Science.gov

Sample records for chemical reactions consuming

  1. Chemical Demonstrations with Consumer Chemicals: The Black and White Reaction

    NASA Astrophysics Data System (ADS)

    Wright, Stephen W.

    2002-01-01

    A color-change reaction is described in which two colorless solutions are combined to afford a black mixture. Two more colorless solutions are combined to afford a white mixture. The black and white mixtures are then combined to afford a clear, colorless solution. The reaction uses chemicals that are readily available on the retail market: vitamin C, tincture of iodine, vinegar, ammonia, bleach, Epsom salt, and laundry starch.

  2. Chemical Demonstrations with Consumer Chemicals: The Black and White Reaction.

    ERIC Educational Resources Information Center

    Wright, Stephen W.

    2002-01-01

    Describes a dramatic chemical demonstration in which chemicals that are black and white combine to produce a colorless liquid. Reactants include tincture of iodine, bleach, white vinegar, Epsom salt, vitamin C tablets, and liquid laundry starch. (DDR)

  3. Chemical Demonstrations with Consumer Chemicals: The Black and White Reaction.

    ERIC Educational Resources Information Center

    Wright, Stephen W.

    2002-01-01

    Describes a dramatic chemical demonstration in which chemicals that are black and white combine to produce a colorless liquid. Reactants include tincture of iodine, bleach, white vinegar, Epsom salt, vitamin C tablets, and liquid laundry starch. (DDR)

  4. CHARACTERIZATION OF INDIVIDUAL CHEMICAL REACTIONS CONSUMING ACID DURING NUCLEAR WASTE PROCESSING AT THE SAVANNAH RIVER SITE - 136B

    SciTech Connect

    Koopman, D.; Pickenheim, B.; Lambert, D.; Newell, J.; Stone, M.

    2009-09-02

    Conversion of legacy radioactive high-level waste at the Savannah River Site into a stable glass waste form involves a chemical pretreatment process to prepare the waste for vitrification. Waste slurry is treated with nitric and formic acids to achieve certain goals. The total quantity of acid added to a batch of waste slurry is constrained by the catalytic activity of trace noble metal fission products in the waste that can convert formic acid into hydrogen gas at many hundreds of times the radiolytic hydrogen generation rate. A large block of experimental process simulations were performed to characterize the chemical reactions that consume acid prior to hydrogen generation. The analysis led to a new equation for predicting the quantity of acid required to process a given volume of waste slurry.

  5. Microfluidic chemical reaction circuits

    SciTech Connect

    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.

  6. Chemical burn or reaction

    MedlinePlus

    ... this page: //medlineplus.gov/ency/article/000059.htm Chemical burn or reaction To use the sharing features on this page, please enable JavaScript. Chemicals that touch skin can lead to a reaction on the skin, throughout the body, or both. ...

  7. Chemical Reaction Problem Solving.

    ERIC Educational Resources Information Center

    Veal, William

    1999-01-01

    Discusses the role of chemical-equation problem solving in helping students predict reaction products. Methods for helping students learn this process must be taught to students and future teachers by using pedagogical skills within the content of chemistry. Emphasizes that solving chemical reactions should involve creative cognition where…

  8. Consumer reaction to healthcare advertising.

    PubMed

    Klein, R F

    1998-07-01

    How do consumers view healthcare advertising? This question, along with many others, was addressed in a national survey conducted by Market Strategies for The Alliance For Healthcare Strategy And Marketing, and presented during The Alliance's annual advertising and promotion conference last June.

  9. Oscillating Chemical Reactions

    ERIC Educational Resources Information Center

    Hawkins, M. D.; And Others

    1975-01-01

    Describes several oscillating chemical reactions which can be used in undergraduate chemistry laboratories. In one such reaction, ferroin oscillates from red (reducing solution) to blue (oxidizing solution) for about an hour at a frequency which can readily be shown to depend on such factors as the temperature, type of solvent, and concentration…

  10. Suspect Screening of Chemicals in Consumer Products

    EPA Science Inventory

    This presentation details a pilot suspect screening analysis (SSA) of common consumer products done under the Rapid Exposure and Dosimetry project of CSS. This work presents methods which can rapidly characterize chemicals identified in consumer products including formulations (s...

  11. Translated chemical reaction networks.

    PubMed

    Johnston, Matthew D

    2014-05-01

    Many biochemical and industrial applications involve complicated networks of simultaneously occurring chemical reactions. Under the assumption of mass action kinetics, the dynamics of these chemical reaction networks are governed by systems of polynomial ordinary differential equations. The steady states of these mass action systems have been analyzed via a variety of techniques, including stoichiometric network analysis, deficiency theory, and algebraic techniques (e.g., Gröbner bases). In this paper, we present a novel method for characterizing the steady states of mass action systems. Our method explicitly links a network's capacity to permit a particular class of steady states, called toric steady states, to topological properties of a generalized network called a translated chemical reaction network. These networks share their reaction vectors with their source network but are permitted to have different complex stoichiometries and different network topologies. We apply the results to examples drawn from the biochemical literature.

  12. Chemical Reactions at Surfaces

    SciTech Connect

    Michael Henderson and Nancy Ryan Gray

    2010-04-14

    Chemical reactions at surfaces underlie some of the most important processes of today, including catalysis, energy conversion, microelectronics, human health and the environment. Understanding surface chemical reactions at a fundamental level is at the core of the field of surface science. The Gordon Research Conference on Chemical Reactions at Surfaces is one of the premiere meetings in the field. The program this year will cover a broad range of topics, including heterogeneous catalysis and surface chemistry, surfaces in environmental chemistry and energy conversion, reactions at the liquid-solid and liquid-gas interface, electronic materials growth and surface modification, biological interfaces, and electrons and photons at surfaces. An exciting program is planned, with contributions from outstanding speakers and discussion leaders from the international scientific community. The conference provides a dynamic environment with ample time for discussion and interaction. Attendees are encouraged to present posters; the poster sessions are historically well attended and stimulate additional discussions. The conference provides an excellent opportunity for junior researchers (e.g. graduate students or postdocs) to present their work and interact with established leaders in the field.

  13. Enhancing chemical reactions

    DOEpatents

    Morrey, John R.

    1978-01-01

    Methods of enhancing selected chemical reactions. The population of a selected high vibrational energy state of a reactant molecule is increased substantially above its population at thermal equilibrium by directing onto the molecule a beam of radiant energy from a laser having a combination of frequency and intensity selected to pump the selected energy state, and the reaction is carried out with the temperature, pressure, and concentrations of reactants maintained at a combination of values selected to optimize the reaction in preference to thermal degradation by transforming the absorbed energy into translational motion. The reaction temperature is selected to optimize the reaction. Typically a laser and a frequency doubler emit radiant energy at frequencies of .nu. and 2.nu. into an optical dye within an optical cavity capable of being tuned to a wanted frequency .delta. or a parametric oscillator comprising a non-centrosymmetric crystal having two indices of refraction, to emit radiant energy at the frequencies of .nu., 2.nu., and .delta. (and, with a parametric oscillator, also at 2.nu.-.delta.). Each unwanted frequency is filtered out, and each desired frequency is focused to the desired radiation flux within a reaction chamber and is reflected repeatedly through the chamber while reactants are fed into the chamber and reaction products are removed therefrom.

  14. Chemical Reactions in Clusters

    DTIC Science & Technology

    1992-11-04

    NH 3)n, n _> 4, clusters has been attributed to the (solvated) naphtholate anion.3a A single picosecond decay measurement has been reported which...vibrational energy in the cluster Sl state. The data are summarized in Table I. A model to explain these decay results can be constructed based on a proton...11 TITLE (Include Security Classification) Chemical Reactions in Clusters 12 PERSONAL AUTHOR(S) Elliot R. Bernstein 13a TYPE OF REPORT 13b TIME COVERED

  15. Chemical Reactions in DSMC

    NASA Astrophysics Data System (ADS)

    Bird, G. A.

    2011-05-01

    DSMC simulations of chemically reacting gas flows have generally employed procedures that convert the macroscopic chemical rate equations to reaction cross-sections at the microscopic level. They therefore depend on the availability of experimental data that has been fitted to equations of the Arrhenius form. This paper presents a physical model for dissociation and recombination reactions and a phenomenological model for exchange and chain reactions. These are based on the vibrational states of the colliding molecules and do not require any experimentally-based data. The simplicity of the models allows the corresponding rate equations to be written down and, while these are not required for the implementation of the models, they facilitate their validation. The model is applied to a typical hypersonic atmospheric entry problem and the results are compared with the corresponding results from the traditional method. It is also used to investigate both spontaneous and forced ignition as well as the structure of a deflagration wave in an oxygen-hydrogen mixture.

  16. Chemical Reactions in DSMC

    SciTech Connect

    Bird, G. A.

    2011-05-20

    DSMC simulations of chemically reacting gas flows have generally employed procedures that convert the macroscopic chemical rate equations to reaction cross-sections at the microscopic level. They therefore depend on the availability of experimental data that has been fitted to equations of the Arrhenius form. This paper presents a physical model for dissociation and recombination reactions and a phenomenological model for exchange and chain reactions. These are based on the vibrational states of the colliding molecules and do not require any experimentally-based data. The simplicity of the models allows the corresponding rate equations to be written down and, while these are not required for the implementation of the models, they facilitate their validation. The model is applied to a typical hypersonic atmospheric entry problem and the results are compared with the corresponding results from the traditional method. It is also used to investigate both spontaneous and forced ignition as well as the structure of a deflagration wave in an oxygen-hydrogen mixture.

  17. Concordant Chemical Reaction Networks

    PubMed Central

    Shinar, Guy; Feinberg, Martin

    2015-01-01

    We describe a large class of chemical reaction networks, those endowed with a subtle structural property called concordance. We show that the class of concordant networks coincides precisely with the class of networks which, when taken with any weakly monotonic kinetics, invariably give rise to kinetic systems that are injective — a quality that, among other things, precludes the possibility of switch-like transitions between distinct positive steady states. We also provide persistence characteristics of concordant networks, instability implications of discordance, and consequences of stronger variants of concordance. Some of our results are in the spirit of recent ones by Banaji and Craciun, but here we do not require that every species suffer a degradation reaction. This is especially important in studying biochemical networks, for which it is rare to have all species degrade. PMID:22659063

  18. Mass Transfer with Chemical Reaction.

    ERIC Educational Resources Information Center

    DeCoursey, W. J.

    1987-01-01

    Describes the organization of a graduate course dealing with mass transfer, particularly as it relates to chemical reactions. Discusses the course outline, including mathematics models of mass transfer, enhancement of mass transfer rates by homogeneous chemical reaction, and gas-liquid systems with chemical reaction. (TW)

  19. Mass Transfer with Chemical Reaction.

    ERIC Educational Resources Information Center

    DeCoursey, W. J.

    1987-01-01

    Describes the organization of a graduate course dealing with mass transfer, particularly as it relates to chemical reactions. Discusses the course outline, including mathematics models of mass transfer, enhancement of mass transfer rates by homogeneous chemical reaction, and gas-liquid systems with chemical reaction. (TW)

  20. A Salicylate Sympathetic Ink from Consumer Chemicals

    ERIC Educational Resources Information Center

    Journal of Chemical Education, 2005

    2005-01-01

    A new sympathetic ink that produces a violet color upon development was developed to develop chemical demonstrations using consumer chemicals. The demonstration was to have a simple, relatively safe reagent system that could be used to make a brightly colored, highly visible "magic sign" for use in science outreach programs.

  1. A Salicylate Sympathetic Ink from Consumer Chemicals

    ERIC Educational Resources Information Center

    Journal of Chemical Education, 2005

    2005-01-01

    A new sympathetic ink that produces a violet color upon development was developed to develop chemical demonstrations using consumer chemicals. The demonstration was to have a simple, relatively safe reagent system that could be used to make a brightly colored, highly visible "magic sign" for use in science outreach programs.

  2. Advancing Consumer Product Composition and Chemical ...

    EPA Pesticide Factsheets

    This presentation describes EPA efforts to collect, model, and measure publically available consumer product data for use in exposure assessment. The development of the ORD Chemicals and Products database will be described, as will machine-learning based models for predicting chemical function. Finally, the talk describes new mass spectrometry-based methods for measuring chemicals in formulation and articles. This presentation is an invited talk to the ICCA-LRI workshop "Fit-For-Purpose Exposure Assessments For Risk-Based Decision Making". The talk will share EPA efforts to characterize the components of consumer products for use in exposure assessment with the international exposure science community.

  3. Chemical scavenging of post-consumed clothes.

    PubMed

    Barot, Amit A; Sinha, Vijay Kumar

    2015-12-01

    Aiming toward the rectification of fiber grade PET waste accumulation as well as recycling and providing a technically viable route leading to preservation of the natural resources and environment, the post consumed polyester clothes were chemically recycled. Post consumed polyester clothes were recycled into bis(2-hydroxyethyl) terephthalate (BHET) monomer in the presence of ethylene glycol as depolymerising agent and zinc acetate as catalyst. Depolymerized product was characterized by chemical as well as analytical techniques. The fiber grade PET was eventually converted into BHET monomer with nearly 90% yield by employing 1% catalyst concentration and at optimum temperature of 180°C without mechanical input of stirring condition.

  4. More on Chemical Reaction Balancing.

    ERIC Educational Resources Information Center

    Swinehart, D. F.

    1985-01-01

    A previous article stated that only the matrix method was powerful enough to balance a particular chemical equation. Shows how this equation can be balanced without using the matrix method. The approach taken involves writing partial mathematical reactions and redox half-reactions, and combining them to yield the final balanced reaction. (JN)

  5. Speeding chemical reactions by focusing.

    PubMed

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

    2013-04-14

    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).

  6. Speeding chemical reactions by focusing

    NASA Astrophysics Data System (ADS)

    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.

  7. Reduction of chemical reaction models

    NASA Technical Reports Server (NTRS)

    Frenklach, Michael

    1991-01-01

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

  8. Fragranced consumer products: Chemicals emitted, ingredients unlisted

    SciTech Connect

    Steinemann, Anne C.; MacGregor, Ian C.; Gordon, Sydney M.; Gallagher, Lisa G.; Davis, Amy L.; Ribeiro, Daniel S.; Wallace, Lance A.

    2011-04-15

    Fragranced consumer products are pervasive in society. Relatively little is known about the composition of these products, due to lack of prior study, complexity of formulations, and limitations and protections on ingredient disclosure in the U.S. We investigated volatile organic compounds (VOCs) emitted from 25 common fragranced consumer products-laundry products, personal care products, cleaning supplies, and air fresheners-using headspace analysis with gas chromatography/mass spectrometry (GC/MS). Our analysis found 133 different VOCs emitted from the 25 products, with an average of 17 VOCs per product. Of these 133 VOCs, 24 are classified as toxic or hazardous under U.S. federal laws, and each product emitted at least one of these compounds. For 'green' products, emissions of these compounds were not significantly different from the other products. Of all VOCs identified across the products, only 1 was listed on any product label, and only 2 were listed on any material safety data sheet (MSDS). While virtually none of the chemicals identified were listed, this nonetheless accords with U.S. regulations, which do not require disclosure of all ingredients in a consumer product, or of any ingredients in a mixture called 'fragrance.' Because the analysis focused on compounds emitted and listed, rather than exposures and effects, it makes no claims regarding possible risks from product use. Results of this study contribute to understanding emissions from common products, and their links with labeling and legislation.

  9. Kinematically complete chemical reaction dynamics

    NASA Astrophysics Data System (ADS)

    Trippel, S.; Stei, M.; Otto, R.; Hlavenka, P.; Mikosch, J.; Eichhorn, C.; Lourderaj, U.; Zhang, J. X.; Hase, W. L.; Weidemüller, M.; Wester, R.

    2009-11-01

    Kinematically complete studies of molecular reactions offer an unprecedented level of insight into the dynamics and the different mechanisms by which chemical reactions occur. We have developed a scheme to study ion-molecule reactions by velocity map imaging at very low collision energies. Results for the elementary nucleophilic substitution (SN2) reaction Cl- + CH3I → ClCH3 + I- are presented and compared to high-level direct dynamics trajectory calculations. Furthermore, an improved design of the crossed-beam imaging spectrometer with full three-dimensional measurement capabilities is discussed and characterization measurements using photoionization of NH3 and photodissociation of CH3I are presented.

  10. . Cheminformatic exploration of the chemical landscape of consumer products

    EPA Science Inventory

    Although Consumer products are a primary source of chemical exposures, little information is available on the chemical ingredients of these products and the concentrations at which they are present. To address this data gap, we have created a database of chemicals in consumer pro...

  11. . Cheminformatic exploration of the chemical landscape of consumer products

    EPA Science Inventory

    Although Consumer products are a primary source of chemical exposures, little information is available on the chemical ingredients of these products and the concentrations at which they are present. To address this data gap, we have created a database of chemicals in consumer pro...

  12. Experimental Demonstrations in Teaching Chemical Reactions.

    ERIC Educational Resources Information Center

    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…

  13. Experimental Demonstrations in Teaching Chemical Reactions.

    ERIC Educational Resources Information Center

    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…

  14. The Oxidation Of Iron In A Gel Using Consumer Chemicals

    ERIC Educational Resources Information Center

    Wright, Stephen W.; Folger, Marsha R.; Quinn, Ryan P.; Sauls, Frederick C.; Krone, Diane

    2005-01-01

    An experiment is conducted for the oxidation of iron in a gel using consumer chemicals, which is pertinent to the students' understanding of redox chemistry and of the relative oxidation potentials of various metals. The experiment can be carried out with consumer chemicals that might be purchased at a supermarket and commonly found in the home.

  15. The Oxidation Of Iron In A Gel Using Consumer Chemicals

    ERIC Educational Resources Information Center

    Wright, Stephen W.; Folger, Marsha R.; Quinn, Ryan P.; Sauls, Frederick C.; Krone, Diane

    2005-01-01

    An experiment is conducted for the oxidation of iron in a gel using consumer chemicals, which is pertinent to the students' understanding of redox chemistry and of the relative oxidation potentials of various metals. The experiment can be carried out with consumer chemicals that might be purchased at a supermarket and commonly found in the home.

  16. (Laser enhanced chemical reaction studies)

    SciTech Connect

    Not Available

    1992-01-01

    Experimental studies of dynamic molecular processes are described with particular emphasis on the use of a powerful infrared diode laser probe technique developed in our laboratory. This technique allows us to determine the final states of CO{sub 2} (and other molecules) produced by collisions, photofragmentation, or chemical reactions with a spectral resolution of 0.0003 cm{sup {minus}1} and a time resolution of 10{sup {minus}7} sec. Such high spectral resolution provides a detailed picture of the vibrational and rotational states of molecules produced by these dynamic events. We have used this experimental method to probe collisions between hot hydrogen/deuterium atoms and CO{sub 2}, between O({sup 1}D) atoms and CO{sub 2}, to study the final states of DC1 molecules produced as a result of the reactions of hot Cl atoms, and to investigate the dynamics of the reaction between OH and CO molecules. Advances in our techniques over the past two years have allowed us to identify and study more than 200 final rotational states in ten different vibrational levels of CO{sub 2} encompassing all 3 normal modes, many overtones, and combination states of the molecule. We have extended the technique to probe a variety of new molecules such as OCS, N{sub 2}O, DCl, and CS{sub 2}. All of this work is aimed at providing experimental tests for polyatomic molecule potential energy surfaces, chemical transition states in complex systems, and theories of reaction dynamic in molecules with more than 3 atoms.

  17. A reversible nanoconfined chemical reaction.

    PubMed

    Nielsen, Thomas K; Bösenberg, Ulrike; Gosalawit, Rapee; Dornheim, Martin; Cerenius, Yngve; Besenbacher, Flemming; Jensen, Torben R

    2010-07-27

    Hydrogen is recognized as a potential, extremely interesting energy carrier system, which can facilitate efficient utilization of unevenly distributed renewable energy. A major challenge in a future "hydrogen economy" is the development of a safe, compact, robust, and efficient means of hydrogen storage, in particular, for mobile applications. Here we report on a new concept for hydrogen storage using nanoconfined reversible chemical reactions. LiBH4 and MgH2 nanoparticles are embedded in a nanoporous carbon aerogel scaffold with pore size Dmax approximately 21 nm and react during release of hydrogen and form MgB2. The hydrogen desorption kinetics is significantly improved compared to bulk conditions, and the nanoconfined system has a high degree of reversibility and stability and possibly also improved thermodynamic properties. This new scheme of nanoconfined chemistry may have a wide range of interesting applications in the future, for example, within the merging area of chemical storage of renewable energy.

  18. Learning to predict chemical reactions.

    PubMed

    Kayala, Matthew A; Azencott, Chloé-Agathe; Chen, Jonathan H; Baldi, Pierre

    2011-09-26

    Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles, respectively, are not high throughput, are not generalizable or scalable, and lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry data set consisting of 1630 full multistep reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top-ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of nonproductive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system

  19. Learning to Predict Chemical Reactions

    PubMed Central

    Kayala, Matthew A.; Azencott, Chloé-Agathe; Chen, Jonathan H.

    2011-01-01

    Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles respectively are not high-throughput, are not generalizable or scalable, or lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry dataset consisting of 1630 full multi-step reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval, problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of non-productive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system

  20. Chemical reactions at aqueous interfaces

    NASA Astrophysics Data System (ADS)

    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

  1. Chemical reactions in endoreversible thermodynamics

    NASA Astrophysics Data System (ADS)

    Wagner, Katharina; Hoffmann, Karl Heinz

    2016-01-01

    Endoreversible thermodynamics is a theory for the (approximate) description of thermodynamic non-equilibrium systems, which allows us to capture the ever present irreversibilities of real processes. For instance in heat engines the dissipation due to finite heat transport capabilities, as well as the resulting limitations in the energy fluxes, can be incorporated into the theory. It has thus been very successful in closing the gap between observed and theoretically predicted efficiencies. Here an extension of the theory is provided, with which chemical reactions can be included in the formalism. This opens up a wide field of applications for endoreversible modeling and the investigation of dissipative processes, for instance in fuel cells or batteries.

  2. Modular verification of chemical reaction network encodings via serializability analysis.

    PubMed

    Lakin, Matthew R; Stefanovic, Darko; Phillips, Andrew

    2016-06-13

    Chemical reaction networks are a powerful means of specifying the intended behaviour of synthetic biochemical systems. A high-level formal specification, expressed as a chemical reaction network, may be compiled into a lower-level encoding, which can be directly implemented in wet chemistry and may itself be expressed as a chemical reaction network. Here we present conditions under which a lower-level encoding correctly emulates the sequential dynamics of a high-level chemical reaction network. We require that encodings are transactional, such that their execution is divided by a "commit reaction" that irreversibly separates the reactant-consuming phase of the encoding from the product-generating phase. We also impose restrictions on the sharing of species between reaction encodings, based on a notion of "extra tolerance", which defines species that may be shared between encodings without enabling unwanted reactions. Our notion of correctness is serializability of interleaved reaction encodings, and if all reaction encodings satisfy our correctness properties then we can infer that the global dynamics of the system are correct. This allows us to infer correctness of any system constructed using verified encodings. As an example, we show how this approach may be used to verify two- and four-domain DNA strand displacement encodings of chemical reaction networks, and we generalize our result to the limit where the populations of helper species are unlimited.

  3. Reaction Decoder Tool (RDT): extracting features from chemical reactions

    PubMed Central

    Rahman, Syed Asad; Torrance, Gilliean; Baldacci, Lorenzo; Martínez Cuesta, Sergio; Fenninger, Franz; Gopal, Nimish; Choudhary, Saket; May, John W.; Holliday, Gemma L.; Steinbeck, Christoph; Thornton, Janet M.

    2016-01-01

    Summary: Extracting chemical features like Atom–Atom Mapping (AAM), Bond Changes (BCs) and Reaction Centres from biochemical reactions helps us understand the chemical composition of enzymatic reactions. Reaction Decoder is a robust command line tool, which performs this task with high accuracy. It supports standard chemical input/output exchange formats i.e. RXN/SMILES, computes AAM, highlights BCs and creates images of the mapped reaction. This aids in the analysis of metabolic pathways and the ability to perform comparative studies of chemical reactions based on these features. Availability and implementation: This software is implemented in Java, supported on Windows, Linux and Mac OSX, and freely available at https://github.com/asad/ReactionDecoder Contact: asad@ebi.ac.uk or s9asad@gmail.com PMID:27153692

  4. Reaction Decoder Tool (RDT): extracting features from chemical reactions.

    PubMed

    Rahman, Syed Asad; Torrance, Gilliean; Baldacci, Lorenzo; Martínez Cuesta, Sergio; Fenninger, Franz; Gopal, Nimish; Choudhary, Saket; May, John W; Holliday, Gemma L; Steinbeck, Christoph; Thornton, Janet M

    2016-07-01

    Extracting chemical features like Atom-Atom Mapping (AAM), Bond Changes (BCs) and Reaction Centres from biochemical reactions helps us understand the chemical composition of enzymatic reactions. Reaction Decoder is a robust command line tool, which performs this task with high accuracy. It supports standard chemical input/output exchange formats i.e. RXN/SMILES, computes AAM, highlights BCs and creates images of the mapped reaction. This aids in the analysis of metabolic pathways and the ability to perform comparative studies of chemical reactions based on these features. This software is implemented in Java, supported on Windows, Linux and Mac OSX, and freely available at https://github.com/asad/ReactionDecoder : asad@ebi.ac.uk or s9asad@gmail.com. © The Author 2016. Published by Oxford University Press.

  5. 2005 Chemical Reactions at Surfaces

    SciTech Connect

    Cynthia M. Friend

    2006-03-14

    The Gordon Research Conference (GRC) on 2005 Chemical Reactions at Surfaces was held at Ventura Beach Marriott, Ventura California from February 13, 2005 through February 18, 2005. The Conference was well-attended with 124 participants (attendees list attached). The attendees represented the spectrum of endeavor in this field coming from academia, industry, and government laboratories, both U.S. and foreign scientists, senior researchers, young investigators, and students. In designing the formal speakers program, emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate lively discussion about the key issues in the field today. Time for formal presentations was limited in the interest of group discussions. In order that more scientists could communicate their most recent results, poster presentation time was scheduled. Attached is a copy of the formal schedule and speaker program and the poster program. In addition to these formal interactions, 'free time' was scheduled to allow informal discussions. Such discussions are fostering new collaborations and joint efforts in the field.

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

    ERIC Educational Resources Information Center

    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…

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

    ERIC Educational Resources Information Center

    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…

  8. Modular verification of chemical reaction network encodings via serializability analysis

    PubMed Central

    Lakin, Matthew R.; Stefanovic, Darko; Phillips, Andrew

    2015-01-01

    Chemical reaction networks are a powerful means of specifying the intended behaviour of synthetic biochemical systems. A high-level formal specification, expressed as a chemical reaction network, may be compiled into a lower-level encoding, which can be directly implemented in wet chemistry and may itself be expressed as a chemical reaction network. Here we present conditions under which a lower-level encoding correctly emulates the sequential dynamics of a high-level chemical reaction network. We require that encodings are transactional, such that their execution is divided by a “commit reaction” that irreversibly separates the reactant-consuming phase of the encoding from the product-generating phase. We also impose restrictions on the sharing of species between reaction encodings, based on a notion of “extra tolerance”, which defines species that may be shared between encodings without enabling unwanted reactions. Our notion of correctness is serializability of interleaved reaction encodings, and if all reaction encodings satisfy our correctness properties then we can infer that the global dynamics of the system are correct. This allows us to infer correctness of any system constructed using verified encodings. As an example, we show how this approach may be used to verify two- and four-domain DNA strand displacement encodings of chemical reaction networks, and we generalize our result to the limit where the populations of helper species are unlimited. PMID:27325906

  9. Chemical reactions in low-g

    NASA Technical Reports Server (NTRS)

    Grodzka, P. G.; Facemire, B. R.

    1978-01-01

    The Apollo-Soyuz flight experiment, 'Chemical Foams' demonstrated that foams and air/liquid dispersions are much more stable in low-gravity than on the ground. It thus should be possible to conduct unique chemical reactions in space foams. The low-g results and subsequent ground work on the formaldehyde clock reaction indicate that the reaction is strongly influenced by (1) dissociated and undissociated solution species being adsorbed at solid/liquid and gas/liquid surfaces and (2) chemical reaction rates apparently being affected by long-range forces determined by the liquid mass and the extent and nature of all surface interfaces.

  10. Chemical reactions in low-g

    NASA Technical Reports Server (NTRS)

    Grodzka, P. G.; Facemire, B. R.

    1978-01-01

    The Apollo-Soyuz flight experiment, 'Chemical Foams' demonstrated that foams and air/liquid dispersions are much more stable in low-gravity than on the ground. It thus should be possible to conduct unique chemical reactions in space foams. The low-g results and subsequent ground work on the formaldehyde clock reaction indicate that the reaction is strongly influenced by (1) dissociated and undissociated solution species being adsorbed at solid/liquid and gas/liquid surfaces and (2) chemical reaction rates apparently being affected by long-range forces determined by the liquid mass and the extent and nature of all surface interfaces.

  11. Microfabricated electrochemiluminescence cell for chemical reaction detection

    DOEpatents

    Northrup, M. Allen; Hsueh, Yun-Tai; Smith, Rosemary L.

    2003-01-01

    A detector cell for a silicon-based or non-silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The detector cell is an electrochemiluminescence cell constructed of layers of silicon with a cover layer of glass, with spaced electrodes located intermediate various layers forming the cell. The cell includes a cavity formed therein and fluid inlets for directing reaction fluid therein. The reaction chamber and detector cell may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The ECL cell may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

  12. 'GREENER' CHEMICAL SYNTHESES USING ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    Microwave (MW) irradiation in conjunction with water as reaction media has proven to be a greener chemical approach for expeditious N-alkylation reactions of amines and hydrazines wherein the reactions under mildly basic conditions afford tertiary amines and double N-alkylation t...

  13. Modelling Students' Visualisation of Chemical Reaction

    ERIC Educational Resources Information Center

    Cheng, Maurice M. W.; Gilbert, John K.

    2017-01-01

    This paper proposes a model-based notion of "submicro representations of chemical reactions". Based on three structural models of matter (the simple particle model, the atomic model and the free electron model of metals), we suggest there are two major models of reaction in school chemistry curricula: (a) reactions that are simple…

  14. 'GREENER' CHEMICAL SYNTHESES USING ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    Microwave (MW) irradiation in conjunction with water as reaction media has proven to be a greener chemical approach for expeditious N-alkylation reactions of amines and hydrazines wherein the reactions under mildly basic conditions afford tertiary amines and double N-alkylation t...

  15. Why Leading Consumer Product Companies Develop Proactive Chemical Management Strategies.

    PubMed

    Scruggs, Caroline E; Van Buren, Harry J

    2016-05-01

    Scholars have studied the various pressures that companies face related to socially responsible behavior when stakeholders know the particular social issues under consideration. Many have examined social responsibility in the context of environmental responsibility and the general approaches companies take regarding environmental management. The issue of currently unregulated, but potentially hazardous, chemicals in consumer products is not well understood by the general public, but a number of proactive consumer product companies have voluntarily adopted strategies to minimize use of such chemicals. These companies are exceeding regulatory requirements by restricting from their products chemicals that could harm human or environmental health, despite the fact that these actions are costly. They do not usually advertise the details of their strategies to end consumers. This article uses interviews with senior environmental directors of 20 multinational consumer product companies to investigate why these companies engage in voluntary chemicals management. The authors conclude that the most significant reasons are to achieve a competitive advantage and stay ahead of regulations, manage relationships and maintain legitimacy with stakeholders, and put managerial values into practice. Many of the characteristics related to the case of chemicals management are extendable to other areas of stakeholder management in which risks to stakeholders are either unknown or poorly understood.

  16. Why Leading Consumer Product Companies Develop Proactive Chemical Management Strategies

    PubMed Central

    Scruggs, Caroline E.; Van Buren, Harry J.

    2014-01-01

    Scholars have studied the various pressures that companies face related to socially responsible behavior when stakeholders know the particular social issues under consideration. Many have examined social responsibility in the context of environmental responsibility and the general approaches companies take regarding environmental management. The issue of currently unregulated, but potentially hazardous, chemicals in consumer products is not well understood by the general public, but a number of proactive consumer product companies have voluntarily adopted strategies to minimize use of such chemicals. These companies are exceeding regulatory requirements by restricting from their products chemicals that could harm human or environmental health, despite the fact that these actions are costly. They do not usually advertise the details of their strategies to end consumers. This article uses interviews with senior environmental directors of 20 multinational consumer product companies to investigate why these companies engage in voluntary chemicals management. The authors conclude that the most significant reasons are to achieve a competitive advantage and stay ahead of regulations, manage relationships and maintain legitimacy with stakeholders, and put managerial values into practice. Many of the characteristics related to the case of chemicals management are extendable to other areas of stakeholder management in which risks to stakeholders are either unknown or poorly understood. PMID:27471326

  17. Nature-Inspired Chemical Reaction Optimisation Algorithms.

    PubMed

    Siddique, Nazmul; Adeli, Hojjat

    2017-01-01

    Nature-inspired meta-heuristic algorithms have dominated the scientific literature in the areas of machine learning and cognitive computing paradigm in the last three decades. Chemical reaction optimisation (CRO) is a population-based meta-heuristic algorithm based on the principles of chemical reaction. A chemical reaction is seen as a process of transforming the reactants (or molecules) through a sequence of reactions into products. This process of transformation is implemented in the CRO algorithm to solve optimisation problems. This article starts with an overview of the chemical reactions and how it is applied to the optimisation problem. A review of CRO and its variants is presented in the paper. Guidelines from the literature on the effective choice of CRO parameters for solution of optimisation problems are summarised.

  18. Chemical potential and reaction electronic flux in symmetry controlled reactions.

    PubMed

    Vogt-Geisse, Stefan; Toro-Labbé, Alejandro

    2016-07-15

    In symmetry controlled reactions, orbital degeneracies among orbitals of different symmetries can occur along a reaction coordinate. In such case Koopmans' theorem and the finite difference approximation provide a chemical potential profile with nondifferentiable points. This results in an ill-defined reaction electronic flux (REF) profile, since it is defined as the derivative of the chemical potential with respect to the reaction coordinate. To overcome this deficiency, we propose a new way for the calculation of the chemical potential based on a many orbital approach, suitable for reactions in which symmetry is preserved. This new approach gives rise to a new descriptor: symmetry adapted chemical potential (SA-CP), which is the chemical potential corresponding to a given irreducible representation of a symmetry group. A corresponding symmetry adapted reaction electronic flux (SA-REF) is also obtained. Using this approach smooth chemical potential profiles and well defined REFs are achieved. An application of SA-CP and SA-REF is presented by studying the Cs enol-keto tautomerization of thioformic acid. Two SA-REFs are obtained, JA'(ξ) and JA'' (ξ). It is found that the tautomerization proceeds via an in-plane delocalized 3-center 4-electron O-H-S hypervalent bond which is predicted to exist only in the transition state (TS) region. © 2016 Wiley Periodicals, Inc.

  19. Chemical-reaction model for Mexican wave

    NASA Astrophysics Data System (ADS)

    Nagatani, Takashi

    2003-05-01

    We present a chemical-reaction model to describe the Mexican wave ( La Ola) in football stadia. The spectator's action is described in terms of chemical reactions. The model is governed by three reaction rates k 1, k 2, and k3. We study the nonlinear waves on one- and two-dimensional lattices. The Mexican wave is formulated as a clockwise forwardly propagating wave. Waves are growing or disappear, depending on the values of reaction rates. In the specific case of k1= k2= k3=1, the nonlinear-wave equation produces a propagating pulse like soliton.

  20. Vibrational Participation in Chemical Reactions.

    DTIC Science & Technology

    1986-08-22

    Cesaro Xue-Feng Yang .. V-. V 8. IV. BIBLIOGRAPHY, AFOSR-SPONSORED RESEARCH, 1981 - 1984 1981 Vibrational Excitation of Ozone and Molecular Fluorine...Phys. Chem. 87, 2142 (1983). G.C. Pimentel, S.N. Cesaro and H. Frei. 11. Selective Vibronic Excitation of Singlet Oxygen-Furan Reactions in Cryogenic

  1. Modeling of turbulent chemical reaction

    NASA Technical Reports Server (NTRS)

    Chen, J.-Y.

    1995-01-01

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

  2. Microfabricated sleeve devices for chemical reactions

    SciTech Connect

    Northrup, M. Allen

    2003-01-01

    A silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and non-silicon based materials to provide the thermal properties desired. For example, the chamber may combine a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

  3. Chemical Reactions at Surfaces. Final Progress Report

    SciTech Connect

    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.

  4. Chemical Reactions in Turbulent Mixing Flows

    DTIC Science & Technology

    1993-07-15

    investigations of turbulent mixing, chemical reaction and combustion processes in turbulent, subsonic and supersonic flows. The program was comprised of...34) n•4I Abstract The purpose of this research is to conduct fundamental investigations of tur- bulent mixing, chemical reaction and combustion processes ...Another issue to consider is that different data- processing used on the different sets of data might result in differences between sets of data. To this end

  5. Explorations into Chemical Reactions and Biochemical Pathways.

    PubMed

    Gasteiger, Johann

    2016-12-01

    A brief overview of the work in the research group of the present author on extracting knowledge from chemical reaction data is presented. Methods have been developed to calculate physicochemical effects at the reaction site. It is shown that these physicochemical effects can quite favourably be used to derive equations for the calculation of data on gas phase reactions and on reactions in solution such as aqueous acidity of alcohols or carboxylic acids or the hydrolysis of amides. Furthermore, it is shown that these physicochemical effects are quite effective for assigning reactions into reaction classes that correspond to chemical knowledge. Biochemical reactions constitute a particularly interesting and challenging task for increasing our understanding of living species. The BioPath.Database is a rich source of information on biochemical reactions and has been used for a variety of applications of chemical, biological, or medicinal interests. Thus, it was shown that biochemical reactions can be assigned by the physicochemical effects into classes that correspond to the classification of enzymes by the EC numbers. Furthermore, 3D models of reaction intermediates can be used for searching for novel enzyme inhibitors. It was shown in a combined application of chemoinformatics and bioinformatics that essential pathways of diseases can be uncovered. Furthermore, a study showed that bacterial flavor-forming pathways can be discovered.

  6. Kinetic studies of elementary chemical reactions

    SciTech Connect

    Durant, J.L. Jr.

    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.

  7. Entropy Generation in a Chemical Reaction

    ERIC Educational Resources Information Center

    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…

  8. Chemical Principles Revisited: Annotating Reaction Equations.

    ERIC Educational Resources Information Center

    Tykodi, R. J.

    1987-01-01

    Urges chemistry teachers to have students annotate the chemical reactions in aqueous-solutions that they see in their textbooks and witness in the laboratory. Suggests this will help students recognize the reaction type more readily. Examples are given for gas formation, precipitate formation, redox interaction, acid-base interaction, and…

  9. Entropy Generation in a Chemical Reaction

    ERIC Educational Resources Information Center

    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…

  10. The quantum dynamics of chemical reactions

    NASA Astrophysics Data System (ADS)

    Kuppermann, A.

    1983-03-01

    In this project, we developed accurate and approximate methods for calculating cross sections of elementary reactions. These methods were applied to systems of importance for the fundamental aspects of chemical dynamics and for advanced technologies of interest to the United States Air Force. The application included calculations of three-atom exchange reactions, break-up and three-body recombination collisions and vibrational quenching by reaction. These calculations improved our understanding of such processes and permitted an assessment of some approximate methods.

  11. Chemical Reactions in Turbulent Mixing Flows

    DTIC Science & Technology

    1989-10-15

    GROUP Turbulence, shear layers, jets, mixing, combustion , 21 ni numerical simulation, light detection diagnostics 21 02 9. ABSTRACT (Conmmna on...mixing chemical reactions and combustion processes in turbulent, subsonic and supersonic flows. This program is comprised of several efforts. In...permit the full chemical kinetics of the combustion process to be incorporated. Our recent analytical efforts have concentrated on a 20

  12. Ultrafast Dynamics of Chemical Reactions.

    DTIC Science & Technology

    2007-11-02

    Michael R. Berman 11 SUPPLEMENTARY NOTES 12a D!STRIBUTION AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE 13 Ap’-,T,,,ACT `’,Ii "•--200words) The research and...Caltech), Professor K. Wilson (UC, San Diego), and Professor J. Polanyi (Toronto). 3 6. Publications (1995/1996) Books Collected Works (up to 1994...1995) Direct Observation of The Transition State J. C. Polanyi and A. H. Zewail Accounts of Chemical Research (Holy-Grail Special Issue), 28,119 (1995

  13. Topologically invariant reaction coordinates for simulating multistate chemical reactions.

    PubMed

    Mones, Letif; Csányi, Gábor

    2012-12-27

    Evaluating free energy profiles of chemical reactions in complex environments such as solvents and enzymes requires extensive sampling, which is usually performed by potential of mean force (PMF) techniques. The reliability of the sampling depends not only on the applied PMF method but also the reaction coordinate space within the dynamics is biased. In contrast to simple geometrical collective variables that depend only on the positions of the atomic coordinates of the reactants, the E(gap) reaction coordinate (the energy difference obtained by evaluating a suitable force field using reactant and product state topologies) has the unique property that it is able to take environmental effects into account leading to better convergence, a more faithful description of the transition state ensemble and therefore more accurate free energy profiles. However, E(gap) requires predefined topologies and is therefore inapplicable for multistate reactions, in which the barrier between the chemically equivalent topologies is comparable to the reaction activation barrier, because undesired "side reactions" occur. In this article, we introduce a new energy-based collective variable by generalizing the E(gap) reaction coordinate such that it becomes invariant to equivalent topologies and show that it yields more well behaved free energy profiles than simpler geometrical reaction coordinates.

  14. Chemical Reactions in Supercritical Carbon Dioxide

    NASA Astrophysics Data System (ADS)

    Wai, Chien M.; Hunt, Fred; Ji, Min; Chen, Xiaoyuan

    1998-12-01

    Utilizing supercritical fluids as environmentally benign solvents for chemical synthesis is one of the new approaches in the "greening" of chemistry. Carbon dioxide is the most widely used gas for supercritical fluid studies because of its moderate critical constants, nontoxic nature, and availability in pure form. One unique property of supercritical carbon dioxide (sc-CO2) is its high solubility for fluorinated compounds. Thus sc-CO2 can be used to replace Freons that are conventionally used as solvents for synthesis of perfluoro-polymers. Another property of sc-CO2 is its miscibility with gases such as H2. Heterogeneous reactions involving these gases may become homogeneous reactions in sc-CO2. Reactions in sc-CO2 may offer several advantages including controlling phase behavior and products, increasing speed of reactions, and obtaining specific reaction channels. This paper describes the following nine types of chemical reactions reported in the literature utilizing sc-CO2 as a solvent to illustrate the unique properties of the supercritical fluid reaction systems: (i) hydrogenation and hydroformylation, (ii) synthesis of organometallic compounds, (iii) metal chelation and extraction, (iv) preparation of inorganic nanoparticles, (v) stereo-selectivity of lipase-catalyzed reactions, (vi) asymmetric catalytic hydrogenation, (vii) polymerization, (viii) Diels-Alder reaction, and (ix) free radical reactions.

  15. Endocrine Disruptors and Asthma-Associated Chemicals in Consumer Products

    PubMed Central

    Nishioka, Marcia; Standley, Laurel J.; Perovich, Laura J.; Brody, Julia Green; Rudel, Ruthann A.

    2012-01-01

    Background: Laboratory and human studies raise concerns about endocrine disruption and asthma resulting from exposure to chemicals in consumer products. Limited labeling or testing information is available to evaluate products as exposure sources. Objectives: We analytically quantified endocrine disruptors and asthma-related chemicals in a range of cosmetics, personal care products, cleaners, sunscreens, and vinyl products. We also evaluated whether product labels provide information that can be used to select products without these chemicals. Methods: We selected 213 commercial products representing 50 product types. We tested 42 composited samples of high-market-share products, and we tested 43 alternative products identified using criteria expected to minimize target compounds. Analytes included parabens, phthalates, bisphenol A (BPA), triclosan, ethanolamines, alkylphenols, fragrances, glycol ethers, cyclosiloxanes, and ultraviolet (UV) filters. Results: We detected 55 compounds, indicating a wide range of exposures from common products. Vinyl products contained > 10% bis(2-ethylhexyl) phthalate (DEHP) and could be an important source of DEHP in homes. In other products, the highest concentrations and numbers of detects were in the fragranced products (e.g., perfume, air fresheners, and dryer sheets) and in sunscreens. Some products that did not contain the well-known endocrine-disrupting phthalates contained other less-studied phthalates (dicyclohexyl phthalate, diisononyl phthalate, and di-n-propyl phthalate; also endocrine-disrupting compounds), suggesting a substitution. Many detected chemicals were not listed on product labels. Conclusions: Common products contain complex mixtures of EDCs and asthma-related compounds. Toxicological studies of these mixtures are needed to understand their biological activity. Regarding epidemiology, our findings raise concern about potential confounding from co-occurring chemicals and misclassification due to variability in

  16. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    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).

  17. Chemical reactions confined within carbon nanotubes.

    PubMed

    Miners, Scott A; Rance, Graham A; Khlobystov, Andrei N

    2016-08-22

    In this critical review, we survey the wide range of chemical reactions that have been confined within carbon nanotubes, particularly emphasising how the pairwise interactions between the catalysts, reactants, transition states and products of a particular molecular transformation with the host nanotube can be used to control the yields and distributions of products of chemical reactions. We demonstrate that nanoscale confinement within carbon nanotubes enables the control of catalyst activity, morphology and stability, influences the local concentration of reactants and products thus affecting equilibria, rates and selectivity, pre-arranges the reactants for desired reactions and alters the relative stability of isomeric products. We critically evaluate the relative advantages and disadvantages of the confinement of chemical reactions inside carbon nanotubes from a chemical perspective and describe how further developments in the controlled synthesis of carbon nanotubes and the incorporation of multifunctionality are essential for the development of this ever-expanding field, ultimately leading to the effective control of the pathways of chemical reactions through the rational design of multi-functional carbon nanoreactors.

  18. Anatomy of an Elementary Chemical Reaction

    NASA Astrophysics Data System (ADS)

    Alexander, Andrew J.; Zare, Richard N.

    1998-09-01

    The alchemists of old sought the knowledge to transform one material to another-for example, base metals into gold-as a path to the elixir of life. As chemists have concerned themselves with the transformation from compound to compound, so they have become involved in trying to uncover the structures of molecules and the pathways that reactions follow. Classically, the study of reaction mechanisms in chemistry encompasses reaction kinetics, the study of velocities or rates of reactions, and reaction dynamics, the study of the nanoscopic motion and rearrangement of atoms during a reactive event. An essential aim of this article is to bring the reader to a favorable vantage point with a brief introduction to reactive dynamics, and from there to describe some examples of recent strategies that have been employed to promote a fundamental understanding of the anatomy of elementary chemical reactions. In the final section we ponder future directions for this rapidly evolving field of research.

  19. Grip on complexity in chemical reaction networks

    PubMed Central

    2017-01-01

    A new discipline of “systems chemistry” is emerging, which aims to capture the complexity observed in natural systems within a synthetic chemical framework. Living systems rely on complex networks of chemical reactions to control the concentration of molecules in space and time. Despite the enormous complexity in biological networks, it is possible to identify network motifs that lead to functional outputs such as bistability or oscillations. To truly understand how living systems function, we need a complete understanding of how chemical reaction networks (CRNs) create function. We propose the development of a bottom-up approach to design and construct CRNs where we can follow the influence of single chemical entities on the properties of the network as a whole. Ultimately, this approach should allow us to not only understand such complex networks but also to guide and control their behavior. PMID:28845192

  20. Grip on complexity in chemical reaction networks.

    PubMed

    Wong, Albert S Y; Huck, Wilhelm T S

    2017-01-01

    A new discipline of "systems chemistry" is emerging, which aims to capture the complexity observed in natural systems within a synthetic chemical framework. Living systems rely on complex networks of chemical reactions to control the concentration of molecules in space and time. Despite the enormous complexity in biological networks, it is possible to identify network motifs that lead to functional outputs such as bistability or oscillations. To truly understand how living systems function, we need a complete understanding of how chemical reaction networks (CRNs) create function. We propose the development of a bottom-up approach to design and construct CRNs where we can follow the influence of single chemical entities on the properties of the network as a whole. Ultimately, this approach should allow us to not only understand such complex networks but also to guide and control their behavior.

  1. Aerosol simulation including chemical and nuclear reactions

    SciTech Connect

    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.

  2. Theoretical study of chemical reactions in solution

    SciTech Connect

    Yokogawa, D.

    2015-12-31

    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.

  3. Classification of Chemical Reactions: Stages of Expertise

    ERIC Educational Resources Information Center

    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…

  4. Computer Animation of a Chemical Reaction.

    ERIC Educational Resources Information Center

    Eaker, Charles W.; Jacobs, Edwin L.

    1982-01-01

    Taking a prototype chemical reaction (molecular hydrogen plus hydrogen atom), constructs an accurate semiempirical, generalized diatomics-in-molecules potential energy surface, calculates motions of these atoms on this surface using REACTS trajectory program, and presents results as moving picture on a microcomputer graphics system. Provides…

  5. Classification of Chemical Reactions: Stages of Expertise

    ERIC Educational Resources Information Center

    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…

  6. Visualization of chemical reaction dynamics: Toward understanding complex polyatomic reactions

    PubMed Central

    SUZUKI, Toshinori

    2013-01-01

    Polyatomic molecules have several electronic states that have similar energies. Consequently, their chemical dynamics often involve nonadiabatic transitions between multiple potential energy surfaces. Elucidating the complex reactions of polyatomic molecules is one of the most important tasks of theoretical and experimental studies of chemical dynamics. This paper describes our recent experimental studies of the multidimensional multisurface dynamics of polyatomic molecules based on two-dimensional ion/electron imaging. It also discusses ultrafast photoelectron spectroscopy of liquids for elucidating nonadiabatic electronic dynamics in aqueous solutions. PMID:23318678

  7. Visualization of chemical reaction dynamics: toward understanding complex polyatomic reactions.

    PubMed

    Suzuki, Toshinori

    2013-01-01

    Polyatomic molecules have several electronic states that have similar energies. Consequently, their chemical dynamics often involve nonadiabatic transitions between multiple potential energy surfaces. Elucidating the complex reactions of polyatomic molecules is one of the most important tasks of theoretical and experimental studies of chemical dynamics. This paper describes our recent experimental studies of the multidimensional multisurface dynamics of polyatomic molecules based on two-dimensional ion/electron imaging. It also discusses ultrafast photoelectron spectroscopy of liquids for elucidating nonadiabatic electronic dynamics in aqueous solutions. (Communicated by Hiroo INOKUCHI, M.J.A.)

  8. Lagrangian descriptors of driven chemical reaction manifolds

    NASA Astrophysics Data System (ADS)

    Craven, Galen T.; Junginger, Andrej; Hernandez, Rigoberto

    2017-08-01

    The persistence of a transition state structure in systems driven by time-dependent environments allows the application of modern reaction rate theories to solution-phase and nonequilibrium chemical reactions. However, identifying this structure is problematic in driven systems and has been limited by theories built on series expansion about a saddle point. Recently, it has been shown that to obtain formally exact rates for reactions in thermal environments, a transition state trajectory must be constructed. Here, using optimized Lagrangian descriptors [G. T. Craven and R. Hernandez, Phys. Rev. Lett. 115, 148301 (2015), 10.1103/PhysRevLett.115.148301], we obtain this so-called distinguished trajectory and the associated moving reaction manifolds on model energy surfaces subject to various driving and dissipative conditions. In particular, we demonstrate that this is exact for harmonic barriers in one dimension and this verification gives impetus to the application of Lagrangian descriptor-based methods in diverse classes of chemical reactions. The development of these objects is paramount in the theory of reaction dynamics as the transition state structure and its underlying network of manifolds directly dictate reactivity and selectivity.

  9. Lagrangian descriptors of driven chemical reaction manifolds.

    PubMed

    Craven, Galen T; Junginger, Andrej; Hernandez, Rigoberto

    2017-08-01

    The persistence of a transition state structure in systems driven by time-dependent environments allows the application of modern reaction rate theories to solution-phase and nonequilibrium chemical reactions. However, identifying this structure is problematic in driven systems and has been limited by theories built on series expansion about a saddle point. Recently, it has been shown that to obtain formally exact rates for reactions in thermal environments, a transition state trajectory must be constructed. Here, using optimized Lagrangian descriptors [G. T. Craven and R. Hernandez, Phys. Rev. Lett. 115, 148301 (2015)PRLTAO0031-900710.1103/PhysRevLett.115.148301], we obtain this so-called distinguished trajectory and the associated moving reaction manifolds on model energy surfaces subject to various driving and dissipative conditions. In particular, we demonstrate that this is exact for harmonic barriers in one dimension and this verification gives impetus to the application of Lagrangian descriptor-based methods in diverse classes of chemical reactions. The development of these objects is paramount in the theory of reaction dynamics as the transition state structure and its underlying network of manifolds directly dictate reactivity and selectivity.

  10. Documentation of Chemical Reactions. I. A Faceted Classification

    ERIC Educational Resources Information Center

    Osinga, M.; Verrijn Stuart, A. A.

    1973-01-01

    Existing methods for coding chemical compounds are discussed and evaluated as to their suitability for documentation of chemical reactions, a new classification for chemical reactions is presented, and possibilities of automatic encoding are studied. (24 references) (Author)

  11. Chemical Reactions at Surfaces [Conference summary report

    SciTech Connect

    Henderson, Michael; Gray, Nancy Ryan

    2010-04-14

    Chemical reactions at surfaces underlie some of the most important processes of today, including catalysis, energy conversion, microelectronics, human health and the environment. Understanding surface chemical reactions at a fundamental level is at the core of the field of surface science. The Gordon Research Conference on Chemical Reactions at Surfaces is one of the premiere meetings in the field. The program this year will cover a broad range of topics, including heterogeneous catalysis and surface chemistry, surfaces in environmental chemistry and energy conversion, reactions at the liquid-solid and liquid-gas interface, electronic materials growth and surface modification, biological interfaces, and electrons and photons at surfaces. An exciting program is planned, with contributions from outstanding speakers and discussion leaders from the international scientific community. The conference provides a dynamic environment with ample time for discussion and interaction. Attendees are encouraged to present posters; the poster sessions are historically well attended and stimulate additional discussions. The conference provides an excellent opportunity for junior researchers (e.g. graduate students or postdocs) to present their work and interact with established leaders in the field.

  12. Chemical reactions in reverse micelle systems

    DOEpatents

    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.

  13. Chemical computing with reaction-diffusion processes.

    PubMed

    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. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  14. Uncertainty Quantification for Nonlinear Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Srinivasan, G.; Robinson, B. A.; Aceves, A. B.; Tartakovsky, D. M.

    2006-12-01

    Systems of coupled chemical reactions are greatly affected by the inherent uncertainties in natural phenomena. These uncertainties can be parametric in nature due to measurement errors or insufficient data. Modeling uncertainties also arise at the molecular level when determining what fraction of the population of each chemical species participates in a chemical reaction at any given time. We present different methods used to quantify both modeling and parametric uncertainties. The application we focus on is that of chemical reactions in the subsurface that greatly affect the transport of contaminants in groundwater. The example considered here is the sorption of Neptunium Np-237 through a competitive ion exchange process. Np-237 is a key radio-nuclide of concern for the Yucca Mountain High Level Waste storage site due to its relatively long half-life, high solubility and low sorption properties. By quantifying the effects of modeling and parametric uncertainties, we can estimate the error associated with Np-237 sorptivity and hence its transport.

  15. Shock-driven chemical reaction in phenylacetylene

    NASA Astrophysics Data System (ADS)

    Dattelbaum, Dana; Sheffield, Stephen; Coe, Joshua; Shock and Detonation Physics Team; Physics and Chemistry of Materials Team

    2013-06-01

    Phenylacetylene (PA) comprises a covalently-linked benzene ring and acetylene moiety, presenting an interesting molecular structure for study of shock driven chemical reactions. In the present work, gas gun-driven embedded electromagnetic gauging experiments produced in situ particle velocity wave profiles at multiple Lagrangian positions at several shock input conditions. The input shock wave evolves over time and distance into a complex multiple wave structure, with a fast risetime 2nd wave, slower risetime 3rd wave, and unusual wave dynamics in the 1st wave. From the shock and particle velocities, the Hugoniot reaction condition, and intermediate and final states associated with the chemical reactions have been obtained. For example, at shock inputs just above the cusp condition, an induction time of 200 ns was observed, with the evolved first wave traveling at Us = 4.2 km/s, P = 5.6 GPa; reaction rates of a few to 10 microsec-1 were inferred. A thermodynamically complete unreacted equation of state was calibrated to estimate the temperature rise along the shock locus. Use of this EOS with the measured wave risetimes yielded highly state-sensitive global reaction rates.

  16. MRI of chemical reactions and processes.

    PubMed

    Britton, Melanie M

    2017-08-01

    As magnetic resonance imaging (MRI) can spatially resolve a wealth of molecular information available from nuclear magnetic resonance (NMR), it is able to non-invasively visualise the composition, properties and reactions of a broad range of spatially-heterogeneous molecular systems. Hence, MRI is increasingly finding applications in the study of chemical reactions and processes in a diverse range of environments and technologies. This article will explain the basic principles of MRI and how it can be used to visualise chemical composition and molecular properties, providing an overview of the variety of information available. Examples are drawn from the disciplines of chemistry, chemical engineering, environmental science, physics, electrochemistry and materials science. The review introduces a range of techniques used to produce image contrast, along with the chemical and molecular insight accessible through them. Methods for mapping the distribution of chemical species, using chemical shift imaging or spatially-resolved spectroscopy, are reviewed, as well as methods for visualising physical state, temperature, current density, flow velocities and molecular diffusion. Strategies for imaging materials with low signal intensity, such as those containing gases or low sensitivity nuclei, using compressed sensing, para-hydrogen or polarisation transfer, are discussed. Systems are presented which encapsulate the diversity of chemical and physical parameters observable by MRI, including one- and two-phase flow in porous media, chemical pattern formation, phase transformations and hydrodynamic (fingering) instabilities. Lastly, the emerging area of electrochemical MRI is discussed, with studies presented on the visualisation of electrochemical deposition and dissolution processes during corrosion and the operation of batteries, supercapacitors and fuel cells. Crown Copyright © 2017. Published by Elsevier B.V. All rights reserved.

  17. Concordant chemical reaction networks and the Species-Reaction Graph.

    PubMed

    Shinar, Guy; Feinberg, Martin

    2013-01-01

    In a recent paper it was shown that, for chemical reaction networks possessing a subtle structural property called concordance, dynamical behavior of a very circumscribed (and largely stable) kind is enforced, so long as the kinetics lies within the very broad and natural weakly monotonic class. In particular, multiple equilibria are precluded, as are degenerate positive equilibria. Moreover, under certain circumstances, also related to concordance, all real eigenvalues associated with a positive equilibrium are negative. Although concordance of a reaction network can be decided by readily available computational means, we show here that, when a nondegenerate network's Species-Reaction Graph satisfies certain mild conditions, concordance and its dynamical consequences are ensured. These conditions are weaker than earlier ones invoked to establish kinetic system injectivity, which, in turn, is just one ramification of network concordance. Because the Species-Reaction Graph resembles pathway depictions often drawn by biochemists, results here expand the possibility of inferring significant dynamical information directly from standard biochemical reaction diagrams.

  18. Concordant Chemical Reaction Networks and the Species-Reaction Graph

    PubMed Central

    Shinar, Guy; Feinberg, Martin

    2015-01-01

    In a recent paper it was shown that, for chemical reaction networks possessing a subtle structural property called concordance, dynamical behavior of a very circumscribed (and largely stable) kind is enforced, so long as the kinetics lies within the very broad and natural weakly monotonic class. In particular, multiple equilibria are precluded, as are degenerate positive equilibria. Moreover, under certain circumstances, also related to concordance, all real eigenvalues associated with a positive equilibrium are negative. Although concordance of a reaction network can be decided by readily available computational means, we show here that, when a nondegenerate network’s Species-Reaction Graph satisfies certain mild conditions, concordance and its dynamical consequences are ensured. These conditions are weaker than earlier ones invoked to establish kinetic system injectivity, which, in turn, is just one ramification of network concordance. Because the Species-Reaction Graph resembles pathway depictions often drawn by biochemists, results here expand the possibility of inferring significant dynamical information directly from standard biochemical reaction diagrams. PMID:22940368

  19. Minimum Energy Pathways for Chemical Reactions

    NASA Technical Reports Server (NTRS)

    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.

  20. Theoretical studies of chemical reaction dynamics

    SciTech Connect

    Schatz, G.C.

    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.

  1. Quantum Theory of Fast Chemical Reactions

    SciTech Connect

    Light, John C

    2007-07-30

    The aims of the research under this grant were to develop a theoretical understanding and predictive abiility for a variety of processes occurring in the gas phase. These included bimolecular chemical exchange reactions, photodissociation, predissociation resonances, unimolecular reactions and recombination reactions. In general we assumed a knowledge, from quantum chemistry, of the interactions of the atoms and molecular fragments involved. Our focus was primarily on the accurate (quantum) dynamics of small molecular systems. This has been important for many reactions related to combustion and atmospheric chemistry involving light atom transfer reactions and, for example, resonances in dissociation and recombination reactions. The rates of such reactions, as functions of temperature, internal states, and radiation (light), are fundamental for generating models of overall combustion processes. A number of new approaches to these problems were developed inclluding the use of discrete variable representations (DVR's) for evaluating rate constants with the flux-flux correlation approach, finite range approaches to exact quantum scattering calculations, energy selected basis representations, transition state wave packet approaches and improved semiclassical approaches. These (and others) were applied to a number of reactive systems and molecular systems of interest including (many years ago) the isotopic H + H2 exchange reactions, the H2 + OH (and H + H2O) systems, Ozone resonances, van der Waals molecule reactions, etc. A total of 7 graduate students, and 5 post-doctoral Research Associates were supported, at least in part, under this grant and seven papers were published with a total of 10 external collaborators. The majority of the 36 publications under this grant were supported entirely by DOE.

  2. Chemical reactions directed Peptide self-assembly.

    PubMed

    Rasale, Dnyaneshwar B; Das, Apurba K

    2015-05-13

    Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly.

  3. Chemical Reactions Directed Peptide Self-Assembly

    PubMed Central

    Rasale, Dnyaneshwar B.; Das, Apurba K.

    2015-01-01

    Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly. PMID:25984603

  4. Chemical Reaction Networks for Computing Polynomials.

    PubMed

    Salehi, Sayed Ahmad; Parhi, Keshab K; Riedel, Marc D

    2017-01-20

    Chemical reaction networks (CRNs) provide a fundamental model in the study of molecular systems. Widely used as formalism for the analysis of chemical and biochemical systems, CRNs have received renewed attention as a model for molecular computation. This paper demonstrates that, with a new encoding, CRNs can compute any set of polynomial functions subject only to the limitation that these functions must map the unit interval to itself. These polynomials can be expressed as linear combinations of Bernstein basis polynomials with positive coefficients less than or equal to 1. In the proposed encoding approach, each variable is represented using two molecular types: a type-0 and a type-1. The value is the ratio of the concentration of type-1 molecules to the sum of the concentrations of type-0 and type-1 molecules. The proposed encoding naturally exploits the expansion of a power-form polynomial into a Bernstein polynomial. Molecular encoders for converting any input in a standard representation to the fractional representation as well as decoders for converting the computed output from the fractional to a standard representation are presented. The method is illustrated first for generic CRNs; then chemical reactions designed for an example are mapped to DNA strand-displacement reactions.

  5. Suppression of Ostwald Ripening by Chemical Reactions

    NASA Astrophysics Data System (ADS)

    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.

  6. Excited state quenching via "unsuccessful" chemical reactions.

    PubMed

    Sinicropi, Adalgisa; Nau, Werner M; Olivucci, Massimo

    2002-08-01

    We discuss the results of recent photochemical reaction path computations on 1n,pi* azoalkanes interacting with a single quencher molecule. We provide computational and experimental evidence that there are two basic mechanisms for the true quenching of 1n,pi* states both based on unsuccessful chemical reactions. The first mechanism is based upon an unsuccessful hydrogen atom transfer and may occur through two different (direct and stepwise) routes. The second mechanism is based on an unsuccessful charge transfer reaction that occurs exclusively in a direct fashion. We show that the efficiency of the two quenching mechanisms is substantially due to the existence of two different types of conical intersections between the excited and ground state potential energy surfaces of the reacting bimolecular system.

  7. Stochastic thermodynamics of chemical reaction networks.

    PubMed

    Schmiedl, Tim; Seifert, Udo

    2007-01-28

    For chemical reaction networks in a dilute solution described by a master equation, the authors 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 of the medium. The latter is given by the exchanged heat identified through the first law. Total entropy production is constrained by an integral fluctuation theorem for networks arbitrarily driven by time-dependent rates and a detailed fluctuation theorem for networks in the steady state. Further exact relations such as a generalized Jarzynski relation and a generalized Clausius inequality are discussed. The authors illustrate these results for a three-species cyclic reaction network which exhibits nonequilibrium steady states as well as transitions between different steady states.

  8. Novel tubing microreactor for monitoring chemical reactions.

    PubMed

    Nielsen, Charles A; Chrisman, Ray W; LaPointe, Robert E; Miller, Theodore E

    2002-07-01

    There is an expanding interest in small-scale methods to evaluate catalysts and chemical reactions at a variety of conditions, ranging up to 6.9 MPa (1000 psig) and 300 degrees C. Multiwell parallel batch techniques are most commonly applied in high-throughput screening systems. In contrast, we describe here a rapid, serial, highly controllable method based on LC-type steel tubing rated for high pressures. The tube, containing a variety of flowing ingredients, such as carrier solvents, catalyst formulations, and reactants, is self-heated ohmically using electrical current from a power supply monitored and regulated with a precision of 0.01%. An array of voltage taps arranged along its length serves to sense the real-time temperature profile of the tube. Reactions are seen as temperature pulses progressing through the reactor, in zones of 200 microL each, and tracked with a temperature precision of 0.1 degrees C. A unique pressure controller was devised to maintain constant reactor pressures despite effluent viscosity fluctuations due to polymerization. Several chemical reaction systems have been characterized to date, including decomposition reactions of di-tert-butyl peroxide, polymerizations of styrene, formation of polyethylene from ethylene, and copolymerization of ethylene with 1-octene. For ethylene polymerization, the amount of mass of polymer formed is proportional to the responses observed.

  9. Identity theft and consumers' reaction to preventive technological innovations.

    PubMed

    Ainscough, Thomas L; Brody, Richard G; Trocchia, Philip J

    2007-08-01

    The use of identification technology by commercial entities has broad and, for some consumers, disturbing social implications. This two-phase study was done to specify consumers' concerns regarding various identification technologies which may be encountered in retail environments. From the qualitative findings, a 26-item survey was constructed to quantify identified areas of concern with 303 survey participants (147 women and 156 men), whose mean age category was 30 to 39 years. Using exploratory factor analysis (principal components with varimax rotation), five dimensions of consumers' concern emerged: privacy, ethics, health, humanity, and complexity.

  10. Stochastic flux analysis of chemical reaction networks.

    PubMed

    Kahramanoğulları, Ozan; Lynch, James F

    2013-12-07

    Chemical reaction networks provide an abstraction scheme for a broad range of models in biology and ecology. The two common means for simulating these networks are the deterministic and the stochastic approaches. The traditional deterministic approach, based on differential equations, enjoys a rich set of analysis techniques, including a treatment of reaction fluxes. However, the discrete stochastic simulations, which provide advantages in some cases, lack a quantitative treatment of network fluxes. We describe a method for flux analysis of chemical reaction networks, where flux is given by the flow of species between reactions in stochastic simulations of the network. Extending discrete event simulation algorithms, our method constructs several data structures, and thereby reveals a variety of statistics about resource creation and consumption during the simulation. We use these structures to quantify the causal interdependence and relative importance of the reactions at arbitrary time intervals with respect to the network fluxes. This allows us to construct reduced networks that have the same flux-behavior, and compare these networks, also with respect to their time series. We demonstrate our approach on an extended example based on a published ODE model of the same network, that is, Rho GTP-binding proteins, and on other models from biology and ecology. We provide a fully stochastic treatment of flux analysis. As in deterministic analysis, our method delivers the network behavior in terms of species transformations. Moreover, our stochastic analysis can be applied, not only at steady state, but at arbitrary time intervals, and used to identify the flow of specific species between specific reactions. Our cases study of Rho GTP-binding proteins reveals the role played by the cyclic reverse fluxes in tuning the behavior of this network.

  11. Stochastic flux analysis of chemical reaction networks

    PubMed Central

    2013-01-01

    Background Chemical reaction networks provide an abstraction scheme for a broad range of models in biology and ecology. The two common means for simulating these networks are the deterministic and the stochastic approaches. The traditional deterministic approach, based on differential equations, enjoys a rich set of analysis techniques, including a treatment of reaction fluxes. However, the discrete stochastic simulations, which provide advantages in some cases, lack a quantitative treatment of network fluxes. Results We describe a method for flux analysis of chemical reaction networks, where flux is given by the flow of species between reactions in stochastic simulations of the network. Extending discrete event simulation algorithms, our method constructs several data structures, and thereby reveals a variety of statistics about resource creation and consumption during the simulation. We use these structures to quantify the causal interdependence and relative importance of the reactions at arbitrary time intervals with respect to the network fluxes. This allows us to construct reduced networks that have the same flux-behavior, and compare these networks, also with respect to their time series. We demonstrate our approach on an extended example based on a published ODE model of the same network, that is, Rho GTP-binding proteins, and on other models from biology and ecology. Conclusions We provide a fully stochastic treatment of flux analysis. As in deterministic analysis, our method delivers the network behavior in terms of species transformations. Moreover, our stochastic analysis can be applied, not only at steady state, but at arbitrary time intervals, and used to identify the flow of specific species between specific reactions. Our cases study of Rho GTP-binding proteins reveals the role played by the cyclic reverse fluxes in tuning the behavior of this network. PMID:24314153

  12. Chemical Reactions in a Sonoluminescing Bubble

    NASA Astrophysics Data System (ADS)

    Yasui, Kyuichi

    1997-09-01

    Rates of chemical reactions in an air bubble are calculatednumerically under a condition of the single-bubble sonoluminescence(SBSL) and that of non-light-emission. In the calculations, effect of non-equilibrium evaporation and condensationof water vapor at the bubble wall andthat of thermal conduction both inside and outside the bubbleare taken into account.Numerical calculations reveal that appreciable amounts of OH, H2O2, HO2, O3, H2, H, and O moleculesare created in a bubble under the condition of SBSL.The amounts of chemical products containing nitrogen such as NOx, NHx, and HNOx are much less than those of the above products at least in the first few acoustic cycles.Numerical calculations also reveal that no chemical reactionstake place under a condition of non-light-emission.Connection with sonoluminescence is also discussed.

  13. Chemical reactions in shear-free turbulence

    NASA Astrophysics Data System (ADS)

    de Bruyn Kops, Stephen M.; Riley, James J.

    2000-11-01

    Understanding and predicting the reaction of chemical species in shear-free turbulence is important in research addressing natural as well as technological problems. In the configuration considered here, two initially separated species mix and react downstream of a turbulence-generating grid in a wind tunnel. Results are reported from high resolution, direct numerical simulations in which the evolution of the conserved scalar field accurately matches that of the temperature field in existing laboratory experiments. Superimposed on the flow are passive, single-step, temperature-dependent reactions with a wide range of activation energies and stoichiometric ratios. Several aspects of the flow are investigated here with the conclusions that (1) reactions in which r ne 1 are more accurately modeled by frozen and equilibrium chemistry limits than are reactions in which r=1; (2) an existing definition of a reduced Damköhler number that includes temperature and stoichiometry effects is a very good measure of reaction rate; and (3) existing theoretical models for the coherence and phase of fuel-oxidizer cross-spectra and the spectrum of the equilibrium fuel mass fraction when r=1 yield accurate predictions. (Supported by NSF and AFOSR.)

  14. Characterization and Prediction of Chemical Functions and Weight Fractions in Consumer Products

    EPA Science Inventory

    Assessing exposures from the thousands of chemicals in commerce requires quantitative information on the chemical constituents of consumer products. Unfortunately, gaps in available composition data prevent assessment of exposure to chemicals in many products. Here we propose fil...

  15. The smallest chemical reaction system with bistability

    PubMed Central

    Wilhelm, Thomas

    2009-01-01

    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 simple systems and for

  16. Chemical and radiation-chemical radical reactions in lignocellulose materials

    NASA Astrophysics Data System (ADS)

    Kuzina, Svetlana I.; Shilova, Irina A.; Mikhailov, Al'fa I.

    2011-09-01

    Chemical and radiation-chemical radical reactions in lignocellulose materials were explored by 3-cm and 2-mm ESR spectroscopy. Background (intrinsic) singlet signals at g=2.003 from wood pulp and lignin and those arising during reaction of lignocellulose materials with acids and chlorine were attributed to radicals with conjugated CC bonds. The 2-mm ESR signal with 3D anisotropy of g-factor from o-semiquinone radical ions formed in reaction of lignin with NaOH was recorded for the first time. The singlet signals derived from cellulose γ-irradiated at 77 K and marked out during post-thermal reactions were assigned to radicals with conjugated bonds. In wetted cellulose, a triplet signal with αβH≅2.7 mT and imposed quadruplet structure (0.5-0.7 mT) from three γ-protons was detected at 300 K and attributed to С 4-radicals. The triplet signals derived from С 2- and С 3-radicals in pyranose cycles of cellulose exhibited higher values of αβH (3.0-3.2 mT) and lower thermal stability (up to 250 K). In radiolyzed cotton pulp, detected were ESR signals derived from formyl radicals formed upon rupture of the С 5С 6 bond in pyranose cycles. Heating up irradiated samples under О 2 was accompanied by formation of peroxide radicals. Photoinduced recombination of trapped electrons with С 1-radicals was found to proceed as a chain reaction with a kinetic length of about 25 units. Photolysis ( λ≥360 nm) of radiolyzed cellulose enhanced the disclosure of pyranose cycles and, as a result, the evolution of CO 2 by a factor of 2-2.5.

  17. Quantum dynamics of fast chemical reactions

    SciTech Connect

    Light, J.C.

    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.

  18. [Laser enhanced chemical reaction studies]. [Progress report

    SciTech Connect

    Not Available

    1992-04-01

    Experimental studies of dynamic molecular processes are described with particular emphasis on the use of a powerful infrared diode laser probe technique developed in our laboratory. This technique allows us to determine the final states of CO{sub 2} (and other molecules) produced by collisions, photofragmentation, or chemical reactions with a spectral resolution of 0.0003 cm{sup {minus}1} and a time resolution of 10{sup {minus}7} sec. Such high spectral resolution provides a detailed picture of the vibrational and rotational states of molecules produced by these dynamic events. We have used this experimental method to probe collisions between hot hydrogen/deuterium atoms and CO{sub 2}, between O({sup 1}D) atoms and CO{sub 2}, to study the final states of DC1 molecules produced as a result of the reactions of hot Cl atoms, and to investigate the dynamics of the reaction between OH and CO molecules. Advances in our techniques over the past two years have allowed us to identify and study more than 200 final rotational states in ten different vibrational levels of CO{sub 2} encompassing all 3 normal modes, many overtones, and combination states of the molecule. We have extended the technique to probe a variety of new molecules such as OCS, N{sub 2}O, DCl, and CS{sub 2}. All of this work is aimed at providing experimental tests for polyatomic molecule potential energy surfaces, chemical transition states in complex systems, and theories of reaction dynamic in molecules with more than 3 atoms.

  19. Law of Localization in Chemical Reaction Networks

    NASA Astrophysics Data System (ADS)

    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.

  20. Strategies for chemical reaction searching in SciFinder

    PubMed

    Ridley

    2000-09-01

    The bibliographic, chemical structure, and chemical reaction databases produced by Chemical Abstracts Service allow a number of possibilities for chemical reaction searching. While these same databases may be searched through the STN network, many end-users find the intuitive software interface SciFinder simpler, but there still are issues to address. Searching may be performed through keywords, chemical structures, or chemical reactions, and the answers may vary with respect to precision and comprehension. Often combinations of search options may be needed to best solve the problem. Retrosynthetic analyses are easily performed in the chemical reaction database and can give unique insights into synthetic alternatives.

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

    ERIC Educational Resources Information Center

    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…

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

    ERIC Educational Resources Information Center

    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…

  3. Exploring consumer exposure pathways and patterns of use for chemicals in the environment through the Chemical/Product Categories Database

    EPA Pesticide Factsheets

    Exploring consumer exposure pathways and patterns of use for chemicals in the environment through the Chemical/Product Categories Database (CPCat) (Presented by: Kathie Dionisio, Sc.D., NERL, US EPA, Research Triangle Park, NC (1/23/2014).

  4. Quantum theory of chemical reaction rates

    SciTech Connect

    Miller, W.H. |

    1994-10-01

    If one wishes to describe a chemical reaction at the most detailed level possible, i.e., its state-to-state differential scattering cross section, then it is necessary to solve the Schroedinger equation to obtain the S-matrix as a function of total energy E and total angular momentum J, in terms of which the cross sections can be calculated as given by equation (1) in the paper. All other physically observable attributes of the reaction can be derived from the cross sections. Often, in fact, one is primarily interested in the least detailed quantity which characterizes the reaction, namely its thermal rate constant, which is obtained by integrating Eq. (1) over all scattering angles, summing over all product quantum states, and Boltzmann-averaging over all initial quantum states of reactants. With the proper weighting factors, all of these averages are conveniently contained in the cumulative reaction probability (CRP), which is defined by equation (2) and in terms of which the thermal rate constant is given by equation (3). Thus, having carried out a full state-to-state scattering calculation to obtain the S-matrix, one can obtain the CRP from Eq. (2), and then rate constant from Eq. (3), but this seems like ``overkill``; i.e., if one only wants the rate constant, it would clearly be desirable to have a theory that allows one to calculate it, or the CRP, more directly than via Eq. (2), yet also correctly, i.e., without inherent approximations. Such a theory is the subject of this paper.

  5. Solving moment hierarchies for chemical reaction networks

    NASA Astrophysics Data System (ADS)

    Krishnamurthy, Supriya; Smith, Eric

    2017-10-01

    The study of chemical reaction networks (CRN’s) is a very active field. Earlier well-known results (Feinberg 1987 Chem. Enc. Sci. 42 2229, Anderson et al 2010 Bull. Math. Biol. 72 1947) identify a topological quantity called deficiency, for any CRN, which, when exactly equal to zero, leads to a unique factorized steady-state for these networks. No results exist however for the steady states of non-zero-deficiency networks. In this paper, we show how to write the full moment-hierarchy for any non-zero-deficiency CRN obeying mass-action kinetics, in terms of equations for the factorial moments. Using these, we can recursively predict values for lower moments from higher moments, reversing the procedure usually used to solve moment hierarchies. We show, for non-trivial examples, that in this manner we can predict any moment of interest, for CRN’s with non-zero deficiency and non-factorizable steady states.

  6. Extracting Chemical Reactions from Biological Literature

    DTIC Science & Technology

    2014-05-16

    noun   phrase , and prepositional  phrase ) are relevant to the  reaction. An extremely general top down pattern may match any sentence that contains these...illuminates an important aspect of our pattern­based  approach . Patterns are designed to capture commonalities in  phrases  used to describe chemical...limitations in our  approach  and outline future works (Section 7) before concluding.  2. Related Works  Semantic relationship extraction is the task of

  7. Evaluation of Consumer Product Co-occurrence to Inform Chemical Exposure

    EPA Science Inventory

    Consumer products are an important target of chemical innovation. Used daily for personal hygiene, home care, disinfection and cleaning, consumer products provide a host of benefits, and also an efficient delivery vehicle for a variety of chemicals into our homes and bodies. Al...

  8. Evaluation of Consumer Product Co-occurrence to Inform Chemical Exposure

    EPA Science Inventory

    Consumer products are an important target of chemical innovation. Used daily for personal hygiene, home care, disinfection and cleaning, consumer products provide a host of benefits, and also an efficient delivery vehicle for a variety of chemicals into our homes and bodies. Al...

  9. Silicon-based sleeve devices for chemical reactions

    DOEpatents

    Northrup, M.A.; Mariella, R.P. Jr.; Carrano, A.V.; Balch, J.W.

    1996-12-31

    A silicon-based sleeve type chemical reaction chamber is described that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis. 32 figs.

  10. Silicon-based sleeve devices for chemical reactions

    DOEpatents

    Northrup, M. Allen; Mariella, Jr., Raymond P.; Carrano, Anthony V.; Balch, Joseph W.

    1996-01-01

    A silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

  11. Regimes of chemical reaction waves initiated by nonuniform initial conditions for detailed chemical reaction models.

    PubMed

    Liberman, M A; Kiverin, A D; Ivanov, M F

    2012-05-01

    Regimes of chemical reaction wave propagation initiated by initial temperature nonuniformity in gaseous mixtures, whose chemistry is governed by chain-branching kinetics, are studied using a multispecies transport model and a detailed chemical model. Possible regimes of reaction wave propagation are identified for stoichiometric hydrogen-oxygen and hydrogen-air mixtures in a wide range of initial pressures and temperature levels, depending on the initial non-uniformity steepness. The limits of the regimes of reaction wave propagation depend upon the values of the spontaneous wave speed and the characteristic velocities of the problem. It is shown that one-step kinetics cannot reproduce either quantitative neither qualitative features of the ignition process in real gaseous mixtures because the difference between the induction time and the time when the exothermic reaction begins significantly affects the ignition, evolution, and coupling of the spontaneous reaction wave and the pressure wave, especially at lower temperatures. We show that all the regimes initiated by the temperature gradient occur for much shallower temperature gradients than predicted by a one-step model. The difference is very large for lower initial pressures and for slowly reacting mixtures. In this way the paper provides an answer to questions, important in practice, about the ignition energy, its distribution, and the scale of the initial nonuniformity required for ignition in one or another regime of combustion wave propagation.

  12. Regimes of chemical reaction waves initiated by nonuniform initial conditions for detailed chemical reaction models

    NASA Astrophysics Data System (ADS)

    Liberman, M. A.; Kiverin, A. D.; Ivanov, M. F.

    2012-05-01

    Regimes of chemical reaction wave propagation initiated by initial temperature nonuniformity in gaseous mixtures, whose chemistry is governed by chain-branching kinetics, are studied using a multispecies transport model and a detailed chemical model. Possible regimes of reaction wave propagation are identified for stoichiometric hydrogen-oxygen and hydrogen-air mixtures in a wide range of initial pressures and temperature levels, depending on the initial non-uniformity steepness. The limits of the regimes of reaction wave propagation depend upon the values of the spontaneous wave speed and the characteristic velocities of the problem. It is shown that one-step kinetics cannot reproduce either quantitative neither qualitative features of the ignition process in real gaseous mixtures because the difference between the induction time and the time when the exothermic reaction begins significantly affects the ignition, evolution, and coupling of the spontaneous reaction wave and the pressure wave, especially at lower temperatures. We show that all the regimes initiated by the temperature gradient occur for much shallower temperature gradients than predicted by a one-step model. The difference is very large for lower initial pressures and for slowly reacting mixtures. In this way the paper provides an answer to questions, important in practice, about the ignition energy, its distribution, and the scale of the initial nonuniformity required for ignition in one or another regime of combustion wave propagation.

  13. Plasmon-driven sequential chemical reactions in an aqueous environment.

    PubMed

    Zhang, Xin; Wang, Peijie; Zhang, Zhenglong; Fang, Yurui; Sun, Mengtao

    2014-06-24

    Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H(+) in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight.

  14. Plasmon-driven sequential chemical reactions in an aqueous environment

    PubMed Central

    Zhang, Xin; Wang, Peijie; Zhang, Zhenglong; Fang, Yurui; Sun, Mengtao

    2014-01-01

    Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H+ in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight. PMID:24958029

  15. Plasmon-driven sequential chemical reactions in an aqueous environment

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Wang, Peijie; Zhang, Zhenglong; Fang, Yurui; Sun, Mengtao

    2014-06-01

    Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H+ in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight.

  16. Development of a consumer product ingredient database for chemical exposure screening and prioritization.

    PubMed

    Goldsmith, M-R; Grulke, C M; Brooks, R D; Transue, T R; Tan, Y M; Frame, A; Egeghy, P P; Edwards, R; Chang, D T; Tornero-Velez, R; Isaacs, K; Wang, A; Johnson, J; Holm, K; Reich, M; Mitchell, J; Vallero, D A; Phillips, L; Phillips, M; Wambaugh, J F; Judson, R S; Buckley, T J; Dary, C C

    2014-03-01

    Consumer products are a primary source of chemical exposures, yet little structured information is available on the chemical ingredients of these products and the concentrations at which ingredients are present. To address this data gap, we created a database of chemicals in consumer products using product Material Safety Data Sheets (MSDSs) publicly provided by a large retailer. The resulting database represents 1797 unique chemicals mapped to 8921 consumer products and a hierarchy of 353 consumer product "use categories" within a total of 15 top-level categories. We examine the utility of this database and discuss ways in which it will support (i) exposure screening and prioritization, (ii) generic or framework formulations for several indoor/consumer product exposure modeling initiatives, (iii) candidate chemical selection for monitoring near field exposure from proximal sources, and (iv) as activity tracers or ubiquitous exposure sources using "chemical space" map analyses. Chemicals present at high concentrations and across multiple consumer products and use categories that hold high exposure potential are identified. Our database is publicly available to serve regulators, retailers, manufacturers, and the public for predictive screening of chemicals in new and existing consumer products on the basis of exposure and risk.

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

    PubMed

    Rappoport, Dmitrij; Galvin, Cooper J; Zubarev, Dmitry Yu; Aspuru-Guzik, Alán

    2014-03-11

    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 reactive potential energy surfaces and are combined here with quantum chemical structure optimizations, which yield the structures and energies of the reaction intermediates and products. Application of heuristics-aided quantum chemical methodology to the formose reaction reproduces the experimentally observed reaction products, major reaction pathways, and autocatalytic cycles.

  18. Heterogeneous chemical reactions: Preparation of monodisperse latexes

    NASA Technical Reports Server (NTRS)

    Vanderhoff, J. W.; Micale, F. J.; El-Aasser, M. S.; Sterk, A. A.; Bethke, G. W.

    1977-01-01

    It is demonstrated that a photoinitiated emulsion polymerization can be carried out to a significant conversion in a SPAR rocket prototype polymerization vessel within the six minutes allowed for the experiment. The percentage of conversion was determined by both dilatometry and gravimetric methods with good agreement. The experimental results lead to the following conclusions: (1) emulsion polymerizations can be carried out to conversions as high as 75%, using a stable micellized styrene-SLS system plus photoinitiator; (2) dilatometry can be used to accurately determine both the rate and conversion of polymerization; (3) thermal expansion due to the light source and heat of reaction is small and can be corrected for if necessary; (4) although seeded emulsion polymerizations are unfavorable in photoinitiation, as opposed to chemical initiation, polymerizations can be carried out to at least 15% conversion using 7940A seed particles, with 0.05% solids; and (5) photoinitiation should be used to initiate polymerization in the SPAR rocket experiments because of the mechanical simplicity of the experiment.

  19. Spectroscopy and reactions of molecules important in chemical evolution

    NASA Technical Reports Server (NTRS)

    Becker, R. S.

    1974-01-01

    The research includes: (1) hot hydrogen atom reactions in terms of the nature of products produced, mechanism of the reactions and the implication and application of such reactions for molecules existing in interstellar clouds, in planetary atmospheres, and in chemical evolution; (2) photochemical reactions that can lead to molecules important in chemical evolution, interstellar clouds and as constituents in planetary atmospheres; and (3) spectroscopic and theoretical properties of biomolecules and their precursors and where possible, use these to understand their photochemical behavior.

  20. GREEN CHEMICAL SYNTHESIS THROUGH CATALYSIS AND ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    Green chemical synthesis through catalysis and alternate reaction conditions

    Encompassing green chemistry techniques and methodologies, we have initiated several projects at the National Risk Management Research laboratory that focus on the design and development of chemic...

  1. Prediction and Prevention of Chemical Reaction Hazards: Learning by Simulation.

    ERIC Educational Resources Information Center

    Shacham, Mordechai; Brauner, Neima; Cutlip, Michael B.

    2001-01-01

    Points out that chemical hazards are the major cause of accidents in chemical industry and describes a safety teaching approach using a simulation. Explains a problem statement on exothermic liquid-phase reactions. (YDS)

  2. GREEN CHEMICAL SYNTHESIS THROUGH CATALYSIS AND ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    Green chemical synthesis through catalysis and alternate reaction conditions

    Encompassing green chemistry techniques and methodologies, we have initiated several projects at the National Risk Management Research laboratory that focus on the design and development of chemic...

  3. Prediction and Prevention of Chemical Reaction Hazards: Learning by Simulation.

    ERIC Educational Resources Information Center

    Shacham, Mordechai; Brauner, Neima; Cutlip, Michael B.

    2001-01-01

    Points out that chemical hazards are the major cause of accidents in chemical industry and describes a safety teaching approach using a simulation. Explains a problem statement on exothermic liquid-phase reactions. (YDS)

  4. Shaking Catalysts Accelerating Chemical Reaction in Micro Reactors

    NASA Astrophysics Data System (ADS)

    Suzumori, Koichi; Nagata, Takashi; Kanda, Takefumi; Sakata, Yusaku; Muto, Akinori

    Efficient uniform mixing is an essential process for chemical reaction. However, it is difficult to fabricate many tiny stirrers on reactor chips. This paper shows a new method promoting high-efficient chemical reaction in micro chamber. To stir chemicals and to accelerate reaction catalytic particles are driven electrostatically in micro chamber. Two driving methods have been evaluated; AC drive and DC drive. Evaluation of chemical reactions revealed the effect of this developed devices. In addition conveyance system of catalytic particles is necessary for particles exchange.

  5. Parameter estimation in complex flows with chemical reactions

    NASA Astrophysics Data System (ADS)

    Robinson, Daniel J.

    electrochemical parameters examined again show very close agreement to the experimental values. The usual method of determining chemical reaction rates by measurement is lengthy and time consuming, especially where the chemistry and chemical processes are of a more complex nature. This computational method and associated algorithms has shown to deliver accurate correlations to the experimental data for three-dimensional models, demonstrated in these new unique applications of the technique.

  6. Classification of chemical reactions and chemoinformatic processing of enzymatic transformations.

    PubMed

    Latino, Diogo A R S; Aires-de-Sousa, João

    2011-01-01

    The automatic perception of chemical similarities between chemical reactions is required for a variety of applications in chemistry and connected fields, namely with databases of metabolic reactions. Classification of enzymatic reactions is required, e.g., for genome-scale reconstruction (or comparison) of metabolic pathways, computer-aided validation of classification systems, or comparison of enzymatic mechanisms. This chapter presents different current approaches for the representation of chemical reactions enabling automatic reaction classification. Representations based on the encoding of the reaction center are illustrated, which use physicochemical features, Reaction Classification (RC) numbers, or Condensed Reaction Graphs (CRG). Representation of differences between the structures of products and reactants include reaction signatures, fingerprint differences, and the MOLMAP approach. The approaches are illustrated with applications to real datasets.

  7. Semiclassical methods in chemical reaction dynamics

    SciTech Connect

    Keshavamurthy, Srihari

    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.

  8. Incidents of chemical reactions in cell equipment

    SciTech Connect

    Baldwin, N.M.; Barlow, C.R.

    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.

  9. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.

    1990-01-01

    The objective was to obtain accurate potential energy surfaces (PES's) for a number of reactions which are important in the H/N/O combustion process. The interest in this is centered around the design of the SCRAM jet engine for the National Aerospace Plane (NASP), which was envisioned as an air-breathing hydrogen-burning vehicle capable of reaching velocities as large as Mach 25. Preliminary studies indicated that the supersonic flow in the combustor region of the scram jet engine required accurate reaction rate data for reactions in the H/N/O system, some of which was not readily available from experiment. The most important class of combustion reactions from the standpoint of the NASP project are radical recombinaton reactions, since these reactions result in most of the heat release in the combustion process. Theoretical characterizations of the potential energy surfaces for these reactions are presented and discussed.

  10. Chemical Looping Combustion Reactions and Systems

    SciTech Connect

    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.

  11. Development of a Consumer Product Ingredient Database for Chemical ExposureScreening and Prioritization

    EPA Science Inventory

    Consumer products are a primary source of chemical exposures, yet little structured information is available on the chemical ingredients of these products and the concentrations at which ingredients are present. To address this data gap, we created a database of chemicals in cons...

  12. Development of a Consumer Product Ingredient Database for Chemical ExposureScreening and Prioritization

    EPA Science Inventory

    Consumer products are a primary source of chemical exposures, yet little structured information is available on the chemical ingredients of these products and the concentrations at which ingredients are present. To address this data gap, we created a database of chemicals in cons...

  13. Stereodynamics: From elementary processes to macroscopic chemical reactions

    SciTech Connect

    Kasai, Toshio; Che, Dock-Chil; Tsai, Po-Yu; Lin, King-Chuen; Palazzetti, Federico; Aquilanti, Vincenzo

    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.

  14. Chemical kinetics computer program for static and flow reactions

    NASA Technical Reports Server (NTRS)

    Bittker, D. A.; Scullin, V. J.

    1972-01-01

    General chemical kinetics computer program for complex gas mixtures has been developed. Program can be used for any homogeneous reaction in either one dimensional flow or static system. It is flexible, accurate, and easy to use. It can be used for any chemical system for which species thermodynamic data and reaction rate constant data are known.

  15. Negative Temperature Coefficient in Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Leenson, I. A.; Sergeev, Gleb B.

    1984-05-01

    A systematic analysis of reactions whose rate decreases with increase of temperature is presented. The possibility of a negative temperature coefficient in the elementary reactions is examined from the standpoint of the transition state theory and of collision theory. The mechanisms of complex reactions in which the temperature dependence of the rate is anomalous are discussed, and possible reasons for the anomaly are examined. The bibliography contains 175 references.

  16. Mesoscale simulations of shockwave energy dissipation via chemical reactions.

    PubMed

    Antillon, Edwin; Strachan, Alejandro

    2015-02-28

    We use a particle-based mesoscale model that incorporates chemical reactions at a coarse-grained level to study the response of materials that undergo volume-reducing chemical reactions under shockwave-loading conditions. We find that such chemical reactions can attenuate the shockwave and characterize how the parameters of the chemical model affect this behavior. The simulations show that the magnitude of the volume collapse and velocity at which the chemistry propagates are critical to weaken the shock, whereas the energetics in the reactions play only a minor role. Shock loading results in transient states where the material is away from local equilibrium and, interestingly, chemical reactions can nucleate under such non-equilibrium states. Thus, the timescales for equilibration between the various degrees of freedom in the material affect the shock-induced chemistry and its ability to attenuate the propagating shock.

  17. Chemical and genomic evolution of enzyme-catalyzed reaction networks.

    PubMed

    Kanehisa, Minoru

    2013-09-02

    There is a tendency that a unit of enzyme genes in an operon-like structure in the prokaryotic genome encodes enzymes that catalyze a series of consecutive reactions in a metabolic pathway. Our recent analysis shows that this and other genomic units correspond to chemical units reflecting chemical logic of organic reactions. From all known metabolic pathways in the KEGG database we identified chemical units, called reaction modules, as the conserved sequences of chemical structure transformation patterns of small molecules. The extracted patterns suggest co-evolution of genomic units and chemical units. While the core of the metabolic network may have evolved with mechanisms involving individual enzymes and reactions, its extension may have been driven by modular units of enzymes and reactions. Copyright © 2013 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

  18. Versatile Dual Photoresponsive System for Precise Control of Chemical Reactions.

    PubMed

    Xu, Can; Bing, Wei; Wang, Faming; Ren, Jinsong; Qu, Xiaogang

    2017-08-22

    A versatile method for photoregulation of chemical reactions was developed through a combination of near-infrared (NIR) and ultraviolet (UV) light sensitive materials. This regulatory effect was achieved through photoresponsive modulation of reaction temperature and pH values, two prominent factors influencing reaction kinetics. Photothermal nanomaterial graphene oxide (GO) and photobase reagent malachite green carbinol base (MGCB) were selected for temperature and pH regulation, respectively. Using nanocatalyst- and enzyme-mediated chemical reactions as model systems, we demonstrated the feasibility and high efficiency of this method. In addition, a photoresponsive, multifunctional "Band-aid"-like hydrogel platform was presented for programmable wound healing. Overall, this simple, efficient, and reversible system was found to be effective for controlling a wide variety of chemical reactions. Our work may provide a method for remote and sustainable control over chemical reactions for industrial and biomedical applications.

  19. Using Chemical Principles to Encourage Critical Thinking in Consumer Chemistry.

    ERIC Educational Resources Information Center

    Hill, John W.

    1988-01-01

    Discusses methods that can be used to encourage students to use chemical principles to evaluate claims made in advertising. Considers weight loss diets, structure and properties, and reproducibility of evidence. (CW)

  20. Using Chemical Principles to Encourage Critical Thinking in Consumer Chemistry.

    ERIC Educational Resources Information Center

    Hill, John W.

    1988-01-01

    Discusses methods that can be used to encourage students to use chemical principles to evaluate claims made in advertising. Considers weight loss diets, structure and properties, and reproducibility of evidence. (CW)

  1. Steric Control of Complex Chemical Reactions

    DTIC Science & Technology

    2014-05-31

    reactants. When the infrared (IR) laser was directed in the source chamber to excite the methane reactants, we probed the stereodynamics by...The reaction of Cl + CH4 is of great importance in atmosphere chemistry as being a primary competing process to the ozone -hole catalytic reaction

  2. An Analysis of the Algebraic Method for Balancing Chemical Reactions.

    ERIC Educational Resources Information Center

    Olson, John A.

    1997-01-01

    Analyzes the algebraic method for balancing chemical reactions. Introduces a third general condition that involves a balance between the total amount of oxidation and reduction. Requires the specification of oxidation states for all elements throughout the reaction. Describes the general conditions, the mathematical treatment, redox reactions, and…

  3. Chemical redox reactions in ES-MS: Study of electrode reactions

    SciTech Connect

    Zhou, Feimeng; VAn Berkel, G.J.

    1995-12-31

    The authors previously demonstrated that chemical redox reactions can be used to ionize neutral commpounds for electrospray mass spectrometric (ES-MS) detection. Two different compounds, viz, C{sub 60}F{sub 48} and {beta}-carotene were used to demonstrate the utility of chemical redox reactions with on-line ES-MS for the elucidation of mechanisms of complicated electron transfer reactions and for the kinetic study of electrode reactions in which relatively short-lived intermediates are involved.

  4. Formal modeling of a system of chemical reactions under uncertainty.

    PubMed

    Ghosh, Krishnendu; Schlipf, John

    2014-10-01

    We describe a novel formalism representing a system of chemical reactions, with imprecise rates of reactions and concentrations of chemicals, and describe a model reduction method, pruning, based on the chemical properties. We present two algorithms, midpoint approximation and interval approximation, for construction of efficient model abstractions with uncertainty in data. We evaluate computational feasibility by posing queries in computation tree logic (CTL) on a prototype of extracellular-signal-regulated kinase (ERK) pathway.

  5. Trends in Exposure to Chemicals in Personal Care and Consumer Products.

    PubMed

    Calafat, Antonia M; Valentin-Blasini, Liza; Ye, Xiaoyun

    2015-12-01

    Synthetic organic chemicals can be used in personal care and consumer products. Data on potential human health effects of these chemicals are limited-sometimes even contradictory-but because several of these chemicals are toxic in experimental animals, alternative compounds are entering consumer markets. Nevertheless, limited information exists on consequent exposure trends to both the original chemicals and their replacements. Biomonitoring (measuring concentrations of chemicals or their metabolites in people) provides invaluable information for exposure assessment. We use phthalates and bisphenol A-known industrial chemicals-and organophosphate insecticides as case studies to show exposure trends to these chemicals and their replacements (e.g., other phthalates, non-phthalate plasticizers, various bisphenols, pyrethroid insecticides) among the US general population. We compare US trends to national trends from Canada and Germany. Exposure to the original compounds is still prevalent among these general populations, but exposures to alternative chemicals may be increasing.

  6. The How and Why of Chemical Reactions

    ERIC Educational Resources Information Center

    Schubert, Leo

    1970-01-01

    Presents a discussion of some of the fundamental concepts in thermodynamics and quantum mechanics including entropy, enthalpy, free energy, the partition function, chemical kinetics, transition state theory, the making and breaking of chemical bonds, electronegativity, ion sizes, intermolecular energies and of their role in explaining the nature…

  7. FACILITATED CHEMICAL SYNTHESIS UNDER ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    The chemical research in the late 1990's witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into the atmo...

  8. The How and Why of Chemical Reactions

    ERIC Educational Resources Information Center

    Schubert, Leo

    1970-01-01

    Presents a discussion of some of the fundamental concepts in thermodynamics and quantum mechanics including entropy, enthalpy, free energy, the partition function, chemical kinetics, transition state theory, the making and breaking of chemical bonds, electronegativity, ion sizes, intermolecular energies and of their role in explaining the nature…

  9. FACILITATED CHEMICAL SYNTHESIS UNDER ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    The chemical research in the late 1990's witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into the atmo...

  10. Chemical Reaction Experiment for the Undergraduate Laboratory.

    ERIC Educational Resources Information Center

    Kwon, K. C.; And Others

    1987-01-01

    Provides an overview of an experiment on reaction kinetics of the anthracene-hydrogen system. Includes a description of the laboratory equipment, procedures, and data analysis requirements. Points out the advantages of the recommended technique. (ML)

  11. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.; Levin, Eugene

    1993-01-01

    A new global potential energy surface (PES) is being generated for O(P-3) + H2 yields OH + H. This surface is being fit using the rotated Morse oscillator method, which was used to fit the previous POL-CI surface. The new surface is expected to be more accurate and also includes a much more complete sampling of bent geometries. A new study has been undertaken of the reaction N + O2 yields NO + O. The new studies have focused on the region of the surface near a possible minimum corresponding to the peroxy form of NOO. A large portion of the PES for this second reaction has been mapped out. Since state to state cross sections for the reaction are important in the chemistry of high temperature air, these studies will probably be extended to permit generation of a new global potential for reaction.

  12. Kinetics of Chemical Reactions in Flames

    NASA Technical Reports Server (NTRS)

    Zeldovich, Y.; Semenov, N.

    1946-01-01

    In part I of the paper the theory of flame propagation is developed along the lines followed by Frank-Kamenetsky and one of the writers. The development of chain processes in flames is considered. A basis is given for the application of the method of stationary concentrations to reactions in flames; reactions with branching chains are analyzed. The case of a diffusion coefficient different from the coefficient of temperature conductivity is considered.

  13. A Method for Generating Oxygen from Consumer Chemicals

    NASA Astrophysics Data System (ADS)

    Wright, Stephen W.

    2003-10-01

    The rapidly accelerated combustion of wood, paper, carbon, a candle, and steel wool in oxygen gas is presented. The oxygen gas is generated as needed in the bottles used for the demonstration using chemicals readily available on the retail market: liquid chlorine bleach and 3% hydrogen peroxide.

  14. Thin liquid films with time-dependent chemical reactions sheared by an ambient gas flow

    NASA Astrophysics Data System (ADS)

    Bender, Achim; Stephan, Peter; Gambaryan-Roisman, Tatiana

    2017-08-01

    Chemical reactions in thin liquid films are found in many industrial applications, e.g., in combustion chambers of internal combustion engines where a fuel film can develop on pistons or cylinder walls. The reactions within the film and the turbulent outer gas flow influence film stability and lead to film breakup, which in turn can lead to deposit formation. In this work we examine the evolution and stability of a thin liquid film in the presence of a first-order chemical reaction and under the influence of a turbulent gas flow. Long-wave theory with a double perturbation analysis is used to reduce the complexity of the problem and obtain an evolution equation for the film thickness. The chemical reaction is assumed to be slow compared to film evolution and the amount of reactant in the film is limited, which means that the reaction rate decreases with time as the reactant is consumed. A linear stability analysis is performed to identify the influence of reaction parameters, material properties, and environmental conditions on the film stability limits. Results indicate that exothermic reactions have a stabilizing effect whereas endothermic reactions destabilize the film and can lead to rupture. It is shown that an initially unstable film can become stable with time as the reaction rate decreases. The shearing of the film by the external gas flow leads to the appearance of traveling waves. The shear stress magnitude has a nonmonotonic influence on film stability.

  15. Phthalate exposure through food and consumers' risk perception of chemicals in food.

    PubMed

    Dickson-Spillmann, Maria; Siegrist, Michael; Keller, Carmen; Wormuth, Matthias

    2009-08-01

    Phthalates have been detected in various types of retail foods. Consumers' exposure to phthalates is common. Consumers are concerned about chemicals in food. Our aim was to investigate the relationships between consumers' exposure to phthalates through food, consumers' interest in a natural and healthy diet, risk perception of food chemicals, and consumers' diet patterns. We collected data through a mail survey in the adult Swiss-German population (N = 1,200). We modeled exposure to di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), benzyl butyl phthalate (BBP), and diethyl phthalate (DEP) based on a food frequency questionnaire and phthalate concentrations reported from food surveys. Using rating scales, we assessed risk perceptions of chemicals in food and interest in a natural and healthy diet. Higher risk perceptions and higher natural and healthy diet interest were associated with higher daily doses of DEHP, BBP, and DEP. No health risk from phthalates in food was identified for the vast majority of the population. Four consumers' diet clusters were discerned, with differences in phthalate exposure, risk perceptions, and interest in a natural and healthy diet. This study shows that even those consumers who express strong interest in natural food and low acceptance of food chemicals, and who try to make respective food choices, are exposed to contaminants such as phthalates.

  16. Toward crustacean without chemicals: a descriptive analysis of consumer response using price comparisons.

    PubMed

    Okpala, Charles Odilichukwu R; Bono, Gioacchino; Pipitone, Vito; Vitale, Sergio; Cannizzaro, Leonardo

    2016-01-01

    To date, there seems to be limited-to-zero emphasis about how consumers perceive crustacean products subject to either chemical and or non-chemical preservative treatments. In addition, studies that investigated price comparisons of crustacean products subject to either chemical or chemical-free preservative methods seem unreported. This study focused on providing some foundational knowledge about how consumers perceive traditionally harvested crustaceans that are either chemical-treated and or free of chemicals, incorporating price comparisons using a descriptive approach. The study design employed a questionnaire approach via interview using a computer-assisted telephone system and sampled 1,540 participants across five key locations in Italy. To actualize consumer sensitivity, 'price' was the focus given its crucial role as a consumption barrier. Prior to this, variables such as demographic characteristics of participants, frequency of purchasing, quality attributes/factors that limit the consumption of crustaceans were equally considered. By price comparisons, consumers are likely to favor chemical-free (modified atmosphere packaging) crustacean products amid a price increase of up to 15%. But, a further price increase such as by 25% could markedly damage consumers' feelings, which might lead to a considerable number opting out in favor of either chemical-treated or other seafood products. Comparing locations, the studied variables showed no statistical differences (p>0.05). On the contrary, the response weightings fluctuated across the studied categories. Both response weightings and coefficient of variation helped reveal more about how responses deviated per variable categories. This study has revealed some foundational knowledge about how consumers perceive traditionally harvested crustaceans that were either chemical-treated or subject to chemical-free preservative up to price sensitivity using Italy as a reference case, which is applicable to other parts

  17. Chemical tailoring of teicoplanin with site-selective reactions.

    PubMed

    Pathak, Tejas P; Miller, Scott J

    2013-06-05

    Semisynthesis of natural product derivatives combines the power of fermentation with orthogonal chemical reactions. Yet, chemical modification of complex structures represents an unmet challenge, as poor selectivity often undermines efficiency. The complex antibiotic teicoplanin eradicates bacterial infections. However, as resistance emerges, the demand for improved analogues grows. We have discovered chemical reactions that achieve site-selective alteration of teicoplanin. Utilizing peptide-based additives that alter reaction selectivities, certain bromo-teicoplanins are accessible. These new compounds are also scaffolds for selective cross-coupling reactions, enabling further molecular diversification. These studies enable two-step access to glycopeptide analogues not available through either biosynthesis or rapid total chemical synthesis alone. The new compounds exhibit a spectrum of activities, revealing that selective chemical alteration of teicoplanin may lead to analogues with attenuated or enhanced antibacterial properties, in particular against vancomycin- and teicoplanin-resistant strains.

  18. An autonomous organic reaction search engine for chemical reactivity

    PubMed Central

    Dragone, Vincenza; Sans, Victor; Henson, Alon B.; Granda, Jaroslaw M.; Cronin, Leroy

    2017-01-01

    The exploration of chemical space for new reactivity, reactions and molecules is limited by the need for separate work-up-separation steps searching for molecules rather than reactivity. Herein we present a system that can autonomously evaluate chemical reactivity within a network of 64 possible reaction combinations and aims for new reactivity, rather than a predefined set of targets. The robotic system combines chemical handling, in-line spectroscopy and real-time feedback and analysis with an algorithm that is able to distinguish and select the most reactive pathways, generating a reaction selection index (RSI) without need for separate work-up or purification steps. This allows the automatic navigation of a chemical network, leading to previously unreported molecules while needing only to do a fraction of the total possible reactions without any prior knowledge of the chemistry. We show the RSI correlates with reactivity and is able to search chemical space using the most reactive pathways. PMID:28598440

  19. An autonomous organic reaction search engine for chemical reactivity

    NASA Astrophysics Data System (ADS)

    Dragone, Vincenza; Sans, Victor; Henson, Alon B.; Granda, Jaroslaw M.; Cronin, Leroy

    2017-06-01

    The exploration of chemical space for new reactivity, reactions and molecules is limited by the need for separate work-up-separation steps searching for molecules rather than reactivity. Herein we present a system that can autonomously evaluate chemical reactivity within a network of 64 possible reaction combinations and aims for new reactivity, rather than a predefined set of targets. The robotic system combines chemical handling, in-line spectroscopy and real-time feedback and analysis with an algorithm that is able to distinguish and select the most reactive pathways, generating a reaction selection index (RSI) without need for separate work-up or purification steps. This allows the automatic navigation of a chemical network, leading to previously unreported molecules while needing only to do a fraction of the total possible reactions without any prior knowledge of the chemistry. We show the RSI correlates with reactivity and is able to search chemical space using the most reactive pathways.

  20. An autonomous organic reaction search engine for chemical reactivity.

    PubMed

    Dragone, Vincenza; Sans, Victor; Henson, Alon B; Granda, Jaroslaw M; Cronin, Leroy

    2017-06-09

    The exploration of chemical space for new reactivity, reactions and molecules is limited by the need for separate work-up-separation steps searching for molecules rather than reactivity. Herein we present a system that can autonomously evaluate chemical reactivity within a network of 64 possible reaction combinations and aims for new reactivity, rather than a predefined set of targets. The robotic system combines chemical handling, in-line spectroscopy and real-time feedback and analysis with an algorithm that is able to distinguish and select the most reactive pathways, generating a reaction selection index (RSI) without need for separate work-up or purification steps. This allows the automatic navigation of a chemical network, leading to previously unreported molecules while needing only to do a fraction of the total possible reactions without any prior knowledge of the chemistry. We show the RSI correlates with reactivity and is able to search chemical space using the most reactive pathways.

  1. Consumers.

    PubMed

    Brophy, Lisa M; Roper, Catherine E; Hamilton, Bridget E; Tellez, Juan José; McSherry, Bernadette M

    2016-03-03

    Objective This paper examines the perspectives of consumers and their supporters regarding the use of seclusion and restraint in mental health settings.Methods Five focus groups for consumers and five focus groups for supporters were conducted in four Australian cities and in one rural location. The 66 participants were asked about strategies to reduce or eliminate the use of seclusion and restraint in mental health settings.Results All participants supported the reduction of the use of seclusion and restraint. Barriers to reducing these practices related to the environment, the effects of drug and alcohol issues, lack of a human rights focus and poor recognition of trauma, stigma and discrimination. Strategies for reducing or eliminating seclusion and restraint included workforce development, environmental and cultural changes.Conclusions Participants clearly identified that the status quo needs to change and conveyed urgency for action. Participants suggested that the involvement of supporters and a range of consumer roles are integral to reducing the use of seclusion and restraint. The findings support the current policy emphasis of working towards the elimination of these practices.What is known about the topic? Mental health policies across many jurisdictions support the reduction and elimination of restraint and seclusion. Evidence suggests those subjected to restraint and seclusion largely experience a range of harmful consequences. No studies focus on the views of supporters of consumers regarding the reduction and elimination of seclusion and restraint, whereas the views of consumers appear in a minority of international studies.What does this paper add? The research enabled an opportunity to hear from people who have been personally affected by and/or have lived experience of these coercive practices. Participants identified local reforms that can uphold the human rights of consumers. They suggested practices to increase accountability, peer support and

  2. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Heinemann, K.; Walch, Stephen P.

    1992-01-01

    The work on the NH + NO system which was described in the last progress report was written up and a draft of the manuscript is included in the appendix. The appendix also contains a draft of a manuscript on an Ar + H + H surface. New work which was completed in the last six months includes the following: (1) calculations on the (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO product channels in the CH3 + OH reaction; (2) calculations for the NH2 + O reaction; (3) calculations for the CH3 + O2 reaction; and (4) calculations for CH3O and the two decomposition channels--CH2OH and H + H2CO. Detailed descriptions of this work will be given in manuscripts; however, brief descriptions of the CH3 + OH and CH3 + O2 projects are given.

  3. Morphological changes of amphiphilic molecular assemblies induced by chemical reactions.

    PubMed

    Nakagawa, Koh M; Noguchi, Hiroshi

    2015-02-04

    Shape transformations of amphiphilic molecular assemblies induced by chemical reactions are studied using coarse-grained molecular simulations. A binding reaction between hydrophilic and hydrophobic molecules is considered. It is found that the reaction induces transformation of an oil droplet to a tubular vesicle via bicelles and vesicles with discoidal arms. The discoidal arms close into vesicles, which are subsequently fused into the tubular vesicle. Under the chemical reaction, the bicelle-to-vesicle transition occurs at smaller sizes than in the absence of the hydrophobic molecules. It is revealed that the enhancement of this transition is due to embedded hydrophobic particles that reduce the membrane bending rigidity.

  4. Non-equilibrium effects in high temperature chemical reactions

    NASA Technical Reports Server (NTRS)

    Johnson, Richard E.

    1987-01-01

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

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

    PubMed

    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.

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

    ERIC Educational Resources Information Center

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

    1998-01-01

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

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

    ERIC Educational Resources Information Center

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

    1998-01-01

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

  8. Mineralization of hazardous chemicals by heme reaction

    SciTech Connect

    Kang, G.; Jung, J.; Park, K.; Stevens, D.K.

    1995-12-31

    The catalytic degradation of pentachlorophenol contaminated soil by heme and hydrogen peroxide has been reported. Here we studied evidence for the mechanism and mineralization by the heme catalyzed reaction for hazardous organopollutants. Ferryl heme radical and non-radical ferryl heme were generated rapidly by the interaction of heme and hydrogen peroxide (H{sub 2}O{sub 2}). The activated heme radical could initiate the oxidation of 5-aminosalicylic acid (5-ASA). The reactions by heme with H{sub 2}O{sub 2} could support the redox cycling between the ferryl species of heme and 5-ASA as the mechanistic routes of the heme catalyzed reaction. Hazardous compounds such as pentachlorophenol, phenanthrene and benzota[a]pyrene were mineralized 20, 6, and 7%, respectively, with 30 mM heme and 1500 mM H{sub 2}O{sub 2} after 24 hr reaction. This catalyzed degradation of organopollutants could be used as a novel technology for hazardous waste remediation.

  9. Steric Control of Complex Chemical Reactions - 1

    DTIC Science & Technology

    2011-12-26

    their contrasting behaviors upon vibrational and translational excitations can serve as benchmark for gaining deeper insights into polyatomic reaction...equipped with a uniquely designed ion velocity map imaging detector capable of measuring the product pair correlation. The ultrafast femtosecond laser...From A + BC to Polyatomic Systems” K. Liu, Adv. in Chem. Phys. 149, (in press). Invited Review Invited talks at Conferences (* denoting

  10. Femtosecond Diffraction and Spectroscopy of Chemical Reactions

    DTIC Science & Technology

    2008-03-31

    bifurcation into phytical and chemical channels, redefines structural dynamics of the energy landscape in radiationless processes. Paper 6. In this... acid bilayers. In 4DUEM we are now able, using timed single-electron packets, to image nano-to-micro scale structures of materials and biological

  11. Experiments on Rate of Chemical Reactions.

    ERIC Educational Resources Information Center

    United Nations Educational, Scientific, and Cultural Organization, Bangkok (Thailand).

    This laboratory manual, part of a series of instruction books on basic experimental chemistry, is designed to provide the secondary school students of developing countries in Asia with laboratory experiences that bring out the fundamental concepts and ideas of chemical kinetics. Taking into consideration the possibility of limited facilities of…

  12. Toward crustacean without chemicals: a descriptive analysis of consumer response using price comparisons

    PubMed Central

    Okpala, Charles Odilichukwu R.; Bono, Gioacchino; Pipitone, Vito; Vitale, Sergio; Cannizzaro, Leonardo

    2016-01-01

    Background To date, there seems to be limited-to-zero emphasis about how consumers perceive crustacean products subject to either chemical and or non-chemical preservative treatments. In addition, studies that investigated price comparisons of crustacean products subject to either chemical or chemical-free preservative methods seem unreported. Objective This study focused on providing some foundational knowledge about how consumers perceive traditionally harvested crustaceans that are either chemical-treated and or free of chemicals, incorporating price comparisons using a descriptive approach. Design The study design employed a questionnaire approach via interview using a computer-assisted telephone system and sampled 1,540 participants across five key locations in Italy. To actualize consumer sensitivity, ‘price’ was the focus given its crucial role as a consumption barrier. Prior to this, variables such as demographic characteristics of participants, frequency of purchasing, quality attributes/factors that limit the consumption of crustaceans were equally considered. Results By price comparisons, consumers are likely to favor chemical-free (modified atmosphere packaging) crustacean products amid a price increase of up to 15%. But, a further price increase such as by 25% could markedly damage consumers’ feelings, which might lead to a considerable number opting out in favor of either chemical-treated or other seafood products. Comparing locations, the studied variables showed no statistical differences (p>0.05). On the contrary, the response weightings fluctuated across the studied categories. Both response weightings and coefficient of variation helped reveal more about how responses deviated per variable categories. Conclusions This study has revealed some foundational knowledge about how consumers perceive traditionally harvested crustaceans that were either chemical-treated or subject to chemical-free preservative up to price sensitivity using Italy as

  13. Force-activated reactivity switch in a bimolecular chemical reaction.

    PubMed

    Garcia-Manyes, Sergi; Liang, Jian; Szoszkiewicz, Robert; Kuo, Tzu-Ling; Fernández, Julio M

    2009-06-01

    The effect of mechanical force on the free-energy surface that governs a chemical reaction is largely unknown. The combination of protein engineering with single-molecule force-clamp spectroscopy allows us to study the influence of mechanical force on the rate at which a protein disulfide bond is reduced by nucleophiles in a bimolecular substitution reaction (S(N)2). We found that cleavage of a protein disulfide bond by hydroxide anions exhibits an abrupt reactivity 'switch' at ∼500 pN, after which the accelerating effect of force on the rate of an S(N)2 chemical reaction greatly diminishes. We propose that an abrupt force-induced conformational change of the protein disulfide bond shifts its ground state, drastically changing its reactivity in S(N)2 chemical reactions. Our experiments directly demonstrate the action of a force-activated switch in the chemical reactivity of a single molecule.

  14. 29. NORTHWEST VIEW OF BOILER FEEDWATER CHEMICAL REACTION TANKS, WITH ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    29. NORTHWEST VIEW OF BOILER FEEDWATER CHEMICAL REACTION TANKS, WITH FORMER GENERAL OFFICE BUILDING IN BACKGROUND. - U.S. Steel Duquesne Works, Fuel & Utilities Plant, Along Monongahela River, Duquesne, Allegheny County, PA

  15. Computed Potential Energy Surfaces for Chemical Reactions

    NASA Technical Reports Server (NTRS)

    Heinemann, K.; Walch, Stephen P.; Levin, Eugene

    1993-01-01

    A manuscript describing the calculations on the (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO product channels in the CH3 + OH reaction, which were described in the last progress report, has been accepted for publication in J. Chem. Phys., and a copy of the manuscript is included in the appendix. The production of (1)CH2 in this reaction is important in hydrocarbon combustion since (1)CH2 is highly reactive and would be expected to insert into N2, possibly leading to a new source for prompt NO(x) (vide infra). During the last six months new calculations have been carried out for the NH2 + NO system, which is important in the thermal de-NO(x) process.

  16. Nucleic Acid Templated Reactions for Chemical Biology.

    PubMed

    Di Pisa, Margherita; Seitz, Oliver

    2017-06-21

    Nucleic acid directed bioorthogonal reactions offer the fascinating opportunity to unveil and redirect a plethora of intracellular mechanisms. Nano- to picomolar amounts of specific RNA molecules serve as templates and catalyze the selective formation of molecules that 1) exert biological effects, or 2) provide measurable signals for RNA detection. Turnover of reactants on the template is a valuable asset when concentrations of RNA templates are low. The idea is to use RNA-templated reactions to fully control the biodistribution of drugs and to push the detection limits of DNA or RNA analytes to extraordinary sensitivities. Herein we review recent and instructive examples of conditional synthesis or release of compounds for in cellulo protein interference and intracellular nucleic acid imaging. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

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

    USGS Publications Warehouse

    Grove, David B.; Stollenwerk, Kenneth G.

    1987-01-01

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

  18. Colloidal Assemblies Effect on Chemical Reactions.

    DTIC Science & Technology

    1986-07-01

    MICROEMULSIONS - SURFACTANTS - OXIDATION - PHOTOCATALYSIS - DEGRADATION - HALOAROMATIC COMPOUNDS - REACTION MECHANISM - KINETICS 20. ABmT’AcT (cthwe - 0...phase model accounting for the observed rate constants was proposed. The complexing and extracting properties of a functionalized surfactant family...micelles were studied. The proper conditions for an efficient iron(III) complexation and extraction were determined. SECURY C - fa ;c --r 2 - SECURITY

  19. Chemical reactions of organic compounds on clay surfaces.

    PubMed Central

    Soma, Y; Soma, M

    1989-01-01

    Chemical reactions of organic compounds including pesticides at the interlayer and exterior surfaces of clay minerals and with soil organic matter are reviewed. Representative reactions under moderate conditions possibly occurring in natural soils are described. Attempts have been made to clarify the importance of the chemical nature of molecules, their structures and their functional groups, and the Brönsted or Lewis acidity of clay minerals. PMID:2533556

  20. Coherent Radiative Control of Chemical Reactions

    DTIC Science & Technology

    1992-01-01

    effective were determined and successful control was displayed using a model of Stilbene isomerization. F. Control over Chemically Distinct Products...than, the stilbene molecule for which Si(t>to) = Ia(to)Il14ru-(I’ f = 1, II11 (3) there is a vast array of data available art for which...mechanical o calculation of ground and first excited electronic potential surfaces _o for trans- and cis- stilbene . To minimize computational cost we 0

  1. Phase Waves in Oscillatory Chemical Reactions.

    DTIC Science & Technology

    number of waves emitted from a center of heterogeneous catalysis , the rate of wave emission. the lifetime of each wave, the asymptotic wave pattern, the...A theory is presented for the effect of heterogeneity on an oscillatory chemically reactive system in a stable limit cycle such as in heterogeneous ... catalysis . A perturbation technique is developed free of secular behavior for the solution of the non-linear partial differential equations. The

  2. Modelling of chemical reactions in plasma

    NASA Astrophysics Data System (ADS)

    Aktaev, N. E.; Remnev, G. E.; Yalovets, A. P.

    2017-01-01

    The paper is devoted to theoretical investigation of interaction of pulsed high current electron beam with gas substance. As a result of the interaction the formation of chemical active plasma can be observed. One of the key parameter for theoretical analyze of the process is the electron distribution function. Within the framework of the Boltzmann approach we obtained the dynamical equation for electron distribution function depending on the electron energy, coordinate and time.

  3. Quantifying chemical reactions by using mixing analysis.

    PubMed

    Jurado, Anna; Vázquez-Suñé, Enric; Carrera, Jesús; Tubau, Isabel; Pujades, Estanislao

    2015-01-01

    This work is motivated by a sound understanding of the chemical processes that affect the organic pollutants in an urban aquifer. We propose an approach to quantify such processes using mixing calculations. The methodology consists of the following steps: (1) identification of the recharge sources (end-members) and selection of the species (conservative and non-conservative) to be used, (2) identification of the chemical processes and (3) evaluation of mixing ratios including the chemical processes. This methodology has been applied in the Besòs River Delta (NE Barcelona, Spain), where the River Besòs is the main aquifer recharge source. A total number of 51 groundwater samples were collected from July 2007 to May 2010 during four field campaigns. Three river end-members were necessary to explain the temporal variability of the River Besòs: one river end-member is from the wet periods (W1) and two are from dry periods (D1 and D2). This methodology has proved to be useful not only to compute the mixing ratios but also to quantify processes such as calcite and magnesite dissolution, aerobic respiration and denitrification undergone at each observation point.

  4. Quantum chemical approach to estimating the thermodynamics of metabolic reactions.

    PubMed

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

    2014-11-12

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed Central

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

    2014-01-01

    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. PMID:25387603

  7. Accelerated Chemical Reactions and Organic Synthesis in Leidenfrost Droplets.

    PubMed

    Bain, Ryan M; Pulliam, Christopher J; Thery, Fabien; Cooks, R Graham

    2016-08-22

    Leidenfrost levitated droplets can be used to accelerate chemical reactions in processes that appear similar to reaction acceleration in charged microdroplets produced by electrospray ionization. Reaction acceleration in Leidenfrost droplets is demonstrated for a base-catalyzed Claisen-Schmidt condensation, hydrazone formation from precharged and neutral ketones, and for the Katritzky pyrylium into pyridinium conversion under various reaction conditions. Comparisons with bulk reactions gave intermediate acceleration factors (2-50). By keeping the volume of the Leidenfrost droplets constant, it was shown that interfacial effects contribute to acceleration; this was confirmed by decreased reaction rates in the presence of a surfactant. The ability to multiplex Leidenfrost microreactors, to extract product into an immiscible solvent during reaction, and to use Leidenfrost droplets as reaction vessels to synthesize milligram quantities of product is also demonstrated. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Plasmonic smart dust for probing local chemical reactions.

    PubMed

    Tittl, Andreas; Yin, Xinghui; Giessen, Harald; Tian, Xiang-Dong; Tian, Zhong-Qun; Kremers, Christian; Chigrin, Dmitry N; Liu, Na

    2013-04-10

    Locally probing chemical reactions or catalytic processes on surfaces under realistic reaction conditions has remained one of the main challenges in materials science and heterogeneous catalysis. Where conventional surface interrogation techniques usually require high-vacuum conditions or ensemble average measurements, plasmonic nanoparticles excel in extreme light focusing and can produce highly confined electromagnetic fields in subwavelength volumes without the need for complex near-field microscopes. Here, we demonstrate an all-optical probing technique based on plasmonic smart dust for monitoring local chemical reactions in real time. The silica shell-isolated gold nanoparticles that form the smart dust can work as strong light concentrators and optically report subtle environmental changes at their pinning sites on the probed surface during reaction processes. As a model system, we investigate the hydrogen dissociation and subsequent uptake trajectory in palladium with both "dust-on-film" and "film-on-dust" platforms. Using time-resolved single particle measurements, we demonstrate that our technique can in situ encode chemical reaction information as optical signals for a variety of surface morphologies. The presented technique offers a unique scheme for real-time, label-free, and high-resolution probing of local reaction kinetics in a plethora of important chemical reactions on surfaces, paving the way toward the development of inexpensive and high-output reaction sensors for real-world applications.

  9. Is the simplest chemical reaction really so simple?

    PubMed

    Jankunas, Justin; Sneha, Mahima; Zare, Richard N; Bouakline, Foudhil; Althorpe, Stuart C; Herráez-Aguilar, Diego; Aoiz, F Javier

    2014-01-07

    Modern computational methods have become so powerful for predicting the outcome for the H + H2 → H2 + H bimolecular exchange reaction that it might seem further experiments are not needed. Nevertheless, experiments have led the way to cause theorists to look more deeply into this simplest of all chemical reactions. The findings are less simple.

  10. Is the simplest chemical reaction really so simple?

    PubMed Central

    Jankunas, Justin; Sneha, Mahima; Zare, Richard N.; Bouakline, Foudhil; Althorpe, Stuart C.; Herráez-Aguilar, Diego; Aoiz, F. Javier

    2014-01-01

    Modern computational methods have become so powerful for predicting the outcome for the H + H2 → H2 + H bimolecular exchange reaction that it might seem further experiments are not needed. Nevertheless, experiments have led the way to cause theorists to look more deeply into this simplest of all chemical reactions. The findings are less simple. PMID:24367084

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

    ERIC Educational Resources Information Center

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

    2011-01-01

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

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

    ERIC Educational Resources Information Center

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

    2011-01-01

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

  13. Chemical reactions driven by concentrated solar energy

    NASA Astrophysics Data System (ADS)

    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.

  14. Design and development of computer-aided chemical systems: representation and balance of inorganic chemical reactions

    PubMed

    Ruiz; Martinez-Pedrajas; Gomez-Nieto

    2000-05-01

    A model for the tracking of inorganic chemical reactions is proposed. Designed to acquire, process, and solve a great number of inorganic reactions, this model will hopefully contribute to the development of powerful computer-aided chemistry teaching systems for use within or without the environment of a virtual laboratory. Using full representation of an inorganic reaction to allow the extraction of chemical knowledge, incomplete reactions (where species are absent) may be completed by adding the necessary species, and reactions may be solved and balanced. Various types of reaction are classified, and a layer-based model is defined for the solution of different reaction types, establishing the basis for the construction of a system which, based on a wide set of production rules, is capable of solving an incomplete inorganic chemical reaction.

  15. Chemical Reactions in Turbulent Mixing Flows.

    DTIC Science & Technology

    1987-06-01

    soot particles are also often formed at the reaction interface, so the feasibility study was intenced to determine whether the two sources of particles...buoyancy effects (i.e. gravity is ipored). it can be shown that the disturbance eigentunction , satisfies the equation .0 .....o ... P I ./Pl...34 * (o’’o) *’t [a" U L" + I ’ U’/g ""* where ( )’ corresponds to d/dy. The equation * above reduces to the Rayleigh equation when the -4.0 d ensity is

  16. Laser cutting with chemical reaction assist

    SciTech Connect

    Gettemy, D.J.

    1991-04-08

    This invention is comprised of a method for cutting with a laser beam where an oxygen-hydrocarbon reaction is used to provide auxiliary energy to a metal workpiece to supplement the energy supplied by the laser. Oxygen is supplied to the laser focus point on the workpiece by a nozzle through which the laser beam also passes. A liquid hydrocarbon is supplied by coating the workpiece along the cutting path with the hydrocarbon prior to laser irradiation or by spraying a stream of hydrocarbon through a nozzle aimed at a point on the cutting path which is just ahead of the focus point during irradiation.

  17. Laser cutting with chemical reaction assist

    DOEpatents

    Gettemy, D.J.

    1992-11-17

    A method is described for cutting with a laser beam where an oxygen-hydrocarbon reaction is used to provide auxiliary energy to a metal workpiece to supplement the energy supplied by the laser. Oxygen is supplied to the laser focus point on the workpiece by a nozzle through which the laser beam also passes. A liquid hydrocarbon is supplied by coating the workpiece along the cutting path with the hydrocarbon prior to laser irradiation or by spraying a stream of hydrocarbon through a nozzle aimed at a point on the cutting path which is just ahead of the focus point during irradiation. 1 figure.

  18. Laser cutting with chemical reaction assist

    DOEpatents

    Gettemy, Donald J.

    1992-01-01

    A method for cutting with a laser beam where an oxygen-hydrocarbon reaction is used to provide auxiliary energy to a metal workpiece to supplement the energy supplied by the laser. Oxygen is supplied to the laser focus point on the workpiece by a nozzle through which the laser beam also passes. A liquid hydrocarbon is supplied by coating the workpiece along the cutting path with the hydrocarbon prior to laser irradiation or by spraying a stream of hydrocarbon through a nozzle aimed at a point on the cutting path which is just ahead of the focus point during irradiation.

  19. Do Health Professionals have Positive Perception Towards Consumer Reporting of Adverse Drug Reactions?

    PubMed

    Alshakka, Mohammed Ahmed; Ibrahim, Mohamed Izham Mohamed; Hassali, Mohamed Azmi Ahmad

    2013-10-01

    The aim of this study was to evaluate the perceptions of general practitioners (GPs) and community pharmacists (CPs) in Penang, Malaysia, towards consumer reporting of Adverse Drug Reactions (ADRs). A cross-sectional mail survey was adopted for the performance of the study. Survey questionnaires were sent to 192 CPs and 400 GPs in the state of Penang, Malaysia. Reminders were sent to all the non-respondents after 3 weeks of the initial mailing. Data which were collected from the questionnaires were analyzed by using the Statistical Package for Social Science (SPSS), version 15. The Chi-square test was used to determine as to whether there was any significant difference between expected and observed frequencies at the alpha level of 0.05. Only 104 respondents (47 CPs and 57 GPs) returned the survey, with a response rate of 18.0%- a figure which could be considered to be low. This study indicated that GPs and CPs were aware about the importance and benefits of consumer reporting. A majority of them (88.0%) thought that consumer reporting would add more benefits to the existing pharmacovigilance program. Similarly, 97% of the respondents agreed that reporting of ADRs was necessary and 87.0% respondents had seen ADRs among their patients. However, 57 of them (6.0%), had not been aware that the national program in Malaysia allowed consumers to report ADRs. A majority of them (97.0%) agreed that consumers needed more education regarding ADR reporting. Most of them (84.0%) thought that consumers could not write valid reports which were similar to reports which were made by healthcare professionals (HCPs). A majority of the respondents (68.0%) had not heard about the consumer reporting program in Malaysia and half of them did not believe that consumer reporting could overcome under-reporting, which was the main problem of the national pharmacovigilance program in Malaysia. The GPs and CPs were aware about the importance and benefits of consumer reporting. Such reporting

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

    ERIC Educational Resources Information Center

    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…

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

    ERIC Educational Resources Information Center

    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…

  2. Modelling Chemical Reasoning to Predict and Invent Reactions.

    PubMed

    Segler, Marwin H S; Waller, Mark P

    2016-11-11

    The ability to reason beyond established knowledge allows organic chemists to solve synthetic problems and invent novel transformations. Herein, we propose a model that 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. The 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 achieved in a sub-second time frame, the model can be used as a high-throughput generator of reaction hypotheses for reaction discovery.

  3. Elementary reaction modeling of solid oxide electrolysis cells: Main zones for heterogeneous chemical/electrochemical reactions

    NASA Astrophysics Data System (ADS)

    Li, Wenying; Shi, Yixiang; Luo, Yu; Cai, Ningsheng

    2015-01-01

    A theoretical model of solid oxide electrolysis cells considering the heterogeneous elementary reactions, electrochemical reactions and the transport process of mass and charge is applied to study the relative performance of H2O electrolysis, CO2 electrolysis and CO2/H2O co-electrolysis and the competitive behavior of heterogeneous chemical and electrochemical reactions. In cathode, heterogeneous chemical reactions exist near the outside surface and the electrochemical reactions occur near the electrolyte. According to the mathematical analysis, the mass transfer flux D ∇c determines the main zone size of heterogeneous chemical reactions, while the charge transfer flux σ ∇V determines the other one. When the zone size of heterogeneous chemistry is enlarged, more CO2 could react through heterogeneous chemical pathway, and polarization curves of CO2/H2O co-electrolysis could be prone to H2O electrolysis. Meanwhile, when the zone size of electrochemistry is enlarged, more CO2 could react through electrochemical pathway, and polarization curves of CO2/H2O co-electrolysis could be prone to CO2 electrolysis. The relative polarization curves, the ratio of CO2 participating in electrolysis and heterogeneous chemical reactions, the mass and charge transfer flux and heterogeneous chemical/electrochemical reaction main zones are simulated to study the effects of cathode material characteristics (porosity, particle diameter and ionic conductivity) and operating conditions (gas composition and temperature).

  4. Chemical reactions on solid surfaces using molecular beam techniques

    NASA Astrophysics Data System (ADS)

    Palmer, R. L.

    1980-07-01

    Thermal energy molecular beams have been used to study chemical interactions with metal surfaces. Chemisorption of simple molecules such as H2, O2, CH4, C2Hx and CO was investigated on single and polycrystalline surfaces of Pt, Ni, Co, and Ag. Kinetic parameters and reaction mechanisms were determined for model catalytic reactions including CO and C2Hx oxidation and methanation from H2/CO mixtures. Chemical reactions of NOx with CO and D2 on Pt(111) and other surfaces have been surveyed and the kinetics of NO and O2 chemisorption have been measured. The theory of adsorption/desorption kinetics is reviewed and certain deficiencies identified.

  5. Chemical memory reactions induced bursting dynamics in gene expression.

    PubMed

    Tian, Tianhai

    2013-01-01

    Memory is a ubiquitous phenomenon in biological systems in which the present system state is not entirely determined by the current conditions but also depends on the time evolutionary path of the system. Specifically, many memorial phenomena are characterized by chemical memory reactions that may fire under particular system conditions. These conditional chemical reactions contradict to the extant stochastic approaches for modeling chemical kinetics and have increasingly posed significant challenges to mathematical modeling and computer simulation. To tackle the challenge, I proposed a novel theory consisting of the memory chemical master equations and memory stochastic simulation algorithm. A stochastic model for single-gene expression was proposed to illustrate the key function of memory reactions in inducing bursting dynamics of gene expression that has been observed in experiments recently. The importance of memory reactions has been further validated by the stochastic model of the p53-MDM2 core module. Simulations showed that memory reactions is a major mechanism for realizing both sustained oscillations of p53 protein numbers in single cells and damped oscillations over a population of cells. These successful applications of the memory modeling framework suggested that this innovative theory is an effective and powerful tool to study memory process and conditional chemical reactions in a wide range of complex biological systems.

  6. Exact stochastic simulation of coupled chemical reactions with delays

    NASA Astrophysics Data System (ADS)

    Cai, Xiaodong

    2007-03-01

    Gillespie's exact stochastic simulation algorithm (SSA) [J. Phys. Chem. 81, 2350 (1977)] has been widely used to simulate the stochastic dynamics of chemically reacting systems. In this algorithm, it is assumed that all reactions occur instantly. While this is true in many cases, it is also possible that some chemical reactions, such as gene transcription and translation in living cells, take certain time to finish after they are initiated. Thus, the product of such reactions will emerge after certain delays. Apparently, Gillespie's SSA is not an exact algorithm for chemical reaction systems with delays. In this paper, the author develops an exact SSA for chemical reaction systems with delays, based upon the same fundamental premise of stochastic kinetics used by Gillespie in the development of his SSA. He then shows that an algorithm modified from Gillespie's SSA by Barrio et al. [PLOS Comput. Biol. 2, 1017 (2006)] is also an exact SSA for chemical reaction systems with delays, but it needs to generate more random variables than the author's algorithm.

  7. Chemical kinetic reaction mechanism for the combustion of propane

    NASA Technical Reports Server (NTRS)

    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. Direct-to-consumer (DTC) antidepressant advertising and consumer misperceptions about the chemical imbalance theory of depression: the moderating role of skepticism.

    PubMed

    Park, Jin Seong; Ahn, Ho-Young Anthony

    2013-01-01

    Based on a survey with members of an online consumer panel (N= 699), this study revealed that: (a) a substantial percentage of consumers held misperceptions about the chemical imbalance theory of depression; (b) personal and interpersonal experiences with depression positively related to such misperceptions; (c) overall, exposure to direct-to-consumer (DTC) antidepressant advertising did not significantly relate to misperceptions; and (d) DTC exposure magnified misperceptions when consumers were highly trustful of DTC advertising, whereas exposure diluted misperceptions when consumers were highly skeptical. Theoretical and practical implications of the research are discussed, especially in light of the social responsibility of DTC advertising.

  9. Single-molecule chemical reaction reveals molecular reaction kinetics and dynamics.

    PubMed

    Zhang, Yuwei; Song, Ping; Fu, Qiang; Ruan, Mingbo; Xu, Weilin

    2014-06-25

    Understanding the microscopic elementary process of chemical reactions, especially in condensed phase, is highly desirable for improvement of efficiencies in industrial chemical processes. Here we show an approach to gaining new insights into elementary reactions in condensed phase by combining quantum chemical calculations with a single-molecule analysis. Elementary chemical reactions in liquid-phase, revealed from quantum chemical calculations, are studied by tracking the fluorescence of single dye molecules undergoing a reversible redox process. Statistical analyses of single-molecule trajectories reveal molecular reaction kinetics and dynamics of elementary reactions. The reactivity dynamic fluctuations of single molecules are evidenced and probably arise from either or both of the low-frequency approach of the molecule to the internal surface of the SiO2 nanosphere or the molecule diffusion-induced memory effect. This new approach could be applied to other chemical reactions in liquid phase to gain more insight into their molecular reaction kinetics and the dynamics of elementary steps.

  10. ReactionMap: an efficient atom-mapping algorithm for chemical reactions.

    PubMed

    Fooshee, David; Andronico, Alessio; Baldi, Pierre

    2013-11-25

    Large databases of chemical reactions provide new data-mining opportunities and challenges. Key challenges result from the imperfect quality of the data and the fact that many of these reactions are not properly balanced or atom-mapped. Here, we describe ReactionMap, an efficient atom-mapping algorithm. Our approach uses a combination of maximum common chemical subgraph search and minimization of an assignment cost function derived empirically from training data. We use a set of over 259,000 balanced atom-mapped reactions from the SPRESI commercial database to train the system, and we validate it on random sets of 1000 and 17,996 reactions sampled from this pool. These large test sets represent a broad range of chemical reaction types, and ReactionMap correctly maps about 99% of the atoms and about 96% of the reactions, with a mean time per mapping of 2 s. Most correctly mapped reactions are mapped with high confidence. Mapping accuracy compares favorably with ChemAxon's AutoMapper, versions 5 and 6.1, and the DREAM Web tool. These approaches correctly map 60.7%, 86.5%, and 90.3% of the reactions, respectively, on the same data set. A ReactionMap server is available on the ChemDB Web portal at http://cdb.ics.uci.edu .

  11. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.

    1988-01-01

    The minimum energy path for the addition of a hydrogen atom to N2 is characterized in CASSCF/CCI calculations using the (4s3p2d1f/3s2p1d) basis set, with additional single point calculations at the stationary points of the potential energy surface using the (5s4p3d2f/4s3p2d) basis set. These calculations represent the most extensive set of ab initio calculations completed to date, yielding a zero point corrected barrier for HN2 dissociation of approx. 8.5 kcal mol/1. The lifetime of the HN2 species is estimated from the calculated geometries and energetics using both conventional Transition State Theory and a method which utilizes an Eckart barrier to compute one dimensional quantum mechanical tunneling effects. It is concluded that the lifetime of the HN2 species is very short, greatly limiting its role in both termolecular recombination reactions and combustion processes.

  12. Consumer products as sources of chemical exposures to children: case study of triclosan.

    PubMed

    Ginsberg, Gary L; Balk, Sophie J

    2016-04-01

    Consumer products are often overlooked as sources of children's exposures to toxic chemicals. Various regulatory bodies have developed lists of chemicals of concern that can be found in products contacted by children. However, this information has not been summarized for health practitioners. This review organizes such chemicals and products into four categories, with the antibacterial agent triclosan used to illustrate the potential risks to children from a common ingredient in consumer products. Biomonitoring, house dust, indoor air, and product testing document children's exposures to a wide variety of chemicals. An increasing number of epidemiology studies have shown associations between these exposures and health effects in children. Triclosan is an example of a chemical contained in high contact products (e.g., soaps, lotions, and toothpaste) not necessarily designed for children. Triclosan exposure in children has been associated with increased responsiveness to airway allergens, with it also capable of endocrine disruption. However, the utility and necessity of this chemical in consumer products has not been demonstrated in most cases. Triclosan and the other examples provided show that a changing marketplace with little regulatory oversight of chemical uses can lead to unanticipated exposures and potential health risks to children.

  13. Chemical Looping Combustion Reactions and Systems

    SciTech Connect

    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.

  14. Automatic NMR-Based Identification of Chemical Reaction Types in Mixtures of Co-Occurring Reactions

    PubMed Central

    Latino, Diogo A. R. S.; Aires-de-Sousa, João

    2014-01-01

    The combination of chemoinformatics approaches with NMR techniques and the increasing availability of data allow the resolution of problems far beyond the original application of NMR in structure elucidation/verification. The diversity of applications can range from process monitoring, metabolic profiling, authentication of products, to quality control. An application related to the automatic analysis of complex mixtures concerns mixtures of chemical reactions. We encoded mixtures of chemical reactions with the difference between the 1H NMR spectra of the products and the reactants. All the signals arising from all the reactants of the co-occurring reactions were taken together (a simulated spectrum of the mixture of reactants) and the same was done for products. The difference spectrum is taken as the representation of the mixture of chemical reactions. A data set of 181 chemical reactions was used, each reaction manually assigned to one of 6 types. From this dataset, we simulated mixtures where two reactions of different types would occur simultaneously. Automatic learning methods were trained to classify the reactions occurring in a mixture from the 1H NMR-based descriptor of the mixture. Unsupervised learning methods (self-organizing maps) produced a reasonable clustering of the mixtures by reaction type, and allowed the correct classification of 80% and 63% of the mixtures in two independent test sets of different similarity to the training set. With random forests (RF), the percentage of correct classifications was increased to 99% and 80% for the same test sets. The RF probability associated to the predictions yielded a robust indication of their reliability. This study demonstrates the possibility of applying machine learning methods to automatically identify types of co-occurring chemical reactions from NMR data. Using no explicit structural information about the reactions participants, reaction elucidation is performed without structure elucidation of the

  15. Automatic NMR-based identification of chemical reaction types in mixtures of co-occurring reactions.

    PubMed

    Latino, Diogo A R S; Aires-de-Sousa, João

    2014-01-01

    The combination of chemoinformatics approaches with NMR techniques and the increasing availability of data allow the resolution of problems far beyond the original application of NMR in structure elucidation/verification. The diversity of applications can range from process monitoring, metabolic profiling, authentication of products, to quality control. An application related to the automatic analysis of complex mixtures concerns mixtures of chemical reactions. We encoded mixtures of chemical reactions with the difference between the (1)H NMR spectra of the products and the reactants. All the signals arising from all the reactants of the co-occurring reactions were taken together (a simulated spectrum of the mixture of reactants) and the same was done for products. The difference spectrum is taken as the representation of the mixture of chemical reactions. A data set of 181 chemical reactions was used, each reaction manually assigned to one of 6 types. From this dataset, we simulated mixtures where two reactions of different types would occur simultaneously. Automatic learning methods were trained to classify the reactions occurring in a mixture from the (1)H NMR-based descriptor of the mixture. Unsupervised learning methods (self-organizing maps) produced a reasonable clustering of the mixtures by reaction type, and allowed the correct classification of 80% and 63% of the mixtures in two independent test sets of different similarity to the training set. With random forests (RF), the percentage of correct classifications was increased to 99% and 80% for the same test sets. The RF probability associated to the predictions yielded a robust indication of their reliability. This study demonstrates the possibility of applying machine learning methods to automatically identify types of co-occurring chemical reactions from NMR data. Using no explicit structural information about the reactions participants, reaction elucidation is performed without structure elucidation of

  16. Taking the plunge: chemical reaction dynamics in liquids.

    PubMed

    Orr-Ewing, Andrew J

    2017-07-06

    The dynamics of chemical reactions in liquid solutions are now amenable to direct study using ultrafast laser spectroscopy techniques and advances in computer simulation methods. The surrounding solvent affects the chemical reaction dynamics in numerous ways, which include: (i) formation of complexes between reactants and solvent molecules; (ii) modifications to transition state energies and structures relative to the reactants and products; (iii) coupling between the motions of the reacting molecules and the solvent modes, and exchange of energy; (iv) solvent caging of reactants and products; and (v) structural changes to the solvation shells in response to the changing chemical identity of the solutes, on timescales which may be slower than the reactive events. This article reviews progress in the study of bimolecular chemical reaction dynamics in solution, concentrating on reactions which occur on ground electronic states. It illustrates this progress with reference to recent experimental and computational studies, and considers how the various ways in which a solvent affects the chemical reaction dynamics can be unravelled. Implications are considered for research in fields such as mechanistic synthetic chemistry.

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

    PubMed

    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.

  18. Incorporation of Chemical Reactions into Building-scale Flow

    SciTech Connect

    Humphreys, T D; Jayaweera, T M; Lee, R L

    2003-10-30

    Many hazardous atmospheric releases involve chemical reactions that occur within a few kilometers of the source. Reactions with commonly occurring atmospheric compounds such as the OH radical, can transform and potentially neutralize original release compounds. Especially in these cases, accurately resolving flow around nearby structures and over surrounding topography can be critical to correctly predicting material dispersion, and thus, the extent of any hazard. Accurate prediction of material dispersion around complex geometries near the source of an atmospheric release requires high-resolution computation. Further complications arise if the compounds released undergo chemical reactions which could alter the extent of the main plume. The reaction products form dispersion patterns separate from, and often more complicated than, the original plume. Directions for future work include expanding the library of chemical reaction mechanisms, adding capabilities for aqueous and heterogeneous reactions, and integrating this model within larger-scale models. We plan that the larger-scale models will provide meteorological and chemical boundary conditions, and that this model could provide a source term in larger-scale models, both for momentum and for dispersed compounds.

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

    NASA Technical Reports Server (NTRS)

    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.

  20. Asymmetric chemical reactions by polarized quantum beams

    NASA Astrophysics Data System (ADS)

    Takahashi, Jun-Ichi; Kobayashi, Kensei

    One of the most attractive hypothesis for the origin of homochirality in terrestrial bio-organic compounds (L-amino acid and D-sugar dominant) is nominated as "Cosmic Scenario"; a chiral impulse from asymmetric excitation sources in space triggered asymmetric reactions on the surfaces of such space materials as meteorites or interstellar dusts prior to the existence of terrestrial life. 1) Effective asymmetric excitation sources in space are proposed as polarized quantum beams, such as circularly polarized light and spin polarized electrons. Circularly polarized light is emitted as synchrotron radiation from tightly captured electrons by intense magnetic field around neutron stars. In this case, either left-or right-handed polarized light can be observed depending on the direction of observation. On the other hand, spin polarized electrons is emitted as beta-ray in beta decay from radioactive nuclei or neutron fireballs in supernova explosion. 2) The spin of beta-ray electrons is longitudinally polarized due to parity non-conservation in the weak interaction. The helicity (the the projection of the spin onto the direction of kinetic momentum) of beta-ray electrons is universally negative (left-handed). For the purpose of verifying the asymmetric structure emergence in bio-organic compounds by polarized quantum beams, we are now carrying out laboratory simulations using circularly polarized light from synchrotron radiation facility or spin polarized electron beam from beta-ray radiation source. 3,4) The target samples are solid film or aqueous solution of racemic amino acids. 1) K.Kobayashi, K.Kaneko, J.Takahashi, Y.Takano, in Astrobiology: from simple molecules to primitive life; Ed. V.Basiuk; American Scientific Publisher: Valencia, 2008. 2) G.A.Gusev, T.Saito, V.A.Tsarev, A.V.Uryson, Origins Life Evol. Biosphere. 37, 259 (2007). 3) J.Takahashi, H.Shinojima, M.Seyama, Y.Ueno, T.Kaneko, K.Kobayashi, H.Mita, M.Adachi, M.Hosaka, M.Katoh, Int. J. Mol. Sci. 10, 3044

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Mining chemical reactions using neighborhood behavior and condensed graphs of reactions approaches.

    PubMed

    de Luca, Aurélie; Horvath, Dragos; Marcou, Gilles; Solov'ev, Vitaly; Varnek, Alexandre

    2012-09-24

    This work addresses the problem of similarity search and classification of chemical reactions using Neighborhood Behavior (NB) and Condensed Graphs of Reaction (CGR) approaches. The CGR formalism represents chemical reactions as a classical molecular graph with dynamic bonds, enabling descriptor calculations on this graph. Different types of the ISIDA fragment descriptors generated for CGRs in combination with two metrics--Tanimoto and Euclidean--were considered as chemical spaces, to serve for reaction dissimilarity scoring. The NB method has been used to select an optimal combination of descriptors which distinguish different types of chemical reactions in a database containing 8544 reactions of 9 classes. Relevance of NB analysis has been validated in generic (multiclass) similarity search and in clustering with Self-Organizing Maps (SOM). NB-compliant sets of descriptors were shown to display enhanced mapping propensities, allowing the construction of better Self-Organizing Maps and similarity searches (NB and classical similarity search criteria--AUC ROC--correlate at a level of 0.7). The analysis of the SOM clusters proved chemically meaningful CGR substructures representing specific reaction signatures.

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Structural simplification of chemical reaction networks in partial steady states.

    PubMed

    Madelaine, Guillaume; Lhoussaine, Cédric; Niehren, Joachim; Tonello, Elisa

    2016-11-01

    We study the structural simplification of chemical reaction networks with partial steady state semantics assuming that the concentrations of some but not all species are constant. We present a simplification rule that can eliminate intermediate species that are in partial steady state, while preserving the dynamics of all other species. Our simplification rule can be applied to general reaction networks with some but few restrictions on the possible kinetic laws. We can also simplify reaction networks subject to conservation laws. We prove that our simplification rule is correct when applied to a module of a reaction network, as long as the partial steady state is assumed with respect to the complete network. Michaelis-Menten's simplification rule for enzymatic reactions falls out as a special case. We have implemented an algorithm that applies our simplification rules repeatedly and applied it to reaction networks from systems biology. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  5. STM CONTROL OF CHEMICAL REACTIONS: Single-Molecule Synthesis

    NASA Astrophysics Data System (ADS)

    Hla, Saw-Wai; Rieder, Karl-Heinz

    2003-10-01

    The fascinating advances in single atom/molecule manipulation with a scanning tunneling microscope (STM) tip allow scientists to fabricate atomic-scale structures or to probe chemical and physical properties of matters at an atomic level. Owing to these advances, it has become possible for the basic chemical reaction steps, such as dissociation, diffusion, adsorption, readsorption, and bond-formation processes, to be performed by using the STM tip. Complete sequences of chemical reactions are able to induce at a single-molecule level. New molecules can be constructed from the basic molecular building blocks on a one-molecule-at-a-time basis by using a variety of STM manipulation schemes in a systematic step-by-step manner. These achievements open up entirely new opportunities in nanochemistry and nanochemical technology. In this review, various STM manipulation techniques useful in the single-molecule reaction process are reviewed, and their impact on the future of nanoscience and technology are discussed.

  6. Finding Chemical Reaction Paths with a Multilevel Preconditioning Protocol

    DOE PAGES

    Kale, Seyit; Sode, Olaseni; Weare, Jonathan; ...

    2014-11-07

    Finding transition paths for chemical reactions can be computationally costly owing to the level of quantum-chemical theory needed for accuracy. Here, we show that a multilevel preconditioning scheme that was recently introduced (Tempkin et al. J. Chem. Phys. 2014, 140, 184114) can be used to accelerate quantum-chemical string calculations. We demonstrate the method by finding minimum-energy paths for two well-characterized reactions: tautomerization of malonaldehyde and Claissen rearrangement of chorismate to prephanate. For these reactions, we show that preconditioning density functional theory (DFT) with a semiempirical method reduces the computational cost for reaching a converged path that is an optimum undermore » DFT by several fold. In conclusion, the approach also shows promise for free energy calculations when thermal noise can be controlled.« less

  7. Finding Chemical Reaction Paths with a Multilevel Preconditioning Protocol

    SciTech Connect

    Kale, Seyit; Sode, Olaseni; Weare, Jonathan; Dinner, Aaron R.

    2014-11-07

    Finding transition paths for chemical reactions can be computationally costly owing to the level of quantum-chemical theory needed for accuracy. Here, we show that a multilevel preconditioning scheme that was recently introduced (Tempkin et al. J. Chem. Phys. 2014, 140, 184114) can be used to accelerate quantum-chemical string calculations. We demonstrate the method by finding minimum-energy paths for two well-characterized reactions: tautomerization of malonaldehyde and Claissen rearrangement of chorismate to prephanate. For these reactions, we show that preconditioning density functional theory (DFT) with a semiempirical method reduces the computational cost for reaching a converged path that is an optimum under DFT by several fold. In conclusion, the approach also shows promise for free energy calculations when thermal noise can be controlled.

  8. Finding Chemical Reaction Paths with a Multilevel Preconditioning Protocol

    PubMed Central

    2015-01-01

    Finding transition paths for chemical reactions can be computationally costly owing to the level of quantum-chemical theory needed for accuracy. Here, we show that a multilevel preconditioning scheme that was recently introduced (Tempkin et al. J. Chem. Phys.2014, 140, 184114) can be used to accelerate quantum-chemical string calculations. We demonstrate the method by finding minimum-energy paths for two well-characterized reactions: tautomerization of malonaldehyde and Claissen rearrangement of chorismate to prephanate. For these reactions, we show that preconditioning density functional theory (DFT) with a semiempirical method reduces the computational cost for reaching a converged path that is an optimum under DFT by several fold. The approach also shows promise for free energy calculations when thermal noise can be controlled. PMID:25516726

  9. Advancing Consumer Product Composition and Chemical Use Information to Facilitate Risk-Based Decision Making

    EPA Science Inventory

    This presentation describes EPA efforts to collect, model, and measure publically available consumer product data for use in exposure assessment. The development of the ORD Chemicals and Products database will be described, as will machine-learning based models for predicting ch...

  10. Maximum probability reaction sequences in stochastic chemical kinetic systems.

    PubMed

    Salehi, Maryam; Perkins, Theodore J

    2010-01-01

    The detailed behavior of many molecular processes in the cell, such as protein folding, protein complex assembly, and gene regulation, transcription and translation, can often be accurately captured by stochastic chemical kinetic models. We investigate a novel computational problem involving these models - that of finding the most-probable sequence of reactions that connects two or more states of the system observed at different times. We describe an efficient method for computing the probability of a given reaction sequence, but argue that computing most-probable reaction sequences is EXPSPACE-hard. We develop exact (exhaustive) and approximate algorithms for finding most-probable reaction sequences. We evaluate these methods on test problems relating to a recently-proposed stochastic model of folding of the Trp-cage peptide. Our results provide new computational tools for analyzing stochastic chemical models, and demonstrate their utility in illuminating the behavior of real-world systems.

  11. Maximum Probability Reaction Sequences in Stochastic Chemical Kinetic Systems

    PubMed Central

    Salehi, Maryam; Perkins, Theodore J.

    2010-01-01

    The detailed behavior of many molecular processes in the cell, such as protein folding, protein complex assembly, and gene regulation, transcription and translation, can often be accurately captured by stochastic chemical kinetic models. We investigate a novel computational problem involving these models – that of finding the most-probable sequence of reactions that connects two or more states of the system observed at different times. We describe an efficient method for computing the probability of a given reaction sequence, but argue that computing most-probable reaction sequences is EXPSPACE-hard. We develop exact (exhaustive) and approximate algorithms for finding most-probable reaction sequences. We evaluate these methods on test problems relating to a recently-proposed stochastic model of folding of the Trp-cage peptide. Our results provide new computational tools for analyzing stochastic chemical models, and demonstrate their utility in illuminating the behavior of real-world systems. PMID:21629860

  12. ReactionPredictor: prediction of complex chemical reactions at the mechanistic level using machine learning.

    PubMed

    Kayala, Matthew A; Baldi, Pierre

    2012-10-22

    Proposing reasonable mechanisms and predicting the course of chemical reactions is important to the practice of organic chemistry. Approaches to reaction prediction have historically used obfuscating representations and manually encoded patterns or rules. Here we present ReactionPredictor, a machine learning approach to reaction prediction that models elementary, mechanistic reactions as interactions between approximate molecular orbitals (MOs). A training data set of productive reactions known to occur at reasonable rates and yields and verified by inclusion in the literature or textbooks is derived from an existing rule-based system and expanded upon with manual curation from graduate level textbooks. Using this training data set of complex polar, hypervalent, radical, and pericyclic reactions, a two-stage machine learning prediction framework is trained and validated. In the first stage, filtering models trained at the level of individual MOs are used to reduce the space of possible reactions to consider. In the second stage, ranking models over the filtered space of possible reactions are used to order the reactions such that the productive reactions are the top ranked. The resulting model, ReactionPredictor, perfectly ranks polar reactions 78.1% of the time and recovers all productive reactions 95.7% of the time when allowing for small numbers of errors. Pericyclic and radical reactions are perfectly ranked 85.8% and 77.0% of the time, respectively, rising to >93% recovery for both reaction types with a small number of allowed errors. Decisions about which of the polar, pericyclic, or radical reaction type ranking models to use can be made with >99% accuracy. Finally, for multistep reaction pathways, we implement the first mechanistic pathway predictor using constrained tree-search to discover a set of reasonable mechanistic steps from given reactants to given products. Webserver implementations of both the single step and pathway versions of Reaction

  13. Exploring consumer exposure pathways and patterns of use for chemicals in the environment.

    PubMed

    Dionisio, Kathie L; Frame, Alicia M; Goldsmith, Michael-Rock; Wambaugh, John F; Liddell, Alan; Cathey, Tommy; Smith, Doris; Vail, James; Ernstoff, Alexi S; Fantke, Peter; Jolliet, Olivier; Judson, Richard S

    2015-01-01

    Humans are exposed to thousands of chemicals in the workplace, home, and via air, water, food, and soil. A major challenge in estimating chemical exposures is to understand which chemicals are present in these media and microenvironments. Here we describe the Chemical/Product Categories Database (CPCat), a new, publically available (http://actor.epa.gov/cpcat) database of information on chemicals mapped to "use categories" describing the usage or function of the chemical. CPCat was created by combining multiple and diverse sources of data on consumer- and industrial-process based chemical uses from regulatory agencies, manufacturers, and retailers in various countries. The database uses a controlled vocabulary of 833 terms and a novel nomenclature to capture and streamline descriptors of chemical use for 43,596 chemicals from the various sources. Examples of potential applications of CPCat are provided, including identifying chemicals to which children may be exposed and to support prioritization of chemicals for toxicity screening. CPCat is expected to be a valuable resource for regulators, risk assessors, and exposure scientists to identify potential sources of human exposures and exposure pathways, particularly for use in high-throughput chemical exposure assessment.

  14. Method and apparatus for controlling gas evolution from chemical reactions

    DOEpatents

    Skorpik, James R.; Dodson, Michael G.

    1999-01-01

    The present invention is directed toward monitoring a thermally driven gas evolving chemical reaction with an acoustic apparatus. Signals from the acoustic apparatus are used to control a heater to prevent a run-away condition. A digestion module in combination with a robotic arm further automate physical handling of sample material reaction vessels. The invention is especially useful for carrying out sample procedures defined in EPA Methods SW-846.

  15. Method and apparatus for controlling gas evolution from chemical reactions

    DOEpatents

    Skorpik, J.R.; Dodson, M.G.

    1999-05-25

    The present invention is directed toward monitoring a thermally driven gas evolving chemical reaction with an acoustic apparatus. Signals from the acoustic apparatus are used to control a heater to prevent a run-away condition. A digestion module in combination with a robotic arm further automate physical handling of sample material reaction vessels. The invention is especially useful for carrying out sample procedures defined in EPA Methods SW-846. 8 figs.

  16. Chemical reactions in viscous liquids under space conditions

    NASA Astrophysics Data System (ADS)

    Kondyurin, A.; Lauke, B.; Richter, E.

    A long-term human flight needs a large-size space ships with artificial self-regulating ecological life-support system. The best way for creation of large-size space ship is a synthesis of light construction on Earth orbit, that does not need a high energy transportation carriers from Earth surface. The construction can be created by the way of chemical polymerisation reaction under space environment. But the space conditions are very specific for chemical reactions. A high vacuum, high energy particles, X-rays, UV- and VUV-irradiations, atomic oxygen, microgravity have a significant influence on chemical reactions. Polymerisation reactions in liquid active mixture were studied in simulated space environment. The epoxy resins based on Bisphenol A and amine curing agents were investigated under vacuum, microwave plasma discharge and ion beam. An acceleration of polymerisation reaction with free radicals formation was observed. The polymerisation reaction can be carried out under space environment. The study was supported by Alexander von Humboldt Foundation (A. Kondyurin) and European Space Agency, ESTEC (contract 17083/03/NL/Sfe "Space Environmental Effects on the Polymerisation of Composite Structures").

  17. Adverse drug reactions reported by consumers for nervous system medications in Europe 2007 to 2011

    PubMed Central

    2013-01-01

    Background Reporting of adverse drug reactions (ADRs) has traditionally been the sole province of healthcare professionals. In the European Union, more countries have allowed consumers to report ADRs directly to the regulatory agencies. The aim of this study was to characterize ADRs reported by European consumer for nervous system medications. Methods ADRs reported by consumers for nervous system medications (ATC group N) from 2007 to 2011 and located in the European ADR database, EudraVigilance, were analysed. Data were categorized with respect to age and sex, category and seriousness of reported ADRs and medications. The unit of analysis was one ADR. Results We located 4766 ADRs reported for nervous system medications, and one half of these were serious including 19 deaths. Less than 5% of ADRs were reported in children. Totally, 58% of ADRs were reported for women, 42% for men. The majority of reported ADRs were of the types “nervous system disorders” (18% of total ADRs) followed by “psychiatric disorders” (18% of total ADRs) and “general disorders” (15% of total ADRs) which also were the system organ classes in which the majority of serious ADRs were found. ADR reports encompassed medicines from the therapeutic groups: antiepileptics (ATC group N03) (36% of total ADRs), parasympathomimetics (ATC group N07) (22% of total ADRs) and antidepressants ATC group N06A (9% of total ADRs). Antiepileptics were the therapeutic group with the highest share of serious ADRs (60%) followed by antidepressants (15%). Many serious ADRs were reported for pregabalin and varenicline. Conclusions The majority of ADRs from nervous system mediations reported by consumers that were identified from the EudraVigilance database were serious. The value of consumer reports in pharmacovigilance still remains unclarified. PMID:23763896

  18. Poison politics: a contentious history of consumer protection against dangerous household chemicals in the United States.

    PubMed

    Jones, Marian Moser; Benrubi, Isidore Daniel

    2013-05-01

    The history of consumer protection against household poisons presents a key case study of the uniquely American struggle to balance public health and safety with the interests of business. By the late 19th century, package designs, warning labels, and state statutes had formed an uneven patchwork of protective mechanisms against accidental poisonings. As household chemicals proliferated in the early 20th century, physicians concerned with childhood poisonings pressured the federal government to enact legislation mandating warning labels on packaging for these substances. Manufacturers of household chemicals agreed to labeling requirements for caustic poisons but resisted broader regulation. Accidental poisonings of children continued to increase until the enactment of broad labeling and packaging legislation in the 1960s and 1970s. This history suggests that voluntary agreements between government agencies and manufacturers are inadequate to protect consumers against household poisonings and that, in the United States, protective household chemical regulation proceeds in a reactive rather than a precautionary manner.

  19. POISON POLITICS: A Contentious History of Consumer Protection Against Dangerous Household Chemicals in the United States

    PubMed Central

    Benrubi, Isidore Daniel

    2013-01-01

    The history of consumer protection against household poisons presents a key case study of the uniquely American struggle to balance public health and safety with the interests of business. By the late 19th century, package designs, warning labels, and state statutes had formed an uneven patchwork of protective mechanisms against accidental poisonings. As household chemicals proliferated in the early 20th century, physicians concerned with childhood poisonings pressured the federal government to enact legislation mandating warning labels on packaging for these substances. Manufacturers of household chemicals agreed to labeling requirements for caustic poisons but resisted broader regulation. Accidental poisonings of children continued to increase until the enactment of broad labeling and packaging legislation in the 1960s and 1970s. This history suggests that voluntary agreements between government agencies and manufacturers are inadequate to protect consumers against household poisonings and that, in the United States, protective household chemical regulation proceeds in a reactive rather than a precautionary manner. PMID:23488510

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

    PubMed

    Lubensky, David K

    2010-06-01

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

  1. Uncertainty quantification for quantum chemical models of complex reaction networks.

    PubMed

    Proppe, Jonny; Husch, Tamara; Simm, Gregor N; Reiher, Markus

    2016-12-22

    For the quantitative understanding of complex chemical reaction mechanisms, it is, in general, necessary to accurately determine the corresponding free energy surface and to solve the resulting continuous-time reaction rate equations for a continuous state space. For a general (complex) reaction network, it is computationally hard to fulfill these two requirements. However, it is possible to approximately address these challenges in a physically consistent way. On the one hand, it may be sufficient to consider approximate free energies if a reliable uncertainty measure can be provided. On the other hand, a highly resolved time evolution may not be necessary to still determine quantitative fluxes in a reaction network if one is interested in specific time scales. In this paper, we present discrete-time kinetic simulations in discrete state space taking free energy uncertainties into account. The method builds upon thermo-chemical data obtained from electronic structure calculations in a condensed-phase model. Our kinetic approach supports the analysis of general reaction networks spanning multiple time scales, which is here demonstrated for the example of the formose reaction. An important application of our approach is the detection of regions in a reaction network which require further investigation, given the uncertainties introduced by both approximate electronic structure methods and kinetic models. Such cases can then be studied in greater detail with more sophisticated first-principles calculations and kinetic simulations.

  2. Modeling Second-Order Chemical Reactions using Cellular Automata

    NASA Astrophysics Data System (ADS)

    Hunter, N. E.; Barton, C. C.; Seybold, P. G.; Rizki, M. M.

    2012-12-01

    Cellular automata (CA) are discrete, agent-based, dynamic, iterated, mathematical computational models used to describe complex physical, biological, and chemical systems. Unlike the more computationally demanding molecular dynamics and Monte Carlo approaches, which use "force fields" to model molecular interactions, CA models employ a set of local rules. The traditional approach for modeling chemical reactions is to solve a set of simultaneous differential rate equations to give deterministic outcomes. CA models yield statistical outcomes for a finite number of ingredients. The deterministic solutions appear as limiting cases for conditions such as a large number of ingredients or a finite number of ingredients and many trials. Here we present a 2-dimensional, probabilistic CA model of a second-order gas phase reaction A + B → C, using a MATLAB basis. Beginning with a random distribution of ingredients A and B, formation of C emerges as the system evolves. The reaction rate can be varied based on the probability of favorable collisions of the reagents A and B. The model permits visualization of the conversion of reagents to products, and allows one to plot concentration vs. time for A, B and C. We test hypothetical reaction conditions such as: limiting reagents, the effects of reaction probabilities, and reagent concentrations on the reaction kinetics. The deterministic solutions of the reactions emerge as statistical averages in the limit of the large number of cells in the array. Modeling results for dynamic processes in the atmosphere will be presented.

  3. Chemical pathways in ultracold reactions of SrF molecules

    SciTech Connect

    Meyer, Edmund R.; Bohn, John L.

    2011-03-15

    We present a theoretical investigation of the chemical reaction SrF + SrF {yields} products, focusing on reactions at ultralow temperatures. We find that bond swapping SrF + SrF {yields} Sr{sub 2} + F{sub 2} is energetically forbidden at these temperatures. Rather, the only energetically allowed reaction is SrF + SrF {yields} SrF{sub 2} + Sr, and even then only singlet states of the SrF{sub 2} trimer can form. A calculation along a reduced reaction path demonstrates that this abstraction reaction is barrierless and proceeds by one SrF molecule ''handing off'' a fluorine atom to the other molecule.

  4. Universality and chaoticity in ultracold K+KRb chemical reactions

    NASA Astrophysics Data System (ADS)

    Croft, J. F. E.; Makrides, C.; Li, M.; Petrov, A.; Kendrick, B. K.; Balakrishnan, N.; Kotochigova, S.

    2017-07-01

    A fundamental question in the study of chemical reactions is how reactions proceed at a collision energy close to absolute zero. This question is no longer hypothetical: quantum degenerate gases of atoms and molecules can now be created at temperatures lower than a few tens of nanokelvin. Here we consider the benchmark ultracold reaction between, the most-celebrated ultracold molecule, KRb and K. We map out an accurate ab initio ground-state potential energy surface of the K2Rb complex in full dimensionality and report numerically-exact quantum-mechanical reaction dynamics. The distribution of rotationally resolved rates is shown to be Poissonian. An analysis of the hyperspherical adiabatic potential curves explains this statistical character revealing a chaotic distribution for the short-range collision complex that plays a key role in governing the reaction outcome.

  5. Researches on Preliminary Chemical Reactions in Spark-Ignition Engines

    NASA Technical Reports Server (NTRS)

    Muehlner, E.

    1943-01-01

    Chemical reactions can demonstrably occur in a fuel-air mixture compressed in the working cylinder of an Otto-cycle (spark ignition) internal-combustion engine even before the charge is ignited by the flame proceeding from the sparking plug. These are the so-called "prelinminary reactions" ("pre-flame" combustion or oxidation), and an exact knowledge of their characteristic development is of great importance for a correct appreciation of the phenomena of engine-knock (detonation), and consequently for its avoidance. Such reactions can be studied either in a working engine cylinder or in a combustion bomb. The first method necessitates a complicated experimental technique, while the second has the disadvantage of enabling only a single reaction to be studied at one time. Consequently, a new series of experiments was inaugurated, conducted in a motored (externally-driven) experimental engine of mixture-compression type, without ignition, the resulting preliminary reactions being detectable and measurable thermometrically.

  6. Universality and chaoticity in ultracold K+KRb chemical reactions

    PubMed Central

    Croft, J. F. E.; Makrides, C.; Li, M.; Petrov, A.; Kendrick, B. K.; Balakrishnan, N.; Kotochigova, S.

    2017-01-01

    A fundamental question in the study of chemical reactions is how reactions proceed at a collision energy close to absolute zero. This question is no longer hypothetical: quantum degenerate gases of atoms and molecules can now be created at temperatures lower than a few tens of nanokelvin. Here we consider the benchmark ultracold reaction between, the most-celebrated ultracold molecule, KRb and K. We map out an accurate ab initio ground-state potential energy surface of the K2Rb complex in full dimensionality and report numerically-exact quantum-mechanical reaction dynamics. The distribution of rotationally resolved rates is shown to be Poissonian. An analysis of the hyperspherical adiabatic potential curves explains this statistical character revealing a chaotic distribution for the short-range collision complex that plays a key role in governing the reaction outcome. PMID:28722014

  7. Reduction of chemical reaction networks through delay distributions

    NASA Astrophysics Data System (ADS)

    Barrio, Manuel; Leier, André; Marquez-Lago, Tatiana T.

    2013-03-01

    Accurate modelling and simulation of dynamic cellular events require two main ingredients: an adequate description of key chemical reactions and simulation of such chemical events in reasonable time spans. Quite logically, posing the right model is a crucial step for any endeavour in Computational Biology. However, more often than not, it is the associated computational costs which actually limit our capabilities of representing complex cellular behaviour. In this paper, we propose a methodology aimed at representing chains of chemical reactions by much simpler, reduced models. The abridgement is achieved by generation of model-specific delay distribution functions, consecutively fed to a delay stochastic simulation algorithm. We show how such delay distributions can be analytically described whenever the system is solely composed of consecutive first-order reactions, with or without additional "backward" bypass reactions, yielding an exact reduction. For models including other types of monomolecular reactions (constitutive synthesis, degradation, or "forward" bypass reactions), we discuss why one must adopt a numerical approach for its accurate stochastic representation, and propose two alternatives for this. In these cases, the accuracy depends on the respective numerical sample size. Our model reduction methodology yields significantly lower computational costs while retaining accuracy. Quite naturally, computational costs increase alongside network size and separation of time scales. Thus, we expect our model reduction methodologies to significantly decrease computational costs in these instances. We anticipate the use of delays in model reduction will greatly alleviate some of the current restrictions in simulating large sets of chemical reactions, largely applicable in pharmaceutical and biological research.

  8. Program Helps To Determine Chemical-Reaction Mechanisms

    NASA Technical Reports Server (NTRS)

    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.

  9. Program Helps To Determine Chemical-Reaction Mechanisms

    NASA Technical Reports Server (NTRS)

    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.

  10. Effects of incomplete mixing on chemical reactions under flow heterogeneities.

    NASA Astrophysics Data System (ADS)

    Perez, Lazaro; Hidalgo, Juan J.; Dentz, Marco

    2016-04-01

    Evaluation of the mixing process in aquifers is of primary importance when assessing attenuation of pollutants. In aquifers different hydraulic and chemical properties can increase mixing and spreading of the transported species. Mixing processes control biogeochemical transformations such as precipitation/dissolution reactions or degradation reactions that are fast compared to mass transfer processes. Reactions are local phenomena that fluctuate at the pore scale, but predictions are often made at much larger scales. However, aquifer heterogeities are found at all scales and generates flow heterogeneities which creates complex concentration distributions that enhances mixing. In order to assess the impact of spatial flow heterogeneities at pore scale we study concentration profiles, gradients and reaction rates using a random walk particle tracking (RWPT) method and kernel density estimators to reconstruct concentrations and gradients in two setups. First, we focus on a irreversible bimolecular reaction A+B → C under homogeneous flow to distinguish phenomena of incomplete mixing of reactants from finite-size sampling effects. Second, we analise a fast reversible bimolecular chemical reaction A+B rightleftharpoons C in a laminar Poiseuille flow reactor to determine the difference between local and global reaction rates caused by the incomplete mixing under flow heterogeneities. Simulation results for the first setup differ from the analytical solution of the continuum scale advection-dispersion-reaction equation studied by Gramling et al. (2002), which results in an overstimation quantity of reaction product (C). In the second setup, results show that actual reaction rates are bigger than the obtained from artificially mixing the system by averaging the concentration vertically. - LITERATURE Gramling, C. M.,Harvey, C. F., Meigs, and L. C., (2002). Reactive transport in porous media: A comparison of model prediction with laboratory visualization, Environ. Sci

  11. Reaction Hamiltonian and state-to-state description of chemical reactions

    SciTech Connect

    Ruf, B.A.; Kresin, V.Z.; Lester, W.A. Jr.

    1985-08-01

    A chemical reaction is treated as a quantum transition from reactants to products. A specific reaction Hamiltonian (in second quantization formalism) is introduced. The approach leads to Franck-Condon-like factor, and adiabatic method in the framework of the nuclear motion problems. The influence of reagent vibrational state on the product energy distribution has been studied following the reaction Hamiltonian method. Two different cases (fixed available energy and fixed translational energy) are distinguished. Results for several biomolecular reactions are presented. 40 refs., 5 figs.

  12. Supersonic molecular beam experiments on surface chemical reactions.

    PubMed

    Okada, Michio

    2014-10-01

    The interaction of a molecule and a surface is important in various fields, and in particular in complex systems like biomaterials and their related chemistry. However, the detailed understanding of the elementary steps in the surface chemistry, for example, stereodynamics, is still insufficient even for simple model systems. In this Personal Account, I review our recent studies of chemical reactions on single-crystalline Cu and Si surfaces induced by hyperthermal oxygen molecular beams and by oriented molecular beams, respectively. Studies of oxide formation on Cu induced by hyperthermal molecular beams demonstrate a significant role of the translational energy of the incident molecules. The use of hyperthermal molecular beams enables us to open up new chemical reaction paths specific for the hyperthermal energy region, and to develop new methods for the fabrication of thin films. On the other hand, oriented molecular beams also demonstrate the possibility of understanding surface chemical reactions in detail by varying the orientation of the incident molecules. The steric effects found on Si surfaces hint at new ways of material fabrication on Si surfaces. Controlling the initial conditions of incoming molecules is a powerful tool for finely monitoring the elementary step of the surface chemical reactions and creating new materials on surfaces.

  13. Prediction of Rate Constants for Catalytic Reactions with Chemical Accuracy.

    PubMed

    Catlow, C Richard A

    2016-08-01

    Ex machina: A computational method for predicting rate constants for reactions within microporous zeolite catalysts with chemical accuracy has recently been reported. A key feature of this method is a stepwise QM/MM approach that allows accuracy to be achieved while using realistic models with accessible computer resources.

  14. Mapping students' ideas about chemical reactions at different educational levels

    NASA Astrophysics Data System (ADS)

    Yan, Fan

    Understanding chemical reactions is crucial in learning chemistry at all educational levels. Nevertheless, research in science education has revealed that many students struggle to understand chemical processes. Improving teaching and learning about chemical reactions demands that we develop a clearer understanding of student reasoning in this area and of how this reasoning evolves with training in the discipline. Thus, we have carried out a qualitative study using semi-structured interviews as the main data collection tool to explore students reasoning about reaction mechanism and causality. The participants of this study included students at different levels of training in chemistry: general chemistry students (n=22), organic chemistry students (n=16), first year graduate students (n=13) and Ph.D. candidates (n=14). We identified major conceptual modes along critical dimensions of analysis, and illustrated common ways of reasoning using typical cases. Main findings indicate that although significant progress is observed in student reasoning in some areas, major conceptual difficulties seem to persist even at the more advanced educational levels. In addition, our findings suggest that students struggle to integrate important concepts when thinking about mechanism and causality in chemical reactions. The results of our study are relevant to chemistry educators interested in learning progressions, assessment, and conceptual development.

  15. Chemical Reaction Engineering: Current Status and Future Directions.

    ERIC Educational Resources Information Center

    Dudukovic, M. P.

    1987-01-01

    Describes Chemical Reaction Engineering (CRE) as the discipline that quantifies the interplay of transport phenomena and kinetics in relating reactor performance to operating conditions and input variables. Addresses the current status of CRE in both academic and industrial settings and outlines future trends. (TW)

  16. WATER AS A REACTION MEDIUM FOR CLEAN CHEMICAL PROCESSES.

    EPA Science Inventory

    Green chemistry is a rapid developing new field that provides us a pro-active avenue for the sustainable development of future science and technologies. When designed properly, clean chemical technology can be developed in water as a reaction media. The technologies generated f...

  17. Quantum and semiclassical theories of chemical reaction rates

    SciTech Connect

    Miller, W.H. |

    1995-09-01

    A rigorous quantum mechanical theory (and a semiclassical approximation thereto) is described for calculating chemical reaction rates ``directly``, i.e., without having to solve the complete state-to-state reactive scattering problem. The approach has many vestiges of transition state theory, for which it may be thought of as the rigorous generalization.

  18. Chemical Reaction Engineering: Current Status and Future Directions.

    ERIC Educational Resources Information Center

    Dudukovic, M. P.

    1987-01-01

    Describes Chemical Reaction Engineering (CRE) as the discipline that quantifies the interplay of transport phenomena and kinetics in relating reactor performance to operating conditions and input variables. Addresses the current status of CRE in both academic and industrial settings and outlines future trends. (TW)

  19. Molecular codes in biological and chemical reaction networks.

    PubMed

    Görlich, Dennis; Dittrich, Peter

    2013-01-01

    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.

  20. WATER AS A REACTION MEDIUM FOR CLEAN CHEMICAL PROCESSES.

    EPA Science Inventory

    Green chemistry is a rapid developing new field that provides us a pro-active avenue for the sustainable development of future science and technologies. When designed properly, clean chemical technology can be developed in water as a reaction media. The technologies generated f...

  1. Perspective: chemical dynamics simulations of non-statistical reaction dynamics.

    PubMed

    Ma, Xinyou; Hase, William L

    2017-04-28

    Non-statistical chemical dynamics are exemplified by disagreements with the transition state (TS), RRKM and phase space theories of chemical kinetics and dynamics. The intrinsic reaction coordinate (IRC) is often used for the former two theories, and non-statistical dynamics arising from non-IRC dynamics are often important. In this perspective, non-statistical dynamics are discussed for chemical reactions, with results primarily obtained from chemical dynamics simulations and to a lesser extent from experiment. The non-statistical dynamical properties discussed are: post-TS dynamics, including potential energy surface bifurcations, product energy partitioning in unimolecular dissociation and avoiding exit-channel potential energy minima; non-RRKM unimolecular decomposition; non-IRC dynamics; direct mechanisms for bimolecular reactions with pre- and/or post-reaction potential energy minima; non-TS theory barrier recrossings; and roaming dynamics.This article is part of the themed issue 'Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces'. © 2017 The Author(s).

  2. 2011 Chemical Reactions at Surfaces Gordon Research Conference

    SciTech Connect

    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.

  3. Stabilization of miscible viscous fingering by chemical reaction decreasing viscosity

    NASA Astrophysics Data System (ADS)

    Arai, Shuntaro; Nagatsu, Yuichiro; Shukla, Priyanka; de Wit, Anne

    2016-11-01

    Viscous fingering (VF) occurs when a more viscous fluid is displaced by a less viscous one in porous media or Hele-Shaw cells. In this study, experiment on miscible VF with chemical reaction is conducted by using a Hele-Shaw cell. Here, the chemical reaction takes place between a polymer dissolved in the more viscous solution and hydrochloric acid (HCl) dissolved in the less viscous one in the miscible interface region. The reaction decreases the viscosity of the polymer solution. The experiment shows that the reaction stabilizes VF when the flow rate is small. In the present study, the corresponding numerical simulation is also conducted. The simulation is able to reproduce the experimental results mentioned above when different diffusion coefficients are considered meaning that HCl diffuses faster than the polymer. However, the stabilization cannot be found under conditions of the same diffusivity of the reactants. These numerical results show that the different diffusivity is responsible for the stabilization of miscible VF by the chemical reaction decreasing viscosity.

  4. Chemical markup, XML, and the world wide web. 6. CMLReact, an XML vocabulary for chemical reactions.

    PubMed

    Holliday, Gemma L; Murray-Rust, Peter; Rzepa, Henry S

    2006-01-01

    A set of components (CMLReact) for managing chemical and biochemical reactions has been added to CML. These can be combined to support most of the strategies for the formal representation of reactions. The elements, attributes, and types are formally defined as XMLSchema components, and their semantics are developed. New syntax and semantics in CML are reported and illustrated with 10 examples.

  5. The role of chemical reactions in the Chernobyl accident

    SciTech Connect

    Grishanin, E. I.

    2010-12-15

    It is shown that chemical reactions played an essential role in the Chernobyl accident at all of its stages. It is important that the reactor before the explosion was at maximal xenon poisoning, and its reactivity, apparently, was not destroyed by the explosion. The reactivity release due to decay of Xe-235 on the second day after the explosion led to a reactor power of 80-110 MW. Owing to this power, the chemical reactions of reduction of uranium, plutonium, and other metals at a temperature of about 2000 Degree-Sign C occurred in the core. The yield of fission products thus sharply increased. Uranium and other metals flew down in the bottom water communications and rooms. After reduction of the uranium and its separation from the graphite, the chain reaction stopped, the temperature of the core decreased, and the activity yield stopped.

  6. Multiscale stochastic simulations of chemical reactions with regulated scale separation

    SciTech Connect

    Koumoutsakos, Petros; Feigelman, Justin

    2013-07-01

    We present a coupling of multiscale frameworks with accelerated stochastic simulation algorithms for systems of chemical reactions with disparate propensities. The algorithms regulate the propensities of the fast and slow reactions of the system, using alternating micro and macro sub-steps simulated with accelerated algorithms such as τ and R-leaping. The proposed algorithms are shown to provide significant speedups in simulations of stiff systems of chemical reactions with a trade-off in accuracy as controlled by a regulating parameter. More importantly, the error of the methods exhibits a cutoff phenomenon that allows for optimal parameter choices. Numerical experiments demonstrate that hybrid algorithms involving accelerated stochastic simulations can be, in certain cases, more accurate while faster, than their corresponding stochastic simulation algorithm counterparts.

  7. Mixing, chemical reaction and flow field development in ducted rockets

    SciTech Connect

    Vanka, S.P.; Craig, R.R.; Stull, F.D.

    1984-09-01

    Calculations have been made of the three-dimensional mixing, chemical reaction, and flow field development in a typical ducted rocket configuration. The governing partial differential equations are numerically solved by an iterative finite-difference solution procedure. The physical models include the k approx. epsilon turbulence model, one-step reaction, and mixing controlled chemical reaction rate. Radiation is neglected. The mean flow structure, fuel dispersal patterns, and temperature field are presented in detail for a base configuration with 0.058 m (2 in.) dome height, 45/sup 0/ side arm inclination, and with gaseous ethylene injected from the dome plate at an eccentric location. In addition, the influences of the geometrical parameters such as dome height, inclination of the side arms, and location of the fuel injector are studied.

  8. Multiscale stochastic simulations of chemical reactions with regulated scale separation

    NASA Astrophysics Data System (ADS)

    Koumoutsakos, Petros; Feigelman, Justin

    2013-07-01

    We present a coupling of multiscale frameworks with accelerated stochastic simulation algorithms for systems of chemical reactions with disparate propensities. The algorithms regulate the propensities of the fast and slow reactions of the system, using alternating micro and macro sub-steps simulated with accelerated algorithms such as τ and R-leaping. The proposed algorithms are shown to provide significant speedups in simulations of stiff systems of chemical reactions with a trade-off in accuracy as controlled by a regulating parameter. More importantly, the error of the methods exhibits a cutoff phenomenon that allows for optimal parameter choices. Numerical experiments demonstrate that hybrid algorithms involving accelerated stochastic simulations can be, in certain cases, more accurate while faster, than their corresponding stochastic simulation algorithm counterparts.

  9. Coriolis coupling and nonadiabaticity in chemical reaction dynamics.

    PubMed

    Wu, Emilia L

    2010-12-01

    The nonadiabatic quantum dynamics and Coriolis coupling effect in chemical reaction have been reviewed, with emphasis on recent progress in using the time-dependent wave packet approach to study the Coriolis coupling and nonadiabatic effects, which was done by K. L. Han and his group. Several typical chemical reactions, for example, H+D(2), F+H(2)/D(2)/HD, D(+)+H(2), O+H(2), and He+H(2)(+), have been discussed. One can find that there is a significant role of Coriolis coupling in reaction dynamics for the ion-molecule collisions of D(+)+H(2), Ne+H(2)(+), and He+H(2)(+) in both adiabatic and nonadiabatic context.

  10. Chemical cues induce consumer-specific defenses in a bloom-forming marine phytoplankton

    PubMed Central

    Long, Jeremy D.; Smalley, Gabriela W.; Barsby, Todd; Anderson, Jon T.; Hay, Mark E.

    2007-01-01

    Blooms of the phytoplankton Phaeocystis can comprise 85% of total production and generate major biogeochemical signals across broad oceanic regions. The success of Phaeocystis may result from its ability to change size by many orders of magnitude when it shifts from small cells of 4–6 μm to large colonies of up to 30,000 μm in diameter. Single cells are consumed by ciliates but not copepods, whereas colonies are consumed by copepods but not ciliates. We demonstrate that chemical cues associated with each of these grazers induce consumer-specific, but opposing, morphological transformations in the bloom-forming species Phaeocystis globosa. Chemical cues from grazing copepods suppress colony formation by a significant 60–90%, a response that should be adaptive because copepods feed four times more on colonies versus solitary cells. In contrast, chemical cues from grazing ciliates enhance colony formation by >25%, a response that should be adaptive because ciliates grow three times faster when fed solitary cells versus colonies. Because size-selective predation fundamentally alters community structure and ecosystem function, this chemically cued shift may redirect energy and nutrients from food webs supporting fisheries to those fueling detrital pathways, thus potentially altering ecosystem-level processes such as productivity, carbon storage, and nutrient release. PMID:17563379

  11. Petri Nets - A Mathematical Formalism to Analyze Chemical Reaction Networks.

    PubMed

    Koch, Ina

    2010-12-17

    In this review we introduce and discuss Petri nets - a mathematical formalism to describe and analyze chemical reaction networks. Petri nets were developed to describe concurrency in general systems. We find most applications to technical and financial systems, but since about twenty years also in systems biology to model biochemical systems. This review aims to give a short informal introduction to the basic formalism illustrated by a chemical example, and to discuss possible applications to the analysis of chemical reaction networks, including cheminformatics. We give a short overview about qualitative as well as quantitative modeling Petri net techniques useful in systems biology, summarizing the state-of-the-art in that field and providing the main literature references. Finally, we discuss advantages and limitations of Petri nets and give an outlook to further development.

  12. Diabatic models with transferrable parameters for generalized chemical reactions

    NASA Astrophysics Data System (ADS)

    Reimers, Jeffrey R.; McKemmish, Laura K.; McKenzie, Ross H.; Hush, Noel S.

    2017-05-01

    Diabatic models applied to adiabatic electron-transfer theory yield many equations involving just a few parameters that connect ground-state geometries and vibration frequencies to excited-state transition energies and vibration frequencies to the rate constants for electron-transfer reactions, utilizing properties of the conical-intersection seam linking the ground and excited states through the Pseudo Jahn-Teller effect. We review how such simplicity in basic understanding can also be obtained for general chemical reactions. The key feature that must be recognized is that electron-transfer (or hole transfer) processes typically involve one electron (hole) moving between two orbitals, whereas general reactions typically involve two electrons or even four electrons for processes in aromatic molecules. Each additional moving electron leads to new high-energy but interrelated conical-intersection seams that distort the shape of the critical lowest-energy seam. Recognizing this feature shows how conical-intersection descriptors can be transferred between systems, and how general chemical reactions can be compared using the same set of simple parameters. Mathematical relationships are presented depicting how different conical-intersection seams relate to each other, showing that complex problems can be reduced into an effective interaction between the ground-state and a critical excited state to provide the first semi-quantitative implementation of Shaik’s “twin state” concept. Applications are made (i) demonstrating why the chemistry of the first-row elements is qualitatively so different to that of the second and later rows, (ii) deducing the bond-length alternation in hypothetical cyclohexatriene from the observed UV spectroscopy of benzene, (iii) demonstrating that commonly used procedures for modelling surface hopping based on inclusion of only the first-derivative correction to the Born-Oppenheimer approximation are valid in no region of the chemical

  13. Students' Understandings of Chemical Bonds and the Energetics of Chemical Reactions.

    ERIC Educational Resources Information Center

    Boo, Hong Kwen

    1998-01-01

    Investigates Grade 12 students' understandings of the nature of chemical bonds and the energetics elicited across five familiar chemical reactions following a course of instruction. Discusses the many ways in which students can misconstruct concepts and principles. Contains 63 references. (DDR)

  14. Development of a chemical oxygen - iodine laser with production of atomic iodine in a chemical reaction

    SciTech Connect

    Censky, M; Spalek, O; Jirasek, V; Kodymova, J; Jakubec, I

    2009-11-30

    The alternative method of atomic iodine generation for a chemical oxygen - iodine laser (COIL) in chemical reactions with gaseous reactants is investigated experimentally. The influence of the configuration of iodine atom injection into the laser cavity on the efficiency of the atomic iodine generation and small-signal gain is studied. (lasers)

  15. Students' Understandings of Chemical Bonds and the Energetics of Chemical Reactions.

    ERIC Educational Resources Information Center

    Boo, Hong Kwen

    1998-01-01

    Investigates Grade 12 students' understandings of the nature of chemical bonds and the energetics elicited across five familiar chemical reactions following a course of instruction. Discusses the many ways in which students can misconstruct concepts and principles. Contains 63 references. (DDR)

  16. Interplay between chemical reactions and transport in structured spaces

    NASA Astrophysics Data System (ADS)

    Konkoli, Zoran

    2005-07-01

    The main motivation behind this study is to understand the interplay between the reactions and transport in a geometries that are not compact. Typical examples of compact geometries are a box or a sphere. A network made of containers C1,C2,…,CN and tubes is an example of the space that is structured and noncompact. In containers, particles react with the rate λ . Tubes connecting containers allow for the exchange of chemicals with the transport rate D . A situation is considered where a number of reactants is small and kinetics is noise dominated. A method is presented that can be used to calculate the average and higher moments of the reaction time. A number of different chemical reactions are studied and their performance compared in various ways. Two schemes are discussed in general, the reaction on a fixed geometry ensemble (ROGE) and the geometry on a fixed reaction ensemble, examples are given in the ROGE case. The most important findings are as follows. (i) There is a large number of reactions that run faster in a networklike geometry. Such reactions contain antagonistic catalytic influences in the intermediate stages of a reaction scheme that are best dealt with in a networklike structure. (ii) Antagonistic catalytic influences are hard to identify since they are strongly connected to the pattern of injected molecules (inject pattern) and depend on the choice of molecules that have to be synthesized at the end (task pattern). (iii) The reaction time depends strongly on the details of the inject and task patterns.

  17. Consumer Product Chemicals in Indoor Dust: A Quantitative Meta-analysis of U.S. Studies

    PubMed Central

    2016-01-01

    Indoor dust is a reservoir for commercial consumer product chemicals, including many compounds with known or suspected health effects. However, most dust exposure studies measure few chemicals in small samples. We systematically searched the U.S. indoor dust literature on phthalates, replacement flame retardants (RFRs), perfluoroalkyl substances (PFASs), synthetic fragrances, and environmental phenols and estimated pooled geometric means (GMs) and 95% confidence intervals for 45 chemicals measured in ≥3 data sets. In order to rank and contextualize these results, we used the pooled GMs to calculate residential intake from dust ingestion, inhalation, and dermal uptake from air, and then identified hazard traits from the Safer Consumer Products Candidate Chemical List. Our results indicate that U.S. indoor dust consistently contains chemicals from multiple classes. Phthalates occurred in the highest concentrations, followed by phenols, RFRs, fragrance, and PFASs. Several phthalates and RFRs had the highest residential intakes. We also found that many chemicals in dust share hazard traits such as reproductive and endocrine toxicity. We offer recommendations to maximize comparability of studies and advance indoor exposure science. This information is critical in shaping future exposure and health studies, especially related to cumulative exposures, and in providing evidence for intervention development and public policy. PMID:27623734

  18. Consumer Product Chemicals in Indoor Dust: A Quantitative Meta-analysis of U.S. Studies.

    PubMed

    Mitro, Susanna D; Dodson, Robin E; Singla, Veena; Adamkiewicz, Gary; Elmi, Angelo F; Tilly, Monica K; Zota, Ami R

    2016-10-04

    Indoor dust is a reservoir for commercial consumer product chemicals, including many compounds with known or suspected health effects. However, most dust exposure studies measure few chemicals in small samples. We systematically searched the U.S. indoor dust literature on phthalates, replacement flame retardants (RFRs), perfluoroalkyl substances (PFASs), synthetic fragrances, and environmental phenols and estimated pooled geometric means (GMs) and 95% confidence intervals for 45 chemicals measured in ≥3 data sets. In order to rank and contextualize these results, we used the pooled GMs to calculate residential intake from dust ingestion, inhalation, and dermal uptake from air, and then identified hazard traits from the Safer Consumer Products Candidate Chemical List. Our results indicate that U.S. indoor dust consistently contains chemicals from multiple classes. Phthalates occurred in the highest concentrations, followed by phenols, RFRs, fragrance, and PFASs. Several phthalates and RFRs had the highest residential intakes. We also found that many chemicals in dust share hazard traits such as reproductive and endocrine toxicity. We offer recommendations to maximize comparability of studies and advance indoor exposure science. This information is critical in shaping future exposure and health studies, especially related to cumulative exposures, and in providing evidence for intervention development and public policy.

  19. Robust Stochastic Chemical Reaction Networks and Bounded Tau-Leaping

    PubMed Central

    2009-01-01

    Abstract The behavior of some stochastic chemical reaction networks is largely unaffected by slight inaccuracies in reaction rates. We formalize the robustness of state probabilities to reaction rate deviations, and describe a formal connection between robustness and efficiency of simulation. Without robustness guarantees, stochastic simulation seems to require computational time proportional to the total number of reaction events. Even if the concentration (molecular count per volume) stays bounded, the number of reaction events can be linear in the duration of simulated time and total molecular count. We show that the behavior of robust systems can be predicted such that the computational work scales linearly with the duration of simulated time and concentration, and only polylogarithmically in the total molecular count. Thus our asymptotic analysis captures the dramatic speedup when molecular counts are large, and shows that for bounded concentrations the computation time is essentially invariant with molecular count. Finally, by noticing that even robust stochastic chemical reaction networks are capable of embedding complex computational problems, we argue that the linear dependence on simulated time and concentration is likely optimal. PMID:19254187

  20. Inverse electron demand Diels-Alder reactions in chemical biology.

    PubMed

    Oliveira, B L; Guo, Z; Bernardes, G J L

    2017-08-14

    The emerging inverse electron demand Diels-Alder (IEDDA) reaction stands out from other bioorthogonal reactions by virtue of its unmatchable kinetics, excellent orthogonality and biocompatibility. With the recent discovery of novel dienophiles and optimal tetrazine coupling partners, attention has now been turned to the use of IEDDA approaches in basic biology, imaging and therapeutics. Here we review this bioorthogonal reaction and its promising applications for live cell and animal studies. We first discuss the key factors that contribute to the fast IEDDA kinetics and describe the most recent advances in the synthesis of tetrazine and dienophile coupling partners. Both coupling partners have been incorporated into proteins for tracking and imaging by use of fluorogenic tetrazines that become strongly fluorescent upon reaction. Selected notable examples of such applications are presented. The exceptional fast kinetics of this catalyst-free reaction, even using low concentrations of coupling partners, make it amenable for in vivo radiolabelling using pretargeting methodologies, which are also discussed. Finally, IEDDA reactions have recently found use in bioorthogonal decaging to activate proteins or drugs in gain-of-function strategies. We conclude by showing applications of the IEDDA reaction in the construction of biomaterials that are used for drug delivery and multimodal imaging, among others. The use and utility of the IEDDA reaction is interdisciplinary and promises to revolutionize chemical biology, radiochemistry and materials science.

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

    NASA Astrophysics Data System (ADS)

    Malijevský, Alexandr; Lísal, Martin

    2009-04-01

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

  2. PDF calculation of scalar mixing layer with simple chemical reactions

    NASA Astrophysics Data System (ADS)

    Kanzaki, Takao; Pope, Stephen B.

    1999-11-01

    A joint velocity-composition-turbulent frequency PDF(JPDF) model is used to simulate reactive mixing layer in a grid-generated turbulence with the influence of second-order irreversible chemical reactions. To investigate the effects of molecular mixing, a gas flow and a liquid flow are simulated. For a gas flow, the oxidation reaction (NO+ O3 arrow NO2 +O2 ) between nitricoxide (NO) and ozone (O3 ) is used. For a liquid flow, the saponification reaction(NaOH+HCOOCH3 arrow HCOONa+CH_3OH) between sodiumhydroxide(NaOH) and methylformate(HCOOCH_3) is used. The both cases are moderately fast reactions. Therefore, reactive scalar statistics are affected by turbulent mixing. The results of caliculation are compared with experimental data of Komori et al.(1994) and Bilger et al.(1991)

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

    PubMed

    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.

  4. Quantum Chemical Modeling of the Dehalogenation Reaction of Haloalcohol Dehalogenase.

    PubMed

    Hopmann, Kathrin H; Himo, Fahmi

    2008-07-01

    The dehalogenation reaction of haloalcohol dehalogenase HheC from Agrobacterium radiobacter AD1 was investigated theoretically using hybrid density functional theory methods. HheC catalyzes the enantioselective conversion of halohydrins into their corresponding epoxides. The reaction is proposed to be mediated by a catalytic Ser132-Tyr145-Arg149 triad, and a distinct halide binding site is suggested to facilitate halide displacement by stabilizing the free ion. We investigated the HheC-mediated dehalogenation of (R)-2-chloro-1-phenylethanol using three quantum chemical models of various sizes. The calculated barriers and reaction energies give support to the suggested reaction mechanism. The dehalogenation occurs in a single concerted step, in which Tyr145 abstracts a proton from the halohydrin substrate and the substrate oxyanion displaces the chloride ion, forming the epoxide. Characterization of the involved stationary points is provided. Furthermore, by using three different models of the halide binding site, we are able to assess the adopted modeling methodology.

  5. Risk management measures for chemicals in consumer products: documentation, assessment, and communication across the supply chain.

    PubMed

    Bruinen de Bruin, Yuri; Hakkinen, Pertti Bert; Lahaniatis, Majlinda; Papameletiou, Demosthenes; Del Pozo, Carlos; Reina, Vittorio; Van Engelen, Jacqueline; Heinemeyer, Gerhard; Viso, Anne Catherine; Rodriguez, Carlos; Jantunen, Matti

    2007-12-01

    This paper analyzes the way risk management measures (RMMs) for consumer products have been used to date in authority and industry risk assessments. A working concept for consumer product RMMs is developed, aimed at controlling, limiting or avoiding exposures, and helping to insure the safe use (or handling) of a substance as part of a consumer product. Particular focus is placed on new requirements introduced by REACH (registration, evaluation, and authorization of chemicals). A RMMs categorization approach is also developed, dividing consumer product RMMs into those that are product integrated and those that are communicated to consumers. For each of these categories, RMMs for normal use, accidental use or misuse need to be distinguished. The level of detail for documenting, assessing and communicating RMMs across supply chains can vary, depending on the type of the assessment (tiered approach). Information on RMMs was collected from published sources to demonstrate that a taxonomical approach using standard descriptors for RMMs libraries is needed for effective information exchange across supply chains.

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

    NASA Astrophysics Data System (ADS)

    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

  7. Deblocking reaction of chemically amplified ArF positive resists

    NASA Astrophysics Data System (ADS)

    Yamana, Mitsuharu; Itani, Toshiro; Yoshino, Hiroshi; Hashimoto, Shuichi; Tanabe, Hiroyoshi; Kasama, Kunihiko

    1998-06-01

    Deblocking reaction mechanisms and lithographic performance in chemically amplified positive ArF resists were investigated by analyzing acid concentration and blocking level. The resists consisted of triphenylsulfonium triflate as a acid generator and either the copolymer, poly(carboxy- tetracyclododecyl methacrylate70-co- tetrahydropyranylcarboxy-tetracyclododecyl methacrylate30) or the terpolymer, poly(tricyclodecylacrylate60- co-tetrahydropyranylmethacrylate20-co-methacrylic acid20). The deblocking reaction mechanisms were evaluated from Arrhenius plots of the deblocking reaction rate constant. It was found that the deblocking reaction of both resists is ruled by two rate-determining steps, i.e., reaction-controlled in the low-temperature region and acid- diffusion-controlled in the high-temperature region. Furthermore, the copolymer resist had better post-exposure- delay (PED) stability. To clarify this result, acid loss caused by air-born contamination effect on deblocking reaction was investigated. The change of amount of blocking group by acid loss was small for the copolymer. Therefore the copolymer resist had better PED stability. Furthermore, the post-exposure bake (PEB) sensitivity of linewidth of the copolymer resist was smaller than that of the terpolymer resist. Both deblocking reaction rate constant and reverse reaction rate constant of the copolymer resist increased with PEB temperature. As a result, equilibrium constant of the copolymer was not valuable with temperature. This is the reason why the copolymer resist has low PEB sensitivity. It is concluded that small acid loss effect on deblocking reaction induces better PED stability. A resist with reverse reaction has an advantage for PEB temperature sensitivity.

  8. Photo-induced chemical reaction of trans-resveratrol.

    PubMed

    Zhao, Yue; Shi, Meng; Ye, Jian-Hui; Zheng, Xin-Qiang; Lu, Jian-Liang; Liang, Yue-Rong

    2015-03-15

    Photo-induced chemical reaction of trans-resveratrol has been studied. UV B, liquid state and sufficient exposure time are essential conditions to the photochemical change of trans-resveratrol. Three principal compounds, cis-resveratrol, 2,4,6-phenanthrenetriol and 2-(4-hydroxyphenyl)-5,6-benzofurandione, were successively generated in the reaction solution of trans-resveratrol (0.25 mM, 100% ethanol) under 100 μW cm(-2) UV B radiation for 4h. cis-Resveratrol, originated from isomerization of trans-resveratrol, resulted in 2,4,6-phenanthrenetriol through photocyclisation reaction meanwhile loss of 2 H. 2,4,6-Phenanthrenetriol played a role of photosensitizer producing singlet oxygen in the reaction pathway. The singlet oxygen triggered [4+2] cycloaddition reaction of trans-resveratrol, and then resulted in the generation of 2-(4-hydroxyphenyl)-5,6-benzofurandione through photorearrangement and oxidation reaction. The singlet oxygen reaction was closely related to the substrate concentration of trans-resveratrol in solution. Copyright © 2014 Elsevier Ltd. All rights reserved.

  9. Information-Theoretical Complexity Analysis of Selected Elementary Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Molina-Espíritu, M.; Esquivel, R. O.; Dehesa, J. S.

    We investigate the complexity of selected elementary chemical reactions (namely, the hydrogenic-abstraction reaction and the identity SN2 exchange reaction) by means of the following single and composite information-theoretic measures: disequilibrium (D), exponential entropy(L), Fisher information (I), power entropy (J), I-D, D-L and I-J planes and Fisher-Shannon (FS) and Lopez-Mancini-Calbet (LMC) shape complexities. These quantities, which are functionals of the one-particle density, are computed in both position (r) and momentum (p) spaces. The analysis revealed that the chemically significant regions of these reactions can be identified through most of the single information-theoretic measures and the two-component planes, not only the ones which are commonly revealed by the energy, such as the reactant/product (R/P) and the transition state (TS), but also those that are not present in the energy profile such as the bond cleavage energy region (BCER), the bond breaking/forming regions (B-B/F) and the charge transfer process (CT). The analysis of the complexities shows that the energy profile of the abstraction reaction bears the same information-theoretical features of the LMC and FS measures, however for the identity SN2 exchange reaction does not hold a simple behavior with respect to the LMC and FS measures. Most of the chemical features of interest (BCER, B-B/F and CT) are only revealed when particular information-theoretic aspects of localizability (L or J), uniformity (D) and disorder (I) are considered.

  10. Laser studies of chemical reaction and collision processes

    SciTech Connect

    Flynn, G.

    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.

  11. Towards chemically accurate simulation of molecule-surface reactions.

    PubMed

    Kroes, Geert-Jan

    2012-11-21

    This perspective addresses four challenges facing theorists whose aim is to make quantitatively accurate predictions for reactions of molecules on metal surfaces, and suggests ways of meeting these challenges, focusing on dissociative chemisorption reactions of H(2), N(2), and CH(4). Addressing these challenges is ultimately of practical importance to a more accurate description of overall heterogeneously catalysed reactions, which play a role in the production of more than 90% of man-made chemicals. One challenge is to describe the interaction of a molecule with a metal surface with chemical accuracy, i.e., with errors in reaction barrier heights less than 1 kcal mol(-1). In this framework, the potential of a new implementation of specific reaction parameter density functional theory (SRP-DFT) will be discussed, with emphasis on applications to reaction of H(2) with metal surfaces. Two additional challenges are to come up with improved descriptions of the effects of phonons and electron-hole pairs on reaction of molecules like N(2) on metal surfaces. Phonons can be tackled using sudden approximations in quantum dynamics, and through Ab Initio Molecular Dynamics (AIMD) calculations using classical dynamics. To additionally achieve an accurate description of the effect of electron-hole pair excitation on dissociative chemisorption within a classical dynamics framework, it may be possible to combine AIMD with electronic friction. The fourth challenge we will consider is how to achieve an accurate quantum mechanical description of the dissociative chemisorption of a polyatomic molecule, like methane, on a metal surface. A method of potential interest is the Multi-Configuration Time-Dependent Hartree (MCTDH) method.

  12. Chemical reaction fouling model for single-phase heat transfer

    SciTech Connect

    Panchal, C.B.; Watkinson, A.P.

    1993-08-01

    A fouling model was developed on the premise that the chemical reaction for generation of precursor can take place in the bulk fluid, in the thermalboundary layer, or at the fluid/wall interface, depending upon the interactive effects of flu id dynamics, heat and mass transfer, and the controlling chemical reaction. The analysis was used to examine the experimental data for fouling deposition of polyperoxides produced by autoxidation of indene in kerosene. The effects of fluid and wall temperatures for two flow geometries were analyzed. The results showed that the relative effects of physical parameters on the fouling rate would differ for the three fouling mechanisms; therefore, it is important to identify the controlling mechanism in applying the closed-flow-loop data to industrial conditions.

  13. Advanced chemical heat pumps using liquid-vapor reactions

    NASA Astrophysics Data System (ADS)

    Kirol, L.

    Chemical heat pumps utilizing liquid-vapor reactions can be configured in forms analogous to electric drive vapor-compression heat pumps and heat activated absorption heat pumps. Basic thermodynamic considerations eliminate some heat pumps and place restrictive working fluid requirements on others, but two thermodynamically feasible systems have significant potential advantage over conventional technology. An electric drive reactive heat pump can use smaller heat exchangers and compressor than a vapor-compression machine, and have more flexible operating characteristics. A waste heat driven heat pump (temperature amplifier) using liquid-vapor chemical reactions can operate with higher coefficient of performance and smaller heat exchangers than an absorption temperature amplifying heat pump. Higher temperatures and larger temperature lifts should also be possible.

  14. What can we learn from consumer reports on psychiatric adverse drug reactions with antidepressant medication? Experiences from reports to a consumer association.

    PubMed

    Vilhelmsson, Andreas; Svensson, Tommy; Meeuwisse, Anna; Carlsten, Anders

    2011-10-25

    According to the World Health Organization (WHO) the cost of adverse drug reactions (ADRs) in the general population is high and under-reporting by health professionals is a well-recognized problem. Another way to increase ADR reporting is to let the consumers themselves report directly to the authorities. In Sweden it is mandatory for prescribers to report serious ADRs to the Medical Products Agency (MPA), but there are no such regulations for consumers. The non-profit and independent organization Consumer Association for Medicines and Health, KILEN has launched the possibility for consumers to report their perceptions and experiences from their use of medicines in order to strengthen consumer rights within the health care sector. This study aimed to analyze these consumer reports. All reports submitted from January 2002 to April 2009 to an open web site in Sweden where anyone could report their experience with the use of pharmaceuticals were analyzed with focus on common psychiatric side effects related to antidepressant usage. More than one ADR for a specific drug could be reported. In total 665 reports were made during the period. 442 reports concerned antidepressant medications and the individual antidepressant reports represented 2392 ADRs and 878 (37%) of these were psychiatric ADRs. 75% of the individual reports concerned serotonin-reuptake inhibitor (SSRI) and the rest serotonin-norepinephrine reuptake inhibitor (SNRI). Women reported more antidepressant psychiatric ADRs (71%) compared to men (24%). More potentially serious psychiatric ADRs were frequently reported to KILEN and withdrawal symptoms during discontinuation were also reported as a common issue. The present study indicates that consumer reports may contribute with important information regarding more serious psychiatric ADRs following antidepressant treatment. Consumer reporting may be considered a complement to traditional ADR reporting.

  15. Crossed molecular beam studies of atmospheric chemical reaction dynamics

    SciTech Connect

    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 + O3 → ClO + O2 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 + O3 → ClO + O2 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 + O3 reaction. The Br + O3 reaction has a direct reaction mechanism similar to that of the Cl + O3 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 + NO2 → 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 NO2

  16. Stochastic Generator of Chemical Structure. 3. Reaction Network Generation

    SciTech Connect

    FAULON,JEAN-LOUP; SAULT,ALLEN G.

    2000-07-15

    A new method to generate chemical reaction network is proposed. The particularity of the method is that network generation and mechanism reduction are performed simultaneously using sampling techniques. Our method is tested for hydrocarbon thermal cracking. Results and theoretical arguments demonstrate that our method scales in polynomial time while other deterministic network generator scale in exponential time. This finding offers the possibility to investigate complex reacting systems such as those studied in petroleum refining and combustion.

  17. Separation of the isotopes of boron by chemical exchange reactions

    DOEpatents

    McCandless, Frank P.; Herbst, Ronald S.

    1995-01-01

    The isotopes of boron, .sup.10 B and .sup.11 B, are separated by means of a gas-liquid chemical exchange reaction involving the isotopic equilibrium between gaseous BF.sub.3 and a liquid BF.sub.3 . donor molecular addition complex formed between BF.sub.3 gas and a donor chosen from the group consisting of: nitromethane, acetone, methyl isobutyl ketone, or diisobutyl ketone.

  18. New Method to Acquire Chemomechanical Parameters of Diverse Chemical Reactions

    DTIC Science & Technology

    2011-01-30

    susceptibility of electrophilic sites in polymers to nucleophilic attack (e.g., by water ), which is thought to be a major initiation mechanism of strain...reactions offers unique attributes, e.g., potentially fast actuation cycles , high chemical and mechanical stability, flexible device design and...a model for reversible and pseudoreversible isothermal photoactuation based on the Carnot -type formalism and used it to estimate the maximum single

  19. Exploring chemical diversity via a modular reaction pairing strategy

    PubMed Central

    Loh, Joanna K; Yoon, Sun Young; Samarakoon, Thiwanka B; Rolfe, Alan; Porubsky, Patrick; Neuenswander, Benjamin; Lushington, Gerald H

    2012-01-01

    Summary The efficient synthesis of an 80-member library of unique benzoxathiazocine 1,1-dioxides by a microwave-assisted, intermolecular nucleophilic aromatic substitution (SNAr) diversification pathway is reported. Eight benzofused sultam cores were generated by means of a sulfonylation/SNAr/Mitsunobu reaction pairing protocol, and subsequently diversified by intermolecular SNAr with ten chiral, non-racemic amine/amino alcohol building blocks. Computational analyses were employed to explore and evaluate the chemical diversity of the library. PMID:23019462

  20. Shock-Induced Chemical Reactions in Condensed Matter.

    DTIC Science & Technology

    1982-08-01

    Technical, 4/1/78 - 6/30/82 Matter 6. PERFORMING ORG. REPORT NUMBER 7. AUTHOR(s) S. CONTRACT OR GRANT NUMUER(e) George E. Duvall, Principal Investigator...CHEMICAL REACTIONS IN CONDENSED MATTER George E. Duvall, Principal Investigator Stephen A. Sheffield* Kendal M. OgilvieT 4 C. Robert Wilson Paul...Temperture," in Sixth Symposium (International on Detonation (Office of Naval Research, Arlington, 1976), ACR-Z21, p. 36. 24. G. Gamow , "Tentative

  1. A microvascular system for chemical reactions using surface waste heat.

    PubMed

    Nguyen, Du Thai; Esser-Kahn, Aaron P

    2013-12-16

    Coffee-powered chemistry: Low-grade waste heat on surfaces can be used to drive chemical reactions, including the regeneration of a CO2 capture solution. Flowing two-phase heat transfer has been implemented within microvascular systems. This stripping system can be adapted to pre-fabricated surfaces, as demonstrated by a coffee mug containing a 1.2 m long microchannel. MEA=monoethanolamine.

  2. Solution of Chemical Master Equations for Nonlinear Stochastic Reaction Networks.

    PubMed

    Smadbeck, Patrick; Kaznessis, Yiannis N

    2014-08-01

    Stochasticity in the dynamics of small reacting systems requires discrete-probabilistic models of reaction kinetics instead of traditional continuous-deterministic ones. The master probability equation is a complete model of randomly evolving molecular populations. Because of its ambitious character, the master equation remained unsolved for all but the simplest of molecular interaction networks. With the first solution of chemical master equations, a wide range of experimental observations of small-system interactions may be mathematically conceptualized.

  3. Solution of Chemical Master Equations for Nonlinear Stochastic Reaction Networks

    PubMed Central

    Smadbeck, Patrick; Kaznessis, Yiannis N.

    2014-01-01

    Stochasticity in the dynamics of small reacting systems requires discrete-probabilistic models of reaction kinetics instead of traditional continuous-deterministic ones. The master probability equation is a complete model of randomly evolving molecular populations. Because of its ambitious character, the master equation remained unsolved for all but the simplest of molecular interaction networks. With the first solution of chemical master equations, a wide range of experimental observations of small-system interactions may be mathematically conceptualized. PMID:25215268

  4. Separation of the isotopes of boron by chemical exchange reactions

    DOEpatents

    McCandless, F.P.; Herbst, R.S.

    1995-05-30

    The isotopes of boron, {sup 10}B and {sup 11}B, are separated by means of a gas-liquid chemical exchange reaction involving the isotopic equilibrium between gaseous BF{sub 3} and a liquid BF{sub 3} donor molecular addition complex formed between BF{sub 3} gas and a donor chosen from the group consisting of: nitromethane, acetone, methyl isobutyl ketone, or diisobutyl ketone. 1 Fig.

  5. Nitrosonium cation in chemical and biochemical reactions: achievements and prospects

    NASA Astrophysics Data System (ADS)

    Borodkin, G. I.; Shubin, V. G.

    2017-01-01

    Data on the reactivity of nitrosonium cation in chemical reactions are systematized and integrated. The review demonstrates the structural diversity of nitrosonium complexes resulting from the specific features of the electronic structure of NO+. The use of nitrosonium salts in the synthesis of heterocyclic compounds and for the preparation of modern materials, including nanomaterials, is considered. The participation of NO+ in oxidative, catalytic and biochemical processes is discussed. The bibliography includes 332 references.

  6. Exploring chemical reaction mechanisms through harmonic Fourier beads path optimization.

    PubMed

    Khavrutskii, Ilja V; Smith, Jason B; Wallqvist, Anders

    2013-10-28

    Here, we apply the harmonic Fourier beads (HFB) path optimization method to study chemical reactions involving covalent bond breaking and forming on quantum mechanical (QM) and hybrid QM∕molecular mechanical (QM∕MM) potential energy surfaces. To improve efficiency of the path optimization on such computationally demanding potentials, we combined HFB with conjugate gradient (CG) optimization. The combined CG-HFB method was used to study two biologically relevant reactions, namely, L- to D-alanine amino acid inversion and alcohol acylation by amides. The optimized paths revealed several unexpected reaction steps in the gas phase. For example, on the B3LYP∕6-31G(d,p) potential, we found that alanine inversion proceeded via previously unknown intermediates, 2-iminopropane-1,1-diol and 3-amino-3-methyloxiran-2-ol. The CG-HFB method accurately located transition states, aiding in the interpretation of complex reaction mechanisms. Thus, on the B3LYP∕6-31G(d,p) potential, the gas phase activation barriers for the inversion and acylation reactions were 50.5 and 39.9 kcal∕mol, respectively. These barriers determine the spontaneous loss of amino acid chirality and cleavage of peptide bonds in proteins. We conclude that the combined CG-HFB method further advances QM and QM∕MM studies of reaction mechanisms.

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

    NASA Technical Reports Server (NTRS)

    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.

  8. Exploring chemical reaction mechanisms through harmonic Fourier beads path optimization

    NASA Astrophysics Data System (ADS)

    Khavrutskii, Ilja V.; Smith, Jason B.; Wallqvist, Anders

    2013-10-01

    Here, we apply the harmonic Fourier beads (HFB) path optimization method to study chemical reactions involving covalent bond breaking and forming on quantum mechanical (QM) and hybrid QM/molecular mechanical (QM/MM) potential energy surfaces. To improve efficiency of the path optimization on such computationally demanding potentials, we combined HFB with conjugate gradient (CG) optimization. The combined CG-HFB method was used to study two biologically relevant reactions, namely, L- to D-alanine amino acid inversion and alcohol acylation by amides. The optimized paths revealed several unexpected reaction steps in the gas phase. For example, on the B3LYP/6-31G(d,p) potential, we found that alanine inversion proceeded via previously unknown intermediates, 2-iminopropane-1,1-diol and 3-amino-3-methyloxiran-2-ol. The CG-HFB method accurately located transition states, aiding in the interpretation of complex reaction mechanisms. Thus, on the B3LYP/6-31G(d,p) potential, the gas phase activation barriers for the inversion and acylation reactions were 50.5 and 39.9 kcal/mol, respectively. These barriers determine the spontaneous loss of amino acid chirality and cleavage of peptide bonds in proteins. We conclude that the combined CG-HFB method further advances QM and QM/MM studies of reaction mechanisms.

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

    NASA Technical Reports Server (NTRS)

    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.

  10. Variably severe systemic allergic reactions after consuming foods with unlabelled lupin flour: a case series

    PubMed Central

    2014-01-01

    Introduction Lupin allergy remains a significant cause of food-induced allergic reactivity and anaphylaxis. Previous work suggests a strong association with legume allergy and peanut allergy in particular. Both doctors and the public have little awareness of lupin as an allergen. Case presentation Case 1 was a 41-year-old Caucasian woman without previous atopy who developed facial swelling, widespread urticaria with asthma and hypotension within minutes of eating a quiche. Her lupin allergy was confirmed by both blood and skin tests. Her lupin sensitivity was so severe that even the miniscule amount of lupin allergen in the skin testing reagent produced a mild reaction. Case 2 was a 42-year-old mildly atopic Caucasian woman with three episodes of worsening urticaria and asthma symptoms over 6 years occurring after the consumption of foods containing lupin flour. Blood and skin tests were positive for lupin allergy. Case 3 was a 38-year-old Caucasian woman with known oral allergy syndrome who had two reactions associated with urticaria and vomiting after consuming foods containing lupin flour. Skin testing confirmed significant responses to a lupin flour extract and to one of the foods inducing her reaction. Case 4 was a 54-year-old mildly atopic Caucasian woman with a 7 year history of three to four episodes each year of unpredictable oral tingling followed by urticaria after consuming a variety of foods. The most recent episode had been associated with vomiting. She had developed oral tingling with lentil and chickpeas over the previous year. Skin and blood tests confirmed lupin allergy with associated sensitivity to several legumes. Conclusions Lupin allergy can occur for the first time in adults without previous atopy or legume sensitivity. Although asymptomatic sensitisation is frequent, clinical reactivity can vary in severity from severe anaphylaxis to urticaria and vomiting. Lupin allergy may be confirmed by skin and specific immunoglobulin E estimation

  11. Nanochemistry - Chemical Reactions of Iron and Benzene Within Molecular Clusters

    NASA Astrophysics Data System (ADS)

    Feigerle, C. S.; Bililign, S.; Miller, John C.

    2000-06-01

    Molecular clusters represent a nanoscale test tube where chemical reactions can be examined in a unique way for the effects of the local environment and the possibility of size-dependent reactions. Previous experiments have shown that the ionization/dissociation of iron pentacarbonyl clusters can lead to the formation of iron ions and iron cluster ions and that these species can further react with dopant molecules to yield chemically rearranged products. The present experiments characterize similar reactions with benzene molecules and clusters. Heteroclusters of the form [Fe(CO)5]m(C6H6)nArp are created in an expanding supersonic jet of the component molecules. Following ionization by a 30 ps, 266 nm laser pulse, extensive dissociation, aggregation, and chemical rearrangement occurs leading to ionic products which are characterized by mass spectrometry. Cluster ions of the type Fem(C6H6)n + are observed as products. The stability of the sandwich form of the ion, Fe(benzene)2 +, is inferred from the data. Evidence for a similar special stability for the double-decker, Fe2(benzene)3 +, is presented.

  12. Review of the Literature on Determinants of Chemical Hazard Information Recall among Workers and Consumers.

    PubMed

    Sathar, Farzana; Dalvie, Mohamed Aqiel; Rother, Hanna-Andrea

    2016-05-31

    In many low and middle income countries (LMIC), workers' and consumers' only access to risk and hazard information in relation to the chemicals they use or work with is on the chemical label and safety data sheet. Recall of chemical hazard information is vital in order for label warnings and precautionary information to promote effective safety behaviors. A literature review, therefore, was conducted on determinants of chemical hazard information recall among workers and consumers globally. Since comprehension and recall are closely linked, the determinants of both were reviewed. Literature was reviewed from both online and print peer reviewed journals for all study designs and countries. This review indicated that the level of education, previous training and the inclusion of pictograms on the hazard communication material are all factors that contribute to the recall of hazard information. The influence of gender and age on recall is incongruent and remains to be explored. More research is required on the demographic predictors of the recall of hazard information, the effect of design and non-design factors on recall, the effect of training on the recall among low literate populations and the examining of different regions or contexts.

  13. Phase and chemical equilibria in multicomponent fluid systems with a chemical reaction

    NASA Astrophysics Data System (ADS)

    Toikka, A. M.; Samarov, A. A.; Toikka, M. A.

    2015-04-01

    Studies of the phase and chemical equilibria in the systems with chemical reaction cover a wide range of problems related to both experimental determination of physicochemical characteristics of these systems and various aspects of thermodynamic analysis of the phase and chemical processes occurring there. The main goal of this review consists in systematization and analysis of available experimental data concerning the vapour-liquid and liquid-liquid equilibria in multicomponent systems where chemical reactions occur. The studies considered here have been mainly published in recent years, and they include rather detailed data on physicochemical properties, phase transitions and chemical processes in fluid systems, i.e., the data which are essential for thermodynamic analysis. Available approaches to the thermodynamic analysis of heterogeneous systems with chemical reactions are also discussed. Particular attention is paid to the studies of the simultaneous phase and chemical equilibria. We hope that this review could be useful both for fundamental studies of heterogeneous reactive systems and for solving applied problems on the design of combined reactive and mass-transfer processes. The bibliography includes 79 references.

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

    SciTech Connect

    Gray, S.K.

    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.

  15. Laser-initiated chemical reactions in carbon suspensions.

    SciTech Connect

    McGrath, T. E.; Diebold, G. J.; Bartels, D. M.; Crowell, R. A.; Chemistry; Brown Univ.

    2002-10-31

    We report on laser-initiated chemical reactions in colloidal carbon suspensions. Irradiation of carbon particles ranging in size from 13 to 75 nm in diameter suspended in water, toluene, and benzene with high power nanosecond, picosecond, and femtosecond laser pulses leads to the formation of a number of gaseous hydrocarbons as well as a series of liquid-phase products. In the product gas above irradiated carbon suspensions in water, H{sub 2} and CO, the main reaction products of the carbon-steam reaction, and numerous hydrocarbons ranging from C{sub 1}-C{sub 4} were detected. Irradiation of particulate carbon in toluene and benzene gave H{sub 2} as the main gas product with small amounts of C{sub 1}-C{sub 3} hydrocarbons. Bibenzyl and biphenyl were found as the main liquid products produced in toluene and benzene suspensions, respectively, but with numerous polycyclic aromatic hydrocarbons in smaller concentrations. The amount of products generated by pulsed laser irradiation is shown to depend on particle size and concentration, as well as the laser fluence and pulse width. The chemical reactions reported take place under conditions characterized by extremely high temperatures and pressures of short duration.

  16. Effect of aspect ratio on chemical reactions on microchip.

    PubMed

    Shimizu, Takahiro; Masaki, Hiroyuki; Korenaga, Takashi

    2006-01-01

    Parallel two-phase laminar flow, which is formed when two solutions flow in microchannels, has been developed and has advanced unique research in the area of microchip analysis. In two-phase laminar flow, channel size has a significant effect on the efficiency of chemical reactions. However, the sizes of microchannels vary greatly in many studies. In this paper, we report on the effect of microchannel size on chemical reactions on a microchip. Aspect ratio is defined as the ratio of depth to width of a microchannel. Five microchips with different aspect ratios (from 0.50 to 2.00) were fabricated by mechanical machining. The reaction of nitrous acid and Saltzman reagent was carried out on these microchips and the absorbance was measured on-line in a capillary tube, which was attached to the outlet on the microchip. The results showed that the color reaction occurred more efficiently as the aspect ratio increased. This result is expected to be useful when determining the size of microchannels.

  17. Arbitrarily Complex Chemical Reactions on Particles

    NASA Astrophysics Data System (ADS)

    Benson, D. A.; Bolster, D.

    2016-12-01

    Previous particle-tracking (PT) algorithms for chemical reaction conceptualize each particle being composed of one species. Reactions occur by either complete or partial birth/death processes between interacting particles. Here we extend the method by placing any number of chemical species on each particle, thereby allowing the single-step calculation of arbitrarily complex reactions using standard methods. The algorithm relies on calculating the correct mass transfer of species between particles, which is exactly given by our previous probabilistic algorithm. The various novel components of the new method are verified against analytic solutions where possible. The potential benefits of the method have been discussed elsewhere in the context of simple bimolecular reactions: the PT method does not artificially mix constituents by numerical dispersion, the particles do not have a Courant number criterion for stability, and the number of particles is very often going to be smaller than the number of cells in a typical grid-based simulation, so that the number of numerical geochemical calculations is similarly smaller.

  18. The nature of chemical reaction-driven tip-streaming

    NASA Astrophysics Data System (ADS)

    Mayer, H. C.; Krechetnikov, R.

    2013-05-01

    The discovery of chemical reaction-driven tip-streaming (also known as "an amazing drop") was made about a decade ago during measurements of the dynamic interfacial tension of a water-alkali pendant droplet immersed in oil-linoleic acid. A plausible explanation for this self-sustained ejection of micron sized droplets from the tip of the macroscopic pendant drop was offered at that time and attributed to Marangoni stresses driving the reaction-produced surfactant along the interface. Later, asymptotic theory based on the analysis of a complete fluid dynamical formulation supported this hypothesis. As this discovery promised a way of microdroplet generation without the need for complex microchannel geometries or externally imposed flow or electric fields, we were recently motivated to study the influence of the reagent concentrations and reaction rate on the droplet generation. However, in an attempt to recreate the original experiments, we revealed that the cause for tip-streaming is not what it originally seemed to be. This led to a series of experiments clarifying the role of the Marangoni stresses and the crucial differences from similar phenomena. As the mechanism by which the phenomenon was originally thought to operate was supported by recent theoretical studies, the present work leads to new intriguing questions of existence and conditions under which a chemical reaction alone can drive Marangoni stresses capable of self-sustaining the process of tip-streaming.

  19. [Recent results in research on oscillatory chemical reactions].

    PubMed

    Poros, Eszter; Kurin-Csörgei, Krisztina

    2014-01-01

    The mechanisms of the complicated periodical phenomenas in the nature (e.g. hearth beat, sleep cycle, circadian rhythms, etc) could be understood with using the laws of nonlinear chemical systems. In this article the newest result in the research of the subfield of nonlinear chemical dynamics aimed at constructing oscillatory chemical reactions, which are novel either in composition or in configuration, are presented. In the introductory part the concept of chemical periodicity is defined, then the forms as it can appear in time and space and the methods of their study are discussed. Detailed description of the experimental work that has resulted in two significant discoveries is provided. A method was developed to design pH-oscillators which are capable of operating under close conditions. The batch pH-oscillators are more convenient to use in some proposed applications than the equivalent CSTR variant. A redox oscillator that is new in composition was found. The permanganate oxidation of some amino acids was shown to take place according to oscillatory kinetics in a narrow range of the experimental parameters. The KMnO4 - glycine - Na2HPO4 system represents the first example in the family of manganese based oscillators where amino acids is involved. In the conclusion formal analogies between the simple chemical and some more complicated biological oscillatory phenomena are mentioned and the possibility of modeling periodic processes with the use of information gained from the studies of chemical oscillations is pointed out.

  20. Physio-chemical reactions in recycle aggregate concrete.

    PubMed

    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.

  1. Mesoscale simulations of shockwave energy dissipation via chemical reactions

    NASA Astrophysics Data System (ADS)

    Antillon, Edwin; Strachan, Alejandro

    2015-06-01

    We use a particle-based mesoscale model that incorporates chemical reactions at a coarse-grained level to study the response of materials under shockwave-loading conditions. An additional implicit variable (the particle size) is used to describe volume-reducing chemical reactions using an intra-molecular potential inspired by Transition State Theory, while the dynamics of the center-of-mass motion evolves according to inter-particle forces. The equations of motion are derived from a Hamiltonian and the model captures both: total energy conservation and Galilean invariance. We demonstrate that this model captures complex thermo-mechanical-chemical processes, and we use these features to explore materials with the capabilities to dissipate shocks-wave energy due to ballistic impacts. Our results characterize how the parameters of the chemical model affect shock-wave attenuation, and we elucidate on how the coupling between the different energy-transferring mechanisms influences nucleation of chemistry for conditions away from equilibrium.

  2. Reversible chemical reactions for single-color multiplexing microscopy.

    PubMed

    Brox, Dominik; Schwering, Michael; Engelhardt, Johann; Herten, Dirk-Peter

    2014-08-04

    Recent developments in biology demand an increasing number of simultaneously imaged structures with standard fluorescence microscopy. However, the number of multiplexed channels is limited for most multiplexing modalities, such as spectral multiplexing or fluorescence-lifetime imaging. We propose extending the number of imaging channels by using chemical reactions, controlling the emissive state of fluorescent dyes. As proof of concept, we reversibly switch a fluorescent copper sensor to enable successive imaging of two different structures in the same spectral channel. We also show that this chemical multiplexing is orthogonal to existing methods. By using two different dyes, we combine chemical with spectral multiplexing for the simultaneous imaging of four different structures with only two spectrally different channels. We characterize and discuss the approach and provide perspectives for extending imaging modalities in stimulated emission depletion microscopy, for which spectral multiplexing is technically demanding.

  3. Humidity independent mass spectrometry for gas phase chemical analysis via ambient proton transfer reaction.

    PubMed

    Zhu, Hongying; Huang, Guangming

    2015-03-31

    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.

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

    SciTech Connect

    Nguyen, H.D.

    1991-11-01

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

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

    SciTech Connect

    Nguyen, H.D.

    1991-11-01

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

  6. 'Would you eat cultured meat?': Consumers' reactions and attitude formation in Belgium, Portugal and the United Kingdom.

    PubMed

    Verbeke, Wim; Marcu, Afrodita; Rutsaert, Pieter; Gaspar, Rui; Seibt, Beate; Fletcher, Dave; Barnett, Julie

    2015-04-01

    Cultured meat has evolved from an idea and concept into a reality with the August 2013 cultured hamburger tasting in London. Still, how consumers conceive cultured meat is largely an open question. This study addresses consumers' reactions and attitude formation towards cultured meat through analyzing focus group discussions and online deliberations with 179 meat consumers from Belgium, Portugal and the United Kingdom. Initial reactions when learning about cultured meat were underpinned by feelings of disgust and considerations of unnaturalness. Consumers saw few direct personal benefits but they were more open to perceiving global societal benefits relating to the environment and global food security. Both personal and societal risks were framed in terms of uncertainties about safety and health, and possible adverse societal consequences dealing with loss of farming and eating traditions and rural livelihoods. Further reflection pertained to skepticism about 'the inevitable' scientific progress, concern about risk governance and control, and need for regulation and proper labeling.

  7. Compare and contrast the reaction coordinate diagrams for chemical reactions and cytoskeletal force generators

    PubMed Central

    Scholey, Jonathan M.

    2013-01-01

    Reaction coordinate diagrams are used to relate the free energy changes that occur during the progress of chemical processes to the rate and equilibrium constants of the process. Here I briefly review the application of these diagrams to the thermodynamics and kinetics of the generation of force and motion by cytoskeletal motors and polymer ratchets as they mediate intracellular transport, organelle dynamics, cell locomotion, and cell division. To provide a familiar biochemical context for discussing these subcellular force generators, I first review the application of reaction coordinate diagrams to the mechanisms of simple chemical and enzyme-catalyzed reactions. My description of reaction coordinate diagrams of motors and polymer ratchets is simplified relative to the rigorous biophysical treatment found in many of the references that I use and cite, but I hope that the essay provides a valuable qualitative representation of the physical chemical parameters that underlie the generation of force and motility at molecular scales. In any case, I have found that this approach represents a useful interdisciplinary framework for understanding, researching, and teaching the basic molecular mechanisms by which motors contribute to fundamental cell biological processes. PMID:23408787

  8. Compare and contrast the reaction coordinate diagrams for chemical reactions and cytoskeletal force generators.

    PubMed

    Scholey, Jonathan M

    2013-02-01

    Reaction coordinate diagrams are used to relate the free energy changes that occur during the progress of chemical processes to the rate and equilibrium constants of the process. Here I briefly review the application of these diagrams to the thermodynamics and kinetics of the generation of force and motion by cytoskeletal motors and polymer ratchets as they mediate intracellular transport, organelle dynamics, cell locomotion, and cell division. To provide a familiar biochemical context for discussing these subcellular force generators, I first review the application of reaction coordinate diagrams to the mechanisms of simple chemical and enzyme-catalyzed reactions. My description of reaction coordinate diagrams of motors and polymer ratchets is simplified relative to the rigorous biophysical treatment found in many of the references that I use and cite, but I hope that the essay provides a valuable qualitative representation of the physical chemical parameters that underlie the generation of force and motility at molecular scales. In any case, I have found that this approach represents a useful interdisciplinary framework for understanding, researching, and teaching the basic molecular mechanisms by which motors contribute to fundamental cell biological processes.

  9. [Anaphylactic reactions to low-molecular weight chemicals].

    PubMed

    Nowak, Daria; Panaszek, Bernard

    2015-02-06

    Low-molecular weight chemicals (haptens) include a large group of chemical compounds occurring in work environment, items of everyday use (cleaning products, clothing, footwear, gloves, furniture), jewelry (earrings, bracelets), drugs, especially in cosmetics. They cause type IV hypersensitive reactions. During the induction phase of delayed-type hypersensitivity, haptens form complexes with skin proteins. After internalization through antigen presenting cells, they are bound to MHC class II molecules. Next, they are exposed against specific T-lymphocytes, what triggers activation of Th1 cells mainly. After repeating exposition to that hapten, during effector phase, Th1 induce production of cytokines affecting non-specific inflammatory cells. Usually, it causes contact dermatitis. However, occasionally incidence of immediate generalized reactions after contact with some kinds of haptens is noticed. A question arises, how the hapten does induce symptoms which are typical for anaphylaxis, and what contributes to amplification of this mechanism. It seems that this phenomenon arises from pathomechanism occurring in contact urticaria syndrome in which an anaphylactic reaction may be caused either by contact of sensitized skin with protein antigens, high-molecular weight allergens, or haptens. One of the hypotheses indicates the leading role of basophiles in this process. Their contact with haptens, may cause to release mediators of immediate allergic reaction (histamine, eicosanoids) and to produce cytokines corresponding to Th2 cells profile. Furthermore, Th17 lymphocytes secreting pro-inflammatory interleukin-17 might be engaged into amplifying hypersensitivity into immediate reactions and regulatory T-cells may play role in the process, due to insufficient control of the activity of effector cells.

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

    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)

  12. Chemical reaction network approaches to Biochemical Systems Theory.

    PubMed

    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. Copyright © 2015 Elsevier Inc. All rights reserved.

  13. Chemical reaction optimization for solving shortest common supersequence problem.

    PubMed

    Khaled Saifullah, C M; Rafiqul Islam, Md

    2016-10-01

    Shortest common supersequence (SCS) is a classical NP-hard problem, where a string to be constructed that is the supersequence of a given string set. The SCS problem has an enormous application of data compression, query optimization in the database and different bioinformatics activities. Due to NP-hardness, the exact algorithms fail to compute SCS for larger instances. Many heuristics and meta-heuristics approaches were proposed to solve this problem. In this paper, we propose a meta-heuristics approach based on chemical reaction optimization, CRO_SCS that is designed inspired by the nature of the chemical reactions. For different optimization problems like 0-1 knapsack, quadratic assignment, global numeric optimization problems CRO algorithm shows very good performance. We have redesigned the reaction operators and a new reform function to solve the SCS problem. The outcomes of the proposed CRO_SCS algorithm are compared with those of the enhanced beam search (IBS_SCS), deposition and reduction (DR), ant colony optimization (ACO) and artificial bee colony (ABC) algorithms. The length of supersequence, execution time and standard deviation of all related algorithms show that CRO_SCS gives better results on the average than all other algorithms. Copyright © 2016 Elsevier Ltd. All rights reserved.

  14. Chemical resolution of Pu+ from U+ and Am+ using a band-pass reaction cell inductively coupled plasma mass spectrometer.

    PubMed

    Tanner, Scott D; Li, Chunsheng; Vais, Vladimir; Baranov, Vladimir I; Bandura, Dmitry R

    2004-06-01

    Determination of the concentration and distribution of the Pu and Am isotopes is hindered by the isobaric overlaps between the elements themselves and U, generally requiring time-consuming chemical separation of the elements. A method is described in which chemical resolution of the elemental ions is obtained through ion-molecule reactions in a reaction cell of an ICPMS instrument. The reactions of "natural" U(+), (242)Pu(+), and (243)Am(+) with ethylene, carbon dioxide, and nitric oxide are reported. Since the net sensitivities to the isotopes of an element are similar, chemical resolution is inferred when one isobaric element reacts rapidly with a given gas and the isobar (or in this instance surrogate isotope) is unreactive or slowly reactive. Chemical resolution of the m/z 238 isotopes of U and Pu can be obtained using ethylene as a reaction gas, but little improvement in the resolution of the m/z 239 isobars is obtained. However, high efficiency of reaction of U(+) and UH(+) with CO(2), and nonreaction of Pu(+), allows the sub-ppt determination of (239)Pu, (240)Pu, and (242)Pu (single ppt for (238)Pu) in the presence of 7 orders of magnitude excess U matrix without prior chemical separation. Similarly, oxidation of Pu(+) by NO, and nonreaction of Am(+), permit chemical resolution of the isobars of Pu and Am over 2-3 orders of magnitude relative concentration. The method provides the potential for analysis of the actinides with reduced sample matrix separation.

  15. Determination of caffeine using oscillating chemical reaction in a CSTR.

    PubMed

    Gao, Jinzhang; Ren, Jie; Yang, Wu; Liu, XiuHui; Yang, Hua

    2003-07-14

    A new analytical method for the determination of caffeine by the sequential perturbation caused by different amounts of caffeine on the oscillating chemical system involving the manganese(II)-catalyzed reaction between potassium bromate and tyrosine in acidic medium in a CSTR was proposed. The method exposed for the first time in this work. It relies on the relationship between the changes in the oscillation amplitude of the chemical system and the concentration of caffeine. The calibration curve fits a second-order polynomial equation very well when the concentration of caffeine over the range 4.0 x 10(-6) - 1.2 x 10(-4) M (r = 0.9968). The effect of influential variables, such as the concentration of reaction components, injection point, temperature, flow rate and stirring rate were studied. Some aspects of the potential mechanism of action of caffeine on the chemical oscillating system were also discussed. A real sample was determined and the result was satisfactory.

  16. Coupled near-field and far-field exposure assessment framework for chemicals in consumer products.

    PubMed

    Fantke, Peter; Ernstoff, Alexi S; Huang, Lei; Csiszar, Susan A; Jolliet, Olivier

    2016-09-01

    Humans can be exposed to chemicals in consumer products through product use and environmental emissions over the product life cycle. Exposure pathways are often complex, where chemicals can transfer directly from products to humans during use or exchange between various indoor and outdoor compartments until sub-fractions reach humans. To consistently evaluate exposure pathways along product life cycles, a flexible mass balance-based assessment framework is presented structuring multimedia chemical transfers in a matrix of direct inter-compartmental transfer fractions. By matrix inversion, we quantify cumulative multimedia transfer fractions and exposure pathway-specific product intake fractions defined as chemical mass taken in by humans per unit mass of chemical in a product. Combining product intake fractions with chemical mass in the product yields intake estimates for use in life cycle impact assessment and chemical alternatives assessment, or daily intake doses for use in risk-based assessment and high-throughput screening. Two illustrative examples of chemicals used in personal care products and flooring materials demonstrate how this matrix-based framework offers a consistent and efficient way to rapidly compare exposure pathways for adult and child users and for the general population. This framework constitutes a user-friendly approach to develop, compare and interpret multiple human exposure scenarios in a coupled system of near-field ('user' environment), far-field and human intake compartments, and helps understand the contribution of individual pathways to overall human exposure in various product application contexts to inform decisions in different science-policy fields for which exposure quantification is relevant. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

  17. Massively parallel computation of 3D flow and reactions in chemical vapor deposition reactors

    SciTech Connect

    Salinger, A.G.; Shadid, J.N.; Hutchinson, S.A.; Hennigan, G.L.; Devine, K.D.; Moffat, H.K.

    1997-12-01

    Computer modeling of Chemical Vapor Deposition (CVD) reactors can greatly aid in the understanding, design, and optimization of these complex systems. Modeling is particularly attractive in these systems since the costs of experimentally evaluating many design alternatives can be prohibitively expensive, time consuming, and even dangerous, when working with toxic chemicals like Arsine (AsH{sub 3}): until now, predictive modeling has not been possible for most systems since the behavior is three-dimensional and governed by complex reaction mechanisms. In addition, CVD reactors often exhibit large thermal gradients, large changes in physical properties over regions of the domain, and significant thermal diffusion for gas mixtures with widely varying molecular weights. As a result, significant simplifications in the models have been made which erode the accuracy of the models` predictions. In this paper, the authors will demonstrate how the vast computational resources of massively parallel computers can be exploited to make possible the analysis of models that include coupled fluid flow and detailed chemistry in three-dimensional domains. For the most part, models have either simplified the reaction mechanisms and concentrated on the fluid flow, or have simplified the fluid flow and concentrated on rigorous reactions. An important CVD research thrust has been in detailed modeling of fluid flow and heat transfer in the reactor vessel, treating transport and reaction of chemical species either very simply or as a totally decoupled problem. Using the analogy between heat transfer and mass transfer, and the fact that deposition is often diffusion limited, much can be learned from these calculations; however, the effects of thermal diffusion, the change in physical properties with composition, and the incorporation of surface reaction mechanisms are not included in this model, nor can transitions to three-dimensional flows be detected.

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

    ERIC Educational Resources Information Center

    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…

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

    ERIC Educational Resources Information Center

    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…

  20. A review of models for near-field exposure pathways of chemicals in consumer products.

    PubMed

    Huang, Lei; Ernstoff, Alexi; Fantke, Peter; Csiszar, Susan A; Jolliet, Olivier

    2017-01-01

    Exposure to chemicals in consumer products has been gaining increasing attention, with multiple studies showing that near-field exposures from products is high compared to far-field exposures. Regarding the numerous chemical-product combinations, there is a need for an overarching review of models able to quantify the multiple transfers of chemicals from products used near-field to humans. The present review therefore aims at an in-depth overview of modeling approaches for near-field chemical release and human exposure pathways associated with consumer products. It focuses on lower-tier, mechanistic models suitable for life cycle assessments (LCA), chemical alternative assessment (CAA) and high-throughput screening risk assessment (HTS). Chemicals in a product enter the near-field via a defined "compartment of entry", are transformed or transferred to adjacent compartments, and eventually end in a "human receptor compartment". We first focus on models of physical mass transfers from the product to 'near-field' compartments. For transfers of chemicals from article interior, adequate modeling of in-article diffusion and of partitioning between article surface and air/skin/food is key. Modeling volatilization and subsequent transfer to the outdoor is crucial for transfers of chemicals used in the inner space of appliances, on object surfaces or directly emitted to indoor air. For transfers from skin surface, models need to reflect the competition between dermal permeation, volatilization and fraction washed-off. We then focus on transfers from the 'near-field' to 'human' compartments, defined as respiratory tract, gastrointestinal tract and epidermis, for which good estimates of air concentrations, non-dietary ingestion parameters and skin permeation are essential, respectively. We critically characterize for each exposure pathway the ability of models to estimate near-field transfers and to best inform LCA, CAA and HTS, summarizing the main characteristics of the

  1. Nature of the chemical reaction for furfural modified asphalt

    SciTech Connect

    Memon, G.M.; Chollar, B.H.

    1994-12-31

    Three of the most serious problems of asphalt pavements today are rutting, cracking, and susceptibility to moisture damage (stripping). Asphalt manufacturers have been mixing asphalts with polymers to produce polymer-modified asphalts with improved rheological properties. However, the costs for these improved polymer-modified asphalts are almost double that of regular asphalts. FHWA researchers have found that asphalt modified by the chemical, furfural (which is prepared by simple elimination reaction of aldopentoses obtained from oat hulls), exhibited better stripping properties and was less temperature susceptible than the virgin asphalt while costing less than polymer-modified asphalts. This paper discusses the possible structure of the furfural-modified asphalt, data for the virgin and furfural-modified asphalts and their Corbett fractions, data from a model reaction between phenol and furfural, and a possible explanation of this structure based on these data.

  2. Chemical characteristics of mineral trioxide aggregate and its hydration reaction

    PubMed Central

    2012-01-01

    Mineral trioxide aggregate (MTA) was developed in early 1990s and has been successfully used for root perforation repair, root end filling, and one-visit apexification. MTA is composed mainly of tricalcium silicate and dicalcium silicate. When MTA is hydrated, calcium silicate hydrate (CSH) and calcium hydroxide is formed. Formed calcium hydroxide interacts with the phosphate ion in body fluid and form amorphous calcium phosphate (ACP) which finally transforms into calcium deficient hydroxyapatite (CDHA). These mineral precipitate were reported to form the MTA-dentin interfacial layer which enhances the sealing ability of MTA. Clinically, the use of zinc oxide euginol (ZOE) based materials may retard the setting of MTA. Also, the use of acids or contact with excessive blood should be avoided before complete set of MTA, because these conditions could adversely affect the hydration reaction of MTA. Further studies on the chemical nature of MTA hydration reaction are needed. PMID:23429542

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

    NASA Technical Reports Server (NTRS)

    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.

  4. Predicting the evolution of fast chemical reactions in chaotic flows.

    PubMed

    Tsang, Yue-Kin

    2009-08-01

    We study the fast irreversible bimolecular reaction in a two-dimensional chaotic flow. The reactants are initially segregated and together fill the whole domain. Simulations show that the reactant concentration decays exponentially with rate lambda and then crosses over to the algebraic law of chemical kinetics in the final stage of the reaction. We estimate the crossover time from the reaction rate constant and the flow parameters. The exponential decay phase of the reaction can be described in terms of an equivalent passive scalar problem, allowing us to predict lambda using the theory of passive scalar advection. Depending on the relative length scale between the velocity and the concentration fields, lambda is either related to the distribution of the finite-time Lyapunov exponent of the flow or given in terms of an effective diffusivity which is independent of the small-scale stretching properties of the flow. For the former case, we suggest an optimal choice of flow parameters at which lambda is maximum.

  5. Confinement effects on chemical reactions in nanostructured carbon materials

    NASA Astrophysics Data System (ADS)

    George, Aaron; Kostov, Milen; Buongiorno Nardelli, Marco

    2005-03-01

    Chemical reactions are frequently carried out in nano-structured media, such as micellar or colloidal solutions, nano-porous media, hydrogels or organogels, or in systems involving nano-particles. Nanostructured environments have been shown to enhance reaction rates through a variety of catalytic effects, such as high surface area, interactions with the nano-structure or confinement. In this work, we have used state-of-the-art electronic structure techniques to study the prototypical example of the hydrogen-producing reaction of formaldehyde dissociation (H2CO -> H2 + CO) within various configurations of a graphitic pore. Using the Nudged Elastic Band (NEB) method for transition states analysis, we have found that the activation energy of the dissociation can be influenced by the presence of a graphitic pore. In particular, while a graphene surface reduces the activation barrier for the reaction, this catalytic effect is enhanced by the presence of two planar sheets, which mimic the geometry of a nano-pore. These findings will be discussed in terms of the charge transfer and/or polarization mechanism associated with the catalytic process.

  6. Chemical Kinetic Reaction Mechanisms for Combustion of Hydrocarbon and Other Types of Chemical Fuels

    DOE Data Explorer

    The central feature of the Combustion Chemistry project at LLNL is the development, validation, and application of detailed chemical kinetic reaction mechanisms for the combustion of hydrocarbon and other types of chemical fuels. For the past 30 years, LLNL's Chemical Sciences Division has built hydrocarbon mechanisms for fuels from hydrogen and methane through much larger fuels including heptanes and octanes. Other classes of fuels for which models have been developed include flame suppressants such as halons and organophosphates, and air pollutants such as soot and oxides of nitrogen and sulfur. Reaction mechanisms have been tested and validated extensively through comparisons between computed results and measured data from laboratory experiments (e.g., shock tubes, laminar flames, rapid compression machines, flow reactors, stirred reactors) and from practical systems (e.g., diesel engines, spark-ignition engines, homogeneous charge, compression ignition (HCCI) engines). These kinetic models are used to examine a wide range of combustion systems.

  7. Spatially resolved chemical reaction monitoring using magnetic resonance imaging.

    PubMed

    Feindel, Kirk W

    2016-06-01

    Over the previous three decades, the use of MRI for studying dynamic physical and chemical processes of materials systems has grown significantly. This mini-review provides a brief introduction to relevant principles of MRI, including methods of spatial localization, factors contributing to image contrast, and chemical shift imaging. A few historical examples of (1) H MRI for reaction monitoring will be presented, followed by a review of recent research including (1) H MRI studies of gelation and biofilms, (1) H, (7) Li, and (11) B MRI studies of electrochemical systems, in vivo glucose metabolism monitored with (19) F MRI, and in situ temperature monitoring with (27) Al MRI. Copyright © 2015 John Wiley & Sons, Ltd.

  8. Scaling Laws for Pulsed Chain-Reaction Chemical Lasers.

    DTIC Science & Technology

    1981-08-07

    HOFLANO, J3 S WHITTIER FOR701-SO-C-OOB1 UCASFE0TR-006i167213 -1 SO-TR-61-57 N MEL LEYELi two Scaling Laws for Pulsed Chain-Reaction Chemical Lasers H...44 CNN u-i LU C=, C= Ca . C= -IN HAND Mil C C" 41 U c-iG- Ca1 ~-J4J -~40) c.Ji C-4- C= G’H Io sifld 83ld A91:3N3 1i7- For small K,te is of the order

  9. Exploring chemical diversity via a modular reaction pairing strategy.

    PubMed

    Loh, Joanna K; Yoon, Sun Young; Samarakoon, Thiwanka B; Rolfe, Alan; Porubsky, Patrick; Neuenswander, Benjamin; Lushington, Gerald H; Hanson, Paul R

    2012-01-01

    The efficient synthesis of an 80-member library of unique benzoxathiazocine 1,1-dioxides by a microwave-assisted, intermolecular nucleophilic aromatic substitution (S(N)Ar) diversification pathway is reported. Eight benzofused sultam cores were generated by means of a sulfonylation/S(N)Ar/Mitsunobu reaction pairing protocol, and subsequently diversified by intermolecular S(N)Ar with ten chiral, non-racemic amine/amino alcohol building blocks. Computational analyses were employed to explore and evaluate the chemical diversity of the library.

  10. Mechanism and nonlinear dynamics of an oscillating chemical reaction

    SciTech Connect

    Zhabotinsky, A.M.; Rovinsky, A.B.

    1987-09-01

    A mechanism and a model of a ferroin-catalyzed oscillating chemical system are described. This reaction presents an excellent example of a far-from-equilibrium system that forms spatial and temporal dissipative structures. The model shows that while the well-stirred system has a unique and stable stationary state, the same reagent spread in a thin layer may form complex spatiotemporal patterns. Stationary periodic patterns of both small and large amplitude, standing waves, and inhomogeneous chaotic oscillations are found in the model.

  11. Mechanism and nonlinear dynamics of an oscillating chemical reaction

    NASA Astrophysics Data System (ADS)

    Zhabotinsky, A. M.; Rovinsky, A. B.

    1987-09-01

    A mechanism and a model of a ferroin-catalyzed oscillating chemical system are descrined. This reaction presents an excellent example of a far-from-equilibrium system that forms spatial and temporal dissipative structures. The model shows that while the well-stirred system has a unique and stable stationary state, the same reagent spread in a thin layer may form complex spatiotemporal paterns. Stationary periodic patterns of both small and large amplitude, standing waves, and inhomogeneous chaotic oscillations are found in the model.

  12. Method for detecting pollutants. [through chemical reactions and heat treatment

    NASA Technical Reports Server (NTRS)

    Rogowski, R. S.; Richards, R. R.; Conway, E. J. (Inventor)

    1976-01-01

    A method is described for detecting and measuring trace amounts of pollutants of the group consisting of ozone, nitrogen dioxide, and carbon monoxide in a gaseous environment. A sample organic solid material that will undergo a chemical reaction with the test pollutant is exposed to the test environment and thereafter, when heated in the temperature range of 100-200 C., undergoes chemiluminescence that is measured and recorded as a function of concentration of the test pollutant. The chemiluminescence of the solid organic material is specific to the pollutant being tested.

  13. Peptide Bond Synthesis by a Mechanism Involving an Enzymatic Reaction and a Subsequent Chemical Reaction.

    PubMed

    Abe, Tomoko; Hashimoto, Yoshiteru; Zhuang, Ye; Ge, Yin; Kumano, Takuto; Kobayashi, Michihiko

    2016-01-22

    We recently reported that an amide bond is unexpectedly formed by an acyl-CoA synthetase (which catalyzes the formation of a carbon-sulfur bond) when a suitable acid and l-cysteine are used as substrates. DltA, which is homologous to the adenylation domain of nonribosomal peptide synthetase, belongs to the same superfamily of adenylate-forming enzymes, which includes many kinds of enzymes, including the acyl-CoA synthetases. Here, we demonstrate that DltA synthesizes not only N-(d-alanyl)-l-cysteine (a dipeptide) but also various oligopeptides. We propose that this enzyme catalyzes peptide synthesis by the following unprecedented mechanism: (i) the formation of S-acyl-l-cysteine as an intermediate via its "enzymatic activity" and (ii) subsequent "chemical" S → N acyl transfer in the intermediate, resulting in peptide formation. Step ii is identical to the corresponding reaction in native chemical ligation, a method of chemical peptide synthesis, whereas step i is not. To the best of our knowledge, our discovery of this peptide synthesis mechanism involving an enzymatic reaction and a subsequent chemical reaction is the first such one to be reported. This new process yields peptides without the use of a thioesterified fragment, which is required in native chemical ligation. Together with these findings, the same mechanism-dependent formation of N-acyl compounds by other members of the above-mentioned superfamily demonstrated that all members most likely form peptide/amide compounds by using this novel mechanism. Each member enzyme acts on a specific substrate; thus, not only the corresponding peptides but also new types of amide compounds can be formed. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

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

    SciTech Connect

    Valentini, J.J.

    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.

  15. Review of the Literature on Determinants of Chemical Hazard Information Recall among Workers and Consumers

    PubMed Central

    Sathar, Farzana; Dalvie, Mohamed Aqiel; Rother, Hanna-Andrea

    2016-01-01

    In many low and middle income countries (LMIC), workers’ and consumers’ only access to risk and hazard information in relation to the chemicals they use or work with is on the chemical label and safety data sheet. Recall of chemical hazard information is vital in order for label warnings and precautionary information to promote effective safety behaviors. A literature review, therefore, was conducted on determinants of chemical hazard information recall among workers and consumers globally. Since comprehension and recall are closely linked, the determinants of both were reviewed. Literature was reviewed from both online and print peer reviewed journals for all study designs and countries. This review indicated that the level of education, previous training and the inclusion of pictograms on the hazard communication material are all factors that contribute to the recall of hazard information. The influence of gender and age on recall is incongruent and remains to be explored. More research is required on the demographic predictors of the recall of hazard information, the effect of design and non-design factors on recall, the effect of training on the recall among low literate populations and the examining of different regions or contexts. PMID:27258291

  16. Community Detection Using Dual-Representation Chemical Reaction Optimization.

    PubMed

    Chang, Honghao; Feng, Zuren; Ren, Zhigang

    2016-09-23

    Many complex networks have been shown to have community structures. Detecting those structures is very important for understanding the organization and function of networks. Because this problem is NP-hard, it is appropriate to resort to evolutionary algorithms. Chemical reaction optimization (CRO) is a novel evolutionary algorithm inspired by the interactions among molecules during chemical reactions. In this paper, we propose a CRO variant named dual-representation CRO (DCRO) to address the community detection problem. DCRO encodes a solution in two representations: one is locus-based and the other is vector-based. The former representation can ensure the validity of a solution and fits for diversification search, and the latter is convenient for intensification search. We thus design two operators for CRO based on these two representations. Their cooperation enables DCRO to achieve a good balance between exploration and exploitation. Experimental results on synthetic and real-life networks show that DCRO can find community structures close to the actual ones and is capable of achieving solutions comparable to several state-of-the-art methods.

  17. Community Detection Using Dual-Representation Chemical Reaction Optimization.

    PubMed

    Chang, Honghao; Feng, Zuren; Ren, Zhigang

    2016-09-23

    Many complex networks have been shown to have community structures. Detecting those structures is very important for understanding the organization and function of networks. Because this problem is NP-hard, it is appropriate to resort to evolutionary algorithms. Chemical reaction optimization (CRO) is a novel evolutionary algorithm inspired by the interactions among molecules during chemical reactions. In this paper, we propose a CRO variant named dual-representation CRO (DCRO) to address the community detection problem. DCRO encodes a solution in two representations: one is locus-based and the other is vector-based. The former representation can ensure the validity of a solution and fits for diversification search, and the latter is convenient for intensification search. We thus design two operators for CRO based on these two representations. Their cooperation enables DCRO to achieve a good balance between exploration and exploitation. Experimental results on synthetic and real-life networks show that DCRO can find community structures close to the actual ones and is capable of achieving solutions comparable to several state-of-the-art methods.

  18. New Possibilities for Magnetic Control of Chemical and Biochemical Reactions.

    PubMed

    Buchachenko, Anatoly; Lawler, Ronald G

    2017-02-20

    Chemistry is controlled by Coulomb energy; magnetic energy is lower by many orders of magnitude and may be confidently ignored in the energy balance of chemical reactions. The situation becomes less clear, however, when reaction rates are considered. In this case, magnetic perturbations of nearly degenerate energy surface crossings may produce observable, and sometimes even dramatic, effects on reactions rates, product yields, and spectroscopic transitions. A case in point that has been studied for nearly five decades is electron spin-selective chemistry via the intermediacy of radical pairs. Magnetic fields, external (permanent or oscillating) and the internal magnetic fields of magnetic nuclei, have been shown to overcome electron spin selection rules for pairs of reactive paramagnetic intermediates, catalyzing or inhibiting chemical reaction pathways. The accelerating effects of magnetic stimulation may therefore be considered to be magnetic catalysis. This type of catalysis is most commonly observed for reactions of a relatively long-lived radical pair containing two weakly interacting electron spins formed by dissociation of molecules or by electron transfer. The pair may exist in singlet (total electron spin is zero) or triplet (total spin is unity) spin states. In virtually all cases, only the singlet state yields stable reaction products. Magnetic interactions with nuclear spins or applied fields may therefore affect the reactivity of radical pairs by changing the angular momentum of the pairs. Magnetic catalysis, first detected via its effect on spin state populations in nuclear and electron spin resonance, has been shown to function in a great variety of well-characterized reactions of organic free radicals. Considerably less well studied are examples suggesting that the basic mechanism may also explain magnetic effects that stimulate ATP synthesis, eliminating ATP deficiency in cardiac diseases, control cell proliferation, killing cancer cells, and

  19. Reaction Paths and Chemical Activation Reactions of 2-Methyl-5-Furanyl Radical with (3)O2.

    PubMed

    Hudzik, Jason M; Bozzelli, Joseph W

    2017-10-05

    Interest in high-energy substituted furans has been increasing due to their occurrence in biofuel production and their versatility in conversion to other useful products. Methylfurans are the simplest substituted furans and understanding their reaction pathways, thermochemical properties, including intermediate species stability, and chemical kinetics would aid in the study of larger furans. Furan ring C-H bonds have been shown to be extremely strong, approximately 120 kcal mol(-1), due in part to the placement of the oxygen atom and aromatic-like resonance, both within the ring. The thermochemistry and kinetics of the oxidation of 2-methyfuran radical at position 5 of the furan ring, 2-methyl-5-furanyl radical (2MF5j), is analyzed. The resulting chemically activated species, 2MF5OOj radical, has a well depth of 51 kcal mol(-1) below the 2MF5j + O2 reactants; this is 4-5 kcal mol(-1) deeper than that of phenyl and vinyl radical plus O2, with both of these reactions known to undergo chain branching. Important, low-energy reaction pathways include chain branching dissociations, intramolecular abstractions, group transfers, and radical oxygen additions. Enthalpies of formation, entropies, and heat capacities for the stable molecules, radicals, and transition-state species are analyzed using computational methods. Calculated ΔH(°)f 298 values were determined using an isodesmic work reaction from the CBS-QB3 composite method. Elementary rate parameters are from saddle point transition-state structures and compared to variational transition-state analysis for the barrierless reactions. Temperature- and pressure-dependent rate constants which are calculated using QRRK and master equation analysis is used for falloff and stabilization.

  20. Kinetic study of irreversible inhibition of an enzyme consumed in the reaction it catalyses. Application to the inhibition of the puromycin reaction by spiramycin and hydroxylamine.

    PubMed

    Dinos, G P; Coutsogeorgopoulos, C

    1997-06-01

    A systematic procedure for the kinetic study of irreversible inhibition when the enzyme is consumed in the reaction which it catalyses, has been developed and analysed. Whereas in most reactions the enzymes are regenerated after each catalytic event and serve as reusable transacting effectors, in the consumed enzymes each catalytic center participates only once and there is no enzyme turnover. A systematic kinetic analysis of irreversible inhibition of these enzyme reactions is presented. Based on the algebraic criteria proposed in this work, it should be possible to evaluate either the mechanism of inhibition (complexing or non-complexing), or the type of inhibition (competitive, non-competitive, uncompetitive, mixed non-competitive). In addition, all kinetic constants involved in each case could be calculated. An experimental application of this analysis is also presented, concerning peptide bond formation in vitro. Using the puromycin reaction, which is a model reaction for the study of peptide bond formation in vitro and which follows the same kinetic law as the enzymes under study, we have found that: (i) the antibiotic spiramycin inhibits the puromycin reaction as a competitive irreversible inhibitor in a one step mechanism with an association rate constant equal to 1.3 x 10(4) M-1 s-1 and, (ii) hydroxylamine inhibits the same reaction as an irreversible non-competitive inhibitor also in a one step mechanism with a rate constant equal to 1.6 x 10(-3) M-1 s-1.

  1. The quantum dynamics of electronically nonadiabatic chemical reactions

    NASA Technical Reports Server (NTRS)

    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

  2. Assessment of reaction-rate predictions of a collision-energy approach for chemical reactions in atmospheric flows.

    SciTech Connect

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

    2010-06-01

    A recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates is assessed 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 non-equilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological nonequilibrium 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, significant differences can be found. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

  3. Miscible viscous fingering with a chemical reaction involving precipitation.

    PubMed

    Nagatsu, Yuichiro; Bae, Si-Kyun; Kato, Yoshihito; Tada, Yutaka

    2008-06-01

    We experimentally investigated the effects of a chemical reaction involving precipitation on the miscible viscous fingering pattern formed in a Hele-Shaw cell. The precipitation concentration, the ratio of the reactant concentrations initially included in the more- and less-viscous liquids, and the Péclet number were varied. For a Péclet number at the stoichiometric ratio the precipitation had significant effects on the fingering pattern when its concentration exceeded a threshold value. Interestingly, the type of effect of the precipitation on the pattern depended on its concentration. At moderate concentration, a straight-shaped finger was observed. At high concentration, the finger was bent in an almost perpendicular direction. The effect of precipitation on the pattern also depended on the ratio of reactant concentrations.

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

    NASA Astrophysics Data System (ADS)

    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. Chemical Reactions in the Processing of Mosi2 + Carbon Compacts

    NASA Technical Reports Server (NTRS)

    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.

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

    NASA Technical Reports Server (NTRS)

    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.

  7. Waste Heat Recovery from Blast Furnace Slag by Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Qin, Yuelin; Lv, Xuewei; Bai, Chenguang; Qiu, Guibao; Chen, Pan

    2012-08-01

    Blast furnace (BF) slag, which is the main byproduct in the ironmaking process, contains large amounts of sensible heat. To recover the heat, a new waste heat-recovery system—granulating molten BF slag by rotary multinozzles cup atomizer and pyrolyzing printed circuited board with obtained hot BF slag particle—was proposed in this study. The feasibility of the waste heat-recovery system was verified by dry granulation and pyrolyzation experiments. The energy of hot BF slag could be converted to chemical energy through the pyrolysis reaction, and a large amount of combustible gas like CO, H2, C m H n , and CH4 can be generated during the process.

  8. Noble metal-free hydrazine fuel cell catalysts: EPOC effect in competing chemical and electrochemical reaction pathways.

    PubMed

    Sanabria-Chinchilla, Jean; Asazawa, Koichiro; Sakamoto, Tomokazu; Yamada, Koji; Tanaka, Hirohisa; Strasser, Peter

    2011-04-13

    We report the discovery of a highly active Ni-Co alloy electrocatalyst for the oxidation of hydrazine (N(2)H(4)) and provide evidence for competing electrochemical (faradaic) and chemical (nonfaradaic) reaction pathways. The electrochemical conversion of hydrazine on catalytic surfaces in fuel cells is of great scientific and technological interest, because it offers multiple redox states, complex reaction pathways, and significantly more favorable energy and power densities compared to hydrogen fuel. Structure-reactivity relations of a Ni(60)Co(40) alloy electrocatalyst are presented with a 6-fold increase in catalytic N(2)H(4) oxidation activity over today's benchmark catalysts. We further study the mechanistic pathways of the catalytic N(2)H(4) conversion as function of the applied electrode potential using differentially pumped electrochemical mass spectrometry (DEMS). At positive overpotentials, N(2)H(4) is electrooxidized into nitrogen consuming hydroxide ions, which is the fuel cell-relevant faradaic reaction pathway. In parallel, N(2)H(4) decomposes chemically into molecular nitrogen and hydrogen over a broad range of electrode potentials. The electroless chemical decomposition rate was controlled by the electrode potential, suggesting a rare example of a liquid-phase electrochemical promotion effect of a chemical catalytic reaction ("EPOC"). The coexisting electrocatalytic (faradaic) and heterogeneous catalytic (electroless, nonfaradaic) reaction pathways have important implications for the efficiency of hydrazine fuel cells.

  9. Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks

    SciTech Connect

    Ziaul Huque

    2007-08-31

    This is the final technical report for the project titled 'Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks'. The aim of the project was to develop an efficient chemistry model for combustion simulations. The reduced chemistry model was developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) was used via a new network topology known as Non-linear Principal Components Analysis (NPCA). A commonly used Multilayer Perceptron Neural Network (MLP-NN) was modified to implement NPCA-NN. The training rate of NPCA-NN was improved with the GEneralized Regression Neural Network (GRNN) based on kernel smoothing techniques. Kernel smoothing provides a simple way of finding structure in data set without the imposition of a parametric model. The trajectory data of the reaction mechanism was generated based on the optimization techniques of genetic algorithm (GA). The NPCA-NN algorithm was then used for the reduction of Dimethyl Ether (DME) mechanism. DME is a recently discovered fuel made from natural gas, (and other feedstock such as coal, biomass, and urban wastes) which can be used in compression ignition engines as a substitute for diesel. An in-house two-dimensional Computational Fluid Dynamics (CFD) code was developed based on Meshfree technique and time marching solution algorithm. The project also provided valuable research experience to two graduate students.

  10. Nonequilibrium Thermodynamics of Chemical Reaction Networks: Wisdom from Stochastic Thermodynamics

    NASA Astrophysics Data System (ADS)

    Rao, Riccardo; Esposito, Massimiliano

    2016-10-01

    We build a rigorous nonequilibrium thermodynamic description for open chemical reaction networks of elementary reactions. Their dynamics is described by deterministic rate equations with mass action kinetics. Our most general framework considers open networks driven by time-dependent chemostats. The energy and entropy balances are established and a nonequilibrium Gibbs free energy is introduced. The difference between this latter and its equilibrium form represents the minimal work done by the chemostats to bring the network to its nonequilibrium state. It is minimized in nondriven detailed-balanced networks (i.e., networks that relax to equilibrium states) and has an interesting information-theoretic interpretation. We further show that the entropy production of complex-balanced networks (i.e., networks that relax to special kinds of nonequilibrium steady states) splits into two non-negative contributions: one characterizing the dissipation of the nonequilibrium steady state and the other the transients due to relaxation and driving. Our theory lays the path to study time-dependent energy and information transduction in biochemical networks.

  11. Electrokinetics for control of on-chip chemical reactions.

    NASA Astrophysics Data System (ADS)

    Erickson, David; Venditti, Roberto

    2005-03-01

    It is well known that electrokinetics affords precise control over flow and species transport in microfluidic systems through simple manipulation of externally applied electric potentials. In this work it is demonstrated how electrokinetic effects can be extended to provide simultaneous control over on-chip chemical reactions through manipulation of the local thermal (ohmic/joule heating), shear (electroosmosis) and electrical (electrophoresis) energies at the reaction site. The coupling of the electrical, flow and ``whole-chip'' thermal effects in both the fluidic and substrate domains are investigated through extensive finite element simulations and experimentally validated using microscale fluorescence thermometry. The simulations reveal changes in viscosity and local conductivity on the order of 50% induced by changes in the fluidic geometry. General chip design guidelines for maximizing or minimizing these effects will also be discussed. The degree of precision available and clinical utility of the technique is demonstrated through the detection of a single base pair mutation (single nucleotide polymorphism) in a DNA microarray integrated into a PDMS/glass microfluidic chip.

  12. Chemically Reversible Reactions of Hydrogen Sulfide with Metal Phthalocyanines

    PubMed Central

    2015-01-01

    Hydrogen sulfide (H2S) is an important signaling molecule that exerts action on various bioinorganic targets. Despite this importance, few studies have investigated the differential reactivity of the physiologically relevant H2S and HS– protonation states with metal complexes. Here we report the distinct reactivity of H2S and HS– with zinc(II) and cobalt(II) phthalocyanine (Pc) complexes and highlight the chemical reversibility and cyclability of each metal. ZnPc reacts with HS–, but not H2S, to generate [ZnPc-SH]−, which can be converted back to ZnPc by protonation. CoPc reacts with HS–, but not H2S, to form [CoIPc]−, which can be reoxidized to CoPc by air. Taken together, these results demonstrate the chemically reversible reaction of HS– with metal phthalocyanine complexes and highlight the importance of H2S protonation state in understanding the reactivity profile of H2S with biologically relevant metal scaffolds. PMID:24785654

  13. Stochastic analysis of Chemical Reaction Networks using Linear Noise Approximation.

    PubMed

    Cardelli, Luca; Kwiatkowska, Marta; Laurenti, Luca

    2016-11-01

    Stochastic evolution of Chemical Reactions Networks (CRNs) over time is usually analyzed through solving the Chemical Master Equation (CME) or performing extensive simulations. Analysing stochasticity is often needed, particularly when some molecules occur in low numbers. Unfortunately, both approaches become infeasible if the system is complex and/or it cannot be ensured that initial populations are small. We develop a probabilistic logic for CRNs that enables stochastic analysis of the evolution of populations of molecular species. We present an approximate model checking algorithm based on the Linear Noise Approximation (LNA) of the CME, whose computational complexity is independent of the population size of each species and polynomial in the number of different species. The algorithm requires the solution of first order polynomial differential equations. We prove that our approach is valid for any CRN close enough to the thermodynamical limit. However, we show on four case studies that it can still provide good approximation even for low molecule counts. Our approach enables rigorous analysis of CRNs that are not analyzable by solving the CME, but are far from the deterministic limit. Moreover, it can be used for a fast approximate stochastic characterization of a CRN.

  14. Stochastic Analysis of Chemical Reaction Networks Using Linear Noise Approximation.

    PubMed

    Cardelli, Luca; Kwiatkowska, Marta; Laurenti, Luca

    2016-10-28

    Stochastic evolution of Chemical Reactions Networks (CRNs) over time is usually analysed through solving the Chemical Master Equation (CME) or performing extensive simulations. Analysing stochasticity is often needed, particularly when some molecules occur in low numbers. Unfortunately, both approaches become infeasible if the system is complex and/or it cannot be ensured that initial populations are small. We develop a probabilistic logic for CRNs that enables stochastic analysis of the evolution of populations of molecular species. We present an approximate model checking algorithm based on the Linear Noise Approximation (LNA) of the CME, whose computational complexity is independent of the population size of each species and polynomial in the number of different species. The algorithm requires the solution of first order polynomial differential equations. We prove that our approach is valid for any CRN close enough to the thermodynamical limit. However, we show on four case studies that it can still provide good approximation even for low molecule counts. Our approach enables rigorous analysis of CRNs that are not analyzable by solving the CME, but are far from the deterministic limit. Moreover, it can be used for a fast approximate stochastic characterization of a CRN. Copyright © 2016. Published by Elsevier Ireland Ltd.

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

    NASA Technical Reports Server (NTRS)

    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

  16. Inorganic chemicals in an effluent-dominated stream as indicators for chemical reactions and streamflows

    NASA Astrophysics Data System (ADS)

    Kim, Kangjoo; Lee, Ji Sun; Oh, Chang-Whan; Hwang, Gab-Soo; Kim, Jinsam; Yeo, Sungku; Kim, Yeongkyoo; Park, Seongmin

    2002-07-01

    The chemical behavior of major inorganic ions in the streams of the Mankyung River area (South Korea) was investigated. Mixing with effluent from the Jeonju STP (a municipal sewage treatment plant in Jeonju City) was the most important process in regulating the water chemistry of the streams. The effluent was chemically distinct relative to the stream waters in inorganic composition. Behavior of various ions was evaluated by comparing their concentrations with the concentration of chloride, a conservative chemical species. It was revealed that concentrations of chloride and sulfate, the total concentration of major cations, and electrical conductivity in the stream were controlled only by mixing, indicating their conservative behavior similar to chloride. Alkalinity and concentration of nitrate, however, were regulated by various reactions such as mixing, photosynthesis, respiration, and decomposition of organic matter. Streamflows were estimated by observing chemical composition of the effluent and those of up/downstream waters. Estimated flows based on the conservative chemical parameters were nearly the same as those directly measured using an area-velocity method, indicating the validity of the chemistry-based method.

  17. Binuclear metallohydrolases: complex mechanistic strategies for a simple chemical reaction.

    PubMed

    Schenk, Gerhard; Mitić, Nataša; Gahan, Lawrence R; Ollis, David L; McGeary, Ross P; Guddat, Luke W

    2012-09-18

    Binuclear metallohydrolases are a large family of enzymes that require two closely spaced transition metal ions to carry out a plethora of hydrolytic reactions. Representatives include purple acid phosphatases (PAPs), enzymes that play a role in bone metabolism and are the only member of this family with a heterovalent binuclear center in the active form (Fe(3+)-M(2+), M = Fe, Zn, Mn). Other members of this family are urease, which contains a di-Ni(2+) center and catalyzes the breakdown of urea, arginase, which contains a di-Mn(2+) center and catalyzes the final step in the urea cycle, and the metallo-β-lactamases, which contain a di-Zn(2+) center and are virulence factors contributing to the spread of antibiotic-resistant pathogens. Binuclear metallohydrolases catalyze numerous vital reactions and are potential targets of drugs against a wide variety of human disorders including osteoporosis, various cancers, antibiotic resistance, and erectile dysfunctions. These enzymes also tend to catalyze more than one reaction. An example is an organophosphate (OP)-degrading enzyme from Enterobacter aerogenes (GpdQ). Although GpdQ is part of a pathway that is used by bacteria to degrade glycerolphosphoesters, it hydrolyzes a variety of other phosphodiesters and displays low levels of activity against phosphomono- and triesters. Such a promiscuous nature may have assisted the apparent recent evolution of some binuclear metallohydrolases to deal with situations created by human intervention such as OP pesticides in the environment. OP pesticides were first used approximately 70 years ago, and therefore the enzymes that bacteria use to degrade them must have evolved very quickly on the evolutionary time scale. The promiscuous nature of enzymes such as GpdQ makes them ideal candidates for the application of directed evolution to produce new enzymes that can be used in bioremediation and against chemical warfare. In this Account, we review the mechanisms employed by binuclear

  18. Low-energy electron-stimulated chemical reactions of CO in water ice

    NASA Astrophysics Data System (ADS)

    Yamamoto, S.; Beniya, A.; Mukai, K.; Yamashita, Y.; Yoshinobu, J.

    2004-04-01

    We investigated low-energy electron-stimulated chemical reactions between CO and water molecules in low-temperature ice using infrared reflection absorption spectroscopy. Carbon dioxide, the formyl radical, formaldehyde, and methanol were produced by electron irradiation of the water/CO/water layered ice. The electron energy threshold and temperature dependence for the chemical reactions were investigated to elucidate the reaction mechanisms.

  19. CH 1 Introduction to Chemistry. Study Guide to Minicourse I - 13 Chemical Reaction Principles.

    ERIC Educational Resources Information Center

    Schlenker, Richard

    Provided is a study guide for an introductory minicourse to the principles of chemical reactions. This written text is designed to accompany a series of audio tapes and 35mm slides which the student studies at his own pace. The course presents chemical kinetics, reaction mechanisms, reaction rates, and equilibrium. (SL)

  20. Progression in High School Students' (Aged 16-18) Conceptualizations about Chemical Reactions in Solution.

    ERIC Educational Resources Information Center

    Boo, Hong-Kwen; Watson, J. R.

    2001-01-01

    Explores the development over time of students' understandings of the concept of chemical reaction in the context of two familiar reactions in solution. Based on interviews (n=48), results show that students made some progress in their understanding of the concept of chemical reaction but some fundamental misconceptions remained. (Author/MM)

  1. Transport Properties of a Kinetic Model for Chemical Reactions without Barriers

    SciTech Connect

    Alves, Giselle M.; Kremer, Gilberto M.; Soares, Ana Jacinta

    2011-05-20

    A kinetic model of the Boltzmann equation for chemical reactions without energy barrier is considered here with the aim of evaluating the reaction rate and characterizing the transport coefficient of shear viscosity for the reactive system. The Chapman-Enskog solution of the Boltzmann equation is used to compute the chemical reaction effects, in a flow regime for which the reaction process is close to the final equilibrium state. Some numerical results are provided illustrating that the considered chemical reaction without energy barrier can induce an appreciable influence on the reaction rate and on the transport coefficient of shear viscosity.

  2. Experiences from consumer reports on psychiatric adverse drug reactions with antidepressant medication: a qualitative study of reports to a consumer association

    PubMed Central

    2012-01-01

    Background The new European pharmacovigilance legislation has been suggested as marking the beginning of a new chapter in drug safety, making patients an important part of pharmacovigilance. In Sweden since 2008 it has been possible for consumers to report adverse drug reactions (ADRs) to the Medical Products Agency (MPA), and these reports are now understood as an increasingly valuable contribution in the monitoring of safety aspects in medicines. Already in 2002 it was possible to report experiences with medicines to the non-profit and independent organization Consumer Association for Medicines and Health (KILEN) through a web-based report form with an opportunity to describe ADR experiences in free text comments. The aim of this study was to qualitatively analyze the free text comments appended to consumer reports on antidepressant medication. Methods All reports of suspected adverse reactions regarding antidepressant medications submitted from January 2002 to April 2009 to KILEN’s Internet-based reporting system in Sweden were analyzed according to reported narrative experience(s). Content analysis was used to interpret the content of 181 reports with free text comments. Results Three main categories emerged from the analyzed data material: (1) Experiences of drug treatment with subcategories (a) Severe psychiatric adverse reactions, and (b) Discontinuation symptoms; (2) Lack of communication and (3) Trust and distrust. A majority of the reports to KILEN were from patients experiencing symptoms of mental disturbances (sometimes severe) affecting them in many different ways, especially during discontinuation. Several report included narratives of patients not receiving information of potential ADRs from their doctor, but also that there were no follow-ups of the treatment. Trust was highlighted as especially important and some patients reported losing confidence in their doctor when they were not believed about the suspected ADRs they experienced, making them

  3. Functionalization of Hydrogenated Chemical Vapour Deposition-Grown Graphene by On-Surface Chemical Reactions.

    PubMed

    Drogowska, Karolina; Kovaříček, Petr; Kalbáč, Martin

    2017-03-23

    The reactivity of hydrogenated graphene when treated with oxidising agents, KMnO4 and KIO4 , as well as alkylated with benzyl bromide (BnBr) was studied. The probed reactions are strictly limited to the partly hydrogenated form of graphene in which most of the hydrogen atoms are located in activated benzylic/allylic positions. This, in turn, clearly demonstrates the presence of hydrogen attached to the graphene lattice. Attachment of the benzyl group was also unequivocally demonstrated by characteristic vibrations recorded in the surface-enhanced Raman spectra, and all reactions were shown to proceed solely on hydrogenated graphene as evidenced by the comparison with pristine chemical vapour deposition-grown graphene.

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

    USGS Publications Warehouse

    Friedly, John C.; Rubin, Jacob

    1992-01-01

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

  5. A Case Study in Chemical Kinetics: The OH + CO Reaction.

    ERIC Educational Resources Information Center

    Weston, Ralph E., Jr.

    1988-01-01

    Reviews some important properties of the bimolecular reaction between the hydroxyl radical and carbon monoxide. Investigates the kinetics of the reaction, the temperature and pressure dependence of the rate constant, the state-to-state dynamics of the reaction, and the reverse reaction. (MVL)

  6. A Case Study in Chemical Kinetics: The OH + CO Reaction.

    ERIC Educational Resources Information Center

    Weston, Ralph E., Jr.

    1988-01-01

    Reviews some important properties of the bimolecular reaction between the hydroxyl radical and carbon monoxide. Investigates the kinetics of the reaction, the temperature and pressure dependence of the rate constant, the state-to-state dynamics of the reaction, and the reverse reaction. (MVL)

  7. Capillary Action may Cool Systems and Precisely balance Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Kriske, Richard

    2011-10-01

    It is well known that it takes no work for Water to rise in a Capillary tube against the force of Gravity. There is a precise balance in this system that resembles Robert Millikan's ``Oil Drop'' experiment, where mass was balanced against the electrostatic force. If at the top of the capillary tube there is evaporation, one can see that the system is cooled as another water molecule has room to move up the column. Furthermore, if the evaporation process can be controlled one photon at a time, a precise balance is created between a photon, and the height/mass of the column. If other molecules are place in the column, they can be moved up and down the column, in a chromatograph way, in a fairly precise manner, by controlling evaporation and molecular weight. If in addition to all of this, the interface of the solution against the walls of the column have Fermi levels, it can be seen as a very precise Electrochemical Device. In the situation of nanotubes, as opposed to trees and plants, these properties can be used to create measure environmental properties and to Balance Chemical Reactions. Forests, and Plants may cool themselves and their environment using this process, and using this process coupled with more energetic photons through photosynthesis.

  8. Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks

    SciTech Connect

    Nelson Butuk

    2005-12-01

    This is an annual technical report for the work done over the last year (period ending 9/30/2005) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the development of a novel procedure to speed up the training of NPCA. The same procedure termed L{sub 2}Boost can be used to increase the order of approximation of the Generalized Regression Neural Network (GRNN). It is pointed out that GRNN is a basic procedure for the emerging mesh free CFD. Also reported is an efficient simple approach of computing the derivatives of GRNN function approximation using complex variables or the Complex Step Method (CSM). The results presented demonstrate the significance of the methods developed and will be useful in many areas of applied science and engineering.

  9. Heat Diffusion in Gases, Including Effects of Chemical Reaction

    NASA Technical Reports Server (NTRS)

    Hansen, C. Frederick

    1960-01-01

    The diffusion of heat through gases is treated where the coefficients of thermal conductivity and diffusivity are functions of temperature. The diffusivity is taken proportional to the integral of thermal conductivity, where the gas is ideal, and is considered constant over the temperature interval in which a chemical reaction occurs. The heat diffusion equation is then solved numerically for a semi-infinite gas medium with constant initial and boundary conditions. These solutions are in a dimensionless form applicable to gases in general, and they are used, along with measured shock velocity and heat flux through a shock reflecting surface, to evaluate the integral of thermal conductivity for air up to 5000 degrees Kelvin. This integral has the properties of a heat flux potential and replaces temperature as the dependent variable for problems of heat diffusion in media with variable coefficients. Examples are given in which the heat flux at the stagnation region of blunt hypersonic bodies is expressed in terms of this potential.

  10. Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks

    SciTech Connect

    Nelson Butuk

    2004-12-01

    This is an annual technical report for the work done over the last year (period ending 9/30/2004) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the development of a procedure to speed up the training of NPCA. The developed procedure is based on the non-parametric statistical technique of kernel smoothing. When this smoothing technique is implemented as a Neural Network, It is know as Generalized Regression Neural Network (GRNN). We present results of implementing GRNN on a test problem. In addition, we present results of an in house developed 2-D CFD code that will be used through out the project period.

  11. Detailed Chemical Kinetic Reaction Mechanism for Biodiesel Components Methyl Stearate and Methyl Oleate

    SciTech Connect

    Naik, C; Westbrook, C K; Herbinet, O; Pitz, W J; Mehl, M

    2010-01-22

    New chemical kinetic reaction mechanisms are developed for two of the five major components of biodiesel fuel, methyl stearate and methyl oleate. The mechanisms are produced using existing reaction classes and rules for reaction rates, with additional reaction classes to describe other reactions unique to methyl ester species. Mechanism capabilities were examined by computing fuel/air autoignition delay times and comparing the results with more conventional hydrocarbon fuels for which experimental results are available. Additional comparisons were carried out with measured results taken from jet-stirred reactor experiments for rapeseed methyl ester fuels. In both sets of computational tests, methyl oleate was found to be slightly less reactive than methyl stearate, and an explanation of this observation is made showing that the double bond in methyl oleate inhibits certain low temperature chain branching reaction pathways important in methyl stearate. The resulting detailed chemical kinetic reaction mechanism includes more approximately 3500 chemical species and more than 17,000 chemical reactions.

  12. Influence of nonlinear chemical reactions on the transport coefficients in oscillatory Couette flow

    NASA Astrophysics Data System (ADS)

    Barik, Swarup; Dalal, D. C.

    2016-10-01

    A multiple-scale method of averaging is applied to the study of transport of a chemical species in oscillatory Couette flow where the species may undergoes a reversible phase exchange with the boundary wall and nonlinear chemical reactions both within the fluid and at the boundary wall. Analytical expressions are obtained for transport coefficients. The results shows how the transport coefficients are influenced by the reversible phase exchange reaction kinetics and the rate and degree of the nonlinear decay chemical reaction.

  13. Chemical reactions between Venus' surface and atmosphere - An update. (Invited)

    NASA Astrophysics Data System (ADS)

    Treiman, A. H.

    2013-12-01

    The surface of Venus, at ~740K, is hot enough to allow relatively rapid chemical reactions between it and the atmosphere, i.e. weathering. Venus chemical weathering has been explored in detail [1], to the limits of available data. New data from Venus Express (VEx) and new ideas from exoplanets have sparked a modest renewal of interest in Venus weathering. Venus' surface cannot be observed in visible light, but there are several NIR ';windows' through its atmosphere that allow surface imaging. The VIRTIS spectrometer on VEx viewed the surface through one window [2]; emissivity variations among lava flows on Imdr and Themis Regios have been explained as varying degrees of weathering, and thus age [3]. The VMC camera on VEx also provides images through a NIR window, which suggest variable degrees of weathering on some basaltic plains [4]. Indirect evidence for weathering may come from varying SO2 abundance at Venus' cloud tops; repeated rapid increases and gradual declines may represent volcanic eruptions followed by weathering to form sulfate minerals [5]. Continued geochemical modeling relevant to Venus weathering is motivated by expolanet studies [6]. Models have been extended to hypothetical exo-Venuses of different temperatures and surface compositions [7]. The idea that Venus' atmosphere composition can be buffered by reaction with its surface was explored in detail, and the derived constraint extended to other types of planets [8]. Several laboratories are investigating Venus weathering, motivated in part by the hope that they can provide real constraints on timescales of Venus volcanism [3]. Aveline et al. [9] are extending early studies [10] by reacting rocks and minerals with concentrated SO2 (to accelerate reaction rates to allow detectability of products). Kohler et al. [11] are investigating the stability of metals and chalcogenides as possible causes of the low-emissivity surfaces at high elevations. Berger and Aigouy [12] studied rock alteration on a

  14. [Consumer reaction to information on the labels of genetically modified food].

    PubMed

    Sebastian-Ponce, Miren Itxaso; Sanz-Valero, Javier; Wanden-Berghe, Carmina

    2014-02-01

    To analyze consumer opinion on genetically modified foods and the information included on the label. A systematic review of the scientific literature on genetically modified food labeling was conducted consulting bibliographic databases (Medline - via PubMed -, EMBASE, ISI-Web of knowledge, Cochrane Library Plus, FSTA, LILACS, CINAHL and AGRICOLA) using the descriptors "organisms, genetically modified" and "food labeling". The search covered the first available date, up to June 2012, selecting relevant articles written in English, Portuguese or Spanish. Forty articles were selected after applying the inclusion and exclusion criteria. All of them should have conducted a population-based intervention focused on consumer awareness of genetically modified foods and their need or not, to include this on the label. The consumers expressed a preference for non-genetically modified products, and added that they were prepared to pay more for this but, ultimately, the product bought was that with the best price, in a market which welcomes new technologies. In 18 of the articles, the population was in favor of obligatory labelling, and in six, in favor of this being voluntary; seven studies showed the consumer knew little about genetically modified food, and in three, the population underestimated the quantity they consumed. Price was an influencing factor in all cases. Label should be homogeneous and clarify the degree of tolerance of genetically modified products in humans, in comparison with those non-genetically modified. Label should also present the content or not of genetically modified products and how these commodities are produced and should be accompanied by the certifying entity and contact information. Consumers express their preference for non-genetically modified products and they even notice that they are willing to pay more for it, but eventually they buy the item with the best price, in a market that welcomes new technologies.

  15. Consumer reaction to information on the labels of genetically modified food

    PubMed Central

    Sebastian-Ponce, Miren Itxaso; Sanz-Valero, Javier; Wanden-Berghe, Carmina

    2014-01-01

    OBJECTIVE To analyze consumer opinion on genetically modified foods and the information included on the label. METHODS A systematic review of the scientific literature on genetically modified food labeling was conducted consulting bibliographic databases (Medline – via PubMed –, EMBASE, ISI-Web of knowledge, Cochrane Library Plus, FSTA, LILACS, CINAHL and AGRICOLA) using the descriptors “organisms, genetically modified” and “food labeling”. The search covered the first available date, up to June 2012, selecting relevant articles written in English, Portuguese or Spanish. RESULTS Forty articles were selected after applying the inclusion and exclusion criteria. All of them should have conducted a population-based intervention focused on consumer awareness of genetically modified foods and their need or not, to include this on the label. The consumers expressed a preference for non-genetically modified products, and added that they were prepared to pay more for this but, ultimately, the product bought was that with the best price, in a market which welcomes new technologies. In 18 of the articles, the population was in favor of obligatory labelling, and in six, in favor of this being voluntary; seven studies showed the consumer knew little about genetically modified food, and in three, the population underestimated the quantity they consumed. Price was an influencing factor in all cases. CONCLUSIONS Label should be homogeneous and clarify the degree of tolerance of genetically modified products in humans, in comparison with those non-genetically modified. Label should also present the content or not of genetically modified products and how these commodities are produced and should be accompanied by the certifying entity and contact information. Consumers express their preference for non-genetically modifiedproducts and they even notice that they are willing to pay more for it, but eventually they buy the item with the best price, in a market that welcomes

  16. Chemical Reactions and Atomic Removal Dynamics during Gallium Nitride Chemical Mechanical Polishing Process: Quantum Chemical Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Kentaro; Higuchi, Yuji; Ozawa, Nobuki; Kubo, Momoji

    2015-03-01

    The chemical mechanical polishing (CMP) is promising for efficient polishing of the GaN substrate, and it is essential for manufacturing of GaN devices. However, the detailed CMP mechanisms are unclear, and then the design of efficient and precise CMP process is difficult. We performed polishing simulations of a GaN substrate by a SiO2 abrasive grain in a solution including OH radicals in order to reveal effects of OH radicals on the polishing process. The OH radicals in the solution are adsorbed on the GaN surface and occupy the hollow sites on the surface. Then, a surface-adsorbed O atom is generated by the chemical reaction between the surface-adsorbed OH species and a OH radical in the solution. In the friction interface between the GaN substrate and the abrasive grain, the surface-adsorbed O atom is mechanically pushed into the GaN substrate by the abrasive grain. This O atom intrusion induces the dissociation of Ga-N bonds of the GaN substrate. Moreover, volatile N2 molecules and soluble Ga(OH)3 molecules are generated due to the dissociation of Ga-N bonds. Then, we suggested that the GaN CMP process efficiently proceeds by the mechanically induced chemical reactions: a surface-adsorbed O atom is generated and pushed into the GaN bulk by the abrasive grain.

  17. Plasmon-assisted chemical reactions revealed by high-vacuum tip-enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Lu, Shuaicheng; Sheng, Shaoxiang; Zhang, Zhenglong; Xu, Hongxing; Zheng, Hairong

    2014-08-01

    Tip-enhanced Raman spectroscopy (TERS) is the technique that combines the nanoscale spatial resolution of a scanning probe microscope and the highly sensitive Raman spectroscopy enhanced by the surface plasmons. It is suitable for chemical analysis at nanometer scale. Recently, TERS exhibited powerful potential in analyzing the chemical reactions at nanoscale. The high sensitivity and spatial resolution of TERS enable us to learn the reaction processes more clearly. More importantly, the chemical reaction in TERS is assisted by surface plasmons, which provides us an optical method to manipulate the chemical reactions at nanoscale. Here using our home-built high-vacuum tip-enhanced Raman spectroscopy (HV-TERS) setup, we successfully observed the plasmon-assisted molecule dimerization and dissociation reactions. In HV-TERS system, under laser illumination, 4-nitrobenzenethiol (4NBT) molecules can be dimerized to p,p'-dimercaptoazobenzene (DMAB), and dissociation reaction occurs for malachite green (MG) molecules. Using our HV-TERS setup, the dynamic processes of the reactions are clearly revealed. The chemical reactions can be manipulated by controlling the plasmon intensity through changing the power of the incident laser, the tunneling current and the bias voltage. We also investigated the role of plasmonic thermal effect in the reactions by measuring both the Stokes and anti- Stokes Raman peaks. Our findings extend the applications of TERS, which can help to study the chemical reactions and understand the dynamic processes at single molecular level, and even design molecules by the plasmon-assisted chemical reactions.

  18. On-line reaction monitoring by mass spectrometry, modern approaches for the analysis of chemical reactions.

    PubMed

    Ray, Andrew; Bristow, Tony; Whitmore, Chris; Mosely, Jackie

    2017-06-19

    The application of on-line mass spectrometry for direct analysis of chemical and other types of process continues to grow in importance and impact. The ability of the technique to characterize many aspects of a chemical reaction such as product and impurity formation, along with reactant consumption in a single experiment is key to its adoption and development. Innovations in ionization techniques and mass spectrometry instrumentation are enabling this adoption. An increasing range of ambient ionization techniques make on-line mass spectrometry applicable to a large range of chemistries. The academic development and commercialization of small footprint portable/transportable mass spectrometers is providing technology that can be positioned with any process under investigation. These developments, coupled with research into new ways of sampling representatively from both the condensed and gaseous phases, are positioning mass spectrometry as an essential technology for on-line process optimization, understanding and intelligent control. It is recognized that quantitative capability of mass spectrometry in this application can cause some resistance to its adoption, but research activities to tackle this limitation are on-going. © 2017 Wiley Periodicals, Inc.

  19. Narrow-and-sharp or broad-and-blunt--regulations of hazardous chemicals in consumer products in the European Union.

    PubMed

    Molander, Linda; Rudén, Christina

    2012-04-01

    Chemicals are incorporated into a vast number of consumer products, and it has been recognized that considerable exposures of humans and the environment to chemicals are due to diffuse emissions from everyday products. Different approaches to the management of risks concerning chemicals in products are discussed on the international arena, but no general strategy has yet been adopted. The aim of this study is to investigate how health and environmental risks associated with chemicals in consumer products are currently managed in European Union legislations, mainly by the Toys Directive, the RoHS Directive, and REACH. Significant differences were found between the risk reduction strategies in these legislations, including substance prioritization, type of restrictions and requirements, and information dissemination to consumers. REACH regulates chemicals in products to a limited extent, and via quite complicated processes. Product-specific rules are therefore useful supplements to REACH for regulating chemicals in products. The combined effects of the RoHS and WEEE directives seem to be effective in promoting substitution of substances identified as problematic in electrical and electronic equipment, and it is recommended that the possibility to develop similar systems should be considered also for other product categories.

  20. [Chemical composition, dietary fiber and mineral content of frequently consumed foods in northwest Mexico].

    PubMed

    Haro, M I; Caire, G; Sánchez, A; Valencia, M E

    1995-06-01

    Nutrient composition in foods is very important specially in evaluation of nutritional status in populations. In this study the proximate composition, dietary fiber (DF) and mineral content of 15 frequently consumed foods in Northwest Mexico were determined. The procedures used were AOAC (1984) official methods, chemical-enzymatic method for DF and atomic absorption spectrophometry for minerals. Foods were grouped into cereals, legumes, meat and dairy products, fat was the most variable component in all foods (0,41 to 21,1 g/100 g). Fired beans (Phaseolus vulgaris: variedad pinto) had the highest DF content (9,21 g/100g); as is basis). Sodium among the minerales was also highly variable mainly due to the addition of salt during preparation of foods, except in corn tortillas were salt is not added. In contrast wheat flour tortillas had the highest sodium content of the foods analysed. Fresh white cheese had the highest calcium content (563 mg/100g). The meat group had the highest content of Fe and Zn (2,4-5,4 and 4,2-5,4 mg/100 g respectively). This study has provided information with current analytical techniques of important foods in northwest Mexico that will contribute to food composition tables in Latin America.

  1. Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes.

    PubMed

    Kabbani, Mohamad A; Tiwary, Chandra Sekhar; Autreto, Pedro A S; Brunetto, Gustavo; Som, Anirban; Krishnadas, K R; Ozden, Sehmus; Hackenberg, Ken P; Gong, Yongi; Galvao, Douglas S; Vajtai, Robert; Kabbani, Ahmad T; Pradeep, Thalappil; Ajayan, Pulickel M

    2015-06-15

    Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations.

  2. Chemical Products in the Home, Workshop and Garden. Proceed with Caution; Consumer Safety in the Home, II.

    ERIC Educational Resources Information Center

    Saskatchewan Consumer and Commercial Affairs, Regina.

    The average home has chemical products to clean floors, kill insects, clean ovens, thin paint, remove grease, and perform countless other chores. Many consumers remain unaware of the dangers these products bring into the home. This booklet provides information on the safe use, storage, and disposal of these products. The compounds found in…

  3. Chemical Products in the Home, Workshop and Garden. Proceed with Caution; Consumer Safety in the Home, II.

    ERIC Educational Resources Information Center

    Saskatchewan Consumer and Commercial Affairs, Regina.

    The average home has chemical products to clean floors, kill insects, clean ovens, thin paint, remove grease, and perform countless other chores. Many consumers remain unaware of the dangers these products bring into the home. This booklet provides information on the safe use, storage, and disposal of these products. The compounds found in…

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

    NASA Astrophysics Data System (ADS)

    Nagaoka, Masataka

    2015-12-01

    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.

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

    SciTech Connect

    Nagaoka, Masataka

    2015-12-31

    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.

  6. On the mechanism of effective chemical reactions with turbulent mixing of reactants and finite rate of molecular reactions

    NASA Astrophysics Data System (ADS)

    Vorotilin, V. P.

    2017-01-01

    A generalization of the theory of chemical transformation processes under turbulent mixing of reactants and arbitrary values of the rate of molecular reactions is presented that was previously developed for the variant of an instantaneous reaction [13]. The use of the features of instantaneous reactions when considering the general case, namely, the introduction of the concept of effective reaction for the reactant volumes and writing a closing conservation equation for these volumes, became possible due to the partition of the whole amount of reactants into "active" and "passive" classes; the reactants of the first class are not mixed and react by the mechanism of instantaneous reactions, while the reactants of the second class approach each other only through molecular diffusion, and therefore their contribution to the reaction process can be neglected. The physical mechanism of reaction for the limit regime of an ideal mixing reactor (IMR) is revealed and described. Although formally the reaction rate in this regime depends on the concentration of passive fractions of the reactants, according to the theory presented, the true (hidden) mechanism of the reaction is associated only with the reaction of the active fractions of the reactants with vanishingly small concentration in the volume of the reactor. It is shown that the rate constant of fast chemical reactions can be evaluated when the mixing intensity of reactants is much less than that needed to reach the mixing conditions in an IMR.

  7. Computational Analyses of Complex Flows with Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Bae, Kang-Sik

    The heat and mass transfer phenomena in micro-scale for the mass transfer phenomena on drug in cylindrical matrix system, the simulation of oxygen/drug diffusion in a three dimensional capillary network, and a reduced chemical kinetic modeling of gas turbine combustion for Jet propellant-10 have been studied numerically. For the numerical analysis of the mass transfer phenomena on drug in cylindrical matrix system, the governing equations are derived from the cylindrical matrix systems, Krogh cylinder model, which modeling system is comprised of a capillary to a surrounding cylinder tissue along with the arterial distance to veins. ADI (Alternative Direction Implicit) scheme and Thomas algorithm are applied to solve the nonlinear partial differential equations (PDEs). This study shows that the important factors which have an effect on the drug penetration depth to the tissue are the mass diffusivity and the consumption of relevant species during the time allowed for diffusion to the brain tissue. Also, a computational fluid dynamics (CFD) model has been developed to simulate the blood flow and oxygen/drug diffusion in a three dimensional capillary network, which are satisfied in the physiological range of a typical capillary. A three dimensional geometry has been constructed to replicate the one studied by Secomb et al. (2000), and the computational framework features a non-Newtonian viscosity model for blood, the oxygen transport model including in oxygen-hemoglobin dissociation and wall flux due to tissue absorption, as well as an ability to study the diffusion of drugs and other materials in the capillary streams. Finally, a chemical kinetic mechanism of JP-10 has been compiled and validated for a wide range of combustion regimes, covering pressures of 1atm to 40atm with temperature ranges of 1,200 K--1,700 K, which is being studied as a possible Jet propellant for the Pulse Detonation Engine (PDE) and other high-speed flight applications such as hypersonic

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

    PubMed

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

    2007-06-16

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-06-01

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

  10. Risk assessment of low-level chemical exposures from consumer products under the U.S. Consumer Product Safety Commission chronic hazard guidelines.

    PubMed

    Babich, M A

    1998-02-01

    The U.S. Consumer Product Safety Commission (CPSC) is an independent regulatory agency that was created in 1973. The CPSC has jurisdiction over more the 15,000 types of consumer products used in and around the home or by children, except items such as food, drugs, cosmetics, medical devices, pesticides, certain radioactive materials, products that emit radiation (e.g., microwave ovens), and automobiles. The CPSC has investigated many low-level exposures from consumer products, including formaldehyde emissions from urea-formaldehyde foam insulation and pressed wood products, CO and NO2 emmissions from combustion appliances, and dioxin in paper products. Many chemical hazards are addressed under the Federal Hazardous Substances Act (FHSA), which applies to acute and chronic health effects resulting from high- or low-level exposures. In 1992 the Commission issued guidelines for assessing chronic hazards under the FHSA, including carcinogenicity, neurotoxicity, reproductive/developmental toxicity, exposure, bioavailability, risk assessment, and acceptable risk. The chronic hazard guidelines describe a series of default assumptions, which are used in the absence of evidence to the contrary. However, the guidelines are intended to be sufficiently flexible to incorporate the latest scientific information. The use of alternative procedures is permissible, on a case-by-case basis, provided that the procedures used are scientifically defensible and supported by appropriate data. The application of the chronic hazard guidelines in assessing the risks from low-level exposures is discussed.

  11. Risk assessment of low-level chemical exposures from consumer products under the U.S. Consumer Product Safety Commission chronic hazard guidelines.

    PubMed Central

    Babich, M A

    1998-01-01

    The U.S. Consumer Product Safety Commission (CPSC) is an independent regulatory agency that was created in 1973. The CPSC has jurisdiction over more the 15,000 types of consumer products used in and around the home or by children, except items such as food, drugs, cosmetics, medical devices, pesticides, certain radioactive materials, products that emit radiation (e.g., microwave ovens), and automobiles. The CPSC has investigated many low-level exposures from consumer products, including formaldehyde emissions from urea-formaldehyde foam insulation and pressed wood products, CO and NO2 emmissions from combustion appliances, and dioxin in paper products. Many chemical hazards are addressed under the Federal Hazardous Substances Act (FHSA), which applies to acute and chronic health effects resulting from high- or low-level exposures. In 1992 the Commission issued guidelines for assessing chronic hazards under the FHSA, including carcinogenicity, neurotoxicity, reproductive/developmental toxicity, exposure, bioavailability, risk assessment, and acceptable risk. The chronic hazard guidelines describe a series of default assumptions, which are used in the absence of evidence to the contrary. However, the guidelines are intended to be sufficiently flexible to incorporate the latest scientific information. The use of alternative procedures is permissible, on a case-by-case basis, provided that the procedures used are scientifically defensible and supported by appropriate data. The application of the chronic hazard guidelines in assessing the risks from low-level exposures is discussed. PMID:9539035

  12. Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks

    SciTech Connect

    Nelson Butuk

    2006-09-21

    This is an annual technical report for the work done over the last year (period ending 9/30/2005) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the significant development made in developing a truly meshfree computational fluid dynamics (CFD) flow solver to be coupled to NPCA. First, the procedure of obtaining nearly analytic accurate first order derivatives using the complex step method (CSM) is extended to include computation of accurate meshfree second order derivatives via a theorem described in this report. Next, boosted generalized regression neural network (BGRNN), described in our previous report is combined with CSM and used to obtain complete solution of a hard to solve wave dominated sample second order partial differential equation (PDE): the cubic Schrodinger equation. The resulting algorithm is a significant improvement of the meshfree technique of smooth particle hydrodynamics method (SPH). It is suggested that the demonstrated meshfree technique be termed boosted smooth particle hydrodynamics method (BSPH). Some of the advantages of BSPH over other meshfree methods include; it is of higher order accuracy than SPH; compared to other meshfree methods, it is completely meshfree and does not require any background meshes; It does not involve any construction of shape function with their associated solution of possibly ill conditioned matrix equations; compared to some SPH techniques, no equation for the smoothing parameter is required; finally it is easy to program.

  13. CHEMICAL SYNTHESIS USING 'GREENER' ALTERNATIVE REACTION CONDITIONS AND MEDIA

    EPA Science Inventory

    The chemical research during the last decade has witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into ...

  14. CHEMICAL SYNTHESIS USING 'GREENER' ALTERNATIVE REACTION CONDITIONS AND MEDIA

    EPA Science Inventory

    The chemical research during the last decade has witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into ...

  15. An Informatics Approach to Evaluating Combined Chemical Exposures from Consumer Products: A Case Study of Asthma-Associated Chemicals and Potential Endocrine Disruptors

    PubMed Central

    Gabb, Henry A.; Blake, Catherine

    2016-01-01

    Background: Simultaneous or sequential exposure to multiple environmental stressors can affect chemical toxicity. Cumulative risk assessments consider multiple stressors but it is impractical to test every chemical combination to which people are exposed. New methods are needed to prioritize chemical combinations based on their prevalence and possible health impacts. Objectives: We introduce an informatics approach that uses publicly available data to identify chemicals that co-occur in consumer products, which account for a significant proportion of overall chemical load. Methods: Fifty-five asthma-associated and endocrine disrupting chemicals (target chemicals) were selected. A database of 38,975 distinct consumer products and 32,231 distinct ingredient names was created from online sources, and PubChem and the Unified Medical Language System were used to resolve synonymous ingredient names. Synonymous ingredient names are different names for the same chemical (e.g., vitamin E and tocopherol). Results: Nearly one-third of the products (11,688 products, 30%) contained ≥ 1 target chemical and 5,229 products (13%) contained > 1. Of the 55 target chemicals, 31 (56%) appear in ≥ 1 product and 19 (35%) appear under more than one name. The most frequent three-way chemical combination (2-phenoxyethanol, methyl paraben, and ethyl paraben) appears in 1,059 products. Further work is needed to assess combined chemical exposures related to the use of multiple products. Conclusions: The informatics approach increased the number of products considered in a traditional analysis by two orders of magnitude, but missing/incomplete product labels can limit the effectiveness of this approach. Such an approach must resolve synonymy to ensure that chemicals of interest are not missed. Commonly occurring chemical combinations can be used to prioritize cumulative toxicology risk assessments. Citation: Gabb HA, Blake C. 2016. An informatics approach to evaluating combined chemical

  16. SUBSTITUTION REACTIONS FOR THE DETOXIFICATION OF HAZARDOUS CHEMICALS

    EPA Science Inventory

    Chemical Treatment is one of several treatment techniques used for the remediation of toxic and hazardous chemicals. Chemical treatment in this report is defined as substitution of halogens by hydrogens for the conversion of halogenated organic toxicant into its native hydrocarb...

  17. SUBSTITUTION REACTIONS FOR THE DETOXIFICATION OF HAZARDOUS CHEMICALS

    EPA Science Inventory

    Chemical Treatment is one of several treatment techniques used for the remediation of toxic and hazardous chemicals. Chemical treatment in this report is defined as substitution of halogens by hydrogens for the conversion of halogenated organic toxicant into its native hydrocarb...

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

    PubMed

    Berg, Nikolaj Drimer; Linneberg, Allan; Thyssen, Jacob Pontoppidan; Dirksen, Asger; Elberling, Jesper

    2011-06-01

    Multiple chemical sensitivity (MCS) is characterised by adverse effects due to exposure to low levels of chemical substances. The aetiology is unknown, but chemical related respiratory symptoms have been found associated with positive patch test. The purpose of this study was to investigate the 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 and the two most severe groups of self-reported sensitivity to airborne chemicals. When adjusting for confounding, associations were weakened, and only non-allergic cutaneous reactions were significantly associated with individuals most severely affected by inhalation of airborne chemicals (odds ratio = 2.5, p = 0.006). Our results suggest that individuals with self-reported chemical sensitivity show increased non-allergic cutaneous reactions based on day 2 readings of patch tests.

  19. Insta-Grams: The Effect of Consumer Weight on Reactions to Healthy Food Posts.

    PubMed

    Kinard, Brian R

    2016-08-01

    Each day, social networking sites become increasingly inundated with food imagery. Since many of these images are of fresh, vibrant, and healthy eats, photo sharing of food through social media should have a long-term positive effect on consumption habits. Yet, obesity rates in the United States continue to rise, suggesting that people are spending more time posting images of healthy foods and paying less attention to the actual foods they consume. This confounding relationship could be explained by consumer weight, in that overweight consumers desire to engage with social media maybe for the purpose of expressing, presenting, and identifying with a healthy lifestyle. In the context of food posts, individuals higher in body mass index may be more likely to engage in social media activity (e.g., likes, shares, comments) that validates healthy food choices to others in their online community. A between-subjects experimental design tested this proposed effect using a manipulated Instagram post of a healthy food item (i.e., black bean veggie burger). Results indicate that obese individuals are more likely to engage with healthy food posts compared with their normal weight and overweight counterparts. The effect is even more pronounced when posts are absent of prior social media activity. Based upon these results, obese individuals are encouraged to establish and maintain social network connections with others who routinely post images of healthy food in their social media feeds. Limitations and directions for future research are provided.

  20. Chemical Defense of the Eastern Newt (Notophthalmus viridescens): Variation in Efficiency against Different Consumers and in Different Habitats

    PubMed Central

    Marion, Zachary H.; Hay, Mark E.

    2011-01-01

    Amphibian secondary metabolites are well known chemically, but their ecological functions are poorly understood—even for well-studied species. For example, the eastern newt (Notophthalmus viridescens) is a well known secretor of tetrodotoxin (TTX), with this compound hypothesized to facilitate this salamander's coexistence with a variety of aquatic consumers across the eastern United States. However, this assumption of chemical defense is primarily based on observational data with low replication against only a few predator types. Therefore, we tested the hypothesis that N. viridescens is chemically defended against co-occurring fishes, invertebrates, and amphibian generalist predators and that this defense confers high survivorship when newts are transplanted into both fish-containing and fishless habitats. We found that adult eastern newts were unpalatable to predatory fishes (Micropterus salmoides, Lepomis macrochirus) and a crayfish (Procambarus clarkii), but were readily consumed by bullfrogs (Lithobates catesbeianus). The eggs and neonate larvae were also unpalatable to fish (L. macrochirus). Bioassay-guided fractionation confirmed that deterrence is chemical and that ecologically relevant concentrations of TTX would deter feeding. Despite predatory fishes rejecting eastern newts in laboratory assays, field experiments demonstrated that tethered newts suffered high rates of predation in fish-containing ponds. We suggest that this may be due to predation by amphibians (frogs) and reptiles (turtles) that co-occur with fishes rather than from fishes directly. Fishes suppress invertebrate consumers that prey on bullfrog larvae, leading to higher bullfrog densities in fish containing ponds and thus considerable consumption of newts due to bullfrog tolerance of newt chemical defenses. Amphibian chemical defenses, and consumer responses to them, may be more complex and indirect than previously appreciated. PMID:22164212

  1. Acid-Base Chemistry According to Robert Boyle: Chemical Reactions in Words as well as Symbols

    ERIC Educational Resources Information Center

    Goodney, David E.

    2006-01-01

    Examples of acid-base reactions from Robert Boyle's "The Sceptical Chemist" are used to illustrate the rich information content of chemical equations. Boyle required lengthy passages of florid language to describe the same reaction that can be done quite simply with a chemical equation. Reading or hearing the words, however, enriches the student's…

  2. Method of operating a thermal engine powered by a chemical reaction

    DOEpatents

    Ross, John; Escher, Claus

    1988-01-01

    The invention involves a novel method of increasing the efficiency of a thermal engine. Heat is generated by a non-linear chemical reaction of reactants, said heat being transferred to a thermal engine such as Rankine cycle power plant. The novel method includes externally perturbing one or more of the thermodynamic variables of said non-linear chemical reaction.

  3. Acid-Base Chemistry According to Robert Boyle: Chemical Reactions in Words as well as Symbols

    ERIC Educational Resources Information Center

    Goodney, David E.

    2006-01-01

    Examples of acid-base reactions from Robert Boyle's "The Sceptical Chemist" are used to illustrate the rich information content of chemical equations. Boyle required lengthy passages of florid language to describe the same reaction that can be done quite simply with a chemical equation. Reading or hearing the words, however, enriches the student's…

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

    ERIC Educational Resources Information Center

    Tellinghuisen, Joel

    2006-01-01

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

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

    ERIC Educational Resources Information Center

    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…

  6. Method of operating a thermal engine powered by a chemical reaction

    DOEpatents

    Ross, J.; Escher, C.

    1988-06-07

    The invention involves a novel method of increasing the efficiency of a thermal engine. Heat is generated by a non-linear chemical reaction of reactants, said heat being transferred to a thermal engine such as Rankine cycle power plant. The novel method includes externally perturbing one or more of the thermodynamic variables of said non-linear chemical reaction. 7 figs.

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

    ERIC Educational Resources Information Center

    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…

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

    ERIC Educational Resources Information Center

    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…

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

    ERIC Educational Resources Information Center

    Tellinghuisen, Joel

    2006-01-01

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

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

    NASA Technical Reports Server (NTRS)

    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.

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

    ERIC Educational Resources Information Center

    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…

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

    ERIC Educational Resources Information Center

    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…

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

    NASA Technical Reports Server (NTRS)

    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.

  14. Evolution of Complex Maillard Chemical Reactions, Resolved in Time.

    PubMed

    Hemmler, Daniel; Roullier-Gall, Chloé; Marshall, James W; Rychlik, Michael; Taylor, Andrew J; Schmitt-Kopplin, Philippe

    2017-06-12

    In this study, we monitored the thermal formation of early ribose-glycine Maillard reaction products over time by ion cyclotron resonance mass spectrometry. Here, we considered sugar decomposition (caramelization) apart from compounds that could only be produced in the presence of the amino acid. More than 300 intermediates as a result of the two initial reactants were found after ten hours (100 °C) to participate in the interplay of the Maillard reaction cascade. Despite the large numerical variety the majority of intermediates follow simple and repetitive reaction patterns. Dehydration, carbonyl cleavage, and redox reactions turned out to have a large impact on the diversity the Maillard reaction causes. Although the Amadori breakdown is considered as the main Maillard reaction pathway, other reactive intermediates, often of higher molecular weight than the Amadori rearrangement product, contribute to a large extent to the multitude of intermediates we observed.

  15. Control of Maillard Reactions in Foods: Strategies and Chemical Mechanisms.

    PubMed

    Lund, Marianne N; Ray, Colin A

    2017-06-14

    Maillard reactions lead to changes in food color, organoleptic properties, protein functionality, and protein digestibility. Numerous different strategies for controlling Maillard reactions in foods have been attempted during the past decades. In this paper, recent advances in strategies for controlling the Maillard reaction and subsequent downstream reaction products in food systems are critically reviewed. The underlying mechanisms at play are presented, strengths and weaknesses of each strategy are discussed, and reasonable reaction mechanisms are proposed to reinforce the evaluations. The review includes strategies involving addition of functional ingredients, such as plant polyphenols and vitamins, as well as enzymes. The resulting trapping or modification of Maillard targets, reactive intermediates, and advanced glycation endproducts (AGEs) are presented with their potential unwanted side effects. Finally, recent advances in processing for control of Maillard reactions are discussed.

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

    NASA Technical Reports Server (NTRS)

    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.

  17. Calculation of the power consumed for mixing in incompletely filled horizontal reactions

    SciTech Connect

    Sychev, G.M.; Zhurba, A.M.; Kurilov, S.V.; Oblogin, V.V.

    1988-01-01

    Horizontally sectioned liquid-phase reactors with a filling coefficient of 0.2-0.6 are finding wider use in the production of highly viscous polyesters and polyamides. The power of their electric motors fluctuates in the range of 2-70 kW. In this paper, in order to provide design and efficiency criteria for the electric motors and other components of the reactors, parameters are determined for calculating the power consumed during the mixing process. The fluids are considered highly viscous and Newtonian. Experimental data in support of the calculations are derived using a multicomponent xylitol solution that is close in rheological properties to polyethylene terephthalate.

  18. Novel chemical kinetics for a single enzyme reaction: relationship between substrate concentration and the second moment of enzyme reaction time.

    PubMed

    Jung, Won; Yang, Seongeun; Sung, Jaeyoung

    2010-08-05

    We report a robust quadratic relation between the inverse substrate concentration and the second moment, , of the catalytic turnover time distribution for enzyme reactions. The results hold irrespective of the mechanism and dynamics of the enzyme reaction and suggest a novel single molecule experimental analysis that provides information about reaction processes of the enzyme-substrate complex and ergodicity of the enzyme reaction system, which is beyond the reach of the conventional analysis for the mean reaction time, . It turns out that - 2(2) is linear in inverse substrate concentration for an ergodic homogeneous enzyme system given that the enzyme substrate encounter is a simple rate process, and its value at the high substrate concentration limit provides direct information about if any non-Poisson reaction process of the enzyme-substrate complex. For a nonergodic heterogeneous reaction system, the corresponding quantity becomes a quadratic function of the inverse substrate concentration. This leads us to suggest an ergodicity measure for single enzyme reaction systems. We obtain a simple analytic expression of the randomness parameter for the single catalytic turnover time, which could provide a quantitative explanation about the previously reported randomness data of the beta-galactosidase enzyme. In obtaining the results, we introduce novel chemical kinetics applicable to a non-Poisson reaction network with arbitrary connectivity, as a generalization of the conventional chemical kinetics.

  19. Phase and chemical equilibria in the transesterification reaction of vegetable oils with supercritical lower alcohols

    NASA Astrophysics Data System (ADS)

    Anikeev, V. I.; Stepanov, D. A.; Ermakova, A.

    2011-08-01

    Calculations of thermodynamic data are performed for fatty acid triglycerides, free fatty acids, and fatty acid methyl esters, participants of the transesterification reaction of vegetable oils that occurs in methanol. Using the obtained thermodynamic parameters, the phase diagrams for the reaction mixture are constructed, and the chemical equilibria of the esterification reaction of free fatty acids and the transesterification reaction of fatty acid triglycerides attained upon treatment with supercritical methanol are determined. Relying on our analysis of the obtained equilibria for the esterification reaction of fatty acids and the transesterification reaction of triglycerides attained upon treatment with lower alcohols, we select the optimum conditions for performing the reaction in practice.

  20. The canonical and other mechanisms of elementary chemical reactions.

    PubMed

    Aldegunde, Jesús; Aoiz, F Javier; Sáez-Rábanos, Vicente; Kendrick, Brian K; de Miranda, Marcelo P

    2007-11-21

    This article introduces a definition of the concept of elementary reaction mechanism that, while conforming to the traditional view of reaction mechanisms as dynamical processes whereby reagents are transformed into products, sharpens it by requiring reagent and product states to be completely specified and fully correlated. This leads to well-defined mathematical requirements for classification of a dynamical process as a reaction mechanism and also to a straightforward mathematical procedure for the determination of a special class of independent collision mechanisms that are dubbed "canonical". Canonical mechanisms result from an exact decomposition of the differential cross section of the reaction and form a complete orthogonal basis in terms of which all reaction mechanisms can be described. Examples involving the benchmark F + H2 and D + H2 reactions at energies ranging from ultralow to hyperthermal illustrate how canonical and other reaction mechanisms can be visualised and also how analysis of a reaction in terms of its canonical mechanisms can provide insight into its dynamics.

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

    ERIC Educational Resources Information Center

    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…

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

    ERIC Educational Resources Information Center

    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…

  3. Ab initio Quantum Chemical Reaction Kinetics: Recent Applications in Combustion Chemistry (Briefing Charts)

    DTIC Science & Technology

    2015-06-28

    Charts 3. DATES COVERED (From - To) June 2015-June 2015 4. TITLE AND SUBTITLE AB INITIO QUANTUM CHEMICAL REACTION KINETICS: RECENT APPLICATIONS IN...Unlimited. 13. SUPPLEMENTARY NOTES Briefing Charts presented at 9th Int. Conf. Chemical Kinetics; Ghent, Belgium; 28 Jun 2015. PA#15351. 14. ABSTRACT...ghanshyam.vaghjiani@us.af.mil Ab initio Quantum Chemical Reaction Kinetics: Recent Applications in Combustion Chemistry Ghanshyam L. Vaghjiani* DISTRIBUTION A

  4. A new extension of the polarizable continuum model: Toward a quantum chemical description of chemical reactions at extreme high pressure.

    PubMed

    Cammi, Roberto

    2015-11-15

    A quantum chemical method for studying potential energy surfaces of reactive molecular systems at extreme high pressures is presented. The method is an extension of the standard Polarizable Continuum Model that is usually used for Quantum Chemical study of chemical reactions at a standard condition of pressure. The physical basis of the method and the corresponding computational protocol are described in necessary detail, and an application of the method to the dimerization of cyclopentadiene (up to 20 GPa) is reported.

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

    PubMed

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

    2016-04-27

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

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

    PubMed Central

    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

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

    ERIC Educational Resources Information Center

    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…

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

    ERIC Educational Resources Information Center

    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…

  10. Aerosols formed from the chemical reaction of monoterpenes and ozone

    NASA Astrophysics Data System (ADS)

    Yokouchi, Y.; Ambe, Y.

    Chamber experiments were conducted to study the aerosol products from the ozonolysis of the major atmospheric monoterpenes; α-pinene, β-pinene and limonene. It was found that the α-pinene-O 3 reaction produced mainly 2', 2'-dimethyl-3'-acetyl cyclobutyl ethanal (pinonaldehyde), the β-pinene-O 3 reaction, mainly 6,6-dimethyl-bicyclo [3.1.1] heptan-2-one and the limonene-O 3 reaction, several unidentified products. These products were sought in forest aerosols and pinonaldehyde was detected in the atmosphere.

  11. Aerosols formed from the chemical reaction of monoterpenes and ozone

    NASA Astrophysics Data System (ADS)

    Yokouchi, Y.; Ambe, Y.

    Chamber experiments were conducted to study the aerosol products from the ozonolysis of the major atmospheric monoterpenes; α-pinene, β-pinene and limonene. It was found that the α-pinend-O 3 reaction produced mainly 2'. 2'-dimethyl-3'-acetyl cyclobutyl ethanal (pinonaldehyde), the β-pinene-O 3 reaction, mainly 6,6-dimethyl-bicyclo [3.1.1] heptan-2-one and the limonene-O 3 reaction, several unidentified products. These products were sought in forest aerosols and pinonaldehyde was detected in the atmosphere.

  12. Consumer reactions to risk information on bovine spongiform encephalopathy in Japan

    PubMed Central

    Yasunaga, Hideo; Obana, Naoya; Ogawa, Toshio; Imamura, Tomoaki

    2010-01-01

    Objectives To investigate the impact of information on foodborne disease on consumers, we quantified consumers’ anxiety, purchasing behaviors, and willingness-to-pay (WTP) in response to the reading of newspaper articles published in 2001 that documented the first cow in Japan to be infected with bovine spongiform encephalopathy (BSE). Methods An online questionnaire survey of 993 females aged 20–59 years was conducted in 2007. The participants were randomly selected from the general population via the Internet and were divided into three groups. Each group was assigned a different number of BSE-related articles to read, namely, two, four, and six articles, respectively. Each participant described her personal level of anxiety, underlying reasons for her anxiety, and changes in purchasing behavior after reading the articles. The respondents who wanted to buy guaranteed-safe beef were asked to state their maximal WTP. Results The level of anxiety was significantly lower and distrust of the relevant administration significantly greater in the group asked to read six articles than in the other groups. The WTP value for guaranteed beef was approximately 1.3-fold higher than the regular purchase price, with significant differences between groups. In the ‘six-article’ group, the ratio between WTP and the regular purchase price was significantly less than that in the ‘four-article’ group. Conclusions These findings suggest that the anxiety of consumers can be reduced if they receive an appropriate amount of published information. WTP may be linked to the contents of the articles. PMID:21432560

  13. Chemical Reactions Impacting the Potential of Planetary Habitability

    NASA Astrophysics Data System (ADS)

    Kamakolanu, U. G.

    2017-02-01

    The formation of building blocks of life might have been a two-step process. 1) Acid catalyzed cyclization reaction, resulting in the formation of substituted pyran moiety, and 2) ring opening of pyran resulting in chiral prebiotic precursor molecule.

  14. Identifying Slow Molecular Motions in Complex Chemical Reactions.

    PubMed

    Piccini, GiovanniMaria; Polino, Daniela; Parrinello, Michele

    2017-09-07

    We have studied the cyclization reaction of deprotonated 4-chloro-1-butanethiol to tetrahydrothiophene by means of well-tempered metadynamics. To properly select the collective variables, we used the recently proposed variational approach to conformational dynamics within the framework of metadyanmics. This allowed us to select the appropriate linear combinations from a set of collective variables representing the slow degrees of freedom that best describe the slow modes of the reaction. We performed our calculations at three different temperatures, namely, 300, 350, and 400 K. We show that the choice of such collective variables allows one to easily interpret the complex free-energy surface of such a reaction by univocal identification of the conformers belonging to reactants and product states playing a fundamental role in the reaction mechanism.

  15. Predictive Models and Tools for Screening Chemicals under TSCA: Consumer Exposure Models 1.5

    EPA Pesticide Factsheets

    CEM contains a combination of models and default parameters which are used to estimate inhalation, dermal, and oral exposures to consumer products and articles for a wide variety of product and article use categories.

  16. Propagation of a Chemical Reaction through Heterogeneous Lithium- Polytetrafluoroethylene Mixtures

    DTIC Science & Technology

    1975-12-11

    kg - K) E* Dimensicnless parameter defined by Equetion (2.15) E aActivation energy in PTFE thermal decomposition rate law, Ea Equation (2.4) (Ji/rol...approximately 0.035 seconds , corresponding tc an average velocity of about 5.5 m/s. The arrival of the reaction front at each subsequent thermocouple...get some more basic information on the characteristics or this reaction. The second series of test runs in the cylindrical configuration was carried

  17. Identification of sensory attributes, instrumental and chemical measurements important for consumer acceptability of grilled lamb Longissimus lumborum.

    PubMed

    Oltra, O R; Farmer, L J; Gordon, A W; Moss, B W; Birnie, J; Devlin, D J; Tolland, E L C; Tollerton, I J; Beattie, A M; Kennedy, J T; Farrell, D

    2015-02-01

    In this study, important eating quality attributes that influence consumer liking for grilled lamb loin have been identified using preference mapping techniques. The eating quality attributes identified as driving the consumer liking of lamb loin steaks were “tenderness”, “sweet flavour”, “meaty aftertaste”, “roast lamb flavour” and “roast lamb aftertaste”. In contrast, the texture attribute “rubbery” and the flavour attributes “bitter flavour” and "bitter aftertaste" had a negative influence on consumer perceptions. Associations were observed between eating quality and a number of instrumental and chemical measurements. Warner Bratzler Shear Force showed an association with “rubbery” texture and a negative association with “tenderness” and consumer liking scores. The compounds, glucose, glucose-6-phosphate, inosine, inosine monophosphate and adenosine monophosphate were associated with the attributes, “sweet flavour”,“meaty aftertaste”, “roast lamb flavour”, “roast lamb aftertaste” and with consumer scores for liking of lamb which is probably caused by the role some of these compounds play as precursors of flavour and as taste compounds.

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

    SciTech Connect

    Sakai, Osamu Nobuto, Kyosuke; Miyagi, Shigeyuki; Tachibana, Kunihide

    2015-10-15

    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 CH{sub 3} 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.

  19. Why Do Lithium-Oxygen Batteries Fail: Parasitic Chemical Reactions and Their Synergistic Effect.

    PubMed

    Yao, Xiahui; Dong, Qi; Cheng, Qingmei; Wang, Dunwei

    2016-09-12

    As an electrochemical energy-storage technology with the highest theoretical capacity, lithium-oxygen batteries face critical challenges in terms of poor stabilities and low charge/discharge round-trip efficiencies. It is generally recognized that these issues are connected to the parasitic chemical reactions at the anode, electrolyte, and cathode. While the detailed mechanisms of these reactions have been studied separately, the possible synergistic effects between these reactions remain poorly understood. To fill in the knowledge gap, this Minireview examines literature reports on the parasitic chemical reactions and finds the reactive oxygen species a key chemical mediator that participates in or facilitates nearly all parasitic chemical reactions. Given the ubiquitous presence of oxygen in all test cells, this finding is important. It offers new insights into how to stabilize various components of lithium-oxygen batteries for high-performance operations and how to eventually materialize the full potentials of this promising technology.

  20. Why Do Lithium–Oxygen Batteries Fail: Parasitic Chemical Reactions and Their Synergistic Effect

    PubMed Central

    Yao, Xiahui; Dong, Qi; Cheng, Qingmei

    2016-01-01

    Abstract As an electrochemical energy‐storage technology with the highest theoretical capacity, lithium–oxygen batteries face critical challenges in terms of poor stabilities and low charge/discharge round‐trip efficiencies. It is generally recognized that these issues are connected to the parasitic chemical reactions at the anode, electrolyte, and cathode. While the detailed mechanisms of these reactions have been studied separately, the possible synergistic effects between these reactions remain poorly understood. To fill in the knowledge gap, this Minireview examines literature reports on the parasitic chemical reactions and finds the reactive oxygen species a key chemical mediator that participates in or facilitates nearly all parasitic chemical reactions. Given the ubiquitous presence of oxygen in all test cells, this finding is important. It offers new insights into how to stabilize various components of lithium–oxygen batteries for high‐performance operations and how to eventually materialize the full potentials of this promising technology. PMID:27381169

  1. Cutaneous reactions in nuclear, biological and chemical warfare.

    PubMed

    Arora, Sandeep

    2005-01-01

    Nuclear, biological and chemical warfare have in recent times been responsible for an increasing number of otherwise rare dermatoses. Many nations are now maintaining overt and clandestine stockpiles of such arsenal. With increasing terrorist threats, these agents of mass destruction pose a risk to the civilian population. Nuclear and chemical attacks manifest immediately while biological attacks manifest later. Chemical and biological attacks pose a significant risk to the attending medical personnel. The large scale of anticipated casualties in the event of such an occurrence would need the expertise of all physicians, including dermatologists, both military and civilian. Dermatologists are uniquely qualified in this respect. This article aims at presenting a review of the cutaneous manifestations in nuclear, chemical and biological warfare and their management.

  2. Real time monitoring of accelerated chemical reactions by ultrasonication-assisted spray ionization mass spectrometry.

    PubMed

    Lin, Shu-Hsuan; Lo, Ta-Ju; Kuo, Fang-Yin; Chen, Yu-Chie

    2014-01-01

    Ultrasonication has been used to accelerate chemical reactions. It would be ideal if ultrasonication-assisted chemical reactions could be monitored by suitable detection tools such as mass spectrometry in real time. It would be helpful to clarify reaction intermediates/products and to have a better understanding of reaction mechanism. In this work, we developed a system for ultrasonication-assisted spray ionization mass spectrometry (UASI-MS) with an ~1.7 MHz ultrasonic transducer to monitor chemical reactions in real time. We demonstrated that simply depositing a sample solution on the MHz-based ultrasonic transducer, which was placed in front of the orifice of a mass spectrometer, the analyte signals can be readily detected by the mass spectrometer. Singly and multiply charged ions from small and large molecules, respectively, can be observed in the UASI mass spectra. Furthermore, the ultrasonic transducer used in the UASI setup accelerates the chemical reactions while being monitored via UASI-MS. The feasibility of using this approach for real-time acceleration/monitoring of chemical reactions was demonstrated. The reactions of Girard T reagent and hydroxylamine with steroids were used as the model reactions. Upon the deposition of reactant solutions on the ultrasonic transducer, the intermediate/product ions are readily generated and instantaneously monitored using MS within 1 s. Additionally, we also showed the possibility of using this reactive UASI-MS approach to assist the confirmation of trace steroids from complex urine samples by monitoring the generation of the product ions.

  3. Accelerating chemical reactions: exploring reactive free-energy surfaces using accelerated ab initio molecular dynamics.

    PubMed

    Pierce, Levi C T; Markwick, Phineus R L; McCammon, J Andrew; Doltsinis, Nikos L

    2011-05-07

    A biased potential molecular dynamics simulation approach, accelerated molecular dynamics (AMD), has been implemented in the framework of ab initio molecular dynamics for the study of chemical reactions. Using two examples, the double proton transfer reaction in formic acid dimer and the hypothetical adiabatic ring opening and subsequent rearrangement reactions in methylenecyclopropane, it is demonstrated that ab initio AMD can be readily employed to efficiently explore the reactive potential energy surface, allowing the prediction of chemical reactions and the identification of metastable states. An adaptive variant of the AMD method is developed, which additionally affords an accurate representation of both the free-energy surface and the mechanism associated with the chemical reaction of interest and can also provide an estimate of the reaction rate.

  4. Accelerating chemical reactions: Exploring reactive free-energy surfaces using accelerated ab initio molecular dynamics

    PubMed Central

    Pierce, Levi C. T.; Markwick, Phineus R. L.; McCammon, J. Andrew; Doltsinis, Nikos L.

    2011-01-01

    A biased potential molecular dynamics simulation approach, accelerated molecular dynamics (AMD), has been implemented in the framework of ab initio molecular dynamics for the study of chemical reactions. Using two examples, the double proton transfer reaction in formic acid dimer and the hypothetical adiabatic ring opening and subsequent rearrangement reactions in methylenecyclopropane, it is demonstrated that ab initio AMD can be readily employed to efficiently explore the reactive potential energy surface, allowing the prediction of chemical reactions and the identification of metastable states. An adaptive variant of the AMD method is developed, which additionally affords an accurate representation of both the free-energy surface and the mechanism associated with the chemical reaction of interest and can also provide an estimate of the reaction rate. PMID:21548673

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

    SciTech Connect

    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.

  6. Analyzing consumers' reactions to news coverage of the 2011 Escherichia coli O104:H4 outbreak, using the Extended Parallel Processing Model.

    PubMed

    De Vocht, Melanie; Cauberghe, Verolien; Sas, Benedikt; Uyttendaele, Mieke

    2013-03-01

    This article describes and analyzes Flemish consumers' real-life reactions after reading online newspaper articles related to the enterohemorrhagic Escherichia coli (EHEC) O104:H4 outbreak associated with fresh produce in May and June 2011 in Germany. Using the Extended Parallel Processing Model (EPPM) as the theoretical framework, the present study explored the impact of Flemish (Belgian) online news coverage on consumers' perception of the risk induced by the EHEC outbreak and their behavioral intentions as consumers of fresh produce. After the consumers read a newspaper article related to the outbreak, EPPM concepts were measured, namely, perceived severity, susceptibility, self-efficacy, and affective response, combined with behavioral intentions to eat less fresh produce, to rinse fresh produce better, and to alert loved ones concerning the risk. The consumers' reactions were measured by inserting a link to an online survey below every online newspaper article on the EHEC outbreak that appeared in two substantial Flemish newspapers. The reactions of 6,312 respondents were collected within 9 days for 17 different online newspaper articles. Looking at the perceived values of the EPPM concepts, the perceived severity and the perceived susceptibility of the risk were, as expected, high. However, the consumers thought they could prevent the risk from happening, which stresses the importance of increasing consumers' knowledge of emerging food safety risks. Furthermore, analyses showed the moderating role of government trust and its influence on the way consumers perceived the risk, how worried they were, and their behavioral intentions.

  7. Understanding chemical binding using the Berlin function and the reaction force

    NASA Astrophysics Data System (ADS)

    Chakraborty, Debajit; Cárdenas, Carlos; Echegaray, Eleonora; Toro-Labbe, Alejandro; Ayers, Paul W.

    2012-06-01

    We use the derivative of the electron density with respect to the reaction coordinate, interpreted through the Berlin binding function, to identify portions of the reaction path where chemical bonds are breaking and forming. The results agree with the conventional description for SN2 reactions, but they are much more general and can be used to elucidate other types of reactions also. Our analysis offers support for, and detailed information about, the use of the reaction force profile to separate the reaction coordinates into intervals, each with characteristic extents of geometry change and electronic rearrangement.

  8. Chemical and mathematical modeling of asphaltene reaction pathways

    SciTech Connect

    Salvage, P.E.

    1986-01-01

    Precipitated asphaltene was subjected to pyrolysis and hydropyrolysis, both neat and in solvents, and catalytic hydroprocessing. A solvent extraction procedure defined gas, maltene, asphaltene, and coke product fractions. The apparent first order rate constant for asphaltene conversion at 400/sup 0/C was relatively insensitive to the particular reaction scheme. The yield of gases likewise showed little variation and was always less than 10%. On the other hand, the maltene and coke yields were about 20% and 60%, respectively, from neat pyrolysis, and about 60% and less than 5%, respectively, from catalytic reactions. The temporal variations of the product fractions allowed discernment of asphaltene reaction pathways. The primary reaction of asphaltene was to residual asphaltene, maltenes, and gases. The residual asphaltene reacted thermally to coke and catalytically to maltenes at the expense of coke. Secondary degradation of these primary products led to lighter compounds. Reaction mechanism for pyrolysis of asphaltene model compounds and alkylaromstics were determined. The model compound kinetics results were combined with a stochastic description of asphaltene structure in a mathematical model of asphaltene pyrolysis. Individual molecular product were assigned to either the gas, maltene, asphaltene, or coke product fractions, and summation of the weights of each constituted the model's predictions. The temporal variation of the product fractions from simulated asphaltene pyrolysis compared favorably with experimental results.

  9. The design of dextran-based hypoxia-inducible hydrogels via in situ oxygen consuming reaction

    PubMed Central

    Park, Kyung Min; Blatchley, Michael R.; Gerecht, Sharon

    2014-01-01

    Hypoxia plays a critical role in development and the wound healing process, as well as a number of pathological conditions. Here, we report dextran–based hypoxia–inducible (Dex–HI) hydrogels formed with in situ oxygen consumption via laccase–medicated reaction. Oxygen levels and gradients were accurately predicted by mathematical simulation. We demonstrate that Dex–HI hydrogels provide prolonged hypoxic conditions up to 12 h. The Dex–HI hydrogel offers an innovative approach to delineate not only the mechanism by which hypoxia regulates cellular responses, but may facilitate the discovery of new pathways involved in the generation of hypoxic and oxygen gradient environments. PMID:25303104

  10. Quantitative structure-property relationships for chemical functional use and weight fractions in consumer articles

    EPA Science Inventory

    Chemical functional use -- the functional role a chemical plays in processes or products -- may be a useful heuristic for predicting human exposure potential in that it comprises information about the compound's likely physical properties and the product formulations or articles ...

  11. Quantitative structure-property relationships for chemical functional use and weight fractions in consumer articles

    EPA Science Inventory

    Chemical functional use -- the functional role a chemical plays in processes or products -- may be a useful heuristic for predicting human exposure potential in that it comprises information about the compound's likely physical properties and the product formulations or articles ...

  12. Predicting rare events in chemical reactions: Application to skin cell proliferation.

    PubMed

    Lee, Chiu Fan

    2010-08-01

    In a well-stirred system undergoing chemical reactions, fluctuations in the reaction propensities are approximately captured by the corresponding chemical Langevin equation. Within this context, we discuss in this work how the Kramers escape theory can be used to predict rare events in chemical reactions. As an example, we apply our approach to a recently proposed model on cell proliferation with relevance to skin cancer [P. B. Warren, Phys. Rev. E 80, 030903 (2009)]. In particular, we provide an analytical explanation for the form of the exponential exponent observed in the onset rate of uncontrolled cell proliferation.

  13. Solvation and chemical reaction of sodium in water clusters

    NASA Astrophysics Data System (ADS)

    Bobbert, C.; Schulz, C. P.

    Nam(H2O)n Clusters ( n = 1...200, m = 1...50) are formed in a recently build pick-up arrangement. Preformed water clusters traverse a sodium oven, where sodium atoms are picked up. At low sodium vapour pressure ( < 1×10-4 mbar) pure Na(H2O)n clusters are observed in the mass spectra. At high sodium vapour pressure ( > 1×10-3 mbar) the water cluster pick up more than 50 Na atoms and reaction products Na(NaOH)n ( n = 2, 4...50) dominate the mass spectra. The even number of NaOH units in the products indicate that also in a finite cluster the reaction occurs in pairs as in the macroscopic reaction.

  14. Sensitivity and network topology in chemical reaction systems

    NASA Astrophysics Data System (ADS)

    Okada, Takashi; Mochizuki, Atsushi

    2017-08-01

    In living cells, biochemical reactions are catalyzed by specific enzymes and connect to one another by sharing substrates and products, forming complex networks. In our previous studies, we established a framework determining the responses to enzyme perturbations only from network topology, and then proved a theorem, called the law of localization, explaining response patterns in terms of network topology. In this paper, we generalize these results to reaction networks with conserved concentrations, which allows us to study any reaction system. We also propose network characteristics quantifying robustness. We compare E. coli metabolic network with randomly rewired networks, and find that the robustness of the E. coli network is significantly higher than that of the random networks.

  15. Modeling the Dynamics of Chemical Reactions Involving Multidimensional Tunneling

    NASA Astrophysics Data System (ADS)

    Liu, Yi-Ping

    The direct dynamics approach is employed to study prototype reactions including hydrogen and hydride transfer. The dynamics are treated with variational transition state theory including multidimensional semiclassical tunneling corrections, and the force field is modeled with semiempirical molecular orbital theory. The primary kinetic isotope effect for the (1,5) sigmatropic rearrangement reaction of cis-1,3-pentadiene is predicted and compared to experiment. The force field is obtained by molecular orbital theory with the AM1, PM3, and MINDO/3 parameterizations. The kinetic isotope effects calculated with the MINDO/3 and PM3 Hamiltonians agree with those calculated by AM1 within 13%, and the latter agree with experiment within 13%. The tunneling contributions to the kinetic isotope effects are analyzed, and the nature of the vibrationally assisted tunneling process is elucidated. The kinetic isotope effects of the reactions of CF_3 with CD_3H are studied including all internal degrees of freedom. The force field necessary for the dynamics calculations is evaluated using the neglect of diatomic differential overlap (NDDO) molecular orbital theory with semiempirical specific -reaction parameters (SRP), which are based on the standard AM1 parameterization adjusted to improve the agreement between experiment and the calculated quantities such as the vibrational frequencies of reactants and products and the classical barrier. The kinetic isotope effects are calculated using two different SRP force fields, and they are in good agreement with the experimental measurements. The picture of the corner cutting tunneling process that emerges is discussed graphically. The two NDDO-SRP models are further used to study the hydrogen abstraction reactions of CF_3 with CH_4, CD_4, and C_2 H_6, and very good agreement with experiment is obtained. Finally, a simple model hydride transfer reaction of formic acid is investigated usine the AM1 and PM3 Hamiltonians, and the results are

  16. Energy storage and transport by reversible chemical reactions

    NASA Astrophysics Data System (ADS)

    Beghi, G.

    Reversible thermochemical reactions are one of the possibilities to store and transport high temperature heat (800 K up to 1300 K). There are open cycles and closed cycles. Some reversible systems are described, as the SO2-SO3 system. A typical example of open cycle is the reaction for water decomposition. Results of a pilot plant to verify the decomposition of sulfuric acid are described; the technological feasibility of this method for hydrogen production is shown. The possibility to use other high temperature sources, as solar energy is discussed.

  17. Conditions for extinction events in chemical reaction networks with discrete state spaces.

    PubMed

    Johnston, Matthew D; Anderson, David F; Craciun, Gheorghe; Brijder, Robert

    2017-09-26

    We study chemical reaction networks with discrete state spaces and present sufficient conditions on the structure of the network that guarantee the system exhibits an extinction event. The conditions we derive involve creating a modified chemical reaction network called a domination-expanded reaction network and then checking properties of this network. Unlike previous results, our analysis allows algorithmic implementation via systems of equalities and inequalities and suggests sequences of reactions which may lead to extinction events. We apply the results to several networks including an EnvZ-OmpR signaling pathway in Escherichia coli.

  18. Chemical Reactions and Properties of Organosilicon Compounds to New Materials

    DTIC Science & Technology

    1988-09-30

    for Synthesis of (Me2Si)e by Gas Chromatography , S.-M. Chen and R. West, Huaxue Xuebao, 43, 365-368 (1985). 4. Metal Halide Catalyzed Rearrangements...Addition of Hydrogen Halides, H. Stuger and R. West, Macromolecules, 18, 2349-2352 (1985). 3. Study of the Reaction of Dimethyldichlorosilane with Lithium

  19. Theoretical Studies of Chemical Reactions following Electronic Excitation

    NASA Technical Reports Server (NTRS)

    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.

  20. Raman spectroscopic studies of gas/aerosol chemical reactions

    SciTech Connect

    Aardahl, C.L.; Davis, E.J.

    1995-12-31

    Reactions between sorbent particles and SO{sub 2} can be used to reduce atmospheric pollution either by {open_quotes}dry scrubbing{close_quotes} or {open_quotes}wet scrubbing{close_quotes} processes. This paper reports Raman spectroscopy results for single electrodynamically levitated droplets of NaOH reacting with SO{sub 2} and studies of the dehydration reactions of some hygroscopic salt species. The NaOH/SO{sub 2} reaction products and the liquid or solid state of the products are shown to depend on the gas phase SO{sub 2} concentration. Deliquesced particles of NaOH exhibit enhanced light scattering intensities associated with morphological resonances of the incident laser light, but crystalline materials show no such resonances. Raman-active hygroscopic salts exhibit bond frequencies characteristic of the stretching vibrations of the anionic group, but these frequencies are different in the presence of water because hydrogen bonding changes the bond force. This allows efficient tracking of the dehydration reactions in hygroscopic aerosols by Raman spectroscopy as the intensities of the two different modes are related to the degree of dehydration in the particle.