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1

An open-framework three-dimensional indium oxalate: [In(OH)(C 2O 4)(H 2O)] 3H 2O  

NASA Astrophysics Data System (ADS)

By hydrothermal reaction of In 2O 3 with H 2C 2O 42H 2O in the presence of H 3BO 3 at 155 C, an open-framework three-dimensional indium oxalate of formula [In(OH)(C 2O 4)(H 2O)] 3H 2O ( 1) has been obtained. The compound crystallizes in the trigonal system, space group R3 c with a=18.668(3) , c=7.953(2) , V=2400.3(7) 3, 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 In 2O 3.

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

2005-12-01

2

Synthesis and Crystal Structure of a Novel 1D Coordinated Polymer {[NaNi(mal)2(??H2O)(H2O)3](H2O)2}n(H2mal=malonic acid)  

Microsoft Academic Search

A novel 1D coordinated polymer, {[NaNi(mal)2(??H2O)(H2O)3](H2O)2}n (H2mal=malonic acid), has been synthesized and its crystal structure is determined by X?ray diffraction analysis. Its crystal structure belongs to orthorhombic system with space group p2(1)2(1)2(1). The coordination environment around Ni(II) is described as a distorted octahedron constructed by four oxygen atoms from two trans?coordinated malonates and two oxygen atoms from two trans?coordinated water,

Rui Yang

2006-01-01

3

The structure of {[Co(pht)(bpy)(H2O)]3H2O}n (pht is phthalate and bpy is 4,4'-bipyridine) and the role of solvent water clusters in structure stability.  

PubMed

The Co(II) cation in poly[[aqua(?-benzene-1,2-dicarboxylato-?(3)O(1),O(2):O(1))(?-4,4'-bipyridine-?(2)N:N')cobalt(II)] trihydrate], {[Co(C8H4O4)(C10H8N2)(H2O)]3H2O}n, is octahedrally coordinated by two N atoms of two 4,4'-bipyridine ligands, three O atoms from phthalate anions and a fourth O atom from a coordinated water molecule. The packing consists of planes of coordination polymers linked by hydrogen bonds mediated by three solvent water molecules; the linkage is achieved by the water molecules forming intricate oligomeric clusters which also involve the O atoms of the phthalate ligands. PMID:24816009

Harvey, Miguel Angel; Suarez, Sebastin; Doctorovich, Fabio; Cukiernik, Fabio D; Baggio, Ricardo

2014-05-01

4

Synthesis, crystal structure and properties of a new complex constructed from coordinated Dy(III) unit and the polyanion [SiMo12O40]: [Dy(NMP)4(H2O)3]H[SiMo12O40]2NMP  

Microsoft Academic Search

The synthesis, X-ray crystal structure, IR, UV and ESR spectra, and thermal properties of the new complex formulated [Dy(NMP)4(H2O)3]H[SiMo12O40]2NMP (NMP = N-methyl-2-pyrrolidone), are reported. The crystal structure indicates that the coordinated ion combines with [SiMo12O40] by an electrostatic force. There are several kinds of hydrogen bonding in the complex and the crystal structure shows that the water molecules in the

Jingping Wang; Qiuxia Han; Jingyang Niu

2004-01-01

5

Kinetics of Exchange Reactions in a Cation-Exchange Resin  

Microsoft Academic Search

The kinetics of the exchange reactions of several cations from aqueous solution by protons from a sulfonated polystyrene resin have been studied in detail. The reaction rate is first-order with respect to both the resin and the cation concentrations and increases with the stirring velocity. The activation parameters for the exchange of Mg, Cu, Cr, and Fe ions have been

Fernando Mata-perez; Felix A. Castro; Joaquin F. Perez-benito

1987-01-01

6

Charge exchange reactions in astrophysical plasmas  

Microsoft Academic Search

A review is presented of charge exchange reactions of multiply charged ions with atomic hydrogen and helium at thermal-eV energies, typical of the physical conditions encountered in planetary nebulae. The basic features of the processes are analyzed in the framework of the molecular model of atomic collisions. A discussion is given of the different theoretical approaches to the calculation of

R. McCarroll; P. Valiron; L. Opradolce

1983-01-01

7

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

8

Charge exchange reactions and applications to astrophysics  

NASA Astrophysics Data System (ADS)

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 12C. 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.

2012-11-01

9

The Mirror Charge Exchange Reaction CARBON-13  

NASA Astrophysics Data System (ADS)

Differential cross sections have been measured near 0^circ for the dominant channels in the mirror reaction ^ {13}C(^{13}N,^{13 }C)^{13}N at E/A = 57 and 105 MeV. The cross sections of the peaks in the excitation spectrum are discussed in terms of the Gamow-Teller and Fermi transition strengths in the target and the projectile. The cross section per unit Gamow-Teller strength is found to be enhanced relative to that for unit Fermi strength when compared with previous results from (p,n) reactions. The use of heavy ions as probes for weak-interaction strengths in radioactive nuclei is discussed. The present work represents the first use of mirror symmetry to study heavy-ion charge exchange as well as the first application of the developing radioactive nuclear beam field to this area.

Steiner, Mathias

10

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

11

Delta excitation in nuclei: the lesson of charge exchange reactions.  

National Technical Information Service (NTIS)

We present an attempt of theoretical interpretation of charge exchange reactions on nuclei in the region of the delta resonance. Special care is taken to insure consistency with the constraints from pion and photon excitation channels. Good agreement with...

J. Delorme P. A. M. Guichon

1989-01-01

12

Surface modification of gold nanorods through a place exchange reaction inside an ionic exchange resin.  

PubMed

A place exchange reaction between 11-mercaptoundecanoic acids (MUA) and cetyltrimethylammonium bromide (CTAB)-protected gold nanorods (GNRs) was conducted inside an ionic exchange resin; this modification resulted in functional gold nanorods soluble in both polar and nonpolar organic solvents. PMID:18566704

Dai, Qiu; Coutts, Janelle; Zou, Jianhua; Huo, Qun

2008-07-01

13

Elastic pion double charge exchange reactions  

Microsoft Academic Search

Results of simple sequential model calculations are presented and compared with experimental data covering a wide variety of targets and energies. The model is fairly successful at higher energies (greater than about 200 MeV) but fails badly at lower energies. [NUCLEAR REACTIONS (pi+,pi-) cross sections calculated and compared with experiment: 80 MeV<=Epi<=300 MeV.

Gerald A. Miller

1981-01-01

14

Cesium exchange reaction on natural and modified clinoptilolite zeolites  

Microsoft Academic Search

Cesium cation exchange reaction with K, Na, Ca and Mg ions on natural and modified clinoptilolite has been studied. Batch\\u000a cation-exchange experiments were performed by placing 0.5 g of clinoptilolite into 10 ml or 20 ml of 110?3M CsCl solution for differing times. Two type deposits of clinoptilolite zeolites from, Nin Hrabovec (NH), Slovakia and\\u000a Metaxades (MX), Greece were used

P. Rajec; K. Domianov

2008-01-01

15

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

16

Successful plasma exchange in type 1 leprosy reversal reaction.  

PubMed Central

A 24 year old man admitted to hospital with borderline lepromatous leprosy was treated with rifampicin, dapsone, and clofazimine. After four months he developed a reversal reaction and the diagnosis was modified to borderline tuberculoid leprosy. The dose of clofazimine was raised and prednisolone added to the regimen without any symptomatic response. His condition improved dramatically after five plasma exchanges on five successive days.

Lucht, F; Rifle, G; Portier, H; Chalopin, J M; Bonhomme, J

1984-01-01

17

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

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

Pion charge-exchange reactions: The analog state transitions  

SciTech Connect

The general features of pion charge-exchange reactions leading to nuclear-isobaric-analog states (IAS) and double-isobaric-analog states (DIAS), as they have emerged from studies over the past ten years, are reviewed. The energy range investigated is 20 to 550 MeV for IAS transitions and 20 to 300 MeV for DIAS transitions. These data are seen to play an important role in characterizing the pion optical potential, in determining the ..delta..-N interaction in nuclei, and in the study of nucleon correlations in nuclei. Recent progress achieved in understanding the role of such correlations in double-charge-exchange reactions is reviewed. 55 refs., 43 figs., 3 tabs.

Baer, H.W.

1987-01-01

20

EXFOR SYSTEMS MANUAL NUCLEAR REACTION DATA EXCHANGE FORMAT.  

SciTech Connect

EXFOR is an exchange format designed to allow transmission of nuclear reaction data between the members of the Nuclear Data Centers Network. This document has been written for use by the members of the Network and includes matters of procedure and protocol, as well as detailed rules for the compilation of data. Users may prefer to consult EXFOR Basics' for a brief description of the format.

MCLANE,V.; NUCLEAR DATA CENTER NETWORK

2000-05-19

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.

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

1995-01-01

22

Test of Weak Reaction Rates of Importance for Late Stellar Evolution Using Charge-exchange Reactions.  

NASA Astrophysics Data System (ADS)

Weak reactions (electron captures and beta decays) on nuclei play an important role in the evolution of pre-supernovae stars and their eventual core collapse. The rates are usually predicted in shell-model and mean-field calculations. Experimental information on Gamow-Teller strength distributions is needed to test these calculations. At the NSCL, the (t,^3He) charge-exchange reaction at 115 MeV/nucleon is employed for such studies. In addition, the (^3He,t) reaction at 140 MeV/nucleon (at RCNP, Osaka) is used for detailed studies of the charge-exchange reaction mechanism, which is important for understanding the uncertainties in the experimentally extracted Gamow-Teller strength distributions. Besides a comparison between experimental and theoretical Gamow-Teller strength distributions, the work also includes the calculation of electron-capture rates, so that the sensitivity of the rates on differences between theoretical and experimental rates can be gauged. A significant fraction of the nuclei relevant for late stellar evolution are unstable. Hence, to ensure accurate weak reaction rates for such nuclei, charge-exchange experiments on rare isotopes are crucial, but the techniques have to be developed. At the NSCL, a program has been initiated to study charge-exchange reactions on rare isotopes.

Zegers, R. G. T.

2009-05-01

23

Selenocysteine in Thiol/Disulfide-Like Exchange Reactions  

PubMed Central

Abstract Significance: Among trace elements used as cofactors in enzymes, selenium is unique in that it is incorporated into proteins co-translationally in the form of an amino acid, selenocysteine (Sec). Sec differs from cysteine (Cys) by only one atom (selenium versus sulfur), yet this switch dramatically influences important aspects of enzyme reactivity. Recent Advances: The main focus of this review is an updated and critical discussion on how Sec might be used to accelerate thiol/disulfide-like exchange reactions in natural selenoenzymes, compared with their Cys-containing homologs. Critical Issues: We discuss in detail three major aspects associated with thiol/disulfide exchange reactions: (i) nucleophilicity of the attacking thiolate (or selenolate); (ii) electrophilicity of the center sulfur (or selenium) atom; and (iii) stability of the leaving group (sulfur or selenium). In all these cases, we analyze the benefits that selenium might provide in these types of reactions. Future Directions: It is the biological thiol oxidoreductase-like function that benefits from the use of Sec, since Sec functions to chemically accelerate the rate of these reactions. We review various hypotheses that could help explain why Sec is used in enzymes, particularly with regard to competitive chemical advantages provided by the presence of the selenium atom in enzymes. Ultimately, these chemical advantages must be connected to biological functions of Sec. Antioxid. Redox Signal. 18, 16751689.

Marino, Stefano M.

2013-01-01

24

Lewis-acid-assisted methyl exchange reactions in silylated aminodichloroarsanes.  

PubMed

Lewis-acid-assisted methyl/chlorine, methyl/azide, and methyl/triflate exchange reactions between silicon and arsenic centers have been studied and applied to different silylated aminoarsane species leading to a number of new methylarsane compounds: bis(trimethylsilyl)amino(dichloro)arsane (3) was reacted with GaCl(3) yielding a bis(chlorodimethylsilyl)-tetramethyl-cyclo-disilazane (4) accompanied by the release of Me(2)AsCl, while trimethylsilyl(m-terphenyl)amino(dichloro)arsane (5) (m-terphenyl = 2,6-Mes(2)-C(6)H(3), Mes = 2,4,6-Me(3)C(6)H(2)) reacted with GaCl(3) to give dichloromethylsilyl(m-terphenyl)aminodimethylarsane (6). In the presence of trimethylsilylazide, trimethylsilyl(m-terphenyl)amino(dichloro)arsane displays a methyl/azide exchange triggered by the action of GaCl(3) yielding azidodimethylsilyl(m-terphenyl)amino(chloro)methylarsane (7). Moreover, methyl/triflate exchange reactions have been observed in the reaction of trimethylsilyl(m-terphenyl)amino(dichloro)arsane (i) with 1 equiv of AgOTf (OTf = triflate) yielding N-(trifluoromethylsulfonatodimethylsilyl)-N-(m-terphenyl)amino(methyl)chloroarsane (8) and (ii) with 2 equiv of AgOTf yielding N-(trifluoromethylsulfonatodimethylsilyl)-N-(m-terphenyl)trifluoromethylsulfonatomethylarsane (9). All new compounds (3-9) have been fully characterized by means of vibrational spectroscopy, X-ray, CHN analysis, MS, and NMR studies. A possible reaction mechanism is discussed starting from an initial chloride abstraction and the intermediate formation of a cationic iminoarsane species. In a second step, a methyl shift from the silicon to the arsenic center occurs. PMID:19006290

Michalik, Dirk; Schulz, Axel; Villinger, Alexander

2008-12-15

25

Clay catalysis of aromatic hydrogen-exchange reactions  

NASA Astrophysics Data System (ADS)

The exchange of aromatic hydrogen in the presence of clay catalysts has been studied by measuring the rates of detritiation of some tritiated naphthalene derivatives on homoionic bentonites. The rate of reaction is influenced by the position of tritium on the ring, the presence of a methoxysubstituent on the ring and the acidity of the clay catalyst. It is inferred that the mechanism of exchange involves an adsorbed species similar to the arenium ion intermediate of electrophilic aromatic substitutions in homogeneous systems. In some cases exchange of hydrogen between acidic clay surfaces and naphthalene derivatives could be detected at temperatures as low as 23C, and in aqueous slurries at 70C. This observed reactivity suggests that these reactions could occur in sedimentary environments where organic matter, such as petroleum hydrocarbons, is in contact with clay surfaces. The hydrogen isotopic composition of aromatic hydrogen in petroleum may therefore be related to that of the acidic water adsorbed on clay surfaces with which the petroleum has been in contact.

Alexander, Robert; Kagi, Robert Ian; Larcher, Alfons Valentino

1982-02-01

26

EXFOR systems manual: Nuclear reaction data exchange format  

SciTech Connect

This document describes EXFOR, the exchange format designed to allow transmission of nuclear reaction data between the members of the Nuclear Data Centers Network. 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. The exchange format, as outlined, is designed to allow 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).

McLane, V. [ed.

1996-07-01

27

Nuclear field shift effect in chemical exchange reactions  

NASA Astrophysics Data System (ADS)

The classic theory of stable isotope fractionation in chemical exchange reactions has been established by Bigeleisen, Mayer, and Urey in 1947. The theory was based on the difference of molecular vibrational energies of isotopomers that are proportional to the respective masses, and hence, results in mass-dependent isotope effect only. In 1996, this conventional mass-dependent theory has been expanded by Bigeleisen to include a mass-independent term named the nuclear field shift effect. The nuclear field shift is an isotope shift in orbital electrons, which results from the isotopic difference in nuclear size and shape. The new equation defined by Bigeleisen (at a constant temperature) can be simply expressed as, ln ? = ? A + (? m/mm') B, where ? is the isotope separation factor, ? isotopic difference in mean-square nuclear charge radius, ?m difference between isotopic masses m and m'. A and B are scaling factors of the nuclear field shift effect and the conventional mass effect, respectively. Since this new theory was presented, the mass-independent isotope fractionation of various elements, e.g, Ti, Cr, Ni, Zn, Sr, Zr, Mo, Ru, Cd, Te, Ba, Nd, Sm, Gd, Yb, and U, found in chemical exchange systems has been successfully explained as the nuclear field shift effect. In our most recent studies, the nuclear field shift effect of Cr, Mo, Ru, Cd, and Te isotopes has been found in laboratory scale experiments. The isotopes of these elements were fractionated by using a liquid-liquid extraction system (a ligand exchange system) at room temperature. The isotopic analysis was performed by the multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) with a typical precision of <100 ppm (at ENS Lyon or UC Davis). Isotope enrichment factors did not show mass-dependent trend, but possessed a similar variation of their nuclear charge radii. For Cr, we tested a different chemical exchange system (a redox system): at high temperature (723-1023 K), an eutectic melt was contacted with a liquid metal. In this system, the nuclear field shift effect of Cr was also found. All these experimental results suggest that the nuclear field shift effect may occur in every chemical exchange reaction at various temperatures to various degrees. Therefore, isotopic anomalies found in a natural system might be partly or largely affected by the nuclear field shift effect via chemical reactions occurred in the nature. In order to clarify the degree and significance of its contribution, we may need to pay more attention to the nuclear field shift effect created chemically.

Fujii, T.; Moynier, F.; Yin, Q.; Albarde, F.

2007-12-01

28

Reactive Resonances in N+N2 Exchange Reaction  

NASA Technical Reports Server (NTRS)

Rich reactive resonances are found in a 3D quantum dynamics study of the N + N2 exchange reaction using a recently developed ab initio potential energy surface. This surface is characterized by a feature in the interaction region called Lake Eyring , that is, two symmetric transition states with a shallow minimum between them. An L2 analysis of the quasibound states associated with the shallow minimum confirms that the quasibound states associated with oscillations in all three degrees of freedom in Lake Eyring are responsible for the reactive resonances in the state-to-state reaction probabilities. The quasibound states, mostly the bending motions, give rise to strong reasonance peaks, whereas other motions contribute to the bumps and shoulders in the resonance structure. The initial state reaction probability further proves that the bending motions are the dominating factors of the reaction probability and have longer life times than the stretching motions. This is the first observation of reactive resonances from a "Lake Eyring" feature in a potential energy surface.

Wang, Dunyou; Huo, Winifred M.; Dateo, Christopher E.; Schwenke, David W.; Stallcop, James R.

2003-01-01

29

Satellite Capture via Binary Exchange Reactions: Application to Triton  

NASA Astrophysics Data System (ADS)

The recent observational discovery of satellites orbiting asteroids and Kuiper belt objects has revealed a whole new constituency of solar system objects (see Merline et al. 2002 for a review). Binaries appear to be ubiquitous among the minor planets, representing 16% of near-Earth asteroids (Margot et al. 2002), at least 2% of asteroids in the main belt (Merline et al. 2002), and a growing number of Kuiper belt objects (currently estimated at 14%, Noll 2005). Given the existence and prevalence of binaries, 3-body encounters between a binary pair and a third body become an inevitable and frequent occurrence in the dynamical evolution of the solar system. This type of encounter has been studied previously in the context of stellar clusters where binary-single star encounters represent an important process in the evolution of binary star populations (see e.g. Hills 1975, Heggie & Hut 1993). The possible outcomes of these encounters include physical collisions, hardening, softening or disruption of the binary, and exchange reactions in which one member of a binary is expelled and its place taken by the third body. In the context of solar system dynamics, the significance of 3-body encounters is only beginning to be examined and appreciated (Funato et al. 2004). We are studying exchange reactions during planet-binary encounters as a new pathway for the capture of irregular planetary satellites from initially heliocentric orbits. Satellite capture via exchange reaction requires gravitational disruption of the binary and retention of one member by the planet. In general, we find that exchange capture is efficient when binaries approach the planet to a distance less than the appropriate Roche radius of the system and with sufficiently low encounter velocities. As application of this capture mechanism, we consider the possibility that Neptune's massive retrograde satellite Triton may have been captured during a gravitational encounter between Neptune and a binary composed of Triton and a third body. We find that Triton's capture can be realized from a variety of binaries, including ones resembling the Pluto-Charon pair (i.e. mass ratio mPluto}/m{Charon = 8 and semi-major axis to primary radius ratio aB/RPluto = 17.3). We will discuss the encounter dynamics required for capture via this mechanism, compare this mode of satellite capture to others suggested for Triton, and relate them to the dynamical environment of Neptune's accretion and putative migration.

Agnor, C. B.; Hamilton, D. P.

2005-05-01

30

Synthesis of temperature-responsive anion exchanger via click reaction.  

PubMed

The temperature-responsive anion exchanger was synthesized by immobilizing the poly(N-isopropylacrylamide) (PNIPAM), a kind of the temperature-responsive polymer, on the external surface of mesoporous silica via click reaction. The structure of this synthesized composite was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), elemental analysis, and nitrogen adsorption experiment. The amount of PNIPAM immobilized on the external surface of mesoporous silica, which was calculated from the weight loss measured by thermogravimetry, increased from 5.3 wt.% to 12.9 wt.% (dry) depending on the amount of PNIPAM added in the click reaction. The adsorption-desorption behavior of methyl orange (MO) ions in this synthesized anion exchanger was affected by the temperature of aqueous solution: the MO ions were adsorbed and desorbed reversibly and repeatedly with changing the pH of the solution at 25 C, while the amount of adsorbed MO ions remained nearly constant at about 0.05 mmol/g independent of the pH of the solution at 40 C. Also, the amount of PNIPAM immobilized on the mesoporous silica influenced the adsorption rate of MO ions, suggesting that the adsorption rate in this composite is controlled by the diffusion of MO ions through the PNIPAM layer. PMID:22446148

Murakami, Kenji; Yu, Xue; Kato, Takahiro; Inoue, Yukihiko; Sugawara, Katsuyasu

2012-06-15

31

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

32

Satellite Capture via Binary Exchange Reactions: Application to Triton  

NASA Astrophysics Data System (ADS)

The recent observational discovery of satellites orbiting asteroids and Kuiper belt objectss has revealed a whole new constituency of solar system objects (see Merline et al. 2002 for a review). Binaries appear to be ubiquitous among the minor planets, representing 16% of near-Earth asteroids (Margo et al. 2002), 2% of asteroids in the main belt (Merline et al. 2002), and 5% of KBOs (Noll et al. 2003). Here we consider the possibility that Triton may have been captured during a gravitational encounter between Neptune and a binary composed of Triton and a third body. Given the existence and prevalence of binaries, 3-body encounters between a binary pair and a third body become an inevitable and frequent occurrence in the dynamical evolution of the solar system. This type of encounter has been studied previously in the context of stellar clusters where binary-single star encounters represent an important process in the evolution of binary star populations (see e.g. Hills 1975, Heggie & Hut 1993). The possible outcomes of these encounters include physical collisions, hardening, softening or disrupting the binary, and exchange reactions in which one member of a binary is expelled and its place taken by the third body. In the context of solar system dynamics, the significance of 3-body encounters is only beginning to be examined and appreciated (Funato et al. 2004). We will report on progress in our study of 3-body encounters between a planet and a binary and discuss the implications of this dynamical process for the origin and evolution of major and minor planet satellites. In particular we will address how exchange reactions during planet-binary encounters represent a new pathway for the capture of Triton and other irregular planetary satellites from initially heliocentric orbits.

Agnor, C. B.; Hamilton, D. P.

2004-11-01

33

Satellite Capture via Binary Exchange Reactions: Application to Triton  

NASA Astrophysics Data System (ADS)

The recent observational discovery of satellites orbiting asteroids and Kuiper belt objects has revealed a whole new constituency of solar system objects. Binaries appear to be ubiquitous among the minor planets, representing about 16% of near-Earth asteroids (Margot et al.~2002), at least 2% of asteroids in the main belt (Merline et al.~2002), and a growing number of Kuiper belt objects (currently estimated at about 14%, Noll 2005). Given the existence and prevalence of binaries, 3-body encounters between a binary pair and a third body become an inevitable and frequent occurrence in the dynamical evolution of the solar system. While 3-body encounters have been studied extensively in the context of stellar clusters, their significance in the context of solar system dynamics is only beginning to be examined and appreciated (Funato et al.~2004). We are examining how exchange reactions during planet-binary encounters (i.e.~an encounter in which one member of a binary is expelled and its place taken by the planet) represent a new pathway for the capture of planetary satellites. This new capture mechanism may be relevant to origin and evolution of several small body populations in the solar system (e.g.~the icy and irregular satellites of the giant planets). Using numerical integrations of 3-body encounters and analytic arguments we have developed a simple model to describe this purely gravitational mode of satellite capture. Capture via exchange reaction requires gravitational disruption of the binary and retention of one member by the planet. In general, we have found that exchange capture is efficient when binaries approach the planet to a distance less than the appropriate Roche radius of the system and with sufficiently low encounter velocities. As a first application of this capture mechanism, we have explored the possibility that Neptune's massive retrograde satellite Triton was captured during a gravitational encounter between Neptune and a binary composed of Triton and a third body. We have found that Triton's capture can be realized from a variety of binaries, including ones in which Triton is the more massive member and those resembling the Pluto-Charon pair (i.e.~mass ratio mPluto/mCharon = 8 and semi-major axis to primary radius ratio a_B/RPluto = 17.3). We will discuss the encounter dynamics required for capture via this mechanism, relate them to the dynamical environment of Neptune's accretion and putative migration and discuss the conditions in which this mode of satellite capture is favored over others suggested for Triton (e.g.~collisional capture, Goldreich et al.~1989, gas drag capture, McKinnon and Leith 1994).

Agnor, C.; Hamilton, D. P.

2005-12-01

34

Isotopic exchange reactions of amines. II. Amino-amide proton exchange in the potassium methylamide-methylamine system  

Microsoft Academic Search

The kinetics of the methylamine-potassium methylamide amino proton exchange reaction were studied by ¹H NMR as a function of temperature and catalyst concentration. Rates were determined by analysis of the line shapes of both the amino and methyl peaks. The exchange kinetics cannot be described by a single bimolecular rate constant based on solvent and stoichiometric amide concentration. By using

James D. Halliday; Patrick E. Bindner

1979-01-01

35

Monte-carlo simulation of ester exchange reactions in PET\\/PEN blends  

Microsoft Academic Search

Monte-Carlo kinetic simulations are performed to study exchange reactions in PET\\/PEN blends. Chain distribution of the blend is simulated at various mixing conditions. The average length of PET and PEN repeating units decreases with increasing exchange reactions. Derivative of heat flow is modeled at T g region during mixing. Two peaks are observed on the derivative of heat flow curve

A. a Mahjub; S.H.a Jafari; H. A. b Khonakdar; U. c Wagenknecht; G. c Heinrich

2013-01-01

36

The formation of Kuiper-belt binaries through exchange reactions  

NASA Astrophysics Data System (ADS)

Recent observations have revealed that an unexpectedly high fraction-a few per cent-of the trans-Neptunian objects (TNOs) that inhabit the Kuiper belt are binaries. The components have roughly equal masses, with very eccentric orbits that are wider than a hundred times the radius of the primary. Standard theories of binary asteroid formation tend to produce close binaries with circular orbits, so two models have been proposed to explain the unique characteristics of the TNOs. Both models, however, require extreme assumptions regarding the size distribution of the TNOs. Here we report a mechanism that is capable of producing binary TNOs with the observed properties during the early stages of their formation and growth. The only required assumption is that the TNOs were initially formed through gravitational instabilities in the protoplanetary dust disk. The basis of the mechanism is an exchange reaction in which a binary whose primary component is much more massive than the secondary interacts with a third body, whose mass is comparable to that of the primary. The low-mass secondary component is ejected and replaced by the third body in a wide but eccentric orbit.

Funato, Yoko; Makino, Junichiro; Hut, Piet; Kokubo, Eiichiro; Kinoshita, Daisuke

2004-02-01

37

Ligand exchange reactions in Cu(III) complexes: mechanistic insights by combined NMR and DFT studies.  

PubMed

NMR studies of (13)C/(12)C isotopic patterns in Cu(iii) intermediates and reaction products together with DFT calculations of possible reaction pathways indicate an intermolecular S(N)2 like substitution mechanism for ligand exchange reactions in square planar Cu(iii) complexes, which is proposed to be slow compared to reductive elimination at synthetic conditions. PMID:20461240

Grtner, Tobias; Yoshikai, Naohiko; Neumeier, Maria; Nakamura, Eiichi; Gschwind, Ruth M

2010-07-01

38

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

39

Invited Parallel Talk: Forward pion-nucleon charge exchange reaction and Regge constraints  

NASA Astrophysics Data System (ADS)

We present our recent study of pion-nucleon charge exchange amplitudes above 2 GeV. We analyze the forward pion-nucleon charge exchange reaction data in a Regge model and compare the resulting amplitudes with those from the Karlsruhe-Helsinki and George-Washington-University partial-wave analyses. We explore possible high-energy constraints for theoretical baryon resonance analyses in the energy region above 2 GeV. Our results show that for the pion-nucleon charge exchange reaction, the appropriate energy region for matching meson-nucleon dynamics to diffractive scattering should be around 3 GeV for the helicity flip amplitude.

Huang, Fei; Sibirtsev, A.; Krewald, S.; Hanhart, C.; Haidenbauer, J.; Meiner, U.-G.

2009-12-01

40

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

National Technical Information Service (NTIS)

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 conser...

Z. Weinfeld

1993-01-01

41

Quantum resonance effects in exchange, photodissociation, and recombination reactions  

SciTech Connect

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This project studied quantum resonance effects on chemical reactions. The authors accurate reactive scattering calculations showed that quantum resonance phenomena dominate most chemical reactions and are essential to any real understanding of reactivity. It was found that, as long-lived metastable states of the colliding system, resonances can decay to reactants, products, or a mixture of both. Only the latter contribute to reaction. Conditions under which resonances can be neglected or treated statistically were studied. Important implications about the mechanism of recombination reactions were discovered, and some remarkable effects of geometric phases on the symmetries and energies of resonances were also discovered. Calculations were completed for the reaction H + O{sub 2} {yields} OH + O, which is the rate limiting step in the combustion of all hydrocarbons and the single most important reaction in all of combustion chemistry.

Pack, R.; Kendrick, B.; Kress, J.; Walker, R. [Los Alamos National Lab., NM (United States); Hayes, E. [Ohio State Univ., Columbus, OH (United States); Lagana, A. [Univ. of Perugia (Italy); Parker, G. [Univ. of Oklahoma, Norman, OK (United States); Butcher, E. [Auburn Univ., AL (United States)

1996-04-01

42

Pion double-charge-exchange reaction: Shell model formalism  

SciTech Connect

A quite general formalism which allows one to compute the pion double-charge-exchange differential cross section in the context of the shell model has been developed. Compact formulas taking into account the full momentum and spin dependence of the elementary amplitude are given. These formulas hold for any nuclear angular momenta as well as any pion-nucleus partial waves. Thus the differential cross section depends on a quantity {ital B}{sub {ital l}1}{ital l2}{ital ifJ}({ital k}{sub 1},{ital k}{sub 2}) which is a function of the magnitude of the pion momenta {ital k}{sub 1},{ital k}{sub 2} and is composed of three factors: (1) the nuclear matrix element involving the states ({ital i}) and ({ital f}) expressed in terms of tensor operators {ital T}({ital a}{sup {dagger}}{ital a}); (2) the essentially geometric'' aspects of the elementary double-charge-exchange amplitude which are pretty independent of any specific model; (3) a radial integral which contains the ingredients of specific models as well as the distortion of the mesons involved.

Vergados, J.D. (Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (US) Department of Physics, University of Ioannina, Ioannina, Greece)

1991-07-01

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

Rlla, G; Bowen, W H

1978-01-01

44

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

45

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

46

Sulfo cation-exchange resins as heterogeneous catalysts for the reaction of styrene with formaldehyde  

Microsoft Academic Search

1.Macroporous and gel sulfo cation-exchange resins are active catalysts for the condensation of styrene with formaldehyde. The product, 4-phenyl-1,3-dioxane was obtained in up to 97% yield.2.The activity of macroporous sulfo cation-exchange resins increases with decreasing particle diameter but in the case of the gel samples, granule size has only a slight effect on the reaction rate.3.The enhanced activity of sulfo

K. A. Kasymova; V. Z. Sharf; E. F. Litvin; E. N. Grigor'eva

1987-01-01

47

Competition between abstraction and exchange channels in H + HCN reaction: Full-dimensional quantum dynamics  

SciTech Connect

Dynamics of the title reaction is investigated on an ab initio based potential energy surface using a full-dimensional quantum wave packet method within the centrifugal sudden approximation. It is shown that the reaction between H and HCN leads to both the hydrogen exchange and hydrogen abstraction channels. The exchange channel has a lower threshold and larger cross section than the abstraction channel. It also has more oscillations due apparently to quantum resonances. Both channels are affected by long-lived resonances supported by potential wells. Comparison with experimental cross sections indicates underestimation of the abstraction barrier height.

Jiang, Bin; Guo, Hua, E-mail: hguo@unm.edu [Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131 (United States)] [Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131 (United States)

2013-12-14

48

Charge exchange and chemical reactions with trapped thorium ions  

NASA Astrophysics Data System (ADS)

Most atomic nuclei have excitation energies ranging from keV to MeV. A unique exception is the ^229Th nucleus, which has an excited state just several eV above the nuclear ground state.ootnotetextB. R. Beck et al., Phys. Rev. Lett. 98, 142501 (2007). Th^3+ provides a convenient level structure for laser cooling in an rf Paul trap.ootnotetextC. J. Campbell et al., Phys. Rev. Lett 102, 233004 (2009). Unlike many ions commonly utilized in precision measurements, the trap lifetime of Th^3+ is limited to only several minutes. This is a severe limitation to experiments involving ^229Th as it is only available in minute quantities. Here we have studied the loss mechanisms by introduction of various contaminants and analyzed reaction products using trapped ion mass spectrometry techniques.ootnotetextL. R. Churchill et al., Phys. Rev. A 83, 012710 (2011).

Depalatis, Michael; Churchill, Layne; Chapman, Michael

2011-06-01

49

Reaction chemistry and ligand exchange at cadmium selenide nanocrystal surfaces  

SciTech Connect

Chemical modification of nanocrystal surfaces is fundamentally important to their assembly, their implementation in biology and medicine, and greatly impacts their electrical and optical properties. However, it remains a major challenge owing to a lack of analytical tools to directly determine nanoparticle surface structure. Early nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) studies of CdSe nanocrystals prepared in tri-n-octylphosphine oxide (1) and tri-n-octylphosphine (2), suggested these coordinating solvents are datively bound to the particle surface. However, assigning the broad NMR resonances of surface-bound ligands is complicated by significant concentrations of phosphorus-containing impurities in commercial sources of 1, and XPS provides only limited information about the nature of the phosphorus containing molecules in the sample. More recent reports have shown the surface ligands of CdSe nanocrystals prepared in technical grade 1, and in the presence of alkylphosphonic acids, include phosphonic and phosphinic acids. These studies do not, however, distinguish whether these ligands are bound datively, as neutral, L-type ligands, or by X-type interaction of an anionic phosphonate/phosphinate moiety with a surface Cd{sup 2+} ion. Answering this question would help clarify why ligand exchange with such particles does not proceed generally as expected based on a L-type ligand model. By using reagents with reactive silicon-chalcogen and silicon-chlorine bonds to cleave the ligands from the nanocrystal surface, we show that our CdSe and CdSe/ZnS core-shell nanocrystal surfaces are likely terminated by X-type binding of alkylphosphonate ligands to a layer of Cd{sup 2+}/Zn{sup 2+} ions, rather than by dative interactions. Further, we provide spectroscopic evidence that 1 and 2 are not coordinated to our purified nanocrystals.

Owen, Jonathan; Park, Jungwon; Trudeau, Paul-Emile; Alivisatos, A. Paul

2008-12-02

50

Exchange-diffusion reactions in HfSiON during annealing studied by Rutherford backscattering spectrometry, nuclear reaction analysis and narrow resonant nuclear reaction profiling  

Microsoft Academic Search

HfSiON films deposited on Si (001) by reactive sputtering were submitted to rapid thermal annealing at 1000 C in vacuum, N2 and O2 atmospheres. The stability of the dielectric was evaluated by measuring the atomic transport and exchange of the chemical species, using Rutherford backscattering spectrometry, nuclear reaction analysis and narrow resonant nuclear reaction profiling. Annealing in O2 ambient reduced

L. Miotti; K. P. Bastos; G. V. Soares; C. Driemeier; R. P. Pezzi; J. Morais; I. J. R. Baumvol; A. L. P. Rotondaro; M. R. Visokay; J. J. Chambers; M. Quevedo-Lopez; L. Colombo

2004-01-01

51

Energy-loss cross sections for inclusive charge-exchange reactions at intermediate energies  

NASA Technical Reports Server (NTRS)

Charge-exchange reactions for scattering to the continuum are considered in a high-energy multiple scattering model. Calculations for (p,n) and (He-3,H-3) reactions are made and compared with experimental results for C-12, O-16, and Al-27 targets. Coherent effects are shown to lead to an important role for inelastic multiple scattering terms when light projectiles are considered.

Cucinotta, Francis A.; Townsend, Lawrence W.; Dubey, Rajendra R.

1993-01-01

52

Cation and proton exchange, pH variations, and carbonate reactions in a freshening aquifer  

NASA Astrophysics Data System (ADS)

Freshening of aquifers is accompanied by sequential elution of the saltwater (seawater) cations from the sediment's exchange complex. The resulting Chromatographic patterns are modeled with a one-dimensional geochemical transport model that can handle the complex interplay of transport and mineral and ion exchange equilibria. The transport part is based on the mixing cell approach, with different time steps for advective and diffusive transport used when required by small grid size. The chemical reactions are calculated explicitly after each time step with the geochemical model PHREEQE. Ion exchange is included in the form of association half reactions, which allows simulation of the dynamic nature of the exchange process. The variation in the constant for proton association is obviated with an activity coefficient for H-X that is derived from the constant capacitance model. All coefficients for the exchange model are obtained by fitting to literature data to be able to perform the modeling as realistically as possible. The code is applied to a laboratory column experiment, and subsequently used to demonstrate Chromatographic development of solute profiles in a freshening aquifer. Sequential peaks of Mg2+, K+, and Na+ along a flow path in the Aquia aquifer in Maryland are modeled, and the results confirm that the variation of water qualities in this aquifer has basically a Chromatographic origin. Proton exchange acts here as a source of acid in NaHCO3 water in which calcite dissolves. This explains the Na+ to HCO3- ratio and high ?13C observed in these waters.

Appelo, C. A. J.

1994-10-01

53

Theoretical rate coefficients for the exchange reaction OH + D--> OD + H.  

PubMed

In this work quasiclassical trajectory calculations were carried out to determine directly the rate coefficients for the isotopic exchange reaction, OH + D-->OD + H, using a potential-energy surface that carefully accounts for the long-range interactions. The calculated thermal rate coefficients are in good agreement with the experimental results. PMID:16497034

Wang, Wenli; Santos, Emanuel; Brando, Joo

2006-02-21

54

Further studies on vinamidinium salt amine exchange reactions, borohydride reductions and subsequent transformations  

PubMed Central

Studies directed at the amine exchange reaction of vinamidinium salts followed by sodium borohydride reduction to secondary and tertiary allylic amines are described. The tertiary allylic amines were alkylated and subjected to base mediated rearrangement to yield a variety of highly functionalized tertiary homoallylic amines.

Gupton, John T.; Telang, Nakul; Jia, Xin; Giglio, Benjamin C.; Eaton, James E.; Barelli, Peter J.; Hovaizi, Mona; Hall, Kayleigh E.; Welden, R. Scott; Keough, Matthew J.; Worrall, Eric F.; Finzel, Kara L.; Kluball, Emily J.; Kanters, Rene P.F.; Smith, Timothy M.; Smith, Stanton Q.; Nunes, Shane R.; Wright, Mathew T.; Birnstihl, Jennifer M.

2010-01-01

55

Ion Exchange Reactions in Soils and Plants: Three Year Summary Report.  

National Technical Information Service (NTIS)

This report covers activities during three years, including studies of ion exchange reactions of Cs with soil and clay materials and studies concerned with the effects of acid soil conditions on accumulation of ions by plants. During this period we commen...

W. A. Jackson D. L. Craig

1965-01-01

56

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

57

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

58

Exchange-diffusion reactions in HfSiON during annealing studied by Rutherford backscattering spectrometry, nuclear reaction analysis and narrow resonant nuclear reaction profiling  

NASA Astrophysics Data System (ADS)

HfSiON films deposited on Si (001) by reactive sputtering were submitted to rapid thermal annealing at 1000 C in vacuum, N2 and O2 atmospheres. The stability of the dielectric was evaluated by measuring the atomic transport and exchange of the chemical species, using Rutherford backscattering spectrometry, nuclear reaction analysis and narrow resonant nuclear reaction profiling. Annealing in O2 ambient reduced the N concentration mainly from near-surface regions where oxygen was incorporated in comparable amounts. Vacuum annealing, on the other hand, induced N loss preferentially from the Si/dielectric interface and O loss preferentially from near-surface regions. The results are explained in terms of exchange-diffusion reactions occurring in the HfSiON.

Miotti, L.; Bastos, K. P.; Soares, G. V.; Driemeier, C.; Pezzi, R. P.; Morais, J.; Baumvol, I. J. R.; Rotondaro, A. L. P.; Visokay, M. R.; Chambers, J. J.; Quevedo-Lopez, M.; Colombo, L.

2004-11-01

59

Competition between charge exchange and chemical reaction - The D2/+/ + H system  

NASA Technical Reports Server (NTRS)

Study of the special features of molecular charge exchange and its competition with chemical reaction in the case of the D2(+) + H system. The trajectory surface hopping (TSH) model proposed by Tully and Preston (1971) is used to study this competition for a number of reactions involving the above system. The diatomics-in-molecules zero-overlap approximation is used to calculate the three adiabatic surfaces - one triplet and two singlet - which are needed to describe this system. One of the significant results of this study is that the chemical reaction and charge exchange are strongly coupled. It is also found that the number of trajectories passing into the chemical regions of the three surfaces depends very strongly on the surface crossings.-

Preston, R. K.; Cross, R. J., Jr.

1973-01-01

60

Alkoxy/halogen exchange reaction of molybdenum complexes containing phosphite with boron trihalides  

SciTech Connect

The ability of boron trihalides, BX/sub 3/, to extract an OR group or halogens on a carbon atom has been applied to the preparation of transition-metal carbyne complexes from Fischer-type carbyne complexes and to the halogen exchange of transition-metal perfluoroalkyl carbonyl complexes. The specific reaction studied was that of fac-(Mo(bpy)-(CO)/sub 3/(P(OR)/sub 3/)) where bpy = 2,2'-bipyridine with BF/sub 3//center dot/OEt/sub 2/ and BCl/sub 3/. Reaction with the former resulted in replacement of one OR group by F, while in the latter reaction, two OR groups were replaced with two Cl atoms. In the first reaction, geometrical retention around the Mo atom was retained; but in the latter reaction, a change in geometry around the Mo atom was noted. 9 refs.

Nakazawa, H.; Ohta, M.; Yoneda, H.

1988-03-23

61

Nucleon-nucleon correlations detected via pion double-charge-exchange reactions  

SciTech Connect

Double-charge-exchange reactions induced by pions are shown to furnish a direct means of detecting nucleon-nucleon correlations in nuclei. For the particular case of double isobaric analog transitions the effect of correlations is easily isolated and quite strong. Examination of the properties of the position correlations implicit in the nuclear shell model provides an explanation of several experimentally observed features of double-charge-exchange reactions, including in particular, their dependence on the number of valence neutrons present. An explicit demonstration of the role played by nucleon-nucleon correlations is presented for the double-charge-exchange cross-sections of /sup 42/Ca, /sup 44/Ca and /sup 48/Ca, recently measured at LAMPF. Our analysis explains why the cross section for the double-charge-exchange reaction on /sup 48/Ca, in which 28 neutron pairs participate, is comparable and indeed smaller than the corresponding cross-section for /sup 42/Ca with its single valence neutron pair. It also predicts the variation of angular distributions over the family of isotopes. 13 refs., 3 figs.

Bleszynski, E.; Bleszynski, M.; Glauber, R.J.

1987-01-01

62

Hyperthermal O-atom exchange reaction O2 + CO2 through a CO4 intermediate.  

PubMed

O(2) and CO(2) do not react under ordinary conditions because of the thermodynamic stability of CO(2) and the large activation energy required for multiple double-bond cleavage. We present evidence for a gas-phase O-atom exchange reaction between neutral O(2) and CO(2) at elevated collision energies (approximately 160 kcal mol(-1)) from crossed-molecular-beam experiments. CCSD(T)/aug-cc-pVTZ calculations demonstrate that isotope exchange can occur on the ground triplet potential energy surface through a short-lived CO(4) intermediate that isomerizes via a symmetric CO(4) transition state containing a bridging oxygen atom. We propose a plausible adiabatic mechanism for this reaction supported by additional spin-density calculations. PMID:19743846

Yeung, Laurence Y; Okumura, Mitchio; Paci, Jeffrey T; Schatz, George C; Zhang, Jianming; Minton, Timothy K

2009-10-01

63

Dynamic NMR study of ligand exchange reactions in U(VI)-phosphonic acid systems  

SciTech Connect

The rates of hydrogen ion exchange on phosphonic acid ligands and that of phosphonate ligand exchange on selected uranyl-phosphonate complexes have been investigated by dynamic NMR spectroscopy. The spin-spin relaxation time (ln(1/T{sub 2})) for H{sup +} exchange on the fee ligands exhibits a parabolic dependence on reciprocal temperature (1/T (K{sup {minus}1})). The empirical fit parameters are correlated with the activation parameters ({Delta}H{sup *}, {Delta}S{sup *}, {Delta}C{sub p}{sup *}) by adapting the statistical mechanical framework developed by Braibanti et al. to the Eyring activated complex theory. The correlation of the apparent activation enthalpy with temperature indicates that 6--11 water molecules participate in the transition from reactants to activated complex for ligand proton exchange reactions, depending on the ligand. Mechanistic details of ligand exchange reactions of phosphonic acid complexants onto the corresponding uranium(VI) complexes are not fully developed, but the negative values for {Delta}S{sup *} imply increased order in the transition to the activated complex. Though {Delta}H{sup *} for ligand exchange covers a range of 15 kJ/mol, the free energy of activation ({Delta}G{sup *}) is nearly constant for the series of ligands, implying substantial entropy compensation in the activation process. Application of the Marcus relationship defines a correlation between {Delta}G{sup *} and the thermodynamic stability ({Delta}G{degree}) for the 1:2 uranyl complexes with methanediphosphonic acid and 1-hydroxyethane-1,1-diphosphonic acid.

Muntean, J.V.; Nash, K.L.; Rickert, P.G.; Sullivan, J.C. [Argonne National Lab., IL (United States). Chemistry Div.] [Argonne National Lab., IL (United States). Chemistry Div.

1999-05-06

64

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

65

Nitroxyl Radical plus Hydroxylamine Pseudo Self-Exchange Reactions: Tunneling in Hydrogen Atom Transfer  

PubMed Central

Bimolecular rate constants have been measured for reactions that involve hydrogen atom transfer (HAT) from hydroxylamines to nitroxyl radicals, using the stable radicals TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical), 4-oxo-TEMPO (2,2,6,6-tetramethyl-4-oxo-piperidine-1-oxyl radical), di-tert-butylnitroxyl (tBu2NO), and the hydroxylamines TEMPO-H, 4-oxo-TEMPO-H, 4-MeO-TEMPO-H (2,2,6,6-tetramethyl-N-hydroxy-4-methoxy-piperidine), and tBu2NOH. The reactions have been monitored by UV-vis stopped-flow methods, using the different optical spectra of nitroxyl radicals. The HAT reactions all have |?Go| ? 1.4 kcal mol?1 and therefore are close to self-exchange reactions. The reaction of 4-oxo-TEMPO + TEMPO-H ? 4-oxo-TEMPO-H + TEMPO occurs with k2H,MeCN = 10 1 M?1 s?1 in MeCN at 298 K (K2H,MeCN = 4.5 1.8). Surprisingly, the rate constant for the analogous deuterium atom transfer reaction is much slower: k2D,MeCN = 0.44 0.05 M?1 s?1 with k2H,MeCN/k2D,MeCN = 23 3 at 298 K. The same large kinetic isotope effect (KIE) is found in CH2Cl2, 23 4, suggesting that the large KIE is not caused by solvent dynamics or hydrogen bonding to solvent. The related reaction of 4-oxo-TEMPO with 4-MeO-TEMPO-H(D) also has a large KIE, k3H/k3D = 21 3 in MeCN. For these three reactions, the EaD EaH values, between 0.3 0.6 and 1.3 0.6 kcal mol?1, and the log(AH/AD) values, between 0.5 0.7 and 1.1 0.6, indicate that hydrogen tunneling plays an important role. The related reaction of tBu2NO + TEMPO-H(D) in MeCN has a large KIE, 16 3 in MeCN, and very unusual isotopic activation parameters, EaD EaH = ?2.6 0.4 and log(AH/AD) = 3.1 0.6. Computational studies, using POLYRATE, also indicate substantial tunneling in the (CH3)2NO + (CH3)2NOH model reaction for the experimental self-exchange processes. Additional calculations on TEMPO(/H), tBu2NO(/H), and Ph2NO(/H) self-exchange reactions reveal why the phenyl groups make the last of these reactions several orders of magnitude faster than the first two. By inference, the calculations also suggest why tunneling appears to be more important in the self-exchange reactions of dialkylhydroxylamines than of arylhydroxylamines.

Wu, Adam; Mader, Elizabeth A.; Datta, Ayan; Hrovat, David A.; Borden, Weston Thatcher; Mayer, James M.

2009-01-01

66

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

67

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

68

EXFOR systems manual: Nuclear reaction data exchange format. Revision 97/1  

SciTech Connect

This document describes EXFOR, the exchange format designed to allow transmission of nuclear reaction data between the members of the Nuclear Data Center Network. 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 rather than optimization of data processing in order to meet the diverse needs of the nuclear reaction data centers. 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 exchange format, as outlined, is designed to allow 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).

McLane, V. [ed.] [comp.

1997-07-01

69

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

70

Tuning anti-microbial activity of poly(4-vinyl 2-hydroxyethyl pyridinium) chloride by anion exchange reactions  

Microsoft Academic Search

A series of new bioactive polymers with pendant choline analogous group was prepared by anion exchange reaction direct at\\u000a the quaternary nitrogen of the polycation. Poly(4-vinyl 2-hydroxyethyl pyridinium) chloride was prepared in situ by simultaneous\\u000a polymerization and quaternization of 4-vinyl pyridine with 2-chloroethanol that also acts as catalyst. The counter anion (Cl?) of the polycation was exchanged by anion exchange

Sunil K. Sharma; Ghanshyam S. Chauhan; Reena Gupta; J.-H. Ahn

2010-01-01

71

Oxygen Isotope Exchange between Metabolites and Water during Biochemical Reactions Leading to Cellulose Synthesis.  

PubMed

Cellulose was produced heterotrophically from different carbon substrates by carrot tissue cultures and Acetobacter xylinum (a cellulose-producing bacterium) and by castor bean seeds germinated in the dark, in each case in the presence of water having known concentration of oxygen-18 ((18)O). We used the relationship between the amount of (18)O in the water and in the cellulose that was synthesized to determine the number and (18)O content of the substrate oxygens that exchanged with water during the reactions leading to cellulose synthesis. Our observations support the hypothesis that oxygen isotope ratios of plant cellulose are determined by isotopic exchange occurring during hydration of carbonyl groups of the intermediates of cellulose synthesis. PMID:16665045

Sternberg, L da S; Deniro, M J; Savidge, R A

1986-10-01

72

Effects of the anion salt nature on the rate constants of the aqueous proton exchange reactions.  

PubMed

The proton-transfer ground-state rate constants of the xanthenic dye 9-[1-(2-methyl-4-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (TG-II), recovered by Fluorescence Lifetime Correlation Spectroscopy (FLCS), have proven to be useful to quantitatively reflect specific cation effects in aqueous solutions (J. M. Paredes, L. Crovetto, A. Orte, J. M. Alvarez-Pez and E. M. Talavera, Phys. Chem. Chem. Phys., 2011, 13, 1685-1694). Since these phenomena are more sensitive to anions than to cations, in this paper we have accounted for the influence of salts with the sodium cation in common, and the anion classified according to the empirical Hofmeister series, on the proton transfer rate constants of TG-II. We demonstrate that the presence of ions accelerates the rate of the ground-state proton-exchange reaction in the same order than ions that affect ion solvation in water. The combination of FLCS with a fluorophore undergoing proton transfer reactions in the ground state, along with the desirable feature of a pseudo-dark state when the dye is protonated, allows one unique direct determination of kinetic rate constants of the proton exchange chemical reaction. PMID:22421957

Paredes, Jose M; Garzon, Andres; Crovetto, Luis; Orte, Angel; Lopez, Sergio G; Alvarez-Pez, Jose M

2012-04-28

73

Oxygen isotope evolution in the protosolar disk induced by isotopic exchange reactions  

NASA Astrophysics Data System (ADS)

Oxygen isotopic heterogeneity is one of the most extensively studied and debated topics in planetary science, though no consensus has been achieved yet. We quantitatively examine the role of exchange reactions in mass-dependent oxygen isotope fractionation during evaporation and recondensation of silicate melts in gas with isotopically identical and distinct gases. The results are applied to the CCAM line, mass-dependent oxygen isotopic fractionation of FUN inclusions, and oxygen isotopic variations of Allende chondrules. We examine the role of oxygen isotopic exchange for silicate melt and ambient gas during evaporation and recondensation in a closed system that monotonically cools from high temperature. Silicate dust aggregates are assumed to be instantaneously heated to an above liquidus temperature. There are three free parameters; one is the efficiency of the isotope ex-change, the second is the cooling rate of the system, and the third is the amount of initial oxygen in the ambient gas. We found following results : (1) Evolution of oxygen isotopic fractionation is decoupled with chemical fractionation of silicate melt; oxygen isotopic fractionation goes more rapidly than chemical fractionation, of which timing depends on the isotopic exchange efficiency. (2) Mass-dependent oxygen isotopic fractionation of silicate melt is suppressed by isotopic exchange during evaporation/recondensation. If isotopic exchange does not work, oxygen isotopic composition of silicate melt spheres after evaporation / recondensation becomes lighter than the initial one if the silicate and gas have identical oxygen isotopic composition due to more abundance of 16O in the gas. Isotopic exchange homogenizes the compositions effectively to result in the same composition between silicate and gas. (3) Cooling rate of the system affects the evolution time of oxygen isotopic mass fractionation, but the final composition is not affected. In a system with initially different oxygen isotopic compositions between silicate melt and gas, deviation from a straight mixing line to the ?18O-rich side on a three-oxygen isotope plot is inevitable through evaporation/recondensation and isotope exchange. (4) Abundance of oxygen in the initial gas largely affects the degree of deviation from a simple mixing line during the cooling process. The average oxygen abundance in gas of protosolar disk relative to that in silicate (~10), and silicate melt gets oxygen isotopic composition very close to the gas. (5) Isotopic exchange efficiency plays an important role on evolution and final oxygen isotopic composition of silicate melt heated in gas. Effective isotopic exchange largely suppresses mass dependent isotopoic fractionation, which tends to result in forming a straight "mixing line", whereas, smaller efficiency causes larger degree of mass-dependent isotopic fractionation, and deviation from a straight "mixing line" becomes larger. (6) A straight mixing line such as CCAM line requires the presence of oxygen in the ambient gas more than the average protosolar disk. (7) The mass-dependent oxygen isotope fractionation of FUN inclusions by ~40 or more is not achieved by evaporation in a closed system, and almost vacuum condition is required, which was possible by almost complete continuous separation of gas and silicate melt during evaporation. If FUN inclusions were formed from oxygen isotopically light solid, they have suffered a reaction between isotopically heavy gas after vacuum evaporation, where the gas abundance must have been more than 10 times of the average protosolar gas. In summary, a series of oxygen isotopic composition of CAIs and chondrules reflects the ambient physical conditions such as dust/gas ratio and dust/gas separation of a protosolar disk.

Nagahara, H.

2012-04-01

74

Neutron skin thickness of Zr90 determined by charge exchange reactions  

NASA Astrophysics Data System (ADS)

Charge exchange spin-dipole (SD) excitations of Zr90 are studied by the Zr90(p,n) and Zr90(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: 14812fm2. The neutron skin thickness of Zr90 is determined to be 0.070.04fm from the SD sum rule value.

Yako, K.; Sagawa, H.; Sakai, H.

2006-11-01

75

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

2013-03-01

76

Quantum statistical study of O + O2 isotopic exchange reactions: cross sections and rate constants.  

PubMed

Using a wave packet based statistical model, we compute cross sections and thermal rate constants for various isotopic variants of the O + O2 exchange reaction on a recently modified ab initio potential energy surface. The calculation predicts a highly excited rotational distribution and relatively cold vibrational distribution for the diatomic product. A small but important threshold effect was identified for the (16)O + 18O2 reaction, which is suggested to contribute to the experimentally observed negative temperature dependence of the rate ratio, k(18O + 16O2)/k(16O + 18O2). Despite reasonable agreement with quasiclassical trajectory results, however, the calculated thermal rate constants are smaller than experimental measurements by a factor from 2 to 5. The experimentally observed negative temperature dependence of the rate constants is not reproduced. Possible reasons for the theory-experiment discrepancies are discussed. PMID:16623456

Lin, Shi Ying; Guo, Hua

2006-04-27

77

Dynamics of the molecular and atomic mechanisms for the hydrogen-iodine exchange reaction.  

NASA Technical Reports Server (NTRS)

The molecular and atomic mechanisms for the hydrogen-iodine exchange reaction are treated theoretically by means of extensive classical trajectories calculated on a reasonable potential energy surface on which the single adjustable parameter is the iodine-core effective charge. The analysis shows the molecular mechanism to be dynamically forbidden, but gives an over-all rate constant for the atomic mechanism that is in agreement with the experimental values. It is indicated that the formation of a weak H2I complex plays an important dynamical role if the atomic mechanism is limited to reactions with collision complexes involving no more than two hydrogen atoms and two iodine atoms. Excellent agreement with experiment is obtained for the rate constant for the recombination I+I+H2 yields I2+H2 and its negative temperature coefficient.

Raff, L. M.; Thompson, D. L.; Sims, L. B.; Porter, R. N.

1972-01-01

78

Pt loaded carbon aerogel catalyst for catalytic exchange reactions between water and hydrogen gas  

NASA Astrophysics Data System (ADS)

We report development and characterization of platinum doped carbon aerogel catalyst for catalytic exchange reactions between water and hydrogen gas. The carbon aerogel with uniformly dispersed platinum nanoparticles was prepared by adding platinum precursor during the sol-gel process. Thereafter colloidal PTFE was mixed with the platinum doped carbon aerogel powder and coated on Dixon rings to obtain hydrophobic catalyst with required mechanical strength. Detailed studies have been carried out to observe the effect of physical characteristics of the catalyst powder (surface area and pore size of aerogels, Pt cluster size and its valence state etc) and the different coating parameters (PTFE to Pt-CA ratio and Pt loading on Dixon ring) on volume transfer rate (Ky.a) for H/D reaction. Ky.a values of ~0.8 m3 (STP).s-1. m-3 were obtained for Pt loading of 7% and Pt cluster size of 3 nm at atmospheric pressure.

Singh, Rashmi; Singh, Ashish; Kohli, D. K.; Singh, M. K.; Gupta, P. K.

2013-06-01

79

Excitation of vacuum UV transitions of alkali-metal atoms by charge-exchange reactions  

SciTech Connect

The authors investigate the vacuum UV radiation spectra of atoms and ions of Rb, Cs, He, Ne, and Ar in a discharge plasma of their mixtures at different concentration of metal vapors in rare gases. The reactions leading to population and deactivation of resonant states of rare-gas atoms were studied. The observation of lines 109.1, 119.6, and 124.7 nm, corresponding to the radiation transitions from the 5p{sup 5}5d6s{sup 4}P{sub 5/2} quasi-metastable autoionizing level of cesium, allowed the authors to estimate experimentally the cross section {sigma} = (9 {+-} 3) {center_dot} 10{sup {minus}15} cm{sup 2} of the charge-exchange reaction of the metastable cesium ion on the cesium atom, giving as a result the above-mentioned quasi-metastable state of cesium.

Ter-Avetisyan, S.A.; Nersisyan, G.Ts.; Papanyan, V.O. [Institute of Physical Research, Ashtarak (Armenia)

1995-03-01

80

Electrochemical study of the thermodynamics of hydrogen isotope exchange reactions in the water-hydrogen isotope exchange reactions in the water-hydrogen sulfide system  

SciTech Connect

The changes in thermodynamic functions ..delta..G/sup 0/, ..delta..H/sup 0/ and ..delta..S/sup 0/ for the solution phase isotope exchange reaction OD/sup -/(aqD) + HS/sup -/(aq) in equilibrium OH/sup -/(aq) + ..delta..S/sup -/(aqD) (1) at 298.15K were experimentally determined to be ..delta..G/sup 0/ = 1.555 +/- 0.054kJ, ..delta..H/sup 0/ = 3.65 +/- 0.53kJ and ..delta..S/sup 0/ = 7.0 +/- 1.8 JK/sup -1/ by cell potential measurement on electrochemical cells. Statistical-thermodynamical calculations were conducted based on an unhydrated species model and a hydrated species model. The results suggest that in aqueous solution, OH/sup -/ can be considered as existing in the monohydrated form H/sub 3/O/sub 2//sup -/, and HS/sup -/ can be considered a existing in the unhydrated form.

Chang, O.K.

1985-01-01

81

O2 activation by binuclear Cu sites: Noncoupled versus exchange coupled reaction mechanisms  

NASA Astrophysics Data System (ADS)

Binuclear Cu proteins play vital roles in O2 binding and activation in biology and can be classified into coupled and noncoupled binuclear sites based on the magnetic interaction between the two Cu centers. Coupled binuclear Cu proteins include hemocyanin, tyrosinase, and catechol oxidase. These proteins have two Cu centers strongly magnetically coupled through direct bridging ligands that provide a mechanism for the 2-electron reduction of O2 to a -2:2 side-on peroxide bridged species. This side-on bridged peroxo-CuII2 species is activated for electrophilic attack on the phenolic ring of substrates. Noncoupled binuclear Cu proteins include peptidylglycine -hydroxylating monooxygenase and dopamine -monooxygenase. These proteins have binuclear Cu active sites that are distant, that exhibit no exchange interaction, and that activate O2 at a single Cu center to generate a reactive CuII/O2 species for H-atom abstraction from the C-H bond of substrates. O2 intermediates in the coupled binuclear Cu enzymes can be trapped and studied spectroscopically. Possible intermediates in noncoupled binuclear Cu proteins can be defined through correlation to mononuclear CuII/O2 model complexes. The different intermediates in these two classes of binuclear Cu proteins exhibit different reactivities that correlate with their different electronic structures and exchange coupling interactions between the binuclear Cu centers. These studies provide insight into the role of exchange coupling between the Cu centers in their reaction mechanisms.

Chen, Peng; Solomon, Edward I.

2004-09-01

82

TraML--A Standard Format for Exchange of Selected Reaction Monitoring Transition Lists*  

PubMed Central

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.

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

2012-01-01

83

Dianion formation from anion-alkali metal charge exchange reactions: TCNQ^- + Na -> TCNQ^-- + Na^+  

NASA Astrophysics Data System (ADS)

The interaction of an electron with an anion is characterized by a long-range coulomb repulsion and a short range polarizability attraction giving rise to a coulomb barrier. The permanent addition of an extra electron to a negatively charged anion requires tunneling through the barrier or attachment of the electron over the top of this coulomb barrier followed by disposal of the excess energy. Charge-exchange collisions of an anion with an alkali atom utilize the latter channel to produce permanent dianions with cross sections of 1 ^2. We have previously examined the reaction TCNQ-F4^- + Xe -> TCNQ-F4^-- + Xe^+ and reported a delayed threshold and quantum phase interference effects in the charge exchange cross section.ootnotetextS. Yu. Ovchinnikov, et al. Phys. Rev. A, 73, 64704(2006) Employing sodium as the collision partner, the cross section is seen to increase with decreasing energy with a threshold below 180 eV (com). A new apparatus has been constructed to allow measurements down to energies below the expected threshold (41 eV, laboratory energy based upon a 1 eV second electron affinity). This method has been used to study the reaction TCNQ^- + NA -> TCNQ^-- + Na^+ and will provide one of the first measurements of second electron affinities for molecular anions.

Smith, Byron; Compton, Robert; Ovchinnikov, Serge; Holm, Anne; Nielsen, Steen

2011-10-01

84

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 Earths 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

85

A model theoretical study on ligand exchange reactions of CooA.  

PubMed

Rr-CooA is a CO-sensor heme protein, where binding of CO with the heme group stimulates a transcriptional activator activity of CooA. In this process, the heme undergoes a series of ligand exchanges. In the ferric form, the heme has Cys75 and Pro2 as the axial ligands. In the reduced ferrous form, the heme has His77 instead of Cys75 as an axial ligand with Pro2. Only in the reduced form, CooA can bind CO that replaces Pro2. Model calculations are carried out to elucidate the ligand exchange reactions of CooA. The coordinated proline is found to be the neutral, protonated form. The ligand exchange of cysteine for histidine is reproduced by a relatively small model. This exchange would be mainly due to difference in stability of the non-bonding sulfur p-orbital in Cys75 between the ferric and ferrous states. The selectivity of gas molecules among CO, NO, and O2 in the proteins is explained by the relative stability of products for Rr-CooA. This is also the case for Ch-CooA, where the amino group of the N-terminus and a histidine are coordinated to the iron ion both in the ferric and ferrous states. The ability to bind the gas molecules is a little stronger in Rr-CooA than in Ch-CooA. In the ferric form of Rr-CooA, heme is deformed to a ruffled form whereas heme is planar in the ferrous form, which leads to a red-shifted Q-band in the former. PMID:23511331

Ishida, Toshimasa; Aono, Shigetoshi

2013-04-28

86

Classical trajectory studies of alkali atom-alkali dimer exchange reactions : Na Li2 and Li Na2  

Microsoft Academic Search

The endoergic and exoergic alkali atom-alkali dimer exchange reactions, Na+Li2-->NaLi+Li and Li+Na2-->LiNa+Na, have been studied using classical trajectory methods on LEPS surfaces exhibiting shallow potential wells at small internuclear separations. For both systems the total reaction cross section, collision lifetime, differential reaction cross section and product energy disposal were calculated for a range of initial collisional energies. Comparison with the

J. C. Whitehead

1976-01-01

87

Isotope exchange reaction between 235UF5 nanoparticles and 238UF6 gas  

NASA Astrophysics Data System (ADS)

The equilibrium in the isotope exchange reaction between 235U-enriched UF5 nanoparticles and natural UF6 gas was experimentally investigated. From the relationship between the isotopic fraction of UF6 gas at equilibrium and the specific surface area of the UF5 nanoparticles, it was experimentally demonstrated for the first time that all UF5 molecules on the outermost layer of the particles participated in the reaction until the isotopic fraction of UF5 on the outermost layer became equal to that of the UF6 gas. A fast rate process during the early period of the reaction and a subsequent slow rate process were quantitatively observed. These facts contradict the previously reported assumption not supported by experimental evidence that the UF5 molecules in the underlying layer of the particle participate in the reaction. A new model based on our experimental findings was proposed. Our model suggests that there are two kinds of molecules on the outermost layer with different reactivities and all UF5 molecules on the outermost layer contribute to the reaction. The rate equations were derived from the proposed model and analytically solved. The time dependency of the isotopic fraction of the UF6 gas and UF5 particles was expressed by three kinetic parameters such as the rate constant of the high reactivity molecule, ks, the rate constant of the low reactivity molecule, ks', and the fraction of high reactivity molecules on the outermost layer, ?. Our model reproduced well all the experimental data determined in the present study with ks=5.510-20 cm3/(s molecules), ks'=4.510-22 cm3/(s molecules), and ?=0.078.

Kuga, Yoshikazu; Takeuchi, Kazuo

1998-03-01

88

Reprint of: A numerical modelling of gas exchange mechanisms between air and turbulent water with an aquarium chemical reaction  

NASA Astrophysics Data System (ADS)

This paper proposes a new numerical modelling to examine environmental chemodynamics of a gaseous material exchanged between the air and turbulent water phases across a gas-liquid interface, followed by an aquarium chemical reaction. This study uses an extended concept of a two-compartment model, and assumes two physicochemical substeps to approximate the gas exchange processes. The first substep is the gas-liquid equilibrium between the air and water phases, A(g)?A(aq), with Henry's law constant H. The second is a first-order irreversible chemical reaction in turbulent water, A(aq)+H2O?B(aq)+H+ with a chemical reaction rate ?A. A direct numerical simulation (DNS) technique has been employed to obtain details of the gas exchange mechanisms and the chemical reaction in the water compartment, while zero velocity and uniform concentration of A is considered in the air compartment. The study uses the different Schmidt numbers between 1 and 8, and six nondimensional chemical reaction rates between 10(?0) to 101 at a fixed Reynolds number. It focuses on the effects of the Schmidt number and the chemical reaction rate on fundamental mechanisms of the gas exchange processes across the interface.

Nagaosa, Ryuichi S.

2014-08-01

89

Delta excitations and shell-model information in heavy-ion, charge-exchange reactions  

NASA Technical Reports Server (NTRS)

We calculate total cross sections for coherent pion production using localized plane-wave approximations for the shell-structure of valence nucleons that are excited to delta particles in the intermediate state in the (12C, 12B) and (12C, 12N) charge-exchange, heavy-ion reactions. We find comparable agreement to projectile downshift data for 12C(12C, 12B)12N. Then we improve the formalism by replacing the localized plane wave bound states with harmonic oscillator states which are imbedded in a multipole expansion approach and calculate pion differential cross sections to test for the sensitivity of the spectra to the single-particle mass parameter.

Deutchman, P. A.; Maung, K. M.; Norbury, J. W.; Rasmussen, J. O.; Townsend, L. W.

1986-01-01

90

Direct calculation of equilibrium constants for isotopic exchange reactions by ab initio molecular orbital theory  

SciTech Connect

The ability of simple levels of ab initio molecular orbital theory to describe with reasonable accuracy the energetics of isotopic exchange processes is demonstrated. Three levels of ab initio molecular orbital theory have been surveyed. The first two levels are single-determinant Hartree-Foch methods utilizing the 3-21G split-valence and 6-31G* polarization basis sets. The third level, which is computationally the most complex, uses the 6-31G* basis set but allows for partial account of electron correlation by way of Moller-Plesset perturbation theory terminated at second order. Theoretical and spectroscopic equilibrium constants for reactions XH + XD reversible XD + H/sub 2/ where XD is a hydride of the first row of the periodic table are tabulated. (BLM)

Hout, R.F. Jr.; Wolfsberg, M.; Hehre, W.J.

1980-04-23

91

Pion nucleus single charge exchange reactions above the. delta. (1232) resonance  

SciTech Connect

Forward-angle differential cross sections for the (..pi../sup +/, ..pi../sup 0/) reaction leading to the Isobaric Analog State in the residual nuclei at 300, 425, 500 and 550 MeV have been measured. Targets ranged in mass from /sup 7/Li to /sup 208/Pb. A description of the experimental setup and the analysis is presented. The 0/sup 0/ cross sections are found to rise markedly between 300 and 425 MeV, contrary to the extrapolation from the lower energy data and to the behavior of the free pion-nucleon single charge exchange process. The angular distributions are sharply forward peaked. Systematics of the data indicate increased volume penetration with increasing pion beam energy. The cross sections are compared with the results of Glauber model calculations indicating the significance of higher order processes even at these energies. 67 refs., 40 figs., 22 tabs.

Rokni, S.H.

1987-06-01

92

Photo-induced hydrogen exchange reaction between methanol and glyoxal: formation of hydroxyketene.  

PubMed

We study the structure and photochemistry of the glyoxal-methanol system (G-MeOH) by means of FTIR matrix isolation spectroscopy and ab initio calculations. The FTIR spectra show that the non-hydrogen-bonded complex, G-MeOH-1, is present in an inert environment of solid argon. MP2/aug-cc-pVDZ calculations indicate that G-MeOH-1 is the most stable complex among the five optimized structures. The interaction energy partitioned according to the symmetry-adapted perturbation theory (SAPT) scheme demonstrates that the dispersion energy gives a larger contribution to the stabilization of a non-hydrogen-bonded G-MeOH-1 complex than compared to the hydrogen-bonded ones. The irradiation of G-MeOH-1 with the filtered output of a mercury lamp (lambda>370 nm) leads to its photo-conversion into the hydroxyketene-methanol complex HK-MeOH-1. The identity of HK-MeOH-1 is confirmed by both FTIR spectroscopy and MP2/aug-cc-pVDZ calculations. An experiment with deuterated methanol (CH(3)OD) evidences that hydroxyketene is formed in a photo-induced hydrogen exchange reaction between glyoxal and methanol. The pathway for the photo-conversion of G-MeOH-1 to HK-MeOH-1 is studied by a coupled-cluster method [CR-CC(2,3)]. The calculations confirm our experimental findings that the reaction proceeds via hydrogen atom exchange between the OH group of methanol and CH group of glyoxal. PMID:18613199

Mielke, Zofia; Mucha, Ma?gorzata; Bil, Andrzej; Golec, Barbara; Coussan, Stephane; Roubin, Pascale

2008-08-25

93

Isotope exchange reaction between tritiated water and hydrogen on SiC  

NASA Astrophysics Data System (ADS)

SiC has been considered as a primary candidate material for a first wall component in future fusion reactor because it has been claimed that SiC has excellent high-temperature properties, good chemical stability and low activation. However, the behavior of tritium on SiC has not been discussed yet. In this study, tritium trapping capacity on the surface of SiC was experimentally obtained at the temperature range of 25-800 C in consideration of tritium trapping to the experimental system. The capacity, which was independent of the water vapor pressure in the gas phase and the temperature, was determined as about 10 6 Bq/cm 2. The isotope exchange reaction rate between tritiated water in a gas phase and hydrogen on the surface was quantified at the temperature of 25, 500 and 700 C in consideration of the behavior of tritium trapping at change of experimental condition by the numerical curve fitting method applying the serial reactor model. The reaction rate was observed to be constant as 3.48 10 -5 m/s. Additionally tritium release behavior from the surface of SiC in water vapor atmosphere was predicted and compared with that for graphite and stainless steel.

Katayama, K.; Nishikawa, M.; Takeishi, T.

2003-11-01

94

Reversible Dissociation and Ligand-Glutathione Exchange Reaction in Binuclear Cationic Tetranitrosyl Iron Complex with Penicillamine  

PubMed Central

This paper describes a comparative study of the decomposition of two nitrosyl iron complexes (NICs) with penicillamine thiolic ligands [Fe2(SC5H11NO2)2(NO)4]SO45H2O (I) and glutathione- (GSH-) ligands [Fe2(SC10H17N3O6)2(NO)4]SO42H2O (II), which spontaneously evolve to NO in aqueous medium. NO formation was measured by a sensor electrode and by spectrophotometric methods by measuring the formation of a hemoglobin- (Hb-) NO complex. The NO evolution reaction rate from (I)??k1 = (4.6 0.1)10?3?s?1 and the elimination rate constant of the penicillamine ligand k2 = (1.8 0.2)10?3?s?1 at 25C in 0.05?M phosphate buffer, ?pH 7.0, was calculated using kinetic modeling based on the experimental data. Both reactions are reversible. Spectrophotometry and mass-spectrometry methods have firmly shown that the penicillamine ligand is exchanged for GS? during decomposition of 1.510?4?M (I) in the presence of 10?3?M GSH, with 76% yield in 24?h. As has been established, such behaviour is caused by the resistance of (II) to decomposition due to the higher affinity of iron to GSH in the complex. The discovered reaction may impede S-glutathionylation of the essential enzyme systems in the presence of (I) and is important for metabolism of NIC, connected with its antitumor activity.

Syrtsova, Lidia; Sanina, Natalia; Lyssenko, Konstantin; Kabachkov, Evgeniy; Psikha, Boris; Shkondina, Natal'ja; Pokidova, Olesia; Kotelnikov, Alexander; Aldoshin, Sergey

2014-01-01

95

Reversible dissociation and ligand-glutathione exchange reaction in binuclear cationic tetranitrosyl iron complex with penicillamine.  

PubMed

This paper describes a comparative study of the decomposition of two nitrosyl iron complexes (NICs) with penicillamine thiolic ligands [Fe2(SC5H11NO2)2(NO)4]SO4 5H2O (I) and glutathione- (GSH-) ligands [Fe2(SC10H17N3O6)2(NO)4]SO4 2H2O (II), which spontaneously evolve to NO in aqueous medium. NO formation was measured by a sensor electrode and by spectrophotometric methods by measuring the formation of a hemoglobin- (Hb-) NO complex. The NO evolution reaction rate from (I)??k 1 = (4.6 0.1)10(-3)?s(-1) and the elimination rate constant of the penicillamine ligand k 2 = (1.8 0.2)10(-3)?s(-1) at 25C in 0.05?M phosphate buffer, ?pH 7.0, was calculated using kinetic modeling based on the experimental data. Both reactions are reversible. Spectrophotometry and mass-spectrometry methods have firmly shown that the penicillamine ligand is exchanged for GS(-) during decomposition of 1.510(-4)?M (I) in the presence of 10(-3)?M GSH, with 76% yield in 24?h. As has been established, such behaviour is caused by the resistance of (II) to decomposition due to the higher affinity of iron to GSH in the complex. The discovered reaction may impede S-glutathionylation of the essential enzyme systems in the presence of (I) and is important for metabolism of NIC, connected with its antitumor activity. PMID:24790592

Syrtsova, Lidia; Sanina, Natalia; Lyssenko, Konstantin; Kabachkov, Evgeniy; Psikha, Boris; Shkondina, Natal'ja; Pokidova, Olesia; Kotelnikov, Alexander; Aldoshin, Sergey

2014-01-01

96

Mechanism of the anion exchange reactions of the layered double hydroxides (LDHs) of Ca and Mg with Al  

Microsoft Academic Search

The nitrate containing layered double hydroxide (LDH) of Ca with Al on reaction with aqueous solutions of Na2CO3 and Na3PO4 yields CaCO3 and Ca5(PO4)3OH respectively rather than the carbonate\\/phosphate containing LDHs. The LDH of Mg with Al on reacting with dissolved phosphate ions also leads to the formation of unitary phosphates. This shows that the anion exchange reactions of layered

A. V. Radha; P. Vishnu Kamath; C. Shivakumara

2005-01-01

97

Modelling of geochemical reactions and experimental cation exchange in MX 80 bentonite.  

PubMed

Bentonites are widely used for waste repository systems because of their hydrodynamic, surface and chemical-retention properties. MX 80 bentonite (bentonite of Wyoming) contains approximately 85% Na/Ca-montmorillonite and 15% accessory minerals. The dominant presence of Na/Ca-montmorillonite in this clay mineral could cause it to perform exceptionally well as an engineered barrier for a radioactive waste repository because this buffer material is expected to fill up by swelling the void between canisters containing waste and the surrounding ground. However, the Na/Ca-montmorillonite could be transformed to other clay minerals as a function of time under repository conditions. Previous modelling studies based on the hydrolysis reactions have shown that the Na/Ca-montmorillonite-to-Ca-montmorillonite conversion is the most significant chemical transformation. In fact, this chemical process appears to be a simple cation exchange into the engineered barrier. The purpose of the present study was two-fold. Firstly, it was hoped to predict the newly formed products of bentonite-fluid reactions under repository conditions by applying a thermokinetic hydrochemical code (KIRMAT: Kinetic Reactions and Mass Transport). The system modelled herein was considered to consist of a 1-m thick zone of water-saturated engineered barrier. This non-equilibrated system was placed in contact with a geological fluid on one side, which was then allowed to diffuse into the barrier, while the other side was kept in contact with iron-charged water. Reducing initial conditions ( [P(O)2 approximately equals 0] ; Eh=-200 mV) and a constant reaction temperature (100 degrees C) were considered. Secondly, it was hoped to estimate the influence of inter-layer cations (Ca and Na) on the swelling behaviour of the MX 80 bentonite by using an isothermal system of water vapour adsorption and an environmental scanning electron microscope (ESEM) coupled with a digital image analysis (DIA) program. Here, the MX 80 bentonite was previously treated with concentrated solutions (1N) of calcium and sodium chlorides. The results confirmed that the Na/Ca-montmorillonite-to-Ca-montmorillonite conversion was the main chemical transformation in the bentonite barrier under repository conditions. A simplified method (based on volume balance) has shown that the swelling capacity of the engineered barrier would be slightly affected after 1000 years of diffusion-reaction because the volume of neo-formed swelling clays is almost directly proportional to the volume of transformed initial-montmorillonite. Minimal neo-formation of saponites, vermiculites and chlorites was also observed. In addition, an isothermal system of water adsorption and ESEM-DIA methods showed that in the raw-bentonite-to-Ca-bentonite exchange there is a small decrease in the amount of adsorbed water and the swelling potential. PMID:15946786

Montes-H, G; Fritz, B; Clement, A; Michau, N

2005-10-01

98

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

99

Beyond personal LeaderMember Exchange (LMX) quality: The effects of perceived LMX variability on employee reactions  

Microsoft Academic Search

A fundamental tenet of LeaderMember Exchange (LMX) theory is that leaders develop different quality relationships with their employees; however, little research has investigated the impact of LMX differentiation on employee reactions. The current research investigates whether perceptions of LMX variability (the extent to which LMX relationships are perceived to vary within a team) affects employee job satisfaction and wellbeing beyond

Danica T. Hooper; Robin Martin

2008-01-01

100

Effect of the geometric phase on the dynamics of the hydrogen-exchange reaction  

NASA Astrophysics Data System (ADS)

A recent puzzle in nonadiabatic quantum dynamics is that geometric phase (GP) effects are present in the state-to-state opacity functions of the hydrogen-exchange reaction, but cancel out in the state-to-state integral cross sections (ICSs). Here the authors explain this result by using topology to separate the scattering amplitudes into contributions from Feynman paths that loop in opposite senses around the conical intersection. The clockwise-looping paths pass over one transition state (1-TS) and scatter into positive deflection angles; the counterclockwise-looping paths pass over two transition states (2-TS) and scatter into negative deflection angles. The interference between the 1-TS and 2-TS paths thus integrates to a very small value, which cancels the GP effects in the ICS. Quasiclassical trajectory (QCT) calculations reproduce the scattering of the 1-TS and 2-TS paths into positive and negative deflection angles and show that the 2-TS paths describe a direct insertion mechanism. The inserting atom follows a highly constrained ``S-bend'' path, which allows it to avoid both the other atoms and the conical intersection and forces the product diatom to scatter into high rotational states. By contrast, the quantum 2-TS paths scatter into a mainly statistical distribution of rotational states, so that the quantum 2-TS total ICS is roughly twice the QCT ICS at 2.3 eV total energy. This suggests that the S-bend constraint is relaxed by tunneling in the quantum system. These findings on H+H2 suggest that similar cancellations or reductions in GP effects are likely in many other reactions.

Juanes-Marcos, Juan Carlos; Althorpe, Stuart C.; Wrede, Eckart

2007-01-01

101

Kinetics and utilization studies of the oxygen reduction and hydrogen oxidation reactions in a proton exchange membrane fuel cell  

NASA Astrophysics Data System (ADS)

The current/voltage relation of a proton exchange membrane fuel cell (PEMFC) has been austerely studied through carefully designed experiments to support models developed theoretically using kinetic, thermodynamic and mass transport principles. In order to develop a complete model description of voltage losses for a PEMFC gas phase mass transport free environment, individual experiments on; (i) the kinetics of the hydrogen oxidation reaction (HOR); (ii) the kinetic dependence of the oxygen reduction reaction (ORR), occurring on a PVC catalyst, on oxygen partial pressure and cell temperature; (iii) the voltage loss associated with proton transport and distribution of the oxygen reduction reaction in a porous proton exchange membrane fuel cell cathode; (iv) the effect of relative humidity, or water content, on the kinetics of the oxygen reduction reaction were performed. These studies revealed that; (i) the voltage loss associated with the HOR is negligible due to its very high exchange current density (235--600 mA/cm2), (ii) the exchange current density, activation energy, and reaction order for the ORR are 2.5 x 10-8 A/cm2, 67 kJ/mol, and 0.5 respectively, (iii) the voltage loss resulting from a balance of proton transport and oxygen reduction reaction kinetics can be precisely predicted using a simple figure (4.2), which was developed from a solution to the conservation of charge equation in the cathode electrode and (iv) the effect of RH on ORR kinetics is negligible above 60% relative humidity. A PEMFC model that can accurately depict the voltage loss associated with each of the above material/process relationships was developed using differential cell experiments (i.e., experiments in which concentrations of reactants and products varied in only the through plane direction) and corresponding simplified 1-D models.

Neyerlin, Kenneth Charles (K. C.)

102

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

103

Noncatalytic kinetic study on site-selective H/D exchange reaction of phenol in sub- and supercritical water  

NASA Astrophysics Data System (ADS)

The site-selective H/D exchange reaction of phenol in sub- and supercritical water is studied without added catalysts. In subcritical water in equilibrium with steam at 210-240 C, the H/D exchange proceeds both at the ortho and para sites in the phenyl ring, with no exchange observed at the meta site. The pseudo-first-order rate constants are of the order of 10-4 s-1 50% larger for the ortho than for the para site. In supercritical water, the exchange is observed also at the meta site with the rate constant in the range of 10-6-10-4 s-1. As the bulk density decreases, the exchange slows down and the site selectivity toward the ortho is enhanced. The enhancement is due to the phenol-water interaction preference at the atomic resolution. The site selectivity toward the ortho is further enhanced when the reaction is carried out in benzene/water solution. Using such selectivity control and the reversible nature of the hydrothermal deuteration/protonation process, it is feasible to synthesize phenyl compounds that are deuterated at any topological combination of ortho, meta, and para sites.

Kubo, Masahito; Takizawa, Takeyuki; Wakai, Chihiro; Matubayasi, Nobuyuki; Nakahara, Masaru

2004-07-01

104

A Computational Study of a Recreated G Protein-GEF Reaction Intermediate Competent for Nucleotide Exchange: Fate of the Mg Ion  

Microsoft Academic Search

Small G-proteins of the superfamily Ras function as a molecular switches, interacting with different cellular partners according to their activation state. G-protein activation involves the dissociation of bound GDP and its replacement by GTP, in an exchange reaction that is accelerated and regulated in the cell by guanine-nucleotide exchange factors (GEFs). Large conformational changes accompany the exchange reaction, and our

Mriam Ben Hamida-Reba; Charles H. Robert

2010-01-01

105

Facile synthesis of magnetic metal (Mn, Fe, Co, and Ni) oxides nanocrystals via a cation-exchange reaction  

NASA Astrophysics Data System (ADS)

Magnetic metal (Mn, Fe, Co, and Ni) oxides nanocrystals with small size and uniform size distribution are synthesized via a cation-exchange reaction. Two experimental stages are included in the synthesis of metal oxides nanocrystals. Firstly, Cu(OH)2 decomposes to CuO nanocrystals, induced by free metal cations. Compared to CuO nanocrystals produced without any free metal cation, the free metal cation has an important influence on the shape and size of CuO. Secondly, free metal cations exchange with the Cu2+ cation in the CuO nanocrystals to get Mn3O4, Fe2O3, CoO and NiO nanocrystals by cation-exchange reactions. The magnetic properties of these metal oxides nanocrystals have been investigated, all the nanocrystals are superparamagnetic at room temperature.Magnetic metal (Mn, Fe, Co, and Ni) oxides nanocrystals with small size and uniform size distribution are synthesized via a cation-exchange reaction. Two experimental stages are included in the synthesis of metal oxides nanocrystals. Firstly, Cu(OH)2 decomposes to CuO nanocrystals, induced by free metal cations. Compared to CuO nanocrystals produced without any free metal cation, the free metal cation has an important influence on the shape and size of CuO. Secondly, free metal cations exchange with the Cu2+ cation in the CuO nanocrystals to get Mn3O4, Fe2O3, CoO and NiO nanocrystals by cation-exchange reactions. The magnetic properties of these metal oxides nanocrystals have been investigated, all the nanocrystals are superparamagnetic at room temperature. Electronic supplementary information (ESI) available: XPS of Fe2O3 nanoparticles, TEM images of Fe2O3 and Mn3O4 nanocrystals produced with different molar ratios of precursors, TEM images and XRD patterns of CuO nanocrystals produced without any free cations and XRD patterns of the transformation from Cu(OH)2 to metal oxide nanocrystals, photographs of color change when reaction solution was exposed to air. See DOI: 10.1039/c0nr00684j

Ning, Jiajia; Xiao, Guanjun; Wang, Li; Zou, Bo; Liu, Bingbing; Zou, Guangtian

2011-02-01

106

Synthesis of free-standing metal sulfide nanoarrays via anion exchange reaction and their electrochemical energy storage application.  

PubMed

Metal sulfides are an emerging class of high-performance electrode materials for solar cells and electrochemical energy storage devices. Here, a facile and powerful method based on anion exchange reactions is reported to achieve metal sulfide nanoarrays through a topotactical transformation from their metal oxide and hydroxide preforms. Demonstrations are made to CoS and NiS nanowires, nanowalls, and core-branch nanotrees on carbon cloth and nickel foam substrates. The sulfide nanoarrays exhibit superior redox reactivity for electrochemical energy storage. The self-supported CoS nanowire arrays are tested as the pseudo-capacitor cathode, which demonstrate enhanced high-rate specific capacities and better cycle life as compared to the powder counterparts. The outstanding electrochemical properties of the sulfide nanoarrays are a consequence of the preservation of the nanoarray architecture and rigid connection with the current collector after the anion exchange reactions. PMID:24809111

Xia, Xinhui; Zhu, Changrong; Luo, Jingshan; Zeng, Zhiyuan; Guan, Cao; Ng, Chin Fan; Zhang, Hua; Fan, Hong Jin

2014-02-26

107

The loss rates of O+ in the inner magnetosphere caused by both magnetic field line curvature scattering and charge exchange reactions  

NASA Astrophysics Data System (ADS)

With consideration of magnetic field line curvature (FLC) pitch angle scattering and charge exchange reactions, the O+ (>300 keV) in the inner magnetosphere loss rates are investigated by using an eigenfunction analysis. The FLC scattering provides a mechanism for the ring current O+ to enter the loss cone and influence the loss rates caused by charge exchange reactions. Assuming that the pitch angle change is small for each scattering event, the diffusion equation including a charge exchange term is constructed and solved; the eigenvalues of the equation are identified. The resultant loss rates of O+ are approximately equal to the linear superposition of the loss rate without considering the charge exchange reactions and the loss rate associated with charge exchange reactions alone. The loss time is consistent with the observations from the early recovery phases of magnetic storms.

Ji, Y.; Shen, C.

2014-03-01

108

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

NASA Astrophysics Data System (ADS)

The production cross sections of four N=127 isotones (207Hg, 206Au, 205Pt, and 204Ir) have been measured using (p,n) charge-exchange reactions, induced in collisions of a 208Pb 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.; Agramunt, J.; Algora, A.; Alkhomashi, N.; lvarez-Pol, H.; Boutachkov, P.; Bruce, A. M.; Cceres, L. S.; Casarejos, E.; Denis Bacelar, A. M.; Doornenbal, P.; Dragosavac, D.; Farrelly, G.; Gadea, A.; Gelletly, W.; Gerl, J.; Grska, M.; Grebosz, J.; Kojouharov, I.; Molina, F.; Prez-Loureiro, D.; Pietri, S.; Podolyk, Z.; Regan, P. H.; Rubio, B.; Shaffner, H.; Steer, S. J.; Tashenov, S.; Verma, S.; Wollersheim, H. J.

2011-07-01

109

Solid-state NMR studies of methanol-to-aromatics reaction over silver exchanged HZSM-5 zeolite  

Microsoft Academic Search

Solid-state NMR spectroscopy was used to study the conversion of methanol to aromatics (MTA) over silver exchanged HZSM-5 zeolites. It is the silver oxide rather than silver cation that plays a crucial role for the MTA reaction. The aromatic products (mainly toluene and benzene) are formed at the expense of the small alkanes (mainly propane and isobutane). AgZSM-5 zeolite calcined

Danlin Zeng; Jun Yang; Jiqing Wang; Jun Xu; Yongxia Yang; Chaohui Ye; Feng Deng

2007-01-01

110

Investigation of alkali ion exchange processes in waste glasses using Rutherford backscattering spectrometry and nuclear reaction analysis  

Microsoft Academic Search

A series of dissolution experiments using isotopic labeled (D2 18O) aqueous solution were carried out to investigate the ion exchange mechanism in Na2O-Al2O3-SiO2 glasses with fixed Na2O and variable Al2O3 concentrations. The sodium removal and the deuterium and oxygen uptake in the glass coupons were measured using ion beam methods such as Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis

V. Shutthanandan; Suntharampillai Thevuthasan; Donald R. Baer; Evan M. Adams; Saravanamuthu Maheswaran; Mark H. Engelhard; Jonathan P. Icenhower; B. Peter McGrail

2001-01-01

111

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

112

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

113

Inelastic process observed in charge-exchange reactions of 56Fe at 500 MeV/u  

NASA Astrophysics Data System (ADS)

The inelastic (IE) component of the reaction product, which is produced through charge-exchange reactions at relativistic energies of E ~ 1 GeV/u, is one of the hopeful probes used to study the nuclear medium effect on ? excitation. In the present study, the longitudinal-momentum (PL) distribution of 56Co, produced by bombarding C-and CH2-target with a primary beam of 56Fe at E=500 MeV/u, was observed by means of the spectrometer at HIMAC facility. The IE peak of 56Co, produced from H and C targets, was successfully observed in energy transfer spectrum. The behaviors of the IE peaks are consistent with those observed in previous experiments. A remarkable reduction of the energy transfer for the IE process was also observed with C target compared with H target. The present results have shown the feasibility to investigate the energy transfer in charge-exchange reactions for heavy reaction system at the energy down to 500 MeV/u.

Momota, S.; Yamaguchi, T.; Suzuki, T.; Suzuki, F.; Sato, K.; Yamaki, S.; Kouno, J.; Ozawa, A.; Nishikiori, R.; Nishimura, D.; Fukuda, M.; Suzuki, S.; Nagashima, M.; Kitagawa, A.; Sato, S.

2014-03-01

114

Quantal Study of the Exchange Reaction for N + N2 using an ab initio Potential Energy Surface  

NASA Technical Reports Server (NTRS)

The N + N2 exchange rate is calculated using a time-dependent quantum dynamics method on a newly determined ab initio potential energy surface (PES) for the ground A" state. This ab initio PES shows a double barrier feature in the interaction region with the barrier height at 47.2 kcal/mol, and a shallow well between these two barriers, with the minimum at 43.7 kcal/mol. A quantum dynamics wave packet calculation has been carried out using the fitted PES to compute the cumulative reaction probability for the exchange reaction of N + N2(J=O). The J - K shift method is then employed to obtain the rate constant for this reaction. The calculated rate constant is compared with experimental data and a recent quasi-classical calculation using a LEPS PES. Significant differences are found between the present and quasiclassical results. The present rate calculation is the first accurate 3D quantal dynamics study for N + N2 reaction system and the ab initio PES reported here is the first such surface for N3.

Wang, Dunyou; Stallcop, James R.; Huo, Winifred M.; Dateo, Christopher E.; Schwenke, David W.; Partridge, Harry; Kwak, Dochan (Technical Monitor)

2002-01-01

115

A homogeneous quenching resonance energy transfer assay for the kinetic analysis of the GTPase nucleotide exchange reaction.  

PubMed

A quenching resonance energy transfer (QRET) assay for small GTPase nucleotide exchange kinetic monitoring is demonstrated using nanomolar protein concentrations. Small GTPases are central signaling proteins in all eukaryotic cells acting as a "molecular switches" that are active in the GTP-state and inactive in the GDP-state. GTP-loading is highly regulated by guanine nucleotide exchange factors (GEFs). In several diseases, most prominently cancer, this process in misregulated. The kinetics of the nucleotide exchange reaction reports on the enzymatic activity of the GEF reaction system and is, therefore, of special interest. We determined the nucleotide exchange kinetics using europium-labeled GTP (Eu-GTP) in the QRET assay for small GTPases. After GEF catalyzed GTP-loading of a GTPase, a high time-resolved luminescence signal was found to be associated with GTPase bound Eu-GTP, whereas the non-bound Eu-GTP fraction was quenched by soluble quencher. The association kinetics of the Eu-GTP was measured after GEF addition, whereas the dissociation kinetics could be determined after addition of unlabeled GTP. The resulting association and dissociation rates were in agreement with previously published values for H-Ras(Wt), H-Ras(Q61G), and K-Ras(Wt), respectively. The broader applicability of the QRET assay for small GTPases was demonstrated by determining the kinetics of the Ect2 catalyzed RhoA(Wt) GTP-loading. The QRET assay allows the use of nanomolar protein concentrations, as more than 3-fold signal-to-background ratio was achieved with 50nM GTPase and GEF proteins. Thus, small GTPase exchange kinetics can be efficiently determined in a HTS compatible 384-well plate format. PMID:24760397

Kopra, Kari; Ligabue, Alessio; Wang, Qi; Syrjnp, Markku; Blaevit, Olga; Veltel, Stefan; van Adrichem, Arjan J; Hnninen, Pekka; Abankwa, Daniel; Hrm, Harri

2014-07-01

116

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

2011-12-15

117

Protonated serine octamer cluster: structure elucidation by gas-phase H/D exchange reactions.  

PubMed

The H/D exchange kinetics of the protonated serine octamer was investigated by both flow-tube and FT-ICR experiments. The exchange was observed to be bimodal in agreement with previous observations. Quantitative analysis of the experimental results led to site-specific H/D exchange rate constants on the basis of which the structures of both ion populations were deduced. We observe the two separate conformers exchanging 33 hydrogens each-in an independent manner and at different rates. This result was achieved through a probabilistic algorithm that groups together equivalent hydrogen atoms having equal rate constants. The slower exchanging population A is assigned an all-zwitterionic structure. Its faster exchanging counterpart B is assigned an all-neutral structure. Population A was found to be more stable toward collision-induced activation than population B. All of these findings are consistent with previous experimental results, thus comprising a self-consistent picture of the protonated serine octamer and its gas-phase properties. PMID:16838981

Mazurek, Ulf; Geller, Orit; Lifshitz, Chava; McFarland, Melinda A; Marshall, Alan G; Reuben, Bryan G

2005-03-17

118

Properties of lnAsxP1-x layer formed by P-As exchange reaction on (001)lnP surface exposed to As4 beam  

NASA Astrophysics Data System (ADS)

The P-As exchange reaction on InP surface exposed to As4 beam was studied using photoluminescence (PL) and x-ray diffraction measurements as well as ultra-high vacuum scanning tunneling microscopy observation. It was found that as high as 90 95% of P can be exchanged by As and that the average depth of exchange reaction increases with the increase of As exposure time, being as deep as 5.5 ML for a long exposure. The splitting of PL peak takes place when the reaction depth exceeds 2 ML and the number of the split subpeaks increases with the increase of As exposure time. The PL peak splitting originates from the fluctuation of well thickness, caused by formation of InAs islands for strain relief during the exchange reaction.

Yang, B. X.; He, L.; Hasegawa, H.

1996-03-01

119

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

120

Studies in the reaction-separation method for the preparation of barium chloride from barite using ion exchange  

SciTech Connect

The authors report the application of an ion-exchange process as a reaction-separation strategy for the preparation of barium chloride from barite ore and sodium chloride. Experimental studies were carried out to evaluate the process efficiency and purity/yield of barium chloride using a strong acid cation-exchange resin, Tulsion T-42. The effects of various process parameters such as concentration of barium sulfide and concentration of sodium chloride were investigated, and optimization of the experimental variables was attempted. The results indicate the developed strategy to be attractive and an alternative route to existing processes. The methodology developed has large potential for the inorganic chemical process industry in general.

Gokarn, A.N.; Gaikwad, A.G.; Phalak, C.A.; Bhandari, V.M. [National Chemical Lab., Pune (India). Chemical Engineering Div.] [National Chemical Lab., Pune (India). Chemical Engineering Div.

1999-06-01

121

The reaction mechanism for CD38. A single intermediate is responsible for cyclization, hydrolysis, and base-exchange chemistries.  

PubMed

Human recombinant CD38 catalyzes the formation of both cyclic ADP-ribose and ADP-ribose products from NAD+ and hydrolyzes cyclic ADP-ribose to ADP-ribose. The corresponding GDP products are formed from NGD+. The enzyme was characterized by substrate and inhibition kinetics, exchange studies, rapid-quench reactions, and stopped-flow-fluorescence spectroscopy to establish the reaction mechanism and energetics for individual steps. Noncyclizable substrates NMN+ and nicotinamide-7-deaza-hypoxanthine dinucleotide (7-deaza NHD+) were rapidly hydrolyzed by the enzyme. The kcat for NMN+ was 5-fold higher than that of NAD+ and has the greatest reported kcat of any substrate for CD38. 7-deaza-NHD+ was hydrolyzed at approximately one-third the rate of NHD+ but does not form a cyclic product. These results establish that a cyclic intermediate is not required for substrate hydrolysis. The ratio of methanolysis to hydrolysis for cADPR and NAD+ catalyzed by CD38 increases linearly with MeOH concentration. Both reactions produce predominantly the beta-methoxy riboside compound, with a relative nucleophilicity of MeOH to H2O of 11. These results indicate the existence of a stabilized cationic intermediate for all observed chemistries in the active site of CD38. The partitioning of this intermediate between cyclization, hydrolysis, and nicotinamide-exchange unites the mechanisms of CD38 chemistries. Steady-state and pre-steady-state parameters for the partition and exchange mechanisms allowed full characterization of the reaction coordinate. Stopped-flow methods indicate a burst of cGDPR formation followed by the steady-state reaction rate. A lag phase, which was NGD+ concentration dependent, was also observed. The burst size indicates that the dimeric enzyme has a single catalytic site formed by two subunits. Pre-steady-state quench experiments did not detect covalent intermediates. Nicotinamide hydrolysis of NGD+ precedes cyclization and the chemical quench decomposes the enzyme-bound species to a mixture of cyclic and hydrolysis products. The time dependence of this ratio indicated that nicotinamide bond-breakage occurs 4 times faster than the conversion of the intermediate to products. Product release is the overall rate-limiting step for enzyme reaction with NGD+. PMID:9748331

Sauve, A A; Munshi, C; Lee, H C; Schramm, V L

1998-09-22

122

Calculated formation and reaction energies of 3d transition metal oxides using a hierachy of exchange-correlation functionals  

NASA Astrophysics Data System (ADS)

The formation and oxidation reaction energies of 16 transition metal oxides (TMOs) are benchmarked against experiments with an increasing complexity of the exchange-correlation (xc) functionals: PBE, PBE + U with a single U for each transition metal element, PBE0 (25% exact exchange included), EXX (100% exact exchange), and EXX + RPA (random phase approximation for the correlation energy). Although rather challenging on standard CPU computing facilities, the RPA calculations were performed efficiently on graphic processing units (GPUs). For the formation energies, the PBE + U, PBE0, EXX + RPA improves significantly over PBE with mean absolute errors (MAE) of 0.83 (PBE), 0.39 (PBE + U), 0.34 (PBE0), and 0.39 (EXX + RPA) eV per oxygen. In addition, EXX + RPA improves over the other xc functionals on the oxidation reaction energies, with MAE of 0.27 (PBE), 0.28 (PBE + U), 0.30 (PBE0), to 0.13 (EXX + RPA) eV per oxygen. The distinct trend observed for the calculated oxidation reaction energies compared to the formation energies is due to that the errors in formation energies for PBE and EXX + RPA are systematic; while for PBE + U and PBE0 the deviations have both signs, so that the error cancellations between different valence states work better for PBE and EXX + RPA. Finally, we compared the performance of the EXX + RPA for total energies and G0W0, which uses the random phase approximation in constructing the W kernel, for band gaps, and discuss a few challenges for the EXX + RPA method on TMOs.

Yan, Jun; Nrskov, Jens K.

2013-12-01

123

Ab initio study of the H + HONO reaction: Direct abstraction versus indirect exchange processes  

Microsoft Academic Search

The mechanism of the H + HONO reaction (for which no experimental data are available) has been elucidated by ab initio molecular orbital calculations using modified G2 and BAC-MP4 methods. These results indicate that the reaction occurs predominantly by two indirect metathetical processes. One produces OH + HNO and HO + NO from the decomposition of vibrationally excited hydroxyl nitroxide,

C.-C. Hsu; M. C. Lin; A. M. Mebel; C. F. Melius

1997-01-01

124

Shrinking core model for multispecies uptake onto an ion exchange resin involving distinct reaction fronts  

Microsoft Academic Search

A shrinking core model is derived for multispecies ion exchange when the counter-ions advance through the resin at different rates, leading to regions with distinctly different occupancies across the particle profile. The model generalizes an earlier version by accounting for the displacement between the various ions at the interfaces separating the regions. The model is applied to the uptake of

Mark Pritzker

2005-01-01

125

Nucleon exchange properties of the E / A =8. 5 MeV sup 74 Ge+ sup 165 Ho reaction  

SciTech Connect

Mass and charge distributions have been measured for damped projectile-like fragments in the reaction {sup 74}Ge+{sup 165}Ho at 8.5 MeV per nucleon bombarding energy. Coincidences were measured between {ital Z}- and {ital A}-identified projectile-like fragments and angle-correlated heavy reaction partners in order to derive the primary mass distribution for projectile-like fragments. Centroids and variances of the primary and post-evaporative {ital Z}, {ital N}, and {ital A} distributions are presented. The evolution of the primary {ital N} and {ital Z} distributions as a function of energy loss is found to deviate from predictions of the nucleon exchange transport model.

Planeta, R.; Kwiatkowski, K.; Zhou, S.H.; Viola, V.E. (Department of Chemistry, Indiana University, Bloomington, Indiana 47405 (USA) Indiana University Cyclotron Facility, Indiana University, Bloomington, Indiana 47405 (USA)); Breuer, H. (Department of Physics, University of Maryland, College Park, Maryland 20742 (USA)); McMahan, M.A. (Accelerator and Fusion Research Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720 (USA)); Kehoe, W.; Mignerey, A.C. (Department of Chemistry, University of Maryland, College Park, Maryland 20742 (USA))

1990-03-01

126

On the size evolution of monolayer-protected gold clusters during ligand place-exchange reactions: the effect of solvents.  

PubMed

Ligand place-exchange (LPE) reactions are extensively applied for the post-functionalization of monolayer-protected gold clusters (MPCs) by using excessive incoming ligands to displace initial ones. However, the modified MPCs are often enlarged or degraded; this results in ill-defined size-dependent properties. The growth of MPCs essentially involves an unprotected surface that is subsequently has gold atoms added or is fused with other gold cores owing to collision. Reported herein is a guideline for the selection of solvents to suppress unwanted MPC growth. Favorable solvents are those with significant affinity to gold or with low solubility for desorbed ligands because these properties retard LPE reactions and minimize the time available for unprotected gold cores. This finding provides a general and convenient approach to regulate the size of functionalized MPCs. PMID:24347109

Kuo, Chun-Ting; Chen, Chiu-Feng; Gu, Meng-Wen; Su, Man-Nung; Huang, Jhih-Fong; Huang, Min-Jie; Chen, Chun-Hsien

2014-03-01

127

Mechanism of C-3 hydrogen exchange and the elimination of ammonia in the 3-methylaspartate ammonia-lyase reaction.  

PubMed

The enzyme 3-methylaspartate ammonia-lyase (EC 4.3.1.2) catalyzes the exchange of the C-3 hydrogen of the substrate, (2S,3S)-3-methylaspartic acid, with solvent hydrogen. The mechanism of the exchange reaction was probed using (2S,3S)-3-methylaspartic acid and its C-3-deuteriated isotopomer. Incubations conducted in tritiated water allowed the rate of protium or deuterium wash-out from the substrates to be measured as tritium wash-in. The primary deuterium isotope effects for the exchange under essentially Vmax conditions ( [S] much greater than Km) were 1.6, 1.5, and 1.5 at pH 9.0, 7.6, and 6.5. The deamination reaction, measured spectrophotometrically on the same incubations, showed isotope effects of 1.7, 1.6, and 1.4 at pH 9.0, 7.6, and 6.5, in agreement with the values of DV and D(V/K) reported previously [Botting, N.P., Akhtar, M., Cohen, M.A., & Gani, D. (1988) Biochemistry 27, 2956-2959]. The ratio of the rate of exchange to the rate of deamination, however, varied widely with pH. Together with the identical values of the primary isotope effects for the two reactions, this result indicates that the partition between reaction pathways occurs after the slowest steps in the common part of the reaction coordinate pathway, almost certainly after the cleavage of the C-N bond at the level of the enzyme-ammonia-mesaconic acid complex, and not at the putative carbanion level as was previously suggested. The enzyme requires both K+ and Mg2+ ions for activity, although ammonium ion is also able to bind in the K+ site and act as an activator. Variation of the metal ion concentration alters the magnitude of the primary deuterium isotope effects. The variation of potassium ion concentration causes the most marked changes: at 1.6 mM K+, DV and D(V/K) are 1.7, whereas at 50 mM K+, DV and D(V/K) are reduced to 1.0. The isotope effects are also reduced at low K+ concentration due to the emergence of a slow-acting high K+ affinity monopotassium form of the enzyme. The binding order and role of the metal ion cofactors and their influence in determining the formal mechanism of the reaction is discussed, and the failure of previous workers to observe primary deuterium isotope effects for the deamination process is explained. The product desorption order was tested by product inhibition, alternative product inhibition, and isotope exchange experiments. Ammonia and mesaconic acid debind in a random fashion.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:1531295

Botting, N P; Gani, D

1992-02-11

128

Hyporheic Exchange and Humic Redox Reactions in an Alpine Stream/Wetland Ecosystem  

NASA Astrophysics Data System (ADS)

We studied the influence of hyporheic zone interactions on the redox state of the humic fraction of dissolved organic material and other redox active species in an alpine stream in the Colorado Front Range, USA. A constant-injection tracer experiment was conducted using bromide (Br-) to determine hydrologic characteristics of the stream system. The information gained from this experiment allowed us to determine that there were high rates of exchange between the main stream channel and a storage zone with a large cross-sectional area. Fluorescence spectroscopy results showed that the humic substances in filtered whole water samples from the hyporheic zone were more reduced than humic substances from the stream. Our results suggest that through hyporheic exchange reduced humic substances are transported from the hyporheic zone to the stream where they are being rapidly oxidized. In turn, hyporheic exchange from the stream carries water containing oxidized humic substances back to the hyporheic zone. These results indicate that hyporheic zone interactions influence the oxidation state of dissolved humic substances as well as other redox active species and may play an important role in determining energy flow through the entire stream system.

Miller, M.; McKnight, D.; Cory, R.; Williams, M.; Runkel, R.

2005-12-01

129

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

130

Sequential chemical bath deposition of Cu(2-x)Se/CdS film by suppressing ion-exchange reaction.  

PubMed

Chemical bath deposition is an attractive technique to form single- and multilayered metal oxide/chalcogenide films on electrode surfaces. However, the occurrence of desorption and/or ion-exchange reaction during subsequent chemical bath deposition has so far limited preparation of multilayered metal oxide/chalcogenide films. In this paper, we report a method to prevent desorption and ion-exchange reaction of metal oxide/chalcogenide on electrode surfaces using a polyelectrolyte multilayer during sequential chemical bath deposition. By controlling the ion permeability of the polyelectrolyte multilayer, Cu(2-x)Se film was successfully deposited on the CdS film. The Cu(2-x)Se/CdS film is confirmed by UV-vis absorption spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis, and X-ray powder diffractometer. Furthermore, the Cu(2-x)Se/CdS films were investigated as photoinduced charge transfer devices which showed photocurrents of 0.22 mA/cm(2) under illumination (I = 100 mW/cm(2)). PMID:22650229

Cai, Gangri; Lim, Iseul; Lee, Deok Yeon; Shrestha, Nabeen K; Lee, Joong Kee; Nah, Yoon-Chae; Lee, Wonjoo; Han, Sung-Hwan

2012-06-21

131

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

NASA Astrophysics Data System (ADS)

The time-delayed forward scattering mechanism recently identified by Althorpe et al. [Nature (London) 416, 67 (2002)] for the H+D2(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.

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

2008-04-01

132

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

NASA Astrophysics Data System (ADS)

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 3A'' and 3A' 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 coe?cients 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 coe?cients 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.

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

2013-09-01

133

Excitation of the delta Resonance in Relativistic Heavy Ion Charge Exchange Reactions.  

National Technical Information Service (NTIS)

Excitation of the delta resonance has been observed for the first time in a heavy ion reaction. The strength of the delta signal depends on the projectile nuclear structure. In the same incident energy range, about 900 MeV per nucleon, we observe - a stro...

M. Roy-Stephan D. Bachelier J. L. Boyard

1985-01-01

134

Charge exchange (p,n) reactions to the isobaric analog states of high Z nuclei: 73<=Z<=92  

NASA Astrophysics Data System (ADS)

Differential cross sections have been measured for the (p,n) reaction to the isobaric analog states of 181Ta, 197Au, 209Bi, 232Th, and 238U at an incident energy of 27 MeV. Because of the importance of collective effects in this mass region, coupled-channel calculations have been carried out in the analysis of the data. Optical potentials obtained from the Lane model for the charge exchange reaction have been used in the simultaneous analysis of coupled proton and neutron channels. The sensitivity of the calculations to the different couplings between the levels and to the magnitude of the isovector potentials, V1 and W1, is discussed. The good agreement obtained between the measured and calculated (p,n) angular distributions to the analog state confirms the validity of the Lane formalism for high-Z nuclei (Z>=50). Elastic neutron differential cross sections inferred from the coupled-channel analysis are compared with measurements available in the literature in the energy range 7-8 MeV. The results of these calculations agree with the measured values as well as the results of calculations made using global neutron optical potential parameters optimized to fit neutron data. NUCLEAR REACTIONS 181Ta, 197Au, 209Bi, 232Th, 238U(p,n)IAS; E=27 MeV; Measured ?(?) for ground-state analog transition; deduced (n,n)?(?), E=7-8 MeV; coupled-channel analysis.

Hansen, L. F.; Grimes, S. M.; Poppe, C. H.; Wong, C.

1983-11-01

135

Ion exchange kinetics of cesium for various reaction designs using crystalline silicotitanate, UOP IONSIV IE-911  

NASA Astrophysics Data System (ADS)

Through collaborative efforts at Texas A&M University and Sandia National Laboratories, a crystalline silicotitanate (CST), which shows extremely high selectivity for radioactive cesium removal in highly concentrated sodium solutions, was synthesized. The effect of hydrogen peroxide on a CST under cesium ion exchange conditions has been investigated. The experimental results with hydrogen peroxide showed that the distribution coefficient of cesium decreased and the tetragonal phase, the major component of CST, slowly dissolved at hydrogen peroxide concentrations greater than 1 M. A simple and novel experimental apparatus for a single-layer ion exchange column was developed to generate experimental data for estimation of the intraparticle effective diffusivity. A mathematical model is presented for estimation of effective diffusivities for a single-layer column of CST granules. The intraparticle effective diffusivity for Cs was estimated as a parameter in the analytical solution. By using the least square method, the effective diffusivities of 1.56 +/- 0.14 x 10-11 m2/s and 0.68 +/- 0.09 x 10-11 m2/s, respectively, were obtained. The difference in the two values was due to the different viscosities of the solutions. A good fit of the experimental data was obtained which supports the use of the homogeneous model for this system. A counter-current ion exchange (CCIX) process was designed to treat nuclear waste at the Savannah River Site. A numerical method based on the orthogonal collocation method was used to simulate the concentration profile of cesium in the CCIX loaded with CST granules. To maximize cesium loading onto the CST and minimize the volume of CST, two design cases of a moving bed, where the fresh CST is pulsed into the column at certain periods or at certain concentration of cesium, were investigated. Simulation results showed that cesium removal behavior in the pilot-scale test of CCIX experiment, where the column length is 22 ft and the CST is pulsed 1 ft in every 24 hours, was well predicted by using the values of the effective diffusivities of 1.0 to 6.0 x 10 -11 m2/s.

Kim, Sung Hyun

136

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

137

Viking gas exchange reaction - Simulation on UV-irradiated manganese dioxide substrate  

NASA Technical Reports Server (NTRS)

The exchange of O2 for H2O, analogous to that recorded on Mars by the Viking GEX experiment, has been observed on humidifying powdered beta-MnO2 (pyrolusite) which had been irradiated by UV in a humidified analog of the Martian atmosphere. Pyrolusite irradiated in a dry atmosphere did not release O2 on humidification. The XPS spectra of Mn and O of the reactive pyrolusite were shifted toward higher binding energies during UV irradiation. These shifts are consistent with the creation of a surface layer of a Mn(V) or Mn(VI) compound. The destruction of such a layer on humidification could account for the observed O2 release. Although manganese has not been identified in the Martian regolith, the upper limit of the Mn concentration is sufficiently high that O2 release from pyrolusite could have been responsible for the results of the Viking GEX experiment.

Blackburn, T. R.; Holland, H. D.; Ceasar, G. P.

1979-01-01

138

Solvent effects on the kinetics of the chlorine isotopic exchange reaction between chloride ion and O,O-diphenyl phosphorochloridate or O,O-diphenyl phosphorchloridothioate  

SciTech Connect

The effect of solvent on the kinetics of the chlorine isotopic exchange reaction between /sup 36/Cl- ions and O,O-diphenyl phosphorochloridate or O,O-diphenyl phosphorochloridothioate has been investigated in nitromethane, acetonitrile, propylene carbonate, benzonitrile, nitrobenzene, and hexamethyl-phosphoric triamide. The rate constants decrease with increasing electrophilicity of the solvent. A good correlation between the logarithm of the rate constants and acceptor number (AN) of the solvent was obtained with identical slopes for reactions with phosphoryl and thiophosporyl compounds. The slopes for the dependence of ..delta..H or T..delta..S vs. AN for chlorine isotopic exchange in (PHO)/sub 2/ pace are opposite those for the exchange reaction in (PHO)/sub 2/ PSCl, so a constant ratio of k/sub p=O//k/sub p=s/ is observed, resulting from compensation of ..delta..H by ..delta..S. The effect of solvent on the initial state (from solubility measurements) and the transition state of the reaction between (PhO)/sub 2/PSCl and the Cl- ion was evaluated. Changes of solvation of (PHO)/sub 2/ PSCE have practically no effect on the kinetics of the reactions. Changes of solvation of the chloride ion and of the transition state primarily influence the rate constants and activation parameters of the investigated isotopic-exchange reaction.

Mikolajczyk, M. (Polish Academy of Sciences, Boczna, Poland); Slebocka-Tilk, H.; Reimschussel, W.

1982-03-26

139

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

PubMed Central

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

2010-01-01

140

On the possibility to measure nuclear matrix elements of neutrinoless double beta decay in charge-exchange reactions  

NASA Astrophysics Data System (ADS)

As shown in Rodin and Faessler (2009) [7], the Fermi nuclear matrix element MF0? of neutrinoless double beta (0???) decay can be reconstructed if one is able to measure the isospin-forbidden single Fermi transition matrix element from the ground state of the final nucleus to the isobaric analog state (IAS) of the initial nucleus, for instance by means of charge-exchange reactions of the (n,p)-type. Here, simple estimates for 82Se are made which show that indeed the tiny cross-section ?(0f+?IAS) is dominated by the admixture of the double IAS in the ground state of the final nucleus provided that the isospin mixing is weak and can be treated perturbatively. A measurement of such a cross-section would definitely be a very difficult task, but it can advance a lot our knowledge of the 0??? nuclear matrix element.

Rodin, Vadim; Faessler, Amand

2011-04-01

141

Hydrogen bonding induced proton exchange reactions in dense D2-NH3 and D2-CH4 mixtures  

NASA Astrophysics Data System (ADS)

We have investigated high-pressure behaviors of simple binary mixtures of NH3 and D2 to 50 GPa and CH4 and D2 to 30 GPa using confocal micro-Raman spectroscopy. The spectral data indicate strong proton exchange reactions occur in dense D2-NH3 mixture, producing different isotopes of ammonia such as NH3, NH2D, NHD2, and ND3. In contrast, the proton exchange process in dense D2-CH4 mixture is highly limited, and no vibration feature is apparent for deuterated methane. The vibrational modes of H2 isotopes in D2-NH3 are blue shifted from those of pure H2 isotopes, whereas the modes of D2-CH4 show overall agreement with those in pure D2 and CH4. In turn, this result advocates the presence of strong repulsion and thereby internal pressure in D2-NH3 mixture, which are absent in D2-CH4. In fact, the bond length of hydrogen molecules in D2-NH3, calculated from the present spectral data, is shorter than that observed in pure hydrogen - supporting the enhanced intermolecular interaction in the mixture. Comparing the present spectral results with those previously observed in D2-H2O mixtures further suggests that the strength of repulsive interaction or the magnitude of internal pressure in the mixtures is proportional to the strength of hydrogen bonding in H2O, NH3, and CH4 in decreasing order. Hence, we suggest that the proton exchange is assisted by hydrogen bonding in these molecules.

Borstad, Gustav M.; Yoo, Choong-Shik

2014-01-01

142

Drug interactions with potential rubber closure extractables. Identification of thiol-disulfide exchange reaction products of captopril and thiurams.  

PubMed

Mixtures of thiuram disulfides are frequently used as accelerators in rubber stoppers for injectables and sterilized powders for injection. Rapid reactions of thiuram disulfides between themselves and with thiols yield mixed disulfides due to thiol-disulfide exchange. The possibility of exchange reactions of thiuram disulfides extracted from rubber stoppers and drug products containing pendant thiol groups have not been reported in the analysis of potential stopper extractables. In this paper we report the formation and identification of mixed thiuram disulfides of N,N,N',N'-dimethylthiuram disulfide (TMTD), N,N,N',N'-dibutylthiuram disulfide (TBTD), and captopril (a thiol-containing drug). A reversed-phase HPLC method was developed for the determination of TMTD, TBTD, captopril and their disulfides in aqueous vehicles, using a YMC ODS AQ column at 35 degrees C and mobile phases A and B consisting of acetonitrile:water:trifluoroacetic acid (TFA) (20:80:0.1) and acetonitrile:TFA (100:0.1), respectively. The captopril-TBTD and captopril-TMTD disulfides were identified by MS, with molecular ions at m/z 420.9 and m/z of 337.1, respectively. Possible structures for the fragment ions in the spectra are provided. Mixed captopril-thiuram formation was studied as a function of pH. Captopril-TMTD formation was enhanced at pH 6.0, reaching a maximum of 31.3% in 4.1h. At pH 4.0 and 2.2, the mixed captopril adduct product was still detected in solution after 20h. The impact of the formation of mixed disulfide products of thiol-containing drugs with thiurams in the HPLC profile of extractables and leachables studies is discussed. PMID:19041978

Corredor, Claudia; Tomasella, Frank P; Young, Joel

2009-01-01

143

Simple ligand exchange reactions enabling excellent dispersibility and stability of magnetic nanoparticles in polar organic, aromatic, and protic solvents.  

PubMed

The use of magnetic nanoparticles (MNPs) in real-world applications is often limited by the lack of stable solutions of monodisperse NPs in appropriate solvents. We report a facile one-pot ligand exchange reaction that is fast, efficient, and thorough for the synthesis of hydrophilic MNPs that are readily dispersed in polar organic and protic solvents (polarity index = 3.9-7.2) including alcohols, THF, DMF, and DMSO for years without precipitation. We emphasize the rational selection of small-molecule ligands such as 4-hydroxybenzoic acid (HBA), 3-(4-hydroxyphenyl)propionic acid (HPP), and gallic acid (GAL) that provide strong bonding with the MNP (FePt and FeOx) surfaces, hydrophilic termini to match the polarity of target solvents, and offer the potential for hydrogen-bonding interactions to facilitate incorporation into polymers and other media. Areal ligand densities (?) calculated based on the NP core size from transmission electron microscopy (TEM) images, and the inorganic fractions of NPs derived from thermogravimetric analysis (TGA) indicated a significant (2-4 times) increase in the ligand coverage after the exchange reactions. Fourier transform infrared spectrometry (FTIR) and (1)H nuclear magnetic resonance (NMR) studies also confirmed anchoring of carboxyl groups on NP surfaces. In addition, we demonstrate a facile one-step in situ synthesis of FePt NPs with aromatic ligands for better dispersibility in solvents of intermediate polarity (polarity index = 1.0-3.5) such as toluene, chlorobenzene, and dichloromethane. The creation of stable dispersions of NPs in solvents across the polarity spectrum opens up new applications and new processing widows for creating NP composites in a variety of host materials. PMID:24460074

Wang, Xinyu; Tilley, Richard D; Watkins, James J

2014-02-18

144

Additional Evidence That Transaldolase Exchange, Isotope Discrimination During the Triose-Isomerase Reaction, or Both Occur in Humans  

PubMed Central

OBJECTIVE To determine whether deuterium enrichment on carbons 5 and 3 (C5/C3) in plasma glucose is influenced by processes other than gluconeogenesis and, if so, whether these processes are altered by type 2 diabetes. RESEARCH DESIGN AND METHODS In this study, 10 obese diabetic and 10 obese nondiabetic subjects were infused intravenously with [3,5-2H2] galactose enriched at a C5-to-C3 ratio of 1.0 as well as the enrichment of deuterium on C5 and C3 of plasma glucose, measured with nuclear magnetic resonance using the acetaminophen glucuronide method. RESULTS The ratio of deuterium enrichment on C5 and C3 of glucose was <1 (P < 0.001) in all of the diabetic and nondiabetic subjects, resulting in a means SE C5-to-C3 ratio that did not differ between groups (0.81 0.01 vs. 0.79 0.01, respectively). CONCLUSIONS That the C5-to-C3 glucose ratio is <1 indicates that transaldolase exchange, selective retention of deuterium at the level of the triose-isomerase reaction, or both occur in humans. This also indicates that the net effect of these processes on the C5-to-C3 ratio is the same in people with and without type 2 diabetes. The possible effects of transaldolase exchange or selective retention of deuterium (or tritium) at the level of the triose-isomerase reaction on tracee labeling and tracer metabolism should be considered when the deuterated water method is used to measure gluconeogenesis or [3-3H] glucose is used to measure glucose turnover in humans.

Basu, Rita; Chandramouli, Visvanthan; Schumann, William; Basu, Ananda; Landau, Bernard R.; Rizza, Robert A.

2009-01-01

145

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 (k(ex)) 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

2013-12-01

146

Swi5-Sfr1 protein stimulates Rad51-mediated DNA strand exchange reaction through organization of DNA bases in the presynaptic filament.  

PubMed

The Swi5-Sfr1 heterodimer protein stimulates the Rad51-promoted DNA strand exchange reaction, a crucial step in homologous recombination. To clarify how this accessory protein acts on the strand exchange reaction, we have analyzed how the structure of the primary reaction intermediate, the Rad51/single-stranded DNA (ssDNA) complex filament formed in the presence of ATP, is affected by Swi5-Sfr1. Using flow linear dichroism spectroscopy, we observe that the nucleobases of the ssDNA are more perpendicularly aligned to the filament axis in the presence of Swi5-Sfr1, whereas the bases are more randomly oriented in the absence of Swi5-Sfr1. When using a modified version of the natural protein where the N-terminal part of Sfr1 is deleted, which has no affinity for DNA but maintained ability to stimulate the strand exchange reaction, we still observe the improved perpendicular DNA base orientation. This indicates that Swi5-Sfr1 exerts its activating effect through interaction with the Rad51 filament mainly and not with the DNA. We propose that the role of a coplanar alignment of nucleobases induced by Swi5-Sfr1 in the presynaptic Rad51/ssDNA complex is to facilitate the critical matching with an invading double-stranded DNA, hence stimulating the strand exchange reaction. PMID:24304898

Fornander, Louise H; Renodon-Cornire, Axelle; Kuwabara, Naoyuki; Ito, Kentaro; Tsutsui, Yasuhiro; Shimizu, Toshiyuki; Iwasaki, Hiroshi; Nordn, Bengt; Takahashi, Masayuki

2014-02-01

147

Investigation of neutron-deuteron charge-exchange reaction at small transfer momentum  

SciTech Connect

Analysis of the nd {sup {yields}} p(nn) reaction in the GeV energy region is performed in the framework based on the multiple-scattering theory for a few-nucleon system. The special kinematic condition where momentum transfer from neutron beam to final proton is close to zero is considered. The possibility of extracting the spin-dependent term of the elementary np {sup {yields}} pn amplitude from the nd breakup process is investigated. The energy dependence of the ratio R = {sigma}(R = frac d{sigma}{sub nd}) d {omega} and frac d{sigma}{sub np}) d{omega}) is obtained taking account of the final state interaction of the two outgoing neutrons in the {sup 1}S{sub 0} state.

Ladygina, N. B. [Joint Institute for Nuclear Research (Russian Federation)], E-mail: ladygina@sunhe.jinr.ru

2008-01-15

148

EPR study on the ligand-exchange reaction between bis(diethyldiselenocarbamato)copper(II) and bis(octyldithiocarbonato)copper(II).  

PubMed

EPR study on the ligand-exchange reaction between bis(diethyldiselenocarbamato)copper(II), Cu(Et2dsc)2, and bis(octyldithiocarbonato)copper(II), Cu(octxant)2, in CH2Cl2, CHCl3, CCl4, C6H6 and C6H5.CH3 is reported for the first time. Mixing of equimolar amounts of the parents (chromophores CuSe4 and CuS4, respectively) in C6H6, C6H5.CH3 and CH2Cl2 makes EPR signals of both parents superimposed by the spectrum of a mixed-chelate Cu(xant)(dsc) complex (chromophore CuS2Se2). A new additional EPR spectrum appears in CHCl3 or CCl4 due to a five-coordinate mixed-ligand complex with the chromophore Cu(S3Se)S as follows by comparing the g-values of parents and mixed-ligand complexes. The appearance of this complex could be explained having in mind donor-acceptor properties of complexes, solvents and the resultant reaction of Cu(octxant)2 with the ester of diselenocarbamic acid yielded in Cu(Et2dsc)2 destruction by CCl4 or CHCl3. PMID:16490389

Yordanov, Nicola D; Dimitrova, Anna

2006-03-13

149

EPR study on the ligand-exchange reaction between bis(diethyldiselenocarbamato)copper(II) and bis(octyldithiocarbonato)copper(II)  

NASA Astrophysics Data System (ADS)

EPR study on the ligand-exchange reaction between bis(diethyldiselenocarbamato)copper(II), Cu(Et 2dsc) 2, and bis(octyldithiocarbonato)copper(II), Cu(octxant) 2, in CH 2Cl 2, CHCl 3, CCl 4, C 6H 6 and C 6H 5CH 3 is reported for the first time. Mixing of equimolar amounts of the parents (chromophores CuSe 4 and CuS 4, respectively) in C 6H 6, C 6H 5CH 3 and CH 2Cl 2 makes EPR signals of both parents superimposed by the spectrum of a mixed-chelate Cu(xant)(dsc) complex (chromophore CuS 2Se 2). A new additional EPR spectrum appears in CHCl 3 or CCl 4 due to a five-coordinate mixed-ligand complex with the chromophore Cu(S 3Se)S as follows by comparing the g-values of parents and mixed-ligand complexes. The appearance of this complex could be explained having in mind donor-acceptor properties of complexes, solvents and the resultant reaction of Cu(octxant) 2 with the ester of diselenocarbamic acid yielded in Cu(Et 2dsc) 2 destruction by CCl 4 or CHCl 3.

Yordanov, Nicola D.; Dimitrova, Anna

2006-03-01

150

Time dependent three-dimensional body frame quantal wave packet treatment of the H + H2 exchange reaction on the Liu-Siegbahn-Truhlar-Horowitz (LSTH) surface  

NASA Technical Reports Server (NTRS)

The first successful application of the three-dimensional quantum body frame wave packet approach to reactive scattering is reported for the H + H2 exchange reaction on the LSTH potential surface. The method used is based on a procedure for calculating total reaction probabilities from wave packets. It is found that converged, vibrationally resolved reactive probabilities can be calculated with a grid that is not much larger than required for the pure inelastic calculation. Tabular results are presented for several energies.

Neuhauser, Daniel; Baer, Michael; Judson, Richard S.; Kouri, Donald J.

1989-01-01

151

Similarity between the kinetic parameters of the buffer-mediated proton exchange reaction of a xanthenic derivative in its ground- and excited-state.  

PubMed

Buffer-mediated proton exchange reactions of a xanthenic dye were studied in the ground and the excited state by single molecule and bulk fluorescence techniques, respectively. The rate constant obtained supported the uniformity of the process in the ground and the excited state, and the need of adequate character of the buffer species to be able to promote excited-state reactions. PMID:20023807

Paredes, Jose M; Orte, Angel; Crovetto, Luis; Alvarez-Pez, Jose M; Rios, Ramon; Ruedas-Rama, Maria J; Talavera, Eva M

2010-01-14

152

Mass-independent isotopic fractionation of tin in a chemical exchange reaction  

NASA Astrophysics Data System (ADS)

Tin isotopes were fractionated by the liquid-liquid extraction technique with a crown ether, dicyclohexano-18- crown-6 (DC18C6). Tin dichloride was dissolved in HCl to create solutions, 0.1 mol dm-3 (M) Sn(II) in various [HCl]. The organic phase was 0.1 M DC18C6 in 1,2-dichloroethane. A 5 cm3 aqueous solution and a 5 cm3 organic solution were mixed in a glass vial with a stirrer bar, and the glass vial was sealed. The two phases were stirred by a magnetic stirrer, and after the equilibrium, the two phases were separated by centrifugation. An aliquot of the upper aqueous solution was taken for analysis. These procedures were carried out at room temperature. The Sn concentration in the equilibrated aqueous phase was analyzed by ICP-AES. In order to avoid any matrix effect, possible trace of organic materials from DC18C6 was separated from the Sn on a micro-column anion-exchange resin in HBr/HNO3. An aliquot of the aqueous phase was once dried by heating and then dissolved into a HBr solution. Sn was strongly adsorbed while organic materials went through. Finally Sn was collected in a HNO3 solution. A solution containing 300 ppb of Sn in 0.05 M HNO3 was prepared for isotopic analysis. Isotopic ratios of Sn in all samples were analyzed with the MC-ICP-MS Nu plasma 500 HR at ENS Lyon coupled with a desolvating nebulizer Nu DSN-100 (with a typical precision of <100 ppm). The instrumental mass bias was controlled by bracketing each of the samples with standards. Because 120Sn is the most abundant isotopes, the isotope ratios have been measured as mSn/120Sn (m : 116, 117, 118, 119, 122, and 124). 114Sn and 115Sn were not analyzed due to their low abundances. Possible interferences with Cd on the masses 116, with Te on the mass 120, 122 and 124 were verified to be under the detection of the ICP-MS. Odd atomic mass isotopes (117Sn and 119Sn) showed deficits of enrichment comparing to the even atomic mass isotopes (116Sn, 118Sn, 122Sn, and 124Sn). This odd-even staggering property would originate from the nuclear field shift effect which has been proposed by Bigeleisen in 1996.

Fujii, T.; Moynier, F.

2008-12-01

153

Catalytic C-H bond activation at nanoscale Lewis acidic aluminium fluorides: H/D exchange reactions at aromatic and aliphatic hydrocarbons.  

PubMed

Nanoscopic amorphous Lewis acidic aluminium fluorides, such as aluminium chlorofluoride (ACF) and high-surface aluminium fluoride (HS-AlF(3)), are capable of activating C-H bonds of aliphatic hydrocarbons. H/D exchange reactions are catalysed under mild conditions (40?C). PMID:22125129

Prechtl, Martin H G; Teltewskoi, Michael; Dimitrov, Anton; Kemnitz, Erhard; Braun, Thomas

2011-12-16

154

Superhydrophobic pure silver surface with flower-like structures by a facile galvanic exchange reaction with [Ag(NH3)2]OH.  

PubMed

Superhydrophobic pure silver film composed of flower-like microstructures built by interconnected silver nanoplates on a copper plate without any modification was prepared by a facile galvanic exchange reaction between the aqueous [Ag(NH3)2]OH and the copper plate, giving rise to a contact angle as high as 157 degrees . PMID:18535710

Cao, Zongwei; Xiao, Debao; Kang, Longtian; Wang, Zhongliang; Zhang, Shuxiao; Ma, Ying; Fu, Hongbing; Yao, Jiannian

2008-06-21

155

Measurement of spin transfer parameters in the p-bar p yields n-bar n charge-exchange reaction at LEAR.  

National Technical Information Service (NTIS)

The experiment PS199 at LEAR investigates the spin structure of the charge-exchange reaction p-bar p yields n-bar n. Data for the measurement of the spin transfer parameters for both neutron and antineutron were collected during 1990 and preliminary resul...

J. Arvieux M. Agnello A. Ahmidouch M. Lamanna

1991-01-01

156

Study of the isotope effect in the isotope exchange reaction between Pu{sup IV} and Pu{sup III} by extraction redox-chromatography  

SciTech Connect

The equilibrium isotope effect in the isotope exchange reaction between Pu{sup IV} extracted with tributyl phosphate and Pu{sup III} in an aqueous nitric acid solution has been studied by extraction chromatography. For the {sup 238/242}Pu isotope pair the isotope separation coefficient ({alpha}) at 25{degrees}C has been found to be 1.0022{+-}0.0005.

Nikitenko, S.I.; Dzyubenko, V.I. [Institute of Physical Chemistry, Moscow (Russian Federation)

1995-03-01

157

Control of the fixed charge distribution in an ion-exchange membrane via diffusion and the reaction rate of the monomer.  

PubMed

The fixed charge distribution of the ion-exchange membranes was controlled by introducing ion-exchangeable groups onto the glycidyl methacrylate (GMA)-g-polypropylene (PP) membranes. The membranes were prepared by plasma-induced graft polymerization with uniform or nonuniform graft distributions over the cross section. The effects of reaction conditions on the graft distribution in plasma-induced graft polymerization were investigated to obtain the GMA-g-PP membranes with different graft distributions. The examined reaction conditions were plasma power, gas pressure of the plasma, solvent, concentration of the monomer solution, and reaction temperature. The graft distribution of the membranes was directly observed by a microscopic Fourier transform infrared mapping method and field-emission scanning electron microscopy. Also, the graft distribution was correlated with the relative magnitude of the reaction rate to the diffusion rate, which may determine the grafting yield as a function of the distance from the surface. A high rate of diffusion compared to the reaction rate resulted in a more uniform graft distribution. Among the grafting conditions, control of the reaction temperature was found to be the most effective for selectively preparing both uniform and nonuniform graft distribution. Uniform graft distribution was achieved when the reaction was conducted at 1 degrees C because of the relatively rapid diffusion and the slow reaction of the monomer, while nonuniform graft distribution occurred at higher reaction temperatures. Consequently, uniformly and nonuniformly charged cation-exchange membranes were prepared through sulfonation of the corresponding GMA-g-PP membranes at temperatures of 1 and 40 degrees C, respectively. PMID:17518493

Choi, Eun-Young; Bae, Byungchan; Moon, Seung-Hyeon

2007-06-14

158

Hyporheic exchange and fulvic acid redox reactions in an alpine stream/wetland ecosystem, Colorado front range  

USGS Publications Warehouse

The influence of hyporheic zone interactions on the redox state of fulvic acids and other redox active species was investigated in an alpine stream and adjacent wetland, which is a more reducing environment. A tracer injection experiment using bromide (Br-) was conducted in the stream system. Simulations with a transport model showed that rates of exchange between the stream and hyporheic zone were rapid (?? ??? 10-3 s -1). Parallel factor analysis of fluorescence spectra was used to quantify the redox state of dissolved fulvic acids. The rate coefficient for oxidation of reduced fulvic acids (?? = 6.5 ?? 10-3 s -1) in the stream indicates that electron-transfer reactions occur over short time scales. The rate coefficients for decay of ammonium (?? = 1.2 ?? 10-3 s-1) and production of nitrate (?? = -1.0 ?? 10-3 s-1) were opposite in sign but almost equal in magnitude. Our results suggest that fulvic acids are involved in rapid electron-transfer processes in and near the stream channel and may be important in determining ecological energy flow at the catchment scale. ?? 2006 American Chemical Society.

Miller, M. P.; McKnight, D. M.; Cory, R. M.; Williams, M. W.; Runkel, R. L.

2006-01-01

159

Iridium-decorated palladium-platinum core-shell catalysts for oxygen reduction reaction in proton exchange membrane fuel cell.  

PubMed

Carbon-supported Pt, Pd, Pd-Pt core-shell (Pt(shell)-Pd(core)/C) and Ir-decorated Pd-Pt core-shell (Ir-decorated Pt(shell)-Pd(core)/C) catalysts were synthesized, and their physical properties, electrochemical behaviors, oxygen reduction reaction (ORR) characteristics and proton exchange membrane fuel cell (PEMFC) performances were investigated herein. From the XRD patterns and TEM images, Ir-decorated Pt(shell)-Pd(core)/C has been confirmed that Pt was deposited on the Pd nanoparticle which had the core-shell structure. Ir-decorated Pt(shell)-Pd(core)/C has more positive OH reduction peak than Pt/C, which is beneficial to weaken the binding energy of Pt-OH during the ORR. Thus, Ir-decorated Pt(shell)-Pd(core)/C has higher ORR activity than Pt/C. The maximum power density of H2-O2 PEMFC using Ir-decorated Pt(shell)-Pd(core)/C is 792.2 mW cm(-2) at 70C, which is 24% higher than that using Pt/C. The single-cell accelerated degradation test of PEMFC using Ir-decorated Pt(shell)-Pd(core)/C shows good durability by the potential cycling of 40,000 cycles. This study concludes that Ir-decorated Pt(shell)-Pd(core)/C has the low Pt content, but it can facilitate the low-cost and high-efficient PEMFC. PMID:24388448

Wang, Chen-Hao; Hsu, Hsin-Cheng; Wang, Kai-Ching

2014-08-01

160

Effects of arginine and some analogues of the partial adenosine triphosphate-adenosine diphosphate exchange reaction catalysed by arginine kinase. Evolutionary divergence in the mechanism of action of a monomer and a dimer arginine kinase.  

PubMed Central

1. Both the monomer arginine kinase from lobster muscle and the dimer arginine kinase from Holothuria forskali catalyse the ATP-ADP partial exchange reaction at rates equal to 3 and 0.6% of the normal rate of transphosphorylation respectively. The Mg2+-nucleotide complex is the substrate for this as it is for the kinase reaction. 2. Analogues of arginine inhibit the exchange reaction of the lobster enzyme but enhance that of the Holothuria enzyme. 3. With the lobster enzyme NO3- has no effect on the exchange reaction alone and inhibit only slightly the apparent enhancement of the exchange reaction produced by the addition of arginine. This is compatible with previous findings for this enzyme that formation of the anion-stabilized dead-end complex, enzyme-arginine-MgADP-NO3-, does not occur to any marked degree. 4. About 80% of the ADP-ATP exchange reaction of the lobster enzyme remains after inhibition with iodoacetamide. This is further decreased to 65% by the addition of L-arginine, indicating that this substrate does bind to the thiolmodified enzyme. 5. It is concluded that the partial exchange reaction is a genuine phenomenon not mediated by trace amounts of arginine. From the effects of arginine and related compounds it would appear that during the normal kinase reaction the partial ATP-ADP exchange reaction is suppressed in the lobster enzyme but enhanced in the Holothuria enzyme. This reflects a remarkable evolutionary divergence of two homologous enzymes.

Anosike, E O; Watts, D C

1976-01-01

161

Exchangeable Template Reaction.  

National Technical Information Service (NTIS)

The invention provides a method for the synthesis of DNA based on a cyclic mechanism of combining deoxyoligonucleotides comprising combining: (1) a series of unique single-stranded deoxypolynucleotides, each having a 5' sequence which, when in double-stra...

Y. Khudyakov H. A. Fields

1992-01-01

162

Study of the gas-phase oxygen-hydrogen exchange reaction of O(3P) + i-C3H7 ? H(2S) + CH3COCH3.  

PubMed

The gas-phase oxygen-hydrogen exchange reaction dynamics of O((3)P) + i-C3H7 (isopropyl) ? H((2)S) + CH3OCH3 (acetone) was first investigated by the vacuum-ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy in a crossed beam configuration. The nascent H-atom Doppler-profile analysis shows that the average translation energy of the products and the fraction of the total available energy released as the transitional energy were determined to be 33.3 1.64 kcal mol(-1) and 0.38, respectively. With the aid of the CBS-QB3 level of ab initio theory and statistical calculations, it was found that the title reaction is one of the major reaction pathways and proceeds through the formation of dynamical, short-lived addition complexes. On the basis of a systematic comparison with several exchange reactions of hydrocarbon radicals, the large variation in the fractions of translational energy release can be understood in terms of the unique geometrical features of the transition states along the reaction coordinates on the doublet potential energy surfaces. PMID:23789742

Park, Min-Jin; Jang, Su-Chan; Choi, Jong-Ho

2013-11-21

163

Trimerization of isobutene over cation exchange resins: Effect of physical properties of the resins and reaction conditions  

Microsoft Academic Search

Oligomerization of isobutene has been investigated using several cation exchange resins in order to produce triisobutenes that are useful feedstock for heavy alkylates and neo-acids. Trimers selectivity increases with increasing isobutene conversion. High isobutene conversion is obtained at high temperature and low space velocity by using macroporous cation exchange resins that have high concentration of sulfonic acid groups. Under selected

Ji Woong Yoon; Jong-San Chang; Hee-Du Lee; Tae-Jin Kim; Sung Hwa Jhung

2006-01-01

164

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 MH n or MD n hydrides (M = As, Sb, Bi, n = 3; M = Ge, Sn, n = 4) taking place when they are in contact with H 2O or D 2O solution at different pH or pD values (interval of pH = [0,13]) have been investigated using gas chromatography-mass spectrometry (GC-MS). MH n or MD n 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 MH n or MD n 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 (AsH nD 3- n , SbH nD 3- n, BiH nD 3- n, n = 0-3; GeH nD 4- n, SnH nD 4- 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 MH n or MD n compounds placed in contact with H 2O or D 2O 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

165

Ex situ scanning force microscopic observation of growth and dissolution phenomena on {0 1 0} surfaces of potassium hydrogen phthalate crystals (KAP) caused by isomorphic exchange reactions  

NASA Astrophysics Data System (ADS)

Ex situ scanning force microscopic observations reveal characteristic phenomena of growth and dissolution on {0 1 0} surfaces of potassium hydrogen phthalate crystals (KHC 8H 4O 4 or KAP) in contact with a saturated solution of rubidium hydrogen phthalate (RbHC 8H 4O 4 or RbAP) due to an isomorphic exchange reaction. An array of small torpedo-shaped inclusions elongated parallel to the crystallographic c-axis covers the initially smooth cleaved surfaces in less than 1 s. Even in such a short time, almost simultaneous very tiny acicular crystals crystallize parallel to the borders of the elongated etch pits. Moreover, protuberances on the step edges of these etch pits and isometric crystals on the surface are formed as well. When KAP {0 1 0} surfaces are wetted during 10 s with a saturated solution of RbAP, these phenomena are much better visible. After 15 s of wetting numerous elongated crystals cover the surface and the channels. After 30 s, the {0 1 0} surface becomes almost too rough for SFM observations since the etch pits are overgrown by precipitates. These phenomena of nearly simultaneous dissolution and consequent crystallization are the initial stages of the monocrystalline isomorphic exchange process on nanometric scale. It is a very fast process, which unfortunately could not be followed in situ. Our observations corroborate the importance of the volume effect on the isomorphic exchange reactions.

Woensdregt, Cornelis F.; Glikin, Arkady E.

2005-10-01

166

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.

167

Geometrical and geochemical properties of isotope exchange and reaction fronts in the Alta aureole, Utah: evidence for scale-dependent heterogeneity and anisotropy in permeability of marbles  

NASA Astrophysics Data System (ADS)

A carbon isotope exchange front, periclase reaction front and an oxygen isotope exchange front are developed with increasing distance from the igneous contact in dolomitic marbles of the south Alta aureole, Utah in response to infiltration-driven metamorphism of the marbles. Their relative distances from the igneous contact, approx. 100, 200 and 350 m, respectively, are consistent with down-temperature infiltration of water-rich fluid that was equilibrated isotopically with the adjacent Alta stock. At the aureole scale both the C and O isotope exchange fronts exhibit significant dispersion: there is significant variation in both ?18O and ?13C values at any given position for >100m to either side of the geometric centers of both fronts. Applications of one-dimensional models of advection-dispersion to these aureole-scale dispersed fronts yield a minimum dispersion coefficient of 2E-8 m2/sec. However at outcrop and bedding scale, steep, coherent gradients in both ?18O and ?13C exist at or near bedding boundaries between marble layers of contrasting lithology and isotopic compositions; modeling of these profiles requires much lower diffusion/dispersion coefficients in the range of 7E-12 to 1E-14 m2/sec. The periclase reaction front (isograd) can be mapped as a fairly regular surface at the aureole scale, located an average 200 m from the igneous contact, and normally of narrow width (<10 m). However at two locations, lenses of dolomite and periclase marble interfinger for distances up to 40-50 m closer to, and farther from, the igneous contact, compared to the average location of the reaction front. This intermixing can be interpreted to result from dispersion of the reaction front owing to heterogeneity in permeability rather than to reaction kinetics, because at outcrop and bedding scales where exposed, the boundary separating dolomite- from periclase-marble is sharp (<1 cm width). Additionally, at the two locations where measurements have been made, steep ?18O and ?13C gradients accompany the sharp reaction boundary between periclase and dolomite marble. The variable characteristics of the exchange and reaction fronts can be explained by scale-dependent heterogeneity and anisotropy in permeability of the marbles. Both the exchange and reaction fronts are characterized by significant dispersion at the aureole scale because of significant bed-to-bed variations in permeability, which are reflected by significant bed-to-bed variations in ?18O and ?13C values. As original sedimentary bedding is sub-horizontal and fluid infiltration is outward from the igneous contact and bedding concordant, the bedding-controlled variations in permeability also lead to significant permeability anisotropy, with effective permeability parallel to bedding>>permeability normal to bedding. In contrast, permeability within individual beds appears to be relatively homogeneous, as suggested by relatively consistent mineral modes and homogeneous ?18O and ?13C values within individual beds, and by steep, highly coherent ?18O and ?13C gradients preserved at or near bedding boundaries.

Bowman, J. R.

2012-12-01

168

Multivalency in the gas phase: H/D exchange reactions unravel the dynamic "rock 'n' roll" motion in dendrimer-dendrimer complexes.  

PubMed

Noncovalent dendrimer-dendrimer complexes were successfully ionized by electrospray ionization of partly protonated amino-terminated polypropylene amine (POPAM) and POPAM dendrimers fully functionalized with benzo[21]crown-7 on all branches. Hydrogen/deuterium exchange (HDX) experiments conducted on dendrimer-dendrimer complexes in the high vacuum of a mass spectrometer give rise to a complete exchange of all labile NH hydrogen atoms. As crown ethers represent noncovalent protective groups against HDX reactions on the ammonium group to which they are coordinated, this result provides evidence for a very dynamic binding situation: each crown is mobile enough to move from one ammonium binding site to another. Schematically, one might compare this motion with two rock 'n' roll dancers that swirl around each other without completely losing all contact at any time. Although the multivalent attachment certainly increases the overall affinity, the "microdynamics" of individual site binding and dissociation remains fast. PMID:24105808

Qi, Zhenhui; Schlaich, Christoph; Schalley, Christoph A

2013-10-25

169

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 40C, 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

170

Electrochemistry of Oxygenation Catalysts. 3.(1) Thermodynamic Characterization of Electron Transfer and Solvent Exchange Reactions of Co(salen)/[Co(salen)](+) in DMF, Pyridine, and Their Mixtures.  

PubMed

Redox and ligand exchange reactions of the oxygenation catalyst (N,N '-bis(salicylidene)ethylenediaminato)cobalt(II), Co(salen), and its one-electron oxidation product, Co(salen)(+), are investigated in DMF, pyridine, and mixtures of these solvents. Electron transfers and solvent exchange reactions involving three neutral Co(II) and three cationic Co(III) complexes with different axially bound solvent molecules (two DMF, one DMF and one pyridine, or two pyridine molecules) form a three-rung ladder scheme. All formal potentials E(0) and equilibrium constants K in this scheme are determined from electrochemical or spectrophotometric experiments or the construction of thermodynamic cycles. The latter are also used to prove consistency of the results. Values for the E(0) and K are discussed in terms of the Co coordination geometry, solvent effects on the potentials, the thermodynamics of cross reactions, and the distribution of Co(II) and Co(III) species as a function of the solvent composition. Some peculiarities found in the oxygenation of flavonols and indoles are explained. PMID:11669996

Eichhorn, Emerich; Rieker, Anton; Speiser, Bernd; Stahl, Hartmut

1997-07-16

171

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

NASA Astrophysics Data System (ADS)

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 interface between the two fluids. By solving the Bloch-Torrey equations with new generalized boundary conditions describing this localized interfacial reaction we show how the N.M.R. spectral lineshape and relaxation times depend on the morphology of the system as well as on the rates of diffusion and interfacial reaction. Our results differ fundamentally from the traditional phenomenological description of exchange based on the Bloch-McConnell or Zimmerman-Brittin equations which take no explicit account of these factors. In order to illustrate these differences exact analytical solutions are derived for the simplest geometry where the two phases are lamellar. More complicated geometries can be treated by numerical methods.

Belton, P. S.; Hills, B. P.

172

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

173

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. PMID:23625472

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

2013-10-01

174

Comparative studies on exchange reactions of hexafluoroacetylacetonate in bis(hexafluoroacetylacetonato)(dimethyl sulfoxide)dioxouranium(VI) in nonaqueous solvent and supercritical CO(2).  

PubMed

Exchange reactions of hexafluoroacetylacetonate (hfacac) in UO2(hfacac)2DMSO (DMSO = dimethyl sulfoxide) in o-C6D4Cl2 and supercritical CO2 (sc-CO2) have been studied using the NMR line-broadening method to compare reactivity in a nonaqueous solvent with that in sc-CO2. It was found that the exchange rates of hfacac in both systems are dependent on the concentration of the enol isomer ([Henol]) of hexafluoroacetylacetone and become slow with an increase in the concentration of free DMSO ([DMSO]). The exchange reaction between free and coordinated DMSO in UO2(hfacac)2DMSO has been also examined in o-C6D4Cl2 and sc-CO2. As a result, the exchange rate of DMSO was found to depend on [DMSO]. From these results, the hfacac exchange reactions in UO2(hfacac)2DMSO in o-C6D4Cl2 and sc-CO2 were proposed to proceed through the mechanism that the ring-opening for one of two coordinated hfacac in UO2(hfacac)2DMSO is the rate-determining step, and the resulting vacant site is coordinated by the incoming Henol, followed by the proton transfer from Henol to hfacac and the ring closure of unidentate hfacac. The rate constants at 60 degrees C and the activation parameters (DeltaH and DeltaS) for the ring-opening path are 35.8 +/- 3.2 s(-1), 57.8 +/- 2.7 kJ.mol(-1), and -42.9 +/- 7.7 J.mol(-1).K(-1) for the o-C6D4Cl2 system, and 518 +/- 50 s(-1), 18.9 +/- 1.8 kJ.mol(-1), and -138 +/- 5 J.mol(-1).K(-1) for the sc-CO2 system, respectively. Differences in kinetic parameters between sc-CO2 and o-C6D4Cl2 systems were proposed to be attributed to the solute-solvent interactions such as Lewis acid-Lewis base interactions and hydrogen bondings between sc-CO2 and beta-diketones. PMID:18062686

Kachi, Yoshihiro; Kayaki, Yoshihito; Tsukahara, Takehiko; Ikariya, Takao; Ikeda, Yasuhisa

2008-01-01

175

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 [CaSO42H2O] and bassanite [CaSO40.5H2O] 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

176

Energy deposition accompanying pion double charge exchange: Radiochemical study of the 209Bi(pi+, pi-xn)209xAt reactions  

Microsoft Academic Search

The pion double charge exchange reactions, 209Bi(pi+, pi-xn)209-xAt, have been studied by radiochemical techniques for incident pion energies of 100, 180, and 300 MeV. Cross sections for the chemically separated At isotopes A=205-209 were determined by alpha-particle and gamma-ray spectroscopy. The contribution of secondary processes, such as 209Bi(pi+, 3,4He)X followed by 209Bi(4He, xn)213-xAt and 209Bi(3He, xn)212-xAt, which mimic the double

J. L. Clark; P. E. Haustein; T. J. Ruth; J. Hudis; A. A. Caretto Jr.

1983-01-01

177

Absorptive corrections to the reaction gammap-->npi in the one pion exchange model with gauge invariant extension  

Microsoft Academic Search

Absorptive corrections have been calculated for photoproduction of N *. Two versions for the uncorrected production amplitude are used. First, the one pion exchange Born approximation in the Coulomb gauge and second, a gauge invariant extension, restricted to the orbital electromagnetic current and to the isospin I=1-amplitude in the t-channel. We found the second restriction to be unimportant. Numerical values

M. P. Locher; W. Sandhas

1966-01-01

178

Invited paper: Composition-dependent electrical properties of ternary AgxSb1-xTey thin films synthesized by cationic exchange reaction  

NASA Astrophysics Data System (ADS)

Ternary silver antimony telluride (AgxSb1-xTey) thin films with tailored compositions were synthesized by a cationic exchange reaction of thermally evaporated antimony telluride thin films, as a simple and costeffective approach. The composition of AgxSb1-xTey thin films was controlled by the reaction time. Temperaturedependent electrical properties of the AgxSb1-xTey thin films demonstrated phase transition behavior from 323 K to 343 K. The composition-dependent thermoelectric properties (i.e., electrical resistivity (?), Seebeck coefficient (S) and power factor (S2?)) of the as-deposited Sb54Te46, the transformed AgxSb1-xTey and the annealed AgxSb1-xTey thin films were investigated as a function of temperature.

Jung, Hyunsung; Park, Hosik; Choa, Yongho; Myung, Nosang V.

2012-04-01

179

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

180

Ultrasound-mediated synthesis of high-molecular weight polystyrene-grafted silver nanoparticles by facile ligand exchange reactions in suspension.  

PubMed

Ultrasound mediated facile ligand exchange method in suspension for the formation of polystyrene-grafted silver nanoparticles is reported. Amazingly, this method allows even grafting of very high molecular weight polystyrenes (up to 217 200 g mol(-1) ) having a single terminal thiol group at the chain end. Detailed studies are carried out to gain insights in the role of molecular weight of the ligands and the mechanism of the ligand exchange reactions. Key factors are determined to be the droplet formation by ultrasonification and low silver content, which enhances the availability of the terminal thiol end group significantly. The extraordinary compatibility of the ligand exchange method in particular regarding high molecular weights is attributed to hydrophilic orientation of the terminal thiol groups at the liquid-liquid interphase. This is proved conclusively by using an in situ method as a reference approach in which agglomeration occurs at considerably lower molecular weights due to the absence of preferred end group orientation within the polymer coil. In homogeneous phase only the chain length is found to be the crucial factor in stabilization of silver nanoparticles. PMID:24038884

Pletsch, Holger; Peng, Ling; Mitschang, Fabian; Schaper, Andreas; Hellwig, Michael; Nette, David; Seubert, Andreas; Greiner, Andreas; Agarwal, Seema

2014-01-15

181

Alkali-exchanged sepiolites containing palladium as bifunctional (basic sites and noble metal) catalysts for the Heck and Suzuki reactions  

Microsoft Academic Search

Alkali-exchanged sepiolites-containing PdCl2 act as bifunctional heterogeneous catalysts for the Heck and Suzuki cross-coupling in the absence of extrinsic base. The catalyst becomes deactivated upon reuse and partial reactivation can be achieved by mild steaming at 150C. Sodium sepiolites were found the most suitable support of the series. Surprisingly, natural sepiolite exhibiting very weak basicity being not able to catalyse

Avelino Corma; Hermenegildo Garc??a; Antonio Leyva; Ana Primo

2004-01-01

182

Electron-transfer reactions of technetium complexes. 1. Rate of the self-exchange reaction of the Tc(I)/Tc(II) couple (Tc(DMPE)/sub 3//sup +/2+/, where DMPE = 1,2-bis(dimethylphosphino)ethane  

SciTech Connect

The rate of the self-exchange electron-transfer reaction between (Tc(DMPE)/sub 3/)/sup +/ and (Tc(DMPE)/sub 3/)/sup 2 +/ has been determined by two independent applications of the Marcus theory. The rates and equilibrium constants governing the cross-reactions between (Tc(DMPE)/sub 3/)/sup +/2+/ and ((NH/sub 3/)/sub 5/RuL)/sup 2+/3+ (L = isonicotinamide, pyridine, 4-picoline) were measured in aqueous LiCl/HCl solutions. The known self-exchange rate of ((NH/sub 3/)/sub 5/Ru(py))/sup2+/3+/ was then used within the Marcus cross relationship to calculate three values of k/sub ex/ for (Tc(DMPE)/sub 3/)/sup =/2+/. These values fall within the range (0.8-4.0) x 10/sup 6/ M/sup -1/ s/sup -1/ (25 /sup 0/C, ..mu.. = 0.10 M). Estimated activation parameters for this reaction are ..delta..H/sub ex//sup */ = 7 +/- 3 kcal/mol and ..delta..S/sub ex//sup */ = -8 +/- 4 eu. Available bond length data show that, because of extensive ..pi..-back-bonding from Tc to P, the Tc-P bond expands by about 0.068 A upon oxidation of the technetium center. This information combined with estimates for the radius of the complex (4.8 A) and for the force constant of the Tc-P bond (1.64 x 10/sup 5/ dyn/cm), can be used within the Marcus formalism to calculate k/sub ex/. The resulting calculated value is 3 x 10/sup 6/ M/sup -1/ s/sup -1/ (25/sup 0/C), in excellent agreement with the median value determined kinetically. This agreement between kinetically and structurally determined values of k/sub ex/ demonstrates that the self-exchange reaction of the extensively ..pi..-back-bonded (Tc(DMPE)/sub 3/)/sup +/2+ system is adequately described within the Marcus formalism. Moreover, the value of k/sub ex/ for this d/sup 6//d/sup 5/ couple is in good agreement with the value of k/sub ex/ (2.2 x 10/sup 6/ M/sup -1/ s/sup -1/; 25/sup 0/X, ..mu.. = 0.10 M) observed for ((NH/sub 3/)/sub 4/Ru(bpy))/sup 2+/3+/, a predominantly sigma-bonded d/sup 6//d/sup 5/ couple of similar radius (4.4 A).

Doyle, M.N.; Libson, K.; Woods, M.; Sullivan, J.C.; Deutsch, E.

1986-09-10

183

Anion-exchange reactions on a robust phosphonium photopolymer for the controlled deposition of ionic gold nanoclusters.  

PubMed

UV curing (photopolymerization) is ubiquitous in many facets of industry ranging from the application of paints, pigments, and barrier coatings all the way to fiber optic cable production. To date no reports have focused on polymerizable phosphonium salts under UV irradiation, and despite this dearth of examples, they potentially offer numerous substantial advantages to traditional UV formulation components. We have generated a highly novel coating based on UV-curable trialkylacryloylphosphonium salts that allow for the fast (seconds) and straightforward preparation of ion-exchange surfaces amenable to a roll-to-roll process. We have quantified the surface charges and exploited their accessibility by employing these surfaces in an anion exchange experiment by which [Au25L18](-) (L = SCH2CH2Ph) nanocrystals can be assembled into the solid state. This unprecedented application of such surfaces offers a paradigm shift in the emerging chemistry of Au25 research where the nanocrystals remain single and intact and where the integrity of the cluster and its solution photophysical properties are resilient in the solid state. The specific loading of [Au25L18](-) on the substrates has been determined and the completely reversible loading and unloading of intact nanocrystals to and from the surface has been established. In the solid state, the assembly has an incredible mechanical resiliency, where the surface remains undamaged even when subjected to repeated Scotch tests. PMID:23472738

Guterman, Ryan; Hesari, Mahdi; Ragogna, Paul J; Workentin, Mark S

2013-05-28

184

Rapid formation of AgnX(X = S, Cl, PO4, C2O4) nanotubes via an acid-etching anion exchange reaction  

NASA Astrophysics Data System (ADS)

This work presents a rapid nanotube fabrication method for a series of silver compounds AgnX, such as Ag2S, AgCl, Ag3PO4, and Ag2C2O4, from pregrown Ag2CO3 nanorod templates. The anion exchange process involved takes place in non-aqueous solutions just at room temperature and completes within 10 minutes. An acid-etching anion exchange reaction mechanism has been proved underneath the transformation process from Ag2CO3 nanorods to AgnX nanotubes by the observation of an intermediate yolk-shell nanostructure. It has been found that the final structure of the products can be conveniently controlled by simply varying the concentration of HnX acids, and the organic solvents employed play a vital role in the formation of the nanotubes by effectively controlling the diffusion rates of different species of reacting ions. As a demonstration, the as-prepared AgCl and Ag3PO4 nanotubes exhibit enhanced photocatalytic activity and favorable recyclability for the photodegradation of rhodamine B (RhB) under visible-light irradiation.This work presents a rapid nanotube fabrication method for a series of silver compounds AgnX, such as Ag2S, AgCl, Ag3PO4, and Ag2C2O4, from pregrown Ag2CO3 nanorod templates. The anion exchange process involved takes place in non-aqueous solutions just at room temperature and completes within 10 minutes. An acid-etching anion exchange reaction mechanism has been proved underneath the transformation process from Ag2CO3 nanorods to AgnX nanotubes by the observation of an intermediate yolk-shell nanostructure. It has been found that the final structure of the products can be conveniently controlled by simply varying the concentration of HnX acids, and the organic solvents employed play a vital role in the formation of the nanotubes by effectively controlling the diffusion rates of different species of reacting ions. As a demonstration, the as-prepared AgCl and Ag3PO4 nanotubes exhibit enhanced photocatalytic activity and favorable recyclability for the photodegradation of rhodamine B (RhB) under visible-light irradiation. Electronic supplementary information (ESI) available: Detailed experimental procedures, additional SEM images, XRD pattern. See DOI: 10.1039/c4nr00364k

Li, Jingjing; Yang, Wenlong; Ning, Jiqiang; Zhong, Yijun; Hu, Yong

2014-05-01

185

Novel support effects on the mechanism of propene-deuterium: Addition and exchange reactions over dispersed ZrO{sub 2}  

SciTech Connect

The effect on the rate and mechanisms of propene-deuterium reactions of dispersing ZrO{sub 2} on various supports such as silica, alumina, and titanium dioxide has been studied by microwave spectroscopic analysis of monodeuteropropene as well as by kinetic investigation. By dispersal of ZrO{sub 2} on these supports, the rate of the C{sub 3}H{sub 6}{minus}D{sub 2} reactions is increased considerbly compared to that over unsupported ZrO{sub 2}, with the decrease of activation energy. Hydrogen exchange in propene proceeds simultaneously with addition via the associative mechanism through n-propyl and s-propyl intermediates. Through XPS analysis of ZrO{sub 2}/SiO{sub 2}, it was found that a monolayer of ZrO{sub 2} is formed over the silica support. The monolayer catalyst exhibits catalytic behavior quite different from that of unsupported ZrO{sub 2}. On the other hand, alumina surfaces modified by ZrO{sub 2} layers may be the main active sites in the case of ZrO{sub 2}/Al{sub 2}O{sub 3}. The marked enhancement of the reaction rate in the lower loading region of ZrO{sub 2}/TiO{sub 2} may be explained by the strong interaction of atomically dispersed zirconium ions with active centers on TiO{sub 2}. 28 refs., 10 figs., 1 tab.

Naito, Shuichi [Kanagawa Univ., Yokohama (Japan)] [Kanagawa Univ., Yokohama (Japan); Tanimoto, Mitsutoshi [Shizuoka Univ. (Japan)] [Shizuoka Univ. (Japan)

1995-07-01

186

Influence of varying hydraulic conditions on hyporheic exchange and reactions in an in-stream gravel bar  

NASA Astrophysics Data System (ADS)

In the hyporheic zone (HZ) important biogeochemical transformations occur with crucial impact on nutrient cycling in fluvial systems. Here we investigate the interplay between stream flow and HZ exchange of a natural in-stream gravel bar (ISGB), by using three-dimensional steady state simulations of a coupled surface and subsurface numerical model. Stream flow is simulated by the open source computational fluid dynamics (CFD) software OpenFOAM. It is sequentially coupled by the hydraulic head distribution to the top boundary of the groundwater model code MIN3P, simulating flow, solute transport, aerobic respiration (AR) and denitrification (DN) in the HZ. The modelling approach is validated to the stream rating curve and the subsurface travel times in the ISGB based on field measurements. Hydraulic conditions are varied by stream discharge, ranging from low discharge, sufficient to allow stream water flow through both stream channels surrounding the ISGB (0.1 m/s), to conditions where the ISGB is completely submerged (5.0 m/s). Ambient groundwater flow is assigned by constant head boundaries upstream and downstream of the ISGB. By varying stream discharge or ambient groundwater heads the general flow field of the ISGB can be adjusted from losing via neutral to gaining conditions. Reactive transport scenarios consider stream water as the primary source of dissolved oxygen and dissolved organic carbon. Furthermore, two nitrate sources originated from the stream water and ambient groundwater are included in the model. Results show that highest hyporheic exchange and longest residence times occur under neutral conditions, where the extent of the hyporheic flow cell is at a maximum. Hence, the stronger the system is gaining and losing, the smaller is the hyporheic exchange flux and the shorter are the residence times in the HZ of the ISGB. AR and DN efficiencies of the ISGB are lowest under gaining conditions because infiltrating solutes are restriced to the hyporheic flow cells and hence to small reactive areas. In contrast, under losing conditions stream solutes infiltrate deep into the HZ and overreach the extent of the hyporheic flow cells, resulting in large reactive areas with highest AR and DN efficiencies.

Trauth, Nico; Schmidt, Christian; Maier, Uli; Fleckenstein, Jan H.

2014-05-01

187

Transition state dynamics of the OH + H2O hydrogen exchange reaction studied by dissociative photodetachment of H3O2-.  

PubMed

Dynamics in the transition state region of the bimolecular OH + H2O-->H2O + OH hydrogen exchange reaction have been studied by photoelectron-photofragment coincidence spectroscopy of the H3O2- negative ion and its deuterated analog D3O2-. The data reveal vibrationally resolved product translational energy distributions. The total translational energy distribution shows a vibrational progression indicating excitation of the antisymmetric stretch of the water product. Electronic structure calculations at the QCISD level of theory support this analysis. Examination of the translational energy release between the neutral products reveals a dependence on the product vibrational state. These data should provide a critical test of ab initio potential energy surfaces and dynamics calculations. PMID:11040507

Deyerl, H J; Luong, A K; Clements, T G; Continetti, R E

2000-01-01

188

Rapid formation of AgnX(X = S, Cl, PO4, C2O4) nanotubes via an acid-etching anion exchange reaction.  

PubMed

This work presents a rapid nanotube fabrication method for a series of silver compounds AgnX, such as Ag2S, AgCl, Ag3PO4, and Ag2C2O4, from pregrown Ag2CO3 nanorod templates. The anion exchange process involved takes place in non-aqueous solutions just at room temperature and completes within 10 minutes. An acid-etching anion exchange reaction mechanism has been proved underneath the transformation process from Ag2CO3 nanorods to AgnX nanotubes by the observation of an intermediate yolk-shell nanostructure. It has been found that the final structure of the products can be conveniently controlled by simply varying the concentration of HnX acids, and the organic solvents employed play a vital role in the formation of the nanotubes by effectively controlling the diffusion rates of different species of reacting ions. As a demonstration, the as-prepared AgCl and Ag3PO4 nanotubes exhibit enhanced photocatalytic activity and favorable recyclability for the photodegradation of rhodamine B (RhB) under visible-light irradiation. PMID:24744113

Li, Jingjing; Yang, Wenlong; Ning, Jiqiang; Zhong, Yijun; Hu, Yong

2014-06-01

189

Quasiclassical trajectory studies of 18O(3P) + NO2 isotope exchange and reaction to O2 + NO on D0 and D1 potentials  

NASA Astrophysics Data System (ADS)

We report quasiclassical trajectory calculations for the bimolecular reaction 18O(3P) + NO2 on the recent potential energy surfaces of the ground (D0) and first excited (D1) states of NO3 [B. Fu, J. M. Bowman, H. Xiao, S. Maeda, and K. Morokuma, J. Chem. Theory. Comput. 9, 893 (2013)]. The branching ratio of isotope exchange versus O2 + NO formation, as well as the product angular distributions and energy and rovibrational state distributions are presented. The calculations are done at the collision energy of relevance to recent crossed beam experiments [K. A. Mar, A. L. Van Wyngarden, C.-W. Liang, Y. T. Lee, J. J. Lin, and K. A. Boering, J. Chem. Phys. 137, 044302 (2012)]. Very good agreement is achieved between the current calculations and these experiments for the branching ratio and final translational energy and angular distributions of isotope exchange products 16O(3P) + NO2 and O2 + NO formation products. The reactant 18O atom results in 18O16O but not N18O for the O2 + NO formation product channel, consistent with the experiment. In addition, the detailed vibrational and rotational state information of diatomic molecules calculated currently for the 34O2 + NO formation channel on D0 and D1 states are in qualitative agreement with the previous experimental and theoretical results of the photodissociation of NO3 and are consistent with older thermal bimolecular kinetics measurements.

Fu, Bina; Zhang, Dong H.; Bowman, Joel M.

2013-07-01

190

The super-allowed Fermi type charge exchange reaction for studies of isovector non-spin-flip monopole resonance  

NASA Astrophysics Data System (ADS)

In order to establish the HICE using the super-allowed Fermi type reaction that is selective to isovector the non-spin-flip mode, the 90Zr(10C,10B(IAS)) experiment at 200 MeV/u was performed. We successfully observed the signature of the isovector non-spin-flip transition by detecting the gamma-ray emitted from 10B(IAS). We also observed strength at around more than Ex > 20 MeV in 90Nb coincident with 1022-keV gamma-ray which indicates the non-spin-flip transition.

Sasamoto, Y.; Uesaka, T.; Shimoura, S.; Michimasa, S.; Ota, S.; Tokieda, H.; Miya, H.; Kawase, S.; Kikuchi, Y.; Kisamori, K.; Takaki, M.; Dozono, M.; Mathubara, H.; Yako, K.; Noji, S.; Miki, K.; Sakai, H.; Kubo, T.; Yanagisawa, Y.; Takeda, H.; Yoshida, K.; Ohnishi, T.; Fukuda, N.; Kameda, D.; Inabe, N.; Aoi, N.; Takeuchi, S.; Ichihara, T.; Baba, H.; Sakaguchi, S.; Doornenbal, P.; Wang, H.; Chen, R.; Shimizu, Y.; Kawahara, T.; Kawabata, T.; Yokota, N.; Maeda, Y.; Miyasako, H.; Berg, G. P. A.

2013-09-01

191

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

192

Synthesis of stoichiometric and bulk CrN through a solid-state ion-exchange reaction.  

PubMed

Chromium mononitride (CrN) exhibits interesting magnetic, structural, and electronic properties for technological applications. Experimental reports on these properties are often inconsistent owing to differences in the degree of nonstoichiometry in CrN(x). To date, the preparation of bulk and stoichiometric CrN has been challenging; most products are in the form of a thin film produced by non-equilibrium processes, and are often nonstoichiometric and poorly crystallized. In this work, we formulated a solid-state ion-exchange route for the synthesis of CrN under high pressure. The final CrN product is phase-pure, stoichiometric, and well-crystallized in the bulk form. Near-stoichiometric and well-crystallized CrN can be synthesized using the same route at atmospheric pressure, making massive and industrial-scale production technologically feasible. The successful synthesis of stoichiometric and bulk CrN is expected to open new opportunities in diverse areas of fundamental research. PMID:23059561

Chen, Miao; Wang, Shanmin; Zhang, Jianzhong; He, Duanwei; Zhao, Yusheng

2012-11-26

193

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

194

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.

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

2008-09-01

195

Reaction of copper(II) with ferrocene and 1,1'-dimethylferrocene in aqueous acetonitrile: the copper(II/I) self-exchange rate.  

PubMed

The kinetics of the reactions of copper(II) with ferrocene (Fc) and 1,1'-dimethylferrocene (Dmfc) have been studied at 25 degrees C in aqueous acetonitrile (AN) containing 50-97.5 vol % AN. With increasing % AN, the rate constant increases along with the driving-force for the reaction. The results are analyzed in terms of Marcus theory to estimate the Cu(II/I) electron self-exchange rate constant (k11) for the system. Over the solvent range studied, the calculated k11)changes from 1.1 x 10(-9) to 17 x 10(-9) M(-1) s(-1), with an average value of 5 x 10(-9). In addition, the structures of the trifluoromethanesulfonate salts of [Cu(AN)4]+, [Cu(OH2)2(AN)2]2+, and [Cu(AN)4]2+ are reported. It is found that the Cu-NCCH3 bond-length difference between the Cu(I) and Cu(II) oxidation states is only approximately 0.02 A. PMID:15733005

Irangu, Japhet; Ferguson, Michael J; Jordan, Robert B

2005-03-01

196

Isotopic exchange reactions occurring in the hydrogenation of (1,5-cyclooctadiene)dialkylplatinum(II) complexes over platinum black  

SciTech Connect

This paper analyzes the reactivity of platinum-surface alkyls with two types of deuterium-labeling experiments. In the first, the extent of deuterium incorporation into cyclooctane during reduction of CODPt(R/sup D/)/sub 2/ (COD = 1,5-cyclooctadiene; R/sup D/ = a deuterium-labeled alkyl group) complexes with dihydrogen over platinum black is determined as a function of the structure of R/sup D/ and the position of the deuterium label in it. Reduction of CODPt(CD/sub 2/CH/sub 3/)/sub 2/ yields cyclooctane containing substantially more deuterium than that obtained by reduction of CODPt(CH/sub 2/CD/sub 3/)/sub 2/ yields cyclooctane containing substantially more deuterium than that obtained by reduction of CODPt(CH/sub 2/CD/sub 3/)/sub 2/. Reduction of CODPt(CD/sub 2/C(CH/sub 3/)/sub 3/)/sub 2/ yields cyclooctane containing less deuterium than that obtained by reduction of CODPt(CD/sub 2/CH/sub 2/CH/sub 3/)/sub 2/. The quantity of deuterium incorporated into cyclooctane from reduction of complexes of the type CODPt(CH/sub 2/C(CH/sub 3/)/sub 2/(CH/sub 2/)/sub n/CD/sub 3/)/sub 2/ (n = 1-3) decreases from n = 1 to 3. The second type of experiment compares the isotopic compositions of alkanes obtained by reduction of CODPtR/sub 2/ complexes with D/sub 2/ over platinum black with that of the same alkanes from reduction of the corresponding alkenes with D/sub 2/. The relative rates of exchange with surface hydrogen (deuterium) and reductive elimination for the platinum surface ethyl species produced from deuteriogenation of CODPt(CH/sub 2/CH/sub 3/)/sub 2/ and ethylene are similar. Propanes from deuteriogenation of CODPt(CH/sub 2/CH/sub 2/CH/sub 3/)/sub 2/ and CODPt(CH(CH/sub 3/)/sub 2/)/sub 2/ contain deuterium principally at C/sub 1/ and C/sub 2/, respectively.

Miller, T.M.; Whitesides, G.M.

1988-05-11

197

Active microchannel heat exchanger  

DOEpatents

The present invention is an active microchannel heat exchanger with an active heat source and with microchannel architecture. The 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 exhaust through the exhaust chamber and by conduction through a containment wall to the working fluid in the heat exchanger chamber thereby raising a temperature of the working fluid. The invention is particularly useful as a liquid fuel vaporizer and/or a steam generator for fuel cell power systems, and as a heat source for sustaining endothermic chemical reactions and initiating exothermic reactions.

Tonkovich, Anna Lee Y. (Pasco, WA) [Pasco, WA; Roberts, Gary L. (West Richland, WA) [West Richland, WA; Call, Charles J. (Pasco, WA) [Pasco, WA; Wegeng, Robert S. (Richland, WA) [Richland, WA; Wang, Yong (Richland, WA) [Richland, WA

2001-01-01

198

Weathering reactions and hyporheic exchange controls on stream water chemistry in a glacial meltwater stream in the McMurdo Dry Valleys  

NASA Astrophysics Data System (ADS)

In the McMurdo Dry Valleys, Antarctica, dilute glacial meltwater flows down well-established streambeds to closed basin lakes during the austral summer. During the 6-12 week flow season, a hyporheic zone develops in the saturated sediment adjacent to the streams. Longer Dry Valley streams have higher concentrations of major ions than shorter streams. The longitudinal increases in Si and K suggest that primary weathering contributes to the downstream solute increase. The hypothesis that weathering reactions in the hyporheic zone control stream chemistry was tested by modeling the downstream increase in solute concentration in von Guerard Stream in Taylor Valley. The average rates of solute supplied from these sources over the 5.2 km length of the stream were 6.1 10-9 mol Si L-1 m-1 and 3.7 10-9 mol K L-1 m-1, yielding annual dissolved Si loads of 0.02-1.30 mol Si m-2 of watershed land surface. Silicate minerals in streambed sediment were analyzed to determine the representative surface area of minerals in the hyporheic zone subject to primary weathering. Two strategies were evaluated to compute sediment surface area normalized weathering rates. The first applies a best linear fit to synoptic data in order to calculate a constant downstream solute concentration gradient, dC/dx (constant weathering rate contribution, CRC method); the second uses a transient storage model to simulate dC/dx, representing both hyporheic exchange and chemical weathering (hydrologic exchange, HE method). Geometric surface area normalized dissolution rates of the silicate minerals in the stream ranged from 0.6 10-12 mol Si m-2 s-1 to 4.5 10-12 mol Si m-2 s-1 and 0.4 10-12 mol K m-2 s-1 to 1.9 10-12 mol K m-2 s-1. These values are an order of magnitude lower than geometric surface area normalized weathering rates determined in laboratory studies and are an order of magnitude greater than geometric surface area normalized weathering rates determined in a warmer, wetter setting in temperate basins, despite the cold temperatures, lack of precipitation and lack of organic material. These results suggest that the continuous saturation and rapid flushing of the sediment due to hyporheic exchange facilitates weathering in Dry Valley streams.

Gooseff, Michael N.; McKnight, Diane M.; Lyons, W. Berry; Blum, Alex E.

2002-12-01

199

Weathering reactions and hyporheic exchange controls on stream water chemistry in a glacial meltwater stream in the McMurdo Dry Valleys  

USGS Publications Warehouse

In the McMurdo Dry Valleys, Antarctica, dilute glacial meltwater flows down well-established streambeds to closed basin lakes during the austral summer. During the 6-12 week flow season, a hyporheic zone develops in the saturated sediment adjacent to the streams. Longer Dry Valley streams have higher concentrations of major ions than shorter streams. The longitudinal increases in Si and K suggest that primary weathering contributes to the downstream solute increase. The hypothesis that weathering reactions in the hyporheic zone control stream chemistry was tested by modeling the downstream increase in solute concentration in von Guerard Stream in Taylor Valley. The average rates of solute supplied from these sources over the 5.2 km length of the stream were 6.1 ?? 10-9 mol Si L-1 m-1 and 3.7 ?? 10-9 mol K L-1 m-1, yielding annual dissolved Si loads of 0.02-1.30 tool Si m-2 of watershed land surface. Silicate minerals in streambed sediment were analyzed to determine the representative surface area of minerals in the hyporheic zone subject to primary weathering. Two strategies were evaluated to compute sediment surface area normalized weathering rates. The first applies a best linear fit to synoptic data in order to calculate a constant downstream solute concentration gradient, dC/dx (constant weathering rate contribution, CRC method); the second uses a transient storage model to simulate dC/dx, representing both hyporheic exchange and chemical weathering (hydrologic exchange, HE method). Geometric surface area normalized dissolution rates of the silicate minerals in the stream ranged from 0.6 ?? 10-12 mol Si m-2 s-1 to 4.5 ?? 10-12 mol Si m-2 s-1 and 0.4 ?? 10-12 mol K m-2 s-1 to 1.9 ?? 10-12 mol K m-2 s-1. These values are an order of magnitude lower than geometric surface area normalized weathering rates determined in laboratory studies and are an order of magnitude greater than geometric surface area normalized weathering rates determined in a warmer, wetter setting in temperate basins, despite the cold temperatures, lack of precipitation and lack of organic material. These results suggest that the continuous saturation and rapid flushing of the sediment due to hyporheic exchange facilitates weathering in Dry Valley streams.

Gooseff, M. N.; McKnight, D. M.; Lyons, W. B.; Blum, A. E.

2002-01-01

200

Speciation analysis of ultratrace chromium in water by on-line reaction/concentration/separation method using a cation-exchange column.  

PubMed

A cation-exchange column (TSK IC-Cation, 4.6 mm i.d., 10 mm) was used as a reaction/concentration/separation medium in an HPLC system. Cr(VI) and 1,5-diphenylcarbazide (DPC) were on-line mixed and reacted in a flow tube. When the reagents flowed into the column, both DPC and the complex were concentrated on the column, and the higher DPC concentration accelerated the remaining Cr(VI) to quickly complete the reaction with the DPC on the column. After the complexation and preconcentration, the complex and the extra DPC were eluted by a mixed solution containing lanthanum chloride and 1-propanol. The absorbance of the Cr(III)-DPCO complex at 540 nm was continuously monitored. In addition, the dissolved Cr(III) could be oxidized to Cr(VI) by 185-nm irradiation using a low pressure ultraviolet (UV) lamp for 8 min, and then analyzed by the present method as total chromium, thus the quantitative speciation analysis of Cr(III) and Cr(VI) was realized. In the range of 1 ng dm? - 100 ?g dm? Cr(VI) concentration, the calibration curve was linear. The analytical time was 8 min for Cr(VI) and 24 min for total Cr. The detection limit (3?) of the method was 0.6 ng dm? for Cr(VI) and 0.8 ng dm? for total chromium when using a 3.9-cm water sample. The present method could be successfully applied to the speciation analysis of dissolved chromium in natural water, and the leaching test of Cr(III) and Cr(VI) from stainless steel. PMID:23934564

Sarenqiqige; Ashitomi, Masaki; Yoshimura, Kazuhisa

2013-01-01

201

Kinetics of ¹³CO exchange with ¹²CO in (HM(¹²CO))⁻ and (DM(¹²CO))⁻ (M = Ru or Os): relationship between exchange pathway and catalytic activity in the catalysis of the water gas shift reaction  

Microsoft Academic Search

The roles of the anions (HRu(CO))⁻ and (HOs(CO))⁻ in the catalysis of the water gas shift reaction are investigated. The kinetics of ¹³CO exchange with ¹²CO provides confirmation of the greater activity of the ruthenium based anion.

M. W. Payne; D. L. Leussing; S. G. Shore

1987-01-01

202

First measurement of the cross-section ratio R dp(0) in charge-exchange (np) reactions on H2/D2 at 0o and T n = 1 GeV Dubna ``Delta-Sigma experiment''  

NASA Astrophysics Data System (ADS)

The first results of the measurement of 0o of the cross-section ratio R dp=0.500.02 in charge-exchange (np) reaction on H2/D2 targets at the neutron beam kinetic energie 1.0 GeV are presented. As a result the value of the ratio of non spin-flip to spin-flip contribution in np? pn charge-exchange at 0o r {/np?pn /nf/fl }=0.330.03 was obtained.

Morozov, A. A.; Antonenko, V. G.; Borzakov, S. B.; Borzunov, Yu. T.; Chernykh, E. V.; Chumakov, V. F.; Dolgii, S. A.; Finger, M.; Finger, M.; Golovanov, L. B.; Janata, A.; Kirillov, A. D.; Kovalenko, A. D.; Krasnov, V. A.; Kuzmin, N. A.; Lehar, F.; Livanov, A. N.; Maniakov, P. K.; Matyushevsky, E. A.; Nikolaevsky, G. P.; Nomofilov, A. A.; Panteleev, Tz.; Pisarev, I. L.; Polunin, Yu. P.; Prokofiev, A. N.; Prytkov, V. Yu.; Rukoyatkin, P. A.; Sharov, V. I.; Shindin, R. A.; Slune?ka, M.; Slune?kov, V.; Starikov, A. Yu.; Strunov, L. N.; Vorobiev, E. I.; Yudin, I. P.; Zaitsev, I. V.; Zhdanov, A. A.; Zhmyrov, V. N.

2005-01-01

203

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

204

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

205

Degradation of salicylic acid by photo-assisted Fenton reaction using Fe ions on strongly acidic ion exchange resin as catalyst  

Microsoft Academic Search

The photo-assisted Fenton degradation of salicylic acid (SA) was studied by using strongly acidic ion exchange resin (SAIER) exchanged with Fe ions as catalyst in the presence of UV light (254nm) and H2O2. The X-ray photoelectron spectroscopy (XPS) results revealed that the Fe ions are indeed anchored by the sulfonate groups on the surface of the SAIER and are Fe3+.

Jiyun Feng; Xijun Hu; Po Lock Yue

2004-01-01

206

Characteristic features of Raman band shifts of scheelite-type molybdate catalysts exchanged with the {sup 18}O tracer via redox reactions  

SciTech Connect

The oxide oxygen of scheelite-type {alpha}-MnMoO{sub 4}, {beta}-CoMoO{sub 4}, and {alpha}-Bi{sub 2}Mo{sub 3}O{sub 12} were exchanged with the {sup 18}O tracer using a reduction-oxidation method. The Raman band shifts in the spectra of these catalysts were examined. Normal coordination analysis and diatomic approximation reported in previous literature have shown that the Raman bands are correlated to the Mo-O stretchings of these molybdate catalysts. With {alpha}-MnMoO{sub 4}, the band at 945 cm{sup {minus}1} corresponding to the shortest Mo=O of a Mo tetrahedron was exchanged preferentially while with {beta}-CoMoO{sub 4} which is isotypic with {alpha}-MnMoO{sub 4}, all the oxygen of Mo tetrahedra were exchanged with an increase in the {sup 18}O exchange. With {alpha}-Bi{sub 2}Mo{sub 3}O{sub 12} which has two twin Mo tetrahedra, the bands at 865 and 845 cm{sup {minus}1} were shifted preferentially. Oxygen insertion seems to take place more selectively on the Mo tetrahedron sites where Bi ions are present. A comparative study and discussions on the preferential exchange in these molybdates and reoxidation sites have been reported here. 29 refs., 7 figs., 7 tabs.

Ono, Takehiko; Ogata, Nobuaki; Miyaryo, Yasuhiro [Univ. of Osaka Prefecture (Japan)] [Univ. of Osaka Prefecture (Japan)

1996-06-01

207

Baryon Exchange in the Reaction pi exp - p Implies n* exp 0 pi exp 0 at 9GEV/C and 12GEV/C.  

National Technical Information Service (NTIS)

In pi exp - p interactions at 9GeV/c and 12GeV/c, the forward production of N*1680 and N*1520 has been observed with features of nucleon exchange. The production of delta 1232 is strongly suppressed. (Atomindex citation 08:339504)

A. Rouge, G. de Rosny, P. Fleury

1977-01-01

208

Total cross sections of the charge exchange reaction ({pi}{sup +},{pi}{sup 0}) on {sup 2}H, {sup 3}He, and {sup 4}He across the {Delta}(1232) resonance  

SciTech Connect

Results from a 4{pi} solid angle measurement of the inclusive reaction ({pi}{sup +},{pi}{sup 0}) on {sup 2}H, {sup 3}He, and {sup 4}He at incident pion energies of T{sub {pi}{sup +}}=70, 118, 162, 239, and 330 MeV are presented. The single charge exchange total cross sections were determined, and are compared to previous results and simple models of {pi}{endash}few-nucleon interactions. On the helium isotopes a strong damping of the cross sections in the {Delta}(1232) energy region is observed. Total cross sections of the breakup reaction {pi}{sup +}+{sup 2}H {r_arrow}{pi}{sup +}pn are also given. {copyright} {ital 1999} {ital The American Physical Society}

Lehmann, A.; Backenstoss, G.; Koehler, J.; Kroedel, M.; Weyer, H.J.; Wildi, M. [University of Basel, CH-4056 Basel (Switzerland)] [University of Basel, CH-4056 Basel (Switzerland); Hoffart, A.; Trezeciak, R.; Ullrich, H. [University of Karlsruhe, D-76128 Karlsruhe (Germany)] [University of Karlsruhe, D-76128 Karlsruhe (Germany); Gram, P.A. [Los Alamos Meson Physics Facility, Los Alamos, New Mexico 87545 (United States)] [Los Alamos Meson Physics Facility, Los Alamos, New Mexico 87545 (United States); Lehmann, A.; Gregory, N.K.; Mateos, A.O.; Redwine, R.P.; Rowntree, D.; Simicevic, N.; Wilson, K.E. [Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)] [Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Kyle, G. [New Mexico State University, Las Cruces, New Mexico 88003 (United States)] [New Mexico State University, Las Cruces, New Mexico 88003 (United States); Dooling, T.; Klein, A. [Old Dominion University, Norfolk, Virginia 23529 (United States)] [Old Dominion University, Norfolk, Virginia 23529 (United States); Hoffart, A.; Ingram, C.H.; Koch, K.; Kotlinski, B.; Michaelian, K.; Weyer, H.J. [Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland)] [Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Androic, D.; Bosnar, D.; Furic, M.; Petkovic, T.; Planinic, M. [University of Zagreb, HR-10000 Zagreb (Croatia)] [University of Zagreb, HR-10000 Zagreb (Croatia)

1999-08-01

209

ION EXCHANGE  

EPA Science Inventory

The IONEX program's name is a contraction of "ion exchange." The IONEX program performs calculations related to removing radium and/or uranium from water with the ion exchange process. IONEX provides a quick method of calculating whether a proposed ion exchange process will m...

210

Synthesis and crystal structure of Mg{sub 0.5}NbO{sub 2}: An ion-exchange reaction with Mg{sup 2+} between trigonal [NbO{sub 2}]{sup -} layers  

SciTech Connect

A new layered niobate, Mg{sub 0.5}NbO{sub 2}, was synthesized from LiNbO{sub 2} through a cation-exchange reaction with Mg{sup 2+} at 450-550 Degree-Sign C. This is the first example of a topotactic reaction with an aliovalent cation between trigonal [NbO{sub 2}]{sup -} layers. It is proposed to be isostructural with LiNbO{sub 2} (space group; P6{sub 3}/mmc) with lattice parameters of a=2.9052(6) A, c=10.625(15) A. The lattice parameters and formation energy of Mg{sub 0.5}NbO{sub 2} crystallized in LiNbO{sub 2} form and other layered CaNb{sub 2}O{sub 4} one were calculated by density functional theory. - Graphical abstract: A new layered niobate, Mg{sub 0.5}NbO{sub 2}, was synthesized from LiNbO{sub 2} through a cation-exchange reaction with Mg{sup 2+} at 450-550 Degree-Sign C. It is isostructural with LiNbO{sub 2} with lattice parameters of a=2.9052(6) A, c=10.625(15) A. Mg{sup 2+} are described in spheres located between [NbO{sub 2}]{sup -} trigonal layers and its occupancy is 0.5. Highlights: Black-Right-Pointing-Pointer A new layered niobate, Mg{sub 0.5}NbO{sub 2}, was synthesized from LiNbO{sub 2}. Black-Right-Pointing-Pointer Cation-exchange reaction converted two monovalent Li{sup +} into one divalent Mg{sup 2+} at 450-550 Degree-Sign C. Black-Right-Pointing-Pointer Mg{sub 0.5}NbO{sub 2} was isostructural with LiNbO{sub 2} (space group; P6{sub 3}/mmc). Black-Right-Pointing-Pointer Its lattice parameters were a=2.9052(6) A and c=10.625(15) A. Black-Right-Pointing-Pointer Synthesized Mg{sub 0.5}NbO{sub 2} was calculated to be thermodynamically more favorable.

Miura, Akira, E-mail: amiura@yamanashi.ac.jp [Center for Crystal Science and Technology, University of Yamanashi (Japan); Takei, Takahiro; Kumada, Nobuhiro [Center for Crystal Science and Technology, University of Yamanashi (Japan)

2013-01-15

211

Diabatic excited states of the (HeH 2) + molecular ion for the charge exchange-excitation reaction: He + + H 2 ? HeH + + H ?  

Microsoft Academic Search

An extensive set of data has been determined for a few low lying diabatic states of the (HeH2)+ system with a view to make possible future theoretical investigations of the He+ + H2 ? HeH+ + H? (n=2) reaction dynamics The data are produced in two steps. Firstly, ab initio calculations are carried out which follow a similar scheme to

V. Sidis

1996-01-01

212

An Easy Student Synthesis of a Substituted 1,3-Dioxane by Use of an Ion-Exchange Resin as Catalyst: Clean Illustration of the Prins Reaction.  

ERIC Educational Resources Information Center

Background information and experimental procedures are provided for a Prins reaction (condensation of an aldehyde with an alkene). The preparation of 4-(4-hydroxy, 3-methoxy-phenyl) 5-methyl, 1,3-dioxane realized from isoeugenol (natural plant product, commercially available) can be completed in a three-hour laboratory period. (Author/JN)

Delmas, Michael; And Others

1982-01-01

213

The mechanism of proton exchange: guided ion beam studies of the reactions, H(H2O)n+ (n=1-4)+D2O and D(D2O)n+ (n=1-4)+H2O.  

PubMed

Reactions of protonated water clusters, H(H(2)O)(n) (+) (n=1-4) with D(2)O and their "mirror" reactions, D(D(2)O)(n) (+) (n=1-4) with H(2)O, are studied using guided-ion beam mass spectrometry. Absolute reaction cross sections are determined as a function of collision energy from thermal energy to over 10 eV. At low collision energies, we observe reactions in which H(2)O and D(2)O molecules are interchanged and reactions where H-D exchange has occurred. As the collision energy is increased, the H-D exchange products decrease and the water exchange products become dominant. At high collision energies, processes in which one or more water molecules are lost from the reactant ions become important, with simple collision-induced dissociation processes, i.e., those without H-D exchange, being dominant. Threshold energies of endothermic channels are measured and used to determine binding energies of the proton bound complexes, which are consistent with those determined by thermal equilibrium measurements and previous collision-induced dissociation studies. A kinetic scheme that relies only on the ratio of isomerization and dissociation rate constants successfully accounts for the kinetic energy dependence observed in the branching ratios for H-D and water exchange products in all systems. Rice-Ramsperger-Kassel-Marcus theory and ab initio calculations confirm the feasibility and establish the details of this kinetic model. PMID:15511151

Honma, Kenji; Armentrout, P B

2004-11-01

214

High-resolution 100Mo(3He,t)100Tc charge-exchange experiment and the impact on double-? decays and neutrino charged-current reactions  

NASA Astrophysics Data System (ADS)

The Gamow-Teller (GT) strength distribution has been investigated in a high-resolution (3He,t) charge-exchange experiment on the double-beta (??) decaying nucleus 100Mo. The experiment was carried out at the Osaka University Research Center for Nuclear Physics (RCNP) with a 420 MeV incident 3He beam and the Grand Raiden magnetic spectrometer. A final-state energy resolution of 33 keV was achieved. It was found that nearly the entire low-energy (up to ?4 MeV) GT- strength is concentrated in the ground-state transition to 100Tc, which is interpreted as a result of the particular neutron and proton sub-shell occupancies. The impact on the matrix elements for the two-neutrino double-beta (2???) decay and the use of 100Mo as a neutrino detection material is discussed.

Thies, J. H.; Adachi, T.; Dozono, M.; Ejiri, H.; Frekers, D.; Fujita, H.; Fujita, Y.; Fujiwara, M.; Grewe, E.-W.; Hatanaka, K.; Heinrichs, P.; Ishikawa, D.; Khai, N. T.; Lennarz, A.; Matsubara, H.; Okamura, H.; Oo, Y. Y.; Puppe, P.; Ruhe, T.; Suda, K.; Tamii, A.; Yoshida, H. P.; Zegers, R. G. T.

2012-10-01

215

Application of FeOCl derivative for a secondary lithium battery; Discharge and charge characteristics of amorphous FeOOH prepared by ion exchange reaction of FeOCl including aniline  

SciTech Connect

This paper discusses a derivative of FeOCl chemically prepared by ion exchanging Cl{sup {minus}} ions with OH{sup {minus}} ions. This modification was made in order to improve the discharge and charge characteristics of a secondary lithium battery made with this material as the cathode. The preparation was accomplished by using the intercalation compound of FeOCl and aniline as an intermediate which has a high reactivity with water. The x-ray diffraction patterns of the reactant and product indicate that a structural change occurred, and the product structure became amorphous. The FT-IR spectrum of the reaction product indicates that an organic compound, which is similar to a secondary phenyl amine, remains in the interlayer space of this product. The discharge and charge characteristics of a lithium battery using this cathode were examined using a coin-type cell. The small cell showed excellent cycleability.

Kanamura, K.; Sakaebe, H.; Zhen, C.; Takehara, Z. (Dept. of Industrial Chemistry, Faculty of Engineering, Kyoto Univ., Yoshida-Hommachi, Sakyo-ku, Kyoto 606 (JP))

1991-10-01

216

Switching of PET fluorescence signals induced by ligand exchange reactions of N-(9-anthrylmethyl)amine on Cu(II) complexes and its application to postcolumn detection of glyphosate.  

PubMed

N-(9-Anthrylmethyl)amines which combine a fluorescent subunit and a chelate forming fragment have revealed a signal switching property in an aqueous solution upon complexation (off) with Cu(II) and liberation (on) of the probe molecule by substitution with an other ligand. The ligand exchange reaction between N-(phosphonomethyl)glycine (glyphosate), a typical herbicide, with N-(9-anthrylmethyl)amines on Cu(II) ion leads the fluorescence signal intensity to revive, providing an indirect detection system of glyphosate available in water of neutral pH region. The present system has been applied to the post column detection in the ion chromatographic separation of glyphosate and its metabolite aminomethylphosphonic acid (AMPA). PMID:15844337

Tanaka, David A Pacheco; Alvarado, Mario S Cuentas; Tanco, Margot A Llosa; Takahashi, Yukiko; Chatterjee, Abhijit; Suzuki, Hiroshi; Suzuki, Toshishige M

2005-04-01

217

Platinum-cobalt catalysts for the oxygen reduction reaction in high temperature proton exchange membrane fuel cells - Long term behavior under ex-situ and in-situ conditions  

NASA Astrophysics Data System (ADS)

Platinum cobalt catalysts (Pt-Co) have attracted much interest as cathode catalysts for proton exchange membrane fuel cells (PEMFCs) due to their high activity toward oxygen reduction reaction (ORR). Many of the reported catalysts show outstanding performance in ex-situ experiments. However, the laborious synthesis protocols of these Pt-Co catalysts disable an efficient and economic production of membrane electrode assemblies (MEAs). We present an economic, flexible and continuous Pt-M/C catalyst preparation method as part of a large scale membrane electrode assembly manufacturing. In comparison, the as-prepared Pt-Co/C based high temperature (HT)-PEM MEA showed an equal performance to a commercially available HT-PEM MEA during 600h of operation under constant load, although the commercial one had a significantly higher Pt loading at the cathode.

Schenk, Alexander; Grimmer, Christoph; Perchthaler, Markus; Weinberger, Stephan; Pichler, Birgit; Heinzl, Christoph; Scheu, Christina; Mautner, Franz-Andreas; Bitschnau, Brigitte; Hacker, Viktor

2014-11-01

218

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

219

Slowdown of H/D exchange reaction rate and water dynamics in ionic liquids: deactivation of solitary water solvated by small anions in 1-butyl-3-methyl-imidazolium chloride.  

PubMed

The H/D exchange reaction and the rotational dynamics of heavy water (D2O) are studied at 50 degrees C in the ionic liquid, 1-butyl-3-methylimidazolium chloride ([bmim][Cl]), in the [D2O] range of 3-55 M. The initial H/D exchange rates are observed as 1.0 x 10(-7), 4.5 x 10(-6), 1.0 x 10(-5), 4.1 x 10(-5), 1.1 x 10(-4), and 3.7 x 10(-4) s(-1), respectively, at [D2O] of 2.8, 7.1, 8.1, 11, 15, and 25 M. The rate is very slow and less than 10(-5) s(-1) at [D2O] below approximately 7 M. It steeply increases to the order of 10(-4)s(-1) for 7 M < [D2O] < 10 M, and linearly increases with [D2O] in the more water-rich region. The intercept of the linear region at [D2O] = approximately 9 M is interpreted by considering that each chloride anion deactivates 1.6 equiv water molecules due to the strong solvation. Correspondingly, the rotational correlation time of D2O at [D2O] < 7 M is 1 order of magnitude larger than that in water-rich conditions. PMID:17249739

Yasaka, Yoshiro; Wakai, Chihiro; Matubayasi, Nobuyuki; Nakahara, Masaru

2007-02-01

220

C?H Bond Activation during and after the Reactions of a Metallacyclic Amide with Silanes: Formation of a ?-Alkylidene Hydride Complex, Its H-D Exchange, and ?-H Abstraction by a Hydride Ligand.  

PubMed

Metallacyclic complex [(Me2 N)3 Ta(?(2) -CH2 SiMe2 NSiMe3 )] (3) undergoes C?H activation in its reaction with H3 SiPh to afford a Ta/?-alkylidene/hydride complex, [(Me2 N)2 {(Me3 Si)2 N}Ta(?-H)2 (?-C-?(2) -CHSiMe2 NSiMe3 )Ta(NMe2 )2 ] (4). Deuterium-labeling studies with [D3 ]SiPh show H-D exchange between the Ta?D?Ta unit and all methyl groups in [(Me2 N)2 {(Me3 Si)2 N}Ta(?-D)2 (?-C-?(2) -CHSiMe2 NSiMe3 )Ta(NMe2 )2 ] ([D2 ]-4) to give the partially deuterated complex [Dn ]-4. In addition, 4 undergoes ?-H abstraction between a hydride and an NMe2 ligand and forms a new complex [(Me2 N){(Me3 Si)2 N}Ta(?-H)(?-N-?(2) -C,N-CH2 NMe)(?-C-?(2) -C,N-CHSiMe2 NSiMe3 )Ta(NMe2 )2 ] (5) with a cyclometalated, ?(2) -imine ligand. These results indicate that there are two simultaneous processes in [Dn ]-4: 1)?H-D exchange through ?-bond metathesis, and 2)?H?D elimination through ?-H abstraction (to give [Dn ]-5). Both 4 and 5 have been characterized by single-crystal X-ray diffraction studies. PMID:24682935

Wang, Li; Hunter, Seth C; Song, Zhimin; Steren, Carlos A; Chen, Tianniu; Wei, Zhenhong; Cai, Hu; Xue, Zi-Ling

2014-05-12

221

Catalysis with Metal Cation-Exchanged Resins  

Microsoft Academic Search

There have been a paucity of reports dealing with catalytic reactions involving metal or metal cations incorporated into ion-exchange resins. It is the objective of this review to summarize these reactions and to discuss in detail one such resin, a perfluorinated Exchange polymer, PFIEP. here survey two resin types, polystyrene sulfonic acid (PSSA) and PFIEP or Nafion [11. Acid catalysis

F. J. Waller

1986-01-01

222

The Third Dimension of a More O'Ferrall-Jencks Diagram for Hydrogen Atom Transfer in the Isoelectronic Hydrogen Exchange Reactions of (PhX)2H with X = O, NH, and CH2  

PubMed Central

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 OFerrall-Jencks diagram can be represented to determine the step-wise and concerted nature of the reaction. Although the More OFerrall-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 OFerrall-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)2H, where X = O, NH, and CH2, 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 PhNH2 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.

Cembran, Alessandro; Provorse, Makenzie R.; Wang, Changwei

2012-01-01

223

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

2012-11-13

224

Videotape Exchange  

ERIC Educational Resources Information Center

Describes a videotape exchange between students in a New York City school and a classroom of students in Charleston, South Carolina, explaining what the students learned about themselves and others from the personally-made tapes. (RB)

Mack, Teresa

1975-01-01

225

Heat exchanger  

SciTech Connect

A heat exchanger having primary and secondary conduits in heat-exchanging relationship is described comprising: at least one serpentine tube having parallel sections connected by reverse bends, the serpentine tube constituting one of the conduits; a group of open-ended tubes disposed adjacent to the parallel sections, the open-ended tubes constituting the other of the conduits, and forming a continuous mass of contacting tubes extending between and surrounding the serpentine tube sections; and means securing the mass of tubes together to form a predetermined cross-section of the entirety of the mass of open-ended tubes and tube sections.

Drury, C.R.

1988-02-02

226

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

NASA Technical Reports Server (NTRS)

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.

2010-01-01

227

Effect of nitration on the activity of bovine erythrocyte Cu,Zn-superoxide dismutase (BESOD) and a kinetic analysis of its dimerization-dissociation reaction as examined by subunit exchange between the native and nitrated BESODs.  

PubMed

Bovine erythrocyte Cu,Zn-superoxide dismutase (BESOD) is a dimeric enzyme composed of identical subunits associated through unusually strong non-covalent interactions. The state of the unique tyrosyl residue (Tyr 108) of BESOD was examined, and the kinetics of subunit exchange was studied using Tyr 108 as a probe. UV-absorption difference spectra demonstrate that Tyr 108 is exposed to the solvent, and that the accessibilities to ethanol, ethylene glycol, and polyethylene glycol 600 are 53.5, 52.0, and 44.6%, respectively. Tyr 108 was fully nitrated by tetranitromethane. The pK(a) values of the phenolic hydroxyl group of native and nitrated Tyr 108 were determined to be 11.3 and 7.9, whereas those of model compounds, L-tyrosine and 3-nitro-L-tyrosine, are 9.8 and 6.8, respectively. When the native and nitrated BESODs of an equal concentration were mixed, the hybrid dimer was formed. From the amount of hybrid dimer formed, the rate constant (k(-1)) of the subunit dissociation at pH 7.8, 25 degrees C was assessed to be (4.17 +/- 0.13) x 10(-6) s(-1). The activation energy of the subunit dissociation at pH 7.8 was determined to be 117 +/- 4 kJ.mol(-1). The k(-1) value remains constant at BESOD concentrations ranging from 0.62 to 6.8 micro M and at pH ranging from 6.0 to 10.0, but increased remarkably with a decrease in the dielectric constant of the reaction mixture. It is suggested that hydrophobic interaction may play a significant role in the subunit interaction. PMID:14688234

Oneda, Hiroshi; Inouye, Kuniyo

2003-11-01

228

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

229

Segmented heat exchanger  

DOEpatents

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

230

Textile Exchange  

NSDL National Science Digital Library

From crochet machines to the uses of acrylic yarn, the Textile Exchange website has rather fine comprehensive coverage across the nooks and crannies of the textile industry. Visitors to the homepage will find a search engine and a very thorough products directory which includes topical headings like "Textile Products", "Fibers, Yarns & Threads", and "Textile Chemicals". After looking over a few of these areas, visitors will definitely want to peruse the "Knowledge Center". Here they can learn more about fiber and textile history, and the types of weaves. One section that should not be missed is the "Textile Personalities" area. For those individuals who've been pining to learn about giants of the textile industry such as John Mercer, John Kay (who patented the flying shuttle), and Richard Roberts, this area will be quite the eye-opener.

231

Weathering Reactions and Soil-Groundwater Reactions  

NSDL National Science Digital Library

This 11-page PDF document is part of an environmental geochemistry course taught by Dr. David Sherman at the University of Bristol. The lecture explores the weathering reactions that convert primary minerals into quartz or phyllosilicate clays and iron oxide hydroxides, and the mineral-water reactions that buffer pH and the dissolved ion concentration of groundwater. Also discussed is the manner in which phyllosilicate clays, iron oxides and hydroxides sorb pollutants via ion exchange and adsorption. Helpful diagrams and illustrations accompany the text.

Sherman, David M.; Bristol, University O.

232

Biological Ion Exchanger Resins  

PubMed Central

The cell is presented as a biological ion exchanger resin. The similarities between ion accumulating cells and ion exchanger resins are correlated. The kinetic characteristics of biological ion exchange are shown to be amenable to analysis by a model commonly used for ion exchanger resins. The theories of ion exchange equilibria currently in use with ion exchanger resins are reviewed with their suitability for adaptation to biological ion exchange in mind. ImagesFIGURE 1

Damadian, Raymond

1971-01-01

233

A novel pulse isotopic exchange technique for rapid determination of the oxygen surface exchange rate of oxide ion conductors.  

PubMed

We demonstrate the use of a novel pulse (18)O-(16)O isotopic exchange technique for the rapid determination of the oxygen surface exchange rate of oxide ion conductors while simultaneously providing insight into the mechanism of the oxygen exchange reaction, which contributes to the efficient development of devices incorporating these solids, such as solid oxide fuel cells and oxygen transport membranes. PMID:19851540

Bouwmeester, Henny J M; Song, Chunlin; Zhu, Jianjun; Yi, Jianxin; van Sint Annaland, Martin; Boukamp, Bernard A

2009-11-14

234

Educator Exchange Resource Guide.  

ERIC Educational Resources Information Center

This resource guide was developed for teachers and administrators interested in participating in intercultural and international exchange programs or starting an exchange program. An analysis of an exchange program's critical elements discusses exchange activities; orientation sessions; duration of exchange; criteria for participation; travel,

Garza, Cris; Rodriguez, Victor

235

Reactions of 2-benzo[b]thienyl (2-BTyl) complexes with acid to give Cp(PMe[sub 3])[sub 2]Ru([eta][sup 1](S)-BT)[sup +] and Cp(CO)(PPh[sub 3])Ru([eta][sup 1](S)-BT[sup +]): A model for benzo[b]thiophene (BT) deuterium exchange on hydrodesulfurization catalysis  

SciTech Connect

Hydrodesulfurization (HDS) of benzo[b]thiophene (BT) over Co-Mo/Al[sub 2]O[sub 3] catalysts to give ethylbenzene and H[sub 2]S is proposed to occur by two mechanistic pathways either by initial hydrogenation to give 2,3-dihydrobenzothiophene followed by desulfurization to form the final products or by initial desulfurization to give vinylbenzene followed by hydrogenation to ethylbenzene. Regardless of the pathway, the reaction involves only the thiophenic part of BT as the benzene ring is not hydrogenated. Also, deuterium exchange of BT, when passed with D[sub 2] over HDS catalysts, occurs predominantly in the 2- and 3-positions of the thiophene rather than in the benzene ring. A mechanism which accounts for this deuterium exchange has been proposed by Cowley. In order to probe the possibility that [sigma]-coordination of 2-benzothienyl (2-BTyl) to a metal accounts for deuterium exchange at the 2-position as proposed by Cowley, the authors describe herein the synthesis of 2-BTyl complexes of Ru and examine their reactions with CF[sub 3]SO[sub 3]H. 19 refs., 2 figs.

Benson, J.W.; Angelici, R.J. (Iowa State Univ., Ames (United States))

1993-04-28

236

Pion exchange at high energies  

SciTech Connect

The state of Regge pion exchange calculations for high-energy reactions is reviewed. Experimental evidence is summarized to show that (i) the pion trajectory has a slope similar to that of other trajectories; (ii) the pion exchange contribution can dominate contributions of higher trajectories up to quite a large energy; (iii) many two-body cross sections with large pion contributions can be fit only by models which allow for kinematical conspiracy at t=0. The theory of kinematic conspiracy is reviewed for two-body amplitudes, and calculations of the conspiring pion--Pomeron cut discussed. The author then summarizes recent work on pion exchange in Reggeized Deck models for multiparticle final states, with emphasis on the predictions of various models (with and without resonances) for phases of the partial wave amplitudes.

Jones, L.M.

1980-07-01

237

Drug Reactions  

MedlinePLUS

... adverse drug reaction. One medicine might cause an adverse reaction if its taken with another medicine. One way ... reaction. Are prescription medicines the only cause of adverse reactions? No. Even medicines that you don't need ...

238

Fundamental reaction pathways during coprocessing. Tenth quarterly technical progress report and milestone status report.  

National Technical Information Service (NTIS)

Deuterium incorporation into Lloydminster resid and asphaltene was accomplished via acid and base-catalyzed hydrogen-deuterium exchange reactions. More specifically, the acid-catalyzed exchanged reaction was carried out with trifluoromethanesulfonic acid-...

L. M. Stock

1991-01-01

239

Crystal structure of the external aldimine of Citrobacter freundii methionine ?-lyase with glycine provides insight in mechanisms of two stages of physiological reaction and isotope exchange of ?- and ?-protons of competitive inhibitors.  

PubMed

The three-dimensional structure of the external aldimine of Citrobacter freundii methionine ?-lyase with competitive inhibitor glycine has been determined at 2.45? resolution. It revealed subtle conformational changes providing effective binding of the inhibitor and facilitating labilization of C?-protons of the external aldimine. The structure shows that 1, 3-prototropic shift of C?-proton to C4'-atom of the cofactor may proceed with participation of active site Lys210 residue whose location is favorable for performing this transformation by a concerted mechanism. The observed stereoselectivity of isotopic exchange of enantiotopic C?-protons of glycine may be explained on the basis of external aldimine structure. The exchange of C?-pro-(R)-proton of the external aldimine might proceed in the course of the concerted transfer of the proton from C?-atom of glycine to C4'-atom of the cofactor. The exchange of C?-pro-(S)-proton may be performed with participation of Tyr113 residue which should be present in its basic form. The isotopic exchange of ?-protons, which is observed for amino acids bearing longer side groups, may be effected by two catalytic groups: Lys210 in its basic form, and Tyr113 acting as a general acid. PMID:24463191

Revtovich, Svetlana V; Faleev, Nicolai G; Morozova, Elena A; Anufrieva, Natalya V; Nikulin, Alexey D; Demidkina, Tatyana V

2014-06-01

240

Dbl family guanine nucleotide exchange factors  

Microsoft Academic Search

The Dbl family of guanine nucleotide exchange factors are multifunctional molecules that transduce diverse intracellular signals leading to the activation of Rho GTPases. The tandem Dbl-homology and pleckstrin-homology domains shared by all members of this family represent the structural module responsible for catalyzing the GDPGTP exchange reaction of Rho proteins. Recent progress in genomic, genetic, structural and biochemical studies has

Yi Zheng

2001-01-01

241

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

242

The rates of the exchange reactions between [Gd(DTPA)]2- and the endogenous ions Cu2+ and Zn2+: a kinetic model for the prediction of the in vivo stability of [Gd(DTPA)]2-, used as a contrast agent in magnetic resonance imaging.  

PubMed

The kinetic stability of the complex [Gd(DTPA)]2- (H5DTPA = diethylenetriamine-N,N,N',N",N"-pentaacetic acid), used as a contrast-enhancing agent in magnetic resonance imaging (MRI), is characterised by the rates of the exchange reactions that take place with the endogenous ions Cu2+ and Zn2+. The reactions predominantly occur through the direct attack of Cu2+ and Zn2+ on the complex (rate constants are 0.93+/-0.17 M(-1) s(-1) and (5.6+/-0.4) x 10(-2)M(-1) S(-1), respectively). The proton-assisted dissociation of [Gd(DTPA)]2- is relatively slow (k1 = 0.58+/-0.22 M(-1) s(-1)), and under physiological conditions the release of Gd3+ predominantly occurs through the reactions of the complex with the Cu2+ and Zn2+ ions. To interpret the rate data, the rate-controlling role of a dinuclear intermediate was assumed in which a glycinate fragment of DTPA is coordinated to Cu2+ or Zn2+. In the exchange reactions between [Gd-(DTPA)]2- and Eu3+, smaller amounts of Cu2+ and Zn2+ and their complexes with the amino acids glycine and cysteine have a catalytic effect. In a model of the fate of the complex in the body fluids, the excretion and the "dissociation" of [Gd(DTPA)]2- are regarded as parallel first-order processes, and by 10 h after the intravenous administration the ratio of the amounts of "dissociated" and excreted [Gd(DTPA)]2- is constant. From about this time, 1.71% of the injected dose of [Gd(DTPA)]2- is "dissociated". The results of equilibrium calculations indicate that the Gd3+ released from the complex is in the form of Gd3+-citrate. PMID:10807182

Sarka, L; Burai, L; Brcher, E

2000-02-18

243

Concerted hydrogen atom exchange between three HF molecules  

NASA Technical Reports Server (NTRS)

The termolecular reaction involving concerted hydrogen-atom exchange between three HF molecules was investigated with particular attention given to the effects of correlation at the various stationary points along the reaction. Using large segmented Gaussian basis sets to locate the (HF)3 stationary points at the SCF level, the geometries of the stable hydrogen-bonded trimer, which is of C(3h) symmetry, were located, together with the transition state for hydrogen exchange, which is of D(3h) symmetry. Then, using a large atomic natural orbital basis and correlating all valence electrons, the energetics of the exchange reaction were evaluated at the correlated level.

Komornicki, Andrew; Dixon, David A.; Taylor, Peter R.

1992-01-01

244

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.

245

Differential cross sections of the charge-exchange reaction {pi}{sup -}p{yields}{pi}{sup 0}n in the momentum range from 103 to 178 MeV/c  

SciTech Connect

Measured values of the differential cross sections for pion-nucleon charge exchange, {pi}{sup -}p{yields}{pi}{sup 0}n, are presented for {pi}{sup -} momenta of 103,112,120,130,139,152, and 178 MeV/c. Complete angular distributions were obtained by using the Crystal Ball detector at the Alternating Gradient Synchrotron at Brookhaven National Laboratory. Statistical uncertainties of the differential cross sections vary from 3 to 6% in the backward angle region and from 6 to about 20% in the forward region with the exception of the two most forward angles. The systematic uncertainties are estimated to be about 3% for all momenta.

Mekterovic, D.; Supek, I. [Ruder Boskovic Institute, Zagreb 10000 (Croatia); Abaev, V.; Bekrenev, V.; Kozlenko, N.; Kulbardis, A.; Kruglov, S.; Lopatin, I. [Petersburg Nuclear Physics Institute, Gatchina RU-188350 (Russian Federation); Bircher, C.; Isenhover, D.; Jerkins, M.; Joy, M.; Sadler, M. E.; Watson, S. [Abilene Christian University, Abilene, Texas 79699-7963 (United States); Briscoe, W. J.; Shafi, A.; Strakovsky, I. [George Washington University, Washington, DC 20052-0001 (United States); Cadman, R. V.; Spinka, H. [Argonne National Laboratory, Argonne, Illinois 60439-4815 (United States); Clajus, M. [University of California, Los Angeles, California 90095-1547 (United States)] (and others)

2009-11-15

246

New Trifluorosilyl Exchange Reagent: Reactions of Cd(SiF3)2.glyme (glyme = dimethoxyethane) with Dibromo Metal Phosphine Complexes of Platinum, Palladium, and Nickel yield Trifluorosilyl Substituted Dialkyl Compounds.  

National Technical Information Service (NTIS)

The reaction of excess Cd(SiF3)2.glyme (glyme = dimethoxyethane) with trimethylphospine metal dibromides of platinum, palladium, and nickel yielded the trifluorosilyl substituted dialkyl compounds trans-Pt(SiF3)2(PMe3)2, Pd(SiF3)2(PMe3)2, and Ni(SiF3)2(PM...

M. A. Guerra R. J. Lagow

1990-01-01

247

Semi-Classical Treatment of Exchange Processes.  

National Technical Information Service (NTIS)

The chemical exchange reaction A+BC to AB+C is treated in the approximation where the mass of the atom B is very small compared to those of the atoms A and C. Furthermore, A and C are taken to be essentially identical, so that an impact parameter treatmen...

C. Nyeland T. A. Bak

1964-01-01

248

THE IRRADIATION OF ION EXCHANGERS IN JEEP  

Microsoft Academic Search

Several organic and inorganic ion exchanger materials were irradiated in ; JEEP. Radiation effects are dcscribed and dependence on dose rate and quality of ; the radiation is discussed. By comparing the action of different kinds of ; ionizing radiation, possible reaction mechanisms are discussed. (authl;

Nater

1959-01-01

249

Exchange rates and fundamentals  

Microsoft Academic Search

Standard economic models hold that exchange rates are influenced by fundamental variables such as relative money supplies, outputs, inflation rates and interest rates. Nonetheless, it has been well documented that such variables little help predict changes in floating exchange rates that is, exchange rates follow a random walk. We show that the data do exhibit a related link suggested

Charles Engel; Kenneth D. West

2003-01-01

250

Exchange rates and fundamentals  

Microsoft Academic Search

Standard economic models hold that exchange rates are influenced by fundamental variables such as relative money supplies, outputs, inflation rates and interest rates. Nonetheless, it has been well documented that such variables little help predict changes in floating exchange rates - that is, exchange rates follow a random walk. We show that the data do exhibit a related link suggested

Charles Engel; Kenneth D. West

2003-01-01

251

Bifunctional anion-exchange resins with improved selectivity and exchange kinetics  

DOEpatents

Disclosed herein are a class of anion exchange resins containing two different exchange sites with improved selectivity and sorptive capability for chemical species in solution, such as heptavalent technetium (as pertechnetate anion, TcO.sub.4.sup.-). The resins are prepared by first reacting haloalkylated crosslinked copolymer beads with a large tertiary amine in a solvent in which the resin beads can swell, followed by reaction with a second, smaller, tertiary amine to more fully complete the functionalization of the resin. The resins have enhanced selectivity, capacity, and exchange kinetics.

Alexandratos, Spiro D. (Knoxville, TN) [Knoxville, TN; Brown, Gilbert M. (Knoxville, TN) [Knoxville, TN; Bonnesen, Peter V. (Knoxville, TN) [Knoxville, TN; Moyer, Bruce A. (Oak Ridge, TN) [Oak Ridge, TN

2000-01-01

252

Formaldehyde reactions in dark clouds  

NASA Technical Reports Server (NTRS)

The low-pressure reactions of formaldehyde (H2CO) with D(+), D2(+), D3(+), and He(+) are studied by the ion-cyclotron resonance technique. These reactions are potential loss processes for formaldehyde in cores of dark interstellar clouds. The deuterated reactants represent direct analogs for protons. Rate coefficients and branching ratios of product channels have been measured. Charge transfer is observed to be the dominant reaction of H2CO with D(+), D2(+), and He(+) ions. Only the D3(+) reaction exhibits a proton-transfer channel. All reactions proceed at rate coefficients near the collision limit. Proton-deuteron exchange reactions are found to be inefficient processes in the formaldehyde system.

Sen, A. D.; Anicich, V. G.; Federman, S. R.

1992-01-01

253

CaMn exchange between grossular and MnCl 2 solutions at 2 kbar and 600C: reaction mechanism and evidence for non-ideal mixing in spessartine-grossular garnets  

Microsoft Academic Search

The hydrothermal reaction between grossular and 1 molar manganese chloride solution was studied at 2?kbar and 600?C at various\\u000a bulk Ca\\/(Ca+Mn) compositions:\\u000a \\u000a Ca3Al2Si3O12+3Mn2+(aq)???Mn3Al2Si3O12+3Ca2+(aq)\\u000a \\u000a \\u000a \\u000a The reaction products are garnets of the spessartine-grossular solid-solution series which discontinuously armour the dissolving\\u000a grossular grains. The first garnet to crystallize is spessartine rich (X\\u000a gt\\u000a Mn?0.95), reflecting the high Mn content of the solution, but

Ittai Gavrieli; Alan Matthews; J. B. Holland

1996-01-01

254

Epoxide Reactions  

NASA Astrophysics Data System (ADS)

This puzzle presents 16 numbered reactions of epoxides and 11 possible products designated by letters. The reactions are matched with the letters corresponding to the products to answer a playful question.

Bertolini, Thomas

2002-07-01

255

Exchangeable and partially exchangeable random partitions  

Microsoft Academic Search

Summary Call a random partition of the positive integerspartially exchangeable if for each finite sequence of positive integersn1,...,nk, the probability that the partition breaks the firstn1+...+nk integers intok particular classes, of sizesn1,...,nk in order of their first elements, has the same valuep(n1,...,nk) for every possible choice of classes subject to the sizes constraint. A random partition is exchangeable iff it

Jim Pitman

1995-01-01

256

Reaction time  

Microsoft Academic Search

Reviews five studies of reaction time published during 1917-1918. The Studies pertain to (a) effect of continuous, intermittent, continuous-intermittent auditory distraction upon sensory reactions to auditory stimuli (b) processes involved in the fore-period, main period and after-period of the controlled associative reaction with special reference to the analysis of fore-period (c) use of reaction key suspended as a pendulum and

V. A. C. Henmon

1918-01-01

257

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

258

Enzyme Reactions  

NSDL National Science Digital Library

This video shows an enzyme reaction lab. The teacher demonstrates how the enzyme, catalase, reacts with hydrogen peroxide (a substrate found in cells). The teacher first demonstrates a normal enzyme reaction. He or she then goes on to show how manipulating temperature and pH will affect the reaction of an enzyme.

School, Minerva D.

2011-10-03

259

Electron-transfer reactions of technetium and rhenium complexes. 2. Relative self-exchange rate of the M(I)/M(II) couples (M(DMPE)/sub 3/)/sup +/2+/, where M = Tc or Re and DMPE = 1,2-bis(dimethylphosphino)ethane  

SciTech Connect

The relative rates of self-exchange of the closely related d/sup 6//d/sup 5/ couples (Tc(DMPE)/sub 3/)/sup +/2+/ and (Re(DMPE)/sub 3/)/sup +/2+/ have been determined by two independent applications of the Marcus theory. (1) The rates and equilibrium constants governing the cross-reactions between (Re(DMPE)/sub 3/)/sup +/ and ((NH/sub 3/)/sub 5/RuL)/sup 3+/ (L = 4-picoline, pyridine, and isonicotinamide) were measured in a 0.100 M LiCl and 0.001 M HCl aqueous medium and compared to equivalent data previously obtained for the reaction of (Tc(DMPE)/sub 3/)/sup +/ with the same three Ru(III) complexes in this medium. (2) EXAFS measurements were used to obtain average Re(I)-P and Re(II)-P bond lengths for the (Re(DMPE)/sub 3/)/sup +2/2+/ complexes, and these data were compared to equivalent data available for the (Tc(DMPE)/sub 3/)/sup +/2+/ complexes. The difference in bond lengths, (M/sup II/-P) - (M/sup I/-P), is less for the Re couple than for the Tc couple (0.054 vs 0.068 /angstrom/), and within the Marcus formalism this leads directly to a structurally determined value of k/sub ex//sup Re//k/sub ex//sup Tc/ = 2. Thus, the kinetically observed, slightly greater rate of self-exchange of the (Re(DMPE)/sub 3/)/sup +/2+/ couple is seen to be due entirely to the somewhat smaller structural distortions suffered by the inner coordination sphere of the Re complex during electron transfer. The absolute self-exchange rates of the (Re(DMPE)/sub 3/)/sup +/2+/ and (Tc(DMPE)/sub 3/)/sup +/2+/ couples are calculated to be 4 /times/ 10/sup 6/ M/sup /minus/1/ s/sup /minus/1/ and 2 /times/ 10/sup 6/ M/sup /minus/1/ s/sup /minus/1/, respectively (25/degree/C, /mu/ = 0.10 M). 17 refs., 2 figs., 5 tabs.

Libson, K.; Woods, M.; Sullivan, J.C.; Watkins, J.W. II; Elder, R.C.; Deutsch, E.

1988-03-23

260

Ceramics in heat exchangers  

Microsoft Academic Search

This book presents the papers given at a conference on the testing of ceramics for heat exchangers. Topics considered at the conference included advanced heat-transfer systems, heat recovery equipment, air-to-air heat exchangers, fluidized bed heat-recovery boilers, industrial heat recovery, potential materials, materials development and evaluation, chemical vapor deposition, product testing, fracture properties, and the durability of silicon carbide heat-exchanger tubes

B. D. Foster; J. B. Patton

1984-01-01

261

Convertible Exchangeable Preferred Stock  

Microsoft Academic Search

Convertible exchangeable preferred stock includes an option for the issuer to exchange the preferred for convertible bonds with identical pre-tax cash flows and conversion terms. In other respects this innovative corporate security is identical to traditional convertible preferred stock. The exchange feature provides the issuer with a potentially valuable option to swap a non-tax-deductible expense for a tax-deductible one. The

Arnold R. Cowan

1996-01-01

262

Quaternized polyethersulfone Cardo anion exchange membranes for direct methanol alkaline fuel cells  

Microsoft Academic Search

A novel anion exchange membrane, quaternized polyethersulfone Cardo, was prepared. Polyethersulfone Cardo was chloromethylated with the complex solution of chloromethylether and chloride zinc. Subsequent reaction with trimethylamine and ion exchange with sodium hydroxide yields alkaline anion exchange membrane. The quaternized polyethersulfone Cardo (QPES-C) membrane may be suitable for use in low temperature direct methanol alkaline fuel cells. Ionic conductivity and

Lei Li; Yuxin Wang

2005-01-01

263

Text Exchange System  

NASA Technical Reports Server (NTRS)

Text Exchange System (TES) exchanges and maintains organized textual information including source code, documentation, data, and listings. System consists of two computer programs and definition of format for information storage. Comprehensive program used to create, read, and maintain TES files. TES developed to meet three goals: First, easy and efficient exchange of programs and other textual data between similar and dissimilar computer systems via magnetic tape. Second, provide transportable management system for textual information. Third, provide common user interface, over wide variety of computing systems, for all activities associated with text exchange.

Snyder, W. V.; Hanson, R. J.

1986-01-01

264

Shale oil denitrogenation with ion exchange  

SciTech Connect

The nitrogen-containing aromatics normally found in crude retorted shale oils have been shown to be involved in reactions leading to the deposition of insoluble gums and sediments. These nitrogen-containing compounds must be removed in order to permit the effective utilization of the shale oil product. A process is proposed in which the nitrogen-containing compounds found in raw shale oil are removed by mild hydrodenitrogenation followed by resin ion exchange. Ion exchange data from experimentation involving six jet fuel (154-271C) and diesel fuel (271-343C) boiling point cuts are presented. Amberlyst A-15, a macroreticular, strongly acidic, cation exchange resin is used in this study. Three types of experiments were performed: batch sorption equilibrium experiments, batch sorption kinetics experiments, and dynamic ion-exchange column performance tests. The Langmuir isotherm was found to describe the equilibrium sorption behavior of the shale oil/ion-exchange resin system fairly well. The sorption kinetics are described using a quadratic-driving force model. Dynamic modeling, assuming intraparticle (solid) diffusion control and including the results of the batch equilibrium and batch kinetics experiments, provides reasonable prediction of the results of dynamic ion-exchange column performance tests.

Prudich, M.E.; Cronauer, D.C.; Marcelin, G.

1987-01-01

265

ZEOLITE PERFORMANCE AS AN ANION EXCHANGER FOR ARSENIC SEQUESTRATION IN WATER  

EPA Science Inventory

Zeolites are well known for their use in ion exchange and acid catalysis reactions. The use of zeolites in anion or ligand exchange reactions is less studied. The NH4+ form of zeolite Y (NY6, Faujasite) has been tested in this work to evaluate its performance for arsenic removal...

266

Higher Education Exchange, 2005  

ERIC Educational Resources Information Center

The "Higher Education Exchange" is part of a movement to strengthen higher education's democratic mission and foster a more democratic culture throughout American society. Working in this tradition, the "Higher Education Exchange" publishes case studies, analyses, news, and ideas about efforts within higher education to develop more democratic

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

2005-01-01

267

Serpentine heat exchanger  

Microsoft Academic Search

This patent describes a furnace having a burner means for providing hot products of combustion, and an air flow means for circulating conditioned air, a heat exchanger for transferring heat from products of combustion to conditioned air. The heat exchanger comprises first and second matched clamshell plates assembled together. The plates connected at their respective edges by a sealing means

1991-01-01

268

Higher Education Exchange, 2010  

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.

2010-01-01

269

Money and exchange  

Microsoft Academic Search

This paper endorses Marx's deduction of the need for money to actualise value before exchange can be considered, so that, in exchange, money's function as means of purchase follows from money's ability to actualise value. This is contrasted with the Uno school, whose proponents mix concepts from Capital chapters 1 and 2. The paper goes beyond Marx in presenting a

Christopher J. Arthur

2006-01-01

270

Higher Education Exchange, 2008  

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.

2008-01-01

271

Higher Education Exchange, 2007  

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" discuss the concept of growing public scholars; each contribution incorporates a student component. Articles include: (1) "Foreword"

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

2007-01-01

272

Higher Education Exchange, 2004  

ERIC Educational Resources Information Center

The Higher Education Exchange is part of a movement to strengthen higher education's democratic mission and foster a more democratic culture throughout American society. Working in this tradition, the Higher Education Exchange publishes case studies, analyses, news, and ideas about efforts within higher education to develop more democratic

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

2004-01-01

273

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

274

Higher Education Exchange, 2011  

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.

2011-01-01

275

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

276

Computational Science - Stack Exchange  

NSDL National Science Digital Library

This is a free, community driven Q&A for scientists using computers to solve scientific problems. It is a part of the Stack Exchange network of Q&A websites, and it was created through the open democratic process defined at Stack Exchange Area 51.

277

Reaction Time  

NSDL National Science Digital Library

In this activity, learners explore reaction time and challenge themselves to improve their coordination. Do you want to move faster? Catch that ball that you never seem to see in time? Use a simple test to help you improve your reaction (or response) time.

Science, New Y.

1999-01-01

278

Reaction Kinetics  

NASA Astrophysics Data System (ADS)

Detonation, which is the result of a reacting high explosive, is not a simple chemical reaction. Instead it is a complex process of rapid chemical changes that give rise to equally rapid mechanical and physical changes. Initially, as the explosive is initiated or Subscriptjected to a stimulus such as a shock wave, energy is transferred to the material causing mechanical deformation and heating. The transferred energy and heating produce chemically excited species, leading to initial bond-breaking or reaction initiation. These processes are thought to occur in a Hot-Molecule Zone (HMZ). Once reaction is initiated, sequences of chemical reactions follow resulting in the liberation of chemical energy and the production of gaseous reaction products.

Peiris, Suhithi M.

279

Systematics of pion double charge exchange  

SciTech Connect

Differential cross sections have been measured for pion-induced double-charge-exchange (DCX) reactions leading to double-isobaric-analog states (DIAS) and low-lying nonanalog states in the residual nuclei. A description of the experimental details and data analysis is presented. The experimentally observed systematics of reactions leading to DIAS, to nonanalog ground states, and to low-lying 2 states are described. Lowest-order optical-model calculations of DIAS DCX are compared to the data. Efforts to understand the anomalies by invoking additional reaction-mechanism amplitudes and a higher-order optical potential are described. Calculations of nonanalog DCX reactions leading to J/sup / = 0 states were performed within a distorted-wave impulse-approximation framework. The sensitivities of these calculations to input parameters are discussed. 58 refs., 41 figs., 16 tabs.

Gilman, R.A.

1985-10-01

280

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

281

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

282

Microtube strip heat exchanger  

SciTech Connect

This progress report is for the September--October 1991 quarter. 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.

1991-10-16

283

Heat and mass exchanger  

DOEpatents

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

284

Heat and mass exchanger  

DOEpatents

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)

2011-06-28

285

[Periosteal reaction].  

PubMed

The periosteal membrane covers the cortical bone except for the articular surface. The deep layer of the periosteum contains bone-forming mesenchymal cells, capillaries, and nerves. This layer is more active in infants than in adults. Prostaglandin osteopathy, infantile cortical hyperostosis, hypervitaminosis A, and congenital syphilis are examples of periostitis in infants. Incidental asymptomatic periosteal reactions are usually either physiological changes or cortical bone irregularities simulating periostitis. On the other hand, symptomatic periosteal reactions of single bone, such as bone tumor, tumor-like lesion, infection, and trauma, are always pathologic. Careful radiological analysis of periosteal reactions is needed to evaluate the activity and aggressiveness of the lesions. Periosteal reactions of multiple bones usually show solid smooth or undulating patterns. They include pachydermoperiostosis, secondary hypertrophic osteoarthropathy, vascular insufficiency, renal osteodystrophy, and thyroid acropachy. These are usually skeletal manifestations of systemic disorders. PMID:10429428

Fukuda, K

1999-06-01

286

Drug Reactions  

MedlinePLUS

... can also cause unwanted reactions. One problem is interactions, which may occur between Two drugs, such as ... and diseases, such as aspirin and peptic ulcers Interactions can change the actions of one or both ...

287

Development of Experimental Nuclear Reaction Data File for Astrophysics  

SciTech Connect

Experimental nuclear reaction data compilation activity in Japan for the NRDF database and international collaboration of experimental nuclear reaction data exchange by the EXFOR format are presented. Recent development of an experimental nuclear reaction data file (NRDF/A) for astrophysics, which is based on the EXFOR compilation, is also introduced. All services are available at http://www.jcprg.org/.

Otuka, N. [Nuclear Reaction Data Centre (JCPRG), Faculty of Science, Hokkaido University, Sapporo 060-0810 (Japan); Nuclear Data Center, Japan Atomic Energy Agency, Tokai 319-1195 (Japan); Aikawa, M. [OpenCourseWare, Hokkaido University, Sapporo 060-0811 (Japan); Hirabayashi, Y. [Information Initiative Centre, Hokkaido University, Sapporo 060-0811 (Japan); Nuclear Reaction Data Centre (JCPRG), Faculty of Science, Hokkaido University, Sapporo 060-0810 (Japan); Ohnishi, A.; Kato, K. [Department of Physics, Faculty of Science, Hokkaido University, Sapporo 060-0810 (Japan); Nuclear Reaction Data Centre (JCPRG), Faculty of Science, Hokkaido University, Sapporo 060-0810 (Japan)

2008-05-21

288

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

289

Heterogeneous exchange of precipitates  

Microsoft Academic Search

SummaryThe heterogeneous exchange of ferric ion between a labelled aqueous ferric chloride solution and the colloidal?-FeOOH, prepared by slow hydrolysis of a ferric chloride solution at 100 C, was investigated at room temperature.\\u000a \\u000a Contrary to previously described ferric (hydr)oxides, originating from freshly formed amorphous precipitate, the?-FeOOH showed no exchange. This was attributed to a well ordered crystal lattice related to

R. H. H. Wolf; M. Mirnik; B. Teak

1965-01-01

290

Compact, super heat exchanger  

NASA Technical Reports Server (NTRS)

Heat exchanger uses porous media to enhance heat transfer through walls of cooling channels, thereby lowering wall temperature. Porous media within cooling channel increases internal surface area from which heat can be transferred to coolant. Comparison data shows wall has lower temperature and coolant has higher temperature when porous medium is used within heat exchanger. Media can be sintered powedered metal, metal fibers, woven wire layers, or any porous metal having desired permeability and porosity.

Fortini, A.; Kazaroff, J. M.

1980-01-01

291

New tobermorite cation exchangers  

Microsoft Academic Search

Tobermorite minerals, calcium silicate hydrates substituted with Al3+ and alkali, exhibit cation exchange and selectivity properties. The total cation exchange capacities of the Al3+ and alkali substituted tobermorites synthesized here range from 128 to 197 meq per 100g. These substituted tobermorites also have high selectivity for caesium and rubidium. For examples, a tobermorite synthesized from Na2SiO3, AlCl3 and CaO has

Sridhar Komarneni; Della M. Roy

1985-01-01

292

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

293

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

294

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

295

Reaction of silicon ion (/sup 2/P) with silane (SiH/sub 4/, SiD/sub 4/). Heats of formation of SiH/sub n/, SiH/sub n//sup +/ (n = 1, 2, 3), and SiH/sub n//sup +/ (n = 0, 1, 2, 3). Remarkable isotope exchange reaction involving four hydrogen shifts  

SciTech Connect

The reaction of ground-state silicon ion with silane is investigated by using a guided ion beam tandem mass spectrometer. Reaction cross sections of all possible fragments, Si/sub m/H/sub n//sup +/ (m = 1, 2; n = 0, 1, 2, 3), as a function of relative kinetic energy are determined. All thermal energies, the major product is Si/sub 2/H/sub 2//sup +/. One remarkable reaction, the interchange of the projectile silicon ion with the target silicon atom, is observed at near zero kinetic energy. Labeling experiments employing /sup 30/Si/sup +/ for the beam or SiD/sub 4/ for the reactant indicate the intermediacy of the disilicon hydrides for the formation of the observed products. From the endothermicities of several reactions, the 298 K heats of formation for several ionic and neutral silicon hydrides are derived: ..delta..H/sub f//sup 0/(SiH) = 90.0 +/- 1.7, ..delta..H/sub f//sup 0/(SiH/sub 2/) = 69.0 +/- 2, ..delta..H/sub f//sup 0/(SiH/sub 3/) = 48.5 +/- 1.6, ..delta..H/sub f//sup 0/(SiH/sub 2//sup +/) = 276.1 +/- 1.7, ..delta..H/sub f//sup 0/(SiH/sub 3//sup +/) = 237.1 +/- 2, ..delta..H/sub f//sup 0/(Si/sub 2//sup +/) less than or equal to 328.0 +/- 2, ..delta..H/sub f//sup 0/(Si/sub 2/H/sup +/) less than or equal to 304.4 +/- 1.6, ..delta..H/sub f//sup 0/(Si/sub 2/H/sub 2/) less than or equal to 268.0 +/- 2.6, ..delta..H/sub f//sup 0/(Si/sub 2/H/sub 3//sup +/) = 266 +/- 2, all in kcal/mol. From an evaluation of these and other experiments, values of ..delta..H/sub f//sup 0/(SiH/sub 2//sup +/) and ..delta..H/sub f//sup 0/(SiH/sub 2/) of 278.0 +/- 1.4 and 68.5 +/- 1.5 kcal/mol, respectively, are recommended.

Boo, B.H.; Armentrout, P.B.

1987-06-10

296

FASTGAS: Fast Gas Sampling for palladium exchange tests  

SciTech Connect

A mass spectrometric technique for measuring the composition of gas flows in rapid H/D exchange reactions in palladium compacts has been developed. This method, called FASTGAS (Fast Gas Sampling)'' has been used at atmospheric pressures and above with a time response of better than 100 ms. The current implementation of the FASTGAS technique is described in detail and examples of its application to palladium hydride exchange tests are given. 12 refs., 10 figs.

Malinowski, M.E.; Stewart, K.D.; VerBerkmoes, A.A.

1991-06-01

297

An ESCA study of rhodium(III)-exchanged zeolite catalysts  

SciTech Connect

An ESCA study of rhodium(III)-exchanged zeolite catalysts which are active in hydrogenation and other reactions, showed that activation at 300/sup 0/C and 0.002 mm Hg reduced rhodium(III) in Y zeolite to metallic rhodium but did not affect rhodium(III) in A zeolite. This reduction occurred under milder conditions than known for other metal ions in zeolites, and the reduced species is probably the active catalyst in rhodium-exchanged zeolite.

Kuznicki, S.M.; Eyring, E.M.

1980-09-01

298

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

299

Cation exchange resins from chemically modified poly(vinyl chloride)  

Microsoft Academic Search

Poly(vinyl chloride) has been modified chemically to a cation exchange resin by halogen displacement reactions with phenol sulfonic acid, bisphenol-A sulfonic acid and phenolpthalein sulfonic acid. Ion-exchange capacity, salt-splitting capacity and pH-titration characteristics of these resins have been evaluated. pH-titration behaviour of these resins is consistent with that of a polyfunctional cation-exchanger having pK1=2 and pK2=910 corresponding to -SO3H and

Subrata Moitra; Mukul Biswas

1987-01-01

300

Scaling relations for hadron charge exchange continuum scattering from carbon  

NASA Astrophysics Data System (ADS)

Two scaling relations, familiar from analyses of electron scattering and successful over limited kinematic ranges for hadron scattering, are applied to 45 charge exchange spectra from beams of protons and pions on carbon. As with scattering without charge exchange, the conditions that underlie scaling analyses of quasifree scattering are in doubt for intermediate energy hadron beams, and scaling analyses are tests of strong assumptions. Scaling for charge exchange reactions is found in the sense that scaled responses for both beam species and all beam energies are in near agreement over a limited but useful range of momentum transfers, especially at small energy losses where nucleon dynamic effects are strong.

Peterson, R. J.

2013-12-01

301

Reactions Governing Coal Solubilization. First Quarterly Progress Report, July 15, 1983-October 15, 1983.  

National Technical Information Service (NTIS)

Work during the first quarter concerned the hydrogen atom abstraction reactions of macerals. The influence of macerals from several bituminous coals on the hydrogen-deuterium exchange reaction between tetralin-d sub 12 and diphenylmethane and on the reduc...

L. M. Stock

1983-01-01

302

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

2012-04-17

303

Reaction Time  

NSDL National Science Digital Library

In this activity, learners conduct an experiment to test how fast they can react. Learners try to catch a piece of paper with a ruler printed on it (or a ruler) as quickly as they can. Learners collect data and compare the reaction times of friends and family.

Boston, Wgbh

2003-01-01

304

Reaction time  

Microsoft Academic Search

Reviews the studies on RT by H. E. Burtt, A. T. Poffenberger, T. Topciu, and H. Woodrow (1915-1916). It was found that the with shorter intervals, the time of the 1st reaction was lengthened through the inhibiting and distracting influence of the 2nd stimulus. The RT to the cessation of sound and light stimuli and to beginning of the stimuli

V. A. C. Henmon

1916-01-01

305

Ultratrace Determination of Metals Using Coordination Chain Reactions.  

National Technical Information Service (NTIS)

A chemical kinetic method is proposed for the detection and determination of ultratrace quantities of metal ions. A coordination chain reaction system involving the exchange of triethylenetetramine-nickel(ll) and (ethylenedinitrilo) tetraacetatocuprate(ll...

D. W. Margerum R. K. Steinhaus

1964-01-01

306

Ion/molecule reactions of the protonated serine octamer.  

PubMed

The protonated homochiral octamer of serine exchanges all 33 of its labile hydrogens with CH(3)OD and undergoes ligand switching reactions with amines in a quadrupole ion trap mass spectrometer. PMID:15340613

Gronert, Scott; O'Hair, Richard A J; Fagin, Adelaide E

2004-09-01

307

Laser Assisted Emittance Exchange  

SciTech Connect

We describe here the laser assisted emittance exchange (LAEE) technique. A laser operating in the transverse mode (TEM10 or TEM01) is used to interact with the electron beam in a dispersive region and to initiate the transverse-to-longitudinal emittance exchange. It is shown that with the LAEE one can generate an electron beam with ultralow transverse emittance, which allows one to significantly bring down the size of an X-ray free electron laser (FEL) and greatly extend the availability of these light sources. The technique can also be used to enhance the performances of X-ray FELs in storage rings. The timing and energy jitter problems for the standard emittance exchange and LAEE techniques are also discussed.

Xiang, Dao; /SLAC

2012-06-11

308

Microgravity condensing heat exchanger  

NASA Technical Reports Server (NTRS)

A heat exchanger having a plurality of heat exchanging aluminum fins with hydrophilic condensing surfaces which are stacked and clamped between two cold plates. The cold plates are aligned radially along a plane extending through the axis of a cylindrical duct and hold the stacked and clamped portions of the heat exchanging fins along the axis of the cylindrical duct. The fins extend outwardly from the clamped portions along approximately radial planes. The spacing between fins is symmetric about the cold plates, and are somewhat more closely spaced as the angle they make with the cold plates approaches 90.degree.. Passageways extend through the fins between vertex spaces which provide capillary storage and communicate with passageways formed in the stacked and clamped portions of the fins, which communicate with water drains connected to a pump externally to the duct. Water with no entrained air is drawn from the capillary spaces.

Thomas, Christopher M. (Inventor); Ma, Yonghui (Inventor); North, Andrew (Inventor); Weislogel, Mark M. (Inventor)

2011-01-01

309

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).

310

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

311

Microscale Regenerative Heat Exchanger  

NASA Technical Reports Server (NTRS)

The device described herein is designed primarily for use as a regenerative heat exchanger in a miniature Stirling engine or Stirling-cycle heat pump. A regenerative heat exchanger (sometimes called, simply, a "regenerator" in the Stirling-engine art) is basically a thermal capacitor: Its role in the Stirling cycle is to alternately accept heat from, then deliver heat to, an oscillating flow of a working fluid between compression and expansion volumes, without introducing an excessive pressure drop. These volumes are at different temperatures, and conduction of heat between these volumes is undesirable because it reduces the energy-conversion efficiency of the Stirling cycle.

Moran, Matthew E.; Stelter, Stephan; Stelter, Manfred

2006-01-01

312

Heat exchanger panel  

NASA Technical Reports Server (NTRS)

The present invention relates to a heat exchanger panel which has broad utility in high temperature environments. The heat exchanger panel has a first panel, a second panel, and at least one fluid containment device positioned intermediate the first and second panels. At least one of the first panel and the second panel have at least one feature on an interior surface to accommodate the at least one fluid containment device. In a preferred embodiment, each of the first and second panels is formed from a high conductivity, high temperature composite material. Also, in a preferred embodiment, the first and second panels are joined together by one or more composite fasteners.

Warburton, Robert E. (Inventor); Cuva, William J. (Inventor)

2005-01-01

313

Ceramic Spheres From Cation Exchange Beads  

NASA Technical Reports Server (NTRS)

Porous ZrO2 and hollow TiO2 spheres were synthesized from a strong acid cation exchange resin. Spherical cation exchange beads, polystyrene based polymer, were used as a morphological-directing template. Aqueous ion exchange reaction was used to chemically bind (ZrO)(2+) ions to the polystyrene structure. The pyrolysis of the polystyrene at 600 C produces porous ZrO2 spheres with a surface area of 24 sq m/g with a mean sphere size of 42 microns. Hollow TiO2 spheres were synthesized by using the beads as a micro-reactor. A direct surface reaction - between titanium isopropoxide and the resin beads forms a hydrous TiO2 shell around the polystyrene core. The pyrolysis of the polystyrene core at 600 C produces hollow anatase spheres with a surface area of 42 sq m/g with a mean sphere size of 38 microns. The formation of ceramic spheres was studied by XRD, SEM and B.E.T. nitrogen adsorption measurements.

Dynys, F. W.

2003-01-01

314

Exam Question Exchange: A Popular Approach to Reaction Kinetics.  

ERIC Educational Resources Information Center

Presents an undergraduate physical chemistry question and its acceptable solution. This question, presented to share exam questions with other teachers, shows the analogy between molecular kinetics and population dynamics. (HM)

Collins, Michael P. S.; Alexander, John J., Ed.

1979-01-01

315

Recuperative coupling of exothermic and endothermic reactions  

Microsoft Academic Search

Coupling energy intensive endothermic reaction systems with suitable exothermic reactions improves the thermal efficiency of processes and reduces the size of the reactors. One type of reactor suitable for such a type of coupling is the heat exchanger reactor. In this work, a one-dimensional pseudo-homogeneous plug flow model is used to analyze and compare the performance of co-current and counter-current

R. C. Ramaswamy; P. A. Ramachandran; M. P. Dudukovi?

2006-01-01

316

Benchmark calculations of chemical reactions in density functional theory: Comparison of the accurate Kohn-Sham solution with generalized gradient approximations for the H2+H and H2+H2 reactions  

Microsoft Academic Search

The Kohn-Sham (KS) solution is constructed from an accurate CI density and the KS exchange and correlation energies Ex and Ec, as well as the corresponding exchange and exchange-correlation energy densities ?x(r) and ?xc(r), which are obtained for the hydrogen abstraction reaction H+H2 and the symmetrical four-center exchange reaction H2+H2. The KS quantities are compared with those of the standard

P. R. T. Schipper; O. V. Gritsenko; E. J. Baerends

1999-01-01

317

Quark-exchange versus meson-exchange in D(e,e'p)Delta  

SciTech Connect

We demonstrate that the meson-exchange contribution to D(e,e'p)Delta(T{sub p} {approx} 0.7-1 GeV and being at rest) is small compared to the six-quark contribution. The cross-section is large enough to be measured at CEBAF. It means that through this reaction we could observe and study the quark degrees of freedom in the deuteron.

L. Ya. Glozman; A. Faessler

1994-05-01

318

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

319

Thermosyphon heat exchanger  

NASA Technical Reports Server (NTRS)

Report summarizes final development, testing, and certification of pumpless, liquid-to-air heat exchanger for solar heating. System requires blower but no pump in water loop. Output is 35,000 Btu/hr when water temperature is 49 C.

Hankins, J. D.

1980-01-01

320

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

321

Chimney heat exchanger  

SciTech Connect

A heat exchanger for installation on the top of a chimney of a building includes a housing having a lower end receiving the top of the chimney and an upper end with openings permitting the escape of effluent from the chimney and a heat exchanger assembly disposed in the housing including a central chamber and a spirally arranged duct network defining an effluent spiral path between the top of the chimney and the central chamber and a fresh air spiral path between an inlet disposed at the lower end of the housing and the central chamber, the effluent and fresh air spiral paths being in heat exchange relationship such that air passing through the fresh air spiral path is heated by hot effluent gases passing upward through the chimney and the effluent spiral path for use in heating the building. A pollution trap can be disposed in the central chamber of the heat exchanger assembly for removing pollutants from the effluent, the pollution trap including a rotating cage carrying pumice stones for absorbing pollutants from the effluent with the surface of the pumice gradually ground off to reveal fresh stone as the cage rotates.

Whiteley, I.C.

1981-09-01

322

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

323

Charge and Exchange  

NASA Technical Reports Server (NTRS)

Even though comets are basically giant dirty snowballs, a few years ago they surprised astronomers by emitting X-radiation. These X-rays are not produced by multi-million degree gas (as is often the case) but rather by a process called 'charge exchange'. In this process, ionized atoms (which have lost one or more electrons) which are carried within the solar wind collide with neutral atoms in the comet's coma. The solar wind ion can collide with and capture an electron from the neutral comet atom, and in doing so some of the energy of the collision is observed in the form of X-rays. This produces a glow of X-rays on the sunward side of the comet's atmosphere. Charge exchange can occur in a variety of astrophysical settings, and cometary charge exchange provides astronomers a means to study this process up close. The image above is a pretty picture of comet 73P/Schwassmann-Wachmann 3 passing by the Ring Nebula. This image was obtained by the ultraviolet and optical telescope (UVOT) on the Swift gamma-ray burst hunter. The UVOT observations help astronomers to study the structure and chemistry of the comet, while Swift's X-ray Telescope (XRT) simultaneously monitors the charge exchange process. Comet 73P/Schwassmann-Wachmann 3 is currently in the process of breaking up, and the UVOT observations show important details of how this breakup is occurring.

2008-01-01

324

The Pizza Exchange  

NSDL National Science Digital Library

The students will receive paper pizzas that are divided into different fractional parts. They will decorate their pizza, and then make equal trades with classmates to explore equivalence of fractions. The students will be able to explain equivalence of fractions based on their pizza exchanges and will be able to compare and order the fractional parts by their size.

Gehron, Elizabeth

2012-07-20

325

Model optimizes exchanger cleaning  

Microsoft Academic Search

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

Casado

1990-01-01

326

The Science Exchange Program.  

ERIC Educational Resources Information Center

Describes the Science Exchange Program that aims at increasing children's knowledge and use of the Internet and teaching them how commonplace items such as shells, rocks, and other natural materials differ throughout the world. Involves students from different countries connecting through the Internet. (JRH)

Holden, Janet C.

1996-01-01

327

(18O,18Ne) double charge-exchange with MAGNEX  

NASA Astrophysics Data System (ADS)

An experimental study concerning Double Gamow-Teller (DGT) modes in (18O,18Ne) Double Charge-Exchange reactions has been very recently performed at INFN-LNS laboratory in Catania. The experiment was performed using a 40Ca solid target and a 18O Cyclotron beam at 270 MeV incident energy. Charged ejectiles produced in the reaction were momentum analyzed and identified by MAGNEX spectrometer at very forward angles. Preliminary results are presented in the present paper.

Bond, M.; Cappuzzello, F.; Agodi, C.; Carbone, D.; Cavallaro, M.; Cunsolo, A.; De Napoli, M.; Foti, A.; Nicolosi, D.; Tropea, S.

2014-05-01

328

Fe atom exchange between aqueous Fe2+ and magnetite.  

PubMed

The reaction between magnetite and aqueous Fe(2+) has been extensively studied due to its role in contaminant reduction, trace-metal sequestration, and microbial respiration. Previous work has demonstrated that the reaction of Fe(2+) with magnetite (Fe(3)O(4)) results in the structural incorporation of Fe(2+) and an increase in the bulk Fe(2+) content of magnetite. It is unclear, however, whether significant Fe atom exchange occurs between magnetite and aqueous Fe(2+), as has been observed for other Fe oxides. Here, we measured the extent of Fe atom exchange between aqueous Fe(2+) and magnetite by reacting isotopically "normal" magnetite with (57)Fe-enriched aqueous Fe(2+). The extent of Fe atom exchange between magnetite and aqueous Fe(2+) was significant (54-71%), and went well beyond the amount of Fe atoms found at the near surface. Mssbauer spectroscopy of magnetite reacted with (56)Fe(2+) indicate that no preferential exchange of octahedral or tetrahedral sites occurred. Exchange experiments conducted with Co-ferrite (Co(2+)Fe(2)(3+)O(4)) showed little impact of Co substitution on the rate or extent of atom exchange. Bulk electron conduction, as previously invoked to explain Fe atom exchange in goethite, is a possible mechanism, but if it is occurring, conduction does not appear to be the rate-limiting step. The lack of significant impact of Co substitution on the kinetics of Fe atom exchange, and the relatively high diffusion coefficients reported for magnetite suggest that for magnetite, unlike goethite, Fe atom diffusion is a plausible mechanism to explain the rapid rates of Fe atom exchange in magnetite. PMID:22577839

Gorski, Christopher A; Handler, Robert M; Beard, Brian L; Pasakarnis, Timothy; Johnson, Clark M; Scherer, Michelle M

2012-11-20

329

Lysine uptake and exchange in Corynebacterium glutamicum.  

PubMed Central

Resting cells of Corynebacterium glutamicum (ATCC 13032) accumulate [14C]lysine by a transport system with a relatively high affinity (10 microMs) and a low maximum velocity (0.15 nmol/min per mg [dry weight]). Uptake of lysine was not inhibited by uncouplers or by ionophores affecting the ion gradients and the energetic state of the cell. Analysis of intracellular amino acid concentrations during the transport reaction as well as kinetic studies revealed that the observed uptake of lysine in fact represents a homologous antiport between extracellular [14C]lysine and intracellular unlabeled lysine. Intracellular [14C]lysine could only be released by the addition of unlabeled lysine to the bacterial suspension. In contrast to this homologous antiport reaction, we observed net uptake of lysine in lysine-depleted cells of a lysine auxotrophic strain. This net uptake was found to be electrogenic and could also be observed as a heterologous antiport reaction in wild-type cells under particular conditions. In this case exchange was mediated between internal lysine and external alanine, isoleucine, or valine. This antiport was electrogenic, since the substrates differ in charge. The cells can switch between electroneutral homologous exchange and electrogenic heterologous antiport mode during fermentation because of changing metabolic conditions.

Broer, S; Kramer, R

1990-01-01

330

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

331

Reactions of silicon carbide with oxidizing atmospheres  

Microsoft Academic Search

During the operation of silicon carbide materials in thermally stressed elements of electrothermal, metallurgical, and power plants (various types of lining, heat exchangers, electric heating elements, etc.) heterogeneous reactions take place between the solid silicon carbide and chemically active gaseous media (air, organic fuel combustion products, and the like). Air and combustion products consist mainly of nitrogen, oxygen, water vapor,

I. A. Yavorskii; V. I. Elchin; G. G. Gnesin

1978-01-01

332

Metal Reactions  

NSDL National Science Digital Library

This is written as a static display, but can easily be adapted to a hands-on experiment for learners to conduct. Sodium phosphate, a clear colorless solution, is combined with six different metal ion solutions. Each metal (copper, nickel, iron, silver, cobalt, and barium) forms a different color and texture precipitate. Learners discover that a chemical reaction can be identified by a color change, and formation of a precipitate. They also learn that metals can be identified by their precipitates. For safety reasons, this activity should be conducted as a demonstration for younger audiences.

Industry, Oregon M.

1997-01-01

333

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

334

Phosphonic acid based exchange resins  

DOEpatents

An ion exchange resin is described 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. 10 figs.

Horwitz, E.P.; Alexandratos, S.D.; Gatrone, R.C.; Chiarizia, R.

1995-09-12

335

Hydrogen Isotope Exchange Properties of Porous Solids Containing Hydrogen  

SciTech Connect

Porous solids such as activated alumina, silica and molecular sieves generally contain significant amounts of hydrogen atoms in the form of H2O or OH even at high temperature and low humidity environment. A significant amount of this hydrogen is available for reversible isotopic exchange. This exchange reaction is slow under normal conditions and does not render itself to practical applications. But if the exchange kinetics is improved this reaction has the potential to be used for tritium removal from gas streams or for hydrogen isotopic separation.The use of catalysts to improve the exchange kinetics between hydrogen isotope in the gas phase and that in the solid phase was investigated. Granules of alumina, silica and molecular sieve were coated with platinum or palladium as the catalyst. The granules were packed in a 2-cm diameter column for isotope exchange tests. Gas streams containing different concentrations of deuterium in nitrogen or argon were fed through the protium saturated column. Isotope concentration in column effluent was monitored to generate isotope break-through curves. The curves were analyzed to produce information on the kinetics and capacity of the material. The results showed that all materials tested provided some extent of isotope exchange but some were superior both in kinetics and capacity. This paper will present the test results.

HEUNG, LEUNGK.

2004-08-18

336

Quark exchange model for charmonium dissociation in hot hadronic matter.  

National Technical Information Service (NTIS)

A diagrammatic approach to quark exchange processes in meson-meson scattering is applied to the case of inelastic reactions of the type (Q anti Q)+(q anti q)(yields)(Q anti q)+(q anti Q), where Q and q refer to heavy and light quarks, respectively. This s...

K. Martins, D. Blaschke, E. Quack

1994-01-01

337

Meson baryon interaction in the hadron exchange picture  

NASA Astrophysics Data System (ADS)

Elastic ?N scattering and the related reactions ?N-->K?, K? are described simultaneously in a unitary coupled-channel approach which respects analyticity and other general properties of the S-matrix. SU(3) flavor symmetry is used to relate the t- and u- channel exchanges that dirve the meson-baryon interaction in the different channels.

Dring, M.

2012-04-01

338

Isomerization of ?-pinene over ion-exchanged natural zeolites  

Microsoft Academic Search

Catalysts prepared by ion exchange of clinoptilolite-based natural zeolite tuffs with NH4+, Ba2+ and Pb2+ were investigated in the isomerization reaction of ?-pinene at atmospheric pressure under nitrogen flow. Activity and selectivity to mono-, bi- and tricyclic products were correlated with acidity strength.

Fehime zkan; Gnl Gndz; Oguz Akpolat; Nurgun Be?n; Dmitry Yu. Murzin

2003-01-01

339

Charge exchange ion number density distribution in Hall thruster plume  

Microsoft Academic Search

The charge exchange (CEX) ions by the collisions between energetic ions and slow neutral particles in a Hall thruster plume are thought a source of the ions coming back to the satellite. Therefore, mechanical plume shielding has been proposed to prevent the CEX ions from spreading out from near exit region. In order to optimize the shield length, CEX reactions

Shigeru Yokota; Daichi Sakoh; Makoto Matsui; Kimiya Komurasaki; Yoshihiro Arakawa

2008-01-01

340

Dehydrogenation process utilizing indirect heat exchange and direct combustion heating  

Microsoft Academic Search

A multiple reaction zone process for dehydrogenating light hydrocarbons, preferably propane, is disclosed. The feed stream and intermediate streams are first heated by indirect heat exchange to temperatures slightly below the desired inlet temperature of the dehydrogenation catalyst beds. These streams are then transported to a location which is in close proximity of the dehydrogenation catalyst bed and further heated

Vora

1983-01-01

341

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

342

Synthesis and characterisation of a new anion exchangeable layered hydroxyiodide.  

PubMed

Lu4O(OH)9I3H2O is a new member of the anion exchangeable lanthanide hydroxyanion family of materials which has been synthesised hydrothermally. Its structure comprises positively charged [Lu4O(OH)9(H2O)3](+) layers with exchangeable charge balancing iodide anions located in the interlayer gallery. It has been found to undergo facile anion exchange reactions with dicarboxylate anions such as succinate and terephthalate at room temperature but reacts less readily with disulfonate anions such as 1,5- and 2,6-naphthalenedisulfonate under the same conditions. At reaction temperatures above 200 C the cationic inorganic framework Lu3O(OH)6I2H2O forms instead of the layered phase. PMID:24590319

Southworth, Faye Y; Wilson, Claire; Coles, Simon J; Fogg, Andrew M

2014-07-21

343

Serial tempering without exchange.  

PubMed

Serial tempering is a computational method that turns the temperature T (or more generally any independent ? parameter) into a dynamical variable. It is shown that, under conditions for which this variable is fast, serial tempering is equivalent to the umbrella sampling method with a single effective potential. This equivalence is demonstrated using both a small one-dimensional system and a small solvated peptide. The suggestion is then made to replace the serial tempering protocol with the equivalent umbrella sampling calculation. This approach, serial tempering without exchange (STeWiE), has the same performance as serial tempering in the limit that exchanges are frequent, is simpler to implement, and has fewer adjustable parameters than conventional serial tempering. The equivalence of serial tempering and STeWiE also provides a convenient route for estimating and optimizing the performance of serial tempering simulations and other generalized-ensemble methods. PMID:20866132

Nymeyer, Hugh

2010-09-21

344

Serial tempering without exchange  

NASA Astrophysics Data System (ADS)

Serial tempering is a computational method that turns the temperature T (or more generally any independent ? parameter) into a dynamical variable. It is shown that, under conditions for which this variable is fast, serial tempering is equivalent to the umbrella sampling method with a single effective potential. This equivalence is demonstrated using both a small one-dimensional system and a small solvated peptide. The suggestion is then made to replace the serial tempering protocol with the equivalent umbrella sampling calculation. This approach, serial tempering without exchange (STeWiE), has the same performance as serial tempering in the limit that exchanges are frequent, is simpler to implement, and has fewer adjustable parameters than conventional serial tempering. The equivalence of serial tempering and STeWiE also provides a convenient route for estimating and optimizing the performance of serial tempering simulations and other generalized-ensemble methods.

Nymeyer, Hugh

2010-09-01

345

Serpentine heat exchanger  

SciTech Connect

This patent describes a furnace having a burner means for providing hot products of combustion, and an air flow means for circulating conditioned air, a heat exchanger for transferring heat from products of combustion to conditioned air. The heat exchanger comprises first and second matched clamshell plates assembled together. The plates connected at their respective edges by a sealing means for providing a seal thereat, each the plate having an internal surface defining a depression. The depressions together defining a serpentine passageway, an entrance and exhaust ported formed in the passageway. The surfaces including elongated ribs for obstructing fluid flow adjacent the exhaust portal and for directing fluid flow to under-utilized portions in the passageway.

Tomlinson, R.S.

1991-01-08

346

AGRICULTURAL EXCHANGE RATE DATA SHEET  

EPA Science Inventory

The ERS data set contains annual and monthly data for exchange rates important to U.S. agriculture. It includes both nominal and real exchange rates for 80 countries (plus the European Union) as well as real trade-weighted exchange rate indexes for many commodities and aggregatio...

347

Exchange Rate Regimes: Middling Through  

Microsoft Academic Search

The appropriate exchange rate regime, in the context of integration of currency markets with financial markets and of large international capital flows, continues to be a policy dilemma. It is found that the majority of countries are moving towards somewhat higher exchange and lower interest rate volatility. Features of foreign exchange (forex) markets could be partly motivating these choices. A

Ashima Goyal

2006-01-01

348

Heat exchange fluids and techniques  

Microsoft Academic Search

The book presents detailed technical information based on United States patents issued since January, 1975 on heat exchange fluids and techniques, emphasizing the potential energy savings attainable. Attention is given to general heat exchanger construction and design, including tubular and other constructions, particulate exchange mediums and surface treatments, and to the compositions of heat transfer fluids. Refrigerant processes and fluids

M. W. Ranney

1979-01-01

349

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

350

Exchange and Resource Theories  

Microsoft Academic Search

Conceptual frameworks are often organized around a metaphor (Gergen et al., 1980). When the metaphor is powerful and embraced by the culture, the framework is easily understood and readily adapted\\u000a to explain a wide range of phenomenon. During the 1960s, the social exchange framework was formally advanced in the work of\\u000a sociologists George Homans (1961) and Peter Blau (1964a) and

Ronald M. Sabatelli; Constance L. Shehan

351

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

352

Selective Cu{sup 2+} and Pb{sup 2+} exchange with highly charged cation exchanger of Na-4-mica  

SciTech Connect

Selective cation exchange for Cu and Pb has been demonstrated with the high-charge-density sodium fluorophlogopite mica, Na-4-mica. The 2Na{sup +} {yields} M{sup 2+} exchange reaction (M = Cu or Pb) was investigated with Na-4-micas prepared by two different synthetic processes. One was easily and economically prepared by crystallization from a mixture of NaF, MgO, and metakaolin, the latter serves as an inexpensive aluminosilicate source. Another was prepared by solution-sol-gel processing. Ion-exchange isotherms for Cu{sup 2+} and Pb{sup 2+} were obtained at room temperature. The thermodynamic functions for the initial ion-exchange reactions were calculated because the isotherms were not completed., High selectivities for both copper and lead exchange were found on the highly crystallized Na-4-mica prepared from metakaolin. Their ion-exchange capacities were 225 and 257 milliequivalents per 100 g of dry clay for Cu{sup 2+} and Pb{sup 2+}, respectively. This high level decontamination of copper and lead with the highly crystallized Na-4-mica from metakaolin will be a very important separation required for purification of drinking water as well as for wastewater treatment and disposal.

Kodama, Tatsuya; Komarneni, Sridhar [Pennsylvania State Univ., University Park, PA (United States)] [Pennsylvania State Univ., University Park, PA (United States)

1999-09-01

353

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

354

The exchangeability of shape  

PubMed Central

Background Landmark based geometric morphometrics (GM) allows the quantitative comparison of organismal shapes. When applied to systematics, it is able to score shape changes which often are undetectable by traditional morphological studies and even by classical morphometric approaches. It has thus become a fast and low cost candidate to identify cryptic species. Due to inherent mathematical properties, shape variables derived from one set of coordinates cannot be compared with shape variables derived from another set. Raw coordinates which produce these shape variables could be used for data exchange, however they contain measurement error. The latter may represent a significant obstacle when the objective is to distinguish very similar species. Results We show here that a single user derived dataset produces much less classification error than a multiple one. The question then becomes how to circumvent the lack of exchangeability of shape variables while preserving a single user dataset. A solution to this question could lead to the creation of a relatively fast and inexpensive systematic tool adapted for the recognition of cryptic species. Conclusions To preserve both exchangeability of shape and a single user derived dataset, our suggestion is to create a free access bank of reference images from which one can produce raw coordinates and use them for comparison with external specimens. Thus, we propose an alternative geometric descriptive system that separates 2-D data gathering and analyzes.

2010-01-01

355

Ceramic oxides with high oxygen exchange: The system SrCoO  

Microsoft Academic Search

Oxide compositions in the system SrCoO were prepared by solid-state reaction. The oxideoxygen reactions were investigated by thermo-gravimetric measurements. Equilibration was controlled by an amperometric lambda sensor. Thermodynamic data for the oxideoxygen reaction were calculated. For the reaction CoO\\/Co3O4 with complete change of crystal structure between ferrite-and NaCl-types, the amount of oxygen exchanged (?=1), and the absolute values of changes

E. Girdauskaite; H. Ullmann; V. Vashook; M. Blow; U. Guth

2006-01-01

356

Behavior of carboxyl-bound potassium during combustion of an ion-exchanged lignite  

Microsoft Academic Search

The reactions of potassium during combustion of a potassium-ion-exchanged Beulah lignite have been investigated. Combustion was carried out in a drop-tube furnace and CCSEM and XAFS spectroscopy were used to characterize the coal and ash samples. The reactions of the ion-exchanged potassium were quite similar to those of carboxyl-bound sodium in the original coal. The principal K-containing ash phases observed

Anup D. Shah; Gerald P. Huffman; Frank E. Huggins; Naresh Shah; Joseph J. Helble

1995-01-01

357

Sorption of iron(III) from chromate solution by the aminocarboxylic ion exchanger ANKB-2  

SciTech Connect

The possibility of iron(III) sorption by the amphoteric ion exchanger ANKB-2 from chromate solution and its superiority over the cation exchanger KU-23 (10/60) have been demonstrated. By means of IR spectroscopy it has been shown that iron(III) sorption from chromate solution by ANKB-2 proceeds via both ionic and coordination reactions. The proportion of these kinds of reaction does not depend on the Cr(VI) content of the initial solution.

Stoyanova, O.F.; Izmailova, D.R.; Kurolap, N.S.; Uglyanskaya, V.A.

1986-12-20

358

Reaction energetics on long-range corrected density functional theory: Diels-Alder reactions.  

PubMed

The possibility of quantitative reaction analysis on the orbital energies of long-range corrected density functional theory (LC-DFT) is presented. First, we calculated the Diels-Alder reaction enthalpies that have been poorly given by conventional functionals including B3LYP functional. As a result, it is found that the long-range correction drastically improves the reaction enthalpies. The barrier height energies were also computed for these reactions. Consequently, we found that dispersion correlation correction is also crucial to give accurate barrier height energies. It is, therefore, concluded that both long-range exchange interactions and dispersion correlations are essentially required in conventional functionals to investigate Diels-Alder reactions quantitatively. After confirming that LC-DFT accurately reproduces the orbital energies of the reactant and product molecules of the Diels-Alder reactions, the global hardness responses, the halves of highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps, along the intrinsic reaction coordinates of two Diels-Alder reactions were computed. We noticed that LC-DFT results satisfy the maximum hardness rule for overall reaction paths while conventional functionals violate this rule on the reaction pathways. Furthermore, our results also show that the HOMO-LUMO gap variations are close to the reaction enthalpies for these Diels-Alder reactions. Based on these results, we foresee quantitative reaction analysis on the orbital energies. PMID:23037888

Singh, Raman K; Tsuneda, Takao

2013-02-15

359

Single- and double-charge exchange at low pion energies  

SciTech Connect

A review is given of pion single- and double-charge exchange reactions at incident energies of 25 to 65 MeV leading to isobaric analog states, and in the case of double-charge exchange leading to the ground state of the residual nucleus. The crucial role of the higher nuclear transparency at low pion energies for the analysis of the data in terms of single and double scattering is demonstrated. The large effects on double-charge exchange produced by the spatial correlations in nuclear wave functions are evident. The data on 1f{sub 7/2} nuclei at 35 MeV are used to establish the general validity of a shell-model-based two-amplitude model for these transitions. Recent measurements of the energy dependence between 25 and 65 MeV of double-charge exchange cross sections at forward angles are presented and discussed. 33 refs., 19 figs.

Baer, H.W.

1991-01-01

360

Kinetic theory of oxygen isotopic exchange between minerals and water  

USGS Publications Warehouse

Kinetic and mass conservation equations are used to describe oxygen isotopic exchange between minerals and water in "closed" and open hydrothermal systems. In cases where n coexisting mineral phases having different reaction rates are present, the exchange process is described by a system of n + 1 simultaneous differential equations consisting of n pseudo first-order rate equations and a conservation of mass equation. The simultaneous solutions to these equations generate curved exchange trajectories on ??-?? plots. Families of such trajectories generated under conditions allowing for different fluid mole fractions, different fluid isotopic compositions, or different fluid flow rates are connected by positive-sloped isochronous lines. These isochrons reproduce the effects observed in hydrothermally exchanged mineral pairs including 1) steep positive slopes, 2) common reversals in the measured fractionation factors (??), and 3) measured fractionations that are highly variable over short distances where no thermal gradient can be geologically demonstrated. ?? 1987.

Criss, R. E.; Gregory, R. T.; Taylor, Jr. , H. P.

1987-01-01

361

Lightweight long life heat exchanger  

NASA Technical Reports Server (NTRS)

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), and both the core air passes and slurpers were hydrophilic coated to enhance wettability. The test program included performance tests which demonstrated the adequacy of the design and confirmed the predicted weight savings.

Moore, E. K.

1976-01-01

362

Improved corporate governance: market reaction and liquidity implications  

Microsoft Academic Search

We study the market price reaction and liquidity impact that firms experience when they are incorporated into the differentiated corporate governance listing segments of the Sao Paulo Stock Exchange. The Brazilian market is of special interest since it allows us to analyze the effect of improved governance while keeping the market microstructure unchanged. The market price reaction is positive and

GONZALO CHAVEZ

2006-01-01

363

Reaction steps for the water-gas shift reaction and NOx storage\\/reduction catalysts studied by FTIR methods  

Microsoft Academic Search

Proton exchange membrane (PEM) fuel cells are an environmentally friendly source of energy since they are roughly twice as fuel efficient as internal combustion engines. The source of H2 is generally from hydrocarbons through the catalytic reforming and water-gas shift (WGS) reactions. The challenge on the WGS reaction is to find a catalyst that is more stable but has the

Joshua Lynn Ratts

2008-01-01

364

Sorption and binary exchange of nitrate, sulfate, and uranium on an anion-exchange resin.  

PubMed

Competitive ion-exchange reactions were studied on a strong-base anion-exchange resin to remove NO3- and uranium from a contaminated groundwater containing high levels of NO3- (approximately 140 mM), SO4(2-) (approximately 10 mM), and U(VI) (approximately 0.2 mM). Results indicate that although SO4(2-) carries divalent negative charges, it showed the least selectivity for sorption by the Purolite A-520E resin, which is functionalized with triethylamine exchange sites. Nitrate was the most strongly sorbed. Sorption selectivity followed the order of NO3- > Cl- > SO4(2-) under the experimental conditions. Nitrate competitively sorbed and displaced previously sorbed SO4(2-) in a column flow-through experiment and resulted in a high elution front of SO4(2-) in the effluent. Although the concentration of uranium in groundwater is orders of magnitude lower than that of NO3- or SO4(2-), it was found to be strongly sorbed by the anion-exchange resin. Because the most stable uranium species in oxic and suboxic environments is the UO2(2+) cation, its strong sorption by anion-exchange resins is hypothesized to be the result of the co-ion effect of NO3- by forming anionic UO2(NO3)3- complexes in the resin matrix. These observations point out a potential alternative remediation strategy that uses strong-base anion-exchange resins to remove uranium from this site-specific groundwater, which has a low pH and a relatively high NO3- concentration. PMID:15224753

Gu, Baohua; Ku, Yee-Kyoung; Jardine, Philip M

2004-06-01

365

Calculations of ion-molecule deuterium fractionation reactions involving HD  

NASA Technical Reports Server (NTRS)

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 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.

Maluendes, Sergio A.; Mclean, A. D.; Herbst, Eric

1992-01-01

366

Direct contact heat exchangers for space  

Microsoft Academic Search

Direct contact heat exchanger concepts have been investigated for use in space, including droplet vortex heat exchangers, coflowing droplet heat exchangers, electrostatically driven heat exchangers, and belt and disk heat exchangers. These concepts are characterized by a low heat exchanger mass per unit of heat transferred, low pressure losses, high reliability, and compactness in design. Operation in zero-G poses unique

R. T. Taussig; W. J. Thayer; V. C. H. Lo; K. M. Sakins; A. P. Bruckner

1985-01-01

367

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

368

Kinetics of tritium removal from heavy water by exchange with deuterochloroform  

SciTech Connect

A technique was developed to determine the rate and equilibrium constants for the base-catalyzed exchange of tritium from ehavy water to deuterochloroform. An activation energy and entropy were also calculated. These quantities are comparable with those reported in the literature for a similar reaction involving the exchange of deuterium from deuterochloroform to water. It was found that the exchange reaction occurred predominately between the dissolved reactants in the D/sub 2/O and CDCl/sub 3/ phases. The rate constant is a strong direct function of temperature while the equilibrium constant is a weak inverse function.

Hsiao, P.

1983-03-14

369

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

370

Isotopic fractionation by isotope-exchange reactions as a function of temperature: (2)H and (18)O in OH(-) + H sub 2 O and H sub 3 O(+) + H sub 2 O and (15)N in N sub 2 H(+) + N sub 2  

Microsoft Academic Search

A simple model is used to predict the fractionation of isotopes as a function of temperature via ion-molecule reactions. It is developed for reactions proceeding via a single intermediate, where the isotopic mixing is completed within the lifetime of the intermediate such that the reaction is under thermodynamic control. The fractionation efficiency is K\\/(K + 1) where K is the

M. Henchman; J. F. Paulson

1989-01-01

371

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

372

Gas Exchange of Algae  

PubMed Central

The oxygen production of a photosynthetic gas exchanger containing Chlorella pyrenoidosa (1% packed cell volume) was measured when various concentrations of carbon dioxide were present within the culture unit. The internal carbon dioxide concentrations were obtained by manipulating the entrance gas concentration and the flow rate. Carbon dioxide percentages were monitored by means of electrodes placed directly in the nutrient medium. The concentration of carbon dioxide in the nutrient medium which produced maximal photosynthesis was in the range of 1.5 to 2.5% by volume. Results were unaffected by either the level of carbon dioxide in the entrance gas or the rate of gas flow. Entrance gases containing 2% carbon dioxide flowing at 320 ml/min, 3% carbon dioxide at 135 ml/min, and 4% carbon dioxide at 55 ml/min yielded optimal carbon dioxide concentrations in the particular unit studied. By using carbon dioxide electrodes implanted directly in the gas exchanger to optimize the carbon dioxide concentration throughout the culture medium, it should be possible to design more efficient large-scale units.

Ammann, Elizabeth C. B.; Lynch, Victoria H.

1967-01-01

373

Concerted hydrogen atom exchange between three HF molecules  

NASA Technical Reports Server (NTRS)

We have investigated the termolecular reaction involving concerted hydrogen exchange between three HF molecules, with particular emphasis on the effects of correlation at the various stationary points along the reaction. Using an extended basis, we have located the geometries of the stable hydrogen-bonded trimer, which is of C(sub 3h) symmetry, and the transition state for hydrogen exchange, which is of D(sub 3h) symmetry. The energies of the exchange reation were then evaluated at the correlated level, using a large atomic natural orbital basis and correlating all valence electrons. Several correlation treatments were used, namely, configration interaction with single and double excitations, coupled-pair functional, and coupled-cluster methods. We are thus able to measure the effect of accounting for size-extensivity. Zero-point corrections to the correlated level energetics were determined using analytic second derivative techniques at the SCF level. Our best calculations, which include the effects of connected triple excitations in the coupled-cluster procedure, indicate that the trimer is bound by 9 +/- 1 kcal/mol relative to three separate monomers, in excellent agreement with previous estimates. The barrier to concerted hydrogen exchange is 15 kcal/mol above the trimer, or only 4.7 kcal/mol above three separated monomers. Thus the barrier to hydrogen exchange between HF molecules via this termolecular process is very low.

Komornicki, Andrew; Dixon, David A.; Taylor, Peter R.

1992-01-01

374

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

375

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

376

Interfacial Spins in Exchange Biased Pairs  

NASA Astrophysics Data System (ADS)

Today's magnetic storage devices consist of magnetic multilayers that are magnetically coupled across their interface. While the interface itself is supposed to dominate the magnetic behavior of the entire system, the identification and characterization of its magnetic properties remains an experimental challenge. A prominent example is the loop shift (unidirectional anisotropy, exchange bias) and the coercivity increase (uniaxial anisotropy) found if a ferromagnet is coupled to an antiferromagnet. The exchange bias effect is utilized in magnetic data storage device to form a pinned magnetic reference layer. Although exchange bias was discovered over 40 years ago by Meiklejohn our understanding of its origin is still poor. We use dichroism x-ray absorption spectromicroscopy in a photoemission electron microscope to study the magnetic coupling between antiferromagnetic NiO(001) and ferromagnetic Co across its interface. We observe large (1-20 ?m) antiferromagnetic domains at the surface of bare NiO(001) single crystals. Upon in situ deposition of thin ferromagnetic Co layers (1.5 nm) a reorientation of the antiferromagnetic axes takes place. The uniaxial anisotropy axes of the ferromagnet and the antiferromagnet are then aligned parallel domain by domain. In another experiment the role of uncompensated spins in exchange biased coupled has been investigated. Uncompensated spins are found to be produced at the interface either by chemical reaction (Co/NiO) or intermixing (Co/IrMn, Co/PtMn). Two kinds of uncompensated spins are detected. Spins that follow the external field and such that remain pinned. An imbalance between free and pinned interfacial moments as origin of the unidirectional anisotropy will be discussed in the talk [1] H. Ohldag, A. Scholl et al., Phys. Rev. Lett. 86(13), pp. 2878, 2001. [2] F. U. Hillebrecht, H. Ohldag et al., Phys. Rev. Lett. 86(15), pp. 3419, 2001. [3] H. Ohldag, A. Scholl et al., Phys. Rev. Lett. 87, art. no. 247201 (2001).

Ohldag, Hendrik; Scholl, Andreas; Regan, Thomas J.; Nolting, Frithjof; Arenholz, Elke; Carey, Matt C.; Maat, Stefan; Sthr, Joachim

2002-03-01

377

Optimistic protocols for fair exchange  

Microsoft Academic Search

We describe a generic protocol for fair exchange of electronic goods with non-repudiation. Goods can be signatures (i.e., non-repudiation tokens of public data), confidential data, or payments. The protocol does not involve a third party in the exchange in the fault-less case but only for recovery. Many commercial transactions can be modelled as a sequence of exchanges of electronic goods

N. Asokan; Matthias Schunter; Michael Waidner

1997-01-01

378

The rate of oxygen isotope exchange between nitrate and water  

NASA Astrophysics Data System (ADS)

The oxygen isotope exchange rate between nitrate and water was measured at a temperature of 50-80 C and pH -0.6 to 1.1. Oxygen isotope exchange is a first-order reaction, with the exchange rate being strongly affected by both reaction temperature and pH, with increased rates of isotope exchange at higher temperatures and lower pH values. The rate of oxygen isotope exchange under natural conditions is extremely slow, with an estimated half-life for isotope exchange of 5.5 109 years at 25 C and pH 7. The extremely slow rate of oxygen isotope exchange between nitrate and water under typical environmental conditions illustrates that nitrate-?18O signatures (and also nitrate ?17O and ?17O signatures) associated with various nitrate sources, as well as isotope compositions produced by biogeochemical processes, will be preserved. Hence, it is valid to use the value of nitrate-?18O to investigate the sources and biogeochemical behavior of nitrate, in a similar manner to the use of sulfate-?18O signatures to study the sources and biogeochemical behavior of sulfate. Equilibrium oxygen isotope fractionation factors have been determined, although quantification of the nitrate-water equilibrium fractionation factor is not possible due to the presence of nitrate as both protonated (i.e. HNO3) and unprotonated forms (i.e. NO3-) under the experimental conditions, and the difficulty in accurately calculating nitrate speciation in low pH, high ionic strength solutions.

Kaneko, Masanori; Poulson, Simon R.

379

Ion-exchange hollow fibers  

NASA Technical Reports Server (NTRS)

An ion-exchange hollow fiber is prepared by introducing into the wall of the fiber polymerizable liquid monomers, and polymerizing the monomers therein to form solid, insoluble, cross-linked, ion-exchange resin particles which embed in the wall of the fiber. Excess particles blocking the central passage or bore of the fiber are removed by forcing liquid through the fiber. The fibers have high ion-exchange capacity, a practical wall permeability and good mechanical strength even with very thin wall dimensions. Experimental investigation of bundles of ion-exchange hollow fibers attached to a header assembly have shown the fiber to be very efficient in removing counterions from solution.

Rembaum, Alan (Inventor); Yen, Shiao-Ping S. (Inventor); Klein, Elias (Inventor)

1977-01-01

380

Ion-exchange hollow fibers  

NASA Technical Reports Server (NTRS)

An ion-exchange hollow fiber is prepared by introducing into the wall of the fiber polymerizable liquid monomers, and polymerizing the monomers therein to form solid, insoluble, cross-linked, ion-exchange resin particles which embed in the wall of the fiber. Excess particles blocking the central passage or bore of the fiber are removed by forcing liquid through the fiber. The fibers have high ion-exchange capacity, a practical wall permeability and good mechanical strength even with very thin wall dimensions. Experimental investigation of bundles of ion-exchange hollow fibers attached to a header assembly have shown the fiber to be very efficient in removing counterions from solution.

Rembaum, Alan (Inventor); Yen, Shiao-Ping S. (Inventor); Klein, Elias (Inventor)

1980-01-01

381

On-line preconcentration of phosphate onto molybdate form anion exchange column  

Microsoft Academic Search

In this paper, we describe an automated flow injection system for measuring the concentration of phosphate based on a fluorescence quenching reaction between Rhoadamine 6G and phosphomolybdate with a preconcentration column, which was packed with a molybdate-form ion exchange resin to collect and preconcentrate the phosphate in the sample solution. Rhodamine 6G was chosen because the reaction with phosphomolybdate was

Tetsuyuki Taniai; Masaaki Sukegawa; Akio Sakuragawa; Atsushi Uzawa

2003-01-01

382

Gas-Phase Hydrogen Isotope Exchange in HF + D sub 2 O.  

National Technical Information Service (NTIS)

The gas-phase isotope exchange reaction of HF and D sub 2 O has been studied by flow tube and matrix isolation techniques over a range of concentrations and reaction times. The matrix isolation/FTIR gas sampling and analysis technique proved capable of de...

L. D. Trowbridge

1982-01-01

383

South Atlantic interbasin exchange  

NASA Technical Reports Server (NTRS)

The exchange of mass and heat between the South Atlantic and the neighboring ocean basins was estimated using hydrographic data and inverse methods, in order to gain information on the links between the deep-water formation processes occurring within the Atlantic and the global thermohaline circulation. Results demonstrate that the global thermohaline cell associated with the formation and export of North Atlantic deep water (NADW) is closed primarily by a 'cold water path' in which deep water leaving the Atlantic ultimately returns as intermediate water entering the basin through Drake Passage. This conclusion conflicts with the suggestion by Gordon (1986) that the global thermohaline circulation associated with the formation of NADW is closed primarily by a 'warm water path', in which the export of NADW is compensated by an inflow of warm Indian Ocean thermocline water south of Africa.

Rintoul, Stephen Rich

1991-01-01

384

Biological Ion Exchanger Resins  

PubMed Central

Biological selectivity is shown to vary with medium osmotic strength and temperature. Selectivity reversals occur at 4C and at an external osmolality of 0.800 indicating that intracellular hydration and endosolvent (intracellular water) structure are important determinants in selectivity. Magnetic resonance measurements of line width by steady-state nuclear magnetic resonance (NMR) indicate a difference in the intracellular water signal of 16 Hz between the K form and Na form of Escherichia coli, providing additional evidence that changes in the ionic composition of cells are accompanied by changes in endosolvent structure. The changes were found to be consistent with the thermodynamic and magnetic resonance properties of aqueous electrolyte solutions. Calculation of the dependence of ion-pairing forces on medium dielectric reinforces the role of endosolvent structure in determining ion exchange selectivity.

Damadian, Raymond; Goldsmith, Michael; Zaner, K. S.

1971-01-01

385

Hybrid Heat Exchangers  

NASA Technical Reports Server (NTRS)

A hybrid light-weight heat exchanger concept has been developed that uses high-conductivity carbon-carbon (C-C) composites as the heat-transfer fins and uses conventional high-temperature metals, such as Inconel, nickel, and titanium as the parting sheets to meet leakage and structural requirements. In order to maximize thermal conductivity, the majority of carbon fiber is aligned in the fin direction resulting in 300 W/m.K or higher conductivity in the fin directions. As a result of this fiber orientation, the coefficient of thermal expansion (CTE) of the C-C composite in both non-fiber directions matches well with the CTE of various high-temperature metal alloys. This allows the joining of fins and parting sheets by using high-temperature braze alloys.

Tu, Jianping Gene; Shih, Wei

2010-01-01

386

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

387

Monogroove liquid heat exchanger  

NASA Technical Reports Server (NTRS)

A liquid supply control is disclosed for a heat transfer system which transports heat by liquid-vapor phase change of a working fluid. An assembly (10) of monogroove heat pipe legs (15) can be operated automatically as either heat acquisition devices or heat discharge sources. The liquid channels (27) of the heat pipe legs (15) are connected to a reservoir (35) which is filled and drained by respective filling and draining valves (30, 32). Information from liquid level sensors (50, 51) on the reservoir (35) is combined (60) with temperature information (55) from the liquid heat exchanger (12) and temperature information (56) from the assembly vapor conduit (42) to regulate filling and draining of the reservoir (35), so that the reservoir (35) in turn serves the liquid supply/drain needs of the heat pipe legs (15), on demand, by passive capillary action (20, 28).

Brown, Richard F. (Inventor); Edelstein, Fred (Inventor)

1990-01-01

388

Biofuels Information Exchange  

NSDL National Science Digital Library

As biofuels grow in importance, there is more interest in finding places where professionals, scientists, and policymakers with a passion for the subject can come together and exchange ideas. CABI, a non-profit science-based development and information organization, has created this website to allow just that to happen. What can you do on the site? Well, for starters you can peruse the "What's in the News" area to learn about timely reports from different news outlets and scholarly sources regarding biofuels technology. Dedicated users should sign up on the site so that they can create their own group to discuss shared interests with other colleagues on the site and so that they may create a profile. The site also has a blog, a section dedicated to relevant publications, and a RSS feed of activities from registered users.

Holmes, Tim

389

Reaction and Anomalous Transport: Effective Reaction Rate Coefficients from the Multirate Model  

NASA Astrophysics Data System (ADS)

One cause of anomalous transport is a distribution of exchange rates between fast- and slow-moving water. Slow-moving water is frequently the preferred location of the most significant reactions, such as in biofilms. We express transport and reaction using the multirate model and we assume first-order reaction from parent to daughter. In this case, the effective rate coefficient can be expressed ? _a = int_0^{infty } frac{alpha p(alpha) ? }{alpha +? } dalpha where alpha is the mass transfer rate coefficient, ?mda is the reaction rate coefficient, and p(alpha) is the density function of mass transfer rate coefficients in the multirate model. Exchange rates much slower than ?mda contribute relatively little to the effective rate coefficient, while exchange rates similar to or faster than ?mda contribute most to the effective rate coefficient. Consequently, a conservative solute may experience anomalous transport, but a reacting solute may exhibit behavior that is not significantly different from Fickian transport with reaction.

Haggerty, R.

2012-12-01

390

Novel Gas Phase Ion Molecule Reactions of C60(++) with NH3. (Reannouncement with New Availability Information).  

National Technical Information Service (NTIS)

We have observed an associative charge exchange reaction for C60 2+ with ammonia which does not occur for C60 + under identical experimental conditions. We believe that this is indicative of a new family of charge-exchange reactions for C60 2+ which will ...

J. Stry M. T. Coolbaugh E. Turros J. F. Garvey

1992-01-01

391

The reaction 3 cordierite = 2 garnet + 4 sillimanite + 5 quartz as a geological thermometer in the Opinicon Lake region, Ontario  

Microsoft Academic Search

In equilibrated metamorphic rocks containing coexisting garnet, cordierite, quartz and sillimanite, the exchange of iron and magnesium between cordierite and garnet offers a highly favourable geological thermometer and barometer, because this exchange reaction is insensitive to pressure. Thermodynamic analysis shows that this thermometer may be calibrated from knowledge of the breakdown reactions for iron and magnesian cordierite end members to

K. L. Currie

1971-01-01

392

Liquid/liquid heat exchanger  

NASA Technical Reports Server (NTRS)

Conceptual design for heat exchanger, utilizing two immiscible liquids with dissimilar specific gravities in direct contact, is more efficient mechanism of heat transfer than conventional heat exchangers with walls or membranes. Concept could be adapted for collection of heat from solar or geothermal sources.

Miller, C. G.

1980-01-01

393

Corrosion of furnace heat exchangers  

Microsoft Academic Search

Systematic investigations and field data indicate that corrosion of furnace heat exchangers is affected primarily by condensation tendencies caused by installation, design, and operating conditions and aggravated by the presence of contaminants, reports the Canadian Gas Research Institute. Designing for maximum heat-transfer efficiency can cause excessive chilling in some areas of the heat exchanger, resulting in condensation of combustion products

S. W. Khoo; F. D. Williamson

1976-01-01

394

The Transatlantic Orientation Exchange Project  

ERIC Educational Resources Information Center

The Transatlantic Orientation Exchange/Multiplikatorenschulung im transatlan-tischen Austausch is a collaboration between volunteers and staff in both the US and German AFS organizations. The goal of the project is to increase the level of intercultural learning of German and US secondary education exchange participants and their host families.

Gisevius, Annette; Weber, Robin A.

2009-01-01

395

Risk, Uncertainty and Exchange Rates  

Microsoft Academic Search

This paper explores a new direction for empirical models of exchange rate determination. The motivation arises from two well documented facts, the failure of log-linear empirical exchange rate models of the 1970's and the variability of risk premiums in the forward market. Rational maximizing models of economic behavior imply that changes in the conditional variances of exogenous processes, such as

Robert J. Hodrick

1989-01-01

396

Evidence for Exchange Degeneracy Reanalysed.  

National Technical Information Service (NTIS)

A detailed analysis is presented of Kp and pi p total cross-sections with a view to investigating the validity of strong exchange degeneracy which has recently been questioned. Kp CEX data is used to extract the rho-A sub 2 exchange. This contribution is ...

R. G. Roberts R. V. Gavai D. P. Roy

1977-01-01

397

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

398

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

399

Airway heat and gas exchange  

Microsoft Academic Search

The usual approach to analysis of pulmonary gas exchange deals with the airways as a dead space that does not participate in gas exchange and acts simply as a conduit for the passage of air between the outside environment and the alveoli. In reality, however, inspired air undergoes some change during its trans-airway passage. The relatively cool and dry air

M P Hlastala

1992-01-01

400

Mirage of Floating Exchange Rates  

Microsoft Academic Search

This note summarizes some of the highlights of my longer paper with Guillermo CalvoFear of Floating. Many emerging market countries have suffered financial crises. One view blames soft pegs for these crises. Adherents to that view suggest that countries move to corner solutions--hard pegs or floating exchange rates. We analyze the behavior of exchange rates, reserves, and interest rates to

Carmen M. Reinhart

2000-01-01

401

TWISTED TUBE HEAT EXCHANGER TECHNOLOGY  

Microsoft Academic Search

Over 85% of all new heat exchanger applications in oil refining, chemical, petro-chemical, and power generation are accommodated through the use of conventional shell and tube type heat exchangers. The fundamental basis for this statistic is shell and tube technology is a cost effective, proven solution for a wide variety of heat transfer requirements. However, there are limitations associated with

R. Donald Morgan

402

Development of Chemical Exchange Process.  

National Technical Information Service (NTIS)

This study is concerned with the development of a process to achieve low enrichment of uranium (3-4% exp 235 U) by a chemical exchange method. In our experiment, we chose the ion exchange process among the solid-liquid contacting operations first. In 1981...

H. J. Lee W. Y. Kim J. W. Park Y. M. Park D. S. Kang

1982-01-01

403

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

404

Hydrodesulfurization of thiophenic compounds: the reaction mechanism  

SciTech Connect

It has often been assumed that catalytic hydrodesulfurization of thiophene and related compounds proceeds via a one-point end-on adsorption involving bonding of the sulfur atom with Mo ions at an anion vacancy on the catalyst surface. This interpretation is inadequate, failing to account for hydrogen-deuterium exchange results, the reactivities of benzothiophene and dibenzothiophene, and the small steric effects of methyl substituents on the adsorption and reaction of compounds in the thiophene, benzothiopene, and dibenzothiophene families of homologs. An alternative mechanism, presented here, involves a multipoint adsorption of the reactant, with a C=C bond interacting with a Mo cation, and the S atom of the reactant interacting with an S ion on the surface. The new mechanism accounts for the observed deuterium exchange and hydrodesulfurization reactions and is consistent with the observed steric effects. 24 references, 5 figures.

Kwart, H.; Schuit, G.C.A.; Gates, B.C.

1980-01-01

405

The microtube strip heat exchanger  

SciTech Connect

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 reliability. The problems of manufacturing heat exchangers suited to laminar flow are discussed. A method of manufacture is outlined that allows compact, modular design. Experience with this method of manufacture is described. Experimental results with a prototype heat exchanger bank are presented: these results show good agreement with theory at moderate levels of effectiveness (75--85%), but fall below predicted values at higher levels. It is argued that this discrepancy results from flow maldistribution. The problem of fouling and flow maldistribution are briefly discussed, and some possible applications are mentioned.

Doty, F.D.; Hosford, G.; Spitzmesser, J.B. (Doty Scientific, Inc., Columbia, SC (United States)); Jones, J.D. (Simon Fraser Univ., Burnaby, British Columbia (Canada). School of Engineering Science)

1991-01-01

406

Heat exchanger leakage problem location  

NASA Astrophysics Data System (ADS)

Recent compact heat exchangers are very often assembled from numerous parts joined together to separate heat transfer fluids and to form the required heat exchanger arrangement. Therefore, the leak tightness is very important property of the compact heat exchangers. Although, the compact heat exchangers have been produced for many years, there are still technological problems associated with manufacturing of the ideal connection between the individual parts, mainly encountered with special purpose heat exchangers, e.g. gas turbine recuperators. This paper describes a procedure used to identify the leakage location inside the prime surface gas turbine recuperator. For this purpose, an analytical model of the leaky gas turbine recuperator was created to assess its performance. The results obtained are compared with the experimental data which were acquired during the recuperator thermal performance analysis. The differences between these two data sets are used to indicate possible leakage areas.

Hej?k, Ji?; Jcha, Miroslav

2012-04-01

407

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

408

GXL: Toward a Standard Exchange Format  

Microsoft Academic Search

This paper describes ongoing work toward the devel- opment of a standard software exchange format (SEF), for exchanging information among tools that analyze com- puter programs. A particular exchange format called GXL (Graph Exchange Language) is proposed. GXL can be viewed as a merger of well known formats (e. g. GraX, PRO- GRES, RPA, RSF, and TA) for exchanging typed,

Richard C. Holt; Andreas Winter; Andy Schiirr

2000-01-01

409

Fault-Tolerant Heat Exchanger  

NASA Technical Reports Server (NTRS)

A compact, lightweight heat exchanger has been designed to be fault-tolerant in the sense that a single-point leak would not cause mixing of heat-transfer fluids. This particular heat exchanger is intended to be part of the temperature-regulation system for habitable modules of the International Space Station and to function with water and ammonia as the heat-transfer fluids. The basic fault-tolerant design is adaptable to other heat-transfer fluids and heat exchangers for applications in which mixing of heat-transfer fluids would pose toxic, explosive, or other hazards: Examples could include fuel/air heat exchangers for thermal management on aircraft, process heat exchangers in the cryogenic industry, and heat exchangers used in chemical processing. The reason this heat exchanger can tolerate a single-point leak is that the heat-transfer fluids are everywhere separated by a vented volume and at least two seals. The combination of fault tolerance, compactness, and light weight is implemented in a unique heat-exchanger core configuration: Each fluid passage is entirely surrounded by a vented region bridged by solid structures through which heat is conducted between the fluids. Precise, proprietary fabrication techniques make it possible to manufacture the vented regions and heat-conducting structures with very small dimensions to obtain a very large coefficient of heat transfer between the two fluids. A large heat-transfer coefficient favors compact design by making it possible to use a relatively small core for a given heat-transfer rate. Calculations and experiments have shown that in most respects, the fault-tolerant heat exchanger can be expected to equal or exceed the performance of the non-fault-tolerant heat exchanger that it is intended to supplant (see table). The only significant disadvantages are a slight weight penalty and a small decrease in the mass-specific heat transfer.

Izenson, Michael G.; Crowley, Christopher J.

2005-01-01

410

Do ?-conjugative effects facilitate SN2 reactions?  

PubMed

Rigorous quantum chemical investigations of the SN2 identity exchange reactions of methyl, ethyl, propyl, allyl, benzyl, propargyl, and acetonitrile halides (X = F(-), Cl(-)) refute the traditional view that the acceleration of SN2 reactions for substrates with a multiple bond at C? (carbon adjacent to the reacting C? center) is primarily due to ?-conjugation in the SN2 transition state (TS). Instead, substrate-nucleophile electrostatic interactions dictate SN2 reaction rate trends. Regardless of the presence or absence of a C? multiple bond in the SN2 reactant in a series of analogues, attractive C?(?(+))X(?(-)) interactions in the SN2 TS lower net activation barriers (E(b)) and enhance reaction rates, whereas repulsive C?(?(-))X(?(-)) interactions increase E(b) barriers and retard SN2 rates. Block-localized wave function (BLW) computations confirm that ?-conjugation lowers the net activation barriers of SN2 allyl (1t, coplanar), benzyl, propargyl, and acetonitrile halide identity exchange reactions, but does so to nearly the same extent. Therefore, such orbital interactions cannot account for the large range of E(b) values in these systems. PMID:24450965

Wu, Chia-Hua; Galabov, Boris; Wu, Judy I-Chia; Ilieva, Sonia; Schleyer, Paul von R; Allen, Wesley D

2014-02-26

411

Zeolite catalysts for the water gas shift reaction  

Microsoft Academic Search

Cu- and Cu,Zn-ZSM-5 zeolite catalysts were prepared using different cation exchange procedures. The samples were characterized by TPR; CO-FTIR; O2-TPD, XRD; BET and XPS. These catalysts showed appreciable activity and selectivity for the water gas shift reaction at 300400C and vapor\\/gas ratio=3. The Cu,Zn-ZSM-5 catalysts deactivated after a long exposure to steam, at high temperature. The catalytic activity of co-exchanged

Tnia Regina Oliveira de Souza; Suzana Modesto de Oliveira Brito; Heloysa Martins Carvalho Andrade

1999-01-01

412

Nuclear Chain Reaction  

NSDL National Science Digital Library

This simulation shows a chain reaction. The visitor can introduce a neutron and observe how it produces an additional reaction or escapes. The chain reaction can be paused in order to analyze the process.

Bauer, W. (Wolfgang), 1959-

2011-11-29

413

Catalysis of Photochemical Reactions.  

ERIC Educational Resources Information Center

Offers a classification system of catalytic effects in photochemical reactions, contrasting characteristic properties of photochemical and thermal reactions. Discusses catalysis and sensitization, examples of catalyzed reactions of excepted states, complexing ground state substrates, and catalysis of primary photoproducts. (JM)

Albini, A.

1986-01-01

414

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

1981-03-03

415

Synthesis of Di- and trivalent. beta. -aluminas by ion exchange  

SciTech Connect

Many of the mono- di-, and trivalent cations in the periodic chart diffuse rapidly in the ..beta..-alumina structure. ..beta..-Aluminas containing multivalent cations can be synthesized by ion exchange reactions starting with the sodium form of the compound. These facile reactions make it possible to prepare a wide variety of ..beta..-alumina compositions, many of which are metastable and inaccessible by normal synthetic means. This paper describes the methods used to synthesize multivalent ..beta..-aluminas and the preparation of a number of specific transition metal and lanthanide forms of these compounds.

Sattar, S.; Ghosal, B.; Underwood, M.L.; Mertwoy, H.; Saltzberg, M.A.; Frydrych, W.S.; Rohrer, G.S.; Farrington, G.C.

1986-11-15

416

In situ coating on cation exchange resin catalyst, Amberlyst-15, and its impact on the hydration of dicyclopentadiene  

Microsoft Academic Search

New phenomenon of in situ coating by the reactant\\/product on ion exchange resin catalyst, Amberlyst-15, that helps to improve the reaction kinetics of dicyclopentadiene (DCPD) hydration has been reported.

Sandip Talwalkar; Pramod Kumbhar; Sanjay Mahajani

2006-01-01

417

Method for regenerating ion exchange resin.  

National Technical Information Service (NTIS)

This invention is comprised of a method for regenerating ion exchange resin consisting of a mixed resin containing granular cation exchange resin and anion exchange resin contaminated during condensation treatment in steam power generating plants, charact...

M. Ogihara, K. Ichikawa, T. Idemizu

1991-01-01

418

22 CFR 41.62 - Exchange visitors.  

Code of Federal Regulations, 2010 CFR

...2009-04-01 2009-04-01 false Exchange visitors. 41.62 Section 41.62 Foreign Relations...NATIONALITY ACT, AS AMENDED Students and Exchange Visitors § 41.62 Exchange visitors. (a) J-1 classification. An...

2009-04-01

419

22 CFR 41.62 - Exchange visitors.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 false Exchange visitors. 41.62 Section 41.62 Foreign Relations...NATIONALITY ACT, AS AMENDED Students and Exchange Visitors § 41.62 Exchange visitors. (a) J-1 classification. An...

2010-04-01

420

Novel silica-based ion exchange resin.  

National Technical Information Service (NTIS)

Eichrom's highly successful Diphonixo resin resembles a conventional ion exchange resin in its use of sulfonic acid ligands on a styrene- divinylbenzene matrix. Diphonix resin exhibits rapid exchange kinetics that allow economical operation of ion exchang...

1997-01-01

421

Virial exchange energies from model exact-exchange potentials.  

PubMed

It is shown by the example of Slater's averaged exchange potential that a poor approximation to the optimized effective potential (OEP) can yield a deceptively accurate energy via the conventional Kohn-Sham energy functional. For a trial exchange potential to be correct, its Kohn-Sham energy must coincide with the value obtained by the Levy-Perdew virial relation. Significant discrepancies between Kohn-Sham and the virial exchange energies are found for self-consistent Slater, Becke-Johnson, and effective local potentials (ELPs); their relative magnitudes are used to argue that, as approximations to the exact-exchange OEP, ELPs are the most accurate. Virial energy discrepancies vanish for Yang-Wu OEPs when the orbital and auxiliary basis sets are balanced, and remain surprisingly small for oscillatory OEPs obtained with unbalanced basis sets. PMID:18513004

Gaiduk, Alex P; Staroverov, Viktor N

2008-05-28

422

Meson-baryon interaction in the meson exchange picture  

NASA Astrophysics Data System (ADS)

Elastic ?N scattering and the reaction ?+p-->K+?+ are described simultaneously in a unitary coupled-channels approach which respects analyticity. SU(3) flavor symmetry is used to relate the t- and u- channel exchanges that drive the meson-baryon interaction in the different channels. Angular distributions, polarizations, and spin-rotation parameters are compared with available experimental data. The pole structure of the amplitudes is extracted from the analytic continuation.

Dring, M.

2011-10-01

423

Meson-baryon interaction in the meson exchange picture  

SciTech Connect

Elastic {pi}N scattering and the reaction {pi}{sup +}p{yields}K{sup +}{Sigma}{sup +} are described simultaneously in a unitary coupled-channels approach which respects analyticity. SU(3) flavor symmetry is used to relate the t- and u- channel exchanges that drive the meson-baryon interaction in the different channels. Angular distributions, polarizations, and spin-rotation parameters are compared with available experimental data. The pole structure of the amplitudes is extracted from the analytic continuation.

Doering, M. [Institut fuer Kernphysik and Juelich Center for Hadron Physics, Forschungszentrum Juelich, D-52425 Juelich (Germany)

2011-10-24

424

Meson baryon interaction in the hadron exchange picture  

SciTech Connect

Elastic {pi}N scattering and the reaction {pi}{sup +}p{yields}K{sup +}{Sigma}{sup +} are described simultaneously in a unitary coupled-channels approach which respects analyticity. SU(3) flavor symmetry is used to relate the t- and u- channel exchanges that drive the meson-baryon interaction in the different channels. Angular distributions, polarizations, and spin-rotation parameters are compared with available experimental data. The pole structure of the amplitudes is extracted from the analytic continuation.

Doering, M. [Helmholtz-Institut fuer Strahlen- und Kernphysik (Theorie), Universitaet Bonn, Nussallee 14-16, D-53115 Bonn (Germany)

2011-10-21

425

Meson baryon interaction in the hadron exchange picture  

NASA Astrophysics Data System (ADS)

Elastic ?N scattering and the reaction ?+p-->K+?+ are described simultaneously in a unitary coupled-channels approach which respects analyticity. SU(3) flavor symmetry is used to relate the t- and u- channel exchanges that drive the meson-baryon interaction in the different channels. Angular distributions, polarizations, and spin-rotation parameters are compared with available experimental data. The pole structure of the amplitudes is extracted from the analytic continuation.

Dring, M.

2011-10-01

426

Insoluble polyelectrolyte and ion-exchange hollow fiber impregnated therewith  

NASA Technical Reports Server (NTRS)

The number of quaternary sites and ion exchange capacity of a polyquaternary, cross linked, insoluble copolymer of a vinyl pyridine and a dihalo organic compound is increased by about 15-35% by reaction of the polymer with an amine followed by quaternization, if required. The polymer forms spontaneously in the presence of a substrate such as within the pores of a hollow fiber. The improved resin impregnated fiber may be utilized to remove ions from waste or process steams.

Rembaum, A. (inventor)

1977-01-01

427

Heat exchanger using graphite foam  

DOEpatents

A heat exchanger is disclosed. The heat exchanger may have an inlet configured to receive a first fluid and an outlet configured to discharge the first fluid. The heat exchanger may further have at least one passageway configured to conduct the first fluid from the inlet to the outlet. The at least one passageway may be composed of a graphite foam and a layer of graphite material on the exterior of the graphite foam. The layer of graphite material may form at least a partial barrier between the first fluid and a second fluid external to the at least one passageway.

Campagna, Michael Joseph; Callas, James John

2012-09-25

428

Heat exchanger with ceramic elements  

DOEpatents

An annular heat exchanger assembly includes a plurality of low thermal growth ceramic heat exchange members with inlet and exit flow ports on distinct faces. A mounting member locates each ceramic member in a near-annular array and seals the flow ports on the distinct faces into the separate flow paths of the heat exchanger. The mounting member adjusts for the temperature gradient in the assembly and the different coefficients of thermal expansion of the members of the assembly during all operating temperatures.

Corey, John A. (North Troy, NY) [North Troy, NY

1986-01-01

429

IAESTE Exchange Development and Participation  

NASA Astrophysics Data System (ADS)

The International Association for the Exchange of Students for Technical Experience is an Association of National Committees representing academic, industrial and students interests. Participation in the IAESTE exchange is open to bona fide students attending courses at Universities, Institutes of Technology and similar Institutions of Higher Education. This Report contains the Activities of IAESTE with its history and the detail on the bilateral exchanges, study fields, training periods and other useful information. We also look to the future as we continue our journey to improve our Association in partnership with our Academics, Employers and Students.

Ishita, Yusuke

430

Sorption studies of chromium(VI) onto new ion exchanger with tertiary amine, quaternary ammonium and ketone groups  

Microsoft Academic Search

A new acrylic anion exchanger with both tertiary and quaternary ammonium as well as ketone groups in the structural unit has been prepared by the nucleophilic substitution reaction of aminolyzed vinylacetate:acrylonitrile:divinylbenzene copolymer of porosity structure in the swelling state with 2-chloroacetone as a halogenated compound. The new compound exhibits better qualities of strong base exchange capacity than the weak base

Grzegorz Wjcik; Violeta Neagu; Ion Bunia

2011-01-01

431

Hear Exchange Assembly  

DOEpatents

A heat exchange assembly comprises a plurality of plates disposed in a spaced-apart arrangement, each of the plurality of plates includes a plurality of passages extending internally from a first end to a second end for directing flow of a heat transfer fluid in a first plane, a plurality of first end-piece members equaling the number of plates and a plurality of second end-piece members also equaling the number of plates, each of the first and second end-piece members including a recessed region adapted to fluidly connect and couple with the first and second ends of the plate, respectively, and further adapted to be affixed to respective adjacent first and second end-piece members in a stacked formation, and each of the first and second end-piece members further including at least one cavity for enabling entry of the heat transfer fluid into the plate, exit of the heat transfer fluid from the plate, or 180.degree. turning of the fluid within the plate to create a serpentine-like fluid flow path between points of entry and exit of the fluid, and at least two fluid conduits extending through the stacked plurality of first and second end-piece members for providing first fluid connections between the parallel fluid entry points of adjacent plates and a fluid supply inlet, and second fluid connections between the parallel fluid exit points of adjacent plates and a fluid discharge outlet so that the heat transfer fluid travels in parallel paths through each respective plate.

Lowenstein, Andrew (Princeton, NJ); Sibilia, Marc (Princeton, NJ); Miller, Jeffrey (Rocky Hill, NJ); Tonon, Thomas S. (Princeton, NJ)

2003-05-27

432

Use of ion-exchange membranes in a reactor for esterification of oleic acid and methanol at room temperature  

Microsoft Academic Search

Full and complete esterification of oleic acid and methanol, catalyzed by cationic activation, is performed quickly at room temperature in a new kind of reactor, REMI, fitted with cation-exchange membranes.Use of ion-exchange membranes involves liquid phases, prevents the appearance of the compensating ion of the proton which catalyses the reaction, in the reaction medium and allows pertraction of water from

B. Chemseddine; R. Audinos

1996-01-01

433

Surface Exchange and Bulk Diffusivity of LSCF as SOFC Cathode: Electrical Conductivity Relaxation and Isotope Exchange Characterizations  

SciTech Connect

The oxygen diffusion coefficient (D) and surface exchange coefficient (k) of a typical SOFC cathode material, La{sub 0.6}Sr{sub 0.4}Co{sub 0.2}Fe{sub 0.8}O{sub 3-?} (LSCF) were characterized by both electrical conductivity relaxation (ECR) and oxygen isotope exchange (IE) methods. Conductivity relaxation experiments were conducted at 800C for small step changes in partial pressure of oxygen (P{sub O{sub 2}} ), both decreasing and increasing, from 0.02 atm to 0.20 atm. The results revealed P{sub O{sub 2}} dependent hysteresis with the reduction process requiring more equilibration time than oxidation. Analysis of the experimental data indicated that the surface exchange coefficient is a function of the final oxygen partial pressure in an isothermal system. In addition, both forward and backward oxygen reduction reaction constants, which are vital for the fundamental understanding of SOFC cathode reaction mechanisms, are investigated based on the relationship between surface exchange coefficient and P{sub O{sub 2}} . The direct comparisons between the results from both ECR and IE were presented and the possible experimental errors in both methods were discussed.

Li, Yihong; Gerdes, Kirk; Horita, Teruhisa; Liu, Xingbo

2013-05-05

434

Solar system X-rays from charge exchange processes  

NASA Astrophysics Data System (ADS)

While X-ray astronomy began in 1962 and has made fast progress since then in expanding our knowledge about where in the Universe X-rays are generated by which processes, it took one generation before the importance of a fundamentally different process was recognized. This happened in our immediate neighborhood, when in 1996 comets were discovered as a new class of X-ray sources, directing our attention to charge exchange reactions. Charge exchange is fundamentally different from other processes which lead to the generation of X-rays, because the X-rays are not produced by hot electrons, but by ions picking up electrons from cold gas. Thus it opens up a new window, making it possible to detect cool gas in X-rays (like in comets), while all the other processes require extremely high temperatures or otherwise extreme conditions. After having been overlooked for a long time, the astrophysical importance of charge exchange for the generation of X-rays is now receiving increased general attention. In our solar system, charge exchange induced X-rays have now been established to originate in comets, in all the planets from Venus to Jupiter, and even in the heliosphere itself. In addition to that, evidence for this X-ray emission mechanism has been found at various locations across the Universe. Here we summarize the current knowledge about solar system X-rays resulting from charge exchange processes.

Dennerl, K.; Lisse, C. M.; Bhardwaj, A.; Christian, D. J.; Wolk, S. J.; Bodewits, D.; Zurbuchen, T. H.; Combi, M.; Lepri, S.

2012-04-01

435

Direct-Contact Heat Exchanger.  

National Technical Information Service (NTIS)

The working principle of direct contact heat exchanger, where heat transfer takes place between two immiscible fluids coming into direct contact, is described. Typical direct contact devices are outlined. A better understanding of the principles involved ...

A. Bricard

1991-01-01

436

Combined Electrolysis Catalytic Exchange (CECE).  

National Technical Information Service (NTIS)

Starting from an effort to control airborne emissions, the Mound tritium containment program has evolved to include development of the Combined Electrolysis Catalytic Exchange (CECE) process. This process separates tritiated aqueous streams into detritiat...

R. E. Ellis T. K. Mills M. L. Rogers

1980-01-01

437

Gas Exchange under Environmental Stress.  

National Technical Information Service (NTIS)

The purpose of this project was threefold: (1) to assemble available information concerning the effects of various environmental factors such as altitude, acceleration, and breathing gas composition on gas exchange, (2) to initiate a mathematical simulati...

H. I. Modell M. P. Hlastala

1978-01-01

438

Exchange couplings in magnetic films  

NASA Astrophysics Data System (ADS)

Recent advances in the study of exchange couplings in magnetic films are introduced. To provide a comprehensive understanding of exchange coupling, we have designed different bilayers, trilayers and multilayers, such as anisotropic hard-/soft-magnetic multilayer films, ferromagnetic/antiferromagnetic/ferromagnetic trilayers, [Pt/Co]/NiFe/NiO heterostructures, Co/NiO and Co/NiO/Fe trilayers on an anodic aluminum oxide (AAO) template. The exchange-coupling interaction between soft- and hard-magnetic phases, interlayer and interfacial exchange couplings and magnetic and magnetotransport properties in these magnetic films have been investigated in detail by adjusting the magnetic anisotropy of ferromagnetic layers and by changing the thickness of the spacer layer, ferromagnetic layer, and antiferromagnetic layer. Some particular physical phenomena have been observed and explained.

Liu, Wei; Liu, Xiong-Hua; Cui, Wei-Bin; Gong, Wen-Jie; Zhang, Zhi-Dong

2013-02-01

439

Thin cation-exchange foils  

Microsoft Academic Search

Treatment of commercial polystyrene sheets with fuming sulfuric acid ; produced a thin layer of cation exchanger. The ion exchange capacity of the ; layer was measured by an isotope dilution procedure which utilizes Th²²⁸ ; and Th²³². At the same time the thickness was found from the yield of Ra\\/; sup 224\\/ which escapes from the foils as alpha

S. Bjoernholm; C. M. Lederer

1962-01-01

440

Vitrification of ion exchange resins  

DOEpatents

The present invention relates to vitrification of ion exchange resins that have become loaded with hazardous or radioactive wastes, in a way that produces a homogenous and durable waste form and reduces the disposal volume of the resin. The methods of the present invention involve directly adding borosilicate glass formers and an oxidizer to the ion exchange resin and heating the mixture at sufficient temperature to produce homogeneous glass.

Cicero-Herman, Connie A. (Aiken, SC); Workman, Rhonda Jackson (North Augusta, SC)

2001-01-01

441

Ion exchange - Simulation and experiment  

NASA Technical Reports Server (NTRS)

A FORTRAN program for simulating multicomponent adsorption by ion-exchange resins was adapted for use as both an ASPEN-callable module and as a free-standing simulator of the ion-exchange bed. Four polystyrene-divinylbenzene sulfonic acid resins have been characterized for three principal ions. It is concluded that a chelating resin appears appropriate as a heavy-metal trap. The same ASPEN-callable module is used to model this resin when Wilson parameters can be obtained.

Herrmann, Cal C.; Finn, John E.

1991-01-01