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1

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, Sebastián; Doctorovich, Fabio; Cukiernik, Fabio D; Baggio, Ricardo

2014-05-01

2

U(IV)/Ln(III) mixed site in polymetallic oxalato complexes. Part III: Structure of Na[Yb(C 2O 4) 2(H 2O)]·3H 2O and the derived quadratic series (NH 4+) 1-x[ Ln1-xU x (C 2O 4) 2(H 2O)]·(3+ x) H 2O, Ln=Y, Pr-Sm, Gd, Tb  

NASA Astrophysics Data System (ADS)

Single crystals of a new sodium ytterbium oxalate Na[Yb(C 2O 4) 2(H 2O)]·3H 2O ( 1) and six mixed lanthanide (III)-uranium (IV) oxalates (NH 4+) 1-x[ Ln1-xU x (C 2O 4) 2(H 2O)]·(3+ x) H 2O, Ln=Y, x=0.47 ( 2), Ln=Pr, x=0.42 ( 3), Ln=Nd, x=0.60 ( 4), Ln=Sm, x=0.55 ( 5), Ln=Gd, x=0.25 ( 6) and Ln=Tb, x=0.52 ( 7) have been grown using slow diffusion through silica gels. The crystal structures of all the compounds have been determined by single-crystal X-ray diffraction. For compound 1 the symmetry is monoclinic, space group Pc, cell dimensions a=8.559(2) Å, b=8.564(2) Å, c=14.938(3) Å, ?=103.062(3), Z=4. The structure of 1 is isotypic with Na[Y(C 2O 4) 2(H 2O)]·3H 2O and consists of layers formed by four-membered rings of Yb connected through oxalate ions. The ytterbium atom is nine-coordinated by oxygen from four bis-bidentate oxalate ligands and one water molecule which alternate up and down the layer. Na + ions and supplementary water molecules are located between the layers. The six mixed lanthanide (III)-uranium (IV) oxalates, 2- 7, are isotypic, the symmetry is tetragonal, space group P4/ n, the unit cell parameters are in the range 8.7239(12)-8.9116(6) and 7.854(2)-7.9487(9) Å for a and c, respectively, Z=2. The structure of the six compounds is built from the same two-dimensional arrangement of alternating metallic and oxalate ions forming four-membered rings. The layers are similar to that observed in 1 and the mixed Ln(III)/U(IV) oxalate layers are obtained by partial substitution of Ln(III) by U(IV) in a nine-coordinated site, the charge surplus being compensated by removal of monovalent cations in the interlayer space. The ammonium ions and the water molecules are disordered in the same crystallographic site. Thus these compounds form the third series of mixed lanthanide (III)-uranium (IV) oxalates, the tetragonal one, that completes the two others previously reported, the hexagonal and the triclinic series.

Chapelet-Arab, B.; Duvieubourg, L.; Nowogrocki, G.; Abraham, F.; Grandjean, S.

2006-12-01

3

Nucleon exchange in damped nuclear reactions  

SciTech Connect

Starting from the general context of one-body nuclear dynamics, the nucleon-exchange mechanism in damped nuclear reactions is discussed. Some of its characteristic effects on various dinuclear observables are highlighted and a few recent advances are described.

Randrup, J.

1986-04-01

4

Individual Differences in Reactions to Inequitable Exchanges  

Microsoft Academic Search

This study investigated the role of sociopathic tendencies in reactions to inequitable exchanges. Subjects were 273 males and females classified as high or low in sociopathy. High sociopathic subjects were further divided into primary or secondary sociopaths on the basis of their levels of anxiety and guilt. Subjects read narratives of inequitable exchanges and assumed the role of the exploiter

Barbara B. Ellis; Louis A. Penner

1983-01-01

5

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

6

Hyporheic Exchange and Fulvic Acid Redox Reactions in an Alpine  

E-print Network

Hyporheic Exchange and Fulvic Acid Redox Reactions in an Alpine Stream/Wetland Ecosystem, Colorado to provide insight into redox reactions in hyporheiczones The influence of hyporheic zone interactions on the redox state of fulvic acids and other redox active species

Williams, Mark W.

7

Hydrogen\\/chlorine exchange reactions of gaseous carbanions  

Microsoft Academic Search

Gas-phase reactions of three typical carbanions CH2NO2?, CH2CN?, and CH2S(O)CH3? with the chloromethanes CH2Cl2, CHCl3, and CCl4, examined by tandem mass spectrometry, show a novel hydrogen\\/chlorine exchange reaction. For example, reaction between the\\u000a nitromethyl anion CH2NO2? and carbon tetrachloride CCl4 forms the ion CHClNO2?. The suggested reaction mechanism involves nucleophilic attack by CH2NO2? at the chlorine of CCl4 followed by

Hao Chen; R. Graham Cooks; Eduardo C. Meurer; Marcos N. Eberlin

2005-01-01

8

Guest Exchange in an Encapsulation Complex: A Supramolecular Substitution Reaction  

Microsoft Academic Search

Encapsulation complexes are reversibly formed assemblies in which small molecule guests are completely surrounded by large molecule hosts. The assemblies are held together by weak intermolecular forces and are dynamic: they form and dissipate on time scales ranging from milliseconds to days--long enough for many interactions, even reactions, to take place within them. Little information is available on the exchange

Javier Santamaria; Tomas Martin; Goran Hilmersson; Stephen L. Craig; Julius Rebek Jr.

1999-01-01

9

The effect of various cropping systems upon organic matter, total nitrogen, cation exchange capacity, exchangeable cations, conductivity and reaction  

E-print Network

&IBRARY A 4 N COLLEGE OF TEXAS THE EFFECT OF VARIOUS CROPPING SYSTEMS UPON ORGANIC MATTER, TOTAL NITROGEN, CATION EXCHANGE CAPACITY, EXCHANGEABLE CATIONS, CONDUCTIVITY AND REACTION. A Thesis By MOHAMMAD ABDUL MANNAN Submitted... NITROGEN, CATION EXCHANGE CAPACITY, EXCHANGEABLE CATIONS, CONDUCTIVITY AND REACTION A Thesis By Approved as to style and content by: Chairman of Committe ~Head of the Department f Agronomy Nay 1958 ACKNOWLE DGNEHTS Thanks are due to Mr. M. E...

Mannan, Mohammad Abdul

1958-01-01

10

Guest exchange in an encapsulation complex: A supramolecular substitution reaction  

PubMed Central

Encapsulation complexes are reversibly formed assemblies in which small molecule guests are completely surrounded by large molecule hosts. The assemblies are held together by weak intermolecular forces and are dynamic: they form and dissipate on time scales ranging from milliseconds to days—long enough for many interactions, even reactions, to take place within them. Little information is available on the exchange process, how guests get in and out of these complexes. Here we report that these events can be slow enough for conventional kinetic studies, and reactive intermediates can be detected. Guest exchange has much in common with familiar chemical substitution reactions, but differs in some respects: no covalent bonds are made or broken, the substrate is an assembly rather than a single molecule, and at least four molecules are involved in multiple rate-determining steps. PMID:10411877

Santamaría, Javier; Martín, Tomás; Hilmersson, Göran; Craig, Stephen L.; Rebek, Julius

1999-01-01

11

Guest exchange in an encapsulation complex: a supramolecular substitution reaction.  

PubMed

Encapsulation complexes are reversibly formed assemblies in which small molecule guests are completely surrounded by large molecule hosts. The assemblies are held together by weak intermolecular forces and are dynamic: they form and dissipate on time scales ranging from milliseconds to days-long enough for many interactions, even reactions, to take place within them. Little information is available on the exchange process, how guests get in and out of these complexes. Here we report that these events can be slow enough for conventional kinetic studies, and reactive intermediates can be detected. Guest exchange has much in common with familiar chemical substitution reactions, but differs in some respects: no covalent bonds are made or broken, the substrate is an assembly rather than a single molecule, and at least four molecules are involved in multiple rate-determining steps. PMID:10411877

Santamaría, J; Martín, T; Hilmersson, G; Craig, S L; Rebek, J

1999-07-20

12

Charge exchange reactions and solar neutrino detection in 81Br  

NASA Astrophysics Data System (ADS)

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

Liu, K. F.; Gabbard, F.

1983-01-01

13

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

14

Separation of the isotopes of boron by chemical exchange reactions  

DOEpatents

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

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

1995-05-30

15

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

16

Polarization relations in charge and hypercharge exchange reactions  

NASA Astrophysics Data System (ADS)

Relations between polarizations in charge and hyperchange exchange reactions are derived. The idea is that K ?(890) and K ??(1400) exchange, including unspecified absorptive corrections, are related to ? and A 2 exchanges by SU(3) octet symmetry, with a scale factor to represent symmetry breaking between the ?- A2 and the K ?-K ?? trajectories. This hypothesis is consistent with the present data on overlineKN ? ??(??) and ?N ? K ?(K ?). It leads to simple relations between the polarized cross sections P d ?/d t, relating the above reactions to K-p ? overlineKon, K +n ? K op, ?-p ? ?on, ?-p ? ?on. Predictions are made, on this basis, for polarization in K -p ? K on, K +n ? K op and ?-p ? ?on at 4 GeV/ c and for K-p ? overlineKon at 7 GeV/ c. Finally, some supplementary conjectures lead to predictions about polarization in baryon-baryon and baryon-anti-baryon reactions, np ? pn, overlinepp ? overlinenn, overlinepp ? overline?? , etc., and also in K Lop ? K Sop regeneration.

Martin, A. D.; Michael, C.; Phillips, R. J. N.

1972-06-01

17

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, 1675–1689. PMID:23121622

Marino, Stefano M.

2013-01-01

18

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

19

Deuteron-proton charge exchange reaction at small transfer momentum  

E-print Network

The charge-exchange reaction pd -> npp at 1 GeV projectile proton energy is studied. This reaction is considered in a special kinematics, when the transfer momentum from the beam proton to fast outgoing neutron is close to zero. Our approach is based on the Alt-Grassberger-Sandhas formulation of the multiple-scattering theory for the three-nucleon system. The matrix inversion method has been applied to take account of the final state interaction (FSI) contributions. The differential cross section, tensor analyzing power $C_{0,yy}$, vector-vector $C_{y,y}$ and vector-tensor $C_{y,xz}$ spin correlation parameters of the initial particles are presented. It is shown, that the FSI effects play a very important role under such kinematical conditions. The high sensitivity of the considered observables to the elementary nucleon-nucleon amplitudes has been obtained.

N. B. Ladygina; A. V. Shebeko

2004-11-17

20

Charge-exchange reactions with a radioactive triton beam  

SciTech Connect

A high-resolution (t, {sup 3}He) test experiment has been performed recently by making use of a secondary triton beam produced by fragmentation of {alpha}-particles. The purpose of this charge-exchange experiment was to achieve good energy resolution in an (n,p)-type reaction at intermediate bombarding energies. The experiment was carried out with the K1200 cyclotron at the National Superconducting Cyclotron Laboratory using the A1200 beam-analysis system and the S800 magnetic spectrometer. The beam-analysis system was used to transport the energy-dispersed radioactive triton beam from the production target to the target position, and the magnetic spectrometer was used to focus the dispersion-matched {sup 3}He particles from the (t, {sup 3}He) reaction at 0 degree sign onto the focal plane of the spectrometer. An energy resolution of 200-250 keV was achieved.

Jaenecke, J. [University of Michigan, Ann Arbor, Michigan 48109-1120 (United States)

1998-12-21

21

Mechanism of the Exchange Reaction in HRAS from Multiscale Modeling  

PubMed Central

HRAS regulates cell growth promoting signaling processes by cycling between active (GTP-bound) and inactive (GDP-bound) states. Understanding the transition mechanism is central for the design of small molecules to inhibit the formation of RAS-driven tumors. Using a multiscale approach involving coarse-grained (CG) simulations, all-atom classical molecular dynamics (CMD; total of 3.02 µs), and steered molecular dynamics (SMD) in combination with Principal Component Analysis (PCA), we identified the structural features that determine the nucleotide (GDP) exchange reaction. We show that weakening the coupling between the SwitchI (residues 25–40) and SwitchII (residues 59–75) accelerates the opening of SwitchI; however, an open conformation of SwitchI is unstable in the absence of guanine nucleotide exchange factors (GEFs) and rises up towards the bound nucleotide to close the nucleotide pocket. Both I21 and Y32, play a crucial role in SwitchI transition. We show that an open SwitchI conformation is not necessary for GDP destabilization but is required for GDP/Mg escape from the HRAS. Further, we present the first simulation study showing displacement of GDP/Mg away from the nucleotide pocket. Both SwitchI and SwitchII, delays the escape of displaced GDP/Mg in the absence of GEF. Based on these results, a model for the mechanism of GEF in accelerating the exchange process is hypothesized. PMID:25272152

Kapoor, Abhijeet; Travesset, Alex

2014-01-01

22

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

23

Surface characterization of chromia for chlorine/fluorine exchange reactions.  

PubMed

The dismutation of CCl(2)F(2) was used to probe the effect of halogenation of chromia by Cl/F exchange reactions to find out the difference between the halogenated inactive and active catalysts. The heterogeneous reactions were performed in a continuous flow Ni reactor and also under simulated reaction conditions in a reactor where after the reaction X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES) analyses are possible without air exposure of the catalyst, i.e., under so-called "in situ" conditions. The Cr(III) 2p XP spectra, which revealed multiplet splitting features and satellite emission, were used for chemical analysis by using a simple evaluation procedure which neglects this inherent complexity. Chemical analysis was also applied by using chemical state plots for Cr 3s in order to cross-check Cr 2p related results. Both ex and in situ XPS show that as soon as Cr(2)O(3) is exposed to CCl(2)F(2) at 390 degrees C fluorination as well as chlorination takes place at the catalyst surface. When the XPS surface composition reaches approximately 4 at. % fluorination and 6 at. % chlorination, maximum catalytic activity was obtained. Application of longer reaction times did not change significantly the obtained surface composition of the activated chromia. The fluorination and chlorination of chromia was further investigated by various HF and HCl treatments. The activated chromia samples and the Cr(2)O(3), Cr(OH)(3), CrF(2)OH, CrF(3) x H(2)O, alpha-CrF(3), beta-CrF(3), and CrCl(3) reference samples with well-known chemical structures were also characterized by X-ray absorption near edge structure (XANES), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), pyridine-FTIR, wet chemical (F and Cl) analysis, X-ray powder diffraction (XRD), and surface area (BET) analysis. The results suggest that the formation of chromium oxide chloride fluoride species, e.g., chromium oxide halides, at the surface is sufficient to provide catalytic activity. The presence of any CrF(3) and/or CrCl(3) phases on the activated chromia samples was not found. PMID:16851173

Unveren, Ercan; Kemnitz, Erhard; Lippitz, Andreas; Unger, Wolfgang E S

2005-02-10

24

Dynamics of the hydrogen exchange reaction using the photoloc technique  

NASA Astrophysics Data System (ADS)

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

Fernandez-Alonso, Felix

2000-08-01

25

Measurement of positional isotope exchange rates in enzyme catalyzed reactions by fast atom bombardment mass spectrometry  

E-print Network

MEASUREMENT OF POSITIONAL ISOTOPE EXCHANGE RATES IN ENZYME CATALYZED REACTIONS BY FAST ATOM BOMBARDMENT MASS SPECTROMETRY A Thesis by LARRY NAYNE HILSCHER Submitted to the Gradu te College of Texas A&M University in partial fulfil" mert... of the requiremer ts for the degree of MASTEP. QF SCIENCE August 1985 Major Subject: Chemistry MEASUREMENT OF POSITIONAL ISOTOPE EXCHANGE RATES IN ENZYME CATALYZED REACTIONS BY FAST ATOM BOMBARDMENT MASS SPECTROMETRY A Thesis LARRY NAYNE HILSCHER Approved...

Hilscher, Larry Wayne

1985-01-01

26

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

SciTech Connect

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

Baer, H.W.

1987-01-01

27

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

28

Isotope exchange reactions with radiolabeled sulfur compounds in anoxic seawater  

Microsoft Academic Search

The isotope exchange between35S-labeled sulfur compounds of sulfate (SO42-), elemental sulfur (S0), polysulfide (Sn2-), hydrogen sulfide (SHS-: H2S + HS- + S2-), iron sulfide (FeS), and pyrite (FeS2) was studied at pH 7.6 and 20 °C in anoxic, sterile seawater. Isotope exchange was observed between S0, S22- SHS-, and FeS, but not between35S labeled SO42- or FeS2 and the other

Henrik Fossing; Bo Ba Jørgensen

1990-01-01

29

Comparison of meson-exchange and QCD calculations of. gamma. d. -->. np reaction  

SciTech Connect

We report a calculation of ..gamma..d ..-->.. np reaction up to GeV energy region, based on a meson-exchange theory developed in the study of intermediate energy NN and ..pi..d reactions. The result is in a sharp disagreement with a QCD prediction by Brodsky and Hiller. 11 refs., 7 figs.

Lee, T.S.H.; Ohta, K.

1989-01-01

30

Rare events via multiple reaction channels sampled by path replica exchange  

Microsoft Academic Search

Transition path sampling (TPS) was developed for studying activated processes in complex systems with unknown reaction coordinate. Transition interface sampling (TIS) allows efficient evaluation of the rate constants. However, when the transition can occur via more than one reaction channel separated by a high barrier, TPS and TIS are ineffective in sampling both channels. The combination of replica exchange with

Peter G. Bolhuis

2008-01-01

31

Multistrange Baryon production from strangeness-exchange reactions  

E-print Network

Using a gauged flavor SU(3) invariant hadronic Lagrangian, we study [] production from [ ] induced reactions on[] and [] in a coupled-channel approach. Including the four channels of [], and [], we solve the Bethe-Salpeter equation in the K...

Li, Changhui

2012-06-07

32

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

NASA Astrophysics Data System (ADS)

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

Alavi, Saman; Taghikhani, Mahdi

2012-06-01

33

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

34

General Potential-Energy Function for Exchange Reactions  

Microsoft Academic Search

A general potential-energy function for linear triatomic systems has been developed for use in connection with reaction kinetics calculations. The function is a generalization of the Morse function with a sufficient number of adjustable parameters to permit arbitrary fixing of the location and curvatures of the saddle point of the potential energy surface. The function reduces, of course, to the

Frederick T. Wall; Richard N. Porter

1962-01-01

35

Hydrotalcite-like compounds obtained by anion exchange reactions  

Microsoft Academic Search

The synthesis of nickel aluminium hydroxypicrate, [Ni3Al(OH)8] (C6O7N3H2)·nH2O, and lithium aluminium hydroxypicrate, [Al2Li(OH)6] (C6O7N3H2)·nH2O by anion exchange is described. Picric acid and the corresponding hydroxycarbonates were used as starting materials. The new compounds were characterized by chemical analyses, electron microscopy, infrared spectroscopy and X-ray diffraction. The results obtained indicate that both are hydrotalcite-like compounds where the picrate anion lies between

M. A. Ulibarri; M. J. Hernandez; J. Cornejo

1991-01-01

36

Probing the mechanisms and dynamics of gas phase hydrogen-deuterium exchange reactions of sodiated polyglycines.  

PubMed

The rate constants for H-D exchange reactions of sodiated polyglycines (GnNa(+), n = 2-8) and polyalanines (AnNa(+), n = 2, 3 and 5) with ND3 have been measured in the cell of an FT-ICR mass spectrometer. All peptides except G2Na(+) are found to undergo three exchange reactions, all of which are consecutive with no sign of multiple exchanges within a single collision event. This information has been used to construct full mechanistic scenarios with the help of detailed quantum chemical calculations of the possible reaction paths for H-D exchange. The first exchange is always located at the C terminus however with different mechanisms depending upon whether the peptide termini can (larger peptides) or cannot (smaller peptides) interact directly without strong energy penalty. The most favourable mechanisms for the second and third exchanges of the N terminus protons, are found to be different from those for the first for all peptide sizes. The peptide distortions that are necessary in order for some of these reactions to occur are made possible by the energy reservoir provided by the favorable interaction of the peptide ion with ND3. Their occurrence and variety preclude any general relationship between H-D exchange kinetics and the most stable ion structures. There is however a break at G7Na(+) in the kinetics trend, with a first exchange rate which is much smaller than for all other peptide sizes. This break can be directly related to a different structural type in which the C terminus is neither free nor close to the N terminus. PMID:25573245

McMahon, T B; Ohanessian, G

2015-01-28

37

Arrhenius' law in turbulent media and an equivalent tunnel effect. [in binary exchange chemical reactions  

NASA Technical Reports Server (NTRS)

The indeterminacy inherent to the formal extension of Arrhenius' law to reactions in turbulent flows is shown to be surmountable in the case of a binary exchange reaction with a sufficiently high activation energy. A preliminary calculation predicts that the turbulent reaction rate is invariant in the Arrhenius form except for an equivalently lowered activation energy. This is a reflection of turbulence-augmented molecular vigor, and causes an appreciable increase in the reaction rate. A similarity to the tunnel effect in quantum mechanics is indicated. The anomaly associated with the mild ignition of oxy-hydrogen mixtures is discussed in this light.

Tsuge, S.; Sagara, K.

1978-01-01

38

New charge exchange model of GEANT4 for 9Be(p,n)9B reaction  

NASA Astrophysics Data System (ADS)

A new data-based charge exchange model of GEANT4 dedicated to the 9Be(p,n)9B reaction is developed by taking the ENDF/B-VII.1 differential cross-section data as input. Our model yields results that are in good agreement with the experimental neutron yield spectrum data obtained for proton beams of energy (20-35) MeV. In particular, in contrast to all the considered GEANT4 hadronic models, the peak structure resulting from the discrete neutrons generated by the charge-exchange reaction is observed to be accurately reproduced in our model.

Shin, Jae Won; Park, Tae-Sun

2015-01-01

39

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

SciTech Connect

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

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

2011-01-15

40

Study of deuteron-proton charge exchange reaction at small transfer momentum  

E-print Network

The charge-exchange reaction pd->npp at 1 GeV projectile proton energy is studied in the multiple-scattering expansion technique. This reaction is considered in a special kinematics, when the transfer momentum from the beam proton to fast neutron is close to zero. The differential cross section and a set of polarization observables are calculated. It was shown that contribution of the final state interaction between two protons is very significant.

N. B. Ladygina; A. V. Shebeko

2004-04-15

41

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

42

Ethene/alkyne exchange reaction at an intramolecular frustrated Lewis pair.  

PubMed

A vicinal ethylene bridged S/B frustrated Lewis pair (FLP) in situ generated by a hydroboration reaction of phenyl vinyl sulfide, reacts with p-tert-butylphenylacetylene by ethene/alkyne exchange and subsequent 1,2-addition of a second alkyne equivalent to give a zwitterionic sulfonium/borate product. PMID:24409458

Eller, Christina; Bussmann, Kathrin; Kehr, Gerald; Wibbeling, Birgit; Daniliuc, Constantin G; Erker, Gerhard

2014-02-25

43

A catalytic heat-exchanging tubular reactor for combining of high temperature exothermic and endothermic reactions  

Microsoft Academic Search

A multifunctional catalytic heat-exchanging (HEX) tubular reactor for combining exothermic and endothermic reactions has been developed and tested for catalytic methane oxidation and methane steam reforming. The methane combustion and steam reforming catalysts were synthesized on the heat-conducting metal foam support materials by application of preliminary plasma spraying of alumina in order to increase adhesive properties of the active layer.

Z. R Ismagilov; V. V Pushkarev; O. Yu Podyacheva; N. A Koryabkina; H Veringa

2001-01-01

44

Analytical solutions for flow in porous media with multicomponent cation exchange reactions  

NASA Astrophysics Data System (ADS)

cation exchange reactions have important applications in groundwater remediation, disposal of nuclear wastes as well as enhanced oil recovery. The hyperbolic theory of conservation laws can be used to explain the nature of displacements observed during flow with cation exchange reactions between flowing aqueous phase and stationary solid phase. Analytical solutions have been developed to predict the effluent profiles for a particular case of heterovalent cations (Na+, Ca2+ and Mg2+) and an anion (Cl-) for any combination of constant injection and constant initial composition using this theory. We assume local equilibrium, neglect dispersion and model the displacement as a Riemann problem using mass action laws, the charge conservation equation and the cation exchange capacity equation. The theoretical predictions have been compared with experimental data available at two scales—the laboratory scale and the field scale. The theory agrees well with the experimental data at both scales. Analytical theory predictions show good agreement with numerical model, developed using finite differences.

Venkatraman, Ashwin; Hesse, Marc A.; Lake, Larry W.; Johns, Russell T.

2014-07-01

45

Immunoassay principle based on exchange reactions: investigations on agarose gel and silanized quartz.  

PubMed

Preliminary studies of a new immunoassay principle based on exchange reactions is reported. Exchange of 125I-labelled insulin with unlabelled insulin from immobilized monoclonal antibodies was investigated. From antibody immobilized on a gel substrate the tagged insulin was exchanged according to a first-order process. With antibody immobilized on a quartz substrate by two different methods, the kinetics was changed dramatically, probably because of the non-specific interaction between the ligand and the surface. The recorded adsorption isotherms could not be described by the Langmuir adsorption equation, and a model allowing for non-specific adsorption of the ligand was developed. This model gave a satisfactory fit to the experimental data, allowing computation of adsorption parameters. It is concluded that even the best method used to immobilize receptors on quartz is not adequate for an exchange assay to be made. However, this coating method may lead to more sensitive receptor-based assays of more conventional type. PMID:1379052

Weber, A; Ogendal, L H

1992-01-01

46

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

47

Synthesis of Single-Crystalline Niobate Nanorods via Ion-Exchange Based on Molten-Salt Reaction  

E-print Network

Synthesis of Single-Crystalline Niobate Nanorods via Ion-Exchange Based on Molten-Salt Reaction by employing hydrothermal reaction2 or templates,3 molten-salt syn- thesis,4 and composite- exchange approach for the synthesis of single-crystal sodium and calcium niobates nanorods based on molten-salt

Wang, Zhong L.

48

Reactivity of hydroxybenzoic acids in the hydrogen-isotope exchange reaction.  

PubMed

The hydrogen-isotope exchange reaction (T-for-H exchange reaction) between tritiated water vapor (HTO vapor) and 3-hydroxy-4-methoxybenzoic acid (and it's analog; 4-hydroxy-3-methoxybenzoic acid) were observed at 50 and 70 degrees C in a gas-solid system to reveal the reactivity of a functional group in an aromatic compound having two substituents in the aromatic ring. Further, it was shown that (a) the reactivity of the compounds used in this work follows the Hammett's rule, and (b) the reactivity of trisubstituted aromatic compound could be analyzed by applying the additive property of the Hammett's rule even if the compound contains a substituent at the ortho-position. PMID:17261367

Zhao, D; Imaizumi, H; Lei, Q; Wu, J

2007-05-01

49

Induced Nucleon Polarization and Meson-Exchange Currents in (e,e'p) Reactions  

E-print Network

Nucleon recoil polarization observables in $(e,e'\\vec{p})$ reactions are investigated using a semi-relativistic distorted-wave model which includes one- and two-body currents with relativistic corrections. Results for the induced polarization asymmetry are shown for closed-shell nuclei and a comparison with available experimental data for $^{12}$C is provided. A careful analysis of meson exchange currents shows that they may affect significantly the induced polarization for high missing momentum.

F. Kazemi Tabatabaei; J. E. Amaro; J. A. Caballero

2004-02-02

50

Synthesis and processing of AgInO 2 delafossite compounds by cation exchange reactions  

Microsoft Academic Search

In recent years, ternary noble metal oxide compounds based on the delafossite structure have attracted great interest because of their potential use as transparent conductors. In this work, the experimental conditions which affect the synthesis and properties of Ag-based compounds by the cation exchange technique was explored. The reaction between AgNO3 and NaInO2 was performed at temperatures ranging from 200

Jane E Clayton; David P Cann; Nathan Ashmore

2002-01-01

51

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

52

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

53

Double-Regge Exchange Limit for the $?p\\rightarrow K^+K^-p$ Reaction  

E-print Network

We apply the generalized Veneziano model ($B_5$ model) in the double-Regge exchange limit to the $\\gamma p \\to K^+ K^- p$ reaction. Four different cases defined by the possible combinations of the signature factors of leading Regge exchanges (($K^*,a_2/f_2$), ($K^*,\\rho/\\omega$), ($K_2^*,a_2/f_2$), and ($K_2^*,\\rho/\\omega$)) have been simulated through the Monte Carlo method. Suitable event candidates for the double-Regge exchange high-energy limit were selected employing \\textit{Van Hove} plots as a better alternative to kinematical cuts in the $K^+ K^- p$ Dalitz plot. In this way we predict and analyze the double-Regge contribution to the $K^+ K^- p$ Dalitz plot, which constitutes one of the major backgrounds in the search for strangeonia, hybrids and exotics using $\\gamma p\\rightarrow K^+K^-p$ reaction. We expect that data currently under analysis, and that to come in the future, will allow verification of the double-Regge behavior and a better assessment of this component of the amplitude.

M. Shi; I. V. Danilkin; C. Fernández-Ramírez; V. Mathieu; M. R. Pennington; D. Schott; A. P. Szczepaniak

2014-11-23

54

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

55

Intermediates in the Guanine Nucleotide Exchange Reaction of Rab8 Protein Catalyzed by Guanine Nucleotide Exchange Factors Rabin8 and GRAB*  

PubMed Central

Small G-proteins of the Ras superfamily control the temporal and spatial coordination of intracellular signaling networks by acting as molecular on/off switches. Guanine nucleotide exchange factors (GEFs) regulate the activation of these G-proteins through catalytic replacement of GDP by GTP. During nucleotide exchange, three distinct substrate·enzyme complexes occur: a ternary complex with GDP at the start of the reaction (G-protein·GEF·GDP), an intermediary nucleotide-free binary complex (G-protein·GEF), and a ternary GTP complex after productive G-protein activation (G-protein·GEF·GTP). Here, we show structural snapshots of the full nucleotide exchange reaction sequence together with the G-protein substrates and products using Rabin8/GRAB (GEF) and Rab8 (G-protein) as a model system. Together with a thorough enzymatic characterization, our data provide a detailed view into the mechanism of Rabin8/GRAB-mediated nucleotide exchange. PMID:24072714

Guo, Zhong; Hou, Xiaomin; Goody, Roger S.; Itzen, Aymelt

2013-01-01

56

Influence of evaporation and exchange reactions at the surface on the evolution of an arbitrary tracer distribution by diffusion  

E-print Network

11 Influence of evaporation and exchange reactions at the surface on the evolution of an arbitrary-dimensional diffusion with evaporation of the sample and exchange of the diffusant with the ambient at the surface has-vs-depth) to a theoretical one which takes into account different mechanisms occurring during the annealing. Evapor- ation

Paris-Sud XI, Université de

57

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

SciTech Connect

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

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

1989-02-09

58

Interfacial energy exchange and reaction dynamics in collisions of gases on model organic surfaces  

NASA Astrophysics Data System (ADS)

Molecular beam scattering experiments and molecular dynamics simulations have been combined to develop an atomic-level understanding of energy transfer, accommodation, and reactions during collisions between gases and model organic surfaces. The work highlighted in this progress report has been motivated by the scientific importance of understanding fundamental interfacial chemical reactions and the relevance of reactions on organic surfaces to many areas of environmental chemistry. The experimental investigations have been accomplished by molecular beam scattering from ?-functionalized self-assembled monolayers (SAMs) on gold. Molecular beams provide a source of reactant molecules with precisely characterized collision energy and flux; SAMs afford control over the order, structure, and chemical nature of the surface. The details of molecular motion that affect energy exchange and scattering have been elucidated through classical-trajectory simulations of the experimental data using potential energy surfaces derived from ab initio calculations. Our investigations began by employing rare-gas scattering to explore how alkanethiol chain length and packing density, terminal group relative mass, orientation, and chemical functionality influence energy transfer and accommodation at organic surfaces. Subsequent studies of small molecule scattering dynamics provided insight into the influence of internal energy, molecular orientation, and gas-surface attractive forces in interfacial energy exchange. Building on the understanding of scattering dynamics in non-reactive systems, our work has recently explored the reaction probabilities and mechanisms for O3 and atomic fluorine in collisions with a variety of functionalized SAM surfaces. Together, this body of work has helped construct a more comprehensive understanding of reaction dynamics at organic surfaces.

Lu, Jessica W.; Day, B. Scott; Fiegland, Larry R.; Davis, Erin Durke; Alexander, William A.; Troya, Diego; Morris, John R.

2012-09-01

59

Low energy of activation for amide hydrogen exchange reactions in proteins supports a local unfolding model.  

PubMed

Hydrogen exchange reactions of amides in hen egg white lysozyme that are pH dependent and have a low energy of activation have been shown to be in accordance with a reaction mechanism in two steps, an equilibrium step and an exchange step. These results are not in agreement with the model, proposed by C.K. Woodward & B.D. Hilton, known as the penetration model. Therefore our results suggest that this model should be revised. The amide hydrogen/deuterium exchange rates in hen egg white lysozyme were measured at 4 degrees C, 10 degrees C, 15 degrees C and 25 degrees C at pH 7.0 by 1H nuclear magnetic resonance spectroscopy. Activation energies of the exchange reactions in the range from 20 kJ mol-1 to 333 kJ mol-1 were obtained for 32 of the 129 residues in the protein. The amides of lysozyme studied here could be divided into two groups, one group of amides are characterized by an observed amide exchange rate (ko) in the range 10(-4) to 10(-6) s-1, an equilibrium constant k1/k2 close to 10(-5), a low energy of activation (20 to 50 kJ mol-1) and a distance less than 6 A from solvent. The other group of amides are characterized by a ko less than 10(-6) s-1, a k1/k2 close to 10(-7), higher energies of activation (40 to 330 kJ mol-1) and a distance more than 4 A from solvent. In terms of structure the amides of the last group are from the core of the protein. They are typically involved in a hydrogen bond and form part of the secondary structure either as interior alpha-helices or central strands of beta-sheets. The first group consists of amides that are in the shell of the protein between the core and the surface. These amides are typically hydrogen bonded and involved in secondary structure such as external alpha-helices or outer strands of beta-sheets and turns. PMID:8230202

Thomsen, N K; Poulsen, F M

1993-11-01

60

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

Microsoft Academic Search

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

Michael J. O'Leary; Richard O. Sack

1987-01-01

61

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

Microsoft Academic Search

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

Michael J. O'Leary; Richard O. Sack

1987-01-01

62

Mineral carbonation of gaseous carbon dioxide using a clay-hosted cation exchange reaction.  

PubMed

The mineral carbonation method is still a challenge in practical application owing to: (1) slow reaction kinetics, (2) high reaction temperature, and (3) continuous mineral consumption. These constraints stem from the mode of supplying alkaline earth metals through mineral acidification and dissolution. Here, we attempt to mineralize gaseous carbon dioxide into calcium carbonate, using a cation exchange reaction of vermiculite (a species of expandable clay minerals). The mineralization is operated by draining NaCI solution through vermiculite powders and continuously dropping into the pool of NaOH solution with CO2 gas injected. The mineralization temperature is regulated here at 293 and 333 K for 15 min. As a result of characterization, using an X-ray powder diffractometer and a scanning electron microscopy, two types of pure CaCO3 polymorphs (vaterite and calcite) are identified as main reaction products. Their abundance and morphology are heavily dependent on the mineralization temperature. Noticeably, spindle-shaped vaterite, which is quite different from a typical vaterite morphology (polycrystalline spherulite), forms predominantly at 333 K (approximately 98 wt%). PMID:24617079

Kang, Il-Mo; Roh, Ki-Min

2013-01-01

63

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

SciTech Connect

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

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

2009-07-06

64

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 µ-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

65

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

PubMed

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

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

2007-01-01

66

The neutron-proton charge-exchange amplitudes measured in the dp ? ppn reaction  

NASA Astrophysics Data System (ADS)

The unpolarised differential cross section and the two deuteron tensor analysing powers A xx and A yy of the ?c dp to \\{ pp\\} _s n charge-exchange reaction have been measured with the ANKE spectrometer at the COSY storage ring. Using deuteron beams with energies 1.2, 1.6, 1.8, and 2.27GeV, data were obtained for small momentum transfers to a { pp} s system with low excitation energy. The results at the three lower energies are consistent with impulse approximation predictions based upon the current knowledge of the neutron-proton amplitudes. However, at 2.27GeV, where these amplitudes are far more uncertain, agreement requires a reduction in the overall double-spin-flip contribution, with an especially significant effect in the longitudinal direction. These conclusions are supported by measurements of the deuteron-proton spin-correlation parameters C x,x and C y,y that were carried out in the ?c d?c p to \\{ pp\\} _s n reaction at 1.2 and 2.27GeV. The values obtained for the proton analysing power A {/y p } also suggest the need for a radical re-evaluation of the neutron-proton elastic scattering amplitudes at the higher energy. It is therefore clear that such measurements can provide a valuable addition to the neutron-proton database in the charge-exchange region.

Mchedlishvili, D.; Barsov, S.; Carbonell, J.; Chiladze, D.; Dymov, S.; Dzyuba, A.; Engels, R.; Gebel, R.; Glagolev, V.; Grigoryev, K.; Goslawski, P.; Hartmann, M.; Kacharava, A.; Kamerdzhiev, V.; Keshelashvili, I.; Khoukaz, A.; Komarov, V.; Kulessa, P.; Kulikov, A.; Lehrach, A.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Maier, R.; Merzliakov, S.; Mielke, M.; Mikirtychyants, M.; Mikirtychyants, S.; Nioradze, M.; Ohm, H.; Papenbrock, M.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Seyfarth, H.; Stein, H. J.; Steffens, E.; Stockhorst, H.; Ströher, H.; Tabidze, M.; Trusov, S.; Uzikov, Yu.; Valdau, Yu.; Wilkin, C.

2013-04-01

67

Catalytic activity of anion-exchange resins modified with metal-porphine in oxidative reactions of phenols.  

PubMed

Anion-exchange resins modified with metal-porphine (M-Pr) have been investigated to develop a solid catalyst in the oxidative reaction of phenols by O2 in air. Co-Pr, which is easily prepared and separable from the reaction mixture, has been proved to accelerate the oxidative reaction of phenols such as 3,5-di-tertbutyl-4-hydroxyanisole. The resulting main oxidative products were identified to be quinones by using the GC-MS method. PMID:11086930

Iwado, A; Mifune, M; Kato, J; Oda, J; Chikuma, M; Motohashi, N; Saito, Y

2000-11-01

68

Green condensation reaction of aromatic aldehydes with active methylene compounds catalyzed by anion-exchange resin under ultrasound irradiation.  

PubMed

To realize a practical and green chemistry, two important challenges need to be addressed, namely the effective process for the activation of reaction and efficient, eco-friendly and robust chemical methods for the reaction conversion to target products via highly selective catalytic and reactions. Ultrasonic energy promotes the conversion process through its special cavitational effects. Combined with anion-exchange resin as a heterogeneous, reusable and efficient catalyst, Ultrasonic energy enhances the Knoevenagel condensation and leads to reduced reaction time at lower reaction temperature with less amounts of solvent and catalyst. PMID:25112685

Ammar, Hafedh Belhadj; Chtourou, Manef; Frikha, Mohamed Hédi; Trabelsi, Mahmoud

2015-01-01

69

Hydrogen exchange in some coal-related reactions at 400/sup 0/C  

SciTech Connect

Data are available for kinetics of the transfer of hydrogen from tetralin and other hydrogen-rich solvents, but not much is known about the detailed mechanism involving individual linkages or groups in coal. In order to obtain some of this information, we have chosen to work with the pure compounds, 1,2-diphenylethane (bibenzyl), and diphenylmethane as models for certain linkages in coal. Because the thermolysis of the compound gives some different products when heated alone or when heated in the presence of a good hydrogen donor, such as tetralin, it was of interest to know where the cleavage fragments derive their hydrogen to give the final product. While the source of hydrogen needed to cap off the thermolysis fragments is obvious when bibenzyl is heated alone, its origin is ambiguous when tetralin is present. In order to resolve this aspect of the reaction, we prepared bibenzyl completely deuterated (99.8%) in the dimethylene linkage, and pyrolyzed it in the presence of ordinary tetralin. The products were isolated and their hydrogen and deuterium content were determined. From the data we conclude that the benzyl radical, formed by cleavage of bibenzyl, gives toluene by abstracting hydrogen from tetralin. The product after 1 percent conversion was PhCD/sub 2/H. Further, it was observed that, upon heating the mixture for eight hours, deuterium appeared in all the compounds. A considerable amount of deuterium exchange had taken place. In fact, in this mixture, tetralin-bibenzyl-d/sub 4/ at 400/sup 0/C, deuterium is lost from bibenzyl by exchange 3 to 4 times faster than it undergoes carbon-carbon bond scission. Thus, the chemistry of bibenzyl at 400/sup 0/ is dominated by hydrogen exchange reactions.

Benjamin, B.M.; Michalczyk, M.J.; Woody, M.C.

1980-01-01

70

Ligand exchange reactions and hydroamination with tris(oxazolinyl)borato yttrium compounds.  

PubMed

Ligand substitution reactions and catalytic hydroamination/cyclization of aminoalkenes have been studied with a new oxazolinylborato yttrium compound, tris(4,4-dimethyl-2-oxazolinyl)phenylborato bis(trimethylsilylmethyl)yttrium ([Y(kappa(3)-To(M))(CH(2)SiMe(3))(2)(THF)], 1). THF exchange in 1 is rapid at room temperature, and activation parameters obtained by simulation of (1)H NMR spectra acquired from 190 to 280 K are consistent with a dissociative mechanism (DeltaS(++) = 30 +/- 1 e.u., DeltaG(++) = 11.9 kcal mol(-1) at 243 K). The related phosphine oxide adduct [Y(kappa(3)-To(M))(CH(2)SiMe(3))(2)(OPPh(3))] (2) also undergoes exchange via OPPh(3) dissociation with a much higher barrier (DeltaG(++) = 15.0 kcal mol(-1) at 320 K). Compound 1 reacts with the amines (t)BuNH(2), para-MeC(6)H(4)NH(2), and 2,6-(i)Pr(2)C(6)H(3)NH(2) to provide six-coordinate [Y(kappa(3)-To(M))(NHR)(2)(THF)] (3: R = (t)Bu; 4: R = para-MeC(6)H(4)) and five-coordinate [Y(kappa(3)-To(M))(NH-2,6-(i)Pr(2)C(6)H(3))(2)] (6). These oxazolinylborato yttrium compounds are precatalysts for the cyclization of aminoalkenes; the kinetics of catalytic conversion indicate zero-order substrate dependence and first-order catalyst dependence. Kinetic investigations of ligand exchange processes and hydroamination reactions indicate that the tris(oxazolinyl)borato-yttrium interaction is robust even in the presence of excess phosphine oxide and primary and secondary amines. PMID:19586044

Pawlikowski, Andrew V; Ellern, Arkady; Sadow, Aaron D

2009-08-17

71

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

NASA Astrophysics Data System (ADS)

Microprobe and fluid inclusion analyses of hydrothermal ore deposits containing the subassemblage sphalerite+ tetrahedrite-tennantite ˜[(Cu, Ag)10(Fe, Zn)2(As,Sb)4S13] reveal that the Gibbs energies of the reciprocal reaction Cu10Zn2Sb4S13 + Cu10Fe2As4S13 = Cu10Fe2Sb4S13 + Cu10Zn2As4S13 and the Fe-Zn exchange reaction 1/2Cu10Fe2Sb4S13 + ZnS = 1/2Cu10Zn2Sb4S13 + FeS are within the uncertainties of the values established by Sack and Loucks (1985) and Raabe and Sack (1984), 2.59±0.14 and 2.07±0.07 kcal/gfw. However, this study suggests that the Fe-Zn exchange reaction between sphalerite and Sb and Ag-rich tetrahedrites does not obey the simple systematics suggested by Sack and Loucks (1985) wherein tetrahedrite is assumed to behave as an “ideal” reciprocal solution. Instead these studies show that the configurational Gibbs energy of this exchange reaction, RTln[( X Fe/ X Zn)TET( X ZnS/ X FeS)SPH], corrected for sphalerite nonideality exhibits both a local maximum and minimum as a function of Ag/(Cu+Ag) ratio at a given X {FeS/SPH}and temperature. The local maximum for X {FeS/SPH}˜0.10 corresponds to the position of the cell edge maximum established for natural tetrahedrites by Riley (1974), Ag/(Ag+Cu)˜0.4. These studies and the results of structural refinements of Ag-bearing tetrahedrites suggest that in low silver tetrahedrites Ag is preferentially incorporated in trigonal-planar sites but that in tetrahedrites with intermediate and greater Ag/(Ag+Cu) ratio, Ag is preferentially incorporated in tetrahedral sites. A nonconvergent site ordering model for tetrahedrite is developed to quantify and extrapolate these predictions.

O'Leary, Michael J.; Sack, Richard O.

1987-12-01

72

EXCHANGE  

SciTech Connect

EXCHANGE is published monthly by the Idaho National Engineering Laboratory (INEL), a multidisciplinary facility operated for the US Department of Energy (DOE). The purpose of EXCHANGE is to inform computer users about about recent changes and innovations in both the mainframe and personal computer environments and how these changes can affect work being performed at DOE facilities.

Boltz, J.C. (ed.)

1992-09-01

73

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=5.5×10-20 cm3/(s molecules), ks'=4.5×10-22 cm3/(s molecules), and ?=0.078.

Kuga, Yoshikazu; Takeuchi, Kazuo

1998-03-01

74

Proton and light ion induced charge exchange reactions in nuclei This article has been downloaded from IOPscience. Please scroll down to see the full text article.  

E-print Network

Proton and light ion induced charge exchange reactions in nuclei This article has been downloaded Scripta. Vol. 48, 101-104, 1993 Proton and Light Ion Induced Charge Exchange Reactions in Nuclei E. Oset) reaction on the neutron target is different to the one with the proton target and has its strength shifted

Fernández de Córdoba, Pedro

75

Rare events via multiple reaction channels sampled by path replica exchange.  

PubMed

Transition path sampling (TPS) was developed for studying activated processes in complex systems with unknown reaction coordinate. Transition interface sampling (TIS) allows efficient evaluation of the rate constants. However, when the transition can occur via more than one reaction channel separated by a high barrier, TPS and TIS are ineffective in sampling both channels. The combination of replica exchange with TIS can overcome this problem. This work shows how, by including both the backward and forward reactions, the corresponding rate constants, as well as the free energy barrier can be computed in a single simulation. The method is illustrated on a two dimensional potential using the Langevin dynamics. In addition, a simpler algorithm based on only forward shooting from the interfaces is shown to give equally accurate results, and forms a bridge between the transition interface and the forward flux sampling methods. The diffusive behavior of the replicas can be used to assess the quality of the choice of the order parameter used for the interfaces. PMID:19044951

Bolhuis, Peter G

2008-09-21

76

Rare events via multiple reaction channels sampled by path replica exchange  

NASA Astrophysics Data System (ADS)

Transition path sampling (TPS) was developed for studying activated processes in complex systems with unknown reaction coordinate. Transition interface sampling (TIS) allows efficient evaluation of the rate constants. However, when the transition can occur via more than one reaction channel separated by a high barrier, TPS and TIS are ineffective in sampling both channels. The combination of replica exchange with TIS can overcome this problem. This work shows how, by including both the backward and forward reactions, the corresponding rate constants, as well as the free energy barrier can be computed in a single simulation. The method is illustrated on a two dimensional potential using the Langevin dynamics. In addition, a simpler algorithm based on only forward shooting from the interfaces is shown to give equally accurate results, and forms a bridge between the transition interface and the forward flux sampling methods. The diffusive behavior of the replicas can be used to assess the quality of the choice of the order parameter used for the interfaces.

Bolhuis, Peter G.

2008-09-01

77

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.

2014-01-01

78

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

79

Ion-molecule reaction chemistry of ionic transition-metal carbonyl clusters fragments. 1. Ligand-exchange reactions of Cr sub 2 (CO) sub y sup + ions  

SciTech Connect

The ligand-exchange ion-molecule reaction chemistry of Cr{sub 2}(CO){sub y}{sup +} ionic transition metal cluster fragments has been investigated by using a two-section ion cell Fourier transform ion cyclotron resonance mass spectrometer. Simple ligand-exchange reactions involving ligand (L) addition followed by metal-ligand (M---CO) bond cleavage (i.e., an associative ligand-exchange mechanism) as well as ligand exchange involving metal-metal cleavage (i.e. addition of L to Cr{sub 2}(CO){sub y}{sup +} followed by metal-metal bond cleavage) are observed. The branching ratios for reactions involving metal-metal bond cleavage increase as the metal-to-ligand ratio decreases. In addition, the ratio for simple ligand exchange to metal-metal bond cleavage is strongly dependent upon the nature of the reacting ligand (L). These data combined with collision-induced dissociation data for Cr{sub 2}(CO){sub y}{sup +} ionic cluster fragments suggest that the Cr-Cr bond strength decreases as y is increased; i.e., the Cr---Cr bond order is strongly dependent upon the ligand environment.

Sellers-Hahn, L.; Russell, D.H. (Texas A and M Univ., College Station (USA))

1990-08-01

80

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

81

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

PubMed

Reactions involving minerals and glasses in water are slow and difficult to probe spectroscopically but are fundamental to the performance of oxide materials in green technologies such as automotive thermoelectric power generation, CO2 capture and storage and water-oxidation catalysis; these must be made from geochemically common elements and operate in hydrous environments. Polyoxometalate ions (POMs) have structures similar to condensed oxide phases and can be used as molecular models of the oxide/water interface. Oxygen atoms in POM exchange isotopes at different rates, but, at present, there is no basis for predicting how the coordination environment and metal substitution influences rates and mechanisms. Here we identify low-energy metastable configurations that form from the breaking of weak bonds between metals and underlying highly coordinated oxygen atoms, followed by facile hydroxide, hydronium or water addition. The mediation of oxygen exchange by these stuffed structures suggests a new view of the relationship between structure and reactivity at the oxide/solution interface. PMID:22231599

Rustad, James R; Casey, William H

2012-03-01

82

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

NASA Astrophysics Data System (ADS)

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

Rustad, James R.; Casey, William H.

2012-03-01

83

The effects of phosphorous ligands on the gas phase ligand exchange reactions of dichromium ionic cluster fragments  

E-print Network

between Cr, (CO), ' and PEt, . 21 8. Temporal plot of the ligand exchange products of the ion-molecule reaction between Cr, (CO), ' and PEt, . 22 9. Temporal plot of the ligand exchange products of the ion-molecule reaction between Cr, (CO), ' and P...L, + L. For example, Musco and co-workers' " studied the equilibria PdL, =PdL, + L PdL, + L and found that the extent of L dissociation is dominated by steric effects, increasing in the order PMe, ? PMe, Ph ? PMePh, & PEt, ? PBu, ? PPh, & PBz3 & P...

Nguyen, Hanh Duc

2012-06-07

84

Bidirectional exchange of biogenic volatiles with vegetation: emission sources, reactions, breakdown and deposition  

PubMed Central

Biogenic volatile organic compound (BVOC) emissions are widely modeled as inputs to atmospheric chemistry simulations. However, BVOC may interact with cellular structures and neighboring leaves in a complex manner during volatile diffusion from the sites of release to leaf boundary layer and during turbulent transport to the atmospheric boundary layer. Furthermore, recent observations demonstrate that the BVOC emissions are bidirectional, and uptake and deposition of BVOC and their oxidation products are the rule rather than the exception. This review summarizes current knowledge of within-leaf reactions of synthesized volatiles with reactive oxygen species (ROS), uptake, deposition and storage of volatiles and their oxidation products as driven by adsorption on leaf surface and solubilization and enzymatic detoxification inside leaves. The available evidence indicates that due to reactions with ROS and enzymatic metabolism, the BVOC gross production rates are much larger than previously thought. The degree to which volatiles react within leaves and can be potentially taken up by vegetation depends on compound reactivity, physicochemical characteristics, as well as their participation in leaf metabolism. We argue that future models should be based on the concept of bidirectional BVOC exchange and consider modification of BVOC sink/source strengths by within-leaf metabolism and storage. PMID:24635661

Niinemets, Ülo; Fares, Silvano; Harley, Peter; Jardine, Kolby J.

2014-01-01

85

Bidirectional exchange of biogenic volatiles with vegetation: emission sources, reactions, breakdown and deposition.  

PubMed

Biogenic volatile organic compound (BVOC) emissions are widely modelled as inputs to atmospheric chemistry simulations. However, BVOC may interact with cellular structures and neighbouring leaves in a complex manner during volatile diffusion from the sites of release to leaf boundary layer and during turbulent transport to the atmospheric boundary layer. Furthermore, recent observations demonstrate that the BVOC emissions are bidirectional, and uptake and deposition of BVOC and their oxidation products are the rule rather than the exception. This review summarizes current knowledge of within-leaf reactions of synthesized volatiles with reactive oxygen species (ROS), uptake, deposition and storage of volatiles, and their oxidation products as driven by adsorption on leaf surface and solubilization and enzymatic detoxification inside leaves. The available evidence indicates that because of the reactions with ROS and enzymatic metabolism, the BVOC gross production rates are much larger than previously thought. The degree to which volatiles react within leaves and can be potentially taken up by vegetation depends upon compound reactivity, physicochemical characteristics, as well as upon their participation in leaf metabolism. We argue that future models should be based upon the concept of bidirectional BVOC exchange and consider modification of BVOC sink/source strengths by within-leaf metabolism and storage. PMID:24635661

Niinemets, Ülo; Fares, Silvano; Harley, Peter; Jardine, Kolby J

2014-08-01

86

Combination of 31P-NMR magnetization transfer and radioisotope exchange methods for assessment of an enzyme reaction mechanism: rate-determining steps of the creatine kinase reaction.  

PubMed

The theoretical analysis of a reversible enzyme reaction performed in this work shows that the 31P-NMR magnetization (saturation) transfer technique combined with a radioisotope exchange method may potentially provide information on the position of rate-determining step(s). It depends on chemical shifts of NMR signals of nuclei of interest in free and enzyme-bound forms of substrate(s) and product(s) of the reaction. The creatine kinase reaction (MgATP + creatine----MgADP + P-creatine) has been used as a model. Chemical shifts of 31P in binary, ternary and transitional state substrate-enzyme complexes have been estimated by the variable frequency saturation transfer (VFST) method. This method is based on selective irradiation of numerous points in the spectrum and observation of changes in the intensity of visible line(s) which occur due to chemical exchange between it and lines which are not visible in the routine spectrum. Also, dissociation rate constants of MgADP-containing complexes were determined. Magnetization exchange rates, P-creatine----[gamma-P]MgATP and [beta-P]MgADP----[beta-P]MgATP, were compared with radioisotope exchange rates, [gamma-32P-MgATP----P-creatine and [3H]MgADP----MgATP at different [P-creatine]/[creatine] ratios and at different temperatures. All these exchange rates were close to each other at 30-37 degrees C and [PCr]/[Cr] ratios lower than 2. It is concluded that phosphoryl group transfer is the rate-determining step of the overall creatine kinase reaction under these conditions. However, at lower temperatures (below 25 degrees C) or at high [PCr]/[Cr] ratios ([ADP] less than 20 microM) the rate-determining step seems to be shifted toward dissociation of nucleotide substrates from enzyme-substrate complexes, since exchange rates became significantly different. This approach is useful for analysis of mechanism of enzymatic reactions and also can be applied to non-enzymatic reactions and evaluation of small rapidly exchangeable metabolite pools. PMID:2248962

Kupriyanov, V V; Balaban, R S; Lyulina, N V; Steinschneider AYa; Saks, V A

1990-12-01

87

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]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)??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 25°C 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 1.5·10?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

88

D/H Exchange Reactions in Salts Extracted from LEW 85320  

NASA Astrophysics Data System (ADS)

Understanding the effects of terrestrial weathering on meteorites has been shown to be critical in distinguishing primary chemical and isotopic features from secondary alterations [1]. To further constrain weathering effects we report here the D/H composition of water thermally extracted from three distinct generations of efflorescence (,98, ,99, and ,102) occurring on the Antarctic H-5 chondrite LEW85320. To better understand the hydrogen isotope exchange systematics of these precipitates, an experiment was performed to characterize the rate of isotope exchange between a synthetic analog to the predominant weathering product, nesquehonite (Mg(HCO3)(OH).2H2O), found on the exterior of LEW85320 [2], and water. Synthetic nesquehonite, produced following the procedure of Ming and Franklin [3], a dehydrated CaSO4 standard, and deuterium-spiked water (deltaD = +701 permil SMOW) were placed together in a closed box and allowed to exchange hydrogen isotopes at constant temperature and humidity (30 degrees +- 2 degrees C and 75% +- 5%). Samples of each solid phase were taken initially and at 1, 3, 20, and 30 days. These samples along with three generations of efflorescence on LEW85320 (,98, ,99, and ,102) were weighed and loaded into separate high-purity, prebaked, 9-mm (O.D) quartz tubes. After degassing for two hours under high vacuum, samples were heated to 625 degrees C for 4 hr while all condensable gases were collected in a trap immersed in liquid nitrogen. CO2 was separated from water by exchanging the LN2 trap with a dry ice/alcohol mixture. All evolved water was frozen into a tube containing Zn turnings, which was then heated to 450 degrees C for 30 min, producing hydrogen gas for isotopic analysis. Results of our exchange experiment show that the CaSO4 standard quickly assumes the deltaD composition of the water (from -29 permil to +581 permil in 30 days). On the other hand, nesquehonite becomes only slightly enriched in deltaD (from -29 permil to +51 permil). Mass balance calculations reveal that absorption of the spiked water is stoichiometric with respect to the formation of CaSO4.2H2O, while within limits of sampling error no net change of weight was observed for the nesquehonite. Assuming that the change in deltaDnesq. is due entirely to exchange (i.e., no absorption), mass balance constraints dictate that less than 5 wt% of water exchanged. These data suggest that nesquehonite retains its original deltaD composition even under conditions of relatively high temperature and humidity. Hydrogen isotope data of water extracted from three generations of nesquehonite on LEW85320 are plotted as a function of the theoretical delta18O composition of water in equilibrium with the carbonate at 0 degrees C (where delta18Onesq. is derived by phosphoric acid digestion of the carbonate, assuming a calcite-CO2 fractionation factor of 1.01012). Our data plot very near the meteoric water line indicating formation from slightly enriched Antarctic meltwater. Water extracted from generations II (,99), salts consisting mostly of hydromagnesite (Mg5(CO3)4(OH)2.4H2O) (Gooding, 1993, personal communication), and III (,102), with mineralogy as yet unknown, is enriched in D (deltaD = -55 and -75 permil, respectively) and plot above the meteoric water line. Both generations precipitated in the Houston curatorial facility. Data suggest either that hydrogen isotopes have exchanged at least partially with local (i.e., Houston) water, or that the exchange reactions differ between structural sites within or among the various generations of efflorescent salts. Hydrogen isotopes extracted from hydrous weathering products can reveal information about the environment of crystal growth. However, hydrogen isotope exchange systematics could be complicated if water within the crystal structure of the mineral is located in multiple sites. Furthermore, these results could have profound implications for curation and long-term storage strategies in curatorial facilities. References: [1] Socki R. A. et al., (1991) Meteoritics, 26, 396-397. [2] Gooding J. L. e

Socki, R. A.; Romanek, C. S.; Gibson, E. K., Jr.

1993-07-01

89

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

90

13C NMR Characterization of an Exchange Reaction between CO and CO2 Catalyzed by Carbon Monoxide Dehydrogenase†  

PubMed Central

Carbon monoxide dehydrogenase (CODH) catalyzes the reversible oxidation of CO to CO2 at a nickel?iron?sulfur cluster (the C-cluster). CO oxidation follows a ping-pong mechanism involving two-electron reduction of the C-cluster followed by electron transfer through an internal electron transfer chain to external electron acceptors. We describe 13C NMR studies demonstrating a CODH-catalyzed steady-state exchange reaction between CO and CO2 in the absence of external electron acceptors. This reaction is characterized by a CODH-dependent broadening of the 13CO NMR resonance; however, the chemical shift of the 13CO resonance is unchanged, indicating that the broadening is in the slow exchange limit of the NMR experiment. The 13CO line broadening occurs with a rate constant (1080 s?1 at 20 °C) that is approximately equal to that of CO oxidation. It is concluded that the observed exchange reaction is between 13CO and CODH-bound 13CO2 because 13CO line broadening is pH-independent (unlike steady-state CO oxidation), because it requires a functional C-cluster (but not a functional B-cluster) and because the 13CO2 line width does not broaden. Furthermore, a steady-state isotopic exchange reaction between 12CO and 13CO2 in solution was shown to occur at the same rate as that of CO2 reduction, which is approximately 750-fold slower than the rate of 13CO exchange broadening. The interaction between CODH and the inhibitor cyanide (CN?) was also probed by 13C NMR. A functional C-cluster is not required for 13CN? broadening (unlike for 13CO), and its exchange rate constant is 30-fold faster than that for 13CO. The combined results indicate that the 13CO exchange includes migration of CO to the C-cluster, and CO oxidation to CO2, but not release of CO2 or protons into the solvent. They also provide strong evidence of a CO2 binding site and of an internal proton transfer network in CODH. 13CN? exchange appears to monitor only movement of CN? between solution and its binding to and release from CODH. PMID:18589895

2008-01-01

91

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

SciTech Connect

With consideration of magnetic field line curvature (FLC) pitch angle scattering and charge exchange reactions, the O{sup +} (>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{sup +} 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{sup +} 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., E-mail: yji@spaceweather.ac.cn [State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China); College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049 (China); Shen, C. [State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China)] [State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China)

2014-03-15

92

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

NASA Astrophysics Data System (ADS)

The nitrate containing layered double hydroxide (LDH) of Ca with Al on reaction with aqueous solutions of Na 2CO 3 and Na 3PO 4 yields CaCO 3 and Ca 5(PO 4) 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 double hydroxides take place by the dissolution-reprecipitation mechanism rather than by the topotactic mechanism.

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

2005-10-01

93

Modeling of surface exchange reactions and diffusion in composites including transport processes at grain and interphase boundaries  

Microsoft Academic Search

Surface exchange reactions and diffusion of oxygen in ceramic composites consisting of a dilute and random distribution of\\u000a inclusions in a polycrystalline matrix (host phase) are modeled phenomenologically by employing the finite element method.\\u000a The microstructure of the mixed conducting composite is described by means of a square grain model, including grain boundaries\\u000a of the matrix and interphase boundaries between

Wolfgang Preis

94

Polarization effects in the reaction $\\bar p+p\\to e^++e^-$ in presence of two-photon exchange  

E-print Network

Polarization observables for the reaction $\\bar p+p\\to e^++e^-$ are given in terms of three independent complex amplitudes, in presence of two photon exchange. General expressions for the differential cross section and the polarization observables are given and model independent properties are derived. Polarization effects depending on the polarization of the antiproton beam, the target and of the electron in the final state, have been calculated.

G. I. Gakh; E. Tomasi--Gustafsson

2005-04-06

95

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

96

Testing the TPSS meta-generalized-gradient-approximation exchange-correlation functional in calculations of transition states and reaction barriers  

NASA Astrophysics Data System (ADS)

We have studied the performance of local and semilocal exchange-correlation functionals [meta-generalized-gradient-approximation (GGA)-TPSS, GGA-Perdew-Burke-Ernzerhof (PBE), and local density approximation (LDA)] in the calculation of transition states, reaction energies, and barriers for several molecular and one surface reaction, using the plane-wave pseudopotential approach. For molecular reactions, these results have been compared to all-electron Gaussian calculations using the B3LYP hybrid functional, as well as to experiment and high level quantum chemistry calculations, when available. We have found that the transition state structures are accurately identified irrespective of the level of the exchange-correlation functional, with the exception of a qualitatively incorrect LDA prediction for the H-transfer reaction in the hydrogen bonded complex between a water molecule and a OH radical. Both the meta-GGA-TPSS and the GGA-PBE functionals improve significantly the calculated LDA barrier heights. The meta-GGA-TPSS further improves systematically, albeit not always sufficiently, the GGA-PBE barriers. We have also found that, on the Si(001) surface, the meta-GGA-TPSS barriers for hydrogen adsorption agree significantly better than the corresponding GGA-PBE barriers with quantum Monte Carlo cluster results and experimental estimates.

Kanai, Yosuke; Wang, Xiaofei; Selloni, Annabella; Car, Roberto

2006-12-01

97

Stereo-dynamics of the exchange reaction Ha+LiHb?LiHa+Hb and its isotopic variants  

NASA Astrophysics Data System (ADS)

The quasi-classical trajectory (QCT) method is used to calculate the stereo-dynamics of the exchange reaction Ha+LiHb?LiHa+Hb and its isotopic variants based on an accurate potential energy surface reported by Prudente et al. [Prudente F V, Marques J M C and Maniero A M 2009 Chem. Phys. Lett. 474 18]. The reactive probability of the title reaction is computed. The vector correlations and four polarization-dependent generalized differential cross sections (PDDCSs) at different collision energies are presented. The influences of the collision energy and the reagent rotation on the product polarization are studied in the present work. The results indicate that the product rotational angular momentum j' is not only aligned, but also oriented along the direction perpendicular to the scattering plane. The product polarization distributions of the title reaction and its isotopic variants exhibit distinct differences which may arise from different mass combinations.

Zhai, Hong-Sheng; Yin, Shu-Hui

2012-12-01

98

Modulation of the reaction cycle of the Na+:Ca2+, K+ exchanger.  

PubMed

Ca(2+) concentration in retinal photoreceptor rod outer segment (OS) strongly affects the generator potential kinetics and the receptor light adaptation. The response to intense light stimuli delivered in the dark produce potential changes exceeding 40 mV: since the Ca(2+) extrusion in the OS is entirely controlled by the Na(+):Ca(2+), K(+) exchanger, it is important to assess how the exchanger ion transport rate is affected by the voltage and, in general, by intracellular factors. It is indeed known that the cardiac Na(+):Ca(2+) exchanger is regulated by Mg-ATP via a still unknown metabolic pathway. In the present work, the Na(+):Ca(2+), K(+) exchanger regulation was investigated in isolated OS, recorded in whole-cell configuration, using ionic conditions that activated maximally the exchanger in both forward and reverse mode. In all species examined (amphibia: Rana esculenta and Ambystoma mexicanum; reptilia: Gecko gecko), the forward (reverse) exchange current increased about linearly for negative (positive) voltages and exhibited outward (inward) rectification for positive (negative) voltages. Since hyperpolarisation increases Ca(2+) extrusion rate, the recovery of the dark level of Ca(2+) (and, in turn, of the generator potential) after intense light stimuli results accelerated. Mg-ATP increased the size of forward and reverse exchange current by a factor of approximately 2.3 and approximately 2.6, respectively, without modifying their voltage dependence. This indicates that Mg-ATP regulates the number of active exchanger sites and/or the exchanger turnover number, although via an unknown mechanism. PMID:17415556

Vedovato, Natascia; Rispoli, Giorgio

2007-09-01

99

Analysis of ping-pong reaction mechanisms by positional isotope exchange. Application to galactose-1-phosphate uridyltransferase  

SciTech Connect

A new positional isotope exchange method has been developed that can be used for the analysis of enzyme-catalyzed reactions which have ping-pong kinetic mechanisms. The technique can be used to measure the relative rates of ligand dissociation from enzyme-product complexes. Enzyme is incubated with the labeled substrate and an excess of the corresponding unlabeled product. The partitioning of the enzyme-product complex back toward free enzyme is determined from the rate of positional isotope exchange within the original labeled substrate. The partitioning of the enzyme-product complex forward toward free enzyme is determined from the rate of formation of totally unlabeled substrate. It has been shown that the ratio of the two rates provides a lower limit for the release of product from the enzyme-product complex. The technique has been applied to the reaction catalyzed by galactose-1-phosphate uridyltransferase. The lower limit for the release of glucose 1-phosphate from the uridyl-enzyme relative to the maximal velocity of the reverse reaction was determined to be 3.4 +/- 0.5.

Hester, L.S.; Raushel, F.M.

1987-09-05

100

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

SciTech Connect

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

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

1985-07-01

101

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

102

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; Nørskov, Jens K.

2013-12-01

103

Complex-Regge-Pole Model Consistent with the Dual Absorption Picture: Meson-Baryon Charge-Exchange Reactions  

Microsoft Academic Search

The reactions pi-p-->pi0n, pi-p-->etan, K-p-->K¯0n, and K+n-->K0p, where rho and\\/or A2 exchanges are involved, are considered within the complex-pole model with the amplitudes given by gamma+xi+salpha++gamma-xi-salpha-. Our fits confirm the prediction of the dual absorption model in that we find the real part of the residue function, gammaR, to be ~Jn with n=0, 1. For the imaginary part, gammaI, we

N. Barik; Bipin R. Desai

1972-01-01

104

Charge-exchange and fusion reaction measurements during compression experiments with neutral beam heating in the Tokamak Fusion Test Reactor  

SciTech Connect

Adiabatic toroidal compression experiments were performed in conjunction with high power neutral beam injection in the Tokamak Fusion Test Reactor (TFTR). Acceleration of beam ions to energies nearly twice the injection energy was measured with a charge-exchange neutral particle analyzer. Measurements were also made of 2.5 MeV neutrons and 15 MeV protons produced in fusion reactions between the deuterium beam ions and the thermal deuterium and /sup 3/He ions, respectively. When the plasma was compressed, the d(d,n)/sup 3/He fusion reaction rate increased a factor of five, and the /sup 3/He(d,p)/sup 4/He rate by a factor of twenty. These data were simulated with a bounce-averaged Fokker-Planck program, which assumed conservation of angular momentum and magnetic moment during compression. The results indicate that the beam ion acceleration was consistent with adiabatic scaling.

Kaita, R.; Heidbrink, W.W.; Hammett, G.W.; Chan, A.A.; England, A.C.; Hendel, H.W.; Medley, S.S.; Nieschmidt, E.; Roquemore, A.L.; Scott, S.D.

1986-04-01

105

Ion exchange kinetics of cesium for various reaction designs using crystalline silicotitanate, UOP IONSIV IE911  

Microsoft Academic Search

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

Sung Hyun Kim

2003-01-01

106

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

NASA Astrophysics Data System (ADS)

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

Collins, Michael A.; Radom, Leo

2003-04-01

107

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

NASA Astrophysics Data System (ADS)

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

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

2009-10-01

108

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

109

Chemically modified reaction centers of photosystem II: Exchange of pheophytin a with 7-deformyl-7-hydroxymethyl-pheophytin b.  

PubMed

The native pheophytin a (Pheo a) in isolated reaction centers of photosystem II (PSII RCs) has been chemically exchanged with extraneous 7-deformyl-7-hydroxymethyl-Pheo b (7(1)-OH-Pheo b) which differs from Pheo a by the C-7 substituent (hydroxymethyl instead of methyl). The two pigments have similar reduction potentials in vitro [M. Meyer, Dissertation, Universität München, 1997], while their absorption spectra show small but distinct differences in the visible region. The resulting 7(1)-OH-Pheo b-modified reaction center preparations were characterized by high-performance liquid chromatography, electronic absorption and light-induced Fourier transform infra red absorption difference spectroscopies, together with photoaccumulation of the reduced pheophytin electron acceptor and NaBH4-treatment. About 70% of the total Pheo a molecules are found to be replaced by 7(1)-OH-Pheo b molecules in modified preparations, indicating that both the photochemically active (PheoD1) and inactive (PheoD2) binding sites were subjected to pigment exchange. The 7(1)-OH-Pheo b molecule located at the PheoD1 site is able to functionally replace the native Pheo a, participating in primary charge separation as an electron acceptor. The Qx absorption band of this modified pheophytin molecule is localized at ~546nm; its Qy band is blue-shifted with respect to the absorption of other reaction center core pigments, being located at ~665nm. The Qy and Qx optical transitions of the 7(1)-OH-Pheo b molecule exchanged into the PheoD2 site are identified at 677 and 543.5nm, respectively. The photochemically active double-modified PSII RCs additionally containing 7-deformyl-7-hydroxymethyl-13(1)-deoxo-13(1)-hydroxy-Pheo b at the PheoD2 site were obtained by treatment of the 7(1)-OH-Pheo b-modified RCs with NaBH4. PMID:25172518

Zabelin, Alexey A; Shkuropatova, Valentina A; Makhneva, Zoya K; Moskalenko, Andrey A; Shuvalov, Vladimir A; Shkuropatov, Anatoly Ya

2014-11-01

110

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

111

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

112

Review of quasi-elastic charge-exchange data in the nucleon-deuteron breakup reaction  

NASA Astrophysics Data System (ADS)

The available data on the forward charge exchange of nucleons on the deuteron up to 2 GeV/nucleon are reviewed. The value of the inclusive nd ? pnn/ np ? pn cross section ratio is sensitive to the fraction of spin-independent neutron-proton backward scattering. The measurements of the polarisation transfer in d( n, p){ nn} or the deuteron analysing power in p{ d, { pp}) n in high-resolution experiments, where the final nn or pp pair emerge at low excitation energy, depend upon the longitudinal and transverse spin-spin up amplitudes. The relation between these types of experiments is discussed and the results compared with predictions of the impulse approximation model in order to see what new constraints they can bring to the neutron-proton database.

Lehar, F.; Wilkin, C.

2010-07-01

113

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

114

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-Cornière, Axelle; Kuwabara, Naoyuki; Ito, Kentaro; Tsutsui, Yasuhiro; Shimizu, Toshiyuki; Iwasaki, Hiroshi; Nordén, Bengt; Takahashi, Masayuki

2014-02-01

115

Isospin and spin-isospin modes in charge-exchange reactions  

SciTech Connect

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

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

1999-11-16

116

Sulfur(VI) fluoride exchange (SuFEx): another good reaction for click chemistry.  

PubMed

Aryl sulfonyl chlorides (e.g. Ts-Cl) are beloved of organic chemists as the most commonly used S(VI) electrophiles, and the parent sulfuryl chloride, O2 S(VI) Cl2 , has also been relied on to create sulfates and sulfamides. However, the desired halide substitution event is often defeated by destruction of the sulfur electrophile because the S(VI) ?Cl bond is exceedingly sensitive to reductive collapse yielding S(IV) species and Cl(-) . Fortunately, the use of sulfur(VI) fluorides (e.g., R-SO2 -F and SO2 F2 ) leaves only the substitution pathway open. As with most of click chemistry, many essential features of sulfur(VI) fluoride reactivity were discovered long ago in Germany.6a Surprisingly, this extraordinary work faded from view rather abruptly in the mid-20th century. Here we seek to revive it, along with John Hyatt's unnoticed 1979 full paper exposition on CH2 ?CH-SO2 -F, the most perfect Michael acceptor ever found.98 To this history we add several new observations, including that the otherwise very stable gas SO2 F2 has excellent reactivity under the right circumstances. We also show that proton or silicon centers can activate the exchange of S?F bonds for S?O bonds to make functional products, and that the sulfate connector is surprisingly stable toward hydrolysis. Applications of this controllable ligation chemistry to small molecules, polymers, and biomolecules are discussed. PMID:25112519

Dong, Jiajia; Krasnova, Larissa; Finn, M G; Sharpless, K Barry

2014-09-01

117

Active microchannel heat exchanger  

Microsoft Academic Search

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

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

2001-01-01

118

Presolvated electron reactions with methyl acetoacetate: electron localization, proton-deuteron exchange, and H-atom abstraction.  

PubMed

Radiation-produced electrons initiate various reaction processes that are important to radiation damage to biomolecules. In this work, the site of attachment of the prehydrated electrons with methyl acetoacetate (MAA, CH3-CO-CH2-COOCH3) at 77 K and subsequent reactions of the anion radical (CH3-CO•--CH2-COOCH3) in the 77 to ca. 170 K temperature range have been investigated in homogeneous H2O and D2O aqueous glasses by electron spin resonance (ESR) spectroscopy. At 77 K, the prehydrated electron attaches to MAA forming the anion radical in which the electron is delocalized over the two carbonyl groups. This species readily protonates to produce the protonated electron adduct radical CH3-C(•)OH-CH2-COOCH3. The ESR spectrum of CH3-C(•)OH-CH2-COOCH3 in H2O shows line components due to proton hyperfine couplings of the methyl and methylene groups. Whereas, the ESR spectrum of CH3-C(•)OH-CH2-COOCH3 in D2O glass shows only the line components due to proton hyperfine couplings of CH3 group. This is expected since the methylene protons in MAA are readily exchangeable in D2O. On stepwise annealing to higher temperatures (ca. 150 to 170 K), CH3-C(•)OH-CH2-COOCH3 undergoes bimolecular H-atom abstraction from MAA to form the more stable radical, CH3-CO-CH•-COOCH3. Theoretical calculations using density functional theory (DFT) support the radical assignments. PMID:25255751

Petrovici, Alex; Adhikary, Amitava; Kumar, Anil; Sevilla, Michael D

2014-01-01

119

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

120

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 70°C, 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

121

Ion-exchange reactions on clay minerals coupled with advection/dispersion processes. Application to Na+/Ca2+ exchange on vermiculite: Reactive-transport modeling, batch and stirred flow-through reactor experiments  

NASA Astrophysics Data System (ADS)

The present study aims at testing the validity of using an Na+/Ca2+ ion-exchange model, derived from batch data to interpret experimental Ca2+-for-Na+ exchange breakthrough curves obtained on vermiculite (a common swelling clay mineral in surface environments). The ion-exchange model was constructed considering the multi-site nature of the vermiculite surface as well as the exchange of all aqueous species (Mg2+ derived from the dissolution of the solid and H+). The proposed ion-exchange model was then coupled with a transport model, and the predicted breakthrough curves were compared with the experimental ones obtained using a well stirred flow-through reactor. For a given solute residence time in the reactor (typically 50 min), our thermodynamic model based on instantaneous equilibrium was found to accurately reproduce several of the experimental breakthrough curves, depending on the Na+ and Ca2+ concentrations of the influents pumped through the reactor. However the model failed to reproduce experimental breakthrough curves obtained at high flow rates and low chemical gradient between the exchanger phase and the solution. An alternative model based on a hybrid equilibrium/kinetic approach was thus used and allowed predicting experimental data. Based on these results, we show that a simple parameter can be used to differentiate between thermodynamic and kinetic control of the exchange reaction with water flow. The results of this study are relevant for natural systems where two aquatic environments having contrasted chemistries interact. Indeed, the question regarding the attainment of a full equilibrium in such a system during the contact time of the aqueous phase with the particle/colloid remains most often open. In this context, we show that when a river (a flow of fresh water) encounters marine colloids, a systematic full equilibrium can be assumed (i.e., the absence of kinetic effects) when the residence time of the solute in 1 m3 of the system is ?6200 h.

Tertre, E.; Hubert, F.; Bruzac, S.; Pacreau, M.; Ferrage, E.; Prêt, D.

2013-07-01

122

Characterization of the dynamic oxygen migration over Pt\\/CeO 2-ZrO 2 catalysts by 18 O\\/ 16 O isotopic exchange reaction  

Microsoft Academic Search

To characterize the oxygen mobility over metal supported catalysts on a dynamic and in situ base, 18O\\/16O isotopic exchange reaction combined with CO oxidation was designed and exemplified on three kinds of three way catalysts of Pt\\/CeO2-ZrO2 (CZ-O, CZ-D and CZ-R). The obtained oxygen diffusion coefficients, oxygen release rate, and oxygen storage capacity were discussed and correlated with XRD spectra

F Dong; A Suda; T Tanabe; Y Nagai; H Sobukawa; H Shinjoh; M Sugiura; C Descorme; D Duprez

2004-01-01

123

218 Inorg. Chem. 1993, 32, 218-222 Synthesis, X-ray CrystalStructure, and Phosphine-Exchange Reactions of the  

E-print Network

-Exchange Reactions of the Hafnium(III)-Hafnium(II1)Dimer HfiCb(PEt& Matthew E.Riehl, Scott R. Wilson, and Gregory S of PEt3 yields the dark green hafnium(II1)- hafnium(II1) dimer HfiC&(PEt,)d. The X-ray crystal structure shows that moleculesof Hf2C&(PEt3)4consistof two octahedral hafnium centers that are connected

Girolami, Gregory S.

124

/sup 1/H NMR study of the base-pairing reactions of d(GGAATTCC): salt and polyamine effects on the imino proton exchange  

SciTech Connect

Salts and polyamines have a variety of effects on the physical properties of DNA, including stabilization against thermal melting. The authors wished to gain greater insight into the mechanism of this stabilization by ascertaining its effect on the dynamics of base opening and closing reactions, as measured by NMR. Since the binding of spermidine (3+) is influenced by salt, and since spermidine may act as a base catalyst in proton exchange reactions, they have undertaken a study of salt and base catalyst effects on the imino proton exchange kinetics of a model oligomeric DNA. The selective longitudinal NMR relaxation rates of the hydrogen-bonded imino protons of the self-complementary octadeoxyribonucleotide d(GGAATTCC) monitor the rate of the base-catalyzed chemical exchange of these protons with solvent water. The exchange rates thus obtained provide a sensitive measure of the base-pair opening reactions of the DNA duplex. Under conditions of low pH and no added base catalyst, the NMR relaxation rates allow the determination of k/sub d/, the rate constant for the dissociation of the octameric duplex into single strands. Titration with the base catalyst tris(hydroxymethyl) aminomethane allows the determination of k/sub op/, the rate constant for the localized opening of individual base pairs, prior to dissociation. The activation energy for helix dissociation is not dependent on the sodium ion concentration. In agreement with previous results, no measurable salt dependence is found for k/sub op/. Under low-salt conditions, the trivalent cation spermidine decreases the rate of helix dissociation, again without affecting the activation energy for this process.

Braunlin, W.H.; Bloomfield, V.A.

1988-02-23

125

Mechanistic information from volume profiles for water exchange and complex-formation reactions of aquated Ni(II). pH, buffer and medium effects.  

PubMed

Rate and activation parameters for the complex-formation reaction of Ni(2+) with 4-(2-pyridylazo)-N,N-dimethyl aniline (PADA) were studied as a function of pH in different buffers in both aqueous and sodium dodecyl sulfate (SDS) micelle solutions. In aqueous Tris buffer solution, the forward and backward rate constants increased with increasing pH, while the complex-formation constant decreased due to a larger increase in the backward rate constant. The activation entropy, DeltaS(#), and activation volume, DeltaV(#), changed with increasing pH from positive to negative values, suggesting an apparent changeover from a dissociative to a more associative mechanism. Complex-formation reactions with 2,2'-bipyridine in Tris buffer showed almost no increase in the forward and backward rate constants on increasing the pH, but the DeltaS(#) and DeltaV(#) values became more negative. N-ethylmorpholine buffer showed no pH effect on the rate constants and activation parameters. Water exchange reactions of aquated Ni(2+) were also studied as a function of pH under the same conditions. The reported rate and activation parameters for water exchange in Tris and N-ethylmorpholine buffers are consistent with those found for the complex-formation reactions of Ni(2+) with PADA. The observed pH and buffer effects for both the complex-formation and water exchange reactions of aquated Ni(2+) can be accounted for in terms of the formation of a Ni(2+)-Tris complex in Tris buffer and general base catalysis by the buffer components. In SDS micelle solution, the complex-formation reaction with PADA was much faster than in aqueous solution, but the increase in rate constant with increasing pH was less significant, while DeltaS(#) and DeltaV(#) became more positive, pointing to a more dissociative mechanism. For SDS micelle solutions there was no effect on the water exchange rate constant or activation volume. Mechanistic interpretations are offered for all observed pH, buffer and medium effects. PMID:19859604

Gazzaz, Hanaa Asaad; Ember, Erika; Zahl, Achim; van Eldik, Rudi

2009-11-21

126

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.

127

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

128

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

SciTech Connect

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

Clark, J.L.

1980-01-01

129

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

130

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

PubMed

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

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

2003-10-31

131

Calcite dissolution and Ca/Na ion-exchange reactions in columns with different flow rates through high ESR soil  

E-print Network

The leaching of a Na?-affected calcareous soil with water results in two concurrent recesses: (i) CaCO? dissolution, and (ii) replacement of Na? on the cation-exchange complex by Ca²?. In the current study, Woodward soil (coarse-silty, mixed...

Navarre, Audrey

2012-06-07

132

Determination of labile Fe(II) species complexed with seawater extractable organic matter under seawater conditions based on the kinetics of ligand-exchange reactions with ferrozine.  

PubMed

A fertilizer, comprised of a mixture of steel slag and compost, was used to restore seaweed beds in barren coastal areas. Complex Fe(II) species, supplied by steel slag, play a significant role in supplying Fe(II) to coastal areas and stimulating seaweed growth. Seawater extractable organic matter (SWEOM) from compost is generally assumed to serve as a chelator of Fe(II) in the fertilizer. It is considered that the bioavailability of Fe(II)-SWEOM complexes is higher in the dissociable (labile) species. In the present study, a method for determining labile species of Fe(II)-SWEOM complexes in seawater (pH 8.0, I = 0.7) was developed. The method is based on a ligand-exchange reaction between SWEOM and ferrozine (FZ). Because Fe(II) is readily oxidized to Fe(III) under normal seawater conditions, ascorbic acid was added as an antioxidant. The coloring for the Fe-FZ complex in the presence of SWEOM was retarded. This retarding can be attributed to a ligand-exchange reaction between FZ and labile Fe(II)-SWEOM complexes. Conditional binding constants for the labile Fe(II)-SWEOM complexes and binding capacities of labile sites in SWEOM to Fe(II) were evaluated for a variety of total Fe(II) concentrations. PMID:23842415

Iwai, Hisanori; Fukushima, Masami; Yamamoto, Mitsuo

2013-01-01

133

Study of the $\\vec{p}d \\to n\\{pp\\}_{s}$ charge-exchange reaction using a polarised deuterium target  

E-print Network

The vector and tensor analysing powers, $A_y$ and $A_{yy}$, of the $\\vec{p}d \\to n\\{pp\\}_{s}$ charge-exchange reaction have been measured at a beam energy of 600 MeV at the COSY-ANKE facility by using an unpolarised proton beam incident on an internal storage cell target filled with polarised deuterium gas. The low energy recoiling protons were measured in a pair of silicon tracking telescopes placed on either side of the target. Putting a cut of 3 MeV on the diproton excitation energy ensured that the two protons were dominantly in the $^{1}S_{0}$ state, here denoted by $\\{pp\\}_{s}$. The polarisation of the deuterium gas was established through measurements in parallel of proton-deuteron elastic scattering. By analysing events where both protons entered the same telescope, the charge-exchange reaction was measured for momentum transfers $q\\geq 160$ MeV/$c$. These data provide a good continuation of the earlier results at $q\\leq 140$ MeV/$c$ obtained with a polarised deuteron beam. They are also consistent with impulse approximation predictions with little sign evident for any modifications due to multiple scatterings.

B. Gou; D. Mchedlishvili; Z. Bagdasarian; S. Barsov; D. Chiladze; S. Dymov; R. Engels; M. Gaisser; R. Gebel; K. Grigoryev; M. Hartmann; A. Kacharava; A. Khoukaz; P. Kulessa; A. Kulikov; A. Lehrach; Z. Li; N. Lomidze; B. Lorentz; G. Macharashvili; S. Merzliakov; M. Mielke; M. Mikirtychyants; S. Mikirtychyants; M. Nioradze; H. Ohm; D. Prasuhn; F. Rathmann; V. Serdyuk; H. Seyfarth; V. Shmakova; H. Ströher; M. Tabidze; S. Trusov; D. Tsirkov; Yu. Uzikov; Yu. Valdau; T. Wang; C. Weidemann; C. Wilkin; X. Yuan

2014-08-08

134

Fully converged integral cross sections of collision induced dissociation, four-center, and single exchange reactions, and accuracy of the centrifugal sudden approximation in H2 + D2 reaction.  

PubMed

The initial state selected time-dependent wave packet method was employed to calculate the integral cross sections for the H(2) + D(2) reaction with and without the centrifugal sudden (CS) approximation by including all important K (the projection of the total angular momentum on the body-fixed axis) blocks. With a full-dimensional model, the first fully converged coupled-channel (CC) cross sections for different competitive processes from the ground rotational state were obtained: collision induced dissociation (CID), four-center (4C) reaction and single exchange (SE) reaction. The effect of the total angular momentum J on the reaction dynamics of H(2) + D(2) and the accuracy of the CS approximation have also been studied. It was found that the CID and SE processes occur in a wide range of J values while the 4C process can only take place in a narrow window of J values. For this reason, the CC cross section for the 4C channel is merely comparable to the SE channel. A comparison of the integral cross sections from CC and CS calculations showed that the CS approximation works well for the CID process but not for the 4C and SE processes, and the discrepancy between the CC and CS cross sections grows larger as the translational energy and/or the vibrational energy increase(s). PMID:22443764

Song, Hongwei; Lu, Yunpeng; Lee, Soo-Y

2012-03-21

135

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

136

Theoretical studies of the alteration of spodumene, petalite, eucryptite and pollucite in granitic pegmatites: exchange reactions with alkali feldspars  

Microsoft Academic Search

The ratios Na\\/Li, K\\/Li, Na\\/Cs and K\\/Cs have been calculated for exchange equilibria among the Li and Cs silicates spodumene, petalite, eucryptite, and pollucite, and the alkali feldspars albite and K-feldspar plus quartz, in pure water and in chloride solutions at temperatures from 100° to 700°C and pressures from 0.5 to 4 kbar, using available thermodynamic data for minerals and

Scott A. Wood; Anthony E. Williams-Jones

1993-01-01

137

Determination of D / H ratios of nonexchangeable hydrogen in cellulose: A method based on the cellulose-water exchange reaction  

NASA Astrophysics Data System (ADS)

We have established a simple technique for the determination of D/H ratios of nonexchangeable hydrogen in cellulose. This technique is based on equilibrating cellulose prepared from raw wood or cotton with water of known isotopic composition. A temperature of 0°C was selected for the exchange experiments. This allowed the rapid freezing and subsequent sublimation of the ice without affecting the isotopic composition of the equilibrated hydroxyl hydrogen. A sodium hydroxide treatment of the cellulose is necessary to achieve equilibrium between cellulose and water within 24 hours. The best sodium hydroxide treatment procedure was found to be overnight soaking of cellulose in a 17% NaOH solution at near 0°C, followed by rinsing and transferring the cellulose to the exchange vessels without drying. We have obtained a very good reproducibility for the ?D analysis of the equilibrated cellulose treated with this procedure (1? < 2%.). The resulting ?D values of nonexchangeable hydrogen, using the equilibration technique, were compared with those obtained using the nitration technique. The agreement between the two techniques is ±3.3%. (1?), and the analytical accuracy of the equilibration method is ±2.5%. (1?). This method may be useful in dealing with the nitration of ancient plant materials, which is sometimes not possible. In addition, the technique may be extended to the isotopic analysis of other organic compounds that contain exchangeable hydrogen.

Feng, Xiahong; Krishnamurthy, R. V.; Epstein, Samuel

1993-09-01

138

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

SciTech Connect

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

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

2009-07-15

139

Isotope effects in the transient phases of the reaction catalyzed by ethanolamine ammonia-lyase: determination of the number of exchangeable hydrogens in the enzyme-cofactor complex.  

PubMed

Transient phases of the reaction catalyzed by ethanolamine ammonia-lyase (EAL) from Salmonella typhimurium have been investigated by stopped-flow visible spectrophotometry and deuterium kinetic isotope effects. The cleavage of adenosylcobalamin (coenzyme B(12)) to form cob(II)alamin (B(12r)) with ethanolamine as the substrate occurred within the dead time of the instrument whenever coenzyme B(12) was preincubated with enzyme prior to mixing with substrate. The rate was, however, slowed sufficiently to be measured with perdeutero ethanolamine as the substrate. Optical spectra indicate that, during the steady states of the reactions with ethanolamine and with S-2-aminopropanol as substrates, approximately 90% of the active sites contain B(12r). Reformation of the carbon-cobalt bond of the cofactor occurs following depletion of substrate in the reaction mixtures, and the rate constant for this process reflects k(cat) of the respective substrates. This late phase of the reaction also exhibits (2)H isotope effects similar to those measured for the overall reaction with (2)H-labeled substrates. With unlabeled substrates, the rate of cofactor reassembly is independent of the number of substrate molecules turned over in the steady-state phase. However, with (2)H-labeled substrates, kinetic isotope effects appear in the reassembly phase, and these isotope effects are maximal after only approximately 2 equiv of substrate/active site are processed. With 5'-deuterated coenzyme B(12) and deuterated substrate, the isotope effect on reassembly is independent of the number of substrate molecules that are turned over. These results indicate that the pool of exchangeable hydrogens in the enzyme-cofactor complex is two-a finding consistent with the hydrogens in the C5' methylene of coenzyme B(12). PMID:11009622

Bandarian, V; Reed, G H

2000-10-01

140

Dose-dependent effects of Chlamydia psittaci infection on pulmonary gas exchange, innate immunity and acute-phase reaction in a bovine respiratory model.  

PubMed

The respiratory pathogen Chlamydia psittaci naturally occurs in bovine herds and was recently shown to impair calf health in a dose-dependent manner. The aim of this study was to determine whether the functional consequences and immunological reactions of infection were dose related by quantifying the consequences of acute respiratory chlamydial infection on respiratory signs, disturbances of pulmonary gas exchange, response of the innate immune system, and acute-phase reaction. Fourteen calves were challenged intrabronchially with different C. psittaci doses (from 10(6) to 10(9)inclusion-forming units (ifu) per animal). Ten controls received either UV-inactivated chlamydiae or cell culture medium. Compared to the controls, all animals challenged with live C. psittaci developed hypoxaemia linked to reduced haemoglobin oxygen saturation, increased alveolar-arterial oxygen partial pressure difference (A-aO2) and pulmonary shunt, with symptoms following a dose-dependent pattern. Increases in lipopolysaccharide-binding protein (LBP) and leukocytes were also dose-dependent and accompanied by a regenerative left shift in neutrophil granulocytes. With the exception of LBP, which reflected the load of chlamydial cell components in the host, pathophysiological reactions were only detected in calves challenged with viable chlamydiae. These results indicate that the pathophysiological consequences of respiratory C. psittaci infections are strongly dependent on the challenge dose of chlamydiae. For further studies, challenge doses between 10(6) and 10(8)ifu/calf are recommended. PMID:23265868

Ostermann, Carola; Schroedl, Wieland; Schubert, Evelyn; Sachse, Konrad; Reinhold, Petra

2013-06-01

141

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

142

Heisenberg model for radical reactions. Part 3. Direct exchange coupling between transition metal ions and triplet methylene  

NASA Astrophysics Data System (ADS)

Ab initio UHF calculations have been carried out for naked transition metal-methylene ions. The low-spin open-shell states are found to be the ground states of these ions, in accord with the GVB-CI results. The low-spin transition metal-methylene ions are regarded as direct exchange-coupled systems formed from high-spin transition metal ions and the triplet monocentric diradical. The direct exchange couplings between these species can be described on the basis of the Heisenberg model. The CASSCF calculations using UHF natural orbitals (UNOs) have been carried out for low-spin states, showing that UNOs and their occupation numbers are good trials. However, they provide poor binding energies for the transition metal-carbon double bonds and indicate the necessity for dynamical correlation corrections. The approximate spin-projected UHF Møller-Plesset and UHF coupled-cluster methods provide reasonable binding energies for the transition metal-methylene ions, which are close to those of modified coupled-pair functional (CPF) and average CPF methods.

Yamanaka, S.; Kawamura, T.; Noro, T.; Yamaguchi, K.

1994-07-01

143

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

NASA Astrophysics Data System (ADS)

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

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

1995-06-01

144

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 m³/s), to conditions where the ISGB is completely submerged (5.0 m³/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

145

Hydrogen bonding induced proton exchange reactions in dense D{sub 2}-NH{sub 3} and D{sub 2}-CH{sub 4} mixtures  

SciTech Connect

We have investigated high-pressure behaviors of simple binary mixtures of NH{sub 3} and D{sub 2} to 50 GPa and CH{sub 4} and D{sub 2} to 30 GPa using confocal micro-Raman spectroscopy. The spectral data indicate strong proton exchange reactions occur in dense D{sub 2}-NH{sub 3} mixture, producing different isotopes of ammonia such as NH{sub 3}, NH{sub 2}D, NHD{sub 2}, and ND{sub 3}. In contrast, the proton exchange process in dense D{sub 2}-CH{sub 4} mixture is highly limited, and no vibration feature is apparent for deuterated methane. The vibrational modes of H{sub 2} isotopes in D{sub 2}-NH{sub 3} are blue shifted from those of pure H{sub 2} isotopes, whereas the modes of D{sub 2}-CH{sub 4} show overall agreement with those in pure D{sub 2} and CH{sub 4}. In turn, this result advocates the presence of strong repulsion and thereby internal pressure in D{sub 2}-NH{sub 3} mixture, which are absent in D{sub 2}-CH{sub 4}. In fact, the bond length of hydrogen molecules in D{sub 2}-NH{sub 3}, 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 D{sub 2}-H{sub 2}O 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 H{sub 2}O, NH{sub 3}, and CH{sub 4} in decreasing order. Hence, we suggest that the proton exchange is assisted by hydrogen bonding in these molecules.

Borstad, Gustav M.; Yoo, Choong-Shik, E-mail: csyoo@wsu.edu [Institute for Shock Physics, Department of Physics and Department of Chemistry, Washington State University, Pullman, Washington 99164 (United States)] [Institute for Shock Physics, Department of Physics and Department of Chemistry, Washington State University, Pullman, Washington 99164 (United States)

2014-01-28

146

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)], 10.1021/ct3009792. 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)], 10.1063/1.4736567. 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

147

Implications of weak Donnan potential in ion-exchange reactions. An alternate strategy for modeling sorption processes  

SciTech Connect

Donnan potential generated during an ion-exchange process is conventionally believed to play an important role in partitioning co-ions in the resin and solution phases; most earlier studies implied near total exclusion of co-ions from the resin pores. The present work attempts to investigate implications of weak Donnan potential with specific reference to the sorption of acids on weak base resins. An alternate mathematical treatment has been proposed to describe the sorption behavior of any type of acid by assuming diffusion and sorption of single species, the composite acid molecule, in the resin pores. Fick`s law is then used to characterize the diffusion process. The proposed model is validated using data reported in the literature for the sorption of a strong monobasic acid (HCl) and also for a weak monobasic acid (HCOOH). The fit of the model is excellent, and the regressed values of the effective diffusion coefficient are shown to be reasonable and correct to the order of magnitude. The model is expected to offer a simpler and unified approach for modeling sorption behavior of different types of acids and will be more useful in problems of acid separation from mixtures.

Bhandari, V.M. [National Chemical Lab., Pune (India). Chemical Engineering Div.

1998-09-01

148

Nitrogenase of Klebsiella pneumoniae. Reversibility of the reductant-independent MgATP-cleavage reaction is shown by MgADP-catalysed phosphate/water oxygen exchange.  

PubMed Central

The steady-state kinetics of reductant-independent ATP hydrolysis by Klebsiella pneumoniae nitrogenase at 23 degrees C at pH 7.4 were determined as a function of component protein ratio (optimal at an oxidized Fe protein/MoFe protein ratio of 3:1) and MgATP concentration (Km 400 microM). Competitive inhibition was observed for MgADP (Ki 145 microM), [beta gamma-methylene]ATP (Mgp[CH2]ppA) (Ki 115 microM), [beta gamma-monofluoromethylene]ATP (Mgp[CHF]ppA) (Ki 53 microM) and [beta gamma-difluoromethylene]ATP (Mgp[CF2]ppA) (Ki 160 microM). The tighter binding of MgADP to free oxidized Fe protein (KD less than 10 microM) than to the oxidized Fe protein-MoFe protein complex (Ki 145 microM) is proposed as the driving force that induces rate-limiting protein dissociation in the catalytic cycle of nitrogenase. The reversible nature of the reductant-independent MgATP-cleavage reaction was demonstrated by an MgADP-induced enhancement of the rate of the phosphate/water oxygen exchange reaction with 18O-labelled phosphate ion. This enhancement, like the reductant-independent ATPase reaction, only occurred with the complex formed by oxidized Fe protein and MoFe protein and not with the individual proteins. The results are discussed in terms of the mechanism of ATP hydrolysis by nitrogenase and other systems involving protein-protein interactions. PMID:1872810

Thorneley, R N; Ashby, G A; Julius, C; Hunter, J L; Webb, M R

1991-01-01

149

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

150

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

151

Toward a protecting-group-free halogen-metal exchange reaction: practical, chemoselective metalation of functionalized aromatic halides using dianion-type zincate, tBu4ZnLi2.  

PubMed

A versatile preparation method for aromatic zincate compounds through a halogen-zinc exchange reaction using dilithium tetra-tert-butylzincate (tBu4ZnLi2) has been developed. This reagent permits efficient preparation of highly functionalized aromatic zincates, particularly, those with electrophilic functional groups, such as ester, amide, alcohol, and phenol. Halogen-zinc exchange reactions followed by electrophilic trapping (with allyl bromide or benzaldehyde) proved to be a powerful tool for C-C bond formation on functionalized aromatic rings. The functionalized aromatic zincate intermediate was also found to undergo copper- and palladium-catalyzed C-C bond-forming reactions with good yields and high chemoselectivity. PMID:16802798

Uchiyama, Masanobu; Furuyama, Taniyuki; Kobayashi, Minoru; Matsumoto, Yotaro; Tanaka, Kentaro

2006-07-01

152

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?³ - 100 ?g dm?³ 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?³ for Cr(VI) and 0.8 ng dm?³ for total chromium when using a 3.9-cm³ 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

153

Gram-level synthesis of core-shell structured catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

Over the past decade, Pt based core-shell structured alloys have been studied extensively as oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cells (PEMFCs) because of their distinctive electrochemical performance and low Pt loading. In this paper, a facile route based on microwave-assisted polyol method and chemical dealloying process is proposed to synthesize carbon supported core-shell structured nanoparticles (NPs) in gram-level for ORR electrocatalysis in PEMFCs. The obtained samples are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). These physical characterization indicate that the final synthesized NPs are highly dispersed on the carbon support, and in a core-shell structure with CuPt alloy as the core and Pt as the shell. Electrochemical measurements, conducted by cyclic voltammetry (CV) and rotating disk electrode (RDE) tests, show the core-shell structured catalyst exhibit a 3× increase in mass activity and a 2× increase in specific activity over the commercial Pt/C catalyst, respectively. These results demonstrate that this route can be a reliable way to synthesize low-Pt catalyst in large-scale for PEMFCs.

Luo, Mingchuan; Wei, Lingli; Wang, Fanghui; Han, Kefei; Zhu, Hong

2014-12-01

154

Microfluidic chemical reaction circuits  

DOEpatents

New microfluidic devices, useful for carrying out chemical reactions, are provided. The devices are adapted for on-chip solvent exchange, chemical processes requiring multiple chemical reactions, and rapid concentration of reagents.

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

2012-06-26

155

Ion Exchange in Nonaqueous and Mixed Media  

Microsoft Academic Search

Enough experimental data on nonaqueous ion-exchange separations have been gathered to show that one is dealing with a field whose theoretical aspects are infinitely complicated. The separations can be based on several different types of chemical reactions. Apart from true ion exchange, sorption can take place by non-exchange reactions such as acid-base reactions or complex-formation, either by hydrogen bonding or

Walter R. Heumann; James S. Fritz

1971-01-01

156

Differential cross sections of the charge-exchange reaction pip>pi0n in the momentum range from 103 to 178 MeV\\/c  

Microsoft Academic Search

Measured values of the differential cross sections for pion-nucleon charge exchange, pi-p-->pi0n, are presented for pi- 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

D. Mekterovic; I. Supek; V. Abaev; V. Bekrenev; C. Bircher; W. J. Briscoe; R. V. Cadman; M. Clajus; J. R. Comfort; K. Craig; D. Grosnick; D. Isenhover; M. Jerkins; M. Joy; N. Knecht; D. D. Koetke; N. Kozlenko; A. Kulbardis; S. Kruglov; G. Lolos; I. Lopatin; D. M. Manley; R. Manweiler; A. Marusic; S. McDonald; B. M. K. Nefkens; J. Olmsted; Z. Papandreou; D. Peaslee; J. Peterson; N. Phaisangittisakul; S. N. Prakhov; J. W. Price; A. Ramirez; M. E. Sadler; A. Shafi; H. Spinka; S. Stanislaus; A. Starostin; H. M. Staudenmaier; I. Strakovsky; W. B. Tippens; S. Watson

2009-01-01

157

Anion exchange behavior of nobelium  

Microsoft Academic Search

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

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

2003-01-01

158

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

159

Synthesis and characterization of sulfonated polytriazole-clay proton exchange membrane by in situ polymerization and click reaction for direct methanol fuel cells  

NASA Astrophysics Data System (ADS)

Sulfonated polytriazole-clay (SPTA-clay) nanocomposites are successfully prepared by in situ polymerization of SPTA using click chemistry in the presence of propargyl-functionality modified clay. The clay layers are exfoliated and well dispersed within the SPTA matrix resulting in improvements in thermal stability, mechanical strength, methanol permeability, water retention, ion channel size, and ionic cluster distribution. The SPTA-clay nanocomposite membranes with small amounts of clay in the SPTA matrices possess higher selectivity's; defined as the ratio of proton conductivity to methanol permeability, and thus have potential as proton exchange membranes (PEMs) in direct methanol fuel cells (DMFCs).

Huang, Yao-Jheng; Ye, Yun-Sheng; Syu, Yu-Jyuan; Hwang, Bing-Joe; Chang, Feng-Chih

2012-06-01

160

Using positive-ion electrospray ionization mass spectrometry and H/D exchange study phosphoryl group transfer reactions involved in amino acid ester isopropyl phosphoramidates of Brefeldin A.  

PubMed

As mini-chemical models, amino acid ester isopropyl phosphoramidates of Brefeldin A (compounds 2a-2d) were synthesized and investigated by electrospray ionization tandem mass spectrometry in combination with H/D exchange. To further confirm the fragments's structures, off-line Fourier transform resonance tandem mass spectrometry (FT-ICR-MS/MS) was also performed. The fragmentation rules of compounds 2a-2d have been summarized and the plausible schemes for the fragmentation pathways were proposed. In this study, one dephosphorylated ion and two phosphorylated ions were observed in ESI-MS(2) spectra of [M+Na](+) ions for compounds 2a-2d. The possible mechanisms about phosphorylation and dephosphorylation were proposed and confirmed by H/D exchange. For the "dephosphorylation" rearrangement, a nitrogen atom was migrated from the phosphoryl group to the carbon atom of Brefeldin A's backbone with losing a molecule of C3H7PO3 (122Da). For the "phosphorylation" rearrangement, an oxygen atom of one phosphoryl group attacked the sideward phosphorus atom to form a nine-member ring intermediate, then two steps of CH covalent bond cleavage with consecutive migration of hydrogen atom to lose a molecule of C16H20O2 (244Da). The two proposed rearrangement mechanisms about phosphoryl group transfer might be valuable for the structure analysis of other analogs and provide insights into elucidating the dynamic process of the phosphorylation-dephosphorylation of proteins. PMID:25467484

Fang, Mei-Juan; Zhang, He; Liao, Chao; Qiu, Ying-Kun; Fang, Hua; Zheng, Zhen-Yu; Gao, Xiang; Zhao, Yu-Fen; Wu, Zhen

2015-01-01

161

Non-precious Co3O4 nano-rod electrocatalyst for oxygen reduction reaction in anion-exchange membrane fuel cells  

E-print Network

Non-precious Co3O4 nano-rod electrocatalyst for oxygen reduction reaction in anion 2011 DOI: 10.1039/c1ee01431e We report preparation of carbon-supported Co3O4 electrocatalysts with nano that the non-precious Co3O4 electrocatalyst with the nano-rod structure ($12 nm in length and $5.1 nm

Zhao, Tianshou

162

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

163

High performance fluorine doped (Sn,Ru)O2 oxygen evolution reaction electro-catalysts for proton exchange membrane based water electrolysis  

NASA Astrophysics Data System (ADS)

Identification of electro-catalysts containing non-noble metal or significantly reduced amounts of expensive noble metals (e.g. RuO2) is highly desirable. Development of such a catalyst with comparable electrochemical performance to the standard noble metal oxide for proton exchange membrane (PEM) based water electrolysis would constitute a pioneering breakthrough in hydrogen generation by water electrolysis. In line with these goals, by exploiting a two-pronged theoretical first principles and experimental approach herein we demonstrate that a nano-structured solid solution of SnO2:10 wt% F containing only 20 at.% RuO2 [e.g. (Sn0.80Ru0.20)O2:10F] displays a remarkably similar electrochemical activity and moreover, comparable or even much improved electrochemical stability and durability compared to pure the noble metal counterpart, RuO2. Density functional theory calculations have demonstrated direct dependence of the catalytic activity on the electronic structure peculiarities of the F-doped (Ru,Sn)O2 which corresponds well with the experimental results.

Kadakia, Karan; Datta, Moni Kanchan; Velikokhatnyi, Oleg I.; Jampani, Prashanth; Park, Sung Kyoo; Chung, Sung Jae; Kumta, Prashant N.

2014-01-01

164

Cumulative reaction probabilities and transition state properties: A study of the H{sup +}+H{sub 2} and H{sup +}+D{sub 2} proton exchange reactions  

SciTech Connect

Cumulative reaction probabilities (CRPs) have been calculated by accurate (converged, close coupling) quantum mechanical (QM), quasiclassical trajectory (QCT), and statistical QCT (SQCT) methods for the H{sup +}+H{sub 2} and H{sup +}+D{sub 2} reactions at collision energies up to 1.2 eV and total angular momentum J=0-4. A marked resonance structure is found in the QM CRP, most especially for the H{sub 3}{sup +} system and J=0. When the CRPs are resolved in their ortho and para contributions, a clear steplike structure is found associated with the opening of internal states of reactants and products. The comparison of the QCT results with those of the other methods evinces the occurrence of two transition states, one at the entrance and one at the exit. At low J values, except for the quantal resonance structure and the lack of quantization in the product channel, the agreement between QM and QCT is very good. The SQCT model, that reflects the steplike structure associated with the opening of initial and final states accurately, clearly tends to overestimate the value of the CRP as the collision energy increases. This effect seems more marked for the H{sup +}+D{sub 2} isotopic variant. For sufficiently high J values, the growth of the centrifugal barrier leads to an increase in the threshold of the CRP. At these high J values the discrepancy between SQCT and QCT becomes larger and is magnified with growing collision energy. The total CRPs calculated with the QCT and SQCT methods allowed the determination of the rate constant for the H{sup +}+D{sub 2} reaction. It was found that the rate, in agreement with experiment, decreases with temperature as expected for an endothermic reaction. In the range of temperatures between 200 and 500 K the differences between SQCT and QCT rate results are relatively minor. Although exact QM calculations are formidable for an exact determination of the k(T), it can be reliably expected that their value will lie between those given by the dynamical and statistical trajectory methods.

Jambrina, P. G. [Departamento de Quimica Fisica, Universidad de Salamanca, 37008 Salamanca (Spain); Departamento de Quimica Fisica, Facultad de Quimica, Universidad Complutense, 28040 Madrid (Spain); Aoiz, F. J. [Departamento de Quimica Fisica, Facultad de Quimica, Universidad Complutense, 28040 Madrid (Spain); Eyles, C. J. [Department of Chemistry, The Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ (United Kingdom); Herrero, V. J. [Instituto de Estructura de la Materia (CSIC), Serrano 123, 28006 Madrid (Spain); Saez Rabanos, V. [Departamento de Quimica y Bioquimica, ETS Ingenieros de Montes, Universidad Politecnica, 28040 Madrid (Spain)

2009-05-14

165

Test procedure for cation exchange chromatography  

SciTech Connect

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

Cooper, T.D.

1994-08-24

166

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

167

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 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)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. PMID:23226989

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

2012-01-01

168

Electron paramagnetic resonance investigation of photosynthetic reaction centers from Rhodobacter sphaeroides R-26 in which Fe2+ was replaced by Cu2+. Determination of hyperfine interactions and exchange and dipole-dipole interactions between Cu2+ and QA-.  

PubMed Central

We report electron paramagnetic resonance (EPR) experiments in frozen solutions of unreduced and reduced photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides R-26 in which Fe2+ has been chemically replaced by the isotope 65Cu2+. Samples in which the primary quinone acceptor QA is unreduced (Cu2+QA:RCs) give a powder EPR spectrum typical for Cu2+ having axial symmetry, corresponding to a d(x2 - y2) ground state orbital, with g values g parallel = 2.314 +/- 0.001 and g perpendicular = 2.060 +/- 0.003. The spectrum shows a hyperfine structure for the nuclear spin of copper (65I = 3/2) with A parallel = (-167 +/- 1) x 10(-4) cm-1 and /A perpendicular/ = (16 +/- 2) x 10(-4) cm-1, and hyperfine couplings with three nitrogen ligands. This has been verified in samples containing the naturally occurring 14N isotope (l = 1), and in samples where the nitrogen ligands to copper were replaced by the isotope 15N (l = 1/2). We introduce a model for the electronic structure at the position of the metal ion which reflects the recently determined three-dimensional structure of the RCs of Rb. sphaeroides (Allen, J. P., G. Feher, T. O. Yeates, H. Komiya, and D. C. Rees. 1987. Proc. Natl. Acad. Sci. USA. 84:5730: Allen, J. P., G. Feher, T. O. Yeates, H. Komiya, and D. C. Rees. 1988. Proc. Natl. Acad. Sci. USA, 85:8487) as well as our EPR results. In this model the copper ion is octahedrally coordinated to three nitrogens from histidine residues and to one carboxylate oxygen from a glutamic acid, forming a distorted square in the plane of the d(x2 = y2) ground state orbital. It is also bound to a nitrogen of another histidine and to the other carboxylate oxygen of the same glutamic acid residue, in a direction approximately normal to this plane. The EPR spectrum changes drastically when the quinone acceptor QA is chemically reduced (Cu2+QA-:RCs); the change is due to the exchange and dipole-dipole interactions between the Cu2+ and QA- spins. A model spin Hamiltonian proposed for this exchange coupled cooper-quinone spin dimer accounts well for the observed spectra. From a comparison of the EPR spectra of the Cu2+QA:RC and CU2+QA-:RC complexes we obtain the values /J0/ = (0.30 +/- 0.02) K for the isotropic exchange coupling, and /d/ = (0.010 +/- 0.002) K for the projection of the dipole-dipole interaction tensor on the symmetry axis of the copper spin. From the EPR experiments only the relative signs of J0 and d can be deduced; it was determined that they have the same sign. The magnitude of the exchange coupling calculated for Cu2+QA-:RC is similar to that observed for the Fe2+QA-:RC complex (J0 = -0.43K). The exchange coupling is discussed in terms of the superexchange paths connecting the Cu2+ ion and the quinone radical using the structural data for the RCs of Rb. sphaeroides. From the value of the dipole-dipole interaction, d, we determined R approximately 8.4 A for the weighted distance between the metal ion and the quinone in reduced RCs, which is to be compared with 10 A obtained from x-ray analysis of unreduced RCs. This points to a shortening of the Cu2+ -QA- distance upon reduction of the quinone, as has been proposed by Allen et al. (1988). PMID:2166597

Calvo, R; Passeggi, M C; Isaacson, R A; Okamura, M Y; Feher, G

1990-01-01

169

Specific dicyclohexylcarbodiimide inhibition of the E-P + H/sub 2/O equilibrium E + P /sub i/ reaction and ATP equilibrium P /sub i/ exchange in sarcoplasmic reticulum adenosinetriphosphatase  

SciTech Connect

Treatment of sarcoplasmic reticulum adenosinetriphosphatase (ATPase) with N,N'-dicyclohexylcarbodiimide is known to produce total inhibition of calcium binding and enzyme activity. However, we now find that treatment with lower reagent:protein ratios produces selective inhibition of hydrolytic P /sub i/ cleavage, enzyme phosphorylation with P /sub i/, and ATP in equilibrium P /sub i/ exchange, while calcium binding and enzyme phosphorylation with ATP remain largely unaffected. This specific inhibition is attributed to derivatization of residues which are normally involved in acid-base-assisted catalysis of the hydrolytic reaction and its reversal, but are not involved in calcium binding or in the mechanism of phosphoryl transfer from ATP to the enzyme. This specific inhibition is prevented by the presence of micromolar calcium during the incubation with the inhibitor, evidently through an allosteric effect of calcium binding on the catalytic site. We also find that the initial adducts formed between ATPase residues and N,N'-dicyclo(/sup 14/C)carbodiimide undergo further degradation with release of radioactive product into the medium, while the protein residues remain inactivated probably by linkage with neighboring residues. Therefore, the stoichiometry of radioactive labeling underestimates the actual number of inactivated residues.

Scofano, H.M.; Barrabin, H.; Lewis, D.; Inesi, G.

1985-02-12

170

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

171

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

NASA Astrophysics Data System (ADS)

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

Liechty, Derek S.; Lewis, Mark J.

2011-05-01

172

Closed cycle ion exchange method for regenerating acids, bases, and salts  

Microsoft Academic Search

A method is described for conducting a chemical reaction in acidic, basic, or neutral solution as required and then regenerating the acid, base, or salt by means of ion exchange in a closed cycle reaction sequence which comprises contacting the spent acid, base, or salt with an ion exchanger. The ion exchanger is preferably a synthetic organic ion-exchange resin so

Dreyfuss

1976-01-01

173

Spin uncoupling in chemical reactions  

Microsoft Academic Search

Spin pairing is the main attribute of the covalent chemical bond. Exchange repulsion between closed shell molecules being responsible for activation barriers in bimolecular reactions can be explained by a high weight of the intermolecular triplet spin pairing. Intermolecular exchange interaction switches to a strong attraction when the molecules are in excited triplet states. This is the reason for that

Boris F. Minaev; Hans Ågren

2001-01-01

174

Law on Exchange InternationalExchangeProgram  

E-print Network

Law on Exchange InternationalExchangeProgram Law students have a range of exchange options available both at the faculty level and through University- wide exchange partners. Law students can spend a maximum of one semester on exchange in the last year of their Bachelor of Law or Juris Doctor course. Law

Viglas, Anastasios

175

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

PubMed

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

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

2012-10-16

176

Job Exchange  

NSDL National Science Digital Library

Job Exchange, provided by BioMedNet (discussed in the February 14, 1997 Scout Report) is a searchable database of jobs in molecular biology, genetics, general biology, and the biomedical sciences. Employment opportunities are updated frequently and may be searched or browsed by position type (Academic/Research Institution, Government/Private Research, Hospital/Medical Institution, Industry/Other), international region, or specialty. Typical returns include full job details, including summary of duties, salary range, duration of position, and contact information.

1998-01-01

177

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.

178

Exchange Rate Regime Shift in Reaction to a Changing Environment: A Case Study of Kuwait - Modifiche del regime dei tassi di cambio a seguito di modifiche nelle condizioni del sistema: il caso del Kuwait  

Microsoft Academic Search

Two propositions are verified about the exchange rate regime of a basket peg, which is adopted by some developing countries. The first is that by pegging the domestic currency to an import-weighted basket, the economy can be insulated from the imported inflation resulting purely from change in exchange rates. The second proposition is that profitable arbitrage can be conducted by

Imad A. Moosa

2011-01-01

179

Heat exchanger  

DOEpatents

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

Brackenbury, Phillip J. (Richland, WA)

1986-01-01

180

Heat exchanger  

DOEpatents

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

Brackenbury, P.J.

1983-12-08

181

Agriculture on Exchange InternationalExchangeProgram  

E-print Network

Agriculture on Exchange InternationalExchangeProgram Students enrolled in courses offered through the Faculty of Agriculture and Environment are welcome to apply for exchange. However, to ensure that you Academic Adviser before submitting an exchange application. Undergraduate Agriculture students normally go

Viglas, Anastasios

182

Drug Reactions  

MedlinePLUS

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

183

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

184

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.

185

The adsorption of valine on cation-exchanged montmorillonites  

Microsoft Academic Search

The interfacial reaction of valine was systematically studied on the surface of different cation-exchanged montmorillonites, namely calcium-, copper-, zinc-montmorillonite, and montmorillonite KSF. The exchanged cations were selected on the basis of stability of their valine complexes. At first the interfacial acid\\/base properties of cation exchanged montmorillonites were studied: the stability constants of the ion exchange processes on the layer charges

Noémi M. Nagy; József Kónya

2004-01-01

186

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

187

Closed cycle ion exchange method for regenerating acids, bases and salts  

Microsoft Academic Search

A method for conducting a chemical reaction in acidic, basic, or neutral solution as required and then regenerating the acid, base, or salt by means of ion exchange in a closed cycle reaction sequence which comprises contacting the spent acid, base, or salt with an ion exchanger, preferably a synthetic organic ion-exchange resin, so selected that the counter ions thereof

Dreyfuss; Robert M

1976-01-01

188

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

189

Corrosive resistant heat exchanger  

DOEpatents

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

Richlen, Scott L. (Annandale, VA)

1989-01-01

190

Psychology on Exchange InternationalExchangeProgram  

E-print Network

Psychology on Exchange InternationalExchangeProgram Psychology majors are welcome to apply Honours, you need to take into account the advice from the Department of Psychology (http://sydney.edu.au/ current_students/student_exchange/forms_downloads.shtml). Timing To meet Australian Psychology

Viglas, Anastasios

191

Reaction times  

Microsoft Academic Search

Reviews 11 studies dealing with reaction times (1910-1911). Reaction time has been utilized to study a variety of problems. The studies indicate that accurate results can not be obtained without careful attention to the technique of the method of reaction time. The topics covered include effect of intensity of stimulus on reaction time, rapidity of perception of sound and light

Herbert Woodrow

1911-01-01

192

Woven heat exchanger  

DOEpatents

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

Piscitella, Roger R. (Idaho Falls, ID)

1987-01-01

193

Woven heat exchanger  

DOEpatents

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

Piscitella, R.R.

1984-07-16

194

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

195

Community, exchange and diversity: The Carrick Exchange  

Microsoft Academic Search

The Carrick Exchange is a significant new online service that will provide communication and collaboration services, and learning and teaching resources across the Australian and international higher education sectors. The Carrick Exchange is sponsored by the Carrick Institute for Learning and Teaching in Higher Education. It is for those who teach, manage and lead learning and teaching in Australian higher

Robyn Phillip; Geraldine E. Lefoe; Meg OReilly; Dominique Parrish

2007-01-01

196

THE THERMODYNAMICS OF ANION EXCHANGE OF THE RARE EARTH ETHYLENEDIAMINETETRAACETATES  

Microsoft Academic Search

Distribution coefficients for the ion exchange reaction of the rare ; earth ethylenediaminetetraacetates in the system strongly basic anion exchange ; resin Amberlite IRA-400-aq. solution of di-Na-ethylenediaminetetraacetate were ; determined by column method with the use of radioactive tracers. From tuese ; data, partial molal free energy ( DELTA G\\/sup *\\/), enthalpy ( DELTA H\\/sup *\\/), ; entropy ( DELTA

Dybczynski

1963-01-01

197

Reversible Reactions  

NSDL National Science Digital Library

Watch a reaction proceed over time. How does total energy affect a reaction rate? Vary temperature, barrier height, and potential energies. Record concentrations and time in order to extract rate coefficients. Do temperature dependent studies to extract Arrhenius parameters. This simulation is best used with teacher guidance because it presents an analogy of chemical reactions.

Simulations, Phet I.; Barbera, Jack; Koch, Linda; Lemaster, Ron; Adams, Wendy

2005-09-01

198

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

199

Chemical Reactions  

NSDL National Science Digital Library

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

National Science Teachers Association (NSTA)

2009-05-01

200

77 FR 8304 - Self-Regulatory Organizations; Chicago Board Options Exchange, Incorporated; Order Approving...  

Federal Register 2010, 2011, 2012, 2013, 2014

...agrees with the Exchange that the five-minute RFQ Reaction Period should be sufficient time for the Submitting Trading Permit Holder to determine...market movements that may occur during the RFQ Reaction...

2012-02-14

201

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

2000-01-01

202

Phase change heat exchanger  

Microsoft Academic Search

A heat exchanger for a phase change material having a solid density greater than its liquid density, the heat exchanger is described comprising a container holding the phase change material, a tube surrounding the container to define an annular space there between, means for connecting the tube in fluid communication with a first source of heat exchange fluid to allow

R. L. Longardner; W. J. Longardner

1993-01-01

203

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

PubMed

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

Farazdaghi, Hadi

2011-02-01

204

Oxygen exchange measurements on perovskites as cathode materials for solid oxide fuel cells  

Microsoft Academic Search

Oxygen exchange measurements have been applied to determine simultaneously the chemical diffusion coefficient and the surface exchange coefficient of oxide perovskites. The oxygen partial pressure is changed in a step-wise manner and the relaxation of the oxide ceramics is followed as a function of time. Instead of recording the amount of exchanged oxygen, the rate of oxygen incorporation reactions is

W. Preis; E. Bucher; W. Sitte

2002-01-01

205

A stylized exchange rate pass-through model of crude oil price formation  

Microsoft Academic Search

This paper presents a stylized exchange rate pass-through model of crude oil price formation for the purpose of understanding the price reactions of OPEC Member Countries to changes in the exchange rate of the US dollar against major currencies and the prices of other Members. Our empirical results suggest that, in response to changes in the exchange rate, exporting countries

Ayoub Yousefi; Tony S. Wirjanto

2005-01-01

206

Intrinsic Barriers for Electron and Hydrogen Atom Transfer Reactions of Biomimetic Iron Complexes  

E-print Network

Intrinsic Barriers for Electron and Hydrogen Atom Transfer Reactions of Biomimetic Iron Complexes: Self-exchange reactions between high-spin iron complexes of 2,2-bi-imidazoline (H2bim) have been.3 ( 0.3 at 324 K, whereas no such effect is detected in the electron exchange reaction. Proton self

Roth, Justine P.

207

Electrical and magnetic properties of ion-exchangeable layered ruthenates  

SciTech Connect

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

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

2004-12-01

208

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...

209

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

210

Reaction product imaging  

SciTech Connect

Over the past few years the author has investigated the photochemistry of small molecules using the photofragment imaging technique. Bond energies, spectroscopy of radicals, dissociation dynamics and branching ratios are examples of information obtained by this technique. Along with extending the technique to the study of bimolecular reactions, efforts to make the technique as quantitative as possible have been the focus of the research effort. To this end, the author has measured the bond energy of the C-H bond in acetylene, branching ratios in the dissociation of HI, the energetics of CH{sub 3}Br, CD{sub 3}Br, C{sub 2}H{sub 5}Br and C{sub 2}H{sub 5}OBr dissociation, and the alignment of the CD{sub 3} fragment from CD{sub 3}I photolysis. In an effort to extend the technique to bimolecular reactions the author has studied the reaction of H with HI and the isotopic exchange reaction between H and D{sub 2}.

Chandler, D.W. [Sandia National Laboratories, Livermore, CA (United States)

1993-12-01

211

Chicago Climate Exchange, Inc. 2010 Chicago Climate Exchange 1 The Role of Exchanges and Standardization  

E-print Network

Chicago Climate Exchange®, Inc.© 2010 Chicago Climate Exchange 1 The Role of Exchanges and Standardization in Reducing Emissions at Scale Michael J. Walsh, Ph.D. Executive Vice President Chicago Climate Exchange, Inc. #12;Chicago Climate Exchange®, Inc.© 2010 Chicago Climate Exchange Pacala-Socolow GHG

212

Application of biological samples treated by wet-digested mineralization to cation-exchange high-performance liquid chromatography with post-column reaction by 4-(2-pyridylazo)-resorcinol.  

PubMed

To quantify metals in biological samples, we tried to find good conditions for wet-digested mineralization of the samples and for separation of metal ions in chromatography. A 500 microliters volume of aliquot was transferred to a glass tube, and was evapolated at 100 degrees C for 2 hours. A 5.5 ml volume of a mixture of concentrated nitric acid-70% perchloric acid (10: 1, v/v) was added and heated, consecutively, at 80 degrees C for 12 hours, at 140 degrees C for 2 hours, at 180 degrees C for 2 hours, and finally at 190 degrees C for 1 hour to evapolate the residual acids. After addition of 500 microliters of 10 mM nitric acid, the metals were extracted by a suspension mixer (32 r.p.m., 1 hour). One hundred microliters of the extracted solution was applied to the chromatographic system: cation-exchange column, TSKgel IC-Cation SW (Tosoh Co.); eluent, 0.35 M lactic acid-0.35 M sodium lactate (pH 3.0); flow rate, 0.7 ml/minute; column temperature, 30 degrees C. After adding a color-forming reagent (100 mg/l 4-(2-pyridylazo)-resorcinol in 40 g/l Na2CO3; flow rate, 0.7 ml/minute) to the effluent, five different metal ions of Cd2+, Co2+, Cu2+, Ni2+ and Zn2+ were detected at 520 nm. The peaks were separated in approximately 25 minutes, and were quantified even at the 1-10 ppb levels. The present procedures were considered to provide simultaneous detection and accurate quantitation of the above five metals in the biological samples. PMID:1798062

Sudo, J; Hayashi, T; Suzue, T; Terui, J

1991-11-01

213

Equal Exchange: Determining a  

E-print Network

Equal Exchange: Determining a Fair Price for Carbon P E RS P E C T I V E S S E R I E S 20 07 #12;Equal Exchange: Determining a Fair Price for Carbon P e rs P e c t i v e s s e r i e s 20 07 Glenn Hodes. Printed on environmentally friendly paper. #12;editors' introduction Equal Exchange: Determining a Fair

214

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

215

Preparation of Pt-Co nanoparticles by galvanostatic pulse electrochemical codeposition on in situ electrochemical reduced graphene nanoplates based carbon paper electrode for oxygen reduction reaction in proton exchange membrane fuel cell  

NASA Astrophysics Data System (ADS)

Nanocomposite films of Pt-Co nanoparticles deposited on graphene nanoplate based gas diffusion layer electrode are fabricated via an electrochemical route involving a series of electrochemical process. Pt-Co nanoparticles of 11.37 nm in average size are prepared by galvanostatic codeposition in 0.5 M NaCl at PH of 2.5 at 300 mA cm-2 on the surface of in situ reduced graphene nanoplates on carbon paper. The topographical features, structure, morphology and composition of the prepared film samples are characterized by Atomic Force microscopy, Raman Spectroscopy, FTIR analysis, X-ray Diffraction, FESEM and EDS. At the same time, the catalytic activities of prepared electrodes for the oxygen reduction reaction are evaluated through cyclic voltammetry, linear sweep voltammetry and chronoamperometry and electrochemical impedance spectroscopy measurements. Raman spectroscopy measurements confirmed the graphitic structure of the produced graphene nanoplates. The nanoparticles in the film were observed to be uniform spherical objects and well distributed. Catalytic properties of Pt-Co/GNP/GDL electrode were compared with Pt/C/GDL using half cell polarization measurements based on both mass activity and specific activity. The as prepared Pt-Co/GNP/GDL electrode exhibits high catalytic activity for the ORR, which may be attributed to structural changes caused by alloying and the high specific surface area of graphene nanoplates catalyst support. The mass activity peak current is found to be as high as 728.25 mA mgPt-1.

Yaldagard, Maryam; Seghatoleslami, Naser; Jahanshahi, Mohsen

2014-10-01

216

Chemical properties of anion-exchangers prepared from waste natural materials  

Microsoft Academic Search

Waste natural materials (WNM) were converted into anion-exchangers through consecutive chemical reactions with thionylchloride, N,N-Dimethylformamide (DMF), dimethylamine and formaldehyde as crosslinking agents. The final products obtained were weak-base anion-exchangers with tertiary amines as major functional exchange groups. WNM containing small amounts of extractives gave higher yields. Also, anion-exchangers produced from WNM with higher lignin content gave higher maximum nitrate adsorption

T. Okuda; A. U. Baes; W. Nishijima; M. Okada

2003-01-01

217

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

218

Drug Reactions  

MedlinePLUS

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

219

Enzyme Reactions  

NSDL National Science Digital Library

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

Maryland Virtual High School

220

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

221

Building Relationships through Exchange  

ERIC Educational Resources Information Center

From the moment of birth, children form and develop relationships with others in their world based on exchange. Children recognize that engaging in such encounters offers them the opportunity to enter into a relationship with another individual and to nurture that relationship through the exchange of messages and gifts, items and ideas. At Boulder…

Primavera, Angi; Hall, Ellen

2011-01-01

222

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

223

Direct fired heat exchanger  

DOEpatents

A gas-to-liquid heat exchanger system which transfers heat from a gas, generally the combustion gas of a direct-fired generator of an absorption machine, to a liquid, generally an absorbent solution. The heat exchanger system is in a counterflow fluid arrangement which creates a more efficient heat transfer.

Reimann, Robert C. (Lafayette, NY); Root, Richard A. (Spokane, WA)

1986-01-01

224

Isotope exchange between 12-molybdocerate(IV) and sodium molybdate- 99 Mo in aqueous media  

Microsoft Academic Search

12-molybdocerate(IV) gel labelled with99Mo has been prepared via isotope exchange between a column of inactive molybdate matrix and a mobile solution of99-Mo-sodium molybdate(VI) in 0.1 mol·dm–3 HNO3. The composition and nature of the reaction mixture, concentration of Mo(VI) in the reactants, reaction temperature and\\/or drying temperature of the gel matrix on the exchange yeild of99Mo and time of reaction are

M. A. El-Absy; M. Abou El-Enein; M. Raieh; H. F. Aly

1997-01-01

225

Single event kinetic modeling of solid acid alkylation of isobutane with butenes over proton-exchanged Y-Zeolites  

E-print Network

Complex reaction kinetics of the solid acid alkylation of isobutane with butenes over a proton-exchanged Y-zeolite has been modeled at the elementary step level. Starting with a computer algorithm that generated the reaction network based...

Martinis Coll, Jorge Maximiliano

2006-04-12

226

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

227

Chemical Reactions in DSMC  

SciTech Connect

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

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

2011-05-20

228

Taxol reactions.  

PubMed

Paclitaxel (Taxol) a taxane antineoplastic agent causing irreversible microtubule aggregation with activity against breast, ovarian, lung, head and neck, bladder, testicular, esophageal, endometrial and other less common tumors was derived from the bark of the Pacific yew (Taxus brevifolia). Phase I trials conducted in the late 1980s were almost halted because of the high frequency of hypersensitivity-like reactions. Respiratory distress (dyspnea and/or bronchospasm), hypotension, and angioedema were the major manifestations, but flushing, urticaria, chest, abdomen, and extremity pains were described also. Reactions occurred on first exposure in the majority of cases raising etiologic questions. The vehicle for paclitaxel Cremophor EL (polyoxyethylated castor oil in 50% ethanol) was strongly suspect as a direct (non-immunoglobulin E dependent) histamine releaser. Premedication regimens and longer infusion times lowered the incidence of reactivity allowing phase II and III trials to progress through the early 1990s. The mechanism(s) underlying paclitaxel hypersensitivity-like reactions is still unknown, and clinical data on probable complement and mast cell activation are lacking. The original clinical trial protocols for paclitaxel required discontinuation of therapy for patients who experienced hypersensitivity-like reactions. Here, we review the current etiologic knowledge of these reactions and describe our clinical approach to allow completion of chemotherapy with this powerful plant-derived agent. PMID:12125509

Price, Kursteen S; Castells, Mariana C

2002-01-01

229

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

230

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

231

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

232

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

233

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

234

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

235

Reaction Time  

NSDL National Science Digital Library

This lab is not an inquiry activity. There are some students whose reaction times will not allow them to catch a 12 inch ruler. They may use a dowel, stick, strip of cardboard, etc. Although the students are led to believe that the point of the lab is to

Horton, Michael

2009-05-30

236

Exchange effects and cidep  

Microsoft Academic Search

Summary  We have presented a review of a number of different electron exchange interactions, which range from rieisenberg spin exchange\\u000a to energy transfer. We have chosen to present most of this material largely from the perspective of esr experiments, but that\\u000a is an arbitrary choice. One could build experiments around energy transfer or nmr experiments (or several other things!) and\\u000a make

William S. Jenks; Nicholas J. Turro

1990-01-01

237

Exchange enrollment, round 2.  

PubMed

Enrollment approaches hospitals plan to undertake during the second open-enrollment period for the insurance exchanges, or marketplaces, include: Deploying mobile units to help eligible consumers sign up for coverage or assistance. Working with insurers to more easily identify patients who received coverage through the exchanges. Clarifying details of coverage with patients who have marketplace coverage. Limiting use of hospital charity care programs among those who qualify for Medicaid or marketplace coverage. PMID:25650475

Daly, Rich

2014-10-01

238

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

239

Deuterium Exchange in the Systems of H2O+/H2O and H3O+/H2O  

NASA Technical Reports Server (NTRS)

Using tandem mass spectrometry various water ion interactions were observed. These reactions consisted of a series of charge transfer, proton transfer, and isotopic exchange steps. The experimental data sets consist of variations of ion abundances over a neutral pressure range. An expected sequence of isotopic exchange reactions is given along with differential equation solutions & reaction rate data.

Anicich, V. G.; Sen, A. D.

1995-01-01

240

Measuring hydrogen exchange rates in invisible protein excited states  

PubMed Central

Hydrogen exchange rates have become a valuable probe for studying the relationship between dynamics and structure and for dissecting the mechanism by which proteins fold to their native conformation. Typically measured rates correspond to averages over all protein states from which hydrogen exchange can occur. Here we describe a new NMR experiment based on chemical exchange saturation transfer that provides an avenue for obtaining uncontaminated, per-residue amide hydrogen exchange rates for interconverting native and invisible states so long as they can be separated on the basis of distinct 15N chemical shifts. The approach is applied to the folding reaction of the Fyn SH3 domain that exchanges between a highly populated, NMR-visible native state and a conformationally excited, NMR-invisible state, corresponding to the unfolded ensemble. Excellent agreement between experimentally derived hydrogen exchange rates of the excited state at a pair of pHs is obtained, taking into account the expected dependence of exchange on pH. Extracted rates for the unfolded ensemble have been used to test hydrogen exchange predictions based on the primary protein sequence that are used in many analyses of solvent exchange rates, with a Pearson correlation coefficient of 0.84 obtained. PMID:24889628

Long, Dong; Bouvignies, Guillaume; Kay, Lewis E.

2014-01-01

241

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

242

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

243

Heat exchange device  

SciTech Connect

A heat exchange device is adapted to recover heat from the fire box of a wood burning stove or the like for heating ambient air in a room or other enclosed space. The heat exchange device is adapted to mount in a recess in a stove top in place of a lid which is normally supplied with the stove. The device according to the invention includes heat exchange means which extend into the fire box of the stove below the top surface thereof. The heat from the heat exchange device is transmitted into a main cavity of the device where the heat is transferred to air forced through the main cavity by a blower mounted to an outside surface of the device. Air exit means are provided on a surface opposite to the surface on which the blower is mounted to provide a passage for heated air into the room or other enclosed space to be heated. The device may also include a top mounted isolated handle for ease in handling the device such as for moving from one area to another. In a second embodiment of the device, a high temperature heat exchange glass plate is mounted on the surface of the device which is in contact with the fire box. Heat is transmitted by heat exchange plate to the main cavity of the device where the air is heated and blown into the room as above.

Callison, G.

1984-01-17

244

Heat exchanger for fuel cell power plant reformer  

DOEpatents

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

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

1988-01-01

245

Microscopic Theory of Cation Exchange in CdSe Nanocrystals  

NASA Astrophysics Data System (ADS)

Although poorly understood, cation-exchange reactions are increasingly used to dope or transform colloidal semiconductor nanocrystals (quantum dots). We use density-functional theory and kinetic Monte Carlo simulations to develop a microscopic theory that explains structural, optical, and electronic changes observed experimentally in Ag-cation-exchanged CdSe nanocrystals. We find that Coulomb interactions, both between ionized impurities and with the polarized nanocrystal surface, play a key role in cation exchange. Our theory also resolves several experimental puzzles related to photoluminescence and electrical behavior in CdSe nanocrystals doped with Ag.

Ott, Florian D.; Spiegel, Leo L.; Norris, David J.; Erwin, Steven C.

2014-10-01

246

Determination of the cation-exchange capacity of muscovite mica  

SciTech Connect

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

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

2000-04-01

247

RecA as a Motor Protein TESTING MODELS FOR THE ROLE OF ATP HYDROLYSIS IN DNA STRAND EXCHANGE*  

E-print Network

RecA as a Motor Protein TESTING MODELS FOR THE ROLE OF ATP HYDROLYSIS IN DNA STRAND EXCHANGE, Madison, Wisconsin 53706 ATP hydrolysis (by RecA protein) fundamentally al- ters the properties of RecA protein-mediated DNA strand exchange reactions. ATP hydrolysis renders DNA strand exchange unidirectional

Cox, Michael M.

248

PROTEINS Structure, Function, and Genetics 17:87-92 (1993) Isotope Effects in Peptide Group Hydrogen Exchange  

E-print Network

Hydrogen Exchange Gregory P.Connelly, Yawen Bai, Mei-Fen Jeng, and S. Walter Englander The Johnson Research 29104-6059 ABSTRACT Kinetic and equilibrium iso- tope effects in peptide group hydrogen ex- change reactions were evaluated. Unlike many other reactions,kinetic isotope effects in amide hydrogen exchange

Englander, S. Walter

249

Controlling chemical reactions of a single particle  

NASA Astrophysics Data System (ADS)

Traditionally, chemical reactions have been investigated by tuning thermodynamic parameters, such as temperature or pressure. More recently, laser or magnetic field control methods have emerged to provide new experimental possibilities, in particular in the realm of cold collisions. The control of reaction pathways is also a critical component to implement molecular quantum information processing. For these studies, single particles provide a clean and well-controlled experimental system. Here, we report on the experimental tuning of the exchange reaction rates of a single trapped ion with ultracold neutral atoms by exerting control over both their quantum states. We observe the influence of the hyperfine interaction on chemical reaction rates and branching ratios, and monitor the kinematics of the reaction products. These investigations advance chemistry with single trapped particles towards achieving quantum-limited control of chemical reactions and indicate limits for buffer-gas cooling of single-ion clocks.

Ratschbacher, Lothar; Zipkes, Christoph; Sias, Carlo; Köhl, Michael

2012-09-01

250

Oxygen diffusion and reactions in Hf-based dielectrics L. V. Goncharova,a  

E-print Network

Oxygen diffusion and reactions in Hf-based dielectrics L. V. Goncharova,a M. Dalponte, D. G Oxygen transport in and reactions with thin hafnium oxide and hafnium silicate films have been. The exchange rate is faster for pure hafnium oxides than for silicates. The amount of exchanged oxygen

Gustafsson, Torgny

251

Fluid exchange flows  

NASA Astrophysics Data System (ADS)

Flow flows from one container to another play important roles in many natural and industrial situations. The talk will describe the latest work on some of these. 1. The exchange flow of relatively dense, viscous fluid in a container connected by a vertical pipe to a container beneath it, initially full of relatively light fluid, will be discussed. This mimics the important exchange flow between a volcanic crater and a deep magma reservoir. A quantitative analysis of the flow will be presented. For the volcanic situation this allows the conduit radius to be evaluated from observations of the sulphur dioxide flux from the crater to the atmosphere. 2. A closed container initially full of liquid, which can drain into the atmosphere through a very long tube, displays different phenomena, which are associated with the compressibility of the air that exchanges space with the liquid. Three distinct regimes are observed, which we term: `popping'; `glugging'; and `slugging'. During each of these the container drains at a quite different rate. 3. Hot air in a house can be exchanged through doors and windows with the cooler air outside. The form and rate of exchange and its dependence on window geometry is of considerable architectural interest at the moment, if only to make our working environment as green as possible. New experiments and the associated concepts for this problem will be discussed.

Huppert, Herbert

2006-11-01

252

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

253

The formate-pyruvate exchange reaction by Streptococcus faecalis  

E-print Network

, Ii Q. Kalckaf . 'i ?. '~'. , 1947 Dlffersiltisl spectrophotometry of purine co~- pounds by nisans of !ilpe. Iflc sn 'ycis, j. Biol, beni. i . '. 67q 461-475. yAinirsky, G. and ". 'erkvwn, C. II. 1943 'Inc anaerobic dissimilation of pyruvats...

Yeager, Robert Lee

1960-01-01

254

Search for R-parity breaking sneutrino exchange at LEP  

Microsoft Academic Search

We report on a search for R-parity breaking effects due to supersymmetric tau-sneutrino exchange in the reactions e+e? ? e+e? and e+e? ? ?+?? at centre-of-mass energies from 91 GeV to 172 GeV, using the L3 detector at LEP. No evidence for deviations from the Standard Model expectations of the measured cross sections and forward-backward asymmetries for these reactions is

M. Acciarri; O Adriani; M. Aguilar-Benitez; S P Ahlen; J Alcaraz; G. Alemanni; James V Allaby; A Aloisio; G. Alverson; M. G. Alviggi; G. Ambrosi; H Anderhub; V. P Andreev; T Angelescu; F Anselmo; A Arefiev; T Azemoon; T Aziz; P Bagnaia; L Baksay; S Banerjee; K Banicz; A Barczyk; R Barillère; L Barone; P Bartalini; A Baschirotto; M Basile; R Battiston; A Bay; F Becattini; U Becker; F Behner; J Berdugo; P Berges; B Bertucci; B. L Betev; S Bhattacharya; M Biasini; A Biland; G. M Bilei; J. J Blaising; S. C Blyth; Gerjan J Bobbink; R K Böck; A Böhm; L Boldizsar; B Borgia; D Bourilkov; Maurice Bourquin; S Braccini; J. G Branson; V Brigljevic; I. C Brock; A Buffini; A Buijs; J. D Burger; W. J Burger; J K Busenitz; A M Button; X. D Cai; M Campanelli; M Capell; G Cara Romeo; G Carlino; A. M Cartacci; J Casaus; G Castellini; F Cavallari; N Cavallo; C Cecchi; M Cerrada-Canales; F Cesaroni; M Chamizo-Llatas; Y. H Chang; U. K Chaturvedi; S. V Chekanov; M Chemarin; A Chen; G Chen; H. F Chen; H. S Chen; X J Chéreau; G Chiefari; C. Y Chien; Luisa Cifarelli; F Cindolo; C Civinini; I Clare; R Clare; H. O Cohn; G Coignet; A. P Colijn; N Colino; V Commichau; S Costantini; F Cotorobai; B de la Cruz; Akos Csilling; T. S Dai; R D'Alessandro; R de Asmundis; A Degré; K Deiters; D della Volpe; P Denes; F DeNotaristefani; Daryl DiBitonto; M Diemoz; D N Van Dierendonck; F Di Lodovico; C Dionisi; Michael Dittmar; A Dominguez; A Doria; M. T Dova; D Duchesneau; P Duinker; I Duran; S Dutta; S Easo; Yu V Efremenko; H El Mamouni; A Engler; F. J Eppling; F. C Erné; J. P Ernenwein; Pierre Extermann; M Fabre; R Faccini; S Falciano; A Favara; J Fay; O Fedin; Marta Felcini; B Fenyi; T Ferguson; F Ferroni; H S Fesefeldt; E Fiandrini; J. H Field; Frank Filthaut; P. H Fisher; I Fish; G Forconi; L Fredj; Klaus Freudenreich; C Furetta; Yu Galaktionov; S. N Ganguli; P Garcia-Abia; S. S Gau; S Gentile; N Gheordanescu; S Giagu; S Goldfarb; J Goldstein; Z. F Gong; Andreas Gougas; Giorgio Gratta; M. W Gruenewald; V. K Gupta; A Gurtu; L. J Gutay; B Hartmann; A Hasan; D Hatzifotiadou; T Hebbeker; A Hervé; W. C van Hoek; H Hofer; S. J Hong; H Hoorani; S. R Hou; G Hu; Vincenzo Innocente; K Jenkes; B. N Jin; L. W Jones; P de Jong; I Josa-Mutuberria; A Kasser; R. A Khan; D Kamrad; Yu A Kamyshkov; J. S Kapustinsky; Yu Karyotakis; M Kaur; M. N Kienzle-Focacci; D Kim; J. K Kim; S. C Kim; Y. G Kim; W. W Kinnison; A Kirkby; D Kirkby; Jasper Kirkby; D Kiss; W Kittel; A Klimentov; A. C König; A Kopp; I Korolko; V F Koutsenko; R. W Kraemer; W Krenz; A Kunin; P Ladron de Guevara; I Laktineh; G Landi; C Lapoint; K M Lassila-Perini; P Laurikainen; M Lebeau; A Lebedev; P Lebrun; P Lecomte; P Lecoq; P Le Coultre; H. J Lee; J. M Le Goff; R Leiste; E Leonardi; P Levtchenko; Li Chuan; C. H Lin; W. T Lin; Frank L Linde; L Lista; Z. A Liu; W Lohmann; E Longo; W Lu; Y. S Lu; K Lübelsmeyer; C Luci; D Luckey; L Luminari; W Lustermann; W. G Ma; M Maity; G Majumder; L Malgeri; A Malinin; C Maña; D J J Mangeol; S Mangla; P A Marchesini; A Marin; J. P Martin; F Marzano; G. G. G Massaro; D McNally; R. R McNeil; S Mele; L Merola; M Meschini; W. J Metzger; M von der Mey; Y Mi; A Mihul; A. J. W van Mil; H Milcent; G Mirabelli; J Mnich; P Molnar; B Monteleoni; R Moore; S Morganti; T Moulik; R Mount; S Müller; F Muheim; A. J. M Muijs; S Nahn; M Napolitano; F Nessi-Tedaldi; H Newman; T Niessen; A Nippe; A Nisati; H Nowak; Yu D Oh; H Opitz; G Organtini; R Ostonen; C Palomares; D Pandoulas; S Paoletti; P Paolucci; H. K Park; I. H Park; G Pascale; G Passaleva; S Patricelli; T Paul; M Pauluzzi; C Paus; Felicitas Pauss; D Peach; Y. J Pei; S Pensotti; D Perret-Gallix; B Petersen; S Petrak; A Pevsner; D Piccolo; M Pieri; P. A Piroué; E Pistolesi; V Plyaskin; M Pohl; V Pozhidaev; H Postema; N Produit; D Prokofiev; G Rahal-Callot; N Raja; P. G Rancoita; M Rattaggi; P Razis; K Read; D Ren; M Rescigno; S Reucroft; T van Rhee; S Riemann; K Riles; A Robohm; J Rodin; B. P Roe; L Romero; S Rosier-Lees; Ph Rosselet; W van Rossum; S Roth; J. A Rubio; D Ruschmeier; H Rykaczewski; J Salicio; E Sanchez; M. P Sanders; M. E Sarakinos; S Sarkar; M Sassowsky; C Schäfer; V Schegelsky; S Schmidt-Kaerst; D Schmitz; P Schmitz; N Scholz; H Schopper; D. J Schotanus; J Schwenke; G Schwering; C Sciacca; D Sciarrino; L Servoli; S Shevchenko; N Shivarov; V Shoutko; J Shukla; E Shumilov; A Shvorob; T Siedenburg; D Son; A Sopczak; B Smith; P Spillantini; M Steuer; D. P Stickland; A Stone; H Stone; B Stoyanov; A Straessner; K Strauch; K Sudhakar; G Sultanov; L. Z Sun; G. F Susinno; H Suter; J. D Swain; X. W Tang; L Tauscher; L Taylor; Samuel C. C Ting; S. M Ting; M Tonutti; S. C Tonwar; J Tóth; C Tully; H Tuchscherer; K. L Tung; Y Uchida; J Ulbricht; U Uwer; E Valente; R. T Van de Walle; G Vesztergombi; I Vetlitsky; G Viertel; M Vivargent; R Völkert; H Vogel; H Vogel; I Vorobiev; A. A Vorobyov; A Vorvolakos; M Wadhwa; W Wallraff

1997-01-01

255

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

256

Ion exchange phenomena  

SciTech Connect

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

Bourg, I.C.; Sposito, G.

2011-05-01

257

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.

2011-11-01

258

Polyneutrons as agents for cold nuclear reactions  

SciTech Connect

In this paper new nuclear reactions are described where polyneutrons exchange neutron pairs with charged nuclides, liberating substantial energy with only minor production of neutrons and tritium. It is postulated that polyneutrons are bound in a totally paired collective phase analogous to the Bardeen-Cooper-Schrieffer superconducting phase, that massive precursor hydrogen nuclides are bound in the same collective phase, and the polyneutrons are generated from precursor hydrogen by reaction with neutrons. The concentration and disposition of precursor hydrogen, of lithium, and of neutron-moderating and neutron-absorbing materials in the reactor environment emerge as key variables in cold nuclear reaction processes.

Fisher, J.C. (Thomas Paine Associates, Carpinteria, CA (United States))

1992-12-01

259

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

260

Reactions of alkenes on lanthana  

SciTech Connect

Reactions of ethene, propene, butenes, 2-methylpropene, cyclopentene, 2,3-dimethylbut-1-ene, and 3,3-dimethylbut-1-ene have been studied with hydrogen, and sometimes deuterium, on lanthana catalysts. Many alkene/lanthana systems show evidence of self-poisoning which is more marked with straight-chain hydrocarbons than with branched hydrocarbons and at higher temperatures; the catalysts are also highly sensitive to impurities. The temperature required to attain a fixed rate of hydrogenation (10/sup 16/ molecules s/sup -1/ m/sup -2/) varied from 220 K for ethene to over 373 K for the 2,3-dimethylbutenes. Fast hydrogenation without accompanying deuterium exchange was observed with alkenes which cannot form allylic species. The ability to form such species led to rapid isomerization of the butenes below 273 K and of 2-3-dimethylbut-1-ene at 373 K, and to exchange rates with deuterium which were comparable to (propene) or faster than (2-methylpropene) addition reactions at 380 K. Deuterium NMR spectroscopy was used for analysis of the products from the reactions with deuterium. Although the hydrogenation of 3,3-dimethylbut-1-ene occurred readily at 245 K, no isomerization was detected even at 510 K.

Bird, R.; Kemball, C.; Leach, H.F.

1987-05-01

261

Metal implants and surface reactions.  

PubMed

A metal in living tissue is prone to corrosion. The interaction of the foreign body with the tissue involves the redox reaction (an electron exchange) at the interface, the hydrolysis (a proton exchange) of oxide-hydrates as products of corrosion, and the formation of metal-organic complexes in the electrolyte. Denatured tissue in contact with the foreign body is the consequence. But behaviour of metals is variable; gold, stainless steel and most other metals react as described while few others like titanium and tantalum do not. The absence of a foreign body effect of a chemical kind is, without doubt, favorable in terms of tissue susceptibility to infection in the presence of titanium. PMID:9039349

Steinemann, S G

1996-01-01

262

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. Mössbauer 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

263

Zeolite an efficient catalyst for the Biginelli condensation reaction  

Microsoft Academic Search

A zeolite catalyzed, single step and environmentally friendly process for synthesis of classical Biginelli reaction was investigated.\\u000a For this reaction Transition metal\\/Y zeolites were prepared by microwave solid-state and aqueous solution ion-exchange methods.\\u000a The yield of reactions was increased in order of CuY > CoY > NiY > MnY ? FeY > VY > CrY > ZnY for the solid-state zeolite\\u000a ion-exchange and CuY > CoY > NiY > MnY > CrY > VY > ZnY > FeY for the aqueous solution ion-exchange. The solid-state ion-exchange\\u000a zeolite by

Mojgan Zendehdel; A. Mobinikhaledi; A. Asgari

2008-01-01

264

Is the simplest chemical reaction really so simple?  

PubMed Central

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

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

2014-01-01

265

J/psi absorption by nucleons in the meson-exchange model  

E-print Network

We reinvestigate the J/Psi dissociation processes induced by the reactions with nucleons, J/Psi + N -> D-(*) + Lambda(c), in the meson- exchange model. Main constraints used in this work are vector- meson dominance and charm vector...

Oh, Yongseok; Liu, Wei; Ko, Che Ming.

2007-01-01

266

Poincare invariant exchange model of pion-nucleon scattering Yasser Elmessiri and Michael G. Fuda  

E-print Network

Poincare´ invariant exchange model of pion-nucleon scattering Yasser Elmessiri and Michael G. Fuda, and the reaction N~ N. Fuda and Zhang have developed a variation of this ap- proach, in which an effective mass

Fuda, Michael G.

267

Higher Education Exchange 2006  

ERIC Educational Resources Information Center

Contributors to this issue of the Higher Education Exchange debate the issues around knowledge production, discuss the acquisition of deliberative skills for democracy, and examine how higher education prepares, or does not prepare, students for citizenship roles. Articles include: (1) "Foreword" (Deborah Witte); (2) "Knowledge, Judgment and…

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

2006-01-01

268

Dublin, Ireland Exchange Program  

E-print Network

Dublin, Ireland Exchange Program Dublin Institute of Technology Dublin, the capital of Ireland, culture, and hip shops. Dublin is vibrant, cosmopolitan and is a truly captivating city. The city of Dublin is surrounded by unspoiled countryside with authentic rural life, breathtaking scenery

Fernandez, Eduardo

269

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

270

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

271

The Creative Learning Exchange  

NSDL National Science Digital Library

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

The Creative Learning Exchange

272

Ion Exchange Membrane Processes  

SciTech Connect

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

Wallace, R.M.

2002-10-30

273

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

274

Visiting Scholar Exchange Reports.  

ERIC Educational Resources Information Center

Provides reports of four United States scholars who visited China as part of the Visiting Scholar Exchange Program. The titles of the reports are (1) "China Journey: A Political Scientist's Look at Yan'an," (2) "The Social Consequences of Land Reclamation in Chinese Coastal Ecosystems," (3) "Anthropology Lectures in South China," and (4) "The Use…

Rubin, Kyna, Ed.

1986-01-01

275

Higher Education Exchange, 2009  

ERIC Educational Resources Information Center

This volume begins with an essay by Noelle McAfee, a contributor who is familiar to readers of Higher Education Exchange (HEX). She reiterates Kettering's president David Mathews' argument regarding the disconnect between higher education's sense of engagement and the public's sense of engagement, and suggests a way around the epistemological…

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

2009-01-01

276

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.

277

Exchange Programs 2011 International  

E-print Network

of California. Longitudinally, Korea lies straight north of the Philippines and central Australia. The meridianExchange Programs 2011 International CHUNG-ANG UNIVERSITY,KOREA #12;CONTENTS 5 Introduction, Chung-Ang University of Korea is running through ceaseless changes to be a global leader in education

Petriu, Emil M.

278

Currency Exchange Rates.  

ERIC Educational Resources Information Center

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

Siler, Carl R.

279

A corrosive resistant heat exchanger  

DOEpatents

A corrosive and erosive resistant heat exchanger which recovers heat from a contaminated heat stream. The heat exchanger utilizes a boundary layer of innocuous gas, which is continuously replenished, to protect the heat exchanger surface from the hot contaminated gas. The innocuous gas is pumped through ducts or perforations in the heat exchanger wall. Heat from the heat stream is transferred by radiation to the heat exchanger wall. Heat is removed from the outer heat exchanger wall by a heat recovery medium. 3 figs., 3 tabs.

Richlen, S.L.

1987-08-10

280

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

281

Carbon monoxide poisoning of proton-exchange membrane fuel cells  

Microsoft Academic Search

The platinum-alloy catalyst used in proton-exchange membrane (PEM) fuel cell anodes is highly susceptible to carbon monoxide (CO) poisoning. CO reduces the catalyst activity by blocking active catalyst sites normally available for hydrogen chemisorption and dissociation. The reaction kinetics at the anode catalyst surface can be used to estimate the decrease in cell voltage due to various levels of CO

Aida Rodrigues; John C. Amphlett; Ronald F. Mann; Brant A. Peppley; Pierre R. Roberge

1997-01-01

282

PREPARATION AND UTILIZATION OF CARBOXYL-CONTAINING CATION EXCHANGE CELLULOSE  

Microsoft Academic Search

A cation-exchange resin was synthesized by esterification of cellulose fibers, with ?-hydroxy polycarboxylic acids (citric acid (CA), malic acid, or tartaric acid) in presence of sodium hypophosphite (SHP) as an esterification catalyst, followed by curing at high temperature. Factors affecting the reaction such as CA concentration, CA\\/SHP molar ratio, curing conditions (temperature and time), type of polycarboxylic acid, and type

M. H. Abo-Shosha; N. A. Ibrahim; E. I. Elnagdy; M. A. Gaffar

2002-01-01

283

ION-EXCHANGE PROCESSES AND MECHANISMS IN GLASSES  

EPA Science Inventory

Recent performance assessment calculations of a disposal system at Hanford, Washington for low activity waste glass show that a Na ion-exchange reaction can effectively increase the radionuclide release rate by over a factor of 1000 and so is a major factor that currently limits ...

284

Counterflow Regolith Heat Exchanger  

NASA Technical Reports Server (NTRS)

A problem exists in reducing the total heating power required to extract oxygen from lunar regolith. All such processes require heating a great deal of soil, and the heat energy is wasted if it cannot be recycled from processed material back into new material. The counterflow regolith heat exchanger (CoRHE) is a device that transfers heat from hot regolith to cold regolith. The CoRHE is essentially a tube-in-tube heat exchanger with internal and external augers attached to the inner rotating tube to move the regolith. Hot regolith in the outer tube is moved in one direction by a right-hand - ed auger, and the cool regolith in the inner tube is moved in the opposite direction by a left-handed auger attached to the inside of the rotating tube. In this counterflow arrangement, a large fraction of the heat from the expended regolith is transferred to the new regolith. The spent regolith leaves the heat exchanger close to the temperature of the cold new regolith, and the new regolith is pre-heated close to the initial temperature of the spent regolith. Using the CoRHE can reduce the heating requirement of a lunar ISRU system by 80%, reducing the total power consumption by a factor of two. The unique feature of this system is that it allows for counterflow heat exchange to occur between solids, instead of liquids or gases, as is commonly done. In addition, in variants of this concept, the hydrogen reduction can be made to occur within the counterflow heat exchanger itself, enabling a simplified lunar ISRU (in situ resource utilization) system with excellent energy economy and continuous nonbatch mode operation.

Zubrin, Robert; Jonscher, Peter

2013-01-01

285

Hydrogen exchange studies of protein structure Tanya M Raschke and Susan Marqusee*  

E-print Network

80 Hydrogen exchange studies of protein structure Tanya M Raschke and Susan Marqusee* Hydrogen partially folded ensembles present at equilibrium. Analysis of hydrogen exchange mechanisms has revealed intrinsicexchangerate kobs observedexchangerate NH amide hydrogen AGHx free energy of the opening reaction Introduction

Raschke, Tanya M.

286

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

287

Oxygen isotopic exchange: A useful tool for characterizing oxygen conducting oxides  

E-print Network

Oxygen isotopic exchange: A useful tool for characterizing oxygen conducting oxides Bassat J we obtain in both cases data concerning the oxygen diffusion in the bulk and the oxygen exchange with regards to the oxygen reduction reaction. Detailed experimental and analytical processes are given

Paris-Sud XI, Université de

288

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

289

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

290

Softhard exchange-coupled layered structures with modulated exchange coupling  

E-print Network

, Tuscaloosa, Alabama 35487-0209 Received 8 April 2003; accepted 28 June 2003 Magnetically soft/hard exchange mag- netization of the soft phase can be combined in an exchange- spring magnet due to strong exchange coupling between the two phases. In this way the composite magnet can show a hysteresis loop like a single

Garmestani, Hamid

291

Clearing Algorithms for Barter Exchange Markets: Enabling Nationwide Kidney Exchanges  

E-print Network

Clearing Algorithms for Barter Exchange Markets: Enabling Nationwide Kidney Exchanges David J national kidney-exchange mar- ket, where patients with kidney disease can obtain compat- ible donors kidney in the US, this market is seen as the only ethical way to significantly reduce the 4,000 deaths

Blum, Avrim

292

WMS International Exchange Scholarships WMS International Exchange Scholarships Regulations  

E-print Network

WMS International Exchange Scholarships WMS International Exchange Scholarships Regulations I N T R O D U C T I O N These scholarships have been established to enhance awareness and foster interest in exchange programmes offered by the University of Waikato. The scholarships are offered: To encourage

Waikato, University of

293

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

294

Ecosystem Restoration through Interdisciplinary Exchange  

E-print Network

Ecosystem Restoration through Interdisciplinary Exchange David M. Blersch dblersch Shade of Blue and You 21 September 2010 #12;National Science Foundation Ecosystem Restoration through;National Science Foundation Ecosystem Restoration through Interdisciplinary Exchange UB's ERIE Program www

Sachs, Frederick

295

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

296

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

297

Advanced Chemical Heat Pumps Using Liquid-Vapor Reactions  

E-print Network

ADVANCED CHEMICAL HEAT PUMPS USING LIQUID-VAPOR REACTIONS LANCE KIROL Senior Program Specialist Idaho National Engineering Laboratory Idaho Falls, Idaho . ABSTRACT Chemical heat pumps utilizing liquid-vapor reactions can be configured... characteristics. A waste heat driven heat pump (temperature amplifier) using liquid-vapor chem1cal reactions- can oper ate with higher coefficient of performance and smaller heat exchangers than an absorption temp erature amplifying heat pump. Higher tempera...

Kirol, L.

298

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, H.P., Jr.

1987-01-01

299

DNA Strand Exchange and RecA Homologs in Meiosis.  

PubMed

Homology search and DNA strand-exchange reactions are central to homologous recombination in meiosis. During meiosis, these processes are regulated such that the probability of choosing a homolog chromatid as recombination partner is enhanced relative to that of choosing a sister chromatid. This regulatory process occurs as homologous chromosomes pair in preparation for assembly of the synaptonemal complex. Two strand-exchange proteins, Rad51 and Dmc1, cooperate in regulated homology search and strand exchange in most organisms. Here, we summarize studies on the properties of these two proteins and their accessory factors. In addition, we review current models for the assembly of meiotic strand-exchange complexes and the possible mechanisms through which the interhomolog bias of recombination partner choice is achieved. PMID:25475089

Brown, M Scott; Bishop, Douglas K

2014-12-01

300

Exchange Rates and Financial Fragility  

Microsoft Academic Search

In this paper we analyze three views of the relationship between the exchange rate and financial fragility: (1) the moral hazard hypothesis, according to which pegged exchange rates offer implicit insurance against exchange risk and thereby encourage reckless borrowing and lending; (2) the original sin hypothesis, which emphasizes an incompleteness in financial markets which prevents the domestic currency from being

Barry Eichengreen; Ricardo Hausmann

1999-01-01

301

COMPACT EXCHANGERS FOR PHASE CHANGE  

Microsoft Academic Search

Compact heat exchangers are being increasingly considered for duties involving phase change processes of boiling and condensation. In many cases such applications are completely new and no previous experience or information on exchanger performance is available. Understanding the thermal-hydraulic characteristics of flow passages of compact heat exchangers for phase change duties is therefore vitally important. Even for those compact heat

Vishwas V. Wadekar

302

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...

303

Diverse secondary interactions between ions exchanged into the resin phase and their analytical applications.  

PubMed

The research activities by the author's group to elucidate the chemical states of ions within the ion exchange resin phase are summarized. The resin with the higher exchange capacity has the smaller space available for ion exchange, and the higher cross linking degree interferes more with swelling of the resin. As a result, diverse secondary interactions between exchanged ions are observed on the resins of high exchange capacities and high cross linking degrees: the van der Waals contact results in incomplete exchange or enhanced dehydration of ions, hydrogen bond formation between acidic anions, and coadsorption of anions with metal ions. Contribution of the simple ion exchange mechanism to the reactions of iminodiactate-type chelating resins with metal ions in the acidic media is quantitatively discussed. The resulting complexes were successfully applied to preconcentration and separation of anions. PMID:24420244

Yuchi, Akio

2014-01-01

304

Origins of Linear Partitioning in Binary Solutions: the Exchange Coefficient  

NASA Astrophysics Data System (ADS)

Linear partitioning occurs when, as often in petrologic systems and perhaps always in azeotropes, a straight- line relationship occurs when the partition coefficient D = X1S/X1L is plotted against the solid composition X2S and runs from an intercept value KD at pure (2) to 1.0 at pure (1). The equation is then D = KD*X2S + X1S (Morse 1997, JGeol 105:471; 2000 GCA, 64:2309). The notation KD was taken from its long-standing familiarity in binary solutions (Roeder & Emslie 1970, CMP 29:275) and described as the exchange coefficient (Beattie et al. 1993 GCA 57:1605). But the binary loop is not in itself an exchange equilibrium; it is a transfer equilibrium marching to a different drummer, and that causes a problem (Kretz 2005, CanMin 43:1349). In at least three ways, the binary loop qualifies as an exchange reaction and justifies calling the intercept KD. To the experimentalist this issue never arises. In a perfect liquidus experiment, an infinitesimal mass of liquid is indeed transferred to the crystal. A second bulk composition is then made, and at the new liquidus a second mass transfer occurs. The ensemble of all such perfect partitioning experiments in sufficient number then completely delineates the binary loop without any continuous transfer at changing T having taken place. The partitionings are therefore truly independent of the path. Moreover, each equilibrium pair defines a common tangent in G-X space whose intercept at pure (2) unarguably gives the value of the common chemical potential, a partial Gibbs energy. But where is the exchange reaction? The real experimentalist makes no perfect experiments, and neither does nature. In reality, the barrier to nucleation (particularly formidable in the case of plagioclase) dictates that the crystals nucleate only at some supercooling. They therefore have some composition between the initial solidus and the liquid lying at the bulk composition (BC). Over time the two phases may drift apart by diffusion, the crystal going to the solidus and the liquid going to the liquidus, with evolution of latent heat and a gain in T. The parting of the two compositions is a true exchange reaction, revealed by kinetics. An isothermal exchange reaction occurs in the petrologically important adcumulus growth (Wager et al. 1960, JPet. 1:73; Walker et al. 1985, EOS 66:362). In this process, a porous cumulate becomes solidified by the expulsion of low-melting components in the pore liquid to an infinite reservoir (the main magma) with the concomitant return of refractory components to the crystals, a perfect open-system exchange process involving the complete transit of the local bulk composition from that of the liquid to that of the crystals. Ideally, the exchange operates on a constant G-X tangent and constant chemical potential with constant D and T but with extraction of latent heat to the surroundings. Here again the Gibbs function is described by KD. In metamorphic systems, for a bulk composition between biotite and garnet in the AFM projection, the two phases are in true Fe-Mg exchange as a function of T, following the usual association of KD with T. But when the BC encounters the 3-phase triangle Bi-Gt-Sill, the reaction becomes a transfer reaction, still, however, responding to the linear partitioning principle (Morse 2000). Here the transfer reaction is a limiting case of an exchange reaction. In linear partitioning, the exchange coefficient is a constant anchor for all T, and only D tracks the temperature. The big surprise, of course, is that KD is, in this limiting case, an isothermal function, with consequences explored elsewhere (Morse, 2000).

Morse, S. A.

2006-05-01

305

Solar heat exchanger  

SciTech Connect

A solar heat exchanger comprising a frame having an inner surface area defined by upstanding walls, ends and bottom wherein an insulation layer of relatively uniform thickness is spread throughout the inner surface. A plurality of channels are spaced throughout the frame. The channels may be arranged in a serpentine or manifold design and may comprise an outer curved wall and an inner curved wall wherein water flows through the inner and outer curved wall and spaced between the inner and outer curved wall in a restricted manner. Additionally, the frame may include a top insulation layer comprising generally parallel panels spanning the frame and creating a greenhouse effect upon the channels. Inlet and outlet means are provided within the frame to allow cooler water to enter the exchanger and warmer water to exit.

Kitzmiller, G.

1982-08-31

306

Intergranular exchange coupling  

NASA Astrophysics Data System (ADS)

We evaluate the exchange interaction between neighboring grains of a polycrystalline magnetic material with uniaxial magnetocrystalline anisotropy, based on the energy of the domain wall formed at the portion of the interface in atomic contact. The analysis suggests that previous work [J.-G. Zhu and H. N. Bertram, in Solid State Physics Vol. 46, edited by H. Ehrenreich and T. Turnbull (Academic, San Diego, 1992)] may underestimate the interaction, and it predicts a different dependence on grain size.

Muller, M. W.; Indeck, R. S.

1994-02-01

307

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

308

Emittance and Phase Space Exchange  

SciTech Connect

Alternative chicane-type beam lines are proposed for exact emittance exchange between horizontal phase space (x; x{prime}) and longitudinal phase space (z; {delta}). Methods to achieve exact phase space exchanges, i.e. mapping x to z, x{prime} to {delta}, z to x and {delta} to x{prime} are suggested. Methods to mitigate the thick-lens effect of the transverse cavity on emittance exchange are discussed. Some applications of the phase space exchanger and the feasibility of an emittance exchange experiment with the proposed chicane-type beam line at SLAC are discussed.

Xiang, Dao; Chao, Alex; /SLAC

2011-08-19

309

Chem 115Lithium-Halogen ExchangeMyers RLi + R'X RX + R'Li  

E-print Network

Chem 115Lithium-Halogen ExchangeMyers RLi + R'X RX + R'Li Lithium-halogen exchange reactions are essentially inert. 2 t-BuLi t-BuI + RLi t-BuLi isobutene + isobutane + LiI Lithium-halogen exchange reactions, and lithium iodide. H OEtBr H H OEtLi H1.1 eq n-BuLi Et2O, !80 °C Lau, K. S.; Schlosser, M. J. Org. Chem. 1978

310

Performance simulation of a wall-type reactor in which exothermic and endothermic reactions proceed simultaneously, comparing with that of a fixed-bed reactor  

Microsoft Academic Search

By combining endothermic and exothermic reactions in one reactor, a mutual utilization of thermal energy involved in reactions is expected to produce a saving energy and a cost-down for running in industrial reaction process. In this case, a wall-type reaction system is thought to be suitable because such reaction system is good at exchangeability of thermal energy by conductive heat

Choji Fukuhara; Akira Igarashi

2005-01-01

311

Selective Facet Reactivity During Cation Exchange in Cadmium Sulfide Nanorods  

SciTech Connect

The partial transformation of ionic nanocrystals through cation exchange has been used to synthesize nanocrystal heterostructures. We demonstrate that the selectivity for cation exchange to take place at different facets of the nanocrystal plays an important role in determining the resulting morphology of the binary heterostructure. In the case of copper I (Cu+) cation exchange in cadmium sulfide (CdS) nanorods, the reaction starts preferentially at the ends of the nanorods such that copper sulfide (Cu2S) grows inwards from either end. The resulting morphology is very different from the striped pattern obtained in our previous studies of silver I (Ag+) exchange in CdS nanorods where non-selective nucleation of silver sulfide (Ag2S) occurs. From interface formation energies calculated for several models of epitaxialconnections between CdS and Cu2S or Ag2S, we infer the relative stability of each interface during the nucleation and growth of Cu2S or Ag2S within the CdS nanorods. The epitaxial connections of Cu2S to the end facets of CdS nanorods minimize the formation energy, making these interfaces stable throughout the exchange reaction. However, as the two end facets of wurtzite CdS nanorods are crystallographically nonequivalent, asymmetric heterostructures can be produced.

Sadtler, Bryce; Demchenko, Denis; Zheng, Haimei; Hughes, Steven; Merkle, Maxwell; Dahmen, Ulrich; Wang, Lin-Wang; Alivisatos, A. Paul

2008-12-18

312

0022-3530/90 $3.00 Reaction Between Ultramafic Rock and Fractionating  

E-print Network

reaction between peridotite and fractionating tholeiitic basalt in simple and complex silicate systems, the result of reactions between 'basalt' and 'peridotite' may be treated as a combination of Fe-Mg exchange with peridotite, and crystal products of such reactions will be dunite. Liquids saturated in clinopyroxene

313

Nuclear Physics A 587 (1995) 787-801 (3He,t) reactions on unstable nuclei  

E-print Network

ELSEVIER NUCLEAR PHYSICS A Nuclear Physics A 587 (1995) 787-801 (3He,t) reactions on unstable,t) reactions on unstable nuclei theoretically. Since this charge-exchange reaction takes place on the nuclear in nuclear physics since we got a new tool, "beams of unstable nuclei" [1,2]. Many experimentalists have

Fernández de Córdoba, Pedro

314

Surface diffusion upon oxygen isotopic exchange on oxide-supported metal nanoclusters  

Microsoft Academic Search

A newly developed real-time kinetic model is presented. The model was used for the characterization of supported metal catalysts' properties in the oxygen isotopic exchange reaction. This model is based on rate equations and includes several elementary processes: adsorption on the metal nanoclusters, reactions on the metal nanoclusters, desorption from the metal nanoclusters, surface and bulk diffusion on\\/in the oxide

A Galdikas; C Descorme; D Duprez

2004-01-01

315

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

316

The Gift Exchange Problem  

E-print Network

The aim of this paper is to solve the "gift exchange" problem: you are one of n players, and there are n wrapped gifts on display; when your turn comes, you can either choose any of the remaining wrapped gifts, or you can "steal" a gift from someone who has already unwrapped it, subject to the restriction that no gift can be stolen more than a total of S times. The problem is to determine the number of ways that the game can be played out, for given values of S and n. Several recurrences and explicit formulas are given for these numbers, although some open questions remain.

Applegate, David

2009-01-01

317

6.RP Currency Exchange  

NSDL National Science Digital Library

This is a task from the Illustrative Mathematics website that is one part of a complete illustration of the standard to which it is aligned. Each task has at least one solution and some commentary that addresses important asects of the task and its potential use. Here are the first few lines of the commentary for this task: Joe was planning a business trip to Canada, so he went to the bank to exchange \\$200 U.S. dollars for Canadian (CDN) dollars (at a rate of \\$1.02 CDN p...

318

Spinnability of silica sols: The role of alkoxy group exchange  

SciTech Connect

The exchange and spinnability of several systems with the general form Si(OR){sub 4} (where R = CH{sub 3}, C{sub 2}H{sub 5}) in ethanol, propanol and butanol were investigated. We have followed the alkoxy group exchange, hydrolysis and condensation reactions, and Q distributions of these systems using {sup 29}Si and {sup 17}O NMR. Observed differences in spinnability of the various sol-gel systems are attributed to the effect of the bulkiness of the alkoxy group on its reactivity.

Prabakar, S. [New Mexico Univ., Albuquerque, NM (United States). Center for Micro-Engineered Ceramics; Assink, R.A. [Sandia National Labs., Albuquerque, NM (United States); Irwin, A.D. [Butler Univ., Indianapolis, IN (United States)

1993-12-31

319

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

320

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

321

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

322

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

323

Health Science on Exchange InternationalExchangeProgram  

E-print Network

courses: · Bachelor of Health Science · Bachelor of Applied Science (Exercise and Sports ScienceHealth Science on Exchange InternationalExchangeProgram Students enrolled in Health Sciences) · Bachelor of Applied Science (Exercise and Sports Science) and Master of Nutrition and Dietetics · Bachelor

Viglas, Anastasios

324

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

325

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

326

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

327

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

328

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

329

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

330

New Standards Based Data Exchange \\  

Microsoft Academic Search

ISO\\/STEP Standards are providing international product data exchange models and versioning procedures for the purpose of capturing and sharing more complete enterprise- wide design, analysis and manufacturing data. In particular, the STEP AP209 Standard (presently at Draft International Standard (DIS) status) is focused on the product design and analysis (simulation) disciplines, and provides for data exchanges that include: • design

Keith Hunten; John Klintworth; Narendra Pitre; Tom Mack

331

Flow maldistribution in heat exchangers  

Microsoft Academic Search

Based on the study of gross flow maldistribution in an experimental electrical heater, this paper presents the effect of flow nonuniformity on the performance of heat exchangers. First, it is shown that it is much more important to understand maldistributions for electrical heaters than for two-fluid heat exchangers. The study of the flow distribution in a particular heater shows that

S. Lalot; P. Florent; S. K. Lang; A. E. Bergles

1999-01-01

332

Deniable authentication and key exchange  

Microsoft Academic Search

We extend the denitional work of Dwork, Naor and Sahai from deniable authentication to deniable key-exchange protocols. We then use these denitions to prove the deniability features of SKEME and SIGMA, two natural and ecient protocols which serve as basis for the Internet Key Exchange (IKE) protocol. The two protocols require distinct approaches to their deniability analysis, hence highlighting im-

Mario Di Raimondo; Rosario Gennaro; Hugo Krawczyk

2006-01-01

333

PHOSPHORUS EXCHANGE IN MARINE PHYTOPLANKTON  

E-print Network

PHOSPHORUS EXCHANGE IN MARINE PHYTOPLANKTON BY THEODORE R. RICE FISHERY BULLETIN 80 UNITED STATES;ABSTRACT Phosphorus exchange in Nitzschia· clostai'iu.In, isoiated and grown in pure culture, was demunstrated by using rudioactive phosphorus find was ~h()\\\\"n to "IlI'Y with changes in the phosphorus

334

Mirage of Floating Exchange Rates  

Microsoft Academic Search

This note summarizes some of the highlights of my longer paper with Guillermo Calvo”Fear 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

335

Jamaica's foreign exchange black market  

Microsoft Academic Search

As in many other less developed nations, the imposition of foreign exchange controls promoted the growth of a foreign exchange black market in Jamaica. This article explains the structure and functioning of the market in recent years. Under controls initially imposed in 1954, this market grew to about US$1.7 billion of transaction value per year by 1990. During the 1980s

Robert Grosse

1994-01-01

336

EXCHANGE. Volume 9-92  

SciTech Connect

EXCHANGE is published monthly by the Idaho National Engineering Laboratory (INEL), a multidisciplinary facility operated for the US Department of Energy (DOE). The purpose of EXCHANGE is to inform computer users about about recent changes and innovations in both the mainframe and personal computer environments and how these changes can affect work being performed at DOE facilities.

Boltz, J.C. [ed.] [ed.

1992-09-01

337

Cation exchange: cemical flooding experiments  

Microsoft Academic Search

Mass action equilibria equations provide a good description of cation exchange effects in laboratory floods with solutions containing sodium, calcium, and magnesium cations. These equations can aid in the design of prefloods for surfactant and polymer processes. Cation exchange in the presence of a surfactant system is found to be significantly complicated by interaction between surfactant and divalent cations. The

H. J. Hill; L. W. Lake

1977-01-01

338

Exchange Rates and Old People.  

ERIC Educational Resources Information Center

Extends earlier work on aging as a process of exchange by focusing on the issue of exchange rates and how they are negotiated. Access to power resources declines with age, placing the old person in the position of negotiating from weakness. (Author)

Dowd, James J.

1980-01-01

339

The Glyoxal Clock Reaction  

ERIC Educational Resources Information Center

Research on the glyoxal clock reaction has led to adaptation of the clock reaction to a general chemistry experiment. This particular reaction is just one of many that used formaldehyde in the past. The kinetics of the glyoxal clock makes the reaction suitable as a general chemistry lab using a Calculator Based Laboratory (CBL) or a LabPro. The…

Ealy, Julie B.; Negron, Alexandra Rodriguez; Stephens, Jessica; Stauffer, Rebecca; Furrow, Stanley D.

2007-01-01

340

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

341

Stock Exchange Mergers and Market Efficiency  

E-print Network

EA 4272 Stock Exchange Mergers and Market Efficiency Amélie Charles* Olivier Darné** Jae H. Kim efficiency of the markets. We consider a range of factors in relation to the stock exchange merger, that can markets; large stock exchange mergers ver- sus small stock exchange mergers; and domestic stock exchange

Paris-Sud XI, Université de

342

Hydrogen atom scrambling in ion-molecule reactions of methane and ethylene.  

NASA Technical Reports Server (NTRS)

The extent of hydrogen atom exchange in the reaction, CH3(+) + CH4 yields C2H5(+) + H2, is determined by examining the product distribution for the reactions CH3(+) + CD4 and CD3(+) + CH4 as a function of relative kinetic energy from thermal energies to 10 eV. It is found that the reaction of CH4(+) with the parent neutral proceeds both via proton transfer and hydrogen abstraction accompanied by approximately 10% hydrogen atom exchange during the reaction.

Huntress, W. T., Jr.

1972-01-01

343

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

344

Natural Zeolites: Cation Exchange, Cation Arrangement and Dehydration Behavior  

Microsoft Academic Search

Still 50 years ago natural zeolites mainly from vugs and fissures of volcanic rocks were considered a rare curiosity of nature.\\u000a About 100 years ago chemists recognized that these minerals with a tetrahedral framework structure, characterized by internal\\u000a porous space in form of cavities and connecting channels, can be used for ion exchange, molecular sieving, and catalytic reactions.\\u000a Thus in

Thomas Armbruster

345

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

346

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

347

Deuterium isotopic exchangeability of resin and amber at low thermal stress under hydrous conditions  

NASA Astrophysics Data System (ADS)

Hydrous deuterium-exchange experiments have shown that a significant fraction of the original D/H composition of bulk kerogens, bitumens and expelled oils may participate in isotopic exchange reactions during burial diagenesis. However, it is unknown to what extent plant-derived secondary metabolites, namely resins and their fossil counterpart amber, exchange hydrogen isotopes following their biosynthesis. This situation hinders the application of resin D/H measurements in paleoenvironmental reconstruction. Here, we assess explicitly hydrogen exchange in resins and ambers using a series of immersion experiments in deuterated (D-enriched) waters over a period of several months at several temperatures. We are especially interested in assessing whether significant H-isotopic exchange occurs between resins and meteoric waters during early thermal maturation and polymerization. At 90°C, equivalent to ~3km of burial in most diagenetic regimes, modern conifer and angiosperm resins have an average post-metabolic H exchange of 4.6%, compared to only 1.1% for mature, polymerized ambers. At 55°C the degree of exchange is considerably lower: 1.9% for resins and 0.6% for ambers. These results indicate that most D/H isotopic exchange occurs prior to polymerization reactions, thereby confirming that D/H measurements from amber constitute a potentially sensitive proxy for environmental change.

Gonzalez, G.; Tappert, R.; Wolfe, A. P.; Muehlenbachs, K.

2012-04-01

348

Structural Insight into the Ion-Exchange Mechanism of the Sodium/Calcium Exchanger  

SciTech Connect

Sodium/calcium (Na{sup +}/Ca{sup 2+}) exchangers (NCX) are membrane transporters that play an essential role in maintaining the homeostasis of cytosolic Ca{sup 2+} for cell signaling. We demonstrated the Na{sup +}/Ca{sup 2+}-exchange function of an NCX from Methanococcus jannaschii (NCX{_}Mj) and report its 1.9 angstrom crystal structure in an outward-facing conformation. Containing 10 transmembrane helices, the two halves of NCX{_}Mj share a similar structure with opposite orientation. Four ion-binding sites cluster at the center of the protein: one specific for Ca{sup 2+} and three that likely bind Na{sup +}. Two passageways allow for Na{sup +} and Ca{sup 2+} access to the central ion-binding sites from the extracellular side. Based on the symmetry of NCX{_}Mj and its ability to catalyze bidirectional ion-exchange reactions, we propose a structure model for the inward-facing NCX{_}Mj.

Liao, Jun; Li, Hua; Zeng, Weizhong; Sauer, David B.; Belmares, Ricardo; Jiang, Youxing (UTSMC)

2012-06-19

349

Structure, dynamics, and surface reactions of bioactive glasses  

Microsoft Academic Search

Three bioactive glasses (45S5, 55S4.3, and 60S3.8) have been investigated using atomic-scale molecular dynamics simulations in attempt to explain differences in observed macroscopic bioactivity. Bulk and surface structures and bulk dynamics have been characterized. Ion exchange and hydrolysis reactions, the first two stages in Hench's model describing the reactions of bioactive glass surfaces in vivo, have been investigated in detail.

Todd R. Zeitler

2006-01-01

350

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 800°C 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

351

77 FR 33531 - Self-Regulatory Organizations; BATS Exchange, Inc.; BATS Y-Exchange, Inc.; NASDAQ OMX BX, Inc...  

Federal Register 2010, 2011, 2012, 2013, 2014

...Incorporated; C2 Options Exchange, Incorporated; Chicago Stock Exchange, Inc.; EDGA Exchange, Inc.; EDGX Exchange...International Securities Exchange LLC; The NASDAQ Stock Market LLC; New York Stock Exchange LLC; NYSE Amex LLC; NYSE Arca,...

2012-06-06

352

Refractive lens exchange.  

PubMed

Advances in small incision surgery have enabled cataract surgery to evolve from being concerned primarily with the safe removal of the opaque crystalline lens to a procedure refined to yield the best possible postoperative refractive result. As the outcomes of cataract surgery have improved, the use of lens surgery as a refractive modality in patients without cataracts (clear lens extraction) has increased in popularity. The removal of the crystalline lens for refractive purposes, or so-called refractive lens exchange (RLE), offers distinct advantages over corneal refractive surgery in selected cases. Nevertheless, in some middle-aged patients with high refractive errors, corneal refractive surgery can be a safe and effective treatment. In addition, the use of multifocal lenses offers an alternative for the correction of presbyopia. A further advantage of RLE is that it simultaneously eliminates the need for cataract surgery in the future. The keys for success in RLE are effectiveness and consistency in the refractive outcome, providing at the same time surgical and postoperative safety. To achieve these goals, adequate indications following strict risk/benefit criteria and refractive precision based on accurate preoperative protocols for IOL calculation and selection are mandatory, together with an appropriate choice of surgical procedure based on the surgeon's skills, minimizing complications. PMID:25127929

Alio, Jorge L; Grzybowski, Andrzej; El Aswad, Amr; Romaniuk, Dorota

353

Modular heat exchanger  

DOEpatents

A shell and tube heat exchanger is described having a plurality of individually removable tube bundle modules. A lattice of structural steel forming rectangular openings therein is placed at each end of a cylindrical shell. Longitudinal structural members are placed in the shell between corners of the rectangular openings situated on opposite ends of the shell. Intermediate support members interconnect the longitudinal supports so as to increase the longitudinal supports rigidity. Rectangular parallelepiped tube bundle modules occupy the space defined by the longitudinal supports and end supports and each include a rectangular tube sheet situated on each end of a plurality of tubes extending there through, a plurality of rectangular tube supports located between the tube sheets, and a tube bundle module stiffening structure disposed about the bundle's periphery and being attached to the tube sheets and tube supports. The corners of each tube bundle module have longitudinal framework members which are mateable with and supported by the longitudinal support members. Intermediate support members constitute several lattices, each of which is situated in a plane between the end support members. The intermediate support members constituting the several lattices extend horizontally and vertically between longitudinal supports of adjacent tube module voids. An alternative embodiment for intermediate support members constitute a series of structural plates situated at the corners of the module voids and having recesses therein for receiving the respective longitudinal support members adjacent thereto, protrusions separating the recesses, and a plurality of struts situated between protrusions of adjacent structural plates. 12 figs.

Giardina, A.R.

1981-03-03

354

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

355

Reaction cycle and thermodynamics in bacteriorhodopsin  

NASA Technical Reports Server (NTRS)

Light causes the all-trans to 13-cis isomerization of the retinal in bacteriorhodopsin; the thermal relaxation leading back to the initial state drives proton transport first via proton transfer between the retinal Schiff base and D85 and then between the Schiff base and D96. The reaction sequence and thermodynamics of this photocycle are described by measuring time-resolved absorption changes with a gated multichannel analyzer between 100 ns and 100 ms, at six temperatures between 5 degrees C and 30 degrees C. Analysis of the energetics of the chromophore reaction sequence is on the basis of a recently proposed model (Varo & Lanyi, Biochemistry 30, 5016-5022, 1991) which consists of a single cycle and many reversible reactions: BR -hv-->K<==>L<==>M1-->M2<==>N<==>O-->BR. The existence of the M1-->M2 reaction, which functions as the switch in the proton transfer, is confirmed by spectroscopic evidence. The calculated thermodynamic parameters indicate that the exchange of free energy between the protein and the protons is at the switch step. Further, a large entropy decrease at this reaction suggests a protein conformation change which will conserve delta G for driving the completion of the reaction cycle. The results provide insights to mechanism and energy coupling in this system, with possible relevance to the general question of how ion pumps function.

Lanyi, J. K.

1992-01-01

356

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)

1986-01-01

357

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

358

Matrix-type heat exchangers  

NASA Astrophysics Data System (ADS)

Problems related to the analysis, design, and fabrication of compact matrix-type heat exchangers are discussed. Particular attention is given to the general characteristics describing the intensity of heat transfer and the hydrodynamic resistance of the matrices, an analysis of the efficiency of perforated ribs, and an evaluation of the efficiency of the matrix heat exchange surfaces. The effect of longitudinal heat conduction on heat transfer in the heat exchanger is examined, and a method is proposed whereby this factor can be allowed for in the analysis.

Mikulin, E. I.; Shevich, Iu. A.

359

Semilocal density functional obeying a strongly tightened bound for exchange.  

PubMed

Because of its useful accuracy and efficiency, density functional theory (DFT) is one of the most widely used electronic structure theories in physics, materials science, and chemistry. Only the exchange-correlation energy is unknown, and needs to be approximated in practice. Exact constraints provide useful information about this functional. The local spin-density approximation (LSDA) was the first constraint-based density functional. The Lieb-Oxford lower bound on the exchange-correlation energy for any density is another constraint that plays an important role in the development of generalized gradient approximations (GGAs) and meta-GGAs. Recently, a strongly and optimally tightened lower bound on the exchange energy was proved for one- and two-electron densities, and conjectured for all densities. In this article, we present a realistic "meta-GGA made very simple" (MGGA-MVS) for exchange that respects this optimal bound, which no previous beyond-LSDA approximation satisfies. This constraint might have been expected to worsen predicted thermochemical properties, but in fact they are improved over those of the Perdew-Burke-Ernzerhof GGA, which has nearly the same correlation part. MVS exchange is however radically different from that of other GGAs and meta-GGAs. Its exchange enhancement factor has a very strong dependence upon the orbital kinetic energy density, which permits accurate energies even with the drastically tightened bound. When this nonempirical MVS meta-GGA is hybridized with 25% of exact exchange, the resulting global hybrid gives excellent predictions for atomization energies, reaction barriers, and weak interactions of molecules. PMID:25561554

Sun, Jianwei; Perdew, John P; Ruzsinszky, Adrienn

2015-01-20

360

Surface Exchange and Shape Transitions of PbSe Quantum Dots during Overgrowth  

SciTech Connect

Epitaxial overgrowth of PbSe quantum dots is shown to drastically affect their shape and composition due to anion exchange reactions. As shown by scanning tunneling microscopy, for PbTe capping layers this results in a complete truncation of the dots. Introduction of EuTe into the cap layer leads to an effective suppression of the anion exchange process. This preserves the original dot pyramids and induces a large stress concentration on the surface which further alters the overgrowth process.

Abtin, L.; Springholz, G. [Institut fuer Halbleiter- und Festkoerperphysik, Johannes Kepler Universitaet, A-4040 Linz (Austria); Holy, V. [Charles University, Faculty of Mathematics and Physics, Prague (Czech Republic)

2006-12-31

361

Room-temperature alkane reactivity in zeolites: an H/D exchange study.  

PubMed

As evidenced by H/D exchange with acidic zeolites, isoalkanes react readily at room temperature whereas linear alkanes do not. The observed regioselectivity of the exchange process demonstrates that the main factor controlling the reaction is not the accessibility to the acid sites, but the intrinsic reactivity of the alkane. The mechanism is best rationalized by classic organic chemistry involving carbocationic intermediates including the Markovnikov rule. PMID:20108278

Sido, Abdelkarim Sani Souna; Walspurger, Stéphane; Barbiche, Jérémy; Sommer, Jean

2010-03-01

362

Numerical simulation of heat exchanger  

SciTech Connect

Accurate and detailed knowledge of the fluid flow field and thermal distribution inside a heat exchanger becomes invaluable as a large, efficient, and reliable unit is sought. This information is needed to provide proper evaluation of the thermal and structural performance characteristics of a heat exchanger. It is to be noted that an analytical prediction method, when properly validated, will greatly reduce the need for model testing, facilitate interpolating and extrapolating test data, aid in optimizing heat-exchanger design and performance, and provide scaling capability. Thus tremendous savings of cost and time are realized. With the advent of large digital computers and advances in the development of computational fluid mechanics, it has become possible to predict analytically, through numerical solution, the conservation equations of mass, momentum, and energy for both the shellside and tubeside fluids. The numerical modeling technique will be a valuable, cost-effective design tool for development of advanced heat exchangers.

Sha, W.T.

1985-01-01

363

Heat pipe array heat exchanger  

DOEpatents

A heat pipe arrangement for exchanging heat between two different temperature fluids. The heat pipe arrangement is in a ounterflow relationship to increase the efficiency of the coupling of the heat from a heat source to a heat sink.

Reimann, Robert C. (Lafayette, NY)

1987-08-25

364

Ion cyclotron resonance studies of some reactions of N/+/ ions  

NASA Technical Reports Server (NTRS)

Product distributions and rate constants for the reactions of ground-state N(+) ions with CO, NO, CO2, and CH4 were measured. Rate constants were obtained using ion-cyclotron-resonance trapped-ion methods, and product distributions were obtained using a tandem (Dempster-ICR) mass spectrometer. Rapid nitrogen isotope exchange was also observed in N(+)-N2 collisions.

Anicich, V. G.; Huntress, W. T., Jr.; Futrell, J. H.

1977-01-01

365

Optimization of Heat Exchanger Cleaning  

E-print Network

. Material is not only continuously deposited on the heat exchange surface but is also continuously removed. In order to predict the optimum cleaning time and calculate the TFRE, it is necessary to develop a mathematical relationship for the rate... OPTIMIZATION OF HEAT EXCHANGER CLEANING Jeffrey H. Siegell Exxon Research and Engineering Company Florham Park, New Jersey ABSTRACT The performance of heat integration systems is quantified in terms of the amount of heat that is recovered...

Siegell, J. H.

366

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

367

CO2 exchange of plants  

Microsoft Academic Search

The CO2 exchange of shoots of Trifolium repens, Fragaria chiloensis × virginiana, Celmisia spectabilis, Lycopersicum esculentum, Lolium perenne, and Chionochloa rubra were determined at exposed leaf temperatures of 4° to 55°c and five light intensities. The maximum rates of exchange for the first three species at a photosynthetic irradiance of 340 W.m were 58, 23, and 5 mg CO2.g.hr respectively,

D. Scott; P. H. Menalda

1970-01-01

368

Microscale Thermite Reactions.  

ERIC Educational Resources Information Center

Describes the adaptation of thermite (aluminum with metal oxides) reactions from whole-class demonstrations to student-run micro-reactions. Lists detailed directions and possible variations of the experiment. (WRM)

Arnaiz, Francisco J.; Aguado, Rafael; Arnaiz, Susana

1998-01-01

369

Classification of clock reactions.  

PubMed

Autocatalytic systems are sometimes designated as clock reactions or reactions that exhibit clock behavior. To resolve the recent dispute over the term clock reaction, we describe a new approach to classify systems featuring clock behavior into three distinct groups: substrate-depletive clock reactions, autocatalysis-driven clock reactions, and systems that have pseudo clock behavior. Many of the well-known classical and recently discovered reactions can conveniently be put into these categories. We also provide a convincing argument for classifying some autocatalytic processes as clock reactions, but it does not necessarily mean that all autocatalytic processes should be classified as autocatalysis-driven clock reactions. This classification can be conveniently performed if the kinetic nature of the given system has been completely elucidated and understood. PMID:25425415

Horváth, Attila K; Nagypál, István

2015-02-23

370

Chemical Reactions (Netorials)  

NSDL National Science Digital Library

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

371

Synthesis, structural characterization, and catalytic properties of tungsten-exchanged H-ZSM5  

SciTech Connect

W-exchanged H-ZSM5 was prepared by sublimation of WCl6 at 673 K followed by hydrolysis of exchanged WClx species at 523 K. D2 exchange with residual OH groups showed that each W initially replaced about two zeolitic protons for W/Al ratios of 0.29 and 0.44, consistent with the formation of (WO2)2+ containing W6+ species bridging two cation exchange sites. As temperatures reached973 K during D2-OH exchange, these species reduced to (WO2)+ with the concurrent formation of one OD group. CH4 conversion turnover rates (per W) and C2-C1 2 selectivities are very similar to those observed on a Mo/H-ZSM5 sample with similar cation exchange level. As in the case of Mo/H-ZSM5, WOx/H-ZSM5 precursors are initially inactive in CH4 reactions, but they activate during induction with the concurrent evolution of CO, H2O, and an excess amount of H2. The reduction and carburization processes occurring during CH4 reactions and the structure of the exchanged WOx precursors was probed using in situ X-ray absorption spectroscopy (XAS). XAS studies confirmed the isolated initial nature of the exchanged WOx precursors after hydrolysis and dehydration and the formation of WCx clusters 0.6 nm in diameter during CH4 reactions at 973 K. The structural and catalytic resemblance between W- and Mo-exchanged H-ZSM5 is not unexpected, in view of chemical similarities between oxides or carbides of Mo and W. The synthesis of exchanged WOx precursors and their subsequent carburization during CH4 reactions, however, are more difficult than the corresponding processes for the MoOx counterparts. This may account for previous reports of lower CH4 reaction rates and aromatics selectivities on W/H-ZSM5 compared with those observed on Mo/H-ZSM5 and with those reported here for rigorously exchanged W/H-ZSM5.

Ding, Weiping; Meitzner, George D.; Marler, David O.; Iglesia, Enrique

2001-01-18

372

Anion exchange polymer electrolytes  

DOEpatents

Solid anion exchange polymer electrolytes and compositions comprising chemical compounds comprising a polymeric core, a spacer A, and a guanidine base, wherein said chemical compound is uniformly dispersed in a suitable solvent and has the structure: ##STR00001## wherein: i) A is a spacer having the structure O, S, SO.sub.2, --NH--, --N(CH.sub.2).sub.n, wherein n=1-10, --(CH.sub.2).sub.n--CH.sub.3--, wherein n=1-10, SO.sub.2-Ph, CO-Ph, ##STR00002## wherein R.sub.5, R.sub.6, R.sub.7 and R.sub.8 each are independently --H, --NH.sub.2, F, Cl, Br, CN, or a C.sub.1-C.sub.6 alkyl group, or any combination of thereof; ii) R.sub.9, R.sub.10, R.sub.11, R.sub.12, or R.sub.13 each independently are --H, --CH.sub.3, --NH.sub.2, --NO, --CH.sub.nCH.sub.3 where n=1-6, HC.dbd.O--, NH.sub.2C.dbd.O--, --CH.sub.nCOOH where n=1-6, --(CH.sub.2).sub.n--C(NH.sub.2)--COOH where n=1-6, --CH--(COOH)--CH.sub.2--COOH, --CH.sub.2--CH(O--CH.sub.2CH.sub.3).sub.2, --(C.dbd.S)--NH.sub.2, --(C.dbd.NH)--N--(CH.sub.2).sub.nCH.sub.3, where n=0-6, --NH--(C.dbd.S)--SH, --CH.sub.2--(C.dbd.O)--O--C(CH.sub.3).sub.3, --O--(CH.sub.2).sub.n--CH--(NH.sub.2)--COOH, where n=1-6, --(CH.sub.2).sub.n--CH.dbd.CH wherein n=1-6, --(CH.sub.2).sub.n--CH--CN wherein n=1-6, an aromatic group such as a phenyl, benzyl, phenoxy, methylbenzyl, nitrogen-substituted benzyl or phenyl groups, a halide, or halide-substituted methyl groups; and iii) wherein the composition is suitable for use in a membrane electrode assembly.

Kim, Yu Seung; Kim, Dae Sik; Lee, Kwan-Soo

2013-07-23

373

Disintegration of the deuteron by reactor antineutrinos and the axial meson exchange current effects  

NASA Astrophysics Data System (ADS)

Using the realistic NN interaction we study the influence of the axial meson exchange current effects on the cross sections and spectra in the weak neutral and charged disintegration of deuterons. In the hard pion approach we estimate these effects to be ?8%. We suggest that an accurate experimental study of the problem may reveal the existence of the axial meson exchange current effects and the isobar configurations in nuclear physics. NUCLEAR REACTIONS d(?¯e,?'e)np, (?¯e,e), reactor antineutrinos. Calculated cross sections and spectra. Hard pion approach to exchange currents.

Hošek, J.; Truhlík, E.

1981-02-01

374

Chemical Reactions and Stoichiometry  

NSDL National Science Digital Library

In this activity, students explore reactions in which chemical bonds are formed and broken. Students experiment with changing the temperature and the concentration of the atoms in order to see how these affect reaction rates. They also learn how to communicate what happens during a chemical reaction by writing the ratios of reactants and products, known as stoichiometry.

The Concord Consortium

2011-12-11

375

Vapor-phase catalytic oxidesulfurization (ODS) of organosulfur compounds over supported metal oxide catalysts  

NASA Astrophysics Data System (ADS)

Sulfur in transportation fuels remains a leading source of SOx emissions from vehicle engines and is a major source of air pollution. The very low levels of sulfur globally mandated for transportation fuels in the near future cannot be achieved by current practices of hydrodesulfurization (HDS) for sulfur removal, which operate under severe conditions (high T, P) and use valuable H2. Novel vapor-phase catalytic oxidesulfurization (ODS) processes of selectively oxidizing various organosulfur compounds (carbonyl sulfide, carbon disulfide, methanethiol, dimethyl sulfide (DMS), dimethyl disulfide (DMDS), thiophene, 2,5-dimenthylthiophene) typically found in various industrial streams (e.g., petroleum refining, pulp and paper) into valuable chemical intermediates (H 2CO, CO, H2, maleic anhydride and concentrated SO2) has been extensively studied. This research has primarily focused on establishing the fundamental kinetics and mechanisms of these selective oxidation reactions over well-defined supported metal oxide catalysts. The selective oxidation reactions of COS + O2 ? CO + SO2; 2CS2 + 5O2 ? 2CO + 4SO2; CH3SH + 2O 2 ? H2CO + SO2 + H2O; C4 H4S + 3O2 ? C4H2O 3 + H2O + SO2; were studied. Raman spectroscopy revealed that the supported metal oxide phases were 100% dispersed on the oxide substrate. All the catalysts were highly active and selective for the oxidesulfurization of carbonyl sulfide, carbon disulfide, methanethiol, and thiophene between 290--330°C, 230--270°C, 350--400°C, and 250--400°C, respectively and did not deactivate. The TOFs (turnover frequency, normalized activity per active catalytic site) for all ODS reactions over supported vanadia catalysts, only containing molecularly dispersed surface vanadia species, varied within one order of magnitude and revealed the V-O-Support bridging bond was involved in the critical rate-determining kinetic steps. The surface reaction mechanism for each reaction was revealed by in situ IR (infrared) and temperature programmed surface reaction-mass spectroscopy (TPSR-MS). The systematic investigation of vapor-phase oxidesulfurization (ODS) reactions of organosulfur compounds over catalytic supported metal oxides revealed the facile S-O exchange mechanisms allow for the efficient removal of sulfur while producing value-added chemicals and represents the discovery of a new series of catalytic reactions.

Choi, Sukwon

376

Removal of catalyst in polybutene production by treatment with ion exchange resin  

SciTech Connect

The development of process technology for removal of AlCl/sub 3/ from the reaction mass obtained in the polymerization of butenes by treatment with ion exchange resins is reported. This work also investigated certain reactions that take place in this treatment. It is proposed that the polymerized product should be treated with KU-2-8 cation exchange resin in the H form. The study demonstrates that by the use of resin treatment of the polymerized product that has been prehomogenized with alcohols, it becomes possible to produce low molecular weight polybutenes in a low waste process.

Vlasov, A.V.; Prokof'ev, K.V.; Sangalov, Yu.A.; Kotov, S.V.

1988-09-01

377

Reaction coordinates for electron transfer reactions  

SciTech Connect

The polarization fluctuation and energy gap formulations of the reaction coordinate for outer sphere electron transfer are linearly related to the constant energy constraint Lagrangian multiplier m in Marcus' theory of electron transfer. The quadratic dependence of the free energies of the reactant and product intermediates on m and m+1, respectively, leads to similar dependence of the free energies on the reaction coordinates and to the same dependence of the activation energy on the reorganization energy and the standard reaction free energy. Within the approximations of a continuum model of the solvent and linear response of the longitudinal polarization to the electric field in Marcus' theory, both formulations of the reaction coordinate are expected to lead to the same results.

Rasaiah, Jayendran C. [Department of Chemistry, University of Maine, Orono, Maine 04469 (United States); Zhu Jianjun [Department of Chemistry, State University of New York, Stonybrook, New York 11790 (United States) and Department of Chemistry, Henan Normal University, Xinxiang, Henan (China)

2008-12-07

378

Chemical Reactions: Investigating Exothermic and Endothermic Reactions  

NSDL National Science Digital Library

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

379

Effects of diatomic reagent alignment on the A + BC reaction  

NASA Technical Reports Server (NTRS)

A computational study is reported on the A + BC - AB + C bimolecular exchange reaction in which BC is aligned with respect to the approach direction of atom A so that the initial rotational angular momentum vector of BC is either parallel (or equivalently antiparallel) or perpendicular to the initial velocity vector of A. The calculations employ a modification of the extended LEPS potential, which permits straightforward generation of noncollinear minimum energy reaction paths. The calculations clearly demonstrate that diatomic reagent alignment can markedly affect the nature of reaction product early partitioning; they also demonstrate that diatomic reagent alignment affects reactive cross sections.

Pattengill, M. D.; Zare, R. N.; Jaffe, R. L.

1987-01-01

380

K. Toyota et al.: Air-snowpack exchange of bromine and ozone (Supplement) 1 Supplement to "Air-snowpack exchange of bromine, ozone and  

E-print Network

K. Toyota et al.: Air-snowpack exchange of bromine and ozone (Supplement) 1 Supplement to "Air: In-snow bromine activation and its impact on ozone" K. Toyota1,2 , J. C. McConnell1, , R. M. Staebler-phase reactions and their rate constants Correspondence to: K. Toyota (kenjiro.toyota@ec.gc.ca) Table S1. List

Meskhidze, Nicholas

381

Exchange rate expectations of chartists and fundamentalists  

Microsoft Academic Search

This paper provides novel evidence on exchange rate expectations of both chartists and fundamentalists separately. These groups indeed form expectations differently. Chartists change their expectations more often; however, all professionals' expectations vary considerably as they generally follow strong exchange rate trends. In line with non-linear exchange rate-modeling, professionals expect mean reversion only if exchange rates deviate much from PPP. Chartists

Christian D. Dick; Lukas Menkhoff

2012-01-01

382

Conflict and Fairness in Social Exchange  

ERIC Educational Resources Information Center

Inherent to all social exchange relations are elements of both cooperation and competition. We develop and test a theoretical model which proposes that the relative salience of the competitive, conflictual elements of exchange mediate and explain the negative effects of negotiated exchange, as compared with reciprocal exchange, on actors'…

Molm, Linda D.; Collett, Jessica L.; Schaefer, David R.

2006-01-01

383

NASA data exchange standards for computational fluid dynamics  

NASA Technical Reports Server (NTRS)

This paper covers the following topics in viewgraph format: purpose of data exchange standards; data exchange in engineering analysis/CFD; geometry data exchange through existing product data exchange standards, NASA Data Exchange Committee, and NASA-IGES (Initial Graphics Exchange Specification); CFD grid and solution data exchange; and data exchange for multi-disciplinary engineering.

Blake, Matthew

1993-01-01

384

Unraveling the chemical dynamics of bimolecular reactions of ground state boron atoms, B(2  

E-print Network

Unraveling the chemical dynamics of bimolecular reactions of ground state boron atoms, B(2 PjArticle on the web 8th March 2004 The reaction dynamics of atomic boron, B(2 P), with acetylene, C2H2(X 1 Sg þ molecular beams technique. Only the atomic boron versus hydrogen atom exchange pathway was observed. Forward

Kaiser, Ralf I.

385

On the mechanism of prograde metamorphic reactions in quartz-bearing pelitic rocks  

Microsoft Academic Search

An empirical method is described whereby the sequence of textural changes in pelitic rocks from one zone to the next may be reconciled with the balanced metamorphic reaction inferred to have been in progress. It consists in deducing from the textures of a single thin section a set of metasomatic cation-exchange reactions, which proceed in different microscopic domains of the

Dugald M. Carmichael

1969-01-01

386

Inverse Modeling of Tracer Tests in Streams Undergoing Hyporheic Exchange  

NASA Astrophysics Data System (ADS)

Hyporheic exchange has been identified as a key process in solute transport, biogeochemical cycling, and ecosystem functioning of streams. Physical solute transport through the hyporheic zone may be characterized by the total flux of water exchange and the distribution of hyporheic travel times. The classical method of obtaining travel-time distributions is an artificial-tracer experiment, in which an easy to detect compound is injected into the river, and the breakthrough curve (BTC) is measured at an observation point further downstream in the river. This BTC is affected by in-stream transport and hyporheic exchange as expressed in the transient storage model for linear solute transport in rivers undergoing hyporheic exchange: (? ) ?c+ v-?c- D ?2c-= q tp(?)c(t- ?)exp(- ??)d? - c(t) + q (c - c(t)) ?t ?x ?x2 he 0 in in (1) in which v and D are the velocity and dispersion coefficient, respectively, qhe is the hyporheic exchange flux, ? is the travel-time coordinate in the hyporheic zone, p(?) is the probability density function of ?, ? is a first-order rate coefficient quantifying potential decay within the hyporheic zone, qin expresses lateral inflow, and cin is the corresponding concentration within that inflow. The target quantities are the exchange flux qhe and the nonnegative travel time distribution p(?) in the hyporheic zone. Common transient storage models use parametric distribution functions, such as the exponential, power-law, or log-normal distributions. By predefining the functional form of p(?), however, important features such as multimodality may remain unnoticed. We present a nonparametric approach of obtaining p(?) jointly with the other transport parameters by fitting BTCs of conservative and reactive solutes. For regularization p(?) is assumed autocorrelated, and nonnegativity is enforced by the method of Lagrange multipliers. The method extends a nonparametric deconvolution approach for the determination of transfer functions. It requires successive linearization (Gauss-Newton scheme), stabilized by a line-search, and forward simulation in the Laplace domain with numerical back-transformation. Once the hyporheic travel-time distribution p(?) has been identified, the transport model can be extended to include nonlinear reactions of river-borne compound within the hyporheic zone thus facilitating the simulation of biogeochemical cycling in streams undergoing hyporheic exchange. This method has been tested by virtual conservative and reactive tracer experiments undergoing hyporheic exchange. Joint inversion of conservative and reactive tracer BTCs is essential for distinguishing the effects of in-stream dispersion from hyporheic exchange. Applications to field data are on the way.

Liao, Zijie; Arie Cirpka, Olaf

2010-05-01

387

Krypton charge exchange cross sections for Hall effect thruster models  

SciTech Connect

Following discharge from a Hall effect thruster, charge exchange occurs between ions and un-ionized propellant atoms. The low-energy cations produced can disturb operation of onboard instrumentation or the thruster itself. Charge-exchange cross sections for both singly and doubly charged propellant atoms are required to model these interactions. While xenon is the most common propellant currently used in Hall effect thrusters, other propellants are being considered, in particular, krypton. We present here guided-ion beam measurements and comparisons to semiclassical calculations for Kr{sup +} + Kr and Kr{sup 2+} + Kr cross sections. The measurements of symmetric Kr{sup +} + Kr charge exchange are in good agreement with both the calculations including spin-orbit effects and previous measurements. For the symmetric Kr{sup 2+} + Kr reaction, we present cross section measurements for center-of-mass energies between 1 eV and 300 eV, which spans energies not previously examined experimentally. These cross section measurements compare well with a simple one-electron transfer model. Finally, cross sections for the asymmetric Kr{sup 2+} + Kr {yields} Kr{sup +} + Kr{sup +} reaction show an onset near 12 eV, reaching cross sections near constant value of 1.6 A{sup 2} with an exception near 70-80 eV.

Hause, Michael L. [Institute for Scientific Research, Boston College, Chestnut Hill, Massachusetts 02159 (United States); Prince, Benjamin D.; Bemish, Raymond J. [Air Force Research Laboratory, Space Vehicles Directorate, Kirtland AFB, New Mexico 87117 (United States)

2013-04-28

388

Cooling exothermic regenerator with endothermic reactions  

SciTech Connect

A fluidized catalytic cracking (FCC) process is described wherein a heavy hydrocarbon feed having a boiling point above about 650 F is catalytically cracked in an FCC unit by direct contact with an inventory of hot regenerated cracking catalyst to lighter products and spent catalyst which is regenerated to produce hot regenerated catalyst, by: a. catalytically cracking the feed in a catalytic cracking reactor operating at conditions to produce a cracking reactor effluent mixture comprising cracked products and spent catalyst containing coke and strippable hydrocarbons; b. separating the cracking reactor effluent mixture into a cracked product rich vapor phase and a solids rich spent catalyst phase comprising strippable hydrocarbons and coked catalyst; c. stripping at least a portion of the spent catalyst phase to produce stripped coked catalyst; d. regenerating at least a portion of the stripped coked catalyst in a catalyst regeneration means to produce hot regenerated catalyst which is recycled to the catalytic cracking reactor; the process characterized by cooling at least a portion of the FCC catalyst inventory by indirect heat exchange against an endothermic chemical reaction in an endothermic cooler having two isolated sections, an FCC catalyst side section and an endothermic cooler reactant side section by: e. removing at least a portion of the FCC catalyst from the FCC unit and charging same to an inlet of the endothermic cooler; f. charging an endothermically reactive reactant selected from the group of ethane, propane, butane, light naphtha, and heavy naphtha to an inlet of the endothermic cooler reactant side of the heat exchange means; g. heating the endothermically reactive reactant, by indirect heat exchange with the FCC catalyst, to a temperature sufficient to drive the endothermic reaction and produce endothermic reaction products which are removed as a product and simultaneously remove heat from the FCC catalyst and produce cooled FCC catalyst.

Sapre, A.V.

1993-06-01

389

Structure, dynamics, and surface reactions of bioactive glasses  

NASA Astrophysics Data System (ADS)

Three bioactive glasses (45S5, 55S4.3, and 60S3.8) have been investigated using atomic-scale molecular dynamics simulations in attempt to explain differences in observed macroscopic bioactivity. Bulk and surface structures and bulk dynamics have been characterized. Ion exchange and hydrolysis reactions, the first two stages in Hench's model describing the reactions of bioactive glass surfaces in vivo, have been investigated in detail. The 45S5 composition shows a much greater network fragmentation: it is suggested that this fragmentation can play a role in at least the first two stages of Hench's model for HCA formation on the surfaces of bioactive glasses. In terms of dynamic behavior, long-range diffusion was only observed for sodium. Calcium showed only jumps between adjacent sites, while phosphorus showed only local vibrations. Surface simulations show the distinct accumulation of sodium at the immediate surface for each composition. Surface channels are also shown to exist and are most evident for 45S5 glass. Results for a single ion exchange showed that the ion-exchange reaction is preferred (more exothermic) for Na+ ions near Si, rather than P. A range of reaction energies were found, due to a range of local environments, as expected for a glass surface. The average reaction energies are not significantly different among the three glass compositions. The results for bond hydrolysis on as-created surfaces show no significant differences among the three compositions for simulations involving Si-O-Si or Si-O-P. All average values are greater than zero, indicating endothermic reactions that are not favorable by themselves. However, it is shown that the hydrolysis reactions became more favorable (in fact, exothermic for 45S5 and 55S4.3) when simulated on surfaces that had already been ion-exchanged. This is significant because it gives evidence supporting Hench's proposed reaction sequence. Perhaps even more significantly, the reaction energies for hydrolysis following ion exchange directly relate to the glass composition; the 45S5 composition is most favorable and 60S3.8 is least favorable. This correlates directly with the observed macroscopic in vivo bioactivity of these glasses.

Zeitler, Todd R.

390

Wood burning stove heat exchanger  

SciTech Connect

A wood burning stove includes a water circulating grate within the stove fire chamber which includes horizontally extending, vertically spaced, first and second tubular manifolds. Fuel supporting pipes, including bottom portions which define a ''V'', physically and fluidly interconnect the manifolds. An inlet pipe extends throughout the majority of the length of the bottom manifold, and the top manifold is connected-through a container having a larger cross-sectional area than the cross-sectional area of the manifold-to an outlet. The inlet to and outlet from the manifold are connected up to a hydronic space heating system. The container supports a heat exchanger comprising a finned copper tube, so that the heat exchanger extends generally horizontally and within the first manifold. The heat exchanger is connected up to a domestic hot water supply. The container also supports one or more electric resistance heating coils, which heat liquid within the container in emergency situations.

Manno, J. T.

1985-08-13

391

Ion Exchange Properties of the Canine Carotid Artery  

PubMed Central

Properties of the ion exchange mechanisms in the arterial wall were investigated by comparing water and electrolyte contents, and by measuring the steady-state entry of 22Na, 42K, and 26Cl under similar in vitro conditions. Overnight incubation of freshly dissected slices at 2°C resulted in an accumulation of sodium, chloride, and water and a loss of potassium. Subsequent incubation at 37°C in a physiological solution resulted in a reversal of these processes. Loss of water, sodium, and chloride at 37°C could also take place into a potassium-free solution. Under all conditions studied the quantity of fast exchanging electrolyte (half time less than 3 min) exceeded that contained in the inulin and sucrose spaces. The excess could not be attributed to connective tissue adsorption. A kinetic model was applied to the flux data which incorporated two simultaneous processes: bulk diffusion and a reversible reaction. The assumption that the cell membrane behaved as a discrete barrier for the exchange of all cell electrolyte was relaxed in this approach. A theory based upon the physicochemical properties of proteins, ions, and water in biological systems provided a physical basis for the kinetic model, and for interpreting the ion exchange properties of the vascular wall. PMID:5791547

Jones, A. W.; Karreman, G.

1969-01-01

392

Ion-exchangeable, electronically conducting layered perovskite oxyfluorides.  

PubMed

Cation-exchangeable d(0) layered perovskites are amenable to intercalation, exfoliation, and a variety of topochemical reactions, but they lack the interesting electronic and magnetic functionalities of mixed-valent perovskites. Conversely, electronically and magnetically interesting layered perovskites lack scope in terms of interlayer chemistry. To bridge this gap, the insulating, cation-exchangeable layered perovskites RbLaNb(2)O(7), KCa(2)Nb(3)O(10), and NaYTiO(4) were reacted with poly(tetrafluoroethylene) under inert atmosphere conditions to yield layer perovskites in which some of the oxygen is substituted by fluorine. In the fluorinated materials, the B-site cations are reduced to a mixed-valent state without introducing oxygen vacancies into the anion sublattice. The resulting electronically conducting solids can be exposed to air and water and even ion-exchanged in acid without oxidation of the B-site cations. Electronic transport measurements on the air-stable RbLaNb(2)O(6)F reveal room-temperature conductivity (2-7 x 10(2) ohms x cm) via a variable-range hopping mechanism, which is not substantially changed after aqueous proton exchange to H(1-x)Rb(x)LaNb(2)O(6)F (x approximately = 0.2). PMID:19548670

Kobayashi, Yoji; Tian, Mingliang; Eguchi, Miharu; Mallouk, Thomas E

2009-07-22

393

Oscillating-Coolant Heat Exchanger  

NASA Technical Reports Server (NTRS)

Devices useful in situations in which heat pipes inadequate. Conceptual oscillating-coolant heat exchanger (OCHEX) transports heat from its hotter portions to cooler portions. Heat transported by oscillation of single-phase fluid, called primary coolant, in coolant passages. No time-averaged flow in tubes, so either heat removed from end reservoirs on every cycle or heat removed indirectly by cooling sides of channels with another coolant. Devices include leading-edge cooling devices in hypersonic aircraft and "frost-free" heat exchangers. Also used in any situation in which heat pipe used and in other situations in which heat pipes not usable.

Scotti, Stephen J.; Blosser, Max L.; Camarda, Charles J.

1992-01-01

394

Grafted methylenediphosphonate ion exchange resins  

DOEpatents

An ion exchange resin is disclosed that is comprised of an insoluble copolymer onto which are grafted pendent groups that provide 1.0 to about 10 mmol/g dry weight phosphorous. The pendent groups have the formula ##STR1## wherein R is hydrogen, a cation or mixtures thereof; and R.sup.1 is hydrogen or an C.sub.1 -C.sub.2 alkyl group. The resin also contains zero to about 5 mmol/g dry weight of pendent aromatic sulfonate groups. Processes for making and using an ion exchange-resin are also disclosed.

Trochimcznk, Andrzej W. (Knoxville, TN); Gatrone, Ralph C. (Plymouth, PA); Alexandratos, Spiro (Knoxville, TN); Horwitz, E. Philip (Naperville, IL)

1998-01-27

395

Grafted methylenediphosphonate ion exchange resins  

DOEpatents

An ion exchange resin is disclosed that is comprised of an insoluble copolymer onto which are grafted pendent groups that provide 1.0 to about 10 mmol/g dry weight phosphorus. The pendent groups have the formula as shown in the patent wherein R is hydrogen, a cation or mixtures thereof; and R{sup 1} is hydrogen or an C{sub 1}-C{sub 2} alkyl group. The resin also contains zero to about 5 mmol/g dry weight of pendent aromatic sulfonate groups. Processes for making and using an ion exchange resin are also disclosed.

Trochimcznk, A.W.; Gatrone, R.C.; Alexandratos, S.; Horwitz, E.P.

1997-04-08

396

Grafted methylenediphosphonate ion exchange resins  

DOEpatents

An ion exchange resin is disclosed that is comprised of an insoluble copolymer onto which are grafted pendent groups that provide 1.0 to about 10 mmol/g dry weight phosphorous. The pendent groups have the formula ##STR1## wherein R is hydrogen, a cation or mixtures thereof; and R.sup.1 is hydrogen or an C.sub.1 -C.sub.2 alkyl group. The resin also contains zero to about 5 mmol/g dry weight of pendent aromatic sulfonate groups. Processes for making and using an ion exchange resin are also disclosed.

Trochimcznk, Andrzej W. (Knoxbille, TN); Gatrone, Ralph C. (Plymouth, PA); Alexandratos, Spiro (Knoxville, TN); Horwitz, E. Philip (Naperville, IL)

1997-01-01

397

Ceramic-heat-exchanger technology  

NASA Astrophysics Data System (ADS)

Technology for pressurized, high temperature, ceramic tube heat exchangers was established by environmental, design, and fabrication studies. The design study includes the finite element stress analysis of the ceramic components contained in the DOE ceramic heat exchanger test module. This test module contains 28, 4.56-m long ceramic tubes with a 11.43-cm dia ceramic header. It was operated successfully for 125 h up to firing temperatures of 17000K (26000F) and outlet air temperatures of 15330K (23000F) at 689.4 kPa (100 psia). This unit was then fired with a pulverized coal burner under EPRI sponsorship for 25 h.

Ward, M. E.; Kubasco, A. J.

1983-03-01

398

The Electrically Controlled Exchange Bias  

NASA Astrophysics Data System (ADS)

Controlling magnetism via voltage in the virtual absence of electric current is the key to reduce power consumption while enhancing processing speed, integration density and functionality in comparison with present-day information technology. Almost all spintronic devices rely on tailored interface magnetism. Controlling magnetism at thin-film interfaces, preferably by purely electrical means, is therefore a key challenge to better spintronics. However, there is no direct interaction between magnetization and electric fields, thus making voltage control of magnetism in general a scientific challenge. The significance of controlled interface magnetism started with the exchange-bias effect. Exchange bias is a coupling phenomenon at magnetic interfaces that manifests itself prominently in the shift of the ferromagnetic hysteresis loop along the magnetic-field axis. Various attempts on controlling exchange bias via voltage utilizing different scientific principles have been intensively studied recently. The majority of present research is emphasizing on various complex oxides. Our approach can be considered as a paradigm shift away from complex oxides. We focus on a magnetoelectric antiferromagnetic simple oxide Cr2O3. From a combination of experimental and theoretical efforts, we show that the (0001) surface of magnetoelectric Cr2O3 has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr2O3 single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This is a significant scientific breakthrough providing a new route towards potentially revolutionizing information technology. In addition, a second path of electrically controlled exchange bias is introduced by exploiting the piezoelectric property of BaTiO3. An exchange-bias Co/CoO bilayer is deposited on the surface of BaTiO 3 substrate which allows for tunable stress in the adjacent Co thin film. This stress induces strain in the Co film thus alters its magnetic anisotropy. The change of the magnetization orientation at the Co/CoO interface tunes its exchange bias and coercivity and provides a route to study the interface magnetism of the exchange bias heterostructure from a new perspective.

Harper, Jacob

399

Mechanisms in Knockout Reactions  

NASA Astrophysics Data System (ADS)

We report the first detailed study of the relative importance of the stripping and diffraction mechanisms involved in nucleon knockout reactions, by the use of a coincidence measurement of the residue and fast proton following one-proton knockout reactions. The measurements used the S800 spectrograph in combination with the HiRA detector array at the NSCL. Results for the reactions Be9(C9,B8+X)Y and Be9(B8,Be7+X)Y are presented and compared with theoretical predictions for the two reaction mechanisms calculated using the eikonal model. The data show a clear distinction between the stripping and diffraction mechanisms and the measured relative proportions are very well reproduced by the reaction theory. This agreement adds support to the results of knockout reaction analyses and their applications to the spectroscopy of rare isotopes.

Bazin, D.; Charity, R. J.; de Souza, R. T.; Famiano, M. A.; Gade, A.; Henzl, V.; Henzlova, D.; Hudan, S.; Lee, J.; Lukyanov, S.; Lynch, W. G.; McDaniel, S.; Mocko, M.; Obertelli, A.; Rogers, A. M.; Sobotka, L. G.; Terry, J. R.; Tostevin, J. A.; Tsang, M. B.; Wallace, M. S.

2009-06-01

400

Information Exchange for theInformation Exchange for the Development of SustainableDevelopment of Sustainable  

E-print Network

Information Exchange for theInformation Exchange for the Development of SustainableDevelopment influenced the development ofthe development of sustainable wood process industrysustainable wood process industry substantiallysubstantially .. Information Exchange for the development of Sustainable Wood Process

401

Sleeve reaction chamber system  

DOEpatents

A chemical reaction chamber system that combines devices such as doped polysilicon for heating, bulk silicon for convective cooling, and thermoelectric (TE) coolers to augment the heating and cooling rates of the reaction chamber or chambers. In addition the system includes non-silicon-based reaction chambers such as any high thermal conductivity material used in combination with a thermoelectric cooling mechanism (i.e., Peltier device). The heat contained in the thermally conductive part of the system can be used/reused to heat the device, thereby conserving energy and expediting the heating/cooling rates. The system combines a micromachined silicon reaction chamber, for example, with an additional module/device for augmented heating/cooling using the Peltier effect. This additional module is particularly useful in extreme environments (very hot or extremely cold) where augmented heating/cooling would be useful to speed up the thermal cycling rates. The chemical reaction chamber system has various applications for synthesis or processing of organic, inorganic, or biochemical reactions, including the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction.

Northrup, M. Allen (Berkeley, CA); Beeman, Barton V. (San Mateo, CA); Benett, William J. (Livermore, CA); Hadley, Dean R. (Manteca, CA); Landre, Phoebe (Livermore, CA); Lehew, Stacy L. (Livermore, CA); Krulevitch, Peter A. (Pleasanton, CA)

2009-08-25

402

Radical reactions of borohydrides.  

PubMed

Borohydrides are an important class of reagents in both organic and inorganic chemistry. Though popular as hydride-transfer reagents for reduction, since earlier work from the 1970s, borohydride reagents have also been known to serve as hydrogen-transfer reagents. In pursuit of greener tin hydride substitutes, recent progress has been made to mediate radical C-C bond forming reactions, including Giese reactions, radical carbonylation and addition to HCHO reactions, with borohydride reagents. This review article focuses on state-of-the-art borohydride based radical reactions, also covering earlier work, kinetics and some DFT calculations with respect to the hydrogen transfer mechanism. PMID:25349957

Kawamoto, Takuji; Ryu, Ilhyong

2014-12-28

403

Evidence for a SN2-type pathway in the exchange of phosphines at a [PhSe]+ centre.  

PubMed

A range of thio- and seleno-phosphonium cationic complexes [RE(PR'3)](+)[X](-) (R = Me, Ph; E = S, Se; X = GaCl4, SbF6) have been synthesised and structurally characterised. Reaction of [PhSPPh3][GaCl4] and [PhSePPh3][GaCl4] with P(t)Bu3 results in the ready transfer of the "RS(+)" and "RSe(+)" fragments from PPh3 to the stronger electron donor P(t)Bu3. NMR experiments combined with an Eyring analysis on the corresponding degenerate phosphine exchange reaction allowed the thermodynamic values for the phosphine exchange reaction of the sulfur cation (?H(‡) 18.7 ± 12.0 kJ mol(-1); ?S(‡) -99.3 ± 36.3 J mol(-1) K(-1)) to be compared with the corresponding values (?H(‡) 2.4 ± 1.1 kJ mol(-1) and ?S(‡) -58.1 ± 5.0 J mol(-1) K(-1)) for the [PhSePPh3](+) system. Importantly, the large negative entropy of activation and linear dependence on the rate of exchange are compatible with an SN2-type exchange process. This conclusion is supported by DFT calculations which confirm that the phosphine exchange process occurs via an associative mechanism. The rate of exchange was found to increase from sulfur to selenium and those with aryl substituents underwent exchange faster than those with alkyl substituents. PMID:25318556

Forfar, Laura C; Green, Michael; Haddow, Mairi F; Hussein, Sharifa; Lynam, Jason M; Slattery, John M; Russell, Christopher A

2015-01-01

404

Evaluation of anion exchange resins Tulsion A-30 and Indion-930A by application of radioanalytical technique  

NASA Astrophysics Data System (ADS)

Radioanalytical technique using 131I and 82Br was employed to evaluate organic based anion exchange resins Tulsion A-30 and Indion-930A. The evaluation was based on performance of these resins during iodide and bromide ion-isotopic exchange reactions. It was observed that for iodide ion-isotopic exchange reaction by using Tulsion A-30 resin, the values of specific reaction rate (min-1), amount of iodide ion exchanged (mmol), initial rate of iodide ion exchange (mmol/min) and log K d were 0.238, 0.477, 0.114, and 11.0, respectively, which was higher than 0.155, 0.360, 0.056, and 7.3, respectively as that obtained by using Indion-930A resins under identical experimental conditions of 40.0°C, 1.000 g of ion exchange resins and 0.003 M labeled iodide ion solution. Also at a constant temperature of 40.0°C, as the concentration of labeled iodide ion solution increases 0.001 to 0.004 M, for Tulsion A-30 resins the percentage of iodide ions exchanged increases from 59.0 to 65.1%, and from 46.4 to 48.8% for Indion-930A resins under identical experimental conditions. The identical trend was observed for both the resins during bromide ion-isotopic exchange reactions. The overall results indicate that under identical experimental conditions, Tulsion A-30 show superior performance over Indion-930A resins. The results of present experimental work have demonstrated that the radioanalytical technique used here can be successfully applied for characterization of different ion exchange resins so as to evaluate their performance under various process parameters.

Singare, P. U.

2014-07-01

405

Primer on nuclear exchange models  

SciTech Connect

Basic physics is applied to nuclear force exchange models between two nations. Ultimately, this scenario approach can be used to try and answer the age old question of 'how much is enough?' This work is based on Chapter 2 of Physics of Societal Issues: Calculations on National Security, Environment and Energy (Springer, 2007 and 2014)

Hafemeister, David [Physics Department, Cal Poly University, San Luis Obispo, California (United States)

2014-05-09

406

Knowledge Exchange with Sistema Scotland  

ERIC Educational Resources Information Center

This paper reports on a knowledge exchange project, funded by the Scottish Funding Council and undertaken by a group of researchers from three higher education institutions in Scotland and the project partner, Sistema Scotland. This newly established charity is attempting to implement a major programme of social change, developed in Venezuela,…

Allan, Julie; Moran, Nikki; Duffy, Celia; Loening, Gica

2010-01-01

407

Gambling, exchange systems, and moralities.  

PubMed

History and ethnography show us that, across societies of the past and present, gambling varies considerably with respect to its organization, social meanings, and how it is regarded in moral terms. This paper presents a basic scheme for analyzing the relationship between gambling and society. A theoretical starting point is that reciprocity is fundamental to social and economic systems. An anthropological theory of exchange systems makes a broad distinction between a structural dimension (generalized versus balanced reciprocity) and a normative dimension (from voluntary to involuntary). A model of four basic forms of reciprocity, each having a characteristic exchange mode and morality, can thus be constructed. Gambling is here understood as an exchange system embedded in the reciprocal orders of society and having a necessary relationship to these; it can take on the characteristics of such an order or it can be regarded as conflicting with it. Much of the variation in the form and morality of gambling therefore emerges as systematic and explainable by a theory of forms of reciprocal exchange. PMID:16311877

Binde, Per

2005-01-01

408

The Picture Exchange Communication System  

Microsoft Academic Search

A variety of strategies have been used to help children with autism acquire functional communication skills. The Picture Exchange Communication System (PECS) is a unique communication training program that was developed as a means of circumventing some shortcomings associatd with these strategies. A description of the steps within PECS is provided. Long-term group data have indicated that a large proportion

Andrew S. Bondy; Lori A. Frost

1994-01-01

409

Lightweight long life heat exchanger  

NASA Technical Reports Server (NTRS)

The design, fabrication, and evaluation of a full scale shuttle-type condensing heat exchanger constructed of aluminum and utilizing aluminum clad titanium parting sheets is described. A long term salt spray test of candidate parting sheet specimens is described. The results of an investigation into an alternate method of making composite sheet material are discussed.

Moore, E. K.

1975-01-01

410

GAS EXCHANGE Respiration: An Introduction  

E-print Network

Bohr effect Effect of the proton concentration (pH) on the oxygen affinity of hemoglobin. Carbonic cascade A model of gas exchange in which gas is viewed as flowing through a series of resistances from the environment to the tissues or vice versa. The model is based on the analogy of water flowing down a series

Wood, Spencer

411

Sister chromatid exchanges in barley  

Microsoft Academic Search

A mean frequency of 20.6 sister chromatid exchanges (SCEs) per cell has been observed in a reconstructed karyotype of Hordeum vulgare by application of the FPG technique after unifilar incorporation of BrdU into chromosomes. The involvement in SCEs of the 48 segments into which the chromosome set had been subdivided was, with a single deviation, length proportional and independent of

I. Schubert; G. Künzel; H. Bretschneider; R. Rieger; H. Nicoloff

1980-01-01

412

Kinetic Modeling of Hyperpolarized 13C Label Exchange between Pyruvate and Lactate in Tumor Cells*  

PubMed Central

Measurements of the kinetics of hyperpolarized 13C label exchange between [1-13C]pyruvate and lactate in suspensions of intact and lysed murine lymphoma cells, and in cells in which lactate dehydrogenase expression had been modulated by inhibition of the PI3K pathway, were used to determine quantitatively the role of enzyme activity and membrane transport in controlling isotope flux. Both steps were shown to share in the control of isotope flux in these cells. The kinetics of label exchange were well described by a kinetic model that employed rate constants for the lactate dehydrogenase reaction that had been determined previously from steady state kinetic studies. The enzyme showed pyruvate inhibition in steady state kinetic measurements, which the kinetic model predicted should also be observed in the isotope exchange measurements. However, no such pyruvate inhibition was observed in either intact cells or cell lysates and this could be explained by the much higher enzyme concentrations present in the isotope exchange experiments. The kinetic analysis presented here shows how lactate dehydrogenase activity can be determined from the isotope exchange measurements. The kinetic model should be useful for modeling the exchange reaction in vivo, particularly as this technique progresses to the clinic. PMID:21596745

Witney, Timothy H.; Kettunen, Mikko I.; Brindle, Kevin M.

2011-01-01

413

Implementation of a vibrationally linked chemical reaction model for DSMC  

NASA Technical Reports Server (NTRS)

A new procedure closely linking dissociation and exchange reactions in air to the vibrational levels of the diatomic molecules has been implemented in both one- and two-dimensional versions of Direct Simulation Monte Carlo (DSMC) programs. The previous modeling of chemical reactions with DSMC was based on the continuum reaction rates for the various possible reactions. The new method is more closely related to the actual physics of dissociation and is more appropriate to the particle nature of DSMC. Two cases are presented: the relaxation to equilibrium of undissociated air initially at 10,000 K, and the axisymmetric calculation of shuttle forebody heating during reentry at 92.35 km and 7500 m/s. Although reaction rates are not used in determining the dissociations or exchange reactions, the new method produces rates which agree astonishingly well with the published rates derived from experiment. The results for gas properties and surface properties also agree well with the results produced by earlier DSMC models, equilibrium air calculations, and experiment.

Carlson, A. B.; Bird, Graeme A.

1994-01-01

414

Iron-Exchanged Zeolite as Effective Catalysts for Friedel–Crafts Alkylation with Alkyl Halides  

Microsoft Academic Search

Friedel–Crafts alkylation of benzene and ethylbenzene with butyl halides has been investigated in the presence of iron-exchanged zeolites. The catalysts showed high conversions and selectivity for monoalkylated products with tertiary and secondary halides under mild reaction conditions (45–60°C). Alkylation of ethylbenzene with 2-chlorobutane can be achieved in 99% yield and 100% selectivity to the monoalkylated product.

Antônio M. F. Bidart; Ana P. S. Borges; Leonardo Nogueira; Elizabeth R. Lachter; Claudio J. A. Mota

2001-01-01

415

Effects of Exchange Energy and Spin-Orbit Coupling on Bond Energies  

ERIC Educational Resources Information Center

Since chemical reactions involve the breaking and making of bonds, understanding the relative strengths of bonds is of paramount importance in the study, teaching, and practice of chemistry. Further, it is showed that free atoms having p(super n) configuration with n = 2,3, or 4 are stabilized by exchange energy, and by spin-orbit coupling for n =…

Smith, Derek W.

2004-01-01

416

Conducting polymer-coated corrosion resistant metallic bipolar plates for proton exchange membrane fuel cells  

Microsoft Academic Search

Concerns over depleting stocks of natural resources and a growing awareness of the environmental damage caused by widespread burning of fossil fuels, and more energy demands brought the idea of alternative energy systems. Proton Exchange Membrane (PEM) fuel cells are one of the fast growing alternative energy technologies. PEM fuel cells generate electricity from an electrochemical reaction between hydrogen and

Shine Joseph

2005-01-01

417

Electrochemical Removal of Carbon Monoxide in Reformate Hydrogen for Fueling Proton Exchange Membrane  

E-print Network

Electrochemical Removal of Carbon Monoxide in Reformate Hydrogen for Fueling Proton Exchange, Austria, Meeting of the Society, October 4­9, 2009. Carbon monoxide CO in hydrogen reformed from carbon by poisoning the anode active sites, as shown in Reaction 1 1-4 Pt + CO Pt­CO 1 To mitigate the detrimental

Weidner, John W.

418

Acetone and Water on TiO?(110): H/D Exchange  

SciTech Connect

Isotopic H/D exchange between coadsorbed acetone and water on the TiO?(110) surface was examined using temperature programmed desorption (TPD) as a function of coverage and two surface pretreatments (oxidation and reduction). Coadsorbed acetone and water interact repulsively on reduced TiO?(110) based on results from the companion paper to this study, with water exerting a greater influence in destabilizing acetone and acetone having only a nominal influence on water. Despite the repulsive interaction between these coadsorbates, about 0.02 ML of a 1 ML d6-acetone on the reduced surface exhibits H/D exchange with coadsorbed water, with the exchange occurring exclusively in the high temperature region of the d?-acetone TPD spectrum at {approx}340 K. The effect was confirmed with combinations of d?-acetone and D?O. The extent of exchange decreased on the reduced surface with water coverages above {approx}0.3 ML due to the ability of water to displace coadsorbed acetone from first layer sites to the multilayer. In contrast, the extent of exchange increased by a factor of 3 when the surface was pre-oxidized prior to coadsorption. In this case, there was no evidence for the negative influence of high water coverages on the extent of H/D exchange. Comparison of the TPD spectra from the exchange products (either d?- or d?-acetone depending on the coadsorption pairing) suggests that, in addition to the 340 K exchange process seen on the reduced surface, a second exchange process was observed on the oxidized surface at {approx}390 K. In both cases (oxidized and reduced), desorption of the H/D exchange products appeared to be reaction limited and to involve the influence of OH/OD groups (or water formed during recombinative desorption of OH/OD groups) instead of molecularly adsorbed water. The 340 K exchange process is assigned to reaction at step sites and the 390 K exchange process is attributed to the influence of oxygen adatoms deposited during surface oxidation. The H/D exchange mechanism likely involves an enolate or propenol surface intermediate formed transiently during the desorption of oxygen-stabilized acetone molecules.

Henderson, Michael A.

2005-04-12

419

Intensification of the solvent-free catalytic hydroformylation of cyclododecatriene: Comparison of a stirred batch reactor and a heat-exchange reactor  

Microsoft Academic Search

The potential of heat-exchange reactors with mm-scale channels to provide process intensification for homogeneously catalysed gas–liquid reactions was explored. The solvent-free hydroformylation of cyclododecatriene using a homogeneous catalyst was carried out in a heat-exchange (HEx) reactor with mm-scale thin channels, and in a stirred batch autoclave for comparative purposes. The reaction was carried out using generally a concentration of 0.3mol%

Dan I. Enache; William Thiam; Delphine Dumas; Simon Ellwood; Graham J. Hutchings; Stuart H. Taylor; Steve Hawker; E. H. Stitt

2007-01-01

420

Kinetics of Ion Exchange on Clay Minerals and Soil: II. Elucidation of Rate-limiting Steps1 R. A. OGWADA ANDD. L. SPARKS2  

E-print Network

Kinetics of Ion Exchange on Clay Minerals and Soil: II. Elucidation of Rate-limiting Steps1 R. A, diffusion, reaction kinetics, K-ion selective electrode, energies of activation. Ogwada, R.A., and D.L. Sparks. 1986. Kinetics of ion exchange on clay minerals and soil: II. Elucidation of rate-limiting steps

Sparks, Donald L.

421

Dispersion of reactive species with reversible and irreversible wall reactions  

NASA Astrophysics Data System (ADS)

The longitudinal dispersion of a chemical species released in an oscillatory flow through an annular tube has been studied in presence of two kinds of first order reactions between the species and tube-wall. The species is supposed to undergo kinetic reversible phase exchange with the outer-wall material and irreversible absorption into the wall. Due to the variation of velocity across the tube section, the chemical species may spread out axially along the tube at a much faster rate than that produced by the molecular diffusion. A finite-difference implicit scheme has been adopted to solve the unsteady convection-diffusion equation for all time period based on the Aris method of moments. Axial distributions of mean concentration are determined from the first four central moments using Hermite polynomial representation for the periodic flow with and without non-zero mean flow. The study brings forward the coupled effects of reversible phase exchange and irreversible absorption on dispersion coefficient. Both the reversible and irreversible reactions are found to inhabit the dispersion process at early times, but at developed stage dispersion may be enhanced by the reversible phase exchange, provided the velocity comprises time invariant component. The decrease of peak of the mean concentration distribution with the increase of reaction rate is found irrespective of the nature of reaction.

Mazumder, B. S.; Paul, Suvadip

2012-06-01

422

Electrode kinetics: reactions  

Microsoft Academic Search

This is Volume 27 in the Comprehensive Chemical Kinetics series. The contributors are Calvo (Argentina), Hamnett (England), O'Sullivan (United States), and Weaver (United States). The book's chapters cover Redox Reactions at Metal-Solution Interfaces, Semiconductor Electrochemistry, and Reactions at Metal Oxide Electrodes. The references date from the 1960s to the mid-1980s. An index is included.

1987-01-01

423

Reactions to Attitudinal Deviancy.  

ERIC Educational Resources Information Center

This paper presents a critical review of empirical and theoretical treatments of group reaction to attitudinal deviancy. Inspired by Festinger's (1950) ideas on resolution of attitudinal discrepancies in groups, Schachter (1951) conducted an experiment that has greatly influenced subsequent research and theory concerning reaction to attitudinal…

Levine, John M.; Allen, Vernon L.

424

Clock Reaction: Outreach Attraction  

ERIC Educational Resources Information Center

Chemistry students are often introduced to the concept of reaction rates through demonstrations or laboratory activities involving the well-known iodine clock reaction. For example, a laboratory experiment involving thiosulfate as an iodine scavenger is part of the first-year general chemistry laboratory curriculum at Dalhousie University. With…

Carpenter, Yuen-ying; Phillips, Heather A.; Jakubinek, Michael B.

2010-01-01

425

Smell the Maillard Reaction  

NSDL National Science Digital Library

In this activity, learners cook amino acids and sugar to explore the range of aromas released. When amino acids and sugars are heated, learners will observe a phenomenon known as the Maillard reaction, also known as the browning reaction. Caution!: Kids, please don't try this at home without the help of an adult. The corn syrup can get very hot, very quickly.

Exploratorium

2012-10-03

426

Oscillating Chemical Reactions  

ERIC Educational Resources Information Center

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

Hawkins, M. D.; And Others

1975-01-01

427

Alternative Anode Reaction for Copper Electrowinning  

SciTech Connect

This report describes a project funded by the Department of Energy, with additional funding from Bechtel National, to develop a copper electrowinning process with lower costs and lower emissions than the current process. This new process also includes more energy efficient production by using catalytic-surfaced anodes and a different electrochemical couple in the electrolyte, providing an alternative oxidation reaction that requires up to 50% less energy than is currently required to electrowin the same quantity of copper. This alternative anode reaction, which oxidizes ferric ions to ferrous, with subsequent reduction back to ferric using sulfur dioxide, was demonstrated to be technically and operationally feasible. However, pure sulfur dioxide was determined to be prohibitively expensive and use of a sulfur burner, producing 12% SO{sub 2}, was deemed a viable alternative. This alternate, sulfur-burning process requires a sulfur burner, waste heat boiler, quench tower, and reaction towers. The electrolyte containing absorbed SO{sub 2} passes through activated carbon to regenerate the ferrous ion. Because this reaction produces sulfuric acid, excess acid removal by ion exchange is necessary and produces a low concentration acid suitable for leaching oxide copper minerals. If sulfide minerals are to be leached or the acid unneeded on site, hydrogen was demonstrated to be a potential reductant. Preliminary economics indicate that the process would only be viable if significant credits could be realized for electrical power produced by the sulfur burner and for acid if used for leaching of oxidized copper minerals on site.

Not Available

2005-07-01

428

The load and release characteristics on a strong cationic ion-exchange fiber: kinetics, thermodynamics, and influences  

PubMed Central

Ion-exchange fibers were different from conventional ion-exchange resins in their non-cross-linked structure. The exchange was located on the surface of the framework, and the transport resistance reduced significantly, which might mean that the exchange is controlled by an ionic reaction instead of diffusion. Therefore, this work aimed to investigate the load and release characteristics of five model drugs with the strong cationic ion-exchange fiber ZB-1. Drugs were loaded using a batch process and released in United States Pharmacopoeia (USP) dissolution apparatus 2. Opposing exchange kinetics, suitable for the special structure of the fiber, were developed for describing the exchange process with the help of thermodynamics, which illustrated that the load was controlled by an ionic reaction. The molecular weight was the most important factor to influence the drug load and release rate. Strong alkalinity and rings in the molecular structures made the affinity between the drug and fiber strong, while logP did not cause any profound differences. The drug–fiber complexes exhibited sustained release. Different kinds and concentrations of counter ions or different amounts of drug–fiber complexes in the release medium affected the release behavior, while the pH value was independent of it. The groundwork for in-depth exploration and further application of ion-exchange fibers has been laid. PMID:25114504

Yuan, Jing; Gao, Yanan; Wang, Xinyu; Liu, Hongzhuo; Che, Xin; Xu, Lu; Yang, Yang; Wang, Qifang; Wang, Yan; Li, Sanming

2014-01-01

429

Surface-Water Exchanges for Streams Entering Lakes Compared with Shoreline Exchanges in General  

NASA Astrophysics Data System (ADS)

Streamflow and thermal patterns suggest that stream/streambed exchanges are more dynamic than lake/sediment exchanges along the nearby shoreline. A synoptic field program was carried out in September 2012 for Lake Tahoe NV, when baseflow is dominant and diurnal temperature patterns are large as alpine night temperatures cool tributary waters to well below lake water temperatures. Two streams with significant adjoining lakeshores were chosen for thermal and hydraulic instrumentation, with continuous logging and periodic water quality sampling. Due to partial channelization, Incline Creek flows and discharges nearly perpendicular to the shoreline on the lake's north shore, while in a natural setting Marlette Creek forms a summer barrier sandbar at its mouth on the lake's eastern shore. A suite of measurements were gathered, including continuous surface and subsurface water levels and temperatures, as well as periodic samples of nutrients and field parameters. For Incline Creek, the thermal and hydraulic patterns were monitored 1.3 m upstream of the mouth, across the mouth of the stream, and 1.3 m into the lake. These data were compared with data collected at equivalent locations along the shoreline away from the stream. Initial results reveal considerably more dynamic spatial and temporal patterns of exchange associated with the stream. For Marlette Creek, a barrier sandbar forms and spreads across the mouth as baseflow recession extends to the fall, and by September streamflow only directly reaches the lake during predawn hours when evapotranspiration is at a minimum. During September 2012, there was ponding behind the barrier sandbar resulting in stream-originated groundwater rapidly flowing through the sandbar, with high dissolved oxygen gradients approaching the lake. As a result of these synoptic results, a more extensive monitoring program was developed for September 2013, with additional instrumentation including automated seepage meters and infrared imaging across the shoreline and stream margins at and near the lake, to detect relatively uniform thermal patterns (and thus flux patterns) along the lakeshore compared with stream mouths. Initial results demonstrate several important issues with practical implications, including: (1) the generally unique nature of stream-mouth sediment exchanges compared with adjacent lakeshores are possibly significant with respect to nutrient transport and overall stream ecology at both streams, and (2) for Marlette Creek there's clear potential importance of barrier sandbars to impact nutrient reactions before stream-originated groundwater discharges to lakes.

Naranjo, R. C.; Allander, K.; Neilson, B. T.; Niswonger, R. G.; Constantz, J. E.

2013-12-01

430

Second Law Optimization of Heat Exchangers  

E-print Network

A new method for optimizing heat exchangers is developed in this paper. It is based on second law efficiency relationships rather than on the traditional heat exchanger effectiveness concept. The cost of energy is based on its availability level...

Witte, L. C.

431

New Challenges in Multihospital Kidney Exchange  

E-print Network

The growth of kidney exchange presents new challenges for the design of kidney exchange clearinghouses. The players now include directors of transplant centers, who see sets of patient-donor pairs, and can choose to reveal ...

Ashlagi, Itai

432

Modular Heat Exchanger With Integral Heat Pipe  

NASA Technical Reports Server (NTRS)

Modular heat exchanger with integral heat pipe transports heat from source to Stirling engine. Alternative to heat exchangers depending on integrities of thousands of brazed joints, contains only 40 brazed tubes.

Schreiber, Jeffrey G.

1992-01-01

433

Integrated Approach to Revamping Heat Exchangers Networks  

E-print Network

A heat exchanger network constitutes the core of the plant energy systems interlinking the core process operation and the utility systems. This paper will illustrate an integrated approach for the revamp of a heat exchanger network by bringing...

Glass, K. E.; Dhole, V.; Wang, Y.

434

Phosphonic acid based ion 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. 9 figures.

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

1994-01-25

435

Synergistic diffuser/heat-exchanger design  

E-print Network

The theoretical and numerical evaluation of synergistic diffusing heat-exchanger design is presented. Motivation for this development is based on current diffuser and heat-exchange technologies in cogeneration plants, which ...

Lazzara, David S. (David Sergio), 1980-

2004-01-01

436

Protein hydrogen exchange mechanism: Local fluctuations  

E-print Network

Protein hydrogen exchange mechanism: Local fluctuations HARIPADA MAITY, WOON KI LIM,1 JON N. RUMBLEY, AND S. WALTER ENGLANDER The Johnson Research Foundation, Department of Biochemistry & Biophysics the dynamic structural motions that determine protein hydrogen exchange (HX) behavior. The replacement

Englander, S. Walter

437

Phosphonic acid based ion 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.

1996-07-23

438

Phosphonic acid based ion 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)

1996-01-01

439

Phosphonic acid based ion 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 disphosphonic 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)

1994-01-01

440

Mechanisms in knockout reactions  

NASA Astrophysics Data System (ADS)

We report on the first detailed study of the mechanisms involved in knockout reactions, via a coincidence measurement of the residue and fast proton in one-proton knockout reactions, using the S800 spectrograph in combination with the HiRA detector array at the NSCL. Results on the reactions ^9Be(^9C,^8B+X)Y and ^9Be(^8B,^7Be+X)Y are presented. They are compared with theoretical predictions for both the diffraction (elastic breakup) and stripping (inelastic breakup) reaction mechanisms, as calculated in the eikonal model. The data shows a clear distinction between the two reaction mechanisms, and the observed respective proportions are very well reproduced by the reaction theory. This agreement supports the results of knockout reaction analyses and their applications to the spectroscopy of rare isotopes. In particular, this add considerable support to the use of the eikonal model as a quantitative tool, able, for example, to determine single-particle spectroscopic strengths in rare isotopes.

Bazin, D.; Charity, R. J.; de Souza, R. T.; Famiano, M. A.; Gade, A.; Henzl, V.; Henzlova, D.; Hudan, S.; Lee, J.; Lukyanov, S.; Lynch, W. G.; McDaniel, S.; Mocko, M.; Obertelli, A.; Rogers, A. M.; Sobotka, L. G.; Terry, J. R.; Tostevin, J. A.; Tsang, M. B.; Wallace, M. S.

2009-10-01

441

Helium escape from the Earth's atmosphere - The charge exchange mechanism revisited  

NASA Technical Reports Server (NTRS)

We have studied the escape of neutral helium from the terrestrial atmosphere through exothermic charge exchange reactions between He(+) ions and the major atmospheric constituents N2, O2 and O. Elastic collisions with the neutral background particles were treated quantitatively using a recently developed kinetic theory approach. An interhemispheric plasma transport model was employed to provide a global distribution of He(+) ions as a function of altitude, latitude and local solar time and for different levels of solar ionization. Combining these ion densities with neutral densities from an MSIS model and best estimates for the reaction rate coefficients of the charge exchange reactions, we computed the global distribution of the neutral He escape flux. The escape rates show large diurnal and latitudinal variations, while the global average does not vary by more than a factor of three over a solar cycle. We find that this escape mechanism is potentially important for the overall balance of helium in the Earth's atmosphere. However, more accurate values for the reaction rate coefficients of the charge exchange reactions are required to make a definitive assessment of its importance.

Lie-Svendsen, O.; Rees, M. H.; Stamnes, K.

1992-01-01

442

Mass transfer and kinetics of ion exchange  

Microsoft Academic Search

These papers were written by leading scientists and technologists working in the field of ion exchange, and they discuss the synthesis, equilibria, transport phenomena, kinetics and design of ion exchange resins and membranes, both systematically and progressively. This volume also reflects recent developments in the field, with sections dealing with novel areas of application for ion exchange, such as, pollution

L. Liberti; F. L. Helfferich

1983-01-01

443

Pharmaceutical Applications of Ion-Exchange Resins  

ERIC Educational Resources Information Center

The historical uses of ion-exchanged resins and a summary of the basic chemical principles involved in the ion-exchanged process are discussed. Specific applications of ion-exchange are provided that include drug stabilization, pharmaceutical excipients, taste-masking agents, oral sustained-release products, topical products for local application…

Elder, David

2005-01-01

444

MODELING PARTICLE DEPOSITION ON HVAC HEAT EXCHANGERS  

E-print Network

LBNL-49339 MODELING PARTICLE DEPOSITION ON HVAC HEAT EXCHANGERS J.A. Siegel1,3 * and W.W. Nazaroff2 Fouling of fin-and-tube heat exchangers by particle deposition leads to diminished effectiveness on heat exchanger surfaces. We present a model that accounts for impaction, diffusion, gravitational

445

Proceedings Article Failure-Aware Kidney Exchange  

E-print Network

Proceedings Article Failure-Aware Kidney Exchange JOHN P. DICKERSON, Computer Science Department in fielded kidney exchanges do not result in an actual transplant. In this paper, we address the problem that failure-aware kidney exchange can significantly increase the expected number of lives saved (i) in theory

Gordon, Geoffrey J.

446

Heat Exchanger Network Design, Monitoring and Optimization  

Microsoft Academic Search

In process industries, heat exchanger networks represent an important part of the plant structure. The purpose of the networks is to maximize heat recovery, thereby lowering the overall plant costs. Previously published research on heat exchanger networks deals with two categories:\\u000a• Synthesis of heat exchanger networks with the goal of designing a structure that provides the lowest total (capital

Uma Maheshwar Kiran Ati

2009-01-01

447

Self-disclosure as an exchange process  

Microsoft Academic Search

Found the exchange of self-disclosures in a laboratory setting to function in a manner consistent with social exchange theory. The intimacy of disclosures exchanged tended to follow the norm of reciprocity. More intimate initial disclosures were made to those who were initially better liked. In turn, final liking was higher for those who made more intimate disclosures. The authoritarianism of

Morgan Worthy; Albert L. Gary; Gay M. Kahn

1969-01-01

448

Information Exchange, Responsiveness and Logistics Provider Performance  

Microsoft Academic Search

The impact of information exchange on suppliers' performance is investigated in the context of trade relationships formed between manufacturers and third party providers of international logistics services. A conceptual model that predicts the important linkages among information exchange, responsiveness and performance is introduced and tested. The research shows that information exchange positively affects customers' perceptions of third party logistics providers'

Theodore P. Stank; Patricia J. Daugherty; Alexander E. Ellinger

1996-01-01

449

Pressurized bellows flat contact heat exchanger interface  

NASA Technical Reports Server (NTRS)

Disclosed is an interdigitated plate-type heat exchanger interface. The interface includes a modular interconnect to thermally connect a pair or pairs of plate-type heat exchangers to a second single or multiple plate-type heat exchanger. The modular interconnect comprises a series of parallel, plate-type heat exchangers arranged in pairs to form a slot therebetween. The plate-type heat exchangers of the second heat exchanger insert into the slots of the modular interconnect. Bellows are provided between the pairs of fins of the modular interconnect so that when the bellows are pressurized, they drive the plate-type heat exchangers of the modular interconnect toward one another, thus closing upon the second heat exchanger plates. Each end of the bellows has a part thereof a thin, membrane diaphragm which readily conforms to the contours of the heat exchanger plates of the modular interconnect when the bellows is pressurized. This ensures an even distribution of pressure on the heat exchangers of the modular interconnect thus creating substantially planar contact between the two heat exchangers. The effect of the interface of the present invention is to provide a dry connection between two heat exchangers whereby the rate of heat transfer can be varied by varying the pressure within the bellows.

Voss, Fred E. (inventor); Howell, Harold R. (inventor); Winkler, Roger V. (inventor)

1990-01-01

450

Cryogenic Heat Exchanger with Turbulent Flows  

ERIC Educational Resources Information Center

An evaporator-type cryogenic heat exchanger is designed and built for introducing fluid-solid heat exchange phenomena to undergraduates in a practical and efficient way. The heat exchanger functions at liquid nitrogen temperature and enables cooling of N[subscript 2] and He gases from room temperatures. We present first the experimental results of…

Amrit, Jay; Douay, Christelle; Dubois, Francis; Defresne, Gerard

2012-01-01

451

Trust and Transitions in Modes of Exchange  

ERIC Educational Resources Information Center

In this study, we investigate the relationship between uncertainty and trust in exogenous shifts in modes of social exchange (i.e., those that are not initiated by the individuals in a given exchange system). We explore how transitions from a high uncertainty environment (reciprocal exchange) to lower-uncertainty environments (nonbinding or…

Cheshire, Coye; Gerbasi, Alexandra; Cook, Karen S.

2010-01-01

452

Solute transport with equilibrium aqueous complexation and either sorption or ion exchange: Simulation methodology and applications  

USGS Publications Warehouse

Methodologies that account for specific types of chemical reactions in the simulation of solute transport can be developed so they are compatible with solution algorithms employed in existing transport codes. This enables the simulation of reactive transport in complex multidimensional flow regimes, and provides a means for existing codes to account for some of the fundamental chemical processes that occur among transported solutes. Two equilibrium-controlled reaction systems demonstrate a methodology for accommodating chemical interaction into models of solute transport. One system involves the sorption of a given chemical species, as well as two aqueous complexations in which the sorbing species is a participant. The other reaction set involves binary ion exchange coupled with aqueous complexation involving one of the exchanging species. The methodology accommodates these reaction systems through the addition of nonlinear terms to the transport equations for the sorbing species. Example simulation results show (1) the effect equilibrium chemical parameters have on the spatial distributions of concentration for complexing solutes; (2) that an interrelationship exists between mechanical dispersion and the various reaction processes; (3) that dispersive parameters of the porous media cannot be determined from reactive concentration distributions unless the reaction is accounted for or the influence of the reaction is negligible; (4) how the concentration of a chemical species may be significantly affected by its participation in an aqueous complex with a second species which also sorbs; and (5) that these coupled chemical processes influencing reactive transport can be demonstrated in two-dimensional flow regimes. ?? 1987.

Lewis, F.M.; Voss, C.I.; Rubin, J.

1987-01-01

453

Inflationary trispectrum from graviton exchange  

SciTech Connect

We compute the connected four-point correlation function of the primordial curvature perturbation generated during inflation with standard kinetic terms, where the correlation is established via exchange of a graviton between two pairs of scalar fluctuations. Any such correlation yields a contribution to the scalar trispectrum of the order of the tensor to scalar ratio r. This contribution is numerically one order of magnitude larger than the one previously calculated on the basis of scalar perturbations interacting at a point and satisfies a simple relation in the limit where the momentum of the graviton which is exchanged becomes much smaller than the external momenta. We conclude that the total non-linearity parameter generated by single-field models of slow-roll inflation is at maximum |{tau}{sub NL}| {approx} r.

Seery, David [Department of Applied Mathematics and Theoretical Physics, Wilberforce Road, Cambridge, CB3 0WA (United Kingdom)] [Department of Applied Mathematics and Theoretical Physics, Wilberforce Road, Cambridge, CB3 0WA (United Kingdom); Sloth, Martin S. [Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C (Denmark)] [Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C (Denmark); Vernizzi, Filippo, E-mail: djs61@cam.ac.uk, E-mail: sloth@phys.au.dk, E-mail: filippo.vernizzi@cea.fr [CEA, IPhT, 91191 Gif-sur-Yvette cedex, France CNRS, URA-2306, 91191 Gif-sur-Yvette cedex (France)] [CEA, IPhT, 91191 Gif-sur-Yvette cedex, France CNRS, URA-2306, 91191 Gif-sur-Yvette cedex (France)

2009-03-15

454

The NESACS Exchange with Germany  

NASA Astrophysics Data System (ADS)

In August 2007, the Northeastern Section of the American Chemical Society (NESACS), its Younger Chemists Committee (YCC), and its Education Committee will host a visit to Boston by representatives of the Young Chemists Forum (JCF) of the German Chemical Society (GDCh) as the seventh annual event of the exchange program between NESACS and GDCh. The German delegation of 14 graduate students and Kurt Begitt, Deputy Executive Director of the GDCh, will spend a week in Boston during the ACS National Meeting.

Hoffman, Morton Z.; Tanner, Ruth; Strem, Michael

2007-08-01

455

Improved Ceramic for Heat Exchangers  

NASA Technical Reports Server (NTRS)

Most promising composition developed in investigation consisted of mixed oxides described generically as ZrMAS. Has been commercially designated as GE-7808. Material was obtained from low-cost clay/talc mixture. Overall assessment of ZrMAS indicates it is a viable candidate for heat-exchanger application in automotive gas-turbine engines and possibly other areas that require dielectric materials of moderate refractoriness, good corrosion resistance, and excellent thermal-shock resistance.

Herbell, T. P.; Rauch, H. W.; Mccreeght, L. R.

1982-01-01

456

The Hollywood Stock Exchange (HSX)  

NSDL National Science Digital Library

The Hollywood Stock Exchange (HSX) is a stock market game based on the entertainment industry (registration required). According to the logic of HSX, stars have a bond rating based on their popularity and the potential gross sales of films may be traded as stocks. Players are encouraged to research their "MovieStocks" and "StarBonds" via Variety.com or the HSX Journal. Complete game instructions, a glossary of terms, and registration information are provided online.

1996-01-01

457

Authentication and Authenticated Key Exchanges  

Microsoft Academic Search

We discuss two-party mutual authentication protocols providing authenticated key exchange, focusing on those using asymmetric techniques. A simple, efficient protocol referred to as the station-to-station (STS) protocol is introduced, examined in detail, and considered in relation to existing protocols. The definition of a secure protocol is considered, and desirable characteristics of secure protocols are discussed. The goal of an authentication

Whitfield Diffie; Paul C. Van Oorschot; Michael J. Wiener

1992-01-01

458

On exchangeable continuous variable systems  

NASA Astrophysics Data System (ADS)

We investigate permutation-invariant continuous variable quantum states and their covariance matrices. We provide a complete characterization of the latter with respect to permutation invariance and exchangeability and representing convex combinations of tensor power states. On the level of the respective density operators this leads to necessary criteria for all these properties which become necessary and sufficient for Gaussian states. For these we use the derived results to provide de Finetti-type theorems for various distance measures.

König, Robert; Wolf, Michael M.

2009-01-01

459

Exchanging clinical knowledge via Internet.  

PubMed

The need for effective and efficient exchange of clinical knowledge is increasing. Paper based methods for managing clinical knowledge are not meeting the demand for knowledge and this has undoubtedly contributed to the widely reported failures of clinical guidelines. Internet affords both opportunities and dangers for clinical knowledge. Systems such as Wax have demonstrated the importance of intuitive structure in the management of knowledge. We report on a new initiative for the global management of clinical knowledge. PMID:9506390

Buchan, I E; Hanka, R

1997-11-01

460

Science Policy Exchange September 21, 2009 Columbia River Estuary Science-Policy Exchange  

E-print Network

Science Policy Exchange September 21, 2009 Summary 1 Columbia River Estuary Science-Policy Exchange and Conservation Council hosted a science-policy exchange in Astoria, Oregon. The Council supports strategies Science Advisory Board (ISAB) and the Independent Scientific Review Panel (ISRP) attended the exchange

461

Kinetic models of immediate exchange  

NASA Astrophysics Data System (ADS)

We propose a novel kinetic exchange model differing from previous ones in two main aspects. First, the basic dynamics is modified in order to represent economies where immediate wealth exchanges are carried out, instead of reshufflings or uni-directional movements of wealth. Such dynamics produces wealth distributions that describe more faithfully real data at small values of wealth. Secondly, a general probabilistic trading criterion is introduced, so that two economic units can decide independently whether to trade or not depending on their profit. It is found that the type of the equilibrium wealth distribution is the same for a large class of trading criteria formulated in a symmetrical way with respect to the two interacting units. This establishes unexpected links between and provides a microscopic foundations of various kinetic exchange models in which the existence of a saving propensity is postulated. We also study the generalized heterogeneous version of the model in which units use different trading criteria and show that suitable sets of diversified parameter values with a moderate level of heterogeneity can reproduce realistic wealth distributions with a Pareto power law.

Heinsalu, Els; Patriarca, Marco

2014-08-01

462

Effective method for recovering and enriching tritium from tritiated water by dual-temperature HâO-Hâ exchange process  

Microsoft Academic Search

The composite packing with the hydrophobic platinum catalyst for the isotope exchange reaction in HâO-Hâ system was improved to be appreciably active. Therefore, it became realistic to design a process for tritium recovery by the dual-temperature exchange method. The separation performance of dual-temperature 5stage cascade (S3-E2) was simulated. The process was designed to be operated under the condition of P

A. Kitamoto; M. Shimizu; Y. Takashima

1985-01-01

463

Selective catalytic reduction of nitric oxide by methane over cerium and silver ion-exchanged ZSM-5 zeolites  

Microsoft Academic Search

A new catalyst comprising cerium and silver ion-exchanged ZSM-5 zeolite is reported in this paper, for the reduction of nitric oxide by methane in the presence of excess oxygen. The bi-cation exchanged Ce—Ag-ZSM-5 catalyst was very active for this reaction, while either Ce-ZSM-5 or Ag-ZSM-5 alone showed low activity. The presence of oxygen in the feed gas mixture enhanced the

Zhijiang Li; Maria Flytzani-Stephanopoulos

1997-01-01

464

Magnetic properties and composition range of non-stoichiometric m-type hexagonal ferrites prepared by ion exchange  

Microsoft Academic Search

Single crystals of Ba, Sr M-type hexagonal ferrites were prepared by ion exchange in Ba, Sr containing molten salts from single crystals of beta'' -ferrites. A fast diffusion of the divalent Ba2+, Sr2+ is observed leading to a non-stoichiometric M-type ferrite with chemical formula: Ba1+xFe10.5Co0.25O17+x (0 <= x <= 0.25). x depending on the exchange reaction time. Saturation magnetization ranges

O. Kalogirou; D. Samaras; A. C. Stergiou

1990-01-01

465

Oral Hypersensitivity Reactions  

MedlinePLUS

... Million NIDCR/NIH Grant 2015 AAOM Call for Abstract Submissions Upcoming Events 2015 Annual Conference Registration is Now Open 2016 Annual Meeting in Atlanta - Save the Date! Oral Hypersensitivity Reactions ...

466

Types of Allergic Reactions  

MedlinePLUS

... allergies. Substances that don't bother some people (including certain medications) can trigger allergic reactions in others. ... | Terms and Conditions © 1996-2015 Academy of General Dentistry. All Rights Reserved.

467

Chemisorption And Precipitation Reactions  

EPA Science Inventory

The transport and bioavailability of chemical components within soils is, in part, controlled by partitioning between solids and solution. General terms used to describe these partitioning reactions include chemisorption and precipitation. Chemisorption is inclusive of the suit...

468

Untoward penicillin reactions  

PubMed Central

The literature on untoward reactions following the administration of penicillin is reviewed. These reactions, including a certain number of deaths which have been reported, are of particular interest to health administrations and to WHO in view of the large-scale programmes for controlling the treponematoses which are now under way—programmes affecting millions of people in many parts of the world. The most serious problems are anaphylactic sensitivity phenomena and superinfection or cross-infection with penicillin-resistant organisms, and the reactions involved range in intensity from the mildest to the fatal; the incidence of the latter is estimated at 0.1-0.3 per million injections. The authors point out that with increasing use of penicillin, more persons are likely to become sensitized and the number of reactions can therefore be expected to rise. The best prevention against such an increase is the restriction of the unnecessary use of penicillin. PMID:13596877

Guthe, T.; Idsöe, O.; Willcox, R. R.

1958-01-01

469

Polymerase Chain Reaction  

NSDL National Science Digital Library

This interactive activity adapted from the University of Nebraska's Library of Crop Technologies depicts steps in the polymerase chain reaction (PCR) technique and explains how it is used to efficiently copy sections of DNA for analysis.

WGBH Educational Foundation

2009-12-07

470

An Illuminating Reaction.  

ERIC Educational Resources Information Center

Describes the use of carbide lights as an excellent mechanism for introducing or reviewing many basic chemistry concepts including elements and compounds, endothermic and exothermic reactions, physical and chemical changes, and balancing chemical equations. (JRH)

Matthews, Catherine E.

1996-01-01

471

EXCHANGE  

SciTech Connect

This report contains the following news headlines: ADPE acquisition process made easy with SRP; scientific reference material available; ORPS WordPerfect macro setup procedure; system managed storage is here; LIBSPOOL for MVS mainframe end-users; training center course schedule for February 1993; enjoy NJOY; scientific user services staff decreased; new release of Forwarn, a static source code analysis tool for FORTRAN programs; out of the cold with HEAT; coping cells from one table to another in word perfect; used PC equipment pool; and video training.

Boltz, J.C. (ed.)

1993-01-01

472

SAFE gas turbine cycle primary heat exchangers  

NASA Astrophysics Data System (ADS)

Los Alamos National Laboratory and Marshall Space Flight Center are jointly developing two modular heat pipe heat exchangers, collectively named FIGMENT (Fission Inert Gas Metal Exchanger for Non-nuclear Testing). The FIGMENT heat exchangers are designed to transfer power from the SAFE nuclear reactor cores to gas turbine energy converters. A stainless steel prototype heat exchanger will be built during 2002 in preparation for the construction of a larger refractory metal version. Two promising FIGMENT stainless steel heat exchanger concepts are reviewed here. .

Reid, Robert S.; Kapernick, Richard J.

2002-01-01

473

Nitropyridines: Synthesis and reactions  

Microsoft Academic Search

Reaction of pyridine and substituted pyridines with N2O5 in an organic solvent gives the N-nitropyridinium ion. When this is reacted with SO2\\/HSO3 - in water, 3-nitropyri- dine is obtained (77 % yield). With substituted pyridines, the method gives good yields for 4-substituted and moderate yields for 3-substituted pyridines. The reaction mechanism is not an electrophilic aromatic substitution, but one in

Jan M. Bakke

2003-01-01

474

Safety of chlorination reactions  

Microsoft Academic Search

Chlorination reactions are part of various processes in the chemical industry, to manufacture heavy chemicals, specialty chemicals, pesticides and pharmaceuticals, in inorganic and organic chemistry. They are a valuable tool in organic synthesis.The hazard of processing chlorine involves:u- Gas phase explosion;- Runaway reaction or thermal explosion in the condensed phase.Gas phase explosion hazard with chlorine as an oxidizer is present

Jean-Louis Gustin; Alexandre Fines

1996-0