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1

OLIGOSACCHARIDE STRUCTURES STUDIED BY HYDROGEN-DEUTERIUM EXCHANGE (HX) AND MALDI-TOF MASS SPECTROMETRY  

Technology Transfer Automated Retrieval System (TEKTRAN)

Hydrogen-deuterium exchange matrix-assisted laser desorption/ionization - time-of-flight mass spectrometry (HX-MALDI-TOF MS) is reported for the first time for the determination of exchangeable protons in diverse oligosaccharide and glycoconjugate structures. The method is generally analogous to th...

2

Pulsed hydrogen/deuterium exchange mass spectrometry for time-resolved membrane protein folding studies.  

PubMed

Kinetic folding experiments by pulsed hydrogen/deuterium exchange (HDX) mass spectrometry (MS) are a well-established tool for water-soluble proteins. To the best of our knowledge, the current study is the first that applies this approach to an integral membrane protein. The native state of bacteriorhodopsin (BR) comprises seven transmembrane helices and a covalently bound retinal cofactor. BR exposure to sodium dodecyl sulfate (SDS) induces partial unfolding and retinal loss. We employ a custom-built three-stage mixing device for pulsed-HDX/MS investigations of BR refolding. The reaction is triggered by mixing SDS-denatured protein with bicelles. After a variable folding time (10?ms to 24?h), the protein is exposed to excess D(2) O buffer under rapid exchange conditions. The HDX pulse is terminated by acid quenching after 24?ms. Subsequent off-line analysis is performed by size exclusion chromatography and electrospray MS. These measurements yield the number of protected backbone N-H sites as a function of folding time, reflecting the recovery of secondary structure. Our results indicate that much of the BR secondary structure is formed quite late during the reaction, on a time scale of 10?s and beyond. It is hoped that in the future it will be possible to extend the pulsed-HDX/MS approach employed here to membrane proteins other than BR. PMID:23280751

Khanal, Anil; Pan, Yan; Brown, Leonid S; Konermann, Lars

2012-12-01

3

Hydrogen/Deuterium Exchange Study of Subtilisin Carlsberg During Prolonged Exposure to Organic Solvents  

PubMed Central

It has been previously reported that prolonged exposure of an enzyme to organic solvents leads to substantial decrease of activity. This effect was found to be unrelated to the catalysts’ structure or their possible aggregation in organic solvents, and up to the present day the cause for activity loss remains unclear. In the present work, the structural dynamics of the serine protease subtilisin Carlsberg (SC) have been investigated during prolonged exposure to two organic solvents by following hydrogen/deuterium (H/D) exchange of mobile protons. The enzyme, after lyophilization, was incubated in organic solvents at controlled deuteriated water activity for different times and the H/D exchange was allowed to take place. The amount of deuterium exchanged was evaluated by 2H NMR, which in turn gave us a picture of the changing dynamics of our model enzyme during incubation and under different experimental conditions. Our results show that the flexibility of SC decreases during prolonged storage in 1,4-dioxane (Diox) and acetonitrile (ACN) as indicated by the observed 3- to 10-fold decrease in the apparent rate constants of exchange (k) of fast exchangeable protons (FEP) and slow exchangeable protons (SEP) in the protein. Our study also shows that SC is more flexible in ACN than in Diox (k 3?20 times higher in ACN for the FEP and SEP), suggesting that enzyme dynamics are affected by solvent physicochemical properties. Additionally, the enzyme dynamics are also affected by the method of preparation: decreased flexibility (k decreases 3- to 10-fold for FEP and SEP) is observed when the enzyme is chemically modified with poly ethylene glycol (PEGylated) or colyophilized with crown ethers. A possible relationship between activity, enantioselectivity (E), and structural dynamics is discussed, demonstrating that direct correlations, as have been attempted in the past, are hampered by the multi-variable nature and complexity of the system.

Fasoli, Ezio; Ferrer, Amaris; Barletta, Gabriel L.

2009-01-01

4

The Utility of Hydrogen/Deuterium Exchange Mass Spectrometry in Biopharmaceutical Comparability Studies  

PubMed Central

The function, efficacy, and safety of protein biopharmaceuticals are tied to their three-dimensional structure. The analysis and verification of this higher-order structure are critical in demonstrating manufacturing consistency and in establishing the absence of structural changes in response to changes in production. It is, therefore, essential to have reliable, high-resolution and high sensitivity biophysical tools capable of interrogating protein structure and conformation. Here, we demonstrate the use of hydrogen/deuterium exchange mass spectrometry (H/DX-MS) in biopharmaceutical comparability studies. H/DX-MS measurements can be conducted with good precision, consume only picomoles of protein, interrogate nearly the entire molecule with peptide level resolution, and can be completed in a few days. Structural comparability or lack of comparability was monitored for different preparations of interferon-?-1a. We present specific graphical formats for the display of H/DX-MS data that aid in rapidly making both the qualitative (visual) and quantitative assessment of comparability. H/DX-MS is capable of making significant contributions in biopharmaceutical characterization by providing more informative and confident comparability assessments of protein higher order structure than are currently available within the biopharmaceutical industry.

Houde, Damian; Berkowitz, Steven A.; Engen, John R.

2011-01-01

5

Infrared spectroscopic study of photoreceptor membrane and purple membrane. Protein secondary structure and hydrogen deuterium exchange  

SciTech Connect

Infrared spectroscopy in the interval from 1800 to 1300 cm-1 has been used to investigate the secondary structure and the hydrogen/deuterium exchange behavior of bacteriorhodopsin and bovine rhodopsin in their respective native membranes. The amide I' and amide II' regions from spectra of membrane suspensions in D2O were decomposed into constituent bands by use of a curve-fitting procedure. The amide I' bands could be fit with a minimum of three theoretical components having peak positions at 1664, 1638, and 1625 cm-1 for bacteriorhodopsin and 1657, 1639, and 1625 cm-1 for rhodopsin. For both of these membrane proteins, the amide I' spectrum suggests that alpha-helix is the predominant form of peptide chain secondary structure, but that a substantial amount of beta-sheet conformation is present as well. The shape of the amide I' band was pH-sensitive for photoreceptor membranes, but not for purple membrane, indicating that membrane-bound rhodopsin undergoes a conformation change at acidic pH. Peptide hydrogen exchange of bacteriorhodopsin and rhodopsin was monitored by observing the change in the ratio of integrated absorbance (Aamide II'/Aamide I') during the interval from 1.5 to 25 h after membranes were introduced into buffered D2O. The fraction of peptide groups in a very slowly exchanging secondary structure was estimated to be 0.71 for bacteriorhodopsin at pD 7. The corresponding fraction in vertebrate rhodopsin was estimated to be less than or equal to 0.60. These findings are discussed in relationship to previous studies of hydrogen exchange behavior and to structural models for both proteins.

Downer, N.W.; Bruchman, T.J.; Hazzard, J.H.

1986-03-15

6

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

Microsoft Academic Search

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

1962-01-01

7

Usefulness of the hydrogen–deuterium exchange method in the study of drug metabolism using liquid chromatography-tandem mass spectrometry  

Microsoft Academic Search

The usefulness of the hydrogen–deuterium (H-D) exchange method in the study of drug metabolism was investigated. Metabolite samples of denopamine and promethazine prepared in vitro were introduced to a triple stage quadrupole tandem mass spectrometer via a high performance liquid chromatography (HPLC) system using a deuterated mobile phase. Mass spectra by various ionization modes and collisionally induced dissociation (CID) mass

Noriko Ohashi; Satoshi Furuuchi; Masayoshi Yoshikawa

1998-01-01

8

Characterization of Low-Salt and High-Salt Conformation of Poly(dI-dC) by Hydrogen-Deuterium Exchange Kinetics: A Classical Raman Spectroscopy Study  

Microsoft Academic Search

Poly(dI-dC) in H2O and D2O solution can undergo different equilibrium geometries which strongly depend on the salt nature and concentration. These structures were studied by classical Raman spectroscopy in order to monitor a hydrogen-deuterium exchange kinetics in 8- CH group in inosine. Spectral and isotopic exchange rate changes depending on NaCl concentration were observed and interpreted on the basis of

G. Fabriciova; P. Miskovsky; D. Jancura; V. Lisy

1998-01-01

9

Protein structure change studied by hydrogen-deuterium exchange, functional labeling, and mass spectrometry  

PubMed Central

An automated high-throughput, high-resolution deuterium exchange HPLC-MS method (DXMS) was used to extend previous hydrogen exchange studies on the position and energetic role of regulatory structure changes in hemoglobin. The results match earlier highly accurate but much more limited tritium exchange results, extend the analysis to the entire sequence of both hemoglobin subunits, and identify some energetically important changes. Allosterically sensitive amide hydrogens located at near amino acid resolution help to confirm the reality of local unfolding reactions and their use to evaluate resolved structure changes in terms of allosteric free energy.

Englander, Joan J.; Del Mar, Charyl; Li, Will; Englander, S. Walter; Kim, Jack S.; Stranz, David D.; Hamuro, Yoshitomo; Woods, Virgil L.

2003-01-01

10

Studies of negative ions by collision-induced decomposition and hydrogen-deuterium exchange techniques.  

PubMed Central

Development of two new techniques for studying the gas phase chemistry of negative ions is reported. Collision induced dissociation (CID) of (M-1)- ions has been accomplished in a newly constructed triple stage quadrupole mass spectrometer. This instrument was assembled by adding two additional Finnigan quadrupole mass filters to a Finnigan Model 3200 CI mass spectrometer. Generation of (M-1)- ions is accomplished by allowing OH- and sample to react under CI conditions in the ion source. The first quadrupole mass filter, Q1, is then employed to selectively pass the (M-1)- ion into a second quadrupole filter containing argon or neon at 10(-3) torr. On collision with the inert gas the (M-1)- ions dissociate into fragments which are then mass analyzed in the third quadrupole filter, CID spectra of (M-1)- ions from twelve carbonyl compounds are presented in this paper. Ion molecule isotope exchange reactions in the CI ion source can be used to count the number of hydrogen atoms in many different chemical environments. Collisions between sample (M-1)- ions and deuterium-labeled reagent gases (ND3, D2O, EtOD) facilitate incorporation of deuterium into the negative ion if the basicities of the sample and reagent anions are similar. Thus it is possible to selectively incorporate deuterium into many organic samples by controlling the exothermicity of the acid base, ion-molecule chemistry.

Hunt, D F; Sethi, S K; Shabanowitz, J

1980-01-01

11

Probing backbone dynamics with hydrogen/deuterium exchange mass spectrometry.  

PubMed

Protein dynamics can be probed by the solution technique amide hydrogen/deuterium exchange. The exchange rate of hydrogen for deuterium along a peptide backbone is dependent on the extent of hydrogen bonding from secondary structure, accessibility by D2O, and protein motions. Both global and local conformational changes that alter bonding or structure will lead to changes in the amount of deuterium incorporated. The deuterium can be localized via pepsin digestion of the protein and quantified by electrospray ionization mass spectrometry through the mass shifts of the resulting peptides. The technique is emerging as an essential tool to study protein structure in solution due to the exceptional capability of examining both dynamic and structural changes related to protein function. PMID:24061917

Singh, Harsimran; Busenlehner, Laura S

2014-01-01

12

Hydrogen-deuterium exchange in bulk LiBH4.  

PubMed

Because of its apparent simplicity, diffusion of hydrogen in solids can be regarded as a general model system for diffusion. However, only rudimentary knowledge exists for the dynamics of hydrogen in complex hydrides. Insight into the specific diffusion process is given by hydrogen-deuterium exchange experiments. Thermogravimetry and Raman spectroscopy are used to measure the hydrogen-deuterium exchange during the decomposition of LiBH4. At a temperature of 523 K the self-diffusion constant of deuterium in LiBH4 is estimated to be D approximately 7 x 10(-14) m(2) s(-1). A careful analysis of the Raman spectra shows that hydrogen is statistically exchanged by deuterium in LiBH4; i.e., the diffusing species is assumed to be the single hydrogen atom. PMID:18461915

Borgschulte, A; Züttel, A; Hug, P; Racu, A-M; Schoenes, J

2008-05-08

13

Probing protein ensemble rigidity and hydrogen–deuterium exchange  

NASA Astrophysics Data System (ADS)

Protein rigidity and flexibility can be analyzed accurately and efficiently using the program floppy inclusion and rigid substructure topography (FIRST). Previous studies using FIRST were designed to analyze the rigidity and flexibility of proteins using a single static (snapshot) structure. It is however well known that proteins can undergo spontaneous sub-molecular unfolding and refolding, or conformational dynamics, even under conditions that strongly favor a well-defined native structure. These (local) unfolding events result in a large number of conformers that differ from each other very slightly. In this context, proteins are better represented as a thermodynamic ensemble of ‘native-like’ structures, and not just as a single static low-energy structure. Working with this notion, we introduce a novel FIRST-based approach for predicting rigidity/flexibility of the protein ensemble by (i) averaging the hydrogen bonding strengths from the entire ensemble and (ii) by refining the mathematical model of hydrogen bonds. Furthermore, we combine our FIRST-ensemble rigidity predictions with the ensemble solvent accessibility data of the backbone amides and propose a novel computational method which uses both rigidity and solvent accessibility for predicting hydrogen–deuterium exchange (HDX). To validate our predictions, we report a novel site specific HDX experiment which characterizes the native structural ensemble of Acylphosphatase from hyperthermophile Sulfolobus solfataricus (Sso AcP). The sub-structural conformational dynamics that is observed by HDX data, is closely matched with the FIRST-ensemble rigidity predictions, which could not be attained using the traditional single ‘snapshot’ rigidity analysis. Moreover, the computational predictions of regions that are protected from HDX and those that undergo exchange are in very good agreement with the experimental HDX profile of Sso AcP.

Sljoka, Adnan; Wilson, Derek

2013-10-01

14

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

Microsoft Academic Search

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

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

1962-01-01

15

Interdependence of coenzyme-induced conformational work and binding potential in yeast alcohol and porcine heart lactate dehydrogenases: a hydrogen-deuterium exchange study  

SciTech Connect

Binding of NAD coenzymes to yeast alcohol dehydrogenase (YADH) and porcine heart lactate dehydrogenase (PHLDH) was studied by hydrogen-deuterium exchange with the infrared technique. Conformational changes in the enzymes specific to the coenzymes and their fragments were observed, and the pH dependence of the exchange reaction shows that it conforms to the EX-2 scheme. In both YADH and PHLDH the magnitude of the conformational change as measured by exchange retardation is considerably larger for the NAD/sup +/ than for NADH. Studies with coenzyme fragments like ADP-ribose, ADP, and AMP also highlight the lack of rigorous correlation between structural features such as charge and size and their influence on exchange behavior. Ternary complexes such as YADH-NAD/sup +/-pyrazole, PHLDH-NAD/sup +/-oxalate, and PHLDH-NADH-oxamate, which mimic the transition state, have a significantly more pronounced effect on exchange rates than the corresponding binary complexes. The outstanding feature of this study is the demonstration that in the binary enzyme-coenzyme complexes the more loosely bound NAD/sup +/ is more effective in retarding exchange than the more firmly bound NADH. These differences are attributed to the unequal structural constraints exerted by the two coenzymes upon the enzymes, which translate to unequal expenditure of transconformational work in the formation of the two complexes. The opposing variation in the free energy of binding and the transconformational work expended can be viewed as an unequal partitioning of the net free energy gain resulting from the protein-ligand interaction into a binding term and that required for conformational change.

De Weck, Z.; Pande, J.; Kaegi, J.H.R.

1987-07-28

16

A Membrane Cell for On-line Hydrogen/Deuterium Exchange to Study Protein Folding and Protein-Protein Interactions by Mass Spectrometry*  

PubMed Central

A membrane cell for hydrogen and deuterium exchange on-line with mass spectrometry has been developed to monitor protein-protein interactions and protein conformations. It consists of two channels separated by a semipermeable membrane, where one channel carries the protein sample and the other deuterium oxide. The membrane allows transfer of deuterium oxide into the sample flow. The labeling time is controlled via the flow rate in the sample channel. This cell was validated against three models commonly used in hydrogen-deuterium exchange mass spectrometry: monitoring of folded and unfolded states in a protein, mapping the protein secondary structure at the peptide level, and detection of protein and antibody interactions. The system avoids the conventionally used sample dilution and handling, allowing for potential automation.

Astorga-Wells, Juan; Landreh, Michael; Johansson, Jan; Bergman, Tomas; Jornvall, Hans

2011-01-01

17

Oligomerization Interface of RAGE Receptor Revealed by MS-Monitored Hydrogen Deuterium Exchange.  

PubMed

Activation of the receptor for advanced glycation end products (RAGE) leads to a chronic proinflammatory signal, affecting patients with a variety of diseases. Potentially beneficial modification of RAGE activity requires understanding the signal transduction mechanism at the molecular level. The ligand binding domain is structurally uncoupled from the cytoplasmic domain, suggesting receptor oligomerization is a requirement for receptor activation. In this study, we used hydrogen-deuterium exchange and mass spectrometry to map structural differences between the monomeric and oligomeric forms of RAGE. Our results indicated the presence of a region shielded from exchange in the oligomeric form of RAGE and led to the identification of a new oligomerization interface localized at the linker region between domains C1 and C2. Based on this finding, a model of a RAGE dimer and higher oligomeric state was constructed. PMID:24098480

Sitkiewicz, Ewa; Tarnowski, Krzysztof; Pozna?ski, Jaros?aw; Kulma, Magdalena; Dadlez, Michal

2013-10-01

18

Oligomerization Interface of RAGE Receptor Revealed by MS-Monitored Hydrogen Deuterium Exchange  

PubMed Central

Activation of the receptor for advanced glycation end products (RAGE) leads to a chronic proinflammatory signal, affecting patients with a variety of diseases. Potentially beneficial modification of RAGE activity requires understanding the signal transduction mechanism at the molecular level. The ligand binding domain is structurally uncoupled from the cytoplasmic domain, suggesting receptor oligomerization is a requirement for receptor activation. In this study, we used hydrogen-deuterium exchange and mass spectrometry to map structural differences between the monomeric and oligomeric forms of RAGE. Our results indicated the presence of a region shielded from exchange in the oligomeric form of RAGE and led to the identification of a new oligomerization interface localized at the linker region between domains C1 and C2. Based on this finding, a model of a RAGE dimer and higher oligomeric state was constructed.

Poznanski, Jaroslaw; Kulma, Magdalena; Dadlez, Michal

2013-01-01

19

Localized hydration in lyophilized myoglobin by hydrogen-deuterium exchange mass spectrometry. 2. Exchange kinetics.  

PubMed

Solid-state hydrogen-deuterium exchange with mass spectrometric analysis (ssHDX) is a promising method for characterizing proteins in amorphous solids. Though analysis of HDX kinetics is informative and well-established in solution, application of these methods to solid samples is complicated by possible heterogeneities in the solid. The studies reported here provide a detailed analysis of the kinetics of hydration and ssHDX for equine myoglobin (Mb) in solid matrices containing sucrose or mannitol. Water sorption was rapid relative to ssHDX, indicating that ssHDX kinetics was not limited by bulk water transport. Deuterium uptake in solids was well-characterized by a biexponential model; values for regression parameters provided insight into differences between the two solid matrices. Analysis of the widths of peptide mass envelopes revealed that, in solution, an apparent EX2 mechanism prevails, consistent with native conformation of the protein. In contrast, in mannitol-containing samples, a smaller non-native subpopulation exchanges by an EX1-like mechanism. Together, the results indicate that the analysis of ssHDX kinetic data and of the widths of peptide mass envelopes is useful in screening solid formulations of protein drugs for the presence of non-native species that cannot be detected by amide I FTIR. PMID:22352990

Sophocleous, Andreas M; Topp, Elizabeth M

2012-02-29

20

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

PubMed Central

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

Niemeyer, Emily D.; Brodbelt, Jennifer S.

2007-01-01

21

Transitions between Elongated Conformations of Ubiquitin [M+11H]11+ Enhance Hydrogen/Deuterium Exchange  

PubMed Central

Hydrogen/deuterium (H/D) exchange reactions between different elongated conformations of [M+11H]11+ ions of ubiquitin and D2O are studied by a combination of ion mobility spectrometry (IMS) and mass spectrometry techniques. Three conformers (B, C, and D), resolved in the IMS separation, each exchange ~27 hydrogens upon exposure to 0.06 torr of D2O vapor for ~35 to 40 ms. However, a region of the IMS spectrum that appears between the C and D states (corresponding to ions that undergo a structural transition during the mobility separation) undergoes substantially more exchanges (~39 total sites, 44% more than the B, C, and D states). Selection and activation of the individual B, C, and D states reveals that the increased H/D exchange occurs during the transition between structures. Overall, these studies suggest a key process in establishing the maximum exchange levels involves structural transitions, which allow protected sites to be exposed for some fraction of the reaction time. Analysis of changes in exchange levels upon structural transitions can provide insight about common regions of structure that exist in the B, C, and D conformations.

Bohrer, Brian C.; Atlasevich, Natalya; Clemmer, David E.

2011-01-01

22

Hydrogen-deuterium exchange in KD2PO4  

NASA Astrophysics Data System (ADS)

Depth profiles of 1H and 2D in rapidly grown KD2xH2(1-x)PO4 single crystals are studied by elastic recoil detection analysis. Results show that, under ambient conditions, deuteration in the first ~500 nm from the sample surface significantly decreases within the first several days after D2O surface polishing. This effect is attributed to deuterium-hydrogen exchange. The effective diffusion coefficient of this process is strongly dependent on both the degree of deuteration and the sample growth conditions. Physical mechanisms of D/H exchange are discussed.

Kucheyev, S. O.; Felter, T. E.; Siekhaus, W. J.; Nelson, A. J.; Hamza, A. V.

2004-02-01

23

Tracking hydrogen/deuterium exchange at glycan sites in glycoproteins by mass spectrometry  

PubMed Central

Hydrogen deuterium exchange coupled to mass spectrometry (HDX-MS) has emerged as a technique for studying glycoproteins, which are often refractory to classical methods. Glycan chains are generally assumed to exchange protons very rapidly making them invisible to this technique. Here we show that under conditions commonly used for HDX-MS, acetamido groups within glycan chains retain a significant amount of deuterium. Using mono and polysaccharide standards along with glycopeptides from a panel of glycoproteins, we demonstrate that N-acetyl hexosamines, along with modified Asn sidechains are responsible for this effect. Model compounds for sialic acid also displayed similar exchange kinetics, but terminal sialic acids in the context of an entire glycan chain did not contribute to deuterium retention. Furthermore, the presence of sialic acid appears to enhance the exchange rate of the nearby N-acetyl glucosamines. The ability to detect deuterium exchange at the glycan level opens the possibility of applying HDX-MS to monitor glycan interactions and dynamics.

Guttman, M.; Scian, M.; Lee, K.K.

2011-01-01

24

Improved protein hydrogen/deuterium exchange mass spectrometry platform with fully automated data processing.  

PubMed

Protein hydrogen/deuterium exchange (HDX) followed by protease digestion and mass spectrometric (MS) analysis is accepted as a standard method for studying protein conformation and conformational dynamics. In this article, an improved HDX MS platform with fully automated data processing is described. The platform significantly reduces systematic and random errors in the measurement by introducing two types of corrections in HDX data analysis. First, a mixture of short peptides with fast HDX rates is introduced as internal standards to adjust the variations in the extent of back exchange from run to run. Second, a designed unique peptide (PPPI) with slow intrinsic HDX rate is employed as another internal standard to reflect the possible differences in protein intrinsic HDX rates when protein conformations at different solution conditions are compared. HDX data processing is achieved with a comprehensive HDX model to simulate the deuterium labeling and back exchange process. The HDX model is implemented into the in-house developed software MassAnalyzer and enables fully unattended analysis of the entire protein HDX MS data set starting from ion detection and peptide identification to final processed HDX output, typically within 1 day. The final output of the automated data processing is a set (or the average) of the most possible protection factors for each backbone amide hydrogen. The utility of the HDX MS platform is demonstrated by exploring the conformational transition of a monoclonal antibody by increasing concentrations of guanidine. PMID:22571272

Zhang, Zhongqi; Zhang, Aming; Xiao, Gang

2012-05-15

25

HYDROGEN-DEUTERIUM EXCHANGE IN PHOTOLYZED METHANE-WATER ICES  

SciTech Connect

Previous work has concluded that H-D exchange occurs readily in polycyclic aromatic hydrocarbons frozen in deuterated water (D{sub 2}O) irradiated with ultraviolet light. Here, we examine H-D exchange in methane-water ices following exposure to ultraviolet radiation and analyze the products formed as a result. We find that H-D exchange also occurs in methane-water ices by means of ultraviolet photolysis. Exchange proceeds through a radical mechanism that implies that almost all organic species will undergo significant H-D exchange with the matrix in water ices exposed to ultraviolet radiation. Given sufficient energetic processing of the ice, the H/D ratio of an ice matrix may be transferred to the organic species in the ice.

Weber, Amanda S.; Hodyss, Robert; Johnson, Paul V.; Willacy, Karen; Kanik, Isik, E-mail: Robert.P.Hodyss@jpl.nasa.go [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

2009-09-20

26

Analysis of Overlapped and Noisy Hydrogen/Deuterium Exchange Mass Spectra  

NASA Astrophysics Data System (ADS)

Noisy and overlapped mass spectrometry data hinder the sequence coverage that can be obtained from hydrogen deuterium exchange analysis, and places a limit on the complexity of the samples that can be studied by this technique. Advances in instrumentation have addressed these limits, but as the complexity of the biological samples under investigation increases, these problems are re-encountered. Here we describe the use of binomial distribution fitting with asymmetric linear squares regression for calculating the accurate deuterium content for mass envelopes of low signal or that contain significant overlap. The approach is demonstrated with a test data set of HIV Env gp140 wherein inclusion of the new analysis regime resulted in obtaining exchange data for 42 additional peptides, improving the sequence coverage by 11 %. At the same time, the precision of deuterium uptake measurements was improved for nearly every peptide examined. The improved processing algorithms also provide an efficient method for deconvolution of bimodal mass envelopes and EX1 kinetic signatures. All these functions and visualization tools have been implemented in the new version of the freely available software, HX-Express v2.

Guttman, Miklos; Weis, David D.; Engen, John R.; Lee, Kelly K.

2013-09-01

27

Substrate binding and conformational changes of Clostridium glutamicum diaminopimelate dehydrogenase revealed by hydrogen/deuterium exchange and electrospray mass spectrometry.  

PubMed Central

C. glutamicum meso-diaminopimelate dehydrogenase is an enzyme of the L-lysine biosynthetic pathway in bacteria. The binding of NADPH and diaminopimelate to the recombinant, overexpressed enzyme has been analyzed using hydrogen/deuterium exchange and electrospray ionization/mass spectrometry. NADPH binding reduces the extent of deuterium exchange, as does the binding of diaminopimelate. Pepsin digestion of the deuterated enzyme and enzyme-substrate complexes coupled with liquid chromatography/mass spectrometry have allowed the identification of eight peptides whose deuterium exchange slows considerably upon the binding of the substrates. These peptides represent regions known or thought to bind NADPH and diaminopimelate. One of these peptides is located at the interdomain hinge region and is proposed to be exchangeable in the "open," catalytically inactive, conformation but nonexchangeable in the "closed," catalytically active conformation formed after NADPH and diaminopimelate binding and domain closure. Furthermore, the dimerization region has been localized by this method, and this study provides an example of detecting protein-protein interface regions using hydrogen/deuterium exchange and electrospray ionization.

Wang, F.; Scapin, G.; Blanchard, J. S.; Angeletti, R. H.

1998-01-01

28

Differential hydrogen/deuterium exchange mass spectrometry analysis of protein-ligand interactions  

PubMed Central

Functional regulation of ligand-activated receptors is driven by alterations in the conformational dynamics of the protein upon ligand binding. Differential hydrogen/deuterium exchange (HDX) coupled with mass spectrometry has emerged as a rapid and sensitive approach for characterization of perturbations in conformational dynamics of proteins following ligand binding. While this technique is sensitive to detecting ligand interactions and alterations in receptor dynamics, it also can provide important mechanistic insights into ligand regulation. For example, HDX has been used to determine a novel mechanism of ligand activation of the nuclear receptor peroxisome proliferator activated receptor-?, perform detailed analyses of binding modes of ligands within the ligand-binding pocket of two estrogen receptor isoforms, providing insight into selectivity, and helped classify different types of estrogen receptor-? ligands by correlating their pharmacology with the way they interact with the receptor based solely on hierarchical clustering of receptor HDX signatures. Beyond small-molecule–receptor interactions, this technique has also been applied to study protein–protein complexes, such as mapping antibody–antigen interactions. In this article, we summarize the current state of the differential HDX approaches and the future outlook. We summarize how HDX analysis of protein–ligand interactions has had an impact on biology and drug discovery.

Chalmers, Michael J; Busby, Scott A; Pascal, Bruce D; West, Graham M; Griffin, Patrick R

2011-01-01

29

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

NASA Astrophysics Data System (ADS)

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

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

2006-07-01

30

Hydrogen/deuterium exchange of hydrophobic peptides in model membranes by electrospray ionization mass spectrometry.  

PubMed

We demonstrate here that the hydrogen/deuterium solvent exchange (HDX) properties of the transmembrane fragment of the M2 protein of Influenza A (M2-TM) incorporated into lipid vesicles or detergent micelles can be studied with straightforward electrospray (ESI) and nanospray mass spectrometry (MS) configurations provided that key factors, including sample preparation techniques, are optimized. Small unilamellar vesicle preparations were obtained by solubilizing dimyristoyl phosphatidylcholine (DMPC) and the M2-TM peptide in aqueous solution with n-octyl-beta-D-glycopyranoside, followed by dialysis to remove the detergent. Electron microscopy experiments revealed that subsequent concentration by centrifugation introduced large multilamellar aggregates that were not compatible with ESI-MS. By contrast, a lyophilization-based concentration procedure, followed by thawing above the liquid crystal transition temperature of the lipid component, maintained the liposome size profile and yielded excellent ion fluxes in both ESI-MS and nano-ESI-MS. Using these methods the global HDX profile of M2-TM in aqueous DMPC vesicles was compared with that in methanol, demonstrating that several amide sites were protected from exchange by the lipid membrane. We also show that hydrophobic peptides can be detected by ESI-MS in the presence of a large molar excess of the detergent Triton X-100. The rate of HDX of M2-TM in Triton X-100 micelles was faster than that in DMPC vesicles but slower than when the peptide had been denatured in methanol. These results indicate that the accessibility of backbone amide sites to the solvent can be profoundly affected by membrane protein structure and dynamics, as well as the properties of model bilayer systems. PMID:12484457

Hansen, Raino K; Broadhurst, R William; Skelton, Paul C; Arkin, Isaiah T

2002-12-01

31

Pulsed hydrogen-deuterium exchange mass spectrometry probes conformational changes in amyloid beta (A?) peptide aggregation.  

PubMed

Probing the conformational changes of amyloid beta (A?) peptide aggregation is challenging owing to the vast heterogeneity of the resulting soluble aggregates. To investigate the formation of these aggregates in solution, we designed an MS-based biophysical approach and applied it to the formation of soluble aggregates of the A?42 peptide, the proposed causative agent in Alzheimer's disease. The approach incorporates pulsed hydrogen-deuterium exchange coupled with MS analysis. The combined approach provides evidence for a self-catalyzed aggregation with a lag phase, as observed previously by fluorescence methods. Unlike those approaches, pulsed hydrogen-deuterium exchange does not require modified A?42 (e.g., labeling with a fluorophore). Furthermore, the approach reveals that the center region of A?42 is first to aggregate, followed by the C and N termini. We also found that the lag phase in the aggregation of soluble species is affected by temperature and Cu(2+) ions. This MS approach has sufficient structural resolution to allow interrogation of A? aggregation in physiologically relevant environments. This platform should be generally useful for investigating the aggregation of other amyloid-forming proteins and neurotoxic soluble peptide aggregates. PMID:23959898

Zhang, Ying; Rempel, Don L; Zhang, Jun; Sharma, Anuj K; Mirica, Liviu M; Gross, Michael L

2013-08-19

32

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

PubMed Central

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

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

2001-01-01

33

Hydrogen/Deuterium Exchange Analysis of HIV-1 Capsid Assembly and Maturation  

PubMed Central

Summary Following budding, HIV-1 virions undergo a maturation process where the gag polyprotein in the immature virus is cleaved by the viral protease and rearranges to form the mature, infectious virion. Despite the wealth of structures of isolated capsid domains and an in vitro assembled mature lattice, models of the immature lattice do not provide an unambiguous model of capsid molecule orientation and no structural information is available for the capsid maturation pathway. Here we have applied hydrogen/deuterium exchange mass spectrometry to immature, mature and mutant gag particles (CA5) blocked at the final gag cleavage event to examine the molecular basis of capsid assembly and maturation. Capsid packing arrangements were very similar for all virions while immature and CA5 virions contained an additional intermolecular interaction at the hexameric, three-fold axis. Additionally, the N-terminal ?-hairpin was observed to form as a result of capsid-SP1 cleavage rather than driving maturation as previously postulated.

Monroe, Eric B.; Kang, Sebyung; Kyere, Sampson K.; Li, Rui; Prevelige, Peter E.

2010-01-01

34

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

PubMed

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

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

2008-05-29

35

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

Microsoft Academic Search

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

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

2006-01-01

36

Cooperative alpha-helix unfolding in a protein-DNA complex from hydrogen-deuterium exchange.  

PubMed

We present experimental evidence for a cooperative unfolding transition of an alpha-helix in the lac repressor headpiece bound to a symmetric variant of the lac operator, as inferred from hydrogen-deuterium (H-D) exchange experiments monitored by NMR spectroscopy. In the EX1 limit, observed exchange rates become pH-independent and exclusively sensitive to local structure fluctuations that expose the amide proton HN to exchange. Close to this regime, we measured decay rates of individual backbone HN signals in D2O, and of their mutual HN-HN NOE by time-resolved two-dimensional (2D) NMR experiments. The data revealed correlated exchange at the center of the lac headpiece recognition helix, Val20-Val23, and suggested that the correlation breaks down at Val24, at the C terminus of the helix. A lower degree of correlation was observed for the exchange of Val9 and Ala10 at the center of helix 1, while no correlation was observed for Val38 and Glu39 at the center of helix 3. We conclude that HN exchange in the recognition helix and, to some extent, in helix 1 is a cooperative event involving the unfolding of these helices, whereas the HN exchange in helix 3 is dominated by random local structure fluctuations. PMID:16751603

Salinas, Roberto K; Diercks, Tammo; Kaptein, Robert; Boelens, Rolf

2006-06-02

37

In electrospray ionization source hydrogen\\/deuterium exchange LCMS and LCMS\\/MS for characterization of metabolites  

Microsoft Academic Search

A new method is described for performing hydrogen\\/deuterium (H\\/D) exchange in an electrospray ionization (ESI) source. The\\u000a use of liquid chromatography (LC)-mass spectrometer equipped with an ESI source and deuterium oxide (D2O) as the sheath liquid allows H\\/D exchange experiments to be performed on-line. This directly provides information for determining\\u000a the number and position of exchangeable hydrogens, aiding in the

Wing Lam; Ragu Ramanathan

2002-01-01

38

Characterizing rapid, activity-linked conformational transitions in proteins via sub-second hydrogen deuterium exchange mass spectrometry.  

PubMed

This review outlines the application of time-resolved electrospray ionization mass spectrometry (TRESI-MS) and hydrogen-deuterium exchange (HDX) to study rapid, activity-linked conformational transitions in proteins. The method is implemented on a microfluidic chip which incorporates all sample-handling steps required for a 'bottom-up' HDX workflow: a capillary mixer for sub-second HDX labeling, a static mixer for HDX quenching, a microreactor for rapid protein digestion, and on-chip electrospray. By combining short HDX labeling pulses with rapid digestion, this approach provides a detailed characterization of the structural transitions that occur during protein folding, ligand binding, post-translational modification and catalytic turnover in enzymes. This broad spectrum of applications in areas largely inaccessible to conventional techniques means that microfluidics-enabled TRESI-MS/HDX is a unique and powerful approach for investigating the dynamic basis of protein function. PMID:23663649

Resetca, Diana; Wilson, Derek J

2013-06-11

39

Defining the Interacting Regions between Apomyoglobin and Lipid Membrane by Hydrogen\\/Deuterium Exchange Coupled to Mass Spectrometry  

Microsoft Academic Search

Sperm whale myoglobin can be considered as the model protein of the globin family. The pH-dependence of the interactions of apomyoglobin with lipid bilayers shares some similarities with the behavior of pore-forming domains of bacterial toxins belonging also to the globin family. Two different states of apomyoglobin bound to a lipid bilayer have been characterized by using hydrogen\\/deuterium exchange experiments

Petr Man; Caroline Montagner; Grégory Vernier; Bernard Dublet; Alexandre Chenal; Eric Forest; Vincent Forge

2007-01-01

40

Conformational stability of ribonuclease T1 determined by hydrogen-deuterium exchange.  

PubMed Central

The hydrogen-deuterium exchange kinetics of 37 backbone amide residues in RNase T1 have been monitored at 25, 40, 45, and 50 degrees C at pD 5.6 and at 40 and 45 degrees C at pD 6.6. The hydrogen exchange rate constants of the hydrogen-bonded residues varied over eight orders of magnitude at 25 degrees C with 13 residues showing exchange rates consistent with exchange occurring as a result of global unfolding. These residues are located in strands 2-4 of the central beta-pleated sheet. The residues located in the alpha-helix and the remaining strands of the beta-sheet exhibited exchange behaviors consistent with exchange occurring due to local structural fluctuations. For several residues at 25 degrees C, the global free energy change calculated from the hydrogen exchange data was over 2 kcal/mol greater than the free energy of unfolding determined from urea denaturation experiments. The number of residues showing this unexpected behavior was found to increase with temperature. This apparent inconsistency can be explained quantitatively if the cis-trans isomerization of the two cis prolines, Pro-39 and Pro-55, is taken into account. The cis-trans isomerization equilibrium calculated from kinetic data indicates the free energy of the unfolded state will be 2.6 kcal/mol higher at 25 degrees C when the two prolines are cis rather than trans (Mayr LM, Odefey CO, Schutkowski M, Schmid FX. 1996. Kinetic analysis of the unfolding and refolding of ribonuclease T1 by a stopped-flow double-mixing technique. Biochemistry 35: 5550-5561). The hydrogen exchange results are consistent with the most slowly exchanging hydrogens exchanging from a globally higher free energy unfolded state in which Pro-55 and Pro-39 are still predominantly in the cis conformation. When the conformational stabilities determined by hydrogen exchange are corrected for the proline isomerization equilibrium, the results are in excellent agreement with those from an analysis of urea denaturation curves.

Mullins, L. S.; Pace, C. N.; Raushel, F. M.

1997-01-01

41

Gas-phase noncovalent interactions between vancomycin-group antibiotics and bacterial cell-wall precursor peptides probed by hydrogen\\/deuterium exchange  

Microsoft Academic Search

Gas-phase structures of noncovalent complexes between the glycopeptide antibiotics vancomycin, eremomycin, ristocetin, and\\u000a pseudo aglyco-ristocetin and the cell-wall mimicking peptides N-acetyl-D-Alanyl-D-Alanine, N-acetyl-Glycyl-D-Alanine, and\\u000a N,N?-di-acetyl L-Lysyl-D-Alanyl-D-Alanine have been probed by hydrogen\\/deuterium (H\\/D) exchange using ND3 as reagent gas. The noncovalent complexes were transferred from solution to the vacuum using electrospray ionization. The\\u000a H\\/D exchange of the solvent-free ions was studied in

Albert J. R. Heck; Thomas J. D. Jørgensen; Mary O’Sullivan; Markus von Raumer; Peter J. Derrick

1998-01-01

42

Gas-phase hydrogen/deuterium exchange in a travelling wave ion guide for the examination of protein conformations  

PubMed Central

Accumulating evidence suggests that solution-phase conformations of small globular proteins and large molecular protein assemblies can be preserved for milliseconds after electrospray ionization. Thus, the study of proteins in the gas-phase on this time-scale is highly desirable. Here we demonstrate that a travelling wave ion guide (TWIG) of a Synapt mass spectrometer offers a highly suitable environment for rapid and efficient gas-phase hydrogen/deuterium exchange (HDX). Gaseous ND3 was introduced into either the source TWIG or the TWIG located just after the ion mobility cell, such that ions underwent HDX as they passed through the ND3 on the way to the time-of-flight analyzer. The extent of deuterium labeling could be controlled by varying the quantity of ND3 or the speed of the travelling wave. The gas-phase HDX of model peptides corresponded to labeling of primarily fast exchanging sites due to the short labeling times (ranging from 0.1 to 10 ms). In addition to peptides, gas-phase HDX of ubiquitin, cytochrome c, lysozyme and apomyoglobin were examined. We conclude that HDX of protein ions in a TWIG is highly sensitive to protein conformation, enables the detection of conformers present on sub-milliseconds timescales and can readily be combined with ion mobility spectrometry.

Rand, Kasper D.; Pringle, Steven D.; Murphy, James P.; Fadgen, Keith E.; Brown, Jeff; Engen, John R.

2009-01-01

43

Structural Insights of Glucan Phosphatase Dynamics using Amide Hydrogen/Deuterium Exchange Mass Spectrometry  

PubMed Central

Laforin and Starch Excess 4 (SEX4) are founding members of a class of phosphatases that dephosphorylate phosphoglucans. Each protein contains a carbohydrate binding module (CBM) and a dual specificity phosphatase (DSP) domain. The gene encoding laforin is mutated in a fatal neurodegenerative disease called Lafora disease (LD). In the absence of laforin function, insoluble glucans accumulate that are hyperphosphorylated and exhibit sparse branching. It is hypothesized that these accumulations trigger the neurodegeneration and premature death of LD patients. We recently demonstrated that laforin removes phosphate from phosphoglucans and hypothesized that this function inhibits insoluble glucan accumulation. Loss of SEX4 function in plants yields a similar cellular phenotype; cells accumulate an excess amount of insoluble, hyperphosphorylated glucans. While multiple groups have shown that these phosphatases dephosphorylate phosphoglucans, there is no structure of a glucan phosphatase and little is known about the mechanism whereby they perform this action. We utilized hydrogen-deuterium exchange mass spectrometry (DXMS) and structural modeling to probe the conformational and structural dynamics of the glucan phosphatase SEX4. We found that the enzyme does not undergo a global conformational change upon glucan binding, but instead undergoes minimal rearrangement upon binding. The CBM undergoes increased protection from deuteration when bound to glucans, confirming its role in glucan binding. More interestingly, we identified structural components of the DSP that also undergo increased protection from deuteration upon glucan addition. To determine the position of these regions, we generated a homology model of the SEX4 DSP. The homology model shows that all of these regions are adjacent the DSP active site. Therefore, our results suggest that these regions of the DSP participate in presenting the phosphoglucan to the active site and provide the first structural analysis and mode of action of this unique class of phosphatases.

Hsu, Simon; Kim, Youngjun; Li, Sheng; Durrant, Eric S.; Pace, Rachel M.; Woods, Virgil L.; Gentry, Matthew S.

2009-01-01

44

Platform dependencies in bottom-up hydrogen/deuterium exchange mass spectrometry.  

PubMed

Hydrogen-deuterium exchange mass spectrometry is an important method for protein structure-function analysis. The bottom-up approach uses protein digestion to localize deuteration to higher resolution, and the essential measurement involves centroid mass determinations on a very large set of peptides. In the course of evaluating systems for various projects, we established two (HDX-MS) platforms that consisted of a FT-MS and a high-resolution QTOF mass spectrometer, each with matched front-end fluidic systems. Digests of proteins spanning a 20-110 kDa range were deuterated to equilibrium, and figures-of-merit for a typical bottom-up (HDX-MS) experiment were compared for each platform. The Orbitrap Velos identified 64% more peptides than the 5600 QTOF, with a 42% overlap between the two systems, independent of protein size. Precision in deuterium measurements using the Orbitrap marginally exceeded that of the QTOF, depending on the Orbitrap resolution setting. However, the unique nature of FT-MS data generates situations where deuteration measurements can be inaccurate, because of destructive interference arising from mismatches in elemental mass defects. This is shown through the analysis of the peptides common to both platforms, where deuteration values can be as low as 35% of the expected values, depending on FT-MS resolution, peptide length and charge state. These findings are supported by simulations of Orbitrap transients, and highlight that caution should be exercised in deriving centroid mass values from FT transients that do not support baseline separation of the full isotopic composition. PMID:23197788

Burns, Kyle M; Rey, Martial; Baker, Charles A H; Schriemer, David C

2012-11-28

45

Atmospheric Pressure Photo Ionization Hydrogen/Deuterium Exchange Mass Spectrometry—a Method to Differentiate Isomers by Mass Spectrometry  

NASA Astrophysics Data System (ADS)

In this report, a method for in-source hydrogen/deuterium (H/D) exchange at atmospheric pressure is reported. The method was named atmospheric pressure photo ionization hydrogen/deuterium exchange mass spectrometry (APPI HDX MS). H/D exchange was performed by mixing samples dissolved in toluene with CH3OD solvent and analyzing the mixture using atmospheric pressure photo ionization mass spectrometry (APPI-MS). The APPI HDX spectra obtained with contact times between the analyte solution and methanol-OD (CH3OD) of < 0.5 s or 1 h showed the same pattern of H/D exchange. Therefore, it was concluded that APPI HDX occurred in the source but not in the solution. The proposed method does not require a specific type of mass spectrometer and can be performed at atmospheric pressure. H/D exchange can be performed in any laboratory with a mass spectrometer and a commercial APPI source. Using this method, multiple H/D exchanges of aromatic hydrogen and/or H/D exchange of active hydrogen were observed. These results demonstrated that H/D exchange can be used to distinguish between isomers containing primary, secondary, and tertiary amines, as well as pyridine and pyrrole functional groups.

Ahmed, Arif; Kim, Sunghwan

2013-09-01

46

Functional Unfolding of ?1-Antitrypsin Probed by Hydrogen-Deuterium Exchange Coupled with Mass Spectrometry*S?  

PubMed Central

The native state of ?1-antitrypsin (?1AT), a member of the serine protease inhibitor (serpin) family, is considered a kinetically trapped folding intermediate that converts to a more stable form upon complex formation with a target protease. Although previous structural and mutational studies of ?1AT revealed the structural basis of the native strain and the kinetic trap, the mechanism of how the native molecule overcomes the kinetic barrier to reach the final stable conformation during complex formation remains unknown. We hypothesized that during complex formation, a substantial portion of the molecule undergoes unfolding, which we dubbed functional unfolding. Hydrogen-deuterium exchange coupled with ESI-MS was used to analyze this serpin in three forms: native, complexing, and complexed with bovine ?-trypsin. Comparing the deuterium content at the corresponding regions of these three samples, we probed the unfolding of ?1AT during complex formation. A substantial portion of the ?1AT molecule unfolded transiently during complex formation, including not only the regions expected from previous structural studies, such as the reactive site loop, helix F, and the following loop, but also regions not predicted previously, such as helix A, strand 6 of ?-sheet B, and the N terminus. Such unfolding of the native interactions may elevate the free energy level of the kinetically trapped native serpin sufficiently to cross the transition state during complex formation. In the current study, we provide evidence that protein unfolding has to accompany functional execution of the protein molecule.

Baek, Je-Hyun; Yang, Won Suk; Lee, Cheolju; Yu, Myeong-Hee

2009-01-01

47

Separation and identification of structural isomers by quadrupole collision-induced dissociation-hydrogen\\/deuterium exchange-infrared multiphoton dissociation (QCID-HDX-IRMPD)  

Microsoft Academic Search

A new approach that uses a hybrid Q-FTICR instrument and combines quadrupole collision-induced dissociation, hydrogen-deuterium\\u000a exchange, and infrared multiphoton dissociation (QCID-HDX-IRMPD) has been shown to effectively separate and differentiate\\u000a isomeric fragment ion structures present at the same m\\/z. This method was used to study protonated YAGFL-OH (free acid), YAGFL-NH2 (amide), cyclic YAGFL, and YAGFL-OCH3 (methyl ester). QCID-HDX of m\\/z 552.28

Ashley C. Gucinski; Árpád Somogyi; Julia Chamot-Rooke; Vicki H. Wysocki

2010-01-01

48

A two-stage differential hydrogen deuterium exchange method for the rapid characterization of protein/ligand interactions.  

PubMed

The peroxisome proliferator-activated receptor is a member of the nuclear receptor superfamily of transcriptional regulators. Regulation of the nuclear receptors occurs through changes to the structure and dynamics of the ligand-binding domain. Therefore, the need has arisen for a rapid method capable of detecting changes in the dynamics of nuclear receptors following ligand binding. We recently described how solution-phase amide hydrogen/deuterium exchange (HDX) provides a biophysical technique for probing changes in protein dynamics induced by ligand interaction. Building from this platform, we have optimized the robustness of the differential HDX experiment by minimizing systematic errors, and have increased the efficiency of the chromatographic separation through the use of high-pressure liquid chromatography. Using knowledge gained previously from comprehensive HDX experiments of PPARgamma, a modest throughput method to probe changes in the dynamics of key regions of the receptor was developed. A collection of ten synthetic and endogenous PPARgamma ligands were characterized with this new method requiring approximately 24 h of analysis. This is a dramatic improvement over the 10 d of analysis that would have been required with our previous approach for comprehensive differential HDX analysis. In addition to demonstrating the utility of this approach, the study presented here is the first to measure changes to the dynamics of PPARgamma upon the binding of putative endogenous ligands. PMID:17916792

Chalmers, Michael J; Busby, Scott A; Pascal, Bruce D; Southern, Mark R; Griffin, Patrick R

2007-09-01

49

Conformational analysis of dynorphin A (1-13) using hydrogen-deuterium exchange and tandem mass spectrometry.  

PubMed

Trifluoroethanol (TFE)-induced conformational changes in dynorphin A (1-13) were investigated using charge-state distribution (CSD) and hydrogen-deuterium exchange (HDX), combined with electrospray ionization (ESI) mass spectrometry (MS). Individual amino acids involved in secondary structural elements were identified by collision-induced dissociation-tandem mass spectrometry (MS/MS). It was observed that dynorphin A (1-13) largely exists in an unfolded conformation and a folded structure in increasing concentrations of TFE. In 50% TFE, it forms an alpha-helix that encompasses residues 1-9 and remains flexible from residues 10 to 13. PMID:18417761

Cai, Xianmei; Dass, Chhabil

2007-01-01

50

Dissecting the mechanism of Epac activation by hydrogen/deuterium exchange FT-IR and structural modeling*  

PubMed Central

Exchange proteins directly activated by cAMP (Epac) is a family of cAMP-binding domain containing proteins that play important roles in mediating the effects of cAMP through the activation of down-stream small GTPases, Ras-proximate proteins. To delineate the mechanism of Epac activation, we probed the conformation and structural dynamics of Epac using amide hydrogen/deuterium (H/D) exchange coupled with Fourier transform infrared spectroscopy (FT-IR) and structural modeling. Our studies show that unlike that of cAMP-dependent protein kinase (PKA), the classic intracellular cAMP receptor, binding of cAMP to Epac does not induce significant changes in overall secondary structure and structural dynamics, as measured by FT-IR and the rate of H/D exchange, respectively. These results suggest that Epac activation does not involve significant changes in the amount of exposed surface areas as in the case of PKA activation and conformational changes induced by cAMP in Epac are most likely confined to small local regions. Homology modeling and comparative structural analyses of the CBDs of Epac and PKA lead us to propose a model of Epac activation. Based on our model, Epac activation by cAMP employs the same underlying structural principal utilized by PKA although the detailed structural and conformational changes associated with Epac and PKA activation are significantly different. In addition, we predict that during Epac activation the first ? strand of the switchboard switches conformation to a ?-helix, which folds back to the ? barrel core of the CBD and interacts directly with cAMP to form the base of the cAMP-binding pocket.

Yu, Shaoning; Fan, Fenghui; Flores, Samuel C.; Mei, Fang; Cheng, Xiaodong

2008-01-01

51

Structural Dynamics of Soluble Chloride Intracellular Channel Protein CLIC1 Examined by Amide Hydrogen-Deuterium Exchange Mass Spectrometry (DXMS)†  

PubMed Central

Chloride intracellular channel protein 1 (CLIC1) functions as an anion channel in plasma and nuclear membranes when its soluble monomeric form converts to an integral-membrane form. The transmembrane region of CLIC1 is located in its thioredoxin-like domain 1 but the mechanism whereby the protein converts to its membrane conformation has yet to be determined. Since channel formation in membranes is enhanced at low pH (5 to 5.5), a condition that is found at the surface of membranes, the structural dynamics of soluble CLIC1 was studied at pH 7 and at pH 5.5 in the absence of membranes by amide hydrogen-deuterium exchange mass spectrometry (DXMS). Rapid hydrogen exchange data indicate that CLIC1 displays a similar core structure at these pH values. Domain 1 is less stable than the all-helical domain 2 and, while the structure of domain 1 remains intact, its conformational flexibility is further increased in an acidic environment (pH 5.5). In the absence of membrane, an acidic environment appears to prime the solution structure of CLIC1 by destabilising domain 1 in order to lower the activation energy barrier for its conversion to the membrane-insertion conformation. The significantly enhanced H/D-exchange rates at pH 5.5 displayed by two segments (peptides 11-31 and 68-82) could be due to the protonation of acidic residues in salt bridges. One of these segments (peptide 11-31) includes part of the transmembrane region which, in the solution structure, consists of helix ?1. This helix is intrinsically stable and is most likely retained in the membrane conformation. Strand ?2, another element of the transmembrane region, displays a propensity to form a helical structure and has putative N- and C-capping motifs, suggesting that it too most likely forms a helix in a lipid bilayer.

Stoychev, Stoyan H.; Nathaniel, Christos; Fanucchi, Sylvia; Brock, Melissa; Li, Sheng; Asmus, Kyle; Woods, Virgil L.; Dirr, Heini W.

2009-01-01

52

Hydrogen/deuterium exchange-LC-MS approach to characterize the action of heparan sulfate C5-epimerase.  

PubMed

Heparan sulfate (HS) proteoglycans regulate a number of biological functions in many systems. Most of the functions of HS are attributed to its unique structure, consisting of sulfated and non-sulfated domains, arising from the differential presence of iduronyl and glucuronyl residues along the polysaccharide chain. A single glucuronyl C5-epimerase enzyme acts on HS precursors, converts glucuronyl residues into iduronyl residues, and modulates subsequent biosynthetic steps in vivo. Previously, the ratios of non-sulfated epimers within the polysaccharide chain have been calculated by resolving radiolabeled GlcA-(A)Man(R) and IdoA-(A)Man(R) disaccharides using a tedious paper chromatography technique. This radioactive assay, based on measuring either the release or incorporation of (3)H at C5 carbon of uronyl residues of (3)H-labeled HS precursor substrate, has been in use over three decades to characterize the action of HS C5-epimerase. We have developed a non-radioactive assay to estimate the epimerase activity through resolving GlcA-(A)Man(R) and IdoA-(A)Man(R) disaccharides on high-performance liquid chromatography in conjunction with hydrogen/deuterium exchange upon epimerization protocol-liquid chromatography mass spectrometry (DEEP-LC-MS). Utilizing this new, non-radioactive-based assay, DEEP-LC-MS, we were able to determine the extent of both forward and reverse reactions on the same substrate catalyzed by C5-epimerase. The results from this study also provide insights into the action of C5-epimerase and provide an opportunity to delineate snapshots of biosynthetic events that occur during the HSPG assembly in the Golgi. PMID:21573838

Babu, Ponnusamy; Victor, Xylophone V; Nelsen, Emily; Nguyen, Thao Kim Nu; Raman, Karthik; Kuberan, Balagurunathan

2011-05-15

53

Hydrogen/Deuterium Exchange-LC-MS Approach to Characterize the Action of Heparan Sulfate C5-Epimerase  

PubMed Central

Heparan sulfate (HS) proteoglycans regulate a number of biological functions in many systems. Most of the functions of HS are attributed to its unique structure, consisting of sulfated and non-sulfated domains, arising from the differential presence of iduronyl and glucuronyl residues along the polysaccharide chain. A single glucuronyl C5-epimerase enzyme acts on heparan sulfate precursor, converts glucuronyl residues into iduronyl residues and modulates subsequent biosynthetic steps in vivo. The ratios of non-sulfated epimers within the polysaccharide chain have been calculated by resolving radiolabeled GlcA-AManR and IdoA-AManR disaccharides using a tedious paper chromatography technique. Radioactive assay, based on measuring either the release or incorporation of 3H at C5 carbon of uronyl residues of 3H-labeled HS precursor substrate, has been in use over three decades to characterize the action of HS C5-epimerase. We have developed a non-radioactive assay to estimate the epimerase activity through resolving GlcA-AManR and IdoA-AManR disaccharides on HPLC in conjunction with hydrogen/deuterium exchange upon epimerization protocol-liquid chromatography mass spectrometry (DEEP-LC-MS). Utilizing this new, non-radioactive based assay, DEEP-LC-MS, we were able to determine the extent of both forward and reverse reaction on the same substrate catalyzed by C5-epimerase. Results from this study also provide insights into the action of C5-epimerase and provide an opportunity to delineate snapshots of biosynthetic events that occur during the HSPG assembly in the Golgi.

Babu, Ponnusamy; Victor, Xylophone V.; Nelsen, Emily; Nguyen, Thao Kim Nu; Raman, Karthik; Kuberan, Balagurunathan

2011-01-01

54

ALKYL AND HYDRIDE BIS (TRIMETHYLSILYL)AMIDO DERIVATIVES OF THE ACTINIDE ELEMENTS: PREPARATION AND HYDROGEN-DEUTERIUM EXCHANGE  

SciTech Connect

The monomeric, hydrocarbon-soluble monohydrides and monodeuterides of the actinide metals (thorium or uranium) of the type HM[N(SiMe{sub 3}){sub 2}]{sub 3} have been prepared. Their reaction chemistry, n-BuLi followed by MeBr yields MeM[N(SiMe{sub 3}){sub 2}]{sub 3} and borane in tetrahydrofuran yields BH{sub 4}M[N(SiMe{sub 3}){sub 2}]{sub 3}, suggests that the hydrogen atom is hydridic. Pyrolysis of the hydrides yields the novel, four-membered ring metallocycle, [(Me{sub 3}Si){sub 2}N]{sub 2} - MCH{sub 2}Si(Me){sub 2}NSiMe{sub 3} where M is Th or U. These metallocycles are the key intermediates in the hydrogen-deuterium exchange reaction that yields {[(CD{sub 3}){sub 3}Si]{sub 2}N}{sub 3}MD.

Simpson, Stephen J.; Turner, Howard W.; Andersen, Richard A.

1980-09-01

55

Hydrogen/deuterium exchange of mass-selected peptide ions with ND3 in a tandem sector mass spectrometer  

NASA Astrophysics Data System (ADS)

Hydrogen/deuterium exchange of mass-selected protonated peptide ions with ND3 is investigated in a four sector tandem mass spectrometer equipped with a high-pressure collision cell. The dependence of H/D exchange on the pressure of ND3, on collision energy and on proton affinities (PAs) of the peptides is examined. For leucine enkephalin, a peptide without strongly basic residues, the maximum number of H/D exchanges observed can correspond to the maximum number of active hydrogen atoms in the ions. In peptides with basic residues such as arginine, the H/D exchange proceeds more slowly and more selectively. H/D exchange is observed for renin substrate whose PA is estimated to be higher than ND3 by more than 50 kcal mol-. The pattern of H/D exchange of leucine enkephalin shows discrepancy with the number of hydrogen atoms in the peptide ion expected to undergo fast H/D exchange, thus indicating possible conformational effects. When protonated leucine enkephalin is reacted with ND3 under predominantly single-collision conditions, the incorporation of deuterium into fragment ions is found to vary, depending on the type of fragment ion. This differential incorporation of deuterium may be informative about the nature of the processes leading to the formation of fragment ions.

Cheng, Xueheng; Fenselau, Catherine

1992-12-01

56

An electrospray ms-coupled microfluidic device for sub-second hydrogen/deuterium exchange pulse-labelling reveals allosteric effects in enzyme inhibition.  

PubMed

In this work, we introduce an integrated, electrospray mass spectrometry-coupled microfluidic chip that supports the complete workflow for 'bottom up' hydrogen/deuterium exchange (HDX) pulse labelling experiments. HDX pulse labelling is used to measure structural changes in proteins that occur after the initiation of a reaction, most commonly folding. In the present case, we demonstrate the device on the ?-lactamase enzyme TEM-1, identifying active site changes that occur upon acylation by a covalent inhibitor and subtle changes in conformational dynamics that occur away from the active site over a period of several second after the inhibitor is bound. Our results demonstrate the power of microfluidics-enabled sub-second HDX pulse labelling as a tool for studying allostery and show some intriguing correlations with mutagenesis studies. PMID:23426018

Rob, Tamanna; Gill, Preet Kamal; Golemi-Kotra, Dasantila; Wilson, Derek J

2013-02-21

57

Application of atmospheric pressure photo ionization hydrogen/deuterium exchange high-resolution mass spectrometry for the molecular level speciation of nitrogen compounds in heavy crude oils.  

PubMed

We report here for the first time the application of atmospheric pressure photo ionization hydrogen/deuterium exchange (APPI HDX) coupled to high-resolution mass spectrometry for molecular level speciation of nitrogen containing compounds in crude oils. The speciation was done based on different combinations of ions produced from nitrogen containing compounds with various functional groups. To prove the concept, 20 nitrogen containing standard compounds were analyzed. As a result, it was shown that the nitrogen containing compound (M) with a primary amine functional group mainly produced a combination of [M - 2H + 2D](•+) and ([M - 2H + 2D] + D)(+) ions, one with a secondary amine including alkylated or phenylated pyrrole a combination of [M - H + D](•+) and ([M - H + D] + D)(+), one with a tertiary amine including N-alkylated or phenylated pyrrole a combination of [M](•+) and [M + D](+), and one with a pyridine functional group mostly [M + D](+) ions. The concept was successfully applied to do nitrogen speciation of resins fractions of two oil samples. Combined with the subsequent investigation of double bond equivalence distribution, it was shown that resins of Qinhuangdao crude oil sample contained mostly alkylated pyrrole and N-alkylated pyrrole type compounds but resins of shale oil extract contained mostly pyridine type nitrogen compounds. It was also shown that the speciation of individual elemental composition was also possible by use of this method. Overall, this study clearly shows that atmospheric pressure photo ionization hydrogen/deuterium exchange (APPI HDX) coupled to high-resolution mass spectrometry is a powerful analytical method to do nitrogen speciation of crude oil compounds at the molecular level. PMID:24033284

Cho, Yunju; Ahmed, Arif; Kim, Sunghwan

2013-09-30

58

Polarized Fourier transform infrared spectroscopy of bacteriorhodopsin. Transmembrane alpha helices are resistant to hydrogen/deuterium exchange.  

PubMed Central

The secondary structure of bacteriorhodopsin has been investigated by polarized Fourier transform infrared spectroscopy combined with hydrogen/deuterium exchange, isotope labeling and resolution enhancement methods. Oriented films of purple membrane were measured at low temperature after exposure to H2O or D2O. Resolution enhancement techniques and isotopic labeling of the Schiff base were used to assign peaks in the amide I region of the spectrum. alpha-helical structure, which exhibits strong infrared dichroism, undergoes little H/D exchange, even after 48 h of D2O exposure. In contrast, non-alpha-helical structure, which exhibits little dichroism, undergoes rapid H/D exchange. A band at 1,640 cm-1, which has previously been assigned to beta-sheet structure, is found to be due in part to the C = N stretching vibration of protonated Schiff base of the retinylidene chromophore. We conclude that the membrane spanning regions of bR consist predominantly of alpha-helical structure whereas most beta-type structure is located in surface regions directly accessible to water.

Earnest, T N; Herzfeld, J; Rothschild, K J

1990-01-01

59

Gas-phase hydrogen/deuterium exchange of dinucleotides and 5'-monophosphate dinucleotides in a quadrupole ion trap  

NASA Astrophysics Data System (ADS)

Gas-phase hydrogen/deuterium (H/D) exchange reactions of four deprotonated dinucleotides (dAA, dAG, dGA, dGG) and their 5'-monophosphate analogs (5'-dAA, 5'-dAG, 5'-dGA, 5'-dGG) with D2O were performed in a quadrupole ion trap mass spectrometer. Significant differences in the rates and extents of exchange were found when the 5'-hydroxyl group of the dinucleotides was replaced by a phosphate functionality. Extensive and nucleobase-dependent exchange occurred for the deprotonated 5'-monophosphate dinucleotides, whereas the dinucleotides all exhibited essentially the same limited exchange. Results for the isomeric 5'-monophosphates, 5'-dAG and 5'-dGA, were remarkably different, indicating that the H/D exchange reaction was sequence dependent. An elaborate array of computations was performed to investigate the gas-phase structures of the ions individually and also as participants in ion-molecule complexes with D2O. Integration of the experimental and theoretical results supports a relay exchange mechanism and suggests that the exchange behavior depends highly on the identity and sequence of the nucleobases as well as their ability to interact with the deprotonation site. Finally, a shuttling mechanism is proposed to possibly account for the bimodal H/D exchange behavior observed for deprotonated 5'P-dGA. In this case, hydrogen bonding between the nucleobases in concert with interaction from the deuterating agent creates an ion-molecule complex in which hydrogen and deuterium atoms may be shuttled amongst the hydrogen-bonded participants.

Chipuk, Joseph E.; Brodbelt, Jennifer S.

2009-10-01

60

The Effect of Inhibitors on the Hydrogen-Deuterium Exchange Reaction  

Microsoft Academic Search

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

M. J. Stephen; C. J. Danby

1955-01-01

61

Dynamic motions of free and bound O29 scaffolding protein identified by hydrogen deuterium exchange mass spectrometry.  

PubMed

In the double-stranded DNA containing bacteriophages, hundreds of copies of capsid protein subunits polymerize to form icosahedral shells, called procapsids, into which the viral genome is subsequently packaged to form infectious virions. High assembly fidelity requires the assistance of scaffolding protein molecules, which interact with the capsid proteins to insure proper geometrical incorporation of subunits into the growing icosahedral lattices. The interactions between the scaffolding and capsid proteins are transient and are subsequently disrupted during DNA packaging. Removal of scaffolding protein is achieved either by proteolysis or alternatively by some form of conformational switch that allows it to dissociate from the capsid. To identify the switch controlling scaffolding protein association and release, hydrogen deuterium exchange was applied to Bacillus subtilis phage Ø29 scaffolding protein gp7 in both free and procapsid-bound forms. The H/D exchange experiments revealed highly dynamic and cooperative opening motions of scaffolding molecules in the N-terminal helix-loop-helix (H-L-H) region. The motions can be promoted by destabilizing the hydrophobic contact between two helices. At low temperature where high energy motions were damped, or in a mutant in which the helices were tethered through the introduction of a disulfide bond, this region displayed restricted cooperative opening motions as demonstrated by a switch in the exchange kinetics from correlated EX1 exchange to uncorrelated EX2 exchange. The cooperative opening rate was increased in the procapsid-bound form, suggesting this region might interact with the capsid protein. Its dynamic nature might play a role in the assembly and release mechanism. PMID:16522798

Fu, Chi-Yu; Prevelige, Peter E

2006-03-07

62

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

Microsoft Academic Search

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

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

2001-01-01

63

Defining the interacting regions between apomyoglobin and lipid membrane by hydrogen/deuterium exchange coupled to mass spectrometry.  

PubMed

Sperm whale myoglobin can be considered as the model protein of the globin family. The pH-dependence of the interactions of apomyoglobin with lipid bilayers shares some similarities with the behavior of pore-forming domains of bacterial toxins belonging also to the globin family. Two different states of apomyoglobin bound to a lipid bilayer have been characterized by using hydrogen/deuterium exchange experiments and mass spectrometry. When bound to the membrane at pH 5.5, apomyoglobin remains mostly native-like and interacts through alpha-helix A. At pH 4, the binding is related to the stabilization of a partially folded state. In that case, alpha-helices A and G are involved in the interaction. At this pH, alpha-helix G, which is the most hydrophobic region of apomyoglobin, is available for interaction with the lipid bilayer because of the loss of the tertiary structure. Our results show the feasibility of such experiments and their potential for the characterization of various membrane-bound states of amphitropic proteins such as pore-forming domains of bacterial toxins. This is not possible with other high-resolution methods, because these proteins are usually in partially folded states when interacting with membranes. PMID:17346745

Man, Petr; Montagner, Caroline; Vernier, Grégory; Dublet, Bernard; Chenal, Alexandre; Forest, Eric; Forge, Vincent

2007-02-13

64

Thermodynamic and kinetic characterization of hydrogen-deuterium exchange in beta-phase palladium.  

PubMed

A Sieverts' apparatus coupled with a residual gas analyzer (RGA) is an effective method to detect composition variations during isotopic exchange. This experimental setup provides a tool for the thermodynamic and kinetic characterization of H-D isotope exchange on Pd. The H or D concentrations in the gas and solid phases during the exchanges starting from (H(2) + Pd(x)D) and (D(2) + Pd(x)H) in beta-phase Pd were monitored over a temperature range from 173 to 298 K. The equilibrium properties, i.e., the H-D separation factors alpha and equilibrium constants K(HD), were obtained and found to be very close to those in the literature. The values of equilibrium constant reported here are the only experimental K(HD) data for H-D-Pd system. The H-D exchange rates on beta-Pd were measured for both exchange directions. A comprehensive kinetic model is proposed that correlates the exchange rate and the driving force composed of the reactant concentrations and the extent of deviation from equilibrium. The rate constants were obtained using this model for two exchange directions. The rates for the two exchange directions were found to be close to each other at 173 K, but they differ with temperature increase in such a way that the (D(2) + Pd(x)H) has a higher rate than (H(2) + Pd(x)D). The exchange activation energies obtained are 2.0 and 3.5 kJ/mol for the (H(2) + Pd(x)D) and (D(2) + Pd(x)H) directions, respectively. The difference in activation energies results from the difference in the energy states of (H(2) + Pd(x)D) and (D(2) + Pd(x)D). The calculated exchange profiles using this model agree with the experimental values reasonably well. PMID:19735117

Luo, Weifang; Cowgill, Donald F; Causey, Rion A

2009-10-01

65

Construct optimization for protein NMR structure analysis using amide hydrogen/deuterium exchange mass spectrometry.  

PubMed

Disordered or unstructured regions of proteins, while often very important biologically, can pose significant challenges for resonance assignment and three-dimensional structure determination of the ordered regions of proteins by NMR methods. In this article, we demonstrate the application of (1)H/(2)H exchange mass spectrometry (DXMS) for the rapid identification of disordered segments of proteins and design of protein constructs that are more suitable for structural analysis by NMR. In this benchmark study, DXMS is applied to five NMR protein targets chosen from the Northeast Structural Genomics project. These data were then used to design optimized constructs for three partially disordered proteins. Truncated proteins obtained by deletion of disordered N- and C-terminal tails were evaluated using (1)H-(15)N HSQC and (1)H-(15)N heteronuclear NOE NMR experiments to assess their structural integrity. These constructs provide significantly improved NMR spectra, with minimal structural perturbations to the ordered regions of the protein structure. As a representative example, we compare the solution structures of the full length and DXMS-based truncated construct for a 77-residue partially disordered DUF896 family protein YnzC from Bacillus subtilis, where deletion of the disordered residues (ca. 40% of the protein) does not affect the native structure. In addition, we demonstrate that throughput of the DXMS process can be increased by analyzing mixtures of up to four proteins without reducing the sequence coverage for each protein. Our results demonstrate that DXMS can serve as a central component of a process for optimizing protein constructs for NMR structure determination. PMID:19306341

Sharma, Seema; Zheng, Haiyan; Huang, Yuanpeng J; Ertekin, Asli; Hamuro, Yoshitomo; Rossi, Paolo; Tejero, Roberto; Acton, Thomas B; Xiao, Rong; Jiang, Mei; Zhao, Li; Ma, Li-Chung; Swapna, G V T; Aramini, James M; Montelione, Gaetano T

2009-09-01

66

Comparative Analysis of Oxy-Hemoglobin and Aquomet-Hemoglobin by Hydrogen/Deuterium Exchange Mass Spectrometry  

NASA Astrophysics Data System (ADS)

The function of hemoglobin (Hb) as oxygen transporter is mediated by reversible O2 binding to Fe(2+) heme in each of the ? and ? subunits. X-ray crystallography revealed different subunit arrangements in oxy-Hb and deoxy-Hb. The deoxy state is stabilized by additional contacts, causing a rigidification that results in strong protection against hydrogen/deuterium exchange (HDX). Aquomet-Hb is a dysfunctional degradation product with four water-bound Fe(3+) centers. Heme release from aquomet-Hb is relatively facile, triggering oxidative damage of membrane lipids. Aquomet-Hb crystallizes in virtually the same conformation as oxy-Hb. Hence, it is commonly implied that the solution-phase properties of aquomet-Hb should resemble those of the oxy state. This work compares the structural dynamics of oxy-Hb and aquomet-Hb by HDX mass spectrometry (MS). It is found that the aquomet state exhibits a solution-phase structure that is significantly more dynamic, as manifested by elevated HDX levels. These enhanced dynamics affect the aquomet ? and ? subunits in a different fashion. The latter undergoes global destabilization, whereas the former shows elevated HDX levels only in the heme binding region. It is proposed that these enhanced dynamics play a role in facilitating heme release from aquomet-Hb. Our findings should be of particular interest to the MS community because oxy-Hb and aquomet-Hb serve as widely used test analytes for probing the relationship between biomolecular structure in solution and in the gas phase. We are not aware of any prior comparative HDX/MS experiments on oxy-Hb and aquomet-Hb.

Sowole, Modupeola A.; Konermann, Lars

2013-05-01

67

Histidine Hydrogen-Deuterium Exchange Mass Spectrometry for Probing the Microenvironment of Histidine Residues in Dihydrofolate Reductase  

PubMed Central

Background Histidine Hydrogen-Deuterium Exchange Mass Spectrometry (His-HDX-MS) determines the HDX rates at the imidazole C2-hydrogen of histidine residues. This method provides not only the HDX rates but also the pKa values of histidine imidazole rings. His-HDX-MS was used to probe the microenvironment of histidine residues of E. coli dihydrofolate reductase (DHFR), an enzyme proposed to undergo multiple conformational changes during catalysis. Methodology/Principal Findings Using His-HDX-MS, the pKa values and the half-lives (t1/2) of HDX reactions of five histidine residues of apo-DHFR, DHFR in complex with methotrexate (DHFR-MTX), DHFR in complex with MTX and NADPH (DHFR-MTX-NADPH), and DHFR in complex with folate and NADP+ (DHFR-folate-NADP+) were determined. The results showed that the two parameters (pKa and t1/2) are sensitive to the changes of the microenvironment around the histidine residues. Although four of the five histidine residues are located far from the active site, ligand binding affected their pKa, t1/2 or both. This is consistent with previous observations of ligand binding-induced distal conformational changes on DHFR. Most of the observed pKa and t1/2 changes could be rationalized using the X-ray structures of apo-DHFR, DHFR-MTX-NADPH, and DHFR-folate-NADP+. The availability of the neutron diffraction structure of DHFR-MTX enabled us to compare the protonation states of histidine imidazole rings. Conclusions/Significance Our results demonstrate the usefulness of His-HDX-MS in probing the microenvironments of histidine residues within proteins.

Ahmad, Md. Faiz; Gokulrangan, Giridharan; Tomechko, Sara E.; Bennett, Brad; Dealwis, Chris

2011-01-01

68

Ultra performance liquid chromatography (UPLC) further improves hydrogen\\/deuterium exchange mass spectrometry  

Microsoft Academic Search

Ultra performance liquid chromatography (UPLC) employs particles smaller than 2 µm in diameter to achieve superior resolution,\\u000a speed, and sensitivity compared with high-performance liquid chromatography (HPLC). We have tested the suitability of UPLC\\u000a for the analysis of deuterated peptides in hydrogen exchange mass spectrometry experiments. Superior resolution and sample\\u000a throughput were obtained with UPLC versus HPLC. For highly deuterated model

Yan Wu; John R. Engen; William B. Hobbins

2006-01-01

69

Gas-phase hydrogen\\/deuterium exchange of 5?- and 3?-mononucleotides in a quadrupole ion trap: Exploring the role of conformation and system energy  

Microsoft Academic Search

Gas-phase hydrogen\\/deuterium (H\\/D) exchange reactions for deprotonated 2?-deoxy-5?-monophosphate and 2?-deoxy-3?-monophosphate\\u000a nucleotides with D2O were performed in a quadrupole ion trap mass spectrometer. To augment these experiments, molecular modeling was also conducted\\u000a to identify likely deprotonation sites and potential gas-phase conformations of the anions. A majority of the 5?-monophosphates\\u000a exchanged extensively with several of the compounds completely incorporating deuterium in place

Joseph E. Chipuk; Jennifer S. Brodbelt

2007-01-01

70

Hydrogen/Deuterium Exchange Mass Spectrometry and Site-Directed Disulfide Cross-Linking Suggest an Important Dynamic Interface between the Two Lysostaphin Domains  

PubMed Central

Lysostaphin is a peptidoglycan hydrolase secreted by Staphylococcus simulans. It can specifically lyse Staphylococcus aureus and is being tested as a novel antibacterial agent. The protein contains an N-terminal catalytic domain and a C-terminal cell wall targeting domain. Although the two domains from homologous enzymes were structurally determined, the structural organization of lysostaphin domains remains unknown. We used hydrogen/deuterium exchange mass spectrometry (H/DX-MS) and site-directed disulfide cross-linking to probe the interface between the lysostaphin catalytic and targeting domains. H/DX-MS-mediated comparison of peptides from full-length lysostaphin and the separated domains identified four peptides of lower solvent accessibility in the full-length protein. Cross-linking analysis using cysteine pair substitutions within those peptides showed that two pairs of cysteines can form disulfide bonds, supporting the domain association role of the targeted peptides. The cross-linked mutant exhibited a binding capacity to S. aureus that was similar to that of the wild-type protein but reduced bacteriolytic activity probably because of restraint in conformation. The diminished activity was further reduced with increasing NaCl concentrations that can cause contractions of bacterial peptidoglycan. The lytic activity, however, could be fully recovered by reducing the disulfide bonds. These results suggest that lysostaphin may require dynamic association of the two domains for coordinating substrate binding and target cleavage on the elastic peptidoglycan. Our study will help develop site-specific PEGylated lysostaphin to treat systemic S. aureus infections.

Lu, Hai-Rong; Gu, Mei-Gang; Huang, Qiang; Huang, Jin-Jiang; Lu, Wan-Ying; Lu, Hong

2013-01-01

71

Conformational dynamics of the bovine mitochondrial ADP/ATP carrier isoform 1 revealed by hydrogen/deuterium exchange coupled to mass spectrometry.  

PubMed

The mitochondrial adenine nucleotide carrier (Ancp) catalyzes the transport of ADP and ATP across the mitochondrial inner membrane, thus playing an essential role in cellular energy metabolism. During the transport mechanism the carrier switches between two different conformations that can be blocked by two toxins: carboxyatractyloside (CATR) and bongkrekic acid. Therefore, our understanding of the nucleotide transport mechanism can be improved by analyzing structural differences of the individual inhibited states. We have solved the three-dimensional structure of bovine carrier isoform 1 (bAnc1p) in a complex with CATR, but the structure of the carrier-bongkrekic acid complex, and thus, the detailed mechanism of transport remains unknown. Improvements in sample processing in the hydrogen/deuterium exchange technique coupled to mass spectrometry (HDX-MS) have allowed us to gain novel insights into the conformational changes undergone by bAnc1p. This paper describes the first study of bAnc1p using HDX-MS. Results obtained with the CATR-bAnc1p complex were fully in agreement with published results, thus, validating our approach. On the other hand, the HDX kinetics of the two complexes displays marked differences. The bongkrekic acid-bAnc1p complex exhibits greater accessibility to the solvent on the matrix side, whereas the CATR-bAnc1p complex is more accessible on the intermembrane side. These results are discussed with respect to the structural and biochemical data available on Ancp. PMID:20805227

Rey, Martial; Man, Petr; Clémençon, Benjamin; Trézéguet, Véronique; Brandolin, Gérard; Forest, Eric; Pelosi, Ludovic

2010-08-30

72

Conformational studies of the robust 2-Cys peroxiredoxin Salmonella typhimurium AhpC by solution phase hydrogen/deuterium (H/D) exchange monitored by electrospray ionization mass spectrometry  

PubMed Central

This is the first comprehensive HX-MS study of a “robust” 2-Cys peroxiredoxin (Prx), namely Salmonella typhimurium AhpC (StAhpC). Prx proteins control intracellular peroxide levels and are abundant antioxidant proteins in eukaryotes, archaea and bacteria. Crystal structural analyses and structure/activity studies of several bacterial and mammalian 2-Cys Prxs have revealed that the activity of 2-Cys Prxs is regulated by redox-dependent oligmerization and a sensitivity of the active site cysteine residue to overoxidation. The propensity to overoxidation is linked to the conformational flexibility of the peroxidatic active site loop. The HX-MS results emphasize the modulation of the conformational motility of the active site loop by disulfide formation. To obtain information on the conformational impact of decamer formation on the active site loop motility, mutants with Thr77 substituted by Ile, a decamer-disrupting mutation or by Val, a decamer-stabilizing mutation, were studied. For the isoleucine mutant, enhanced mobility was observed for regions encompassing the ?4 helix located in the dimer-dimer interface and regions surrounding the peroxidatic loop. In contrast, the T77V mutation resulted in an increase in conformational stability in most regions of the protein except for the active site loop and the region encompassing the resolving cysteine.

Nirudodhi, Sasidhar; Parsonage, Derek; Karplus, P. Andrew; Poole, Leslie B.; Maier, Claudia S.

2010-01-01

73

Interrupted hydrogen/deuterium exchange reveals the stable core of the remarkably helical molten globule of alpha-beta parallel protein flavodoxin.  

PubMed

Kinetic intermediates that appear early during protein folding often resemble the relatively stable molten globule intermediates formed by several proteins under mildly denaturing conditions. Molten globules have a substantial amount of secondary structure but lack virtually all tertiary side-chain packing characteristics of natively folded proteins. Due to exposed hydrophobic groups, molten globules are prone to aggregation, which can have detrimental effects on organisms. The molten globule that is observed during folding of alpha-beta parallel flavodoxin from Azotobacter vinelandii is a remarkably non-native species. This folding intermediate is helical and contains no beta-sheet and is kinetically off-pathway to the native state. It can be trapped under native-like conditions by substituting residue Phe(44) for Tyr(44). To characterize this species at the residue level, in this study, use is made of interrupted hydrogen/deuterium exchange detected by NMR spectroscopy. In the molten globule of flavodoxin, the helical region comprising residues Leu(110)-Val(125) is shown to be better protected against exchange than the other ordered parts of the folding intermediate. This helical region is better buried than the other helices, causing its context-dependent stabilization against unfolding. Residues Leu(110)-Val(125) thus form the stable core of the helical molten globule of alpha-beta parallel flavodoxin, which is almost entirely structured. Non-native docking of helices in the molten globule of flavodoxin prevents formation of the parallel beta-sheet of native flavodoxin. Hence, to produce native alpha-beta parallel protein molecules, the off-pathway species needs to unfold. PMID:19959481

Nabuurs, Sanne M; van Mierlo, Carlo P M

2009-12-03

74

Hydrogen/deuterium exchange mass spectrometry and site-directed disulfide cross-linking suggest an important dynamic interface between the two lysostaphin domains.  

PubMed

Lysostaphin is a peptidoglycan hydrolase secreted by Staphylococcus simulans. It can specifically lyse Staphylococcus aureus and is being tested as a novel antibacterial agent. The protein contains an N-terminal catalytic domain and a C-terminal cell wall targeting domain. Although the two domains from homologous enzymes were structurally determined, the structural organization of lysostaphin domains remains unknown. We used hydrogen/deuterium exchange mass spectrometry (H/DX-MS) and site-directed disulfide cross-linking to probe the interface between the lysostaphin catalytic and targeting domains. H/DX-MS-mediated comparison of peptides from full-length lysostaphin and the separated domains identified four peptides of lower solvent accessibility in the full-length protein. Cross-linking analysis using cysteine pair substitutions within those peptides showed that two pairs of cysteines can form disulfide bonds, supporting the domain association role of the targeted peptides. The cross-linked mutant exhibited a binding capacity to S. aureus that was similar to that of the wild-type protein but reduced bacteriolytic activity probably because of restraint in conformation. The diminished activity was further reduced with increasing NaCl concentrations that can cause contractions of bacterial peptidoglycan. The lytic activity, however, could be fully recovered by reducing the disulfide bonds. These results suggest that lysostaphin may require dynamic association of the two domains for coordinating substrate binding and target cleavage on the elastic peptidoglycan. Our study will help develop site-specific PEGylated lysostaphin to treat systemic S. aureus infections. PMID:23380729

Lu, Hai-Rong; Gu, Mei-Gang; Huang, Qiang; Huang, Jin-jiang; Lu, Wan-Ying; Lu, Hong; Huang, Qing-Shan

2013-02-04

75

Role of Calcium in the Conformational Dynamics of Factor XIII Activation Examined by Hydrogen/Deuterium Exchange Coupled with MALDI-TOF MS  

PubMed Central

Factor XIII catalyzes formation of ?-glutamyl-?-lysyl crosslinks within fibrin clots. FXIII A2 can be activated proteolytically with thrombin and low mM Ca2+ or nonproteolytically with high monovalent/divalent cations along with low mM Ca2+. Physiologically, FXIII A2 is poised to respond to transient influxes of Ca2+ in a Na+ containing environment. A successful strategy to monitor FXIII conformational events is hydrogen-deuterium exchange (HDX) coupled with mass spectrometry. FXIII A2 was examined in the presence of different cations (Ca2+, Mg2+, Ba2+, Cu2+, Na+, TMAC+, and EDA2+) ranging from 1–2 mM, physiological Ca2+ concentration, to 50–500mM for nonproteolytic activation. Increases in FXIII solvent exposure could already be observed at 1 mM Ca2+ for the dimer interface, the catalytic site, and glutamine substrate regions. By contrast, solvent protection was observed at the secondary cleavage site. These events occurred even though 1mM Ca2+ is insufficient for FXIII activation. The metals 1mM Mg2+, 1mM Ba2+, and 1mM Cu2+ each led to conformational changes, many in the same FXIII regions as Ca2+. FXIII could also be activated nonproteolytically with 500mM tetramethylammonium chloride (TMAC+) and 500mM ethylenediamine (EDA2+), both with 2mM Ca2+. These different HDX studies help reveal the first FXIII segments that respond to physiological Ca2+ levels.

Woofter, Ricky T.; Maurer, Muriel C.

2011-01-01

76

Role of calcium in the conformational dynamics of factor XIII activation examined by hydrogen-deuterium exchange coupled with MALDI-TOF MS.  

PubMed

Factor XIII catalyzes formation of ?-glutamyl-?-lysyl crosslinks within fibrin clots. FXIII A(2) can be activated proteolytically with thrombin and low mM Ca(2+) or nonproteolytically with high monovalent/divalent cations along with low mM Ca(2+). Physiologically, FXIII A(2) is poised to respond to transient influxes of Ca(2+) in a Na(+) containing environment. A successful strategy to monitor FXIII conformational events is hydrogen-deuterium exchange (HDX) coupled with mass spectrometry. FXIII A(2) was examined in the presence of different cations (Ca(2+), Mg(2+), Ba(2+), Cu(2+), Na(+), TMAC(+), and EDA(2+)) ranging from 1 to 2mM, physiological Ca(2+) concentration, to 50-500mM for nonproteolytic activation. Increases in FXIII solvent exposure could already be observed at 1mM Ca(2+) for the dimer interface, the catalytic site, and glutamine substrate regions. By contrast, solvent protection was observed at the secondary cleavage site. These events occurred even though 1mM Ca(2+) is insufficient for FXIII activation. The metals 1mM Mg(2+), 1mM Ba(2+), and 1mM Cu(2+) each led to conformational changes, many in the same FXIII regions as Ca(2+). FXIII could also be activated nonproteolytically with 500mM tetramethylammonium chloride (TMAC(+)) and 500mM ethylenediamine (EDA(2+)), both with 2mM Ca(2+). These different HDX studies help reveal the first FXIII segments that respond to physiological Ca(2+) levels. PMID:21640701

Woofter, Ricky T; Maurer, Muriel C

2011-05-26

77

Dynamics of Cleft Closure of the GluA2 Ligand-binding Domain in the Presence of Full and Partial Agonists Revealed by Hydrogen-Deuterium Exchange.  

PubMed

The majority of excitatory neurotransmission in the CNS is mediated by tetrameric AMPA receptors. Channel activation begins with a series of interactions with an agonist that binds to the cleft between the two lobes of the ligand-binding domain of each subunit. Binding leads to a series of conformational transitions, including the closure of the two lobes of the binding domain around the ligand, culminating in ion channel opening. Although a great deal has been learned from crystal structures, determining the molecular details of channel activation, deactivation, and desensitization requires measures of dynamics and stabilities of hydrogen bonds that stabilize cleft closure. The use of hydrogen-deuterium exchange at low pH provides a measure of the variation of stability of specific hydrogen bonds among agonists of different efficacy. Here, we used NMR measurements of hydrogen-deuterium exchange to determine the stability of hydrogen bonds in the GluA2 (AMPA receptor) ligand-binding domain in the presence of several full and partial agonists. The results suggest that the stabilization of hydrogen bonds between the two lobes of the binding domain is weaker for partial than for full agonists, and efficacy is correlated with the stability of these hydrogen bonds. The closure of the lobes around the agonists leads to a destabilization of the hydrogen bonding in another portion of the lobe interface, and removing an electrostatic interaction in Lobe 2 can relieve the strain. These results provide new details of transitions in the binding domain that are associated with channel activation and desensitization. PMID:23940029

Ahmed, Ahmed H; Ptak, Christopher P; Fenwick, Michael K; Hsieh, Ching-Lin; Weiland, Gregory A; Oswald, Robert E

2013-08-12

78

Polymorphic Triple ?-Sheet Structures Contribute to Amide Hydrogen/Deuterium (H/D) Exchange Protection in the Alzheimer Amyloid ?42 Peptide*  

PubMed Central

Characterization of the polymorphic structural range of A? oligomers is important to the understanding of the mechanisms of toxicity. Yet for highly polymorphic ensembles, experimental structural elucidation is difficult. Here, we use a combination of NMR solvent protection experiments and computational structural screening to identify major species in the amyloid conformational ensemble. We examined the polymorphic pentamer and fibril seeds of A?42 and its mutants and compared the theoretical backbone amide protection obtained from simulations with experimental hydrogen/deuterium (H/D) exchange protection ratio. We observed that highly flexible pentamers do not share structural similarities with fibril seed oligomers, except the turn regions. We found that a novel amyloid structural motif of a triple ?-sheet, with the N-terminal residues interacting with the core (Lys17–Glu22) ?-sheet region, correlates with H/D exchange protection. The triple ?-sheet A?42 oligomer has a minimal exposure of hydrophobic residues and is further stabilized by the E22Q (Dutch) mutation in Alzheimer disease. The experimental H/D exchange solvent protection ratio implies that triple ?-sheet fibrils and globulomers could coexist in the A?42 ensemble, pointing to a broad heterogeneous aggregate population. Our results suggest that an approach that combines computational modeling with NMR protection data can be a useful strategy for obtaining clues to the preferred conformational species of the assemblies in solution and help in alleviating experimental difficulties and consequently possible errors in the exchange data for A?42 fibrils.

Ma, Buyong; Nussinov, Ruth

2011-01-01

79

Evidence for site-specific intra-ionic hydrogen/deuterium exchange in the low-energy collision-induced dissociation product ion spectra of protonated small molecules generated by electrospray ionisation.  

PubMed

The experimental investigation of site-specific intra-ionic hydrogen/deuterium (H/D) exchange in the low-energy collision-induced dissociation (CID) product ion spectra of protonated small molecules generated by electrospray ionisation (ESI) is presented. The observation of intra-ionic H/D exchange in such ions under low-energy CID conditions has hitherto been rarely reported. The data suggest that the intra-ionic H/D exchange takes place in a site-specific manner between the ionising deuteron, localised at either a tertiary amine or a tertiary amine-N-oxide, and a gamma-hydrogen relative to the nitrogen atom. Nuclear magnetic resonance (NMR) spectroscopy measurements showed that no H/D exchange takes place in solution, indicating that the reaction occurs in the gas phase. The compounds analysed in this study suggested that electron-withdrawing groups bonded to the carbon atom bearing the gamma-hydrogen can preclude exchange. The effect of the electron-withdrawing group appears dependent upon its electronegativity, with lower chi value groups still allowing exchange to take place. However, the limited dataset available in this study prevented robust conclusions being drawn regarding the effect of the electron-withdrawing group. The observation of site-specific intra-ionic H/D exchange has application in the area of structural elucidation, where it could be used to introduce an isotopic label into the carbon skeleton of a molecule containing specific structural features. This could increase the throughput, and minimise the cost, of such studies due to the obviation of the need to produce a deuterium-labelled analogue by synthetic means. PMID:20069530

Holman, Stephen W; Wright, Patricia; Wells, Neil J; Langley, G John

2010-04-01

80

Distinct interaction modes of an AKAP bound to two regulatory subunit isoforms of protein kinase A revealed by amide hydrogen/deuterium exchange.  

PubMed

The structure of an AKAP docked to the dimerization/docking (D/D) domain of the type II (RIIalpha) isoform of protein kinase A (PKA) has been well characterized, but there currently is no detailed structural information of an AKAP docked to the type I (RIalpha) isoform. Dual-specific AKAP2 (D-AKAP2) binds in the nanomolar range to both isoforms and provided us with an opportunity to characterize the isoform-selective nature of AKAP binding using a common docked ligand. Hydrogen/deuterium (H/D) exchange combined with mass spectrometry (DXMS) was used to probe backbone structural changes of an alpha-helical A-kinase binding (AKB) motif from D-AKAP2 docked to both RIalpha and RIIalpha D/D domains. The region of protection upon complex formation and the magnitude of protection from H/D exchange were determined for both interacting partners in each complex. The backbone of the AKB ligand was more protected when bound to RIalpha compared to RIIalpha, suggesting an increased helical stabilization of the docked AKB ligand. This combined with a broader region of backbone protection induced by the AKAP on the docking surface of RIalpha indicated that there were more binding constraints for the AKB ligand when bound to RIalpha. This was in contrast to RIIalpha, which has a preformed, localized binding surface. These distinct modes of AKAP binding may contribute to the more discriminating nature of the RIalpha AKAP-docking surface. DXMS provides valuable structural information for understanding binding specificity in the absence of a high-resolution structure, and can readily be applied to other protein-ligand and protein-protein interactions. PMID:16260760

Burns-Hamuro, Lora L; Hamuro, Yoshitomo; Kim, Jack S; Sigala, Paul; Fayos, Rosa; Stranz, David D; Jennings, Patricia A; Taylor, Susan S; Woods, Virgil L

2005-10-31

81

Distinct interaction modes of an AKAP bound to two regulatory subunit isoforms of protein kinase A revealed by amide hydrogen/deuterium exchange  

PubMed Central

The structure of an AKAP docked to the dimerization/docking (D/D) domain of the type II (RII?) isoform of protein kinase A (PKA) has been well characterized, but there currently is no detailed structural information of an AKAP docked to the type I (RI?) isoform. Dual-specific AKAP2 (D-AKAP2) binds in the nanomolar range to both isoforms and provided us with an opportunity to characterize the isoform-selective nature of AKAP binding using a common docked ligand. Hydrogen/deuterium (H/D) exchange combined with mass spectrometry (DXMS) was used to probe backbone structural changes of an ?-helical A-kinase binding (AKB) motif from D-AKAP2 docked to both RI? and RII? D/D domains. The region of protection upon complex formation and the magnitude of protection from H/D exchange were determined for both interacting partners in each complex. The backbone of the AKB ligand was more protected when bound to RI? compared to RII?, suggesting an increased helical stabilization of the docked AKB ligand. This combined with a broader region of backbone protection induced by the AKAP on the docking surface of RI? indicated that there were more binding constraints for the AKB ligand when bound to RI?. This was in contrast to RII?, which has a preformed, localized binding surface. These distinct modes of AKAP binding may contribute to the more discriminating nature of the RI? AKAP-docking surface. DXMS provides valuable structural information for understanding binding specificity in the absence of a high-resolution structure, and can readily be applied to other protein–ligand and protein–protein interactions.

Burns-Hamuro, Lora L.; Hamuro, Yoshitomo; Kim, Jack S.; Sigala, Paul; Fayos, Rosa; Stranz, David D.; Jennings, Patricia A.; Taylor, Susan S.; Woods, Virgil L.

2005-01-01

82

Structure and Dynamics of NBD1 from CFTR Characterized Using Crystallography and Hydrogen/Deuterium Exchange Mass Spectrometry  

SciTech Connect

The {Delta}F508 mutation in nucleotide-binding domain 1 (NBD1) of the cystic fibrosis transmembrane conductance regulator (CFTR) is the predominant cause of cystic fibrosis. Previous biophysical studies on human F508 and {Delta}F508 domains showed only local structural changes restricted to residues 509-511 and only minor differences in folding rate and stability. These results were remarkable because {Delta}F508 was widely assumed to perturb domain folding based on the fact that it prevents trafficking of CFTR out of the endoplasmic reticulum. However, the previously reported crystal structures did not come from matched F508 and {Delta}F508 constructs, and the {Delta}F508 structure contained additional mutations that were required to obtain sufficient protein solubility. In this article, we present additional biophysical studies of NBD1 designed to address these ambiguities. Mass spectral measurements of backbone amide {sup 1}H/{sup 2}H exchange rates in matched F508 and {Delta}F508 constructs reveal that {Delta}F508 increases backbone dynamics at residues 509-511 and the adjacent protein segments but not elsewhere in NBD1. These measurements also confirm a high level of flexibility in the protein segments exhibiting variable conformations in the crystal structures. We additionally present crystal structures of a broader set of human NBD1 constructs, including one harboring the native F508 residue and others harboring the {Delta}F508 mutation in the presence of fewer and different solubilizing mutations. The only consistent conformational difference is observed at residues 509-511. The side chain of residue V510 in this loop is mostly buried in all non-{Delta}F508 structures but completely solvent exposed in all {Delta}F508 structures. These results reinforce the importance of the perturbation {Delta}F508 causes in the surface topography of NBD1 in a region likely to mediate contact with the transmembrane domains of CFTR. However, they also suggest that increased exposure of the 509-511 loop and increased dynamics in its vicinity could promote aggregation in vitro and aberrant intermolecular interactions that impede trafficking in vivo.

Lewis, H.A.; Wang, C.; Zhao, X.; Hamuro, Y.; Conners, K.; Kearins, M.C.; Lu, F.; Sauder, J.M.; Molnar, K.S.; Coales, S.J.; Maloney, P.C.; Guggino, W.B.; Wetmore, D.R.; Weber, P.C.; Hunt, J.F. (SGX); (ExSAR); (Cystic); (JHU-MED); (Columbia)

2012-04-30

83

Conformational changes of the glucocorticoid receptor ligand binding domain induced by ligand and cofactor binding, and the location of cofactor binding sites determined by hydrogen/deuterium exchange mass spectrometry  

PubMed Central

HXMS (hydrogen/deuterium exchange mass spectrometry) of the glucocorticoid receptor ligand-binding domain (GR LBD) complexed with the agonist dexamethasone and the antagonist RU-486 is described. Variations in the rates of exchange were observed in regions consistent with the published crystal structures of GR LBD complexed with RU-486 when compared with the GR dexamethasone complex. We also report the HXMS results for agonist-bound GR LBD with the coactivator transcriptional intermediary factor 2 (TIF2) and anatagonist-bound GR LBD with nuclear receptor corepressor (NCoR). Alterations in exchange rates observed for agonist-bound GR LBD with TIF2 present were consistent with the published crystal structural contacts for the complex. Alterations in exchange rates observed for antagonist-bound GR LBD with NCoR were a subset of those observed with TIF2 binding, suggesting a common or overlapping binding site for coactivator and corepressor.

Frego, Lee; Davidson, Walter

2006-01-01

84

Computational Investigation and Hydrogen/Deuterium Exchange of the Fixed Charge Derivative Tris(2,4,6-Trimethoxyphenyl)Phosphonium: Implications for the Aspartic Acid Cleavage Mechanism  

SciTech Connect

Aspartic acid (Asp)-containing peptides with the fixed charge derivative tris(2,4,6-trimethoxyphenyl) phosphonium (tTMP-P+) were explored computationally and experimentally by H/D exchange and fragmentation studies in order to probe the phenomenon of selective cleavage C-terminal to Asp in the absence of a ''mobile'' proton. Ab initio modeling of the tTMP-P+ electrostatic potential demonstrates the positive charge is distributed on the phosphonium group and therefore is not initiating or directing fragmentation as would a ''mobile'' proton. Geometry optimizations and vibrational analyses of different aspartic acid conformations show the aspartic acid structure with a hydrogen bond between the side chain hydroxy and backbone carbonyl lies 2.8 kcal/mol above the lowest energy conformer. In reactions with D2O, the phosphonium-derived doubly charged peptide (H+)P+LDIFSDF rapidly exchanges all 12 of its exchangeable hydrogens for deuterium and also displays a non-exchanging population. With no added proton, P+LDIFSDF exchanges a maximum of four of eleven exchangeable hydrogens for deuterium. No exchange is observed when all acidic groups are converted to the corresponding methyl esters. Together, these H/D exchange results indicate that the acidic hydrogens are ''mobile locally'' because they are able to participate in exchange even in the absence of an added proton. Fragmentation of two distinct (H+)P+LDIFSDF ion populations shows the non-exchanging population displays selective cleavage, while the exchanging population fragments more evenly across the peptide backbone. This result demonstrates that H/D exchange can sometimes distinguish between and provide a means of separation of different protonation motifs, and that these protonation motifs can have an effect on the fragmentation.

Herrmann, Kristin A.; Wysocki, Vicki H.; Vorpagel, Erich R.

2005-05-25

85

Characterization of water exchange and two-phase flow in porous gas diffusion materials by hydrogen-deuterium contrast neutron radiography  

NASA Astrophysics Data System (ADS)

Liquid water exchange in two-phase flows within hydrophobic porous gas diffusion materials of polymer electrolyte membrane fuel cells was investigated spatially resolved with H-D contrast neutron radiography. A commonly used one-phase model is sufficient to describe water exchange characteristics at low water production rates. At higher rates, however, a significantly higher exchange velocity is found than predicted by a simple model. A new model for the water transport is derived based on an eruptive mechanism guided by Haines jumps, which is supported by recent experimental findings and leads to a very good agreement with the experiments.

Manke, Ingo; Hartnig, Christoph; Kardjilov, Nikolay; Messerschmidt, Matthias; Hilger, André; Strobl, Markus; Lehnert, Werner; Banhart, John

2008-06-01

86

Probing Lactate Dehydrogenase Activity in Tumors by Measuring Hydrogen/Deuterium Exchange in Hyperpolarized l-[1-13C,U-2H]Lactate  

PubMed Central

13C magnetic resonance spectroscopy and spectroscopic imaging measurements of hyperpolarized 13C label exchange between exogenously administered [1-13C]pyruvate and endogenous lactate, catalyzed by lactate dehydrogenase (LDH), has proved to be a powerful approach for probing tissue metabolism in vivo. This experiment has clinical potential, particularly in oncology, where it could be used to assess tumor grade and response to treatment. A limitation of the method is that pyruvate must be administered in vivo at supra-physiological concentrations. This problem can be avoided by using hyperpolarized [1-13C]lactate, which can be used at physiological concentrations. However, sensitivity is limited in this case by the relatively small pyruvate pool size, which would result in only low levels of labeled pyruvate being observed even if there was complete label equilibration between the lactate and pyruvate pools. We demonstrate here a more sensitive method in which a doubly labeled lactate species can be used to measure LDH-catalyzed exchange in vivo. In this experiment exchange of the C2 deuterium label between injected hyperpolarized l-[1-13C,U-2H]lactate and endogenous unlabeled lactate is observed indirectly by monitoring phase modulation of the spin-coupled hyperpolarized 13C signal in a heteronuclear 1H/13C spin–echo experiment.

2012-01-01

87

Hydrogen-exchange mass spectrometry for the study of intrinsic disorder in proteins.  

PubMed

Amide hydrogen/deuterium exchange detected by mass spectrometry (HXMS) is seeing wider use for the identification of intrinsically disordered parts of proteins. In this review, we discuss examples of how discovery of intrinsically disordered regions and their removal can aid in structure determination, biopharmaceutical quality control, the characterization of how post-translational modifications affect weak structuring of disordered regions, the study of coupled folding and binding, and the characterization of amyloid formation. This article is part of a Special Issue entitled: Mass spectrometry in structural biology. PMID:23099262

Balasubramaniam, Deepa; Komives, Elizabeth A

2012-10-22

88

Structural elucidation studies of 15-membered azalide macrocycles using H/D exchange and ESI-MS(n.).  

PubMed

A comprehensive study of fragmentation pathways of 15-membered azalide macrocycles using electrospray ionisation with multistage mass spectrometry (ESI-MS(n)) is presented in this work. Hydrogen/deuterium (H/D) exchange experiments and high-resolution mass spectrometry were used to investigate the proposed fragmentation pathways. In addition, the fragmentation patterns of sodium adduct ions [M+Na](+) of the macrocycles were also investigated as the presence of an alkali metal interacting with the aglycone ring influences the product-ion spectra. PMID:23973790

Gembarovski, Dubravka; Markovi?, Vesna Gabelica; Gali?, Nives

2013-08-02

89

Hydrogen (deuterium) vibron frequency as a pressure comparison gauge at multi-Mbar pressures  

NASA Astrophysics Data System (ADS)

The Raman spectra of compressed hydrogen (deuterium) have been measured in the multi-Mbar pressure range in the diamond anvil cell using the position of the stressed first-order Raman diamond edge (DE) to estimate pressure. We find that the Raman spectra are very consistent in repeated experiments for the critical frequencies of the hydrogen (deuterium) bands at the phase transition pressure-temperature (P-T) points. However, measurements of pressure determined from the DE in different experiments vary substantially with virtually identical Raman spectra of H2 (D2), giving in some cases a pressure variation as high as 20 GPa. These variations do not only depend on sample and sample chamber geometry but also on the P-T path taken, thus making the DE pressure determination uncertain. Therefore, we propose in experiments on hydrogen (deuterium) to use the Raman frequency of the intramolecular vibration (vibron) of H2(D2) as a pressure sensor. By comparing the vibron frequencies and considering the geometrical changes of the sample chamber caused by very high pressures, we propose an alternative explanation to the recent claims of a transformation to a metallic liquid state of hydrogen (deuterium).

Howie, Ross T.; Gregoryanz, Eugene; Goncharov, Alexander F.

2013-08-01

90

Sequence-Specific Conformational Flexibility of SNARE Transmembrane Helices Probed by Hydrogen\\/Deuterium Exchange  

Microsoft Academic Search

SNARE proteins mediate fusion of intracellular eukaryotic membranes and their ?-helical transmembrane domains are known to contribute to lipid bilayer mixing. Synthetic transmembrane domain peptides were previously shown to mimic the function of SNARE proteins in that they trigger liposome fusion in a sequence-specific fashion. Here, we performed a detailed investigation of the conformational dynamics of the transmembrane helices of

Walter Stelzer; Bernhard C. Poschner; Holger Stalz; Albert J. Heck; Dieter Langosch

2008-01-01

91

Hydrogen--Deuterium Exchange in Water Vapor: The Mass Spectrometric Sensitivities and the Equilibrium Constant.  

National Technical Information Service (NTIS)

The equilibrium constant, K/sub HDO/, for the reaction H sub 2 O + D sub 2 O = 2HDO can be expressed as an intensity ratio, I, measured mass spectrometrically, times a sensitivity ratio, S, measured in mass spectrometric calibration experiments. The latte...

J. W. Pyper R. J. Dupzyk R. D. Friesen S. L. Bernasek C. A. May

1976-01-01

92

Hydrogen\\/Deuterium Exchange Monitored by Liquid Chromatography Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry-Method Optimization and Applications to the Study of Protein Conformation and Protein-Drug Interactions  

Microsoft Academic Search

Proteins are the most versatile macromolecules in the cell. Major biochemical functions of proteins include binding; catalysis; and serving as structural components of cells and organisms. Proteins are made of amino acids that are linearly connected by peptide bonds. The linear protein sequence, determined by a gene, can fold into higher-level structures. Proper protein structure\\/conformation is important to maintain its

Hui-Min Zhang

2009-01-01

93

The torque dependence of the H-mode power threshold in hydrogen, deuterium and helium plasmas in DIII-D  

SciTech Connect

On DIII-D, the H-mode power threshold has been determined for hydrogen, deuterium and helium plasmas heated by neutral beam injection and/or by electron cyclotron heating and as a function of the applied torque plasmas for plasma configurations in the favourable ion grad-B drift direction. The H-mode threshold power has been determined to increase with input torque for all the main ion species (hydrogen, deuterium and helium). The H-mode threshold power for similar plasma parameters and configurations is the least for deuterium, followed by helium and hydrogen in that order. The plasma geometry also affects the power threshold, which is dependent on the X-point height.

Gohil, P. [General Atomics; Jernigan, T. C. [Oak Ridge National Laboratory (ORNL); Osborne, T.H. [General Atomics, San Diego; Scoville, J. T. [General Atomics, San Diego; Strait, E. J. [General Atomics

2010-01-01

94

Nano-scaled TiO(OD)2: a time resolved 1H/2D isotope exchange study observed in situ with neutron scattering at 20 °C and 40 °C.  

PubMed

In situ neutron diffraction measurements of the nanocrystalline deuterated oxyhydroxide TiO(OD)(2) compound were performed as a function of time and temperature under NH(3) gas flow in order to study the hydrogen-deuterium exchange mechanism. Data were collected on the instrument D20 at the ILL (France) and the analysis of the kinetics was directly based on the contrast variation of the incoherent neutron cross section of hydrogen and deuterium. The time evolution of the hydrogenated phase fraction was described using the well-known Kolmogorov-Johnson-Mehl-Avrami (KJMA) expression. The H/D exchange reaction is complete within 140 s at 20 °C and within 120 s at 40 °C. The activation energy for the H/D exchange reaction is estimated to be 37 kJ mol(-1). PMID:23328794

Legrand, Vincent; Merdrignac-Conanec, Odile; Paulus, Werner

2013-01-17

95

Performance of a hydrogen/deuterium polarized gas target in a storage ring  

NASA Astrophysics Data System (ADS)

The performance of a high-density polarized hydrogen/deuterium gas target internal to a medium-energy electron storage ring is presented. Compared to our previous electron scattering experiments with tensor-polarized deuterium at NIKHEF (Zhou et al., Nucl. Instr. and Meth. A 378 /(1996) 40; Ferro-Luzzi et al., Phys. Rev. Lett. 77 /(1996) 2630; Van den Brand et al., Phys. Rev. Lett. 78 /(1997) 1235; Bouwhuis et al., Phys. Rev. Lett. 82 /(1999) 687; Zhou et al., Phys. Rev. Lett. 82 /(1999) 687) the target figure of merit, (polarization)2×luminosity, was improved by more than an order of magnitude. The target density was increased by upgrading the flux of nuclear-polarized atoms injected into the storage cell and by using a longer (60cm) and colder (~70K) storage cell. A maximal target thickness of 1.2(1.1)+/-0.1×1014nuclei/cm2 was achieved with deuterium (hydrogen). With typical beam currents of 110mA, this corresponds to a luminosity of about 8.4(7.8)+/-0.8×1031e-nucleicm- 2s-1. By reducing the molecular background and using a stronger target guide field, a higher polarization was achieved. The target was used in combination with a 720MeV polarized electron beam stored in the AmPS ring (NIKHEF) to measure spin observables in electron-proton and electron-deuteron scattering. Scattered electrons were detected in a large acceptance magnetic spectrometer. Ejected hadrons were detected in a single time-of-flight scintillator array. The product of beam and target vector polarization, PePt, was determined from the known spin-correlation parameters of /e'p quasi-elastic (or elastic) scattering. With the deuterium (hydrogen) target, values up to PePt=0.49+/-0.03 /(0.32+/-0.03) were obtained with an electron beam polarization of Pe=0.62+/-0.04 /(0.56+/-0.03) as measured with a Compton backscattering polarimeter (Passchier et al., Nucl. Instr. and Meth. A 414 /(1998) 4988). From this, we deduce a cell-averaged target polarization of Pt=0.78+/-0.07 (/0.58+/-0.07), including the dilution by unpolarized molecules.

van Buuren, L. D.; Szczerba, D.; van den Brand, J. F. J.; Bulten, H. J.; Ferro-Luzzi, M.; Klous, S.; Kolster, H.; Lang, J.; Mul, F. A.; Poolman, H. R.; Simani, M. C.

2001-12-01

96

Investigation of the role of the micro-porous layer in polymer electrolyte fuel cells with hydrogen deuterium contrast neutron radiography.  

PubMed

In this study, the high resolution hydrogen-deuterium contrast radiography method was applied to elucidate the impact of the micro-porous layer (MPL) on water distribution in the porous fuel cell media. At the steady state, deuterium replaced hydrogen in the anode stream, and the large difference in neutron attenuation of the D(2)O produced at the cathode was used to track the produced water. It was found that the water content peaked in the cathode-side diffusion media (DM) for the cell without MPL, but with an MPL on the anode and cathode DM, the peak water amount was pushed toward the anode, resulting in a relatively flattened water profile through components and demonstrating a liquid barrier effect. Additionally, the dynamic water behavior in diffusion media was analyzed to understand the effect of a MPL and operating conditions. The water content in the DM changed with applied current, although there is a significant amount of residual liquid content that does not appear to be part of capillary channels. The effect of the MPL on irreducible saturation in DM and cell performance was also investigated. PMID:22337210

Cho, Kyu Taek; Mench, Matthew M

2012-02-15

97

Staphylococcal Nuclease Folding Intermediate Characterized by Hydrogen Exchange and NMR Spectroscopy  

Microsoft Academic Search

Pulsed hydrogen-deuterium exchange during refolding was used to probe the protection of backbone amide hydrogens from solvent exchange of the staphylococcal nuclease Pro117 --> Gly variant. The extent of exchange for 39 residues was determined by two-dimensional proton NMR after refolding for 5 ms to 10 s. Three kinetic phases are inferred. Modest protection of amides in the early refolding

Mard D. Jacobs; Robert O. Fox

1994-01-01

98

Application of h/d exchange to hydrogen bonding in small molecules.  

PubMed

Do you recognize me? A series of simple amides has been used to demonstrate the application of hydrogen/deuterium exchange in small-molecule hydrogen bonding. By comparison with similar controls, the degree of protection from H/D exchange can provide insight into the degree of hydrogen bonding. PMID:24123654

Schneider, Tanya L; Halloran, Kevin T; Hillner, Julie A; Conry, Rebecca R; Linton, Brian R

2013-10-02

99

Effects of hydrogen/deuterium absorption on the magnetic properties of Co/Pd multilayers  

NASA Astrophysics Data System (ADS)

The effects of hydrogen and deuterium absorption were studied in two Co/Pd multilayers with perpendicular magnetic anisotropy using Polarized Neutron Reflectivity (PNR). PNR measurements were performed with the field in the plane of the sample with the magnetization M saturated at H = 6.0 T and unsaturated at 0.65 T. The nominal thicknesses of the Co/Pd layers were 2.5 å/21 å. Therefore, the actual layer chemical composition, thickness, and interface width parameters were defined from the nuclear scattering length density (SLD) profile obtained from both x-ray reflectivity (XRR) and PNR and their derivatives. The nuclear PNR SLD profile showed that although deuterium absorption occurred throughout the sample, the multilayer stack did not expand. The magnetic SLD showed that M in both the Pd and Co layers was affected. At saturation, M decreased, while at H = 0.65 T M increased upon deuterium exposure. Magnetization measurements confirmed hydrogen absorption decreased the total M at saturation and increased the component of M parallel to the field when not at saturation. These results indicate that hydrogen or deuterium absorption decreases both the perpendicular anisotropy and total magnetization of the samples.

Munbodh, Kineshma; Perez, Felio; Keenan, Cameron; Lederman, David; Zhernenkov, Mikhail; Fitzsimmons, Michael

2011-03-01

100

HK97 Maturation Studied by Crystallography and H/[superscript 2]H Exchange Reveals the Structural Basis for Exothermic Particle Transitions  

SciTech Connect

HK97 is an exceptionally amenable system for characterizing major conformational changes associated with capsid maturation in double-stranded DNA bacteriophage. HK97 undergoes a capsid expansion of {approx}20%, accompanied by major subunit rearrangements during genome packaging. A previous 3.44-{angstrom}-resolution crystal structure of the mature capsid Head II and cryo-electron microscopy studies of other intermediate expansion forms of HK97 suggested that, primarily, rigid-body movements facilitated the maturation process. We recently reported a 3.65-{angstrom}-resolution structure of the preexpanded particle form Prohead II (P-II) and found that the capsid subunits undergo significant refolding and twisting of the tertiary structure to accommodate expansion. The P-II study focused on major twisting motions in the P-domain and on refolding of the spine helix during the transition. Here we extend the crystallographic comparison between P-II and Head II, characterizing the refolding events occurring in each of the four major domains of the capsid subunit and their effect on quaternary structure stabilization. In addition, hydrogen/deuterium exchange, coupled to mass spectrometry, was used to characterize the structural dynamics of three distinct capsid intermediates: P-II, Expansion Intermediate, and the nearly mature Head I. Differences in the solvent accessibilities of the seven quasi-equivalent capsid subunits, attributed to differences in secondary and quaternary structures, were observed in P-II. Nearly all differences in solvent accessibility among subunits disappear after the first transition to Expansion Intermediate. We show that most of the refolding is coupled to this transformation, an event associated with the transition from asymmetric to symmetric hexamers.

Gertsman, Ilya; Komives, Elizabeth A.; Johnson, John E. (Scripps); (UCSD)

2010-03-22

101

Identification of a drug degradation product found in a stressed dosage form using LC/MSn, LC/TOF MS and on-line H/D exchange MS.  

PubMed

An unknown degradation product was found when a dosage form was stressed under base and heat. Comprehensive LC-MS studies have been conducted to identify this degradation product. The approach included the use of an ion-trap MS for MS(n) ion fragmentation patterns, a time-of-flight (TOF) MS to measure the accurate mass for its potential chemical formula, and on-line hydrogen/deuterium (H/D) exchange LC-MS to determine the number of exchangeable hydrogen atoms in the gradation product. Based upon the above LC-MS results, the unknown was identified to result from the conversion of a trifluoromethyl moiety in the drug substance to a carboxylic acid under the combination of thermal and base stress. Different ion fragmentation pathways between the drug substance and its degradation product were discussed. The reaction mechanism was proposed to be nucleophilic substitution through S(N)2 mechanism. PMID:21906899

Pan, Changkang; Jiang, Yanjing; Wen, Hong; Motto, Michael

2011-08-22

102

Exchange of deeply trapped and interstitial hydrogen in silicon  

SciTech Connect

Using {ital ab initio} density-functional calculations, we examine possible exchange mechanisms between an interstitial hydrogen atom and a deeply bound H at a silicon-hydrogen bond. We determine a low-energy pathway for exchange, which involves an intermediate, metastable {equivalent_to}SiH{sub 2} complex with both hydrogen atoms strongly bound to the silicon atom. The energy barrier for the exchange process is E{sub ex}{lt}0.2 eV, consistent with observations of hydrogen-deuterium exchange in a-Si:H(D) films. {copyright} {ital 1999} {ital The American Physical Society}

Tuttle, B. [Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States); Van de Walle, C.G. [Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, California 94304 (United States); Adams, J.B. [Department of Chemical, Bio and Materials Engineering, Arizona State University, Tempe, Arizona 85287-6006 (United States)

1999-02-01

103

Hydrogen-deuterium isotope shift: From the 1S-2S-transition frequency to the proton-deuteron charge-radius difference  

SciTech Connect

We analyze and review the theory of the hydrogen-deuterium isotope shift for the 1S-2S transition, which is one of the most accurately measured isotope shifts in any atomic system, in view of a recently improved experiment. A tabulation of all physical effects that contribute to the isotope shift is given. These include the Dirac binding energy, quantum electrodynamic effects, including recoil corrections, and the nuclear-size effect, including the pertaining relativistic and radiative corrections. From a comparison of the theoretical result {Delta}f{sub th}=670 999 566.90(66)(60) kHz (exclusive of the nonrelativistic nuclear-finite-size correction) and the experimental result {Delta}f{sub expt}=670 994 334 605(15) Hz, we infer the deuteron-proton charge-radius difference {sub d}-{sub p}=3.820 07(65) fm{sup 2} and the deuteron structure radius r{sub str}=1.975 07(78) fm.

Jentschura, U.D. [Department of Physics, Missouri University of Science and Technology, Rolla, Missouri 65409-0640 (United States); Matveev, A.; Parthey, C.G.; Alnis, J.; Pohl, R.; Udem, Th.; Kolachevsky, N.; Haensch, T.W. [Max-Planck-Institut fuer Quantenoptik, DE-85748 Garching (Germany)

2011-04-15

104

Fragmentation of doubly-protonated peptide ion populations labeled by H\\/D exchange with CD3OD  

Microsoft Academic Search

Doubly-protonated bradykinin (RPPGFSPFR) and an angiotensin III analogue (RVYIFPF) were subjected to hydrogen\\/deuterium (H\\/D) exchange with CD3OD in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. A bimodal distribution of deuterium incorporation was present for bradykinin after H\\/D exchange for 90 s at a CD3OD pressure of 4 × 10-7 Torr, indicating the existence of at least two distinct

Kristin A. Herrmann; Krishna Kuppannan; Vicki H. Wysocki

2006-01-01

105

Exchange Studies as Actor-Networks: Following Korean Exchange Students in Swedish Higher Education  

ERIC Educational Resources Information Center

|This article explores how Korean exchange students organized their studies during exchange programs in Swedish higher education. For most students, the programs became a disordered period in relation to their education. The value of exchange studies seems mainly to be extra-curricular. Drawing upon actor network theory, the article argues that…

Ahn, Song-ee

2011-01-01

106

PAS Domain Allostery and Light-induced Conformational Changes in Photoactive Yellow Protein upon I 2 Intermediate Formation, Probed with Enhanced Hydrogen\\/Deuterium Exchange Mass Spectrometry  

Microsoft Academic Search

Photoactive yellow protein (PYP) is a small bacterial photoreceptor that undergoes a light-activated reaction cycle. PYP is also the prototypical Per-Arnt-Sim (PAS) domain. PAS domains, found in diverse multi-domain proteins from bacteria to humans, mediate protein–protein interactions and function as sensors and signal transducers. Here, we investigate conformational and dynamic changes in solution in wild-type PYP upon formation of the

Ronald Brudler; Chris R. Gessner; Sheng Li; Sammy Tyndall; Elizabeth D. Getzoff; Virgil L. Woods Jr

2006-01-01

107

The prohormone proenkephalin possesses differential conformational features of subdomains revealed by rapid H-D exchange mass spectrometry  

PubMed Central

Active enkephalin and related peptide hormones or neurotransmitters are generated by proteolytic processing of inactive prohormone precursors. Little is known about the relative accessibilities of prohormone cleavage sites and conformations of subdomains that undergo proteolytic processing. Therefore, this study investigated the conformational features of the prohormone proenkephalin (PE) by rapid hydrogen-deuterium exchange mass spectrometry (DXMS). DXMS analyzes rates of hydrogen exchange of the polypeptide backbone of PE with deuterium from D2O (heavy water) by mass spectrometry, accomplished at sub-second and multisecond time periods. Results showed differential accessibilities of cleavage sites and adjacent subdomains of PE to the aqueous environment. Importantly, protease cleavage sites of PE with greater relative accessibilities correspond to sites most readily cleaved by processing proteases to generate active peptide neurotransmitters. For comparison, peptides derived from PE (by pepsin digestion) displayed greater accessibility to the solvent environment, illustrated by their higher rates of H-D exchange compared to that of intact PE protein. The more limited H-D exchange accessibilities of PE protein, compared to peptides derived from PE, indicate that PE possesses tertiary conformation. These results demonstrate that differential tertiary conformations of PE subdomains undergo ordered proteolytic processing to generate active enkephalin peptides for cell-cell communication in the nervous and endocrine systems.

Lu, Weiya D; Liu, Tong; Li, Sheng; Woods, Virgil L; Hook, Vivian

2012-01-01

108

Multidimensional separations of ubiquitin conformers in the gas phase: Relating ion cross sections to H\\/D exchange measurements  

Microsoft Academic Search

Investigating gas-phase structures of protein ions can lead to an improved understanding of intramolecular forces that play\\u000a an important role in protein folding. Both hydrogen\\/deuterium (H\\/D) exchange and ion mobility spectrometry provide insight\\u000a into the structures and stabilities of different gas-phase conformers, but how best to relate the results from these two methods\\u000a has been hotly debated. Here, high-field asymmetric

Errol W. Robinson; Evan R. Williams

2005-01-01

109

Chiral sum frequency generation for in situ probing proton exchange in antiparallel ?-sheets at interfaces.  

PubMed

Studying hydrogen/deuterium (H/D) exchange in proteins can provide valuable insight on protein structure and dynamics. Several techniques are available for probing H/D exchange in the bulk solution, including NMR, mass spectroscopy, and Fourier transform infrared spectroscopy. However, probing H/D exchange at interfaces is challenging because it requires surface-selective methods. Here, we introduce the combination of in situ chiral sum frequency generation (cSFG) spectroscopy and ab initio simulations of cSFG spectra as a powerful methodology to probe the dynamics of H/D exchange at interfaces. This method is applied to characterize H/D exchange in the antiparallel ?-sheet peptide LK7?. We report here for the first time that the rate of D-to-H exchange is about 1 order of magnitude faster than H-to-D exchange in the antiparallel structure at the air/water interface, which is consistent with the existing knowledge that O-H/D dissociation in water is the rate-limiting step, and breaking the O-D bond is slower than breaking the O-H bond. The reported analysis also provides fundamental understanding of several vibrational modes and their couplings in peptide backbones that have been difficult to characterize by conventional methods, including Fermi resonances of various combinations of peptide vibrational modes such as amide I and amide II, C-N stretch, and N-H/N-D bending. These results demonstrate cSFG as a sensitive technique for probing the kinetics of H/D exchange in proteins at interfaces, with high signal-to-noise N-H/N-D stretch bands that are free of background from the water O-H/O-D stretch. PMID:23394622

Fu, Li; Xiao, Dequan; Wang, Zhuguang; Batista, Victor S; Yan, Elsa C Y

2013-02-19

110

Preliminary design study of heat pipe heat exchangers  

Microsoft Academic Search

A preliminary design study was conducted in order to identify the important design parameters which can be varied to optimize overall performance of heat pipe heat exchangers. A computer program was developed to analyze the heat exchanger performance using conventional design procedures for finned tube heat exchangers and using conventional design procedures for three-puddle-artery heat pipes.

K. T. Feldman; D. C. Lu

1976-01-01

111

Study on dynamic characteristics of heat exchanger  

NASA Astrophysics Data System (ADS)

Temperature regulation in aircraft air conditioning systems is considered. The structural form of a dynamic mathematical model for a heat exchanger with the form of lumped parameter model is theoretically deduced. An experimental way to obtain the model parameters is proposed and the appropriate calculation formulas are deduced. A method for calculating the dynamic characteristics of a heat exchanger is pointed out. An example is given.

Ying, Wenjiang

1993-04-01

112

Gas phase RNA and DNA ions 2. Conformational dependence of the gas-phase H\\/D exchange of nucleotide-5?-monophosphates  

Microsoft Academic Search

The conformational dependence of the gas-phase hydrogen\\/deuterium (H\\/D) exchange of nucleotide-5-monophosphate anions with\\u000a the H\\/D exchange reagent D2S is reported here. The electrospray-generated [M ? H]? anions of adenosine-5?-monophosphate, adenosine-5?-carboxylic acid, ribitol-5-phosphate, and 2-deoxy-ribitol-5-phosphate\\u000a were reacted with D2S in the gas phase. Their reactivity (adenosine-5?-monophosphate exchanged 2 of 5 labile hydrogens, adenosine-5?-carboxylic\\u000a acid exchanged 1 of 4, ribitol-5-phosphate exchanged 2

Michael A. Freitas; Alan G. Marshall

2001-01-01

113

Ceramic heat-exchanger applications study  

NASA Astrophysics Data System (ADS)

To put the potential benefits of ceramic heat exchangers (CHX) applications into quantitative perspective, several industrial cogeneration and electric utility power generation systems were evaluated. Coal based fuel fired applications, for which system performance and economic assessments were made were studied. Seven CHX applications were selected for evaluation. These include: (1) gasified coal fired gas turbine; (2) pressurized fluidized bed combustor (PFBC) gas turbine; (3) atmospheric fluidized bed combustor (AFBC) gas turbine; (4) and (5) AFBC combined cycle with and without reheat; and (6) and (7) indirect coal fired gas turbine and combined cycle. The performance and economics of these cogeneration systems were evaluated and compared with other competing systems. For the electric utility power generation sector five applications utilizing a CHX were selected and evaluated; their performance and cost factors were compared to those of a reference pulverized coal fired steam plant with flue gas desulfurization. The five applications included: PFBC combined cycle, AFBC combined cycle, industrial coal gasifier combined cycle, indirect coal fired combined cycle, and indirect coal fired simple cycle. Of the five CHX applications evaluated in the power generation sector, only the AFBC system shows a clear gain over the reference pulverized coal system.

McFarlin, D. J.; Sgamboti, C. T.; Lessard, R. D.

1982-10-01

114

Ceramic heat-exchanger applications study  

SciTech Connect

To put the potential benefits of ceramic heat exchangers (CHX) applications into quantitative perspective, several industrial cogeneration and electric utiity power generation systems were surveyed and evaluated. This study was focused on coal-based fuel fired applications, for which system performance and economic assessments were made. Seven CHX applications in the industrial cogeneration sector were selected for evaluation. These include (1) Gasified Coal-Fired Gas Turbine, (2) Pressurized Fluidized Bed Combustor (PFBC)-Gas Turbine, (3) Atmospheric Fluidized Bed Combustor (AFBC)-Gas Turbine, (4 and 5) AFBC Combined Cycle with and without reheat and (6 and 7) Indirect Coal-Fired Gas Turbine and Combined Cycle. The performance and economics of these cogeneration systems were evaluated and compared with other competing systems (both advanced and State-of-the-Art). For the electric utility power generation sector five applications utilizing a CHX were selected and evaluated; their performance and cost factors were compared to those of a reference pulverized coal-fired steam plant with flue gas desulfurization. These five applications included (1) PFBC-Combined Cycle, (2) AFBC-Combined Cycle, (3) Industrial Coal Gasifier-Combined Cycle, (4) Indirect Coal-Fired Combined Cycle, and (5) Indirect Coal-Fired Simple Cycle. Of the five CHX applications evaluated in the power generation sector, only the AFBC system showed a clear gain over the reference pulverized coal system.

McFarlin, D.J.; Sgamboti, C.T.; Lessard, R.D.

1982-10-01

115

Strategies for characterization of drug metabolites using liquid chromatography–tandem mass spectrometry in conjunction with chemical derivatization and on-line H\\/D exchange approaches  

Microsoft Academic Search

Strategies using high performance liquid chromatography–tandem mass spectrometry (LC–MS\\/MS) in conjunction with techniques such as chemical derivatization and on-line hydrogen\\/deuterium (H\\/D) exchange for structural elucidation of drug metabolites in crude samples are reviewed. Useful mass spectrometric scan techniques discussed include product ion scan, constant neutral-loss scan, precursor ion scan, multistage MSn, and accurate mass measurements. In biological systems, xenobiotics are

David Q. Liu; Cornelis E. C. A. Hop

2005-01-01

116

Strong Anion Exchange for Studying Protein-DNA Interactions by H/D Exchange Mass Spectrometry  

PubMed Central

The use of mass spectrometry to study protein-ligand interactions is expanding into more complex systems including protein-DNA interactions. The excess amount of a model DNA, or more typically an oligodeoxynucleotide (ODN), needed to study such interactions in an amide H/D exchange experiment, for example, causes serious signal suppression in the protein analysis. We describe here a modification of the traditional H/D exchange protocol whereby we utilize a strong anion exchange column to remove rapidly the ODN from solution before MS analysis. We showed the successful incorporation of such a column in a study of two protein-ODN systems: (1) the DNA-binding domain of human telomeric repeat binding factor 2 with a telomeric oligodeoxynucleotide and (2) thrombin with the thrombin-binding aptamer. The approach gave no appreciable difference in back-exchange compared to a method in which no SAX is used.

Sperry, Justin B.; Wilcox, J. Micah; Gross, Michael L.

2008-01-01

117

International Exchange as a Transformative Learning Experience: A Case Study  

ERIC Educational Resources Information Center

This study examines the role of international exchange programs on the transformative learning of English-speaking students. A student exchange program at a South Korean university is used for this case study. It explores how learning experiences are translated by participants onto their perceptions about the host country. An analysis of a pre-…

Choi, Sheena; Slaubaugh, Michael; Kim, Ae-Sook

2012-01-01

118

A Longitudinal Study of Premarital Couples: A Social Exchange Perspective.  

ERIC Educational Resources Information Center

|The attributes of couples planning to marry can affect their future relationship satisfaction. To study this phenomenon, a social exchange model was applied to a sample of couples planning to marry to assess the predictive validity of a measure of positive exchange. The longitudinal design of the two-and-a-half year investigation provided direct…

Markman, Howard J.

119

Protein-peptide affinity determination using an h/d exchange dilution strategy: application to antigen-antibody interactions.  

PubMed

A new methodology using hydrogen/deuterium amide exchange (HDX) to determine the binding affinity of protein-peptide interactions is reported. The method, based on our previously established approach, protein ligand interaction by mass spectrometry, titration, and H/D exchange (PLIMSTEX) [J. Am. Chem. Soc.2003, 125, 5252-5253], makes use of a dilution strategy (dPLIMSTEX) for HDX, using the mass of the peptide ligand as readout. We employed dPLIMSTEX to study the interaction of calcium-saturated calmodulin with the opioid peptide ?-endorphin as a model system; the affinity results are in good agreement with those from traditional PLIMSTEX and with literature values obtained by using other methods. We show that the dPLIMSTEX method is feasible to quantify an antigen-antibody interaction involving a 3-nitrotyrosine modified peptide in complex with a monoclonal anti-nitrotyrosine antibody. A dissociation constant in the low nanomolar range was determined, and a binding stoichiometry of antibody/peptide of 1:2 was confirmed. In addition, we determined that the epitope in the binding interface contains a minimum of five amino acids. The dPLIMSTEX approach is a sensitive and powerful tool for the quantitative determination of peptide affinities with antibodies, complementary to conventional immuno-analytical techniques. PMID:20444623

Tu, Tingting; Dr?gu?anu, Mihaela; Petre, Brîndu?a-Alina; Rempel, Don L; Przybylski, Michael; Gross, Michael L

2010-03-28

120

Protein-peptide affinity determination using an H/D exchange dilution strategy: Application to antigen-antibody interactions  

PubMed Central

A new methodology using hydrogen/deuterium amide exchange (HDX) to determine the binding affinity of protein-peptide interactions is reported. The method, based on our previously established approach, PLIMSTEX (Protein Ligand Interaction by Mass Spectrometry, Titration and H/D Exchange) [J. Am. Chem. Soc. 2003, 125, 5252–5253], makes use of a dilution strategy (dPLIMSTEX) for HDX, using the mass of the peptide ligand as readout. We employed dPLIMSTEX to study the interaction of calcium-saturated calmodulin with the opioid peptide ?-endorphin as a model system; the affinity results are in good agreement with those from traditional PLIMSTEX and with literature values obtained by using other methods. We show that the dPLIMSTEX method is feasible to quantify an antigen-antibody interaction involving a 3-nitrotyrosine modified peptide in complex with a monoclonal anti-nitrotyrosine antibody. A dissociation constant in the low nanomolar range, was determined, and a binding stoichiometry of antibody/peptide of 1:2 was confirmed. In addition, we determined that the epitope in the binding interface contains a minimum of five amino acids. The dPLIMSTEX approach is a sensitive and powerful tool for the quantitative determination of peptide affinities with antibodies, complementary to conventional immuno-analytical techniques.

Tu, Tingting; Dragusanu, Mihaela; Petre, Brindusa-Alina; Rempel, Don L.; Przybylski, Michael; Gross, Michael L.

2010-01-01

121

Studies of spin-exchange optical pumping  

NASA Astrophysics Data System (ADS)

Although we still do not understand fully the alkali-alkali relaxation at pressures of an atmosphere or more, an important part of the spin-relaxation comes from the classical dipole-dipole anisotropic spin-axis interaction acting in triplet dimer molecules. The key observation is the existence of magnetic resonances in the magnetic decoupling curves which are predicted from the spin-axis interaction. We identified a new gas-phase, room temperature spin relaxation that is due to the spin-rotation coupling in bound 129Xe-Xe van der Waals molecules. This 129Xe-Xe molecular spin-relaxation is more than an order of magnitude stronger than the well-known 129 Xe-Xe binary spin-relaxation and is the fundamental spin-relaxation process at gas densities below 14 amagat. With external cavity diode laser array bar, we find, based on tests of several cells, that the power required to reach the same polarization is typically three times lower for the spectrally narrowed laser as compared to the unnarrowed diode array bar. This last result indicates that spectrally narrowed lasers are critical to obtaining the highest noble gas polarizations. Furthermore, we find, circularly polarized light propagating at an angle as small as a few degrees to the external magnetic field does not optically pump the atoms to full transparency and causes excess absorption of the pump beam. We measured the Rb-3He spin-exchange rate coefficients using three different methods. We obtained 6.73 +/- 0.12 x 10 -20 cm3/s for the repolarization method. We deduced the spin-exchange rate coefficient to be 6.61 +/- 0.12 x 10 -20 cm3/s for the rate balance method. The third method uses a temperature dependence relaxation of 3He and the deduced value is 8.85 +/- 0.32 x 10-20 cm3/s. This is about 30% higher than the other two methods. This implies a temperature-dependence wall-relaxation or a large value of anisotropic spin-exchange rate coefficient for Rb-3He and would explain the shortfall 3He measured polarization.

Chann, Bien

122

Studies of inertial deposition of particles onto heat exchanger elements  

SciTech Connect

This thesis examines gas-side fouling mechanisms in heat exchangers that involve the inertial impaction of small particles onto tubular exchanger surfaces. An aerosol processes wind tunnel was constructed that facilitates quantitative studies of particle interactions with heat-exchanger surfaces. Three sets of experiments were performed. First, single heat-exchanger tubes were exposed to a cross flow of particle-laden air. Stainless steel tubes coated with a thin layer of grease to ensure that particle collisions resulted in capture were used to verify a numerical model for the inertial transport of ammonium fluorescein particles to the tube surface. Particle bound was quantified for the case of clean tubes and solid particles. Second, the transient deposition of particles onto single heat-exchanger tubes in cross flow was studied. It was found that a steady-state condition could be reached for cases in which particle bounce occurred. Finally, the deposition patterns for the aerosol particles as they passed through a tube bank were studied. The quantities of aerosol deposited on various tubes depended on tube surface condition, tube position within the tube bank, and the overall geometry of the bank. Using these findings, heat exchangers can be designed that will resist gas-side fouling.

Fuhs, S.E.

1988-01-01

123

Detection of oligonucleotide gas-phase conformers: H\\/D exchange and ion mobility as complementary techniques  

Microsoft Academic Search

Gas-phase hydrogen\\/deuterium exchange of small oligonucleotides (dTG, dC6 and C6) with CD3OD was performed in the second hexapole of a Fourier transform ion-cyclotron resonance (FTICR) mass spectrometer. Ion activation\\u000a experiments were conducted by accelerating the ions at the entrance of the H\\/D exchange cell under conditions promoting exclusively\\u000a collisional isomerization. These experiments allowed us to assess the presence of several

Dorothée Balbeur; Joëlle Widart; Bernard Leyh; Laetitia Cravello; Edwin De Pauw

2008-01-01

124

HDX Workbench: Software for the Analysis of H/D Exchange MS Data  

PubMed Central

Hydrogen/deuterium exchange mass spectrometry (HDX-MS) is an established method for the interrogation of protein conformation and dynamics. While the data analysis challenge of HDX-MS has been addressed by a number of software packages, new computational tools are needed to keep pace with the improved methods and throughput of this technique. To address these needs, we report an integrated desktop program titled HDX Workbench, which facilitates automation, management, visualization, and statistical cross-comparison of large HDX data sets. Using the software, validated data analysis can be achieved at the rate of generation. The application is available at the project home page http://hdx.florida.scripps.edu.

Pascal, Bruce D.; Willis, Scooter; Lauer, Janelle L.; Landgraf, Rachelle R.; West, Graham M.; Marciano, David; Novick, Scott; Goswami, Devrishi; Chalmers, Michael J.; Griffin, Patrick R.

2013-01-01

125

HDX Workbench: Software for the Analysis of H/D Exchange MS Data  

NASA Astrophysics Data System (ADS)

Hydrogen/deuterium exchange mass spectrometry (HDX-MS) is an established method for the interrogation of protein conformation and dynamics. While the data analysis challenge of HDX-MS has been addressed by a number of software packages, new computational tools are needed to keep pace with the improved methods and throughput of this technique. To address these needs, we report an integrated desktop program titled HDX Workbench, which facilitates automation, management, visualization, and statistical cross-comparison of large HDX data sets. Using the software, validated data analysis can be achieved at the rate of generation. The application is available at the project home page http://hdx.florida.scripps.edu.

Pascal, Bruce D.; Willis, Scooter; Lauer, Janelle L.; Landgraf, Rachelle R.; West, Graham M.; Marciano, David; Novick, Scott; Goswami, Devrishi; Chalmers, Michael J.; Griffin, Patrick R.

2012-09-01

126

Event Study of Russian Foreign Exchange Market.  

National Technical Information Service (NTIS)

This paper will seek to identify events in Russian and world economic and political news that significantly affected the value of the Russian ruble. Most conventional events studies name the events in question first, and then test for significance. This p...

M. P. Barry

2000-01-01

127

W-F substitutions in apomyoglobin increase the local flexibility of the N-terminal region causing amyloid aggregation: a H/D exchange study.  

PubMed

Myoglobin is an ?-helical globular protein containing two highly conserved tryptophanyl residues at positions 7 and 14 in the N-terminal region. The simultaneous substitution of the two residues impairs the productive folding of the protein making the polypeptide chain highly prone to aggregate forming amyloid fibrils at physiological pH and room temperature. The role played by tryptophanyl residues in driving the productive folding process was investigated by providing structural details at low resolution of compact intermediate of three mutated apomyoglobins, i.e., W7F, W14F and the amyloid forming mutant W7FW14F. In particular, we followed the hydrogen/deuterium exchange rate of protein segments using proteolysis with pepsin followed by mass spectrometry analysis. The results revealed significant differences in the N-terminal region, consisting in an alteration of the physico-chemical properties of the 7-11 segment for W7F and in an increase of local flexibility of the 12-29 segment for W14F. In the double trypthophanyl substituted mutant, these effects are additive and impair the formation of native-like contacts and favour inter-chain interactions leading to protein aggregation and amyloid formation at physiological pH. PMID:23343142

Infusini, Giuseppe; Iannuzzi, Clara; Vilasi, Silvia; Maritato, Rosa; Birolo, Leila; Pagnozzi, Daniela; Pucci, Piero; Irace, Gaetano; Sirangelo, Ivana

2013-08-01

128

Experimental study of copper-alkali ion exchange in glass  

NASA Astrophysics Data System (ADS)

Copper-alkali ion exchange was performed by immersing different silicate glasses (soda-lime and BK7) in different molten eutectic salt baths (CuSO4:Na2SO4 and CuSO4:K2SO4). The obtained optical waveguides were characterized by m-lines spectroscopy for the determination of refractive index profiles, and by secondary ion mass spectrometry for the concentration profiles of the ion species involved in the exchange process. The different oxidation states of copper inside the glass structure were studied by electron paramagnetic resonance and x-ray absorption techniques. Interdiffusion copper coefficients were also determined. The Cu-alkali exchange was observed to give rise to local structural rearrangement of the atoms in the glass matrix. The Cu+ ion was found to mainly govern the exchange process, while competition between Cu-Na and K-Na exchanges occurred when a potassium sulfate bath was used. In this case, significant waveguide modal birefringence was observed.

Gonella, F.; Caccavale, F.; Bogomolova, L. D.; D'Acapito, F.; Quaranta, A.

1998-02-01

129

TRACER STUDY OF VERTICAL EXCHANGE BY CUMULUS CLOUDS  

EPA Science Inventory

The exchange of material by convective cloud processes between the mixed layer and the overlying free troposphere is examined. The paper describes results of a field experiment that was conducted in Lexington, Kentucky during the period from July 20 to August 24, 1983 to study th...

130

Conformational characterization of the charge variants of a human IgG1 monoclonal antibody using H/D exchange mass spectrometry.  

PubMed

MAb1, a human IgG1 monoclonal antibody produced in a NS0 cell line, exhibits charge heterogeneity because of the presence of variants formed by processes such as N-terminal glutamate cyclization, C-terminal lysine truncation, deamidation, aspartate isomerization and sialylation in the carbohydrate moiety. Four major charge variants of MAb1 were isolated and the conformations of these charge variants were studied using hydrogen/deuterium exchange mass spectrometry, including the H/D exchange time course (HX-MS) and the stability of unpurified proteins from rates of H/D exchange (SUPREX) techniques. HX-MS was used to evaluate the conformation and solution dynamics of MAb1 charge variants by measuring their deuterium buildup over time at the peptide level. The SUPREX technique evaluated the unfolding profile and relative stability of the charge variants by measuring the exchange properties of globally protected amide protons in the presence of a chemical denaturant. The H/D exchange profiles from both techniques were compared among the four charge variants of MAb1. The two techniques together offered extensive understanding about the local and subglobal/global unfolding of the charge variants of MAb1. Our results demonstrated that all four charge variants of MAb1 were not significantly different in conformation, solution dynamics and chemical denaturant-induced unfolding profile and stability, which aids in understanding the biofunctions of the molecules. The analytical strategy used for conformational characterization may also be applicable to comparability studies done for antibody therapeutics. PMID:23222183

Tang, Liangjie; Sundaram, Shanmuuga; Zhang, Jingming; Carlson, Ping; Matathia, Alice; Parekh, Babita; Zhou, Qinwei; Hsieh, Ming-Ching

2012-12-06

131

An inelastic neutron scattering study of the dynamics of hydrogenated and deuterated amorphous silicon  

NASA Astrophysics Data System (ADS)

A short summary is presented of inelastic neutron scattering studies of hydrogenated and deuterated amorphous silicon with particular emphasis on the structural role played by the hydrogen (deuterium) atoms. It is concluded that the data are consistent with the existence of molecular H2 (D2) trapped within the cages of the amorphous covalent network. Present address: Airco Coating Technology, Concord, CA 94524, USA.

Wright, Adrian C.; Brunier, Thierry M.; Guy, Carlo A.; Sinclair, Roger N.; Hannon, Alex C.; Jansen, Frank

1993-12-01

132

Correlation between solution and gas-phase protein conformation: H/D exchange, IRMPD, and ESI FT-ICR MS  

NASA Astrophysics Data System (ADS)

Infrared multiphoton dissociation (IRMPD) of the hydrogen/deuterium (H/D) exchanged 12+ charge state of gas-phase bovine ubiquitin was performed on a Fourier transform ion cyclotron resonance mass spectrometer. The H/D exchange of the 12+ charge state revealed two distinct isotopic distributions indicating the presence of at least two distinct conformations of the 12+ charge state. Following H/D exchange, IRMPD was used to dissociate the conformations. The fragments clearly showed little or no deuterium scrambling as evidenced by a nonstatistical distribution of deuterium incorporation. Analysis of the deuterium incorporation for the five most abundant fragment ions indicated a slow exchanging region of the fast exchanging conformation that corresponds to a stable (beta) - sheet observed by NMR in alcoholic solutions. The data suggest that protection of the amide hydrogens in the (beta) -sheet may result in the observed slow exchange rate and provides further evidence for the retention of secondary structure in gas phase.

Freitas, Michael A.; Hendrickson, Christopher L.; Marshall, Alan G.

2000-03-01

133

Ion-exchange studies with some complex ions on ion-exchange resins  

SciTech Connect

The ion exchange equilibria of Cr(NH{sub 3}){sub 6}{sup 3+}, Cr(NH{sub 3}){sub 5}Cl{sup 2+}, cis-Cr(en){sub 2}Cl{sub 2}{sup +}, trans-Cr(en){sub 2}(SCN){sub 2}{sup +}, Cr(H{sub 2}O){sub 6}{sup 3+} complex ions against La{sup 3+} ions were studied. The effect of the ionic charge, radius and composition of various chromium complex ions on the selectivity were discussed. The logarithms of the selectivity constants were plotted versus mole fraction of complex ions in the resin phase. Linear variations with negative slopes were observed in experiments except for the Cr(H{sub 2}O){sub 6}{sup 3+}-La{sup 3+} system. 17 refs., 5 figs.

Besirli, N. [Karadeniz Technical Univ., Trabzon (Turkey); Baysal, B.M. [Istanbul Technical Univ., Istanbul (Turkey)

1993-07-01

134

John Locke's seed lists: a case study in botanical exchange.  

PubMed

This paper gives a detailed analysis of four seed lists in the journals of John Locke. These lists provide a window into a fascinating open network of botanical exchange in the early 1680s which included two of the leading botanists of the day, Pierre Magnol of Montpellier and Jacob Bobart the Younger of Oxford. The provenance and significance of the lists are assessed in relation to the relevant extant herbaria and plant catalogues from the period. The lists and associated correspondence provide the main evidence for Locke's own important, though modest contribution to early modern botany, a contribution which he would have regarded as a small part of the broader project of constructing a natural history of plants. They also provide a detailed case study of the sort of open and informal network of knowledge exchange in the early modern period that is widely recognised by historians of science, but all too rarely illustrated. PMID:19917484

Harris, Stephen A; Anstey, Peter R

2009-11-03

135

Combining H/D exchange mass spectroscopy and computational docking reveals extended DNA-binding surface on uracil-DNA glycosylase  

PubMed Central

X-ray crystallography provides excellent structural data on protein–DNA interfaces, but crystallographic complexes typically contain only small fragments of large DNA molecules. We present a new approach that can use longer DNA substrates and reveal new protein–DNA interactions even in extensively studied systems. Our approach combines rigid-body computational docking with hydrogen/deuterium exchange mass spectrometry (DXMS). DXMS identifies solvent-exposed protein surfaces; docking is used to create a 3-dimensional model of the protein–DNA interaction. We investigated the enzyme uracil-DNA glycosylase (UNG), which detects and cleaves uracil from DNA. UNG was incubated with a 30 bp DNA fragment containing a single uracil, giving the complex with the abasic DNA product. Compared with free UNG, the UNG–DNA complex showed increased solvent protection at the UNG active site and at two regions outside the active site: residues 210–220 and 251–264. Computational docking also identified these two DNA-binding surfaces, but neither shows DNA contact in UNG–DNA crystallographic structures. Our results can be explained by separation of the two DNA strands on one side of the active site. These non-sequence-specific DNA-binding surfaces may aid local uracil search, contribute to binding the abasic DNA product and help present the DNA product to APE-1, the next enzyme on the DNA-repair pathway.

Roberts, Victoria A.; Pique, Michael E.; Hsu, Simon; Li, Sheng; Slupphaug, Geir; Rambo, Robert P.; Jamison, Jonathan W.; Liu, Tong; Lee, Jun H.; Tainer, John A.; Ten Eyck, Lynn F.; Woods, Virgil L.

2012-01-01

136

Combining H/D exchange mass spectroscopy and computational docking reveals extended DNA-binding surface on uracil-DNA glycosylase.  

PubMed

X-ray crystallography provides excellent structural data on protein-DNA interfaces, but crystallographic complexes typically contain only small fragments of large DNA molecules. We present a new approach that can use longer DNA substrates and reveal new protein-DNA interactions even in extensively studied systems. Our approach combines rigid-body computational docking with hydrogen/deuterium exchange mass spectrometry (DXMS). DXMS identifies solvent-exposed protein surfaces; docking is used to create a 3-dimensional model of the protein-DNA interaction. We investigated the enzyme uracil-DNA glycosylase (UNG), which detects and cleaves uracil from DNA. UNG was incubated with a 30 bp DNA fragment containing a single uracil, giving the complex with the abasic DNA product. Compared with free UNG, the UNG-DNA complex showed increased solvent protection at the UNG active site and at two regions outside the active site: residues 210-220 and 251-264. Computational docking also identified these two DNA-binding surfaces, but neither shows DNA contact in UNG-DNA crystallographic structures. Our results can be explained by separation of the two DNA strands on one side of the active site. These non-sequence-specific DNA-binding surfaces may aid local uracil search, contribute to binding the abasic DNA product and help present the DNA product to APE-1, the next enzyme on the DNA-repair pathway. PMID:22492624

Roberts, Victoria A; Pique, Michael E; Hsu, Simon; Li, Sheng; Slupphaug, Geir; Rambo, Robert P; Jamison, Jonathan W; Liu, Tong; Lee, Jun H; Tainer, John A; Ten Eyck, Lynn F; Woods, Virgil L

2012-04-06

137

Nucleotide-induced conformational changes of tetradecameric GroEL mapped by H/D exchange monitored by FT-ICR mass spectrometry.  

PubMed

Here we employ hydrogen/deuterium exchange mass spectrometry (HDX-MS) to access E. coli chaperonin GroEL conformation. The ~800 kDa tetradecameric GroEL plays an essential role in the proper folding of many proteins. Previous studies of the structural dynamics of GroEL upon ATP binding have been inconsistent, showing either minimal or major allosteric changes. Our results, based on the native, non-mutated, protein under physiological conditions in solution demonstrate substantial changes in conformation and/or flexibility upon ATP binding. We capture the pivotal step in its functional cycle by use of a non-hydrolyzable ATP analog, ATP?S, to mimic the ATP-bound GroEL state. Comparison of HDX-MS results for apo GroEL and GroEL-ATP?S enables the characterization of the nucleotide-regulated conformational changes throughout the entire protein with high sequence resolution. The 14-mer GroEL complex is the largest protein assembly yet accessed by HDX-MS, with sequence resolution of segments of as few as five amino acids. PMID:23409238

Zhang, Qian; Chen, Jin; Kuwajima, Kunihiro; Zhang, Hui-Min; Xian, Feng; Young, Nicolas L; Marshall, Alan G

2013-02-13

138

Determination of vibrational energy relaxation rates of CH,D,T stretching modes on hydrogen, deuterium, and tritium-terminated H,D,T\\/C(111) and H,D,T\\/C(110) diamond surfaces using molecular dynamics simulation: Thermal effect  

Microsoft Academic Search

Molecular dynamics simulations were carried out to determine the vibrational energy relaxation rates for C-H,D,T stretches on hydrogen-, deuterium-, and tritium-terminated H,D,T\\/C(111) and H,D,T\\/C(110) diamond surfaces at high temperatures based on the Bloch-Redfield theory and the calculated power spectra of fluctuating force along C-H,D,T stretches. The lifetime of C-H stretches on H\\/(110) surfaces at room temperature was found to be

Hsiu-Feng Lu; Ming-Shun Ho; Sho-Ching Hong; Ai-Hsin Liu; Pei-Fang Wu; Ying-Chieh Sun

1998-01-01

139

Studies of ion-exchange resin complex of chloroquine phosphate.  

PubMed

High-potency adsorbates of chloroquine phosphate (CQP) were prepared by the batch method using a polyacrylic acid ion-exchange resin. Taste evaluation of the adsorbates shows significant masking of the bitterness of the drug. The complex formation was complete at pH 6.0. Stability studies at 37 degrees C, 45 degrees C, and 60 degrees C indicated that the complex was stable at all conditions for 1 month. In vitro release studies revealed complete drug elution from the complex at pH 1.2 and 2.0. PMID:10872097

Agarwal, R; Mittal, R; Singh, A

2000-07-01

140

77 FR 57055 - Regulatory New Drug Review: Solutions for Study Data Exchange Standards; Notice of Meeting...  

Federal Register 2010, 2011, 2012, 2013

...FDA-2012-N-0780] Regulatory New Drug Review: Solutions for Study Data Exchange Standards; Notice of Meeting; Request for Comments...entitled ``Regulatory New Drug Review: Solutions for Study Data Exchange Standards.'' The document was published...

2012-09-17

141

Case studies in applying recoflo ion-exchange technology  

NASA Astrophysics Data System (ADS)

Recoflo ion-exchange technology offers improvements over conventional ion-exchange equipment through the use of fine mesh resins; short-depth, fully packed ion-exchange columns; and counter-current regeneration. The system is particularly suited for hydrometallurgical applications due to its ability to process more concentrated feed solutions, the recovery of concentrated-metal product streams, and the much smaller required volume of ion-exchange resin.

Sheedy, Michael

1998-10-01

142

Fragmentation of doubly-protonated peptide ion populations labeled by H/D exchange with CD3OD  

NASA Astrophysics Data System (ADS)

Doubly-protonated bradykinin (RPPGFSPFR) and an angiotensin III analogue (RVYIFPF) were subjected to hydrogen/deuterium (H/D) exchange with CD3OD in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. A bimodal distribution of deuterium incorporation was present for bradykinin after H/D exchange for 90 s at a CD3OD pressure of 4 × 10-7 Torr, indicating the existence of at least two distinct populations. Bradykinin ion populations corresponding to 0-2 and 5-11 deuteriums (i.e., D0, D1, D2, D5, D6, D7, D8, D9, D10, and D11) were each monoisotopically selected and fragmented via sustained off-resonance irradiation (SORI) collision-induced dissociation (CID). The D0-D2 ion populations, which correspond to the slower exchanging population, consistently require lower SORI amplitude to achieve a similar precursor ion survival yield as the faster-reacting (D5-D11) populations. These results demonstrate that conformation/protonation motif has an effect on fragmentation efficiency for bradykinin. Also, the partitioning of the deuterium atoms into fragment ions suggests that the C-terminal arginine residue exchanges more rapidly than the N-terminal arginine. Total deuterium incorporation in the b1/y8 and b2/y7 ion pairs matches very closely the theoretical values for all ion populations studied, indicating that the ions of a complementary pair are likely formed during the same fragmentation event, or that no scrambling occurs upon SORI. Deuterium incorporation into the y1/a8 pseudo-ion pair does not closely match the expected theoretical values. The other peptide, doubly-protonated RVYIFPF, has a trimodal distribution of deuterium incorporation upon H/D exchange with CD3OD at a pressure of 1 × 10-7 Torr for 600 s, indicating at least three distinct ion populations. After 90 s of H/D exchange where at least two distinct populations are detected, the D0-D7 ion populations were monoisotopically selected and fragmented via SORI-CID over a range of SORI amplitudes. The precursor ion survival yield as a function of SORI amplitude falls into two distinct behaviors corresponding to slower- and faster-reacting ion populations. The slower-reacting population requires larger SORI amplitudes to achieve the same precursor ion survival yield as the faster exchanging population. Total deuterium incorporation into the y2/b5 ion pairs matches closely the theoretical values over all ion populations and SORI amplitudes studied. This result indicates the y2 and b5 ions are likely formed by the same mechanism over the SORI amplitudes studied.

Herrmann, Kristin A.; Kuppannan, Krishna; Wysocki, Vicki H.

2006-03-01

143

Fragmentation of doubly-protonated peptide ion populations labeled by H/D exchange with CD3OD  

PubMed Central

Doubly-protonated bradykinin (RPPGFSPFR) and an angiotensin III analogue (RVYIFPF) were subjected to hydrogen/deuterium (H/D) exchange with CD3OD in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. A bimodal distribution of deuterium incorporation was present for bradykinin after H/D exchange for 90 s at a CD3OD pressure of 4 × 10?7 Torr, indicating the existence of at least two distinct populations. Bradykinin ion populations corresponding to 0–2 and 5–11 deuteriums (i.e., D0, D1, D2, D5, D6, D7, D8, D9, D10, and D11) were each monoisotopically selected and fragmented via sustained off-resonance irradiation (SORI) collision-induced dissociation (CID). The D0–D2 ion populations, which correspond to the slower exchanging population, consistently require lower SORI amplitude to achieve a similar precursor ion survival yield as the faster-reacting (D5–D11) populations. These results demonstrate that conformation/protonation motif has an effect on fragmentation efficiency for bradykinin. Also, the partitioning of the deuterium atoms into fragment ions suggests that the C-terminal arginine residue exchanges more rapidly than the N-terminal arginine. Total deuterium incorporation in the b1/y8 and b2/y7 ion pairs matches very closely the theoretical values for all ion populations studied, indicating that the ions of a complementary pair are likely formed during the same fragmentation event, or that no scrambling occurs upon SORI. Deuterium incorporation into the y1/a8 pseudo-ion pair does not closely match the expected theoretical values. The other peptide, doubly-protonated RVYIFPF, has a trimodal distribution of deuterium incorporation upon H/D exchange with CD3OD at a pressure of 1 × 10?7 Torr for 600 s, indicating at least three distinct ion populations. After 90 s of H/D exchange where at least two distinct populations are detected, the D0–D7 ion populations were monoisotopically selected and fragmented via SORI-CID over a range of SORI amplitudes. The precursor ion survival yield as a function of SORI amplitude falls into two distinct behaviors corresponding to slower- and faster-reacting ion populations. The slower-reacting population requires larger SORI amplitudes to achieve the same precursor ion survival yield as the faster exchanging population. Total deuterium incorporation into the y2/b5 ion pairs matches closely the theoretical values over all ion populations and SORI amplitudes studied. This result indicates the y2 and b5 ions are likely formed by the same mechanism over the SORI amplitudes studied.

Herrmann, Kristin A.; Kuppannan, Krishna; Wysocki, Vicki H.

2008-01-01

144

Studying MHC class I peptide loading and exchange in vitro.  

PubMed

In the endoplasmic reticulum (ER), MHC class I molecules associate with several specialized proteins, forming a large macromolecular complex referred to as the "peptide-loading complex" (PLC). In the PLC, antigenic peptides undergo a stringent selection process for binding onto MHC class I molecules. This ensures that the immune system elicits robust CD8+ T-cell responses to viruses and solid tumors. The ability to reconstitute in vitro MHC class I molecules in association with key proteins of the PLC provides a mean for studying at the molecular level how antigenic peptides are selected for presentation to CD8+ T-cells. Here, we describe practical procedures for generating a cell-free system involving MHC class I molecules and tapasin, a critical protein of the PLC, that can be used as a versatile tool for biochemical and mechanistic studies of peptide loading and exchange. PMID:23329480

Bouvier, Marlene

2013-01-01

145

Interlayer diffusion studies of a Laves phase exchange spring superlattice  

NASA Astrophysics Data System (ADS)

Rare earth Laves phase (RFe2) superlattice structures grown at different temperatures are studied using x-ray reflectivity (XRR), x-ray diffraction, and transmission electron microscopy. The optimized molecular beam epitaxy growth condition is matched with the XRR simulation, showing minimum diffusion/roughness at the interfaces. Electron microscopy characterization reveals that the epitaxial growth develops from initial 3D islands to a high quality superlattice structure. Under this optimum growth condition, chemical analysis by electron energy loss spectroscopy with high spatial resolution is used to study the interface. The analysis shows that the interface roughness is between 0.6 and 0.8 nm and there is no significant interlayer diffusion. The locally sharp interface found in this work explains the success of simple structural models in predicting the magnetic reversal behavior of Laves exchange spring superlattices.

Wang, C.; Kohn, A.; Wang, S. G.; Ward, R. C. C.

2011-03-01

146

Study on heat transfer of heat exchangers in the Stirling engine - Performance of heat exchangers in the test Stirling engine  

NASA Astrophysics Data System (ADS)

The heat transfer performance of the actual heat exchangers obtained from the experimental results of the test Stirling engine is presented. The heater for the test engine has 120 heat transfer tubes that consist of a bare-tube part and a fin-tube part. These tubes are located around the combustion chamber and heated by the combustion gas. The cooler is the shell-and-tube-type heat exchanger and is chilled by water. It is shown that the experimental results of heat transfer performance of the heater and cooler of the test Stirling engine are in good agreement with the results calculated by the correlation proposed in our previous heat transfer study under the periodically reversing flow condition. Our correlation is thus confirmed to be applicable to the evaluation of the heat transfer coefficient and the thermal design of the heat exchangers in the Stirling engine.

Kanzaka, Mitsuo; Iwabuchi, Makio

1992-11-01

147

Exchange bias  

Microsoft Academic Search

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

J. Nogués; Ivan K Schuller

1999-01-01

148

The Effective Factors on Absorbing Investment of Real People in Stock Exchange Market (Case Study: Isfahan Regional Stock Exchange)  

Microsoft Academic Search

Today, recognizing the economic objectives of any country is unconceiveable without general sharing its people. One of the ways for participation is stock exchange, because in this way, small and wandering savings of people will be led to productive and manu facturing direction, heane the production and economy circle will move on. The main objective of the present study is

M. Abzari; S. Samadi; A. Safari

149

Is sterilised foreign exchange intervention effective after all? an event study approach  

Microsoft Academic Search

This study provides evidence supporting the effectiveness of sterilised foreign exchange market intervention by central banks using an event study approach. An event study framework is better suited to the study of sporadic and intense periods of official intervention, juxtaposed with continuously changing exchange rates, than standard time-series studies. Focusing on daily Bundesbank and US official intervention operations, we identify

Rasmus Fatum; Michael M. Hutchison

2003-01-01

150

An efficient and inexpensive refrigerated LC system for H/D exchange mass spectrometry.  

PubMed

Loss of deuterium label during the LC step in amide hydrogen/deuterium exchange mass spectrometry (H/D-MS) is minimized by maintaining an acidic mobile phase pH and low temperature (pH 2.5, 0 °C). Here we detail the construction and performance of a low-cost, thermoelectrically refrigerated enclosure to house high-performance liquid chromatography (HPLC) components and cool mobile phases. Small volume heat exchangers rapidly decrease mobile phase temperature and keep the temperature stable to ±0.2 °C. Using a superficially porous reversed-phase column, we obtained excellent chromatographic performance in the separation of peptides with a median peak width of 4.4 s. Average deuterium recovery was 80.2% with an average relative precision of 0.91%. PMID:21953202

Keppel, Theodore R; Jacques, Martin E; Young, Robert W; Ratzlaff, Kenneth L; Weis, David D

2011-05-15

151

Structural Study of Monomethylammonium and Dimethylammonium-Exchanged Vermiculites  

Microsoft Academic Search

Vermiculite crystals from Santa Olalla, Spain, were first Na exchanged and then intercalated with monomethylammonium (= NH3(CH3) +, MMA) and dimethylammonium (= NH2(CH3)2 +, DMA) molecules, respectively, by immersion in 1 M ammonium-chloride solutions at 65~ for 2-3 wk. MMA- and DMA-exchange with vermiculite resulted in crystals with near perfect three-dimensional stacking, suitable for single crystal X-ray diffraction analysis. Unit

A. Vahedi-Faridi; STEPHEN GUGGENHEIM

1999-01-01

152

Exchangeable Potassium Study in Patients Undergoing Chronic Haemodialysis  

PubMed Central

Seven patients with chronic renal failure treated with haemodialysis for 4 to 24 months were found to have low exchangeable potassium levels. Before dialysis the plasma potassium was normal or somewhat raised (possibly owing to acidosis), though the exchangeable potassium was low. Acidosis was corrected during dialysis; plasma potassium levels fell, but clinical and electrocardiographic changes of hypokalaemia were absent. The level of 1 mEq/litre in the dialysate fluid may be too low for use in prolonged haemodialysis.

Seedat, Y. K.

1969-01-01

153

Parametric performance studies on fluidized-bed heat exchangers  

NASA Astrophysics Data System (ADS)

The performance of single and multistage shallow fluidized beds is investigated for possible application to the recovery of heat from sources such as waste heat, and coal combustion or coal gasification. Tests are conducted to (1) investigate the effects of fouling due to liquid condensate in the gas stream on fluidized bed heat exchanger performance, (2) investigate the performance of fluidized beds which are staged using baffle plates, and (3) investigate the effects of different heat exchanger surface geometries. Work is progressing in selecting the conditions for that portion of the program involving fouling by a liquid condensate, and in modifying the fluidized bed heat exchanger facility for the fouling experiments. Preliminary tests were conducted with water vapor injection. Water vapor and glycerol vapor were chosen as the condensates. The results are summarized as follows: (1) heat exchanger performance is seriously degraded by condensation when the dew point temperature exceeds the heat exchanger wall temperature; and (2) the performance decrease occurs as a result of particle adherence to the heat exchanger surface and not as a result of particle agglomeration.

Stoeffler, R. C.

1982-01-01

154

Study of isovector resonances with pion charge exchange  

SciTech Connect

Studies with the pion charge exchange reactions (..pi../sup +-/,..pi../sup 0/) at 164 MeV using the LAMPF ..pi../sup 0/ spectrometer are yielding new results on the existence and systematic features of isovector resonances in nuclei. These experiments possess an unusually high signal/background ratio for isovector resonances of low-multipolarity. Results obtained to date are: (1) observation and angular disribution measurement of the giant dipole resonance in nuclei /sup 12/C, /sup 40/Ca, /sup 90/Zr, and /sup 120/Sn; and (2) observation and angular distribution measurements in the (..pi../sup -/,..pi../sup 0/) reaction on /sup 90/Zr and /sup 120/Sn of large signals possessing the expected angular distribution shapes and magnitudes for the isovector monopole resonance. Excitation energies are near the hydrodynamical model values 170 A/sup -//sup 1/3/ MeV. Differential cross sections are approximately 0.7 J/sub 1//sup 2/(qR) mb/sr. An overview of this experimental program, with emphasis on new results and how they correlate with existing knowledge on the isovector resonances, is presented.

Baer, H.W.; Bolton, R.; Bowman, J.D.

1982-01-01

155

Conformational lability in the class II MHC 310 helix and adjacent extended strand dictate HLA-DM susceptibility and peptide exchange  

PubMed Central

HLA-DM is required for efficient peptide exchange on class II MHC molecules, but its mechanism of action is controversial. We trapped an intermediate state of class II MHC HLA-DR1 by substitution of ?F54, resulting in a protein with increased HLA-DM binding affinity, weakened MHC-peptide hydrogen bonding as measured by hydrogen-deuterium exchange mass spectrometry, and increased susceptibility to DM-mediated peptide exchange. Structural analysis revealed a set of concerted conformational alterations at the N-terminal end of the peptide-binding site. These results suggest that interaction with HLA-DM is driven by a conformational change of the MHC II protein in the region of the ?-subunit 310 helix and adjacent extended strand region, and provide a model for the mechanism of DM-mediated peptide exchange.

Painter, Corrie A.; Negroni, Maria P.; Kellersberger, Katherine A.; Zavala-Ruiz, Zarixia; Evans, James E.; Stern, Lawrence J.

2011-01-01

156

Micromagnetic studies on exchange-coupled composite media  

NASA Astrophysics Data System (ADS)

In order to understand the recording characteristics of the media, the magnetic dynamics of a total recording system with a single pole head (SPH) and exchange-coupled composite media with recording layer (RL) and semi-hard layer (SHL) were examined by a 3-D micromagnetic model. Effects of the interlayer exchange coupling (Jex) between the RL and the SHL as well as thickness, anisotropy constant (Ku), intergranular exchange coupling (A*) of the SHL on SNR were investigated. As the Jex increases, writability increases due to the increase of the interlayer exchange coupling but over-all SNR decreases due to the reversed grains in a bit. The increase of the SHL thickness improves writability, but causes SNR to decrease. As Ku of the SHL decreases, both writability and SNR increase. The reduction of Ku of the SHL is important to get high SNR and good writability. Magnetically well-isolated grains in the SHL are apt for high SNR in exchange-coupled composite media.

Lee, T. D.; Lee, S. C.; Tahk, Y. W.

2006-08-01

157

Nucleotide exchange factors: Kinetic analyses and the rationale for studying kinetics of GEFs.  

PubMed

Exchange factors are enzymes that catalyze the exchange of GTP for GDP on guanine nucleotide binding proteins. Progress in understanding the molecular basis of action and the cellular functions of these enzymes has largely come from structural determinations (e.g., crystal structures) and studying effects on cells when expression levels of the exchange factors are perturbed or mutated exchange factors are expressed. Proportionally little effort has been expended on studying the kinetics of exchange; however, reaction rates are central to understanding enzymes. Here, we discuss the importance of kinetic analysis of exchange factors for guanine nucleotide binding proteins, with a focus on ADP-ribosylation factor (Arf) and heterotrimeric G proteins, for providing unique insights into molecular mechanisms and regulation as well as how kinetic analyses are used to complement other approaches. PMID:23181196

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

2012-07-01

158

Experimental studies on coherent synchrotron radiation at an emittance exchange beam line  

NASA Astrophysics Data System (ADS)

One of the goals of the Fermilab A0 photoinjector is to investigate experimentally the transverse to longitudinal emittance exchange (EEX) principle. Coherent synchrotron radiation in the emittance exchange line could limit the performance of the emittance exchanger at short bunch lengths. In this paper, we present experimental and simulation studies of the coherent synchrotron radiation (CSR) in the emittance exchange line at the A0 photoinjector. We report on time-resolved CSR studies using a skew-quadrupole technique. We also demonstrate the advantages of running the EEX with an energy-chirped beam.

Thangaraj, J. C. T.; Thurman-Keup, R.; Ruan, J.; Johnson, A. S.; Lumpkin, A. H.; Santucci, J.

2012-11-01

159

Parametric performance studies on fluidized-bed heat exchangers  

NASA Astrophysics Data System (ADS)

The performance of single and multistage shallow fluidized beds for possible application to the recovery of heat from sources as waste heat, and coal combustion or coal gasification were investigated. The following tests are investigated: (1) the effects of fouling due to liquid condensate in the gas stream of fluidized beds which are staged using baffle plates; and (3) the effects of different heat exchanger surface geometries. The conditions fouling by a liquid condensate are selected. Modifications are made to the fluidized bed heat exchanger facility for the fouling experiments.

Stoffler, R. C.

1981-10-01

160

Field theoretical study of a spin-1/2 ladder with unequal chain exchanges  

NASA Astrophysics Data System (ADS)

We study the low-energy properties of a Heisenberg spin-1/2 zigzag ladder with different exchange constants on the two chains. Using a nonlinear ?-model field theory and Abelian bosonization, we find that the excitations are gapless, with a finite spin-wave velocity, if the values of the chain exchanges are small. If the chain exchanges are large, the system is gapped, and the energy spectra of the kink and antikink excitations are different from each other.

Sarkar, Sujit; Sen, Diptiman

2002-05-01

161

The Kuroshio edge exchange processes (KEEP) study — an introduction to hypotheses and highlights  

Microsoft Academic Search

The Kuroshio edge exchange processes (KEEP) study is a multidisciplinary study on the internal cycling of material, especially carbon, within the East China Sea Shelf and the exchange of material between this Shelf and its adjoining Kuroshio. The project has been ongoing since 1989. The East China Sea Shelf is a net sink of atmospheric carbon dioxide. Rich supplies of

George T. F. Wong; Shenn-Yu Chao; Yuan-Hui Li; Fuh-Kwo Shiah

2000-01-01

162

Study of Multiferroic Manganites using Double-Exchange Models  

NASA Astrophysics Data System (ADS)

The double exchange (DE) model, supplemented by lattice distortions and superexchange between the t2g spins, has been very successful in describing the physics of manganites, such as La1-xCaxMnO3, including the presence of colossal magnetoresistance in Monte Carlo simulations [1]. In this presentation, we describe the first steps toward the application of the theoretical framework previously used for CMR manganites now to the study of multiferroic manganites. An encouraging result was recently obtained when S. Dong et al. [2] showed that the addition to the DE model of a next-nearest-neighbor antiferromagnetic t2g coupling J2 was found to produce a phase diagram that correctly predicts a transition from an A-type AF to a spiral phase and finally to an E-type AF state with increasing J2, as in experiments. This result paves the way for a variety of investigations and theoretical predictions now varying both the hole doping x and J2. Other issues in the area of multiferroics will also be addressed in this presentation, including the prediction of ferroelectricity in the spin zigzag E-type AF state [3]. 0.2cm [1] C. Sen et al., Phys. Rev. Lett. 98, 127202 (2007); R. Yu et al., Phys. Rev. B 77, 214434 (2008); and references therein. 0.1cm [2] S. Dong, R. Yu, S. Yunoki, J.-M. Liu, and E. Dagotto, Phys. Rev. B 78, 155121 (2008). 0.1cm [3] I. A. Sergienko et al., Phys. Rev. Lett. 97, 227204 (2006); S. Picozzi et al., Phys. Rev. Lett. 99, 227201 (2007).

Dagotto, Elbio

2009-03-01

163

Fast Reversed-Phase Liquid Chromatography to Reduce Back Exchange and Increase Throughput in H/D Exchange Monitored by FT-ICR Mass Spectrometry  

PubMed Central

In solution-phase hydrogen/deuterium exchange (HDX), it is essential to minimize the back exchange level of H for D after the exchange has been quenched, to accurately assign protein conformation and protein-protein or protein-ligand interactions. Reversed-phase HPLC is conducted at low pH and low temperature to desalt and separate proteolytic fragments. However, back exchange averages ?30% due to long exposure to H2O in the mobile phase. In this paper, we first show that there is no significant backbone amide hydrogen back exchange during quenching and digestion; backbone exchange occurs primarily during subsequent LC separation. We then show that a rapid reversed-phase separation reduces back exchange for HDX by at least 25%, due to dramatically reduced retention time of the peptide fragments on the column. The influence of retention time on back exchange was also evaluated. The rapid separation coupled with high resolution FT-ICR MS at 14.5T provides high amino acid sequence coverage, high sample throughput, and high reproducibility and reliability.

Zhang, Hui-Min; Bou-Assaf, George M.; Emmett, Mark R.; Marshall, Alan G.

2009-01-01

164

Positional isotope exchange studies on enzyme using NMR spectroscopy  

SciTech Connect

The isotopically enriched compounds, /sup 18/O-..beta..,..gamma..-ATP and /sup 18/O bridge-labeled pyrophosphate, synthesized previously in this laboratory, were used to investigate and measure the exchange vs. turnover of substrates and products from their central complexes in four selected enzyme systems. Using hi-field /sup 31/P NMR, we were able to differentiate between /sup 18/O labeled in the bridge vs. the non-bridge positions by virtue of the isotope shift upon the phosphorus nuclei. The bridge to non-bridge scrambling of the label was quantitated and the exchange vs. turnover ratios under a variety of conditions was determined. Using the substrate inhibitor carboxycreatinine, PIX experiments with /sup 18/O-..beta..,..gamma..-ATP and creatine kinase were conducted. It was shown that carboxycreatinine and creatine kinase promoted exchange of the /sup 18/O label as determined by NMR. We have concluded that carboxycreatinine is either a substrate that catalyzes very slow turnover or it catalyzes exchange by a dissociative (SN/sub 1//sub P/) type of mechanism

Matsunaga, T.O.

1987-01-01

165

Study of frost melting on a heat pump heat exchanger  

SciTech Connect

This experimental work was carried out to obtain basic information on frost melting on a heat exchanger used as a heat pump air conditioner. The heat exchanger working fluid used in this experiment was a 50 wt% propylene glycol aqueous solution. The flow amount G and the temperature T{sub b} of the working fluid were 0.1 {lt} G m{sup 3}/hour {lt} 0.2 and 10 {lt} T{sub b}0{degrees}C {lt} 34, respectively. A melting thermal efficiency {eta} is defined in this paper as the ratio of the net heat for melting to the heat supplied to the heat exchanger until the critical time for melting t{sub c}. {eta} strongly depends on t{sub c}, and t{sub c} is strongly affected by G and T{sub b}. In conclusion, it was found that the heat supplied to the heat exchanger can be utilized with a high {eta} when t{sub c} becomes small.

Sugawara, M.; Kirihoshi, C.; Fujita, T. (Dept. of Mechanical Engineering, Akita Univ. (JP)); Uemura, S.; Yajima, R. (Daikin Industries, Ltd. (JP))

1990-01-01

166

Parametric performance studies on fluidized-bed heat exchangers  

Microsoft Academic Search

The performance of single and multistage shallow fluidized beds is investigated for possible application to the recovery of heat from sources such as waste heat, and coal combustion or coal gasification. Tests are conducted to (1) investigate the effects of fouling due to liquid condensate in the gas stream on fluidized bed heat exchanger performance, (2) investigate the performance of

R. C. Stoeffler

1982-01-01

167

Forecasting of currency exchange rates using ANN: a case study  

Microsoft Academic Search

In today's global economy, accuracy in forecasting the foreign exchange rate or at least predicting the trend correctly is of crucial importance for any future investment. The use of computational intelligence based techniques for forecasting has been proved extremely successful in recent times. In this paper, we developed and investigated three artificial neural network (ANN) based forecasting model using standard

Joarder Kamruzzaman; Ruhul A Sarker

2003-01-01

168

Conformational changes and orientation of Humicola lanuginosa lipase on a solid hydrophobic surface: an in situ interface Fourier transform infrared-attenuated total reflection study.  

PubMed Central

This study was done to better understand how lipases are activated at an interface. We investigated the conformational and solvation changes occurring during the adsorption of Humicola lanuginosa lipase (HLL) onto a hydrophobic surface using Fourier transform infrared-attenuated total reflection spectroscopy. The hydrophobic surfaces were obtained by coating silicon attenuated total reflection crystal with octadecyltrichlorosilane. Analysis of vibrational spectra was used to compare the conformation of HLL adsorbed at the aqueous-solid interface with its conformation in solution. X-ray crystallography has shown that HLL exists in two conformations, the closed and open forms. The conformational changes in HLL caused by adsorption onto the surface were compared with those occurring in three reference proteins, bovine serum albumin, lysozyme, and alpha-chymotrypsin. Adsorbed protein layers were prepared using proteins solutions of 0.005 to 0.5 mg/mL. The adsorptions of bovine serum albumin, lysozyme, and alpha-chymotrypsin to the hydrophobic support were accompanied by large unfoldings of ordered structures. In contrast, HLL underwent no secondary structure changes at first stage of adsorption, but there was a slight folding of beta-structures as the lipase monolayer became complete. Solvation studies using deuterated buffer showed an unusual hydrogen/deuterium exchange of the peptide CONH groups of the adsorbed HLL molecules. This exchange is consistent with the lipase being in the native open conformation at the water/hydrophobic interface.

Noinville, Sylvie; Revault, Madeleine; Baron, Marie-Helene; Tiss, Ali; Yapoudjian, Stephane; Ivanova, Margarita; Verger, Robert

2002-01-01

169

Solution and Gas-Phase H/D Exchange of Protein-Small-Molecule Complexes: Cex and Its Inhibitors  

NASA Astrophysics Data System (ADS)

The properties of noncovalent complexes of the enzyme exo-1,4-?-D-glycanase ("Cex") with three aza-sugar inhibitors, deoxynojirimycin (X2DNJ), isofagomine lactam (X2IL), and isofagomine (X2IF), have been studied with solution and gas-phase hydrogen deuterium exchange (H/Dx) and measurements of collision cross sections of gas-phase ions. In solution, complexes have lower H/Dx levels than free Cex because binding the inhibitors blocks some sites from H/Dx and reduces fluctuations of the protein. In mass spectra of complexes, abundant Cex ions are seen, which mostly are formed by dissociation of complexes in the ion sampling interface. Both complex ions and Cex ions formed from a solution containing complexes have lower cross sections than Cex ions from a solution of Cex alone. This suggests the Cex ions formed by dissociation "remember" their solution conformations. For a given charge, ions of the complexes have greater gas-phase H/Dx levels than ions of Cex. Unlike cross sections, H/Dx levels of the complexes do not correlate with the relative gas-phase binding strengths measured by MS/MS. Cex ions from solutions with or without inhibitors, which have different cross sections, show the same H/Dx level after 15 s, indicating the ions may fold or unfold on the seconds time scale of the H/Dx experiment. Thus, cross sections show that complexes have more compact conformations than free protein ions on the time scale of ca. 1 ms. The gas-phase H/Dx measurements show that at least some complexes retain different conformations from the Cex ions on a time scale of seconds.

Kang, Yang; Terrier, Peran; Ding, Chuanfan; Douglas, D. J.

2012-01-01

170

Experimental Study of Coherent Synchrotron Radiation in the Emittance Exchange Line at the A0-Photoinjector  

SciTech Connect

Next generation accelerators will require a high current, low emittance beam with a low energy spread. Such accelerators will employ advanced beam conditioning systems such as emittance exchangers to manipulate high brightness beams. One of the goals of the Fermilab A0 photoinjector is to investigate the transverse to longitudinal emittance exchange principle. Coherent synchrotron radiation could limit high current operation of the emittance exchanger. In this paper, we report on the preliminary experimental and simulation study of the coherent synchroton radiation (CSR) in the emittance exchange line at the A0 photoinjector.

Thangaraj, Jayakar C. T.; Thurman-Keup, R.; Johnson, A.; Lumpkin, A. H.; Edwards, H.; Ruan, J.; Santucci, J.; Sun, Y. E.; Church, M. [Fermi National Accelerator Labaratory, Batavia, IL, 60510 (United States); Piot, P. [Fermi National Accelerator Labaratory, Batavia, IL, 60510 (United States); Department of Physics, DeKalb, IL, 60115 (United States)

2010-11-04

171

Analytical lessons learned from selected therapeutic protein drug comparability studies.  

PubMed

The successful implementation of process and product changes for a therapeutic protein drug, both during clinical development and after commercialization, requires a detailed evaluation of their impact on the protein's structure and biological functionality. This analysis is called a comparability exercise and includes a data driven assessment of biochemical equivalence and biological characterization using a cadre of analytical methodologies. This review focuses on describing analytical results and lessons learned from selected published therapeutic protein comparability case studies both for bulk drug substance and final drug product. An overview of the currently available analytical methodologies typically used is presented as well as a discussion of new emerging analytical techniques. The potential utility of several novel analytical approaches to comparability studies is discussed including distribution and stability of protein drugs in vivo, and enhanced evaluation of higher-order protein structure in actual formulations using hydrogen/deuterium exchange mass spectrometry, two-dimensional nuclear magnetic resonance fingerprinting or empirical phase diagrams. In addition, new methods for detecting and characterizing protein aggregates and particles are presented as these degradants are of current industry-wide concern. The critical role that analytical methodologies play in elucidating the structure-function relationships for therapeutic protein products during the overall assessment of comparability is discussed. PMID:23146362

Federici, Marcia; Lubiniecki, Anthony; Manikwar, Prakash; Volkin, David B

2012-11-10

172

Theoretical and experimental study of solar water heater with internal exchanger using thermosiphon system  

Microsoft Academic Search

This study presents a theoretical and experimental analysis of the thermal performance of a solar water heater prototype with an internal exchanger using a thermosiphon system. The heat exchanger made of a rolled copper tube is placed diagonally in the storage tank so that the hot fluid crosses a significant mass of stored water. The results focus mainly on the

P. M. E. Koffi; H. Y. Andoh; P. Gbaha; S. Touré; G. Ado

2008-01-01

173

Coqblin–Schrieffer versus local exchange coupling: a perturbative renormalization group study  

Microsoft Academic Search

As a model for the competition between local exchange (LE) and hybridization in rare earth systems we study a Hamiltonian given by the Coqblin–Schrieffer (CS) interaction, plus the exchange interaction derived from LE. The last term breaks the SU(N) symmetry of the CS model. By using the perturbative renormalization group, we show that the ground state of the model is

Eva Pavarini; Lucio Claudio Andreani

1999-01-01

174

Microstructural studies of glass-metal composites produced by ion-exchange and hydrogen treatments  

Microsoft Academic Search

Detailed electron micrographic studies have been carried out on float glass surface subjected to sodium ? copper ion-exchange in molten salts followed by a reduction treatment in hydrogen. Spherical copper particles of diameters ranging from 50 to 300 å are formed in the glass matrix depending on the ion-exchange and reduction temperatures. The nucleus density of these particles is maximum

D. Chakravorty; A. Shuttleworth; P. H. Gaskell

1975-01-01

175

High Performance Liquid Chromatographic Studies of the Ion Exchange Selectivity of Nafion.  

National Technical Information Service (NTIS)

Nafion films were coated on 5 micron octadecyl-derivatized silica. HPLC columns were packed with this film-modified ODS and the ion exchange selectivity of Nafion was studied. A homologous series of organic cations was used to probe the ion exchange prope...

R. B. Moore J. E. Wilkerson C. R. Martin

1984-01-01

176

ESR Studies of Heisenberg Spin Exchange. II. Effects of Radical Charge and Size  

Microsoft Academic Search

The Heisenberg spin exchange behavior of several radical–solvent systems has been studied. This work has shown that k, the second-order rate constant for bimolecular encounters, and | J | ?1 (where | J | is twice the exchange integral and ?1 is the lifetime of the collision pair) depend markedly on the ionic strength of the solution and upon the

Michael P. Eastman; Gerald V. Bruno; Jack H. Freed

1970-01-01

177

Empirical Study of an Air-to-Air Heat Pipe Heat Exchanger in Tropical Climates  

Microsoft Academic Search

This article presents the empirical study of a heat pipe heat exchanger that was directly experiencing the ambient tropical air in its evaporator section. The performance of the heat pipe heat exchanger was monitored during two weeks of operation to determine the performance curves. The temperature of return air was controlled at about 22°C as the representative temperature of inside

Y. H. Yau; M. Ahmadzadehtalatapeh

2011-01-01

178

Feasibility Study of Secondary Heat Exchanger Concepts for the Advanced High Temperature Reactor  

SciTech Connect

The work reported herein represents a significant step in the preliminary design of heat exchanger options (material options, thermal design, selection and evaluation methodology with existing challenges). The primary purpose of this study is to aid in the development and selection of the required heat exchanger for power production using either a subcritical or supercritical Rankine cycle.

Piyush Sabharwall

2011-09-01

179

Experimental Study on Impact/Fretting Wear in Heat Exchanger Tubes.  

National Technical Information Service (NTIS)

A data bank of field experiences with heat exchanger tube vibration reveals numerous cases of tube failures at, or near, the baffle. The objective of this study is to provide qualitative impact/fretting wear information for heat exchanger tubes through th...

J. H. Cha M. W. Wambsganss J. A. Jendrzejczyk

1985-01-01

180

Vulnerable youth, dialogic exchanges and resilience: Some preliminary findings from an exploratory study in East London  

Microsoft Academic Search

There has been little exploration in the literature of the dialogic exchanges among marginalized youth, including the kinds of associations they may have, if any, with resilience. Based on preliminary findings from an ethnographic study in East London, we explore some of the dialogic exchanges about resilience among ethnically diverse groups of vulnerable youth to suggest alternative ways in which

Anne-Marie Tupuola; Vicky Cattell; Stephen Stansfeld

2008-01-01

181

Computational studies of water exchange around aqueous Li+ with polarizable potential models  

NASA Astrophysics Data System (ADS)

To enhance our understanding of the mechanism of water-exchange around aqueous Li+, we carried out a systematic study on this system using molecular dynamics simulations with polarizable potential models. The mechanistic properties associated with the water-exchange process, such as potentials of mean force, time dependent transmission coefficients, and the corresponding rate constants, were examined using transition rate theory, the reactive flux method, and Grote-Hynes treatments of the dynamic response of the solvent. We compared the computed rate theory results with results from previous corresponding studies in which classical non-polarizable force fields were used. Our computed barrier heights for water exchange are significantly larger than those obtained using classical non-polarizable force fields. We also studied the effect of pressure on water-exchange rates and the corresponding activation volume. Our computed rate results for water exchange increase with pressure; therefore, a small negative activation volume is observed.

Dang, Liem X.; Annapureddy, Harsha V. R.

2013-08-01

182

The use of stable isotopes to study ecosystem gas exchange  

Microsoft Academic Search

Stable isotopes are a powerful research tool in environmental sciences and their use in ecosystem research is increasing.\\u000a In this review we introduce and discuss the relevant details underlying the use of carbon and oxygen isotopic compositions\\u000a in ecosystem gas exchange research. The current use and potential developments of stable isotope measurements together with\\u000a concentration and flux measurements of CO2

D. Yakir; L. da S. L. Sternberg

2000-01-01

183

Study of Multiferroic Manganites using Double-Exchange Models  

Microsoft Academic Search

The double exchange (DE) model, supplemented by lattice distortions and superexchange between the t2g spins, has been very successful in describing the physics of manganites, such as La1-xCaxMnO3, including the presence of colossal magnetoresistance in Monte Carlo simulations [1]. In this presentation, we describe the first steps toward the application of the theoretical framework previously used for CMR manganites now

Elbio Dagotto

2009-01-01

184

Cost-effectiveness study of heat pipe heat exchangers  

Microsoft Academic Search

The initial costs of three types of heat pipe heat exchangers are presented: aluminum-Freon 11 for the temperature range from -23 C to 121 C, copper-water for 38 C to 232 C, and carbon steel-Dowtherm A for 120 C to 400 C. An optimization computer program for the cost-effectiveness analysis is developed, which takes into consideration the costs for equipment,

D. C. Lu; K. T. Feldman Jr.

1977-01-01

185

Gas exchange strategy in the Nile crocodile: a morphometric study  

Microsoft Academic Search

The respiratory surface area (SAR) per kilogram body mass (MB), the harmonic mean thickness of the air-blood barrier (thtR) in the gas exchange tissue, and the anatomical diffusion factor (ADF=SAR\\/thtR per MB) were calculated for four juvenile Nile crocodiles. The ADF of three small specimens (mean MB=3.59 kg) was 625 cm2·µm-1·kg-1. The values varied considerably among individuals and were similar

S. F. Perry

1990-01-01

186

NMR study of chemical exchange in mesoporous material MCM-41  

NASA Astrophysics Data System (ADS)

In this work we will explore behaviour of water molecules inside pores of mesoporous material MCM-41 and their interactions to the surface hydration sites, using proton NMR techniques. In NMR MAS experiments involving hydrated porous media, it is generally observed that the water and surface OH proton resonances tend to coalesce with increasing moisture content. It has been suggested that chemical exchange between surface OH groups and water may not be the only mechanism producing the coalescence in the mesoporous material MCM-41. [Chem. Eur. J. 10 (2004) 5689] Here the importance of such exchange was investigated in MCM-41, hydrated to one water molecule per OH group, using both NMR time domain and MAS techniques. The results suggest that the surface - water chemical exchange rate is too small to produce substantive proton spectral coalescence in the MCM-41 material at low hydration level. In the next step a hopping model for water molecules on surface of porous material has been introduced and resulting average resonance position for different proton species in mesoporous material MCM-41 based on this model, has been compared to experimental data.

Niknam, Mohamad; Liang, Jianzhen; Peemoeller, Hartwig

2012-02-01

187

Mossbauer Effect Study of the Fe Spin Structure in Exchange-Bias and Exchange-Spring Systems.  

National Technical Information Service (NTIS)

Theoretical and experimental issues connected with exchange-bias and exchange-spring behavior are briefly reviewed, and the potential of conversion electron Moessbauer spectroscopy (CEMS), including the (sup 57)Fe probe layer technique, to reveal the spin...

W. Keune V. E. Kuncser J. S. Jiang S. D. Bader

2002-01-01

188

Moessbauer effect study of the Fe spin structure in exchange-bias and exchange-spring systems.  

SciTech Connect

Theoretical and experimental issues connected with exchange-bias and exchange-spring behavior are briefly reviewed, and the potential of conversion electron Moessbauer spectroscopy (CEMS), including the {sup 57}Fe probe layer technique, to reveal the spin structure in layered systems is emphasized. First experimental results are reported for the new exchange-bias system FeSn{sub 2}/Fe and for the exchange-spring system Sm-Co/Fe.

Keune, W.; Kuncser, V. E.; Doi, M.; Askin, M.; Spies, H.; Sahoo, B.; Duman, E.; Acet, M.; Jiang, J. S.; Bader, S. D.

2002-03-14

189

HDX workbench: software for the analysis of H/D exchange MS data.  

PubMed

Hydrogen/deuterium exchange mass spectrometry (HDX-MS) is an established method for the interrogation of protein conformation and dynamics. While the data analysis challenge of HDX-MS has been addressed by a number of software packages, new computational tools are needed to keep pace with the improved methods and throughput of this technique. To address these needs, we report an integrated desktop program titled HDX Workbench, which facilitates automation, management, visualization, and statistical cross-comparison of large HDX data sets. Using the software, validated data analysis can be achieved at the rate of generation. The application is available at the project home page http://hdx.florida.scripps.edu . PMID:22692830

Pascal, Bruce D; Willis, Scooter; Lauer, Janelle L; Landgraf, Rachelle R; West, Graham M; Marciano, David; Novick, Scott; Goswami, Devrishi; Chalmers, Michael J; Griffin, Patrick R

2012-06-13

190

Individual Basepair Stability of DNA and RNA Studied by NMR-Detected Solvent Exchange  

PubMed Central

In this study, we have optimized NMR methodology to determine the thermodynamic parameters of basepair opening in DNA and RNA duplexes by characterizing the temperature dependence of imino proton exchange rates of individual basepairs. Contributions of the nuclear Overhauser effect to exchange rates measured with inversion recovery experiments are quantified, and the influence of intrinsic and external catalysis exchange mechanisms on the imino proton exchange rates is analyzed. Basepairs in DNA and RNA have an approximately equal stability, and the enthalpy and entropy values of their basepair dissociation are correlated linearly. Furthermore, the compensation temperature, Tc, which is derived from the slope of the correlation, coincides with the melting temperature, and duplex unfolding occurs at that temperature where all basepairs are equally thermodynamically stable. The impact of protium-deuterium exchange of the imino hydrogen on the free energy of RNA basepair opening is investigated, and it is found that two A·U basepairs show distinct fractionation factors.

Steinert, Hannah S.; Rinnenthal, Jorg; Schwalbe, Harald

2012-01-01

191

Individual basepair stability of DNA and RNA studied by NMR-detected solvent exchange.  

PubMed

In this study, we have optimized NMR methodology to determine the thermodynamic parameters of basepair opening in DNA and RNA duplexes by characterizing the temperature dependence of imino proton exchange rates of individual basepairs. Contributions of the nuclear Overhauser effect to exchange rates measured with inversion recovery experiments are quantified, and the influence of intrinsic and external catalysis exchange mechanisms on the imino proton exchange rates is analyzed. Basepairs in DNA and RNA have an approximately equal stability, and the enthalpy and entropy values of their basepair dissociation are correlated linearly. Furthermore, the compensation temperature, T(c), which is derived from the slope of the correlation, coincides with the melting temperature, and duplex unfolding occurs at that temperature where all basepairs are equally thermodynamically stable. The impact of protium-deuterium exchange of the imino hydrogen on the free energy of RNA basepair opening is investigated, and it is found that two A·U basepairs show distinct fractionation factors. PMID:22713572

Steinert, Hannah S; Rinnenthal, Jörg; Schwalbe, Harald

2012-06-05

192

Continuation of Studies on Development of ODS Heat Exchanger Tubing  

SciTech Connect

The Department of Energy (DOE), National Energy Technology Center (NETL), has initiated a strategic plan for the development of advanced technologies needed to design and build fossil fuel plants with very high efficiency and environmental performance. These plants, referred to as 'Vision 21' and FutureGen programs by DOE, will produce electricity, chemicals, fuels, or a combination of these products, and possibly secondary products such as steam/heat for industrial use. MA956 is a prime candidate material being considered for a high temperature heat exchanger in the 'Vision 21' and FutureGen programs. This material is an oxide dispersion strengthened (ODS) alloy; however, there are some gaps in the data required to commit to the use of these alloys in a full-size plant. To fill the technology gaps for commercial production and use of the material for 'Advanced Power Generation Systems' this project has performed development activity to significant increase in circumferential strength of MA956 as compared to currently available material, investigated bonding technologies for bonding tube-to-tube joints through joining development, and performed tensile, creep and fire-side corrosion tests to validate the use and fabrication processes of MA956 to heat exchanger tubing applications. Development activities within this projected has demonstrated increased circumferential strength of MA956 tubes through flow form processing. Of the six fabrication technologies for bonding tube-to-tube joints, inertia friction welding (IFW) and flash butt welding (FBW) were identified as processes for joining MA956 tubes. Tensile, creep, and fire-side corrosion test data were generated for both base metal and weld joints. The data can be used for design of future systems employing MA956. Based upon the positive development activities, two test probes were designed and fabricated for field exposure testing at 1204 C ({approx}2200 F) flue gas. The probes contained tube portions with FBW and IFW welded MA956. Field testing of the probes and remaining heat exchanger design activity will be performed by Oak Ridge National Laboratory under DOE Contract DE-AC05-00OR22725.

Lawrence Brown; David Workman; Bimal Kad; Gaylord Smith; Archie Robertson; Ian Wright

2008-04-15

193

Studies of Spin-Exchange Optical Pumping of Helium-3  

NASA Astrophysics Data System (ADS)

Recent experiments on spin-exchange optical pumping of ^3He with diode laser sources have only acheived spin-polarizations of 50-55%, in opposition to models that predict polarizations in excess of 80%. Using a frequency narrowed diode array and long lifetime cells provided by T. Gentile's group at NIST, we have obtained He polarizations of over 70% over a temperature range of 140-180 C. In order to understand the difference between broad and narrow band pumping, and the difference between the experiment and models, we have heavily instrumented our experiment with diagnostics for absolute Rb density and polarization, absolute He polarization, and Rb and He relaxation rates. We find that the He wall relaxation rate scales approximately linearly with Rb density over more than an order of magnitude change in Rb density.

Chann, B.; Babcock, Earl; Anderson, L. W.; Walker, T. G.

2002-05-01

194

Patients' Attitudes Toward Electronic Health Information Exchange: Qualitative Study  

PubMed Central

Background In many countries, there has been substantial progress in establishing the electronic transmission of patients’ health information between health care providers, but little is known about how best to engage patients in the process. Objective We explored patients’ views about sharing of electronic health information and their preferences for learning about and participating in this process. Methods Patients in one Massachusetts community in the northeastern United States were recruited to participate in focus-group discussions. Prior to discussion, participants completed a written questionnaire that captured their reactions to draft educational materials and a consent form. The discussion moderator and two physicians analyzed the moderator’s detailed notes from each session and participants’ written comments, using an immersion-crystallization approach. Results Three dominant themes emerged: (1) concerns about privacy and security, (2) the potential benefit to a person’s health, and (3) the desire for more information about the consent process. On the pre-discussion questionnaire, 55 out of 62 participants (88%) indicated that they would provide consent for their information to be shared electronically among their health care providers, given the materials they had reviewed. Conclusions Patients are enthusiastic about electronic health information exchange, recognizing its capacity to improve the quality and safety of health care; however, they are also concerned about its potential to result in breached privacy and misuse of health data. As the exchange of electronic health information becomes more widespread, policy makers will need to ensure that patients have access to concise educational materials and opportunities to engage in conversations about the risks and benefits of participation.

Evans, J Stewart; Benjamin, Alison; Delano, David; Bates, David W

2009-01-01

195

Study of Gas and Plasma Conditions in the High Isp VASIMR Thruster  

Microsoft Academic Search

Internal electrode-free VASIMR thruster [1-3] consists of three major sections: plasma production, plasma heating, and plasma exhaust. In our previous works [6-10] we have performed an extensive study of plasma dynamics in the plasma source. We have developed several models of helicon plasma discharge utilizing hydrogen (deuterium) gas, and analyzed its performance in the experimental set-up [4-5]. In the present

O. Batishchev; K. Molvig

2002-01-01

196

Solvent Influenced Fluxionality Studied by Ultrafast Chemical Exchange Spectroscopy  

NASA Astrophysics Data System (ADS)

Two-dimensional infrared spectroscopy (2DIR) allows unprecedentedly detailed understanding of the dynamics of chemical systems in the condensed phase. Carbonyl vibrations of small transition metal complexes report intramolecular dynamics and solvent-solute interactions due to their strong oscillator strengths and moderate environmental sensitivity. We studed the fluxional dynamics of iron pentacarbonyl (Fe(CO)5), which is unique in that it contains nearly perfectly uncoupled vibrational modes. We seek to probe the ``molecularity'' of condensed phase activated barrier crossings beyond the continuum Kramers theory picture. Using 2DIR chemical exchange spectroscopy, we show how the dynamics of Berry pseudorotation, the only significant mechanism for vibrational mode mixing on our experimental timescale, is sensitive to interactions with the environment. In a wide range of solvents, we have investigated the effects of hydrogen bonding with alcohols and friction from high viscosity alkanes. In addition, we have monitored vibrational energy redistribution as a solvation shell probe. Moreover, recently implemented mid-infrared pulse shaper based methods allow increased flexibility in experimental design, enabling experimental techniques that are not possible using passive optics.

Ross, Matthew; Kubarych, Kevin

2012-02-01

197

ESR study of titanium(III)-exchanged zeolite A  

SciTech Connect

A comparison of the chemical reactivity of Ti(III) cations in A-type and Y-type zeolite lattices has been performed by the use of electron spin resonance. While the state of the Ti(III) cation, as observed by ESR spectroscopy, appears similar in the two types of lattices, the reactions of adsorbed gases with the two types of titanium(III)-exchanged zeolites are strikingly different. The adsorption of sulfur dioxide leads to the formation of Ti(IV)-SO/sub 2//sup -/ in the zeolite Y lattice while Ti(IV)-SO/sub 3//sup -/ is formed in the A-type lattice. Adsorption of oxygen results in the formation of Ti(IV)-O/sub 2//sup -/ in the Y-type lattice, as it does in the A-type lattice at low pressures. However, at elevated oxygen pressure a new radical is formed in the A-type lattice which ESR and ESCA evidence strongly suggests is of the form Ti(IV)-O/sub 4//sup -/.

Kuznicki, S.M.; DeVries, K.L.; Eyring, E.M.

1980-03-06

198

Radiolytic and chemical degradation of strong acidic ion-exchange resins: Study of ligands formed  

Microsoft Academic Search

The formation of water-soluble organic ligands by radiolytic and chemical degradation of several strong acidic ion-exchange resins was investigated under conditions close to those of the near field of a cementitious repository. The most important degradation products were studied and their complexing properties evaluated. Irradiation of strong acidic cation exchange resins (Powder PCH and Lewatite S-100) resulted in the formation

L. R. van Loon; W. Hummel

1999-01-01

199

COLLABORATIVE E-MAIL EXCHANGE FOR TEACHING SECONDARY ESL: A CASE STUDY IN HONG KONG  

Microsoft Academic Search

This article presents data from a qualitative case study examining secondary ESL students' attitudes toward and perceptions of a collaborative e-mail exchange between a Form 4 (10th grade) ESL class in Hong Kong and an 11th grade English class in Iowa. The exchange was based on a researcher-designed instructional model, utilizing widely accepted theories and methods for modern second language

Roseanne Greenfield

2003-01-01

200

The structure of mixed surfactants adsorbed at the air-liquid interface, as studied by specular neutron reflection  

NASA Astrophysics Data System (ADS)

The specular reflection of neutrons is now finding widespread application in a range of problems in surface chemistry. Recent studies have shown that by the use of hydrogen-deuterium isotopic substitution, it is possible to determine surface excesses and detailed surface structures of surfactants adsorbed at the air-liquid interface. Recent results on the adsorption of mixed nonionic/cationic surfactants at the air-liquid interface are presented.

Cummins, P. G.; Penfold, J.; Thomas, R. K.; Simister, E.; Staples, E.

1992-06-01

201

PMR study of the kinetics of H/D exchange of b-hydroxypyridinecarboxylic acids  

SciTech Connect

The kinetics of isotope exchange of 3-hydroxyisonicotinic (3-HINA), 5-hydroxynicotinic (5-HNA) and 5-hydroxypicolinic (5-HPA) acids in aqueous solution at 160/sup 0/C in the region pD 5.0-10.0 was studied. Based on kinetic regularities of the H/D exchange of hydrogen in 5-hydroxynicotinic, 5-hydroxypicolinic, and 3-hydroxyisonicotinic acids, results indicated that the reaction follows an electrophilic mechanism and that the ..cap alpha.. position of the ring, vicinal to the OH group, is the most reactive. The proton exchange rate constants were determined which characterize the contribution of the anionic form of the B-hydroxypyridinecarboxylic acids to the H/D exchange reaction.

Lezina, V.P.; Shirokova, L.V.; Stolyarova, L.G.; Smirnov, L.D.

1982-04-10

202

Exchange and correlation in the Si atom: A quantum Monte Carlo study  

SciTech Connect

We have studied the pair-correlation function, the exchange-correlation hole, and the exchange-correlation energy density of the valence electrons in the Si atom using the Coulomb-coupling constant integration technique with the variational quantum Monte Carlo method. These quantities are compared to those derived from various approximate models within the Kohn-Sham density functional theory. We find that the charge density prefactor in the expression for the exchange-correlation hole dominates the errors found in the local spin density approximation (LSDA), that the generalized gradient approximation improves energy calculations by improving the LSDA at long ranges, and that the weighted spin density approximation, which uses the correct charge density prefactor, gives the lowest root mean square error for the exchange-correlation energy density.

Puzder, Aaron; Chou, M. Y.; Hood, Randolph Q.

2001-08-01

203

[Immunoglobulins or plasma exchange? Synchronization of plasma exchange and intravenous polyvalent immunoglobulins. A consecutive study of 11 patients].  

PubMed

Synchronization is defined as a prescription sequence aimed at obtaining synergic response or potentialization. THEORETICAL BASIS--The concept of synchronization is based on clinical and biological observations such as similar indications and transient effectiveness. Certain mechanisms of action such as reduction of pathological autoantibodies and accelerated elimination of immune complexes are common to both methods. Inversely, long-term effects differ. Plasma exchange cannot control the synthesis (or could aggravate) of autoantibodies while gammaglobulins have a suppressor effect on autoreactive clones. The aim is to obtain a summation effect by eliminating immediately cytotoxic factors. The potentializing effect of gammaglobulin anti-idiotypes on the modification of the immunologic repertory is favoured by prior reduction in the level of circulating pathogenic antibodies. RESULTS--It is difficult to evaluate the efficacy of this therapeutic association. Only a few trials have been conducted in refractory autoimmune thrombopenic purpura (n = 8), in intra-uterine Rhesus disease (n = 3), and HIV associated pathologies. We report our experience in 11 patients in a situation of therapeutic failure including three cases of renal transplantation, two cases each of chronic polyradiculoneuritis and neurological paraneoplastic syndromes, and one case each of Wegener's syndrome, polymyositis, sclerokeratitis, and antiphospholipid antibodies during pregnancy. Immunoglobulins were injected at an initial dose of 2 g/kg following at least 3 plasma exchanges. Consolidation cures were then administered every 3 weeks at a dose of 1 g/kg. Two major complications occurred and required interruption of the treatment: acute regressive oligo-anuric renal failure (Wegener) and exacerbation of sclerokeratitis inflammatory lesions. The disease process was controlled in 7 patients. CONCLUSIONS--Despite these promising preliminary results, the proposed combination therapy is not devoid of complications and its cost is high (cost of PE for 500 mg/kg Ig is about 5,000 FF). The next step should be the study of experimental models and prospective trials on pathologies with well characterized immunological features. PMID:8179243

Bussel, A; Boulechfar, H; Naim, R

1993-01-01

204

Multi-Lorentzian representation of deuterium spectrum to study water spin magnetization exchange in MCM-41.  

PubMed

Water behavior on the pore surface of nano-silica MCM-41, at a hydration level corresponding to one water molecule per OH group, is studied using (2)H NMR spectra in the temperature range 213 to 313 K. In an earlier study [J. Hassan, E. Reardon, H. Peemoeller, Microporous Mesoporous Materials, 122 (2009) 121-127] it was shown that at this hydration level, deuterons of water at single OH sites exhibit a Lorentzian line shape and deuterons of water at hydrogen-bonded OH sites exhibit a powder pattern. Here it is shown that magnetization exchange occurs between these two deuteron spin groups. This exchange cannot be described using the common, two-site exchange model, involving two Lorentzians. We successfully apply a multi-Lorentzian exchange model, prompted by Woessner's work [D. E. Woessner, Mol. Phys. 34, 4, (1977) 899-920] on the effects of motion on the shape of water spin resonance lines exhibiting doublet splitting. For this low hydration sample the rate of magnetization exchange out of the hydration site, where the water deuterons exhibit a Lorentzian line in the (2)H spectra, is 1.3 ms(-1) and the activation energy for the exchange is found to be 3.4±0.1 kcal/mole. PMID:22647224

Hassan, J; Reardon, E; Peemoeller, H

2012-05-07

205

Experimental studies on coherent synchrotron radiaiton in the emittance exchange line at the Fermilab A0 Photoinjector  

Microsoft Academic Search

Future accelerators will employ advanced beam conditioning systems such as emittance exchangers to manipulate high brightness beams. Coherent synchrotron radiation (CSR) in the dipoles could limit the performance of the emittance exchanger. In this paper, we report the experimental studies on measuring CSR and its effects on the beam at the A0 photoinjector in the emittance exchange line. After reporting

J. C. T. Thangaraj; R. Keup; A. Johnson; J. ruan; P. Piot; M. Church; H. Edwards; A. Lumpkin; Y.-E. Sun; J. Santucci

2011-01-01

206

Advances and challenges in analytical characterization of biotechnology products: mass spectrometry-based approaches to study properties and behavior of protein therapeutics  

PubMed Central

Biopharmaceuticals are a unique class of medicines due to their extreme structural complexity. The structure of these therapeutic proteins is critically important for their efficacy and safety, and the ability to characterize it at various levels (from sequence to conformation) is critical not only at the quality control stage, but also throughout the discovery and design stages. Biological mass spectrometry (MS) offers a variety of approaches to study structure and behavior of complex protein drugs and has already become a default tool for characterizing the covalent structure of protein therapeutics, including sequence and post-translational modifications. Recently, MS-based methods have also begun enjoying a dramatic growth in popularity as a means to provide information on higher order structure and dynamics of biotechnology products. In particular, hydrogen/deuterium exchange MS and charge state distribution analysis of protein ions in electrospray ionization (ESI)MS offer a convenient way to assess the integrity of protein conformation. Native ESI MS also allows the interactions of protein drugs with their therapeutic targets and other physiological partners to be monitored using simple model systems. MS-based methods are also applied to study pharmacokinetics of biopharmaceutical products, where they begin to rival traditional immunoassays. MS already provides valuable support to all stages of development of biopharmaceuticals, from discovery to post-approval monitoring, and its impact on the field of biopharmaceutical analysis will undoubtedly continue to grow.

Kaltashov, Igor A.; Bobst, Cedric E.; Abzalimov, Rinat R.; Wang, Guanbo; Baykal, Burcu; Wang, Shunhai

2011-01-01

207

The Experimental Study on Heat Transfer Characteristics of The External Heat Exchanger  

NASA Astrophysics Data System (ADS)

Using the external heat exchanger in large-scale CFB boilers can control combustion and heat transfer separately, make the adjustments of bed temperature and steam temperature convenient. The state of gas-solid two phase flow in the external heat exchanger is bubbling fluidized bed, but differs from the regular one as there is a directional flow in it. Consequently, the temperature distribution changes along the flow direction. In order to study the heat transfer characteristics of the water cooled tubes in the bubbling fluidized bed and ensure the uniformity of heat transfer in the external heat exchanger, a physical model was set up according to the similarity principle and at the geometric ratio of 1?28 to an external heat exchanger of a 300MW CFB boiler. The model was connected with an electrically heated CFB test-bed which provides the circulating particles. The influencing factors and the distribution rule of the particles' heat transfer coefficient in the external heat exchanger were assessed by measuring the temperature changes of the water in the tubes and different parts of particles flow along the flow direction. At the end, an empirical correlation of particles' heat transfer coefficient in external heat exchanger was given by modifying the Veedendery empirical correlation.

Ji, X. Y.; Lu, X. F.; Yang, L.; Liu, H. Z.

208

Russian studies of the safety of anion exchange in nitric acid  

SciTech Connect

Synthetic ion exchange resins came into use in the Soviet Union in the 1950`s, and domestic anion exchange resins based on quaternary amine groups have long been used in the Russian nuclear industry. These resins are similar to resins used in the West, and include pyridine-based resins, as well as the more conventional aryl polymers with substituted methyl amines. (Slide 1) The sensitivity of these amines to reaction with nitric acid and other oxidants has been a concern in Russia as in the West, and numerous laboratory studies have been conducted on the reactions involved. Several incidents involving pressure or temperature excursions have provided incentives for such studies. (Slide 2) This report briefly summarizes this work. A report by the Russian authors of this paper providing greater detail is to be issued as a U.S. Dept. of Energy document. Additionally, a second report by these authors, describing new studies on anion exchange resin safety, will also be issued as a DOE report. The separation of plutonium, neptunium, etc. from other materials by ion exchange requires rather strong nitric acid (6-8 M). In some systems, such as the processing of {sup 238}Pu, intense ionizing radiation may also be present during ion exchange separation. As a result, it is necessary to consider not only thermal hydrolysis and oxidation and their effects on the resin, but also radiolysis. All of these were investigated in the Russian studies.

Hyder, M.L.; Bartenev, S.A.; Lazarev, L.N. [and others

1997-07-01

209

Experimental study of a novel manifold structure of micro-channel heat exchanger  

NASA Astrophysics Data System (ADS)

Refrigerant flow distribution with phase change heat transfer was experimentally studied for a micro-channel heat exchanger having horizontal headers. In order to solve the problem of maldistribution, a novel manifold structure with orifice and bypass tube was proposed and experimentally studied compared to the conventional structure. Tests were conducted with downward flow for mass flux from 70 to 110 kg m-2s-1 (air side flow velocity from 1 to 2ms-1). The surface temperature distribution of the heat exchanger recorded by thermal imager and the square deviation of it were used to judge the uniformity of flow distribution. It is shown that as mass flux increased, better flow distribution is obtained (small square deviation of temperature distribution means better flow distribution: conventional structure from 32 to 27, novel structure from 19 to 14), and flow distribution of the novel structure was much better than that of the conventional one. The heat transfer performances of the two heat exchangers were also studied. The cooling capacity of the novel heat exchanger was 14.8% higher than that of the conventional because of the better flow distribution. And the refrigerant pressure drop was 120% higher because of bigger mass flow and the resistance of the orifice. It's worth noting that the air pressure drop of novel heat exchanger was also higher (about 28.3%)than that of the conventional one, even when they have same fin and flat tube structure. From the pictures of the heat exchanger surfaces, it was found that some surface area of the conventional heat exchanger was not wet because of the low mass flow and high superheat, which leaded to a poor performance and relatively small air pressure drop.

Xu, Bo; Xu, Kunhao; Wei, Wei; Han, Qing; Chen, Jiangping

2013-07-01

210

Crossed Molecular Beam Studies of Substitution and Exchange Reactions.  

National Technical Information Service (NTIS)

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

G. N. Robinson

1987-01-01

211

CO2 gas exchange and ocean acidification studies in the coastal Gulf of Maine  

Microsoft Academic Search

The University of New Hampshire is studying CO2 gas exchange, ocean acidification, air-sea dynamics, and associated biological processes in the western Gulf of Maine. Three buoys and shipboard cruises have provided data to support these studies. The first, a CO2 monitoring buoy, is deployed jointly with NOAA's Pacific Marine Environmental Laboratory and has been moored in 70 m of water

James Irish; Douglas Vandemark; Shawn Shellito; Joseph Salisbury; Amanda Plagge; Kevin Hanley; Marc Emond

2010-01-01

212

Acetylcholinesterase-catalyzed acetate - water oxygen exchange studied by /sup 13/C-NMR  

SciTech Connect

The kinetics of the oxygen exchange reaction between (l-/sup 13/C,/sup 18/O/sub 2/)acetate and H/sub 2//sup 16/O catalyzed by homogeneous acetyl-cholinesterase from the electric eel, Electrophorus electricus, was studied using the /sup 18/O-isotope-induced shift on /sup 13/C-nuclear magnetic resonance spectra. Pseudo-first-order rate constants for the exchange reactions were determined at pH values from 4.5 to 8. The exchange reaction exhibits a maximum at pH 5.8. The apparent catalytic rate constant for the exchange reaction is 10/sup 2/ to 10/sup 4/ times smaller than that for the deacylation of the acetyl-enzyme intermediate over the pH range tested. Oxygen exchange occurs by a random sequential pathway rather than by multiple (coupled) exchange. The inhibition of acetylcholinesterase by sodium acetate showed a sigmoidal dependence on pH, with K/sub i/ increasing 2.5 orders of magnitude over the pH range. Protonation of an active site residue having an apparent pKa of 6.8 is associated with an increase in acetate binding. Deacylation also exhibits a sigmoidal dependence on (H/sup +/). The experimental data fits titration curves with inflection points at 5.0 +/- 0.3 and 6.7 +/-0.1. Results support the role of histidine in acetylation of the active site serine, but the conjugate base of another active site residue with a pKa of 5.0 appears necessary for maximal catalytic activity in both the deacylation and exchange reactions.

Van Etten, R.L.; Dayton, B.; Cortes, S.

1986-05-01

213

Folding of the KIX domain: characterization of the equilibrium analog of a folding intermediate using 15N/13C relaxation dispersion and fast 1H/2H amide exchange NMR spectroscopy.  

PubMed

The KIX domain of the transcription co-activator CBP is a three-helix bundle protein that folds via rapid accumulation of an intermediate state, followed by a slower folding phase. Recent NMR relaxation dispersion studies revealed the presence of a low-populated (excited) state of KIX that exists in equilibrium with the natively folded form under non-denaturing conditions, and likely represents the equilibrium analog of the folding intermediate. Here, we combine amide hydrogen/deuterium exchange measurements using rapid NMR data acquisition techniques with backbone (15)N and (13)C relaxation dispersion experiments to further investigate the equilibrium folding of the KIX domain. Residual structure within the folding intermediate is detected by both methods, and their combination enables reliable quantification of the amount of persistent residual structure. Three well-defined folding subunits are found, which display variable stability and correspond closely to the individual helices in the native state. While two of the three helices (alpha(2) and alpha(3)) are partially formed in the folding intermediate (to approximately 50% and approximately 80%, respectively, at 20 degrees C), the third helix is disordered. The observed helical content within the excited state exceeds the helical propensities predicted for the corresponding peptide regions, suggesting that the two helices are weakly mutually stabilized, while methyl (13)C relaxation dispersion data indicate that a defined packing arrangement is unlikely. Temperature-dependent experiments reveal that the largest enthalpy and entropy changes along the folding reaction occur during the final transition from the intermediate to the native state. Our experimental data are consistent with a folding mechanism where helices alpha(2) and alpha(3) form rapidly, although to different extents, while helix alpha(1) consolidates only as folding proceeds to complete the native state-structure. PMID:18565542

Schanda, Paul; Brutscher, Bernhard; Konrat, Robert; Tollinger, Martin

2008-05-24

214

Density functional study on anisotropic magnetic exchange couplings in iron-based superconductors  

NASA Astrophysics Data System (ADS)

Iron-based superconductors exhibit many different antiferromagnetically ordered ground states. An understanding of the magnetic exchange couplings and ground-state Hamiltonian in the parent compounds of these materials is important because such an information could be the basis to unveil the mechanism of unconventional superconductivity. By performing first-principles calculations of the electronic and magnetic properties with non-collinear spin configurations, we study the anisotropic magnetic exchange couplings in iron-based superconductors. We obtain magnetic excitations using the anisotropic magnetic exchange couplings, and compare the results with published inelastic neutron scattering data. This work was supported by the NRF of Korea (Grant No. 2011-0018306). Computational resources have been provided by KISTI Supercomputing Center (Project No. KSC-2012-C2-14).

Oh, Hyungju; Choi, Hyoung Joon

2013-03-01

215

Plasma Exchange vs. Intravenous Immunoglobulin for Myasthenia Gravis Crisis: An Acute Hospital Cost Comparison Study  

PubMed Central

Objective To compare the short term financial costs of treating a patient in myasthenia gravis crisis (MGC) with intravenous immunoglobulin (IVIG) versus plasma exchange (PLEX). Methods An itemized comparative cost-minimization analysis of IVIG vs. plasma exchange for MGC was performed. Calculations were based on each therapy’s implementation cost, associated hospitalization times, and predicted cost to treat known complications. A cost superiority determination was proposed based on the total cost profile of each therapy. Results The difference in total cost favored IVIG over PLEX with an average savings of $22,326 per patient. Sensitivity analysis demonstrated that overall costs are highly dependent on IVIG dosing, hospital lengths of stay, and the number of plasma exchange days required. Conclusions The use of IVIG for MGC may be a short term cost minimizing therapy compared to PLEX. Additional prospective studies are required to evaluate the extended cost profile and efficacy of these therapies.

Heatwole, Chad; Johnson, Nicholas; Holloway, Robert; Noyes, Katia

2011-01-01

216

Polarised neutron reflectometry study of Co/CoO exchange-biased multilayers  

NASA Astrophysics Data System (ADS)

We have investigated via SQUID magnetometry and polarised neutron reflectivity the exchange-bias effect in CoO/Co sputtered multilayers. In particular, we studied the magnetisation reversal and the time relaxation of the exchange-bias field close to the coercive field Hc1. Neutron intensities of all four cross sections (I++, I+-, I-+, I-) were recorded at the position of the first multilayer Bragg peak while scanning the magnetic field. From such scans we infer that the magnetisation reversal for the ascending as well as for the descending branch of the magnetic hysteresis occurs not by in-plane rotation but through domain-wall movements. The exchange-bias field, HEB, is strongly affected by thermal fluctuations. HEB decreases, following an exponential decay function with a half-life time of about 580s at T=240K.

Radu, F.; Etzkorn, M.; Leiner, V.; Schmitte, T.; Schreyer, A.; Westerholt, K.; Zabel, H.

217

Structural Studies of NH4-exchanged Natrolites at Ambient Conditions and High Temperature  

SciTech Connect

We report here for the first time that fully and partially NH{sub 4}-exchanged natrolites can be prepared in hydrated states using the solution exchange method with potassium-natrolite. The structural models of the as-prepared hydrated phases and their dehydrated forms at elevated temperature were refined in space group Fdd2 using in situ synchrotron X-ray powder diffraction data and Rietveld methods. The unit-cell volumes of the hydrated NH{sub 4}-exchanged natrolites at ambient conditions, (NH{sub 4}){sub 16(2)}Al{sub 16}Si{sub 24}O{sub 80}{center_dot}14.1(9)H{sub 2}O and (NH{sub 4}){sub 5.1(1)}K{sub 10.9(1)}Al{sub 16}Si{sub 24}O{sub 80}{center_dot}15.7(3)H{sub 2}O, are found to be larger than that the original sodium-natrolite by ca. 15.6% and 12.8%, respectively. Upon temperature increase, the fully NH{sub 4}-exchanged natrolite undergoes dehydration at ca. 150 C with ca. 16.4% contraction in the unit-cell volume. The dehydrated phase of the fully NH{sub 4}-exchanged natrolite exhibits marginal volume expansion up to 425 C and then becomes amorphized during temperature decrease and exposure to atmospheric condition. In the case of the partially NH{sub 4}-exchanged natrolite, the dehydration starts from ca. 175 C with {approx}15.1% volume contraction and leads to a partial phase separation to show a phase related to the dehydrated K-natrolite. The degree of the phase separation decreases with temperature increase up to 475 C, concomitant to the gradual volume contraction occurring in the partially NH{sub 4}-exchanged natrolite in the dehydrared state. Upon temperature decrease and exposure to atmospheric condition, only the dehydrated K-natrolite is recovered as a crystalline phase from the partially NH{sub 4}-exchanged natrolite. In the hydrated model of the fully NH{sub 4}-exchanged natrolite, the ammonium cations and water molecules are statistically distributed along the elliptical channels, similar to the disordered pattern observed in natrolites exchanged with larger alkali metal cations such as the K-, Rb-, and Cs-forms. The dehydrated model of the fully NH{sub 4}-exchanged natrolite at 400 C is essentially same as the one reported previously from the sample prepared by direct melt exchange method using sodium-natrolite. Both the hydrated and dehydrated structures of the partially NH{sub 4}-exchanged natrolite at RT and at 400 C, respectively, are characterized by having two separate sites for the ammonium and potassium cations. Comparing the structural models of the monovalent cation forms studied so far, we find that the rotation angle of the natrolite chain is inversely proportional to the cation radius both in the hydrated and dehydrated phases. The distribution pattern of the non-framework species along the natrolite channel also seems to be related to the non-framework cation radius and hence to the chain rotation angle.

Y Lee; D Seoung; Y Jang; J Bai; Y Lee

2011-12-31

218

AB INITIO STUDY OF ELECTRIC TRANSPOR T AND INTERLA YER EXCHANGE COUPLING IN  

Microsoft Academic Search

We present a rst principles study of the magnetoresistance (MR) perpendicular to the planes of atoms and the interlayer exchange cou- pling (IEC) in Fe\\/Si\\/Fe trilayers. In both cases the dependence on the number of spacer layers is investigated, whereby the spacer thickness ranges between 3 and 21 A for the IEC and extends to 33 A for the MR

H. C. HERPER; P. WEINBERGER; L. SZUNYOGH; C. SOMMERS; P. ENTEL

2003-01-01

219

sup 1 H NMR study of water exchange in bis(nitrato)diaquodioxouranium(VI)  

SciTech Connect

Kinetics of water exchange of bis(nitrato)diaquodioxouranium(VI) in 96.7% acetone-water have been studied by {sup 1}H NMR spectroscopy, and the activation parameters {Delta}H{sup {double dagger}} = 21.0 kJ mol{sup {minus}1}, {Delta}S{sup {double dagger}} = {minus}86.5 J K{sup {minus}1} determined.

Azenha, M.E.D.G.; Burrows, H.D.; Formosinho, S.J.; Gil, V.M.S.; Miguel, M.D.G. (Univ. de Coimbra (Portugal))

1991-01-01

220

Experimental study and modeling of the ``adiabatic'' section of the constrained vapor bubble heat exchanger  

Microsoft Academic Search

A constrained vapor bubble heat exchanger, CVB, with capillarity to recirculate the liquid was modeled and experimentally studied. Using a relatively simple pentane\\/quartz system the fundamental parameters governing the CVB, namely, temperature, pressure, and menisci curvature, were measured. An ``adiabatic'' section wherein the temperature remained nearly constant was identified. A one-dimensional steady state model of this ``adiabatic'' section was developed

M. Karthikeyan; Jianming Huang; Joel L. Plawsky; Peter C. Wayner

1997-01-01

221

Experimental study and modeling of the “adiabatic” section of the constrained vapor bubble heat exchanger  

Microsoft Academic Search

A constrained vapor bubble heat exchanger, CVB, with capillarity to recirculate the liquid was modeled and experimentally studied. Using a relatively simple pentane\\/quartz system the fundamental parameters governing the CVB, namely, temperature, pressure, and menisci curvature, were measured. An “adiabatic” section wherein the temperature remained nearly constant was identified. A one-dimensional steady state model of this “adiabatic” section was developed

M. ‘Karthik’ Karthikeyan; Jianming Huang; Joel L. Plawsky; Peter C. Wayner

1997-01-01

222

Multicultural Contacts in Education: A Case Study of an Exchange Project between Different Ethnic Groups  

ERIC Educational Resources Information Center

|One important aim of citizenship education is learning to deal with cultural diversity. To this end, schools organise exchange projects to bring students into contact with different social and cultural groups. The aim of this study is to investigate the effects of intergroup contact in educational settings and to understand what the most…

Schuitema, Jaap; Veugelers, Wiel

2011-01-01

223

Multicultural contacts in education: a case study of an exchange project between different ethnic groups  

Microsoft Academic Search

One important aim of citizenship education is learning to deal with cultural diversity. To this end, schools organise exchange projects to bring students into contact with different social and cultural groups. The aim of this study is to investigate the effects of intergroup contact in educational settings and to understand what the most favourable conditions are. The paper discusses a

Jaap Schuitema; Wiel Veugelers

2011-01-01

224

Monte Carlo simulation study of exchange biased hysteresis loops in nanoparticles  

Microsoft Academic Search

We present the results of Monte Carlo simulations of the magnetic properties of a model for a single nanoparticle consisting in a ferromagnetic core surrounded by an antiferromagnetic shell. The simulations of hysteresis loops after cooling in a magnetic field display exchange bias effects. In order to understand the origin of the loop shifts, we have studied the thermal dependence

Òscar Iglesias; Amílcar Labarta

2006-01-01

225

Multicultural Contacts in Education: A Case Study of an Exchange Project between Different Ethnic Groups  

ERIC Educational Resources Information Center

One important aim of citizenship education is learning to deal with cultural diversity. To this end, schools organise exchange projects to bring students into contact with different social and cultural groups. The aim of this study is to investigate the effects of intergroup contact in educational settings and to understand what the most…

Schuitema, Jaap; Veugelers, Wiel

2011-01-01

226

Research on Study Abroad, Mobility, and Student Exchange in Comparative Education Scholarship  

ERIC Educational Resources Information Center

|For many years there has been research on study abroad, student mobility and international student exchange; however in the last two decades the volume and scope of this work has increased significantly. There are now specific academic journals, a host of new books each year, expansive reports by international research organizations, and an…

Streitwieser, Bernhard T.; Le, Emily; Rust, Val

2012-01-01

227

Determining carbon isotope signatures from micrometeorological measurements: Implications for studying biosphere-atmosphere exchange processes  

Microsoft Academic Search

In recent years considerable effort has been focused on combining micrometeorological and stable isotope techniques to partition netfluxes and to study biosphere-atmosphere exchange processes. While much progress has been achieved over the last decade, some new issues are beginning to emerge as technological advances, such as laser spectroscopy, permit isotopic fluxes to be measured more easily and continuously in the

T. J. Griffis; J. Zhang; J. M. Baker; N. Kljun; K. Billmark

2006-01-01

228

Studies on the Electrical Transport of Cations Through Cation Exchange Membranes.  

National Technical Information Service (NTIS)

A study is presented of the influence on cation mobilities in ion exchange membranes, caused by the charge of migrating cations and by the partial substitution of water by non-aqueous solvents of lower permitivity. For this purpose measurements of the par...

H. Voss

1981-01-01

229

Mechanistic study of the low temperature activity of transition metal exchanged zeolite SCR catalysts  

Microsoft Academic Search

Reactor activity measurements and FTIR spectroscopy were applied to study the transient and steady state behavior of Cu and Fe exchanged zeolite catalysts for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with NH3 at 200°C. Different surface NOx adsorption complexes were observed on the two catalysts. IR bands assigned to surface nitrate\\/nitrite groups were apparent on the Cu

Joseph M. Fedeyko; Bin Chen; Hai-Ying Chen

2010-01-01

230

Study on heat transfer of heat exchangers in the Stirling engine - Performance of heat exchangers in the test Stirling engine  

Microsoft Academic Search

The heat transfer performance of the actual heat exchangers obtained from the experimental results of the test Stirling engine is presented. The heater for the test engine has 120 heat transfer tubes that consist of a bare-tube part and a fin-tube part. These tubes are located around the combustion chamber and heated by the combustion gas. The cooler is the

Mitsuo Kanzaka; Makio Iwabuchi

1992-01-01

231

Lead exchange in teeth and bone--a pilot study using stable lead isotopes.  

PubMed Central

Stable lead isotopes and lead concentrations were measured in the enamel and dentine of permanent (n = 37) and deciduous teeth (n = 14) from 47 European immigrants to Australia to determine whether lead exchange occurs in teeth and how it relates to lead exchange in bone. Enamel exhibits no exchange of its European-origin lead with lead from the Australian environment. In contrast, dentine lead exchanges with Australian lead to the extent of approximately 1% per year. In one subject, trabecular bone from the tooth socket exchanged almost all its European lead with Australian lead over a a 15-year period (turnover of approximately 6% per year), similar to the approximately 8% per year proposed for lead turnover in trabecular bone. The repository characteristics of intact circumpulpal dentine were investigated by analyses of four sets of contiguous slices from six teeth: 1) a set consisting of slices with intact circumpulpal dentine and cementum; 2) a set in which these areas were removed; 3) another set consisting of slices with intact circumpulpal dentine and cementum; and 4) a set without cementum. These analyses show relatively small differences in isotopic composition between contiguous slices except that circumpulpal dentine appears to be the dominant control on lead concentration. There is a significant correlation (R2 = 0.19, p = 0.01, n = 34) of dentine lead concentration and rate of exchange with residence time from the country of origin and Australian lead, but there is no such correlation with enamel lead concentration. Analyses of permanent and deciduous teeth of subjects from other countries who have resided in Australia for varying lengths of time should resolve some of the questions arising from this pilot study. Images Figure 1.

Gulson, B L; Gillings, B R

1997-01-01

232

Computing H/D-Exchange rates of single residues from data of proteolytic fragments  

PubMed Central

Background Protein conformation and protein/protein interaction can be elucidated by solution-phase Hydrogen/Deuterium exchange (sHDX) coupled to high-resolution mass analysis of the digested protein or protein complex. In sHDX experiments mutant proteins are compared to wild-type proteins or a ligand is added to the protein and compared to the wild-type protein (or mutant). The number of deuteriums incorporated into the polypeptides generated from the protease digest of the protein is related to the solvent accessibility of amide protons within the original protein construct. Results In this work, sHDX data was collected on a 14.5 T FT-ICR MS. An algorithm was developed based on combinatorial optimization that predicts deuterium exchange with high spatial resolution based on the sHDX data of overlapping proteolytic fragments. Often the algorithm assigns deuterium exchange with single residue resolution. Conclusions With our new method it is possible to automatically determine deuterium exchange with higher spatial resolution than the level of digested fragments.

2010-01-01

233

CFD Simulation Studies on the Performance of Rectangular Coil Heat Exchanger  

NASA Astrophysics Data System (ADS)

The simulation studies are made to understand the concept of heat transfer by convection in a rectangular coiled type heat exchanger. The rectangular coil heat exchanger consists of inner and outer coil arrangements with several straight portions and bends so that the exterior flow is very similar to flow within tube-bundles. The present work focuses mainly on exploring the various flow pattern and temperature distribution through the pipe. Computer simulation studies were performed for four different angle of tube bundle inclination (0°, 30°, 60°, and 90°) with two set flow arrangements (inline and staggered arrangement) in the shell side of the heat exchanger. The simulation results show that the effect of the tube bundle inclination on the fluid velocity distribution and the heat transfer performance is observed maximum for the coil with tube bundle inclination angle between 30 degrees and 60 degrees with the staggered arrangement than with the inline arrangement due to proper mixing in the shell side and the outside flow over the tube bundle helps to create turbulence without increasing the velocity in the shell side of the heat exchanger.

Samsudeen, N.; Anantharaman, N.; Raviraj, Pol.

2010-10-01

234

Point Defiance: a case study of the United States’ first public needle exchange in Tacoma, Washington  

Microsoft Academic Search

The first publicly funded needle exchange program in the United States began in Tacoma, Washington, in August 1988. The exchange's history is characterized by a series of firsts: the first American publicly funded exchange; the first pharmacy exchange; the first American needle delivery program; and the first state Supreme Court ruling not only supporting the existence of a needle exchange

Susan G. Sherman; Dave Purchase

2001-01-01

235

Fragmentation of doubly-protonated peptide ion populations labeled by H/D exchange with CD(3)OD.  

PubMed

Doubly-protonated bradykinin (RPPGFSPFR) and an angiotensin III analogue (RVYIFPF) were subjected to hydrogen/deuterium (H/D) exchange with CD(3)OD in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. A bimodal distribution of deuterium incorporation was present for bradykinin after H/D exchange for 90 s at a CD(3)OD pressure of 4 x 10(-7) Torr, indicating the existence of at least two distinct populations. Bradykinin ion populations corresponding to 0-2 and 5-11 deuteriums (i.e., D(0), D(1), D(2), D(5), D(6), D(7), D(8), D(9), D(10), and D(11)) were each monoisotopically selected and fragmented via sustained off-resonance irradiation (SORI) collision-induced dissociation (CID). The D(0)-D(2) ion populations, which correspond to the slower exchanging population, consistently require lower SORI amplitude to achieve a similar precursor ion survival yield as the faster-reacting (D(5)-D(11)) populations. These results demonstrate that conformation/protonation motif has an effect on fragmentation efficiency for bradykinin. Also, the partitioning of the deuterium atoms into fragment ions suggests that the C-terminal arginine residue exchanges more rapidly than the N-terminal arginine. Total deuterium incorporation in the b(1)/y(8) and b(2)/y(7) ion pairs matches very closely the theoretical values for all ion populations studied, indicating that the ions of a complementary pair are likely formed during the same fragmentation event, or that no scrambling occurs upon SORI. Deuterium incorporation into the y(1)/a(8) pseudo-ion pair does not closely match the expected theoretical values. The other peptide, doubly-protonated RVYIFPF, has a trimodal distribution of deuterium incorporation upon H/D exchange with CD(3)OD at a pressure of 1 x 10(-7) Torr for 600 s, indicating at least three distinct ion populations. After 90 s of H/D exchange where at least two distinct populations are detected, the D(0)-D(7) ion populations were monoisotopically selected and fragmented via SORI-CID over a range of SORI amplitudes. The precursor ion survival yield as a function of SORI amplitude falls into two distinct behaviors corresponding to slower- and faster-reacting ion populations. The slower-reacting population requires larger SORI amplitudes to achieve the same precursor ion survival yield as the faster exchanging population. Total deuterium incorporation into the y(2)/b(5) ion pairs matches closely the theoretical values over all ion populations and SORI amplitudes studied. This result indicates the y(2) and b(5) ions are likely formed by the same mechanism over the SORI amplitudes studied. PMID:18802500

Herrmann, Kristin A; Kuppannan, Krishna; Wysocki, Vicki H

2006-01-01

236

SEA-0400, a potent inhibitor of the Na+/Ca2+ exchanger, as a tool to study exchanger ionic and metabolic regulation.  

PubMed

The effects of a new, potent, and selective inhibitor of the Na(+)/Ca(2+) exchange, SEA-0400 (SEA), on steady-state outward (forward exchange), inward (reverse exchange), and Ca(2+)/Ca(2+) transport exchange modes were studied in internally dialyzed squid giant axons from both the extra- and intracellular sides. Inhibition by SEA takes place preferentially from the intracellular side of the membrane. Its inhibition has the following characteristics: it increases synergic intracellular Na(+) (Na(i)(+)) + intracellular H(+) (H(i)(+)) inactivation, is antagonized by ATP and intracellular alkalinization, and is enhanced by intracellular acidification even in the absence of Na(+). Inhibition by SEA is still present even after 1 h of its removal from the experimental solutions, whereas removal of the cointeracting agents of inhibition, Na(i)(+) and H(i)(+), even in the continuous presence of SEA, releases inhibition, indicating that SEA facilitates the reversible attachment of the natural H(i)(+) and Na(i)(+) synergic inhibitors. On the basis of a recent model of squid Na(+)/Ca(2+) exchange regulation (DiPolo R and Beauge L. J Physiol 539: 791-803, 2002), we suggest that SEA acts on the H(i)(+) + Na(i)(+) inactivation process and can interact with the Na(+)-free and Na(+)-bound protonized carrier. Protection by ATP concurs with the antagonism of the nucleotide by H(i)(+) + Na(i)(+) synergic inhibition. PMID:15703202

Beaugé, Luis; DiPolo, Reinaldo

2005-02-09

237

Ion-exchange of monovalent and bivalent cations with NaA zeolite membranes : a molecular dynamics study  

NASA Astrophysics Data System (ADS)

Molecular simulations using the method of molecular dynamics have been carried out to study the dynamics and energetics of ion exchanges between monovalent and bivalent cations in supercritical and subcritical (liquid) electrolyte solutions (here Li+, and Ca++ in aqueous solutions of LiCl and CaCl2) and an ion exchange membrane (NaA zeolite) using direct simulations of up to a nanosecond or more. NaA zeolites are widely used in many commercial ion-exchange processes including detergents. Results show that with appropriate driving forces, such ion exchange processes can be clearly witnessed and investigated using molecular simulations at these timescales, especially for supercritical solutions. An attempt is made to understand the phenomenon of ion exchange at the molecular level. Results have shown that the ion-exchange process is primarily energetically driven and entropic forces do not appear to be playing a significant role in the exchanges observed. For supercritical LiCl solutions, small differences were found between the energy of the Li+ inside and outside the membrane. In contrast, for Na+ there was a considerable energetic advantage in being outside the membrane, making the overall exchange process energetically favourable. In subcritical (liquid) LiCl solutions an exchange was found to be more favourable energetically than supercritical solutions. For Ca++ similar trends were observed, except the differences in the energies were much larger (compared to the corresponding Li+ exchanges), making them more energetically efficient, as has also been observed experimentally. In addition to clarifying the molecular basis for these exchanges, simulations can also potentially be very useful to determine the behaviour (e.g. state dependence, etc.) of hydrodynamic parameters commonly used to characterize ion-exchange processes at a fundamental molecular level, and to determine if the hydrodynamic equations used for ion-exchange processes are applicable to nano-systems that can be studied using simulations.

Murad, S.; Jia, W.; Krishnamurthy, M.

2004-01-01

238

Experimental study of mixed convection heat transfer in vertical helically coiled tube heat exchangers  

SciTech Connect

In this study the mixed convection heat transfer in a coil-in-shell heat exchanger for various Reynolds numbers, various tube-to-coil diameter ratios and different dimensionless coil pitch was experimentally investigated. The experiments were conducted for both laminar and turbulent flow inside coil. Effects of coil pitch and tube diameters on shell-side heat transfer coefficient of the heat exchanger were studied. Different characteristic lengths were used in various Nusselt number calculations to determine which length best fits the data and several equations were proposed. The particular difference in this study in comparison with the other similar studies was the boundary conditions for the helical coils. The results indicate that the equivalent diameter of shell is the best characteristic length. (author)

Ghorbani, N. [School of Mechanical Engineering, University of Leeds, Leeds, England (United Kingdom); Taherian, H. [Department of Engineering Technology and Industrial Distribution, Texas A and M University, College Station, TX (United States); Gorji, M. [Department of Mechanical Engineering, Babol Noushirvani University of Technology, Babol (Iran); Mirgolbabaei, H. [Department of Mechanical Engineering, Islamic Azad University, Jouybar branch, Jouybar (Iran)

2010-10-15

239

Effects of temperature and pH on the water exchange through erythrocyte membranes: Nuclear magnetic resonance studies  

Microsoft Academic Search

Summary The temperature and pH dependence of water exchange has been studied on isolated erythrocytes suspended in isotonic buffered solutions. At pH 7.4 a break in the Arrhenius plot of water exchange time at around 26°C was found. The mean value of the apparent activation energy of the water exchange time at temperatures higher than that of the discontinuity was

Vasile V. Morariu; Victor I. Pop; Octavian Popescu; Gheorghe Benga

1981-01-01

240

Crystallographic study of the ammonium\\/potassium 12-molybdophosphate ion-exchange system  

Microsoft Academic Search

Ammonium and potassium 12-molybdophosphate crystals obtained by gel-diffusion methods, as well as the products obtained by subjecting the parent compounds to ion exchange in solutions containing the alternate cations, have been studied by single-crystal X-ray diffraction studies, using automatic counting techniques. Details of the structures of five compounds of the type (K, NH4, H3O)3(PO4)Mo12O36, which have all been refined to

J. C. A. Boeyens; Gloria J. McDougal; J. van R. Smit

1976-01-01

241

Mechanism of framework oxygen exchange in Fe-zeolites: a combined DFT and mass spectrometry study.  

PubMed

The role of framework oxygen atoms in N(2)O decomposition [N(2)O(g)?N(2)(g) and 1/2O(2)(g)] over Fe-ferrierite is investigated employing a combined experimental (N(2)(18)O decomposition in batch experiments followed by mass spectroscopy measurements) and theoretical (density functional theory calculations) approach. The occurrence of the isotope exchange indicates that framework oxygen atoms are involved in the N(2)O decomposition catalyzed by Fe-ferrierite. Our study, using an Fe-ferrierite sample with iron exclusively present as Fe(II) cations accommodated in the cationic sites, shows that the mobility of framework oxygen atoms in the temperature range: 553 to 593 K is limited to the four framework oxygen atoms of the two AlO(4)(-) tetrahedra forming cationic sites that accomodate Fe(II). They exchange with the Fe extra-framework (18)O atom originating from the decomposed N(2)(18)O. We found, using DFT calculations, that O(2) molecules facilitate the oxygen exchange. However, the corresponding calculated energy barrier of 87 kcal? mol(-1) is still very high and it is higher than the assumed experimental value based on the occurrence of the sluggish oxygen exchange at 553 K. PMID:23319377

Andrikopoulos, Prokopis C; Sobalik, Zdenek; Novakova, Jana; Sazama, Petr; Sklenak, Stepan

2013-01-14

242

Studies of Ion Exchange and Chelation Compounds Adsorbed on Granular Graphite.  

National Technical Information Service (NTIS)

Several compounds that have particular ion exchange or chelation properties have been adsorbed on granular graphite and coke. The resulting materials exhibit ion exchange and chelation properties similar to typical commercial exchange resins used for sepa...

J. L. Hern

1976-01-01

243

Experimental study on corrugated cross-flow air-cooled plate heat exchangers  

SciTech Connect

Experimental study on cross-flow air-cooled plate heat exchangers (PHEs) was performed. The two prototype PHEs were manufactured in a stack of single-wave plates and double-wave plates in parallel. Cooling air flows through the PHEs in a crosswise direction against internal cooling water. The heat exchanger aims to substitute open-loop cooling towers with closed-loop water circulation, which guarantees cleanliness and compactness. In this study, the prototype PHEs were tested in a laboratory scale experiments. From the tests, double-wave PHE shows approximately 50% enhanced heat transfer performance compared to single-wave PHE. However, double-wave PHE costs 30% additional pressure drop. For commercialization, a wide channel design for air flow would be essential for reliable performance. (author)

Kim, Minsung; Baik, Young-Jin; Park, Seong-Ryong; Ra, Ho-Sang [Solar Thermal and Geothermal Research Center, Korea Institute of Energy Research, Daejeon 305-343 (Korea); Lim, Hyug [Research and Development Center, LHE Co., Ltd., Gimhae 621-874 (Korea)

2010-11-15

244

Solar Wind Charge Exchange Studies Of Highly Charged Ions On Atomic Hydrogen  

Microsoft Academic Search

Accurate studies of low-energy charge exchange (CX) are critical to understanding underlying soft X-ray radiation processes in the interaction of highly charged ions from the solar wind with the neutral atoms and molecules in the heliosphere, cometary comas, planetary atmospheres, interstellar winds, etc.. Particularly important are the CX cross sections for bare, H-like, and He-like ions of C, N, O

I. N. Draganic´; D. G. Seely; D. McCammon; C. C. Havener

2011-01-01

245

A NMR study of the hydration of sulfo and carboxyl groups in perfluorinated cation exchange membranes  

Microsoft Academic Search

The mobility of the polymer matrix and the structure of the hydration complex in the acid forms of perfluorinated ion exchange\\u000a membranes MF-4SK and F-4KF depending on moisture content were studied by 1H, 13C, and 19F solid-state high-resolution NMR. A correlation between an increase in mobility of separate polymer matrix segments under\\u000a hydration conditions and their hydrophilic properties was observed.

S. L. Shestakov; A. A. Pavlov; A. V. Maksimychev; A. V. Chernyak; V. I. Volkov; S. V. Timofeev

2010-01-01

246

The combined effect of rain and wind on air–water gas exchange: A feasibility study  

Microsoft Academic Search

A series of experiments were conducted at University of Delaware's Air–Sea Interaction Laboratory to examine the combined effects of rain and wind on air–water gas exchange. During this study, ASIL WRX I, a combination of 3 rain rates and 4 wind speeds were used, for a total of 12 different environmental conditions. The SF6 evasion method was used to determine

David T. Ho; Fabrice Veron; Emily Harrison; Larry F. Bliven; Nicholas Scott; Wade R. McGillis

2007-01-01

247

Determining carbon isotope signatures from micrometeorological measurements: Implications for studying biosphere–atmosphere exchange processes  

Microsoft Academic Search

In recent years considerable effort has been focused on combining micrometeorological and stable isotope techniques to partition\\u000a net fluxes and to study biosphere–atmosphere exchange processes. While much progress has been achieved over the last decade,\\u000a some new issues are beginning to emerge as technological advances, such as laser spectroscopy, permit isotopic fluxes to be\\u000a measured more easily and continuously in

T. J. Griffis; J. Zhang; J. M. Baker; N. Kljun; K. Billmark

2007-01-01

248

Benefits and problems of electronic information exchange as perceived by health care professionals: an interview study  

Microsoft Academic Search

BACKGROUND: Various countries are currently implementing a national electronic patient record (n-EPR). Despite the assumed positive effects of n-EPRs, their overall adoption remains low and meets resistance from health care providers. This study aims to increase our understanding of health care providers' attitude towards the n-EPR, by investigating their perceptions of the benefits and problems of electronic information exchange in

M. Zwaanswijk; R. A. Verheij; F. J. Wiesman; R. D. Friele

2011-01-01

249

Tunable diode laser absorption spectroscopy for stable isotope studies of ecosystem–atmosphere CO 2 exchange  

Microsoft Academic Search

The stable isotope content of atmospheric CO2 provides information about ecosystem carbon–water relations and biosphere–atmosphere carbon exchange. Virtually every isotope study within these fields has required air sample collection at remote locations followed by isotope analysis at a laboratory. This requirement severely limits sampling frequency and experiment duration. In this paper, we evaluate a tunable diode laser absorption spectrometer (TDL)

David R. Bowling; Steve D. Sargent; Bert D. Tanner; James R. Ehleringer

2003-01-01

250

A Study of Jordanian University Students' Perceptions of Using Email Exchanges with Native English Keypals for Improving Their Writing Competency  

ERIC Educational Resources Information Center

|English foreign language learners generally tend to consider email exchanges with native speakers (NSs) as an effective tool for improving their foreign language proficiency. This study investigated Jordanian university students' perceptions of using email exchanges with native English keypals (NEKs) for improving their writing competency. A…

Mahfouz, Safi Mahmoud

2010-01-01

251

A study on the thermal contact conductance in fin–tube heat exchangers with 7 mm tube  

Microsoft Academic Search

The thermal contact resistance has been frequently neglected in the process of design of heat exchangers because of the difficulty of measurement and the lack of accurate data. However, the thermal contact resistance is one of principal parameters in heat transfer mechanism of fin–tube heat exchangers. The objective of the present study is to investigate new factors such as fin

Jin Jeong; Chang Nyung Kim; Baek Youn

2006-01-01

252

A Motivation Case Study of English/Japanese Language Exchange Partners Using Computer Mediated Communication and Telecommunication.  

ERIC Educational Resources Information Center

This case study examines the motivation of two intermediate foreign language learners engaged in a remote language exchange partnership. A learner of English in Japan and a learner of Japanese in Australia completed language exchange activities using the telephone, Internet text chat, and e-mail over 10 weeks. Quantitative and qualitative methods…

Long, Robert Harrison

253

Fe magnetic moment formation and exchange interaction in Fe2P: A first-principles study  

NASA Astrophysics Data System (ADS)

Electronic structure and magnetic properties of Fe2P have been studied by a first-principles density functional theory calculation. The ground state is ferromagnetic and the calculated magnetic moments for Fe1 (3f) and Fe2 (3g) are 0.83 and 2.30?B, respectively. The nearest neighbor inter-site magnetic exchange coupling parameter at the Fe1 layer (0.02 mRy) is much smaller than that at the Fe2 layer (1.29 mRy). The Fe moment at the 3f site is metastable and sensitive to the inter-site exchange interaction with its magnetic neighbors, which is responsible for the first order magnetic transition and large magneto-caloric effect around TC.

Liu, X. B.; Ping Liu, J.; Zhang, Qiming; Altounian, Z.

2013-03-01

254

Study of a market model with conservative exchanges on complex networks  

NASA Astrophysics Data System (ADS)

Many models of market dynamics make use of the idea of conservative wealth exchanges among economic agents. A few years ago an exchange model using extremal dynamics was developed and a very interesting result was obtained: a self-generated minimum wealth or poverty line. On the other hand, the wealth distribution exhibited an exponential shape as a function of the square of the wealth. These results have been obtained both considering exchanges between nearest neighbors or in a mean field scheme. In the present paper we study the effect of distributing the agents on a complex network. We have considered archetypical complex networks: Erdös-Rényi random networks and scale-free networks. The presence of a poverty line with finite wealth is preserved but spatial correlations are important, particularly between the degree of the node and the wealth. We present a detailed study of the correlations, as well as the changes in the Gini coefficient, that measures the inequality, as a function of the type and average degree of the considered networks.

Braunstein, Lidia A.; Macri, Pablo A.; Iglesias, J. R.

2013-04-01

255

Water exchange in plant tissue studied by proton NMR in the presence of paramagnetic centers.  

PubMed Central

The proton NMR relaxation of water in maize roots in the presence of paramagnetic centers, Mn2+, Mn- EDTA2 -, and dextran-magnetite was measured. It was shown that the NMR method of Conlon and Outhred (1972, Biochem. Biophys. Acta. 288:354-361) can be applied to a heterogenous multicellular system, and the water exchange time between cortical cells and the extracellular space can be calculated. The water exchange is presumably controlled by the intracellular unstirred layers. The Mn- EDTA2 - complex is a suitable paramagnetic compound for complex tissue, while the application of dextran-magnetite is probably restricted to studies of water exchange in cell suspensions. The water free space of the root and viscosity of the cells cytoplasm was estimated with the use of Mn- EDTA2 -. The convenience of proton NMR for studying the multiphase uptake of paramagnetic ions by plant root as well as their transport to leaves is demonstrated. A simple and rapid NMR technique (spin-echo recovery) for continuous measurement of the uptake process is presented.

Bacic, G; Ratkovic, S

1984-01-01

256

Lead exchange into zeolite and clay minerals: A 29Si, 27Al, 23Na solid-state NMR study  

NASA Astrophysics Data System (ADS)

Chabazite, vermiculite, montmorillonite, hectorite, and kaolinite were used to remove Pb, through ion exchange, from 0.01 M aqueous Pb(NO 3) 2 solutions. These minerals contained 27 (Nachabazite), 16, 9, 9, and 0.4 wt% of Pb, respectively, after equilibration with the solutions. Ion exchange reached equilibrium within 24 h for Na-chabazite and vermiculite, but in less than 5 min for montmorillonite and hectorite. Na-chabazite took up more Pb than natural (Ca, Na)-chabazite (7 wt% Pb), whereas no such difference was observed in different cation forms of the clay minerals. Calcite impurities, associated with the clay minerals, effectively removed Pb from the aqueous solutions by the precipitation of cerussite (PbCO 3). 29Si, 27Al, and 23Na magic angle spinning (MAS) nuclear magnetic resonance (NMR), 23Na double rotation (DOR) NMR, and 23Na variable-temperature MAS NMR were used to study the ion exchange mechanisms. In Na-chabazite, cations in all three possible sites take part in the fast chemical exchange. The chemical exchange passes from the fast exchange regime to the slow regime at -80 to -100°C. One site contains a relatively low population of exchangeable cations. The other two more shielded sites contain most of the exchangeable cation. The exchangeable cations in chabazite and vermiculite were found to be close to the SiO 4 and AlO 4 tetrahedra, while those in the other clay minerals were more distant. Two sites (or groups of sites) for exchangeable cations were observed in hectorite. Lead tended to occupy the one which corresponds to the -8 ppm peak on the 23Na MAS NMR spectrum. The behaviour of the exchangeable cations in the interlayer sites was similar in all the clay minerals studied.

Liang, Jian-Jie; Sherriff, Barbara L.

257

International biomedical engineering exchanges  

Microsoft Academic Search

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

S. Somerwil; T. Easty

1995-01-01

258

Laboratory Studies of X-ray Spectra Formed by Charge Exchange  

NASA Astrophysics Data System (ADS)

Charge exchange between ions and neutral atoms or molecules has been accepted at an important soft producing process in our solar system. By extension, charge exchange may contribute to the X-ray emission of circumstellar material. It may also produce X-ray emission at the boundaries of supernova ejecta and star burst galaxies, or whenever hot plasma collides with neutral matter. X-ray spectra of K-shell and L-shell ions formed by charge exchange have now been studied in a variety of laboratory settings. These experiments have shown several characteristic features of line formation by charge exchange when compared to the X-ray emission produced by electron-impact excitation, e.g., enhancement emission of forbidden lines and of lines from levels with high principal quantum number. They have also shown a dependence on the interaction gas and on the energy of the ion-neutral collision. Moreover, the transfer of multiple electrons is typically preferred, provided the donor molecules or atoms have multiple valence-shell electrons. The laboratory measurements are in qualitative agreement with theory. However, the details of the observed X-ray spectra, especially those recorded with high spectral resolution, can differ substantially from predictions, especially for spectra produced at collision velocities equal to or lower than those found in thermal plasmas or produced with neutral gases other than atomic hydrogen. Puzzling discrepancies can be noted, such as enhanced emission from an upper level with the 'wrong' principal quantum number. Even more puzzling is a recent experiment in which two, co-mixed bare ion species of similar atomic number produce very different Lyman series emission upon charge exchange with a given neutral gas, defying both theoretical predictions and empirical scaling. Laboratory measurements have also shown that some of the characteristic features of charge exchange can be reproduced by radiative electron capture, i.e., by capture of a continuum electron. This process dominates in cold, photo-ionized plasmas, or when hot and cold plasmas mix. Work was performed under the auspices of the DOE by LLNL under contract DE-AC52-07NA27344 and supported in part by an award from NASA's APRA program.

Beiersdorfer, Peter; Ali, R.; Brown, G. V.; Koutroumpa, D.; Kelley, R. L.; Kilbourne, C.; Leutenegger, M. A.; Porter, F.

2013-04-01

259

Exchange-bias in amorphous ferromagnetic and polycrystalline antiferromagnetic bilayers: Structural study and micromagnetic modeling  

NASA Astrophysics Data System (ADS)

We study the role of the structure of antiferromagnetic polycrystalline metallic films in determining the magnetic properties of an exchange-coupled amorphous ferromagnetic layer. The bilayers are sputter-deposited, highly textured {111} Ir22Mn78 and Co65.5Fe14.5B20 thin films. We focus on structural characterization of Ir22Mn78 as a function of layer thickness in the range having the strongest influence over the exchange-bias field and training effect. We have used transmission electron microscopy to characterize defects in the form of interface steps and roughness, interdiffusion, twin- and grain-boundaries. Such defects can result in uncompensated magnetic spins in the antiferromagnet, which then contribute to exchange-bias. These experimental results form the basis of a general model, which uses finite element micromagnetic simulations. The model incorporates the experimental structural parameters of the bilayer by implementing a surface integral technique that allows numerical calculations to solve the transition from an amorphous to a granular structure. As a result, a detailed calculation of the underlying magnetic structure within the antiferromagnetic material is achieved. These calculations are in good agreement with micromagnetic imaging using Lorentz transmission electron microscopy and the macro-magnetic properties of these bilayers.

Kohn, A.; Dean, J.; Kovacs, A.; Zeltser, A.; Carey, M. J.; Geiger, D.; Hrkac, G.; Schrefl, T.; Allwood, D.

2011-04-01

260

Microfluidic device for rapid solution exchange to study kinetics of cell physiology  

NASA Astrophysics Data System (ADS)

Exchanging the extracellular solution of the cell rapidly (less than 10ms) is an important requirement in study the kinetics of cell physiology. A microfluidic device is developed to exchange the solution around the cells as they flow through a junction at the intersection of two microfluidic channels. The solution exchange time is measured experimentally by fluorescently labeling the cell surface membranes with a styryl dye, FM1-43 or FM 2-10, and then observing the time course of cell fluorescence decay following the rapid drop in the extracellular concentration of the FM dye that occurs as the cell flows past the fluidic junction. A numerical model is developed to guide the experimental design of microfluidic device. In the model, the motion of a single cell through a fluid junction is simulated and the mixing process of the solutions is solved. The model also includes the kinetics of departitioning of FM dyes from the cell membrane. The departitioning time constants for the FM dyes are determined from fitting the measured data of the cell fluorescence decay. This departitioning kinetics is important as FM dyes are commonly used to label cell membranes for the purpose of measuring the release of neurotransmitter from synaptic vesicles via exocytosis and the subsequent reuptake of vesicular membrane by endocytosis.

Hu, Howard; Honnatti, Meghana; Gillis, Kevin

2006-11-01

261

The use of multiple AUVs in FASTNEt: a study of Ocean Shelf Exchange  

NASA Astrophysics Data System (ADS)

We present early results and future plans from the £ 4.5M UK NERC-funded project FASTNEt (Fluxes Across the Sloping Topography of the North East Atlantic). The shelf edge is the controlling gateway to exchange of nutrients and carbon between oceanic and shelf waters, with impacts on global climate and on regional resources. As a result the shelf edge has been the focus of a number of studies which have improved our understanding of exchange processes. However, there are significant deficiencies in the current understanding of shelf edge exchange transport due largely to the sparseness of observations. Gliders and long-endurance AUVs look set to change this and are an important aspect of FASTNEt. We will report on the evolution of physical processes during the breakdown of seasonal stratification at the Celtic shelf edge observed by Glider pairs from June 2012 to January 2013. Glider CTD profiles have been ported realtime onto the GTS, and assimilation into UK Met Office forecast models has been trialled. We will report on 9-days of continuous Glider-based microstructure profiling made near the shelf break in June 2012, revealing the temporal variability of shelf-break generated turbulent mixing. Finally we will present plans to use long endurance AUVs to quantify the seasonal variations in the off-shelf bottom Ekman drain at the Malin Shelf edge during 2013/14.

Inall, Mark; Sherwin, Toby; Smeed, David; Palmer, Matthew; Porter, Marie; Dumont, Estelle

2013-04-01

262

A continuous stirred tank reactor study on chromic acid removal by ion exchange  

SciTech Connect

Dilute chromic acid removal by anion exchange was studied using a continuous stirred tank reactor (CSTR) system. A rate model based on film diffusion control was formulated for quantitative study on the chromate removal. For simplicity, the rate and mass balance equations were formulated for total Cr(VI) concentration. Equations were derived for the effluent concentration history as well as the time-dependent Cr(VI) concentration in the resin. The derived equations for solid and liquid phase Cr(VI) concentration variations were tested and verified by the experimental results obtained. Effects of various operating conditions, such as resin size, feed concentration, and flow rate, were also discussed.

Tan, Henry K.S. [National Chiao Tung Univ., Hsinchu (Taiwan, Province of China). Dept. of Applied Chemistry

1998-06-01

263

Comparative study of density-functional theories of the exchange-correlation hole and energy in silicon  

SciTech Connect

We present a detailed study of the exchange-correlation hole and exchange-correlation energy per particle in the Si crystal as calculated by the variational Monte Carlo method and predicted by various density-functional models. Nonlocal density-averaging methods prove to be successful in correcting severe errors in the local-density approximation (LDA) at low densities where the density changes dramatically over the correlation length of the LDA hole, but fail to provide systematic improvements at higher densities where the effects of density inhomogeneity are more subtle. Exchange and correlation considered separately show a sensitivity to the nonlocal semiconductor-crystal environment, particularly within the Si bond, which is not predicted by the nonlocal approaches based on density averaging. The exchange hole is well described by a bonding-orbital picture, while the correlation hole has a significant component due to the polarization of the nearby bonds, which partially screens out the anisotropy in the exchange hole.

Cancio, A. C.; Chou, M. Y.; Hood, Randolph Q.

2001-09-15

264

Hydrogen\\/deuterium Polarized Target at Mit-Bates  

Microsoft Academic Search

MIT-Bates Linear Accelerator Center conducts experiments with a polarized internal target in the electron storage ring. The target includes an Atomic Beam Source (ABS), a storage cell and a polarimeter. Bates ABS is the first installation of the kind operated inside a magnetic spectrometer in the presence of a magnetic field exceeding 2 kG. The paper describes the specific features

E. Ihloff; H. Kolster; N. Meitanis; R. Milner; A. Shinozaki; E. Tsentalovich; V. Ziskin; Y. Xiao; C. Zhang

2005-01-01

265

Kinetic Method for Hydrogen-Deuterium-Tritium Mixture Distillation Simulation  

SciTech Connect

Simulation of hydrogen distillation plants requires mathematical procedures suitable for multicomponent systems. In most of the present-day simulation methods a distillation column is assumed to be composed of theoretical stages, or plates. However, in the case of a multicomponent mixture theoretical plate does not exist.An alternative kinetic method of simulation is depicted in the work. According to this method a system of mass-transfer differential equations is solved numerically. Mass-transfer coefficients are estimated with using experimental results and empirical equations.Developed method allows calculating the steady state of a distillation column as well as its any non-steady state when initial conditions are given. The results for steady states are compared with ones obtained via Thiele-Geddes theoretical stage technique and the necessity of using kinetic method is demonstrated. Examples of a column startup period and periodic distillation simulations are shown as well.

Sazonov, A.B.; Kagramanov, Z.G.; Magomedbekov, E.P. [Mendeleyev University of Chemical Technology of Russia (Russian Federation)

2005-07-15

266

Follow-Up Study of Infants with Blood Incompatibilities and Idiopathic Hyperbilirubinemia with Emphasis on Exchange Transfusions.  

National Technical Information Service (NTIS)

This study was undertaken to investigate whether the administration of extraneous agents in exchange transfusions which may contain latent viruses result in any diseases in later life (leukemia in particular) over and above control populations which did n...

E. Schlesinger

1970-01-01

267

Experimental Study of Heat Transfer and Pressure Drop Characteristics of Air\\/Water and Air-Steam\\/Water Heat Exchange in a Polymer Compact Heat Exchanger  

Microsoft Academic Search

Experiments of heat transfer and pressure drop in a polymer compact heat exchanger made of PolyVinyliDene-Fluoride were conducted under various conditions for air\\/water heat exchange and air-steam\\/water heat exchange, respectively. The overall heat transfer coefficients of air-steam\\/water heat exchange (150 to 600 W\\/mK) are much greater than that of air\\/water heat exchange (80 to 130 W\\/mK). The pressure drops of

Lixin Cheng; CEES W. M. VAN DER GELD

2005-01-01

268

Mathematical Model for the Study of Hemorrhagic Shock and Fluid Resuscitation: Transcapillary Exchange.  

National Technical Information Service (NTIS)

Mathematical models used to predict plasma volume responses to hemorrhage and fluid resuscitation must consider both fluid and solute exchange across the capillary wall. In this paper, we review four models of transcapillary exchange that might be incorpo...

T. J. Doherty

1993-01-01

269

A study of spin-exchange polarization transfer in hydrogen-rubidium collisions  

NASA Astrophysics Data System (ADS)

The results of experimental studies of basic limitations on optical pumping of high density rubidium vapor are presented. A maximum 40% proton polarization was obtained in a spin exchange optically pumped polarized H- ion source using a 30 cm long dry-film coated cell. About 50% polarization was measured with a 90 cm long copper uncoated cell at a Rb thickness of 8×1014 atoms/cm2. A pulsed Ti:sapphire laser was used for optical pumping of Rb with up to 1 kW pulsed power, 200 ?sec pulse duration, and 10-15 GHz linewidth.

Zelenski, A. N.; Kokhanovski, S. A.

1993-12-01

270

Monte Carlo simulation study of exchange biased hysteresis loops in nanoparticles  

NASA Astrophysics Data System (ADS)

We present the results of Monte Carlo simulations of the magnetic properties of a model for a single nanoparticle consisting in a ferromagnetic core surrounded by an antiferromagnetic shell. The simulations of hysteresis loops after cooling in a magnetic field display exchange bias effects. In order to understand the origin of the loop shifts, we have studied the thermal dependence of the shell and interface magnetizations under field cooling. These results, together with inspection of the snapshots of the configurations attained at low temperature, show the existence of a net magnetization at the interface which is responsible for the bias of the hysteresis loops.

Iglesias, Òscar; Labarta, Amílcar

2006-02-01

271

Study of cation-exchange capacity of soil near fluorspar mining with special reference to Kadipani mine (Gujarat, India).  

PubMed

One of the important functions of soil is exchange of cations, whereby essential trace metals are made available to plants as nutrients. Both minerals and organics fractions of soil exchange the cations. Clay minerals exchange cation because of the presence of negatively charged sites on the mineral while organic materials exchange cations by means of their carboxylate groups and other basic functional groups. Cation exchange in soil provides trace metal nutrients to plant. The metal ions are taken up by the roots while H+ is exchanged for the metal ions. Therefore, the measurement of Cation Exchange Capacity (CEC) of soil is important and this becomes more significant when the mining activity is carried out in the surrounding environment as mining activity may adversely impact the soil texture and organic matter content and sometimes changes the pH which is the main regulator of CEC in soil. The studies related to the assessment of CEC of soil were carried out. 14 soil samples, including one sample of mine site, were collected during summer season from different villages within 10 km radius from the mine site. These samples were then analyzed. The efforts were made to establish the CEC of soil quality of Kadipani, Distt. Vadodara, Gujarat, India. This study is useful for making the decisions regarding the environmental measures required for mining activity. PMID:23505823

Pradhan, Alka; Deshmukh, Jitendra P

2011-10-01

272

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

Microsoft Academic Search

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

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

1996-01-01

273

Condensing heat exchanger microbial growth and control study-phase 2  

Microsoft Academic Search

The Space Station Temperature and Humidity Control Condensing Heat Exchangers will be utilized to collect and remove atmospheric water vapor generated by the metabolic and hygienic activity of crew members. The porous hydrophillic coating within the heat exchangers will always be wet. Cabin air will continuously flow through the heat exchangers during system operation which makes them a potential site

R. W. Marsh; M. E. Caron; C. Metselaar; J. Steele

1993-01-01

274

Experimental studies on coherent synchrotron radiaiton in the emittance exchange line at the Fermilab A0 Photoinjector  

SciTech Connect

Future accelerators will employ advanced beam conditioning systems such as emittance exchangers to manipulate high brightness beams. Coherent synchrotron radiation (CSR) in the dipoles could limit the performance of the emittance exchanger. In this paper, we report the experimental studies on measuring CSR and its effects on the beam at the A0 photoinjector in the emittance exchange line. After reporting the CSR power measurements, we report on the diagnostic scheme based on a weak skew quad in the emittance exchange line to study the CSR effects on the beam and other beam dynamics. In this work, we have reported on CSR measurements and the effect of skew quad on the dogleg line with the 5-cell turned on and off. We plan to study CSR effects on the bunch with the 5-cell on at larger chirp. This is will not only increase the CSR self-effect but also reduce the beamsize at the screen for convenient beamsize measurements.

Thangaraj, J.C.T.; Keup, R.; Johnson, A.; ruan, J.; Piot, P.; Church, M.; Edwards, H.; Lumpkin, A.; Sun, Y.-E.; Santucci, J.; /Fermilab

2011-03-01

275

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

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

276

Moessbauer studies of exchange-coupled two-iron centers in proteins  

SciTech Connect

This study reports Moessbauer measurements on three derivatives of the oxygen-transport protein hemerythrin and on the oxidized and reduced forms of uteroferrin, a purple acid phosphatase isolated from porcine uterine fluid. Both proteins contain an exchange-coupled pair of iron atoms coordinated directly to amino acid side chains. A model that takes account of both the exchange coupling and the zero-field splitting at each site is presented and used to describe the magnetic properties of the ground spin multiplet of a pair of coupled spins. One notable feature of the model is the fact that the g- and A-tensors of the coupled system may be quite anisotropic even if the corresponding single-site tensors are not. Preliminary studies of some non-Kramers systems are also presented. The Moessbauer spectrum of an azide derivative of deoxyhemerythrin broadens in a small applied field, indicating the presence of a near degeneracy. The spectrum of oxidized uteroferrin broadens as the temperature is raised, even in the absence of an applied field. No fully adequate explanation for the latter observation is apparent.

Sage, J.T.

1986-01-01

277

Theoretical study of annealed proton-exchanged Nd:LiNbO3 channel waveguide lasers with variational method  

Microsoft Academic Search

The controllable fabrication parameters, including anneal time, initial exchange time, channel width, dependences of TM00 mode size, corresponding effective refractive index, effective pump area, and coupling efficiency between pump and laser modes in z-cut annealed proton-exchanged (APE) Nd:LiNbO3 channel waveguide lasers were studied by using variational method. The effect of channel width on the surface index increment and the waveguide

Delong Zhang; Bo Wu; Yuanguo Xie; Guilan Ding; Yuming Cui; Caihe Chen

2001-01-01

278

Kinetics study on separation of cadmium from tellurium in acidic solution media using ion-exchange resins  

Microsoft Academic Search

The feasibility of using ion-exchange resins to separate cadmium from tellurium in acidic solutions of the two metals was investigated. We studied the competitive adsorption of cadmium and tellurium in such resins under varying acid strengths and contact time. We found that low sulfuric acid strength (i.e., 0.5M) was most effective in removing cadmium from solutions. Different ion-exchange resins were

Wenming Wang; Vasilis Fthenakis

2005-01-01

279

Experimental thermal performance study of an inclined heat pipe heat exchanger operating in high humid tropical HVAC systems  

Microsoft Academic Search

In an earlier paper [Y.H. Yau, Application of a heat pipe heat exchanger to dehumidification enhancement in tropical HVAC systems – a baseline performance characteristics study, International Journal of Thermal Sciences 46 (2) (2007) 164–171], the author had established the baseline performance characteristics of the eight-row wickless heat pipe heat exchanger (HPHX) for a vertical configuration under a range of

Y. H. Yau

2007-01-01

280

Study of the reductive solid-state ion exchange of indium into an NH 4-beta zeolite  

Microsoft Academic Search

The incorporation of indium(i) cations into zeolite beta by reductive solid-state ion exchange has been studied by TPR\\/TPO techniques, FTIR spectroscopy and a catalytic test reaction (isomerization of m-xylene). Among the hydroxyl groups observed in zeolite beta, those vibrating at 3610cm?1 (bridged hydroxyls) were found to be preferentially involved in the exchange process, resulting in In+ lattice cations. Reoxidation leads

R. M. Mihályi; H. K. Beyer; V. Mavrodinova; Ch. Minchev; Y. Neinska

1998-01-01

281

Impurity transport studies on Alcator C-Mod tokamak using Charge Exchange Recombination Spectroscopy  

NASA Astrophysics Data System (ADS)

A Charge-Exchange Recombination Spectroscopy (CXRS) diagnostic has been installed on Alcator C-Mod to study the transport of light impurities in plasma. The system provides spatially (1 cm) and temporally (12.5 msec) resolved measurements of the impurity density, temperature and flow velocities of the particular impurity. Two optical arrays: poloidal (19 channels) and toroidal (10 channels), collect the light emitted from excited impurity ion populated by charge exchange process from the Diagnostic Neutral Beam (DNB) particle. The attention of this dissertation is focused on the B4+ (n = 7 ? 6) spectral line emitted by B4+ ion formed in the following charge exchange reaction (H0 + B5+ ? H+ + B4+*). A complex spectral model was developed to simulate emission. The high magnetic fields of C-Mod result in broad Zeeman patterns which must be taken into account for the interpretation of the line shift and broadening in terms of impurity ion velocity and temperature. After the spectral line fitting and careful identification of the charge exchange component, the calculated Doppler broadening and shifts of the spectral line profile yield information on the ion temperature and rotation. Together with the calculation of the beam density, the absolute calibration of the CXRS optical system provides us with B5+ density measurement capabilities. One of the main objectives of this work was to use the acquired impurity density, temperature and flow velocity profiles to investigate plasma transport behavior and infer the radial electric field ER from plasma force balance equation. The focus here was placed on the region of the Internal Transport Barrier (ITB) formation 0.35 < rho < 0.8. Radial electric field ER is readily calculated in the region of the ITB foot using measured B5+ profiles. ExB velocity shearing turbulence stabilization are believed to play an important role in the physics of the ITB formation. The computed ER profiles demonstrated the large difference between the H-mode and ITB discharges. Linear gyrokinetic stability analysis (GS2) demonstrated that shearing rate oExB prevails over the linear Ion Temperature Gradient (ITG) growth rates gammamax in the region where ITB forms.

Bespamyatnov, Igor Olegovich

282

Structural features of interferon-? aggregation revealed by hydrogen exchange  

PubMed Central

Using hydrogen-deuterium exchange (HX) and electrospray ionization mass spectrometry, we have investigated the stability and structural changes of recombinant human interferon-? (IFN-?) during aggregation induced by guanidine hydrochloride (GdnHCl) and potassium thiocyanate. First, HX labeling was initiated after the amorphous aggregates were formed to probe the tertiary structure of the aggregated state. Second, labeling was performed at low protein concentrations to assess stability under aggregation prone conditions. In 1 M GdnHCl, the stability of IFN-? was greatly reduced and much less protection from HX in solution was observed. Exchange under these conditions was slower in helix C than in the rest of the protein. Aggregates formed in 1 M GdnHCl showed a HX pattern consistent with a partially unfolded state with an intact helix C. Although aggregates formed in 0.3 M KSCN exhibited a HX pattern similar to those formed in GdnHCl, the solution phase HX pattern in 0.3 M KSCN was surprisingly comparable to that of the native state. Varying the aggregation time before performing HX revealed that KSCN first precipitated native protein and then facilitated partial unfolding of the precipitated protein. These results show that helix C, which forms the hydrophobic core of the IFN-? dimer, is highly protected from HX under native conditions, is more stable in GdnHCl than the rest of the protein and remains intact in both GdnHCl- and KSCN-induced aggregates. This suggests that native-state HX patterns may presage regions of the protein susceptible to unfolding during aggregation.

Tobler, Scott A.; Fernandez, Erik J.

2002-01-01

283

Stability of Coupling in Exchange Spring and Exchange Bias Systems.  

National Technical Information Service (NTIS)

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

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

2001-01-01

284

Study of interface wall energy in exchange-coupled double-layer film  

SciTech Connect

Recently, exchange-coupled multilayer films have been investigated intensively for the magneto-optical recording medium. We studied the interface wall energy density ({sigma}{sub {ital w}}) in the exchange-coupled double-layer TbFeCo films which were prepared by the dc-sputtering method. The composition of the first layer was Tb{sub {ital x}}(Fe{sub 85}Co{sub 15}){sub 100{minus}{ital x}} ({ital x}=14.0--35.0), and that of the second layer was fixed at the compensation composition of Tb{sub 23.8}(Fe{sub 85}Co{sub 15}){sub 76.2}. The magnitude of {sigma}{sub {ital w}} stored in the boundary was determined by the shift field of the minor hysteresis loop of the first layer measured with VSM. It was found that {sigma}{sub {ital w}} depended on the Tb content of the first layer. As a result, {sigma}{sub {ital w}} was correlated with the perpendicular anisotropy ({ital K}{sub {ital u}}), and well explained by the formula, {sigma}{sub {ital w}}{proportional to}({ital K}{sub {ital u}}){sup 1/2}. We can treat the interface wall energy practically as Bloch wall energy; however, {sigma}{sub {ital w}} was determined by the magnetic properties of both layers.

Tokunaga, T.; Taguchi, M.; Fukami, T.; Nakaki, Y.; Tsutsumi, K. (Mitsubishi Electric Corporation, 8-1-1, Tsukaguchi-Honmach, Amagasaki, Hyogo 661, Japan (JP))

1990-05-01

285

Experimental study of a two-phase thermosiphon-loop heat exchanger  

SciTech Connect

An experimental study of the performance of an air-to-air, multi-loop, two-phase thermosiphon heat-exchanger system, utilizing R-11 as the working fluid, has been carried out to investigate the effect of its previous thermal history for hot air to cold air temperature differences up to 50 Celsius degrees. Tests were run on a four loop system with equal face velocities of 1.3, 2.2 and 3.1 m/s at each coil and on a single loop system with a face velocity of 2.2 m/s. An hysterisis loop was found to exist on each plot of heat-exchanger effectiveness vs. overall temperature difference for temperature differences below 45 Celsius degrees. Boiling was not initiated until a difference of 13 degrees was reached. However, once initiated, boiling was not completely stopped until the temperature difference dropped below 4 degrees. The shape of the two bounding curves which form these hysteresis loops could be approximated very well by exponential curves.

Stauder, F.A.; McDonald, T.W.

1986-01-01

286

Sorption of sunset yellow dye by weak base anion exchanger-kinetic and equilibrium studies.  

PubMed

The sorption equilibrium and kinetics of Sunset Yellow dye in aqueous solutions on the weak base anion exchange resin Amberlite FPA51 were examined in this paper. The influences of phase contact time, solution pH, initial dye concentration and temperature were studied by the batch method. The amounts of dye sorbed at equilibrium changed from 9.9 to 48.7 mg/g with increasing initial dye concentration in the range 100-500 mg/L. The experimental data were analysed by the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models of adsorption. The maximum monolayer capacity was 130.6 mg/g. The sorption free energy was equal to 14.6 kJ/mol and revealed the nature of the ion exchange mechanism in this system. The kinetic data were modelled using the pseudo-first-order, pseudo-second-order (types 1-5) and intraparticle diffusion equations. The experimental data were well described by types 1-3 of the pseudo-second-order kinetic model. PMID:21780713

Wawrzkiewicz, Monika

287

Study of dipole interaction in micron-width NiFe/Cu/NiFe/NiO wire using exchange anisotropy  

SciTech Connect

The dipole interaction between a NiFe layer pinned by a NiO and a free NiFe layer in a micron-wide NiFe/Cu/NiFe/NiO wire was studied by changing the direction of the exchange bias from the NiO layer. The effect of the dipole interaction when the exchange bias was perpendicular to the wire axis was larger than that when the exchange bias was parallel to the wire axis, and was consistently explained by the stray field caused by the magnetic charges of the pinned layer. It was demonstrated that this method, using exchange anisotropy, is useful for investigating the dipole interaction between ferromagnetic materials separated by a nonmagnetic material in small-scale magnetic multilayers. {copyright} 2001 American Institute of Physics.

Kimura, Takashi; Itagaki, Yoshio; Wakaya, Fujio; Gamo, Kenji

2001-06-18

288

Growth, DNA repair, sister chromatid exchange and chromosome studies in fibroblasts from Huntington's disease patients.  

PubMed

Fibroblast cultures from six unrelated Huntington's Disease (HD) patients and controls and one affected relative of an HD patient were used in studies of cell growth, DNA repair, sister chromatid exchange (SCE) and chromosome aberrations. There were no significant differences in background levels of SCEs or of chromosome aberrations between HD cultures and controls. Preliminary results using epidermal growth factor indicated that HD cells may have a lowered relative response to this polypeptide hormone. Cell growth studies showed no correlation between growth rate and HD. Increased cell saturation density was recorded in cell lines from four of the HD patients; the remaining three lines from affected individuals (two of them related) were indistinguishable from control cultures. This variation may reflect genetic heterogeneity in HD. An apparent deficiency in DNA repair capacity following UV irradiation in cultures from three HD patients was subsequently shown to be the result of the increased cell saturation densities in these cultures. PMID:6459055

Delhanty, J D; Parrington, J M; Casey, G; Attwood, J; West, L; Kirk, D; Corney, G

1981-05-01

289

Theory of the Protein Equilibrium Population Snapshot by H/D Exchange Electrospray Ionization Mass Spectrometry (PEPS-HDX-ESI-MS) Method used to obtain Protein Folding Energies/Rates and Selected Supporting Experimental Evidence.  

PubMed

Protein equilibrium snapshot by hydrogen/deuterium exchange electrospray ionization mass spectrometry (PEPS-HDX-ESI-MS or PEPS) is a method recently introduced for estimating protein folding energies and rates. Herein we describe the basis for this method using both theory and new experiments. Benchmark experiments were conducted using ubiquitin because of the availability of reference data for folding and unfolding rates from NMR studies. A second set of experiments was also conducted to illustrate the surprising resilience of the PEPS to changes in HDX time, using staphylococcal nuclease and time frames ranging from a few seconds to several minutes. Theory suggests that PEPS experiments should be conducted at relatively high denaturant concentrations, where the protein folding/unfolding rates are slow with respect to HDX and the life times of both the closed and open states are long enough to be sampled experimentally. Upon deliberate denaturation, changes in folding/unfolding are correlated with associated changes in the ESI-MS signal upon fast HDX. When experiments are done quickly, typically within a few seconds, ESI-MS signals, corresponding to the equilibrium population of the native (closed) and denatured (open) states can both be detected. The interior of folded proteins remains largely un-exchanged. Amongst MS methods, the simultaneous detection of both states in the spectrum is unique to PEPS and provides a "snapshot" of these populations. The associated ion intensities are used to estimate the protein folding equilibrium constant (or the free energy change, ?G). Linear extrapolation method (LEM) plots of derived ?G values for each denaturant concentration can then be used to calculate ?G in the absence of denaturant, ?G(H(2)O). In accordance with the requirement for detection of signals for both the folded and unfolded states, this theoretical framework predicts that PEPS experiments work best at the middle of the denaturation curve where natured and denatured protein molecules are equilibrated at easily detectable ratios, namely 1:1. It also requires that closed and open states have lifetimes measurable in the time frame of the HDX experiment. Because both conditions are met by PEPS, these measurements can provide an accurate assessment of closed/open state populations and thus protein folding energies/rates. PMID:23436981

Liyanage, Rohana; Devarapalli, Nagarjuna; Pyland, Derek B; Puckett, Latisha M; Phan, N H; Starch, Joel A; Okimoto, Mark R; Gidden, Jennifer; Stites, Wesley E; Lay, Jackson O

2012-10-23

290

Comparative studies on electrochemical characterization of homogeneous and heterogeneous type of ion-exchange membranes  

Microsoft Academic Search

Interpolymer films of poly-ethylene and styrene-divinyl benzene copolymer were subjected to chlorosulfonation or chloromethylation then amination for the preparation of homogeneous type of cation- or anion-exchange membranes, respectively. Heterogeneous types of ion-exchange membranes were prepared from polyvinyl chloride (PVC) as binder and ion-exchange resin powder in tetrahydrofuran solvent. Membrane potential and conductance measurements have been carried out in NaCl(aq), CuCl2(aq)

G. S. Gohil; Vinod K. Shahi; R. Rangarajan

2004-01-01

291

Study of parallel and perpendicular exchange biases in FePt-FeMn multilayers  

SciTech Connect

A systematic investigation of parallel and perpendicular exchange biases in [FePt/FeMn]{sub 10} multilayers deposited onto MgO(100) substrates by ion beam sputter-deposition system is performed. The thickness (FeMn) dependences of exchange bias field and blocking temperature are discussed. The blocking temperature increases with the increase of FeMn thickness and becomes nearly constant as the FeMn thickness is beyond a critical value. Of interest is the blocking temperature of the parallel exchange bias which is higher than that of the perpendicular one. Also, the angular dependence of parallel and perpendicular exchange biases is investigated.

Phuoc, Nguyen N.; Suzuki, Takao [Information Storage Materials Laboratory, Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan)

2006-04-15

292

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

Microsoft Academic Search

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

Kenzi Hori; Yuji Hashitani; Yuji Kaku; Katsutoshi Ohkubo

1999-01-01

293

Thrombotic thrombocytopenic purpura: outcome in 24 patients with renal impairment treated with plasma exchange. Canadian Apheresis Study Group.  

PubMed

The Canadian Apheresis Study Group recently completed a randomized clinical trial involving 102 patients with thrombotic thrombocytopenic purpura (TTP), in which treatment with plasma infusion and treatment with plasma exchange were compared. Thirty-three other patients were ineligible or refused to be randomly assigned in the trial. Of the 33 patients, 24 were assessed as ineligible because they would be unable to tolerate the fluid input that would occur if they were randomly assigned to receive plasma infusion. All 24 patients had oliguria and elevated creatinine and/or blood urea nitrogen level. These 24 patients were treated with acetylsalicyclic acid, dipyridamole, and plasma exchange according to the standardized protocol defined in the trial. Blood for tests of factors possibly involved in the pathogenesis of TTP was drawn before exchange and at intervals during and after exchange. The mean platelet count before exchange was 35.5 x 10(9) per L. In 12 of the 24 patients, the platelet count reached 150 x 10(9) per L or greater by 7 days after the initiation of plasma exchange. Three patients responded partially, in that their platelet count increased to at least twice that at presentation, but remained below 150 x 10(9) per L. One patient died during the first week. Of the eight other patients who experienced treatment failure at the 7-day assessment point, six subsequently responded, four while continuing to receive plasma exchange and two after plasma exchange had been discontinued. Of the 15 patients who either responded fully or responded partially by the end of the first cycle, all survived.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1412677

Rock, G; Shumak, K; Kelton, J; Blanchette, V S; Buskard, N; Nair, R; Spasoff, R

1992-10-01

294

A kinetic simulation study of the mechanisms of aluminum induced layer exchange process  

NASA Astrophysics Data System (ADS)

The aluminum induced layer exchange (ALILE) process allows the formation of thin polycrystalline Si (poly-Si) layers of large grain size on foreign substrates such as glass at low process temperatures. This paper is devoted to a computer simulation study of the kinetics of the ALILE process taking into account the mechanisms of its separate stages: Si diffusion in the AlOx membrane, nucleation and growth of grains, and the formation of preferential (100) orientation. The characteristics of the ALILE process are explained based on the evolution of the Si concentration within the Al layer. In particular it is demonstrated that the characteristic suppression of nucleation after short annealing times results from a decrease in the Si concentration in the Al layer due to the growth of existing grains. A number of important parameters of ALILE process are estimated comparing the results of simulation to the experimental data.

Sarikov, Andrey; Schneider, Jens; Berghold, Juliane; Muske, Martin; Sieber, Ina; Gall, Stefan; Fuhs, Walther

2010-06-01

295

Study of X(3872) from effective field theory with pion-exchange interaction.  

PubMed

We study DD[over ¯]* (D*D[over ¯]) scattering in the framework of unitarized heavy meson chiral perturbation theory with pion exchange and a contact interaction. 3S1-3D1 mixing effects are taken into account. A loosely bound state X(3872), with the pole position being Mpole}=(3871.70-i0.39)??MeV, is found. The result is not sensitive to the strength of the contact interaction. Our calculation provides a theoretical confirmation of the existence of the 1++ state X(3872). The light quark mass dependence of the pole position indicates it has a predominately DD[over ¯]* (D*D[over ¯]) molecular nature. When the ? mass is larger than 142 MeV, the pole disappears, which makes impossible the lattice simulation of this state at large quark mass. PMID:23931357

Wang, P; Wang, X G

2013-07-24

296

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

PubMed

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

Vissers, Gé W M; McCoy, Anne B

2006-05-11

297

Air-Snow Exchange and Snow Photochemistry Studies at Summit, Greenland  

NASA Astrophysics Data System (ADS)

Summit has hosted nearly continuous investigations into air-snow exchange processes since the station was created to support deep drilling in 1989. Over the past 14 years many of these studies have targeted improved understanding of the photochemical processes occurring in the near surface snow and how these enhance the emission or uptake of reactive gases, and modify chemical cycling in the air just above the snow. Physical characteristics of the snow control snow photochemical processes through impacts on; the penetration of light, movement of firn air and reactive gases in firn air, uptake of surface active products, and surfaces available for heterogeneous reactions. Recent snow photochemistry campaigns at Summit will be summarized. New chemical instrumentation and sampling techniques that have been deployed will be briefly described. Most of these campaigns have also made measurements of select physical properties, but these have not generally been adequate to fully constrain the complex coupled physical-chemical system. Critical open questions will be presented.

Dibb, J. E.

2011-12-01

298

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

299

Protein adsorption dynamics in cation-exchange chromatography quantitatively studied by confocal laser scanning microscopy  

Microsoft Academic Search

A self-contained research system based on the technique of confocal laser scanning microscopy (CLSM) was put up to quantitatively analyze the dynamics of protein adsorption to porous cation exchanger by mathematical modeling. Bovine serum albumin adsorption to the cation exchanger SP Sepharose FF was performed by batch adsorption and micro-flow cell in which protein concentration in single absorbent was visualized

Kun Yang; Shu Bai; Yan Sun

2008-01-01

300

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

301

Comparative Study of Rotating Regenerators and Heat-Pipe Heat Exchangers. Final Report.  

National Technical Information Service (NTIS)

The aim of this research was to make a comparison between two types of heat exchangers operating in a practical environment. The heat wheel (rotating regenerator) and the heat pipe heat exchanger were intended to have efficiencies of between 60 and 80% an...

D. B. A . Macmichael D. A. F. E. Reay

1980-01-01

302

Kinetics of starch hydrolysis and glucose mutarotation studied by NMR chemical exchange saturation transfer (CEST)  

Microsoft Academic Search

The –OH resonance on –C1 of the ? and ?-anomers of glucose that are normally invisible in 1H NMR spectra, was used to monitor the reaction kinetics of starch hydrolysis in aqueous solutions. The exchangeable protons on glucose were detected indirectly through their exchange with water protons, and hence the water resonance, by using selective radiofrequency (RF) saturation at the

Anthony C. Dona; Guilhem Pages; Philip W. Kuchel

2011-01-01

303

CODEPENDENT VOLATILITY PATTERNS IN DAILY FOREIGN EXCHANGE AND INTEREST RATES: A CASE STUDY OF TURKEY  

Microsoft Academic Search

ABSTRACT In this paper, the main purpose is to detect the possible cross relationships between the volatilities of foreign exchange and interest rates in Turkey. In Turkey, it is seen that the volatilities of foreign exchange returns and daily interest yields are strongly correlated. This is because of the fact that Turkish financial markets are not deep enough to attract

Dundar Murat DEMIROZ

304

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

SciTech Connect

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

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

1999-04-01

305

Study of multi-electron ionization and charge exchange in HIBF  

NASA Astrophysics Data System (ADS)

Beam ion stripping on background gases or plasma in a Heavy Ion Beam Fusion (HIBF) chamber increases the charge state of the beam and the diameter of the focus, complicating the final focusing on the focusing target. To model beam transport in the chamber, it is necessary to know the beam charge-state evolution, including both ionization and charge exchange dynamics. The main objective of this research is to explore theoretical approaches including scaling law. Improved models are developed to calculate multi-electron loss, especially ion stripping and charge exchange cross sections, for both near-term experiments and future power plant scale HIBF research. First, a new space-charge neutralization approach that uses electron injection is proposed for the ion beam transport in HIBF chamber. An analytical study was performed to illustrate the plasma dynamics and final neutralization effects with this technique. The results examine the effect of different injected electron profiles. Next, to improve the accuracy of such simulations, methods to improve cross sections of ionization and charge exchange are studied. Both classical and quantum mechanical approaches are examined. Attention is focused on the interaction by low-charge-state heavy ions. Multi-electron processes for dressed ions, including screening and anti-screening effects, internuclear forces, are given special attention, This analysis is complex and requires a combining several different theoretical approaches. Finally, a Classic Trajectory Monte Carlo (CTMC) model based on an improvement of Olson's n-body CTMC method is presented. This model solves the n-body ion-atom ionization problem in a regime of intent to HIBF. In the paper, a new and complete computational module for these interactions has been developed. The cross section data for Xe, Cs, and Bi ions colliding with various background gases (Xe, N2, Ar and Flibe) is presented. After the calculation of the cross section data, the predicted energy dependence of the beam ion and background gas target is analyzed and scaling laws are developed to give a larger range of energies. Due to the scarcity of prior experimental and theoretical data, comparisons between the calculated data and prior data is limited to selected cases, The cross section data is being implemented into the Large Scale Plasmas (LSP) code package, a beam transport code that is widely used for HIBF studies. This improved LSP package can be used to study the effects of ionization on neutralized drift compression and focusing in HIBF. This code package studied will provide further physical insight into current neutralized transport experiments, and future HIBF studies. In addition to the study of atomic effects for HIBF, plasma dynamics in a low-energy radio frequency (RF) discharge is studied through the implementation of a new Monte Carlo Collision (MCC) module developed for including into a Particle-In-Cell (PIC) package, The MCC module uses available cross section data for the light ion-atom collisions as the input. The results illustrate the collision effects on particle transport in the discharge.

Wu, Linchun

306

Process Model for Studying Regional 13C Stable Isotope Exchange between Vegetation and Atmosphere  

NASA Astrophysics Data System (ADS)

The variation of the stable isotope 13CO2 in the air in exchange with land ecosystems results from fractionation processes in both plants and soil during photosynthesis and respiration. Its diurnal and seasonal variations therefore contain information on the carbon cycle. We developed a model (BEPS-iso) to simulate its exchange between vegetation and the atmosphere. To be useful for regional carbon cycle studies, the model has the following characteristics: (i) it considers the turbulent mixing in the vertical profile from the soil surface to the top of the planetary boundary layer (PBL); (ii) it scales individual leaf photosynthetic discrimination to the whole canopy through the separation of sunlit and shaded leaf groups; (iii) through simulating leaf-level photosynthetic processes, it has the capacity to mechanistically examine isotope discrimination resulting from meteorological forcings, such as radiation, precipitation and humidity; and (iv) through complete modeling of radiation, energy and water fluxes, it also simulates soil moisture and temperature needed for estimating ecosystem respiration and the 13C signal from the soil. After validation using flask data acquired at 20 m level on a tower near Fraserdale, Ontario, Canada, during intensive campaigns (1998-2000), the model has been used for several purposes: (i) to investigate the diurnal and seasonal variations in the disequilibrium in 13C fractionation between ecosystem respiration and photosynthesis, which is an important step in using 13C measurements to separate these carbon cycle components; (ii) to quantify the 13C rectification in the PBL, which differs significantly from CO2 rectification because of the diurnal and seasonal disequilibriums; and (iii) to model the 13C spatial and temporal variations over the global land surface for the purpose of CO2 inversion using 13C as an additional constraint.

Chen, J. M.; Chen, B.; Huang, L.; Tans, P.; Worthy, D.; Ishizawa, M.; Chan, D.

2007-12-01

307

Macrophyte biological methods used in the study of the exchange between the Rhine river and the groundwater  

Microsoft Academic Search

The purpose of this study is to demonstrate the efficiency of two biological methods in the study of the exchange between the canalized Rhine river and its riverside aquifer. The infiltration of Rhine water into the groundwater is revealed by a high level of eutrophicants and the micropollutant mercury. One method made use of the aquatic macrophyte communities as bioindicators

Isabelle Eglin; Ute Roeck; Fabienne Robach; Michèle Tremolieres

1997-01-01

308

Employee responses to relational fulfilment and work-life benefits : A social exchange study in the German public administration  

Microsoft Academic Search

Purpose – Investigating employee responses to relational fulfilment of the psychological contract and work-life benefits of a telecommuting program, this study aims to contribute to the literature on social exchange in employment. Design\\/methodology\\/approach – The setting of the study was the German public administration. Survey data from 947 Civil Servants were analyzed in structural equation models. Analysis of mean structure

Severin Hornung; Jürgen Glaser

2010-01-01

309

A preliminary study of amorphous silica deposition in a bench-scale liquid fluidized bed heat exchanger  

Microsoft Academic Search

Deposition of silica scale on heat transfer surfaces is a problem which must be solved before economic power generation from many high temperature geothermal brines will be possible. As a part of the liquid fluidized bed heat exchanger development project, a preliminary silica deposition study was conducted using a laboratory bench scale unit. The purpose of this study was to

K. L. Wagner; C. A. Allen

1976-01-01

310

Photoemission study of the upper limit to the change of the local exchange splitting at finite temperature  

NASA Astrophysics Data System (ADS)

A photoemission study at both room temperature and at 80 K of the valence bands of the disordered alloys PdFe, PdNi, PdCo, and PtFe is presented. The Cooper-minimum effect is used to study the impurity contribution to the photoemission signal, and hence the local density of states at the impurity site. The observed differences in the photoemission signal are discussed in terms of the local exchange splitting and an attempt is presented to quantify the change in the local exchange splitting by comparison to spectra calculated with an impurity model.

Kappert, R. J. H.; Borsje, H. R.; van Acker, J. F.; Horn, K.; Haak, H.; Buschow, K. H. J.; Fuggle, J. C.

1991-02-01

311

Toward a checklist for exchange and interpretation of data from a toxicology study.  

PubMed

Data from toxicology and toxicogenomics studies are valuable, and can be combined for meta-analysis using public data repositories such as Chemical Effects in Biological Systems Knowledgebase, ArrayExpress, and Gene Expression Omnibus. In order to fully utilize the data for secondary analysis, it is necessary to have a description of the study and good annotation of the accompanying data. This study annotation permits sophisticated cross-study comparison and analysis, and allows data from comparable subjects to be identified and fully understood. The Minimal Information About a Microarray Experiment Standard was proposed to permit deposition and sharing of microarray data. We propose the first step toward an analogous standard for a toxicogenomics/toxicology study, by describing a checklist of information that best practices would suggest be included with the study data. When the information in this checklist is deposited together with the study data, the checklist information helps the public explore the study data in context of time, or identify data from similarly treated subjects, and also explore/identify potential sources of experimental variability. The proposed checklist summarizes useful information to include when sharing study data for publication, deposition into a database, or electronic exchange with collaborators. It is not a description of how to carry out an experiment, but a definition of how to describe an experiment. It is anticipated that once a toxicology checklist is accepted and put into use, then toxicology databases can be configured to require and output these fields, making it straightforward to annotate data for interpretation by others. PMID:17442663

Fostel, Jennifer M; Burgoon, Lyle; Zwickl, Craig; Lord, Peter; Corton, J Christopher; Bushel, Pierre R; Cunningham, Michael; Fan, Liju; Edwards, Stephen W; Hester, Susan; Stevens, James; Tong, Weida; Waters, Michael; Yang, ChiHae; Tennant, Raymond

2007-04-17

312

Experimental study of an integral catalytic combustor: heat exchanger for Stirling engines  

SciTech Connect

An experimental study was conducted to determine the feasibility of using catalytic combustion with heat removal for the Stirling engine to reduce exhaust emissions and also improve heat transfer to the working fluid. The study was conducted using spaced parallel plates. An internally air-cooled heat exchnger was placed between two noble metal catalytic plates. A preheated fuel-air mixture passed between the plates and reacted on the surface of the catalyzed plates. Heat was removed from the catalytic surface by radiation and convection to the air-cooled heat exchangers to control temperature and minimize thermal NO/sub x/ emissions. The study was conducted at inlet combustion air temperatures from 850 to 900 K, inlet velocities of about 10 m/s, equivalence ratios from 0.5 to 0.9, and pressures from 1.3 x 10/sup 5/ to 2.0 x 10/sup 5/ Pa. Propane fuel was used for all testing. Combustion efficiencies greater than 99.5% were measured. NO/sub x/ emissions ranged from 1.7 to 3.3 g NO/sub 2//kg fuel. The results demonstrate the feasibility of the concept and indicate that further investigation of the concept is warranted.

Bulzan, D.L.

1982-01-01

313

Exchange transfusion in the neonate: a controlled study using frozen-stored erythrocytes resuspended in plasma.  

PubMed

During a nine-month period 43 consecutive infants who needed exchange transfusions for the management of their hyperbilirubinemia randomly received whole blood less than 5 days old (control group) or frozen erythrocytes diluted in plasma (experimental groups). There was no different prior to and after exchange transfusions in total protein, albumin, globulin, immunoglobulins, bilirubin, and hematocrit in the control group versus the experimental group. The efficacies of bilirubin removal, as measured by delta bilirubin, were the same in the two groups. Advantages of exchange transfusion with freeze-preserved erythrocytes suspended in type-specific plasma are discussed. PMID:945688

Grajwer, L A; Pildes, R S; Zarif, M; Ainis, H; Agrawal, B L; Patel, A

1976-07-01

314

Mechanism of the vapor-phase dehydration of cyclohexanol to cyclohexanone on a copper-magnesium catalyst  

Microsoft Academic Search

1.Study has been made of the hydrogen-deuterium exchange, in cyclohexanol under dehydrogenation conditions and in cyclohexanone under hydrogenation conditions, on a copper-magnesium cataiyst. The overall rate of exchange in the alcohol and the rates of exchange in the hydroxyl group and in thea positions are higher than the rate of dehydrogenation.2.Kinetic isotope effects have been measured for the replacement of

O. N. Medvedeva; B. S. Gudkov; A. S. Badrian; S. L. Kiperman

1977-01-01

315

Deuterium exchange and mass spectrometry reveal the interaction differences of two synthetic modulators of RXR? LBD  

PubMed Central

Protein amide hydrogen/deuterium (H/D) exchange was used to compare the interactions of two antagonists, UVI 2112 and UVI 3003, with that of the agonist, 9-cis-retinoic acid, upon binding to the human retinoid X receptor alpha ligand-binding domain (hRXR? LBD) homodimer. Analysis of the H/D content by mass spectrometry showed that in comparison to 9-cis-retinoic acid, the antagonists provide much greater protection toward deuterium exchange-in throughout the protein, suggesting that the protein–antagonist complex adopts a more restricted conformation or ensemble of conformations in which solvent accesses to amide protons are reduced. A comparison between the two antagonists shows that UVI 3003 is more protective in the C-terminal region due to the extra hydrophobic interactions derived from the atoms in the benzene ring of the carboxylic acid chain. It was less protective within regions comprising peptides 271–278 and 326–330 due to differences in conformational orientation, and/or shorter carboxylic acid chain length. Decreased deuterium exchange-in in the segment 234–239 where the residues do not involve interactions with the ligand was observed with the two antagonists, but not with 9-cis-RA. The amide protons of helix 12 of the agonist- or antagonist-occupied protein in solution have the same deuterium exchange rates as the unliganded protein, supporting a suggestion made previously that helix 12 can cover the occupied binding cavity only with the cofactor present to adjust its location.

Yan, Xuguang; Perez, Efren; Leid, Mark; Schimerlik, Michael I.; de Lera, Angel R.; Deinzer, Max L.

2007-01-01

316

Impact: a case study examining the closure of a large urban fixed site needle exchange in Canada  

PubMed Central

Introduction In 2008, one of the oldest fixed site needle exchanges in a large urban city in Canada was closed due to community pressure. This service had been in existence for over 20 years. Case Description This case study focuses on the consequences of the switch to mobile needle exchange services immediately after the closure and examines the impact of the closure on changes in risk behavior related to drug use, needle distribution and access to services The context surrounding the closure was also examined. Discussion and Evaluation After the closure of the fixed site exchange, access to needle exchange services decreased as evidenced by the sharp decline in numbers of clients reached, and the numbers of needles distributed and collected monthly. Reports related to needle reuse and selling of syringes suggest changes in risk behaviors. Thousands of needles remain unaccounted for in the community. To date, a new fixed site has not been found. Conclusion Closing the fixed site needle exchange had an adverse effect on already vulnerable clients and reduced access to comprehensive harm reduction services. While official public policy supports a fixed site, politicization of the issue has meant a significant setback for harm reduction with reduced potential to meet public health targets related to reducing the spread of blood borne diseases. This situation is unacceptable from a public health perspective.

2010-01-01

317

A tall-tower study of carbon exchange from developed land use in the U.S. Upper Midwest  

NASA Astrophysics Data System (ADS)

A central goal of the North American Carbon Program is to reconcile differences in regional carbon exchange predictions from atmospheric and ground-based approaches. Within any large region there are embedded areas where land cover and land use have been strongly modified by development. However, studies involving continuous measurement of CO2 exchange in developed land have begun only recently. These areas represent a significant percentage of the Upper Midwest region. U.S. Census housing density data show that while high-density urban areas occupy 3% of the land area, low-density residential land uses (generally suburbs) occupy >11% of the land area. We established a new tall-tower site to study CO2, water vapor, and energy exchange from developed land use in the in the Minneapolis-Saint Paul metropolitan area. The objectives of the study are: 1. To quantify the components of the net ecosystem exchange of CO2 (NEE) of developed land use and their variation over diurnal, synoptic, seasonal, and interannual time scales. 2. To determine the specific ecosystem controls on the net exchanges of CO2, water vapor, and energy by analyzing the relationships between the fluxes and a suite of biophysical properties measured within the footprint of the flux tower. 3. To evaluate the relationship of the MODIS vegetation index, land surface temperature, and snow cover products to temporal dynamics of net ecosystem exchange of CO2 and water vapor at a range scales from the flux tower to the metropolitan area. The design, implementation, and first results of the site will be presented. The long-term goal of this research is to understand how developed land use affects regional- to continental-scale carbon dynamics, how these effects may change with urban growth and development, and ultimately, how they could be managed to mitigate carbon sources and maximize sinks.

McFadden, J. P.; Widboom, A. A.; Bauer, M. E.; Yuan, F.

2004-12-01

318

Comparative Study of Some Layered Hydroxide Salts Containing Exchangeable Interlayer Anions  

NASA Astrophysics Data System (ADS)

Anion-exchange reactions of layered Zn, Cu, Ni, or La hydroxide nitrates with the organic anions acetate, terephthalate, and benzoate are compared. Powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetry combined with mass spectrometry (TG-MS) are used to characterize the materials. Exchange of the interlayer nitrate anions for these organic anions is generally possible, although no exchange is observed for the parent nickel hydroxide material. The organo derivatives obtained may be considered inorganic-organic hybrids, consisting of alternating hydroxide and A- layers, where A is the incorporated organic anion. The materials are structurally similar to the layered double hydroxide family of materials, which also exhibit an anion-exchange capacity.

Newman, Steven P.; Jones, William

1999-11-01

319

Heat exchangers for cardioplegia systems: in vitro study of four different concepts.  

PubMed

The aim of this work is the evaluation of four different heat exchangers used for myocardium during cardioplegic system in cardiac surgeries. Four types of shell and tube heat exchangers made of different exchange elements were constructed, as follows: stainless steel tubes, aluminium tubes, polypropylene hollow fiber, and bellows type. The evaluation was performed by in vitro tests of parameters such as heat transfer, pressure drop, and hemolysis tendency. The result has shown that all four systems tested were able to achieve the heat performance, and to offer low resistance to flow, and safety, as well as have low tendency to hemolysis. However, we can emphasize that the bellows type heat exchanger has a significant difference with regard to the other three types. PMID:12752210

Drummond, Mário; Novello, Waldyr Parorali; de Arruda, Antonio Celso Fonseca; Braile, Domingo Marcolino

2003-05-01

320

Planning and Conducting an International Seismic Data Exchange Experiment at the Center for Seismic Studies.  

National Technical Information Service (NTIS)

This report covers preparations for and the conduct of an international seismic data exchange experiment sponsored by the Group of Scientific Experts, U.N. Conference on Disarmament. Seismic data reports from 37 countries were transmitted over circuits of...

C. Romney L. Huszar G. A. Frazier A. Campanella M. A. Tiberio

1986-01-01

321

An ALC study of spin exchange of a muoniated cosurfactant in lamellar phase surfactant dispersions  

NASA Astrophysics Data System (ADS)

The Avoided Level Crossing muon spin resonance (ALC-?SR) technique has been used to measure the Heisenberg spin exchange rate between the Mu adducts of 2-phenylethanol (PEA) and Ni in a concentrated lamellar phase dispersion composed of the dichain cationic surfactant 2,3-diheptadecyl ester ethoxypropyl-1,1,1-trimethylammonium chloride (DHTAC) and water. Ni is only dissolved in the aqueous phase, therefore information about the local environment of the PEA can be extracted from the spin exchange rate. In the high-temperature (L) phase the spin exchange is very slow, revealing that PEA preferentially resides in the headgroup regime of the surfactant. In the low-temperature (L) phase the spin exchange is diffusion controlled, because the PEA is expelled into the water region between the bilayers.

Dilger, H.; Martyniak, A.; Scheuermann, R.; Vujoševic`, D.; Tucker, I. M.; McKenzie, I.; Roduner, E.

2006-03-01

322

Knowledge flow and exchange in interdisciplinary primary health care teams (PHCTs): an exploratory study  

PubMed Central

Objective: Improving the process of evidence-based practice in primary health care requires an understanding of information exchange among colleagues. This study explored how clinically oriented research knowledge flows through multidisciplinary primary health care teams (PHCTs) and influences clinical decisions. Methods: This was an exploratory mixed-methods study with members of six PHCTs in Ontario, Canada. Quantitative data were collected using a questionnaire and analyzed with social network analysis (SNA) using UCINet. Qualitative data were collected using semi-structured interviews and analyzed with content analysis procedures using NVivo8. Results: It was found that obtaining research knowledge was perceived to be a shared responsibility among team members, whereas its application in patient care was seen as the responsibility of the team leader, usually the senior physician. PHCT members acknowledged the need for resources for information access, synthesis, interpretation, or management. Conclusion: Information sharing in interdisciplinary teams is a complex and multifaceted process. Specific interventions need to be improved such as formalizing modes of communication, better organizing knowledge-sharing activities, and improving the active use of allied health professionals. Despite movement toward team-based models, senior physicians are often gatekeepers of uptake of new evidence and changes in practice.

Sibbald, Shannon L.; Wathen, C. Nadine; Kothari, Anita; Day, Adam M. B.

2013-01-01

323

Light Impurity Studies on Text Using Charge-Exchange Recombination Spectroscopy.  

NASA Astrophysics Data System (ADS)

Intrinsic fully stripped low-Z (light) impurities present in the TEXT tokamak have been studied via charge -exchange recombination spectroscopy (CXRS). Transitions induced by charge exchange with injected energetic hydrogen neutrals have been observed in the ultraviolet with a spatially imaging, time-resolving monochromator constructed for these experiments. It has been used to obtain fully stripped impurity radial profiles. The role of sawtoothing in determining light impurity transport is explored by studying sawtoothing and non-sawtoothing discharges of low and high density. In the low density case, both C^{+6} and O^{+8} are seen to peak on axis during discharges without sawteeth, as opposed to the broader profiles observed during sawtoothing discharges. Sawtoothing gas-puff-fueled high density discharges are compared to non-sawtoothing discharges obtained with fueling by frozen hydrogen pellets. The impurity profiles obtained during the gas-puff-fueled discharges are fairly broad, being slightly more peaked than the electron density. However, profiles obtained following pellet fueling are found to be strongly peaked on axis. Central impurity concentrations increase in the pellet case as compared to the gas-puff case. Impurity profile shapes in this case are highly suggestive of neoclassical behavior. Measured transport coefficients are larger than predicted by neoclassical theory, but are an order of magnitude less than those obtained by impurity injection during sawtoothing discharges. The dynamics of light impurities during a sawtooth period have also been explored. No evidence for impurity reduction in the center of the plasma during precursor MHD activity is found. Evidence for differences in behavior in the central region of the plasma during discharges at low density vs. high density is seen. In particular, influx of impurities is not seen between sawtooth crashes during low density discharges. However, at somewhat higher density, light impurities are seen to undergo changes in concentration in the center of the plasma. Transport coefficients obtained in the latter cases are somewhat larger than predicted by neoclassical theory but are of the same order of magnitude.

Synakowski, Edmund John

324

Experimental studies of alunite: II. Rates of alunite-water alkali and isotope exchange  

USGS Publications Warehouse

Rates of alkali exchange between alunite and water have been measured in hydrothermal experiments of 1 hour to 259 days duration at 150 to 400??C. Examination of run products by scanning electron microscope indicates that the reaction takes place by dissolution-reprecipitation. This exchange is modeled with an empirical rate equation which assumes a linear decrease in mineral surface area with percent exchange (f) and a linear dependence of the rate on the square root of the affinity for the alkali exchange reaction. This equation provides a good fit of the experimental data for f = 17% to 90% and yields log rate constants which range from -6.25 moles alkali m-2s-1 at 400??C to - 11.7 moles alkali m-2s-1 at 200??C. The variation in these rates with temperature is given by the equation log k* = -8.17(1000/T(K)) + 5.54 (r2 = 0.987) which yields an activation energy of 37.4 ?? 1.5 kcal/mol. For comparison, data from O'Neil and Taylor (1967) and Merigoux (1968) modeled with a pseudo-second-order rate expression give an activation energy of 36.1 ?? 2.9 kcal/mol for alkali-feldspar water Na-K exchange. In the absence of coupled alkali exchange, oxygen isotope exchange between alunite and water also occurs by dissolution-reprecipitation but rates are one to three orders of magnitude lower than those for alkali exchange. In fine-grained alunites, significant D-H exchange occurs by hydrogen diffusion at temperatures as low as 100??C. Computed hydrogen diffusion coefficients range from -15.7 to -17.3 cm2s-1 and suggest that the activation energy for hydrogen diffusion may be as low as 6 kcal/mol. These experiments indicate that rates of alkali exchange in the relatively coarse-grained alunites typical of hydrothermal ore deposits are insignificant, and support the reliability of K-Ar age data from such samples. However, the fine-grained alunites typical of low temperature settings may be susceptible to limited alkali exchange at surficial conditions which could cause alteration of their radiometric ages. Furthermore, the rapid rate of hydrogen diffusion observed at 100-150??C suggests that fine-grained alunites are susceptible to rapid D-H re-equilibration even at surficial conditions. ?? 1994.

Stoffregen, R. E.; Rye, R. O.; Wasserman, M. D.

1994-01-01

325

An experimental study on the thermal performance of ground heat exchanger  

SciTech Connect

A knowledge of ground thermal properties is most important for the proper design of large GHE (ground heat exchanger) systems. Thermal response tests have so far been used primarily not only for in situ determination of design data for GHE systems, but also for the evaluation of grout material, heat exchanger types and groundwater effects. The main purpose has been to determine in situ values of effective ground thermal conductivity, including the effect of groundwater flow and natural convection in boreholes. (author)

Lim, Kyoungbin; Lee, Sanghoon [Department of Mechanical Engineering, Hanbat University, Daejon (Korea); Lee, Changhee [Department of Mechanical Engineering, Hanyang University, 1271 Sa1 Ansan, Kyungki-do 425791 (Korea)

2007-08-15

326

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

Microsoft Academic Search

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

R. Fujiyoshi; A. Aono; M. Katayama

1992-01-01

327

Concurrent studies of enhanced heat transfer and materials in ocean thermal heat exchangers  

Microsoft Academic Search

Vertical shell-and-tube condensers and evaporators with axially ridged tubes produce high heat fluxes under OTEC conditions. Shell-side pressure drop is inconsequential and there are only minimal problems associated with the operation of large exchangers. Yet the cost effectiveness of ridged-tube units is reduced by added material and labor costs to the point where the possible advantages of these exchangers must

Rothfus

1981-01-01

328

STUDY OF BEHAVIOR IN THE HEAT EXCHANGER OF A MIXED GAS JOULE-THOMSON COOLER  

Microsoft Academic Search

The object of the investigation is a mixed gas Joule-Thomson (J-T) cooler. A computa- tional model was developed, which makes it possible to investigate the steady state behavior of the refrigerant in the heat exchanger of a mixed gas J-T system. The calculations show that the temperature distribution as well as the pressure distribution in the heat exchanger channels depends

A. Alexeev; A. Thiel; Ch. Haberstroh; H. Quack

329

Study of toponium production including the effects of Higgs-boson exchange  

SciTech Connect

The production rates for toponium in {ital e}{sup +}{ital e{minus}} collisions are calculated for a top-quark mass in the range of 100--200 GeV including the effects of standard-model Higgs-boson exchange. The effects due to this exchange fall off rapidly with the Higgs-boson mass, but lead to changes comparable to those due to uncertainties in {Lambda} for a light Higgs boson.

Feigenbaum, J. (Physics Department, Case Western Reserve University, Cleveland, Ohio 44106 (US) )

1991-01-01

330

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

SciTech Connect

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

Gober, J.R.

1988-01-01

331

Low Reynolds number flow heat exchangers; Proceedings of the Fourth Advanced Study Institute, Ankara, Turkey, July 13-24, 1981  

NASA Astrophysics Data System (ADS)

A review of thermal-hydraulic fundamental principles is presented, focusing on the design of heat exchangers with low-Reynolds number flows. Attention is given to aspects of laminar forced convection, low-Reynolds number turbulent flow, and laminar non-Newtonian flow. The investigations were performed in tubes, tube bundles, and in a gravity flow over vertical or horizontal tubes. Heat exchanger configurations and materials were examined, as were compact and noncompact versions and heat transfer and fouling. Finally, research directions that are necessary to further characterize thermal design parameters, produce better flow visualization, and study single-phase fluid flows in heat exchangers are discussed. No individual items are abstracted in this volume

Kakac, S.; Shah, R. K.; Bergles, A. E.

332

Study on the adsorption property of lysozyme on weak cation exchanger based on monodisperse poly(glycidymethacrylate-co-ethylenedimethacrylate) beads.  

PubMed

A type of weak cation exchanger was prepared based on poly(glycidylmethacrylate-co-ethylenedimethacrylate). The effects of pH and ionic strength on the adsorption behavior were studied, and the results suggested that the adsorption of lysozyme onto a weak cation exchanger is electrostatic interaction, and that the adsorption behavior is in accordance with the Langmuir adsorption model with a correlation coefficient greater than 0.99. It was also found that increasing ionic strength led to a decrease of the adsorption of lysozyme from 49.50 to 28.09 mg/g. Preliminary chromatographic experiments were conducted to test the separation properties of the weak cation exchanger, and the results demonstrated that the retention time of different proteins could be predicted in order of their isoelectric point. PMID:22776738

Zhang, Jing; Han, Yan-Ting; Bu, Xin-Li; Yue, Xuan-Feng

2012-07-09

333

Equilibrium and kinetic ion exchange studies of Pb 2+, Cr 3+, Fe 3+ and Cu 2+ on natural clinoptilolite  

Microsoft Academic Search

In the present study ion exchange of Pb2+, Cu2+, Fe3+ and Cr3+ on natural clinoptilolite is examined at 27±1°C and initial concentration of 10meq\\/dm3. Equilibrium is favorable for Pb2+, unfavorable for Cu2+ and sigmoid for Cr3+ and Fe3+. Selectivity series deduced from equilibrium isotherms is Pb2+>Cr3+>Fe3+>Cu2+, while when maximum exchange levels (MELs) are considered, selectivity series is Pb2+>Cr3+?Cu2+?Fe3+. Cu2+ manifests

V. J. Inglezakis; M. D. Loizidou; H. P. Grigoropoulou

2002-01-01

334

Study on the Heat-flow Controlable Heat Exchanger (first report)  

NASA Astrophysics Data System (ADS)

Heat generating devices and heat recovery systems are desired to control the heat flow and the temperature, contrary to the prior thermo-siphon uncontrolable heat flow. Then, authors have developed a heat flow controlable heat exchanger having a bubble pump mechanism without movable par t. The heat exchanger is consisted of evaporator, condenser, vapor passage pipe, liquid return pipe with a reverse-U type pipe, and heater located on the reverse pipe. Further the system encloses evaporating liquid and is possible to control heat flow between the evaporator to the condenser by adjusting the heater power. This paper presents experimental results on the system. The following results are obtained. (1) The heat exchanger can control heat flow between the evaporator to the condenser by adjusting the heater input which is smaller about 1/20 the above heat flow. (2) The complex heat flow controlable heat exchanger system is possible to control the output temperature by changing its operating heat exchanger number. (3) This heat exchanger is useful to the heat recovery at the room, the temperature control at the space, and the system joining heat storage system.

Hamano, Masayoshi; Yanadori, Michio; Kawano, Tomohiro

335

A multinuclear NMR study of the active site of an endoglucanase from a strain of Bacillus. Use of Trp residues as structural probes.  

PubMed

In the hydrolytic reaction catalyzed by an endoglucanase from a Bacillus strain (endoglucanase K), 2 of 12 Trp residues, Trp174 and Trp243, are responsible for binding of the substrate and/or for the catalysis (Kawaminami, S., Ozaki, K., Sumitomo, N., Hayashi, Y., Ito, S., Shimada, I., and Arata, Y. (1994) J. Biol. Chem. 269, 28752-28756). Here we report results of a stable isotope-aided NMR analysis of the active site of endoglucanase K, using Trp174 and Trp243 as structural probes. Hydrogen-deuterium exchange experiments performed for the NH protons of main and side chains of Trp residues revealed that Trp174 and Trp243 are located in the hydrophilic and hydrophobic microenvironments in the active site, respectively. We also carried out pH titration experiments for indole C2 proton resonances of Trp residues and measured the pH dependence of specific activities for wild-type endoglucanase K and its mutants in which Glu or Asp residues are replaced with their respective amide forms. On the basis of the results obtained from the present study, we conclude that (a) Glu130 and Asp191, which are in spatial proximity to Trp174 and Trp243 in the active site, play a crucial role in the enzymatic activity; (b) Glu130 and Asp191 interact with each other in the active site, leading to an increase in the pKa values to 5.5 for both amino acid residues; and (c) the pKa values of Glu130 and Asp191 would lead to an unusually narrow pH-activity profile of the endoglucanase K. PMID:10391926

Kawaminami, S; Takahashi, H; Ito, S; Arata, Y; Shimada, I

1999-07-01

336

Orientation and Electronic Structure of Ion Exchanged Dye Molecules on Mica: An X-Ray Absorption Study  

Microsoft Academic Search

Dye molecules are frequently used to determine the specific surface area and the ion exchange capacity of high-surface-area materials such as mica. The organic molecules are often considered to be planar and to adsorb in a flat orientation. In the present study we have investigated the orientation and electronic structure of crystal violet (CV) and malachite green (MG) on muscovite

Dorothee Fischer; Walter R. Caseri; Georg Hähner

1998-01-01

337

Study of Land Acquisitions and Exchanges Related to Retention and Management or Disposition of the Federal Public Lands.  

National Technical Information Service (NTIS)

The study was designed to provide information that will determine whether the existing system for land acquisition and exchanges is adequate and proper in the context of assuring that the public lands of the United States are retained and managed or dispo...

C. F. Wheatley

1970-01-01

338

An experimental and numerical study of an air-to-air heat exchanger using liquid reservoir variable conductance heat pipes  

Microsoft Academic Search

This report documents a study of a prototype air-to-air heat exchanger of which the thermal conductivity is governed by the reservoir temperature of the heat pipes. The work is introduced with a brief review of the basic operating principles of heat pipes and of the various existing schemes for variable conductance. An experimental facility, incorporating a computerized data acquisition system,

S. Drouilhet; J. M. Buchlin

1982-01-01

339

ANION EXCHANGE METHOD FOR THE DETERMINATION OF PLUTONIUM IN WATER: SINGLE-LABORATORY EVALUATION AND INTERLABORATORY COLLABORATIVE STUDY  

EPA Science Inventory

This report gives the results of a single-laboratory evaluation and an interlaboratory collaborative study of a method for determining plutonium in water. The method was written for the analysis of 1-liter samples and involved coprecipitation, acid dissolution, anion exchange, el...

340

COMPETITIVE INTELLIGENCE COMPARISON BASED ON THE TYPES OF INDUSTRY. CASE STUDY: LISTED COMPANIES IN TEHRAN STOCK EXCHANGE (TSE)  

Microsoft Academic Search

The purpose of this study is to compare competitive intelligence based on the types of industry. In order to do this, the listed companies in Tehran Stock Exchange (TSE) during a five year period (2004-2008) have been selected. These companies’ products are grouped into five industrial categories; that are, food & drink, tile & ceramic, petrochemical, automobile & parts manufacturing,

Mortazavi Mahdy; Javadi Pour Far Mahnoosh

2011-01-01

341

In Situ X-ray Diffraction Study of Cesium Exchange in Synthetic Umbite  

SciTech Connect

The exchange of Cs{sup +} into H{sub 1.22}K{sub 0.84}ZrSi{sub 3}O{sub 9} {center_dot} 2.16H{sub 2}O (umbite-(HK)) was followed in situ using time-resolved X-ray diffraction at the National Synchrotron Light Source. The umbite framework (space group P2{sub 1}/c with cell dimensions of a = 7.2814(3) {angstrom}, b = 10.4201(4) {angstrom}, c = 13.4529(7) {angstrom}, and {beta} = 90.53(1){sup o}) consists of wollastonite-like silicate chains linked by isolated zirconia octahedra. Within umbite-(HK) there are two unique ion exchange sites in the tunnels running parallel to the a-axis. Exchange Site 1 is marked by 8 member-ring (MR) windows in the bc-plane and contains K{sup +} cations. Exchange Site 2 is marked by a larger 8-MR channel parallel to [100], and contains H{sub 2}O molecules. The occupancy of the Cs{sup +} cations through these channels was modeled by Rietveld structure refinements of the diffraction data and demonstrated that there is a two-step exchange process. The incoming Cs{sup +} ions populated the larger 8-MR channel (Exchange Site 2) first and then migrated into the smaller 8-MR channel. During the exchange process a structural change occurs, transforming the exchanger from monoclinic P2{sub 1}/c to orthorhombic P2{sub 1}2{sub 1}2{sub 1}. This structural change occurs when Cs{sup +} occupancy in the small cavity becomes greater than 0.50. The final in situ ion exchange diffraction pattern was refined to yield umbite-(CsK) with the molecular formula H{sub 0.18}K{sub 0.45}Cs{sub 1.37}ZrSi{sub 3}O{sub 9} {center_dot} 0.98H{sub 2}O and possessing an orthorhombic unit cell with dimensions a = 10.6668(8) {angstrom}, b = 13.5821(11) {angstrom}, c = 7.3946(6) {angstrom}. Solid state {sup 133}Cs MAS NMR showed there is only a slight difference between the two cavities electronically. Valence bond sums for the completely occupied Exchange Site 1 demonstrate that Cs-O bonds of up to 3.8 {angstrom} contribute to the coordination of the Cs{sup +} cation.

C Fewox; A Clearfield; A Celestian

2011-12-31

342

Preliminary study of iron removal from hydrochloric pickling liquor by ion exchange  

SciTech Connect

Hydrochloric acid from exhausted pickling baths is a residue that has to be managed adequately because of its high pollutant potential. In this work, an ion exchange treatment for removing iron from the spent acid was studied in an attempt to make the re-utilization of said acid viable for industry while reducing the amount of waste generated. Several cationic, anionic, and chelating resins were tested. Cationic and chelating resins are able to remove Fe(II) that is present as a cation in the acid, whereas anionic resins are able to remove Fe(III) that forms anionic complexes with the chloride anion. The capacity of the cationic and chelating resins, although not high, does improve as the iron concentration in the hydrochloric acid increases and when the acid concentration decreases, because there is less competition between the ferrous cation and the protons. The anionic resins showed higher capacity for removing iron, especially the Lewatit MP-500, and this capacity also increased with iron concentration.

Maranon, E.; Suarez, F.; Alonso, F.; Fernandez, Y.; Sastre, H. [Univ. of Oviedo, Asturias (Spain). Dept. of Chemical and Environmental Engineering

1999-07-01

343

Solar Wind Charge Exchange Studies of Highly Charged Ions on Atomic Hydrogen  

SciTech Connect

Accurate studies of low energy charge exchange (CX) are critical to understanding underlying soft X ray radiation processes in the interaction of highly charged ions from the solar wind with the neutral atoms and molecules in the heliosphere, cometary comas, planetary atmospheres, interstellar winds, etc.. Particularly important are the CX cross sections for bare, H like, and He like ions of C, N, O and Ne, which are the dominant charge states for these heavier elements in the solar wind. Absolute total cross sections for single electron capture by H like ions of C, N, O and fully stripped O ions from atomic hydrogen have been measured in an expanded range of relative collision energies (5 eV u 20 keV u) and compared to previous H oven measurements. The present measurements are performed using a merged beams technique with intense highly charged ion beams extracted from a 14.5 GHz ECR ion source installed on a high voltage platform at the Oak Ridge National Laboratory. For the collision energy range of 0.3 keV u 3.3 keV u, which corresponds to typical ion velocities in the solar wind, the new measurements are in good agreement with previous H oven measurements. The experimental results are discussed in detail and compared with theoretical calculations where available.

Draganic, Ilija N [ORNL; Seely, D. G. [Albion College; McCammon, D [University of Wisconsin, Madison; Havener, Charles C [ORNL

2011-01-01

344

Solar Wind Charge Exchange Studies Of Highly Charged Ions On Atomic Hydrogen  

SciTech Connect

Accurate studies of low-energy charge exchange (CX) are critical to understanding underlying soft X-ray radiation processes in the interaction of highly charged ions from the solar wind with the neutral atoms and molecules in the heliosphere, cometary comas, planetary atmospheres, interstellar winds, etc.. Particularly important are the CX cross sections for bare, H-like, and He-like ions of C, N, O and Ne, which are the dominant charge states for these heavier elements in the solar wind. Absolute total cross sections for single electron capture by H-like ions of C, N, O and fully-stripped O ions from atomic hydrogen have been measured in an expanded range of relative collision energies (5 eV/u-20 keV/u) and compared to previous H-oven measurements. The present measurements are performed using a merged-beams technique with intense highly charged ion beams extracted from a 14.5 GHz ECR ion source installed on a high voltage platform at the Oak Ridge National Laboratory. For the collision energy range of 0.3 keV/u-3.3 keV/u, which corresponds to typical ion velocities in the solar wind, the new measurements are in good agreement with previous H-oven measurements. The experimental results are discussed in detail and compared with theoretical calculations where available.

Draganic, I. N.; Havener, C. C. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Seely, D. G. [Department of Physics, Albion College, Albion, MI 49224 (United States); McCammon, D. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States)

2011-06-01

345

Inhibiting the Na+/H+ exchanger reduces reperfusion injury: a small animal MRI study.  

PubMed

We used magnetic resonance imaging (MRI) to assess the efficacy of Na+/H+ exchanger isoform 1 (NHE-1) inhibition following cerebral ischemia. Transient focal cerebral ischemia was induced in wild-type controls (NHE-1(+/+)), NHE-1 genetic knockdown mice (NHE-1(+/-)), and NHE-1(+/+) mice treated with the selective NHE-1 inhibitor HOE642. Diffusion weighted imaging (DWI) revealed a brain lesion as early as 1 hour following reperfusion and illustrated significant protection in NHE-1(+/-) mice (16.2 +/- 7.9 mm3 in NHE-1(+/-) mice vs. 47.5 +/- 16.6 mm3 in NHE-1(+/+) mice). Knockdown of NHE-1 showed significantly smaller infarct at 72 hours on T2 imaging (21.2 +/- 12.6 mm3 in NHE-1(+/-) mice vs. 64.6 +/- 2.5 mm3 in NHE-1(+/+) mice). Administration of HOE642 prior to reperfusion or during early reperfusion reduced ischemic damage. Thus, high resolution T2 images can be used for consistent and precise calculation of lesion volumes, while changes of DWI are a sensitive early marker of ischemic injury. The results of this study demonstrate the therapeutic potential for inhibition of NHE-1 in treating cerebral ischemia. PMID:21196287

Ferrazzano, Peter; Shi, Yejie; Manhas, Namratta; Wang, Yanping; Hutchinson, Beth; Chen, Xinzhi; Chanana, Vishal; Gerdts, Josiah; Meyerand, Mary Elizabeth; Sun, Dandan

2011-01-01

346

The model study of water mass and energy exchange between the inland water body and atmosphere  

NASA Astrophysics Data System (ADS)

Based on a one-dimensional eddy diffusion model, a model to study the water mass and energy exchange between the water body (such as lake and wetland) and the atmosphere is developed, which takes the phase change process due to the seasonal melting and freezing of water and the convection mixing process of energy caused by temperature stratification into consideration. The model uses enthalpy instead of temperature as predictive variable, which will help to deal with the phase change process and to design an efficient numerical scheme for obtaining the solution more easily. The performance of the model and the rationality of taking convection mixing into the consideration are validated by using observed data of Kinneret Lake in Israel and Lower Two Medicine Lake in Montana State in America. The comparison of model results with observed data indicates that the model presented here is capable of describing the physical process of water mass and energy between the water body (lake and wetland) and atmosphere. Comparison of the result from wetland with shallow and deep lakes under the same forcing conditions shows that the evaporation from wetland is much greater than that from lakes, which accords with the real observation fact and physical mechanism.

Sun, Shufen; Yan, Jinfeng; Xia, Nan; Li, Qian

2008-08-01

347

Inhibiting the Na+/H+ exchanger reduces reperfusion injury: a small animal MRI study  

PubMed Central

We used magnetic resonance imaging (MRI) to assess the efficacy of Na+/H+ exchanger isoform 1 (NHE-1) inhibition following cerebral ischemia. Transient focal cerebral ischemia was induced in wild-type controls (NHE-1+/+), NHE-1 genetic knockdown mice (NHE-1+/?), and NHE-1+/+ mice treated with the selective NHE-1 inhibitor HOE642. Diffusion weighted imaging (DWI) revealed a brain lesion as early as 1 hour following reperfusion and illustrated significant protection in NHE-1+/? mice (16.2 +/? 7.9 mm3 in NHE-1+/? mice vs. 47.5 +/? 16.6 mm3 in NHE-1+/+ mice). Knockdown of NHE-1 showed significantly smaller infarct at 72 hours on T2 imaging (21.2 +/? 12.6 mm3 in NHE-1+/? mice vs. 64.6 +/? 2.5 mm3 in NHE-1+/+ mice). Administration of HOE642 prior to reperfusion or during early reperfusion reduced ischemic damage. Thus, high resolution T2 images can be used for consistent and precise calculation of lesion volumes, while changes of DWI are a sensitive early marker of ischemic injury. The results of this study demonstrate the therapeutic potential for inhibition of NHE-1 in treating cerebral ischemia.

Ferrazzano, Peter; Shi, Yejie; Manhas, Namratta; Wang, Yanping; Hutchinson, Beth; Chen, Xinzhi; Chanana, Vishal; Gerdts, Josiah; Meyerand, Mary Elizabeth; Sun, Dandan

2010-01-01

348

Magnetic state and exchange interaction in GdScGe: Ab initio study  

NASA Astrophysics Data System (ADS)

The electronic structure and magnetic properties for GdScGe system have been studied via a first-principles density functional calculation. The energy band structure has been calculated in a generalized gradient approximation, plus Hubbard U approach. For Gd atoms, seven spin-up 4f bands are fully occupied and situated at the bottom of Ge 4s-like states, while the spin-down 4f hole levels are completely unoccupied and well above the Fermi level. The calculated magnetic moment is 7.6 ?B per formula unit and is not sensitive to the change of the unit cell volume. The exchange interaction increases with decreasing unit cell volume, which results in a pressure induced enhancement of the Curie temperature (TC). TC increases from about 345 K to 410 K as external pressure increases from 0 to 18 GPa. With the experimental lattice constants, the calculated TC is 353 K, which is in good agreement with the experimental value (TCexp.=349K).

Liu, X. B.; Altounian, Z.; Han, Xianghua; Poudyal, Narayan; Ping Liu, J.

2013-05-01

349

Study of scale-removal methods in a double-pipe heat exchanger  

SciTech Connect

The objective of the present study was to examine the effectiveness of four cleaning methods for the removal of tube-side fouling in a double-pipe heat exchanger. The four cleaning methods are (1) hydrolazing with 10,000-psi head pressure, (2) hydrolazing with 20,000-psi head pressure, (3) chemical cleaning, and (4) brush punching. Fouled tubes were prepared using water from a cooling tower. Each test started with a brand new tube. When the overall heat transfer coefficient dropped by 40% from the initial peak value, scales in the fouled tubes were removed using one of the above four methods. Both the overall heat transfer coefficient and inside diameter were measured before and after fouling, by which the effectiveness of a particular cleaning method was evaluated. The chemical cleaning method was found to be most effective, whereas the brush punching was least effective. When a fouled tube was kept dry, brush punching completely removed scales, indicating that surface wetness plays an important role in scale removal.

Cho, Y.I.; Liu, R.; McFarland, W.J.; Fusegni, L.

2000-06-01

350

The radon cycle and its daughters - an application to the study of troposphere-stratosphere exchanges  

NASA Astrophysics Data System (ADS)

The global activities of the natural radioactive nuclides Rn-222, Pb-210, Bi-210, and Po-210 in the whole atmosphere are studied. A two-box model which assumes the existence of a steady state for the whole atmosphere is employed since the residence times of the aerosols and air masses are different in the troposphere and in the stratosphere. In each reservoir, the production of a nuclide by radioactive decay of its precursor is balanced simultaneously by its own radioactivity, by the flux of atoms transferred to or from the other reservoir, and in the case of the troposphere, by scavenging. The model is used to consider an unknown emanation of Rn-222 from the soil of the continents and also the existence of possible volcanic sources for each nuclide. Among other results, it is found that the Rn-222 emanation rate from the surface of the continents is 0.72 atom/sq cm-sec, and about 2 percent of this flux is able to reach the stratosphere. The scavenging constant of the submicronic aerosols in the troposphere is determined to be 0.00011/min, which corresponds to a mean residence time of 6.5 days in the global troposphere. The flux of air exchanged across the tropopause is determined to be between 4.2-9 x 10 to the 12th kg/min, which corresponds to a mean residence time in the stratosphere between 0.23-0.50 year.

Lambert, G.; Polian, G.; Jegou, A.; Sanak, J.; Ardouin, B.; Buisson, A.; Le Roulley, J. C.

1982-12-01

351

Essays on exchange rate economics  

Microsoft Academic Search

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

Yan Shu

2008-01-01

352

Essays on Exchange Rate Economics  

Microsoft Academic Search

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

Yan Shu

2008-01-01

353

Parametric performance studies on fluidized-bed heat exchangers. Task 1: Fouling characteristics  

NASA Astrophysics Data System (ADS)

Analyses and experiments are being performed to investigate the heat transfer performance of single and multistage shallow fluidized beds for application to the recovery of heat from sources such as waste heat, and coal combustion or coal gasification. Tests were conducted to investigate the effects of liquid condensate fouling on fluidized bed heat exchanger performance. Liquid condensates used in these tests were water and glycerol (which is more viscous than water). The tests showed that fluidized bed heat exchanger performance is degraded by condensation within the bed and the degradation is caused by bed particles adhering to the heat exchanger surface, not by particle agglomeration. Liquid condensate did not continuously build up within the bed. After a period of dry out, heat transfer equal to that obtained prior to condensation was again obtained.

Stoeffler, R. C.

1982-09-01

354

Magnetization processes in exchange-biased MnPd/Fe bilayers studied by polarized neutron reflectivity  

NASA Astrophysics Data System (ADS)

The magnetization processes in exchange-biased MnPd/Fe bilayers have been investigated using polarized neutron reflectivity and vibrating sample magnetometry. The measurements show that by breaking the symmetry of the intrinsic cubic fourfold anisotropy of the Fe film the induced unidirectional anisotropy radically changes the magnetization processes. If the exchange bias is large the induced unidirectional anisotropy is able to pull the net magnetization of the sample to the bias direction after saturation along any of the magnetic hard Fe<110> directions. However, if the exchange bias is small it will only give rise to a difference in net magnetization along the magnetic easy axes adjacent to the saturation direction. Thus, the net magnetic moment along the bias direction depends on the relative magnitudes of the cubic and the unidirectional anisotropies.

Blomqvist, P.; Krishnan, Kannan M.; Srinath, S.; Te Velthuis, S. G. E.

2004-12-01

355

Laboratory studies of exchange between a polar and a subpolar basin  

SciTech Connect

Experiments on the exchange of a freshwater surface layer between two basins in a rotating tank demonstrate the contrasting roles of wind and buoyancy forces. Buoyancy-driven exchange occurs primarily in narrow boundary currents along the walls. Wind-driven exchange has a complex flow pattern with net transfer controlled by the sign of wind stress curl. Freshwater is transferred from the basin with positive curl to the one with negative curl. These results are related to freshwater flow from the Arctic Ocean to the Greenland Sea in which the southward flow of freshwater under buoyancy forces may be either increased or decreased by wind stress depending upon the sign of the curl. At present there is a negative stress curl over the Arctic Ocean which leads to a deep surface layer and no deep convection while opposite conditions in the Greenland Sea tend to remove the surface layer and allow deep convection.

Hunkins, K.

1992-03-01

356

Studies on the kinetics of Na + \\/H + exchange in OK cells: Introduction of a new device for the analysis of polarized transport in cultured epithelia  

Microsoft Academic Search

Summary The present study describes a new perfusion technique—based on the use of a routine spectrofluorometer—which enables fluorometric evaluation of polarity, regulation and kinetics of Na+\\/H+ exchange at the level of an intact monolayer. Na+\\/ H+ exchange was evaluated in bicarbonate-free solutions in OK (opossum kidney) cells, a renal epithelial cell line. Na+\\/H+ exchange activity was measured by monitoring changes

Danuta Krayer-Pawlowska; Corinna Helmle-Kolb; Marshall H. Montrose; Reto Krapf; Heini Murer

1991-01-01

357

Solvation of exchangeable Cu\\/sup 2 +\\/ cations by primary alcohols in montmorillonite clay studied by electron spin resonance and electron spin echo modulation spectroscopies  

Microsoft Academic Search

A montmorillonite clay (STx-1), with Mg\\/sup 2 +\\/ as the major exchangeable cation and Cu\\/sup 2 +\\/ exchanged into 5% of the Mg\\/sup 2 +\\/ sites, is used to study the interaction between the exchangeable cations and adsorbed primary alcohols, methanol, ethanol, and 1-propanol, in the clay interlayer region. Electron spin resonance (ESR) shows that, on saturation of the clay

D. R. Brown; L. Kevan

1988-01-01

358

Corrosion study of heat exchanger tubes in pressurized water cooled nuclear reactors by conversion electron Mössbauer spectroscopy  

Microsoft Academic Search

57Fe-conversion electron Mössbauer spectroscopy (CEMS) — a sensitive tool to analyze the phase composition of corrosion products\\u000a on the surface of stainless steel — was applied to study real specimens from the Paks Nuclear Power Plant, Hungary. The primary\\u000a circuit side of the heat exchanger tubes was studied on selected samples cut out from the steam generators during regular\\u000a maintenance.

Z. Homonnay; P. Á. Szilágyi; E. Kuzmann; K. Varga; Z. Németh; A. Szabó; K. Radó; J. Schunk; P. Tilky; G. Patek

2007-01-01

359

Retrospective Study of Rapid-Exchange Monorail Versus Over-the-Wire Technique for Femoropopliteal Angioplasty  

SciTech Connect

PurposeThe purpose of this study was to compare procedural outcome of rapid-exchange (RX) monorail versus conventional over-the-wire (OTW) technique for femoropopliteal angioplasty.Materials and MethodsDemographic data, procedure details, angioplasty success, and complications of 328 consecutive percutaneous transluminal angioplasties (PTAs) were collected from a prospective database and retrospectively analyzed. Procedure details included duration of fluoroscopy, area-dose product, amount of contrast agent, sheath sizes, access route, length of stenosis, presence of total occlusion, technical and anatomical success (residual stenosis <30% in the absence of complications), need for bail-out stenting, and periprocedural complications. The RX technique alone was used in 102 of 328 cases (31%); the OTW technique, in 226 of 328 of cases (68%).ResultsTechnical success was 98% for the RX versus 95.4% for the OTW technique (p = 0.2). A significantly greater number of stents had to be implanted due to angioplasty failure when the OTW technique was used (RX, 5.9%; OTW, 13.7%; p = 0.04). There were no significant differences in fluorocopy time, dose-area product, or amount of contrast medium used. The RX system facilitated the use of smaller sheath sizes (5 Fr = 38% and 6 Fr = 59% for RX versus 5 Fr = 16.8% and {>=}6 Fr = 82.5% for OTW) but showed only a tendency toward lower overall complication rates (16.6% [17/102] in the RX group versus 19.9% [45/226] in the OTW group; p = 0.09). There was no effect on length of hospitalization. RX monorail systems were not associated with higher procedural costs when compared to conventional OTW technique.ConclusionWe conclude that RX monorail systems seem to enhance the technical success of femoropopliteal angioplasty. Although smaller sheath sizes can be used due to the lower profile of the RX systems, there is only a tendency toward lower complication rates.

Jahnke, Thomas, E-mail: jahnke@prontomail.com; Schaefer, Jost Philipp; Bolte, Hendrik; Schaefer, Fritz; Michalek, Jens; Charalambous, Nicholas [University Hospital Schleswig-Holstein, Klinik fuer Diagnostische Radiologie (Germany); Sapoval, Marc [Radiologie Vasculaire, Hopital Europeen Georges Pompidou (France); Mueller-Huelsbeck, Stefan [University Hospital Schleswig-Holstein, Klinik fuer Diagnostische Radiologie (Germany)

2008-09-15

360

Optimizing Exchange Transfusion for Severe Unconjugated Hyperbilirubinemia: Studies in the Gunn Rat  

PubMed Central

Background Severe unconjugated hyperbilirubinemia carries the risk of neurotoxicity. Phototherapy (PT) and exchange transfusion (ET) are cornerstones in the treatment of unconjugated hyperbilirubinemia. Studies to improve ET efficacy have been hampered by the low application of ET in humans and by the lack of an in vivo model. The absence of an appropriate animal model has also prevented to determine the efficacy of adjunct or alternative treatment options such as albumin (Alb) administration. Aim To establish an in vivo model for ET and to determine the most effective treatment (combination) of ET, PT and Alb administration. Methods Gunn rats received either PT, PT+Alb, ET, ET+PT, ET+PT+Alb or sham operation (each n?=?7). ET was performed via the right jugular vein in ?20 min. PT (18 µW/cm2/nm) was started after ET or at T0. Albumin i.p. injections (2.5 g/kg) were given after ET or before starting PT. Plasma unconjugated bilirubin (UCB), plasma free bilirubin (Bf), and brain bilirubin concentrations were determined. Results We performed ET in 21 Gunn rats with 100% survival. At T1, ET was profoundly more effective in decreasing both UCB ?44%, p<0.01) and Bf ?81%, p<0.05) than either PT or PT+Alb. After 48 h, the combination of ET+PT+Alb showed the strongest hypobilirubinemic effect (?54% compared to ET). Conclusions We optimized ET for severe unconjugated hyperbilirubinemia in the Gunn rat model. Our data indicate that ET is the most effective treatment option, in the acute as well as the follow-up situation.

Schreuder, Andrea B.; Vanikova, Jana; Vitek, Libor; Havinga, Rick; Ahlfors, Charles E.; Hulzebos, Christian V.; Verkade, Henkjan J.

2013-01-01

361

John Locke’s seed lists: a case study in botanical exchange  

Microsoft Academic Search

This paper gives a detailed analysis of four seed lists in the journals of John Locke. These lists provide a window into a fascinating open network of botanical exchange in the early 1680s which included two of the leading botanists of the day, Pierre Magnol of Montpellier and Jacob Bobart the Younger of Oxford. The provenance and significance of the

Stephen A. Harris; Peter R. Anstey

2009-01-01

362

EPR Studies of Spin-Spin Exchange Processes: A Physical Chemistry Experiment.  

ERIC Educational Resources Information Center

|Theoretical background, experimental procedures, and analysis of experimental results are provided for an undergraduate physical chemistry experiment on electron paramagnetic resonance (EPR) linewidths. Source of line broadening observed in a spin-spin exchange process between radicals formed in aqueous solutions of potassium peroxylamine…

Eastman, Michael P.

1982-01-01

363

Parametric performance studies on fluidized-bed heat exchangers. Task 1: Fouling characteristics  

Microsoft Academic Search

Analyses and experiments are being performed to investigate the heat transfer performance of single and multistage shallow fluidized beds for application to the recovery of heat from sources such as waste heat, and coal combustion or coal gasification. Tests were conducted to investigate the effects of liquid condensate fouling on fluidized bed heat exchanger performance. Liquid condensates used in these

R. C. Stoeffler

1982-01-01

364

A kinetic study of the aldol condensation of acetone using an anion exchange resin catalyst  

Microsoft Academic Search

The rate of the reversible aldol condensation of acetone (Ac) to diacetone alcohol (DAA) catalysed by Amberlite IRA-900 anion exchange resin in the hydroxide form is measured in the liquid phase, without solvent, using batch and continuous reactors. The desired reaction product is DAA, but its dehydration leads to the formation of mesityl oxide (MO) as a byproduct. Although the

G. G. Podrebarac; F. T. T. Ng; G. L. Rempel

1997-01-01

365

Investor herding during financial crisis: A clinical study of the Jakarta Stock Exchange  

Microsoft Academic Search

Jakarta Stock Exchange (JSX) data is used to analyse the investment patterns of foreign and domestic investors for evidence of herding and positive feedback trading before, during, and after the 1997 Asian crisis. Results indicate that both investor classes herd, foreigners herd more than locals, and foreign herding increases following the onset of the crisis. Domestic herding does not increase

Michael Bowe; Daniela Domuta

2004-01-01

366

“Actually, I Wanted to Learn”: Study-related knowledge exchange on social networking sites  

Microsoft Academic Search

Social media open up multiple options to add a new dimension to learning and knowledge processes. Particularly, social networking sites allow students to connect formal and informal learning settings. Students can find like-minded people and organize informal knowledge exchange for educational purposes. However, little is known about in which way students use social networking sites for informal learning and about

Katrin Wodzicki; Eva Schwämmlein; Johannes Moskaliuk

367

Concurrent studies of enhanced heat transfer and materials in ocean thermal heat exchangers  

Microsoft Academic Search

Vertical shell and tube condensors and evaporators with axially ridged tubes produce high heat fluxes under OTEC conditions. Shell side pressure drop is inconsequential and there are only minimal problems associated with the operation of large exchangers. Yet the cost effectiveness of ridged tube units is reduced by added material and labor costs to the point where the possible advantages

R. R. Bothfus

1981-01-01

368

Comparative study of rotating regenerators and heat-pipe heat exchangers  

Microsoft Academic Search

A heat wheel was purchased and installed for air to air heat recovery on a Terylene fiber drying and setting oven at ICI Wilton. At the same time a heat pipe heat exchanger was prepared at IRD and tested under controlled conditions. The heat wheel was then replaced by the heat pipe unit. During this procedure measurements were made regularly

D. B. A. MacMichael; D. A. Reay; E. L. Foster

1980-01-01

369

RUSSIAN STUDIES OF THE SAFETY OF ANION EXCHANGE IN NITRIC ACID  

Microsoft Academic Search

The Russian literature pertinent to the thermal (chemical) and radiolytic degradation of anion-exchange resins has been reviewed, and some of the results are summarized. The review covers strongly basic resins of both the conventional (divinylbenzene-styrene) and the more recently developed pyridinium types. Thermal and radiolytic degradation causes loss of functional groups (primarily in the conventional resins) and induces reactions in

M. L. Hyder; S. A. Bartenev; L. N. Lazarev; V. N. Romanovskiy; S. A. Strelkov; G. M. Zachinyaev; E. R. Nazin; A. I. Aldochin; Y. V. Glagolenko; A. I. Maliych; S. I. Rovniy

1999-01-01

370

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

Microsoft Academic Search

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

Weinfeld

1993-01-01

371

Extratropical case study of stratosphere–troposphere exchange using multivariate analyses from mozaic aircraft data  

Microsoft Academic Search

A multivariate analysis methodology, applied to ozone, water vapour and potential temperature data collected from MOZAIC aircraft allowed to identify and to quantify three types of air masses directly linked to stratosphere-troposphere exchanges (STE). These air masses occurred in February 1997 over the North Atlantic during the development of a Rossby wave, which is manifested in the form of four

François Borchi; Emmanouil Oikonomou; Alain Marenco

2005-01-01

372

"Actually, I Wanted to Learn": Study-Related Knowledge Exchange on Social Networking Sites  

ERIC Educational Resources Information Center

|Social media open up multiple options to add a new dimension to learning and knowledge processes. Particularly, social networking sites allow students to connect formal and informal learning settings. Students can find like-minded people and organize informal knowledge exchange for educational purposes. However, little is known about in which way…

Wodzicki, Katrin; Schwammlein, Eva; Moskaliuk, Johannes

2012-01-01

373

Study Abroad Programs: Elements of Effective International Student and Faculty Exchange Programs. CRB 09-006  

ERIC Educational Resources Information Center

As part of Assembly Concurrent Resolution 146 (Solorio), the California Research Bureau was asked to report on the programmatic and funding elements of an effective international student and faculty exchange program, including good practices nationally, with an emphasis on public higher education institutions in California and Mexico. The CRB…

Martin, Pam

2009-01-01

374

Promoting Intercultural Exchanges with Blogs and Podcasting: A Study of Spanish-American Telecollaboration  

ERIC Educational Resources Information Center

|Blogs and podcasts open new ways for global communication and development of intercultural awareness. This article reports a Spanish-American telecollaborative project through which students created blogs and podcasts for intercultural exchanges in light of the sociocultural perspectives. The article outlines the methodology for the project…

Lee, Lina

2009-01-01

375

Implications of the Modigliani-Miller Theorem for the Study of Exchange Rate  

Microsoft Academic Search

We extend the Modigliani-Miller Theorem to the composition of the public debt and show that in a deterministic model the structure of a govern- ment's assets and liabilities is undetermined. Hence, a floating exchange rate regime can implement any attainable competitive equilibrium. Concerning sto- chastic economies, if the government issues nominal bonds of several maturities, then the same result may

Alexandre B. Cunha

376

Perturbed angular correlation study of the ion exchange of indium into silicalite zeolites  

NASA Astrophysics Data System (ADS)

Two indium-containing silicalite zeolites (In/H ZSM5) catalysts prepared by wet impregnation and ionic exchange were characterized by the Perturbed Angular Correlation (PAC) technique using 111In as probe to determine the nature of the indium species. Some of these species take part in the catalytic reaction of the selective reduction (SCR) of NOx with methane. PAC experiments were performed at 500ºC in air before and after reduction reoxidation treatments on the catalysts in order to determine the origin of the different hyperfine interactions and then the degree of ionic exchange. Complementary catalytic activity characterizations were also performed. PAC experiments performed on the catalyst obtained by wet impregnation showed that all In-atoms form In2O3 crystallites while almost 70% of In-atoms form In2O3 in the catalyst obtained by ionic exchange. The PAC experiments of both catalysts performed after the reduction reoxidation treatment revealed the presence of two hyperfine interactions, different from those corresponding to indium in In2O3. These hyperfine interactions should be associated to disperse In species responsible of the catalytic activity located in the ionic exchange-sites of the zeolites.

Ramallo-López, J. M.; Requejo, F. G.; Rentería, M.; Bibiloni, A. G.; Miró, E. E.

1999-09-01

377

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

National Technical Information Service (NTIS)

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

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

1995-01-01

378

[Animal experiment studies on hemodynamics following partial and total blood exchange with a pyridoxalated polyhemoglobin solution].  

PubMed

The effects of a pyridoxalated polyhaemoglobin (SFH-PLP)n-solution on haemodynamics were investigated in a model of partial (hct = 12%) and total blood exchange (hct less than 1%) in 7 dogs. Partial blood exchange resulted in a slight increase in right atrial pressure (RAP) and pulmonary capillary wedge pressure (PCWP) and in a marked decrease in heart rate (HR). Cardiac output (CO) did not increase as would be expected from haemodilution. After total blood exchange, arterial pressure, HR, RAP, PCWP and CO were unchanged compared to the pre-exchange values during the 90 minutes of observation. However, pronounced pulmonary vasoconstriction was observed in 4 dogs. The beneficial effects on haemodynamics are due to the long intravascular persistance of the polymerized haemoglobin molecules (plasma half-disappearance time = 36 hours) and the addition of albumin supplying a sufficient colloid-osmotic pressure of the solution. These characteristics and the good oxygen unloading capacity of the pyridoxalated polyhaemoglobin resulted in longterm survival of three dogs. These results demonstrate a better haemodynamic efficacy of the (SFH-PLP)n-solution compared to previous investigations with unmodified haemoglobin solutions. However, there are still many problems, which have to be clarified prior to its clinical application. PMID:3931496

Hobbhahn, J; Jesch, F; Conzen, P; Brendel, W; Peter, K

1985-08-01

379

EPR Studies of Spin-Spin Exchange Processes: A Physical Chemistry Experiment.  

ERIC Educational Resources Information Center

Theoretical background, experimental procedures, and analysis of experimental results are provided for an undergraduate physical chemistry experiment on electron paramagnetic resonance (EPR) linewidths. Source of line broadening observed in a spin-spin exchange process between radicals formed in aqueous solutions of potassium peroxylamine…

Eastman, Michael P.

1982-01-01

380

Nucleotide exchange factors  

PubMed Central

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

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

2012-01-01

381

Folding analysis of hormonal polypeptide calcitonins and the oxidized calcitonins using electrospray ionization mass spectrometry combined with H/D exchange.  

PubMed

Conformational change of calcitonins has been examined by measuring the rate of hydrogen/deuterium (H/D) exchange in amino acids. Time dependent m/z shift caused by H/D exchange was monitored by electrospray ionization quadrupole ion trap mass spectrometry (ESI-QIT MS). The rate constants of H/D exchange were calculated from apparent first-order kinetics. The time course of H/D exchange exhibited two phases of faster and slower exchange. The smaller rate constant (k2) estimated from the slower H/D exchange was correlated with an alpha-helix content that reflected the folding state. The order of k2 values obtained for human calcitonin (hCT), porcine calcitonin (pCT), salmon calcitonin (sCT), and elcatonin (ECT) was hCT > pCT approximately sCT > ECT. Although the amino acid sequence of sCT is similar to that of ECT, their k2 values were considerably different. The results suggest that ECT is relatively rigid on the N-terminal side cyclic structure in the folded state. Further, the effect of methionine oxidation on k2 has been examined. In the oxidized pCT that possesses similar biological activity with the intact pCT, the k2 values obtained were nearly equal. The k2 of hCT increased via methionine oxidation, and the biological activity was weakened by oxidation. This suggested that methionine oxidation of hCT produced unfolding in the secondary structure and that oxidative unfolding of hCT led to the loss of biological activity. The results indicate that the H/D exchange rate constant may be used as an informative parameter to elucidate the relationship between the folded state and biological activity of polypeptides like calcitonins with secondary structure. PMID:15519222

Nabuchi, Yoshiaki; Asoh, Yoshinori; Takayama, Mitsuo

2004-11-01

382

Ferromagnetic resonance studies of exchange coupled ultrathin Py/Cr/Py trilayers  

NASA Astrophysics Data System (ADS)

Magnetic properties of ultrathin Py/Cr/Py trilayers have been investigated as a function of Cr spacer layer thickness by using ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques. The Cr spacer layer thickness was increased from 4 to 40 A? with 1 A? steps to determine the dependence of interlayer exchange coupling between ferromagnetic layers on the spacer layer thickness. Two strong and well resolved peaks were observed which correspond to a strong (acoustic) and weak (optic) modes of magnetization precession in the effective dc field due to the exciting external microwave field as the external dc field orientation comes close to the film normal. The separation of the two modes in the field axis depends on the thickness of Cr spacer layer. An interchange in the relative positions of the acoustic and optic modes has been observed for a particular thickness of Cr spacer layer as well. A computer program for magnetically exchange coupled N magnetic layers was written to simulate the experimental FMR spectra and to obtain the magnetic parameters of ultrathin Py/Cr/Py trilayers. FMR data have been analyzed from every aspect by using this program and interlayer exchange coupling constant was calculated for the prepared structures. It was found that the relative position of the peaks depends on the nature (sign) of the interlayer exchange coupling between ferromagnetic layers through Cr spacer layer. In Py/Cr/Py trilayers, strength of the interlayer exchange coupling constant oscillates and changes its sign with Cr spacer layer thickness with a period of about 11 A?.

Topkaya, R.; Erkovan, M.; Öztürk, A.; Öztürk, O.; Akta?, B.; Özdemir, M.

2010-07-01

383

Experimental and theoretical studies of magnetic exchange in silole-bridged diradicals.  

PubMed

Five bis(tert-butylnitroxide) diradicals connected by a silole (7 a-d) or a thiophene (12) ring as a coupler were studied. Compound 12 crystallizes in the orthorhombic space group Pna2(1) with a = 20.752(5), b = 5.826(5), and c = 34.309(5) A. X-ray crystal structure determination, electronic spectroscopy, variable-temperature EPR spectroscopy, SQUID measurements and DFT computations (UB3LYP/6-31+G*) were used to study the molecular conformations and electronic spin coupling in this series of molecules. Whereas compounds 7 b, 7 c, and 7 d are quite stable both in solution and in the solid state, 7 a and 12 undergo a partial electronic rearrangement to both a diamagnetic quinonoidal form and a monoradical species owing to the fact that they correspond to the open form of a pi-conjugated Kekulé structure. In the solid state, magnetic measurements indicate that the diradicals are all antiferromagnetically coupled, as expected from their topology. These interactions are best reproduced by means of a "Bleaney-Bowers" model that gives values of J = -142.0 cm(-1) for 7 a, -1.8 cm(-1) for 7 b, -1.3 cm(-1) for 7 c, -4.2 cm(-1) for 7 d, and -248.0 cm(-1) for 12. The temperature dependence of the EPR half-field transition in frozen dichloromethane solutions is consistent with singlet ground states and thermally accessible triplet states for diradicals 7 b, 7 c, and 7 d with DeltaE(T-S) values of 3.48, 2.09, and 8 cm(-1), respectively. No evidence of a populated triplet state was found for diradicals 7 a and 12. Similarities between the DeltaE(T-S) and J values (DeltaE(T-S) = -2 J) clearly show the intramolecular origin of the observed antiferromagnetic interaction. Analyses of the data with a "Karplus-Conroy"-type equation enabled us to establish that the silole ring, as a whole, allows a more efficient magnetic coupling of the two nitroxide radicals attached to its 2,5-positions than the thiophene ring. This superiority probably originates from the nonaromaticity of the silole which thus permits a better magnetic interaction through it. DFT calculations also support the experimental results, indicating that the magnetic exchange pathway preferentially involves the carbon pi system of the silole. PMID:16680786

Roques, Nans; Gerbier, Philippe; Schatzschneider, Ulrich; Sutter, Jean-Pascal; Guionneau, Philippe; Vidal-Gancedo, José; Veciana, Jaume; Rentschler, Eva; Guérin, Christian

2006-07-17

384

Exchange interaction in binuclear complexes with rare-earth and copper ions: A many-body model study  

Microsoft Academic Search

We have used a many-body model Hamiltonian to study the nature of the magnetic ground state of heterobinuclear complexes involving rare-earth and copper ions. We have taken into account all diagonal repulsions involving the rare-earth 4f and 5d orbitals and the copper 3d orbital. In addition, we have included direct exchange interaction, crystal field splitting of the rare-earth atomic levels

Indranil Rudra; C. Raghu; S. Ramasesha

2002-01-01

385

Perceived reciprocity in social exchange and health functioning in early old age: Prospective findings from the GAZEL study  

Microsoft Academic Search

Objectives: To assess prospectively the effects of perceived non-reciprocity of exchange in three different types of social engagement on health functioning in early old age.Methods: In the frame of the prospective French GAZEL cohort study, data on reciprocity in three types of role-related social engagement (principal regular activity in everyday life, marital role relationship, trusting relationships in civic life) were

Morten Wahrendorf; Celine Ribet; Marie Zins; Marcel Goldberg; Johannes Siegrist

2010-01-01

386

Surface magnetic phase transition of the double-exchange ferromagnet: Schwinger-boson mean-field study  

SciTech Connect

Surface magnetic phase transition of a double-exchange model for colossal magnetoresiscance manganites is studied using a Schwinger-boson mean-field method. About three unit cell wide surface layers are identified. The magnetic moment in these layers decreases more rapidly than that in the bulk when temperature is increased. This behavior is consistent with experimental observations. Are also discussed implication to the tunneling magnetoresistance effect using manganites and possible improvement of the magnetoresistance effect near bulk Curie temperature.

Okamoto, Satoshi [ORNL

2009-01-01

387

Magnetization reversal in exchange-coupled GdFe\\/TbFe studied by x-ray magnetic circular dichroism  

Microsoft Academic Search

This work is dedicated to the study of magnetization reversal processes in a ferromagnetically exchange coupled ferrimagnetic\\/ferrimagnetic bilayer system made of a soft magnetic GdFe layer and a hard TbFe layer. Regular magnetization measurements and x-ray magnetic circular dichroism (XMCD) measurements performed at the ESRF on a GdFe (100 nm)\\/TbFe (3 nm) bilayer at different temperatures are presented and compared.

S. Mangin; C. Bellouard; S. Andrieu; F. Montaigne; P. Ohresser; N. B. Brookes; B. Barbara

2004-01-01

388

Influence of thermal energy on exchange-bias studied by finite-element simulations  

NASA Astrophysics Data System (ADS)

In this article we describe the thermal relaxation in anti-ferromagnetic/ferromagnetic bilayers using a hybrid method that combines a kinetic Monte Carlo technique with magnetization dynamics following the Landau Lifshitz Gilbert equation. A granular anti-ferromagnetic layer is exchange coupled to an amorphous ferromagnetic layer and discretized using a finite element method. Calculations are made to help clarify how the underlying magnetic structure is related to the measured exchange bias fields as a function of temperature for the case of amorphous Co65.5Fe14.5B20/granular Ir22Mn78 bilayers. Our calculations are in excellent agreement with experimentally measured macro-magnetic properties of these bilayers.

Dean, J.; Kohn, A.; Kovács, A.; Allwood, D. A.; Suess, D.; Schrefl, T.

2013-07-01

389

Estimating Net Ecosystem Exchange in Complex Terrain: A Case Study from a Subalpine, Montane Forest System.  

NASA Astrophysics Data System (ADS)

Through ecosystem measurement networks such as Ameriflux and FLUXNET, carbon cycling studies are becoming increasingly linked. However, important gaps in this carbon flux data set occur in the vast montane forests typical of the Rocky Mountains and similar areas throughout the world. Problematically, these areas can exhibit complex terrain and tall canopies, which often invalidate assumptions of turbulent transport theory used in eddy covariance techniques. This is particularly true when the atmosphere is stably stratified, which is often the case at night. Though direct investigations into the resulting advection phenomena are underway, they are costly, involving the erection of multiple towers to obtain a three-dimensional control volume capable of including horizontal fluxes in the mass balance equation. It is therefore of great interest to investigate methods of data treatment that can effectively circumvent problematic conditions, while providing reliable results. A 40-meter tower outfitted to FLUXNET specifications was erected over a lodgepole pine-dominated system in the Tenderfoot Creek Experimental Forest, Montana. In order to account for surmised underestimation of nocturnal ecosystem respiration, data were conservatively filtered, excluding measurements under a friction velocity (u*) of 0.4 m/s. Resultant data gaps were filled with nocturnal respiration measurements obtained from soil and leaf chambers, and compared to nighttime eddy flux measurements obtained in sufficiently turbulent conditions. Initial results indicate that on particularly stable nights (u* <0.1), subcanopy concentrations of CO2 became elevated to ~100ppm above levels measured on sufficiently turbulent nights (u*>0.4). Resultant turbulent flux, as shown by the unfiltered eddy covariance system, exhibit nocturnal carbon emissions that are much larger in times of high turbulence, and much smaller in times of low turbulence. The difference can be an order of magnitude. Presumably, this is due to understory-atmosphere decoupling in times of stability. Since, this storage term is not recovered in the morning hours, we assume that an unmeasured advection component is at work. Encouragingly, estimates of net ecosystem exchange derived from chamber measurements compare very favorably with eddy covariance measurements from turbulent conditions indicating the potential for reliable gap-filing for a single tower system on complex terrain.

Muth, D. J.; Epstein, H.; McGlynn, B.; Welsch, D.

2006-12-01

390

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

Microsoft Academic Search

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

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

1999-01-01

391

Induced anisotropy and positive exchange bias: A temperature, angular, and cooling field study by ferromagnetic resonance  

Microsoft Academic Search

Exchange-biased MnF2\\/Fe bilayers, examined by variable angle and temperature ferromagnetic resonance (FMR), exhibit a sudden onset of a unidirectional and fourfold anisotropy below the MnF2 Néel temperature. This unexpected fourfold symmetry arises from frustrated perpendicular coupling between the MnF2 and the Fe overlayer in the presence of twinning in the antiferromagnet layer. These data are consistent with earlier polarized-neutron-reflectometry results.

Michael J. Pechan; Douglas Bennett; Nienchtze Teng; C. Leighton; J. Nogués; Ivan K. Schuller

2002-01-01

392

X and Q-band ferromagnetic resonance studies of exchange biased Co\\/MnPt bilayers  

Microsoft Academic Search

In a recent in-plane ferromagnetic resonance (FMR) experiment using X-band (9.57GHz) spectrometer, we observed a large unidirectional anisotropy HE = 480 Oe in exchange biased Co(8nm)\\/MnPt(25nm) bilayer systems[1]. Non-saturation of the magnetization gave rise to interesting hysteresis effects enabling us to measure in-plane angular variation of coercivity and loop asymmetry. In this work, we report the in-plane angular variation data

A. Punnoose; E. H. Morales; D. Lederman; M. S. Seehra

2003-01-01

393

A gas-exchange study of photosynthesis and isoprene emission in Quercus rubra L  

Microsoft Academic Search

We have investigated the signals which affect the rate of isoprene emission from photosynthesizing leaves of red oak (Quercus rubra L.) using analytical gas-exchange techniques, chlorophyll-fluorescence measurements, and inhibitor feeding. Isoprene emission\\u000a increased with increasing photon flux density at low CO2 but much less so at high CO2 partial pressure. Photosynthetic CO2 assimilation exhibited the opposite behavior. In CO2-free air,

Francesco Loreto; Thomas D. Sharkey

1990-01-01

394

Study on the property rights exchange models for privatization of state-owned enterprises  

Microsoft Academic Search

The information search cost of Anglo-American model and the brokerage cost of Chinese model, obstruct the privatization process of state-owned enterprises (SOEs) to different extents. This paper theoretically explains the differences between Anglo-American model and Chinese model from the perspective of information search cost and brokerage cost in the process of property rights exchange. We then argue that all governments

Zheng Xiaoping; Wang Xiaolu

2010-01-01

395

Planning and conducting an international seismic data exchange experiment at the center for seismic studies  

NASA Astrophysics Data System (ADS)

This report covers preparations for and the conduct of an international seismic data exchange experiment sponsored by the Group of Scientific Experts, U.N. Conference on Disarmament. Seismic data reports from 37 countries were transmitted over circuits of the WMO/GTS. The data were analyzed at centers in Washington, Moscow and Stockholm and epicenter lists were broadcast to participants. The experiment tested a number of aspects of a proposed nuclear test monitoring system.

Romney, C.; Huszar, L.; Frazier, G. A.; Campanella, A.; Tiberio, M. A.

1986-01-01

396

Case study: effectiveness of plasma exchange in an adolescent with systemic lupus erythematosus and catatonia.  

PubMed

Catatonia is a rare but severe condition in adolescents that can be associated with both psychiatric and organic causes. The present report notes that systemic lupus erythematosus should be considered among possible causes of catatonia and shows that plasma exchange could be an efficient treatment option for such neuropsychiatric manifestations of systemic lupus erythematosus, to avoid the use of electroconvulsive therapy in young patients. PMID:12649638

Perisse, Didier; Amoura, Zahir; Cohen, David; Saintigny, Pierre; Mekhloufi, Fatiha; Mazet, Philippe; Piette, Jean-Charles

2003-04-01

397

The Relationship between Corporate Governance Indicators and Firm Value : A Case Study of Karachi Stock Exchange  

Microsoft Academic Search

We investigated whether differences in quality of firm-level corporate governance can explain the firm-level performance in a cross-section of companies listed at Karachi Stock Exchange. Therefore, we analysed the relationship between firm-level value as measured by Tobins Q and total Corporate Governance Index (CGI) and three sub-indices : Board, Shareholdings and Ownership, and Disclosures and Transparency for a sample of

Attiya Y. Javed; Robina Iqbal

2007-01-01

398

Atom exchange between aqueous Fe(II) and goethite: an Fe isotope tracer study.  

PubMed

The reaction of aqueous Fe(II) with Fe(III) oxides is a complex process, comprising sorption, electron transfer, and in some cases, reductive dissolution and transformation to secondary minerals. To better understand the dynamics of these reactions, we measured the extent and rate of Fe isotope exchange between aqueous Fe(II) and goethite using a 57Fe isotope tracer approach. We observed near-complete exchange of Fe atoms between the aqueous phase and goethite nanorods over a 30-day time period. Despite direct isotopic evidence for extensive mixing between the aqueous and goethite Fe, no phase transformation was observed, nor did the size or shape of the goethite rods change appreciably. High-resolution transmission electron microscopy images, however, appear to indicate that some recrystallization of the goethite particles may have occurred. Near-complete exchange of Fe between aqueous Fe(II) and goethite, coupled with negligible change in the goethite mineralogy and morphology, suggests a mechanism of coupled growth (via sorption and electron transfer) and dissolution at separate crystallographic goethite sites. We propose that sorption and dissolution sites are linked via conduction through the bulk crystal, as was recently demonstrated for hematite. Extensive mixing between aqueous Fe(II) and goethite, a relatively stable iron oxide, has significant implications for heavy metal sequestration and release (e.g., arsenic and uranium), as well as reduction of soil and groundwater contaminants. PMID:19320165

Handler, Robert M; Beard, Brian L; Johnson, Clark M; Scherer, Michelle M

2009-02-15

399

Results from the US/USSR exchange for heat load material studies of simulated tokamak disruptions  

NASA Astrophysics Data System (ADS)

This paper presents recent results from exchange I.2 of the US/USSR Exchange Program of Cooperation for Magnetic Confinement Fusion. Previous results from this exchange demonstrated much lower than expected ablation of graphites when the graphites were exposed to disruption like heat fluxes delivered by plasma gun sources. This lower than expected ablation has been accounted for by the 'vapor shielding' effect. Vapor shielding occurs when material is ablated from the surface of the graphite target early in the plasma pulse. This ablated material then shields the surface of the target from the rest of the incoming plasma pulse. Vapor shielding has been inferred from diagnostics and ablation data at all participating laboratories, and clear evidence of the effect has been found by laser interferometry at Kurchatov (Troitsk) in the 2MK-200 machine. Recent results from Kurchatov on the 2MK-200 and MKT experiments continue to indicate that the erosion of graphite exposed to disruption like heat fluxes is much lower than expected. Work from the University of New Mexico on the PLAIDS experiment confirms earlier important work conducted on the VIKA experiment at Efremov. This is particularly interesting in that PLAIDS and VIA have very similar plasma pulse characteristics.

Gahl, J. M.; Crawford, J. F.; McDonald, J. M.; McGrath, R. T.; Zakharov, A.

400

In situ heat exchanger tube fouling thickness measurements using ultrasonics. Final report on a laboratory feasibility study  

SciTech Connect

The growth of fouling layers on heat exchanger surfaces and the corrosion of heat exchanger materials exposed to seawater have been recognized since the beginning of OTEC research as basic problems which could render the concept uneconomical. Consequently, a significant effort has been directed toward predicting, measuring, identifying, explaining and solving potential biofouling and corrosion phenomena. To address this problem, the feasibility of establishing a practical microacoustic technique to measure fouling film thickness in situ on typical OTEC heat exchanger tasks was studied. Seven techniques were studied for this application, including velocity measurements, acoustic diffraction, acoustic interferometer, Doppler flow velocity, pulse echo, critical angle, and surface (shear) wave effects. Of these, the latter five were laboratory tested using conventional microacoustic system components in various configuratons. Only the pulse echo technique yielded promising results. On fouled aluminum plates, thin film layers of 40 ..mu..m and greater were measured using a focused 30 MHz ceramic transducer operated at 25 MHz; this represents a resolution of about 2/3 wavelength. Measurements made on the inside of fouled 1'' aluminum pipes yielded film thicknesses of 75 to 125 ..mu..m. The thinnest layer resolved was approximately 1-1/4 wavelength. The resolution of slime layer thicknesses in the magnitudes of OTEC interest (5 to 30 ..mu..m) using pulse echo microacoustics will require transducer development. In particular, a higher operating frequency (150 to 200 MHz) and advanced material construction is recommended for further research.

Hirshman, J; Munier, R S.C.

1980-09-01

401

IMPACT OF SMALL COLUMN ION EXCHANGE STREAMS ON DWPF GLASS FORMULATION MELT RATE STUDIES  

SciTech Connect

This study was undertaken to evaluate the potential impacts of the Small Column Ion Exchange (SCIX) streams - particularly the addition of Monosodium Titanate (MST) and Crystalline Silicotitanate (CST) - on the melt rate of simulated feed for the Defense Waste Processing Facility (DWPF). Additional MST was added to account for contributions from the Salt Waste Processing Facility (SWPF). The Savannah River National Laboratory (SRNL) Melt Rate Furnace (MRF) was used to evaluate four melter feed compositions: two with simulated SCIX and SWPF material and two without. The Slurry-fed Melt Rate Furnace (SMRF) was then used to compare two different feeds: one with and one without bounding concentrations of simulated SCIX and SWPF material. Analyses of the melter feed materials confirmed that they met their targeted compositions. Four feeds were tested in triplicate in the MRF. The linear melt rates were determined by using X-ray computed tomography to measure the height of the glass formed along the bottom of the beakers. The addition of the SCIX and SWPF material reduced the average measured melt rate by about 10% in MRF testing, although there was significant scatter in the data. Two feeds were tested in the SMRF. It was noted that the ground CST alone (ground CST with liquid in a bucket) was extremely difficult to resuspend during preparation of the feed with material from SCIX and SWPF. This feed was also more difficult to pump than the material without MST and CST due to settling occurring in the melter feed line, although the yield stress of both feeds was high relative to the DWPF design basis. Steady state feeding conditions were maintained for about five hours for each feed. There was a reduction in the feed and pour rates of approximately 15% when CST and MST were added to the feed, although there was significant scatter in the data. Analysis of samples collected from the SMRF pour stream showed that the composition of the glass changed as expected when MST and CST were added to the feed. These reductions in melt rate are consistent with previous studies that showed a negative impact of increased TiO{sub 2} concentrations on the rate of melting. The impact of agitating the melt pool via bubbling was not studied as part of this work, but may be of interest for further testing. It is recommended that additional melt rate testing be performed should a potential reduction in melt rate of 10-15% be considered an issue of concern, or should the anticipated composition of the glass with the addition of material from salt waste processing be modified significantly from the current projections, either due to changes in sludge batch preparation or changes in the composition or volume of SCIX and SWPF material.

Fox, K.; Miller, D.; Koopman, D.

2011-04-26

402

Higher Education Exchange, 2012  

ERIC Educational Resources Information Center

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

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

2012-01-01

403

Gas exchange function through the middle ear mucosa in piglets: comparative study of normal and inflamed ears.  

PubMed

The gas exchange function through the middle ear (ME) mucosa was investigated by comparing normal and inflamed ears in an animal model. Piglets were examined (n = 15) because their tympanic bulla closely resembles the human mastoid air cell system. Four untreated ears served as controls. Eleven ears were injected with glycerin into the tympanic bulla to induce inflammation and were studied as inflamed ears. Two respiratory conditions, spontaneous respiration and hyperventilation by a ventilator, were alternated repeatedly. ME pressure was measured intermittently by a tympanometer and blood gas was measured simultaneously. In all four normal ears, both ME pressure and carbon dioxide (CO2) partial pressure in the blood decreased in parallel following alternation of the respiratory conditions from spontaneous respiration to hyperventilation, while both pressure levels increased in parallel when respiration was changed from hyperventilation to spontaneous respiration. This result indicates that there is a gas exchange between the ME and the blood through the mucosa. However, ME pressure change in inflamed ears was limited, though the change in CO2 partial pressure in the blood was the same as that in normal ears. There was a significant difference in the degree of ME pressure change occurring in normal ears compared to that in inflamed ears, suggesting that inflammation of the mucosa reduced gas exchange function in the ME. PMID:10219389

Yamamoto, Y

1999-01-01

404

An XML Model of an Enhanced Data Dictionary to Facilitate the Exchange of Clinical Research Data in International Studies  

PubMed Central

The clinical research data sets exchanged in international epidemiology research often lack the elements needed to assess their suitability for use in multi-region meta-analyses. While the missing information is generally known to local investigators, it is not contained in the files exchanged between sites. Instead, such content must be solicited by the study coordinating center though a series of lengthy phone and electronic communications: an informal process whose reproducibility and accuracy decays over time. This report describes a set of supplemental information needed to assess whether clinical research data from diverse research sites are truly comparable, and what metadata (“data about the data”) should be preserved when a data set is archived for future use. We propose a structured Extensible Markup Language (XML) model that captures this information. The authors hope this model will be a first step towards preserving the metadata associated with clinical research data sets, thereby improving the quality of international data exchange, data archiving, and merged-data research using data collected in many different countries, languages and care settings.

Duda, Stephany N.; Cushman, Clint; Masys, Daniel R.

2013-01-01

405

Perceived reciprocity in social exchange and health functioning in early old age: prospective findings from the GAZEL study  

PubMed Central

Objectives To assess prospectively the effects of perceived non-reciprocity of exchange in three different types of social engagement on health functioning in early old age. Methods In the frame of the prospective French Gazel cohort study, data on reciprocity in three types of role-related social engagement (principal regular activity in everyday life, marital role relationship, trusting relationships in civic life) were collected in 8679 men and 2742 women (mean age: 60.4 years) in 2005. Two years later, health functioning was assessed, using the SF-36 mental and physical component scores, as well as self perceived health. Multivariate regressions were calculated, controlling for important confounders including baseline self-perceived health. Results Consistent effects of perceived non-reciprocity in all three types of social exchange on mental and physical health functioning were observed. After adjustment for relevant confounders including baseline self-perceived, health effect were attenuated, but largely remained significant. Conclusions Findings underline the importance of the quality of social exchange (reciprocity vs. non-reciprocity) for health functioning in early old age.

Wahrendorf, Morten; Ribet, Celine; Zins, Marie; Goldberg, Marcel; Siegrist, Johannes

2010-01-01

406

Ion exchange and dehydration experimental studies of clinoptilolite: Implications to zeolite dating  

SciTech Connect

Variable effects were noted on the argon (Ar) and potassium (K) contents of clinoptilolite fractions used in ion-exchange and dehydration experiments. The K contents of clinoptilolite fractions were differently affected during cation exchange with Ca-, Cs-, K-, and Na-chloride solutions. Ar was generally less affected during these experiments, except for a Na-clinoptitolite fraction exchanged for five days. Loss of Ar during organic heavy-liquid treatment and cleaning using acetone and deionized water does occur, as indicated by comparing the amounts of radiogenic Ar of treated and untreated fractions. Moreover, a regular decrease in radiogenic Ar contents was noted in clinoptilolite fractions during dehydration experiments at different temperatures for 16 hours. Comparable losses do not occur from saturated samples that were heated in 100 C for more than five months. Water appears to play a vital role in stabilizing the clinoptilolite framework structure and in the retention of Ar. The radiogenic Ar depletion pattern noted in clinoptilolite fractions dehydrated in unsaturated environment at different temperatures is similar to variations in the amount of radiogenic Ar observed in clinoptilolite samples from the unsaturated zone of an altered tuff. These results can be used to evaluate the extent of zeolitic water (and hence Ar) retention in unsaturated geologic settings. The utility of alkali zeolites (e.g., phillipsite, clinoptilolite, and mordenite) from low-temperature, open-hydrologic alteration as potential dateable minerals was evaluated using the K/Ar method as part of the Yucca Mountain Site Characterization Project, which is evaluating Yucca Mountain, Nevada, as a potential high-level radioactive waste repository site.

WoldeGabriel, G.

1995-02-01

407

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

408

Study of electron scattering by CO/sub 2/ at the static-exchange level  

SciTech Connect

We present results for the scattering of low-energy electrons by CO/sub 2/ at the static-exchange level. The collision equations were solved by the iterative Schwinger method. All necessary partial-wave expansions have been carried out to high order so as to assure convergence of the scattering solutions. Of special interest are our calculated position and width for the /sup 2/product/sub u/ resonance of 5.39 and 0.64 eV, respectively, which differ significantly from previously published results.

Lucchese, R.R.; McKoy, V.

1982-04-01

409

Neutron scattering study of MnSi proving no ''exchange hole''  

SciTech Connect

Neutron scattering experiments have been performed on MnSi below T/sub C/ with the double-axis powder scattering technique using unpolarized neutrons, and also with the polarization analysis technique. The magnetic scattering intensity has not shown any anomaly around q = 0.5 A/sup -1/, in contrast to the previous results of Ziebeck et al. who found a large intensity peak at this momentum transfer. Thus, the hypothesis of Ziebeck et al. of observing an ''exchange hole'' is excluded.

Uemura, Y.J.; Majkrzak, C.F.; Shirane, G.; Ishikawa, Y.

1984-03-20

410

Neutron scattering study of MnSi proving no exchange hole  

SciTech Connect

Neutron scattering experiments have been performed in MnSi below T/sub c/ with the double-axis powder scattering technique using unpolarized neutrons, and also with the polarization analysis technique. The magnetic scattering intensity has not shown any anomaly around q = 0.5 A/sup -1/, in contrast to the previous results of Ziebeck et al. who found a large intensity peak at this momentum transfer. Thus the hypothesis of Ziebeck et al. of observing an Exchange Hole is excluded.

Uemura, Y.J.; Majkrzak, C.F.; Shirane, G.; Ishikawa, Y.

1983-01-01

411

Isotope Fractionation of chlorine in Aqueous System: One Study on Anion-Exchange Chromatography.  

NASA Astrophysics Data System (ADS)

Stable chlorine isotopes such as 37Cl and 35Cl have been paid attention as useful tool identifying the source, and monitoring the transport process and natural fate of chlorinated organic pollutants in air and groundwater. However, it is not established yet whether any isotope effects accompany biodegradation or reductive dehalogenation of the pollutants (Clark and Fritz, 1997). Here we first present an experimental determination of isotope fractionation factor of chlorine in aqueous system by using anion-exchange chromatographic technique. Into the Cl-free anion exchange resin (Muromac, OH- form) packed in a 30 cm long pyrex glass column and controlled temperature at 25 oC, hydrochloric solution was fed with controlling the flow rate constant. Effluent from the column was recovered by an automatic fraction collector and prepared for Cl isotope analysis. The Cl isotope ratio (? 37Cl vs. SMOC) was measured by IR-MS at the Utrecht University with precision of 0.06 per-mil. Magnitude of the factor obtained was 1.00035 at 25 oC. The result indicates that the lighter isotope (35Cl) was preferably fractionated into the resin phase, while the heavier one (37Cl) was enriched into the aqueous phase. This trend suggests that molecular structure of hydrolysis with Cl in aqueous phase may be more stable than that of Cl ionically bonding with the resin. This result may offer physico-chemical insights into behavior and fate of the pollutants.

Musashi, M.; Oi, T.; Eggenkamp, H.; Van Cappellen, P.

2001-05-01

412

Estudio de zeolitas de hierro por el efecto Moessbauer y la resonancia paramagnetica electronica. (Study of iron exchanged zeolites by Moessbauer effect and electron spin resonance spectroscopy).  

National Technical Information Service (NTIS)

Crystalline iron exchanged NaY zeolites, prepared from aqueous solutions and calcined at atmospheric conditions, have been studied and characterized by XRD, Moessbauer and EPR spectroscopies and TGA analysis. Three iron sites are clearly distinguished fro...

C. E. Aguirre Campuzano

1993-01-01

413

A study of wet catalytic oxidation of radioactive spent ion exchange resin by hydrogen peroxide  

SciTech Connect

The decomposition behavior of cationic, anionic, and mixed ion-exchange resins was investigated in the H{sub 2}O{sub 2}-Ni{sup 2+}/Cu{sup 2+}, H{sub 2}O{sub 2}-Mn{sup 2+}/Cu{sup 2+}, H{sub 2}O{sub 2}-Fe{sup 2+}, H{sub 2}O{sub 2}-Cu{sup 2+}, and H{sub 2}O{sub 2}-Fe{sup 2+}/Cu{sup 2+} systems for volume reduction and improvement in the capacity of the cemented product. The effects on reaction processes and the consequences of many other factors were analyzed. No radioactivity was detected in the off-gas. The cementation process of encapsulation of the concentrated decomposition residue could produce qualified cemented products with excellent properties for long-term storage in a volume-reduced state.

Xingchao Jian; Tianbao Wu; Guichun Yun [Tsinghua Univ., Beijing (China)

1996-04-01

414

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

NASA Astrophysics Data System (ADS)

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

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

1999-10-01

415

A study of nutritional transport in capillary-tissue exchange system.  

PubMed

A two region flow model has been developed for a capillary-tissue exchange unit. Nutrient dissolved in plasma enters into the tissue from capillary through diffusion, filtration and osmosis. The governing non-linear coupled partial differential equations in the two regions (capillary and tissue) have been solved separately with suitable boundary and matching conditions. The results for the variation of Taylor's-Diffusivity Coefficient and concentration of a nutrient in the tissue region have been brought out for various values of the parameters involved in the analysis and discussed. It has been particularly noted that the penetration depth in the tissue for the nutritional transport can be considered as an important diagnostic parameter for many cardiovascular diseases. PMID:1551732

Tandon, P N; Kushwaha, K

1992-01-01

416

Experimental Background Studies in the Two Photon Exchange (TPE) Experiment at Jefferson Lab  

SciTech Connect

This work is based on the improvement of an existing simulation for the two photon exchange (TPE) experiment at Jefferson Lab developed within the GEANT4 framework. This experiment will determine the ratio of the positron-proton elastic scattering cross section and the electron-proton elastic scattering cross section with high precision. To accomplish this measurement requires the use of a variety of devices and complex arrangements, creating background particles that manage to reach the detector system (CLAS). A number of test runs have identified the sources of background in the detector guided by previous simulations. Even so, the remaining background can be reduced considerably by the microscopic identification and locating of the background sources performed by our new simulation.

Pena, Cristian; Brooks, W. K.; Hakobyan, Hayk [Universidad Tecnica Federico Santa Maria, Valparaiso (Chile)

2010-08-04

417

Experimental Background Studies in the Two Photon Exchange (TPE) Experiment at Jefferson Lab  

NASA Astrophysics Data System (ADS)

This work is based on the improvement of an existing simulation for the two photon exchange (TPE) experiment at Jefferson Lab developed within the GEANT4 framework. This experiment will determine the ratio of the positron-proton elastic scattering cross section and the electron-proton elastic scattering cross section with high precision. To accomplish this measurement requires the use of a variety of devices and complex arrangements, creating background particles that manage to reach the detector system (CLAS). A number of test runs have identified the sources of background in the detector guided by previous simulations. Even so, the remaining background can be reduced considerably by the microscopic identification and locating of the background sources performed by our new simulation.

Peña, Cristian; Brooks, W. K.; Hakobyan, Hayk

2010-08-01

418

Parametric Performance Studies on Fluidized-Bed Heat Exchangers. Quarterly Technical Progress Report, 1 April-30 June 1982.  

National Technical Information Service (NTIS)

In the previous report period, the effects of water condensate on fluidized bed heat exchanger performance was investigated. During the quarter ending 30 June 1982 the Fluidized Bed Heat Exchanger (FBHEX) was tested using glycerol injection, thus completi...

1982-01-01

419

Density functional study of the spin exchange interactions, magnetic structures and ferroelectric polarizations of multiferroics driven by magnetic order  

NASA Astrophysics Data System (ADS)

The electronic structures of magnetic insulators LiCuVO4, LiCu2O2, TbMnO3, Ca3CoMnO6, MnWO4, CuFeO2, Ba2CoGe2O7 and CuBr were examined on the basis of first principles DFT+U+SOC calculations to evaluate their spin exchange parameters and account for their ordered magnetic structures. We then explored how the electric polarizations of these compounds are related to the magnetic ordering and spin-orbit coupling. In this talk results of our studies will be presented.

Whangbo, Mike

2009-03-01

420

Magnetization reversal processes in ErFe2\\/YFe2 exchange spring multilayer studied by xray magnetic circular dichroism  

Microsoft Academic Search

X-ray magnetic circular dichroism at the Er M4,5 edge is used to study the switching behavior of the hard ErFe2 layers in an epitaxial [ErFe2(70{\\\\AA})\\/YFe2 (150{\\\\AA})]{\\\\times}25 exchange-spring superlattice. Magnetic hysteresis loops for the Er magnetization, at temperatures T 200 K reveal a crossover to a regime with two types of switching processes. Computational modelling for this system gives a semi-quantitative

G. B. G. Stenning; A. R. Buckingham; G. J. Bowden; R. C. C. Ward; G. van der Laan; L. R. Shelford; F. Maccherozzi; S. S. Dhesi; P. A. J. de Groot

2011-01-01

421

Preparation, physico-chemical characterization and electrical conductivity measurement studies of an organic–inorganic nanocomposite cation-exchanger: Poly o-toluidine Zr(IV) phosphate  

Microsoft Academic Search

An organic–inorganic nanocomposite cation-exchanger, i.e. poly-o-toluidine Zr(IV) phosphate was synthesized via sol–gel mixing of an electrical conducting polymer poly-o-toluidine into the matrices of inorganic precipitate of Zr(IV) phosphate. The ion-exchange capacity, chemical stability, effect of eluant concentration, elution behavior, pH titration and thermal studies were also carried out to understand the ion-exchange capabilities. The physico-chemical properties of the material were

Asif Ali Khan; Tabassum Akhtar

2008-01-01

422

Ion Exchange  

Microsoft Academic Search

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

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

423

Simulating forest productivity and surface-atmosphere carbon exchange in the BOREAS study region.  

PubMed

A process-based, general ecosystem model (BIOME-BGC) was used to simulate daily gross primary production, maintenance and heterotrophic respiration, net primary production and net ecosystem carbon exchange of boreal aspen, jack pine and black spruce stands. Model simulations of daily net carbon exchange of the ecosystem (NEE) explained 51.7% (SE = 1.32 g C m(-2) day(-1)) of the variance in daily NEE derived from stand eddy flux measurements of CO(2) during 1994. Differences between measured and simulated results were attributed to several factors including difficulties associated with measuring nighttime CO(2) fluxes and model assumptions of site homogeneity. However, comparisons between simulations and field data improved markedly at coarser time-scales. Model simulations explained 66.1% (SE = 0.97 g C m(-2) day(-1)) of the variance in measured NEE when 5-day means of daily results were compared. Annual simulations of aboveground net primary production ranged from 0.6-2.4 Mg C ha(-1) year(-1) and were concurrent with results derived from tree increment core measurements and allometric equations. Model simulations showed that all of the sites were net sinks (0.1-4.1 Mg C ha(-1) year(-1)) of atmospheric carbon for 1994. Older conifer stands showed narrow margins between uptake of carbon by net photosynthesis and carbon release through respiration. Younger stands were more productive than older stands, primarily because of lower maintenance respiration costs. However, all sites appeared to be less productive than temperate forests. Productivity simulations were strongly linked to stand morphology and site conditions. Old jack pine and aspen stands showed decreased productivity in response to simulated low soil water contents near the end of the 1994 growing season. Compared with the aspen stand, the jack pine stand appeared better adapted to conserve soil water through lower daily evapotranspiration losses but also exhibited a narrower margin between daily net photosynthesis and respiration. Stands subjected to water stress during the growing season may exist on the edge between being annual sources or sinks for atmospheric carbon. PMID:14759832

Kimball, John S.; Thornton, Peter E.; White, Mike A.; Running, Steven W.

424

A Study on a Performance of Water-Spray-Type Ice Thermal Energy Storage Vessel with Vertical Heat Exchanger Plates  

NASA Astrophysics Data System (ADS)

A system with a water-embedded-trpe ice storage vessel is widely used because of its simple structure and compactness. However, the water-embedded-type ice storage vessel has a disadvantage, that is, the solidification rate is very small. The use of falling water film seems to be one of promising ways for solving this disadvantage. We have found in a previous study that the use of the falling water film is very effective, especially for high initial water temperatures. In the present study, we eexamined the performance of a faling-water-film-type ice thermal energy storage vessel with pratical size, having vertical heat exchanger plates. The ice making performance coefficient, ?, increases with time, and it becomes am aximum value of 2.5, after that, it decreases gradually. In order to make ice efficiently, it is necessary to set a flow rate of refrigerant properly and to adjust a difference between the evaporating temperature of refrigerant and the freezing point of water so that the refrigerant evaporates in the heat exchanger plates overall.

Yoshimura, Kenji; Sasaguchi, Kengo; Fukuda, Toshihito; Koyama, Shigeru

425

The Grammar of Exchange: A Comparative Study of Reciprocal Constructions Across Languages  

PubMed Central

Cultures are built on social exchange. Most languages have dedicated grammatical machinery for expressing this. To demonstrate that statistical methods can also be applied to grammatical meaning, we here ask whether the underlying meanings of these grammatical constructions are based on shared common concepts. To explore this, we designed video stimuli of reciprocated actions (e.g., “giving to each other”) and symmetrical states (e.g., “sitting next to each other”), and with the help of a team of linguists collected responses from 20 languages around the world. Statistical analyses revealed that many languages do, in fact, share a common conceptual core for reciprocal meanings but that this is not a universally expressed concept. The recurrent pattern of conceptual packaging found across languages is compatible with the view that there is a shared non-linguistic understanding of reciprocation. But, nevertheless, there are considerable differences between languages in the exact extensional patterns, highlighting that even in the domain of grammar semantics is highly language-specific.

Majid, Asifa; Evans, Nicholas; Gaby, Alice; Levinson, Stephen C.

2010-01-01

426

Three Dimensional Computational Study on Proton Exchange Membrane Fuel Cell by Operation Conditions  

NASA Astrophysics Data System (ADS)

A single-phase, fully three-dimensional simulation model for a proton exchange membrane(PEM) fuel cell was used to examine the interdigitated flow field with electrochemical reaction and ion, electron, and water transport(electro-osmotic drag flux and back diffusion flux) through the polymer membrane. The numerical results showed that the fuel cell with an interdigitated flow field resulted in better performance than a fuel cell with a conventional flow field due to its strong convective transport across gas diffusion layer(GDL). However, the pressure drop in an interdigitated flow field is much greater than in conventional flow field. To investigate the effect of relative humidity on the performance of a PEM fuel cell, the humidification condition was set to 100% at the anode flow field and was changed by 0-100% at the cathode flow field. Maximum power density was obtained for a 70% humidified condition at the cathode where the oxygen concentration is moderately high while maintaining high ion conductivity at the polymer membrane.

Lee, Pil Hyong; Park, Bong Il; Hwang, Sang Soon

427

Studies on biologically induced corrosion in heat exchanger systems at the Savannah River Plant, Aiken, SC  

SciTech Connect

Biological fouling and corrosion of stainless steel tubes in the heat exchangers in nuclear reactors at the Savannah River Plant have caused decreased heat transfer efficiency and reduced operational life. This report addresses the microbiology and chemistry of the films present on these tubes, and the relation of this data to the corrosion of the tube material (304L stainless steel). Very few microorganisms other than bacteria were found in the biofilm. Bacteria capable of producing H/sub 2/S, organic acids, anaerobic conditions, and slime have all been isolated from these films. All of these have been implicated in corrosion processes. The most remarkable chemical finding was the inability to detect chloride in the film around areas of presumed chloride induced stress corrosion cracking. Three model systems were used to test the fouling and corrosion potential of metal specimens under a variety of environmental conditions including various biocide regimes. Using these systems, potential improvements in the use of chlorine as a biocidal agent have been observed. It was also shown that larger bacterial populations (including viable and killed cells) were associated with corroded areas as compared to noncorroded areas on the same specimen.

Pope, D.H. (Rensselaer Polytechnic Inst., Troy, NY); Soracco, R.J.; Wilde, E.W.

1982-07-01