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1

An open-framework three-dimensional indium oxalate: [In(OH)(C2O4)(H2O)]3·H2O  

NASA Astrophysics Data System (ADS)

By hydrothermal reaction of In2O3 with H2C2O4·2H2O in the presence of H3BO3 at 155 °C, an open-framework three-dimensional indium oxalate of formula [In(OH)(C2O4)(H2O)]3·H2O (1) has been obtained. The compound crystallizes in the trigonal system, space group R3c with a=18.668(3)Å, c=7.953(2)Å, V=2400.3(7)Å, Z=6, R1=0.0352 at 298 K. The small pores in 1 are filled with water molecules. It loses its filled water at about 180 °C without the change of structure, then the bounded water at 260 °C, and completely decompounds at 324 °C. The residue is confirmed to be In2O3.

Yang, Sihai; Li, Guobao; Tian, Shujian; Liao, Fuhui; Lin, Jianhua

2005-12-01

2

A new binuclear germanium(IV) and copper(II) complex with 1,3-diamino-2-propanoltetraacetic acid: Crystal and molecular structure of [(H 2 O)(OH)Ge(?-Hpdta)Cu(H 2 O)] · 3H 2 O  

Microsoft Academic Search

A heteronuclear germanium(IV) and copper(II) complex with 1,3-diamino-2-propanoltetraacetic acid (H5Hpdta) has been synthesized for the first time. The compound has been characterized by elemental analysis, X-ray diffraction,\\u000a thermogravimetry, and IR spectroscopy. The structure of the complex [(H2O)(OH)Ge(?-Hpdta)Cu(H2O)] · 3H2O (I) has been determined by single-crystal X-ray diffraction. The crystals of I are monoclinic, a = 1 5.327(4) Å, b =

E. E. Martsinko; L. Kh. Minacheva; V. S. Sergienko; E. A. Chebanenko; I. I. Seifullina

2010-01-01

3

Extended networks, porous sheets, and chiral frameworks. Thorium materials containing mixed geometry anions: Structures and properties of Th(SeO3)(SeO4), Th(IO3)2(SeO4)(H2O)3·H2O, and Th(CrO4)(IO3)2  

NASA Astrophysics Data System (ADS)

Three novel Th(IV) compounds containing heavy oxoanions, Th(SeO3)(SeO4) (1), Th(IO3)2(SeO4)(H2O)3·H2O (2), and Th(CrO4)(IO3)2 (3), have been synthesized under mild hydrothermal conditions. Each of these three distinct structures contain trigonal pyramidal and tetrahedral oxoanions. Compound 1 adopts a three-dimensional structure formed from ThO9 tricapped trigonal prisms, trigonal pyramidal selenite, SeO32 , anions containing Se(IV), and tetrahedral selenate, SeO42 , anions containing Se(VI). The structure of 2 contains two-dimensional porous sheets and occluded water molecules. The Th centers are found as isolated ThO9 tricapped trigonal prisms and are bound by four trigonal pyramidal iodate anions, two tetrahedral selenate anions, and three coordinating water molecules. In the structure of 3, the Th(IV) cations are found as ThO9 tricapped trigonal prisms. Each Th center is bound by six IO31 anions and three CrO42 anions forming a chiral three-dimensional structure. Second-harmonic generation of 532 nm light from 1064 nm radiation by a polycrystalline sample of 3 was observed. Crystallographic data (193 K, MoK?, ?=0.71073): 1; monoclinic, P21/c; a=7.0351(5)Å, b=9.5259(7)Å, c=9.0266(7)Å, ?=103.128(1), Z=4, R(F)=2.47% for 91 parameters with 1462 reflections with I>2?(I); 2, monoclinic, P21/n, a=7.4889(9)Å, b=8.002(1)Å, c=20.165(3)Å, ?=100.142(2), Z=4, R(F)=4.71% for 158 parameters with 2934 reflections with I>2?(I); 3, orthorhombic, P212121, a=7.3672(5)Å, b=9.3617(6)Å, c=11.9201(7)Å, Z=4, R(F)=2.04% for 129 parameters with 2035 reflections with I>2?(I).

Sullens, Tyler A.; Almond, Philip M.; Byrd, Jessica A.; Beitz, James V.; Bray, Travis H.; Albrecht-Schmitt, Thomas E.

2006-04-01

4

The Kinetics of Isotopic Exchange Reactions.  

ERIC Educational Resources Information Center

|Discussed are the kinetic interactions of these chemical processes and the determination of the actual order of such reactions. Included are multiple exchange, catalytic exchange with deuterium, and depletion of the original substrate. (CW)|

Logan, S. R.

1990-01-01

5

Exchange reaction between epoxides and chlorohydrins  

Microsoft Academic Search

We determined the equilibrium constant of the exchange reaction between epichlorohydrin and 1-chloro-2-hydroxy-3-phenoxypropane, which leads to the formation of phenyl glycidyl ether and glycerol 1,3-dichlorohydrin.

M. A. Markevich; T. S. Zarkhina; S. Z. Rogovina; V. A. Pekarskii; M. G. Brusilovskii; A. I. Nepomnyashchii; N. S. Enikolopyan

1979-01-01

6

Charge exchange reactions and applications to astrophysics  

SciTech Connect

Neutrino-induced reactions have been known to play important roles as the neutrino process on the nucleosynthesis in core collapsing supernovae (SNe) explosions because expected neutrino flux and energy are sufficiently high enough to excite many relevant nuclei in spite of small cross sections of the weak interaction. However, we do not have enough data for the neutrino reaction to be exploited in the network calculation. Only a sparse data in the relevant energy range is known, in specific, for {sup 12}C. Therefore we have to rely on theoretical estimation of the reaction, which has two different modes, charge current (CC) and neutral current (NC). In particular, CC reactions are closely related to charge exchange reactions (CEXRs) which are feasible in the experiment, such as, (p,n) or (n,p) reactions. These CEXRs are usually dominated by the Gamow-Teller (GT) transition in the lower energy region. In this respect, any theoretical approaches for the neutrino reaction should be investigated for the CEXR because we have and expect more useful experimental data. After confirming our models to the GT strength deduced from the CEXR, we calculated neutrino-induced reactions in the energy range below the quasielastic region for nuclei of astrophysical importance. Our calculations are carried out with the Quasi-particle Random Phase Approximation (QRPA), which successfully described the nuclear beta decays of relevant nuclei. To describe neutrino-nucleus reactions, general multipole transitions by the weak interaction are considered for CC and NC reactions. Both reactions are described in a theoretical framework. Our results are shown to well reproduce the data from CEXRs and the sparse experimental data related to the neutrino-induced reaction, and further extended for neutrino reactions on various nuclear targets. Parts of the results are reported in this talk.

Cheoun, Myung-Ki; Ha, Eunja; Kajino, T. [Department of Physics, Soongsil University, Seoul, 156-743 (Korea, Republic of); National Astronomical Observatory, Mitaka, Tokyo 181-8589 (Japan) and Department of Astronomy, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033 (Japan)

2012-11-12

7

Quantum Normal Form Approach to Reactive Scattering: The Cumulative Reaction Probability for Collinear Exchange Reactions.  

National Technical Information Service (NTIS)

The quantum normal form approach to quantum transition state theory is used to compute the cumulative reaction probability for collinear exchange reactions. It is shown that for heavy atom systems like the nitrogen exchange reaction the quantum normal for...

A. Goussev H. Waalkens R. Schubert S. Wiggins

2009-01-01

8

Ion-Molecule Reactions in NO(+)--H2O System.  

National Technical Information Service (NTIS)

The following reaction sequence which occurs in ionized NO--H2O or air--H2O mixtures has been studied: NO(+) + H2O + M goes to NO(+)(H2O) + M, NO(+)(H2O) + H2O + M goes to NO(+)(H2O)2 + M, NO(+)(H2O)2 + H2O + M goes to NO(+)(H2O)3 + M, NO(+)(H2O)3 + H2O g...

F. C. Fehsenfeld M. Mosesman E. E. Ferguson

1971-01-01

9

Samarium Ion Exchanged Montmorillonite for High Temperature Cumene Cracking Reaction  

NASA Astrophysics Data System (ADS)

Montmorillonite clay is cation exchanged with samarium and its catalytic influence in cumene cracking reaction is investigated. Effect of exchange with sodium ions on further exchange with samarium ions is also noted. Acidity measurements are done using Temperature Programmed Desorption (TPD) of ammonia. The retention of basic structure is proved from FTIR spectra and XRD patterns. Elemental analysis result shows that samarium exchange has occurred, which is responsible for the higher catalytic activity. Surface area and pore volume remains more or less unaffected upon exchange. Thermogravimetric analysis indicates the enhanced thermal stability on exchanging. Cumene cracking reaction is carried out at atmospheric pressure in a fixed bed glass reactor at 673 K. The predominance of Brønsted acidity is confirmed from high selectivity to benzene.

Binitha, N. N.; Silija, P. P.; Suraj, V.; Yaakob, Z.; Sugunan, S.

2011-02-01

10

Using reactive artificial muscles to determine water exchange during reactions  

NASA Astrophysics Data System (ADS)

Artificial muscles based on films of conducting polymers translate film volume variations, driven by electrochemical reactions (Faradaic motors), into macroscopic movements with generation of mechanical energy. The reaction promotes exchange of counterions (anions here) and solvent molecules with the electrolyte. Attributing here both the film volume variation and the movement originated by these exchanges of ions and solvent, the described angles can be used to quantify the exchanged solvent. Different angles described by bending muscles consuming equal driving charges in electrolytes having the same cation and different anions were measured. The number of exchanged counterions is given by the consumed charge and the ion valence: this is a Faradaic reaction. The described angle fraction due to the exchanged anions is given by the number of anions and the crystallographic radius. Taking as reference the anion giving the shorter angle, whatever the consumed charge, the relative number of solvent molecules exchanged by the polymeric membrane during a reversible reaction was determined. Actuators and artificial muscles can be used as useful tools for, at least, an initial study of the solvent exchange during reactions in reactive gels.

Otero, T. F.; Martínez, J. G.; Zaifoglu, B.

2013-10-01

11

Carbonyl-Olefin Exchange Reaction and Related Chemistry  

NASA Astrophysics Data System (ADS)

A new carbon—carbon double bond forming reaction (carbonyl olefin exchange reaction) mediated by transition metal catalytic systems has been discovered. The catalytic systems used (transition metal halides or oxohalides alone or in combination with Lewis acids) are active only in the case when the two reacting groups are in one molecules and are conjugated. In addition these systems accelerate other reactions which run simultaneously with the carbonyl olefin metathesis rendering a detailed investigation of the process very complicated.

Jossifov, Christo; Kalinova, Radostina

12

Carbonyl–Olefin Exchange Reaction: Present State and Outlook  

Microsoft Academic Search

The carbonyl–olefin exchange reaction (COER) is a new reaction between carbonyl group and olefin double bond, which has a\\u000a formal similarity with the olefin metathesis (OM) – one carbon atom in the latter is replaced with an oxygen atom. Till now\\u000a the new reaction is performed successfully only when the two functional groups (carbonyl group and olefin double bond) are

Radostina Kalinova; Christo Jossifov

2007-01-01

13

Heat exchanger development at Reaction Engines Ltd.  

NASA Astrophysics Data System (ADS)

The SABRE engine for SKYLON has a sophisticated thermodynamic cycle with heat transfer between the fluid streams. The intake airflow is cooled in an efficient counterflow precooler, consisting of many thousand small bore thin wall tubes. Precooler manufacturing technology has been under investigation at REL for a number of years with the result that flightweight matrix modules can now be produced. A major difficulty with cooling the airflow to sub-zero temperatures at low altitude is the problem of frost formation. Frost control technology has been developed which enables steady state operation. The helium loop requires a top cycle heat exchanger (HX3) to deliver a constant inlet temperature to the main turbine. This is constructed in silicon carbide and the feasibility of manufacturing various matrix geometries has been investigated along with suitable joining techniques. A demonstration precooler will be made to run in front of a Viper jet engine at REL's B9 test facility in 2011. This precooler will incorporate full frost control and be built from full size SABRE engine modules. The facility will incorporate a high pressure helium loop that rejects the absorbed heat to a bath of liquid nitrogen.

Varvill, Richard

2010-05-01

14

Lock-exchange experiments with an autocatalytic reaction front  

NASA Astrophysics Data System (ADS)

A viscous lock-exchange gravity current corresponds to the reciprocal exchange of two fluids of different densities in a horizontal channel. The resulting front between the two fluids spreads as the square root of time, with a diffusion coefficient reflecting the buoyancy, viscosity, and geometrical configuration of the current. On the other hand, an autocatalytic reaction front between a reactant and a product may propagate as a solitary wave, namely, at a constant velocity and with a stationary concentration profile, resulting from the balance between molecular diffusion and chemical reaction. In most systems, the fluid left behind the front has a different density leading to a lock-exchange configuration. We revisit, with a chemical reaction, the classical situation of lock-exchange. We present an experimental analysis of buoyancy effects on the shape and the velocity of the iodate arsenous acid autocatalytic reaction fronts, propagating in horizontal rectangular channels and for a wide range of aspect ratios (1/3 to 20) and cylindrical tubes. We do observe stationary-shaped fronts, spanning the height of the cell and propagating along the cell axis. Our data support the contention that the front velocity and its extension are linked to each other and that their variations scale with a single variable involving the diffusion coefficient of the lock-exchange in the absence of chemical reaction. This analysis is supported by results obtained with lattice Bathnagar-Gross-Krook (BGK) simulations Jarrige et al. [Phys. Rev. E 81, 06631 (2010)], in other geometries (like in 2D simulations by Rongy et al. [J. Chem. Phys. 127, 114710 (2007)] and experiments in cylindrical tubes by Pojman et al. [J. Phys. Chem. 95, 1299 (1991)]), and for another chemical reaction Schuszter et al. [Phys. Rev. E 79, 016216 (2009)].

Malham, I. Bou; Jarrige, N.; Martin, J.; Rakotomalala, N.; Talon, L.; Salin, D.

2010-12-01

15

Conditions on exchange mechanisms for polarization effects in inclusive reactions  

Microsoft Academic Search

In the framework of Mueller-Regge phenomenology we investigate under which conditions one could expect to observe polarization effects in the fragmentation region for inclusive reactions. On the basis of kinematical considerations and parity relations only, we find that this requires exchange of states with mixed naturalities.

Ph. Salin; J. Soffer

1974-01-01

16

Carbonyl-Olefin Exchange Reaction: Present State and Outlook  

NASA Astrophysics Data System (ADS)

The carbonyl-olefin exchange reaction (COER) is a new reaction between carbonyl group and olefin double bond, which has a formal similarity with the olefin metathesis (OM) - one carbon atom in the latter is replaced with an oxygen atom. Till now the new reaction is performed successfully only when the two functional groups (carbonyl group and olefin double bond) are in one molecule and are conjugated. The ?, ?-unsaturated carbonyl compounds (substituted propenones) are the compounds with such a structure. They polymerize giving substituted polyacetylenes. The chain propagation step of this polymerization is in fact the COER. The question arises: is it possible the COER to take place when the two functional groups are not in one molecule and are not conjugated, and could this reaction became an alternative of the existing carbonyl olefination reactions?

Kalinova, Radostina; Jossifov, Christo

17

Phosphatidylethanolamine synthesis by castor bean endosperm : a base exchange reaction.  

PubMed

A base exchange reaction for synthesis of phosphatidylethanolamine by the endoplasmic reticulum of castor bean (Ricinus comminus L. var Hale) endosperm has been examined. The calculated Michaelis-Menten constant of the enzyme for ethanolamine was 5 micromolar and the optimal pH was 7.8 in the presence of 2 millimolar CaCl(2). l-Serine, N-methylethanolamine and N,N-dimethylethanolamine all reduced ethanolamine incorporation, while d-serine and myo-inositol had little effect. These inhibitions of ethanolamine incorporation were found to be noncompetitive and ethanolamine also noncompetitively inhibited l-serine incorporation by exchange. The activity of the ethanolamine base exchange enzyme was affected by several detergents, with the best activity being obtained with the zwitterionic defjtergent 3-3-cholamidopropyl) dimethylammonio-2-hydroxyl-1-propanesulfonate. PMID:16667427

Shin, S; Moore, T S

1990-05-01

18

Cross-ligation and exchange reactions catalyzed by hairpin ribozymes.  

PubMed Central

The negative strand of the satellite RNA of tobacco ringspot virus (sTobRV(-)) contains a hairpin catalytic domain that shows self-cleavage and self-ligation activities in the presence of magnesium ions. We describe here that the minimal catalytic domain can catalyze a cross-ligation reaction between two kinds of substrates in trans. The cross-ligated product increased when the reaction temperature was decreased during the reaction from 37 degrees C to 4 degrees C. A two-stranded hairpin ribozyme, divided into two fragments between G45 and U46 in a hairpin loop, showed higher ligation activity than the nondivided ribozyme. The two stranded ribozyme also catalyzed an exchange reaction of the 3'-portion of the cleavage site. Images

Komatsu, Y; Koizumi, M; Sekiguchi, A; Ohtsuka, E

1993-01-01

19

Charge exchange reactions and solar neutrino detection in 81Br  

NASA Astrophysics Data System (ADS)

The feasibility of 81Br as the detector of the solar neutrino flux hinges upon the knowledge of the Gamow-Teller matrix element from the ground state of 81Br to the 52- state at 0.457 MeV in 81Kr. The possibility of obtaining this matrix element is discussed in terms of the (p, n) and (3He, t) charge exchange reactions. NUCLEAR REACTIONS 81Br(p, n)81Kr and 81Br(3He, t)81Kr Gamow-Teller transitions; solar neutrino detection.

Liu, K. F.; Gabbard, F.

1983-01-01

20

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

21

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

22

Charge-exchange reactions and nuclear matrix elements for ?? decay  

NASA Astrophysics Data System (ADS)

Charge-exchange reactions of (n, p) and (p, n) type at intermediate energies are a powerful tool for the study of nuclear matrix element in ?? decay. The present paper reviews some of the most recent experiments in this context. Here, the (n, p) type reactions are realized through (d, 2He), where 2He refers to two protons in a singlet 1S0 state and where both of these are momentum analyzed and detected by the same spectrometer and detector. These reactions have been developed and performed exclusively at KVI, Groningen (NL), using an incident deuteron energy of 183 MeV. Final state resolutions of about 100 keV have routinely been available. On the other hand, the (3He, t) reaction is of (p, n) type and was developed at the RCNP facility in Osaka (JP). Measurements with an unprecedented high resolution of 30 keV at incident energies of 420 MeV are now readily possible. Using both reaction types one can extract the Gamow-Teller transition strengths B(GT+) and B(GT-), which define the two ``legs'' of the ?? decay matrix elements for the 2v?? decay The high resolution available in both reactions allows a detailed insight into the excitations of the intermediate odd-odd nuclei and, as will be shown, some unexpected features are being unveiled.

Frekers, D.

2009-11-01

23

Synthesis of layered sodium lanthanum selenide through ion exchange reactions  

SciTech Connect

Layered hexagonal KLaSe2 ({alpha}-NaFeO{sub 2}-type) was synthesized using the reactive flux method and analyzed by powder XRD to determine its lattice constants (space group R-3m, a = 4.40508(5) A, c = 22.7838(5) A). NaLaSe{sub 2}, which normally crystallizes as a disordered rock salt structure with mixed Na+/La + 3 sites, was synthesized through a solid state ion exchange reaction at 585 deg. C from a 1:3 molar ratio mixture of KLaSe{sub 2}:NaI. The product of this reaction was hexagonally layered NaLaSe{sub 2} (space group R-3m, a = 4.3497(3) A, c = 20.808(2) A) isostructural to KLaSe{sub 2}. This product was analyzed by comparison with members of the set of solid solutions Na{sub (1-x)}K{sub (x)}LaSe{sub 2} to confirm that the extent ion exchange in this reaction was complete. Cubic (disordered) NaLaSe{sub 2} was also reacted with KI to yield the poorly crystalline hexagonally layered product with the approximate formula Na{sub 0.79}K{sub 0.21}LaSe{sub 2}.

Butts, Laura J.; Strickland, Nicholas [Department of Chemistry, Texas State University - San Marcos, 601 University Drive, San Marcos, TX 78666 (United States); Martin, Benjamin R. [Department of Chemistry, Texas State University - San Marcos, 601 University Drive, San Marcos, TX 78666 (United States)], E-mail: bmartin@txstate.edu

2009-04-02

24

Optical absorption assay for strand-exchange reactions in unlabeled nucleic acids  

Microsoft Academic Search

The nucleic acid exchange reaction is a common feature for genetic recombination, DNA replication and transcription. Due to the fact that in the strand- exchange reactions the reactant and product mole- cules have similar or identical nucleotide sequences, the reaction is undetectable. As a rule, the nucleic acids with radioactive or fluorescence labels are used in such studies. Besides the

Besik I. Kankia

2004-01-01

25

Spin-Isospin responses via charge exchange reactions of RI beams at SHARAQ  

SciTech Connect

Nuclear spectroscopy via direct reactions of RI beams is discussed focusing on characteristics of charge-exchange reactions of RI beams. Recent experiments using the SHARAQ spectrometer at the RIBF are presented, where isovector spin monopole and spin-non-flip monopole responses are studied by charge exchange reaction of RI beams. Some experimental plans and perspectives are also presented.

Shimoura, Susumu [Center for Nuclear Study (CNS), University of Tokyo Wako, Saitama 351-0198 (Japan)

2012-11-12

26

Meson Exchange Contributions to the pparrow pp?^0 Reaction  

NASA Astrophysics Data System (ADS)

The reaction pparrow pp ?^0 remains a challenging theoretical problem. Long--range contributions as dictated from chiral perturbation theory from the impulse and pion rescattering diagrams interfere destructively and fail to account for the observed cross--section near threshold ( T.D. Cohen, J.L. Friar, G.A. Miller, and U. van Kolck, Phys. Rev. C 53) (1996) 2661; B.-Y. Park, F. Myhrer, J.R. Morones, T. Meissner, and K. Kubodera, Phys. Rev. C 53 (1996) 1519.. Here we discuss shorter--ranged mechanisms in which the pion is emitted by heavier mesons that are exchanged between nucleons. In particular, we show that ?-? and ?-a0 exchanges, when combined with previously suggested ( T.-S.H. Lee and D.O. Riska, Phys. Rev. Lett. 70) (1993) 2237; C.J. Horowitz, H.O. Meyer, and D.K. Griegel, Phys. Rev. C 49 (1994) 1337. ?, ? pair diagrams, can reproduce the observed cross--section, within the theoretical uncertainty associated with long--range mechanisms and the two--nucleon wave function.

van Kolck, U.; Miller, G. A.; Riska, D. O.

1996-10-01

27

Neutrino and antineutrino charge-exchange reactions on C12  

NASA Astrophysics Data System (ADS)

We extend the formalism of weak interaction processes, obtaining new expressions for the transition rates, which greatly facilitate numerical calculations, for both neutrino-nucleus reactions and muon capture. Explicit violation of the conserved vector current hypothesis by the Coulomb field, as well as development of a sum-rule approach for inclusive cross sections, has been worked out. We have done a thorough study of exclusive (ground-state) properties of B12 and N12 within the projected quasiparticle random phase approximation (PQRPA). Good agreement with experimental data achieved in this way put into evidence the limitations of the standard RPA and QRPA models, which come from the inability of the RPA to open the p3/2 shell and from the nonconservation of the number of particles in the QRPA. The inclusive neutrino/antineutrino (?/?˜) reactions C12(?,e-)12N and C12(?˜,e+)12B are calculated within both the PQRPA and the relativistic QRPA. It is found that (i) the magnitudes of the resulting cross sections are close to the sum-rule limit at low energy, but significantly smaller than this limit at high energies, for both ? and ?˜; (ii) they increase steadily when the size of the configuration space is augmented, particularly for ?/?˜ energies >200 MeV; and (iii) they converge for sufficiently large configuration space and final-state spin. The quasi-elastic C12(?,?-)12N cross section recently measured in the MiniBooNE experiment is briefly discussed. We study the decomposition of the inclusive cross section based on the degree of forbiddenness of different multipoles. A few words are dedicated to the ?/?˜-C12 charge-exchange reactions related to astrophysical applications.

Samana, A. R.; Krmpoti?, F.; Paar, N.; Bertulani, C. A.

2011-02-01

28

Scaling hyporheic exchange and its influence on biogeochemical reactions in aquatic ecosystems  

Microsoft Academic Search

Hyporheic exchange and biogeochemical reactions are difficult to quantify because of the range in fluid-flow and sediment conditions inherent to streams, wetlands, and nearshore marine ecosystems. Field measurements of biogeochemical reactions in aquatic systems are impeded by the difficulty of measuring hyporheic flow simultaneously with chemical gradients in sediments. Simplified models of hyporheic exchange have been developed using Darcy's law

Ben L. O'Connor; Judson W. Harvey

2008-01-01

29

Dynamics of the hydrogen exchange reaction using the photoloc technique  

NASA Astrophysics Data System (ADS)

The dynamics of the H + D2 exchange reaction has been studied experimentally using laser, velocity- sensitive time-of-flight (TOF) methods. Chemical reaction is initiated by laser photolysis of a suitable HX precursor resulting in a collision energy spread of 50 MeV. HD(v ', J') products are detected via (2+1) resonance-enhanced multiphoton ionization (REMPI) inside a Wiley-McLaren time-of-flight spectrometer. Integral cross section measurements are performed by measuring the total ion yield into different product rovibrational states. In addition, core extraction of the ion packet prior to detection allows an unambiguous inversion of the laboratory product velocity distribution into a corresponding center-of-mass differential cross section with an angular resolution ranging from 3° for backward to 15° for forward scattering. The measured rotational distributions for the HD(v' = 1, 2, J) vibrational manifolds at collision energies ca. 1.6 eV agree closely with quasiclassical trajectory calculations. These distributions are colder than the ``prior'' limit indicating that other constraints besides energy conservation are dictating energy disposal into the rotational degree of Freedom of the diatomic product. Further insight into the dynamics of this reaction is given by the differential cross section measurements into particular HD(v' = 1, J') and HD(v' = 2, J') quantum states. In each vibrational manifold, the product angular distributions are completely back ward scattered for low- J' states, and they shift toward side scattering as the rotational excitation of the product increases. Experimental data at a lower angular resolution for HD(v' = 3, J' ) also show a similar trend in the angular distributions. The differential cross section data can be qualitatively explained by invoking a line- of-centers with nearly elastic specular scattering model which links the most probable scattering angle for a given HD(v', J') product state with initial impact parameter. Within the framework of this model, the angular distributions for HD(v' = 1, J ') and HD(v' = 2, J') only show differences that can be attributed to a smaller hard-sphere radius leading to the more vibrationally excited product.

Fernandez-Alonso, Felix

2000-08-01

30

The kinetics and mechanism of bromide ion isotope exchange reaction in strongly basic anion-exchange resin duolite A-162 determined by the radioactive tracer technique  

NASA Astrophysics Data System (ADS)

In the present investigation, 82Br radioactive isotope was used as a tracer to study the kinetics and mechanism of exchange reaction between an ion exchange resin and an external bromide ion solution. In an attempt to study the reversible bromide ion isotopic exchange reaction kinetics, it was expected that whether the initial step was the exchange of radioactive bromide ions from the solution into the ion exchange resin (forward reaction) or from the ion exchange resin into the solution (reverse reaction), two ion isotopic exchange reactions should occur simultaneously, which was further confirmed by the experimental specific reaction rates of 0.130 and 0.131 min-1, respectively. The results can be used to standardize process parameters so as to optimize the utilization of ion exchange resins in various industrial applications.

Lokhande, R. S.; Singare, P. U.; Karthikeyan, P.

2007-11-01

31

The hydrogen atom, hydrogen molecule exchange reaction: Experimental evidence for dynamical resonances in chemical reactions  

NASA Astrophysics Data System (ADS)

The hydrogen exchange reaction, H + H2 --> H2 + H, and its isotopic variants are considered to be the simplest of all bimolecular reactions. Quasibound collision complexes (dynamic resonances) have been predicted to play a role in this reaction since 1971, but experimental observation of these effects has been achieved only recently. We co-expand a mixture of HBr and D2 into a vacuum chamber and initiate the reaction H + D2 --> HD + D by photolyzing HBr with a laser pulse. Approximately 15 nanoseconds after initiating the reaction we ionize the HD(v', j') products with a second laser pulse. We detect the HD+ ions with a time-of-flight mass spectrometer that allows us to measure the amount of a particular HD(v ', j') product state as well as the distribution of its lab-frame speeds. Because the reaction is initiated via the photolysis of HBr, we can control the center-of-mass collision energy by changing the wavelength of the photolysis laser. From these measurements we construct energy-dependent distributions of product states (relative integral cross sections) and distributions of scattering angles for individual states (differential cross sections). Differential and integral cross sections were measured for H + D 2 --> HD(v' = 1-3, j') + D reactions at collision energies near 1.6 eV. The cross section measurements for the HD(v' = 1,2) products agree with a simple hard-sphere model, however the results for the HD(v' = 3) products deviate from predictions. These deviations are most notable in the differential cross sections of the HD(v' = 3, j' = 0,1) products where forward scattering is prominent. Quasiclassical trajectory calculations suggest that this forward scattering is the result of a short-lived collision complex (Feshbach resonance). This interpretation is reinforced with a series of HD(v' = 3, j' = 0) experimental differential cross sections spanning 1.39-1.75 eV in which the forward scattered portion is observed to rise and fall as a function of collision energy. The observed peak can be fit to a Lorentzian line shape having a full width at half maximum (FWHM) of 0.07 eV. This FWHM suggests a collision complex lifetime on the order of 10 fs, far too short for the rotation of the H-D-D complex.

Bean, Brian David

2000-09-01

32

Catalysis of the exchange reactions between tetralin-dââ and diphenylmethane by inorganic compounds  

Microsoft Academic Search

In an attempt to determine the mechanism of how effective catalysts alter the rate and the product distributions in the coal gasification reaction, an investigation of the influence of inorganic substances on the exchange reactions between the hydrogen atoms in the benzylic positions and the hydrogen atoms in the aromatic positions was undertaken. The reactions of diphenylmethane and tetralin-dââ at

C. B. Huang; H. H. King; L. M. Stock

1981-01-01

33

Reaction mechanism and nuclear correlations study by low energy pion double charge exchange  

Microsoft Academic Search

In pion double-charge-exchange (DCX) reactions, a positive (negative) pion is incident on a nucleus and a negative (positive) pion emerges. These reactions are of fundamental interest since the process must involve at least two nucleons in order to conserve charge. Although two nucleon processes are present in many reactions they are usually masked by the dominant single nucleon processes. DCX

Weinfeld

1993-01-01

34

The Effect of Inhibitors on the Hydrogen-Deuterium Exchange Reaction  

Microsoft Academic Search

The exchange reaction between hydrogen and deuterium in silica vessels at temperatures in the region of 560 degrees C has been studied, the rate of formation of HD being determined by mass-spectrometer analysis. Nitric oxide and propylene are effective inhibitors of the reaction: both reduce the rate to the same limit. The fully inhibited reaction is approximately of the first

M. J. Stephen; C. J. Danby

1955-01-01

35

The reaction of isotopic exchange of hydrogen with alkyl halides  

Microsoft Academic Search

1.We have studied the kinetics of hydrogen exchange in 2-chloro-2-methylpentane and 1-chloro-1 -methylcyclohexane in anhydrous acetic acid in the presence of the Lewis acids: FeCl3, SbCl5, SnCl4, ZnCl2, HgCl2, and BF3. Under the same conditions, the rate constants of hydrogen exchange in the alkyl chlorides depend essentially on their structures.2.On the basis of the results of hydrogen exchange in different

D. N. Kursanov; E. V. Bykova; V. N. Setkina

1961-01-01

36

Isomeric Differentiation of Green Tea Catechins using Gas-Phase Hydrogen/Deuterium Exchange Reactions  

PubMed Central

Hydrogen/deuterium exchange reactions in a quadrupole ion trap mass spectrometer are used to differentiate galloylated catechin stereoisomers (catechin gallate and epicatechin gallate; gallocatechin gallate and epigallocatechin gallate) and the non-galloylated analogs (catechin and epicatechin, gallocatechin and epigallocatechin). Significant differences in the hydrogen/deuterium exchange behavior of the four pairs of deprotonated catechin stereoisomers are observed upon reaction with D2O. Interestingly, the non-galloylated catechins undergo H/D exchange to a much greater extent than the galloylated species, incorporating deuterium at both aromatic/allylic and active phenolic sites. Non-galloylated catechin isomers are virtually indistinguishable by their H/D exchange kinetics over a wide range of reaction times (0.05 to 10 s). Our experimental results are explained using high-level ab initio calculations to elucidate the subtle structural variations in the catechin stereoisomers that lead to their differing H/D exchange kinetics.

Niemeyer, Emily D.; Brodbelt, Jennifer S.

2007-01-01

37

Analysis of the galactosyltransferase reaction by positional isotope exchange and secondary deuterium isotope effects  

Microsoft Academic Search

The mechanism of the galactosyltransferase-catalyzed reaction was probed using positional isotope exchange, alpha-secondary deuterium isotope effects, and inhibition studies with potential transition state analogs. Incubation of (beta-18O2, alpha beta-18O)UDP-galactose and alpha-lactalbumin with galactosyltransferase from bovine milk did not result in any positional isotope exchange. The addition of 4-deoxy-4-fluoroglucose as a dead-end inhibitor did not induce any detectable positional isotope exchange.

S. C. Kim; A. N. Singh; F. M. Raushel

1988-01-01

38

Pion single- and double-charge-exchange reactions at low energies  

SciTech Connect

The general features of pion charge-exchange reactions at energies of 20 to 80 MeV leading to nuclear isobaric-analog states (IAS) and double-isobaric-analog states (DIAS) are reviewed. The recent progress achieved in understanding the role of short-range N-N correlations in the double-charge-exchange reactions is presented. 36 refs., 21 figs., 2 tabs.

Baer, H.W.

1987-01-01

39

Substrate preferences for lipase-mediated acyl-exchange reactions with butteroil are concentration-dependent  

Microsoft Academic Search

Substrate preferences for pancreatic lipase-mediated acyl-exchange reactions with butteroil were concentration-dependent for\\u000a the series of acyl donors and alcohol acceptors evaluated. For acidolysis reactions, the initial reaction rates and percent\\u000a reaction yields after 18 h at 50 µmol acyl donor per gram substrate mixture were similar forn-fatty acids and their methyl and glycerol esters. At 400–500 µmol g?1 (and greater),

Shu-Jung Kuo; Kirk L. Parkin

1993-01-01

40

Fast Neutral Generation by Charge Exchange Reaction and Its Effect on Neutron Production Rate in Inertial Electrostatic Confinement Fusion Systems  

Microsoft Academic Search

Fast neutral generation by charge exchange reaction in inertial electrostatic confinement plasmas is studied by solving the Poisson equation and the Boltzmann equation for fast neutrals. Fusion reactions carried by the charge exchange fast neutrals become appreciable compared with ion-background fusion reaction. It is shown that the fusion reaction between fast neutral and background gas is sensitively affected by experimental

S. Yoshinaga; H. Matsuura; Y. Nakao; K. Kudo

2005-01-01

41

Proton exchange in acid-base complexes induced by reaction coordinates with heavy atom motions  

NASA Astrophysics Data System (ADS)

We extend previous work on nitric acid-ammonia and nitric acid-alkylamine complexes to illustrate that proton exchange reaction coordinates involve the rocking motion of the base moiety in many double hydrogen-bonded gas phase strong acid-strong base complexes. The complexes studied involve the biologically and atmospherically relevant glycine, formic, acetic, propionic, and sulfuric acids with ammonia/alkylamine bases. In these complexes, the magnitude of the imaginary frequencies associated with the proton exchange transition states are <400 cm-1. This contrasts with widely studied proton exchange reactions between symmetric carboxylic acid dimers or asymmetric DNA base pair and their analogs where the reaction coordinate is localized in proton motions and the magnitude of the imaginary frequencies for the transition states are >1100 cm-1. Calculations on complexes of these acids with water are performed for comparison. Variations of normal vibration modes along the reaction coordinate in the complexes are described.

Alavi, Saman; Taghikhani, Mahdi

2012-06-01

42

Crossed Molecular Beam Studies of Substitution and Exchange Reactions.  

National Technical Information Service (NTIS)

Atom + alkene/aromatic and radical + iodoalkane reactions have been studied. F + C sub 2 H sub 4 -> (C sub 2 H sub 4 F)* implies H + C sub 2 H sub 3 F was studied at low collision energies. The substitution cross section decreases with increasing E/sub c/...

G. N. Robinson

1987-01-01

43

Surface adsorption of fluoride and ionic exchange reactions on hydroxyapatite.  

PubMed

The experiments showed that a part of the fluoride which was taken up by hydroxyapatite or teeth at low concentrations of fluoride at neutral pH was soluble in alkali (IN KOH, 24 h) and was thus not fluoroapatite. Calcium fluoride could not form under the present conditions because the solubility of this compound was not exceeded. It is suggested that the alkali soluble fluoride is adsorbed to calcium ions bound as counterions in the hydration layer of the hydroxyapatite or the enamel. This is consistent with previous findings in this laboratory, showing that fluoride displaced acidic proteins adsorbed to calcium receptors on the hydroxyapatite surface in the same way as other anions displace proteins. It could also be shown that polyanions and polycations adsorbed to hydroxyapatite surfaces by ionic exchange, displacing phosphate or phosphate and calcium respectively in the process. A model is suggested which differs slightly from that proposed by Bernardi. PMID:280116

Rölla, G; Bowen, W H

1978-01-01

44

Role of the aerosol phase state in ammonia/amines exchange reactions.  

PubMed

The exchange reaction of ammonia in (NH4)2SO4 with an amine and the corresponding reverse reaction of amines in aminium sulfates with ammonia were investigated using an electrodynamic balance coupled with a Raman spectrometer. The temporal changes in particle mass, chemical composition, and phase state were simultaneously monitored. When the salt particles were in an aqueous state at elevated relative humidities (RHs), the exchange of ammonia/amine vapors in the particle phase was reversible. The exchange rates of aqueous particles were in general higher than those of their corresponding solid counterparts. An aqueous phase was essential for the effective displacement of ammonia and amines. Aminium salts in different phase states and with different evaporation characteristics showed remarkably different reaction behaviors in ammonia vapor. The less compact amorphous aminium sulfate solids were more susceptible to ammonia exchange than the crystalline solids. The aminium salts in a liquid state exhibited substantial amine evaporation at <3% RH and formed acidic bisulfate. Under ammonia exposure, these acidic aminium droplets underwent both neutralization and displacement reactions. Stable solid salts containing ammonium, aminium, sulfate, and bisulfate were formed and hindered further reactions. The result suggests that ambient aminium sulfates may be acidic. Overall, the phase states of the ammonium and aminium salt particles crucially determine the heterogeneous reaction rates and final product properties and identities. PMID:23668831

Chan, Lap P; Chan, Chak K

2013-05-24

45

An extension of CVDV model to Zeldovich exchange reactions for hypersonic non-equilibrium air flows  

NASA Astrophysics Data System (ADS)

A new preferential vibration-dissociation-exchange reactions coupling model - labelled CVDEV - resulting from an extension of the well-known Treanor and Marrone CVDV model, has been derived to take into account the coupling between the vibrational excitation of the N2 and O2 molecules and the two Zeldovich exchange reactions. Analytical expressions for the exchange reactions coupling factor and for the average vibrational energy lost - or gained - by a molecule through an exchange reaction have been developed. The influence of such a coupling has been shown by means of numerical simulations of hypersonic air flows through normal and bow shock waves. Code-to-code comparisons between our model and other recent approaches have been conducted. The infrared radiation of nitric oxide behind a normal shock wave resulting from computations with the CVDEV model has been compared with other coupling model results and to recent shock tube experimental data. These comparisons have shown a good agreement of our model results with the experimental data. In this context, the results show the prominent influence of N2 vibration coupling on the first Zeldovich reaction, and the absence of O2 vibration coupling effects on the second Zeldovich reaction.

Séror, S.; Schall, E.; Druguet, M.-C.; Zeitoun, D. E.

46

Studies on metal exchange reaction between Mn-PAN and * Zn-EDTA complexes  

Microsoft Academic Search

A metal exchange reaction between*Zn-EDTA and Mn-PAN complexes has been investigated to evaluate the possibility of Mn determination in geological samples radiometrically. Exchange ratios (E) of Mn(II) to Zn(II) were obtained from measuring the activity of65ZnPAN2 extracted into an organic phase. Values of E increased rapidly with increasing pH of the aqueous solution. Suitable conditions for the determination of Mn(II)

R. Fujiyoshi; A. Aono; M. Katayama

1992-01-01

47

CATALYTIC REACTIONS ON SEMICONDUCTORS: HYDROGEN-DEUTERIUM EXCHANGE AND FORMIC ACID DECOMPOSITION ON CHEMICALLY DOPED GERMANIUM  

Microsoft Academic Search

Hydrogen--deuterium exchange and the decomposition of formic acid were ; studied from 100 to 400 deg over samples of germanium doped with 10¹⁶ to ; 10²° atoms per cc. of n- and p-type impurities. Over these wide ranges of ; electronic chemical potentials (Fermi level) and temperature the rate and ; activation energy of the exchange reaction varied definitely with

George E. Moore; Hilton A. Smith; Ellison H. Taylor

1962-01-01

48

EXFOR BASICS A SHORT GUIDE TO THE NEUTRON REACTION DATA EXCHANGE FORMAT.  

SciTech Connect

This manual is intended as a guide to users of nuclear reaction data compiled in the EXFOR format, and is not intended as a complete guide to the EXFOR System. EXFOR is the exchange format designed to allow transmission of nuclear reaction data between the Nuclear Reaction Data Centers. In addition to storing the data and its' bibliographic information, experimental information is also compiled. The status (e.g., the source of the data) and history (e.g., date of last update) of the data set is also included. EXFOR is designed for flexibility in order to meet the diverse needs of the nuclear reaction data centers. It was originally conceived for the exchange of neutron data and was developed through discussions among personnel from centers situated in Saclay, Vienna, Livermore and Brookhaven. It was accepted as the official exchange format of the neutron data centers at Saclay, Vienna, Brookhaven and Obninsk, at a meeting held in November 1969. As a result of two meetings held in 1975 and 1976 and attended by several charged-particle data centers, the format was further developed and adapted to cover all nuclear reaction data. The exchange format should not be confused with a center-to-user format. Although users may obtain data from the centers in the EXFOR format, other center-to-user formats have been developed to meet the needs of the users within each center's own sphere of responsibility. The EXFOR format, as outlined, allows a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in a format: that is machine-readable (for checking and indicating possible errors); that can be read by personnel (for passing judgment on and correcting errors). The data presently included in the EXFOR exchange file include: a complete compilation of experimental neutron-induced reaction data, a selected compilation of charged-particle-induced reaction data, a selected compilation of photon-induced reaction data.

MCLANE,V.; NUCLEAR DATA CENTER NETWORK

2000-05-19

49

EXFOR BASICS A SHORT GUIDE TO THE NEUTRON REACTION DATA EXCHANGE FORMAT.  

SciTech Connect

This manual is intended as a guide to users of nuclear reaction data compiled in the EXFOR format, and is not intended as a complete guide to the EXFOR System. EXFOR is the exchange format designed to allow transmission of nuclear reaction data between the Nuclear Reaction Data Centers. In addition to storing the data and its' bibliographic information, experimental information is also compiled. The status (e.g., the source of the data) and history (e.g., date of last update) of the data set is also included. EXFOR is designed for flexibility in order to meet the diverse needs of the nuclear reaction data centers. It was originally conceived for the exchange of neutron data and was developed through discussions among personnel from centers situated in Saclay, Vienna, Livermore and Brookhaven. It was accepted as the official exchange format of the neutron data centers at Saclay, Vienna, Brookhaven and Obninsk, at a meeting held in November 1969.3 As a result of two meetings held in 1975 and 1976 and attended by several charged-particle data centers, the format was further developed and adapted to cover all nuclear reaction data. The exchange format should not be confused with a center-to-user format. Although users may obtain data from the centers in the EXFOR format, other center-to-user formats have been developed to meet the needs of the users within each center's own sphere of responsibility. The EXFOR format, as outlined, allows a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in a format: l that is machine-readable (for checking and indicating possible errors); l that can be read by personnel (for passing judgment on and correcting errors). The data presently included in the EXFOR exchange file include: a complete compilation of experimental neutron-induced reaction data, a selected compilation of charged-particle-induced reaction data, a selected compilation of photon-induced reaction data.

MCLANE,V.; NUCLEAR DATA CENTER NETWORK

2000-05-19

50

Real time observation of strand exchange reaction with high spatiotemporal resolution  

PubMed Central

RecA binds to single stranded (ss) DNA to form a helical filament that catalyzes strand exchange with a homologous double stranded (ds) DNA. The study of strand exchange in ensemble assays is limited by the diffusion limited homology search process which masks the subsequent strand exchange reaction. We developed a single molecule fluorescence assay with a few basepair and milliseconds resolution which can separate initial docking from the subsequent propagation of joint molecule formation. Our data suggests that propagation occurs in 3 bp increments with destabilization of the incoming dsDNA and concomitant pairing with the reference ssDNA. Unexpectedly, we discovered the formation of a dynamic complex between RecA and the displaced DNA that remains bound transiently after joint molecule formation. This finding could have important implications for the irreversibility of strand exchange. Our model for strand exchange links structural models of RecA to its catalytic function.

Ragunathan, Kaushik; Joo, Chirlmin; Ha, Taekjip

2011-01-01

51

Deuterium isotope exchange reaction between hydrogen and water over polyester-supported platinum catalysts  

SciTech Connect

Deuterium transfer between hydrogen and water over polyester-supported platinum has been found to follow a two-step process, namely, an initial fast step followed by a slower one. The faster exchange step was more susceptible to water poisoning while the other step continued to be active for H/D exchange reaction during prolonged contact with liquid water. The results are in agreement with the existence of heterogeneous metal sites with varying degrees of catalytic activity and support the mechanism whereby the chemisorption of both the water and hydrogen molecules at metal sites leads to the deuterium exchange process.

Gupta, N.M.; Mishra, K.; Belapurkar, A.D.; Rama Rao, K.V.S.; Iyer, R.M. (Bhabha Atomic Research Centre, Bombay (India))

1990-02-01

52

Charge exchange and chemical reactions with trapped Th{sup 3+}  

SciTech Connect

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

Churchill, L. R.; DePalatis, M. V.; Chapman, M. S. [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430 (United States)

2011-01-15

53

ION EXCHANGE APPLIED TO RECOVERY OF URANIUM FROM SPRINGFIELDS CALCIUM FLUORIDE REACTION SLAG  

Microsoft Academic Search

Uraniferous liquor obtained by leaching Springfields' calcium fluoride ; reaction slag with 10% sulfuric acid containing manganese dioxide oxidizing agent ; was stripped of uranium by single column and multiple column ion exchange ; operations. The work was done on a laboratory scale using Dowex-1, a strong-base ; resin, in the nitrate form, which absorbs uranium as an anionic sulfate

Ware

1953-01-01

54

Carbon Dioxide Exchange at the Air–Sea Interface: Flux Augmentation by Chemical Reaction  

Microsoft Academic Search

Numerical results for typical ocean conditions indicate that for film thicknesses less than, say, 400tz. oceanic exchange is not influenced by the hydration\\/dehydration reactions of dissolved carbon dioxide. This conclusion is in substantial agreement with the approximate analysis of Bolin [1960]. However, if suitable catalysts are present in the ocean (there is recent evidence to suggest that this may be

J. A. Quinn; N. C. Otto

1971-01-01

55

Isotope Exchange Rates. Iv. The Homogeneous Reaction Between Methane and Deuterium.  

National Technical Information Service (NTIS)

The rate of exchange of deuterium for hydrogen in the homogeneous gas-phase reaction between D2 and CH4 (highly diluted in argon) was measured behind reflected shocks in a single-pulse shock tube of the 'magic hole' design. The studies covered the tempera...

W. S. Watt P. Borrell D. Lewis S. H. Bauer

1965-01-01

56

Elastic scattering and charge exchange reaction studies with (sup 6)He, (sup 10,11)Be.  

National Technical Information Service (NTIS)

The elastic scattering and charge exchange reaction of (sup 6)He, (sup 10,11)Be secondary beams on proton and (sup 12)C targets have been measured. The combined use of SISSI and SPEG allowed to obtain very good quality data in terms of energy and angular ...

P. Roussel-Chomaz M. D. Cortina-Gil W. Mittig J. M. Casandjian M. Chartier

1995-01-01

57

Fast Neutral Generation by Charge Exchange Reaction and Its Effect on Neutron Production Rate in Inertial Electrostatic Confinement Fusion Systems  

SciTech Connect

Fast neutral generation by charge exchange reaction in inertial electrostatic confinement plasmas is studied by solving the Poisson equation and the Boltzmann equation for fast neutrals. Fusion reactions carried by the charge exchange fast neutrals become appreciable compared with ion-background fusion reaction. It is shown that the fusion reaction between fast neutral and background gas is sensitively affected by experimental parameters (grid voltage, background gas pressure) and ion distribution function.

Yoshinaga, S.; Matsuura, H.; Nakao, Y.; Kudo, K. [Kyushu University (Japan)

2005-05-15

58

Kinetic study on the reaction between CO2-CO and wustite using the isotope exchange method  

NASA Astrophysics Data System (ADS)

To investigate the reaction between CO2-CO and wustite using the isotope exchange method at 1073, 1173, 1273, and 1373 K, the experiment apparatus was designed to simulate the fluidized bed. The chemical rate constant was estimated by considering the effect of gas phase mass transfer on the reaction. It is found that the chemical rate constant is inversely decreased with the increase in the ratio of CO2/CO by volume. The activation energy of reaction is in a linear relationship with the ratio of CO2/CO by volume, and the average activation energy is 155.37 kJ/mol.

Zhang, Teng; Hu, Xiao-jun; Chou, Kuo-Chih

2013-02-01

59

Incorporation of monomethylethanolamine into phosphatidylcholine by way of an exchange reaction followed by methylation  

SciTech Connect

Recent evidence by Datko and Mudd indicates that phosphatidylcholine (PC) may be synthesized by methylation of phosphatidylmonomethyl-ethanolamine (PMME), but perhaps not by utilization of phosphatidylethanolamine (PE) as a source of PMME. They provided evidence that a CDP derivative of monomethylethanolamine (MME) might be the source of the headgroup. Another possibility is incorporation of MME by an exchange reaction. We tested this by incubating MME with ER from castor bean endosperm and radiolabeled S- adenosylmethionine under conditions which would allow incorporation of the headgroup and methylation to PC. Under these conditions the reaction proceeded, with radiolabel appearing in both PC and phosphatidyldimethylethanolamine. Neither ethanolamine nor L-serine, both of which are known to undergo exchange reactions, yielded PC under the same conditions.

Moore, T.S. Jr. (Louisiana State Univ., Baton Rouge (USA))

1989-04-01

60

Chemical surface modification of self-assembled monolayers by radical nitroxide exchange reactions.  

PubMed

This article describes the application of nitroxide exchange reactions of surface-bound alkoxyamines as a tool for reversible chemical modification of self-assembled monolayers (SAMs). This approach is based on radical chemistry, which allows for introduction of various functional groups and can be used to reversibly introduce functionalities at surfaces. To investigate the scope of this surface chemistry, alkoxyamines with different functionalities were synthesized and were then applied to the immobilization of, for example, dyes, sugars, or biotin. Surface analysis was carried out by contact angle, X-ray photoelectron spectroscopy, and fluorescence microscopy measurements. The results show that this reaction is highly efficient, reversible, and mild and allows for immobilization of various sensitive functional groups. In addition, Langmuir-Blodgett lithography was used to generate structured SAMs. Site-selective immobilization of a fluorescent dye could be achieved by nitroxide exchange reactions. PMID:21732441

Wagner, Hendrik; Brinks, Marion K; Hirtz, Michael; Schäfer, Andreas; Chi, Lifeng; Studer, Armido

2011-07-05

61

Adenosine triphosphate-pyrophosphate isotopic exchange reaction: a tool for determination of tryptophan  

SciTech Connect

Quantitative determination of tryptophan at the picomole level is described, using the ATP-(/sup 32/P)PPi isotopic exchange reaction catalyzed by tryptophanyl-tRNA synthetase. Sensitivity limits of 500 fmol were obtained. The presence of other amino acids at a 1000-fold excess over tryptophan did not interfere significantly with the quantitative determination of tryptophan. The specificity of the reaction was checked using five tryptophan analogs. These analogs did not prevent the determination of tryptophan when present in the same concentration range as tryptophan. When sensitive determination of a single amino acid is needed, the ATP-(/sup 32/P)PPi exchange reaction catalyzed by aminoacyl-tRNA synthetases is suggested as a general method and as an alternative to HPLC procedures.

Trezeguet, V.; Labouesse, B.

1986-05-01

62

Surface exchange reactions and fast grain boundary diffusion in polycrystalline materials: Application of a spherical grain model  

Microsoft Academic Search

Laplace transforms of the solution functions to the diffusion equations for surface exchange reactions and fast grain boundary diffusion in polycrystalline materials of finite thickness have been derived by applying a spherical grain model. Diffusion profiles have been calculated for semi-infinite diffusion systems as well as thin films by application of numerical Laplace inversion. The surface exchange reaction at the

W. Preis; W. Sitte

2005-01-01

63

Kinetics of sulfur isotope exchange between aqueous sulfide and thiosulfate involving intra- and intermolecular reactions at hydrothermal conditions  

Microsoft Academic Search

Sulfur isotope exchange between sulfide (H2S) and thiosulfate (HSSO3H) can be described by the general rate law for a two-compound system (X and AB) with three exchangeable atoms (X, A, and B) proposed by [X. Chu, H. Ohmoto, Kinetics of isotope exchange reactions involving intra- and intermolecular reactions: I. Rate law for a system with two chemical compounds and three

Xuelei Chu; Hiroshi Ohmoto; David R. Cole

2004-01-01

64

The steady-state kinetics of isotope exchange for one substrate-one product enzymic reactions  

PubMed Central

Steady-state kinetic equations for isotope exchange are derived for a number of one substrate–one product enzymic mechanisms in which two molecules of substrate or product can be combined with an enzyme molecule at the one time (e.g. allosteric mechanisms). The usual assumption, that the radioactive material is distributed among the substrate and product components according to a first-order law, is not valid. One can recognize whether isotope-exchange kinetics of an enzyme reaction follows first-order behaviour by using various initial concentrations of the labelled substance added to a mixture.

Darvey, Ivan G.

1973-01-01

65

Cl/F-exchange reaction in COCl 2/SbF 5 system: A theoretical investigation  

NASA Astrophysics Data System (ADS)

The mechanism and kinetic of a Cl/F-exchange SbF 5-mediated reaction are studied for halocarbonyl COCl 2 by means of theoretical calculations at the B3LYP level. Two energetic pathways are described in which antimony containing four-centre transition states are localized. The lowest energy barrier of 19.5 kcal/mol corresponds to a transition state in which the formally 16-valence electron triatomic ClCO + species is linked to hexacoordinated SbF 5Cl - anion. The rate constant for this Cl/F-exchange reaction is predicted by transition state theory and evaluated at kTST = 2.2 × 10 -3 s -1 when T = 293 K.

Bachmann, Christian; Frapper, Gilles

2008-05-01

66

On the interaction of isotopic exchange processes with photochemical reactions in atmospheric oxides of nitrogen  

Microsoft Academic Search

Gas-phase isotopic exchange between NO and NO2 enriches the heavier N-15 isotope in the more oxidized form. In the atmosphere the concentration of both gases, NO and NO2, is controlled during daytime by the Leighton relationship through the oxidation of NO with O3 and the photolytic reaction of NO2 to NO. For atmospheric concentrations (e.g., NO(x), about 10 ppb), isotopic

H. D. Freyer; D. Kley; A. Volz-Thomas; K. Kobel

1993-01-01

67

Charge exchange reaction of the neutron-halo nucleus 11Li  

NASA Astrophysics Data System (ADS)

Charge exchange reactions of the 11Li nucleus have been measured by means of the inverse kinematics on proton and deuteron targets at 63 A MeV. The isobaric analog state of the 11Li nucleus has been found at Ex(11Be) = 21.14 +/- 0.03 MeV with the width ? = 0.25 +0.2-0.1 MeV. Neutron halo effects and configuration of halo nucleons are discussed.

Shimoura, S.; Teranishi, T.; Ando, Y.; Hirai, M.; Iwasa, N.; Kikuchi, T.; Moriya, S.; Motobayashi, T.; Murakami, T.; Nakamura, T.; Nishio, T.; Sakurai, H.; Uchibori, T.; Wabanabe, Y.; Yanagisawa, Y.; Ishihara, M.

1997-02-01

68

DETECTION OF BIOTIN BASED ON AN EXCHANGE REACTION WITH AVIDIN-HABA COMPLEX USING CAPILLARY ELECTROPHORESIS  

Microsoft Academic Search

The detection of biotin at lower concentration in UV-visible region is difficult because of the low adsorption coefficients. In order to improve this problem, a new migration system, using an exchange reaction between biotin injected and avidin- HABA (2[4’-hydroxyazobenzene] benzoic acid) complex added in running buffer, was developed in the capillary electrophoresis (CE). The use of combination of zwitterionic surfactant

Shunitz Tanaka; Masanobu Mori; Kokoro Kodama; Wenzhi Hu

2000-01-01

69

EXFOR basics: A short guide to the nuclear reaction data exchange format  

SciTech Connect

This manual is intended as a guide to users of nuclear reaction data compiled in the EXFOR format, and is not intended as a complete guide to the EXFOR System. EXFOR is the exchange format designed to allow transmission of nuclear data between the Nuclear Reaction Data Centers. In addition to storing the data and its` bibliographic information, experimental information, including source of uncertainties, is also compiled. The status and history of the data set is also included, e.g., the source of the data, any updates which have been made, and correlations to other data sets. EXFOR is designed for flexibility in order to meet the diverse needs of the nuclear data compilation centers. This format should not be confused with a center-to-user format. Although users may obtain data from the centers in the EXFOR format, other center-to-user formats have been developed to meet the needs of the users within each center`s own sphere of responsibility. The exchange format, as outlined, allows a large variety of numerical data tables with explanatory and bibliographic information to be transmitted in an easily machine-readable format (for checking and indicating possible errors) and a format that can be read by personnel (for passing judgment on and correcting any errors indicated by the machine). The data presently included in the EXFOR exchange include: a complete compilation of experimental neutron-induced reaction data, a selected compilation of charged-particle induced reaction data, a selected compilation of photon-induced reaction data.

McLane, V.

1996-07-01

70

Reaction mechanism and nuclear correlations study by low energy pion double charge exchange. [25 to 65 MeV  

Microsoft Academic Search

In pion double-charge-exchange (DCX) reactions, a positive (negative) pion is incident on a nucleus and a negative (positive) pion emerges. These reactions are of fundamental interest since the process must involve at least two nucleons in order to conserve charge. Although two nucleon processes are present in many reactions they are usually masked by the dominant single nucleon processes. DCX

Weinfeld

1993-01-01

71

Towards rotationally state-resolved differential cross sections for the hydrogen exchange reaction  

SciTech Connect

The hydrogen exchange reaction H + H{sub 2} {yields} H{sub 2} + H (and its isotopic variants) plays a pivotal role in chemical reaction dynamics. It is the only chemical reaction for which fully converged quantum scattering calculations have been carried out using a potential energy surface which is considered to be chemically accurate. To improve our ability to test the theory, a `perfect experiment`, measuring differential cross sections with complete specification of the reactant and product states, is called for. In this thesis, the design of an experiment is described that aims at achieving this goal for the D + H{sub 2} reaction. A crossed molecular beam arrangement is used, in which a photolytic D atom beam is crossed by a pulsed beam of H{sub 2} molecules. DH molecules formed in the D + H{sub 2} reaction are state-specifically ionized using Doppler-free (2+1) Resonance-Enhanced Multi-Photon Ionization (REMPI) and detected using a Position-sensitive microchannel plate detector. This detection technique has an unprecedented single shot detection sensitivity of 6.8 10{sup 3} molecules/cc. This thesis does not contain experimental results for the D + H{sub 2} reaction yet, but progress that has been made towards achieving this goal is reported. In addition, results are reported for a study of the Rydberg spectroscopy of the water molecule.

Vrakking, M.J.J.

1992-11-01

72

Towards rotationally state-resolved differential cross sections for the hydrogen exchange reaction  

SciTech Connect

The hydrogen exchange reaction H + H[sub 2] [yields] H[sub 2] + H (and its isotopic variants) plays a pivotal role in chemical reaction dynamics. It is the only chemical reaction for which fully converged quantum scattering calculations have been carried out using a potential energy surface which is considered to be chemically accurate. To improve our ability to test the theory, a 'perfect experiment', measuring differential cross sections with complete specification of the reactant and product states, is called for. In this thesis, the design of an experiment is described that aims at achieving this goal for the D + H[sub 2] reaction. A crossed molecular beam arrangement is used, in which a photolytic D atom beam is crossed by a pulsed beam of H[sub 2] molecules. DH molecules formed in the D + H[sub 2] reaction are state-specifically ionized using Doppler-free (2+1) Resonance-Enhanced Multi-Photon Ionization (REMPI) and detected using a Position-sensitive microchannel plate detector. This detection technique has an unprecedented single shot detection sensitivity of 6.8 10[sup 3] molecules/cc. This thesis does not contain experimental results for the D + H[sub 2] reaction yet, but progress that has been made towards achieving this goal is reported. In addition, results are reported for a study of the Rydberg spectroscopy of the water molecule.

Vrakking, M.J.J.

1992-11-01

73

Detection of the strand exchange reaction using DNAzyme and Thermotoga maritima recombinase A.  

PubMed

We have designed multiple detection systems for the DNA strand exchange process. Thermostable Thermotoga maritima recombinase A (TmRecA), a core protein in homologous recombination, and DNAzyme, a catalytic DNA that can cleave a specific DNA sequence, are introduced in this work. In a colorimetric method, gold nanoparticles (AuNPs) modified with complementary DNAs (cDNAs) were assembled by annealing. Aggregated AuNPs were then separated irreversibly by TmRecA and DNAzyme, leading to a distinct color change in the particles from purple to red. For the case of fluorometric detection, fluorescein isothiocyanate (FITC)-labeled DNA as a fluorophore and black hole quencher 1 (BHQ1)-labeled DNA as a quencher were used; successful strand exchange was clearly detected by variations in fluorescence intensity. In addition, alterations in the impedance of a gold electrode with immobilized DNA were employed to monitor the regular exchange of DNA strands. All three methods provided sufficient evidence of efficient strand exchange reactions and have great potential for applications in the monitoring of recombination, discovery of new DNAzymes, detection of DNAzymes, and measurement of other protein activities. PMID:22178915

Jo, Hunho; Lee, Seonghwan; Min, Kyoungin; Ban, Changill

2011-11-16

74

The analysis of reactions {pi}N {yields} two mesons + N within reggeon exchanges. Basic formulas for fit  

SciTech Connect

We present technical aspects of the fitting procedure given in the paper by V.V. Anisovich and A.V. Sarantsev 'The analysis of reactions {pi}N {yields} two mesons + N within reggeon exchanges. Fit and results.'

Anisovich, V. V., E-mail: anisovic@thd.pnpi.spb.ru; Sarantsev, A. V. [Russian Academy of Sciences, Petersburg Nuclear Physics Institute (Russian Federation)

2009-11-15

75

Controlling plasmonic "hot spots" in nanoparticle assemblies using ligand place-exchange reactions  

NASA Astrophysics Data System (ADS)

This thesis describes the 1) selective attachment of Au nanoparticles (NPs) to the edges of Au nanoplates via ligand place-exchange reactions, 2) preparation of coupled Au nanoplates via ligand place-exchange reactions, 3) attachment of Au NPs to Au nanorods via ligand place-exchange reactions, 4) study of the dynamics of ligand place-exchange reactions on Au nanoplates, 5) study of the changes in the optical properties of Au nanoplates upon attachment of Au NPs by observing the shift in the localized surface plasmon resonance (LSPR) band, and 6) study of the surface-enhanced Raman spectroscopy (SERS) enhancement of analyte molecules located in the "hot-spots" of coupled Au nanoplate-Au NP structures. We regio-selectively attached 20 nm Au NPs to Au nanoplates by first assembling hexanethiol (HT) onto Au nanoplates, then exchanging HT with 4-aminothiophenol (4-ATP) using different reaction times, and finally electrostatically attaching the negatively-charged Au NPs to the positively-charged 4-ATP ligands bound to the Au nanoplates. We prepared nanoplate-NP assemblies with 100% of the NPs attached to vertex sites or 100% attached to vertex and edge sites using 1 h and 2 h exchange times, respectively. The location and number of bound Au NPs to the nanoplates as a function of exchange time provided information about the mechanism of the ligand place-exchange reaction on the Au nanoplate surface. Ligand place-exchange starts from the vertex sites, then proceeds at the edge sites and finally occurs at smooth terrace sites for longer times. Direct exchange at terraces is possible but the data suggests it occurs mostly through lateral migration of the 4-ATP ligands from vertex/edge sites to the terrace. The data also suggests that phase segregation of 4-ATP ligands and HT ligands occurs on the terrace sites for longer times. The ligand place-exchange strategy also leads to interesting coupled Au nanoplate-Au nanoplate and Au nanorod-Au NP assemblies. The optical properties of the Au nanoplate-Au NP assemblies were studied by monitoring the shift in the LSPR band of the Au nanoplates upon attachment of Au NPs and by measuring the SERS enhancement of the 4-ATP linker. The LSPR band red shifted about 1 nm upon attachment of each Au NP at the vertex and edge sites. The estimated shift is about 0.1 to 0.6 nm per Au NP for those attached to the terraces sites, where the shift is larger for Au NPs attached to outer terrace sites close to the edge and smaller for the inner terrace sites. Au nanoplate-Au NP assemblies with 100% of the NPs attached on the vertex sites of the nanoplates showed the largest enhancement relative to the Au nanoplates. The intensity was similar to the assemblies with many more NPs, but relatively fewer at the vertex/edge sites, indicating that the "hottest spot" for enhancement is located in the interparticle junction between the vertex of the nanoplate and the attached NP. The relative enhancement of the Au nanoplate-Au NP couple relative to the Au nanoplate alone was about 11 on a per Au NP basis. Fundamentally, the results suggest that a small number of "hottest spots" in the laser beam area dominate the Raman enhancement signal and practically, the nanoplate-NP coupling approach controllably at the vertex/edge sites can be very useful for amplifying the detection of analyte down to the single molecule level. This research provides a simple approach for the preparation of various nanostructure assemblies with high accuracy and reproducibility. At the same time, it can potentially be used to control the location of analyte for LSPR and SERS sensing. Another important contribution of this study is the direct evidence for the mechanism and kinetics of the ligand place-exchange reaction on the nanoplate surfaces, which can be useful for controlling NP attachment to other structures as well.

Bao, Lanlan

76

The CH + CO reaction: Rate coefficient for carbon atom exchange at 294 K  

SciTech Connect

A fast-flow reactor equipped with isotope-specific laser-excited fluorescence detection of CH radicals has been used to study carbon atom exchange in the reaction between CH and CO at 294 K and 2 Torr of total pressure. The rate coefficient for exchange, k{sub 3} = (2.1 {times} 0.3) {times} 10{sup {minus}12} cm{sup 3} s{sup {minus}1}, is about an order of magnitude larger than the bimolecular rate for the addition reaction, k{sub 2} = (2.7 {plus minus} 0.4) {times} 10{sup {minus}13}. High-pressure limiting bimolecular and low-pressure termolecular recombination rate coefficients of 1.1 {times} 10{sup {minus}10} cm{sup 3} s{sup {minus}1} and 4.9 {times} 10{sup {minus}30} cm{sup 6} s{sup {minus}1} are derived. The results are discussed in the context of previous work on the title reaction and on the chemistry of singlet CH{sub 2}.

Anderson, S.M.; McCurdy, K.E.; Kolb, C.E. (Aerodyne Research, Inc., Billerica, MA (USA))

1989-02-09

77

Kinetics and mechanism of ligand-exchange reactions of Cd(II) chelates  

SciTech Connect

Tetrahedral Cd(II) bis(5-thio(or seleno)pyrazole-4-carboxaldiminates) of types II and III have been synthesized for the first time. The kinetics of the degenerate ligand exchange and enantiomerization of the complexes obtained have been studied by dynamic /sup 111/Cd, /sup 77/Se, and /sup 1/H (s = 1/2) NMR. The rate of intramolecular enantiomerization (k = 1/tau) is more than an order of magnitude greater than the corresponding values for processes of degenerate ligand exchange (a second-order reaction) determined from the dynamics of the averaging of the /sup 111/Cd-/sup 77/Se and /sup 111/Cd-N=CH spin-spin coupling constants. The cleavage and formation processes of the Cd-Se and Cd-N bonds are isoenergetic (..delta.. G/sub 298//sup not equal to/ = 14.4 kcal/mole for chelate II with X = Se and R = CH/sub 2/C/sub 6/H/sub 5/). The free energies of activation of degenerate ligand exchange determined form the dynamics of the averaging of the /sup 111/Cd N=CH spin-spin coupling constant increase from 12.7 to 17.9 kcal/mole along the following series for R: C/sub 2/H/sub 5/ < Ar < CH/sub 2/C/sub 6/H/sub 5/ < t-C/sub 4/H/sub 9/ < cyclo-C/sub 6/H/sub 11/. Replacement of the sulfur atom in the chelate ring by selenium results in increases in the rates of ligand exchange. A mechanism of degenerate ligand exchange has been proposed.

Nivorozhkin, L.E.; Kalabin, G.A.; Nivorozhkin, A.L.; Valeev, R.B.; Minkin, V.I.

1987-03-01

78

Charge-exchange reaction induced by 6He and nuclear densities  

NASA Astrophysics Data System (ADS)

The charge-exchange reaction p(6He, 6Li)n is studied in reverse kinematics with a secondary 6He beam at 41.6 MeV/nucleon. The transition connecting the ground state of 6He to its isobaric analog state in 6Li has been measured and analyzed in the context of a microscopic calculation. The angular distribution is shown to be sensitive to the nuclear interaction potential and to the radii of the density distribution of 6He. It is shown that only a coherent microscopic analysis may disentangle the different contributions.

Cortina-Gil, M. D.; Pakou, A.; Alamanos, N.; Mittig, W.; Roussel-Chomaz, P.; Auger, F.; Barrette, J.; Blumenfeld, Y.; Casandjian, J. M.; Chartier, M.; Dietrich, F.; Fekou-Youmbi, V.; Fernandez, B.; Frascaria, N.; Gillibert, A.; Laurent, H.; Lepine-Szily, A.; Orr, N.; Pascalon, V.; Scarpaci, J. A.; Sida, J. L.; Suomijarvi, T.

1998-10-01

79

Neutron skin thickness of {sup 90}Zr determined by charge exchange reactions  

SciTech Connect

Charge exchange spin-dipole (SD) excitations of {sup 90}Zr are studied by the {sup 90}Zr(p,n) and {sup 90}Zr(n,p) reactions at 300 MeV. A multipole decomposition technique is employed to obtain the SD strength distributions in the cross-section spectra. For the first time, a model-independent SD sum rule value is obtained: 148{+-}12 fm{sup 2}. The neutron skin thickness of {sup 90}Zr is determined to be 0.07{+-}0.04 fm from the SD sum rule value.

Yako, K.; Sakai, H. [Department of Physics, University of Tokyo, Bunkyo, Tokyo 113-0033 (Japan); Sagawa, H. [Center for Mathematical Sciences, University of Aizu Aizu-Wakamatsu, Fukushima 965-8580 (Japan)

2006-11-15

80

Adverse tissue reactions in modular exchangeable neck implants: a report of two cases.  

PubMed

Dual-modular femoral stems with exchangeable necks theoretically allow optimization of hip joint biomechanics via selective restoration of femoral anteversion, offset, and limb length. A potential disadvantage is the possible generation of metal ions and debris by fretting and crevice corrosion at the additional stem-neck interface. We present 2 cases of early-onset adverse inflammatory tissue reactions as a result of accelerated corrosion at the stem-neck interface of a dual-modular implant, requiring subsequent revision of well-fixed components. PMID:23141863

Werner, S Douglas; Bono, James V; Nandi, Sumon; Ward, Daniel M; Talmo, Carl T

2012-11-08

81

(NH4)2S, a highly reactive molecular precursor for low temperature anion exchange reactions in nanoparticles.  

PubMed

Ammonium sulfide ((NH4)2S) exhibits high reactivity as a sulfide reagent in anion exchange reactions that transform CoO to cobalt sulfide nanoparticles (NPs). The faster diffusion of Co(2+) and O(2-) than the incoming S(2-) during the anion exchange causes a significant expansion of the NP voids. The low temperature (70 °C) anion exchange reaction produces amorphous cobalt sulfide NPs with Co?:?S ratio of ca. 3?:?4, which are converted into crystalline NPs with a major phase of cubic Co3S4 by annealing at high temperature in an organic solution. PMID:23779083

Zhang, Haitao; Solomon, Louis V; Ha, Don-Hyung; Honrao, Shreyas; Hennig, Richard G; Robinson, Richard D

2013-08-13

82

Fe-Zn exchange reaction between tetrahedrite and sphalerite in natural environments  

Microsoft Academic Search

Microprobe and fluid inclusion analyses of hydrothermal ore deposits containing the subassemblage sphalerite+ tetrahedrite-tennantite ~[(Cu, Ag)10(Fe, Zn)2(As,Sb)4S13] reveal that the Gibbs energies of the reciprocal reaction Cu10Zn2Sb4S13 + Cu10Fe2As4S13 = Cu10Fe2Sb4S13 + Cu10Zn2As4S13 and the Fe-Zn exchange reaction 1\\/2Cu10Fe2Sb4S13 + ZnS = 1\\/2Cu10Zn2Sb4S13 + FeS are within the uncertainties of the values established by Sack and Loucks (1985) and Raabe

Michael J. O'Leary; Richard O. Sack

1987-01-01

83

Weak interaction processes in supernovae: New probes using charge exchange reaction at intermediate energies  

NASA Astrophysics Data System (ADS)

Spin-isospin-flip excitations in nuclei at vanishing momentum transfer are generally referred to as Gamov-Teller (GT) transitions. They are being studied because the simplicity of the excitation makes them an ideal probe for testing nuclear structure models. In astrophysics, GT transitions provide an important input for model calculations and element formation during the explosive phase of a massive star at the end of its life-time. GT transitions in the ?- direction (also referred to as isospin lowering T< transitions) have extensively been studied through (p,n) and (3He,t) charge-exchange reactions [B.D. Anderson et al., Phys. Rev. C 36 (1987) 2195, B.D. Anderson et al., Phys. Rev. C 43 (1991) 50, J. Rapaport et al., Phys. Rev. C 24 (1981) 335, H. Akimune et al., Nucl. Phys. A 569 (1994) 245c, Y. Fujita et al., Phys. Lett. B 365 (1996) 29]. The generally good resolution allows easy extraction of the GT distribution and the total B(GT-) strength in the final nucleus. On the other hand, determination of B(GT+) strength through a charge-exchange reaction in the T> direction were mostly done with secondary neutron beams, and as such, they come with significant experimental difficulties. TRIUMF has pioneered this field in the late 80's and early 90's with a rich and highly successful (n,p) program using a several hundred MeV neutron beam from a 7Li(p,n)7Be reaction [R. Helmer, Can. J. Phys. 65 (1987) 588]. In this paper we present the (d,2He) reaction at intermediate energies as another and potentially even more powerful tool for charge-exchange reactions in the T>, resp. ?+ direction. The key issue here will be the high resolution of order 100 keV, which provides new and sometimes unexpected insight into nuclear structure phenomena. This program has been launched at the AGOR Superconducting Cyclotron Facility at the KVI Groningen. By now, it covers a wide field of physics questions ranging from few-body physics, the structure of halo-nuclei, to questions pertaining to the dynamics of supernova explosions and nuclear synthesis, and more recently to the measurements of (??) decay matrix elements and the determination of half-lives of (??) decaying nuclei.

Frekers, Dieter

2005-04-01

84

Independent control of the shape and composition of ionic nanocrystals through sequential cation exchange reactions  

SciTech Connect

Size- and shape-controlled nanocrystal growth is intensely researched for applications including electro-optic, catalytic, and medical devices. Chemical transformations such as cation exchange overcome the limitation of traditional colloidal synthesis, where the nanocrystal shape often reflects the inherent symmetry of the underlying lattice. Here we show that nanocrystals, with established synthetic protocols for high monodispersity, can be templates for independent composition control. Specifically, controlled interconversion between wurtzite CdS, chalcocite Cu2S, and rock salt PbS occurs while preserving the anisotropic dimensions unique to the as-synthesized materials. Sequential exchange reactions between the three sulfide compositions are driven by the disparate solubilites of the metal ion exchange pair in specific coordinating molecules. Starting with CdS, highly anisotropic PbS nanorods are created, which serve as an important material for studying strong 2-dimensional quantum confinement, as well as for optoelectronic applications. Furthermore, interesting nanoheterostructures of CdS|PbS are obtained by precise control over ion insertion and removal.

Luther, Joseph Matthew; Zheng, Haimei; Sadtler, Bryce; Alivisatos, A. Paul

2009-07-06

85

Phosphatidylinositol synthase of Tetrahymena: inositol isomers as substrates in phosphatidylinositol biosynthesis and headgroup exchange reactions.  

PubMed

Phosphatidylinositol (PtdIns) synthase in microsomal fractions derived from Tetrahymena vorax was studied to determine its activity requirements. The suitability of inositol isomers as substrates for the synthase and in headgroup exchange reactions also was investigated. Tetrahymena PtdIn synthase activity was optimum in the presence of 2 mM MgCl2 plus 2 mM MnCl2, a pH of 7.8, and a temperature of 30 degrees C. The enzyme retained approximately 80% of its activity after incubation at 70 degrees C for 10 min. PtdIns headgroup exchange activity was maximal in the presence of cytidine monophosphate. By following either the accumulation of radiolabeled reaction products or the loss of radiolabel from precursors, each of the inositol isomers tested appeared to serve as substrates for both the PtdIns synthase and PtdIns:inositol phosphatidyl transferase activities. In each case, myo-inositol and scyllo-inositol were the preferred substrates. The data suggest two routes for the formation of phosphatidyl-non-myo-inositols in Tetrahymena and the potential for the production of novel, non-myo-inositol-containing second messengers. PMID:17403152

Riggs, Bridget M; Lansley, Tanya A; Ryals, Phillip E

86

TraML--a standard format for exchange of selected reaction monitoring transition lists.  

PubMed

Targeted proteomics via selected reaction monitoring is a powerful mass spectrometric technique affording higher dynamic range, increased specificity and lower limits of detection than other shotgun mass spectrometry methods when applied to proteome analyses. However, it involves selective measurement of predetermined analytes, which requires more preparation in the form of selecting appropriate signatures for the proteins and peptides that are to be targeted. There is a growing number of software programs and resources for selecting optimal transitions and the instrument settings used for the detection and quantification of the targeted peptides, but the exchange of this information is hindered by a lack of a standard format. We have developed a new standardized format, called TraML, for encoding transition lists and associated metadata. In addition to introducing the TraML format, we demonstrate several implementations across the community, and provide semantic validators, extensive documentation, and multiple example instances to demonstrate correctly written documents. Widespread use of TraML will facilitate the exchange of transitions, reduce time spent handling incompatible list formats, increase the reusability of previously optimized transitions, and thus accelerate the widespread adoption of targeted proteomics via selected reaction monitoring. PMID:22159873

Deutsch, Eric W; Chambers, Matthew; Neumann, Steffen; Levander, Fredrik; Binz, Pierre-Alain; Shofstahl, Jim; Campbell, David S; Mendoza, Luis; Ovelleiro, David; Helsens, Kenny; Martens, Lennart; Aebersold, Ruedi; Moritz, Robert L; Brusniak, Mi-Youn

2011-12-12

87

State-to-state quantum dynamics of O + O2 isotope exchange reactions reveals nonstatistical behavior at atmospheric conditions  

PubMed Central

The O + O2 exchange reaction is a prerequisite for the formation of ozone in Earth’s atmosphere. We report here state-to-state differential and integral cross sections for several O + O2 isotope-exchange reactions obtained by dynamically exact quantum scattering calculations at collision energies relevant to atmospheric conditions. These reactions are shown to be highly nonstatistical, evidenced by dominant forward scattering and deviation of the integral cross section from the statistical limit. Mechanistic analyses revealed that the nonstatistical channel is facilitated by short-lived osculating resonances. The theoretical results provided an in-depth interpretation of a recent molecular beam experiment of the exchange reaction and shed light on the initial step of ozone recombination.

Sun, Zhigang; Liu, Lan; Lin, Shi Ying; Schinke, Reinhard; Guo, Hua; Zhang, Dong H.

2010-01-01

88

Time-dependent wave packet studies on the Cl + HCl hydrogen exchange reaction.  

PubMed

The initiation of the hydrogen exchange reaction Cl((2)P)+HCl --> ClH+Cl((2)P) by excitation of the HCl molecular stretch to v=2 is studied for total angular momentum quantum number J=(1)/(2) and both even and odd parity. The calculations were performed using a time-dependent propagation from an initial quasi-bound state and employed all three relevant potential energy surfaces and the nonadiabatic couplings between them. Coriolis and spin-orbit coupling were also taken into account. The electronic and HCl rotational distributions of the products in both dissociation channels are analyzed, and the results are interpreted using features of the potential energy surfaces. PMID:16671664

Vissers, Gé W M; McCoy, Anne B

2006-05-11

89

Metastable structures and isotope exchange reactions in polyoxometalate ions provide a molecular view of oxide dissolution  

NASA Astrophysics Data System (ADS)

Reactions involving minerals and glasses in water are slow and difficult to probe spectroscopically but are fundamental to the performance of oxide materials in green technologies such as automotive thermoelectric power generation, CO2 capture and storage and water-oxidation catalysis; these must be made from geochemically common elements and operate in hydrous environments. Polyoxometalate ions (POMs) have structures similar to condensed oxide phases and can be used as molecular models of the oxide/water interface. Oxygen atoms in POM exchange isotopes at different rates, but, at present, there is no basis for predicting how the coordination environment and metal substitution influences rates and mechanisms. Here we identify low-energy metastable configurations that form from the breaking of weak bonds between metals and underlying highly coordinated oxygen atoms, followed by facile hydroxide, hydronium or water addition. The mediation of oxygen exchange by these stuffed structures suggests a new view of the relationship between structure and reactivity at the oxide/solution interface.

Rustad, James R.; Casey, William H.

2012-03-01

90

Effect of ADP on Na+-Na+ Exchange Reaction Kinetics of Na,K-ATPase  

PubMed Central

The whole-cell voltage-clamp technique was used in rat cardiac myocytes to investigate the kinetics of ADP binding to phosphorylated states of Na,K-ATPase and its effects on presteady-state Na+-dependent charge movements by this enzyme. Ouabain-sensitive transient currents generated by Na,K-ATPase functioning in electroneutral Na+-Na+ exchange mode were measured at 23°C with pipette ADP concentrations ([ADP]) of up to 4.3 mM and extracellular Na+ concentrations ([Na]o) between 36 and 145 mM at membrane potentials (VM) from ?160 to +80 mV. Analysis of charge-VM curves showed that the midpoint potential of charge distribution was shifted toward more positive VM both by increasing [ADP] at constant Na+o and by increasing [Na]o at constant ADP. The total quantity of mobile charge, on the other hand, was found to be independent of changes in [ADP] or [Na]o. The presence of ADP increased the apparent rate constant for current relaxation at hyperpolarizing VM but decreased it at depolarizing VM as compared to control (no added ADP), an indication that ADP binding facilitates backward reaction steps during Na+-Na+ exchange while slowing forward reactions. Data analysis using a pseudo three-state model yielded an apparent Kd of ?6 mM for ADP binding to and release from the Na,K-ATPase phosphoenzyme; a value of 130 s?1 for k2, a rate constant that groups Na+ deocclusion/release and the enzyme conformational transition E1?P ? E2-P; a value of 162 s?1M?1 for k?2, a lumped second-order VM-independent rate constant describing the reverse reactions; and a Hill coefficient of ?1 for Na+o binding to E2-P. The results are consistent with electroneutral release of ADP before Na+ is deoccluded and released through an ion well. The same approach can be used to study additional charge-moving reactions and associated electrically silent steps of the Na,K-pump and other transporters.

Peluffo, R. Daniel

2004-01-01

91

N/D exchange reaction between CHCl sub 3 and D sub 2 O in two-liquid-phase system  

SciTech Connect

The kinetics of hydrogen isotope exchange between CHCl{sub 3} and D{sub 2}O has been studied by using a system which is composed of 2 liquid phases, a chloroform phase and an aqueous phase. The area of the interface between these two phases was kept constant (5.7 {times} 10{sup {minus}3} m{sup 2}) during the reaction, where the reaction may be controlled by the interfacial transfer of chloroform. The isotopic content of chloroform in the chloroform phase was determined by an infrared absorption measurement. After the reaction, disappearance of deuteroxide ion was observed, which is caused by the chloroform hydrolysis reaction. The experimental results are reasonably explained on the basis of the model in which the reaction process is assumed to be composed of 2 steps: interfacial transfer of chloroform from the chloroform phase to the aqueous phase or vice versa, and the hydrogen isotope exchange reaction between CHCl{sub 3} and D{sub 2}O in the aqueous phase. The rate constants for the interfacial transfer of chloroform and for the exchange reaction in the aqueous phase at 26.0{degree}c were 0.107 {plus minus}0.003 m{sup {minus}2} s{sup {minus}1} and 0.231 {plus minus}0.013 L mol{sup {minus}1} s{sup {minus}1}, respectively.

Iwasaki, Matae; Sakka, Tetsuo; Ohashi, Shigeyuki; Matsushita, Hiroshi (Kyoto Univ. (Japan)); Yokoyama, Atsushi; Suzuki, Kazuya (Japan Atomic Energy Research Institute, Ibaraki (Japan))

1989-06-29

92

Carbon cations and silicon atoms in the ISM: modelling their charge exchange reaction  

NASA Astrophysics Data System (ADS)

The time-dependent rate coefficients for the charge exchange reaction C+ + Si ? C + Si+ for doublet and quartet states have been determined with ab initio quantum calculations coupled with a non-adiabatic transition model based on a simple Landau-Zener picture. This reaction plays a key role in determining the abundances of C, Si and their ions, in the interstellar medium since these abundances affect the fine-structure cooling and hence the star formation rates. We also provide additional calculations to evaluate the differences between the gas evolution as obtained by using the empirical rate estimates found in the current literature and the calculations presented in this work which are based on our more realistic evaluation of such rates from ab initio transition probabilities. We shall thus show here that the new rates yield important differences for metal-rich environments where T < 104 K and the ultraviolet flux is very small, while becoming less important at higher T values and higher photon fluxes.

Satta, M.; Grassi, T.; Gianturco, F. A.

2013-02-01

93

Neutrino and antineutrino charge-exchange reactions on {sup 12}C  

SciTech Connect

We extend the formalism of weak interaction processes, obtaining new expressions for the transition rates, which greatly facilitate numerical calculations, for both neutrino-nucleus reactions and muon capture. Explicit violation of the conserved vector current hypothesis by the Coulomb field, as well as development of a sum-rule approach for inclusive cross sections, has been worked out. We have done a thorough study of exclusive (ground-state) properties of {sup 12}B and {sup 12}N within the projected quasiparticle random phase approximation (PQRPA). Good agreement with experimental data achieved in this way put into evidence the limitations of the standard RPA and QRPA models, which come from the inability of the RPA to open the p{sub 3/2} shell and from the nonconservation of the number of particles in the QRPA. The inclusive neutrino/antineutrino ({nu}/{nu}-tilde) reactions {sup 12}C({nu},e{sup -}){sup 12}N and {sup 12}C({nu}-tilde,e{sup +}){sup 12}B are calculated within both the PQRPA and the relativistic QRPA. It is found that (i) the magnitudes of the resulting cross sections are close to the sum-rule limit at low energy, but significantly smaller than this limit at high energies, for both {nu} and {nu}-tilde; (ii) they increase steadily when the size of the configuration space is augmented, particularly for {nu}/{nu}-tilde energies >200 MeV; and (iii) they converge for sufficiently large configuration space and final-state spin. The quasi-elastic {sup 12}C({nu},{mu}{sup -}){sup 12}N cross section recently measured in the MiniBooNE experiment is briefly discussed. We study the decomposition of the inclusive cross section based on the degree of forbiddenness of different multipoles. A few words are dedicated to the {nu}/{nu}-tilde-{sup 12}C charge-exchange reactions related to astrophysical applications.

Samana, A. R. [Department of Physics, Texas A and M University Commerce, P.O. Box 3011 Commerce, Texas 75429 (United States); Departamento de Ciencias Exactas e Tecnologicas, Universidade Estadual de Santa Cruz, CEP 45662-000, Ilheus, Bahia-BA (Brazil); Krmpotic, F. [Instituto de Fisica La Plata, CONICET, Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, 1900 La Plata (Argentina); Paar, N. [Physics Department, Faculty of Science, University of Zagreb, Bijenicka 32, HR-10002 Zagreb (Croatia); Bertulani, C. A. [Department of Physics, Texas A and M University Commerce, P.O. Box 3011 Commerce, Texas 75429 (United States)

2011-02-15

94

Optical beam deflection approach for studying ion-exchange reactions occurring at a single ion-exchange resin particle  

Microsoft Academic Search

The optical beam deflection method was applied for exploring chemical reactions occurring at a single particle. A probe beam from a diode laser was introduced into a microscope, and focused to the vicinity of a particle. When a chemical reaction occurs at the surface of the particle, concentration gradients exist in the vicinity of the particle due to the diffusion

Xing-Zheng Wu; Yumiko Tsuji; Norio Teramae

2007-01-01

95

One- and two-dimensional chemical exchange nuclear magnetic resonance studies of the creatine kinase catalyzed reaction  

SciTech Connect

The equilibrium chemical exchange dynamics of the creatine kinase enzyme system were studied by one- and two-dimensional {sup 31}P NMR techniques. Pseudo-first-order reaction rate constants were measured by the saturation transfer method under an array of experimental conditions of pH and temperature. Quantitative one-dimensional spectra were collected under the same conditions in order to calculate the forward and reverse reaction rates, the K{sub eq}, the hydrogen ion stoichiometry, and the standard thermodynamic functions. The pure absorption mode in four quadrant two-dimensional chemical exchange experiment was employed so that the complete kinetic matrix showing all of the chemical exchange process could be realized.

Gober, J.R.

1988-01-01

96

Classical Dynamics Studies of the Chlorine' + Hydrogen Chloride(v, j) Exchange Reaction Over AN Extended Collision Energy Range  

Microsoft Academic Search

We have simulated the dynamics of the Cl ^' + HCl(v = 1,j = 3), Cl ^' + HCl(v = 0,j = 1), and Cl ^' + HCl(v = 1,j = 0) exchange reactions over the collision energy range 0-1.5 eV using quasi classical trajectory (QCT) calculations. The results show that the reactivity oscillations do not survive in three dimensions,

John Paul Fulmer

1993-01-01

97

Photochemical Synthesis and Ligand Exchange Reactions of Ru(CO)[subscript 4] (Eta[superscript 2]-Alkene) Compounds  

ERIC Educational Resources Information Center

The photochemical synthesis and subsequent ligand exchange reactions of Ru(CO)[subscript 4] (eta[superscript2]-alkene) compounds has provided a novel experiment for upper-level inorganic chemistry laboratory courses. The experiment is designed to provide a system in which the changing electronic properties of the alkene ligands could be easily…

Cooke, Jason; Berry, David E.; Fawkes, Kelli L.

2007-01-01

98

Detoxification of Wheat Straw Hydrolysis in Formic Acid Reaction System by D311 Ion-exchange Resin  

Microsoft Academic Search

Formic acid hydrolysis is widely used in lignocellulose pretreatment. However, formic acid hydrolysis wheat straw cannot be directly used as a fermentation substrate owing to various fermentation inhibitors, especially the formic acid in reaction system and released during pretreatment. Study found treatment of wheat straw hydrolysate with D311 ion-exchange resin had a good result on reduction formic acid. We investigated

Junping Zhuang; Lu Lin; Chunsheng Pang; Zhen Wu; Ying Liu

2010-01-01

99

Infrared study of H\\/D isotope exchange reaction of alkanes and Brønsted acidic hydroxyl groups on FER zeolite  

Microsoft Academic Search

H\\/D isotope exchange between n-alkanes and the acidic OD groups in ferrierite was observed by infrared spectroscopy. The real activation energies were estimated\\u000a by adding the heats of adsorption to the apparent activation energies, resulting in almost the same value for all n-alkanes. The transition state for the reaction is discussed.

Byongjin Lee; Junko N. Kondo; Fumitaka Wakabayashi; Kazunari Domen

1999-01-01

100

Photochemical Synthesis and Ligand Exchange Reactions of Ru(CO)[subscript 4] (Eta[superscript 2]-Alkene) Compounds  

ERIC Educational Resources Information Center

|The photochemical synthesis and subsequent ligand exchange reactions of Ru(CO)[subscript 4] (eta[superscript2]-alkene) compounds has provided a novel experiment for upper-level inorganic chemistry laboratory courses. The experiment is designed to provide a system in which the changing electronic properties of the alkene ligands could be easily…

Cooke, Jason; Berry, David E.; Fawkes, Kelli L.

2007-01-01

101

SALT EFFECTS ON THE RATE OF EXCHANGE OF THALLOUS AND THALLIC IONS IN WATER AND HEAVY WATER. PART 2. THE EFFECT OF CHLORIDE ON THE SOLVENT REACTION  

Microsoft Academic Search

The chloride inhibition and catalysis of the thallousthallic electron-; exchange reaction in concentrated perchlorate solutions was measured in water and ; in heavy water. In the range of chloride ion concentration in which this ion is ; a catalyst for the exchange reaction, there was no kinetic deuterium isotope ; effect. From spectroscopic observations it was concluded that chloride and

S. Gilks; T. E. Rogers; Gwyneth M. Waind

1961-01-01

102

Spectrophotometric Determination of Captopril and Penicillamine through the Use of Ligand Exchange Complexation Reactions  

PubMed Central

Two spectrophotmetric methods based on combined redox - ligand exchange reactions were developed for the determination of captopril and penicillamine in pure form and in their dosage forms. The first method is based on attenuating the absorbance of a ternary complex: silver (I) - bromopyrogallol red - phenanthroline in a buffer solution of pH6-8. The method has the concentration ranges 2-10 ?g mL-1 and 0.5-1.75 ?g mL-1 for captopril and penicillamine respectively, and the detection limits 7.1 × 10-2 and 5.7 × 10-2 ?g mL-1 for captopril and penicillamine respectively. The second method is based on decreasing the absorbance of a chloroformic solution of copper (II) - oxine chelate when shaken with the drug solution in buffer medium of pH 8. The drugs were determined in the concentrations 30-90 ?g mL-1 and 30-100 ?g mL-1 for captopril and penicillamine respectively, and the detection limits 0.94 and 1.76 ?g mL-1 for captopril and penicillamine respectively. The proposed methods were applied in the analysis of both compounds in their pharmaceutical preparations, and results were favorably compared with reference spectrophotometric methods regarding accuracy and precision.

Belal, Saied; Abdel-Razak, Omayma; El-Walily, Abdel-Fattah; Bakry, Rania

2011-01-01

103

Preparation of poly(aniline-co-o-anisidine)-intercalated mesostructured manganese oxide composites by exchange reaction  

SciTech Connect

Layered mesostructured manganese oxide (mesostructured MnO{sub 2}) was synthesized using manganese chloride and lithium hydroxide as the raw materials and cetyltrimethylammonium bromide (CTAB) as the structure-directing agent. Poly(aniline-co-o-anisidine)-intercalated mesostructured MnO{sub 2} composites (P(An-co-oAs)/MnO{sub 2}) were synthesized in an organic solvent through the exchange reaction between the CTAB in MnO{sub 2} gallery and the P(An-co-oAs). The interlayer spacing (I{sub c} values) of mesostructured MnO{sub 2} enlarged from 2.52 to 4.41 nm as the added amount of P(An-co-oAs) increased from 0 to 0.5 g per 0.5 g of mesostructured MnO{sub 2}. The regularity of the layered structure of the composites was firstly decreased due to intercalation of low amounts of P(An-co-oAs). However, with increasing the intercalated amount of P(An-co-oAs) the layered structure of the composites becomes more regular. The electrical conductivity of the composites is 10{sup 2} to 10{sup 3} times higher than that of the mesostructured MnO{sub 2}.

Wang Gengchao [Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 (China)], E-mail: gengchaow@ecust.edu.cn; Yang Zhenyu; Li Xingwei; Li Chunzhong [Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 (China); Yuan Weikang [UNILAB, State Key Laboratory of Chemical Reaction Engineering, East China University of Science and Technology, Shanghai 200237 (China)

2008-08-04

104

Limiting the extent of a delayed hemolytic transfusion reaction with automated red blood cell exchange.  

PubMed

Delayed hemolytic transfusion reactions (DHTRs) are mediated by blood group antibodies that undergo anamnestic increases following antigen reexposure. Available options for the treatment or prophylaxis of DHTRs are limited. We report the use of automated red blood cell exchange (ARE) to limit hemolysis associated with an emerging DHTR. Following transfusion of 12 red blood cell units, a family member's comments led to the discovery of a patient's history of 4 alloantibodies (anti-E, anti-c, anti-Fy(a), and anti-M). Testing revealed that all 12 units were incompatible for at least 1 antigen. Six days after transfusion, the patient developed a newly positive antibody screen and direct antiglobulin test (DAT) result. To prevent further hemolysis, ARE was performed to replace incompatible red blood cells with antigen-negative units. After ARE, the patient's DAT results were negative and he was discharged without demonstrating symptoms of hemolysis. This case illustrates the use of ARE to limit hemolysis and prevent symptoms of a DHTR. PMID:23721278

Tormey, Christopher A; Stack, Gary

2013-06-01

105

Magnetic isotope effect and theory of atomic orbital hybridization to predict a mechanism of chemical exchange reactions.  

PubMed

A novel approach is suggested to investigate the mechanisms of chemical complexation reactions based on the results of Fujii with co-workers; they have experimentally observed that several metals and metalloids demonstrate mass-independent isotope fractionation during the reactions with the DC18C6 crown ether using solvent-solvent extraction. In this manuscript, the isotope fractionation caused by the magnetic isotope effect is used to understand the mechanisms of chemical exchange reactions. Due to the rule that reactions are allowed for certain electron spin states, and forbidden for others, magnetic isotopes show chemical anomalies during these reactions. Mass-independent fractionation is suggested to take place due to the hyperfine interaction of the nuclear spin with the electron spin of the intermediate product. Moreover, the sign of the mass-independent fractionation is found to be dependent on the element and its species, which is also explained by the magnetic isotope effect. For example, highly negative mass-independent isotope fractionation of magnetic isotopes was observed for reactions of DC18C6 with SnCl(2) species and with several Ru(III) chloro-species, and highly positive for reactions of this ether with TeCl(6)(2-), and with several Cd(II) and Pd(II) species. The atomic radius of an element is also a critical parameter for the reaction with crown ether, particularly the element ions with [Kr]4d(n)5s(m) electron shell fits the best with the DC18C6 crown ring. It is demonstrated that the magnetic isotope effect in combination with the theory of orbital hybridization can help to understand the mechanism of complexation reactions. The suggested approach is also applied to explain previously published mass-independent fractionation of Hg isotopes in other types of chemical exchange reactions. PMID:21709897

Epov, Vladimir N

2011-06-27

106

Experimental Test of Exchange Degeneracy in Hypercharge Exchange Reactions at 7 and 11.5 GeV/C.  

National Technical Information Service (NTIS)

The two pairs of line-reversed reactions: pi exp + p implies K exp + sigma exp + ; K exp - p implies pi exp - sigma exp + and pi exp + p implies K exp + Y*(1385); K exp - p implies pi exp - Y*(1385) at two energies: 7 and 11.5 GeV/c were studied. The expe...

P. A. Baker J. S. Chima P. J. Dornan

1978-01-01

107

Unexpected Toxicity of Monolayer Protected Gold Clusters Eliminated by PEG-Thiol Place Exchange Reactions  

PubMed Central

Monolayer protected clusters (MPCs) are small, metal nanoparticles capped with thiolate ligands that have been widely studied for their size-dependent properties and for their ability to be functionalized for biological applications. Common water-soluble MPCs, functionalized by 2-mercaptopropanoyl) amino acetic acid (tiopronin) or glutathione, have been used previously to interface with biological systems. These MPCs are ideal for biological applications not only due to their water-solubility but also their small size (< 5 nm). These characteristics are expected to enable easy biodistribution and clearance. In this report we show an unexpected toxicity is associated with the tiopronin monolayer protected cluster (TMPC), making it incompatible for potential in vivo applications. This toxicity is linked to significant histological damage to the renal tubules, causing mortality at concentrations above 20 ?M. We further show how the incorporation of poly-ethylene glycol (PEG) by simple place-exchange reaction eliminates this toxicity. We analyzed gold content within blood and urine and found an increased lifetime of the particle within the bloodstream due to the creation of the mixed monolayer. Also shown was the elimination of kidney damage with the use of the mixed-monolayer particle via Multistix™ analysis, MALDI-TOF MS analysis, and histological examination. Final immunological analysis showed no effect on white blood cell (WBC) count for the unmodified particle and a surprising increase in WBC count with injection of mixed monolayer particles at concentrations higher than 30 ?M, suggesting that there may be an immune response to these mixed monolayer nanoparticles at high concentrations; therefore, special attention should be focused on selecting the best capping ligands for use in vivo. These findings make the mixed monolayer an excellent candidate for further biological applications using water-soluble nanoparticles.

Simpson, Carrie A.; Huffman, Brian J.; Gerdon, Aren E.; Cliffel, David E.

2010-01-01

108

Synthesis of N=127 isotones through (p,n) charge-exchange reactions induced by relativistic {sup 208}Pb projectiles  

SciTech Connect

The production cross sections of four N=127 isotones ({sup 207}Hg, {sup 206}Au, {sup 205}Pt, and {sup 204}Ir) have been measured using (p,n) charge-exchange reactions, induced in collisions of a {sup 208}Pb primary beam at 1 A GeV with a Be target. These data allow one to investigate the use of a reaction mechanism to extend the limits of the chart of nuclides toward the important r-process nuclei in the region of the third peak of elemental abundance distribution.

Morales, A. I.; Benlliure, J.; Alvarez-Pol, H.; Casarejos, E.; Dragosavac, D.; Perez-Loureiro, D.; Verma, S. [Universidade de Santiago de Compostela, 15782 Santiago de Compostela (Spain); Agramunt, J.; Molina, F.; Rubio, B. [IFIC, CSIC-Universidad de Valencia, E-46071 Valencia (Spain); Algora, A. [IFIC, CSIC-Universidad de Valencia, E-46071 Valencia (Spain); Institute of Nuclear Research of the Hungarian Academy of Sciences, H-4001 Debrecen (Hungary); Alkhomashi, N.; Farrelly, G.; Gelletly, W.; Pietri, S.; Podolyak, Z.; Regan, P. H.; Steer, S. J. [Department of Physics, University of Surrey, Guildford GU2 7XH (United Kingdom); Boutachkov, P.; Caceres, L. S. [GSI, Planckstrasse 1, D-64291 Darmstadt (Germany)

2011-07-15

109

Electron transfer reactions at metal electrodes: Influence of work function on free energy of activation and exchange current density  

Microsoft Academic Search

The dependence of the free energy of activation on the work function of electrodes, solvation energies, and surface potentials of the reactant species pertaining to electron transfer reactions at metal\\/solution interfaces is derived using thermodynamic considerations. The standard exchange current density is calculated for Fe3++eFe2+ at different metal electrodes and compared with experimental data as well as molecular dynamics simulations.

S. Harinipriya; M. V. Sangaranarayanan

2001-01-01

110

Meson-exchange calculation of the d(. gamma. ,p)n reaction in the GeV energy region  

SciTech Connect

We show that a meson-exchange model of the d({gamma},p) reaction can be constructed to reproduce the energy-dependence of the existing data for the differential cross section at 90{degree}. The prediction of the model in the GeV energy region is found to be radically different from the QCD prediction by Brodsky and Hiller. The results will be compared with the new data presented in a companion paper. 12 refs., 4 figs.

Lee, T.S.H.

1991-01-01

111

Inclusive measurement of (p,pi-xn) double charge exchange reactions on bismuth from threshold to 800 MeV  

Microsoft Academic Search

The energy dependence of the total angle-integrated cross section for the production of astatine isotopes from (p,pi-xn) double charge exchange reactions on bismuth (209Bi) was measured from 120 to 800 MeV using activation and radiochemical techniques. Chemical yields were estimated by direct radioassaying of 211At activity in thin (~1 mg\\/cm2), irradiated bismuth targets. Calculations of the contributions of secondary (two-step)

M. Dombsky; J. M. D'auria; I. Kelson; A. I. Yavin; T. E. Ward; J. L. Clark; T. Ruth; G. Sheffer

1985-01-01

112

Kinetic and Mechanistic Studies of the Deuterium Exchange in Classical Keto-Enol Tautomeric Equilibrium Reactions  

ERIC Educational Resources Information Center

|An extension of the classic keto-enol tautomerization of beta-dicarbonyl compounds into a kinetic analysis of deuterium exchange is presented. It is shown that acetylacetone and ethyl acetoacetate undergo nearly complete deuterium exchange of the alpha-methylene carbon when dissolved in methanol-d[subscript 4]. The extent of deuteration may be…

Nichols, Michael A.; Waner, Mark J.

2010-01-01

113

?-Complex Intermediates in Homogeneous and Heterogeneous Catalytic Exchange Reactions of Hydrocarbons and Derivatives with Metals  

Microsoft Academic Search

The exchange of unsaturated and aromatic hydrocarbons and their derivatives with isotopic hydrogen on group VIII transition metals has been reviewed. Both classical and ?-complex heterogeneous mechanisms proposed to account for the observed behavior have been compared. Evidence to distinguish between the application of the heterogeneous associative and dissociative ?-complex exchange mechanisms is discussed. The recently discovered homogeneous equivalent of

J. L. Garnett

1972-01-01

114

Kinetic and Mechanistic Studies of the Deuterium Exchange in Classical Keto-Enol Tautomeric Equilibrium Reactions  

ERIC Educational Resources Information Center

An extension of the classic keto-enol tautomerization of beta-dicarbonyl compounds into a kinetic analysis of deuterium exchange is presented. It is shown that acetylacetone and ethyl acetoacetate undergo nearly complete deuterium exchange of the alpha-methylene carbon when dissolved in methanol-d[subscript 4]. The extent of deuteration may be…

Nichols, Michael A.; Waner, Mark J.

2010-01-01

115

Reaction Engineering International and Pacific Northwest Laboratory staff exchange: Addressing computational fluid dynamics needs of the chemical process industry  

SciTech Connect

Staff exchanges, such as the one described in this report, are intended to facilitate communications and collaboration among scientists and engineers at Department of Energy (DOE) laboratories, in US industry, and academia. Funding support for these exchanges is provided by the DOE, Office of Energy Research, Laboratory Technology Transfer Program. Funding levels for each exchange typically range from $20,000 to $40,000. The exchanges offer the opportunity for the laboratories to transfer technology and expertise to industry, gain a perspective to industry`s problems, and develop the basis for further cooperative efforts through Cooperative Research and Development Agreements (CRADAS) or other mechanisms. Information in this report on the staff exchange of the Pacific Northwest Laboratory (PNL) staff with Reaction Engineering International (REI) includes the significant accomplishments, significant problems, industry benefits realized, recommended follow-on work and potential benefit of that work. The objectives of this project were as follows: Work with REI to develop an understanding of the computational fluid dynamics (CFD) needs of the chemical process industry; assess the combined capabilities of the PNL and REI software analysis tools to address these needs; and establish a strategy for a future programmatically funded, joint effort to develop a new CFD tool for the chemical process industry.

Fort, J.A.

1995-07-01

116

The Nuclear Responses for Double Beta Neutrinos and Double Spin Isospin Resonances by Using of Double Charge Exchange Heavey Ion Reaction  

NASA Astrophysics Data System (ADS)

To study double spin-isospin responses in view of the ??? decays, double charge-exchange nuclear reactions have measured at RCNP. We have succeeded to measure the double charge exchange reaction by means of heavy ion reaction. From these experiments, we conclude that the (11B,11Li) reaction at 70 MeV/nucleon is a good spectroscopic tool. We believe that the reaction can be well applied to the study of pure spin-flip nuclear responses in higher-excited regions including DGT and higher ?L excitations.

Takahisa, K.; Akimune, H.; Ejiri, H.; Fujimura, H.; Fujiwara, M.; Hara, K.; Hasimoto, H.; Hatanaka, K.; Itahasi, T.; Kawabata, T.; Kawase, K.; Koreeda, Y.; Maehara, N.; Mordechai, S.; Nagai, Y.; Nakanishi, K.; Ninomiya, S.; Shima, T.; Tanaka, M.; Umehara, S.; Umisedo, S.; Yoshida, H. P.; Yoshida, S.; Yoshimura, M.; Yosoi, M.

2005-12-01

117

Isotope exchange for gas-phase acetic acid and ethanol at aqueous interfaces: A study of surface reactions  

SciTech Connect

Isotope exchange for deuterated gas-phase acetic acid and ethanol in contact with water (H{sub 2}O) droplets was studied using a droplet train apparatus. In these experiments, the gas-phase species interacts with liquid droplets and the loss of the species is monitored. The loss of the species may be due to the entry of the molecules into the bulk or to a reaction of the species at the gas-liquid interface, in this case isotope exchange. Studies were conducted as a function of pH in the range 0--14, droplet temperature in the range 291--263 K and gas-liquid interaction time in the range 2--15 ms. For deuterated acetic acid the isotope exchange probability with water molecules at the interface is near unity. On the other hand, isotope exchange probability for ethanol with surface water molecules at the interface is near unity. On the other hand, isotope exchange probability for ethanol with surface water molecules at pH 7 is much smaller, ranging from 0.033 at 263 K to 0.051 at 291 K. Ethanol isotope exchange is both acid and base catalyzed. The exchange probability therefore increases both toward low and high pH and levels off to a plateau at pH 2 and 12, respectively. The maximum value of the isotope exchange probability at the plateau is significant less than 1. It ranges between 0.14 and 0.18 with no clear trend in temperature. Results are explained in terms of a kinetic model in which it is assumed that the surface-adsorbed ethanol molecules are distributed between two distinct forms: a weakly adsorbed state and a partially solvated state. Only the partially solvated molecules can interact with the near-surface ions in the interior of the liquid. A finite rate of entering the partially solvated state is responsible for the observed plateaus in isotope exchange at high and low pH. Parameters describing the gas uptake and isotope exchange processes are examined using two models to describe the surface species: surface nucleation and Gibbs surface excess.

Shi, Q.; Li, Y.Q.; Davidovits, P. [Boston Coll., Chestnut Hill, MA (United States); Jayne, J.T.; Worsnop, D.R.; Mozurkewich, M.; Kolb, C.E. [Aerodyne Research, Inc., Billerica, MA (United States). Center for Aerosol and Cloud Chemistry

1999-04-01

118

A full dimensional time-dependent wave packet study for the H4 four-center, collision induced dissociation, and single exchange reactions: reaction probabilities for J=0.  

PubMed

A time-dependent initial state selected wave packet method has been developed to study the H2(v(1)=10-11,j1=0)+H2'(v2=0,j2=0)-->HH'+HH' four-center (4C) reaction, and two other competing reactions: the H2+H2'-->H+H+H2' collision induced dissociation (CID) and the H2+H2'-->H+HH'+H' single exchange (SE) reaction, in full six dimensions. Initial state-specific total reaction probabilities for these three competing reactions are presented for total angular momentum J=0 and the effects of reagent vibration on reactions are examined. It is found that (a) the CID process is the dominant process over the whole energy range considered in this study, but the 4C and SE processes also have non-negligible probabilities; (b) the SE process has a lower threshold energy than the 4C process, but the SE probability increases slower than the 4C probability as collision energy increases; (c) the vibrational excitation of H2(v1) is much more efficient than translational motion for promoting these processes, in particular to the CID process. PMID:16409016

Lu, Yunpeng; Lee, Soo-Y; Zhang, Dong H

2006-01-01

119

Theoretical study on oxygen exchange accompanying alkaline hydrolysis of esters and amides. The role of water for the exchange reaction 1 Dedicated to Professor Keiji Morokuma in celebration of his 65th birthday. 1  

Microsoft Academic Search

The hydrolysis of esters and amides accompanies a fast reaction, which results in exchange of carbonyl 18O to 16O coming from solvent water. The present study considered two paths as the oxygen exchange mechanism. One, Path 1 called the direct path, is the mechanism that a proton of the OH fragment directly moves from the OH to the 18O fragment

Kenzi Hori; Yuji Hashitani; Yuji Kaku; Katsutoshi Ohkubo

1999-01-01

120

Influence of montmorillonite tactoid size on Na-Ca cation exchange reactions.  

PubMed

The spatial organisation of swelling clay platelets in a suspension depends on the chemical composition of the equilibration solution. Individual clay platelets can be well dispersed, with surfaces entirely in contact with the external solution, or be stacked in tactoids, where part of the surfaces forms parallel alignments embedding interlayer water and cations. External and interlayer surfaces do not exhibit similar affinities for cations having different hydration and charge properties and the clay platelet stacking arrangement influences the clay affinity for these cations. This paper aims to establish the link between exchange properties and clay tactoid size and organisation for Na-Ca exchange on montmorillonite. Different montmorillonite samples behave differently with regards to Na-Ca exchange, from ideal to non-ideal exchange behaviour. A simple model coupling the tactoid stacking size to different Na/Ca relative affinities of the external and interlayer clay surfaces enables these differences to be reproduced. PMID:21920529

Tournassat, Christophe; Bizi, Mohamed; Braibant, Gilles; Crouzet, Catherine

2011-08-16

121

The reaction of exchange rates and interest rates to news releases  

Microsoft Academic Search

This paper examines the response of exchange rates and interest rates--U.S. and foreign--to economic news. The news is associated with the surprise component of the monthly release of six U.S. macroeconomic variables. The results suggest that dollar exchange rates systematically react to news about real economic activity--a surprise of 100,000 on nonfarm payroll employment leads to a 0.2 percent appreciation

Hali J. Edison

1996-01-01

122

The Reaction of Exchange Rates and Interest Rates to News Releases  

Microsoft Academic Search

This paper examines the response of exchange rates and interest rates--US and foreign--to economic news. The news is associated with the surprise component of the monthly release of six US macroeconomic variables. The results suggest that dollar exchange rates systematically react to news about real economic activity--a surprise of 100,000 on non-farm payroll employment leads to a 0.2% appreciation of

Hali J. Edison

1997-01-01

123

Marcado general con tritio de la gentamicina C por intercambio catalitico con agua tritiada. (General Tritium labelling of gentamicin C by catalytic hydrogen exchange reaction with tritiated water).  

National Technical Information Service (NTIS)

Gentamicin C was labelled with tritium by means of a PtO(sub 2) catalyzed hydrogen exchange reaction. Under the conditions of the exchange (100 mg of gentamicin, basic form, 0,3 ml H(sub 2)O-(sup 3)H, and 50 mg of prereduced PtO(sub 2)) the radiochemical ...

C. Suarez D. Diaz

1991-01-01

124

Reaction centers of photosystem II with a chemically-modified pigment composition: exchange of pheophytins with 13 1-deoxo-13 1-hydroxy-pheophytin a  

Microsoft Academic Search

Isolated reaction centers of photosystem II with an altered pigment content were obtained by chemical exchange of the native pheophytin a molecules with externally added 131-deoxo-131-hydroxy-pheophytin a. Judged from a comparison of the absorption spectra and photochemical activities of exchanged and control reaction centers, 70–80% of the pheophytin molecules active in charge separation are replaced by 131-deoxo-131-hydroxy-pheophytin a after double

A. Ya. Shkuropatov; R. A. Khatypov; V. A. Shkuropatova; M. G. Zvereva; T. G. Owens; V. A. Shuvalov

1999-01-01

125

Thermal FT-IR microspectroscopy for rapid detection of solid-state ion-exchange reaction between metoclopramide HCl monohydrate and potassium bromide.  

PubMed

The combination of Fourier transform infrared (FT-IR) microspectroscopy with a thermal analyzer was applied to quickly investigate the solid-state ion-exchange reaction of metoclopramide HCl monohydrate (MCP H(2)O) by clipping MCP H(2)O powder between two KBr or KCl pellets. The physical and ground mixtures of MCP H(2)O or 150 °C-preheated MCP powder and KBr or KCl powders with a weight ratio of 1 : 100 were also prepared and determined by FT-IR microspectroscopy. The samples of MCP H(2)O or 150 °C-preheated MCP were identified by using differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. The results of present study indicate that the ion-exchange reaction was easily induced between MCP H(2)O and KBr by grinding and heating processes. The possible mechanism of ion-exchange reaction may take place between the HCl salt of MCP H(2)O and a KBr matrix by grinding or heating to yield a mixture of HCl and HBr salts of the MCP sample in the presence of hydrated water. The crystal hydrate played an important role to improve this ion-exchange reaction between MCP H(2)O and KBr. However, no ion-exchange reaction occurred between MCP H(2)O and KCl or between 150 °C-preheated MCP and KBr. The solid-state ion-exchange reaction was more easily determined by this novel thermal FT-IR microspectroscopy than other conventional methods. PMID:21183974

Cheng, Wen-Ting; Wang, Shun-Li; Lin, Shan-Yang

2010-12-23

126

Inclusive measurement of (p,. pi. /sup -/xn) double charge exchange reactions on bismuth from threshold to 800 MeV  

SciTech Connect

The energy dependence of the total angle-integrated cross section for the production of astatine isotopes from (p,..pi../sup -/xn) double charge exchange reactions on bismuth (/sup 209/Bi) was measured from 120 to 800 MeV using activation and radiochemical techniques. Chemical yields were estimated by direct radioassaying of /sup 211/At activity in thin (approx.1 mg/cm/sup 2/), irradiated bismuth targets. Calculations of the contributions of secondary (two-step) reactions to these measured astatine yields were performed, based partially upon the observed /sup 211/At activity although even at the highest energies, the contribution to products lighter than /sup 207/At was negligible. These data for products with as many as seven neutrons removed from the doubly coherent product (/sup 210/At) display nearly Gaussian shapes for the mass distributions of the astatine residues, with the maximum occurring for about /sup 204/At. The most probable momentum transfer deduced from these distributions for the initial ..pi../sup -/ production step was 335 MeV/c. The observed excitation functions display a behavior similar to that observed for the yield of /sup 210/Po from a (p,..pi../sup 0/) reaction on /sup 209/Bi, but radically different from that observed for inclusive ..pi../sup -/ reactions on a heavy nucleus. These data are discussed in terms of recent theoretical approaches to negative pion production from bismuth. In addition, a simple, schematic model is developed to treat the rapidly decreasing percentage of the total inclusive ..pi../sup -/ emission which is observed for this double charge exchange reaction. This model reflects the opacity of a nucleus to a source of internal energetic protons.

Dombsky, M.; D'Auria, J.M.; Kelson, I.; Yavin, A.I.; Ward, T.E.; Clark, J.L.; Ruth, T.; Sheffer, G.

1985-07-01

127

Central bank reactions to banking crises in fixed exchange rate regimes  

Microsoft Academic Search

Until recently, speculative attacks and banking crises have been largely treated as separate phenomena. However, the recent experiences of several Southern Cone countries indicates that banking difficulties can lead to a currency crises if in combatting them, the central bank adopts policies which are inconsistent with the fixed exchange rate regime. The paper illustrates how this can be the case

Victoria Miller

2000-01-01

128

Invariant mass spectroscopy of 19,17C and 14B using proton inelastic and charge-exchange reactions  

NASA Astrophysics Data System (ADS)

The neutron-rich carbon isotopes 19,17C and the boron isotope 14B have been investigated, respectively, by the proton inelastic and charge-exchange reactions on a liquid hydrogen target at around 70 MeV/nucleon. The invariant mass method in inverse kinematics was employed to map the energy spectrum above the neutron decay threshold of the residual nuclei. New states on carbon isotopes are reported. An experimental capability of extracting ?-decay strengths via forward angle (p,n) cross sections on unstable nuclei is shown.

Satou, Y.; Nakamura, T.; Fukuda, N.; Sugimoto, T.; Kondo, Y.; Matsui, N.; Hashimoto, Y.; Nakabayashi, T.; Okumura, Y.; Shinohara, M.; Motobayashi, T.; Yanagisawa, Y.; Aoi, N.; Takeuchi, S.; Gomi, T.; Togano, Y.; Kawai, S.; Sakurai, H.; Ong, H. J.; Onishi, T. K.; Shimoura, S.; Tamaki, M.; Kobayashi, T.; Otsu, H.; Endo, N.; Kitayama, M.; Ishihara, M.

2010-03-01

129

Studies on the reaction of the 5'-phosphorimidazolide of adenosine with Cu(II)-exchanged hectorite  

Microsoft Academic Search

The role of clay minerals in the prebiotic synthesis of nucleotide oligomers has received considerable attention in recent years. Scanning force microscopy and matrix-assisted laser desorption\\/ionization time-of-flight mass spectrometry are used to identify oligomers of adenylic acid formed on the clay mineral Cu(II)-exchanged hectorite in simulated prebiotic cycling experiments. Electron-spin resonance and x-ray diffraction data indicate that the monomer (5'-phosphorimidazolide

T. L. Porter; R. Whitehorse; M. P. Eastman; E. D. Bain

1999-01-01

130

Dipole and spin-dipole resonances in charge-exchange reactions on 12C  

Microsoft Academic Search

The 12C(n,p)12B reaction was studied using the white neutron source at the Los Alamos Meson Physics Facility\\/Weapon Neutron Research Center with a continuous incident neutron energy from 60 to 260 MeV. Double differential cross sections were measured in the angular range 11°<=thetalab<=37°. Using the neutron time-of-flight facility at the Indiana University Cyclotron Facility, we also studied the 12C(p,n)12N reaction at

X. Yang; L. Wang; J. Rapaport; C. D. Goodman; C. Foster; Y. Wang; W. Unkelbach; E. Sugarbaker; D. Marchlenski; S. de Lucia; B. Luther; J. L. Ullmann; A. G. Ling; B. K. Park; D. S. Sorenson; L. Rybarcyk; T. N. Taddeucci; C. R. Howell; W. Tornow

1993-01-01

131

Theoretical investigation of the thermodynamic structures and kinetic water-exchange reactions of aqueous Al(III)-salicylate complexes  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) calculations were performed on the structures and water-exchange reactions of aqueous Al(III)-salicylate complexes. Based on the four models (gas phase (GP); polarizable continuum model (PCM), which estimates the bulk solvent effect; supermolecule model (SM), which considers the explicit solvent effect, and supermolecule-polarizable continuum model (SM-PCM), which accounts for both types of solvent effects), we systematically conducted this study by examining three different properties of the complexes. (1) The microscopic properties of the aqueous Al(III)-salicylate complexes were studied by optimizing their various structures (including the possible 1:1 mono- and bidentate complexes, cis and trans isomers of the 1:2 bidentate complexes and 1:3 bidentate complexes) at the B3LYP/6-311+G(d, p) level. (2) The 27Al and 13C NMR chemical shifts were calculated using the GIAO method at the HF/6-311+G(d, p) level. The calculation results show that the values obtained with the SM-PCM models are in good agreement with the experimental data available in the literature, indicating that the models we employed are appropriate for Al(III)-salicylate complexes. (3) The water-exchange reactions of 1:1 mono- and bidentate Al(III)-salicylate complexes were simulated using supermolecule models at the B3LYP/6-311+G(d, p) level. The logarithm of the water-exchange rate constant (log kex) of the 1:1 bidentate complex predicted using the "log kex-dAl-OH2" correlation is 4.0, which is in good agreement with the experimental value of 3.7, whereas the calculated range of log kex of the 1:1 monodentate complexes is 1.3-1.9. By effectively combining the results for the thermodynamic static structures with the simulations of the kinetic water-exchange reactions, this work promotes further understanding of the configurations and formation mechanism of Al(III)-salicylate complexes.

Shi, Wenjing; Jin, Xiaoyan; Dong, Shaonan; Bi, Shuping

2013-11-01

132

Radial electric field formation by the gyrocenter shifts of the charge exchange reactions at the boundary of fusion device  

SciTech Connect

As an important future energy source nuclear fusion researchers have been trying to solve the problem of radial electric field formation: the key factor of H-mode (high confinement mode) phenomena. Although a profound analysis has been developed on the turbulence suppression by ExB flow (E is the electric field and B is the magnetic field) as a basic mechanism of H-mode transition, the origin of the electric field and its relation with the neutrals are not fully explained. In this paper a novel model of radial electric field formation achieved by gyrocenter shifts during the charge exchange reactions and ion elastic scatterings with the neutrals is analyzed. From this analysis the formula of radial current density by the poloidal momentum sink at the reactions of charge exchange with boundary neutrals is developed with an example calculation for a given plasma condition similar to the experiment. The profile and absolute value of the saturated radial electric field are in agreement with the experimental results. An H-mode transition scenario is discussed by the gyrocenter shift model.

Lee, K.C. [Department of Applied Science, University of California, Davis, California 95616 (United States)

2006-06-15

133

Unbound states of ^32Cl studied via the ^32S(^3He,t)^32Cl charge-exchange reaction  

NASA Astrophysics Data System (ADS)

Breakout from the SiP cycle [1], which is closed by the ^31S (p,?)^28P reaction, can occur via the ^31S(p, ?)^32Cl proton-capture reaction. The duration of the cycle influences the timescale of explosive hydrogen burning. At novae temperatures 0.1-0.4 GK, the ^31S(p,?)^32Cl reaction rate is dominated by ^31S+p resonances. Discrepancies in the ^32Cl resonance energies have been reported in previous measurements [1,2]. We have used the ^ 32S(^3He,t)^32Cl charge-exchange reaction to produce unbound states in ^32Cl and determined their excitation energies by detecting the tritons at the focal plane of the Enge Spectrograph at the Yale University's Wright Nuclear Structure Laboratory. To determine the proton branching ratios the decay protons coming from the residual ^32Cl nuclei have been detected using a silicon-strip detector array around the target position. Results from the experiment will be presented. [4pt] [1] S.Vouzoukas et al., PRC 50 (1994) 1185.[0pt] [2] C. Jeanperrin et al., NPA 503 (1989) 77.

Mato&{Caron; S}, M.; Bardayan, D. W.; Blackmon, J. C.; Clark, J. A.; Deibel, C. M.; Linhardt, L.; Nesaraja, C. D.; O'Malley, P. D.; Parker, P. D.; Schmitt, K. T.

2009-10-01

134

Intermediates in Hin-mediated DNA inversion: a role for Fis and the recombinational enhancer in the strand exchange reaction.  

PubMed Central

The site-specific inversion reaction controlling flagellin synthesis in Salmonella involves the function of three proteins: Hin, Fis and HU. The DNA substrate must be supercoiled and contain a recombinational enhancer sequence in addition to the two recombination sites. Using mutant substrates or modified reaction conditions, large amounts of complexes can be generated which are recognized by double-stranded breaks within both recombination sites upon quenching. The cleaved molecules contain 2-bp staggered cuts within the central dinucleotide of the recombination site. Hin is covalently associated with the 5' end while the protruding 3' end contains a free hydoxyl. We demonstrate that complexes generated in the presence of an active enhancer are intermediates that have advanced past the major rate limiting step(s) of the reaction. In the absence of a functional enhancer, Hin is also able to assemble and catalyze site-specific cleavages within the two recombination sites. However, these complexes are kinetically distinct from the complexes assembled with a functional enhancer and cannot generate inversion without an active enhancer. The results suggest that strand exchange leading to inversion is mediated by double-stranded cleavage of DNA at both recombination sites followed by the rotation of strands to position the DNA into the recombinant configuration. The role of the enhancer and DNA supercoiling in these reactions is discussed. Images

Johnson, R C; Bruist, M F

1989-01-01

135

Proton-transport catalysis, proton abstraction, and proton exchange in HF+HOC+ and H2O+HOC+ and analogous deuterated reactions  

NASA Astrophysics Data System (ADS)

Classical simulations of the reactions of HF and H2O with HOC+ have been carried out on interpolated ab initio potential energy surfaces. Rearrangement (X+HOC+-->OCH++X), abstraction (X+HOC+-->XH++OC), (X=HF or H2O), exchange (e.g., DY+HOC+-->HY+DOC+), and exchange-rearrangement (e.g., DY+HOC+-->OCD++YH) (Y=F or HO or DO) reactions are observed. However, the abstraction reaction is dominant for both the HF+HOC+ and H2O+HOC+ systems.

Collins, Michael A.; Radom, Leo

2003-04-01

136

Evidence for cooperative effects in the exchange reaction catalysed by the oxoglutarate translocator of rat-heart mitochondria.  

PubMed

The initial rates of the exchange external oxoglutarate/internal malate through the inner membrane of rat-heart mitochondria, for various concentrations of the two substrates, have been reinvestigated for an extended range of concentrations of the external oxoglutarate. This has been made possible by use of the inhibitor-stop technique that allows 100 times smaller incubation times than the centrifugation-stop technique used previously. Under the experimental conditions the uptake of the external-labelled oxoglutarate into the mitochondrial-matrix space is mediated by the oxoglutarate translocator performing a ono-to-one exchange of the anions oxoglutarate (external) and malate (internal). Two intermediary-plateau regions are observed in the kinetic saturation curve of the translocator by the external oxoglutarate, revealing a complex rate equation which is found to be the product of two one-substrate functions. Analysing these features it is shown that the model, proposed earlier, of a "double carrier" as catalyst in a rapid-equilibrium random bi-bi mechanism, is still applicable but that several external binding sites have to be considered. As already noticed the external and the internal substrates bind to their respective sites independently of each other. Furthermore, some additional requirements imposed by the observed kinetics suggest that the exchange reaction is performed by only one translocator species made of identical interacting subunits. The anion exchange is tentatively viewed as a rotation of a subunit around an axis situated in the plane of the membrane after two independent local configuration changes induced by the binding of the two substrates on this subunit. PMID:1175617

Sluse, F E; Sluse-Goffart, C M; Duyckaerts, C; Liébecq, C

1975-08-01

137

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

PubMed

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

Polak, Micha; Rubinovich, Leonid

2011-08-22

138

Psychotic reaction as a manifestation of multiple sclerosis relapse treated with plasma exchange.  

PubMed

We present a patient with a clinically isolated syndrome suggestive of multiple sclerosis, who developed a full-blown picture of paranoid psychosis with suicidal attempt. Four new lesions were observed on brain MRI, one in the left and one in the right temporal lobe, one subcortically in the cingulate gyrus and one centrally in the tegmentum of the midbrain. The patient was treated with plasma exchange and recovered completely. Psychosis is not so rare symptom of multiple sclerosis as previously reported, and poses a major treatment challenge. A combination of lesions at strategic locations was a presumed mechanism of psychosis in this patient. PMID:21796428

Gabeli?, Tereza; Adamec, Ivan; Mr?en, Anamarija; Radoš, Milan; Brinar, Vesna V; Habek, Mario

2011-07-28

139

A quasiclassical trajectory study of the time-delayed forward scattering in the hydrogen exchange reaction.  

PubMed

The time-delayed forward scattering mechanism recently identified by Althorpe et al. [Nature (London) 416, 67 (2002)] for the H+D(2)(v=0,j=0)-->HD(v(')=3,j(')=0)+D reaction was analyzed by using quasiclassical trajectory (QCT) methodology. The QCT results were found to match the quantum wavepacket snapshots of Althorpe et al., albeit without the quantum scattering effects. Trajectories were analyzed on the fly to investigate the dynamics of the atoms during the reaction. The dominant reaction mechanism progresses from hard collinear impacts, leading to direct recoil, toward glancing impacts. The increased time required for forward scattered trajectories is due to the rotation of the transient HDD complex. Forward scattered trajectories display symmetric stretch vibrations of the transient HDD complex, a signature of the presence of a resonance, or a quantum bottleneck state. PMID:18447439

Greaves, Stuart J; Murdock, Daniel; Wrede, Eckart

2008-04-28

140

Quasiclassical dynamics for the H + HS abstraction and exchange reactions on the (3)A" and the (3)A' states.  

PubMed

A detailed quasiclassical trajectory study of the H + HS reaction yielding an exchange (H + HS) and an abstraction (H2 + S) channel has been performed by employing the new triplet (3)A" and (3)A' surfaces developed by our group. The cross sections for both channels are presented and found to be in good agreement with previous quantum wave packet results. The thermal rate coefficients for abstraction channel at the temperature between 200 and 1000 K have been evaluated by averaging over a Boltzmann distribution of rotational states and compared with the available experimental values. It is found that the thermal rate coefficients exhibit a conventional Arrhenius-type dependence on temperature, which agrees well with the experimental data. Average fractions, vibration and rotation distributions of the products H2 and HS at different collision energies have been also fully investigated. Furthermore, influence of the collision energy on the total and product-state-resolved differential cross sections (DCSs) for both channels are calculated and discussed. Some observations on the mechanism of the title reaction have been made; in particular it was discovered that reactive collisions along the collinear pathway cause the H2 product to scatter backward, while the reactive collisions with large impact parameters b, which are favored deviating from the minimum energy path, produced mainly forward scattering. For the exchange channel, the discrepancies in the DCS are also distinguished through an analysis of individual trajectories and found a double microscopic mechanism, migration or non-migration. The state-to-state DCSs provide a global perspective of the reaction mechanisms and their contribution to the final product internal energy states. The theoretical findings are discussed and compared with a kinematic constraint model. PMID:24028117

Duan, Zhi Xin; Li, Wen Liang; Xu, Wen Wu; Lv, Shuang Jiang

2013-09-01

141

Dipole and spin-dipole resonances in charge-exchange reactions on [sup 12]C  

SciTech Connect

The [sup 12]C([ital n],[ital p])[sup 12]B reaction was studied using the white neutron source at the Los Alamos Meson Physics Facility/Weapon Neutron Research Center with a continuous incident neutron energy from 60 to 260 MeV. Double differential cross sections were measured in the angular range 11[degree][le][theta][sub lab][le]37[degree]. Using the neutron time-of-flight facility at the Indiana University Cyclotron Facility, we also studied the [sup 12]C([ital p],[ital n])[sup 12]N reaction at [ital E][sub [ital p

Yang, X.; Wang, L.; Rapaport, J. (Ohio University, Athens, Ohio 45701 (United States)); Goodman, C.D.; Foster, C.; Wang, Y.; Unkelbach, W. (Indiana University, Indiana University Cyclotron Facility, Bloomington, Indiana 47405 (United States)); Sugarbaker, E.; Marchlenski, D.; de Lucia, S.; Luther, B. (Ohio State University, Columbus, Ohio 43210 (United States)); Ullmann, J.L.; Ling, A.G.; Park, B.K.; Sorenson, D.S.; Rybarcyk, L.; Taddeucci, T.N. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)); Howell, C.R.; Tornow, W. (Department of Physics, Duke University and Triangle Universities Nuclear Laboatory, Durham, North Carolina 27706 (United States))

1993-09-01

142

The H + Li2 bimolecular exchange reaction: Dynamical and kinetical properties at J = 0  

NASA Astrophysics Data System (ADS)

For the first time in the literature, rigorous time-independent quantum scattering formalism was applied, by means of the ABC program, to the H + Li2 --> LiH + Li reaction. The state-to-state probabilities as a function of the total energy have been computed at zero total angular momentum (J = 0) allowing us to evaluate the effect of vibrational/rotational excitation on the reaction promotion/inhibition, the energetic distribution of products, and the temperature dependence of the J-shifting thermal rate coefficients.

Vila, Henrique Vieira Rivera; Leal, Luciano Almeida; Martins, Joa~o. Batista Lopes; Skouteris, Dimitrios; e Silva, Geraldo Magela; Gargano, Ricardo

2012-04-01

143

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

144

One-pot approach to functional nucleosides possessing a fluorescent group using nucleobase-exchange reaction by thymidine phosphorylase.  

PubMed

Herein, we describe ?-selective coupling between a modified uracil and a deoxyribose to produce functionalized nucleosides catalyzed by thymidine phosphorylase derived from Escherichia coli. This enzyme mediates nucleobase-exchange reactions to convert unnatural nucleosides possessing a large functional group such as a fluorescent molecule, coumarin or pyrene, linked via an alkyl chain at the C5 position of uracil. 5-(Coumarin-7-oxyhex-5-yn)uracil (C4U) displayed 57.2% conversion at 40% DMSO concentration in 1.0 mM phosphate buffer pH 6.8 to transfer thymidine to an unnatural nucleoside with C4U as the base. In the case of using 5-(pyren-1-methyloxyhex-5-yn)uracil (P4U) as the substrate, TP also could catalyse the reaction to generate a product with a very large functional group at 50% DMSO concentration (21.6% conversion). We carried out docking simulations using MF myPrest for the modified uracil bound to the active site of TP. The uracil moiety of the substrate binds to the active site of TP, with the fluorescent moiety linked to the C5 position of the nucleobase located outside the surface of the enzyme. As a consequence, the bulky fluorescent moiety binding to uracil has little influence on the coupling reaction. PMID:24057401

Hatano, Akihiko; Kurosu, Masayuki; Yonaha, Susumu; Okada, Munehiro; Uehara, Sanae

2013-09-25

145

Studies on the reaction of the 5'-phosphorimidazolide of adenosine with Cu(II)-exchanged hectorite  

NASA Astrophysics Data System (ADS)

The role of clay minerals in the prebiotic synthesis of nucleotide oligomers has received considerable attention in recent years. Scanning force microscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry are used to identify oligomers of adenylic acid formed on the clay mineral Cu(II)-exchanged hectorite in simulated prebiotic cycling experiments. Electron-spin resonance and x-ray diffraction data indicate that the monomer (5'-phosphorimidazolide of adenosine, or ImpA) penetrates into the intergallery regions of the mineral substrate, and complexes the gallery Cu(II) cations. It is postulated that polymerization of the monomer is initiated in the clay intergallery regions, producing oligomers of adenylic acid up to 8 units in length or more.

Porter, T. L.; Whitehorse, R.; Eastman, M. P.; Bain, E. D.

1999-10-01

146

Hydrogen-deuterium exchange experiments to probe the decomposition reaction of sodium alanate.  

PubMed

NaAlH(4) is the archetypical complex hydride for hydrogen storage. The extraordinary effect of dopants on the sorption kinetics triggered the investigation of this empirical finding. In this paper, a short review of the state of the art is given. To gain further understanding of the mechanisms involved we label the interacting species during the sorption process. This was experimentally realized by hydrogen-deuterium exchange measurements during the decomposition of NaAlH(4) followed by thermogravimetry, Raman spectroscopy and mass spectrometry. By these experiments we are able to obtain specific information on the diffusing species and formation of intermediates. The activation energy of tracer diffusion in NaAlH(4) is found to be 0.28 eV. The results are evidence for a vacancy-mediated desorption process of NaAlH(4). PMID:18597019

Borgschulte, A; Züttel, A; Hug, P; Barkhordarian, G; Eigen, N; Dornheim, M; Bormann, R; Ramirez-Cuesta, A J

2008-05-29

147

Positioning of Platinum Nanoparticles In Cation-exchange Membrane By Galvanic Reaction  

NASA Astrophysics Data System (ADS)

Platinum nanoparticles were formed at the surface of the poly (perfluorosulfonic) acid membrane (Nafion-117) by the galvanic reaction of PtCl62- ions with Ag nanoparticles positioned near the surface of the membrane. The reduction with BH4- ions produced Ag nanoparticles (15+/-4 nm size) mostly positioned near the surface of membrane due to Donnan exclusion of co-ions (BH4-). Energy Dispersive X-ray Fluorescence (EDXRF) analysis of the membrane indicated that galvanic reaction proceeded quantitatively. Transmission Electron Microscopy (TEM) of the cross-sections of membrane samples indicated that the spherical Pt nanoparticles having size 2 to 8 nm were mostly located near the surface of the membrane. The positioning of Pt nanoparticles at surface of the membrane is important for using nano-composite in catalytical application.

Kumar, Rakesh; Pandey, A. K.; Ramagiri, S. V.; Bellare, J. R.; Goswami, A.

2010-12-01

148

Decay of Be populated in the Li(³He,³H) charge-exchange reaction  

Microsoft Academic Search

A complete kinematic measurement of the Li(³He,³H)alphapp reaction is performed at E{sub lab}=50 MeV, to investigate the cluster structure of Be. The energy and angular distributions of the breakup particles, emitted from the ground and first excited states of Be, are compared to three-body resonance and two-body sequential decay calculations. The results indicate a rather pure three-body configuration of the

P. Papka; F. Nemulodi; R. A. Bark; N. Y. Kheswa; E. A. Lawrie; J. J. Lawrie; E. O. Lieder; R. M. Lieder; T. E. Madiba; S. M. Mullins; R. T. Newman; O. Shirinda; T. D. Singo; R. Alvarez-Rodriguez; S. P. Fox; J. Gal; G. Kalinka; J. Molnar; B. M. Nyako; J. Timar

2010-01-01

149

Development of Functional Inorganic Materials by Soft Chemical Process Using Ion-Exchange Reactions  

NASA Astrophysics Data System (ADS)

Our study on soft chemical process using the metal oxide and metal hydroxide nanosheets obtained by exfoliation their layered compounds were reviewed. Ni(OH)2?MnO2 sandwich layered nanostructure can be prepared by layer by-layer stacking of exfoliated manganese oxide nanosheets and nickel hydroxide layers. Manganese oxide nanotubes can be obtained by curling the manganese oxide nanosheets using the cationic surfactants as the template. The layered titanate oriented thin film can be prepared by restacking the titanate nanosheets on a polycrystalline substrate, and transformed to the oriented BaTiO3 and TiO2 thin films by the topotactic structural transformation reactions, respectively. The titanate nanosheets can be transformed anatase-type TiO2 nanocrystals under hydrothermal conditions. The TiO2 nanocrystals are formed by a topotactic structural transformation reaction. The TiO2 nanocrystals prepared by this method expose specific crystal plane on their surfaces, and show high photocatalytic activity and high dye adsorption capacity for high performance dye-sensitized solar cell. A series of layered basic metal salt (LBMS) compounds were prepared by hydrothermal reactions of transition metal hydroxides and organic acids. We succeeded in the exfoliation of these LBMS compounds in alcohol solvents, and obtained the transition metal hydroxide nanosheets for the first time.

Feng, Qi

150

Gas-phase ion\\/molecule isotope-exchange reactions: methodology for counting hydrogen atoms in specific organic structural environments by chemical ionization mass spectrometry  

Microsoft Academic Search

Ion\\/molecule reactions are described which facilitate exchange of hydrogens for deuteriums in a variety of different chemical environments. Aromatic hydrogens in alkylbenzenes, oxygenated benzenes, m-toluidine, m-phenylenediamine, thiophene, and several polycyclic aromatic hydrocarbons and metallocenes are exchanged under positive ion CI conditions by using either DâO, EtOD, or NDâ as the reagent gas. Aromatic hydrogens, benzylic hydrogens, and hydrogens on carbon

Donald F. Hunt; Satinder K. Sethi

1980-01-01

151

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

152

The T{sub z} = -1{yields}T{sub z} =0 beta decays and comparison with Charge Exchange reactions  

SciTech Connect

Gamow-Teller (GT) transitions can be studied in both {beta} decay and charge exchange (CE) reactions. If isospin is a good quantum number, then the Tz = -1{yields}0 and Tz = +1{yields}0GT mirror transitions, are identical. Therefore, a comparison of the results from studies of {beta} decay and CE should shed light on this assumption. Accordingly we have studied the {beta} decay of the Tz = -1 fp-shell nuclei, {sup 54}Ni, {sup 50}Fe, {sup 46}Cr, and {sup 42}Ti, produced in fragmentation and we have compared our results with the spectra from ({sup 3}He, t) measurements on the mirror Tz = +1 target nuclei studied in high resolution at RCNP, Osaka. The {beta} decay experiments were performed as part of the STOPPED beam RISING campaign at GSI.

Molina, F.; Rubio, B. [Instituto de Fisica Corpuscular, CSIC-Universidad de Valencia, E-46071 Valencia (Spain); Fujita, Y. [Department of Physics, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Gelletly, W. [Department of Physics, University of Surrey, Guildford GU7XH, Surrey (United Kingdom); Collaboration: Santiago Collaboration

2011-11-30

153

The analysis of reactions {pi}{sub N} {yields} two mesons + N within reggeon exchanges. Fit and results  

SciTech Connect

The novel point of this analysis is a direct use of reggeon-exchange technique for the description of the reactions {pi}N {yields} two mesons + N at large energies of the initial pion. This approach allows us to describe simultaneously distributions over M (invariant mass of two mesons) and t (momentum transfer squared to nucleons). Making use of this technique, the following resonances (as well as corresponding bare states), produced in the {pi}N {yields} {pi}{sup 0}{pi}{sup 0}N reaction are studied: f{sub 0}(980), f{sub 0}(1300) (f{sub 0}(1370) in PDG notation), f{sub 0}(1200-1600), f{sub 0}(1500), f{sub 0}(1750), f{sub 2}(1270), f{sub 2}(1525), f{sub 2}(1565), f{sub 2}(2020), f{sub 4}(2025). Adding data for the reactions p{bar p}(at rest, from liquid H{sub 2}) {yields} {pi}{sup 0}{pi}{sup 0}{pi}{sup 0}, {pi}{sup 0}{eta}, {pi}{sup 0}{eta}{eta} and p{bar p}(at rest, from gaseous H{sub 2}) {yields} {pi}{sup 0}{pi}{sup 0}{pi}{sup 0}, {pi}{sup 0}{pi}{sup 0}{eta}, {pi}{sup 0}{eta}{eta}, we have performed simultaneous K-matrix fit of two-meson spectra in all these reactions. The results of combined fits to the above-listed isoscalar f{sub J} states and to isovector ones, a{sub 0}(980), a{sub 0}(1475), a{sub 2}(1320), are presented.

Anisovich, V. V., E-mail: anisovic@thd.pnpi.spb.ru; Sarantsev, A. V. [Russian Academy of Sciences, Petersburg Nuclear Physics Institute (Russian Federation)

2009-11-15

154

Spin-dipole stength observed in charge exchange reactions on P-shell nuclei  

SciTech Connect

The (p,n) reactions on {sup 6,7}Li, {sup 10,11}B, and {sup 12,13}C targets have been studied at 186 MeV using the IUCF time-of-flight facilities. The authors use a multipole decomposition analysis to obtain the spectral distribution of states characterized with {Delta}L = 1 transfer. At this incident energy the states that also have {Delta}S = 1 and form the giant spin-dipole resonance (GSDR) are strongly excited. The energy distribution of the GSDR in these nuclei will be presented and compared with theoretical predictions.

Yang, X.; Wang, L.; Rapaport, J. [and others

1993-04-01

155

Enhanced bimolecular exchange reaction through programmed coordination of a five-coordinate oxovanadium complex for efficient redox mediation in dye-sensitized solar cells.  

PubMed

Electrochemical reversibility and fast bimolecular exchange reaction found for VO(salen) gave rise to a highly efficient redox mediation to enhance the photocurrent of a dye-sensitized solar cell, leading to an excellent photovoltaic performance with a conversion efficiency of 5.4%. A heterogeneous electron-transfer rate constant at an electrode (k0) and a second-order rate constant for an electron self-exchange reaction (kex) were proposed as key parameters that dominate the charge transport property, which afforded a novel design concept for the mediators based on their kinetic aspects. PMID:23985896

Oyaizu, Kenichi; Hayo, Noriko; Sasada, Yoshito; Kato, Fumiaki; Nishide, Hiroyuki

2013-08-29

156

Isospin and Spin-Isospin Modes in Charge-Exchange Reactions  

SciTech Connect

The microscopic structure of the Gamow-Teller resonance (GTR) and spin-dipole resonance (SDR) in {sup 208}Bi has been investigated in the {sup 208}Pb({sup 3}He,tp){sup 207}Pb reaction at E{sup 3}He=450 MeV and very forward scattering angles. The partial and total branching ratios and the escape widths for GTR and SDR decay to the residual neutron-hole states in {sup 207}Pb were deduced. These are found to be in good agreement with recent theoretical estimates. The ({sup 3}He,tp) reaction on Pb at E({sup 3}He)=177 MeV was also studied in order to locate isovector monopole strength corresponding to 2{Dirac_h}{omega} transitions. Monopole strength at excitation energies above 25 MeV was discovered and compared to calculated strength due to the isovector giant monopole resonance and the spin-flip isovector monopole resonance. Calculations in a normal-mode framework show that all isovector monopole strength can be accounted for if the branching ratio for decay by proton emission is 20%.

Harakeh, M.N.; Akimune, H.; van den Berg, A.M.; Brandenburg, S.; Fujiwara, M.; Laurent, H.; Willis, A.; Zegers, R.G.T.

1999-12-31

157

Isospin and spin-isospin modes in charge-exchange reactions  

SciTech Connect

The microscopic structure of the Gamow-Teller resonance (GTR) and spin-dipole resonance (SDR) in {sup 208}Bi has been investigated in the {sup 208}Pb({sup 3}He,tp){sup 207}Pb reaction at E({sup 3}He)=450 MeV and very forward scattering angles. The partial and total branching ratios and the escape widths for GTR and SDR decay to the residual neutron-hole states in {sup 207}Pb were deduced. These are found to be in good agreement with recent theoretical estimates. The ({sup 3}He,tp) reaction on Pb at E({sup 3}He)=177 MeV was also studied in order to locate isovector monopole strength corresponding to 2({Dirac_h}/2{pi}){omega} transitions. Monopole strength at excitation energies above 25 MeV was discovered and compared to calculated strength due to the isovector giant monopole resonance and the spin-flip isovector monopole resonance. Calculations in a normal-mode framework show that all isovector monopole strength can be accounted for if the branching ratio for decay by proton emission is 20%.

Harakeh, M. N.; Berg, A. M. van den; Brandenburg, S.; Zegers, R. G. T. [Kernfysisch Versneller Instituut, Zernikelaan 25, 9747AA Groningen (Netherlands); Akimune, H.; Fujiwara, M. [Research Center for Nuclear Physics, Osaka University, Mihogaoka 10-1 Ibaraki, Osaka 657-0047 (Japan); Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Laurent, H.; Willis, A. [Institut de Physique Nucleaire, IN2PS, Universite de Paris-Sud, Orsay Cedex (France)

1999-11-16

158

Insight into the reaction mechanism of the Escherichia coli cyclopropane fatty acid synthase: isotope exchange and kinetic isotope effects.  

PubMed

Cyclopropanation of unsaturated lipids is an intriguing enzymatic reaction and a potential therapeutic target in Mycobacterium tuberculosis. Cyclopropane fatty acid synthase from Escherichia coli is the only in vitro model available to date for mechanistic and inhibition studies. While the overall reaction mechanism of this enzymatic process is now well accepted, some mechanistic issues are still debated. Using homogeneous E. coli enzyme we have shown that, contrary to previous report based on in vivo experiments, there is no exchange of the cylopropane methylene protons with the solvent during catalysis, as probed by ultra high resolution mass spectrometry. Using [methyl-14C]-labeled and [methyl-³H?]-S-adenosyl-L-methionine we have measured a significant intermolecular primary tritium kinetic isotope effect ((T)V/K(app)=1.8 ± 0.1) consistent with a partially rate determining deprotonation step. We conclude that both chemical steps of this enzymatic cyclopropanation, the methyl addition onto the double bond and the deprotonation step, are rate determining, a common situation in efficient enzymes. PMID:20538038

Guangqi, E; Lesage, Denis; Ploux, Olivier

2010-06-09

159

Excitation of isovector giant resonances in /sup 27/Al by heavy ion charge exchange reaction  

SciTech Connect

Excitation of isovector giant resonances in /sup 27/Al was studied by using the /sup 27/Al(/sup 7/Li, /sup 7/Be)/sup 27/Mg reaction at incident energies of 100, 150, and 180 MeV. We observed the analog of the giant dipole resonance at E-italic/sub x-italic/ = 14.3 MeV in /sup 27/Mg. From the observed excitation function, we suggest that a peak at E-italic/sub x-italic/ = 9.5 MeV is a resonance with a higher multipolarity than one. In the excitation energy region higher than the giant dipole resonance, no resonance was observed.

Nakayama, S.; Yamagata, T.; Yuasa, K.; Tanaka, M.; Inoue, M.; Itahashi, T.; Ogata, H.

1986-07-01

160

Exchange mechanisms and energy dependence of isospin amplitudes for the reaction pN --> NNpi in the energy range 5-1480 GeV  

Microsoft Academic Search

Data on the reactions pp --> pppi0, pp --> pnpi+ and new data on pn --> pppi- at 19 GeV\\/c are used to study the reaction N1N2 --> N3(N4pi) in terms of the three isospin amplitudes MIIx, where Ix and I are the isospins of the exchanged particle and the N4pi combination respectively. The result is that the amplitude with

E. Dahl-Jensen; I. Dahl-Jensen; J. D. Hansen; R. Möllerud; J. Mäkelä; M. Pimiä; E. Sundell; V. Bakken; J. Haldorsen; T. Jacobsen; G. Skjevling; G. Ekspong; H. Johansson; P. Lundborg; B. Selldén

1975-01-01

161

Metal chalcogenide nanoparticle gel networks: Their formation mechanism and application for novel material generation and heavy metal water remediation via cation exchange reactions  

Microsoft Academic Search

The dissertation research is focused on (1) uncovering the mechanism of metal chalcogenide nanoparticle gel formation; (2) extending the cation exchange reaction protocol to zinc sulfide gel networks, with the goal of accessing new aerogel chemistries and understanding the factors that drive the process; and (3) conducting a quantitative analysis of the ability of ZnS aerogels to remove heavy metal

Irina R Pala

2012-01-01

162

The effects of exchange and interfacial reaction in two-phase systems on N.M.R. lineshapes and relaxation processes  

Microsoft Academic Search

The effects of molecular exchange between two immiscible fluid phases are of considerable importance when interpreting N.M.R. lineshapes and relaxation times in systems such as emulsions or coacervates, but have not been fully explored theoretically. In general the nuclei in each phase must be considered as belonging to distinct chemical species which are interchanged by chemical reaction localized at the

P. S. Belton; B. P. Hills

1988-01-01

163

Active microchannel heat exchanger  

Microsoft Academic Search

The present invention is an active microchannel heat exchanger with an active heat source and with microchannel architecture. The active microchannel heat exchanger has (a) an exothermic reaction chamber; (b) an exhaust chamber; and (c) a heat exchanger chamber in thermal contact with the exhaust chamber, wherein (d) heat from the exothermic reaction chamber is convected by an exothermic reaction

Anna Lee Y. Tonkovich; Gary L. Roberts; Charles J. Call; Robert S. Wegeng; Yong Wang

2001-01-01

164

Experimental study and baryonic exchange interpretation of the reaction 2H(d, n)3He in the intermediate energy region  

NASA Astrophysics Data System (ADS)

We present a complete set of eight differential cross sections of the reactions 2H(d, n)3He and 2H(d, p)3H in the 0-60° c.m. angular range for incident deuteron momenta between 1.1 and 2.5 GeV/c. A simple phenomenological interpretation of the energy dependence of the total cross section ?T and of d?dt at fixed t shows, in the reaction, the contribution of a nucleon exchange process to which we must add a mechanism implying the ?33 resonance excitation in the direct channel. NUCLEAR REACTION 2H(d, n)3He, 2H(d, p)3H Ed=0.3-1.25 GeV; measured ?(Ed, ?) intermediate energy; phenomenological analysis of the baryonic exchange mechanisms.

Bizard, G.; Laville, J. L.; Le Brun, C.; Lecolley, J. F.; Lefebvres, F.; Osmont, A.; Regimbart, R.; Steckmeyer, J. C.; Berger, J.; Duflo, J.; Goldzahl, L.; Oostens, J.; Plouin, F.; Fabbri, F. L.; Picozza, P.; Satta, L.

1980-10-01

165

Measurement of the analyzing power of the charge-exchange p¯p-->n¯n reaction in the momentum range 546-875 MeV\\/c at LEAR  

Microsoft Academic Search

Results are given for the analysing power of the p¯p-->n¯n charge-exchange reaction at four incident beam momenta. The measurement is part of an experimental programme to study the spin structure of this reaction at LEAR. The analyzing power shows strong angular and energy dependence, which at present is not reproduced by the existing meson-exchange potential models.

R. Birsa; F. Bradamante; A. Bressan; S. dalla Torre-Colautti; M. Giorgi; M. Lamanna; A. Martin; A. Penzo; P. Schiavon; F. Tessarotto; M. P. Macciotta; A. Masoni; G. Puddu; S. Serci; T. Niinikoshi; A. Rijllart; A. Ahmidouch; E. Heer; R. Hess; C. Lechanoine-Le Luc; C. Mascarini; D. Rapin; J. Arvieux; R. Bertini; H. Catz; J. C. Faivre; R. A. Kunne; F. Perrot-Kunne; M. Agnello; F. Iazzi; B. Minetti; T. Bressani; E. Chiavassa; N. de Marco; A. Musso; A. Piccotti

1991-01-01

166

Nonenzymatically evoked and cytochrome P450-dependent lipid peroxidation inhibits synthesis of phosphatidylethanolaminevia the ethanolamine base exchange reaction in rat liver microsomes.  

PubMed

In the present study the relationship between lipid peroxidation, changes in the redox state of membrane and phosphatidylethanolamine (PE) synthesis via base exchange reaction in rat liver microsomes was investigated. It was found that PE synthesis is enhanced in the presence of antioxidants, butylated hydroxytoluene (BHT), or unsaturated free fatty acids. Prooxidants, tert-butyl hydroxyperoxide (BHP), ferrous ions combined with ascorbate or NADPH (via cytochrome P450-dependent proteins), increased the amount of lipid peroxidation products in the membrane, and in consequence inhibited the reaction. The effect of BHP was fully reversed by reduced glutathione and dithiothreitol (DTT), whereas the effect of other compounds could be reversed only by BHT. In contrast, a reversal of the inhibitory effect of cadmium ions on base exchange activity was observed in the presence of DTT, but not BHT. Therefore, both the -SH/-S-S- ratio in the membrane, affected by BHP and cadmium ions, and the lipid hydroxyperoxides (rather than aldehydes), generated by ferrous ions and ascorbate or NADPH, are equally responsible for the inactivation of the ethanolamine base exchange enzyme in rat liver microsomes. This may suggest that the synthesis of PE via the base exchange reaction may be considered an element of the superfine cellular machinery involved in the repair of damage to unsaturated fatty acid chains of phospholipids caused by reactive oxygen species under oxidative stress. PMID:8635598

Jasínka, R; Rakowska, M; Lenart, J; Kománska, I; Pikuta, S

1996-05-13

167

31P NMR studies of the arginine kinase reaction. Equilibrium constants and exchange rates at stoichiometric enzyme concentration.  

PubMed

The arginine kinase reaction, the reversible transfer of the terminal phosphoryl group of ATP to L-arginine, has been investigated by the technique of 31P NMR at catalytic and stoichiometric concentrations of the enzyme. Three of the four substrates, ATP, ADP, and P-arginine produce easily distinguishable resonances in the 31P NMR spectrum, thus permitting a determination of equilibrium constants from the integrated areas of the resonances. From the linewidths, the exchange rates between reactants and products may be evaluated. At pH 7.25 and a temperature of 12 degrees, the equilibrium constant at catalytic enzyme concentration: Keq = [MgADP] [P-arginine]/[MgATP] [L-arginine], is found to be 0.10 +/- 0.02 and that at stoichiometric enzyme concentration: K'eq = [E-MgADP] [E-P-arginine]/[E-MgATP] [E-arginine] to be 1.56 +/- 0.5. Thus, as the enzyme concentration increased, the production of P-arginine is increasingly favored. From the NMR line shapes in the presence of excess enzyme, the rate of the single step, the transfer of the phosphoryl group on the surface of the enzyme is found to be 192 +/- 15 s-1 in the forward direction, i.e. from E-MgATP, and 154 +/- 15 s-1 in the reverse direction from E-P-argine. At 12 degrees and pH 7.25, the rate of the overall reaction in the forward direction was determined from kinetic measurements to be 19 s-1, an order of magnitude slower than the rate measured by NMR. It can, therefore, be concluded that the interconversion of substrates on the surface of the enzyme is not the rate-determining step in the overal reaction. From the equilibrium constants and other known data the dissociation constant of P-arginine from its enzyme complex can be determined and is found to be 100 muM. PMID:186451

Rao, B D; Buttlaire, D H; Cohn, M

1976-11-25

168

Metal chalcogenide nanoparticle gel networks: their formation mechanism and application for novel material generation and heavy metal remediation via cation exchange reactions  

Microsoft Academic Search

METAL CHALCOGENIDE NANOPARTICLE GEL NETWORKS: THEIR FROMATION MECHANISM AND APPLICATION FOR NOVEL MATERIAL GENERATION AND HEAVY METAL REMEDIATION VIA CATION EXCHANGE REACTIONS\\u000aby\\u000aIRINA R. PALA\\u000aFebruary 2012\\u000aAdvisor: Dr. Stephanie L. Brock\\u000aMajor: Chemistry\\u000aDegree: Doctor of Philosophy\\u000aThe dissertation research is focused on (1) uncovering the mechanism of metal chalcogenide nanoparticle gel formation; (2) extending the cation exchange

Irina Ramona Pala

2012-01-01

169

Exchange Reactions Carboxy Radicals.  

National Technical Information Service (NTIS)

The article briefly summarizes the problems centered around the detailed mechanisms of the decompositions of peroxide molecules. The methods of study included secondary deuterium kinetic isotope effects. Further study of these isotope effects on the decom...

T. Koenig

1969-01-01

170

Kinetics of liquid-solid ion-exchange reactions of transition metal ions in tin(IV) phosphate  

NASA Astrophysics Data System (ADS)

A simple approach to liquid-solid ion exchange kinetics of Cu2+, Zn2+, Cd2+, Co2+ ions in tin(IV) phosphate under different conditions of temperature, exchange ion concentration, and the particle size of the exchanger has been reported. The kinetics were controlled by particle diffusion and the t1/2 law operated to about 65-75% of exchange. The diffusion coefficients and activation energies were calculated. The activation energies of Cu2+ and Co2+ ions were found to be low when compared with Zn2+ and Cd2+ ions due to Jahn-Teller distortion.

Thind, Pritam S.; Gandhi, Jatinder S.

1985-11-01

171

Spin structure of the "Forward" nucleon charge-exchange reaction n + p ? p + n and the deuteron charge-exchange breakup  

NASA Astrophysics Data System (ADS)

The structure of the nucleon charge-exchange process n + p ? p + n is investigated basing on the isotopic invariance of the nucleon-nucleon scattering. Using the operator of permutation of the spin projections of the neutron and proton, the connection between the spin matrices, describing the amplitude of the nucleon charge-exchange process at zero angle and the amplitude of the elastic scattering of the neutron on the proton in the "backward" direction, has been considered. Due to the optical theorem, the spin-independent part of the differential cross section of the process n + p ? p + n at zero angle for unpolarized particles is expressed through the difference of total cross sections of unpolarized proton-proton and neutron-proton scattering. Meantime, the spin-dependent part of this cross section is proportional to the differential cross section of the deuteron charge-exchange breakup d + p ? ( pp) + n at zero angle at the deuteron momentum k d = 2 k n ( k n is the initial neutron momentum). Analysis shows that, assuming the real part of the spin-independent term of the "forward" amplitude of the process n + p ? p + n to be smaller or of the same order as compared with the imaginary part, in the wide range of neutron laboratory momenta k n > 700 MeV/ c the main contribution into the differential cross section of the process n + p ? p + n at zero angle is provided namely by the spin-dependent term.

Lyuboshitz, V. L.; Lyuboshitz, V. V.

2011-02-01

172

Gas phase hydrogen deuterium exchange reactions of a model peptide: FT-ICR and computational analyses of metal induced conformational mutations  

Microsoft Academic Search

We utilized gas phase hydrogen\\/deuterium (H\\/D) exchange reactions and ab initio calculations to investigate the complexation\\u000a between a model peptide (Arg-Gly-Asp?RGD) with various alkali metal ions. The peptide conformation is drastically altered\\u000a upon alkali metal ion complexation. The associated conformational changes depend on both the number and type of complexing\\u000a alkali metal ions. Sodium has a smaller ionic diameter and

T. Solouki; R. C. Fort; A. Alomary; A. Fattahi

2001-01-01

173

Platinum\\/multiwalled carbon nanotubes-platinum\\/carbon composites as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell  

Microsoft Academic Search

Pt-loaded multiwalled carbon nanotubes (Pt\\/MWCNTs) have been prepared by chemical reduction method using functionalized MWCNT synthesized by pyrolysis of acetylene over MmNi2 (Mm denotes misch metal) hydride catalyst. Composites of Pt\\/MWCNT and commercial Pt-loaded carbon black (Pt\\/C) have been used as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell (PEMFC). Cathode catalyst with 50% Pt\\/MWCNT and 50%

M. M. Shaijumon; S. Ramaprabhu; N. Rajalakshmi

2006-01-01

174

Carbon Dioxide Catalysis of Reactions of Chromium(III). I. Oxygen Exchange of Hydroxopentaamminechromium(III) Ion.  

National Technical Information Service (NTIS)

Carbon dioxide catalyzes the exchange between Cr(NH3)5OH(2+) and solvent water. At 25C in buffered perchlorate solutions of ionic strength 0.1, the rate of exchange was determined. Also, 18O introduced as HCO3*- rapidly appears in CR(NH3)5OH(2+). These re...

J. E. Earley W. Alexander

1969-01-01

175

Gas chromatography mass spectrometry study of hydrogen deuterium exchange reactions of volatile hydrides of As, Sb, Bi, Ge and Sn in aqueous media  

NASA Astrophysics Data System (ADS)

The H D exchange processes in MHn or MDn hydrides (M = As, Sb, Bi, n = 3; M = Ge, Sn, n = 4) taking place when they are in contact with H2O or D2O solution at different pH or pD values (interval of pH = [0,13]) have been investigated using gas chromatography mass spectrometry (GC-MS). MHn or MDn compounds were injected into the headspace of reaction vials (4 12 ml) containing 1 2 ml of buffered solution maintained under stirring or shaking conditions. The isotopic composition of the gaseous phase hydrides/deuterides was determined at regular intervals in the range of time 0 15 min. The MHn or MDn compounds were synthesized in separate vials and their purity was checked separately before injection into the reaction vials. The mass spectra were deconvoluted in order to estimate the relative abundance of each species formed following the H D exchange process (AsHnD3-n , SbHnD3-n, BiHnD3-n, n = 0 3; GeHnD4-n, SnHnD4-n, n = 0 4) and the relative abundance of H and D. In the investigated pH (or pD) interval arsanes and stibanes undergo H D exchange in alkaline media for pH > 7. No H D exchange was detected for the other hydrides, where the prevailing process is their decomposition in the aqueous phase. A reaction model, based on the formation of protonated or deprotonated intermediates is proposed for H D exchange of MHn or MDn compounds placed in contact with H2O or D2O at different pH or pD values. The H D exchange in the already formed hydrides can be source of the interference in mechanistic studies on hydride formation performed using labeled reagents; no H D exchange was detected within the following pH intervals that can be considered free from interference: arsanes pH = [0,7), stibanes pH = [0,7), bismuthanes, germanes and stannanes pH = [0,13].

D'Ulivo, Alessandro; Mester, Zoltan; Meija, Juris; Sturgeon, Ralph E.

2006-07-01

176

Spin structure of the 'Forward' nucleon charge-exchange reaction n + p {yields} p + n and the deuteron charge-exchange breakup  

SciTech Connect

The structure of the nucleon charge-exchange process n + p {yields} p + n is investigated basing on the isotopic invariance of the nucleon-nucleon scattering. Using the operator of permutation of the spin projections of the neutron and proton, the connection between the spin matrices, describing the amplitude of the nucleon charge-exchange process at zero angle and the amplitude of the elastic scattering of the neutron on the proton in the 'backward' direction, has been considered. Due to the optical theorem, the spin-independent part of the differential cross section of the process n + p {yields} p + n at zero angle for unpolarized particles is expressed through the difference of total cross sections of unpolarized proton-proton and neutron-proton scattering. Meantime, the spin-dependent part of this cross section is proportional to the differential cross section of the deuteron charge-exchange breakup d + p {yields} (pp) + n at zero angle at the deuteron momentum k{sub d} = 2 k{sub n} (k{sub n} is the initial neutron momentum). Analysis shows that, assuming the real part of the spin-independent term of the 'forward' amplitude of the process n + p {yields} p + n to be smaller or of the same order as compared with the imaginary part, in the wide range of neutron laboratory momenta k{sub n} > 700 MeV/c the main contribution into the differential cross section of the process n + p {yields} p + n at zero angle is provided namely by the spin-dependent term.

Lyuboshitz, V. L., E-mail: Valery.Lyuboshitz@jinr.ru; Lyuboshitz, V. V. [Joint Institute for Nuclear Research (Russian Federation)

2011-02-15

177

Ionic atmosphere effects on the energetics of thermal and optical electron-exchange reactions: Application to ferrocenium-ferrocene self exchange. Technical report  

SciTech Connect

A treatment of ionic-atmosphere effects upon symmetrical electron-transfer reactions resulting from added electrolyte is outlined. Relationships are derived on the basis of the extended Debye-Huckel model for the increase in the activation free energy, associated with reorganization of the ionic atmosphere for homogeneous-phase reactions involving a pair of spherical reactants with varying internuclear distance R. Similar relationships apply to the energetics of symmetrical optical electron transfer, since the increase in the optical transition energy, should equal the corresponding ionic atmosphere reorganization energy, under the anticipated linear response conditions.

Kuznetsov, A.M.; Phelps, D.K.; Weaver, M.J.

1990-05-01

178

Metal chalcogenide nanoparticle gel networks: Their formation mechanism and application for novel material generation and heavy metal water remediation via cation exchange reactions  

NASA Astrophysics Data System (ADS)

The dissertation research is focused on (1) uncovering the mechanism of metal chalcogenide nanoparticle gel formation; (2) extending the cation exchange reaction protocol to zinc sulfide gel networks, with the goal of accessing new aerogel chemistries and understanding the factors that drive the process; and (3) conducting a quantitative analysis of the ability of ZnS aerogels to remove heavy metal ions from aqueous solutions. The mechanism of metal chalcogenide nanoparticle gel formation was investigated using Raman spectroscopy and X-ray Photoelectron Spectroscopy to probe the chemical changes that occur during the gelation process. These techniques suggest that the bonding between the particles in the CdSe nanoparticle gels is due to the oxidation of surface selenide species, forming covalent Se--Se bonds. Treating the gel networks with a suitable reducing agent, such as a thiol, breaks the covalent bond and disperses the gel network. The addition of sodium borohydride, a "pure" reducing agent, also breaks down the gel network, strengthening the hypothesis that the reducing character of the thiols, not their ligation ability, is responsible for the gel network breakdown. UV-Vis spectroscopy, Transmission Electron Microscopy and Powder X-ray Diffraction were used to analyze the particles after successive gelation-dispersion cycles. The primary particle size decreases after repeated oxidation-reduction cycles, due to nanoparticle surface etching. This trend is observed for CdSe and CdS gel networks, allowing for the proposition that the oxidative-reductive mechanism responsible for the formation-dispersion of the gels is general, applying to other metal chalcogenide nanocrystals as well. The cation exchange reaction previously demonstrated for CdSe gels was extended to ZnS gel networks. The exchange occurs under mild reaction conditions (room temperature, methanol solvent) with exchanging ions of different size, charge and mobility (Ag+, Pb2+, Cd2+ , Cu2+). The overall reaction is kinetically controlled, since systems with similar solubility, and thus similar thermodynamic driving force (e.g. PbS and CdS) exchange at very different rates. A correlation exists between the speed of the reaction and the difference between the reduction potential of the incoming cation and that of Zn2+; the larger the difference, the faster the exchange. At the same time, the porosity of the aerogels and the surfactant-free surfaces hold great importance for the exchange reactions, allowing for exchange between cations of similar size and charge (i.e. Pb2+ for Zn2+), a phenomenon that was previously reported as impossible in ligand-capped metal chalcogenide nanoparticles. These observations allowed for a better understanding of the factors governing the cation exchange reaction in nanoscale metal chalcogenides. Quaternary ZnS-CuInS2 gels were obtained by cation exchange with Cu+ and In3+, but the pure CuInS2 phase was not obtained under the mild reaction conditions used, probably due to the very different mobility of the two exchanging cations. The kinetically fast cation exchange process and the propensity of the soft chalcogenide gel networks to bind heavy metal ions selectively, suggest that these materials could also be suitable for the removal of heavy metal ions from the environment. The dissertation research studied the capacity of ZnS aerogels to sequester heavy metal ions such as Pb2+ and Hg2+ from water. The materials are efficient in removing the heavy metal ions from aqueous solutions with a wide range of initial concentrations. For initial concentrations that mimic an environmental spill (i.e. 100 ppb Pb2+), the treatment with the aerogel affords a final concentration lower than the 15 ppm action level recommended by the EPA. Under thermodynamically forcing conditions, the water remediation capacity of the ZnS nanoparticle aerogels was determined to be 14.2 mmol Pb2+ / g ZnS aerogel, which is the highest value reported to date.

Palhares, Leticia F.

179

Developing Single-Molecule TPM Experiments for Direct Observation of Successful RecA-Mediated Strand Exchange Reaction  

PubMed Central

RecA recombinases play a central role in homologous recombination. Once assembled on single-stranded (ss) DNA, RecA nucleoprotein filaments mediate the pairing of homologous DNA sequences and strand exchange processes. We have designed two experiments based on tethered particle motion (TPM) to investigate the fates of the invading and the outgoing strands during E. coli RecA-mediated pairing and strand exchange at the single-molecule level in the absence of force. TPM experiments measure the tethered bead Brownian motion indicative of the DNA tether length change resulting from RecA binding and dissociation. Experiments with beads labeled on either the invading strand or the outgoing strand showed that DNA pairing and strand exchange occurs successfully in the presence of either ATP or its non-hydrolyzable analog, ATP?S. The strand exchange rates and efficiencies are similar under both ATP and ATP?S conditions. In addition, the Brownian motion time-courses suggest that the strand exchange process progresses uni-directionally in the 5?-to-3? fashion, using a synapse segment with a wide and continuous size distribution.

Fan, Hsiu-Fang; Cox, Michael M.; Li, Hung-Wen

2011-01-01

180

Radiochemical study of the medium energy pion double charge exchange reactions: /sup 209/Bi(pi/sup +/pi/sup -/)/sup 209-x/At  

SciTech Connect

Carrier-free radiochemical techniques have been used to measure cross sections for the double charge exchange reactions of the type /sup 209/Bi(pi/sup +/, pi/sup -/xn)/sup 209-x/At for 100, 180, and 300 MeV incident pions. The observed formation of astatine products with mass numbers ranging from 208 to 205 is interpreted as evidence of processes in which energy deposited in the initial double charge exchange interaction is subsequently dissipated through neutron evaporation. The excitation functions for these reactions are seen to rise rapidly with decreasing incident pion energy with the maximum results for this study at 100 MeV. The astatine production cross secions measured for these positive pion irradiations of thick bismuth targets must be corrected for secondary processes, particularly the pion induced production of fast alpha particles which can contribute to the total cross sections through reactions like /sup 209/Bi(alpha,xn)/sup 213-x/At. The importance of these secondary contributions was studied through a series of negative pion irradiations of bismuth in which secondary pathways furnish the only means of producing astatine. The failure of evaporation calculations to reproduce the astatine product mass yields observed in these secondary studies suggests that direct mechanisms for energetic complex particle formation are quite important. Values for the alpha decay branches of /sup 207/At, /sup 208/At, and /sup 209/At were determined through a study of the electron capture and alpha decay characteristics of chemically purified astatine fractions.

Clark, J.L.

1980-01-01

181

Exchange reactions between whey proteins and caseins in heated soya oil-in-water emulsion systems — overall aspects of the reaction  

Microsoft Academic Search

The heat-induced exchange of caseins and serum proteins on the interfaces of oil-in-water emulsion droplets has been studied. At temperatures above 40°C, the proteins from whey protein isolate were capable of displacing adsorbed caseins. As the whey proteins ?-lactoglobulin and ?-lactalbumin adsorbed, ?s1- and ?-caseins were desorbed, principally the former. The ?s2- and ?-caseins were not displaced. The rate of

Douglas G Dalgleish; H. Douglas Goff; Jacqueline M Brun; Beibei Luan

2002-01-01

182

Ab initio calculation of transition state normal mode properties and rate constants for the H(T)+CH4(CD4) abstraction and exchange reactions  

NASA Astrophysics Data System (ADS)

We present ab initio (GVB-POL-CI) calculations for enough of the region about the abstraction and exchange saddle points for H(T)+CH4(CD4) to perform a full normal mode analysis of the transition states. The resulting normal mode frequencies are compared to four other published surfaces: an ab initio UHF-SCF calculation by Carsky and Zahradnik, a semiempirical surface by Raff, and two semiempirical surfaces by Kurylo, Hollinden, and Timmons. Significant quantitative and qualitative differences exist between the POL-CI results and those of the other surfaces. Transition state theory rate constants and vibrationally adiabatic reaction threshold energies were computed for all surfaces and compared to available experimental values. For abstraction, the POL-CI rates are in good agreement with experimental rates and in better agreement than are the rates of any of the other surfaces. For exchange, uncertainties in the experimental values and in the importance of vibrationally nonadiabatic effects cloud the comparison of theory to experiment. Tentative conclusions are that the POL-CI barrier is too low by several kcal. Unless vibrationaly nonadiabatic effects are severe, the POL-CI surface is still in better agreement with experiment than are the other surfaces. The rates for a simple 3-atom transition state theory model (where CH3 is treated as an atom) are compared to the rates for the full 6-atom model. The kinetic energy coupling of reaction coordinate modes to methyl group modes is identified as being of primary importance in determining the accuracy of the 3-atom model for this system. Substantial coupling in abstraction, but not exchange, causes the model to fail for abstraction but succeed for exchange.

Schatz, George C.; Walch, Stephen P.; Wagner, Albert F.

1980-11-01

183

New reactions and theory in organic photochemistry: The 1,3-vinyl migration and its relevance to exchange integral control*  

PubMed Central

The photochemistry of 1,1,4-triphenyl-1,4-pentadiene was investigated. Sensitized irradiation of this compound labeled at carbon 3 with 2H led to a degenerate rearrangement wherein the diphenylvinyl moiety migrated 1,3, thus affording diene with 2H substitution at carbon 5. In contrast, direct irradiation of the triphenyl pentadiene led to 1,3,3-triphenylbicyclo[2.1.0]pentane by a [2 + 2] cycloaddition. This multiplicity dependence of the photochemistry is understood on the basis of triplet reactants preferring a linearly conjugated diradical mechanism with a large exchange integral (K) and singlet reactants preferring an electrocyclic mechanism with a small exchange integral.

Zimmerman, Howard E.; Penn, John H.; Johnson, Mark R.

1981-01-01

184

Ratiometric analysis in hyperpolarized NMR (I): test of the two-site exchange model and the quantification of reaction rate constants.  

PubMed

Conventional methods for the analysis of in vivo hyperpolarized (13) C NMR data from the lactate dehydrogenase (LDH) reaction usually make assumptions on the stability of rate constants and/or the validity of the two-site exchange model. In this study, we developed a framework to test the validity of the assumption of stable reaction rate constants and the two-site exchange model in vivo via ratiometric fitting of the time courses of the signal ratio L(t)/P(t). Our analysis provided evidence that the LDH enzymatic kinetics observed by hyperpolarized NMR are in near-equilibrium and satisfy the two-site exchange model for only a specific time window. In addition, we quantified both the forward and reverse exchange rate constants of the LDH reaction for the transgenic and mouse xenograft models of breast cancer using the ratio fitting method developed, which includes only two modeling parameters and is less sensitive to the influence of instrument settings/protocols, such as flip angles, degree of polarization and tracer dosage. We further compared the ratio fitting method with a conventional two-site exchange modeling method, i.e. the differential equation fitting method, using both the experimental and simulated hyperpolarized NMR data. The ratio fitting method appeared to fit better than the differential equation fitting method for the reverse rate constant on the mouse tumor data, with less relative errors on average, whereas the differential equation fitting method also resulted in a negative reverse rate constant for one tumor. The simulation results indicated that the accuracy of both methods depends on the width of the transport function, noise level and rate constant ratio; one method may be more accurate than the other based on the experimental/biological conditions aforementioned. We were able to categorize our tumor models into specific conditions of the computer simulation and to estimate the errors of rate quantification. We also discussed possible approaches to the development of more accurate rate quantification methods for hyperpolarized NMR. Copyright © 2013 John Wiley & Sons, Ltd. PMID:23625472

Li, Lin Z; Kadlececk, Stephen; Xu, He N; Daye, Dania; Pullinger, Benjamin; Profka, Harrilla; Chodosh, Lewis; Rizi, Rahim

2013-04-29

185

Formation of gypsum and bassanite by cation exchange reactions in the absence of free-liquid H2O: Implications for Mars  

NASA Astrophysics Data System (ADS)

Smectites and hydrated Mg sulfate minerals have been identified in close association at various locations on the Martian surface. The hydration states of sulfates and smectites are dependent on temperature and relative humidity (RH), and therefore these minerals have the potential to affect cycling and bioavailability of H2O on Mars. We have conducted X-ray powder diffraction experiments to investigate cycling of H2O within mixtures of Ca-bearing smectites and hydrated Mg sulfate minerals under conditions of varying RH similar to those that exist at or just beneath the Martian surface. Our experiments show that under conditions of varying RH, cation-exchange reactions occur between these two potential components of the Martian regolith, producing gypsum [CaSO4·2H2O] and bassanite [CaSO4·˜0.5H2O] in the absence of free-liquid H2O. Cation-exchange reactions were accompanied by significant loss of porosity, warping of the sample surface and, in some cases, volume expansion. The formation of Ca sulfate minerals in these experiments provides evidence for the development of thin films of H2O at mineral surfaces and suggests that similar processes may operate at the arid surface of Mars. Humidity-driven cation-exchange reactions between smectites and hydrated Mg sulfate minerals may therefore play a role in shaping the present-day Martian surface and could have provided a transient source of H2O and nutrients (e.g., major and trace elements and possibly organic micro/macronutrients) for putative microorganisms.

Wilson, Siobhan A.; Bish, David L.

2011-09-01

186

Adsorption isotherms in ion exchange reactions. Further treatments and remarks on the application of the Langmuir isotherm  

Microsoft Academic Search

In a previous work, the author gave an adsorption isotherm for the general case of single-site heterovalent exchange and simpler approximate equations having linear forms involving the same plot used for the Langmuir isotherm. The present work gives a substantiation of these equations by calculations involving some potential practical examples. It also extends the equations to the case of two-site

Nasr Z. Misak

1995-01-01

187

A STUDY OF CATALYTIC REACTIONS ON SEMICONDUCTORS: HYDROGEN-DEUTERIUM EXCHANGE AND FORMIC ACID DECOMPOSITION ON CHEMICALLYDOPED GERMANIUM  

Microsoft Academic Search

Rates and activation energies for the hydrogen-deuterium exchange and ; formic acid vapor decomposition were measured on a series of chemically doped ; germanium catalysts over the temperature range 100 to 400 deg C. The germanium ; catalysts were intriosic and n- or p-type extrinsic semiconductors; the position ; of the Fermi level of the solid was located suitably in

1962-01-01

188

Modeling and experiment reveal an unexpected stereoelectronic effect on conformation and scalar couplings of alpha-aminoorganostannanes, with possible relevance to the tin-lithium exchange reaction.  

PubMed

The solution conformation of N-methyl-2-(tributylstannyl)piperidines has been determined through the use of vicinal 119Sn-13C coupling constants, revealing a conformational distortion caused by an unexpected stereoelectronic effect in some cases. Specifically, the "equatorial" conformer is distorted into a half-chair, in which the nitrogen lone pair eclipses the C-Sn bond. This distortion, which "costs" approximately 1 kcal/mol, correlates with a conformational dependence of geminal 119Sn-15N couplings and a possible correlation with reactivity in the tin-lithium exchange reaction. PMID:14575474

Santiago, Marcelina; Low, Eddy; Chambournier, Gilles; Gawley, Robert E

2003-10-31

189

Synthesis and crystal structure of Mg0.5NbO2: An ion-exchange reaction with Mg2+ between trigonal [NbO2]- layers  

NASA Astrophysics Data System (ADS)

A new layered niobate, Mg0.5NbO2, was synthesized from LiNbO2 through a cation-exchange reaction with Mg2+ at 450-550 °C. This is the first example of a topotactic reaction with an aliovalent cation between trigonal [NbO2]- layers. It is proposed to be isostructural with LiNbO2 (space group; P63/mmc) with lattice parameters of a=2.9052(6) Å, c=10.625(15) Å. The lattice parameters and formation energy of Mg0.5NbO2 crystallized in LiNbO2 form and other layered CaNb2O4 one were calculated by density functional theory.

Miura, Akira; Takei, Takahiro; Kumada, Nobuhiro

2013-01-01

190

Production of the neutron-rich hypernucleus 10LambdaLi in the (pi-,K+) double charge-exchange reaction.  

PubMed

In order to produce a neutron-rich Lambda hypernucleus for the first time, we carried out an experiment by utilizing the (pi-,K+) double charge-exchange reaction on a 10B target. We observed the production of a 10LambdaLi hypernucleus. The cross section for the Lambda bound region was found to be 11.3+/-1.9 nb/sr with the 1.2 GeV/c incident momentum, which is compared with the 10LambdaB hypernucleus production cross section, 7.8+/-0.3 microb/sr, in the (pi+,K+) reaction with a 1.05 GeV/c incident momentum beam. PMID:15783631

Saha, P K; Fukuda, T; Imoto, W; Ahn, J K; Ajimura, S; Aoki, K; Bhang, H C; Fujioka, H; Hotchi, H; Hwang, J I; Itabashi, T; Kang, B H; Kim, H D; Kim, M J; Kishimoto, T; Krutenkova, A; Maruta, T; Miura, Y; Miwa, K; Nagae, T; Noumi, H; Outa, H; Ohtaki, T; Sakaguchi, A; Sato, Y; Sekimoto, M; Shimizu, Y; Tamura, H; Tanida, K; Toyoda, A; Ukai, M; Yim, H J

2005-02-09

191

Platinum/multiwalled carbon nanotubes-platinum/carbon composites as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell  

NASA Astrophysics Data System (ADS)

Pt-loaded multiwalled carbon nanotubes (Pt/MWCNTs) have been prepared by chemical reduction method using functionalized MWCNT synthesized by pyrolysis of acetylene over MmNi2 (Mm denotes misch metal) hydride catalyst. Composites of Pt/MWCNT and commercial Pt-loaded carbon black (Pt/C) have been used as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell (PEMFC). Cathode catalyst with 50% Pt/MWCNT and 50% Pt/C showed best performance due to better dispersion and good accessibility of MWCNT support and Pt electrocatalysts for oxygen reduction reaction in PEMFC. A maximum performance of 540 mV at a current density of around 535 mA cm-2 has been obtained.

Shaijumon, M. M.; Ramaprabhu, S.; Rajalakshmi, N.

2006-06-01

192

Evidence for o-atom exchange in the O(1D) + N2O reaction as the source of mass-independent isotopic fractionation in atmospheric N2O.  

SciTech Connect

Recent experiments have shown that in the oxygen isotopic exchange reaction for O({sup 1}D) + CO{sub 2} the elastic channel is approximately 50% that of the inelastic channel [Perri et al., 2003]. We propose an analogous oxygen atom exchange reaction for the isoelectronic O({sup 1}D) + N{sub 2}O system to explain the mass-independent isotopic fractionation (MIF) in atmospheric N{sub 2}O. We apply quantum chemical methods to compute the energetics of the potential energy surfaces on which the O({sup 1}D) + N{sub 2}O reaction occurs. Preliminary modeling results indicate that oxygen isotopic exchange via O({sup 1}D) + N{sub 2}O can account for the MIF oxygen anomaly if the oxygen atom isotopic exchange rate is 30-50% that of the total rate for the reactive channels.

Miller, Charles E. (Jet Propulsion Laboratory, Pasadena, CA); Liang, Mao-Chang (California Institute of Technology, Pasadena, CA); Blake, Geoffrey A. (California Institute of Technology, Pasadena, CA); Muller, Richard Partain; Yung, Yuk L. (California Institute of Technology, Pasadena, CA)

2004-07-01

193

Pt nanoparticle-dispersed graphene-wrapped MWNT composites as oxygen reduction reaction electrocatalyst in proton exchange membrane fuel cell.  

PubMed

Chemical and electrical synergies between graphite oxide and multiwalled carbon nanotube (MWNT) for processing graphene wrapped-MWNT hybrids has been realized by chemical vapor deposition without any chemical functionalization. Potential of the hybrid composites have been demonstrated by employing them as electrocatalyst supports in proton exchange membrane fuel cells. The defects present in the polyelectrolyte, which have been wrapped over highly dispersed MWNT, act as anchoring sites for the homogeneous deposition of platinum nanoparticles. Single-cell proton exchange membrane fuel cells show that the power density of the hybrid composite-based fuel cells is higher compared to the pure catalyst-support-based fuel cells, because of enhanced electrochemical reactivity and good surface area of the nanocomposites. PMID:22850438

Aravind, S S Jyothirmayee; Ramaprabhu, Sundara

2012-08-10

194

Tracing the Steps of Photoinduced Chemical Reactions in Organic Molecules by Coherent Two-Dimensional Electronic Spectroscopy Using Triggered Exchange  

NASA Astrophysics Data System (ADS)

We establish coherent triggered-exchange two-dimensional (TE2D) electronic spectroscopy as an expansion of pump-repump-probe transient absorption spectroscopy and uniquely elucidate the role of higher-lying electronic states in ultrafast photochemistry. As an example, this is demonstrated for a molecular switch present in two ring-open conformations. The formation of a new species—the radical cation—is observed and its precursor state is identified via TE2D.

Ruetzel, Stefan; Kullmann, Martin; Buback, Johannes; Nuernberger, Patrick; Brixner, Tobias

2013-04-01

195

Kinetic dissection of two distinct proton binding sites in Na+/H+ exchangers by measurement of reverse mode reaction.  

PubMed

We examined the effect of intracellular acidification on the reverse mode of Na+/H+ exchange by measuring 22Na+ efflux from 22Na+-loaded PS120 cells expressing the Na+/H+ exchanger (NHE) isoforms NHE1, NHE2, and NHE3. The 5-(N-ethyl-N-isopropyl)amiloride (EIPA)- or amiloride-sensitive fraction of 22Na+ efflux was dramatically accelerated by cytosolic acidification as opposed to thermodynamic prediction, supporting the concept that these NHE isoforms are activated by protonation of an internal binding site(s) distinct from the H+ transport site. Intracellular pH (pHi) dependence of 22 Na+ efflux roughly exhibited a bell-shaped profile; mild acidification from pHi 7.5 to 7 dramatically accelerated 22Na+ efflux, whereas acidification from pHi 6.6 gradually decreased it. Alkalinization above pHi 7.5 completely suppressed EIPA-sensitive 22Na+ efflux. Cell ATP depletion and mutation of NHE1 at Arg440 (R440D) caused a large acidic shift of the pHi profile for 22Na+ efflux, whereas mutation at Gly455 (G455Q) caused a significant alkaline shift. Because these mutations and ATP depletion cause correspondingly similar effects on the forward mode of Na+/H+ exchange, it is most likely that they alter exchange activity by modulating affinity of the internal modifier site for protons. The data provide substantial evidence that a proton modifier site(s) distinct from the transport site controls activities of at least three NHE isoforms through cooperative interaction with multiple protons. PMID:12928437

Wakabayashi, Shigeo; Hisamitsu, Takashi; Pang, Tianxiang; Shigekawa, Munekazu

2003-08-19

196

Reactions involving isotopic exchange of heterocyclic compounds with D 2 O in the presence of transition metals (review)  

Microsoft Academic Search

The results of isotopic exchange with D2O of various O-, N-, and S-containing heterocycles and some hydrocarbons on transition metals are discussed from the positions of the theory of ?-complex adsorption. The effect of various fragments of the molecules (the aromatic or alicyclic ring, electron-donor or electron-acceptor substituents, double bonds, and the number and nature of the heteroatoms) on the

É. A. Karakhanov; A. G. Dedov

1982-01-01

197

A theoretical study of the iminoxyl/oxime self-exchange reaction. A five-center, cyclic proton-coupled electron transfer.  

PubMed

In solution, the self-exchange reactions for oxygen-centered pi-radicals, e.g., PhO. + PhOH <==>PhOH + PhO., are known to occur with low activation enthalpies (E(a) approximately equal to 2 kcal/mol). For the PhO./PhOH couple and, we conclude, for other O-centered pi-radicals, exchange occurs by proton-coupled electron transfer (PCET) with the proton transferred between oxygen electron pairs while the electron migrates between oxygen orbitals orthogonal to the -O- - -H- - -O- transition state plane (Mayer et al. J. Am. Chem. Soc. 2002, 123, 11142). Iminoxyls, R(2)C=NO., are sigma-radicals with substantial spin density on the nitrogen. The R(2)C=NO./R(2)C=NOH self-exchange has a significant E(a) (Mendenhall et al. J. Am. Chem. Soc. 1973, 95, 627). For this exchange, DFT calculations have revealed a counterintuitive cisoid transition state in which the seven atoms, >C=NO- - -H- - -ON=C<, lie in a plane (R = H, Me) or, for steric reasons, two planes twisted at 45.2 degrees (R = Me(3)C). The planar transition state has the two N-O dipoles close to each other and pointing in the same direction and an O- - -H- - -O angle of 165.4 degrees . A transoid transition state for R = H lies 3.4 kcal/mol higher in energy than the cisoid despite a more favorable arrangement of the dipoles and a near linear O- - -H- - -O. It is concluded that iminoxyl/oxime self-exchange reactions occur by a five-center, cyclic PCET mechanism with the proton being transferred between electron pairs on the oxygens and the electron migrating between in-plane orbitals on the two nitrogens (R(N-N) = 2.65 A). The calculated E(a) values (8.8-9.9 kcal/mol) are in satisfactory agreement with the limited experimental data. PMID:15869291

DiLabio, Gino A; Ingold, K U

2005-05-11

198

Interaction between the reaction medium and an ion-exchange resin catalyst in the etherification of isoamylenes  

Microsoft Academic Search

tert-Amyl methyl ether (2-methoxy-2-methylbutane, TAME) is synthesised in a liquid-phase reaction of methanol (MeOH) and isoamylenes (2-methyl-1-butene (2M1B), and 2-methyl-2-butene (2M2B)). The reaction rates of the formation of TAME were measured in a continuous stirred tank reactor (CSTR) at the temperature range between 323 and 353K. The molar ratio of methanol to isoamylenes and the concentration of the reagents were

Liisa K Rihko-Struckmann; Petri V Latostenmaa; A. Outi I Krause

2001-01-01

199

Human immunodeficiency virus-1 protease. 1. Initial velocity studies and kinetic characterization of reaction intermediates by sup 18 O isotope exchange  

SciTech Connect

The peptidolytic reaction HIV-1 protease has been investigated by using four oligopeptide substrates, Ac-Ser-Gln-Asn-Pro-Val-Val-NH{sub 2}, Ac-Arg-Ala-Ser-Gln-Asn-Tyr-Pro-Val-Val-NH{sub 2}, Ac-Ser-Gln-Ser-Tyr-Pro-Val-Val-NH{sub 2}, and Ac-Arg-Lys-Ile-Leu-Phe-Leu-Asp-Gly-NH{sub 2} that resemble two cleavage sites found within the naturally occurring polyprotein substrates Pr55{sup gag} and Pr160{sup gag-pol}. By use of a variety of inorganic salts, it was concluded that the peptidolytic reaction is nonspecifically activated by increasing ionic strength. V/K increased in an apparently parabolic fashion with increasing ionic strength, while V was either increased or decreased slightly. From product inhibition studies, the kinetic mechanism of the protease is either random or ordered uni-bi, depending on the substrate studied. The protease-catalyzed exchange of an atom of {sup 18}O from H{sub 2}{sup 18}O into the re-formed substrates occurred at a rate which was 0.01-0.12 times that the forward peptidolytic reaction. The results of these studies are in accord with the formation of a kinetically competent enzyme-bound amide hydrate intermediate, the collapse of which is the rate-limiting chemical step in the reaction pathway.

Hyland, L.J.; Tomaszek, T.A. Jr.; Roberts, G.D.; Carr, S.A.; Magaard, V.W.; Bryan, H.L.; Fakhoury, S.A.; Moore, M.L.; Minnich, M.D.; Culp, J.S.; DesJarlais, R.L.; Meek, T.D. (Smline Beecham Pharmaceuticals, King of Prussia, PA (United States))

1991-08-27

200

Oxygen isotope biogeochemistry of pore water sulfate in the deep biosphere: Dominance of isotope exchange reactions with ambient water during microbial sulfate reduction (ODP Site 1130)  

NASA Astrophysics Data System (ADS)

Microbially mediated sulfate reduction affects the isotopic composition of dissolved and solid sulfur species in marine sediments. Experiments and field data show that the ?18O composition is also modified in the presence of sulfate-reducing microorganisms. This has been attributed either to a kinetic isotope effect during the reduction of sulfate to sulfite, cell-internal exchange reactions between enzymatically-activated sulfate (APS), and/or sulfite with cytoplasmic water. The isotopic fingerprint of these processes may be further modified by the cell-external reoxidation of sulfide to elemental sulfur, and the subsequent disproportionation to sulfide and sulfate or by the oxidation of sulfite to sulfate. Here we report ?18O values from interstitial water samples of ODP Leg 182 (Site 1130) and provide the mathematical framework to describe the oxygen isotope fractionation of sulfate during microbial sulfate reduction. We show that a purely kinetic model is unable to explain our ?18O data, and that the data are well explained by a model using oxygen isotope exchange reactions. We propose that the oxygen isotope exchange occurs between APS and cytoplasmic water, and/or between sulfite and adenosine monophosphate (AMP) during APS formation. Model calculations show that cell external reoxidation of reduced sulfur species would require up to 3000 mol/m3 of an oxidant at ODP Site 1130, which is incompatible with the sediment geochemical data. In addition, we show that the volumetric fluxes required to explain the observed ?18O data are on average 14 times higher than the volumetric sulfate reduction rates (SRR) obtained from inverse modeling of the porewater data. The ratio between the gross sulfate flux into the microbes and the net sulfate flux through the microbes is depth invariant, and independent of sulfide concentrations. This suggests that both fluxes are controlled by cell density and that cell-specific sulfate reduction rates remain constant with depth.

Wortmann, Ulrich G.; Chernyavsky, Boris; Bernasconi, Stefano M.; Brunner, Benjamin; Böttcher, Michael E.; Swart, Peter K.

2007-09-01

201

Anion exchanger as a reaction/separation medium-absorptiometric determination of trace amounts of boron in waters by on-line complexation with chromotropic acid presorbed on the anion-exchange column.  

PubMed

A novel method of on-line absorptiometric determination for trace amounts of boron was developed based on the complexation with chromotropic acid presorbed on an anion-exchange column. On-line reaction and separation were achieved by controlling pH conditions in solutions to accelerate the 1:2 complex formation in the concentration process at pH 3 and to stabilize the complex in the separation process at pH 8. About 75% of the boron introduced into the stream was kinetically collected as the 1:2 complex on the column under the experimental conditions. The 1:2 complex was satisfactorily separated from excess reagent and matrix components by changing the concentration of NaClO4 in the eluent and its peak height on the chromatogram monitored at 350 nm was used for calibration. The sensitivity could be enhanced by increasing the sample amount introduced and the detection limits (3sigma) were 162 ng dm(-3) and 45 ng dm(-3) of boron, when 5.0 cm3 and 13.4 cm3 of the samples were used, respectively. The method has been successfully applied to the determination of boron in samples of river water, tap water and ion-exchanged water. PMID:12537369

Shao, Chaoying; Matsuoka, Shiro; Miyazaki, Yoshinobu; Yoshimura, Kazuhisa

2002-12-01

202

Two-pion-exchange and other higher-order contributions to the pp{yields}pp{pi}{sup 0} reaction  

SciTech Connect

Much effort has been invested on effective-field-theoretical studies of the near-threshold NN{yields}NN{pi} reactions and, in order to deal with the somewhat large three-momentum transfers involved, the momentum counting scheme (MCS) was proposed as an alternative to the usual Weinberg counting scheme. Given the fact that a quantitative explanation of the existing high-precision NN{yields}NN{pi} data requires a careful examination of higher chiral order contributions to the transition operator, we make a detailed numerical investigation of the convergence property of MCS for a pilot case of the pp{yields}pp{pi}{sup 0} reaction. Our study indicates that MCS is superior to the Weinberg scheme in identifying dominant higher order contributions to the NN{yields}NN{pi} reactions.

Kim, Y. [Department of Physics and Astronomy, University of South Carolina, Columbia, South Carolina 29208 (United States); School of Physics, Korea Institute for Advanced Study, Seoul 130-012 (Korea, Republic of); Sato, T. [Department of Physics, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Myhrer, F.; Kubodera, K. [Department of Physics and Astronomy, University of South Carolina, Columbia, South Carolina 29208 (United States)

2009-07-15

203

Cumulative reaction probabilities and transition state properties: A study of the H++H2 and H++D2 proton exchange reactions  

NASA Astrophysics Data System (ADS)

Cumulative reaction probabilities (CRPs) have been calculated by accurate (converged, close coupling) quantum mechanical (QM), quasiclassical trajectory (QCT), and statistical QCT (SQCT) methods for the H++H2 and H++D2 reactions at collision energies up to 1.2 eV and total angular momentum J=0-4. A marked resonance structure is found in the QM CRP, most especially for the H3+ system and J=0. When the CRPs are resolved in their ortho and para contributions, a clear steplike structure is found associated with the opening of internal states of reactants and products. The comparison of the QCT results with those of the other methods evinces the occurrence of two transition states, one at the entrance and one at the exit. At low J values, except for the quantal resonance structure and the lack of quantization in the product channel, the agreement between QM and QCT is very good. The SQCT model, that reflects the steplike structure associated with the opening of initial and final states accurately, clearly tends to overestimate the value of the CRP as the collision energy increases. This effect seems more marked for the H++D2 isotopic variant. For sufficiently high J values, the growth of the centrifugal barrier leads to an increase in the threshold of the CRP. At these high J values the discrepancy between SQCT and QCT becomes larger and is magnified with growing collision energy. The total CRPs calculated with the QCT and SQCT methods allowed the determination of the rate constant for the H++D2 reaction. It was found that the rate, in agreement with experiment, decreases with temperature as expected for an endothermic reaction. In the range of temperatures between 200 and 500 K the differences between SQCT and QCT rate results are relatively minor. Although exact QM calculations are formidable for an exact determination of the k(T), it can be reliably expected that their value will lie between those given by the dynamical and statistical trajectory methods.

Jambrina, P. G.; Aoiz, F. J.; Eyles, C. J.; Herrero, V. J.; Sáez Rábanos, V.

2009-05-01

204

Layered alkali rhodium oxides A/sub x/RhO/sub 2/: topotactic solvation, exchange, and redox reactions  

SciTech Connect

The intercalation/deintercalation properties of the layered oxides LiRhO/sub 2/, and KRhO/sub 2/ have been investigated with respect to redox and exchange processes. The chemical reactivity was found to be strongly dependent upon the alkali cation. Only KRhO/sub 2/ is able to form hydrated phases and to undergo quantitative K/sup +//H/sup +/ exchange, resulting in the formation of the new layered hydrogen bronze HRhO/sub 2/. HRhO/sub 2/ has a limited phase range up to H/sub 1.1/RhO/sub 2/ and exhibits no Broensted acid character. LiRhO/sub 2/ and NaRhO/sub 2/ both show a limited cycling range in aprotic Li/sup +/ or Na/sup +/ electrolytes beyond which irreversible lattice disorder is observed. The origin of the significant differences in topotactic reactivity between layered dichalcogenide and oxide systems is discussed.

Mendiboure, A.; Eickenbusch, H.; Schoellhorn, R.; Subba Rao, G.V.

1987-11-01

205

Modeling Multi-Species Transport With Non-Linear Reactions and Mass Exchange Between Mobile Fluid and Stationary Porous Medium  

Microsoft Academic Search

We present a novel approach to numerically solve the mathematical model of reactive mass transport in porous media. The main objective is to solve a multi-species transport problem with non-linear reactions. In this system, the transfer of mass from the mobile fluid to the stationary medium is considered as an important transport mechanism. Examples of this type of problem include

I. Mendoza-Sanchez; J. A. Cunningham

2006-01-01

206

Density functional theory study of the carbonyl-ene reaction of encapsulated formaldehyde in Cu(I), Ag(I), and Au(I) exchanged FAU zeolites.  

PubMed

Carbonyl-ene reactions, which involve C-C bond formation, are essential in many chemical syntheses. The formaldehyde-propene reaction catalyzed by several of the group 11 metal cations, Cu(+), Ag(+), and Au(+) exchanged on the faujasite zeolite (metal-FAU) has been investigated by density functional theory at the M06-L/6-31G(d,p) level. The Au-FAU exhibits a higher activity than the others due to the high charge transfer between the Au and the reactant molecules, even though it is located at a negatively charged site of the zeolite. This site enables it to compensate for the charge of the Au(+) ion. The NBO analysis reveals that the 6s orbital of the Au atom plays an important role, inducing a charge on the probe molecules. Moreover, the effect of the zeolite framework makes the Au-FAU more active than the others by stabilizing the high charge induced transition structure. The activation energy of the reaction catalyzed by Au-FAU is 13.0 kcal/mol whereas that of Cu and Ag-FAU is found to be around 17 kcal/mol. The product desorption needs to be improved for Au-FAU; however, we suggest that catalysts with high charge transfer might provide a promising activity. PMID:21942893

Wannakao, Sippakorn; Khongpracha, Pipat; Limtrakul, Jumras

2011-09-26

207

Hydrogen isotope exchange reactions between hydrous minerals and molecular hydrogen: I. A new approach for the determination of hydrogen isotope fractionation at moderate temperatures  

NASA Astrophysics Data System (ADS)

Molecular hydrogen was used as an exchange medium to make indirect determinations of hydrogen isotope fractionation factors between hydrous minerals (epidote, kaolinite, muscovite, biotite, and hornblende) and water at temperatures between 150 and 400°C. Hydrogen isotope exchange between hydrous minerals and H 2 is found to be unusually rapid at these temperatures and, in the absence of reducible iron, may represent true diffusive exchange. Two methods were used for the exchange: (1) the molecular hydrogen provided an "infinite" reservoir of H 2 and (2) the mineral provided an "infinite" reservoir of H 2. Results of these methods are in good agreement for epidote and kaolinite, suggesting that "surface effects" are not important for these experiments. Fractionation factors in the epidote-H 2 system, expressed as 1000 ln?, increase linearly with increasing 1/T 2 (or decreasing temperature) between temperatures of 150 and 400°C. This behavior is also true for epidote-water fractionation factors calculated from published H 2O (vapor) - H 2 and H 2O (vapor) - H 2O(liquid) fractionation factors. Values of 1000 ln? for kaolinite-H 2 and muscovite-H 2 fractionation factors are similar and also decrease linearly with increasing 1/T 2 between 200 and 275°C, and 200 and 400°C, respectively. There is a small departure from such linearity at temperatures of less than 200°C for the kaolinite-H 2 system. The trends of the calculated kaolinite-H 2O fractionation factors with temperature are similar to those previously published, with a maximum at about 200°C. Muscovite-H 2O fractionation factors also decrease with decreasing temperatures and become increasingly positive at temperatures lower than about 225°C. Problems of reduction of iron and a concomitant increase in the amount of water were encountered in exchange experiments involving biotite, hornblende, and, to a lesser extent, muscovite. The consequences of these reactions were the production of apparent relatively small mineral-H 2 and large mineral-H 2O equilibrium fractionation factors and support the hypothesis that hydroxyl groups are added to sites linked to iron and that there is indeed a compositional effect on hydrogen isotope fractionations in mineral-H 2O systems. The new equilibrium fractionation factors determined in this study do not unambiguously resolve serious conflicts in data published by previous workers, but do provide some important constraints on the direction and magnitude of the D/H fractionation factors between water and the common rock-forming minerals.

Vennemann, Torsten W.; O'neil, James R.

1996-07-01

208

Mass-dependent dynamics of the luminescent exchange reactions C+(2P), P+(3P) + H2, D2, HD  

NASA Astrophysics Data System (ADS)

Chemiluminescent ion/molecule reactions of ground state C+ and P+ ions with H2, D2 and HD have been studied in an ion beam/target gas cell arrangement. Emission spectra of CH+, CD+ (A 1II) and of PH+, PD+ (A 2[Delta]) were observed with up to 1 Å FWHM resolution and at collision energies from threshold ([approximate] 3 eV) to 8 eVc.m. (centre-of-mass) and 15eVc.m., respectively. Very detailed computer simulations of the spectral contours were done, including ab initio transition moments and, in the case of PH+/PD+, the effects of predissociation. In simulating the spectra obtained with HD, the overlapped hydride and deuteride product ion spectra could be isolated by varying the respective weighting factors to achieve an optimum overall fit. In the case of C+ + HD, the two components were found to have very similar rovibrational distributions as with the products from C+ + H2 and C+ + D2. In the P+ case, however, the rotational, although not the vibrational, distributions were found to be significantly different for the isotopically mixed and the pure reactions. The cross-sections showed an intermolecular isotope effect only for C+ + H2 vs. C+ + D2 at high energies. However, both with C+ + HD and P+ + HD, a very strong intramolecular isotope effect, i.e. an energy-dependent branching ratio, was observed: at low energies deuteride formation prevails, at high energies hydride. This behaviour is discussed in terms of an impulsive collision model, assuming the "pairwise" relative kinetic energy between the reacting atoms to be the determining factor. On the basis of the measured cross-section curves for the H2 and D2 reactions, the energy-dependent hydride/deuteride ratio in the HD reaction can then be predicted. The agreement with the experimental results is excellent in the P+ case, but only moderate for the C+ reactions. Even the P+ reaction, however, does not occur via the spectator stripping mechanisms. The spectra show an energy-independent vibrational excitation, contrary to the stripping model assumption. The impulsive model was also extended to an analysis of the relative mean product angular momenta. Again it performs well for P+ + H2, D2, HD, but cannot fit the C+ + HD case.

Glenewinkel-Meyer, Th; Hoppe, U.; Kowalski, A.; Ottinger, Ch; Rabenda, D.

1995-06-01

209

Sonochemistry of alcohol-water mixtures: Spin-trapping evidence for thermal decomposition and isotope-exchange reactions  

Microsoft Academic Search

The sonochemistry of argon-saturated water-alcohol mixtures has been studied by ESR and spin trapping with 3,5-dibromo-4-nitrosobenzenesulfonate. Free-radical intermediates induced by 50-kHz ultrasound in aqueous solutions of ethanol, 1-propanol, 2-propanol, and 2-methyl-2-propanol were identified. Spin adducts typical of thermal decomposition of the alcohols and of H- and OH-induced abstraction reactions were observed. In the sonolysis of mixed-isotope systems of the type

C. Murali Krishna; Takashi Kondo; Peter Riesz

1989-01-01

210

Irreversible Li +\\/H + ion-exchange reaction between cubic HNbO 3 and rhombohedral LiNbO 3 and NMR study of Li xH 1?xNbO 3  

Microsoft Academic Search

The Li+\\/H+ ion-exchange reaction was examined between cubic niobic acid (c-HNbO3) and rhombohedral lithium niobate (r-LiNbO3). The proton exchange of r-LiNbO3 in concentrated nitric acid occurred through an apparent eutectic mixture of c-HNbO3 and r-LiNbO3. The X-ray diffraction peaks of r-LiNbO3 simply decreased while those of c-HNbO3 increased inversely. The conversion to c-HNbO3 was almost 100%. The reverse lithium ion-exchange

Tohru Ohsaka; Yasushi Kanzaki; Mitsuo Abe

2001-01-01

211

Complex formation of uranyl ion with triphenylphosphine oxide and its ligand exchange reaction in 1-butyl-3-methylimidazolium nonafluorobutanesulfonate ionic liquid.  

PubMed

Complex formation of the uranyl ion (UO(2)(2+)) with triphenylphosphine oxide (OPPh(3)) in 1-butyl-3-methylimidazolium nonafluorobutanesulfonate ([BMI][NfO]) ionic liquid was investigated by means of (31)P NMR spectroscopy. In [BMI][NfO], coordination of OPPh(3) to UO(2)(2+) was found, and its coordination number was 4.1 +/- 0.2, indicating UO(2)(OPPh(3))(4)(2+). From the [BMI][NfO] solution containing UO(2)(2+) and OPPh(3), yellow crystals of UO(2)(OPPh(3))(4)(ClO(4))(2) deposited, and its molecular and crystal structures were determined by using single-crystal X-ray analysis. An OPPh(3) exchange reaction of UO(2)(OPPh(3))(4)(2+) in [BMI][NfO] was also examined. The apparent first-order rate constant (k(obs)) showed the first-order dependence on [OPPh(3)] (k(obs) = k(4)[OPPh(3)](free)), suggesting the "associative" (A) mechanism. Its activation parameters were DeltaH(4)(++) = 55.3 +/- 2.8 kJ mol(-1) and DeltaS(4)(++) = 16.1 +/- 7.9 J mol(-1) K(-1). To compare the reactivity of UO(2)(OPPh(3))(4)(2+) in [BMI][NfO] with that in an ordinary organic solvent, the same reaction in CD(2)Cl(2) was studied. In the CD(2)Cl(2) system, an equilibrium between UO(2)(OPPh(3))(4)(2+) and UO(2)(OPPh(3))(5)(2+) was observed. The k(obs) values of the OPPh(3) exchange reactions in UO(2)(OPPh(3))(4)(2+) (k(4obs)) and UO(2)(OPPh(3))(5)(2+) (k(5obs)) in CD(2)Cl(2) are expressed as k(4obs) = k(4)[OPPh(3)](free) and k(5obs) = k(5), respectively, indicating that the exchange reactions in UO(2)(OPPh(3))(4)(2+) and UO(2)(OPPh(3))(5)(2+) are categorized in A and "dissociative" (D) mechanisms, respectively. The activation parameters of these reactions were also estimated (UO(2)(OPPh(3))(4)(2+): DeltaH(4)(++) = 7.1 +/- 0.3 kJ mol(-1) and DeltaS(4)(++) = -122 +/- 1 J mol(-1) K(-1), UO(2)(OPPh(3))(5)(2+): DeltaH(5)(++) = 62.4 +/- 1.0 kJ mol(-1) and DeltaS(5)(++) = 68.4 +/- 4.2 J mol(-1) K(-1)). A large difference in the reactivity of UO(2)(OPPh(3))(4)(2+) was found between [BMI][NfO] and CD(2)Cl(2). This was explained by the formation of a specific solvation barrier of NfO(-) around UO(2)(OPPh(3))(4)(2+) in [BMI][NfO]. PMID:19138105

Takao, Koichiro; Takahashi, Takafumi; Ikeda, Yasuhisa

2009-02-16

212

A Structure-Function Study of RecA: The Structural Basis for ATP Specificity in the Strand Exchange Reaction  

NASA Astrophysics Data System (ADS)

The terms "structure" and "function" can assume a variety of meanings. In biochemistry, the "structure" of a protein can refer to its sequence of amino acids, the three-dimensional arrangement of atoms within a subunit, or the arrangement of subunits into a larger oligomeric or filamentous state. Likewise, the function of biological macromolecules can be examined at many levels. The function of a protein can be described by its role in an organism's survival or by a chemical reaction that it promotes. We have designed a three-part biochemical laboratory experiment that characterizes the structure and function of the Escherichia coli RecA protein. The first part examines the importance of RecA in the survival of bacteria that have been exposed to UV light. This is the broadest view of function of the enzyme. Second, the students use an in vitro assay of RecA whereby the protein promotes homologous recombination. Because RecA functions not catalytically, but rather stoichiometrically, in this recombination reaction, the oligomeric state of RecA in complex with DNA must also be discussed. Finally, through molecular modeling of X-ray crystallographic structures, students identify functionally important features of the ATP cofactor binding site of RecA.

Gegner, Julie; Spruill, Natalie; Plesniak, Leigh A.

1999-11-01

213

A facile route to violet- to orange-emitting CdxZn1-xSe alloy nanocrystals via cation exchange reaction  

NASA Astrophysics Data System (ADS)

The most advanced CdSe-based binary semiconductor system does not work well for emission in the short wavelength spectral region from 420 to 500 nm, which is of special interest for the preparation of nanocrystal-based blue LEDs and white light generation. CdxZn1-xSe alloy nanocrystals are proven to be an attractive alternative as their emission color can be tuned from the UV spectral region (ZnSe) to the red region (CdSe) by changing the composition of the Zn/Cd ratio in the alloy. Herein we report a facile and 'green' alloying approach for the preparation of highly luminescent CdxZn1-xSe nanocrystals via cation exchange reaction of the pre-prepared ZnSe nanocrystals with Cd2+ at intermediate temperatures. Through this new synthetic strategy, high-quality alloy QDs with different desired emission wavelengths or colors (ranging from 370 to 600 nm) can be made reproducibly and precisely by varying the predetermined amounts of the reaction precursors.

Zhong, Xinhua; Feng, Yaoyu; Zhang, Yuliang; Gu, Zhenyu; Zou, Lei

2007-09-01

214

Charge exchange, surface-induced dissociation and reactions of doubly charged molecular ions SF42+ upon impact on a stainless steel surface  

NASA Astrophysics Data System (ADS)

Collisions of SF42+ and SF4+ ions with hydrocarbon-covered stainless steel surface at room temperature were investigated. The projectile ions were mass selected by a two-sector-field mass spectrometer and decelerated to incident energies of 60 to a few eV. Product ions were measured with the use of a time-of-flight spectrometer and their relative abundances determined as a function of the incident energy of the projectile ions (collision-energy-resolved mass spectra, CERMS curves). The mass spectra of product ions were dominated by fragment ions SF3+, SF2+, and SF+ at incident energies below 40 eV, while sputtering of contaminant adsorbates prevailed at higher energies. The results indicate that the likely major reaction sequence responsible for the observed CERMS curves of product ions from SF42+ collisions is charge exchange to form singly charged projectile ions followed by subsequent unimolecular fragmentation. In addition, chemical reactions between projectile ions and hydrocarbon adsorbates were observed leading to SF2CH3+, SFCH2+, and SCH+ ions.

Feketeová, L.; Grill, V.; Zappa, F.; Endstrasser, N.; Rasul, B.; Herman, Z.; Scheier, P.; Märk, T. D.

2008-09-01

215

Development of a High-Speed Real-Time Polymerase Chain Reaction System Using a Circulating Water-Based Rapid Heat-Exchange  

NASA Astrophysics Data System (ADS)

Polymerase chain reaction (PCR) is a powerful technique to detect microorganisms, viruses, or cells by amplifying a single copy or a few copies of a fragment of a particular DNA sequence. To reduce acquisition time, it is necessary to decrease the temperature transition time between denaturation and extension. We have developed a simple rapid real-time microlitter-sample droplet PCR system accomplished by the rapid liquid-based heat-exchange of sample droplets by quick switching of two circulating hot waters of denaturation and extension, a microlitter-sized droplet and a thin-film aluminum chip. Using this system, rapid PCR amplification of a set of droplets lined up on an aluminum chip was conducted successfully as shown by the increase in fluorescence intensity, and was accomplished within 3.5 min in 40 cycles of 1 s denaturation and 3 s extension reaction, which is one magnitude faster than conventional fast PCR systems. This method allows the rapid detection of DNA fragments and has a possibility for measuring multiple samples simultaneously in a miniaturized microfluidic chip.

Hideyuki Terazono,; Hiroyuki Takei,; Akihiro Hattori,; Kenji Yasuda,

2010-06-01

216

Phosphorylation of adenosine in renal brush-border membrane vesicles by an exchange reaction catalysed by adenosine kinase.  

PubMed Central

Uptake of [3H]adenosine in brush-border membrane (BBM) vesicles from either rat or pig kidney leads to an accumulation of intravesicular [3H]AMP. The lack of significant levels of ATP and the presence of AMP in BBM indicated that a phosphotransfer between [3H]adenosine and AMP occurs. The phosphotransfer activity is inhibited by iodotubercidin, which suggests that it is performed by adenosine kinase acting in an ATP-independent manner. The existence of a similar phosphotransferase activity was demonstrated in membrane-free extracts from pig kidney. From the compounds tested it was shown that a variety of mononucleotides could act as phosphate donors. The results suggest that phosphotransfer reactions may be physiologically relevant in kidney.

Sayos, J; Solsona, C; Mallol, J; Lluis, C; Franco, R

1994-01-01

217

Isobaric analog states in rare-earth nuclei studied with the (3He, t) charge-exchange reaction at ?L = 0°  

NASA Astrophysics Data System (ADS)

The (3He, t) charge-exchange reaction leading to the ground-state isobaric analog states (IAS) of 152, 154, 156, 158, 160Gd, 160,162Dy, 162,164,166,168,170Er, 170, 172, 174, 176Yb and 176, 178, 180Hf has been studied at ?L = 0° and E(3He) = 60.5 MeV. The reaction 28Si(3He, t)28P was used for energy calibration. The centroid energies of most IAS were determined to +/-6 keV. Coulomb displacement energies have been extracted from the measured Q-values. They display the influence of non-spherical nuclear shapes which increase the rms radii and lower the Coulomb displacement energies. The dependence on both quadrupole and hexadecapole deformations is apparent with deformation parameters in good agreement with results from other measurements. The total widths ? of the IAS are in the range 30 to 110 keV. They increase more strongly with neutron excess than is known for the IAS of the Sn and Te isotopes. The width of the IAS of 176Yb is anomalously low. The zero-degree (3He, t) cross sections are in the range 5 to 20 ?b/sr. They generally increase with neutron excess except for the sequence of Yb isotopes. No systematic dependence on (N - Z) appears to exist. Excitation energies and zero-degree cross sections for the reactions 28Si(3He, t)28P, 16O(3He,t)16F and 12C(3He,t)12N are reported.

Jänecke, J.; Aarts, E. H. L.; Drentje, A. G.; Harakeh, M. N.; Gaarde, C.

1983-02-01

218

Effects of donor-acceptor electronic interactions on the rates of gas-phase metallocene electron-exchange reactions  

SciTech Connect

Rate constants for electron self-exchange, k{sub ex}, of five cobaltocenium-cobaltocene and ferrocenium-ferrocene couples in the gas phase have been measured by means of Fourier transform ion cyclotron resonance mass spectrometry in order to explore the possible effects of donor-acceptor electronic coupling on gas-phase redox reactivity. The systems studied, Cp{sub 2}Co{sup +/0}, Cp{sub 2}Fe{sup +/0} (Cp = cyclopentadienyl), the decamethyl derivative Cp{prime}{sub 2}Fe{sup +/0}, carboxymethyl(cobaltocenium-cobaltocene) (Cp{sub 2}{sup e}Co{sup +/0}), and hydroxymethyl(ferrocenium-ferrocene) (HMFc{sup +/0}), were selected in view of the substantial variations in electronic coupling inferred on the basis of their solvent-dependent reactivities and theoretical grounds. The sequence of k{sub ex} values determined in the gas phase, Cp{sub 2}{sup e}Co{sup +/0} {approx} Cp{sub 2}Co{sup +/0} > Cp{prime}{sub 2}Fe{sup +/0} > HMFc{sup +/0} > Cp{sub 2}Fe{sup +/0}, is roughly similar to that observed in solution, although the magnitude (up to 5-fold) of the k{sub ex} variations is smaller in the former case. The likely origins of these differences in gas-phase reactivity are discussed in light of the known variations in the electronic coupling matrix element H{sub 12}, inner-shell reorganization energy {Delta}E*, and gas-phase ion-molecule interaction energy {Delta}E{sub w} extracted from solution-phase rates, structural data, and theoretical calculations. It is concluded that the observed variations in gas-phase k{sub ex} values, especially for Cp{sub 2}Fe{sup +/0} versus Cp{sub 2}Co{sup +/0}, arise predominantly from the presence of weaker donor-acceptor orbital overlap for the ferrocene couples, yielding inefficient electron tunneling for a substantial fraction of the gas-phase ion-molecule encounters. The anticipated differences as well as similarities of such nonadiabatic effects for gas-phase and solution electron-transfer processes are briefly outlined.

Phelps, D.K.; Gord, J.R.; Freiser, B.S.; Weaver, M.J. (Purdue Univ., West Lafayette, IN (United States))

1991-05-30

219

Evaluation of the degree of transformation for exchange reactions with simultaneous diffusion of steel with chromium, vanadium, and aluminum  

SciTech Connect

In analyzing the correlation between aluminum content and an impregnating chromium-vanadium mixture with phase and chemical composition of the diffusion layer on forging steel 5KhNM, it has been found that the capacity of the diffusion source affects to a considerable extent the content of aluminum, chromium, and vanadium in the steel surface layer. It has been established that with a low aluminum content in the impregnating mixture a layer forms at the surface of Me/sub 7/C/sub 3/ type carbides distributed in ferrite or in superstructures: Fe/sub 3/Al or FeAl. With a high aluminum content in the mixture the concentration of chromium and vanadium at the surface decreases sharply and an intermetallic layer of FeAl forms. In view of this, they have made an attempt to analyze the chemical affinity of the process of multicomponent impregnation and also to evaluate by calculation the effect of reaction mixture composition and temperature of process on preferential deposition of the main elements (Cr, V, Al) at the steel surface.

Sokolova, N.K.; Karpman, M.G.; Sokolov, V.S.

1986-11-01

220

THE APPLICATION OF LIQUID ION-EXCHANGE RESINS IN ANALYSIS. PART II. THE REACTIONS OF ZIRCONIUM, TITANIUM AND VANADIUM IN SULPHURIC ACID MEDIA  

Microsoft Academic Search

S> With the advent of liquid ion-exchange resins which are insoluble in ; water but soluble in organic solvents, it is now possible to remove ions from ; solutions by solvent extraction techniques using ion exchange. In Part I, the ; results were given of an investigation into the degree of extraction obtained ; with a liquid anion-exchange resin in

1962-01-01

221

Isovector giant resonances in 6He, 12B, 90Y, 120In, and 208Tl observed in the (7Li,7Be) charge-exchange reaction  

NASA Astrophysics Data System (ADS)

The (7Li,7Be) and (7Li,7Be?) reactions have been studied at bombarding energies of 50 A MeV on targets of 6Li, 12C, 90Zr, 120Sn, 208Pb, and polystyrene. The detection of Doppler-shifted ?-rays from excited 7Be permits the identification of the spinflip and non-spinflip characteristics. Transitions to over 20 discrete states and resonances have been observed. Angular distributions for 6Li and 12C are well described by microscopic one-step distorted-waves calculations with shell-model transition amplitudes. The transitions to the ground states of 6He and 12C exhibit significant Gamow-Teller strength, but ~7% and ~17%, respectively, of the calculated cross sections at ?~ 0? arise from the tensor interaction. A broad resonance at ~5.6 MeV in the halo nucleus 6He with J?=(2+,1-,0+) seems to correspond to a structure predicted at this excitation energy containing soft modes of excitation with J?=0+ and/or 2+. A resonance in 12B at ~4.5 MeV is described by a superposition of known 2- and 4- states, and another one at ~7.5 MeV is dominated by a transition to a 2- state with weaker contributions from two 1- states (spin dipole and giant dipole). Four to six resonances each, mostly spin-dipole resonances, were identified in the final nuclei 90Y, 120In, and 208Tl. The non-resonant quasi-free charge-exchange reaction pbound(7Li,7Be)nfree was observed for all targets up to effective excitation energies of 50 MeV. The mechanism is related to that on free protons. The effective number of participating protons was determined.

Annakkage, T.; Jänecke, J.; Winfield, J. S.; Berg, G. P. A.; Brown, J. A.; Crawley, G.; Danczyk, S.; Fujiwara, M.; Mercer, D. J.; Pham, K.; Roberts, D. A.; Stasko, J.; Yoo, G. H.

1999-03-01

222

Heat exchanger antifoulant  

SciTech Connect

Disclosed is a process for reducing the fouling in a heat exchanger in which a hydrocarbon stream is heated or cooled as it passes through the heat exchanger. From 1 to 500 parts per million of the reaction product of a polyalkylene amine and a hydroxy fatty acid are added to the stream to reduce fouling.

Ferm, R.L.

1984-02-14

223

Effect of solvent on the lithium-bromine exchange of aryl bromides: reactions of n-butyllithium and tert-butyllithium with 1-bromo-4-tert-butylbenzene at 0 degrees C.  

PubMed

The outcome of reactions of 1-bromo-4-tert-butylbenzene (1), a representative aryl bromide, with n-BuLi or t-BuLi at 0 degrees C in a variety of solvent systems has been investigated. The products of reactions of 1 with n-BuLi vary significantly with changes in solvent composition: 1 does not react with n-BuLi in pure heptane; the exchange reaction to give (4-tert-butylphenyl)lithium, which is slow in pure diethyl ether, is virtually quantitative in heptane containing a small quantity of THF; and the reaction of 1 with n-BuLi in THF leads to considerable coupling. Lithium-bromine exchange is the virtually exclusive outcome of reactions of 1 with t-BuLi in every solvent studied except pure heptane: the presence of a small quantity of any of a variety of structurally diverse ethers (Et(2)O, THF, THP, MTBE) in the predominantly hydrocarbon medium affords (4-tert-butylphenyl)lithium, assayed as tert-butylbenzene, in yields exceeding 97%. The only side products observed from reactions of 1 with t-BuLi are small amounts of benzyne-derived hydrocarbons. PMID:16555838

Bailey, William F; Luderer, Mark R; Jordan, Kevin P

2006-03-31

224

Simulated annealing and density functional theoretical prediction of macrocyclic ligand conformations, protonation sites and complex metal-ligand exchange reaction directions.  

PubMed

The prediction of conformations and protonation sites for the macrocyclic ligands H2DO2A (1,4,7,10-tetraazacyclododecane-1,7-diacetic acid) and H2ODO2A (1-oxa-4,7,10-triazacyclododecane-4,10-diacetic acid) has been performed employing the simulated annealing (SA) method and density functional theory (DFT) calculations using the B3LYP/6-31G* method in a vacuum and aqueous solution. These SA method/DFT calculations reveal that, in contrast to the H2ODO2A ligand system, the H2DO2A ligand system is (i) pre-organized for trivalent lanthanide (Ln) and other metal ion complexation, (ii) structurally more symmetrical and slightly more compact in aqueous solution (i.e. more and/or shorter intra-molecular hydrogen bonds), and (iii) with a greater degree of partial positive charge accumulation on the hydrogen atoms bonded to macrocyclic ring nitrogen atoms when protonated. The H2ODO2A ligand system is not pre-organized. These observations are in accord with the experimental findings that the LnODO2A(+) complexes are less thermodynamically stable and kinetically more labile as compared to those of the corresponding LnDO2A(+) complexes. The results on the prediction of the ligand protonation sites are consistent with those experimentally obtained via NMR spectroscopy. The calculations of the first and second protonation constants are, however, not as accurate as compared to those experimentally determined using either the thermodynamic cycle (TC) or the isodesmic reaction (IRn) methodology, although the latter gave relatively better results. The lowest energy structures of the LnL(+) and ZnL (Ln = Eu, Y; L = DO2A, ODO2A) complexes are also calculated using the same method. The Gibb's free energies (?Gaq) for a number of ligand and/or metal ion exchange reactions such as LnDO2A(+) + HnODO2A((2-n)-) -->/<-- LnODO2A(+) + HnDO2A((2-n)-) (Ln = Eu, Y; n = 0, 1, 2), LnDO2A(+) + Ln'ODO2A(+) -->/<-- LnODO2A(+) + Ln'DO2A(+) (Ln = Eu, Ln' = Y), LnDO2A(+) + Ln'(3+) -->/<-- Ln'ODO2A(+) + Ln(3+) (Ln = Eu, Ln' = Y) and LnDO2A(+) + ZnODO2A -->/<-- LnODO2A(+) + ZnDO2A (Ln = Eu, Y) have been calculated in aqueous phase and the reaction directions in some cases could be predicted to be consistent with experimental or expected results. The errors between the calculated and experimental Gibb's free energy data are in the range ?G(aq,calc) - ?G(aq,exp) = -1.89 to +7.00 kcal mol(-1) in seven selected cases involving LnDO2A(+), LnODO2A(+) (Ln = Eu, Y), ZnDO2A and ZnODO2A complexes. The predicted reaction directions with the small core effective core potential (ECP) data are not necessarily better than those using large core ECP. However, the former takes much longer computer time to obtain the energy data. PMID:23462882

Chang, C Allen; Lee, Hwa Yu; Chen, Cheng-Lung

2013-05-14

225

Dynamics of the C/H and C/F exchanges in the reaction of 3P carbon atoms with vinyl fluoride  

NASA Astrophysics Data System (ADS)

Two product channels C3H2F + H and C3H3 + F were identified in the reaction of C(3P) atoms with vinyl fluoride (C2H3F) at collision energy 3.7 kcal mol-1 in a crossed molecular-beam apparatus using selective photoionization. Time-of-flight (TOF) spectra of products C3H2F and C3H3 were measured at 12-16 laboratory angles as well as a TOF spectrum of atomic F, a counter part of C3H3, was recorded at single laboratory angle. From the best simulation of product TOF spectra, translational-energy distributions at seven scattering angles and a nearly isotropic (forward and backward peaked) angular distribution were derivable for exit channel C3H2F + H (C3H3 + F) that has average kinetic-energy release of 14.5 (4.9) kcal mol-1. Products C3H2F + H and C3H3 + F were estimated to have a branching ratio of ~53:47. Furthermore, TOF spectra and photoionization spectra of products C3H2F and C3H3 were measured at laboratory angle 62° with photoionization energy ranging from 7 eV to 11.6 eV. The appearance of TOF spectra is insensitive to photon energy, implying that only single species overwhelmingly contributes to products C3H2F and C3H3. HCCCHF (H2CCCH) was identified as the dominant species based on the measured ionization threshold of 8.3 +/- 0.2 (8.6 +/- 0.2) eV and the maximal translational-energy release. The C/H and C/F exchange mechanisms are stated.

Lee, Shih-Huang; Chen, Wei-Kan; Chin, Chih-Hao; Huang, Wen-Jian

2013-08-01

226

Nucleotide exchange factors  

PubMed Central

Exchange factors are enzymes that catalyze the exchange of GTP for GDP on guanine nucleotide binding proteins. Progress in understanding the molecular basis of action and the cellular functions of these enzymes has largely come from structural determinations (e.g., crystal structures) and studying effects on cells when expression levels of the exchange factors are perturbed or mutated exchange factors are expressed. Proportionally little effort has been expended on studying the kinetics of exchange; however, reaction rates are central to understanding enzymes. Here, we discuss the importance of kinetic analysis of exchange factors for guanine nucleotide binding proteins, with a focus on ADP-ribosylation factor (Arf) and heterotrimeric G proteins, for providing unique insights into molecular mechanisms and regulation as well as how kinetic analyses are used to complement other approaches.

Northup, John K.; Jian, Xiaoying; Randazzo, Paul A.

2012-01-01

227

Formation of abundant [Pb(H2O)]2+ by ligand-exchange reaction between [Pb(N2)n]2+ (n = 1-3) and H2O.  

PubMed

Doubly charged lead monohydrate, [Pb(H2O)]2+, was predicted to be unstable in the gas phase, but it has recently been observed to form in low yield via ligand change between [Pb(CH3CN)]2+ and H2O [Shi, T.; Orlova, G.; Guo, J.; Bohme, D. K.; Hopkinson, A. C.; Siu, K. W. M. J. Am. Chem. Soc. 2004, 126, 7975-7980]. Here we report that abundant [Pb(H2O)]2+ is formed in the gas phase by ligand-exchange reaction between [Pb(N2)n]2+ (n = 1-3) and water after collisional activation. Density functional theory has been used to examine the ligand-exchange reaction profile. A comparison of the potential-energy surfaces between [Pb(N2)]2+ and [Pb(CH3CN)]2+ reacting with H2O provides strong evidence that the ligand-exchange reaction of [Pb(N2)]2+ with H2O to form [Pb(H2O)]2+ is more efficient than that of [Pb(CH3CN)]2+ with H2O. PMID:16852285

Shi, Tujin; Zhao, Junfang; Hopkinson, Alan C; Siu, K W Michael

2005-06-01

228

Novel protonated and hydrated n=1 Ruddlesden-Popper phases, H{sub x}Na{sub 1-x}LaTiO{sub 4}.yH{sub 2}O, formed by ion-exchange/intercalation reaction  

SciTech Connect

New derivatives of layered perovskite compounds with H{sub 3}O{sup +} ions, H{sup +} ions and water molecules in the interlayer, H{sub x}Na{sub 1-x}LaTiO{sub 4}.yH{sub 2}O, were successfully synthesized by an ion-exchange/intercalation reaction with dilute HCl solution, using an n=1 member of Ruddlesden-Popper phase, NaLaTiO{sub 4}. Powder X-ray diffraction revealed that the layered structure changed from space group P4/nmm with a=3.776(1) and c=13.028(5)A to I4/mmm with a=3.7533(3) and c=28.103(4)A after the ion-exchange/intercalation reaction at pH 5. The change of space group indicates that the perovskite layers are transformed from staggered to an eclipsed configuration through the ion-exchange/intercalation reaction. Thermogravimetric analysis and high-temperature powder X-ray diffraction suggested the existence of the secondary hydrated phase by dehydrating H{sub x}Na{sub 1-x}LaTiO{sub 4}.yH{sub 2}O at 100{sup o}C.

Nishimoto, Shunsuke [Faculty of Environmental Science and Technology, Department of Environmental Chemistry and Materials, Okayama University, Tsushima-Naka, Okayama 700-8530 (Japan); Matsuda, Motohide [Faculty of Environmental Science and Technology, Department of Environmental Chemistry and Materials, Okayama University, Tsushima-Naka, Okayama 700-8530 (Japan); Miyake, Michihiro [Faculty of Environmental Science and Technology, Department of Environmental Chemistry and Materials, Okayama University, Tsushima-Naka, Okayama 700-8530 (Japan)]. E-mail: mmiyake@cc.okayama-u.ac.jp

2005-03-15

229

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

230

Exchange bias  

Microsoft Academic Search

We review the phenomenology of exchange bias and related effects, with emphasis on layered antiferromagnetic (AFM)–ferromagnetic (FM) structures. A compilation of materials exhibiting exchange bias and some of the techniques used to study them is given. Some of the applications of exchange bias are discussed. The leading theoretical models are summarized. Finally some of the factors controlling exchange bias as

J. Nogués; Ivan K Schuller

1999-01-01

231

H/Br exchange in BBr3 by HSiR3 (R = H, CH3, C2H5): origin of DFT failures to describe a seemingly innocuous reaction barrier.  

PubMed

We investigate the suitability of density functional theory (DFT) and second order Møller-Plesset perturbation theory (MP2) for the title reaction, which serves as a model to represent the key step in a recently developed B-C bond formation reaction. CBS-QB3 is employed as a reference throughout this study. The classical barrier height associated with the concerted transition state for the H/Br exchange reaction poses a serious challenge to most standard GGAs or hybrid functionals. In particular the popular B3LYP hybrid functional shows dramatically overestimated reaction barriers (by 12 kcal mol(-1)) for the largest system with R = C(2)H(5). We find that a proper description of intramolecular dispersion interactions arising in the transition state is crucial for a correct assessment of this reaction and that the inclusion of Grimme's empirical dispersion correction effectively compensates for most of the errors to a large extent. In conclusion we find a pleasing performance of the dispersion corrected functionals B2PLYP-D or B3LYP-D for the present set of systems if used in combination with basis sets of triple-zeta quality, which we recommend for future quantum chemical studies on related systems. Also the recently devised M05-2X hybrid meta-GGA shows an excellent performance, in particular if used in combination with the small SVP basis. PMID:19780522

Rakow, Julia R; Tüllmann, Sandor; Holthausen, Max C

2009-10-29

232

H/Br Exchange in BBr3 by HSiR3 (R = H, CH3, C2H5): Origin of DFT Failures to Describe a Seemingly Innocuous Reaction Barrier  

NASA Astrophysics Data System (ADS)

We investigate the suitability of density functional theory (DFT) and second order Møller-Plesset perturbation theory (MP2) for the title reaction, which serves as a model to represent the key step in a recently developed B-C bond formation reaction. CBS-QB3 is employed as a reference throughout this study. The classical barrier height associated with the concerted transition state for the H/Br exchange reaction poses a serious challenge to most standard GGAs or hybrid functionals. In particular the popular B3LYP hybrid functional shows dramatically overestimated reaction barriers (by 12 kcal mol-1) for the largest system with R = C2H5. We find that a proper description of intramolecular dispersion interactions arising in the transition state is crucial for a correct assessment of this reaction and that the inclusion of Grimme's empirical dispersion correction effectively compensates for most of the errors to a large extent. In conclusion we find a pleasing performance of the dispersion corrected functionals B2PLYP-D or B3LYP-D for the present set of systems if used in combination with basis sets of triple-? quality, which we recommend for future quantum chemical studies on related systems. Also the recently devised M05-2X hybrid meta-GGA shows an excellent performance, in particular if used in combination with the small SVP basis.

Rakow, Julia R.; Tüllmann, Sandor; Holthausen, Max C.

2009-09-01

233

Activity enhancement of mesoporous silicate FSM-16 by metal ion-exchange and sulfiding with hydrogen sulfide for acid-catalyzed reactions  

Microsoft Academic Search

The modification of mesoporous silicate FSM-16 by metal ion-exchange and sulfiding with hydrogen sulfide was studied through the isomerization of 1-butène, cis-2-butene and cyclopropane. It was revealed that the catalytic activities of MeFSM-16 were remarkably enhanced by sulfiding with hydrogen sulfide due to the formation of new Brönsted acid sites

M. Sugioka; L Andalaluna; J. K. A. Dapaah

2000-01-01

234

Inorganic ion exchangers for the removal of scandium and rare earth elements in neutron activation analysis of geological samples. [Neutron reactions  

Microsoft Academic Search

Sorption properties of inorganic ion exchangers have been investigated for use in radiochemical separation of elements in geological samples subjected to neutron activation analysis. Samples were allowed to decay for two weeks, dissolved in hydrofluoric acid, and saturated boric acid was added to dissolve any fluoride complexes. Samples were placed onto the COX column and eluted with nitric acid. Retained

K. Akilimali; B. Lumu; W. Mwamba

1979-01-01

235

Anion exchange behavior of nobelium  

Microsoft Academic Search

The anion exchange behavior of 255No produced by the 248Cm(12C,5n) reaction has been investigated in 11.5M HCl, 4M HCl and 8M HNO3 to deduce the behavior of 'primordial 257No' produced via 248Cm(18O,5n)261Rf 257No before anion exchange separation in the 261Rf experiment. It was found that 255No is mostly eluted from the anion exchange column with these solutions. The contribution of

A. Toyoshima; K. Tsukada; H. Haba; M. Asai; S. Goto; K. Akiyama; I. Nishinaka; S. Ichikawa; Y. Nagame; A. Shinohara

2003-01-01

236

Charge Exchange and Production of eta Mesons and Multiple Neutral Pions in pi-p Reactions between 654 and 1247 MeV\\/c  

Microsoft Academic Search

An experiment designed to study the pi-p total neutral cross section and its breakdown into several channels has been performed at eleven incident pion momenta ranging from 654 to 1247 MeV\\/c. Angular distributions for the charge exchange pi0 and for eta0 production are given in terms of Legendre-polynomial expansion coefficients. Forward and backward differential cross sections are presented for the

F. Bulos; R. E. Lanou; A. E. Pifer; A. M. Shapiro; C. A. Bordner; A. E. Brenner; M. E. Law; E. E. Ronat; F. D. Rudnick; K. Strauch; J. J. Szymanski; P. Bastien; B. B. Brabson; Y. Eisenberg; B. T. Feld; V. K. Kistiakowsky; I. A. Pless; L. Rosenson; R. K. Yamamoto; G. Calvelli; F. Gasparini; L. Guerriero; G. A. Salandin; A. Tomasin; L. Ventura; C. Voci; F. Waldner

1969-01-01

237

Effect of the salt melt composition, temperature, and interaction time on the contact exchange reaction in the MCl-PbCl 2 MeN systems  

Microsoft Academic Search

The interaction of titanium, zirconium, and aluminum nitrides with a mixture of fused alkali-metal chlorides with lead chloride\\u000a at 870–1070 K is studied. It is shown that as a result of the contact exchange interaction, which occurs in no more than 5\\u000a h, a large fraction of the powdered nitrides transforms into a soluble state, and lead precipitates in a

L. A. Elshina; V. Ya. Kudyakov; N. G. Molchanova

2008-01-01

238

Gas chromatography mass spectrometry study of hydrogen deuterium exchange reactions of volatile hydrides of As, Sb, Bi, Ge and Sn in aqueous media  

Microsoft Academic Search

The H D exchange processes in MHn or MDn hydrides (M = As, Sb, Bi, n = 3; M = Ge, Sn, n = 4) taking place when they are in contact with H2O or D2O solution at different pH or pD values (interval of pH = [0,13]) have been investigated using gas chromatography mass spectrometry (GC-MS). MHn or MDn

Alessandro D'Ulivo; Zoltan Mester; Juris Meija; Ralph E. Sturgeon

2006-01-01

239

Reaction between amorphous Si and crystalline Al in Al\\/Si and Si\\/Al bilayers: microstructural and thermodynamic analysis of layer exchange  

Microsoft Academic Search

Aluminium-induced crystallization of amorphous silicon (a-Si) in Al\\/Si and Si\\/Al bilayers was studied upon annealing at 250 °C by X-ray diffraction and Auger electron spectroscopy. The Al\\/a-Si bilayers and a-Si\\/Al bilayers were prepared by sputter deposition on single-crystal silicon wafers with a silicon-oxide film on top. During the isothermal annealing a layer-exchange process occurred in both types of bilayers. A

D. He; J. Y. Wang; E. J. Mittemeijer

2005-01-01

240

Reaction between amorphous Si and crystalline Al in Al\\/Si and Si\\/Al bilayers: microstructural and thermodynamic analysis of layer exchange  

Microsoft Academic Search

Aluminium-induced crystallization of amorphous silicon (a-Si) in Al\\/Si and Si\\/Al bilayers was studied upon annealing at 250 °C by X-ray diffraction and Auger electron spectroscopy. The Al\\/a-Si bilayers and a-Si\\/Al bilayers were prepared by sputter deposition on single-crystal silicon wafers with a silicon-oxide film on top. During the isothermal annealing a layer-exchange process occurred in both types of bilayers. A continuous

D. He; J. Y. Wang; E. J. Mittemeijer

2005-01-01

241

Reaction between amorphous Si and crystalline Al in Al/Si and Si/Al bilayers: microstructural and thermodynamic analysis of layer exchange  

NASA Astrophysics Data System (ADS)

Aluminium-induced crystallization of amorphous silicon (a-Si) in Al/Si and Si/Al bilayers was studied upon annealing at 250 °C by X-ray diffraction and Auger electron spectroscopy. The Al/a-Si bilayers and a-Si/Al bilayers were prepared by sputter deposition on single-crystal silicon wafers with a silicon-oxide film on top. During the isothermal annealing a layer-exchange process occurred in both types of bilayers. A continuous polycrystalline silicon (poly-Si) film was formed within, and thereby gradually replacing, the initial Al metal layer. The sublayer sequence in the original bilayer influenced the speed of the poly-Si formation and the layer-exchange process. After annealing, the Al fiber texture in the as-deposited bilayers had become stronger, the Al crystallites had grown laterally, and the macrostress in the Al layer had been released. The amorphous Si layer had crystallized into an aggregate of nanocrystals with {111} planes parallel to the surface, with a crystallite size of about 15 25 nm. An extensive analysis of the Gibbs energy change due to annealing showed that the layer exchange may be promoted by the release of elastic energy and grain growth for the Al phase.

He, D.; Wang, J. Y.; Mittemeijer, E. J.

2005-02-01

242

Effects which will not blur the message of the 1H (11Li, 9Li) 3H reaction: observation of phonon-exchange pairing correlations in nuclei  

NASA Astrophysics Data System (ADS)

The results of the 1H (11Li, 9Li) 3H experiment carried out recently at TRIUMF have given detailed information concerning the structure and the reaction mechanism at work in the case of halo, exotic nuclei, providing important stepping stones for an eventual quantitative description of superfluidity in finite nuclei. In fact, the central role played by renormalization processes as testified by the excitation of the 1/2- (2.69 MeV) member of the 9Li (2+ otimesp3/2(?))j- multiplet (nuclear structure) together with the post-prior symmetry (reaction), testify to the fact that a detailed knowledge of the "bare" quantities, like e.g. the NN-interaction is likely to be less important, in a unified Nuclear Field Theory description of the structure and the reaction aspects of the experiment, than previously thought.

Vigezzi, E.; Potel, G.; Barranco, F.; Broglia, R. A.

2011-09-01

243

Measurement of the analysing power of the charge-exchange pp --> nn reaction in the momentum range 546-1287 MeV\\/c at LEAR  

Microsoft Academic Search

Final results of the measurement of the analysing power AOn of the pp --> nn reaction are presented. Eight measurements in the range 546-1287 MeV\\/c incoming p momentum have been performed over the full angular range using a solid polarized proton target and the Low Energy Antiproton Ring (LEAR) at CERN antiproton extracted beams.

R. Birsa; F. Bradamante; A. Bressan; S. dalla Torre-Colautti; M. Giorgi; M. Lamanna; A. Martin; A. Penzo; P. Schiavon; F. Tessarotto; M. P. Macciotta; A. Masoni; G. Puddu; S. Serci; T. Niinikoski; A. Rijllart; A. Ahmidouch; E. Heer; R. Hess; C. Lechanoine-Le Luc; C. Mascarini; D. Rapin; H. Catz; J. C. Faivre; F. Perrot-Kunne; J. Arvieux; R. Bertini; R. A. Kunne; M. Agnello; F. Iazzi; B. Minetti; T. Bressani; E. Chiavassa; N. de Marco; A. Musso; A. Piccotti

1993-01-01

244

Reactant-product decoupling method for state-to-state reactive scattering: A case study for 3D H+H{sub 2} exchange reaction (J=0)  

SciTech Connect

In this paper, we present theoretical and computational details of implementing the recently developed reactant-product decoupling (RPD) method (J. Chem. Phys. {bold 105}, 6072 (1996)) for state-to-state quantum reactive scattering calculations of the prototypical H + H{sub 2} reaction in three dimensions. The main purpose of this paper is to explore important features of the RPD scheme for use as a general and efficient computational approach to study state-to-state quantum dynamics for polyatomic reactions by using 3D H + H{sub 2} as an example. Specific computational techniques and numerical details are explicitly provided for efficient application of this method in the time-dependent (TD) implementation. Using the RPD method, the calculated state-to-state reaction probabilities for the 3D H + H{sub 2} reaction are in excellent agreement with those from the time-independent variational calculations, and the computational cost of the RPD method is significantly lower than other existing TD methods for state-to-state dynamics calculations. {copyright} {ital 1997 American Institute of Physics.}

Zhu, W.; Peng, T.; Zhang, J.Z. [Department of Chemistry, New York University, New York, New York 10003 (United States)

1997-02-01

245

Two-nucleon processes in pion-induced double charge exchange in {sup 4}He: A coincidence measurement of the {sup 4}He({pi}{sup +},{pi}{sup {minus}} {ital p})3{ital p} reaction  

SciTech Connect

Inclusive measurements of pion double-charge-exchange in {sup 3}He[1] and {sup 4}He[2] in the {Delta}(1232) resonance region suggest the dominance of a two-step sequential single-charge-exchange mechanism involving quasi-free nucleons. To investigate this reaction mechanism, we have observed protons in coincidence with the outgoing pion in {pi}{sup +}+{sup 4}He{r_arrow}{pi}{sup {minus}}+4{ital p} at {ital T}{sub {pi}{sup +}}=240 MeV. Pions were detected in a magnetic spectrometer at {theta}{sub {pi}{sup {minus}}}=32{degree}, while protons were detected in a close-packed array of plastic scintillator telescopes covering {theta}{sub {ital p}}=67.5{degree}--157.5{degree} on the same side of the beam as the spectrometer, and {theta}{sub {ital p}}=22.5{degree}--157.5{degree} on the opposite side. We will present preliminary results for the distributions in energy and angle of the coincident protons. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Pate, S.F.; Fong, W.; Harvey, M.T.; Matthews, J.L.; Park, H.T.; Vidos, L.L.; Zelevinsky, V.V. [Laboratory for Nuclear Science, MIT, Cambridge, Massachusetts 02139 (United States); Saunders, A.; Holcomb, M.D.; Kinney, E.R.; Kriss, B.J. [Department of Physics, University of Colorado, Boulder, Colorado 80309 (United States); Gram, P.A.M. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Roberts, D.A. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States)

1995-05-10

246

The Dynamics of Multilateral Exchange  

NASA Astrophysics Data System (ADS)

The article formulates a dynamic mathematical model where arbitrarily many players produce, consume, exchange, loan, and deposit arbitrarily many goods over time to maximize utility. Consuming goods constitutes a benefit, and producing, exporting, and loaning away goods constitute a cost. Utilities are benefits minus costs, which depend on the exchange ratios and bargaining functions. Three-way exchange occurs when one player acquires, through exchange, one good from another player with the sole purpose of using this good to exchange against the desired good from a third player. Such a triple handshake is not merely a set of double handshakes since the player assigns no interest to the first good in his benefit function. Cognitive and organization costs increase dramatically for higher order exchanges. An exchange theory accounting for media of exchange follows from simple generalization of two-way exchange. The examples of r-way exchange are the triangle trade between Africa, the USA, and England in the 17th and 18th centuries, the hypothetical hypercycle involving RNAs as players and enzymes as goods, and reaction-diffusion processes. The emergence of exchange, and the role of trading agents are discussed. We simulate an example where two-way exchange gives zero production and zero utility, while three-way exchange causes considerable production and positive utility. Maximum utility for each player is reached when exchanges of the same order as the number of players in society are allowed. The article merges micro theory and macro theory within the social, natural, and physical sciences.

Hausken, Kjell; Moxnes, John F.

247

Test procedure for cation exchange chromatography  

SciTech Connect

The purpose of this test plan is to demonstrate the synthesis of inorganic antimonate ion exchangers and compare their performance against the standard organic cation exchangers. Of particular interest is the degradation rate of both inorganic and organic cation exchangers. This degradation rate will be tracked by determining the ion exchange capacity and thermal stability as a function of time, radiation dose, and chemical reaction.

Cooper, T.D.

1994-08-24

248

Ion Exchange  

Microsoft Academic Search

\\u000a Several processes can be used to attract soluble ions from the liquid phase to the solid phase and among these is ion exchange,\\u000a which is arguably the most widely used in the water treatment industry for this purpose (1-4). Ion exchange (IX) provides\\u000a a means for transferring one or more ionic species from one liquid phase to another via intermediate

J. Paul Chen; Lei Yang; Wun-Jern Ng; Lawrence K. Wang; Sook-Leng Thong

249

Exploring the dynamics of C/H and C/Cl exchanges in the C(3P) + C2H3Cl reaction  

NASA Astrophysics Data System (ADS)

The dynamics of the C(3P) + C2H3Cl reaction at collision energy 3.8 kcal mol-1 was investigated in a crossed molecular-beam apparatus using synchrotron vacuum-ultraviolet ionization. Time-of-flight spectra of products C3H2Cl, C3H3, and Cl were recorded at various laboratory scattering angles, from which translational-energy distributions and angular distributions of product channels C3H2Cl + H and C3H3 + Cl were derived. Cl correlates satisfactorily with C3H3 in linear momentum and angular distributions, which confirms the production of C3H3 + Cl. The H-loss (Cl-loss) channel has average translational-energy release 14.3 (8.8) kcal mol-1 corresponding to a fraction 0.30 (0.14) of available energy into the translational degrees of freedom of product HCCCHCl + H (H2CCCH + Cl). The branching ratio of channel H to channel Cl was determined approximately as 12:88. The measurements of translational-energy releases and photoionization thresholds cannot distinguish HCCCHCl from H2CCCCl because both isomers have similar enthalpy of formation and ionization energy; nevertheless, the Rice-Ramsperger-Kassel-Marcus calculation prefers HCCCHCl. The measurement of photoionization spectra identifies product C3H3 as H2CCCH (propargyl). Both products C3H2Cl + H and C3H3 + Cl might correlate to the same triplet intermediate H2CCCHCl but have distinct angular distributions; the former is nearly isotropic whereas the latter is forward biased. A comparison with the C(3P) + C2H3F reaction is stated.

Lee, Shih-Huang; Chen, Wei-Kan; Chin, Chih-Hao; Huang, Wen-Jian

2013-10-01

250

Cyclometalated iridium complexes of bis(aryl) phosphine ligands: catalytic C-H/C-D exchanges and C-C coupling reactions.  

PubMed

This work details the synthesis and structural identification of a series of complexes of the (?(5)-C5Me5)Ir(III) unit coordinated to cyclometalated bis(aryl)phosphine ligands, PR'(Ar)2, for R' = Me and Ar = 2,4,6-Me3C6H2, 1b; 2,6-Me2-4-OMe-C6H2, 1c; 2,6-Me2-4-F-C6H2, 1d; R' = Et, Ar = 2,6-Me2C6H3, 1e. Both chloride- and hydride-containing compounds, 2b-2e and 3b-3e, respectively, are described. Reactions of chlorides 2 with NaBArF (BArF = B(3,5-C6H3(CF3)2)4) in the presence of CO form cationic carbonyl complexes, 4(+), with ?(CO) values in the narrow interval 2030-2040 cm(-1), indicating similar ?-basicity of the Ir(III) center of these complexes. In the absence of CO, NaBArF forces ?(4)-P,C,C',C? coordination of the metalated arm (studied for the selected complexes 5b, 5d, and 5e), a binding mode so far encountered only when the phosphine contains two benzylic groups. A base-catalyzed intramolecular, dehydrogenative, C-C coupling reaction converts the ?(4) species 5d and 5e into the corresponding hydrido phosphepine complexes 6d and 6e. Using CD3OD as the source of deuterium, the chlorides 2 undergo deuteration of their 11 benzylic positions whereas hydrides 3 experience only D incorporation into the Ir-H and Ir-CH2 sites. Mechanistic schemes that explain this diversity have come to light thanks to experimental and theoretical DFT studies that are also reported. PMID:23675910

Campos, Jesús; Espada, María F; López-Serrano, Joaquín; Carmona, Ernesto

2013-05-15

251

Exploring the dynamics of C?H and C?Cl exchanges in the C((3)P) + C2H3Cl reaction.  

PubMed

The dynamics of the C((3)P) + C2H3Cl reaction at collision energy 3.8 kcal mol(-1) was investigated in a crossed molecular-beam apparatus using synchrotron vacuum-ultraviolet ionization. Time-of-flight spectra of products C3H2Cl, C3H3, and Cl were recorded at various laboratory scattering angles, from which translational-energy distributions and angular distributions of product channels C3H2Cl + H and C3H3 + Cl were derived. Cl correlates satisfactorily with C3H3 in linear momentum and angular distributions, which confirms the production of C3H3 + Cl. The H-loss (Cl-loss) channel has average translational-energy release 14.3 (8.8) kcal mol(-1) corresponding to a fraction 0.30 (0.14) of available energy into the translational degrees of freedom of product HCCCHCl + H (H2CCCH + Cl). The branching ratio of channel H to channel Cl was determined approximately as 12:88. The measurements of translational-energy releases and photoionization thresholds cannot distinguish HCCCHCl from H2CCCCl because both isomers have similar enthalpy of formation and ionization energy; nevertheless, the Rice-Ramsperger-Kassel-Marcus calculation prefers HCCCHCl. The measurement of photoionization spectra identifies product C3H3 as H2CCCH (propargyl). Both products C3H2Cl + H and C3H3 + Cl might correlate to the same triplet intermediate H2CCCHCl but have distinct angular distributions; the former is nearly isotropic whereas the latter is forward biased. A comparison with the C((3)P) + C2H3F reaction is stated. PMID:24116562

Lee, Shih-Huang; Chen, Wei-Kan; Chin, Chih-Hao; Huang, Wen-Jian

2013-10-01

252

The Third Dimension of a More O'Ferrall-Jencks Diagram for Hydrogen Atom Transfer in the Isoelectronic Hydrogen Exchange Reactions of (PhX)(2)H(•) with X = O, NH, and CH(2).  

PubMed

A critical element in theoretical characterization of the mechanism of proton-coupled electron transfer (PCET) reactions, including hydrogen atom transfer (HAT), is the formulation of the electron and proton localized diabatic states, based on which a More O'Ferrall-Jencks diagram can be represented to determine the step-wise and concerted nature of the reaction. Although the More O'Ferrall-Jencks diabatic states have often been used empirically to develop theoretical models for PCET reactions, the potential energy surfaces for these states have never been determined directly based on first principles calculations using electronic structure theory. The difficulty is due to a lack of practical method to constrain electron and proton localized diabatic states in wave function or density functional theory calculations. Employing a multistate density functional theory (MSDFT), in which the electron and proton localized diabatic configurations are constructed through block-localization of Kohn-Sham orbitals, we show that distinction between concerted proton-electron transfer (CPET) and HAT, which are not distinguishable experimentally from phenomenological kinetic data, can be made by examining the third dimension of a More O'Ferrall-Jencks diagram that includes both the ground and excited state potential surfaces. In addition, we formulate a pair of effective two-state valence bond models to represent the CPET and HAT mechanisms. We found that the lower energy of the CPET and HAT effective diabatic states at the intersection point can be used as an energetic criterion to distinguish the two mechanisms. In the isoelectronic series of hydrogen exchange reaction in (PhX)(2)H(•), where X = O, NH, and CH(2), there is a continuous transition from a CPET mechanism for the phenoxy radical-phenol pair to a HAT process for benzyl radical and toluene, while the reaction between PhNH(2) and PhNH(•) has a mechanism intermediate of CPET and HAT. The electronically nonadiabatic nature of the CPET mechanism in the phenol system can be attributed to the overlap interactions between the ground and excited state surfaces, resulting in roughly orthogonal minimum energy paths on the adiabatic ground and excited state potential energy surfaces. On the other hand, the minimum energy path on the adiabatic ground state for the HAT mechanism coincides with that on the excited state, producing a large electronic coupling that separates the two surfaces by more than 120 kcal/mol. PMID:23226989

Cembran, Alessandro; Provorse, Makenzie R; Wang, Changwei; Wu, Wei; Gao, Jiali

2012-09-01

253

Synthesis, structure, theoretical studies, and Ligand exchange reactions of monomeric, T-shaped arylpalladium(II) halide complexes with an additional, weak agostic interaction.  

PubMed

A series of monomeric arylpalladium(II) complexes LPd(Ph)X (L = 1-AdPtBu2, PtBu3, or Ph5FcPtBu2 (Q-phos); X = Br, I, OTf) containing a single phosphine ligand have been prepared. Oxidative addition of aryl bromide or aryl iodide to bis-ligated palladium(0) complexes of bulky, trialkylphosphines or to Pd(dba)2 (dba = dibenzylidene acetone) in the presence of 1 equiv of phosphine produced the corresponding arylpalladium(II) complexes in good yields. In contrast, oxidative addition of phenyl chloride to the bis-ligated palladium(0) complexes did not produce arylpalladium(II) complexes. The oxidative addition of phenyl triflate to PdL2 (L = 1-AdPtBu2, PtBu3, or Q-phos) also did not form arylpalladium(II) complexes. The reaction of silver triflate with (1-AdPtBu2)Pd(Ph)Br furnished the corresponding arylpalladium(II) triflate in good yield. The oxidative addition of phenyl bromide and iodide to Pd(Q-phos)2 was faster than oxidative addition to Pd(1-AdPtBu2)2 or Pd(PtBu3)2. Several of the arylpalladium complexes were characterized by X-ray diffraction. All of the arylpalladium(II) complexes are T-shaped monomers. The phenyl ligand, which has the largest trans influence, is located trans to the open coordination site. The complexes appear to be stabilized by a weak agostic interaction of the metal with a ligand C-H bond positioned at the fourth-coordination site of the palladium center. The strength of the Pd.H bond, as assessed by tools of density functional theory, depended upon the donating properties of the ancillary ligands on palladium. PMID:14746489

Stambuli, James P; Incarvito, Christopher D; Bühl, Michael; Hartwig, John F

2004-02-01

254

Thermostability of endo-1,4-beta-xylanase II from Trichoderma reesei studied by electrospray ionization Fourier-transform ion cyclotron resonance MS, hydrogen/deuterium-exchange reactions and dynamic light scattering.  

PubMed Central

Endo-1,4-beta-xylanase II (XYNII) from Trichoderma reesei is a 21 kDa enzyme that catalyses the hydrolysis of xylan, the major plant hemicellulose. It has various applications in the paper, food and feed industries. Previous thermostability studies have revealed a significant decrease in enzymic activity of the protein at elevated temperatures in citrate buffer [Tenkanen, Puls and Poutanen (1992) Enzyme Microb. Technol. 14, 566-574]. Here, thermostability of XYNII was investigated using both conventional and nanoelectrospray ionization Fourier-transform ion cyclotron resonance MS and hydrogen/deuterium (H/D)-exchange reactions. In addition, dynamic light scattering (DLS) was used as a comparative method to observe possible changes in both tertiary and quaternary structures of the protein. We observed a significant irreversible conformational change and dimerization when the protein was exposed to heat. H/D exchange revealed two distinct monomeric protein populations in a narrow transition temperature region. The conformational change in both the water and buffered solutions occurred in the same temperature region where enzymic-activity loss had previously been observed. Approx. 10-30% of the protein was specifically dimerized when exposed to the heat treatment. However, adding methanol to the solution markedly lowered the transition temperature of conformational change as well as increased the dimerization up to 90%. DLS studies in water confirmed the change in conformation observed by electrospray ionization MS. We propose that the conformational change is responsible for the loss of enzymic activity at temperatures over 50 degrees C and that the functioning of the active site in the enzyme is unfeasible in a new, more labile solution conformation.

Janis, J; Rouvinen, J; Leisola, M; Turunen, O; Vainiotalo, P

2001-01-01

255

Science exchanges  

NASA Astrophysics Data System (ADS)

Dwindling scientific and technical exchange between the United States and the Soviet Union and prospects for enhancing such exchanges were discussed at an August 2 hearing by the Foreign Affairs Committee of the U.S. House of Representatives. The committee also heard overviews on the United States' approach to international exchange of science and technology. The hearing was the first in a series on current and future international science and technology programs.Four of eight science and technology agreements with the USSR that have expired in the last 15 months, including one on space, have not been renewed. The remaining four agreements have been extended into 1987 and 1988. Two others, including one on oceanography, are scheduled to run out in 1984.

Richman, Barbara T.

256

NEUTRONIC REACTION SYSTEM  

DOEpatents

A nuclear reactor system is described for breeding fissionable material, including a heat-exchange tank, a high- and a low-pressure chamber therein, heat- exchange tubes connecting these chambers, a solution of U/sup 233/ in heavy water in a reaction container within the tank, a slurry of thorium dioxide in heavy water in a second container surrounding the first container, an inlet conduit including a pump connecting the low pressure chamber to the reaction container, an outlet conduit connecting the high pressure chamber to the reaction container, and means of removing gaseous fission products released in both chambers. (AEC)

Wigner, E.P.

1963-09-01

257

Heat exchanger  

Microsoft Academic Search

A heat exchanger is described in which the main component is formed of a plurality of elongated strips of rigid heat conductive material. Each of the strips has a cross-sectional configuration which is elongated in a direction transverse to the elongated extent of the strip so as to provide a pair of spaced relatively thin end edges and a pair

1982-01-01

258

Heat exchanger  

DOEpatents

A heat exchanger of the straight tube type in which different rates of thermal expansion between the straight tubes and the supply pipes furnishing fluid to those tubes do not result in tube failures. The supply pipes each contain a section which is of helical configuration.

Wolowodiuk, Walter (New Providence, NJ)

1976-01-06

259

Heat exchanger  

DOEpatents

A heat exchanger is provided having first and second fluid chambers for passing primary and secondary fluids. The chambers are spaced apart and have heat pipes extending from inside one chamber to inside the other chamber. A third chamber is provided for passing a purge fluid, and the heat pipe portion between the first and second chambers lies within the third chamber.

Daman, Ernest L. (Westfield, NJ); McCallister, Robert A. (Mountain Lakes, NJ)

1979-01-01

260

Heat exchanger  

DOEpatents

A heat exchanger comparising a shell attached at its open end to one side of a tube sheet and a detachable head connected to the other side of said tube sheet. The head is divided into a first and second chamber in fluid communication with a nozzle inlet and nozzle outlet, respectively, formed in said tube sheet. A tube bundle is mounted within said shell and is provided with inlets and outlets formed in said tube sheet in communication with said first and second chambers, respectively.

Brackenbury, P.J.

1983-12-08

261

Two-dimensional peptide separation improving sensitivity of selected reaction monitoring-based quantitative proteomics in mouse liver tissue: comparing off-gel electrophoresis and strong cation exchange chromatography.  

PubMed

Protein expression analysis is one of the most powerful tools to further the understanding of biological systems. Progress in the field of mass spectrometry has shifted focus from gel-based approaches to the upcoming LC-selected reaction monitoring (SRM) technique which combines high technical accuracy with absolute quantification of proteins and the capability for high-throughput analyses. Due to these properties, LC-SRM has the potential to become the foundation for biomarker analysis, targeted hypothesis driven proteomic studies and contribute to the field of systems biology. While the performance of LC-SRM applied to samples from various bodily fluids, particularly plasma, and microorganisms has been extensively investigated, there is only little experience with its application to animal tissue samples. Here, we show that a conventional one-dimensional LC-SRM workflow applied to mouse liver tissue suffers from a shortcoming in terms of sensitivity for lower abundance proteins. This problem could be solved through the extension of the standard workflow by an additional dimension of separation at the peptide level prior to online LC-SRM. For this purpose, we used off-gel electrophoresis (OGE) which is also shown to outperform strong cation exchange (SCX) in terms of resolution, gain of signal intensity, and predictability of separation. The extension of the SRM workflow by a high resolving peptide separation technique is an ideal combination as it allows the addition of stable isotope standards directly after trytic digestion and will increase the dynamic range of protein abundances amenable by SRM in animal tissue. PMID:22994301

Schäfer, Alexander; von Toerne, Christine; Becker, Silke; Sarioglu, Hakan; Neschen, Susanne; Kahle, Melanie; Hauck, Stefanie M; Ueffing, Marius

2012-10-04

262

Scraped surface heat exchangers.  

PubMed

Scraped surface heat exchangers (SSHEs) are commonly used in the food, chemical, and pharmaceutical industries for heat transfer, crystallization, and other continuous processes. They are ideally suited for products that are viscous, sticky, that contain particulate matter, or that need some degree of crystallization. Since these characteristics describe a vast majority of processed foods, SSHEs are especially suited for pumpable food products. During operation, the product is brought in contact with a heat transfer surface that is rapidly and continuously scraped, thereby exposing the surface to the passage of untreated product. In addition to maintaining high and uniform heat exchange, the scraper blades also provide simultaneous mixing and agitation. Heat exchange for sticky and viscous foods such as heavy salad dressings, margarine, chocolate, peanut butter, fondant, ice cream, and shortenings is possible only by using SSHEs. High heat transfer coefficients are achieved because the boundary layer is continuously replaced by fresh material. Moreover, the product is in contact with the heating surface for only a few seconds and high temperature gradients can be used without the danger of causing undesirable reactions. SSHEs are versatile in the use of heat transfer medium and the various unit operations that can be carried out simultaneously. This article critically reviews the current understanding of the operations and applications of SSHEs. PMID:16527753

Rao, Chetan S; Hartel, Richard W

2006-01-01

263

Extension of a Kinetic-Theory Approach for Computing Chemical-Reaction Rates to Reactions with Charged Particles  

NASA Astrophysics Data System (ADS)

Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction rate information) are extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

Liechty, Derek S.; Lewis, Mark J.

2011-05-01

264

Segmented heat exchanger  

SciTech Connect

A segmented heat exchanger system for transferring heat energy from an exhaust fluid to a working fluid. The heat exchanger system may include a first heat exchanger for receiving incoming working fluid and the exhaust fluid. The working fluid and exhaust fluid may travel through at least a portion of the first heat exchanger in a parallel flow configuration. In addition, the heat exchanger system may include a second heat exchanger for receiving working fluid from the first heat exchanger and exhaust fluid from a third heat exchanger. The working fluid and exhaust fluid may travel through at least a portion of the second heat exchanger in a counter flow configuration. Furthermore, the heat exchanger system may include a third heat exchanger for receiving working fluid from the second heat exchanger and exhaust fluid from the first heat exchanger. The working fluid and exhaust fluid may travel through at least a portion of the third heat exchanger in a parallel flow configuration.

Baldwin, Darryl Dean (Lafayette, IN); Willi, Martin Leo (Dunlap, IL); Fiveland, Scott Byron (Metamara, IL); Timmons, Kristine Ann (Chillicothe, IL)

2010-12-14

265

Electrical and magnetic properties of ion-exchangeable layered ruthenates  

Microsoft Academic Search

An ion-exchangeable ruthenate with a layered structure, K0.2RuO2.1, was prepared by solid-state reactions. The interlayer cation was exchanged with H+, C2H5NH3+, and ((C4H9)4N+) through proton-exchange, ion-exchange, and guest-exchange reactions. The electrical and magnetic properties of the products were characterized by DC resistivity and susceptibility measurements. Layered K0.2RuO2.1 exhibited metallic conduction between 300 and 13K. The products exhibited similar magnetic behavior

Wataru. Sugimoto; Masashi Omoto; Katsunori Yokoshima; Yasushi Murakami; Yoshio Takasu

2004-01-01

266

Heat exchanger sourcebook  

SciTech Connect

This book covers techniques brought about by economical computing capabilities. It is divided into the following sections: general design information; shell-and-tube heat exchangers; reboilers and condensers; plate heat exchangers; heat exchange enhancement; techniques; and fouling.

Palen, J.W.

1986-01-01

267

Foreign Exchange Markets and Foreign Exchange Rates  

Microsoft Academic Search

A foreign exchange market is a market where a convertible currency is exchanged for another convertible currency or other\\u000a convertible currencies. In the transaction or execution of conversion, one currency is considered domestic and the other is\\u000a regarded as foreign, from a certain geographical or sovereign point of view, so is the term foreign exchange derived. Foreign\\u000a exchange markets are

Peijie Wang

268

Corrosive resistant heat exchanger  

DOEpatents

A corrosive and errosive resistant heat exchanger which recovers heat from a contaminated heat stream. The heat exchanger utilizes a boundary layer of innocuous gas, which is continuously replenished, to protect the heat exchanger surface from the hot contaminated gas. The innocuous gas is conveyed through ducts or perforations in the heat exchanger wall. Heat from the heat stream is transferred by radiation to the heat exchanger wall. Heat is removed from the outer heat exchanger wall by a heat recovery medium.

Richlen, Scott L. (Annandale, VA)

1989-01-01

269

High temperature heat exchangers  

SciTech Connect

This book contains the proceedings from the XVII Symposium of the International Center for Heat and Mass Transfer on High Temperature Heat Exchangers, held August 1985 in Yugoslavia. Papers were presented under the following topics: High Temperature Heat Exchangers Development; Basic Problem in High Temperature Heat Exchangers; Heat Exchangers for High Temperature Recovery; and High Temperature Heat Exchangers for Future Power Plants and Industrial Process Application. Some of the papers' titles are: Future Development of High Temperature Heat Exchangers; Regenerative and Direct Contact High Temperature Heat Exchangers; Heat Exchangers for Heat Recovery; High Temeprature Heat Transfer Augmentation; and Development of a BOF Slag Granulating and Heat Recovering System.

Mori, Y.; Sheindlin, A.E.; Afgan, N.

1986-01-01

270

Oxygen self-diffusion and surface exchange studies of oxide electrolytes having the fluorite structure  

Microsoft Academic Search

Isotopic Exchange Depth Profiling (IEDP) using Secondary Ion Mass Spectrometry (SIMS) has been used to investigate oxygen self-diffusion and surface exchange reactions in the related fluorites, yttria stabilised zirconia (YSZ) and gadolinia doped ceria (CGO). The nature of the exchange reaction between the gas and the surface of the solid has been explored using the gas phase analysis technique. Both

P. S. Manning; J. D. Sirman; J. A. Kilner

1996-01-01

271

Woven heat exchanger  

DOEpatents

In a woven ceramic heat exchanger using the basic tube-in-shell design, each heat exchanger consisting of tube sheets and tube, is woven separately. Individual heat exchangers are assembled in cross-flow configuration. Each heat exchanger is woven from high temperature ceramic fiber, the warp is continuous from tube to tube sheet providing a smooth transition and unitized construction.

Piscitella, Roger R. (Idaho Falls, ID)

1987-01-01

272

Industrial heat exchangers  

Microsoft Academic Search

This book presents the papers given at a symposium on the use of heat exchangers in the industrial plants. Topics considered include the US DOE and GRI research programs, advanced fixed boundary heat exchanger technology, commercial heat exchanger applications, thermo-hydraulic performance of heat-transfer equipment, field tests, the corrosion of heat exchanger materials, economics, cost benefit analysis, payback, and advanced assembly

A. J. Hayes; W. W. Liang; S. L. Richlen; E. S. Tabb

1985-01-01

273

International biomedical engineering exchanges  

Microsoft Academic Search

This is a pilot study of the feasibility of having biomedical engineers exchange jobs in other countries for a period of time. The exchange is a way of learning what our fellow biomedical engineers do. An exchange is the best way to exchange information since the exchangee actually works in the other person's job whereas at a conference there is

S. Somerwil; T. Easty

1995-01-01

274

Water Network-Dependent Charge Translocation in the NO^+ \\\\cdot (H_2O)_3 Clusters: AN Old Riddle of the Ionosphere Brings a Microscopic Grotthuss Mechanism Down to Earth  

Microsoft Academic Search

The dominant ions in the D-region of the ionosphere are proton hydrates, H^+ \\\\cdot (H_2O)_n, which are formed through a complex mechanism involving clustering, and a water network-mediated reaction, NO^+ \\\\cdot (H_2O)_3 + H_2O ? H^+ \\\\cdot (H_2O)_3 + HNO_2, that proceeds to products only upon addition of the fourth water molecule. The presence of reactive and non-reactive isomers of

Rachael Relph; Ben Elliott; Michael Kamrath; Mark A. Johnson; Anne B. McCoy; Albert A. Viggiano; Eldon E. Ferguson

2009-01-01

275

PdZn=Cu: Can an Intermetallic Compound Replace an Element?  

Microsoft Academic Search

An intermetallic compound, PdZn, exhibits a similar valence electron density of states as pure Cu, which has been confirmed by energy band calculation and X-ray photoelectron spectroscopy. The catalytic function was verified to be identical for PdZn and Cu. This explains the origin of the high selectivity of PdZn for the steam reforming of methanol (SRM), CH3OH+H2O-->3H2+CO2, a chemical reaction

An Pang Tsai; Satoshi Kameoka; Yasushi Ishii

2004-01-01

276

Field Based Constraints on Reaction Rates in the Crust  

Microsoft Academic Search

Modern research in plate boundary processes involving metamorphism frequently employs complex physical models. Such models require some quantification (or assumption) of the rate at which metamorphic reactions, or chemical exchange, proceed in natural systems. Here, a compilation of available quantitative field-based constraints on high temperature reaction rates will be presented. These include quantifications based on isotopic exchange, porphyroblast and reaction

E. F. Baxter

2004-01-01

277

Reactions & Rates  

NSDL National Science Digital Library

Explore what makes a reaction happen by colliding atoms and molecules. Design experiments with different reactions, concentrations, and temperatures. When are reactions reversible? What affects the rate of a reaction?

Simulations, Phet I.; Koch, Linda; Lemaster, Ron; Loeblein, Trish; Perkins, Kathy; Gratny, Mindy

2006-12-01

278

Drug Reactions  

MedlinePLUS

... version Drug Reactions Drug Reactions What is an adverse drug reaction? Medicines can treat or prevent illness ... medicines can cause problems. These problems are called adverse drug reactions. You should know what to do ...

279

H\\/Br Exchange in BBr3 by HSiR3 (R = H, CH3, C2H5): Origin of DFT Failures to Describe a Seemingly Innocuous Reaction Barrier  

Microsoft Academic Search

We investigate the suitability of density functional theory (DFT) and second order Møller-Plesset perturbation theory (MP2) for the title reaction, which serves as a model to represent the key step in a recently developed B-C bond formation reaction. CBS-QB3 is employed as a reference throughout this study. The classical barrier height associated with the concerted transition state for the H\\/Br

Julia R. Rakow; Sandor Tüllmann; Max C. Holthausen

2009-01-01

280

Reactor for exothermic reactions  

DOEpatents

A liquid phase process is described for oligomerization of C[sub 4] and C[sub 5] isoolefins or the etherification thereof with C[sub 1] to C[sub 6] alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120 to 300 F. Wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

Smith, L.A. Jr.; Hearn, D.; Jones, E.M. Jr.

1993-03-02

281

Reactor for exothermic reactions  

DOEpatents

A liquid phase process for oligomerization of C.sub.4 and C.sub.5 isoolefins or the etherification thereof with C.sub.1 to C.sub.6 alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120.degree. to 300.degree. F. Wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

Smith, Jr., Lawrence A. (Bellaire, TX); Hearn, Dennis (Houston, TX); Jones, Jr., Edward M. (Friendswood, TX)

1993-01-01

282

Sizing plate heat exchangers  

SciTech Connect

Since their commercial debut in the 1930s, plate heat exchangers have found widespread use in the chemical process industries (CPI). Today, more than two dozen firms market this space-saving and highly efficient type of heat exchanger. One reason for the popularity of plate heat exchangers is that their overall heat-transfer coefficient (U) is superior to that of shell-and-tube heat exchangers [1,2,3,4]. In clean water-to-water service, for example, a shell-and-tube heat exchanger has a U value of 350 Btu/ft[sup 2]-h-F, much lower than the 1,000 of a plate design at the same pressure drop. However, the plate heat exchanger's much higher U values also mean that fouling factors have a much greater effect on calculations of exchanger surface area. The right fouling factor is the key to specifying plate heat exchanger areas correctly.

Kerner, J. (Alberts and Associates, Inc., Philadelphia, PA (United States))

1993-11-01

283

The Television News Exchange  

ERIC Educational Resources Information Center

|A special issue with extensive coverage of The Television News Exchange. Contributing authors from all over the world give their perspectives on the current status and future prospects of The Television News Exchange. (HB)|

Boni, Vittorio; And Others

1975-01-01

284

Screened Exchange in Semiconductors.  

National Technical Information Service (NTIS)

The exchange contribution to the band gap is calculated in a simple model to illustrate the various processes and approximations involved. It is shown how the exchange contributes a large and approximately constant fraction of the semiconductor band gap. ...

J. C. Inkson

1973-01-01

285

Heavy-ion charge exchange in the eikonal approximation  

NASA Astrophysics Data System (ADS)

In high-energy collisions (Elab > 50 MeV/nucleon) the eikonal approximation provides a transparent description of heavy-ion exchange reactions. The formalism is applied to the reaction 13N(13C, 13N)13C at 70 MeV/nucleon. The relative contributions of pion- and rho-exchange are determined. It is found that heavy-ion reactions are more sensitive to the one-pion exchange component of the interaction than nucleon-induced charge exchange. The cross section for double charge exchange are estimated, which could be useful for future experiments. Permanent address: Instituto de Física, Universidade Federal do Rio de Janeiro, 21945 Rio de Janeiro, Brazil.

Bertulani, C. A.

1993-03-01

286

Fluid dynamic energy exchanger  

Microsoft Academic Search

A gas-to-gas energy exchanger utilizing a commutator repetitively diverts a jet of a first pressurized gas between an energy exchange conduit and an exhaust outlet. Upon entering the energy exchange conduit, the first gas creates a pressure wave which traverses the conduit at sonic velocity and, in so doing, compresses a second gas in the conduit. The now pressurized second

1982-01-01

287

Data of Ion Exchange.  

National Technical Information Service (NTIS)

Behavior of ion exchange of several elements are compiled as 30 figures in the sequence of periodic system. Exchangers are Dowex, Diaion and inorganic ion exchangers. Data of adsorption on charcoal and silica gel are also given. (Atomindex citation 09:367...

E. Akatsu

1977-01-01

288

Parisian exchange options  

Microsoft Academic Search

The option to exchange one asset for another is one of the oldest and one of the most popular exotic options. In the present article, we extend the existing literature on options to Parisian exchange options, i.e. the option to exchange one asset for the other contingent on the occurrence of the Parisian time. Thus, these options are a special

An Chen; Michael Suchanecki

2010-01-01

289

The Tacoma Syringe Exchange  

Microsoft Academic Search

For over a year, the Tacoma Syringe Exchange has been operating in spite of existing drug paraphernalia laws. One hundred fifty-four subjects have been interviewed regarding drug injection practices for the month prior to first use of the exchange and for the most recent month since using the exchange. Statistically significant reductions in mean frequency of obtaining used syringes, and

Holly Hagan; Don C. Des Jarlais; David Purchase; Terry Reid; Samuel R Friedman

1991-01-01

290

Microtube strip heat exchanger  

Microsoft Academic Search

The purpose of this contract has been to explore the limits of miniaturization of heat exchangers with the goals of (1) improving the theoretical understanding of laminar heat exchangers, (2) evaluating various manufacturing difficulties, and (3) identifying major applications for the technology. A low-cost, ultra-compact heat exchanger could have an enormous impact on industry in the areas of cryocoolers and

F. D. Doty

1992-01-01

291

Exchange Rate Economics  

Microsoft Academic Search

This book describes and evaluates the literature on exchange rate economics. It provides a wide-ranging survey, with background on the history of international monetary regimes and the institutional characteristics of foreign exchange markets, an overview of the development of conceptual and empirical models of exchange rate behavior, and perspectives on the key issues that policymakers confront in deciding whether, and

Peter Isard

292

Charge exchange system  

DOEpatents

An improved charge exchange system for substantially reducing pumping requirements of excess gas in a controlled thermonuclear reactor high energy neutral beam injector. The charge exchange system utilizes a jet-type blanket which acts simultaneously as the charge exchange medium and as a shield for reflecting excess gas.

Anderson, Oscar A. (Berkeley, CA)

1978-01-01

293

Synthesis and anion exchange reactions of a layered copper-zinc hydroxy double salt, Cu 1.6 Zn 0.4 (OH) 3 (OAc)·H 2 O  

Microsoft Academic Search

A mixed-metal hydroxysalt of formula Cu1.6Zn0.4(OH)3(OAc)·H2O has been synthesized by an acetate hydrolysis route. Acetate ions can be exchanged with simple inorganic anions such as\\u000a chloride and nitrate, and organic anions such as benzoate and large surfactant anions such as dodecyl sulphate. Structures\\u000a of these hydroxysalts are derived from that of Cu2(OH)3NO3·H2O with some of the Cu2+ ions being replaced

Jacqueline Therese Rajamathi; Sylvia Britto; Michael Rajamathi

2005-01-01

294

A combined experimental, theoretical, and Van't Hoff model study for identity methyl, proton, hydrogen atom, and hydride exchange reactions. Correlation with three-center four-, three-, and two-electron systems  

NASA Astrophysics Data System (ADS)

We have studied carbon transfer reactions following an SN2 reaction profile. With ab initio calculations and experimental geometries concerning the nature of the various complexes indicated as stable, intermediate, and transition state we were able to show the additional value of van't Hoff's tetrahedral configuration by changing its geometry via a trigonal pyramid into a trigonal bipyramid. The ratio of the apical bond and corresponding tetrahedral bond distances is then nearly 1.333. The relevance of this approach has also been shown for identity proton-(hydrogen atom-, and hydride-) in-line reactions. The use of this geometrical transmission will be demonstrated for the hydrogen bonding distances in e.g., DNA duplexes and other biological (supra) molecular systems.

Buck, Henk M.

295

Nitron base fibrous cation exchange materials  

Microsoft Academic Search

The high chemical stability of the carbon chain in the macromolecule of polyacrylonitrile and the reaction capacity of the nitrile groups in polymeric conversion processes \\/I\\/ are factors which render the production of ion exchange materials based on fibres spun from polyacrylonitrile polymers and copoiymers of interest. The alkaline saponification of polyacrylonitrile (PAN) is a process which has been studied

Zh. A. Zgibneva; A. A. Geller; B. E. Geller; M. V. Polovnikova; A. G. Ereshchenko; R. I. Khomenko

1974-01-01

296

RELATIONSHIP BETWEEN ISOTOPICALLY EXCHANGABLE CALCIUM AND ABSORPTION BY PLANTS  

Microsoft Academic Search

When soils are suspended in solutions of calcium chloride labeled with ; radioactive tracer, isotopic exchange with the labile soil-calcium occurs rapidly. ; This may be followed by a slow secondary exchange reaction, but its magnitude is ; not great and equilibrium is nearly, if not completely, attained with 7 days. ; When, however, plants are grown in soil throughout

P. Newbould

1963-01-01

297

Allelic exchange in Francisella tularensis using PCR products  

Microsoft Academic Search

We describe here a technique for allelic exchange in Francisella tularensis subsp. novicida utilizing polymerase chain reaction (PCR) products. Linear PCR fragments containing gene deletions with an erythromycin resistance cassette insertion were transformed into F. tularensis. The subsequent ErmR progeny were found to have undergone allelic exchange at the correct location in the genome; the minimum flanking homology necessary was

Crystal M. Lauriano; Jeffrey R. Barker; Francis E. Nano; Bernard P. Arulanandam; Karl E. Klose

2003-01-01

298

Reactions on ZSM-5-type zeolite catalysts  

Microsoft Academic Search

Catalytic reactions and sorption measurements have been carried out with ZSM-5 and silicalite catalysts which are distinguished by variation in skeletal heteroatom concentration. The catalysts were used in both the hydrogen-exchanged and sodium-exchanged forms. Sorption measurements were made with the hydrocarbons n-hexane, 3-methylpentane, and 2,2-dimethyl-butane, and with the bases ammonia, n-butylamine, t-butylamine, and 4-methylquinoline. Catalytic reactions were carried out on

J. R. Anderson; K. Foger; T. Mole; R. A. Rajadhyaksha; J. V. Sanders

1979-01-01

299

Isotopic fractionation in low temperature ion--molecule exchange reactions: Enrichment of sup 22 Ne in Ne sup + sub n clusters formed by association in an ionized free jet  

SciTech Connect

Cationic clusters of neon atoms (Ne{sup +}{sub {ital n}} ) formed by association of neutrals onto seed ions in an ionized supersonic expansion are found to favor incorporation of the heavier isotope ({sup 22}Ne) {ital by} {ital as} {ital much} {ital as} {ital a} {ital factor} {ital of} 15 (in the dimer and trimer ions) when compared to a simple statistical distribution based on natural abundances. This enrichment is attributed to the small difference in zero-point energies among species formed with the two major isotopes of neon ({sup 20}Ne and {sup 22}Ne), which is of the same order as the collisional energy of particles in the expanding jet. This enrichment is anticipated by current models of isotope exchange which are invoked to explain the anomalous isotope abundance patterns in interstellar clouds.

DeLuca, M.J.; Cyr, D.M.; Chupka, W.A.; Johnson, M.A. (Yale University, Department of Chemistry, New Haven, Connecticut 06511-8118 (US))

1990-06-15

300

Reciprocity theory of homogeneous reactions  

NASA Astrophysics Data System (ADS)

The reciprocity formalism is applied to the homogeneous gaseous reactions in which the structure of the participating molecules changes upon collision with one another, resulting in a change in the composition of the gas. The approach is applied to various classes of dissociation, recombination, rearrangement, ionizing, and photochemical reactions. It is shown that for the principle of reciprocity to be satisfied it is necessary that all chemical reactions exist in complementary pairs which consist of the forward and backward reactions. The backward reaction may be described by either the reverse or inverse process. The forward and backward processes must satisfy the same reciprocity equation. Because the number of dynamical variables is usually unbalanced on both sides of a chemical equation, it is necessary that this balance be established by including as many of the dynamical variables as needed before the reciprocity equation can be formulated. Statistical transformation models of the reactions are formulated. The models are classified under the titles free exchange, restricted exchange and simplified restricted exchange. The special equations for the forward and backward processes are obtained. The models are consistent with the H theorem and Le Chatelier's principle. The models are also formulated in the context of the direct simulation Monte Carlo method.

Agbormbai, Adolf A.

1990-03-01

301

The single-process biochemical reaction of Rubisco: a unified theory and model with the effects of irradiance, CO? and rate-limiting step on the kinetics of C? and C? photosynthesis from gas exchange.  

PubMed

Photosynthesis is the origin of oxygenic life on the planet, and its models are the core of all models of plant biology, agriculture, environmental quality and global climate change. A theory is presented here, based on single process biochemical reactions of Rubisco, recognizing that: In the light, Rubisco activase helps separate Rubisco from the stored ribulose-1,5-bisphosphate (RuBP), activates Rubisco with carbamylation and addition of Mg²(+), and then produces two products, in two steps: (Step 1) Reaction of Rubisco with RuBP produces a Rubisco-enediol complex, which is the carboxylase-oxygenase enzyme (Enco) and (Step 2) Enco captures CO? and/or O? and produces intermediate products leading to production and release of 3-phosphoglycerate (PGA) and Rubisco. PGA interactively controls (1) the carboxylation-oxygenation, (2) electron transport, and (3) triosephosphate pathway of the Calvin-Benson cycle that leads to the release of glucose and regeneration of RuBP. Initially, the total enzyme participates in the two steps of the reaction transitionally and its rate follows Michaelis-Menten kinetics. But, for a continuous steady state, Rubisco must be divided into two concurrently active segments for the two steps. This causes a deviation of the steady state from the transitional rate. Kinetic models are developed that integrate the transitional and the steady state reactions. They are tested and successfully validated with verifiable experimental data. The single-process theory is compared to the widely used two-process theory of Farquhar et al. (1980. Planta 149, 78-90), which assumes that the carboxylation rate is either Rubisco-limited at low CO? levels such as CO? compensation point, or RuBP regeneration-limited at high CO?. Since the photosynthesis rate cannot increase beyond the two-process theory's Rubisco limit at the CO? compensation point, net photosynthesis cannot increase above zero in daylight, and since there is always respiration at night, it leads to progressively negative daily CO? fixation with no possibility of oxygenic life on the planet. The Rubisco-limited theory at low CO? also contradicts all experimental evidence for low substrate reactions, and for all known enzymes, Rubisco included. PMID:21093535

Farazdaghi, Hadi

2010-11-18

302

Emittance exchange results  

SciTech Connect

The promise of next-generation light sources depends on the availability of ultra-low emittance electron sources. One method of producing low transverse emittance beams is to generate a low longitudinal emittance beam and exchange it with a large transverse emittance. Experiments are underway at Fermilab's A0 Photoinjector and ANL's Argonne Wakefield Accelerator using the exchange scheme of Kim and Sessler. The experiment at the A0 Photoinjector exchanges a large longitudinal emittance with a small transverse emittance. AWA expects to exchange a large transverse emittance with a small longitudinal emittance. In this paper we discuss recent results at A0 and AWA and future plans for these experiments.

Fliller, R.P., III; /Brookhaven; Koeth, T.; /Rutgers U., Piscataway

2009-09-01

303

Emittance Exchange Results  

SciTech Connect

The promise of next-generation light sources depends on the availability of ultra-low emittance electron sources. One method of producing low transverse emittance beams is to generate a low longitudinal emittance beam and exchange it with a large transverse emittance. Experiments are underway at Fermilab's A0 Photoinjector and ANL's Argonne Wakefield Accelerator using the exchange scheme of Kim and Sessler. The experiment at the A0 Photoinjector exchanges a large longitudinal emittance with a small transverse emittance. AWA expects to exchange a large transverse emittance with a small longitudinal emittance. In this paper we discuss recent results at A0 and AWA and future plans for these experiments.

Fliller III,R.; Koeth, T.

2009-05-04

304

Microtube strip heat exchanger  

SciTech Connect

During the last quarter, Doty Scientific, Inc. (DSI) continued to make progress on the microtube strip (MTS) heat exchanger. DSI completed a heat exchanger stress analysis of the ten-module heat exchanger bank; and, performed a shell-side flow inhomogeneity analysis of the three-module heat exchanger bank. The company produced 50 tubestrips using an in-house CNC milling machine and began pressing them onto tube arrays. DSI revised some of the tooling required to encapsulate a tube array and press tubestrips into the array to improve some of the prototype tooling. 2 refs., 4 figs.

Doty, F.D.

1991-07-08

305

Modeling of surface reactions  

SciTech Connect

Mathematical models are used to elucidate properties of the monomer-monomer and monomer-dimer type chemical reactions on a two-dimensional surface. The authors use mean-field and lattice gas models, detailing similarities and differences due to correlations in the lattice gas model. The monomer-monomer, or AB surface reaction model, with no diffusion, is investigated for various reaction rates k. Study of the exact rate equations reveals that poisoning always occurs if the adsorption rates of the reactants are unequal. If the adsorption rates of the reactants are equal, simulations show slow poisoning, associated with clustering of reactants. This behavior is also shown for the two-dimensional voter model. The authors analyze precisely the slow poisoning kinetics by an analytic treatment for the AB reaction with infinitesimal reaction rate, and by direct comparison with the voter model. They extend the results to incorporate the effects of place-exchange diffusion, and they compare the AB reaction with infinitesimal reaction rate and no diffusion to the voter model with diffusion at rate 1/2. They also consider the relationship of the voter model to the monomer-dimer model, and investigate the latter model for small reaction rates. The monomer-dimer, or AB[sub 2] surface reaction model is also investigated. Specifically, they consider the ZGB-model for CO-oxidation, and in generalizations of this model which include adspecies diffusion. A theory of nucleation to describe properties of non-equilibrium first-order transitions, specifically the evolution between [open quote]reactive[close quote] steady states and trivial adsorbing states, is derived. The behavior of the [open quote]epidemic[close quote] survival probability, P[sub s], for a non-poisoned patch surrounded by a poisoned background is determined below the poisoning transition.

Ray, T.R.

1993-01-01

306

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

307

Electrical and magnetic properties of ion-exchangeable layered ruthenates  

SciTech Connect

An ion-exchangeable ruthenate with a layered structure, K{sub 0.2}RuO{sub 2.1}, was prepared by solid-state reactions. The interlayer cation was exchanged with H{sup +}, C{sub 2}H{sub 5}NH{sub 3}{sup +}, and ((C{sub 4}H{sub 9}){sub 4}N{sup +}) through proton-exchange, ion-exchange, and guest-exchange reactions. The electrical and magnetic properties of the products were characterized by DC resistivity and susceptibility measurements. Layered K{sub 0.2}RuO{sub 2.1} exhibited metallic conduction between 300 and 13K. The products exhibited similar magnetic behavior despite the differences in the type of interlayer cation, suggesting that the ruthenate sheet in the protonated form and the intercalation compounds possesses metallic nature.

Sugimoto, Wataru [Faculty of Textile Science and Technology, Department of Fine Materials Engineering, Shinshu University, 3-15-1 Tokida, Ueda 386-8567 (Japan)]. E-mail: wsugi@shinshu-u.ac.jp; Omoto, Masashi [Faculty of Textile Science and Technology, Department of Fine Materials Engineering, Shinshu University, 3-15-1 Tokida, Ueda 386-8567 (Japan); Yokoshima, Katsunori [Faculty of Textile Science and Technology, Department of Fine Materials Engineering, Shinshu University, 3-15-1 Tokida, Ueda 386-8567 (Japan); Murakami, Yasushi [Faculty of Textile Science and Technology, Department of Fine Materials Engineering, Shinshu University, 3-15-1 Tokida, Ueda 386-8567 (Japan); Takasu, Yoshio [Faculty of Textile Science and Technology, Department of Fine Materials Engineering, Shinshu University, 3-15-1 Tokida, Ueda 386-8567 (Japan)

2004-12-01

308

SYNTHETIC INORGANIC ION-EXCHANGE MATERIALS. II. HYDROUS ZIRCONIUM OXIDE AND OTHER OXIDES  

Microsoft Academic Search

The oxides ZrOâ, ThOâ, and TiOâ behave as anion ; exchangers in acid and neutral solution and cation exchangers in alkaline ; solution, the pH at which their behavior changes depending upon the oxide itself ; and Possibly also upon the nature of the exchanging ion. The oxides have been ; prepared in granular form and their reversible reactions with

C. B. Amphlett; L. A. McDonald; M. J. Redman

1958-01-01

309

Water Network-Dependent Charge Translocation in the NO^+ \\cdot (H_2O)_3 Clusters: AN Old Riddle of the Ionosphere Brings a Microscopic Grotthuss Mechanism Down to Earth  

NASA Astrophysics Data System (ADS)

The dominant ions in the D-region of the ionosphere are proton hydrates, H^+ \\cdot (H_2O)_n, which are formed through a complex mechanism involving clustering, and a water network-mediated reaction, NO^+ \\cdot (H_2O)_3 + H_2O ? H^+ \\cdot (H_2O)_3 + HNO_2, that proceeds to products only upon addition of the fourth water molecule. The presence of reactive and non-reactive isomers of NO^+ \\cdot (H_2O)_3 has been invoked to explain the relatively slow rate of HNO_2 formation from the trihydrate. To address this hypothesis, we have employed isomer-selective, pump-probe spectroscopy to determine the infrared signatures of species nominally present in the NO^+ \\cdot (H_2O)_3 ion packet prepared in a supersonic jet ion source. Indeed two isomers are found to be present. Strong differences in the spectral patterns of the two isomers suggest that they have quite different geometries, which would be consistent with the isomer-specific reactivity model. One of the patterns yields strongly red-shifted activity in the OH stretching region around 2800 cm^{-1}, which is readily explained by the expected behavior of the bridging hydrogen atoms in a chain structure. The motion of these protons is reminiscent of the von Grotthuss mechanism where sequential dissociation and reformation of OH bonds translocates a proton over large distances by passing through a series of small, pairwise exchanges.

Relph, Rachael; Elliott, Ben; Kamrath, Michael; Johnson, Mark A.; McCoy, Anne B.; Viggiano, Albert A.; Ferguson, Eldon E.

2009-06-01

310

Heat exchanger antifoulant  

SciTech Connect

Disclosed is a process for reducing the fouling in a heat exchanger in which a hydrocarbon stream is heated or cooled as it passes through the heat exchanger. From 1 to 500 parts per million of a saturated sulfoxide is added to the stream to reduce fouling.

Ferm, R.L.

1984-09-04

311

Heat exchanger antifoulant  

SciTech Connect

Disclosed is a process for reducing the fouling in a heat exchanger in which a hydrocarbon stream is heated or cooled as it passes through the heat exchanger. From 1 to 500 parts per million of an alkylamino alkylphenol is added to the stream to reduce fouling.

Ferm, R.L.; Kray, L.R.

1984-03-06

312

Heat exchanger antifoulant  

SciTech Connect

Disclosed is a process for reducing the fouling in a heat exchanger in which a hydrocarbon stream is heated or cooled as it passes through the heat exchanger. From 1 to 500 parts per million of an organic hydroxylamine is added to the stream to reduce fouling.

Ferm, R. L.

1985-11-05

313

Money and Exchange.  

ERIC Educational Resources Information Center

This teaching guide begins with an explanation of the role of money in the economy, focusing on its circulation or exchange. The use of money as a unit of account, a store of value, and a medium of exchange are explained. Three brief teaching units are included. The grade K-2 unit, "Money Counts," provides games and activities which develop the…

Walstad, William B.; And Others

1982-01-01

314

Data Exchange in Bauhaus  

Microsoft Academic Search

In the context of the Bauhaus project, reengineering environments to support program understanding of legacy code are being developed. Bauhaus defines two formats to represent information that has been extracted from source code. One of these formats, RG, is suitable as an exchange format. This paper introduces RG, describes how it is rep- resented as an exchange format, and discusses

Jörg Czeranski; Thomas Eisenbarth; Holger M. Kienle; Rainer Koschke; Erhard Plödereder; Daniel Simon; Yan Zhang V; Jean-francois Girard; Martin Würthner

2000-01-01

315

Verifying Exchange Rate Regimes  

Microsoft Academic Search

July 2000One reason intermediate exchange rate regimes have fallen out of favor is that they are not transparent or easy to verify. A simple peg or a simple float may be easier for market participants to verify than a more complicated intermediate regime.Credibility and transparency are at the core of the current debate about exchange rate regimes. The steady growth

Sergio Schmukler; Jeffrey Frankel; Eduardo Fajnzylber

1999-01-01

316

Higher Education Exchange, 2012  

ERIC Educational Resources Information Center

|"Higher Education Exchange" publishes case studies, analyses, news, and ideas about efforts within higher education to develop more democratic societies. Contributors to this issue of the "Higher Education Exchange" examine whether institutions of higher learning are doing anything to increase the capacity of citizens to shape their future.…

Brown, David W., Ed.; Witte, Deborah, Ed.

2012-01-01

317

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

318

Special Reactions  

NSDL National Science Digital Library

The basics of chemical reactions were covered in the first chemistry book, including how to write and balance chemical equations that represent those reactions. There is also a quick review of chemical reactions in Chapter 1 of this book. We're going to d

Robertson, William C.

2010-03-01

319

Lightweight long life heat exchanger  

Microsoft Academic Search

A shuttle orbiter flight configuration aluminum heat exchanger was designed, fabricated, and tested. The heat exchanger utilized aluminum clad titanium composite parting sheets for protection against parting sheet pin hole corrosion. The heat exchanger, which is fully interchangeable with the shuttle condensing heat exchanger, includes slurpers (a means for removing condensed water from the downstream face of the heat exchanger),

E. K. Moore

1976-01-01

320

Stability of Coupling in Exchange Spring and Exchange Bias Systems.  

National Technical Information Service (NTIS)

We have studied the magnetic stability in exchange bias and exchange spring systems prepared via epitaxial sputter deposition. The two interracial exchange coupled systems, Fe/Cr(2 11) double superlattices consisting of a ferromagnetic and an antiferromag...

J. S. Jiang A. Inomata C. Y. You J. E. Pearson S. D. Bader

2001-01-01

321

Solvent effect in the Walden inversion reactions  

NASA Astrophysics Data System (ADS)

The solvent effect on the fluoride exchange reaction has been studied by means of ab initio calculations using the 3-21G basis set. It is shown that the motion of the solvent molecules is an important part of the reaction coordinate.

Jaume, J.; Lluch, J. M.; Oliva, A.; Bertrán, J.

1984-04-01

322

Polarization Effects in Exclusive Hyperon Production Reactions  

Microsoft Academic Search

Extensive experimental evidence for sizable polarizations of hyperons produced in inclusive reactions at high energies have stimulated various quark-based or meson-exchange models of the mechanism responsible for this spin preference. We are in the final stages of preparing an experiment to distinguish among such models by the study of the exclusive reactions pp --> p K^+ Lambda and pp -->

M. Dzemidzic

1996-01-01

323

Heat and mass exchanger  

SciTech Connect

A mass and heat exchanger includes at least one first substrate with a surface for supporting a continuous flow of a liquid thereon that either absorbs, desorbs, evaporates or condenses one or more gaseous species from or to a surrounding gas; and at least one second substrate operatively associated with the first substrate. The second substrate includes a surface for supporting the continuous flow of the liquid thereon and is adapted to carry a heat exchange fluid therethrough, wherein heat transfer occurs between the liquid and the heat exchange fluid.

Lowenstein, Andrew (Princeton, NJ); Sibilia, Marc J. (Princeton, NJ); Miller, Jeffrey A. (Hopewell, NJ); Tonon, Thomas (Princeton, NJ)

2007-09-18

324

Cryptographic Securities Exchanges  

NASA Astrophysics Data System (ADS)

While transparency in financial markets should enhance liquidity, its exploitation by unethical and parasitic traders discourages others from fully embracing disclosure of their own information. Traders exploit both the private information in upstairs markets used to trade large orders outside traditional exchanges and the public information present in exchanges' quoted limit order books. Using homomorphic cryptographic protocols, market designers can create "partially transparent" markets in which every matched trade is provably correct and only beneficial information is revealed. In a cryptographic securities exchange, market operators can hide information to prevent its exploitation, and still prove facts about the hidden information such as bid/ask spread or market depth.

Thorpe, Christopher; Parkes, David C.

325

Anion exchange membrane  

DOEpatents

An anion exchange membrane and fuel cell incorporating the anion exchange membrane are detailed in which proazaphosphatrane and azaphosphatrane cations are covalently bonded to a sulfonated fluoropolymer support along with anionic counterions. A positive charge is dispersed in the aforementioned cations which are buried in the support to reduce the cation-anion interactions and increase the mobility of hydroxide ions, for example, across the membrane. The anion exchange membrane has the ability to operate at high temperatures and in highly alkaline environments with high conductivity and low resistance.

Verkade, John G; Wadhwa, Kuldeep; Kong, Xueqian; Schmidt-Rohr, Klaus

2013-05-07

326

Wound tube heat exchanger  

DOEpatents

What is disclosed is a wound tube heat exchanger in which a plurality of tubes having flattened areas are held contiguous adjacent flattened areas of tubes by a plurality of windings to give a double walled heat exchanger. The plurality of windings serve as a plurality of effective force vectors holding the conduits contiguous heat conducting walls of another conduit and result in highly efficient heat transfer. The resulting heat exchange bundle is economical and can be coiled into the desired shape. Also disclosed are specific embodiments such as the one in which the tubes are expanded against their windings after being coiled to insure highly efficient heat transfer.

Ecker, Amir L. (Duncanville, TX)

1983-01-01

327

TOSS Exchange Center.  

National Technical Information Service (NTIS)

The interim technical report documents the detailed system specifications for the Terminal Oriented Support System (TOSS) Exchange Center (TEC) as required under RADC Contract. TEC is a software system design which enables a mini-computer to function as a...

R. Taylor D. Lewis R. Hicks B. Montcalm C. Shorter

1974-01-01

328

Understanding heat exchanger systems  

SciTech Connect

Many of the complaints heard about steam heat exchangers--water hammer, corrosion, and freezing--often are not caused by the unit itself but, rather, are problems within the system. Diagnosing and overcoming problems in existing systems or designing new ones properly requires a thorough understanding not only of the heat exchanger, but all of the components that make up the overall system. Many types of heat exchangers are available today (shell-and-tube, plate-and-frame, coil, tank heaters, and plate coils). The same basic principles and similar controls apply to all. Although the examples in this article consider the shell-and-tube style, the concepts apply to all types of steam heat exchangers.

Hughes, B. [ITT Fluid Technology, Guelph, Ontario (Canada)

1997-04-01

329

Greywater Heat Exchanger.  

National Technical Information Service (NTIS)

A kilowatt meter and water meter were installed to monitor pregreywater usage. The design considerations, the heat exchanger construction and installation, and the monitoring of usage levels are described. (ERA citation 09:040361)

D. Holmberg

1983-01-01

330

Greywater heat exchanger  

SciTech Connect

A kilowatt meter and water meter were installed to monitor pregreywater usage. The design considerations, the heat exchanger construction and installation, and the monitoring of usage levels are described.

Holmberg, D.

1983-11-21

331

TOSS Exchange Center.  

National Technical Information Service (NTIS)

This final Technical Report documents the TOSS Exchange Center (TEC). TEC is the communications utility subsystem of the Terminal Oriented Support System (TOSS). TEC was designed to provide all the facilities needed to handle the transfer of data between ...

R. Taylor D. Lewis S. Adams R. Hicks R. Montcalm

1975-01-01

332

Hibernation and gas exchange.  

PubMed

Hibernation in endotherms and ectotherms is characterized by an energy-conserving metabolic depression due to low body temperatures and poorly understood temperature-independent mechanisms. Rates of gas exchange are correspondly reduced. In hibernating mammals, ventilation falls even more than metabolic rate leading to a relative respiratory acidosis that may contribute to metabolic depression. Breathing in some mammals becomes episodic and in some small mammals significant apneic gas exchange may occur by passive diffusion via airways or skin. In ectothermic vertebrates, extrapulmonary gas exchange predominates and in reptiles and amphibians hibernating underwater accounts for all gas exchange. In aerated water diffusive exchange permits amphibians and many species of turtles to remain fully aerobic, but hypoxic conditions can challenge many of these animals. Oxygen uptake into blood in both endotherms and ectotherms is enhanced by increased affinity of hemoglobin for O? at low temperature. Regulation of gas exchange in hibernating mammals is predominately linked to CO?/pH, and in episodic breathers, control is principally directed at the duration of the apneic period. Control in submerged hibernating ectotherms is poorly understood, although skin-diffusing capacity may increase under hypoxic conditions. In aerated water blood pH of frogs and turtles either adheres to alphastat regulation (pH ?8.0) or may even exhibit respiratory alkalosis. Arousal in hibernating mammals leads to restoration of euthermic temperature, metabolic rate, and gas exchange and occurs periodically even as ambient temperatures remain low, whereas body temperature, metabolic rate, and gas exchange of hibernating ectotherms are tightly linked to ambient temperature. PMID:23737179

Milsom, William K; Jackson, Donald C

2011-01-01

333

Superconductivity and information exchange  

NASA Astrophysics Data System (ADS)

The author was invited to visit several institutions in Europe for the purposes of collaboration, information exchange, and presentation of seminars. Extensive exchanges of information regarding the current state of the field in high-temperature superconductivity took place. Five seminars on the recent work of Klemm and Liu on interlayer pairing were given, and the response was very favorable. A new collaboration on the role of gap anisotropy on the physical properties of high-temperature superconductors was begun.

Klemm, R. A.

1990-08-01

334

Microtube strip heat exchanger  

SciTech Connect

The purpose of this contract has been to explore the limits of miniaturization of heat exchangers with the goals of (1) improving the theoretical understanding of laminar heat exchangers, (2) evaluating various manufacturing difficulties, and (3) identifying major applications for the technology. A low-cost, ultra-compact heat exchanger could have an enormous impact on industry in the areas of cryocoolers and energy conversion. Compact cryocoolers based on the reverse Brayton cycle (RBC) would become practical with the availability of compact heat exchangers. Many experts believe that hardware advances in personal computer technology will rapidly slow down in four to six years unless lowcost, portable cryocoolers suitable for the desktop supercomputer can be developed. Compact refrigeration systems would permit dramatic advances in high-performance computer work stations with conventional'' microprocessors operating at 150 K, and especially with low-cost cryocoolers below 77 K. NASA has also expressed strong interest in our MTS exchanger for space-based RBC cryocoolers for sensor cooling. We have demonstrated feasibility of higher specific conductance by a factor of five than any other work in high-temperature gas-to-gas exchangers. These laminar-flow, microtube exchangers exhibit extremely low pressure drop compared to alternative compact designs under similar conditions because of their much shorter flow length and larger total flow area for lower flow velocities. The design appears to be amenable to mass production techniques, but considerable process development remains. The reduction in materials usage and the improved heat exchanger performance promise to be of enormous significance in advanced engine designs and in cryogenics.

Doty, F.D.

1992-07-09

335

Microtube Strip Heat Exchanger  

SciTech Connect

Doty Scientific (DSI) believes their Microtube-Strip Heat Exchanger will contribute significantly to (a) the closed Brayton cycles being pursued at MIT, NASA, and elsewhere; (b) reverse Brayton cycle cryocoolers, currently being investigated by NASA for space missions, being applied to MRI superconducting magnets; and (c) high-efficiency cryogenic gas separation schemes for CO{sub 2} removal from exhaust stacks. The goal of this current study is to show the potential for substantial progress in high-effectiveness, low-cost, gas-to-gas heat exchangers for diverse applications at temperatures from below 100 K to above 1000 K. To date, the highest effectiveness measured is about 98%, and relative pressure drops below 0.1% with a specific conductance of about 45 W/kgK are reported. During the pre-award period DSI built and tested a 3-module heat exchanger bank using 103-tube microtube strip (MTS) modules. To add to their analytical capabilities, DSI has acquired computational fluid dynamics (CFD) software. This report describes the pre-award work and the status of the ten tasks of the current project, which are: analyze flow distribution and thermal stresses within individual modules; design a heat exchanger bank of ten modules with 400 microtube per module; obtain production quality tubestrip die and AISI 304 tubestrips; obtain production quality microtubing; construct revised MTS heat exchanger; construct dies and fixtures for prototype heat exchanger; construct 100 MTS modules; assemble 8-10 prototype MTS heat exchangers; test prototype MTS heat exchanger; and verify test through independent means. 7 refs., 9 figs. 1 tab. (CK)

Doty, F.D.

1990-12-27

336

Microtube strip heat exchanger  

NASA Astrophysics Data System (ADS)

The purpose of this contract has been to explore the limits of miniaturization of heat exchangers with the goals of (1) improving the theoretical understanding of laminar heat exchangers, (2) evaluating various manufacturing difficulties, and (3) identifying major applications for the technology. A low-cost, ultra-compact heat exchanger could have an enormous impact on industry in the areas of cryocoolers and energy conversion. Compact cryocoolers based on the reverse Brayton cycle (RBC) would become practical with the availability of compact heat exchangers. Many experts believe that hardware advances in personal computer technology will rapidly slow down in four to six years unless lowcost, portable cryocoolers suitable for the desktop supercomputer can be developed. Compact refrigeration systems would permit dramatic advances in high-performance computer work stations with 'conventional' microprocessors operating at 150 K, and especially with low-cost cryocoolers below 77 K. NASA has also expressed strong interest in our MTS exchanger for space-based RBC cryocoolers for sensor cooling. We have demonstrated feasibility of higher specific conductance by a factor of five than any other work in high-temperature gas-to-gas exchangers. These laminar-flow, microtube exchangers exhibit extremely low pressure drop compared to alternative compact designs under similar conditions because of their much shorter flow length and larger total flow area for lower flow velocities. The design appears to be amenable to mass production techniques, but considerable process development remains. The reduction in materials usage and the improved heat exchanger performance promise to be of enormous significance in advanced engine designs and in cryogenics.

Doty, F. D.

1992-07-01

337

Cryptographic Combinatorial Securities Exchanges  

NASA Astrophysics Data System (ADS)

We present a useful new mechanism that facilitates the atomic exchange of many large baskets of securities in a combinatorial exchange. Cryptography prevents information about the securities in the baskets from being exploited, enhancing trust. Our exchange offers institutions who wish to trade large positions a new alternative to existing methods of block trading: they can reduce transaction costs by taking advantage of other institutions’ available liquidity, while third party liquidity providers guarantee execution—preserving their desired portfolio composition at all times. In our exchange, institutions submit encrypted orders which are crossed, leaving a “remainder”. The exchange proves facts about the portfolio risk of this remainder to third party liquidity providers without revealing the securities in the remainder, the knowledge of which could also be exploited. The third parties learn either (depending on the setting) the portfolio risk parameters of the remainder itself, or how their own portfolio risk would change if they were to incorporate the remainder into a portfolio they submit. In one setting, these third parties submit bids on the commission, and the winner supplies necessary liquidity for the entire exchange to clear. This guaranteed clearing, coupled with external price discovery from the primary markets for the securities, sidesteps difficult combinatorial optimization problems. This latter method of proving how taking on the remainder would change risk parameters of one’s own portfolio, without revealing the remainder’s contents or its own risk parameters, is a useful protocol of independent interest.

Thorpe, Christopher; Parkes, David C.

338

Radial flow heat exchanger  

DOEpatents

A radial flow heat exchanger (20) having a plurality of first passages (24) for transporting a first fluid (25) and a plurality of second passages (26) for transporting a second fluid (27). The first and second passages are arranged in stacked, alternating relationship, are separated from one another by relatively thin plates (30) and (32), and surround a central axis (22). The thickness of the first and second passages are selected so that the first and second fluids, respectively, are transported with laminar flow through the passages. To enhance thermal energy transfer between first and second passages, the latter are arranged so each first passage is in thermal communication with an associated second passage along substantially its entire length, and vice versa with respect to the second passages. The heat exchangers may be stacked to achieve a modular heat exchange assembly (300). Certain heat exchangers in the assembly may be designed slightly differently than other heat exchangers to address changes in fluid properties during transport through the heat exchanger, so as to enhance overall thermal effectiveness of the assembly.

Valenzuela, Javier (Hanover, NH)

2001-01-01

339

Vacuum powered heat exchanger  

SciTech Connect

In an internal combustion engine including an oil lubrication system, a liquid cooling system, and an improved air intake system is described. The improved air intake system comprises: a housing including a first opening in one end, which opening is open to the atmosphere and a second opening comprising an air outlet opening in the other end open to the air intake manifold of the engine, a heat exchanger positioned in the first opening. The heat exchanger consists of a series of coils positioned in the flow path of the atmospheric air as it enters the housing, the heat exchanger being fluidly connected to either the engine lubrication system or the cooling system to provide a warm heat source for the incoming air to the housing, acceleration means positioned in the housing downstream of the heat exchanger, the acceleration means comprising a honeycomb structure positioned across the air intake flow path. The honey-comb structure includes a multitude of honey combed mini-venturi cells through which the heated air flows in an accelerated mode, a removable air filter positioned between the heat exchanger and the acceleration means and a single opening provided in the housing through which the air filter can be passed and removed, and additional openings in the housing positioned downstream of the heat exchanger and upstream of the air filter, the additional openings including removable flaps for opening and closing the openings to control the temperature of the air flowing through the housing.

Ruffolo, R.F.

1986-06-24

340

Azoxy rearrangement reactions  

NASA Astrophysics Data System (ADS)

The mechanisms of several types of azoxy compound (XN(O)NY) rearrangement reactions have been studied using density functional theory (DFT) with the B3LYP exchange-correlation potential. The substituents X and Y are taken from the set H, CH , F, C H , Cl and CN. The 6-311 + G(d,p) basis set was used to optimize up to ten equilibrium and transition state structures for a given pair of X and Y substituents; except for azoxybenzene where a 6- 311(+)G(d) basis set was used. All geometric structures were characterized by a frequency calculation. The reaction path for converting XN (O)N Y to XN N (O)Y via a concerted intramolecular shift of the oxygen atom from N to N involves three equilibrium and two saddle-point structures. The relatively high (about 70-80 kcalmol1) calculated barrier height to reaction and its independence of the nature of the X and Y substituents is attributed to characteristic orbital, atomic charge and structural factors along the reaction path. Cis trans isomerization across N-- N in the NH(O)NH azoxy compound and across N-N in the ring XNONY oxadiaziridine intermediate is found to have a barrier height of at least - 1 about 30 kcalmol . Single-point CCSD(T)/DFT energy differences are found to be somewhat smaller than the DFT calculated values. 3 6 5

Basch, Harold; Hoz, Tova

341

Named Reactions  

NSDL National Science Digital Library

This Web site lists 95 of the most important named reactions in organic chemistry. Each is linked to a Web page that gives the primary reference and equations for one or more recent literature examples that illustrate the use of the reaction.

342

Empirical tests for ecological exchangeability  

Microsoft Academic Search

The concept of ecological exchangeability, together with genetic exchangeability, is central to both the Cohesion Species Concept as well as to some definitions of Evolutionarily Significant Units. While there are well- established criteria for measuring genetic exchangeability, the concept of ecological exchangeability has generated considerable confusion. We describe a procedure that uses the complementary strengths, while recognising the limitations, of

Russell B. Rader; Mark C. Belk; Dennis K. Shiozawa; Keith A. Crandall

2005-01-01

343

Essays on exchange rate economics  

Microsoft Academic Search

Exchange rate economics has achieved substantial development in the past few decades. Despite extensive research, a large number of unresolved problems remain in the exchange rate debate. This dissertation studied three puzzling issues aiming to improve our understanding of exchange rate behavior. Chapter Two used advanced econometric techniques to model and forecast exchange rate dynamics. Chapter Three and Chapter Four

Yan Shu

2008-01-01

344

Essays on Exchange Rate Economics  

Microsoft Academic Search

Exchange rate economics has achieved substantial development in the past few decades. Despite extensive research, a large number of unresolved problems remain in the exchange rate debate. This dissertation studied three puzzling issues aiming to improve our understanding of exchange rate behavior. Chapter Two used advanced econometric techniques to model and forecast exchange rate dynamics. Chapter Three and Chapter Four

Yan Shu

2008-01-01

345

Understand spiral heat exchangers  

SciTech Connect

Shell-and-tube heat exchangers are standard in most chemical process industries (CPI) applications. However, they do have limitations related to thermal efficiency, mechanical design, and maintenance requirements that will not allow the standard straight-tube fixed-tubesheet shell-and-tube (S and T) heat exchanger to work properly in certain applications. It is in these problem areas that spiral heat exchangers (SHEs) have been used successfully worldwide for over 60 years. The SHE can be a viable alternative to the complex and often expensive shell-and-tube heat exchanger. The SHEs' unique spiral countercurrent monochannel design gives them exceptionally high heat-transfer rates and low fouling tendencies. The mechanical configuration of the SHE also allows full access to all heat-transfer surfaces for simplified inspection, maintenance, and cleaning. This article describes how SHEs operate, discusses their advantages in terms of thermal efficiency, fouling, mechanical design, and maintenance characteristics, and provides guidance on choosing between spiral and tubular exchangers.

Bailey, K.M.

1994-05-01

346

Heat exchanger restart evaluation  

SciTech Connect

On December 24, 1991, the K-Reactor was in the shutdown mode with full AC process water flow and full cooling water flow. Safety rod testing was being performed as part of the power ascension testing program. The results of cooling water samples indicated tritium concentrations higher than allowable. Further sampling and testing confirmed a Process Water System to Cooling Water System leak in heat exchanger 4A (HX 4A). The heat exchanger was isolated and the plant shutdown. Heat exchanger 4A was removed from the plant and moved to C-Area prior to performing examinations and diagnostic testing. This included locating and identifying the leaking tube or tubes, eddy current examination of the leaking tube and a number of adjacent tubes, visually inspecting the leaking tube from both the inside as well as the area surrounding the identified tube. The leaking tube was removed and examined metallurgically to determine the failure mechanism. In addition ten other tubes that either exhibited eddy current indications or would represent a baseline condition were removed from heat exchanger 4A for metallurgical examination. Additional analysis and review of heat exchanger leakage history was performed to determine if there are any patterns which can be used for predictive purposes. Compensatory actions have been taken to improve the sensitivity and response time to any future events of this type. The results of these actions are summary herein.

Morrison, J.M.; Hirst, C.W.; Lentz, T.F.

1992-03-18

347

Syringe exchange in Germany.  

PubMed

Syringe exchange in Germany is clearly linked to a recent shift of local responses to drug-use(r) associated problem. Since the end of the 1980s, metropolitan communities in Northern and Central Germany-concerned by the emergence of "Open Drug Scenes," increasing HIV and mortality rates among drug users, and drug-use-related property crime-began to favor measures of survival-oriented drug-user help. While the Federal Government still favors repression and law enforcement efforts, they nevertheless made syringe exchange explicitly legal in 1992-some 5 years after the creation of local Syringe Exchange Programs. In general, the new approach of local authorities includes a variety of services, such as housing facilities, crisis intervention centers, primary medical care, maintenance with substitute drugs, and syringe exchange programs. The creation of pilot heroin maintenance programs is planned for Frankfurt and Hamburg. While the established programs are successfully functioning in large cities such as Hamburg, Bremen, and Frankfurt, the demand for sterile needles and syringes remains unmet in smaller cities and in the conservative governed Bundeslander (states), where pharmacies remain the primary and often single legal supply source for syringes. Another major problem continues to be the drug-use situation in prisons. Although injection drug use is common in prisons, injection equipment is not legally available for the 10,000 injecting drug users imprisoned at any given time. Two of Germany's 220 prisons started an experimental syringe exchange in 1996. PMID:9596378

Weber, U; Schneider, W

1998-04-01

348

Equilibrious Strand Exchange Promoted by DNA Conformational Switching  

NASA Astrophysics Data System (ADS)

Most of DNA strand exchange reactions in vitro are based on toehold strategy which is generally nonequilibrium, and intracellular strand exchange mediated by proteins shows little sequence specificity. Herein, a new strand exchange promoted by equilibrious DNA conformational switching is verified. Duplexes containing c-myc sequence which is potentially converted into G-quadruplex are designed in this strategy. The dynamic equilibrium between duplex and G4-DNA is response to the specific exchange of homologous single-stranded DNA (ssDNA). The SER is enzyme free and sequence specific. No ATP is needed and the displaced ssDNAs are identical to the homologous ssDNAs. The SER products and exchange kenetics are analyzed by PAGE and the RecA mediated SER is performed as the contrast. This SER is a new feature of G4-DNAs and a novel strategy to utilize the dynamic equilibrium of DNA conformations.

Wu, Zhiguo; Xie, Xiao; Li, Puzhen; Zhao, Jiayi; Huang, Lili; Zhou, Xiang

2013-01-01

349

Ion exchanged potassium titanoniobate as photocatalyst under visible light  

Microsoft Academic Search

Potassium titanoniobate (KTiNbO5) was synthesized by solid-state reaction. The potassium ion of KTiNbO5 was exchanged for hydrogen ion in hydrochloric acid, and the sample was heat-treated. The shrinkage of the distance between\\u000a titanoniobate layers that arise from ion-exchange was observed by using X-ray diffraction. The absorption edges of the UV–Vis\\u000a spectra for the ion exchanged samples which were treated at

Koichi Inoue; Satoshi Suzuki; Masayuki Nagai

2010-01-01

350

Heat exchanger for fuel cell power plant reformer  

DOEpatents

A heat exchanger uses the heat from processed fuel gas from a reformer for a fuel cell to superheat steam, to preheat raw fuel prior to entering the reformer and to heat a water-steam coolant mixture from the fuel cells. The processed fuel gas temperature is thus lowered to a level useful in the fuel cell reaction. The four temperature adjustments are accomplished in a single heat exchanger with only three heat transfer cores. The heat exchanger is preheated by circulating coolant and purge steam from the power section during startup of the latter.

Misage, Robert (Manchester, CT); Scheffler, Glenn W. (Tolland, CT); Setzer, Herbert J. (Ellington, CT); Margiott, Paul R. (Manchester, CT); Parenti, Jr., Edmund K. (Manchester, CT)

1988-01-01

351

Synthesis and Magnetic Properties of Partially Exchanged Nonstoichiometric Hexaferrites  

Microsoft Academic Search

Nonstoichiometric hexaferrite particles containing both Ba and K, with typical composition K0.8Ba0.6Fe10.5Co0.25O17, have been prepared by partial ion exchange in an aqueous solution of Ba(NO3)2at 40–80°C, from ?? ferrite precursor phase K2Fe10.5Co0.25O17. The ?? structure is maintained after the exchange reaction and the hexaferrite structure is formed by heating atT> 600°C. Exchange of K+by H3O+also takes place in the aqueous

G. Litsardakis; A. C. Stergiou; J. Georgiou; D. Samaras

1996-01-01

352

Method for conducting exothermic reactions  

DOEpatents

A liquid phase process for oligomerization of C[sub 4] and C[sub 5] isoolefins or the etherification thereof with C[sub 1] to C[sub 6] alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120 to 300 F. wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

Smith, L. Jr.; Hearn, D.; Jones, E.M. Jr.

1993-01-05

353

Method for conducting exothermic reactions  

DOEpatents

A liquid phase process for oligomerization of C.sub.4 and C.sub.5 isoolefins or the etherification thereof with C.sub.1 to C.sub.6 alcohols wherein the reactants are contacted in a reactor with a fixed bed acid cation exchange resin catalyst at an LHSV of 5 to 20, pressure of 0 to 400 psig and temperature of 120.degree. to 300.degree. F. wherein the improvement is the operation of the reactor at a pressure to maintain the reaction mixture at its boiling point whereby at least a portion but less than all of the reaction mixture is vaporized. By operating at the boiling point and allowing a portion of the reaction mixture to vaporize, the exothermic heat of reaction is dissipated by the formation of more boil up and the temperature in the reactor is controlled.

Smith, Jr., Lawrence (Bellaire, TX); Hearn, Dennis (Houston, TX); Jones, Jr., Edward M. (Friendswood, TX)

1993-01-01

354

Ion exchange phenomena  

SciTech Connect

Ion exchange phenomena involve the population of readily exchangeable ions, the subset of adsorbed solutes that balance the intrinsic surface charge and can be readily replaced by major background electrolyte ions (Sposito, 2008). These phenomena have occupied a central place in soil chemistry research since Way (1850) first showed that potassium uptake by soils resulted in the release of an equal quantity of moles of charge of calcium and magnesium. Ion exchange phenomena are now routinely modeled in studies of soil formation (White et al., 2005), soil reclamation (Kopittke et al., 2006), soil fertilitization (Agbenin and Yakubu, 2006), colloidal dispersion/flocculation (Charlet and Tournassat, 2005), the mechanics of argillaceous media (Gajo and Loret, 2007), aquitard pore water chemistry (Tournassat et al., 2008), and groundwater (Timms and Hendry, 2007; McNab et al., 2009) and contaminant hydrology (Chatterjee et al., 2008; van Oploo et al., 2008; Serrano et al., 2009).

Bourg, I.C.; Sposito, G.

2011-05-01

355

IEL Policy Exchange  

NSDL National Science Digital Library

The Institute for Educational Leadership (IEL) Policy Exchange is a "hands-on" think tank that attempts to make "the connection between ideas and leaders in all domestic policy arenas" at all levels of government in the areas of education, vocational training, health, social services, welfare, juvenile justice, and housing. The IEL Policy exchange unites leaders with ideas through policy research, published reports, and hands-on workshops for policy makers. Two of the 1998 special reports issued by the IEL Policy Exchange are "Mixed Results: Lessons Learned from a Case Study of Interagency Collaboration" by Margaret C. Dunkle and Stephanie A. Surles, and "The Measure of Success: What are the Policy Implications of the New National Indicators of Child Well-Being?" by Jeanne Jehl (both available in .pdf and WordPerfect formats).

356

Determination of the cation-exchange capacity of muscovite mica  

SciTech Connect

High cation-exchange capacity (CEC) muscovite mica with a homoionic surface was prepared by replacing the Li{sup +} surface ions of partially delaminated Li-mica with K{sup +}. The CEC of this K-mica was determined by exchanging its surface cations with Cs{sup +}, NH{sub 4}{sup +}, methylene blue (MB{sup +}), and copper triethylenetetramine [Cu(trien){sup 2+}]. The kinetics of these exchange reactions were studied and showed large differences depending on their relative affinities to mica. The NH{sub 4}{sup +}/K{sup +} exchange was slow, while the Cs{sup +} and Cu(trien){sup 2+}/K{sup +} exchange was fast. The MB{sup +}/K{sup +} exchange was quite slow and was not completed even after 99 h. Insufficient reaction time is one of the main reasons for the contradictory results reported in the literature for the CEC of aluminosilicates obtained by different methods. The CEC of mica can be photometrically measured by exchanging its surface cations with Cu(trien){sup 2+}.

Osman, M.A.; Suter, U.W.

2000-04-01

357

Rate of oxygen isotope exchange between selenate and water.  

PubMed

The rate of oxygen isotope exchange between selenate and water was investigated at conditions of 10 to 80 °C and pH -0.6 to 4.4. Oxygen isotope exchange proceeds as a first-order reaction, and the exchange rate is strongly affected by reaction temperature and pH, with increased rates of isotope exchange at higher temperature and lower pH. Selenate speciation (HSeO(4)(-) vs SeO(4)(2-)) also has a significant effect on the rate of isotope exchange. The half-life for isotope exchange at example natural conditions (25 °C and pH 7) is estimated to be significantly in excess of 10(6) years. The very slow rate of oxygen isotope exchange between selenate and water under most environmental conditions demonstrates that selenate-?(18)O signatures produced by biogeochemical processes will be preserved and hence that it will be possible to use the value of selenate-?(18)O to investigate the biogeochemical behavior of selenate, in an analogous fashion to the use of sulfate-?(18)O to study the biogeochemical behavior of sulfate. PMID:22428618

Kaneko, Masanori; Poulson, Simon R

2012-03-29

358

Nuclear excitations and reaction mechanisms  

NASA Astrophysics Data System (ADS)

Research concerning nuclear excitations and reaction mechanisms is described. Among the various subjects discussed are: photon scattering, consistency condition between seagull quadrapole terms and the absorption sum rule, Raman scattering to negative-parity states, non-local terms due to exchange and retardation effects in charge-transfer equations, consistency and meaning of various approximate channel coupling array equations, derivation of equations used in empirical nuclear reaction analyses, multi-cluster n-particle scattering theory, converged molecular bound state calculations, and WKB-type approximation in angular momenta for central potentials.

Fallieros, S.; Levin, S. F.; Li, C. T.

1980-10-01

359

Direct Reactions of Borromean Nuclei  

SciTech Connect

There are so-called Borromean nuclei on the drip-line in the nuclear chart, where any two-body subsystem has no bound state. The exotic structure and responses of Borromean nuclei have been studied by measurements of three-body (final-state) channels produced via direct reactions. Measurement of the three-body decay of the isospin partner of light drip-line nuclei populated by the charge exchange reaction is discussed as a means for studying the neutron halo structure. Experimental efforts to study nuclei beyond the drip-line, where many-body resonances may appear, are also presented.

Shimoura, S. [Center for Nuclear Study (CNS), University of Tokyo, Wako branch at RIKEN, Wako, Saitama 351-0198 (Japan)

2008-04-29

360

Drug Reactions  

MedlinePLUS

Most of the time, medicines make our lives better. They reduce aches and pains, fight infections, and control problems such as high blood pressure or diabetes. But medicines can also cause unwanted reactions. One problem is ...

361

Heat exchanger support  

SciTech Connect

This patent describes a support structure for in-bed heat exchanger tubes of a fluidzed bed boiler having wall means defining a fluidized bed region and a freeboard region above the fluidized bed region, the wall means including tubular means disposed near a transition zone between the fluidized bed and freeboard regions, the structure comprising support tubes having opposite ends extending respectively through the wall means and over the tubular means for support thereby, each support tube having at least one upright portion disposed in the fluidized bed region, and at least one heat exchanger tube being supportingly secured to the upright portion.

McDonald, D.K.; Weitzel, P.S.

1988-09-13

362

Model optimizes exchanger cleaning  

SciTech Connect

There are many simple models about fouling in the literature that calculate the optimum period for heat exchanger operation. Because of the assumptions and simplifications they contain, these models always yield, and often incorrectly, an optimum point. However, a more rigorous analysis indicates that the trend of fouling costs (which we try to minimize) can be increasing or decreasing, and certain conditions must be achieved for the existence of that optimum. This analysis applies to shell-and-tube heat exchangers in a crude oil preheat train, but it can be made suitable for any case with adequate changes.

Casado, E. (Centromin Peru' S.A., Lima (PE))

1990-08-01

363

Enzyme Reactions  

NSDL National Science Digital Library

The enzyme reaction rate activity allows students to simulate the effects of variables such as temperature and pH on the reaction rate of the enzyme catalase. This computer simulation is best used after the students have done a wet lab experiment. The value of the simulation is that it requires the students to interpret and analyze the graphical representation of data and it enables the running of mutiple experiments in a short amount of time.

School, Maryland V.

364

Gas exchange measurements in natural systems  

SciTech Connect

Direct knowledge of the rates of gas exchange in lakes and the ocean is based almost entirely on measurements of the isotopes /sup 14/C, /sup 222/Rn and /sup 3/He. The distribution of natural radiocarbon has yielded the average rate of CO/sub 2/ exchange for the ocean and for several closed basin lakes. That of bomb produced radiocarbon has been used in the same systems. The /sup 222/Rn to /sup 226/Ra ratio in open ocean surface water has been used to give local short term gas exchange rates. The radon method generally cannot be used in lakes, rivers, estuaries or shelf areas because of the input of radon from sediments. A few attempts have been made to use the excess /sup 3/He produced by decay of bomb produced tritium in lakes to give gas transfer rates. The uncertainty in the molecular diffusivity of helium and in the diffusivity dependence of the rate of gas transfer holds back the application of this method. A few attempts have been made to enrich the surface waters of small lakes with /sup 226/Ra and /sup 3/H in order to allow the use of the /sup 222/Rn and /sup 3/He methods. While these studies give broadly concordant results, many questions remain unanswered. The wind velocity dependence of gas exchange rate has yet to be established in field studies. The dependence of gas exchange rate on molecular diffusivity also remains in limbo. Finally, the degree of enhancement of CO/sub 2/ exchange through chemical reactions has been only partially explored. 49 references, 2 figures, 2 tables.

Broecker, W.S.; Peng, T.H.

1983-01-01

365

Energy absorber for sodium-heated heat exchanger  

DOEpatents

A heat exchanger is described in which water-carrying tubes are heated by liquid sodium and in which the results of accidental contact between the water and the sodium caused by failure of one or more of the water tubes is minimized. An energy absorbing chamber contains a compressible gas and is connected to the body of flowing sodium by a channel so that, in the event of a sodium-water reaction, products of the reaction will partially fill the energy absorbing chamber to attenuate the rise in pressure within the heat exchanger.

Essebaggers, J.

1975-12-01

366

Elastic electron-deuteron scattering beyond one-photon exchange  

SciTech Connect

We discuss elastic electron-deuteron (ed) scattering beyond the Born approximation. The reaction amplitude contains six generalized form factors, but only three linearly independent combinations of them (generalized charge, quadrupole, and magnetic form factors) contribute to the reaction cross section in second-order perturbation theory. We examine the two-photon exchange and find that it includes two types of diagrams, where two virtual photons are interacting with the same nucleon and where the photons are interacting with different nucleons. It is shown that the two-photon-exchange amplitude is strongly connected with the deuteron wave function at short distances.

Kobushkin, A. P.; Krivenko-Emetov, Ya. D.; Dubnicka, S. [Bogolyubov Institute for Theoretical Physics, Metrologicheskaya Street 14B, 03680 Kiev (Ukraine); Institute for Nuclear Research, Prospekt Nauki 47, 03680 Kiev (Ukraine); Institute of Physics, Slovak Academy of Sciences, Bratislava (Slovakia)

2010-05-15

367

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

368

Anion exchange in Zn-Al layered double hydroxides: In situ X-ray diffraction study  

NASA Astrophysics Data System (ADS)

Anion exchange capacity is a key factor for the application of Zn-Al layered double hydroxides (LDHs) as nano-containers in active corrosion protection. In this work, the nitrate-pyrovanadate anion exchange/re-exchange processes in these LDHs were investigated in situ. We demonstrate that the exchange reactions lead to a decrease of the average crystallite size of LDHs as a result of mechanical fragmentation of the crystallites rather than dissolution/recrystallization. The fragmentation occurs due to fast anion exchange in the initial stage, and can be controlled by changing the ratio of the available substituent anions to the replacement anions and application of a mechanical activation.

Salak, Andrei N.; Tedim, João; Kuznetsova, Alena I.; Zheludkevich, Mikhail L.; Ferreira, Mário G. S.

2010-07-01

369

Currency Exchange Rates.  

ERIC Educational Resources Information Center

|This curriculum unit of the Muncie (Indiana) Southside High School is to simulate the dynamics of foreign currency exchange rates from the perspectives of: (1) a major U.S. corporation, ABB Power T & D Company, Inc., of Muncie, Indiana, a manufacturer of large power transformers for the domestic and foreign markets; and (2) individual consumers…

Siler, Carl R.

370

High Flux Heat Exchanger.  

National Technical Information Service (NTIS)

This interim report documents the results of the first two phases of a four-phase program to develop a high flux heat exchanger for cooling future high performance aircraft electronics. Phase I defines future needs for high flux heat removal in advanced m...

E. M. Flynn M. J. Mackowski

1993-01-01

371

Dimensions of Consumer Exchange  

Microsoft Academic Search

A systematic sequence of psychometric procedures was used to develop a scale of consumer exchange. Initially, a diversity of psychological attraction concepts from widely published sources was selected for scale development. Scale content reflected concepts of passion, intimacy, affection, friendship\\/attraction, affiliation, freedom\\/creativity, cooperation, satisfaction, compliance, and dependence. The reduced scale appeared acceptable in both interpersonal attraction and apparently nonpersonal consumer

Diane M. McConocha; Jack A. Lesser

1990-01-01

372

Organizing Equity Exchanges  

NASA Astrophysics Data System (ADS)

In the last years equity exchanges have diversified their operations into business areas such as derivatives trading, post-trading services, and software sales. Securities trading and post-trading are subject to economies of scale and scope. The integration of these functions into one institution ensures efficiency by economizing on transactions costs.

Schaper, Torsten

373

Conquer heat exchanger fouling  

SciTech Connect

Fouling plays a dominant role in heat exchanger performance. It is extremely important to choose the most appropriate type of heat exchanger for a particular application and adopt proper values for fouling resistance. A design practice for shell-and-tube heat exchangers that will limit fouling to a minimum and thus ensure trouble-free operation is essential. Due to the availability of specialized software, the thermal design of heat exchangers has become precise and scientific. The results occasionally have to be tempered with practical experience and engineering judgment, but generally these computer programs are very reliable and authentic. However, the above is true only for determining heat-transfer coefficients and pressure drop. One important area that cannot possibly be addressed by design software is fouling. While a proper selection of fouling resistance is extremely difficult due to the numerous factors involved, a sound design practice will minimize any errors. However, it is important to first understand the phenomenon of fouling. The paper describes what fouling is, types of fouling, factors affecting fouling, providing a fouling allowance, selecting a fouling resistance, and overcoming fouling through better design.

Mukherjee, R. [Engineers India Ltd., New Delhi (India)

1996-01-01

374

Chicago Mercantile Exchange  

NSDL National Science Digital Library

The Chicago Mercantile Exchange, the World's Largest Marketplace, trading approximately $200 trillion annually in underlying value of financial and agricultural futures and options, now has a Web page. Accessible from the CME Home Page are background and product information, volume and membership-price information and charts, and the CME Model for Federal Financial Regulation, a proposal for streamlining government oversight of financial institutions.

1994-01-01

375

The Creative Learning Exchange  

NSDL National Science Digital Library

This site is the homepage of The Creative Learning Exchange. CLE encourages a view of education for primary and secondary schools based on discovery as the essence of the learning process and advocates systems education implemented through learner-centered learning. Links to a downloadable introductory packet and models and lesson plans are also included.

Exchange, The C.

376

Ion Exchange Membrane Processes  

SciTech Connect

Techniques were developed, and promising preliminary tests were completed in an exploratory study of the applicability of ion exchange membrane processes to such chemical operations as the separation of plutonium from uranium, the separation of americium from curium, the isolation of individual rare earths, the removal of strontium from process waste streams. This report discusses results of those tests.

Wallace, R.M.

2002-10-30

377

Exchange-Rate Determination  

Microsoft Academic Search

This volume is intended to provide a survey of thought about exchange-rate determination as it emerged in the decade of the 1970s. This survey differs from many, however, in that the field itself is in a state of rapid change. Understanding the changes and the reasons for them is therefore essential if the reader is to have a basis for

Anne O. Krueger

378

Nature's Heat Exchangers.  

ERIC Educational Resources Information Center

Discusses the heat-transfer systems of different animals. Systems include heat conduction into the ground, heat transferred by convection, heat exchange in lizards, fish and polar animals, the carotid rete system, electromagnetic radiation from animals and people, and plant and animal fiber optics. (MDH)

Barnes, George

1991-01-01

379

Nature's Heat Exchangers.  

ERIC Educational Resources Information Center

|Discusses the heat-transfer systems of different animals. Systems include heat conduction into the ground, heat transferred by convection, heat exchange in lizards, fish and polar animals, the carotid rete system, electromagnetic radiation from animals and people, and plant and animal fiber optics. (MDH)|

Barnes, George

1991-01-01

380

Interpersonal Exchange in Isolation.  

National Technical Information Service (NTIS)

The study explored interpersonal exchange in isolated and non-isolated groups. Nine dyads formed at different levels on need achievement, need dominance, need affiliation and dogmatism worked out lived in a small room for ten days, with no outside contact...

I. Altman W. W. Haythorn

1965-01-01

381

Exchange bias theory  

Microsoft Academic Search

Research on the exchange bias (EB) phenomenon has witnessed a flurry of activity during recent years, which stems from its use in magnetic sensors and as stabilizers in magnetic reading heads. EB was discovered in 1956 but it attracted only limited attention until these applications, closely related to giant magnetoresistance, were developed during the last decade. In this review, I

Miguel Kiwi

2001-01-01

382

Process for operating equilibrium controlled reactions  

DOEpatents

A cyclic process for operating an equilibrium controlled reaction in a plurality of reactors containing an admixture of an adsorbent and a reaction catalyst suitable for performing the desired reaction which is operated in a predetermined timed sequence wherein the heating and cooling requirements in a moving reaction mass transfer zone within each reactor are provided by indirect heat exchange with a fluid capable of phase change at temperatures maintained in each reactor during sorpreaction, depressurization, purging and pressurization steps during each process cycle.

Nataraj, Shankar (Allentown, PA); Carvill, Brian Thomas (Orefield, PA); Hufton, Jeffrey Raymond (Fogelsville, PA); Mayorga, Steven Gerard (Allentown, PA); Gaffney, Thomas Richard (Allentown, PA); Brzozowski, Jeffrey Richard (Bethlehem, PA)

2001-01-01

383

Fluid dynamic energy exchanger  

SciTech Connect

A gas-to-gas energy exchanger utilizing a commutator repetitively diverts a jet of a first pressurized gas between an energy exchange conduit and an exhaust outlet. Upon entering the energy exchange conduit, the first gas creates a pressure wave which traverses the conduit at sonic velocity and, in so doing, compresses a second gas in the conduit. The now pressurized second gas opens a first check valve and egresses through a primary outlet. When the first gas is diverted to the exhaust passage, a rarefaction wave is created in the energy exchange conduit and traverses the conduit at sonic velocity plus the velocity of the first gas still in the conduit. The energy exchange conduit length may be selected such that the rarefaction wave reaches the downstream end of the conduit before the previously entered slug of first gas to thereby prevent mixing of the first and second gases in the primary outlet; alternatively, the conduit length may be selected to permit any desired degree of such mixing. The rarefaction wave closes the first check valve and opens a second check valve which permits the second gas to enter the downstream end of the conduit. The rarefaction wave also reverses the flow direction of first fluid passed by the wave so that the first fluid is caused to flow back upstream in the conduit to be aspirated into the exhaust passage by the jet of first gas. The commutator is preferably a fluidic oscillator, but may be a mechanically driven device; in either case the frequency is selected to provide desired operation consistent with the conduit length. Two such commutators may be employed, operating in 180/sup 0/ phase relation, so that a constant flow of the second gas may be provided from half cycle to half cycle.

Bauer, P.

1982-10-19

384

Reciprocal Exchange: A Self-Sustaining System  

Microsoft Academic Search

Reciprocal exchange, or gift exchange, remains a widespread means of obtaining goods and services. This paper examines the persistence of reciprocal exchange by formalizing the interaction between self-enforcing exchange agreements and monetary market exchange. When more people engage in reciprocal exchange, market search costs increase, reciprocity is easier to enforce and yields higher utility. Thus, personalized exchange can persist even

Rachel E Kranton

1996-01-01

385

Polymethylmethacrylate open tubular ion exchange columns: nondestructive measurement of very small ion exchange capacities.  

PubMed

We describe an approach to prepare an open tubular ion exchange (OTIE) column by coating a monolayer of anion exchange nanoparticle to a 16-20 ?m bore polymethylmethacrylate (PMMA) capillary. The latex nanoparticle was electrostatically attached to carboxylate groups on the inner wall of capillary, pretreated with strong base for hydrolyzing the ester. Several approaches to nondestructively measure ion exchange capacities (IEC) of the columns were examined: (a) adsorption-desorption of an intensely fluorescent ion, e.g. fluorescein, and off-line fluorometry, (b) loading a weakly retained ion (e.g., IO3(-)), frontal displacement by a strongly bound ion (e.g., Cl(-)), and online optical or conductometric boundary detection, and (c) similar to the above except displacement being accompanied by reaction (e.g., acid-base titration). To our knowledge, this is the first time on-column titration has been used to measure capacities. By using different pH displacer solutions, we demonstrate for the first time the possibility of pKa-differentiated ion exchange capacity measurements. The cation exchange capacity of bare PMMA capillaries was on the order of 1 pequiv/mm(2) with little dependence on time and temperature of hydrolysis conditions. After AS18 latex coating, the strong base anion exchange capacity was on the order of 10 pequiv/mm(2), very close to what would be estimated on the basis of monolayer coverage of the surface by individual latex particles. The latex used contained a significant, additional amount of weak base character, about the same as the strong base ion exchange capacity. PMID:23875750

Zhang, Min; Yang, Bingcheng; Dasgupta, Purnendu K

2013-08-07

386

Phosphonic acid based exchange resins  

DOEpatents

An ion exchange resin for extracting metal ions from a liquid waste stream. An ion exchange resin is prepared by copolymerizing a vinylidene diphosphonic acid with styrene, acrylonitrile and divinylbenzene.

Horwitz, E. Philip (Naperville, IL); Alexandratos, Spiro D. (Knoxville, TN); Gatrone, Ralph C. (Naperville, IL); Chiarizia, Ronato (Oak Park, IL)

1995-01-01

387

Two-stage heat exchanger  

SciTech Connect

Improved furnaces are described in which secondary and tertiary heat exchanges are incorporated into new and existing hot-air furnace systems for controlled cooling of hot combustion products by co-current and countercurrent heat exchanges. Hot combustion products are cooled to a temperature at which latent heat of water vapor contained in combustion gases are substantially recovered. In one embodiment of our invention, a secondary heat exchanger comprises inter alia a closed hollow annular drum concentric with and spaced from a cylindrical combustion chamber, said annular drum having an upper annulus preferably filled with randomly packed refractory material. A second embodiment of our invention comprises a closed double annuli drum heat exchanger concentric with and spaced from a cylindrical combustion chamber. Finned tube or thermosiphon heat exchangers can be arranged sequentially with the primary heat exchanger combustion chamber to function as a secondary heat exchanger or as a tertiary heat exchanger.

Overall, J.C.; Schaus, O.O.

1981-06-30

388

Oxygen-exchange Pathways in Aluminum Polyoxocations  

SciTech Connect

Using molecular dynamics simulations and electronic structure methods, we postulate a mechanism to explain the complicated reactivity trends that are observed for oxygen isotope exchange reactions between sites in aluminum polyoxocations of the E-Keggin type and bulk solution. Experimentally, the molecules have four nonequivalent oxygens that differ considerably in reactivity both within a molecule, and between molecules in the series: Al13, GaAl12, and GeAl12 [MO4Al12(OH)24(H2O)12 n*(aq); with M=Al(III) for Al13, n=7; M=Ga(III) for GaAl12, n=7; M=Ge(IV) for GeAl12, n=8]. We find that a partly dissociated, metastable intermediate molecule of expanded volume is necessary for exchange of both sets of u2-OH and that the steady-state concentration of this intermediate reflects the bond strengths between the central metal and the u4-O. Thus the central metal exerts extraordinary control over reactions at hydroxyl bridges, although these are three bonds away. This mechanism not only explains the reactivity trends for oxygen isotope exchange in u2-OH and u-OH2 sites in the E-Keggin aluminum molecules, but also explains the observation that the reactivities of minerals tend to reflect the presence of highly coordinated oxygens, such as the u4-O in boehmite, a-, and y-Al2O3 and their Fe(III) analogs. The partial dissociation of these highly coordinated oxygens, coupled with simultaneous activation and displacement of neighboring metal centers, may be a fundamental process by which metals atoms undergo ligand exchanges at mineral surfaces.

Rustad, James R.; Loring, J. S.; Casey, William H.

2004-07-15

389

Reaction Time  

NSDL National Science Digital Library

This lab is not an inquiry activity. There are some students whose reaction times will not allow them to catch a 12 inch ruler. They may use a dowel, stick, strip of cardboard, etc. Although the students are led to believe that the point of the lab is to

Horton, Michael

2009-05-30

390

Exchange Rates and Financial Fragility  

Microsoft Academic Search

In this paper we analyze three views of the relationship between the exchange rate and financial fragility: (1) the moral hazard hypothesis, according to which pegged exchange rates offer implicit insurance against exchange risk and thereby encourage reckless borrowing and lending; (2) the original sin hypothesis, which emphasizes an incompleteness in financial markets which prevents the domestic currency from being

Barry Eichengreen; Ricardo Hausmann

1999-01-01

391

SNOWPACK ENERGY EXCHANGE: BASIC THEORY  

Technology Transfer Automated Retrieval System (TEKTRAN)

The exchange of energy between the snowpack and its environment ultimately determines the rate of snowpack water losses due to melting and evaporation/sublimation. Energy exchange primarily occurs at the snowpack surface through exchange of shortwave and longwave radiation and turbulent or convect...

392

The Economics of Exchange Rates  

Microsoft Academic Search

Reviews the literature on exchange rate economics over the last two decades, with particular reference to recent developments. Topics surveyed include the evidence on foreign exchange market efficiency and forward discount bias, chewed interest parity and purchasing power parity, the theory and evidence relating to the determination of exchange rates (the flexible-price monetary model, the stickyprice monetary model, the equilibrium

Mark P. Taylor

1995-01-01

393

Cryptographic Commitment and Simultaneous Exchange  

Microsoft Academic Search

Remark 1 Version 1.6.9 Mutually beneficial exchange is a fundamental building block in the conceptual framework through which economists view the world. Yet simultaneous exchange is not entirely unprob- lematic. Unless the exchange is truly simultaneous, there is a risk that the person who first relinquishes control of their asset will be left with nothing if the other person does

Peter Bardsley; Andrew Clausen; Vanessa Teague

394

Plug for heat exchanger tubes  

Microsoft Academic Search

A heat exchanger tube plug is described for sealing the ends of heat exchanger tubes, comprising a cylindrical housing member sized for insertion within the end portion of one of the heat exchanger tubes, the housing member having a longitudinal blind bore comprising a smooth portion communicating with a threaded portion. An eccentric locking means is mounted on the housing

Epstein

1987-01-01

395

Serial replica exchange.  

PubMed

Parallel tempering (or the replica exchange method (REM)) is a powerful method for speeding up the sampling of conformational states of systems with rough energy landscapes, like proteins, where stable conformational states can be separated by large energy barriers. The usual implementation of the REM is performed on local computer clusters (or parallel processors) where the different replicas must be run synchronously. Here, we present serial replica exchange (SREM), a method that is equivalent to the standard REM in terms of efficiency yet runs asynchronously on a distributed network of computers. A second advantage is the method's greatly enhanced fault tolerance, which enables the study of biological systems on worldwide distributed computing environments, such as Folding@Home. For proof of concept, we apply the SREM to a single alanine dipeptide molecule in explicit water. We show that the SREM reproduces the thermodynamic and structural properties determined by the REM. PMID:17249714

Hagen, Morten; Kim, Byungchan; Liu, Pu; Friesner, Richard A; Berne, B J

2007-01-24

396

Serial Replica Exchange  

PubMed Central

Parallel tempering (or the replica exchange method (REM)) is a powerful method for speeding up the sampling of conformational states of systems with rough energy landscapes, like proteins, where stable conformational states can be separated by large energy barriers. The usual implementation of the REM is performed on local computer clusters (or parallel processors) where the different replicas must be run synchronously. Here, we present serial replica exchange (SREM), a method that is equivalent to the standard REM in terms of efficiency yet runs asynchronously on a distributed network of computers. A second advantage is the method’s greatly enhanced fault tolerance, which enables the study of biological systems on worldwide distributed computing environments, such as Folding@Home.1 For proof of concept, we apply the SREM to a single alanine dipeptide molecule in explicit water. We show that the SREM reproduces the thermodynamic and structural properties determined by the REM.

Hagen, Morten; Kim, Byungchan; Liu, Pu; Friesner, Richard A.; Berne, B. J.

2009-01-01

397

Nucleophilic substitution at the halogen atom (halogenophilic reactions)  

NASA Astrophysics Data System (ADS)

The key features of halogenophilic reactions defining their role in organic chemistry are considered. The results of studies of mechanisms involving a nucleophilic attack at the halogen atom (SN2Hal) are summarized. The main mechanistic evidence comes from the studies of halogen-metal exchange reactions. Primary attention is paid to the role of halogenophilic reaction as a competing process or a concealed mechanism in ordinary nucleophilic substitution reaction at carbon atoms. The bibliography includes 249 references.

Sazonov, Petr K.; Artamkina, Galina A.; Beletskaya, Irina P.

2012-04-01

398

Reconstitution and Pigment Exchange  

Microsoft Academic Search

Reconstitution and pigment exchange are two experimental techniques that have proven extremely useful to elucidate structure-function\\u000a relationships in chlorophyll (Chl)-protein complexes. In reconstitution experiments the Chl-binding apoproteins, usually in\\u000a their recombinant form, are folded in the presence of pigments to form pigment-protein complexes that are often virtually\\u000a indistinguishable from their native counterparts. Since both the protein and the pigment building

Harald Paulsen

399

Thermoelectric heat exchange element  

DOEpatents

A thermoelectric heat exchange module includes a first substrate including a heat receptive side and a heat donative side and a series of undulatory pleats. The module may also include a thermoelectric material layer having a ZT value of 1.0 or more disposed on at least one of the heat receptive side and the heat donative side, and an electrical contact may be in electrical communication with the thermoelectric material layer.

Callas, James J. (Peoria, IL); Taher, Mahmoud A. (Peoria, IL)

2007-08-14

400

Repeated Reasoning: Valentine Exchange  

NSDL National Science Digital Library

This professional development video clip shows students engaged in Common Core Practice Standard #8-Look for and express regularity in repeated reasoning. In this video clip fourth grade students are developing their algebraic thinking skills by problem solving the question: "How many cards would be needed if all 24 students in the class were to exchange cards with each other?" Additional resources include a video transcript, teaching tips, and a link to a professional development reflection activity based upon the video.

Boston, Wghb

2013-01-01

401

Christmas Gift Exchange Games  

Microsoft Academic Search

The Christmas gift exchange is a popular party game played around Christmas. Each participant brings a Christmas present to\\u000a the party, and a random ordering of the participants, according to which they will choose gifts, is announced. When a participant’s\\u000a turn comes, she can either open a new gift with unknown value, or steal an already opened gift with known

Arpita Ghosh; Mohammad Mahdian

402

Divalent ion exchange with alkali  

SciTech Connect

In micellar polymer and alkaline floodings in order to increase the oil production of strata, Ca-cation(2) ions and Mg-cation(2) ions in the stratum water are placed in reaction with anionic surfacants (PAV), reducing the effectiveness of using these particular methods. To determine the capability of sedimenting the divalent ions in the form of salts with pumping of alkaline margins, a chromatographic theory of simultaneous ion exchange and salt sedimentation is proposed. Data are presented for the cases of pulsation and continuous pumping of OH-anion ions into cores and the results are cited for equilibrium of a solution with a sediment and for imbalance with which the sediment is not redisolved. A conclusion is drawn about the possibility of repeat solution of the sedimented salts in practice, which was not established in laboratory conditions. In predicting, the sedimentation of silicates should be considered, as well as the phenomena of dispersion. On the whole, the theoretical model agrees well with experimental results.

Bunge, A.L.; Radke, C.J.

1983-01-01

403

ION-EXCHANGE PROCESSES AND MECHANISMS IN GLASSES  

EPA Science Inventory

Recent performance assessment calculations of a disposal system at Hanford, Washington for low activity waste glass show that a Na ion-exchange reaction can effectively increase the radionuclide release rate by over a factor of 1000 and so is a major factor that currently limits ...

404

New Advances in Catalysis by Ion-exchange Resins  

Microsoft Academic Search

Current research on the general problems, methods and theory of catalysis by ion-exchange resins as well as new advances in its application in hydrolytic, hydration, and dehydration reactions, the synthesis of esters, alkylation, polymerisation, isomerisation, and condensation are surveyed. The bibliography includes 276 references.

N. G. Polyanskii; V. K. Sapozhnikov

1977-01-01

405

REMOVAL OF PESTICIDES FROM WATER BY BIOMOLECULE-EXCHANGED CLAYS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Replacement of natural inorganic cations of clay minerals with organic cations through ion exchange reactions has been proposed as an strategy to improve the adsorptive capacity of clay minerals for organic compounds, including pesticides. The organic cations most commonly used for this purpose have...

406

Evaporation heat transfer and pressure drop of refrigerant R-134a in a plate heat exchanger  

Microsoft Academic Search

Plate heat exchangers (PHE) have been widely used in food processing, chemical reaction processes, and other industrial applications for many years. Particularly, in the last 20 years plate heat exchangers have been introduced to the refrigeration and air conditioning systems as evaporators or condensers for their high efficiency and compactness. Here, the evaporation heat transfer coefficient and pressure drop for

Y.-Y. Yan; T.-F. Lin

1999-01-01

407

Kinetics of starch hydrolysis and glucose mutarotation studied by NMR chemical exchange saturation transfer (CEST)  

Microsoft Academic Search

The –OH resonance on –C1 of the ? and ?-anomers of glucose that are normally invisible in 1H NMR spectra, was used to monitor the reaction kinetics of starch hydrolysis in aqueous solutions. The exchangeable protons on glucose were detected indirectly through their exchange with water protons, and hence the water resonance, by using selective radiofrequency (RF) saturation at the

Anthony C. Dona; Guilhem Pages; Philip W. Kuchel

2011-01-01

408

Dynamic phenomena of SCR-catalysts containing Fe-exchanged zeolites – experiments and computer simulations  

Microsoft Academic Search

The dynamic behaviour of the NO SCR-reaction on Fe-exchanged zeolites was investigated by the transient response method (TRM).\\u000a The results were used to develop a mathematical model for catalysts containing Fe-exchanged zeolites capable of describing\\u000a the dynamic phenomena observed.

S. Malmberg; M. Votsmeier; J. Gieshoff; N. Söger; L. Mußmann; A. Schuler; A. Drochner

2007-01-01

409

Compact heat exchangers  

SciTech Connect

This report aims to increase the market penetration of compact heat exchangers (CHEs) in industry by detailing current experience of their use. CHEs are characterized by having a comparatively large amount of surface area in a given volume, compared to traditional heat exchangers, in particular the shell-and-tube type. The most basic CHEs have volumes of less than 50% of that of a comparable shell-and-tube heat exchanger, for a given duty. Some new designs can, under appropriate process conditions, have only 5% of the volume of traditional equivalents. An essential component of many of these compact concepts is heat (and mass) transfer enhancement. This report also details some of the main enhancement methods which are used in the implementation of compact systems. CHEs are of interest for a number of reasons. As well as being, in general, highly efficient, allowing greater amounts of energy to be recovered between process streams, they are more versatile in terms of the number of process streams that can be handled. Some CHEs can handle only two streams. Others can handle four or more with ease. That, coupled with the availability of units to cater for most operating temperatures and pressures, makes them of interest to operators of complex thermal processing plants. Of even greater long-term importance to the process industries is the ability to use CHE manufacturing technology to integrate effective heat transfer with other unit operations, such as reactors, in one unit. This radical approach to process plant design has fostered many exciting concepts for combined unit operations, some of which are discussed in this report. Topics covered are: types of CHE; (2) the role of heat transfer enhancement; (3) benefits and perceived limitations of CHEs; (4) costs; (5) fouling; (6) specification, installation and operating procedures; (7) the new opportunities; and (8) conclusions.

NONE

1999-11-01

410

California Data Exchange Center  

NSDL National Science Digital Library

At the California Data Exchange Center website, the California Department of Water Resources provides access to an array of operational hydrologic data. Within the River Stages and Flow Data link, visitors will find river stage maps, river schematics, information on various rivers, and daily hydrologic summaries. The website provides snow information including snow sensor plots, water supply conditions, reservoir data, and reports. Individuals can view numerous satellite images and water- and weather-related forecasts. The data query tools offer an easy way to search historical and current data, data plots and graphs, and station information.

411

Exchange functional by a range-separated exchange hole  

NASA Astrophysics Data System (ADS)

An approximation to the exchange-hole density is proposed for the evaluation of the exact exchange energy in electronic structure calculations within the density-functional theory and the Kohn-Sham scheme. Based on the localized nature of density matrix, the exchange hole is divided into the short-range (SR) and long-range (LR) parts by using an adequate filter function, where the LR part is deduced by matching of moments with the exactly calculated SR counterpart, ensuring the correct asymptotic -1/r behavior of the exchange potential. With this division, the time-consuming integration is truncated at a certain interaction range, largely reducing the computation cost. The total energies, exchange energies, exchange potentials, and eigenvalues of the highest-occupied orbitals are calculated for the noble-gas atoms. The close agreement of the results with the exact values suggests the validity of the approximation.

Toyoda, Masayuki; Ozaki, Taisuke

2011-03-01

412

Molecular recognition in cation-exchanged zeolites  

NASA Astrophysics Data System (ADS)

The concepts of confinement- and molecular recognition-driven chemical reactivity of cation-exchanged zeolites is illustrated by our recent results from periodic and cluster density functional theory (DFT) calculations. The reactivity of alkali-earth- and alkaline-exchanged low-silica zeolites for selective photo-oxidation of alkenes with molecular oxygen and for N2O4 disproportionation is shown to be mainly due to the specific arrangement and the size of the cations in the zeolite cage. An attempt is made to separate the effects of basicity of the framework, the Lewis acidity of the extra-framework cations and the electrostatic field in the zeolite cage as well as its geometrical properties for the respective reactions. The importance of the favorable adsorption fashion of the reagents controlled by noncovalent interactions with the microporous matrix is shown. The role of the weak interactions with the zeolite walls and the factors, which determine the preference for a particular adsorption mode, are discussed by the example of light alkanes adsorption to Mg- and Ca-exchanged faujasites.

Pidko, Evgeny A.; van Santen, Rutger A.

413

Competing interfacial exchange and Zeeman energies in exchange biased bilayers  

Microsoft Academic Search

The exchange bias in antiferromagnet (MnF2)\\/ferromagnet (Fe) bilayers has been studied as a function of temperature, cooling field, and interfacial roughness. Positive exchange bias is observed under certain conditions, along with a nonmonotonic roughness dependence. The unusual cooling field dependence can be understood within a simple model in which the exchange bias is determined by a competition between a roughness-dependent

C. Leighton; J. Nogués; Harry Suhl; Ivan K. Schuller

1999-01-01

414

Heat exchanger-accumulator  

DOEpatents

What is disclosed is a heat exchanger-accumulator for vaporizing a refrigerant or the like, characterized by an upright pressure vessel having a top, bottom and side walls; an inlet conduit eccentrically and sealingly penetrating through the top; a tubular overflow chamber disposed within the vessel and sealingly connected with the bottom so as to define an annular outer volumetric chamber for receiving refrigerant; a heat transfer coil disposed in the outer volumetric chamber for vaporizing the liquid refrigerant that accumulates there; the heat transfer coil defining a passageway for circulating an externally supplied heat exchange fluid; transferring heat efficiently from the fluid; and freely allowing vaporized refrigerant to escape upwardly from the liquid refrigerant; and a refrigerant discharge conduit penetrating sealingly through the top and traversing substantially the length of the pressurized vessel downwardly and upwardly such that its inlet is near the top of the pressurized vessel so as to provide a means for transporting refrigerant vapor from the vessel. The refrigerant discharge conduit has metering orifices, or passageways, penetrating laterally through its walls near the bottom, communicating respectively interiorly and exteriorly of the overflow chamber for controllably carrying small amounts of liquid refrigerant and oil to the effluent stream of refrigerant gas.

Ecker, Amir L. (Dallas, TX)

1980-01-01

415

Exam Question Exchange.  

ERIC Educational Resources Information Center

|Two exam questions are presented. One suitable for advanced undergraduate or beginning graduate courses in organic chemistry, is on equivalent expressions for the description of several pericyclic reactions. The second, for general chemistry students, asks for an estimation of the rate of decay of a million-year-old Uranium-238 sample. (BB)|

Alexander, John J., Ed.

1978-01-01

416

Ion exchange technology assessment report  

SciTech Connect

In the execution of its charter, the SRS Ion Exchange Technology Assessment Team has determined that ion exchange (IX) technology has evolved to the point where it should now be considered as a viable alternative to the SRS reference ITP/LW/PH process. The ion exchange media available today offer the ability to design ion exchange processing systems tailored to the unique physical and chemical properties of SRS soluble HLW's. The technical assessment of IX technology and its applicability to the processing of SRS soluble HLW has demonstrated that IX is unquestionably a viable technology. A task team was chartered to evaluate the technology of ion exchange and its potential for replacing the present In-Tank Precipitation and proposed Late Wash processes to remove Cs, Sr, and Pu from soluble salt solutions at the Savannah River Site. This report documents the ion exchange technology assessment and conclusions of the task team.

Duhn, E.F.

1992-01-01

417

Ion exchange technology assessment report  

SciTech Connect

In the execution of its charter, the SRS Ion Exchange Technology Assessment Team has determined that ion exchange (IX) technology has evolved to the point where it should now be considered as a viable alternative to the SRS reference ITP/LW/PH process. The ion exchange media available today offer the ability to design ion exchange processing systems tailored to the unique physical and chemical properties of SRS soluble HLW`s. The technical assessment of IX technology and its applicability to the processing of SRS soluble HLW has demonstrated that IX is unquestionably a viable technology. A task team was chartered to evaluate the technology of ion exchange and its potential for replacing the present In-Tank Precipitation and proposed Late Wash processes to remove Cs, Sr, and Pu from soluble salt solutions at the Savannah River Site. This report documents the ion exchange technology assessment and conclusions of the task team.

Duhn, E.F.

1992-12-31

418

[Studies on the reactions of unsaturated chloride polyether polyol with trimethyl phosphite by FTIR].  

PubMed

The reactions of unsaturated chloride polyether polyol with trimethyl phosphite have been studied by FTIR, which was prepared by copolymerization of ethanediol, allyl glycidyl ether and epoxychloropropane. The experimental results showed that the reaction included ester-exchange reaction, ester-exchange polymerization and Arbuzov rearrangement. The process conditions such as catalyst, mass rate and reaction time were determined through the experiments. The analytic results indicated that the reaction temperature was the key controlling the process and the reaction products are suitable for reactive multifunctional flame retarders. PMID:15762469

Zhang, Tian-lin; Li, Zai-feng; Jia, Zhen; Wang, Jun-hong

2004-11-01

419

Studies on the mechanism of the peroxyoxalate chemiluminescence reaction  

Microsoft Academic Search

Further consideration has been given to the reaction pathway of a model peroxyoxalate chemiluminescence system. Again utilising doubly labelled oxalyl chloride and anhydrous hydrogen peroxide, 2D EXSY 13C nuclear magnetic resonance (NMR) spectroscopy experiments allowed for the characterisation of unknown products and key intermediate species on the dark side of the peroxyoxalate chemiluminescence reaction. Exchange spectroscopy afforded elucidation of a

Sarah A. Tonkin; Richard Bos; Gail A. Dyson; Kieran F. Lim; Richard A. Russell; Simon P. Watson; Christopher M. Hindson; Neil W. Barnett

2008-01-01

420

In vitro exchangeable erythrocytic zinc  

Microsoft Academic Search

Exchangeable erythrocytic zinc is measured by65Zn uptake in and release from erythrocytes under standarized and near, physiological conditions: 7.6 ?M zinc and 580 ?M albumin in the medium. The intracellular exchangeable erythrocytic zinc pool in healthy volunteers amounts to 5 ?mol zinc\\/L\\u000a packed cells. The half-time of the exchange is 7 h, its activation energy 84 kJ\\/mol. The effects of

JACOBUS P. VAIl WOUWE; Marcel Veldhuizen; Jeroen J. M. De Goeij; Cornelis J. A. Van den Hamer

1990-01-01

421

The Microtube Strip Heat Exchanger  

Microsoft Academic Search

The advantages of designing heat exchangers in the laminar-flow regime are discussed from a theoretical standpoint. It is argued that laminar-flow designs have the advantages of reducing thermodynamic and hydrodynamic irreversibilities, and hence increasing system efficiency. More concretely, laminar-flow heat exchangers are free from the turbulence-induced vibration common in conventional heat exchangers, and can thus offer longer life and greater

F. DAVID DOTY; GREG HOSFORD; J. B. SPITZMESSER; I JOHN DEWEY JONES

1991-01-01

422

Potential reactions among indoor pollutants  

NASA Astrophysics Data System (ADS)

Reactions among indoor pollutants can produce products that, otherwise, might not be present in an indoor environment. To be relevant in an indoor setting, a chemical reaction must occur within a time interval shorter than or comparable to the residence time for a packet of indoor air. At typical air exchange rates, the reactions that meet this criterion include those of ozone with nitric oxide, nitrogen dioxide, and selected unsaturated hydrocarbons; thermal decomposition of peroxyacyl nitrates; numerous free radical reactions; and selected heterogeneous processes. Stable products include aldehydes, ketones, carboxylic acids and various organic nitrates. These reactions also generate free radicals, starting with the nitrate radical, Criegree biradicals, and peroxyacyl radicals, and leading to the hydroxyl, alkyl, alkylperoxy, hydroperoxy, and alkoxy radicals. Such radicals can react with other indoor species yielding additional aldehydes, ketones, carboxylic acids, dinitrates and peroxyacyl nitrates. Some of the potential products are known or suspected to be irritating (e.g. methacrolein, nonanoic acid, 1,2-propanediol dinitrate, peroxybenzoyl nitrate, and radical anions of the type [Cl… NO 2] -) However, some of these same products are difficult to detect using the sampling and analysis techniques currently applied to indoor air.

Weschler, Charles J.; Shields, Helen C.

423

The separation of Zn and Cu using chelating ion exchangers and temperature variations  

SciTech Connect

This paper reports the results of a study on the ion-exchange equilibrium of Cu{sup 2+} and Zn{sup 2+} at different temperatures on chelating ion-exchange resins: Amberlite IRC-718 (iminodiacetic acid based functional groups), VPC-l (picolinic acid based) and thiourea-based resins. The separation factors and the conditional equilibrium constants of the ion-exchange reaction were determined in temperature range from 15 to 75 {degrees}C. An estimation of thermodynamic functions has also been carried out. Possibility of the separation of Cu and Zn mixture by dual temperature ion-exchange method has been demonstrated.

Zagorodni, A.A.; Muhammed, M.; Muiraviev, D.N. [Royal Inst. of Technology, Stockholm (Sweden)

1997-01-01

424

Ion Exchange Properties of New Crystalline Inorganic Ion Exchangers.  

National Technical Information Service (NTIS)

Micro crystals of both alpha-FeOOH and mono-clinic zirconia (ZrO2) were prepared. They possess weak acidic or weak basic or amphoteric ion exchange behavior. Using new pH titration techniques, detailed studies were made on these exchangers. They were show...

H. U. Rehman

1987-01-01

425

Clearing algorithms for barter exchange markets: enabling nationwide kidney exchanges  

Microsoft Academic Search

In barter-exchange markets, agents seek to swap their items with one another, in order to improve their own utilities. These swaps consist of cycles of agents, with each agent receiving the item of the next agent in the cycle. We fo- cus mainly on the upcoming national kidney-exchange mar- ket, where patients with kidney disease can obtain compat- ible donors

David J. Abraham; Avrim Blum; Tuomas Sandholm

2007-01-01

426

The Engineering Exchange  

NSDL National Science Digital Library

Under the banner of "developed by engineers for engineers," the Engineering Exchange functions as a global educational networking community for engineers. The materials on the site are divided into eight primary areas, which include Groups, Videos, Images, Events, Blogs, and Resources. Sections such as the Top Blog Posts showcase some of the most popular insights, which include updates like Manufacturing Productivity Through Design Efficiency and technical pieces on engineering software. Moving on, the Groups area is a great way for visitors to learn from other professionals with sub-sections that include Green Engineering, Water & Wastewater, and Solar Power Development. The Videos section is another gem that features over 1400 items such as Additive Manufacturing: When will it arrive? and The Safest Key-Smart Key. Additionally, visitors can search all of the videos and create their own playlists.

Matheson, Marshall

2013-01-01

427

DHE (Downhole Heat Exchangers)  

NASA Astrophysics Data System (ADS)

The use of downhole heat exchangers (DHE) for residential or commercial space and domestic water heating and other applications has several desirable features. Systems are nearly or completely passive -- that is, no or very little geothermal water or steam is produced from the well either reducing or completely eliminating surface environmental concerns and the need for disposal systems or injection wells. Initial cost of pumps and installation are eliminated or reduced along with pumping power costs and maintenance costs associated with pumping often corrosive geothermal fluids. Many residential and small commercial systems do not require circulating pumps because the density difference in the incoming and outgoing sides of the loop are sufficient to overcome circulating friction losses in the entire system. The major disadvantage of DHEs is their dependence on natural heat flow. In areas where geological conditions provide high permeability and a natural hydraulic gradient, DHEs can provide a substantial quantity of heat. A single 500-ft (152 m) well in Klamath Falls, Oregon, supplies over one megawatt thermal and output is apparently limited by the surface area of pipe that can be installed in the well bore. In contrast, DHEs used in conjunction with heat pumps may supply less than 8 KW from a well of similar depth. Here output is limited by conductive heat flow with perhaps a small contribution from convection near the well bore. The highest capacity DHE reported to date, in Turkey, supplies 6 MW thermal from an 820-ft (250 m) well. There were two main goals for this project. The first was to gather, disseminate and exchange internationally information on DHES. The second was to perform experiments that would provide insight into well bore/aquifer interaction and thereby provide more information on which to base DHE designs.

Culver, G.

1990-11-01

428

Viscous exchange flows  

NASA Astrophysics Data System (ADS)

Gravitationally driven exchange flows of viscous fluids with different densities are analysed theoretically and investigated experimentally within a horizontal channel. Following initiation from rest when there is a vertical boundary dividing the two fluids, the denser fluid slumps under the less dense along the underlying boundary, while the less dense fluid intrudes along the upper boundary. The motion is driven by the pressure gradients associated with the density differences between the two fluids, resisted by viscous stresses, and mathematically modelled by a similarity solution that depends on the ratio of the viscosities of the two fluids. When the viscosity of the less dense fluid is much smaller than the viscosity of the denser fluid, the shape of the interface between the fluids varies rapidly close to the upper boundary and depends weakly on the viscosity ratio within the interior of the flow. Matched asymptotic expansions are employed in this regime to determine the shape of the interface and the rates of its propagation along the boundaries. The similarity solutions are shown to be linearly stable and thus are expected to represent the intermediate asymptotics of the flow. Experiments confirm the similarity form of solutions and demonstrate close agreement with the theoretical predictions when the viscosities of the fluids are comparable, but exhibit some discrepancies when the viscosities differ more substantially. It is suggested that these discrepancies may be due to mixing between the fluids close to the boundaries, which is induced by the no-slip boundary condition. Exchange flows within porous domains are also investigated to determine the shape of the interface as a function of the ratio of the viscosities of the two fluids and using asymptotic analysis, this shape is determined when this ratio is much larger, or smaller, than unity.

Matson, Gary P.; Hogg, Andrew J.

2012-02-01

429

Spinnability of silica sols: The role of alkoxy group exchange  

SciTech Connect

The exchange and spinnability of several systems with the general form Si(OR){sub 4} (where R = CH{sub 3}, C{sub 2}H{sub 5}) in ethanol, propanol and butanol were investigated. We have followed the alkoxy group exchange, hydrolysis and condensation reactions, and Q distributions of these systems using {sup 29}Si and {sup 17}O NMR. Observed differences in spinnability of the various sol-gel systems are attributed to the effect of the bulkiness of the alkoxy group on its reactivity.

Prabakar, S. [New Mexico Univ., Albuquerque, NM (United States). Center for Micro-Engineered Ceramics; Assink, R.A. [Sandia National Labs., Albuquerque, NM (United States); Irwin, A.D. [Butler Univ., Indianapolis, IN (United States)

1993-12-31

430

Calculations of ion-molecule deuterium fractionation reactions involving HD.  

PubMed

Gas-phase chemical models of deuterium fractionation in dense interstellar clouds utilize a small number of exothermic reactions to achieve fractionation. Although HD is a major repository of deuterium, it appears not to exchange deuterium with many molecular ions. Useful semiquantitative reasons have been given for the unusual lack of reactivity of exothermic ion-HD deuterium exchange systems, but quantum chemical studies are needed to understand these ideas in more detail and to determine if the lack of reactivity pertains at very low temperatures not studied in the laboratory, or whether tunneling can drive the reactions. Accordingly, the potential energy surfaces of three representative ion-molecule exchange reactions involving protonated ions (H3+, CH3+, HCO+) and HD have been investigated with ab initio quantum chemical techniques. Our results generally confirm the semiquantitative picture as to which reactions are likely to occur and show that tunneling at low temperatures is unlikely to alter this picture. PMID:11538407

Maluendes, S A; McLean, A D; Herbst, E

1992-10-01

431

Amorphous solid water's isotopic exchange kinetics  

NASA Astrophysics Data System (ADS)

The mechanism for isotopic exchange by proton hopping and subsequent reorientation of H2O molecules in vapor-deposited, 0.1 mol % 2-naphthol containing amorphous solid water [M. Fischer and J. P. Devlin, J. Phys. Chem. 99, 11584 (1995)] has been reconsidered and an alternative mechanism in terms of diffusion controlled reactions is proposed. In this mechanism, H2O molecules diffuse within the H-bonded clusters, with or without a net increase in the number of H bonds, and isotopic exchange occurs by two processes: (i) Random diffusion of molecules in two clusters, one containing D2O and the other H3O+, leads to formation of an intercluster H bond, which in turn provides a path for proton hopping and converts one D2O (plus one H2)O to two coupled HODs by proton translocation and subsequent orientation. (ii) One H bond between two HOD neighbors in a cluster breaks and reforms with another H2O in the same cluster or in a different cluster, and hence a coupled HOD is converted to an uncoupled HOD. The decrease in D2O and the increase in HOD concentrations with time follow a stretched exponential kinetics, with exponent of 0.65 for the former and 0.54 for the latter process at 122 K. This is equivalent to the time-dependent rate constant in Plonka's formalism [J. Chem. Phys. 96, 1128 (1992)] and is seen as characteristic of dispersive kinetics. Because fluctuation of the environment is slower than the time scale of overall barrier crossing, the mass-controlled kinetics equations do not apply to a consecutive reaction scheme. The known variation of the isotopic species concentration with time seems to be consistent with this reaction kinetics.

Johari, G. P.

2002-08-01

432

?- and ? ?-meson production in the reaction pn? dM near threshold  

Microsoft Academic Search

The two-step model with ?, ? and ? exchanges taken into account is applied to investigate the reactions pn?d? and pn?d?? near the corresponding thresholds. The existing experimental data on the reaction pn?d? are analyzed and predictions for the cross section of the reaction pn?d?? are presented. It is found that ?- as well as ?-meson exchanges yield significant contributions

V. Yu. Grishina; L. A. Kondratyuk; M. Büscher; J. Haidenbauer; C. Hanhart; J. Speth

2000-01-01

433

Mechanisms of Ligand Exchange in Complexes of Cobalt, Nickel and Zinc  

Microsoft Academic Search

One of the simplest types of reactions encountered in inorganic chemistry involves the exchange of a molecule coordinated to a metal ion (the ligand) with another molecule free in solution. This type of reaction is fundamental to much of synthetic inorganic chemistry and also constitutes the building blocks from which the complex multistep mechanisms typical of homogeneous catalysis are built.

Kyaw Zaw

1973-01-01

434

Exchange Rates and Old People.  

ERIC Educational Resources Information Center

|Extends earlier work on aging as a process of exchange by focusing on the issue of exchange rates and how they are negotiated. Access to power resources declines with age, placing the old person in the position of negotiating from weakness. (Author)|

Dowd, James J.

1980-01-01

435

Predicate-Based Key Exchange  

Microsoft Academic Search

We provide the first description of and security model for authenticated key exchange protocols with predicate-based authentication. In addition to the standard goal of session key security, our security model also provides for credential privacy: a participating party learns nothing more about the other party's credentials than whether they satisfy the given predicate. Our model also encompasses attribute-based key exchange

James Birkett; Douglas Stebila

2010-01-01

436

How to exchange (secret) keys  

Microsoft Academic Search

A protocol is presented whereby two adversaries may exchange secrets, although neither trusts the other. The secrets are the prime factors of their publicly announced composite numbers. The two adversaries can exchange their secrets bit by bit, but each fears the other will cheat by sending \\

Manuel Blum

1983-01-01

437

Flow maldistribution in heat exchangers  

Microsoft Academic Search

Based on the study of gross flow maldistribution in an experimental electrical heater, this paper presents the effect of flow nonuniformity on the performance of heat exchangers. First, it is shown that it is much more important to understand maldistributions for electrical heaters than for two-fluid heat exchangers. The study of the flow distribution in a particular heater shows that

S. Lalot; P. Florent; S. K. Lang; A. E. Bergles

1999-01-01

438

Technology Performance Exchange (Fact Sheet)  

SciTech Connect

This fact sheet, 'The Technology Performance Exchange' will be presented at the ET Summit, held at the Pasadena Convention Center on October 15-17, 2012. The Technology Performance Exchange will be a centralized, Web-based portal for finding and sharing energy performance data for commercial building technologies.

Not Available

2012-10-01

439

Rotating fluidized bed heat exchanger  

Microsoft Academic Search

A rotating fluidized bed heat exchanger particularly adaptable as a heat exchange unit in the recuperator section of conventional gas turbine engines is disclosed comprising an annular fluidized bed, defined by inner and outer spaced apart coaxial cylindrical, perforated walls, which rotates about the longitudinal axis of the cylinders. The bed is comprised of pulverulent inert particulate material and includes

W. H. Belke; A. Goloff; G. B. Grim

1982-01-01

440

The NESACS Exchange with Germany  

ERIC Educational Resources Information Center

The Northeastern Section of the American Chemical Society (NESACS) is going to host visit to the representatives of the German Chemical Society (GDCh) at their annual exchange program this year. The delegation is expected to spotlight the ACS international effects, in addition to the advantages of the exchange between the two organizations.

Hoffman, Morton Z.; Tanner, Ruth; Strem, Michael

2007-01-01

441

Troubleshooting problems with heat exchangers  

SciTech Connect

Problems encountered during routine use of shell and tube heat exchangers are identified and discussed. Most problems which affect unit performance fall into two basic categories: thermal design and mechanical design. This article approaches the troubleshooting of heat exchangers using this categorization.

Mehra, D.K.

1985-08-01

442

Flexible Exchange Rates and Interdependence  

Microsoft Academic Search

The paper was prepared for the NBER-IMF conference on Exchange Rate Policy and Interdependence. It reviews the experience with flexible exchange rates and the main policy alternatives that have been suggested. The theoretical part develops a modern open economy macro model with an emphasis on capital mobility, real and nominal wage stickiness and expectations. The impact of disturbances is discussed

Rudiger Dornbusch

1983-01-01

443

Heat exchanger performance monitoring guidelines  

SciTech Connect

Fouling can occur in many heat exchanger applications in a way that impedes heat transfer and fluid flow and reduces the heat transfer or performance capability of the heat exchanger. Fouling may be significant for heat exchanger surfaces and flow paths in contact with plant service water. This report presents guidelines for performance monitoring of heat exchangers subject to fouling. Guidelines include selection of heat exchangers to monitor based on system function, safety function and system configuration. Five monitoring methods are discussed: the heat transfer, temperature monitoring, temperature effectiveness, delta P and periodic maintenance methods. Guidelines are included for selecting the appropriate monitoring methods and for implementing the selected methods. The report also includes a bibliography, example calculations, and technical notes applicable to the heat transfer method.

Stambaugh, N. (Duke Power Co., Charlotte, NC (United States)); Closser, W. Jr. (Toledo Edison Co., Oak Harbor,OH (United States)); Mollerus, F.J. (Mollerus Engineering Corp., Los Gatos, CA (United States))

1991-12-01

444

High Temperature Heat Exchanger Project  

SciTech Connect

The UNLV Research Foundation assembled a research consortium for high temperature heat exchanger design and materials compatibility and performance comprised of university and private industry partners under the auspices of the US DOE-NE Nuclear Hydrogen Initiative in October 2003. The objectives of the consortium were to conduct investigations of candidate materials for high temperature heat exchanger componets in hydrogen production processes and design and perform prototypical testing of heat exchangers. The initial research of the consortium focused on the intermediate heat exchanger (located between the nuclear reactor and hydrogen production plan) and the components for the hydrogen iodine decomposition process and sulfuric acid decomposition process. These heat exchanger components were deemed the most challenging from a materials performance and compatibility perspective

Anthony E. Hechanova, Ph.D.

2008-09-30

445

Nucleotide exchange factors: Kinetic analyses and the rationale for studying kinetics of GEFs.  

PubMed

Exchange factors are enzymes that catalyze the exchange of GTP for GDP on guanine nucleotide binding proteins. Progress in understanding the molecular basis of action and the cellular functions of these enzymes has largely come from structural determinations (e.g., crystal structures) and studying effects on cells when expression levels of the exchange factors are perturbed or mutated exchange factors are expressed. Proportionally little effort has been expended on studying the kinetics of exchange; however, reaction rates are central to understanding enzymes. Here, we discuss the importance of kinetic analysis of exchange factors for guanine nucleotide binding proteins, with a focus on ADP-ribosylation factor (Arf) and heterotrimeric G proteins, for providing unique insights into molecular mechanisms and regulation as well as how kinetic analyses are used to complement other approaches. PMID:23181196

Northup, John K; Jian, Xiaoying; Randazzo, Paul A

2012-07-01

446

78 FR 46622 - Application of Topaz Exchange, LLC for Registration as a National Securities Exchange; Findings...  

Federal Register 2010, 2011, 2012, 2013

...Topaz Exchange, LLC for Registration as a National Securities Exchange; Findings...an Application for Registration as a National Securities Exchange (``Form 1...Application.\\6\\ Topaz Exchange submitted a detailed response to comments on July...

2013-08-01

447

The heat pipe exchanger with controllable heat exchanging area  

NASA Astrophysics Data System (ADS)

The heat transfer rate through the heat exchanger in an industrial boiler that burns heavy oils must be controlled so as not to decrease the exhaust gas temperature below the dew point of sulfuric acid. Two systems of heat pipe exchangers are examined: one controls the heat exchange area of the condenser section of the heat pipes and the other uses the variable conductance heat pipes. The characteristics of these two systems are described. The temperatures at various points and the gas quantity are plotted against the boiler loads. The maintainability and operational reliability of both systems are demonstrated.

Oshiro, M.; Takasu, S.; Kurihara, M.; Taneda, K.; Nakamoto, T.; Nakayama, H.

1984-03-01

448

Modular heat exchanger  

DOEpatents

A shell and tube heat exchanger is described having a plurality of individually removable tube bundle modules. A lattice of structural steel forming rectangular openings therein is placed at each end of a cylindrical shell. Longitudinal structural members are placed in the shell between corners of the rectangular openings situated on opposite ends of the shell. Intermediate support members interconnect the longitudinal supports so as to increase the longitudinal supports rigidity. Rectangular parallelepiped tube bundle modules occupy the space defined by the longitudinal supports and end supports and each include a rectangular tube sheet situated on each end of a plurality of tubes extending there through, a plurality of rectangular tube supports located between the tube sheets, and a tube bundle module stiffening structure disposed about the bundle's periphery and being attached to the tube sheets and tube supports. The corners of each tube bundle module have longitudinal framework members which are mateable with and supported by the longitudinal support members. Intermediate support members constitute several lattices, each of which is situated in a plane between the end support members. The intermediate support members constituting the several lattices extend horizontally and vertically between longitudinal supports of adjacent tube module voids. An alternative embodiment for intermediate support members constitute a series of structural plates situated at the corners of the module voids and having recesses therein for receiving the respective longitudinal support members adjacent thereto, protrusions separating the recesses, and a plurality of struts situated between protrusions of adjacent structural plates. 12 figs.

Giardina, A.R.

1981-03-03

449

Energy-Exchange Project  

SciTech Connect

The purpose of the study was to determine what energy savings can be achieved by coordinating the resources and requirements of two facilities, the 26th Ward Water Pollution Control Plant (WPCP) and a housing development named Starrett City with its own total energy system. It was determined that three energy exchange options were economically and technically feasible. These include: the transfer of digester gas produced at the 26th Ward to the boilers at the Starrett City's total energy plant (TEP); the transfer of hot water heated at the TEP to the 26th Ward for space and process heating; and the transfer of coal effluent waste water from the 26th Ward to the condenser cooling systems at the TEP. Technical information is presented to support the findings. The report addresses those tasks of the statement of work dedicated to data acquisition, analysis, and energy conservation strategies internal to the Starrett City TEP and the community it supplies as well as to the 26th Ward WPCP. (MCW)

Not Available

1982-04-01

450

Compact heat exchanger  

SciTech Connect

A compact heat exchanger apparatus is described which consists of: a cluster of hollow shells, the shell having an outer surface and an inner surface, the shells being clustered to connect portions of their outer surfaces with portions of the outer surfaces of adjacent the shells to form a substantially contiguous interstitial space between the unconnected portions of the outer surfaces, the inner surfaces forming cavities which are interconnected by inner passages through the connecting portions of the shells' outer furfaces to cavaties in adjacent shells, at least some of the cavities and inner passages comprising a contiguous inner space within the inner surfaces of the cluster, fluid communication between the interstitial space and the inner space being prevented by the shells; a first side of the cluster bonded to a first bonding layer which seals the interstitial space on the first side of the cluster, the first side of the cluster being open to the exterior side of the first bonding layer to make the inner space accessible to a first manifold connected to the exterior side of the first bonding layer; a second side of the cluster bonded to a second bonding layer which seals the interstitial space on the second side of the cluster, the second side of the cluster being open to the exterior side of the second bonding layer.

Wood, C.D. III; Benson, H.S.

1986-07-15

451

Modular heat exchanger  

DOEpatents

A shell and tube heat exchanger having a plurality of individually removable tube bundle modules. A lattice of structural steel forming rectangular openings therein is placed at each end of a cylindrical shell. Longitudinal structural members are placed in the shell between corners of the rectangular openings situated on opposite ends of the shell. Intermediate support members interconnect the longitudinal supports so as to increase the longitudinal supports rigidity. Rectangular parallelpiped tube bundle moldules occupy the space defined by the longitudinal supports and end supports and each include a rectangular tube sheet situated on each end of a plurality of tubes extending therethrough, a plurality of rectangular tube supports located between the tube sheets, and a tube bundle module stiffening structure disposed about the bundle's periphery and being attached to the tube sheets and tube supports. The corners of each tube bundle module have longitudinal framework members which are mateable with and supported by the longitudinal support members. Intermediate support members constitute several lattice, each of which is situate d in a plane between the end support members. The intermediate support members constituting the several lattice extend horizontally and vertically between longitudinal supports of adjacent tube module voids. An alternative embodiment for intermediate support members constitute a series of structural plates situated at the corners of the module voids and having recesses therein for receiving the respective longitudinal support members adjacent thereto, protrusions separating the recesses, and a plurality of struts situated between protrusions of adjacent structural plates.

Giardina, Angelo R. (Marple Township, Delaware County, PA)

1981-01-01

452

Charge Transfer Reactions  

NASA Astrophysics Data System (ADS)

Charge transfer, or charge exchange, describes a process in which an ion takes one or more electrons from another atom. Investigations of this fundamental process have accompanied atomic physics from its very beginning, and have been extended to astrophysical scenarios already many decades ago. Yet one important aspect of this process, i.e. its high efficiency in generating X-rays, was only revealed in 1996, when comets were discovered as a new class of X-ray sources. This finding has opened up an entirely new field of X-ray studies, with great impact due to the richness of the underlying atomic physics, as the X-rays are not generated by hot electrons, but by ions picking up electrons from cold gas. While comets still represent the best astrophysical laboratory for investigating the physics of charge transfer, various studies have already spotted a variety of other astrophysical locations, within and beyond our solar system, where X-rays may be generated by this process. They range from planetary atmospheres, the heliosphere, the interstellar medium and stars to galaxies and clusters of galaxies, where charge transfer may even be observationally linked to dark matter. This review attempts to put the various aspects of the study of charge transfer reactions into a broader historical context, with special emphasis on X-ray astrophysics, where the discovery of cometary X-ray emission may have stimulated a novel look at our universe.

Dennerl, Konrad

2010-12-01

453

10 CFR Appendix E to Part 110 - Illustrative List of Chemical Exchange or Ion Exchange Enrichment Plant Equipment and Components...  

Code of Federal Regulations, 2010 CFR

...Illustrative List of Chemical Exchange or Ion Exchange Enrichment Plant Equipment and...Illustrative List of Chemical Exchange or Ion Exchange Enrichment Plant Equipment and...liquid-liquid chemical exchange and solid-liquid ion exchange. A. In the...

2009-01-01

454

Hydrogen exchange equilibria in thiols.  

PubMed

Cysteine, cysteinyl-glycine, glutathione, phenylalanyl-cysteinyl-glycine, and histidyl-cysteinyl-glycine were dissolved in acidic and neutral D(2)O in the presence of the radical generator 2,2'-azobis(2-methylpropionamidine) dihydrochloride and radical mediator compounds (benzyl alcohol and 2-propanol). An exchange of H-atoms by D-atoms took place in these peptides due to intramolecular H-abstraction equilibria. NMR measurements allow one to follow the extent of H-D exchanges and to identify the sites where these exchanges take place. Significant exchanges occur in acidic media in GSH at positions Glu-? and Glu-?, in Phe-Cys-Gly at positions Phe ortho, Phe-?, Cys-?, Cys-?, and Gly-?, and in His-Cys-Gly at positions His H1, His H2, His ?, Cys ?, and Gly ?. In neutral media, exchanges occur in Cys-Gly at position Cys ? and in GSH at position Cys ?. Phe-Cys-Gly and His-Cys-Gly were not examined in neutral media. Sites participating in the radical exchange equilibria are highly dependent on structure and pH; the availability of electron density in the form of lone pairs appears to increase the extent of exchange. Interestingly, and unexpectedly, 2D NMR experiments show that GSH rearranges itself in acidic solution: the signals shift, but their patterns do not change. The formation of a thiolactone from Gly and Cys residues matches the changes observed. PMID:22712484

Hofstetter, Dustin; Thalmann, Basil; Nauser, Thomas; Koppenol, Willem H

2012-07-03

455

Exchange of Publications with Developing Countries.  

National Technical Information Service (NTIS)

This paper encourages the exchange of publications between industrialized and developing countries, and discusses the following topics: financial concerns contributing to the importance of exchange, problems arising in the course of exchange efforts, misc...

F. Vanwijngaerden

1979-01-01