynamic properties of chemical systems. Information essential in design and analysis of such equipment as compressors, turbines, nozzles, engines, shock tubes, heat exchangers, and chemical-processing equipment. CET93 is general program that calculates chemical equilibrium compositions and properties of mixtures for any chemical system for which thermodynamic data are available. Includes thermodynamic data for more than 1,300 gaseous and condensed species and thermal-transport data for 151 gases. Written in FORTRAN 77.

  5. An Elementary Discussion of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    David, Carl W.

    1988-01-01

    This discussion uses a more difficult reaction as the prototype to derive the standard equation for chemical equilibrium. It can be used by students who can understand and use partial derivatives. (CW)

  6. Spreadsheet Templates for Chemical Equilibrium Calculations.

    ERIC Educational Resources Information Center

    Joshi, Bhairav D.

    1993-01-01

    Describes two general spreadsheet templates to carry out all types of one-equation chemical equilibrium calculations encountered by students in undergraduate chemistry courses. Algorithms, templates, macros, and representative examples are presented to illustrate the approach. (PR)

  7. Chemical equilibrium and reaction modeling of arsenic and selenium in soils

    USDA-ARS?s Scientific Manuscript database

    The chemical processes and soil factors that affect the concentrations of As and Se in soil solution were discussed. Both elements occur in two redox states differing in toxicity and reactivity. Methylation and volatilization reactions occur in soils and can act as detoxification pathways. Precip...

  8. Tautomeric equilibrium of uracil and thymine in model protein-nucleic acid contacts. Spectroscopic and quantum chemical approach.

    PubMed

    Samijlenko, Svitlana P; Yurenko, Yevgen P; Stepanyugin, Andriy V; Hovorun, Dmytro M

    2010-01-28

    This work deals with tautomeric transformations of uracil (Ura) and thymine (Thy) in their model complexes with the deprotonated carboxylic group. Essential changes in the UV spectra of the bases upon their interaction with NaAc, vanishing signals of both imino protons in (1)H NMR spectra, and a perceptible decrease in intensity of both IR bands, related to the stretching vibrations nu(C=O) of the carbonyl groups, imply involvement of enolic tautomers. Results of quantum chemical calculations of the double complexes of the Ura(Thy) tautomers with CH(3)COO(-) at the MP2/6-311++G(2df,pd)//B3LYP/6-311++G(d,p) level of theory proved to be incompatible with the spectral features: despite the fact that the complexes of the enolic tautomers are much closer in energy to the diketo ones as compared to isolated tautomers, the energy gap between them is such that in tautomeric equilibrium dominate diketo forms. Calculations of triple complexes of the type CH(3)COO(-):Ura(Thy) tautomer:Na(+), taking into account the effect of the Na(+) coordination with tautomers, show that three triple complexes formed by enolic tautomers appeared more stable than those formed by diketo ones. This makes the UV and (1)H NMR data understandable, but the high residual intensity of the nu(C=O) bands in the IR spectra remains unclear. At that ion, Na(+) itself was not able to disturb the tautomeric equilibrium in the coordination complexes of the type Ura(Thy) tautomer:Na(+). To evaluate the DMSO effect, the CPCM solvation model was applied to triple complexes of the Ura tautomers. It appeared that in the solution there is coexistence between the diketo and enolic tautomers in a ratio of 53%:47%. This makes possible reconciliation of our experimental data. The biological significance of high-energy tautomers of nucleotide bases is discussed.

  9. Caustic-Side Solvent Extraction Chemical and Physical Properties: Equilibrium Modeling of Distribution Behavior.

    SciTech Connect

    Delmau, LH

    2001-12-18

    A multivariate mathematical model describing the extraction of cesium from different mixtures of sodium hydroxide, sodium nitrate, sodium chloride, and sodium nitrite containing potassium at variable concentrations has been established. It was determined based on the cesium, potassium, and sodium distribution ratios obtained with simple systems containing single salts. These experimental data were modeled to obtain the formation constants of complexes formed in the organic phase based on specified concentrations of components in both organic and aqueous phases. The model was applied to five different SRS waste simulants, and the corresponding cesium extraction results were predicted satisfactorily, thus validating the model.

  10. Has Chemical Education Reached Equilibrium?

    NASA Astrophysics Data System (ADS)

    Moore, John W.

    1997-06-01

    The other day I got to thinking about whether something akin to Le Chatelier's principle operates in chemical education. That is, whenever someone alters the conditions under which we interact with students, there is a shift in the system that attempts to minimize or counteract the change.

  11. Teaching Chemical Equilibrium with the Jigsaw Technique

    NASA Astrophysics Data System (ADS)

    Doymus, Kemal

    2008-03-01

    This study investigates the effect of cooperative learning (jigsaw) versus individual learning methods on students’ understanding of chemical equilibrium in a first-year general chemistry course. This study was carried out in two different classes in the department of primary science education during the 2005-2006 academic year. One of the classes was randomly assigned as the non-jigsaw group (control) and other as the jigsaw group (cooperative). Students participating in the jigsaw group were divided into four “home groups” since the topic chemical equilibrium is divided into four subtopics (Modules A, B, C and D). Each of these home groups contained four students. The groups were as follows: (1) Home Group A (HGA), representin g the equilibrium state and quantitative aspects of equilibrium (Module A), (2) Home Group B (HGB), representing the equilibrium constant and relationships involving equilibrium constants (Module B), (3) Home Group C (HGC), representing Altering Equilibrium Conditions: Le Chatelier’s principle (Module C), and (4) Home Group D (HGD), representing calculations with equilibrium constants (Module D). The home groups then broke apart, like pieces of a jigsaw puzzle, and the students moved into jigsaw groups consisting of members from the other home groups who were assigned the same portion of the material. The jigsaw groups were then in charge of teaching their specific subtopic to the rest of the students in their learning group. The main data collection tool was a Chemical Equilibrium Achievement Test (CEAT), which was applied to both the jigsaw and non-jigsaw groups The results indicated that the jigsaw group was more successful than the non-jigsaw group (individual learning method).

  12. Algorithm For Hypersonic Flow In Chemical Equilibrium

    NASA Technical Reports Server (NTRS)

    Palmer, Grant

    1989-01-01

    Implicit, finite-difference, shock-capturing algorithm calculates inviscid, hypersonic flows in chemical equilibrium. Implicit formulation chosen because overcomes limitation on mathematical stability encountered in explicit formulations. For dynamical portion of problem, Euler equations written in conservation-law form in Cartesian coordinate system for two-dimensional or axisymmetric flow. For chemical portion of problem, equilibrium state of gas at each point in computational grid determined by minimizing local Gibbs free energy, subject to local conservation of molecules, atoms, ions, and total enthalpy. Major advantage: resulting algorithm naturally stable and captures strong shocks without help of artificial-dissipation terms to damp out spurious numerical oscillations.

  13. Computational non-chemically equilibrium model on the current zero simulation in a model N2 circuit breaker under the free recovery condition

    NASA Astrophysics Data System (ADS)

    Sun, Hao; Tanaka, Yasunori; Tomita, Kentaro; Wu, Yi; Rong, Mingzhe; Uesugi, Yoshihiko; Ishijima, Tatsuo

    2016-02-01

    A non-chemically equilibrium (non-CE) model was established to investigate the N2 arc plasma in the decaying phase during the arc interruption, and was validated by comparison with the experimental results based on laser Thomson scattering. Unlike the conventional model assuming the local thermodynamic equilibrium (LTE), in this non-CE model, the magneto-hydro-dynamics (MHD) method was coupled with the reaction kinetics to obtain the time-dependent species compositions and properties. The current calculation took into account five species in hot gas and 22 chemical reactions in total. The time-dependent species compositions of hot N2 were derived from the mass conservation equation for each species, considering the effect of the convection, diffusion and the chemical reaction. The influence of the non-CE compositions on the arc decaying behavior was realized by updating the thermodynamic and transport properties at each iterative step. The results indicate that the non-CE model can result in the departure of the arc decaying behavior from the LTE model, because it alters the time evolution of the species composition and consequently changes the thermodynamic and transport properties. At the edge of the arc, the time evolutions of the species are dominant by both the diffusion and the chemical reactions while at the center of the arc they are mainly influenced by the chemical reactions. Generally, the non-CE effect can lead to the delay of all the particles’ variations, particularly the electron decay, so that the arc interruption performance will be reduced compared with that in the LTE model.

  14. Teaching Chemical Equilibrium with the Jigsaw Technique

    ERIC Educational Resources Information Center

    Doymus, Kemal

    2008-01-01

    This study investigates the effect of cooperative learning (jigsaw) versus individual learning methods on students' understanding of chemical equilibrium in a first-year general chemistry course. This study was carried out in two different classes in the department of primary science education during the 2005-2006 academic year. One of the classes…

  15. Calculating Shocks In Flows At Chemical Equilibrium

    NASA Technical Reports Server (NTRS)

    Eberhardt, Scott; Palmer, Grant

    1988-01-01

    Boundary conditions prove critical. Conference paper describes algorithm for calculation of shocks in hypersonic flows of gases at chemical equilibrium. Although algorithm represents intermediate stage in development of reliable, accurate computer code for two-dimensional flow, research leading up to it contributes to understanding of what is needed to complete task.

  16. Teaching Chemical Equilibrium with the Jigsaw Technique

    ERIC Educational Resources Information Center

    Doymus, Kemal

    2008-01-01

    This study investigates the effect of cooperative learning (jigsaw) versus individual learning methods on students' understanding of chemical equilibrium in a first-year general chemistry course. This study was carried out in two different classes in the department of primary science education during the 2005-2006 academic year. One of the classes…

  17. Modeling the Non-Equilibrium Process of the Chemical Adsorption of Ammonia on GaN(0001) Reconstructed Surfaces Based on Steepest-Entropy-Ascent Quantum Thermodynamics

    PubMed Central

    Kusaba, Akira; von Spakovsky, Michael R.; Kangawa, Yoshihiro; Kakimoto, Koichi

    2017-01-01

    Clearly understanding elementary growth processes that depend on surface reconstruction is essential to controlling vapor-phase epitaxy more precisely. In this study, ammonia chemical adsorption on GaN(0001) reconstructed surfaces under metalorganic vapor phase epitaxy (MOVPE) conditions (3Ga-H and Nad-H + Ga-H on a 2 × 2 unit cell) is investigated using steepest-entropy-ascent quantum thermodynamics (SEAQT). SEAQT is a thermodynamic-ensemble based, first-principles framework that can predict the behavior of non-equilibrium processes, even those far from equilibrium where the state evolution is a combination of reversible and irreversible dynamics. SEAQT is an ideal choice to handle this problem on a first-principles basis since the chemical adsorption process starts from a highly non-equilibrium state. A result of the analysis shows that the probability of adsorption on 3Ga-H is significantly higher than that on Nad-H + Ga-H. Additionally, the growth temperature dependence of these adsorption probabilities and the temperature increase due to the heat of reaction is determined. The non-equilibrium thermodynamic modeling applied can lead to better control of the MOVPE process through the selection of preferable reconstructed surfaces. The modeling also demonstrates the efficacy of DFT-SEAQT coupling for determining detailed non-equilibrium process characteristics with a much smaller computational burden than would be entailed with mechanics-based, microscopic-mesoscopic approaches. PMID:28809816

  18. Modeling the Non-Equilibrium Process of the Chemical Adsorption of Ammonia on GaN(0001) Reconstructed Surfaces Based on Steepest-Entropy-Ascent Quantum Thermodynamics.

    PubMed

    Kusaba, Akira; Li, Guanchen; von Spakovsky, Michael R; Kangawa, Yoshihiro; Kakimoto, Koichi

    2017-08-15

    Clearly understanding elementary growth processes that depend on surface reconstruction is essential to controlling vapor-phase epitaxy more precisely. In this study, ammonia chemical adsorption on GaN(0001) reconstructed surfaces under metalorganic vapor phase epitaxy (MOVPE) conditions (3Ga-H and Nad-H + Ga-H on a 2 × 2 unit cell) is investigated using steepest-entropy-ascent quantum thermodynamics (SEAQT). SEAQT is a thermodynamic-ensemble based, first-principles framework that can predict the behavior of non-equilibrium processes, even those far from equilibrium where the state evolution is a combination of reversible and irreversible dynamics. SEAQT is an ideal choice to handle this problem on a first-principles basis since the chemical adsorption process starts from a highly non-equilibrium state. A result of the analysis shows that the probability of adsorption on 3Ga-H is significantly higher than that on Nad-H + Ga-H. Additionally, the growth temperature dependence of these adsorption probabilities and the temperature increase due to the heat of reaction is determined. The non-equilibrium thermodynamic modeling applied can lead to better control of the MOVPE process through the selection of preferable reconstructed surfaces. The modeling also demonstrates the efficacy of DFT-SEAQT coupling for determining detailed non-equilibrium process characteristics with a much smaller computational burden than would be entailed with mechanics-based, microscopic-mesoscopic approaches.

  19. Measurement and estimation of ammonia emissions from lagoon-atmosphere interface using a coupled mass transfer and chemical reactions model, and an equilibrium model

    NASA Astrophysics Data System (ADS)

    Bajwa, Kanwardeep S.; Aneja, Viney P.; Pal Arya, S.

    Ammonia has recently gained importance for its increasing atmospheric concentrations and its role in the formation of aerosols. The anaerobic lagoon and spray method, commonly used for waste storage and disposal in confined animal feeding operations (CAFO), is a significant source of ammonia emissions. An accurate emission model for ammonia from aqueous surfaces can help in the development of emission factors. Data collected from field measurements made at hog waste lagoons in south eastern North Carolina, using the flow through dynamic chamber technique, were used to evaluate the Coupled mass transfer and Chemical reactions model and Equilibrium model developed by Aneja et al. [2001a. Measurement and modeling of ammonia emissions at waste treatment lagoon-Atmospheric Interface. Water, Air and Soil pollution: Focus 1, 177-188]. Sensitivity analysis shows that ammonia flux increases exponentially with lagoon temperature and pH, but a linear increase was observed with an increase in total ammoniacal nitrogen (TAN). Ammonia flux also shows a nonlinear increase with increasing wind speed. Observed ammonia fluxes were generally lower in the cold season than in the warm season when lagoon temperatures are higher. About 41% of the equilibrium model predictions and 43% of the Coupled model predictions are found to be within a factor of two of the observed fluxes. Several model performance statistics were used to evaluate the performance of the two models against the observed flux data. These indicate that the simpler Equilibrium model does as well as the Coupled model. The possible effects of the "artificial" environment within the chamber, which is different from that in the ambient atmospheric conditions above the open lagoon surface, on the measured fluxes are also recognized.

  20. THE ABUNDANCE OF MOLECULAR HYDROGEN AND ITS CORRELATION WITH MIDPLANE PRESSURE IN GALAXIES: NON-EQUILIBRIUM, TURBULENT, CHEMICAL MODELS

    SciTech Connect

    Mac Low, Mordecai-Mark; Glover, Simon C. O. E-mail: glover@uni-heidelberg.de

    2012-02-20

    Observations of spiral galaxies show a strong linear correlation between the ratio of molecular to atomic hydrogen surface density R{sub mol} and midplane pressure. To explain this, we simulate three-dimensional, magnetized turbulence, including simplified treatments of non-equilibrium chemistry and the propagation of dissociating radiation, to follow the formation of H{sub 2} from cold atomic gas. The formation timescale for H{sub 2} is sufficiently long that equilibrium is not reached within the 20-30 Myr lifetimes of molecular clouds. The equilibrium balance between radiative dissociation and H{sub 2} formation on dust grains fails to predict the time-dependent molecular fractions we find. A simple, time-dependent model of H{sub 2} formation can reproduce the gross behavior, although turbulent density perturbations increase molecular fractions by a factor of few above it. In contradiction to equilibrium models, radiative dissociation of molecules plays little role in our model for diffuse radiation fields with strengths less than 10 times that of the solar neighborhood, because of the effective self-shielding of H{sub 2}. The observed correlation of R{sub mol} with pressure corresponds to a correlation with local gas density if the effective temperature in the cold neutral medium of galactic disks is roughly constant. We indeed find such a correlation of R{sub mol} with density. If we examine the value of R{sub mol} in our local models after a free-fall time at their average density, as expected for models of molecular cloud formation by large-scale gravitational instability, our models reproduce the observed correlation over more than an order-of-magnitude range in density.

  1. The Conceptual Change Approach to Teaching Chemical Equilibrium

    ERIC Educational Resources Information Center

    Canpolat, Nurtac; Pinarbasi, Tacettin; Bayrakceken, Samih; Geban, Omer

    2006-01-01

    This study investigates the effect of a conceptual change approach over traditional instruction on students' understanding of chemical equilibrium concepts (e.g. dynamic nature of equilibrium, definition of equilibrium constant, heterogeneous equilibrium, qualitative interpreting of equilibrium constant, changing the reaction conditions). This…

  2. The Conceptual Change Approach to Teaching Chemical Equilibrium

    ERIC Educational Resources Information Center

    Canpolat, Nurtac; Pinarbasi, Tacettin; Bayrakceken, Samih; Geban, Omer

    2006-01-01

    This study investigates the effect of a conceptual change approach over traditional instruction on students' understanding of chemical equilibrium concepts (e.g. dynamic nature of equilibrium, definition of equilibrium constant, heterogeneous equilibrium, qualitative interpreting of equilibrium constant, changing the reaction conditions). This…

  3. Domino effects within a chemical cluster: a game-theoretical modeling approach by using Nash-equilibrium.

    PubMed

    Reniers, Genserik; Dullaert, Wout; Karel, Soudan

    2009-08-15

    Every company situated within a chemical cluster faces domino effect risks, whose magnitude depends on every company's own risk management strategies and on those of all others. Preventing domino effects is therefore very important to avoid catastrophes in the chemical process industry. Given that chemical companies are interlinked by domino effect accident links, there is some likelihood that even if certain companies fully invest in domino effects prevention measures, they can nonetheless experience an external domino effect caused by an accident which occurred in another chemical enterprise of the cluster. In this article a game-theoretic approach to interpret and model behaviour of chemical plants within chemical clusters while negotiating and deciding on domino effects prevention investments is employed.

  4. Thermo-chemical dynamics and chemical quasi-equilibrium of plasmas in thermal non-equilibrium

    NASA Astrophysics Data System (ADS)

    Massot, Marc; Graille, Benjamin; Magin, Thierry E.

    2011-05-01

    We examine both processes of ionization by electron and heavy-particle impact in spatially uniform plasmas at rest in the absence of external forces. A singular perturbation analysis is used to study the following physical scenario, in which thermal relaxation becomes much slower than chemical reactions. First, electron-impact ionization is investigated. The dynamics of the system rapidly becomes close to a slow dynamics manifold that allows for defining a unique chemical quasi-equilibrium for two-temperature plasmas and proving that the second law of thermodynamics is satisfied. Then, all ionization reactions are taken into account simultaneously, leading to a surprising conclusion: the inner layer for short time scale (or time boundary layer) directly leads to thermal equilibrium. Global thermo-chemical equilibrium is reached within a short time scale, involving only chemical reactions, even if thermal relaxation through elastic collisions is assumed to be slow.

  5. Thermo-chemical dynamics and chemical quasi-equilibrium of plasmas in thermal non-equilibrium

    SciTech Connect

    Massot, Marc; Graille, Benjamin; Magin, Thierry E.

    2011-05-20

    We examine both processes of ionization by electron and heavy-particle impact in spatially uniform plasmas at rest in the absence of external forces. A singular perturbation analysis is used to study the following physical scenario, in which thermal relaxation becomes much slower than chemical reactions. First, electron-impact ionization is investigated. The dynamics of the system rapidly becomes close to a slow dynamics manifold that allows for defining a unique chemical quasi-equilibrium for two-temperature plasmas and proving that the second law of thermodynamics is satisfied. Then, all ionization reactions are taken into account simultaneously, leading to a surprising conclusion: the inner layer for short time scale (or time boundary layer) directly leads to thermal equilibrium. Global thermo-chemical equilibrium is reached within a short time scale, involving only chemical reactions, even if thermal relaxation through elastic collisions is assumed to be slow.

  6. NMR spectroscopic studies of a TAT-derived model peptide in imidazolium-based ILs: influence on chemical shifts and the cis/trans equilibrium state.

    PubMed

    Wiedemann, Christoph; Ohlenschläger, Oliver; Mrestani-Klaus, Carmen; Bordusa, Frank

    2017-09-13

    NMR spectroscopy was used to study systematically the impact of imidazolium-based ionic liquid (IL) solutions on a TAT-derived model peptide containing Xaa-Pro peptide bonds. The selected IL anions cover a wide range of the Hofmeister series of ions. Based on highly resolved one- and two-dimensional NMR spectra individual (1)H and (13)C peptide chemical shift differences were analysed and a classification of IL anions according to the Hofmeister series was derived. The observed chemical shift changes indicate significant interactions between the peptide and the ILs. In addition, we examined the impact of different ILs towards the cis/trans equilibrium state of the Xaa-Pro peptide bonds. In this context, the IL cations appear to be of exceptional importance for inducing an alteration of the native cis/trans equilibrium state of Xaa-Pro bonds in favour of the trans-isomers.

  7. Helical axis stellarator equilibrium model

    SciTech Connect

    Koniges, A.E.; Johnson, J.L.

    1985-02-01

    An asymptotic model is developed to study MHD equilibria in toroidal systems with a helical magnetic axis. Using a characteristic coordinate system based on the vacuum field lines, the equilibrium problem is reduced to a two-dimensional generalized partial differential equation of the Grad-Shafranov type. A stellarator-expansion free-boundary equilibrium code is modified to solve the helical-axis equations. The expansion model is used to predict the equilibrium properties of Asperators NP-3 and NP-4. Numerically determined flux surfaces, magnetic well, transform, and shear are presented. The equilibria show a toroidal Shafranov shift.

  8. Investigating High School Students' Understanding of Chemical Equilibrium Concepts

    ERIC Educational Resources Information Center

    Karpudewan, Mageswary; Treagust, David F.; Mocerino, Mauro; Won, Mihye; Chandrasegaran, A. L.

    2015-01-01

    This study investigated the year 12 students' (N = 56) understanding of chemical equilibrium concepts after instruction using two conceptual tests, the "Chemical Equilibrium Conceptual Test 1" ("CECT-1") consisting of nine two-tier multiple-choice items and the "Chemical Equilibrium Conceptual Test 2"…

  9. Analytical formulation of chemical derivatives in equilibrium plasma flows.

    PubMed

    Orsini, Alessio

    2008-12-01

    Chemical derivatives are used in the mathematical modeling of transport phenomena in equilibrium plasma flows when chemical element diffusion and mixing or demixing effects are accounted for. They measure the variation of mixture chemical composition in response to changes in element fractions, pressure, or temperature. Currently, these quantities are calculated numerically, using finite differences. This approach, other than being computationally expensive and prone to numerical error, does not provide any insight into flow physics. Our work is aimed at introducing a fully analytical method for the calculation of chemical derivatives which bypasses the computational cost. It also provides a simple means of estimating their order of magnitude.

  10. Thermodynamic derivations of conditions for chemical equilibrium and of Onsager reciprocal relations for chemical reactors.

    PubMed

    Beretta, Gian Paolo; Gyftopoulos, Elias P

    2004-08-08

    For an isolated chemical reactor, we derive the conditions for chemical equilibrium in terms of either energy, volume, and amounts of constituents or temperature, pressure, and composition, with special emphasis on what is meant by temperature and chemical potentials as the system proceeds through nonequilibrium states towards stable chemical equilibrium. For nonequilibrium states, we give both analytical expressions and pictorial representations of the assumptions and implications underlying chemical dynamics models. In the vicinity of the chemical equilibrium state, we express the affinities of the chemical reactions, the reaction rates, and the rate of entropy generation as functions of the reaction coordinates and derive Onsager reciprocal relations without recourse to statistical fluctuations, time reversal, and the principle of microscopic reversibility.

  11. Chemical zonation in garnet: kinetics or chemical equilibrium?

    NASA Astrophysics Data System (ADS)

    Ague, Jay; Chu, Xu; Axler, Jennifer

    2015-04-01

    Chemical zonation in garnet is widely used to reconstruct the pressure (P), temperature (T), time (t), and fluid (f) histories of mountain belts. Zonation is thought to result largely from changing P - T - t - f conditions during growth as well as post-growth intracrystalline diffusion. Chemical zonation is conventionally interpreted to mean that at least some of the garnet interior was out of chemical equilibrium with the matrix during metamorphism. In this case, thermally-activated diffusion in garnet is too slow to equalize chemical potentials. However, in their groundbreaking paper, Tajčmanová et al. (2014) postulate that in high-grade rocks, chemical zonation may actually reflect attainment of equilibrium. In this scenario, diffusion is fast but viscous relaxation is slow such that the zonation patterns directly mirror internal pressure gradients within garnet. Such zoning would likely be very different than typical concentric growth zonation. Furthermore, Baumgartner et al. (2010) hypothesize that given significant variations in the molar volumes of garnet endmembers, diffusional relaxation may produce internal pressure gradients if the garnet behaves as a near constant-volume system. Consequently, growth zoning could be preserved by pressure variations within the garnet that equalize chemical potentials and slow or stop diffusion (i.e., the garnet is chemically heterogeneous but maintains internal chemical equilibrium due to the pressure variations). This mechanism predicts that areas of garnet with small compositional contrasts would undergo more diffusional relaxation than areas with large contrasts. Moreover, generation of large internal pressure gradients approaching 1 GPa would be expected to induce deformation (e.g., fracturing) in regions of large compositional gradients. Strongly growth-zoned amphibolite facies garnet from the Barrovian zones, Scotland (Ague and Baxter, 2007) shows neither of these features. The sharp compositional gradients are

  12. Development of Accurate Chemical Equilibrium Models for the Hanford Waste Tanks: New Thermodynamic Measurements and Model Applications

    SciTech Connect

    Felmy, Andrew R.; Mason, Marvin; Qafoku, Odeta; Xia, Yuanxian; Wang, Zheming; MacLean, Graham

    2003-03-27

    Developing accurate thermodynamic models for predicting the chemistry of the high-level waste tanks at Hanford is an extremely daunting challenge in electrolyte and radionuclide chemistry. These challenges stem from the extremely high ionic strength of the tank waste supernatants, presence of chelating agents in selected tanks, wide temperature range in processing conditions and the presence of important actinide species in multiple oxidation states. This presentation summarizes progress made to date in developing accurate models for these tank waste solutions, how these data are being used at Hanford and the important challenges that remain. New thermodynamic measurements on Sr and actinide complexation with specific chelating agents (EDTA, HEDTA and gluconate) will also be presented.

  13. Equilibriumlike behavior in chemical reaction networks far from equilibrium.

    PubMed

    Lubensky, David K

    2010-06-01

    In an equilibrium chemical reaction mixture, the number of molecules present obeys a Poisson distribution. We report that, surprisingly, the same is true of a large class of nonequilibrium reaction networks. In particular, we show that certain topological features imply a Poisson distribution, whatever the reaction rates. Such driven systems also obey an analog of the fluctuation-dissipation theorem. Our results shed light on the fundamental question of when equilibrium concepts might apply to nonequilibrium systems and may have applications to models of noise in biochemical networks.

  14. Chemical Equilibrium Problems Treated by Geometric and Transcendental Programming

    DTIC Science & Technology

    1975-04-01

    RCRPONMINO ORCANIZATION NAMt AND ADORCU Department of Operations Research Stanford University Stanford, CA 95305 M. CONTROLLINO OFFICE NAME AND...Equilibrium 86 6.2 Verification of the Model 88 6.3 Sensitivity Analysis 92 6.4 Coaling Problems 99 7 A DUAL CHEMICAL ALGORITHM 108 7.1 Introduction...experience and judgment. In general the choice of species is up to the designer of the model. The mathematical analysis of the system assumes a given set

  15. Equilibrium properties of chemically reacting gases

    NASA Technical Reports Server (NTRS)

    1976-01-01

    The equilibrium energy, enthalpy, entropy, specific heat at constant volume and constant pressure, and the equation of state of the gas are all derived for chemically reacting gas mixtures in terms of the compressibility, the mol fractions, the thermodynamic properties of the pure gas components, and the change in zero point energy due to reaction. Results are illustrated for a simple diatomic dissociation reaction and nitrogen is used as an example. Next, a gas mixture resulting from combined diatomic dissociation and atomic ionization reactions is treated and, again, nitrogen is used as an example. A short discussion is given of the additional complexities involved when precise solutions for high-temperature air are desired, including effects caused by NO produced in shuffle reactions and by other trace species formed from CO2, H2O and Ar found in normal air.

  16. Spectral Quasi-Equilibrium Manifold for Chemical Kinetics.

    PubMed

    Kooshkbaghi, Mahdi; Frouzakis, Christos E; Boulouchos, Konstantinos; Karlin, Iliya V

    2016-05-26

    The Spectral Quasi-Equilibrium Manifold (SQEM) method is a model reduction technique for chemical kinetics based on entropy maximization under constraints built by the slowest eigenvectors at equilibrium. The method is revisited here and discussed and validated through the Michaelis-Menten kinetic scheme, and the quality of the reduction is related to the temporal evolution and the gap between eigenvalues. SQEM is then applied to detailed reaction mechanisms for the homogeneous combustion of hydrogen, syngas, and methane mixtures with air in adiabatic constant pressure reactors. The system states computed using SQEM are compared with those obtained by direct integration of the detailed mechanism, and good agreement between the reduced and the detailed descriptions is demonstrated. The SQEM reduced model of hydrogen/air combustion is also compared with another similar technique, the Rate-Controlled Constrained-Equilibrium (RCCE). For the same number of representative variables, SQEM is found to provide a more accurate description.

  17. On the Concept "Chemical Equilibrium": The Associative Framework.

    ERIC Educational Resources Information Center

    Gussarsky, Esther; Gorodetsky, Malka

    1990-01-01

    Word associations were used to map high school students' concepts of "chemical equilibrium" and "equilibrium." It was found that the preconception of the two concepts was differentiated on noncritical dimensions. (Author/CW)

  18. On the Concept "Chemical Equilibrium": The Associative Framework.

    ERIC Educational Resources Information Center

    Gussarsky, Esther; Gorodetsky, Malka

    1990-01-01

    Word associations were used to map high school students' concepts of "chemical equilibrium" and "equilibrium." It was found that the preconception of the two concepts was differentiated on noncritical dimensions. (Author/CW)

  19. A Lakatosian Conceptual Change Teaching Strategy Based on Student Ability To Build Models with Varying Degrees of Conceptual Understanding of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Niaz, Mansoor

    1998-01-01

    Reports on a study that constructs a Lakatosian teaching strategy that can facilitate conceptual change in students' understanding of chemical equilibrium. Results indicate that the experimental group performed better on tests. Contains 81 references. (DDR)

  20. Computations of fluid mixtures including solid carbon at chemical equilibrium

    NASA Astrophysics Data System (ADS)

    Bourasseau, Emeric

    2013-06-01

    One of the key points of the understanding of detonation phenomena is the determination of equation of state of the detonation products mixture. Concerning carbon rich explosives, detonation products mixtures are composed of solid carbon nano-clusters immersed in a high density fluid phase. The study of such systems where both chemical and phase equilibriums occur simultaneously represents an important challenge and molecular simulation methods appear to be one of the more promising way to obtain some answers. In this talk, the Reaction Ensemble Monte Carlo (RxMC) method will be presented. This method allows the system to reach the chemical equilibrium of a mixture driven by a set of linearly independent chemical equations. Applied to detonation product mixtures, it allows the calculation of the chemical composition of the mixture and its thermodynamic properties. Moreover, an original model has been proposed to take explicitly into account a solid carbon meso-particle in thermodynamic and chemical equilibrium with the fluid. Finally our simulations show that the intrinsic inhomogeneous nature of the system (i.e. the fact that the solid phase is immersed in the fluid phase) has an important impact on the thermodynamic properties, and as a consequence must be taken into account.

  1. Implementing an Equilibrium Law Teaching Sequence for Secondary School Students to Learn Chemical Equilibrium

    ERIC Educational Resources Information Center

    Ghirardi, Marco; Marchetti, Fabio; Pettinari, Claudio; Regis, Alberto; Roletto, Ezio

    2015-01-01

    A didactic sequence is proposed for the teaching of chemical equilibrium law. In this approach, we have avoided the kinetic derivation and the thermodynamic justification of the equilibrium constant. The equilibrium constant expression is established empirically by a trial-and-error approach. Additionally, students learn to use the criterion of…

  2. Implementing an Equilibrium Law Teaching Sequence for Secondary School Students to Learn Chemical Equilibrium

    ERIC Educational Resources Information Center

    Ghirardi, Marco; Marchetti, Fabio; Pettinari, Claudio; Regis, Alberto; Roletto, Ezio

    2015-01-01

    A didactic sequence is proposed for the teaching of chemical equilibrium law. In this approach, we have avoided the kinetic derivation and the thermodynamic justification of the equilibrium constant. The equilibrium constant expression is established empirically by a trial-and-error approach. Additionally, students learn to use the criterion of…

  3. Sparse Partial Equilibrium Tables in Chemically Resolved Reactive Flow

    NASA Astrophysics Data System (ADS)

    Vitello, Peter; Fried, Laurence E.; Pudliner, Brian; McAbee, Tom

    2004-07-01

    The detonation of an energetic material is the result of a complex interaction between kinetic chemical reactions and hydrodynamics. Unfortunately, little is known concerning the detailed chemical kinetics of detonations in energetic materials. CHEETAH uses rate laws to treat species with the slowest chemical reactions, while assuming other chemical species are in equilibrium. CHEETAH supports a wide range of elements and condensed detonation products and can also be applied to gas detonations. A sparse hash table of equation of state values is used in CHEETAH to enhance the efficiency of kinetic reaction calculations. For large-scale parallel hydrodynamic calculations, CHEETAH uses parallel communication to updates to the cache. We present here details of the sparse caching model used in the CHEETAH coupled to an ALE hydrocode. To demonstrate the efficiency of modeling using a sparse cache model we consider detonations in energetic materials.

  4. Sparse Partial Equilibrium Tables in Chemically Resolved Reactive Flow

    SciTech Connect

    Vitello, P; Fried, L E; Pudliner, B; McAbee, T

    2003-07-14

    The detonation of an energetic material is the result of a complex interaction between kinetic chemical reactions and hydrodynamics. Unfortunately, little is known concerning the detailed chemical kinetics of detonations in energetic materials. CHEETAH uses rate laws to treat species with the slowest chemical reactions, while assuming other chemical species are in equilibrium. CHEETAH supports a wide range of elements and condensed detonation products and can also be applied to gas detonations. A sparse hash table of equation of state values, called the ''cache'' is used in CHEETAH to enhance the efficiency of kinetic reaction calculations. For large-scale parallel hydrodynamic calculations, CHEETAH uses MPI communication to updates to the cache. We present here details of the sparse caching model used in the CHEETAH. To demonstrate the efficiency of modeling using a sparse cache model we consider detonations in energetic materials.

  5. Teaching Chemical Equilibrium and Thermodynamics in Undergraduate General Chemistry Classes.

    ERIC Educational Resources Information Center

    Banerjee, Anil C.

    1995-01-01

    Discusses some of the conceptual difficulties encountered by undergraduate students in learning certain aspects of chemical equilibrium and thermodynamics. Discusses teaching strategies for dealing with these difficulties. (JRH)

  6. Teaching Chemical Equilibrium and Thermodynamics in Undergraduate General Chemistry Classes.

    ERIC Educational Resources Information Center

    Banerjee, Anil C.

    1995-01-01

    Discusses some of the conceptual difficulties encountered by undergraduate students in learning certain aspects of chemical equilibrium and thermodynamics. Discusses teaching strategies for dealing with these difficulties. (JRH)

  7. Misconceptions of Students and Teachers in Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Banerjee, Anil C.

    1991-01-01

    Written test was developed and administered to diagnose misconceptions in different areas of chemical equilibrium among 162 undergraduate chemistry students and 69 teachers of chemistry. Responses reveal widespread misconceptions among students and teachers in areas related to the prediction of equilibrium conditions, rate and equilibrium,…

  8. Boltzmann equation solver adapted to emergent chemical non-equilibrium

    SciTech Connect

    Birrell, Jeremiah; Wilkening, Jon; Rafelski, Johann

    2015-01-15

    We present a novel method to solve the spatially homogeneous and isotropic relativistic Boltzmann equation. We employ a basis set of orthogonal polynomials dynamically adapted to allow for emergence of chemical non-equilibrium. Two time dependent parameters characterize the set of orthogonal polynomials, the effective temperature T(t) and phase space occupation factor ϒ(t). In this first paper we address (effectively) massless fermions and derive dynamical equations for T(t) and ϒ(t) such that the zeroth order term of the basis alone captures the particle number density and energy density of each particle distribution. We validate our method and illustrate the reduced computational cost and the ability to easily represent final state chemical non-equilibrium by studying a model problem that is motivated by the physics of the neutrino freeze-out processes in the early Universe, where the essential physical characteristics include reheating from another disappearing particle component (e{sup ±}-annihilation)

  9. Non-equilibrium effects in high temperature chemical reactions

    NASA Technical Reports Server (NTRS)

    Johnson, Richard E.

    1987-01-01

    Reaction rate data were collected for chemical reactions occurring at high temperatures during reentry of space vehicles. The principle of detailed balancing is used in modeling kinetics of chemical reactions at high temperatures. Although this principle does not hold for certain transient or incubation times in the initial phase of the reaction, it does seem to be valid for the rates of internal energy transitions that occur within molecules and atoms. That is, for every rate of transition within the internal energy states of atoms or molecules, there is an inverse rate that is related through an equilibrium expression involving the energy difference of the transition.

  10. The Lewis Chemical Equilibrium Program with parametric study capability

    NASA Technical Reports Server (NTRS)

    Sevigny, R.

    1981-01-01

    The program was developed to determine chemical equilibrium in complex systems. Using a free energy minimization technique, the program permits calculations such as: chemical equilibrium for assigned thermodynamic states; theoretical rocket performance for both equilibrium and frozen compositions during expansion; incident and reflected shock properties; and Chapman-Jouget detonation properties. It is shown that the same program can handle solid coal in an entrained flow coal gasification problem.

  11. Conceptual Integration of Chemical Equilibrium by Prospective Physical Sciences Teachers

    ERIC Educational Resources Information Center

    Ganaras, Kostas; Dumon, Alain; Larcher, Claudine

    2008-01-01

    This article describes an empirical study concerning the mastering of the chemical equilibrium concept by prospective physical sciences teachers. The main objective was to check whether the concept of chemical equilibrium had become an integrating and unifying concept for them, that is to say an operational and functional knowledge to explain and…

  12. Using Analogies to Prevent Misconceptions about Chemical Equilibrium

    ERIC Educational Resources Information Center

    Sahin Pekmez, Esin

    2010-01-01

    The main purpose of this study was to find the effectiveness of using analogies to prevent misconceptions about chemical equilibrium. Nineteen analogies, which were based on dynamic aspects of chemical equilibrium and application of Le Chatelier's principle, were developed. The participations of this study consisted of 11th grade students (n: 151)…

  13. Conceptual Integration of Chemical Equilibrium by Prospective Physical Sciences Teachers

    ERIC Educational Resources Information Center

    Ganaras, Kostas; Dumon, Alain; Larcher, Claudine

    2008-01-01

    This article describes an empirical study concerning the mastering of the chemical equilibrium concept by prospective physical sciences teachers. The main objective was to check whether the concept of chemical equilibrium had become an integrating and unifying concept for them, that is to say an operational and functional knowledge to explain and…

  14. Using Analogies to Prevent Misconceptions about Chemical Equilibrium

    ERIC Educational Resources Information Center

    Sahin Pekmez, Esin

    2010-01-01

    The main purpose of this study was to find the effectiveness of using analogies to prevent misconceptions about chemical equilibrium. Nineteen analogies, which were based on dynamic aspects of chemical equilibrium and application of Le Chatelier's principle, were developed. The participations of this study consisted of 11th grade students (n: 151)…

  15. Chemical Equilibrium Models for the S3 State of the Oxygen-Evolving Complex of Photosystem II.

    PubMed

    Isobe, Hiroshi; Shoji, Mitsuo; Shen, Jian-Ren; Yamaguchi, Kizashi

    2016-01-19

    We have performed hybrid density functional theory (DFT) calculations to investigate how chemical equilibria can be described in the S3 state of the oxygen-evolving complex in photosystem II. For a chosen 340-atom model, 1 stable and 11 metastable intermediates have been identified within the range of 13 kcal mol(-1) that differ in protonation, charge, spin, and conformational states. The results imply that reversible interconversion of these intermediates gives rise to dynamic equilibria that involve processes with relocations of protons and electrons residing in the Mn4CaO5 cluster, as well as bound water ligands, with concomitant large changes in the cluster geometry. Such proton tautomerism and redox isomerism are responsible for reversible activation/deactivation processes of substrate oxygen species, through which Mn-O and O-O bonds are transiently ruptured and formed. These results may allow for a tentative interpretation of kinetic data on substrate water exchange on the order of seconds at room temperature, as measured by time-resolved mass spectrometry. The reliability of the hybrid DFT method for the multielectron redox reaction in such an intricate system is also addressed.

  16. Use of a chemical equilibrium model to describe surface properties and uptake of cadmium, strontium, and lead by Chlorella (UTEX 252)

    SciTech Connect

    Hassett, J.M.

    1988-01-01

    Metal-aquatic biota interactions are important in both natural and engineered systems. In this study, the uptake of cadmium, strontium and lead by the unicellular green alga Chlorella (UTEX 252) was investigated. Variables included metal concentration, pH, and ionic strength. Data gathered included dry weights (mg/l), cell counts (cells/ml), electrophoretic mobilities (EPMs, {mu}m/sec/V/cm) of metal-free and metal-exposed cells, and metal uptake - difference in concentration in filtrate of cell-metal and cell-free metal solutions. Derived data included cell volumes and surface area, uptake on a {mu}M/m{sup 2} basis, {zeta}-potentials, diffuse layer potentials and charge densities. Typical uptake values were 1.1, 5.2, and 6 {mu}M/m{sup 2} for Cd, Pb, and Sr, respectively, from solutions of pH 6, ionic strength 0.02M, and metal concentration 10{sup {minus}4} M. Cell EPMs were insensitive to metal; under certain conditions, however, (pM > 4, pH > 8), cadmium exposed cells exhibited a reversal in surface charge from negative to positive. The chemical equilibrium model MINEQL1 + STANFORD was used to model algal surface properties and metal uptake. Input data included site pK, density, and {Delta}pK, estimated from EPM-pH data. The model described surface properties of Chlorella (UTEX 252) as judged by a close fit of {zeta}-potentials and model-derived diffuse layer potentials. Metal uptake was modelled by adjusting site density and/or metal-surface site equilibrium constants. Attempts to model surface properties and metal uptake simultaneously were not successful.

  17. Nanomechanics Model for Static Equilibrium

    NASA Astrophysics Data System (ADS)

    Jung, Sunghoon

    2002-09-01

    This study presented a computational technique to model and simulate atomistic behavior of materials under static loads, Interatomic potential energy was used to maintain equilibrium among atoms under static loads and constraints, In addition, the atomistic model was coupled with the finite element analysis model so that more flexible loads and constraints could be applied to the atomistic model A multi-scale technique was also presented for some single wall nanotubes of both zigzag and armchair and then their effective stiffness were estimated Those designed nanotubes are woven into fabric composites, which can be used in various military applications including body armored, vehicles, and infantry transportation vehicles because advanced nano- composites could be much lighter and stronger than current ones, Some example problems were presented to illustrate the developed technique for the nano-composites and SWNTs, The proposed technique for nanomechanics can be used for design and analysis of materials at the atomic or molecular level,

  18. Transverse-momentum spectra of strange particles produced in Pb+Pb collisions at = 2.76 TeV in the chemical non-equilibrium model

    NASA Astrophysics Data System (ADS)

    Florkowski, Wojciech

    2017-01-01

    It is first shown that recent problems in heavy-ion collisions at the LHC energies, connected with thermal description of the proton yield and the pion spectra at low transverse-momenta, can be simultaneously explained within a chemical non-equilibrium statistical hadronization framework. Then the predictions of this approach for the production of strange particles are presented.

  19. Chemical Equilibrium Composition of Aqueous Systems

    SciTech Connect

    1996-12-30

    MINEQL is a subroutine package to calculate equilibrium composition of an aqueous system, accounting for mass transfer. MINEQL-EIR contains an additional base on enthalpy and heat capacity data and has the option to do calculations at temperatures different from 25 degrees C.

  20. Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks

    ERIC Educational Resources Information Center

    Cloonan, Carrie A.; Nichol, Carolyn A.; Hutchinson, John S.

    2011-01-01

    Chemical reaction kinetics and equilibrium are essential core concepts of chemistry but are challenging topics for many students, both at the high school and undergraduate university level. Visualization at the molecular level is valuable to aid understanding of reaction kinetics and equilibrium. This activity provides a discovery-based method to…

  1. Thermodynamic and transport properties of gaseous tetrafluoromethane in chemical equilibrium

    NASA Technical Reports Server (NTRS)

    Hunt, J. L.; Boney, L. R.

    1973-01-01

    Equations and in computer code are presented for the thermodynamic and transport properties of gaseous, undissociated tetrafluoromethane (CF4) in chemical equilibrium. The computer code calculates the thermodynamic and transport properties of CF4 when given any two of five thermodynamic variables (entropy, temperature, volume, pressure, and enthalpy). Equilibrium thermodynamic and transport property data are tabulated and pressure-enthalpy diagrams are presented.

  2. A Better Way of Dealing with Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Tykodi, Ralph J.

    1986-01-01

    Discusses how to address the concept of chemical equilibrium through the use of thermodynamic activities. Describes the advantages of setting up an equilibrium constant in terms of activities and demonstrates how to approximate those activities by practical measures such as partial pressures, mole fractions, and molar concentrations. (TW)

  3. Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks

    ERIC Educational Resources Information Center

    Cloonan, Carrie A.; Nichol, Carolyn A.; Hutchinson, John S.

    2011-01-01

    Chemical reaction kinetics and equilibrium are essential core concepts of chemistry but are challenging topics for many students, both at the high school and undergraduate university level. Visualization at the molecular level is valuable to aid understanding of reaction kinetics and equilibrium. This activity provides a discovery-based method to…

  4. Students' Systematic Errors When Solving Kinetic and Chemical Equilibrium Problems.

    ERIC Educational Resources Information Center

    BouJaoude, Saouma

    Although students' misconceptions about the concept of chemical equilibrium has been the focus of numerous investigations, few have investigated students' systematic errors when solving equilibrium problems at the college level. Students (n=189) enrolled in the second semester of a first year chemistry course for science and engineering majors at…

  5. Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and >3D< Models. II. Chemical Properties of the Galactic Metal-poor Disk and the Halo

    NASA Astrophysics Data System (ADS)

    Bergemann, Maria; Collet, Remo; Schönrich, Ralph; Andrae, Rene; Kovalev, Mikhail; Ruchti, Greg; Hansen, Camilla Juul; Magic, Zazralt

    2017-09-01

    From exploratory studies and theoretical expectations it is known that simplifying approximations in spectroscopic analysis (local thermodynamic equilibrium (LTE), 1D) lead to systematic biases of stellar parameters and abundances. These biases depend strongly on surface gravity, temperature and, in particular, for LTE versus non-LTE (NLTE), on metallicity of the stars. Here we analyze the [Mg/Fe] and [Fe/H] plane of a sample of 326 stars, comparing LTE and NLTE results obtained using 1D hydrostatic models and averaged <3D> models. We show that compared to the <3D> NLTE benchmark, the other three methods display increasing biases toward lower metallicities, resulting in false trends of [Mg/Fe] against [Fe/H], which have profound implications for interpretations by chemical evolution models. In our best <3D> NLTE model, the halo and disk stars show a clearer behavior in the [Mg/Fe]–[Fe/H] plane, from the knee in abundance space down to the lowest metallicities. Our sample has a large fraction of thick disk stars and this population extends down to at least [Fe/H] ∼ ‑1.6 dex, further than previously proven. The thick disk stars display a constant [Mg/Fe] ≈ 0.3 dex, with a small intrinsic dispersion in [Mg/Fe] that suggests that a fast SN Ia channel is not relevant for the disk formation. The halo stars reach higher [Mg/Fe] ratios and display a net trend of [Mg/Fe] at low metallicities, paired with a large dispersion in [Mg/Fe]. These indicate the diverse origin of halo stars from accreted low-mass systems to stochastic/inhomogeneous chemical evolution in the Galactic halo.

  6. Evidence-Based Approaches to Improving Chemical Equilibrium Instruction

    ERIC Educational Resources Information Center

    Davenport, Jodi L.; Leinhardt, Gaea; Greeno, James; Koedinger, Kenneth; Klahr, David; Karabinos, Michael; Yaron, David J.

    2014-01-01

    Two suggestions for instruction in chemical equilibrium are presented, along with the evidence that supports these suggestions. The first is to use diagrams to connect chemical reactions to the effects of reactions on concentrations. The second is the use of the majority and minority species (M&M) strategy to analyze chemical equilibrium…

  7. Evidence-Based Approaches to Improving Chemical Equilibrium Instruction

    ERIC Educational Resources Information Center

    Davenport, Jodi L.; Leinhardt, Gaea; Greeno, James; Koedinger, Kenneth; Klahr, David; Karabinos, Michael; Yaron, David J.

    2014-01-01

    Two suggestions for instruction in chemical equilibrium are presented, along with the evidence that supports these suggestions. The first is to use diagrams to connect chemical reactions to the effects of reactions on concentrations. The second is the use of the majority and minority species (M&M) strategy to analyze chemical equilibrium…

  8. Chemical equilibrium model for interfacial activity of crude oil in aqueous alkaline solution: the effects of pH, alkali and salt

    SciTech Connect

    Chan, M.; Yen, T.F.

    1980-11-01

    A chemical equilibrium model for interfacial activity of crude in aqueous alkaline solution is proposed. The model predicts the observed effects of pH and concentrations of alkali and salt on the interfacial tension (IFT). The model proposed was shown to describe the observed effects of acid content, pH, and sodium ions on the interfacial activity of crude oil in water. Once the pH of the interface reaches the pKa of the acids, sometimes with the help of addition of some salt, the IFT experiences a sudden steep drop to the range of 10/sup -2/ dynes/cm. After that, further addition of sodium either in the form of NaOH or NaCl is going to increase the IFT due to a shift of equilibriumn to the formation of undissociated soap. This was confirmed by the difference in the observed effect of sodium on the IFT of the extracted soap molecules which are dissociated easily and those which are associated highly and precipitated easily. These soap molecules have dissociation constant values ranging from below 10/sup -2/ to above one. 13 references.

  9. Thermal Conductivity of Gas Mixtures in Chemical Equilibrium

    NASA Technical Reports Server (NTRS)

    Brokaw, Richard S.

    1960-01-01

    The expression for the thermal conductivity of gas mixtures in chemical equilibrium is presented in a simpler and less restrictive form. This new form is shown to be equivalent to the previous equations.

  10. Chemical Equilibrium, Unit 3: Chemical Equilibrium Calculations. A Computer-Enriched Module for Introductory Chemistry. Student's Guide and Teacher's Guide.

    ERIC Educational Resources Information Center

    Jameson, Cynthia J.

    Presented are the teacher's guide and student materials for one of a series of self-instructional, computer-based learning modules for an introductory, undergraduate chemistry course. The student manual for this unit on chemical equilibrium calculations includes objectives, prerequisites, a discussion of the equilibrium constant (K), and ten…

  11. Speleothems as Examples of Chemical Equilibrium Processes.

    ERIC Educational Resources Information Center

    Wilson, James R.

    1984-01-01

    The chemical formation of speleothems such as stalactites and stalagmites is poorly understood by introductory geology instructors and misrepresented in most textbooks. Although evaporation may be a controlling factor in some caves, it is necessary to consider chemical precipitation as more important in controlling the diagenesis of calcium…

  12. Speleothems as Examples of Chemical Equilibrium Processes.

    ERIC Educational Resources Information Center

    Wilson, James R.

    1984-01-01

    The chemical formation of speleothems such as stalactites and stalagmites is poorly understood by introductory geology instructors and misrepresented in most textbooks. Although evaporation may be a controlling factor in some caves, it is necessary to consider chemical precipitation as more important in controlling the diagenesis of calcium…

  13. Wave propagation in a quasi-chemical equilibrium plasma

    NASA Technical Reports Server (NTRS)

    Fang, T.-M.; Baum, H. R.

    1975-01-01

    Wave propagation in a quasi-chemical equilibrium plasma is studied. The plasma is infinite and without external fields. The chemical reactions are assumed to result from the ionization and recombination processes. When the gas is near equilibrium, the dominant role describing the evolution of a reacting plasma is played by the global conservation equations. These equations are first derived and then used to study the small amplitude wave motion for a near-equilibrium situation. Nontrivial damping effects have been obtained by including the conduction current terms.

  14. Multicomponent Equilibrium Models for Testing Geothermometry Approaches

    SciTech Connect

    Cooper, D. Craig; Palmer, Carl D.; Smith, Robert W.; McLing, Travis L.

    2013-02-01

    Geothermometry is an important tool for estimating deep reservoir temperature from the geochemical composition of shallower and cooler waters. The underlying assumption of geothermometry is that the waters collected from shallow wells and seeps maintain a chemical signature that reflects equilibrium in the deeper reservoir. Many of the geothermometers used in practice are based on correlation between water temperatures and composition or using thermodynamic calculations based a subset (typically silica, cations or cation ratios) of the dissolved constituents. An alternative approach is to use complete water compositions and equilibrium geochemical modeling to calculate the degree of disequilibrium (saturation index) for large number of potential reservoir minerals as a function of temperature. We have constructed several “forward” geochemical models using The Geochemist’s Workbench to simulate the change in chemical composition of reservoir fluids as they migrate toward the surface. These models explicitly account for the formation (mass and composition) of a steam phase and equilibrium partitioning of volatile components (e.g., CO2, H2S, and H2) into the steam as a result of pressure decreases associated with upward fluid migration from depth. We use the synthetic data generated from these simulations to determine the advantages and limitations of various geothermometry and optimization approaches for estimating the likely conditions (e.g., temperature, pCO2) to which the water was exposed in the deep subsurface. We demonstrate the magnitude of errors that can result from boiling, loss of volatiles, and analytical error from sampling and instrumental analysis. The estimated reservoir temperatures for these scenarios are also compared to conventional geothermometers. These results can help improve estimation of geothermal resource temperature during exploration and early development.

  15. Insights: Simple Models for Teaching Equilibrium and Le Chatelier's Principle.

    ERIC Educational Resources Information Center

    Russell, Joan M.

    1988-01-01

    Presents three models that have been effective for teaching chemical equilibrium and Le Chatelier's principle: (1) the liquid transfer model, (2) the fish model, and (3) the teeter-totter model. Explains each model and its relation to Le Chatelier's principle. (MVL)

  16. Insights: Simple Models for Teaching Equilibrium and Le Chatelier's Principle.

    ERIC Educational Resources Information Center

    Russell, Joan M.

    1988-01-01

    Presents three models that have been effective for teaching chemical equilibrium and Le Chatelier's principle: (1) the liquid transfer model, (2) the fish model, and (3) the teeter-totter model. Explains each model and its relation to Le Chatelier's principle. (MVL)

  17. A Lakatosian Conceptual Change Teaching Strategy Based on Student Ability to Build Models with Varying Degrees of Conceptual Understanding of Chemical Equilibrium

    NASA Astrophysics Data System (ADS)

    Niaz, M.

    The main objective of this study is to construct a Lakatosian teaching strategy that can facilitate conceptual change in students'' understanding of chemical equilibrium. The strategy is based on the premise that cognitive conflicts must have been engendered by the students themselves in trying to cope with different problem solving strategies. Results obtained (based on Venezuelan freshman students) show that the performance of the experimental group of students was generally better (especially on the immediate post tests) than that of the control group. It is concluded that a conceptual change teaching strategy must take into consideration the following aspects: a) core beliefs of the students in the topic (cf. ''hard core'', Lakatos 1970); b) exploration of the relationship between core beliefs and student alternative conceptions (misconceptions); c) cognitive complexity of the core belief can be broken down into a series of related and probing questions; d) students resist changes in their core beliefs by postulating ''auxiliary hypotheses'' in order to resolve their contradictions; e) students'' responses based on their alternative conceptions must be considered not as wrong, but rather as models, perhaps in the same sense as used by scientists to break the complexity of a problem; and f) students'' misconceptions be considered as alternative conceptions (theories) that compete with the present scientific theories and at times recapitulate theories scientists held in the past.

  18. The conceptual change approach to teaching chemical equilibrium

    NASA Astrophysics Data System (ADS)

    Canpolat, Nurtaç; Pınarbaşı, Tacettin; Bayrakçeken, Samih; Geban, Omer

    2006-11-01

    This study investigates the effect of a conceptual change approach over traditional instruction on students’ understanding of chemical equilibrium concepts (e.g. dynamic nature of equilibrium, definition of equilibrium constant, heterogeneous equilibrium, qualitative interpreting of equilibrium constant, changing the reaction conditions). This study consisted of 85 undergraduate students from two classes enrolled on an introductory chemistry course. One of the classes was assigned randomly to the control group, and the other class was assigned randomly to the experimental group. During teaching of the topic of chemical equilibrium concepts in the chemistry curriculum, the conceptual change approach was applied in the experimental group whereas ‘traditional instruction’ was followed in the control group. The data were analyzed using analysis of covariance. The results showed that the students in the experimental group performed better compared to the control group. The average percent of correct responses of the experimental group was 70%, and that of the control group was 51%, after treatment. In addition, it was found that students’ science process skills made a statistically significant contribution to the variation in students’ understanding of chemical equilibrium concepts.

  19. Non-equilibrium modelling of transferred arcs

    NASA Astrophysics Data System (ADS)

    Haidar, J.

    1999-02-01

    A two-temperature, variable-density, arc model has been developed for description of high-current free-burning arcs, including departures from thermodynamic and chemical equilibrium in the plasma. The treatment includes the arc, the anode and the cathode and considers the separate energy balance of the electrons and the heavy particles, together with the continuity equations for these species throughout the plasma. The output includes a two-dimensional distribution for the temperatures and densities both of the electrons and of the heavy particles, plasma velocity, current density and electrical potential throughout the arc. For a 200 A arc in pure argon at 1 atm, we calculate large differences between the temperatures of the electrons and the heavy particles in the plasma region near the cathode tip, together with large departures from local chemical plasma equilibrium. In the main body of the arc at high plasma temperatures, we predict minor differences between the temperatures of the electrons and the heavy particles, which are inconsistent with recent measurements using laser-scattering techniques showing differences of up to several thousand degrees. However, we find that, for the region in front of the cathode tip, the ground-state level of the neutral atoms is overpopulated relative to the corresponding populations under conditions of LTE, in agreement with experimental observations. These departures from LTE are caused by the injection of a large mass flow of cold gas into the arc core due to arc constriction at the tip of the cathode.

  20. Temporal assessment of copper speciation, bioavailability and toxicity in UK freshwaters using chemical equilibrium and biotic ligand models: Implications for compliance with copper environmental quality standards.

    PubMed

    Lathouri, Maria; Korre, Anna

    2015-12-15

    Although significant progress has been made in understanding how environmental factors modify the speciation, bioavailability and toxicity of metals such as copper in aquatic environments, the current methods used to establish water quality standards do not necessarily consider the different geological and geochemical characteristics of a given site and the factors that affect copper fate, bioavailability potential and toxicity. In addition, the temporal variation in the concentration and bioavailable metal fraction is also important in freshwater systems. The work presented in this paper illustrates the temporal and seasonal variability of a range of water quality parameters, and Cu speciation, bioavailability and toxicity at four freshwaters sites in the UK. Rivers Coquet, Cree, Lower Clyde and Eden (Kent) were selected to cover a broad range of different geochemical environments and site characteristics. The monitoring data used covered a period of around six years at almost monthly intervals. Chemical equilibrium modelling was used to study temporal variations in Cu speciation and was combined with acute toxicity modelling to assess Cu bioavailability for two aquatic species, Daphnia magna and Daphnia pulex. The estimated copper bioavailability, toxicity levels and the corresponding ecosystem risks were analysed in relation to key water quality parameters (alkalinity, pH and DOC). Although copper concentrations did not vary much during the sampling period or between the seasons at the different sites; copper bioavailability varied markedly. In addition, through the chronic-Cu BLM-based on the voluntary risk assessment approach, the potential environmental risk in terms of the chronic toxicity was assessed. A much higher likelihood of toxicity effects was found during the cold period at all sites. It is suggested that besides the metal (copper) concentration in the surface water environment, the variability and seasonality of other important water quality

  1. CET89 - CHEMICAL EQUILIBRIUM WITH TRANSPORT PROPERTIES, 1989

    NASA Technical Reports Server (NTRS)

    Mcbride, B.

    1994-01-01

    Scientists and engineers need chemical equilibrium composition data to calculate the theoretical thermodynamic properties of a chemical system. This information is essential in the design and analysis of equipment such as compressors, turbines, nozzles, engines, shock tubes, heat exchangers, and chemical processing equipment. The substantial amount of numerical computation required to obtain equilibrium compositions and transport properties for complex chemical systems led scientists at NASA's Lewis Research Center to develop CET89, a program designed to calculate the thermodynamic and transport properties of these systems. CET89 is a general program which will calculate chemical equilibrium compositions and mixture properties for any chemical system with available thermodynamic data. Generally, mixtures may include condensed and gaseous products. CET89 performs the following operations: it 1) obtains chemical equilibrium compositions for assigned thermodynamic states, 2) calculates dilute-gas transport properties of complex chemical mixtures, 3) obtains Chapman-Jouguet detonation properties for gaseous species, 4) calculates incident and reflected shock properties in terms of assigned velocities, and 5) calculates theoretical rocket performance for both equilibrium and frozen compositions during expansion. The rocket performance function allows the option of assuming either a finite area or an infinite area combustor. CET89 accommodates problems involving up to 24 reactants, 20 elements, and 600 products (400 of which may be condensed). The program includes a library of thermodynamic and transport properties in the form of least squares coefficients for possible reaction products. It includes thermodynamic data for over 1300 gaseous and condensed species and transport data for 151 gases. The subroutines UTHERM and UTRAN convert thermodynamic and transport data to unformatted form for faster processing. The program conforms to the FORTRAN 77 standard, except for

  2. CET89 - CHEMICAL EQUILIBRIUM WITH TRANSPORT PROPERTIES, 1989

    NASA Technical Reports Server (NTRS)

    Mcbride, B.

    1994-01-01

    Scientists and engineers need chemical equilibrium composition data to calculate the theoretical thermodynamic properties of a chemical system. This information is essential in the design and analysis of equipment such as compressors, turbines, nozzles, engines, shock tubes, heat exchangers, and chemical processing equipment. The substantial amount of numerical computation required to obtain equilibrium compositions and transport properties for complex chemical systems led scientists at NASA's Lewis Research Center to develop CET89, a program designed to calculate the thermodynamic and transport properties of these systems. CET89 is a general program which will calculate chemical equilibrium compositions and mixture properties for any chemical system with available thermodynamic data. Generally, mixtures may include condensed and gaseous products. CET89 performs the following operations: it 1) obtains chemical equilibrium compositions for assigned thermodynamic states, 2) calculates dilute-gas transport properties of complex chemical mixtures, 3) obtains Chapman-Jouguet detonation properties for gaseous species, 4) calculates incident and reflected shock properties in terms of assigned velocities, and 5) calculates theoretical rocket performance for both equilibrium and frozen compositions during expansion. The rocket performance function allows the option of assuming either a finite area or an infinite area combustor. CET89 accommodates problems involving up to 24 reactants, 20 elements, and 600 products (400 of which may be condensed). The program includes a library of thermodynamic and transport properties in the form of least squares coefficients for possible reaction products. It includes thermodynamic data for over 1300 gaseous and condensed species and transport data for 151 gases. The subroutines UTHERM and UTRAN convert thermodynamic and transport data to unformatted form for faster processing. The program conforms to the FORTRAN 77 standard, except for

  3. From Chemical Forces to Chemical Rates: A Historical/Philosophical Foundation for the Teaching of Chemical Equilibrium

    ERIC Educational Resources Information Center

    Quilez, Juan

    2009-01-01

    With this paper, our main aim is to contribute to the realisation of the chemical reactivity concept, tracing the historical evolution of the concept of chemical affinity that eventually supported the concept of chemical equilibrium. We will concentrate on searching for the theoretical grounds of three key chemical equilibrium ideas: "incomplete…

  4. From Chemical Forces to Chemical Rates: A Historical/Philosophical Foundation for the Teaching of Chemical Equilibrium

    ERIC Educational Resources Information Center

    Quilez, Juan

    2009-01-01

    With this paper, our main aim is to contribute to the realisation of the chemical reactivity concept, tracing the historical evolution of the concept of chemical affinity that eventually supported the concept of chemical equilibrium. We will concentrate on searching for the theoretical grounds of three key chemical equilibrium ideas: "incomplete…

  5. Developing Secondary Students' Conceptions of Chemical Reactions: The Introduction of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Van Driel, Jan H.; De Vos, Wobbe; Verloop, Nico; Dekkers, Hetty

    1998-01-01

    Describes an empirical study concerning the introduction of the concept of chemical equilibrium in chemistry classrooms in a way which challenges students' initial conceptions of chemical reactions. Contains 23 references. (DDR)

  6. Developing Secondary Students' Conceptions of Chemical Reactions: The Introduction of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Van Driel, Jan H.; De Vos, Wobbe; Verloop, Nico; Dekkers, Hetty

    1998-01-01

    Describes an empirical study concerning the introduction of the concept of chemical equilibrium in chemistry classrooms in a way which challenges students' initial conceptions of chemical reactions. Contains 23 references. (DDR)

  7. Chemical-equilibrium calculations for aqueous geothermal brines

    SciTech Connect

    Kerrisk, J.F.

    1981-05-01

    Results from four chemical-equilibrium computer programs, REDEQL.EPAK, GEOCHEM, WATEQF, and SENECA2, have been compared with experimental solubility data for some simple systems of interest with geothermal brines. Seven test cases involving solubilities of CaCO/sub 3/, amorphous SiO/sub 2/, CaSO/sub 4/, and BaSO/sub 4/ at various temperatures from 25 to 300/sup 0/C and in NaCl or HCl solutions of 0 to 4 molal have been examined. Significant differences between calculated results and experimental data occurred in some cases. These differences were traced to inaccuracies in free-energy or equilibrium-constant data and in activity coefficients used by the programs. Although currently available chemical-equilibrium programs can give reasonable results for these calculations, considerable care must be taken in the selection of free-energy data and methods of calculating activity coefficients.

  8. Modeling of thermal and chemical non-equilibrium in a laser-induced aluminum plasma by means of a Collisional-Radiative model

    NASA Astrophysics Data System (ADS)

    Morel, V.; Bultel, A.; Chéron, B. G.

    2010-09-01

    A 0D numerical approach including a Collisional-Radiative model is elaborated in the purpose of describing the behavior of the nascent plasma resulting from the interaction between a 4 ns/65 mJ/532 nm Q-switched Nd:YAG laser pulse and an aluminum sample in vacuum. The heavy species considered are Al, Al +, Al 2+ and Al 3+ on their different excited states and free electrons. The translation temperatures of free electrons and heavy species are assumed different ( T e and TA respectively). Numerous elementary processes are accounted for as electron impact induced excitation and ionization, elastic collisions, multiphoton ionization and inverse Bremsstrahlung. Atoms passing from the sample to gas phase are described by using classical vaporization theory so that the surface temperature is arbitrarily limited to values less than the critical point one at 6700 K. The laser flux density considered in the study is therefore moderate with a fluence lower than 7 J cm - 2 . This model puts forward the major influence of multiphoton ionization in the plasma formation, whereas inverse Bremsstrahlung turns out to be quasi negligible. The increase of electron temperature is mainly due to multiphoton ionization and Te does not exceed 10,000 K. The electron induced collisions play an important role during the subsequent phase which corresponds to the relaxation of the excited states toward Boltzmann equilibrium. The electron density reaches its maximum during the laser pulse with a value ≈ 10 22, 10 23 m - 3 depending highly on the sample temperature. The ionization degree is of some percents in our conditions.

  9. Chemical Equilibrium and Polynomial Equations: Beware of Roots.

    ERIC Educational Resources Information Center

    Smith, William R.; Missen, Ronald W.

    1989-01-01

    Describes two easily applied mathematical theorems, Budan's rule and Rolle's theorem, that in addition to Descartes's rule of signs and intermediate-value theorem, are useful in chemical equilibrium. Provides examples that illustrate the use of all four theorems. Discusses limitations of the polynomial equation representation of chemical…

  10. Computer program determines chemical composition of physical system at equilibrium

    NASA Technical Reports Server (NTRS)

    Kwong, S. S.

    1966-01-01

    FORTRAN 4 digital computer program calculates equilibrium composition of complex, multiphase chemical systems. This is a free energy minimization method with solution of the problem reduced to mathematical operations, without concern for the chemistry involved. Also certain thermodynamic properties are determined as byproducts of the main calculations.

  11. Modified NASA-Lewis chemical equilibrium code for MHD applications

    NASA Technical Reports Server (NTRS)

    Sacks, R. A.; Geyer, H. K.; Grammel, S. J.; Doss, E. D.

    1979-01-01

    A substantially modified version of the NASA-Lewis Chemical Equilibrium Code was recently developed. The modifications were designed to extend the power and convenience of the Code as a tool for performing combustor analysis for MHD systems studies. The effect of the programming details is described from a user point of view.

  12. Clarifying the Concept of Equilibrium in Chemically Reacting Systems.

    ERIC Educational Resources Information Center

    Harris, W. F.

    1982-01-01

    Offers a critique of the conventional approach to teaching of equilibrium in chemically reacting systems and outlines a more satisfactory approach. This approach is based not in kinetics but in the basic principles of thermodynamics. The approach is especially useful for the advanced student. (Author/JN)

  13. Computer Series, 108. Computer Simulation of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Cullen, John F., Jr.

    1989-01-01

    Presented is a computer simulation called "The Great Chemical Bead Game" which can be used to teach the concepts of equilibrium and kinetics to introductory chemistry students more clearly than through an experiment. Discussed are the rules of the game, the application of rate laws and graphical analysis. (CW)

  14. Chemical equilibrium of ablation materials including condensed species

    NASA Technical Reports Server (NTRS)

    Stroud, C. W.; Brinkley, K. L.

    1975-01-01

    Equilibrium is determined by finding chemical composition with minimum free energy. Method of steepest descent is applied to quadratic representation of free-energy surface. Solution is initiated by selecting arbitrary set of mole fractions, from which point on free-energy surface is computed.

  15. Chemical Equilibrium and Polynomial Equations: Beware of Roots.

    ERIC Educational Resources Information Center

    Smith, William R.; Missen, Ronald W.

    1989-01-01

    Describes two easily applied mathematical theorems, Budan's rule and Rolle's theorem, that in addition to Descartes's rule of signs and intermediate-value theorem, are useful in chemical equilibrium. Provides examples that illustrate the use of all four theorems. Discusses limitations of the polynomial equation representation of chemical…

  16. Composition and Thermodynamic Properties of Air in Chemical Equilibrium

    NASA Technical Reports Server (NTRS)

    Moeckel, W E; Weston, Kenneth C

    1958-01-01

    Charts have been prepared relating the thermodynamic properties of air in chemical equilibrium for temperatures to 15,000 degrees k and for pressures 10(-5) to 10 (plus 4) atmospheres. Also included are charts showing the composition of air, the isentropic exponent, and the speed of sound. These charts are based on thermodynamic data calculated by the National Bureau of Standards.

  17. Treatment of Chemical Equilibrium without Using Thermodynamics or Statistical Mechanics.

    ERIC Educational Resources Information Center

    Nelson, P. G.

    1986-01-01

    Discusses the conventional approaches to teaching about chemical equilibrium in advanced physical chemistry courses. Presents an alternative approach to the treatment of this concept by using Boltzmann's distribution law. Lists five advantages to using this method as compared with the other approaches. (TW)

  18. On the calculation of equilibrium thermodynamic properties and the establishment of statistical-thermodynamically-consistent finite bound-state partition functions in nonideal multicomponent plasma mixtures within the chemical model

    SciTech Connect

    Zaghloul, Mofreh R.

    2010-12-15

    The problem of the calculation of equilibrium thermodynamic properties and the establishment of statistical-thermodynamically consistent finite bound-state partition functions in nonideal multicomponent plasma systems is revised within the chemical picture. The present exploration accompanied by the introduction of a generalized consistent formulation, in terms of the solution of the inverse problem, clears ambiguities and gives a better understanding of the problem on top of pointing out weaknesses and inaccuracies/inconsistencies buried in widely used models in literature.

  19. An analytical model of crater count equilibrium

    NASA Astrophysics Data System (ADS)

    Hirabayashi, Masatoshi; Minton, David A.; Fassett, Caleb I.

    2017-06-01

    Crater count equilibrium occurs when new craters form at the same rate that old craters are erased, such that the total number of observable impacts remains constant. Despite substantial efforts to understand this process, there remain many unsolved problems. Here, we propose an analytical model that describes how a heavily cratered surface reaches a state of crater count equilibrium. The proposed model formulates three physical processes contributing to crater count equilibrium: cookie-cutting (simple, geometric overlap), ejecta-blanketing, and sandblasting (diffusive erosion). These three processes are modeled using a degradation parameter that describes the efficiency for a new crater to erase old craters. The flexibility of our newly developed model allows us to represent the processes that underlie crater count equilibrium problems. The results show that when the slope of the production function is steeper than that of the equilibrium state, the power law of the equilibrium slope is independent of that of the production function slope. We apply our model to the cratering conditions in the Sinus Medii region and at the Apollo 15 landing site on the Moon and demonstrate that a consistent degradation parameterization can successfully be determined based on the empirical results of these regions. Further developments of this model will enable us to better understand the surface evolution of airless bodies due to impact bombardment.

  20. Clouds Composition in Super-Earth Atmospheres: Chemical Equilibrium Calculations

    NASA Astrophysics Data System (ADS)

    Kempton, Eliza M.-R.; Mbarek, Rostom

    2015-12-01

    Attempts to determine the composition of super-Earth atmospheres have so far been plagued by the presence of clouds. Yet the theoretical framework to understand these clouds is still in its infancy. For the super-Earth archetype GJ 1214b, KCl, Na2S, and ZnS have been proposed as condensates that would form under the condition of chemical equilibrium, if the planet’s atmosphere has a bulk composition near solar. Condensation chemistry calculations have not been presented for a wider range of atmospheric bulk composition that is to be expected for super-Earth exoplanets. Here we provide a theoretical context for the formation of super-Earth clouds in atmospheres of varied composition by determining which condensates are likely to form, under the assumption of chemical equilibrium. We model super-Earth atmospheres assuming they are formed by degassing of volatiles from a solid planetary core of chondritic material. Given the atomic makeup of these atmospheres, we minimize the global Gibbs free energy of over 550 gases and condensates to obtain the molecular composition of the atmospheres over a temperature range of 350-3,000 K. Clouds should form along the temperature-pressure boundaries where the condensed species appear in our calculations. The super-Earth atmospheres that we study range from highly reducing to oxidizing and have carbon to oxygen (C:O) ratios that are both sub-solar and super-solar, thereby spanning a diverse range of atmospheric composition that is appropriate for low-mass exoplanets. Some condensates appear across all of our models. However, the majority of condensed species appear only over specific ranges of H:O and C:O ratios. We find that for GJ 1214b, KCl is the primary cloud-forming condensate at solar composition, in agreement with previous work. However, for oxidizing atmospheres, where H:O is less than unity, K2SO4 clouds form instead. For carbon-rich atmospheres with super-solar C:O ratios, graphite clouds additionally appear. At

  1. Problem solving and chemical equilibrium: Successful versus unsuccessful performance

    NASA Astrophysics Data System (ADS)

    Camacho, Moises; Good, Ron

    The purpose of this study was to describe the problem-solving behaviors of experts and novices engaged in solving seven chemical equilibrium problems. Thirteen novices (five high-school students, five undergraduate majors, and three nonmajors) and ten experts (six doctoral students and four faculty members) were videotaped as they individually solved standard chemical equilibrium problems. The nature of the problems was such that they required more than mere recall or algorithmic learning and yet simple enough to provide the novices a reasonable chance of solving them. Extensive analysis of the think-aloud protocols produced 27 behavioral tendencies that can be used to describe and differentiate between successful and unsuccessful problem solvers. Successful solvers' perceptions of the problem were characterized by careful analysis and reasoning of the task, use of related principles and concepts to justify their answers, frequent checks of the consistency of answers and reasons, and better quality of procedural and strategic knowledge. Unsuccessful subjects had many knowledge gaps and misconceptions about the nature of chemical equilibrium. Even faculty experts were sometimes unable to correctly apply common chemical principles during the problem-solving process. Important theoretical concepts such as molar enthalpy, heat of reaction, free energy of formation, and free energy of reaction were rarely used by novices in explaining problems.

  2. The efficiency of driving chemical reactions by a physical non-equilibrium is kinetically controlled.

    PubMed

    Göppel, Tobias; Palyulin, Vladimir V; Gerland, Ulrich

    2016-07-27

    An out-of-equilibrium physical environment can drive chemical reactions into thermodynamically unfavorable regimes. Under prebiotic conditions such a coupling between physical and chemical non-equilibria may have enabled the spontaneous emergence of primitive evolutionary processes. Here, we study the coupling efficiency within a theoretical model that is inspired by recent laboratory experiments, but focuses on generic effects arising whenever reactant and product molecules have different transport coefficients in a flow-through system. In our model, the physical non-equilibrium is represented by a drift-diffusion process, which is a valid coarse-grained description for the interplay between thermophoresis and convection, as well as for many other molecular transport processes. As a simple chemical reaction, we consider a reversible dimerization process, which is coupled to the transport process by different drift velocities for monomers and dimers. Within this minimal model, the coupling efficiency between the non-equilibrium transport process and the chemical reaction can be analyzed in all parameter regimes. The analysis shows that the efficiency depends strongly on the Damköhler number, a parameter that measures the relative timescales associated with the transport and reaction kinetics. Our model and results will be useful for a better understanding of the conditions for which non-equilibrium environments can provide a significant driving force for chemical reactions in a prebiotic setting.

  3. Exploring Chemical Equilibrium with Poker Chips: A General Chemistry Laboratory Exercise

    ERIC Educational Resources Information Center

    Bindel, Thomas H.

    2012-01-01

    A hands-on laboratory exercise at the general chemistry level introduces students to chemical equilibrium through a simulation that uses poker chips and rate equations. More specifically, the exercise allows students to explore reaction tables, dynamic chemical equilibrium, equilibrium constant expressions, and the equilibrium constant based on…

  4. Exploring Chemical Equilibrium with Poker Chips: A General Chemistry Laboratory Exercise

    ERIC Educational Resources Information Center

    Bindel, Thomas H.

    2012-01-01

    A hands-on laboratory exercise at the general chemistry level introduces students to chemical equilibrium through a simulation that uses poker chips and rate equations. More specifically, the exercise allows students to explore reaction tables, dynamic chemical equilibrium, equilibrium constant expressions, and the equilibrium constant based on…

  5. GEOMETRIC PROGRAMMING, CHEMICAL EQUILIBRIUM, AND THE ANTI-ENTROPY FUNCTION*

    PubMed Central

    Duffin, R. J.; Zener, C.

    1969-01-01

    The culmination of this paper is the following duality principle of thermodynamics: maximum S = minimum S*. (1) The left side of relation (1) is the classical characterization of equilibrium. It says to maximize the entropy function S with respect to extensive variables which are subject to certain constraints. The right side of (1) is a new characterization of equilibrium and concerns minimization of an anti-entropy function S* with respect to intensive variables. Relation (1) is applied to the chemical equilibrium of a mixture of gases at constant temperature and volume. Then (1) specializes to minimum F = maximum F*, (2) where F is the Helmholtz function for free energy and F* is an anti-Helmholtz function. The right-side of (2) is an unconstrained maximization problem and gives a simplified practical procedure for calculating equilibrium concentrations. We also give a direct proof of (2) by the duality theorem of geometric programming. The duality theorem of geometric programming states that minimum cost = maximum anti-cost. (30) PMID:16591769

  6. Chemical equilibrium in high pressure molecular fluid mixtures

    SciTech Connect

    Shaw, M.S.

    1993-09-01

    The N{sub atoms}PT Monte Carlo simulation method has been reformulated to incorporate multiple species and chemical reactions with changes in total number of molecules. While maintaining a constant number of each type of atom, the number of molecules is changed by turning on and off the interactions of any particular position with other molecules. Chemical reactions are allowed as a correlated move of atoms to differnt molecular locations. Equilibrium chemical composition is determined as an average over the simulation along with equation of state quantities. A large set of simulations has been made with the system N{sub 2} + O{sub 2} {rightleftharpoons} NO covering a wide range in P and T. Both Hugoniot states and the CJ point have been determined and are shown to be sensitive to the potentials between unlike species.

  7. Equilibrium-based bipolar neurological modeling.

    PubMed

    Zhang, Wen-Ran; Pandurangi, Anand K; Peace, Karl E

    2006-01-01

    This work introduces an equilibrium-based dynamic model for the characterization, classification, and diagnostic analysis of bipolar disorder, a psychiatric syndrome with manic and depressive phases. The new model extends the traditional spectrum model of mood states from a static and closed world to a dynamic open-world of equilibria with a bipolar universal modus ponens (BUMP). The utility of the new model is illustrated in diagnostic analysis of depression and clinical psychopharmacology of different phases of this disorder.

  8. Students' and Teachers' Misapplication of Le Chatelier's Principle: Implications for the Teaching of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Quilez-Pardo, Juan; Solaz-Portoles, Joan Josep

    1995-01-01

    Study of strategies and procedures of 170 students and 40 teachers when solving chemical equilibrium problems found misconceptions emerging through: misapplication of Le Chatelier's Principle, use of rote-learning recall, incorrect control of variables, limited use of chemical equilibrium law, lack of mastery of chemical equilibrium principles,…

  9. Students' and Teachers' Misapplication of Le Chatelier's Principle: Implications for the Teaching of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Quilez-Pardo, Juan; Solaz-Portoles, Joan Josep

    1995-01-01

    Study of strategies and procedures of 170 students and 40 teachers when solving chemical equilibrium problems found misconceptions emerging through: misapplication of Le Chatelier's Principle, use of rote-learning recall, incorrect control of variables, limited use of chemical equilibrium law, lack of mastery of chemical equilibrium principles,…

  10. Solute transport with multiple equilibrium-controlled or kinetically controlled chemical reactions

    USGS Publications Warehouse

    Friedly, John C.; Rubin, Jacob

    1992-01-01

    A new approach is applied to the problem of modeling solute transport accompanied by many chemical reactions. The approach, based on concepts of the concentration space and its stoichiometric subspaces, uses elements of the subspaces as primary dependent variables. It is shown that the resulting model equations are compact in form, isolate the chemical reaction expressions from flow expressions, and can be used for either equilibrium or kinetically controlled reactions. The implications of the results on numerical algorithms for solving the equations are discussed. The application of the theory is illustrated throughout with examples involving a simple but broadly representative set of reactions previously considered in the literature. Numerical results are presented for four interconnected reactions: a homogeneous complexation reaction, two sorption reactions, and a dissolution/precipitation reaction. Three cases are considered: (1) four kinetically controlled reactions, (2) four equilibrium-controlled reactions, and (3) a system with two kinetically controlled reactions and two equilibrium-controlled reactions.

  11. Chemical tension and global equilibrium in VLS nanostructure growth process: from nanohillocks to nanowires

    NASA Astrophysics Data System (ADS)

    Li, N.; Tan, T. Y.; Gösele, U.

    2007-03-01

    We formulate a global equilibrium model to describe the growth of one-dimensional nanostructures in the VLS process by including also the chemical tension in addition to the physical tensions, i.e. surface energies. The chemical tension derives from the Gibbs free energy change due to the growth of a crystal layer of an elementary thickness. The system global equilibrium is arrived at via the balance of the static physical tensions and the dynamic chemical tension. The model predicts and provides conditions for the growth of nanowires of all sizes exceeding a lower thermodynamic limit. The model also predicts the conditions distinguishing the growth of nanohillocks from nanowires. These predictions will allow the verification of the model by future experiments specifically designed for this purpose.

  12. Early quark production and approach to chemical equilibrium

    NASA Astrophysics Data System (ADS)

    Gelfand, D.; Hebenstreit, F.; Berges, J.

    2016-04-01

    We perform real-time lattice simulations of out-of-equilibrium quark production in non-Abelian gauge theory in 3 +1 dimensions. Our simulations include the backreaction of quarks onto the dynamical gluon sector, which is particularly relevant for strongly correlated quarks. We observe fast isotropization and universal behavior of quarks and gluons at weak coupling and establish a quantitative connection to previous pure glue results. In order to understand the strongly correlated regime, we perform simulations for a large number of flavors and compare them to those obtained with two light quark flavors. By doing this we are able to provide estimates of the chemical equilibration time.

  13. General Equilibrium Models: Improving the Microeconomics Classroom

    ERIC Educational Resources Information Center

    Nicholson, Walter; Westhoff, Frank

    2009-01-01

    General equilibrium models now play important roles in many fields of economics including tax policy, environmental regulation, international trade, and economic development. The intermediate microeconomics classroom has not kept pace with these trends, however. Microeconomics textbooks primarily focus on the insights that can be drawn from the…

  14. General Equilibrium Models: Improving the Microeconomics Classroom

    ERIC Educational Resources Information Center

    Nicholson, Walter; Westhoff, Frank

    2009-01-01

    General equilibrium models now play important roles in many fields of economics including tax policy, environmental regulation, international trade, and economic development. The intermediate microeconomics classroom has not kept pace with these trends, however. Microeconomics textbooks primarily focus on the insights that can be drawn from the…

  15. Diffusion approximations to the chemical master equation only have a consistent stochastic thermodynamics at chemical equilibrium

    SciTech Connect

    Horowitz, Jordan M.

    2015-07-28

    The stochastic thermodynamics of a dilute, well-stirred mixture of chemically reacting species is built on the stochastic trajectories of reaction events obtained from the chemical master equation. However, when the molecular populations are large, the discrete chemical master equation can be approximated with a continuous diffusion process, like the chemical Langevin equation or low noise approximation. In this paper, we investigate to what extent these diffusion approximations inherit the stochastic thermodynamics of the chemical master equation. We find that a stochastic-thermodynamic description is only valid at a detailed-balanced, equilibrium steady state. Away from equilibrium, where there is no consistent stochastic thermodynamics, we show that one can still use the diffusive solutions to approximate the underlying thermodynamics of the chemical master equation.

  16. Diffusion approximations to the chemical master equation only have a consistent stochastic thermodynamics at chemical equilibrium.

    PubMed

    Horowitz, Jordan M

    2015-07-28

    The stochastic thermodynamics of a dilute, well-stirred mixture of chemically reacting species is built on the stochastic trajectories of reaction events obtained from the chemical master equation. However, when the molecular populations are large, the discrete chemical master equation can be approximated with a continuous diffusion process, like the chemical Langevin equation or low noise approximation. In this paper, we investigate to what extent these diffusion approximations inherit the stochastic thermodynamics of the chemical master equation. We find that a stochastic-thermodynamic description is only valid at a detailed-balanced, equilibrium steady state. Away from equilibrium, where there is no consistent stochastic thermodynamics, we show that one can still use the diffusive solutions to approximate the underlying thermodynamics of the chemical master equation.

  17. Pulse-density modulation control of chemical oscillation far from equilibrium in a droplet open-reactor system

    PubMed Central

    Sugiura, Haruka; Ito, Manami; Okuaki, Tomoya; Mori, Yoshihito; Kitahata, Hiroyuki; Takinoue, Masahiro

    2016-01-01

    The design, construction and control of artificial self-organized systems modelled on dynamical behaviours of living systems are important issues in biologically inspired engineering. Such systems are usually based on complex reaction dynamics far from equilibrium; therefore, the control of non-equilibrium conditions is required. Here we report a droplet open-reactor system, based on droplet fusion and fission, that achieves dynamical control over chemical fluxes into/out of the reactor for chemical reactions far from equilibrium. We mathematically reveal that the control mechanism is formulated as pulse-density modulation control of the fusion–fission timing. We produce the droplet open-reactor system using microfluidic technologies and then perform external control and autonomous feedback control over autocatalytic chemical oscillation reactions far from equilibrium. We believe that this system will be valuable for the dynamical control over self-organized phenomena far from equilibrium in chemical and biomedical studies. PMID:26786848

  18. Pulse-density modulation control of chemical oscillation far from equilibrium in a droplet open-reactor system.

    PubMed

    Sugiura, Haruka; Ito, Manami; Okuaki, Tomoya; Mori, Yoshihito; Kitahata, Hiroyuki; Takinoue, Masahiro

    2016-01-20

    The design, construction and control of artificial self-organized systems modelled on dynamical behaviours of living systems are important issues in biologically inspired engineering. Such systems are usually based on complex reaction dynamics far from equilibrium; therefore, the control of non-equilibrium conditions is required. Here we report a droplet open-reactor system, based on droplet fusion and fission, that achieves dynamical control over chemical fluxes into/out of the reactor for chemical reactions far from equilibrium. We mathematically reveal that the control mechanism is formulated as pulse-density modulation control of the fusion-fission timing. We produce the droplet open-reactor system using microfluidic technologies and then perform external control and autonomous feedback control over autocatalytic chemical oscillation reactions far from equilibrium. We believe that this system will be valuable for the dynamical control over self-organized phenomena far from equilibrium in chemical and biomedical studies.

  19. Pulse-density modulation control of chemical oscillation far from equilibrium in a droplet open-reactor system

    NASA Astrophysics Data System (ADS)

    Sugiura, Haruka; Ito, Manami; Okuaki, Tomoya; Mori, Yoshihito; Kitahata, Hiroyuki; Takinoue, Masahiro

    2016-01-01

    The design, construction and control of artificial self-organized systems modelled on dynamical behaviours of living systems are important issues in biologically inspired engineering. Such systems are usually based on complex reaction dynamics far from equilibrium; therefore, the control of non-equilibrium conditions is required. Here we report a droplet open-reactor system, based on droplet fusion and fission, that achieves dynamical control over chemical fluxes into/out of the reactor for chemical reactions far from equilibrium. We mathematically reveal that the control mechanism is formulated as pulse-density modulation control of the fusion-fission timing. We produce the droplet open-reactor system using microfluidic technologies and then perform external control and autonomous feedback control over autocatalytic chemical oscillation reactions far from equilibrium. We believe that this system will be valuable for the dynamical control over self-organized phenomena far from equilibrium in chemical and biomedical studies.

  20. Application of a coupled ecosystem-chemical equilibrium model, DayCent-Chem, to stream and soil chemistry in a Rocky Mountain watershed

    USGS Publications Warehouse

    Hartman, M.D.; Baron, J.S.; Ojima, D.S.

    2007-01-01

    Atmospheric deposition of sulfur and nitrogen species have the potential to acidify terrestrial and aquatic ecosystems, but nitrate and ammonium are also critical nutrients for plant and microbial productivity. Both the ecological response and the hydrochemical response to atmospheric deposition are of interest to regulatory and land management agencies. We developed a non-spatial biogeochemical model to simulate soil and surface water chemistry by linking the daily version of the CENTURY ecosystem model (DayCent) with a low temperature aqueous geochemical model, PHREEQC. The coupled model, DayCent-Chem, simulates the daily dynamics of plant production, soil organic matter, cation exchange, mineral weathering, elution, stream discharge, and solute concentrations in soil water and stream flow. By aerially weighting the contributions of separate bedrock/talus and tundra simulations, the model was able to replicate the measured seasonal and annual stream chemistry for most solutes for Andrews Creek in Loch Vale watershed, Rocky Mountain National Park. Simulated soil chemistry, net primary production, live biomass, and soil organic matter for forest and tundra matched well with measurements. This model is appropriate for accurately describing ecosystem and surface water chemical response to atmospheric deposition and climate change. ?? 2006 Elsevier B.V. All rights reserved.

  1. Chemical bonding and the equilibrium composition of Grignard reagents in ethereal solutions.

    PubMed

    Henriques, André M; Barbosa, André G H

    2011-11-10

    A thorough analysis of the electronic structure and thermodynamic aspects of Grignard reagents and its associated equilibrium composition in ethereal solutions is performed. Considering methylmagnesium halides containing fluorine, chlorine, and bromine, we studied the neutral, charged, and radical species associated with their chemical equilibrium in solution. The ethereal solvents considered, tetrahydrofuran (THF) and ethyl ether (Et(2)O), were modeled using the polarizable continuum model (PCM) and also by explicit coordination to the Mg atoms in a cluster. The chemical bonding of the species that constitute the Grignard reagent is analyzed in detail with generalized valence bond (GVB) wave functions. Equilibrium constants were calculated with the DFT/M06 functional and GVB wave functions, yielding similar results. According to our calculations and existing kinetic and electrochemical evidence, the species R(•), R(-), (•)MgX, and RMgX(2)(-) must be present in low concentration in the equilibrium. We conclude that depending on the halogen, a different route must be followed to produce the relevant equilibrium species in each case. Chloride and bromide must preferably follow a "radical-based" pathway, and fluoride must follow a "carbanionic-based" pathway. These different mechanisms are contrasted against the available experimental results and are proven to be consistent with the existing thermodynamic data on the Grignard reagent equilibria.

  2. Minimizing the Free Energy: A Computer Method for Teaching Chemical Equilibrium Concepts.

    ERIC Educational Resources Information Center

    Heald, Emerson F.

    1978-01-01

    Presents a computer method for teaching chemical equilibrium concepts using material balance conditions and the minimization of the free energy. Method for the calculation of chemical equilibrium, the computer program used to solve equilibrium problems and applications of the method are also included. (HM)

  3. Minimizing the Free Energy: A Computer Method for Teaching Chemical Equilibrium Concepts.

    ERIC Educational Resources Information Center

    Heald, Emerson F.

    1978-01-01

    Presents a computer method for teaching chemical equilibrium concepts using material balance conditions and the minimization of the free energy. Method for the calculation of chemical equilibrium, the computer program used to solve equilibrium problems and applications of the method are also included. (HM)

  4. Transport Coefficients for the NASA Lewis Chemical Equilibrium Program

    NASA Technical Reports Server (NTRS)

    Svehla, Roger A.

    1995-01-01

    The new transport property data that will be used in the NASA Lewis Research Center's Chemical Equilibrium and Applications Program (CEA) is presented. It complements a previous publication that documented the thermodynamic and transport property data then in use. Sources of the data and a brief description of the method by which the data were obtained are given. Coefficients to calculate the viscosity, thermal conductivity, and binary interactions are given for either one, or usually, two temperature intervals, typically 300 to 1000 K and 1000 to 5000 K. The form of the transport equation is the same as used previously. The number of species was reduced from the previous database. Many species for which the data were estimated were eliminated from the database. Some ionneutral interactions were added.

  5. Turbulence modeling for non-equilibrium flow

    NASA Technical Reports Server (NTRS)

    Durbin, P. A.

    1995-01-01

    The work performed during this year has involved further assessment and extension of the k-epsilon-v(exp 2) model, and initiation of work on scalar transport. The latter is introduced by the contribution of Y. Shabany to this volume. Flexible, computationally tractable models are needed for engineering CFD. As computational technology has progressed, the ability and need to use elaborate turbulence closure models has increased. The objective of our work is to explore and develop new analytical frameworks that might extend the applicability of the modeling techniques. In past years the development of a method for near-wall modeling was described. The method has been implemented into a CFD code and its viability has been demonstrated by various test cases. Further tests are reported herein. Non-equilibrium near-wall models are needed for some heat transfer applications. Scalar transport seems generally to be more sensitive to non-equilibrium effects than is momentum transport. For some applications turbulence anisotropy plays a role and an estimate of the full Reynolds stress tensor is needed. We have begun work on scalar transport per se, but in this brief I will only report on an extension of the k-epsilon-v(exp 2) model to predict the Reynolds stress tensor.

  6. Incorporation of a Chemical Equilibrium Equation of State into LOCI-Chem

    NASA Technical Reports Server (NTRS)

    Cox, Carey F.

    2005-01-01

    Renewed interest in development of advanced high-speed transport, reentry vehicles and propulsion systems has led to a resurgence of research into high speed aerodynamics. As this flow regime is typically dominated by hot reacting gaseous flow, efficient models for the characteristic chemical activity are necessary for accurate and cost effective analysis and design of aerodynamic vehicles that transit this regime. The LOCI-Chem code recently developed by Ed Luke at Mississippi State University for NASA/MSFC and used by NASA/MSFC and SSC represents an important step in providing an accurate, efficient computational tool for the simulation of reacting flows through the use of finite-rate kinetics [3]. Finite rate chemistry however, requires the solution of an additional N-1 species mass conservation equations with source terms involving reaction kinetics that are not fully understood. In the equilibrium limit, where the reaction rates approach infinity, these equations become very stiff. Through the use of the assumption of local chemical equilibrium the set of governing equations is reduced back to the usual gas dynamic equations, and thus requires less computation, while still allowing for the inclusion of reacting flow phenomenology. The incorporation of a chemical equilibrium equation of state module into the LOCI-Chem code was the primary objective of the current research. The major goals of the project were: (1) the development of a chemical equilibrium composition solver, and (2) the incorporation of chemical equilibrium solver into LOCI-Chem. Due to time and resource constraints, code optimization was not considered unless it was important to the proper functioning of the code.

  7. Predicting equilibrium sorption of neutral organic chemicals into various polymeric sorbents with COSMO-RS.

    PubMed

    Goss, Kai-Uwe

    2011-07-01

    There is an increasing use of polymers in analytical chemistry as sorbents for organic chemicals in sampling, cleanup, and chromatography. In order to find the optimal polymer for a given purpose, one needs to know the equilibrium partition constants of the chemicals of interest in a wide range of polymers. COSMOtherm, a quantum-chemically based software, is designed to predict such equilibrium partition constants based only on the molecular structure as input information. In this work, literature data for such equilibrium partition constants were collected for a wide range of different polymers and used to evaluate the performance of COSMOtherm. The results show good agreement between the predicted and experimental data from water and air for most of the tested polymers. The relative preference of analytes to sorb in a given polymer represented by the molecular structure of a monomer can be predicted without any calibration. If absolute values for the partition constants are required, then a few experimental values are needed to establish a log-linear regression between the model output and the experimental values. COSMOtherm appears to be a helpful tool for selecting the best sorbent polymer for a given task or for designing new polymers. The present evaluation is limited to chemicals with a rather simple structure. Further evaluation with complex chemicals that possess multiple functionalities is still warranted.

  8. Surface-dependent chemical equilibrium constants and capacitances for bare and 3-cyanopropyldimethylchlorosilane coated silica nanochannels.

    PubMed

    Andersen, Mathias Bækbo; Frey, Jared; Pennathur, Sumita; Bruus, Henrik

    2011-01-01

    We present a combined theoretical and experimental analysis of the solid-liquid interface of fused-silica nanofabricated channels with and without a hydrophilic 3-cyanopropyldimethylchlorosilane (cyanosilane) coating. We develop a model that relaxes the assumption that the surface parameters C(1), C(2), and pK(+) are constant and independent of surface composition. Our theoretical model consists of three parts: (i) a chemical equilibrium model of the bare or coated wall, (ii) a chemical equilibrium model of the buffered bulk electrolyte, and (iii) a self-consistent Gouy-Chapman-Stern triple-layer model of the electrochemical double layer coupling these two equilibrium models. To validate our model, we used both pH-sensitive dye-based capillary filling experiments as well as electro-osmotic current-monitoring measurements. Using our model we predict the dependence of ζ potential, surface charge density, and capillary filling length ratio on ionic strength for different surface compositions, which can be difficult to achieve otherwise.

  9. Computer program for calculation of complex chemical equilibrium compositions and applications. Part 1: Analysis

    NASA Technical Reports Server (NTRS)

    Gordon, Sanford; Mcbride, Bonnie J.

    1994-01-01

    This report presents the latest in a number of versions of chemical equilibrium and applications programs developed at the NASA Lewis Research Center over more than 40 years. These programs have changed over the years to include additional features and improved calculation techniques and to take advantage of constantly improving computer capabilities. The minimization-of-free-energy approach to chemical equilibrium calculations has been used in all versions of the program since 1967. The two principal purposes of this report are presented in two parts. The first purpose, which is accomplished here in part 1, is to present in detail a number of topics of general interest in complex equilibrium calculations. These topics include mathematical analyses and techniques for obtaining chemical equilibrium; formulas for obtaining thermodynamic and transport mixture properties and thermodynamic derivatives; criteria for inclusion of condensed phases; calculations at a triple point; inclusion of ionized species; and various applications, such as constant-pressure or constant-volume combustion, rocket performance based on either a finite- or infinite-chamber-area model, shock wave calculations, and Chapman-Jouguet detonations. The second purpose of this report, to facilitate the use of the computer code, is accomplished in part 2, entitled 'Users Manual and Program Description'. Various aspects of the computer code are discussed, and a number of examples are given to illustrate its versatility.

  10. Thermodynamics and Kinetics of Chemical Equilibrium in Solution.

    ERIC Educational Resources Information Center

    Leenson, I. A.

    1986-01-01

    Discusses theory of thermodynamics of the equilibrium in solution and dissociation-dimerization kinetics. Describes experimental procedure including determination of molar absorptivity and equilibrium constant, reaction enthalpy, and kinetics of the dissociation-dimerization reaction. (JM)

  11. Thermodynamics and Kinetics of Chemical Equilibrium in Solution.

    ERIC Educational Resources Information Center

    Leenson, I. A.

    1986-01-01

    Discusses theory of thermodynamics of the equilibrium in solution and dissociation-dimerization kinetics. Describes experimental procedure including determination of molar absorptivity and equilibrium constant, reaction enthalpy, and kinetics of the dissociation-dimerization reaction. (JM)

  12. Evaluating role of interactive visualization tool in improving students' conceptual understanding of chemical equilibrium

    NASA Astrophysics Data System (ADS)

    Sampath Kumar, Bharath

    The purpose of this study is to examine the role of partnering visualization tool such as simulation towards development of student's concrete conceptual understanding of chemical equilibrium. Students find chemistry concepts abstract, especially at the microscopic level. Chemical equilibrium is one such topic. While research studies have explored effectiveness of low tech instructional strategies such as analogies, jigsaw, cooperative learning, and using modeling blocks, fewer studies have explored the use of visualization tool such as simulations in the context of dynamic chemical equilibrium. Research studies have identified key reasons behind misconceptions such as lack of systematic understanding of foundational chemistry concepts, failure to recognize the system is dynamic, solving numerical problems on chemical equilibrium in an algorithmic fashion, erroneous application Le Chatelier's principle (LCP) etc. Kress et al. (2001) suggested that external representation in the form of visualization is more than a tool for learning, because it enables learners to make meanings or express their ideas which cannot be readily done so through a verbal representation alone. Mixed method study design was used towards data collection. The qualitative portion of the study is aimed towards understanding the change in student's mental model before and after the intervention. A quantitative instrument was developed based on common areas of misconceptions identified by research studies. A pilot study was conducted prior to the actual study to obtain feedback from students on the quantitative instrument and the simulation. Participants for the pilot study were sampled from a single general chemistry class. Following the pilot study, the research study was conducted with a total of 27 students (N=15 in experimental group and N=12 in control group). Prior to participating in the study, students have completed their midterm test on the topic of chemical equilibrium. Qualitative

  13. Self-organization of grafted polyelectrolyte layers via the coupling of chemical equilibrium and physical interactions.

    PubMed

    Tagliazucchi, Mario; de la Cruz, Mónica Olvera; Szleifer, Igal

    2010-03-23

    The competition between chemical equilibrium, for example protonation, and physical interactions determines the molecular organization and functionality of biological and synthetic systems. Charge regulation by displacement of acid-base equilibrium induced by changes in the local environment provides a feedback mechanism that controls the balance between electrostatic, van der Waals, steric interactions and molecular organization. Which strategies do responsive systems follow to globally optimize chemical equilibrium and physical interactions? We address this question by theoretically studying model layers of end-grafted polyacids. These layers spontaneously form self-assembled aggregates, presenting domains of controlled local pH and whose morphologies can be manipulated by the composition of the solution in contact with the film. Charge regulation stabilizes micellar domains over a wide range of pH by reducing the local charge in the aggregate at the cost of chemical free energy and gaining in hydrophobic interactions. This balance determines the boundaries between different aggregate morphologies. We show that a qualitatively new form of organization arises from the coupling between physical interactions and protonation equilibrium. This optimization strategy presents itself with polyelectrolytes coexisting in two different and well-defined protonation states. Our results underline the need of considering the coupling between chemical equilibrium and physical interactions due to their highly nonadditive behavior. The predictions provide guidelines for the creation of responsive polymer layers presenting self-organized patterns with functional properties and they give insights for the understanding of competing interactions in highly inhomogeneous and constrained environments such as those relevant in nanotechnology and those responsible for biological cells function.

  14. Modeling Equilibrium of microRNA Expression

    PubMed Central

    Chan, Lawrence W. C.

    2011-01-01

    MicroRNAs are a class of non-coding RNAs and the dysregulated expression of these short RNA molecules was frequently observed in cancer cells. The steady state level of microRNA concentration may differentiate the biological function of the cells between normal and impaired. To understand the steady state or equilibrium of microRNAs, their interactions with transcription factors and target genes need to be explored and visualized through prediction and network analysis algorithms. This article discusses the application of mathematical model for simulating the dynamics of network feedback loop so as to decipher the mechanism of microRNA regulation. PMID:22303331

  15. Chemical Derivatives and Elemental Transport Coefficients in Plasma Flows Near Local Equilibrium

    SciTech Connect

    Orsini, Alessio; Kustova, Elena V.

    2011-05-20

    Elemental transport coefficients are extensively used for modeling chemically reacting and plasma flows when the proximity to local equilibrium is exploited to combine the ordinary transport coefficients into a few elemental coefficients. A deeper insight into the physics of chemically reacting flows near local equilibrium can be achieved by looking only at a reduced number of relevant parameters in the expression of the flow transport properties.A new technique to calculate chemical derivatives using an analytical method which strongly reduces computational effort and numerical errors is introduced. A general formalism for elemental diffusion velocities, heat flux and electric current for plasma flows near local equilibrium is then derived. An order of magnitude analysis shows how to identify the main contributions to the transport fluxes among: elemental fractions gradients, pressure or temperature gradients, electric field. The resulting theoretical framework is particularly suitable for numerical implementation.The present contribution aims to provide a summary of the theoretical framework described above. Numerical examples of chemical derivatives and elemental transport coefficients are given. Results are presented for a carbon dioxide mixture of practical interest for aerospace applications and atmospheric entry problems.

  16. Phase-field model of oxidation: Equilibrium

    NASA Astrophysics Data System (ADS)

    Sherman, Q. C.; Voorhees, P. W.

    2017-03-01

    A phase-field model of an oxide relevant to corrosion resistant alloys for film thicknesses below the Debye length LD, where charge neutrality in the oxide does not occur, is formulated. The phase-field model is validated in the Wagner limit using a sharp interface Gouy-Chapman model for the electrostatic double layer. The phase-field simulations show that equilibrium oxide films below the Wagner limit are charged throughout due to their inability to electrostatically screen charge over the length of the film, L . The character of the defect and charge distribution profiles in the oxide vary depending on whether reduced oxygen adatoms are present on the gas-oxide interface. The Fermi level in the oxide increases for thinner films, approaching the Fermi level of the metal in the limit L /LD→0 , which increases the driving force for adsorbed oxygen reduction at the gas-oxide interface.

  17. Chemical equilibrium of minced turkey meat in organic acid solutions.

    PubMed

    Goli, T; Abi Nakhoul, P; Zakhia-Rozis, N; Trystram, G; Bohuon, P

    2007-02-01

    The distribution of acid (HA), anions (A(-)), free protons (H(3)O(+)) and bound protons (H(b)), in homogenized turkey meat was evaluated at various meat/water mass ratios of (1/4-1/10) during titration with acetic acid (0.25N) or lactic acid (0.2N). H(b) concentration was determined by titration with hydrochloric acid (0.075N) and a correlation for [H(b)]=f(pH) was proposed. A procedure was used to calculate the fractions of the various species in equilibrium, starting from an initial acid concentration in a meat/water system and assuming the accuracy of the pK(a) value of the pure weak acids despite the chemical complexity of meat. Calculated results were in very good agreement (±0.15) with experimental pH values, whatever the acid, meat batch or meat/water mass ratios used. Less than 1% of the total protons were free (H(3)O(+)) and determined the meat pH.

  18. Chemical equilibrium. [maximizing entropy of gas system to derive relations between thermodynamic variables

    NASA Technical Reports Server (NTRS)

    1976-01-01

    The entropy of a gas system with the number of particles subject to external control is maximized to derive relations between the thermodynamic variables that obtain at equilibrium. These relations are described in terms of the chemical potential, defined as equivalent partial derivatives of entropy, energy, enthalpy, free energy, or free enthalpy. At equilibrium, the change in total chemical potential must vanish. This fact is used to derive the equilibrium constants for chemical reactions in terms of the partition functions of the species involved in the reaction. Thus the equilibrium constants can be determined accurately, just as other thermodynamic properties, from a knowledge of the energy levels and degeneracies for the gas species involved. These equilibrium constants permit one to calculate the equilibrium concentrations or partial pressures of chemically reacting species that occur in gas mixtures at any given condition of pressure and temperature or volume and temperature.

  19. Chemical equilibrium. [maximizing entropy of gas system to derive relations between thermodynamic variables

    NASA Technical Reports Server (NTRS)

    1976-01-01

    The entropy of a gas system with the number of particles subject to external control is maximized to derive relations between the thermodynamic variables that obtain at equilibrium. These relations are described in terms of the chemical potential, defined as equivalent partial derivatives of entropy, energy, enthalpy, free energy, or free enthalpy. At equilibrium, the change in total chemical potential must vanish. This fact is used to derive the equilibrium constants for chemical reactions in terms of the partition functions of the species involved in the reaction. Thus the equilibrium constants can be determined accurately, just as other thermodynamic properties, from a knowledge of the energy levels and degeneracies for the gas species involved. These equilibrium constants permit one to calculate the equilibrium concentrations or partial pressures of chemically reacting species that occur in gas mixtures at any given condition of pressure and temperature or volume and temperature.

  20. The Lack of Chemical Equilibrium does not Preclude the Use of the Classical Nucleation Theory in Circumstellar Outflows

    NASA Technical Reports Server (NTRS)

    Paquette, John A.; Nuth, Joseph A., III

    2011-01-01

    Classical nucleation theory has been used in models of dust nucleation in circumstellar outflows around oxygen-rich asymptotic giant branch stars. One objection to the application of classical nucleation theory (CNT) to astrophysical systems of this sort is that an equilibrium distribution of clusters (assumed by CNT) is unlikely to exist in such conditions due to a low collision rate of condensable species. A model of silicate grain nucleation and growth was modified to evaluate the effect of a nucleation flux orders of magnitUde below the equilibrium value. The results show that a lack of chemical equilibrium has only a small effect on the ultimate grain distribution.

  1. APOLLO: A computer program for the calculation of chemical equilibrium and reaction kinetics of chemical systems

    SciTech Connect

    Nguyen, H.D.

    1991-11-01

    Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a ``glass like`` material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.

  2. APOLLO: A computer program for the calculation of chemical equilibrium and reaction kinetics of chemical systems

    SciTech Connect

    Nguyen, H.D.

    1991-11-01

    Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a glass like'' material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.

  3. Identification and Analysis of Student Conceptions Used To Solve Chemical Equilibrium Problems.

    ERIC Educational Resources Information Center

    Voska, Kirk W.; Heikkinen, Henry W.

    2000-01-01

    Identifies and quantifies the chemistry conceptions used by students when solving chemical equilibrium problems requiring application of LeChatelier's Principle, and explores the feasibility of designing a paper and pencil test to accomplish these purposes. Eleven prevalent incorrect student conceptions about chemical equilibrium were identified…

  4. Promoting Pre-Service Elementary Students' Understanding of Chemical Equilibrium through Discussions in Small Groups

    ERIC Educational Resources Information Center

    Bilgin, Ibrahim

    2006-01-01

    The purpose of this study was to investigate the effectiveness of small group discussion on students' conceptual understanding of chemical equilibrium. Students' understanding of chemical equilibrium concepts was measured using the Misconception Identification Test. The test consisted of 30 items and administered as pre-posttests to a total of 81…

  5. Response to Contradiction: Conflict Resolution Strategies Used by Students in Solving Problems of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Niaz, Mansoor

    2001-01-01

    Illustrates how a novel problem of chemical equilibrium based on a closely related sequence of items can facilitate students' conceptual understanding. Students were presented with a chemical reaction in equilibrium to which a reactant was added as an external effect. Three studies were conducted to assess alternative conceptions. (Author/SAH)

  6. Effectiveness of Instruction Based on the Constructivist Approach on Understanding Chemical Equilibrium Concepts

    ERIC Educational Resources Information Center

    Akkus, Huseyin; Kadayifci, Hakki; Atasoy, Basri; Geban, Omer

    2003-01-01

    The purpose of this study was to identify misconceptions concerning chemical equilibrium concepts and to investigate the effectiveness of instruction based on the constructivist approach over traditional instruction on 10th grade students' understanding of chemical equilibrium concepts. The subjects of this study consisted of 71 10th grade…

  7. A Colorful Demonstration to Visualize and Inquire into Essential Elements of Chemical Equilibrium

    ERIC Educational Resources Information Center

    Eilks, Ingo; Gulacar, Ozcan

    2016-01-01

    One of the topics that chemistry teachers have a great challenge introducing is chemical equilibrium. When being introduced to chemical equilibrium, many students have difficulties in understanding that some reactions do not go to completion, as this contrasts most of their supposed prior experiences in chemistry lessons. Students may also…

  8. Promoting Pre-Service Elementary Students' Understanding of Chemical Equilibrium through Discussions in Small Groups

    ERIC Educational Resources Information Center

    Bilgin, Ibrahim

    2006-01-01

    The purpose of this study was to investigate the effectiveness of small group discussion on students' conceptual understanding of chemical equilibrium. Students' understanding of chemical equilibrium concepts was measured using the Misconception Identification Test. The test consisted of 30 items and administered as pre-posttests to a total of 81…

  9. Response to Contradiction: Conflict Resolution Strategies Used by Students in Solving Problems of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Niaz, Mansoor

    2001-01-01

    Illustrates how a novel problem of chemical equilibrium based on a closely related sequence of items can facilitate students' conceptual understanding. Students were presented with a chemical reaction in equilibrium to which a reactant was added as an external effect. Three studies were conducted to assess alternative conceptions. (Author/SAH)

  10. Teachers' Misconceptions about the Effects of Addition of More Reactants or Products on Chemical Equilibrium

    ERIC Educational Resources Information Center

    Cheung, Derek; Ma, Hong-jia; Yang, Jie

    2009-01-01

    The importance of research on misconceptions about chemical equilibrium is well recognized by educators, but in the past, researchers' interest has centered on student misconceptions and has neglected teacher misconceptions. Focusing on the effects of adding more reactants or products on chemical equilibrium, this article discusses the various…

  11. Identification and Analysis of Student Conceptions Used To Solve Chemical Equilibrium Problems.

    ERIC Educational Resources Information Center

    Voska, Kirk W.; Heikkinen, Henry W.

    2000-01-01

    Identifies and quantifies the chemistry conceptions used by students when solving chemical equilibrium problems requiring application of LeChatelier's Principle, and explores the feasibility of designing a paper and pencil test to accomplish these purposes. Eleven prevalent incorrect student conceptions about chemical equilibrium were identified…

  12. The Adverse Effects of Le Chatelier's Principle on Teacher Understanding of Chemical Equilibrium

    ERIC Educational Resources Information Center

    Cheung, Derek

    2009-01-01

    Although the scientific inadequacy of Le Chatelier's principle has long been documented in the literature, the principle is still treated as a central concept of chemical equilibrium by textbook writers and teachers in many countries. In the past, researchers' interest has focused on student misconceptions about chemical equilibrium and has…

  13. Effectiveness of Instruction Based on the Constructivist Approach on Understanding Chemical Equilibrium Concepts

    ERIC Educational Resources Information Center

    Akkus, Huseyin; Kadayifci, Hakki; Atasoy, Basri; Geban, Omer

    2003-01-01

    The purpose of this study was to identify misconceptions concerning chemical equilibrium concepts and to investigate the effectiveness of instruction based on the constructivist approach over traditional instruction on 10th grade students' understanding of chemical equilibrium concepts. The subjects of this study consisted of 71 10th grade…

  14. Teachers' Misconceptions about the Effects of Addition of More Reactants or Products on Chemical Equilibrium

    ERIC Educational Resources Information Center

    Cheung, Derek; Ma, Hong-jia; Yang, Jie

    2009-01-01

    The importance of research on misconceptions about chemical equilibrium is well recognized by educators, but in the past, researchers' interest has centered on student misconceptions and has neglected teacher misconceptions. Focusing on the effects of adding more reactants or products on chemical equilibrium, this article discusses the various…

  15. A Colorful Demonstration to Visualize and Inquire into Essential Elements of Chemical Equilibrium

    ERIC Educational Resources Information Center

    Eilks, Ingo; Gulacar, Ozcan

    2016-01-01

    One of the topics that chemistry teachers have a great challenge introducing is chemical equilibrium. When being introduced to chemical equilibrium, many students have difficulties in understanding that some reactions do not go to completion, as this contrasts most of their supposed prior experiences in chemistry lessons. Students may also…

  16. The Adverse Effects of Le Chatelier's Principle on Teacher Understanding of Chemical Equilibrium

    ERIC Educational Resources Information Center

    Cheung, Derek

    2009-01-01

    Although the scientific inadequacy of Le Chatelier's principle has long been documented in the literature, the principle is still treated as a central concept of chemical equilibrium by textbook writers and teachers in many countries. In the past, researchers' interest has focused on student misconceptions about chemical equilibrium and has…

  17. Radiative equilibrium model of Titan's atmosphere

    NASA Technical Reports Server (NTRS)

    Samuelson, R. E.

    1983-01-01

    The present global radiative equilibrium model for the Saturn satellite Titan is restricted to the two-stream approximation, is vertically homogeneous in its scattering properties, and is spectrally divided into one thermal and two solar channels. Between 13 and 33% of the total incident solar radiation is absorbed at the planetary surface, and the 30-60 ratio of violet to thermal IR absorption cross sections in the stratosphere leads to the large temperature inversion observed there. The spectrally integrated mass absorption coefficient at thermal wavelengths is approximately constant throughout the stratosphere, and approximately linear with pressure in the troposphere, implying the presence of a uniformly mixed aerosol in the stratosphere. There also appear to be two regions of enhanced opacity near 30 and 500 mbar.

  18. Radiative equilibrium model of Titan's atmosphere

    NASA Astrophysics Data System (ADS)

    Samuelson, R. E.

    1983-02-01

    The present global radiative equilibrium model for the Saturn satellite Titan is restricted to the two-stream approximation, is vertically homogeneous in its scattering properties, and is spectrally divided into one thermal and two solar channels. Between 13 and 33% of the total incident solar radiation is absorbed at the planetary surface, and the 30-60 ratio of violet to thermal IR absorption cross sections in the stratosphere leads to the large temperature inversion observed there. The spectrally integrated mass absorption coefficient at thermal wavelengths is approximately constant throughout the stratosphere, and approximately linear with pressure in the troposphere, implying the presence of a uniformly mixed aerosol in the stratosphere. There also appear to be two regions of enhanced opacity near 30 and 500 mbar.

  19. Radiative equilibrium model of Titan's atmosphere

    NASA Technical Reports Server (NTRS)

    Samuelson, R. E.

    1983-01-01

    The present global radiative equilibrium model for the Saturn satellite Titan is restricted to the two-stream approximation, is vertically homogeneous in its scattering properties, and is spectrally divided into one thermal and two solar channels. Between 13 and 33% of the total incident solar radiation is absorbed at the planetary surface, and the 30-60 ratio of violet to thermal IR absorption cross sections in the stratosphere leads to the large temperature inversion observed there. The spectrally integrated mass absorption coefficient at thermal wavelengths is approximately constant throughout the stratosphere, and approximately linear with pressure in the troposphere, implying the presence of a uniformly mixed aerosol in the stratosphere. There also appear to be two regions of enhanced opacity near 30 and 500 mbar.

  20. Modeling of turbulent chemical reaction

    NASA Technical Reports Server (NTRS)

    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. Clouds in Super-Earth Atmospheres: Chemical Equilibrium Calculations

    NASA Astrophysics Data System (ADS)

    Mbarek, Rostom; Kempton, Eliza M.-R.

    2016-08-01

    Recent studies have unequivocally proven the existence of clouds in super-Earth atmospheres. Here we provide a theoretical context for the formation of super-Earth clouds by determining which condensates are likely to form under the assumption of chemical equilibrium. We study super-Earth atmospheres of diverse bulk composition, which are assumed to form by outgassing from a solid core of chondritic material, following Schaefer & Fegley. The super-Earth atmospheres that we study arise from planetary cores made up of individual types of chondritic meteorites. They range from highly reducing to oxidizing and have carbon to oxygen (C:O) ratios that are both sub-solar and super-solar, thereby spanning a range of atmospheric composition that is appropriate for low-mass exoplanets. Given the atomic makeup of these atmospheres, we minimize the global Gibbs free energy of formation for over 550 gases and condensates to obtain the molecular composition of the atmospheres over a temperature range of 350-3000 K. Clouds should form along the temperature-pressure boundaries where the condensed species appear in our calculation. We find that the composition of condensate clouds depends strongly on both the H:O and C:O ratios. For the super-Earth archetype GJ 1214b, KCl and ZnS are the primary cloud-forming condensates at solar composition, in agreement with previous work. However, for oxidizing atmospheres, K2SO4 and ZnO condensates are favored instead, and for carbon-rich atmospheres with super-solar C:O ratios, graphite clouds appear. For even hotter planets, clouds form from a wide variety of rock-forming and metallic species.

  2. Equilibrium simulations of proteins using molecular fragment replacement and NMR chemical shifts.

    PubMed

    Boomsma, Wouter; Tian, Pengfei; Frellsen, Jes; Ferkinghoff-Borg, Jesper; Hamelryck, Thomas; Lindorff-Larsen, Kresten; Vendruscolo, Michele

    2014-09-23

    Methods of protein structure determination based on NMR chemical shifts are becoming increasingly common. The most widely used approaches adopt the molecular fragment replacement strategy, in which structural fragments are repeatedly reassembled into different complete conformations in molecular simulations. Although these approaches are effective in generating individual structures consistent with the chemical shift data, they do not enable the sampling of the conformational space of proteins with correct statistical weights. Here, we present a method of molecular fragment replacement that makes it possible to perform equilibrium simulations of proteins, and hence to determine their free energy landscapes. This strategy is based on the encoding of the chemical shift information in a probabilistic model in Markov chain Monte Carlo simulations. First, we demonstrate that with this approach it is possible to fold proteins to their native states starting from extended structures. Second, we show that the method satisfies the detailed balance condition and hence it can be used to carry out an equilibrium sampling from the Boltzmann distribution corresponding to the force field used in the simulations. Third, by comparing the results of simulations carried out with and without chemical shift restraints we describe quantitatively the effects that these restraints have on the free energy landscapes of proteins. Taken together, these results demonstrate that the molecular fragment replacement strategy can be used in combination with chemical shift information to characterize not only the native structures of proteins but also their conformational fluctuations.

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

    NASA Technical Reports Server (NTRS)

    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.

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

    NASA Technical Reports Server (NTRS)

    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.

  5. Formation of nitric acid hydrates - A chemical equilibrium approach

    NASA Technical Reports Server (NTRS)

    Smith, Roland H.

    1990-01-01

    Published data are used to calculate equilibrium constants for reactions of the formation of nitric acid hydrates over the temperature range 190 to 205 K. Standard enthalpies of formation and standard entropies are calculated for the tri- and mono-hydrates. These are shown to be in reasonable agreement with earlier calorimetric measurements. The formation of nitric acid trihydrate in the polar stratosphere is discussed in terms of these equilibrium constants.

  6. SOME MODELS OF STEADY STATE DYNAMIC EQUILIBRIUM,

    DTIC Science & Technology

    output is maximized, interest rate equals population growth rate and real wage equals output per worker. The second equilibrium called here a sigma...equilibrium because it depends on, peoples propensity to save, has output less than maximum and interest rate either greater than (deflationary) or less than

  7. An Evaluation of the Venous Equilibrium Model for Hepatic Clearance using Isolated Perfused Rainbow Trout Livers

    EPA Science Inventory

    The venous equilibrium model is widely used to describe hepatic clearance (CLH) of chemicals metabolized by the liver. If chemical delivery to the tissue does not limit CLH, this model predicts that CLH will approximately equal the product of intrinsic metabolic clearance and a t...

  8. An Evaluation of the Venous Equilibrium Model for Hepatic Clearance using Isolated Perfused Rainbow Trout Livers

    EPA Science Inventory

    The venous equilibrium model is widely used to describe hepatic clearance (CLH) of chemicals metabolized by the liver. If chemical delivery to the tissue does not limit CLH, this model predicts that CLH will approximately equal the product of intrinsic metabolic clearance and a t...

  9. Modeling rocky coastline evolution and equilibrium

    NASA Astrophysics Data System (ADS)

    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

  10. Equilibrium statistical-thermal models in high-energy physics

    NASA Astrophysics Data System (ADS)

    Tawfik, Abdel Nasser

    2014-05-01

    We review some recent highlights from the applications of statistical-thermal models to different experimental measurements and lattice QCD thermodynamics that have been made during the last decade. We start with a short review of the historical milestones on the path of constructing statistical-thermal models for heavy-ion physics. We discovered that Heinz Koppe formulated in 1948, an almost complete recipe for the statistical-thermal models. In 1950, Enrico Fermi generalized this statistical approach, in which he started with a general cross-section formula and inserted into it, the simplifying assumptions about the matrix element of the interaction process that likely reflects many features of the high-energy reactions dominated by density in the phase space of final states. In 1964, Hagedorn systematically analyzed the high-energy phenomena using all tools of statistical physics and introduced the concept of limiting temperature based on the statistical bootstrap model. It turns to be quite often that many-particle systems can be studied with the help of statistical-thermal methods. The analysis of yield multiplicities in high-energy collisions gives an overwhelming evidence for the chemical equilibrium in the final state. The strange particles might be an exception, as they are suppressed at lower beam energies. However, their relative yields fulfill statistical equilibrium, as well. We review the equilibrium statistical-thermal models for particle production, fluctuations and collective flow in heavy-ion experiments. We also review their reproduction of the lattice QCD thermodynamics at vanishing and finite chemical potential. During the last decade, five conditions have been suggested to describe the universal behavior of the chemical freeze-out parameters. The higher order moments of multiplicity have been discussed. They offer deep insights about particle production and to critical fluctuations. Therefore, we use them to describe the freeze-out parameters

  11. Equilibrium, chemical kinetic, and transport limitations to diamond growth

    NASA Astrophysics Data System (ADS)

    Evans, Edward Anthony

    Because of their extreme properties, diamond films have found some industrial applications, i.e., heat sinks and tool coatings. However, to increase their economic attractiveness, the growth rate must be increased, the deposition temperature must be lowered, and single crystal films must be achieved. We have studied two types of chemical vapor deposition systems, hot-filament and microwave assisted, in order to understand the factors limiting diamond growth rate. From simultaneous microbalance growth rate measurements and mass spectrometer measurements, changes in growth rate are correlated with changes in gas phase composition. Measured reaction orders support the proposal that diamond growth occurs through a single-carbon-atom species, e.g., CHsb3. When a two-carbon atom source gas is used, it is likely that the dissociation to two, single-carbon atom species occurs on the substrate surface (dissociative adsorption). Furthermore, a shift to zero-order suggests that the diamond growth is a surface-site limited process at higher hydrocarbon concentrations. The diamond growth rate maximum with pressure is explained by transport limitations of species within the reaction zone. The reported diamond growth rates in the hot-filament reactor are several times higher than those reported by other research groups. These higher growth rates result from surrounding the substrate with the filament. We have used the measured growth rates, filament temperatures, and thermocouple measurements to calculate activation energies for diamond growth. When the filament temperature is used for the calculation, an activation energy of 73 kcal per mole is obtained; however, based on estimated substrate temperatures, an activation energy of 18 kcal per mole is determined. A dimensional analysis approach was developed to select the most important gas phase reactions occurring during diamond CVD. Steady-state analysis of these reactions and the application of mass transport equations lead to

  12. Evaluation of uncertainties in solid-aqueous-gas chemical equilibrium calculations

    NASA Astrophysics Data System (ADS)

    Novoselov, Alexey A.; Popov, Serguei; de Souza Filho, Carlos Roberto

    2015-06-01

    Thermodynamic calculations are traditionally carried out under the assumption of specified input parameters. Errors associated to the results are not often estimated. Here, we propose a novel algorithm that propagates the uncertainty intervals on thermodynamic constants to the uncertainty in chemical equilibrium compositions. The computing uses a dataset of uncertainties on thermodynamic parameters for minerals, solution species and gases consistent with the SUPCRT92 database. Also the algorithm of nonlinear optimization is thoroughly described and realized on a base of the CRONO software. This code can be incorporated into reactive mass transport models as a core for calculating equilibrium compositions. The performance of the algorithm is tested in an experimental system involving Mont Terri's Opalinus Clay interacting with pore water. Its effectiveness is also evaluated against Monte Carlo simulations and Latin Hypercube sampling.

  13. Stability of high-speed boundary layers in oxygen including chemical non-equilibrium effects

    NASA Astrophysics Data System (ADS)

    Klentzman, Jill; Tumin, Anatoli

    2013-11-01

    The stability of high-speed boundary layers in chemical non-equilibrium is examined. A parametric study varying the edge temperature and the wall conditions is conducted for boundary layers in oxygen. The edge Mach number and enthalpy ranges considered are relevant to the flight conditions of reusable hypersonic cruise vehicles. Both viscous and inviscid stability formulations are used and the results compared to gain insight into the effects of viscosity and thermal conductivity on the stability. It is found that viscous effects have a strong impact on the temperature and mass fraction perturbations in the critical layer and in the viscous sublayer near the wall. Outside of these areas, the perturbations closely match in the viscous and inviscid models. The impact of chemical non-equilibrium on the stability is investigated by analyzing the effects of the chemical source term in the stability equations. The chemical source term is found to influence the growth rate of the second Mack mode instability but not have much of an effect on the mass fraction eigenfunction for the flow parameters considered. This work was supported by the AFOSR/NASA/National Center for Hypersonic Laminar-Turbulent Transition Research.

  14. Net reaction rate and neutrino emissivity for the Urca process in departure from chemical equilibrium

    NASA Astrophysics Data System (ADS)

    Wang, Wei-Hua; Huang, Xi; Zheng, Xiao-Ping

    2017-06-01

    We discuss the effect of compression on Urca shells in the ocean and crust of accreting neutron stars, especially in superbursting sources. We find that Urca shells may be deviated from chemical equilibrium in neutron stars which accrete at several tenths of the local Eddington accretion rate. The deviation depends on the energy threshold of the parent and daughter nuclei, the transition strength, the temperature, and the local accretion rate. In a typical crust model of accreting neutron stars, the chemical departures range from a few tenths of kBT to tens of kBT for various Urca pairs. If the Urca shell can exist in crusts of accreting neutron stars, compression may enhance the net neutrino cooling rate by a factor of about 1 ˜2 relative to the neutrino emissivity in chemical equilibrium. For some cases, such as Urca pairs with small energy thresholds and/or weak transition strength, the large chemical departure may result in net heating rather than cooling, although the released heat can be small. Strong Urca pairs in the deep crust are hard to be deviated even in neutron stars accreting at the local Eddington accretion rate.

  15. A study of diurnal variations of PM2.5 acidity and related chemical species using a new thermodynamic equilibrium model.

    PubMed

    Behera, Sailesh N; Betha, Raghu; Liu, Ping; Balasubramanian, Rajasekhar

    2013-05-01

    Aerosol acidity is one of the most important parameters that can influence atmospheric visibility, climate change and human health. Based on continuous field measurements of inorganic aerosol species and their thermodynamic modeling on a time resolution of 1h, this study has investigated the acidic properties of PM2.5 and their relation with the formation of secondary inorganic aerosols (SIA). The study was conducted by taking into account the prevailing ambient temperature (T) and relative humidity (RH) in a tropical urban atmosphere. The in-situ aerosol pH (pH(IS)) on a 12h basis ranged from -0.20 to 1.46 during daytime with an average value of 0.48 and 0.23 to 1.53 during nighttime with an average value of 0.72. These diurnal variations suggest that the daytime aerosol was more acidic than that caused by the nighttime aerosol. The hourly values of pH(IS) showed a reverse trend as compared to that of in-situ aerosol acidity ([H(+)]Ins). The pH(IS) had its maximum values at 3:00 and at 20:00 and its minimum during 11:00 to 12:00. Correlation analyses revealed that the molar concentration ratio of ammonium to sulfate (R(N/S)), equivalent concentration ratio of cations to anions (RC/A), T and RH can be used as independent variables for prediction of pH(IS). A multi-linear regression model consisting of RN/S, RC/A, T and RH was developed to estimate aerosol pH(IS).

  16. Site-specific functionalization for chemical speciation of Cr(III) and Cr(VI) using polyaniline impregnated nanocellulose composite: equilibrium, kinetic, and thermodynamic modeling

    NASA Astrophysics Data System (ADS)

    Jain, Priyanka; Varshney, Shilpa; Srivastava, Shalini

    2017-07-01

    Site-specific functionalizations are the emergent attention for the enhancement of sorption latent of heavy metals. Limited chemistry has been applied for the fabrication of diafunctionalized materials having potential to tether both environmentally stable oxidation states of chromium (Cr(III) and Cr(VI). Polyaniline impregnated nanocellulose composite (PANI-NCC) has been fabricated using click chemistry and explored for the removal of Cr(III) and Cr(VI) from hydrological environment. The structure, stability, morphology, particle size, surface area, hydrophilicity, and porosity of fabricated PANI-NCC were characterized comprehensively using analytical techniques and mathematical tools. The maximum sorption performance of PANI-NCC was procured for (Cr(III): 47.06 mg g-1; 94.12 %) and (Cr(VI): 48.92 mg g-1; 97.84 %) by equilibrating 0.5 g sorbent dose with 1000 mL of 25 mg L-1 chromium conc. at pH 6.5 and 2.5 for Cr(III) and Cr(VI), respectively. The sorption data showed a best fit to the Langmuir isotherm and pseudo-second-order kinetic model. The negative value of ∆ G° (-8.59 and -11.16 kJ mol-1) and ∆ H° (66.46 × 10-1 and 17.84 × 10-1 kJ mol-1), and positive value of ∆ S° (26.66 and 31.46 J mol-1K-1) for Cr(III) and Cr(VI), respectively, reflect the spontaneous, feasibility, and exothermic nature of the sorption process. The application of fabricated PANI-NCC for removing both the forms of chromium in the presence of other heavy metals was also tested at laboratory and industrial waste water regime. These findings open up new avenues in the row of high performance, scalable, and economic nanobiomaterial for the remediation of both forms of chromium from water streams.

  17. Site-specific functionalization for chemical speciation of Cr(III) and Cr(VI) using polyaniline impregnated nanocellulose composite: equilibrium, kinetic, and thermodynamic modeling

    NASA Astrophysics Data System (ADS)

    Jain, Priyanka; Varshney, Shilpa; Srivastava, Shalini

    2015-10-01

    Site-specific functionalizations are the emergent attention for the enhancement of sorption latent of heavy metals. Limited chemistry has been applied for the fabrication of diafunctionalized materials having potential to tether both environmentally stable oxidation states of chromium (Cr(III) and Cr(VI). Polyaniline impregnated nanocellulose composite (PANI-NCC) has been fabricated using click chemistry and explored for the removal of Cr(III) and Cr(VI) from hydrological environment. The structure, stability, morphology, particle size, surface area, hydrophilicity, and porosity of fabricated PANI-NCC were characterized comprehensively using analytical techniques and mathematical tools. The maximum sorption performance of PANI-NCC was procured for (Cr(III): 47.06 mg g-1; 94.12 %) and (Cr(VI): 48.92 mg g-1; 97.84 %) by equilibrating 0.5 g sorbent dose with 1000 mL of 25 mg L-1 chromium conc. at pH 6.5 and 2.5 for Cr(III) and Cr(VI), respectively. The sorption data showed a best fit to the Langmuir isotherm and pseudo-second-order kinetic model. The negative value of ∆ G° (-8.59 and -11.16 kJ mol-1) and ∆ H° (66.46 × 10-1 and 17.84 × 10-1 kJ mol-1), and positive value of ∆ S° (26.66 and 31.46 J mol-1K-1) for Cr(III) and Cr(VI), respectively, reflect the spontaneous, feasibility, and exothermic nature of the sorption process. The application of fabricated PANI-NCC for removing both the forms of chromium in the presence of other heavy metals was also tested at laboratory and industrial waste water regime. These findings open up new avenues in the row of high performance, scalable, and economic nanobiomaterial for the remediation of both forms of chromium from water streams.

  18. Hysteresis in modeling of poroelastic systems: quasistatic equilibrium.

    PubMed

    Guyer, R A; Kim, H Alicia; Derome, Dominique; Carmeliet, Jan; TenCate, J

    2011-06-01

    The behavior of hysteretic, coupled elastic and fluid systems is modeled. The emphasis is on quasistatic equilibrium in response to prescribed chemical potential (μ) protocols and prescribed stress (σ) protocols. Hysteresis arises in these models either from the presence of hysterons or from the presence of self-trapping internal fields. This latter mechanism is modeled in finite element calculations which serve to illustrate the creation of hysteresis in a range of circumstances that go from conventionally hysteretic systems, a sandstone, to systems like a wood fiber. An essential ingredient in the behavior of these systems, the interaction between the mechanical variables and the fluid variables, is accorded special attention. The proper venue for the exploration of these systems is (μ,σ) space and appropriate μ protocols, σ protocols, and combined μ-σ protocols.

  19. Description of the General Equilibrium Model of Ecosystem Services (GEMES)

    Treesearch

    Travis Warziniack; David Finnoff; Jenny Apriesnig

    2017-01-01

    This paper serves as documentation for the General Equilibrium Model of Ecosystem Services (GEMES). GEMES is a regional computable general equilibrium model that is composed of values derived from natural capital and ecosystem services. It models households, producing sectors, and governments, linked to one another through commodity and factor markets. GEMES was...

  20. A rapid method for the computation of equilibrium chemical composition of air to 15000 K

    NASA Technical Reports Server (NTRS)

    Prabhu, Ramadas K.; Erickson, Wayne D.

    1988-01-01

    A rapid computational method has been developed to determine the chemical composition of equilibrium air to 15000 K. Eleven chemically reacting species, i.e., O2, N2, O, NO, N, NO+, e-, N+, O+, Ar, and Ar+ are included. The method involves combining algebraically seven nonlinear equilibrium equations and four linear elemental mass balance and charge neutrality equations. Computational speeds for determining the equilibrium chemical composition are significantly faster than the often used free energy minimization procedure. Data are also included from which the thermodynamic properties of air can be computed. A listing of the computer program together with a set of sample results are included.

  1. The Adverse Effects of Le Châtelier's Principle on Teacher Understanding of Chemical Equilibrium

    NASA Astrophysics Data System (ADS)

    Cheung, Derek

    2009-04-01

    Although the scientific inadequacy of Le Châtelier's principle has long been documented in the literature, the principle is still treated as a central concept of chemical equilibrium by textbook writers and teachers in many countries. In the past, researchers' interest has focused on student misconceptions about chemical equilibrium and has neglected teacher misconceptions. This study aimed to determine how Le Châtelier's principle adversely affects teachers' ability to solve chemical equilibrium problems. This area of research is critically important because teachers cannot help their students understand what they themselves do not understand. In this study, a misconception test was developed and administered to a sample of 33 secondary chemistry teachers in Hong Kong. The test consisted of three open-ended chemical equilibrium questions. Analysis of teacher responses revealed that most of the 33 teachers failed the test as they relied on Le Châtelier's principle rather than the equilibrium law to tackle the three chemical equilibrium problems. Teachers' misconceptions about chemical equilibrium were categorized. Implications of these findings for chemistry teacher education and selection of curriculum content for school chemistry are discussed.

  2. Effect of a Perturbation on the Chemical Equilibrium: Comparison with Le Chatelier's Principle

    ERIC Educational Resources Information Center

    Torres, Emilio Martinez

    2007-01-01

    This article develops a general thermodynamic treatment to predict the direction of shift in a chemical equilibrium when it is subjected to a stress. This treatment gives an inequality that relates the change in the perturbed variable and the change that the equilibrium shift produces in the conjugated variable. To illustrate the generality of…

  3. Effect of a Perturbation on the Chemical Equilibrium: Comparison with Le Chatelier's Principle

    ERIC Educational Resources Information Center

    Torres, Emilio Martinez

    2007-01-01

    This article develops a general thermodynamic treatment to predict the direction of shift in a chemical equilibrium when it is subjected to a stress. This treatment gives an inequality that relates the change in the perturbed variable and the change that the equilibrium shift produces in the conjugated variable. To illustrate the generality of…

  4. A two-dimensional, TVD numerical scheme for inviscid, high Mach number flows in chemical equilibrium

    NASA Technical Reports Server (NTRS)

    Eberhardt, S.; Palmer, G.

    1986-01-01

    A new algorithm has been developed for hypervelocity flows in chemical equilibrium. Solutions have been achieved for Mach numbers up to 15 with no adverse effect on convergence. Two methods of coupling an equilibrium chemistry package have been tested, with the simpler method proving to be more robust. Improvements in boundary conditions are still required for a production-quality code.

  5. Remarkable nanoconfinement effects on chemical equilibrium manifested in nucleotide dimerization and H-D exchange reactions.

    PubMed

    Polak, Micha; Rubinovich, Leonid

    2011-10-06

    Nanoconfinement entropic effects on chemical equilibrium involving a small number of molecules, which we term NCECE, are revealed by two widely diverse types of reactions. Employing statistical-mechanical principles, we show how the NCECE effect stabilizes nucleotide dimerization observed within self-assembled molecular cages. Furthermore, the effect provides the basis for dimerization even under an aqueous environment inside the nanocage. Likewise, the NCECE effect is pertinent to a longstanding issue in astrochemistry, namely the extra deuteration commonly observed for molecules reacting on interstellar dust grain surfaces. The origin of the NCECE effect is elucidated by means of the probability distributions of the reaction extent and related variations in the reactant-product mixing entropy. Theoretical modelling beyond our previous preliminary work highlights the role of the nanospace size in addition to that of the nanosystem size, namely the limited amount of molecules in the reaction mixture. Furthermore, the NCECE effect can depend also on the reaction mechanism, and on deviations from stoichiometry. The NCECE effect, leading to enhanced, greatly variable equilibrium "constants", constitutes a unique physical-chemical phenomenon, distinguished from the usual thermodynamical properties of macroscopically large systems. Being significant particularly for weakly exothermic reactions, the effects should stabilize products in other closed nanoscale structures, and thus can have notable implications for the growing nanotechnological utilization of chemical syntheses conducted within confined nanoreactors.

  6. Relating Students' Reasoning To the History of Science: The Case of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Van Driel, Jan H.; De Vos, Wobbe; Verloop, Nico

    1998-01-01

    Relates the reasoning of students introduced to the concept of chemical equilibrium to the historical development of the concept. Concludes that the study of authentic historical sources may inspire the design of effective teaching activities. Contains 33 references. (DDR)

  7. Construction and repair of highly ordered 2D covalent networks by chemical equilibrium regulation.

    PubMed

    Guan, Cui-Zhong; Wang, Dong; Wan, Li-Jun

    2012-03-21

    The construction of well-ordered 2D covalent networks via the dehydration of di-borate aromatic molecules was successfully realized through introducing a small amount of water into a closed reaction system to regulate the chemical equilibrium.

  8. Dissolved and labile concentrations of Cd, Cu, Pb, and Zn in the South Fork Coeur d'Alene River, Idaho: Comparisons among chemical equilibrium models and implications for biotic ligand models

    USGS Publications Warehouse

    Balistrieri, L.S.; Blank, R.G.

    2008-01-01

    In order to evaluate thermodynamic speciation calculations inherent in biotic ligand models, the speciation of dissolved Cd, Cu, Pb, and Zn in aquatic systems influenced by historical mining activities is examined using equilibrium computer models and the diffusive gradients in thin films (DGT) technique. Several metal/organic-matter complexation models, including WHAM VI, NICA-Donnan, and Stockholm Humic model (SHM), are used in combination with inorganic speciation models to calculate the thermodynamic speciation of dissolved metals and concentrations of metal associated with biotic ligands (e.g., fish gills). Maximum dynamic metal concentrations, determined from total dissolved metal concentrations and thermodynamic speciation calculations, are compared with labile metal concentrations measured by DGT to assess which metal/organic-matter complexation model best describes metal speciation and, thereby, biotic ligand speciation, in the studied systems. Results indicate that the choice of model that defines metal/organic-matter interactions does not affect calculated concentrations of Cd and Zn associated with biotic ligands for geochemical conditions in the study area, whereas concentrations of Cu and Pb associated with biotic ligands depend on whether the speciation calculations use WHAM VI, NICA-Donnan, or SHM. Agreement between labile metal concentrations and dynamic metal concentrations occurs when WHAM VI is used to calculate Cu speciation and SHM is used to calculate Pb speciation. Additional work in systems that contain wide ranges in concentrations of multiple metals should incorporate analytical speciation methods, such as DGT, to constrain the speciation component of biotic ligand models. ?? 2008 Elsevier Ltd.

  9. Students' and teachers' misapplication of le chatelier's principle: Implications for the teaching of chemical equilibrium

    NASA Astrophysics Data System (ADS)

    Quílez-Pardo, Juan; Solaz-Portolés, Joan Josep

    The aim of this article was to study the reasons, strategies, and procedures that both students and teachers use to solve some chemical equilibrium questions and problems. Inappropriate conceptions on teaching and a lack of knowledge regarding the limited usefulness of Le Chatelier's principle, with its vague and ambiguous formulation and textbook presentation, may be some of the sources of misconceptions about the prediction of the effect of changing conditions on chemical equilibrium. To diagnose misconceptions and their possible sources, a written test was developed and administered to 170 1st-year university chemistry students. A chemical equilibrium problem, relating to the students' test, was solved by 40 chemistry teachers. First, we ascertained that teacher's conceptions might influence the problem-solving strategies of the learner. Based on this first aspect, our discussion also concerns students' and teachers' misconceptions related to the Le Chatelier's principle. Misconceptions emerged through: (a) misapplication and misunderstanding of Le Chatelier's principle; (b) use of rote-learning recall and algorithmic procedures; (c) incorrect control of the variables involved; (d) limited use of the chemical equilibrium law; (e) a lack of mastery of chemical equilibrium principles and difficulty in transferring such principles to new situations. To avoid chemical equilibrium misconceptions, a specific pattern of conceptual and methodological change may be considered.Received: 16 November 1993; Revised: 21 September 1994;

  10. Chemical Equilibrium in Supramolecular Systems as Studied by NMR Spectrometry

    ERIC Educational Resources Information Center

    Gonzalez-Gaitano, Gustavo; Tardajos, Gloria

    2004-01-01

    Undergraduate students are required to study the chemical balance in supramolecular assemblies constituting two or more interacting species, by using proton NMR spectrometry. A good knowledge of physical chemistry, fundamentals of chemical balance, and NMR are pre-requisites for conducting this study.

  11. Chemical Equilibrium in Supramolecular Systems as Studied by NMR Spectrometry

    ERIC Educational Resources Information Center

    Gonzalez-Gaitano, Gustavo; Tardajos, Gloria

    2004-01-01

    Undergraduate students are required to study the chemical balance in supramolecular assemblies constituting two or more interacting species, by using proton NMR spectrometry. A good knowledge of physical chemistry, fundamentals of chemical balance, and NMR are pre-requisites for conducting this study.

  12. Trunk biomechanical models based on equilibrium at a single-level violate equilibrium at other levels

    PubMed Central

    Arjmand, N.; Parnianpour, M.

    2006-01-01

    Accurate estimation of muscle forces in various occupational tasks is critical for a reliable evaluation of spinal loads and subsequent assessment of risk of injury and management of back disorders. The majority of biomechanical models of multi-segmental spine estimate muscle forces and spinal loads based on the balance of net moments at a single level with no consideration for the equilibrium at remaining levels. This work aimed to quantify the extent of equilibrium violation and alterations in estimations when such models are performed at different levels. Results are compared with those of kinematics-driven model that satisfies equilibrium at all levels and EMG data. Regardless of the method used (optimization or EMG-assisted), single-level free body diagram models yielded estimations that substantially altered depending on the level considered (i.e., level dependency). Equilibrium of net moment was also grossly violated at remaining levels with the error increasing in more demanding tasks. These models may, however, be used to estimate spinal compression forces. PMID:17136359

  13. Achieving Chemical Equilibrium: The Role of Imposed Conditions in the Ammonia Formation Reaction

    ERIC Educational Resources Information Center

    Tellinghuisen, Joel

    2006-01-01

    Under conditions of constant temperature T and pressure P, chemical equilibrium occurs in a closed system (fixed mass) when the Gibbs free energy G of the reaction mixture is minimized. However, when chemical reactions occur under other conditions, other thermodynamic functions are minimized or maximized. For processes at constant T and volume V,…

  14. Rapid computation of chemical equilibrium composition - An application to hydrocarbon combustion

    NASA Technical Reports Server (NTRS)

    Erickson, W. D.; Prabhu, R. K.

    1986-01-01

    A scheme for rapidly computing the chemical equilibrium composition of hydrocarbon combustion products is derived. A set of ten governing equations is reduced to a single equation that is solved by the Newton iteration method. Computation speeds are approximately 80 times faster than the often used free-energy minimization method. The general approach also has application to many other chemical systems.

  15. Achieving Chemical Equilibrium: The Role of Imposed Conditions in the Ammonia Formation Reaction

    ERIC Educational Resources Information Center

    Tellinghuisen, Joel

    2006-01-01

    Under conditions of constant temperature T and pressure P, chemical equilibrium occurs in a closed system (fixed mass) when the Gibbs free energy G of the reaction mixture is minimized. However, when chemical reactions occur under other conditions, other thermodynamic functions are minimized or maximized. For processes at constant T and volume V,…

  16. A Unified Graphical Representation of Chemical Thermodynamics and Equilibrium

    ERIC Educational Resources Information Center

    Hanson, Robert M.

    2012-01-01

    During the years 1873-1879, J. Willard Gibbs published his now-famous set of articles that form the basis of the current perspective on chemical thermodynamics. The second article of this series, "A Method of Geometrical Representation of the Thermodynamic Properties of Substances by Means of Surfaces," published in 1873, is particularly notable…

  17. A Unified Graphical Representation of Chemical Thermodynamics and Equilibrium

    ERIC Educational Resources Information Center

    Hanson, Robert M.

    2012-01-01

    During the years 1873-1879, J. Willard Gibbs published his now-famous set of articles that form the basis of the current perspective on chemical thermodynamics. The second article of this series, "A Method of Geometrical Representation of the Thermodynamic Properties of Substances by Means of Surfaces," published in 1873, is particularly notable…

  18. Direct Monte Carlo simulation of the chemical equilibrium composition of detonation products

    SciTech Connect

    Shaw, M.S.

    1993-06-01

    A new Monte Carlo simulation method has been developed by the author which gives the equilibrium chemical composition of a molecular fluid directly. The usual NPT ensemble (isothermal-isobaric) is implemented with N being the number of atoms instead of molecules. Changes in chemical composition are treated as correlated spatial moves of atoms. Given the interaction potentials between molecular products, ``exact`` EOS points including the equilibrium chemical composition can be determined from the simulations. This method is applied to detonation products at conditions in the region near the Chapman- Jouget state. For the example of NO, it is shown that the CJ detonation velocity can be determined to a few meters per second. A rather small change in cross potentials is shown to shift the chemical equilibrium and the CJ conditions significantly.

  19. A time-accurate algorithm for chemical non-equilibrium viscous flows at all speeds

    NASA Technical Reports Server (NTRS)

    Shuen, J.-S.; Chen, K.-H.; Choi, Y.

    1992-01-01

    A time-accurate, coupled solution procedure is described for the chemical nonequilibrium Navier-Stokes equations over a wide range of Mach numbers. This method employs the strong conservation form of the governing equations, but uses primitive variables as unknowns. Real gas properties and equilibrium chemistry are considered. Numerical tests include steady convergent-divergent nozzle flows with air dissociation/recombination chemistry, dump combustor flows with n-pentane-air chemistry, nonreacting flow in a model double annular combustor, and nonreacting unsteady driven cavity flows. Numerical results for both the steady and unsteady flows demonstrate the efficiency and robustness of the present algorithm for Mach numbers ranging from the incompressible limit to supersonic speeds.

  20. A time-accurate algorithm for chemical non-equilibrium viscous flows at all speeds

    NASA Technical Reports Server (NTRS)

    Shuen, J.-S.; Chen, K.-H.; Choi, Y.

    1992-01-01

    A time-accurate, coupled solution procedure is described for the chemical nonequilibrium Navier-Stokes equations over a wide range of Mach numbers. This method employs the strong conservation form of the governing equations, but uses primitive variables as unknowns. Real gas properties and equilibrium chemistry are considered. Numerical tests include steady convergent-divergent nozzle flows with air dissociation/recombination chemistry, dump combustor flows with n-pentane-air chemistry, nonreacting flow in a model double annular combustor, and nonreacting unsteady driven cavity flows. Numerical results for both the steady and unsteady flows demonstrate the efficiency and robustness of the present algorithm for Mach numbers ranging from the incompressible limit to supersonic speeds.

  1. Adaptive Chemical Networks under Non-Equilibrium Conditions: The Evaporating Droplet.

    PubMed

    Armao, Joseph J; Lehn, Jean-Marie

    2016-10-17

    Non-volatile solutes in an evaporating drop experience an out-of-equilibrium state due to non-linear concentration effects and complex flow patterns. Here, we demonstrate a small molecule chemical reaction network that undergoes a rapid adaptation response to the out-of-equilibrium conditions inside the droplet leading to control over the molecular constitution and spatial arrangement of the deposition pattern. Adaptation results in a pronounced coffee stain effect and coupling to chemical concentration gradients within the drop is demonstrated. Amplification and suppression of network species are readily identifiable with confocal fluorescence microscopy. We anticipate that these observations will contribute to the design and exploration of out-of-equilibrium chemical systems, as well as be useful towards the development of point-of-care medical diagnostics and controlled deposition of small molecules through inkjet printing.

  2. Non-equilibrium assembly of microtubules: from molecules to autonomous chemical robots.

    PubMed

    Hess, H; Ross, Jennifer L

    2017-03-22

    Biological systems have evolved to harness non-equilibrium processes from the molecular to the macro scale. It is currently a grand challenge of chemistry, materials science, and engineering to understand and mimic biological systems that have the ability to autonomously sense stimuli, process these inputs, and respond by performing mechanical work. New chemical systems are responding to the challenge and form the basis for future responsive, adaptive, and active materials. In this article, we describe a particular biochemical-biomechanical network based on the microtubule cytoskeletal filament - itself a non-equilibrium chemical system. We trace the non-equilibrium aspects of the system from molecules to networks and describe how the cell uses this system to perform active work in essential processes. Finally, we discuss how microtubule-based engineered systems can serve as testbeds for autonomous chemical robots composed of biological and synthetic components.

  3. Structure, dynamics, and hydration of a collagen model polypeptide, (L-prolyl-L-prolylglycyl)10, in aqueous media: a chemical equilibrium analysis of triple helix-to-single coil transition.

    PubMed

    Shikata, Toshiyuki; Minakawa, Ayako; Okuyama, Kenji

    2009-10-29

    The structure, dynamics, and hydration behavior of a collagen model polypeptide, (L-prolyl-L-prolylglycyl)(10) (PPG10), were investigated in pure water and dilute acetic acid over a wide temperature range using broadband dielectric relaxation (DR) techniques that spanned frequencies from 1 kHz to 20 GHz. All samples showed pronounced dielectric dispersion with two major relaxation processes around 3 MHz and 20 GHz. Because DR measurements sensitively probe dipoles and their dynamics, the structures and ionization states of the carboxy and amino termini of aqueous PPG10 were precisely determined from the relaxation times and strengths in the 3 MHz frequency range. In solution, PPG10 formed mixtures of monodisperse rods as triple helices with lengths and diameters of 8.6 and 1.5 nm, respectively, and monomeric random coils with radii of approximately 1.4 nm. Ionization of the C-terminus was suppressed by the addition of acetic acid in both states. The fraction of random coils (f(coil)) was found to be a function of temperature (T) and the concentration of PPG10 (c). At low temperatures, small f(coil) values were found, which increased with temperature to reach f(coil) = 1 at approximately 60 degrees C, irrespective of c. This phenomenon, well-known as a triple helix-to-single coil transition, is discussed on the basis of the chemical reaction, (PPG10)(3) <==> 3PPG10, with an equilibrium constant of K = 3(c/55.6)(2)f(coil)(3)(1 - f(coil))(-1). The standard enthalpy change evaluated from Arrhenius plots (ln K versus T(-1)) was found to change dramatically at the same transition temperature that was previously determined by using optical rotation experiments. The other major DR process, observed at approximately 20 GHz, was assigned to free and hydrated water molecules and used to determine the average hydration number (m) per PPG10. The m values for the triple helix and random coil state at 25 degrees C were evaluated to be m(th) = 60-70 and m(coil) = 250-270. The m

  4. Turbulence modeling for non-equilibrium flows

    NASA Technical Reports Server (NTRS)

    Durbin, Paul A.

    1993-01-01

    Two projects are reported. The first is the development and testing of an eddy viscosity transport model. This project also is a starting point for our work on developing computational tools for solving turbulence models in complex geometries. The second project is a stochastic analysis of the realizability of Reynolds stress transport models.

  5. Equilibrium Distribution of Mutators in the Single Fitness Peak Model

    NASA Astrophysics Data System (ADS)

    Tannenbaum, Emmanuel; Deeds, Eric J.; Shakhnovich, Eugene I.

    2003-09-01

    This Letter develops an analytically tractable model for determining the equilibrium distribution of mismatch repair deficient strains in unicellular populations. The approach is based on the single fitness peak model, which has been used in Eigen’s quasispecies equations in order to understand various aspects of evolutionary dynamics. As with the quasispecies model, our model for mutator-nonmutator equilibrium undergoes a phase transition in the limit of infinite sequence length. This “repair catas­trophe” occurs at a critical repair error probability of ɛr=Lvia/L, where Lvia denotes the length of the genome controlling viability, while L denotes the overall length of the genome. The repair catastrophe therefore occurs when the repair error probability exceeds the fraction of deleterious mutations. Our model also gives a quantitative estimate for the equilibrium fraction of mutators in Escherichia coli.

  6. Phylogenies support out-of-equilibrium models of biodiversity.

    PubMed

    Manceau, Marc; Lambert, Amaury; Morlon, Hélène

    2015-04-01

    There is a long tradition in ecology of studying models of biodiversity at equilibrium. These models, including the influential Neutral Theory of Biodiversity, have been successful at predicting major macroecological patterns, such as species abundance distributions. But they have failed to predict macroevolutionary patterns, such as those captured in phylogenetic trees. Here, we develop a model of biodiversity in which all individuals have identical demographic rates, metacommunity size is allowed to vary stochastically according to population dynamics, and speciation arises naturally from the accumulation of point mutations. We show that this model generates phylogenies matching those observed in nature if the metacommunity is out of equilibrium. We develop a likelihood inference framework that allows fitting our model to empirical phylogenies, and apply this framework to various mammalian families. Our results corroborate the hypothesis that biodiversity dynamics are out of equilibrium.

  7. A kinetic and equilibrium analysis of silicon carbide chemical vapor deposition on monofilaments

    NASA Technical Reports Server (NTRS)

    Gokoglu, S. A.; Kuczmarski, M. A.

    1993-01-01

    Chemical kinetics of atmospheric pressure silicon carbide (SiC) chemical vapor deposition (CVD) from dilute silane and propane source gases in hydrogen is numerically analyzed in a cylindrical upflow reactor designed for CVD on monofilaments. The chemical composition of the SiC deposit is assessed both from the calculated total fluxes of carbon and silicon and from chemical equilibrium considerations for the prevailing temperatures and species concentrations at and along the filament surface. The effects of gas and surface chemistry on the evolution of major gas phase species are considered in the analysis.

  8. Control of Chemical Equilibrium by Solvent: A Basis for Teaching Physical Chemistry of Solutions

    ERIC Educational Resources Information Center

    Prezhdo, Oleg V.; Craig, Colleen F.; Fialkov, Yuriy; Prezhdo, Victor V.

    2007-01-01

    The study demonstrates that the solvent present in a system can highly alter and control the chemical equilibrium of a system. The results show that the dipole moment and polarizibility of a system can be highly altered by using different mixed solvents.

  9. The Effect of a Conceptual Change Approach on Understanding of Students' Chemical Equilibrium Concepts

    ERIC Educational Resources Information Center

    Atasoy, Basri; Akkus, Huseyin; Kadayifci, Hakki

    2009-01-01

    The purpose of this study was to compare the effects of a conceptual change approach over traditional instruction on tenth-grade students' conceptual achievement in understanding chemical equilibrium. The study was conducted in two classes of the same teacher with participation of a total of 44 tenth-grade students. In this study, a…

  10. A Teaching Sequence for Learning the Concept of Chemical Equilibrium in Secondary School Education

    ERIC Educational Resources Information Center

    Ghirardi, Marco; Marchetti, Fabio; Pettinari, Claudio; Regis, Alberto; Roletto, Ezio

    2014-01-01

    A novel didactic sequence is proposed for the teaching of chemical equilibrium. This teaching sequence takes into account the historical and epistemological evolution of the concept, the alternative conceptions and learning difficulties highlighted by teaching science and research in education, and the need to focus on both the students'…

  11. Strategies Reported Used by Instructors to Address Student Alternate Conceptions in Chemical Equilibrium

    ERIC Educational Resources Information Center

    Piquette, Jeff S.; Heikkinen, Henry W.

    2005-01-01

    This study explores general-chemistry instructors' awareness of and ability to identify and address common student learning obstacles in chemical equilibrium. Reported instructor strategies directed at remediating student alternate conceptions were investigated and compared with successful, literature-based conceptual change methods. Fifty-two…

  12. Analogies in the Teaching of Chemical Equilibrium: A Synthesis/Analysis of the Literature

    ERIC Educational Resources Information Center

    Raviolo, Andres; Garritz, Andoni

    2009-01-01

    This paper presents a thorough literature review of the analogies used to teach chemical equilibrium. The main objective is to compile all the analogies that have been found to be of service to the teacher and the student. Additionally, we categorize and analyze analogies in relation to the following aspects: representation of the dynamic nature…

  13. Argumentation Practices in Classroom: Pre-Service Teachers' Conceptual Understanding of Chemical Equilibrium

    ERIC Educational Resources Information Center

    Kaya, Ebru

    2013-01-01

    This study examines the impact of argumentation practices on pre-service teachers' understanding of chemical equilibrium. The sample consisted of 100 pre-service teachers in two classes of a public university. One of these classes was assigned as experimental and the other as control group, randomly. In the experimental group, the subject of…

  14. Systematic Approach to Calculate the Concentration of Chemical Species in Multi-Equilibrium Problems

    ERIC Educational Resources Information Center

    Baeza-Baeza, Juan Jose; Garcia-Alvarez-Coque, Maria Celia

    2011-01-01

    A general systematic approach is proposed for the numerical calculation of multi-equilibrium problems. The approach involves several steps: (i) the establishment of balances involving the chemical species in solution (e.g., mass balances, charge balance, and stoichiometric balance for the reaction products), (ii) the selection of the unknowns (the…

  15. Using Think-Aloud Protocols to Investigate Secondary School Chemistry Teachers' Misconceptions about Chemical Equilibrium

    ERIC Educational Resources Information Center

    Cheung, Derek

    2009-01-01

    Secondary school chemistry teachers' understanding of chemical equilibrium was investigated through interviews using the think-aloud technique. The interviews were conducted with twelve volunteer chemistry teachers in Hong Kong. Their teaching experience ranged from 3 to 18 years. They were asked to predict what would happen to the equilibrium…

  16. A time-accurate implicit method for chemical non-equilibrium flows at all speeds

    NASA Technical Reports Server (NTRS)

    Shuen, Jian-Shun

    1992-01-01

    A new time accurate coupled solution procedure for solving the chemical non-equilibrium Navier-Stokes equations over a wide range of Mach numbers is described. The scheme is shown to be very efficient and robust for flows with velocities ranging from M less than or equal to 10(exp -10) to supersonic speeds.

  17. Student Misconceptions in Chemical Equilibrium as Related to Cognitive Level and Achievement.

    ERIC Educational Resources Information Center

    Wheeler, Alan E.; Kass, Heidi

    Reported is an investigation to determine the nature and extent of student misconceptions in chemical equilibrium and to ascertain the degree to which certain misconceptions are related to chemistry achievement and to performance on specific tasks involving cognitive transformations characteristic of the concrete and formal operational stages of…

  18. Exploring the Impact of Argumentation on Pre-Service Science Teachers' Conceptual Understanding of Chemical Equilibrium

    ERIC Educational Resources Information Center

    Aydeniz, Mehmet; Dogan, Alev

    2016-01-01

    This study examines the impact of argumentation on pre-service science teachers' (PST) conceptual understanding of chemical equilibrium. The sample consisted of 57 first-year PSTs enrolled in a teacher education program in Turkey. Thirty two of the 57 PSTs who participated in this study were in the experimental group and 25 in the control group.…

  19. The Effect of a Conceptual Change Approach on Understanding of Students' Chemical Equilibrium Concepts

    ERIC Educational Resources Information Center

    Atasoy, Basri; Akkus, Huseyin; Kadayifci, Hakki

    2009-01-01

    The purpose of this study was to compare the effects of a conceptual change approach over traditional instruction on tenth-grade students' conceptual achievement in understanding chemical equilibrium. The study was conducted in two classes of the same teacher with participation of a total of 44 tenth-grade students. In this study, a…

  20. Control of Chemical Equilibrium by Solvent: A Basis for Teaching Physical Chemistry of Solutions

    ERIC Educational Resources Information Center

    Prezhdo, Oleg V.; Craig, Colleen F.; Fialkov, Yuriy; Prezhdo, Victor V.

    2007-01-01

    The study demonstrates that the solvent present in a system can highly alter and control the chemical equilibrium of a system. The results show that the dipole moment and polarizibility of a system can be highly altered by using different mixed solvents.

  1. A Simple Method to Calculate the Temperature Dependence of the Gibbs Energy and Chemical Equilibrium Constants

    ERIC Educational Resources Information Center

    Vargas, Francisco M.

    2014-01-01

    The temperature dependence of the Gibbs energy and important quantities such as Henry's law constants, activity coefficients, and chemical equilibrium constants is usually calculated by using the Gibbs-Helmholtz equation. Although, this is a well-known approach and traditionally covered as part of any physical chemistry course, the required…

  2. Analogies in the Teaching of Chemical Equilibrium: A Synthesis/Analysis of the Literature

    ERIC Educational Resources Information Center

    Raviolo, Andres; Garritz, Andoni

    2009-01-01

    This paper presents a thorough literature review of the analogies used to teach chemical equilibrium. The main objective is to compile all the analogies that have been found to be of service to the teacher and the student. Additionally, we categorize and analyze analogies in relation to the following aspects: representation of the dynamic nature…

  3. A Teaching Sequence for Learning the Concept of Chemical Equilibrium in Secondary School Education

    ERIC Educational Resources Information Center

    Ghirardi, Marco; Marchetti, Fabio; Pettinari, Claudio; Regis, Alberto; Roletto, Ezio

    2014-01-01

    A novel didactic sequence is proposed for the teaching of chemical equilibrium. This teaching sequence takes into account the historical and epistemological evolution of the concept, the alternative conceptions and learning difficulties highlighted by teaching science and research in education, and the need to focus on both the students'…

  4. Using Think-Aloud Protocols to Investigate Secondary School Chemistry Teachers' Misconceptions about Chemical Equilibrium

    ERIC Educational Resources Information Center

    Cheung, Derek

    2009-01-01

    Secondary school chemistry teachers' understanding of chemical equilibrium was investigated through interviews using the think-aloud technique. The interviews were conducted with twelve volunteer chemistry teachers in Hong Kong. Their teaching experience ranged from 3 to 18 years. They were asked to predict what would happen to the equilibrium…

  5. Argumentation Practices in Classroom: Pre-Service Teachers' Conceptual Understanding of Chemical Equilibrium

    ERIC Educational Resources Information Center

    Kaya, Ebru

    2013-01-01

    This study examines the impact of argumentation practices on pre-service teachers' understanding of chemical equilibrium. The sample consisted of 100 pre-service teachers in two classes of a public university. One of these classes was assigned as experimental and the other as control group, randomly. In the experimental group, the subject of…

  6. Strategies Reported Used by Instructors to Address Student Alternate Conceptions in Chemical Equilibrium

    ERIC Educational Resources Information Center

    Piquette, Jeff S.; Heikkinen, Henry W.

    2005-01-01

    This study explores general-chemistry instructors' awareness of and ability to identify and address common student learning obstacles in chemical equilibrium. Reported instructor strategies directed at remediating student alternate conceptions were investigated and compared with successful, literature-based conceptual change methods. Fifty-two…

  7. Exploring the Impact of Argumentation on Pre-Service Science Teachers' Conceptual Understanding of Chemical Equilibrium

    ERIC Educational Resources Information Center

    Aydeniz, Mehmet; Dogan, Alev

    2016-01-01

    This study examines the impact of argumentation on pre-service science teachers' (PST) conceptual understanding of chemical equilibrium. The sample consisted of 57 first-year PSTs enrolled in a teacher education program in Turkey. Thirty two of the 57 PSTs who participated in this study were in the experimental group and 25 in the control group.…

  8. The Effectiveness of Conceptual Change Texts in Remediating High School Students' Alternative Conceptions Concerning Chemical Equilibrium

    ERIC Educational Resources Information Center

    Ozmen, Haluk

    2007-01-01

    This study investigated the effectiveness of conceptual change texts in remediating high school students' alternative conceptions concerning chemical equilibrium. A quasi-experimental design was used in this study. The subjects for this study consisted of a total 78 tenth-grade students, 38 of them in the experimental group and 40 of them in the…

  9. Systematic Approach to Calculate the Concentration of Chemical Species in Multi-Equilibrium Problems

    ERIC Educational Resources Information Center

    Baeza-Baeza, Juan Jose; Garcia-Alvarez-Coque, Maria Celia

    2011-01-01

    A general systematic approach is proposed for the numerical calculation of multi-equilibrium problems. The approach involves several steps: (i) the establishment of balances involving the chemical species in solution (e.g., mass balances, charge balance, and stoichiometric balance for the reaction products), (ii) the selection of the unknowns (the…

  10. A Simple Method to Calculate the Temperature Dependence of the Gibbs Energy and Chemical Equilibrium Constants

    ERIC Educational Resources Information Center

    Vargas, Francisco M.

    2014-01-01

    The temperature dependence of the Gibbs energy and important quantities such as Henry's law constants, activity coefficients, and chemical equilibrium constants is usually calculated by using the Gibbs-Helmholtz equation. Although, this is a well-known approach and traditionally covered as part of any physical chemistry course, the required…

  11. Model-based analysis of coupled equilibrium-kinetic processes: indirect kinetic studies of thermodynamic parameters using the dynamic data.

    PubMed

    Emami, Fereshteh; Maeder, Marcel; Abdollahi, Hamid

    2015-05-07

    Thermodynamic studies of equilibrium chemical reactions linked with kinetic procedures are mostly impossible by traditional approaches. In this work, the new concept of generalized kinetic study of thermodynamic parameters is introduced for dynamic data. The examples of equilibria intertwined with kinetic chemical mechanisms include molecular charge transfer complex formation reactions, pH-dependent degradation of chemical compounds and tautomerization kinetics in micellar solutions. Model-based global analysis with the possibility of calculating and embedding the equilibrium and kinetic parameters into the fitting algorithm has allowed the complete analysis of the complex reaction mechanisms. After the fitting process, the optimal equilibrium and kinetic parameters together with an estimate of their standard deviations have been obtained. This work opens up a promising new avenue for obtaining equilibrium constants through the kinetic data analysis for the kinetic reactions that involve equilibrium processes.

  12. Coupling microscopic and mesoscopic scales to simulate chemical equilibrium between a nanometric carbon cluster and detonation products fluid.

    PubMed

    Bourasseau, Emeric; Maillet, Jean-Bernard

    2011-04-21

    This paper presents a new method to obtain chemical equilibrium properties of detonation products mixtures including a solid carbon phase. In this work, the solid phase is modelled through a mesoparticle immersed in the fluid, such that the heterogeneous character of the mixture is explicitly taken into account. Inner properties of the clusters are taken from an equation of state obtained in a previous work, and interaction potential between the nanocluster and the fluid particles is derived from all-atoms simulations using the LCBOPII potential (Long range Carbon Bond Order Potential II). It appears that differences in chemical equilibrium results obtained with this method and the "composite ensemble method" (A. Hervouet et al., J. Phys. Chem. B, 2008, 112.), where fluid and solid phases are considered as non-interacting, are not significant, underlining the fact that considering the inhomogeneity of such system is crucial.

  13. Uncertainty of mantle geophysical properties computed from phase equilibrium models

    NASA Astrophysics Data System (ADS)

    Connolly, J. A. D.; Khan, A.

    2016-05-01

    Phase equilibrium models are used routinely to predict geophysically relevant mantle properties. A limitation of this approach is that nonlinearity of the phase equilibrium problem precludes direct assessment of the resultant uncertainties. To overcome this obstacle, we stochastically assess uncertainties along self-consistent mantle adiabats for pyrolitic and basaltic bulk compositions to 2000 km depth. The dominant components of the uncertainty are the identity, composition and elastic properties of the minerals. For P wave speed and density, the latter components vary little, whereas the first is confined to the upper mantle. Consequently, P wave speeds, densities, and adiabatic temperatures and pressures predicted by phase equilibrium models are more uncertain in the upper mantle than in the lower mantle. In contrast, uncertainties in S wave speeds are dominated by the uncertainty in shear moduli and are approximately constant throughout the model depth range.

  14. A novel local equilibrium model for shaped tokamak plasmas

    SciTech Connect

    Yu Weihong; Zhou Deng; Xiang Nong

    2012-07-15

    A model is proposed for a local up-down symmetric equilibrium in the vicinity of a specified magnetic surface with given elongation and triangularity. Different from the Miller's model [R. L. Miller et al., Phys. Plasmas 5, 973 (1998)], the derivative of the Shafranov shift in the present model is self-consistently determined. The equilibrium accounts for all the essential features, like the elongation, the triangularity, and the Shafranov shift etc., of a shaped cross section. Hence, it can be used for investigation of radially localized plasma modes, like reversed shear Alfvenic eigenmodes and ballooning mode, etc., and it is also suitable for local equilibrium construction used for flux tube plasma simulations.

  15. Heavy ion collisions and the pre-equilibrium exciton model

    SciTech Connect

    Betak, E.

    2012-10-20

    We present a feasible way to apply the pre-equilibrium exciton model in its masterequation formulation to heavy-ion induced reactions including spin variables. Emission of nucleons, {gamma}'s and also light clusters is included in our model.

  16. Atomistic modeling of thermodynamic equilibrium of plutonium

    NASA Astrophysics Data System (ADS)

    Lee, Tongsik; Valone, Steve; Baskes, Mike; Chen, Shao-Ping; Lawson, Andrew

    2012-02-01

    Plutonium metal has complex thermodynamic properties. Among its six allotropes at ambient pressure, the fcc delta-phase exhibits a wide range of anomalous behavior: extraordinarily high elastic anisotropy, largest atomic volume despite the close-packed structure, negative thermal expansion, strong elastic softening at elevated temperature, and extreme sensitivity to dilute alloying. An accurate description of these thermodynamic properties goes far beyond the current capability of first-principle calculations. An elaborate modeling strategy at the atomic level is hence an urgent need. We propose a novel atomistic scheme to model elemental plutonium, in particular, to reproduce the anomalous characteristics of the delta-phase. A modified embedded atom method potential is fitted to two energy-volume curves that represent the distinct electronic states of plutonium in order to embody the mechanism of the two-state model of Weiss, in line with the insight originally proposed by Lawson et al. [Philos. Mag. 86, 2713 (2006)]. By the use of various techniques in Monte Carlo simulations, we are able to provide a unified perspective of diverse phenomenological aspects among thermal expansion, elasticity, and phase stability.

  17. A numerical model of non-equilibrium thermal plasmas. II. Governing equations

    SciTech Connect

    Li HePing; Zhang XiaoNing; Xia Weidong

    2013-03-15

    Governing equations and the corresponding physical properties of the plasmas are both prerequisites for studying the fundamental processes in a non-equilibrium thermal plasma system numerically. In this paper, a kinetic derivation of the governing equations used for describing the complicated thermo-electro-magneto-hydrodynamic-chemical coupling effects in non-equilibrium thermal plasmas is presented. This derivation, which is achieved using the Chapman-Enskog method, is completely consistent with the theory of the transport properties reported in the previous paper by the same authors. It is shown, based on this self-consistent theory, that the definitions of the specific heat at constant pressure and the reactive thermal conductivity of two-temperature plasmas are not necessary. The governing equations can be reduced to their counterparts under local thermodynamic equilibrium (LTE) and local chemical equilibrium (LCE) conditions. The general method for the determination of the boundary conditions of the solved variables is also discussed briefly. The two papers establish a self-consistent physical-mathematical model that describes the complicated physical and chemical processes in a thermal plasma system for the cases both in LTE or LCE conditions and under non-equilibrium conditions.

  18. An implicit flux-split algorithm to calculate hypersonic flowfields in chemical equilibrium

    NASA Technical Reports Server (NTRS)

    Palmer, Grant

    1987-01-01

    An implicit, finite-difference, shock-capturing algorithm that calculates inviscid, hypersonic flows in chemical equilibrium is presented. The flux vectors and flux Jacobians are differenced using a first-order, flux-split technique. The equilibrium composition of the gas is determined by minimizing the Gibbs free energy at every node point. The code is validated by comparing results over an axisymmetric hemisphere against previously published results. The algorithm is also applied to more practical configurations. The accuracy, stability, and versatility of the algorithm have been promising.

  19. Derivation of the chemical-equilibrium rate coefficient using scattering theory

    NASA Technical Reports Server (NTRS)

    Mickens, R. E.

    1977-01-01

    Scattering theory is applied to derive the equilibrium rate coefficient for a general homogeneous chemical reaction involving ideal gases. The reaction rate is expressed in terms of the product of a number of normalized momentum distribution functions, the product of the number of molecules with a given internal energy state, and the spin-averaged T-matrix elements. An expression for momentum distribution at equilibrium for an arbitrary molecule is presented, and the number of molecules with a given internal-energy state is represented by an expression which includes the partition function.

  20. Thermal And Chemical Non-Equilibrium Effects In The Wake Of A Boundary-Layer Sized Object In Hypersonic Flows

    NASA Astrophysics Data System (ADS)

    Birrer, Marcel; Stemmer, Christian; Adams, Nikolaus N.

    2011-05-01

    Investigations of hypersonic boundary-layer flows around a cubical obstacle with a height in the order of half the boundary layer thickness were carried out in this work. Special interest was laid on the influence of chemical non-equilibrium effects on the wake flow of the obstacle. Direct numerical simulations were conducted using three different gas models, a caloric perfect, an equilibrium and a chemical non-equilibrium gas model. The geometry was chosen as a wedge with a six degree half angle, according to the aborted NASA HyBoLT free flight experiment. At 0.5 m downstream of the leading edge, a surface trip was positioned. The free-stream flow was set to Mach 8.5 with air conditions taken from the 1976 standard atmosphere at an altitude of 42 km according to the predicted flight path. The simulations were done in three steps for all models. First, two-dimensional calculations of the whole configuration including the leading edge and the obstacle were conducted. These provide constant span-wise profiles for detailed, steady three-dimensional simulations around the close vicinity of the obstacle. A free-stream Mach number of about 6.3 occurs behind the shock. A cross-section in the wake of the object then delivers the steady inflow for detailed unsteady simulations of the wake. Perturbations at unstable frequencies, obtained from a bi-global secondary stability analysis, were added to these profiles. The solutions are time-Fourier transformed to investigate the unsteady downstream development of the different modes due to the interaction with the base-flow containing two counter-rotating vortices. Results will be presented that show the influence of the presence of chemical non-equilibrium on the instability in the wake of the object leading to a laminar or a turbulent wake.

  1. Effect of a Perturbation on the Chemical Equilibrium: Comparison with Le Châtelier's Principle

    NASA Astrophysics Data System (ADS)

    Martínez Torres, Emilio

    2007-03-01

    This article develops a general thermodynamic treatment to predict the direction of shift in a chemical equilibrium when it is subjected to a stress. This treatment gives an inequality that relates the change in the perturbed variable and the change that the equilibrium shift produces in the conjugated variable. To illustrate the generality of this approach, it has been applied to predict the direction of shift caused by changes of pressure, volume, and amount of substance. In this last case, the well-known unexpected shift in the ammonia synthesis equilibrium upon addition of nitrogen is easily explained. From the above referred inequality and the stability criteria of thermodynamics some conclusions have been obtained about the direction of shift in terms of extensive and extensive variables. This article is suitable for physical chemistry courses.

  2. Evolution of light hydrocarbon gases in subsurface processes: Constraints from chemical equilibrium

    NASA Astrophysics Data System (ADS)

    Sugisaki, Ryuichi; Nagamine, Koichiro

    1995-06-01

    The behaviour of CH 4, C 2H 6 and C 3H 8 in subsurface processes such as magma intrusion, volcanic gas discharge and natural gas generation have been examined from the viewpoint of chemical equilibrium. It seems that equilibrium among these three hydrocarbons is attainable at about 200°C. When a system at high temperatures is cooled, re-equilibration is continued until a low temperature is reached. The rate at which re-equilibration is achieved, however, steadily diminishes and, below 200°C, the reaction between the hydrocarbons stops and the gas composition at this time is frozen in, and it remains unchanged in a metastable state for a long period of geological time. Natural gas compositions from various fields have shown that, when a hydrocarbon system out of chemical equilibrium is heated, it gradually approaches equilibrium above 150°C. On the way towards equilibration, compositions of thermogenic gases apparently temporarily show a thermodynamic equilibrium constant at a temperature that is higher than the real equilibrium temperature expected from the ambient temperature of the samples; in contrast, biogenic gases indicate a lower temperature. In lower temperature regions, kinetic effects probably control the gas composition; the compositions are essentially subjected to genetic processes operating on the gases (such as pyrolysis of organic material and bacterial activity) and they fluctuate substantially. Examination of volcanic gases and pyrolysis experimental data, however, have suggested that the equilibration rate of these hydrocarbons is sluggish in comparison with that of reactive inorganic species such as H 2S and SO 2. The view presented in this study will be helpful in understanding the genetic processes that create oil and gas and the migration of these hydrocarbons and in interpreting the origins of magmatic gases.

  3. Phase Transitions and Equilibrium Measures in Random Matrix Models

    NASA Astrophysics Data System (ADS)

    Martínez-Finkelshtein, A.; Orive, R.; Rakhmanov, E. A.

    2015-02-01

    The paper is devoted to a study of phase transitions in the Hermitian random matrix models with a polynomial potential. In an alternative equivalent language, we study families of equilibrium measures on the real line in a polynomial external field. The total mass of the measure is considered as the main parameter, which may be interpreted also either as temperature or time. Our main tools are differentiation formulas with respect to the parameters of the problem, and a representation of the equilibrium potential in terms of a hyperelliptic integral. Using this combination we introduce and investigate a dynamical system (system of ODEs) describing the evolution of families of equilibrium measures. On this basis we are able to systematically derive a number of new results on phase transitions, such as the local behavior of the system at all kinds of phase transitions, as well as to review a number of known ones.

  4. A Study of Interactions between Mixing and Chemical Reaction Using the Rate-Controlled Constrained-Equilibrium Method

    NASA Astrophysics Data System (ADS)

    Hadi, Fatemeh; Janbozorgi, Mohammad; Sheikhi, M. Reza H.; Metghalchi, Hameed

    2016-10-01

    The rate-controlled constrained-equilibrium (RCCE) method is employed to study the interactions between mixing and chemical reaction. Considering that mixing can influence the RCCE state, the key objective is to assess the accuracy and numerical performance of the method in simulations involving both reaction and mixing. The RCCE formulation includes rate equations for constraint potentials, density and temperature, which allows taking account of mixing alongside chemical reaction without splitting. The RCCE is a dimension reduction method for chemical kinetics based on thermodynamics laws. It describes the time evolution of reacting systems using a series of constrained-equilibrium states determined by RCCE constraints. The full chemical composition at each state is obtained by maximizing the entropy subject to the instantaneous values of the constraints. The RCCE is applied to a spatially homogeneous constant pressure partially stirred reactor (PaSR) involving methane combustion in oxygen. Simulations are carried out over a wide range of initial temperatures and equivalence ratios. The chemical kinetics, comprised of 29 species and 133 reaction steps, is represented by 12 RCCE constraints. The RCCE predictions are compared with those obtained by direct integration of the same kinetics, termed detailed kinetics model (DKM). The RCCE shows accurate prediction of combustion in PaSR with different mixing intensities. The method also demonstrates reduced numerical stiffness and overall computational cost compared to DKM.

  5. Chemistry and Chemical Equilibrium Dynamics of BMAA and Its Carbamate Adducts.

    PubMed

    Diaz-Parga, Pedro; Goto, Joy J; Krishnan, V V

    2017-09-18

    Beta-N-methylamino-L-alanine (BMAA) has been demonstrated to contribute to the onset of the ALS/Parkinsonism-dementia complex (ALS/PDC) and is implicated in the progression of other neurodegenerative diseases. While the role of BMAA in these diseases is still debated, one of the suggested mechanisms involves the activation of excitatory glutamate receptors. In particular, the excitatory effects of BMAA are shown to be dependent on the presence of bicarbonate ions, which in turn forms carbamate adducts in physiological conditions. The formation of carbamate adducts from BMAA and bicarbonate is similar to the formation of carbamate adducts from non-proteinogenic amino acids. Structural, chemical, and biological information related to non-proteinogenic amino acids provide insight into the formation of and possible neurological action of BMAA. This article reviews the carbamate formation of BMAA in the presence of bicarbonate ions, with a particular focus on how the chemical equilibrium of BMAA carbamate adducts may affect the molecular mechanism of its function. Highlights of nuclear magnetic resonance (NMR)-based studies on the equilibrium process between free BMAA and its adducts are presented. The role of divalent metals on the equilibrium process is also explored. The formation and the equilibrium process of carbamate adducts of BMAA may answer questions on their neuroactive potency and provide strong motivation for further investigations into other toxic mechanisms.

  6. Equilibrium and Disequilibrium Dynamics in Cobweb Models with Time Delays

    NASA Astrophysics Data System (ADS)

    Gori, Luca; Guerrini, Luca; Sodini, Mauro

    2015-06-01

    This paper aims to study price dynamics in two different continuous time cobweb models with delays close to [Hommes, 1994]. In both cases, the stationary equilibrium may be not representative of the long-term dynamics of the model, since it is possible to observe endogenous and persistent fluctuations (supercritical Hopf bifurcations) even if a deterministic context without external shocks is considered. In the model in which markets are in equilibrium every time, we show that the existence of time delays in the expectations formation mechanism may cause chaotic dynamics similar to those obtained in [Hommes, 1994] in a discrete time context. From a mathematical point of view, we apply the Poincaré-Lindstedt perturbation method to study the local dynamic properties of the models. In addition, several numerical experiments are used to investigate global properties of the systems.

  7. Knowledge Management through the Equilibrium Pattern Model for Learning

    NASA Astrophysics Data System (ADS)

    Sarirete, Akila; Noble, Elizabeth; Chikh, Azeddine

    Contemporary students are characterized by having very applied learning styles and methods of acquiring knowledge. This behavior is consistent with the constructivist models where students are co-partners in the learning process. In the present work the authors developed a new model of learning based on the constructivist theory coupled with the cognitive development theory of Piaget. The model considers the level of learning based on several stages and the move from one stage to another requires learners' challenge. At each time a new concept is introduced creates a disequilibrium that needs to be worked out to return back to its equilibrium stage. This process of "disequilibrium/equilibrium" has been analyzed and validated using a course in computer networking as part of Cisco Networking Academy Program at Effat College, a women college in Saudi Arabia. The model provides a theoretical foundation for teaching especially in a complex knowledge domain such as engineering and can be used in a knowledge economy.

  8. Sensitivity of an exothermic chemical wave front to a departure from local equilibrium.

    PubMed

    Nowakowski, B; Lemarchand, A

    2007-11-07

    We study the propagation of an exothermic chemical wave front in a reactive dilute gas and show that the particle velocity distribution departs from the Maxwellian form in the front zone. The analytical corrections to the balance equations for concentrations, temperature, and stream velocity induced by the departure from local equilibrium are derived from a perturbative solution of the Boltzmann equation. Our analytical predictions of the front properties, including its propagation speed, compare well with microscopic simulations of the particle dynamics.

  9. Viscous shock layer solutions for turbulent flow of radiating gas mixtures in chemical equilibrium

    NASA Technical Reports Server (NTRS)

    Anderson, E. C.; Moss, J. N.

    1975-01-01

    The viscous shock layer equations for hypersonic laminar and turbulent flows of radiating or nonradiating gas mixtures in chemical equilibrium are presented for two-dimensional and axially symmetric flow fields. Solutions are obtained using an implicit finite difference scheme and results are presented for hypersonic flow over spherically blunted cone configurations at free stream conditions representative of entry into the atmosphere of Venus. These data are compared with solutions obtained using other methods of analysis.

  10. Viscous-shock-layer solutions for turbulent flow of radiating gas mixtures in chemical equilibrium

    NASA Technical Reports Server (NTRS)

    Anderson, E. C.; Moss, J. N.

    1975-01-01

    The viscous-shock-layer equations for hypersonic laminar and turbulent flows of radiating or nonradiating gas mixtures in chemical equilibrium are presented for two-dimensional and axially-symmetric flow fields. Solutions were obtained using an implicit finite-difference scheme and results are presented for hypersonic flow over spherically-blunted cone configurations at freestream conditions representative of entry into the atmosphere of Venus. These data are compared with solutions obtained using other methods of analysis.

  11. A Quasi-Equilibrium Kinetic Model of HF Air Breakdown

    DTIC Science & Technology

    1991-09-01

    Ref. 141, which we shall call the BVB model. They assume all transport and rate coefficients are functions of electron temperature or mean energy េ...collisions. The lack of large deviations is encouraging. It explains why the BVB model gives reasonable behavior; the difference between a non-equilibrium...Thus, the slow relaxation of ɡ> (not to be confused with the relaxation of the energy transfer rate) casts doubt on the basic premise of the BVB

  12. Argumentation Practices in Classroom: Pre-service teachers' conceptual understanding of chemical equilibrium

    NASA Astrophysics Data System (ADS)

    Kaya, Ebru

    2013-05-01

    This study examines the impact of argumentation practices on pre-service teachers' understanding of chemical equilibrium. The sample consisted of 100 pre-service teachers in two classes of a public university. One of these classes was assigned as experimental and the other as control group, randomly. In the experimental group, the subject of chemical equilibrium was taught by using argumentative practices and the participants were encouraged to participate in the lessons actively. However, the instructor taught the same subject by using the lecturing method without engaging argumentative activities in the control group. The Chemical Equilibrium Concept Test and Written Argumentation Survey were administered to all participants to assess their conceptual understanding and the quality of their arguments, respectively. The analysis of covariance results indicate that argumentation practices significantly improved conceptual understanding of the experimental group when compared to the control group. Furthermore, the results show that the pre-service teachers exposed to argumentative practices constructed more quality arguments than those in the control group after the instruction. Based on these results, it can be concluded that the instruction based on argumentative practices is effective in concept teaching in science education. Therefore, argumentation should be explicitly taught in teacher education besides elementary and secondary education.

  13. Activity Enhancement Based on the Chemical Equilibrium of Multiple-Subunit Nitrile Hydratase from Bordetella petrii.

    PubMed

    Liu, Yi; Liu, Ping; Lin, Lu; Zhao, Yueqin; Zhong, Wenjuan; Wu, Lunjie; Zhou, Zhemin; Sun, Weifeng

    2016-09-01

    The maturation mechanism of nitrile hydratase (NHase) of Pseudomonas putida NRRL-18668 was discovered and named as "self-subunit swapping." Since the NHase of Bordetella petrii DSM 12804 is similar to that of P. putida, the NHase maturation of B. petrii is proposed to be the same as that of P. putida. However, there is no further information on the application of NHase according to these findings. We successfully rapidly purified NHase and its activator through affinity his tag, and found that the cell extracts of NHase possessed multiple types of protein ingredients including α, β, α2β2, and α(P14K)2 who were in a state of chemical equilibrium. Furthermore, the activity was significantly enhanced through adding extra α(P14K)2 to the cell extracts of NHase according to the chemical equilibrium. Our findings are useful for the activity enhancement of multiple-subunit enzyme and for the first time significantly increased the NHase activity according to the chemical equilibrium.

  14. New quasi-steady-state and partial-equilibrium methods for integrating chemically reacting systems

    NASA Astrophysics Data System (ADS)

    Mott, David Ray

    1999-11-01

    We present new quasi-steady-state (QSS) and partial- equilibrium (PE) methods for integrating systems of ordinary differential equations (ODEs) that arise from chemical reactions. These methods were developed for use in process-split reacting-flow simulations. The new QSS integrator is a second-order predictor- corrector method that is A-stable for linear equations. The method is accurate regardless of the timescales of the individual ODEs in the system and works well for problems typical of hydrocarbon combustion. The method has very low start-up costs, making it ideal for process- split reacting-flow simulations which require the solution of an initial-value problem in each computational cell in the flowfield for every global timestep. For problems of extreme stiffness, PE tools can be used in combination with the QSS integrator. PE methods remove the fastest reactions in the mechanism from the kinetic integration when their effects can be calculated using algebraic equilibrium constraints. Conservation constraints are used to write an ODE for the reaction's progress variable. The solution of this equation provides a new method for identifying reactions in equilibrium. A systematic method for finding a set of conserved scalars for an arbitrary group of reactions is presented, and this method is used to eliminate reactions that produce redundant equilibrium constraints. Since the equilibrium reactions must compensate for changes in the system that disturb their equilibrium, the equilibrium source terms are not forced identically to zero. Equilibrium is imposed by driving these source terms to the average value required to compensate for the perturbations caused by the other processes. Integration results for a cesium-air mechanism, a hydrogen-air mechanism, and a thermonuclear mechanism used in astrophysics are presented. One-dimensional flame and detonation results are presented for a single-step hydrogen mechanism and the thermonuclear mechanism, respectively

  15. Visualising the equilibrium distribution and mobility of organic contaminants in soil using the chemical partitioning space.

    PubMed

    Wong, Fiona; Wania, Frank

    2011-06-01

    Assessing the behaviour of organic chemicals in soil is a complex task as it is governed by the physical chemical properties of the chemicals, the characteristics of the soil as well as the ambient conditions of the environment. The chemical partitioning space, defined by the air-water partition coefficient (K(AW)) and the soil organic carbon-water partition coefficient (K(OC)), was employed to visualize the equilibrium distribution of organic contaminants between the air-filled pores, the pore water and the solid phases of the bulk soil and the relative importance of the three transport processes removing contaminants from soil (evaporation, leaching and particle erosion). The partitioning properties of twenty neutral organic chemicals (i.e. herbicides, pharmaceuticals, polychlorinated biphenyls and volatile chemicals) were estimated using poly-parameter linear free energy relationships and superimposed onto these maps. This allows instantaneous estimation of the equilibrium phase distribution and mobility of neutral organic chemicals in soil. Although there is a link between the major phase and the dominant transport process, such that chemicals found in air-filled pore space are subject to evaporation, those in water-filled pore space undergo leaching and those in the sorbed phase are associated with particle erosion, the partitioning coefficient thresholds for distribution and mobility can often deviate by many orders of magnitude. In particular, even a small fraction of chemical in pore water or pore air allows for evaporation and leaching to dominate over solid phase transport. Multiple maps that represent soils that differ in the amount and type of soil organic matter, water saturation, temperature, depth of surface soil horizon, and mineral matters were evaluated.

  16. Equilibrium and stability properties of detonation waves in the hydrodynamic limit of a kinetic model

    NASA Astrophysics Data System (ADS)

    Marques, Wilson, Jr.; Jacinta Soares, Ana; Pandolfi Bianchi, Miriam; Kremer, Gilberto M.

    2015-06-01

    A shock wave structure problem, like the one which can be formulated for the planar detonation wave, is analyzed here for a binary mixture of ideal gases undergoing the symmetric reaction {{A}1}+{{A}1}\\rightleftharpoons {{A}2}+{{A}2}. The problem is studied at the hydrodynamic Euler limit of a kinetic model of the reactive Boltzmann equation. The chemical rate law is deduced in this frame with a second-order reaction rate, in a chemical regime such that the gas flow is not far away from the chemical equilibrium. The caloric and the thermal equations of state for the specific internal energy and temperature are employed to close the system of balance laws. With respect to other approaches known in the kinetic literature for detonation problems with a reversible reaction, this paper aims to improve some aspects of the wave solution. Within the mathematical analysis of the detonation model, the equation of the equilibrium Hugoniot curve of the final states is explicitly derived for the first time and used to define the correct location of the equilibrium Chapman-Jouguet point in the Hugoniot diagram. The parametric space is widened to investigate the response of the detonation solution to the activation energy of the chemical reaction. Finally, the mathematical formulation of the linear stability problem is given for the wave detonation structure via a normal-mode approach, when bidimensional disturbances perturb the steady solution. The stability equations with their boundary conditions and the radiation condition of the considered model are explicitly derived for small transversal deviations of the shock wave location. The paper shows how a second-order chemical kinetics description, derived at the microscopic level, and an analytic deduction of the equilibrium Hugoniot curve, lead to an accurate picture of the steady detonation with reversible reaction, as well as to a proper bidimensional linear stability analysis.

  17. Phase-field-crystal models and mechanical equilibrium

    NASA Astrophysics Data System (ADS)

    Heinonen, V.; Achim, C. V.; Elder, K. R.; Buyukdagli, S.; Ala-Nissila, T.

    2014-03-01

    Phase-field-crystal (PFC) models constitute a field theoretical approach to solidification, melting, and related phenomena at atomic length and diffusive time scales. One of the advantages of these models is that they naturally contain elastic excitations associated with strain in crystalline bodies. However, instabilities that are diffusively driven towards equilibrium are often orders of magnitude slower than the dynamics of the elastic excitations, and are thus not included in the standard PFC model dynamics. We derive a method to isolate the time evolution of the elastic excitations from the diffusive dynamics in the PFC approach and set up a two-stage process, in which elastic excitations are equilibrated separately. This ensures mechanical equilibrium at all times. We show concrete examples demonstrating the necessity of the separation of the elastic and diffusive time scales. In the small-deformation limit this approach is shown to agree with the theory of linear elasticity.

  18. Mixing and non-equilibrium chemical reaction in a compressible mixing layer. M.S. Thesis Final Report

    NASA Technical Reports Server (NTRS)

    Steinberger, Craig J.

    1991-01-01

    The effects of compressibility, chemical reaction exothermicity, and non-equilibrium chemical modeling in a reacting plane mixing layer were investigated by means of two dimensional direct numerical simulations. The chemical reaction was irreversible and second order of the type A + B yields Products + Heat. The general governing fluid equations of a compressible reacting flow field were solved by means of high order finite difference methods. Physical effects were then determined by examining the response of the mixing layer to variation of the relevant non-dimensionalized parameters. The simulations show that increased compressibility generally results in a suppressed mixing, and consequently a reduced chemical reaction conversion rate. Reaction heat release was found to enhance mixing at the initial stages of the layer growth, but had a stabilizing effect at later times. The increased stability manifested itself in the suppression or delay of the formation of large coherent structures within the flow. Calculations were performed for a constant rate chemical kinetics model and an Arrhenius type kinetic prototype. The choice of the model was shown to have an effect on the development of the flow. The Arrhenius model caused a greater temperature increase due to reaction than the constant kinetic model. This had the same effect as increasing the exothermicity of the reaction. Localized flame quenching was also observed when the Zeldovich number was relatively large.

  19. Development of Accurate Chemical Equilibrium Models for the Hanford Waste Tanks: The System Na-Ca-Sr-OH-CO3-NO3-EDTA-HEDTA-H2O from 25 to 75°C

    SciTech Connect

    Felmy, Andrew R.; Mason, Marvin J.; Qafoku, Odeta; Dixon, David A.

    2005-04-19

    This symposium manuscript describes the development of an accurate aqueous thermodynamic model for predicting the speciation of Sr in the waste tanks at the Hanford site. A systematic approach is described that details the studies performed to define the most important inorganic and organic complexation reactions as well as the effects of other important metal ions that compete with Sr for complexation reactions with the chelates. By using this approach we were able to define a reduced set of inorganic complexation, organic complexation, and competing metal reactions that best represent the much more complex waste tank chemical system. A summary is presented of the final thermodynamic model for the system Na-Ca-Sr-OH-CO3-NO3-EDTA-HEDTA-H2O from 25 to 75 ºC that was previously published in a variety of sources. Previously unpublished experimental data are also given for the competing metal Ni as well for certain chemical systems, Na-Sr-CO3-PO4-H2O, and for the solubility of amorphous iron hydroxide in the presence of several organic chelating agents. These data were not used in model development but were key to the final selection of the specific chemical systems prioritized for detailed study.

  20. NON-EQUILIBRIUM IONIZATION MODELING OF THE CURRENT SHEET IN A SIMULATED SOLAR ERUPTION

    SciTech Connect

    Shen Chengcai; Reeves, Katharine K.; Raymond, John C.; Murphy, Nicholas A.; Ko, Yuan-Kuen; Lin Jun; Mikic, Zoran; Linker, Jon A.

    2013-08-20

    The current sheet that extends from the top of flare loops and connects to an associated flux rope is a common structure in models of coronal mass ejections (CMEs). To understand the observational properties of CME current sheets, we generated predictions from a flare/CME model to be compared with observations. We use a simulation of a large-scale CME current sheet previously reported by Reeves et al. This simulation includes ohmic and coronal heating, thermal conduction, and radiative cooling in the energy equation. Using the results of this simulation, we perform time-dependent ionization calculations of the flow in a CME current sheet and construct two-dimensional spatial distributions of ionic charge states for multiple chemical elements. We use the filter responses from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory and the predicted intensities of emission lines to compute the count rates for each of the AIA bands. The results show differences in the emission line intensities between equilibrium and non-equilibrium ionization. The current sheet plasma is underionized at low heights and overionized at large heights. At low heights in the current sheet, the intensities of the AIA 94 A and 131 A channels are lower for non-equilibrium ionization than for equilibrium ionization. At large heights, these intensities are higher for non-equilibrium ionization than for equilibrium ionization inside the current sheet. The assumption of ionization equilibrium would lead to a significant underestimate of the temperature low in the current sheet and overestimate at larger heights. We also calculate the intensities of ultraviolet lines and predict emission features to be compared with events from the Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric Observatory, including a low-intensity region around the current sheet corresponding to this model.

  1. Non-Equilibrium Turbulence and Two-Equation Modeling

    NASA Technical Reports Server (NTRS)

    Rubinstein, Robert

    2011-01-01

    Two-equation turbulence models are analyzed from the perspective of spectral closure theories. Kolmogorov theory provides useful information for models, but it is limited to equilibrium conditions in which the energy spectrum has relaxed to a steady state consistent with the forcing at large scales; it does not describe transient evolution between such states. Transient evolution is necessarily through nonequilibrium states, which can only be found from a theory of turbulence evolution, such as one provided by a spectral closure. When the departure from equilibrium is small, perturbation theory can be used to approximate the evolution by a two-equation model. The perturbation theory also gives explicit conditions under which this model can be valid, and when it will fail. Implications of the non-equilibrium corrections for the classic Tennekes-Lumley balance in the dissipation rate equation are drawn: it is possible to establish both the cancellation of the leading order Re1/2 divergent contributions to vortex stretching and enstrophy destruction, and the existence of a nonzero difference which is finite in the limit of infinite Reynolds number.

  2. Equilibrium chemical vapor deposition growth of Bernal-stacked bilayer graphene.

    PubMed

    Zhao, Pei; Kim, Sungjin; Chen, Xiao; Einarsson, Erik; Wang, Miao; Song, Yenan; Wang, Hongtao; Chiashi, Shohei; Xiang, Rong; Maruyama, Shigeo

    2014-11-25

    Using ethanol as the carbon source, self-limiting growth of AB-stacked bilayer graphene (BLG) has been achieved on Cu via an equilibrium chemical vapor deposition (CVD) process. We found that during this alcohol catalytic CVD (ACCVD) a source-gas pressure range exists to break the self-limitation of monolayer graphene on Cu, and at a certain equilibrium state it prefers to form uniform BLG with a high surface coverage of ∼94% and AB-stacking ratio of nearly 100%. More importantly, once the BLG is completed, this growth shows a self-limiting manner, and an extended ethanol flow time does not result in additional layers. We investigate the mechanism of this equilibrium BLG growth using isotopically labeled (13)C-ethanol and selective surface aryl functionalization, and results reveal that during the equilibrium ACCVD process a continuous substitution of graphene flakes occurs to the as-formed graphene and the BLG growth follows a layer-by-layer epitaxy mechanism. These phenomena are significantly in contrast to those observed for previously reported BLG growth using methane as precursor.

  3. Development and application of a numerical model of kinetic and equilibrium microbiological and geochemical reactions (BIOKEMOD)

    NASA Astrophysics Data System (ADS)

    Salvage, Karen M.; Yeh, Gour-Tsyh

    1998-08-01

    This paper presents the conceptual and mathematical development of the numerical model titled BIOKEMOD, and verification simulations performed using the model. BIOKEMOD is a general computer model for simulation of geochemical and microbiological reactions in batch aqueous solutions. BIOKEMOD may be coupled with hydrologic transport codes for simulation of chemically and biologically reactive transport. The chemical systems simulated may include any mixture of kinetic and equilibrium reactions. The pH, pe, and ionic strength may be specified or simulated. Chemical processes included are aqueous complexation, adsorption, ion-exchange and precipitation/dissolution. Microbiological reactions address growth of biomass and degradation of chemicals by microbial metabolism of substrates, nutrients, and electron acceptors. Inhibition or facilitation of growth due to the presence of specific chemicals and a lag period for microbial acclimation to new substrates may be simulated if significant in the system of interest. Chemical reactions controlled by equilibrium are solved using the law of mass action relating the thermodynamic equilibrium constant to the activities of the products and reactants. Kinetic chemical reactions are solved using reaction rate equations based on collision theory. Microbiologically mediated reactions for substrate removal and biomass growth are assumed to follow Monod kinetics modified for the potentially limiting effects of substrate, nutrient, and electron acceptor availability. BIOKEMOD solves the ordinary differential and algebraic equations of mixed geochemical and biogeochemical reactions using the Newton-Raphson method with full matrix pivoting. Simulations may be either steady state or transient. Input to the program includes the stoichiometry and parameters describing the relevant chemical and microbiological reactions, initial conditions, and sources/sinks for each chemical species. Output includes the chemical and biomass concentrations

  4. On cooperative quasi-equilibrium models of transcriptional regulation.

    PubMed

    Mjolsness, Eric

    2007-04-01

    Mechanistic models for transcriptional regulation are derived using the methods of equilibrium statistical mechanics, to model equilibrating processes that occur at a fast time scale. These processes regulate slower changes in the synthesis and expression of transcription factors that feed back and cooperatively regulate transcription, forming a gene regulation network (GRN). We rederive and extend two previous quasi-equilibrium models of transcriptional regulation, and demonstrate circumstances under which they can be approximated at each transcription complex by feed-forward artificial neural network (ANN) models. A single-level mechanistic model can be approximated by a successfully applied phenomenological model of GRNs which is based on single-layer analog-valued ANNs. A two-level hierarchical mechanistic model, with separate activation states for modules and for the whole transcription complex, can be approximated by a two-layer feed-forward ANN in several related ways. The sufficient conditions demonstrated for the ANN approximations correspond biologically to large numbers of binding sites each of which have a small effect. A further extension to the single-level and two-level models allows one-dimensional chains of overlapping and/or energetically interacting binding sites within a module. Partition functions for these models can be constructed from stylized diagrams that indicate energetic and logical interactions between binary-valued state variables. All parameters in the mechanistic models, including the two approximations, can in principle be related to experimentally measurable free energy differences, among other observables.

  5. Understanding Chemical Equilibrium Using Entropy Analysis: The Relationship between [delta]S[subscript tot](sys[superscript o]) and the Equilibrium Constant

    ERIC Educational Resources Information Center

    Bindel, Thomas H.

    2010-01-01

    Entropy analyses as a function of the extent of reaction are presented for a number of physicochemical processes, including vaporization of a liquid, dimerization of nitrogen dioxide, and the autoionization of water. Graphs of the total entropy change versus the extent of reaction give a visual representation of chemical equilibrium and the second…

  6. Understanding Chemical Equilibrium Using Entropy Analysis: The Relationship between [delta]S[subscript tot](sys[superscript o]) and the Equilibrium Constant

    ERIC Educational Resources Information Center

    Bindel, Thomas H.

    2010-01-01

    Entropy analyses as a function of the extent of reaction are presented for a number of physicochemical processes, including vaporization of a liquid, dimerization of nitrogen dioxide, and the autoionization of water. Graphs of the total entropy change versus the extent of reaction give a visual representation of chemical equilibrium and the second…

  7. Density functional study of chemical reaction equilibrium for dimerization reactions in slit and cylindrical nanopores

    NASA Astrophysics Data System (ADS)

    Malijevský, Alexandr; Lísal, Martin

    2009-04-01

    We present a theoretical study of the effects of confinement on chemical reaction equilibrium in slit and cylindrical nanopores. We use a density functional theory (DFT) to investigate the effects of temperature, pore geometry, bulk pressure, transition layering, and capillary condensation on a dimerization reaction that mimics the nitric oxide dimerization reaction, 2NO⇌(NO)2, in carbonlike slit and cylindrical nanopores in equilibrium with a vapor reservoir. In addition to the DFT calculations, we also utilize the reaction ensemble Monte Carlo method to supplement the DFT results for reaction conversion. This work is an extension of the previous DFT study by Tripathi and Chapman [J. Chem. Phys. 118, 7993 (2003)] on the dimerization reactions confined in the planar slits.

  8. Reactive solute transport in streams. 1. Development of an equilibrium- based model

    USGS Publications Warehouse

    Runkel, R.L.; Bencala, K.E.; Broshears, R.E.; Chapra, S.C.

    1996-01-01

    An equilibrium-based solute transport model is developed for the simulation of trace metal fate and transport in streams. The model is formed by coupling a solute transport model with a chemical equilibrium submodel based on MINTEQ. The solute transport model considers the physical processes of advection, dispersion, lateral inflow, and transient storage, while the equilibrium submodel considers the speciation and complexation of aqueous species, precipitation/dissolution and sorption. Within the model, reactions in the water column may result in the formation of solid phases (precipitates and sorbed species) that are subject to downstream transport and settling processes. Solid phases on the streambed may also interact with the water column through dissolution and sorption/desorption reactions. Consideration of both mobile (water-borne) and immobile (streambed) solid phases requires a unique set of governing differential equations and solution techniques that are developed herein. The partial differential equations describing physical transport and the algebraic equations describing chemical equilibria are coupled using the sequential iteration approach.

  9. Reactive Solute Transport in Streams: 1. Development of an Equilibrium-Based Model

    NASA Astrophysics Data System (ADS)

    Runkel, Robert L.; Bencala, Kenneth E.; Broshears, Robert E.; Chapra, Steven C.

    1996-02-01

    An equilibrium-based solute transport model is developed for the simulation of trace metal fate and transport in streams. The model is formed by coupling a solute transport model with a chemical equilibrium submodel based on MINTEQ. The solute transport model considers the physical processes of advection, dispersion, lateral inflow, and transient storage, while the equilibrium submodel considers the speciation and complexation of aqueous species, precipitation/dissolution and sorption. Within the model, reactions in the water column may result in the formation of solid phases (precipitates and sorbed species) that are subject to downstream transport and settling processes. Solid phases on the streambed may also interact with the water column through dissolution and sorption/desorption reactions. Consideration of both mobile (water-borne) and immobile (streambed) solid phases requires a unique set of governing differential equations and solution techniques that are developed herein. The partial differential equations describing physical transport and the algebraic equations describing chemical equilibria are coupled using the sequential iteration approach.

  10. Revealing model dependencies in "Assessing the RAFT equilibrium constant via model systems: an EPR study".

    PubMed

    Junkers, Thomas; Barner-Kowollik, Christopher; Coote, Michelle L

    2011-12-01

    In a recent article (W. Meiser, M. Buback, Assessing the RAFT Equilibrium Constant via Model Systems: An EPR Study, Macromol. Rapid Commun. 2011, 18, 1490-1494), it is claimed that evidence is found that unequivocally proves that quantum mechanical calculations assessing the equilibrium constant and fragmentation rate coefficients in dithiobenzoate-mediated reversible addition fragmentation transfer (RAFT) systems are beset with a considerable uncertainty. In the present work, we show that these claims made by Meiser and Buback are beset with a model dependency, as a critical key parameter in their data analysis - the addition rate coefficient of the radicals attacking the C=S double bond in the dithiobenzoate - induces a model insensitivity into the data analysis. Contrary to the claims made by Meiser and Buback, their experimental results can be brought into agreement with the quantum chemical calculations if a lower addition rate coefficient of cyanoisopropyl radicals (CIP) to the CIP dithiobenzoate (CPDB) is assumed. To resolve the model dependency, the addition rate coefficient of CIP radicals to CPDB needs to be determined as a matter of priority.

  11. Understanding Chemical Equilibrium: The Role of Gas Phases and Mixing Contributions in the Minimum of Free Energy Plots

    ERIC Educational Resources Information Center

    Tomba, J. Pablo

    2017-01-01

    The use of free energy plots to understand the concept of thermodynamic equilibrium has been shown to be of great pedagogical value in materials science. Although chemical equilibrium is also amenable to this kind of analysis, it is not part of the agenda of materials science textbooks. Something similar is found in chemistry branches, where free…

  12. Rates of coalescence for common epidemiological models at equilibrium

    PubMed Central

    Koelle, Katia; Rasmussen, David A.

    2012-01-01

    Coalescent theory provides a mathematical framework for quantitatively interpreting gene genealogies. With the increased availability of molecular sequence data, disease ecologists now regularly apply this body of theory to viral phylogenies, most commonly in attempts to reconstruct demographic histories of infected individuals and to estimate parameters such as the basic reproduction number. However, with few exceptions, the mathematical expressions at the core of coalescent theory have not been explicitly linked to the structure of epidemiological models, which are commonly used to mathematically describe the transmission dynamics of a pathogen. Here, we aim to make progress towards establishing this link by presenting a general approach for deriving a model's rate of coalescence under the assumption that the disease dynamics are at their endemic equilibrium. We apply this approach to four common families of epidemiological models: standard susceptible-infected-susceptible/susceptible-infected-recovered/susceptible-infected-recovered-susceptible models, models with individual heterogeneity in infectivity, models with an exposed but not yet infectious class and models with variable distributions of the infectious period. These results improve our understanding of how epidemiological processes shape viral genealogies, as well as how these processes affect levels of viral diversity and rates of genetic drift. Finally, we discuss how a subset of these coalescent rate expressions can be used for phylodynamic inference in non-equilibrium settings. For the ones that are limited to equilibrium conditions, we also discuss why this is the case. These results, therefore, point towards necessary future work while providing intuition on how epidemiological characteristics of the infection process impact gene genealogies. PMID:21920961

  13. Stepwise kinetic equilibrium models of quantitative polymerase chain reaction

    PubMed Central

    2012-01-01

    Background Numerous models for use in interpreting quantitative PCR (qPCR) data are present in recent literature. The most commonly used models assume the amplification in qPCR is exponential and fit an exponential model with a constant rate of increase to a select part of the curve. Kinetic theory may be used to model the annealing phase and does not assume constant efficiency of amplification. Mechanistic models describing the annealing phase with kinetic theory offer the most potential for accurate interpretation of qPCR data. Even so, they have not been thoroughly investigated and are rarely used for interpretation of qPCR data. New results for kinetic modeling of qPCR are presented. Results Two models are presented in which the efficiency of amplification is based on equilibrium solutions for the annealing phase of the qPCR process. Model 1 assumes annealing of complementary targets strands and annealing of target and primers are both reversible reactions and reach a dynamic equilibrium. Model 2 assumes all annealing reactions are nonreversible and equilibrium is static. Both models include the effect of primer concentration during the annealing phase. Analytic formulae are given for the equilibrium values of all single and double stranded molecules at the end of the annealing step. The equilibrium values are then used in a stepwise method to describe the whole qPCR process. Rate constants of kinetic models are the same for solutions that are identical except for possibly having different initial target concentrations. Analysis of qPCR curves from such solutions are thus analyzed by simultaneous non-linear curve fitting with the same rate constant values applying to all curves and each curve having a unique value for initial target concentration. The models were fit to two data sets for which the true initial target concentrations are known. Both models give better fit to observed qPCR data than other kinetic models present in the literature. They also give

  14. Computation of eigenfrequencies for equilibrium models including turbulent pressure

    NASA Astrophysics Data System (ADS)

    Sonoi, T.; Belkacem, K.; Dupret, M.-A.; Samadi, R.; Ludwig, H.-G.; Caffau, E.; Mosser, B.

    2017-03-01

    Context. The space-borne missions CoRoT and Kepler have provided a wealth of highly accurate data. However, our inability to properly model the upper-most region of solar-like stars prevents us from making the best of these observations. This problem is called "surface effect" and a key ingredient to solve it is turbulent pressure for the computation of both the equilibrium models and the oscillations. While 3D hydrodynamic simulations help to include properly the turbulent pressure in the equilibrium models, the way this surface effect is included in the computation of stellar oscillations is still subject to uncertainties. Aims: We aim at determining how to properly include the effect of turbulent pressure and its Lagrangian perturbation in the adiabatic computation of the oscillations. We also discuss the validity of the gas-gamma model and reduced gamma model approximations, which have been used to compute adiabatic oscillations of equilibrium models including turbulent pressure. Methods: We use a patched model of the Sun with an inner part constructed by a 1D stellar evolution code (CESTAM) and an outer part by the 3D hydrodynamical code (CO5BOLD). Then, the adiabatic oscillations are computed using the ADIPLS code for the gas-gamma and reduced gamma model approximations and with the MAD code imposing the adiabatic condition on an existing time-dependent convection formalism. Finally, all those results are compared to the observed solar frequencies. Results: We show that the computation of the oscillations using the time-dependent convection formalism in the adiabatic limit improves significantly the agreement with the observed frequencies compared to the gas-gamma and reduced gamma model approximations. Of the components of the perturbation of the turbulent pressure, the perturbation of the density and advection term is found to contribute most to the frequency shift. Conclusions: The turbulent pressure is certainly the dominant factor responsible for the

  15. Equilibrium slab models of Lyman-alpha clouds

    NASA Technical Reports Server (NTRS)

    Charlton, Jane C.; Salpeter, Edwin E.; Hogan, Craig J.

    1993-01-01

    Solutions for the equilibrium configuration of a slab with ionizing radiation incident equally from both sides are explored. Radiation effects (photoionization, Ly-alpha photon trapping, and mock gravity) as well as external pressure and self gravity (with and without dark matter) are included. The general formalism is applied to structure growth on small scales at very high z due to mock gravity on dust. Emphasis is placed on the application of slab models at z of less than 5, particularly those that may correspond to Ly-alpha forest, Lyman limit, and damped Ly-alpha systems. The regime with a dominant outward force contributed by trapping of Ly-alpha photons is discussed. General expressions are given for the equilibrium, including dark matter, assuming various relationships between the density of the dark matter halo and the total gas column density.

  16. Chemical kinetics and relaxation of non-equilibrium air plasma generated by energetic photon and electron beams

    NASA Astrophysics Data System (ADS)

    Maulois, Melissa; Ribière, Maxime; Eichwald, Olivier; Yousfi, Mohammed; Azaïs, Bruno

    2016-04-01

    The comprehension of electromagnetic perturbations of electronic devices, due to air plasma-induced electromagnetic field, requires a thorough study on air plasma. In the aim to understand the phenomena at the origin of the formation of non-equilibrium air plasma, we simulate, using a volume average chemical kinetics model (0D model), the time evolution of a non-equilibrium air plasma generated by an energetic X-ray flash. The simulation is undertaken in synthetic air (80% N2 and 20% O2) at ambient temperature and atmospheric pressure. When the X-ray flash crosses the gas, non-relativistic Compton electrons (low energy) and a relativistic Compton electron beam (high energy) are simultaneously generated and interact with the gas. The considered chemical kinetics scheme involves 26 influent species (electrons, positive ions, negative ions, and neutral atoms and molecules in their ground or metastable excited states) reacting following 164 selected reactions. The kinetics model describing the plasma chemistry was coupled to the conservation equation of the electron mean energy, in order to calculate at each time step of the non-equilibrium plasma evolution, the coefficients of reactions involving electrons while the energy of the heavy species (positive and negative ions and neutral atoms and molecules) is assumed remaining close to ambient temperature. It has been shown that it is the relativistic Compton electron beam directly created by the X-ray flash which is mainly responsible for the non-equilibrium plasma formation. Indeed, the low energy electrons (i.e., the non-relativistic ones) directly ejected from molecules by Compton collisions contribute to less than 1% on the creation of electrons in the plasma. In our simulation conditions, a non-equilibrium plasma with a low electron mean energy close to 1 eV and a concentration of charged species close to 1013 cm-3 is formed a few nanoseconds after the peak of X-ray flash intensity. 200 ns after the flash

  17. Chemical kinetics and relaxation of non-equilibrium air plasma generated by energetic photon and electron beams

    SciTech Connect

    Maulois, Melissa; Azaïs, Bruno

    2016-04-15

    The comprehension of electromagnetic perturbations of electronic devices, due to air plasma-induced electromagnetic field, requires a thorough study on air plasma. In the aim to understand the phenomena at the origin of the formation of non-equilibrium air plasma, we simulate, using a volume average chemical kinetics model (0D model), the time evolution of a non-equilibrium air plasma generated by an energetic X-ray flash. The simulation is undertaken in synthetic air (80% N{sub 2} and 20% O{sub 2}) at ambient temperature and atmospheric pressure. When the X-ray flash crosses the gas, non-relativistic Compton electrons (low energy) and a relativistic Compton electron beam (high energy) are simultaneously generated and interact with the gas. The considered chemical kinetics scheme involves 26 influent species (electrons, positive ions, negative ions, and neutral atoms and molecules in their ground or metastable excited states) reacting following 164 selected reactions. The kinetics model describing the plasma chemistry was coupled to the conservation equation of the electron mean energy, in order to calculate at each time step of the non-equilibrium plasma evolution, the coefficients of reactions involving electrons while the energy of the heavy species (positive and negative ions and neutral atoms and molecules) is assumed remaining close to ambient temperature. It has been shown that it is the relativistic Compton electron beam directly created by the X-ray flash which is mainly responsible for the non-equilibrium plasma formation. Indeed, the low energy electrons (i.e., the non-relativistic ones) directly ejected from molecules by Compton collisions contribute to less than 1% on the creation of electrons in the plasma. In our simulation conditions, a non-equilibrium plasma with a low electron mean energy close to 1 eV and a concentration of charged species close to 10{sup 13 }cm{sup −3} is formed a few nanoseconds after the peak of X-ray flash intensity

  18. Evaluation of a predictive model for air/surface adsorption equilibrium constants and enthalpies.

    PubMed

    Arp, Hans Peter H; Goss, Kai-Uwe; Schwarzenbach, René P

    2006-01-01

    A model used to predict equilibrium adsorption to surfaces using a poly-parameter linear free-energy relationship as well as an empirical model used to predict enthalpies of adsorption of volatile compounds were evaluated with new experimental data to cover semivolatile compounds and a larger variability of compound classes. Equilibrium adsorption constants on a quartz surface ranging over seven orders of magnitude were measured for 142 compounds, and enthalpies of adsorption on a quartz surface from -33.7 to -99.8 kJ/mol were measured for 76 compounds. Agreement between experimental and predicted data was within a factor of two (82.1%) or three (100.0%) for the equilibrium adsorption constants and within 20% for the enthalpy of adsorption values. Thus, the scatter in the validation data sets reported here were practically the same as that for the calibration data sets used to derive the models. The few outliers that we identified in the prediction of equilibrium adsorption constants likely are caused by either shortcomings of the reported sorbate parameters or the occurrence of chemical speciation in the water layer on the surface of the quartz.

  19. General Reynolds analogy on curved surfaces in hypersonic rarefied gas flows with non-equilibrium chemical reactions

    NASA Astrophysics Data System (ADS)

    Xingxing, Chen; Zhihui, Wang; Yongliang, Yu

    2016-11-01

    Hypersonic chemical non-equilibrium gas flows around blunt nosed bodies are studied in the present paper to investigate the Reynolds analogy relation on curved surfaces. With a momentum and energy transfer model being applied through boundary layers, influences of molecular dissociations and recombinations on skin frictions and heat fluxes are separately modeled. Expressions on the ratio of Cf / Ch (skin friction coefficient to heat flux) are presented along the surface of circular cylinders under the ideal dissociation gas model. The analysis indicates that molecular dissociations increase the linear distribution of Cf / Ch, but the nonlinear Reynolds analogy relation could ultimately be obtained in flows with larger Reynolds numbers and Mach numbers, where the decrease of wall heat flux by molecular recombinations signifies. The present modeling and analyses are also verified by the DSMC calculations on nitrogen gas flows.

  20. Pharmaceutical industry and trade liberalization using computable general equilibrium model.

    PubMed

    Barouni, M; Ghaderi, H; Banouei, Aa

    2012-01-01

    Computable general equilibrium models are known as a powerful instrument in economic analyses and widely have been used in order to evaluate trade liberalization effects. The purpose of this study was to provide the impacts of trade openness on pharmaceutical industry using CGE model. Using a computable general equilibrium model in this study, the effects of decrease in tariffs as a symbol of trade liberalization on key variables of Iranian pharmaceutical products were studied. Simulation was performed via two scenarios in this study. The first scenario was the effect of decrease in tariffs of pharmaceutical products as 10, 30, 50, and 100 on key drug variables, and the second was the effect of decrease in other sectors except pharmaceutical products on vital and economic variables of pharmaceutical products. The required data were obtained and the model parameters were calibrated according to the social accounting matrix of Iran in 2006. The results associated with simulation demonstrated that the first scenario has increased import, export, drug supply to markets and household consumption, while import, export, supply of product to market, and household consumption of pharmaceutical products would averagely decrease in the second scenario. Ultimately, society welfare would improve in all scenarios. We presents and synthesizes the CGE model which could be used to analyze trade liberalization policy issue in developing countries (like Iran), and thus provides information that policymakers can use to improve the pharmacy economics.

  1. Pharmaceutical Industry and Trade Liberalization Using Computable General Equilibrium Model

    PubMed Central

    Barouni, M; Ghaderi, H; Banouei, AA

    2012-01-01

    Background Computable general equilibrium models are known as a powerful instrument in economic analyses and widely have been used in order to evaluate trade liberalization effects. The purpose of this study was to provide the impacts of trade openness on pharmaceutical industry using CGE model. Methods: Using a computable general equilibrium model in this study, the effects of decrease in tariffs as a symbol of trade liberalization on key variables of Iranian pharmaceutical products were studied. Simulation was performed via two scenarios in this study. The first scenario was the effect of decrease in tariffs of pharmaceutical products as 10, 30, 50, and 100 on key drug variables, and the second was the effect of decrease in other sectors except pharmaceutical products on vital and economic variables of pharmaceutical products. The required data were obtained and the model parameters were calibrated according to the social accounting matrix of Iran in 2006. Results: The results associated with simulation demonstrated that the first scenario has increased import, export, drug supply to markets and household consumption, while import, export, supply of product to market, and household consumption of pharmaceutical products would averagely decrease in the second scenario. Ultimately, society welfare would improve in all scenarios. Conclusion: We presents and synthesizes the CGE model which could be used to analyze trade liberalization policy issue in developing countries (like Iran), and thus provides information that policymakers can use to improve the pharmacy economics. PMID:23641393

  2. Significance of vapor phase chemical reactions on CVD rates predicted by chemically frozen and local thermochemical equilibrium boundary layer theories

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.

    1988-01-01

    This paper investigates the role played by vapor-phase chemical reactions on CVD rates by comparing the results of two extreme theories developed to predict CVD mass transport rates in the absence of interfacial kinetic barrier: one based on chemically frozen boundary layer and the other based on local thermochemical equilibrium. Both theories consider laminar convective-diffusion boundary layers at high Reynolds numbers and include thermal (Soret) diffusion and variable property effects. As an example, Na2SO4 deposition was studied. It was found that gas phase reactions have no important role on Na2SO4 deposition rates and on the predictions of the theories. The implications of the predictions of the two theories to other CVD systems are discussed.

  3. Significance of vapor phase chemical reactions on CVD rates predicted by chemically frozen and local thermochemical equilibrium boundary layer theories

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.

    1988-01-01

    This paper investigates the role played by vapor-phase chemical reactions on CVD rates by comparing the results of two extreme theories developed to predict CVD mass transport rates in the absence of interfacial kinetic barrier: one based on chemically frozen boundary layer and the other based on local thermochemical equilibrium. Both theories consider laminar convective-diffusion boundary layers at high Reynolds numbers and include thermal (Soret) diffusion and variable property effects. As an example, Na2SO4 deposition was studied. It was found that gas phase reactions have no important role on Na2SO4 deposition rates and on the predictions of the theories. The implications of the predictions of the two theories to other CVD systems are discussed.

  4. A tightly coupled non-equilibrium model for inductively coupled radio-frequency plasmas

    SciTech Connect

    Munafò, A. Alfuhaid, S. A. Panesi, M.; Cambier, J.-L.

    2015-10-07

    The objective of the present work is the development of a tightly coupled magneto-hydrodynamic model for inductively coupled radio-frequency plasmas. Non Local Thermodynamic Equilibrium (NLTE) effects are described based on a hybrid State-to-State approach. A multi-temperature formulation is used to account for thermal non-equilibrium between translation of heavy-particles and vibration of molecules. Excited electronic states of atoms are instead treated as separate pseudo-species, allowing for non-Boltzmann distributions of their populations. Free-electrons are assumed Maxwellian at their own temperature. The governing equations for the electro-magnetic field and the gas properties (e.g., chemical composition and temperatures) are written as a coupled system of time-dependent conservation laws. Steady-state solutions are obtained by means of an implicit Finite Volume method. The results obtained in both LTE and NLTE conditions over a broad spectrum of operating conditions demonstrate the robustness of the proposed coupled numerical method. The analysis of chemical composition and temperature distributions along the torch radius shows that: (i) the use of the LTE assumption may lead to an inaccurate prediction of the thermo-chemical state of the gas, and (ii) non-equilibrium phenomena play a significant role close the walls, due to the combined effects of Ohmic heating and macroscopic gradients.

  5. One-Dimensional Transport with Equilibrium Chemistry (OTEQ) - A Reactive Transport Model for Streams and Rivers

    USGS Publications Warehouse

    Runkel, Robert L.

    2010-01-01

    OTEQ is a mathematical simulation model used to characterize the fate and transport of waterborne solutes in streams and rivers. The model is formed by coupling a solute transport model with a chemical equilibrium submodel. The solute transport model is based on OTIS, a model that considers the physical processes of advection, dispersion, lateral inflow, and transient storage. The equilibrium submodel is based on MINTEQ, a model that considers the speciation and complexation of aqueous species, acid-base reactions, precipitation/dissolution, and sorption. Within OTEQ, reactions in the water column may result in the formation of solid phases (precipitates and sorbed species) that are subject to downstream transport and settling processes. Solid phases on the streambed may also interact with the water column through dissolution and sorption/desorption reactions. Consideration of both mobile (waterborne) and immobile (streambed) solid phases requires a unique set of governing differential equations and solution techniques that are developed herein. The partial differential equations describing physical transport and the algebraic equations describing chemical equilibria are coupled using the sequential iteration approach. The model's ability to simulate pH, precipitation/dissolution, and pH-dependent sorption provides a means of evaluating the complex interactions between instream chemistry and hydrologic transport at the field scale. This report details the development and application of OTEQ. Sections of the report describe model theory, input/output specifications, model applications, and installation instructions. OTEQ may be obtained over the Internet at http://water.usgs.gov/software/OTEQ.

  6. Entropy and equilibrium state of free market models

    NASA Astrophysics Data System (ADS)

    Iglesias, J. R.; de Almeida, R. M. C.

    2012-03-01

    Many recent models of trade dynamics use the simple idea of wealth exchanges among economic agents in order to obtain a stable or equilibrium distribution of wealth among the agents. In particular, a plain analogy compares the wealth in a society with the energy in a physical system, and the trade between agents to the energy exchange between molecules during collisions. In physical systems, the energy exchange among molecules leads to a state of equipartition of the energy and to an equilibrium situation where the entropy is a maximum. On the other hand, in a large class of exchange models, the system converges to a very unequal condensed state, where one or a few agents concentrate all the wealth of the society while the wide majority of agents shares zero or almost zero fraction of the wealth. So, in those economic systems a minimum entropy state is attained. We propose here an analytical model where we investigate the effects of a particular class of economic exchanges that minimize the entropy. By solving the model we discuss the conditions that can drive the system to a state of minimum entropy, as well as the mechanisms to recover a kind of equipartition of wealth.

  7. Modeling Inflation Using a Non-Equilibrium Equation of Exchange

    NASA Technical Reports Server (NTRS)

    Chamberlain, Robert G.

    2013-01-01

    Inflation is a change in the prices of goods that takes place without changes in the actual values of those goods. The Equation of Exchange, formulated clearly in a seminal paper by Irving Fisher in 1911, establishes an equilibrium relationship between the price index P (also known as "inflation"), the economy's aggregate output Q (also known as "the real gross domestic product"), the amount of money available for spending M (also known as "the money supply"), and the rate at which money is reused V (also known as "the velocity of circulation of money"). This paper offers first a qualitative discussion of what can cause these factors to change and how those causes might be controlled, then develops a quantitative model of inflation based on a non-equilibrium version of the Equation of Exchange. Causal relationships are different from equations in that the effects of changes in the causal variables take time to play out-often significant amounts of time. In the model described here, wages track prices, but only after a distributed lag. Prices change whenever the money supply, aggregate output, or the velocity of circulation of money change, but only after a distributed lag. Similarly, the money supply depends on the supplies of domestic and foreign money, which depend on the monetary base and a variety of foreign transactions, respectively. The spreading of delays mitigates the shocks of sudden changes to important inputs, but the most important aspect of this model is that delays, which often have dramatic consequences in dynamic systems, are explicitly incorporated.macroeconomics, inflation, equation of exchange, non-equilibrium, Athena Project

  8. How is PCK embodied in the instructional decisions teachers make while teaching chemical equilibrium?

    NASA Astrophysics Data System (ADS)

    Shannon, Joseph Charles

    Much of the research concerning pedagogical content knowledge (PCK) in science education has been focused on its nature and development rather than how it is dynamically employed in the classroom with respect to specific topics. Research on how PCK is linked with actual classroom decisions has been limited since its tacit nature makes it challenging to identify what dimensions of PCK a teacher employs in various aspects of their practice. This study, using a multi-method case study design, examined four chemistry teachers' (two 1 st year and two 3rd year) decision-making during the planning, teaching, and reflection stages of their practice to determine PCK's influence for the topic of chemical equilibrium. The research occurred in undergraduate chemistry classrooms and special emphasis was placed on examining discourse to illuminate the relationships between how a teacher recognizes the need for a decision, what pedagogical 'moves' were chosen for implementation, and how talk was utilized to execute it. Findings indicated there were distinct differences between 1st and 3rd year teachers' PCK and how they employed it in their practice. The various types of knowledge and beliefs supporting the teachers' model of PCK such as subject matter knowledge, knowledge of student understanding, knowledge of instructional strategies as well as knowledge and beliefs about teaching and their learners influenced their decision-making ability during pre-lesson planning which subsequently influenced their communicative approach in the classroom. Two patterns were observed. Teachers with less teaching experience displayed a model of PCK characterized by an underdeveloped and sometimes fragmented understanding of the topic as well as a fragile knowledge of student understanding. As a result of having limited resources to draw on in the classroom they relied on a controlling communicative approach, thereby inhibiting the elicitation and incorporation of student thinking and

  9. Out-of-equilibrium catalysis of chemical reactions by electronic tunnel currents.

    PubMed

    Dzhioev, Alan A; Kosov, Daniel S; von Oppen, Felix

    2013-04-07

    We present an escape rate theory for current-induced chemical reactions. We use Keldysh nonequilibrium Green's functions to derive a Langevin equation for the reaction coordinate. Due to the out of equilibrium electronic degrees of freedom, the friction, noise, and effective temperature in the Langevin equation depend locally on the reaction coordinate. As an example, we consider the dissociation of diatomic molecules induced by the electronic current from a scanning tunnelling microscope tip. In the resonant tunnelling regime, the molecular dissociation involves two processes which are intricately interconnected: a modification of the potential energy barrier and heating of the molecule. The decrease of the molecular barrier (i.e., the current induced catalytic reduction of the barrier) accompanied by the appearance of the effective, reaction-coordinate-dependent temperature is an alternative mechanism for current-induced chemical reactions, which is distinctly different from the usual paradigm of pumping vibrational degrees of freedom.

  10. Chemicals loading in acetylated bamboo assisted by supercritical CO2 based on phase equilibrium data

    NASA Astrophysics Data System (ADS)

    Silviana, Petermann, M.

    2015-12-01

    Indonesia has a large tropical forest. However, the deforestation still appears annually and vastly. This reason drives a use of bamboo as wood alternative. Recently, there are many modifications of bamboo in order to prolong the shelf life. Unfortunately, the processes need more chemicals and time. Based on wood modification, esterifying of bamboo was undertaken in present of a dense gas, i.e. supercritical CO2. Calculation of chemicals loading referred to ASTM D1413-99 by using the phase equilibrium data at optimum condition by a statistical design. The results showed that the acetylation of bamboo assisted by supercritical CO2 required 14.73 kg acetic anhydride/m3 of bamboo for a treatment of one hour.

  11. Out-of-equilibrium catalysis of chemical reactions by electronic tunnel currents

    NASA Astrophysics Data System (ADS)

    Dzhioev, Alan A.; Kosov, Daniel S.; von Oppen, Felix

    2013-04-01

    We present an escape rate theory for current-induced chemical reactions. We use Keldysh nonequilibrium Green's functions to derive a Langevin equation for the reaction coordinate. Due to the out of equilibrium electronic degrees of freedom, the friction, noise, and effective temperature in the Langevin equation depend locally on the reaction coordinate. As an example, we consider the dissociation of diatomic molecules induced by the electronic current from a scanning tunnelling microscope tip. In the resonant tunnelling regime, the molecular dissociation involves two processes which are intricately interconnected: a modification of the potential energy barrier and heating of the molecule. The decrease of the molecular barrier (i.e., the current induced catalytic reduction of the barrier) accompanied by the appearance of the effective, reaction-coordinate-dependent temperature is an alternative mechanism for current-induced chemical reactions, which is distinctly different from the usual paradigm of pumping vibrational degrees of freedom.

  12. Self-consistent treatment of dynamics and chemistry in the winds from carbon-rich AGB stars. I. Tests of the equilibrium and kinetic chemical codes

    NASA Astrophysics Data System (ADS)

    Pułecka, M.; Schmidt, M. R.; Shematovich, V. I.; Szczerba, R.

    2007-07-01

    Aims:The main aim of this paper was to test our (chemical and kinetic) codes, which will be used during self-consistent modelling of dynamics and chemistry in the winds from C-rich AGB stars. Methods: We used the thermodynamical equilibrium code to test the different databases of dissociation constants. We also calculated the equilibrium content of the gas using the kinetic code that includes the chemical network of neutral-neutral reactions. The influence of reaction rates updated using the UMIST database for Astrochemistry 2005 (UDFA05) was tested. Results: The local thermodynamical equilibrium calculations show that the NIST database reproduces equilibrium concentrations fairly well in comparison with previous computations, while consistency for the other, commonly used, dissociation constants is worse. The most important finding is that the steady state solution obtained with the kinetic code for the reactions network is different from the thermodynamical equilibrium solution. In particular, the important opacity sources CN and C2 are underabundant relative to thermodynamical equilibrium, while O-bearing molecules (like SiO, H{2}O, and OH) are overabundant. After updating the reaction rates by data from the UDFA05 database, the consistency in O-bearing species becomes much better, however the disagreement in C-bearing species is still present. Figures 3-5 and 7 are only available in electronic form at http://www.aanda.org

  13. Iron chelators in medicinal applications - chemical equilibrium considerations in pharmaceutical activity.

    PubMed

    Manning, Thomas; Kean, Greg; Thomas, Jessica; Thomas, Khaleh; Corbitt, Michael; Gosnell, Donna; Ware, Ronald; Fulp, Sonya; Jarrard, Joey; Phillips, Dennis

    2009-01-01

    Iron chelators are being examined as a potential class of pharmaceutical agents to battle different types of cancer as well as iron overload diseases. In recent studies, iron binding species such as desferrioxamine, triapine, tachpyridine, Dp44Mt, and PIH have been tested in cell line tests and clinical trials. Using published chemical equilibrium values (stability constants, equilibrium constants), it is argued that an iron chelator cannot competitively remove iron from a heme-containing biomolecule (i.e. hemoglobin (Hb), myoglobin) causing a cancerous cell to die. This type of reaction (DFO(aq) + [Fe(2+,3+)-Hb] --> [Fe(2+,3+)-DFO] + Hb) has been proposed in a number of published studies using circumstantial evidence. It is argued that iron chelators can potentially interact with iron from ferritin or iron that has precipitated or flocculated as oxyhydroxide under physiological pH's. It is argued that chelators can interfere with various physiological processes by binding cations such as Ca(2+), Zn(2+) or K(+). A number of siderophores and natural products that have the ability to bind Fe(3+)/Fe(2+) as well as other cations are discussed in terms of their potential pharmaceutical activity as chelators. Chemical equilibria between cations and pharmaceutical agents, which are rarely quantitated in explaining medicinal mechanisms, are used to show that chelators can bind and remove iron and other cations from physiologically important systems required for cell survival and propagation.

  14. First-principles models of equilibrium tellurium isotope fractionation

    NASA Astrophysics Data System (ADS)

    Haghnegahdar, M. A.; Schauble, E. A.; Fornadel, A. P.; Spry, P. G.

    2013-12-01

    In this study, equilibrium mass-dependent isotopic fractionation among representative Te-bearing species is estimated with first-principles thermodynamic calculations. Tellurium is a group 16 element (along with O, S, and Se) with eight stable isotopes ranging in mass from 120Te to 130Te, and six commonly-occurring oxidation states: -II, -I, 0, +II, +IV, and +VI. In its reduced form, Te(-II), tellurium has a unique crystal-chemical role as a bond partner for gold and silver in epithermal and orogenic gold deposits, which likely form when oxidized Te species (e.g., H2TeO3, TeO32-) or perhaps polytellurides (e.g., Te22-) interact with precious metals in hydrothermal solution. Te(IV) is the most common oxidation state at the Earth's surface, including surface outcrops of telluride ore deposits, where tellurite and tellurate minerals form by oxidation. In the ocean, dissolved tellurium tends to be scavenged by particulate matter. Te(VI) is more abundant than Te(IV) in the ocean water (1), even though it is thought to be less stable thermodynamically. This variety of valence states in natural systems and range of isotopic masses suggest that tellurium could exhibit geochemically useful isotope abundance variations. Tellurium isotope fractionations were determined for representative molecules and crystals of varying complexity and chemistry. Gas-phase calculations are combined with supermolecular cluster models of aqueous and solid species. These in turn are compared with plane-wave density functional theory calculations with periodic boundary conditions. In general, heavyTe/lightTe is predicted to be higher for more oxidized species, and lower for reduced species, with 130Te/125Te fractionations as large as 4‰ at 100οC between coexisting Te(IV) and Te(-II) or Te(0) compounds. This is a much larger fractionation than has been observed in naturally occurring redox pairs (i.e., Te (0) vs. Te(IV) species) so far, suggesting that disequilibrium processes may control

  15. A Metastable Equilibrium Model for the Relative Abundances of Microbial Phyla in a Hot Spring

    PubMed Central

    Dick, Jeffrey M.; Shock, Everett L.

    2013-01-01

    Many studies link the compositions of microbial communities to their environments, but the energetics of organism-specific biomass synthesis as a function of geochemical variables have rarely been assessed. We describe a thermodynamic model that integrates geochemical and metagenomic data for biofilms sampled at five sites along a thermal and chemical gradient in the outflow channel of the hot spring known as “Bison Pool” in Yellowstone National Park. The relative abundances of major phyla in individual communities sampled along the outflow channel are modeled by computing metastable equilibrium among model proteins with amino acid compositions derived from metagenomic sequences. Geochemical conditions are represented by temperature and activities of basis species, including pH and oxidation-reduction potential quantified as the activity of dissolved hydrogen. By adjusting the activity of hydrogen, the model can be tuned to closely approximate the relative abundances of the phyla observed in the community profiles generated from BLAST assignments. The findings reveal an inverse relationship between the energy demand to form the proteins at equal thermodynamic activities and the abundance of phyla in the community. The distance from metastable equilibrium of the communities, assessed using an equation derived from energetic considerations that is also consistent with the information-theoretic entropy change, decreases along the outflow channel. Specific divergences from metastable equilibrium, such as an underprediction of the relative abundances of phototrophic organisms at lower temperatures, can be explained by considering additional sources of energy and/or differences in growth efficiency. Although the metabolisms used by many members of these communities are driven by chemical disequilibria, the results support the possibility that higher-level patterns of chemotrophic microbial ecosystems are shaped by metastable equilibrium states that depend on both the

  16. Equilibrium model constraints on baryon cycling across cosmic time

    NASA Astrophysics Data System (ADS)

    Mitra, Sourav; Davé, Romeel; Finlator, Kristian

    2015-09-01

    Galaxies strongly self-regulate their growth via energetic feedback from stars, supernovae, and black holes, but these processes are among the least understood aspects of galaxy formation theory. We present an analytic galaxy evolution model that directly constrains such feedback processes from observed galaxy scaling relations. The equilibrium model, which is broadly valid for star-forming central galaxies that dominate cosmic star formation, is based on the ansatz that galaxies live in a slowly evolving equilibrium between inflows, outflows, and star formation. Using a Bayesian Monte Carlo Markov chain approach, we constrain our model to match observed galaxy scaling relations between stellar mass and halo mass, star formation rate, and metallicity from 0 < z < 2. A good fit (χ2 ≈ 1.6) is achieved with eight free parameters. We further show that constraining our model to any two of the three data sets also produces a fit to the third that is within reasonable systematic uncertainties. The resulting best-fitting parameters that describe baryon cycling suggest galactic outflow scalings intermediate between energy and momentum-driven winds, a weak dependence of wind recycling time on mass, and a quenching mass scale that evolves modestly upwards with redshift. This model further predicts a stellar mass-star formation rate relation that is in good agreement with observations to z ˜ 6. Our results suggest that this simple analytic framework captures the basic physical processes required to model the mean evolution of stars and metals in galaxies, despite not incorporating many canonical ingredients of galaxy formation models such as merging or disc formation.

  17. LLNL Chemical Kinetics Modeling Group

    SciTech Connect

    Pitz, W J; Westbrook, C K; Mehl, M; Herbinet, O; Curran, H J; Silke, E J

    2008-09-24

    The LLNL chemical kinetics modeling group has been responsible for much progress in the development of chemical kinetic models for practical fuels. The group began its work in the early 1970s, developing chemical kinetic models for methane, ethane, ethanol and halogenated inhibitors. Most recently, it has been developing chemical kinetic models for large n-alkanes, cycloalkanes, hexenes, and large methyl esters. These component models are needed to represent gasoline, diesel, jet, and oil-sand-derived fuels.

  18. Modeling dune response using measured and equilibrium bathymetric profiles

    USGS Publications Warehouse

    Fauver, Laura A.; Thompson, David M.; Sallenger, Asbury H.

    2007-01-01

    Coastal engineers typically use numerical models such as SBEACH to predict coastal change due to extreme storms. SBEACH model inputs include pre-storm profiles, wave heights and periods, and water levels. This study focuses on the sensitivity of SBEACH to the details of pre-storm bathymetry. The SBEACH model is tested with two initial conditions for bathymetry, including (1) measured bathymetry from lidar, and (2) calculated equilibrium profiles. Results show that longshore variability in the predicted erosion signal is greater over measured bathymetric profiles, due to longshore variations in initial surf zone bathymetry. Additionally, patterns in predicted erosion can be partially explained by the configuration of the inner surf zone from the shoreline to the trough, with surf zone slope accounting for 67% of the variability in predicted erosion volumes.

  19. Non-Equilibrium Zeldovich-Von Neumann-Doring Theory and Reactive Flow Modeling of Detonation

    SciTech Connect

    Tarver, C M; Forbes, J W; Urtiew, P A

    2002-05-02

    This paper discusses the Non-Equilibrium Zeldovich - von Neumann - Doring (NEZND) theory of self-sustaining detonation waves and the Ignition and Growth reactive flow model of shock initiation and detonation wave propagation in solid explosives. The NEZND theory identified the non-equilibrium excitation processes that precede and follow the exothermic decomposition of a large high explosive molecule into several small reaction product molecules. The thermal energy deposited by the leading shock wave must be distributed to the vibrational modes of the explosive molecule before chemical reactions can occur. The induction time for the onset of the initial endothermic reactions can be calculated using high pressure, high temperature transition state theory. Since the chemical energy is released well behind the leading shock front of a detonation wave, a physical mechanism is required for this chemical energy to reinforce the leading shock front and maintain its overall constant velocity. This mechanism is the amplification of pressure wavelets in the reaction zone by the process of de-excitation of the initially highly vibrationally excited reaction product molecules. This process leads to the development of the three-dimensional structure of detonation waves observed for all explosives. For practical predictions of shock initiation and detonation in hydrodynamic codes, phenomenological reactive flow models have been developed. The Ignition and Growth reactive flow model of shock initiation and detonation in solid explosives has been very successful in describing the overall flow measured by embedded gauges and laser interferometry. This reactive flow model uses pressure and compression dependent reaction rates, because time resolved experimental temperature data is not yet available. Since all chemical reaction rates are ultimately controlled by temperature, the next generation of reactive flow models will use temperature dependent reaction rates. Progress on a

  20. Non-Equilibrium Ionization Modeling of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Rimple, Remington; Murphy, Nicholas Arnold; Shen, Chengcai

    2017-01-01

    Coronal Mass Ejections, or CMEs, are solar events that eject plasma and magnetic flux into interplanetary space. Contemporary sources have noted that the onset of CMEs are caused by some instability of the coronal magnetic field, and further allows heating of plasma upon expansion. Additionally, plasma that leaves the lower solar corona does not remain in ionization equilibrium due to the rapid expansion of plasma. We investigate the evolution of charge states of CME plasma using non-equilibrium ionization (NEI) modeling. These NEI models include radiative cooling and serve as baseline studies for special cases where no heat is being added to the plasma. Each of the simulated CMEs have initial conditions characteristic of active regions. Various function inputs, such as initial temperature, density and final velocity, allow us to examine the influence of certain parameters on the charge state evolution. The results of our project show that plasma originating from active regions display charge state evolutions substantially dependent on initial density and temperature. The CMEs starting with higher plasma density often show an abundance of lower charge states above the freeze-in height. Simulations starting from higher temperatures often show abundance peaks at charge states with closed electron shells.

  1. Development of a continuum/rarefied hybrid scheme for flows with thermal and chemical non-equilibrium

    NASA Astrophysics Data System (ADS)

    Michaelis, Christopher Harold

    2001-07-01

    The motion of a gas may be studied from the microscopic or macroscopic point of view. At the microscopic level, molecules are constantly moving and colliding, and occasionally reacting to form new species. The accepted model for describing gases at the microscopic level is the Boltzmann equation. In contrast, macroscopic models rely on the conservation laws, combined with constitutive relations, which approximate the molecular relaxation in a gas. The resulting set of equations, called the Navier- Stokes equations, represent an approximation to the Boltzmann equation for small non-equilibrium. For flows that are sufficiently rarefied, the Navier- Stokes equations no longer represent an accurate approximation of the Boltzmann equation. Numerical solutions of the Boltzmann equation may be obtained through the direct simulation of molecular motion. Such approaches are termed Monte Carlo, or particle methods. In principle, particle methods can be used to simulate all flows, regardless of the degree of non-equilibrium. There are many instances where neither approach is ideal. One such example is the reentry of a blunt body through the atmosphere. Ahead of the body, there is a very strong shock wave that cannot be adequately modeled by the Navier-Stokes equations, due to the degree of non- equilibrium. At the surface of the blunt body, the temperature is substantially colder than the surrounding flow, resulting in a large increase in the density next to the surface. In this region, where the flow is near- continuum, particle methods are not computationally efficient. A numerical method that utilizes the Navier-Stokes equations in regions of near-continuum flow and a particle method everywhere else is ideal. In this study, a hybrid scheme, for the efficient numerical simulation of flows with thermal and chemical non-equilibrium, is successfully demonstrated. The hybrid method was applied to extreme, high Mach number flows, where vibrational and chemical relaxation are

  2. Chemical kinetics modeling

    SciTech Connect

    Westbrook, C.K.; Pitz, W.J.

    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.

  3. Equilibrium modeling of cadmium biosorption from aqueous solution by compost.

    PubMed

    Ahmad, Iftikhar; Akhtar, Muhammad Javed; Jadoon, Iram Bashir Khan; Imran, Muhammad; Imran, Muhammad; Ali, Shahid

    2017-02-01

    One of the most serious environmental issues of the present century is metal contamination of the aqueous environment due to the release of metal-containing effluents into the water bodies. Cadmium (Cd) is one of the toxic heavy metals which is not biodegradable thereby causing high risks to animals, plants, and humans. In the present study, potential and feasibility of compost derived from fruits and vegetables for Cd biosorption from aqueous solution were investigated. The batch biosorption experiments were performed to evaluate the effects of Cd concentrations (5, 15, 30, and 60 mg/L), compost biomass (0.5, 1.0, and 1.5 g/100 mL), pH (4, 6, and 8), contact time (1, 4, and 19 h), and temperature (28 and 35 °C) on Cd sorption and removal by compost. The biosorption of Cd was found to be highly dependent on initial Cd concentration, sorbent biomass, pH, contact time, and temperature of aqueous solution. It was observed that Cd sorption by compost was rapid up to 4 h, and then it became slow and stable as the contact time shifted towards equilibrium state (19 h). At equilibrium, the Cd sorption (q = 0.33-5.43 mg/g compost) and removal (45-99%) were observed at pH 6 and temperature 28 °C depending upon Cd concentrations and sorbent biomass in aqueous solution. The equilibrium experimental data were fitted well with Langmuir adsorption isotherm model (q max = 6.35-7.14 mg/g compost, R (2) = 0.77-0.98). FTIR spectrum of the compost indicated the presence of hydroxyl and carboxyl groups, which might be involved in the biosorption of Cd through ion exchange and complexation mechanisms. The optimal environmental conditions (pH 6, sorbent biomass 0.5 g/100 mL, and temperature 28 °C) induced more Cd sorption on compost at equilibrium. Results show compost as a cost-effective adsorbent material having high potential for heavy metal remediation from aqueous solution.

  4. A radial non-uniform helicon equilibrium discharge model

    NASA Astrophysics Data System (ADS)

    Cheng, Yu-Guo; Cheng, Mou-Sen; Wang, Mo-Ge; Li, Xiao-Kang

    2014-10-01

    Helicon discharges have attracted great attention in the electric propulsion community in recent years. To acquire the equilibrium properties, a self-consistent model is developed, which combines the helicon/Trivelpiece—Gould (TG) waves-plasma interaction mechanism and the plasma flow theory under the confinement of the magnetic field. The calculations reproduce the central peak density phenomenon observed in the experiments. The results show that when operating in the wave coupling mode, high magnetic field strength B0 results in the deviation of the central density versus B0 from the linear relationship, while the density rise becomes flatter as the radiofrequency (rf) input power Prf grows, and the electron temperature Te radial profile is mainly determined by the characteristic of the rf energy deposition. The model could provide suggestions in choosing the B0 and Prf for medium power helicon thrusters.

  5. Equilibrium model for biodegradation and adsorption of mixtures in GAC columns

    SciTech Connect

    Erlanson, B.C.; Dvorak, B.I.; Speitel, G.E. Jr.; Lawler, D.F.

    1997-05-01

    Microbial activity in granular activated carbon (GAC) columns has received much attention over the last 15 years because biodegradation of one or more chemicals might increase the GAC service life, thereby decreasing costs. An equilibrium model for simultaneous biodegradation and adsorption was developed and verified with existing data. For simplicity the model was restricted to only two components: one biodegradable and one not. The results from modeling over 300 hypothetical situations identified conditions where biodegradation significantly extends the service life of granular activated carbon (GAC) columns. When the nonbiodegradable chemical controls the service life, the only significant gains in service life occurred when the biodegradable and nonbiodegradable chemical had similar adsorbabilities. When the biodegradable chemical controls the service life, the service life was 1.2--7 times that with adsorption alone, depending on the relative adsorbability of the two chemicals. The increase in service life can be maximized by ensuring that biodegradation begins as soon as possible after start-up. The model provides a good screening tool for initial assessments of process feasibility, preliminary economic analyses, and planning of detailed experimental and computer modeling studies. Examples are presented using benzene and TCE to illustrate how the general trends presented apply to specific cases.

  6. Equilibrium modeling of the TFCX poloidal field coil system

    SciTech Connect

    Strickler, D.J.; Miller, J.B.; Rothe, K.E.; Peng, Y.K.M.

    1984-04-01

    The Toroidal Fusion Core Experiment (TFCX) isproposed to be an ignition device with a low safety factor (q approx. = 2.0), rf or rf-assisted startup, long inductive burn pulse (approx. 300 s), and an elongated plasma cross section (kappa = 1.6) with moderate triangularity (delta = 0.3). System trade studies have been carried out to assist in choosing an appropriate candidate for TFCX conceptual design. This report describes an important element in these system studies - the magnetohydrodynamic (MHD) equilibrium modeling of the TFCX poloidal field (PF) coil system and its impact on the choice of machine size. Reference design points for the all-super-conducting toroidal field (TF) coil (TFCX-S) and hybrid (TFCX-H) options are presented that satisfy given PF system criteria, including volt-second requirements during burn, mechanical configuration constraints, maximum field constraints at the superconducting PF coils, and plasma shape parameters. Poloidal coil current waveforms for the TFCX-S and TFCX-H reference designs consistent with the equilibrium requirements of the plasma startup, heating, and burn phases of a typical discharge scenario are calculated. Finally, a possible option for quasi-steady-state operation is discussed.

  7. Microscopic Models for Chemical Thermodynamics

    NASA Astrophysics Data System (ADS)

    Malyshev, V. A.

    2005-06-01

    We introduce an infinite particle system dynamics, which includes stochastic chemical kinetics models, the classical Kac model and free space movement. We study energy redistribution between two energy types (kinetic and chemical) in different time scales, similar to energy redistribution in the living cell. One example is considered in great detail, where the model provides main formulas of chemical thermodynamics.

  8. Non-equilibrium radiation from viscous chemically reacting two-phase exhaust plumes

    NASA Technical Reports Server (NTRS)

    Penny, M. M.; Smith, S. D.; Mikatarian, R. R.; Ring, L. R.; Anderson, P. G.

    1976-01-01

    A knowledge of the structure of the rocket exhaust plumes is necessary to solve problems involving plume signatures, base heating, plume/surface interactions, etc. An algorithm is presented which treats the viscous flow of multiphase chemically reacting fluids in a two-dimensional or axisymmetric supersonic flow field. The gas-particle flow solution is fully coupled with the chemical kinetics calculated using an implicit scheme to calculate chemical production rates. Viscous effects include chemical species diffusion with the viscosity coefficient calculated using a two-equation turbulent kinetic energy model.

  9. Adsorption laboratory experiment for undergraduate chemical engineering: Introducing kinetic, equilibrium and thermodynamic concepts

    NASA Astrophysics Data System (ADS)

    Muryanto, S.; Djatmiko Hadi, S.

    2016-11-01

    Adsorption laboratory experiment for undergraduate chemical engineering program is discussed. The experiment demonstrated adsorption of copper ions commonly found in wastewater using bio-sorbent, i.e. agricultural wastes. The adsorption was performed in a batch mode under various parameters: adsorption time (up to 120 min), initial pH (2 to 6), adsorbent dose (2.0 to 12.0 g L-1), adsorbent size (50 to 170 mesh), initial Cu2+ concentration (25 to 100 ppm) and temperatures (room temp to 40°C). The equilibrium and kinetic data of the experiments were calculated using the two commonly used isotherms: Langmuir and Lagergren pseudo-first-order kinetics. The maximum adsorption capacity for Cu2+ was found as 94.34 mg g-1. Thermodynamically, the adsorption process was spontaneous and endothermic. The calculated activation energy for the adsorption was observed as high as 127.94 kJ mol-1. Pedagogically, the experiment was assumed to be important in increasing student understanding of kinetic, equilibrium and thermodynamic concepts.

  10. Operating mechanisms of electrolytes in magnesium ion batteries: chemical equilibrium, magnesium deposition, and electrolyte oxidation.

    PubMed

    Kim, Dong Young; Lim, Younhee; Roy, Basab; Ryu, Young-Gyoon; Lee, Seok-Soo

    2014-12-21

    Since the early nineties there have been a number of reports on the experimental development of Mg electrolytes based on organo/amide-magnesium chlorides and their transmetalations. However, there are no theoretical papers describing the underlying operating mechanisms of Mg electrolytes, and there is no clear understanding of these mechanisms. We have therefore attempted to clarify the operating mechanisms of Mg electrolytes by studying the characteristics of Mg complexes, solvation, chemical equilibrium, Mg-deposition processes, electrolyte-oxidation processes, and oxidative degradation mechanism of RMgCl-based electrolytes, using ab initio calculations. The formation and solvation energies of Mg complexes highly depend on the characteristics of R groups. Thus, changes in R groups of RMgCl lead to changes in the equilibrium position and the electrochemical reduction and oxidation pathways and energies. We first provide a methodological scheme for calculating Mg reduction potential values in non-aqueous electrolytes and electrochemical windows. We also describe a strategy for designing Mg electrolytes to maximize the electrochemical windows and oxidative stabilities. These results will be useful not only for designing improved Mg electrolytes, but also for developing new electrolytes in the future.

  11. Development of (19)F-NMR chemical shift detection of DNA B-Z equilibrium using (19)F-NMR.

    PubMed

    Nakamura, S; Yang, H; Hirata, C; Kersaudy, F; Fujimoto, K

    2017-06-28

    Various DNA conformational changes are in correlation with biological events. In particular, DNA B-Z equilibrium showed a high correlation with translation and transcription. In this study, we developed a DNA probe containing 5-trifluoromethylcytidine or 5-trifluoromethylthymidine to detect DNA B-Z equilibrium using (19)F-NMR. Its probe enabled the quantitative detection of B-, Z-, and ss-DNA based on (19)F-NMR chemical shift change.

  12. Estimated Performance of Radial-Flow Exit Nozzles for Air in Chemical Equilibrium

    NASA Technical Reports Server (NTRS)

    Englert, Gerald W.; Kochendorfer, Fred D.

    1959-01-01

    The thrust, boundary-layer, and heat-transfer characteristics were computed for nozzles having radial flow in the divergent part. The working medium was air in chemical equilibrium, and the boundary layer was assumed to be all turbulent. Stagnation pressure was varied from 1 to 32 atmospheres, stagnation temperature from 1000 to 6000 R, and wall temperature from 1000 to 3000 R. Design pressure ratio was varied from 5 to 320, and operating pressure ratio was varied from 0.25 to 8 times the design pressure ratio. Results were generalized independent of divergence angle and were also generalized independent of stagnation pressure in the temperature range of 1000 to 3000 R. A means of determining the aerodynamically optimum wall angle is provided.

  13. Review and analysis of high temperature chemical reactions and the effect of non-equilibrium conditions

    NASA Technical Reports Server (NTRS)

    Johnson, R. E.

    1986-01-01

    Chemical reactions at high temperatures have been considered extensively because of their importance to the heating effects on re-entry of space vehicles. Data on these reactions however, are not abundant and even when found there are discrepancies in data collected by various investigators. In particular, data for recombination reactions are calculated from the dissociation reactions or vice versa through the equilibrium constant. This involves the use of the principle of detailed balancing. This principle is discussed in reference to conditions where it is valid as well as to those where it is not valid. Related topics that merit further study or for which applicable information was available are briefly mentioned in an appendix to this report.

  14. Review and analysis of high temperature chemical reactions and the effect of non-equilibrium conditions

    NASA Technical Reports Server (NTRS)

    Johnson, R. E.

    1986-01-01

    Chemical reactions at high temperatures have been considered extensively because of their importance to the heating effects on re-entry of space vehicles. Data on these reactions however, are not abundant and even when found there are discrepancies in data collected by various investigators. In particular, data for recombination reactions are calculated from the dissociation reactions or vice versa through the equilibrium constant. This involves the use of the principle of detailed balancing. This principle is discussed in reference to conditions where it is valid as well as to those where it is not valid. Related topics that merit further study or for which applicable information was available are briefly mentioned in an appendix to this report.

  15. An Analytical Investigation of Three General Methods of Calculating Chemical-Equilibrium Compositions

    NASA Technical Reports Server (NTRS)

    Zeleznik, Frank J.; Gordon, Sanford

    1960-01-01

    The Brinkley, Huff, and White methods for chemical-equilibrium calculations were modified and extended in order to permit an analytical comparison. The extended forms of these methods permit condensed species as reaction products, include temperature as a variable in the iteration, and permit arbitrary estimates for the variables. It is analytically shown that the three extended methods can be placed in a form that is independent of components. In this form the Brinkley iteration is identical computationally to the White method, while the modified Huff method differs only'slightly from these two. The convergence rates of the modified Brinkley and White methods are identical; and, further, all three methods are guaranteed to converge and will ultimately converge quadratically. It is concluded that no one of the three methods offers any significant computational advantages over the other two.

  16. Master equation for a chemical wave front with perturbation of local equilibrium.

    PubMed

    Dziekan, P; Lemarchand, A; Nowakowski, B

    2011-08-28

    In order to develop a stochastic description of gaseous reaction-diffusion systems, which includes a reaction-induced departure from local equilibrium, we derive a modified expression of the master equation from analytical calculations based on the Boltzmann equation. We apply the method to a chemical wave front of Fisher-Kolmogorov-Petrovsky-Piskunov type, whose propagation speed is known to be sensitive to small perturbations. The results of the modified master equation are compared successfully with microscopic simulations of the particle dynamics using the direct simulation Monte Carlo method. The modified master equation constitutes an efficient tool at the mesoscopic scale, which incorporates the nonequilibrium effect without need of determining the particle velocity distribution function.

  17. An improved flux-split algorithm applied to hypersonic flows in chemical equilibrium

    NASA Technical Reports Server (NTRS)

    Palmer, Grant

    1988-01-01

    An explicit, finite-difference, shock-capturing numerical algorithm is presented and applied to hypersonic flows assumed to be in thermochemical equilibrium. Real-gas chemistry is either loosely coupled to the gasdynamics by way of a Gibbs free energy minimization package or fully coupled using species mass conservation equations with finite-rate chemical reactions. A scheme is developed that maintains stability in the explicit, finite-rate formulation while allowing relatively high time steps. The codes use flux vector splitting to difference the inviscid fluxes and employ real-gas corrections to viscosity and thermal conductivity. Numerical results are compared against existing ballistic range and flight data. Flows about complex geometries are also computed.

  18. Tropospheric chemical models

    NASA Technical Reports Server (NTRS)

    Prinn, R. G.

    1992-01-01

    The differences in atmospheric composition over the globe and the short- and long-term variations in this composition are the net effect of several atmospheric and biospheric processes: biospheric emissions, atmospheric circulation, atmospheric chemical transformations and finally deposition back to the surface. Accurate and realistic atmospheric chemistry and circulation models are essential to interpret the observed global distributions and trends of atmospheric species in terms of these underlying processes. Comparisons between model predictions and observations test current understanding of these processes and models used in conjunction with inverse methods allow deductions of the rates of these processes from the observations. With the planned inclusion of at least CO and CH4 observations on the Earth Observing System (EOS) satellites, together with the large global data set expected from in situ observations under the International Global Atmospheric Chemistry (IGAC) Project, the further development of global three-dimensional high-resolution atmospheric chemistry and circulation models in order to interpret this new data is a high-priority endeavor.

  19. LIFE Chamber Chemical Equilibrium Simulations with Additive Hydrogen, Oxygen, and Nitrogen

    SciTech Connect

    DeMuth, J A; Simon, A J

    2009-09-03

    In order to enable continuous operation of a Laser Inertial confinement Fusion Energy (LIFE) engine, the material (fill-gas and debris) in the fusion chamber must be carefully managed. The chamber chemical equilibrium compositions for post-shot mixtures are evaluated to determine what compounds will be formed at temperatures 300-5000K. It is desired to know if carbon and or lead will deposit on the walls of the chamber, and if so: at what temperature, and what elements can be added to prevent this from happening. The simulation was conducted using the chemical equilibrium solver Cantera with a Matlab front-end. Solutions were obtained by running equilibrations at constant temperature and constant specific volume over the specified range of temperatures. It was found that if nothing is done, carbon will deposit on the walls once it cools to below 2138K, and lead below 838K. Three solutions to capture the carbon were found: adding pure oxygen, hydrogen/nitrogen combo, and adding pure nitrogen. The best of these was the addition of oxygen which would readily form CO at around 4000K. To determine the temperature at which carbon would deposit on the walls, temperature solutions to evaporation rate equations needed to be found. To determine how much carbon or any species was in the chamber at a given time, chamber flushing equations needed to be developed. Major concerns are deposition of carbon and/or oxygen on the tungsten walls forming tungsten oxides or tungsten carbide which could cause embrittlement and cause failure of the first wall. Further research is needed.

  20. Equilibrium unfolding of A. niger RNase: pH dependence of chemical and thermal denaturation.

    PubMed

    Kumar, Gundampati Ravi; Sharma, Anurag; Kumari, Moni; Jagannadham, Medicherla V; Debnath, Mira

    2011-08-01

    Equilibrium unfolding of A. niger RNase with chemical denaturants, for example GuHCl and urea, and thermal unfolding have been studied as a function of pH using fluorescence, far-UV, near-UV, and absorbance spectroscopy. Because of their ability to affect electrostatic interactions, pH and chemical denaturants have a marked effect on the stability, structure, and function of many globular proteins. ANS binding studies have been conducted to enable understanding of the folding mechanism of the protein in the presence of the denaturants. Spectroscopic studies by absorbance, fluorescence, and circular dichroism and use of K2D software revealed that the enzyme has α + β type secondary structure with approximately 29% α-helix, 24% β-sheet, and 47% random coil. Under neutral conditions the enzyme is stable in urea whereas GuHCl-induced equilibrium unfolding was cooperative. A. niger RNase has little ANS binding even under neutral conditions. Multiple intermediates were populated during the pH-induced unfolding of A. niger RNase. Urea and temperature-induced unfolding of A. niger RNase into the molten globule-like state is non-cooperative, in contrast to the cooperativity seen with the native protein, suggesting the presence of two parts/domains, in the molecular structure of A. niger RNase, with different stability that unfolds in steps. Interestingly, the GuHCl-induced unfolding of the A state (molten globule state) of A. niger RNase is unique, because a low concentration of denaturant not only induces structural change but also facilitates transition from one molten globule like state (A(MG1)) into another (I(MG2)).

  1. Radiative-convective equilibrium models of Uranus and Neptune

    SciTech Connect

    Appleby, J.F.

    1986-03-01

    The present study of Uranus and Neptune radiative-convective equilibrium models gives emphasis to such aspects of the stratospheric energy balance as the influence of aerosol heating and convective penetration. The results obtained for Uranus imply that a continuum absorber may be a significant factor in the stratosphere despite the great distance from the sun. The results obtained for Neptune show that such a continuum absorber could significantly contribute to the energy balance within a localized stratospheric region, although it probably cannot furnish sufficient power to account for the observed IR spectrum irrespective of its vertical distribution. Attention is accordingly given to the convective penetration that could arise under such rapid vertical mixing that CH4's condensation cannot occur before the gas is carried above the condensation region. 64 references.

  2. Computable general equilibrium model fiscal year 2013 capability development report

    SciTech Connect

    Edwards, Brian Keith; Rivera, Michael Kelly; Boero, Riccardo

    2016-05-17

    This report documents progress made on continued developments of the National Infrastructure Simulation and Analysis Center (NISAC) Computable General Equilibrium Model (NCGEM), developed in fiscal year 2012. In fiscal year 2013, NISAC the treatment of the labor market and tests performed with the model to examine the properties of the solutions computed by the model. To examine these, developers conducted a series of 20 simulations for 20 U.S. States. Each of these simulations compared an economic baseline simulation with an alternative simulation that assumed a 20-percent reduction in overall factor productivity in the manufacturing industries of each State. Differences in the simulation results between the baseline and alternative simulations capture the economic impact of the reduction in factor productivity. While not every State is affected in precisely the same way, the reduction in manufacturing industry productivity negatively affects the manufacturing industries in each State to an extent proportional to the reduction in overall factor productivity. Moreover, overall economic activity decreases when manufacturing sector productivity is reduced. Developers ran two additional simulations: (1) a version of the model for the State of Michigan, with manufacturing divided into two sub-industries (automobile and other vehicle manufacturing as one sub-industry and the rest of manufacturing as the other subindustry); and (2) a version of the model for the United States, divided into 30 industries. NISAC conducted these simulations to illustrate the flexibility of industry definitions in NCGEM and to examine the simulation properties of in more detail.

  3. Equilibrium Slab Models of Lyman-Alpha Clouds

    NASA Technical Reports Server (NTRS)

    Charlton, Jane C.; Salpeter, Edwin E.; Hogan, Craig J.

    1993-01-01

    We model the L(sub y(alpha)) clouds as slabs of hydrogen with an ionizing extragalactic radiation field incident from both sides. In general, the equilibrium configuration of a slab at redshift z approx. less than 5 is determined by a balance of the gas pressure, gravity (including the effects of a dark matter halo), and the pressure exerted by the inter-galactic medium, P(sub ext). These models have been used to make predictions of the number of slabs as a function of the neutral hydrogen column density, N(sub H). A break in the curve is predicted at the transition between regimes where gravity and pressure are the dominant confining forces, with a less rapid decrease at larger N(sub H). The transition from optically thin to optically thick slabs leads to a gap in the distribution, whose location is governed largely by the spectrum of ionizing radiation. There are certain parallels between lines of sight through the outer HI disk of spiral galaxy with increasing radius, and the progression from damped, to Lyman limit, to forest clouds. We discuss briefly the possibility that at least some of the observed low z forest clouds may be a separate population, associated with galaxies, as suggested by the observations of Bahcall et al. This population could dominate the forest at present if the dark matter attached to galaxies should lead to gravity confinement for this disk population, while the isolated clouds remain pressure confined. The formalism developed in this paper will allow a more detailed study. We also discuss a more general parameter study of the equilibrium configuration of slabs, including mock gravity and L(sub y(alpha)) photon trapping.

  4. The invariant constrained equilibrium edge preimage curve method for the dimension reduction of chemical kinetics

    NASA Astrophysics Data System (ADS)

    Ren, Zhuyin; Pope, Stephen B.; Vladimirsky, Alexander; Guckenheimer, John M.

    2006-03-01

    This work addresses the construction and use of low-dimensional invariant manifolds to simplify complex chemical kinetics. Typically, chemical kinetic systems have a wide range of time scales. As a consequence, reaction trajectories rapidly approach a hierarchy of attracting manifolds of decreasing dimension in the full composition space. In previous research, several different methods have been proposed to identify these low-dimensional attracting manifolds. Here we propose a new method based on an invariant constrained equilibrium edge (ICE) manifold. This manifold (of dimension nr) is generated by the reaction trajectories emanating from its (nr-1)-dimensional edge, on which the composition is in a constrained equilibrium state. A reasonable choice of the nr represented variables (e.g., nr "major" species) ensures that there exists a unique point on the ICE manifold corresponding to each realizable value of the represented variables. The process of identifying this point is referred to as species reconstruction. A second contribution of this work is a local method of species reconstruction, called ICE-PIC, which is based on the ICE manifold and uses preimage curves (PICs). The ICE-PIC method is local in the sense that species reconstruction can be performed without generating the whole of the manifold (or a significant portion thereof). The ICE-PIC method is the first approach that locally determines points on a low-dimensional invariant manifold, and its application to high-dimensional chemical systems is straightforward. The "inputs" to the method are the detailed kinetic mechanism and the chosen reduced representation (e.g., some major species). The ICE-PIC method is illustrated and demonstrated using an idealized H2/O system with six chemical species. It is then tested and compared to three other dimension-reduction methods for the test case of a one-dimensional premixed laminar flame of stoichiometric hydrogen/air, which is described by a detailed mechanism

  5. The invariant constrained equilibrium edge preimage curve method for the dimension reduction of chemical kinetics.

    PubMed

    Ren, Zhuyin; Pope, Stephen B; Vladimirsky, Alexander; Guckenheimer, John M

    2006-03-21

    This work addresses the construction and use of low-dimensional invariant manifolds to simplify complex chemical kinetics. Typically, chemical kinetic systems have a wide range of time scales. As a consequence, reaction trajectories rapidly approach a hierarchy of attracting manifolds of decreasing dimension in the full composition space. In previous research, several different methods have been proposed to identify these low-dimensional attracting manifolds. Here we propose a new method based on an invariant constrained equilibrium edge (ICE) manifold. This manifold (of dimension nr) is generated by the reaction trajectories emanating from its (nr-1)-dimensional edge, on which the composition is in a constrained equilibrium state. A reasonable choice of the nr represented variables (e.g., nr "major" species) ensures that there exists a unique point on the ICE manifold corresponding to each realizable value of the represented variables. The process of identifying this point is referred to as species reconstruction. A second contribution of this work is a local method of species reconstruction, called ICE-PIC, which is based on the ICE manifold and uses preimage curves (PICs). The ICE-PIC method is local in the sense that species reconstruction can be performed without generating the whole of the manifold (or a significant portion thereof). The ICE-PIC method is the first approach that locally determines points on a low-dimensional invariant manifold, and its application to high-dimensional chemical systems is straightforward. The "inputs" to the method are the detailed kinetic mechanism and the chosen reduced representation (e.g., some major species). The ICE-PIC method is illustrated and demonstrated using an idealized H2O system with six chemical species. It is then tested and compared to three other dimension-reduction methods for the test case of a one-dimensional premixed laminar flame of stoichiometric hydrogen/air, which is described by a detailed mechanism

  6. Equilibrium and Kinetic Models for Colloid Release Under Transient Solution Chemistry Conditions

    NASA Astrophysics Data System (ADS)

    Bradford, S. A.; Torkzaban, S.; Leij, F. J.; Simunek, J.

    2014-12-01

    Colloid retention and release is well known to depend on a wide variety of physical, chemical, and microbiological factors that may vary temporally in the subsurface environment. We present equilibrium, kinetic, combined equilibrium and kinetic, and two-site kinetic models of colloid release during transient physicochemical conditions. Our mathematical modeling approach relates colloid release under transient conditions to changes in the fraction of the solid surface area that contributes to retention. The developed models were subsequently applied to experimental colloid release datasets to investigate the influence of variations in ionic strength (IS), pH, cation exchange, colloid size, and water velocity on release. Various combinations of equilibrium and/or kinetic release models were needed to describe the experimental data depending on the transient conditions and colloid type. Release of E. coli D21g was promoted by a decrease in solution IS and an increase in pH, similar to expected trends for a reduction in the secondary minimum and nanoscale chemical heterogeneity, respectively. The retention and release of 20 nm carboxyl modified latex nanoparticles (NPs) were demonstrated to be more sensitive to the presence of Ca2+ than D21g. Specifically, retention of NPs was greater than D21g in the presence of 2 mM CaCl2 solution, and release of NPs only occurred after exchange of Ca2+ by Na+ and then a reduction in the solution IS. These findings highlight the limitations of conventional interaction energy calculations to describe colloid retention and release, and point to the need to consider Born repulsion and nanoscale heterogeneity. Temporal changes in the water velocity did not have a large influence on the release of D21g. This insensitivity was likely due to factors that reduce the applied hydrodynamic torque and/or increase the resisting adhesive torque. Collectively, experimental and modeling results indicate that episodic colloid transport in the

  7. Multiscale stochastic simulation algorithm with stochastic partial equilibrium assumption for chemically reacting systems

    SciTech Connect

    Cao Yang . E-mail: ycao@cs.ucsb.edu; Gillespie, Dan . E-mail: GillespieDT@mailaps.org; Petzold, Linda . E-mail: petzold@engineering.ucsb.edu

    2005-07-01

    In this paper, we introduce a multiscale stochastic simulation algorithm (MSSA) which makes use of Gillespie's stochastic simulation algorithm (SSA) together with a new stochastic formulation of the partial equilibrium assumption (PEA). This method is much more efficient than SSA alone. It works even with a very small population of fast species. Implementation details are discussed, and an application to the modeling of the heat shock response of E. Coli is presented which demonstrates the excellent efficiency and accuracy obtained with the new method.

  8. Chemical reactions simulated by ground-water-quality models

    USGS Publications Warehouse

    Grove, David B.; Stollenwerk, Kenneth G.

    1987-01-01

    Recent literature concerning the modeling of chemical reactions during transport in ground water is examined with emphasis on sorption reactions. The theory of transport and reactions in porous media has been well documented. Numerous equations have been developed from this theory, to provide both continuous and sequential or multistep models, with the water phase considered for both mobile and immobile phases. Chemical reactions can be either equilibrium or non-equilibrium, and can be quantified in linear or non-linear mathematical forms. Non-equilibrium reactions can be separated into kinetic and diffusional rate-limiting mechanisms. Solutions to the equations are available by either analytical expressions or numerical techniques. Saturated and unsaturated batch, column, and field studies are discussed with one-dimensional, laboratory-column experiments predominating. A summary table is presented that references the various kinds of models studied and their applications in predicting chemical concentrations in ground waters.

  9. Paper spray mass spectrometry applied in the monitoring of a chemical system in dynamic chemical equilibrium: the redox process of methylene blue.

    PubMed

    de Paula, Camila Cristina Almeida; Valadares, Alberto; Jurisch, Marina; Piccin, Evandro; Augusti, Rodinei

    2016-05-15

    The monitoring of chemical systems in dynamic equilibrium is not an easy task. This is due to the high rate at which the system returns to equilibrium after being perturbed, which hampers the possibility of following the aftereffects of the disturbance. In this context, it is necessary to use a fast analytical technique that requires no (or minimal) sample preparation, and which is capable of monitoring the species constituting the system in equilibrium. Paper spray ionization mass spectrometry (PS-MS), a recently introduced ambient ionization technique, has such characteristics and hence was chosen for monitoring a model system: the redox process of methylene blue. The model system evaluated herein was composed of three cationic species of methylene blue (MB), which coexist in a dynamic redox system: (1) [MB](+) of m/z 284 (cationic MB); (2) [MB + H + e](+•) of m/z 285 (the protonated form of a transient species resulting from the reduction of [MB](+) ); (3) [MB + 2H + 2e](+) or [leuco-MB + H](+) of m/z 286 (the protonated leuco form of MB). Aliquots of a MB solution were collected before and after the addition of a reducing agent (metallic zinc) and directly analyzed by PS-MS for identification of the predominant cationic species at different conditions. The mass spectra revealed that before the addition of the reducing agent the ion of m/z 284 (cationic MB) is the unique species. Upon the addition of the reducing agent and acid, however, the solution continuously undergo discoloration while reduced species derived directly from cationic MB (m/z 285 and 286) are detected in the mass spectra with increasing intensities. Fragmentation patterns obtained for each ionic species, i.e. [MB](+) , [MB + H + e](+•) and [leuco-MB + H](+) , shown to be consistent with the proposed structures. The PS-MS technique proved to be suitable for an in situ and 'near' real-time analysis of the dynamic equilibrium involving the redox of MB in aqueous medium. The data clearly

  10. Coupling of an average-atom model with a collisional-radiative equilibrium model

    SciTech Connect

    Faussurier, G. Blancard, C.; Cossé, P.

    2014-11-15

    We present a method to combine a collisional-radiative equilibrium model and an average-atom model to calculate bound and free electron wavefunctions in hot dense plasmas by taking into account screening. This approach allows us to calculate electrical resistivity and thermal conductivity as well as pressure in non local thermodynamic equilibrium plasmas. Illustrations of the method are presented for dilute titanium plasma.

  11. Revised method for calculating cloud densities in equilibrium models

    NASA Astrophysics Data System (ADS)

    Wong, M. H.; Atreya, S. K.; Kuhn, W. R.

    2013-12-01

    Models of cloud condensation under thermodynamic equilibrium in planetary atmospheres are simple but still useful for several reasons. They calculate the wet adiabatic lapse rate, they determine saturation-limited mixing ratios of condensing species, and they calculate the stabilizing effect of latent heat release and molecular weight stratification. Equilibrium cloud condensation models (ECCMs) also calculate a type of condensate density---a condensate "unit density"---that only equates to cloud density under specific circumstances, because microphysics and dynamics are not considered in ECCMs. Unit densities are calculated for every model altitude by requiring that condensed material remains at the level where it condenses. Many ECCMs in use trace their heritage to Weidenschilling and Lewis (1973; Icarus 20, 465--476; hereafter WL73), which contains an error that affects only the calculation of condensate unit density. The error led to densities too high by a factor of the atmospheric scale height divided by unit length, which is about 3x10^6 at Jupiter's ammonia cloud level. We will describe the condensate unit density calculation error in WL73, and provide a new algorithm based on the local change in vapor mixing ratio, rather than the difference between integrated column masses as in WL73. The new algorithm satisfies conservation of mass. Using a simple scaling law to parameterize dynamics in terms of updraft speed and duration, condensate unit densities from ECCMs can be converted to cloud densities. We validate the technique for the terrestrial case, by comparing model predictions with representative densities of cirrus and cumulus clouds. For cirrus and cumulus updraft parameters, respectively, we find cloud densities of 0.01--0.2 g m-3 and 0.8--7 g m-3, in excellent agreement with observations and models of terrestrial clouds of these types. Implications for models of planetary and exoplanetary atmospheres will be discussed. [This material is based upon

  12. Chemical earth models

    NASA Astrophysics Data System (ADS)

    Javoy, Marc

    1999-10-01

    This article presents a critical review of method, concepts and prejudices used bv modelists of the Earth's chemical composition over approximate the last fifty years and of the resulting compositions. Brief descriptions are given of admitted accretion mechanisms, of the starting materials most often considered and of the major parameters and recurrent concepts: 'reduced" state, mantle homogeneity vs heterogeneity, 'low pressure' core formation, 'great impact', refractory, lithophile, siderophile, compatible, incompatible character of elements, depleted and degassed mantle, Urey ratio, as well as the description of a commonly-used instrument, possibly harmful to Iogic, the famous Ockham's razor. Differences between models are now restricted to the lower mantle composition:the 'primary' (before crust differentiation) upper mentle varies little from model to model and the idea of a 10-15% combined Si-O-S concentration as representing the necessary light elements in the core is gaining more and more ground. The dominant type of model derives more or less directly from the CI cabonaceous composition by complete devolatilization and reduction. Its mantle is homogeneous and convecting mainly in a one-level mode, in accordence with dominant geophysicists' views but in rather strong disagreement with geochemical data and models which insist on the strong decoupling between lower and upper mantle. Its low Si excess is generally supposed to have been absorbed by the core, whereas its high refractory lithophile element (RLE) content creates mass balance problems relative to presently observed mantle and crust concentrations. The alternative type is a two-lavel mantle with a Si and Fe-rich, RLE-poor, lower mantle, previously based mainly on seismic and mineral physics data, and now also on geochemical and cosmochemical arguments.

  13. Ising Model Reprogramming of a Repeat Protein's Equilibrium Unfolding Pathway.

    PubMed

    Millership, C; Phillips, J J; Main, E R G

    2016-05-08

    Repeat proteins are formed from units of 20-40 aa that stack together into quasi one-dimensional non-globular structures. This modular repetitive construction means that, unlike globular proteins, a repeat protein's equilibrium folding and thus thermodynamic stability can be analysed using linear Ising models. Typically, homozipper Ising models have been used. These treat the repeat protein as a series of identical interacting subunits (the repeated motifs) that couple together to form the folded protein. However, they cannot describe subunits of differing stabilities. Here we show that a more sophisticated heteropolymer Ising model can be constructed and fitted to two new helix deletion series of consensus tetratricopeptide repeat proteins (CTPRs). This analysis, showing an asymmetric spread of stability between helices within CTPR ensembles, coupled with the Ising model's predictive qualities was then used to guide reprogramming of the unfolding pathway of a variant CTPR protein. The designed behaviour was engineered by introducing destabilising mutations that increased the thermodynamic asymmetry within a CTPR ensemble. The asymmetry caused the terminal α-helix to thermodynamically uncouple from the rest of the protein and preferentially unfold. This produced a specific, highly populated stable intermediate with a putative dimerisation interface. As such it is the first step in designing repeat proteins with function regulated by a conformational switch.

  14. Stochastic Modeling of Non-equilibrium Bedload Transport

    NASA Astrophysics Data System (ADS)

    Kuai, Z.; Tsai, C. W.

    2009-05-01

    Traditional stochastic bed load models aimed to solve for the equilibrium bedload transport rate by matching the rate of bed erosion with the rate of deposition. Bedload transport can be in nonequilibrium even under the steady flow condition, as the quantity of moving particles in the bedload layer may vary. In a nonequilibrium condition, the interchange of sediment particles occurs not only between the bedload layer and the bed surface, but also across the interface between bedload and suspended load. The proposed approach attempts to add a new bedload-suspended load interchange layer to a stochastic bedlod transport model based on the Markov chain. The bedload transport rate is the product of the total particle volume in saltation and the average saltating velocity. We can quantify the number of saltating particles by modeling the occupancy probabilities vector of particles staying in three states (i.e., bed surface, bedload layer, and the interchange layer between the bedload and the suspended load.). The new stochastic bedload relation is validated against existing bedload model. The sudden change of flow and/or sediment condition leads to changes in the transition probabilities. The influence of sudden changes in flow-sediment properties on the bedload transport rate is investigated in this preliminary study. It is found that the neglecting the exchange process between the bedload layer and the suspended layer may lead to non-negligible errors in bedload calculation when the flow and/or sediment conditions change.

  15. An Equilibrium-Based Model of Gas Reaction and Detonation

    SciTech Connect

    Trowbridge, L.D.

    2000-04-01

    During gaseous diffusion plant operations, conditions leading to the formation of flammable gas mixtures may occasionally arise. Currently, these could consist of the evaporative coolant CFC-114 and fluorinating agents such as F2 and ClF3. Replacement of CFC-114 with a non-ozone-depleting substitute is planned. Consequently, in the future, the substitute coolant must also be considered as a potential fuel in flammable gas mixtures. Two questions of practical interest arise: (1) can a particular mixture sustain and propagate a flame if ignited, and (2) what is the maximum pressure that can be generated by the burning (and possibly exploding) gas mixture, should it ignite? Experimental data on these systems, particularly for the newer coolant candidates, are limited. To assist in answering these questions, a mathematical model was developed to serve as a tool for predicting the potential detonation pressures and for estimating the composition limits of flammability for these systems based on empirical correlations between gas mixture thermodynamics and flammability for known systems. The present model uses the thermodynamic equilibrium to determine the reaction endpoint of a reactive gas mixture and uses detonation theory to estimate an upper bound to the pressure that could be generated upon ignition. The model described and documented in this report is an extended version of related models developed in 1992 and 1999.

  16. Conversion of Chemical Reaction Energy into Useful Work in the Van't Hoff Equilibrium Box

    ERIC Educational Resources Information Center

    Bazhin, N. M.; Parmon, V. N.

    2007-01-01

    The ideal van't Hoff equilibrium box is described in detail. It shows that van't Hoff equilibrium box divided in two parts can simultaneously produce heat and useful work without violation of the first law of thermodynamics.

  17. Conversion of Chemical Reaction Energy into Useful Work in the Van't Hoff Equilibrium Box

    ERIC Educational Resources Information Center

    Bazhin, N. M.; Parmon, V. N.

    2007-01-01

    The ideal van't Hoff equilibrium box is described in detail. It shows that van't Hoff equilibrium box divided in two parts can simultaneously produce heat and useful work without violation of the first law of thermodynamics.

  18. Fluid/mineral equilibrium calculations for geothermal fluids and chemical geothermometry

    SciTech Connect

    Tole, M.P. . School of Environmental Studies); Armannsson, H. ); Pang Zhonghe . Lab. for Geothermal); Arnorsson, S. . Science Inst.)

    1993-02-01

    Aquifer temperatures of 13 geothermal wells in Iceland whose measured reservoir temperatures range from 47 to 325 C have been estimated from the chemical composition of the discharged fluid by considering simultaneously temperature dependent equilibria between many mineral phases and the solution. This approach to chemical geothermometry was initially proposed by Reed and Spycher. Its advantage over individual solute geothermometers such as the silica and the Na-K and Na-K-Ca geothermometers is that it allows a distinction to be made between equilibrated and non-equilibrated waters. However, care should be taken in interpreting the results of multi-mineral/solute equilibria as the results depend on both the thermodynamic data base used for mineral solubilities and the activities of end-member minerals in solid solutions. When using old analytical data attention has to be paid to analytical methods, especially in the case of important constituents present at low concentrations in the fluid, such as aluminium, for which analytical results obtained by two methods yielded very different equilibrium temperatures. The results for selected wells in Iceland, presented here, indicate that the geothermometry results are with few exceptions within 20 C of measured aquifer temperatures, and within 10 C for about half the wells considered. The method responds rapidly to changes such as cooling or mixing.

  19. New radiative-convective equilibrium models for EGPs

    NASA Astrophysics Data System (ADS)

    Goukenleuque, C.

    2001-11-01

    A radiative equilibrium atmospheric model for HD 209458 b is presented. Opacity from alkalii metals (K, Na) in the visible have been included, using vertical abundance profiles of alkalii atoms calculated by Tim Brown (preprint, 2001) and accounting for photoionization by the parent star's radiation. Absorption from the neutral Potassium and Sodium atoms strongly reduces the planetary reflected flux in the 0.4-0.8 μ m wavelength range. Although these atoms (whose modelling of the line profiles may overestimate the absorption in the wings and underestimate the absorption in the line cores) are remarkably depleted in the upper atmosphere (above the 1-mbar level) through photoionization, they tend to increase the effective temperature of the planet by more than 100 K. In addition, convective adjustment and correction for water vapor abundance have been applied to a model for a Jupiter-like planet at 1 AU orbiting a solar-type star. This work was made possible thanks to the National Research Council Research Associate Program.

  20. VHTR Prismatic Super Lattice Model for Equilibrium Fuel Cycle Analysis

    SciTech Connect

    G. S. Chang

    2006-09-01

    The advanced Very High Temperature gas-cooled Reactor (VHTR), which is currently being developed, achieves simplification of safety through reliance on innovative features and passive systems. One of the VHTRs innovative features is the reliance on ceramic-coated fuel particles to retain the fission products under extreme accident conditions. The effect of the random fuel kernel distribution in the fuel prismatic block is addressed through the use of the Dancoff correction factor in the resonance treatment. However, if the fuel kernels are not perfect black absorbers, the Dancoff correction factor is a function of burnup and fuel kernel packing factor, which requires that the Dancoff correction factor be updated during Equilibrium Fuel Cycle (EqFC) analysis. An advanced Kernel-by-Kernel (K-b-K) hexagonal super lattice model can be used to address and update the burnup dependent Dancoff effect during the EqFC analysis. The developed Prismatic Super Homogeneous Lattice Model (PSHLM) is verified by comparing the calculated burnup characteristics of the double-heterogeneous Prismatic Super Kernel-by-Kernel Lattice Model (PSK-b-KLM). This paper summarizes and compares the PSHLM and PSK-b-KLM burnup analysis study and results. This paper also discusses the coupling of a Monte-Carlo code with fuel depletion and buildup code, which provides the fuel burnup analysis tool used to produce the results of the VHTR EqFC burnup analysis.

  1. A Synthesis of Equilibrium and Historical Models of Landform Development.

    ERIC Educational Resources Information Center

    Renwick, William H.

    1985-01-01

    The synthesis of two approaches that can be used in teaching geomorphology is described. The equilibrium approach explains landforms and landform change in terms of equilibrium between landforms and controlling processes. The historical approach draws on climatic geomorphology to describe the effects of Quaternary climatic and tectonic events on…

  2. A Synthesis of Equilibrium and Historical Models of Landform Development.

    ERIC Educational Resources Information Center

    Renwick, William H.

    1985-01-01

    The synthesis of two approaches that can be used in teaching geomorphology is described. The equilibrium approach explains landforms and landform change in terms of equilibrium between landforms and controlling processes. The historical approach draws on climatic geomorphology to describe the effects of Quaternary climatic and tectonic events on…

  3. Equilibrium sampling of environmental pollutants in fish: comparison with lipid-normalized concentrations and homogenization effects on chemical activity.

    PubMed

    Jahnke, Annika; Mayer, Philipp; Adolfsson-Erici, Margaretha; McLachlan, Michael S

    2011-07-01

    Equilibrium sampling of organic pollutants into the silicone polydimethylsiloxane (PDMS) has recently been applied in biological tissues including fish. Pollutant concentrations in PDMS can then be multiplied with lipid/PDMS distribution coefficients (D(Lipid,PDMS) ) to obtain concentrations in fish lipids. In the present study, PDMS thin films were used for equilibrium sampling of polychlorinated biphenyls (PCBs) in intact tissue of two eels and one salmon. A classical exhaustive extraction technique to determine lipid-normalized PCB concentrations, which assigns the body burden of the chemical to the lipid fraction of the fish, was additionally applied. Lipid-based PCB concentrations obtained by equilibrium sampling were 85 to 106% (Norwegian Atlantic salmon), 108 to 128% (Baltic Sea eel), and 51 to 83% (Finnish lake eel) of those determined using total extraction. This supports the validity of the equilibrium sampling technique, while at the same time confirming that the fugacity capacity of these lipid-rich tissues for PCBs was dominated by the lipid fraction. Equilibrium sampling was also applied to homogenates of the same fish tissues. The PCB concentrations in the PDMS were 1.2 to 2.0 times higher in the homogenates (statistically significant in 18 of 21 cases, p < 0.05), indicating that homogenization increased the chemical activity of the PCBs and decreased the fugacity capacity of the tissue. This observation has implications for equilibrium sampling and partition coefficients determined using tissue homogenates.

  4. Identification and analysis of student conceptions used to solve chemical equilibrium problems

    NASA Astrophysics Data System (ADS)

    Voska, Kirk William

    This study identified and quantified chemistry conceptions students use when solving chemical equilibrium problems requiring the application of Le Chatelier's principle, and explored the feasibility of designing a paper and pencil test for this purpose. It also demonstrated the utility of conditional probabilities to assess test quality. A 10-item pencil-and-paper, two-tier diagnostic instrument, the Test to Identify Student Conceptualizations (TISC) was developed and administered to 95 second-semester university general chemistry students after they received regular course instruction concerning equilibrium in homogeneous aqueous, heterogeneous aqueous, and homogeneous gaseous systems. The content validity of TISC was established through a review of TISC by a panel of experts; construct validity was established through semi-structured interviews and conditional probabilities. Nine students were then selected from a stratified random sample for interviews to validate TISC. The probability that TISC correctly identified an answer given by a student in an interview was p = .64, while the probability that TISC correctly identified a reason given by a student in an interview was p=.49. Each TISC item contained two parts. In the first part the student selected the correct answer to a problem from a set of four choices. In the second part students wrote reasons for their answer to the first part. TISC questions were designed to identify students' conceptions concerning the application of Le Chatelier's principle, the constancy of the equilibrium constant, K, and the effect of a catalyst. Eleven prevalent incorrect conceptions were identified. This study found students consistently selected correct answers more frequently (53% of the time) than they provided correct reasons (33% of the time). The association between student answers and respective reasons on each TISC item was quantified using conditional probabilities calculated from logistic regression coefficients. The

  5. Calculation of individual isotope equilibrium constants for implementation in geochemical models

    USGS Publications Warehouse

    Thorstenson, Donald C.; Parkhurst, David L.

    2002-01-01

    Theory is derived from the work of Urey to calculate equilibrium constants commonly used in geochemical equilibrium and reaction-transport models for reactions of individual isotopic species. Urey showed that equilibrium constants of isotope exchange reactions for molecules that contain two or more atoms of the same element in equivalent positions are related to isotope fractionation factors by , where is n the number of atoms exchanged. This relation is extended to include species containing multiple isotopes, for example and , and to include the effects of nonideality. The equilibrium constants of the isotope exchange reactions provide a basis for calculating the individual isotope equilibrium constants for the geochemical modeling reactions. The temperature dependence of the individual isotope equilibrium constants can be calculated from the temperature dependence of the fractionation factors. Equilibrium constants are calculated for all species that can be formed from and selected species containing , in the molecules and the ion pairs with where the subscripts g, aq, l, and s refer to gas, aqueous, liquid, and solid, respectively. These equilibrium constants are used in the geochemical model PHREEQC to produce an equilibrium and reaction-transport model that includes these isotopic species. Methods are presented for calculation of the individual isotope equilibrium constants for the asymmetric bicarbonate ion. An example calculates the equilibrium of multiple isotopes among multiple species and phases.

  6. A non-equilibrium neutral model for analysing cultural change.

    PubMed

    Kandler, Anne; Shennan, Stephen

    2013-08-07

    Neutral evolution is a frequently used model to analyse changes in frequencies of cultural variants over time. Variants are chosen to be copied according to their relative frequency and new variants are introduced by a process of random mutation. Here we present a non-equilibrium neutral model which accounts for temporally varying population sizes and mutation rates and makes it possible to analyse the cultural system under consideration at any point in time. This framework gives an indication whether observed changes in the frequency distributions of a set of cultural variants between two time points are consistent with the random copying hypothesis. We find that the likelihood of the existence of the observed assemblage at the end of the considered time period (expressed by the probability of the observed number of cultural variants present in the population during the whole period under neutral evolution) is a powerful indicator of departures from neutrality. Further, we study the effects of frequency-dependent selection on the evolutionary trajectories and present a case study of change in the decoration of pottery in early Neolithic Central Europe. Based on the framework developed we show that neutral evolution is not an adequate description of the observed changes in frequency. Copyright © 2013 Elsevier Ltd. All rights reserved.

  7. Reduction of chemical reaction models

    NASA Technical Reports Server (NTRS)

    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.

  8. Evaporation from Soils Under Thermal Boundary Conditions: Experimental and Modeling Investigation to Compare Equilibrium and Non-Equilibrium Based Approaches

    NASA Astrophysics Data System (ADS)

    Smits, K. M.; Cihan, A.; Sakaki, T.; Illangasekare, T. H.

    2010-12-01

    In the shallow subsurface immediately below the land-atmosphere interface, it is widely recognized that the movement of water vapor is closely coupled to thermal processes. However, their mutual interactions are rarely considered in most soil water modeling efforts or in practical applications where it becomes necessary to understand and predict the spatial and temporal distribution of soil moisture. The validation of numerical models that are designed to capture these processes is difficult due to the inherent complexities of the problem in field systems and the scarcity of field or laboratory data with accurately known hydraulic and thermal parameters of soils, thus limiting the testing and refinement of heat and water transfer theories. In addition, it is often assumed in traditional soil physics applications that water vapor concentration in the air adjacent to the water phase in soil pores is always in equilibrium with liquid water, i.e., vaporization occurs instantaneously, which can result in over prediction of evaporation from soil. The goal of this work is to perform controlled experiments under transient conditions of soil moisture and temperature using soil with accurately known hydraulic/thermal properties and use this data to test existing theories and develop appropriate numerical models. In this work, water vapor flow under varying temperature gradients was implemented based on a concept that allows non-equilibrium liquid/gas phase change with gas phase vapor diffusion. In order to validate this new approach, we developed a long column apparatus equipped with a network of sensors and generated data under well-controlled thermal boundary conditions at the soil surface. Water saturation, capillary pressure, temperature, relative humidity and column weight to record total mass of water in the column were continuously monitored. Results from numerical simulations based on the conventional equilibrium and non-equilibrium approaches were compared with

  9. Modeling of ion-cyclotron resonant heating in Wendelstein 7-X equilibrium

    NASA Astrophysics Data System (ADS)

    Faustin, J. M.; Cooper, W. A.; Graves, J. P.; Pfefferlé, D.

    2014-11-01

    W7X stellarator 3D equilibrium has been computed with the equilibrium code ANIMEC (Anisotropic Neumann Inverse Moments Equilibrium Code). This equilibrium was used to model ICRH minority heating in 4He(H) plasma with the 3D full-wave code LEMan (Low frequency ElectroMagnetic wave propagation). The coupled power spatial distribution is shown for different resonance positions within the range of frequencies foreseen for the ICRH antenna. It is found that for the high mirror equilibrium examined, the antenna frequency can be chosen to optimise the power deposition in the plasma core while limiting the absorption at the edge.

  10. Testing Equilibrium Models of Molecular Gas in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Wong, Tony

    We propose to study the molecular gas fractions and physical conditions of diffuse molecular clouds in the Magellanic Clouds using ultraviolet (UV) and optical absorption spectra, principally from the Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble Space Telescope (HST) archives. We will use these data to constrain the abundance of molecular hydrogen (H_2) undetectable in CO emission surveys and to test equilibrium models that seek to predict the H_2 mass fraction and the H_2/HI ratio as functions of metallicity, column density, and thermal pressure. Our approach complements HI and CO surveys by providing direct estimates of HI and H_2 column densities. For sight lines where sufficiently high resolution spectra are available, we will use the excitation of CI to determine thermal pressures, allowing us to test models that assume thermodynamic equilibrium in order to determine the HI-H_2 balance. The recently completed Spitzer Legacy surveys of the MCs provide images of PAH emission on sub-parsec scales, which may provide a means to model the distribution and small-scale clumping of gas in the vicinity of the absorption sight lines, and thus connect the absorption data with the much coarser resolution radio data. We will investigate this possibility and the implications that small-scale clumping have for comparisons with theoretical models. A preliminary analysis of the FUSE and HST data is already underway, and we present a few early results. We seek support to continue this effort over the next two years and to disseminate our results. Our methodology is novel in several respects. It includes the use of high-resolution optical spectra to derive component models for the FUSE absorption spectra, in order to derive more accurate column densities, especially for the higher J transitions of H_2 which provide key diagnostics of density and radiation field strength. Such component models will also aid in the analysis of the CI spectra. We will work to increase

  11. Determination of Students' Alternative Conceptions about Chemical Equilibrium: A Review of Research and the Case of Turkey

    ERIC Educational Resources Information Center

    Ozmen, Haluk

    2008-01-01

    This study aims to determine prospective science student teachers' alternative conceptions of the chemical equilibrium concept. A 13-item pencil and paper, two-tier multiple choice diagnostic instrument, the Test to Identify Students' Alternative Conceptions (TISAC), was developed and administered to 90 second-semester science student teachers…

  12. The Effect of Cooperative Learning Approach Based on Conceptual Change Condition on Students' Understanding of Chemical Equilibrium Concepts

    ERIC Educational Resources Information Center

    Bilgin, Ibrahim; Geban, Omer

    2006-01-01

    The purpose of this study is to investigate the effects of the cooperative learning approach based on conceptual change conditions over traditional instruction on 10th grade students' conceptual understanding and achievement of computational problems related to chemical equilibrium concepts. The subjects of this study consisted of 87 tenth grade…

  13. Studying Equilibrium in the Chemical Reaction between Ferric and Iodide Ions in Solution Using a Simple and Inexpensive Approach

    ERIC Educational Resources Information Center

    Nikolaychuk, Pavel Anatolyevich; Kuvaeva, Alyona Olegovna

    2016-01-01

    A laboratory experiment on the study of the chemical equilibrium based on the reaction between ferric and iodide ions in solution with the formation of ferrous ions, free iodine, and triiodide ions is developed. The total concentration of iodide and triiodide ions in the reaction mixture during the reaction is determined by the argentometric…

  14. Studying Equilibrium in the Chemical Reaction between Ferric and Iodide Ions in Solution Using a Simple and Inexpensive Approach

    ERIC Educational Resources Information Center

    Nikolaychuk, Pavel Anatolyevich; Kuvaeva, Alyona Olegovna

    2016-01-01

    A laboratory experiment on the study of the chemical equilibrium based on the reaction between ferric and iodide ions in solution with the formation of ferrous ions, free iodine, and triiodide ions is developed. The total concentration of iodide and triiodide ions in the reaction mixture during the reaction is determined by the argentometric…

  15. Reviewing Some Crucial Concepts of Gibbs Energy in Chemical Equilibrium Using a Computer-Assisted, Guided-Problem-Solving Approach

    ERIC Educational Resources Information Center

    Borge, Javier

    2015-01-01

    G, G°, ?rG, ?rG°, ?G, and ?G° are essential quantities to master the chemical equilibrium. Although the number of publications devoted to explaining these items is extremely high, it seems that they do not produce the desired effect because some articles and textbooks are still being written with some of these quantities that appear to be…

  16. Determination of Students' Alternative Conceptions about Chemical Equilibrium: A Review of Research and the Case of Turkey

    ERIC Educational Resources Information Center

    Ozmen, Haluk

    2008-01-01

    This study aims to determine prospective science student teachers' alternative conceptions of the chemical equilibrium concept. A 13-item pencil and paper, two-tier multiple choice diagnostic instrument, the Test to Identify Students' Alternative Conceptions (TISAC), was developed and administered to 90 second-semester science student teachers…

  17. Functional Fixedness and Functional Reduction as Common Sense Reasonings in Chemical Equilibrium and in Geometry and Polarity of Molecules.

    ERIC Educational Resources Information Center

    Furio, C.; Calatayud, M. L.; Barcenas, S. L.; Padilla, O. M.

    2000-01-01

    Focuses on learning difficulties in procedural knowledge, and assesses the procedural difficulties of grade 12 and first- and third-year university students based on common sense reasoning in two areas of chemistry--chemical equilibrium and geometry, and polarity of molecules. (Contains 55 references.) (Author/YDS)

  18. The Effect of Cooperative Learning Approach Based on Conceptual Change Condition on Students' Understanding of Chemical Equilibrium Concepts

    ERIC Educational Resources Information Center

    Bilgin, Ibrahim; Geban, Omer

    2006-01-01

    The purpose of this study is to investigate the effects of the cooperative learning approach based on conceptual change conditions over traditional instruction on 10th grade students' conceptual understanding and achievement of computational problems related to chemical equilibrium concepts. The subjects of this study consisted of 87 tenth grade…

  19. The Effect of Context-Based Chemical Equilibrium on Grade 11 Students' Learning, Motivation and Constructivist Learning Environment

    ERIC Educational Resources Information Center

    ilhan, Nail; Yildirim, Ali; Yilmaz, Sibel Sadi

    2016-01-01

    In recent years, many countries have adopted a context-based approach for designing science curricula for education at all levels. The aim of this study was to determine the effectiveness of a Context-Based Chemistry Course (CBCC) as compared with traditional/existing instruction, on 11th grade students' learning about chemical equilibrium,…

  20. Reviewing Some Crucial Concepts of Gibbs Energy in Chemical Equilibrium Using a Computer-Assisted, Guided-Problem-Solving Approach

    ERIC Educational Resources Information Center

    Borge, Javier

    2015-01-01

    G, G°, ?rG, ?rG°, ?G, and ?G° are essential quantities to master the chemical equilibrium. Although the number of publications devoted to explaining these items is extremely high, it seems that they do not produce the desired effect because some articles and textbooks are still being written with some of these quantities that appear to be…

  1. Functional Fixedness and Functional Reduction as Common Sense Reasonings in Chemical Equilibrium and in Geometry and Polarity of Molecules.

    ERIC Educational Resources Information Center

    Furio, C.; Calatayud, M. L.; Barcenas, S. L.; Padilla, O. M.

    2000-01-01

    Focuses on learning difficulties in procedural knowledge, and assesses the procedural difficulties of grade 12 and first- and third-year university students based on common sense reasoning in two areas of chemistry--chemical equilibrium and geometry, and polarity of molecules. (Contains 55 references.) (Author/YDS)

  2. Equilibrium Models of Coronal Loops That Involve Curvature and Buoyancy

    NASA Astrophysics Data System (ADS)

    Hindman, Bradley W.; Jain, Rekha

    2013-12-01

    We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.

  3. Equilibrium models of coronal loops that involve curvature and buoyancy

    SciTech Connect

    Hindman, Bradley W.; Jain, Rekha

    2013-12-01

    We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.

  4. Development of Accurate Chemical Equilibrium Models for Oxalate Species to High Ionic Strength in the System: Na-Ba-Ca-Mn-Sr-Cl-NO3-PO4-SO4-H2O at 25°C

    SciTech Connect

    Qafoku, Odeta; Felmy, Andrew R.

    2007-01-01

    The development of an accurate aqueous thermodynamic model is described for oxalate species in the Na-Ba-Ca-Mn-Sr-Cl-NO3-PO4-SO4-H2O system at 25°C. The model is valid to high ionic strength (as high as 10m) and from very acid (10m H2SO4) to neutral and basic conditions. The model is based upon the equations of Pitzer and co-workers. The necessary ion-interaction parameters are determined by comparison with experimental data taken from the literature or determined in this study. The proposed aqueous activity and solubility model is valid for a range of applications from interpretation of studies on mineral dissolution at circumneutral pH to the dissolution of high-level waste tank sludges under acidic conditions.

  5. Model atmospheres for cool stars. [varying chemical composition

    NASA Technical Reports Server (NTRS)

    Johnson, H. R.

    1974-01-01

    This report contains an extensive series of model atmospheres for cool stars having a wide range in chemical composition. Model atmospheres (temperature, pressure, density, etc.) are tabulated, along with emergent energy flux distributions, limb darkening, and information on convection for selected models. The models are calculated under the usual assumptions of hydrostatic equilibrium, constancy of total energy flux (including transport both by radiation and convection) and local thermodynamic equilibrium. Some molecular and atomic line opacity is accounted for as a straight mean. While cool star atmospheres are regimes of complicated physical conditions, and these atmospheres are necessarily approximate, they should be useful for a number of kinds of spectral and atmospheric analysis.

  6. The role of non-equilibrium fluxes in the relaxation processes of the linear chemical master equation

    SciTech Connect

    Oliveira, Luciana Renata de; Bazzani, Armando; Giampieri, Enrico; Castellani, Gastone C.

    2014-08-14

    We propose a non-equilibrium thermodynamical description in terms of the Chemical Master Equation (CME) to characterize the dynamics of a chemical cycle chain reaction among m different species. These systems can be closed or open for energy and molecules exchange with the environment, which determines how they relax to the stationary state. Closed systems reach an equilibrium state (characterized by the detailed balance condition (D.B.)), while open systems will reach a non-equilibrium steady state (NESS). The principal difference between D.B. and NESS is due to the presence of chemical fluxes. In the D.B. condition the fluxes are absent while for the NESS case, the chemical fluxes are necessary for the state maintaining. All the biological systems are characterized by their “far from equilibrium behavior,” hence the NESS is a good candidate for a realistic description of the dynamical and thermodynamical properties of living organisms. In this work we consider a CME written in terms of a discrete Kolmogorov forward equation, which lead us to write explicitly the non-equilibrium chemical fluxes. For systems in NESS, we show that there is a non-conservative “external vector field” whose is linearly proportional to the chemical fluxes. We also demonstrate that the modulation of these external fields does not change their stationary distributions, which ensure us to study the same system and outline the differences in the system's behavior when it switches from the D.B. regime to NESS. We were interested to see how the non-equilibrium fluxes influence the relaxation process during the reaching of the stationary distribution. By performing analytical and numerical analysis, our central result is that the presence of the non-equilibrium chemical fluxes reduces the characteristic relaxation time with respect to the D.B. condition. Within a biochemical and biological perspective, this result can be related to the “plasticity property” of biological systems

  7. The role of non-equilibrium fluxes in the relaxation processes of the linear chemical master equation.

    PubMed

    de Oliveira, Luciana Renata; Bazzani, Armando; Giampieri, Enrico; Castellani, Gastone C

    2014-08-14

    We propose a non-equilibrium thermodynamical description in terms of the Chemical Master Equation (CME) to characterize the dynamics of a chemical cycle chain reaction among m different species. These systems can be closed or open for energy and molecules exchange with the environment, which determines how they relax to the stationary state. Closed systems reach an equilibrium state (characterized by the detailed balance condition (D.B.)), while open systems will reach a non-equilibrium steady state (NESS). The principal difference between D.B. and NESS is due to the presence of chemical fluxes. In the D.B. condition the fluxes are absent while for the NESS case, the chemical fluxes are necessary for the state maintaining. All the biological systems are characterized by their "far from equilibrium behavior," hence the NESS is a good candidate for a realistic description of the dynamical and thermodynamical properties of living organisms. In this work we consider a CME written in terms of a discrete Kolmogorov forward equation, which lead us to write explicitly the non-equilibrium chemical fluxes. For systems in NESS, we show that there is a non-conservative "external vector field" whose is linearly proportional to the chemical fluxes. We also demonstrate that the modulation of these external fields does not change their stationary distributions, which ensure us to study the same system and outline the differences in the system's behavior when it switches from the D.B. regime to NESS. We were interested to see how the non-equilibrium fluxes influence the relaxation process during the reaching of the stationary distribution. By performing analytical and numerical analysis, our central result is that the presence of the non-equilibrium chemical fluxes reduces the characteristic relaxation time with respect to the D.B. condition. Within a biochemical and biological perspective, this result can be related to the "plasticity property" of biological systems and to their

  8. Non-equilibrium Ionization Modeling of Simulated Pseudostreamers in a Solar Corona Model

    NASA Astrophysics Data System (ADS)

    Shen, Chengcai; Raymond, John C.; Mikić, Zoran; Linker, Jon; Reeves, Katharine K.; Murphy, Nicholas A.

    2015-04-01

    Time-dependent ionization is important for diagnostics of coronal streamers, where the thermodynamic time scale could be shorter than the ionization or recombination time scales, and ions are therefor in non-equilibrium ionization states. In this work, we perform post-processing time-dependent ionization calculations for a three dimensional solar corona and inner heliosphere model from Predictive Sciences Inc. (Mikić & Linker 1999) to analyze the influence of non-equilibrium ionization on emission from coronal streamers. Using the plasma temperature, density, velocity and magnetic field distributions provided by the 3D MHD simulation covering the Whole Sun Month (Carrington rotation CR1913, 1996 August 22 to September 18), we calculate non-equilibrium ionization states in the region around a pseudostreamer. We then obtain the synthetic emissivities with the non-equilibrium ion populations. Under the assumption that the corona is optically thin, we also obtain intensity profiles of several emission lines. We compare our calculations with intensities of Lyman-alpha lines and OVI lines from SOHO/Ultraviolet Coronagraph Spectrometer (UVCS) observations at 14 different heights. The results show that intensity profiles of both Lyman-alpha and OVI lines match well UVCS observations at low heights. At large heights, OVI intensites are higher for non-equilibrium ionization than equilibrium ionization inside this pseudostreamer. The assumption of ionization equilibrium would lead to a underestimate of the OVI intensity by about ten percent at a height of 2 solar radii, and the difference between these two ionization cases increases with height. The intensity ratio of OVI 1032 line to OVI 1037 lines is also obtained for non-equilibrium ionization modeling.

  9. The Coupling of Related Demonstrations to Illustrate Principles in Chemical Kinetics and Equilibrium

    NASA Astrophysics Data System (ADS)

    Pacer, Richard A.

    1997-05-01

    Two very simple lecture demonstrations, both involving the reaction of magnesium with one or more dilute acids, are linked together to illustrate principles in chemical kinetics and equilibrium. In the first, crumpled Mg ribbon is placed in the nipple of a baby bottle holding 200 mL of 0.40 M HCl. The bottle is inverted into a large beaker of water, and the volume of H2 gas generated in one minute is measured. the experiment is repeated with 0.60 M HCl. The rate law, Rate = k[H+]n, is developed from the data. In the second, equal lengths of Mg ribbon are placed in small beakers or Petri dishes, on an overhead projector, containing equal (0.80 to 1.0 M) concentrations of HCl, H3BO3, and CH3CO2H. Acids are not identified; students are merely told that 'Acids A, B, and C are of the same molarity.' Students are then asked to explain why the rates are so different, which serves as a lead-in for the instructor to explain the meaning of a Ka value. Students readily conclude that one of the acids must be a strong acid, but are puzzled by the other two. [The enormous difference in the Ka values of acetic and boric acids results in a striking difference in their reaction rates.

  10. Silicon Oxysulfide, OSiS: Rotational Spectrum, Quantum-Chemical Calculations, and Equilibrium Structure.

    PubMed

    Thorwirth, Sven; Mück, Leonie Anna; Gauss, Jürgen; Tamassia, Filippo; Lattanzi, Valerio; McCarthy, Michael C

    2011-06-02

    Silicon oxysulfide, OSiS, and seven of its minor isotopic species have been characterized for the first time in the gas phase at high spectral resolution by means of Fourier transform microwave spectroscopy. The equilibrium structure of OSiS has been determined from the experimental data using calculated vibration-rotation interaction constants. The structural parameters (rO-Si = 1.5064 Å and rSi-S = 1.9133 Å) are in very good agreement with values from high-level quantum chemical calculations using coupled-cluster techniques together with sophisticated additivity and extrapolation schemes. The bond distances in OSiS are very short in comparison with those in SiO and SiS. This unexpected finding is explained by the partial charges calculated for OSiS via a natural population analysis. The results suggest that electrostatic effects rather than multiple bonding are the key factors in determining bonding in this triatomic molecule. The data presented provide the spectroscopic information needed for radio astronomical searches for OSiS.

  11. Influence of boundary slip effect on thermal environment in thermo-chemical non-equilibrium flow

    NASA Astrophysics Data System (ADS)

    Miao, Wenbo; Zhang, Liang; Li, Junhong; Cheng, Xiaoli

    2014-12-01

    A kind of new hypersonic vehicle makes long-time flight in transitional flow regime where boundary slip effect caused by low gas density will have an important influence on the thermal environment around the vehicles. Numerical studies on the boundary slip effect as hypersonic vehicles fly in high Mach number has been carried out. The method for solving non-equilibrium flows considering slip boundary, surface catalysis and chemical reactions has been built up, and been validated by comparing the thermal environment results with STS-2 flight test data. The mechanism and rules of impact on surface heat flux by different boundary slip level (Knudsen number from 0.01 to 0.05) has been investigated in typical hypersonic flow conditions. The results show that the influence mechanisms of boundary slip effect are different on component diffusion heat flux and convective heat flux; slip boundary increases the near wall temperature which diminish the convective heat; whereas enhances the near wall gas diffusion heat because of the internal energy's growing. Component diffusion heat flux takes a smaller portion of the total heat flux, so the slip boundary reduces the total wall heat flux. As Knudsen number goes up, the degree of rarefaction increases, the influences of slip boundary on convective and component diffusion heat flux are both enhanced, total heat flux grows by a small margin, and boundary slip effect is more distinct.

  12. Non-invasive estimation of dissipation from non-equilibrium fluctuations in chemical reactions.

    PubMed

    Muy, S; Kundu, A; Lacoste, D

    2013-09-28

    We show how to extract an estimate of the entropy production from a sufficiently long time series of stationary fluctuations of chemical reactions. This method, which is based on recent work on fluctuation theorems, is direct, non-invasive, does not require any knowledge about the underlying dynamics and is applicable even when only partial information is available. We apply it to simple stochastic models of chemical reactions involving a finite number of states, and for this case, we study how the estimate of dissipation is affected by the degree of coarse-graining present in the input data.

  13. HTR Spherical Super Lattice Model for Equilibrium Fuel Cycle Analysis

    SciTech Connect

    Gray S. Cahng

    2005-09-01

    Advanced High Temperature gas-cooled Reactors (HTR) currently being developed (GFR, VHTR - Very High Temperature gas-cooled Reactor, PBMR, and GT-MHR) are able to achieve a simplification of safety through reliance on innovative features and passive systems. One of the innovative features in these HTRs is reliance on ceramic-coated fuel particles to retain the fission products even under extreme accident conditions. The effect of the random fuel kernel distribution in the fuel pebble / block is addressed through the use of the Dancoff correction factor in the resonance treatment. In addition, the Dancoff correction factor is a function of burnup and fuel kernel packing factor, which requires that the Dancoff correction factor be updated during Equilibrium Fuel Cycle (EqFC) analysis. Although HTR fuel is rather homogeneously dispersed in the fuel graphite matrix, the heterogeneity effects in between fuel kernels and pebbles cannot be ignored. The double-heterogeneous lattice model recently developed at the Idaho National Engineering and Environmental Laboratory (INEEL) contains tens of thousands of cubic fuel kernel cells, which makes it very difficult to deplete the fuel, kernel by kernel (KbK), for the EqFC analysis. In addition, it is not possible to preserve the cubic size and packing factor in a spherical fuel pebble. To avoid these difficulties, a newly developed and validated HTR pebble-bed Kernel-by-Kernel spherical (KbK-sph) model, has been developed and verified in this study. The objective of this research is to introduce the KbK-sph model and super whole Pebble lattice model (PLM). The verified double-heterogeneous KbK-sph and pebble homogeneous lattice model (HLM) are used for the fuel burnup chracteristics analysis and important safety parameters validation. This study summarizes and compares the KbK-sph and HLM burnup analyzed results. Finally, we discus the Monte-Carlo coupling with a fuel depletion and buildup code - Origen-2 as a fuel burnup

  14. HTR Spherical Super Lattice Model for Equilibrium Fuel Cycle Analysis

    SciTech Connect

    Gray S. Cahng

    2005-09-01

    Advanced High Temperature gas-cooled Reactors (HTR) currently being developed (GFR, VHTR - Very High Temperature gas-cooled Reactor, PBMR, and GT-MHR) are able to achieve a simplification of safety through reliance on innovative features and passive systems. One of the innovative features in these HTRs is reliance on ceramic-coated fuel particles to retain the fission products even under extreme accident conditions. The effect of the random fuel kernel distribution in the fuel pebble / block is addressed through the use of the Dancoff correction factor in the resonance treatment. In addition, the Dancoff correction factor is a function of burnup and fuel kernel packing factor, which requires that the Dancoff correction factor be updated during Equilibrium Fuel Cycle (EqFC) analysis. Although HTR fuel is rather homogeneously dispersed in the fuel graphite matrix, the heterogeneity effects in between fuel kernels and pebbles cannot be ignored. The double-heterogeneous lattice model recently developed at the Idaho National Engineering and Environmental Laboratory (INEEL) contains tens of thousands of cubic fuel kernel cells, which makes it very difficult to deplete the fuel, kernel by kernel (KbK), for the EqFC analysis. In addition, it is not possible to preserve the cubic size and packing factor in a spherical fuel pebble. To avoid these difficulties, a newly developed and validated HTR pebble-bed Kernel-by-Kernel spherical (KbK-sph) model, has been developed and verified in this study. The objective of this research is to introduce the KbK-sph model and super whole Pebble lattice model (PLM). The verified double-heterogeneous KbK-sph and pebble homogeneous lattice model (HLM) are used for the fuel burnup chracteristics analysis and important safety parameters validation. This study summarizes and compares the KbK-sph and HLM burnup analyzed results. Finally, we discus the Monte-Carlo coupling with a fuel depletion and buildup code - Origen-2 as a fuel burnup

  15. Making Models of Chemical Compounds.

    ERIC Educational Resources Information Center

    Hoehn, Robert G.

    1992-01-01

    Describes the benefits and techniques of having students create models of chemical compounds. This hands-on approach uses colored paper and other inexpensive materials to construct the models. A step-by-step approach provides objectives, materials, an explanation on how to calculate chemical ratios, procedures, follow-up activities, and a resource…

  16. Equilibrium structural model of liquid water: Evidence from heat capacity, spectra, density, and other properties

    NASA Astrophysics Data System (ADS)

    Dougherty, Ralph C.; Howard, Louis N.

    1998-11-01

    Hydrogen bond strength depends on both temperature and pressure. The gradient for hydrogen bond strength with temperature, or pressure, depends upon the hydrogen bonded structure. These features create an intimate connection between quantum mechanics and thermodynamics in the structure of liquid water. The equilibrium structural model of liquid water developed from analysis of the heat capacity at constant pressure is complex. The model is based on the assumptions that: (i) the hydrogen bond length and molecular packing density of water both vary with temperature; (ii) the number of different geometries for hydrogen bonding is limited to a small set; (iii) water molecules that possess these hydrogen bonding geometries are in equilibrium with each other under static conditions; (iv) significant changes in the slope of the heat capacity, Cp, and to a lesser extent other properties of the liquid, reflect the onset of significant changes in the chemical structure of the liquid; (v) the partial molal enthalpies and entropies of the different water arrays generated from these building blocks differ from each other in their dependence upon temperature; and (vi) the structure of the liquid is a random structural network of the structural components. The equilibrium structural model for liquid water uses four structural components and the assumptions listed above. At the extrapolated-homogeneous nucleation temperature, 221 K, a disordered hexagonal-diamond lattice (tetrahedrally hydrogen bonded water clusters) is the structure of liquid water. At the homogeneous nucleation temperature, ˜238 K, liquid water is a mixture of disordered tetrahedral water arrays and pentagonal water arrays. The abundance of tetrahedral water structures at this temperature causes the system to self-nucleate. As the temperature increases to 266 K the proportion of disordered pentagonal water clusters in the equilibrium mixture increases. At 256 K, the temperature of the previously unrecognized

  17. Use of the augmented Young-Laplace equation to model equilibrium and evaporating extended menisci

    SciTech Connect

    DasGupta, S.; Schonberg, J.A.; Kim, I.Y.; Wayner, P.C.Jr. )

    1993-05-01

    The generic importance of fluid flow and change-of-phase heat transfer in the contact line region of an extended meniscus has led to theoretical and experimental research on the details of these transport processes. Numerical solutions of equilibrium and nonequilibrium models based on the augmented Young-Laplace equation were successfully used to evaluate experimental data for an extended meniscus. The data for the equilibrium and nonequilibrium meniscus profiles were obtained optically using ellipsometry and image processing interferometry. A Taylor series expansion of the fourth-order nonlinear transport model was used to obtain the extremely sensitive initial conditions at the interline. The solid-liquid-vapor Hamaker constants for the systems were obtained from the experimental data. The consistency of the data was demonstrated by using the combining rules to calculate the unknown value of the Hamaker constant for the experimental substrate. The sensitivity of the meniscus profile to small changes in the environment was demonstrated. Both temperature and intermolecular forces need to be included in modeling transport processes in the contact line region because the chemical potential is a function of both temperature and pressure.

  18. Modelling of Equilibrium Between Mantle and Core: Refractory, Volatile, and Highly Siderophile Elements

    NASA Technical Reports Server (NTRS)

    Righter, K.; Danielson, L.; Pando, K.; Shofner, G.; Lee, C. -T.

    2013-01-01

    Siderophile elements have been used to constrain conditions of core formation and differentiation for the Earth, Mars and other differentiated bodies [1]. Recent models for the Earth have concluded that the mantle and core did not fully equilibrate and the siderophile element contents of the mantle can only be explained under conditions where the oxygen fugacity changes from low to high during accretion and the mantle and core do not fully equilibrate [2,3]. However these conclusions go against several physical and chemical constraints. First, calculations suggest that even with the composition of accreting material changing from reduced to oxidized over time, the fO2 defined by metal-silicate equilibrium does not change substantially, only by approximately 1 logfO2 unit [4]. An increase of more than 2 logfO2 units in mantle oxidation are required in models of [2,3]. Secondly, calculations also show that metallic impacting material will become deformed and sheared during accretion to a large body, such that it becomes emulsified to a fine scale that allows equilibrium at nearly all conditions except for possibly the length scale for giant impacts [5] (contrary to conclusions of [6]). Using new data for D(Mo) metal/silicate at high pressures, together with updated partitioning expressions for many other elements, we will show that metal-silicate equilibrium across a long span of Earth s accretion history may explain the concentrations of many siderophile elements in Earth's mantle. The modeling includes refractory elements Ni, Co, Mo, and W, as well as highly siderophile elements Au, Pd and Pt, and volatile elements Cd, In, Bi, Sb, Ge and As.

  19. A vertical equilibrium model for assessing nonaqueous phase liquid contamination and remediation of groundwater systems

    SciTech Connect

    Wu, Y.S.; Huyakorn, P.S.; Park, N.S. )

    1994-04-01

    The areal numerical model was developed to simulate the simultaneous flow of ground water and a nonaqueous phase liquid (NAPL) for specific application to petroleum or chemical spills and leaks and remedial design and evaluation. The gravity-capillary vertical equilibrium (GCVE) formulation incorporates history-dependent pseudo capillary and relative permeability functions. These functions were developed to allow realistic simulations of migration and remediation scenarios involving partly contaminated ground water systems and significant residual NAPL saturations. Robust and efficient mass-conservative numerical solution techniques were implemented to allow complete analyses of site-specific field problems. Simulation examples were provided to demonstrate the model verification and utility. Both analytical and rigorous multiphase numerical solutions were used to check the results from the GCVE formulation. For the various test cases the GCVE performed remarkably well, yielding good accuracy in predicting of vertical profiles of NAPL saturation and cumulative recovery curves.

  20. Modeling of equilibrium hollow objects stabilized by electrostatics.

    PubMed

    Mani, Ethayaraja; Groenewold, Jan; Kegel, Willem K

    2011-05-18

    The equilibrium size of two largely different kinds of hollow objects behave qualitatively differently with respect to certain experimental conditions. Yet, we show that they can be described within the same theoretical framework. The objects we consider are 'minivesicles' of ionic and nonionic surfactant mixtures, and shells of Keplerate-type polyoxometalates. The finite-size of the objects in both systems is manifested by electrostatic interactions. We emphasize the importance of constant charge and constant potential boundary conditions. Taking these conditions into account, indeed, leads to the experimentally observed qualitatively different behavior of the equilibrium size of the objects.

  1. Equilibrium and kinetic models for colloid release under transient solution chemistry conditions

    USDA-ARS?s Scientific Manuscript database

    We present continuum models to describe colloid release in the subsurface during transient physicochemical conditions. Our modeling approach relates the amount of colloid release to changes in the fraction of the solid surface area that contributes to retention. Equilibrium, kinetic, equilibrium and...

  2. Computation of drying stresses in red oak using equilibrium and non-equilibrium creep models

    SciTech Connect

    Park, J.H.; Kyanka, G.H.; Smith, W.B.

    1995-12-31

    A comprehensive model which shows the development of drying stresses in red oak is presented. The elastic, visco-elastic and mechano-sorptive mechanisms of strain behavior are all included. The results show the dominant effects of mechano-sorptive creep on stress relaxation and give insights on the effects of temperature on stress. Some of the results indicate that model has value for people who are involved with commerical drying systems.

  3. Dynamic non-equilibrium wall-modeling for large eddy simulation at high Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Kawai, Soshi; Larsson, Johan

    2013-01-01

    A dynamic non-equilibrium wall-model for large-eddy simulation at arbitrarily high Reynolds numbers is proposed and validated on equilibrium boundary layers and a non-equilibrium shock/boundary-layer interaction problem. The proposed method builds on the prior non-equilibrium wall-models of Balaras et al. [AIAA J. 34, 1111-1119 (1996)], 10.2514/3.13200 and Wang and Moin [Phys. Fluids 14, 2043-2051 (2002)], 10.1063/1.1476668: the failure of these wall-models to accurately predict the skin friction in equilibrium boundary layers is shown and analyzed, and an improved wall-model that solves this issue is proposed. The improvement stems directly from reasoning about how the turbulence length scale changes with wall distance in the inertial sublayer, the grid resolution, and the resolution-characteristics of numerical methods. The proposed model yields accurate resolved turbulence, both in terms of structure and statistics for both the equilibrium and non-equilibrium flows without the use of ad hoc corrections. Crucially, the model accurately predicts the skin friction, something that existing non-equilibrium wall-models fail to do robustly.

  4. The lagRST Model: A Turbulence Model for Non-Equilibrium Flows

    NASA Technical Reports Server (NTRS)

    Lillard, Randolph P.; Oliver, A. Brandon; Olsen, Michael E.; Blaisdell, Gregory A.; Lyrintzis, Anastasios S.

    2011-01-01

    This study presents a new class of turbulence model designed for wall bounded, high Reynolds number flows with separation. The model addresses deficiencies seen in the modeling of nonequilibrium turbulent flows. These flows generally have variable adverse pressure gradients which cause the turbulent quantities to react at a finite rate to changes in the mean flow quantities. This "lag" in the response of the turbulent quantities can t be modeled by most standard turbulence models, which are designed to model equilibrium turbulent boundary layers. The model presented uses a standard 2-equation model as the baseline for turbulent equilibrium calculations, but adds transport equations to account directly for non-equilibrium effects in the Reynolds Stress Tensor (RST) that are seen in large pressure gradients involving shock waves and separation. Comparisons are made to several standard turbulence modeling validation cases, including an incompressible boundary layer (both neutral and adverse pressure gradients), an incompressible mixing layer and a transonic bump flow. In addition, a hypersonic Shock Wave Turbulent Boundary Layer Interaction with separation is assessed along with a transonic capsule flow. Results show a substantial improvement over the baseline models for transonic separated flows. The results are mixed for the SWTBLI flows assessed. Separation predictions are not as good as the baseline models, but the over prediction of the peak heat flux downstream of the reattachment shock that plagues many models is reduced.

  5. Turbulence Modeling Effects on the Prediction of Equilibrium States of Buoyant Shear Flows

    NASA Technical Reports Server (NTRS)

    Zhao, C. Y.; So, R. M. C.; Gatski, T. B.

    2001-01-01

    The effects of turbulence modeling on the prediction of equilibrium states of turbulent buoyant shear flows were investigated. The velocity field models used include a two-equation closure, a Reynolds-stress closure assuming two different pressure-strain models and three different dissipation rate tensor models. As for the thermal field closure models, two different pressure-scrambling models and nine different temperature variance dissipation rate, Epsilon(0) equations were considered. The emphasis of this paper is focused on the effects of the Epsilon(0)-equation, of the dissipation rate models, of the pressure-strain models and of the pressure-scrambling models on the prediction of the approach to equilibrium turbulence. Equilibrium turbulence is defined by the time rate (if change of the scaled Reynolds stress anisotropic tensor and heat flux vector becoming zero. These conditions lead to the equilibrium state parameters. Calculations show that the Epsilon(0)-equation has a significant effect on the prediction of the approach to equilibrium turbulence. For a particular Epsilon(0)-equation, all velocity closure models considered give an equilibrium state if anisotropic dissipation is accounted for in one form or another in the dissipation rate tensor or in the Epsilon(0)-equation. It is further found that the models considered for the pressure-strain tensor and the pressure-scrambling vector have little or no effect on the prediction of the approach to equilibrium turbulence.

  6. Study of equilibrium solubility measurement by saturation shake-flask method using hydrochlorothiazide as model compound.

    PubMed

    Baka, Edit; Comer, John E A; Takács-Novák, Krisztina

    2008-01-22

    The experimental conditions that affect equilibrium solubility values measured by the classical saturation shake-flask method have been examined, using hydrochlorothiazide as a model compound. Modifications in temperature, sedimentation time, composition of aqueous buffer and the technique of separation of solid and liquid phases were all found to influence the equilibrium solubility results strongly. However, variations in the amount of solid excess and stirring time were found to have less influence. In the light of these observations, a new, shorter protocol has been developed for measurements of equilibrium solubility, together with recommendations for good analytical practice. The equilibrium solubilities of five other drugs were measured to verify the new protocol.

  7. Non-Equilibrium Modeling of Inductively Coupled RF Plasmas

    DTIC Science & Technology

    2015-01-01

    other provision of law , no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a...Navier-Stokes and Maxwell equa- tions [2]. In literature, the Local Thermodynamic Equi- librium (LTE) assumption is often used to describe the state of...the gas in the discharge region [4–17]. However, Non Local Thermodynamic Equilibrium (NLTE) simula- tions of Argon [18, 19] and air plasmas [20], have

  8. Constant Entropy Properties for an Approximate Model of Equilibrium Air

    NASA Technical Reports Server (NTRS)

    Hansen, C. Frederick; Hodge, Marion E.

    1961-01-01

    Approximate analytic solutions for properties of equilibrium air up to 15,000 K have been programmed for machine computation. Temperature, compressibility, enthalpy, specific heats, and speed of sound are tabulated as constant entropy functions of temperature. The reciprocal of acoustic impedance and its integral with respect to pressure are also given for the purpose of evaluating the Riemann constants for one-dimensional, isentropic flow.

  9. Equilibrium and volumetric data and model development of coal fluids

    SciTech Connect

    Robinson, R.L. Jr.; Gasem, K.A.M.; Park, J.

    1992-04-28

    The long term goal of our efforts is to develop accurate predictive methods for description of equilibrium phase properties for a variety of types of mixtures and operating conditions. The specific objectives of the work specified herein include: (1) development of an experimental facility having the capability to provide data on equilibrium phase compositions (solubilities) and liquid densities, and doing so with greater accuracy and speed than our previous facility, (2) measurement of equilibrium phase properties for systematically-selected mixtures-specifically those containing important solute gases (such as hydrogen, carbon monoxide, methane, ethane, carbonyl sulfide, ammonia) in a series of heavy paraffinic, naphthenic and aromatic solvents (e.g., n-decane, n-eicosane, n-octacosane, n-hexatriacontane, cyclohexane, Decalin, perhydrophenanthrene, perhydropyrene, benzene, naphthalene, phenanthrene, pyrene), (3) testing/development of correlation frameworks for representing the phase behavior of fluids of the type encountered in coal conversion processes, and (4) generalization of parameters in the correlation frameworks to enable accurate predictions for systems of the type studied, permitting predictions to be made for systems and conditions other than those for which experimental data are available.

  10. Near-equilibrium chemical vapor deposition of high-quality single-crystal graphene directly on various dielectric substrates.

    PubMed

    Chen, Jianyi; Guo, Yunlong; Jiang, Lili; Xu, Zhiping; Huang, Liping; Xue, Yunzhou; Geng, Dechao; Wu, Bin; Hu, Wenping; Yu, Gui; Liu, Yunqi

    2014-03-05

    By using near-equilibrium chemical vapor deposition, it is demonstrated that high-quality single-crystal graphene can be grown on dielectric substrates. The maximum size is about 11 μm. The carrier mobility can reach about 5650 cm(2) V(-1) s(-1) , which is comparable to those of some metal-catalyzed graphene crystals, reflecting the good quality of the graphene lattice.

  11. Spectral Modeling in Astrophysics - The Physics of Non-equilibrium Clouds

    NASA Astrophysics Data System (ADS)

    Ferland, Gary; Williams, Robin

    2016-02-01

    Collisional-radiative spectral modeling plays a central role in astrophysics, probing phenomena ranging from the chemical evolution of the Universe to the energy production near supermassive black holes in distant quasars. The observed emission lines form in non-equilibrium clouds that have very low densities by laboratory standards, and are powered by energy sources which themselves are not in equilibrium. The spectrum is the result of a large number of microphysical processes, thermal statistics often do not apply, and analytical theory cannot be used. Numerical simulations are used to understand the physical state and the resulting spectrum. The greatest distinction between astrophysical modeling and conventional plasma simulations lies in the range of phenomena that must be considered. A single astronomical object will often have gas with kinetic temperatures of T˜10^6 K, 10^4 K, and T≤ 10^3 K, with the physical state ranging from molecular to fully ionized, and emitting over all wavelengths between the radio and x-ray. Besides atomic, plasma, and chemical physics, condensed matter physics is important because of the presence of small solid `grains' which affect the gas through catalytic reactions and the infrared emission they produce. The ionization, level populations, chemistry, and grain properties must be determined self-consistently, along with the radiation transport, to predict the observed spectrum. Although the challenge is great, so are the rewards. Numerical spectral simulations allow us to read the message contained in the spectrum emitted by objects far from the Earth that existed long ago.

  12. Novel non-equilibrium modelling of a DC electric arc in argon

    NASA Astrophysics Data System (ADS)

    Baeva, M.; Benilov, M. S.; Almeida, N. A.; Uhrlandt, D.

    2016-06-01

    A novel non-equilibrium model has been developed to describe the interplay of heat and mass transfer and electric and magnetic fields in a DC electric arc. A complete diffusion treatment of particle fluxes, a generalized form of Ohm’s law, and numerical matching of the arc plasma with the space-charge sheaths adjacent to the electrodes are applied to analyze in detail the plasma parameters and the phenomena occurring in the plasma column and the near-electrode regions of a DC arc generated in atmospheric pressure argon for current levels from 20 A up to 200 A. Results comprising electric field and potential, current density, heating of the electrodes, and effects of thermal and chemical non-equilibrium are presented and discussed. The current-voltage characteristic obtained is in fair agreement with known experimental data. It indicates a minimum for arc current of about 80 A. For all current levels, a field reversal in front of the anode accompanied by a voltage drop of (0.7-2.6) V is observed. Another field reversal is observed near the cathode for arc currents below 80 A.

  13. Preparing "Chameleon Balls" from Natural Plants: Simple Handmade pH Indicator and Teaching Material for Chemical Equilibrium

    NASA Astrophysics Data System (ADS)

    Kanda, Naoki; Asano, Takayuki; Itoh, Toshiyuki; Onoda, Makoto

    1995-12-01

    Anthocyanins are found in the flowers and fruits of natural plants. Since their color depends on pH, they are sometines used as a pH indicator. Since these sequences are reversible, they are also useful in demonstrating chemical equilibrium in the repetitive color changes of anthocyanins from flowers by controlling pH conditions. We prepared the polysaccharide beads conatining water extracts of red cabbage as calcium alginate. The beads showed a clear red color under acidic conditions, turned blue at neutral pH of 7, and orange-yellow at pH of 13. This color change could be demonstrated over and over. Because the color changes of these polysaccharide beads depended darmatically on pH, junior high students in science classes called them "chameleon balls" when we demonstrated this reaction for them. In this paper we describe how polysaccharide beads, which are made from calcium alginate with natural pigments, served as a teaching tool for the chemical equilibrium of anthocyanins under different pH conditions. Preparation of the chameleon ball is very easy. The most important thing is that making the chameleon ball is great fun. The ball should therefore be viewed not only as a handmade pH indicator but also an interesting teaching tool of the chemical equilibrium reaction.

  14. Chemical Equilibrium of the Dissolved Uranium in Groundwaters From a Spanish Uranium-Ore Deposit

    SciTech Connect

    Garralon, Antonio; Gomez, Paloma; Turrero, Maria Jesus; Buil, Belen; Sanchez, Lorenzo

    2007-07-01

    The main objectives of this work are to determine the hydrogeochemical evolution of an uranium ore and identify the main water/rock interaction processes that control the dissolved uranium content. The Mina Fe uranium-ore deposit is the most important and biggest mine worked in Spain. Sageras area is located at the north part of the Mina Fe, over the same ore deposit. The uranium deposit was not mined in Sageras and was only perturbed by the exploration activities performed 20 years ago. The studied area is located 10 Km northeast of Ciudad Rodrigo (Salamanca) at an altitude over 650 m.a.s.l. The uranium mineralization is related to faults affecting the metasediments of the Upper Proterozoic to Lower Cambrian schist-graywacke complex (CEG), located in the Centro-Iberian Zone of the Hesperian Massif . The primary uranium minerals are uraninite and coffinite but numerous secondary uranium minerals have been formed as a result of the weathering processes: yellow gummite, autunite, meta-autunite, torbernite, saleeite, uranotile, ianthinite and uranopilite. The water flow at regional scale is controlled by the topography. Recharge takes place mainly in the surrounding mountains (Sierra Pena de Francia) and discharge at fluvial courses, mainly Agueda and Yeltes rivers, boundaries S-NW and NE of the area, respectively. Deep flows (lower than 100 m depth) should be upwards due to the river vicinity, with flow directions towards the W, NW or N. In Sageras-Mina Fe there are more than 100 boreholes drilled to investigate the mineral resources of the deposit. 35 boreholes were selected in order to analyze the chemical composition of groundwaters based on their depth and situation around the uranium ore. Groundwater samples come from 50 to 150 m depth. The waters are classified as calcium-bicarbonate type waters, with a redox potential that indicates they are slightly reduced (values vary between 50 to -350 mV). The TOC varies between <0.1 and 4.0 mgC/L and the dissolved

  15. Disequilibrium Textures vs Equilibrium Modelling: Geochronology at the Crossroads

    NASA Astrophysics Data System (ADS)

    Villa, I. M.

    2007-12-01

    Observations made by electron microscopy show the processes affecting minerals at the atomic scale. The majority of reported analyses demonstrate chemical disequilibrium. A classic example are overgrowths of one mineral generation by a secondary one, which may be recognized on textural grounds. Disequilibrium recrystallization is promoted by water, which is everywhere on this planet (granites, contact aureoles, regional metamorphism, faults). It is mostly easier and energetically less costly to recrystallize a mineral at any temperature than to induce genuine volume diffusion in it. However, these observations are only relevant to geochronologists if chemical disequilibria are also accompanied by isotopic disequilibria. If a mineral mixture gives a mixed isotope record, then the interpretation of ages does not come cheap. If, on the contrary, diffusive reequilibration of the isotopic record is faster than that of chemical heterogeneities, then the petrology and microchemistry of a mineral could be ignored and its apparent age termed a "cooling age". First principle arguments and experimental data of the last decade concordantly show that the diffusivity of radiogenic isotopes is never higher than that of major elements forming the mineral structure. And indeed, end- member ages of mineral mixtures can be unravelled if the petrogenesis is understood. This was first shown by CL images of zircon grains (Gebauer et al, Schweiz Min Pet Mitt 68 (1988) 485-490). Similar progress was reported on monazite (Williams et al, Ann Rev Earth Planet Sci 35 (2007) 137-175), amphibole (Belluso et al, Eur J Mineral 12 (2000) 45-62), K-feldspar (Nyfeler et al, Schweiz Min Pet Mitt 78 (1998) 11-21), biotite (Villa et al, Water Rock Interaction 10 (2001) 1589-92). The mechanism for resetting the isotope record in nature thus seems more dependent on the availability of water to enhance disequilibrium recrystallization than on reaching a preset temperature. Intercomparison of laboratory

  16. Particle orbits in two-dimensional equilibrium models for the magnetotail

    NASA Technical Reports Server (NTRS)

    Karimabadi, H.; Pritchett, P. L.; Coroniti, F. V.

    1990-01-01

    Assuming that there exist an equilibrium state for the magnetotail, particle orbits are investigated in two-dimensional kinetic equilibrium models for the magnetotail. Particle orbits in the equilibrium field are compared with those calculated earlier with one-dimensional models, where the main component of the magnetic field (Bx) was approximated as either a hyperbolic tangent or a linear function of z with the normal field (Bz) assumed to be a constant. It was found that the particle orbits calculated with the two types of models are significantly different, mainly due to the neglect of the variation of Bx with x in the one-dimensional fields.

  17. Equilibrium and kinetic models for colloid release under transient solution chemistry conditions.

    PubMed

    Bradford, Scott A; Torkzaban, Saeed; Leij, Feike; Simunek, Jiri

    2015-10-01

    We present continuum models to describe colloid release in the subsurface during transient physicochemical conditions. Our modeling approach relates the amount of colloid release to changes in the fraction of the solid surface area that contributes to retention. Equilibrium, kinetic, equilibrium and kinetic, and two-site kinetic models were developed to describe various rates of colloid release. These models were subsequently applied to experimental colloid release datasets to investigate the influence of variations in ionic strength (IS), pH, cation exchange, colloid size, and water velocity on release. Various combinations of equilibrium and/or kinetic release models were needed to describe the experimental data depending on the transient conditions and colloid type. Release of Escherichia coli D21g was promoted by a decrease in solution IS and an increase in pH, similar to expected trends for a reduction in the secondary minimum and nanoscale chemical heterogeneity. The retention and release of 20nm carboxyl modified latex nanoparticles (NPs) were demonstrated to be more sensitive to the presence of Ca(2+) than D21g. Specifically, retention of NPs was greater than D21g in the presence of 2mM CaCl2 solution, and release of NPs only occurred after exchange of Ca(2+) by Na(+) and then a reduction in the solution IS. These findings highlight the limitations of conventional interaction energy calculations to describe colloid retention and release, and point to the need to consider other interactions (e.g., Born, steric, and/or hydration forces) and/or nanoscale heterogeneity. Temporal changes in the water velocity did not have a large influence on the release of D21g for the examined conditions. This insensitivity was likely due to factors that reduce the applied hydrodynamic torque and/or increase the resisting adhesive torque; e.g., macroscopic roughness and grain-grain contacts. Our analysis and models improve our understanding and ability to describe the amounts

  18. Characterization of the conformational equilibrium between the two major substates of RNase A using NMR chemical shifts.

    PubMed

    Camilloni, Carlo; Robustelli, Paul; De Simone, Alfonso; Cavalli, Andrea; Vendruscolo, Michele

    2012-03-07

    Following the recognition that NMR chemical shifts can be used for protein structure determination, rapid advances have recently been made in methods for extending this strategy for proteins and protein complexes of increasing size and complexity. A remaining major challenge is to develop approaches to exploit the information contained in the chemical shifts about conformational fluctuations in native states of proteins. In this work we show that it is possible to determine an ensemble of conformations representing the free energy surface of RNase A using chemical shifts as replica-averaged restraints in molecular dynamics simulations. Analysis of this surface indicates that chemical shifts can be used to characterize the conformational equilibrium between the two major substates of this protein.

  19. Passive samplers of hydrophobic organic chemicals reach equilibrium faster in the laboratory than in the field.

    PubMed

    Booij, Kees; Tucca, Felipe

    2015-09-15

    The use of passive sampling methods for monitoring hydrophobic organic chemicals frequently requires the determination of equilibration times and partition coefficients in the laboratory. These experiments are often carried out by exposing passive samplers in a finite water volume, and errors are easily made when the obtained results are applied to the field, where water volumes are essentially infinite. The effect of water volume on the equilibration rate constant is discussed, using a mechanistic model. Application of this model to two literature reports illustrates that aqueous concentrations in the field may be underestimated by a factor of 10 or more, when the water volume effect is neglected. Finally, it is shown that the concept of "sorption capacity" (sampler mass times partition coefficient) allows for a more intuitive understanding of the passive sampling process in small and large water volumes, which may reduce the risk of laboratory-field extrapolation errors. Copyright © 2015 Elsevier Ltd. All rights reserved.

  20. Equilibrium points, stability and numerical solutions of fractional-order predator-prey and rabies models

    NASA Astrophysics Data System (ADS)

    Ahmed, E.; El-Sayed, A. M. A.; El-Saka, H. A. A.

    2007-01-01

    In this paper we are concerned with the fractional-order predator-prey model and the fractional-order rabies model. Existence and uniqueness of solutions are proved. The stability of equilibrium points are studied. Numerical solutions of these models are given. An example is given where the equilibrium point is a centre for the integer order system but locally asymptotically stable for its fractional-order counterpart.

  1. Computer model of one-dimensional equilibrium controlled sorption processes

    USGS Publications Warehouse

    Grove, D.B.; Stollenwerk, K.G.

    1984-01-01

    A numerical solution to the one-dimensional solute-transport equation with equilibrium-controlled sorption and a first-order irreversible-rate reaction is presented. The computer code is written in FORTRAN language, with a variety of options for input and output for user ease. Sorption reactions include Langmuir, Freundlich, and ion-exchange, with or without equal valance. General equations describing transport and reaction processes are solved by finite-difference methods, with nonlinearities accounted for by iteration. Complete documentation of the code, with examples, is included. (USGS)

  2. A dynamic physicochemical model for chemical phosphorus removal.

    PubMed

    Hauduc, H; Takács, I; Smith, S; Szabo, A; Murthy, S; Daigger, G T; Spérandio, M

    2015-04-15

    A dynamic physico-chemical model for chemical phosphorus removal in wastewater is presented as a tool to optimize chemical dosing simultaneously while ensuring compliant effluent phosphorus concentration. This new model predicts the kinetic and stoichiometric variable processes of precipitation of hydrous ferric oxides (HFO), phosphates adsorption and co-precipitation. It is combined with chemical equilibrium and physical precipitation reactions in order to model observed bulk dynamics in terms of pH. The model is calibrated and validated based on previous studies and experimental data from Smith et al. (2008) and Szabo et al. (2008) as a first step for full-plant implementation. The simulation results show that the structure of the model describes adequately the mechanisms of adsorption and co-precipitation of phosphate species onto HFO and that the model is robust under various experimental conditions.

  3. Stability of equilibrium points in intraguild predation model with disease with SI model

    NASA Astrophysics Data System (ADS)

    Hassan, Aimi Nuraida binti Ali; Bujang, Noriham binti; Mahdi, Ahmad Faisal Bin

    2017-04-01

    Intraguild Predation (IGP) is classified as killing and eating among potential competitors. Intraguild Predation is a universal interaction, differing from competition or predation. Lotka Volterra competition model and Intraguild predation model has been analyze. The assumption for this model is no any immigration or migration involves. This paper is only considered IGP model for susceptible and infective (SI) only. The analysis of stability of the equilibrium points of Intraguild Predation Models with disease using Routh Hurwitz criteria will be illustrated using some numerical example.

  4. Chemical Process Modeling and Control.

    ERIC Educational Resources Information Center

    Bartusiak, R. Donald; Price, Randel M.

    1987-01-01

    Describes some of the features of Lehigh University's (Pennsylvania) process modeling and control program. Highlights the creation and operation of the Chemical Process Modeling and Control Center (PMC). Outlines the program's philosophy, faculty, technical program, current research projects, and facilities. (TW)

  5. Vertical sorting and the morphodynamics of bed-form-dominated rivers: An equilibrium sorting model

    NASA Astrophysics Data System (ADS)

    Blom, Astrid; Parker, Gary; Ribberink, Jan S.; de Vriend, Huib J.

    2006-02-01

    A modeling framework is developed for taking into account the effects of sediment sorting in the morphodynamic modeling of bed-form-dominated rivers for the case of equilibrium or stationary conditions dominated by bed load transport. To this end, the Blom and Parker (2004) framework for sediment continuity is reduced to an equilibrium sorting model. The predicted equilibrium sorting profile is mainly determined by the probability density function (PDF) of bed form trough elevations and by a lee sorting function. The PDF of trough elevations needs to be known from either model predictions or measurements. A simple formulation for the lee sorting function is suggested, yet data on the avalanche mechanism down lee faces of dunes is required so as to improve the function and make it generic. The equilibrium sorting model is calibrated and verified using data from flume experiments. The agreement between the predicted and measured equilibrium sorting profiles is reasonable, although the model does not reproduce an observed coarse top layer. In a hydraulic-morphodynamic model this equilibrium sorting model may be applied instantaneously if the timescale of large-scale morphological changes is much larger than the ones of changes in vertical sorting and dune dimensions.

  6. HYDROBIOGEOCHEM: A coupled model of HYDROlogic transport and mixed BIOGEOCHEMical kinetic/equilibrium reactions in saturated-unsaturated media

    SciTech Connect

    Yeh, G.T.; Salvage, K.M.; Gwo, J.P.; Zachara, J.M.; Szecsody, J.E.

    1998-07-01

    The computer program HYDROBIOGEOCHEM is a coupled model of HYDROlogic transport and BIOGEOCHEMical kinetic and/or equilibrium reactions in saturated/unsaturated media. HYDROBIOGEOCHEM iteratively solves the two-dimensional transport equations and the ordinary differential and algebraic equations of mixed biogeochemical reactions. The transport equations are solved for all aqueous chemical components and kinetically controlled aqueous species. HYDROBIOGEOCHEM is designed for generic application to reactive transport problems affected by both microbiological and geochemical reactions in subsurface media. Input to the program includes the geometry of the system, the spatial distribution of finite elements and nodes, the properties of the media, the potential chemical and microbial reactions, and the initial and boundary conditions. Output includes the spatial distribution of chemical and microbial concentrations as a function of time and space, and the chemical speciation at user-specified nodes.

  7. TICKET-UWM: a coupled kinetic, equilibrium, and transport screening model for metals in lakes.

    PubMed

    Farley, Kevin J; Carbonaro, Richard F; Fanelli, Christopher J; Costanzo, Robert; Rader, Kevin J; Di Toro, Dominic M

    2011-06-01

    The tableau input coupled kinetic equilibrium transport-unit world model (TICKET-UWM) has been developed as a screening model for assessing potential environmental risks associated with the release of metals into lakes. The model is based on a fully implicit, one-step solution algorithm that allows for simultaneous consideration of dissolved and particulate phase transport; metal complexation to organic matter and inorganic ligands; precipitation of metal hydroxides, carbonates, and sulfides; competitive interactions of metals and major cations with biotic ligands; a simplified description of biogeochemical cycling of organic carbon and sulfur; and dissolution kinetics for metal powders, massives, and other solid forms. Application of TICKET-UWM to a generalized lake in the Sudbury area of the Canadian Shield is presented to demonstrate the overall cycling of metals in lakes and the nonlinear effects of chemical speciation on metal responses. In addition, the model is used to calculate critical loads for metals, with acute toxicity of Daphnia magna as the final endpoint. Model results show that the critical loads for Cu, Ni, Pb, and Zn varied from 2.5 to 39.0 g metal/m(2) -year and were found to be one or more orders of magnitude higher than comparable loads for pesticides (lindane, 4,4'-DDT) and several polyaromatic hydrocarbon (PAH) compounds. In sensitivity calculations, critical metal-loading rates were found to vary significantly as a function of the hydraulic detention time, water hardness, and metal dissolution kinetic rates.

  8. The Separatory Cylinder: A Novel Solvent Extraction System for the Study of Chemical Equilibrium in Solution.

    ERIC Educational Resources Information Center

    Cwikel, Dori; And Others

    1986-01-01

    Dicusses the use of the separatory cylinder in student laboratory experiments for investigating equilibrium distribution of a solute between immiscible phases. Describes the procedures for four sets of experiments of this nature. Lists of materials needed and quantities of reagents are provided. (TW)

  9. The Fizz Keeper, a Case Study in Chemical Education, Equilibrium, and Kinetics.

    ERIC Educational Resources Information Center

    Howald, Reed A.

    1999-01-01

    The loss of carbon dioxide from carbonated beverages provides an interesting case of the combination of equilibrium and kinetic principles. Adding air with a commercial device (the Fizz Keeper) has a negligible effect on various equilibria present but will slow diffusion in the gas space of a resealed bottle, decreasing the rate at which…

  10. Does the Addition of Inert Gases at Constant Volume and Temperature Affect Chemical Equilibrium?

    ERIC Educational Resources Information Center

    Paiva, Joao C. M.; Goncalves, Jorge; Fonseca, Susana

    2008-01-01

    In this article we examine three approaches, leading to different conclusions, for answering the question "Does the addition of inert gases at constant volume and temperature modify the state of equilibrium?" In the first approach, the answer is yes as a result of a common students' alternative conception; the second approach, valid only for ideal…

  11. Does the Addition of Inert Gases at Constant Volume and Temperature Affect Chemical Equilibrium?

    ERIC Educational Resources Information Center

    Paiva, Joao C. M.; Goncalves, Jorge; Fonseca, Susana

    2008-01-01

    In this article we examine three approaches, leading to different conclusions, for answering the question "Does the addition of inert gases at constant volume and temperature modify the state of equilibrium?" In the first approach, the answer is yes as a result of a common students' alternative conception; the second approach, valid only for ideal…

  12. The Fizz Keeper, a Case Study in Chemical Education, Equilibrium, and Kinetics.

    ERIC Educational Resources Information Center

    Howald, Reed A.

    1999-01-01

    The loss of carbon dioxide from carbonated beverages provides an interesting case of the combination of equilibrium and kinetic principles. Adding air with a commercial device (the Fizz Keeper) has a negligible effect on various equilibria present but will slow diffusion in the gas space of a resealed bottle, decreasing the rate at which…

  13. Equilibrium chemical reaction of supersonic hydrogen-air jets (the ALMA computer program)

    NASA Technical Reports Server (NTRS)

    Elghobashi, S.

    1977-01-01

    The ALMA (axi-symmetrical lateral momentum analyzer) program is concerned with the computation of two dimensional coaxial jets with large lateral pressure gradients. The jets may be free or confined, laminar or turbulent, reacting or non-reacting. Reaction chemistry is equilibrium.

  14. Vapor-liquid equilibrium thermodynamics of N2 + CH4 - Model and Titan applications

    NASA Technical Reports Server (NTRS)

    Thompson, W. R.; Zollweg, John A.; Gabis, David H.

    1992-01-01

    A thermodynamic model is presented for vapor-liquid equilibrium in the N2 + CH4 system, which is implicated in calculations of the Titan tropospheric clouds' vapor-liquid equilibrium thermodynamics. This model imposes constraints on the consistency of experimental equilibrium data, and embodies temperature effects by encompassing enthalpy data; it readily calculates the saturation criteria, condensate composition, and latent heat for a given pressure-temperature profile of the Titan atmosphere. The N2 content of condensate is about half of that computed from Raoult's law, and about 30 percent greater than that computed from Henry's law.

  15. Vapor-liquid equilibrium thermodynamics of N2 + CH4 - Model and Titan applications

    NASA Technical Reports Server (NTRS)

    Thompson, W. R.; Zollweg, John A.; Gabis, David H.

    1992-01-01

    A thermodynamic model is presented for vapor-liquid equilibrium in the N2 + CH4 system, which is implicated in calculations of the Titan tropospheric clouds' vapor-liquid equilibrium thermodynamics. This model imposes constraints on the consistency of experimental equilibrium data, and embodies temperature effects by encompassing enthalpy data; it readily calculates the saturation criteria, condensate composition, and latent heat for a given pressure-temperature profile of the Titan atmosphere. The N2 content of condensate is about half of that computed from Raoult's law, and about 30 percent greater than that computed from Henry's law.

  16. Vapor-liquid equilibrium thermodynamics of N2 + CH4 - Model and Titan applications

    NASA Astrophysics Data System (ADS)

    Thompson, W. R.; Zollweg, John A.; Gabis, David H.

    1992-06-01

    A thermodynamic model is presented for vapor-liquid equilibrium in the N2 + CH4 system, which is implicated in calculations of the Titan tropospheric clouds' vapor-liquid equilibrium thermodynamics. This model imposes constraints on the consistency of experimental equilibrium data, and embodies temperature effects by encompassing enthalpy data; it readily calculates the saturation criteria, condensate composition, and latent heat for a given pressure-temperature profile of the Titan atmosphere. The N2 content of condensate is about half of that computed from Raoult's law, and about 30 percent greater than that computed from Henry's law.

  17. The cosmic dust analyzer: Experimental evaluation of an impact ionization model. [considering thermal equilibrium plasma

    NASA Technical Reports Server (NTRS)

    Friichtenicht, J. F.; Roy, N. L.; Becker, D. G.

    1973-01-01

    A thermal equilibrium plasma model is used to process data from an impact ionization time-of-flight mass spectrometer in order to convert the raw ion data to relative abundances of the elemental constituents of cosmic dust particles.

  18. Experimental testing of olivine-melt equilibrium models at high temperatures

    NASA Astrophysics Data System (ADS)

    Krasheninnikov, S. P.; Sobolev, A. V.; Batanova, V. G.; Kargaltsev, A. A.; Borisov, A. A.

    2017-08-01

    Data are presented on the equilibrium compositions of olivine and melts in the products of 101 experiments performed at 1300-1600°C, atmospheric pressure, and controlled oxygen fugacity by means of new equipment at the Vernadsky Institute. It was shown that the available models of the olivine-melt equilibrium describe with insufficient adequacy the natural systems at temperatures over 1400°C. The most adequate is the model by Ford et al. (1983). However, this model overestimates systematically the equilibrium temperature with underestimating by 20-40°C at 1450-1600°C. These data point to the need for developing a new, improved quantitative model of the olivine-melt equilibrium for high-temperature magnesian melts, as well as to the possibility of these studies on the basis of the equipment presented.

  19. Quantum chemical calculation of the equilibrium structures of small metal atom clusters

    NASA Technical Reports Server (NTRS)

    Kahn, L. R.

    1981-01-01

    A decomposition of the molecular energy is presented that is motivated by the atom superposition and electron delocalization physical model of chemical binding. The energy appears in physically transparent form consisting of a classical electrostatic interaction, a zero order two electron exchange interaction, a relaxation energy, and the atomic energies. Detailed formulae are derived in zero and first order of approximation. The formulation extends beyond first order to any chosen level of approximation leading, in principle, to the exact energy. The structure of this energy decomposition lends itself to the fullest utilization of the solutions to the atomic sub problems to simplify the calculation of the molecular energy. If nonlinear relaxation effects remain minor, the molecular energy calculation requires at most the calculation of two center, two electron integrals. This scheme thus affords the prospects of substantially reducing the computational effort required for the calculation of molecular energies.

  20. NNEPEQ: Chemical equilibrium version of the Navy/NASA Engine Program

    NASA Technical Reports Server (NTRS)

    Fishbach, Laurence H.; Gordon, Sanford

    1988-01-01

    The Navy NASA Engine Program, NNEP, currently is in use at a large number of government agencies, commercial companies and universities. This computer code has bee used extensively to calculate the design and off-design (matched) performance of a broad range of turbine engines, ranging from subsonic turboprops to variable cycle engines for supersonic transports. Recently, there has been increased interest in applications for which NNEP was not capable of simulating, namely, high Mach applications, alternate fuels including cryogenics, and cycles such as the gas generator air-turbo-rocker (ATR). In addition, there is interest in cycles employing ejectors such as for military fighters. New engine component models had to be created for incorporation into NNEP, and it was found necessary to include chemical dissociation effects of high temperature gases. The incorporation of these extended capabilities into NNEP is discussed and some of the effects of these changes are illustrated.

  1. NNEPEQ - Chemical equilibrium version of the Navy/NASA Engine Program

    NASA Technical Reports Server (NTRS)

    Fishbach, L. H.; Gordon, S.

    1989-01-01

    The Navy NASA Engine Program, NNEP, currently is in use at a large number of government agencies, commercial companies and universities. This computer code has been used extensively to calculate the design and off-design (matched) performance of a broad range of turbine engines, ranging from subsonic turboprops to variable cycle engines for supersonic transports. Recently, there has been increased interest in applications for which NNEP was not capable of simulating, namely, high Mach applications, alternate fuels including cryogenics, and cycles such as the gas generator air-turbo-rocker (ATR). In addition, there is interest in cycles employing ejectors such as for military fighters. New engine component models had to be created for incorporation into NNEP, and it was found necessary to include chemical dissociation effects of high temperature gases. The incorporation of these extended capabilities into NNEP is discussed and some of the effects of these changes are illustrated.

  2. Revised lattice Boltzmann model for traffic flow with equilibrium traffic pressure

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Lu, Wei-Zhen; Xue, Yu; He, Hong-Di

    2016-02-01

    A revised lattice Boltzmann model concerning the equilibrium traffic pressure is proposed in this study to tackle the phase transition phenomena of traffic flow system. The traditional lattice Boltzmann model has limitation to investigate the complex traffic phase transitions due to its difficulty for modeling the equilibrium velocity distribution. Concerning this drawback, the equilibrium traffic pressure is taken into account to derive the equilibrium velocity distribution in the revised lattice Boltzmann model. In the proposed model, a three-dimensional velocity-space is assumed to determine the equilibrium velocity distribution functions and an alternative, new derivative approach is introduced to deduct the macroscopic equations with the first-order accuracy level from the lattice Boltzmann model. Based on the linear stability theory, the stability conditions of the corresponding macroscopic equations can be obtained. The outputs indicate that the stability curve is divided into three regions, i.e., the stable region, the neutral stability region, and the unstable region. In the stable region, small disturbance appears in the initial uniform flow and will vanish after long term evolution, while in the unstable region, the disturbance will be enlarged and finally leads to the traffic system entering the congested state. In the neutral stability region, small disturbance does not vanish with time and maintains its amplitude in the traffic system. Conclusively, the stability of traffic system is found to be enhanced as the equilibrium traffic pressure increases. Finally, the numerical outputs of the proposed model are found to be consistent with the recognized, theoretical results.

  3. Equilibrium models of mass distribution and collisional lifetimes of asteroids

    NASA Technical Reports Server (NTRS)

    Williams, David R.; Wetherill, George

    1993-01-01

    An understanding of the steady state distribution expected in the present day asteroid belt is important to our understanding of the collisional evolution of the asteroids and their physical properties. We have extended earlier work to show that, in the absence of gravity, a simple power law distribution as a function of mass with constant exponent will give an equilibrium distribution of asteroids for all bodies much smaller than the largest asteroids. This result holds for realistic fragmentation mechanisms and is independent of the physical properties of the asteroids. Inclusion of the effects of gravity on disruption and fragmentation of asteroids precludes an analytic solution to this problem, and rules out a simple power law distribution. We are currently calculating numerical solutions in order to determine the expected steady state mass distribution in the asteroid belt.

  4. Models of supply function equilibrium with applications to the electricity industry

    NASA Astrophysics Data System (ADS)

    Aromi, J. Daniel

    Electricity market design requires tools that result in a better understanding of incentives of generators and consumers. Chapter 1 and 2 provide tools and applications of these tools to analyze incentive problems in electricity markets. In chapter 1, models of supply function equilibrium (SFE) with asymmetric bidders are studied. I prove the existence and uniqueness of equilibrium in an asymmetric SFE model. In addition, I propose a simple algorithm to calculate numerically the unique equilibrium. As an application, a model of investment decisions is considered that uses the asymmetric SFE as an input. In this model, firms can invest in different technologies, each characterized by distinct variable and fixed costs. In chapter 2, option contracts are introduced to a supply function equilibrium (SFE) model. The uniqueness of the equilibrium in the spot market is established. Comparative statics results on the effect of option contracts on the equilibrium price are presented. A multi-stage game where option contracts are traded before the spot market stage is considered. When contracts are optimally procured by a central authority, the selected profile of option contracts is such that the spot market price equals marginal cost for any load level resulting in a significant reduction in cost. If load serving entities (LSEs) are price takers, in equilibrium, there is no trade of option contracts. Even when LSEs have market power, the central authority's solution cannot be implemented in equilibrium. In chapter 3, we consider a game in which a buyer must repeatedly procure an input from a set of firms. In our model, the buyer is able to sign long term contracts that establish the likelihood with which the next period contract is awarded to an entrant or the incumbent. We find that the buyer finds it optimal to favor the incumbent, this generates more intense competition between suppliers. In a two period model we are able to completely characterize the optimal mechanism.

  5. An Initial Non-Equilibrium Porous-Media Model for CFD Simulation of Stirling Regenerators

    NASA Technical Reports Server (NTRS)

    Tew, Roy C.; Simon, Terry; Gedeon, David; Ibrahim, Mounir; Rong, Wei

    2006-01-01

    The objective of this paper is to define empirical parameters for an initial thermal non-equilibrium porous-media model for use in Computational Fluid Dynamics (CFD) codes for simulation of Stirling regenerators. The two codes currently used at Glenn Research Center for Stirling modeling are Fluent and CFD-ACE. The codes porous-media models are equilibrium models, which assume solid matrix and fluid are in thermal equilibrium. This is believed to be a poor assumption for Stirling regenerators; Stirling 1-D regenerator models, used in Stirling design, use non-equilibrium regenerator models and suggest regenerator matrix and gas average temperatures can differ by several degrees at a given axial location and time during the cycle. Experimentally based information was used to define: hydrodynamic dispersion, permeability, inertial coefficient, fluid effective thermal conductivity, and fluid-solid heat transfer coefficient. Solid effective thermal conductivity was also estimated. Determination of model parameters was based on planned use in a CFD model of Infinia's Stirling Technology Demonstration Converter (TDC), which uses a random-fiber regenerator matrix. Emphasis is on use of available data to define empirical parameters needed in a thermal non-equilibrium porous media model for Stirling regenerator simulation. Such a model has not yet been implemented by the authors or their associates.

  6. The intrinsic role of nanoconfinement in chemical equilibrium: evidence from DNA hybridization.

    PubMed

    Rubinovich, Leonid; Polak, Micha

    2013-05-08

    Recently we predicted that when a reaction involving a small number of molecules occurs in a nanometric-scale domain entirely segregated from the surrounding media, the nanoconfinement can shift the position of equilibrium toward products via reactant-product reduced mixing. In this Letter, we demonstrate how most-recently reported single-molecule fluorescence measurements of partial hybridization of ssDNA confined within nanofabricated chambers provide the first experimental confirmation of this entropic nanoconfinement effect. Thus, focusing separately on each occupancy-specific equilibrium constant, quantitatively reveals extra stabilization of the product upon decreasing the chamber occupancy or size. Namely, the DNA hybridization under nanoconfined conditions is significantly favored over the identical reaction occurring in bulk media with the same reactant concentrations. This effect, now directly verified for DNA, can be relevant to actual biological processes, as well as to diverse reactions occurring within molecular capsules, nanotubes, and other functional nanospaces.

  7. The Fizz Keeper, a Case Study in Chemical Education, Equilibrium, and Kinetics

    NASA Astrophysics Data System (ADS)

    Howald, Reed

    1999-02-01

    The chemistry of the loss of carbonation from carbonated beverages on storage was considered. Increasing the pressure of CO2(g) will restore carbonation, but an increase in pressure adding air should not affect the equilibria. It can and does, however, affect the kinetics-the rate at which a new equilibrium is established. Thus the Fizz Keeper is effective for storage of resealed pop containers for hours, but not for periods of weeks or months.

  8. Addition to the Lewis Chemical Equilibrium Program to allow computation from coal composition data

    NASA Technical Reports Server (NTRS)

    Sevigny, R.

    1980-01-01

    Changes made to the Coal Gasification Project are reported. The program was developed by equilibrium combustion in rocket engines. It can be applied directly to the entrained flow coal gasification process. The particular problem addressed is the reduction of the coal data into a form suitable to the program, since the manual process is involved and error prone. A similar problem in relating the normal output of the program to parameters meaningful to the coal gasification process is also addressed.

  9. Out-of-equilibrium relaxation of the thermal Casimir effect in a model polarizable material.

    PubMed

    Dean, David S; Démery, Vincent; Parsegian, V Adrian; Podgornik, Rudolf

    2012-03-01

    Relaxation of the thermal Casimir or van der Waals force (the high temperature limit of the Casimir force) for a model dielectric medium is investigated. We start with a model of interacting polarization fields with a dynamics that leads to a frequency dependent dielectric constant of the Debye form. In the static limit, the usual zero frequency Matsubara mode component of the Casimir force is recovered. We then consider the out-of-equilibrium relaxation of the van der Waals force to its equilibrium value when two initially uncorrelated dielectric bodies are brought into sudden proximity. For the interaction between dielectric slabs, it is found that the spatial dependence of the out-of-equilibrium force is the same as the equilibrium one, but it has a time dependent amplitude, or Hamaker coefficient, which increases in time to its equilibrium value. The final relaxation of the force to its equilibrium value is exponential in systems with a single or finite number of polarization field relaxation times. However, in systems, such as those described by the Havriliak-Negami dielectric constant with a broad distribution of relaxation times, we observe a much slower power law decay to the equilibrium value.

  10. A two-phase restricted equilibrium model for combustion of metalized solid propellants

    NASA Technical Reports Server (NTRS)

    Sabnis, J. S.; Dejong, F. J.; Gibeling, H. J.

    1992-01-01

    An Eulerian-Lagrangian two-phase approach was adopted to model the multi-phase reacting internal flow in a solid rocket with a metalized propellant. An Eulerian description was used to analyze the motion of the continuous phase which includes the gas as well as the small (micron-sized) particulates, while a Lagrangian description is used for the analysis of the discrete phase which consists of the larger particulates in the motor chamber. The particulates consist of Al and Al2O3 such that the particulate composition is 100 percent Al at injection from the propellant surface with Al2O3 fraction increasing due to combustion along the particle trajectory. An empirical model is used to compute the combustion rate for agglomerates while the continuous phase chemistry is treated using chemical equilibrium. The computer code was used to simulate the reacting flow in a solid rocket motor with an AP/HTPB/Al propellant. The computed results show the existence of an extended combustion zone in the chamber rather than a thin reaction region. The presence of the extended combustion zone results in the chamber flow field and chemical being far from isothermal (as would be predicted by a surface combustion assumption). The temperature in the chamber increases from about 2600 K at the propellant surface to about 3350 K in the core. Similarly the chemical composition and the density of the propellant gas also show spatially non-uniform distribution in the chamber. The analysis developed under the present effort provides a more sophisticated tool for solid rocket internal flow predictions than is presently available, and can be useful in studying apparent anomalies and improving the simple correlations currently in use. The code can be used in the analysis of combustion efficiency, thermal load in the internal insulation, plume radiation, etc.

  11. A two-phase restricted equilibrium model for combustion of metalized solid propellants

    NASA Technical Reports Server (NTRS)

    Sabnis, J. S.; Dejong, F. J.; Gibeling, H. J.

    1992-01-01

    An Eulerian-Lagrangian two-phase approach was adopted to model the multi-phase reacting internal flow in a solid rocket with a metalized propellant. An Eulerian description was used to analyze the motion of the continuous phase which includes the gas as well as the small (micron-sized) particulates, while a Lagrangian description is used for the analysis of the discrete phase which consists of the larger particulates in the motor chamber. The particulates consist of Al and Al2O3 such that the particulate composition is 100 percent Al at injection from the propellant surface with Al2O3 fraction increasing due to combustion along the particle trajectory. An empirical model is used to compute the combustion rate for agglomerates while the continuous phase chemistry is treated using chemical equilibrium. The computer code was used to simulate the reacting flow in a solid rocket motor with an AP/HTPB/Al propellant. The computed results show the existence of an extended combustion zone in the chamber rather than a thin reaction region. The presence of the extended combustion zone results in the chamber flow field and chemical being far from isothermal (as would be predicted by a surface combustion assumption). The temperature in the chamber increases from about 2600 K at the propellant surface to about 3350 K in the core. Similarly the chemical composition and the density of the propellant gas also show spatially non-uniform distribution in the chamber. The analysis developed under the present effort provides a more sophisticated tool for solid rocket internal flow predictions than is presently available, and can be useful in studying apparent anomalies and improving the simple correlations currently in use. The code can be used in the analysis of combustion efficiency, thermal load in the internal insulation, plume radiation, etc.

  12. Modeling Mathematical Programs with Equilibrium Constraints in Pyomo

    SciTech Connect

    Hart, William E.; Siirola, John Daniel

    2015-07-01

    We describe new capabilities for modeling MPEC problems within the Pyomo modeling software. These capabilities include new modeling components that represent complementar- ity conditions, modeling transformations for re-expressing models with complementarity con- ditions in other forms, and meta-solvers that apply transformations and numeric optimization solvers to optimize MPEC problems. We illustrate the breadth of Pyomo's modeling capabil- ities for MPEC problems, and we describe how Pyomo's meta-solvers can perform local and global optimization of MPEC problems.

  13. Modeling Complex Chemical Systems: Problems and Solutions

    NASA Astrophysics Data System (ADS)

    van Dijk, Jan

    2016-09-01

    Non-equilibrium plasmas in complex gas mixtures are at the heart of numerous contemporary technologies. They typically contain dozens to hundreds of species, involved in hundreds to thousands of reactions. Chemists and physicists have always been interested in what are now called chemical reduction techniques (CRT's). The idea of such CRT's is that they reduce the number of species that need to be considered explicitly without compromising the validity of the model. This is usually achieved on the basis of an analysis of the reaction time scales of the system under study, which identifies species that are in partial equilibrium after a given time span. The first such CRT that has been widely used in plasma physics was developed in the 1960's and resulted in the concept of effective ionization and recombination rates. It was later generalized to systems in which multiple levels are effected by transport. In recent years there has been a renewed interest in tools for chemical reduction and reaction pathway analysis. An example of the latter is the PumpKin tool. Another trend is that techniques that have previously been developed in other fields of science are adapted as to be able to handle the plasma state of matter. Examples are the Intrinsic Low Dimension Manifold (ILDM) method and its derivatives, which originate from combustion engineering, and the general-purpose Principle Component Analysis (PCA) technique. In this contribution we will provide an overview of the most common reduction techniques, then critically assess the pros and cons of the methods that have gained most popularity in recent years. Examples will be provided for plasmas in argon and carbon dioxide.

  14. Equilibrium and nonequilibrium attractors for a discrete, selection-migration model

    Treesearch

    James F. Selgrade; James H. Roberds

    2003-01-01

    This study presents a discrete-time model for the effects of selection and immigration on the demographic and genetic compositions of a population. Under biologically reasonable conditions, it is shown that the model always has an equilibrium. Although equilibria for similar models without migration must have real eigenvalues, for this selection-migration model we...

  15. A facilitated diffusion model constrained by the probability isotherm: a pedagogical exercise in intuitive non-equilibrium thermodynamics.

    PubMed

    Chapman, Brian

    2017-06-01

    This paper seeks to develop a more thermodynamically sound pedagogy for students of biological transport than is currently available from either of the competing schools of linear non-equilibrium thermodynamics (LNET) or Michaelis-Menten kinetics (MMK). To this end, a minimal model of facilitated diffusion was constructed comprising four reversible steps: cis-substrate binding, cis→trans bound enzyme shuttling, trans-substrate dissociation and trans→cis free enzyme shuttling. All model parameters were subject to the second law constraint of the probability isotherm, which determined the unidirectional and net rates for each step and for the overall reaction through the law of mass action. Rapid equilibration scenarios require sensitive 'tuning' of the thermodynamic binding parameters to the equilibrium substrate concentration. All non-equilibrium scenarios show sigmoidal force-flux relations, with only a minority of cases having their quasi-linear portions close to equilibrium. Few cases fulfil the expectations of MMK relating reaction rates to enzyme saturation. This new approach illuminates and extends the concept of rate-limiting steps by focusing on the free energy dissipation associated with each reaction step and thereby deducing its respective relative chemical impedance. The crucial importance of an enzyme's being thermodynamically 'tuned' to its particular task, dependent on the cis- and trans-substrate concentrations with which it deals, is consistent with the occurrence of numerous isoforms for enzymes that transport a given substrate in physiologically different circumstances. This approach to kinetic modelling, being aligned with neither MMK nor LNET, is best described as intuitive non-equilibrium thermodynamics, and is recommended as a useful adjunct to the design and interpretation of experiments in biotransport.

  16. A facilitated diffusion model constrained by the probability isotherm: a pedagogical exercise in intuitive non-equilibrium thermodynamics

    PubMed Central

    2017-01-01

    This paper seeks to develop a more thermodynamically sound pedagogy for students of biological transport than is currently available from either of the competing schools of linear non-equilibrium thermodynamics (LNET) or Michaelis–Menten kinetics (MMK). To this end, a minimal model of facilitated diffusion was constructed comprising four reversible steps: cis-substrate binding, cis→trans bound enzyme shuttling, trans-substrate dissociation and trans→cis free enzyme shuttling. All model parameters were subject to the second law constraint of the probability isotherm, which determined the unidirectional and net rates for each step and for the overall reaction through the law of mass action. Rapid equilibration scenarios require sensitive ‘tuning’ of the thermodynamic binding parameters to the equilibrium substrate concentration. All non-equilibrium scenarios show sigmoidal force–flux relations, with only a minority of cases having their quasi-linear portions close to equilibrium. Few cases fulfil the expectations of MMK relating reaction rates to enzyme saturation. This new approach illuminates and extends the concept of rate-limiting steps by focusing on the free energy dissipation associated with each reaction step and thereby deducing its respective relative chemical impedance. The crucial importance of an enzyme's being thermodynamically ‘tuned’ to its particular task, dependent on the cis- and trans-substrate concentrations with which it deals, is consistent with the occurrence of numerous isoforms for enzymes that transport a given substrate in physiologically different circumstances. This approach to kinetic modelling, being aligned with neither MMK nor LNET, is best described as intuitive non-equilibrium thermodynamics, and is recommended as a useful adjunct to the design and interpretation of experiments in biotransport. PMID:28680687

  17. Global stability of endemic equilibrium of an epidemic model with birth and death on complex networks

    NASA Astrophysics Data System (ADS)

    Wei, Xiaodan; Xu, Gaochao; Liu, Lijun; Zhou, Wenshu

    2017-07-01

    We study global stability of endemic equilibrium of an epidemic model with birth and death on complex networks. Under some conditions, the local asymptotic stability of the endemic equilibrium was established by Zhang and Jin (2011) for correlated networks, and the global asymptotic stability was obtained by Chen and Sun (2014) for uncorrelated networks. In this work, we remove those conditions, and prove by constructing a Lyapunov function that the endemic equilibrium is globally asymptotically stable. Numerical simulations are also presented to illustrate the feasibility of the result.

  18. Parametrizing coarse grained models for molecular systems at equilibrium

    NASA Astrophysics Data System (ADS)

    Kalligiannaki, E.; Chazirakis, A.; Tsourtis, A.; Katsoulakis, M. A.; Plecháč, P.; Harmandaris, V.

    2016-10-01

    Hierarchical coarse graining of atomistic molecular systems at equilibrium has been an intensive research topic over the last few decades. In this work we (a) review theoretical and numerical aspects of different parametrization methods (structural-based, force matching and relative entropy) to derive the effective interaction potential between coarse-grained particles. All methods approximate the many body potential of mean force; resulting, however, in different optimization problems. (b) We also use a reformulation of the force matching method by introducing a generalized force matching condition for the local mean force in the sense that allows the approximation of the potential of mean force under both linear and non-linear coarse graining mappings (E. Kalligiannaki, et al., J. Chem. Phys. 2015). We apply and compare these methods to: (a) a benchmark system of two isolated methane molecules; (b) methane liquid; (c) water; and (d) an alkane fluid. Differences between the effective interactions, derived from the various methods, are found that depend on the actual system under study. The results further reveal the relation of the various methods and the sensitivities that may arise in the implementation of numerical methods used in each case.

  19. Combustion of hydrogen-air jets in local chemical equilibrium: A guide to the CHARNAL computer program

    NASA Technical Reports Server (NTRS)

    Spalding, D. B.; Launder, B. E.; Morse, A. P.; Maples, G.

    1974-01-01

    A guide to a computer program, written in FORTRAN 4, for predicting the flow properties of turbulent mixing with combustion of a circular jet of hydrogen into a co-flowing stream of air is presented. The program, which is based upon the Imperial College group's PASSA series, solves differential equations for diffusion and dissipation of turbulent kinetic energy and also of the R.M.S. fluctuation of hydrogen concentration. The effective turbulent viscosity for use in the shear stress equation is computed. Chemical equilibrium is assumed throughout the flow.

  20. Calculating the mean time to capture for tethered ligands and its effect on the chemical equilibrium of bound ligand pairs.

    PubMed

    Shen, Lu; Decker, Caitlin G; Maynard, Heather D; Levine, Alex J

    2016-09-01

    We present here the calculation of the mean time to capture of a tethered ligand to the receptor. This calculation is then used to determine the shift in the partitioning between (1) free, (2) singly bound, and (3) doubly bound ligands in chemical equilibrium as a function of the length of the tether. These calculations are used in the research article Fibroblast Growth Factor 2 Dimer with Superagonist in vitro Activity Improves Granulation Tissue Formation During Wound Healing (Decker et al., in press [1]) to explain quantitatively how changes in polymeric linker length in the ligand dimers modifies the efficacy of these molecules relative to that of free ligands.

  1. Non equilibrium dynamics of isolated disordered systems: the classical Hamiltonian p-spin model

    NASA Astrophysics Data System (ADS)

    Cugliandolo, Leticia F.; Lozano, Gustavo S.; Nessi, Emilio N.

    2017-08-01

    We study the dynamics of a classical disordered macroscopic model completely isolated from the environment reproducing, in a classical setting, the ‘quantum quench’ protocol. We show that, depending on the pre and post quench parameters, the system approaches equilibrium, succeeding to act as a bath on itself, or remains out of equilibrium, in two different ways. In the latter one, the system stays confined in a metastable state in which it undergoes stationary dynamics characterised by a single temperature. In the other, the system ages and its dynamics are characterised by two temperatures associated with observations made at short and long time differences (high and low frequencies). The parameter dependence of the asymptotic states is rationalised in terms of a dynamic phase diagram with one equilibrium and two out of equilibrium phases. Aspects of pre-thermalisation are observed and discussed. Similarities and differences with the dynamics of the dissipative model are also explained.

  2. Development of Plasma Equilibrium Response Model for Optimized Plasma Control of KSTAR tokamak

    NASA Astrophysics Data System (ADS)

    Jeon, Youngmu; Park, Jong-Kyu; Park, Young-Seok; Hwang, Y. S.

    2004-11-01

    Plasma equilibrium response models for an optimized control system design are developed with KSTAR tokamak configurations. In a simple filament model, plasma column is assumed as a single ring filament with rigid displacements, and constitutes circuits with external conductors (coils, passive plate, and vacuum vessel segments). Perturbed equilibrium response model, based on CREATE-L deformable plasma response model [1], assumes that the plasma evolves through a sequence of MHD equilibria. Prediction characteristics of both models are described in terms of open loop characteristics of vertical motion of plasma, and validated by comparison with TSC (Tokamak Simulation Code) simulations. Additionally, applications of the plasma equilibrium response models to design of optimal plasma controllers are described. [1] R. Albanese, and F. Villone, Nucl. Fusion 38 723 (1998)

  3. Chemical vapour deposition of silicon under reduced pressure in a hot-wall reactor: Equilibrium and kinetics

    NASA Astrophysics Data System (ADS)

    Langlais, Francis; Hottier, François; Cadoret, Robert

    1982-02-01

    Silicon chemical vapour deposition (SiH 2Cl 2/H 2 system), under reduced pressure conditions, in a hot-wall reactor, is presented. The vapour phase composition is assessed by evaluating two distnct equilbria. The "homogeneous equilibrium", which assumes that the vapour phase is not in equilibrium with solid silicon, is thought to give an adequate description of the vapour phase in the case of low pressure, high gas velocities, good temperature homogeneity conditions. A comparison with "heterogeneous equilibrium" enables us to calculate the supersaturation so evidencing a highly irreversible growth system. The experimental determination of the growth rate reveals two distinct temperature ranges: below 1000°C, polycrystalline films are usually obtained with a thermally activated growth rate (+40 kcal mole -1) and a reaction order, with respect to the predominant species SiCl 2, close to one; above 1000°C, the films are always monocrystalline and their growth rate exhibits a much lower or even negative activation energy, the reaction order in SiCl 2 remaining about one.

  4. Distance-dependent diffusion-controlled reaction of •NO and O2•- at chemical equilibrium with ONOO-.

    PubMed

    Botti, Horacio; Möller, Matías N; Steinmann, Daniel; Nauser, Thomas; Koppenol, Willem H; Denicola, Ana; Radi, Rafael

    2010-12-16

    The fast reaction of (•)NO and O(2)(•-) to give ONOO(-) has been extensively studied at irreversible conditions, but the reasons for the wide variations in observed forward rate constants (3.8 ≤ k(f) ≤ 20 × 10(9) M(-1) s(-1)) remain unexplained. We characterized the diffusion-dependent aqueous (pH > 12) chemical equilibrium of the form (•)NO + O(2)(•-) = ONOO(-) with respect to its dependence on temperature, viscosity, and [ONOO(-)](eq) by determining [ONOO(-)](eq) and [(•)NO](eq). The equilibrium forward reaction rate constant (k(f)(eq)) has negative activation energy, in contrast to that found under irreversible conditions. In contradiction to the law of mass action, we demonstrate that the equilibrium constant depends on ONOO(-) concentration. Therefore, a wide range of k(f)(eq) values could be derived (7.5-21 × 10(9) M(-1) s(-1)). Of general interest, the variations in k(f) can thus be explained by its dependence on the distance between ONOO(-) particles (sites of generation of (•)NO and O(2)(•-)).

  5. A hierarchical analysis of terrestrial ecosystem model Biome-BGC: Equilibrium analysis and model calibration

    SciTech Connect

    Thornton, Peter E; Wang, Weile; Law, Beverly E.; Nemani, Ramakrishna R

    2009-01-01

    The increasing complexity of ecosystem models represents a major difficulty in tuning model parameters and analyzing simulated results. To address this problem, this study develops a hierarchical scheme that simplifies the Biome-BGC model into three functionally cascaded tiers and analyzes them sequentially. The first-tier model focuses on leaf-level ecophysiological processes; it simulates evapotranspiration and photosynthesis with prescribed leaf area index (LAI). The restriction on LAI is then lifted in the following two model tiers, which analyze how carbon and nitrogen is cycled at the whole-plant level (the second tier) and in all litter/soil pools (the third tier) to dynamically support the prescribed canopy. In particular, this study analyzes the steady state of these two model tiers by a set of equilibrium equations that are derived from Biome-BGC algorithms and are based on the principle of mass balance. Instead of spinning-up the model for thousands of climate years, these equations are able to estimate carbon/nitrogen stocks and fluxes of the target (steady-state) ecosystem directly from the results obtained by the first-tier model. The model hierarchy is examined with model experiments at four AmeriFlux sites. The results indicate that the proposed scheme can effectively calibrate Biome-BGC to simulate observed fluxes of evapotranspiration and photosynthesis; and the carbon/nitrogen stocks estimated by the equilibrium analysis approach are highly consistent with the results of model simulations. Therefore, the scheme developed in this study may serve as a practical guide to calibrate/analyze Biome-BGC; it also provides an efficient way to solve the problem of model spin-up, especially for applications over large regions. The same methodology may help analyze other similar ecosystem models as well.

  6. Modelling non-equilibrium thermodynamic systems from the speed-gradient principle

    NASA Astrophysics Data System (ADS)

    Khantuleva, Tatiana A.; Shalymov, Dmitry S.

    2017-03-01

    The application of the speed-gradient (SG) principle to the non-equilibrium distribution systems far away from thermodynamic equilibrium is investigated. The options for applying the SG principle to describe the non-equilibrium transport processes in real-world environments are discussed. Investigation of a non-equilibrium system's evolution at different scale levels via the SG principle allows for a fresh look at the thermodynamics problems associated with the behaviour of the system entropy. Generalized dynamic equations for finite and infinite number of constraints are proposed. It is shown that the stationary solution to the equations, resulting from the SG principle, entirely coincides with the locally equilibrium distribution function obtained by Zubarev. A new approach to describe time evolution of systems far from equilibrium is proposed based on application of the SG principle at the intermediate scale level of the system's internal structure. The problem of the high-rate shear flow of viscous fluid near the rigid plane plate is discussed. It is shown that the SG principle allows closed mathematical models of non-equilibrium processes to be constructed. This article is part of the themed issue 'Horizons of cybernetical physics'.

  7. Modelling non-equilibrium thermodynamic systems from the speed-gradient principle.

    PubMed

    Khantuleva, Tatiana A; Shalymov, Dmitry S

    2017-03-06

    The application of the speed-gradient (SG) principle to the non-equilibrium distribution systems far away from thermodynamic equilibrium is investigated. The options for applying the SG principle to describe the non-equilibrium transport processes in real-world environments are discussed. Investigation of a non-equilibrium system's evolution at different scale levels via the SG principle allows for a fresh look at the thermodynamics problems associated with the behaviour of the system entropy. Generalized dynamic equations for finite and infinite number of constraints are proposed. It is shown that the stationary solution to the equations, resulting from the SG principle, entirely coincides with the locally equilibrium distribution function obtained by Zubarev. A new approach to describe time evolution of systems far from equilibrium is proposed based on application of the SG principle at the intermediate scale level of the system's internal structure. The problem of the high-rate shear flow of viscous fluid near the rigid plane plate is discussed. It is shown that the SG principle allows closed mathematical models of non-equilibrium processes to be constructed.This article is part of the themed issue 'Horizons of cybernetical physics'.

  8. The Entropy Criterion for Chemical Equilibrium: An Exercise in the Second Law.

    ERIC Educational Resources Information Center

    Smith, Norman O.

    1985-01-01

    Describes an exercise in which the entropy maximum is illustrated with a chemical example. The exercise allows students to work with an isolated, chemically reactive system and shows that the entropy of a nonisolated system can pass through a maximum but does so at a nonequilibrium point. (JN)

  9. Temporal cross-correlation asymmetry and departure from equilibrium in a bistable chemical system.

    PubMed

    Bianca, C; Lemarchand, A

    2014-06-14

    This paper aims at determining sustained reaction fluxes in a nonlinear chemical system driven in a nonequilibrium steady state. The method relies on the computation of cross-correlation functions for the internal fluctuations of chemical species concentrations. By employing Langevin-type equations, we derive approximate analytical formulas for the cross-correlation functions associated with nonlinear dynamics. Kinetic Monte Carlo simulations of the chemical master equation are performed in order to check the validity of the Langevin equations for a bistable chemical system. The two approaches are found in excellent agreement, except for critical parameter values where the bifurcation between monostability and bistability occurs. From the theoretical point of view, the results imply that the behavior of cross-correlation functions cannot be exploited to measure sustained reaction fluxes in a specific nonlinear system without the prior knowledge of the associated chemical mechanism and the rate constants.

  10. An interactive computer code for calculation of gas-phase chemical equilibrium (EQLBRM)

    NASA Technical Reports Server (NTRS)

    Pratt, B. S.; Pratt, D. T.

    1984-01-01

    A user friendly, menu driven, interactive computer program known as EQLBRM which calculates the adiabatic equilibrium temperature and product composition resulting from the combustion of hydrocarbon fuels with air, at specified constant pressure and enthalpy is discussed. The program is developed primarily as an instructional tool to be run on small computers to allow the user to economically and efficiency explore the effects of varying fuel type, air/fuel ratio, inlet air and/or fuel temperature, and operating pressure on the performance of continuous combustion devices such as gas turbine combustors, Stirling engine burners, and power generation furnaces.

  11. On a variational formulation of the maximum energy dissipation principle for non-equilibrium chemical thermodynamics

    NASA Astrophysics Data System (ADS)

    Moroz, Adam

    2008-05-01

    In this work we revise the applicability of the optimal control and variational approach to the maximum energy dissipation (MED) principle in non-equilibrium thermodynamics. The optimal control analogies for the kinetical and potential parts of thermodynamic Lagrangian (in the form of a sum of the positively defined thermodynamic potential and positively defined dissipative function) have been considered. An interpretation of thermodynamic momenta is discussed with respect to standard optimal control applications, which employ dynamic constraints. Also included is interpretation in terms of the least action principle.

  12. The Sulfur-Iodine Cycle: Process Analysis and Design Using Comprehensive Phase Equilibrium Measurements and Modeling

    SciTech Connect

    Thies, Mark C.; O'Connell, J. P.; Gorensek, Maximilian B.

    2010-01-10

    Of the 100+ thermochemical hydrogen cycles that have been proposed, the Sulfur-Iodine (S-I) Cycle is a primary target of international interest for the centralized production of hydrogen from nuclear power. However, the cycle involves complex and highly nonideal phase behavior at extreme conditions that is only beginning to be understood and modeled for process simulation. The consequence is that current designs and efficiency projections have large uncertainties, as they are based on incomplete data that must be extrapolated from property models. This situation prevents reliable assessment of the potential viability of the system and, even more, a basis for efficient process design. The goal of this NERI award (05-006) was to generate phase-equilibrium data, property models, and comprehensive process simulations so that an accurate evaluation of the S-I Cycle could be made. Our focus was on Section III of the Cycle, where the hydrogen is produced by decomposition of hydroiodic acid (HI) in the presence of water and iodine (I2) in a reactive distillation (RD) column. The results of this project were to be transferred to the nuclear hydrogen community in the form of reliable flowsheet models for the S-I process. Many of the project objectives were achieved. At Clemson University, a unique, tantalum-based, phase-equilibrium apparatus incorporating a view cell was designed and constructed for measuring fluid-phase equilibria for mixtures of iodine, HI, and water (known as HIx) at temperatures to 350 °C and pressures to 100 bar. Such measurements were of particular interest for developing a working understanding of the expected operation of the RD column in Section III. The view cell allowed for the IR observation and discernment of vapor-liquid (VL), liquid-liquid, and liquid-liquid-vapor (LLVE) equilibria for HIx systems. For the I2-H2O system, liquid-liquid equilibrium (LLE) was discovered to exist at temperatures up to 310-315 °C, in contrast to the models and

  13. Collective Flocking Dynamics: Long Rang Order in a Non-Equilibrium 2D XY Model

    NASA Astrophysics Data System (ADS)

    Tu, Yuhai

    1996-03-01

    We propose and study a non-equilibrium continuum dynamical model for the collective motion of large groups of biological organisms (e.g., flocks of birds, slime molds, schools of fishs, etc.) (J. Toner and Y. Tu, Phys. Rev. Lett.), 75(23), 4326(1995) Our model becomes highly non-trivial, and different from the equilibrium model, for dequilibrium systems, our model exhibits a broken continuous symmetry even in d=2. Our model describes a large universality class of microscopic rules, including those recently simulated by Vicsek et. al.( T. Vicsek et. al. , Phys. Rev. Lett.) 75, 1226(95).

  14. General and Partial Equilibrium Modeling of Sectoral Policies to Address Climate Change in the United States

    SciTech Connect

    Pizer, William; Burtraw, Dallas; Harrington, Winston; Newell, Richard; Sanchirico, James; Toman, Michael

    2003-03-31

    This document provides technical documentation for work using detailed sectoral models to calibrate a general equilibrium analysis of market and non-market sectoral policies to address climate change. Results of this work can be found in the companion paper, "Modeling Costs of Economy-wide versus Sectoral Climate Policies Using Combined Aggregate-Sectoral Model".

  15. The Navy/NASA Engine Program (NNEP89): Interfacing the program for the calculation of complex Chemical Equilibrium Compositions (CEC)

    NASA Technical Reports Server (NTRS)

    Gordon, Sanford

    1991-01-01

    The NNEP is a general computer program for calculating aircraft engine performance. NNEP has been used extensively to calculate the design and off-design (matched) performance of a broad range of turbine engines, ranging from subsonic turboprops to variable cycle engines for supersonic transports. Recently, however, there has been increased interest in applications for which NNEP is not capable of simulating, such as the use of alternate fuels including cryogenic fuels and the inclusion of chemical dissociation effects at high temperatures. To overcome these limitations, NNEP was extended by including a general chemical equilibrium method. This permits consideration of any propellant system and the calculation of performance with dissociation effects. The new extended program is referred to as NNEP89.

  16. Characterization of sodium carboxymethylcellulose-gelatin complex coacervation by chemical analysis of the coacervate and equilibrium fluid phases.

    PubMed

    Koh, G L; Tucker, I G

    1988-05-01

    The complex coacervation of sodium carboxymethylcellulose (SCMC) and gelatin has been characterized by chemical analyses of the coacervate and equilibrium fluid phases. The phenol-sulphuric acid (for SCMC) and Lowry (for gelatin) assays were used. Chemically analysed coacervate yield was used to predict optimum coacervation conditions, which occurred at a SCMC-gelatin mixing ratio of 3:7 at pH 3.5. The effects of pH, colloid mixing ratio and total colloid concentration on coacervate yield and composition were studied. The colloid mixing ratio, at which the peak coacervate yields occurred varied with coacervation pH. Increase in the total colloid concentration suppressed coacervation, resulting in a coacervate of higher water content. A similar coacervation mechanism was seen for two viscosity grades SCMC. However, because of the different degree of substitution of these two grades the SCMC-gelatin coacervates had different SCMC contents.

  17. Simulating adsorption of U(VI) under transient groundwater flow and hydrochemistry – Physical versus non-equilibrium model

    SciTech Connect

    Greskowiak, Janek; Hay, Michael B.; Prommer, Henning; Liu, Chongxuan; Post, Vincent; Ma, Rui; Davis, James A.; Zheng, Chunmiao; Zachara, John M.

    2011-08-03

    Coupled intra-grain diffusional mass-transfer and non-linear surface complexation processes play an important role for the transport behaviour of U(VI) in contaminated aquifers. Two alternative model approaches for simulating these coupled processes have been analysed and compared: (i) the physical non-equilibrium approach that explicitly accounts for aqueous speciation and instantaneous surface complexation reactions in the intra-grain regions and approximates the diffusive mass exchange between the immobile intra-grain pore water and the advective pore water as multi-rate 1st-order mass transfer and (ii) the chemical non-equilibrium approach that approximates the diffusion-limited intra-grain surface complexation reactions by a set of multiple 1st-order surface complexation reaction kinetics, thereby eliminating the explicit treatment of aqueous speciation in the intra grain pore water. Model comparison has been carried out for column and field scale scenarios, representing the highly transient hydrological and geochemical conditions in the U(VI)-contaminated aquifer at the Hanford 300A site, Washington, USA. It was found that the response of apparent U(VI) adsorption/desorption kinetic behaviour to hydrogeochemically induced changes in U(VI) sorption strength is more pronounced in the physical than in the chemical non-equilibrium model. The magnitude of the differences in model behaviour depends particularly on the degree of disequilibrium between the advective and immobile phase U(VI) concentrations. While a clear difference in U(VI) transport behaviour between the two models was noticeable for the column-scale scenarios, only minor differences were found for the Hanford 300A field scale scenarios, where the model-generated disequilibrium conditions were less pronounced as a result of high frequent groundwater flow reversals.

  18. Self-consistent chemical model of partially ionized plasmas

    SciTech Connect

    Arkhipov, Yu. V.; Baimbetov, F. B.; Davletov, A. E.

    2011-01-15

    A simple renormalization theory of plasma particle interactions is proposed. It primarily stems from generic properties of equilibrium distribution functions and allows one to obtain the so-called generalized Poisson-Boltzmann equation for an effective interaction potential of two chosen particles in the presence of a third one. The same equation is then strictly derived from the Bogolyubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy for equilibrium distribution functions in the pair correlation approximation. This enables one to construct a self-consistent chemical model of partially ionized plasmas, correctly accounting for the close interrelation of charged and neutral components thereof. Minimization of the system free energy provides ionization equilibrium and, thus, permits one to study the plasma composition in a wide range of its parameters. Unlike standard chemical models, the proposed one allows one to study the system correlation functions and thereby to obtain an equation of state which agrees well with exact results of quantum-mechanical activity expansions. It is shown that the plasma and neutral components are strongly interrelated, which results in the short-range order formation in the corresponding subsystem. The mathematical form of the results obtained enables one to both firmly establish this fact and to determine a characteristic length of the structure formation. Since the cornerstone of the proposed self-consistent chemical model of partially ionized plasmas is an effective pairwise interaction potential, it immediately provides quite an efficient calculation scheme not only for thermodynamical functions but for transport coefficients as well.

  19. Non-Equilibrium Sediment Transport Modeling - Extensions and Applications

    DTIC Science & Technology

    2013-01-01

    waves, in vegetated water bodies, and by overland flow. Even though different flow models are used in these cases, the sediment transport models are...the flow model adopts the phase-averaged shallow water flow equations with wave-induced radiation stresses coupled with a spectral wave...case of vegetated channels, the vegetation drag and inertia forces are considered in the momentum equations and the sediment transport capacity is

  20. Equilibrium and kinetic modeling of adsorption of reactive dye on cross-linked chitosan beads.

    PubMed

    Chiou, Ming Shen; Li, Hsing Ya

    2002-07-22

    The adsorption of reactive dye (Reactive Red 189) from aqueous solutions on cross-linked chitosan beads was studied in a batch system. The equilibrium isotherms at different particle sizes (2.3-2.5, 2.5-2.7 and 3.5-3.8mm) and the kinetics of adsorption with respect to the initial dye concentration (4320, 5760 and 7286 g/m(3)), temperature (30, 40 and 50 degrees C), pH (1.0, 3.0, 6.0 and 9.0), and cross-linking ratio (cross-linking agent/chitosan weight ratio: 0.2, 0.5, 0.7 and 1.0) were investigated. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherms and isotherm constants. Equilibrium data fitted very well to the Langmuir model in the entire saturation concentration range (0-1800 g/m(3)). The maximum monolayer adsorption capacities obtained from the Langmuir model are very large, which are 1936, 1686 and 1642 g/kg for small, mediumand large particle sizes, respectively, at pH 3.0, 30 degrees C, and the cross-linking ratio of 0.2. The pseudo first- and second-order kinetic models were used to describe the kinetic data, and the rate constants were evaluated. The experimental data fitted well to the second-order kinetic model, which indicates that the chemical sorption is the rate-limiting step, instead of mass transfer. The initial dye concentration and the solution pH both significantly affect the adsorption capacity, but the temperature and the cross-linking ratio are relatively minor factors. An increase in initial dye concentration results in the increase of adsorption capacity, which also increases with decreasing pH. The activation energy is 43.0 kJ/mol for the adsorption of the dye on the cross-linked chitosan beads at pH 3.0 and initial dye concentration 3768 g/m(3).