WorldWideScience

Sample records for chemical reaction system

  1. Chemical reaction systems with toric steady states

    CERN Document Server

    Millan, Mercedes Perez; Shiu, Anne; Conradi, Carsten

    2011-01-01

    Mass-action chemical reaction systems are frequently used in Computational Biology. The corresponding polynomial dynamical systems are often large, consisting of tens or even hundreds of ordinary differential equations, and poorly parameterized (due to noisy measurement data and a small number of data points and repetitions). Therefore, it is often difficult to establish the existence of (positive) steady states or to determine whether more complicated phenomena such as multistationarity exist. If, however, the steady state ideal of the system is a binomial ideal, then we show that these questions can be answered easily. The focus of this work is on systems with this property, and we say that such systems have toric steady states. Our main result gives sufficient conditions for a chemical reaction system to have toric steady states. Furthermore, we analyze the capacity of such a system to exhibit positive steady states and multistationarity. Examples of systems with toric steady states include weakly-reversib...

  2. Chemical reactions in reverse micelle systems

    Science.gov (United States)

    Matson, Dean W.; Fulton, John L.; Smith, Richard D.; Consani, Keith A.

    1993-08-24

    This invention is directed to conducting chemical reactions in reverse micelle or microemulsion systems comprising a substantially discontinuous phase including a polar fluid, typically an aqueous fluid, and a microemulsion promoter, typically a surfactant, for facilitating the formation of reverse micelles in the system. The system further includes a substantially continuous phase including a non-polar or low-polarity fluid material which is a gas under standard temperature and pressure and has a critical density, and which is generally a water-insoluble fluid in a near critical or supercritical state. Thus, the microemulsion system is maintained at a pressure and temperature such that the density of the non-polar or low-polarity fluid exceeds the critical density thereof. The method of carrying out chemical reactions generally comprises forming a first reverse micelle system including an aqueous fluid including reverse micelles in a water-insoluble fluid in the supercritical state. Then, a first reactant is introduced into the first reverse micelle system, and a chemical reaction is carried out with the first reactant to form a reaction product. In general, the first reactant can be incorporated into, and the product formed in, the reverse micelles. A second reactant can also be incorporated in the first reverse micelle system which is capable of reacting with the first reactant to form a product.

  3. The smallest chemical reaction system with bistability

    Directory of Open Access Journals (Sweden)

    Wilhelm Thomas

    2009-09-01

    Full Text Available Abstract Background Bistability underlies basic biological phenomena, such as cell division, differentiation, cancer onset, and apoptosis. So far biologists identified two necessary conditions for bistability: positive feedback and ultrasensitivity. Results Biological systems are based upon elementary mono- and bimolecular chemical reactions. In order to definitely clarify all necessary conditions for bistability we here present the corresponding minimal system. According to our definition, it contains the minimal number of (i reactants, (ii reactions, and (iii terms in the corresponding ordinary differential equations (decreasing importance from i-iii. The minimal bistable system contains two reactants and four irreversible reactions (three bimolecular, one monomolecular. We discuss the roles of the reactions with respect to the necessary conditions for bistability: two reactions comprise the positive feedback loop, a third reaction filters out small stimuli thus enabling a stable 'off' state, and the fourth reaction prevents explosions. We argue that prevention of explosion is a third general necessary condition for bistability, which is so far lacking discussion in the literature. Moreover, in addition to proving that in two-component systems three steady states are necessary for bistability (five for tristability, etc., we also present a simple general method to design such systems: one just needs one production and three different degradation mechanisms (one production, five degradations for tristability, etc.. This helps modelling multistable systems and it is important for corresponding synthetic biology projects. Conclusion The presented minimal bistable system finally clarifies the often discussed question for the necessary conditions for bistability. The three necessary conditions are: positive feedback, a mechanism to filter out small stimuli and a mechanism to prevent explosions. This is important for modelling bistability with

  4. Chemical Looping Combustion Reactions and Systems

    Energy Technology Data Exchange (ETDEWEB)

    Sarofim, Adel; Lighty, JoAnn; Smith, Philip; Whitty, Kevin; Eyring, Edward; Sahir, Asad; Alvarez, Milo; Hradisky, Michael; Clayton, Chris; Konya, Gabor; Baracki, Richard; Kelly, Kerry

    2014-03-01

    , they performed a sensitivity analysis for velocity, height and polydispersity and compared results against literature data for experimental studies of CLC beds with no reaction. Finally, they present an optimization space using simple non-reactive configurations. In Subtask 5.3, through a series of experimental studies, behavior of a variety of oxygen carriers with different loadings and manufacturing techniques was evaluated under both oxidizing and reducing conditions. The influences of temperature, degree of carrier conversion and thermodynamic driving force resulting from the difference between equilibrium and system O{sub 2} partial pressures were evaluated through several experimental campaigns, and generalized models accounting for these influences were developed to describe oxidation and oxygen release. Conversion of three solid fuels with widely ranging reactivities was studied in a small fluidized bed system, and all but the least reactive fuel (petcoke) were rapidly converted by oxygen liberated from the CLOU carrier. Attrition propensity of a variety of carriers was also studied, and the carriers produced by freeze granulation or impregnation of preformed substrates displayed the lowest rates of attrition. Subtask 5.4 focused on gathering kinetic data for a copper-based oxygen carrier to assist with modeling of a functioning chemical looping reactor. The kinetics team was also responsible for the development and analysis of supported copper oxygen carrier material.

  5. Thermo effect of chemical reaction in irreversible electrochemical systems

    International Nuclear Information System (INIS)

    From first law of thermodynamics the expressions of statistical calculation of 'Fundamental' and 'Thermo-chemical' thermal effects are obtained. Besides, method of calculation of thermal effect of chemical reactions in non-equilibrium electro-chemical systems is accurately discussed. (author). 7 refs

  6. Chemical Looping Combustion Reactions and Systems

    Energy Technology Data Exchange (ETDEWEB)

    Sarofim, Adel; Lighty, JoAnn; Smith, Philip; Whitty, Kevin; Eyring, Edward; Sahir, Asad; Alvarez, Milo; Hradisky, Michael; Clayton, Chris; Konya, Gabor; Baracki, Richard; Kelly, Kerry

    2011-07-01

    Chemical Looping Combustion (CLC) is one promising fuel-combustion technology, which can facilitate economic CO2 capture in coal-fired power plants. It employs the oxidation/reduction characteristics of a metal, or oxygen carrier, and its oxide, the oxidizing gas (typically air) and the fuel source may be kept separate. This work focused on two classes of oxygen carrier, one that merely undergoes a change in oxidation state, such as Fe3O4/Fe2O3 and one that is converted from its higher to its lower oxidation state by the release of oxygen on heating, i.e., CuO/Cu2O. This topical report discusses the results of four complementary efforts: (1) the development of process and economic models to optimize important design considerations, such as oxygen carrier circulation rate, temperature, residence time; (2) the development of high-performance simulation capabilities for fluidized beds and the collection, parameter identification, and preliminary verification/uncertainty quantification (3) the exploration of operating characteristics in the laboratory-scale bubbling bed reactor, with a focus on the oxygen carrier performance, including reactivity, oxygen carrying capacity, attrition resistance, resistance to deactivation, cost and availability (4) the identification of mechanisms and rates for the copper, cuprous oxide, and cupric oxide system using thermogravimetric analysis.

  7. Model Reduction of Chemical Reaction Systems using Elimination

    OpenAIRE

    Boulier, François; Lefranc, Marc; Lemaire, François; Morant, Pierre-Emmanuel

    2007-01-01

    There exist different schemes of model reduction for parametric ordinary differential systems arising from chemical reaction systems. In this paper, we focus on some schemes which rely on quasi-steady states approximations. We show that these schemes can be formulated by means of differential and algebraic elimination. Our formulation is simpler than the classical ones. It permitted us to obtain an approximation of the basic enzymatic reaction system which is different from those of Henri-Mic...

  8. Chemical reaction network approaches to Biochemical Systems Theory.

    Science.gov (United States)

    Arceo, Carlene Perpetua P; Jose, Editha C; Marin-Sanguino, Alberto; Mendoza, Eduardo R

    2015-11-01

    This paper provides a framework to represent a Biochemical Systems Theory (BST) model (in either GMA or S-system form) as a chemical reaction network with power law kinetics. Using this representation, some basic properties and the application of recent results of Chemical Reaction Network Theory regarding steady states of such systems are shown. In particular, Injectivity Theory, including network concordance [36] and the Jacobian Determinant Criterion [43], a "Lifting Theorem" for steady states [26] and the comprehensive results of Müller and Regensburger [31] on complex balanced equilibria are discussed. A partial extension of a recent Emulation Theorem of Cardelli for mass action systems [3] is derived for a subclass of power law kinetic systems. However, it is also shown that the GMA and S-system models of human purine metabolism [10] do not display the reactant-determined kinetics assumed by Müller and Regensburger and hence only a subset of BST models can be handled with their approach. Moreover, since the reaction networks underlying many BST models are not weakly reversible, results for non-complex balanced equilibria are also needed. PMID:26363083

  9. Studying chemical reactions in biological systems with MBN Explorer

    DEFF Research Database (Denmark)

    Sushko, Gennady B.; Solov'yov, Ilia A.; Verkhovtsev, Alexey V.;

    2016-01-01

    The concept of molecular mechanics force field has been widely accepted nowadays for studying various processes in biomolecular systems. In this paper, we suggest a modification for the standard CHARMM force field that permits simulations of systems with dynamically changing molecular topologies....... applied for studying processes where rupture of chemical bonds plays an essential role, e.g., in irradiation- or collision-induced damage, and also in transformation and fragmentation processes involving biomolecular systems....

  10. Introduction to chemical reaction engineering

    International Nuclear Information System (INIS)

    This deals with chemical reaction engineering with thirteen chapters. The contents of this book are introduction on reaction engineering, chemical kinetics, thermodynamics and chemical reaction, abnormal reactor, non-isothermal reactor, nonideal reactor, catalysis in nonuniform system, diffusion and reaction in porosity catalyst, design catalyst heterogeneous reactor in solid bed, a high molecule polymerization, bio reaction engineering, reaction engineering in material process, control multi-variable reactor process using digital computer.

  11. Microfluidic chemical reaction circuits

    Science.gov (United States)

    Lee, Chung-cheng; Sui, Guodong; Elizarov, Arkadij; Kolb, Hartmuth C.; Huang, Jiang; Heath, James R.; Phelps, Michael E.; Quake, Stephen R.; Tseng, Hsian-rong; Wyatt, Paul; Daridon, Antoine

    2012-06-26

    New microfluidic devices, useful for carrying out chemical reactions, are provided. The devices are adapted for on-chip solvent exchange, chemical processes requiring multiple chemical reactions, and rapid concentration of reagents.

  12. Chemical modeling of irreversible reactions in nuclear waste-water-rock systems

    International Nuclear Information System (INIS)

    Chemical models of aqueous geochemical systems are usually built on the concept of thermodynamic equilibrium. Though many elementary reactions in a geochemical system may be close to equilibrium, others may not be. Chemical models of aqueous fluids should take into account that many aqueous redox reactions are among the latter. The behavior of redox reactions may critically affect migration of certain radionuclides, especially the actinides. In addition, the progress of reaction in geochemical systems requires thermodynamic driving forces associated with elementary reactions not at equilibrium, which are termed irreversible reactions. Both static chemical models of fluids and dynamic models of reacting systems have been applied to a wide spectrum of problems in water-rock interactions. Potential applications in nuclear waste disposal range from problems in geochemical aspects of site evaluation to those of waste-water-rock interactions. However, much further work in the laboratory and the field will be required to develop and verify such applications of chemical modeling

  13. On the study of nonlinear dynamics of complex chemical reaction systems

    Institute of Scientific and Technical Information of China (English)

    XIN; Houwen; HOU; Zhonghuai

    2006-01-01

    With ever-increasing attentions being paid to complex systems such as the life system, soft matter, and nano-systems, theoretical studies of non-equilibrium nonlinear problems involved in chemical dynamics are now of general interest. In this mini-review, we mainly give a brief introduction to some frontier topics in this field, namely, nonlinear state-state dynamics, nonlinear chemical dynamics on complex networks, and nonlinear dynamics in mesoscopic chemical reaction systems. Deep study of these topics will make great contribution to discovering new laws of chemical dynamics, to exploring new control methods of complex chemical processes, to figuring out the very roles of chemical processes in the life system, and to crosslinking the scientific study of chemistry, physics and biology.

  14. Chemical transport reactions

    CERN Document Server

    Schäfer, Harald

    2013-01-01

    Chemical Transport Reactions focuses on the processes and reactions involved in the transport of solid or liquid substances to form vapor phase reaction products. The publication first offers information on experimental and theoretical principles and the transport of solid substances and its special applications. Discussions focus on calculation of the transport effect of heterogeneous equilibria for a gas motion between equilibrium spaces; transport effect and the thermodynamic quantities of the transport reaction; separation and purification of substances by means of material transport; and

  15. Mathematical Formalism of Nonequilibrium Thermodynamics for Nonlinear Chemical Reaction Systems with General Rate Law

    CERN Document Server

    Ge, Hao

    2016-01-01

    This paper studies a mathematical formalism of nonequilibrium thermodynamics for chemical reaction models with $N$ species, $M$ reactions, and general rate law. We establish a mathematical basis for J. W. Gibbs' macroscopic chemical thermodynamics under G. N. Lewis' kinetic law of entire equilibrium (detailed balance in nonlinear chemistry kinetics). In doing so, the equilibrium thermodynamics is then naturally generalized to nonequilibrium settings without detailed balance. The kinetic models are represented by a Markovian jumping process. A generalized macroscopic chemical free energy function and its associated balance equation with nonnegative source and sink are the major discoveries. The proof is based on the large deviation principle of this type of Markov processes. A general fluctuation dissipation theorem for stochastic reaction kinetics is also proved. The mathematical theory illustrates how a novel macroscopic dynamic law can emerges from the mesoscopic kinetics in a multi-scale system.

  16. On the graph and systems analysis of reversible chemical reaction networks with mass action kinetics

    NARCIS (Netherlands)

    Rao, Shodhan; Jayawardhana, Bayu; Schaft, Arjan van der

    2012-01-01

    Motivated by the recent progresses on the interplay between the graph theory and systems theory, we revisit the analysis of reversible chemical reaction networks described by mass action kinetics by reformulating it using the graph knowledge of the underlying networks. Based on this formulation, we

  17. Nonequilibrium thermodynamic formalism of nonlinear chemical reaction systems with Waage-Guldberg's law of mass action

    Science.gov (United States)

    Ge, Hao; Qian, Hong

    2016-06-01

    Macroscopic entropy production rate σ (tot) in the general nonlinear isothermal chemical reaction system with mass action kinetics is decomposed into a free energy dissipation rate and a house-keeping heat dissipation rate: σ (tot) =σ (fd) +σ (hk) ; σ (fd) = -d A /d t , where A is a generalized free energy function. This yields a novel nonequilibrium free energy balance equation d A /d t = -σ (tot) +σ (hk) , which is on a par with celebrated entropy balance equation d S /d t =σ (tot) +η (ex) where η (ex) is the rate of entropy exchange with the environment. For kinetic systems with complex balance, σ (fd) and σ (hk) are the macroscopic limits of stochastic free energy dissipation rate and house-keeping heat dissipation rate, which are both nonnegative, in the Delbrück-Gillespie description of the stochastic chemical kinetics. A full kinetic and thermodynamic theory of chemical reaction systems that transcends mesoscopic and macroscopic levels emerges.

  18. Fundamentals of chemical reaction engineering

    CERN Document Server

    Davis, Mark E

    2012-01-01

    Appropriate for a one-semester undergraduate or first-year graduate course, this text introduces the quantitative treatment of chemical reaction engineering. It covers both homogeneous and heterogeneous reacting systems and examines chemical reaction engineering as well as chemical reactor engineering. The authors take a chemical approach, helping students develop an intuitive feeling for concepts, rather than an engineering approach, which tends to overlook the inner workings of systems and objects.Each chapter contains numerous worked-out problems and real-world vignettes involving commercia

  19. Chemical reaction of hexagonal boron nitride and graphite nanoclusters in mechanical milling systems

    Energy Technology Data Exchange (ETDEWEB)

    Muramatsu, Y.; Grush, M.; Callcott, T.A. [Univ. of Tennessee, Knoxville, TN (United States)] [and others

    1997-04-01

    Synthesis of boron-carbon-nitride (BCN) hybrid alloys has been attempted extensively by many researchers because the BCN alloys are considered an extremely hard material called {open_quotes}super diamond,{close_quotes} and the industrial application for wear-resistant materials is promising. A mechanical alloying (MA) method of hexagonal boron nitride (h-BN) with graphite has recently been studied to explore the industrial synthesis of the BCN alloys. To develop the MA method for the BCN alloy synthesis, it is necessary to confirm the chemical reaction processes in the mechanical milling systems and to identify the reaction products. Therefore, the authors have attempted to confirm the chemical reaction process of the h-BN and graphite in mechanical milling systems using x-ray absorption near edge structure (XANES) methods.

  20. Speeding chemical reactions by focusing

    Science.gov (United States)

    Lacasta, A. M.; Ramírez-Piscina, L.; Sancho, J. M.; Lindenberg, K.

    2013-04-01

    We present numerical results for a chemical reaction of colloidal particles which are transported by a laminar fluid and are focused by periodic obstacles in such a way that the two components are well mixed and consequently the chemical reaction is speeded up. The roles of the various system parameters (diffusion coefficients, reaction rate, and obstacles sizes) are studied. We show that focusing speeds up the reaction from the diffusion limited rate ˜t-1/2 to very close to the perfect mixing rate, ˜t-1.

  1. Speeding chemical reactions by focusing

    CERN Document Server

    Lacasta, A M; Sancho, J M; Lindenberg, K

    2012-01-01

    We present numerical results for a chemical reaction of colloidal particles which are transported by a laminar fluid and are focused by periodic obstacles in such a way that the two components are well mixed and consequently the chemical reaction is speeded up. The roles of the various system parameters (diffusion coefficients, reaction rate, obstacles sizes) are studied. We show that focusing speeds up the reaction from the diffusion limited rate (t to the power -1/2) to very close to the perfect mixing rate, (t to the power -1).

  2. Chemical kinetics of gas reactions

    CERN Document Server

    Kondrat'Ev, V N

    2013-01-01

    Chemical Kinetics of Gas Reactions explores the advances in gas kinetics and thermal, photochemical, electrical discharge, and radiation chemical reactions. This book is composed of 10 chapters, and begins with the presentation of general kinetic rules for simple and complex chemical reactions. The next chapters deal with the experimental methods for evaluating chemical reaction mechanisms and some theories of elementary chemical processes. These topics are followed by discussions on certain class of chemical reactions, including unimolecular, bimolecular, and termolecular reactions. The rema

  3. On the graph and systems analysis of reversible chemical reaction networks with mass action kinetics

    OpenAIRE

    Rao, Shodhan; Jayawardhana, Bayu; der Schaft, Arjan van

    2012-01-01

    Motivated by the recent progresses on the interplay between the graph theory and systems theory, we revisit the analysis of reversible chemical reaction networks described by mass action kinetics by reformulating it using the graph knowledge of the underlying networks. Based on this formulation, we can characterize the space of equilibrium points and provide simple dynamical analysis on the state space modulo the space of equilibrium points.

  4. The study of thermodynamic properties and transport properties of multicomponent systems with chemical reactions

    Directory of Open Access Journals (Sweden)

    Samujlov E.

    2013-04-01

    Full Text Available In case of system with chemical reaction the most important properties are heat conductivity and heat capacity. In this work we have considered the equation for estimate the component of these properties caused by chemical reaction and ionization processes. We have evaluated the contribution of this part in heat conductivity and heat capacity too. At the high temperatures contribution in heat conductivity from ionization begins to play an important role. We have created a model, which describe partial and full ionization of gases and gas mixtures. In addition, in this work we present the comparison of our result with experimental data and data from numerical simulation. We was used the data about transport properties of middle composition of Russian coals and the data of thermophysical properties of natural gas for comparison.

  5. Nobel Prize 1992: Rudolph A. Marcus: theory of electron transfer reactions in chemical systems

    International Nuclear Information System (INIS)

    A review of the theory developed by Rudolph A. Marcus is presented, who for his rating to the theory of electron transfer in chemical systems was awarded the Nobel Prize in Chemistry in 1992. Marcus theory has constituted not only a good extension of the use of a spectroscopic principle, but also has provided an energy balance and the application of energy conservation for electron transfer reactions. A better understanding of the reaction coordinate is exposed in terms energetic and establishing the principles that govern the transfer of electrons, protons and some labile small molecular groups as studied at present. Also, the postulates and equations described have established predictive models of reaction time, very useful for industrial environments, biological, metabolic, and others that involve redox processes. Marcus theory itself has also constituted a large contribution to the theory of complex transition

  6. Programmability of Chemical Reaction Networks

    Science.gov (United States)

    Cook, Matthew; Soloveichik, David; Winfree, Erik; Bruck, Jehoshua

    Motivated by the intriguing complexity of biochemical circuitry within individual cells we study Stochastic Chemical Reaction Networks (SCRNs), a formal model that considers a set of chemical reactions acting on a finite number of molecules in a well-stirred solution according to standard chemical kinetics equations. SCRNs have been widely used for describing naturally occurring (bio)chemical systems, and with the advent of synthetic biology they become a promising language for the design of artificial biochemical circuits. Our interest here is the computational power of SCRNs and how they relate to more conventional models of computation. We survey known connections and give new connections between SCRNs and Boolean Logic Circuits, Vector Addition Systems, Petri nets, Gate Implementability, Primitive Recursive Functions, Register Machines, Fractran, and Turing Machines. A theme to these investigations is the thin line between decidable and undecidable questions about SCRN behavior.

  7. Performance and cost of energy transport and storage systems for dish applications using reversible chemical reactions

    Science.gov (United States)

    Schredder, J. M.; Fujita, T.

    1984-01-01

    The use of reversible chemical reactions for energy transport and storage for parabolic dish networks is considered. Performance and cost characteristics are estimated for systems using three reactions (sulfur-trioxide decomposition, steam reforming of methane, and carbon-dioxide reforming of methane). Systems are considered with and without storage, and in several energy-delivery configurations that give different profiles of energy delivered versus temperature. Cost estimates are derived assuming the use of metal components and of advanced ceramics. (The latter reduces the costs by three- to five-fold). The process that led to the selection of the three reactions is described, and the effects of varying temperatures, pressures, and heat exchanger sizes are addressed. A state-of-the-art survey was performed as part of this study. As a result of this survey, it appears that formidable technical risks exist for any attempt to implement the systems analyzed in this study, especially in the area of reactor design and performance. The behavior of all components and complete systems under thermal energy transients is very poorly understood. This study indicates that thermochemical storage systems that store reactants as liquids have efficiencies below 60%, which is in agreement with the findings of earlier investigators.

  8. Chemical reaction and separation method

    NARCIS (Netherlands)

    Jansen, J.C.; Kapteijn, F.; Strous, S.A.

    2005-01-01

    The invention is directed to process for performing a chemical reaction in a reaction mixture, which reaction produces water as by-product, wherein the reaction mixture is in contact with a hydroxy sodalite membrane, through which water produced during the reaction is removed from the reaction mixtu

  9. Chemical morphogenesis: recent experimental advances in reaction-diffusion system design and control.

    Science.gov (United States)

    Szalai, István; Cuiñas, Daniel; Takács, Nándor; Horváth, Judit; De Kepper, Patrick

    2012-08-01

    In his seminal 1952 paper, Alan Turing predicted that diffusion could spontaneously drive an initially uniform solution of reacting chemicals to develop stable spatially periodic concentration patterns. It took nearly 40 years before the first two unquestionable experimental demonstrations of such reaction-diffusion patterns could be made in isothermal single phase reaction systems. The number of these examples stagnated for nearly 20 years. We recently proposed a design method that made their number increase to six in less than 3 years. In this report, we formally justify our original semi-empirical method and support the approach with numerical simulations based on a simple but realistic kinetic model. To retain a number of basic properties of real spatial reactors but keep calculations to a minimal complexity, we introduce a new way to collapse the confined spatial direction of these reactors. Contrary to similar reduced descriptions, we take into account the effect of the geometric size in the confinement direction and the influence of the differences in the diffusion coefficient on exchange rates of species with their feed environment. We experimentally support the method by the observation of stationary patterns in red-ox reactions not based on oxihalogen chemistry. Emphasis is also brought on how one of these new systems can process different initial conditions and memorize them in the form of localized patterns of different geometries. PMID:23919126

  10. Mathematical Formalism of Nonequilibrium Thermodynamics for Nonlinear Chemical Reaction Systems with General Rate Law

    OpenAIRE

    Ge, Hao; Qian, Hong

    2016-01-01

    This paper studies a mathematical formalism of nonequilibrium thermodynamics for chemical reaction models with $N$ species, $M$ reactions, and general rate law. We establish a mathematical basis for J. W. Gibbs' macroscopic chemical thermodynamics under G. N. Lewis' kinetic law of entire equilibrium (detailed balance in nonlinear chemistry kinetics). In doing so, the equilibrium thermodynamics is then naturally generalized to nonequilibrium settings without detailed balance. The kinetic model...

  11. Nonequilibrium Thermodynamic Formalism of Nonlinear Chemical Reaction Systems with Waage-Guldberg's Law of Mass Action

    CERN Document Server

    Ge, Hao

    2016-01-01

    Macroscopic entropy production $\\sigma^{(tot)}$ in the general nonlinear isothermal chemical reaction system with mass action kinetics is decomposed into a free energy dissipation and a house-keeping heat: $\\sigma^{(tot)}=\\sigma^{(fd)}+\\sigma^{(hk)}$; $\\sigma^{(fd)}=-\\rd A/\\rd t$, where $A$ is a generalized free enegy function. This yields a novel nonequilibrium free energy balance equation $\\rd A/\\rd t=-\\sigma^{(tot)}+\\sigma^{(hk)}$, which is on a par with celebrated entropy balance equation $\\rd S/\\rd t=\\sigma^{(tot)}+\\eta^{(ex)}$ where $\\eta^{(ex)}$ is the rate of entropy exchange with the environment.For kinetic system with complex balance,$\\sigma^{(fd)},\\sigma^{(hk)}\\ge 0$: $\\sigma^{(fd)}$ characterizes the irreversibility of a transient relaxation kinetics; while $\\sigma^{(hk)}$ is positive even in a steady state, representing irreversibility in open,driven chemical systems with a chemostat.For kinetic system withoutcomplex balance, negative $\\sigma^{(fd)}$ is a necessary condition for multistability, w...

  12. Methods and systems for carrying out a pH-influenced chemical and/or biological reaction

    Science.gov (United States)

    Stern, Michael C.; Simeon, Fritz; Hatton, Trevor Alan

    2016-04-05

    The present invention generally relates to methods and systems for carrying out a pH-influenced chemical and/or biological reaction. In some embodiments, the pH-influenced reaction involves the conversion of CO.sub.2 to a dissolved species.

  13. Laser-induced chemical reactions

    International Nuclear Information System (INIS)

    A classical model for the interaction of laser radiation with a molecular system is derived. This model is used to study the enhancement of a chemical reaction via a collision induced absorption. It was found that an infrared laser will in general enhance the rate of a chemical reaction, even if the reactants are infrared inactive. Results for an illustrative analytically solvable model are presented, as well as results from classical trajectory studies on a number of systems. The collision induced absorption spectrum in these systems can be written as the Fourier transform of a particular dipole correlation function. This is used to obtain the collision induced absorption spectrum for a state-selected, mono-energetic reactive collision system. Examples treated are a one-dimensional barrier problem, reactive and nonreactive collisions of H + H2, and a modified H + H2 potential energy surface which leads to a collision intermediate. An extension of the classical model to treat laser-induced electronically nonadiabatic collision processes is constructed. The model treats all degrees of freedom, molecular, electronic and radiation, in a dynamically consistent framework within classical mechanics. Application is made to several systems. Several interesting phenomena are discovered including a Franck-Condon-like effect causing maxima in the reaction probability at energies much below the classical threshold, laser de-enhancement of chemical reactions and an isotope effect. In order to assess the validity of the classical model for electronically nonadiabatic process (without a laser field), a model problem involving energy transfer in a collinear atom-diatom system is studied, and the results compared to the available quantum mechanical calculation. The calculations are in qualitative agreement

  14. A Novel Approach for Modeling Chemical Reaction in Generalized Fluid System Simulation Program

    Science.gov (United States)

    Sozen, Mehmet; Majumdar, Alok

    2002-01-01

    The Generalized Fluid System Simulation Program (GFSSP) is a computer code developed at NASA Marshall Space Flight Center for analyzing steady state and transient flow rates, pressures, temperatures, and concentrations in a complex flow network. The code, which performs system level simulation, can handle compressible and incompressible flows as well as phase change and mixture thermodynamics. Thermodynamic and thermophysical property programs, GASP, WASP and GASPAK provide the necessary data for fluids such as helium, methane, neon, nitrogen, carbon monoxide, oxygen, argon, carbon dioxide, fluorine, hydrogen, water, a hydrogen, isobutane, butane, deuterium, ethane, ethylene, hydrogen sulfide, krypton, propane, xenon, several refrigerants, nitrogen trifluoride and ammonia. The program which was developed out of need for an easy to use system level simulation tool for complex flow networks, has been used for the following purposes to name a few: Space Shuttle Main Engine (SSME) High Pressure Oxidizer Turbopump Secondary Flow Circuits, Axial Thrust Balance of the Fastrac Engine Turbopump, Pressurized Propellant Feed System for the Propulsion Test Article at Stennis Space Center, X-34 Main Propulsion System, X-33 Reaction Control System and Thermal Protection System, and International Space Station Environmental Control and Life Support System design. There has been an increasing demand for implementing a combustion simulation capability into GFSSP in order to increase its system level simulation capability of a liquid rocket propulsion system starting from the propellant tanks up to the thruster nozzle for spacecraft as well as launch vehicles. The present work was undertaken for addressing this need. The chemical equilibrium equations derived from the second law of thermodynamics and the energy conservation equation derived from the first law of thermodynamics are solved simultaneously by a Newton-Raphson method. The numerical scheme was implemented as a User

  15. Chemical Effects of the (n, p) Reaction in Gaseous Systems: Simple Alkanes and their Chloroderivatives

    International Nuclear Information System (INIS)

    The chemical effects accompanying the reaction Cl35(n, p)S35 in organic system, have been studied in this paper. Chemical species in which the hot S35 atoms are stabilized were studied in the first part of this article. Methyl chloride, ethyl chloride and methane-hydrogen chloride mixture in gaseous state were used as target materials. All samples were prepared by vacuum technique and irradiated in a horizontal channel of the VVR-S reactor. The irradiated samples were analysed by radio-gas chromatography. The pressure dependence of yields of individual species has been also investigated in methyl chloride and ethyl chloride with no additives. Only a slight effect of pressure (in the range of 200-500 mm Hg) was found for irradiated methyl chloride, while the apparent increase of the yield of some simple S35-labelled compounds appeared in ethyl chloride under the same conditions. The reactions of recoil S35 atoms with gaseous methane have been examined in detail. For this purpose, the methane-hydrogen chloride mixture with additives were irradiated under constant conditions. Argon and nitric oxide were used as moderator and scavenger respectively. The composition of irradiated samples varied in the range of 20-260 mm Hg of methane and argon, 0.02-12 mm Hg of nitric oxide, the partial pressure of hydrogen chloride keeping constant (100 mm Hg). The S35-labelled hydrogen sulphide and methyl mercaptane were found as main products in irradiated samples. The results obtained show that the yield of hydrogen sulphide is mostly affected by the concentration of nitric oxide. On the other hand the amount of methyl mercaptane formed is determined mainly by the concentration of argon. (author)

  16. Sensitivity of chemical reaction networks: a structural approach 3. Regular multimolecular systems

    CERN Document Server

    Brehm, Bernhard

    2016-01-01

    We present a systematic mathematical analysis of the qualitative steady-state response to rate perturbations in large classes of reaction networks. This includes multimolecular reactions and allows for catalysis, enzymatic reactions, multiple reaction products, nonmonotone rate functions, and non-closed autonomous systems. Our structural sensitivity analysis is based on the stoichiometry of the reaction network, only. It does not require numerical data on reaction rates. Instead, we impose mild and generic nondegeneracy conditions of algebraic type. From the structural data, only, we derive which steady-state concentrations are sensitive to, and hence influenced by, changes of any particular reaction rate - and which are not. We also establish transitivity properties for influences involving rate perturbations. This allows us to derive an influence graph which globally summarizes the influence pattern of the given network. The influence graph allows the computational, but meaningful, automatic identification ...

  17. Density functional theory of chemical reactivity indices in some ion-molecule reaction systems

    International Nuclear Information System (INIS)

    Three isoelectronic reactions, proton transfer (PT), hydrogen abstraction (HA), and electron transfer (ET), of NH3+ with NH3, H2O, and HF have been studied using ab initio molecular orbital calculations. For the reaction of NH3+ + H2O, the energy of the transition state (TS) is higher than that of the reactants. This is consistent with the experimental observation that the rate constant is less than the average dipole orientation (ADO) rate constant. It seems reasonable that the reaction rate for the reaction NH3+ + H2O would hardly depend on the V2 mode of NH3+ at least for low-lying excited states (Eint≤ 0.714 eV) of the V2 mode, because the V2 contributes mainly to the normal mode orthogonal to the reaction coordinate at the TS. This is consistent with experimental observation. A similiar prediction can be made for the NH3+ + HF reaction. The electron transfer processes for the HA reactions have been examined in terms of the intrinsic reaction coordinate (IRC). The order of reactivity with NH3+ is NH3>H2O>HF. It is found that the degree of the electron transfer and the reactivity are correlated with the absolute hardness η of NH3, H2O, and HF. this is accord with the softness as the chemical reactivity index in the density functional theory. 25 refs., 6 fig., 4 tab

  18. Chemical burn or reaction

    Science.gov (United States)

    ... and buy only as much as needed. Many household products are made of toxic chemicals. It is important ... follow label instructions, including any precautions. Never store household products in food or drink containers. Leave them in ...

  19. Modelling Chemical Reasoning to Predict Reactions

    CERN Document Server

    Segler, Marwin H S

    2016-01-01

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

  20. Reduction of chemical reaction models

    Science.gov (United States)

    Frenklach, Michael

    1991-01-01

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

  1. Tabulation of thermodynamic data for chemical reactions involving 58 elements common to radioactive waste package systems

    International Nuclear Information System (INIS)

    The rate of release and migration of radionuclides from a nuclear waste repository to the biosphere is dependent on chemical interactions between groundwater, the geologic host rock, and the radioactive waste package. For the purpose of this report, the waste package includes the wasteform, canister, overpack, and repository backfill. Chemical processes of interest include sorption (ion exchange), dissolution, complexation, and precipitation. Thermochemical data for complexation and precipitation calculations for 58 elements common to the radioactive waste package are presented. Standard free energies of formation of free ions, complexes, and solids are listed. Common logarithms of equilibrium constants (log K's) for speciation and precipitation reactions are listed. Unless noted otherwise, all data are for 298.150K and one atmosphere

  2. Fast stochastic simulation of biochemical reaction systems by alternative formulations of the chemical Langevin equation

    KAUST Repository

    Mélykúti, Bence

    2010-01-01

    The Chemical Langevin Equation (CLE), which is a stochastic differential equation driven by a multidimensional Wiener process, acts as a bridge between the discrete stochastic simulation algorithm and the deterministic reaction rate equation when simulating (bio)chemical kinetics. The CLE model is valid in the regime where molecular populations are abundant enough to assume their concentrations change continuously, but stochastic fluctuations still play a major role. The contribution of this work is that we observe and explore that the CLE is not a single equation, but a parametric family of equations, all of which give the same finite-dimensional distribution of the variables. On the theoretical side, we prove that as many Wiener processes are sufficient to formulate the CLE as there are independent variables in the equation, which is just the rank of the stoichiometric matrix. On the practical side, we show that in the case where there are m1 pairs of reversible reactions and m2 irreversible reactions there is another, simple formulation of the CLE with only m1 + m2 Wiener processes, whereas the standard approach uses 2 m1 + m2. We demonstrate that there are considerable computational savings when using this latter formulation. Such transformations of the CLE do not cause a loss of accuracy and are therefore distinct from model reduction techniques. We illustrate our findings by considering alternative formulations of the CLE for a human ether a-go-go related gene ion channel model and the Goldbeter-Koshland switch. © 2010 American Institute of Physics.

  3. Molecular dynamics simulation of a chemical reaction

    International Nuclear Information System (INIS)

    Molecular dynamics is used to study the chemical reaction A+A→B+B. It is shown that the reaction rate constant follows the Arrhenius law both for Lennard-Jones and hard sphere interaction potentials between substrate particles. A. For the denser systems the reaction rate is proportional to the value of the radial distribution function at the contact point of two hard spheres. 10 refs, 4 figs

  4. Nonlinear Stochastic Dynamics of Complex Systems, I: A Chemical Reaction Kinetic Perspective with Mesoscopic Nonequilibrium Thermodynamics

    CERN Document Server

    Qian, Hong

    2016-01-01

    We distinguish a mechanical representation of the world in terms of point masses with positions and momenta and the chemical representation of the world in terms of populations of different individuals, each with intrinsic stochasticity, but population wise with statistical rate laws in their syntheses, degradations, spatial diffusion, individual state transitions, and interactions. Such a formal kinetic system in a small volume $V$, like a single cell, can be rigorously treated in terms of a Markov process describing its nonlinear kinetics as well as nonequilibrium thermodynamics at a mesoscopic scale. We introduce notions such as open, driven chemical systems, entropy production, free energy dissipation, etc. Then in the macroscopic limit, we illustrate how two new "laws", in terms of a generalized free energy of the mesoscopic stochastic dynamics, emerge. Detailed balance and complex balance are two special classes of "simple" nonlinear kinetics. Phase transition is intrinsically related to multi-stability...

  5. Nonlinear Stochastic Dynamics of Complex Systems, I: A Chemical Reaction Kinetic Perspective with Mesoscopic Nonequilibrium Thermodynamics

    OpenAIRE

    Qian, Hong

    2016-01-01

    We distinguish a mechanical representation of the world in terms of point masses with positions and momenta and the chemical representation of the world in terms of populations of different individuals, each with intrinsic stochasticity, but population wise with statistical rate laws in their syntheses, degradations, spatial diffusion, individual state transitions, and interactions. Such a formal kinetic system in a small volume $V$, like a single cell, can be rigorously treated in terms of a...

  6. Apparent tunneling in chemical reactions

    DEFF Research Database (Denmark)

    Henriksen, Niels Engholm; Hansen, Flemming Yssing; Billing, G. D.

    2000-01-01

    A necessary condition for tunneling in a chemical reaction is that the probability of crossing a barrier is non-zero, when the energy of the reactants is below the potential energy of the barrier. Due to the non-classical nature (i.e, momentum uncertainty) of vibrational states this is, however...

  7. Apparent tunneling in chemical reactions

    DEFF Research Database (Denmark)

    Henriksen, Niels Engholm; Hansen, Flemming Yssing; Billing, G. D.

    A necessary condition for tunneling in a chemical reaction is that the probability of crossing a barrier is non-zero, when the energy of the reactants is below the potential energy of the barrier. Due to the non-classical nature (i.e, momentum uncertainty) of vibrational states this is, however...

  8. A higher-order numerical framework for stochastic simulation of chemical reaction systems.

    KAUST Repository

    Székely, Tamás

    2012-07-15

    BACKGROUND: In this paper, we present a framework for improving the accuracy of fixed-step methods for Monte Carlo simulation of discrete stochastic chemical kinetics. Stochasticity is ubiquitous in many areas of cell biology, for example in gene regulation, biochemical cascades and cell-cell interaction. However most discrete stochastic simulation techniques are slow. We apply Richardson extrapolation to the moments of three fixed-step methods, the Euler, midpoint and θ-trapezoidal τ-leap methods, to demonstrate the power of stochastic extrapolation. The extrapolation framework can increase the order of convergence of any fixed-step discrete stochastic solver and is very easy to implement; the only condition for its use is knowledge of the appropriate terms of the global error expansion of the solver in terms of its stepsize. In practical terms, a higher-order method with a larger stepsize can achieve the same level of accuracy as a lower-order method with a smaller one, potentially reducing the computational time of the system. RESULTS: By obtaining a global error expansion for a general weak first-order method, we prove that extrapolation can increase the weak order of convergence for the moments of the Euler and the midpoint τ-leap methods, from one to two. This is supported by numerical simulations of several chemical systems of biological importance using the Euler, midpoint and θ-trapezoidal τ-leap methods. In almost all cases, extrapolation results in an improvement of accuracy. As in the case of ordinary and stochastic differential equations, extrapolation can be repeated to obtain even higher-order approximations. CONCLUSIONS: Extrapolation is a general framework for increasing the order of accuracy of any fixed-step stochastic solver. This enables the simulation of complicated systems in less time, allowing for more realistic biochemical problems to be solved.

  9. Experimental Demonstrations in Teaching Chemical Reactions.

    Science.gov (United States)

    Hugerat, Muhamad; Basheer, Sobhi

    2001-01-01

    Presents demonstrations of chemical reactions by employing different features of various compounds that can be altered after a chemical change occurs. Experimental activities include para- and dia-magnetism in chemical reactions, aluminum reaction with base, reaction of acid with carbonates, use of electrochemical cells for demonstrating chemical…

  10. A New Method for Determining the Nanocrystallite Size Distribution in Systems Where Chemical Reaction between Solid and a Gas Phase Occurs

    Directory of Open Access Journals (Sweden)

    Rafał Pelka

    2013-01-01

    Full Text Available The proposed method, based on measuring the chemical reaction rate in solid phase, is, therefore, limited to such systems where reaction between nanocrystalline materials and a gas phase occurs. Additionally, assumptions of the model of reaction between nanocrystalline materials and a gas phase, where the surface chemical reaction rate is the rate limiting step, are used. As an example of such a reaction, nitriding (with ammonia of the prereduced industrial iron catalysts for ammonia synthesis of different average crystallite sizes was used. To measure the reaction rate, the differential reactor equipped with systems for thermogravimetric measurements and analysis of the chemical composition of the gas phase was used. The crystallites mass and size distributions for the analyzed samples of catalyst were determined.

  11. Aerosol simulation including chemical and nuclear reactions

    Energy Technology Data Exchange (ETDEWEB)

    Marwil, E.S.; Lemmon, E.C.

    1985-01-01

    The numerical simulation of aerosol transport, including the effects of chemical and nuclear reactions presents a challenging dynamic accounting problem. Particles of different sizes agglomerate and settle out due to various mechanisms, such as diffusion, diffusiophoresis, thermophoresis, gravitational settling, turbulent acceleration, and centrifugal acceleration. Particles also change size, due to the condensation and evaporation of materials on the particle. Heterogeneous chemical reactions occur at the interface between a particle and the suspending medium, or a surface and the gas in the aerosol. Homogeneous chemical reactions occur within the aersol suspending medium, within a particle, and on a surface. These reactions may include a phase change. Nuclear reactions occur in all locations. These spontaneous transmutations from one element form to another occur at greatly varying rates and may result in phase or chemical changes which complicate the accounting process. This paper presents an approach for inclusion of these effects on the transport of aerosols. The accounting system is very complex and results in a large set of stiff ordinary differential equations (ODEs). The techniques for numerical solution of these ODEs require special attention to achieve their solution in an efficient and affordable manner. 4 refs.

  12. Chemical reactions at aqueous interfaces

    Science.gov (United States)

    Vecitis, Chad David

    2009-12-01

    Interfaces or phase boundaries are a unique chemical environment relative to individual gas, liquid, or solid phases. Interfacial reaction mechanisms and kinetics are often at variance with homogeneous chemistry due to mass transfer, molecular orientation, and catalytic effects. Aqueous interfaces are a common subject of environmental science and engineering research, and three environmentally relevant aqueous interfaces are investigated in this thesis: 1) fluorochemical sonochemistry (bubble-water), 2) aqueous aerosol ozonation (gas-water droplet), and 3) electrolytic hydrogen production and simultaneous organic oxidation (water-metal/semiconductor). Direct interfacial analysis under environmentally relevant conditions is difficult, since most surface-specific techniques require relatively `extreme' conditions. Thus, the experimental investigations here focus on the development of chemical reactors and analytical techniques for the completion of time/concentration-dependent measurements of reactants and their products. Kinetic modeling, estimations, and/or correlations were used to extract information on interfacially relevant processes. We found that interfacial chemistry was determined to be the rate-limiting step to a subsequent series of relatively fast homogeneous reactions, for example: 1) Pyrolytic cleavage of the ionic headgroup of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) adsorbed to cavitating bubble-water interfaces during sonolysis was the rate-determining step in transformation to their inorganic constituents carbon monoxide, carbon dioxide, and fluoride; 2) ozone oxidation of aqueous iodide to hypoiodous acid at the aerosol-gas interface is the rate-determining step in the oxidation of bromide and chloride to dihalogens; 3) Electrolytic oxidation of anodic titanol surface groups is rate-limiting for the overall oxidation of organics by the dichloride radical. We also found chemistry unique to the interface, for example: 1

  13. Chemical reaction and radiation absorption effects on MHD micropolar fluid past a vertical porous plate in a rotating system

    International Nuclear Information System (INIS)

    This paper considers the effect of radiation absorption and chemical reaction on MHD free convection heat and mass transfer flow of a micropolar fluid in a rotating system. A uniform magnetic field acts perpendicular to the porous surface in which absorbs micropolar fluid with a constant suction velocity. The entire system rotates about the axes normal to the plate with uniform angular velocity Ω. The governing dimensionless equations for this investigation are solved analytically by using regular perturbation method. The effects of the various flow parameters and physical properties on the velocity, microrotation, temperature and concentration profiles across the boundary layer are investigated through graphs. Also the numerical results of velocity profiles of micropolar fluids are compared with the corresponding flow problems for a Newtonian fluid. (author)

  14. An Experiment on Mining Chemical Reaction Databases

    OpenAIRE

    Berasaluce, Sandra; Laurenço, Claude; Napoli, Amedeo; Niel, Gilles

    2004-01-01

    In this paper, we present an experiment on knowledge discovery in chemical reaction databases. Chemical reactions are the main elements on which relies synthesis in organic chemistry, and this is why chemical reactions databases are of first importance. From a problem-solving process perspective, synthesis in organic chemistry must be considered at several levels of abstraction: mainly a strategic level where general synthesis methods are involved, and a tactic level where actual chemical rea...

  15. Minimum Energy Pathways for Chemical Reactions

    Science.gov (United States)

    Walch, S. P.; Langhoff, S. R. (Technical Monitor)

    1995-01-01

    Computed potential energy surfaces are often required for computation of such parameters as rate constants as a function of temperature, product branching ratios, and other detailed properties. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method to obtain accurate energetics, gives useful results for a number of chemically important systems. The talk will focus on a number of applications to reactions leading to NOx and soot formation in hydrocarbon combustion.

  16. Neural Networks in Chemical Reaction Dynamics

    CERN Document Server

    Raff, Lionel; Hagan, Martin

    2011-01-01

    This monograph presents recent advances in neural network (NN) approaches and applications to chemical reaction dynamics. Topics covered include: (i) the development of ab initio potential-energy surfaces (PES) for complex multichannel systems using modified novelty sampling and feedforward NNs; (ii) methods for sampling the configuration space of critical importance, such as trajectory and novelty sampling methods and gradient fitting methods; (iii) parametrization of interatomic potential functions using a genetic algorithm accelerated with a NN; (iv) parametrization of analytic interatomic

  17. Dynamic Reaction Figures: An Integrative Vehicle for Understanding Chemical Reactions

    Science.gov (United States)

    Schultz, Emeric

    2008-01-01

    A highly flexible learning tool, referred to as a dynamic reaction figure, is described. Application of these figures can (i) yield the correct chemical equation by simply following a set of menu driven directions; (ii) present the underlying "mechanism" in chemical reactions; and (iii) help to solve quantitative problems in a number of different…

  18. A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

    OpenAIRE

    De Lucia, M.; Kempka, T.; Kühn, M.

    2014-01-01

    Fully-coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i) that the presence of CO2 is the only driving force for chemical reactions and (ii) that its migration in the reservoir is only marginally affected by immobilization due to chemical reac...

  19. Chemical behaviour of plutonium in natural, aquatic systems: Hydrolysis, carbonate complexation and redox reactions

    International Nuclear Information System (INIS)

    In order to clear up the geochemical behaviour of plutonium and its migration mechanisms in groundwater, hydrolysis, redox behaviour, compound formation in carbonate solutions and colloid formation were examined in groundwater conditions, i.e. at pH values between 5 and 8 and at redox potentials of between -300 and +700 mV. Solubility measurements, spectroscopic processes (UV, VIS, IR spectroscopy and laser induced photoacoustic spectroscopy) and electrochemical processes (cyclic voltammetry, differential pulse polarography) are used as methods of investigation. The hydrolysis constants of Pu IV and Pu VI and the solubility product of Pu (OH)4 were determined and hydrolysis products of divalent and trivalent type are described. From solubility experiments, the stability constants for Pu (IV) carbonate compounds and the solubility product for the carbonate system of stable bodies of Pu (OH)2 CO3 were calculated. Using absorption spectroscopy, the disproportionate kinetics of Pu (V) in carbonate was determined at various pH values. A slow, but continuous, reduction in Pu (VI) was found in carbonate solution, which was derived from radiolytic effects. The speed of this auto-reduction was determined, depending on various experimental parameters. (orig./RB)

  20. Suppression of Ostwald Ripening by Chemical Reactions

    Science.gov (United States)

    Zwicker, David; Hyman, Anthony A.; Jülicher, Frank

    2015-03-01

    Emulsions consisting of droplets immersed in a fluid are typically unstable and coarsen over time. One important coarsening process is Ostwald ripening, which is driven by the surface tension of the droplets. Ostwald ripening must thus be suppressed to stabilize emulsions, e.g. to control the properties of pharmaceuticals, food, or cosmetics. Suppression of Ostwald ripening is also important in biological cells, which contain stable liquid-like compartments, e.g. germ granules, Cajal-bodies, and centrosomes. Such systems are often driven away from equilibrium by chemical reactions and can thus be called active emulsions. Here, we show that non-equilibrium chemical reactions can suppress Ostwald Ripening, leading to stable, monodisperse emulsions. We derive analytical approximations of the typical droplet size, droplet count, and time scale of the dynamics from a coarse-grained description of the droplet dynamics. We also compare these results to numerical simulations of the continuous concentration fields. Generally, we thus show how chemical reactions can be used to stabilize emulsions and to control their properties in technology and nature.

  1. Chemical reaction and radiation absorption effects on the flow and heat transfer of a nanofluid in a rotating system

    Science.gov (United States)

    Venkateswarlu, B.; Satya Narayana, P. V.

    2015-03-01

    The aim of this paper is to study the effects of radiation absorption and chemical reaction on MHD free convection heat transfer flow of a nanofluid bounded by a semi-infinite flat plate in a rotating frame of reference. The plate is assumed to oscillate in time with steady frequency so that the solutions of the boundary layer are the similar oscillatory kind. The entire system rotates about the axes normal to the plate. The dimensionless governing differential equations for this investigation are solved analytically using perturbation method. The effects of various important parameters entering into the problem on velocity, temperature, skin friction and Nusselt number within the boundary layer are discussed for Cu-water-based nanofluid with the help of graphs. The predicted consequences obviously point out that the presence of nanoparticles in the base fluid improves the heat transfer process significantly. The results also show that the values of Nusselt number in case of nanofluid are more pronounced than that of micropolar fluid.

  2. Transport-induced shifts in condensate dew-point and composition in multicomponent systems with chemical reaction

    Science.gov (United States)

    Rosner, D. E.; Nagarajan, R.

    1985-01-01

    Partial heterogeneous condensation phenomena in multicomponent reacting systems are analyzed taking into consideration the chemical element transport phenomena. It is demonstrated that the dew-point surface temperature in chemically reactive systems is not a purely thermodynamic quantity, but is influenced by the multicomponent diffusion and Soret-mass diffusion phenomena. Several distinct dew-points are shown to exist in such systems and, as a result of transport constraints, the 'sharp' locus between two chemically distinct condensates is systematically moved to a difference mainstream composition.

  3. Stochastic thermodynamics of chemical reaction networks

    OpenAIRE

    Schmiedl, Tim; Seifert, Udo

    2006-01-01

    For chemical reaction networks described by a master equation, we define energy and entropy on a stochastic trajectory and develop a consistent nonequilibrium thermodynamic description along a single stochastic trajectory of reaction events. A first-law like energy balance relates internal energy, applied (chemical) work and dissipated heat for every single reaction. Entropy production along a single trajectory involves a sum over changes in the entropy of the network itself and the entropy o...

  4. A Unified Theory of Chemical Reactions

    CERN Document Server

    Aubry, S

    2014-01-01

    We propose a new and general formalism for elementary chemical reactions where quantum electronic variables are used as reaction coordinates. This formalism is in principle applicable to all kinds of chemical reactions ionic or covalent. Our theory reveals the existence of an intermediate situation between ionic and covalent which may be almost barrierless and isoenegetic and which should be of high interest for understanding biochemistry.

  5. Chemical Reaction Dynamics in Nanoscle Environments

    Energy Technology Data Exchange (ETDEWEB)

    Evelyn M. Goldfield

    2006-09-26

    The major focus of the research in this program is the study of the behavior of molecular systems confined in nanoscale environments. The goal is to develop a theoretical framework for predicting how chemical reactions occur in nanoscale environments. To achieve this goal we have employed ab initio quantum chemistry, classical dynamics and quantum dynamics methods. Much of the research has focused on the behavior of molecules confined within single-walled carbon nanotubes (SWCNTs). We have also studied interactions of small molecules with the exterior surface of SWCNTs. Nonequilibrium molecular dynamics of interfaces of sliding surface interfaces have also been performed.

  6. Complex Chemical Reaction Networks from Heuristics-Aided Quantum Chemistry

    OpenAIRE

    Rappoport, Dmitrij; Galvin, Cooper J.; Zubarev, Dmitry; Aspuru-Guzik, Alan

    2014-01-01

    While structures and reactivities of many small molecules can be computed efficiently and accurately using quantum chemical methods, heuristic approaches remain essential for modeling complex structures and large-scale chemical systems. Here, we present a heuristics-aided quantum chemical methodology applicable to complex chemical reaction networks such as those arising in cell metabolism and prebiotic chemistry. Chemical heuristics offer an expedient way of traversing high-dimensional reacti...

  7. Chemical reactions in solvents and melts

    CERN Document Server

    Charlot, G

    1969-01-01

    Chemical Reactions in Solvents and Melts discusses the use of organic and inorganic compounds as well as of melts as solvents. This book examines the applications in organic and inorganic chemistry as well as in electrochemistry. Organized into two parts encompassing 15 chapters, this book begins with an overview of the general properties and the different types of reactions, including acid-base reactions, complex formation reactions, and oxidation-reduction reactions. This text then describes the properties of inert and active solvents. Other chapters consider the proton transfer reactions in

  8. Flows and chemical reactions in heterogeneous mixtures

    CERN Document Server

    Prud'homme, Roger

    2014-01-01

    This book - a sequel of previous publications 'Flows and Chemical Reactions' and 'Chemical Reactions in Flows and Homogeneous Mixtures' - is devoted to flows with chemical reactions in heterogeneous environments.  Heterogeneous media in this volume include interfaces and lines. They may be the site of radiation. Each type of flow is the subject of a chapter in this volume. We consider first, in Chapter 1, the question of the generation of environments biphasic individuals: dusty gas, mist, bubble flow.  Chapter 2 is devoted to the study at the mesoscopic scale: particle-fluid exchange of mom

  9. Quantum dynamics of fast chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Light, J.C. [Univ. of Chicago, IL (United States)

    1993-12-01

    The aims of this research are to explore, develop, and apply theoretical methods for the evaluation of the dynamics of gas phase collision processes, primarily chemical reactions. The primary theoretical tools developed for this work have been quantum scattering theory, both in time dependent and time independent forms. Over the past several years, the authors have developed and applied methods for the direct quantum evaluation of thermal rate constants, applying these to the evaluation of the hydrogen isotopic exchange reactions, applied wave packet propagation techniques to the dissociation of Rydberg H{sub 3}, incorporated optical potentials into the evaluation of thermal rate constants, evaluated the use of optical potentials for state-to-state reaction probability evaluations, and, most recently, have developed quantum approaches for electronically non-adiabatic reactions which may be applied to simplify calculations of reactive, but electronically adiabatic systems. Evaluation of the thermal rate constants and the dissociation of H{sub 3} were reported last year, and have now been published.

  10. An alternative to fully coupled reactive transport simulations for long-term prediction of chemical reactions in complex geological systems

    Science.gov (United States)

    De Lucia, Marco; Kempka, Thomas; Kühn, Michael

    2014-05-01

    Fully-coupled reactive transport simulations involving multiphase hydrodynamics and chemical reactions in heterogeneous settings are extremely challenging from a computational point of view. This often leads to oversimplification of the investigated system: coarse spatial discretization, to keep the number of elements in the order of few thousands; simplified chemistry, disregarding many potentially important reactions. A novel approach for coupling non-reactive hydrodynamic simulations with the outcome of single batch geochemical simulations was therefore introduced to assess the potential long-term mineral trapping at the Ketzin pilot site for underground CO2 storage in Germany [1],[2]. The advantage of the coupling is the ability to use multi-million grid non-reactive hydrodynamics simulations on one side and few batch 0D geochemical simulations on the other, so that the complexity of both systems does not need to be reduced. This contribution shows the approach which was taken to validate this simplified coupling scheme. The procedure involved batch simulations of the reference geochemical model, then performing both non-reactive and fully coupled 1D and 3D reactive transport simulations and finally applying the simplified coupling scheme based on the non-reactive and geochemical batch model. The TOUGHREACT/ECO2N [3] simulator was adopted for the validation. The degree of refinement of the spatial grid and the complexity and velocity of the mineral reactions, along with a cut-off value for the minimum concentration of dissolved CO2 allowed to originate precipitates in the simplified approach were found out to be the governing parameters for the convergence of the two schemes. Systematic discrepancies between the approaches are not reducible, simply because there is no feedback between chemistry and hydrodynamics, and can reach 20 % - 30 % in unfavourable cases. However, even such discrepancy is completely acceptable, in our opinion, given the amount of

  11. Non-equilibrium thermo-chemical heat storage in porous media: Part 2 – A 1D computational model for a calcium hydroxide reaction system

    International Nuclear Information System (INIS)

    Thermal energy storage technologies can facilitate the transition to an energy system based largely on renewable sources and enable efficiency gains for industrial processes in general. Due to their specific advantages, various concepts of thermo-chemical storage systems are being developed. They share characteristic features of mass and heat transport that are strongly coupled through a variety of physical and chemical phenomena. To facilitate the understanding of the coupled multi-physics processes inside such systems, a versatile conceptual model for directly permeated reactive beds was developed in part 1 of this work. It was based on thermodynamic principles and the Theory of Porous Media. The model was then implemented into OpenGeoSys, a scientific finite element simulation software. In this article, the model is specified to the well-studied calcium hydroxide reaction system to illustrate its practical applicability. Sensitivity analyses reveal the influence of particle diameter, porosity, permeability, mass flux, and reaction rate. Two distinct “reaction waves” are identified to migrate through the reactor. The power required to pump the gas stream was decomposed into parts related to the classical mechanical pressure drop and to the chemical reaction. The results can be used for the optimization of thermochemical heat storage systems. - Highlights: • Detailed investigation of coupled multiphysics in thermochemical heat storage. • Thermodynamically consistent model for thermochemical heat storage systems. • Analysis of thermal power depending on material and process parameters. • Two reaction waves are identified that traverse the reactor. • Mechanical pumping power splits into mechanically and chemically induced parts

  12. Chemical kinetics and reaction dynamics

    CERN Document Server

    Houston, Paul L

    2006-01-01

    This text teaches the principles underlying modern chemical kinetics in a clear, direct fashion, using several examples to enhance basic understanding. It features solutions to selected problems, with separate sections and appendices that cover more technical applications.Each chapter is self-contained and features an introduction that identifies its basic goals, their significance, and a general plan for their achievement. This text's important aims are to demonstrate that the basic kinetic principles are essential to the solution of modern chemical problems, and to show how the underlying qu

  13. Modeling of turbulent chemical reaction

    Science.gov (United States)

    Chen, J.-Y.

    1995-01-01

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

  14. A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

    OpenAIRE

    De Lucia, M.; Kempka, T.; Kühn, M.

    2015-01-01

    Fully coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i) that the presence of CO2 is the only driving force for chemical reactions and (ii) that its migration in the reservoir is only marginally affected by immobilisation due to chem...

  15. CHEMICAL REACTIONS AT NANOMETAL PARTICLES

    OpenAIRE

    GALO CÁRDENAS-TRIVIÑO

    2005-01-01

    The concept of nanochemistry and the reactions involved are discussed. The work is focused on nanoparticles obtained from colloidal dispersions. The colloidal particles by transmission electron microscopy of low and high resolution were analyzed. The high resolution electron miscroscopy (HRTEM) allow us to classify the nanostructure of the metal particles in some polyhedral models: cubooctahedron, truncated octahedron, tetracai decahedron and icosahedron. Some HRTEM of Pd-2 propanol and Ge-2-...

  16. Chemical Reactions at Surfaces. Final Progress Report

    Energy Technology Data Exchange (ETDEWEB)

    None

    2003-02-21

    The Gordon Research Conference (GRC) on Chemical Reactions at Surfaces was held at Holiday Inn, Ventura, California, 2/16-21/03. Emphasis was placed on current unpublished research and discussion of the future target areas in this field.

  17. Inelastic Collisions and Chemical Reactions of Molecules at Ultracold Temperatures

    OpenAIRE

    Quéméner, Goulven; Balakrishnan, Naduvalath; Dalgarno, Alexander

    2010-01-01

    This paper summarizes the recent theoretical works on inelastic collisions and chemical reactions at cold and ultracold temperatures involving neutral or ionic systems of atoms and molecules. Tables of zero-temperature rate constants of various molecules are provided.

  18. Kinetic studies of elementary chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Durant, J.L. Jr. [Sandia National Laboratories, Livermore, CA (United States)

    1993-12-01

    This program concerning kinetic studies of elementary chemical reactions is presently focussed on understanding reactions of NH{sub x} species. To reach this goal, the author is pursuing experimental studies of reaction rate coefficients and product branching fractions as well as using electronic structure calculations to calculate transition state properties and reaction rate calculations to relate these properties to predicted kinetic behavior. The synergy existing between the experimental and theoretical studies allow one to gain a deeper insight into more complex elementary reactions.

  19. Temperature waves in chemical reaction-diffusion-heat conduction systems with two ends respectively subject to Dirichlet and no-flux conditions

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Taking the Lindemann model as a sample system in which there exist chemical reactions, diffusion and heat conduction, we found the theoretical framework of linear stability analysis for a unidimensional nonhomogeneous two-variable system with one end subject to Dirichlet conditions, while the other end no-flux conditions. Furthermore, the conditions for the emergence of temperature waves are found out by the linear stabiliy analysis and verified by a diagram for successive steps of evolution of spatial profile of temperature during a period that is plotted by numerical simulations on a computer. Without doubt, these results are in favor of the heat balance in chemical reactor designs.

  20. Acoustic wave propagation in fluids with coupled chemical reactions

    International Nuclear Information System (INIS)

    This investigation presents a hydroacoustic theory which accounts for sound absorption and dispersion in a multicomponent mixture of reacting fluids (assuming a set of first-order acoustic equations without diffusion) such that several coupled reactions can occur simultaneously. General results are obtained in the form of a biquadratic characteristic equation (called the Kirchhoff-Langevin equation) for the complex propagation variable chi = - (α + iω/c) in which α is the attenuation coefficient, c is the phase speed of the progressive wave and ω is the angular frequency. Computer simulations of sound absorption spectra have been made for three different chemical systems, each comprised of two-step chemical reactions using physico-chemical data available in the literature. The chemical systems studied include: (1) water-dioxane, (2) aqueous solutions of glycine and (3) cobalt polyphosphate mixtures. Explicit comparisons are made between the exact biquadratic characteristic solution and the approximate equation (sometimes referred to as a Debye equation) previously applied to interpret the experimental data for the chemical reaction contribution to the absorption versus frequency. The relative chemical reaction and classical viscothermal contributions to the sound absorption are also presented. Several discrepancies that can arise when estimating thermodynamic data (chemical reaction heats or volume changes) for multistep chemical reaction systems when making dilute solution or constant density assumptions are discussed

  1. Entropy Generation in a Chemical Reaction

    Science.gov (United States)

    Miranda, E. N.

    2010-01-01

    Entropy generation in a chemical reaction is analysed without using the general formalism of non-equilibrium thermodynamics at a level adequate for advanced undergraduates. In a first approach to the problem, the phenomenological kinetic equation of an elementary first-order reaction is used to show that entropy production is always positive. A…

  2. Genetic Recombination as a Chemical Reaction Network

    OpenAIRE

    Müller, Stefan; Hofbauer, Josef

    2015-01-01

    The process of genetic recombination can be seen as a chemical reaction network with mass-action kinetics. We review the known results on existence, uniqueness, and global stability of an equilibrium in every compatibility class and for all rate constants, from both the population genetics and the reaction networks point of view.

  3. Potential energy surfaces for chemical reactions

    International Nuclear Information System (INIS)

    Research into potential energy surfaces for chemical reactions at Lawrence Berkeley Laboratory during 1976 is described. Topics covered include: the fuzzy interface between surface chemistry catalysis and organometallic chemistry; potential energy surfaces for elementary fluorine hydrogen reactions; structure, energetics, and reactivity of carbenes; and the theory of self-consistent electron pairs

  4. Computed potential energy surfaces for chemical reactions

    Science.gov (United States)

    Walch, Stephen P.

    1994-01-01

    Quantum mechanical methods have been used to compute potential energy surfaces for chemical reactions. The reactions studied were among those believed to be important to the NASP and HSR programs and included the recombination of two H atoms with several different third bodies; the reactions in the thermal Zeldovich mechanism; the reactions of H atom with O2, N2, and NO; reactions involved in the thermal De-NO(x) process; and the reaction of CH(squared Pi) with N2 (leading to 'prompt NO'). These potential energy surfaces have been used to compute reaction rate constants and rates of unimolecular decomposition. An additional application was the calculation of transport properties of gases using a semiclassical approximation (and in the case of interactions involving hydrogen inclusion of quantum mechanical effects).

  5. Chemical characteristics and enhanced hepatoprotective activities of Maillard reaction products derived from milk protein-sugar system.

    Science.gov (United States)

    Oh, Nam Su; Young Lee, Ji; Lee, Hyun Ah; Joung, Jae Yeon; Shin, Yong Kook; Kim, Sae Hun; Kim, Younghoon; Lee, Kwang Won

    2016-02-01

    The objective of this study was to investigate the characteristics, antioxidative properties, and hepatoprotective effects of Maillard reaction products (MRP) from milk protein reacted with sugars. The MRP were obtained from milk protein, whey protein concentrates and sodium caseinate, using 2 types of sugars, lactose and glucose, by heating the mixture at 55°C for 7d in a sodium phosphate buffer (pH 7.4). Changes in the chemical modification of the milk protein were monitored by measuring the protein-bound carbonyls and PAGE protein profiles. The results showed that the amount of protein-bound carbonyls increased after Maillard reaction (MR). In addition, sodium dodecyl sulfate-PAGE analysis indicated a formation of high-molecular weight complexes through MR. The modification sites induced by MR of milk protein were monitored by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of tryptic-digested gel spots of MRP. As a result, modification and their localization in AA sequence of MRP was identified. Also, the MRP showed higher antioxidant activities than the intact milk protein, and they reduced intracellular reactive oxygen species production and inhibited the depletion of the reduced glutathione concentrations in the HepG2 cells. In particular, glucose-sodium caseinate MRP showed the highest biological activities among all MRP. Therefore, these results suggest that the MRP from milk protein reacting with sugars possess effective antioxidant activity and have a protective ability against oxidative damage. PMID:26627852

  6. A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

    Directory of Open Access Journals (Sweden)

    M. De Lucia

    2014-09-01

    Full Text Available Fully-coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i that the presence of CO2 is the only driving force for chemical reactions and (ii that its migration in the reservoir is only marginally affected by immobilization due to chemical reactions. In the simplified coupling, the exposure time to CO2 of each element of the hydrodynamic grid is estimated by non-reactive simulations and the reaction path of one single batch geochemical model is applied to each grid element during its exposure time. In heterogeneous settings, analytical scaling relationships provide the dependency of velocity and amount of reactions to porosity and gas saturation. The analysis of TOUGHREACT fully coupled reactive transport simulations of CO2 injection in saline aquifer, inspired to the Ketzin pilot site (Germany, both in homogeneous and heterogeneous settings, confirms that the reaction paths predicted by fully coupled simulations in every element of the grid show a high degree of self-similarity. A threshold value for the minimum concentration of dissolved CO2 considered chemically active is showed to mitigate the effects of the discrepancy between dissolved CO2 migration in non-reactive and fully coupled simulations. In real life, the optimal threshold value is unknown and has to be estimated, e.g., by means of 1-D or 2-D simulations, resulting in an uncertainty ultimately due to the process de-coupling. However, such uncertainty is more than acceptable given that the alternative coupling enables using grids in the order of million elements, profiting from much better description of heterogeneous reservoirs at a fraction of the calculation time of fully coupled models.

  7. A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

    Science.gov (United States)

    De Lucia, M.; Kempka, T.; Kühn, M.

    2015-02-01

    Fully coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i) that the presence of CO2 is the only driving force for chemical reactions and (ii) that its migration in the reservoir is only marginally affected by immobilisation due to chemical reactions. In the simplified coupling, the exposure time to CO2 of each element of the hydrodynamic grid is estimated by non-reactive simulations and the reaction path of one single batch geochemical model is applied to each grid element during its exposure time. In heterogeneous settings, analytical scaling relationships provide the dependency of velocity and amount of reactions to porosity and gas saturation. The analysis of TOUGHREACT fully coupled reactive transport simulations of CO2 injection in saline aquifer, inspired to the Ketzin pilot site (Germany), both in homogeneous and heterogeneous settings, confirms that the reaction paths predicted by fully coupled simulations in every element of the grid show a high degree of self-similarity. A threshold value for the minimum concentration of dissolved CO2 considered chemically active is shown to mitigate the effects of the discrepancy between dissolved CO2 migration in non-reactive and fully coupled simulations. In real life, the optimal threshold value is unknown and has to be estimated, e.g. by means of 1-D or 2-D simulations, resulting in an uncertainty ultimately due to the process de-coupling. However, such uncertainty is more than acceptable given that the alternative coupling enables using grids of the order of millions of elements, profiting from much better description of heterogeneous reservoirs at a fraction of the calculation time of fully coupled models.

  8. A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

    Directory of Open Access Journals (Sweden)

    M. De Lucia

    2015-02-01

    Full Text Available Fully coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i that the presence of CO2 is the only driving force for chemical reactions and (ii that its migration in the reservoir is only marginally affected by immobilisation due to chemical reactions. In the simplified coupling, the exposure time to CO2 of each element of the hydrodynamic grid is estimated by non-reactive simulations and the reaction path of one single batch geochemical model is applied to each grid element during its exposure time. In heterogeneous settings, analytical scaling relationships provide the dependency of velocity and amount of reactions to porosity and gas saturation. The analysis of TOUGHREACT fully coupled reactive transport simulations of CO2 injection in saline aquifer, inspired to the Ketzin pilot site (Germany, both in homogeneous and heterogeneous settings, confirms that the reaction paths predicted by fully coupled simulations in every element of the grid show a high degree of self-similarity. A threshold value for the minimum concentration of dissolved CO2 considered chemically active is shown to mitigate the effects of the discrepancy between dissolved CO2 migration in non-reactive and fully coupled simulations. In real life, the optimal threshold value is unknown and has to be estimated, e.g. by means of 1-D or 2-D simulations, resulting in an uncertainty ultimately due to the process de-coupling. However, such uncertainty is more than acceptable given that the alternative coupling enables using grids of the order of millions of elements, profiting from much better description of heterogeneous reservoirs at a fraction of the calculation time of fully coupled models.

  9. The Chemical Master Equation Approach to Nonequilibrium Steady-State of Open Biochemical Systems: Linear Single-Molecule Enzyme Kinetics and Nonlinear Biochemical Reaction Networks

    Directory of Open Access Journals (Sweden)

    Lisa M. Bishop

    2010-09-01

    Full Text Available We develop the stochastic, chemical master equation as a unifying approach to the dynamics of biochemical reaction systems in a mesoscopic volume under a living environment. A living environment provides a continuous chemical energy input that sustains the reaction system in a nonequilibrium steady state with concentration fluctuations. We discuss the linear, unimolecular single-molecule enzyme kinetics, phosphorylation-dephosphorylation cycle (PdPC with bistability, and network exhibiting oscillations. Emphasis is paid to the comparison between the stochastic dynamics and the prediction based on the traditional approach based on the Law of Mass Action. We introduce the difference between nonlinear bistability and stochastic bistability, the latter has no deterministic counterpart. For systems with nonlinear bistability, there are three different time scales: (a individual biochemical reactions, (b nonlinear network dynamics approaching to attractors, and (c cellular evolution. For mesoscopic systems with size of a living cell, dynamics in (a and (c are stochastic while that with (b is dominantly deterministic. Both (b and (c are emergent properties of a dynamic biochemical network; We suggest that the (c is most relevant to major cellular biochemical processes such as epi-genetic regulation, apoptosis, and cancer immunoediting. The cellular evolution proceeds with transitions among the attractors of (b in a “punctuated equilibrium” manner.

  10. The chemical master equation approach to nonequilibrium steady-state of open biochemical systems: linear single-molecule enzyme kinetics and nonlinear biochemical reaction networks.

    Science.gov (United States)

    Qian, Hong; Bishop, Lisa M

    2010-01-01

    We develop the stochastic, chemical master equation as a unifying approach to the dynamics of biochemical reaction systems in a mesoscopic volume under a living environment. A living environment provides a continuous chemical energy input that sustains the reaction system in a nonequilibrium steady state with concentration fluctuations. We discuss the linear, unimolecular single-molecule enzyme kinetics, phosphorylation-dephosphorylation cycle (PdPC) with bistability, and network exhibiting oscillations. Emphasis is paid to the comparison between the stochastic dynamics and the prediction based on the traditional approach based on the Law of Mass Action. We introduce the difference between nonlinear bistability and stochastic bistability, the latter has no deterministic counterpart. For systems with nonlinear bistability, there are three different time scales: (a) individual biochemical reactions, (b) nonlinear network dynamics approaching to attractors, and (c) cellular evolution. For mesoscopic systems with size of a living cell, dynamics in (a) and (c) are stochastic while that with (b) is dominantly deterministic. Both (b) and (c) are emergent properties of a dynamic biochemical network; We suggest that the (c) is most relevant to major cellular biochemical processes such as epi-genetic regulation, apoptosis, and cancer immunoediting. The cellular evolution proceeds with transitions among the attractors of (b) in a "punctuated equilibrium" manner. PMID:20957107

  11. Theoretical study of chemical reactions in solution

    International Nuclear Information System (INIS)

    Quantum chemical calculations in solution are becoming more and more important in chemistry. Reference interaction site model self-consistent field (RISM-SCF) is one of the powerful approaches to perform quantum chemical calculations in solution. In this work, we developed a new generation of RISM-SCF, where a robust fitting method was newly introduced. We applied the new method to tautomerization reaction of cytosine in aqueous phase. Our calculation reproduced experimentally obtained relative stabilities and relative free energies correctly

  12. Classification of Chemical Reactions: Stages of Expertise

    Science.gov (United States)

    Stains, Marilyne; Talanquer, Vicente

    2008-01-01

    In this study we explore the strategies that undergraduate and graduate chemistry students use when engaged in classification tasks involving symbolic and microscopic (particulate) representations of different chemical reactions. We were specifically interested in characterizing the basic features to which students pay attention when classifying…

  13. Mathematical model on surface reaction diffusion in the presence of front chemical reaction

    OpenAIRE

    Permikin, D. V.; Zverev, V. S.

    2013-01-01

    The article discusses a mathematical model of solid-phase diffusion over substance surface accompanied a frontal chemical reaction. The purpose of our article is to describe the concentration distribution and surface reacted layer growth. The model is a system parabolic equations, complicated with the presence of mobile front. It takes account of diffusive fluxes redistribution, sublimation from the surface, chemical reaction reversibility. The asymptotic approximation of the obtained nonline...

  14. Heterogeneous Bunsen reaction : Analysis and experimental study of chemical absorption of sulfur dioxide and dissolution of iodine into aqueous reacting system

    International Nuclear Information System (INIS)

    Bunsen reaction is one of the three main reaction steps of Iodine-Sulphur (I-S) thermochemical water splitting process for production of hydrogen, utilizing nuclear heat. This complex multiphase-multispecies reaction has to be carried out optimally for harnessing the potential of I-S process for large scale production of hydrogen. Apart from strong influence of operating conditions, contacting scheme, reactor type and size have severe bearing on issues like overall process efficiency, product purity, separation, conversion etc. In this study sulphur dioxide (gas) and iodine (solid) are reacted in aqueous solution (liquid) with gas sparging and mechanical agitation at room temperature. Experimental results of this reacting ternary system are analyzed in terms of film theory of mass transfer. Chemical absorption of sulphur dioxide and enhanced dissolution of iodine solid into Bunsen reacting system are interpreted to deduce crucial engineering information like controlling resistance, regime, enhancement factor etc, which will help in selection of suitable contacting scheme and design of multiphase absorber-reactor for large-scale production of hydrogen. Behavior of this fluid-fluid-solid absorber - reactor can be construed kinetically as 'Fast psuedo first order reaction system'. (author)

  15. Semiclassical methods in chemical reaction dynamics

    International Nuclear Information System (INIS)

    Semiclassical approximations, simple as well as rigorous, are formulated in order to be able to describe gas phase chemical reactions in large systems. We formulate a simple but accurate semiclassical model for incorporating multidimensional tunneling in classical trajectory simulations. This model is based on the existence of locally conserved actions around the saddle point region on a multidimensional potential energy surface. Using classical perturbation theory and monitoring the imaginary action as a function of time along a classical trajectory we calculate state-specific unimolecular decay rates for a model two dimensional potential with coupling. Results are in good comparison with exact quantum results for the potential over a wide range of coupling constants. We propose a new semiclassical hybrid method to calculate state-to-state S-matrix elements for bimolecular reactive scattering. The accuracy of the Van Vleck-Gutzwiller propagator and the short time dynamics of the system make this method self-consistent and accurate. We also go beyond the stationary phase approximation by doing the resulting integrals exactly (numerically). As a result, classically forbidden probabilties are calculated with purely real time classical trajectories within this approach. Application to the one dimensional Eckart barrier demonstrates the accuracy of this approach. Successful application of the semiclassical hybrid approach to collinear reactive scattering is prevented by the phenomenon of chaotic scattering. The modified Filinov approach to evaluating the integrals is discussed, but application to collinear systems requires a more careful analysis. In three and higher dimensional scattering systems, chaotic scattering is suppressed and hence the accuracy and usefulness of the semiclassical method should be tested for such systems

  16. Semiclassical methods in chemical reaction dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Keshavamurthy, S.

    1994-12-01

    Semiclassical approximations, simple as well as rigorous, are formulated in order to be able to describe gas phase chemical reactions in large systems. We formulate a simple but accurate semiclassical model for incorporating multidimensional tunneling in classical trajectory simulations. This model is based on the existence of locally conserved actions around the saddle point region on a multidimensional potential energy surface. Using classical perturbation theory and monitoring the imaginary action as a function of time along a classical trajectory we calculate state-specific unimolecular decay rates for a model two dimensional potential with coupling. Results are in good comparison with exact quantum results for the potential over a wide range of coupling constants. We propose a new semiclassical hybrid method to calculate state-to-state S-matrix elements for bimolecular reactive scattering. The accuracy of the Van Vleck-Gutzwiller propagator and the short time dynamics of the system make this method self-consistent and accurate. We also go beyond the stationary phase approximation by doing the resulting integrals exactly (numerically). As a result, classically forbidden probabilties are calculated with purely real time classical trajectories within this approach. Application to the one dimensional Eckart barrier demonstrates the accuracy of this approach. Successful application of the semiclassical hybrid approach to collinear reactive scattering is prevented by the phenomenon of chaotic scattering. The modified Filinov approach to evaluating the integrals is discussed, but application to collinear systems requires a more careful analysis. In three and higher dimensional scattering systems, chaotic scattering is suppressed and hence the accuracy and usefulness of the semiclassical method should be tested for such systems.

  17. Chemical computing with reaction-diffusion processes.

    Science.gov (United States)

    Gorecki, J; Gizynski, K; Guzowski, J; Gorecka, J N; Garstecki, P; Gruenert, G; Dittrich, P

    2015-07-28

    Chemical reactions are responsible for information processing in living organisms. It is believed that the basic features of biological computing activity are reflected by a reaction-diffusion medium. We illustrate the ideas of chemical information processing considering the Belousov-Zhabotinsky (BZ) reaction and its photosensitive variant. The computational universality of information processing is demonstrated. For different methods of information coding constructions of the simplest signal processing devices are described. The function performed by a particular device is determined by the geometrical structure of oscillatory (or of excitable) and non-excitable regions of the medium. In a living organism, the brain is created as a self-grown structure of interacting nonlinear elements and reaches its functionality as the result of learning. We discuss whether such a strategy can be adopted for generation of chemical information processing devices. Recent studies have shown that lipid-covered droplets containing solution of reagents of BZ reaction can be transported by a flowing oil. Therefore, structures of droplets can be spontaneously formed at specific non-equilibrium conditions, for example forced by flows in a microfluidic reactor. We describe how to introduce information to a droplet structure, track the information flow inside it and optimize medium evolution to achieve the maximum reliability. Applications of droplet structures for classification tasks are discussed. PMID:26078345

  18. Study on a Bioethanol Solar Reforming System with the Solar Insolation Fluctuation in Consideration of Heat Chemical Reaction

    Science.gov (United States)

    Obara, Shin'ya; El-Sayed, Abeer Galal

    A bioethanol reforming system (FBSR) with a sunlight heat source is developed as a potential fuel supply system for distributed fuel cells. The temperature distribution of a catalyst layer in the reactor is not stable under conditions of unstable solar radiation and unstable outside air temperature; therefore, it is thought that the inversion rate of a reforming reaction will decrease. In this paper, heat transmission analysis was used in the catalyst layer of the reforming component of an FBSR, and temperature distribution, inversion rate, and process gas composition were investigated. Based on the results, the relationship between weather conditions and a hydrogen-generating rate was determined. When solar insolation was unstable, it turned out that the efficiency of the reforming component is reduced. Fluctuations of the solar insolation over a short period of time affect the hydrogen generating rate of an FBSR. Moreover, the amount of hydrogen production of an FBSR was simulated using meteorological data from a day in March and a day in August in a cold region (Sapporo). The analysis showed that efficiency of the reforming component exceeded 40% for both of the days.

  19. Theoretical studies of chemical reaction dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Schatz, G.C. [Argonne National Laboratory, IL (United States)

    1993-12-01

    This collaborative program with the Theoretical Chemistry Group at Argonne involves theoretical studies of gas phase chemical reactions and related energy transfer and photodissociation processes. Many of the reactions studied are of direct relevance to combustion; others are selected they provide important examples of special dynamical processes, or are of relevance to experimental measurements. Both classical trajectory and quantum reactive scattering methods are used for these studies, and the types of information determined range from thermal rate constants to state to state differential cross sections.

  20. Reaction diffusion and solid state chemical kinetics handbook

    CERN Document Server

    Dybkov, V I

    2010-01-01

    This monograph deals with a physico-chemical approach to the problem of the solid-state growth of chemical compound layers and reaction-diffusion in binary heterogeneous systems formed by two solids; as well as a solid with a liquid or a gas. It is explained why the number of compound layers growing at the interface between the original phases is usually much lower than the number of chemical compounds in the phase diagram of a given binary system. For example, of the eight intermetallic compounds which exist in the aluminium-zirconium binary system, only ZrAl3 was found to grow as a separate

  1. Molecular codes in biological and chemical reaction networks.

    Directory of Open Access Journals (Sweden)

    Dennis Görlich

    Full Text Available Shannon's theory of communication has been very successfully applied for the analysis of biological information. However, the theory neglects semantic and pragmatic aspects and thus cannot directly be applied to distinguish between (bio- chemical systems able to process "meaningful" information from those that do not. Here, we present a formal method to assess a system's semantic capacity by analyzing a reaction network's capability to implement molecular codes. We analyzed models of chemical systems (martian atmosphere chemistry and various combustion chemistries, biochemical systems (gene expression, gene translation, and phosphorylation signaling cascades, an artificial chemistry, and random reaction networks. Our study suggests that different chemical systems possess different semantic capacities. No semantic capacity was found in the model of the martian atmosphere chemistry, the studied combustion chemistries, and highly connected random networks, i.e. with these chemistries molecular codes cannot be implemented. High semantic capacity was found in the studied biochemical systems and in random reaction networks where the number of second order reactions is twice the number of species. We conclude that our approach can be applied to evaluate the information processing capabilities of a chemical system and may thus be a useful tool to understand the origin and evolution of meaningful information, e.g. in the context of the origin of life.

  2. Optimization of a Chemical Reaction Train

    Directory of Open Access Journals (Sweden)

    Bahar Sansar

    2010-01-01

    Full Text Available This project consists of the optimization of a chemical reactor train. The reactor considered here is the continuous stirred tank reactor (CSTR, one of the reactor models used in engineering. Given the design equation for the CSTR and the cost function for a reactor, the following values are determined; the optimum number of reactors in the reaction train, the volume of each reactor and the total cost.

  3. Optimization of a Chemical Reaction Train

    OpenAIRE

    Bahar Sansar

    2010-01-01

    This project consists of the optimization of a chemical reactor train. The reactor considered here is the continuous stirred tank reactor (CSTR), one of the reactor models used in engineering. Given the design equation for the CSTR and the cost function for a reactor, the following values are determined; the optimum number of reactors in the reaction train, the volume of each reactor and the total cost.

  4. Variable elimination in chemical reaction networks with mass action kinetics

    OpenAIRE

    Feliu, Elisenda; Wiuf, Carsten

    2011-01-01

    We consider chemical reaction networks taken with mass action kinetics. The steady states of such a system are solutions to a system of polynomial equations. Even for small systems the task of finding the solutions is daunting. We develop an algebraic framework and procedure for linear elimination of variables. The procedure reduces the variables in the system to a set of "core" variables by eliminating variables corresponding to a set of non-interacting species. The steady states are paramet...

  5. On the steady states of weakly reversible chemical reaction networks

    OpenAIRE

    Deng, Jian; Jones, Christopher; Feinberg, Martin; Nachman, Adrian

    2011-01-01

    A natural condition on the structure of the underlying chemical reaction network, namely weak reversibility, is shown to guarantee the existence of an equilibrium (steady state) in each positive stoichiometric compatibility class for the associated mass-action system. Furthermore, an index formula is given for the set of equilibria in a given stoichiometric compatibility class.

  6. Chemical selforganization of composite catalysts during catalytic reactions

    Energy Technology Data Exchange (ETDEWEB)

    Imbihl, Ronald, E-mail: imbihl@pci.uni-hannover.de [Institut fuer Physikalische Chemie und Elektrochemie, Leibniz-Universitaet Hannover, Callinstrasse 3-3a, D-30167 Hannover (Germany)

    2012-10-15

    Highlights: Black-Right-Pointing-Pointer Selforganization of composite catalysts under reaction conditions. Black-Right-Pointing-Pointer Reactive phase separation causes demixing of catalysts. Black-Right-Pointing-Pointer Condensation patterns in supported oxide catalysts. -- Abstract: Recent progress in the study of selforganization phenomena in catalytic reactions on multi-component surfaces is reviewed. As chemically more complex systems a Rh(1 1 1) surface with ultra-thin vanadium oxide layers ({theta}{sub V} < 0.5 MLE) and a bimetallic Rh(1 1 1)/Ni surface, both subjected to the H{sub 2} + O{sub 2} reaction, were chosen. Applying spatially resolving methods in situ, it is shown that under reaction conditions a reversible redistribution of the components of the catalyst occurs. The redistribution processes are essentially driven by the different chemical affinities of the components to reacting species.

  7. Chemical reaction due to stronger Ramachandran interaction

    Indian Academy of Sciences (India)

    Andrew Das Arulsamy

    2014-05-01

    The origin of a chemical reaction between two reactant atoms is associated with the activation energy, on the assumption that, high-energy collisions between these atoms, are the ones that overcome the activation energy. Here, we show that a stronger attractive van der Waals (vdW) and electron-ion Coulomb interactions between two polarized atoms are responsible for initiating a chemical reaction, either before or after the collision. We derive this stronger vdW attraction formula exactly using the quasi one-dimensional Drude model within the ionization energy theory and the energy-level spacing renormalization group method. Along the way, we expose the precise physical mechanism responsible for the existence of a stronger vdW interaction for both long and short distances, and also show how to technically avoid the electron-electron Coulomb repulsion between polarized electrons from these two reactant atoms. Finally, we properly and correctly associate the existence of this stronger attraction with Ramachandran’s `normal limits’ (distance shorter than what is allowed by the standard vdW bond) between chemically nonbonded atoms.

  8. Kinetics of Hydrogen Radical Reactions with Toluene Including Chemical Activation Theory Employing System-Specific Quantum RRK Theory Calibrated by Variational Transition State Theory.

    Science.gov (United States)

    Bao, Junwei Lucas; Zheng, Jingjing; Truhlar, Donald G

    2016-03-01

    Pressure-dependent reactions are ubiquitous in combustion and atmospheric chemistry. We employ a new calibration procedure for quantum Rice-Ramsperger-Kassel (QRRK) unimolecular rate theory within a chemical activation mechanism to calculate the pressure-falloff effect of a radical association with an aromatic ring. The new theoretical framework is applied to the reaction of H with toluene, which is a prototypical reaction in the combustion chemistry of aromatic hydrocarbons present in most fuels. Both the hydrogen abstraction reactions and the hydrogen addition reactions are calculated. Our system-specific (SS) QRRK approach is adjusted with SS parameters to agree with multistructural canonical variational transition state theory with multidimensional tunneling (MS-CVT/SCT) at the high-pressure limit. The new method avoids the need for the usual empirical estimations of the QRRK parameters, and it eliminates the need for variational transition state theory calculations as a function of energy, although in this first application we do validate the falloff curves by comparing SS-QRRK results without tunneling to multistructural microcanonical variational transition state theory (MS-μVT) rate constants without tunneling. At low temperatures, the two approaches agree well with each other, but at high temperatures, SS-QRRK tends to overestimate falloff slightly. We also show that the variational effect is important in computing the energy-resolved rate constants. Multiple-structure anharmonicity, torsional-potential anharmonicity, and high-frequency-mode vibrational anharmonicity are all included in the rate computations, and torsional anharmonicity effects on the density of states are investigated. Branching fractions, which are both temperature- and pressure-dependent (and for which only limited data is available from experiment), are predicted as a function of pressure. PMID:26841076

  9. Sonoluminescence air bubbles as chemical reaction chambers

    CERN Document Server

    Lohse, D; Dupont, T F; Hilgenfeldt, S; Johnston, B; Lohse, Detlef; Brenner, Michael P; Dupont, Todd F; Hilgenfeldt, Sascha; Johnston, Blaine

    1996-01-01

    Sound driven gas bubbles can emit light pulses, a phenomenon called sonoluminescence. Air is found to be one of the most friendly gases towards this phenomenon, but only if it contains 1\\% argon. We suggest a chemical mechanism to account for the strong dependence on the gas mixture, based on the dissociation of nitrogen at high temperatures and reactions which form \\rm{NO}_3^- and \\rm{NH}_4^+, among other ions; the reaction products should be investigated experimentally. Inert gases are crucial for stable sonoluminescence because they do not react with the fluid. Our phase diagram in the concentration vs forcing pressure space is applicable to any gas mixture and in good agreement with latest measurements of the UCLA group.

  10. Law of Localization in Chemical Reaction Networks

    Science.gov (United States)

    Okada, Takashi; Mochizuki, Atsushi

    2016-07-01

    In living cells, chemical reactions are connected by sharing their products and substrates, and form complex networks, e.g., metabolic pathways. Here we developed a theory to predict the sensitivity, i.e., the responses of concentrations and fluxes to perturbations of enzymes, from network structure alone. Nonzero response patterns turn out to exhibit two characteristic features, localization and hierarchy. We present a general theorem connecting sensitivity with network topology that explains these characteristic patterns. Our results imply that network topology is an origin of biological robustness. Finally, we suggest a strategy to determine real networks from experimental measurements.

  11. Law of localization in chemical reaction networks

    CERN Document Server

    Okada, Takashi

    2016-01-01

    In living cells, chemical reactions are connected by sharing their products and substrates, and form complex networks, e.g. metabolic pathways. Here we developed a theory to predict the sensitivity, i.e. the responses of concentrations and fluxes to perturbations of enzymes, from network structure alone. Responses turn out to exhibit two characteristic patterns, $localization$ and $hierarchy$. We present a general theorem connecting sensitivity with network topology that explains these characteristic patterns. Our results imply that network topology is an origin of biological robustness. Finally, we suggest a strategy to determine real networks from experimental measurements.

  12. Development of Green and Sustainable Chemical Reactions

    DEFF Research Database (Denmark)

    Taarning, Esben

    Abstract This thesis entitled Development of Green and Sustainable Chemical Reactions is divided into six chapters involving topics and projects related to green and sustainable chemistry. The chapters can be read independently, however a few concepts and some background information is introduced...... in chapter one and two which can be helpful to know when reading the subsequent chapters. The first chapter is an introduction into the fundamentals of green and sustainable chemistry. The second chapter gives an overview of some of the most promising methods to produce value added chemicals from biomass...... and only leads to small amounts of waste formation due to the all-catalytic nature of the procedure. This chapter involves the use of transition metal catalysis as well as classic organic chemistry. In chapter four, supported gold nanoparticles are used as catalysts for the aerobic oxidation of primary...

  13. Program Helps To Determine Chemical-Reaction Mechanisms

    Science.gov (United States)

    Bittker, D. A.; Radhakrishnan, K.

    1995-01-01

    General Chemical Kinetics and Sensitivity Analysis (LSENS) computer code developed for use in solving complex, homogeneous, gas-phase, chemical-kinetics problems. Provides for efficient and accurate chemical-kinetics computations and provides for sensitivity analysis for variety of problems, including problems involving honisothermal conditions. Incorporates mathematical models for static system, steady one-dimensional inviscid flow, reaction behind incident shock wave (with boundary-layer correction), and perfectly stirred reactor. Computations of equilibrium properties performed for following assigned states: enthalpy and pressure, temperature and pressure, internal energy and volume, and temperature and volume. Written in FORTRAN 77 with exception of NAMELIST extensions used for input.

  14. A network dynamics approach to chemical reaction networks

    Science.gov (United States)

    van der Schaft, A. J.; Rao, S.; Jayawardhana, B.

    2016-04-01

    A treatment of a chemical reaction network theory is given from the perspective of nonlinear network dynamics, in particular of consensus dynamics. By starting from the complex-balanced assumption, the reaction dynamics governed by mass action kinetics can be rewritten into a form which allows for a very simple derivation of a number of key results in the chemical reaction network theory, and which directly relates to the thermodynamics and port-Hamiltonian formulation of the system. Central in this formulation is the definition of a balanced Laplacian matrix on the graph of chemical complexes together with a resulting fundamental inequality. This immediately leads to the characterisation of the set of equilibria and their stability. Furthermore, the assumption of complex balancedness is revisited from the point of view of Kirchhoff's matrix tree theorem. Both the form of the dynamics and the deduced behaviour are very similar to consensus dynamics, and provide additional perspectives to the latter. Finally, using the classical idea of extending the graph of chemical complexes by a 'zero' complex, a complete steady-state stability analysis of mass action kinetics reaction networks with constant inflows and mass action kinetics outflows is given, and a unified framework is provided for structure-preserving model reduction of this important class of open reaction networks.

  15. Molecular Dynamics Simulations of Chemical Reactions for Use in Education

    Science.gov (United States)

    Qian Xie; Tinker, Robert

    2006-01-01

    One of the simulation engines of an open-source program called the Molecular Workbench, which can simulate thermodynamics of chemical reactions, is described. This type of real-time, interactive simulation and visualization of chemical reactions at the atomic scale could help students understand the connections between chemical reaction equations…

  16. Systematic Error Estimation for Chemical Reaction Energies

    CERN Document Server

    Simm, Gregor N

    2016-01-01

    For the theoretical understanding of the reactivity of complex chemical systems accurate relative energies between intermediates and transition states are required. Despite its popularity, density functional theory (DFT) often fails to provide sufficiently accurate data, especially for molecules containing transition metals. Due to the huge number of intermediates that need to be studied for all but the simplest chemical processes, DFT is to date the only method that is computationally feasible. Here, we present a Bayesian framework for DFT that allows for error estimation of calculated properties. Since the optimal choice of parameters in present-day density functionals is strongly system dependent, we advocate for a system-focused re-parameterization. While, at first sight, this approach conflicts with the first-principles character of DFT that should make it in principle system independent, we deliberately introduce system dependence because we can then assign a stochastically meaningful error to the syste...

  17. Mass transfer with complex reversible chemical reactions. II: Parallel reversible chemical reactions

    NARCIS (Netherlands)

    Versteeg, G.F.; Kuipers, J.A.M.; Beckum, van F.P.H.; Swaaij, van W.P.M.

    1990-01-01

    An absorption model has been developed which can be used to calculate rapidly absorption rates for the phenomenon mass transfer accompanied by multiple complex parallel reversible chemical reactions. This model can be applied for the calculation of the mass transfer rates, enhancement factors and co

  18. Flow-Injection Responses of Diffusion Processes and Chemical Reactions

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov

    2000-01-01

    manifold may be characterised by a diffusion coefficient that depends on flow rate, denoted as the kinematic diffusion coefficient. The description was applied to systems involving species of chromium, both in the case of simple diffusion and in the case of chemical reactions. It is suggested that it may...... be used in the resolution of FIA profiles to obtain information about the content of interference’s, in the study of chemical reaction kinetics and to measure absolute concentrations within the FIA-detector cell.......The technique of Flow-injection Analysis (FIA), now aged 25 years, offers unique analytical methods that are fast, reliable and consuming an absolute minimum of chemicals. These advantages together with its inherent feasibility for automation warrant the future applications of FIA as an attractive...

  19. Thermodynamic performance for a chemical reactions model

    International Nuclear Information System (INIS)

    This paper presents the analysis efficiency of a chemical reaction model of four states, such that their activated states can occur at any point (fixed but arbitrary) of the transition from one state to another. This mechanism operates under a single heat reservoir temperature, unlike the internal combustion engines where there are two thermal sources. Different efficiencies are compared to this model, which operate at different optimum engine regimes. Thus, some analytical methods are used to give an approximate expression, facilitating the comparison between them. Finally, the result is compared with that obtained by other authors considered a general model of an isothermal molecular machine. Taking into account the above, the results seems to follow a similar behaviour for all the optimized engines, which resemble that observed in the case of heat engine efficiencies

  20. Internal Active Thermal Control System (IATCS) Sodium Bicarbonate/Carbonate Buffer in an Open Aqueous Carbon Dioxide System and Corollary Electrochemical/Chemical Reactions Relative to System pH Changes

    Science.gov (United States)

    Stegman, Thomas W.; Wilson, Mark E.; Glasscock, Brad; Holt, Mike

    2014-01-01

    The International Space Station (ISS) Internal Active Thermal Control System (IATCS) experienced a number of chemical changes driven by system absorption of CO2 which altered the coolant’s pH. The natural effects of the decrease in pH from approximately 9.2 to less than 8.4 had immediate consequences on system corrosion rates and corrosion product interactions with specified coolant constituents. The alkalinity of the system was increased through the development and implementation of a carbonate/bicarbonate buffer that would increase coolant pH to 9.0 – 10.0 and maintain pH above 9.0 in the presence of ISS cabin concentrations of CO2 up to twenty times higher than ground concentrations. This paper defines how a carbonate/bicarbonate buffer works in an open carbon dioxide system and summarizes the analyses performed on the buffer for safe and effective application in the on-orbit system. The importance of the relationship between the cabin environment and the IATCS is demonstrated as the dominant factor in understanding the system chemistry and pH trends before and after addition of the carbonate/bicarbonate buffer. The paper also documents the corollary electrochemical and chemical reactions the system has experienced and the rationale for remediation of these effects with the addition of the carbonate/bicarbonate buffer.

  1. Mathematical description of the nonlinear chemical reactions with oscillatory inflow to the reaction field

    Indian Academy of Sciences (India)

    Aldona Krupska

    2015-06-01

    In this paper the arduous attempt to find a mathematical solution for the nonlinear autocatalytic chemical processes with a time-varying and oscillating inflow of reactant to the reaction medium has been taken. Approximate analytical solution is proposed. Numerical solutions and analytical attempts to solve the non-linear differential equation indicates a phase shift between the oscillatory influx of intermediate reaction reagent to the medium of chemical reaction and the change of its concentration in this medium. Analytical solutions indicate that this shift may be associated with the reaction rate constants 1 and 2 and the relaxation time . The relationship between the phase shift and the oscillatory flow of reactant seems to be similar to that obtained in the case of linear chemical reactions, as described previously, however, the former is much more complex and different. In this paper, we would like to consider whether the effect of forced phase shift in the case of nonlinear and non-oscillatory chemical processes occurring particularly in the living systems have a practical application in laboratory.

  2. Accelerated Stochastic Simulation of Large Chemical Systems

    Institute of Scientific and Technical Information of China (English)

    CHEN Xiao; AO Ling

    2007-01-01

    For efficient simulation of chemical systems with large number of reactions, we report a fast and exact algorithm for direct simulation of chemical discrete Markov processes. The approach adopts the scheme of organizing the reactions into hierarchical groups. By generating a random number, the selection of the next reaction that actually occurs is accomplished by a few successive selections in the hierarchical groups. The algorithm which is suited for simulating systems with large number of reactions is much faster than the direct method or the optimized direct method. For a demonstration of its efficiency, the accelerated algorithm is applied to simulate the reaction-diffusion Brusselator model on a discretized space.

  3. A chemical reaction network solver for the astrophysics code NIRVANA

    Science.gov (United States)

    Ziegler, U.

    2016-02-01

    Context. Chemistry often plays an important role in astrophysical gases. It regulates thermal properties by changing species abundances and via ionization processes. This way, time-dependent cooling mechanisms and other chemistry-related energy sources can have a profound influence on the dynamical evolution of an astrophysical system. Modeling those effects with the underlying chemical kinetics in realistic magneto-gasdynamical simulations provide the basis for a better link to observations. Aims: The present work describes the implementation of a chemical reaction network solver into the magneto-gasdynamical code NIRVANA. For this purpose a multispecies structure is installed, and a new module for evolving the rate equations of chemical kinetics is developed and coupled to the dynamical part of the code. A small chemical network for a hydrogen-helium plasma was constructed including associated thermal processes which is used in test problems. Methods: Evolving a chemical network within time-dependent simulations requires the additional solution of a set of coupled advection-reaction equations for species and gas temperature. Second-order Strang-splitting is used to separate the advection part from the reaction part. The ordinary differential equation (ODE) system representing the reaction part is solved with a fourth-order generalized Runge-Kutta method applicable for stiff systems inherent to astrochemistry. Results: A series of tests was performed in order to check the correctness of numerical and technical implementation. Tests include well-known stiff ODE problems from the mathematical literature in order to confirm accuracy properties of the solver used as well as problems combining gasdynamics and chemistry. Overall, very satisfactory results are achieved. Conclusions: The NIRVANA code is now ready to handle astrochemical processes in time-dependent simulations. An easy-to-use interface allows implementation of complex networks including thermal processes

  4. Computational Systems Chemical Biology

    OpenAIRE

    Oprea, Tudor I.; May, Elebeoba E.; Leitão, Andrei; Tropsha, Alexander

    2011-01-01

    There is a critical need for improving the level of chemistry awareness in systems biology. The data and information related to modulation of genes and proteins by small molecules continue to accumulate at the same time as simulation tools in systems biology and whole body physiologically-based pharmacokinetics (PBPK) continue to evolve. We called this emerging area at the interface between chemical biology and systems biology systems chemical biology, SCB (Oprea et al., 2007).

  5. Thermodynamic chemical energy transfer mechanisms of non-equilibrium, quasi-equilibrium, and equilibrium chemical reactions

    International Nuclear Information System (INIS)

    Chemical energy transfer mechanisms at finite temperature are explored by a chemical energy transfer theory which is capable of investigating various chemical mechanisms of non-equilibrium, quasi-equilibrium, and equilibrium. Gibbs energy fluxes are obtained as a function of chemical potential, time, and displacement. Diffusion, convection, internal convection, and internal equilibrium chemical energy fluxes are demonstrated. The theory reveals that there are chemical energy flux gaps and broken discrete symmetries at the activation chemical potential, time, and displacement. The statistical, thermodynamic theory is the unification of diffusion and internal convection chemical reactions which reduces to the non-equilibrium generalization beyond the quasi-equilibrium theories of migration and diffusion processes. The relationship between kinetic theories of chemical and electrochemical reactions is also explored. The theory is applied to explore non-equilibrium chemical reactions as an illustration. Three variable separation constants indicate particle number constants and play key roles in describing the distinct chemical reaction mechanisms. The kinetics of chemical energy transfer accounts for the four control mechanisms of chemical reactions such as activation, concentration, transition, and film chemical reactions. - Highlights: • Chemical energy transfer theory is proposed for non-, quasi-, and equilibrium. • Gibbs energy fluxes are expressed by chemical potential, time, and displacement. • Relationship between chemical and electrochemical reactions is discussed. • Theory is applied to explore nonequilibrium energy transfer in chemical reactions. • Kinetics of non-equilibrium chemical reactions shows the four control mechanisms

  6. Chemical dynamics in the gas phase: Time-dependent quantum mechanics of chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Gray, S.K. [Argonne National Laboratory, IL (United States)

    1993-12-01

    A major goal of this research is to obtain an understanding of the molecular reaction dynamics of three and four atom chemical reactions using numerically accurate quantum dynamics. This work involves: (i) the development and/or improvement of accurate quantum mechanical methods for the calculation and analysis of the properties of chemical reactions (e.g., rate constants and product distributions), and (ii) the determination of accurate dynamical results for selected chemical systems, which allow one to compare directly with experiment, determine the reliability of the underlying potential energy surfaces, and test the validity of approximate theories. This research emphasizes the use of recently developed time-dependent quantum mechanical methods, i.e. wave packet methods.

  7. Reaction dynamics in polyatomic molecular systems

    Energy Technology Data Exchange (ETDEWEB)

    Miller, W.H. [Lawrence Berkeley Laboratory, CA (United States)

    1993-12-01

    The goal of this program is the development of theoretical methods and models for describing the dynamics of chemical reactions, with specific interest for application to polyatomic molecular systems of special interest and relevance. There is interest in developing the most rigorous possible theoretical approaches and also in more approximate treatments that are more readily applicable to complex systems.

  8. Chemical Characterization and Reactivity of Fuel-Oxidizer Reaction Product

    Science.gov (United States)

    David, Dennis D.; Dee, Louis A.; Beeson, Harold D.

    1997-01-01

    Fuel-oxidizer reaction product (FORP), the product of incomplete reaction of monomethylhydrazine and nitrogen tetroxide propellants prepared under laboratory conditions and from firings of Shuttle Reaction Control System thrusters, has been characterized by chemical and thermal analysis. The composition of FORP is variable but falls within a limited range of compositions that depend on three factors: the fuel-oxidizer ratio at the time of formation; whether the composition of the post-formation atmosphere is reducing or oxidizing; and the reaction or post-reaction temperature. A typical composition contains methylhydrazinium nitrate, ammonium nitrate, methylammonium nitrate, and trace amounts of hydrazinium nitrate and 1,1-dimethylhydrazinium nitrate. Thermal decomposition reactions of the FORP compositions used in this study were unremarkable. Neither the various compositions of FORP, the pure major components of FORP, nor mixtures of FORP with propellant system corrosion products showed any unusual thermal activity when decomposed under laboratory conditions. Off-limit thruster operations were simulated by rapid mixing of liquid monomethylhydrazine and liquid nitrogen tetroxide in a confined space. These tests demonstrated that monomethylhydrazine, methylhydrazinium nitrate, ammonium nitrate, or Inconel corrosion products can induce a mixture of monomethylhydrazine and nitrogen tetroxide to produce component-damaging energies. Damaging events required FORP or metal salts to be present at the initial mixing of monomethylhydrazine and nitrogen tetroxide.

  9. Cellular automaton model of mass transport with chemical reactions

    International Nuclear Information System (INIS)

    The transport and chemical reactions of solutes are modelled as a cellular automaton in which molecules of different species perform a random walk on a regular lattice and react according to a local probabilistic rule. The model describes advection and diffusion in a simple way, and as no restriction is placed on the number of particles at a lattice site, it is also able to describe a wide variety of chemical reactions. Assuming molecular chaos and a smooth density function, we obtain the standard reaction-transport equations in the continuum limit. Simulations on one-and two-dimensional lattices show that the discrete model can be used to approximate the solutions of the continuum equations. We discuss discrepancies which arise from correlations between molecules and how these discrepancies disappear as the continuum limit is approached. Of particular interest are simulations displaying long-time behaviour which depends on long-wavelength statistical fluctuations not accounted for by the standard equations. The model is applied to the reactions a + b ↔ c and a + b → c with homogeneous and inhomogeneous initial conditions as well as to systems subject to autocatalytic reactions and displaying spontaneous formation of spatial concentration patterns. (author) 9 figs., 34 refs

  10. Deterministic Function Computation with Chemical Reaction Networks

    CERN Document Server

    Chen, Ho-Lin; Soloveichik, David

    2012-01-01

    We study the deterministic computation of functions on tuples of natural numbers by chemical reaction networks (CRNs). CRNs have been shown to be efficiently Turing-universal when allowing for a small probability of error. CRNs that are guaranteed to converge on a correct answer, on the other hand, have been shown to decide only the semilinear predicates. We introduce the notion of function, rather than predicate, computation by representing the output of a function f:N^k --> N^l by a count of some molecular species, i.e., if the CRN starts with n_1,...,n_k molecules of some "input" species X_1,...,X_k, the CRN is guaranteed to converge to having f(n_1,...,n_k) molecules of the "output" species Y_1,...,Y_l. We show that a function f:N^k --> N^l is deterministically computed by a CRN if and only if its graph {(x,y) \\in N^k x N^l | f(x) = y} is a semilinear set. Finally, we show that each semilinear function f can be computed on input x in expected time O(polylog |x|).

  11. Flows and chemical reactions in an electromagnetic field

    CERN Document Server

    Prud'homme, Roger

    2014-01-01

    This book - a sequel of previous publications 'Flows and Chemical Reactions', 'Chemical Reactions Flows in Homogeneous Mixtures' and 'Chemical Reactions and Flows in Heterogeneous Mixtures' - is devoted to flows with chemical reactions in the electromagnetic field. The first part, entitled basic equations, consists of four chapters. The first chapter provides an overview of the equations of electromagnetism in Minkowski spacetime. This presentation is extended to balance equations, first in homogeneous media unpolarized in the second chapter and homogeneous fluid medium polarized in the thir

  12. Mechanisms of chemical reaction initiated by recoil implantation

    International Nuclear Information System (INIS)

    Mechanisms of chemical reactions initiated by recoil implantation were studied in the systems 51Cr+M(acac)3 yields 51Cr(acac)3 where M is a trivalent metal. The yield of 51Cr(acac)3 increased linearly with an increase of inverse of the force constant of metal-oxygen bonding K(M-O). This indicates that there is competition between the implanted 51Cr atom and M. However, exception for this trend was the case of Co(acac)3 catcher, for which the yield of 51Cr(acac)3 was much higher than that expected for a competition reaction. Complex features of the replacement reaction caused by implantation are discussed

  13. Chemical morphogenesis: turing patterns in an experimental chemical system.

    Science.gov (United States)

    Dulos, E; Boissonade, J; Perraud, J J; Rudovics, B; De Kepper, P

    1996-11-01

    Patterns resulting from the sole interplay between reaction and diffusion are probably involved in certain stages of morphogenesis in biological systems, as initially proposed by Alan Turing. Self-organization phenomena of this type can only develop in nonlinear systems (i.e. involving positive and negative feedback loops) maintained far from equilibrium. We present Turing patterns experimentally observed in a chemical system. An oscillating chemical reaction, the CIMA reaction, is operated in an open spatial reactor designed in order to obtain a pure reaction-diffusion system. The two types of Turing patterns observed, hexagonal arrays of spots and parallel stripes, are characterized by an intrinsic wavelength. We identify the origin of the necessary diffusivity between activator and inhibitor. We also describe a pattern growth mechanism by spot splitting that recalls cell division. PMID:8953211

  14. Quantum mechanical calculations of vibrational population inversion in chemical reactions - Numerically exact L-squared-amplitude-density study of the H2Br reactive system

    Science.gov (United States)

    Zhang, Y. C.; Zhang, J. Z. H.; Kouri, D. J.; Haug, K.; Schwenke, D. W.

    1988-01-01

    Numerically exact, fully three-dimensional quantum mechanicl reactive scattering calculations are reported for the H2Br system. Both the exchange (H + H-prime Br to H-prime + HBr) and abstraction (H + HBR to H2 + Br) reaction channels are included in the calculations. The present results are the first completely converged three-dimensional quantum calculations for a system involving a highly exoergic reaction channel (the abstraction process). It is found that the production of vibrationally hot H2 in the abstraction reaction, and hence the extent of population inversion in the products, is a sensitive function of initial HBr rotational state and collision energy.

  15. Incidents of chemical reactions in cell equipment

    Energy Technology Data Exchange (ETDEWEB)

    Baldwin, N.M.; Barlow, C.R. [Uranium Enrichment Organization, Oak Ridge, TN (United States)

    1991-12-31

    Strongly exothermic reactions can occur between equipment structural components and process gases under certain accident conditions in the diffusion enrichment cascades. This paper describes the conditions required for initiation of these reactions, and describes the range of such reactions experienced over nearly 50 years of equipment operation in the US uranium enrichment program. Factors are cited which can promote or limit the destructive extent of these reactions, and process operations are described which are designed to control the reactions to minimize equipment damage, downtime, and the possibility of material releases.

  16. Control of Ultracold Chemical Reactions Through Conical Intersections

    Science.gov (United States)

    Makrides, Constantinos; Petrov, Alexander; Kotochigova, Svetlana

    2016-05-01

    The pioneering work on obtaining a quantum degenerate sample of ground state KRb molecules is one of the great successes in ultracold physics. The early experimental and theoretical investigations to describe quantum chemical reactions of ultracold KRb molecules with residual ultracold K atoms have been based on probing their inelastic collision loss rates. A natural progression towards control of molecular reactivity would be to study the potential landscape of the collisional complex with the inherited degeneracies and intersections between two lowest electronic states. The topology of these surfaces provide us with a qualitative understanding of the reaction mechanism. Here we study how the ability to prepare unique initial states combined with the presence of conical intersections can be used to control the outcome of ultracold chemical reactions of alkali-metal atoms and molecules. We locate and determine properties of conical intersections for the KRbK molecular system and determine signatures of non-adiabatic passage through the conical intersection to distinguish between relaxation and reaction pathways. This work is supported by the ARO-MURI and NSF Grants.

  17. Stereodynamics: From elementary processes to macroscopic chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Kasai, Toshio [Department of Chemistry, National Taiwan University, Taipei 106, Taiwan (China); Graduate School of Science, Department of Chemistry, Osaka University, Toyonaka, 560-0043 Osaka (Japan); Che, Dock-Chil [Graduate School of Science, Department of Chemistry, Osaka University, Toyonaka, 560-0043 Osaka (Japan); Tsai, Po-Yu [Department of Chemistry, National Taiwan University, Taipei 106, Taiwan (China); Department of Chemistry, National Chung Hsing University, Taichung 402, Taiwan (China); Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan (China); Lin, King-Chuen [Department of Chemistry, National Taiwan University, Taipei 106, Taiwan (China); Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan (China); Palazzetti, Federico [Scuola Normale Superiore, Pisa (Italy); Dipartimento di Chimica Biologia e Biotecnologie, Università di Perugia, 06123 Perugia (Italy); Aquilanti, Vincenzo [Dipartimento di Chimica Biologia e Biotecnologie, Università di Perugia, 06123 Perugia (Italy); Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Roma (Italy); Instituto de Fisica, Universidade Federal da Bahia, Salvador (Brazil)

    2015-12-31

    This paper aims at discussing new facets on stereodynamical behaviors in chemical reactions, i.e. the effects of molecular orientation and alignment on reactive processes. Further topics on macroscopic processes involving deviations from Arrhenius behavior in the temperature dependence of chemical reactions and chirality effects in collisions are also discussed.

  18. Stereodynamics: From elementary processes to macroscopic chemical reactions

    International Nuclear Information System (INIS)

    This paper aims at discussing new facets on stereodynamical behaviors in chemical reactions, i.e. the effects of molecular orientation and alignment on reactive processes. Further topics on macroscopic processes involving deviations from Arrhenius behavior in the temperature dependence of chemical reactions and chirality effects in collisions are also discussed

  19. Design criteria for extraction with chemical reaction and liquid membrane permeation

    Science.gov (United States)

    Bart, H. J.; Bauer, A.; Lorbach, D.; Marr, R.

    1988-01-01

    The design criteria for heterogeneous chemical reactions in liquid/liquid systems formally correspond to those of classical physical extraction. More complex models are presented which describe the material exchange at the individual droplets in an extraction with chemical reaction and in liquid membrane permeation.

  20. Fixed Points for Stochastic Open Chemical Systems

    CERN Document Server

    Malyshev, V A

    2011-01-01

    In the first part of this paper we give a short review of the hierarchy of stochastic models, related to physical chemistry. In the basement of this hierarchy there are two models --- stochastic chemical kinetics and the Kac model for Boltzman equation. Classical chemical kinetics and chemical thermodynamics are obtained as some scaling limits in the models, introduced below. In the second part of this paper we specify some simple class of open chemical reaction systems, where one can still prove the existence of attracting fixed points. For example, Michaelis\\tire Menten kinetics belongs to this class. At the end we present a simplest possible model of the biological network. It is a network of networks (of closed chemical reaction systems, called compartments), so that the only source of nonreversibility is the matter exchange (transport) with the environment and between the compartments. Keywords: chemical kinetics, chemical thermodynamics, Kac model, mathematical biology

  1. Transient assembly of active materials fueled by a chemical reaction

    Science.gov (United States)

    Boekhoven, Job; Hendriksen, Wouter E.; Koper, Ger J. M.; Eelkema, Rienk; van Esch, Jan H.

    2015-09-01

    Fuel-driven self-assembly of actin filaments and microtubules is a key component of cellular organization. Continuous energy supply maintains these transient biomolecular assemblies far from thermodynamic equilibrium, unlike typical synthetic systems that spontaneously assemble at thermodynamic equilibrium. Here, we report the transient self-assembly of synthetic molecules into active materials, driven by the consumption of a chemical fuel. In these materials, reaction rates and fuel levels, instead of equilibrium composition, determine properties such as lifetime, stiffness, and self-regeneration capability. Fibers exhibit strongly nonlinear behavior including stochastic collapse and simultaneous growth and shrinkage, reminiscent of microtubule dynamics.

  2. Computational molecular technology towards macroscopic chemical phenomena-molecular control of complex chemical reactions, stereospecificity and aggregate structures

    International Nuclear Information System (INIS)

    A new efficient hybrid Monte Carlo (MC)/molecular dynamics (MD) reaction method with a rare event-driving mechanism is introduced as a practical ‘atomistic’ molecular simulation of large-scale chemically reactive systems. Starting its demonstrative application to the racemization reaction of (R)-2-chlorobutane in N,N-dimethylformamide solution, several other applications are shown from the practical viewpoint of molecular controlling of complex chemical reactions, stereochemistry and aggregate structures. Finally, I would like to mention the future applications of the hybrid MC/MD reaction method

  3. Variable elimination in chemical reaction networks with mass action kinetics

    CERN Document Server

    Feliu, Elisenda

    2011-01-01

    We consider chemical reaction networks taken with mass action kinetics. The steady states of such a system are solutions to a system of polynomial equations. Even for small systems the task of finding the solutions is daunting. We develop an algebraic framework and procedure for linear elimination of variables. The procedure reduces the variables in the system to a set of "core" variables by eliminating variables corresponding to a set of non-interacting species. The steady states are parameterized algebraically by the core variables, and a graphical condition is given for when a steady state with positive core variables necessarily have all variables positive. Further, we characterize graphically the sets of eliminated variables that are constrained by a conservation law and show that this conservation law takes a specific form.

  4. Miscible viscous fingering involving production of gel by chemical reactions

    Science.gov (United States)

    Nagatsu, Yuichiro; Hoshino, Kenichi

    2015-11-01

    We have experimentally investigated miscible viscous fingering with chemical reactions producing gel. Here, two systems were employed. In one system, sodium polyacrylate (SPA) solution and aluminum ion (Al3 +) solution were used as the more and less viscous liquids, respectively. In another system, SPA solution and ferric ion (Fe3 +) solution were used as the more and less viscous liquids, respectively. In the case of Al3 +, displacement efficiency was smaller than that in the non-reactive case, whereas in the case of Fe3 +, the displacement efficiency was larger. We consider that the difference in change of the patterns in the two systems will be caused by the difference in the properties of the gels. Therefore, we have measured the rheological properties of the gels by means of a rheometer. We discuss relationship between the VF patterns and the rheological measurement.

  5. Non-equilibrium effects in high temperature chemical reactions

    Science.gov (United States)

    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.

  6. Communication: Control of chemical reactions using electric field gradients.

    Science.gov (United States)

    Deshmukh, Shivaraj D; Tsori, Yoav

    2016-05-21

    We examine theoretically a new idea for spatial and temporal control of chemical reactions. When chemical reactions take place in a mixture of solvents, an external electric field can alter the local mixture composition, thereby accelerating or decelerating the rate of reaction. The spatial distribution of electric field strength can be non-trivial and depends on the arrangement of the electrodes producing it. In the absence of electric field, the mixture is homogeneous and the reaction takes place uniformly in the reactor volume. When an electric field is applied, the solvents separate and the reactants are concentrated in the same phase or separate to different phases, depending on their relative miscibility in the solvents, and this can have a large effect on the kinetics of the reaction. This method could provide an alternative way to control runaway reactions and to increase the reaction rate without using catalysts. PMID:27208928

  7. Communication: Control of chemical reactions using electric field gradients

    Science.gov (United States)

    Deshmukh, Shivaraj D.; Tsori, Yoav

    2016-05-01

    We examine theoretically a new idea for spatial and temporal control of chemical reactions. When chemical reactions take place in a mixture of solvents, an external electric field can alter the local mixture composition, thereby accelerating or decelerating the rate of reaction. The spatial distribution of electric field strength can be non-trivial and depends on the arrangement of the electrodes producing it. In the absence of electric field, the mixture is homogeneous and the reaction takes place uniformly in the reactor volume. When an electric field is applied, the solvents separate and the reactants are concentrated in the same phase or separate to different phases, depending on their relative miscibility in the solvents, and this can have a large effect on the kinetics of the reaction. This method could provide an alternative way to control runaway reactions and to increase the reaction rate without using catalysts.

  8. Visualizing chemical reactions confined under graphene.

    Science.gov (United States)

    Mu, Rentao; Fu, Qiang; Jin, Li; Yu, Liang; Fang, Guangzong; Tan, Dali; Bao, Xinhe

    2012-05-14

    An undercover agent: graphene has been used as an imaging agent to visualize interfacial reactions under its cover, and exhibits a strong confinement effect on the chemistry of molecules underneath. In a CO atmosphere, CO penetrates into the graphene/Pt(111) interface and reacts with O(2) therein, whereas intercalated CO desorbs from the Pt surface. PMID:22492473

  9. Charge exchange and chemical reactions with trapped Th3+

    International Nuclear Information System (INIS)

    We have measured the reaction rates of trapped, buffer gas cooled Th3+ and various gases and have analyzed the reaction products using trapped ion mass spectrometry techniques. Ion trap lifetimes are usually limited by reactions with background molecules, and the high electron affinity of multiply charged ions such as Th3+ make them more prone to loss. Our results show that reactions of Th3+ with carbon dioxide, methane, and oxygen all occur near the classical Langevin rate, while reaction rates with argon, hydrogen, and nitrogen are orders of magnitude lower. Reactions of Th3+ with oxygen and methane proceed primarily via charge exchange, while simultaneous charge exchange and chemical reaction occurs between Th3+ and carbon dioxide. Loss rates of Th3+ in helium are consistent with reaction with impurities in the gas. Reaction rates of Th3+ with nitrogen and argon depend on the internal electronic configuration of the Th3+.

  10. Charge Exchange and Chemical Reactions with Trapped Th$^{3+}$

    CERN Document Server

    Churchill, L R; Chapman, M S

    2010-01-01

    We have measured the reaction rates of trapped, buffer gas cooled Th$^{3+}$ and various gases and have analyzed the reaction products using trapped ion mass spectrometry techniques. Ion trap lifetimes are usually limited by reactions with background molecules, and the high electron affinity of multiply charged ions such as Th$^{3+}$ make them more prone to loss. Our results show that reactions of Th$^{3+}$ with carbon dioxide, methane, and oxygen all occur near the classical Langevin rate, while reaction rates with argon, hydrogen, and nitrogen are orders of magnitude lower. Reactions of Th$^{3+}$ with oxygen and methane proceed primarily via charge exchange, while simultaneous charge exchange and chemical reaction occurs between Th$^{3+}$ and carbon dioxide. Loss rates of Th$^{3+}$ in helium are consistent with reaction with impurities in the gas. Reaction rates of Th$^{3+}$ with nitrogen and argon depend on the internal electronic configuration of the Th$^{3+}$.

  11. Pyrimidine-specific chemical reactions useful for DNA sequencing.

    OpenAIRE

    Rubin, C M; Schmid, C. W.

    1980-01-01

    Potassium permanganate reacts selectively with thymidine residues in DNA (1) while hydroxylamine hydrochloride at pH 6 specifically attacks cytosine (2). We have adopted these reactions for use with the chemical sequencing method developed by Maxam and Gilbert (3).

  12. CHEMICAL REACTIONS SIMULATED BY GROUND-WATER-QUALITY MODELS.

    Science.gov (United States)

    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.

  13. Dynamical resonance in F+H2 chemical reaction and rotational excitation effect

    Institute of Scientific and Technical Information of China (English)

    YANG XueMing; XIE DaiQian; ZHANG DongHui

    2007-01-01

    Reaction resonance is a frontier topic in chemical dynamics research, and it is also essential to the understanding of mechanisms of elementary chemical reactions. This short article describes an important development in the frontier of research. Experimental evidence of reaction resonance has been detected in a full quantum state resolved reactive scattering study of the F+H2 reaction. Highly accurate full quantum scattering theoretical modeling shows that the reaction resonance is caused by two Feshbach resonance states. Further studies show that quantum interference is present between the two resonance states for the forward scattering product. This study is a significant step forward in our understanding of chemical reaction resonance in the benchmark F+H2 system. Further experimental studies on the effect of H2 rotational excitation on dynamical resonance have been carried out. Dynamical resonance in the F+H2 (j = 1) reaction has also been observed.

  14. Electronic dissipation processes during chemical reactions on surfaces

    CERN Document Server

    Stella, Kevin

    2012-01-01

    Hauptbeschreibung Every day in our life is larded with a huge number of chemical reactions on surfaces. Some reactions occur immediately, for others an activation energy has to be supplied. Thus it happens that though a reaction should thermodynamically run off, it is kinetically hindered. Meaning the partners react only to the thermodynamically more stable product state within a mentionable time if the activation energy of the reaction is supplied. With the help of catalysts the activation energy of a reaction can be lowered. Such catalytic processes on surfaces are widely used in industry. A

  15. Physical Chemistry Chemical Kinetics and Reaction Mechanism

    CERN Document Server

    Trimm, Harold H

    2011-01-01

    Physical chemistry covers diverse topics, from biochemistry to materials properties to the development of quantum computers. Physical chemistry applies physics and math to problems that interest chemists, biologists, and engineers. Physical chemists use theoretical constructs and mathematical computations to understand chemical properties and describe the behavior of molecular and condensed matter. Their work involves manipulations of data as well as materials. Physical chemistry entails extensive work with sophisticated instrumentation and equipment as well as state-of-the-art computers. This

  16. Reaction path analysis of sodium-water chemical reaction field using laser diagnostics

    International Nuclear Information System (INIS)

    In a sodium-cooled fast reactor (SFR), liquid sodium is used as a heat transfer fluid because of its excellent heat transport capability. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow by a breach of heat transfer tubes. Therefore, the study on sodium-water chemical reactions is of importance for security reasons. This study aims to clarify the gas phase sodium-water reaction path and reaction products. Na, Na2, H2O, and reaction products in the counter-flow sodium-water reaction field were measured using laser diagnostics such as Raman scattering and photo-fragmentation. The main product in the sodium-water reaction was determined to be NaOH and its reaction path was discussed using Na-H2O elementally reaction analysis. (author)

  17. Quantum Chemical Approach to Estimating the Thermodynamics of Metabolic Reactions

    Science.gov (United States)

    Jinich, Adrian; Rappoport, Dmitrij; Dunn, Ian; Sanchez-Lengeling, Benjamin; Olivares-Amaya, Roberto; Noor, Elad; Even, Arren Bar; Aspuru-Guzik, Alán

    2014-11-01

    Thermodynamics plays an increasingly important role in modeling and engineering metabolism. We present the first nonempirical computational method for estimating standard Gibbs reaction energies of metabolic reactions based on quantum chemistry, which can help fill in the gaps in the existing thermodynamic data. When applied to a test set of reactions from core metabolism, the quantum chemical approach is comparable in accuracy to group contribution methods for isomerization and group transfer reactions and for reactions not including multiply charged anions. The errors in standard Gibbs reaction energy estimates are correlated with the charges of the participating molecules. The quantum chemical approach is amenable to systematic improvements and holds potential for providing thermodynamic data for all of metabolism.

  18. Chemical reactions driven by concentrated solar energy

    Science.gov (United States)

    Levy, Moshe

    Solar energy can be used for driving endothermic reactions, either photochemically or thermally. The fraction of the solar spectrum that can be photochemically active is quite small. Therefore, it is desirable to be able to combine photochemical and thermal processes in order to increase the overall efficiency. Two thermally driven reactions are being studied: oil shale gasification and methane reforming. In both cases, the major part of the work was done in opaque metal reactors where photochemical reactions cannot take place. We then proceeded working in transparent quartz reactors. The results are preliminary, but they seem to indicate that there may be some photochemical enhancement. The experimental solar facilities used for this work include the 30 kW Schaeffer Solar Furnace and the 3 MW Solar Central Receiver in operation at the Weizmann Institute. The furnace consists of a 96 sq. m flat heliostat, that follows the sun by computer control. It reflects the solar radiation onto a spherical concentrator, 7.3 m in diameter, with a rim angle of 65 degrees. The furnace was characterized by radiometric and calorimetric measurements to show a solar concentration ratio of over 10,000 suns. The central receiver consists of 64 concave heliostats, 54 sq. m each, arranged in a north field and facing a 52 m high tower. The tower has five target levels that can be used simultaneously. The experiments with the shale gasification were carried out at the lowest level, 20 m above ground, which has the lowest solar efficiency and is assigned for low power experiments. We used secondary concentrators to boost the solar flux.

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

    Science.gov (United States)

    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…

  20. A network dynamics approach to chemical reaction networks

    NARCIS (Netherlands)

    van der Schaft, Abraham; Rao, S.; Jayawardhana, B.

    2016-01-01

    A treatment of chemical reaction network theory is given from the perspective of nonlinear network dynamics, in particular of consensus dynamics. By starting from the complex-balanced assumption the reaction dynamics governed by mass action kinetics can be rewritten into a form which allows for a ve

  1. Open complex-balanced mass action chemical reaction networks

    NARCIS (Netherlands)

    Rao, Shodhan; van der Schaft, Arjan; Jayawardhana, Bayu

    2014-01-01

    We consider open chemical reaction networks, i.e. ones with inflows and outflows. We assume that all the inflows to the network are constant and all outflows obey the mass action kinetics rate law. We define a complex-balanced open reaction network as one that admits a complex-balanced steady state.

  2. Chemical Reaction of In-situ Processing of NiAl/Al2O3 Composite by Using Thermite Reaction

    Institute of Scientific and Technical Information of China (English)

    LIU Yin; FAN Xiaonan; ZHANG Mingxu; QIN Xiaoying

    2005-01-01

    NiAl / Al2O3 composite were synthesized by thermite reaction of nickel oxide and aluminum powder mixtures. The phase, the microstructure of the composite, as well as the thermite reaction mechanism, were investigated by X-ray diffractometry ( XRD ), scanning electron microscopy (SEM) combined with differential scanning calorimetry ( DSC). The experimental results show that the thermite reaction leads to the interpenetrating network structure of NiAl/Al2O3 at 1223K for 60min and the chemical reaction apparent activation energy is Eap = 166.960± 13.496 kJ· mol-1 in the NiO/Al system.

  3. Results of the 2010 Survey on Teaching Chemical Reaction Engineering

    Science.gov (United States)

    Silverstein, David L.; Vigeant, Margot A. S.

    2012-01-01

    A survey of faculty teaching the chemical reaction engineering course or sequence during the 2009-2010 academic year at chemical engineering programs in the United States and Canada reveals change in terms of content, timing, and approaches to teaching. The report consists of two parts: first, a statistical and demographic characterization of the…

  4. On the Complexity of Reconstructing Chemical Reaction Networks

    DEFF Research Database (Denmark)

    Fagerberg, Rolf; Flamm, Christoph; Merkle, Daniel;

    2013-01-01

    The analysis of the structure of chemical reaction networks is crucial for a better understanding of chemical processes. Such networks are well described as hypergraphs. However, due to the available methods, analyses regarding network properties are typically made on standard graphs derived from...... the full hypergraph description, e.g. on the so-called species and reaction graphs. However, a reconstruction of the underlying hypergraph from these graphs is not necessarily unique. In this paper, we address the problem of reconstructing a hypergraph from its species and reaction graph and show NP...

  5. Use of radioactive tracers in chemical reactions

    International Nuclear Information System (INIS)

    A method for the determination of small quantities of nickel using radioactive tracers is presented. An analytical application of the displacement reaction between nickel and zinc ethylenediaminetetraacetate labeled with zinc-65 is pursued. This method is based on the extraction of radioactive zinc displaced by nickel from the zinc chelate into a dithizone-carbon tetracloride solution and the subsequent measurement of the activity of an aliquot of the extract. The method is very sensitive and nickel can be measured in concentrations as small as 0.1μg/ml or even less, depending on the specific activity of the radioreagent used. The precision and the accuracy of the method are determined. The problem of interferences, trying to eliminate them by using masking agents or by means of a previous separation between nickel and other interfering metals, is also investigated

  6. A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions.

    Science.gov (United States)

    Brack, Paul; Dann, Sandie; Wijayantha, K G Upul; Adcock, Paul; Foster, Simon

    2016-01-01

    There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) hydrogen fuel cells. Researchers seeking to develop such systems require a method of measuring the generated hydrogen. Herein, we describe a simple, low-cost, and robust method to measure the hydrogen generated from the reaction of solids with aqueous solutions. The reactions are conducted in a conventional one-necked round-bottomed flask placed in a temperature controlled water bath. The hydrogen generated from the reaction in the flask is channeled through tubing into a water-filled inverted measuring cylinder. The water displaced from the measuring cylinder by the incoming gas is diverted into a beaker on a balance. The balance is connected to a computer, and the change in the mass reading of the balance over time is recorded using data collection and spreadsheet software programs. The data can then be approximately corrected for water vapor using the method described herein, and parameters such as the total hydrogen yield, the hydrogen generation rate, and the induction period can also be deduced. The size of the measuring cylinder and the resolution of the balance can be changed to adapt the setup to different hydrogen volumes and flow rates. PMID:27584581

  7. Chemical kinetic reaction mechanism for the combustion of propane

    Science.gov (United States)

    Jachimowski, C. J.

    1984-01-01

    A detailed chemical kinetic reaction mechanism for the combustion of propane is presented and discussed. The mechanism consists of 27 chemical species and 83 elementary chemical reactions. Ignition and combustion data as determined in shock tube studies were used to evaluate the mechanism. Numerical simulation of the shock tube experiments showed that the kinetic behavior predicted by the mechanism for stoichiometric mixtures is in good agrement with the experimental results over the entire temperature range examined (1150-2600K). Sensitivity and theoretical studies carried out using the mechanism revealed that hydrocarbon reactions which are involved in the formation of the HO2 radical and the H2O2 molecule are very important in the mechanism and that the observed nonlinear behavior of ignition delay time with decreasing temperature can be interpreted in terms of the increased importance of the HO2 and H2O2 reactions at the lower temperatures.

  8. Numerical simulation of rising bubble with chemical reaction

    Science.gov (United States)

    Sahu, Kirti; Tripathi, Manoj; Matar, Omar; Karapetsas, George

    2014-11-01

    The dynamics of a rising bubble under the action of gravity and in the presence of an exothermic chemical reaction at the interface is investigated via direct numerical simulation using Volume-of-Fluid (VOF) method. The product of the chemical reaction, and temperature rise due to the exothermic chemical reaction influence the local viscosity and surface tension near the interfacial region, which in turn give rise to many interesting dynamics. The flow is governed by continuity, Navier-Stokes equations along with the convection equation of the volume fraction of the outer fluid and the energy equation. The effects of the Bond, Damkohler, and Reynolds numbers, and of the dimensionless heat of reaction are investigated. The results of this parametric study will be presented at the meeting.

  9. Chemical reaction between single hydrogen atom and graphene

    International Nuclear Information System (INIS)

    We study chemical reaction between a single hydrogen atom and a graphene, which is the elemental reaction between hydrogen and graphitic carbon materials. In the present work, classical molecular dynamics simulation is used with modified Brenner's empirical bond order potential. The three reactions, that is, absorption reaction, reflection reaction and penetration reaction, are observed in our simulation. Reaction rates depend on the incident energy of the hydrogen atom and the graphene temperature. The dependence can be explained by the following mechanisms: (1) The hydrogen atom receives repulsive force by π-electrons in addition to nuclear repulsion. (2) Absorbing the hydrogen atom, the graphene transforms its structure to the 'overhand' configuration such as sp3 state. (3) The hexagonal hole of the graphene is expanded during the penetration of the hydrogen atom. (author)

  10. Chemical reactions of excited nitrogen atoms for short wavelength chemical lasers. Final technical report

    Energy Technology Data Exchange (ETDEWEB)

    1989-12-15

    Accomplishments of this program include the following: (1) Scalable, chemical generation of oxygen atoms by reaction of fluorine atoms and water vapor. (2) Production of nitrogen atom densities of 1 {times} 10{sup 1}5 cm{sup {minus}3} with 5% electrical efficiency by injecting trace amounts of fluorine into microwave discharged nitrogen. (3) Production of cyanide radicals by reaction of high densities of N atoms with cyanogen. (4) Production of carbon atoms by reaction of nitrogen atoms with cyanogen or with fluorine atoms and hydrogen cyanide. (5) Confirmation that the reaction of carbon atoms and carbonyl sulfide produces CS(a{sup 3} {Pi}{sub r}), as predicted by conservation of electron spin and orbital angular momenta and as proposed by others under another SWCL program. (6) Production of cyanide radicals by injection of cyanogen halides into active nitrogen and use as spectroscopic calibration source. (7) Demonstration that sodium atoms react with cyanogen chloride, bromide and iodide and with cyanuric trifluoride to produce cyanide radicals. (8) Demonstration of the potential utility of the fluorine atom plus ammonia reaction system in the production of NF(b{sup l}{Sigma}{sup +}) via N({sup 2}D) + F{sub 2}.

  11. Isotope effects of sulfur in chemical reactions

    International Nuclear Information System (INIS)

    Sulfur is an important component of organic matter because it forms compounds with many elements. Due to high chemical activity of sulfur, it takes part in biological and geological processes in which isotope effects are occurring. It has been shown during last years research of isotope effects that we have take into account not only mass difference but also many other physical properties of nuclides e.g. even or odd number of neutrons in nuclei, shape and distribution of charge, turn of nuclear spin etc. The factor remains that new theoretical ideas have been formed on the base of data, being obtained in fractionation processes of heavy element isotope, particularly uranium. Now it is being well known that effects unconnected with vibration energy have also caused an effect on fractionation of considerably lighter elements like iron and magnesium. The important question is, if these effects would come to light during the separation of sulfur isotopes. Sulfur have three even isotopes M = (32, 34, 36) and one odd M 33). This problem is still open. (author)

  12. LSENS, a general chemical kinetics and sensitivity analysis code for gas-phase reactions: User's guide

    Science.gov (United States)

    Radhakrishnan, Krishnan; Bittker, David A.

    1993-01-01

    A general chemical kinetics and sensitivity analysis code for complex, homogeneous, gas-phase reactions is described. The main features of the code, LSENS, are its flexibility, efficiency and convenience in treating many different chemical reaction models. The models include static system, steady, one-dimensional, inviscid flow, shock initiated reaction, and a perfectly stirred reactor. In addition, equilibrium computations can be performed for several assigned states. An implicit numerical integration method, which works efficiently for the extremes of very fast and very slow reaction, is used for solving the 'stiff' differential equation systems that arise in chemical kinetics. For static reactions, sensitivity coefficients of all dependent variables and their temporal derivatives with respect to the initial values of dependent variables and/or the rate coefficient parameters can be computed. This paper presents descriptions of the code and its usage, and includes several illustrative example problems.

  13. Multispecies reaction-diffusion systems

    OpenAIRE

    Aghamohammadi, A.; Fatollahi, A. H.; Khorrami, M.; Shariati, A.

    2000-01-01

    Multispecies reaction-diffusion systems, for which the time evolution equation of correlation functions become a closed set, are considered. A formal solution for the average densities is found. Some special interactions and the exact time dependence of the average densities in these cases are also studied. For the general case, the large time behaviour of the average densities has also been obtained.

  14. Matrix isolation as a tool for studying interstellar chemical reactions

    Science.gov (United States)

    Ball, David W.; Ortman, Bryan J.; Hauge, Robert H.; Margrave, John L.

    1989-01-01

    Since the identification of the OH radical as an interstellar species, over 50 molecular species were identified as interstellar denizens. While identification of new species appears straightforward, an explanation for their mechanisms of formation is not. Most astronomers concede that large bodies like interstellar dust grains are necessary for adsorption of molecules and their energies of reactions, but many of the mechanistic steps are unknown and speculative. It is proposed that data from matrix isolation experiments involving the reactions of refractory materials (especially C, Si, and Fe atoms and clusters) with small molecules (mainly H2, H2O, CO, CO2) are particularly applicable to explaining mechanistic details of likely interstellar chemical reactions. In many cases, matrix isolation techniques are the sole method of studying such reactions; also in many cases, complexations and bond rearrangements yield molecules never before observed. The study of these reactions thus provides a logical basis for the mechanisms of interstellar reactions. A list of reactions is presented that would simulate interstellar chemical reactions. These reactions were studied using FTIR-matrix isolation techniques.

  15. The role of van der Waals interactions in chemical reactions

    International Nuclear Information System (INIS)

    We are studying the role of van der Waals interactions in the chemical reactions from the theoretical view point, especially, a case related to the tunnel effect. The fist case that the cumulative reaction probability depends on the tunnel effect was increased by the van der waals force. This case was proved by theoretical calculation of the reaction rate constant of the reaction: Mu + F2 → MuF + F. The second case was that a van der Waals well was so deep that pseudo bound state was observed in the reaction: F + H2 → HF + H. A van der Waals complex such as AB(v=j=0)...C was excited to the resonance state of AB(vij)...C and A...BC(v,j) by laser, than the resonance state proceeded to AB + C (predissociation) or A + BC(pre-reaction). We succeeded for the first time to calculate theoretically the pre-reaction by the real three dimentional potential curve. The pre-reaction can be observed only the case that the tunnel probability is larger than the non-adiabatic transition probability. The chemical reactions in solid were explained, too. (S.Y.)

  16. An Efficient Chemical Reaction Optimization Algorithm for Multiobjective Optimization.

    Science.gov (United States)

    Bechikh, Slim; Chaabani, Abir; Ben Said, Lamjed

    2015-10-01

    Recently, a new metaheuristic called chemical reaction optimization was proposed. This search algorithm, inspired by chemical reactions launched during collisions, inherits several features from other metaheuristics such as simulated annealing and particle swarm optimization. This fact has made it, nowadays, one of the most powerful search algorithms in solving mono-objective optimization problems. In this paper, we propose a multiobjective variant of chemical reaction optimization, called nondominated sorting chemical reaction optimization, in an attempt to exploit chemical reaction optimization features in tackling problems involving multiple conflicting criteria. Since our approach is based on nondominated sorting, one of the main contributions of this paper is the proposal of a new quasi-linear average time complexity quick nondominated sorting algorithm; thereby making our multiobjective algorithm efficient from a computational cost viewpoint. The experimental comparisons against several other multiobjective algorithms on a variety of benchmark problems involving various difficulties show the effectiveness and the efficiency of this multiobjective version in providing a well-converged and well-diversified approximation of the Pareto front. PMID:25373137

  17. Plasma-chemical processes and systems

    International Nuclear Information System (INIS)

    The direct applications of plasma technology on chemistry and metallurgy are presented. The physical fundaments of chemically active non-equilibrium plasma, the reaction kinetics, and the physical chemical transformations occuring in the electrical discharges, which are applied in the industry, are analysed. Some plasma chemical systems and processes related to the energy of hydrogen, with the chemical technology and with the metallurgy are described. Emphasis is given to the optimization of the energy effectiveness of these processes to obtain reducers and artificial energetic carriers. (M.C.K.)

  18. Reaction Mechanism Generator: Automatic construction of chemical kinetic mechanisms

    Science.gov (United States)

    Gao, Connie W.; Allen, Joshua W.; Green, William H.; West, Richard H.

    2016-06-01

    Reaction Mechanism Generator (RMG) constructs kinetic models composed of elementary chemical reaction steps using a general understanding of how molecules react. Species thermochemistry is estimated through Benson group additivity and reaction rate coefficients are estimated using a database of known rate rules and reaction templates. At its core, RMG relies on two fundamental data structures: graphs and trees. Graphs are used to represent chemical structures, and trees are used to represent thermodynamic and kinetic data. Models are generated using a rate-based algorithm which excludes species from the model based on reaction fluxes. RMG can generate reaction mechanisms for species involving carbon, hydrogen, oxygen, sulfur, and nitrogen. It also has capabilities for estimating transport and solvation properties, and it automatically computes pressure-dependent rate coefficients and identifies chemically-activated reaction paths. RMG is an object-oriented program written in Python, which provides a stable, robust programming architecture for developing an extensible and modular code base with a large suite of unit tests. Computationally intensive functions are cythonized for speed improvements.

  19. The Electronic Flux in Chemical Reactions. Insights on the Mechanism of the Maillard Reaction

    Science.gov (United States)

    Flores, Patricio; Gutiérrez-Oliva, Soledad; Herrera, Bárbara; Silva, Eduardo; Toro-Labbé, Alejandro

    2007-11-01

    The electronic transfer that occurs during a chemical process is analysed in term of a new concept, the electronic flux, that allows characterizing the regions along the reaction coordinate where electron transfer is actually taking place. The electron flux is quantified through the variation of the electronic chemical potential with respect to the reaction coordinate and is used, together with the reaction force, to shed light on reaction mechanism of the Schiff base formation in the Maillard reaction. By partitioning the reaction coordinate in regions in which different process might be taking place, electronic reordering associated to polarization and transfer has been identified and found to be localized at specific transition state regions where most bond forming and breaking occur.

  20. Clarification of sodium-water chemical reaction using laser diagnostics

    International Nuclear Information System (INIS)

    In a sodium-cooled fast reactor (SFR), liquid sodium is used as a heat transfer fluid because of its excellent heat transport capability. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow by a breach of heat transfer tubes in a steam generator. Therefore the study on sodium-water chemical reactions is of paramount importance for safety reasons. This study aims to clarify the sodium-water reaction mechanisms using laser diagnostics. The sodium-water, sodium-oxygen and sodium-hydrogen counter-flow reactions were measured using laser diagnostics such as Raman, absorption and photo-fragmentation spectroscopies. The measurement results show that the main product of the sodium-water reaction is NaOH. The sodium-water reaction rate is slower than that of the sodium-oxygen reaction and hydrogen does not react noticeably with sodium. (author)

  1. Is There a Minimum Electrophilicity Principle in Chemical Reactions?

    Institute of Scientific and Technical Information of China (English)

    NOORIZADEH,Siamak

    2007-01-01

    For 25 simple reactions, the changes of the hardness (△η), polarizability (△α) and electrophilicity index (△ω)and their cube-roots (△η1/3, △α1/3, △ω1/3) were calculated. It is shown that although the Maximum Hardness and Minimum Polarizability Principles are not valid for all reactions, but in most cases △ω1/3<0, whereas we always find △ω<0. Our observation impliesto this fact that for those chemical reactions in which the number of moles decreases or at least remains constant, the most stable species (reactants or products) have the lowest sum of electrophilicities. In other words "the natural direction of a chemical reaction is toward a state of minimum electrophilicity". This fact may be called Minimum Electrophilicity Principle (MEP).

  2. A comparison of reversible chemical reactions for solar thermochemical power generation

    OpenAIRE

    Williams, O. M.

    1980-01-01

    Reversible chemical reactions operating in a thermochemical energy transfer system have been proposed for solar electricity generation in order to solve not only the problem of energy transport from the solar collection field to a central power plant, but also potentially the long term lossless energy storage problem through underground storage of the reaction products. A number of reactions have been proposed for solar thermochemical power generation and in this paper the thermodynamic and c...

  3. Waste dissolution with chemical reaction, diffusion and advection

    International Nuclear Information System (INIS)

    This paper extends the mass-transfer analysis to include the effect of advective transport in predicting the steady-state dissolution rate, with a chemical-reaction-rate boundary condition at the surface of a waste form of arbitrary shape. This new theory provides an analytic means of predicting the ground-water velocities at which dissolution rate in a geologic environment will be governed entirely to the chemical reaction rate. As an illustration, we consider the steady-state potential flow of ground water in porous rock surrounding a spherical waste solid. 3 refs., 2 figs

  4. Simulation of chemical reaction dynamics on an NMR quantum computer

    CERN Document Server

    Lu, Dawei; Xu, Ruixue; Chen, Hongwei; Gong, Jiangbin; Peng, Xinhua; Du, Jiangfeng

    2011-01-01

    Quantum simulation can beat current classical computers with minimally a few tens of qubits and will likely become the first practical use of a quantum computer. One promising application of quantum simulation is to attack challenging quantum chemistry problems. Here we report an experimental demonstration that a small nuclear-magnetic-resonance (NMR) quantum computer is already able to simulate the dynamics of a prototype chemical reaction. The experimental results agree well with classical simulations. We conclude that the quantum simulation of chemical reaction dynamics not computable on current classical computers is feasible in the near future.

  5. Effects of chemical reactions on the performance of gas dynamic lasers

    Energy Technology Data Exchange (ETDEWEB)

    Rom, J.; Stricker, J.

    1974-01-01

    It is shown that chemical reactions in the stagnation region of a gasdynamic laser in the shock tube may not be completed during the available test time. Therefore, analysis of data obtained in the shock tube must account for the instantaneous composition which may be effected by chemical reactions. A CO/sub 2/--N/sub 2/ gasdynamic laser experimental program in the shock tube including addition of H/sub 2/ into the system is described. This experiment involves reasonably complicated chemical reactions. These chemical reactions result in H/sub 2/O production under certain conditions. The comparison of the experimental results with the calculated results shows that such measurements can also be used to evaluate the energy transfer rates. The small-signal gain measurements indicate that the hydrogen is much more effective in depopulating the ..nu.. sub 3 level to ..nu.. sub 2 than previously assumed.

  6. The Heck reaction in the production of fine chemicals

    OpenAIRE

    Vries, Johannes G. de

    2001-01-01

    An overview is given of the use of the Heck reaction for the production of fine chemicals. Five commercial products have been identified that are produced on a scale in excess of 1 ton/year. The herbicide Prosulfuron™ is produced via a Matsuda reaction of 2-sulfonatobenzenediazonium on 3,3,3-trifluoropropene. The sunscreen agent 2-ethylhexyl p-methoxy-cinnamate has been produced on pilot scale using Pd/C as catalyst. Naproxen™ is produced via the Heck reaction of 2-bromo-6-methoxy-naphthalene...

  7. Variable elimination in chemical reaction networks with mass-action kinetics

    DEFF Research Database (Denmark)

    Feliu, Elisenda; Wiuf, C.

    2012-01-01

    We consider chemical reaction networks taken with mass-action kinetics. The steady states of such a system are solutions to a system of polynomial equations. Even for small systems the task of finding the solutions is daunting. We develop an algebraic framework and procedure for linear elimination...

  8. Chemical reaction mediated self-assembly of PTCDA into nanofibers.

    Science.gov (United States)

    Sayyad, Arshad S; Balakrishnan, Kaushik; Ajayan, Pulickel M

    2011-09-01

    Uniform and crystalline nanofibers of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), an insoluble organic semiconducting molecule, have been achieved by self-assembling the molecules using chemical reaction mediated conversion of an appropriately designed soluble precursor, perylene tetracarboxylic acid (PTCA) using carbodiimide chemistry. PMID:21814688

  9. 2011 Chemical Reactions at Surfaces Gordon Research Conference

    Energy Technology Data Exchange (ETDEWEB)

    Peter Stair

    2011-02-11

    The Gordon Research Conference on Chemical Reactions at Surfaces is dedicated to promoting and advancing the fundamental science of interfacial chemistry and physics by providing surface scientists with the foremost venue for presentation and discussion of research occurring at the frontiers of their fields.

  10. Complex and detailed balancing of chemical reaction networks revisited

    NARCIS (Netherlands)

    van der Schaft, Abraham; Rao, Shodhan; Jayawardhana, Bayu

    2015-01-01

    The characterization of the notions of complex and detailed balancing for mass action kinetics chemical reaction networks is revisited from the perspective of algebraic graph theory, in particular Kirchhoff’s Matrix Tree theorem for directed weighted graphs. This yields an elucidation of previously

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

    Science.gov (United States)

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

    1993-01-01

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

  12. Chemical reactions in organic monomolecular layers. Condensation of hydrazine on carbonyl functions

    International Nuclear Information System (INIS)

    Evidence is given for chemical reactions of hydrazine (NH2-NH2) with different carbonyl functional groups of organic molecules in the solid state, in monomolecular layer structures. The condensation of hydrazine with these molecules leads to conjugated systems by bridging the N-N links, to cyclizations, and also to polycondensations. The reactions investigated were followed up by infrared spectrophotometry, by transmission and metallic reflection. These chemical reactions revealed in the solid phase constitute a polycondensation procedure which is valuable in obtaining organized polymers in monomolecular layers

  13. Modeling Electric Double-Layers Including Chemical Reaction Effects

    DEFF Research Database (Denmark)

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

    2014-01-01

    A physicochemical and numerical model for the transient formation of an electric double-layer between an electrolyte and a chemically-active flat surface is presented, based on a finite elements integration of the nonlinear Nernst-Planck-Poisson model including chemical reactions. The model works...... for symmetric and asymmetric multi-species electrolytes and is not limited to a range of surface potentials. Numerical simulations are presented, for the case of a CaCO3 electrolyte solution in contact with a surface with rate-controlled protonation/deprotonation reactions. The surface charge and...... potential are determined by the surface reactions, and therefore they depends on the bulk solution composition and concentration...

  14. Modeling of Electric Double-Layers Including Chemical Reaction Effects

    International Nuclear Information System (INIS)

    A physicochemical and numerical model for the transient formation of an electric double-layer between an electrolyte and a chemically-active flat surface is presented, based on a finite elements integration of the nonlinear Nernst-Planck-Poisson model including chemical reactions. The model works for symmetric and asymmetric multi-species electrolytes and is not limited to a range of surface potentials. Numerical simulations are presented, for the case of a CaCO3 electrolyte solution in contact with a surface with rate-controlled protonation/deprotonation reactions. The surface charge and potential are determined by the surface reactions, and therefore they depend on the bulk solution composition and concentration

  15. NATO Advanced Study Institute on Advances in Chemical Reaction Dynamics

    CERN Document Server

    Capellos, Christos

    1986-01-01

    This book contains the formal lectures and contributed papers presented at the NATO Advanced Study Institute on. the Advances in Chemical Reaction Dynamics. The meeting convened at the city of Iraklion, Crete, Greece on 25 August 1985 and continued to 7 September 1985. The material presented describes the fundamental and recent advances in experimental and theoretical aspects of, reaction dynamics. A large section is devoted to electronically excited states, ionic species, and free radicals, relevant to chemical sys­ tems. In addition recent advances in gas phase polymerization, formation of clusters, and energy release processes in energetic materials were presented. Selected papers deal with topics such as the dynamics of electric field effects in low polar solutions, high electric field perturbations and relaxation of dipole equilibria, correlation in picosecond/laser pulse scattering, and applications to fast reaction dynamics. Picosecond transient Raman spectroscopy which has been used for the elucidati...

  16. Quantum mechanics of chemical reactions: Recent developments in reactive scattering and in reaction path Hamiltonians

    International Nuclear Information System (INIS)

    Two recent developments in the theory of chemical reaction dynamics are reviewed. First, it has recently been discovered that the S- matrix version of the Kohn variational principle is free of the ''Kohn anomalies'' that have plagued other versions and prevented its general use. This has considerably simplified quantum mechanical reactive scattering calculations, which provide the rigorous characterizations of bimolecular reactions. Second, a new kind of reaction path Hamiltonian has been developed, one based on the ''least motion'' path that interpolates linearly between the reactant and product geometry of the molecule (rather than the previously used minimum energy, or ''intrinsic'' reaction path). The form of Hamiltonian which results is much simpler than the original reaction path Hamiltonian, but more important is the fact that it provides a more physically correct description of hydrogen atom transfer reactions. 44 refs., 4 figs

  17. Single-molecule chemical reactions on DNA origami

    DEFF Research Database (Denmark)

    Voigt, Niels Vinther; Tørring, Thomas; Rotaru, Alexandru;

    2010-01-01

    as templates for building materials with new functional properties. Relatively large nanocomponents such as nanoparticles and biomolecules can also be integrated into DNA nanostructures and imaged. Here, we show that chemical reactions with single molecules can be performed and imaged at a local...... position on a DNA origami scaffold by atomic force microscopy. The high yields and chemoselectivities of successive cleavage and bond-forming reactions observed in these experiments demonstrate the feasibility of post-assembly chemical modification of DNA nanostructures and their potential use as locally......DNA nanotechnology and particularly DNA origami, in which long, single-stranded DNA molecules are folded into predetermined shapes, can be used to form complex self-assembled nanostructures. Although DNA itself has limited chemical, optical or electronic functionality, DNA nanostructures can serve...

  18. A thermodynamic force generated by chemical gradient and adsorption reaction

    CERN Document Server

    Sugawara, Takeshi

    2009-01-01

    Biological units such as macromolecules, organelles, and cells are directed to a proper location under gradients of relevant chemicals. By considering a macroscopic element that has binding sites for a chemical adsorption reaction to occur on its surface, we show the existence of a thermodynamic force that is generated by the gradient and exerted on the element. By assuming local equilibrium and adopting the grand potential from thermodynamics, we derive a formula for such a thermodynamic force, which depends on the chemical potential gradient and Langmuir isotherm. The conditions under which the formula can be applied are demonstrated to hold in intracellular reactions. The role of the force in the partitioning of bacterial chromosome/plasmid during cell division is discussed.

  19. Heat, Mass and Charge Transport, and Chemical Reactions at Surfaces

    Directory of Open Access Journals (Sweden)

    Signe Kjelstrup

    2005-03-01

    Full Text Available In this work we derive the excess entropy production rate for heat, mass and charge transport into, out of and across a surface, using as basic variables the excess densities proposed by Gibbs. With the help of these variables we define the surface as an autonomous system (i.e. a surface in local equilibrium and find its excess entropy production rate. This then determines the conjugate fluxes and forces. Equivalent forms of the entropy production rate are given. The forms contain finite differences of intensive variables into and across the surface as driving forces. The general form of the force-flux relations is given. The expressions for the fluxes serve as boundary conditions for integration across heterogeneous systems. Two examples are discussed in more detail. The first example is the practically important coupled transport of heat and mass into and through a liquid-vapor surface. The second example concerns phenomena at electrode surfaces: the coupled transport of heat, mass and charge and a chemical reaction. By assuming that the two sides of the surface can be described as resistances in series, we are able to reduce the number of unknown transport coefficients considerably. For both examples it is shown that the coupling coefficients for heat and mass flow are large at the surface, when the homogeneous phases have a large enthalpy difference. As a consequence it is not sufficient to use, for instance, Fourier’s law for transport of heat across surfaces.

  20. Cellular automaton model of coupled mass transport and chemical reactions

    International Nuclear Information System (INIS)

    Mass transport, coupled with chemical reactions, is modelled as a cellular automaton in which solute molecules perform a random walk on a lattice and react according to a local probabilistic rule. Assuming molecular chaos and a smooth density function, we obtain the standard reaction-transport equations in the continuum limit. The model is applied to the reactions a + b ↔c and a + b →c, where we observe interesting macroscopic effects resulting from microscopic fluctuations and spatial correlations between molecules. We also simulate autocatalytic reaction schemes displaying spontaneous formation of spatial concentration patterns. Finally, we propose and discuss the limitations of a simple model for mineral-solute interaction. (author) 5 figs., 20 refs

  1. Chemical research on red pigments after adverse reactions to tattoo.

    Science.gov (United States)

    Tammaro, A; Toniolo, C; Giulianelli, V; Serafini, M; Persechino, S

    2016-03-01

    Currently, the incidence of tattooing is on the rise compared to the past, especially among adolescents, and it leads to the urgency of monitoring the security status of tattooing centers, as well as to inform people about the risks of tattoo practice. In our clinical experience, 20% of tattooed patients presented adverse reactions, like allergic contact dermatitis, psoriasis with Koebner's phenomena and granulomatous reactions, with the latter most prevalent and most often related to red pigment. Adverse reactions to tattoo pigments, especially the red one, are well known and described in literature. Great attention has to be focused on the pigments used, especially for the presence of new substances, often not well known. For this reason, we decided to perform a study on 12 samples of red tattoo ink, obtained by patients affected by different cutaneous reactions in the site of tattoo, to analyze their chemical composition. PMID:26934738

  2. Engineering Model Reduction and Entropy-based Lyapunov Functions in Chemical Reaction Kinetics

    OpenAIRE

    Hangos, Katalin M.

    2010-01-01

    In this paper, the structural properties of chemical reaction systems obeying the mass action law are investigated and related to the physical and chemical properties of the system. An entropy-based Lyapunov function candidate serves as a tool for proving structural stability, the existence of which is guaranteed by the second law of thermodynamics. The commonly used engineering model reduction methods, the so-called quasi equilibrium and quasi steady state assumption based reductions, togeth...

  3. Product-form stationary distributions for deficiency zero chemical reaction networks

    OpenAIRE

    Anderson, David F.; Craciun, Gheorghe; Kurtz, Thomas G.

    2008-01-01

    We consider stochastically modeled chemical reaction systems with mass-action kinetics and prove that a product-form stationary distribution exists for each closed, irreducible subset of the state space if an analogous deterministically modeled system with mass-action kinetics admits a complex balanced equilibrium. Feinberg's deficiency zero theorem then implies that such a distribution exists so long as the corresponding chemical network is weakly reversible and has a deficiency of zero. The...

  4. Thermodynamic and Kinetic Investigation of a Chemical Reaction-Based Miniature Heat Pump

    OpenAIRE

    Flueckiger, Scott M.; Volle, Fabien; Garimella, S V; Mongia, Rajiv K.

    2012-01-01

    Representative reversible endothermic chemical reactions (paraldehyde depolymerization and 2-proponal dehydrogenation) are theoretically assessed for their use in a chemical heat pump design for compact thermal management applications. Equilibrium and dynamic simulations are undertaken to explore the operation of the heat pump which upgrades waste heat from near room temperature by approximately 20 in a minimized system volume. A model is developed based on system mass and energy balances cou...

  5. EFFECTIVE SOLUTION METHOD OF CHEMICAL REACTION KINETICS WITH DIFFUSE

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The time integration method with four-order accuracy, self-starting and implicit for the diffuse chemical reaction kinetics equation or the transient instantaneous temperature filed equation was presented. The examples show that both accuracy and stability are better than Runge-Kutta method with four-order. The coefficients of the equation are stored with sparse matrix pattern, so an algorithm is presented which combines a compact storage scheme with reduced computation cost. The computation of the competitive and consecutive reaction in the rotating packed bed, taken as examples,shows that the method is effective.

  6. Laser studies of chemical reaction and collision processes

    Energy Technology Data Exchange (ETDEWEB)

    Flynn, G. [Columbia Univ., New York, NY (United States)

    1993-12-01

    This work has concentrated on several interrelated projects in the area of laser photochemistry and photophysics which impinge on a variety of questions in combustion chemistry and general chemical kinetics. Infrared diode laser probes of the quenching of molecules with {open_quotes}chemically significant{close_quotes} amounts of energy in which the energy transferred to the quencher has, for the first time, been separated into its vibrational, rotational, and translational components. Probes of quantum state distributions and velocity profiles for atomic fragments produced in photodissociation reactions have been explored for iodine chloride.

  7. The phase transition and classification of critical points in the multistability chemical reactions

    Institute of Scientific and Technical Information of China (English)

    ChunhuaZHANG; FugenWU; ChunyanWU; FaOU

    2000-01-01

    In this paper, we study the phase transition and classification of critical points in multistability chemical reaction systems. Referring to the spirit of Landau's theory of phase transitions, this paper deals with the varied transitions and critical phenomena in multistable chemical systems. It is demonstrated that the higher the order of the multistability,the wider the variety of phase transitions will be. A classification scheme of critical points according to the stability criterion and the thermodynamic potential continuity is suggested.It is useful for us to study critical phenomena especially in the non-equilibrium systems including the multi-stable chemical ones.

  8. Crossed molecular beam studies of atmospheric chemical reaction dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Jingsong

    1993-04-01

    The dynamics of several elementary chemical reactions that are important in atmospheric chemistry are investigated. The reactive scattering of ground state chlorine or bromine atoms with ozone molecules and ground state chlorine atoms with nitrogen dioxide molecules is studied using a crossed molecular beams apparatus with a rotatable mass spectrometer detector. The Cl + O{sub 3} {yields} ClO + O{sub 2} reaction has been studied at four collision energies ranging from 6 kcal/mole to 32 kcal/mole. The derived product center-of-mass angular and translational energy distributions show that the reaction has a direct reaction mechanism and that there is a strong repulsion on the exit channel. The ClO product is sideways and forward scattered with respect to the Cl atom, and the translational energy release is large. The Cl atom is most likely to attack the terminal oxygen atom of the ozone molecule. The Br + O{sub 3} {yields} ClO + O{sub 2} reaction has been studied at five collision energies ranging from 5 kcal/mole to 26 kcal/mole. The derived product center-of-mass angular and translational energy distributions are quite similar to those in the Cl + O{sub 3} reaction. The Br + O{sub 3} reaction has a direct reaction mechanism similar to that of the Cl + O{sub 3} reaction. The electronic structure of the ozone molecule seems to play the central role in determining the reaction mechanism in atomic radical reactions with the ozone molecule. The Cl + NO{sub 2} {yields} ClO + NO reaction has been studied at three collision energies ranging from 10.6 kcal/mole to 22.4 kcal/mole. The center-of-mass angular distribution has some forward-backward symmetry, and the product translational energy release is quite large. The reaction proceeds through a short-lived complex whose lifetime is less than one rotational period. The experimental results seem to show that the Cl atom mainly attacks the oxygen atom instead of the nitrogen atom of the NO{sub 2} molecule.

  9. Simulation of underexpanded supersonic jet flows with chemical reactions

    Institute of Scientific and Technical Information of China (English)

    Fu Debin; Yu Yong; Niu Qinglin

    2014-01-01

    To achieve a detailed understanding of underexpanded supersonic jet structures influenced by afterburning and other flow conditions, the underexpanded turbulent supersonic jet with and without combustions are investigated by computational fluid dynamics (CFD) method. A program based on a total variation diminishing (TVD) methodology capable of predicting complex shocks is created to solve the axisymmetric expanded Navier-Stokes equations containing transport equations of species. The finite-rate ratio model is employed to handle species sources in chemical reactions. CFD solutions indicate that the structure of underexpanded jet is typically influenced by the pressure ratio and afterburning. The shock reflection distance and maximum value of Mach number in the first shock cell increase with pressure ratio. Chemical reactions for the rocket exhaust mostly exist in the mixing layer of supersonic jet flows. This tends to reduce the intensity of shocks existing in the jet, responding to the variation of thermal parameters.

  10. Tabletop imaging of structural evolutions in chemical reactions

    CERN Document Server

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

    2014-01-01

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

  11. Implementation of a vibrationally linked chemical reaction model for DSMC

    Science.gov (United States)

    Carlson, A. B.; Bird, Graeme A.

    1994-01-01

    A new procedure closely linking dissociation and exchange reactions in air to the vibrational levels of the diatomic molecules has been implemented in both one- and two-dimensional versions of Direct Simulation Monte Carlo (DSMC) programs. The previous modeling of chemical reactions with DSMC was based on the continuum reaction rates for the various possible reactions. The new method is more closely related to the actual physics of dissociation and is more appropriate to the particle nature of DSMC. Two cases are presented: the relaxation to equilibrium of undissociated air initially at 10,000 K, and the axisymmetric calculation of shuttle forebody heating during reentry at 92.35 km and 7500 m/s. Although reaction rates are not used in determining the dissociations or exchange reactions, the new method produces rates which agree astonishingly well with the published rates derived from experiment. The results for gas properties and surface properties also agree well with the results produced by earlier DSMC models, equilibrium air calculations, and experiment.

  12. Size Dependence of Chemical Reactions in Nanoscale Aerosol Particles

    Czech Academy of Sciences Publication Activity Database

    Levdansky, V.V.; Smolík, Jiří; Moravec, Pavel

    Helsinki : -, 2010, P2L1. ISBN N. [International Aerosol Conference IAC 2010. Helsinki (FI), 29.08.2010-03.09.2010] R&D Projects: GA ČR GA104/07/1093; GA ČR GA101/09/1633; GA AV ČR(CZ) IAA400720804 Institutional research plan: CEZ:AV0Z40720504 Keywords : size effect * nanoparticles * chemical reactions Subject RIV: CF - Physical ; Theoretical Chemistry www.iac2010.fi

  13. Effects of Confinement on Chemical Reaction Equilibrium in Nanoporous Materials

    Czech Academy of Sciences Publication Activity Database

    Smith, W.R.; Lísal, Martin; Brennan, J.K.

    2006-01-01

    Roč. 3984, - (2006), s. 743-751. ISSN 0302-9743 R&D Projects: GA ČR(CZ) GA203/05/0725; GA AV ČR 1ET400720507 Grant ostatní: NRCC(CA) OGP 1041 Institutional research plan: CEZ:AV0Z40720504 Keywords : nanoporous materials * chemical reaction equilibrium Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 0.402, year: 2005

  14. Simulation of chemical reaction dynamics on an NMR quantum computer

    OpenAIRE

    Lu, Dawei; Xu, Nanyang; Xu, Ruixue; Chen, Hongwei; Gong, Jiangbin; Peng, Xinhua; Du, Jiangfeng

    2011-01-01

    Quantum simulation can beat current classical computers with minimally a few tens of qubits and will likely become the first practical use of a quantum computer. One promising application of quantum simulation is to attack challenging quantum chemistry problems. Here we report an experimental demonstration that a small nuclear-magnetic-resonance (NMR) quantum computer is already able to simulate the dynamics of a prototype chemical reaction. The experimental results agree well with classical ...

  15. Chemical sensor system

    Science.gov (United States)

    Darrach, Murray R. (Inventor); Chutjian, Ara (Inventor)

    2008-01-01

    A chemical sensing apparatus and method for the detection of sub parts-per-trillion concentrations of molecules in a sample by optimizing electron utilization in the formation of negative ions is provided. A variety of media may be sampled including air, seawater, dry sediment, or undersea sediment. An electrostatic mirror is used to reduce the kinetic energy of an electron beam to zero or near-zero kinetic energy.

  16. On the Mathematical Structure of Balanced Chemical Reaction Networks Governed by Mass Action Kinetics

    OpenAIRE

    der Schaft, Arjan van; Rao, Shodhan; Jayawardhana, Bayu

    2011-01-01

    Motivated by recent progress on the interplay between graph theory, dynamics, and systems theory, we revisit the analysis of chemical reaction networks described by mass action kinetics. For reaction networks possessing a thermodynamic equilibrium we derive a compact formulation exhibiting at the same time the structure of the complex graph and the stoichiometry of the network, and which admits a direct thermodynamical interpretation. This formulation allows us to easily characterize the set ...

  17. The role of chemical reaction in waste-form performance

    International Nuclear Information System (INIS)

    The dissolution rate of waste solids in a geologic repository is a complex function of waste form geometry, chemical raction rate, exterior flow field, and chemical environment. We present here an analysis to determine the stady-state mass transfer rate, over the entire range of flow conditions relevant to geologic disposal of nuclear waste. The equations for steady-state mass transfer with a chemical-reaction-rate boundary condition are solved by three different mathematical techniques which supplement each other. This theory is illustrated with laboratory leach data for borosilicate-glass and a spherical spent-fuel waste form under typical repository conditions. For borosilicate glass waste in the temperature range of 57/degree/C to 250/degree/C, dissolution rate in a repository is determined for a wide range of chemical reaction rates and for Peclet numbers from zero to well over 100, far beyond any Peclet values expected in a repository. Spent-fuel dissolution in a repository is also investigated, based on the limited leach data now available. 10 refs., 4 figs., 1 tab

  18. Physio-chemical reactions in recycle aggregate concrete.

    Science.gov (United States)

    Tam, Vivian W Y; Gao, X F; Tam, C M; Ng, K M

    2009-04-30

    Concrete waste constitutes the major proportion of construction waste at about 50% of the total waste generated. An effective way to reduce concrete waste is to reuse it as recycled aggregate (RA) for the production of recycled aggregate concrete (RAC). This paper studies the physio-chemical reactions of cement paste around aggregate for normal aggregate concrete (NAC) and RAC mixed with normal mixing approach (NMA) and two-stage mixing approach (TSMA) by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Four kinds of physio-chemical reactions have been recorded from the concrete samples, including the dehydration of C(3)S(2)H(3), iron-substituted ettringite, dehydroxylation of CH and development of C(6)S(3)H at about 90 degrees C, 135 degrees C, 441 degrees C and 570 degrees C, respectively. From the DSC results, it is confirmed that the concrete samples with RA substitution have generated less amount of strength enhancement chemical products when compared to those without RA substitution. However, the results from the TSMA are found improving the RAC quality. The pre-mix procedure of the TSMA can effectively develop some strength enhancing chemical products including, C(3)S(2)H(3), ettringite, CH and C(6)S(3)H, which shows that RAC made from the TSMA can improve the hydration processes. PMID:18718710

  19. Computational analysis of the mechanism of chemical reactions in terms of reaction phases: hidden intermediates and hidden transition States.

    Science.gov (United States)

    Kraka, Elfi; Cremer, Dieter

    2010-05-18

    Computational approaches to understanding chemical reaction mechanisms generally begin by establishing the relative energies of the starting materials, transition state, and products, that is, the stationary points on the potential energy surface of the reaction complex. Examining the intervening species via the intrinsic reaction coordinate (IRC) offers further insight into the fate of the reactants by delineating, step-by-step, the energetics involved along the reaction path between the stationary states. For a detailed analysis of the mechanism and dynamics of a chemical reaction, the reaction path Hamiltonian (RPH) and the united reaction valley approach (URVA) are an efficient combination. The chemical conversion of the reaction complex is reflected by the changes in the reaction path direction t(s) and reaction path curvature k(s), both expressed as a function of the path length s. This information can be used to partition the reaction path, and by this the reaction mechanism, of a chemical reaction into reaction phases describing chemically relevant changes of the reaction complex: (i) a contact phase characterized by van der Waals interactions, (ii) a preparation phase, in which the reactants prepare for the chemical processes, (iii) one or more transition state phases, in which the chemical processes of bond cleavage and bond formation take place, (iv) a product adjustment phase, and (v) a separation phase. In this Account, we examine mechanistic analysis with URVA in detail, focusing on recent theoretical insights (with a variety of reaction types) from our laboratories. Through the utilization of the concept of localized adiabatic vibrational modes that are associated with the internal coordinates, q(n)(s), of the reaction complex, the chemical character of each reaction phase can be identified via the adiabatic curvature coupling coefficients, A(n,s)(s). These quantities reveal whether a local adiabatic vibrational mode supports (A(n,s) > 0) or resists

  20. A Voltammetric Determination of the Rate Constant of a One-Way Homogeneous Chemical Reaction in a System of Two Immiscible Liquid Phases

    Czech Academy of Sciences Publication Activity Database

    Holub, Karel; Brusová, Zuzana; Štulík, K.; Mareček, Vladimír

    2004-01-01

    Roč. 574, č. 1 (2004), s. 101-106. ISSN 0022-0728 R&D Projects: GA ČR GA203/03/0822 Institutional research plan: CEZ:AV0Z4040901 Keywords : liquid|liquid interfaces * homogeneous reaction * voltammetry Subject RIV: CG - Electrochemistry Impact factor: 2.228, year: 2004

  1. Automatic learning for the classification of chemical reactions and in statistical thermodynamics

    OpenAIRE

    Latino, Diogo Alexandre Rosa Serra

    2008-01-01

    This Thesis describes the application of automatic learning methods for a) the classification of organic and metabolic reactions, and b) the mapping of Potential Energy Surfaces(PES). The classification of reactions was approached with two distinct methodologies: a representation of chemical reactions based on NMR data, and a representation of chemical reactions from the reaction equation based on the physico-chemical and topological features of chemical bonds. NMR-based classification of ...

  2. Isothermal Vapour-Liquid Equilibrium with Chemical Reaction in the Quaternary Water + Methanol + Acetic Acid + Methyl Acetate System, and in Five Binary Subsystems.

    Czech Academy of Sciences Publication Activity Database

    Bernatová, Svatoslava; Aim, Karel; Wichterle, Ivan

    2006-01-01

    Roč. 247, 1-2 (2006) , s. 96-101. ISSN 0378-3812 R&D Projects: GA ČR(CZ) GA203/03/1588 Institutional research plan: CEZ:AV0Z40720504 Keywords : esterification * chemical equilibria * phase equilibria Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.680, year: 2006

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

    Science.gov (United States)

    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. PMID:27147197

  4. Discrete formulation of mixed finite element methods for vapor deposition chemical reaction equations

    Institute of Scientific and Technical Information of China (English)

    LUO Zhen-dong; ZHOU Yan-jie; ZHU Jiang

    2007-01-01

    The vapor deposition chemical reaction processes, which are of extremely extensive applications, can be classified as a mathematical modes by the following governing nonlinear partial differential equations containing velocity vector,temperature field,pressure field,and gas mass field.The mixed finite element(MFE)method is employed to study the system of equations for the vapor deposition chemical reaction processes.The semidiscrete and fully discrete MFE formulations are derived.And the existence and convergence(error estimate)of the semidiscrete and fully discrete MFE solutions are deposition chemical reaction processes,the numerical solutions of the velocity vector,the temperature field,the pressure field,and the gas mass field can be found out simultaneonsly.Thus,these researches are not only of important theoretical means,but also of extremely extensive applied vistas.

  5. Chemical reaction and dust formation studies in laboratory hydrocarbon plasmas.

    Science.gov (United States)

    Hippler, Rainer; Majumdar, Abhijit; Thejaswini, H. C.

    Plasma chemical reaction studies with relevance to, e.g., Titan's atmosphere have been per-formed in various laboratory plasmas [1,2]. Chemical reactions in a dielectric barrier discharge at medium pressure of 250-300 mbar have been studied in CH4 /N2 and CH4 /Ar gas mixtures by means of mass spectrometry. The main reaction scheme is production of H2 by fragmenta-tion of CH4 , but also production of larger hydrocarbons like Cn Hm with n up to 10 including formation of different functional CN groups is observed. [1] A. Majumdar and R. Hippler, Development of dielectric barrier discharge plasma processing apparatus for mass spectrometry and thin film deposition, Rev. Sci. Instrum. 78, 075103 (2007) [2] H.T. Do, G. Thieme, M. Frühlich, H. Kersten, and R. Hippler, Ion Molecule and Dust Particle Formation in Ar/CH4 , Ar/C2 H2 and Ar/C3 H6 Radio-frequency Plasmas, Contrib. Plasma Phys. 45, No. 5-6, 378-384 (2005)

  6. Facilitating High School Students' Use of Multiple Representations to Describe and Explain Simple Chemical Reactions

    Science.gov (United States)

    Chandrasegaran, A. L.; Treagust, David F.; Mocerino, Mauro

    2011-01-01

    This study involved the evaluation of the efficacy of a planned instructional program to facilitate understanding of the macroscopic, submicroscopic and symbolic representational systems when describing and explaining chemical reactions by sixty-five Grade 9 students in a Singapore secondary school. A two-tier multiple-choice diagnostic instrument…

  7. Fluctuation Induced Structure in Chemical Reaction with Small Number of Molecules

    Science.gov (United States)

    Suzuki, Yasuhiro

    We investigate the behaviors of chemical reactions of the Lotka-Volterra model with small number of molecules; hence the occurrence of random fluctuations modifies the deterministic behavior and the law of mass action is replaced by a stochastic model. We model it by using Abstract Rewriting System on Multisets, ARMS; ARMS is a stochastic method of simulating chemical reactions and it is based on the reaction rate equation. We confirmed that the magnitude of fluctuations on periodicity of oscillations becomes large, as the number of involved molecules is getting smaller; and these fluctuations induce another structure, which have not observed in the reactions with large number of molecules. We show that the underling mechanism through investigating the coarse grained phase space of ARMS.

  8. Automated Discovery of Elementary Chemical Reaction Steps Using Freezing String and Berny Optimization Methods

    CERN Document Server

    Suleimanov, Yury V

    2015-01-01

    We present a simple protocol which allows fully automated discovery of elementary chemical reaction steps using in cooperation single- and double-ended transition-state optimization algorithms - the freezing string and Berny optimization methods, respectively. To demonstrate the utility of the proposed approach, the reactivity of several systems of combustion and atmospheric chemistry importance is investigated. The proposed algorithm allowed us to detect without any human intervention not only "known" reaction pathways, manually detected in the previous studies, but also new, previously "unknown", reaction pathways which involve significant atom rearrangements. We believe that applying such a systematic approach to elementary reaction path finding will greatly accelerate the possibility of discovery of new chemistry and will lead to more accurate computer simulations of various chemical processes.

  9. Molecular dynamics study of phase separation in fluids with chemical reactions

    Science.gov (United States)

    Krishnan, Raishma; Puri, Sanjay

    2015-11-01

    We present results from the first d =3 molecular dynamics (MD) study of phase-separating fluid mixtures (AB) with simple chemical reactions (A ⇌B ). We focus on the case where the rates of forward and backward reactions are equal. The chemical reactions compete with segregation, and the coarsening system settles into a steady-state mesoscale morphology. However, hydrodynamic effects destroy the lamellar morphology which characterizes the diffusive case. This has important consequences for the phase-separating structure, which we study in detail. In particular, the equilibrium length scale (ℓeq) in the steady state suggests a power-law dependence on the reaction rate ɛ :ℓeq˜ɛ-θ with θ ≃1.0 .

  10. Automated Discovery of Elementary Chemical Reaction Steps Using Freezing String and Berny Optimization Methods.

    Science.gov (United States)

    Suleimanov, Yury V; Green, William H

    2015-09-01

    We present a simple protocol which allows fully automated discovery of elementary chemical reaction steps using in cooperation double- and single-ended transition-state optimization algorithms--the freezing string and Berny optimization methods, respectively. To demonstrate the utility of the proposed approach, the reactivity of several single-molecule systems of combustion and atmospheric chemistry importance is investigated. The proposed algorithm allowed us to detect without any human intervention not only "known" reaction pathways, manually detected in the previous studies, but also new, previously "unknown", reaction pathways which involve significant atom rearrangements. We believe that applying such a systematic approach to elementary reaction path finding will greatly accelerate the discovery of new chemistry and will lead to more accurate computer simulations of various chemical processes. PMID:26575920

  11. Unnatural selection in chemical systems

    Science.gov (United States)

    Orgel, Leslie E.

    1995-01-01

    The theory of evolution through natural selection was proposed by Darwin and Wallace to explain how the characteristics of populations of animals change with time. An examination of their assumptions shows that the theory has much broader application than they originally envisaged. We now know that in appropriate environments RNA molecules or computer viruses, for example, can evolve. The adventure with which we are concerned is the quest for chemical systems that undergo processes analogous to Darwinian selection in the test tube. The search is not restricted to systems that are closely related to nucleic acids, although most of the available experimental evidence concerns such systems. A population of molecules satisfies all the requirements of the theory is there are different kinds of molecules in the population and if each individual molecule can direct the formation of copies of itself, then a population of molecules will adapt to a varying environment by changing its composition so as to maintain as high as possible a rate of replication. Sol Spiegelman is the inventor of 'unnatural selection'. He showed clearly that populations of RNA molecules evolve when replicated repeatedly by Q beta RNA polymerase under a chosen set of adverse reaction conditions. In the systems that he studied, the initial population was fairly homogeneous and much of the variation was created during the course of the experiment by mutation, that is, error of replication. The term 'unnatural selection' will be used loosely to describe evolution of nucleic acids or other replicatable polymers in vitro. The term 'Natural Selection' will be reserved for the evolution of living organisms and their viruses. Natural Section usually involves the coevolution of nucleic acids and proteins, while 'unnatural selection', as practiced so far, allows replicating nucleic acids to evolve but hold constant the enzymes that catalyze replication. It is widely believed that biology based on DNA, RNA, and

  12. Two-scale large deviations for chemical reaction kinetics through second quantization path integral

    Science.gov (United States)

    Li, Tiejun; Lin, Feng

    2016-04-01

    Motivated by the study of rare events for a typical genetic switching model in systems biology, in this paper we aim to establish the general two-scale large deviations for chemical reaction systems. We build a formal approach to explicitly obtain the large deviation rate functionals for the considered two-scale processes based upon the second quantization path integral technique. We get three important types of large deviation results when the underlying two timescales are in three different regimes. This is realized by singular perturbation analysis to the rate functionals obtained by the path integral. We find that the three regimes possess the same deterministic mean-field limit but completely different chemical Langevin approximations. The obtained results are natural extensions of the classical large volume limit for chemical reactions. We also discuss its implication on the single-molecule Michaelis-Menten kinetics. Our framework and results can be applied to understand general multi-scale systems including diffusion processes.

  13. Holistic Metrics for Assessment of the Greenness of Chemical Reactions in the Context of Chemical Education

    Science.gov (United States)

    Ribeiro, M. Gabriela T. C.; Machado, Adelio A. S. C.

    2013-01-01

    Two new semiquantitative green chemistry metrics, the green circle and the green matrix, have been developed for quick assessment of the greenness of a chemical reaction or process, even without performing the experiment from a protocol if enough detail is provided in it. The evaluation is based on the 12 principles of green chemistry. The…

  14. Mass transfer with complex reversible chemical reactions—II. parallel reversible chemical reactions

    NARCIS (Netherlands)

    Versteeg, G.F.; Kuipers, J.A.M.; Beckum, F.P.H. van; Swaaij, W.P.M. van

    1990-01-01

    An absorption model has been developed which can be used to calculate rapidly absorption rates for the phenomenon mass transfer accompanied by multiple complex parallel reversible chemical reactions. This model can be applied for the calculation of the mass transfer rates, enhancement factors and co

  15. A quantum informational approach for dissecting chemical reactions

    CERN Document Server

    Duperrouzel, Corinne; Boguslawski, Katharina; Barcza, Gergerly; Legeza, Örs; Ayers, Paul W

    2014-01-01

    We present a conceptionally different approach to dissect bond-formation processes in metal-driven catalysis using concepts from quantum information theory. Our method uses the entanglement and correlation among molecular orbitals to analyze changes in electronic structure that accompany chemical processes. As a proof-of-principle example, the evolution of nickel-ethene bond-formation is dissected which allows us to monitor the interplay of back-bonding and $\\pi$-donation along the reaction coordinate. Furthermore, the reaction pathway of nickel-ethene complexation is analyzed using quantum chemistry methods revealing the presence of a transition state. Our study supports the crucial role of metal-to-ligand back-donation in the bond-forming process of nickel-ethene.

  16. Chemical reactions of mercury in combustion flue gases

    International Nuclear Information System (INIS)

    Atmospheric Hg is present in different physical and chemical forms, which determine its atmospheric transformation and transport capacities. The chemistry of Hg in flue gases is thus of importance for the deposition pattern around point source emissions. In order to apply Hg cleaning methods in flue gases its speciation is also of importance. To investigate this under realistic conditions, a 17 kW propane fired flue gas generator was used, while the kinetics of specific Hg reactions were investigated in a continuous flow reactor. Elemental Hg is readily oxidized by Cl2 and HCl both at room and at elevated temperatures (up to 900 degree C) but not by NH3, N2O, SO2 or H2S. It reacts with O2 if a catalyst, such as activated carbon, is present. A slow reaction between Hg and NO2 has also been noted. 19 refs., 8 figs., 3 tabs

  17. Thermal energy storage. [by means of chemical reactions

    Science.gov (United States)

    Grodzka, P. G.

    1975-01-01

    The principles involved in thermal energy storage by sensible heat, chemical potential energy, and latent heat of fusion are examined for the purpose of evolving selection criteria for material candidates in the low ( 0 C) and high ( 100 C) temperature ranges. The examination identifies some unresolved theoretical considerations and permits a preliminary formulation of an energy storage theory. A number of candidates in the low and high temperature ranges are presented along with a rating of candidates or potential candidates. A few interesting candidates in the 0 to 100 C region are also included. It is concluded that storage by means of reactions whose reversibility can be controlled either by product removal or by catalytic means appear to offer appreciable advantages over storage with reactions whose reversability cannot be controlled. Among such advantages are listed higher heat storage capacities and more favorable options regarding temperatures of collection, storage, and delivery. Among the disadvantages are lower storage efficiencies.

  18. Modelling of structural effects on chemical reactions in turbulent flows

    Energy Technology Data Exchange (ETDEWEB)

    Gammelsaeter, H.R.

    1997-12-31

    Turbulence-chemistry interactions are analysed using algebraic moment closure for the chemical reaction term. The coupling between turbulence and chemical length and time scales generate a complex interaction process. This interaction process is called structural effects in this work. The structural effects are shown to take place on all scales between the largest scale of turbulence and the scales of the molecular motions. The set of equations describing turbulent correlations involved in turbulent reacting flows are derived. Interactions are shown schematically using interaction charts. Algebraic equations for the turbulent correlations in the reaction rate are given using the interaction charts to include the most significant couplings. In the frame of fundamental combustion physics, the structural effects appearing on the small scales of turbulence are proposed modelled using a discrete spectrum of turbulent scales. The well-known problem of averaging the Arrhenius law, the specific reaction rate, is proposed solved using a presumed single variable probability density function and a sub scale model for the reaction volume. Although some uncertainties are expected, the principles are addressed. Fast chemistry modelling is shown to be consistent in the frame of algebraic moment closure when the turbulence-chemistry interaction is accounted for in the turbulent diffusion. The modelling proposed in this thesis is compared with experimental data for an laboratory methane flame and advanced probability density function modelling. The results show promising features. Finally it is shown a comparison with full scale measurements for an industrial burner. All features of the burner are captured with the model. 41 refs., 33 figs.

  19. Fat versus Thin Threading Approach on GPUs: Application to Stochastic Simulation of Chemical Reactions

    KAUST Repository

    Klingbeil, Guido

    2012-02-01

    We explore two different threading approaches on a graphics processing unit (GPU) exploiting two different characteristics of the current GPU architecture. The fat thread approach tries to minimize data access time by relying on shared memory and registers potentially sacrificing parallelism. The thin thread approach maximizes parallelism and tries to hide access latencies. We apply these two approaches to the parallel stochastic simulation of chemical reaction systems using the stochastic simulation algorithm (SSA) by Gillespie [14]. In these cases, the proposed thin thread approach shows comparable performance while eliminating the limitation of the reaction system\\'s size. © 2006 IEEE.

  20. The hunt for the dynamical resonances in chemical reaction dynamics: a perspective on historical advances

    OpenAIRE

    Yu Angyang; Zhonghua Yang

    2015-01-01

    The theoretical background and basic definition of the resonances in chemical reaction dynamics have been introduced in this article. The historical breakthrough in the experimental search for the reaction resonances has been reviewed in this report, with an emphasis on the crossed molecular beam apparatus. The research of the chemical reaction resonances has attracted many scientists’ attention from 80s of last century. The chemical reaction resonances in the F+H2 reaction were firstly obser...

  1. Single-collision studies of energy transfer and chemical reaction

    Energy Technology Data Exchange (ETDEWEB)

    Valentini, J.J. [Columbia Univ., New York, NY (United States)

    1993-12-01

    The research focus in this group is state-to-state dynamics of reaction and energy transfer in collisions of free radicals such as H, OH, and CH{sub 3} with H{sub 2}, alkanes, alcohols and other hydrogen-containing molecules. The motivation for the work is the desire to provide a detailed understanding of the chemical dynamics of prototype reactions that are important in the production and utilization of energy sources, most importantly in combustion. The work is primarily experimental, but with an important and growing theoretical/computational component. The focus of this research program is now on reactions in which at least one of the reactants and one of the products is polyatomic. The objective is to determine how the high dimensionality of the reactants and products differentiates such reactions from atom + diatom reactions of the same kinematics and energetics. The experiments use highly time-resolved laser spectroscopic methods to prepare reactant states and analyze the states of the products on a single-collision time scale. The primary spectroscopic tool for product state analysis is coherent anti-Stokes Raman scattering (CARS) spectroscopy. CARS is used because of its generality and because the extraction of quantum state populations from CARS spectra is straightforward. The combination of the generality and easy analysis of CARS makes possible absolute cross section measurements (both state-to-state and total), a particularly valuable capability for characterizing reactive and inelastic collisions. Reactant free radicals are produced by laser photolysis of appropriate precursors. For reactant vibrational excitation stimulated Raman techniques are being developed and implemented.

  2. Thermodynamic Branch in the Chemical System Response to External Impact

    CERN Document Server

    Zilbergleyt, B

    2012-01-01

    The paper gives an account of a detailed investigation of the thermodynamic branch as a path of the chemical system deviation from its isolated thermodynamic equilibrium under an external impact. For a combination of direct and reverse reactions in the same chemical system, full thermodynamic branch is presented by an S-shaped curve, whose ends asymptotically achieve appropriate initial states, which, in turn, are logistic ends of the opposite reactions. The slope tangents of the steepest parts of the curves, the areas of the maximum rate of the shift growth vs. the external thermodynamic force, occurred to be directly proportional to the force and, simultaneously, linearly proportional to the thermodynamic equivalent of chemical reaction, which is the ratio between the amount in moles of any reaction participant, transformed in an isolated system, along the reaction way from its initial state to thermodynamic equilibrium, to its stoichiometric coefficient. The found linearity is valid for arbitrary combinati...

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

    Science.gov (United States)

    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. Chemical Specification of Autonomic Systems

    OpenAIRE

    Banâtre, Jean-Pierre; Fradet, Pascal; Radenac, Yann

    2004-01-01

    Autonomic computing provides a vision of information systems allowing self-management of many predefined properties. Such systems take care of their own behavior and of their interactions with other components without any external intervention. One of the major challenges concerns the expression of properties and constraints of autonomic systems. We believe that the {\\em chemical programming paradigm} (represented here by the Gamma formalism) is well-suited to the specification of autonomic s...

  5. The quantum dynamics of electronically nonadiabatic chemical reactions

    Science.gov (United States)

    Truhlar, Donald G.

    1993-01-01

    Considerable progress was achieved on the quantum mechanical treatment of electronically nonadiabatic collisions involving energy transfer and chemical reaction in the collision of an electronically excited atom with a molecule. In the first step, a new diabatic representation for the coupled potential energy surfaces was created. A two-state diabatic representation was developed which was designed to realistically reproduce the two lowest adiabatic states of the valence bond model and also to have the following three desirable features: (1) it is more economical to evaluate; (2) it is more portable; and (3) all spline fits are replaced by analytic functions. The new representation consists of a set of two coupled diabatic potential energy surfaces plus a coupling surface. It is suitable for dynamics calculations on both the electronic quenching and reaction processes in collisions of Na(3p2p) with H2. The new two-state representation was obtained by a three-step process from a modified eight-state diatomics-in-molecules (DIM) representation of Blais. The second step required the development of new dynamical methods. A formalism was developed for treating reactions with very general basis functions including electronically excited states. Our formalism is based on the generalized Newton, scattered wave, and outgoing wave variational principles that were used previously for reactive collisions on a single potential energy surface, and it incorporates three new features: (1) the basis functions include electronic degrees of freedom, as required to treat reactions involving electronic excitation and two or more coupled potential energy surfaces; (2) the primitive electronic basis is assumed to be diabatic, and it is not assumed that it diagonalizes the electronic Hamiltonian even asymptotically; and (3) contracted basis functions for vibrational-rotational-orbital degrees of freedom are included in a very general way, similar to previous prescriptions for locally

  6. The quantum dynamics of electronically nonadiabatic chemical reactions

    Science.gov (United States)

    Truhlar, Donald G.

    1993-04-01

    Considerable progress was achieved on the quantum mechanical treatment of electronically nonadiabatic collisions involving energy transfer and chemical reaction in the collision of an electronically excited atom with a molecule. In the first step, a new diabatic representation for the coupled potential energy surfaces was created. A two-state diabatic representation was developed which was designed to realistically reproduce the two lowest adiabatic states of the valence bond model and also to have the following three desirable features: (1) it is more economical to evaluate; (2) it is more portable; and (3) all spline fits are replaced by analytic functions. The new representation consists of a set of two coupled diabatic potential energy surfaces plus a coupling surface. It is suitable for dynamics calculations on both the electronic quenching and reaction processes in collisions of Na(3p2p) with H2. The new two-state representation was obtained by a three-step process from a modified eight-state diatomics-in-molecules (DIM) representation of Blais. The second step required the development of new dynamical methods. A formalism was developed for treating reactions with very general basis functions including electronically excited states. Our formalism is based on the generalized Newton, scattered wave, and outgoing wave variational principles that were used previously for reactive collisions on a single potential energy surface, and it incorporates three new features: (1) the basis functions include electronic degrees of freedom, as required to treat reactions involving electronic excitation and two or more coupled potential energy surfaces; (2) the primitive electronic basis is assumed to be diabatic, and it is not assumed that it diagonalizes the electronic Hamiltonian even asymptotically; and (3) contracted basis functions for vibrational-rotational-orbital degrees of freedom are included in a very general way, similar to previous prescriptions for locally

  7. The hunt for the dynamical resonances in chemical reaction dynamics: a perspective on historical advances

    Directory of Open Access Journals (Sweden)

    Yu Angyang

    2015-06-01

    Full Text Available The theoretical background and basic definition of the resonances in chemical reaction dynamics have been introduced in this article. The historical breakthrough in the experimental search for the reaction resonances has been reviewed in this report, with an emphasis on the crossed molecular beam apparatus. The research of the chemical reaction resonances has attracted many scientists’ attention from 80s of last century. The chemical reaction resonances in the F+H2 reaction were firstly observed by the researchers of the Chinese Academy of Sciences in 2006. Besides, the partial wave resonances in the chemical reactions have been observed for the first time in 2010.

  8. On a theory of stability for nonlinear stochastic chemical reaction networks

    International Nuclear Information System (INIS)

    We present elements of a stability theory for small, stochastic, nonlinear chemical reaction networks. Steady state probability distributions are computed with zero-information (ZI) closure, a closure algorithm that solves chemical master equations of small arbitrary nonlinear reactions. Stochastic models can be linearized around the steady state with ZI-closure, and the eigenvalues of the Jacobian matrix can be readily computed. Eigenvalues govern the relaxation of fluctuation autocorrelation functions at steady state. Autocorrelation functions reveal the time scales of phenomena underlying the dynamics of nonlinear reaction networks. In accord with the fluctuation-dissipation theorem, these functions are found to be congruent to response functions to small perturbations. Significant differences are observed in the stability of nonlinear reacting systems between deterministic and stochastic modeling formalisms

  9. Numerical simulation of the interaction of transport, diffusion and chemical reactions in an urban plume

    Science.gov (United States)

    Vogel, Bernhard; Vogel, Heike; Fiedler, Franz

    1994-01-01

    A model system is presented that takes into account the main physical and chemical processes on the regional scale here in an area of 100x100 sq km. The horizontal gridsize used is 2x2 sq km. For a case study, it is demonstrated how the model system can be used to separate the contributions of the processes advection, turbulent diffusion, and chemical reactions to the diurnal cycle of ozone. In this way, typical features which are visible in observations and are reproduced by the numerical simulations can be interpreted.

  10. Theory for Diffusion-Limited Oscillating Chemical Reactions

    OpenAIRE

    Bussemaker, H. J.; Brito López, Ricardo

    1996-01-01

    A kinetic description of lattice-gas automaton models for reaction-diffusion systems is presented. It provides corrections to the mean-field rate equations in the diffusion-limited regime. When applied to the two-species Maginu model, the theory gives an excellent quantitative prediction of the effect of slow diffusion on the periodic oscillations of the average concentrations in a spatially homogeneous state.

  11. On the use of chemical reaction rates with discrete internal energies in the direct simulation Monte Carlo method

    Science.gov (United States)

    Gimelshein, S. F.; Gimelshein, N. E.; Levin, D. A.; Ivanov, M. S.; Wysong, I. J.

    2004-07-01

    The conventional chemical reaction models of the direct simulation Monte Carlo method developed with the assumption of continuous rotational or vibrational modes that are shown to exhibit systematic errors when used with discrete energy modes. A reaction model is proposed that is consistent with the use of discrete energy distributions of rotational and vibrational modes, and is equally applicable to diatomic and polyatomic systems. The sensitivity of the model to variations of different reaction rate parameters is examined. The revised chemical reaction model is then applied to the modeling of hypersonic flows over spacecraft in the Martian and Earth atmospheres.

  12. Chemical Reactions in the Processing of Mosi2 + Carbon Compacts

    Science.gov (United States)

    Jacobson, Nathan S.; Lee, Kang N.; Maloy, Stuart A.; Heuer, Arthur H.

    1993-01-01

    Hot-pressing of MoSi2 powders with carbon at high temperatures reduces the siliceous grain boundary phase in the resultant compact. The chemical reactions in this process were examined using the Knudsen cell technique. A 2.3 wt pct oxygen MoSi2 powder and a 0.59 wt pct oxygen MoSi2 powder, both with additions of 2 wt pct carbon, were examined. The reduction of the siliceous grain boundary phase was examined at 1350 K and the resultant P(SiO)/P(CO) ratios interpreted in terms of the SiO(g) and CO(g) isobars on the Si-C-O predominance diagram. The MoSi2 + carbon mixtures were then heated at the hot-pressing temperature of 2100 K. Large weight losses were observed and could be correlated with the formation of a low-melting eutectic and the formation and vaporization of SiC.

  13. Mass transfer in porous media with heterogeneous chemical reaction

    Directory of Open Access Journals (Sweden)

    Souza S.M.A.G.Ulson de

    2003-01-01

    Full Text Available In this paper, the modeling of the mass transfer process in packed-bed reactors is presented and takes into account dispersion in the main fluid phase, internal diffusion of the reactant in the pores of the catalyst, and surface reaction inside the catalyst. The method of volume averaging is applied to obtain the governing equation for use on a small scale. The local mass equilibrium is assumed for obtaining the one-equation model for use on a large scale. The closure problems are developed subject to the length-scale constraints and the model of a spatially periodic porous medium. The expressions for effective diffusivity, hydrodynamic dispersion, total dispersion and the Darcy's law permeability tensors are presented. Solution of the set of final equations permits the variations of velocity and concentration of the chemical species along the packed-bed reactors to be obtained.

  14. Radiation induced chemical reaction of carbon monoxide and hydrogen mixture

    International Nuclear Information System (INIS)

    Previous studies of radiation induced chemical reactions of CO-H2 mixture have revealed that the yields of oxygen containing products were larger than those of hydrocarbons. In the present study, methane was added to CO-H2 mixture in order to increase further the yields of the oxygen containing products. The yields of most products except a few products such as formaldehyde increased with the addition of small amount of methane. Especially, the yields of trioxane and tetraoxane gave the maximum values when CO-H2 mixture containing 1 mol% methane was irradiated. When large amounts of methane were added to the mixture, the yields of aldehydes and carboxylic acids having more than two carbon atoms increased, whereas those of trioxane and tetraoxane decreased. From the study at reaction temperature over the range of 200 to 473 K, it was found that the yields of aldehydes and carboxylic acids showed maxima at 323 K. The studies on the effects of addition of cationic scavenger (NH3) and radical scavenger (O2) on the products yields were also carried out on the CO-H2-CH4 mixture. (author)

  15. Ab Initio Calculation of Rate Constants for Molecule-Surface Reactions with Chemical Accuracy.

    Science.gov (United States)

    Piccini, GiovanniMaria; Alessio, Maristella; Sauer, Joachim

    2016-04-18

    The ab initio prediction of reaction rate constants for systems with hundreds of atoms with an accuracy that is comparable to experiment is a challenge for computational quantum chemistry. We present a divide-and-conquer strategy that departs from the potential energy surfaces obtained by standard density functional theory with inclusion of dispersion. The energies of the reactant and transition structures are refined by wavefunction-type calculations for the reaction site. Thermal effects and entropies are calculated from vibrational partition functions, and the anharmonic frequencies are calculated separately for each vibrational mode. This method is applied to a key reaction of an industrially relevant catalytic process, the methylation of small alkenes over zeolites. The calculated reaction rate constants (free energies), pre-exponential factors (entropies), and enthalpy barriers show that our computational strategy yields results that agree with experiment within chemical accuracy limits (less than one order of magnitude). PMID:27008460

  16. Chemical kinetic analysis of hydrogen-air ignition and reaction times

    Science.gov (United States)

    Rogers, R. C.; Schexnayder, C. J., Jr.

    1981-01-01

    An anaytical study of hydrogen air kinetics was performed. Calculations were made over a range of pressure from 0.2 to 4.0 atm, temperatures from 850 to 2000 K, and mixture equivalence ratios from 0.2 to 2.0. The finite rate chemistry model included 60 reactions in 20 species of the H2-O2-N2 system. The calculations also included an assessment of how small amounts of the chemicals H2O, NOx, H2O2, and O3 in the initial mixture affect ignition and reaction times, and how the variation of the third body efficiency of H2O relative of N2 in certain key reactions may affect reaction time. The results indicate that for mixture equivalence ratios between 0.5 and 1.7, ignition times are nearly constant; however, the presence of H2O and NO can have significant effects on ignition times, depending on the mixture temperature. Reaction time is dominantly influenced by pressure but is nearly independent of initial temperature, equivalence ratio, and the addition of chemicals. Effects of kinetics on reaction at supersonic combustor conditions are discussed.

  17. Effect of Chemical Reactions on the Hydrologic Properties of Fractured and Rubbelized Glass Media

    International Nuclear Information System (INIS)

    Understanding the effect of chemical reactions on the hydrologic properties of geological media, such as porosity, permeability and dispersivity, is critical to many natural and engineered sub-surface systems. Influence of glass corrosion (precipitation and dissolution) reactions on fractured and rubbelized (crushed) forms HAN28 and LAWBP1, two candidate waste glass forms for a proposed immobilized low-activity waste (ILAW) disposal facility at the Hanford, WA site, was investigated. Flow and tracer transport experiments were conducted using fractured and rubbelized forms, before and after subjecting them to corrosion using Vapor Hydration Testing (VHT) at 200 C temperature and 200 psig pressure, causing the precipitation of alteration products. Data were analyzed using analytical expressions and CXTFIT, a transport parameter optimization code, for the estimation of the hydrologic characteristics before and after VHT. It was found that glass reactions significantly influence the hydrologic properties of ILAW glass media. Hydrologic properties of rubbelized glass decreased due to precipitation reactions, whereas those of fractured glass media increased due to reaction which led to unconfined expansion of fracture aperture. The results are unique and useful to better understand the effect of chemical reactions on the hydrologic properties of fractured and rubbelized stony media in general and glass media in particular

  18. Chemical Abstracts Service Chemical Registry System: History, Scope, and Impacts.

    Science.gov (United States)

    Weisgerber, David W.

    1997-01-01

    Describes the history, scope, and applications of the Chemical Abstracts Service Chemical Registry System, a computerized database that uniquely identifies chemical substances on the basis of their molecular structures. Explains searching the system is and discusses its use as an international resource. (66 references) (Author/LRW)

  19. Bayesian inference of chemical kinetic models from proposed reactions

    KAUST Repository

    Galagali, Nikhil

    2015-02-01

    © 2014 Elsevier Ltd. Bayesian inference provides a natural framework for combining experimental data with prior knowledge to develop chemical kinetic models and quantify the associated uncertainties, not only in parameter values but also in model structure. Most existing applications of Bayesian model selection methods to chemical kinetics have been limited to comparisons among a small set of models, however. The significant computational cost of evaluating posterior model probabilities renders traditional Bayesian methods infeasible when the model space becomes large. We present a new framework for tractable Bayesian model inference and uncertainty quantification using a large number of systematically generated model hypotheses. The approach involves imposing point-mass mixture priors over rate constants and exploring the resulting posterior distribution using an adaptive Markov chain Monte Carlo method. The posterior samples are used to identify plausible models, to quantify rate constant uncertainties, and to extract key diagnostic information about model structure-such as the reactions and operating pathways most strongly supported by the data. We provide numerical demonstrations of the proposed framework by inferring kinetic models for catalytic steam and dry reforming of methane using available experimental data.

  20. Chloroaluminum phthalocyanine thin films: chemical reaction and molecular orientation.

    Science.gov (United States)

    Latteyer, Florian; Peisert, Heiko; Uihlein, Johannes; Basova, Tamara; Nagel, Peter; Merz, Michael; Schuppler, Stefan; Chassé, Thomas

    2013-05-01

    The chemical transformation of the polar chloroaluminum phthalocyanine, AlClPc, to μ-(oxo)bis(phthalocyaninato)aluminum(III), (PcAl)2O, in thin films on indium tin oxide is studied and its influence on the molecular orientation is discussed. The studies were conducted using complementary spectroscopic techniques: Raman spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. In addition, density functional theory calculations were performed in order to identify specific vibrations and to monitor the product formation. The thin films of AlClPc were annealed in controlled environmental conditions to obtain (PcAl)2O. It is shown that the chemical transformation in the thin films can proceed only in the presence of water. The influence of the reaction and the annealing on the molecular orientation was studied with Raman spectroscopy and NEXAFS spectroscopy in total electron yield and partial electron yield modes. The comparison of the results obtained from these techniques allows the determination of the molecular orientation of the film as a function of the probing depth. PMID:23494276

  1. Active Chemical Sampling System for Underwater Chemical Source Localization

    OpenAIRE

    Ryuichi Takemura; Hiromi Sakata; Hiroshi Ishida

    2016-01-01

    This paper investigates the effect of active water sampling to enhance chemical reception for small underwater robots. The search for a chemical source in a stagnant water environment is not an easy task because the chemical solution released from the source stays in the close vicinity of the source. No signal is obtained even if a robot with chemical sensors is placed a few centimeters from the chemical source. In the system under study, four electrochemical sensors are aligned in front of a...

  2. A semiclassical non-adiabatic theory for elementary chemical reactions

    CERN Document Server

    Aubry, Serge

    2014-01-01

    Electron Transfer (ET) reactions are modeled by the dynamics of a quantum two-level system (representing the electronic state) coupled to a thermalized bath of classical harmonic oscillators (representing the nuclei degrees of freedom). Unlike for the standard Marcus theory, the complex amplitudes of the electronic state are chosen as reaction coordinates. Then, the dynamical equations at non vanishing temperature become those of an effective Hamiltonian submitted to damping terms and their associated Langevin random forces. The advantage of this new formalism is to extend the original theory by taking into account both ionic and covalent interactions. The standard theory is recovered only when covalent interactions are neglected. Increasing these covalent interactions from zero, the energy barrier predicted by the standard theory first depresses, next vanish (or almost vanish) and for stronger covalent interactions, covalent bond formation takes place of ET. In biochemistry, the standard Marcus theory often ...

  3. Closed loop chemical systems for energy storage and transmission (chemical heat pipe). Final report

    Energy Technology Data Exchange (ETDEWEB)

    Vakil, H.B.; Flock, J.W.

    1978-02-01

    The work documents the anlaysis of closed loop chemical systems for energy storage and transmission, commonly referred to as the Chemical Heat Pipe (CHP). Among the various chemical reaction systems and sources investigated, the two best systems were determined to be the high temperature methane/steam reforming reaction (HTCHP) coupled to a Very High Temperature Gas Cooled Reactor (VHTR) and the lower temperature, cyclohexane dehydrogenation reaction (LTCHP) coupled to existing sources such as coal or light water reactors. Solar and other developing technologies can best be coupled to the LTCHP. The preliminary economic and technical analyses show that both systems could transport heat at an incremental cost of approximately $1.50/GJ/160 km (in excess of the primary heat cost of $2.50/GJ), at system efficiencies above 80%. Solar heat can be transported at an incremental cost of $3/GJ/160 km. The use of the mixed feed evaporator concept developed in this work contributes significantly to reducing the transportation cost and increasing the efficiency of the system. The LTCHP shows the most promise of the two systems if the technical feasibility of the cyclic closed loop chemical reaction system can be established. An experimental program for establishing this feasibility is recommended. Since the VHTR is several years away from commercial demonstration and the HTCHP chemical technology is well developed, future HTCHP programs should be aimed at VHTR and interface problems.

  4. Chemical Reaction and Flow Modeling in Fullerene and Nanotube Production

    Science.gov (United States)

    Scott, Carl D.; Farhat, Samir; Greendyke, Robert B.

    2004-01-01

    The development of processes to produce fullerenes and carbon nanotubes has largely been empirical. Fullerenes were first discovered in the soot produced by laser ablation of graphite [1]and then in the soot of electric arc evaporated carbon. Techniques and conditions for producing larger and larger quantities of fullerenes depended mainly on trial and error empirical variations of these processes, with attempts to scale them up by using larger electrodes and targets and higher power. Various concepts of how fullerenes and carbon nanotubes were formed were put forth, but very little was done based on chemical kinetics of the reactions. This was mainly due to the complex mixture of species and complex nature of conditions in the reactors. Temperatures in the reactors varied from several thousand degrees Kelvin down to near room temperature. There are hundreds of species possible, ranging from atomic carbon to large clusters of carbonaceous soot, and metallic catalyst atoms to metal clusters, to complexes of metals and carbon. Most of the chemical kinetics of the reactions and the thermodynamic properties of clusters and complexes have only been approximated. In addition, flow conditions in the reactors are transient or unsteady, and three dimensional, with steep spatial gradients of temperature and species concentrations. All these factors make computational simulations of reactors very complex and challenging. This article addresses the development of the chemical reaction involved in fullerene production and extends this to production of carbon nanotubes by the laser ablation/oven process and by the electric arc evaporation process. In addition, the high-pressure carbon monoxide (HiPco) process is discussed. The article is in several parts. The first one addresses the thermochemical aspects of modeling; and considers the development of chemical rate equations, estimates of reaction rates, and thermodynamic properties where they are available. The second part

  5. Open chemical reaction networks, steady-state loads and Braess-like paradox

    CERN Document Server

    Banerjee, Kinshuk

    2014-01-01

    Open chemical reaction systems involve matter-exchange with the surroundings. As a result, species can accumulate inside a system during the course of the reaction. We study the role of network topology in governing the concentration build-up inside a fixed reaction volume at steady state, particularly focusing on the effect of additional paths. The problem is akin to that in traffic networks where an extra route, surprisingly, can increase the overall travel time. This is known as the Braess' paradox. Here, we report chemical analogues of such a paradox in suitably chosen reaction networks, where extra reaction step(s) can inflate the total concentration, denoted as `load', at steady state. It is shown that, such counter-intuitive behavior emerges in a qualitatively similar pattern in networks of varying complexities. We then explore how such extra routes affect the load in a biochemical scheme of uric acid degradation. From a thorough analysis of this network, we propose a functional role of some decomposit...

  6. Computed Potential Energy Surfaces and Minimum Energy Pathway for Chemical Reactions

    Science.gov (United States)

    Walch, Stephen P.; Langhoff, S. R. (Technical Monitor)

    1994-01-01

    Computed potential energy surfaces are often required for computation of such observables as rate constants as a function of temperature, product branching ratios, and other detailed properties. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method with the Dunning correlation consistent basis sets to obtain accurate energetics, gives useful results for a number of chemically important systems. Applications to complex reactions leading to NO and soot formation in hydrocarbon combustion are discussed.

  7. Free convection in MHD micropolar fluid with radiation and chemical reaction effects

    OpenAIRE

    Srinivasacharya D.; Mendu Upendar

    2014-01-01

    In this paper, the effects of radiation and first order chemical reaction on free convection heat and mass transfer in a micropolar fluid is considered. A uniform magnetic field is applied normal to the plate. The plate is maintained with variable surface heat and mass fluxes. The governing nonlinear partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations using similarity transformations and then sol...

  8. Ultrafast electron diffraction and direct observation of transient structures in a chemical reaction

    OpenAIRE

    Cao, Jianming; Ihee, Hyotcherl; Zewail, Ahmed H.

    1999-01-01

    Ultrafast electron diffraction is a unique method for the studies of structural changes of complex molecular systems. In this contribution, we report direct ultrafast electron diffraction study of the evolution of short-lived intermediates in the course of a chemical change. Specifically, we observe the transient intermediate in the elimination reaction of 1,2-diiodotetrafluoroethane (C2F4I2) to produce the corresponding ethylene derivative by the breakage of two carbon-iodine, C---I, bonds. ...

  9. Automated Discovery of Elementary Chemical Reaction Steps Using Freezing String and Berny Optimization Methods

    OpenAIRE

    Suleimanov, Yury V.; Green, William H.

    2015-01-01

    We present a simple protocol which allows fully automated discovery of elementary chemical reaction steps using in cooperation single- and double-ended transition-state optimization algorithms - the freezing string and Berny optimization methods, respectively. To demonstrate the utility of the proposed approach, the reactivity of several systems of combustion and atmospheric chemistry importance is investigated. The proposed algorithm allowed us to detect without any human intervention not on...

  10. Study on the key problems of interaction between microwave and chemical reaction

    Institute of Scientific and Technical Information of China (English)

    YANG Xiaoqing; HUANG Kama

    2007-01-01

    Microwave has been found as an efficient heating method in chemical industry.However,in present days the interaction between microwave and chemical reactions has not been deeply understood,which restricts a wider application of high power microwave in chemical industry.In this Paper,the key problems of interaction between microwave and chemical reaction are investigated,such as complex effective permittivity of chemical reaction,simulation of microwave heating on chemical reaction and non-thermal effect of microwave,which will enhance further knowledge of the mechanism of interaction between microwave and chemical reaction.Moreover,such an analysis is beneficial for handling with difficulties in application of microwave chemical industry.

  11. Global solutions of a strongly coupled reaction-diffusion system with different diffusion coefficients

    OpenAIRE

    L. W. Somathilake; Peiris, J. M. J. J.

    2005-01-01

    We deal with a mathematical model for a four-component chemical reaction-diffusion process. The model is described by a system of strongly coupled reaction-diffusion equations with different diffusion rates. The existence of the global solution of this reaction-diffusion system in unbounded domain is proved by using semigroup theory and estimates on the growth of solutions.

  12. Method of Investigating Fast Chemical Reactions Based on μ+-Meson Depolarization

    International Nuclear Information System (INIS)

    When a μ+-meson is slowed down in a substance the hydrogenoid muonium atom formed enters into chemical reactions similar to the corresponding interactions of atomic hydrogen. The observed angular distribution effect of the meson decay is associated with the chemical state of the meson. The absolute constants of the rate of the chemical reactions are determined in relation to the known nuclear physical decay characteristics. The method is independent of the state of aggregation of the substance and can be applied at essentially any temperature. Quantitative identification of the classes of the substances obtained (radical and molecular products are determined separately) is possible, as is individual determination based on variations in the precession of the system of spins in the magnetic field using a number of diatomic molecules as an example. The authors consider the possibility of studying the structural parameters of the radicals and molecules, and of estimating the lifetime of the short-lived intermediate compounds. The elementary steps in fast chemical reactions are investigated. (author)

  13. Uses and abuses of the Langevin equation for chemical reactions in condensed phases

    International Nuclear Information System (INIS)

    The Langevin and Fokker-Planck equations are useful in the description of many classical and quantum mechanical systems. However, these equations are justifiable from molecular considerations under very restricted conditions. These conditions include weak coupling. Brownian motion, and systems with special Hamiltonians. The application of these equations to chemical reactions in condensed phases is fraught with peril, particularly for fluid systems. The authors examine the molecular derivations of these equations and describe the conditions under which they are justifiable. It is, of course, possible that the equations are useful under other conditions

  14. Free convection in MHD micropolar fluid with radiation and chemical reaction effects

    Directory of Open Access Journals (Sweden)

    Srinivasacharya D.

    2014-01-01

    Full Text Available In this paper, the effects of radiation and first order chemical reaction on free convection heat and mass transfer in a micropolar fluid is considered. A uniform magnetic field is applied normal to the plate. The plate is maintained with variable surface heat and mass fluxes. The governing nonlinear partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations using similarity transformations and then solved numerically using the Keller-box method. The numerical results are compared and found to be in good agreement with previously published results as special cases of the present investigation. The dimensionless velocity, microrotation, temperature, concentration and heat and mass transfer rates are presented graphically for various values of coupling number, magnetic parameter, radiation parameter, chemical reaction parameter. The numerical values of the skin friction and wall couple stress for different values of governing parameters are also tabulated.

  15. A transition in the spatially integrated reaction rate of bimolecular reaction-diffusion systems

    Science.gov (United States)

    Arshadi, Masoud; Rajaram, Harihar

    2015-09-01

    Numerical simulations of diffusion with bimolecular reaction demonstrate a transition in the spatially integrated reaction rate—increasing with time initially, and transitioning to a decrease with time. In previous work, this reaction-diffusion problem has been analyzed as a Stefan problem involving a distinct moving boundary (reaction front), leading to predictions that front motion scales as √t, and correspondingly the spatially integrated reaction rate decreases as the square root of time 1/√t. We present a general nondimensionalization of the problem and a perturbation analysis to show that there is an early time regime where the spatially integrated reaction rate scales as √t rather than 1/√t. The duration of this early time regime (where the spatially integrated reaction rate is kinetically rather than diffusion controlled) is shown to depend on the kinetic rate parameters, diffusion coefficients, and initial concentrations of the two species. Numerical simulation results confirm the theoretical estimates of the transition time. We present illustrative calculations in the context of in situ chemical oxidation for remediation of fractured rock systems where contaminants are largely dissolved in the rock matrix. We consider different contaminants of concern (COCs), including TCE, PCE, MTBE, and RDX. While the early time regime is very short lived for TCE, it can persist over months to years for MTBE and RDX, due to slow oxidation kinetics.

  16. Mechanism of the Ferrocyanide-Iodate-Sulfite Oscillatory Chemical Reaction.

    Science.gov (United States)

    Horváth, Viktor; Epstein, Irving R; Kustin, Kenneth

    2016-03-31

    Existing models of the ferrocyanide-iodate-sulfite (FIS) reaction seek to replicate the oscillatory pH behavior that occurs in open systems. These models exhibit significant differences in the amplitudes and waveforms of the concentration oscillations of such intermediates as I(-), I3(-), and Fe(CN)6(3-) under identical conditions and do not include several experimentally found intermediates. Here we report measurements of sulfite concentrations during an oscillatory cycle. Knowing the correct concentration of sulfite over the course of a period is important because sulfite is the main component that determines the buffer capacity, the pH extrema, and the amount of oxidizer (iodate) required for the transition to low pH. On the basis of this new result and recent experimental findings on the rate laws and intermediates of component processes taken from the literature, we propose a mass action kinetics model that attempts to faithfully represent the chemistry of the FIS reaction. This new comprehensive mechanism reproduces the pH oscillations and the periodic behavior in [Fe(CN)6(3-)], [I3(-)], [I(-)], and [SO3(2-)]T with characteristics similar to those seen in experiments in both CSTR and semibatch arrangements. The parameter ranges at which stationary and oscillatory behavior is exhibited also show good agreement with those of the experiments. PMID:26949219

  17. Lie symmetries of nonlinear multidimensional reaction-diffusion systems:

    International Nuclear Information System (INIS)

    We present a complete description of the classical (Lie) symmetries of a coupled system of partial differential equations comprising a pair of semilinear reaction-diffusion equations with constant diffusivities and arbitrary nonlinearities in the reaction terms, in any number of spatial dimensions. Part I (Cherniha R M and King J R 2000 J. Phys. A: Math. Gen. 33 267-82, J. Phys. A: Math. Gen. 33 7839-41) addressed the case of unequal diffusivities; here we complete the analysis by treating the case of equal diffusivities in which the symmetry structure is richer still. Such models arise in the description of numerous physical, chemical and biological systems and we also indicate the possible application in such contexts of some of the specific cases arising from the group classification. Specifically, a variety of Lie's ansaetze and exact solutions of the so-called λ - ω reaction-diffusion systems, of a type that arises in mathematical biology, are constructed

  18. Parametric spatiotemporal oscillation in reaction-diffusion systems.

    Science.gov (United States)

    Ghosh, Shyamolina; Ray, Deb Shankar

    2016-03-01

    We consider a reaction-diffusion system in a homogeneous stable steady state. On perturbation by a time-dependent sinusoidal forcing of a suitable scaling parameter the system exhibits parametric spatiotemporal instability beyond a critical threshold frequency. We have formulated a general scheme to calculate the threshold condition for oscillation and the range of unstable spatial modes lying within a V-shaped region reminiscent of Arnold's tongue. Full numerical simulations show that depending on the specificity of nonlinearity of the models, the instability may result in time-periodic stationary patterns in the form of standing clusters or spatially localized breathing patterns with characteristic wavelengths. Our theoretical analysis of the parametric oscillation in reaction-diffusion system is corroborated by full numerical simulation of two well-known chemical dynamical models: chlorite-iodine-malonic acid and Briggs-Rauscher reactions. PMID:27078346

  19. Chemical reaction path modeling of hydrothermal processes on Mars: Preliminary results

    Science.gov (United States)

    Plumlee, Geoffrey S.; Ridley, W. Ian

    1992-01-01

    Hydrothermal processes are thought to have had significant roles in the development of surficial mineralogies and morphological features on Mars. For example, a significant proportion of the Martian soil could consist of the erosional products of hydrothermally altered impact melt sheets. In this model, impact-driven, vapor-dominated hydrothermal systems hydrothermally altered the surrounding rocks and transported volatiles such as S and Cl to the surface. Further support for impact-driven hydrothermal alteration on Mars was provided by studies of the Ries crater, Germany, where suevite deposits were extensively altered to montmorillonite clays by inferred low-temperature (100-130 C) hydrothermal fluids. It was also suggested that surface outflow from both impact-driven and volcano-driven hydrothermal systems could generate the valley networks, thereby eliminating the need for an early warm wet climate. We use computer-driven chemical reaction path calculation to model chemical processes which were likely associated with postulated Martian hydrothermal systems.

  20. Two-scale large deviations for chemical reaction kinetics through second quantization path integral

    International Nuclear Information System (INIS)

    Motivated by the study of rare events for a typical genetic switching model in systems biology, in this paper we aim to establish the general two-scale large deviations for chemical reaction systems. We build a formal approach to explicitly obtain the large deviation rate functionals for the considered two-scale processes based upon the second quantization path integral technique. We get three important types of large deviation results when the underlying two timescales are in three different regimes. This is realized by singular perturbation analysis to the rate functionals obtained by the path integral. We find that the three regimes possess the same deterministic mean-field limit but completely different chemical Langevin approximations. The obtained results are natural extensions of the classical large volume limit for chemical reactions. We also discuss its implication on the single-molecule Michaelis–Menten kinetics. Our framework and results can be applied to understand general multi-scale systems including diffusion processes. (paper)

  1. Self-similar fast-reaction limits for reaction-diffusion systems on unbounded domains

    Science.gov (United States)

    Crooks, E. C. M.; Hilhorst, D.

    2016-08-01

    We present a unified approach to characterising fast-reaction limits of systems of either two reaction-diffusion equations, or one reaction-diffusion equation and one ordinary differential equation, on unbounded domains, motivated by models of fast chemical reactions where either one or both reactant(s) is/are mobile. For appropriate initial data, solutions of four classes of problems each converge in the fast-reaction limit k → ∞ to a self-similar limit profile that has one of four forms, depending on how many components diffuse and whether the spatial domain is a half or whole line. For fixed k, long-time convergence to these same self-similar profiles is also established, thanks to a scaling argument of Kamin. Our results generalise earlier work of Hilhorst, van der Hout and Peletier to a much wider class of problems, and provide a quantitative description of the penetration of one substance into another in both the fast-reaction and long-time regimes.

  2. Mixing and chemical reaction in sheared and nonsheared homogeneous turbulence

    Science.gov (United States)

    Leonard, Andy D.; Hill, James C.

    1992-01-01

    Direct numerical simulations were made to examine the local structure of the reaction zone for a moderately fast reaction between unmixed species in decaying, homogeneous turbulence and in a homogeneous turbulent shear flow. Pseudospectral techniques were used in domains of 64 exp 3 and higher wavenumbers. A finite-rate, single step reaction between non-premixed reactants was considered, and in one case temperature-dependent Arrhenius kinetics was assumed. Locally intense reaction rates that tend to persist throughout the simulations occur in locations where the reactant concentration gradients are large and are amplified by the local rate of strain. The reaction zones are more organized in the case of a uniform mean shear than in isotropic turbulence, and regions of intense reaction rate appear to be associated with vortex structures such as horseshoe vortices and fingers seen in mixing layers. Concentration gradients tend to align with the direction of the most compressive principal strain rate, more so in the isotropic case.

  3. Coupling sample paths to the partial thermodynamic limit in stochastic chemical reaction networks

    CERN Document Server

    Levien, Ethan

    2016-01-01

    We present a new technique for reducing the variance in Monte Carlo estimators of stochastic chemical reaction networks. Our method makes use of the fact that many stochastic reaction networks converge to piecewise deterministic Markov processes in the large system-size limit. The statistics of the piecewise deterministic process can be obtained much more efficiently than those of the exact process. By coupling sample paths of the exact model to the piecewise deterministic process we are able to reduce the variance, and hence the computational complexity of the Monte Carlo estimator. In addition to rigorous results concerning the asymptotic behavior of our method, numerical simulations are performed on some simple biological models suggesting that significant computational gains are made for even moderate system-sizes.

  4. Mapping Students' Conceptual Modes When Thinking about Chemical Reactions Used to Make a Desired Product

    Science.gov (United States)

    Weinrich, M. L.; Talanquer, V.

    2015-01-01

    The central goal of this qualitative research study was to uncover major implicit assumptions that students with different levels of training in the discipline apply when thinking and making decisions about chemical reactions used to make a desired product. In particular, we elicited different ways of conceptualizing why chemical reactions happen…

  5. Motivational Factors Contributing to Turkish High School Students' Achievement in Gases and Chemical Reactions

    Science.gov (United States)

    Kadioglu, Cansel; Uzuntiryaki, Esen

    2008-01-01

    This study aimed to investigate the contribution of motivational factors to 10th grade students' achievement in gases and chemical reactions in chemistry. Three hundred fifty nine 10th grade students participated in the study. The Gases and Chemical Reactions Achievement Test and the Motivated Strategies for Learning Questionnaire were…

  6. Introducing Stochastic Simulation of Chemical Reactions Using the Gillespie Algorithm and MATLAB: Revisited and Augmented

    Science.gov (United States)

    Argoti, A.; Fan, L. T.; Cruz, J.; Chou, S. T.

    2008-01-01

    The stochastic simulation of chemical reactions, specifically, a simple reversible chemical reaction obeying the first-order, i.e., linear, rate law, has been presented by Martinez-Urreaga and his collaborators in this journal. The current contribution is intended to complement and augment their work in two aspects. First, the simple reversible…

  7. Rate constants of chemical reactions from semiclassical transition state theory in full and one dimension

    Science.gov (United States)

    Greene, Samuel M.; Shan, Xiao; Clary, David C.

    2016-06-01

    Semiclassical Transition State Theory (SCTST), a method for calculating rate constants of chemical reactions, offers gains in computational efficiency relative to more accurate quantum scattering methods. In full-dimensional (FD) SCTST, reaction probabilities are calculated from third and fourth potential derivatives along all vibrational degrees of freedom. However, the computational cost of FD SCTST scales unfavorably with system size, which prohibits its application to larger systems. In this study, the accuracy and efficiency of 1-D SCTST, in which only third and fourth derivatives along the reaction mode are used, are investigated in comparison to those of FD SCTST. Potential derivatives are obtained from numerical ab initio Hessian matrix calculations at the MP2/cc-pVTZ level of theory, and Richardson extrapolation is applied to improve the accuracy of these derivatives. Reaction barriers are calculated at the CCSD(T)/cc-pVTZ level. Results from FD SCTST agree with results from previous theoretical and experimental studies when Richardson extrapolation is applied. Results from our implementation of 1-D SCTST, which uses only 4 single-point MP2/cc-pVTZ energy calculations in addition to those for conventional TST, agree with FD results to within a factor of 5 at 250 K. This degree of agreement and the efficiency of the 1-D method suggest its potential as a means of approximating rate constants for systems too large for existing quantum scattering methods.

  8. Rate constants of chemical reactions from semiclassical transition state theory in full and one dimension.

    Science.gov (United States)

    Greene, Samuel M; Shan, Xiao; Clary, David C

    2016-06-28

    Semiclassical Transition State Theory (SCTST), a method for calculating rate constants of chemical reactions, offers gains in computational efficiency relative to more accurate quantum scattering methods. In full-dimensional (FD) SCTST, reaction probabilities are calculated from third and fourth potential derivatives along all vibrational degrees of freedom. However, the computational cost of FD SCTST scales unfavorably with system size, which prohibits its application to larger systems. In this study, the accuracy and efficiency of 1-D SCTST, in which only third and fourth derivatives along the reaction mode are used, are investigated in comparison to those of FD SCTST. Potential derivatives are obtained from numerical ab initio Hessian matrix calculations at the MP2/cc-pVTZ level of theory, and Richardson extrapolation is applied to improve the accuracy of these derivatives. Reaction barriers are calculated at the CCSD(T)/cc-pVTZ level. Results from FD SCTST agree with results from previous theoretical and experimental studies when Richardson extrapolation is applied. Results from our implementation of 1-D SCTST, which uses only 4 single-point MP2/cc-pVTZ energy calculations in addition to those for conventional TST, agree with FD results to within a factor of 5 at 250 K. This degree of agreement and the efficiency of the 1-D method suggest its potential as a means of approximating rate constants for systems too large for existing quantum scattering methods. PMID:27369506

  9. Effects of gel properties produced by chemical reactions on viscous fingering

    Science.gov (United States)

    Ujiie, Tomohiro; Nagatsu, Yuichiro; Ban, Mitsumasa; Iwata, Shuichi; Kato, Yoshihito; Tada, Yutaka

    2011-11-01

    We have experimentally investigated viscous fingering with chemical reaction producing gel. Here, two systems were employed. In one system, sodium polyacrylate (SPA) solution and ferric ion solution were used as the more and less viscous liquids, respectively. In another system, xthantan gum (XG) solution and the ferric ion solution were used as the more and less viscous liquids, respectively. For high concentration of ferric ion, viscous fingering pattern was changed into spiral pattern in the former system, whereas into fracture pattern in the latter system. We consider that the difference in the change of the patterns in the two systems will be caused by the difference in the properties of the gels. Therefore, we have measured the rheological properties of the gels by means of a rheometer. We have found that the gel in the former case is more elastic. Furthermore, we have discussed the relationship between the measured rheological properties and the observed spiral or fracturing patterns.

  10. A Novel Oscillating Chemical Reaction Using Ninhydrin as Single Organic Substrate

    Institute of Scientific and Technical Information of China (English)

    Fu Wei YANG; Jin Zhang GAO; Wu YANG; Kan Jun SUN

    2006-01-01

    A novel oscillating chemical reaction using ninhydrin as a single organic substrate was represented in this paper. It distinguished from the classically catalyzed BZ oscillating chemical reaction due to there was no active methene (CH2=) and/or enol structure in the ninhydrin molecule, which served as single organic substrate. This suggested that the substrates used in catalyzed BZ reaction were not always the organic compounds containing active methene (CH2=) and/or enol structure and bromination process in this kind of catalyzed chemical oscillating reaction was not also necessary.

  11. Formation of slow molecules in chemical reactions in crossed molecular beams

    Science.gov (United States)

    Tscherbul, T. V.; Barinovs, Ğ.; Kłos, J.; Krems, R. V.

    2008-08-01

    We demonstrate that chemical reactions in collisions of molecular beams can generally produce low-velocity molecules in the laboratory-fixed frame. Our analysis shows that collisions of beams may simultaneously yield slow reactant molecules and slow products. The reaction products are formed in selected rovibrational states and scattered in a specific direction, which can be controlled by tuning the kinetic energies of the incident beams and the angle between the beams. Our calculations indicate that chemical reactions of polar alkali-metal dimers are barrierless and we suggest that chemical reactions involving alkali-metal dimers may be particularly suitable for producing slow molecules in crossed beams.

  12. Probabilistic sensitivity analysis of biochemical reaction systems

    OpenAIRE

    Zhang, Hong-Xuan; Dempsey, William P.; Goutsias, John

    2009-01-01

    Sensitivity analysis is an indispensable tool for studying the robustness and fragility properties of biochemical reaction systems as well as for designing optimal approaches for selective perturbation and intervention. Deterministic sensitivity analysis techniques, using derivatives of the system response, have been extensively used in the literature. However, these techniques suffer from several drawbacks, which must be carefully considered before using them in problems of systems biology. ...

  13. Chemical Pattern Formation in Far-From Systems.

    Science.gov (United States)

    Pearson, John Evan

    The diffusive instability was proposed as a mechanism for pattern formation in chemical systems, in the context of biological morphogenesis, by Alan Turing in 1952. The instability gives rise to a chemical pattern with an intrinsic "chemical wavelength" that is independent of the system size. Since 1952, the diffusive instability, or Turing bifurcation, has been invoked to explain pattern formation in a variety of fields. To date there has been no unambiguous observation of such an instability. Model studies of the instability are usually carried out on systems containing two variables. Such works do not address issues that are of fundamental importance in experimental studies. How does one go about finding Turing bifurcations in systems with many parameters and for which the chemical kinetics are only partially known? What is the chemical wavelength? Turing bifurcations cannot occur in systems with all diffusion coefficients exactly equal. How unequal must the diffusion coefficients be for a system to undergo a Turing bifurcation?. Reacting and diffusing systems obey a partial -differential equation which is a sum of a diffusion term and a reaction term. Dropping the diffusion term results in an ordinary differential equation describing the reaction kinetics in a well-mixed system. In this dissertation it is shown that, for systems with an arbitrary number of variables, Turing bifurcations can occur with diffusion coefficients arbitrarily close to equal, provided the corresponding well-mixed system is sufficiently close to a point of coalescence of Hopf and saddle-node bifurcations. Since the bifurcation set can be obtained directly from experiments, one does not need a detailed microscopic theory of the reaction kinetics. Similarly, the chemical wavelength can be estimated from experimental measurements without knowledge of the reaction kinetics.

  14. Chemical reactions of ultracold alkali dimers in the lowest-energy $^3\\Sigma$ state

    CERN Document Server

    Tomza, Michał; Moszynski, Robert; Krems, Roman V

    2013-01-01

    We show that the interaction of polar alkali dimers in the quintet spin state leads to the formation of a deeply bound reaction complex. The reaction complex can decompose adiabatically into homonuclear alkali dimers (for all molecules except KRb) and into alkali trimers (for all molecules). We show that there are no barriers for these chemical reactions. This means that all alkali dimers in the $a^3\\Sigma^+$ state are chemically unstable at ultracold temperature, and the use of an optical lattice to segregate the molecules and suppress losses may be necessary. In addition, we calculate the minimum energy path for the chemical reactions of alkali hydrides. We find that the reaction of two molecules is accelerated by a strong attraction between the alkali atoms, leading to a barrierless process that produces hydrogen atoms with large kinetic energy. We discuss the unique features of the chemical reactions of ultracold alkali dimers in the $a^3\\Sigma^+$ electronic state.

  15. A multi target approach to control chemical reactions in their inhomogeneous solvent environment

    Science.gov (United States)

    Keefer, Daniel; Thallmair, Sebastian; Zauleck, Julius P. P.; de Vivie-Riedle, Regina

    2015-12-01

    Shaped laser pulses offer a powerful tool to manipulate molecular quantum systems. Their application to chemical reactions in solution is a promising concept to redesign chemical synthesis. Along this road, theoretical developments to include the solvent surrounding are necessary. An appropriate theoretical treatment is helpful to understand the underlying mechanisms. In our approach we simulate the solvent by randomly selected snapshots from molecular dynamics trajectories. We use multi target optimal control theory to optimize pulses for the various arrangements of explicit solvent molecules simultaneously. This constitutes a major challenge for the control algorithm, as the solvent configurations introduce a large inhomogeneity to the potential surfaces. We investigate how the algorithm handles the new challenges and how well the controllability of the system is preserved with increasing complexity. Additionally, we introduce a way to statistically estimate the efficiency of the optimized laser pulses in the complete thermodynamical ensemble.

  16. Chemical Synthesis Accelerated by Paper Spray: The Haloform Reaction

    Science.gov (United States)

    Bain, Ryan M.; Pulliam, Christopher J.; Raab, Shannon A.; Cooks, R. Graham

    2016-01-01

    In this laboratory, students perform a synthetic reaction in two ways: (i) by traditional bulk-phase reaction and (ii) in the course of reactive paper spray ionization. Mass spectrometry (MS) is used both as an analytical method and a means of accelerating organic syntheses. The main focus of this laboratory exercise is that the same ionization…

  17. Evolution of DNA and RNA as catalysts for chemical reactions.

    Science.gov (United States)

    Jäschke, A; Seelig, B

    2000-06-01

    In vitro selection from combinatorial nucleic acid libraries has provided new RNA and DNA molecules that have catalytic properties. Catalyzed reactions now go far beyond self-modifying reactions of nucleic acid molecules. The future application of in vitro selected RNA and DNA catalysts in bioorganic synthesis appears promising. PMID:10826969

  18. Propensity approach to nonequilibrium thermodynamics of a chemical reaction network: Controlling single E-coli β-galactosidase enzyme catalysis through the elementary reaction steps

    Energy Technology Data Exchange (ETDEWEB)

    Das, Biswajit; Gangopadhyay, Gautam, E-mail: gautam@bose.res.in [S. N. Bose National Centre For Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata 700 098 (India); Banerjee, Kinshuk [Department of Chemistry, University of Calcutta, 92 A.P.C. Road, Kolkata 700 009 (India)

    2013-12-28

    In this work, we develop an approach to nonequilibrium thermodynamics of an open chemical reaction network in terms of the elementary reaction propensities. The method is akin to the microscopic formulation of the dissipation function in terms of the Kullback-Leibler distance of phase space trajectories in Hamiltonian system. The formalism is applied to a single oligomeric enzyme kinetics at chemiostatic condition that leads the reaction system to a nonequilibrium steady state, characterized by a positive total entropy production rate. Analytical expressions are derived, relating the individual reaction contributions towards the total entropy production rate with experimentally measurable reaction velocity. Taking a real case of Escherichia coli β-galactosidase enzyme obeying Michaelis-Menten kinetics, we thoroughly analyze the temporal as well as the steady state behavior of various thermodynamic quantities for each elementary reaction. This gives a useful insight in the relative magnitudes of various energy terms and the dissipated heat to sustain a steady state of the reaction system operating far-from-equilibrium. It is also observed that, the reaction is entropy-driven at low substrate concentration and becomes energy-driven as the substrate concentration rises.

  19. Computed Potential Energy Surfaces and Minimum Energy Pathways for Chemical Reactions

    Science.gov (United States)

    Walch, Stephen P.; Langhoff, S. R. (Technical Monitor)

    1994-01-01

    Computed potential energy surfaces are often required for computation of such parameters as rate constants as a function of temperature, product branching ratios, and other detailed properties. For some dynamics methods, global potential energy surfaces are required. In this case, it is necessary to obtain the energy at a complete sampling of all the possible arrangements of the nuclei, which are energetically accessible, and then a fitting function must be obtained to interpolate between the computed points. In other cases, characterization of the stationary points and the reaction pathway connecting them is sufficient. These properties may be readily obtained using analytical derivative methods. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method to obtain accurate energetics, gives usefull results for a number of chemically important systems. The talk will focus on a number of applications including global potential energy surfaces, H + O2, H + N2, O(3p) + H2, and reaction pathways for complex reactions, including reactions leading to NO and soot formation in hydrocarbon combustion.

  20. Surface chemical reactions induced by molecules electronically-excited in the gas

    DEFF Research Database (Denmark)

    Petrunin, Victor V.

    2011-01-01

    alignment are taking place, guiding all the molecules towards the intersections with the ground state PES, where transitions to the ground state PES will occur with minimum energy dissipation. The accumulated kinetic energy may be used to overcome the chemical reaction barrier. While recombination chemical...... be readily produced. Products of chemical adsorption and/or chemical reactions induced within adsorbates are aggregated on the surface and observed by light scattering. We will demonstrate how pressure and spectral dependencies of the chemical outcomes, polarization of the light and interference of...... two laser beams inducing the reaction can be used to distinguish the new process we try to investigate from chemical reactions induced by photoexcitation within adsorbed molecules and/or gas phase photolysis....

  1. Using Drawing Technology to Assess Students' Visualizations of Chemical Reaction Processes

    Science.gov (United States)

    Chang, Hsin-Yi; Quintana, Chris; Krajcik, Joseph

    2014-06-01

    In this study, we investigated how students used a drawing tool to visualize their ideas of chemical reaction processes. We interviewed 30 students using thinking-aloud and retrospective methods and provided them with a drawing tool. We identified four types of connections the students made as they used the tool: drawing on existing knowledge, incorporating dynamic aspects of chemical processes, linking a visualization to the associated chemical phenomenon, and connecting between the visualization and chemistry concepts. We also compared students who were able to create dynamic visualizations with those who only created static visualizations. The results indicated a relationship between students constructing a dynamic view of chemical reaction processes and their understanding of chemical reactions. This study provides insights into the use of visualizations to support instruction and assessment to facilitate students' integrated understanding of chemical reactions.

  2. Multi-scenario modelling of uncertainty in stochastic chemical systems

    International Nuclear Information System (INIS)

    Uncertainty analysis has not been well studied at the molecular scale, despite extensive knowledge of uncertainty in macroscale systems. The ability to predict the effect of uncertainty allows for robust control of small scale systems such as nanoreactors, surface reactions, and gene toggle switches. However, it is difficult to model uncertainty in such chemical systems as they are stochastic in nature, and require a large computational cost. To address this issue, a new model of uncertainty propagation in stochastic chemical systems, based on the Chemical Master Equation, is proposed in the present study. The uncertain solution is approximated by a composite state comprised of the averaged effect of samples from the uncertain parameter distributions. This model is then used to study the effect of uncertainty on an isomerization system and a two gene regulation network called a repressilator. The results of this model show that uncertainty in stochastic systems is dependent on both the uncertain distribution, and the system under investigation. -- Highlights: •A method to model uncertainty on stochastic systems was developed. •The method is based on the Chemical Master Equation. •Uncertainty in an isomerization reaction and a gene regulation network was modelled. •Effects were significant and dependent on the uncertain input and reaction system. •The model was computationally more efficient than Kinetic Monte Carlo

  3. Multi-scenario modelling of uncertainty in stochastic chemical systems

    Energy Technology Data Exchange (ETDEWEB)

    Evans, R. David [Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1 (Canada); Ricardez-Sandoval, Luis A., E-mail: laricardezsandoval@uwaterloo.ca [Department of Chemical Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1 (Canada); Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1 (Canada)

    2014-09-15

    Uncertainty analysis has not been well studied at the molecular scale, despite extensive knowledge of uncertainty in macroscale systems. The ability to predict the effect of uncertainty allows for robust control of small scale systems such as nanoreactors, surface reactions, and gene toggle switches. However, it is difficult to model uncertainty in such chemical systems as they are stochastic in nature, and require a large computational cost. To address this issue, a new model of uncertainty propagation in stochastic chemical systems, based on the Chemical Master Equation, is proposed in the present study. The uncertain solution is approximated by a composite state comprised of the averaged effect of samples from the uncertain parameter distributions. This model is then used to study the effect of uncertainty on an isomerization system and a two gene regulation network called a repressilator. The results of this model show that uncertainty in stochastic systems is dependent on both the uncertain distribution, and the system under investigation. -- Highlights: •A method to model uncertainty on stochastic systems was developed. •The method is based on the Chemical Master Equation. •Uncertainty in an isomerization reaction and a gene regulation network was modelled. •Effects were significant and dependent on the uncertain input and reaction system. •The model was computationally more efficient than Kinetic Monte Carlo.

  4. Chemical Tracking Systems: Not Your Usual Global Positioning System!

    Science.gov (United States)

    Roy, Ken

    2007-01-01

    The haphazard storing and tracking of chemicals in the laboratory is a serious safety issue facing science teachers. To get control of your chemicals, try implementing a "chemical tracking system". A chemical tracking system (CTS) is a database of chemicals used in the laboratory. If implemented correctly, a CTS will reduce purchasing costs,…

  5. A weak comparison principle for reaction-diffusion systems

    CERN Document Server

    Valero, José

    2012-01-01

    In this paper we prove a weak comparison principle for a reaction-diffusion system without uniqueness of solutions. We apply the abstract results to the Lotka-Volterra system with diffusion, a generalized logistic equation and to a model of fractional-order chemical autocatalysis with decay. Morever, in the case of the Lotka-Volterra system a weak maximum principle is given, and a suitable estimate in the space of essentially bounded functions $L^{\\infty}$ is proved for at least one solution of the problem.

  6. A Weak Comparison Principle for Reaction-Diffusion Systems

    Directory of Open Access Journals (Sweden)

    José Valero

    2012-01-01

    Full Text Available We prove a weak comparison principle for a reaction-diffusion system without uniqueness of solutions. We apply the abstract results to the Lotka-Volterra system with diffusion, a generalized logistic equation, and to a model of fractional-order chemical autocatalysis with decay. Moreover, in the case of the Lotka-Volterra system a weak maximum principle is given, and a suitable estimate in the space of essentially bounded functions L∞ is proved for at least one solution of the problem.

  7. Detonation wave solutions and linear stability in a four component gas with bimolecular chemical reaction

    OpenAIRE

    Carvalho, Filipe; De Silva, A.W.; Soares, A. J.

    2015-01-01

    We consider a four component gas undergoing a bimolecular chemical reaction of type A1 + A2 = A3 + A4, described by the Boltzmann equation (BE) for chemically reactive mixtures. We adopt hard-spheres elastic cross sections and modified line-of-centers reactive cross sections depending on both the activation energy and geometry of the reactive collisions. Then we consider the hydrodynamic limit specified by the reactive Euler equations, in an earlier stage of the chemical reaction, when the ga...

  8. A new type of power energy for accelerating chemical reactions: the nature of a microwave-driving force for accelerating chemical reactions.

    Science.gov (United States)

    Zhou, Jicheng; Xu, Wentao; You, Zhimin; Wang, Zhe; Luo, Yushang; Gao, Lingfei; Yin, Cheng; Peng, Renjie; Lan, Lixin

    2016-01-01

    The use of microwave (MW) irradiation to increase the rate of chemical reactions has attracted much attention recently in nearly all fields of chemistry due to substantial enhancements in reaction rates. However, the intrinsic nature of the effects of MW irradiation on chemical reactions remains unclear. Herein, the highly effective conversion of NO and decomposition of H2S via MW catalysis were investigated. The temperature was decreased by several hundred degrees centigrade. Moreover, the apparent activation energy (Ea') decreased substantially under MW irradiation. Importantly, for the first time, a model of the interactions between microwave electromagnetic waves and molecules is proposed to elucidate the intrinsic reason for the reduction in the Ea' under MW irradiation, and a formula for the quantitative estimation of the decrease in the Ea' was determined. MW irradiation energy was partially transformed to reduce the Ea', and MW irradiation is a new type of power energy for speeding up chemical reactions. The effect of MW irradiation on chemical reactions was determined. Our findings challenge both the classical view of MW irradiation as only a heating method and the controversial MW non-thermal effect and open a promising avenue for the development of novel MW catalytic reaction technology. PMID:27118640

  9. A new type of power energy for accelerating chemical reactions: the nature of a microwave-driving force for accelerating chemical reactions

    Science.gov (United States)

    Zhou, Jicheng; Xu, Wentao; You, Zhimin; Wang, Zhe; Luo, Yushang; Gao, Lingfei; Yin, Cheng; Peng, Renjie; Lan, Lixin

    2016-01-01

    The use of microwave (MW) irradiation to increase the rate of chemical reactions has attracted much attention recently in nearly all fields of chemistry due to substantial enhancements in reaction rates. However, the intrinsic nature of the effects of MW irradiation on chemical reactions remains unclear. Herein, the highly effective conversion of NO and decomposition of H2S via MW catalysis were investigated. The temperature was decreased by several hundred degrees centigrade. Moreover, the apparent activation energy (Ea’) decreased substantially under MW irradiation. Importantly, for the first time, a model of the interactions between microwave electromagnetic waves and molecules is proposed to elucidate the intrinsic reason for the reduction in the Ea’ under MW irradiation, and a formula for the quantitative estimation of the decrease in the Ea’ was determined. MW irradiation energy was partially transformed to reduce the Ea’, and MW irradiation is a new type of power energy for speeding up chemical reactions. The effect of MW irradiation on chemical reactions was determined. Our findings challenge both the classical view of MW irradiation as only a heating method and the controversial MW non-thermal effect and open a promising avenue for the development of novel MW catalytic reaction technology. PMID:27118640

  10. Chemical reactions induced by oscillating external fields in weak thermal environments

    CERN Document Server

    Craven, Galen T; Hernandez, Rigoberto

    2015-01-01

    Chemical reaction rates must increasingly be determined in systems that evolve under the control of external stimuli. In these systems, when a reactant population is induced to cross an energy barrier through forcing from a temporally varying external field, the transition state that the reaction must pass through during the transformation from reactant to product is no longer a fixed geometric structure, but is instead time-dependent. For a periodically forced model reaction, we develop a recrossing-free dividing surface that is attached to a transition state trajectory [T. Bartsch, R. Hernandez, and T. Uzer, Phys. Rev. Lett. 95, 058301 (2005)]. We have previously shown that for single-mode sinusoidal driving, the stability of the time-varying transition state directly determines the reaction rate [G. T. Craven, T. Bartsch, and R. Hernandez, J. Chem. Phys. 141, 041106 (2014)]. Here, we extend our previous work to the case of multi-mode driving waveforms. Excellent agreement is observed between the rates pred...

  11. Low-temperature solid-phase chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Baluev, A.V.; Mityakhina, V.S.; Rogozev, B.I.; Silin, M.Yu.

    1987-06-01

    This paper is concerned with the possibility of solid-phase reactions carried out at 20-25 degrees C. A variety of solid complexes are ground and tested for their reaction capacity in the solid phase with acid phosphates, including complexes of iron, cesium, sodium, tin, and uranyl, using Moessbauer and infrared spectroscopy and thermal analysis. The reactions are considered viable not only because they avoid the expenditure of energy otherwise needed to heat the reactants but also because they provide a new method for the preparation of complex coordination compounds.

  12. A ``partitioned leaping'' approach for multiscale modeling of chemical reaction dynamics

    Science.gov (United States)

    Harris, Leonard A.; Clancy, Paulette

    2006-10-01

    We present a novel multiscale simulation approach for modeling stochasticity in chemical reaction networks. The approach seamlessly integrates exact-stochastic and "leaping" methodologies into a single partitioned leaping algorithmic framework. The technique correctly accounts for stochastic noise at significantly reduced computational cost, requires the definition of only three model-independent parameters, and is particularly well suited for simulating systems containing widely disparate species populations. We present the theoretical foundations of partitioned leaping, discuss various options for its practical implementation, and demonstrate the utility of the method via illustrative examples.

  13. Radiation and chemical reaction effects on MHD flow along a moving vertical porous plate

    Science.gov (United States)

    Ramana Reddy, G. V.; Bhaskar Reddy, N.; Gorla, R. S. R.

    2016-02-01

    This paper presents an analysis of the effects of magnetohydrodynamic force and buoyancy on convective heat and mass transfer flow past a moving vertical porous plate in the presence of thermal radiation and chemical reaction. The governing partial differential equations are reduced to a system of self-similar equations using the similarity transformations. The resultant equations are then solved numerically using the fourth order Runge-Kutta method along with the shooting technique. The results are obtained for the velocity, temperature, concentration, skin-friction, Nusselt number and Sherwood number. The effects of various parameters on flow variables are illustrated graphically, and the physical aspects of the problem are discussed.

  14. Modelling of chemical reaction in foods: a multiresponse approach.

    NARCIS (Netherlands)

    Boekel, van M.A.J.S.

    1998-01-01

    The quality of foods depends on several factors. One of these factors is the occurrence of (bio)chemical changes taking place during the post-harvest period and during processing, storage and distribution. In order to optimise quality it is of utmost importance to control (bio)chemical changes as mu

  15. ENGINEERED BARRIER SYSTEM: PHYSICAL AND CHEMICAL ENVIRONMENT

    Energy Technology Data Exchange (ETDEWEB)

    R. Jarek

    2005-08-29

    The purpose of this model report is to describe the evolution of the physical and chemical environmental conditions within the waste emplacement drifts of the repository, including the drip shield and waste package surfaces. The resulting seepage evaporation and gas abstraction models are used in the total system performance assessment for the license application (TSPA-LA) to assess the performance of the engineered barrier system and the waste form. This report develops and documents a set of abstraction-level models that describe the engineered barrier system physical and chemical environment. Where possible, these models use information directly from other reports as input, which promotes integration among process models used for TSPA-LA. Specific tasks and activities of modeling the physical and chemical environment are included in ''Technical Work Plan for: Near-Field Environment and Transport In-Drift Geochemistry Model Report Integration'' (BSC 2005 [DIRS 173782], Section 1.2.2). As described in the technical work plan, the development of this report is coordinated with the development of other engineered barrier system reports. To be consistent with other project documents that address features, events, and processes (FEPs), Table 6.14.1 of the current report includes updates to FEP numbers and FEP subjects for two FEPs identified in the technical work plan (TWP) governing this report (BSC 2005 [DIRS 173782]). FEP 2.1.09.06.0A (Reduction-oxidation potential in EBS), as listed in Table 2 of the TWP (BSC 2005 [DIRS 173782]), has been updated in the current report to FEP 2.1.09.06.0B (Reduction-oxidation potential in Drifts; see Table 6.14-1). FEP 2.1.09.07.0A (Reaction kinetics in EBS), as listed in Table 2 of the TWP (BSC 2005 [DIRS 173782]), has been updated in the current report to FEP 2.1.09.07.0B (Reaction kinetics in Drifts; see Table 6.14-1). These deviations from the TWP are justified because they improve integration with FEPs

  16. ENGINEERED BARRIER SYSTEM: PHYSICAL AND CHEMICAL ENVIRONMENT

    International Nuclear Information System (INIS)

    The purpose of this model report is to describe the evolution of the physical and chemical environmental conditions within the waste emplacement drifts of the repository, including the drip shield and waste package surfaces. The resulting seepage evaporation and gas abstraction models are used in the total system performance assessment for the license application (TSPA-LA) to assess the performance of the engineered barrier system and the waste form. This report develops and documents a set of abstraction-level models that describe the engineered barrier system physical and chemical environment. Where possible, these models use information directly from other reports as input, which promotes integration among process models used for TSPA-LA. Specific tasks and activities of modeling the physical and chemical environment are included in ''Technical Work Plan for: Near-Field Environment and Transport In-Drift Geochemistry Model Report Integration'' (BSC 2005 [DIRS 173782], Section 1.2.2). As described in the technical work plan, the development of this report is coordinated with the development of other engineered barrier system reports. To be consistent with other project documents that address features, events, and processes (FEPs), Table 6.14.1 of the current report includes updates to FEP numbers and FEP subjects for two FEPs identified in the technical work plan (TWP) governing this report (BSC 2005 [DIRS 173782]). FEP 2.1.09.06.0A (Reduction-oxidation potential in EBS), as listed in Table 2 of the TWP (BSC 2005 [DIRS 173782]), has been updated in the current report to FEP 2.1.09.06.0B (Reduction-oxidation potential in Drifts; see Table 6.14-1). FEP 2.1.09.07.0A (Reaction kinetics in EBS), as listed in Table 2 of the TWP (BSC 2005 [DIRS 173782]), has been updated in the current report to FEP 2.1.09.07.0B (Reaction kinetics in Drifts; see Table 6.14-1). These deviations from the TWP are justified because they improve integration with FEPs documents. The updates

  17. Vicher: A Virtual Reality Based Educational Module for Chemical Reaction Engineering.

    Science.gov (United States)

    Bell, John T.; Fogler, H. Scott

    1996-01-01

    A virtual reality application for undergraduate chemical kinetics and reactor design education, Vicher (Virtual Chemical Reaction Model) was originally designed to simulate a portion of a modern chemical plant. Vicher now consists of two programs: Vicher I that models catalyst deactivation and Vicher II that models nonisothermal effects in…

  18. Effects of Surfactants on the Rate of Chemical Reactions

    Directory of Open Access Journals (Sweden)

    B. Samiey

    2014-01-01

    Full Text Available Surfactants are self-assembled compounds that depend on their structure and electric charge can interact as monomer or micelle with other compounds (substrates. These interactions which may catalyze or inhibit the reaction rates are studied with pseudophase, cooperativity, and stoichiometric (classical models. In this review, we discuss applying these models to study surfactant-substrate interactions and their effects on Diels-Alder, redox, photochemical, decomposition, enzymatic, isomerization, ligand exchange, radical, and nucleophilic reactions.

  19. RPMDrate: Bimolecular chemical reaction rates from ring polymer molecular dynamics

    OpenAIRE

    Allen, Joshua W.; Green, William H; Suleimanov, Yu. V.

    2013-01-01

    We present RPMDrate, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett–Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any ...

  20. Precision synthesis of functional materials via RAFT polymerization and click-type chemical reactions

    Science.gov (United States)

    Flores, Joel Diez

    2011-12-01

    The need to tailor polymeric architectures with specific physico-chemical properties via the simplest, cleanest, and most efficient synthetic route possible has become the ultimate goal in polymer synthesis. Recent progress in macromolecular science, such as the discoveries of controlled/"living" free radical polymerization (CRP) methods, has brought about synthetic capabilities to prepare (co)polymers with advanced topologies, predetermined molecular weights, narrow molecular weight distributions, and precisely located functional groups. In addition, the establishment of click chemistry has redefined the selected few highly efficient chemical reactions that become highly useful in post-polymerization modification strategies. Hence, the ability to make well-defined topologies afforded by controlled polymerization techniques and the facile incorporation of functionalities along the chain via click-type reactions have yielded complex architectures, allowing the investigation of physical phenomena which otherwise could not be studied with systems prepared via conventional methods. The overarching theme of the research work described in this dissertation is the fusion of the excellent attributes of reversible addition-fragmentation chain transfer (RAFT) polymerization method, which is one of the CRP techniques, and click-type chemical reactions in the precision of synthesis of advanced functional materials. Chapter IV is divided into three sections. In Section I, the direct RAFT homopolymerization of 2-(acryloyloxy)ethyl isocyanate (AOI) and subsequent post-polymerization modifications are described. The polymerization conditions were optimized in terms of the choice of RAFT chain transfer agent (CTA), polymerization temperature and the reaction medium. Direct RAFT polymerization of AOI requires a neutral CTA, and relatively low reaction temperature to yield AOI homopolymers with low polydispersities. Efficient side-chain functionalization of PAOI homopolymers was

  1. Analysis of weblike network structures of directed graphs for chemical reactions in methane plasmas

    International Nuclear Information System (INIS)

    Chemical reactions of molecular gases like methane are so complicated that a chart of decomposed and/or synthesized species originating from molecules in plasma resembles a weblike network in which we write down species and reactions among them. Here we consider properties of the network structures of chemical reactions in methane plasmas. In the network, atoms/molecules/radical species are assumed to form nodes and chemical reactions correspond to directed edges in the terminology of graph theory. Investigation of the centrality index reveals importance of CH3 in the global chemical reaction, and difference of an index for each radical species between cases with and without electrons clarifies that the electrons are at an influential position to tighten the network structure

  2. Molecule-based approach for computing chemical-reaction rates in upper atmosphere hypersonic flows.

    Energy Technology Data Exchange (ETDEWEB)

    Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

    2009-08-01

    This report summarizes the work completed during FY2009 for the LDRD project 09-1332 'Molecule-Based Approach for Computing Chemical-Reaction Rates in Upper-Atmosphere Hypersonic Flows'. The goal of this project was to apply a recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary nonequilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological non-equilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, the difference between the two models can exceed 10 orders of magnitude. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates. Extensions of the model to reactions typically found in combustion flows and ionizing reactions are also found to be in very good agreement with available measurements, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

  3. Remote and in situ sensing products in chemical reaction using a flexible terahertz pipe waveguide.

    Science.gov (United States)

    You, Borwen; Lu, Ja-Yu

    2016-08-01

    The feasibility of remote chemical detection is experimentally demonstrated by using a Teflon pipe as a scanning arm in a continuous-terahertz wave sensing and imaging system. Different tablets with distinct mixed ratios of aluminum and polyethylene powders are well distinguished by measuring the power reflectivities of 0.4 THz wave associated with their distinct terahertz refractive indices. Given its refractive index sensitivity and fast response, the reflective terahertz sensing system can be used to real-time trace and quantitatively analyze the ammonium-chloride aerosols produced by the chemical reaction between hydrochloric acid and ammonia vapors. With a tightly focusing terahertz beam spot, the spatial and concentration distributions of the generated chemical product are successfully mapped out by the 1D scan of the flexible pipe probe. In consideration of the responsitivity, power stability, and focused spot size of the system, its detection limit for the ammonium-chloride aerosol is estimated to be approximately 165 nmol/mm2. The reliable and compact terahertz pipe scan system is potentially suitable for practical applications, such as biomedical or industrial fiber endoscopy. PMID:27505768

  4. Non-allergic cutaneous reactions in airborne chemical sensitivity--a population based study

    DEFF Research Database (Denmark)

    Berg, Nikolaj Drimer; Linneberg, Allan; Thyssen, Jacob Pontoppidan;

    2011-01-01

    relationship between cutaneous reactions from patch testing and self-reported severity of chemical sensitivity to common airborne chemicals. A total of 3460 individuals participating in a general health examination, Health 2006, were patch tested with allergens from the European standard series and screened...... for chemical sensitivity with a standardised questionnaire dividing the participants into four severity groups of chemical sensitivity. Both allergic and non-allergic cutaneous reactions--defined as irritative, follicular, or doubtful allergic reactions--were analysed in relationship with severity of...... chemical sensitivity. Associations were controlled for the possible confounding effects of sex, age, asthma, eczema, atopic dermatitis, psychological and social factors, and smoking habits. In unadjusted analyses we found associations between allergic and non-allergic cutaneous reactions on patch testing...

  5. Effects of Chemical Reaction on Dissipative Radiative MHD Flow through a Porous Medium over a Nonisothermal Stretching Sheet

    Directory of Open Access Journals (Sweden)

    S. Mohammed Ibrahim

    2014-01-01

    Full Text Available The steady two-dimensional radiative MHD boundary layer flow of an incompressible, viscous, electrically conducting fluid caused by a nonisothermal linearly stretching sheet placed at the bottom of fluid saturated porous medium in the presence of viscous dissipation and chemical reaction is studied. The governing system of partial differential equations is converted to ordinary differential equations by using the similarity transformations, which are then solved by shooting method. The dimensionless velocity, temperature, and concentration are computed for different thermophysical parameters, namely, the magnetic parameter, permeability parameter, radiation parameter, wall temperature parameter, Prandtl number, Eckert number, Schmidt number, and chemical reaction.

  6. Heterogeneously Catalysed Chemical Reactions in Carbon Dioxide Medium

    DEFF Research Database (Denmark)

    Musko, Nikolai E.

    determination of phase equilibria is very time consuming, expensive, and very often reveals very little information. However, these problems can be overcome when thermodynamic modelling is applied. The Cubic-Plus-Association Equation of State (CPA) was used throughout this study; therefore this model is...... studied. Furthermore, the “one-pot” synthesis with 2-butenal was performed using bifunctional and mixed catalysts. The reactions were studied in different reactor types and reaction conditions were optimised using CPA calculations. Extensive catalyst characterisation was carried out in order to understand...... equilibria of the reaction mixture can make the process economically more feasible. Many different thermodynamic models of different capability and applicability have been applied for this task. The CPA model is an advanced model that accounts for complex interactions between associating molecules like water...

  7. RPMDrate: Bimolecular chemical reaction rates from ring polymer molecular dynamics

    KAUST Repository

    Suleimanov, Yu.V.

    2013-03-01

    We present RPMDrate, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH 4, OH+CH4 and H+C2H6 reactions. © 2012 Elsevier B.V. All rights reserved.

  8. Weakly bound systems, continuum effects, and reactions

    CERN Document Server

    Jaganathen, Y; Ploszajczak, M

    2012-01-01

    Structure of weakly bound/unbound nuclei close to particle drip lines is different from that around the valley of beta stability. A comprehensive description of these systems goes beyond standard Shell Model and demands an open quantum system description of the nuclear many-body system. We approach this problem using the Gamow Shell Model which provides a fully microscopic description of bound and unbound nuclear states, nuclear decays, and reactions. We present in this paper the first application of the GSM for a description of the elastic and inelastic scattering of protons on 6He.

  9. Theoretical Studies of Chemical Reactions following Electronic Excitation

    Science.gov (United States)

    Chaban, Galina M.

    2003-01-01

    The use of multi-configurational wave functions is demonstrated for several processes: tautomerization reactions in the ground and excited states of the DNA base adenine, dissociation of glycine molecule after electronic excitation, and decomposition/deformation of novel rare gas molecules HRgF. These processes involve bond brealung/formation and require multi-configurational approaches that include dynamic correlation.

  10. Theoretical studies of the dynamics of chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Wagner, A.F. [Argonne National Laboratory, IL (United States)

    1993-12-01

    Recent research effort has focussed on several reactions pertinent to combustion. The formation of the formyl radical from atomic hydrogen and carbon monoxide, recombination of alkyl radicals and halo-alkyl radicals with halogen atoms, and the thermal dissociation of hydrogen cyanide and acetylene have been studied by modeling. In addition, the inelastic collisions of NCO with helium have been investigated.

  11. Flow-Injection Responses of Diffusion Processes and Chemical Reactions

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov

    2000-01-01

    The technique of Flow-injection Analysis (FIA), now aged 25 years, offers unique analytical methods that are fast, reliable and consuming an absolute minimum of chemicals. These advantages together with its inherent feasibility for automation warrant the future applications of FIA as an attractive...... tool of automated analytical chemistry. The need for an even lower consumption of chemicals and for computer analysis has motivated a study of the FIA peak itself, that is, a theoretical model was developed, that provides detailed knowledge of the FIA profile. It was shown that the flow in a FIA...

  12. Numerical modelling of shock-induced chemical reactions (SICR) in reactive powder mixtures using smoothed particle hydrodynamics (SPH)

    Science.gov (United States)

    S, Siva Prasad A. V.; Basu, Sumit

    2015-10-01

    Shock compaction of reactive powder mixtures to synthesize new materials is one of the oldest material processing techniques and has been studied extensively by several researchers over the past few decades. The quantitative connection between the shock energy imparted and the extent of reaction that can be completed in the small time window associated with the passage of the shock wave is complicated and depends on a large variety of parameters. In particular, our understanding of the complex interplay between the thermo-elasto-viscoplastic behaviour of the granular constituents and their temperature dependent, diffusion-limited reaction mechanism may be enriched through careful numerical simulations. A robust numerical model should be able to handle extremely large deformations coupled with diffusion mediated fast reaction kinetics. In this work, a meshfree discrete particle numerical method based on smoothed particle hydrodynamics (SPH) to simulate shock-induced chemical reactions (SICR) in reactive powder mixtures is proposed. We present a numerical strategy to carry out reactions between reactant powder particles and partition the obtained products between the particles in a manner that accounts for the requirement that the total mass of the entire system remains constant as the reactions occur. Instead of solving the reaction-diffusion problem, we propose a ‘pseudo-diffusion’ model in which a distance dependent reaction rate constant is defined to carry out chemical reaction kinetics. This approach mimics the actual reaction-diffusion process at short times. Our numerical model is demonstrated for the well-studied reaction system Nb  +  2Si \\rightleftharpoons NbSi 2 . The predicted mass fractions of the product obtained from the simulations are in agreement with experimental observations. Finally, the effects of impact speed, particle arrangement and mixing ratio on the predicted product mass fractions are discussed.

  13. Thermodynamically predicted oscillations in closed chemical systems

    CERN Document Server

    Zilbergleyt, B

    2010-01-01

    All known up to now models of chemical oscillations are based exclusively on kinetic considerations. The chemical gross-process equation is split usually by elementary steps, each step is supplied by an arrow and a differential equation, joint solution to such a construction under certain, often ad hoc chosen conditions and with ad hoc numerical coefficients leads to chemical oscillations. Kinetic perception of chemical oscillations reigns without exclusions. However, as it was recently shown by the author for the laser and for the electrochemical systems, chemical oscillations follow also from solutions to the basic expressions of discrete thermodynamics of chemical equilibria. Graphically those solutions are various fork bifurcation diagrams, and, in certain types of chemical systems, oscillations are well pronounced in the bistable bifurcation areas. In this work we describe a general thermodynamic approach to chemical oscillations as opposite to kinetic models, and depict some of their new features like s...

  14. X-ray Microspectroscopy and Chemical Reactions in Soil Microsites

    Energy Technology Data Exchange (ETDEWEB)

    D Hesterberg; M Duff; J Dixon; M Vepraskas

    2011-12-31

    Soils provide long-term storage of environmental contaminants, which helps to protect water and air quality and diminishes negative impacts of contaminants on human and ecosystem health. Characterizing solid-phase chemical species in highly complex matrices is essential for developing principles that can be broadly applied to the wide range of notoriously heterogeneous soils occurring at the earth's surface. In the context of historical developments in soil analytical techniques, we describe applications of bulk-sample and spatially resolved synchrotron X-ray absorption spectroscopy (XAS) for characterizing chemical species of contaminants in soils, and for determining the uniqueness of trace-element reactivity in different soil microsites. Spatially resolved X-ray techniques provide opportunities for following chemical changes within soil microsites that serve as highly localized chemical micro- (or nano-)reactors of unique composition. An example of this microreactor concept is shown for micro-X-ray absorption near edge structure analysis of metal sulfide oxidation in a contaminated soil. One research challenge is to use information and principles developed from microscale soil chemistry for predicting macroscale and field-scale behavior of soil contaminants.

  15. Global solutions of a strongly coupled reaction-diffusion system with different diffusion coefficients

    Directory of Open Access Journals (Sweden)

    L. W. Somathilake

    2005-01-01

    Full Text Available We deal with a mathematical model for a four-component chemical reaction-diffusion process. The model is described by a system of strongly coupled reaction-diffusion equations with different diffusion rates. The existence of the global solution of this reaction-diffusion system in unbounded domain is proved by using semigroup theory and estimates on the growth of solutions.

  16. Kinetically constrained ring-polymer molecular dynamics for non-adiabatic chemical reactions

    International Nuclear Information System (INIS)

    We extend ring-polymer molecular dynamics (RPMD) to allow for the direct simulation of general, electronically non-adiabatic chemical processes. The kinetically constrained (KC) RPMD method uses the imaginary-time path-integral representation in the set of nuclear coordinates and electronic states to provide continuous equations of motion that describe the quantized, electronically non-adiabatic dynamics of the system. KC-RPMD preserves the favorable properties of the usual RPMD formulation in the position representation, including rigorous detailed balance, time-reversal symmetry, and invariance of reaction rate calculations to the choice of dividing surface. However, the new method overcomes significant shortcomings of position-representation RPMD by enabling the description of non-adiabatic transitions between states associated with general, many-electron wavefunctions and by accurately describing deep-tunneling processes across asymmetric barriers. We demonstrate that KC-RPMD yields excellent numerical results for a range of model systems, including a simple avoided-crossing reaction and condensed-phase electron-transfer reactions across multiple regimes for the electronic coupling and thermodynamic driving force

  17. Kinetically constrained ring-polymer molecular dynamics for non-adiabatic chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Menzeleev, Artur R.; Bell, Franziska; Miller, Thomas F., E-mail: tfm@caltech.edu [Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 (United States)

    2014-02-14

    We extend ring-polymer molecular dynamics (RPMD) to allow for the direct simulation of general, electronically non-adiabatic chemical processes. The kinetically constrained (KC) RPMD method uses the imaginary-time path-integral representation in the set of nuclear coordinates and electronic states to provide continuous equations of motion that describe the quantized, electronically non-adiabatic dynamics of the system. KC-RPMD preserves the favorable properties of the usual RPMD formulation in the position representation, including rigorous detailed balance, time-reversal symmetry, and invariance of reaction rate calculations to the choice of dividing surface. However, the new method overcomes significant shortcomings of position-representation RPMD by enabling the description of non-adiabatic transitions between states associated with general, many-electron wavefunctions and by accurately describing deep-tunneling processes across asymmetric barriers. We demonstrate that KC-RPMD yields excellent numerical results for a range of model systems, including a simple avoided-crossing reaction and condensed-phase electron-transfer reactions across multiple regimes for the electronic coupling and thermodynamic driving force.

  18. Sodium-water reaction product flow system

    International Nuclear Information System (INIS)

    Purpose: To provide the subject equipments wherein thermal insulating layers which neither exfoliate nor react by the impact due to high temperature sodium and hydrogen gas and are used for mitigating the thermal impact are provided on the inner surfaces of the emission system equipments, thereby preventing the destruction of the emission system equipments. Constitution: Thermal insulating layers are formed on the inner surfaces of sodium-water reaction product emission system equipments, that is, the inner surface of the emission system pipeline, that of the accommodation vessel and the surface of the cyclone separator, by film treatment, coating or heat resisting coating, and these surfaces are covered with the layers. Each of the layers is made of a material which does not cause a rapid reaction with high temperature sodium or hydrogen gas nor exfoliates and is withstandable for several seconds in which the thermal impact of at least the emission system comes into question, and its thickness is more than one capable of securing the necessary thermal resistance computed by the thermal impact analysis of the emission system. (Yoshihara, H.)

  19. Carbon compounds in the atmosphere and their chemical reactions

    OpenAIRE

    Martišová, Petra

    2013-01-01

    The essay dissert on compounds of carbon in the atmosphere and its reaction. The most important are carbon dioxide, carbon monoxide and methane. Included among important compounds of carbon are volatile organic substances, polycyclic aromatic hydrocarbon and dioxin. Carbon dioxide and methane representing greenhouse gases have also indispensable meaning. As they, together with water vapour, nitrogen monoxide and other gases are causing the major part of greenhouse effect. Primarily because of...

  20. Magnetohydrodynamic (MHD) stretched flow of nanofluid with power-law velocity and chemical reaction

    Science.gov (United States)

    Hayat, Tasawar; Rashid, Madiha; Imtiaz, Maria; Alsaedi, Ahmed

    2015-11-01

    This paper deals with the boundary layer flow of nanofluid over power-law stretched surface. Analysis has been carried out in the presence of applied magnetic field and chemical reaction. Heat and mass transfer characteristics are studied using heat and mass convective conditions. The governing partial differential equations are transferred to the nonlinear ordinary differential equations. Convergent series solutions are obtained for fluid velocity, temperature and concentrations fields. Influences of pertinent parameters including Hartman number, thermal and concentration Biot numbers and chemical reaction parameters are discussed on the velocity, temperature and concentration profiles. Graphical result are presented and discussed. Computations for local Nusselt and Sherwood numbers are carried out. It is observed that the heat transfer rate is enhanced by increasing power-law index, thermal Biot number and chemical reaction parameter while mass transfer rate increases for power-law index and chemical reaction parameter.

  1. NATO Advanced Research Workshop on The Theory of Chemical Reaction Dynamics

    CERN Document Server

    1986-01-01

    The calculation of cross sections and rate constants for chemical reactions in the gas phase has long been a major problem in theoretical chemistry. The need for reliable and applicable theories in this field is evident when one considers the significant recent advances that have been made in developing experimental techniques, such as lasers and molecular beams, to probe the microscopic details of chemical reactions. For example, it is now becoming possible to measure cross sections for chemical reactions state selected in the vibrational­ rotational states of both reactants and products. Furthermore, in areas such as atmospheric, combustion and interstellar chemistry, there is an urgent need for reliable reaction rate constant data over a range of temperatures, and this information is often difficult to obtain in experiments. The classical trajectory method can be applied routinely to simple reactions, but this approach neglects important quantum mechanical effects such as tunnelling and resonances. For al...

  2. Gaussian approximations for stochastic systems with delay: chemical Langevin equation and application to a Brusselator system

    OpenAIRE

    Brett, Tobias; Galla, Tobias

    2013-01-01

    We present a heuristic derivation of Gaussian approximations for stochastic chemical reaction systems with distributed delay. In particular we derive the corresponding chemical Langevin equation. Due to the non-Markovian character of the underlying dynamics these equations are integro-differential equations, and the noise in the Gaussian approximation is coloured. Following on from the chemical Langevin equation a further reduction leads to the linear-noise approximation. We apply the formali...

  3. Properties of Random Complex Chemical Reaction Networks and Their Relevance to Biological Toy Models

    OpenAIRE

    Bigan, Erwan; Steyaert, Jean-Marc; Douady, Stéphane

    2013-01-01

    We investigate the properties of large random conservative chemical reaction networks composed of elementary reactions endowed with either mass-action or saturating kinetics, assigning kinetic parameters in a thermodynamically-consistent manner. We find that such complex networks exhibit qualitatively similar behavior when fed with external nutrient flux. The nutrient is preferentially transformed into one specific chemical that is an intrinsic property of the network. We propose a self-consi...

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

    Science.gov (United States)

    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. Feasibility Study of Venus Surface Cooling Using Chemical Reactions with the Atmosphere

    Science.gov (United States)

    Evans, Christopher

    2013-01-01

    A literature search and theoretical analysis were conducted to investigate the feasibility of cooling a craft on Venus through chemical reformation of materials from the atmosphere. The core concept was to take carbon dioxide (CO2) from the Venus atmosphere and chemically reform it into simpler compounds such as carbon, oxygen, and carbon monoxide. This process is endothermic, taking energy from the surroundings to produce a cooling effect. A literature search was performed to document possible routes for achieving the desired reactions. Analyses indicated that on Venus, this concept could theoretically be used to produce cooling, but would not perform as well as a conventional heat pump. For environments other than Venus, the low theoretical performance limits general applicability of this concept, however this approach to cooling may be useful in niche applications. Analysis indicated that environments with particular atmospheric compositions and temperatures could allow a similar cooling system to operate with very good performance. This approach to cooling may also be useful where the products of reaction are also desirable, or for missions where design simplicity is valued. Conceptual designs for Venus cooling systems were developed using a modified concept, in which an expendable reactant supply would be used to promote more energetically favorable reactions with the ambient CO2, providing cooling for a more limited duration. This approach does not have the same performance issues, but the use of expendable supplies increases the mass requirements and limits the operating lifetime. This paper summarizes the findings of the literature search and corresponding analyses of the various cooling options.

  6. Feasibility Study of Venus Surfuce Cooling Using Chemical Reactions with the Atmosphere

    Science.gov (United States)

    Evans, Christopher

    2013-01-01

    A literature search and theoretical analysis were conducted to investigate the feasibility of cooling a craft on Venus through chemical reformation of materials from the atmosphere. The core concept was to take carbon dioxide (CO2) from the Venus atmosphere and chemically reform it into simpler compounds such as carbon, oxygen, and carbon monoxide. This process is endothermic, taking energy from the surroundings to produce a cooling effect. A literature search was performed to document possible routes for achieving the desired reactions. Analyses indicated that on Venus, this concept could theoretically be used to produce cooling, but would not perform as well as a conventional heat pump. For environments other than Venus, the low theoretical performance limits general applicability of this concept, however this approach to cooling may be useful in niche applications. Analysis indicated that environments with particular atmospheric compositions and temperatures could allow a similar cooling system to operate with very good performance. This approach to cooling may also be useful where the products of reaction are also desirable, or for missions where design simplicity is valued. Conceptual designs for Venus cooling systems were developed using a modified concept, in which an expendable reactant supply would be used to promote more energetically favorable reactions with the ambient CO2, providing cooling for a more limited duration. This approach does not have the same performance issues, but the use of expendable supplies increases the mass requirements and limits the operating lifetime. This paper summarizes the findings of the literature search and corresponding analyses of the various cooling options

  7. Vapor–Liquid Equilibrium Coupled with Chemical Reaction (Transesterification)

    Czech Academy of Sciences Publication Activity Database

    Wichterle, Ivan; Aim, Karel

    - : -, 2005 - (Domanska-Zelazna, U.; Malanowski, S.), s.68-69 ISBN 83-920719-1-3. [European Symposium on Applied Thermodynamics ESAT 2005 /21./. Jurata (PL), 01.06.2005-05.06.2005] R&D Projects: GA ČR(CZ) GA203/03/1588 Institutional research plan: CEZ:AV0Z40720504 Keywords : phase equilibria * chemical equilibria * transesterification Subject RIV: CF - Physical ; Theoretical Chemistry

  8. LSENS: A General Chemical Kinetics and Sensitivity Analysis Code for homogeneous gas-phase reactions. Part 3: Illustrative test problems

    Science.gov (United States)

    Bittker, David A.; Radhakrishnan, Krishnan

    1994-01-01

    LSENS, the Lewis General Chemical Kinetics and Sensitivity Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part 3 of a series of three reference publications that describe LSENS, provide a detailed guide to its usage, and present many example problems. Part 3 explains the kinetics and kinetics-plus-sensitivity analysis problems supplied with LSENS and presents sample results. These problems illustrate the various capabilities of, and reaction models that can be solved by, the code and may provide a convenient starting point for the user to construct the problem data file required to execute LSENS. LSENS is a flexible, convenient, accurate, and efficient solver for chemical reaction problems such as static system; steady, one-dimensional, inviscid flow; reaction behind incident shock wave, including boundary layer correction; and perfectly stirred (highly backmixed) reactor. In addition, the chemical equilibrium state can be computed for the following assigned states: temperature and pressure, enthalpy and pressure, temperature and volume, and internal energy and volume. For static problems the code computes the sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of the dependent variables and/or the three rate coefficient parameters of the chemical reactions.

  9. Effects of reversible chemical reaction on Li diffusion and stresses in spherical composition-gradient electrodes

    International Nuclear Information System (INIS)

    Composition-gradient electrode materials have been proven to be one of the most promising materials in lithium-ion battery. To study the mechanism of mechanical degradation in spherical composition-gradient electrodes, the finite deformation theory and reversible chemical theory are adopted. In homogeneous electrodes, reversible electrochemical reaction may increase the magnitudes of stresses. However, reversible electrochemical reaction has different influences on stresses in composition-gradient electrodes, resulting from three main inhomogeneous factors—forward reaction rate, backward reaction rate, and reaction partial molar volume. The decreasing transition form of forward reaction rate, increasing transition form of backward reaction rate, and increasing transition form of reaction partial molar volume can reduce the magnitudes of stresses. As a result, capacity fading and mechanical degradation are reduced by taking advantage of the effects of inhomogeneous factors

  10. Ca + HF - The anatomy of a chemical insertion reaction

    Science.gov (United States)

    Jaffe, R. L.; Pattengill, M. D.; Mascarello, F. G.; Zare, R. N.

    1987-01-01

    A comprehensive first-principles theoretical investigation of the gas phase reaction Ca + HF - CaF + H is reported. Ab initio potential energy calculations are first discussed, along with characteristics of the computed potential energy surface. Next, the fitting of the computed potential energy points to a suitable analytical functional form is described, and maps of the fitted potential surface are displayed. The methodology and results of a classical trajectory calculation utilizing the fitted potential surface are presented. Finally, the significance of the trajectory study results is discussed, and generalizations concerning dynamical aspects of Ca + HF scattering are drawn.

  11. Selective Chemical-Lithographic Reaction Techniques Using Radiation Technology for Biological Application

    International Nuclear Information System (INIS)

    This report, titled 'selective Chemical-Lithographic Reaction Techniques Using Radiation Technology for Biological Application' contains a research summary, 1) development of selective reaction technology using irradiation of electron beams, 2) preparation of functional surfaces using selective radiation technology on carbon-based nanomaterials, and 3) development of bio-applicable biochips using combinatorial surface modification

  12. Enzyme efficiency: An open reaction system perspective

    Energy Technology Data Exchange (ETDEWEB)

    Banerjee, Kinshuk, E-mail: kb36@rice.edu [Department of Chemistry, University of Calcutta, Rajabazar Science College Campus, Kolkata 700 009 (India); Bhattacharyya, Kamal, E-mail: pchemkb@gmail.com [Department of Chemistry, University of Calcutta, 92 A.P.C. Road, Kolkata 700 009 (India)

    2015-12-21

    A measure of enzyme efficiency is proposed for an open reaction network that, in suitable form, applies to closed systems as well. The idea originates from the description of classical enzyme kinetics in terms of cycles. We derive analytical expressions for the efficiency measure by treating the network not only deterministically but also stochastically. The latter accounts for any significant amount of noise that can be present in biological systems and hence reveals its impact on efficiency. Numerical verification of the results is also performed. It is found that the deterministic equation overestimates the efficiency, the more so for very small system sizes. Roles of various kinetics parameters and system sizes on the efficiency are thoroughly explored and compared with the standard definition k{sub 2}/K{sub M}. Study of substrate fluctuation also indicates an interesting efficiency-accuracy balance.

  13. Enzyme efficiency: An open reaction system perspective

    International Nuclear Information System (INIS)

    A measure of enzyme efficiency is proposed for an open reaction network that, in suitable form, applies to closed systems as well. The idea originates from the description of classical enzyme kinetics in terms of cycles. We derive analytical expressions for the efficiency measure by treating the network not only deterministically but also stochastically. The latter accounts for any significant amount of noise that can be present in biological systems and hence reveals its impact on efficiency. Numerical verification of the results is also performed. It is found that the deterministic equation overestimates the efficiency, the more so for very small system sizes. Roles of various kinetics parameters and system sizes on the efficiency are thoroughly explored and compared with the standard definition k2/KM. Study of substrate fluctuation also indicates an interesting efficiency-accuracy balance

  14. Chemical Kinetics of Hydrocarbon Ignition in Practical Combustion Systems

    Energy Technology Data Exchange (ETDEWEB)

    Westbrook, C.K.

    2000-07-07

    Chemical kinetic factors of hydrocarbon oxidation are examined in a variety of ignition problems. Ignition is related to the presence of a dominant chain branching reaction mechanism that can drive a chemical system to completion in a very short period of time. Ignition in laboratory environments is studied for problems including shock tubes and rapid compression machines. Modeling of the laboratory systems are used to develop kinetic models that can be used to analyze ignition in practical systems. Two major chain branching regimes are identified, one consisting of high temperature ignition with a chain branching reaction mechanism based on the reaction between atomic hydrogen with molecular oxygen, and the second based on an intermediate temperature thermal decomposition of hydrogen peroxide. Kinetic models are then used to describe ignition in practical combustion environments, including detonations and pulse combustors for high temperature ignition, and engine knock and diesel ignition for intermediate temperature ignition. The final example of ignition in a practical environment is homogeneous charge, compression ignition (HCCI) which is shown to be a problem dominated by the kinetics intermediate temperature hydrocarbon ignition. Model results show why high hydrocarbon and CO emissions are inevitable in HCCI combustion. The conclusion of this study is that the kinetics of hydrocarbon ignition are actually quite simple, since only one or two elementary reactions are dominant. However, there are many combustion factors that can influence these two major reactions, and these are the features that vary from one practical system to another.

  15. Production of cold formaldehyde molecules for study and control of chemical reaction dynamics with hydroxyl radicals

    OpenAIRE

    Hudson, Eric R.; Ticknor, Christopher; Sawyer, Brian C.; Taatjes, Craig A.; Lewandowski, H. J.; Bochinski, J. R.; Bohn, John L.; Ye, Jun

    2005-01-01

    We propose a method for controlling a class of low temperature chemical reactions. Specifically, we show the hydrogen abstraction channel in the reaction of formaldehyde (H$_{2}$CO) and the hydroxyl radical (OH) can be controlled through either the molecular state or an external electric field. We also outline experiments for investigating and demonstrating control over this important reaction. To this end, we report the first Stark deceleration of the H$_{2}$CO molecule. We have decelerated ...

  16. Students' Ideas about How and Why Chemical Reactions Happen: Mapping the Conceptual Landscape

    Science.gov (United States)

    Yan, Fan; Talanquer, Vicente

    2015-01-01

    Research in science education has revealed that many students struggle to understand chemical reactions. Improving teaching and learning about chemical processes demands that we develop a clearer understanding of student reasoning in this area and of how this reasoning evolves with training in the domain. Thus, we have carried out a qualitative…

  17. The diagnostic of the chemical reaction zone at the detonation of condensed explosives

    CERN Document Server

    Satonkina, Nataliya P

    2016-01-01

    The highly-sensitive method is proposed for the real-time diagnostics of the von Neumann peak at detonation of brisant high explosives. The absence of the direct link between the pressure and the course of chemical reactions was shown. For TNT (trinitrotoluene), the influence of the structure of charge on the kinetics of chemical peak was demonstrated.

  18. The Technology for Intensification of Chemical Reaction Process Envisaged in the "863" Plan

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    @@ It is learned from the Ministry of Science and Technology that in order to promote the shift of China's chemical industry toward an energy efficient and environmentally friendly product mode, the technology for intensification of chemical reaction processes has been included in the National "863" Project of the "Eleventh Five-Year Plan", and the application for research project proposals is to be accepted.

  19. A study of the chemical effects of metal hydroxides upon cement hydration reactions

    Energy Technology Data Exchange (ETDEWEB)

    Fowler, G.D.; Asavapisit, S.; Cheeseman, C.R.; Perry, R. [Centre for Environmental Control and Waste Management, Civil Engineering Building, Imperial College GB, London (United Kingdom)

    1997-12-31

    By the addition of individual metal hydroxides (Pb(II), Zn(II), Cr(III) and Fe(III)) to ordinary Portland cement in an inert atmosphere, the chemical interactions which occur have been studied by examining changes in the solution chemistry through IC and ICP-AES. The extent of the cement hydration reactions were also studied by following the production of Ca(OH)2 using DTA and the rate of heat evolution as hydration proceeded by isothermal conduction calorimetry. These results showed that the effects of each metal are different. With respect to the effects upon the hydration reactions, Fe(OH){sub 3} accelerates whilst Cr(OH){sub 3} slightly retarded them. The Zn(OH){sub 2} completely suppressed hydration whilst Pb(OH){sub 2} retarded the reaction by about 8 days. With regard to solution effects, reduced levels of Ca{sup 2+} and SO{sub 4}{sup 2-} were released compared to an OPC control and re-solubilization of the metals in the cement system was noted, partially as a result of oxidation effects. By using Ca Cl{sub 2}, it was shown to be possible to partially overcoming the retarding effects of Pb(OH){sub 2}

  20. Rate constants for chemical reactions in high-temperature nonequilibrium air

    Science.gov (United States)

    Jaffe, R. L.

    1986-01-01

    In the nonequilibrium atmospheric chemistry regime that will be encountered by the proposed Aeroassisted Orbital Transfer Vehicle in the upper atmosphere, where air density is too low for thermal and chemical equilibrium to be maintained, the detailed high temperature air chemistry plays a critical role in defining radiative and convective heating loads. Although vibrational and electronic temperatures remain low (less than 15,000 K), rotational and translational temperatures may reach 50,000 K. Attention is presently given to the effects of multiple temperatures on the magnitudes of various chemical reaction rate constants, for the cases of both bimolecular exchange reactions and collisional excitation and dissociation reactions.

  1. Simulation of chemical reactions in solution by a combination of classical and quantum mechanical approach

    Science.gov (United States)

    Onida, Giovanni; Andreoni, Wanda

    1995-09-01

    A classical trajectory mapping method was developed to study chemical reactions in solution and in enzymes. In this method, the trajectories were calculated on a classical potential surface and the free energy profile was obtained by mapping the classical surface to the quantum mechanical surface obtained by the semiempirical AM1 method. There is no need to perform expensive quantum mechanical calculations at each iteration step. This method was applied to proton transfer reactions both in aqueous solution and in papain. The results are encouraging, indicating the applicability of this hybrid method to chemical reactions both in solution and in enzymes.

  2. Heterogeneous nucleation - current transients under chemical reaction control

    CERN Document Server

    D'Ajello-Tettamanzy, P C; Kipervaser, Z G S

    2002-01-01

    Heterogeneous nucleation on catalytic surfaces plunged into a fluid is described through a stochastic model. To generate this non-equilibrium process we assume that the turn on of a electrostatic potential triggers a complex dynamics that includes a free Brownian motion, a reaction kinetic and a stimulated migration before the final adhesion of ions on the surface (electrode). At, when the potential is switched on, the spatial symmetry is broken and a two-stage process is developed. First the ion undergoes a change in its electrochemical character (at some region of the space) and then reacts at some specific points to stick together on the surface. The continuous addition of ions develops a material deposit connected to the current transient signals measured in electrochemical deposition processes. Unlike current models found in the literature, this procedure avoids the computation of the area covered by the diffusion zones, allowing a formalism skill to describe equally well the absorption of ions by channe...

  3. The mass balance approach: application to interpreting the chemical evolution of hydrologic systems.

    Science.gov (United States)

    Plummer, L.N.; Back, W.

    1980-01-01

    Mass balance calculations are applied to observed chemical and isotopic data of three natural water systems involving carbonate reactions in order to define mineral stoichiometry of reactants and products, relative rates of reactions, and mass transfer. One study evaluates reactions in a lagoon on the east coast of the Yucatan Peninsula, Mexico.- from Authors

  4. Small-angle neutron scattering studies of chemical reaction and reaction-induced self-assembly

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, H. [Advanced Science Research Center(ASRC), Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan); Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8501 (Japan); Koizumi, S. [Advanced Science Research Center(ASRC), Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan); Hashimoto, T. [Advanced Science Research Center(ASRC), Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan) and Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8501 (Japan)]. E-mail: hashimoto.takeji@jaea.go.jp; Kurosaki, K. [Department of Materials Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8501 (Japan); Ohmae, M. [Department of Materials Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8501 (Japan); Kobayashi, S. [Department of Materials Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8501 (Japan)

    2006-11-15

    We have investigated a self-assembling process of cellulose artificially synthesized via enzymatic polymerization by means of in-situ and time-resolved small-angle neutron scattering (SANS). The results elucidated the following: (i) cellulose molecules were synthesized at a special reaction site of the enzyme (cellulase) located on or near the smooth surface of the self-assembled enzymes formed in the reaction medium; (ii) the synthesized molecules associated themselves via diffusion-limited aggregation (DLA) and crystallized into fibrils and (iii) the fibrils formed the aggregates, which had the surface fractal dimension D {sub s} increasing from 2 to 2.3 with the reaction time, on the smooth surface of the enzyme aggregates.

  5. Hazardous chemical tracking system (HAZ-TRAC)

    Energy Technology Data Exchange (ETDEWEB)

    Bramlette, J D; Ewart, S M; Jones, C E

    1990-07-01

    Westinghouse Idaho Nuclear Company, Inc. (WINCO) developed and implemented a computerized hazardous chemical tracking system, referred to as Haz-Trac, for use at the Idaho Chemical Processing Plant (ICPP). Haz-Trac is designed to provide a means to improve the accuracy and reliability of chemical information, which enhances the overall quality and safety of ICPP operations. The system tracks all chemicals and chemical components from the time they enter the ICPP until the chemical changes form, is used, or becomes a waste. The system runs on a Hewlett-Packard (HP) 3000 Series 70 computer. The system is written in COBOL and uses VIEW/3000, TurboIMAGE/DBMS 3000, OMNIDEX, and SPEEDWARE. The HP 3000 may be accessed throughout the ICPP, and from remote locations, using data communication lines. Haz-Trac went into production in October, 1989. Currently, over 1910 chemicals and chemical components are tracked on the system. More than 2500 personnel hours were saved during the first six months of operation. Cost savings have been realized by reducing the time needed to collect and compile reporting information, identifying and disposing of unneeded chemicals, and eliminating duplicate inventories. Haz-Trac maintains information required by the Superfund Amendment Reauthorization Act (SARA), the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) and the Occupational Safety and Health Administration (OSHA).

  6. Non-allergic cutaneous reactions in airborne chemical sensitivity--a population based study

    DEFF Research Database (Denmark)

    Linneberg, Allan; Thyssen, Jacob Pontoppidan; Dirksen, Asger;

    2011-01-01

    relationship between cutaneous reactions from patch testing and self-reported severity of chemical sensitivity to common airborne chemicals. A total of 3460 individuals participating in a general health examination, Health 2006, were patch tested with allergens from the European standard series and screened...... chemical sensitivity. Associations were controlled for the possible confounding effects of sex, age, asthma, eczema, atopic dermatitis, psychological and social factors, and smoking habits. In unadjusted analyses we found associations between allergic and non-allergic cutaneous reactions on patch testing...

  7. An in-situ chemical reaction deposition of nanosized wurtzite CdS thin films

    Energy Technology Data Exchange (ETDEWEB)

    Chu Juan [School of Materials Science and Engineering, Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin 300072 (China); Jin Zhengguo, E-mail: zhgjin@tju.edu.cn [School of Materials Science and Engineering, Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin 300072 (China); State Key Laboratory of Silicon Materials and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Cai Shu [School of Materials Science and Engineering, Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin 300072 (China); State Key Laboratory of Silicon Materials and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Yang Jingxia [State Key Laboratory of Silicon Materials and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Hong Zhanglian, E-mail: hong_zhanglian@zju.edu.cn [State Key Laboratory of Silicon Materials and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China)

    2012-01-01

    Nanocrystalline CdS thin films were deposited on glass substrates by an ammonia-free in-situ chemical reaction synthesis technique using cadmium cationic precursor solid films as reaction source and sodium sulfide based solutions as anionic reaction medium. Effects of ethanolamine addition to the cadmium cationic precursor solid films, deposition cycle numbers and annealing treatments in Ar atmosphere on structure, morphology, chemical composition and optical properties of the resultant films were investigated by X-ray diffraction, field emission scanning electron microscope, energy dispersive X-ray analysis and UV-Vis spectra measurements. The results show that CdS thin films deposited by the in-situ chemical reaction synthesis have wurtzite structure with (002) plane preferential orientation and crystallite size is in the range of 16 nm-19 nm. The growth of film thickness is almost constant with deposition cycle numbers and about 96 nm per cycle.

  8. Thermally activated reaction–diffusion-controlled chemical bulk reactions of gases and solids

    Directory of Open Access Journals (Sweden)

    S. Möller

    2015-01-01

    Full Text Available The chemical kinetics of the reaction of thin films with reactive gases is investigated. The removal of thin films using thermally activated solid–gas to gas reactions is a method to in-situ control deposition inventory in vacuum and plasma vessels. Significant scatter of experimental deposit removal rates at apparently similar conditions was observed in the past, highlighting the need for understanding the underlying processes. A model based on the presence of reactive gas in the films bulk and chemical kinetics is presented. The model describes the diffusion of reactive gas into the film and its chemical interaction with film constituents in the bulk using a stationary reaction–diffusion equation. This yields the reactive gas concentration and reaction rates. Diffusion and reaction rate limitations are depicted in parameter studies. Comparison with literature data on tokamak co-deposit removal results in good agreement of removal rates as a function of pressure, film thickness and temperature.

  9. An in-situ chemical reaction deposition of nanosized wurtzite CdS thin films

    International Nuclear Information System (INIS)

    Nanocrystalline CdS thin films were deposited on glass substrates by an ammonia-free in-situ chemical reaction synthesis technique using cadmium cationic precursor solid films as reaction source and sodium sulfide based solutions as anionic reaction medium. Effects of ethanolamine addition to the cadmium cationic precursor solid films, deposition cycle numbers and annealing treatments in Ar atmosphere on structure, morphology, chemical composition and optical properties of the resultant films were investigated by X-ray diffraction, field emission scanning electron microscope, energy dispersive X-ray analysis and UV–Vis spectra measurements. The results show that CdS thin films deposited by the in-situ chemical reaction synthesis have wurtzite structure with (002) plane preferential orientation and crystallite size is in the range of 16 nm–19 nm. The growth of film thickness is almost constant with deposition cycle numbers and about 96 nm per cycle.

  10. Numerical kinetic model including equilibrium and rate equations for chemical reactions of actinide elements

    International Nuclear Information System (INIS)

    Numerical simulation method was examined for chemical reactions of actinide elements U, Pu, Np, and Tc etc. in an aqueous nitric acid solution. It is known that the numerical calculation for the Purex process with chemical reactions and liquid flow becomes stiff, because time constant for the chemical reactions is two to three order of magnitude smaller due to the very fast reactions than that of mass transfer or of reaching distribution equilibrium. Recently in order to increase a time step Δt the partial equilibrium (P.E.) model, in which some very fast reactions are treated by the equilibrium law whereas other reactions are by the rate law, has been proposed. In the present study concentration change of the solutes in an aqueous solution with 30 chemical reactions, of which 4 are expressed by equilibrium equations, has been calculated. Description of the P.E. model and the comparison of the results and cpu time between the kinetic and the P.E. models are given. (author)

  11. From chemical reactions to evolution: Emergence of species

    Science.gov (United States)

    Carletti, T.; Fanelli, D.

    2007-01-01

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

  12. Momentum balance equation for nonelectrolytes in models of coupling between chemical reaction and diffusion in membranes.

    Science.gov (United States)

    Gałdzicki, Z; Miekisz, S

    1984-04-01

    The role of viscosity in coupling between chemical reaction (complex formation) and diffusion in membranes has been investigated. The Fick law was replaced by the momentum balance equation with the viscous term. The irreversible thermodynamics admits coupling of the chemical reaction rate with the gradient of velocity. The proposed model has shown the contrary effect of viscosity and confirmed the experimental results. The chemical reaction rate increases only above the limit value of viscosity. The parameter Q (degree of complex formation) was introduced to investigate coupling. Q equals to the ratio of the chemical contribution into the flux of the complex to the total flux of the substance transported. For different values of the parameters of the model the dependence of Q upon position inside the membrane has been numerically calculated. The assumptions of the model limit it to a specific case and they only roughly model the biological situation. PMID:6537360

  13. Students' Ideas about How and Why Chemical Reactions Happen: Mapping the conceptual landscape

    Science.gov (United States)

    Yan, Fan; Talanquer, Vicente

    2015-12-01

    Research in science education has revealed that many students struggle to understand chemical reactions. Improving teaching and learning about chemical processes demands that we develop a clearer understanding of student reasoning in this area and of how this reasoning evolves with training in the domain. Thus, we have carried out a qualitative study to explore students reasoning about chemical causality and mechanism. Study participants included individuals at different educational levels, from college to graduate school. We identified diverse conceptual modes expressed by students when engaged in the analysis of different types of reactions. Main findings indicate that student reasoning about chemical reactions is influenced by the nature of the process. More advanced students tended to express conceptual modes that were more normative and had more explanatory power, but major conceptual difficulties persisted in their reasoning. The results of our study are relevant to educators interested in conceptual development, learning progressions, and assessment.

  14. Chemical Reaction Rates from Ring Polymer Molecular Dynamics: Theory and Practical Applications

    CERN Document Server

    Suleimanov, Yury V; Guo, Hua

    2016-01-01

    This Feature Article presents an overview of the current status of Ring Polymer Molecular Dynamics (RPMD) rate theory. We first analyze theory and its connection to quantum transition state theory. We then focus on its practical application to prototypical chemical reactions in the gas phase, which demonstrate how accurate and reliable RPMD is for calculating thermal chemical reaction rates in multifarious cases. This review serves as an important checkpoint in RPMD rate theory development, which shows that RPMD is shifting from being just one of recent novel ideas to a well-established and validated alternative to conventional techniques for calculating thermal chemical rates. We also hope it will motivate further applications of RPMD to various chemical reactions.

  15. Chemical Reactions of N13 Recoils from the C12 (d, n)N13 Reaction

    International Nuclear Information System (INIS)

    Earlier studies of N13 recoils produced by the nuclear reaction C12 (d, n) N13 in CH4, CH3OH, CCl4, etc. showed that the final radioactive gaseous products were entirely cyanides such as HCN, CH3CN and ClCN. No ammonia or amines were detected. In this study the investigation has been extended to benzene and CF4. In addition reactions of N+ ions with CCl4 and CF4 have been examined in a tandem mass spectrometer. In the case of N13 recoils reacting with benzene HCN was the main product and small amounts of benzonitrile were formed. No aniline or pyridine were produced. This will be contrasted with reported studies in which active nitrogen produced by electrical discharge reacted with benzene. In the case of CF4, the only radioactive product detected was FCN. In both cases polymeric materials were produced on the walls of the reaction vessels. No other products such as NF3 were detected. Studies of the effect of rare gas additives in the case of methanol indicated that ion-molecule reactions were involved at least in part. For this reason, the reactions of N+ ions with CCI4 and CF4 were studied in a tandem mass spectrometer in the bombarding ion energy range from 2 eV to. 200 eV. In this study the relative cross-sections for various ion production were investigated as a function of energy. In addition to ions composed of carbon and chlorine, various nitrogen-containing ions such as NCl+. CNCl+ and CN+ were detected. The shapes of the cross-section curves were such as to indicate complex formation possibly (CCl4N)+, which decomposed to give the product ions. The above complex was not detected directly. (author)

  16. Automatic reaction to a chemical event detected by a low-cost wireless chemical sensing network

    OpenAIRE

    Beirne, Stephen; Lau, King-Tong; Corcoran, Brian; Diamond, Dermot

    2009-01-01

    A test-scale wireless chemical sensor network (WCSN) has been deployed within a controlled Environmental Chamber (EC). The combined signals from the WCSN were used to initiate a controllable response to the detected chemical event. When a particular sensor response pattern was obtained, a purging cycle was initiated. Sensor data were continuously checked against user-defined action limits, to determine if a chemical event had occurred. An acidic contaminant was used to demonstrate the respons...

  17. Modelling biochemical reaction systems by stochastic differential equations with reflection.

    Science.gov (United States)

    Niu, Yuanling; Burrage, Kevin; Chen, Luonan

    2016-05-01

    In this paper, we gave a new framework for modelling and simulating biochemical reaction systems by stochastic differential equations with reflection not in a heuristic way but in a mathematical way. The model is computationally efficient compared with the discrete-state Markov chain approach, and it ensures that both analytic and numerical solutions remain in a biologically plausible region. Specifically, our model mathematically ensures that species numbers lie in the domain D, which is a physical constraint for biochemical reactions, in contrast to the previous models. The domain D is actually obtained according to the structure of the corresponding chemical Langevin equations, i.e., the boundary is inherent in the biochemical reaction system. A variant of projection method was employed to solve the reflected stochastic differential equation model, and it includes three simple steps, i.e., Euler-Maruyama method was applied to the equations first, and then check whether or not the point lies within the domain D, and if not perform an orthogonal projection. It is found that the projection onto the closure D¯ is the solution to a convex quadratic programming problem. Thus, existing methods for the convex quadratic programming problem can be employed for the orthogonal projection map. Numerical tests on several important problems in biological systems confirmed the efficiency and accuracy of this approach. PMID:26920245

  18. Photochemical reactions of various model protocell systems

    Science.gov (United States)

    Folsome, C. E.

    1986-01-01

    Models for the emergence of cellular life on the primitive Earth, and for physical environments of that era have been studied that embody these assumptions: (1) pregenetic cellular forms were phase-bounded systems primarily photosynthetic in nature, and (2) the early Earth environment was anoxic (lacking appreciable amounts of free hydrogen). It was found that organic structures can also be formed under anoxic conditions (N2, CO3=, H2O) by protracted longwavelength UV radiation. Apparently these structures form initially as organic layers upon CaCO3 crystalloids. The question remains as to whether the UV photosynthetic ability of such phase bounded structures is a curiosity, or a general property of phase bounded systems which is of direct interest to the emergence of cellular life. The question of the requirement and sailient features of a phase boundary for UV photosynthetic abilities was addressed by searching for similar general physical properties which might be manifest in a variety of other simple protocell-like structures. Since it has been shown that laboratory protocell models can effect the UV photosynthesis of low molecular weight compounds, this reaction is being used as an assay to survey other types of structures for similar UV photosynthetic reactions. Various kinds of structures surveyed are: (1) proteinoids; (2) liposomes; (3) reconstituted cell membrane spheroids; (4) coacervates; and (5) model protocells formed under anoxic conditions.

  19. Molecular Beam Studies of Hot Atom Chemical Reactions: Reactive Scattering of Energetic Deuterium Atoms

    Science.gov (United States)

    Continetti, R. E.; Balko, B. A.; Lee, Y. T.

    1989-02-01

    A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H{sub 2} -> DH + H and the substitution reaction D + C{sub 2}H{sub 2} -> C{sub 2}HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible.

  20. Chemical Reactions and Kinetics of the Carbon Monoxide Coupling in the Presence of Hydrogen

    Institute of Scientific and Technical Information of China (English)

    Fandong Meng; Genhui Xu; Zhenhua Li; Pa Du

    2002-01-01

    The chemical reactions and kinetics of the catalytic coupling reaction of carbon monoxide to diethyl oxalate were studied in the presence of hydrogen over a supported palladium catalyst in the gaseous phase at the typical coupling reaction conditions. The experiments were performed in a continuous flow fixed-bed reactor. The results indicated that hydrogen only reacts with ethyl nitrite to form ethanol, and kinetic studies revealed that the rate-determining step is the surface reaction of adsorbed hydrogen and the ethoxy radical (EtO-). A kinetic model is proposed and a comparison of the observed and calculated conversions showed that the rate expressions are of rather high confidence.

  1. Chemical reactions during the thermal processing of borazene polymers

    International Nuclear Information System (INIS)

    A class of borazene polymers was developed which consists of a two-dimensional array of six-membered borazene rings with the borons of adjacent borazene rings separated by -NH- groups. Pyrolysis of these polymers above ∼1000 degrees C leads to crystalline graphite-like boron nitride (h-BN). The thermal chemistry of thin films of one polymer deposited on KOH-etched aluminum was examined by thermal decomposition mass spectroscopy (TDMS) and thermal gravimetric analysis (TGA) and the gas evolution chemistry was found to be essentially complete at temperatures less than 400 degrees C. All products desorb with the same temperature profile and the major desorbing species are NH3 and N2, consistent with a loss of excess nitrogen and hydrogen in the polymer, and HCI from decomposition of byproducts of the synthesis step. Since the formation of ordered crystalline h-BN films requires heating to temperatures of the order of 1000 degrees C, whereas the gas evolution chemistry is complete by roughly 400 degrees C, it is concluded that gas evolution chemical processes are not rate limiting in BN ceramic production

  2. Distribution in flowing reaction-diffusion systems

    KAUST Repository

    Kamimura, Atsushi

    2009-12-28

    A power-law distribution is found in the density profile of reacting systems A+B→C+D and 2A→2C under a flow in two and three dimensions. Different densities of reactants A and B are fixed at both ends. For the reaction A+B, the concentration of reactants asymptotically decay in space as x-1/2 and x-3/4 in two dimensions and three dimensions, respectively. For 2A, it decays as log (x) /x in two dimensions. The decay of A+B is explained considering the effect of segregation of reactants in the isotropic case. The decay for 2A is explained by the marginal behavior of two-dimensional diffusion. A logarithmic divergence of the diffusion constant with system size is found in two dimensions. © 2009 The American Physical Society.

  3. Chemical Reactions Catalyzed by Metalloporphyrin-Based Metal-Organic Frameworks

    Directory of Open Access Journals (Sweden)

    Kelly Aparecida Dias de Freitas Castro

    2013-06-01

    Full Text Available The synthetic versatility and the potential application of metalloporphyrins (MP in different fields have aroused researchers’ interest in studying these complexes, in an attempt to mimic biological systems such as cytochrome P-450. Over the last 40 years, synthetic MPs have been mainly used as catalysts for homogeneous or heterogeneous chemical reactions. To employ them in heterogeneous catalysis, chemists have prepared new MP-based solids by immobilizing MP onto rigid inorganic supports, a strategy that affords hybrid inorganic-organic materials. More recently, materials obtained by supramolecular assembly processes and containing MPs as building blocks have been applied in a variety of areas, like gas storage, photonic devices, separation, molecular sensing, magnets, and heterogeneous catalysis, among others. These coordination polymers, known as metal-organic frameworks (MOFs, contain organic ligands or complexes connected by metal ions or clusters, which give rise to a 1-, 2- or 3-D network. These kinds of materials presents large surface areas, Brønsted or redox sites, and high porosity, all of which are desirable features in catalysts with potential use in heterogeneous phases. Building MOFs based on MP is a good way to obtain solid catalysts that offer the advantages of bioinspired systems and zeolitic materials. In this mini review, we will adopt a historical approach to present the most relevant MP-based MOFs applicable to catalytic reactions such as oxidation, reduction, insertion of functional groups, and exchange of organic functions.

  4. The quantum instanton (QI) model for chemical reaction rates: The 'Simplest' QI with one dividing surface

    International Nuclear Information System (INIS)

    A new version of the quantum instanton (QI) approach to thermal rate constants of chemical reactions is presented, namely, the simplest QI (SQI) approximation with one dividing surface (DS), referred to here as SQI1. (The SQI approximation presented originally was applicable only with two DSs.) As with all versions of the QI approach, the rate is expressed wholly in terms of the (quantum) Boltzmann operator (which, for complex systems, can be evaluated by Monte Carlo path integral methods). Test calculations on some simple model problems show the SQI1 model to be slightly less accurate than the original version of the QI approach, but it is the easiest version to implement; it requires only a constrained free-energy calculation, location of the (transition-state) DS so as to maximize this free energy, and the curvature (second derivative) of the free energy at this maximum

  5. Axisymmetric mixed convective MHD flow over a slender cylinder in the presence of chemically reaction

    Directory of Open Access Journals (Sweden)

    Prasad K.V.

    2016-02-01

    Full Text Available The present analysis is focused on the study of the magnetic effect on coupled heat and mass transfer by mixed convection boundary layer flow over a slender cylinder in the presence of a chemical reaction. The buoyancy effect due to thermal diffusion and species diffusion is investigated. Employing suitable similarity transformations, the governing equations are transformed into a system of coupled non-linear ordinary differential equations and are solved numerically via the implicit, iterative, second order finite difference method. The numerical results obtained are compared with the available results in the literature for some special cases and the results are found to be in excellent agreement. The velocity, temperature, and the concentration profiles are presented graphically and analyzed for several sets of the pertinent parameters. The pooled effect of the thermal and mass Grashof number is to enhance the velocity and is quite the opposite for temperature and the concentration fields.

  6. Chemical Reaction Equilibrium in Nanoporous Materials: NO Dimerization Reaction in Carbon Slit Nanopores

    Czech Academy of Sciences Publication Activity Database

    Lísal, Martin; Brennan, J.K.; Smith, W.R.

    2006-01-01

    Roč. 124, č. 6 (2006), s. 64712.1-64712.14. ISSN 0021-9606 R&D Projects: GA ČR(CZ) GA203/05/0725; GA AV ČR(CZ) 1ET400720507; GA AV ČR(CZ) 1ET400720409 Institutional research plan: CEZ:AV0Z40720504 Keywords : nanopore * NO dimerization * reaction Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.166, year: 2006

  7. Programming chemical kinetics: engineering dynamic reaction networks with DNA strand displacement

    Science.gov (United States)

    Srinivas, Niranjan

    Over the last century, the silicon revolution has enabled us to build faster, smaller and more sophisticated computers. Today, these computers control phones, cars, satellites, assembly lines, and other electromechanical devices. Just as electrical wiring controls electromechanical devices, living organisms employ "chemical wiring" to make decisions about their environment and control physical processes. Currently, the big difference between these two substrates is that while we have the abstractions, design principles, verification and fabrication techniques in place for programming with silicon, we have no comparable understanding or expertise for programming chemistry. In this thesis we take a small step towards the goal of learning how to systematically engineer prescribed non-equilibrium dynamical behaviors in chemical systems. We use the formalism of chemical reaction networks (CRNs), combined with mass-action kinetics, as our programming language for specifying dynamical behaviors. Leveraging the tools of nucleic acid nanotechnology (introduced in Chapter 1), we employ synthetic DNA molecules as our molecular architecture and toehold-mediated DNA strand displacement as our reaction primitive. Abstraction, modular design and systematic fabrication can work only with well-understood and quantitatively characterized tools. Therefore, we embark on a detailed study of the "device physics" of DNA strand displacement (Chapter 2). We present a unified view of strand displacement biophysics and kinetics by studying the process at multiple levels of detail, using an intuitive model of a random walk on a 1-dimensional energy landscape, a secondary structure kinetics model with single base-pair steps, and a coarse-grained molecular model that incorporates three-dimensional geometric and steric effects. Further, we experimentally investigate the thermodynamics of three-way branch migration. Our findings are consistent with previously measured or inferred rates for

  8. A method for incorporating equilibrium chemical reactions into multiphase flow models for CO2 storage

    Science.gov (United States)

    Saaltink, Maarten W.; Vilarrasa, Victor; De Gaspari, Francesca; Silva, Orlando; Carrera, Jesús; Rötting, Tobias S.

    2013-12-01

    CO2 injection and storage in deep saline aquifers involves many coupled processes, including multiphase flow, heat and mass transport, rock deformation and mineral precipitation and dissolution. Coupling is especially critical in carbonate aquifers, where minerals will tend to dissolve in response to the dissolution of CO2 into the brine. The resulting neutralization will drive further dissolution of both CO2 and calcite. This suggests that large cavities may be formed and that proper simulation may require full coupling of reactive transport and multiphase flow. We show that solving the latter may suffice whenever two requirements are met: (1) all reactions can be assumed to occur in equilibrium and (2) the chemical system can be calculated as a function of the state variables of the multiphase flow model (i.e., liquid and gas pressure, and temperature). We redefine the components of multiphase flow codes (traditionally, water and CO2), so that they are conservative for all reactions of the chemical system. This requires modifying the traditional constitutive relationships of the multiphase flow codes, but yields the concentrations of all species and all reaction rates by simply performing speciation and mass balance calculations at the end of each time step. We applied this method to the H2O-CO2-Na-Cl-CaCO3 system, so as to model CO2 injection into a carbonate aquifer containing brine. Results were very similar to those obtained with traditional formulations, which implies that full coupling of reactive transport and multi-phase flow is not really needed for this kind of systems, but the resulting simplifications may make it advisable even for cases where the above requirements are not met. Regarding the behavior of carbonate rocks, we find that porosity development near the injection well is small because of the low solubility of calcite. Moreover, dissolution concentrates at the front of the advancing CO2 plume because the brine below the plume tends to reach

  9. Characteristics of Turbulent/non-turbulent Interface in a Turbulent Planar Jet with a Chemical Reaction

    Science.gov (United States)

    Watanabe, Tomoaki; Sakai, Yasuhiko; Nagata, Kouji; Terashima, Osamu; Ito, Yasumasa; Hayase, Toshiyuki

    2013-11-01

    Characteristics of chemical reaction (A + B --> P) near the turbulent/non-turbulent (T/NT) interface are investigated by using the direct numerical simulation of reactive planar jet. The reactants A and B are separately premixed into the jet and ambient flows, respectively. DNS is performed at three different Damköhler numbers. The conditional statistics conditioned on the distance from the T/NT interface is used to investigate the chemical reaction near the T/NT interface. The conditional mean concentration of product P shows a sharp jump near the T/NT interface, and the product P hardly exists in the non-turbulent region. This implies that the chemical reaction takes place in the turbulent region after the reactant B in the ambient flow is entrained into the turbulent region. The conditional mean scalar dissipation rate of mixture fraction has a large peak value slightly inside the T/NT interface. At the same point, the chemical reaction rate also has a peak value in the case of large Damköhler number. On the other hand, when the Damköhler number is small, the chemical reaction rate near the T/NT interface is smaller than that in the turbulent region. This work was carried out under the Collaborative Research Project of the Institute of Fluid Science, Tohoku University. Part of this work was supported by JSPS KAKENHI Grant Number 25002531 and MEXT KAKENHI Grant Numbers 25289030, 25289031, 2563005.

  10. Magnetic field effects in chemical systems

    OpenAIRE

    Rodgers, CT

    2009-01-01

    Chemical reactions that involve radical intermediates can be influenced by magnetic fields, which act to alter their rate, yield, or product distribution. These effects have been studied extensively in liquids, solids, and constrained media such as micelles. They may be interpreted using the radical pair mechanism (RPM). Such effects are central to the field of spin chemistry of which there have been several detailed and extensive reviews. This review instead presents an introductory account ...

  11. Chemical Characterization and Reactivity Testing of Fuel-Oxidizer Reaction Product (Test Report)

    Science.gov (United States)

    1996-01-01

    The product of incomplete reaction of monomethylhydrazine (MMH) and nitrogen tetroxide (NTO) propellants, or fuel-oxidizer reaction product (FORP), has been hypothesized as a contributory cause of an anomaly which occurred in the chamber pressure (PC) transducer tube on the Reaction Control Subsystem (RCS) aft thruster 467 on flight STS-51. A small hole was found in the titanium-alloy PC tube at the first bend below the pressure transducer. It was surmised that the hole may have been caused by heat and pressure resulting from ignition of FORP. The NASA Johnson Space Center (JSC) White Sands Test Facility (WSTF) was requested to define the chemical characteristics of FORP, characterize its reactivity, and simulate the events in a controlled environment which may have lead to the Pc-tube failure. Samples of FORP were obtained from the gas-phase reaction of MMH with NTO under laboratory conditions, the pulsed firings of RCS thrusters with modified PC tubes using varied oxidizer or fuel lead times, and the nominal RCS thruster firings at WSTF and Kaiser-Marquardt. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), accelerating rate calorimetry (ARC), ion chromatography (IC), inductively coupled plasma (ICP) spectrometry, thermogravimetric analysis (TGA) coupled to FTIR (TGA/FTIR), and mechanical impact testing were used to qualitatively and quantitatively characterize the chemical, thermal, and ignition properties of FORP. These studies showed that the composition of FORP is variable but falls within a limited range of compositions that depends on the fuel loxidizer ratio at the time of formation, composition of the post-formation atmosphere (reducing or oxidizing), and reaction or postreaction temperature. A typical composition contains methylhydrazinium nitrate (MMHN), ammonium nitrate (AN), methylammonium nitrate (MAN), and trace amounts of hydrazinium nitrate and 1,1-dimethylhydrazinium nitrate. The thermal decomposition

  12. Chemical organization theory: towards a theory of constructive dynamical systems

    OpenAIRE

    Dittrich, Peter; di Fenizio, Pietro Speroni

    2005-01-01

    Complex dynamical networks consisting of many components that interact and produce each other are difficult to understand, especially, when new components may appear. In this paper we outline a theory to deal with such systems. The theory consists of two parts. The first part introduces the concept of a chemical organization as a closed and mass-maintaining set of components. This concept allows to map a complex (reaction) network to the set of organizations, providing a new view on the syste...

  13. Combustion chemical vapor desposited coatings for thermal barrier coating systems

    Energy Technology Data Exchange (ETDEWEB)

    Hampikian, J.M.; Carter, W.B. [Georgia Institute of Technology, Atlanta, GA (United States)

    1995-10-01

    The new deposition process, combustion chemical vapor deposition, shows a great deal of promise in the area of thermal barrier coating systems. This technique produces dense, adherent coatings, and does not require a reaction chamber. Coatings can therefore be applied in the open atmosphere. The process is potentially suitable for producing high quality CVD coatings for use as interlayers between the bond coat and thermal barrier coating, and/or as overlayers, on top of thermal barrier coatings.

  14. Photo-induced isomerization and chemical reaction dynamics in superfluid helium droplets

    Science.gov (United States)

    Merritt, Jeremy; Douberly, Gary; Miller, Roger

    2008-03-01

    Near threshold photo-induced isomerization and photo-induced chemical reactions have long been sough after as sensitive probes of the underlying potential energy surface. One of the most important questions asked is how the initially bright quantum state couples to the reaction coordinate, and thus relates to energy transfer in general. Helium droplets have now allowed us to stabilize entrance channel clusters behind very small reaction barriers such that vibrational excitation may result in reaction. Through two examples, namely the isomerization of the 2 binary complexes of HF-HCN Douberly et al. PCCP 2005, 7,463, and the induced reaction of the gallium-HCN complex Merritt et al. JPCA 2007, DOI:10.1021/jp074981e we will show how the branching ratios for reaction and predissociation can determined and the influence of the superfluid He solvent.

  15. Purification of hydrogen under a free or combined form in a gaseous mixture, by chemical reactions with uranium

    International Nuclear Information System (INIS)

    Within the framework of the european fusion program, we are dealing with the purification of hydrogen (tritium) under a free or combined form, from a H2, N2, NH3, CH4, O2, gaseous mixture. The process consists in cracking the hydrogenated molecules and absorbing the impurities by chemical reactions with uranium, without holding back hydrogen. In the temperature range: 950 K < T < 1200 K hydrides are indeed fully decomposed for hydrogen partial pressures lower than ten atmospheres while uranium oxides, nitrides and carbides formation reactions are promoted. The experiments are carried out with massive uranium heated at 973 K in a closed reactor. They confirm that such a process may satisfy our goals, but they point out the importance of interactions occurring between the gaseous and solids systems and interfere with the conversion rates. Gaseous pressure decreases with time according to two successive phases: the first one is governed by a surface kinetic law, while after a short transition time, gas diffusion in the solid products arises and becomes the limiting step of the reactions. Experimental results with pure gases and mixtures, prove that solid products have different structures. An illustrative example is given by nitrogen and methane reactions with uranium: the solid layers are compactely formed with each pure gas and they slow down the chemical kinetic rates; on the contrary the chemical kinetic rates of the mixed gases reactions are clearly increased and the diffusional rates are postponed. Then, the compacity of the solid products merely depends on the operating conditions and the influence of the reactional surface state on the chemical kinetic rates is here pointed out

  16. Two Optimization Methods to Determine the Rate Constants of a Complex Chemical Reaction Using FORTRAN and MATLAB

    Directory of Open Access Journals (Sweden)

    Abdel-Latif A. Seoud

    2010-01-01

    Full Text Available Problem statement: For chemical reactions, the determination of the rate constants is both very difficult and a time consuming process. The aim of this research was to develop computer programs for determining the rate constants for the general form of any complex reaction at a certain temperature. The development of such program can be very helpful in the control of industrial processes as well as in the study of the reaction mechanisms. Determination of the accurate values of the rate constants would help in establishing the optimum conditions of reactor design including pressure, temperature and other parameters of the chemical reaction. Approach: From the experimental concentration-time data, initial values of rate constants were calculated. Experimental data encountered several types of errors, including temperature variation, impurities in the reactants and human errors. Simulations of a second order consecutive irreversible chemical reaction of the saponification of diethyl ester were presented as an example of the complex reactions. The rate equations (system of simultaneous differential equations of the reaction were solved to get the analytical concentration versus time profiles. The simulation results were compared with experimental results at each measured point. All deviations between experimental and calculated values were squared and summed up to form a new function. This function was fed into a minimizer routine that gave the optimal rate constants. Two optimization techniques were developed using FORTRAN and MATLAB for accurately determining the rate constants of the reaction at certain temperature from the experimental data. Results: Results showed that the two proposed programs were very efficient, fast and accurate tools to determine the true rate constants of the reaction with less 1% error. The use of the MATLAB embedded subroutines for simultaneously solving the differential equations and minimization of the error function

  17. System chemical biology studies of endocrine disruptors

    DEFF Research Database (Denmark)

    Taboureau, Olivier; Oprea, Tudor I.

    Endocrine disrupting chemicals (EDCs) alter hormonal balance and other physiological systems through inappropriate developmental or adult exposure, perturbing the reproductive function of further generations. While disruption of key receptors (e.g., estrogen, androgen, and thyroid) at the ligand...

  18. Coherent chemical kinetics as quantum walks. I. Reaction operators for radical pairs

    Science.gov (United States)

    Chia, A.; Tan, K. C.; Pawela, Ł.; Kurzyński, P.; Paterek, T.; Kaszlikowski, D.

    2016-03-01

    Classical chemical kinetics uses rate-equation models to describe how a reaction proceeds in time. Such models are sufficient for describing state transitions in a reaction where coherences between different states do not arise, in other words, a reaction that contains only incoherent transitions. A prominent example of a reaction containing coherent transitions is the radical-pair model. The kinetics of such reactions is defined by the so-called reaction operator that determines the radical-pair state as a function of intermediate transition rates. We argue that the well-known concept of quantum walks from quantum information theory is a natural and apt framework for describing multisite chemical reactions. By composing Kraus maps that act only on two sites at a time, we show how the quantum-walk formalism can be applied to derive a reaction operator for the standard avian radical-pair reaction. Our reaction operator predicts the same recombination dephasing rate as the conventional Haberkorn model, which is consistent with recent experiments [K. Maeda et al., J. Chem. Phys. 139, 234309 (2013), 10.1063/1.4844355], in contrast to previous work by Jones and Hore [J. A. Jones and P. J. Hore, Chem. Phys. Lett. 488, 90 (2010), 10.1016/j.cplett.2010.01.063]. The standard radical-pair reaction has conventionally been described by either a normalized density operator incorporating both the radical pair and reaction products or a trace-decreasing density operator that considers only the radical pair. We demonstrate a density operator that is both normalized and refers only to radical-pair states. Generalizations to include additional dephasing processes and an arbitrary number of sites are also discussed.

  19. Identification of heavy and superheavy nuclides using chemical separator systems

    Science.gov (United States)

    Türler, Andreas

    1999-11-01

    With the recent synthesis of superheavy nuclides produced in the reactions 48Ca+238U and 48Ca+242,244Pu, much longer-lived nuclei than the previously known neutron-deficient isotopes of the heaviest elements have been identified. Half-lives of several hours and up to several years have been predicted for the longest-lived isotopes of these elements. Thus, the sensitivity of radiochemical separation techniques may present a viable alternative to physical separator systems for the discovery of some of the predicted longer-lived heavy and superheavy nuclides. The advantages of chemical separator systems in comparison to kinematic separators lie in the possibility of using thick targets, high beam intensities spread over larger target areas and in providing access to nuclides emitted under large angles and low velocities. Thus, chemical separator systems are ideally suited to study also transfer and (HI, αxn) reaction products. In the following, a study of (HI, αxn) reactions will be presented and prospects to chemically identify heavy and superheavy elements discussed.

  20. Application of laser diagnostics to sodium-water chemical reaction field

    International Nuclear Information System (INIS)

    In a sodium-cooled fast reactor (SFR), liquid sodium is used as a heat transfer fluid because of its excellent heat transport capability. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow by a breach of heat transfer tubes in a steam generator. Therefore the study on sodium-water chemical reactions is of paramount importance for safety reasons. This study aims to clarify the sodium-water reaction mechanisms using laser diagnostics. The sodium-water counter-flow reactions were measured using laser diagnostics such as laser induced fluorescence, CARS, Raman scattering and photo-fragmentation. The measurement results show that the sodium-water reaction proceeds mainly by the reaction Na + H2O → NaOH + H and the main product is NaOH in this reaction. Its forward and backward reaction rates tend to balance with each other and the whole reaction rate reduces as temperature increases. (author)

  1. Chemical production processes and systems

    Science.gov (United States)

    Holladay, Johnathan E; Muzatko, Danielle S; White, James F; Zacher, Alan H

    2015-04-21

    Hydrogenolysis systems are provided that can include a reactor housing an Ru-comprising hydrogenolysis catalyst and wherein the contents of the reactor is maintained at a neutral or acidic pH. Reactant reservoirs within the system can include a polyhydric alcohol compound and a base, wherein a weight ratio of the base to the compound is less than 0.05. Systems also include the product reservoir comprising a hydrogenolyzed polyhydric alcohol compound and salts of organic acids, and wherein the moles of base are substantially equivalent to the moles of salts or organic acids. Processes are provided that can include an Ru-comprising catalyst within a mixture having a neutral or acidic pH. A weight ratio of the base to the compound can be between 0.01 and 0.05 during exposing.

  2. Chemical production processes and systems

    Science.gov (United States)

    Holladay, Johnathan E.; Muzatko, Danielle S.; White, James F.; Zacher, Alan H.

    2014-06-17

    Hydrogenolysis systems are provided that can include a reactor housing an Ru-comprising hydrogenolysis catalyst and wherein the contents of the reactor is maintained at a neutral or acidic pH. Reactant reservoirs within the system can include a polyhydric alcohol compound and a base, wherein a weight ratio of the base to the compound is less than 0.05. Systems also include the product reservoir comprising a hydrogenolyzed polyhydric alcohol compound and salts of organic acids, and wherein the moles of base are substantially equivalent to the moles of salts or organic acids. Processes are provided that can include an Ru-comprising catalyst within a mixture having a neutral or acidic pH. A weight ratio of the base to the compound can be between 0.01 and 0.05 during exposing.

  3. Reaction chemistry of nitrogen species in hydrothermal systems: Simple reactions, waste simulants, and actual wastes

    International Nuclear Information System (INIS)

    Results are presented from hydrothermal reaction systems containing organic components, nitrogen components, and an oxidant. Reaction chemistry observed in simple systems and in simple waste simulants is used to develop a model which presents global nitrogen chemistry in these reactive systems. The global reaction path suggested is then compared with results obtained for the treatment of an actual waste stream containing only C-N-0-H species

  4. Structural dynamics effects on the ultrafast chemical bond cleavage of a photodissociation reaction

    OpenAIRE

    Corrales, Maria E.; Loriot, Vincent; Balerdi, Garikoitz; González-Vázquez, Jesús; de Nalda, Rebeca; Bañares, Luis; Zewail, Ahmed H.

    2014-01-01

    The correlation between chemical structure and dynamics has been explored in a series of molecules with increasing structural complexity in order to investigate its influence on bond cleavage reaction times in a photodissociation event. Femtosecond time-resolved velocity map imaging spectroscopy reveals specificity of the ultrafast carbon–iodine (C–I) bond breakage for a series of linear (unbranched) and branched alkyl iodides, due to the interplay between the pure reaction coordinate and the...

  5. New Approach to the Stability of Chemical Reaction Networks: Piecewise Linear in Rates Lyapunov Functions

    OpenAIRE

    Al-Radhawi, M. Ali; Angeli, David

    2014-01-01

    Piecewise-Linear in Rates (PWLR) Lyapunov functions are introduced for a class of Chemical Reaction Networks (CRNs). In addition to their simple structure, these functions are robust with respect to arbitrary monotone reaction rates, of which mass-action is a special case. The existence of such functions ensures the convergence of trajectories towards equilibria, and guarantee their asymptotic stability with respect to the corresponding stoichiometric compatibility class. We give the definiti...

  6. Reaction of Phosphorylated and O-Glycosylated Peptides by Chemically Targeted Identification at Ambient Temperature

    OpenAIRE

    Rusnak, Felicia; Zhou, Jie; Hathaway, Gary M.

    2004-01-01

    Conditions for carrying out chemically targeted identification of peptides containing phosphorylated or glycosylated serine residues have been investigated. Ba(OH)2 was used at ambient temperature to catalyze the β-elimination reaction at 25°C. Nucleophilic addition of 2-aminoethanethiol was performed in both parallel and tandem experiments. The method was demonstrated by the reaction of β-casein tryptic digest phosphopeptides and an O-glycosylated peptide. Contrary to an earlier report by ot...

  7. A kinetic model for chemical reactions without barriers : transport coefficients and eigenmodes

    OpenAIRE

    Alves, Giselle M.; Marques Júnior, Wilson; Soares, A. J.; Kremer, Gilberto M.

    2011-01-01

    The kinetic model of the Boltzmann equation proposed in the work of Kremer and Soares 2009 for a binary mixture undergoing chemical reactions of symmetric type which occur without activation energy is revisited here, with the aim of investigating in detail the transport properties of the reactive mixture and the influence of the reaction process on the transport coefficients. Accordingly, the non-equilibrium solution of the Boltzmann equation is determined through an expansion in Sonine polyn...

  8. Transformation of Symmetrization Order to Nuclear-Spin Magnetization by Chemical Reaction and Nuclear Magnetic Resonance

    OpenAIRE

    Bowers, C. Russell; Weitekamp, Daniel P.

    1986-01-01

    A method of obtaining very large nuclear-spin polarizations is proposed and illustrated by density-operator calculations. The prediction is that chemical reaction and rf irradiation can convert the scalar parahydrogen state into polarization of order unity on the nuclear spins of the products of molecular-hydrogen addition reactions. A means of extending the resultant sensitivity enhancement to other spins is proposed in which the transfer of order occurs through population differences not as...

  9. Implicit coupling of turbulent diffusion with chemical reaction mechanisms for prognostic atmospheric dispersion models

    Energy Technology Data Exchange (ETDEWEB)

    Berlowitz, D.R.

    1996-11-01

    In the last few decades the negative impact by humans on the thin atmospheric layer enveloping the earth, the basis for life on this planet, has increased steadily. In order to halt, or at least slow down this development, the knowledge and study of these anthropogenic influence has to be increased and possible remedies have to be suggested. An important tool for these studies are computer models. With their help the atmospheric system can be approximated and the various processes, which have led to the current situation can be quantified. They also serve as an instrument to assess short or medium term strategies to reduce this human impact. However, to assure efficiency as well as accuracy, a careful analysis of the numerous processes involved in the dispersion of pollutants in the atmosphere is called for. This should help to concentrate on the essentials and also prevent excessive usage of sometimes scarce computing resources. The basis of the presented work is the EUMAC Zooming Model (ETM), and particularly the component calculating the dispersion of pollutants in the atmosphere, the model MARS. The model has two main parts: an explicit solver, where the advection and the horizontal diffusion of pollutants are calculated, and an implicit solution mechanism, allowing the joint computation of the change of concentration due to chemical reactions, coupled with the respective influence of the vertical diffusion of the species. The aim of this thesis is to determine particularly the influence of the horizontal components of the turbulent diffusion on the existing implicit solver of the model. Suggestions for a more comprehensive inclusion of the full three dimensional diffusion operator in the implicit solver are made. This is achieved by an appropriate operator splitting. A selection of numerical approaches to tighten the coupling of the diffusion processes with the calculation of the applied chemical reaction mechanisms are examined. (author) figs., tabs., refs.

  10. Temperature lowering in cryogenic chemical-synthesis techniques and system

    International Nuclear Information System (INIS)

    When evaluating a chemical synthesis process for a reaction that occurs on the cryogenically cooled walls, it is sometimes necessary to reduce the wall temperatures to enhance the chemical process. To evaluate the chemical process at lower than atmospheric boiling of liquid nitrogen, we built a system and used it to reduce the temperature of the liquid nitrogen. The technique of lowering the liquid nitrogen temperature by reducing the pressure of the boil-off is established knowledge. This paper presents the engineering aspects of the system, design features, equipment requirements, methods of control, and results of the chemical synthesis. The heat input to the system was ∼400 watts, placing a relatively large demand on the pumping system. Our system is a scale-up of the small laboratory experiment, and it provides the information needed to design an effective system. The major problem encountered was the large quantity of liquid escaping the system during the processing, placing a large gas load on the vacuum system

  11. Elucidation of Mechanisms and Selectivities of Metal-Catalyzed Reactions using Quantum Chemical Methodology.

    Science.gov (United States)

    Santoro, Stefano; Kalek, Marcin; Huang, Genping; Himo, Fahmi

    2016-05-17

    Quantum chemical techniques today are indispensable for the detailed mechanistic understanding of catalytic reactions. The development of modern density functional theory approaches combined with the enormous growth in computer power have made it possible to treat quite large systems at a reasonable level of accuracy. Accordingly, quantum chemistry has been applied extensively to a wide variety of catalytic systems. A huge number of problems have been solved successfully, and vast amounts of chemical insights have been gained. In this Account, we summarize some of our recent work in this field. A number of examples concerned with transition metal-catalyzed reactions are selected, with emphasis on reactions with various kinds of selectivities. The discussed cases are (1) copper-catalyzed C-H bond amidation of indoles, (2) iridium-catalyzed C(sp(3))-H borylation of chlorosilanes, (3) vanadium-catalyzed Meyer-Schuster rearrangement and its combination with aldol- and Mannich-type additions, (4) palladium-catalyzed propargylic substitution with phosphorus nucleophiles, (5) rhodium-catalyzed 1:2 coupling of aldehydes and allenes, and finally (6) copper-catalyzed coupling of nitrones and alkynes to produce β-lactams (Kinugasa reaction). First, the methodology adopted in these studies is presented briefly. The electronic structure method in the great majority of these kinds of mechanistic investigations has for the last two decades been based on density functional theory. In the cases discussed here, mainly the B3LYP functional has been employed in conjunction with Grimme's empirical dispersion correction, which has been shown to improve the calculated energies significantly. The effect of the surrounding solvent is described by implicit solvation techniques, and the thermochemical corrections are included using the rigid-rotor harmonic oscillator approximation. The reviewed examples are chosen to illustrate the usefulness and versatility of the adopted methodology in

  12. Research on development of in situ titanium matrix composites and in situ reaction thermodynamics of the reaction systems

    Institute of Scientific and Technical Information of China (English)

    Lifang Cai; Yongzhong Zhang; Likai Shi; Haoqiang Yang; Mingzhe Xi

    2006-01-01

    The in situ synthesis method for titanium matrix composites (TMCs) has obvious technical and economical advantages over other traditional methods. Ultrafine reinforcement particles were formed in situ by chemical reaction between elements or between elements and compounds. Using the approach, contamination at the composite matrix/reinforcement particle interface did not occur,interface bonding was good, and the reinforcement particle was thermodynamically stable. The stage of development of the preparation process for in situ TMCs as well as the thermodynamic analysis of the possible in situ reaction systems was described.

  13. Theoretical considerations of Flow Injection Analysis in the Absence of Chemical Reactions

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov

    2000-01-01

    The fundamental mechanism of flow injection analysis (FIA) is assumed to be simple dissusion and the response of the detector is included in a model description that provide information about the shape of the FIA peak in terms of, basically, five parameters. Two of the five parameters are associa...... any deviation from the features of the present model and the results of a tentative chemical reaction with one of the test compounds, is related to chemical kinetics....

  14. Stochastic innovation as a mechanism by which catalysts might self-assemble into chemical reaction networks

    OpenAIRE

    Bradford, Justin A; Dill, Ken A.

    2007-01-01

    We develop a computer model for how two different chemical catalysts in solution, A and B, could be driven to form AB complexes, based on the concentration gradients of a substrate or product that they share in common. If A's product is B's substrate, B will be attracted to A, mediated by a common resource that is not otherwise plentiful in the environment. By this simple physicochemical mechanism, chemical reactions could spontaneously associate to become chained together in solution. Accord...

  15. In-Space Chemical Propulsion System Model

    Science.gov (United States)

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

    2004-01-01

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

  16. Power optimization of chemically driven heat engine based on first and second order reaction kinetic theory and probability theory

    Science.gov (United States)

    Zhang, Lei; Chen, Lingen; Sun, Fengrui

    2016-03-01

    The finite-time thermodynamic method based on probability analysis can more accurately describe various performance parameters of thermodynamic systems. Based on the relation between optimal efficiency and power output of a generalized Carnot heat engine with a finite high-temperature heat reservoir (heat source) and an infinite low-temperature heat reservoir (heat sink) and with the only irreversibility of heat transfer, this paper studies the problem of power optimization of chemically driven heat engine based on first and second order reaction kinetic theory, puts forward a model of the coupling heat engine which can be run periodically and obtains the effects of the finite-time thermodynamic characteristics of the coupling relation between chemical reaction and heat engine on the power optimization. The results show that the first order reaction kinetics model can use fuel more effectively, and can provide heat engine with higher temperature heat source to increase the power output of the heat engine. Moreover, the power fluctuation bounds of the chemically driven heat engine are obtained by using the probability analysis method. The results may provide some guidelines for the character analysis and power optimization of the chemically driven heat engines.

  17. Engineered Barrier System: Physical and Chemical Environment

    International Nuclear Information System (INIS)

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

  18. A priori modeling of chemical reactions on computational grid platforms: Workflows and data models

    International Nuclear Information System (INIS)

    Graphical abstract: The quantum framework of the Grid Empowered Molecular Simulator GEMS assembled on the European Grid allows the ab initio evaluation of the dynamics of small systems starting from the calculation of the electronic properties. Highlights: ► The grid based GEMS simulator accurately models small chemical systems. ► Q5Cost and D5Cost file formats provide interoperability in the workflow. ► Benchmark runs on H + H2 highlight the Grid empowering. ► O + O2 and N + N2 calculated k (T)’s fall within the error bars of the experiment. - Abstract: The quantum framework of the Grid Empowered Molecular Simulator GEMS has been assembled on the segment of the European Grid devoted to the Computational Chemistry Virtual Organization. The related grid based workflow allows the ab initio evaluation of the dynamics of small systems starting from the calculation of the electronic properties. Interoperability between computational codes across the different stages of the workflow was made possible by the use of the common data formats Q5Cost and D5Cost. Illustrative benchmark runs have been performed on the prototype H + H2, N + N2 and O + O2 gas phase exchange reactions and thermal rate coefficients have been calculated for the last two. Results are discussed in terms of the modeling of the interaction and advantages of using the Grid is highlighted.

  19. Illustrating Chemical Concepts through Food Systems: Introductory Chemistry Experiments.

    Science.gov (United States)

    Chambers, E., IV; Setser, C. S.

    1980-01-01

    Demonstrations involving foods that illustrate chemical concepts are described, including vaporization of liquids and Graham's law of diffusion, chemical reaction rates, adsorption, properties of solutions, colloidal dispersions, suspensions, and hydrogen ion concentration. (CS)

  20. Characterizing Molecular Interactions in Chemical Systems

    OpenAIRE

    Guenther, David; Alvarez-Boto, Roberto; Contreras-Garcia, Julia; Piquemal, Jean-Philip; Tierny, Julien

    2014-01-01

    Interactions between atoms have a major influence on the chemical properties of molecular systems. While covalent interactions impose the structural integrity of molecules, noncovalent interactions govern more subtle phenomena such as protein folding, bonding or self assembly. The understanding of these types of interactions is necessary for the interpretation of many biological processes and chemical design tasks. While traditionally the electron density is analyzed to interpret the quantum ...

  1. Relativistic thermodynamics of irreversible processes I. Heat conduction, diffusion, viscous flow and chemical reactions; formal part

    NARCIS (Netherlands)

    Kluitenberg, G.A.; Groot, S.R. de; Mazur, P.

    1953-01-01

    The relativistic thermodynamics of irreversible processes is developed for an isotropic mixture in which heat conduction, diffusion, viscous flow, chemical reactions and their cross-phenomena may occur. The four-vectors, representing the relative flows of matter, are defined in such a way that, in t

  2. Using Drawing Technology to Assess Students' Visualizations of Chemical Reaction Processes

    Science.gov (United States)

    Chang, Hsin-Yi; Quintana, Chris; Krajcik, Joseph

    2014-01-01

    In this study, we investigated how students used a drawing tool to visualize their ideas of chemical reaction processes. We interviewed 30 students using thinking-aloud and retrospective methods and provided them with a drawing tool. We identified four types of connections the students made as they used the tool: drawing on existing knowledge,…

  3. The Effective Concepts on Students' Understanding of Chemical Reactions and Energy

    Science.gov (United States)

    Ayyildiz, Yildizay; Tarhan, Leman

    2012-01-01

    The purpose of this study was to determine the relationship between the basic concepts related to the unit of "Chemical Reactions and Energy" and the sub-concepts underlying for meaningful learning of the unit and to investigate the effectiveness of them on students' learning achievements. For this purpose, the basic concepts of the unit were…

  4. Mapping Students' Modes of Reasoning When Thinking about Chemical Reactions Used to Make a Desired Product

    Science.gov (United States)

    Weinrich, M. L.; Talanquer, V.

    2016-01-01

    The central goal of this study was to analyze the complexity of students' explanations about how and why chemical reactions happen in terms of the types of causal connections students built between expressed concepts and ideas. We were particularly interested in characterizing differences in the types of reasoning applied by students with…

  5. Impact of supersonic and subsonic aircraft on ozone: Including heterogeneous chemical reaction mechanisms

    Science.gov (United States)

    Kinnison, Douglas E.; Wuebbles, Donald J.

    1994-01-01

    Preliminary calculations suggest that heterogeneous reactions are important in calculating the impact on ozone from emissions of trace gases from aircraft fleets. In this study, three heterogeneous chemical processes that occur on background sulfuric acid aerosols are included and their effects on O3, NO(x), Cl(x), HCl, N2O5, ClONO2 are calculated.

  6. Two Experiments to Approach the Boltzmann Factor: Chemical Reaction and Viscous Flow

    Science.gov (United States)

    Fazio, Claudio; Battaglia, Onofrio R.; Guastella, Ivan

    2012-01-01

    In this paper we discuss a pedagogical approach aimed at pointing out the role played by the Boltzmann factor in describing phenomena usually perceived as regulated by different mechanisms of functioning. Experimental results regarding some aspects of a chemical reaction and of the viscous flow of some liquids are analysed and described in terms…

  7. Turkish, Indian, and American Chemistry Textbooks Use of Inscriptions to Represent "Types of Chemical Reactions"

    Science.gov (United States)

    Aydin, Sevgi; Sinha, Somnath; Izci, Kemal; Volkmann, Mark

    2014-01-01

    The purpose of this study was to investigate inscriptions used in "Types of Chemical Reactions" topic in Turkish, Indian, and American chemistry textbooks. We investigated both the types of inscriptions and how they were used in textbooks to support learning. A conceptual analysis method was employed to determine how those textbooks use…

  8. Influence of Size Effect on Chemical Reactions on Surface of Aerosol Nanoparticles

    Czech Academy of Sciences Publication Activity Database

    Levdansky, V.V.; Smolík, Jiří; Ždímal, Vladimír; Moravec, Pavel

    Prague : Czech Aerosol Society, 2013, C028. ISBN N. [European Aerosol Conference (EAC 2013). Prague (CZ), 01.09.2013-06.09.2013] R&D Projects: GA AV ČR IAA200760905 Institutional support: RVO:67985858 Keywords : aerosol * nanoparticles * chemical reactions Subject RIV: CF - Physical ; Theoretical Chemistry http://eac2013.cz/index.php

  9. Law of Large Numbers in the Supremum Norm for a Chemical Reaction with Diffusion

    OpenAIRE

    Blount, Douglas

    1992-01-01

    A space-time jump Markov process, modeling a chemical reaction with diffusion, is compared in the supremum norm to the usual model, the solution to a partial differential equation. Conditions are given which imply the deviation converges in probability to 0 uniformly on bounded time intervals. Estimates reflecting underlying large deviation behavior are obtained.

  10. Dynamics of chemical reactions of multiply-charged cations: Information from beam scattering experiments

    Czech Academy of Sciences Publication Activity Database

    Herman, Zdeněk

    2015-01-01

    Roč. 378, FEB 2015 (2015), s. 113-126. ISSN 1387-3806 Institutional support: RVO:61388955 Keywords : Multiply-charged ions * Dynamics of chemical reactions * Beam scattering Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.972, year: 2014

  11. Impact of supersonic and subsonic aircraft on ozone: Including heterogeneous chemical reaction mechanisms

    International Nuclear Information System (INIS)

    Preliminary calculations suggest that heterogeneous reactions are important in calculating the impact on ozone from emissions of trace gases from aircraft fleets. In this study, three heterogeneous chemical processes that occur on background sulfuric acid aerosols are included and their effects on O3, NOx, Clx, HCl, N2O5, ClONO2 are calculated

  12. Change of the chemical barrier performance of cement materials altered by hydrothermal reaction

    International Nuclear Information System (INIS)

    Cement has been considered to be a useful material because its chemical property is potentially suitable for immobilization of radioactive waste. In particular, the sorption of radionuclides onto cement material is very important parameter in the TRU waste disposal system containing long-life radionuclides. For the long term, in the disposal environment, cement materials must be altered by dissolution, chemical reaction with ions dissolved in the ground water, and hydrothermal reaction etc. Once the composition or crystallinity of minerals in cement is changed, the chemical properties, especially sorption, might be changed. However, the mechanism of the process of cement alteration and mechanism of radionuclide sorption onto cement are not yet fully understood. In this paper, the hydrothermal alteration process was studied experimentally, and the effect of alteration on the sorption properties of cement was investigated by the bath sorption test for Sr and Se. The results follow: 1) OPC and OPC/BFS-blended cement (hereafter BFS cement) were heated at temperatures up to 70degC in the synthetic cement equilibrated groundwater or distilled water for 1 month. Changes of crystallinity of the minerals were observed. For example, it was observed that the crystallinity of CSH-gel might increase. Ettringite decomposed on heating. For treatment in distilled water, monosulphate was formed only in the case of BFS cement. 2) In the case of Sr (as a representative cation) sorption, the distribution coefficient for hydrothermally altered OPC and BFS cement decreased as the alteration temperature increased. This is mainly caused by the decrease of distribution coefficient for the CSH-gel phase in cement accompanying the change of its crystallinity. In the case of Se(as a model anion, selenite) sorption, the distribution coefficient decreased as the alteration temperature increased for OPC in both distilled water and synthetic ground water, and also for BFS in groundwater. This is

  13. On detonation initiation by a temperature gradient for a detailed chemical reaction models

    International Nuclear Information System (INIS)

    The evolution from a temperature gradient to a detonation is investigated for combustion mixture whose chemistry is governed by a detailed chemical kinetics. We show that a detailed chemical reaction model has a profound effect on the spontaneous wave concept for detonation initiation by a gradient of reactivity. The evolution to detonation due to a temperature gradient is considered for hydrogen-oxygen and hydrogen-air mixtures at different initial pressures. It is shown that the minimal length of the temperature gradient for which a detonation can be ignited is much larger than that predicted from a one-step chemical model. - Highlights: → We study detonation initiation by temperature gradient for detailed chemical models. → Detailed chemical models have a profound effect on the spontaneous wave concept. → Initiating detonation by temperature gradient differs from one-step model. → In real fuels DDT can not be initiated by temperature gradient.

  14. Stability of a laminar premixed supersonic free shear layer with chemical reactions

    Science.gov (United States)

    Menon, S.; Anderson, J. D., Jr.; Pai, S. I.

    1984-01-01

    The stability of a two-dimensional compressible supersonic flow in the wake of a flat plate is discussed. The fluid is a multi-species mixture which is undergoing finite rate chemical reactions. The spatial stability of an infinitesimal disturbance in the fluid is considered. Numerical solutions of the eigenvalue stability equations for both reactive and nonreactive supersonic flows are presented and discussed. The chemical reactions have significant influence on the stability behavior. For instance, a neutral eigenvalue is observed near the freestream Mach number of 2.375 for the nonreactive case, but disappears when the reaction is turned on. For reactive flows, the eigenvalues are not very dependent on the free stream Mach number.

  15. Chemical cleavage reactions of DNA on solid support: application in mutation detection

    Directory of Open Access Journals (Sweden)

    Cotton Richard GH

    2003-05-01

    Full Text Available Abstract Background The conventional solution-phase Chemical Cleavage of Mismatch (CCM method is time-consuming, as the protocol requires purification of DNA after each reaction step. This paper describes a new version of CCM to overcome this problem by immobilizing DNA on silica solid supports. Results DNA test samples were loaded on to silica beads and the DNA bound to the solid supports underwent chemical modification reactions with KMnO4 (potassium permanganate and hydroxylamine in 3M TEAC (tetraethylammonium chloride solution. The resulting modified DNA was then simultaneously cleaved by piperidine and removed from the solid supports to afford DNA fragments without the requirement of DNA purification between reaction steps. Conclusions The new solid-phase version of CCM is a fast, cost-effective and sensitive method for detection of mismatches and mutations.

  16. A study on the improving efficiency for laser-induced chemical reaction process

    International Nuclear Information System (INIS)

    The laser-induced photoreaction process is a very useful technology in environmental aspects as well as atomic energy industry. In this study various factors which affect to the reaction process has been investigated for the increment of efficiency of reaction process. Palladium and silver have been chosen as samples for the reaction and the reaction processes have been monitored very carefully. For palladium nitric acid was identified as the best solvent for the reaction, while oxalic acid was the best reducing agent. As the concentration of the reducing agent increases, the reactivity of the samples were increased. When more laser energy was illuminated to the samples, reactivity increased, too. The wavelength of the laser beam used for the reaction was 3rd harmonic of Nd:YAG laser(355 nm). For silver case perchloric acid and ethanol were the best combination for the optimal reaction condition. As a result of the analysis of the reaction products, pure palladium and silver were the products, not any other forms of chemicals. (author). 12 refs., 3 tabs., 26 figs

  17. Ion-molecule reactions of oxygenated chemical ionization reagents with vincamine.

    Science.gov (United States)

    Bauerle, G F; Hall, B J; Tran, N V; Brodbelt, J S

    1996-03-01

    The ion-molecule reactions of ions from acetone, dimethyl ether, 2-methoxyethanol, and vinyl methyl ether with vincamine were investigated. Reactions with dimethyl ether result in [M+13](+) and [M+45](+) products, reactions with 2-methoxyethanol produce [M+13](+) and [M+89](+) ions, and reactions with acetone or vinyl methyl ether ions generate predominantly [M+43](+) ions. Collision-activated dissociation and deuterium labeling experiments allowed speculation about the product structures and mechanisms of dissociation. The methylene substitution process was shown to occur at the hydroxyl oxygen and the phenyl ring of vincamine for dimethyl ether reactions, but the methylene substitution process was not favored at the hydroxyl oxygen for the 2-methoxyethanol reactions, instead favored at the 12 phenyl position. The reaction site is likely different for the 2-methoxyethanol ion due to its capability for secondary hydrogen-bonding interactions. For the [M+45](+) and [M+89](+) ions, evidence suggests that charge-remote fragmentation processes occur from these products. In general, the use of dimethyl ether ions or 2-methoxyethanol ions for ionmolecule reactions prove highly diagnostic for the characterization of vincamine; both molecular weight and structural information are obtained. Limits of detection for vincamine with dimethyl ether chemical ionization via this technique on a benchtop ion trap gas chromatography-tandem mass spectrometer are in the upper parts per trillion range. PMID:24203296

  18. Chemical reactions at metallic and metal/semiconductor interfaces stimulated by pulsed laser annealing

    Science.gov (United States)

    Petit, E. J.; Caudano, R.

    1992-01-01

    Multilayer Al/Sb thin films have been evaporated on GaSb single crystals in ultra-high vacuum and pulsed-laser irradiated in-situ above the energy density threshold for surface melting. Superficial and interfacial chemical reactions have been characterized in-situ by Auger electron spectroscopy; and later, by X-ray photoelectron spectroscopy profiling, Rutherford backscattering spectrometry and scanning electron microscopy. The chemical reaction between the Al and Sb films is considered as a model reaction for laser-assisted synthesis of high-purity intermetallic compounds. The observation of a strong interfacial reaction between the melted film and the substrate is also a subject of great concern for optical data recording and laser alloying of ohmic contacts on semiconductors. We show that a suitable choice of the substrate and adding a low surface tension element into the metallic film can improve its stability during melting, and prevent inhomogeneous reaction and formation of holes, cracks and particles. Finally, other solutions are suggested to improve the control of these reactions.

  19. Chemical Synthesis of Proanthocyanidins in Vitro and Their Reactions in Aging Wines

    Directory of Open Access Journals (Sweden)

    Qiu-Hong Pan

    2008-12-01

    Full Text Available Proanthocyanidins are present in many fruits and plant products like grapes and wine, and contribute to their taste and health benefits. In the past decades of years, substantial progresses has been achieved in the identification of composition and structure of proanthocyanidins, but the debate concerning the existence of an enzymatic or nonenzymatic mechanism for proanthocyanidin condensation still goes on. Substantial attention has been paid to elucidating the potential mechanism of formation by means of biomimetic and chemical synthesis in vitro. The present paper aims at summarizing the research status on chemical synthesis of proanthocyanidins, including non-enzymatic synthesis of proanthocyanidin precursors, chemical synthesis of proanthocyanidins with direct condensation of flavanols and stereoselective synthesis of proanthocyanidins. Proanthocyanidin-involved reactions in aging wines are also reviewed such as direct and indirect reactions among proanthocyanidins, flavanols and anthocyanins. Topics for future research in this field are also put forward in this paper.

  20. Binomial moment equations for stochastic reaction systems.

    Science.gov (United States)

    Barzel, Baruch; Biham, Ofer

    2011-04-15

    A highly efficient formulation of moment equations for stochastic reaction networks is introduced. It is based on a set of binomial moments that capture the combinatorics of the reaction processes. The resulting set of equations can be easily truncated to include moments up to any desired order. The number of equations is dramatically reduced compared to the master equation. This formulation enables the simulation of complex reaction networks, involving a large number of reactive species much beyond the feasibility limit of any existing method. It provides an equation-based paradigm to the analysis of stochastic networks, complementing the commonly used Monte Carlo simulations. PMID:21568538

  1. Chemical detection, identification, and analysis system

    International Nuclear Information System (INIS)

    The chemical detection, identification, and analysis system (CDIAS) has three major goals. The first is to display safety information regarding chemical environment before personnel entry. The second is to archive personnel exposure to the environment. Third, the system assists users in identifying the stage of a chemical process in progress and suggests safety precautions associated with that process. In addition to these major goals, the system must be sufficiently compact to provide transportability, and it must be extremely simple to use in order to keep user interaction at a minimum. The system created to meet these goals includes several pieces of hardware and the integration of four software packages. The hardware consists of a low-oxygen, carbon monoxide, explosives, and hydrogen sulfide detector; an ion mobility spectrometer for airborne vapor detection; and a COMPAQ 386/20 portable computer. The software modules are a graphics kernel, an expert system shell, a data-base management system, and an interface management system. A supervisory module developed using the interface management system coordinates the interaction of the other software components. The system determines the safety of the environment using conventional data acquisition and analysis techniques. The low-oxygen, carbon monoxide, hydrogen sulfide, explosives, and vapor detectors are monitored for hazardous levels, and warnings are issued accordingly

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

    Science.gov (United States)

    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.

  3. Kinetics and thermodynamics of chemical reactions in Li/SOCl2 cells

    Science.gov (United States)

    Hansen, Lee D.; Frank, Harvey

    1987-01-01

    Work is described that was designed to determine the kinetic constants necessary to extrapolate kinetic data on Li/SOCl2 cells over the temperature range from 25 to 75 C. A second objective was to characterize as far as possible the chemical reactions that occur in the cells since these reactions may be important in understanding the potential hazards of these cells. The kinetics of the corrosion processes in undischarged Li/SOCl2 cells were determined and separated according to their occurrence at the anode and cathode; the effects that switching the current on and off has on the corrosion reactions was determined; and the effects of discharge state on the kinetics of the corrosion process were found. A thermodynamic analysis of the current-producing reactions in the cell was done and is included.

  4. Middle atmosphere heating by exothermic chemical reactions involving odd-hydrogen species

    Science.gov (United States)

    Mlynczak, Martin G.; Solomon, Susan

    1991-01-01

    The rate of heating which occurs in the middle atmosphere due to four exothermic reactions involving members of the odd-hydrogen family is calculated. The following reactions are considered: O + OH yields O2 + H; H + O2 + M yields HO2 + M; H + O3 yields OH + O2; and O + HO2 yields OH + O2. It is shown that the heating rates due to these reactions rival the oxygen-related heating rates conventionally considered in middle-atmosphere models. The conversion of chemical potential energy into molecular translational energy (heat) by these odd-hydrogen reactions is shown to be a significant energy source in the middle atmosphere that has not been previously considered.

  5. Assessment of existing H2/O2 chemical reaction mechanisms at reheat gas turbine conditions

    CERN Document Server

    Weydahl, Torleif; Seljeskog, Morten; Haugen, Nils Erland L

    2011-01-01

    This paper provides detailed comparisons of chemical reaction mechanisms of H2 applicable at high preheat temperatures and pressures relevant to gas turbine and particularly Alstom's reheat gas turbine conditions. It is shown that the available reaction mechanisms exhibit large differences in several important elementary reaction coefficients. The reaction mechanisms are assessed by comparing ignition delay and laminar flame speed results obtained from CHEMKIN with available data, however, the amount of data at these conditions is scarce and a recommended candidate among the mechanisms can presently not be selected. Generally, the results with the GRI-Mech and Leeds mechanisms deviate from the Davis, Li, O'Conaire, Konnov and San Diego mechanisms, but there are also significant deviations between the latter five mechanisms that altogether are better adapted to hydrogen. The differences in ignition delay times between the dedicated hydrogen mechanisms (O'Conaire, Li and Konnov) range from approximately a maxim...

  6. Parent type chemical species formed by recoil implantation reaction in tris(β-diketonato)metal(III)

    International Nuclear Information System (INIS)

    Chemical reactions induced by recoil implantation were studied focussing on parent type species in tris(β-diketonato)metal(III) complexes. The yield of the substitution reaction *M + M(acac)3 → *M(acac)3 + M was dependent on the force constant ratio K(*M-O)/K(M-O), showing that competition occurred between *M and M in the cage of the acetylacetonate complex. In the case of *Cr implantation in Co(acac)3, an exceptionally large yield could be explained by formation of Co(acac)2, whose central metal easily exchanges with *Cr, and by pickup of acac. When different β-diketonate complexes were examined in the reaction *Cr + M(β-dik)3 → *Cr(β-dik)3 + M the yield was dependent on the stability of the M(β-dik)3 complexes. A reaction model to explain these results reasonably was presented. (orig.)

  7. Modelling transport of water and ions and chemical reactions in compacted bentonite - Two flexible modelling platforms

    International Nuclear Information System (INIS)

    Document available in extended abstract form only. Many phenomena and processes have to be understood when considering the safety of the engineering barrier system (EBS) of the spent fuel repository. In this work the main interest is in the bentonite buffer part of the EBS. Bentonite is a certain kind of natural composite material: - smectite layers and the charge-compensating cations; - water, which is partly external and partly internal water more, or tightly on smectite layers; - salts and minerals, of which part is dissolved into external water, and some salinity may penetrate into inter-lamellar space; most minerals in solid state (auxiliary minerals). Therefore, it is understandable that a composite material having interaction between its components already at nano-level can behave in quite a complex and nonlinear way. Bentonite buffer must survive under many conditions, and in many cases the conditions may change far in the future with reactions taking thousands of years to be completed. Therefore, modelling is the only option to study these systems in order to guarantee the proper functioning of bentonite buffer over a planned period of over a hundred thousand years. All modelling is based on experimental work either directly or indirectly via data and ideas. Bentonite is studied intensively in many countries and all experiments produce new data and problems (or new ideas). All of this new information should be applied and tested by modelling, but quite often models are not flexible enough to adopt all the new topics. Therefore, our approach is based on segregation of modelling steps to enable more flexibility: - conceptualization at least partially free of the limitations in code to be applied; - collection of data needed (may be biggest limiting factor in our approach); - creation of mathematical model, again having hopefully bigger freedom concerning the code; - implementation of the model on our two flexible platforms: COMSOL Multiphysics and Numerrin

  8. Effect of water losses by evaporation and chemical reaction in an industrial slaker reactor

    Directory of Open Access Journals (Sweden)

    Ricardo Andreola

    2007-03-01

    Full Text Available A dynamic model of the slaker reactor was developed and validated for Klabin Paraná Papéis causticizing system, responsable for white liquor generation used by the plant. The model considered water losses by evaporation and chemical reaction. The model showed a good agreement with the industrial plant measures of active alkali, total titratable alkali and temperature, without the need of adjustment of any parameter. The simulated results showed that the water consumption by the slaking reaction and evaporation exerted significant influence on the volumetric flow rate of limed liquor, which imposed a decrease of 4.6% in the amount of water in reactor outlet.Foi desenvolvido e testado um modelo dinâmico do reator de apagamento do sistema de caustificação da Klabin Paraná Papéis, responsável pela geração do licor branco utilizado na planta. O modelo contempla perdas de água por evaporação e por reação química e apresentou boa concordância com dados industriais de álcali ativo, álcali total titulável e temperatura, sem a necessidade de ajuste de nenhum parâmetro. Os resultados obtidos a partir de simulações revelam que o consumo de água pela reação de apagamento, bem como pela evaporação, exercem uma influência significativa sobre a vazão volumétrica na saída do reator, impondo uma diminuição de 4,6% sobre o teor de água na corrente de saída do reator em relação à alimentação.

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

    OpenAIRE

    Cianci, Claudia; Smith, Stephen; Grima, Ramon

    2016-01-01

    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 equilibriu...

  10. Engineered Barrier System: Physical and Chemical Environment

    Energy Technology Data Exchange (ETDEWEB)

    P. Dixon

    2004-04-26

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

  11. Coupling of hydrologic transport and chemical reactions in a stream affected by acid mine drainage

    Science.gov (United States)

    Kimball, B.A.; Broshears, R.E.; Bencala, K.E.; McKnight, Diane M.

    1994-01-01

    Experiments in St. Kevin Gulch, an acid mine drainage stream, examined the coupling of hydrologic transport to chemical reactions affecting metal concentrations. Injection of LiCl as a conservative tracer was used to determine discharge and residence time along a 1497-m reach. Transport of metals downstream from inflows of acidic, metal-rich water was evaluated based on synoptic samples of metal concentrations and the hydrologic characteristics of the stream. Transport of SO4 and Mn was generally conservative, but in the subreaches most affected by acidic inflows, transport was reactive. Both 0.1-??m filtered and particulate Fe were reactive over most of the stream reach. Filtered Al partitioned to the particulate phase in response to high instream concentrations. Simulations that accounted for the removal of SO4, Mn, Fe, and Al with first-order reactions reproduced the steady-state profiles. The calculated rate constants for net removal used in the simulations embody several processes that occur on a stream-reach scale. The comparison between rates of hydrologie transport and chemical reactions indicates that reactions are only important over short distances in the stream near the acidic inflows, where reactions occur on a comparable time scale with hydrologic transport and thus affect metal concentrations.

  12. Nanostructured palladium tailored via carbonyl chemical route towards oxygen reduction reaction

    International Nuclear Information System (INIS)

    Graphical Abstract: Mass-depending morphologies of nanostructured Palladium obtained via the carbonyl chemical route. Display Omitted -- Highlights: •Mass-depending morphology was observed in nanostructured palladium supported on carbon prepared by the carbonyl chemical route. •The Morphological effect of carbon supported Pd was investigated towards ORR. -- Abstract: Carbon supported palladium nanostructures were synthesized via the carbonyl chemical route. Compared with nanostructured platinum, prepared via carbonyl chemical route, Pd nanomaterials showed mass-loading morphology, whereas particle size and morphology of Pt nanostructures was constant. The oxygen reduction reaction (ORR) on nanostructured Pd, with different morphology in both acid and alkaline medium was investigated. A relationship, based on X-ray diffraction structural analysis pattern, transmission electron microscope, with the Pd morphological effect on ORR activity was identified

  13. Spatially orthogonal chemical functionalization of a hierarchical pore network for catalytic cascade reactions

    Science.gov (United States)

    Parlett, Christopher M. A.; Isaacs, Mark A.; Beaumont, Simon K.; Bingham, Laura M.; Hondow, Nicole S.; Wilson, Karen; Lee, Adam F.

    2016-02-01

    The chemical functionality within porous architectures dictates their performance as heterogeneous catalysts; however, synthetic routes to control the spatial distribution of individual functions within porous solids are limited. Here we report the fabrication of spatially orthogonal bifunctional porous catalysts, through the stepwise template removal and chemical functionalization of an interconnected silica framework. Selective removal of polystyrene nanosphere templates from a lyotropic liquid crystal-templated silica sol-gel matrix, followed by extraction of the liquid crystal template, affords a hierarchical macroporous-mesoporous architecture. Decoupling of the individual template extractions allows independent functionalization of macropore and mesopore networks on the basis of chemical and/or size specificity. Spatial compartmentalization of, and directed molecular transport between, chemical functionalities affords control over the reaction sequence in catalytic cascades; herein illustrated by the Pd/Pt-catalysed oxidation of cinnamyl alcohol to cinnamic acid. We anticipate that our methodology will prompt further design of multifunctional materials comprising spatially compartmentalized functions.

  14. Coupled chemical oscillators and emergent system properties.

    Science.gov (United States)

    Epstein, Irving R

    2014-09-25

    We review recent work on a variety of systems, from the nanometre to the centimetre scale, including microemulsions, microfluidic droplet arrays, gels and flow reactors, in which chemical oscillators interact to generate novel spatiotemporal patterns and/or mechanical motion. PMID:24835430

  15. Technologies and devices for micro chemical systems

    NARCIS (Netherlands)

    Gardeniers, Han; Schasfoort, Richard; Berg, van den Albert

    2000-01-01

    This article describes recent developments at MESA+ in the field of miniaturised systems for chemical synthesis and analysis, also frequently referred to as "Lab-on-a-Chip". Several examples of siliconbased devices will be discussed, like micro pipettes for DNA studies, chips for cation analysis in

  16. Reaction rate in an evanescent random walkers system

    CERN Document Server

    Ré, Miguel A

    2015-01-01

    Diffusion mediated reaction models are particularly ubiquitous in the description of physical, chemical or biological processes. The random walk schema is a useful tool for formulating these models. Recently, evanescent random walk models have received attention in order to include finite lifetime processes. For instance, activated chemical reactions, such as laser photolysis, exhibit a different asymptotic limit when compared with immortal walker models. A diffusion limited reaction model based on a one dimensional continuous time random walk on a lattice with evanescent walkers is presented here. The absorption probability density and the reaction rate are analytically calculated in the Laplace domain. A finite absorption rate is considered, a model usually referred to as imperfect trapping. Short and long time behaviors are analyzed.

  17. LSENS, a general chemical kinetics and sensitivity analysis code for homogeneous gas-phase reactions. 2: Code description and usage

    Science.gov (United States)

    Radhakrishnan, Krishnan; Bittker, David A.

    1994-01-01

    LSENS, the Lewis General Chemical Kinetics Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part 2 of a series of three reference publications that describe LSENS, provide a detailed guide to its usage, and present many example problems. Part 2 describes the code, how to modify it, and its usage, including preparation of the problem data file required to execute LSENS. Code usage is illustrated by several example problems, which further explain preparation of the problem data file and show how to obtain desired accuracy in the computed results. LSENS is a flexible, convenient, accurate, and efficient solver for chemical reaction problems such as static system; steady, one-dimensional, inviscid flow; reaction behind incident shock wave, including boundary layer correction; and perfectly stirred (highly backmixed) reactor. In addition, the chemical equilibrium state can be computed for the following assigned states: temperature and pressure, enthalpy and pressure, temperature and volume, and internal energy and volume. For static problems the code computes the sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of the dependent variables and/or the three rate coefficient parameters of the chemical reactions. Part 1 (NASA RP-1328) derives the governing equations describes the numerical solution procedures for the types of problems that can be solved by lSENS. Part 3 (NASA RP-1330) explains the kinetics and kinetics-plus-sensitivity-analysis problems supplied with LSENS and presents sample results.

  18. Chemical sensing underclothing system for testing PPE

    International Nuclear Information System (INIS)

    Personal protective equipment (PPE) when worn is subjected to pressure differentials across the garment due to ambient wind flow, by body movement and breathing creating the bellows effect, which may force hazardous chemicals vapor or aerosol through the closures, joints, outlet valves and/or clothing protective fabric. Thus the design, fit, size or improper donning of the protective garment will influence chemical-agent penetration. In order to determine penetration of chemical-protective garments by chemical vapor or aerosol, it is necessary to test the entire suit system, including seams, closures, outlet valves and areas of transition with other protective equipment, that is, at the ankles, waist, wrists, neck etc. In order to identify penetration of chemical vapor or aerosol through protective assembly, the Man-in-Simulant Test (MIST) with passive adsorptive devices (PADs) is used, when adsorbed challenging agent (simulant) is desorbed from the PAD and quantified. The current MIST method is failing in complexity of leak detection, due to limited number of passive collection points fixed on human body or a mannequin and very labor extensive work associated with allocation of 20-40 PADs and quantification of adsorbed agent. The Czech approach to detect and quantify penetration/permeation of chemical agent is based on chemical sensing underclothing enable to change the color when exposed with simulant or even with real CW agent. Color intensity and shape of stains on sensing fabric are processed with Laboratory Universal Computer Image Analysis (LUCIA) allowing determining the quantity and the allocation of the penetrating noxious agent(s). This method allows for example calculate individual doses of exposure, the breakthrough coefficient of protective garment as whole and uniquely precise allocation of penetration/permeation shortfalls. Presentation is providing detailed description of imaging system with nickname 'LUCY' in combination with testing mannequin

  19. Simulations of isoprene: Ozone reactions for a general circulation/chemical transport model

    Science.gov (United States)

    Makar, P. A.; Mcconnell, J. C.

    1994-01-01

    A parameterized reaction mechanism has been created to examine the interactions between isoprene and other tropospheric gas-phase chemicals. Tests of the parameterization have shown that its results match those of a more complex reaction set to a high degree of accuracy. Comparisons between test runs have shown that the presence of isoprene at the start of a six day interval can enhance later ozone concentrations by as much as twenty-nine percent. The test cases used no input fluxes beyond the initial time, implying that a single input of a biogenic hydrocarbon to an airmass can alter its ozone chemistry over a time scale on the order of a week.

  20. Chemical evolution: A solar system perspective

    Science.gov (United States)

    Oro, J.

    1989-01-01

    During the last three decades major advances were made in the understanding of the formation of carbon compounds in the universe and of the occurrence of processes of chemical evolution in the solar system and beyond. This was made possible by the development of new astronomical techniques and by the exploration of the solar system by means of properly instrumented spacecraft. Some of the major findings made as a result of these observations are summarized.

  1. 生化反应的五行归属%Anfive elements classification of bio-chemical reactions

    Institute of Scientific and Technical Information of China (English)

    徐天成

    2015-01-01

    五行学说提供了对事物进行系统分类的合理方法。人类体内充满了复杂的生物化学反应体系,能否用五行学说的基本规律归纳生物化学反应体系值得探讨。在以往相关研究的基础上,本文利用五行思想对生化反应的物质和反应类型进行分类,用简洁的中医学规律研究复杂的生化反应过程,这种新思路对药物研究、中西医结合学科的发展等具有挖掘价值。%Thefive elements theory provides us a system classification of all things so we can do the research in a much reasonable way. Further more, our bodies are full of complicated bio-chemical reactions and thefive elements theory should also be applicable to those reaction systems. This paper will try to make use of thefive elements theory to carry on an innovative classification of different types of bio-chemical reactions with the help of the former foundation of related researches, to make the complicated bio-chemical reactions easy to understand, and point out that this kind of lately academic thought is of great significance to the medicine researches as well as the integrated traditional Chinese and western medicine.

  2. Ab initio studies of equations of state and chemical reactions of reactive structural materials

    Science.gov (United States)

    Zaharieva, Roussislava

    The motivations for the research issues addressed in this thesis are based on the needs of the aerospace structural analysis and the design community. The specific focus is related to the characterization and shock induced chemical reactions of multi-functional structural-energetic materials that are also known as the reactive structural materials and their reaction capabilities. Usually motivation for selection of aerospace structural materials is to realize required strength characteristics and favorable strength to weight ratios. The term strength implies resistance to loads experienced during the service life of the structure, including resistance to fatigue loads, corrosion and other extreme conditions. Thus, basically the structural materials are single function materials that resist loads experienced during the service life of the structure. However, it is desirable to select materials that are capable of offering more than one basic function of strength. Very often, the second function is the capability to provide functions of sensing and actuation. In this thesis, the second function is different. The second function is the energetic characteristics. Thus, the choice of dual functions of the material are the structural characteristics and energetic characteristics. These materials are also known by other names such as the reactive material structures or dual functional structural energetic materials. Specifically the selected reactive materials include mixtures of selected metals and metal oxides that are also known as thermite mixtures, reacting intermetallic combinations and oxidizing materials. There are several techniques that are available to synthesize these structural energetic materials or reactive material structures and new synthesis techniques constitute an open research area. The focus of this thesis, however, is the characterization of chemical reactions of reactive material structures that involve two or more solids (or condensed matter). The

  3. Challenge for real-time and real-space resolved spectroscopy of surface chemical reactions. Aiming at trace of irreversible and inhomogeneous reactions

    International Nuclear Information System (INIS)

    A novel experimental technique, time-resolved wavelength-dispersive soft X-ray imaging spectroscopy, is proposed in order to achieve real-time and real-space resolved spectroscopy for the observation of irreversible and inhomogeneous surface chemical reactions. By combining the wavelength-dispersed soft X rays, in which the X-ray wavelength (photon energy) changes as a function of position on the sample, with the photoelectron emission microscope, the soft X-ray absorption spectra are separately obtained at different positions on the sample without scanning the X-ray monochromator. Therefore, the real-time resolved measurement of site-selective soft X-ray absorption spectroscopy is realized in one event without repeating the chemical reaction. It is expected that the spatial distribution of different chemical species is traced during the surface chemical reaction, which is essential to understand the reaction mechanism. (author)

  4. Explosion of limit cycles and chaotic waves in a simple nonlinear chemical system

    DEFF Research Database (Denmark)

    Brøns, Morten; Sturis, Jeppe

    2001-01-01

    A model of an autocatalytic chemical reaction was employed to study the explosion of limit cycles and chaotic waves in a nonlinear chemical system. The bifurcation point was determined using asymptotic analysis and perturbations. Scaling laws for amplitude and period were derived. A strong...

  5. Self-propelled motion of a fluid droplet under chemical reaction

    CERN Document Server

    Yabunaka, Shunsuke; Yoshinaga, Natsuhiko

    2012-01-01

    We study self-propelled dynamics of a droplet due to a Marangoni effect and chemical reactions in a binary fluid with a dilute third component of chemical product which affects the interfacial energy of a droplet. The equation for the migration velocity of the center of mass of a droplet is derived in the limit of an infinitesimally thin inter- face. We found that there is a bifurcation from a motionless state to a propagating state of droplet by changing the strength of the Marangoni effect.

  6. Lightweight autonomous chemical identification system (LACIS)

    Science.gov (United States)

    Lozos, George; Lin, Hai; Burch, Timothy

    2012-06-01

    Smiths Detection and Intelligent Optical Systems have developed prototypes for the Lightweight Autonomous Chemical Identification System (LACIS) for the US Department of Homeland Security. LACIS is to be a handheld detection system for Chemical Warfare Agents (CWAs) and Toxic Industrial Chemicals (TICs). LACIS is designed to have a low limit of detection and rapid response time for use by emergency responders and could allow determination of areas having dangerous concentration levels and if protective garments will be required. Procedures for protection of responders from hazardous materials incidents require the use of protective equipment until such time as the hazard can be assessed. Such accurate analysis can accelerate operations and increase effectiveness. LACIS is to be an improved point detector employing novel CBRNE detection modalities that includes a militaryproven ruggedized ion mobility spectrometer (IMS) with an array of electro-resistive sensors to extend the range of chemical threats detected in a single device. It uses a novel sensor data fusion and threat classification architecture to interpret the independent sensor responses and provide robust detection at low levels in complex backgrounds with minimal false alarms. The performance of LACIS prototypes have been characterized in independent third party laboratory tests at the Battelle Memorial Institute (BMI, Columbus, OH) and indoor and outdoor field tests at the Nevada National Security Site (NNSS). LACIS prototypes will be entering operational assessment by key government emergency response groups to determine its capabilities versus requirements.

  7. Reaction dynamics and photochemistry of divalent systems

    Energy Technology Data Exchange (ETDEWEB)

    Davis, H.F.

    1992-05-01

    Results are presented of molecular beam studies of bimolecular and unimolecular reactions of Ba. Chapter 1 discusses the reaction Ba + NO{sub 2}. Formation of the dominant BaO({sup 1}{Sigma}) + NO products resulted primarily from decay of long-lived Ba{sup +}NO{sub 2}{sup {minus}} collision complexes. Secondary mechanisms led to formation of forward scattered, internally excited BaO, and BaNO + O. D{sub o}(Ba-NO) = 65{plus_minus}20 kcal/mol. Reactions of ground state and electronically excited Ba with water and alcohols are examined in Chapter 2. Reaction of Ba({sup 1}S) + H{sup 2}O led to BaO + H{sub 2}, whereas excited state Ba({sup 1}D) + H{sub 2}O reacted to form BaOH + H. Collisions between Ba and CH{sub 3}OH led to BaOCH{sub 3} + H. Radical channels involve H-atom migration and are promoted by excitation of the incident Ba atom. In Chapter 3, reactions of Ba({sup 1}S) with ClO{sub 2}2 and O{sub 3} are discussed. Again, direct and complex mechanisms were observed. Formation of BaCl + O{sub 2} from decomposition of Ba{sup +}ClO{sub 2}{sup {minus}} accounted for 10% of total reaction crass section. Although Ba + O{sub 3} {yields} BaO + 0{sub 2} occurs primarily by direct reaction mechanisms, the secondary channel Ba + 0{sub 3} {yields} BaO{sub 2} + 0 involved decay of long lived Ba{sup +}O{sub 3}{sup {minus}} intermediates. D{sub o}(Ba{minus}O{sub 2}) = 120 {plus_minus}20 kcal/mol. Photodissociation dynamics of NO{sub 3} is explored in chapter 4. Visible excitation leads to formation of NO + 0{sub 2} and NO{sub 2} + O. Wavelength dependence of branching ratios is investigated. D{sub o}(O-NO{sub 2}) = 48.55 kcal/mole ;and calculate {Delta}H{sub f}(NO{sub 3}) = 17.75 kcal/mole (298K). Chapter 5 discusses the photodissociation of OClO in a molecular beam. Although ClO({sup 2}II) + O({sup 3}P) is dominant, Cl({sup 2}P) + O{sub 2} also forms, with a max yield of 3.9{plus_minus}0.8% near 404nm.

  8. Extension of a Kinetic-Theory Approach for Computing Chemical-Reaction Rates to Reactions with Charged Particles

    Science.gov (United States)

    Liechty, Derek S.; Lewis, Mark J.

    2010-01-01

    Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction rate information) are extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

  9. Acid-functionalized polyolefin materials and their use in acid-promoted chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Oyola, Yatsandra; Tian, Chengcheng; Bauer, John Christopher; Dai, Sheng

    2016-06-07

    An acid-functionalized polyolefin material that can be used as an acid catalyst in a wide range of acid-promoted chemical reactions, wherein the acid-functionalized polyolefin material includes a polyolefin backbone on which acid groups are appended. Also described is a method for the preparation of the acid catalyst in which a precursor polyolefin is subjected to ionizing radiation (e.g., electron beam irradiation) of sufficient power and the irradiated precursor polyolefin reacted with at least one vinyl monomer having an acid group thereon. Further described is a method for conducting an acid-promoted chemical reaction, wherein an acid-reactive organic precursor is contacted in liquid form with a solid heterogeneous acid catalyst comprising a polyolefin backbone of at least 1 micron in one dimension and having carboxylic acid groups and either sulfonic acid or phosphoric acid groups appended thereto.

  10. Graphene-Semiconductor Catalytic Nanodiodes for Quantitative Detection of Hot Electrons Induced by a Chemical Reaction.

    Science.gov (United States)

    Lee, Hyosun; Nedrygailov, Ievgen I; Lee, Young Keun; Lee, Changhwan; Choi, Hongkyw; Choi, Jin Sik; Choi, Choon-Gi; Park, Jeong Young

    2016-03-01

    Direct detection of hot electrons generated by exothermic surface reactions on nanocatalysts is an effective strategy to obtain insight into electronic excitation during chemical reactions. For this purpose, we fabricated a novel catalytic nanodiode based on a Schottky junction between a single layer of graphene and an n-type TiO2 layer that enables the detection of hot electron flows produced by hydrogen oxidation on Pt nanoparticles. By making a comparative analysis of data obtained from measuring the hot electron current (chemicurrent) and turnover frequency, we demonstrate that graphene's unique electronic structure and extraordinary material properties, including its atomically thin nature and ballistic electron transport, allow improved conductivity at the interface between the catalytic Pt nanoparticles and the support. Thereby, graphene-based nanodiodes offer an effective and facile way to approach the study of chemical energy conversion mechanisms in composite catalysts with carbon-based supports. PMID:26910271

  11. Endocrine Disrupting Chemical Impacts on Aquatic Systems

    Science.gov (United States)

    Jobling, Susan

    2014-07-01

    We often talk about the importance of water, but one area that's often overlooked is the safety of our water supply. How many people actually think about the purity of their water when they turn on the tap? We may have real reason to be concerned because our water delivery systems and treatment technology seem to be stuck in the past, relying on old water treatment and water delivery systems. While these systems still do a great job filtering out particles, parasites and bacteria, they usually fail to remove 21st century contaminants like pesticides, industrial chemicals, lead, pharmaceuticals and arsenic. Indeed our water contains already a whole plethora of things in daily commerce and pharmaceuticals are increasingly showing up in the water supply, including antibiotics, anti-convulsants, mood altering medications and sex hormones. As the world's dependence on chemicals grows, our water supplies will continue to feel the effects, which inevitably will touch every person on this planet...

  12. Metal-Catalyzed Chemical Reaction of Single Molecules Directly Probed by Vibrational Spectroscopy.

    Science.gov (United States)

    Choi, Han-Kyu; Park, Won-Hwa; Park, Chan-Gyu; Shin, Hyun-Hang; Lee, Kang Sup; Kim, Zee Hwan

    2016-04-01

    The study of heterogeneous catalytic reactions remains a major challenge because it involves a complex network of reaction steps with various intermediates. If the vibrational spectra of individual molecules could be monitored in real time, one could characterize the structures of the intermediates and the time scales of reaction steps without ensemble averaging. Surface-enhanced Raman scattering (SERS) spectroscopy does provide vibrational spectra with single-molecule sensitivity, but typical single-molecule SERS signals exhibit spatial heterogeneities and temporal fluctuations, making them difficult to be used in single-molecule kinetics studies. Here we show that SERS can monitor the single-molecule catalytic reactions in real time. The surface-immobilized reactants placed at the junctions of well-defined nanoparticle-thin film structures produce time-resolved SERS spectra with discrete, step-transitions of photoproducts. We interpret that such SERS-steps correspond to the reaction events of individual molecules occurring at the SERS hotspot. The analyses of the yield, dynamics, and the magnitude of such SERS steps, along with the associated spectral characteristics, fully support our claim. In addition, a model that is based on plasmonic field enhancement and surface photochemistry reproduces the key features of experimental observation. Overall, the result demonstrates that it is possible, under well-controlled conditions, to differentiate the chemical and physical processes contributing to the single-molecule SERS signals, and thus shows the use of single-molecule SERS as a tool for studying the metal-catalyzed organic reactions. PMID:26964567

  13. Modeling of Sheath Ion-Molecule Reactions in Plasma Enhanced Chemical Vapor Deposition of Carbon Nanotubes

    Science.gov (United States)

    Hash, David B.; Govindan, T. R.; Meyyappan, M.

    2004-01-01

    In many plasma simulations, ion-molecule reactions are modeled using ion energy independent reaction rate coefficients that are taken from low temperature selected-ion flow tube experiments. Only exothermic or nearly thermoneutral reactions are considered. This is appropriate for plasma applications such as high-density plasma sources in which sheaths are collisionless and ion temperatures 111 the bulk p!asma do not deviate significantly from the gas temperature. However, for applications at high pressure and large sheath voltages, this assumption does not hold as the sheaths are collisional and ions gain significant energy in the sheaths from Joule heating. Ion temperatures and thus reaction rates vary significantly across the discharge, and endothermic reactions become important in the sheaths. One such application is plasma enhanced chemical vapor deposition of carbon nanotubes in which dc discharges are struck at pressures between 1-20 Torr with applied voltages in the range of 500-700 V. The present work investigates The importance of the inclusion of ion energy dependent ion-molecule reaction rates and the role of collision induced dissociation in generating radicals from the feedstock used in carbon nanotube growth.

  14. Propagating fronts in reaction-transport systems with memory

    Energy Technology Data Exchange (ETDEWEB)

    Yadav, A. [Department of Chemistry, Southern Methodist University, Dallas, TX 75275-0314 (United States)], E-mail: ayadav1@lsu.edu; Fedotov, Sergei [School of Mathematics, University of Manchester, Manchester M60 1DQ (United Kingdom)], E-mail: sergei.fedotov@manchester.ac.uk; Mendez, Vicenc [Grup de Fisica Estadistica, Departament de Fisica, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Spain)], E-mail: vicenc.mendez@uab.es; Horsthemke, Werner [Department of Chemistry, Southern Methodist University, Dallas, TX 75275-0314 (United States)], E-mail: whorsthe@smu.edu

    2007-11-26

    In reaction-transport systems with non-standard diffusion, the memory of the transport causes a coupling of reactions and transport. We investigate the effect of this coupling for systems with Fisher-type kinetics and obtain a general analytical expression for the front speed. We apply our results to the specific case of subdiffusion.

  15. Computing multi-species chemical equilibrium with an algorithm based on the reaction extents

    DEFF Research Database (Denmark)

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

    2013-01-01

    A mathematical model for the solution of a set of chemical equilibrium equations in a multi-species and multiphase chemical system is described. The computer-aid solution of model is achieved by means of a Newton-Raphson method enhanced with a line-search scheme, which deals with the non-negative...

  16. Exchange reactions in the systems of alkali metal, silver and thallium, sulfates, niobates and tantalates

    International Nuclear Information System (INIS)

    Investigated are exchange interactions in diagonal cross sections of twenty triple mutual systems with A and A' cations and SO4 and MO3 anions where A and A'-Li, Na, K, Ag, Tl, M-Nb, Ta using the methods of X-ray phase, chemical and differential thermal analyses. Exchange reaction between crystal complex oxide and melted salt are effective synthesis method. These reactions in particular permitted to obtain pure AgNbO3, AgTaO3 and their solid solutions at temperatures hundreds degrees lower than in displacement reactions. Equilibrium samples of AMO3-A'MO3 systems, continuous or discontinuous solid solutions, compounds (except NaMO3-KMO3, and also LiTaO3-KTaO3) are formed in exchange reactions when there is sulfate shortage. Thus, exchange reactions can be applied for solid solution synthesis, and also for phase diagram study

  17. Faradiac Impedance of a Heterogeneous Chemical Reaction and an Adsorption Process

    OpenAIRE

    Qudah MMA

    2015-01-01

    The electrochemical behaviour of stainless steel 302 has been investigated in 0.10 M K2SO4 solution using the impedance technique at several anodic potentials. Stainless steel 302 is passive up to 1300 mV, due to the main formation of Cr2O3. Above this potential stainless steel became active. Faradiac impedances of a heterogeneous chemical reaction and an adsorption process were discussed.

  18. Spatial Heterogeneity and Imperfect Mixing in Chemical Reactions: Visualization of Density-Driven Pattern Formation

    OpenAIRE

    2009-01-01

    Imperfect mixing is a concern in industrial processes, everyday processes (mixing paint, bread machines), and in understanding salt water-fresh water mixing in ecosystems. The effects of imperfect mixing become evident in the unstirred ferroin-catalyzed Belousov-Zhabotinsky reaction, the prototype for chemical pattern formation. Over time, waves of oxidation (high ferriin concentration, blue) propagate into a background of low ferriin concentration (red); their structure reflects in part the ...

  19. Magnetohydrodynamic (MHD) stretched flow of nanofluid with power-law velocity and chemical reaction

    OpenAIRE

    Tasawar Hayat; Madiha Rashid; Maria Imtiaz; Ahmed Alsaedi

    2015-01-01

    This paper deals with the boundary layer flow of nanofluid over power-law stretched surface. Analysis has been carried out in the presence of applied magnetic field and chemical reaction. Heat and mass transfer characteristics are studied using heat and mass convective conditions. The governing partial differential equations are transferred to the nonlinear ordinary differential equations. Convergent series solutions are obtained for fluid velocity, temperature and concentrations fields. Infl...

  20. Studying Equilibrium in the Chemical Reaction between Ferric and Iodide Ions in Solution Using a Simple and Inexpensive Approach

    Science.gov (United States)

    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…

  1. A Microscale Approach to Chemical Kinetics in the General Chemistry Laboratory: The Potassium Iodide Hydrogen Peroxide Iodine-Clock Reaction

    Science.gov (United States)

    Sattsangi, Prem D.

    2011-01-01

    A microscale laboratory for teaching chemical kinetics utilizing the iodine clock reaction is described. Plastic pipets, 3 mL volume, are used to store and deliver precise drops of reagents and the reaction is run in a 24 well plastic tray using a total 60 drops of reagents. With this procedure, students determine the rate of reaction and the…

  2. Drop-by-drop chemical reaction and sample introduction for capillary electrophoresis.

    Science.gov (United States)

    Chen, Fengming; Rang, Ying; Weng, Ying; Lin, Luyao; Zeng, Hulie; Nakajim, Hizuru; Lin, Jin-Ming; Uchiyama, Katsumi

    2015-06-21

    In this paper, we report a novel sample introduction and chemical reaction strategy by drop-by-drop inkjet injection for an electrophoretically mediated microanalysis (EMMA). This method makes it possible to achieve an on-line introduction of reactant solutions by alternately ejecting small plugs, with an overlapping region of the plugs for mixing the reactants by electrophoresis, supporting chemical reactions, followed by electrophoretic separation of the final compounds. As a proof-of-concept of the method, the EMMA of an inkjetted mixture of 4-fluoro-7-nitrobenzofurazan (NBD-F) and amino acids was carried out as a model chemical reaction. The product NBD-amino acids were quantified by detection with laser induced fluorescence. The optimal conditions for the procedure were: inkjet driving voltage: +40-44 V; pulse width: 20-24 μs; drop-by-drop injection of reactant solutions: alternately 2 drops × 25 times for the amino acid solution and the NBD-F solution; zone overlapping voltage and time: 3 kV and 2 s; incubation time after overlapping: 5 min; separation voltage: 18 kV. Under the optimized conditions, a significant enhancement in sensitivity and a sensitive quantitative analysis were realized. The results obtained were comparable with those using the off-line labeling method. This method is rapid, cost-effective, and readily automated for EMMA. PMID:25728632

  3. Production of cold formaldehyde molecules for study and control of chemical reaction dynamics with hydroxyl radicals

    CERN Document Server

    Hudson, E R; Sawyer, B C; Taatjes, C A; Lewandowski, H J; Bochinski, J R; Bohn, J L; Ye, J; Hudson, Eric R.; Ticknor, Christopher; Sawyer, Brian C.; Taatjes, Craig A.; Bohn, John L.; Ye, Jun

    2005-01-01

    We propose a method for controlling a class of low temperature chemical reactions. Specifically, we show the hydrogen abstraction channel in the reaction of formaldehyde (H$_{2}$CO) and the hydroxyl radical (OH) can be controlled through either the molecular state or an external electric field. We also outline experiments for investigating and demonstrating control over this important reaction. To this end, we report the first Stark deceleration of the H$_{2}$CO molecule. We have decelerated a molecular beam of H$_{2}$CO essentially to rest, producing cold molecule packets at a temperature of 100 mK with a few million molecules in the packet at a density of $\\sim10^{6}$ cm$^{-3}$.

  4. FEARCF a multidimensional free energy method for investigating conformational landscapes and chemical reaction mechanisms

    Institute of Scientific and Technical Information of China (English)

    NAIDOO Kevin J.

    2012-01-01

    The development and implementation of a computational method able to produce free energies in multiple dimensions,descriptively named the free energies from adaptive reaction coordinate forces (FEARCF) method is described in this paper.While the method can be used to calculate free energies of association,conformation and reactivity here it is shown in the context of chemical reaction landscapes.A reaction free energy surface for the Claisen rearrangement of chorismate to prephenate is used as an illustration of the method's efficient convergence.FEARCF simulations are shown to achieve fiat histograms for complex multidimensional free energy volumes.The sampling efficiency by which it produces multidimensional free energies is demonstrated on the complex puckering of a pyranose ring,that is described by a three dimensional W(θ1,θ2,θ3) potential of mean force.

  5. Chemically Accurate Simulation of a Polyatomic Molecule-Metal Surface Reaction.

    Science.gov (United States)

    Nattino, Francesco; Migliorini, Davide; Kroes, Geert-Jan; Dombrowski, Eric; High, Eric A; Killelea, Daniel R; Utz, Arthur L

    2016-07-01

    Although important to heterogeneous catalysis, the ability to accurately model reactions of polyatomic molecules with metal surfaces has not kept pace with developments in gas phase dynamics. Partnering the specific reaction parameter (SRP) approach to density functional theory with ab initio molecular dynamics (AIMD) extends our ability to model reactions with metals with quantitative accuracy from only the lightest reactant, H2, to essentially all molecules. This is demonstrated with AIMD calculations on CHD3 + Ni(111) in which the SRP functional is fitted to supersonic beam experiments, and validated by showing that AIMD with the resulting functional reproduces initial-state selected sticking measurements with chemical accuracy (4.2 kJ/mol ≈ 1 kcal/mol). The need for only semilocal exchange makes our scheme computationally tractable for dissociation on transition metals. PMID:27284787

  6. Chemically Accurate Simulation of a Polyatomic Molecule-Metal Surface Reaction

    Science.gov (United States)

    2016-01-01

    Although important to heterogeneous catalysis, the ability to accurately model reactions of polyatomic molecules with metal surfaces has not kept pace with developments in gas phase dynamics. Partnering the specific reaction parameter (SRP) approach to density functional theory with ab initio molecular dynamics (AIMD) extends our ability to model reactions with metals with quantitative accuracy from only the lightest reactant, H2, to essentially all molecules. This is demonstrated with AIMD calculations on CHD3 + Ni(111) in which the SRP functional is fitted to supersonic beam experiments, and validated by showing that AIMD with the resulting functional reproduces initial-state selected sticking measurements with chemical accuracy (4.2 kJ/mol ≈ 1 kcal/mol). The need for only semilocal exchange makes our scheme computationally tractable for dissociation on transition metals. PMID:27284787

  7. Humidity independent mass spectrometry for gas phase chemical analysis via ambient proton transfer reaction

    International Nuclear Information System (INIS)

    Graphical abstract: Direct and humidity independent mass spectrometry analysis of gas phase chemicals could be achieved via ambient proton transfer ionization, ion intensity was found to be stable with humidity ranged from ∼10% to ∼100%. - Highlights: • A humidity independent mass spectrometric method for gas phase samples analysis. • A universal and good sensitivity method. • The method can real time identify plant released raw chemicals. - Abstract: In this work, a humidity independent mass spectrometric method was developed for rapid analysis of gas phase chemicals. This method is based upon ambient proton transfer reaction between gas phase chemicals and charged water droplets, in a reaction chamber with nearly saturate humidity under atmospheric pressure. The humidity independent nature enables direct and rapid analysis of raw gas phase samples, avoiding time- and sample-consuming sample pretreatments in conventional mass spectrometry methods to control sample humidity. Acetone, benzene, toluene, ethylbenzene and meta-xylene were used to evaluate the analytical performance of present method. The limits of detection for benzene, toluene, ethylbenzene and meta-xylene are in the range of ∼0.1 to ∼0.3 ppbV; that of benzene is well below the present European Union permissible exposure limit for benzene vapor (5 μg m−3, ∼1.44 ppbV), with linear ranges of approximately two orders of magnitude. The majority of the homemade device contains a stainless steel tube as reaction chamber and an ultrasonic humidifier as the source of charged water droplets, which makes this cheap device easy to assemble and facile to operate. In addition, potential application of this method was illustrated by the real time identification of raw gas phase chemicals released from plants at different physiological stages

  8. Probing the bioactivity-relevant chemical space of robust reactions and common molecular building blocks.

    Science.gov (United States)

    Hartenfeller, Markus; Eberle, Martin; Meier, Peter; Nieto-Oberhuber, Cristina; Altmann, Karl-Heinz; Schneider, Gisbert; Jacoby, Edgar; Renner, Steffen

    2012-05-25

    In the search for new bioactive compounds, there is a trend toward increasingly complex compound libraries aiming to target the demanding targets of the future. In contrast, medicinal chemistry and traditional library design rely mainly on a small set of highly established and robust reactions. Here, we probe a set of 58 such reactions for their ability to sample the chemical space of known bioactive molecules, and the potential to create new scaffolds. Combined with ~26,000 common available building blocks, the reactions retrieve around 9% of a scaffold-diverse set of compounds active on human target proteins covering all major pharmaceutical target classes. Almost 80% of generated scaffolds from virtual one-step synthesis products are not present in a large set of known bioactive molecules for human targets, indicating potential for new discoveries. The results suggest that established synthesis resources are well suited to cover the known bioactivity-relevant chemical space and that there are plenty of unexplored regions accessible by these reactions, possibly providing valuable "low-hanging fruit" for hit discovery. PMID:22512717

  9. Nuclear quantum effects in chemical reactions via higher-order path-integral calculations

    International Nuclear Information System (INIS)

    Highlights: • The study presents path-integral calculations for chemical reactions. • The path-integrals use higher-order factorizations of the density matrix. • The Eckart potential and the H2 + H reaction are used as test cases for the methods. • The Chin higher order factorization enhances QM transmission convergence. • The higher order factorizations enhance eigenvalue and partition function convergence. - Abstract: A practical approach to treat nuclear quantum mechanical effects in simulations of condensed phases, such as enzymes, is via Feynman path integral (PI) formulations. Typically, the standard primitive approximation (PA) is employed in enzymatic PI simulations. Nonetheless, these PI simulations are computationally demanding due to the large number of beads required to obtain converged results. The efficiency of PI simulations may be greatly improved if higher-order factorizations of the density matrix operator are employed. Herein, we compare the results of model calculations obtained employing the standard PA, the improved operator of Takahashi and Imada (TI), and a gradient-based forward corrector algorithm due to Chin (CH). The quantum transmission coefficient is computed for the Eckart potential while the partition functions and rate constant are computed for the H2 + H hydrogen transfer reaction. These potentials are simple models for chemical reactions. The study of the different factorization methods reveals that in most cases the higher-order action converges faster than the PA and TI approaches, at a moderate computational cost

  10. ENGINEERED BARRIER SYSTEM: PHYSICAL AND CHEMICAL ENVIRONMENT

    Energy Technology Data Exchange (ETDEWEB)

    R. Jarek

    2004-11-23

    The purpose of this report is to describe the evolution of the physical and chemical environmental conditions within the waste emplacement drifts of the repository, including the drip shield and waste package surfaces. The abstraction model is used in the total system performance assessment for the license application (TSPA LA) to assess the performance of the engineered barrier system and the waste form. This report develops and documents a set of these abstraction-level models that describe the engineered barrier system physical and chemical environment. Where possible, these models use information directly from other reports as input, which promotes integration among process models used for TSPA-LA. Specific tasks and activities of modeling the physical and chemical environment are included in ''Technical Work Plan for: Near-Field Environment and Transport In-Drift Geochemistry Model Report Integration'' (BSC 2004 [DIRS 171156], Section 1.2.2). As described in the technical work plan, the development of this report is coordinated with the development of other engineered barrier system reports.

  11. ENGINEERED BARRIER SYSTEM: PHYSICAL AND CHEMICAL ENVIRONMENT

    International Nuclear Information System (INIS)

    The purpose of this report is to describe the evolution of the physical and chemical environmental conditions within the waste emplacement drifts of the repository, including the drip shield and waste package surfaces. The abstraction model is used in the total system performance assessment for the license application (TSPA LA) to assess the performance of the engineered barrier system and the waste form. This report develops and documents a set of these abstraction-level models that describe the engineered barrier system physical and chemical environment. Where possible, these models use information directly from other reports as input, which promotes integration among process models used for TSPA-LA. Specific tasks and activities of modeling the physical and chemical environment are included in ''Technical Work Plan for: Near-Field Environment and Transport In-Drift Geochemistry Model Report Integration'' (BSC 2004 [DIRS 171156], Section 1.2.2). As described in the technical work plan, the development of this report is coordinated with the development of other engineered barrier system reports

  12. Anaphylactoid reaction to intravenous contrast in patient with systemic mastocytosis.

    Science.gov (United States)

    Weingarten, T N; Volcheck, G W; Sprung, J

    2009-07-01

    Systemic mastocytosis is a rare disorder characterised by tissue infiltration of morphologically abnormal mast cells and has been associated with severe anaphylactoid reactions during general anaesthesia. We report the case of a 43-year-old woman who developed a severe anaphylactoid reaction to iodinated contrast media. Persistently elevated serum tryptase levels led to further evaluation and the eventual diagnosis of systemic mastocytosis. This case highlights the importance of repeated measurements of serum tryptase levels following severe anaphylactoid reactions. The anaesthetist should also be aware of the propensity of these patients to develop severe anaphylactoid reactions during general anaesthesia and use treatment strategies to minimise this risk. PMID:19681427

  13. PINS: A field PGNAA chemical identification system

    Energy Technology Data Exchange (ETDEWEB)

    Gehrke, R.J.; Caffrey, A.J.; Krebs, K.M.; Watts, K.D.; Oates, M.A.; McLaughlin, G.D. (Idaho National Engineering Lab., Idaho Falls (United States))

    1993-01-01

    Prompt gamma neutron activation analysis (PGNAA) has long been employed for chemical analysis in process streams and laboratories. Recent improvements in the design of germanium gamma-ray spectrometers, the miniaturization of their associated components, and the development of [open quotes]powerful[close quotes] notebook personal computers (PCs) permit the design of PGNAA systems for truly portable in-field use. Portable isotopic neutron spectrometry (PINS) (of gamma rays) was developed at the Idaho National Engineering Laboratory for in-field inspection and verification of chemical weapon inventories where a system that can be carried into an area inaccessible by wheeled transport (rough terrain, confined spaces, etc.) and that is capable of operating on battery power is required. PINS is now also finding use outside of military applications.

  14. TREATABILITY STUDIES USED TO TEST FOR EXOTHERMIC REACTIONS OF PLUTONIUM DECONTAMINATION CHEMICALS

    International Nuclear Information System (INIS)

    Fluor Hanford is decommissioning the Plutonium Finishing Plant (PFP) at the Hanford site in Eastern Washington. Aggressive chemicals are commonly used to remove transuranic contaminants from process equipment to allow disposal as low level waste. Chemicals being considered for decontamination of gloveboxes in PFP include cerium(IV) nitrate in a nitric acid solution, and proprietary commercial solutions that include acids, degreasers, and sequestering agents. Fluor's decontamination procedure involves application of chemical solutions as a spray on the contaminated surfaces, followed by a wipe-down with rags. This process effectively transfers the transuranic materials to the decontamination liquids, which are then absorbed by rags and packaged for disposal as TRU waste. Concerns regarding the safety of this procedure developed following a fire at Rocky Flats in 2003. The fire occurred in a glovebox that had been treated with cerium nitrate, which is one of the decontamination chemicals that Fluor Hanford has proposed to use. The investigation of the event was hampered by the copious use of chemicals and water to extinguish the fire, and was not conclusive regarding the cause. However, the reviewers noted that rags were found in the glovebox, suggesting that the combination of rags and chemicals may have contributed to the fire. With that uncertainty, Fluor began an investigation into the potential for fire when using the chemicals and materials in the decontamination process. The focus of this work has been to develop a disposal strategy that will provide a chemically stable waste form at expected Hanford waste storage temperatures. Treatability tests under CERCLA were used to assess the use of certain chemicals and wipes during the decontamination process. Chemicals being considered for decontamination of gloveboxes at PFP include cerium (IV) nitrate in a nitric acid solution, and proprietary commercial solutions as RadPro(trademark) that include acids, degreasers

  15. Modeling of multiphase flow with solidification and chemical reaction in materials processing

    Science.gov (United States)

    Wei, Jiuan

    Understanding of multiphase flow and related heat transfer and chemical reactions are the keys to increase the productivity and efficiency in industrial processes. The objective of this thesis is to utilize the computational approaches to investigate the multiphase flow and its application in the materials processes, especially in the following two areas: directional solidification, and pyrolysis and synthesis. In this thesis, numerical simulations will be performed for crystal growth of several III-V and II-VI compounds. The effects of Prandtl and Grashof numbers on the axial temperature profile, the solidification interface shape, and melt flow are investigated. For the material with high Prandtl and Grashof numbers, temperature field and growth interface will be significantly influenced by melt flow, resulting in the complicated temperature distribution and curved interface shape, so it will encounter tremendous difficulty using a traditional Bridgman growth system. A new design is proposed to reduce the melt convection. The geometric configuration of top cold and bottom hot in the melt will dramatically reduce the melt convection. The new design has been employed to simulate the melt flow and heat transfer in crystal growth with large Prandtl and Grashof numbers and the design parameters have been adjusted. Over 90% of commercial solar cells are made from silicon and directional solidification system is the one of the most important method to produce multi-crystalline silicon ingots due to its tolerance to feedstock impurities and lower manufacturing cost. A numerical model is developed to simulate the silicon ingot directional solidification process. Temperature distribution and solidification interface location are presented. Heat transfer and solidification analysis are performed to determine the energy efficiency of the silicon production furnace. Possible improvements are identified. The silicon growth process is controlled by adjusting heating power and

  16. Solar System chemical abundances corrected for systematics

    OpenAIRE

    Gonzalez, Guillermo

    2014-01-01

    The relative chemical abundances between CI meteorites and the solar photosphere exhibit a significant trend with condensation temperature. A trend with condensation temperature is also seen when the solar photospheric abundances are compared to those of nearby solar twins. We use both these trends to determine the alteration of the elemental abundances of the meteorties and the photosphere by fractionation and calculate a new set of primordial Solar System abundances.

  17. Quantifying electron transfer reactions in biological systems

    DEFF Research Database (Denmark)

    Sjulstok, Emil Sjulstok; Olsen, Jógvan Magnus Haugaard; Solov'yov, Ilia A

    2015-01-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling...... quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to...

  18. Multimass thermal desorption spectroscopy as a monitoring device for chemical reaction products

    OpenAIRE

    Zagatta, Gunther; Müller, H; Böwering, N.; Heinzmann, Ulrich

    1994-01-01

    To observe the products of surface reaction mechanisms we combined a standard quadrupole mass spectrometer featuring high-speed scanning options with fast data acquisition and a computer-controlled sample heating system. This combination served to obtain a general view (like a 'fingerprint') of the reaction occurring on a Pt(100) crystal upon heating the adsorbate covered surface, as well as to allow for a detailed analysis of the gas compounds leaving the surface within a single measurement....

  19. Laser induced and controlled chemical reaction of carbon monoxide and hydrogen

    Science.gov (United States)

    du Plessis, Anton; Strydom, Christien A.; Uys, Hermann; Botha, Lourens R.

    2011-11-01

    Bimolecular chemical reaction control of gaseous CO and H2 at room temperature and atmospheric pressure, without any catalyst, using shaped femtosecond laser pulses is presented. High intensity laser radiation applied to a reaction cell facilitates non-resonant bond breakage and the formation of a range of ions, which can then react to form new products. Stable reaction products are measured after irradiation of a reaction cell, using time of flight mass spectroscopy. Bond formation of C-O, C-C, and C-H bonds is demonstrated as CO2+, C2H2+, CH+, and CH3+ were observed in the time of flight mass spectrum of the product gas, analyzed after irradiation. The formation of CO2 is shown to be dependent on laser intensity, irradiation time, and on the presence of H2 in the reaction cell. Using negatively chirped laser pulses more C-O bond formation takes place as compared to more C-C bond formation for unchirped pulses.

  20. Stochastic Modeling and Simulation of Reaction-Diffusion Biochemical Systems

    OpenAIRE

    LI Fei

    2016-01-01

    Reaction Diffusion Master Equation (RDME) framework, characterized by the discretization of the spatial domain, is one of the most widely used methods in the stochastic simulation of reaction-diffusion systems. Discretization sizes for RDME have to be appropriately chosen such that each discrete compartment is "well-stirred" and the computational cost is not too expensive. An efficient discretization size based on the reaction-diffusion dynamics of each species is derived in this disserta...