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1

Chemical reaction in a thermal plasma  

Microsoft Academic Search

A thermal plasma has high potential to instigate a refractory chemical reaction because it has a high temperature and high energy. So thermal plasmas have been utilized for some high-temperature processes in which a chemical reaction occurs, although so far chemical application of thermal plasmas has not been sufficient and their use should be promoted more. In this paper, the

Atsushi Kanzawa

1993-01-01

2

Method of operating a thermal engine powered by a chemical reaction  

DOEpatents

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

Ross, J.; Escher, C.

1988-06-07

3

Chemical reactions and thermal stability of oxygen impurities on graphene  

NASA Astrophysics Data System (ADS)

Oxygen as an impurity is known to degrade conductivity in graphene, but annealing at moderate temperature reverses the effect. Here we report first-principles calculations of oxygen binding and reactions on graphene that elucidate the underlying physics. We find that two O atoms can form an O dimer that can desorb from graphene with an overall activation barrier of 1.3 eV. Oxygen can also be removed in a more complicated reaction in which C atoms in graphene are consumed. We find that structural defects such as Stone-Wales defect and grain boundaries show enhanced binding to O atoms due to the local strain, facilitating the O reaction. If H atoms coexist, an O atom can bind to an H atom forming an OH group, which can also be removed by thermal annealing due to the weak binding, resulting in defect-free graphene.

Wang, Bin; Pantelides, Sokrates

2012-02-01

4

Determination of Activation Energies of Chemical Reactions by Differential Thermal Analysis  

Microsoft Academic Search

A NUMBER of articles have been published dealing with the differential thermal analysis (DTA) of chemical reaction kinetics1-5. Only one of these, however, gives a direct method for determining the activation energy (E) of the chemical reaction4. In this method, DTA curves are recorded at several different rates of heating. The results are then plotted as ln b\\/Tm2 against 1\\/Tm,

G. O. Piloyan; I. D. Ryabchikov; O. S. Novikova

1966-01-01

5

Thermal Analysis of Chemical Reaction Process Forming CuInSe 2 Crystal  

Microsoft Academic Search

In order to establish the preparation method of high-quality CuInSe2 single crystals, we have investigated the chemical reaction process of CuInSe2 by differential thermal analysis and by powder X-ray diffraction measurements. It is confirmed that CuInSe2 compound undergoes a phase transition from chalcopyrite to sphalerite structure at 815°C and melts at 996°C. In the chemical reaction process of a Cu+In+2Se

Hiroaki Matsushita; Takeo Takizawa

1995-01-01

6

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

7

Chemically non-equilibrium modelling of N2 thermal ICP at atmospheric pressure using reaction kinetics  

NASA Astrophysics Data System (ADS)

A two-dimensional hydrodynamic model for an N2 inductively coupled thermal plasma (ICTP or thermal ICP) at atmospheric pressure was developed using reaction rates without the chemical equilibrium (CE) assumption. Particle composition distribution in the N2 ICTP was derived by solving the mass conservation equations for each of the particles, considering diffusion, convection and production terms. The electrical conductivity, mass density and diffusion coefficient were calculated at each of the calculation steps with the derived particle composition distributions. Using this model, the influence of gas flow rate on chemical composition distribution was investigated. The dependence of mass flow of N atom on gas flow rate was obtained. From the result, a large deviation from CE in the distribution of the particle composition was found, especially near the wall of the ICTP.

Tanaka, Y.; Sakuta, T.

2002-03-01

8

Solar photo-thermal catalytic reactions to produce high value chemicals  

SciTech Connect

This report presents a summary of the research work accomplished to date on the utilization of solar photo-thermal energy to convert low cost chemical feedstocks into high $-value chemical products. The rationale is that the solar IR-VIS-UV spectrum is unique, supplying endothermic reaction energy as well as VIS-UV for photochemical activation. Chemical market analysis and product price distribution focused attention on speciality chemicals with prices >$1.00/lb, and a synthesis sequence of n-paraffins to aromatics to partial oxidized products. The experimental work has demonstrated that enhanced reaction effects result from VIS-UV irradiation of catalytically active V2O5/SiO2. Experiments of the past year have been on dehydrogenation and dehydrocyclization of n-paraffins to olefins and aromatics with preference for the latter. Recent results using n-hexane produced 95% conversion with 56% benzene; it is speculated that aromatic yield should reach {approximately}70% by further optimization. Pilot- and commercial-scale reactor configurations have been examined; the odds-on-favorite being a shallow fluid-bed of catalyst with incident radiation from the top. Sequencing for maximum cost effectiveness would be day-time endothermic followed by night-time exothermic reactions to produce the products.

Prengle, H.W. Jr.; Wentworth, W.E. [Houston Univ., TX (United States)

1992-04-01

9

Correlation of shock initiated and thermally initiated chemical reactions in a 1:1 atomic ratio nickel-silicon mixture  

Microsoft Academic Search

Shock initiated chemical reaction experiments have been performed on a 1:1 atomic ratio mixture of 20- to 45-?m nickel and ?325 mesh crystalline silicon powders. It has been observed that no detectable or only minor surface reactions occur between the constituents until a thermal energy threshold is reached, above which the reaction goes to completion. The experiments show the energy

Barry R. Krueger; Andrew H. Mutz; Thad Vreeland

1991-01-01

10

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

NASA Astrophysics Data System (ADS)

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.

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

2010-12-01

11

Mass Transfer with Chemical Reaction on Flow Past an Accelerated Vertical Plate with Variable Temperature and Thermal Radiation  

NASA Astrophysics Data System (ADS)

An exact solution of an unsteady radiative flow past a uniformly accelerated infinite vertical plate with variable temperature and mass diffusion is presented here, taking into account the homogeneous chemical reaction of first order. The plate temperature as well as concentration near the plate is raised linearly with time. The dimensionless governing equations are solved using the Laplace-transform technique. The velocity, temperature and concentration fields are studied for different physical parameters such as the thermal Grashof number, mass Grashof number, Schmidt number, Prandtl number, radiation parameter, chemical reaction parameter and time. It is observed that the velocity increases with increasing values of the thermal Grashof number or mass Grashof number. But the trend is just reversed with respect to the thermal radiation parameter. It is also observed that the velocity increases with the decreasing chemical reaction parameter

Muthucumaraswamy, R.; Balachandran, P.; Ganesan, K.

2013-08-01

12

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

2010-10-22

13

Numerical simulations of heterogeneous chemical reactions coupled to fluid flow in varying thermal fields.  

National Technical Information Service (NTIS)

A numerical simulator of reactive chemical transport with coupling from precipitation-dissolution reactions to fluid flow, via changes of porosity and permeability, is applied to precipitation-dissolution of quartz and calcite in spatially and temporally ...

C. L. Carnahan

1991-01-01

14

Nanoreactors for simultaneous remote thermal activation and optical monitoring of chemical reactions.  

PubMed

We report herein the design of plasmonic hollow nanoreactors capable of concentrating light at the nanometer scale for the simultaneous performance and optical monitoring of thermally activated reactions. These reactors feature the encapsulation of plasmonic nanoparticles on the inner walls of a mesoporous silica capsule. A Diels-Alder cycloaddition reaction was carried out in the inner cavities of these nanoreactors to evidence their efficacy. Thus, it is demonstrated that reactions can be accomplished in a confined volume without alteration of the temperature of the bulk solvent while allowing real-time monitoring of the reaction progress. PMID:24044481

Vázquez-Vázquez, Carmen; Vaz, Belén; Giannini, Vincenzo; Pérez-Lorenzo, Moisés; Alvarez-Puebla, Ramon A; Correa-Duarte, Miguel A

2013-09-09

15

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

16

ARTICLES: Possible thermal self-focusing of light beams influencing chemical reactions  

Microsoft Academic Search

It is shown that self-focusing of light beams may occur as a result of cooling of a mixture of reacting gases in the case of resonant interaction of light with atoms (or molecules) participating in chemical reactions. Estimates of the duration and degree of cooling are obtained. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find

E. P. Orlov

1983-01-01

17

Chemical Reactions (Netorials)  

NSDL National Science Digital Library

Chemical Reactions: this is a resource in the collection "Netorials". The Netorials cover selected topics in first-year chemistry including: Chemical Reactions, Stoichiometry, Thermodynamics, Intermolecular Forces, Acids & Bases, Biomolecules, and Electrochemistry.

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

Chemical Reaction Problem Solving.  

ERIC Educational Resources Information Center

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

Veal, William

1999-01-01

20

Nonadiabatic chemical reactions  

Microsoft Academic Search

A mixed quantum-classical approach where the environment is treated classically and the reactive degrees of freedom are considered to be quantum mechanical can be used to describe many chemical reactions, such as proton and electron transfer processes. We present reactive flux correlation function expressions for the rate constants of nonadiabatic chemical reactions occurring in quantum-classical systems. By means of a

Alessandro Sergi; Raymond Kapral

2005-01-01

21

Theoretical Studies of Chemical Reactions: Dynamics.  

National Technical Information Service (NTIS)

Theoretical studies have been performed on the dynamics of interesting chemical reactions. The systems studied included the recombination reaction of methyl radicals to form ethylene, the addition of hydrogen atoms to carbon monoxide and the thermal disso...

A. F. Wagner M. J. Davis G. C. Schatz R. J. Duchovic R. Steckler

1988-01-01

22

Method and Apparatus for Obtaining Enhanced Production Rate of Thermal Chemical Reactions.  

National Technical Information Service (NTIS)

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 proc...

A. L. Y. Tonkovich R. S. Wegeng Y. Gao Y. Wang

2005-01-01

23

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

24

Chemical Thermal Desorption System.  

National Technical Information Service (NTIS)

A field portable chemical thermal desorption system. The system comprises a desorption tube, an injection needle operatively connected to the desorption tube, a needle valve operatively connected to the injection needle, a heater operatively connected to ...

A. Alcaraz C. Koester J. D. Eckels

2004-01-01

25

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

26

Chemical Reaction Effects on MHD Flow Past a Linearly Accelerated Vertical Plate with Variable Temperature and Mass Diffusion in the Presence of Thermal Radiation  

NASA Astrophysics Data System (ADS)

An exact solution of first order chemical reaction effects on a radiative flow past a linearly accelerated infinite isothermal vertical plate with variable mass diffusion, under the action of a transversely applied magnetic field has been presented. The plate temperature is raised linearly with time and the concentration level near the plate is also raised to C'w linearly with time. The dimensionless governing equations are tackled using the Laplace-transform technique. The velocity, temperature and concentration fields are studied for different physical parameters such as the magnetic field parameter, radiation parameter, chemical reaction parameter, thermal Grashof number, mass Grashof number, Schmidt number, Prandtl number and time. It is observed that velocity increases with decreasing magnetic field parameter or radiation parameter. But the trend is just reversed with respect to the chemical reaction parameter

Muthucumaraswamy, R.; Geetha, E.

2013-08-01

27

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

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

Magnetic Effects in Chemical Reactions  

Microsoft Academic Search

The Review discusses in what elementary chemical reactions the intrinsic angular momentum of electrons and nuclei is conserved and in what reactions it is not conserved, how weak electron-nuclear magnetic interaction and an external magnetic field influence the conservation of angular momentum and what are the consequences of this effect, and what magnetic effects occur in chemical reactions, as well

Anatolii L Buchachenko

1976-01-01

30

Chemical Reactions: Investigating Exothermic and Endothermic Reactions  

NSDL National Science Digital Library

This activity is an inquiry-based investigation where students discover the indicators of chemical reactions (endothermic and exothermic) by collecting data and using that data to develop a testable question for further experimentation.

31

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

32

Thermal hyperspectral chemical imaging  

NASA Astrophysics Data System (ADS)

Several chemical compounds have their strongest spectral signatures in the thermal region. This paper presents three push-broom thermal hyperspectral imagers. The first operates in MWIR (2.8-5 ?m) with 35 nm spectral resolution. It consists of uncooled imaging spectrograph and cryogenically cooled InSb camera, with spatial resolution of 320/640 pixels and image rate to 400 Hz. The second imager covers LWIR in 7.6-12 ?m with 32 spectral bands. It employs an uncooled microbolometer array and spectrograph. These imagers have been designed for chemical mapping in reflection mode in industry and laboratory. An efficient line-illumination source has been developed, and it makes possible thermal hyperspectral imaging in reflection with much higher signal and SNR than is obtained from room temperature emission. Application demonstrations including sorting of dark plastics and mineralogical mapping of drill cores are presented. The third imager utilizes a cryo-cooled MCT array with precisely temperature stabilized optics. The optics is not cooled, but instrument radiation is suppressed by special filtering and corrected by BMC (Background-Monitoring-on-Chip) method. The approach provides excellent sensitivity in an instrument which is portable and compact enough for installation in UAVs. The imager has been verified in 7.6 to 12.3 ?m to provide NESR of 18 mW/(m2 sr ?m) at 10 ?m for 300 K target with 100 spectral bands and 384 spatial samples. It results in SNR of higher than 500. The performance makes possible various applications from gas detection to mineral exploration and vegetation surveys. Results from outdoor and airborne experiments are shown.

Holma, Hannu; Hyvärinen, Timo; Mattila, Antti-Jussi; Kormano, Ilkka

2012-05-01

33

A preliminary study on numerical simulation of microwave heating process for chemical reaction and discussion of hotspot and thermal runaway phenomenon  

NASA Astrophysics Data System (ADS)

The nonlinear process of microwave heating chemical reaction is studied by means of numerical simulation. Especially, the variation of temperature in terms of space and time, as well as the hotspot and thermal runaway phenomena are discussed. Suppose the heated object is a cylinder and the incident electromagnetic (EM) wave is plane wave, the problem turns out to be a coupling calculation of 2D multi-physical fields. The integral equation of EM field is solved using the method of moment (MoM) and the thermal conduction equation is solved using a semi-analysis method. Moreover, a method to determine the equivalent complex permittivity of reactant under the heating is presented in order to perform the calculation. The numerical results for water and a dummy chemical reaction ( A) show that the hotspot is a ubiquitous phenomenon in microwave heating process. When the radius of the heated object is small, the highest temperature occurs somewhere inside the object due to the concentration of the EM wave. While the radius increases to a certain degree, the highest temperature occurs somewhere close to the surface due to the skin effect, and the whole high temperature area shows crescent-shaped. That is in accordance with basic physical principles. If the radius is kept the same in the heating process, the hotspot position of water does not change, while that of reaction A with several radius values varies. For either water or A, the thermal runaway phenomenon in which small difference of radius results in large difference of highest temperature, occurs easily when the radius is small. On the contrary, it is not evident when the radius is large. Moreover, it is notable that the highest temperature in water shows oscillating decreasing trend with the increase of radius, but in reaction A almost decreases monotonously. Further study should be performed to determine if this difference is only an occasional occurrence.

Zhao, Xiang; Huang, Kama; Yan, Liping; Yao, Yuan

2009-04-01

34

Bistable and oscillating chemical reactions  

NASA Astrophysics Data System (ADS)

In the last decade the number and the diversity of isothermal oscillating reactions in homogeneous aqueous solution have tremendously increased. We present an updated classified review of these chemical reactions.

Pacault, A.; Ouyang, Q.; de Kepper, P.

1987-09-01

35

Continuous chemical reaction chromatography  

SciTech Connect

The past three years have been devoted to investigating simulated countercurrent chomatographic moving bed separators (SCMCS) and simulated countercurrent moving bed reactors (SCMCR). These are novel separators and reactors used for separation, or for carrying out a chemical reaction and separation continuously and simultaneously in fixed bed. In the SCMCR and the SCMCS the process aspects of a countercurrent moving bed, in which a stream of solids flows countercurrent to an inert fluid and past stationary reactant inlet, is simulated by successively switching feed and product take-off streams through a series of inlets located at fixed intervals along a fixed bed or between a series of packed columns. The flow of solids past a fixed feed point, characteristic of countercurrent moving beds, is replaced by motion of the feed past a fixed packed bed. Feed enters a particular column for a fixed length of time, and then is switched to the next column. Product streams are also advanced simultaneously. When the feed point has progressed to the end it is returned to the starting position and the process repeated. The shifting of the feed and the product positions in the direction of fluid flow thus simulates the movement of solids in the opposite direction. The requisite motion between the feed and the bed, which is continuous for true countercurrency, is replaced by periodic, discrete steps in simulated countercurrency. The continuous, steady state operation characteristic of true countercurrency is replaced by periodic transients at each switch of the feed.

Aris, R.; Carr, R.W.

1992-01-01

36

Monotonicity in chemical reaction systems  

Microsoft Academic Search

This article discusses the question of when the dynamical systems arising from chemical reaction networks are monotone, preserving an order induced by some proper cone. The reaction systems studied are defined by the reaction network structure while the kinetics is only constrained very weakly. Necessary and sufficient conditions on cones preserved by these systems are presented. Linear coordinate changes which

Murad Banaji

2009-01-01

37

Chemical reaction on polysaccharides  

Microsoft Academic Search

The article discusses the synthesis of pullulan derivatives containing chloroalkyl groups by the reaction of crosslinked pullulan microparticles with different chloroalkyl chlorides in organic basic solvents. These new products may allow the attachment of various bioactive compounds by covalent bonding.

G Mocanu; D Vizitiu; D Mihai; A Carpov

1999-01-01

38

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 ...

39

Speeding chemical reactions by focusing  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

40

Insights into the mechanisms on chemical reactions: reaction paths for chemical reactions. [Li + HF; OH + Hâ  

Microsoft Academic Search

We report reaction paths for two prototypical chemical reactions: Li + HF, an electron transfer reaction, and OH + Hâ, an abstraction reaction. In the first reaction we consider the connection between the energetic terms in the reaction path Hamiltonian and the electronic changes which occur upon reaction. In the second reaction we consider the treatment of vibrational effects in

T. H. Jr. Dunning; E. Rosen; R. A. Eades

1987-01-01

41

Perturbation technique for unsteady MHD mixed convection periodic flow, heat and mass transfer in micropolar fluid with chemical reaction in the presence of thermal radiation  

NASA Astrophysics Data System (ADS)

An analytical study is presented for the problem of unsteady hydromagnetic heat and mass transfer for a micropolar fluid bounded by semi-infinite vertical permeable plate in the presence of first-order chemical reaction, thermal radiation and heat absorption. A uniform magnetic field acts perpendicularly to the porous surface which absorbs the micropolar fluid with a time-dependent suction velocity. The basic partial differential equations are reduced to a system of nonlinear ordinary differential equations which are solved analytically using perturbation technique. Numerical calculations for the analytical expressions are carried out and the results are shown graphically. The effects of the various dimensionless parameters related to the problem on the velocity, angular velocity, temperature and concentration fields are discussed in detail.

Pal, Dulal; Talukdar, Babulal

2012-10-01

42

Modeling and Simulating Chemical Reactions  

Microsoft Academic Search

Abstract Many students are familiar with the idea of modeling chemical reactions in terms of ordinary dieren tial equations. However, these deterministic reaction rate equations are really a certain large-scale limit of a sequence of ner-scale probabilistic models. In studying this hierarchy of models, students can be exposed to a range of modern ideas in applied and compu- tational mathematics.

Desmond J. Higham

2008-01-01

43

Millisecond chemical reactions and reactors  

Microsoft Academic Search

Short contact time chemical reactors have many features which are very different from conventional packed bed reactors in that temperatures are determined by inlet parameters only, performance is nearly unchanged over wide variations in flow rate, and highly nonequilibrium products can be obtained at high conversions. Chemical reactions occur in regions of large gradients in composition and temperature, so the

Lanny D. Schmidt

2000-01-01

44

Critical phenomena in a system with two competing exothermic and endothermic reactions. Part I. Thermal explosion  

Microsoft Academic Search

This article examines the laws of thermal explosion for chemical reactions in which heat is absorbed and liberated simultaneously. The thermal equilibration time is much less than the characteristic times of the chemical reactions if the heats of reaction and activation energies are large. It is determined that the reaction rates vary during the establishment of thermal equilibrium, which alters

M. B. Borovikov; U. I. Gol'dshleger; I. A. Burovoi

1984-01-01

45

Chemical Dynamics Special Feature: Chemical reaction dynamics  

Microsoft Academic Search

Understanding the motions of the constituent atoms in reacting molecules lies at the heart of chemistry and is the central focus of chemical reaction dynamics. The most detailed questions one can ask are about the evolution of molecules prepared in a single quantum state to products in individual states, and both calculations and experiments are providing such detailed understanding of

F. Fleming Crim

2008-01-01

46

Chemical and Thermal Analysis.  

National Technical Information Service (NTIS)

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 bo...

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

1996-01-01

47

Programmability of Chemical Reaction Networks  

NASA Astrophysics Data System (ADS)

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

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

48

A Novel Solar Thermal Cycle with Chemical Looping Combustion  

Microsoft Academic Search

In this paper, we have proposed a thermal cycle with the integration of chemical-looping combustion and solar thermal energy with the temperature of about 500-600°C. Chemical-looping combustion may be carried out in two successive reactions between a reduction of hydrocarbon fuel with metal oxides and a reduced metal with oxygen in the air. This loop of chemical reactions is substituted

Hui Hong; Hongguang Jin

2005-01-01

49

Experimental Demonstrations in Teaching Chemical Reactions.  

ERIC Educational Resources Information Center

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

Hugerat, Muhamad; Basheer, Sobhi

2001-01-01

50

Experimental Demonstrations in Teaching Chemical Reactions.  

ERIC Educational Resources Information Center

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

Hugerat, Muhamad; Basheer, Sobhi

2001-01-01

51

Infrared Laser Catalyzed Chemical Reactions  

Microsoft Academic Search

The development of the laser some twelve years ago has resulted in the creation and\\/or the resuscitation of a number of experimental disciplines involving measurements of energy transfer, chemical reaction rates, high resolution spectroscopy as well as nonlinear effects. In the last three years more and more work involving the use of lasers has been reported on in the literature

A. M. Ronn

1975-01-01

52

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

53

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

54

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

55

Chemical reaction and reactor engineering  

SciTech Connect

This book discusses research and design problems, simplifying reactor design considerations such as choice of reactor configuration, optimization, and scaleup, and modern surface analysis techniques for interpreting catalytic phenomena, and deciding on the most advantageous method for the selection, testing, development, and application of catalysts. It also covers how to develop models and formulate design strategies for gas-solid catalytic and noncatalytic reactions, overcoming such obstacles as complex hydrodynamics and inaccurate chemical kinetics in the modeling of fixed-bed catalytic processes.

Carberry, J.J.; Varma, A.

1987-01-01

56

Binary counting with chemical reactions.  

PubMed

This paper describes a scheme for implementing a binary counter with chemical reactions. The value of the counter is encoded by logical values of "0" and "1" that correspond to the absence and presence of specific molecular types, respectively. It is incremented when molecules of a trigger type are injected. Synchronization is achieved with reactions that produce a sustained three-phase oscillation. This oscillation plays a role analogous to a clock signal in digital electronics. Quantities are transferred between molecular types in different phases of the oscillation. Unlike all previous schemes for chemical computation, this scheme is dependent only on coarse rate categories for the reactions ("fast" and "slow"). Given such categories, the computation is exact and independent of the specific reaction rates. Although conceptual for the time being, the methodology has potential applications in domains of synthetic biology such as biochemical sensing and drug delivery. We are exploring DNA-based computation via strand displacement as a possible experimental chassis. PMID:21121058

Kharam, Aleksandra; Jiang, Hua; Riedel, Marc; Parhi, Keshab

2011-01-01

57

Strontium isotopes as an indicator of water-rock reaction for the Coupled Thermal-Hydrological-Mechanical-Chemical-Biological (THMCB) Experimental Facility at DUSEL  

NASA Astrophysics Data System (ADS)

The Thermal-Hydrological-Mechanical-Chemical-Biological (THMCB) Experimental Facility is a proposed facility at the DUSEL-Homestake that will be used to investigate reactive transport, heat transfer and the resulting biological responses within a natural fractured rock. As part of THMCB facility design we are characterizing the current geochemical conditions and developing geochemical and isotopic indicators for fluid flow paths and reaction rates. The proposed experimental site is located at a depth of 4850 feet, primarily in the Homestake and Poorman Formations. At the experimental site, these formations are a quartz-chlorite-siderite iron formation and alumina-poor metapelite, respectively. Water samples from fractures and boreholes indicate that the pore fluid is a dilute Na-HCO3 water. The strontium isotope 87Sr/86Sr composition of surface waters is approximately 0.7106 based on stream water collected near the DUSEL site. The 87Sr/86Sr of subsurface waters sampled from fractures and boreholes throughout the mine varies from 0.7144 to 0.8145. 87Sr/86Sr and strontium concentrations suggest that calcite precipitation removes strontium and calcium from solution at shallow depths in the mine (< 3000 ft), consistent with pervasive calcite accumulation observed in the tunnels at these levels. 87Sr/86Sr values generally increase with depth and are highest in slow flowing fractures where they approach the isotopic value of the Poorman Formation (ca. 0.83±0.06). Collectively the data suggest that the Sr isotopic composition of the mine water is controlled by the flow rate of water and the extent of exchange with the surrounding rock matrix. Additionally, 87Sr/86Sr and temperature are positively correlated in the Poorman and Homestake Formations suggesting that temperature may be an additional tracer for fluid flow. Other isotopic tracers including 234U/238U, ?18O, ?D, ?13C and ?30Si are also being evaluated for use in the THMCB experimental facility.

Maher, K.; Olsen, N. J.; Harris, C.; Jones, T. L.; Conrad, M. E.; Sonnenthal, E. L.; Elsworth, D.; Uzunlar, N.; Mailloux, B. J.; Lowell, R. P.

2010-12-01

58

Chemical and radiation-chemical radical reactions in lignocellulose materials  

NASA Astrophysics Data System (ADS)

Chemical and radiation-chemical radical reactions in lignocellulose materials were explored by 3-cm and 2-mm ESR spectroscopy. Background (intrinsic) singlet signals at g=2.003 from wood pulp and lignin and those arising during reaction of lignocellulose materials with acids and chlorine were attributed to radicals with conjugated C=C bonds. The 2-mm ESR signal with 3D anisotropy of g-factor from o-semiquinone radical ions formed in reaction of lignin with NaOH was recorded for the first time. The singlet signals derived from cellulose ?-irradiated at 77 K and marked out during post-thermal reactions were assigned to radicals with conjugated bonds. In wetted cellulose, a triplet signal with ??H?2.7 mT and imposed quadruplet structure (0.5-0.7 mT) from three ?-protons was detected at 300 K and attributed to ?4-radicals. The triplet signals derived from ?2- and ?3-radicals in pyranose cycles of cellulose exhibited higher values of ??H (3.0-3.2 mT) and lower thermal stability (up to 250 K). In radiolyzed cotton pulp, detected were ESR signals derived from formyl radicals formed upon rupture of the ?5=?6 bond in pyranose cycles. Heating up irradiated samples under ?2 was accompanied by formation of peroxide radicals. Photoinduced recombination of trapped electrons with ?1-radicals was found to proceed as a chain reaction with a kinetic length of about 25 units. Photolysis (??360 nm) of radiolyzed cellulose enhanced the disclosure of pyranose cycles and, as a result, the evolution of CO2 by a factor of 2-2.5.

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

2011-09-01

59

Temperature-compensated chemical reactions  

NASA Astrophysics Data System (ADS)

Circadian rhythms are daily oscillations in behaviors that persist in constant light/dark conditions with periods close to 24h . A striking feature of these rhythms is that their periods remain fairly constant over a wide range of physiological temperatures, a feature called temperature compensation. Although circadian rhythms have been associated with periodic oscillations in mRNA and protein levels, the question of how to construct a network of chemical reactions that is temperature compensated remains unanswered. We discuss a general framework for building such a network.

Rajan, Kanaka; Abbott, L. F.

2007-02-01

60

Chemical reactions driven by concentrated solar energy  

Microsoft Academic Search

Solar energy can be used for driving endothermic reactions, either photochemically or thermally. The fraction of the solar spectrum that can be photochemically active is quite small. Therefore, it is desirable to be able to combine photochemical and thermal processes in order to increase the overall efficiency. Two thermally driven reactions are being studied: oil shale gasification and methane reforming.

Moshe Levy

1991-01-01

61

Learning to predict chemical reactions.  

PubMed

Being able to predict the course of arbitrary chemical reactions is essential to the theory and applications of organic chemistry. Approaches to the reaction prediction problems can be organized around three poles corresponding to: (1) physical laws; (2) rule-based expert systems; and (3) inductive machine learning. Previous approaches at these poles, respectively, are not high throughput, are not generalizable or scalable, and lack sufficient data and structure to be implemented. We propose a new approach to reaction prediction utilizing elements from each pole. Using a physically inspired conceptualization, we describe single mechanistic reactions as interactions between coarse approximations of molecular orbitals (MOs) and use topological and physicochemical attributes as descriptors. Using an existing rule-based system (Reaction Explorer), we derive a restricted chemistry data set consisting of 1630 full multistep reactions with 2358 distinct starting materials and intermediates, associated with 2989 productive mechanistic steps and 6.14 million unproductive mechanistic steps. And from machine learning, we pose identifying productive mechanistic steps as a statistical ranking, information retrieval problem: given a set of reactants and a description of conditions, learn a ranking model over potential filled-to-unfilled MO interactions such that the top-ranked mechanistic steps yield the major products. The machine learning implementation follows a two-stage approach, in which we first train atom level reactivity filters to prune 94.00% of nonproductive reactions with a 0.01% error rate. Then, we train an ensemble of ranking models on pairs of interacting MOs to learn a relative productivity function over mechanistic steps in a given system. Without the use of explicit transformation patterns, the ensemble perfectly ranks the productive mechanism at the top 89.05% of the time, rising to 99.86% of the time when the top four are considered. Furthermore, the system is generalizable, making reasonable predictions over reactants and conditions which the rule-based expert does not handle. A web interface to the machine learning based mechanistic reaction predictor is accessible through our chemoinformatics portal ( http://cdb.ics.uci.edu) under the Toolkits section. PMID:21819139

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

2011-09-02

62

Mound Facility activities in chemical and physical research: January-June 1980. [OLECULES; VIRIAL EQUATION; CHEMICAL REACTIONS; DEUTERIUM; TRITIUM; CALCIUM NITRATES; HEAVY WATER; THERMAL DIFFUSION; WATER; CROSS SECTIONS; MOLECULAR BEAMS; TEMPERATURE DEPENDENCE; CHELATING AGENTS; CHLOROFORM  

SciTech Connect

I. Low temperature research covered Hydrogen Intermolecular Potential Functions: five potentials have been compared to bound state energies, second virial coefficients, and total and differential scattering cross sections, but none of them consistently fits all of the data. Using a Hartree-Fock-Dispersion form with a modified damping function, three out of the four sets of data can be represented with a single potential function. Reaction Rates of Deuterium-Tritium Mixtures: two mixing chambers are being designed and built for studying D/sub 2/-T/sub 2/ and H/sub 2/-T/sub 2/. Low Temperature Trennschaukel: a bench model trennschaukel has been instrumented. II. Separation research covered Liquid Thermal Diffusion: Isotopic separations as functions of time were measured for methyl chloride, ethyl chloride, 1-chloropropane and 1-chlorobutane. The campaign to enrich chlorine-37 by liquid thermal diffusion of methyl chloride was concluded after 240 g of enriched isotope had been produced. Calcium Isotope Separation: Calcium isotope separation in the Ca(NO/sub 3/)/sub 2/-H/sub 2/O and -D/sub 2/O systems was measured using a 36.5 cm liquid phase thermal diffusion column. The largest separation was a 15% change in the calcium-48 abundance. Molecular Beam Scattering: a supersonic Ne beam through a cell containing Ar was used to measure low-energy, elastic, total cross sections of neon/argon in the velocity range of 4 to 10 (x 10/sup 4/) cm/s. Cross sections at onset of clustering were 7% higher than at minimum cluster conditions. Mutual Diffusion: Study continues on the temperature dependence of the mutal diffusion coefficients for binary noble gas mixtures, particularly argon with helium, neon, and xenon. Metal Chemical Exchange With Macrocyclic Ligands: The equilibrium single-stage separation factor was determined for two additional LiTFA/221 cryptand/CHCl/sub 3/ and two LiTFA/211 cryptand/CHCl/sub 3/ exchange systems.

Not Available

1980-08-29

63

Observation of Individual Chemical Reactions in Solution  

Microsoft Academic Search

Discrete chemical reaction events occurring in solution have been observed by single photon detection of a bimolecular, chemiluminescent reaction. The reactants were generated from 9,10-diphenylanthracene in acetonitrile with potential pulses applied to an ultramicroelectrode. Electrogenerated radical ions of opposite sign react to yield the excited singlet state of the parent compound. The chemical reactions were restricted to a 20-femtoliter volume

Maryanne M. Collinson; R. Mark Wightman

1995-01-01

64

Quantum theory of chemical reaction rates  

SciTech Connect

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

Miller, W.H. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley Lab., CA (United States). Chemical Sciences Div.

1994-10-01

65

Kinetics of Chemical Reactions in Foods  

Microsoft Academic Search

Chemical reactions occur in foods during processing and storage. Some reactions result in a quality loss and must be minimized,\\u000a whereas others result in the formation of a desired flavor or color and must be optimized to obtain the best product quality.\\u000a Kinetics is a science that involves the study of chemical reaction rates and mechanisms. An understanding of reaction

Romeo T. Toledo

66

Dynamic Reaction Figures: An Integrative Vehicle for Understanding Chemical Reactions  

ERIC Educational Resources Information Center

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

Schultz, Emeric

2008-01-01

67

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

68

Fluid flow and chemical reaction kinetics in metamorphic systems  

SciTech Connect

The treatment and effects of chemical reaction kinetics during metamorphism are developed along with the incorporation of fluid flow, diffusion, and thermal evolution. The interplay of fluid flow and surface reaction rates, the distinction between steady state and equilibrium, and the possible overstepping of metamorphic reactions are discussed using a simple analytic model. This model serves as an introduction to the second part of the paper, which develops a reaction model that solves the coupled temperature-fluid flow-chemical composition differential equations relevant to metamorphic processes. Consideration of stable isotopic evidence requires that such a kinetic model be considered for the chemical evolution of a metamorphic aureole. A general numerical scheme is discussed to handle the solution of the model. The results of this kinetic model allow us to reach several important conclusions regarding the factors controlling the chemical evolution of mineral assemblages during a metamorphic event. 41 refs., 19 figs., 5 tabs.

Lasaga, A.C.; Rye, D.M. (Yale Univ., New Haven, CT (United States))

1993-05-01

69

When do chemical reactions promote mixing?  

Microsoft Academic Search

This paper reviews various situations, in which a chemical reaction promotes the mixing (of reactants and products) in an unstirred reactor. One example is an exothermic chemical reaction, which of course increases the local temperature of an unstirred reacting fluid and hence decreases the density. This can produce natural convection. Thus if the walls of the reactor are cooled, there

T. P. Ivleva; A. G. Merzhanov; E. N. Rumanov; N. I. Vaganova; A. N. Campbell; A. N. Hayhurst

2011-01-01

70

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.

71

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

72

Method and apparatus for controlling gas evolution from chemical reactions  

DOEpatents

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

Skorpik, James R. (Kennewick, WA); Dodson, Michael G. (Richland, WA)

1999-01-01

73

Method and apparatus for controlling gas evolution from chemical reactions  

DOEpatents

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

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

1999-05-25

74

Chemical preconcentrator with integral thermal flow sensor  

DOEpatents

A chemical preconcentrator with integral thermal flow sensor can be used to accurately measure fluid flow rate in a microanalytical system. The thermal flow sensor can be operated in either constant temperature or constant power mode and variants thereof. The chemical preconcentrator with integral thermal flow sensor can be fabricated with the same MEMS technology as the rest of the microanlaytical system. Because of its low heat capacity, low-loss, and small size, the chemical preconcentrator with integral thermal flow sensor is fast and efficient enough to be used in battery-powered, portable microanalytical systems.

Manginell, Ronald P. (Albuquerque, NM); Frye-Mason, Gregory C. (Cedar Crest, NM)

2003-01-01

75

Chemical Reactions in High-Speed Flows  

Microsoft Academic Search

Hypersonic flows are distinguished by a capacity to provoke endothermic chemical reactions in their constituent molecules. Interactions of gas-flow and chemical activity also take place in combustible (exothermic) gas mixtures, such as may be found in propulsive devices. After a brief validation of the idea that chemically active flows can be adequately treated via Euler-Prandtl theory, the paper is devoted

J. F. Clarke

1991-01-01

76

Dynamics in Tangible Chemical Reactions  

Microsoft Academic Search

Spatial understanding and the understanding of dynamic change in the spatial structure of molecules during a reaction is essen- tial for designing new molecules. Knowing the physical processes in the reactions helps to speed up the designing process. To support the designer with the correct representation of the designed molecule as well as showing the dynamic behavior of the whole

Patrick Maier; Marcus T; Gudrun Klinker

77

Thermal hazard analyses and incompatible reaction evaluation of hydrogen peroxide by DSC  

Microsoft Academic Search

Hydrogen peroxide (H2O2), historically, due to its broad applications in the chemical industries, has caused many serious fires and explosions worldwide.\\u000a Its thermal hazards may also be incurred by an incompatible reaction with other chemical materials, and a runaway reaction\\u000a may be induced in the last stage. This study applied thermal analytical methods to explore the H2O2 leading to thermal

Sheng-Hung Wu; Jen-Hao Chi; Chun-Chin Huang; Nung-Kai Lin; Jiou-Jhu Peng; Chi-Min Shu

2010-01-01

78

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

79

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

80

Chemical Changes in Lipids Produced by Thermal Processing.  

ERIC Educational Resources Information Center

|Describes heat effects on lipids, indicating that the chemical and physical changes that occur depend on the lipid's composition and conditions of treatment. Thermolytic and oxidation reactions, thermal/oxidative interaction of lipids with other food components and the chemistry of frying are considered. (JN)|

Nawar, Wassef W.

1984-01-01

81

Chemical Reactions and the Overhead Projector.  

ERIC Educational Resources Information Center

|Describes the construction of a simple apparatus that can be used to take advantage of the overhead projector in a spectacular presentation of chemical reactions that complement quantitative approaches of study in the traditional high school science classroom. (JRH)|

Papageorgiou, George; Xenos, John

1996-01-01

82

FAST ELEMENTARY STEPS IN CHEMICAL REACTION MECHANSIMS  

Microsoft Academic Search

A review is presented of studies of fast chemical reaction steps which ; were studied using various relaxation techniques. These studies include ligand ; substitution in metal complexes, proton transfer, and enzymatic hydrolysis. ; (D.L.C.);

M. Eigen

1963-01-01

83

Chemical Reaction Dynamics in Nanoscale Environments.  

National Technical Information Service (NTIS)

The major focus of the research in this program is the study of the behavior of molecular systems confined in nanoscale environments. The goal is to develop a theoretical framework for predicting how chemical reactions occur in nanoscale environments. To ...

E. M. Goldfield H. B. Schlegel W. L. Hase

2006-01-01

84

Aerosol Simulation Including Chemical and Nuclear Reactions.  

National Technical Information Service (NTIS)

The numerical simulation of aerosol transport, including the effects of chemical and nuclear reactions presents a challenging dynamic accounting problem. Particles of different sizes agglomerate and settle out due to various mechanisms, such as diffusion,...

E. C. Lemmon E. S. Marwil

1985-01-01

85

Photo and thermal reactions of ferrous hydroxide  

NASA Astrophysics Data System (ADS)

The reactions of ferrous ion near neutral pH are of interest because of its known presence in the Archaean oceans. We have confirmed the long wavelength ultraviolet photochemical and the thermal reactions of ferrous hydroxide to form hydrogen. We have shown that a claim of the reduction of carbon dioxide to formaldehyde at neutral pH is mistaken. By the use of14C labelled compounds, we have found that less than 1 ppm of carbon dioxide is reduced to formaldehyde and less than 10 ppm of formate ion is so reduced. The thermal reaction to form hydrogen has a small activation energy of 7 kcal mole-1. We conclude that thermal and photochemical formation of hydrogen from ferrous ion in the Archaean ocean could be comparable at pH 8 9. At lower pH, toward its limit at pH 5, the photochemical reaction would predominate. Both the thermal and photochemical reactions are specific for ferrous hydroxide, being far slower for the phosphate (>50- and 7-fold) and the bicarbonate (2- and 30-fold) complexes.

Mauzerall, David; Borowska, Zofia; Zielinski, Irene

1993-04-01

86

Chemical reactions in quantum crystals  

Microsoft Academic Search

Solid parahydrogen, known as a quantum crystal, is a novel matrix for the study of physical and chemical processes of molecules at low temperatures by high-resolution infrared spectroscopy. Ro-vibrational motion of molecules embedded in solid parahydrogen is well quantized on account of the weak interaction in the crystal. In addition, molecules are almost free from the cage effect because of

Takamasa Momose; Mizuho Fushitani; Hiromichi Hoshina

2005-01-01

87

Determining Interconnections in Chemical Reaction Networks  

Microsoft Academic Search

We present a methodology for robust determination of chemical reaction network interconnections. Given time series data that are collected from experiments and taking into account the measurement error, we minimize the 1-norm of the decision variables (reaction rates) keeping the data in close Euler-flt with a general model structure based on mass action kinetics which models the species' dynamics. We

Antonis Papachristodoulou; Ben Recht

2007-01-01

88

Chemical Principles Revisited: Annotating Reaction Equations.  

ERIC Educational Resources Information Center

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

Tykodi, R. J.

1987-01-01

89

Chemical Principles Revisited: Annotating Reaction Equations.  

ERIC Educational Resources Information Center

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

Tykodi, R. J.

1987-01-01

90

Entropy Generation in a Chemical Reaction  

ERIC Educational Resources Information Center

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

Miranda, E. N.

2010-01-01

91

Novel variational principles of chemical reaction  

Microsoft Academic Search

Minimum principles of chemical reaction coordinates are established. IRC (intrinsic reaction coordinate) draws the path of minimum distance from reactant to product. The distance is measured in the rigged configuration Riemannian space whose metric is determined by the distribution of the adiabatic potential energy. Moreover, minimum property of the intrinsic principle of least action is established for the intrinsic dynamism

Akitomo Tachibana; Kenichi Fukui

1980-01-01

92

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

93

Energy transport effects on rapid bimolecular chemical reactions  

NASA Astrophysics Data System (ADS)

Mass diffusion is known to affect the rate of rapid bimolecular chemical reactions in solution. Rate constants are decreased with respect to their collisional values, an effect which can renormalize the bare rate constant by a factor as large as 100. In this paper we explore the added effect of the thermal diffusivity on rapid reaction rates. This effect arises from the coupling of energy fluctuations to density fluctuations either through the activation energy for reaction or from the heat of reaction. Calculations presented here, using statistical nonequilibrium thermodynamics to calculate the nonequilibrium radial distribution function, show that this effect vanishes in dilute solution. In more concentrated solutions the effect remains negligible unless the diffusion constant is much larger than the thermal diffusivity. Even then the effect is only of the order of 10% of the size of mass diffusion effects in concentrated solutions. Present address: Chemistry Department, University of California, La Jolla, CA 92093, USA.

Keizer, Joel; Peacock-Lopez, Enrique

1987-11-01

94

Thermal fluorine atom reactions with 3-chloropropene  

SciTech Connect

The thermal reactions of fluorine atoms with 3-chloropropene have been studied by using YF atoms formed by the ZF(n,2n) YF nuclear reaction in SF6, and moderated to thermal energies by multiple collisions with the SF6. The reactions with CH2ClCH=CH2 are distributed between abstraction and addition in the approximate ratio 1/3. The relative rates of terminal/central attack CH2ClCH=CH2 are 1.55 +/- 0.05 as compared to 1.35 +/- 0.02 for propene, with the difference attributable to the deactivating effect on an olefinic carbon atom of the Cl substituent on the adjacent carbon. Studies of the overall rate of reaction of fluorine atoms with 3-chloropropene vs. each of four competitors at 287 K showed relative rates of 1.63 vs. HI, 0.86 vs. C2H2, 2.6 vs. CH4, and 6.9 vs. H2. The overall reaction rate for thermal chlorine atoms with CH2ClCH=CH2 is (15 +/- 4) x 10 cmT molecule s . 23 references, 3 figures, 6 tables

Iyer, R.S.; Vasi, L.; Rowland, F.S.

1985-11-07

95

Topologically invariant reaction coordinates for simulating multistate chemical reactions.  

PubMed

Evaluating free energy profiles of chemical reactions in complex environments such as solvents and enzymes requires extensive sampling, which is usually performed by potential of mean force (PMF) techniques. The reliability of the sampling depends not only on the applied PMF method but also the reaction coordinate space within the dynamics is biased. In contrast to simple geometrical collective variables that depend only on the positions of the atomic coordinates of the reactants, the E(gap) reaction coordinate (the energy difference obtained by evaluating a suitable force field using reactant and product state topologies) has the unique property that it is able to take environmental effects into account leading to better convergence, a more faithful description of the transition state ensemble and therefore more accurate free energy profiles. However, E(gap) requires predefined topologies and is therefore inapplicable for multistate reactions, in which the barrier between the chemically equivalent topologies is comparable to the reaction activation barrier, because undesired "side reactions" occur. In this article, we introduce a new energy-based collective variable by generalizing the E(gap) reaction coordinate such that it becomes invariant to equivalent topologies and show that it yields more well behaved free energy profiles than simpler geometrical reaction coordinates. PMID:23214508

Mones, Letif; Csányi, Gábor

2012-12-17

96

Thermal reaction processes in a relativistic QED plasma drop  

SciTech Connect

The equilibrium size and temperature limits of thermally and chemically equilibrated e{sup +}e{sup -{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.

Kuznetsova, Inga; Habs, Dieter; Rafelski, Johann [Department of Physics, University of Arizona, Tucson, Arizona 85721 (United States) and Department fuer Physik der Ludwig-Maximilians, Universitaet Muenchen und Maier-Leibnitz-Laboratorium, Am Coulombwall 1, 85748 Garching (Germany)

2010-03-01

97

Chain reaction : chemical reactions, student reactions and mine  

Microsoft Academic Search

This article describes a primary school science unit on 'chemical and change' that the author presented after attending a professional development course. The article describes her detailed preparation, which was necessary to overcome her previous extremely negative attitude to science teaching. The article then describes the author's change in her attitude to teaching science, and the students' extremely positive attitudes

B Dinneen

2008-01-01

98

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

99

Chemical energy storage system for SEGS solar thermal power plant  

SciTech Connect

In October 1988, a symposium was held in Helendale, California, to discuss thermal energy storage (TES) concepts applicable to medium-temperature (200 to 400{degrees}C) solar thermal electric power plants, in general, and the solar electric generating system (SEGS) plants developed by Luz International, in particular. Chemical reaction energy storage based on the reversible reaction between metal oxides and metal hydroxides was identified as a leading candidate for meeting Luz International's cost and performance requirements. The principal objectives of this study were to identify the design conditions, requirements, and potential feasibility for a chemical energy storage system applied to a SEGS solar thermal power plant. The remaining sections of this report begin by providing an overview of the chemical reaction energy storage concept and a SEGS solar thermal power plant. Subsequent sections describe the initial screening of alternative evaporation energy sources and the more detailed evaluation of design alternatives considered for the preferred evaporation energy source. The final sections summarize the results, conclusions, and recommendations. 7 refs., 8 figs., 13 tabs.

Brown, D.R.; LaMarche, J.L.; Spanner, G.E.

1991-09-01

100

Chemical energy storage system for SEGS solar thermal power plant  

NASA Astrophysics Data System (ADS)

In October 1988, a symposium was held in Helendale, California, to discuss thermal energy storage (TES) concepts applicable to medium temperature (200 to 400 C) solar thermal electric power plants, in general, and the solar electric generating system (SEGS) plants developed by Luz International, in particular. Chemical reaction energy storage based on the reversible reaction between metal oxides and metal hydroxides was identified as a leading candidate for meeting Luz International's cost and performance requirements. The principal objectives of this study were to identify the design conditions, requirements, and potential feasibility for a chemical energy storage system applied to a SEGS solar thermal power plant. The remaining sections of this report begin by providing an overview of the chemical reaction energy storage concept and a SEGS solar thermal power plant. Subsequent sections describe the initial screening of alternative evaporation energy sources and the more detailed evaluation of design alternatives considered for the preferred evaporation energy source. The final sections summarize the results, conclusions, and recommendations.

Brown, D. R.; Lamarche, J. L.; Spanner, G. E.

1991-09-01

101

Chemical Demonstrations with Consumer Chemicals: The Black and White Reaction  

NASA Astrophysics Data System (ADS)

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

Wright, Stephen W.

2002-01-01

102

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

103

Chemical reaction rates and solvent friction  

SciTech Connect

The role of the dynamic solvent friction in influencing the rates of chemical reactions in solution is described. Features considered include (a) the bias of the reaction coordinate toward a direction of lesser friction in the diffusive limit, (b) the importance of frequency-dependent friction in atom transfers, tunneling reactions and isomerizations, (c) the dynamic nonequilibrium solvation in charge transfers which leads to a polar solvent molecule reorientation time dependence for the rate, and (d) the importance of internal degrees of freedom in the location of the Kramers turnover for isomerizations.

Hynes, J.T.

1986-01-01

104

Chemical and thermal unfolding of calreticulin.  

PubMed

Calreticulin is a soluble endoplasmic reticulum chaperone, which has a relatively low melting point due to its remarkable structure with a relatively high content of flexible structural elements. Using far ultraviolet circular dichroism (CD) spectroscopy and a fluorescent dye binding thermal shift assay, we have investigated the chemical and thermal stability of calreticulin. When the chemical stability of calreticulin was assessed, a midpoint for calreticulin unfolding was calculated to 3.0M urea using CD data at 222 nm. Using the fluorescent dye binding thermal shift assay, calreticulin was found to obtain a molten structure in urea concentrations between 1-1.5 M urea, and to unfold/aggregate at high and low pH values. The results demonstrated that the fluorescent dye binding assay could measure the thermal stability of calreticulin in aqueous buffers with results comparable to melting points obtained by other techniques. PMID:22998950

Duus, K; Larsen, N; Tran, T A T; Güven, E; Skov, L K; Jespersgaard, C; Gajhede, M; Houen, G

2013-05-01

105

Programmable calculator and kinetics of chemical reactions  

Microsoft Academic Search

This paper suggests the use of simulation techniques using a programmable calculator in the study of chemical reactions.† This article does not deal with the use of programmable calculations for producing ‘experimental’ data (i.e. as a substitute for the laboratory). Readers interested in that direction may refer to [1]. Also, I would like to thank E. W. Jenkins of the

Amos Ehrlich

1980-01-01

106

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

107

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

108

Documentation of Chemical Reactions. I. A Faceted Classification  

ERIC Educational Resources Information Center

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

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

1973-01-01

109

Visualization of chemical reaction dynamics: Toward understanding complex polyatomic reactions  

PubMed Central

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

SUZUKI, Toshinori

2013-01-01

110

Thermal plasma chemical synthesis of powders  

SciTech Connect

Thermal plasma processing has been increasingly used to synthesize submicron powders of high-purity ceramics and metals. The high temperatures generated with the plasma provide a vapor phase reaction zone for elements with high boiling points and refractory materials. An overview is presented on the general plasma technology used in synthesis and on the properties of plasma powders.

Vogt, G.J.; Newkirk, L.R.

1985-01-01

111

Neutral theory of chemical reaction networks  

NASA Astrophysics Data System (ADS)

To what extent do the characteristic features of a chemical reaction network reflect its purpose and function? In general, one argues that correlations between specific features and specific functions are key to understanding a complex structure. However, specific features may sometimes be neutral and uncorrelated with any system-specific purpose, function or causal chain. Such neutral features are caused by chance and randomness. Here we compare two classes of chemical networks: one that has been subjected to biological evolution (the chemical reaction network of metabolism in living cells) and one that has not (the atmospheric planetary chemical reaction networks). Their degree distributions are shown to share the very same neutral system-independent features. The shape of the broad distributions is to a large extent controlled by a single parameter, the network size. From this perspective, there is little difference between atmospheric and metabolic networks; they are just different sizes of the same random assembling network. In other words, the shape of the degree distribution is a neutral characteristic feature and has no functional or evolutionary implications in itself; it is not a matter of life and death.

Lee, Sang Hoon; Bernhardsson, Sebastian; Holme, Petter; Kim, Beom Jun; Minnhagen, Petter

2012-03-01

112

Oscillations in a laser-induced chemical reaction: coupling of chemical reactions with an acoustic effect  

Microsoft Academic Search

An oscillatory phenomenon has been observed in a laser-induced photochemical reaction occurring in a degassed acetone or benzene solution of the complex [}Au[P(C6H4OMe-p)3{]2-(?-C?C)] after flash photolysis. It been confirmed that the observed oscillation is due to the chemical reactions coupling with the photoacoustic effect.

Yu-Xiang Weng; Hong Xiao; Kwok-Chu Chan; Chi-Ming Che

1997-01-01

113

Chemical reaction process and the single crystal growth of CuInS 2 compound  

Microsoft Academic Search

In order to establish the preparation method of high-quality CuInS2 single crystals, we have investigated the chemical reaction process by means of differential thermal analysis and powder X-ray diffraction measurements. In the chemical reaction process of a Cu+In+2S mixture, an explosive exothermic reaction occurs at 640°C, which is ascribed to the formation of products of the In–S system. In the

Hiroaki Matsushita; Tomohiro Mihira; Takeo Takizawa

1999-01-01

114

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

115

Chemical reactions driven by concentrated solar energy  

NASA Astrophysics Data System (ADS)

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

Levy, Moshe

116

Thermal and chemical equilibrium for vaporizing sources  

NASA Astrophysics Data System (ADS)

Vaporized sources produced in collisions between 36Ar and 58Ni at 95 MeV per nucleon have been detected with the multidetector INDRA. Complete information concerning the deexcitation properties of quasi-projectiles, including second moments of chemical composition, is compared to a quantum statistical model describing a gas of fermions and bosons in thermal and chemical equilibrium. Inclusions in the calculation of all known discrete levels of nuclear species which deexcite into light particles and of a final state excluded volume interaction are found decisive to very well reproduce the experimental data, which strongly supports that thermodynamical equilibrium was achieved at freeze-out for such sources.

INDRA Collaboration; Borderie, B.; Gulminelli, F.; Rivet, M. F.; Tassan-Got, L.; Assenard, M.; Auger, G.; Bocage, F.; Bougault, R.; Brou, R.; Buchet, Ph.; Colin, J.; Dayras, R.; Demeyer, A.; Frankland, J. D.; Galichet, E.; Genouin-Duhamel, E.; Gerlic, E.; Germain, M.; Guinet, D.; Lautesse, P.; Laville, J. L.; Lecolley, J. F.; Lefort, T.; Legrain, R.; Le Neindre, N.; Louvel, M.; Maskay, A. M.; Nalpas, L.; Nguyen, A. D.; Parlog, M.; Plagnol, E.; Rahmani, A.; Reposeur, T.; Rosato, E.; Saint-Laurent, F.; Salou, S.; Steckmeyer, J. C.; Stern, M.; Tabacaru, G.; Tamain, B.; Tirel, O.; Vintache, D.; Volant, C.

117

Chemical thermalization in relativistic heavy ion collisions.  

PubMed

We compute by numerical integration of the Dirac equation the number of quark-antiquark pairs initially produced in the classical color fields of colliding ultrarelativistic nuclei. While the number of pairs is parametrically suppressed in the coupling constant, we find that in this classical field model their production rate is comparable to the thermal ratio of gluons/pairs=9Nf/32. After isotropization one thus would have a quark-gluon plasma in chemical equilibrium. PMID:16486690

Gelis, F; Kajantie, K; Lappi, T

2006-01-27

118

Thermal denaturation assays in chemical biology.  

PubMed

Thermal denaturation-based methods are becoming increasingly used to characterize protein stability and interactions. Recent technical advances have made these methods more suitable for high throughput screening. Reasonable throughput and the ability to perform these screens using commonly used instruments, such as RT-PCR machines or simple plate readers equipped with heating devices, facilitate these experiments in almost any laboratory. Introducing an aggregation-based monitoring approach as well as alternative fluorophores has allowed the screening of a wider range of proteins, including membrane proteins, against large chemical libraries. Thermal denaturation-based methods are independent of protein function, which is especially useful for the identification of orphan protein function. Here, we review applications of thermal denaturation-based methods in characterizing protein stability and ligand binding, and also provide information on protocol modifications that may further increase throughput. PMID:22066913

Senisterra, Guillermo; Chau, Irene; Vedadi, Masoud

2011-11-08

119

Effect of Chemical and Nuclear Reactions on Aerosol Transport.  

National Technical Information Service (NTIS)

The inclusion of the effects of chemical and nuclear reactions on aerosol transport is a complex problem in numerical simulation. Heterogeneous chemical reactions occur at the interface between the surface of a particle and the suspending medium, or betwe...

E. C. Lemmon E. S. Marwil

1984-01-01

120

Scattering Resonances in the Simplest Chemical Reaction  

NASA Astrophysics Data System (ADS)

Recent studies of state-resolved angular distributions show the participation of reactive scattering resonances in the simplest chemical reaction. This review is intended for those who wish to learn about the state-of-the-art in the study of the H + H2 reaction family that has made this breakthrough possible. This review is also intended for those who wish to gain insight into the nature of reactive scattering resonances. Following a tour across several fields of physics and chemistry where the concept of resonance has been crucial for the understanding of new phenomena, we offer an operational definition and taxonomy of reactive scattering resonances. We introduce simple intuitive models to illustrate each resonance type. We focus next on the last decade of H + H2 reaction dynamics. Emphasis is placed on the various experimental approaches that have been applied to the search for resonance behavior in the H + H2 reaction family. We conclude by sketching the road ahead in the study of H + H2 reactive scattering resonances.

Fernandez-Alonso, Felix; Zare, Richard N.

2002-10-01

121

Molecular Dynamics Simulations of Chemical Reactions for Use in Education  

ERIC Educational Resources Information Center

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

Qian Xie; Tinker, Robert

2006-01-01

122

(Homogeneous-heterogeneous combustion: Thermal and chemical coupling)  

SciTech Connect

This is a program to characterize fundamental issues and practical applications of homogeneous-heterogeneous reactions. Fundamental studies of reactions at low pressures and of boundary layer characterization give microscopic information on the processes. Ignition and extinction studies over simple geometries give basic bifurcation behavior with which to characterize multiple steady states and their stabilities and hopefully to identify the types of behavior which may occur. Use of catalytic monoliths will permit examination of the chemical and thermal performance of one of the most important types of geometries in which both types of reaction can occur. Modeling will tie all of these aspects together by showing how individual components interact, Predicting performance of monoliths, and providing the framework for translating these ideas into technological contexts.

Not Available

1992-01-01

123

Industrial pyrolysis of cellulosic materials. [Chemical reactions occurring during pyrolysis and analysis of volatile fractions  

Microsoft Academic Search

Industrial pyrolysis of cellulosic materials to various fuels and chemicals requires an understanding of the complex reactions involved and how they can be controlled to provide acceptable yields. Investigation of a variety of model compounds and cellulosic substrates by modern methods of thermal and chemical analysis has shown that initial pyrolysis of glycosidically linked compounds takes place through transglycosylation to

Shafizadeh

1975-01-01

124

Chemical energy storage system for SEGS solar thermal power plant  

NASA Astrophysics Data System (ADS)

The Pacific Northwest Laboratory evaluated the potential feasibility of using chemical energy storage at the Solar Electric Generating System (SEGS) power plants developed by Luz International. Like sensible or latent heat energy storage systems, chemical energy storage can be beneficially applied to solar thermal power plants to dampen the impact of cloud transients, extend the daily operating period, and/or allow a higher fraction of power production to occur during high-valued peak demand periods. Higher energy storage densities make chemical energy storage a potentially attractive option. The results of the evaluation indicated that a system based on the reversible reaction, CaO + H2O = Ca(OH)2, could be technically and economically feasible for this application, but many technical and economic issues must be resolved.

Brown, D. R.; Lamarche, J. L.; Spanner, G. E.

1992-04-01

125

Organic chemical reactions in supercritical water  

SciTech Connect

Water near or above its critical point (374 C, 218 atm) is attracting increased attention as a medium for organic chemistry. Most of this new attention is driven by the search for more green or environmentally benign chemical processes. Using near-critical or supercritical water (SCW) instead of organic solvents in chemical processes offers environmental advantages and may lead to pollution prevention. Interest in doing chemistry in SCW is not entirely new, however. There has been much previous research in this area with applications in synthetic fuels production, biomass processing, waste treatment, materials synthesis, and geochemistry. Water near its critical point possesses properties very different from those of ambient liquid water. The dielectric constant is much lower, and the number and persistence of hydrogen bonds are both diminished. As a result, high-temperature water behaves like many organic solvents in that organic compounds enjoy high solubilities in near-critical water and complete miscibility with SCW. Moreover, gases are also miscible in SCW so employing a SCW reaction environment provides an opportunity to conduct chemistry in a single fluid phase that would otherwise occur in a multiphase system under more conventional conditions. The paper discusses the use of supercritical water in the following reactions: hydrogenation/dehydrogenation; C-C bond formation; rearrangements; hydration/dehydration; elimination; hydrolysis; partial oxidation; H-D exchange; decomposition; and oxidation.

Savage, P.E. [Univ. of Michigan, Ann Arbor, MI (United States). Chemical Engineering Dept.

1999-02-01

126

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

127

Distinguishing solid bitumens formed by thermochemical sulfate reduction and thermal chemical alteration  

Microsoft Academic Search

Insoluble solid bitumens are organic residues that can form by the thermal chemical alteration (TCA) or thermochemical sulfate reduction (TSR) of migrated petroleum. TCA may actually encompass several low temperature processes, such as biodegradation and asphaltene precipitation, followed by thermal alteration. TSR is an abiotic redox reaction where petroleum is oxidized by sulfate. It is difficult to distinguish solid bitumens

Simon R. Kelemen; Clifford C. Walters; Peter J. Kwiatek; Mobae Afeworki; Michael Sansone; Howard Freund; Robert J. Pottorf; Hans G. Machel; Tongwei Zhang; Geoffrey S. Ellis; Yongchun Tang; Kenneth E. Peters

2008-01-01

128

Model based comparison of thermal and plasma chemical vapor deposition of carbon nanotubes  

Microsoft Academic Search

A model-based comparison of thermal and plasma chemical vapor deposition (CVD) techniques for the growth of carbon nanotubes (CNTs) from methane feedstock is presented. In thermal CVD, the feedstock does not dissociate in the gas phase at temperatures commonly used for single- and multiwalled CNT growth (<=900 °C) and the nanotube production is entirely due to surface reaction of CH4

D. B. Hash; M. Meyyappan

2003-01-01

129

Suspended heated silicon platform for rapid thermal control of surface reactions with application to carbon nanotube synthesis  

Microsoft Academic Search

Rapid continuous thermal control of chemical reactions such as those for chemical vapor deposition CVD growth of nanotubes and nanowires cannot be studied using traditional reactors such as tube furnaces, which have large thermal masses. We present the design, modeling, and verification of a simple, low-cost reactor based on resistive heating of a suspended silicon platform. This system achieves slew

Lucas van Laake; Anastasios John Hart; Alexander H. Slocum

2007-01-01

130

Suspended heated silicon platform for rapid thermal control of surface reactions with application to carbon nanotube synthesis  

Microsoft Academic Search

Rapid continuous thermal control of chemical reactions such as those for chemical vapor deposition (CVD) growth of nanotubes and nanowires cannot be studied using traditional reactors such as tube furnaces, which have large thermal masses. We present the design, modeling, and verification of a simple, low-cost reactor based on resistive heating of a suspended silicon platform. This system achieves slew

Lucas van Laake; Anastasios John Hart; Alexander H. Slocum

2007-01-01

131

Thermophoretic transport in impinging flows including chemical reactions  

NASA Astrophysics Data System (ADS)

The research constitutes a fundamental study of transport phenomena that has applications to the fabrication of optical fibers. The flow, heat and mass transfer with chemical reactions, and thermophoretic transport of silica particles are studied. The governing equations have been formulated and solved to determine the velocity, temperature and species concentrations, and the effects of buoyancy, variable properties, chemical reactions, and thermophoretic transport on deposition uniformity and efficiency. A path-line/stream-line approach for determining variable particle concentration stagnation deposition with thermophoretic transport is introduced. The research is of fundamental interest and has applications to optical fiber fabrication. A review of the thermophoresis phenomena is provided including a recommended treatment for the thermophoretic coefficient, K. A discussion of the related chemical reactions is given. A study of a H2-N 2 non-premixed jet flame is performed to appraise the proposed H2 oxidation reaction rate and heat release rate. The present results of the velocity and temperature distributions are in very good agreement with the published experimental data. A study of silica (SiO2) particle transport in a free jet system is carried out. The gas entrainment and the thermophoretic transport are two important parameters that determine the particle transport. Both non-reacting and reacting jet flows are studied. The effects of inclination of jet flows on particle transport are also studied. A path-line/stream-line approach for determining deposition with thermophoretic transport in stagnation flow is introduced. This approach allows a variable particle concentration inlet boundary condition to be used. A closed form solution is achieved using this approach. Numerical studies of deposition on a cylindrical preform for both non-reacting and reacting jets are also investigated. A study of a small scale fiber fabrication is made with a cylindrical preform and two burners. Of special interest are the effects of preform temperature and preform thermal conductivity on the deposition efficiency.

Hsu, Frank Kuan-Chao

132

Chemical Changes in Proteins Produced by Thermal Processing.  

ERIC Educational Resources Information Center

Discusses effects of thermal processing on proteins, focusing on (1) the Maillard reaction; (2) heat denaturation of proteins; (3) aggregation, precipitation, gelation, and degradation; and (4) other thermally induced protein reactions. Also discusses effects of thermal processing on muscle foods, egg proteins, fruits and vegetables, and cereal…

Dutson, T. R.; Orcutt, M. W.

1984-01-01

133

Chemical Changes in Proteins Produced by Thermal Processing.  

ERIC Educational Resources Information Center

|Discusses effects of thermal processing on proteins, focusing on (1) the Maillard reaction; (2) heat denaturation of proteins; (3) aggregation, precipitation, gelation, and degradation; and (4) other thermally induced protein reactions. Also discusses effects of thermal processing on muscle foods, egg proteins, fruits and vegetables, and cereal…

Dutson, T. R.; Orcutt, M. W.

1984-01-01

134

Chemical reactivity test for thermal stability  

SciTech Connect

Lawrence Livermore National Laboratory (LLNL) has developed a thermal stability test procedure that is currently being evaluated by the Department of Defense (DOD) Explosives Safety Board as an equivalent alternate test to the DOD Technical Bulletin 700-2 {open_quotes}Thermal Stability Test at 75{degrees}C{close_quotes}. The LLNL Chemical Reactivity Test (CRT) is significantly more severe than the existing {open_quotes}Thermal Stability Test at 75{degrees}C{close_quotes} and is also quantitative in nature. It has been approved by the Department of Energy (DOE) Explosives Safety Committee as an equivalent alternate thermal stability test and has been in use by LLNL for over 30 years. It is currently used by other DOE and DOD organizations as the standard small-scale safety test for determining thermal stability and material compatibility. The LLNL CRT is run on a 0.250 gm sample for 22 hours at 120{degrees}C rather than the 50 gm sample for 48 hours at 75{degrees}C as required for the Thermal Stability Test. Thus the CRT is a much more severe test since it is run at 120{degrees}C rather than 75{degrees}C. Simple Arrhenius kinetics predict a material decomposition rate of approximately 25 times greater at 120{degrees}C than at 75{degrees}C. Any material under test that exhibits gas evolution exceeding 4 cc/gm (approximately 0.8 % decomposition) is considered suspect and additional testing and/or evaluation is then performed to determine if the material is thermally unstable. In addition to the CRT being significantly more severe and quantitative, there are significant other advantages for using the CRT. These include: (1) the increased safety afforded to operating personnel and equipment by using a fraction of the test material, (2) the cost savings associated with reduced sample heating time and the use of less sample material, and (3) the reduced amount of post-test waste produced.

Prokosch, D.W.; Garcia, F.

1994-07-01

135

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

136

Thermal Oxidative Degradation Reactions of Perfluoroalkylethers.  

National Technical Information Service (NTIS)

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...

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

1981-01-01

137

Modeling enzymatic reactions via chemical Langevin-Levy equation  

Microsoft Academic Search

Chemical Langevin Equation (CLE) describes a useful approximation in stochastic modeling of chemical reactions. CLE-based ?-leaping algoritm updates the quantities of every molecule in a reaction system with a period of ?, firing every reaction in the system so many times that the concentration of each molecule can be assumed to remain in the current concentration state. Substituting the Brownian

Mustafa A. Altinkaya; Ercan E. Kuruoglu

2012-01-01

138

Chemical reactions in reactive powder metal mixtures during shock compression  

Microsoft Academic Search

A heterogeneous chemical reaction model is proposed and used to describe shock-induced chemical reactions that occur in reactive granular mixtures during shock compression. The proposed heterogeneous model is intended for application in mesoscale simulations at locations where reactant particles are in contact. Previous studies have employed homogeneous reaction rate models with Arrhenius type kinetics, in which the material transport mechanism

D. J. Reding; S. Hanagud

2009-01-01

139

Development of the reaction time accelerating molecular dynamics method for simulation of chemical reaction  

Microsoft Academic Search

We present a novel and efficient method to integrate chemical reactions into molecular dynamics to simulate chemical reaction systems. We have dubbed this method RTAMD, an acronym for reaction time accelerating molecular dynamics. The methodology we propose here requires no more than the knowledge of the empirical intermolecular potentials for the species at play as well as the elementary reaction

Hiromitsu Takaba; Shigekazu Hayashi; Huifeng Zhong; Hema Malani; Ai Suzuki; Riadh Sahnoun; Michihisa Koyama; Hideyuki Tsuboi; Nozomu Hatakeyama; Akira Endou; Momoji Kubo; Carlos A. Del Carrpio; Akira Miyamoto

2008-01-01

140

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

141

Host plant adaptation and the evolution of thermal reaction norms.  

PubMed

For most ectotherms, increasing the rearing temperature reduces the final (adult) body size, producing a negative slope for the thermal reaction norm. Recent studies show that this relationship may be reversed under conditions of low resource quality, producing a positive slope for the thermal reaction norm. If populations or species differ in the degree of evolutionary adaptation to a resource, how does this differential adaptation alter their thermal reaction norms? We used a common garden experiment with the tobacco hornworm, Manduca sexta, to address this question. We examined the thermal reaction norms for body size of two populations of M. sexta that differ in their evolutionary exposures to an atypical, low-quality resource (devil's claw; Proboscidea louisianica), but have comparable exposures to a typical, high-quality resource (tobacco; Nicotiana tabacum). Both populations had increased mean larval mortalities and development times when reared on devil's claw compared with tobacco, but the magnitudes of these increases differed between populations. Both populations had similar, negatively sloped thermal reaction norms on the typical, high-quality resource (tobacco), but had divergent, non-negative thermal reaction norms on the atypical, low-quality resource (devil's claw): the population with the longer evolutionary history of exposure to the atypical resource exhibited a flat (rather than positive) reaction norm. These results suggest that population differences in host plant adaptation can predictably influence the slopes of thermal reaction norms. PMID:22127429

Diamond, Sarah E; Kingsolver, Joel G

2011-11-30

142

Thermal Desorption from Si(111) Surfaces with Native Oxides Formed During Chemical Treatments  

Microsoft Academic Search

The thermal desorption process during thermal cleaning of Si(111) surfaces with native oxides formed by various chemical treatments is studied using TDS (thermal desorption spectroscopy) under UHV. The reaction product of the process is identified to be SiO. The surface cleanliness after the cleaning is virtually independent of the oxide formation method. However, the desorption temperature of SiO strongly depends

Yoshihiro Kobayashi; Yukinobu Shinoda; Kiyomasa Sugii

1990-01-01

143

On differential geometric formalization of chemical reaction kinetics statical aspects  

Microsoft Academic Search

In this article the basic mathematical structure of chemical reaction kinetics is investigated. For this purpose the methods of modern differential geometry are used. Using this approach the various aspects of species, reactions and stoichiometry can be separately treated.

L. Ropolyi; P. Réti

1984-01-01

144

Detecting strictly detailed balanced subnetworks in open chemical reaction networks  

Microsoft Academic Search

The notion “strictly detailed balanced subnetwork” is introduced, for chemical reaction networks which are open and spatially homogeneous, to refer to any set of reactions the net rates of which vanish in each asymptotically stable steady state, regardless of the kinetic parameters of any reaction in the whole network. Necessary and sufficient conditions for sets of reactions to be strictly

Stefan Schuster; Ronny Schuster

1991-01-01

145

Variability of the Cell Potential of a Given Chemical Reaction  

Microsoft Academic Search

It is demonstrated in this article that while the value of the free energy change for any chemical reaction is independent of path (a state function), the value of the standard cell potential of a reaction is dependent on the half-cell reactions used to carry out that reaction. That is, the standard cell potential is not a state function, but

Ladislav H. Berka; Ilie Fishtik

2004-01-01

146

Implementation of a vibrationally linked chemical reaction model for DSMC  

Microsoft Academic Search

A new procedure closely linking dissociation and exchange reactions in air to the vibrational levels of the diatomic molecules has been implemented in both one- and two-dimensional versions of Direct Simulation Monte Carlo (DSMC) programs. The previous modeling of chemical reactions with DSMC was based on the continuum reaction rates for the various possible reactions. The new method is more

A. B. Carlson; Graeme A. Bird

1994-01-01

147

Robust Stochastic Chemical Reaction Networks and Bounded Tau-Leaping  

Microsoft Academic Search

The behavior of some stochastic chemical reaction networks is largely unaffected by slight inaccuracies in reaction rates. We formalize the robustness of state probabilities to reaction rate deviations, and describe a formal connection between robustness and efficiency of simulation. Without robustness guarantees, stochastic simulation seems to require computational time proportional to the total number of reaction events. Even if the

David Soloveichik

2008-01-01

148

GREEN CHEMICAL SYNTHESIS THROUGH CATALYSIS AND ALTERNATE REACTION CONDITIONS  

EPA Science Inventory

Green chemical synthesis through catalysis and alternate reaction conditions Encompassing green chemistry techniques and methodologies, we have initiated several projects at the National Risk Management Research laboratory that focus on the design and development of chemic...

149

Chemical functionalization of diamond surfaces by reaction with diaryl carbenes.  

PubMed

A rapid route to the chemical functionalization of hydrogen-terminated diamond surfaces deposited by chemical vapor deposition involving their reaction with substituted diaryl carbenes has been investigated. To avoid difficulties in the handling of highly reactive compounds, the carbene is generated in situ from the thermal decomposition at 400 K of a thin film of the corresponding diaryl diazomethane precursor deposited at the diamond interface. X-ray photoelectron spectroscopy (XPS) has been used to verify that surface functionalization using two starting compounds, bis(4-iodophenyl) diazomethane and bis(4-nitrophenyl) diazomethane, can be achieved using this approach in agreement with recent theoretical studies. The surface grafting density is measured to be around 10(14) cm(-2) in each case. The chemistry observed is found to be insensitive to the detailed properties of the diamond film and to the presence of oxygen contamination at the hydrogen-terminated diamond surface. We further demonstrate the utility of the approach, in the case of the bound nitrophenyl compound, by its reduction to the corresponding primary amine followed by reaction with fluorescein isothiocyanate to achieve fluorescent tagging of the diamond interface. PMID:18177059

Wang, Hao; Griffiths, Jon-Paul; Egdell, Russell G; Moloney, Mark G; Foord, John S

2008-01-05

150

TEOS-based SiO(sub 2) chemical vapor deposition: Reaction kinetics and related surface chemistry.  

National Technical Information Service (NTIS)

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...

M. E. Bartram H. K. Moffat

1995-01-01

151

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

152

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

153

Signatures of chemical reactions in the morphology and fluctuations of giant vesicles  

NASA Astrophysics Data System (ADS)

The behaviour of an amphiphilic membrane is determined by the physical and chemical properties of the molecules which form the bilayer and their interactions with the surrounding medium. Bulk or interfacial chemical reactions modify interaction parameters and/or affect directly the chemical composition of the membrane. We monitor the morphological response and the thermal fluctuations of giant lipid vesicles to chemical reactions in the external vesicle medium using phase-contrast microscopy. Observation of vesicle conformations as a function of time allows us to characterize the statics and dynamics of membrane response as well as the underlying chemical kinetics. As two examples, we present (a) a photochemical reaction of hexacyanoferrate which induces an increase in pH and (b) the enzymatic cleavage of phosphatidyl choline by the phospholipase C from Bacillus cereus.

Döbereiner, Hans-Günther; Petrov, Peter G.; Riske, Karin A.

2003-01-01

154

Chemical reactions of organic compounds on clay surfaces  

SciTech Connect

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 Broensted or Lewis acidity of clay minerals.

Soma, Yuko; Soma, Mitsuyuki (National Institute for Environmental Studies, Ibaraki (Japan))

1989-11-01

155

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.

Soma, Y; Soma, M

1989-01-01

156

Thermophoresis of an Aerosol Sphere with Chemical Reactions  

Microsoft Academic Search

The thermophoretic motion of a spherical aerosol particle undergoing a chemical reaction in a uniformly prescribed temperature gradient is studied theoretically in the quasisteady limit of negligible Peclet and Reynolds numbers. The chemical reaction taking place within the particle can be either endothermic or exothermic. The Knudsen number is assumed to be small (of the order 0.1) so that the

Tzu H. Hsieh; Huan J. Keh

2012-01-01

157

Synthesis of reactive distillation systems with multiple equilibrium chemical reactions  

Microsoft Academic Search

The authors describe a procedure to determine the feasibility of separating mixtures with multiple equilibrium chemical reactions by reactive distillation. The method involves describing the system in terms of new composition coordinates which represent the reactive system in a lower dimensional composition space. The justification for these new variables is that when equilibrium chemical reactions occur in a mixture, the

Sophie Ung; Michael F. Doherty

1995-01-01

158

Exact stochastic simulation of coupled chemical reactions with delays  

Microsoft Academic Search

Gillespie's exact stochastic simulation algorithm (SSA) [J. Phys. Chem. 81, 2350 (1977)] has been widely used to simulate the stochastic dynamics of chemically reacting systems. In this algorithm, it is assumed that all reactions occur instantly. While this is true in many cases, it is also possible that some chemical reactions, such as gene transcription and translation in living cells,

Xiaodong Cai

2007-01-01

159

The effect of chemical reaction on liquid round free jet  

Microsoft Academic Search

In the fluid engineering field, chemical reaction frequently occur. Sodium-water chain reaction in the sodium cooled nuclear reactor can make an explosion that causes the accident during the operation of nuclear reactor. Therefore, it is very important to investigate the characteristic of this chemically reacting type of jet to achieve the reliable design of industrial reactor. Although a number of

Seong Dae Hong; Okamoto Koji; Madarame Haruki

2002-01-01

160

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

ERIC Educational Resources Information Center

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

Wright, Stephen W.

2002-01-01

161

Heat-of-Reaction Chemical Heat Pumps.  

National Technical Information Service (NTIS)

Chemical heat pumps are mechanically driven heat pumps with working fluids that undergo chemical changes or are heat-driven heat pumps in which either the driver (heat engine) or heat pump utilizes a reactive working fluid. As such, chemical heat pumps ca...

C. Bliem L. Kirol

1988-01-01

162

Coupled thermal-hydraulic-chemical modelling of enhanced geothermal systems  

Microsoft Academic Search

The study investigates thermal-, hydraulic- and chemically coupled processes of enhanced geothermal systems (EGS). On the basis of the two existing numerical codes, the finite element program FRACTURE and the geochemical module of CHEMTOUGH, FRACHEM was developed, to simulate coupled thermal-hydraulic-chemical (THC) processes, accounting for the Soultz specific conditions such as the high salinity of the reservoir fluid and the

D. Bächler; T. Kohl

2005-01-01

163

Visualization of electronic properties of molecules in chemical reactions  

Microsoft Academic Search

Modern computational methods allow for the tracking of entire chemical reactions, ranging from initial reactants, through transition states, and to the final products. They also permit the computation of a variety of properties that can change as the reaction proceeds from start to finish. Visualization of these reactions is often difficult and usually limited to static displays of specific steps

Susanna Wei; George R. Famini

1995-01-01

164

LIGAND: database of chemical compounds and reactions in biological pathways  

Microsoft Academic Search

LIGAND is a composite database comprising three sections: COMPOUND for the information about metabolites and other chemical compounds, REACTION for the collection of substrate-product relations representing metabolic and other reactions, and ENZYME for the information about enzyme molecules. The current release (as of September 7, 2001) includes 7298 compounds, 5166 reactions and 3829 enzymes. In addition to the keyword search

Susumu Goto; Yasushi Okuno; Masahiro Hattori; Takaaki Nishioka; Minoru Kanehisa

2002-01-01

165

Quantum control of chemical reaction dynamics in a classical way  

Microsoft Academic Search

A simplified approach to quantum control of chemical reaction dynamics based on a classical, local control theory was developed. The amplitude of the control pulse is proportional to the linear momentum of the reaction system within the dipole approximation for the system-radiation field interaction. The kinetic energy of the system is the controlling parameter. That is, the reaction is controlled

Hiroaki Umeda; Yuichi Fujimura

2000-01-01

166

Droplet heat transfer and chemical reactions during direct containment heating  

SciTech Connect

A simplified model of heat transfer and chemical reaction has been adapted to evaluate the expected behavior of droplets containing unreacted Zircaloy and stainless steel moving through the containment atmosphere during postulated accidents involving direct containment heating. The model includes internal and external diffusive resistances to reaction. The results indicate that reactions will be incomplete for many conditions characteristic of direct containment heating sequences.

Baker, L. Jr.

1986-01-01

167

Thermal and Photochemical Reactions of dihydrodiazines  

Microsoft Academic Search

This thesis describes the results of an investigation into the thermal and photochemical reactivity of dihydrodiazines.In order to prepare the title compounds the diazines and some phenyldiazines are treated with phenyllithium in ether, yielding adducts resulting from attack of phenyllithium on the various positions of the heteroaromatic ring. With pyrimidine addition takes place mainly at C(4), with pyridazine at C(3).

Stoel van der R. E

1979-01-01

168

The Activated Complex in Chemical Reactions  

Microsoft Academic Search

The calculation of absolute reaction rates is formulated in terms of quantities which are available from the potential surfaces which can be constructed at the present time. The probability of the activated state is calculated using ordinary statistical mechanics. This probability multiplied by the rate of decomposition gives the specific rate of reaction. The occurrence of quantized vibrations in the

Henry Eyring

1935-01-01

169

Organic chemical reactions in supercritical water  

Microsoft Academic Search

Water near or above its critical point (374 C, 218 atm) is attracting increased attention as a medium for organic chemistry. Most of this new attention is driven by the search for more green or environmentally benign chemical processes. Using near-critical or supercritical water (SCW) instead of organic solvents in chemical processes offers environmental advantages and may lead to pollution

Phillip E. Savage

1999-01-01

170

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...

171

The Mystery Reaction: A Lesson on Chemical Reactions  

NSDL National Science Digital Library

This teaching resource was developed by a K-12 science teacher in the American Physiologycal Society's 2006 Frontiers in Physiology Program. For more information on this program, please visit www.frontiersinphys.org. The purpose of this lesson is to design an investigation and conduct an experiment that will allow students to explore the differences between physical and chemical changes. In this investigation, they are given the opportunity to develop a list of evidence for determining whether or not a chemical change has occurred.

Tonya Williams (Kelly Miller Middle School)

2006-08-01

172

Stretching the bonds of chemical reactions  

NASA Astrophysics Data System (ADS)

The effects of reagent stretch-excitation on the gas-phase Cl+CH 4 ? HCl+CH3 reaction are examined experimentally using a photoinitiated reaction technique in which the reagents are prepared by direct infrared absorption or stimulated Raman pumping and the products are state-selectively ionized and detected in a time-of-flight mass spectrometer. Our measurements indicate that the rovibrational distributions and state-selected differential cross sections of the HCl and CH3 products from the symmetric and antisymmetric stretch excited reactions are indistinguishable. This result suggests that the mechanisms of these nearly isoenergetic vibrationally excited reactions are similar, despite theoretical and experimental measurements that suggest the symmetric stretch enhances the reaction rate more than the antisymmetric stretch. Furthermore, we have demonstrated mode- and bond-selectivity in the Cl+CH2D2 reaction. Excitation of the first C-H overtone of CH2D2 leads to a preference for hydrogen abstraction over deuterium abstraction by at least a factor of 20, whereas excitation of the first C-D overtone of CH2D2 reverses this preference by at least a factor of 10. Reactions with CH2D 2 prepared in a local mode containing two quanta in one C-H oscillator |2000>- or in a local mode containing one quantum each in two C-H oscillators |1100> lead to products with significantly different rotational, vibrational, and angular distributions, although the vibrational energy for each mode is nearly identical. These measurements represent the first example of mode selectivity observed in a differential cross section, and they demonstrate that vibrational excitation can be used to direct the reaction pathway of the Cl+CH2D2 reaction. Our results indicate that reagent stretch-excitation enhances the reaction rate by localizing energy along the reaction coordinate, thereby widening the cone of acceptance and allowing reactive collisions at high impact parameter. The chlorine atom appears to react with a single C-H oscillator, while the methyl radical is largely a spectator throughout the course of the reaction. Moreover, our results are consistent with a model in which the impact parameter governs the angular distributions of the product.

Bechtel, Hans A.

173

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

ERIC Educational Resources Information Center

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

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

1998-01-01

174

Chemical Reactions in the Helium Impurities Loop.  

National Technical Information Service (NTIS)

The Helium Impurities Loop (HIL) at Brookhaven National Laboratory has been run to study reactions between the three metals and the four major helium oxidation and reduction and on carburization of the metals. Preliminary work on hydrogen diffusion throug...

L. G. Epel D. G. Schweitzer

1978-01-01

175

Coupled Thermal-Chemical-Mechanical Modeling of Validation Cookoff Experiments  

Microsoft Academic Search

The cookoff of energetic materials involves the combined effects of several physical and chemical processes. These processes include heat transfer, chemical decomposition, and mechanical response. The interaction and coupling between these processes influence both the time-to-event and the violence of reaction. The prediction of the behavior of explosives during cookoff, particularly with respect to reaction violence, is a challenging task.

WILLIAM W. ERIKSON; ROBERT G. SCHMITT; A. I. ATWOOD; P. D. CURRAN

2000-01-01

176

Direct imaging of covalent bond structure in single-molecule chemical reactions.  

PubMed

Observing the intricate chemical transformation of an individual molecule as it undergoes a complex reaction is a long-standing challenge in molecular imaging. Advances in scanning probe microscopy now provide the tools to visualize not only the frontier orbitals of chemical reaction partners and products, but their internal covalent bond configurations as well. We used noncontact atomic force microscopy to investigate reaction-induced changes in the detailed internal bond structure of individual oligo-(phenylene-1,2-ethynylenes) on a (100) oriented silver surface as they underwent a series of cyclization processes. Our images reveal the complex surface reaction mechanisms underlying thermally induced cyclization cascades of enediynes. Calculations using ab initio density functional theory provide additional support for the proposed reaction pathways. PMID:23722428

de Oteyza, Dimas G; Gorman, Patrick; Chen, Yen-Chia; Wickenburg, Sebastian; Riss, Alexander; Mowbray, Duncan J; Etkin, Grisha; Pedramrazi, Zahra; Tsai, Hsin-Zon; Rubio, Angel; Crommie, Michael F; Fischer, Felix R

2013-05-30

177

Thermal Explosion Reaction in the Ti-C System under Air Atmosphere  

NASA Astrophysics Data System (ADS)

The ignition temperature of the thermal explosion reaction from the Ti-C system under air is much lower than that under Ar atmosphere. The ignition mechanism for the Ti-C system under air is determined to be a mechanism of chemical oven, and the reaction mechanism is dissolution, reaction, and precipitation. Namely, the heat generated from the oxidation and nitrification of Ti and C can promote the melting of Ti inside the compact; subsequently, the carbon atoms dissolve into the Ti melt and TiC precipitate.

Yang, Y. F.; Wang, H. Y.; Wang, J. G.; Jiang, Q. C.

2009-11-01

178

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

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

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

179

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

180

Two Examples of Deterministic versus Stochastic Modeling of Chemical Reactions  

NASA Astrophysics Data System (ADS)

The numerical simulation of chemical reactions can be carried out using deterministic or stochastic models. The deterministic simulation gives the average behavior of the system, which is a suitable representation of the reaction when the number of molecules involved is large. The stochastic simulation requires stronger mathematical foundations, mainly from probability theory but allows prediction of the so-called stochastic effects, which are relevant when the number of molecules is small. A more accurate representation of processes dependent on the behavior of a small number of molecules is of increasing importance in current chemistry and can be achieved through stochastic modeling. From an educational point of view, the simultaneous use of stochastic and deterministic models in the simulation of chemical reactions results in a better understanding of the chemical dynamics. The two approaches are reviewed in this paper by using two selected examples of chemical reactions and four MATLAB programs, which implement both the deterministic and stochastic modeling of the examples.

Mira, José; González Fernández, Camino; Martínez Urreaga, Joaquín

2003-12-01

181

Chemical reactions during the optical breakdown of dielectric coatings  

NASA Astrophysics Data System (ADS)

It is shown that the destruction of many types of dielectric coatings is connected with chemical reactions (including solid-phase reactions) initiated by laser radiation. Thermodynamic calculations, and microluminescence and microchemical analyses show that coatings containing ZnS, and oxides of zirconium, hafnium, and titanium in combination with SiO2 are chemically unstable. Absorbing microdefects, whose appearance is determined by chemical reactions on catalytically active centers, facilitate the heating of coatings to the reaction-initiation temperature. The reaction rate depends on the radiation power density, the number of active centers in the coating (lattice defects, dislocations, inclusions, etc.), and the reagent diffusion rate. It is concluded that, in order to assure the high radiation resistance of dielectric coatings, it is necessary to use materials of high thermodynamic stability under laser radiation.

Artemev, V. A.; Bonch-Bruevich, A. M.; Chernaia, Iu. I.

1980-10-01

182

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

183

SIMPLIFICATION OF CHEMICAL REACTION SYSTEMS BY TIMESCALE ANALYSIS  

Microsoft Academic Search

In this article, we present a model order reduction method based on time-scale analysis for chemical reaction systems. The method can be applied to any reaction system exhibiting multiple time scales and described by the set or differential equations dc\\/dl = f(c), where c (dimension n) is the vector of chemical species and f is the operator describing the kinetics.

MILES S. OKINO; MICHAEL L. MAVROVOUNIOTIS

1999-01-01

184

Mechanics driven Chemical Reactions in Structural Energetic Materials  

Microsoft Academic Search

Fundamental mechanisms that are responsible for shock-initiation of chemical reactions, are dominated by non-equilibrium processes including changes in reactant particle configurations caused by plastic deformation or by fracture, mixing of constituents in and around the voids, and rapid increases in temperature from mechanical work. Mechanics driven chemical reactions occur in structural energetic mixtures, during the high-pressure shock state in time

Vindhya Narayanan; Derek Redding; Sathya Hanagud

2007-01-01

185

Drying with Chemical Reaction in Cocoa Beans  

Microsoft Academic Search

Desirable flavor qualities of cocoa are dependent on how the cocoa beans are fermented, dried, and roasted. During fermentation and drying, polyphenols such as leucocyanidin and apecatechin are oxidized by polyphenols oxidase to form o-quinone, which later react nonenzymatically with a hydroquinone in a condensation reaction to form browning products and moisture. The objective of this article is to model

Wan Ramli Wan Daud; Meor Zainal Meor Talib; Tin Mar Kyi

2007-01-01

186

Anatomy of an Elementary Chemical Reaction  

Microsoft Academic Search

The alchemists of old sought the knowledge to transform one material to another-for example, base metals into gold-as a path to the elixir of life. As chemists have concerned themselves with the transformation from compound to compound, so they have become involved in trying to uncover the structures of molecules and the pathways that reactions follow. Classically, the study of

Andrew J. Alexander; Richard N. Zare

1998-01-01

187

Laser cutting with chemical reaction assist.  

National Technical Information Service (NTIS)

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...

D. J. Gettemy

1991-01-01

188

Effect of curvature of the reaction path on dynamic effects in endothermic chemical reactions and product energies in exothermic reactions  

Microsoft Academic Search

Collinear quasiclassical trajectories are examined for two realistic potential energy surfaces for atom?diatomic molecule reactions for two reaction attributes: (1) vibrational energy of the products of a thermal?energy exothermic reaction; (2) threshold energy for endothermic reaction of ground?state reagents. Eight different mass combinations are studied. The potential energy surfaces differ primarily in the amount of potential energy released in an

James W. Duff; Donald G. Truhlar

1975-01-01

189

Memory Switches in Chemical Reaction Space  

Microsoft Academic Search

Just as complex electronic circuits are built from simple Boolean gates, diverse biological functions, including signal transduction, differentiation, and stress response, frequently use biochemical switches as a functional module. A relatively small number of such switches have been described in the literature, and these exhibit considerable diversity in chemical topology. We asked if biochemical switches are indeed rare and if

Naren Ramakrishnan; Upinder S. Bhalla

2008-01-01

190

Chemical pathways in ultracold reactions of SrF molecules  

NASA Astrophysics Data System (ADS)

We present a theoretical investigation of the chemical reaction SrF + SrF ? products, focusing on reactions at ultralow temperatures. We find that bond swapping SrF + SrF ? Sr2 + F2 is energetically forbidden at these temperatures. Rather, the only energetically allowed reaction is SrF + SrF ? SrF2 + Sr, and even then only singlet states of the SrF2 trimer can form. A calculation along a reduced reaction path demonstrates that this abstraction reaction is barrierless and proceeds by one SrF molecule “handing off” a fluorine atom to the other molecule.

Meyer, Edmund R.; Bohn, John L.

2011-03-01

191

Chemical pathways in ultracold reactions of SrF molecules  

NASA Astrophysics Data System (ADS)

We present a theoretical investigation of the chemical reaction SrF + SrF -> products, focusing on reactions at ultralow temperatures. We find that bond swapping, SrF + SrF -> Sr2 + F2, is energetically forbidden at these temperatures. Rather, the only energetically allowed reaction is SrF + SrF -> SrF2 + Sr, and even then only singlet states of the SrF2 trimer can form. A calculation along a reduced reaction path demonstrates that this abstraction reaction is barrierless, and proceeds by one SrF molecule ``handing off'' a fluorine atom to the other molecule.

Meyer, Edmund; Bohn, John

2011-06-01

192

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

2013-03-07

193

Using Large Glass Cylinders To Demonstrate Chemical Reactions  

Microsoft Academic Search

This article describes a simple laboratory experiment that aims at pedagogic as well as aesthetic aspects of chemical reactions. In a 0.5- or 1-liter glass cylinder almost completely filled with water, a slow precipitation reaction involving two soluble salts is made to occur by adding a sample of one salt directly to the water and then placing some of the

Wobbe de Vos

1999-01-01

194

Chemical reactions on solid surfaces of astrophysical interest  

Microsoft Academic Search

Observed abundances of chemical species in interstellar clouds can be explained in most cases by reaction schemes involving only species in the gas phase. There is however clear evidence that reactions occurring on the surface of dust grains, helping the formation of key molecules, play a fundamental role into shaping the universe as we see it today. In this chapter

Ofer Biham; Valerio Pirronello; Gianfranco Vidali

2003-01-01

195

Two-photon induced chemical reactions in liquids  

SciTech Connect

A two-photon absorption process has been used for the first time to produce significant quantities of reaction products between halogen containing organic compounds and silver containing inorganic compounds in the condensed phase. The mechanisms for these chemical reactions were also studied and confirmed by two-photon absorption spectra and optoaccoustic methods.

Chen, C.H.; McCann, M.P. (Chemical Physics Section, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6378 (US))

1989-10-20

196

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

197

Evaluated Chemical Kinetic Rate Constants for Various Gas Phase Reactions  

Microsoft Academic Search

The available information, up to mid-1972, for the rate constants of a series of gas phase chemical reactions has been evaluated critically. For each reaction, relevant thermodynamic data are presented and values for the equilibrium constant expressed in mathematical form. Kinetic data are presented in tabular and graphical form together with a discussion of the pertinent details. Recommended rate constant

Keith Schofield

1973-01-01

198

Incorporation of Chemical Reactions into Building-scale Flow  

Microsoft Academic Search

Many hazardous atmospheric releases involve chemical reactions that occur within a few kilometers of the source. Reactions with commonly occurring atmospheric compounds such as the OH radical, can transform and potentially neutralize original release compounds. Especially in these cases, accurately resolving flow around nearby structures and over surrounding topography can be critical to correctly predicting material dispersion, and thus, the

T D Humphreys; T M Jayaweera; R L Lee

2003-01-01

199

Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks  

ERIC Educational Resources Information Center

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

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

2011-01-01

200

A kinetic model for chemical reactions without barriers: transport coefficients and eigenmodes  

NASA Astrophysics Data System (ADS)

The kinetic model of the Boltzmann equation proposed in the work of Kremer and Soares 2009 for a binary mixture undergoing chemical reactions of symmetric type which occur without activation energy is revisited here, with the aim of investigating in detail the transport properties of the reactive mixture and the influence of the reaction process on the transport coefficients. Accordingly, the non-equilibrium solutions of the Boltzmann equations are determined through an expansion in Sonine polynomials up to the first order, using the Chapman-Enskog method, in a chemical regime for which the reaction process is close to its final equilibrium state. The non-equilibrium deviations are explicitly calculated for what concerns the thermal-diffusion ratio and coefficients of shear viscosity, diffusion and thermal conductivity. The theoretical and formal analysis developed in the present paper is complemented with some numerical simulations performed for different concentrations of reactants and products of the reaction as well as for both exothermic and endothermic chemical processes. The results reveal that chemical reactions without energy barrier can induce an appreciable influence on the transport properties of the mixture. Oppositely to the case of reactions with activation energy, the coefficients of shear viscosity and thermal conductivity become larger than those of an inert mixture when the reactions are exothermic. An application of the non-barrier model and its detailed transport picture are included in this paper, in order to investigate the dynamics of the local perturbations on the constituent number densities, and velocity and temperature of the whole mixture, induced by spontaneous internal fluctuations. It is shown that for the longitudinal disturbances there exist two hydrodynamic sound modes, one purely diffusive hydrodynamic mode and one kinetic mode.

Alves, Giselle M.; Kremer, Gilberto M.; Marques, Wilson, Jr.; Jacinta Soares, Ana

2011-03-01

201

Influence of trace impurities on chemical reaction hazards  

Microsoft Academic Search

The influence of trace impurities is frequently mentioned as a possible or probable cause of accidents in the chemical industry. In process conditions where there is a potential for a fast exothermic decomposition or polymerisation reaction, the contamination of pure chemicals by trace impurities may cause problems. Typical examples of this situation are described concerning the processing of organic nitrocompounds

J. L. Gustin

2002-01-01

202

Results of the 2010 Survey on Teaching Chemical Reaction Engineering  

ERIC Educational Resources Information Center

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

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

2012-01-01

203

Results of the 2010 Survey on Teaching Chemical Reaction Engineering  

ERIC Educational Resources Information Center

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

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

2012-01-01

204

Conservation-dissipation structure of chemical reaction systems  

NASA Astrophysics Data System (ADS)

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.

Yong, Wen-An

2012-12-01

205

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

NASA Astrophysics Data System (ADS)

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.

Zhu, Haitao; Han, Dongxiao; Meng, Zhaoguo; Wu, Daxiong; Zhang, Canying

2011-12-01

206

Symmetry numbers and chemical reaction rates  

Microsoft Academic Search

This article shows how to evaluate rotational symmetry numbers for different molecular configurations and how to apply them\\u000a to transition state theory. In general, the symmetry number is given by the ratio of the reactant and transition state rotational\\u000a symmetry numbers. However, special care is advised in the evaluation of symmetry numbers in the following situations: (i)\\u000a if the reaction

Antonio Fernández-Ramos; Benjamin A. Ellingson; Rubén Meana-Pañeda; Jorge M. C. Marques; Donald G. Truhlar

2007-01-01

207

Probing Isotope Effects in Chemical Reactions Using Single Ions  

SciTech Connect

Isotope effects in reactions between Mg{sup +} in the 3p {sup 2}P{sub 3/2} excited state and molecular hydrogen at thermal energies are studied through single reaction events. From only {approx}250 reactions with HD, the branching ratio between formation of MgD{sup +} and MgH{sup +} is found to be larger than 5. From an additional 65 reactions with H{sub 2} and D{sub 2} we find that the overall fragmentation probability of the intermediate MgH{sub 2}{sup +}, MgHD{sup +}, or MgD{sub 2}{sup +} complexes is the same. Our study shows that few single ion reactions can provide quantitative information on ion-neutral reactions. Hence, the method is well suited for reaction studies involving rare species, e.g., rare isotopes or short-lived unstable elements.

Staanum, Peter F.; Hoejbjerre, Klaus; Drewsen, Michael [QUANTOP - Danish National Research Foundation Centre for Quantum Optics, University of Aarhus, 8000 Aarhus (Denmark); Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus (Denmark); Wester, Roland [Physikalisches Institut, Universitaet Freiburg, Hermann-Herder-Strasse 3, 79104 Freiburg (Germany)

2008-06-20

208

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.

Jewett, John C.

2010-01-01

209

Concerted reactions of polynuclear metalloenzymes and their functional chemical models  

NASA Astrophysics Data System (ADS)

The mechanisms of the many-electron oxidation of water by a chemical model of the manganese oxidase cofactor in photosynthesis photosystem II (manganese(IV) clusters) and nitrogen reduction in chemical models of nitrogenase cofactor (vanadium(II) and molybdenum(III) clusters) were considered. The hypothesis was suggested according to which polynuclear enzyme cofactors and their functional chemical models performed two important functions, catalyzed noncomplementary processes and effected many-substrate concerted reactions with decreased activation energies.

Dzhabiev, T. S.; Shilov, A. E.

2011-03-01

210

Thermal and Chemical Properties of Waldo Lake, Oregon  

Microsoft Academic Search

Thermal and chemical profiles were obtained periodically in ultraoligotrophic Waldo Lake, Oregon during years 1986 through 1999. Profiling was done on a seasonal basis between May and October. During this period the lake becomes thermally well-stratified. Epilimnetic temperatures peak in August, then rapidly diminish in response to decreasing solar radiation. By October, the lake nears autumnal turnover. During winter, the

John Salinas

2000-01-01

211

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.

212

Chemical Memory Reactions Induced Bursting Dynamics in Gene Expression  

PubMed Central

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

Tian, Tianhai

2013-01-01

213

Exact stochastic simulation of coupled chemical reactions with delays  

NASA Astrophysics Data System (ADS)

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

Cai, Xiaodong

2007-03-01

214

An in-situ combustion reservoir simulator with a new representation of chemical reactions  

SciTech Connect

Numerical simulation of in-situ combustion processes poses numerical problems related to the representation of chemical reactions in the burning zone. This paper presents a new approach to the description of the combustion front. The fully implicit thermal compositional model developed to simulate oil recovery by wet or dry forward combustion is formulated to handle three dimensions, three phases, gravity and capillary forces, heat transfer by convection and conduction within the reservoir, and conductive heat loss to adjacent strata. Two options are available. The first includes four components and one fuel combustion reaction., The second allows any number of components and several reactions. The first option emphasizes description of the combustion front with a new formulation that uses a heat-release curve to improve numerical stability and to give accurate temperature distribution with large gridblocks. The paper compares different representations of chemical reactions and includes results of a sensitivity study on the mesh size.

Le Thiez, P.A.; Lemonnier, P.A. (Inst. Francais du Petrole (FR))

1990-08-01

215

A robustness screen for the rapid assessment of chemical reactions.  

PubMed

In contrast to the rapidity with which scientific information is published, the application of new knowledge often remains slow, and we believe this to be particularly true of newly developed synthetic organic chemistry methodology. Consequently, methods to assess and identify robust chemical reactions are desirable, and would directly facilitate the application of newly reported synthetic methodology to complex synthetic problems. Here, we describe a simple process for assessing the likely scope and limitations of a chemical reaction beyond the idealized reaction conditions initially reported. Using simple methods and common analytical techniques we demonstrate a rapid assessment of an established chemical reaction, and also propose a simplified analysis that may be reported alongside new synthetic methodology. PMID:23787750

Collins, Karl D; Glorius, Frank

2013-06-09

216

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

217

Thermal reaction of SiC films with tungsten and tungsten–rhenium alloys  

Microsoft Academic Search

Solid-state reactions between SiC films and W–xRe (x = 0, 5 and 25 at%) substrates on thermal annealing between 1673 K and 1873 K for various durations have been investigated.\\u000a SiC coatings were deposited on metallic wires by hot filament chemical vapour deposition (HFCVD) from a gas mixture of tetramethylsilane\\u000a (TMS) and hydrogen at 1373 K under normal pressure. The interface zones were characterized using scanning

Jérome Roger; Fabienne Audubert; Yann Le Petitcorps

2008-01-01

218

Measurements of the thermal neutron cross section of 90Sr(n,gamma)91Sr reaction  

Microsoft Academic Search

The thermal neutron cross section of the 90Sr(n,gamma)91Sr reaction was measured in a D2O moderated reactor with an activation technique. The Cd ratio of the neutron flux at the location of the irradiation is about 30. For reduction of the 90Y high energy beta-ray background strontium-specific columns (Sr. Spec(TM)) were used to chemically separate the Y from Sr before irradiation

M. A. Lone; W. J. Edwards; R. Collins

1993-01-01

219

Analysis of the chemical composition of organic aerosol at the Mt. Sonnblick observatory using a novel high mass resolution thermal-desorption proton-transfer-reaction mass-spectrometer (hr-TD-PTR-MS)  

NASA Astrophysics Data System (ADS)

For the first time a high mass resolution thermal desorption proton transfer reaction mass spectrometer (hr-TD-PTR-MS) was deployed in the field to analyze the composition of the organic fraction of aerosols. We report on measurements from the remote Mt. Sonnblick observatory in the Austrian alps (3108 m a.s.l.) during a 7 week period in summer 2009. A total of 638 mass peaks in the range 18-392 Da were detected and quantified in aerosols. An empirical formula was tentatively attributed to 464 of these compounds by custom-made data analysis routines which consider compounds containing C, H, O, N, and S atoms. Most of the other (unidentified) compounds must contain other elements - most likely halogenated compounds. The mean total concentration of all detected compounds was 1.1 ?g m-3. Oxygenated hydrocarbons constitute the bulk of the aerosol mass (75%) followed by organic nitrogen compounds (9%), inorganic compounds (mostly NH3, 8%), unidentified/halogenated (3.8%), hydrocarbons (2.7%), and organic sulfur compounds (0.8%). The measured O/C ratios are lower than expected and suggest a significant effect from charring. Organic carbon concentrations measured with TD-PTR-MS were about 25% lower than measurements on high volume filter samples.

Holzinger, R.; Kasper-Giebl, A.; Staudinger, M.; Schauer, G.; Röckmann, T.

2010-10-01

220

Analysis of the chemical composition of organic aerosol at the Mt. Sonnblick observatory using a novel high mass resolution thermal-desorption proton-transfer-reaction mass-spectrometer (hr-TD-PTR-MS)  

NASA Astrophysics Data System (ADS)

For the first time a high mass resolution thermal desorption proton transfer reaction mass spectrometer (hr-TD-PTR-MS) was deployed in the field to analyze the composition of the organic fraction of aerosols. We report on measurements from the remote Mt. Sonnblick observatory in the Austrian alps (3108 m a.s.l.) during a 7 week period in summer 2009. A total of 638 mass peaks in the range 18-392 Da were detected and quantified in aerosols. An empirical formula was tentatively attributed to 464 of these compounds by custom-made data analysis routines which consider compounds containing C, H, O, N, and S atoms. Most of the other (unidentified) compounds must contain other elements - most likely halogenated compounds. The mean total concentration of all detected compounds was 1.1 ?g m-3. Oxygenated hydrocarbons constitute the bulk of the aerosol mass (75%) followed by organic nitrogen compounds (9%), inorganic compounds (mostly NH3, 8%), unidentified/halogenated (3.8%), hydrocarbons (2.7%), and organic sulfur compounds (0.8%). The measured O/C ratios are lower than expected and suggest a significant effect from charring. A significant part of the organic nitrogen compounds is non volatile. Organic carbon concentrations measured with TD-PTR-MS were about 25% lower than measurements on high volume filter samples.

Holzinger, R.; Kasper-Giebl, A.; Staudinger, M.; Schauer, G.; Röckmann, T.

2010-06-01

221

Chemical potentials in real-time thermal field theory  

SciTech Connect

In the functional integral formulation of real-time thermal field theory, a time-dependent canonical transformation of the integration variables can remove the chemical potential from the action. The transformation eliminates the chemical potential from the differential equation satisfied by the propagator, but the chemical potential appears in the transformed boundary conditions and the final result for the perturbative Green's functions is unchanged.

Weldon, H. Arthur [Department of Physics, West Virginia University, Morgantown, West Virginia, 26506-6315 (United States)

2007-12-15

222

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

223

Acceleration of chemical reactions within a shock wave front  

NASA Astrophysics Data System (ADS)

The aim of the present numerical study was to illustrate the possible influence of translational nonequilibrium in the front of a shock wave on the rate of the threshold chemical reaction. The Monte Carlo method of nonstationary statistical simulation with variable weighting factors was used. Gas mixtures which contained, ahead of the front, two chemically interacting small additives A1, A2 and an inert light main component were considered. A chemical reaction of the additives started in the front of a shock wave and led to formation of two new low-concentration components A3 and A4. It was shown that for the ratio of molecular number densities of the additives A1, A2 and an inert component A5 of 1:10:200 and for the molecular mass ratio of components A1, A2, A3, A4, A5 of 34.5:8:38.5:4:1 the value of the direct reaction rate obtained in the front exceeds its equilibrium value behind the wave by more than 100 times. As a result, the reaction occurs more intensively in the zone of translational nonequilibrium. It was also shown that for the cases of an exothermic reaction and a weak endothermic reaction, a small amount of the light reaction product has the velocity of the shock wave and is carried by the front.

Kulikov, S. V.

224

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

PubMed

This work addresses the problem of similarity search and classification of chemical reactions using Neighborhood Behavior (NB) and Condensed Graphs of Reaction (CGR) approaches. The CGR formalism represents chemical reactions as a classical molecular graph with dynamic bonds, enabling descriptor calculations on this graph. Different types of the ISIDA fragment descriptors generated for CGRs in combination with two metrics--Tanimoto and Euclidean--were considered as chemical spaces, to serve for reaction dissimilarity scoring. The NB method has been used to select an optimal combination of descriptors which distinguish different types of chemical reactions in a database containing 8544 reactions of 9 classes. Relevance of NB analysis has been validated in generic (multiclass) similarity search and in clustering with Self-Organizing Maps (SOM). NB-compliant sets of descriptors were shown to display enhanced mapping propensities, allowing the construction of better Self-Organizing Maps and similarity searches (NB and classical similarity search criteria--AUC ROC--correlate at a level of 0.7). The analysis of the SOM clusters proved chemically meaningful CGR substructures representing specific reaction signatures. PMID:22894688

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

2012-09-04

225

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

226

Asymmetric chemical reactions by polarized quantum beams  

NASA Astrophysics Data System (ADS)

One of the most attractive hypothesis for the origin of homochirality in terrestrial bio-organic compounds (L-amino acid and D-sugar dominant) is nominated as "Cosmic Scenario"; a chiral impulse from asymmetric excitation sources in space triggered asymmetric reactions on the surfaces of such space materials as meteorites or interstellar dusts prior to the existence of terrestrial life. 1) Effective asymmetric excitation sources in space are proposed as polarized quantum beams, such as circularly polarized light and spin polarized electrons. Circularly polarized light is emitted as synchrotron radiation from tightly captured electrons by intense magnetic field around neutron stars. In this case, either left-or right-handed polarized light can be observed depending on the direction of observation. On the other hand, spin polarized electrons is emitted as beta-ray in beta decay from radioactive nuclei or neutron fireballs in supernova explosion. 2) The spin of beta-ray electrons is longitudinally polarized due to parity non-conservation in the weak interaction. The helicity (the the projection of the spin onto the direction of kinetic momentum) of beta-ray electrons is universally negative (left-handed). For the purpose of verifying the asymmetric structure emergence in bio-organic compounds by polarized quantum beams, we are now carrying out laboratory simulations using circularly polarized light from synchrotron radiation facility or spin polarized electron beam from beta-ray radiation source. 3,4) The target samples are solid film or aqueous solution of racemic amino acids. 1) K.Kobayashi, K.Kaneko, J.Takahashi, Y.Takano, in Astrobiology: from simple molecules to primitive life; Ed. V.Basiuk; American Scientific Publisher: Valencia, 2008. 2) G.A.Gusev, T.Saito, V.A.Tsarev, A.V.Uryson, Origins Life Evol. Biosphere. 37, 259 (2007). 3) J.Takahashi, H.Shinojima, M.Seyama, Y.Ueno, T.Kaneko, K.Kobayashi, H.Mita, M.Adachi, M.Hosaka, M.Katoh, Int. J. Mol. Sci. 10, 3044 (2009). 4) V.I.Burkov, L.A.Goncharova, G.A.Gusev, H.Hashimoto, F.Kaneko, T.Kaneko, K. Kobayashi, H.Mita, E.V.Moiseenko, T.Ogawa, N.G.Poluhina, T.Saito, S.Shima, J.Takahashi, M.Tanaka, Y.Tao, V.A.Tsarev, J.Xu, H.Yabuta, K.Yagi-Watanabe, H.Yan, G.Zhang, Origins Life Evol. Biosphere, 39 295 (2009).

Takahashi, Jun-Ichi; Kobayashi, Kensei

227

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

NASA Astrophysics Data System (ADS)

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

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

2007-11-01

228

Characterization of chemically modified hyperthermophilic enzymes for chemical syntheses and bioremediation reactions. 1998 annual progress report  

SciTech Connect

'Remediation processes frequently involve species possessing limited solubility in water. The authors are interested in novel strategies that use molecularly-engineered enzymes with enhanced activity and stability for the remediation of recalcitrant compounds in organic media. Organic biocatalysis may be motivated by the nature of the substrate itself, or by augmented mass transport, ease of product recovery, or novel reaction pathways afforded by the organic solvent. However, naturally-occurring enzymes are usually subject to quite limited activity and stability in such organic environments. 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. This bioprocessing system will be assessed using PCB''s, DNAPL''s and PAH''s. As of the second of year of a 3-year project, the authors have obtained promising results for both the demonstration of the proposed remediation strategy and fundamental understanding of the enzymatic catalysis in organic media. In one of the efforts, ligninase (LiP) was modified by poly(ethylene glycol) (PEG) and examined for the degradation of pentachlorophenol (PCP) in water-solvent mixtures. In the other efforts, basic catalytic behaviors of the chemically modified hyperthermophilic metalloenzymes including ferredoxin, hydrogenase and aldehyde oxidoreductase were examined in organic solvents.'

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

1998-06-01

229

Multiple Equilibria in Complex Chemical Reaction Networks: II. The Species-Reaction Graph  

Microsoft Academic Search

For mass action kinetics, the capacity for multiple equilibria in an isothermal homo- geneous continuous ?ow stirred tank reactor is determined by the structure of the underlying network of chemical reactions. We suggest a new graph-theoretical method for discriminating between com- plex reaction networks that can admit multiple equilibria and those that cannot. In particular, we associate with each network

Gheorghe Craciun; Martin Feinberg

2006-01-01

230

Simulation of chemical reaction equilibria by the reaction ensemble Monte Carlo method: a review†  

Microsoft Academic Search

Understanding and predicting the equilibrium behaviour of chemically reacting systems in highly non-ideal environments is critical to many fields of science and technology, including solvation, nanoporous materials, catalyst design, combustion and propulsion science, shock physics and many more. A method with recent success in predicting the equilibrium behaviour of reactions under non-ideal conditions is the reaction ensemble Monte Carlo method

C. Heath Turner; John K. Brennan; Martin Lísal; William R. Smith; J. Karl Johnson; Keith E. Gubbins

2008-01-01

231

Shock-induced chemical reactions and synthesis of binary compounds  

SciTech Connect

The results of an experimental program on shock-induced chemical reactions and synthesis of binary compounds are presented. Binary powder mixture systems that are investigated include: (1) intermetallic forming compounds (e.g., Ni--Al, Ni--Si, Nb--Si, etc.) associated with large negative heats of reaction; and (2) isomorphous (e.g., Ni--Cu) and fully immiscible (e.g., Nb--Cu) systems associated with zero (or positive) heat of reaction. The extent of shock induced chemical reactions and the type of shock synthesized compounds formed in these systems are observed to be dependent on (i) shock-loading condition, (ii) the relative volumetric distribution of the mixture constituents, and (iii) differences in respective material properties which affect relative particle flow. 5 refs., 9 figs.

Thadhani, N.N.; Advani, A.; Song, I.; Dunbar, E.; Grebe, A. (New Mexico Inst. of Mining and Technology, Socorro, NM (USA). Center for Explosives Technology Research); Graham, R.A. (Sandia National Labs., Albuquerque, NM (USA))

1990-01-01

232

Kramers problem for nonequilibrium current-induced chemical reactions.  

PubMed

We discuss the use of tunneling electron current to control and catalyze chemical reactions. Assuming the separation of time scales for electronic and nuclear dynamics we employ Langevin equation for a reaction coordinate. The Langevin equation contains nonconservative current-induced forces and gives nonequilibrium, effective potential energy surface for current-carrying molecular systems. The current-induced forces are computed via Keldysh nonequilibrium Green's functions. Once a nonequilibrium, current-depended potential energy surface is defined, the chemical reaction is modeled as an escape of a Brownian particle from the potential well. We demonstrate that the barrier between the reactant and the product states can be controlled by the bias voltage. When the molecule is asymmetrically coupled to the electrodes, the reaction can be catalyzed or stopped depending on the polarity of the tunneling current. PMID:21861578

Dzhioev, Alan A; Kosov, D S

2011-08-21

233

Machine learning of chemical reactivity from databases of organic reactions  

Microsoft Academic Search

Databases of chemical reactions contain knowledge about the reactivity of specific reagents. Although information is in general\\u000a only explicitly available for compounds reported to react, it is possible to derive information about substructures that do\\u000a not react in the reported reactions. Both types of information (positive and negative) can be used to train machine learning\\u000a techniques to predict if a

Gonçalo V. S. M. Carrera; Sunil Gupta; João Aires-de-Sousa

2009-01-01

234

The Chemical Reaction Model Recent Developments and Prospects  

Microsoft Academic Search

In 2001, we gave a survey of more than fifteen years of research on the chemical paradigm which had been a source of inspiration\\u000a in many different research areas. The present article presents a digest of recent advances concerning the chemical reaction\\u000a model. We focus to a large extent on: (1) upgrading the basic model to a higher order formalism

Jean-pierre Banâtre; Pascal Fradet; Yann Radenac

2008-01-01

235

Shrinkage Dynamics of a Vesicle Induced by Chemical Reactions  

NASA Astrophysics Data System (ADS)

We study the shrinkage dynamics of a vesicle out of equilibrium. In our previous paper, we introduced a kinetic theory of a vesicle interacting with surfactant molecules. In the present paper, we extend the theory to cover more variety of chemical reactions. It is shown that the chemical kinetics change drastically the relation between the waiting time of pore formation and the radius of vesicle. Numerical simulations are carried out to confirm our analytical results.

Kaga, Masafumi; Ohta, Takao

2007-09-01

236

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

237

Chemical description of thermal waters in the Fiji Islands  

Microsoft Academic Search

Thermal springs occur in more than 60 locations in the extinct volcanic islands of Fiji. Discharge temperatures are usually 40° to 60°C, but in two areas, temperatures reach boiling. The chemistry of the thermal waters is variable, largely due to mixing of seawater and cool groundwater. Chemical geothermometry indicates subsurface water temperatures of from 90° to 120°C, and to as

Cox

1980-01-01

238

Thermal impurity reactions and structural changes in slightly carbonated hydroxyapatite  

Microsoft Academic Search

Lattice and surface impurity reactions and structural changes induced by them in slightly carbonated hydroxyapatite (SCHA)\\u000a treated at 25–1100ºC were comprehensively studied. The SCHA was processed by a conventional wet synthesis at a high possible\\u000a temperature (96ºC) using ammonium containing parent reagents. IR-spectroscopy, XRD, TG-DTA technique and mass spectrometric\\u000a thermal analysis (MSTA) were employed for characterization of the samples. $$

Z. Z. Zyman; D. V. Rokhmistrov; V. I. Glushko; I. G. Ivanov

2009-01-01

239

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

240

Chemical pathways in ultracold reactions of SrF molecules  

SciTech Connect

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

Meyer, Edmund R.; Bohn, John L. [JILA, NIST, and Department of Physics, University of Colorado, Boulder, Colorado 80309-0440 (United States)

2011-03-15

241

Developing secondary students’ conceptions of chemical reactions: the introduction of chemical equilibrium  

Microsoft Academic Search

This article describes an empirical study concerning the introduction of the chemical equilibrium concept in chemistry classrooms in a way which challenges secondary students’ initial conceptions of chemical reactions. The objectives of this study were to identify the types of reasoning students use in this context and to develop teaching strategies which promote conceptual change in this respect. As a

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

1998-01-01

242

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

243

Chemical reaction mediated self-assembly of PTCDA into nanofibers.  

PubMed

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

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

2011-08-03

244

Quantum and semiclassical theories of chemical reaction rates  

SciTech Connect

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

Miller, W.H. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley National Lab., CA (United States). Chemical Sciences Div.

1995-09-01

245

Chemical reaction engineering using molecularly imprinted polymeric catalysts  

Microsoft Academic Search

Enzymes play an important role as highly specific catalysts in biotechnology [J. Biotechnol. 66 (1998) 3; Hydrolases in Organic Synthesis, Wiley, New York, 1999] as well as in chemical reaction engineering [J. Biotechnol. 59 (1997) 11; Trends Biotechnol. 13 (7) (1995) 253]. However, the drawbacks of these biomaterials are poor durability and relatively high costs of production. Thus, the technique

Oliver Brüggemann

2001-01-01

246

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.

Gorlich, Dennis; Dittrich, Peter

2013-01-01

247

Chemical reaction models for non-equilibrium phase transitions  

Microsoft Academic Search

Chemical model reactions are discussed the steady states of which show the phenomenon of non equilibrium phase transitions. One example shows a phase transition of second order, another one shows a phase transition of first order. If diffusion occurs in the case of first order transition, coexistence of two phases in different domains is possible. For plane boundary layers between

F. Schlögl

1972-01-01

248

Interaction between chemical reactions and mixing on various scales  

Microsoft Academic Search

The way in which reagents are mixed can have a large influence on the product distribution of a chemical reaction. This has been analysed earlier when micromixing is the limiting mixing step. Additional segregation at a larger scale has only been treated in detail when the local turbulent dispersion of a feed stream was relevant. Here additional segregation due to

S. J. Hearn

1997-01-01

249

Turbulent mixing and the selectivity of fast chemical reactions  

Microsoft Academic Search

Assuming that complete information is available about (a) the chemical reactions (mechanism, stoichiometry, thermodynamics, and kinetics) and (b) the turbulent flow field in a reactor (mean velocities and turbulence parameters), we would like to calculate directly the time evolution of the temperature and the concentrations of all species present. No general method is yet available to satisfy this goal. Starting

J. R. Bourne

1991-01-01

250

A multi-scaled approach for simulating chemical reaction systems  

Microsoft Academic Search

In this paper we give an overview of some very recent work, as well as presenting a new approach, on the stochastic simulation of multi-scaled systems involving chemical reactions. In many biological systems (such as genetic regulation and cellular dynamics) there is a mix between small numbers of key regulatory proteins, and medium and large numbers of molecules. In addition,

Kevin Burrage; Tianhai Tian; Pamela Burrage

2004-01-01

251

Chemical Reactions in Non-Aqueous Media and Molten Salts.  

National Technical Information Service (NTIS)

The symposium on Chemical Reactions in Non-aqueous Media and Molten Salts was held at the Osmania University in Hyderabad, India. Forty papers were presented of which four papers were on non-aqueous chemistry in nuclear technology, nine papers on molten s...

M. V. Ramaniah D. D. Sood V. Venugopal

1978-01-01

252

The arbitrary dynamic behavior of open chemical reaction systems  

Microsoft Academic Search

We show that if the kinetic equations describing a set of chemical reactions occurring in a one-phase closed system are only required to obey a very general set of postulates (mass conserved, concentrations nonnegative, vector fields which are continuous with continuous derivatives, existence of equilibrium, stability of equilibrium, existence of potential functions which are extremal at equilibrium, detailed balance, law

Alan S. Perelson; David Wallwork

1977-01-01

253

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

SciTech Connect

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

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

1985-08-01

254

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

255

Automatic modelling of reaction systems using genetic algorithms and its application to chemical vapour deposition processes: advanced utilizations of simulators for chemical systems  

NASA Astrophysics Data System (ADS)

The identification of appropriate reaction models is very helpful for developing chemical vapour deposition (CVD) processes. We introduced novel algorithms to analyse experimental data from CVD processes and identify reaction models automatically using genetic algorithms (GAs). The reaction models, which consist of various deposition species and gas-phase and surface reactions, were determined both quantitatively and qualitatively, based on chemical kinetics. The GA modelling algorithm consists of a process for calculating the predicted results from the reaction model candidates and a process for modifying the candidates by use of the difference between experimental and predicted results. We demonstrate the validity of this approach to successfully identify the appropriate reaction models from synthetic experimental data and real experimental data obtained during thermal CVD of tetraethylorthosilicate.

Takahashi, Takahiro; Funatsu, Kimito; Ema, Yoshinori

2005-01-01

256

Coriolis coupling and nonadiabaticity in chemical reaction dynamics.  

PubMed

The nonadiabatic quantum dynamics and Coriolis coupling effect in chemical reaction have been reviewed, with emphasis on recent progress in using the time-dependent wave packet approach to study the Coriolis coupling and nonadiabatic effects, which was done by K. L. Han and his group. Several typical chemical reactions, for example, H+D(2), F+H(2)/D(2)/HD, D(+)+H(2), O+H(2), and He+H(2)(+), have been discussed. One can find that there is a significant role of Coriolis coupling in reaction dynamics for the ion-molecule collisions of D(+)+H(2), Ne+H(2)(+), and He+H(2)(+) in both adiabatic and nonadiabatic context. PMID:20928846

Wu, Emilia L

2010-12-01

257

Multiscale stochastic simulations of chemical reactions with regulated scale separation  

NASA Astrophysics Data System (ADS)

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; Feigelman, Justin

2013-07-01

258

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

259

Mixing, chemical reaction and flow field development in ducted rockets  

SciTech Connect

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

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

1984-09-01

260

Noise-induced enhancement of chemical reactions in nonlinear flows.  

PubMed

Motivated by the problem of ozone production in atmospheres of urban areas, we consider chemical reactions of the general type: A+B-->2C, in idealized two-dimensional nonlinear flows that can generate Lagrangian chaos. Our aims differ from those in the existing work in that we address the role of transient chaos versus sustained chaos and, more importantly, we investigate the influence of noise. We find that noise can significantly enhance the chemical reaction in a resonancelike manner where the product of the reaction becomes maximum at some optimal noise level. We also argue that chaos may not be a necessary condition for the observed resonances. A physical theory is formulated to understand the resonant behavior. (c) 2002 American Institute of Physics. PMID:12779572

Liu, Zonghua; Lai, Ying-Cheng; Lopez, Juan M.

2002-06-01

261

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

SciTech Connect

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

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

1997-12-01

262

Single-molecule chemical reactions on DNA origami  

NASA Astrophysics Data System (ADS)

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

Voigt, Niels V.; Tørring, Thomas; Rotaru, Alexandru; Jacobsen, Mikkel F.; Ravnsbæk, Jens B.; Subramani, Ramesh; Mamdouh, Wael; Kjems, Jørgen; Mokhir, Andriy; Besenbacher, Flemming; Gothelf, Kurt Vesterager

2010-03-01

263

Reaction Texture Development in Granulites: A Chemical Potential Approach  

NASA Astrophysics Data System (ADS)

Reaction textures in granulites are generally considered disequilibrium features that are attributed to changes in P-T conditions during a rock's evolution. Various types of reaction textures occur in metamorphic rocks, but can broadly be categorized as either closed or open system. In a closed system, simple reaction textures develop where the products and reactants indicate conservation of the chemical components involved in the reaction. In many rocks, however, more complex reaction textures develop where one or more components must enter into the site where the texture is developing, indicating open system behavior. Once nucleation occurs, and reaction products begin to form, chemical potential gradients are established. Complex reaction textures are difficult to investigate using a standard pseudosection approach. Even for simple reaction textures, conventional pseudosections do not yield information about the spatial organization of a texture. One way to investigate this is to calculate the dependence of phase equilibria on the chemical potentials of the more mobile elements involved in the development of textures. This contribution follows this approach in a case study of sapphirine granulites associated with an exposure of eclogite in the Snowbird tectonic zone of the western Canadian Shield in northern Saskatchewan. Peak P-T conditions in the eclogite reached about 750° and 18 kbar followed by development of extensive reaction textures during near-isothermal decompression through granulite facies conditions. The rock investigated is an impure quartzite containing the peak assemblage Grt + Ky + Qtz with development of silica-undersaturated symplectites of Spl + Spr + An around Ky and coronae of Pl + Opx around Grt. Garnet typically contains abundant inclusions of Ky + Qtz and displays strong Ca-zoning with a decrease in the rim adjacent to surrounding Pl. Opx typically separates Pl from Qtz even in the absence of Grt, occurring as a phase between individual quartz grains and plagioclase. We investigate the phase equilibria and spatial relationships of these textures using petrogenetic grids and compatibility diagrams calculated with THERMOCALC, to understand the effects of chemical potential gradients on the spatial organization and P-T conditions of these reaction textures.

Baldwin, J. A.; Powell, R.

2006-05-01

264

Amniotic membrane transplantation in acute chemical and thermal injury  

Microsoft Academic Search

%PURPOSE: To present a case of chemical injury and a case of thermal injury treated by amniotic membrane transplantation in acute phase.METHODS: Case reports. An eye with sodium hydroxide injury, opaque cornea, and limbal ischemia of more than 180 degrees and an eye with hot tea injury, opaque cornea, stromal edema, and scarring were treated by amniotic membrane transplantation within

M. S Sridhar; Aashish K Bansal; Virender S Sangwan; Gullapalli N Rao

2000-01-01

265

Anisotropic thermal conductivity in chemical vapor deposition diamond  

Microsoft Academic Search

The thermal conductivity of thick-film diamond prepared by chemical vapor deposition (CVD) has been measured with heat flowing in a direction perpendicular to the plane of the film. A laser flash technique with fast infrared detection has been devised for measurement of thin samples with high conductivity. The conductivity perpendicular to the plane is observed to be at least 50

J. E. Graebner; S. Jin; G. W. Kammlott; B. Bacon; L. Seibles; W. Banholzer

1992-01-01

266

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

267

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

268

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

269

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

NASA Astrophysics Data System (ADS)

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

Malijevský, Alexandr; Lísal, Martin

2009-04-01

270

Effects of Chemical Reaction on MHD Flow Past an Impulsively Started Infinite Vertical Plate with Uniform Heat and Mass Flux  

NASA Astrophysics Data System (ADS)

Finite difference solutions of the unsteady MHD flow past an impulsively started infinite vertical plate with uniform heat and mass flux are presented here, taking into account the homogeneous chemical reaction of first order. The dimensionless governing equations are solved by an efficient, more accurate, unconditionally stable and fast converging implicit scheme. The effects of velocity, temperature and concentration for different parameters such as chemical reaction parameter, Schmidt number, Prandtl number, thermal Grashof number, mass Grashof number and time are studied. It is observed that due to the presence of a first order chemical reaction, the velocity increases during the generative reaction and decreases in the destructive reaction. It is observed that the velocity decreases in the presence of the magnetic field, as compared to its absence.

Chandrakala, P.

2013-06-01

271

Modelling of gas-solid reaction—Coupling of heat and mass transfer with chemical reaction  

Microsoft Academic Search

A general gas-solid reaction model is formulated. This work is the further development of the previous modelling work of Mazet (1988, Ph.D. Thesis, University of Perpignan) and Goetz (1991, Ph.D. Thesis, University of Perpignan) to simulate reversible gas-solid reactions that have been extensively applied to the new chemical heat pump technology developed at CNRS-IMP. In the present paper, a general

Hui-Bo Lu; Nathalie Mazet; Bernard Spinner

1996-01-01

272

Propagation of Reactions in Thermally-damaged PBX9501  

Microsoft Academic Search

A thermally-initiated explosion in PBX-9501 (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) is observed in situ by flash x-ray imaging, and modeled with the LLNL multi-physics arbitrary-Lagrangian-Eulerian code ALE3D. The containment vessel deformation provides a useful estimate of the reaction pressure at the time of the explosion, which we calculate to be in the range 0.8-1.4 GPa. Closely-coupled ALE3D simulations of these experiments, utilizing the multi-phase

J W Tringe; E A Glascoe; J R Kercher; T M Willey; H K Springer; D W Greenwood; J D Molitoris; L Smilowitz; B F Henson; J L Maienschein

2010-01-01

273

The plasma-chemical reactions of several materials in a rf ion source  

Microsoft Academic Search

The plasma-chemical reactions of several materials are described in this paper. Materials such as quartz and platinum are used for containers of chemical reactions in various fields. Because of their stability chemical reactions do not occur easily, but such reactions can occur within the plasma of a rf ion source, and ion beams of such materials have been extracted from

Bai Gui Bin

1990-01-01

274

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

Microsoft Academic Search

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

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

2010-01-01

275

Gamma and the Chemical Reaction Model: Fifteen Years After  

Microsoft Academic Search

Gamma was originally proposed in 1986 as a formalism for the definition of programs without artificial sequentiality. The\\u000a basic idea underlying the formalism is to describe computation as a form of chemical reaction on a collection of individual pieces of data. Due to the very minimal nature of the language, and its absence of sequential\\u000a bias, it has been possible

Jean-Pierre Ban?tre; Pascal Fradet; Daniel Le Métayer

276

Separation of the isotopes of boron by chemical exchange reactions  

DOEpatents

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

McCandless, Frank P. (Bozeman, MT); Herbst, Ronald S. (Idaho Falls, ID)

1995-01-01

277

Separation of the isotopes of boron by chemical exchange reactions  

DOEpatents

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

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

1995-05-30

278

Laboratory Kinetics of Chemical Reactions occurring in Astrophysical Environments  

Microsoft Academic Search

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

N. G. Adams; L. M. Babcock

2005-01-01

279

Chemical and mathematical modeling of asphaltene reaction pathways  

SciTech Connect

Precipitated asphaltene was subjected to pyrolysis and hydropyrolysis, both neat and in solvents, and catalytic hydroprocessing. A solvent extraction procedure defined gas, maltene, asphaltene, and coke product fractions. The apparent first order rate constant for asphaltene conversion at 400/sup 0/C was relatively insensitive to the particular reaction scheme. The yield of gases likewise showed little variation and was always less than 10%. On the other hand, the maltene and coke yields were about 20% and 60%, respectively, from neat pyrolysis, and about 60% and less than 5%, respectively, from catalytic reactions. The temporal variations of the product fractions allowed discernment of asphaltene reaction pathways. The primary reaction of asphaltene was to residual asphaltene, maltenes, and gases. The residual asphaltene reacted thermally to coke and catalytically to maltenes at the expense of coke. Secondary degradation of these primary products led to lighter compounds. Reaction mechanism for pyrolysis of asphaltene model compounds and alkylaromstics were determined. The model compound kinetics results were combined with a stochastic description of asphaltene structure in a mathematical model of asphaltene pyrolysis. Individual molecular product were assigned to either the gas, maltene, asphaltene, or coke product fractions, and summation of the weights of each constituted the model's predictions. The temporal variation of the product fractions from simulated asphaltene pyrolysis compared favorably with experimental results.

Salvage, P.E.

1986-01-01

280

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

281

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

282

Analysis of initial reactions of MALDI based on chemical properties of matrixes and excitation condition.  

PubMed

This investigation concerns the initial chemical reactions that affect the ionization of matrixes in matrix-assisted laser desorption/ionization (MALDI). The study focuses on the relaxations of photon energy that occur on a comparable time scale to that of ionization, in which the available laser energy is shared and the ionization condition is changed. The relaxations include fluorescence, fragmentation, and nonradiative relaxation from the excited state to the ground state. With high absorption cross section and long excited-state lifetime, photoionization of matrix plays an important role if sufficient laser energy is used. Under other conditions, thermal ionization of the molecule in the ground state is predicted to be one of the important reactions. Evidence of change in the branching ratio of initial reactions with the matrix and the excitation wavelength was obtained with ?-cyano-4-hydroxycinnamic acid, sinapinic acid, 2,5-dihydroxybenzoic acid, and 2,4,6-trihydroxyacetophenone. These matrixes are studied by obtaining their mixed crystal absorption spectra, fluorescence properties, laser-induced infrared emission, and product ions. The exact ionization pathway depends on the chemical properties of matrixes and the excitation conditions. This concept may explain the diversity of experimental results observed in MALDI experiments, which provides an insight into the ensemble of chemical reactions that govern the generation of ions. PMID:22799495

Lai, Yin-Hung; Wang, Chia-Chen; Chen, Chiu Wen; Liu, Bo-Hong; Lin, Sheng Hsien; Lee, Yuan Tseh; Wang, Yi-Sheng

2012-08-01

283

Spatiotemporal regulation of chemical reactions by active cytoskeletal remodeling  

PubMed Central

Efficient and reproducible construction of signaling and sorting complexes, both on the surface and within the living cell, is contingent on local regulation of biochemical reactions by the cellular milieu. We propose that in many cases this spatiotemporal regulation can be mediated by interaction with components of the dynamic cytoskeleton. We show how the interplay between active contractility and remodeling of the cytoskeleton can result in transient focusing of passive molecules to form clusters, leading to a dramatic increase in the reaction efficiency and output levels. The dynamic cytoskeletal elements that drive focusing behave as quasienzymes catalyzing the chemical reaction. These ideas are directly applicable to the cortical actin-dependent clustering of cell surface proteins such as lipid-tethered GPI-anchored proteins, Ras proteins, as well as many proteins that have domains that confer the ability to interact with the actin cytoskeleton. In general such cytoskeletal driven clustering of proteins could be a cellular mechanism to spatiotemporally regulate and amplify local chemical reaction rates in a variety of contexts such as signaling, transcription, sorting, and endocytosis.

Chaudhuri, Abhishek; Bhattacharya, Bhaswati; Gowrishankar, Kripa; Mayor, Satyajit; Rao, Madan

2011-01-01

284

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

285

Physio-chemical reactions in recycle aggregate concrete.  

PubMed

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

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

2008-07-15

286

Electronically excited molecules: Reaction kinetics and emission of light: Nanosecond infrared spectroscopy, electronic emission from chemical reactions  

NASA Astrophysics Data System (ADS)

A time-resolved IR absorption spectrometer capable of detecting chemical transients on the nanosecond timescale was designed, constructed, and successfully implemented. The spectrometer was used to characterize the vibrational relaxation of an open shell radical species, CF3, produced with excess energy from the photolysis of the parent CF3I compound. The effects of vibrational excitation in the CF3 radical on the reaction CF3 + Br2 yields CF3Br + Br were measured. Broadband data collection techniques were used to monitor the reactive and relaxation pathways simultaneously. The energetic radicals react no faster than the thermalized CF3 and may actually have a lower cross section for reaction. The spectrometer was also used to detect the gas phase absorption spectra of the polyatomic radicals. A thorough investigation into ozone-olefin reactions in a cryogenic matrix environment was completed. It was possible to complex ozone with various olefinic partners through careful control of the matrix deposition process, despite the very low (1-5 kcal/mole) activation energies for the ozonolysis reactions. The ground state complexes were observed to form a charge-transfer (CT) complex upon excitation.

Moore, C. B.

1992-02-01

287

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

288

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

289

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

290

Synthesis of aligned carbon nanotubes using thermal chemical vapor deposition  

Microsoft Academic Search

Aligned carbon nanotubes have been synthesized on transition metal-coated silicon substrates with C2H2 using thermal chemical vapor deposition. It was found that nanotubes can be mostly vertically aligned on a large area of plain Si substrates when the density of metal domains reaches a certain value. Pretreatment of Co–Ni alloy by HF dipping and etching with NH3 gas prior to

Cheol Jin Lee; Dae Woon Kim; Tae Jae Lee; Young Chul Choi; Young Soo Park; Young Hee Lee; Won Bong Choi; Nae Sung Lee; Gyeong-Su Park; Jong Min Kim

1999-01-01

291

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

292

Deposition of thermal and hot-wire chemical vapor deposition copper thin films on patterned substrates.  

PubMed

In this work we study the hot-wire chemical vapor deposition (HWCVD) of copper films on blanket and patterned substrates at high filament temperatures. A vertical chemical vapor deposition reactor was used in which the chemical reactions were assisted by a tungsten filament heated at 650 degrees C. Hexafluoroacetylacetonate Cu(I) trimethylvinylsilane (CupraSelect) vapors were used, directly injected into the reactor with the aid of a liquid injection system using N2 as carrier gas. Copper thin films grown also by thermal and hot-wire CVD. The substrates used were oxidized silicon wafers on which trenches with dimensions of the order of 500 nm were formed and subsequently covered with LPCVD W. HWCVD copper thin films grown at filament temperature of 650 degrees C showed higher growth rates compared to the thermally ones. They also exhibited higher resistivities than thermal and HWCVD films grown at lower filament temperatures. Thermally grown Cu films have very uniform deposition leading to full coverage of the patterned substrates while the HWCVD films exhibited a tendency to vertical growth, thereby creating gaps and incomplete step coverage. PMID:22097561

Papadimitropoulos, G; Davazoglou, D

2011-09-01

293

Kinetic and chemical characterization of thermal decomposition of dicumylperoxide in cumene.  

PubMed

Dicumylperoxide (DCP) is one of the most used peroxides in the polymer industry. It has been reported that its thermal decomposition can result in runaway phenomena and thermal explosions with significant economic losses and injuries to people. In the present paper thermal behaviour of dicumylperoxide in cumene was investigated over the temperature range of 393-433 K under aerated and de-aerated conditions. The results indicated that when oxygen was present, the decomposition rate did not follow a simple pseudo-first order kinetic as previously reported in literature. A satisfactory fit of the experimental data was, in this case, achieved by means of kinetic expression derived under the assumption of an autocatalytic scheme of reaction. The reaction rate was, on the contrary, correctly described by a pseudo-first order kinetic in absence of oxygen. Under both aerated and de-aerated conditions, chemical analysis showed that the decomposition mainly resulted in the formation of acetophenone and dimethylphenylcarbinol with minor occurrence of 2,3-dimethyl-2,3-diphenylbutane. The formation of methane and ethane was also invariably observed while the appearance of cumylhydroperoxide as a reaction intermediate was detected under only aerated conditions. Therefore, two reaction schemes were proposed to explain system behaviour in the presence of oxygen and after its purging. PMID:21277085

Di Somma, Ilaria; Marotta, Raffaele; Andreozzi, Roberto; Caprio, Vincenzo

2011-01-13

294

Chemical reactions occurring during direct solar reduction of CO2.  

PubMed

At high temperatures carbon dioxide may absorb solar radiation and react to form carbon monoxide and molecular oxygen. The CO, so produced, may be converted by well-established means to a combustible fuel, such as methanol. We intend to make a future demonstration of the solar reduction of CO2 based on these processes. This paper, however, addresses only the problem of preserving, or even enhancing, the initial photolytic CO by quenching the hot gas with colder H2O or CO2. We present model calculations with a reaction mechanism used extensively in other calculations. If a CO2 gas stream is heated and photolyzed by intense solar radiation and then allowed to cool slowly, it will react back to the initial CO2 by a series of elementary chemical reactions. The back reaction to CO2 can be terminated with the rapid addition of CO2, water, or a mixture. Calculations show that a three-fold quench with pure CO2 will stop the reactions and preserve over 90% of the initial photolytic CO. We find that water has one of two effects. It can either increase the CO level, or it can catalyze the recombination of O and CO to CO2. The gas temperature is the determining factor. If the quench gas is not sufficient to keep the temperature below approximately 1100 K, a chain-branching reaction dominates and the reaction to CO2 occurs. If the temperature stays below that level a chain terminating reaction dominates and the CO is increased. The former case occurs below approximately a fourfold quench with a water/CO2 mixture. The later case occurs when the quench is greater than fourfold. We conclude that CO2, H2O, or a mixture may quench the hot gas stream photolyzed by solar radiation and preserve the photolytic CO. PMID:11589409

Lyma, J L; Jensen, R J

2001-09-28

295

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

296

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

PubMed

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

2013-02-01

297

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.

Scholey, Jonathan M.

2013-01-01

298

Chemical reaction and dust formation studies in laboratory hydrocarbon plasmas.  

NASA Astrophysics Data System (ADS)

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

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

299

The influence of overlap interactions on chemical reactions in confinement  

NASA Astrophysics Data System (ADS)

Chemical reactions are often carried out in nano-structured materials due to their large surface area per unit mass. It is, however, difficult to understand fully the role of the nano-structure in many reactions due to the superposition of multiple effects. Such effects include: the reduced dimensionality of the system, the heterogeneity of the pore surfaces, the selective adsorption of reactants/products, catalytic effects, and transport limitations. Experimental studies often show many of these effects at the same time, making the results difficult to interpret. In this work we present results of density functional theory calculations illustrating the influence of overlap interactions (shape-catalytic effects) on chemical reactions. In particular, we show the effect of confinement in small pores on the rates of rotational isomerizations of n-butane, 1-butene and 1,3-butadiene. We find that the rates of these transitions change as the double exponential of the pore size in the molecular sieving limit. These results are a first step towards an integrated model for the design of catalytic materials.

Santiso, Erik E.; Gubbins, Keith E.; George, Aaron M.; Buongiorno Nardelli, Marco

2007-03-01

300

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

National Technical Information Service (NTIS)

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 previ...

P. A. Glaude C. Melius W. J. Pitz C. K. Westbrook

2001-01-01

301

Shock-induced and Shock-assisted Solid-state Chemical Reactions in Powder Mixtures.  

National Technical Information Service (NTIS)

Shock compression of powder mixtures can lead to chemical reactions, resulting in the formation of equilibrium as well as nonequilibrium compounds, and rapid increases in temperature. The reactions occur as manifestations of enhanced solid-state chemical ...

N. N. Thadhani

1994-01-01

302

Thermal, chemical, and mechanical response of rigid polyurethane foam  

SciTech Connect

Rigid polyurethane foams are frequently used as encapsulants to isolate and support thermally sensitive components within weapon systems. When exposed to abnormal thermal environments, such as fire, the polyurethane foam decomposes to form products having a wide distribution of molecular weights and can dominate the overall thermal response of the system. Mechanical response of the decomposing foam, such as thermal expansion under various loading conditions created by gas generation, remains a major unsolved problem. A constitutive model of the reactive foam is needed to describe the coupling between mechanical response and chemical decomposition of foam exposed to environments such as fire. Towards this end, a reactive elastic-plastic constitutive model based on bubble mechanics describing nucleation, decomposition chemistry, and elastic/plastic mechanical behavior of rigid polyurethane foam has been developed. A local force balance, with mass continuity constraints, forms the basis of the constitutive model requiring input of temperature and the fraction of the material converted to gas. This constitutive model provides a stress-strain relationship which is applicable for a broad class of reacting materials such as explosives, propellants, pyrotechnics, and decomposing foams. The model is applied to a block of foam exposed to various thermal fluxes. The model is also applied to a sphere of foam confined in brass. The predicted mechanical deformation of the foam block and sphere are shown to qualitatively agree with experimental observations.

Hobbs, M.L.

1997-12-01

303

Chemical characteristics of mineral trioxide aggregate and its hydration reaction  

PubMed Central

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

2012-01-01

304

Quantum control of chemical reaction dynamics in a classical way  

NASA Astrophysics Data System (ADS)

A simplified approach to quantum control of chemical reaction dynamics based on a classical, local control theory was developed. The amplitude of the control pulse is proportional to the linear momentum of the reaction system within the dipole approximation for the system-radiation field interaction. The kinetic energy of the system is the controlling parameter. That is, the reaction is controlled by accelerating the representative point on a potential energy surface before crossing over a potential barrier and then by deaccelerating it to the target after passing over the potential barrier. The classical treatment was extended to control of wave packet dynamics by replacing the classical momentum by a quantum mechanically averaged momentum on the basis of the Ehrenfest theorem. The present method was applied to a quantum system of a simple one-dimensional, double-well potential for checking its validity. A restriction of the applicability of the simplified method was also discussed. An isomerization of HCN was treated as a model system for wave packet control of a two-dimensional reaction.

Umeda, Hiroaki; Fujimura, Yuichi

2000-09-01

305

On the chemical reaction of matter with antimatter.  

PubMed

A chemical reaction between the building block antiatomic nucleus, the antiproton (p or H- in chemical notation), and the hydrogen molecular ion (H2+) has been observed by the ATHENA collaboration at CERN. The charged pair interact via the long-range Coulomb force in the environment of a Penning trap which is purpose-built to observe antiproton interactions. The net result of the very low energy collision of the pair is the creation of an antiproton-proton bound state, known as protonium (Pn), together with the liberation of a hydrogen atom. The Pn is formed in a highly excited, metastable, state with a lifetime against annihilation of around 1 micros. Effects are observed related to the temperature of the H2+ prior to the interaction, and this is discussed herein. PMID:17492700

Lodi Rizzini, Evandro; Venturelli, Luca; Zurlo, Nicola

2007-06-01

306

[The reaction of the pulpal blood circulation to thermal stimuli].  

PubMed

The present paper characterizes the reactions of the systemcirculation and microcirculation of the pulpa to the effects of temperature changes from--30 degrees C to +55 degrees C. In the range between 25 degrees C and 50 degrees C an increase of the blood flow rate can be observed. By long-standing action of temperatures above 40 degrees C and below 25 degrees C a dilatation of the blood vessels and a decrease of the blood flow rate are caused, thus leading to aggregations, capillary stoppage, and finally to thrombosis of entire pulpa sections. In addition to the outline of the critical initial alterations of the microcirculation in the course of inflammation the clinical conclusions towards crown and cavity preparation by means of water spray cooling, concerning thermal sensibility tests, and cryo-surgical operations are discussed. PMID:135441

Gängler, P

1976-01-01

307

Monte-Carlo simulations of chemical reactions in molecular crystals  

NASA Astrophysics Data System (ADS)

Chemical reactions in molecular crystals, yielding new entities (dimers, trimers,..., polymers) in the original structure, are simulated for the first time by stochastic Monte Carlo methods. The results are compared with those obtained by deterministic methods. They show that numerical simulation is a tool for understanding the evolution of these mixed systems. They are in kinetic and not in thermodynamic control. Reactive site distributions, x-ray diffuse scattering, and chain length distributions can be simulated. Comparisons are made with deterministic models and experimental results obtained in the case of the solid state dimerization of cinnamic acid in the beta phase and in the case of the solid state polymerization of diacetylenes.

Even, J.; Bertault, M.

1999-01-01

308

Structural cluster analysis of chemical reactions in solution  

NASA Astrophysics Data System (ADS)

We introduce a simple and general approach to the problem of clustering structures from atomic trajectories of chemical reactions in solution. By considering distance metrics which are invariant under permutation of identical atoms or molecules, we demonstrate that it is possible to automatically resolve as distinct structural clusters the configurations corresponding to reactants, products, and transition states, even in presence of atom-exchanges and of hundreds of solvent molecules. Our approach strongly simplifies the analysis of large trajectories and it opens the way to the construction of kinetic network models of activated processes in solution employing the available efficient schemes developed for proteins conformational ensembles.

Gallet, Grégoire A.; Pietrucci, Fabio

2013-08-01

309

A topological stochastic approach to the study of multidimensional potential energy surfaces of chemical reactions  

Microsoft Academic Search

In this article we propose a new approach for investigating the properties of multidimensional potential energy surfaces in chemical reactions, based on relations of each multidimensional surface to its one-dimensional image which is the chemical reaction tree. This approach makes it possible to find a common number of independent channels in chemical reactions for complex systems and to construct the

Igor V. Krivoshey; Liudmila A. Sleta

1976-01-01

310

Modeling the influence of chemical reactions on the mechanisms of ionic transport in porous materials  

Microsoft Academic Search

This paper attempts to critically review various approaches developed to model the effects of chemical reactions on the mechanisms of ionic transport in porous media. A comprehensive overview of the various types of chemical reactions that can occur in reactive porous solids is first presented. Methods to model each of these chemical reactions are then described and analyzed. The ability

E. Samson; J. Marchand; J. J. Beaudoin

2000-01-01

311

A Model for Incorporating Chemical Reactions in Mesoscale Modeling of Laser Ablation of Polymers  

Microsoft Academic Search

We have developed a methodology for including effects of chemical reactions in coarse-grained computer simulations such as those that use the united atom or bead and spring approximations. The new coarse-grained chemical reaction model (CGCRM) adopts the philosophy of kinetic Monte Carlo approaches and includes a probabilistic element to predicting when reactions occur, thus obviating the need for a chemically

Barbara J. Garrison; Yaroslava G. Yingling

2004-01-01

312

[Homogeneous-heterogeneous combustion: Thermal and chemical coupling]. [Annual report] research in progress  

SciTech Connect

This is a program to characterize fundamental issues and practical applications of homogeneous-heterogeneous reactions. Fundamental studies of reactions at low pressures and of boundary layer characterization give microscopic information on the processes. Ignition and extinction studies over simple geometries give basic bifurcation behavior with which to characterize multiple steady states and their stabilities and hopefully to identify the types of behavior which may occur. Use of catalytic monoliths will permit examination of the chemical and thermal performance of one of the most important types of geometries in which both types of reaction can occur. Modeling will tie all of these aspects together by showing how individual components interact, Predicting performance of monoliths, and providing the framework for translating these ideas into technological contexts.

Not Available

1992-01-01

313

Possible application of solar-thermal energy in the chemical industry  

SciTech Connect

Eight chemicals are identified that require substantial amounts of non-recoverable 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 novel solar energy applications are production of caustic soda from thermodynamic cycles, ethylene from ethanol, and butadiene from ethanol.

Martin, L.R.

1982-06-01

314

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

315

Millimeter-wave imaging of thermal and chemical signatures.  

SciTech Connect

Development of a passive millimeter-wave (mm-wave) system is described for remotely mapping thermal and chemical signatures of process effluents with application to arms control and nonproliferation. Because a large amount of heat is usually dissipated in the air or waterway as a by-product of most weapons of mass destruction facilities, remote thermal mapping may be used to detect concealed or open facilities of weapons of mass destruction. We have developed a focal-plane mm-wave imaging system to investigate the potential of thermal mapping. Results of mm-wave images obtained with a 160-GHz radiometer system are presented for different target scenes simulated in the laboratory. Chemical and nuclear facilities may be identified by remotely measuring molecular signatures of airborne molecules emitted from these facilities. We have developed a filterbank radiometer to investigate the potential of passive spectral measurements. Proof of principle is presented by measuring the HDO spectral line at 80.6 GHz with a 4-channel 77-83 GHz radiometer.

Gopalsami, N.

1999-03-30

316

Effects of exothermic chemical reaction on the photoacoustic effect from particulate suspensions  

Microsoft Academic Search

Irradiation of chemically reactive particulate suspensions by high power, pulsed laser radiation initiates reactions at the sites of the particles so that besides the absorbed optical energy, chemical energy is liberated. In addition to the release of chemical energy, chemical reaction can result in gas production both of which result in enhancement in the amplitude of the photoacoustic effect. Here

Han Jung Park; Binbin Wu; Gerald J. Diebold

2011-01-01

317

Free-Electron Lasers, Thermal Diffusion, Chemical Kinetics, and Surgery  

NASA Astrophysics Data System (ADS)

Experiments demonstrate that the Mark-III FEL is a particularly effective tool for etching soft matter with remarkably little damage surrounding the site when tuned to wavelengths near 6.45 microns. Based on these observatons, human neuorsurgical and ophthalmic procedures were developed and have been performed successfully. A thermodynamic model was proposed to account for the wavelength dependence; however, the dynamics have not been well understood. We have theoretically investigated thermal diffusion and chemical kinetics in a system of alternating layers of protein and water as heated by a Mark-III FEL. The model is representative of cornea and the exposure conditions are comparable to previous experimental FEL investigations. A substantial temperature enhancement develops in the surface layer on the ten-nanosecond time scale. We consider the onset of both the helix-coil transition and chemical bond breaking of collagen in terms of the thermal, chemical, and structural properties of the system as well as laser wavelength and pulse structure.

Edwards, Glenn; Hutson, M. Shane

2001-11-01

318

Reduction of WO3 to nano-WC by thermo-chemical reaction route  

NASA Astrophysics Data System (ADS)

Thermo-chemical reaction route has been used to synthesize WC-nanoparticles from WO3. Two different carbon sources are used to study the effect of these sources on synthesis. The as-prepared samples are characterized by using X-ray diffraction (XRD), differential thermal analyzer (DTA), thermo-gravimetric analysis (TGA) and transmission electron microscope (TEM). The results indicate that reduction of WO3 to WC takes place by the adsorption of carbon at the surface of WO3 forming porous structure at the defect sites through which carbon diffuses. As the concentration of adsorbed carbon increases the growth of carbon nanotube starts from this site which ultimately gets converted to carbon nano-fibers of higher chemical activity.

Kumar, Akshay; Singh, K.; Pandey, O. P.

2009-02-01

319

Machine learning of chemical reactivity from databases of organic reactions.  

PubMed

Databases of chemical reactions contain knowledge about the reactivity of specific reagents. Although information is in general only explicitly available for compounds reported to react, it is possible to derive information about substructures that do not react in the reported reactions. Both types of information (positive and negative) can be used to train machine learning techniques to predict if a compound reacts or not with a specific reagent. The whole process was implemented with two databases of reactions, one involving BuNH2 as the reagent, and the other NaCNBH3. Negative information was derived using MOLMAP molecular descriptors, and classification models were developed with Random Forests also based on MOLMAP descriptors. MOLMAP descriptors were based exclusively on calculated physicochemical features of molecules. Correct predictions were achieved for approximately 90% of independent test sets. While NaCNBH3 is a selective reducing reagent widely used in organic synthesis, BuNH2 is a nucleophile that mimics the reactivity of the lysine side chain (involved in an initiating step of the mechanism leading to skin sensitization). PMID:19468693

Carrera, Gonçalo V S M; Gupta, Sunil; Aires-de-Sousa, João

2009-05-26

320

Nanoscale wear as a stress-assisted chemical reaction  

NASA Astrophysics Data System (ADS)

Wear of sliding contacts leads to energy dissipation and device failure, resulting in massive economic and environmental costs. Typically, wear phenomena are described empirically, because physical and chemical interactions at sliding interfaces are not fully understood at any length scale. Fundamental insights from individual nanoscale contacts are crucial for understanding wear at larger length scales, and to enable reliable nanoscale devices, manufacturing and microscopy. Observable nanoscale wear mechanisms include fracture and plastic deformation, but recent experiments and models propose another mechanism: wear via atom-by-atom removal (`atomic attrition'), which can be modelled using stress-assisted chemical reaction kinetics. Experimental evidence for this has so far been inferential. Here, we quantitatively measure the wear of silicon--a material relevant to small-scale devices--using in situ transmission electron microscopy. We resolve worn volumes as small as 25 +/- 5 nm3, a factor of 103 lower than is achievable using alternative techniques. Wear of silicon against diamond is consistent with atomic attrition, and inconsistent with fracture or plastic deformation, as shown using direct imaging. The rate of atom removal depends exponentially on stress in the contact, as predicted by chemical rate kinetics. Measured activation parameters are consistent with an atom-by-atom process. These results, by direct observation, establish atomic attrition as the primary wear mechanism of silicon in vacuum at low loads.

Jacobs, Tevis D. B.; Carpick, Robert W.

2013-02-01

321

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

322

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

323

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

324

Local thermal equilibrium plasma modeling for analyses of gas-phase reactions during reactive-laser ablation  

Microsoft Academic Search

Number densities of atoms, ions, and molecules in plasmas composed of two-element vapor-gas mixtures have been computed assuming local thermal equilibrium. The calculations include the formation of diatomic molecules by chemical reactions between both elements. Temperature range and total number densities of elements have been set to values characteristic for plasmas generated by pulsed-laser ablation of solid targets under low-pressure

J. Hermann; C. Dutouquet

2002-01-01

325

Development of porous solid reactant for thermal-energy storage and temperature upgrade using carbonation\\/decarbonation reaction  

Microsoft Academic Search

Cyclic reaction performances of solid reactants for a CaO–CO2 chemical heat-pump designed for upgrading and storing high-temperature thermal energy were studied. Solid reactants composed of CaO as the reactant and CaTiO3 as the inert framework were prepared using the conventional powder method or the metal alkoxide method. Upon experiments of cyclic operation between CaO carbonation and CaCO3 decarbonation at 1023K,

Masahiko Aihara; Toshiyuki Nagai; Junro Matsushita; Yoichi Negishi; Haruhiko Ohya

2001-01-01

326

Convective--Diffusive Transport with Chemical Reaction in Natural Convection Flows  

Microsoft Academic Search

:  A study of laminar natural convection flow over a semi-infinite vertical plate at constant species concentration is examined.\\u000a The plate is maintained at a given concentration of some chemical species while convection is induced by diffusion into and\\u000a chemical reaction with the ambient fluid. In the absence of chemical reaction, a similarity transform is possible. When chemical\\u000a reaction occurs, perturbation

M. Rahman; I. Mulolani

2000-01-01

327

Non-adiabatic effects within a single thermally averaged potential energy surface: thermal expansion and reaction rates of small molecules.  

PubMed

At non-zero temperature and when a system has low-lying excited electronic states, the ground-state Born-Oppenheimer approximation breaks down and the low-lying electronic states are involved in any chemical process. In this work, we use a temperature-dependent effective potential for the nuclei which can accommodate the influence of an arbitrary number of electronic states in a simple way, while at the same time producing the correct Boltzmann equilibrium distribution for the electronic part. With the help of this effective potential, we show that thermally activated low-lying electronic states can have a significant effect in molecular properties for which electronic excitations are oftentimes ignored. We study the thermal expansion of the Manganese dimer, Mn(2), where we find that the average bond length experiences a change larger than the present experimental accuracy upon the inclusion of the excited states into the picture. We also show that, when these states are taken into account, reaction-rate constants are modified. In particular, we study the opening of the ozone molecule, O(3), and show that in this case the rate is modified as much as a 20% with respect to the ground-state Born-Oppenheimer prediction. PMID:23249070

Alonso, J L; Castro, A; Clemente-Gallardo, J; Echenique, P; Mazo, J J; Polo, V; Rubio, A; Zueco, D

2012-12-14

328

Non-adiabatic effects within a single thermally averaged potential energy surface: Thermal expansion and reaction rates of small molecules  

NASA Astrophysics Data System (ADS)

At non-zero temperature and when a system has low-lying excited electronic states, the ground-state Born-Oppenheimer approximation breaks down and the low-lying electronic states are involved in any chemical process. In this work, we use a temperature-dependent effective potential for the nuclei which can accommodate the influence of an arbitrary number of electronic states in a simple way, while at the same time producing the correct Boltzmann equilibrium distribution for the electronic part. With the help of this effective potential, we show that thermally activated low-lying electronic states can have a significant effect in molecular properties for which electronic excitations are oftentimes ignored. We study the thermal expansion of the Manganese dimer, Mn2, where we find that the average bond length experiences a change larger than the present experimental accuracy upon the inclusion of the excited states into the picture. We also show that, when these states are taken into account, reaction-rate constants are modified. In particular, we study the opening of the ozone molecule, O3, and show that in this case the rate is modified as much as a 20% with respect to the ground-state Born-Oppenheimer prediction.

Alonso, J. L.; Castro, A.; Clemente-Gallardo, J.; Echenique, P.; Mazo, J. J.; Polo, V.; Rubio, A.; Zueco, D.

2012-12-01

329

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

330

Systematic exploration of the mechanism of chemical reactions: the global reaction route mapping (GRRM) strategy using the ADDF and AFIR methods.  

PubMed

Global reaction route mapping (GRRM), a fully-automated search for all important reaction pathways relevant to a given purpose, on the basis of quantum chemical calculations enables systematic elucidation of complex chemical reaction mechanisms. However, GRRM had previously been limited to very simple systems. This is mainly because such calculations are highly demanding even in small systems when a brute-force sampling is considered. Hence, we have developed two independent but complementary methods: anharmonic downward distortion following (ADDF) and artificial force induced reaction (AFIR) methods. ADDF can follow reaction pathways starting from local minima on the potential energy surface (PES) toward transition structures (TSs) and dissociation channels. AFIR can find pathways starting from two or more reactants toward TSs for their associative reactions. In other words, ADDF searches for A ? X type isomerization and A ? X + Y type dissociation pathways, whereas AFIR finds A + B ? X (+ Y) type associative pathways. Both follow special paths called the ADDF path and the AFIR path, and these tend to pass through near TSs of corresponding reaction pathways, giving approximate TSs. Such approximate TSs can easily be re-optimized to corresponding true TSs by standard geometry optimizations. On the basis of these two methods, we have proposed practical strategies of GRRM. The GRRM strategies have been applied to a variety of chemical systems ranging from thermal- and photochemical-reactions in small systems to organometallic- and enzyme-catalysis, on the basis of quantum chemical calculations. In this perspective, we present an overview of the GRRM strategies and some results of applications. Their practical usage for systematic prediction is also discussed. PMID:23389653

Maeda, Satoshi; Ohno, Koichi; Morokuma, Keiji

2013-03-21

331

On-chip isothermal, chemical cycling polymerase chain reaction (ccPCR)  

NASA Astrophysics Data System (ADS)

We demonstrate a novel ccPCR technique for microfluidic DNA amplification where temperature is held constant in space and time. The polymerase chain reaction is a platform of choice for biological assays and typically based on a three-step thermal cycling: DNA denaturation, primers annealing and extension by an enzyme. We here demonstrate a novel technique where high concentration chemical denaturants (solvents) denature DNA. We leverage the high electrophoretic mobility of DNA and the electrical neutrality of denaturants to achieve chemical cycling. We focus DNA with isotachophoresis (ITP); a robust electrophoretic preconcentration technique which generates strong electric field gradients and protects the sample from dispersion. We apply a pressure-driven flow to balance electromigration velocity and keep the DNA sample stationary in a microchannel. We drive the DNA through a series of high denaturant concentration zones. DNA denatures at high denaturant concentration. At low denaturant concentration, the enzyme creates complementary strands. DNA reaction kinetics are slower than buffer reactions involved in ITP. We demonstrate successful ccPCR amplification for detection of E. Coli. The ccPCR has the potential for simpler chemistry than traditional PCR.

Persat, Alexandre; Santiago, Juan

2008-11-01

332

Conversion of concentrated solar thermal energy into chemical energy.  

PubMed

When a concentrated solar beam is irradiated to the ceramics such as Ni-ferrite, the high-energy flux in the range of 1500-2500 kW/m(2) is absorbed by an excess Frenkel defect formation. This non-equilibrium state defect is generated not by heating at a low heating-rate (30 K/min), but by irradiating high flux energy of concentrated solar beam rapidly at a high heating rate (200 K/min). The defect can be spontaneously converted to chemical energy of a cation-excess spinel structure (reduced-oxide form) at the temperature around 1773 K. Thus, the O(2) releasing reaction (?-O(2) releasing reaction) proceeds in two-steps; (1) high flux energy of concentrated solar beam absorption by formation of the non-equilibrium Frenkel defect and (2) the O(2) gas formation from the O(2-) in the Frenkel defect even in air atmosphere. The 2nd step proceeds without the solar radiation. We may say that the 1st step is light reaction, and 2nd step, dark reaction, just like in photosynthesis process. PMID:22434435

Tamaura, Yutaka

2012-01-01

333

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

334

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

335

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

336

Mechanisms of prion disease progression: a chemical reaction network approach.  

PubMed

Fatal neurodegenerative diseases such as bovine spongiform encephalopathy in cattle, scrapie in sheep and Creutzfeldt-Jakob disease in humans are caused by prions. Prion is a protein encoded by a normal cellular gene. The cellular form of the prion, namely PrP(C), is benign but can be converted into a disease-causing form (named scrapie), PrP(Sc), by a conformational change from -helix to -sheets. Prions replicate by this conformational change; that is, PrP(Sc) interacts with PrP(C) producing a new molecule of PrP(Sc). This kind of replication is modelled in this contribution as an autocatalytic process. The kinetic model accounts for two of the three epidemiological manifestations: sporadic and infectious. By assuming irreversibility of the PrP(Sc) replication and describing a first-order reaction for the degradation of cellular tissue, the authors explore dynamical scenarios for prion progression, such as oscillations and conditions for multiplicity of equilibria. Feinberg's chemical reaction network theory is exploited to identify multiple steady states and their associate kinetic constants. PMID:22129030

Méndez, J M; Femat, R

2011-11-01

337

Site remediation via Dispersion by Chemical Reaction (DCR). Special report  

SciTech Connect

The DCR (Dispersion by Chemical Reaction) technologies are a group of patented waste treatment processes using CaO (quicklime) for the immobilization of heavily oiled sludges, oil-contaminated soils, acid-tars, and heavy metals in Ca(OH)2 and CaCO3 matrices. The objectives of this project were to: (1) evaluate the DCR process for remediating soils contaminated with pesticides, petroleum hydrocarbons (oils and fuels), and heavy metals in cold regions and (2) evaluate DCR-treated oil-contaminated soil as a non-frost-susceptible (NFS) construction material. Three major studies evaluated the DCR process to remediate (1) hydrocarbons at Eareckson Air Force Station on Shemya in the Aleutians, (2) pesticide-contaminated soils from Rocky Mt. Arsenal, and (3) heavy-metal contaminated soils from a former zinc smelter site at Palmerton, Pennsylvania. The DCR process was successful in stabilizing liquid organics and heavy metals in contaminated soils. The chemical properties of soils contaminated by solid organics (asphalt tar and pesticides) were not generally improved by the DCR process, but even in these cases, the physical properties were improved for potential reuse as construction materials.

Marion, G.M.; Payne, J.R.; Brar, G.S.

1997-08-01

338

High resolution time-of-flight spectrometer for crossed molecular beam study of elementary chemical reactions  

Microsoft Academic Search

In this article, we describe an apparatus in our laboratory for investigating elementary chemical reactions using the high resolution time-of-flight Rydberg tagging method. In this apparatus, we have adopted a rotating source design so that collision energy can be changed for crossed beam studies of chemical reactions. Preliminary results on the HI photodissociation and the F atom reaction with H2

Minghui Qiu; Li Che; Zefeng Ren; Dongxu Dai; Xiuyan Wang; Xueming Yang

2005-01-01

339

Diffusion of Weak Acids across Lipid Bilayer Membranes: Effects of Chemical Reactions in the Unstirred Layers  

Microsoft Academic Search

Chemical reactions in the aqueous unstirred layers of solution adjacent to a membrane can have dramatic effects on the diffusion of solutes across that membrane. This is demonstrated by the diffusion of labeled salicylate and salicylic acid across a phospholipid bilayer membrane. Two types of chemical reactions are considered. The first is an isotopic exchange reaction between the ionic and

John Gutknecht; D. C. Tosteson

1973-01-01

340

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

341

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

342

On the role of van der Waals interaction in chemical reactions at low temperatures  

Microsoft Academic Search

It is shown that van der Waals interaction potential plays a crucial role in chemical reactions at low temperatures. By taking the Cl+HD reaction as an illustrative example, we demonstrate that quasibound states of the van der Waals potential preferentially undergo chemical reaction rather than vibrational predissociation. Prereaction occurs even when the wave functions of the quasibound states peak far

N. Balakrishnan

2004-01-01

343

Shock-induced and shock-assisted solid-state chemical reactions in powder mixtures  

Microsoft Academic Search

Shock compression of powder mixtures can lead to chemical reactions, resulting in the formation of equilibrium as well as nonequilibrium compounds, and rapid increases in temperature. The reactions occur as manifestations of enhanced solid-state chemical reactivity of powders, caused by configurational changes and defect states introduced during shock compression. Two types of reactions are possible and can be distinguished on

N. N. Thadhani

1994-01-01

344

Simplifying the Jacobian Criterion for precluding multistationarity in chemical reaction networks  

Microsoft Academic Search

Chemical reaction networks taken with mass-action kinetics are dynamical systems that arise in chemical engineering and systems biology. In general, determining whether a chemical reaction network admits multiple steady states is difficult, as this requires determining existence of multiple positive solutions to a large system of polynomials with unknown coefficients. However, in certain cases, various easy criteria can be applied.

Badal Joshi; Anne Shiu

2011-01-01

345

Control of gaseous pollutants from industrial combustion by chemical reaction. Paper 81. 35. 7  

Microsoft Academic Search

The control methods for gaseous emissions from industrial combustion sources by chemical reaction processes is reviewed. The applicability and effectiveness of chemical control techniques, equipment operation and process limitations are discussed. In some cases, the control of gases by chemical reaction may be appropriate for achieving stringest control requirements. 30 refs.

J. D. Mobley; K. J. Lim

1981-01-01

346

Thermal isolation of microchip reaction chambers for rapid non-contact DNA amplification  

Microsoft Academic Search

This paper describes further optimization of a non-contact, infrared-mediated system for microchip DNA amplification via the polymerase chain reaction (PCR). The optimization is focused on heat transfer modeling and subsequent fabrication of thermally isolated reaction chambers in glass devices that are uniquely compatible with non-contact thermal control. With a thermal conductivity approximately an order of magnitude higher than many plastics,

Christopher J Easley; Joseph A C Humphrey; James P Landers

2007-01-01

347

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

PubMed

Binuclear metallohydrolases are a large family of enzymes that require two closely spaced transition metal ions to carry out a plethora of hydrolytic reactions. Representatives include purple acid phosphatases (PAPs), enzymes that play a role in bone metabolism and are the only member of this family with a heterovalent binuclear center in the active form (Fe(3+)-M(2+), M = Fe, Zn, Mn). Other members of this family are urease, which contains a di-Ni(2+) center and catalyzes the breakdown of urea, arginase, which contains a di-Mn(2+) center and catalyzes the final step in the urea cycle, and the metallo-?-lactamases, which contain a di-Zn(2+) center and are virulence factors contributing to the spread of antibiotic-resistant pathogens. Binuclear metallohydrolases catalyze numerous vital reactions and are potential targets of drugs against a wide variety of human disorders including osteoporosis, various cancers, antibiotic resistance, and erectile dysfunctions. These enzymes also tend to catalyze more than one reaction. An example is an organophosphate (OP)-degrading enzyme from Enterobacter aerogenes (GpdQ). Although GpdQ is part of a pathway that is used by bacteria to degrade glycerolphosphoesters, it hydrolyzes a variety of other phosphodiesters and displays low levels of activity against phosphomono- and triesters. Such a promiscuous nature may have assisted the apparent recent evolution of some binuclear metallohydrolases to deal with situations created by human intervention such as OP pesticides in the environment. OP pesticides were first used approximately 70 years ago, and therefore the enzymes that bacteria use to degrade them must have evolved very quickly on the evolutionary time scale. The promiscuous nature of enzymes such as GpdQ makes them ideal candidates for the application of directed evolution to produce new enzymes that can be used in bioremediation and against chemical warfare. In this Account, we review the mechanisms employed by binuclear metallohydrolases and use PAP, the OP-degrading enzyme from Agrobacterium radiobacter (OPDA), and GpdQ as representative systems because they illustrate both the diversity and similarity of the reactions catalyzed by this family of enzymes. The majority of binuclear metallohydrolases utilize metal ion-activated water molecules as nucleophiles to initiate hydrolysis, while some, such as alkaline phosphatase, employ an intrinsic polar amino acid. Here we only focus on catalytic strategies applied by the former group. PMID:22698580

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

2012-06-14

348

Chemical reactions between aluminum and fly ash during synthesis and reheating of Al-fly ash composite  

SciTech Connect

Thermodynamic analysis indicates that there is the possibility of chemical reactions between aluminum melt and cenosphere fly ash particles. These particles contain alumina, silica, and iron oxide, which, during solidification processing of aluminum-fly ash composites or during holding of such composites at temperatures above the melting temperature of the aluminum, are likely to undergo chemical reduction. These chemical reactions between the fly ash and molten aluminum have been studied by metallographic examination, differential thermal analysis (DTA), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX) and X-ray analysis after holding the aluminum-fly ash composites for different periods above the liquidus temperature. The experiments indicate that there is progressive reduction of silica and mullite in the fly ash, and formation of alumina with holding time of composites at a temperature of 850 C. The walls of the cenosphere fly ash particles progressively disintegrate into discrete particles as the reaction progresses. The rate of chemical reaction was high at the start of holding the composite at a temperature of 850 C, and then the rate significantly decreased with time. The reaction was almost complete after 10 hours.

Guo, R.Q.; Rohatgi, P.K. [Univ. of Wisconsin, Milwaukee, WI (United States). Dept. of Materials

1998-06-01

349

Chemical dynamics in the gas phase : quantum mechanics of chemical reactions.  

SciTech Connect

This research program focuses on both the development and application of accurate quantum mechanical methods to describe gas phase chemical reactions and highly excited molecules. Emphasis is often placed on time-dependent or integrative approaches that, in addition to computational simplifications, yield useful mechanistic insights. Applications to systems of current experimental and theoretical interest are emphasized. The results of these calculations also allow one to gauge the quality of the underlying potential energy surfaces and the reliability of more approximate theoretical approaches such as classical trajectories and transition state theories.

Gray, S. K.

1999-07-02

350

Spectroscopy and Reactions of Molecules Important in Chemical Evolution.  

National Technical Information Service (NTIS)

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, a...

R. S. Becker

1974-01-01

351

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

352

Chemical and microstructural characterization of thermally grown alumina scales  

SciTech Connect

An experimental program has been initiated to evaluate the chemical, microstructural, and mechanical integrity of thermally grown oxide scales to establish requirements for improved corrosion performance in terms of composition, structure, and properties. Iron aluminides of several compositions were selected for the study. Oxidation studies were conducted in air and oxygen environments at 1000{degrees}C. The results showed that the scaling kinetics followed a parabolic rate law but that the rates in early stages of oxidation were significantly greater than in later stages; the difference could be attributed to the presence of fast-growing transient iron oxides in the layer during the early stages. Further, scale failure occurred via gross spallation, scale cracking, and nodule formation and was influenced by alloy composition. Auger electron spectroscopy of Ar-exposed specimens of ternary Fe-Cr-Al alloy showed sulfur on the gas/scale side of the interface; the sulfur decreased as the exposure time increased. Raman spectroscopy and ruby fluorescence were used to examine the scale development as a function of oxidation temperature. Ruby-line shift is used to examine phase transformations in alumina and to calculate compressive strains in thermally grown scales.

Natesan, K.; Richier, C.; Veal, B.W. [and others

1995-09-01

353

Modeling of forced flow/thermal gradient chemical vapor infiltration  

SciTech Connect

The forced flow/thermal gradient chemical vapor infiltration process (FCVI) has proven to be a successful technique for fabrication of ceramic matrix composites. It is particularly attractive for thick components which cannot be fabricated using the conventional, isothermal method (ICVI). Although it offers processing times that are at least an order of magnitude shorter than ICVI, FCVI has not been used to fabricate parts of complex geometry and is perceived by some to be unsuitable for such components. The major concern Is that selection and control of the flow pattern and thermal profile for optimum infiltration can be a difficult and costly exercise. In order to reduce this effort, we are developing a computer model for FCVI that simulates the densification process for given component geometry, reactor configuration and operating parameters. Used by a process engineer, this model can dramatically reduce the experimental effort needed to obtain uniform densification. A one-dimensional process model, described in a previous interim report, has demonstrated good agreement with experimental results in predicting overall densification time and density uniformity during processing and the effect of various fiber architectures and operating parameters on these process issues. This model is fundamentally unsuitable for more complex geometries, however, and extension to two- and three-dimensions is necessary. This interim report summarizes our progress since the previous interim report toward development of a ``finite volume`` model for FCVI.

Starr, T.L.; Smith, A.W. [Oak Ridge National Lab., TN (United States)

1992-09-01

354

Modeling of forced flow/thermal gradient chemical vapor infiltration  

SciTech Connect

The forced flow/thermal gradient chemical vapor infiltration process (FCVI) has proven to be a successful technique for fabrication of ceramic matrix composites. It is particularly attractive for thick components which cannot be fabricated using the conventional, isothermal method (ICVI). Although it offers processing times that are at least an order of magnitude shorter than ICVI, FCVI has not been used to fabricate parts of complex geometry and is perceived by some to be unsuitable for such components. The major concern Is that selection and control of the flow pattern and thermal profile for optimum infiltration can be a difficult and costly exercise. In order to reduce this effort, we are developing a computer model for FCVI that simulates the densification process for given component geometry, reactor configuration and operating parameters. Used by a process engineer, this model can dramatically reduce the experimental effort needed to obtain uniform densification. A one-dimensional process model, described in a previous interim report, has demonstrated good agreement with experimental results in predicting overall densification time and density uniformity during processing and the effect of various fiber architectures and operating parameters on these process issues. This model is fundamentally unsuitable for more complex geometries, however, and extension to two- and three-dimensions is necessary. This interim report summarizes our progress since the previous interim report toward development of a finite volume'' model for FCVI.

Starr, T.L.; Smith, A.W. (Oak Ridge National Lab., TN (United States))

1992-09-01

355

Model-free Investigation of Ultrafast Bimolecular Chemical Reactions: Bimolecular Photo Induced Electron Transfer  

NASA Astrophysics Data System (ADS)

Using photoinduced bimolecular electron transfer reactions as example we demonstrate how diffusion controlled bimolecular chemical reactions can be studied in a model-free manner by quantitatively combining different ultrafast spectroscopical tools.

Lang, Bernhard; Rosspeintner, Arnulf; Vauthey, Eric

2013-03-01

356

Aggregation-induced chemical reactions: acid dissociation in growing water clusters.  

PubMed

Understanding chemical reactivity at ultracold conditions, thus enabling molecular syntheses via interstellar and atmospheric processes, is a key issue in cryochemistry. In particular, acid dissociation and proton transfer reactions are ubiquitous in aqueous microsolvation environments. Here, the full dissociation of a HCl molecule upon stepwise solvation by a small number of water molecules at low temperatures, as relevant to helium nanodroplet isolation (HENDI) spectroscopy, is analyzed in mechanistic detail. It is found that upon successive aggregation of HCl with H(2)O molecules, a series of cyclic heteromolecular structures, up to and including HCl(H(2)O)(3), are initially obtained before a precursor state for dissociation, HCl(H(2)O)(3)···H(2)O, is observed upon addition of a fourth water molecule. The latter partially aggregated structure can be viewed as an "activated species", which readily leads to dissociation of HCl and to the formation of a solvent-shared ion pair, H(3)O(+)(H(2)O)(3)Cl(-). Overall, the process is mostly downhill in potential energy, and, in addition, small remaining barriers are overcome by using kinetic energy released as a result of forming hydrogen bonds due to aggregation. The associated barrier is not ruled by thermal equilibrium but is generated by athermal non-equilibrium dynamics. These "aggregation-induced chemical reactions" are expected to be of broad relevance to chemistry at ultralow temperature much beyond HENDI spectroscopy. PMID:21351796

Forbert, Harald; Masia, Marco; Kaczmarek-Kedziera, Anna; Nair, Nisanth N; Marx, Dominik

2011-02-25

357

Experimental results of exothermic reaction with concentration gradient catalyst in a solar chemical heat pump  

Microsoft Academic Search

A solar chemical heat pump can upgrade low-temperature solar heat of about 80°C to about 150-200°C by using the reversible chemical reactions of 2-propanol\\/acetone\\/hydrogen, which are composed of endothermic and exothermic reactions. In the exothermic process of the above reaction, a temperature peak occurs near the inlet of the reaction zone in the case of uniform catalyst arrangement. Such a

T. Takashima; T. Doi; Y. Ando; T. Tanaka; R. Miyahara; J. Kamoshida

1997-01-01

358

Dynamical resonance in F+H 2 chemical reaction and rotational excitation effect  

Microsoft Academic Search

Reaction resonance is a frontier topic in chemical dynamics research, and it is also essential to the understanding of mechanisms\\u000a of elementary chemical reactions. This short article describes an important development in the frontier of research. Experimental\\u000a evidence of reaction resonance has been detected in a full quantum state resolved reactive scattering study of the F+H2 reaction. Highly accurate full

XueMing Yang; DaiQian Xie; DongHui Zhang

2007-01-01

359

Modeling the thermal reactions of benzyl phenyl sulfide  

Microsoft Academic Search

The reactions of benzylphenylsulfide (BPS) neat, in benzene, in tetralin and with added thiophenol were studied. A free-radical mechanism described the neat pyrolysis of BPS to the major products toluene, thiophenol, diphenyldisulfide, and diphenylsulfide. An analytical rate expression deduced from this mechanism was consistent with results from both neat pyrolysis and reaction with additives. The secondary reactions of primary products

M. A. Abraham; M. T. Klein

1988-01-01

360

Modeling the thermal reactions of benzyl phenyl sulfide  

SciTech Connect

The reactions of benzylphenylsulfide (BPS) neat, in benzene, in tetralin and with added thiophenol were studied. A free-radical mechanism described the neat pyrolysis of BPS to the major products toluene, thiophenol, diphenyldisulfide, and diphenylsulfide. An analytical rate expression deduced from this mechanism was consistent with results from both neat pyrolysis and reaction with additives. The secondary reactions of primary products were detailed.

Abraham, M.A.; Klein, M.T.

1988-01-01

361

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

Microsoft Academic Search

Microwave has been found as an efficient heating method in chemical industry. However, in present days the interaction between\\u000a microwave and chemical reactions has not been deeply understood, which restricts a wider application of high power microwave\\u000a in chemical industry. In this paper, the key problems of interaction between microwave and chemical reaction are investigated,\\u000a such as complex effective permittivity

Xiaoqing Yang; Kama Huang

2007-01-01

362

Kinetic Monte Carlo modeling of chemical reactions coupled with heat transfer  

NASA Astrophysics Data System (ADS)

In this paper, we describe two types of effective events for describing heat transfer in a kinetic Monte Carlo (KMC) simulation that may involve stochastic chemical reactions. Simulations employing these events are referred to as KMC-TBT and KMC-PHE. In KMC-TBT, heat transfer is modeled as the stochastic transfer of ``thermal bits'' between adjacent grid points. In KMC-PHE, heat transfer is modeled by integrating the Poisson heat equation for a short time. Either approach is capable of capturing the time dependent system behavior exactly. Both KMC-PHE and KMC-TBT are validated by simulating pure heat transfer in a rod and a square and modeling a heated desorption problem where exact numerical results are available. KMC-PHE is much faster than KMC-TBT and is used to study the endothermic desorption of a lattice gas. Interesting findings from this study are reported.

Castonguay, Thomas C.; Wang, Feng

2008-03-01

363

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

364

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

365

Continuous chemical reaction chromatography. Progress report, January 1989--January 1992  

SciTech Connect

The past three years have been devoted to investigating simulated countercurrent chomatographic moving bed separators (SCMCS) and simulated countercurrent moving bed reactors (SCMCR). These are novel separators and reactors used for separation, or for carrying out a chemical reaction and separation continuously and simultaneously in fixed bed. In the SCMCR and the SCMCS the process aspects of a countercurrent moving bed, in which a stream of solids flows countercurrent to an inert fluid and past stationary reactant inlet, is simulated by successively switching feed and product take-off streams through a series of inlets located at fixed intervals along a fixed bed or between a series of packed columns. The flow of solids past a fixed feed point, characteristic of countercurrent moving beds, is replaced by motion of the feed past a fixed packed bed. Feed enters a particular column for a fixed length of time, and then is switched to the next column. Product streams are also advanced simultaneously. When the feed point has progressed to the end it is returned to the starting position and the process repeated. The shifting of the feed and the product positions in the direction of fluid flow thus simulates the movement of solids in the opposite direction. The requisite motion between the feed and the bed, which is continuous for true countercurrency, is replaced by periodic, discrete steps in simulated countercurrency. The continuous, steady state operation characteristic of true countercurrency is replaced by periodic transients at each switch of the feed.

Aris, R.; Carr, R.W.

1992-07-01

366

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

367

Hydrogenation process for solid carbonaceous feed materials using thermal countercurrent flow reaction zone  

SciTech Connect

Thermal hydrogenation of solids-containing carbonaceous feed materials to produce hydrocarbon gaseous and liquid products is performed in a thermal reaction zone, in which the feed material flows generally downwardly countercurrent to upflowing hydrogen and recycled hydrocarbon liquid. The recycled hydrocarbon liquid is at a rate sufficient to control the settling of solids-containing feed through the reactor, and is obtained from the reaction zone upper end by phase separation from gaseous effluent at reaction conditions. The gaseous effluent material is removed from the thermal reaction zone upper end, and heavy liquid material containing less than about 40 W % solids is withdrawn from the reaction zone bottom end, with both streams being passed to further phase separation and distillation steps for recovery of the hydrocarbon gas and liquid products. The process is useful for hydroconversion of solids-containing tar sand bitumen, shale oil and particularly for coal, with the coal being fed into the thermal reaction zone as a coal-oil slurry. If desired, the heavy liquid bottoms stream withdrawn from the lower end of the thermal reaction zone containing unconverted coal and ash solids can be advantageously passed to a second reaction zone containing an ebullated catalyst bed for further hydrogenation reaction to increase the conversion and yield of low-boiling hydrocarbon liquid products.

Johanson, E.S.; Schuler, P.D.

1985-04-09

368

THERMAL REACTIONS OF WHOLE CRUDE OILS AND RELATED MODEL COMPOUNDS  

Microsoft Academic Search

The quantities of olefins, polyaromatic hydrocarbons and char formed during thermal decomposition in closed systems of alkylbenzenes are substantially reduced if the decomposition takes place in the presence of a good acceptor molecule such as pyrene or adamantane. The chemistry seems to be applicable to the upgrading of whole crude oils by a thermal treatment at 425-450°C in a closed

M. Farcasiu; R. B. LaPierre

1987-01-01

369

Thermal reactions in interstellar ice: A step towards molecular complexity in the interstellar medium  

NASA Astrophysics Data System (ADS)

Complex organic molecules are widely observed in star-forming regions, although their formation mechanisms are not well understood. Solid-state chemistry is thought to play an important role, but the solid-state reaction network is poorly known. We provide a list of purely thermal reactions involving electronically stable reactants to complement existing grain chemistry networks. The kinetic parameters of the reactions are given when available. These reactions lead to the formation of complex organic molecules, which were not considered previously. Eventually, these complex molecules are either released into the gas phase or incorporated into the organic residue found in meteorites. Thermal reactions are important because they are not limited by the UV flux or the slow diffusion of the radicals, and because they involve both surface and mantle molecules. Thermal reactions represent an important step in the formation of complex organic molecules that constitute the primitive material of comets and asteroids.

Theulé, P.; Duvernay, F.; Danger, G.; Borget, F.; Bossa, J. B.; Vinogradoff, V.; Mispelaer, F.; Chiavassa, T.

2013-10-01

370

Thermal, chemical, and mechanical response of rigid polyurethane foam  

Microsoft Academic Search

Rigid polyurethane foams are frequently used as encapsulants to isolate and support thermally sensitive components within weapon systems. When exposed to abnormal thermal environments, such as fire, the polyurethane foam decomposes to form products having a wide distribution of molecular weights and can dominate the overall thermal response of the system. Mechanical response of the decomposing foam, such as thermal

1997-01-01

371

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

NASA Astrophysics Data System (ADS)

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

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

2007-06-01

372

Thermal decomposition of sodium bicarbonate and its effect on the reaction of sodium bicarbonate and sulfur dioxide in a simulated flue gas  

SciTech Connect

The effect of thermally decomposing sodium bicarbonate while simultaneously reacting with SO/sub 2/, was studied. The study was performed by quantitatively determining the rate of thermal decomposition as a function of particle size in an SO/sub 2/ free gas stream. The rate of reaction of sodium carbonate (product of the thermal decomposition) with SO/sub 2/ was then studied, and the data applied to a pore-plugging model which accounts for the loss in reactivity with increased reaction time. The reaction of sodium bicarbonate with SO/sub 2/ was then studied and the results compared to that for sodium carbonate. From the analysis of the data, the activation energy for the thermal decomposition reaction, the SO/sub 2/ sodium carbonate and SO/sub 2/ sodium bicarbonate reaction were derived. The thermal decomposition reaction of sodium biocarbonate was found to be similar to that of calcium carbonate below the point where heat transfer is rate limiting. The degree of conversion of sodium bicarbonate was found to be 12-17 times greater (depending on particle size) than that of sodium carbonate in the temperature range 250/sup 0/-350/sup 0/F (120/sup 0/-177/sup 0/C). This greater conversion was qualitatively explained by hypothesizing the formation of an activated species during thermal decomposition which would be more chemically reactive.

Keener, T.C.

1982-01-01

373

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 significant development made in developing a truly meshfree computational fluid dynamics (CFD) flow solver to be coupled to NPCA. First, the procedure of obtaining nearly analytic accurate first order derivatives using the complex step method (CSM) is extended to include computation of accurate meshfree second order derivatives via a theorem described in this report. Next, boosted generalized regression neural network (BGRNN), described in our previous report is combined with CSM and used to obtain complete solution of a hard to solve wave dominated sample second order partial differential equation (PDE): the cubic Schrodinger equation. The resulting algorithm is a significant improvement of the meshfree technique of smooth particle hydrodynamics method (SPH). It is suggested that the demonstrated meshfree technique be termed boosted smooth particle hydrodynamics method (BSPH). Some of the advantages of BSPH over other meshfree methods include; it is of higher order accuracy than SPH; compared to other meshfree methods, it is completely meshfree and does not require any background meshes; It does not involve any construction of shape function with their associated solution of possibly ill conditioned matrix equations; compared to some SPH techniques, no equation for the smoothing parameter is required; finally it is easy to program.

Nelson Butuk

2006-09-21

374

Heat-of-Reaction Chemical Heat Pumps: Possible Configurations.  

National Technical Information Service (NTIS)

Chemical heat pumps utilize working fluids which undergo reversible chemical changes. Mechanically driven reactive heat pump cycles or, alternatively, heat driven heat pumps in which either heat engine or heat pump working fluid is reactive, are considere...

L. D. Kirol

1986-01-01

375

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 ...

376

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

377

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

ERIC Educational Resources Information Center

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

Kadioglu, Cansel; Uzuntiryaki, Esen

2008-01-01

378

Stochastic simulation of chemical reactions with spatial resolution and single molecule detail  

Microsoft Academic Search

Methods are presented for simulating chemical reaction networks with a spatial resolution that is accurate to nearly the size scale of individual molecules. Using an intuitive picture of chemical reaction systems, each molecule is treated as a point-like particle that diffuses freely in three-dimensional space. When a pair of reactive molecules collide, such as an enzyme and its substrate, a

Steven S. Andrews; Dennis Bray

2004-01-01

379

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…

Goodney, David E.

2006-01-01

380

Micromechanical modeling of shock-induced chemical reactions in heterogeneous multi-material powder mixtures  

Microsoft Academic Search

Shock waves create a unique environment of high pressure, temperature, strain rate, and gradients thereof. Chemical reactions that occur in this regime can lead to the synthesis of new materials that are not possible under conventional conditions. Shock-induced chemical reactions (also known as shock synthesis) is difficult to study experimentally due to the small time and space scales over which

Ian P. H. Do; David J. Benson

2001-01-01

381

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

ERIC Educational Resources Information Center

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

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

2008-01-01

382

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

ERIC Educational Resources Information Center

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

Tellinghuisen, Joel

2006-01-01

383

Tradeoffs and the evolution of thermal reaction norms  

Microsoft Academic Search

Tradeoffs have played a prominent role in the development of theories describing the evolution of reaction norms. Different classes of tradeoffs are known to constrain the evolution of phenotypes, but current theories incorporate only a subset of these tradeoffs. Consequently, these theories cannot account for some of the variation in reaction norms that has been observed within and among species.

Robbie S. Wilson; Carlos A. Navas; Rob S. James

2003-01-01

384

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

SciTech Connect

Waters from the thermal springs of Washington range in chemical composition from dilute Na-HCO/sub 3/ to moderately saline CO/sub 2/-charged Na-HCO/sub 3/-Cl type waters. St. Martin's Hot Spring which discharges a slightly saline Na-Cl water, is the notable exception. The dilute Na-HCO/sub 3/ waters are generally associated with granitic intrusions; the warm to hot CO/sub 2/-charged waters issue on or near the large stratovolcanoes. The dilute waters have oxygen-isotopic compositions that indicate relatively little water-rock exchange. The CO/sub 2/-charged waters are usually more enriched in oxygen-18 due to more extensive water-rock reaction. The carbon-13 in the CO/sub 2/-charged thermal waters is more depleted (-10 to -12 %) than in the cold CO/sub 2/-charged soda springs (-2 to -8%) which are also scattered throughout the Cascades. The hot and cold CO/sub 2/-charged waters are supersaturated with respect to CaCO/sub 3/, but only the hot springs are actively depositing CaCO/sub 3/. Baker, Gamma, Sulphur, and Ohanapecosh hot springs seem to be associated with thermal aquifers of more than 100/sup 0/C. As these springs occur as individual springs or in small clusters, the respective aquifers are probably of restricted size.

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

1982-02-01

385

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

386

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

SciTech Connect

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

Wolery, T.J.

1981-02-01

387

Regenerated fibre Bragg gratings used to map internal reaction temperatures of a modified chemical vapour deposition (MCVD) optical fibre preform lathe  

NASA Astrophysics Data System (ADS)

The temperature profile of the reaction zone inside the substrate tube of a modified chemical vapour deposition (MCVD) optical fibre perform lathe has been characterised using thermal chirp compensated ultra-high temperature stable regenerated optical fibre Bragg gratings (FBGs). Results indicate significant differences in measured internal temperatures than those predicted theoretically or measured externally.

Åslund, Mattias L.; Canagasabey, Albert; Liu, Yang; Cook, Kevin; Canning, John; Peng, Gang-Ding

2011-05-01

388

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

389

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

390

Chemical reaction of SiCp\\/Al composites during multiple remelting  

Microsoft Academic Search

In the present study, the chemical reaction of SiCp\\/Al composites during multiple remelting above the liquidus was investigated using Differential Scanning Calorimetry and Transmission Electron Microscope. The experimental results indicated that the chemical reaction of SiC particles increased with increasing remelting temperature and the number of recycling runs. After reaching a certain degree of reaction, no further change occurred during

Tongxiang Fan; Di Zhang; Guang Yang; Toshiya Shibayanagi; Masaaki Naka; Takao Sakata; Hirotaro Mori

2003-01-01

391

A Unified Approach to the Study of Chemical Reactions in Freshman Chemistry.  

ERIC Educational Resources Information Center

|Provides rationale and objectives for presenting chemical reactions in a unified, logical six-stage approach rather than a piecemeal approach. Stages discussed include: introduction, stable electronic configurations and stable oxidation states, reactions between two free elements, ion transfer/proton transfer reactions, double displacement…

Cassen, T.; DuBois, Thomas D.

1982-01-01

392

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

393

Improving the operation of chemical process systems at thermal power stations using computerized education facilities  

NASA Astrophysics Data System (ADS)

The list and characteristics of computerized systems used for carrying out basic training of the operating personnel of chemical departments are presented. The results from contests of professional skills carried out among comprehensive teams of thermal power stations with participation of the operating personnel of chemical departments are analyzed. The result obtained from using software facilities for improving the operation of chemical process systems at thermal power stations is discussed.

Kopylov, A. S.; Orlov, K. A.; Kondakova, G. Yu.

2011-07-01

394

Quantum chemical and kinetics study of the thermal gas phase decomposition of 2-chloropropene.  

PubMed

A detailed theoretical study of the kinetics of the thermal decomposition of 2-chloropropene over the 600-1400 K temperature range has been done. The reaction takes place through the elimination of HCl with the concomitant formation of propyne or allene products. Relevant molecular properties of the reactant and transition states were calculated for each reaction channel at 14 levels of theory. From information provided by the BMK, MPWB1K, BB1K, M05-2X, and M06-2X functionals, specific for chemical kinetics studies, high-pressure limit rate coefficients of (5.8 ± 1.0) × 10(14) exp[-(67.8 ± 0.4 kcal mol(-1))/RT] s(-1) and (1.1 ± 0.2) × 10(14) exp[-(66.8 ± 0.5 kcal mol(-1))/RT] s(-1) were obtained for the propyne and allene channels, respectively. The pressure effect over the reaction was analyzed through the calculation of the low-pressure limit rate coefficients and falloff curves. An analysis of the branching ratio between the two channels as a function of pressure and temperature, based on these results and on computed specific rate coefficients, show that the propyne forming channel is predominant. PMID:24032406

Tucceri, María E; Badenes, María P; Cobos, Carlos J

2013-10-01

395

Transition State Spectroscopy of Bimolecular Chemical Reactions. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

One of the fundamental goals of chemical physics has been to understand the nature of the potential energy surfaces on which chemical reactions occur. Much of this interest focuses on the transition state region: the region of the surface where chemical b...

D. M. Neumark

1992-01-01

396

Characterization of thermal reaction by peak temperature and height of DTG curves  

Microsoft Academic Search

A relationship between the peak temperature and height in derivative thermogravimetry (DTG) curves was explored to seek their specific combination for addressing the uniqueness of a thermal reaction. The functional relationship between the peak temperature and height was closely related to the activation energy and reaction order, but rarely affected by the preexponential factor and heating rate. Determining peak temperature

Seungdo Kim; Jae K. Park

1995-01-01

397

Solvent effects on the thermal reaction of photochromic dihydroindolizines: Friction or polarizability effect within the alkanes  

Microsoft Academic Search

The thermal reaction to a photochromic dihydroindolizine was studied in six alkane solutions. The reaction rate in the branched iso-octane compared to that in n-alkanes shows a distinct effect of the molecular shape of the solvent. This effect could be rationalized both by solvent friction as well as by solvent polarizability effects. The rates in all the alkanes, however, form

K. Dernbecher; G. Gauglitz

1992-01-01

398

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

399

Characterization and Modeling of a Coupled Thermal-Hydrological-Mechanical-Chemical-Biological Experimental Facility at DUSEL  

NASA Astrophysics Data System (ADS)

A design is being formulated for a large-scale subsurface experimental facility at the 4850 foot level of the Homestake Mine in South Dakota. The purpose of the experiment is to investigate coupled Thermal-Hydrological-Mechanical-Chemical-Biological (THMCB) processes in fractured rock under stress and would be part of the proposed Deep Underground Science and Engineering Laboratory (DUSEL). Key questions we propose to answer are: 1) What are the effective reaction rates for mineral-fluid interaction in fractured rock under stress?; 2) How does mineral and fluid chemistry affect fracture mechanical behavior and permeability changes under stress at elevated temperatures?; and 3) How do microbial communities evolve in fractured rock under a thermal gradient and under changing stress conditions? In addition to the experiment as an in-situ laboratory for studying crustal processes, it has significant benefits for evaluating stimulation and production in Enhanced Geothermal Systems. Design and planning of the experiment included characterization of the geological, chemical, and isotopic characteristics of the rock and seeping fluids, thermal-hydrological and reactive transport modeling. During a reconnaissance study, strong heterogeneity in fracture fluxes and permeability were observed at the block site with some open boreholes continuously flowing at up to 1 liter/minute, and locally elevated fluid temperatures. A two-dimensional thermal-hydrological model was developed to evaluate fluid fluxes and temperatures as a function of heat input and borehole heater configuration. The dual permeability model considers fluid flow and heat transfer between an array of fractures and rock matrix, both having permeability anisotropy. A horizontal rock matrix permeability of 10-18 m2 was based on recent lab measurements, with a vertical matrix permeability estimated to be one order-of-magnitude higher to account for the strong nearly vertical foliation in the Homestake and Poorman formations. The fracture permeability was assumed to be anisotropic with a higher vertical permeability (kH=10-14 m2; kV=10-13 m2) to treat larger fracture apertures perpendicular to the least principal stress. Ten borehole heaters were emplaced at distances of 4 m with a heat input of 5 kW/m. Maximum convective fracture flow velocities of about 10 m/y were predicted after 5 years of heating with temperatures reaching close to 375°C. Reactive-transport models of the THMCB block will be a basis for the prediction of reaction-induced porosity/permeability changes as a function of the observed fracture fluxes and hydrological boundary conditions. The models use constraints from 87Sr/86Sr ratios measured in fluids, as well as other geochemical, mineralogical, and isotopic data.

Sonnenthal, E. L.; Elsworth, D.; Lowell, R. P.; Maher, K.; Mailloux, B. J.; Uzunlar, N.; Conrad, M. E.; Jones, T. L.; Olsen, N. J.

2010-12-01

400

Thermal Reactions of Blood Vessels in Vascular Stroke and Heatstroke  

Microsoft Academic Search

Research on the pathophysiology and treatment of brain damage with special focus on thermal vascular responses is the subject of this minireview. Interruption of cerebral blood supply by vascular obstruction, temporary cardiac arrest or hyperthermia causes a sudden attack of vascular stroke or heatstroke with serious consequences. It may not induce immediate cell death, but can precipitate a complex biochemical

Olav Thulesius

2006-01-01

401

The canonical and other mechanisms of elementary chemical reactions.  

PubMed

This article introduces a definition of the concept of elementary reaction mechanism that, while conforming to the traditional view of reaction mechanisms as dynamical processes whereby reagents are transformed into products, sharpens it by requiring reagent and product states to be completely specified and fully correlated. This leads to well-defined mathematical requirements for classification of a dynamical process as a reaction mechanism and also to a straightforward mathematical procedure for the determination of a special class of independent collision mechanisms that are dubbed "canonical". Canonical mechanisms result from an exact decomposition of the differential cross section of the reaction and form a complete orthogonal basis in terms of which all reaction mechanisms can be described. Examples involving the benchmark F + H2 and D + H2 reactions at energies ranging from ultralow to hyperthermal illustrate how canonical and other reaction mechanisms can be visualised and also how analysis of a reaction in terms of its canonical mechanisms can provide insight into its dynamics. PMID:19462575

Aldegunde, Jesús; Aoiz, F Javier; Sáez-Rábanos, Vicente; Kendrick, Brian K; de Miranda, Marcelo P

2007-11-21

402

Chemical reaction engineering: A multiscale approach to a multiobjective task  

Microsoft Academic Search

A strategy for synthesizing a reaction system to meet various business and technical objectives is outlined. It replaces the conventional paradigm — the sequential evolution of the microreactor, bench-scale reactor, pilot plant reactor and commercial reactor. Starting with a reaction proposed for commercialization, this approach examines the synthesis problem from the viewpoint of the plant, the reactor, hydrodynamics, transport phenomena,

Jan J. Lerou; Ka M. Ng

1996-01-01

403

Nanoscale Pattern Formation in Non-Equilibrium Surface Chemical Reactions  

Microsoft Academic Search

Using examples from surface science, we consider in this article problems of non- equilibrium pattern formation in reactive soft matter. An interplay of reaction, diffusion and energetic interactions between adatoms can produce a variety of non-equilibrium nanos- tructures, both stationary and traveling. These structures are similar to the patterns found in phase-separating binary mixtures under the influence of reactions. Because

Y. De Decker; A. S. Mikhailov

2006-01-01

404

CHEMICAL REACTIONS OF AQUATIC HUMIC MATERIALS WITH SELECTED OXIDANTS  

EPA Science Inventory

A study was conducted to identify the specific organic reaction products of natural aquatic humic materials with selected oxidants (KMnO4, HOCl, Cl02, O3 and monochloramine). Reaction products were identified by GC/MS after solvent extraction and derivatization. The two most reac...

405

Ring-expansion reactions in the thermal decomposition of tert-butyl-1,3-cyclopentadiene.  

PubMed

The thermal decomposition of tert-butyl-1,3-cyclopentadiene has been investigated in single-pulse shock-tube studies at shock pressures of 182-260 kPa and temperatures of 996-1127 K. Isobutene (2-methylpropene), 1,3-cyclopentadiene, and toluene were observed as the major stable products in the thermolysis of dilute mixtures of the substrate in the presence of a free-radical scavenger. Hydrogen atoms were also inferred to be a primary product of the decomposition and could be quantitatively determined on the basis of products derived from the free-radical scavenger. Of particular interest is the formation of toluene, which involves the expansion of the ring from a five- to a six-membered system. The overall reaction mechanism is suggested to include isomerization of the starting material; a molecular elimination channel; and C-C bond fission reactions, with toluene formation occurring via radical intermediates formed in the latter pathway. These radical intermediates are analogous to those believed to be important in soot formation reactions occurring during combustion. Molecular and thermodynamic properties of key species were determined from G3MP2B3 quantum chemistry calculations and are reported. The temperature dependence of the product spectrum was fit with a detailed chemical kinetic model, and best-fit kinetic parameters were derived using a Nelder-Mead simplex minimization algorithm. Our mechanism and rate constants are consistent with and provide experimental support for the H-atom-assisted routes to the conversion of fulvene to benzene that have been proposed in the literature on the basis of theoretical investigations. PMID:17125296

McGivern, W Sean; Manion, Jeffrey A; Tsang, Wing

2006-11-30

406

Hot carrier-selective chemical reactions on Ag(110)  

NASA Astrophysics Data System (ADS)

Here, we show that the pathways, products, and efficiencies of reactions occurring on a metal surface can be spatially modulated by varying the type and energy of hot carriers produced by injecting tunneling electrons or holes from a scanning tunneling microscope tip into the metal surface. Control over the metal surface reactions was demonstrated for the large-scale dissociation reaction of O2 molecules on a Ag(110) surface. Hot electrons (or holes) transported through the metal surface to chemisorbed O2 selectively dissociated the molecule into two oxygen atoms separated along the [110] (or [001]) lattice direction. The reaction selectivity was enhanced compared to the selectivity of a direct reaction involving tunneling carriers.

Hahn, Jae Ryang; Jang, Sang Hoon; Kim, Ki Wan; Son, Seung Bae

2013-08-01

407

Magnetic and other field effects on prochiral chemical reactions  

NASA Astrophysics Data System (ADS)

Experiments are reported in which three prochiral organic reactions were conducted in the presence of a ca. 1T magnetic field which was oriented with reference to the earth's geometric axes. The sign and magnitude of the rotation varied with the macroscopic orientation of the magnetic field and the time that the reaction was performed. Control measurements were in accord with expectations. The fact that the sign of the observed optical rotation of the product was reversed for all three reported reactions when the magnetic field was reversed for reactions conducted on the same day suggests that either the observed asymmetric synthesis was due to the reactions being conducted in a chiral physical field or extremely unusual stochastic processes were involved.

Piotrowska, Krystyna; Edwards, Deborah; Mitch, Alan; Dougherty, Ralph C.

1980-09-01

408

Prediction of incompatible reaction of dibenzoyl peroxide by isothermal calorimetry analysis and green thermal analysis technology  

Microsoft Academic Search

Dibenzoyl peroxide (BPO) has been widely employed in the petrifaction industry. This study determined the unsafe characteristics\\u000a of organic peroxide mixed with incompatible materials so as to help prevent runaway reactions, fires or explosions in the\\u000a process environment. Thermal activity monitor III (TAM III) was applied to assess the kinetic parameters, such as kinetic\\u000a model, reaction order, heat of reaction

Jo-Ming Tseng; Chun-Ping Lin

409

Thermal and chemical evolution of The Geysers geothermal system, California  

SciTech Connect

Fluid inclusions and mineral assemblages provide a reward of the thermal and chemical changes that occurred during the evolution of The Geysers geothermal system. The data document the presence of an extensive liquid dominated geothermal system that developed in response to felsite intrusion and its evolution to a vapor-dominated regime. Temperatures within the early liquid-dominated system ranged from 175 C at a distance of 7200 feet from the felsite to more than 350 C near the contact while salinities varied from 5 equivalent weight percent NaCl (at a distance of 5500 feet) to more than 26 weight percent NaCl. As temperatures around the felsite declined, the liquid-dominated system collapsed upon itself. Downward migration of the low salinity waters resulted in dilution of the fluids present in regions now occupied by the caprock and normal vapor-dominated reservoir. In contrast, dilution was minor in rocks now hosting the high-temperature vapor-dominated reservoir. This suggests that low permeabilities are the primary reason for the development of the high-temperature reservoir. Boiling within the caprock produced late-stage veins of calcite and quartz. As the fluid boiled off, condensate was trapped as low salinity fluid inclusions. Within the main body of the reservoir, a liquid phase with salinities of up to 7 equivalent weight percent NaCl persisted to temperatures between 250 and 270 C. However, except for the presence of vapor-rich inclusions, little evidence of boiling within the reservoir rocks was preserved.

Moore, J.N.

1992-01-01

410

A Representation to Apply Usual Data Mining Techniques to Chemical Reactions  

Microsoft Academic Search

\\u000a Chemical reactions always involve several molecules of two types, reactants and products. Existing data mining techniques,\\u000a eg. Quantitative Structure Activity Relationship (QSAR) methods, deal with individual molecules only. In this article, we\\u000a propose to use Condensed Graph of Reaction (CGR) approach merging all molecules involved in a reaction into one molecular\\u000a graph. This allows one to consider reactions as pseudo-molecules

Frank Hoonakker; Nicolas Lachiche; Alexandre Varnek; Alain Wagner

2010-01-01

411

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

Microsoft Academic Search

Calculations of thermodynamic data are performed for fatty acid triglycerides, free fatty acids, and fatty acid methyl esters,\\u000a participants of the transesterification reaction of vegetable oils that occurs in methanol. Using the obtained thermodynamic\\u000a parameters, the phase diagrams for the reaction mixture are constructed, and the chemical equilibria of the esterification\\u000a reaction of free fatty acids and the transesterification reaction

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

2011-01-01

412

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.

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

2013-03-01

413

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

414

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

415

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

416

Extended transition-state theory and constant-energy chemical-reaction molecular-dynamics method for liquid-phase chemical reactions  

Microsoft Academic Search

An extension of transition-state theory for liquid-phase chemical reactions is presented. The effect of adding a second solvent water molecule on the proton-transfer reaction in a formamidine–water (FW) cluster was studied. Abinitio molecular-orbital calculations were performed for the formamidine–water–water (FWW) system to obtain the adiabatic potential-energy surface. It was expressed in two coordinate systems: (i) the total normal-coordinate system of

Masataka Nagaoka; Yoshishige Okuno; Tokio Yamabe

1992-01-01

417

Innovative processing of porous and cellular materials by chemical reaction  

Microsoft Academic Search

Nickel aluminide foam and porous Ti composite (TiC,TiB(2)\\/Ti) were synthesized. A reaction between Ni and Al was used to make the nickel aluminide foam. Porous Ti composite was fabricated by reactions between (1) Ti and C or (2) Ti and B4C. Gas release from the elemental powders and initial porosity in the green powder compact were the formation mechanisms of

N. Kanetake; M. Kobashi

2006-01-01

418

Nanoscale Pattern Formation in Non-Equilibrium Surface Chemical Reactions  

Microsoft Academic Search

Using examples from surface science, we consider in article problems of non-equilibrium pattern formation in reactive soft matter. An interplay of reaction, diffusion and energetic interactions between adatoms can produce a variety of non-equilibrium nanostructures, both stationary and traveling. These structures are similar to the patterns found in phase-separating binary mixtures under the influence of reactions. Because of their small

Y. D. Decker; A. S. Mikhailov

2006-01-01

419

CFD Analysis of Personal Ventilation with Volumetric Chemical Reactions  

Microsoft Academic Search

This article studies the concentration distribution in the microenvironment of a person and inhalation exposure in a typical office space when modeling first- and second-order reactions. First, wall adsorption of ozone and d-limonene and the resulting volumetric reaction are validated, and 2D computational concentration profiles are compared to the experimental results from Ito (2007b) with reasonable agreement. The validated model

Jackie Russo; H. Ezzat Khalifa

2010-01-01

420

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

421

The Fluctuation Theorem in Stochastic Chemical Reaction Systems  

NASA Astrophysics Data System (ADS)

In this study, we consider a simple discrete model of isomerization-type reaction, which can be described in Markovian kinetics. Then we investigate the validity of FT in that model by using the Gillespie method which gives an ensemble of stochastic paths of successive reactions explicitly. We obtain a result that the validity of the FT is determined by time-scale of the dynamics.

Akuzawa, Naohiro; Akimoto, Mitsuhiro

2008-02-01

422

The Bergman reaction of dynemicin A – a quantum chemical investigation  

Microsoft Academic Search

For the first time, the Bergman reaction of a naturally occurring enediyne, namely dynemicin A, is fully investigated at the DFT level of theory using the B3LYP hybrid functional and VDZ basis sets. The calculated geometry of dynemicin A agrees well with the X-ray structure of deoxydynemicin A. The activation barrier is calculated to be 19.4 kcal\\/mol, while the reaction

Bodil Ahlström; Elfi Kraka; Dieter Cremer

2002-01-01

423

Thermal Evaluation of Two Prototype Aircrew Chemical Defense Ensembles.  

National Technical Information Service (NTIS)

Individual aircrew members are protected against chemical warfare environments by the Aircrew Chemical Defense Ensemble (ACDE). The current regulation ACDE (flight suit coverall worn over an activated charcoal undergarment) inhibits dissipation of body he...

L. P. Krock J. R. Garza J. Wiegman

1989-01-01

424

Spectrometric Studies of Fast Reactions in Chemically Active Systems.  

National Technical Information Service (NTIS)

The report briefly summarizes research concerning the chemical compositon and stability of planetary atmospheres, - primarily oxygenic atmospheres such as that of the earth, but potentially equally important in other atmospheres such as that of Venus. The...

E. J. Bair

1970-01-01

425

Product-state control of bi-alkali-metal chemical reactions  

SciTech Connect

We consider ultracold, chemically reactive scattering collisions of the diatomic molecules KRb. When two such molecules collide in an ultracold gas, we find that they are energetically forbidden from reacting to form the trimer species K{sub 2}Rb or Rb{sub 2}K, and hence can only react via the bond-swapping reaction 2KRb{yields}K{sub 2}+Rb{sub 2}. Moreover, the tiny energy released in this reaction can in principle be set to zero by applying electric or microwave fields, implying a means of controlling the available reaction channels in a chemical reaction.

Meyer, Edmund R.; Bohn, John L. [JILA, NIST, and University of Colorado, Department of Physics, Boulder, Colorado 80309-0440 (United States)

2010-10-15

426

Product-state control of bi-alkali-metal chemical reactions  

NASA Astrophysics Data System (ADS)

We consider ultracold, chemically reactive scattering collisions of the diatomic molecules KRb. When two such molecules collide in an ultracold gas, we find that they are energetically forbidden from reacting to form the trimer species K2Rb or Rb2K, and hence can only react via the bond-swapping reaction 2KRb?K2+Rb2. Moreover, the tiny energy released in this reaction can in principle be set to zero by applying electric or microwave fields, implying a means of controlling the available reaction channels in a chemical reaction.

Meyer, Edmund R.; Bohn, John L.

2010-10-01

427

Thermal neutron cross section and resonance integral of the 159 Tb ( n,gamma ) 160 Tb reaction  

Microsoft Academic Search

The thermal neutron cross section and resonance integral of the reaction 159 Tb ( n,gamma ) 160 Tb in the thermal and 1\\/E regions, respectively, of a thermal reactor neutron spectrum have been experimentally determined. Literature data on the resonance integral of the reaction show a large scatter ranging from 313 to 780 b . On the basis of such

M. U. Rajput; M. Ahmad; W. Ahmad

2003-01-01

428

Characterization of the thermal and photoinduced reactions of photochromic spiropyrans in aqueous solution.  

PubMed

Six water-soluble spiropyran derivatives have been characterized with respect to the thermal and photoinduced reactions over a broad pH-interval. A comprehensive kinetic model was formulated including the spiro- and the merocyanine isomers, the respective protonated forms, and the hydrolysis products. The experimental studies on the hydrolysis reaction mechanism were supplemented by calculations using quantum mechanical (QM) models employing density functional theory. The results show that (1) the substitution pattern dramatically influences the pKa-values of the protonated forms as well as the rates of the thermal isomerization reactions, (2) water is the nucleophile in the hydrolysis reaction around neutral pH, (3) the phenolate oxygen of the merocyanine form plays a key role in the hydrolysis reaction. Hence, the nonprotonated merocyanine isomer is susceptible to hydrolysis, whereas the corresponding protonated form is stable toward hydrolytic degradation. PMID:24143951

Hammarson, Martin; Nilsson, Jesper R; Li, Shiming; Beke-Somfai, Tamás; Andréasson, Joakim

2013-10-21

429

Simulation of gas exothermic chemical reaction in porous media reactor with lattice Boltzmann method  

NASA Astrophysics Data System (ADS)

Exothermic reactor is the main part in a chemical heat pump. It involves complex multi-component exothermal chemical reaction in catalyst-filled porous media. The lattice Boltzmann method (LBM) is developed to simulate the characteristics of fluid flow, heat and mass transfer coupling chemical reaction in the exothermic reactor of the isopropanol/acetone/hydrogen chemical heat pump system. Fractal theory is used to structure a porous medium model in the reactor. The simulation results show that LBM is suitable for the simulation and the conversion has an optimal value with different inlet velocities.

Xin, Fang; Li, Xun-Feng; Xu, Min; Huai, Xiu-Lan; Cai, Jun; Guo, Zhi-Xiong

2013-02-01

430

Ultralocalized thermal reactions in subnanoliter droplets-in-air  

PubMed Central

Miniaturized laboratory-on-chip systems promise rapid, sensitive, and multiplexed detection of biological samples for medical diagnostics, drug discovery, and high-throughput screening. Within miniaturized laboratory-on-chips, static and dynamic droplets of fluids in different immiscible media have been used as individual vessels to perform biochemical reactions and confine the products. Approaches to perform localized heating of these individual subnanoliter droplets can allow for new applications that require parallel, time-, and space-multiplex reactions on a single integrated circuit. Our method positions droplets on an array of individual silicon microwave heaters on chip to precisely control the temperature of droplets-in-air, allowing us to perform biochemical reactions, including DNA melting and detection of single base mismatches. We also demonstrate that ssDNA probe molecules can be placed on heaters in solution, dried, and then rehydrated by ssDNA target molecules in droplets for hybridization and detection. This platform enables many applications in droplets including hybridization of low copy number DNA molecules, lysing of single cells, interrogation of ligand–receptor interactions, and rapid temperature cycling for amplification of DNA molecules.

Salm, Eric; Guevara, Carlos Duarte; Dak, Piyush; Dorvel, Brian Ross; Reddy, Bobby; Alam, Muhammad Ashraf; Bashir, Rashid

2013-01-01

431

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

432

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

433

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

434

Two-loop hard thermal loop pressure at finite temperature and chemical potential  

NASA Astrophysics Data System (ADS)

We calculate the two-loop pressure of a plasma of quarks and gluons at finite temperature and chemical potential using the hard thermal loop perturbation theory reorganization of finite temperature/density quantum chromodynamics. The computation utilizes a high temperature expansion through fourth order in the ratio of the chemical potential to temperature. This allows us to reliably access the region of high temperature and small chemical potential. We compare our final result for the leading-and next-to-leading-order hard thermal loop perturbation theory pressure at finite temperature and chemical potential with perturbative quantum chromodynamics calculations and available lattice quantum chromodynamics results.

Haque, Najmul; Mustafa, Munshi G.; Strickland, Michael

2013-05-01

435

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

436

Fast growth in phase-separating A-B-copolymer ternary mixtures with a chemical reaction.  

PubMed

We study the dynamics of phase separation of a binary A-B- polymer mixture with copolymer C, which is produced by the reaction of two counterpart reactive polymers A and B at the interface via the chemical reaction A+B right harpoon over left harpoon C. For low interfacial energy between the A and B phases, where the copolymer prefers to locate at interfaces, we show that the chemical reaction accelerates the phase separation of the system dramatically, because the backward reaction always drives the creation of immiscible A and B pairs at interfaces, which speed up the phase separation of the system, while the forward reaction process becomes more and more difficult as the interfaces are gradually saturated by copolymers. We also indicate that for a fixed chemical reaction rate constant, as the initial concentration of the copolymers increases, the domain growth at the late stage is speeded up as a result of the backward chemical reaction. However, when the interfacial energy is high, both forward and backward reactions coexist due to the occurrence of unsaturated interfaces, but the relative strength of reaction rates has no appreciable effect on domain growth during spinodal decomposition, because the interfacial energy dominates phase separation. PMID:12636705

Zhu, Yue-Jin; Ma, Yu-Qiang

2003-02-14

437

Organoberyllium compounds and their chemical reactions. XI. Synthesis of diacetylhydrobenzoins  

SciTech Connect

The authors previously determined that the reaction of aromatic aldehydes with acylhaloberyllium in ethyl acetate lead to the formation of stilbene. In this same vein they have found that the final products of this reaction can include not only stilbenes but also diacetylhydrobenzoin and that the product is determined by the nature of the solvent. In this paper they determine that while ethyl acetate indeed leads to the stilbene the use of an ether--diethyl or diisopropyl--leads to diacetylhydrobenzoin. NMR spectroscopy is used to ascertain the structure of the product.

Lapkin, I.I.; Sinani, S.V.

1987-08-10

438

The Bergman reaction of dynemicin A a quantum chemical investigation  

NASA Astrophysics Data System (ADS)

For the first time, the Bergman reaction of a naturally occurring enediyne, namely dynemicin A, is fully investigated at the DFT level of theory using the B3LYP hybrid functional and VDZ basis sets. The calculated geometry of dynemicin A agrees well with the X-ray structure of deoxydynemicin A. The activation barrier is calculated to be 19.4 kcal/mol, while the reaction energy is exothermic by -2.1 kcal/mol, reflecting the destabilization of the enediyne unit by incorporation into a tricyclic ring system. The energetics of dynemicin A reveal that the enediyne is biologically active at body temperature.

Ahlström, Bodil; Kraka, Elfi; Cremer, Dieter

2002-07-01

439

Asymptotic behaviour of a general reversible chemical reaction-diffusion equation  

Microsoft Academic Search

In this work, we prove the existence and the exponential decay to equilibrium of a general reversible chemical reaction-diffusion equation with same but general diffusion. Moreover, we prove the optimal asymptotic behaviour in the \\

Ivan Gentil; Boguslaw Zegarlinski

2009-01-01

440

Spectroscopic Studies of Chemical Adsorption and Reactions at Transition Metal Surfaces.  

National Technical Information Service (NTIS)

The accomplishments of the work under the title 'Spectroscopic Studies of Chemical Adsorption and Reactions at Transition Metal Surfaces' are summarized. Included are studies of flat and stepped surfaces, of surfaces with chemisorbed species and of reacti...

J. E. Demuth G. W. Rubloff

1977-01-01

441

Detailed Chemical Kinetic Reaction Mechanism for Oxidation of Four Small Alkyl Esters in Laminar Premixed Flames.  

National Technical Information Service (NTIS)

A detailed chemical kinetic reaction mechanism has been developed for a group of four small alkyl ester fuels, consisting of methyl formate, methyl acetate, ethyl formate and ethyl acetate. This mechanism is validated by comparisons between computed resul...

C. K. Westbrook F. L. Dryer M. Chaos P. R. Westmoreland W. J. Pitz

2008-01-01

442

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...

443

Comparison of thermal flow and chemical shrink processes for 193 nm contact hole patterning  

NASA Astrophysics Data System (ADS)

This paper compares thermal shrink properties of contact holes and chemical shrink performance for 193 nm lithography. Pitch dependence, shrink properties, contact hole circularity, sidewall roughness, and process window are also discussed. Thermal flow process exhibited more pitch dependence than chemical shrink process. Thermal shrink rate increased substantially at higher bake temperatures. Contact holes in defocused area shrunk non-evenly and DOF deteriorated upon heating. In chemical shrink process, shrink rate was hardly influenced by mixing bake temperature, contact holes from center focus to defocus area shrunk evenly preserving effective DOF and MEF became smaller at smaller CD. Chemical shrink has clear advantages over thermal flow process and sub-70 nm contact holes were obtained with iso-dense overlap DOF 0.25 ?m by optimizing resist formulations and process conditions. Application of shrink processes will pave the way for the next generation LSI production.

Kudo, Takanori; Antonio, Charito; Sagan, John; Chakrapani, Srinivasan; Parthasarathy, Deepa; Hong, Sungeun; Thiyagarajan, Muthiah; Cao, Yi; Padmanaban, Munirathna

2009-03-01

444

Thermal Stress in Seven Types of Chemical Defense Ensembles during Moderate Exercise in Hot Environments.  

National Technical Information Service (NTIS)

United States Air Force -(USAF) personnel must perform their duties in many operational environments, including those with the potential for contamination with toxic chemical warfare (CW) agents. This study evaluated the physiological response to thermal ...

S. H. Bomalaski R. Hengst S. H. Constable

1993-01-01

445

Non-equilibrium thermodynamics for fully coupled thermal hydraulic mechanical chemical processes  

NASA Astrophysics Data System (ADS)

In this paper, a pioneering approach of reactive transport in porous media is introduced, which model thermal-hydraulic-mechanical-chemical processes. The novelties of this approach are: (i) non-equilibrium thermodynamics which is used as a unifying framework relating generalized fluxes to forces and (ii) fully coupled integration of the multi-physics processes, introduced within the framework of large transformations including logarithmic finite strain and co-rotational rates. This formulation opens the horizons for complex simulations which were difficult to conduct previously because of the lacking bridges between non-linear computational mechanics and reactive transport processes. As an illustration of the model, a sample of simple geometry is subjected to a non-linear deformation beyond the reversible regime. This perturbation from equilibrium produces a permanent deformation, an overpressure and a temperature change. The subsequent thermodynamic conditions trigger chemical reactions among the aqueous species which are not necessarily in equilibrium with their environment. The deformation also induces a change of porosity which affects the permeability as well as the pore pressure distribution.

Karrech, A.

2013-03-01

446

Exothermic and endothermic chemical reactions involving very many particles modeled with molecular dynamics  

Microsoft Academic Search

The traditional continuum approach of modeling chemical reactions with specified kinetic rates suffers from numerical difficulties in reactive flows and other highly non-equilibrium situations due to the stiffness of the differential equations in both space and time. These drawbacks can be eliminated within the framework of the discrete-particle approach in which the chemical reactions are modeled by means of two-body

Witold Alda; David A. Yuen; Hans-Peter Lüthi; James R. Rustad

2000-01-01

447

[From a periodic chemical reaction to the dynamics of microbial communities].  

PubMed

The first articles published by Anatol Zhabotinsky have been analyzed. The mechanisms of the Belousov-Zhabotinsky and Bray-Liebhafsky oscillating chemical reactions were compared. It was shown that the traditional chemical kinetics, the new methods of molecular biology as well as isotopic composition analysis made it possible to consider new constraints concerning the degradation of organic matter and microbial dynamics. A mathematical model was developed to describe isotope accumulation in biomass and reaction products. PMID:20067197

Vavilin, V A

448

From simple to complex and backwards. Chemical reactions under very high pressure  

NASA Astrophysics Data System (ADS)

High pressure chemical reactions of molecular systems are discussed considering the various factors that can affect the reactivity. These include steric hindrance and geometrical constraints in the confined environment of crystals at high pressure, changes of the free energy landscape with pressure, photoactivation by two-photon absorption, local and collective effects. A classification of the chemical reactions at high pressure is attempted on the basis of the prevailing factors.

Bini, Roberto; Ceppatelli, Matteo; Citroni, Margherita; Schettino, Vincenzo

2012-04-01

449

Quantum chemical study of aluminum CVD reaction for titanium nitride (111) surface with terminal fluorine  

Microsoft Academic Search

Reaction mechanisms and interface structures in aluminum (Al) chemical vapor deposition (CVD) have been investigated in terms of the surface termination models for TiN by ab initio quantum chemical approach. The B3LYP density functional calculations and coupled-cluster calculations were carried out by using the local structural models in order to investigate reaction mechanisms, and we found Al can be deposited

A. Tachibana; K. Nakamura

2000-01-01

450

Microfluidic sub-millisecond mixers for the study of chemical reaction kinetics  

Microsoft Academic Search

We present a micromachined, high Reynolds number (2000-6000), sub-millisecond liquid mixer for the study of chemical reaction kinetics. This 1 cm×1 cm×1 mm bulk micromachined silicon mixer is capable of initiating and quenching (starting and stopping) chemical reactions in intervals as short as 100 ?s. The centimeter sized mixer chip contains two tee mixers connected by one channel which serves

Amish Desai; D. Bokenkamp; Xing Yang; Yu-Chong Tai; E. Marzluff; S. Mayo

1997-01-01

451

Studies on the Role of Radiation in Chemical Reactions Occurring on Surfaces  

Microsoft Academic Search

The addition of energetic radiation to a gas-solid surface system may initiate or enhance chemical reactions occurring on the surface. Conversely, when a chemical reaction proceeds on a surface, radiation may be spontaneously emitted. The effect of argon ion bombardment on SiO(,2) exposed to XeF(,2) was studied. At room temperature SiO(,2) adsorbs a monolayer of fluorine when exposed to XeF(,2).

Michael Allen Loudiana

1984-01-01

452

EC mechanism of an adsorbed redox couple. Volume vs surface chemical reaction  

Microsoft Academic Search

A theoretical model of a complex electrode mechanism coupled by adsorption of the redox couple and followed by two different types of irreversible chemical reactions is developed:Ox(ads)+ne??Red(ads)?ksP??(Ox(aq))x=0+ne??(Red(aq))x=0?kvPThe theoretical consideration for this specific type of EC mechanism comprises all relevant phenomena such as diffusion mass transport, adsorption equilibria and kinetics of the following irreversible chemical reactions. The adsorbed electroactive product Red(ads)

Valentin Mir?eski; Milivoj Lovri?

2004-01-01

453

Chemical reactions in the low-temperature zone of a laminar rich propane—air flame  

Microsoft Academic Search

The mechanism of chemical reactions in the low-temperature zone of a rich propane—air flame is considered. It is shown that\\u000a at temperatures of 300–700 K, intense chemical reactions proceed with the formation of end products and that the water concentration\\u000a reaches an intermediate equilibrium value even at a temperature of 685 K. In this zone of the front, the diffusion

V. A. Bunev; V. S. Babkin

2006-01-01

454

Transport in chemical vapor deposition reactors: A two-dimensional model including multicomponent and thermal diffusion, and species interdiffusion  

SciTech Connect

The chemical vapor deposition (CVD) process that consists of depositing coatings of silicon nitride from silicon tetrafluoride and ammonia at low-pressure is modeled in a reactor simulation. Combined effects of surface chemical kinetics, multicomponent diffusion, convection, thermal diffusion, species interdiffusion, and variable properties are included in a reactor model. Full multicomponent diffusion is included by solving the StefanMaxwell equations. Species interdiffusion and thermal diffusion are included in the energy and species conservation equations. Results are for five gas phase species with two surface reactions specified for the deposition. Distributions of radial and axial components of velocity, species, temperature, and deposition rate and deposition profile are obtained in a tube reactor. Effects of the combined transport mechanisms noted above are determined. The decomposition of NH{sub 3} into N{sub 2} and H2{sub 2} retards deposition of silicon nitride and dilutes the incoming reactants. This dilution is strongly enhanced by thermal diffusion since the direction of the temperature gradient causes the light species generated by the surface reactions to remain near the surface resulting in smaller and nonmonotonic deposition rates. The effects of a ramp in the surface temperature on the deposition rate and profile and on the transport processes are also determined.

Evans, G. [Sandia National Labs., Livermore, CA (United States); Greif, R. [California Univ., Berkeley, CA (United States). Dept. of Mechanical Engineering

1994-11-01

455

Chemical reactions occurring at a BN?AgTi interface  

Microsoft Academic Search

A plate of cubic boron nitride (BN) whose surface was covered by an AgTi 1.5 layer was subjected to thermal annealing at 950 °C and 3?10?3 Pa for 1 h. After this treatment the sample was polished on the transverse section. The BN-alloy interface was studied using Auger electron spectroscopy (AES). From the studies of the elemental distributions (Ag, Ti,

E. Benko

1996-01-01

456

Chemical Principles Revisited. Redox Reactions and the Electropotential Axis.  

ERIC Educational Resources Information Center

This paper suggests a nontraditional pedagogic approach to the subject of redox reactions and electrode potentials suitable for freshman chemistry. Presented is a method for the representation of galvanic cells without the introduction of the symbology and notation of conventional cell diagrams. (CW)

Vella, Alfred J.

1990-01-01

457

Effects of Chemical Reactions on the Bimolecular Rate Constant  

Microsoft Academic Search

The dependence of the bimolecular rate constant on the reaction rate, degree of anisotropic scattering, mass ratio, and other parameters is investigated by considering the Boltzmann equation for a dilute homogeneous reacting gas. For highly anisotropic elastic scattering, a differential form of the Boltzmann equation is derived and a solution obtained, which yields an analytical expression for the rate constant.

M. D. Kostin

1967-01-01

458

The Quantum Mechanics of Chemical Reactions Involving Conjugate Double Bonds  

Microsoft Academic Search

The various theories of conjugate double bonds are discussed on the basis of quantum mechanics. The potential energy surfaces for the addition of diatomic molecules to such bonds are calculated by the generalized Heitler-London method. It is shown that various mechanisms are possible for such reactions and that such effects as the steric repulsions of the various inactive groups in

Henry Eyring; Albert Sherman; George E. Kimball

1933-01-01

459

Acoustic wave propagation in fluids with coupled chemical reactions  

Microsoft Academic Search

This investigation presents a hydroacoustic theory which accounts for sound absorption and dispersion in a multicomponent mixture of reacting fluids (assuming a set of first-order acoustic equations without diffusion) such that several coupled reactions can occur simultaneously. General results are obtained in the form of a biquadratic characteristic equation (called the Kirchhoff-Langevin equation) for the complex propagation variable chi =

T. S. Margulies; W. H. Schwarz

1984-01-01

460

Spontaneous Motion of a Droplet Coupled with Chemical Reaction  

Microsoft Academic Search

The spontaneous motion of a droplet of Belousov-Zhabotinsky (BZ) reactionmedium was studied experimentally. A propagating chemical wave causes an increase in interfacial tension, which induces convection inside the droplet. This convection causes spontaneous translational motion of the droplet. In this article, we describe the dynamics of the convection inside the droplet and discuss its mechanism.

Hiroyuki Kitahata

2006-01-01