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1

Thermal energy storage. [by means of chemical reactions  

NASA Technical Reports Server (NTRS)

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.

Grodzka, P. G.

1975-01-01

2

The application of reversible chemical reactions to solar thermal energy systems  

Microsoft Academic Search

It has been proposed to use reversible thermochemical reactions as a means for storing thermal energy in solar energy systems. The considered approach involves the storage of thermal energy in the form of chemicals created by endothermic reactions. In addition to the storage applications, there is also interest in applying reversible reactions to solar thermal energy transport and solar thermal

R. Mar

1980-01-01

3

Femtosecond Chemically Activated Reactions: Concept of Nonstatistical Activation at High Thermal Energies  

E-print Network

Femtosecond chemical activation of reactions at very high thermal energies, much above the bond energyFemtosecond Chemically Activated Reactions: Concept of Nonstatistical Activation at High Thermal Energies Sang Kyu Kim, Ju Guo, J. Spencer Baskin, and Ahmed H. Zewail* Arthur Amos Noyes Chemical Physics

Kim, Sang Kyu

4

Chemical Reactions  

NSDL National Science Digital Library

We don't often stop to think about it, but underlying many of our everyday activities are chemical reactions. From the cooking of an egg to the growth of a child, chemical reactions make things happen. Although many of the reactions that support our lives

National Science Teachers Association (NSTA)

2009-05-01

5

Method and apparatus for obtaining enhanced production rate of thermal chemical reactions  

DOEpatents

The present invention is a method and apparatus (vessel) for providing a heat transfer rate from a reaction chamber through a wall to a heat transfer chamber substantially matching a local heat transfer rate of a catalytic thermal chemical reaction. The key to the invention is a thermal distance defined on a cross sectional plane through the vessel inclusive of a heat transfer chamber, reaction chamber and a wall between the chambers. The cross sectional plane is perpendicular to a bulk flow direction of the reactant stream, and the thermal distance is a distance between a coolest position and a hottest position on the cross sectional plane. The thermal distance is of a length wherein the heat transfer rate from the reaction chamber to the heat transfer chamber substantially matches the local heat transfer rate.

Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Wegeng, Robert S [Richland, WA; Gao, Yufei [Kennewick, WA

2003-04-01

6

Chemical Reactions  

NSDL National Science Digital Library

We are going go over a general view of reactions to prepare us for our unit on Chemical Reactions! Have fun learning! WARNING: If you are caught looking at ANY other site, without permission, you will be sent to the ALC, and you will not participate in any other computer activities for the rest of the year. Get your worksheet and begin! Overview Take this quiz and have me come over and sign off on your worksheet when you have completed the quiz! Overview Quiz Next let's take a look at what effect the rate of a chemical reaction. Rates of Reactions Another quiz, another check off by me! Rates of Reactions Quiz Now how do we measure how fast a ...

Hicken, Mrs.

2009-05-04

7

A combined quantum-classical dynamics method for calculating thermal rate constants of chemical reactions in solution  

E-print Network

-flux correlation function for calculating the thermal rate constants of chemical reactions in solutionA combined quantum-classical dynamics method for calculating thermal rate constants of chemical reactions in solution Thanh N. Truong,") J. Andrew McCammon, and Donald J. Kouri Department of Chemistry

Truong, Thanh N.

8

Chemical and thermal stability of N-heterocyclic ionic liquids in catalytic C-H activation reactions.  

PubMed

(1) H-NMR spectrum analyses are applied to study the chemical and thermal stability of selected N-heterocyclic ionic liquids within the reaction system that can highly efficiently activate a C-H bond of methane and convert it into the C-O bond in methanol. Our results indicate that under such reaction conditions involving using a powerful Pt-based catalyst and strong acidic solvent, the aromatic ring of an imidazolium cation becomes unstable generating an ammonium ion (NH4 (+) ). Our results also suggest that the instability of the imidazolium ring is more chemically (participation in reactions) than thermally based. Modifications of the aromatic ring structure such as pyrazolium and triazolium cations can increase the chemical/thermal stability of ionic liquids under these reaction conditions. Copyright © 2014 John Wiley & Sons, Ltd. PMID:24942984

Chen, Guanyi; Kang, Shujuan; Ma, Qisheng; Chen, Weiqun; Tang, Yongchun

2014-11-01

9

Encapsulated nano-heat-sinks for thermal management of heterogeneous chemical reactions.  

PubMed

This paper describes a new way to control temperatures of heterogeneous exothermic reactions such as heterogeneous catalytic reaction and polymerization by using encapsulated nanoparticles of phase change materials as thermally functional additives. Silica-encapsulated indium nanoparticles and silica encapsulated paraffin nanoparticles are used to absorb heat released in catalytic reaction and to mitigate gel effect of polymerization, respectively. The local hot spots that are induced by non-homogenous catalyst packing, reactant concentration fluctuation, and abrupt change of polymerization rate lead to solid to liquid phase change of nanoparticle cores so as to avoid thermal runaway by converting energies from exothermic reactions to latent heat of fusion. By quenching local hot spots at initial stage, reaction rates do not rise significantly because the thermal energy produced in reaction is isothermally removed. Nanoparticles of phase change materials will open a new dimension for thermal management of exothermic reactions to quench local hot spots, prevent thermal runaway of reaction, and change product distribution. PMID:20967399

Zhang, Minghui; Hong, Yan; Ding, Shujiang; Hu, Jianjun; Fan, Yunxiao; Voevodin, Andrey A; Su, Ming

2010-12-01

10

Thermal effect of chemical reactions in interactions of laser pulse with solids  

Microsoft Academic Search

The heat energy released by chemical reactions was measured in the interaction of 50-ns Nd- laser pulse with titanium, germanium, coke, and sulphur samples placed in different gas media. The samples were exposed to focused laser radiation in the intensity range of 1 - 800 MW\\/cm2. It was found that the maximum value of the ratio of released chemical energy

Anatoly Y. Vorobyov

1994-01-01

11

Microfluidic chemical reaction circuits  

DOEpatents

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.

Lee, Chung-cheng (Irvine, CA); Sui, Guodong (Los Angeles, CA); Elizarov, Arkadij (Valley Village, CA); Kolb, Hartmuth C. (Playa del Rey, CA); Huang, Jiang (San Jose, CA); Heath, James R. (South Pasadena, CA); Phelps, Michael E. (Los Angeles, CA); Quake, Stephen R. (Stanford, CA); Tseng, Hsian-rong (Los Angeles, CA); Wyatt, Paul (Tipperary, IE); Daridon, Antoine (Mont-Sur-Rolle, CH)

2012-06-26

12

Application of a reversible chemical reaction system to solar thermal power plants  

Microsoft Academic Search

Three distributed dish solar thermal power systems using various applications of SO2\\/SO3 chemical energy storage and transport technology were comparatively assessed. Each system features various roles for the chemical system: (1) energy storage only, (2) energy transport, or (3) energy transport and storage. These three systems were also compared with the dish-Stirling, using electrical transport and battery storage, and the

E. J. Hanseth; Y. S. Won; L. P. Seibowitz

1980-01-01

13

Growth and characterization of zinc oxide nano\\/micro-fibers by thermal chemical reactions and vapor transport deposition in air  

Microsoft Academic Search

Zinc oxide (ZnO) crystal fibers were prepared on silicon (100) substrate via a simple thermal chemical reactions vapor transport deposition method in air with a mixture of ZnO and carbon powders as reactants. The growth process was carried out at 1100°C in a quartz tube with one side opened to the air. There is no other metal catalyst and carrier

B. J. Chen; X. W. Sun; C. X. Xu; B. K. Tay

2004-01-01

14

Application of a reversible chemical reaction system to solar thermal power plants  

NASA Astrophysics Data System (ADS)

Three distributed dish solar thermal power systems using various applications of SO2/SO3 chemical energy storage and transport technology were comparatively assessed. Each system features various roles for the chemical system: (1) energy storage only, (2) energy transport, or (3) energy transport and storage. These three systems were also compared with the dish-Stirling, using electrical transport and battery storage, and the central receiver Rankine system, with thermal storage, to determine the relative merit of plants employing a thermochemical system. As an assessment criterion, the busbar energy costs were compared. Separate but comparable solar energy cost computer codes were used for distributed receiver and central receiver systems. Calculations were performed for capacity factors ranging from 0.4 to 0.8. The results indicate that SO2/SO3 technology has the potential to be more cost effective in transporting the collected energy than in storing the energy for the storage capacity range studied (2-15 hours)

Hanseth, E. J.; Won, Y. S.; Seibowitz, L. P.

1980-08-01

15

Application of a reversible chemical reaction system to solar thermal power plants  

NASA Technical Reports Server (NTRS)

Three distributed dish solar thermal power systems using various applications of SO2/SO3 chemical energy storage and transport technology were comparatively assessed. Each system features various roles for the chemical system: (1) energy storage only, (2) energy transport, or (3) energy transport and storage. These three systems were also compared with the dish-Stirling, using electrical transport and battery storage, and the central receiver Rankine system, with thermal storage, to determine the relative merit of plants employing a thermochemical system. As an assessment criterion, the busbar energy costs were compared. Separate but comparable solar energy cost computer codes were used for distributed receiver and central receiver systems. Calculations were performed for capacity factors ranging from 0.4 to 0.8. The results indicate that SO2/SO3 technology has the potential to be more cost effective in transporting the collected energy than in storing the energy for the storage capacity range studied (2-15 hours)

Hanseth, E. J.; Won, Y. S.; Seibowitz, L. P.

1980-01-01

16

Formation of Aromatics in Thermally Induced Reactions of Chemically Bonded RP-C18 Stationary Phase.  

PubMed

In continuation of the research on the thermally induced chemical transformation of the silica-based chemically bonded stationary phases (C18), the oxidative cleavage of the silicon-carbon bonds with hydrogen peroxide and potassium fluoride was utilized, followed by the gas chromatography coupled with mass spectrometry (GC-MS) study of the resulting products. These investigations allowed determination of the probable structures of certain thermal modification products as the various different alkyl derivatives of the phenylsilane ligands. Apart from aromatic compounds, the products with unsaturated bonds and carbonyl functionalities were found in the analyzed extracts. The analysis of the GC-MS chromatograms reveals that under the applied working conditions, the investigated process runs with relatively low yields. PMID:24105920

Prus, Wojciech

2014-10-01

17

Chemical Reactions at Surfaces  

Microsoft Academic Search

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

Nancy Ryan Gray Michael Henderson

2010-01-01

18

Vaporization or Chemical Reaction: Which controls the fate of contaminants treated by in situ thermal remediation?  

EPA Science Inventory

Thermal remediation technologies, which includes steam enhanced extraction, electrical resistance heating, and thermal conductive heating, have been developed based on technologies employed by the enhanced oil recovery industry. Although mobilization and/or volatilization of con...

19

Method and apparatus for obtaining enhanced production rate of thermal chemical reactions  

DOEpatents

Reactors and processes are disclosed that can utilize high heat fluxes to obtain fast, steady-state reaction rates. Porous catalysts used in conjunction with microchannel reactors to obtain high rates of heat transfer are also disclosed. Reactors and processes that utilize short contact times, high heat flux and low pressure drop are described. Improved methods of steam reforming are also provided.

Tonkovich, Anna Lee Y. (Pasco, WA); Wang, Yong (Richland, WA); Wegeng, Robert S. (Richland, WA); Gao, Yufei (Kennewick, WA)

2006-05-16

20

Thermal reactions of methyl linoleate. I. Heating conditions, isolation techniques, biological studies and chemical changes  

Microsoft Academic Search

Methyl linoleate, diluted with an equal weight of methyl laurate, was heated without exclusion of air at 200C for 200 hours.\\u000a The reaction mixture was separated by means of molecular distillation, urea adduction, column chromatography, and gas chromatography.\\u000a Cyclic and aromatic materials were detected in the nonurea adductable monomer fractions. The dimer was separated into polar\\u000a and nonpolar fractions. Analytical

W. R. Michael; J. Craig Alexander; Neil R. Artman

1966-01-01

21

Theoretical calculations of the thermal rate constants for the gas-phase chemical reactions H + NH  

SciTech Connect

Rate constants for the title reactions are computed by using variational transition-state theory with semiclassical ground-state adiabatic transmission coefficients for the temperature range from 200 to 2,400 K. The rates are computed from selected information about the potential energy surface along the minimum energy path as parameters of the reaction path Hamiltonian. The potential information is obtained from ab initio electronic structure calculations with an empirical bond additivity correction. The accuracy of this semiempirical technique for obtaining the potential information is tested by comparing the results of the underlying ab initio calculations with higher quality multiconfiguration SCF and multireference CI calculations and by using increasingly higher quality ab initio electronic structure calculations before applying the bond additivity correction. For the reactions H + NH{sub 3} {yields} H{sub 2} + NH{sub 2}, H{sub 2} + NH{sub 2} {yields} H + NH{sub 3}, and D + ND{sub 3} {yields} D{sub 2} + ND{sub 2}, the ultimate test is given by comparison with recent experimental results. Although the agreement is good in general, the comparisons of experiment and theory indicate that the computed barrier height is overestimated by about 1 kcal/mol.

Garrett, B.C. (Chemical Dynamics Corp., Marlboro, MD (USA)); Koszykowski, M.L.; Melius, C.F. (Sandia National Lab., Livermore, CA (USA)); Page, M. (Naval Research Lab., Washington, DC (USA))

1990-09-06

22

Categorizing Chemical Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the second of four Science Objects in the Chemical Reactions SciPack. It provides an

National Science Teachers Association (NSTA)

2009-07-10

23

Rates of Chemical Reactions  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object is the third of four Science Objects in the Chemical Reactions SciPack. It demonstrates

National Science Teachers Association (NSTA)

1900-01-01

24

ESTUDIO DE SISTEMAS DE DESTILACIÓN TÉRMICAMENTE ACOPLADOS CON REACCIÓN QUÍMICA STUDY OF THERMALLY COUPLED DISTILLATION SYSTEMS WITH CHEMICAL REACTION  

Microsoft Academic Search

Thermally coupled distillation systems have been excellent options to save energy and capital investment for the separation of multicomponent mixtures. Latest information about design, operation and control of these systems has been published and it has allowed a practical implementation in the chemical industry. In this paper the ethyl acetate process is studied, using distillation systems with side columns (either

F. O. Barroso-Muñoz; S. Hernández; J. G. Segovia-Hernández; A. F. Aguilera-Alvarado

2006-01-01

25

Chemical Reactions in DSMC  

SciTech Connect

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.

Bird, G. A. [GAB Consulting Pty Ltd, 144/110 Sussex Street, Sydney NSW 2000 (Australia)

2011-05-20

26

Mass Transfer with Chemical Reaction.  

ERIC Educational Resources Information Center

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)

DeCoursey, W. J.

1987-01-01

27

Thermal energy storage with chemical reaction of NaI-NH3 system. I - Region of liquid phase  

NASA Astrophysics Data System (ADS)

It is shown that a liquid phase in the solid sodium iodide-gaseous ammonia reaction offers a thermal energy storage medium at temperatures suitable for air conditioning. The density of the liquid ammoniate varies depending on temperature and pressure, but the maximum value observed in the present experiments was 1.7 g/cu cm. The liquid region extends to temperatures below zero under higher pressure than the atmospheric, allowing a refrigerator employing the system to operate under possitive pressures.

Fujiwara, I.; Nakashima, Y.; Goto, T.

28

Microfabricated electrochemiluminescence cell for chemical reaction detection  

DOEpatents

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.

Northrup, M. Allen (Berkeley, CA); Hsueh, Yun-Tai (Davis, CA); Smith, Rosemary L. (Davis, CA)

2003-01-01

29

Microfabricated sleeve devices for chemical reactions  

DOEpatents

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.

Northrup, M. Allen (Berkeley, CA)

2003-01-01

30

The classification of chemical reactions  

Microsoft Academic Search

The classification and shorthand designation of chemical reactions are considered. It is concluded that single-step reactions can be divided into a finite number of types, each of which could be represented by an unambiguous symbol. The various types are listed and illustrated. Multi-step reactions, however, cannot be classified (in any detail) in a limited number of ways and for such

D. P. N. Satchell

1977-01-01

31

Chemical burn or reaction  

MedlinePLUS

... the skin has come in contact with the toxic substance Rash , blisters , burns on the skin Unconsciousness ... locked cabinet. Avoid mixing different products that contain toxic chemicals such as ammonia and bleach. The mixture ...

32

Chemical and Thermal Analysis  

NASA Technical Reports Server (NTRS)

Thermal decomposition activation energies have been determined using two methods of Thermogravimetric Analysis (TGA), with good correlation being obtained between the two techniques. Initial heating curves indicated a two-component system for Coflon (i.e. polymer plus placticizer) but a single component system for Tefzel. Two widely differing activation energies were for Coflon supported this view, 15 kcl/mol being associated with plasticizer, and 40 kcal/mol with polymer degradation. With Tefzel, values were 40-45 kcal/mol, the former perhaps being associated with a low molecular weight fraction. Appropriate acceleration factors have been determined. Thermomechanical Analysis (TMA) has shown considerable dimensional change during temperature cycles. For unaged pipe sections heating to 100 C and then holding the temperature resulted in a stable thickness increase of 2%, whereas the Coflon thickness decreased continuously, reaching -4% in 2.7 weeks. Previously strained tensile bars of Tefzel expanded on cooling during TMA. SEM performed on H2S-aged Coflon samples showed significant changes in both physical and chemical nature. The first may have resulted from explosive decompression after part of the aging process. Chemically extensive dehydrofluorination was indicated, and sulfur was present as a result of the aging. These observations indicate that chemical attack of PVDF can occur in some circumstances.

Bulluck, J. W.; Rushing, R. A.

1994-01-01

33

LEGO® Chemical Reactions  

NSDL National Science Digital Library

This activity uses LEGO® bricks to represent atoms bonding into molecules and crystals. The lesson plan is for a 2.5 hour workshop (or four 45-minute classes). There is a "wet lab" chemistry experiment (mixing baking soda and calcium chloride with phenol red indicator), followed by a "LEGO lab" modeling phase that includes writing formulas using chemical notation. This lesson is also offered as a 2.5 hour field trip lesson at the MIT Edgerton Center.

Vandiver, Kathleen M.

2009-01-01

34

Thermal explosion of autocatalytic reaction  

Microsoft Academic Search

Analytical and numerical solutions are used to determine the critical conditions for thermal explosion of autocatalytic reaction. The solutions covers both the reaction governed by the Arrhenius kinetics equation and the Frank-Kamenetskii approximation for that equation. The definition of criticality as the point at which d2?\\/d?2=0, d3?\\/d?3=0 and d?\\/d??0 is used here. The study is dealt with low and high

Saad A. El-Sayed

2003-01-01

35

Kinematically complete chemical reaction dynamics  

NASA Astrophysics Data System (ADS)

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.

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

36

Theoretical studies of chemical reaction dynamics  

SciTech Connect

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.

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

1993-12-01

37

Homeostasis in Chemical Reaction Pathways  

E-print Network

We consider stochastic models of chemical reaction networks with time dependent input rates and several types of molecules. We prove that, in despite of strong time dependence of input rates, there is a kind of homeostasis phenomenon: far away from input nodes the mean numbers of molecules of each type become approximately constant (do not depend on time).

V. A. Malyshev; A. D. Manita; A. A. Zamyatin

2011-12-25

38

Homeostasis in Chemical Reaction Pathways  

E-print Network

We consider stochastic models of chemical reaction networks with time dependent input rates and several types of molecules. We prove that, in despite of strong time dependence of input rates, there is a kind of homeostasis phenomenon: far away from input nodes the mean numbers of molecules of each type become approximately constant (do not depend on time).

Malyshev, V A; Zamyatin, A A

2011-01-01

39

Silicon-based sleeve devices for chemical reactions  

DOEpatents

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.

Northrup, M. Allen (Berkeley, CA); Mariella, Jr., Raymond P. (Danville, CA); Carrano, Anthony V. (Livermore, CA); Balch, Joseph W. (Livermore, CA)

1996-01-01

40

Silicon-based sleeve devices for chemical reactions  

DOEpatents

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.

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

1996-12-31

41

Application of Reversible Chemical Reactions for Temperature Amplification  

E-print Network

temperature thermal energy, mechanical and absorption type heat pumps have been proposed and developed so far. This paper addresses itself to the concept of a heat reaction chemical heat pump (HRCHP). The HRCHP concept is aimed to upgrade low temperature...

Ally, M. R.; Rebello, W. J.; Suciu, D. F.

42

Strain-induced chemical reactions  

SciTech Connect

The uniaxial displacements at leading edges of detonation fronts in solids create large shear-strains. These bend the covalent bonds, and cause piezoelectric effects, thereby closing the HOMO-LUMO energy gaps, and leading to ultra-fast athermal chemical reactions. Specific examples are discussed: ammonium, azide, and nitrate ions; and PETN. It is shown that their properties are consistent with the proposed mechanism. [copyright]American Institute of Physics

Gilman, J.J. (Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States))

1994-07-10

43

Simple thermal decomposition reactions for storage of solar thermal energy  

Microsoft Academic Search

Simple thermal decomposition reactions have been investigated for the purpose of solar thermal energy storage. Ten criteria regarding the thermodynamics and kinetics of the reaction and the physical properties of the components of the reaction have been established. One particular reaction, the decomposition of ammonium hydrogen sulfate, has been evaluated in a preliminary manner and appears to satisfy all of

W. E. Wentworth; E. Chen

1976-01-01

44

Quantum dynamics of fast chemical reactions  

SciTech Connect

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.

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

1993-12-01

45

Chemical and Thermal Analysis  

NASA Technical Reports Server (NTRS)

Work has included significant research in several areas aimed at further clarification of the aging and chemical failure mechanism of thermoplastics (PVDF or Tefzel) for pipes. Among the areas investigated were the crystallinity changes associated with both the Coflon and Tefzel after various simulated environmental exposures using X-Ray diffraction analysis. We have found that significant changes in polymer crystallinity levels occur as a function of the exposures. These crystallinity changes may have important consequences on the fracture, fatigue, tensile, and chemical resistance of the materials. We have also noted changes in the molecular weight distribution of the Coflon material using a dual detector Gel Permeation Analysis. Again these changes may result in variation in the mechanical and chemical properties in the material. We conducted numerous analytical studies with methods including X-Ray Diffraction, Gel Permeation Chromatography, Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis, and Differential Scanning Calorimetry. We investigated a number of aged samples of both Tefzel and Coflon that were forwarded from MERL. Pressurized tests were performed in a modified Fluid G, which we will call G2. In this case the ethylene diamine concentration was increased to 3 percent in methanol. Coflon pipe sections and powdered Coflon were exposed in pressure cells at 1700 psi at three separate test temperatures, 70 C, 110 C, and 130 C. The primary purpose of the pressure tests in Fluid G2 was to further elucidate the aging mechanism of PVDF degradation.

Bulluck, J. W.; Rushing, R. A.; Thornton, C. P.

1996-01-01

46

Chemical and Thermal Analysis  

NASA Technical Reports Server (NTRS)

Work during the past three years has included significant research in several areas aimed at further clarification of the aging and chemical failure mechanism of thermoplastics (PVDF or Tefzel) for pipes. Among the areas investigated were the crystallinity changes associated with both the Coflon and Tefzel after various simulated environmental exposures using X-Ray diffraction analysis. We have found that significant changes in polymer crystallinity levels occur as a function of the exposures. These crystallinity changes may have important consequences on the fracture, fatigue, tensile, and chemical resistance of the materials. We have also noted changes in the molecular weight distribution and the increased crosslinking of the Coflon material using Gel Permeation Chromatographic Analysis. Again these changes may result in variations in the mechanical and chemical properties in the material. We conducted numerous analytical studies with methods including X-ray Diffraction, Gel Permeation Chromatography, Fourier Transform Infrared Spectroscopy, and Differential Scanning Calorimetry. We investigated a plethora of aged samples of both Tefzel and Coflon that were forwarded from MERL. Pressurized tests were performed on powdered PVDF in a modified Fluid A, which we will call A-2. In this case the ethylene diamine concentration was increased to 3 percent in methanol. Coflon pipe sections and powdered Coflon were exposed in pressure cells at 1700 psi at three separate test temperatures.

Bulluck, J. W.; Rushing, R. A.

1997-01-01

47

Chemical and Thermal Analysis  

NASA Technical Reports Server (NTRS)

During the past six months we have conducted significant research in several domains in order to clarify and understanding the aging and chemical failure mechanism of thermoplastics (PVDF or Tefzel) for pipes. We organized numerous analytical studies with methods including Fourier Transform Infrared Spectroscopy, Dynamic Mechanical Analysis, Differential Scanning Calorimetry, and Stress Relaxation experiments. In addition we have reanalyzed previous thermogravimetric data concerning the rate of deplasticization of Coflon pipe. We investigated a number of aged samples of both Tefzel and Coflon that were forwarded from MERL. We conducted stress relaxation experiments of Coflon pipe at several temperatures and determined an activation energy. We also examined the dynamic mechanical response PVDF during deplasticization and during methanol plasticization. We performed numerous DSC analyses to research the changing crystalline morphology. We have noted significant changes in crystallinity upon aging for both PVDF and Tefzel. Little variation in elemental composition was noted for many of the aged Coflon and Tefzel samples tested.

Bulluck, J. W.; Rushing, R. A.

1995-01-01

48

Chemical reactions at aqueous interfaces  

NASA Astrophysics Data System (ADS)

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) Adsorption of dilute PFOS(aq) and PFOA(aq) to acoustically cavitating bubble interfaces was greater than equilibrium expectations due to high-velocity bubble radial oscillations; 2) Relative ozone oxidation kinetics of aqueous iodide, sulfite, and thiosulfate were at variance with previously reported bulk aqueous kinetics; 3) Organics that directly chelated with the anode surface were oxidized by direct electron transfer, resulting in immediate carbon dioxide production but slower overall oxidation kinetics. Chemical reactions at aqueous interfaces can be the rate-limiting step of a reaction network and often display novel mechanisms and kinetics as compared to homogeneous chemistry.

Vecitis, Chad David

49

Basic Chemical Principles 1: Reaction Kinetics  

E-print Network

with radiation can cause chemical events: bonds broken, molecules excited { Creation of radicals Molecular state: Lowest energy con#12;guration of electrons in orbitals #15; To form chemical bond, combine atomic, photo-chemical reactions are important: reactions initiated by light #12; { Interaction of matter

Schofield, Jeremy

50

Laser-initiated chemical chain reactions  

Microsoft Academic Search

A detailed kinetic and experimental analysis is presented for chemical chain reaction processes initiated by well-controlled, low power laser pulses. Realtime evolution of the chain reaction is followed by direct detection of infrared chemiluminescence from vibrationally excited HCl product molecules produced by one of the propagation reactions in the chain. By appropriate choice of conditions, the chain reactions may be

David J. Nesbitt; Stephen R. Leone

1980-01-01

51

2005 Chemical Reactions at Surfaces  

SciTech Connect

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.

Cynthia M. Friend

2006-03-14

52

Chemical Kinetics: Rate of Reaction  

NSDL National Science Digital Library

This site offers an interactive tutorial that emphasizes graphical interpretation of chemical kinetics. The stoichiometric coefficients for a chemical equation are determined by comparing the slopes of concentration-time plots for the reactants and products. This tutorial is coupled to others to further guide the student to a better understanding of chemical kinetics.

Blauch, David N.

53

A Unified Theory of Chemical Reactions  

E-print Network

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

Aubry, S

2014-01-01

54

'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...

55

Chemical ReactionsChemical Reactions between the Componentsbetween the Components  

E-print Network

products, one the result of an SN2 reaction, the other an E2 reaction. P O O- OH OP O HO OP O O HO + N(C6H.Abundance 700600500400300200100 m/z negative MS 2 610 m/z 256.82 E2 340.83 SN2 609.93 Triphosphate DianionTriphosphate Dianion SN2: Hexyl triphosphate (m/z 341) is produced E2: Triphosphate anion (m/z 257) is produced P O O- OH

Beauchamp, Jack

56

Modeling of turbulent chemical reaction  

Microsoft Academic Search

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

J.-Y. Chen

1995-01-01

57

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

SciTech Connect

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

Massot, Marc [Laboratoire EM2C, UPR 288 CNRS - Ecole Centrale Paris (France); Graille, Benjamin [Laboratoire de Mathematiques d'Orsay, UMR 8628 CNRS - Universite Paris-Sud (France); Magin, Thierry E. [Aeronautics and Aerospace Department, von Karman Institute for Fluid Dynamics (Belgium)

2011-05-20

58

Kinetic studies of elementary chemical reactions  

SciTech Connect

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.

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

1993-12-01

59

Modeling of turbulent chemical reaction  

NASA Technical Reports Server (NTRS)

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.

Chen, J.-Y.

1995-01-01

60

Modeling of turbulent chemical reaction  

NASA Astrophysics Data System (ADS)

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.

Chen, J.-Y.

1995-03-01

61

Chemical Reactions Among Indoor Pollutants  

Microsoft Academic Search

\\u000a Chemistry takes place all around us, regulating the intensity and nature of our exposure to pollutants in water, air and soil.\\u000a In indoor environments, chemistry can significantly alter the composition of the air we breathe. Transformations reduce our\\u000a exposure to reactants and increase our exposure to products. If this reaction takes place on or in a surface, the relative\\u000a exposure

Glenn Morrison

62

Heterogeneous chemical reactions: Preparation of monodisperse latexes  

NASA Technical Reports Server (NTRS)

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.

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

1977-01-01

63

Photochemical and thermal reactions of kynurenines  

NASA Astrophysics Data System (ADS)

Kynurenine and its derivatives are present in the lens of the human eye, where they perform the function of UV filters. Photochemical and thermal reactions of these compounds, which can result in irreversible modification of the lens proteins, and play an important role in the cataract development, are considered. Bibliography - 123 references.

Tsentalovich, Yu P.; Snytnikova, O. A.; Sagdeev, R. Z.

2008-09-01

64

Mediating chemical reactions using polysaccharides  

NASA Astrophysics Data System (ADS)

We have studied the NaBH4-mediated hydrogenation of select alkenes catalyzed by polysaccharide-stabilized nanoparticles. We compared the catalytic properties of Ni-based nanoparticles or Au/Co-based nanoparticles on the hydrogenation of cinnamic acid, cinnamide, cinnamyl alcohol, and ethyl cinnamate. We evaluated the possibility that the type of stabilizing polysaccharide surrounding the nanoparticle may affect the selectivity towards the alkene compounds that undergo the hydrogenation reaction. We found that the hydrogenation of cinnamide or ethyl cinnamate proceeded readily to 100% completion independent of the type of polysaccharide stabilizing the nanoparticle. However, the extent of the hydrogenation of cinnamyl alcohol and cinnamic acid varied greatly depending on the type of polysaccharide stabilizing the nanoparticle. In the course of these studies, we observed that some polysaccharides by themselves promoted the hydrolysis of ethyl cinnamate. Thus, we have raised the hypothesis that some polysaccharides may act as "esterases" and explored the interaction between select polysaccharides and a variety of ester compounds.

Tyler, Lauren E.

65

Chemical Changes in Carbohydrates Produced by Thermal Processing.  

ERIC Educational Resources Information Center

Discusses chemical changes that occur in the carbohydrates found in food products when these products are subjected to thermal processing. Topics considered include browning reactions, starch found in food systems, hydrolysis of carbohydrates, extrusion cooking, processing of cookies and candies, and alterations in gums. (JN)

Hoseney, R. Carl

1984-01-01

66

Thermal-oxidative aging of DGEBA\\/EPN\\/LMPA epoxy system: Chemical structure and thermal–mechanical properties  

Microsoft Academic Search

The evolvement of chemical structure and thermal–mechanical properties of diglycidyl ether of bisphenol-A and novolac epoxy resin blends cured with low molecular polyamide (DGEBA\\/EPN\\/LMPA system) during thermal-oxidative aging were investigated by Attenuated Total Reflectance Fourier Transform Infrared spectrometry (ATR-FTIR) and Dynamic Mechanical Thermal Analysis (DMTA). The results revealed that the chemical reactions during thermal-oxidative aging contained oxidation and chain scission.

Yan-min Pei; Kai Wang; Mao-sheng Zhan; Wen Xu; Xiao-jun Ding

2011-01-01

67

Formation of ultracold molecules in chemical reactions  

Microsoft Academic Search

We demonstrate that chemical reactions in collisions of high-energy molecular beams can generally produce molecules with zero velocity in the laboratory-fixed frame. Our analysis shows that collisions of beams may simultaneously yield slow reactant molecules and slow products. The reaction products are formed in selected ro-vibrational states and scattered in a specific direction, which can be controlled by tuning the

Timur Tscherbul; Girts Barinovs; Jacek Klos; Roman Krems

2008-01-01

68

Thermal reaction processes in a relativistic QED plasma drop  

E-print Network

The equilibrium size and temperature limits of thermally and chemically equilibrated $e^+e^-\\gamma$ plasma drops are investigated at a given energy content. For a plasma to be equilibrated it must be opaque to electron and photon interactions. The opaqueness condition is determined by comparing plasma size with the mean free electron and photon paths. We calculate those paths using thermal Lorentz-invariant reaction rates for pair production and electron(positron) and photon scattering. The range of the corresponding plasma temperature and size is evaluated numerically. Considering the energy and size we find that the opaque and equilibrated plasma drop may be experimentally attainable.

Inga Kuznetsova; Dieter Habs; Johann Rafelski

2009-11-01

69

Decrease of Entropy and Chemical Reactions  

E-print Network

The chemical reactions are very complex, and include oscillation, condensation, catalyst and self-organization, etc. In these case changes of entropy may increase or decrease. The second law of thermodynamics is based on an isolated system and statistical independence. If fluctuations magnified due to internal interactions exist in the system, entropy will decrease possibly. In chemical reactions there are various internal interactions, so that some ordering processes with decrease of entropy are possible on an isolated system. For example, a simplifying Fokker-Planck equation is solved, and the hysteresis as limit cycle is discussed.

Yi-Fang Chang

2008-07-01

70

Cores from the Salton Sea scientific drilling program: Metamorphic reaction progress as a function of chemical and thermal environment: Final report  

SciTech Connect

The study investigated the downhole progressive metamorphism at the Salton Sea site by monitoring and evaluating discontinuous and continuous metamorphic reactions. The main emphasis was placed on: (1) the addition of petrographic, geochemical, and mineralogical data to the Salton Sea data base; (2) determination of downhole reactions; (3) evaluation of the progress of individual continuous reaction (epsilon) and the overall reaction progress (epsilon/sub T/) during the transition from one metamorphic zone to the next; and (4) evaluation and correlation of mineral reactions and reaction progress with mineral phase and organic material geothermometry. To these ends, thirty-three samples from the Salton Sea core were analyzed for: (1) quantitative modal mineralogy using the x-ray diffraction reference intensity method (RIM), (2) 30 major and trace elements in the whole rock and (3) mineral chemistry and structural state. In addition, a subset of these samples were used for temperature determinations using vitrinite reflectivity.

Papike, J.J.; Shearer, C.K.

1987-05-13

71

Tailoring oxidation degrees of graphene oxide by simple chemical reactions  

SciTech Connect

High quality graphene oxide (GO) with controllable degrees of oxidation was synthesized by simple chemical reactions inspired by approaches to unzip single wall carbon nanotubes using strong oxidizing agents. As compared to the conventional Hummers method, these reactions are less exo-therm involved without emission of toxic gases. The structural characteristics of the synthesized GO with various oxidation degrees were evaluated by x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, thermal gravimetric analysis, and UV-vis-IR spectroscopy. GO with tailored degrees of oxidation displays tunable optoelectronic properties and may have a significant impact on developing graphene- or GO-based platforms for various technological applications.

Wang Gongkai [Key Laboratory for Anisotropy and Texture of Materials of Ministry of Education, Northeastern University, Shenyang, Liaoning 110004 (China); Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Sun Xiang; Lian Jie [Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Liu Changsheng [Key Laboratory for Anisotropy and Texture of Materials of Ministry of Education, Northeastern University, Shenyang, Liaoning 110004 (China)

2011-08-01

72

Computer Animation of a Chemical Reaction.  

ERIC Educational Resources Information Center

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…

Eaker, Charles W.; Jacobs, Edwin L.

1982-01-01

73

Classification of Chemical Reactions: Stages of Expertise  

ERIC Educational Resources Information Center

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…

Stains, Marilyne; Talanquer, Vicente

2008-01-01

74

Coupled thermal/chemical/mechanical modeling of insensitive explosives in thermal environments  

SciTech Connect

The ability to predict the response of a weapon system that contains insensitive explosives to elevated temperatures is important in understanding its safety characteristics. To model such a system at elevated temperatures in a finite element computer code requires a variety of capabilities. These modeling capabilities include thermal diffusion and convection to transport the heat to the explosives in the weapon system, temperature based chemical reaction modeling of the decomposition of the explosive materials, and mechanical modeling of both the metal casing and the unreacted and decomposed explosive. The Chemical TOPAZ code has been developed to model coupled thermal/chemical problems where we do not need to model the mass motion. We have also developed the LYNX2D code, based on PALM2D and Chemical TOPAZ, which is an implicit, two-dimensional coupled thermal/chemical/mechanical finite element model computer code. Some representative examples are shown. {copyright} {ital 1996 American Institute of Physics.}

Nichols, A.L. III [Lawrence Livermore National Laboratory, Livermore, California, 94550 (United States)

1996-05-01

75

Combustion chemical vapor deposited coatings for thermal barrier coating systems  

SciTech Connect

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

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

1995-12-31

76

Quantum Theory of Fast Chemical Reactions  

SciTech Connect

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.

John C. Light

2007-07-30

77

Computed Potential Energy Surfaces for Chemical Reactions  

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

78

Chemical Reaction due to Stronger Ramachandran Interaction  

E-print Network

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

Andrew Das Arulsamy

2011-10-15

79

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

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

80

Reflections on the design of solar thermal chemical reactors: thoughts in transformation  

Microsoft Academic Search

We illustrate a process for designing solar thermal chemical reactors for industrial applications. The process is iterative and involves developing a numerical model of the reactor that links the radiation heat transfer to the other modes of heat transfer and the kinetics of the chemical reaction. Reactors that effectively convert solar energy to chemical energy match well the solar flux

R. Palumbo; M. Keunecke; S. Möller; A. Steinfeld

2004-01-01

81

Thermal maps of gases in heterogeneous reactions.  

PubMed

More than 85 per cent of all chemical industry products are made using catalysts, the overwhelming majority of which are heterogeneous catalysts that function at the gas-solid interface. Consequently, much effort is invested in optimizing the design of catalytic reactors, usually by modelling the coupling between heat transfer, fluid dynamics and surface reaction kinetics. The complexity involved requires a calibration of model approximations against experimental observations, with temperature maps being particularly valuable because temperature control is often essential for optimal operation and because temperature gradients contain information about the energetics of a reaction. However, it is challenging to probe the behaviour of a gas inside a reactor without disturbing its flow, particularly when trying also to map the physical parameters and gradients that dictate heat and mass flow and catalytic efficiency. Although optical techniques and sensors have been used for that purpose, the former perform poorly in opaque media and the latter perturb the flow. NMR thermometry can measure temperature non-invasively, but traditional approaches applied to gases produce signals that depend only weakly on temperature are rapidly attenuated by diffusion or require contrast agents that may interfere with reactions. Here we present a new NMR thermometry technique that circumvents these problems by exploiting the inverse relationship between NMR linewidths and temperature caused by motional averaging in a weak magnetic field gradient. We demonstrate the concept by non-invasively mapping gas temperatures during the hydrogenation of propylene in reactors packed with metal nanoparticles and metal-organic framework catalysts, with measurement errors of less than four per cent of the absolute temperature. These results establish our technique as a non-invasive tool for locating hot and cold spots in catalyst-packed gas-solid reactors, with unprecedented capabilities for testing the approximations used in reactor modelling. PMID:24153305

Jarenwattananon, Nanette N; Glöggler, Stefan; Otto, Trenton; Melkonian, Arek; Morris, William; Burt, Scott R; Yaghi, Omar M; Bouchard, Louis-S

2013-10-24

82

Thermal maps of gases in heterogeneous reactions  

NASA Astrophysics Data System (ADS)

More than 85 per cent of all chemical industry products are made using catalysts, the overwhelming majority of which are heterogeneous catalysts that function at the gas-solid interface. Consequently, much effort is invested in optimizing the design of catalytic reactors, usually by modelling the coupling between heat transfer, fluid dynamics and surface reaction kinetics. The complexity involved requires a calibration of model approximations against experimental observations, with temperature maps being particularly valuable because temperature control is often essential for optimal operation and because temperature gradients contain information about the energetics of a reaction. However, it is challenging to probe the behaviour of a gas inside a reactor without disturbing its flow, particularly when trying also to map the physical parameters and gradients that dictate heat and mass flow and catalytic efficiency. Although optical techniques and sensors have been used for that purpose, the former perform poorly in opaque media and the latter perturb the flow. NMR thermometry can measure temperature non-invasively, but traditional approaches applied to gases produce signals that depend only weakly on temperature are rapidly attenuated by diffusion or require contrast agents that may interfere with reactions. Here we present a new NMR thermometry technique that circumvents these problems by exploiting the inverse relationship between NMR linewidths and temperature caused by motional averaging in a weak magnetic field gradient. We demonstrate the concept by non-invasively mapping gas temperatures during the hydrogenation of propylene in reactors packed with metal nanoparticles and metal-organic framework catalysts, with measurement errors of less than four per cent of the absolute temperature. These results establish our technique as a non-invasive tool for locating hot and cold spots in catalyst-packed gas-solid reactors, with unprecedented capabilities for testing the approximations used in reactor modelling.

Jarenwattananon, Nanette N.; Glöggler, Stefan; Otto, Trenton; Melkonian, Arek; Morris, William; Burt, Scott R.; Yaghi, Omar M.; Bouchard, Louis-S.

2013-10-01

83

Thermal energy harvesting plasmonic based chemical sensors.  

PubMed

Detection of gases such as H2, CO, and NO2 at 500 °C or greater requires materials with thermal stability and reliability. One of the major barriers toward integration of plasmonic-based chemical sensors is the requirement of multiple components such as light sources and spectrometers. In this work, plasmonic sensing results are presented where thermal energy is harvested using lithographically patterned Au nanorods, replacing the need for an external incident light source. Gas sensing results using the harvested thermal energy are in good agreement with sensing experiments, which used an external incident light source. Principal Component Analysis (PCA) was used to reduce the wavelength parameter space from 665 variables down to 4 variables with similar levels of demonstrated selectivity. The combination of a plasmonic-based energy harvesting sensing paradigm with PCA analysis offers a novel path toward simplification and integration of plasmonic-based sensing methods. PMID:25280004

Karker, Nicholas; Dharmalingam, Gnanaprakash; Carpenter, Michael A

2014-10-28

84

Plasmon-driven sequential chemical reactions in an aqueous environment  

PubMed Central

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

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

2014-01-01

85

Reaction, transformation and delamination of samarium zirconate thermal barrier coatings  

E-print Network

Reaction, transformation and delamination of samarium zirconate thermal barrier coatings Hengbei zirconates have attracted interest for thermal barrier coatings (TBCs) because they have very low intrinsic.V. All rights reserved. 1. Introduction Thermal barrier coating (TBC) systems are an enabling materials

Wadley, Haydn

86

Spectroscopy and reactions of molecules important in chemical evolution  

NASA Technical Reports Server (NTRS)

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.

Becker, R. S.

1974-01-01

87

A DFT analysis of thermal decomposition reactions important to natural products.  

PubMed

The thermal decomposition reactions of several important natural flavor and fragrance chemicals have been investigated using density functional theory (DFT, B3LYP/6-31G*). Retro-aldol reactions of glucose, fructose, hernandulcin, epihernandulcin, [3]-gingerol, and [4]-isogingerol; retro-carbonyl-ene reactions of isopulegol, lavandulol, isolyratol, and indicumenone; and pyrolytic syn elimination reactions of linalyl acetate, alpha-terpinyl acetate, and bornyl acetate, have been carried out. The calculations indicate activation enthalpies of around 30 kcal/mol for the retro-aldol reactions and for retro-carbonyl-ene reactions, comparable to pericyclic reactions such as the Cope rearrangement and electrocyclic reactions, and therefore important reactions at elevated temperatures (e.g., boiling aqueous solutions, gas-chromatograph injection ports). Activation enthalpies for pyrolytic eliminations are around 40 kcal/mol and are unlikely to occur during extraction or GC analysis. PMID:20734926

Setzer, William N

2010-07-01

88

A Review on Chemical Reactions of Solid Lubricants During Friction  

Microsoft Academic Search

A historical background on chemical reactions between solids, in which the chemical activation energy is generated by mechanical forces, is presented and a literature review on “mechano-chemical” or “tribo-chemical” reactions occurring between solid lubricants such as MoS2 and Zn2P2O7 and metal surfaces is given. According to the work reviewed, MoS2 reacts with steel surfaces under boundary friction conditions forming FeS

J. Gansheimer

1972-01-01

89

Shock initiated thermal and chemical responses of HMX crystal from ReaxFF molecular dynamics simulation.  

PubMed

To gain an atomistic-level understanding of the thermal and chemical responses of condensed energetic materials under thermal shock, we developed a thermal shock reactive dynamics (TS-RD) computational protocol using molecular dynamics simulation coupled with ReaxFF force field. ?-Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) was selected as a a target explosive due to its wide usage in the military and industry. The results show that a thermal shock initiated by a large temperature gradient between the "hot" region and the "cold" region results in thermal expansion of the particles and induces a thermal-mechanical wave propagating back and forth in the system with an averaged velocity of 3.32 km s(-1). Heat propagating along the direction of thermal shock leads to a temperature increment of the system and thus chemical reaction initiation. Applying a continuum reactive heat conduction model combined with the temperature distribution obtained from the RD simulation, a heat conduction coefficient is derived as 0.80 W m(-1) K(-1). The chemical reaction mechanisms during thermal shock were analyzed, showing that the reaction is triggered by N-NO2 bond breaking followed by HONO elimination and ring fission. The propagation rates of the reaction front and reaction center are obtained to be 0.069 and 0.038 km s(-1), based on the time and spatial distribution of NO2. The pressure effect on the thermal shock was also investigated by employing uniaxial compression before the thermal shock. We find that compression significantly accelerates thermal-mechanical wave propagation and heat conduction, resulting in higher temperature and more excited molecules and thus earlier initiation and faster propagation of chemical reactions. PMID:24899535

Zhou, Tingting; Song, Huajie; Liu, Yi; Huang, Fenglei

2014-07-21

90

TOPICAL REVIEW: Plasma-chemical reactions: low pressure acetylene plasmas  

NASA Astrophysics Data System (ADS)

Reactive plasmas are a well-known tool for material synthesis and surface modification. They offer a unique combination of non-equilibrium electron and ion driven plasma chemistry, energetic ions accelerated in the plasma sheath at the plasma-surface interface, high fluxes of reactive species towards surfaces and a friendly environment for thermolabile objects. Additionally, small negatively charged clusters can be generated, because they are confined in the positive plasma potential. Plasmas in hydrocarbon gases, and especially in acetylene, are a good example for the discussion of different plasma-chemical processes. These plasmas are involved in a plethora of possible applications ranging from fuel conversion to formation of single wall carbon nanotubes. This paper provides a concise overview of plasma-chemical reactions (PCRs) in low pressure reactive plasmas and discusses possible experimental and theoretical methods for the investigation of their plasma chemistry. An up-to-date summary of the knowledge about low pressure acetylene plasmas is given and two particular examples are discussed in detail: (a) Ar/C2H2 expanding thermal plasmas with electron temperatures below 0.3 eV and with a plasma chemistry initiated by charge transfer reactions and (b) radio frequency C2H2 plasmas, in which the energetic electrons mainly control PCRs.

Benedikt, J.

2010-02-01

91

Direct Monte Carlo simulation of chemical reaction systems: Simple bimolecular reactions  

E-print Network

Direct Monte Carlo simulation of chemical reaction systems: Simple bimolecular reactions Shannon D and understanding the behavior of gas phase chemical reaction systems. This Monte Carlo method, originated by Bird useful, and the gas dynamics of many systems is more easily predicted and understood by using Monte Carlo

Anderson, James B.

92

Advanced Chemical Heat Pumps Using Liquid-Vapor Reactions  

E-print Network

-vapor chemical reactions. . ~ Heat pumps using liquid-vapor reactions f (items 1 and 5, above) are the subjects of this paper. Configurations discussed are: r , ! 1. Electric drive 2. Temperature amplifier (TA) using Rankine heat engine and liquid...-vapor reaction heat pump 3. Heat amplifier (HA) using liquid-vapor ' " reaction heat engine and reverse Rankine heat pump 4. HA and TA in which both heat engine and heat pump use liquid-vapor reactions. Thermodynamic requirements for working fluids...

Kirol, L.

93

Investigating Factors Influencing Rates of Chemical Reactions  

NSDL National Science Digital Library

This activity is a lab investigation in which students observe the rate of generation of hydrogen gas from a reaction, and then modify the procedure to compare another variable affecting the rate of this reaction.

Derickson, Paula

94

Coal gasification with CO 2 in molten salt for solar thermal\\/chemical energy conversion  

Microsoft Academic Search

Coal gasification with CO2 in Na2CO3–K2CO3 molten salt that was used as thermal storage for gas\\/solid heterogeneous reaction was studied to apply this system for solar thermal\\/chemical energy conversion. The reactions were performed at 1173 K under various CO2 flow rates, weights of the molten salt and Na2CO3\\/K2CO3 ratios. The CO2 gas consumption rate increased with increasing CO2 flow rate,

J Matsunami; S Yoshida; Y Oku; O Yokota; Y Tamaura; M Kitamura

2000-01-01

95

Solar-Thermal Fluid-Wall Reaction Processing  

DOEpatents

The present invention provides a method for carrying out high temperature thermal dissociation reactions requiring rapid-heating and short residence times using solar energy. In particular, the present invention provides a method for carrying out high temperature thermal reactions such as dissociation of hydrocarbon containing gases and hydrogen sulfide to produce hydrogen and dry reforming of hydrocarbon containing gases with carbon dioxide. In the methods of the invention where hydrocarbon containing gases are dissociated, fine carbon black particles are also produced. The present invention also provides solar-thermal reactors and solar-thermal reactor systems.

Weimer, A. W.; Dahl, J. K.; Lewandowski, A. A.; Bingham, C.; Raska Buechler, K. J.; Grothe, W.

2006-04-25

96

Deterministic Function Computation with Chemical Reaction Networks*  

PubMed Central

Chemical reaction networks (CRNs) formally model chemistry in a well-mixed solution. CRNs are widely used to describe information processing occurring in natural cellular regulatory networks, and with upcoming advances in synthetic biology, CRNs are a promising language for the design of artificial molecular control circuitry. Nonetheless, despite the widespread use of CRNs in the natural sciences, the range of computational behaviors exhibited by CRNs is not well understood. CRNs have been shown to be efficiently Turing-universal (i.e., able to simulate arbitrary algorithms) when allowing for a small probability of error. CRNs that are guaranteed to converge on a correct answer, on the other hand, have been shown to decide only the semilinear predicates (a multi-dimensional generalization of “eventually periodic” sets). We introduce the notion of function, rather than predicate, computation by representing the output of a function f : ?k ? ?l by a count of some molecular species, i.e., if the CRN starts with x1, …, xk molecules of some “input” species X1, …, Xk, the CRN is guaranteed to converge to having f(x1, …, xk) molecules of the “output” species Y1, …, Yl. We show that a function f : ?k ? ?l is deterministically computed by a CRN if and only if its graph {(x, y) ? ?k × ?l ? f(x) = y} is a semilinear set. Finally, we show that each semilinear function f (a function whose graph is a semilinear set) can be computed by a CRN on input x in expected time O(polylog ?x?1).

Chen, Ho-Lin; Doty, David; Soloveichik, David

2013-01-01

97

Incidents of chemical reactions in cell equipment  

SciTech Connect

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.

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

1991-12-31

98

Rate constants for chemical reactions in high-temperature nonequilibrium air  

NASA Technical Reports Server (NTRS)

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

Jaffe, R. L.

1986-01-01

99

Computed potential energy surfaces for chemical reactions  

NASA Technical Reports Server (NTRS)

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.

Walch, Stephen P.

1990-01-01

100

Multidimensional thermal-chemical cookoff modeling  

SciTech Connect

Multidimensional thermal/chemical modeling is an essential step in the development of a predictive capability for cookoff of energetic materials in systems subjected to abnormal thermal environments. COYOTE II is a state-of-the-art two- and three-dimensional finite element code for the solution of heat conduction problems including surface-to-surface thermal radiation heat transfer and decomposition chemistry. Multistep finite rate chemistry is incorporated into COYOTE II using an operator-splitting methodology; rate equations are solved element-by-element with a modified matrix-free stiff solver, CHEMEQ. COYOTE II is purposely designed with a user-oriented input structure compatible with the database, the pre-processing mesh generation, and the post-processing tools for data visualization shared with other engineering analysis codes available at Sandia National Laboratories. As demonstrated in a companion paper, decomposition during cookoff in a confined or semi-confined system leads to significant mechanical behavior. Although mechanical effect are not presently considered in COYOTE II, the formalism for including mechanics in multidimensions is under development.

Baer, M.R.; Gross, R.J.; Gartling, D.K.; Hobbs, M.L.

1994-08-01

101

Master Equation Models for Chemical Reactions of Importance in Combustion  

Microsoft Academic Search

The master equation provides a quantitative description of the interaction between collisional energy transfer and chemical reaction for dissociation, isomerization, and association processes. The approach is outlined for both irreversible and reversible dissociation, isomerization, and association reactions. There is increasing interest, especially in combustion, in association reactions that involve several linked potential wells, with the possibility of isomerization, collisional stabilization,

Michael J. Pilling; Struan H. Robertson

2003-01-01

102

Thermal behaviors, nonisothermal decomposition reaction kinetics, thermal safety and burning rates of BTATz-CMDB propellant.  

PubMed

The composite modified double base (CMDB) propellants (nos. RB0601 and RB0602) containing 3,6-bis (1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine (BTATz) without and with the ballistic modifier were prepared and their thermal behaviors, nonisothermal decomposition reaction kinetics, thermal safety and burning rates were investigated. The results show that there are three mass-loss stages in TG curve and two exothermic peaks in DSC curve for the BTATz-CMDB propellant. The first two mass-loss stages occur in succession and the temperature ranges are near apart, and the decomposition peaks of the two stages overlap each other, inducing only one visible exothermic peak appear in DSC curve during 350-550 K. The reaction mechanisms of the main exothermal decomposition processes of RB0601 and RB0602 are all classified as chemical reaction, the mechanism functions are f(alpha)=(1-alpha)(2), and the kinetic equations are dalpha/dt = 10(19.24)(1-alpha)(2)e(-2.32x10(4)/T) and dalpha/dt = 10(20.32)(1-alpha)(2)e(-2.32x10(4)/T). The thermal safety evaluation on the BTATz-CMDB propellants was obtained. With the substitution of 26% RDX by BTATz and with the help of the ballistic modifier in the CMDB propellant formulation, the burning rate can be improved by 89.0% at 8 MPa and 47.1% at 22 MPa, the pressure exponent can be reduced to 0.353 at 14-20 MPa. PMID:20542638

Yi, Jian-Hua; Zhao, Feng-Qi; Wang, Bo-Zhou; Liu, Qian; Zhou, Cheng; Hu, Rong-Zu; Ren, Ying-Hui; Xu, Si-Yu; Xu, Kang-Zhen; Ren, Xiao-Ning

2010-09-15

103

Systems of Chemical Equations as Reasonable Reaction Mechanisms  

NASA Astrophysics Data System (ADS)

This paper demonstrates that chemical equations may be operated like a kind of LEGO game, with construction of the systems of chemical equations. In my teaching experience, these systems of chemical equations are able to help students to understand the reaction routes. Six general principles of creating the systems are formulated. Three examples from inorganic chemistry are considered and discussed in detail.

Dorozhkin, Sergey V.

2001-07-01

104

Nonstatistical Dynamics in Thermal Reactions of Polyatomic Molecules  

NASA Astrophysics Data System (ADS)

A brief review is presented of post-RRKM models for unimolecular reaction kinetics. The dynamics of the gas-phase SN2 reaction are discussed, and the important role of phase-space bottlenecks is highlighted. The remainder of the review is devoted to experimental and trajectory simulation results on thermal reactions of organic molecules that exhibit nonstatistical dynamics quite unlike that seen in the SN2 reaction. Specifically, the intermediates generated in these reactions decay much faster than RRKM theory would predict, and often with bimodal or multimodal lifetime distributions. A qualitative model for this behavior based on overlaps of transitional regions in the molecular phase space is discussed.

Carpenter, Barry K.

2005-05-01

105

CHEMICAL TAILORING OF TEICOPLANIN WITH SITE-SELECTIVE REACTIONS  

PubMed Central

Semi-synthesis 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 analogs 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 analogs 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 analogs with attenuated or enhanced antibacterial properties, in particular against vancomycin and teicoplanin resistance strains. PMID:23692563

Pathak, Tejas P.; Miller, Scott J.

2013-01-01

106

Chemical tailoring of teicoplanin with site-selective reactions.  

PubMed

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. PMID:23692563

Pathak, Tejas P; Miller, Scott J

2013-06-01

107

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...

108

The How and Why of Chemical Reactions  

ERIC Educational Resources Information Center

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…

Schubert, Leo

1970-01-01

109

Ignition, extinction, and thermal hysteresis of a heterogeneous exothermic reaction  

Microsoft Academic Search

Critical conditions of ignition and extinction are studied theoretically for the case of a heterogeneous exothermic reaction\\u000a proceeding on the uniformly accessible surface of a channel or a pore. Particular emphasis is placed on the thermal-hysteresis\\u000a effect of the reaction (an ignition temperature in excess of the extinction temperature), which ensures stability of the reaction\\u000a against changes in the external

I. G. Assovskii

1998-01-01

110

Photo, thermal and chemical degradation of riboflavin.  

PubMed

Riboflavin (RF), also known as vitamin B2, belongs to the class of water-soluble vitamins and is widely present in a variety of food products. It is sensitive to light and high temperature, and therefore, needs a consideration of these factors for its stability in food products and pharmaceutical preparations. A number of other factors have also been identified that affect the stability of RF. These factors include radiation source, its intensity and wavelength, pH, presence of oxygen, buffer concentration and ionic strength, solvent polarity and viscosity, and use of stabilizers and complexing agents. A detailed review of the literature in this field has been made and all those factors that affect the photo, thermal and chemical degradation of RF have been discussed. RF undergoes degradation through several mechanisms and an understanding of the mode of photo- and thermal degradation of RF may help in the stabilization of the vitamin. A general scheme for the photodegradation of RF is presented. PMID:25246959

Sheraz, Muhammad Ali; Kazi, Sadia Hafeez; Ahmed, Sofia; Anwar, Zubair; Ahmad, Iqbal

2014-01-01

111

Photo, thermal and chemical degradation of riboflavin  

PubMed Central

Summary Riboflavin (RF), also known as vitamin B2, belongs to the class of water-soluble vitamins and is widely present in a variety of food products. It is sensitive to light and high temperature, and therefore, needs a consideration of these factors for its stability in food products and pharmaceutical preparations. A number of other factors have also been identified that affect the stability of RF. These factors include radiation source, its intensity and wavelength, pH, presence of oxygen, buffer concentration and ionic strength, solvent polarity and viscosity, and use of stabilizers and complexing agents. A detailed review of the literature in this field has been made and all those factors that affect the photo, thermal and chemical degradation of RF have been discussed. RF undergoes degradation through several mechanisms and an understanding of the mode of photo- and thermal degradation of RF may help in the stabilization of the vitamin. A general scheme for the photodegradation of RF is presented.

Kazi, Sadia Hafeez; Ahmed, Sofia; Anwar, Zubair; Ahmad, Iqbal

2014-01-01

112

Computed potential energy surfaces for chemical reactions  

NASA Technical Reports Server (NTRS)

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.

Walch, Stephen P.; Levin, Eugene

1993-01-01

113

Kinetics of Chemical Reactions in Flames  

NASA Technical Reports Server (NTRS)

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.

Zeldovich, Y.; Semenov, N.

1946-01-01

114

Chemical versus Thermal Folding of Graphene Edges  

NASA Astrophysics Data System (ADS)

Using molecular dynamics (MD) simulations, we have investigated the kinetics of the graphene edge folding process. The lower limit of the energy barrier is found to be ˜380 meV/å (or about 800 meV per edge atom) and ˜50 meV/å (or about 120 meV per edge atom) for folding the edges of intrinsic clean single-layer graphene (SLG) and double-layer graphene (DLG), respectively. However, the edge folding barriers can be substantially reduced by imbalanced chemical adsorption, such as of H atoms, on the two sides of graphene along the edges. Our studies indicate that thermal folding is not feasible at room temperature (RT) for clean SLG and DLG edges and is feasible at high temperature only for DLG edges, whereas chemical folding (with adsorbates) of both SLG and DLG edges can be spontaneous at RT. These findings suggest that the folded edge structures of suspended graphene observed in some experiments are possibly due to the presence of adsorbates at the edges.

Su, Ninghai; Liu, Miao; Liu, Feng

2012-02-01

115

Log-domain circuit models of chemical reactions  

E-print Network

We exploit the detailed similarities between electronics and chemistry to develop efficient, scalable bipolar or subthreshold log-domain circuits that are dynamically equivalent to networks of chemical reactions. Our ...

Mandal, Soumyajit

116

Design and development of chemical ontologies for reaction representation.  

PubMed

This paper describes the development of chemical ontologies applied to the representation of organic chemical reactions. The ontologies are built using the methodology known as methontology. The hierarchically structured set of terms describing the subdomains, namely, organic reactions, organic compounds, and reagents, are constructed into individual ontologies. The ontologies consist of about 200 concepts and around 125 individuals. A set of binary relations is defined in order to integrate the ontologies with applications. The ontologies are implemented as an XML application with a set of vocabulary describing the domain knowledge. This paper also features an easy-to-use chemical ontological support system (COSS) intended to represent organic chemical reactions automatically. As a model application, the automatic representation of aliphatic nucleophilic substitution reactions is demonstrated using COSS. The paper also describes a keyword-based search system whose functionality is backed with COSS. PMID:17125179

Sankar, Punnaivanam; Aghila, Gnanasekaran

2006-01-01

117

CHEMICAL REACTIONS SIMULATED BY GROUND-WATER-QUALITY MODELS.  

USGS Publications Warehouse

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.

Grove, David, B.; Stollenwerk, Kenneth, G.

1987-01-01

118

Chemical reactions of organic compounds on clay surfaces.  

PubMed Central

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

Soma, Y; Soma, M

1989-01-01

119

Collisions, Chemical Reactions, and Transport Chemistry 223  

E-print Network

. Effusion, Wall Collisions, and Surface Reactions In the previous section, we found the parameter b application of this expression is in effusion though a pinhole. If there is a hole of area A in the surface will escape more slowly (with a 1/mass dependence); hence, effusion through a pinhole is a simple way in which

Ronis, David M.

120

Thermal oxidative degradation reactions of perfluoroalkylethers  

NASA Technical Reports Server (NTRS)

The mechanisms operative in thermal oxidative degradation of Fomblin Z and hexafluoropropene oxide derived fluids and the effect of alloys and additives upon these processes are investigated. The nature of arrangements responsible for the inherent thermal oxidative instability of the Fomblin Z fluids is not established. It was determined that this behavior is not associated with hydrogen end groups or peroxy linkages. The degradation rate of these fluids at elevated temperatures in oxidizing atmospheres is dependent on the surface/volume ratio. Once a limiting ratio is reached, a steady rate appears to be attained. Based on elemental analysis and oxygen consumption data, CF2OCF2CF2O2, no. CF2CF2O, is one of the major arrangements present. The action of the M-50 and Ti(4 Al, 4 Mn) alloys is much more drastic in the case of Fomblin Z fluids than that observed for the hexafluoropropene derived materials. The effectiveness of antioxidation anticorrosion additives, P-3 and phospha-s-triazine, in the presence of metal alloys is very limited at 316 C; at 288 C the additives arrested almost completely the fluid degradation. The phospha-s-triazine appears to be at least twice as effective as the P-3 compound; it also protected the coupon better. The Ti(4 Al, 4 Mn) alloy degraded the fluid mainly by chain scission processes this takes place to a much lesser degree with M-50.

Paciorek, K. L.; Ito, T. I.; Kratzer, R. H.

1981-01-01

121

Quantum chemical approach to estimating the thermodynamics of metabolic reactions.  

PubMed

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

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

2014-01-01

122

Brownian dynamics simulation of a chemical reaction in solution  

Microsoft Academic Search

We present a study, using the brownian dynamics simulation technique, of a simple model of a chemical reaction in solution. The model consists of the transfer of a particle between two substrate species in a reaction complex which interacts with its surroundings through frictional effects and random force terms. We pay particular attention to the regime in which both the

M. P. Allen

1980-01-01

123

Plasmonic smart dust for probing local chemical reactions.  

PubMed

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. PMID:23458121

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

2013-04-10

124

Cu-free click cycloaddition reactions in chemical biology†  

PubMed Central

Bioorthogonal chemical reactions are paving the way for new innovations in biology. These reactions possess extreme selectivity and biocompatibility, such that their participating reagents can form covalent bonds within richly functionalized biological systems—in some cases, living organisms. This tutorial review will summarize the history of this emerging field, as well as recent progress in the development and application of bioorthogonal copper-free click cycloaddition reactions. PMID:20349533

Jewett, John C.

2010-01-01

125

Polymer Reaction Engineering Laboratory Chemical and Biomolecular Engineering  

E-print Network

the instructions up to the step 9. 1. Main power switch on, blower switch off, pressure control switchPolymer Reaction Engineering Laboratory Chemical and Biomolecular Engineering University for chemical purity. The second type of daily activity involves controlling the position of the gloves

Choi, Kyu Yong

126

Conservation-dissipation structure of chemical reaction systems.  

PubMed

In this Brief Report, we show that balanced chemical reaction systems governed by the law of mass action have an elegant conservation-dissipation structure. From this structure a number of important conclusions can be easily deduced. In particular, with the help of this structure we can rigorously justify the classical partial equilibrium approximation in chemical kinetics. PMID:23368081

Yong, Wen-An

2012-12-01

127

LIGAND: Database of Chemical Compounds and Reactions in Biological Pathways  

NSDL National Science Digital Library

The Institute for Chemical Research at Kyoto University provides this frequently updated and well-documented database of enzyme reactions. With more than 9,300 entries, the LIGAND Chemical Database includes over 3,700 entries for enzymes (the Enzyme Reaction Database) and 5,600 entries for compounds (Chemical Compound Database). The database is searchable by keyword using DBGET (which supports numerous other databases and gene catalogs as well) and is accompanied by clear instructions. The LIGAND database, updated weekly, may be downloaded via anonymous FTP.

128

Laser cutting with chemical reaction assist  

DOEpatents

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.

Gettemy, Donald J. (Los Alamos, NM)

1992-01-01

129

Laser cutting with chemical reaction assist  

DOEpatents

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.

Gettemy, D.J.

1992-11-17

130

Laser cutting with chemical reaction assist  

SciTech Connect

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.

Gettemy, D.J.

1991-04-08

131

Chemical kinetic reaction mechanism for the combustion of propane  

NASA Technical Reports Server (NTRS)

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.

Jachimowski, C. J.

1984-01-01

132

Benchmark calculations of thermal reaction rates. I - Quantal scattering theory  

NASA Astrophysics Data System (ADS)

The thermal rate coefficient for the prototype reaction H + H2 yields H2 + H with zero total angular momentum is calculated by summing, averaging, and numerically integrating state-to-state reaction probabilities calculated by time-independent quantum-mechanical scattering theory. The results are very carefully converged with respect to all numerical parameters in order to provide high-precision benchmark results for confirming the accuracy of new methods and testing their efficiency.

Chatfield, David C.; Truhlar, Donald G.; Schwenke, David W.

1991-02-01

133

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

PubMed

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. PMID:24963600

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

2014-01-01

134

Sequential Voronoi diagram calculations using simple chemical reactions  

E-print Network

In our recent paper [de Lacy Costello et al. 2010] we described the formation of complex tessellations of the plane arising from the various reactions of metal salts with potassium ferricyanide and ferrocyanide loaded gels. In addition to producing colourful tessellations these reactions are naturally computing generalised Voronoi diagrams of the plane. The reactions reported previously were capable of the calculation of three distinct Voronoi diagrams of the plane. As diffusion coupled with a chemical reaction is responsible for the calculation then this is achieved in parallel. Thus an increase in the complexity of the data input does not utilise additional computational resource. Additional benefits of these chemical reactions is that a permanent record of the Voronoi diagram calculation (in the form of precipitate free bisectors) is achieved, so there is no requirement for further processing to extract the calculation results. Previously it was assumed that the permanence of the results was also a potenti...

Costello, Ben de Lacy; Adamatzky, Andy

2012-01-01

135

Thermal performance of a packed bed reactor for a high-temperature chemical heat pump  

Microsoft Academic Search

SUMMARY The thermal performance of a chemical heat pump that uses the reaction system of calcium oxide\\/lead oxide\\/carbon dioxide, which is developed for utilization of high-temperature heat above 8003C, is studied experimentally. The thermal performance of a packed-bed reactor of a calcium oxide\\/carbon dioxide reac- tion system, which stores and transforms a high-temperature heat source in the heat pump operation,

Yukitaka Kato; Tadashi O-shim; Yoshio Yoshizawa

2001-01-01

136

The effect of carbon nanotubes on chiral chemical reactions  

NASA Astrophysics Data System (ADS)

The intrinsic helicity of carbon nanotubes influences the formation of chiral molecules in chemical reactions. A racemic mixture of P and M enantiomers of nanotubes affects the enantiomeric excess of the products of the autocatalytic Soai reaction proportional to the amount of nanotubes added in the reaction mixture. An intermediate complex formed between the nanotube and the organometallic reagent is essential and explains the observed correlation between the enantiomeric distribution of products and the curvature of the carbon nanostructure. This Letter establishes a key mechanism for harnessing the helicity of nanoscale carbon surfaces for preparative organic reactions.

Rance, Graham A.; Miners, Scott A.; Chamberlain, Thomas W.; Khlobystov, Andrei N.

2013-02-01

137

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

PubMed

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 the molecules in the mixtures. PMID:24551112

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

2014-01-01

138

Chemical vapor detection with a multispectral thermal imager  

E-print Network

Chemical vapor detection with a multispectral thermal imager Mark 1. G. Aithouse, MEMBER SPIE U.S. Army Chemical Research Development and Engineering Center SMCCR-DDT Aberdeen Proving Ground, Maryland algorithm 7. Conclusions 8. Acknowledgments 9. References 1. INTRODUCTION Detection of chemical vapor clouds

Chang, Chein-I

139

Thermally Induced And Base Catalyzed Reactions Of Naphthoquinone Diazides  

NASA Astrophysics Data System (ADS)

Thermally induced and base catalyzed reactions of a phenol ester of 1,2-naphthoquinone-diazide-5-sulfonic acid (DAM) with p-cresol were investigated. In total seven reaction products were obtained for the thermally induced reaction. The three major products, TR--F4, TR-F6 and TR-F7, were isolated and their structures were determined by means of several advanced spectroscopic techniques like Fourier transform nuclear magnetic resonance (FTNMR) and field desorption mass spectroscopy (FD-MS). Besides a cresol ester of indenecarboxylic acid (TR-F6) and an azo compound which contains two DAM originated moieties and cresol (TR-F7), the formation of a novel compound was found; a phenol ester of 2-cresyl-l-naphthol-5-sulfonic acid. On the other hand, four reaction products were found in the base (a 2.38wt% tetramethylammonium hydroxide aq. solution) catalyzed reaction products of DAM with p-cresol, and two major products, BC-Fl and BC-F3, which appeared at the initial stage of the reaction were isolated. The structure determination of the two major products was carried out in the same manner as described above. It was discovered that BC-Fl was a cresol ester of 1-naphthol while BC-F3 was an azoxy compound. Brief discussions will be made on those reactions of naphthoquinone diazides with a matrix novolak resin with reference to the results obtained by the present study.

Koshiba, Mitsunobu; Murata, Makoto; Matsui, Mariko; Harita, Yoshiyuki

1988-01-01

140

Stratospheric chemical and thermal response to long-term variability in solar UV irradiance  

Microsoft Academic Search

Taking into account the thermal feedback effect on the reaction rates, a theoretical analysis of the chemical response of the stratosphere to the possible long-term variability of solar ultraviolet irradiance is presented. The variability, related to the 11-year solar cycle, is introduced in a two-dimensional stratosphere model simulating the zonally averaged distribution of chemical species related to oxygen, hydrogen, nitrogen

G. Brasseur; P. C. Simon

1981-01-01

141

Chemical Looping Combustion Reactions and Systems  

SciTech Connect

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.

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

142

STM CONTROL OF CHEMICAL REACTIONS: Single-Molecule Synthesis  

NASA Astrophysics Data System (ADS)

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.

Hla, Saw-Wai; Rieder, Karl-Heinz

2003-10-01

143

International chemical identifier for reactions (RInChI)  

PubMed Central

The IUPAC International Chemical Identifier (InChI) provides a method to generate a unique text descriptor of molecular structures. Building on this work, we report a process to generate a unique text descriptor for reactions, RInChI. By carefully selecting the information that is included and by ordering the data carefully, different scientists studying the same reaction should produce the same RInChI. If differences arise, these are most likely the minor layers of the InChI, and so may be readily handled. RInChI provides a concise description of the key data in a chemical reaction, and will help enable the rapid searching and analysis of reaction databases. PMID:24152584

2013-01-01

144

Theoretical studies of the dynamics of chemical reactions  

SciTech Connect

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

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

1993-12-01

145

Rapid chemical reaction workup based on a rigid solvent extraction.  

PubMed

The conventional chemical reaction workup based on liquid-liquid extraction is a time- and labor-consuming practice. We have developed a substantially faster technique for the routine workup that relies on a porous organic polymer (Porelite) supported solvent phase to extract organic products from an aqueous reaction mixture. We call this process rigid solvent extraction. Using this technique, the tedious liquid-liquid extraction can be replaced by a simple filtration, making parallel operation and automation feasible. PMID:25296390

Xu, Bo; Hammond, Gerald B

2014-10-17

146

Waste dissolution with chemical reaction, diffusion and advection  

SciTech Connect

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

Chambre, P.L.; Kang, C.H.; Lee, W.W.L.; Pigford, T.H.

1987-06-01

147

Simulation of chemical reaction dynamics on an NMR quantum computer  

E-print Network

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

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

2011-05-21

148

Mathematical models of thermal and chemical transport in geologic media  

SciTech Connect

Semi-analytical and numerical methods are used to investigate thermal and chemical transport processes in geologic media. The work is divided into two parts: (1) development of semi-analytical models for the analysis of uncoupled isothermal and nonisothermal fluid flow in naturally fractured media, and (2) development of a high resolution numerical code to address coupled nonisothermal chemical transport in geologic media. A semi-analytical model is developed for well test data analysis in naturally fractured reservoirs. A simple approximate analytical solution for pressure buildup and drawdown tests is developed. Methods based on the approximate solution are developed for the evaluation of important reservoir properties. Type curves for nonisothermal fluid flow in naturally fractured media are developed to design injection systems for maximum energy in hydrothermal systems. An accurate finite difference method for the solution of a convection-diffusion type equation is developed. The method is incorporated in a two-dimensional code to investigate free convection in a porous slab and kinetic silica-water reactions in geothermal systems. A multicomponent model considering the variations of pressure, temperature and silica concentration is developed to interpret the evolution of geothermal systems during exploitation.

Lai, C.-H.

1985-12-01

149

Preparation and thermal conductivity of CuO nanofluid via a wet chemical method  

PubMed Central

In this article, a wet chemical method was developed to prepare stable CuO nanofluids. The influences of synthesis parameters, such as kinds and amounts of copper salts, reaction time, were studied. The thermal conductivities of CuO nanofluids were also investigated. The results showed that different copper salts resulted in different particle morphology. The concentration of copper acetate and reaction time affected the size and shape of clusters of primary nanoparticles. Nanofluids with different microstructures could be obtained by changing the synthesis parameters. The thermal conductivities of CuO nanofluids increased with the increase of particle loading. PMID:21711693

2011-01-01

150

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

NASA Technical Reports Server (NTRS)

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

Gokoglu, Suleyman A.

1988-01-01

151

CHARACTERIZATION OF CHEMICALLY MODIFIED HYPERTHERMOPHILIC ENZYMES FOR CHEMICAL SYNTHESES AND BIOREMEDIATION REACTIONS  

EPA Science Inventory

Research developments in the area of biocatalysis in organic solvents are expected to greatly expand the role of bioprocessing in chemical synthesis, fuel processing, and bioremediation technologies. Many biological transformation reactions of interest to DOE site remediation inv...

152

Modeling Second-Order Chemical Reactions using Cellular Automata  

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

153

Reduction of chemical reaction networks through delay distributions  

NASA Astrophysics Data System (ADS)

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.

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

2013-03-01

154

Favorite Demonstration: Demonstrating Indigo Carmine Oxidation-Reduction Reactions--A Choreography for Chemical Reactions  

NSDL National Science Digital Library

The indigo carmine demonstration (Ferguson et al. 1973), also referred to as a traffic-light demonstration (Flinn Scientific 2007a), is an example of a set of oxidation-reduction reactions that occurs within one solution. This type of demonstration can be used to introduce the concept of chemical reaction to undergraduate nonscience majors. Through their observations guided by the instructor, students begin to develop and construct the following concepts: color changes, reaction rates, reversible reactions, energy requirements (endothermic/exothermic), and equilibrium.

Majerich, David M.; Schmuckler, Joseph S.

2008-03-01

155

Modeling pore collapse and chemical reactions in shock-loaded HMX crystals  

NASA Astrophysics Data System (ADS)

The localization of deformation in shock-loaded crystals of high explosive material leads to the formation of hot spots, which, if hot enough, initiate chemical reactions. The collapse of microscopic pores contained within a crystal is one such process that localizes energy and generates hot spots. Given the difficulty of resolving the details of pore collapse in shock compression experiments, it is useful to study the problem using direct numerical simulation. In this work, we focus on simulating the shock-induced closure of a single pore in crystalline ?-HMX using a multiphysics finite element code. To address coupled thermal-mechanical-chemical responses, the model incorporates a crystal-mechanics-based description of thermoelasto-viscoplasticity, the crystal melting behavior, and transformation kinetics for a single-step decomposition reaction. The model is applied to stress wave amplitudes of up to 11 GPa to study the details of pore collapse, energy localization, and the early stages of reaction initiation.

Austin, R. A.; Barton, N. R.; Howard, W. M.; Fried, L. E.

2014-05-01

156

Jet quenching and holographic thermalization with a chemical potential  

NASA Astrophysics Data System (ADS)

We investigate jet quenching of virtual gluons and thermalization of a strongly-coupled plasma with a non-zero chemical potential via the gauge/gravity duality. By tracking a charged shell falling in an asymptotic AdS d+1 background for d = 3 and d = 4, which is characterized by the AdS-Reissner-Nordström-Vaidya (AdS-RN-Vaidya) geometry, we extract a thermalization time of the medium with a non-zero chemical potential. In addition, we study the falling string as the holographic dual of a virtual gluon in the AdS-RN-Vaidya spacetime. The stopping distance of the massless particle representing the tip of the falling string in such a spacetime could reveal the jet quenching of an energetic light probe traversing the medium in the presence of a chemical potential. We find that the stopping distance decreases when the chemical potential is increased in both AdS-RN and AdS-RN-Vaidya spacetimes, which correspond to the thermalized and thermalizing media respectively. Moreover, we find that the soft gluon with an energy comparable to the thermalization temperature and chemical potential in the medium travels further in the non-equilibrium plasma. The thermalization time obtained here by tracking a falling charged shell does not exhibit, generically, the same qualitative features as the one obtained studying non-local observables. This indicates that — holographically — the definition of thermalization time is observer dependent and there is no unambiguos definition.

Caceres, Elena; Kundu, Arnab; Yang, Di-Lun

2014-03-01

157

Molecular Codes in Biological and Chemical Reaction Networks  

PubMed Central

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 posses 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. PMID:23372756

Gorlich, Dennis; Dittrich, Peter

2013-01-01

158

2011 Chemical Reactions at Surfaces Gordon Research Conference  

SciTech Connect

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.

Peter Stair

2011-02-11

159

Supersonic molecular beam experiments on surface chemical reactions.  

PubMed

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. PMID:25044656

Okada, Michio

2014-10-01

160

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...

161

Relaxations, Fluctuations, Phase Transitions and Chemical Reactions in Liquid Water  

Microsoft Academic Search

Fluctuations and collective motions in liquid water and their effects on chemical reactions dynamics are analyzed. Liquid water is a `frustrated' system with multiple random hydrogen bond network structures, and has anomalous microscopic and macroscopic properties. Rearrangement dynamics of the hydrogen bond network induces collective motions of water molecules and energy fluctuations. Vibrational motions of photoexcited molecules strongly resonate to

Iwao Ohmine; Masaki Sasai

1991-01-01

162

Pressure effects in solid state chemical reactions studied by ESR  

Microsoft Academic Search

The first steps of selected solid state chemical reactions were investigated by ESR in spectral and spatial resolution. Use was made of pressure induced changes of the fine structure of Fe and Mn as Well as the dynamic Jahn-Teller effect of Cu . Paramagnetic oxygen centres like Ox were used to monitore the generation and emptying of traps in oxides,

Reinhard Stoesser

1992-01-01

163

Transglycosylation reactions between galactomannans and arabinogalactans during dry thermal treatment.  

PubMed

Aiming to investigate the possible occurrence of transglycosylation reactions between galactomannans and side chains of arabinogalactans during coffee roasting, mixtures of ?-(1 ? 4)-D-mannotriose and ?-(1 ? 5)-L-arabinotriose were subjected to dry thermal treatments at 200 °C. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis allowed identifying polysaccharides composed by pentose and hexose residues with a degree of polymerization up to 18 residues. Methylation analysis showed the occurrence of new types of glycosidic linkages in all thermally treated mixtures, as well as the occurrence of terminally and 5-linked ribose, possibly formed from arabinose isomerization. Also, xylose and lyxose were identified and proposed to be formed from mannose. These results support the occurrence of transglycosylation reactions promoted by roasting involving both oligosaccharides in the starting mixtures, resulting in arabinan and mannan chimeric polysaccharides. These structural features were also found in roasted coffee polysaccharide samples. PMID:25129715

Moreira, Ana S P; Simões, Joana; Pereira, Andreia T; Passos, Cláudia P; Nunes, Fernando M; Domingues, M Rosário M; Coimbra, Manuel A

2014-11-01

164

The role of chemical reactions in the Chernobyl accident  

SciTech Connect

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.

Grishanin, E. I., E-mail: egrishanin@orexovo.net [Russian Research Center Kurchatov Institute (Russian Federation)

2010-12-15

165

The role of chemical reactions in the Chernobyl accident  

NASA Astrophysics Data System (ADS)

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°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.

Grishanin, E. I.

2010-12-01

166

Multiscale stochastic simulations of chemical reactions with regulated scale separation  

SciTech Connect

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 ? 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.

Koumoutsakos, Petros, E-mail: petros@ethz.ch [Chair of Computational Science, Clausiusstrasse 33, ETH Zurich, CH-8092 (Switzerland)] [Chair of Computational Science, Clausiusstrasse 33, ETH Zurich, CH-8092 (Switzerland); Feigelman, Justin [Chair of Computational Science, Clausiusstrasse 33, ETH Zurich, CH-8092 (Switzerland)] [Chair of Computational Science, Clausiusstrasse 33, ETH Zurich, CH-8092 (Switzerland)

2013-07-01

167

Chemical generation of atomic iodine for chemical oxygen–iodine laser. I. Modelling of reaction systems  

Microsoft Academic Search

The mathematical modelling of reaction systems for chemical generation of atomic iodine is presented. This process is aimed to be applied in the chemical oxygen–iodine laser (COIL), where it can save a substantial part of energy of singlet oxygen and so increase the laser output power. In the suggested method, gaseous reactants for I atoms generation are admixed into the

V??t Jirásek; Otomar Špalek; Jarmila Kodymová; Miroslav ?enský

2001-01-01

168

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

SciTech Connect

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)

Censky, M; Spalek, O; Jirasek, V; Kodymova, J [Institute of Physics, Czech Academy of Sciences, Prague (Czech Republic); Jakubec, I [Institute of Inorganic Chemistry, Czech Academy of Sciences, Rez (Czech Republic)

2009-11-30

169

Energetic fuel-coolant interactions considering chemical reactions  

SciTech Connect

A propagation/expansion model developed for large scale vapor explosions was enhanced to consider the possibility of a chemical reaction between metallic fuel and the water coolant during an energetic fuel-coolant interaction (FCI). This lumped volume model, based on a fragmentation concept involving film collapse, coolant jet impingement and entrapment, predicts the correct qualitative trends for recent Sandia NPR experiments involving molten aluminum dropped into water, as a function of fuel composition, coolant temperature, ambient pressure, coolant/fuel mass ratio, and initial constraints. Chemical reactions between the molten metal and the water vapor in the surrounding film are considered and predicts aluminum ignition at 1,225 K compared to the empirically observed chemical assisted vapor explosion at 1,150 K.

Uludogan, A.; Corradini, M.L. [Univ. of Wisconsin, Madison, WI (United States)

1995-12-31

170

Laboratory Kinetics of Chemical Reactions occurring in Astrophysical Environments  

NASA Astrophysics Data System (ADS)

To model the dynamics and molecular evolution of interstellar clouds, a great deal of information on chemical kinetics is required, preferably under the appropriate conditions of kinetic temperature and internal excitation. This kinetics includes (i) gas phase ionic (ion-molecule and electron-ion) and (ii) neutral-neutral reactions and (iii) heterogeneous surface catalysis, all from simple species to those as complex as polyaromatic hydrocarbons and pre-life molecules. The current situation in these three areas will be briefly reviewed with more emphasis on ionic reactions for which the most data are available. The classes of reactions will include charge and proton transfer, atom insertion and abstraction, radiative association, electron-ion and ion-ion recombination, reactions with atoms, reactions involving isotopes, reaction and production of structural isomers, ring formation and destruction, and condensation. Information on rates of reaction, product identity and state of excitation will be presented wherever possible. Some mention will also be made of the reactions of negative ions. Most recent data will be presented, specifically involving the understudied process of electron-ion recombination. Some possible future directions will also be suggested. Funding of my research program by ACF-PRF, NASA and NSF is gratefully acknowledged.

Adams, N. G.; Babcock, L. M.

2005-05-01

171

Chemical applications of solar thermal energy  

SciTech Connect

The technology is known for solar-activated chemical applications ranging from desalination of salt water to producing elemental phosphorous with a high-temperature solar furnace. Researchers have also experimented with solar furnaces in a number of chemical applications including coal gasification and water-splitting cycles to form hydrogen. Federal budget cuts in solar research may concentrate industrial interest in the high-temperature area. 1 figure. (DCK)

Whaley, T.

1983-01-17

172

Chemical analyses of selected thermal springs and wells in Wyoming  

SciTech Connect

Basic chemical data for 27 selected thermal well and springs in Wyoming are presented. The samples were gathered from 1979 through 1982 in an effort to define geothermal resources in Wyoming. The basic data for the 27 analyzed samples generally include location, temperature, flow, date analyzed, and a description of what the sample is from. The chemical analyses for the sample are listed.

Heasler, H.P.

1984-06-01

173

The path from chemical to thermal freeze-out  

E-print Network

The evolution of a hadronic system after its chemical decomposition is described through a model that conserves the hadronic multiplicities to their values at chemical freeze-out. The state of the system is found as function of temperature and the corresponding baryon density is evaluated. The baryon density at thermal decoupling is also computed.

Kapoyannis, A S

2001-01-01

174

Thermal/chemical degradation of inorganic membrane materials  

SciTech Connect

The objective of this program is to evaluate the long-term thermal and chemical degradation of inorganic membranes that are developed to separate gases produced by coal combustion and coal gasification. Membrane materials tested include alumina, vycor, platinum foil, and palladium foils. The porosity, permeability, and characterization of physical and chemical changes after exposure to hot gas streams is described.

Krishnan, G.N.; Damle, A.S.; Sanjurjo, A.; Wood, B.J.; Lau, K.H.

1995-12-01

175

Evaluation on thermal explosion induced by slightly exothermic interface reaction.  

PubMed

An asphalt-salt mixture (ASM), which once caused a fire and explosion in a reprocessing plant, was prepared by imitating the real bituminization process of waste on a lab scale to evaluate its actual thermal hazards. Heat flux reaction calorimeters were used to measure the release of heat for the simulated ASM at a constant heating rate and at a constant temperature, respectively. Experimental results show that the reaction in the ASM below about 250 degrees C is a slightly exothermic interface reaction between the asphalt and the salt particles contained in the asphalt, and that the heat release rate increases sharply above about 250 degrees C due to melting of the salt particles. The reaction rates were formulated on the basis of an assumed reaction model, and the kinetic parameters were determined. Using the model with the kinetic parameters, temperature changes with time and drum-radius axes for the ASM-filled drum were numerically simulated assuming a one-dimensional infinite cylinder system, where the drum was being cooled at an ambient temperature of 50 degrees C. The minimum filling temperature, at which the runaway reaction (MFTRR) can occur for the simulated ASM in the drum is about 194 degrees C. Furthermore, a very good linear correlation exists between this MFTRR and the initial radius of salt particles formed in the bituminization product. The critical filling temperature to the runaway reaction is about 162 degrees C for the asphalt-salt mixture, containing zero-size salt particles, filled in the same drum at an ambient temperature of 50 degrees C. Thus, the runaway reaction will never occur in the drum filled with the asphalt-salt mixture under the conditions of the filling temperature below 162 degrees C and a constant ambient temperature of 50 degrees C. As a consequence, the ASM explosion occurred in the reprocessing plant likely was due to a slightly exothermically reaction and self heating. PMID:15363527

Yu, Ma-Hong; Li, Yong-Fu; Sun, Jin-Hua; Hasegawa, Kazutoshi

2004-09-10

176

A Review of Study on Thermal Energy Transport System by Synthesis and Decomposition Reactions of Methanol  

NASA Astrophysics Data System (ADS)

The study on thermal energy transport system by synthesis and decomposition reactions of methanol was reviewed. To promote energy conservation and global environment protection, a two-step liquid-phase methanol synthesis process, which starts with carbonylation of methanol to methyl formate, then followed by the hydrogenolysis of the formate, was studied to recover wasted or unused discharged heat from industrial sources for the thermal energy demands of residential and commercial areas by chemical reactions. The research and development of the system were focused on the following three points. (1) Development of low-temperature decomposition and synthetic catalysts, (2) Development of liquid phase reactor (heat exchanger accompanying chemical reaction), (3) Simulation of the energy transport efficiency of entire system which contains heat recovery and supply sections. As the result of the development of catalyst, promising catalysts which agree with the development purposes for the methyl formate decomposition reaction and the synthetic reaction are being developed though some studies remain for the methanol decomposition and synthetic reactions. In the fundamental development of liquid phase reactor, the solubilities of CO and H2 gases in methanol and methyl formate were measured by the method of total pressure decrease due to absorption under pressures up to 1500kPa and temperatures up to 140°C. The diffusivity of CO gas in methanol was determined by measuring the diameter and solution time of single CO bubbles in methanol. The chemical reaction rate of methanol synthesis by hydrogenolysis of methyl formate was measured using a plate-type of Raney copper catalyst in a reactor with rectangular channel and in an autoclave reactor. The reaction characteristics were investigated by carrying out the experiments at various temperatures, flow rates and at various catalyst development conditions. We focused on the effect of Raney copper catalyst thickness on the liquid-phase chemical reaction by varying the development time of the catalyst. Investigation results of the catalyst such as surface area, pore radius, lattice size, and photographs of scanning electron microscope (SEM) were also given. In the simulation of energy transport efficiency of this system, by simulating the energy transfer system using two-step liquid phase methanol decomposition and synthetic reactions, and comparing with the technology so far, it can be expected that an innovative energy transfer system is possible to realize.

Liu, Qiusheng; Yabe, Akira; Kajiyama, Shiro; Fukuda, Katsuya

177

Primary reactions of the thermal decomposition of tricyclodecane  

E-print Network

In order to better understand the thermal decomposition of polycyclanes, the pyrolysis of tricyclodecane has been studied in a jet-stirred reactor at temperatures from 848 to 933 K, for residence times between 0.5 and 6 s and at atmospheric pressure, in order to obtain a conversion between 0.01 and 25 %. The main products of the reaction are hydrogen, methane, ethylene, ethane, propene, 1,3-cyclopentadiene, cyclopentene, benzene, 1,5-hexadiene, toluene and 3-cyclopentyl-cyclopentene. A primary mechanism containing all the possible initiation steps, including those involving diradicals, as well as propagation reactions has been developed and allows experimental results to be satisfactorily modeled. The main reaction pathways of consumption of tricyclodecane and of formation of the main products have been derived from flow rate and sensitivity analyses.

Herbinet, Olivier; Bounaceur, Roda; Fournet, René; Battin-Leclerc, Frédérique; Scacchi, Gérard; Marquaire, Paul-Marie

2006-01-01

178

Photo-induced chemical reaction of trans-resveratrol.  

PubMed

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 (0.25mM, 100% ethanol) under 100?Wcm(-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. PMID:25308653

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

2015-03-15

179

Information-Theoretical Complexity Analysis of Selected Elementary Chemical Reactions  

NASA Astrophysics Data System (ADS)

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.

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

180

Laser studies of chemical reaction and collision processes  

SciTech Connect

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.

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

1993-12-01

181

Extinction and Spread of Isothemal Flame Balls in An Autocatalytic Chemical Reaction  

E-print Network

Extinction and Spread of Isothemal Flame Balls in An Autocatalytic Chemical Reaction Junping Shi(?). Remember that there are more than 4000 universities in USA! #12;An isothermal autocatalytic chemical: reaction rate Reaction-diffusion system of chemical reaction: a t = DAa - kabp, b t = DBb + kabp, t > 0, x

Shi, Jun-Ping

182

Controlling ultracold chemical reactions via Rydberg-dressed interactions  

E-print Network

We show that ultracold chemical reactions can be manipulated and controlled by using Rydberg-dressed interactions. Scattering in the ultracold regime is sensitive to long-range interactions, especially when weakly bound (or quasi-bound) states exist near the collision threshold. We investigate how, by Rydberg-dressing a reactant, one enhances its polarizability and modifies the long-range van der Waals collision complex, which can alter chemical reaction rates by shifting the position of near threshold bound states. We carry out a full quantum mechanical scattering calculation for the benchmark system H$_2$+D, and show that resonances can be moved substantially and that rate coefficients at cold and ultracold temperatures can be increased by several orders of magnitude.

Wang, Jia; Simbotin, Ion; Côté, R

2014-01-01

183

Potential for exothermic chemical reactions in waste tanks  

SciTech Connect

The potential for exothermic chemical reactions in waste tanks at Hanford is discussed. Organic chemicals have been added to Hanford waste tanks, particularly as ferrocyanides and when processing sludges at B Plant. Recent planned or ongoing activities involving stored wastes have possibly increased the potential for reaction of these wastes with nitrate salts in the waste tanks. Risk evaluations appear to be deficient in assessing the consequences of a deflagration, and in determining the probability of either a deflagration or detonation. The present question is whether current plans and recent safety-related documentation have given proper consideration to the available information about organic compounds in waste tanks. The principal organic additions to Hanford waste tanks are 1200 tonnes of organic carbon'' and 500 tonnes of Ni{sub 2}Fe(CN){sub 6}. 13 refs.

Van Tuyl, H.H.

1983-02-03

184

Tabletop imaging of structural evolutions in chemical reactions  

E-print Network

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

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

2014-01-01

185

Chemical reaction fouling model for single-phase heat transfer  

SciTech Connect

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.

Panchal, C.B. [Argonne National Lab., IL (United States); Watkinson, A.P. [British Columbia Univ., Vancouver, BC (Canada)

1993-08-01

186

Boundary Effects on Chaotic Advection-Diffusion Chemical Reactions M. Chertkov1  

E-print Network

not sense changes in the chemical concentrations nor heat released in the result of the chemical reactionBoundary Effects on Chaotic Advection-Diffusion Chemical Reactions M. Chertkov1 and V. Lebedev1,2 1 chemical reaction, A B ! C, in a statistically stationary bounded chaotic flow at large Peclet number Pe

Lebedev, Vladimir

187

Quantum Low-Temperature Limit of a Chemical Reaction Rate  

Microsoft Academic Search

The radiation-induced polymerization of formaldehyde has been studied in the solid state. The time of addition of one new link to a polymer chain increases exponentially in accordance with the Arrhenius law at 140 to 80 K, but approaches a constant value (approximately 10-2 second) at temperatures below 10 K. Thus, a low-temperature limit to a chemical reaction rate has

V. I. Goldanskii; M. D. Frank-Kamenetskii; I. M. Barkalov

1973-01-01

188

Chemical Reaction-Induced Multi-molecular Polarization (CRIMP).  

PubMed

Here we present a novel hyperpolarization method, Chemical Reaction-Induced Multi-molecular Polarization (CRIMP), which could be applied to the study of several in vivo processes simultaneously including glycolysis, TCA cycle, fatty acid synthesis and pH mapping. Through the use of non-enzymatic decarboxylation, we generate four hyperpolarized imaging agents from hyperpolarized 1,2-(13)C pyruvic acid. PMID:25224323

Lee, Y; Zacharias, N M; Piwnica-Worms, D; Bhattacharya, P K

2014-10-01

189

Different chemical reaction times between normal and solid cancer cells.  

PubMed

Entropy generation approach has been developed in order to use it for the analysis of complex systems with particular regards to biological systems in order to evaluate their stationary states. The entropy generation is related to the transport processes related to energy flows. Moreover, cancer can be described as an open complex dynamic and self-organizing system. Using the entropy generation approach it is possible to point out different chemical reaction time between normal and solid cancer cells. PMID:23643705

Lucia, Umberto

2013-07-01

190

Great Chemistry! How is Energy Released in Chemical Reactions?  

NSDL National Science Digital Library

The Materials Science and Technology Teacher's Workshop (MAST) provides this activity to look at the ways in which energy is released in chemical reactions. The class will examine plaster of paris, bromthymol blue and the hydration of baking soda. Students will observe the temperature changes of each.The lesson includes step by step directions for the experiment. Discussion questions and teacher notes are also included.

2012-07-23

191

Chemical reactions in the Titan’s troposphere during lightning  

NASA Astrophysics Data System (ADS)

In the lower troposphere of the Titan the temperature is about 90 K, therefore the chemical production of compounds in the CH 4/N 2 atmosphere is extremely slow. However, atmospheric electricity could provide conditions at which chemical reactions are fast. This paper is based on the assumption that there are lightning discharges in the Titan's lower atmosphere. The temporal temperature profile of a gas parcel after lightning was calculated at the conditions of 10 km above the Titan's surface. Using this temperature profile, composition of the after-lightning atmosphere was simulated using a detailed chemical kinetic mechanism consisting of 1829 reactions of 185 species. The main reaction paths leading to the products were investigated. The main products of lighting discharges in the Titan's atmosphere are H 2, HCN, C 2N 2, C 2H 2, C 2H 4, C 2H 6, NH 3 and H 2CN. The annual production of these compounds was estimated in the Titan's atmosphere.

Kovács, Tamás; Turányi, Tamás

2010-06-01

192

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

SciTech Connect

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.

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

1993-12-01

193

A microfabricated suspended-tube chemical reactor for thermally efficient fuel processing  

Microsoft Academic Search

We present a suspended-tube chemical reactor\\/heat exchanger for high-temperature fuel processing in micro energy conversion systems, primarily for hydrogen production in portable fuel cell systems. This reactor, designed to thermally isolate a high-temperature reaction zone, consists of four free-standing silicon nitride tubes comprising two independent U-shaped fluidic channels. Portions of the tubes are encased in silicon to enable heat exchange

Leonel R. Arana; Samuel B. Schaevitz; Aleksander J. Franz; Martin A. Schmidt; Klavs F. Jensen

2003-01-01

194

Raman studies of chemically and thermally reduced graphene oxide  

NASA Astrophysics Data System (ADS)

Reduced graphene oxides were synthesized by chemical reduction of graphite oxide using hydrazine hydrate as well as by high temperature-high vacuum thermal exfoliation at 900-1100°C. The samples were characterized using Raman spectroscopy. From the Raman spectra, it is inferred that hydrazine reduced and thermally exfoliated samples were found to consist of two and three to five layers. The change in the amount of sp2 rings present in GO with increase in exfoliation temperature is studied.

Sahoo, Madhusmita; Antony, Rajini P.; Mathews, Tom; Dash, S.; Tyagi, A. K.

2013-02-01

195

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

SciTech Connect

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.

Nguyen, H.D.

1991-11-01

196

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

SciTech Connect

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.

Nguyen, H.D.

1991-11-01

197

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

PubMed

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 (A(n,s) < 0) the curving of the path, and thus the structural changes of the reaction complex. URVA can show the mechanism of a reaction expressed in terms of reaction phases, revealing the sequence of chemical processes in the reaction complex and making it possible to determine those electronic factors that control the mechanism and energetics of the reaction. The magnitude of adiabatic curvature coupling coefficients is related to strength and polarizability of the bonds being broken. Transient points along the reaction path are associated with hidden intermediates and hidden transition states, which can be converted into real intermediates and transition states when the reaction conditions or the substitution pattern of the reaction complex are appropriately changed. Accordingly, URVA represents a theoretical tool with tremendous experimental potential, offering the chemist the ability to assert greater control over reactions. PMID:20232791

Kraka, Elfi; Cremer, Dieter

2010-05-18

198

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

PubMed Central

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

Scholey, Jonathan M.

2013-01-01

199

EFFECTS OF THERMAL TREATMENTS ON THE CHEMICAL REACTIVITY OF TRICHLOROETHYLENE  

EPA Science Inventory

A series of experiments was completed to investigate abiotic degradation and reaction product formation of trichloroethylene (TCE) when heated. A quartz-tube apparatus was used to study short residence time and high temperature conditions that are thought to occur during thermal ...

200

Reaction Networks for Interstellar Chemical Modelling: Improvements and Challenges  

NASA Astrophysics Data System (ADS)

We survey the current situation regarding chemical modelling of the synthesis of molecules in the interstellar medium. The present state of knowledge concerning the rate coefficients and their uncertainties for the major gas-phase processes—ion-neutral reactions, neutral-neutral reactions, radiative association, and dissociative recombination—is reviewed. Emphasis is placed on those key reactions that have been identified, by sensitivity analyses, as 'crucial' in determining the predicted abundances of the species observed in the interstellar medium. These sensitivity analyses have been carried out for gas-phase models of three representative, molecule-rich, astronomical sources: the cold dense molecular clouds TMC-1 and L134N, and the expanding circumstellar envelope IRC +10216. Our review has led to the proposal of new values and uncertainties for the rate coefficients of many of the key reactions. The impact of these new data on the predicted abundances in TMC-1 and L134N is reported. Interstellar dust particles also influence the observed abundances of molecules in the interstellar medium. Their role is included in gas-grain, as distinct from gas-phase only, models. We review the methods for incorporating both accretion onto, and reactions on, the surfaces of grains in such models, as well as describing some recent experimental efforts to simulate and examine relevant processes in the laboratory. These efforts include experiments on the surface-catalyzed recombination of hydrogen atoms, on chemical processing on and in the ices that are known to exist on the surface of interstellar grains, and on desorption processes, which may enable species formed on grains to return to the gas-phase.

Wakelam, V.; Smith, I. W. M.; Herbst, E.; Troe, J.; Geppert, W.; Linnartz, H.; Öberg, K.; Roueff, E.; Agúndez, M.; Pernot, P.; Cuppen, H. M.; Loison, J. C.; Talbi, D.

2010-10-01

201

A semiclassical non-adiabatic theory for elementary chemical reactions  

E-print Network

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

Aubry, Serge

2014-01-01

202

Thermal reaction studies of organic model compound-mineral matter interactions in solids  

SciTech Connect

The solid-state chemistry of silica-immobilized phenethyl phenyl ethers is being investigated in the presence of interdispersed aluininosilicates at temperatures relevant to coal processing to gain a better understanding of the impact of mineral matter on pyrolysis and liquefaction mechanisms. Results demonstrate the dramatic effect that aluminosilicates can have in altering the normal thermal reaction pathways for these models of ether linkages in lignin and low rank coals. An investigation of the chemistry of these model compounds at low temperatures (ca. 150-200{degrees}C) in the presence of aluminosilicates, including montmorillonite, is currently being investigated to delineate the chemical transformations that can occur during lignin maturation.

Buchanan, A.C. III; Britt, P.F.; Thomas, K.B.

1995-07-01

203

Automated microreactor system for reaction development and online optimization of chemical processes  

E-print Network

Developing the optimal conditions for chemical reactions that are common in fine chemical and pharmaceutics is a difficult and expensive task. Because syntheses in these fields have multiple reaction pathways, a significant ...

McMullen, Jonathan Patrick

2010-01-01

204

Miscible viscous fingering with chemical reaction involving precipitation.  

NASA Astrophysics Data System (ADS)

When a reactive and miscible less-viscous liquid displaces a more-viscous liquid in a Hele-Shaw cell, reactive miscible viscous fingering takes place. The present study has experimentally examined how precipitation produced by chemical reaction affects miscible viscous fingering pattern. A 97 wt % glycerin solution containing iron(III) nitrate (yellow) and a solution containing potassium hexacyano ferrate(II) (colorless) were used as the more- and less-viscous liquids, respectively. In this case, the chemical reaction instantaneously takes place and produces the precipitation being dark blue in color. The experiments were done by varying reactant concentrations, the cell's gap width, and the displacement speed. We compared the patterns involving the precipitation reaction with those in the non-reactive cases. We have found fylfot-like pattern is observed, depending on the experimental condition, which has never been formed in the non-reactive experiments. As the reactant concentrations are increased or the displacement speed is decreased, the effects of the precipitation on the patterns are more pronounced.

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

2007-11-01

205

Mechano-chemical coupling in Belousov-Zhabotinskii reactions.  

PubMed

Mechano-chemical coupling has been recently recognised as an important effect in various systems as chemical reactivity can be controlled through an applied mechanical loading. Namely, Belousov-Zhabotinskii reactions in polymer gels exhibit self-sustained oscillations and have been identified to be reasonably controllable and definable to the extent that they can be harnessed to perform mechanical work at specific locations. In this paper, we use our theoretical work of nonlinear mechano-chemical coupling and investigate the possibility of providing an explanation of phenomena found in experimental research by means of this theory. We show that mechanotransduction occurs as a response to both static and dynamic mechanical stimulation, e.g., volume change and its rate, as observed experimentally and discuss the difference of their effects on oscillations. Plausible values of the quasi-stoichiometric parameter f of Oregonator model are estimated together with its dependence on mechanical stimulation. An increase in static loading, e.g., pressure, is predicted to have stimulatory effect whereas dynamic loading, e.g., rate of volume change, is predicted to be stimulatory only up to a certain threshold. Further, we offer a physically consistent explanation of the observed phenomena why some Belousov-Zhabotinskii gels require an additional mechanical stimulation to show emergence of oscillation or why "revival" of oscillations in Belousov-Zhabotinskii reactions is possible together with indications for further experimental setups. PMID:24697427

Klika, Václav; Grmela, Miroslav

2014-03-28

206

The thermal reactions of CH{sub 3}  

SciTech Connect

The thermal reactions of CH{sub 3}-radicals have been investigated in reflected shock waves experiments at temperatures between 1224--2520 K. The fast dissociation of CH{sub 3}I served as the source of CH{sub 3}. Experiments were performed at three loading pressures with variations in [CH{sub 3}I]{sub 0}. H-atoms formed in the reaction, 2CH{sub 3} {yields} C{sub 2}H{sub 5} + H, were measured by the atomic resonance absorption spectrometric (ARAS) technique. The product ethyl radicals subsequently decompose to give a second H-atom and ethylene. A reaction mechanism was used to fit the data, and the resulting value for the rate constant was 5.25 {times} 10{sup {minus}11} exp({minus}7384 K/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. This value is compared to earlier determinations. At higher temperatures, 2150--2520 K, the H-atom formation rate was dominated by CH{sub 3} thermal dissociation. With simulations, the rate constant for CH{sub 3} + Kr {yields} CH{sub 2} + H + Kr could be determined. The rate constant for this process is: k = 4.68 {times} 10{sup {minus}9} exp({minus}42506 K/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. This result is compared to earlier experimental determinations and also to theoretical calculations using the semi-empirical Troe formalism.

Lim, K.P.; Michael, J.V.

1994-06-01

207

Fuels and chemicals from biomass using solar thermal energy  

NASA Astrophysics Data System (ADS)

The significant nearer term opportunities for the application of solar thermal energy to the manufacture of fuels and chemicals from biomass are summarized, with some comments on resource availability, market potential and economics. Consideration is given to the production of furfural from agricultural residues, and the role of furfural and its derivatives as a replacement for petrochemicals in the plastics industry.

Giori, G.; Leitheiser, R.; Wayman, M.

1981-05-01

208

On-site thermal treatment of chemical and petroleum equipment  

Microsoft Academic Search

Four on-site thermal treatments are recommended to reduce the manufacturing time of chemical and petroleum equipment. First, heating by panel heater of the annular section of the weld, or temper of the annular seam. Properly treated metal plates, cotton-ceramic insulation, and asbestos mats are recommended. Second, gas flame heating by small size units for local heating during minor repairs. This

Tokarev

1983-01-01

209

Engineered Barrier Systems Thermal-Hydraulic-Chemical Column Test Report  

SciTech Connect

The Engineered Barrier System (EBS) Thermal-Hydraulic-Chemical (THC) Column Tests provide data needed for model validation. The EBS Degradation, Flow, and Transport Process Modeling Report (PMR) will be based on supporting models for in-drift THC coupled processes, and the in-drift physical and chemical environment. These models describe the complex chemical interaction of EBS materials, including granular materials, with the thermal and hydrologic conditions that will be present in the repository emplacement drifts. Of particular interest are the coupled processes that result in mineral and salt dissolution/precipitation in the EBS environment. Test data are needed for thermal, hydrologic, and geochemical model validation and to support selection of introduced materials (CRWMS M&O 1999c). These column tests evaluated granular crushed tuff as potential invert ballast or backfill material, under accelerated thermal and hydrologic environments. The objectives of the THC column testing are to: (1) Characterize THC coupled processes that could affect performance of EBS components, particularly the magnitude of permeability reduction (increases or decreases), the nature of minerals produced, and chemical fractionation (i.e., concentrative separation of salts and minerals due to boiling-point elevation). (2) Generate data for validating THC predictive models that will support the EBS Degradation, Flow, and Transport PMR, Rev. 01.

W.E. Lowry

2001-12-13

210

Department of Chemical Engineering Thermal and Flow Engineering Laboratory  

E-print Network

Aug.2013 Department of Chemical Engineering Thermal and Flow Engineering Laboratory Ron Zevenhoven.5 Radiation heat transfer 5.6 Non-stationary ("transient") conductive heat transfer 6. Fluid mechanics 6 Course 424101 Processteknikens grunder ("PTG") Introduction to Process Engineering v. 2013 0 > V (m3/s

Zevenhoven, Ron

211

Department of Chemical Engineering Thermal and Flow Engineering Laboratory  

E-print Network

August 12 Department of Chemical Engineering Thermal and Flow Engineering Laboratory Ron Zevenhoven.5 Radiation heat transfer 5.6 Non-stationary ("transient") conductive heat transfer 6. Fluid mechanics 6 Course 424101 Processteknikens grunder ("PTG") Introduction to Process Engineering v. 2012 0 > V (m3/s

Zevenhoven, Ron

212

Fuels and chemicals from biomass using solar thermal energy  

NASA Technical Reports Server (NTRS)

The significant nearer term opportunities for the application of solar thermal energy to the manufacture of fuels and chemicals from biomass are summarized, with some comments on resource availability, market potential and economics. Consideration is given to the production of furfural from agricultural residues, and the role of furfural and its derivatives as a replacement for petrochemicals in the plastics industry.

Giori, G.; Leitheiser, R.; Wayman, M.

1981-01-01

213

Thermal barrier coatings produced by chemical vapor deposition  

Microsoft Academic Search

Yttria stabilized zirconia (YSZ) can be employed as thermal barrier coatings (TBCs) on Ni-based super alloys in gas turbines and aircraft engines. The YSZ coatings have been fabricated by atmospheric plasma spraying or electron-beam physical vapor deposition. The increase in operation temperature of gas turbines demands another fabrication process to obtain high quality TBCs. Chemical vapor deposition (CVD) can be

J. R. Vargas Garcia; Takashi Goto

2003-01-01

214

A quantum informational approach for dissecting chemical reactions  

E-print Network

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

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

2014-01-01

215

Nature of the chemical reaction for furfural modified asphalt  

SciTech Connect

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.

Memon, G.M.; Chollar, B.H. [FHWA Engineering, Inc., McLean, VA (United States)

1994-12-31

216

Chemical reaction network theory for in-silico biologists Jeremy Gunawardena  

E-print Network

Chemical reaction network theory for in-silico biologists Jeremy Gunawardena Bauer Center@cgr.harvard.edu June 20, 2003 Contents 1 Introduction 1 2 Chemical reaction networks 2 3 Linearity in chemical reaction biological systems evidently exhibit more complex behaviours, such as oscillations, [18], the significance

Gunawardena, Jeremy

217

AURORA: A FORTRAN program for modeling well stirred plasma and thermal reactors with gas and surface reactions  

SciTech Connect

The AURORA Software is a FORTRAN computer program that predicts the steady-state or time-averaged properties of a well mixed or perfectly stirred reactor for plasma or thermal chemistry systems. The software was based on the previously released software, SURFACE PSR which was written for application to thermal CVD reactor systems. AURORA allows modeling of non-thermal, plasma reactors with the determination of ion and electron concentrations and the electron temperature, in addition to the neutral radical species concentrations. Well stirred reactors are characterized by a reactor volume, residence time or mass flow rate, heat loss or gas temperature, surface area, surface temperature, the incoming temperature and mixture composition, as well as the power deposited into the plasma for non-thermal systems. The model described here accounts for finite-rate elementary chemical reactions both in the gas phase and on the surface. The governing equations are a system of nonlinear algebraic relations. The program solves these equations using a hybrid Newton/time-integration method embodied by the software package TWOPNT. The program runs in conjunction with the new CHEMKIN-III and SURFACE CHEMKIN-III packages, which handle the chemical reaction mechanisms for thermal and non-thermal systems. CHEMKIN-III allows for specification of electron-impact reactions, excitation losses, and elastic-collision losses for electrons.

Meeks, E.; Grcar, J.F.; Kee, R.J. [Sandia National Labs., Livermore, CA (United States). Thermal and Plasma Processes Dept.] [Sandia National Labs., Livermore, CA (United States). Thermal and Plasma Processes Dept.; Moffat, H.K. [Sandia National Labs., Albuquerque, NM (United States). Surface Processing Sciences Dept.] [Sandia National Labs., Albuquerque, NM (United States). Surface Processing Sciences Dept.

1996-02-01

218

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

NASA Technical Reports Server (NTRS)

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.

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

1976-01-01

219

Exploring chemical diversity via a modular reaction pairing strategy  

E-print Network

1293 Exploring chemical diversity via a modular reaction pairing strategy Joanna K. Loh1, Sun Young Yoon1, Thiwanka B. Samarakoon1, Alan Rolfe1, Patrick Porubsky2, Benjamin Neuenswander2, Gerald H. Lushington1,2 and Paul R. Hanson*1,2 Full Research... representative compounds. [http://www.beilstein-journals.org/bjoc/content/ supplementary/1860-5397-8-147-S1.pdf] Acknowledgements Financial support of this work was provided by the National Institute of General Medical Sciences and is gratefully acknowl- edged (P...

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

2012-08-15

220

Building robust chemical reaction mechanisms : next generation of automatic model construction software  

E-print Network

Building proper reaction mechanisms is crucial to model the system dynamic properties for many industrial processes with complex chemical reaction phenomena. Because of the complexity of a reaction mechanism, computer-aided ...

Song, Jing, 1972-

2004-01-01

221

Temporal disorder and fluctuation theorem in chemical reactions.  

PubMed

We report the analytical study of a class of chemical reactions described as birth-and-death stochastic processes ruled by a master equation compatible with the mass action law of chemical kinetics. We solve analytically this master equation to find the generating functions of the fluctuating fluxes and of the Lebowitz-Spohn action functional. These generating functions are explicitly shown to obey fluctuation theorems. In the case of fluxes, we derive relations for the nonlinear response coefficients, extending Onsager's reciprocity relations. Moreover, symmetry relations reminiscent of the fluctuation theorem are obtained for the finite-time probability distributions of the fluxes. The temporal disorder of the stochastic process is also characterized and related to the thermodynamic entropy production. PMID:18517359

Andrieux, David; Gaspard, Pierre

2008-03-01

222

Chemical modification of graphene via hyperthermal molecular reaction.  

PubMed

Chemical functionalization of graphene is achieved by hyperthermal reaction with azopyridine molecular ions. The one-step, room temperature process takes place in high vacuum (10(-7) mbar) using an electrospray ion beam deposition (ES-IBD) setup. For ion surface collisions exceeding a threshold kinetic energy of 165 eV, molecular cation beams of 4,4'-azobis(pyridine) covalently attach to chemical vapor deposited (CVD) graphene. A covalent functionalization degree of 3% of the carbon atoms of graphene is reached after 3-5 h of ion exposure of 2 × 10(14) azopyridinium/cm(2) of which 50% bind covalently. This facile approach for the controlled modification of graphene extends the scope of candidate species that would not otherwise react via existing conventional methods. PMID:25185758

Dubey, Girjesh; Urcuyo, Roberto; Abb, Sabine; Rinke, Gordon; Burghard, Marko; Rauschenbach, Stephan; Kern, Klaus

2014-10-01

223

SHEAR LOCALIZATION AND CHEMICAL REACTION IN HIGH-STRAIN, HIGH-STRAIN-RATE DEFORMATION OF  

E-print Network

SHEAR LOCALIZATION AND CHEMICAL REACTION IN HIGH-STRAIN, HIGH-STRAIN-RATE DEFORMATION OF Ti.6±1 mm. Thermodynamic and kinetic calculations yield the reaction rate outside the shear bands a decisive role in accelerating chemical reactions, particularly, converting an exothermic reaction

Meyers, Marc A.

224

Solar-chemical energy conversion via reversible liquid phase Diels-Alder reactions. Final technical report  

SciTech Connect

Thermochemical energy conversion at moderate or low temperature (< about 400/sup 0/C) employing liquid phase components throughout a cycle is suggested as a promising concept for high-efficiency conversion of solar energy to a convenient chemical form. In particular, we propose liquid phase Diels-Alder cycloaddition chemistry as an important class of reversible reactions for such low or moderate temperature thermochemical energy conversion systems. One of the important attributes of thermally driven Diels-Alder reactions is their concerted mechanism, with consequent high yields and efficiencies relative to liquid photochemical systems. Since the systems we propose involve organic species, with thermal stability concerns about 400/sup 0/C, it is important to demonstrate equilibrium shift capability for the highly energetic reactions sought. We have therefore carried out experimental studies with model liquid Diels-Alder systems that clearly demonstrate the degree of control over equilibrium available through substituent entropy effects. These results are of importance as regards subsequent systematic identification of Diels-Alder reactions having ideal thermochemical and physical properties.

Lenz, T.G.; Hegedus, L.S.; Vaughan, J.D.

1983-05-01

225

New approach to thermal analysis kinetics by considering several first order reactions  

Microsoft Academic Search

An approach to thermal decomposition kinetics is proposed in which it is assumed that the thermal decomposition of a given material is produced by a large, but finite, number of first order reactions. Initially a set of first order reaction “covering” the thermal analysis curves is selected. Usually between 500 and 1500 first order curves are generated. Then, the problem

José A. Caballero; Juan A. Conesa

2011-01-01

226

Thermal conversion of biomass to valuable fuels, chemical feedstocks and chemicals  

DOEpatents

A continuous process for the conversion of biomass to form a chemical feedstock is described. The biomass and an exogenous metal oxide, preferably calcium oxide, or metal oxide precursor are continuously fed into a reaction chamber that is operated at a temperature of at least 1400.degree. C. to form reaction products including metal carbide. The metal oxide or metal oxide precursor is capable of forming a hydrolizable metal carbide. The reaction products are quenched to a temperature of 800.degree. C. or less. The resulting metal carbide is separated from the reaction products or, alternatively, when quenched with water, hydolyzed to provide a recoverable hydrocarbon gas feedstock.

Peters, William A. (Lexington, MA); Howard, Jack B. (Winchester, MA); Modestino, Anthony J. (Hanson, MA); Vogel, Fredreric (Villigen PSI, CH); Steffin, Carsten R. (Herne, DE)

2009-02-24

227

Single-collision studies of energy transfer and chemical reaction  

SciTech Connect

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.

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

1993-12-01

228

Single-molecule chemical reactions: Reexamination of the Kramers approach G. Margolin1  

E-print Network

on chemical conformational changes, and simple chemical processes in condensed phase environments, for exampleSingle-molecule chemical reactions: Reexamination of the Kramers approach G. Margolin1 and E; published 2 August 2005 Single-molecule chemical reactions yield insight into fluctuation phenomena

Barkai, Eli

229

Laser enhanced chemical reaction studies. Technical progress report  

SciTech Connect

A powerful infrared diode laser probe was used to determine final states of small (2-5 atom) molecules produced by collisions, photofragmentation, or chemical reactions with spectral resolution 0.0003 cm{sup {minus}1} and time resolution 10{sup {minus}7}s. Besides picturing the vibrational rotational quantum states of product molecules, this also provides a picture of the translational motion of recoiling fragments through the infrared Doppler line width profile. This method was used to probe collisions between cool bath molecules and vibrationally hot molecules, in order to understand the quenching mechanism for unimolecular chemical reactions. Long-range collisions appear to dominate production of bath molecules which become vibrationally excited during this quenching process. Glimpses are being provided of the separate behavior of translational and rotational degrees of freedom of recoiling bath molecules during relaxation of highly vibrationally excited donors. A study was completed of collisions between hot H atoms and CO{sub 2}, by measuring probability for excitation of the antisymmetric vibrational overtone level CO{sub 2}(00{sup 0}2). Comparison with a 00{sup 0}1 fundamental level study suggests that translational and rotational energy distributions in this collision can be described by classical mechanics, but that vibrational excitation probabilities require full quantum treatment. Relaxation of hot pyrazine by CO{sub 2} was studied. Multiphoton ionization studies have been begun.

Flynn, G.

1993-12-31

230

Coupled thermal/chemical/mechanical modeling of energetic materials in ALE3D  

SciTech Connect

We must improve our ability to model the response of energetic ma@ to thmnal stimuli and the processes involved m the energetic response. Traditionally, the analyses of energeuc have mvolved coupled thermal chemical reaction codes. This provides only a reasonable estimate of the dw and location of ensuing rapid reaction. To predict the violence of the reaction, the m cal motion must be included in the wide range of time scales as with the th@ hazard. Ile ALE3D code has been modified to the hazards associated with heaung energetic ma@ in weapons. We have merged the thermal models from TOPAZ3D and the chemistry models &vel@ in Chemical TOPAZ into ALE3D. We have developed and use an impMt time step option to efficiently and accurately compute the hours that the energetic material can take to react. Since on these longer fim scales materials can be expected to have signifimt motion, it is even more important to provide high- ordcr advection for all components, including the chemical species. We will show an example cook-off problem to illustrate these capabilities.

Nichols, A.L.; Couch, R.; Maltby, J.D.; McCallen, R.C.; Otero, I.; Sharp, R.

1996-10-01

231

Materials problems in reversible chemical reaction storage systems for solar energy  

Microsoft Academic Search

Materials problems encountered in the development of thermochemical energy storage systems for solar energy are discussed. Concerns with catalyzed reaction systems include effects of thermal cycling on reactor materials, catalyst availability and lifetime, and undesirable side reactions. Problems have arisen in thermal decomposition systems due to poor or variable kinetics, volume expansion effects, and poor intrinsic heat transfer properties. Reactions

R. W. Mar

1978-01-01

232

Irreversible bimolecular chemical reactions on directed scale-free networks  

NASA Astrophysics Data System (ADS)

Kinetics of irreversible bimolecular chemical reactions A+A?0 and A+B?0 on directed scale-free networks with the in-degree distribution Pin(k)˜k-?in and the out-degree distribution Pout(?)˜?-?out are investigated. Since the correlation between k and ? of each node generally exists in directed networks, we control the correlation with the probability r?[0,1] by two different algorithms for the construction of the directed networks, i.e., the so-called k and ? algorithms. For r=1, the k algorithm gives =, whereas the ? algorithm gives =. For r=0, = for both algorithms. The kinetics of both reactions are analyzed using heterogeneous mean-field (HMF) theory and Monte Carlo simulations. The density of particles (?) algebraically decays in time t as ?(t)˜t-?. The kinetics of both reactions are determined by the same rate equation, d?/dt=a?2+b??-1, apart from coefficients. The exponent ? is determined by the algorithm: ?=?in for the k algorithm (r?0) and ?=?min for the ? algorithm (r>0), where ?min is the smaller exponent between ?in and ?out. For ?>3, one observes the ordinary mean-field kinetics, ?˜1/t (?=1). In contrast, for ?<3, ?(t) anomalously decays with ?=1/(?-2). The HMF predictions are confirmed by the simulations on quenched directed networks.

Kwon, Sungchul; Kim, Yup

2013-10-01

233

Thermal photon v2 with slow quark chemical equilibration  

NASA Astrophysics Data System (ADS)

Elliptic flow of direct photons in high-energy heavy-ion collisions has been a topic of great interest since it was experimentally found to be larger than most hydrodynamic expectations. I discuss the implication of possible late formation of the quark component in a hot QCD medium on the photon elliptic flow, because quarks are the source of thermal photons in the deconfined phase. Hydrodynamic equations are numerically solved with the evolution equations for quark and gluon number densities. The numerical results suggest that thermal photon v2 is visibly enhanced by the slow chemical equilibration of quarks and gluons, reducing the aforementioned problem.

Monnai, Akihiko

2014-08-01

234

Chemical Vapor Deposition of Turbine Thermal Barrier Coatings  

NASA Technical Reports Server (NTRS)

Ceramic thermal barrier coatings extend the operating temperature range of actively cooled gas turbine components, therefore increasing thermal efficiency. Performance and lifetime of existing ceram ic coatings are limited by spallation during heating and cooling cycles. Spallation of the ceramic is a function of its microstructure, which is determined by the deposition method. This research is investigating metalorganic chemical vapor deposition (MOCVD) of yttria stabilized zirconia to improve performance and reduce costs relative to electron beam physical vapor deposition. Coatings are deposited in an induction-heated, low-pressure reactor at 10 microns per hour. The coating's composition, structure, and response to the turbine environment will be characterized.

Haven, Victor E.

1999-01-01

235

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

SciTech Connect

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.

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

2010-06-01

236

Analysis of the chemical composition of organic aerosol at the Mt. Sonnblick observatory (12.95E, 47.05N) using novel thermal-desorption proton transfer reaction mass spectrometer (TD-PTRMS) technique  

NASA Astrophysics Data System (ADS)

A new combination of aerosol collection (humidification aided impaction and controlled thermo-evaporation) and high mass resolution Proton-Transfer-Reaction Mass-Spectrometry (PTR-MS) was used to measure the composition of organic aerosol at the Mt. Sonnblick observatory (~3100 m.a.s.l.) in Austria during a 6 weeks period in summer 2008. Fractional mass differences as low as 0.01 Da were resolved and more than 400 compounds have been tentatively identified by their molecular formula. Besides pure hydrocarbons and oxygenated compounds, we also observed organic compounds containing nitrogen, sulfur, or halogen atoms. The concentration of the detected compounds covered the range of 10s of picogram to 100s of nanogram per cubic meter. During the campaign six distinct periods have been identified which were separated by short periods of low temperature and very low organic aerosol concentrations (most compounds were below the detection limit). The maximum sum concentration of all detected compounds was up to a few microgram per cubic meter which is in agreement with EC/OC analysis of aerosol filter samples and demonstrates that a fraction of >50% of the total organic carbon is detected with our new approach. Different regimes of aerosol processing and ageing are revealed by the measured thermograms. During some periods more low volatility compounds have been detected than during other periods. Entrainment of contaminated air from the boundary layer was regularly observed. Because most of the detected compounds could be identified by their molecular formula the degree of oxygenation can be directly calculated. A higher degree of oxygenation corresponds with lower volatility of the respective aerosol sample, which is in agreement with current understanding of aerosol ageing. It remains to be established how well the calculated oxygenation corresponds with the real degree of oxygenation mostly because a significant fraction of oxygen may be lost when evaporated aerosol compounds are ionized via proton transfer reactions. Several of the observed compounds have the potential to serve as tracers for sources and/or processes of organic aerosol.

Holzinger, Rupert; Kasper-Giebl, Anne; Schauer, Gerhard; Staudinger, Michael; Röckmann, Thomas

2010-05-01

237

Physico-Geometrical Kinetics of Solid-State Reactions in an Undergraduate Thermal Analysis Laboratory  

ERIC Educational Resources Information Center

An undergraduate kinetic experiment of the thermal decomposition of solids by microscopic observation and thermal analysis was developed by investigating a suitable reaction, applicable techniques of thermal analysis and microscopic observation, and a reliable kinetic calculation method. The thermal decomposition of sodium hydrogen carbonate is…

Koga, Nobuyoshi; Goshi, Yuri; Yoshikawa, Masahiro; Tatsuoka, Tomoyuki

2014-01-01

238

Hydrophobic hydration processes thermal and chemical denaturation of proteins.  

PubMed

The hydrophobic hydration processes have been analysed under the light of a mixture model of water that is assumed to be composed by clusters (W(5))(I), clusters (W(4))(II) and free water molecules W(III). The hydrophobic hydration processes can be subdivided into two Classes A and B. In the processes of Class A, the transformation A(-?(w)W(I)??(w)W(II)+?(w)W(III)+cavity) takes place, with expulsion from the bulk of ?(w) water molecules W(III), whereas in the processes of Class B the opposite transformation B(-?(w)W(III)-?(w)W(II)??(w)W(I)-cavity) takes place, with condensation into the bulk of ?(w) water molecules W(III). The thermal equivalent dilution (TED) principle is exploited to determine the number ?(w). The denaturation (unfolding) process belongs to Class A whereas folding (or renaturation) belongs to Class B. The enthalpy ?H(den) and entropy ?S(den) functions can be disaggregated in thermal and motive components, ?H(den)=?H(therm)+?H(mot), and ?S(den)=?S(therm)+?S(mot), respectively. The terms ?H(therm) and ?S(therm) are related to phase change of water molecules W(III), and give no contribution to free energy (?G(therm)=0). The motive functions refer to the process of cavity formation (Class A) or cavity reduction (Class B), respectively and are the only contributors to free energy ?G(mot). The folded native protein is thermodynamically favoured (?G(fold)??G(mot)<0) because of the outstanding contribution of the positive entropy term for cavity reduction, ?S(red)?0. The native protein can be brought to a stable denatured state (?G(den)??G(mot)<0) by coupled reactions. Processes of protonation coupled to denaturation have been identified. In thermal denaturation by calorimetry, however, is the heat gradually supplied to the system that yields a change of phase of water W(III), with creation of cavity and negative entropy production, ?S(for)?0. The negative entropy change reduces and at last neutralises the positive entropy of folding. In molecular terms, this means the gradual disruption by cavity formation of the entropy-driven hydrophobic bonds that had been keeping the chains folded in the native protein. The action of the chemical denaturants is similar to that of heat, by modulating the equilibrium between W(I), W(II), and W(III) toward cavity formation and negative entropy production. The salting-in effect produced by denaturants has been recognised as a hydrophobic hydration process belonging to Class A with cavity formation, whereas the salting-out effect produced by stabilisers belongs to Class B with cavity reduction. Some algorithms of denaturation thermodynamics are presented in the Appendices. PMID:21482019

Fisicaro, E; Compari, C; Braibanti, A

2011-06-01

239

Thermal stresses in chemically hardening elastic media with application to the molding process  

NASA Technical Reports Server (NTRS)

A method has been formulated for the determination of thermal stresses in materials which harden in the presence of an exothermic chemical reaction. Hardening is described by the transformation of the material from an inviscid liquid-like state into an elastic solid, where intermediate states consist of a mixture of the two, in a ratio which is determined by the degree of chemical reaction. The method is illustrated in terms of an infinite slab cast between two rigid mold surfaces. It is found that the stress component normal to the slab surfaces vanishes in the residual state, so that removal of the slab from the mold leaves the remaining residual stress unchanged. On the other hand, the residual stress component parallel to the slab surfaces does not vanish. Its distribution is described as a function of the parameters of the hardening process.

Levitsky, M.; Shaffer, B. W.

1974-01-01

240

Ab initio studies of equations of state and chemical reactions of reactive structural materials  

NASA Astrophysics Data System (ADS)

The motivations for the research issues addressed in this thesis are based on the needs of the aerospace structural analysis and the design community. The specific focus is related to the characterization and shock induced chemical reactions of multi-functional structural-energetic materials that are also known as the reactive structural materials and their reaction capabilities. Usually motivation for selection of aerospace structural materials is to realize required strength characteristics and favorable strength to weight ratios. The term strength implies resistance to loads experienced during the service life of the structure, including resistance to fatigue loads, corrosion and other extreme conditions. Thus, basically the structural materials are single function materials that resist loads experienced during the service life of the structure. However, it is desirable to select materials that are capable of offering more than one basic function of strength. Very often, the second function is the capability to provide functions of sensing and actuation. In this thesis, the second function is different. The second function is the energetic characteristics. Thus, the choice of dual functions of the material are the structural characteristics and energetic characteristics. These materials are also known by other names such as the reactive material structures or dual functional structural energetic materials. Specifically the selected reactive materials include mixtures of selected metals and metal oxides that are also known as thermite mixtures, reacting intermetallic combinations and oxidizing materials. There are several techniques that are available to synthesize these structural energetic materials or reactive material structures and new synthesis techniques constitute an open research area. The focus of this thesis, however, is the characterization of chemical reactions of reactive material structures that involve two or more solids (or condensed matter). The subject of studies of the shock or thermally induced chemical reactions of the two solids comprising these reactive materials, from first principles, is a relatively new field of study. The published literature on ab initio techniques or quantum mechanics based approaches consists of the ab initio or ab initio-molecular dynamics studies in related fields that contain a solid and a gas. One such study in the literature involves a gas and a solid. This is an investigation of the adsorption of gasses such as carbon monoxide (CO) on Tungsten. The motivation for these studies is to synthesize alternate or synthetic fuel technology by Fischer-Tropsch process. In this thesis these studies are first to establish the procedure for solid-solid reaction and then to extend that to consider the effects of mechanical strain and temperature on the binding energy and chemisorptions of CO on tungsten. Then in this thesis, similar studies are also conducted on the effect of mechanical strain and temperature on the binding energies of Titanium and hydrogen. The motivations are again to understand the method and extend the method to such solid-solid reactions. A second motivation is to seek strained conditions that favor hydrogen storage and strain conditions that release hydrogen easily when needed. Following the establishment of ab initio and ab initio studies of chemical reactions between a solid and a gas, the next step of research is to study thermally induced chemical reaction between two solids (Ni+Al). Thus, specific new studies of the thesis are as follows: (1) Ab initio Studies of Binding energies associated with chemisorption of (a) CO on W surfaces (111, and 100) at elevated temperatures and strains and (b) adsorption of hydrogen in titanium base. (2) Equations of state of mixtures of reactive material structures from ab initio methods. (3) Ab initio studies of the reaction initiation, transition states and reaction products of intermetallic mixtures of (Ni+Al) at elevated temperatures and strains. (4) Press-cure synthesis of Nano-nickel and nano-aluminum based reacti

Zaharieva, Roussislava

241

Department of Chemical Engineering Thermal and Flow Engineering Laboratory  

E-print Network

mars 2010 Department of Chemical Engineering Thermal and Flow Engineering Laboratory Ron Zevenhoven Course 424302 Massöverföring & separationsteknik Mass transfer & separation technology version 2010.abo.fi/vt course material: http://users.abo.fi/rzevenho/kursRZ.html #12;F�RORD Fr.o.m. läsåret 2005/2006 föreläses

Zevenhoven, Ron

242

Shock slip-relations for thermal and chemical nonequilibrium flows  

NASA Astrophysics Data System (ADS)

This paper appears to be the first where the multi-temperature shock slip-relations for the thermal and chemical nonequilibrium flows are derived. The derivation is based on analysis of the influences of thermal nonequilibrium and viscous effects on the mass, momentum and emergy flux balance relations at the shock wave. When the relaxation times for all internal energy modes tend to zero, the multi-tmperature shock slip-relations are converted into single-temperature ones for thermal equilibrium flows. The present results can be applied to flow over vehicles of different geometries with or without angles of attack. In addition, the present single-temperature shock slip-relations are compared with those in the literature, and some defects and limitations in the latter are clarified.

Jinrong, Tang

1996-05-01

243

Waste Heat Recovery from Blast Furnace Slag by Chemical Reactions  

NASA Astrophysics Data System (ADS)

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.

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

2012-08-01

244

Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks  

SciTech Connect

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.

Ziaul Huque

2007-08-31

245

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

SciTech Connect

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

Not Available

1989-12-15

246

Direct Monte Carlo simulation of chemical reaction systems: Prediction of ultrafast detonations  

E-print Network

-dimensional flow with the reaction A MB M having variable energy release and rate characteristics. For a slow by the energy released by exothermic chemical reaction within the wave. A com- plete theoretical treatmentDirect Monte Carlo simulation of chemical reaction systems: Prediction of ultrafast detonations

Anderson, James B.

247

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

ERIC Educational Resources Information Center

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)

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

2001-01-01

248

MODEL OF CHEMICAL REACTION EQUILIBRIUM OF SULFURIC ACID SALTS OF TRIOCTYLAMINE  

Microsoft Academic Search

The chemical reaction of trioctylamine (TOA) and sulfuric acid in organic solvent\\/aqueous solution was carried out. TOA salt products of various kinds were obtained based on different conditions of operation and organic solvents. An equilibrium model, based on the chemical reaction of sulfuric acid and trioctylamine, is proposed. The equilibrium constants of various reactions of trioctylamine and sulfuric acid were

MAW-LING WANG; KWAN-HUA HU

1993-01-01

249

Effect of the reversibility of the chemical reaction on triple flames  

Microsoft Academic Search

We examine a new aspect of triple flames, namely the effect of the reversibility of the chemical reaction on flame propagation. The study is carried out in the configuration of the two-dimensional strained mixing layer formed between two opposing streams of fuel and oxidiser. The chemical reaction is modelled as a single reversible reaction following an Arrhenius law in the

Samina Ali; Joel Daou

2007-01-01

250

Experimental Re-Examination of the Law of Conservation of Mass in Chemical Reactions  

Microsoft Academic Search

At the beginning of the century the law of conservation of mass in chemical reactions was checked experimentally by Landolt and various other experimenters. Even though in 8 of the 10 chemical reactions studied by Landolt the validity of conservation of mass was confirmed within the margin of experimental errors, in 2 reactions the pre vs. post comparison of the

KLAUS VOLKAMER; CHRISTOPH STREICHER; KENNETH G. WALTON; JOHN FAGAN

251

A Comprehensive Chemical Kinetic Reaction Mechanism for Oxidation and Pyrolysis of Propane and Propene  

Microsoft Academic Search

Abstract—A detailed chemical kinetic reaction mechanism is developed to describe the oxidation and pyrolysis of propane and propene. The mechanism consists of 163 elementary reactions among 4l chemical species. New rate expressions are developed for a number of reactions of propane, propene, and intermediate hydrocarbon species with radicals including H, 0, and OH. The mechanism is tested by comparisons between

CHARLES K. WESTBROOK; WILLIAM J. PITZ

1984-01-01

252

Process for providing a feed gas for a chemical reaction and for the separation of a gaseous reaction product  

SciTech Connect

A process is claimed for providing a feed gas for a chemical reaction and for separating a gaseous reaction product from the gaseous mixture obtained by the reaction. The feed gas is obtained by the fractionation of a crude gas mixture containing this feed gas proper, as well as a carrier gas or carrier gas mixture, and is reacted only incompletely in the reaction, and the unreacted proportion is recycled into the reaction. The improvement is obtained by conducting the fractionation of the crude gas mixture and the separation of the gaseous reaction product in a single adsorption plant operating by the pressure swing method and containing cyclically reversible adsorbers.

Benkmann, C.; Lassmann, E.

1981-07-28

253

Possible application of solar-thermal energy in the chemical industry  

NASA Astrophysics Data System (ADS)

Eight chemicals are identified that require substantial amounts of nonrecoverable energy for their production. The chemicals are: ethylene, vinyl chloride, styrene, propylene, butadiene, isoprene, hydrogen, and phosphorus. These chemicals are used to produce a wealth of products such as plastics, rubbers and fertilizers. In most cases, these energy intensive materials are at the top of a pyramid of subsequent, exothermic reactions and products that do not require additional thermal energy except for separation processes. Their production at present is centralized and done on a large scale, and most of the organics are produced in refineries where hydrocarbon energy is abundant. This association with refineries means at present that direct substitution of solar energy for hydrocarbon fired heaters may not be convenient, even though scientifically feasible. Other solar energy applications are production of caustic soda from thermodynamic cycles, ethylene from ethanol, and butadiene from ethanol.

Martin, L. R.

1982-06-01

254

Extraction of chemical structures and reactions from the literature  

E-print Network

................................................................................................................................ 193 Appendix C ................................................................................................................................ 194 XIII Glossary AST = Abstract Syntax Tree CAS = Chemical Abstracts Service ChEBI = Chemical...

Lowe, Daniel Mark

2012-10-09

255

Autowave propagation of low-temperature chemical reactions initiated by brittle fracture of the sample. [Gamma radiation  

SciTech Connect

The present work is a study of autowave process in the chain chlorination of butyl chloride (BC) (heat effect Q = 33 +/- 3 kcal/mole) in a glassy bluish-yellow frozen homogeneous solid solution, in which the molar Cl/sub 2/:BC ratio was 1:3. The starting reaction mixture was irradiated at 4.2 and 77/sup 0/K with /sup 60/Co ..gamma..-rays (dose of 2.7 Mrad); this led to the accumulation of free radicals (the radiation yield of their formation is independent of dose up to 15 Mrad; G approx. = 2) and other reactive centers, and caused the samples to darken. The subsequent reaction, during which the active centers were used up, was accompanied by a lightening and a change of sample color; this permitted the propagation of the reaction front to be recorded by motion pictures. Results obtained by studying wave processes in frozen systems also susceptible to brittle fracture provide evidence of the mechanical activation and autoactivation of chemical reactions at low temperatures. These reactions occur during the formation in a matrix of surface dislocations that are created either artificially or by a favorable reciprocal relationship between chemical reaction and mechanical dislocation. But these data are insufficient for an unambiguous choice between the possible mechanisms of crack formation in a traveling front on the basis of wave form: thermal (thermal strain), or nonthermal (change of density and structure as the wave proceeds).

Zanin, A.M.; Kiryukhin, D.P.; Barelko, V.V.; Barkalov, I.M.; Gol'danskii, V.I.

1982-06-01

256

Influence of reaction parameters on synthesis of high-quality single-layer graphene on Cu using chemical vapor deposition  

NASA Astrophysics Data System (ADS)

Large-area monolayer graphene samples grown on polycrystalline copper foil by thermal chemical vapor deposition with differing CH4 flux and growth time are investigated by Raman spectra, scanning electron microscopy, atomic force microscopy, and scanning tunneling microscopy. The defects, number of layers, and quality of graphene are shown to be controllable through tuning the reaction conditions: ideally to 2-3 sccm CH4 for 30 minutes.

Yang, He; Shen, Cheng-Min; Tian, Yuan; Wang, Gao-Qiang; Lin, Shao-Xiong; Zhang, Yi; Gu, Chang-Zhi; Li, Jun-Jie; Gao, Hong-Jun

2014-09-01

257

No electron left behind: a rule-based expert system to predict chemical reactions and reaction mechanisms  

PubMed Central

Predicting the course and major products of arbitrary reactions is a fundamental problem in chemistry, one that chemists must address in a variety of tasks ranging from synthesis design to reaction discovery. Described here is an expert system to predict organic chemical reactions based on a knowledge base of over 1,500 manually composed reaction transformation rules. Novel rule extensions are introduced to enable robust predictions and describe detailed reaction mechanisms at the level of electron flows in elementary reaction steps, ensuring that all reactions are properly balanced and atom-mapped. The core reaction prediction functionalities of this expert system are illustrated with applications including: (1) prediction of detailed reaction mechanisms; (2) computer-based learning in organic chemistry; (3) retro synthetic analysis; and (4) combinatorial library design. Select applications available via http://cdb.ics.uci.edu. PMID:19719121

Chen, Jonathan H.; Baldi, Pierre

2009-01-01

258

Surface Cracking and Interface Reaction Associated Delamination Failure of Thermal and Environmental Barrier Coatings  

NASA Technical Reports Server (NTRS)

In this paper, surface cracking and interface reactions of a BSAS coating and a multi-layer ZTO2-8wt%Y2O3 and mullite/BSAS/Si thermal and environmental barrier coating system on SiC/SiC ceramic matrix composites were characterized after long-term combined laser thermal gradient and furnace cyclic tests in a water vapor containing environment. The surface cracking was analyzed based on the coating thermal gradient sintering behavior and thermal expansion mismatch stress characteristics under the thermal cyclic conditions. The interface reactions, which were largely enhanced by the coating surface cracking in the water vapor environment, were investigated in detail, and the reaction phases were identified for the coating system after the long- term exposure. The accelerated coating delamination failure was attributed to the increased delamination driving force under the thermal gradient cyclic loading and the reduced interface adhesion due to the detrimental interface reactions.

Zhu, Dongming; Choi, Sung R.; Eldridge, Jeffrey I.; Lee, Kang N.; Miller, Robert A.

2003-01-01

259

Enzyme catalysis Enzyme catalysis is the catalysis of chemical reactions by  

E-print Network

Enzyme catalysis Enzyme catalysis is the catalysis of chemical reactions by specialized proteins known as enzymes. Catalysis of biochemical reactions in the cell is vital due to the very low reaction rates of the uncatalysed reactions. The mechanism of enzyme catalysis is similar in principle to other

Cavanagh, John

260

Reduction of Chemical Reactions in Nitrogen and Nitrogen–Hydrogen Plasma Jets Flowing into Atmospheric Air  

Microsoft Academic Search

The large number of possible chemical reactions represents a severe burdenfor modeling of even relatively simple plasma systems. Reduced sets ofchemical reactions have been obtained for numerical simulations of nitrogenand nitrogen-hydrogen plasma jets flowing into an atmospheric airenvironment. The important or active reactions are determined based on asimplified reduction method. A reaction is considered active if it leadsto higher sensitivities

J. H. Park; E. Pfender; C. H. Chang

2000-01-01

261

Progress in an oxygen-carrier reaction kinetics experiment for rotary-bed chemical looping combustion  

E-print Network

The design process for an experimental platform measuring reaction kinetics in a chemical looping combustion (CLC) process is documented and justified. To enable an experiment designed to characterize the reaction kinetics ...

Jester-Weinstein, Jack (Jack L.)

2013-01-01

262

Atomistic-scale simulations of the initial chemical events in the thermal initiation of triacetonetriperoxide.  

PubMed

To study the initial chemical events related to the detonation of triacetonetriperoxide (TATP), we have performed a series of molecular dynamics (MD) simulations. In these simulations we used the ReaxFF reactive force field, which we have extended to reproduce the quantum mechanics (QM)-derived relative energies of the reactants, products, intermediates, and transition states related to the TATP unimolecular decomposition. We find excellent agreement between the QM-predicted reaction products and those observed from 100 independent ReaxFF unimolecular MD cookoff simulations. Furthermore, the primary reaction products and average initiation temperature observed in these 100 independent unimolecular cookoff simulations match closely with those observed from a TATP condensed-phase cookoff simulation, indicating that unimolecular decomposition dominates the thermal initiation of the TATP condensed phase. Our simulations demonstrate that thermal initiation of condensed-phase TATP is entropy-driven (rather than enthalpy-driven), since the initial reaction (which mainly leads to the formation of acetone, O(2), and several unstable C(3)H(6)O(2) isomers) is almost energy-neutral. The O(2) generated in the initiation steps is subsequently utilized in exothermic secondary reactions, leading finally to formation of water and a wide range of small hydrocarbons, acids, aldehydes, ketones, ethers, and alcohols. PMID:16076213

van Duin, Adri C T; Zeiri, Yehuda; Dubnikova, Faina; Kosloff, Ronnie; Goddard, William A

2005-08-10

263

Final Technical Report "Energy Partitioning in Elementary Chemical Reactions"  

SciTech Connect

This is the final technical report of the subject grant. It describes the scientific results obtained during the reporting period. These results are focused on the reactions of atomic oxygen with terminal alkenes. We have studied the production of vinoxy in these reactions. We have characterized the energy disposal in the reactions and have elaborated the reaction mechanism.

Richard Bersohn (deceased); James J. Valentini (reporting investigator)

2005-10-03

264

Thermal, chemical and spectral equilibration in heavy-ion collisions  

E-print Network

We have considered the equilibration in a relativistic heavy ion collision using our transport model. We applied periodic boundary conditions to close the system in a box. We found that the thermal equilibration takes place in the first 20-40 fm/c which time is comparable to the duration of a heavy ion collision. The chemical equilibration is a much slower process and the system does not equilibrate in a heavy ion collision. We have also shown that the mass spectra of broad resonances immediately follows their in-medium spectral functions.

Gábor András Almási; György Wolf

2014-07-08

265

Point defect dynamics and evolution of chemical reactions in alanates by anelastic spectroscopy.  

PubMed

We report the first measurements of elastic modulus and energy dissipation in Ti-doped and undoped sodium aluminum hydride. It is shown that the chemical reactions that occur by varying the sample temperatures or by aging most sensitively affect the elastic constants, such that the modulus variations allow the time and temperature evolution of decomposition to be monitored. After a well-defined thermal treatment at 436 K, a thermally activated relaxation process appears at 70 K in the kilohertz range, denoting the existence of a new species, likely involving hydrogen, having a very high mobility, that is, 10(3) jumps/s at the peak temperature corresponding to a relaxation rate of about 10(11) s(-1) at room temperature. The activation energy of the process is 0.126 eV and the preexponential factor 7 x 10(-14) s, which is typical of point defect relaxation. The peak is very broad with respect to a single Debye process, indicating strong interaction or/and multiple jumping type of the mobile entity. The present data suggest that the models aiming at interpreting the decomposition reactions and kinetics should take into account the indicated point-defect dynamics and stoichiometry defects. PMID:16851077

Palumbo, Oriele; Cantelli, Rosario; Paolone, Annalisa; Jensen, Craig M; Srinivasan, Sesha S

2005-01-27

266

Thermal/chemical degradation of ceramic cross-flow filter materials  

SciTech Connect

This report summarizes the 14-month, Phase 1 effort conducted by Westinghouse on the Thermal/Chemical Degradation of Ceramic Cross-Flow Filter Materials program. In Phase 1 expected filter process conditions were identified for a fixed-bed, fluid-bed, and entrained-bed gasification, direct coal fired turbine, and pressurized fluidized-bed combustion system. Ceramic cross-flow filter materials were also selected, procured, and subjected to chemical and physical characterization. The stability of each of the ceramic cross-flow materials was assessed in terms of potential reactions or phase change as a result of process temperature, and effluent gas compositions containing alkali and fines. In addition chemical and physical characterization was conducted on cross-flow filters that were exposed to the METC fluid-bed gasifier and the New York University pressurized fluidized-bed combustor. Long-term high temperature degradation mechanisms were proposed for each ceramic cross-flow material at process operating conditions. An experimental bench-scale test program is recommended to be conducted in Phase 2, generating data that support the proposed cross-flow filter material thermal/chemical degradation mechanisms. Papers on the individual subtasks have been processed separately for inclusion on the data base.

Alvin, M.A.; Lane, J.E.; Lippert, T.E.

1989-11-01

267

Seismic evidence for thermally-controlled dehydration reaction in subducting oceanic crust  

E-print Network

Seismic evidence for thermally-controlled dehydration reaction in subducting oceanic crust Junichi of the Philippine Sea slab immediately above it. These observations suggest that dehydration reactions accompanied-controlled dehydration reaction in subducting oceanic crust, Geophys. Res. Lett., 36, L03303, doi:10.1029/2008GL036865. 1

Rawlinson, Nick

268

Thermal effects on the diffusive layer convection instability of an exothermic acid-base reaction front  

NASA Astrophysics Data System (ADS)

A buoyancy-driven hydrodynamic instability appearing when an aqueous acid solution of HCl overlies a denser alkaline aqueous solution of NaOH in a vertically oriented Hele-Shaw cell is studied both experimentally and theoretically. The peculiarity of this reactive convection pattern is its asymmetry with regard to the initial contact line between the two solutions as convective plumes develop in the acidic solution only. We investigate here by a linear stability analysis (LSA) of a reaction-diffusion-convection model of a simple A+B?C reaction the relative role of solutal versus thermal effects in the origin and location of this instability. We show that heat effects are much weaker than concentration-related ones such that the heat of reaction only plays a minor role on the dynamics. Computation of density profiles and of the stability analysis eigenfunctions confirm that the convective motions result from a diffusive layer convection mechanism whereby a locally unstable density stratification develops in the upper acidic layer because of the difference in the diffusion coefficients of the chemical species. The growth rate and wavelength of the pattern are determined experimentally as a function of the Brinkman parameter of the problem and compare favorably with the theoretical predictions of both LSA and nonlinear simulations.

Almarcha, C.; Trevelyan, P. M. J.; Grosfils, P.; De Wit, A.

2013-09-01

269

Direct Monte Carlo simulation of chemical reaction systems: Internal energy transfer and an energy-dependent unimolecular reaction  

E-print Network

Direct Monte Carlo simulation of chemical reaction systems: Internal energy transfer and an energy a direct Monte Carlo simulation of an energy-dependent t&molecular reaction system of the type A+ B can be treated by Monte Carlo simulations. One of the most useful methods is Bird's direct simulation

Anderson, James B.

270

Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks  

SciTech Connect

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.

Nelson Butuk

2004-12-01

271

Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks  

SciTech Connect

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.

Nelson Butuk

2005-12-01

272

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

NASA Astrophysics Data System (ADS)

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 hypothetical early Venus with a water-rich atmosphere. Martin et al. [13] investigated the fate of weathered rock when heated (by igneous or impact events). Our understanding of Venus' geological history is stymied by a lack of data - spacecraft observations of and/or at its surface. VMC on VEx may continue to provide new data on surface emissivity, but their interpretation is inherently ambiguous. Laboratory experiments seem the most promising approach - attempting to quantify rates of weathering and thus volcanism [3], and (with luck) framing significant problems that can be directly answered by spacecraft observations. [1] Fegley B.Jr. et al. (1997) In Venus II. U. Ariz. Press. p. 591. [2] Helbert J. et al. (2008) GRL 35, L11201. [3] Smrekar S.E et al. (2010) Science 328, 605-608. [4] Basilevsky A.T. et al. (2012) Icarus 217, 434-450. [5] Marcq E. et al. (2013) Nature Geoscience 6, 25-28. [6] Kane S.R. et al. (2013) Astrophysical J. 770, L20. [7] Schaefer L. & Fegley B.Jr. (2011) Astrophysical J. 729, 6. [8] Treiman A.H. & Bullock M.A. (2012) Icarus 217, 534-541. [9] Aveline D.C. et al. (2011) Lunar Planet. Sci. Conf. 42, Abstr. #2165. [10] Fegley B.Jr. & Prinn R.G. (1989) Nature 337, 55-58. [11] Kohler E. et al. (2012) Lunar Planet. Sci. Conf. 43, Abstr. #2749. [12] Berger G. & Aigouy T. (2011) Lunar Planet. Sci. Conf. 42, Abstr. #1660. [13] Martin A.M. et al. (2012) Earth Planet. Sci. Lett. 331-332, 291-304.

Treiman, A. H.

2013-12-01

273

Examination of lignocellulosic fibers for chemical, thermal, and separations properties: Addressing thermo-chemical stability issues  

NASA Astrophysics Data System (ADS)

Natural fiber-plastic composites incorporate thermoplastic resins with fibrous plant-based materials, sometimes referred to as biomass. Pine wood mill waste has been the traditional source of natural fibrous feedstock. In anticipation of a waste wood shortage other fibrous biomass materials are being investigated as potential supplements or replacements. Perennial grasses, agricultural wastes, and woody biomass are among the potential source materials. As these feedstocks share the basic chemical building blocks; cellulose, hemicellulose, and lignin, they are collectively called lignocellulosics. Initial investigation of a number of lignocellulosic materials, applied to fiber-plastic composite processing and material testing, resulted in varied results, particularly response to processing conditions. Less thermally stable lignocellulosic filler materials were physically changed in observable ways: darkened color and odor. The effect of biomass materials' chemical composition on thermal stability was investigated an experiment involving determination of the chemical composition of seven lignocellulosics: corn hull, corn stover, fescue, pine, soy hull, soy stover, and switchgrass. These materials were also evaluated for thermal stability by thermogravimetric analysis. The results of these determinations indicated that both chemical composition and pretreatment of lignocellulosic materials can have an effect on their thermal stability. A second study was performed to investigate what effect different pretreatment systems have on hybrid poplar, pine, and switchgrass. These materials were treated with hot water, ethanol, and a 2:1 benzene/ethanol mixture for extraction times of: 1, 3, 6, 12, and 24 hours. This factorial experiment demonstrated that both extraction time and medium have an effect on the weight percent of extractives removed from all three material types. The extracted materials generated in the above study were then subjected to an evaluation of thermal stability by thermogravimetric analysis in a subsequent experiment. Overlay plots, combining individual weight loss curves, demonstrate that the experimental factors, solvent system and extraction time, produce effects on the thermal stability of the treated biomass samples. These data also indicated that the individual lignocellulosic materials had unique responses to the type of solvent used for pretreatment. Increasing extraction time had either no correlation with or a positive effect on thermal stability of the biomass samples.

Johnson, Carter David

274

Chemical TOPAZ: Modifications to the heat transfer code TOPAZ: The addition of chemical reaction kinetics and chemical mixtures  

SciTech Connect

This is a report describing the modifications which have been made to the heat flow code TOPAZ to allow the inclusion of thermally controlled chemical kinetics. This report is broken into parts. The first part is an introduction to the general assumptions and theoretical underpinning that were used to develop the model. The second section describes the changes that have been implemented into the code. The third section is the users manual for the input for the code. The fourth section is a compilation of hints, common errors, and things to be aware of while you are getting started. The fifth section gives a sample problem using the new code. This manual addenda is written with the presumption that most readers are not fluent with chemical concepts. Therefore, we shall in this section endeavor to describe the requirements that must be met before chemistry can occur and how we have modeled the chemistry in the code.

Nichols, A.L. III.

1990-06-07

275

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

NASA Astrophysics Data System (ADS)

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

Schredder, J. M.; Fujita, T.

1984-10-01

276

Chemical Model Systems for Cellular Nitros(yl)ation Reactions  

PubMed Central

S-nitros(yl)ation belongs to the redox-based posttranslational modifications of proteins but the underlying chemistry is controversial. In contrast to current concepts involving the autoxidation of nitric oxide (•NO, nitrogen monoxide), we and others have proposed the formation of peroxynitrite (oxoperoxonitrate(1-)) as an essential intermediate. This requires low cellular fluxes of •NO and superoxide (•O2?), for which model systems have been introduced. We here propose two new systems for nitros(yl)ation that avoid the shortcomings of previous models. Based on the thermal decomposition of 3-morpholinosydnonimine, equal fluxes of •NO and •O2? were generated and modulated by the addition of •NO donors or Cu,Zn-superoxide dismutase. As reactants for S-nitros(yl)ation, NADP+-dependent isocitrate dehydrogenase and glutathione were employed, for which optimal S-nitros(yl)ation was observed at nanomolar fluxes of •NO and •O2? at a ratio of about 3:1. The previously used reactants phenol and diaminonaphthalene, (C- and N-nitrosation) demonstrated potential participation of multiple pathways for nitros(yl)ation. According to our data, neither peroxynitrite nor autoxidation of •NO was as efficient as the 3•NO/1•O2? system in mediating S-nitros(yl)ation. In theory this could lead to an elusive nitrosonium (nitrosyl cation)-like species in the first step and to N2O3 in the subsequent reaction. Which of these two species or whether both together will participate in biological S-nitros(yl)ation remains to be elucidated. Finally, we developed several hypothetical scenarios to which the described U flux model could apply, providing conditions that allow either direct electrophilic substitution at a thiolate or S-nitros(yl)ation via transnitrosation from S-nitrosoglutathione. PMID:19477267

Daiber, Andreas; Schildknecht, Stefan; Muller, Johanna; Bachschmid, Markus M.; Ullrich, Volker

2014-01-01

277

Chemical characterization of asphalt using thermal chromatography with mass spectrometry  

SciTech Connect

The authors embarked on a project to assess whether the similarities and differences in chemical composition among asphalt samples can be delineated by thermal chromatography (TC), a unique method for disassembling complex materials for analysis using precise temperature programming in a controlled and well characterized environment. combined with flame ionization detection (FID), TC provides thermal profiles of materials under study: quantity of evolved species as a function of temperature. combined with gas chromatographic (GC) separation and mass spectral (MS) detection, TC/MS allows structures to be assigned to the various components of the asphalt matrix. Their feasibility study focused on examining neat samples obtained from the SHRP Materials Reference Library in Austin, TX, and oxidized materials prepared by other SHRP contractors. They compared thermal profiles obtained from TC/FID analyses of the samples as to temperature range(s) over which species were evolved and relative amounts of materials evolved as a function of temperature. The authors also discuss the nature of these differences as they are revealed in the chromatograms and mass spectra obtained in the TC/MS studies of these same materials.

Gale, P.J.; Bentz, B.L. (David Sarnoff Research Center, Princeton, NJ (United States))

1990-07-01

278

Effect of chemical vapor infiltration on erosion and thermal properties of porous carbon\\/carbon composite thermal insulation  

Microsoft Academic Search

A highly porous carbon\\/carbon composite, known as carbon bonded carbon fiber (CBCF) and used as thermal insulation, was densified by chemical vapor infiltration (CVI). The erosion resistance, thermal conductivity and thermal expansion coefficient were measured with interest to utilization of the CVI densified composite as erosion protection in furnaces that employ inert gas quenching. It was found that the erosion

R. I Baxter; R. D Rawlings; N Iwashita; Y Sawada

2000-01-01

279

Heat-Of-Reaction Chemical Heat Pumps--Possible Configurations  

E-print Network

, forming a new solid. This reaction is exothermic and conducted at required process temperature, with heat being rejected to 'the load. Regeneration is accomplished by operating at reduced system pressure. The reaction with A and C is reversed, with C...-vapor reversible reaction heat pump and heat engine Heat pumps involving reactions of metal hydrides and hydrogen are of this class and have been the subject of considerable investigation for cryogenic refrigeration (15) and heat pumping. Argonne National...

Kirol, L. D.

280

Impact of organic-mineral matter interactions on thermal reaction pathways for coal model compounds  

SciTech Connect

Coal is a complex, heterogeneous solid that includes interdispersed mineral matter. However, knowledge of organic-mineral matter interactions is embryonic, and the impact of these interactions on coal pyrolysis and liquefaction is incomplete. Clay minerals, for example, are known to be effective catalysts for organic reactions. Furthermore, clays such as montmorillonite have been proposed to be key catalysts in the thermal alteration of lignin into vitrinite during the coalification process. Recent studies by Hatcher and coworkers on the evolution of coalified woods using microscopy and NMR have led them to propose selective, acid-catalyzed, solid state reaction chemistry to account for retained structural integrity in the wood. However, the chemical feasibility of such reactions in relevant solids is difficult to demonstrate. The authors have begun a model compound study to gain a better molecular level understanding of the effects in the solid state of organic-mineral matter interactions relevant to both coal formation and processing. To satisfy the need for model compounds that remain nonvolatile solids at temperatures ranging to 450 C, model compounds are employed that are chemically bound to the surface of a fumed silica (Si-O-C{sub aryl}linkage). The organic structures currently under investigation are phenethyl phenyl ether (C{sub 6}H{sub 5}CH{sub 2}CH{sub 2}OC{sub 6}H{sub 5}) derivatives, which serve as models for {beta}-alkyl aryl ether units that are present in lignin and lignitic coals. The solid-state chemistry of these materials at 200--450 C in the presence of interdispersed acid catalysts such as small particle size silica-aluminas and montmorillonite clay will be reported. Initial focus will be on defining the potential impact of these interactions on coal pyrolysis and liquefaction.

Buchanan, A.C. III; Britt, P.F.; Struss, J.A. [Oak Ridge National Lab., TN (United States). Chemical and Analytical Sciences Div.

1995-07-01

281

Computational thermal, chemical, fluid, and solid mechanics for geosystems management.  

SciTech Connect

This document summarizes research performed under the SNL LDRD entitled - Computational Mechanics for Geosystems Management to Support the Energy and Natural Resources Mission. The main accomplishment was development of a foundational SNL capability for computational thermal, chemical, fluid, and solid mechanics analysis of geosystems. The code was developed within the SNL Sierra software system. This report summarizes the capabilities of the simulation code and the supporting research and development conducted under this LDRD. The main goal of this project was the development of a foundational capability for coupled thermal, hydrological, mechanical, chemical (THMC) simulation of heterogeneous geosystems utilizing massively parallel processing. To solve these complex issues, this project integrated research in numerical mathematics and algorithms for chemically reactive multiphase systems with computer science research in adaptive coupled solution control and framework architecture. This report summarizes and demonstrates the capabilities that were developed together with the supporting research underlying the models. Key accomplishments are: (1) General capability for modeling nonisothermal, multiphase, multicomponent flow in heterogeneous porous geologic materials; (2) General capability to model multiphase reactive transport of species in heterogeneous porous media; (3) Constitutive models for describing real, general geomaterials under multiphase conditions utilizing laboratory data; (4) General capability to couple nonisothermal reactive flow with geomechanics (THMC); (5) Phase behavior thermodynamics for the CO2-H2O-NaCl system. General implementation enables modeling of other fluid mixtures. Adaptive look-up tables enable thermodynamic capability to other simulators; (6) Capability for statistical modeling of heterogeneity in geologic materials; and (7) Simulator utilizes unstructured grids on parallel processing computers.

Davison, Scott; Alger, Nicholas; Turner, Daniel Zack; Subia, Samuel Ramirez; Carnes, Brian; Martinez, Mario J.; Notz, Patrick K.; Klise, Katherine A.; Stone, Charles Michael; Field, Richard V., Jr.; Newell, Pania; Jove-Colon, Carlos F.; Red-Horse, John Robert; Bishop, Joseph E.; Dewers, Thomas A.; Hopkins, Polly L.; Mesh, Mikhail; Bean, James E.; Moffat, Harry K.; Yoon, Hongkyu

2011-09-01

282

Verification of chemical reaction rate models in turbulent reacting flows at Schmidt number considerably exceeding 1  

Microsoft Academic Search

Relations widely used in numerical modeling describing the average rate of a chemical reaction have been analyzed. The spontaneous\\u000a distributions of the mixture fraction and reaction products measured simultaneously in different cross-sections of the jet\\u000a mixer under turbulent mixing of chemically reacting incompressible liquid media served as the basis for verification.

A. D. Chornyi; V. L. Zhdanov

2010-01-01

283

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

ERIC Educational Resources Information Center

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…

Goodney, David E.

2006-01-01

284

Design criteria for extraction with chemical reaction and liquid membrane permeation  

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

285

Effect of gravity field on the nonequilibrium\\/nonlinear chemical oscillation reactions  

Microsoft Academic Search

Biological systems have evolved for a long time under the normal gravity. The Belousov-Zhabotinsky (BZ) reaction is a nonlinear chemical system far from the equilibrium that may be considered as a simplified chemical model of the biological systems so as to study the effect of gravity. The reaction solution is comprised of bromate in sulfuric acid as an oxidizing agent,

S. Fujieda; Y. Mori; A. Nakazawa; Y. Mogami

2001-01-01

286

Temperature-compensated chemical reactions Kanaka Rajan and L. F. Abbott  

E-print Network

oscillations in mRNA and protein levels, the question of how to construct a network of chemical reactionsTemperature-compensated chemical reactions Kanaka Rajan and L. F. Abbott Center for Neurobiology Received 21 September 2006; published 23 February 2007 Circadian rhythms are daily oscillations

Columbia University

287

STRAIN-INDUCED STRUCTURAL CHANGES AND CHEMICAL REACTIONSII. MODELLING OF REACTIONS  

E-print Network

STRAIN-INDUCED STRUCTURAL CHANGES AND CHEMICAL REACTIONSÐII. MODELLING OF REACTIONS IN SHEAR BAND V 1997; accepted in revised form 26 April 1998) AbstractÐThe problem on strain-induced chemical reaction (SICR) and structural changes (SCs) in a thin layer inside the shear band is formulated and solved

Meyers, Marc A.

288

Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels  

E-print Network

Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels C.K. Westbrooka chemical kinetic reaction mechanism is developed for the five major components of soy biodiesel and rapeseed biodiesel fuels. These components, methyl stearate, methyl oleate, methyl linoleate, methyl

Paris-Sud XI, Université de

289

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 ...

290

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

E-print Network

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

Tomza, Micha?; Moszynski, Robert; Krems, Roman V

2013-01-01

291

Chemical Diffusivity and Wave Propagation in Surface Reactions: Analysis of the Bistable Monomer-Dimer Reaction Model  

NASA Astrophysics Data System (ADS)

Spatial pattern formation and wave propagation in surface reactions is controlled in part by chemical diffusion of the adsorbed reactant species. While in the simplest treatment, the chemical diffusion coefficients are taken as constant, the diffusion of one species is in fact influenced by the presence of coadsorbed species(M. Tammaro, M. Sabella, and J.W. Evans, J. Chem. Phys. 103 (1995) 10277; M. Tammaro and J.W. Evans, J. Chem. Phys. (submitted)). We thus develop an appropriate theory for chemical diffusion in mixed adlayers of mobile species. This theory is used to analyze the propagation of chemical waves associated with the displacement of the CO-poisoned state by a reactive steady state in the monomer-dimer model for CO-oxidation. We find good agreement between "exact" simulation results and those obtained from reaction-diffusion equations incorporating an appropriate description of the non-linear chemical diffusion.

Tammaro, M.; Evans, J. W.

1997-03-01

292

Phase and chemical equilibria in the transesterification reaction of vegetable oils with supercritical lower alcohols  

NASA Astrophysics Data System (ADS)

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.

Anikeev, V. I.; Stepanov, D. A.; Ermakova, A.

2011-08-01

293

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...

294

On the Presence of Limit-Cycles in a Model Exothermic Chemical Reaction: Sal'nikov's Oscillator with Two Temperature-Dependent Reaction Rates  

Microsoft Academic Search

This paper investigates a model chemical reaction in which a single substance undergoes a two-stage process of decay, first producing an intermediate species and finally giving a product chemical. Each of the two stages involves only simple first-order reaction kinetics, but the governing rate parameter for each of the two reactions is temperature dependent. The reaction vessel is assumed to

Lawrence K. Forbes; Mary R. Myerscough; Brian F. Gray

1991-01-01

295

Chemical reaction model for oil and gas generation from type 1 and type 2 kerogen  

SciTech Connect

A global model for the generation of oil and gas from petroleum source rocks is presented. The model consists of 13 chemical species and 10 reactions, including an alternate-pathway mechanism for kerogen pyrolysis. Reaction rate parameters and stoichiometry coefficients determined from a variety of pyrolysis data are given for both type I and type II kerogen. Use of the chemical reaction model is illustrated for typical geologic conditions.

Braun, R.L.; Burnham, A.K.

1993-06-01

296

JASPERSE CHEM 350 TEST 2 VERSION 3 Ch. 4 The Study of Chemical Reactions  

E-print Network

the following alkyl halides in order of decreasing reactivity toward SN1/E1 reactions (from most reactive 1 toward SN2 reactions (from most reactive 1 to least reactive 4). Br Br Br I 4. Rank the bond strengthJASPERSE CHEM 350 TEST 2 VERSION 3 Ch. 4 The Study of Chemical Reactions Ch. 5 Sterochemistry Ch. 6

Jasperse, Craig P.

297

JASPERSE CHEM 341 TEST 2 VERSION 3 Ch. 5 The Study of Chemical Reactions  

E-print Network

the following alkyl halides in order of decreasing reactivity toward SN1/E1 reactions (from most reactive 1 toward SN2 reactions (from most reactive 1 to least reactive 4). Br Br Br I 4. Rank the bond strength1 JASPERSE CHEM 341 TEST 2 VERSION 3 Ch. 5 The Study of Chemical Reactions Ch. 9 Stereochemistry Ch

Jasperse, Craig P.

298

A comparison of reversible chemical reactions for solar thermochemical power generation  

E-print Network

453 A comparison of reversible chemical reactions for solar thermochemical power generation O. M storage of the reaction products. A number of reactions have been proposed for solar thermochemical power to be a good choice for first generation solar thermochemical power generation. Revue Phys. Appl. 15 (1980) 453

Boyer, Edmond

299

An Integrated Model for the Differentiation of Chemical-Induced Allergic and Irritant Skin Reactions  

Microsoft Academic Search

Contact and photocontact allergic as well as irritant and photoirritant skin reactions represent a major problem in clinical dermatology and during the development of new pharmaceuticals. Furthermore, there is a lack ofin vitroandin vivoassays that provide a clear differentiation between allergic and irritant skin reactions. Here, we describe an integrated model to differentiate between chemical-induced allergic and irritant skin reactions

Bernhard Homey; Christiane von Schilling; Jörg Blümel; Hans-Christian Schuppe; Thomas Ruzicka; Hans Jürgen Ahr; Percy Lehmann; Hans-Werner Vohr

1998-01-01

300

Real-time quantitative investigation of photochemical reaction using thermal lens measurements: Theory and experiment  

SciTech Connect

In this work the time-resolved mode-mismatched thermal lens method is applied to investigate Cr(VI) species in water. An abnormal behavior of the thermal lens transient induced by a photochemical reaction was observed during optical excitation. With the purpose of better understanding this phenomenon, the existing theoretical model of thermal lens effect was generalized in order to take the time dependence of the absorbance of the sample into account due to the changes in concentration resulting from photochemical reaction and diffusion of absorbing species. Consequently, the photochemical reaction rate can be quantitatively evaluated by this technique with the generalized model. The adopted procedure demonstrates the usefulness of the time-resolved thermal lens method for the study of photochemical reactions under the presence of absorbing species diffusion with the advantage of monitoring the processes in a quantitative way and with a temporal resolution of a few milliseconds.

Pedreira, P. R. B.; Hirsch, L. R.; Pereira, J. R. D.; Medina, A. N.; Bento, A. C.; Baesso, M. L.; Rollemberg, Maria C.; Franko, Mladen; Shen Jun [Departamento de Fisica, Universidade Estadual de Maringa, Avenida Colombo 5790, 87020-900, Maringa, Parana (Brazil); Departamento de Quimica, Universidade Estadual de Maringa, 87020-900, Maringa, Parana (Brazil); Laboratory for Environmental Research, University of Nova Gorica, Vipavska 13, SI-5000 Nova Gorica (Slovenia); National Research Council of Canada, Institute for Fuel Cell Innovation, 3250 East Mall, Vancouver, British Columbia V6T 1W5 (Canada)

2006-08-15

301

An investigation of thermal spray structural reaction injection molded composites  

E-print Network

40 40 11 Unldireorional Roving Thermal Spray Core Figure 2. 5 - Sandwich Structure of TS/UNI Architecture removed and checked for correct glass weight and distribution. This procedure is followed for both the flat test plaques and the beams.... Preform fabrication for the 3-layer, sandwich architectures P51-P53 ~uires more effort since manual assembly of the preform is required. Figure 2. 5 shows the desired sandwich structure with a Thermal Spray core and unidirectional roving outer layers. A...

Hill, Bryan William

2012-06-07

302

Thermally safe operation of liquid–liquid semibatch reactors Part II: Single diffusion controlled reactions with arbitrary reaction order  

Microsoft Academic Search

The thermally safe operation of an indirectly cooled semibatch reactor in which an exothermic liquid–liquid reaction occurs corresponds to conditions of potentially very high macrokinetic conversion rates compared with the supply rate of the coreactant, which accumulation in the system remains consequently low. This leads to the definition of a target temperature that can be compared with the real temperature–time

Francesco Maestri; Renato Rota

2005-01-01

303

Thermally Stable Nanocatalyst for High Temperature Reactions: Pt-Mesoporous Silica Core-Shell Nanoparticles  

SciTech Connect

Recent advances in colloidal synthesis enabled the precise control of size, shape and composition of catalytic metal nanoparticles, allowing their use as model catalysts for systematic investigations of the atomic-scale properties affecting catalytic activity and selectivity. The organic capping agents stabilizing colloidal nanoparticles, however, often limit their application in high-temperature catalytic reactions. Here we report the design of a high-temperature stable model catalytic system that consists of Pt metal core coated with a mesoporous silica shell (Pt{at}mSiO{sub 2}). While inorganic silica shells encaged the Pt cores up to 750 C in air, the mesopores directly accessible to Pt cores made the Pt{at}mSiO{sub 2} nanoparticles as catalytically active as bare Pt metal for ethylene hydrogenation and CO oxidation. The high thermal stability of Pt{at}mSiO{sub 2} nanoparticles permitted high-temperature CO oxidation studies, including ignition behavior, which was not possible for bare Pt nanoparticles because of their deformation or aggregation. The results suggest that the Pt{at}mSiO{sub 2} nanoparticles are excellent nanocatalytic systems for high-temperature catalytic reactions or surface chemical processes, and the design concept employed in the Pt{at}mSiO{sub 2} core-shell catalyst can be extended to other metal-metal oxide compositions.

Joo, Sang Hoon; Park, J.Y.; Tsung, C.-K.; Yamada, Y.; Yang, P.; Somorjai, G.A.

2008-10-25

304

TEOS-based SiO{sub 2} chemical vapor deposition: Reaction kinetics and related surface chemistry  

SciTech Connect

We have developed a comprehensive understanding of thermal TEOS (tetracthylorthosificate, Si(OCH{sub 2}CH{sub 3}){sub 4}) surface chemistry at CVD (chemical vapor deposition) temperatures and pressures. This was accomplished by examining how TEOS reaction rate are influenced by factors critical to the heterogeneous reaction. This includes determining the TEOS pressure dependence, testing if reaction by-products inhibit TEOS decomposition, identifying reaction sites on the surface, and establishing the reaction sites coverage dependencies. We evaluated the pressure dependencies and by-product inhibition with GCMS. The experiments in a cold-wall research reactor revealed that the TEOS surface reaction at 1000K (1) was first-order with respect to TEOS pressure (0.10 to 1.50Torr) and (2) was not inhibited by surface reaction by-products (ethylene, ethanol, and water). Reactivities of surface sites and their coverage dependencies were compared with FTIR. Our experiments demonstrated that two-membered siloxane ((Si-O){sub 2}) rings on the SiO{sub 2} surface were consumed almost instantaneously when exposed to TEOS. Our FTIR experiments also revealed that TEOS decomposition was zero-order with respect to coverages of hydroxyl groups and (by indirect evidence) three-membered siloxane ((Si-O){sub 3}) rings. This type of site-independent reactivity is consistent with TEOS reacting with hydroxyl groups and (Si-O){sub 3} rings via a common rate-determining step at 1000K. With respect to deposition uniformity, our results predict that deposition rates will be insensitive to the relative coverages of (Si-O){sub 3} rings and hydroxyls on SiO{sub 2} as well as the re-adsorbed by-products of the surface reaction. Therefore, it is likely that nonuniform SiO{sub 2} depositions from TEOS reactions are due to depletion of TEOS in the gas-phase and/or thermal gradients.

Bartram, M.E.; Moffat, H.K.

1995-11-01

305

Thermal reactions of guaiacol and syringol as lignin model aromatic nuclei  

Microsoft Academic Search

Thermal reactions of guaiacol (2-methoxyphenol) and syringol (2,6-dimethoxyphenol) were compared in a closed ampoule reactor (N2\\/400–600°C\\/40–600s) to obtain information on the thermal reactivities of lignin aromatic nuclei, guaiacyl and syringyl types. For both compounds, the O–CH3 bond homolysis, which was observed at >400°C, initiated their decomposition. This homolysis was followed by several temperature-dependent reactions; radical-induced rearrangement to convert the aromatic

Mohd Asmadi; Haruo Kawamoto; Shiro Saka

2011-01-01

306

Thermal/chemical degradation of inorganic membrane materials  

SciTech Connect

The overall objective of this program is to evaluate the long-term thermal and chemical degradation of inorganic membranes that are being developed to separate gaseous products produced by the gasification or combustion of coal in fixed-, fluidized-, and entrained-bed gasifiers, direct coal-fired turbines, and pressurized-fluidized-bed combustors. Specific objectives of this program are to (1) quantify the extent of the degradation process for the three most detrimental mechanisms by performing laboratory-scale experiments, and (2) develop a predictive model for membrane degradation under operating conditions. At present, no inorganic membranes are commercially available for application in the high-temperature, high-pressure (HTHP) gas environments encountered in integrated gasification combined cycle (IGCC), pressurized fluidized bed combustion (PFBC), and direct coal fired turbine (DCFT) applications. Most of the inorganic membrane development efforts have focused on hydrogen separation membranes which may be used in an IGCC system for maximizing hydrogen production from coal gas or to remove H{sub 2}S and NH{sub 3} contaminants via thermal or catalytic decomposition of these contaminants. The candidate inorganic membranes may be grouped as follows: dense metallic membranes; silica based membranes; alumina based membranes; and carbon based membranes. Results are reported for membrane characterization done so far.

Krishnan, G.N.; Sanjurjo, A.; Damle, A.S.; Wood, B.J.; Lau, K.H.

1994-10-01

307

Chemical characteristics of the major thermal springs of Montana  

USGS Publications Warehouse

Twenty-one thermal springs in western Montana were sampled for chemical, isotope, and gas compositions. Most of the springs issue dilute to slightly saline sodium-bicarbonate waters of neutral to slightly alkaline pH. A few of the springs issue sodium-mixed anion waters of near neutral pH. Fluoride concentrations are high in most of the thermal waters, up to 18 milligramsper litre, while F/Cl ratios range from 3/1 in the dilute waters to 1/10 in the slightly saline waters. Most of the springs are theoretically in thermodynamic equilibrium with respect to calcite and fluorite. Nitrogen is the major gas escaping from most of the hot springs; however, Hunters Hot Springs issue principally methane. The deuterium content of the hot spring waters is typical of meteoric water in western Montana. Geothermal calculations based on silica concentrations and Na-K-Ca ratios indicate that most of the springs are associated with low temperature aquifers (less than 100?C). Chalcedony may be controlling the silica concentrations in these low temperature aquifers even in 'granitic' terranes.

Mariner, R.H.; Presser, T.S.; Evans, W.C.

1976-01-01

308

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

ERIC Educational Resources Information Center

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…

Bell, John T.; Fogler, H. Scott

1996-01-01

309

Studies on the thermal reactions of aluminium oxides and hydroxides  

Microsoft Academic Search

The gibbsite ??-alumina decomposition (in air) and the?-alumina ? boehmite transformation (under hydrothermal conditions) were investigated isothermally. Reaction products were characterized by TG and X-ray diffraction.

C. Novák; G. Pokol; K. Tomor; J. K?míves; S. Gál

1988-01-01

310

Transient Magnetohydrodynamic Free Convective Heat and Mass Transfer Flow with Thermophoresis past a Radiate Inclined Permeable Plate in the Presence of Variable Chemical Reaction and Temperature Dependent Viscosity  

Microsoft Academic Search

In the present study, an analysis is carried out to investiga te the effects of variable chemical reaction, thermophoresis, temperature-dependent viscosity and thermal radiation on an unsteady MHD free convective heat and mass transfer flow of a viscous, incompressible, electrically conducting fluid past an impu lsively started infinite inclined porous plate. The governing nonlinear partial differentia l equations are transformed

M. S. Alam; M. M. Rahman; M. A. Sattar

311

A lattice gas automata model for heterogeneous chemical reactions at mineral surfaces and in pore networks  

SciTech Connect

A lattice gas automata (LGA) model is described, which couples solute transport with chemical reactions at mineral surfaces and in pore networks. Chemical reactions and transport are integrated into a FHP-I LGA code as a module so that the approach is readily transportable to other codes. Diffusion in a box calculations are compared to finite element Fickian diffusion results and provide an approach to quantifying space-time ratios of the models. Chemical reactions at solid surfaces, including precipitation/dissolution, sorption, and catalytic reaction, can be examined with the model because solute diffusion and mineral surface processes are all treated explicitly. The simplicity and flexibility of the LGA approach provides the ability to study the interrelationship between fluid flow and chemical reactions in porous materials, at a level of complexity that has not previously been computationally possible. 20 refs., 8 figs.

Wells, J.T. (Washington Univ., Seattle, WA (USA). Dept. of Geological Sciences); Janecky, D.R.; Travis, B.J. (Los Alamos National Lab., NM (USA))

1990-01-15

312

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

SciTech Connect

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.

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

2009-08-01

313

Control of Mass Transport and Chemical Reaction Kinetics in Ultrasmall Volumes  

NASA Astrophysics Data System (ADS)

This talk will describe means for triggering chemical reactions for studying reaction kinetics under extreme confinement with sub-millisecond temporal resolution, including on-demand generation and fusion of femtoliter (10-15 L) volume water-in-oil droplets, and triggering reactions in femtoliter chambers microfabricated in poly(dimethylsiloxane) (PDMS). We demonstrated a reversible chemical toggle switch, which lays the groundwork for exploring more complex chemical and biochemical reaction sequences triggered and monitored in real time in discrete ultrasmall reactors, such as sequential and coupled enzymatic reactions. We are also developing methods to vary confinement and macromolecular crowding in ultrasmall, water-in-oil droplets and chambers micromolded in PDMS as biomimetic reaction vessels containing minimal synthetic gene circuits, in order to better understand how confinement, reduced dimensionality and macromolecular crowding affect molecular mechanisms involved in the operation and regulation of genetic circuits in living cells.

Collier, Charles

2012-02-01

314

Understanding chemical binding using the Berlin function and the reaction force  

NASA Astrophysics Data System (ADS)

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.

Chakraborty, Debajit; Cárdenas, Carlos; Echegaray, Eleonora; Toro-Labbe, Alejandro; Ayers, Paul W.

2012-06-01

315

A simple model for two competing chemical reactions  

NASA Astrophysics Data System (ADS)

We study a competitive reaction model in one dimension with different reactivity weights for the reactions. We consider the A + A ? A2 auto-catalytic reaction model and the A + B ? AB monomer-monomer reaction model, where A and B are monomers arriving at the surface with probabilities yA and yB, respectively. The model is studied in the site and pair mean field approximations, and by Monte Carlo simulations. The phase diagram of the model displays a line of continuous phase transitions between active and poisoned states, and we determined the critical exponents, ? and ?? of the model. Our results indicate that the critical behavior of the model does not change with the reactivity rate, and it belongs to the directed percolation universality class.

da Costa, E. C.; Figueiredo, W.

2005-12-01

316

Study of chemical reactions under the influence of ultrasound  

SciTech Connect

At Los Alamos the author is interested in sonochemistry because there is potential for accelerating reactions involving the synthesis of certain nitro compounds and for reducing the possibility of decomposition under milder reaction conditions. The author has initiated the study of the nitration of 2,4-dihydro-3H-1,2,4-triazol-3-one with concentrated nitric acid under sonication. The preparation of 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine, and oxidation of 3,6-diamino-1,2,4,5-tetrazine were also studied. Sonication reaction conditions and results of these reactions under ultrasound are discussed in detail.

Lee, Kien-Yin

1993-07-01

317

Study of chemical reactions under the influence of ultrasound  

SciTech Connect

At Los Alamos the author is interested in sonochemistry because there is potential for accelerating reactions involving the synthesis of certain nitro compounds and for reducing the possibility of decomposition under milder reaction conditions. The author has initiated the study of the nitration of 2,4-dihydro-3H-1,2,4-triazol-3-one with concentrated nitric acid under sonication. The preparation of 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine, and oxidation of 3,6-diamino-1,2,4,5-tetrazine were also studied. Sonication reaction conditions and results of these reactions under ultrasound are discussed in detail.

Lee, Kien-Yin.

1993-01-01

318

Thermal reactions of aromatics with CaO. Technical progress report, April 1-August 31, 1983  

SciTech Connect

The pyrolysis of m-cresol and 1-methylanthracene was studied over both CaO and quartz over the temperature range of 350 to 800/sup 0/C. Vapor-phase concentration of the model compound was 5 mole percent for m-cresol and 1.8 mole percent for 1-methylanthracene. The calcium oxide significantly increased the rates and extents of pyrolysis of the aromatics, reducing the temperature for a given amount of conversion by at least 120/sup 0/C. A proposed mechanism for pyrolysis of m-cresol over CaO involves formation of calcium-cresol salts, which then undergo further cracking at temperatures above 500/sup 0/C to yield coke, CO, CH/sub 4/, toluene and C/sub 3/H/sub 6/. Chemical condensation reactions were the predominant reactions observed in the pyrolysis of 1-methylanthracene over CaO. A comparison of the pyrolysis results of 1-methylanthracene with those of 9-methylanthracene (studied earlier) indicated that the 1-methyl isomer was slightly less reactive over both solids, and that some of the thermal reactions over CaO were also structure specific. Deactivation of CaO was studied by measuring loss of cumulative cracking activity during pyrolysis of 1-methylanthracene. The decay of CaO activity with overall utilization time (or cumulative amount of feed reacted), was well-fitted by a power-law model. Coke burnoff in O/sub 2/ at temperatures between 600-700/sup 0/C regenerated approx.80 percent of the CaO initial activity. The 20 percent loss is attributed to either formation of CaCO/sub 3/ from the CaO or sintering of the CaO particles during regeneration. 7 refs., 11 figs., 1 tab.

Longwell, J.P.; Lai, C.K.; Williams, G.C.; Peters, W.A.

1983-11-01

319

Thermal phenomena under microwave field in the organic synthesis processes: Application to the Diels Alder reaction  

SciTech Connect

The influence of the microwave heating on chemical reactions were investigated. The kinetic of the Diels Alder reaction were studied under microwave irradiation at a frequency of 2.45 GHz in a single mode cavity and were compared to the kinetic obtained by a conventional heating. Experiments were carried out in a liquid solvent in order to have a better control of the medium temperature measurement. In a second part, the presence of a catalytic solid phase was introduced. Some thermal fluctuations which are due to an heterogeneity of the electric field were detected in the medium. They reduce the precision of the results and cause problems of experimental reproducibility. A thermoluminescent material allow a good visualization of these phenomena. In addition, the profiles of the electric field intensity were modelled by a 2D finite elements method in the reactor in the presence of a solvent. Despite the small size of the sample and the use of a monomode cavity which both limited the heterogeneities of the medium temperature, the authors showed a great heterogeneity of the electric field intensity and as a result the heterogeneity of the temperature in their sample. In order to avoid these phenomena which induce a lack of reproducibility, a stirring device was developed. The values of the kinetics obtained under the 2 heating modes with the introduction of the stirring device. So, it induces a good control of the medium temperature. All those investigations prompted the authors to the conclusion that there is no difference between microwave heating and a classical heating in the studied reaction.

Saillard, R.; Poux, M.; Audhuy-Peaudecerf, M.

1996-12-31

320

Polymerase chain reaction with phase change as intrinsic thermal control  

NASA Astrophysics Data System (ADS)

This research demonstrated that without any external temperature controller, the capillary convective polymerase chain reaction (ccPCR) powered by a candle can operate with the help of phase change. The candle ccPCR system productively amplified hepatitis B virus 122 base-pairs DNA fragment. The detection sensitivity can achieve at an initial DNA concentration to 5 copies per reaction. The results also show that the candle ccPCR system can operate functionally even the ambient temperature varies from 7 °C to 45 °C. These features imply that the candle ccPCR system can provide robust medical detection services.

Hsieh, Yi-Fan; Yonezawa, Eri; Kuo, Long-Sheng; Yeh, Shiou-Hwei; Chen, Pei-Jer; Chen, Ping-Hei

2013-04-01

321

Investigation of chemical reactions in solution using API-MS  

Microsoft Academic Search

The general concepts, advantages, and applications of on-line and off-line screening to organic reaction mechanistic studies applying API-MS are reviewed. An overview is presented of the development and the present stage of connected microreactors to API ion-sources. Examples of the successful application of API in revealing, elucidating, and helping to consolidate several proposed mechanisms of organic reactions are summarized. Finally,

Leonardo Silva Santos; Larissa Knaack; Jürgen O. Metzger

2005-01-01

322

From elementary reactions to evaluated chemical mechanisms for combustion models  

Microsoft Academic Search

Methods of determining rate data for elementary reactions for combustion applications, using experimental and theoretical methods, are briefly reviewed. The approaches are illustrated by reference to recent research in three areas: (i) reactions of OH with C2H4 and C2H2, where theory, tuned by reference to experiment, has provided a substantial contribution to the determination of rate data for these complex

Michael J. Pilling

2009-01-01

323

Characterization of chemically modified enzymes for bioremediation-reactions. 1997 annual progress report  

SciTech Connect

'Many, if not most, biological transformation reactions of interest to US Department of Energy (DOE) site remediation involve substrates that are only sparingly soluble in aqueous environments. Hence, destruction of these recalcitrant and toxic materials would benefit tremendously if their degradation could be performed in nonaqueous environments. Organic biocatalysis may be motivated by the nature of the substrate itself, augmented mass transport, ease of product recovery, or novel reaction pathways afforded by the organic solvent. For instance, polychlorinated biphenyls (PCBs) are sparingly soluble in water, but may be more effectively processed when solubilized by organic liquids. However, naturally-occurring enzymes are not soluble in organic solvents. Indeed, most spontaneously denature and, depending on the solvent used, typically form inactive and insoluble precipitates. The objective of the current work is to gain a fundamental understanding of the molecular and catalytic properties of enzymes that have been chemically-modified so that they are catalytically-active and chemically-thermally-stable in organic solvents. The premise for this study is that highly stable enzymes which are catalytically active in both water and in a range of organic solvents are optimally suited for bioremediation where substrates of interest are more soluble and may be processed with greater specificity in nonaqueous solvents. The proposed research program will enable the development of nonaqueous bioremediation technologies for the treatment of DOE sites contaminated with aqueous-insoluble organic compounds. Such compounds may include dense nonaqueous phase liquids, trichloroethylene (TCE), trichloroacetic acid, trans-dichloroethylene, diesel fuel, and PCBs. These compounds have been identified as targets for technology development in the ``EM Technology Needs Database,'''' and are contaminants at the following DOE sites: K-25 Site plumes; ORNL WAGS 1, 4, and 5; Paducah plumes; Portsmouth plumes; the X-701B Holding Pond; and the Y-12 Poplar Creek and Bear Creek Watersheds.'

Kaufman, E.N. [Oak Ridge National Lab., TN (US); Adams, M.W.W. [Univ. of Georgia, Athens, GA (US)

1997-09-01

324

Novel thermal gradient chemical vapor infiltration process for carbon-carbon composites  

Microsoft Academic Search

Solid cylindrical carbon-carbon composites were processed using conventional thermal gradient chemical vapor infiltration. High thermal conductivity (55 W\\/m·°C) carbon fibers (48 k) were inserted in the center of a cylindrical low thermal conductivity (0.15 W\\/m·°C) needle punched carbon felt preform, to create a thermal gradient because of the difference in thermal conductivities. The hottest portion (900–1200 °C) was along the

Shameel Farhan; Ke-zhi LI; Ling-jun GUO

2007-01-01

325

Characterization of solid bitumens originating from thermal chemical alteration and thermochemical sulfate reduction  

NASA Astrophysics Data System (ADS)

Solid bitumen can arise from several reservoir processes acting on migrated petroleum. Insoluble solid organic residues can form by oxidative processes associated with thermochemical sulfate reduction (TSR) as well as by thermal chemical alteration (TCA) of petroleum. TCA may follow non-thermal processes, such as biodegradation and asphaltene precipitation, that produce viscous fluids enriched in polar compounds that are then altered into solid bitumens. It is difficult to distinguish solid bitumen formed by TCA from TSR since both processes occur under relatively high temperatures. The focus of the present work is to characterize solid bitumen samples associated with TSR- or TCA-processes using a combination of solid-state X-ray Photoelectron Spectroscopy (XPS), Sulfur X-ray Absorption Near Edge Structure Spectroscopy (S-XANES), and 13C NMR. Naturally occurring solid bitumens from three locations, Nisku Formation, Brazeau River area (TSR-related); La Barge Field, Madison Formation (TSR-related); and, the Alaskan North Slope, Brooks Range (TCA-related), are compared to solid bitumens generated in laboratory simulations of TSR and TCA. The chemical nature of solid bitumens with respect to organic nitrogen and sulfur can be understood in terms of (1) the nature of hydrocarbon precursor molecules, (2) the mode of sulfur incorporation, and (3) their concentration during thermal stress. TSR-solid bitumen is highly aromatic, sulfur-rich, and nitrogen-poor. These heteroatom distributions are attributed to the ability of TSR to incorporate copious amounts of inorganic sulfur (S/C atomic ratio >0.035) into aromatic structures and to initial low levels of nitrogen in the unaltered petroleum. In contrast, TCA-solid bitumen is derived from polar materials that are initially rich in sulfur and nitrogen. Aromaticity and nitrogen increase as thermal stress cleaves aliphatic moieties and condensation reactions take place. TCA-bitumens from the Brooks Range have <75% aromatic carbon. TCA-bitumens exposed to greater thermal stress can have a higher aromaticity, like that observed in TSR-bitumens. Organic sulfur in TCA-organic solids remains relatively constant with increasing maturation (S/C atomic ratio <0.035) due to offsetting preservation and H 2S elimination reactions. Although S-XANES and 13C NMR provide information needed to understand changes in structure and reactivity that occur in the formation of petroleum solids, in some cases XPS analysis is sufficient to determine whether a solid bitumen is formed by TCA or TSR.

Kelemen, Simon R.; Walters, Clifford C.; Kwiatek, Peter J.; Freund, Howard; Afeworki, Mobae; Sansone, Michael; Lamberti, William A.; Pottorf, Robert J.; Machel, Hans G.; Peters, Kenneth E.; Bolin, Trudy

2010-09-01

326

Lithium silicide nanocrystals: synthesis, chemical stability, thermal stability, and carbon encapsulation.  

PubMed

Lithium silicide (LixSi) is the lithiated form of silicon, one of the most promising anode materials for the next generation of lithium-ion batteries (LIBs). In contrast to silicon, LixSi has not been well studied. Herein we report a facile high-energy ball-milling-based synthesis of four phase-pure LixSi (x = 4.4, 3.75, 3.25, and 2.33), using hexane as the lubricant. Surprisingly, the obtained Li3.75Si phase shows significant downward shifts in all X-ray diffraction peak positions, compared with the standard. Our interpretation is that the high-energy ball-mill-synthesized Li3.75Si presents smaller internal pressures and larger lattice constants. The chemical-stability study reveals that only surface reactions occur after Li4.4Si and Li3.75Si are immersed in several battery-assembly-related chemicals. The thermal-stability study shows that Li4.4Si is stable up to 350 °C and Li3.75Si is stable up to 200 °C. This remarkable thermal stability of Li3.75Si is in stark contrast to the long-observed metastability for electrochemically synthesized Li3.75Si. The carbon encapsulation of Li4.4Si has also been studied for its potential applications in LIBs. PMID:25265365

Cloud, Jacqueline E; Wang, Yonglong; Li, Xuemin; Yoder, Tara S; Yang, Yuan; Yang, Yongan

2014-10-20

327

Will water act as a photocatalyst for cluster phase chemical reactions? Vibrational overtone-induced dehydration reaction of methanediol  

SciTech Connect

The possibility of water catalysis in the vibrational overtone-induced dehydration reaction of methanediol is investigated using ab initio dynamical simulations of small methanediol-water clusters. Quantum chemistry calculations employing clusters with one or two water molecules reveal that the barrier to dehydration is lowered by over 20 kcal/mol because of hydrogen-bonding at the transition state. Nevertheless, the simulations of the reaction dynamics following OH-stretch excitation show little catalytic effect of water and, in some cases, even show an anticatalytic effect. The quantum yield for the dehydration reaction exhibits a delayed threshold effect where reaction does not occur until the photon energy is far above the barrier energy. Unlike thermally induced reactions, it is argued that competition between reaction and the irreversible dissipation of photon energy may be expected to raise the dynamical threshold for the reaction above the transition state energy. It is concluded that quantum chemistry calculations showing barrier lowering are not sufficient to infer water catalysis in photochemical reactions, which instead require dynamical modeling.

Kramer, Zeb C.; Takahashi, Kaito; Skodje, Rex T. [Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215 (United States); Vaida, Veronica [Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215 (United States); CIRES, University of Colorado, Boulder, Colorado 80309 (United States)

2012-04-28

328

Will water act as a photocatalyst for cluster phase chemical reactions? Vibrational overtone-induced dehydration reaction of methanediol  

NASA Astrophysics Data System (ADS)

The possibility of water catalysis in the vibrational overtone-induced dehydration reaction of methanediol is investigated using ab initio dynamical simulations of small methanediol-water clusters. Quantum chemistry calculations employing clusters with one or two water molecules reveal that the barrier to dehydration is lowered by over 20 kcal/mol because of hydrogen-bonding at the transition state. Nevertheless, the simulations of the reaction dynamics following OH-stretch excitation show little catalytic effect of water and, in some cases, even show an anticatalytic effect. The quantum yield for the dehydration reaction exhibits a delayed threshold effect where reaction does not occur until the photon energy is far above the barrier energy. Unlike thermally induced reactions, it is argued that competition between reaction and the irreversible dissipation of photon energy may be expected to raise the dynamical threshold for the reaction above the transition state energy. It is concluded that quantum chemistry calculations showing barrier lowering are not sufficient to infer water catalysis in photochemical reactions, which instead require dynamical modeling.

Kramer, Zeb C.; Takahashi, Kaito; Vaida, Veronica; Skodje, Rex T.

2012-04-01

329

Thermal oxidative degradation reactions of linear perfluoroalkyl ethers  

NASA Technical Reports Server (NTRS)

Thermal and thermal oxidative stability studies were performed on linear perfluoroalkyl ether fluids. The effect on degradation by metal catalysts and degradation inhibitors is reported. The linear perfluoroalkyl ethers are inherently unstable at 316 C in an oxidizing atmosphere. The metal catalysts greatly increased the rate of degradation in oxidizing atmospheres. In the presence of these metals in an oxidizing atmosphere, the degradation inhibitors were highly effective in arresting degradation at 288 C. However, the inhibitors had only limited effectiveness at 316 C. The metals promote degradation by chain scission. Based on elemental analysis and oxygen consumption data, the linear perfluoroalkyl ether fluids have a structural arrangement based on difluoroformyl and tetrafluoroethylene oxide units, with the former predominating. Previously announced in STAR as N82-26468

Jones, W. R., Jr.; Paclorek, K. J. L.; Ito, T. I.; Kratzer, R. H.

1983-01-01

330

Chemical and isotopic composition of water from thermal springs and mineral springs of Washington  

USGS Publications Warehouse

Water from thermal springs of Washington range in chemical composition from dilute NaHC03, to moderately saline C02-charged NaHC03-Cl waters. St. Martin 's Hot Spring which discharges a slightly saline NaCl water, is the notable exception. Mineral springs generally discharge a moderately saline C02-charged NaHC03-Cl water. The dilute Na-HC03 waters are generally associated with granite. The warm to hot waters charged with C02 issue on or near the large stratovolcanoes and many of the mineral springs also occur near the large volcanoes. The dilute waters have oxygen isotopic compositions which indicate relatively little water-rock exchange. The C02-charged waters are usually more enriched in oxygen-18 due to more extensive water-rock reaction. Carbon-13 in the C02-charged thermal waters is more depleted (-10 to -12 permil) than in the cold C02-charged soda springs (-2 to -8 permil) which are also scattered throughout the Cascades. The hot and cold C02-charged waters are supersaturated with respect to CaC03, but only the hot springs are actively depositing CaC03. Baker, Gamma, Sulphur , and Ohanapecosh seem to be associated with thermal aquifers of more than 100C. (USGS)

Mariner, R.H.; Presser, T.S.; Evans, W.C.

1982-01-01

331

Modeling the Dynamics of Chemical Reactions Involving Multidimensional Tunneling  

NASA Astrophysics Data System (ADS)

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 compared to experiment.

Liu, Yi-Ping

332

Energy storage and transport by reversible chemical reactions  

NASA Astrophysics Data System (ADS)

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.

Beghi, G.

333

Digital isothermal quantification of nucleic acids via simultaneous chemical initiation of recombinase polymerase amplification reactions on SlipChip.  

PubMed

In this paper, digital quantitative detection of nucleic acids was achieved at the single-molecule level by chemical initiation of over one thousand sequence-specific, nanoliter isothermal amplification reactions in parallel. Digital polymerase chain reaction (digital PCR), a method used for quantification of nucleic acids, counts the presence or absence of amplification of individual molecules. However, it still requires temperature cycling, which is undesirable under resource-limited conditions. This makes isothermal methods for nucleic acid amplification, such as recombinase polymerase amplification (RPA), more attractive. A microfluidic digital RPA SlipChip is described here for simultaneous initiation of over one thousand nL-scale RPA reactions by adding a chemical initiator to each reaction compartment with a simple slipping step after instrument-free pipet loading. Two designs of the SlipChip, two-step slipping and one-step slipping, were validated using digital RPA. By using the digital RPA SlipChip, false-positive results from preinitiation of the RPA amplification reaction before incubation were eliminated. End point fluorescence readout was used for "yes or no" digital quantification. The performance of digital RPA in a SlipChip was validated by amplifying and counting single molecules of the target nucleic acid, methicillin-resistant Staphylococcus aureus (MRSA) genomic DNA. The digital RPA on SlipChip was also tolerant to fluctuations of the incubation temperature (37-42 °C), and its performance was comparable to digital PCR on the same SlipChip design. The digital RPA SlipChip provides a simple method to quantify nucleic acids without requiring thermal cycling or kinetic measurements, with potential applications in diagnostics and environmental monitoring under resource-limited settings. The ability to initiate thousands of chemical reactions in parallel on the nanoliter scale using solvent-resistant glass devices is likely to be useful for a broader range of applications. PMID:21476587

Shen, Feng; Davydova, Elena K; Du, Wenbin; Kreutz, Jason E; Piepenburg, Olaf; Ismagilov, Rustem F

2011-05-01

334

Conceptual Design of Biorefineries Through the Synthesis of Optimal Chemical-reaction Pathways  

E-print Network

on developing new pathways while optimizing existing ones. Here, potential chemicals are added to create a superstructure, then an algorithm is run to enumerate every feasible reaction stoichiometry through a mixed integer linear program (MILP). An optimal...

Pennaz, Eric James

2011-10-21

335

EVALUATION OF CHEMICAL REACTION MECHANISMS FOR PHOTOCHEMICAL SMOG. PART 2. QUANTITATIVE EVALUATION OF THE MECHANISMS (REVISED)  

EPA Science Inventory

Six chemical reaction mechanisms for photochemical smog were analyzed to determine why, under identical conditions, they predict different maximum ozone concentrations. To perform the analysis, a counter species technique was used to determine the contributions of individual reac...

336

Reformulation and solution of the master equation for multiple-well chemical reactions.  

PubMed

We consider an alternative formulation of the master equation for complex-forming chemical reactions with multiple wells and bimolecular products. Within this formulation the dynamical phase space consists of only the microscopic populations of the various isomers making up the reactive complex, while the bimolecular reactants and products are treated equally as sources and sinks. This reformulation yields compact expressions for the phenomenological rate coefficients describing all chemical processes, i.e., internal isomerization reactions, bimolecular-to-bimolecular reactions, isomer-to-bimolecular reactions, and bimolecular-to-isomer reactions. The applicability of the detailed balance condition is discussed and confirmed. We also consider the situation where some of the chemical eigenvalues approach the energy relaxation time scale and show how to modify the phenomenological rate coefficients so that they retain their validity. PMID:24053787

Georgievskii, Yuri; Miller, James A; Burke, Michael P; Klippenstein, Stephen J

2013-11-21

337

React. Kinet. Catal. Lett., Vol. 15, No. 2,245-250 (1980) DYNAMICS OF CHEMICAL REACTIONS AND NONPHYSICAL  

E-print Network

React. Kinet. Catal. Lett., Vol. 15, No. 2,245-250 (1980) DYNAMICS OF CHEMICAL REACTIONS behavior of chemical reactions,in particular,the reasonsfor slow relaxa- tions. IIoKa3aHo, qTO 14[HdpKcaum~. Prolonged transientregimes were found experimentally in chemical reactions in greatlydifferenthomogeneous

Gorban, Alexander N.

338

Exact probability distributions of selected species in stochastic chemical reaction networks.  

PubMed

Chemical reactions are discrete, stochastic events. As such, the species' molecular numbers can be described by an associated master equation. However, handling such an equation may become difficult due to the large size of reaction networks. A commonly used approach to forecast the behaviour of reaction networks is to perform computational simulations of such systems and analyse their outcome statistically. This approach, however, might require high computational costs to provide accurate results. In this paper we opt for an analytical approach to obtain the time-dependent solution of the Chemical Master Equation for selected species in a general reaction network. When the reaction networks are composed exclusively of zeroth and first-order reactions, this analytical approach significantly alleviates the computational burden required by simulation-based methods. By building upon these analytical solutions, we analyse a general monomolecular reaction network with an arbitrary number of species to obtain the exact marginal probability distribution for selected species. Additionally, we study two particular topologies of monomolecular reaction networks, namely (i) an unbranched chain of monomolecular reactions with and without synthesis and degradation reactions and (ii) a circular chain of monomolecular reactions. We illustrate our methodology and alternative ways to use it for non-linear systems by analysing a protein autoactivation mechanism. Later, we compare the computational load required for the implementation of our results and a pure computational approach to analyse an unbranched chain of monomolecular reactions. Finally, we study calcium ions gates in the sarco/endoplasmic reticulum mediated by ryanodine receptors. PMID:25155220

López-Caamal, Fernando; Marquez-Lago, Tatiana T

2014-09-01

339

Materials testing for solar-thermal chemical process heat  

SciTech Connect

Considerable interest has arisen recently in the production of hydrogen from water using solar thermal energy. The most advanced chemical cycles being developed in the United States and abroad all have the decomposition of sulfuric acid at elevated temperatures as the final step in the cycle. Materials required in the production of hydrogen have been tested. The materials tested included ..cap alpha..-SiC, siliconized SiC, MgO, ZrO/sub 2/(Y/sub 2/O/sub 3/ stabilized), ZrO/sub 2/(MgO stabilized), and silicon aluminum oxynitride (or sialon). Ring specimens of these materials were exposed for varying periods of time in a simulated H/sub 2/SO/sub 4/ decomposition environment at 1000 and 1225/sup 0/C. The specimens were examined visually, metallographically, by x-ray diffraction, and with a scanning electron microscope. In addition, the specimens were tested for changes in their fracture stress and weight. The silicon carbide materials, both alpha and siliconized, were the best performers. The other materials tested showed V)-iron(II) oxides was 10 kcal/mol, and the amount of analytical solution. (MHR)

Tiegs, T.N.

1981-10-01

340

A kinetic mechanism inducing oscillations in simple chemical reactions networks  

E-print Network

, for example, cell cycle [1], Ca+ -induced oscillations [8], glycolysis [15, 20, 14], yeast metabolic cycle [19 for this work) is given by ATP in the glycolysis pathway [20]. ATP is a cofactor in some of the reaction steps (e.g. in the step catalyzed by Hexokinase: glucose - glucose-6-phosphate) while a too high

Altafini, Claudio

341

P MATRIX PROPERTIES, INJECTIVITY AND STABILITY IN CHEMICAL REACTION SYSTEMS  

E-print Network

a class of systems consisting of reactions coupled to an external rate-dependent negative feedback process is algorithmically easy to check, and immediately implies the absence of multiple equilibria as long with some external quantity giving rise to a negative feedback process. Necessary and sufficient conditions

Banaji,. Murad

342

Cellulose Oligomers: Preparation from Cellulose Triacetate, Chemical Transformations and Reactions  

Microsoft Academic Search

Cellulose oligomers obtained by a new degradation method (pivaloylysis) are used as starting materials in organic synthesis. On the one hand these oligomers are functionalized to potent glycosyl donors, on the other hand several methods are shown to generate different types of hydroxy compounds (glycosyl acceptors). Glycosidation reactions performed with these two types of building blocks allow an access to

P. Arndt; K. Bockholt; R. Gerdes; S. Huschens; J. Pyplo; H. Redlich; K. Samm

2003-01-01

343

Effect of interfaces on the thermal, mechanical and chemical characteristics of carbon nanotubes  

NASA Astrophysics Data System (ADS)

The primary focus of this work is to explore the effect of interface on thermal, mechanical, and chemical properties of carbon nanotubes (CNTs) and the methods to modify the interface between CNTs and CNTs based composites. CNTs are potentially promising fibers for ultra-high-strength composites. The load transfer between the inner and outer tubes in multiwall nanotubes (MWNTs) has to be clearly understood to realize the potential of MWNTs in composites and other applications such as nano-springs, and nano-bearings. This dissertation studies the load transfer between the walls of MWNTs in both tension and compression using molecular dynamics simulations. It is found that only the minimal load is transferred to the inner nanotube in tension. The load transfer of capped nanotubes in compression is much higher than in tension. In the case of uncapped nanotubes, the inner nanotube is deformed in bending only after the outer nanotube is extensively deformed by buckling. The presence of a few interstitial atoms between the walls of MWNTs can significantly improve the stiffness and enhance the load transfer to the inner nanotubes in both tension and compression. The modification of the interface of CNTs is a key factor for effectively using CNTs in many applications. Many potential applications of CNTs, including high strength composites, nano-sensors, and molecular electronics, can be created by chemical surface modification. The use of molecular statics and dynamics helps exploring ion irradiation as a method for functionalization of CNTs. It is found that ion bombardment of single and Multiwall carbon nanotubes creates vacancies and defects, which can act as high-energy sites for further chemical reactions; furthermore, ion irradiation of CNTs embedded in polymer matrix creates chemical attachments between CNTs and polymer matrix, enhancing the compositing process. Mechanical property simulations based on tension and pullout tests indicate that the chemical links between constituents in CNT-polymer systems result in higher load transfer, and hence, better composite properties. The effect of the interface turns out to be very crucial for printing in nanolithography processes. Molecular dynamics simulation is applied to extract interface properties, such as friction and adhesion, in nanoscale; later, the properties are input into a large-scale FEM model. As found, the protrusion problem is caused by many factors, such as strength of polymer at high temperature, thermal expansion properties, and depth of metal. The results show a possible application of CNTs in polymer for increasing Young's modulus and decreasing thermal expansion of composites; this will result in less protrusion by using CNTs in the composite, and hence, the protrusion problem could be reduced.

Shen, Guo An

344

Approximate reaction rates and probabilities for a class of exothermic chemical reactions  

Microsoft Academic Search

An approximate expression for the total rate constant for certain exothermic reactions is given. The approximation can be expressed simply in terms of integrals in a region about the saddle point. More complicated procedures for computing the total probability for reaction from a given reactant state are presented. This involves solution of a set of coupled differential equations in a

Edward J. Shipsey

1975-01-01

345

High-rate chemical vapor deposition of nanocrystalline silicon carbide films by radio frequency thermal plasma  

E-print Network

thermal plasma F. Liao a , S. Park a , J.M. Larson b , M.R. Zachariah a , S.L. Girshick a,* a Department were deposited by radio frequency thermal plasma chemical vapor deposition (CVD) at rates up to several; Nanomaterials; Silicon carbide; Thermal plasmas; Thin films; Si tetrachlorine precursor Silicon carbide has

Zachariah, Michael R.

346

Interplay of explosive thermal reaction dynamics and structural confinement  

NASA Astrophysics Data System (ADS)

Explosives play a significant role in human affairs; however, their behavior in circumstances other than intentional detonation is poorly understood. Accidents may have catastrophic consequences, especially if additional hazardous materials are involved. Abnormal ignition stimuli, such as impact, spark, friction, and heat may lead to a very violent outcome, potentially including detonation. An important factor influencing the behavior subsequent to abnormal ignition is the strength and inertia of the vessel confining the explosive, i.e., the near-field structural/mechanical environment, also known as confinement (inertial or mechanical). However, a comprehensive and quantified understanding of how confinement affects reaction violence does not yet exist. In the research discussed here, we have investigated a wide range of confinement conditions and related the explosive response to the fundamentals of the combustion process in the explosive. In our experiments, a charge of an octahydrotetranitrotetrazine-based plastic bonded explosive (PBX 9501) was loaded into a gun assembly having variable confinement conditions and subjected to a heating profile. The exploding charge breached the confinement and accelerated a projectile down the gun barrel. High bandwidth pressure and volume measurements were made and a first-law analysis was used to obtain enthalpy and power from the raw data. These results were then used to quantify reaction violence. Enthalpy change and power ranged from 0-1.8 kJ and 0-12 MW for 300 mg charges, respectively. Below a confinement strength of 20 MPa, violence was found to decline precipitously with decreasing confinement, while the violence for the heaviest confinement experiments was found to be relatively constant. Both pressure and pressurization rate were found to have critical values to induce and sustain violent reaction.

Perry, W. Lee; Zucker, Jonathan; Dickson, Peter M.; Parker, Gary R.; Asay, Blaine W.

2007-04-01

347

Thermal, Mechanical and Chemical Analysis for VELOX -Verification Experiments for Lunar Oxygen Production  

NASA Astrophysics Data System (ADS)

One major aspect for the development of a long-term human presence on the moon will be sustainability and autonomy of any kind of a permanent base. Important resources, such as breathable air and water for the survival of the crew on the lunar surface will have to be extracted in-situ from the lunar regolith, the major resource on the Moon, which covers the first meter of the lunar surface and contains about 45 At the DLR Bremen we are interested in a compact and flexible lab experimenting facility, which shall demonstrate the feasibility of this process by extracting oxygen out of lunar Regolith, respectively soil simulants and certain minerals in the laboratory case. For this purpose, we have investigated important boundary conditions such as temperatures during the process, chemical reaction characteristics and material properties for the buildup of the facility and established basic requirements which shall be analyzed within this paper. These requirements have been used for the concept development and outline of the facility, which is currently under construction and will be subject to initial tests in the near future. This paper will focus mainly on the theoretical aspects of the facility development. Great effort has been put into the thermal and mechanical outline and pre-analysis of components and the system in a whole. Basic aspects that have been investigated are: 1. Selection of suitable materials for the furnace chamber configuration to provide a high-temperature capable operating mode. 2. Theoretical heat transfer analysis of the designed furnace chamber assembly with subsequent validation with the aid of measured values of the constructed demonstration plant. 3. Description of chemical conversion processes for Hydrogen reduction of Lunar Regolith with corresponding analysis of thermal and reaction times under different boundary conditions. 4. Investigation of the high-temperature mechanical behavior of the constructed furnace chamber with regard to thermal stability and especially to the hermetically sealed reactor due to internal Hydrogen atmosphere. In the end, we will give a first glimpse into the development of the test setup and first test results on the way to a superior test set-up and infrastructure with pre-and post-processing units such as feeding and extraction units and analysis of reaction products.

Lange, Caroline; Ksenik, Eugen; Braukhane, Andy; Richter, Lutz

348

Numerical simulation of thermal-hydrologic-mechanical-chemical processes in deformable, fractured porous media  

Microsoft Academic Search

A method is introduced to couple the thermal (T), hydrologic (H), and chemical precipitation\\/dissolution (C) capabilities of TOUGHREACT with the mechanical (M) framework of FLAC3D to examine THMC processes in deformable, fractured porous media. The combined influence of stress-driven asperity dissolution, thermal-hydro-mechanical asperity compaction\\/dilation, and mineral precipitation\\/dissolution alter the permeability of fractures during thermal, hydraulic, and chemical stimulation. Fracture and

Joshua Taron; Derek Elsworth; Ki-Bok Min

2009-01-01

349

X-ray Microspectroscopy and Chemical Reactions in Soil Microsites  

SciTech Connect

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

D Hesterberg; M Duff; J Dixon; M Vepraskas

2011-12-31

350

EFFICIENT CHEMICAL TRANSFORMATIONS USING ALTERNATIVE REACTION CONDITIONS AND MEDIA  

EPA Science Inventory

The diverse nature of chemical entities requires various green' strategic pathways in our quest towards attaining sustainability. A solvent-free approach that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable...

351

JASPERSE CHEM 341 TEST 2 VERSION 1 Ch. 5 The Study of Chemical Reactions  

E-print Network

choice question) 4. Which of the following is true regarding an SN1 reaction? a. It would be faster at 25 an alkyl bromide and some nucleophile that you could use to make the following by SN2. (3 points) OCH2CH3 31 JASPERSE CHEM 341 TEST 2 VERSION 1 Ch. 5 The Study of Chemical Reactions Ch. 9 Stereochemistry Ch

Jasperse, Craig P.

352

Nuclear spin selection rules in chemical reactions by angular momentum algebra  

E-print Network

Nuclear spin selection rules in chemical reactions by angular momentum algebra Takeshi Oka by Quack using molecular symmetry group are derived by using angu- lar momentum algebra. Instead: Selection rules; Nuclear spin modifications; Angular momentum algebra; Ion-neutral reactions; Molecular ions

Oka, Takeshi

353

Progression in high school students (aged 16-18) conceptualizations about chemical reactions in solution  

Microsoft Academic Search

The purpose of this study was to explore the development over time of students' understandings of the concept of chemical reaction in the context of two familiar reactions in solution. The study is based on interviews of 48 students, aged 16-18, who had been successful in their year 11 examinations and had selected to study chemistry as one of their

Hong-Kwen Boo; J. R. Watson

2001-01-01

354

JASPERSE CHEM 341 TEST 2 VERSION 2 Ch. 5 The Study of Chemical Reactions  

E-print Network

A Br2, hv 8. Draw the product when the following substance undergoes E2 elimination. ("D" is deuterium1 JASPERSE CHEM 341 TEST 2 VERSION 2 Ch. 5 The Study of Chemical Reactions Ch. 9 Stereochemistry Ch. 10,11 Alkyl Halides and their Reactions: Nucleophilic Substitution and Elimination 1. Rank

Jasperse, Craig P.

355

JASPERSE CHEM 350 TEST 2 VERSION 2 Ch. 4 The Study of Chemical Reactions  

E-print Network

substance undergoes E2 elimination. ("D" is deuterium, basically just a labelled hydrogen). If the startingJASPERSE CHEM 350 TEST 2 VERSION 2 Ch. 4 The Study of Chemical Reactions Ch. 5 Sterochemistry Ch. 6 that is needed in each case) for each of the following reactions. (Minor products or inorganic side products need

Jasperse, Craig P.

356

Dimensional Reduction of the Fokker–Planck Equation for Stochastic Chemical Reactions  

Microsoft Academic Search

The Fokker-Planck equation models chemical reactions on a mesoscale. The solution is a probability density function for the copy number of the dierent molecules. The number of dimensions of the problem can be large making numerical simulation of the reactions computationally intractable. The number of dimensions is reduced here by deriving partial dierential equations for the first moments of some

LARS FERM

2006-01-01

357

Interaction between Large Vortex Structures and Chemical Reactions in Jet Flames  

Microsoft Academic Search

Microscopic structures and their dynamics shaped by vortices and chemical reactions in jet flames are investigated both numerically and experimentally in order to clarify statistical properties of combustion flows. In our direct numerical simulation with multi-step reaction mechanism of an axisymmetric jet flame, it is verified that shear vortices drifting downstream along the edges of flames make complex flame surfaces

Naoto Yokoyama; Kana Saito; Jiro Mizushima

2004-01-01

358

Direct Monte Carlo simulation of chemical reaction systems: Dissociation and recombination  

E-print Network

Direct Monte Carlo simulation of chemical reaction systems: Dissociation and recombination Shannon of Physics. I. INTRODUCTION In earlier studies1­5 we have found the direct Monte Carlo simulation method6 Monte Carlo simulation of dissociation-recombination reac- tions of the type M AB M A B. These reactions

Anderson, James B.

359

A coupled chemical burster: The chlorine dioxide-iodide reaction in two flow reactors  

E-print Network

A coupled chemical burster: The chlorine dioxide-iodide reaction in two flow reactors Miles Dolnika-iodide reaction has been studied in a system consisting of two continuous flow stirred tank reactors (CSTRs). The reactors are coupled by computer monitoring of the electrochemical potential in each reactor, which

Epstein, Irving R.

360

Kinetics of endothermic decomposition reactions. I. Steady-state chemical steps  

Microsoft Academic Search

When the solid product of an endothermic decomposition reaction is porous, the rate-limiting chemical step is usually assumed to be a surface step of the gaseous product or of a precursor of that product. It is shown here that the rate of such a reaction may also depend upon rates of diffusion in the reactant phase, the rate of transfer

Alan W. Searcy; Dario Beruto

1976-01-01

361

Inward Propagating Chemical Waves in a Single-Phase Reaction-Diffusion System  

Microsoft Academic Search

We report our experimental and theoretical studies of inwardly propagating chemical waves (antiwaves) in a single-phase reaction-diffusion (RD) system. The experiment was conducted in an open spatial reactor using chlorite-iodide-malonic acid reaction. When the system was set to near Hopf bifurcation point, antiwaves appeared spontaneously, as predicted using both the reaction-diffusion (RD) equation and the complex Ginzburg-Landau equation (CGLE). Antiwaves

Xin Shao; Yabi Wu; Jinzhong Zhang; Hongli Wang; Qi Ouyang

2008-01-01

362

Continuous chemical reaction chromatography: Progress report, December 1985--December 1988  

SciTech Connect

During the present three year project period we have been investigating continuous gas chromatographic separations, and continuous reaction gas chromatography of solid catalyzed reactions in a countercurrent moving bed. Design and construction of a computer controlled laboratory scale countercurrent moving bed apparatus was completed. In the countercurrent moving bed, a granular solid (typically 30-50 mesh) flows slowly down a vertical tube against an upflowing carrier gas. A mixture to be separated, or a reactant species, is fed continuously at an arbitrary location along the column. We have now carried out experimental investigations of separation of a binary mixture, 1,3,5-trimethylcyclohexane and 1,3,5-trimethylbenzene, and of hydrogenation in the countercurrent moving bed. 8 refs., 2 tabs.

Aris, R.; Carr, R.W.

1989-01-01

363

Theoretical study of the reaction mechanisms involved in the thermal intramolecular reactions of 1,6-fullerenynes.  

PubMed

Substitution of a H atom by an alkyl group on the terminal carbon of the alkyne moiety of 1,6-fullerenynes has a strong impact on the products of the reaction undergone by this species after thermal treatment. While the reaction of 1,6-fullerenynes bearing an unsubstituted alkyne moiety results in the cycloaddition of the alkyne group to the fullerene double bond leading to cyclobutene-fused derivatives, the presence of an alkyl substituent leads to the formation of allenes. In the present work, we have performed an exhaustive theoretical analysis of all possible reaction mechanisms leading to cyclobutene-fused derivatives and allenes to offer an explanation of the reactivity differences observed. The results obtained show that formation of cyclobutene-fused derivatives occurs through a stepwise diradical reaction mechanism, while allene formation proceeds through a concerted way involving an uncommon intramolecular ene process. For the 1,6-fullerenynes bearing a substituted alkyne, the ene reaction path leading to allenes has an energy barrier somewhat lower than the stepwise diradical mechanism for the cyclobutene-fused derivative formation, thus explaining the outcome of the reaction. PMID:17523605

Güell, Mireia; Martín, Nazario; Altable, Margarita; Filippone, Salvatore; Martín-Domenech, Angel; Solà, Miquel

2007-06-21

364

Thermodynamics of coupled reactions by the amplitudes of chemical relaxation  

Microsoft Academic Search

The amplitudes of the relaxation curves, as obtained by the Temperature-jump method have been used to measure simultaneously\\u000a equilibrium constant and enthalpy for the reaction of complex formation of Ni2+ ion by 2,6-dihydroxobenzoic acid in the presence of a buffer. The experiments have been performed by changing the concentration\\u000a of metal ion at constant ligand concentration andpH as in a

F. Secco; Marcella Venturini

1994-01-01

365

Exploring the limits of ultrafast polymerase chain reaction using liquid for thermal heat exchange: A proof of principle  

NASA Astrophysics Data System (ADS)

Thermal ramp rate is a major limiting factor in using real-time polymerase chain reaction (PCR) for routine diagnostics. We explored the limits of speed by using liquid for thermal exchange rather than metal as in traditional devices, and by testing different polymerases. In a clinical setting, our system equaled or surpassed state-of-the-art devices for accuracy in amplifying DNA/RNA of avian influenza, cytomegalovirus, and human immunodeficiency virus. Using Thermococcus kodakaraensis polymerase and optimizing both electrical and chemical systems, we obtained an accurate, 35 cycle amplification of an 85-base pair fragment of E. coli O157:H7 Shiga toxin gene in as little as 94.1 s, a significant improvement over a typical 1 h PCR amplification.

Maltezos, George; Johnston, Matthew; Taganov, Konstantin; Srichantaratsamee, Chutatip; Gorman, John; Baltimore, David; Chantratita, Wasun; Scherer, Axel

2010-12-01

366

Effect of Finite-rate Chemical Reactions on Turbulence in Hypersonic Turbulent Boundary Layers  

E-print Network

Effect of Finite-rate Chemical Reactions on Turbulence in Hypersonic Turbulent Boundary Layers Lian on future air-breathing hypersonic cruise vehicles will be turbulent and chemically reacting. To aid the design of such vehicles, a greater understanding of turbulent hypersonic flows is needed. Although

Martín, Pino

367

Valence-bond description of chemical reactions on Born-Oppenheimer molecular dynamics trajectories  

Microsoft Academic Search

The nature of chemical bonds on dynamic paths was investigated using the complete active space valence-bond (CASVB) method and the Born-Oppenheimer dynamics. To extract the chemical bond picture during reactions, a scheme to collect contributions from several VB (resonance) structures into a small numbers of indices was introduced. In this scheme, a tree diagram for the VB structures is constructed

Nao Noguchi; Haruyuki Nakano

2009-01-01

368

WORKSHOP ON STATUS OF TEST METHODS FOR ASSESSING POTENTIAL OF CHEMICALS TO INDUCE RESPIRATORY ALLERGIC REACTIONS  

EPA Science Inventory

Because of the association between allergy and asthma and the increasing incidence of morbidity and mortality due to asthma, there is growing concern over the potential of industrial chemicals to produce allergic reactions in the respiratory tract. Two classes of chemicals have b...

369

Stochastic resonance in the absence and presence of external signals for a chemical reaction  

E-print Network

Stochastic resonance in the absence and presence of external signals for a chemical reaction Lingfa Yang, Zhonghuai Hou, and Houwen Xina) Department of Chemical Physics, University of Science random perturbation. Noise-induced oscillations and noise-induced frequency shifts have been observed

Yang, Lingfa

370

A comprehensive detailed chemical kinetic reaction mechanism for combustion of nalkane  

E-print Network

A comprehensive detailed chemical kinetic reaction mechanism for combustion of nalkane 94550, USA b University College of Ireland, Galway, Ireland Abstract Detailed chemical, published in "Combustion and Flame 156 (2008) 181-199" DOI : 10.1016/j.combustflame.2008.07.014 #12

Paris-Sud XI, Université de

371

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

E-print Network

and cylindrical nanopores Alexandr Malijevský1,2,a and Martin Lísal2,3 1 Department of Chemical Engineering challenges of the statistical mechanics of liquids presents a desire for reliable description of fluid con, the impact of confinement does not change only the phase behavior of a fluid but affects also its chemical

Lisal, Martin

372

Thermal distributions in stellar plasmas, nuclear reactions and solar neutrinos  

E-print Network

The physics of nuclear reactions in stellar plasma is reviewed with special emphasis on the importance of the velocity distribution of ions. Then the properties (density and temperature) of the weak-coupled solar plasma are analysed, showing that the ion velocities should deviate from the Maxwellian distribution and could be better described by a weakly-nonexstensive (|q-1|<0.02) Tsallis' distribution. We discuss concrete physical frameworks for calculating this deviation: the introduction of higher-order corrections to the diffusion and friction coefficients in the Fokker-Plank equation, the influence of the electric-microfield stochastic distribution on the particle dynamics, a velocity correlation function with long-time memory arising from the coupling of the collective and individual degrees of freedom. Finally, we study the effects of such deviations on stellar nuclear rates, on the solar neutrino fluxes, and on the pp neutrino energy spectrum, and analyse the consequences for the solar neutrino problem.

M. Coraddu; G. Kaniadakis; A. Lavagno; M. Lissia; G. Mezzorani; P. Quarati

1998-11-24

373

KEMOD: A mixed chemical kinetic and equilibrium model of aqueous and solid phase geochemical reactions  

SciTech Connect

This report presents the development of a mixed chemical Kinetic and Equilibrium MODel in which every chemical species can be treated either as a equilibrium-controlled or as a kinetically controlled reaction. The reaction processes include aqueous complexation, adsorption/desorption, ion exchange, precipitation/dissolution, oxidation/reduction, and acid/base reactions. Further development and modification of KEMOD can be made in: (1) inclusion of species switching solution algorithms, (2) incorporation of the effect of temperature and pressure on equilibrium and rate constants, and (3) extension to high ionic strength.

Yeh, G.T.; Iskra, G.A. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Civil Engineering; Szecsody, J.E.; Zachara, J.M.; Streile, G.P. [Pacific Northwest Lab., Richland, WA (United States)

1995-01-01

374

RPMDRATE: Bimolecular chemical reaction rates from ring polymer molecular dynamics  

NASA Astrophysics Data System (ADS)

We present RPMDRATE, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH4, OH+CH4 and H+C2H6 reactions. Catalogue identifier: AENW_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AENW_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: MIT license No. of lines in distributed program, including test data, etc.: 94512 No. of bytes in distributed program, including test data, etc.: 1395674 Distribution format: tar.gz Programming language: Fortran 90/95, Python (version 2.6.x or later, including any version of Python 3, is recommended). Computer: Not computer specific. Operating system: Any for which Python, Fortran 90/95 compiler and the required external routines are available. Has the code been vectorized or parallelized?: The program can efficiently utilize 4096+ processors, depending on problem and available computer. At low temperatures, 110 processors are reasonable for a typical umbrella integration run with an analytic potential energy function and gradients on the latest x86-64 machines.

Suleimanov, Yu. V.; Allen, J. W.; Green, W. H.

2013-03-01

375

Force-activated reactivity switch in a bimolecular chemical reaction at the single molecule level  

NASA Astrophysics Data System (ADS)

Mechanical force is a distinct and usually less explored way to activate chemical reaction because it can deform the reacting molecules along a well-defined direction of the reaction coordinate. However, the effect of mechanical force on the free- energy surface that governs a chemical reaction is still 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 some reducing agents in a bimolecular substitution reaction (so-called SN2). 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 SN2 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 SN2 chemical reactions. Our experiments directly demonstrate the action of a force-activated switch in the chemical reactivity of a single molecule. References: S. Garcia-Manyes, J. Liang, R. Szoszkiewicz, T-L. Kuo and J. M. Fernandez, Nature Chemistry, 1, 236-242, 2009.

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

2009-10-01

376

The Modification of Biocellular Chemical Reactions by Environmental Physicochemicals  

NASA Astrophysics Data System (ADS)

Environmental risk factors affect human biological system to different extent from modification of biochemical reaction to cellular catastrophe. There are considerable public concerns about electromagnetic fields and endocrine disruptors. Their risk assessments have not been fully achieved because of their scientific uncertainty: electromagnetic fields just modify the bioreaction in the restricted cells and endocrine disruptors are quite unique in that their expression is dependent on the exposure periods throughout a life. Thus, we here describe their molecular characterization to establish the new risk assessments for environmental physicochemicals.

Ishido, M.

377

Detailed Chemical Kinetic Reaction Mechanisms for Incineration of Organophosphorus and Fluoro-Organophosphorus Compounds  

SciTech Connect

A detailed chemical kinetic reaction mechanism is developed to describe incineration of the chemical warfare nerve agent sarin (GB), based on commonly used principles of bond additivity and hierarchical reaction mechanisms. The mechanism is based on previous kinetic models of organophosphorus compounds such as TMP, DMMP and DIMP that are often used as surrogates to predict incineration of GB. Kinetic models of the three surrogates and GB are then used to predict their consumption in a perfectly stirred reactor fueled by natural gas to simulate incineration of these chemicals. Computed results indicate that DIMP is the only one of these surrogates that adequately describes combustion of GB under comparable conditions. The kinetic pathways responsible for these differences in reactivity are identified and discussed. The most important reaction in GB and DIMP that makes them more reactive than TMP or DMMP is found to be a six-center molecular elimination reaction producing propene.

Glaude, P A; Melius, C; Pitz, W J; Westbrook, C K

2001-12-13

378

Photothermal-reaction-assisted two-photon lithography of silver nanocrystals capped with thermally cleavable ligands  

SciTech Connect

We report an alternative approach to produce micropatterns of metallic nanoparticles using photothermal-reaction-assisted two-photon direct laser writing. The patterns are achieved using a facile surface treatment of silver nanoparticles (Ag NPs) functionalized with thermally cleavable ligands; N-(tert-butoxycarbonyl)-L-cysteine methyl ester. The ligand cleavage initiated by pulsed laser-induced thermal reaction results in a significant change in dispersiblility of the nanocrystals, thereby enabling a solvent-selective development process after photopatterning. We demonstrated that Ag NP patterns with submicron linewidths can be achieved using near infrared pulsed laser illumination.

Kim, Won Jin; Vidal, Xavier; Baev, Alexander; Jee, Hong Sub; Swihart, Mark T.; Prasad, Paras N. [Department of Chemistry, Institute for Lasers, Photonics, and Biophotonics, University at Buffalo, State University of New York, Buffalo, New York 14260 (United States)

2011-03-28

379

Theoretical Chemical Dynamics Studies of Elementary Combustion Reactions  

SciTech Connect

The objective of this research was to develop and apply methods for more accurate predictions of reaction rates based on high-level quantum chemistry. We have developed and applied efficient, robust methods for fitting global ab initio potential energy surfaces (PESs) for both spectroscopy and dynamics calculations and for performing direct dynamics simulations. Our approach addresses the problem that high-level quantum calculations are often too costly in computer time for practical applications resulting in the use of levels of theory that are often inadequate for reactions. A critical objective was to develop practical methods that require the minimum number of electronic structure calculations for acceptable fidelity to the ab initio PES. Our method does this by a procedure that determines the optimal configurations at which ab initio points are computed, and that ensures that the final fitted PES is uniformly accurate to a prescribed tolerance. Our fitting methods can be done automatically, with little or no human intervention, and with no prior knowledge of the topology of the PES. The methods are based on local fitting schemes using interpolating moving least-squares (IMLS). IMLS has advantages over the very effective modified-Shepard methods developed by Collins and others in that higher-order polynomials can be used and does not require derivatives but can benefit from them if available.

Donald L. Thompson

2009-09-30

380

Thermal and high pressure intramolecular Diels-Alder reaction of vinylsulfonamides.  

PubMed

Vinylsulfonamides with a furan, carbocyclic, semicyclic or acyclic 1,3-diene moiety are synthetized via a domino elimination-amidation reaction of 2-chloroethanesulfonyl chloride. Intramolecular Diels-Alder reaction of these vinylsulfonamides with thermal (toluene, 110 degrees C) or high pressure (dichloromethane, 13 kbar) activation provides efficient access to a range of gamma- and delta-sultams following a 2-3 d long synthetic procedure. Enantiopure sultams are readily obtained from N-1-phenylethyl substituted vinylsulfonamides. PMID:17406571

Rogachev, Victor O; Metz, Peter

2006-01-01

381

Thermal properties of light nuclei from 12 fusion-evaporation reactions2  

E-print Network

Thermal properties of light nuclei from 12 C+12 C1 fusion-evaporation reactions2 L Morelli1 , G-Magurele, POB-MG6, Romania19 E-mail: luca.morelli@bo.infn.it20 Abstract. The 12 C+12 C reaction at 95 MeV has density of light nuclei above the threshold for particle emission. In particular, a fast29 increase

Paris-Sud XI, Université de

382

Atmospheric chemical and thermal structure evolution after one Titan year  

NASA Astrophysics Data System (ADS)

Our radiative transfer code (ARTT) was applied to Cassini Composite Infrared Spectrometer (CIRS) data taken during Titan flybys from 2004-2010 and to the 1980 Voyager 1 flyby values inferred from the re-analysis of the Infrared Radiometer Spectrometer (IRIS) spectra [1], as well as to the intervening ground- and space- based observations (such as with ISO, [2]), providing us with a new view of the stratospheric evolution over a Titanian year (V1 encounter Ls=9° was reached in mid-2010). CIRS nadir and limb spectral [3,4] show variations in temperature and chemical composition in the stratosphere during the Cassini mission, before and after the Northern Spring Equinox (NSE). We find indication for a weakening of the temperature gradient with warming of the stratosphere and cooling of the lower mesosphere. In addition, we infer precise concentrations for the trace gases and their main isotopologues and find that the chemical composition in Titan's stratosphere varied significantly with latitude during the 6 terrestrial years investigated here, with increased mixing ratios towards the northern latitudes. In particular, we find a maximum enhancement of several gases observed at northern latitudes up to 50°N around mid-2009, at the time of the NSE. We find that this raise is followed by a rapid decrease in chemical inventory in 2010 probably due to changes in the cross vortex mixing or northward migration of the vortex boundary [5,6,7] consistent with the weakening thermal gradient. The finding also ties into the location of the maximum temperature gradient, which appears to be moving northward over the winter/spring season. The return of today's abundances close to the Voyager values (at the same season) is an indication that, as for the Earth, the solar radiation dominates over the other energy sources even at 10AU [8]. Nevertheless, the differences observed for some complex hydrocarbons in the North pole indicate that the other processes could be at play as well, for example the variability of the solar insolation itself through the 11-year solar cycle. We show indeed that wrt V1 the stratospheric composition shows higher values near the northern fall equinox (1997) and lower ones at the spring equinox (2009). An additional cause could be spatial changes (due to Titan's inclination) in the energy input to Titan's atmosphere as a driver for changes in the advection patterns, circulation, etc which eventually provide a stronger variability in the latitudinal abundances of photochemical species. Circulation and photochemical models must satisfy the constraints set by these results, but further observations will have to come from the next summer solstice (2017) and for a complete new Titan year in 2027. References: [1] Coustenis, A., Bézard, B., Icarus 115, 126, 1995. [2] Coustenis, A., et al., Icarus 161, 383, 2003. [3] Coustenis, A., et al., Icarus 207, 461, 2010. [4] Vinatier, S., et al., Icarus, 205, 559, 2010. [5] Bampasidis et al., ApJ, 760, 144, 2012. [6] Teanby et al., Astrophys. J. 724, L84-L89 (2010). [7] Teanby et al., Nature, 491, 732, 2012, [8] Coustenis, A., et al., in preparation, 2013.

Coustenis, Athena; Bampasidis, Georgios; Achterberg, Richard; Lavvas, Panayiotis; Vinatier, Sandrine; Nixon, Conor; Jennings, Donald; Teanby, Nicolas; Flasar, F. Michael; Carlson, Ronald; Orton, Glenn; Romani, Paul; Guandique, Ever

2013-04-01

383

Chemical reactions and fluctuations. Exact substitute processes for diffusion-reaction systems with exclusion rules  

NASA Astrophysics Data System (ADS)

Lattice systems with one species diffusion-reaction processes under local complete exclusion rules are studied analytically. We discuss a rigorously derived Fokker-Planck equation for a so-called pseudo-probability. This probability distribution depends on continuous variables in contrast to the original discrete master equation, and their stochastic dynamics may be interpreted as a substitute process which is completely equivalent to the original lattice dynamics. Especially, averages and correlation functions of the continuous variables are connected to corresponding lattice quantities by simple relations. Although the substitute process for diffusion-reaction systems with exclusion rules has some similarities to the well known substitute process for the same system without exclusion rules, their exist a set of remarkable differences. The given approach is not only valid for the discussed single species processes. We give sufficient arguments that arbitrary combinations of uni-molecular and bimolecular lattice reactions under complete local exclusions may be described in terms of our approach.

Schulz, M.

2008-07-01

384

Investigation of shock-induced and shock-assisted chemical reactions in molybdenum-silicon powder mixtures  

NASA Astrophysics Data System (ADS)

In this research, chemical reactions occurring in molybdenum and silicon powder mixtures under "shock-induced" (those occurring during the high-pressure shock state) and "shock-assisted" (those occurring subsequent to the shock event, but due to bulk temperature increases) conditions were investigated. Differences in the densities and yield strengths of the two constituents, in addition to the large heat of reaction associated with molybdenum disilicide (MoSi2) formation can lead to shock-induced as well as shock-assisted reactions, which make this an ideal system to delineate the kinetics and mechanisms of reactions occurring in shock-compressed powder mixtures. Shock recovery experiments performed on Mo + 2 Si powder mixtures employing cylindrical implosion geometry showed thermally initiated reactions. A mixed phase eutectic type microstructure of MoSi2 and Mo 5Si3, resulting from reaction occurring due to melting of both reactants, was observed in axial regions of the cylindrical compacts. In regions surrounding the mach stem, melting of only silicon and reaction occurring via dissolution and re-precipitation forming MoSi2 spherules surrounding molybdenum particles in a melted and solidified silicon matrix was observed. The planar pressure shock recovery geometry showed a single phase MoSi2, microstructure formed due to a solid-state pressure-induced reaction process. The time-resolved instrumented experiments were performed using a single stage gas gun in the velocity range of 500 m/s to 1 km/s, and employed poly-vinyl di-flouride (PVDF) stress gauges placed at the front and rear surfaces of the powder to determine the crush strength, densification history, and reaction initiation threshold conditions. Time-resolved experiments performed on ˜58% dense Mo + 2 Si powder mixtures at input stresses less than 4 GPa, showed characteristics of powder densification and dispersed propagated wave stress profiles with rise time >˜40 nanoseconds. At input stress between 4--6 GPa, the powder mixtures showed a sharp rise time (<˜10 ns) of propagated wave profile and an expanded state of products revealing conclusive evidence of shock-induced reaction. At input stresses greater than 6 GPa, the powder mixtures showed a lower rise time and transition to a low-compressibility (melt) state indicating lack of shock-induced reaction. The results of this work show that (a) premature formation of a melt phase restricts mixing between reactants and inhibits "shock-induced" reaction initiation, although "shock-assisted" reactions can still occur in time scales of thermal equilibrium, and (b) the crush strength of powder mixtures is the most important parameter that controls initiation of a "shock-induced" reaction. Reaction synthesis experiments conducted on 55--95% dense Mo + 2 Si powder mixture compacts under an applied electric field showed that SHS reactions that would have normally become extinguished without the application of electric field, were observed to be self-sustained. Under such conditions, the reaction kinetics were observed to be enhanced and the reaction products showed a highly refined microstructure.

Vandersall, Kevin Stewart

1999-10-01

385

The Unrestricted Hartree-Fock Theory of Chemical Reactions. I The Electronic Instabilities in the Chemical Reactions and the Solutions of the Unrestricted SCF LCAO MO Equation for the Homopolar Two-Center Two-Electron System  

Microsoft Academic Search

It is shown that the conventional closed shell type ground state solution of SCF LCAO MO equation, which satisfies the requirement of the symmetry, may become unstable in the course of chemical reactions. The instability of the conventional SCF ground state in the chemical reactions, is indicated for the dissociation reaction of a hydrogen molecule, the internal rotation of an

Hideo Fukutome

1972-01-01

386

Students' Dilemmas in Reaction Stoichiometry Problem Solving: Deducing the Limiting Reagent in Chemical Reactions  

ERIC Educational Resources Information Center

A qualitative case study was conducted to investigate the understanding of the limiting reagent concept and the strategies used by five Year 11 students when solving four reaction stoichiometry problems. Students' written problem-solving strategies were studied using the think-aloud protocol during problem-solving, and retrospective verbalisations…

Chandrasegaran, A. L.; Treagust, David F.; Waldrip, Bruce G.; Chandrasegaran, Antonia

2009-01-01

387

A study of the effects of solid phase reactions on the thermal degradation and ballistic properties of solid propellants  

NASA Technical Reports Server (NTRS)

The thermal stability of perchlorate composite propellants was studied at 135 and 170 C. The experimental efforts were concentrated on determining the importance of heterogeneous oxidizer-fuel reactions in the thermal degradation process. The experimental approach used to elucidate the mechanisms by which the oxidizer fuel composites thermally degrade was divided into two parts: (1) keeping the fuel constant and varying the nature of the oxidizers, and (2) holding the oxidizer constant and varying the fuel components. The fuel component primarily utilized in the first phase was polyethylene. Oxidizers included KClO4, KClO3, NH4ClO4 and NH4ClO4 doped with materials such as chlorate, phosphate and arsenate. In the second phase the oxidizer used was primarily NH4ClO4 while the fuels included saturated and unsaturated polybutadiene prepolymers and a series of bonding agents. Techniques employed in the current study include thermogravimetric measurements, differential thermal analysis, infrared, mass spectrometry, electron microscopy, and appropriate wet chemical analysis.

Schmidt, W. G.

1974-01-01

388

Dynamic control and information processing in chemical reaction systems by tuning self-organization behavior  

NASA Astrophysics Data System (ADS)

Specific external control of chemical reaction systems and both dynamic control and signal processing as central functions in biochemical reaction systems are important issues of modern nonlinear science. For example nonlinear input-output behavior and its regulation are crucial for the maintainance of the life process that requires extensive communication between cells and their environment. An important question is how the dynamical behavior of biochemical systems is controlled and how they process information transmitted by incoming signals. But also from a general point of view external forcing of complex chemical reaction processes is important in many application areas ranging from chemical engineering to biomedicine. In order to study such control issues numerically, here, we choose a well characterized chemical system, the CO oxidation on Pt(110), which is interesting per se as an externally forced chemical oscillator model. We show numerically that tuning of temporal self-organization by input signals in this simple nonlinear chemical reaction exhibiting oscillatory behavior can in principle be exploited for both specific external control of dynamical system behavior and processing of complex information.

Lebiedz, Dirk; Brandt-Pollmann, Ulrich

2004-09-01

389

Molecular Dynamics Simulations of Nonequilibrium Effects Associated with Thermally Activated Exothermic Reactions  

Microsoft Academic Search

In this paper we discuss the influence of nonequilibrium effects on the rate of a thermally activated, exothermic reaction. The system with a binary process AA B B +?+ + {} energy is considered as an example, on which we compare molecular dynamics simulations with a simple phenomenology based on the assumption that a nonequilibrium state can be characterized by

Jerzy GORECKI; Joanna Natalia GORECKA

390

Nonisothermal Thermal Decomposition Reaction Kinetics of Double-base Propellant Catalyzed with Lanthanum Citrate  

Microsoft Academic Search

The decomposition reaction kinetics of the double-base (DB) rocket propellant composed of the mixed ester of triethyleneglycol dinitrate (TEGDN) and nitroglycerin (NG), and nitrocellulose (NC) with lanthanum citrate as a combustion catalyst was investigated by thermogravimetry and differential thermogravimetry (TG-DTG), and differential scanning calorimetry (DSC) under atmospheric pressure and flowing nitrogen gas conditions. The results showed that the thermal decomposition

Jianhua Yi; Fengqi Zhao; Siyu Xu; Hongxu Gao; Rongzu Hu; Haixia Hao; Qing Pei; Yin Gao

2007-01-01

391

Simplified Combustion Modeling of Double Base Propellant: Gas Phase Chain Reaction Vs. Thermal Decomposition  

Microsoft Academic Search

Simplified combustion modeling of nitrocellulose (NC), nitroglycerin (NG) double base propellant is considered. Two models with simple but rational chemistry are compared: the classical thermal decomposition, high gas activation energy (Eg\\/RT> > 1) Denison-Baum-Williams (DBW) model, and a new chain reaction, low gas activation energy (Eg\\/RT < < 1) model recently proposed by Ward, Son, and Brewster (WSB). Both models

M. Q. BREWSTER; M. J. WARD; S. F. SON

2000-01-01

392

Blends and Reaction Products Prepared from Phenolic Resin and Waste PET. II. Thermal Oxidative Degradation  

Microsoft Academic Search

High ortho novolactype phenolic resin and waste poly(ethylene terephthalate) (PET) were used to prepare blends and reaction products. The effect of PET on the thermal oxidative stability of these products was investigated with thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and fourier transform infrared spectroscopy (FTIR). It was determined that presence of PET in blends improved the stability and in

Tülin Banu ?yim; Saadet Özgümü?; Murat Orbay

2003-01-01

393

Ene reactions between two alkynes? Doors open to thermally induced cycloisomerization of macrocyclic triynes and enediynes.  

PubMed

A domino process is described combining an ene reaction between two alkynes and a Diels-Alder cycloaddition of the vinylallene formed. The process accounts for the thermally induced cycloisomerization of macrocyclic triynes and enediynes to give fused tetracycles in a stereoselective manner. PMID:20386831

González, Iván; Pla-Quintana, Anna; Roglans, Anna; Dachs, Anna; Solà, Miquel; Parella, Teodor; Farjas, Jordi; Roura, Pere; Lloveras, Vega; Vidal-Gancedo, José

2010-05-01

394

Supercritical fluid phase separations induced by chemical reactions  

SciTech Connect

Our statistical mechanical studies predict that a chemically reactive system containing species composed of C, H, N, O atoms can exhibit a phase separation into a N{sub 2}-rich and a N{sub 2}-poor phase. The preset work is concerned with the effect of the fluid phase separation upon addition of F atoms in the system. Our study shows that F atoms mainly appear as a constituent of HF in a N{sub 2}-poor fluid phase up to a certain pressure beyond which they occur as CF{sub 4} in a N{sub 2}-rich phase and that the phase separation may be abrupt in thermodynamic sense. The pressure at the phase boundary can occur at about 30 GPa at 3000 K and about 10 GPa to 20 GPa at 1000 K.Some of these ranges maybe accessible by present-day experimental high-pressure techniques. We discuss implications of this study to detonation physics.

Ree, F.H.; Viecelli, J.A.; van Thiel, M.

1997-11-01

395

Coupling quantum interpretative techniques: another look at chemical mechanisms in organic reactions  

PubMed Central

A cross ELF-NCI analysis is tested over prototypical organic reactions. The synergetic use of ELF and NCI enables the understanding of reaction mechanisms since each method can respectively identify regions of strong and weak electron pairing. Chemically intuitive results are recovered and enriched by the identification of new features. Non covalent interactions are found to foresee the evolution of the reaction from the initial steps. Within NCI, no topological catastrophe is observed as changes are continuous to such an extent that future reaction steps can be predicted from the evolution of the initial NCI critical points. Indeed, strong convergences through the reaction paths between ELF and NCI critical points enable to identify key interactions at the origin of the bond formation. VMD scripts enabling the automatic generation of movies depicting the cross NCI/ELF analysis along a reaction path (or following a Born-Oppenheimer molecular dynamics trajectory) are provided as S.I. PMID:23185140

Gillet, Natacha; Chaudret, Robin; Contreras-Garc?a, Julia; Yang, Weitao; Silvi, Bernard; Piquemal, Jean-Philip

2012-01-01

396

Coupling quantum interpretative techniques: another look at chemical mechanisms in organic reactions.  

PubMed

A cross ELF-NCI analysis is tested over prototypical organic reactions. The synergetic use of ELF and NCI enables the understanding of reaction mechanisms since each method can respectively identify regions of strong and weak electron pairing. Chemically intuitive results are recovered and enriched by the identification of new features. Non covalent interactions are found to foresee the evolution of the reaction from the initial steps. Within NCI, no topological catastrophe is observed as changes are continuous to such an extent that future reaction steps can be predicted from the evolution of the initial NCI critical points. Indeed, strong convergences through the reaction paths between ELF and NCI critical points enable to identify key interactions at the origin of the bond formation. VMD scripts enabling the automatic generation of movies depicting the cross NCI/ELF analysis along a reaction path (or following a Born-Oppenheimer molecular dynamics trajectory) are provided as S.I. PMID:23185140

Gillet, Natacha; Chaudret, Robin; Contreras-Garc?a, Julia; Yang, Weitao; Silvi, Bernard; Piquemal, Jean-Philip

2012-11-13

397

Chemical reactions of conformationally selected 3-aminophenol molecules in a beam with Coulomb-crystallized Ca+ ions  

NASA Astrophysics Data System (ADS)

Many molecules exhibit multiple conformers that often easily interconvert under thermal conditions. Therefore, single conformations are difficult to isolate which renders the study of their distinct chemical reactivities challenging. We have recently reported a new experimental method for the characterization of conformer-specific effects in chemical reactions [Y.-P. Chang, K. D?ugo??cki, J. Küpper, D. Rösch, D. Wild, and S. Willitsch, "Specific chemical reactivities of spatially separated 3-aminophenol conformers with cold Ca+ ions," Science 342, 98-101 (2013)]. Different conformers are spatially separated using inhomogeneous electric fields and reacted with a Coulomb crystal of cold, spatially localized ions in a trap. As a first application, we studied reactions between the two conformers of 3-aminophenol and Ca+. We observed a twofold larger rate constant for the cis compared to the trans conformer which was rationalized in terms of the differences in the long-range ion-molecule interactions. The present article provides a detailed description of the new method and a full account of the experimental results as well as the accompanying theoretical calculations.

Rösch, Daniel; Willitsch, Stefan; Chang, Yuan-Pin; Küpper, Jochen

2014-03-01

398

The Role of Comprehensive Detailed Chemical Kinetic Reaction Mechanisms in Combustion Research  

SciTech Connect

Recent developments by the authors in the field of comprehensive detailed chemical kinetic reaction mechanisms for hydrocarbon fuels are reviewed. Examples are given of how these mechanisms provide fundamental chemical insights into a range of combustion applications. Practical combustion consists primarily of chemical heat release from reactions between a fuel and an oxidizer, and computer simulations of practical combustion systems have become an essential tool of combustion research (Westbrook et al., 2005). At the heart of most combustion simulations, the chemical kinetic submodel frequently is the most detailed, complex and computationally costly part of a system model. Historically, the chemical submodel equations are solved using time-implicit numerical algorithms, due to the extreme stiffness of the coupled rate equations, with a computational cost that varies roughly with the cube of the number of chemical species in the model. While early mechanisms (c. 1980) for apparently simple fuels such as methane (Warnatz, 1980) or methanol (Westbrook and Dryer, 1979) included perhaps 25 species, current detailed mechanisms for much larger, more complex fuels such as hexadecane (Fournet et al., 2001; Ristori et al., 2001; Westbrook et al., 2008) or methyl ester methyl decanoate (Herbinet et al., 2008) have as many as 2000 or even 3000 species. Rapid growth in capabilities of modern computers has been an essential feature in this rapid growth in the size and complexity of chemical kinetic reaction mechanisms.

Westbrook, C K; Pitz, W J; Curran, H J; Mehl, M

2008-07-16

399

The reaction efficiency of thermal energy oxygen atoms with polymeric materials  

NASA Technical Reports Server (NTRS)

The reaction efficiency of several polymeric materials with thermal-energy (0.04 eV translational energy), ground-state (O3P) oxygen atoms was determined by exposing the materials to a room temperature gas containing a known concentration of atomic oxygen. The reaction efficiency measurements were conducted in two flowing afterglow systems of different configuration. Atomic oxygen concentration measurements, flow, transport and surface dose analysis is presented in this paper. The measured reaction efficiencies of Kapton, Mylar, polyethylene, D4-polyethylene and Tedlar are .001 to .0001 those determined with high-energy ground-state oxygen atoms in low earth orbit or in a high-velocity atom beam. D4-polyethylene exhibits a large kinetic isotope effect with atomic oxygen at thermal but not hyperthermal atom energies.

Koontz, S. L.; Nordine, Paul

1990-01-01

400

New chemical hydrogen storage materials exploiting the self-sustaining thermal decomposition of guanidinium borohydride.  

PubMed

Guanidinium borohydride (GBH) was structurally characterized by single-crystal X-ray diffraction and found to release more than 10 wt% H(2) as a fairly pure stream during a self-sustaining thermal decomposition reaction both with and without additives that were identified to reduce the concentration of the main ammonia impurity and control the reaction sustainability. PMID:19462096

Groshens, Thomas J; Hollins, Richard A

2009-06-01

401

A nanochannel fabrication technique using chemical-mechanical polishing (CMP) and thermal oxidation  

NASA Technical Reports Server (NTRS)

We have developed a new nanochannel fabrication technique using chemical-mechanical polishing (CMP) and thermal oxidation. With this technique, it is possible to control the width, length, and depth of the nanochannels without the need for nanolithography.

Lee, C.; Yang, E. H.; Myung, N. V.; George, T.

2003-01-01

402

A partial-propensity formulation of the stochastic simulation algorithm for chemical reaction networks with delays  

NASA Astrophysics Data System (ADS)

Several real-world systems, such as gene expression networks in biological cells, contain coupled chemical reactions with a time delay between reaction initiation and completion. The non-Markovian kinetics of such reaction networks can be exactly simulated using the delay stochastic simulation algorithm (dSSA). The computational cost of dSSA scales with the total number of reactions in the network. We reduce this cost to scale at most with the smaller number of species by using the concept of partial reaction propensities. The resulting delay partial-propensity direct method (dPDM) is an exact dSSA formulation for well-stirred systems of coupled chemical reactions with delays. We detail dPDM and present a theoretical analysis of its computational cost. Furthermore, we demonstrate the implications of the theoretical cost analysis in two prototypical benchmark applications. The dPDM formulation is shown to be particularly efficient for strongly coupled reaction networks, where the number of reactions is much larger than the number of species.

Ramaswamy, Rajesh; Sbalzarini, Ivo F.

2011-01-01

403

Thermal–hydrologic–mechanical–chemical processes in the evolution of engineered geothermal reservoirs  

Microsoft Academic Search

In a companion paper [Taron J, Elsworth D, Min K-B. Numerical simulation of thermal–hydrologic–mechanical–chemical processes in deformable, fractured porous media. Int J Rock Mech Min Sci 2009; doi:10.1016\\/j.ijrmms.2009.01.008] we introduced a new methodology and numerical simulator for the modeling of thermal–hydrologic–mechanical–chemical processes in dual-porosity media. In this paper we utilize the model to examine some of the dominant behaviors and

Joshua Taron; Derek Elsworth

2009-01-01

404

Provenance matters: thermal reaction norms for embryo survival among sockeye salmon Oncorhynchus nerka populations.  

PubMed

Differences in thermal tolerance during embryonic development in Fraser River sockeye salmon Oncorhynchus nerka were examined among nine populations in a controlled common-garden incubation experiment. Forcing embryonic development at an extreme temperature (relative to current values) of 16° C, representing a future climate change scenario, significantly reduced survival compared to the more ecologically moderate temperature of 10° C (55% v. 93%). Survival at 14° C was intermediate between the other two temperatures (85%). More importantly, this survival response varied by provenance within and between temperature treatments. Thermal reaction norms showed an interacting response of genotype and environment (temperature), suggesting that populations of O. nerka may have adapted differentially to elevated temperatures during incubation and early development. Moreover, populations that historically experience warmer incubation temperatures at early development displayed a higher tolerance for warm temperatures. In contrast, thermal tolerance does not appear to transcend life stages as adult migration temperatures were not related to embryo thermal tolerance. The intra-population variation implies potential for thermal tolerance at the species level. The differential inter-population variation in thermal tolerance that was observed suggests, however, limited adaptive potential to thermal shifts for some populations. This infers that the intergenerational effects of increasing water temperatures may affect populations differentially, and that such thermally mediated adaptive selection may drive population, and therefore species, persistence. PMID:23557297

Whitney, C K; Hinch, S G; Patterson, D A

2013-04-01

405

Modeling of multiphase flow with solidification and chemical reaction in materials processing  

NASA Astrophysics Data System (ADS)

Understanding of multiphase flow and related heat transfer and chemical reactions are the keys to increase the productivity and efficiency in industrial processes. The objective of this thesis is to utilize the computational approaches to investigate the multiphase flow and its application in the materials processes, especially in the following two areas: directional solidification, and pyrolysis and synthesis. In this thesis, numerical simulations will be performed for crystal growth of several III-V and II-VI compounds. The effects of Prandtl and Grashof numbers on the axial temperature profile, the solidification interface shape, and melt flow are investigated. For the material with high Prandtl and Grashof numbers, temperature field and growth interface will be significantly influenced by melt flow, resulting in the complicated temperature distribution and curved interface shape, so it will encounter tremendous difficulty using a traditional Bridgman growth system. A new design is proposed to reduce the melt convection. The geometric configuration of top cold and bottom hot in the melt will dramatically reduce the melt convection. The new design has been employed to simulate the melt flow and heat transfer in crystal growth with large Prandtl and Grashof numbers and the design parameters have been adjusted. Over 90% of commercial solar cells are made from silicon and directional solidification system is the one of the most important method to produce multi-crystalline silicon ingots due to its tolerance to feedstock impurities and lower manufacturing cost. A numerical model is developed to simulate the silicon ingot directional solidification process. Temperature distribution and solidification interface location are presented. Heat transfer and solidification analysis are performed to determine the energy efficiency of the silicon production furnace. Possible improvements are identified. The silicon growth process is controlled by adjusting heating power and moving the side insulation layer upward. It is possible to produce high quality crystal with a good combination of heating and cooling. SiC based ceramic materials fabricated by polymer pyrolysis and synthesis becomes a promising candidate for nuclear applications. To obtain high uniformity of microstructure/concentration fuel without crack at high operating temperature, it is important to understand transport phenomena in material processing at different scale levels. In our prior work, a system level model based on reactive porous media theory was developed to account for the pyrolysis process in uranium-ceramic nuclear fabrication In this thesis, a particle level mesoscopic model based on the Smoothed Particle Hydrodynamics (SPH) is developed for modeling the synthesis of filler U3O8 particles and SiC matrix. The system-level model provides the thermal boundary conditions needed in the particle level simulation. The evolution of particle concentration and structure as well as composition of composite produced will be investigated. Since the process temperature and heat flux play the important roles in material quality and uniformity, the effects of heating rate at different directions, filler particle size and distribution on uniformity and microstructure of the final product are investigated. Uncertainty issue is also discussed. For the multiphase flow with directional solidification, a system level based on FVM is established. In this model, melt convection, temperature distribution, phase change and solidification interface can be investigated. For the multiphase flow with chemical reaction, a particle level model based on SPH method is developed to describe the pyrolysis and synthesis process of uranium-ceramic nuclear fuel. Due to its mesh-free nature, SPH can easily handle the problems with multi phases and components, large deformation, chemical reactions and even solidifications. A multi-scale meso-macroscopic approach, which combine a mesoscopic model based on SPH method and macroscopic model based on FVM, FEM and FDM, can be applied to even more com

Wei, Jiuan

406

Reactions of fluorescent probes with normal and chemically modified myelin.  

PubMed

The fluorescent probes 8-anilino-1-naphthalenesulfonate (ANS) and 2-p-toluidinylnaphthalene-6-sulfonate (TNS) bind to highly purified myelin membranes obtained from bovine brain white matter. Binding of the dyes was markedly increased by environmental conditions which reduce the negative surface potential of the membrane, i.e., cations (La-3+ is greater than Ca-2+ is greater than Na-+,K-+), H-+, local anesthetics, and the antibiotic polymyxin B. Chemical alteration of accessible membrane charged groups affected dye binding in a manner consistent with the hypothesis that such binding is primarily dependent upon the membrane surface potential. Thus, binding was increased by blocking of carboxyl groups via carbodiimide activation and subsequent coupling with neutral amino acid esters, and even more so with a basic amino acid ester (e.g., arginine methyl ester). Dye binding was reduced by succinylation of amino groups, and by hydrolysis of choline and ethanolamine head groups of phospho- and sphingolipids by phospholipase C. Phospholipase C treatment of myelin, or sphingomyelin vesicles, reduced or abolished the augmentation of ANS and TNS binding due to cations, local anesthetics, or polymyxin B. Energy transfer from myelin tryptophan residues to bound ANS occurs, but with low efficiency. Oxidation of membrane tryptophan residues with N-bromosuccinimide, or alkylation with 2-hydroxy (or methoxy)-5-nitrobenzyl bromide, markedly reduced intrinsic membrane fluorescence and energy transfer to bound ANS, but did not significantly affect dye binding or the quantum yield of ANS fluorescence when excitation was at 380nm. Proteolytic digestion removed 6-30% of myelin protein, depending upon the enzyme used, but had no effect on fluorescent dye binding. It is concluded that the binding of the anionic fluorescent probes ANS and TNS to myelin is primarily a function of the membrane surface charge density and net surface potential, as is the case with other biological membranes. Conclusions about the degree of dye binding to membrane lipids or membrane proteins cannot be drawn unless additional studies are carried out on isolated water soluble membrane proteins. PMID:238581

Feinstein, M B; Felsenfeld, H

1975-07-15

407

CHEMICAL AND BIOLOGICAL TREATMENT OF THERMALLY CONDITIONED SLUDGE RECYCLE LIQUORS  

EPA Science Inventory

The objective of this research project was to demonstrate and evaluate the feasibility of treating undiluted heat treatment liquor prior to its rerouting back to the head of the sewage treatment plant. Chemical and biological treatment processes were studied. Chemical treatment w...

408

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

Microsoft Academic Search

The use of reversible chemical reactions for energy transport and storage for parabolic dish networks is considered. Performance and cost characteristics are estimated for systems using three reactions (sulfur-trioxide decomposition, steam reforming of methane, and carbon-dioxide reforming of methane). Systems are considered with and without storage, and in several energy-delivery configurations that give different profiles of energy delivered versus temperature.

J. M. Schredder; T. Fujita

1984-01-01

409

Determination of riboflavin by the perturbation of active oxygen on a chemical oscillating reaction  

Microsoft Academic Search

This paper studies the perturbation of active oxygen (O2??H2O2) produced from the irradiated riboflavin on a chemical oscillating reaction, and a new and sensitive methodological approach for the determination of riboflavin is proposed based on it. An automatic experimental setup is designed to combine the irradiation of riboflavin with the analogous Belousov–Zhabotinskii reaction, which is implemented in a continuous-flow stirred

Zhang Ke; Ma Wanhong; Cai Ruxiu; Lin Zhixin; Gan Nanqin

2000-01-01

410

Quantum chemical study on influence of substituents and solvents in reaction complexing ethylene with nickel dithiolene  

Microsoft Academic Search

The influences induced by various terminal substituents and solvents on the reaction mechanism and chemical dynamics of complexing ethylene with Ni dithiolene are theoretically studied by using B3LYP method and Onsager model. It is shown that the reaction should be a two-step process, and the first step is the rate-determining step. We find that the rate constant of the rate-determining

Qing-Zhen Han; Yue-Hong Zhao; Hao Wen

2008-01-01

411

Force-activated reactivity switch in a bimolecular chemical reaction at the single molecule level  

NASA Astrophysics Data System (ADS)

Mechanical force can deform the reacting molecules along a well-defined direction of the reaction coordinate. However, the effect of mechanical force on the free-energy surface that governs a chemical reaction is still largely unknown. The combination of protein engineering with single-molecule AFM force-clamp spectroscopy allows us to study the influence of mechanical force on the rate at which a protein disulfide bond is reduced by some reducing agents in a bimolecular substitution reaction (so-called SN2). 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 SN2 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 SN2 chemical reactions. Our experiments directly demonstrate the action of a force-activated switch in the chemical reactivity of a single molecule. References: Sergi Garcia-Manyes, Jian Liang, Robert Szoszkiewicz, Tzu-Ling Kuo and Julio M. Fernandez, Nature Chemistry, 1, 236-242, 2009.

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

2010-03-01

412

Chemical activity induces dynamical force with global structure in a reaction-diffusion-convection system  

NASA Astrophysics Data System (ADS)

We found a rotating global structure induced by the dynamical force of local chemical activity in a thin solution layer of excitable Belousov-Zhabotinsky reaction coupled with diffusion. The surface flow and deformation associated with chemical spiral waves (wavelength about 1 mm) represents a global unidirectional structure and a global tilt in the entire Petri dish (100 mm in diameter), respectively. For these observations, we scanned the condition of hierarchal pattern selection. From this result, the bromomalonic acid has an important role to induce the rotating global structure. An interaction between a reaction-diffusion process and a surface-tension-driven effect leads to such hierarchal pattern with different scales.

Mahara, Hitoshi; Okada, Koichi; Nomura, Atsushi; Miike, Hidetoshi; Sakurai, Tatsunari

2009-07-01

413

Persistence of transition state structure in chemical reactions driven by fields oscillating in time  

E-print Network

Chemical reactions subjected to time-varying external forces cannot generally be described through a fixed bottleneck near the transition state barrier or dividing surface. A naive dividing surface attached to the instantaneous, but moving, barrier top also fails to be recrossing-free. We construct a moving dividing surface in phase space over a transition state trajectory. This surface is recrossing-free for both Hamiltonian and dissipative dynamics. This is confirmed even for strongly anharmonic barriers using simulation. The power of transition state theory is thereby applicable to chemical reactions and other activated processes even when the bottlenecks are time-dependent and move across space.

Galen T. Craven; Thomas Bartsch; Rigoberto Hernandez

2014-04-29

414

Chemical degradation of peptides and proteins in PLGA: a review of reactions and mechanisms.  

PubMed

Biodegradable poly(lactide-co-glycolide) (PLGA) polymers have been studied extensively for the controlled release of peptide and protein drugs. In addition to polymer biodegradation, chemical degradation of the incorporated peptide/protein has also been reported in PLGA devices, and the role of the polymer in promoting these reactions has been debated. This review summarizes the peptide/protein chemical degradation reactions that have been reported in PLGA systems and their mechanisms. Reported methods for stabilizing peptides and proteins in PLGA devices are also discussed. PMID:17828756

Houchin, M L; Topp, E M

2008-07-01

415

Journal of Chemical Ecology, Vol. 23, No. 4, 1997 REACTIONS OF Gammarus lacustris TO CHEMICAL  

E-print Network

pheromone decreases the capture efficiency of predatory larvaldragonflies (Aeshna umbrosa) (Hews, 1988 and to chemical stimuli from two types of natural predators: dragonfly larvae (Aeshna eremita) and northern pike, alarm pheromone, kairomone, predator avoidance, antipredator behavior, Esox lucius, Aeshna eremita

Wisenden, Brian D.

416

Measurement of Helical Trajectories in Chemical Reactions by Ion Imaging  

SciTech Connect

During the first year of this grant we developed methods to measure the sense of rotation of the nitric oxide molecule (NO) using a circularly polarized laser probe and with ion imaging detection. The method was applied to the measurement of the correlation of rotational angular momentum orientation with recoil direction in the photodissociation of NO{sub 2}. [''Detection of ''ended'' NO recoil in the 355 nm NO2 photodissociation mechanism'', V.K. Nestorov and J.I. Cline, J. Chem. Phys. 111, 5287-5290 (1999)]. The photodissociation work was performed at the University of Nevada with additional, partial support from NSF. In the summer of 1999 this technique was transported to and implemented at the Combustion Research Facility at Sandia National Laboratory in Livermore, CA in a study of rotationally inelastic collisions of NO molecules with Ar atoms. The summer 1999 experiments at Sandia demonstrated that it is possible to detect collision-induced rotational alignment (preferred planes of rotation) for product molecules. During the late summer and fall of 1999 the P.I. and student James Barr developed a theoretical method for quantifying the angular momentum alignment and for extracting it from ion images. During the winter and spring of 2000 (January-May) the P.I. was in residence at Sandia National Laboratory in Livermore during a sabbatical leave from the University of Nevada. During this time the P.I. collaborated with Sandia P.I. Dr. David Chandler and Sandia postdoctorals Thomas Lorenz and Elisabeth Wade in experiments measuring both rotational alignment and rotational orientation (preferred senses of rotation) in collisions of NO with Ar. Graduate student James Barr continued these experiments at Sandia through the end of June 2000. The success of our experimental techniques for measuring collisional alignment and the theoretical methods we have developed for extracting quantitative alignment parameters from ion images. Spectroscopic probing of products by resonance-enhanced multiphoton ionization (REMPI) detected by ion imaging is a powerful method for measuring the product state-resolved differential cross section (DCS) of bimolecular scattering reactions. Polarization of the REMPI probe light also makes imaging data potentially sensitive to product angular momentum polarization, as is well known from imaging studies of photodissociation. We exploit this sensitivity to obtain the state-resolved product angular momentum polarization as a function of recoil angle. Previous measurements of molecular angular momentum polarization in bimolecular scattering have either been constrained to detection in the scattering plane or have averaged around the azimuthal angle of the recoil velocity vector in the collision frame. Imaging detection captures the entire product recoil velocity sphere, enabling a more complete determination of product angular momentum polarization than is possible for experiments of lower detection dimensionality.

Cline, Joseph I.

2003-02-10

417

A coupled THC model of the FEBEX in situ test with bentonite swelling and chemical and thermal osmosis.  

PubMed

The performance assessment of a geological repository for radioactive waste requires quantifying the geochemical evolution of the bentonite engineered barrier. This barrier will be exposed to coupled thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes. This paper presents a coupled THC model of the FEBEX (Full-scale Engineered Barrier EXperiment) in situ test which accounts for bentonite swelling and chemical and thermal osmosis. Model results attest the relevance of thermal osmosis and bentonite swelling for the geochemical evolution of the bentonite barrier while chemical osmosis is found to be almost irrelevant. The model has been tested with data collected after the dismantling of heater 1 of the in situ test. The model reproduces reasonably well the measured temperature, relative humidity, water content and inferred geochemical data. However, it fails to mimic the solute concentrations at the heater-bentonite and bentonite-granite interfaces because the model does not account for the volume change of bentonite, the CO(2)(g) degassing and the transport of vapor from the bentonite into the granite. The inferred HCO(3)(-) and pH data cannot be explained solely by solute transport, calcite dissolution and protonation/deprotonation by surface complexation, suggesting that such data may be affected also by other reactions. PMID:21783271

Zheng, Liange; Samper, Javier; Montenegro, Luis

2011-09-25

418

A Review of the Thermodynamic, Transport, and Chemical Reaction Rate Properties of High-temperature Air  

NASA Technical Reports Server (NTRS)

Thermodynamic and transport properties of high temperature air, and the reaction rates for the important chemical processes which occur in air, are reviewed. Semiempirical, analytic expressions are presented for thermodynamic and transport properties of air. Examples are given illustrating the use of these properties to evaluate (1) equilibrium conditions following shock waves, (2) stagnation region heat flux to a blunt high-speed body, and (3) some chemical relaxation lengths in stagnation region flow.

Hansen, C Frederick; Heims, Steve P

1958-01-01

419

Anomalously high thermal conductivity of amorphous Si deposited by hot-wire chemical vapor deposition  

Microsoft Academic Search

The thermal conductivities of thin films of amorphous Si (a-Si) deposited by hot-wire chemical vapor deposition (HWCVD) are measured by time-domain thermoreflectance (TDTR). Amorphous Si samples prepared at the National Renewable Energy Laboratory (NREL) show an anomalous enhancement in thermal conductivity compared to other forms of a-Si and compared to the prediction of the model of the minimum thermal conductivity.

Ho-Soon Yang; David G. Cahill; X. Liu; J. L. Feldman; R. S. Crandall; B. A. Sperling; J. R. Abelson

2010-01-01

420

Theory of Thermal Explosions with Simultaneous Parallel Reactions. I. Foundations and the One-Dimensional Case  

Microsoft Academic Search

Many real, exothermic systems involve more than one simultaneous reaction. Even when they are chemically independent, interactions must arise through their several responses to the collective generation of heat. A simple and unifying approach is possible to the behaviour of such systems below and up to criticality. It introduces a communal activation energy E as the basis for dimensionless quantities

T. Boddington; P. Gray; G. C. Wake

1984-01-01

421

Ion-Molecule Reactions and Chemical Composition of Emanated from Herculane Spa Geothermal Sources  

PubMed Central

The paper presents a chemical composition analysis of the gases emanated from geothermal sources in the Herculane Spa area (Romania). The upper homologues of methane have been identified in these gases. An ion-molecule reaction mechanism could be implicated in the formation of the upper homologues of methane. The CH4+ ions that appear under the action of radiation are the starting point of these reactions. The presence of hydrogen in the emanated gases may be also a result of these reactions. PMID:19325844

Cosma, Constantin; Suciu, Ioan; Jantschi, Lorentz; Bolboaca, Sorana D.

2008-01-01

422

Quantum-chemical approach to serine formation in the interstellar medium: A possible reaction pathway  

NASA Astrophysics Data System (ADS)

Radical-radical and radical-neutral interaction schemes are very important for the formation of comparatively complex molecules in low-temperature chemistry. The formation of amino acids, such as serine, in the interstellar medium is quite difficult. We explored the possibility of serine formation in the interstellar medium through detected interstellar molecules such as CH, CO, and OH by radical-radical and radical-neutral interactions in the gaseous phase using rigorous quantum-chemical calculations. The reaction energies, the low potential barrier and the structures of all the geometries involved in the reaction path show that serine formation is possible in interstellar space via the reaction paths.

Shivani; Singh, Amresh; Gupta, Vineet; Misra, Alka; Tandon, Poonam

2014-03-01

423

Conservation equations and physical models for hypersonic air flows in thermal and chemical nonequilibrium  

Microsoft Academic Search

The conservation equations for simulating hypersonic flows in thermal and chemical nonequilibrium and details of the associated physical models are presented. These details include the curve fits used for defining thermodynamic properties of the 11 species air model, curve fits for collision cross sections, expressions for transport properties, the chemical kinetics models, and the vibrational and electronic energy relaxation models.

P. A. Gnoffo; R. N. Gupta; J. L. Shinn

1989-01-01

424

Detection of chemical weapon agents and simulants using chemical ionization reaction time-of-flight mass spectrometry.  

PubMed

Chemical ionization reaction time-of-flight mass spectrometry (CIR-TOF-MS) has been used for the analysis of prepared mixtures of chemical weapon agents (CWAs) sarin and sulfur mustard. Detection of the CWA simulants 2-chloroethyl ethyl sulfide, triethyl phosphate, and dimethyl methyl phosphonate has also been investigated. Chemical ionization of all the agents and simulants was shown to be possible using the CIR-TOF-MS technique with a variety of reagent ions, and the sensitivity was optimized by variation of instrument parameters. The ionization process was found to be largely unaffected by sample humidity levels, demonstrating the potential suitability of the method to a range of environmental conditions, including the analysis of CWAs in air and in the breath of exposed individuals. PMID:17894471

Cordell, Rebecca L; Willis, Kerry A; Wyche, Kevin P; Blake, Robert S; Ellis, Andrew M; Monks, Paul S

2007-11-01

425

Chemical reaction of metal-fullerene in gas phase ^  

E-print Network

Chemical reaction of metal-fullerene in gas phase ·^Masamichi Kohno1 , Shuhei·" `··ZZOE±·S ,Q·D"OEfullerenes-ray diffraction study has proven (1) that some metal-fullerenes such as Sc@C82 and Sc2@C84 that were prepared

Maruyama, Shigeo

426

Chemical reaction of metal-fullerene in gas phase (2) >Masamichi Konoa  

E-print Network

f18-068 Chemical reaction of metal-fullerene in gas phase (2) ·>Masamichi Konoa , Syuhei Inoueb.of Tokyo Since the discovery of macroscopic generation and purification procedure of fullerenes and endohedral fullerenes, the geometric structure and the formation mechanism of them has been one of the most

Maruyama, Shigeo

427

Reaction layer formation and fracture at chemically vapor deposited diamond\\/metal interfaces  

Microsoft Academic Search

Chemically vapor deposited (CVD) diamond films have been deposited by a microwave enhanced deposition process on metal substrates including titanium, tungsten, molybdenum, and copper. Boundary reaction layers formed at the interface during the growth of the CVD diamond films have been investigated for each of these systems. In these studies, the interface has been exposed by mechanically deforming the metal

Scott S. Perry; Gabor A. Somorjai

1994-01-01

428

Approximation for the enhancement factor applicable to reversible reactions of finite rate in chemically loaded solutions  

Microsoft Academic Search

A new explicit relation is proposed for the prediction of the enhancement factor for reversible reactions of finite rate in chemically loaded solutions which also allows for unequal diffusivities. The relation for the enhancement factor is not based on an approximation of the absorption process, but is derived from a similarity which can be observed between the results of the

J. A. Hogendoorn; R. D. Vas Bhat; J. A. M. Kuipers; W. P. M. van Swaaij; G. F. Versteeg

1997-01-01

429

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

ERIC Educational Resources Information Center

In this study, we investigated how students used a drawing tool to visualize their ideas of chemical reaction processes. We interviewed 30 students using thinking-aloud and retrospective methods and provided them with a drawing tool. We identified four types of connections the students made as they used the tool: drawing on existing knowledge,…

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

2014-01-01

430

Selective area growth of III-V semiconductors by chemical beam epitaxy: study of reaction mechanisms  

Microsoft Academic Search

The localized growth of III-V epitaxial structures on substrates patterned with dielectric masks provides a flexible technique for the monolithic integration of electronic and optoelectronic devices. Chemical beam epitaxy (CBE) is an attractive growth technique for use in this approach and interest has consequently focussed on the reaction mechanisms which give rise to selective area growth in CBE. In the

Graham J. Davies; P. J. Skevington; J. S. Foord; C. L. French; C. L. Levoguer

1994-01-01

431

Super-Resolution Fingerprinting Detects Chemical Reactions and Idiosyncrasies of Single DNA Pegboards  

E-print Network

Super-Resolution Fingerprinting Detects Chemical Reactions and Idiosyncrasies of Single DNA in nanoscale topography (PAINT) using site-specific DNA probes to acquire two-dimensional density maps of specific features patterned on nanoscale DNA origami pegboards. We show that PAINT has a localization

Walter, Nils G.

432

Detailed chemical kinetic reaction mechanism for biodiesel components methyl stearate and methyl oleate  

E-print Network

Detailed chemical kinetic reaction mechanism for biodiesel components methyl stearate and methyl are developed for two of the five major components of biodiesel fuel, methyl stearate and methyl oleate renewable sources, can reduce net emissions of greenhouse gases. An important class of biodiesel fuels

Paris-Sud XI, Université de

433

DEVELOPMENT AND TESTING OF A SURROGATE SPECIES CHEMICAL REACTION MECHANISM. VOLUME 2  

EPA Science Inventory

A photochemical reaction mechanism has been updated and extensively evaluated. The testing and refinement of the surrogate species mechanism was performed in order to create an improved chemical mechanism for the atmospheric simulation models that are used to develop ozone contro...

434

DEVELOPMENT AND TESTING OF A SURROGATE SPECIES CHEMICAL REACTION MECHANISM. VOLUME 1  

EPA Science Inventory

A photochemical reaction mechanism has been updated and extensively evaluated. The testing and refinement of the surrogate species mechanism was performed in order to create an improved chemical mechanism for the atmospheric simulation models that are used to develop ozone contro...

435

The thermal reaction rate of muonium with methane (and ethane) in the gas phase  

Microsoft Academic Search

Rates for the gas-phase thermal reaction Mu+CH4?MuH+CH3 (Mu=?+e?), have been measured using the ?SR (muon spin rotation) technique, over the temperature range 625–820 K. A good fit is obtained to the usual Arrhenius expression, k=A exp(?Ea\\/RT), giving an activation energy Ea=24.6±0.9 kcal\\/mol, ?12 kcal\\/mol higher than that of the H-atom isotopic variant of this reaction, H+CH4?H2+CH3. This Ea difference is

Rodney Snooks; Donald J. Arseneau; Donald G. Fleming; Masayoshi Senba; James J. Pan; Mee Shelley; Susan Baer

1995-01-01

436

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

PubMed

Nanoconfinement entropic effects on chemical equilibrium involving a small number of molecules, which we term NCECE, are revealed by two widely diverse types of reactions. Employing statistical-mechanical principles, we show how the NCECE effect stabilizes nucleotide dimerization observed within self-assembled molecular cages. Furthermore, the effect provides the basis for dimerization even under an aqueous environment inside the nanocage. Likewise, the NCECE effect is pertinent to a longstanding issue in astrochemistry, namely the extra deuteration commonly observed for molecules reacting on interstellar dust grain surfaces. The origin of the NCECE effect is elucidated by means of the probability distributions of the reaction extent and related variations in the reactant-product mixing entropy. Theoretical modelling beyond our previous preliminary work highlights the role of the nanospace size in addition to that of the nanosystem size, namely the limited amount of molecules in the reaction mixture. Furthermore, the NCECE effect can depend also on the reaction mechanism, and on deviations from stoichiometry. The NCECE effect, leading to enhanced, greatly variable equilibrium "constants", constitutes a unique physical-chemical phenomenon, distinguished from the usual thermodynamical properties of macroscopically large systems. Being significant particularly for weakly exothermic reactions, the effects should stabilize products in other closed nanoscale structures, and thus can have notable implications for the growing nanotechnological utilization of chemical syntheses conducted within confined nanoreactors. PMID:21858361

Polak, Micha; Rubinovich, Leonid

2011-10-01

437

Ab initio molecular dynamics study on the initial chemical events in nitramines: thermal decomposition of CL-20.  

PubMed

CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane or HNIW) is a high-energy nitramine explosive. To improve atomistic understanding of the thermal decomposition of CL-20 gas and solid phases, we performed a series of ab initio molecular dynamics simulations. We found that during unimolecular decomposition, unlike other nitramines (e.g., RDX, HMX), CL-20 has only one distinct initial reaction channelhomolysis of the N-NO2 bond. We did not observe any HONO elimination reaction during unimolecular decomposition, whereas the ring-breaking reaction was followed by NO 2 fission. Therefore, in spite of limited sampling, that provides a mostly qualitative picture, we proposed here a scheme of unimolecular decomposition of CL-20. The averaged product population over all trajectories was estimated at four HCN, two to four NO2, two to four NO, one CO, and one OH molecule per one CL-20 molecule. Our simulations provide a detailed description of the chemical processes in the initial stages of thermal decomposition of condensed CL-20, allowing elucidation of key features of such processes as composition of primary reaction products, reaction timing, and Arrhenius behavior of the system. The primary reactions leading to NO2, NO, N 2O, and N2 occur at very early stages. We also estimated potential activation barriers for the formation of NO2, which essentially determines overall decomposition kinetics and effective rate constants for NO2 and N2. The calculated solid-phase decomposition pathways correlate with available condensed-phase experimental data. PMID:18686996

Isayev, Olexandr; Gorb, Leonid; Qasim, Mo; Leszczynski, Jerzy

2008-09-01

438

Thermal Relaxation Time in Chemically Non-equilibrated Quark- Gluon Plasma  

E-print Network

The definition of thermal relaxation time is extended to chemically non-equilibrated quark-gluon plasma and the chemical non-equilibrated thermal relaxation times for partons are calculated using the non-equilibrium Debye mass as the infrared regulator. The dependence of the thermal relaxation time on the fugacity is given and the influence of the chemical non-equilibration is discussed. We find that there are threshold fugacities $\\lambda_g^*$ and $\\lambda_q^*$ for gluons and quarks. For \\lambda_g \\lambda_g^* (\\lambda_q>\\lambda_q^*$), the ratios are almost 1. It is shown that there is also the two-stage equilibration in a chemically non-equilibrated plasma. We also discussed the effect of using the non-equilibrium Deby mass as the infrared cutoff.

Xiao-Fei Zhang; Wei-Qin Chao

1997-07-09

439

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

DOE Data Explorer

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.[Taken from https://www-pls.llnl.gov/?url=science_and_technology-chemistry-combustion

440

A Spectroscopist's View of Energy States, Energy Transfers, and Chemical Reactions  

NASA Astrophysics Data System (ADS)

This chapter describes a research career beginning at Berkeley in 1960, shortly after Sputnik and the invention of the laser. Following thesis work on vibrational spectroscopy and the chemical reactivity of small molecules, we studied vibrational energy transfers in my own lab. Collision-induced transfers among vibrations of a single molecule, from one molecule to another, and from vibration to rotation and translation were elucidated. My research group also studied the competition between vibrational relaxation and chemical reaction for potentially reactive collisions with one molecule vibrationally excited. Lasers were used to enrich isotopes by the excitation of a predissociative transition of a selected isotopomer. We also tested the hypotheses of transition-state theory for unimolecular reactions of ketene, formaldehyde, and formyl fluoride by (a) resolving individual molecular eigenstates above a dissociation threshold, (b) locating vibrational levels at the transition state, (c) observing quantum resonances in the barrier region for motion along a reaction coordinate, and (d) studying energy release to fragments.

Moore, C. Bradley

2007-05-01

441

Looking for chemical reaction networks exhibiting a drift along a manifold of marginally stable states.  

PubMed

I recently reported some examples of mass-action equations that have a continuous manifold of marginally stable stationary states [Brogioli, D., 2010. Marginally stable chemical systems as precursors of life. Phys. Rev. Lett. 105, 058102; Brogioli, D., 2011. Marginal stability in chemical systems and its relevance in the origin of life. Phys. Rev. E 84, 031931]. The corresponding chemical reaction networks show nonclassical effects, i.e. a violation of the mass-action equations, under the effect of the concentration fluctuations: the chemical system drifts along the marginally stable states. I proposed that this effect is potentially involved in abiogenesis. In the present paper, I analyze the mathematical properties of mass-action equations of marginally stable chemical reaction networks. The marginal stability implies that the mass-action equations obey some conservation law; I show that the mathematical properties of the conserved quantity characterize the motion along the marginally stable stationary state manifold, i.e. they allow to predict if the fluctuations give rise to a random walk or a drift under the effect of concentration fluctuations. Moreover, I show that the presence of the drift along the manifold of marginally stable stationary-states is a critical property, i.e. at least one of the reaction constants must be fine tuned in order to obtain the drift. PMID:23160143

Brogioli, Doriano

2013-02-01

442

Progress toward chemical accuracy in the computer simulation of condensed phase reactions.  

PubMed Central

We describe a procedure for the generation of chemically accurate computer-simulation models to study chemical reactions in the condensed phase. The process involves (i) the use of a coupled semiempirical quantum and classical molecular mechanics method to represent solutes and solvent, respectively; (ii) the optimization of semiempirical quantum mechanics (QM) parameters to produce a computationally efficient and chemically accurate QM model; (iii) the calibration of a quantum/classical microsolvation model using ab initio quantum theory; and (iv) the use of statistical mechanical principles and methods to simulate, on massively parallel computers, the thermodynamic properties of chemical reactions in aqueous solution. The utility of this process is demonstrated by the calculation of the enthalpy of reaction in vacuum and free energy change in aqueous solution for a proton transfer involving methanol, methoxide, imidazole, and imidazolium, which are functional groups involved with proton transfers in many biochemical systems. An optimized semiempirical QM model is produced, which results in the calculation of heats of formation of the above chemical species to within 1.0 kcal/mol (1 kcal = 4.18 kJ) of experimental values. The use of the calibrated QM and microsolvation QM/MM (molecular mechanics) models for the simulation of a proton transfer in aqueous solution gives a calculated free energy that is within 1.0 kcal/mol (12.2 calculated vs. 12.8 experimental) of a value estimated from experimental pKa values of the reacting species. PMID:11607654

Bash, P A; Ho, L L; MacKerell, A D; Levine, D; Hallstrom, P

1996-01-01

443

Unusual reaction paths of SN2 nucleophile substitution reactions CH4 + H- ? CH4 + H- and CH4 + F- ? CH3F + H-: Quantum chemical calculations  

NASA Astrophysics Data System (ADS)

Quantum chemical (CCSD(full)/6-311++G(3df,3pd), CCSD(T)(full)/6-311++G(3df,3pd)) and density function theory (B3LYP/6-311++G(3df,3pd)) calculations were performed for the SN2 nucleophile substitution reactions CH4 + H- ? CH4 + H- and CH4 + F- ? CH3F + H-. The calculated gradient reaction pathways for both reactions have an unusual behavior. An unusual stationary point of index 2 lies on the gradient reaction path. Using Newton trajectories for the reaction path, we can detect VRI point at which the reaction path branches.

Minyaev, Ruslan M.; Quapp, Wolfgang; Schmidt, Benjamin; Getmanskii, Ilya V.; Koval, Vitaliy V.

2013-11-01

444

Ultrasensitive detection of DNA and RNA based on enzyme-free click chemical ligation chain reaction on dispersed gold nanoparticles.  

PubMed

An ultrasensitive colorimetric DNA and RNA assay using a combination of enzyme-free click chemical ligation chain reaction (CCLCR) on dispersed gold nanoparticles (GNPs) and a magnetic separation process has been developed. The click chemical ligation between an azide-containing probe DNA-modified GNP and a dibenzocyclooctyne-containing probe biotinyl DNA occurred through hybridization with target DNA (RNA) to form the biotinyl-ligated GNPs (ligated products). Eventually, both the biotinyl-ligated GNPs and target DNA (RNA) were amplified exponentially using thermal cycling. After separation of the biotinyl-ligated GNPs using streptavidin-modified magnetic beads, the change in intensity of the surface plasmon band at 525 nm in the supernatants was observed by UV/vis measurement and was also evident visually. The CCLCR assay provides ultrasensitive detection (50 zM: several copies) of target DNA that is comparable to PCR-based approaches. Note that target RNA could also be detected with similar sensitivity without the need for reverse transcription to the corresponding cDNA. The amplification efficiency of the CCLCR assay was as high as 82% due to the pseudohomogeneous reaction behavior of CCLCR on dispersed GNPs. In addition, the CCLCR assay was able to discriminate differences in single-base mismatches and to specifically detect target DNA and target RNA from the cell lysate. PMID:25256209

Kato, Daiki; Oishi, Motoi

2014-10-28