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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

Dual Studies on a Hydrogen-Deuterium Exchange of Resorcinol and the Subsequent Kinetic Isotope Effect  

ERIC Educational Resources Information Center

An efficient laboratory experiment has been developed for undergraduate students to conduct hydrogen-deuterium (H-D) exchange of resorcinol by electrophilic aromatic substitution using D[subscript 2]O and a catalytic amount of H[subscript 2]SO[subscript 4]. The resulting labeled product is characterized by [superscript 1]H NMR. Students also…

Giles, Richard; Kim, Iris; Chao, Weyjuin Eric; Moore, Jennifer; Jung, Kyung Woon

2014-01-01

3

Patterns of structural dynamics in RACK1 protein retained throughout evolution: a hydrogen-deuterium exchange study of three orthologs.  

PubMed

RACK1 is a member of the WD repeat family of proteins and is involved in multiple fundamental cellular processes. An intriguing feature of RACK1 is its ability to interact with at least 80 different protein partners. Thus, the structural features enabling such interactomic flexibility are of great interest. Several previous studies of the crystal structures of RACK1 orthologs described its detailed architecture and confirmed predictions that RACK1 adopts a seven-bladed ?-propeller fold. However, this did not explain its ability to bind to multiple partners. We performed hydrogen-deuterium (H-D) exchange mass spectrometry on three orthologs of RACK1 (human, yeast, and plant) to obtain insights into the dynamic properties of RACK1 in solution. All three variants retained similar patterns of deuterium uptake, with some pronounced differences that can be attributed to RACK1's divergent biological functions. In all cases, the most rigid structural elements were confined to B-C turns and, to some extent, strands B and C, while the remaining regions retained much flexibility. We also compared the average rate constants for H-D exchange in different regions of RACK1 and found that amide protons in some regions exchanged at least 1000-fold faster than in others. We conclude that its evolutionarily retained structural architecture might have allowed RACK1 to accommodate multiple molecular partners. This was exemplified by our additional analysis of yeast RACK1 dimer, which showed stabilization, as well as destabilization, of several interface regions upon dimer formation. PMID:24591271

Tarnowski, Krzysztof; Fituch, Kinga; Szczepanowski, Roman H; Dadlez, Michal; Kaus-Drobek, Magdalena

2014-05-01

4

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

PubMed

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. PMID:7428745

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

1980-06-01

5

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. PMID:7428745

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

1980-01-01

6

Crucial role of perfringolysin O D1 domain in orchestrating structural transitions leading to membrane-perforating pores: a hydrogen-deuterium exchange study.  

PubMed

Perfringolysin O (PFO) is a toxic protein that binds to cholesterol-containing membranes, oligomerizes, and forms a ?-barrel transmembrane pore, leading to cell lysis. Previous studies have uncovered the sequence of events in this multistage structural transition to a considerable detail, but the underlying molecular mechanisms are not yet fully understood. By measuring hydrogen-deuterium exchange patterns of peptide bond amide protons monitored by mass spectrometry (MS), we have mapped structural changes in PFO and its variant bearing a point mutation during incorporation to the lipid environment. We have defined all regions that undergo structural changes caused by the interaction with the lipid environment both in wild-type PFO, thus providing new experimental constraints for molecular modeling of the pore formation process, and in a point mutant, W165T, for which the pore formation process is known to be inefficient. We have demonstrated that point mutation W165T causes destabilization of protein solution structure, strongest for domain D1, which interrupts the pathway of structural transitions in other domains necessary for proper oligomerization in the membrane. In PFO, the strongest changes accompanying binding to the membrane focus in D1; the C-terminal part of D4; and strands ?1, ?4, and ?5 of D3. These changes were much weaker for PFO(W165T) lipo where substantial stabilization was observed only in D4 domain. In this study, the application of hydrogen-deuterium exchange analysis monitored by MS provided new insight into conformational changes of PFO associated with the membrane binding, oligomerization, and lytic pore formation. PMID:25164812

Kacprzyk-Stokowiec, Aleksandra; Kulma, Magdalena; Traczyk, Gabriela; Kwiatkowska, Katarzyna; Sobota, Andrzej; Dadlez, Micha?

2014-10-10

7

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

8

Online hydrogen/deuterium exchange performed in the ion mobility cell of a hybrid mass spectrometer.  

PubMed

The present paper describes the performance of online, gas-phase hydrogen/deuterium exchange implemented in the ion mobility cell of a quadrupole time-of-flight mass spectrometer. Deuterium oxide and deuterated methanol were utilized to create deuterated vapor that is introduced into the ion mobility region of the mass spectrometer. Hydrogen/deuterium exchange occurs spontaneously in the milliseconds time frame without the need of switching the instrument into ion mobility mode. The exchange was studied in case of low molecular weight molecules and proteins. The observed number of exchanged hydrogens was equal to the number of theoretically exchangeable hydrogens for all low molecular weight compounds. This method needs only minimal instrumental modifications, is simple, cheap, environment friendly, compatible with ultraperformance liquid chromatography, and can be implemented on commercially available instruments. It does not compromise choice of liquid chromatographic solvents and accurate mass or parallel-fragmentation (MS(E)) methods. The performance of this method was compared to that of conventional alternatives where the deuterated solvent is introduced into the cone gas of the instrument. Although the degree of exchange was similar between the two methods, the "cone gas method" requires 10 times higher deuterated solvent volumes (50 muL/min) and offers reduced sensitivity in the tandem mass spectrometry (MS/MS) mode. The presented method is suggested as a standard future element of mass spectrometers to aid online structural characterization of unknowns and to study conformational changes of proteins with hydrogen/deuterium exchange. PMID:19848411

Nagy, Kornél; Redeuil, Karine; Rezzi, Serge

2009-11-15

9

The Hydrogen-Deuterium Exchange at ?-Carbon Atom in N,N,N-Trialkylglycine Residue: ESI-MS Studies  

NASA Astrophysics Data System (ADS)

Derivatization of peptides as quaternary ammonium salts (QAS) is a known method for sensitive detection by electrospray ionization tandem mass spectrometry. Hydrogens at ?-carbon atom in N, N, N-trialkylglycine residue can be easily exchanged by deuterons. The exchange reaction is base-catalyzed and is dramatically slow at lower pH. Introduced deuterons are stable in acidic aqueous solution and are not back-exchanged during LC-MS analysis. Increased ionization efficiency, provided by the fixed positive charge on QAS group, as well as the deuterium labeling, enables the analysis of trace amounts of peptides.

Rudowska, Magdalena; Wojewska, Dominika; Kluczyk, Alicja; B?chor, Remigiusz; Stefanowicz, Piotr; Szewczuk, Zbigniew

2012-06-01

10

Hydrogen/deuterium exchange in interstellar ice analogs  

NASA Astrophysics Data System (ADS)

Context: For several reasons, methanol is believed to be formed on grain surfaces and, in warm environments, released in the gas phase. In the past, multiply deuterated isotopologues of methanol have been detected in gas phase around several low-mass protostars. In all these sources, there is significantly more CH2DOH than CH3OD. Various hypotheses have been suggested to explain this anomaly, but none is fully convincing. Aims: In this work, we test a new hypothesis experimentally: the spontaneous exchange between hydrogen and deuterium atoms in water ice as responsible for the deficiency of CH3OD with respect to CH2DOH. Methods: We follow the temperature dependence of the composition of interstellar ice analogs initially composed of CD3OD and H2O. To this aim, thin films of intimate H2O:CD3OD ice mixtures, condensed at low temperature (<110 K), are monitored by Fourier transform infrared (FTIR) spectroscopy up to the complete evaporation of CD3OD (~170 K). Results: Rapid hydrogen/deuterium (H/D) exchange is observed, at 120 K and above, through the growth of the ?_OD stretching mode of HDO at ~2425 cm-1. It is also shown that H/D exchange occurs i) on the hydroxyl functional group of methanol, i.e through hydrogen bonds, and ii) before the completion of crystallization. Conclusions: The present results suggest that the much lower abundance of CH3OD compared to CH2DOH in low-mass protostars could reflect H/D exchanges in water ice either prior to or definitely during the grain mantle sublimation. This solid-state depletion mechanism, so far neglected in the astronomical literature, might affect other deuterated molecules with hydrogen bonds.

Ratajczak, A.; Quirico, E.; Faure, A.; Schmitt, B.; Ceccarelli, C.

2009-03-01

11

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

2013-01-01

12

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. PMID:24098480

Pozna?ski, Jaros?aw; Kulma, Magdalena; Dadlez, Michal

2013-01-01

13

Advantages of Isotopic Depletion of Proteins for Hydrogen/Deuterium Exchange Experiments Monitored by Mass Spectrometry  

E-print Network

Advantages of Isotopic Depletion of Proteins for Hydrogen/Deuterium Exchange Experiments Monitored, the peaks overlap and the spectra become more and more crowded because of the presence of heavier isotopes.0 667.0 Isotopic depletion (i.e. elimination of heavier isotopes) reduces the complexity of the spectra

14

Intertwined structured and unstructured regions of exRAGE identified by monitoring hydrogen-deuterium exchange.  

PubMed

Receptor for advanced glycation end products (RAGE) is a multiligand receptor that is engaged in many pathological processes. Potentially beneficial modification of its activity requires sound knowledge of its structural properties. However, up to now, only the structures of its separated domains have been published or deposited in databases. In this work, we used hydrogen-deuterium exchange and mass spectrometry to gain insight into the structural properties of exRAGE (extracellular region of RAGE)--the full extracellular part of the protein. The present work indicates the common and disparate features of full exRAGE as compared to the structural models of its separate domains. The highlight of the present study is the contrasting behavior of the different regions of the protein, with the protected regions neighboring fully exposed parts especially in the N-terminal V domain. PMID:20732329

Kupniewska-Kozak, Anna; Gospodarska, Emilia; Dadlez, Michal

2010-10-15

15

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. PMID:17702600

Niemeyer, Emily D.; Brodbelt, Jennifer S.

2007-01-01

16

Transitions between elongated conformations of ubiquitin [M+11H]11+ enhance hydrogen/deuterium exchange.  

PubMed

Hydrogen/deuterium (H/D) exchange reactions between different elongated conformations of [M + 11H](11+) ions of ubiquitin and D(2)O 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 D(2)O 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. PMID:21449553

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

2011-04-21

17

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. PMID:21449553

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

2011-01-01

18

Ion Mobility Spectrometry-Hydrogen Deuterium Exchange Mass Spectrometry of Anions: Part 1. Peptides to Proteins  

NASA Astrophysics Data System (ADS)

Ion mobility spectrometry (IMS) coupled with hydrogen deuterium exchange (HDX)-mass spectrometry (MS) has been used to study the conformations of negatively-charged peptide and protein ions. Results are presented for ion conformers of angiotensin 1, a synthetic peptide (SP), bovine insulin, ubiquitin, and equine cytochrome c. In general, the SP ion conformers demonstrate a greater level of HDX efficiency as a greater proportion of the sites undergo HDX. Additionally, these ions exhibit the fastest rates of exchange. Comparatively, the angiotensin 1 ions exhibit a lower rate of exchange and HDX level presumably because of decreased accessibility of exchange sites by charge sites. The latter are likely confined to the peptide termini. Insulin ions show dramatically reduced HDX levels and exchange rates, which can be attributed to decreased conformational flexibility resulting from the disulfide bonds. For the larger ubiquitin and protein ions, increased HDX is observed for larger ions of higher charge state. For ubiquitin, a conformational transition from compact to more elongated species (from lower to higher charge states) is reflected by an increase in HDX levels. These results can be explained by a combination of interior site protection by compact conformers as well as decreased access by charge sites. The elongated cytochrome c ions provide the largest HDX levels where higher values correlate with charge state. These results are consistent with increased exchange site accessibility by additional charge sites. The data from these enhanced IMS-HDX experiments are described in terms of charge site location, conformer rigidity, and interior site protection.

Donohoe, Gregory C.; Khakinejad, Mahdiar; Valentine, Stephen J.

2015-04-01

19

Probing protein ligand interactions by automated hydrogen/deuterium exchange mass spectrometry.  

PubMed

Amide hydrogen/deuterium exchange is a powerful biophysical technique for probing changes in protein dynamics induced by ligand interaction. The inherent low throughput of the technology has limited its impact on drug screening and lead optimization. Automation increases the throughput of H/D exchange to make it compatible with drug discovery efforts. Here we describe the first fully automated H/D exchange system that provides highly reproducible H/D exchange kinetics from 130 ms to 24 h. Throughput is maximized by parallel sample processing, and the system can run H/D exchange assays in triplicate without user intervention. We demonstrate the utility of this system to differentiate structural perturbations in the ligand-binding domain (LBD) of the nuclear receptor PPARgamma induced upon binding a full agonist and a partial agonist. PPARgamma is the target of glitazones, drugs used for treatment of insulin resistance associated with type II diabetes. Recently it has been shown that partial agonists of PPARgamma have insulin sensitization properties while lacking several adverse effects associated with full agonist drugs. To further examine the mechanism of partial agonist activation of PPARgamma, we extended our studies to the analysis of ligand interactions with the heterodimeric complex of PPARgamma/RXRalpha LBDs. To facilitate analysis of H/D exchange of large protein complexes, we performed the experiment with a 14.5-T Fourier transform ion cyclotron resonance mass spectrometer capable of measuring mass with accuracy in the ppb range. PMID:16478090

Chalmers, Michael J; Busby, Scott A; Pascal, Bruce D; He, Yuanjun; Hendrickson, Christopher L; Marshall, Alan G; Griffin, Patrick R

2006-02-15

20

Localized Hydration in Lyophilized Myoglobin by Hydrogen-Deuterium Exchange Mass Spectrometry. 1. Exchange Mapping  

PubMed Central

The local effects of hydration on myoglobin (Mb) in solid matrices containing mannitol or sucrose (1:1 w/w, protein:additive) were mapped using hydrogen-deuterium exchange with mass spectrometric analysis (HDX-MS) at 5°C and compared to solution controls. Solid powders were exposed to D2O(g) at controlled activity (aw) followed by reconstitution and analysis of the intact protein and peptides produced by pepsin digestion. HDX varied with matrix type, aw, and position along the protein backbone. HDX was less in sucrose matrices than in mannitol matrices at all aw while the difference in solution was negligible. Differences in HDX in the two matrices were detectable despite similarities in their bulk water content. The extent of exchange in solids is proposed as a measure of the hydration of exchangeable amide groups, as well as protein conformation and dynamics; pepsin digestion allows these effects to be mapped with peptide-level resolution. PMID:22352965

Sophocleous, Andreas M.; Zhang, Jun; Topp, Elizabeth M.

2012-01-01

21

Using hydrogen-deuterium exchange to monitor protein structure in the presence of gold nanoparticles.  

PubMed

The potential applications of protein-functionalized gold nanoparticles (AuNPs) have motivated many studies characterizing protein-AuNP interactions. However, the lack of detailed structural information has hindered our ability to understand the mechanism of protein adsorption on AuNPs. In order to determine the structural perturbations that occur during adsorption, hydrogen/deuterium exchange (HDX) of amide protons was measured for two proteins by NMR. Specifically, we measured both slow (5-300 min) and fast (10-500 ms) H/D exchange rates for GB3 and ubiquitin, two well-characterized proteins. Overall, amide exchange rates are very similar in the presence and absence of AuNPs, supporting a model where the adsorbed protein remains largely folded on the AuNP surface. Small differences in exchange rates are observed for several loop residues, suggesting that the secondary structure remains relatively rigid while loops and surface residues can experience perturbations upon binding. Strikingly, several of these residues are close to lysines, which supports a model where positive surface residues may interact favorably with AuNP-bound citrate. Because these proteins appear to remain folded on AuNP surfaces, these studies suggest that it may be possible to engineer functional AuNP-based nanoconjugates without the use of chemical linkers. PMID:25265213

Wang, Ailin; Vo, Tam; Le, Vu; Fitzkee, Nicholas C

2014-12-11

22

Hydrogen/deuterium exchange mass spectrometry applied to IL-23 interaction characteristics: potential impact for therapeutics.  

PubMed

IL-23 is an important therapeutic target for the treatment of inflammatory diseases. Adnectins are targeted protein therapeutics that are derived from domain III of human fibronectin and have a similar protein scaffold to antibodies. Adnectin 2 was found to bind to IL-23 and compete with the IL-23/IL-23R interaction, posing a potential protein therapeutic. Hydrogen/deuterium exchange mass spectrometry and computational methods were applied to probe the binding interactions between IL-23 and Adnectin 2 and to determine the correlation between the two orthogonal methods. This review summarizes the current structural knowledge about IL-23 and focuses on the applicability of hydrogen/deuterium exchange mass spectrometry to investigate the higher order structure of proteins, which plays an important role in the discovery of new and improved biotherapeutics. PMID:25711416

Iacob, Roxana E; Krystek, Stanley R; Huang, Richard Y-C; Wei, Hui; Tao, Li; Lin, Zheng; Morin, Paul E; Doyle, Michael L; Tymiak, Adrienne A; Engen, John R; Chen, Guodong

2015-04-01

23

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

24

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.

2013-12-01

25

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. PMID:21329427

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

2011-01-01

26

NMR-Based Detection of Hydrogen/Deuterium Exchange in Liposome-Embedded Membrane Proteins  

PubMed Central

Membrane proteins play key roles in biology. Determination of their structure in a membrane environment, however, is highly challenging. To address this challenge, we developed an approach that couples hydrogen/deuterium exchange of membrane proteins to rapid unfolding and detection by solution-state NMR spectroscopy. We show that the method allows analysis of the solvent protection of single residues in liposome-embedded proteins such as the 349-residue Tom40, the major protein translocation pore in the outer mitochondrial membrane, which has resisted structural analysis for many years. PMID:25375235

Yao, Xuejun; Dürr, Ulrich H. N.; Gattin, Zrinka; Laukat, Yvonne; Narayanan, Rhagavendran L.; Brückner, Ann-Kathrin; Meisinger, Chris; Lange, Adam; Becker, Stefan; Zweckstetter, Markus

2014-01-01

27

Probing Conserved Helical Modules of Portal Complexes by Mass Spectrometry based Hydrogen/deuterium Exchange  

PubMed Central

The dsDNA bacteriophage P22 has a ring shaped dodecameric complex composed of the 84 kDa portal protein subunit which forms the central channel of the phage’s DNA packaging motor. The overall morphology of the P22 portal complex is similar to that of the portal complexes of Phi29, SPP1, T3, T7 phages and herpes simplex virus. Secondary structure prediction of P22 portal protein and its threading onto the crystal structure of the Phi29 portal complexes suggested that P22 portal protein complex shares conserved helical modules which were found in the dodecameric interfaces of the Phi29 portal complex. To identify the amino acids involved in inter-subunit contacts in the P22 portal ring complexes and validate the threading model, we performed comparative hydrogen/deuterium exchange analysis of monomeric and in vitro assembled portal proteins of P22 and the dodecameric Phi29 portal. Hydrogen/deuterium exchange experiments provided evidence of inter-subunit interactions in the P22 portal complex similar to those in the Phi29 portal which map to the regions predicted to be conserved helical modules. PMID:18621389

Kang, Sebyung; Poliakov, Anton; Sexton, Jennifer; Renfrow, Matthew B.; Prevelige, Peter E.

2008-01-01

28

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. PMID:11368772

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

2001-01-01

29

state. However, the rates of hydrogen/deuterium exchange demonstrate that the conformation of human PrPC is not  

E-print Network

state. However, the rates of hydrogen/deuterium exchange demonstrate that the conformation of human, and can be Structural mobility of the human prion protein probed by backbone hydrogen exchange Laszlo L. P8 1TD, UK.4Krebs Institute for Biomolecular Research, Dept. of Molecular Biology and Biotechnology

Hosszu, Laszlo

30

Evidence for a bound water molecule next to the retinal Schiff base in bacteriorhodopsin and rhodopsin: a resonance Raman study of the Schiff base hydrogen/deuterium exchange.  

PubMed Central

The retinal chromophores of both rhodopsin and bacteriorhodopsin are bound to their apoproteins via a protonated Schiff base. We have employed continuous-flow resonance Raman experiments on both pigments to determine that the exchange of a deuteron on the Schiff base with a proton is very fast, with half-times of 6.9 +/- 0.9 and 1.3 +/- 0.3 ms for rhodopsin and bacteriorhodopsin, respectively. When these results are analyzed using standard hydrogen-deuteron exchange mechanisms, i.e., acid-, base-, or water-catalyzed schemes, it is found that none of these can explain the experimental results. Because the exchange rates are found to be independent of pH, the deuterium-hydrogen exchange can not be hydroxyl (or acid-)-catalyzed. Moreover, the deuterium-hydrogen exchange of the retinal Schiff base cannot be catalyzed by water acting as a base because in that case the estimated exchange rate is predicted to be orders of magnitude slower than that observed. The relatively slow calculated exchange rates are essentially due to the high pKa values of the Schiff base in both rhodopsin (pKa > 17) and bacteriorhodopsin (pKa approximately 13.5). We have also measured the deuterium-hydrogen exchange of a protonated Schiff base model compound in aqueous solution. Its exchange characteristics, in contrast to the Schiff bases of the pigments, is pH-dependent and consistent with the standard base-catalyzed schemes. Remarkably, the water-catalyzed exchange, which has a half-time of 16 +/- 2 ms and which dominates at pH 3.0 and below, is slower than the exchange rate of the Schiff base in rhodopsin and bacteriorhodopsin. Thus, there are two anomalous results, the inconsistency of the observed hydrogen exchange rates of retinal Schiff base in the two pigments with those predicted from the standard exchange schemes and the enhancement of the rate of hydrogen exchange in the two proteins over the model Schiff base in aqueous solution. We suggest that these results are explained by the presence of a structural water molecule (or molecules) at the retinal binding sites of the two pigments, quite close, probably-hydrogen bonded, to the Schiff base proton. In this case, the rate of exchange can be faster than that found for the model compound due to an "effective water concentration" near the Schiff base that is increased from that found in aqueous solution. PMID:8038384

Deng, H.; Huang, L.; Callender, R.; Ebrey, T.

1994-01-01

31

Time-Resolved Pulsed Hydrogen/Deuterium Exchange Mass Spectrometry Probes Gaseous Proteins Structural Kinetics  

NASA Astrophysics Data System (ADS)

A pulsed hydrogen/deuterium exchange (HDX) method has been developed for rapid monitoring of the exchange kinetics of protein ions with D2O a few milliseconds after electrospray ionization (ESI). The stepwise gradual evolution of HDX of multiply charged protein ions was monitored using the pulsed HDX mass spectrometry technique. Upon introducing a very short pulse of D2O (in the ?s to ms time scale) into the linear ion trap (LIT) of a time-of-flight (TOF) mass spectrometer, bimodal distributions were detected for the ions of cytochrome c and ubiquitin. Mechanistic details of HDX reactions for ubiquitin and cytochrome c in the gas phase were uncovered and the structural transitions were followed by analyzing the kinetics of HDX.

Rajabi, Khadijeh

2015-01-01

32

Difference in Fibril Core Stability between Two Tau Four-Repeat Domain Proteins: A Hydrogen-Deuterium Exchange Coupled to  

E-print Network

Difference in Fibril Core Stability between Two Tau Four-Repeat Domain Proteins: A Hydrogen for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560 065, India *S Supporting hydrogen-deuterium exchange coupled to mass spectrometry as a tool. While the two fibrils are found

33

Activation of AMP-activated protein kinase revealed by hydrogen/deuterium exchange Mass Spectrometry  

PubMed Central

Summary AMP-Activated protein kinase (AMPK) monitors cellular energy, regulates genes involved in ATP synthesis and consumption, and is allosterically activated by nucleotides and synthetic ligands. Analysis of the intact enzyme by hydrogen/deuterium exchange mass spectrometry reveals conformational perturbations of AMPK in response to binding of nucleotides, cyclodextrin and a synthetic small molecule activator, A769662. Results from this analysis clearly show that binding of AMP leads to conformational changes primarily in the ? subunit of AMPK and subtle changes in the ? and ? subunits. In contrast, A769662 causes profound conformational changes in the glycogen binding module of the ? subunit and in the kinase domain of the ? subunit suggesting that the molecular binding site of latter resides between the ? and ? subunits. The distinct short and long-range perturbations induced upon binding of AMP and A769662 suggest fundamentally different molecular mechanisms for activation of AMPK by these two ligands. PMID:24076403

Landgraf, Rachelle R.; Goswami, Devrishi; Rajamohan, Francis; Harris, Melissa S.; Calabrese, Matthew; Hoth, Lise R.; Magyar, Rachelle; Pascal, Bruce D.; Chalmers, Michael J.; Busby, Scott A.; Kurumbail, Ravi; Griffin, Patrick R.

2013-01-01

34

Peptide-Column Interactions and Their Influence on Back Exchange Rates in Hydrogen/Deuterium Exchange-MS  

NASA Astrophysics Data System (ADS)

Hydrogen/deuterium exchange (HDX) methods generate useful information on protein structure and dynamics, ideally at the individual residue level. Most MS-based HDX methods involve a rapid proteolytic digestion followed by LC/MS analysis, with exchange kinetics monitored at the peptide level. Localizing specific sites of HDX is usually restricted to a resolution the size of the host peptide because gas-phase processes can scramble deuterium throughout the peptide. Subtractive methods may improve resolution, where deuterium levels of overlapping and nested peptides are used in a subtractive manner to localize exchange to smaller segments. In this study, we explore the underlying assumption of the subtractive method, namely, that the measured back exchange kinetics of a given residue is independent of its host peptide. Using a series of deuterated peptides, we show that secondary structure can be partially retained under quenched conditions, and that interactions between peptides and reversed-phase LC columns may both accelerate and decelerate residue HDX, depending upon peptide sequence and length. Secondary structure is induced through column interactions in peptides with a solution-phase propensity for structure, which has the effect of slowing HDX rates relative to predicted random coil values. Conversely, column interactions can orient random-coil peptide conformers to accelerate HDX, the degree to which correlates with peptide charge in solution, and which can be reversed by using stronger ion pairing reagents. The dependency of these effects on sequence and length suggest that subtractive methods for improving structural resolution in HDX-MS will not offer a straightforward solution for increasing exchange site resolution.

Sheff, Joey G.; Rey, Martial; Schriemer, David C.

2013-07-01

35

Hydrogen, Deuterium and Tritium in Palladium: An Elastic Constants Study  

SciTech Connect

We have used resonant ultrasound spectroscopy to measure the three independent elastic constants of Pd-H, Pd-D, and Pd-T single crystal at 300K as a function of hydrogen, deuterium, and tritium concentration, respectively. The addition of interstitial H (D, or T) atoms, located at (0,1/2,0) in the fcc Pd lattice, affects all three elastic constants C', C{sub 44}, and B. In the mixed ({alpha}+{beta}) phase, and with increasing H isotope, the shear modulus C' shows an abnormal softening whereas C{sub 44} and B do not. This is explained in terms of Zener-type an elastic relaxations affecting the shape of the hydride phases in the coherent({alpha}+{beta}) two-phase mixture In the single {beta}-phase, C' shows a strong isotope dependence whereas C{sub 44} and B show none. This behavior is explained in terms of differences in the excitation of optical phonons. In Pd-T, {sup 3}He is produced by the radioactive decay of tritium. We have measured in situ the swelling and the change in the elastic constants in Pd-T as a function of aging time. Aging ({sup 3}He formation) affects all three elastic constants. These measurements are being used to understand the early stages of {sup 3}H-{sup 3}He cluster formation in aged Pd-T crystal.

Bach, H.T.; Schwarz, R.B.; Tuggle, D.G. [Los Alamos National Laboratory (United States)

2005-07-15

36

Analysis of oligomeric stability of insulin analogs using hydrogen/deuterium exchange mass spectrometry.  

PubMed

Insulin analog products for subcutaneous injection are prepared as solutions in which insulin analog molecules exist in several oligomeric states. Oligomeric stability can affect their onset and duration of action and has been exploited in designing them. To investigate the oligomeric stability of insulin analog products having different pharmacokinetics, we performed hydrogen/deuterium exchange mass spectrometry (HDX/MS), which is a rapid method to analyze dynamic aspects of protein structures. Two rapid-acting analogs (lispro and glulisine) incorporated deuteriums more and faster than recombinant human insulin, whereas a long-acting analog (glargine) and two intermediate-acting preparations (protamine-containing formulations) incorporated them less and more slowly. Kinetic analysis revealed that the number of slowly exchanged hydrogens (D(s)) (k<0.01 min(-1)) accounted for the difference in HDX reactivity among analogs. Furthermore, we found correlations between HDX kinetics and pharmacokinetics reported previously. Their maximum serum concentration (C(max)) was linearly correlated with D(s) (r=0.88) and the number of maximum exchangeable hydrogens (D(?)) (r=0.89). The maximum drug concentration time (t(max)) was also correlated with reciprocals of D(s) and D(?) (r=0.86 and r=0.96, respectively). Here we demonstrate the ability of HDX/MS to evaluate oligomeric stability of insulin analog products. PMID:21951784

Nakazawa, Shiori; Hashii, Noritaka; Harazono, Akira; Kawasaki, Nana

2012-01-01

37

Real-time Hydrogen/Deuterium Exchange Kinetics via Supercharged Electrospray Ionization Tandem Mass Spectrometry  

PubMed Central

Amide hydrogen/deuterium exchange (HDX) rate constants of bovine ubiquitin in an ammonium acetate solution containing 1% of the electrospray ionization (ESI) “supercharging” reagent m-nitrobenzyl alcohol (m-NBA) were obtained using top-down, electron transfer dissociation (ETD) tandem mass spectrometry (MS). The supercharging reagent replaces the acid and temperature “quench” step in the conventional MS approach to HDX experiments by causing rapid protein denaturation to occur in the ESI droplet. The higher charge state ions that are produced with m-NBA are more unfolded, as measured by ion mobility, and result in higher fragmentation efficiency and higher sequence coverage with ETD. Single amino acid resolution was obtained for 44 of 72 exchangeable amide sites, and summed kinetic data were obtained for regions of the protein where adjacent fragment ions were not observed, resulting in an overall spatial resolution of 1.3 residues. Comparison of these results with previous values from NMR indicates that the supercharging reagent does not cause significant structural changes to the protein in the initial ESI solution, and that scrambling or back-exchange is minimal. This new method for top-down HDX-MS enables real-time kinetic data measurements under physiological conditions, similar to those obtained using NMR, with comparable spatial resolution and significantly better sensitivity. PMID:20942406

Sterling, Harry J.; Williams, Evan R.

2010-01-01

38

Conformational Analysis of Recombinant Monoclonal Antibodies with Hydrogen/Deuterium Exchange Mass Spectrometry  

PubMed Central

Understanding the conformation of antibodies, especially those of therapeutic value, is of great interest. Many of the current analytical methods used to probe protein conformation face issues in the analysis of antibodies, either due to the nature of the antibody itself or the limitations of the method. One method that has recently been utilized for conformational analysis of antibodies is hydrogen/deuterium exchange mass spectrometry (H/DX MS). H/DX MS can be used to probe the conformation and dynamics of proteins in solution, requires small sample quantities, is compatible with many buffer systems, and provides peptide-level resolution. The application of H/DX MS to immunoglobulin gamma 1 (IgG1) recombinant monoclonal antibodies can provide information about IgG1 conformation, dynamics, and changes to conformation as a result of protein modification(s), changes in storage conditions, purification procedures, formulation, and many other parameters. In this article we provide a comprehensive HD/X MS protocol for the analysis of an antibody. PMID:23475726

Houde, Damian; Engen, John R.

2013-01-01

39

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. PMID:9232639

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

1997-01-01

40

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. PMID:19921790

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

2009-01-01

41

Proton nuclear magnetic resonance spectroscopy of human transferrin N-terminal half-molecule: titration and hydrogen-deuterium exchange  

SciTech Connect

The binding of Ga(III) to the proteolytically derived N-terminal half-molecule of human transferrin (HTF/2N) was studied by proton nuclear magnetic resonance spectroscopy. The pH-dependent titration curves of the histidinyl C(2) proton chemical shifts were altered upon formation of the GaIIIHTF/2N(C/sub 2/O/sub 4/) ternary complex. Two high-pK'a histidines failed to titrate when the metal and synergistic anion formed a complex with the protein. These results implicated two histidinyl residues as direct ligands to the metal. The rates of hydrogen-deuterium exchange for the C(2) protons of certain histidinyl residues were substantially decreased by metal ion binding. The two ligand histidines were protected from exchange, and a third, low-pK'a, histidinyl residue was protected. We propose that this third histidinyl residue is involved in anion binding and may serve as the base in the putative proton-relay scheme proposed for complex formation.

Valcour, A.A.; Woodworth, R.C.

1987-06-02

42

Resolving Isotopic Fine Structure to Detect and Quantify Natural Abundance- and Hydrogen/Deuterium Exchange-Derived Isotopomers  

PubMed Central

Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) is used for analyzing protein dynamics, protein folding/unfolding, and molecular interactions. Until this study, HDX MS experiments employed mass spectral resolving powers that afforded only one peak per nominal mass in a given peptide’s isotope distribution, and HDX MS data analysis methods were developed accordingly. A level of complexity that is inherent to HDX MS remained unaddressed, namely, various combinations of natural abundance heavy isotopes and exchanged deuterium shared the same nominal mass and overlapped at previous resolving powers. For example, an A + 2 peak is comprised of (among other isotopomers) a two-2H-exchanged/zero-13C isotopomer, a one-2H-exchanged/one-13C isotopomer, and a zero-2H-exchanged/two-13C isotopomer. Notably, such isotopomers differ slightly in mass as a result of the ~3 mDa mass defect between 2H and 13C atoms. Previous HDX MS methods did not resolve these isotopomers, requiring a natural-abundance-only (before HDX or “time zero”) spectrum and data processing to remove its contribution. It is demonstrated here that high-resolution mass spectrometry can be used to detect isotopic fine structure, such as in the A + 2 profile example above, deconvolving the isotopomer species resulting from deuterium incorporation. Resolving isotopic fine structure during HDX MS therefore permits direct monitoring of HDX, which can be calculated as the sum of the fractional peak magnitudes of the deuterium-exchanged isotopomers. This obviates both the need for a time zero spectrum as well as data processing to account for natural abundance heavy isotopes, saving instrument and analysis time. PMID:24328359

Liu, Qian; Easterling, Michael L.; Agar, Jeffrey N.

2014-01-01

43

Different conformational dynamics of ?-arrestin1 and ?-arrestin2 analyzed by hydrogen/deuterium exchange mass spectrometry.  

PubMed

Arrestins have important roles in G protein-coupled receptor (GPCR) signaling including desensitization of GPCRs and G protein-independent signaling. There have been four arrestins identified: arrestin1, arrestin2 (e.g. ?-arrestin1), arrestin3 (e.g. ?-arrestin2), and arrestin4. ?-Arrestin1 and ?-arrestin2 are ubiquitously expressed and regulate a broad range of GPCRs, while arrestin1 and arrestin4 are expressed in the visual system. Although the functions of ?-arrestin1 and ?-arrestin2 widely overlap, ?-arrestin2 has broader receptor selectivity, and a few studies have suggested that ?-arrestin1 and ?-arrestin2 have distinct cellular functions. Here, we compared the conformational dynamics of ?-arrestin1 and ?-arrestin2 by hydrogen/deuterium exchange mass spectrometry (HDX-MS). We also used the R169E mutant as a pre-activation model system. HDX-MS data revealed that ?-strands II through IV were more dynamic in ?-arrestin2 in the basal state, while the middle loop was more dynamic in ?-arrestin1. With pre-activation, both ?-arrestin1 and ?-arrestin2 became more flexible, but broader regions of ?-arrestin1 became flexible compared to ?-arrestin2. The conformational differences between ?-arrestin1 and ?-arrestin2 in both the basal and pre-activated states might determine their different receptor selectivities and different cellular functions. PMID:25542150

Yun, Youngjoo; Kim, Dong Kyun; Seo, Min-Duk; Kim, Kyeong-Man; Chung, Ka Young

2015-01-30

44

Characterization of Stress-Exposed Granulocyte Colony Stimulating Factor Using ELISA and Hydrogen/Deuterium Exchange Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Information on the higher-order structure is important in the development of biopharmaceutical drugs. Recently, hydrogen/deuterium exchange coupled with mass spectrometry (HDX-MS) has been widely used as a tool to evaluate protein conformation, and unique automated systems for HDX-MS are now commercially available. To investigate the potential of this technique for the prediction of the activity of biopharmaceuticals, granulocyte colony stimulating factor (G-CSF), which had been subjected to three different stress types, was analyzed using HDX-MS and through comparison with receptor-binding activity. It was found that HDX-MS, in combination with ion mobility separation, was able to identify conformational changes in G-CSF induced by stress, and a good correlation with the receptor-binding activity was demonstrated, which cannot be completely determined by conventional peptide mapping alone. The direct evaluation of biological activity using bioassay is absolutely imperative in biopharmaceutical development, but HDX-MS can provide the alternative information in a short time on the extent and location of the structural damage caused by stresses. Furthermore, the present study suggests the possibility of this system being a versatile evaluation method for the preservation stability of biopharmaceuticals.

Tsuchida, Daisuke; Yamazaki, Katsuyoshi; Akashi, Satoko

2014-10-01

45

Polar Aprotic Modifiers for Chromatographic Separation and Back-Exchange Reduction for Protein Hydrogen/Deuterium Exchange Monitored by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Hydrogen/deuterium exchange monitored by mass spectrometry is an important non-perturbing tool to study protein structure and protein-protein interactions. However, water in the reversed-phase liquid chromatography mobile phase leads to back-exchange of D for H during chromatographic separation of proteolytic peptides following H/D exchange, resulting in incorrect identification of fast-exchanging hydrogens as unexchanged hydrogens. Previously, fast high-performance liquid chromatography (HPLC) and supercritical fluid chromatography have been shown to decrease back-exchange. Here, we show that replacement of up to 40% of the water in the LC mobile phase by the modifiers, dimethylformamide (DMF) and N-methylpyrrolidone (NMP) (i.e., polar organic modifiers that lack rapid exchanging hydrogens), significantly reduces back-exchange. On-line LC micro-ESI FT-ICR MS resolves overlapped proteolytic peptide isotopic distributions, allowing for quantitative determination of the extent of back-exchange. The DMF modified solvent composition also improves chromatographic separation while reducing back-exchange relative to conventional solvent.

Valeja, Santosh G.; Emmett, Mark R.; Marshall, Alan G.

2012-04-01

46

Polar Aprotic Modifiers for Chromatographic Separation and Back-Exchange Reduction for Protein Hydrogen/Deuterium Exchange Monitored by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry  

PubMed Central

Hydrogen/deuterium exchange monitored by mass spectrometry is an important non-perturbing tool to study protein structure and protein–protein interactions. However, water in the reversed-phase liquid chromatography mobile phase leads to back-exchange of D for H during chromatographic separation of proteolytic peptides following H/D exchange, resulting in incorrect identification of fast-exchanging hydrogens as unexchanged hydrogens. Previously, fast high-performance liquid chromatography (HPLC) and supercritical fluid chromatography have been shown to decrease back-exchange. Here, we show that replacement of up to 40% of the water in the LC mobile phase by the modifiers, dimethylformamide (DMF) and N-methylpyrrolidone (NMP) (i.e., polar organic modifiers that lack rapid exchanging hydrogens), significantly reduces back-exchange. On-line LC micro-ESI FT-ICR MS resolves overlapped proteolytic peptide isotopic distributions, allowing for quantitative determination of the extent of back-exchange. The DMF modified solvent composition also improves chromatographic separation while reducing back-exchange relative to conventional solvent. PMID:22298288

Valeja, Santosh G.; Emmett, Mark R.; Marshall, Alan G.

2013-01-01

47

Hydrogen/deuterium exchange-protected oligomers populated during A? fibril formation correlate with neuronal cell death.  

PubMed

The aggregation of the amyloid-? peptide (A?) to form fibrils and plaques is strongly associated with Alzheimer's disease (AD). Although it is well established that this process generates neurotoxicity, it is also heterogeneous with a variety of species being formed during the conversion process. This heterogeneity makes it difficult to detect and characterize each of the aggregates formed, which precludes establishing the specific features responsible for the neurotoxicity observed. Here we use pulse-labeling hydrogen-deuterium exchange experiments analyzed by electrospray ionization mass spectrometry (PL-HDX-ESI-MS) to distinguish three ensembles populated during the aggregation of the 40 and 42 residue forms of the A? peptide, A?40 and A?42, on the basis of differences in their persistent structure. Noticeably, two of them are more abundant at the beginning and at the end of the lag phase and are therefore not detectable by conventional assays such as Thioflavin T (ThT). The ensembles populated at different stages of the aggregation process have a surprisingly consistent average degree of exchange, indicating that there are definite structural transitions between the different stages of aggregation. To determine whether an ensemble of species with a given hydrogen exchange pattern correlates with neurotoxicity, we combined PL-HDX-ESI-MS experiments with parallel measurements of the neurotoxicity of the samples under study. The results of this dual approach show that the maximum toxicity correlates with the ensemble comprising HDX protected oligomers, indicating that development of persistent structure within A? oligomers is a determinant of neurotoxicity. PMID:25265274

Serra-Vidal, Bernat; Pujadas, Lluís; Rossi, Daniela; Soriano, Eduardo; Madurga, Sergio; Carulla, Natàlia

2014-11-21

48

Effective Application of Bicelles for Conformational Analysis of G Protein-Coupled Receptors by Hydrogen/Deuterium Exchange Mass Spectrometry  

NASA Astrophysics Data System (ADS)

G protein-coupled receptors (GPCRs) have important roles in physiology and pathology, and 40% of drugs currently on the market target GPCRs for the treatment of various diseases. Because of their therapeutic importance, the structural mechanism of GPCR signaling is of great interest in the field of drug discovery. Hydrogen/deuterium exchange mass spectrometry (HDX-MS) is a useful tool for analyzing ligand binding sites, the protein-protein interaction interface, and conformational changes of proteins. However, its application to GPCRs has been limited for various reasons, including the hydrophobic nature of GPCRs and the use of detergents in their preparation. In the present study, we tested the application of bicelles as a means of solubilizing GPCRs for HDX-MS studies. GPCRs (e.g., ?2-adrenergic receptor [?2AR], ?-opioid receptor, and protease-activated receptor 1) solubilized in bicelles produced better sequence coverage (greater than 90%) than GPCRs solubilized in n-dodecyl-?-D-maltopyranoside (DDM), suggesting that bicelles are a more effective method of solubilization for HDX-MS studies. The HDX-MS profile of ?2AR in bicelles showed that transmembrane domains (TMs) undergo lower deuterium uptake than intracellular or extracellular regions, which is consistent with the fact that the TMs are highly ordered and embedded in bicelles. The overall HDX-MS profiles of ?2AR solubilized in bicelles and in DDM were similar except for intracellular loop 3. Interestingly, we detected EX1 kinetics, an important phenomenon in protein dynamics, at the C-terminus of TM6 in ?2AR. In conclusion, we suggest the application of bicelles as a useful method for solubilizing GPCRs for conformational analysis by HDX-MS.

Duc, Nguyen Minh; Du, Yang; Thorsen, Thor S.; Lee, Su Youn; Zhang, Cheng; Kato, Hideaki; Kobilka, Brian K.; Chung, Ka Young

2015-03-01

49

Effective application of bicelles for conformational analysis of g protein-coupled receptors by hydrogen/deuterium exchange mass spectrometry.  

PubMed

G protein-coupled receptors (GPCRs) have important roles in physiology and pathology, and 40% of drugs currently on the market target GPCRs for the treatment of various diseases. Because of their therapeutic importance, the structural mechanism of GPCR signaling is of great interest in the field of drug discovery. Hydrogen/deuterium exchange mass spectrometry (HDX-MS) is a useful tool for analyzing ligand binding sites, the protein-protein interaction interface, and conformational changes of proteins. However, its application to GPCRs has been limited for various reasons, including the hydrophobic nature of GPCRs and the use of detergents in their preparation. In the present study, we tested the application of bicelles as a means of solubilizing GPCRs for HDX-MS studies. GPCRs (e.g., ?2-adrenergic receptor [?2AR], ?-opioid receptor, and protease-activated receptor 1) solubilized in bicelles produced better sequence coverage (greater than 90%) than GPCRs solubilized in n-dodecyl-?-D-maltopyranoside (DDM), suggesting that bicelles are a more effective method of solubilization for HDX-MS studies. The HDX-MS profile of ?2AR in bicelles showed that transmembrane domains (TMs) undergo lower deuterium uptake than intracellular or extracellular regions, which is consistent with the fact that the TMs are highly ordered and embedded in bicelles. The overall HDX-MS profiles of ?2AR solubilized in bicelles and in DDM were similar except for intracellular loop 3. Interestingly, we detected EX1 kinetics, an important phenomenon in protein dynamics, at the C-terminus of TM6 in ?2AR. In conclusion, we suggest the application of bicelles as a useful method for solubilizing GPCRs for conformational analysis by HDX-MS. PMID:25740347

Duc, Nguyen Minh; Du, Yang; Thorsen, Thor S; Lee, Su Youn; Zhang, Cheng; Kato, Hideaki; Kobilka, Brian K; Chung, Ka Young

2015-05-01

50

Hydrogen-deuterium exchange mass spectrometry as an emerging analytical tool for stabilization and formulation development of therapeutic monoclonal antibodies.  

PubMed

The dynamic nature of the structure of monoclonal antibodies (mAbs) can be probed at a resolution of 5-20 residues using hydrogen-deuterium exchange mass spectrometry (H/D-MS). Recent studies using H/D-MS have shown that distinct regions of IgG1 mAbs experience significant changes in backbone dynamics in response to specific physicochemical alterations, varying solution conditions, or exposure to different environmental stresses. Tracking such changes in local dynamics may therefore serve as a key analytical tool, not only to monitor stability changes, but also to design improved, and more stable formulations of therapeutic mAbs in pharmaceutical dosage forms. This review article describes the H/D-MS method as applied to the analysis of formulations containing mAbs and summarizes recent studies monitoring changes in mAb local dynamics in response to chemical modifications, physical degradation, and presence of stabilizing and destabilizing excipients. Furthermore, the nature of the local dynamics of a highly conserved peptide segment in the CH 2 domain of IgG1 mAbs is reviewed, and the results are correlated with decreased pharmaceutical stability, supporting the identification of a common aggregation hotspot sequence in the Fc region of human IgG1 mAbs. In addition, unresolved challenges (and opportunities) in applying H/D-MS technology for stabilization and formulation development of mAbs are discussed. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 104:327-345, 2015. PMID:25354868

Majumdar, Ranajoy; Middaugh, C Russell; Weis, David D; Volkin, David B

2015-02-01

51

Conformational Difference in Human IgG2 Disulfide Isoforms Revealed by Hydrogen/Deuterium Exchange Mass Spectrometry.  

PubMed

Both recombinant and natural human IgG2 antibodies have several different disulfide bond isoforms, which possess different global structures, thermal stabilities, and biological activities. A detailed mapping of the structural difference among IgG2 disulfide isoforms, however, has not been established. In this work, we employed hydrogen/deuterium exchange mass spectrometry to study the conformation of three major IgG2 disulfide isoforms known as IgG2-B, IgG2-A1, and IgG2-A2 in two recombinant human IgG2 monoclonal antibodies. By comparing the protection factors between amino acid residues in isoforms B and A1 (the classical form), we successfully identified several local regions in which the IgG2-B isoform showed more solvent protection than the IgG2-A1 isoform. On the basis of three-dimensional structural models of IgG2, these identified regions were located on the Fab domains, close to the hinge, centered on the side where the two Fab arms faced each other in spatial proximity. We speculated that in the more solvent-protected B isoform, the two Fab arms were brought into contact by the nonclassical disulfide bonds, resulting in a more compact global structure. Loss of Fab domain flexibility in IgG2-B could limit its ability to access cell-surface epitopes, leading to reduced antigen binding potency. The A2 isoform was previously found to have disulfide linkages similar to those of the classical A1 isoform, but with different biophysical behaviors. Our data indicated that, compared to IgG2-A1, IgG2-A2 had less solvent protection in some heavy-chain Fab regions close the hinge, suggesting that the A2 isoform had more flexible Fab domains. PMID:25730439

Zhang, Aming; Fang, Jing; Chou, Robert Y-T; Bondarenko, Pavel V; Zhang, Zhongqi

2015-03-17

52

Differential isotopic enrichment to facilitate characterization of asymmetric multimeric proteins using hydrogen/deuterium exchange mass spectrometry.  

PubMed

Hydrogen/deuterium exchange (HDX) coupled to mass spectrometry has emerged as a powerful tool for analyzing the conformational dynamics of protein-ligand and protein-protein interactions. Recent advances in instrumentation and methodology have expanded the utility of HDX for the analysis of large and complex proteins; however, asymmetric dimers with shared amino acid sequence present a unique challenge for HDX because assignment of peptides with identical sequence to their subunit of origin remains ambiguous. Here we report the use of differential isotopic labeling to facilitate HDX analysis of multimers using HIV-1 reverse transcriptase (RT) as a model. RT is an asymmetric heterodimer of 51 kDa (p51) and 66 kDa (p66) subunits. The first 440 residues of p51 and p66 are identical. In this study differentially labeled RT was reconstituted from isotopically enriched ((15)N-labeled) p51 and unlabeled p66. To enable detection of (15)N-deuterated RT peptides, the software HDX Workbench was modified to follow a 100% (15)N model. Our results demonstrated that (15)N enrichment of p51 did not affect its conformational dynamics compared to unlabeled p51, but (15)N-labeled p51 did show different conformational dynamics than p66 in the RT heterodimer. Differential HDX-MS of isotopically labeled RT in the presence of the non-nucleoside reverse transcriptase inhibitor (NNRTI) efavirenz (EFV) showed subunit-specific perturbation in the rate of HDX consistent with previously published results and the RT-EFV cocrystal structure. PMID:25763479

Goswami, Devrishi; Tuske, Steve; Pascal, Bruce D; Bauman, Joseph D; Patel, Disha; Arnold, Eddy; Griffin, Patrick R

2015-04-01

53

Enhanced gas-phase hydrogen-deuterium exchange of oligonucleotide and protein ions stored in an external multipole ion reservoir.  

PubMed

Rapid gas-phase hydrogen-deuterium (H-D) exchange from D(2)O and ND(3) into oligonucleotide and protein ions was achieved during storage in a hexapole ion reservoir. Deuterated gas is introduced through a capillary line that discharges directly into the low-pressure region of the reservoir. Following exchange, the degree of H-D exchange is determined using Fourier transform ion cyclotron resonance mass spectrometry. Gas-phase H-D exchange experiments can be conducted more than 100 times faster than observed using conventional in-cell exchange protocols that require lower gas pressures and additional pump-down periods. The short experimental times facilitate the quantitation of the number of labile hydrogens for less reactive proteins and structured oligonucleotides. For ubiquitin, we observe approximately 65 H-D exchanges after 20 s. Exchange rates of > 250 hydrogens s(-1) are observed for oligonucleotide ions when D(2)O or ND(3) is admitted directly into the external ion reservoir owing to the high local pressure in the hexapole. Partially deuterated oligonucleotide ions have been fragmented in the reservoir using infrared multiphoton dissociation (IRMPD). The resulting fragment ions show that exchange predominates at charged sites on the 5'- and 3'-ends of the oligonucleotide, whereas exchange is slower in the core. This hardware configuration is independent of the mass detector and should be compatible with other mass spectrometric platforms including quadrupole ion trap and time-of-flight mass spectrometers. PMID:10633235

Hofstadler, S A; Sannes-Lowery, K A; Griffey, R H

2000-01-01

54

Top-down mass spectrometry and hydrogen/deuterium exchange for comprehensive structural characterization of interferons: implications for biosimilars.  

PubMed

Rapid development in biopharmaceuticals has put high demands on analytical tools that can provide accurate and comprehensive characterization of protein drugs, including biosimilars. Although the enzyme digestion based "bottom-up" approach is usually the method of choice for this purpose, it only gives peptide-level information and sequence coverage is often incomplete. In this work, we used top-down MS with electron capture dissociation (ECD) to characterize both the primary and higher order structures of a therapeutic protein interferon and its variants. Accurate mass measurement at the intact protein level combined with top-down ECD fragmentation enabled unambiguous protein sequence confirmation and identification of all PTMs. Combining hydrogen/deuterium exchange and rapid disulfide reduction with top-down ECD on the LC time scale, we have investigated the differences in higher order structure between the protein variants, as well as the impact of PTMs on protein conformation. PMID:24574185

Pan, Jingxi; Borchers, Christoph H

2014-05-01

55

Mass spectral characterization of ergot alkaloids by electrospray ionization, hydrogen/deuterium exchange, and multiple stage mass spectrometry: Usefulness of precursor ion scan experiments.  

PubMed

Six ergot alkaloids belonging to the lysergic acid derivatives (ergonovine (EGN) and methysergide hydrogen maleinate (MHM)) and peptide-type derivatives (ergocristine (EGR), ergotamine (EGT), ergocornine (EGC) and alpha-ergokryptine (EGK)) were studied by positive electrospray tandem mass spectrometry. The fragmentation mechanisms of these compounds were studied by collision-induced dissociation (CID) using triple quadrupole and ion trap mass spectrometers, and the nature of the major product ions further confirmed by hydrogen/deuterium (H/D) exchange experiments. A common abundant product ion at m/z 223 was characteristic of the two classes of ergot alkaloids. Therefore, a precursor ion scan of m/z 223 that triggers information data acquisition (IDA) in combination with CID experiments was used to identify other potential ergot alkaloids. Using this approach, it was possible to confirm the presence of ergosine, another peptide-type ergot alkaloid, in a rye flour extract at trace levels. PMID:16941545

Mohamed, Rayane; Gremaud, Eric; Tabet, Jean-Claude; Guy, Philippe A

2006-01-01

56

Mapping residual structure in intrinsically disordered proteins at residue resolution using millisecond hydrogen/deuterium exchange and residue averaging.  

PubMed

Measurement of residual structure in intrinsically disordered proteins can provide insights into the mechanisms by which such proteins undergo coupled binding and folding. The present work describes an approach to measure residual structure in disordered proteins using millisecond hydrogen/deuterium (H/D) exchange in a conventional bottom-up peptide-based workflow. We used the exchange mid-point, relative to a totally deuterated control, to quantify the rate of H/D exchange in each peptide. A weighted residue-by-residue average of these midpoints was used to map the extent of residual structure at near single-residue resolution. We validated this approach both by simulating a disordered protein and experimentally using the p300 binding domain of ACTR, a model disordered protein already well-characterized by other approaches. Secondary structure elements mapped in the present work are in good agreement with prior nuclear magnetic resonance measurements. The new approach was somewhat limited by a loss of spatial resolution and subject to artifacts because of heterogeneities in intrinsic exchange. Approaches to correct these limitations are discussed. PMID:25481641

Keppel, Theodore R; Weis, David D

2015-04-01

57

Mapping Residual Structure in Intrinsically Disordered Proteins at Residue Resolution Using Millisecond Hydrogen/Deuterium Exchange and Residue Averaging  

NASA Astrophysics Data System (ADS)

Measurement of residual structure in intrinsically disordered proteins can provide insights into the mechanisms by which such proteins undergo coupled binding and folding. The present work describes an approach to measure residual structure in disordered proteins using millisecond hydrogen/deuterium (H/D) exchange in a conventional bottom-up peptide-based workflow. We used the exchange mid-point, relative to a totally deuterated control, to quantify the rate of H/D exchange in each peptide. A weighted residue-by-residue average of these midpoints was used to map the extent of residual structure at near single-residue resolution. We validated this approach both by simulating a disordered protein and experimentally using the p300 binding domain of ACTR, a model disordered protein already well-characterized by other approaches. Secondary structure elements mapped in the present work are in good agreement with prior nuclear magnetic resonance measurements. The new approach was somewhat limited by a loss of spatial resolution and subject to artifacts because of heterogeneities in intrinsic exchange. Approaches to correct these limitations are discussed.

Keppel, Theodore R.; Weis, David D.

2015-04-01

58

NMR-Based Amide Hydrogen-Deuterium Exchange Measurements for Complex Membrane Proteins: Development and Critical Evaluation  

NASA Astrophysics Data System (ADS)

A method for measuring site-specific amide hydrogen-deuterium exchange rates for membrane proteins in bilayers is reported and evaluated. This method represents an adaptation and extension of the approach of Dempsey and co-workers ( Biophys. J. 70, 1777-1788 (1996)) and is based on reconstituting 15N-labeled membrane proteins into phospholipid bilayers, followed by lyophilization and rehydration with D 2O or H 2O (control). Following incubation for a time t under hydrated conditions, samples are again lyophilized and then solubilized in an organic solvent system, where 1H- 15N HSQC spectra are recorded. Comparison of spectra from D 2O-exposed samples to spectra from control samples yields the extent of the H-D exchange which occurred in the bilayers during time t. Measurements are site specific if specific 15N labeling is used. The first part of this paper deals with the search for a suitable solvent system in which to solubilize complex membrane proteins in an amide "exchange-trapped" form for NMR quantitation of amide peak intensities. The second portion of the paper documents application of the overall procedure to measuring site-specific amide exchange rates in diacylglycerol kinase, a representative integral membrane protein. Both the potential usefulness and the significant limitations of the new method are documented.

Czerski, Lech; Vinogradova, Olga; Sanders, Charles R.

2000-01-01

59

Combining ion mobility spectrometry with hydrogen-deuterium exchange and top-down MS for peptide ion structure analysis.  

PubMed

The gas-phase conformations of electrosprayed ions of the model peptide KKDDDDIIKIIK have been examined by ion mobility spectrometry (IMS) and hydrogen deuterium exchange (HDX)-tandem mass spectrometry (MS/MS) techniques. [M+4H](4+) ions exhibit two conformers with collision cross sections of 418 Å(2) and 471 Å(2). [M+3H](3+) ions exhibit a predominant conformer with a collision cross section of 340 Å(2) as well as an unresolved conformer (shoulder) with a collision cross section of ~367 Å(2). Maximum HDX levels for the more compact [M+4H](4+) ions and the compact and partially-folded [M+3H](3+) ions are ~12.9, ~15.5, and ~14.9, respectively. Ion structures obtained from molecular dynamics simulations (MDS) suggest that this ordering of HDX level results from increased charge-site/exchange-site density for the more compact ions of lower charge. Additionally, a new model that includes two distance calculations (charge site to carbonyl group and carbonyl group to exchange site) for the computer-generated structures is shown to better correlate to the experimentally determined per-residue deuterium uptake. Future comparisons of IMS-HDX-MS data with structures obtained from MDS are discussed with respect to novel experiments that will reveal the HDX rates of individual residues. PMID:25267084

Khakinejad, Mahdiar; Kondalaji, Samaneh Ghassabi; Maleki, Hossein; Arndt, James R; Donohoe, Gregory C; Valentine, Stephen J

2014-12-01

60

Characterization of IgG1 Conformation and Conformational Dynamics by Hydrogen/Deuterium Exchange Mass Spectrometry  

SciTech Connect

Protein function is dictated by protein conformation. For the protein biopharmaceutical industry, therefore, it is important to have analytical tools that can detect changes in protein conformation rapidly, accurately, and with high sensitivity. In this paper we show that hydrogen/deuterium exchange mass spectrometry (H/DX-MS) can play an important role in fulfilling this need within the industry. H/DX-MS was used to assess both global and local conformational behavior of a recombinant monoclonal IgG1 antibody, a major class of biopharmaceuticals. Analysis of exchange into the intact, glycosylated IgG1 (and the Fab and Fc regions thereof) showed that the molecule was folded, highly stable, and highly amenable to analysis by this method using less than a nanomole of material. With improved chromatographic methods, peptide identification algorithms and data-processing steps, the analysis of deuterium levels in peptic peptides produced after labeling was accomplished in 1--2 days. On the basis of peptic peptide data, exchange was localized to specific regions of the antibody. Changes to IgG1 conformation as a result of deglycosylation were determined by comparing exchange into the glycosylated and deglycosylated forms of the antibody. Two regions of the IgG1 (residues 236-253 and 292-308) were found to have altered exchange properties upon deglycosylation. These results are consistent with previous findings concerning the role of glycosylation in the interaction of IgG1 with Fc receptors. Moreover, the data clearly illustrate how H/DX-MS can provide important characterization information on the higher order structure of antibodies and conformational changes that these molecules may experience upon modification.

Houde, Damian; Arndt, Joseph; Domeier, Wayne; Berkowitz, Steven; Engen, John R.; (NEU); (Biogen)

2009-04-22

61

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

62

Activity-regulating structural changes and autoantibody epitopes in transglutaminase 2 assessed by hydrogen/deuterium exchange  

PubMed Central

The multifunctional enzyme transglutaminase 2 (TG2) is the target of autoantibodies in the gluten-sensitive enteropathy celiac disease. In addition, the enzyme is responsible for deamidation of gluten peptides, which are subsequently targeted by T cells. To understand the regulation of TG2 activity and the enzyme’s role as an autoantigen in celiac disease, we have addressed structural properties of TG2 in solution by using hydrogen/deuterium exchange monitored by mass spectrometry. We demonstrate that Ca2+ binding, which is necessary for TG2 activity, induces structural changes in the catalytic core domain of the enzyme. Cysteine oxidation was found to abolish these changes, suggesting a mechanism whereby disulfide bond formation inactivates the enzyme. Further, by using TG2-specific human monoclonal antibodies generated from intestinal plasma cells of celiac disease patients, we observed that binding of TG2 by autoantibodies can induce structural changes that could be relevant for the pathogenesis. Detailed mapping of two of the main epitopes targeted by celiac disease autoantibodies revealed that they are located adjacent to each other in the N-terminal part of the TG2 molecule. PMID:25404341

Iversen, Rasmus; Mysling, Simon; Hnida, Kathrin; Jørgensen, Thomas J. D.; Sollid, Ludvig M.

2014-01-01

63

Automated Hydrogen/Deuterium Exchange Electron Transfer Dissociation High Resolution Mass Spectrometry Measured at Single-Amide Resolution  

NASA Astrophysics Data System (ADS)

Hydrogen deuterium exchange mass spectrometry (HDX-MS) is a well established method for the measurement of solution-phase deuterium incorporation into proteins, which can provide insight into protein conformational mobility. However, most HDX measurements are constrained to regions of the protein where pepsin proteolysis allows detection at peptide resolution. Recently, single-amide resolution deuterium incorporation has been achieved by limiting gas-phase scrambling in the mass spectrometer. This was accomplished by employing a combination of soft ionization and desolvation conditions coupled with the radical-driven fragmentation technique electron transfer dissociation (ETD). Here, a hybrid LTQ-Orbitrap XL is systematically evaluated for its utility in providing single-amide deuterium incorporation for differential HDX analysis of a nuclear receptor upon binding small molecule ligands. We are able to show that instrumental parameters can be optimized to minimize scrambling and can be incorporated into an established and fully automated HDX platform making differential single-amide HDX possible for bottom-up analysis of complex systems. We have applied this system to determine differential single amide resolution HDX data for the peroxizome proliferator activated receptor bound with two ligands of interest.

Landgraf, Rachelle R.; Chalmers, Michael J.; Griffin, Patrick R.

2012-02-01

64

Hexicon 2: Automated Processing of Hydrogen-Deuterium Exchange Mass Spectrometry Data with Improved Deuteration Distribution Estimation  

NASA Astrophysics Data System (ADS)

Hydrogen-deuterium exchange (HDX) experiments analyzed by mass spectrometry (MS) provide information about the dynamics and the solvent accessibility of protein backbone amide hydrogen atoms. Continuous improvement of MS instrumentation has contributed to the increasing popularity of this method; however, comprehensive automated data analysis is only beginning to mature. We present Hexicon 2, an automated pipeline for data analysis and visualization based on the previously published program Hexicon (Lou et al. 2010). Hexicon 2 employs the sensitive NITPICK peak detection algorithm of its predecessor in a divide-and-conquer strategy and adds new features, such as chromatogram alignment and improved peptide sequence assignment. The unique feature of deuteration distribution estimation was retained in Hexicon 2 and improved using an iterative deconvolution algorithm that is robust even to noisy data. In addition, Hexicon 2 provides a data browser that facilitates quality control and provides convenient access to common data visualization tasks. Analysis of a benchmark dataset demonstrates superior performance of Hexicon 2 compared with its predecessor in terms of deuteration centroid recovery and deuteration distribution estimation. Hexicon 2 greatly reduces data analysis time compared with manual analysis, whereas the increased number of peptides provides redundant coverage of the entire protein sequence. Hexicon 2 is a standalone application available free of charge under http://hx2.mpimf-heidelberg.mpg.de.

Lindner, Robert; Lou, Xinghua; Reinstein, Jochen; Shoeman, Robert L.; Hamprecht, Fred A.; Winkler, Andreas

2014-06-01

65

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

PubMed

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

McMahon, T B; Ohanessian, G

2015-01-28

66

Synthesis, Spectroscopy, and Hydrogen/Deuterium Exchange in High-Spin Iron(II) Hydride Complexes  

PubMed Central

Very few hydride complexes are known in which the metals have a high-spin electronic configuration. We describe the characterization of several high-spin iron(II) hydride/deuteride isotopologues and their exchange reactions with one another and with H2/D2. Though the hydride/deuteride signal is not observable in NMR spectra, the choice of isotope has an influence on the chemical shifts of distant protons in the dimers through the paramagnetic isotope effect on chemical shift. This provides the first way to monitor the exchange of H and D in the bridging positions of these hydride complexes. The rate of exchange depends on the size of the supporting ligand, and this is consistent with the idea that H2/D2 exchange into the hydrides occurs through the dimeric complexes rather than through a transient monomer. The understanding of H/D exchange mechanisms in these high-spin iron hydride complexes may be relevant to postulated nitrogenase mechanisms. PMID:24555749

2015-01-01

67

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

2013-07-01

68

Nickel\\/Chromium oxide\\/Zirconium oxide Catalysts for Hydrogen\\/Deuterium Isotopic Exchange  

Microsoft Academic Search

Catalysts composed of nickel and promoted with different metal oxides proved to be suitable for H\\/D isotropic exchange between hydrogen and water vapour. They loss their activity due to water condensation on their surfaces. Several nickel\\/chromium oxide\\/zirconium oxide catalysts of different composition were prepared by the coprecipitation technique. The liquid phase activity of these catalysts were followed using the hydrogen

M. M. Abdel-Badei; A. El-Sharkawi; M. Abdel-Khalik; F. Abou El-Nour

1990-01-01

69

Using Hydrogen/Deuterium Exchange Mass Spectrometry to Define the Specific Interactions of the Phospholipase A2 Superfamily with Lipid Substrates, Inhibitors, and Membranes*  

PubMed Central

The phospholipase A2 (PLA2) superfamily consists of 16 groups and many subgroups and constitutes a diverse set of enzymes that have a common catalytic activity due to convergent evolution. However, different PLA2 types have unique three-dimensional structures and catalytic residues as well as specific tissue localization and distinct biological functions. Understanding how the different PLA2 enzymes associate with phospholipid membranes, specific phospholipid substrate molecules, and inhibitors on a molecular basis has advanced in recent years due to the introduction of hydrogen/deuterium exchange mass spectrometry. Its theory, practical considerations, and application to understanding PLA2/membrane interactions are addressed. PMID:23209293

Cao, Jian; Burke, John E.; Dennis, Edward A.

2013-01-01

70

The combination of hydrogen/deuterium exchange or chemical cross-linking techniques with mass spectrometry: mapping of human 14-3-3? homodimer interface.  

PubMed

Hydrogen/deuterium (H/D) exchange or chemical cross-linking by soluble carbodiimide (EDC) was employed in combination with high-resolution mass spectrometry (MS) to extend our knowledge about contact surface regions involved in the well-characterized model of interaction between two molecules of human 14-3-3? regulatory protein. The H/D exchange experiment provided low resolution mapping of interaction in the homodimeric 14-3-3? complex. A lower level of deuteration, suggesting structural protection, of two sequential segments has been demonstrated for dimeric 14-3-3? wild type relative to the monomeric mutant 14-3-3? S58D. The N-terminal sequence (the first 27 residues) from one subunit interacts with region ?C'and ?D'-helices (residues 45-98) of the other molecule across the dimer interface. To identify interacting amino acid residues within the studied complex, a chemical cross-linking reaction was carried out to produce the covalent homodimer, which was detected by SDS-PAGE. The MS analysis (following tryptic in-gel digestion) employing both high resolution and tandem mass spectrometry revealed cross-linked amino acid residues. Two alternative salt bridges between Glu81 and either Lys9 or the N-terminal amino group have been found to participate in transient interactions of the 14-3-3? isotype homodimerization. The data obtained, which have never previously been reported, were used to modify the published 14-3-3 crystal structure using molecular modeling. Based on our findings, utilization of this combination of experimental approaches, which preserve protein native structures, is suitable for mapping the contact between two proteins and also allows for the description of transient interactions or of regions with flexible structure in the studied protein complexes. PMID:22580067

Haladová, Kate?ina; Mrázek, Hynek; Je?men, Tomáš; Halada, Petr; Man, Petr; Novák, Petr; Chmelík, Josef; Obšil, Tomáš; Šulc, Miroslav

2012-07-01

71

Characterization of the interface structure of enzyme-inhibitor complex by using hydrogen-deuterium exchange and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry.  

PubMed Central

We investigated the interaction between a thiol protease inhibitor, cystatin, and its target enzyme, papain, by hydrogen-deuterium (H/D) exchange in conjunction with successive analysis by collision-induced dissociation (CID) in an rf-only hexapole ion guide with electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR MS). The deuterium incorporation into backbone amide hydrogens of cystatin was analyzed at different time points in the presence or absence of papain, examining the mass of each fragment produced by hexapole-CID. In the absence of papain, amide hydrogens in short amino-terminal fragments, such as b10(2+) and b12(2+), were highly deuterated within 1 min. Although fewer fragments were observed for the cystatin-papain complex in the hexapole-CID spectra, significant reductions in initial deuterium content were recognized throughout the sequence of cystatin. This suggests that complex formation restricted the flexibility of the whole cystatin molecule. Detailed analyses revealed that a marked reduction in deuterium content in the region of residues 1-10 persisted for hours, suggesting that the flexible N-terminal region was tightly fixed in the binding pocket with hydrogen bonds. Our results are consistent with those of previous studies on the structure and inhibition mechanism of cystatin. We demonstrated here that enzyme-inhibitor interactions can be characterized by H/D exchange in combination with CID in a hexapole ion guide using ESI-FTICR MS rapidly and using only a small amount of sample. PMID:11206071

Akashi, S.; Takio, K.

2000-01-01

72

Effect of B-Z transition and nucleic acid structure on the conformational dynamics of bound ethidium dimer measured by hydrogen deuterium exchange kinetics.  

PubMed Central

Ethidium dimer is shown to bind by intercalation, almost equally well, to the B and Z form of poly[(dG-m5dC)].poly[(dG-m5dC)], whereas the ethidium monomer shows a strong preference for the B form. The hydrogen-deuterium (H-D) exchange kinetics of the ethidium dimer bound to the B and Z form of poly [(dG-m5dC)].poly[(dG-m5dC)] could then be compared. The kinetics of the H-D exchange were strikingly slower when the dye was bound to Z DNA as compared to B DNA. The exchange kinetics were also modified when ethidium dimer was bound to tRNA and to a triple stranded structure. It is proposed that a dynamic fluctuation at the level of the nucleic acid could modulate the dynamic fluctuation at the level of the bound ligand. PMID:4011442

Markovits, J; Ramstein, J; Roques, B P; Le Pecq, J B

1985-01-01

73

Conformation and dynamics of interchain cysteine-linked antibody-drug conjugates as revealed by hydrogen/deuterium exchange mass spectrometry.  

PubMed

Antibody-drug conjugates (ADCs) are protein therapeutics in which a target specific monoclonal antibody (mAb) is conjugated with drug molecules. The manufacturing of ADCs involves additional conjugation steps, which are carried out on the parent mAbs, and it is important to evaluate how the drug conjugation process impacts the conformation and dynamics of the mAb. Here, we present a comparative study of interchain cysteine linked IgG1 ADCs and the corresponding mAb by hydrogen/deuterium exchange mass spectrometry (HDX-MS). We found that ?90% of the primary sequence of the ADC conjugated with either monomethyl auristatin E or F (vcMMAE/mcMMAF) displayed the same HDX kinetics as the mAb, indicating the ADCs and mAbs share very similar conformation and dynamics in solution. Minor increases in HDX kinetic rates were observed in two Fc regions in the ADCs relative to the mAb which indicated that both regions become more structurally dynamic and/or more solvent-accessible in the ADCs. The findings led to a subsequent inquiry into whether the local conformational changes were due to the presence of drugs on the interchain cysteine residues or the absence of intact interchain disulfides or both. To address this question, a side-by-side HDX comparison of ADCs, mAbs, reduced mAbs (containing 8 reduced interchain cysteine thiols), and partially reduced mAbs (conjugation process intermediate) was performed. Our results indicated that the slight increase in conformational dynamics detected at the two regions in the ADCs was due to the absence of intact interchain disulfide bonds and not the presence of vcMMAE or mcMMAF on the alkylated interchain cysteine residues. These results highlight the utility of HDX-MS for interrogating the higher-order structure of ADCs and other protein therapeutics. PMID:24512515

Pan, Lucy Yan; Salas-Solano, Oscar; Valliere-Douglass, John F

2014-03-01

74

Enumeration of labile hydrogens in natural organic matter by use of hydrogen/deuterium exchange Fourier transform ion cyclotron resonance mass spectrometry.  

PubMed

A method to enumerate labile hydrogens in all constituents of molecular ensemble of natural organic matter (NOM) based on our previously developed simple hydrogen/deuterium (H/D) exchange (electrospray ionization (ESI) ion source (Kostyukevich et al. Anal. Chem. 2013, 85, 5330) and ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry is presented. The method was applied for analysis of Suwannee River fulvic acid (SRFA), which is an International Humic Substances Society standard, as well as Siberian crude oil; and lignosulfonate. We found that SRFA and lignosulfonate molecules contain 2-5 labile hydrogens, and their number increases with the number of oxygens in the molecule. Also, we observed that compounds of Siberian crude oil ionizing in positive-ESI mode do not have labile hydrogens, while compounds ionizing in negative-ESI mode have one labile hydrogen that detaches during ESI ionization. PMID:24098913

Kostyukevich, Yury; Kononikhin, Alexey; Popov, Igor; Kharybin, Oleg; Perminova, Irina; Konstantinov, Andrey; Nikolaev, Eugene

2013-11-19

75

Automated data reduction for hydrogen/deuterium exchange experiments, enabled by high-resolution Fourier transform ion cyclotron resonance mass spectrometry.  

PubMed

Mass analysis of proteolytic fragment peptides following hydrogen/deuterium exchange offers a general measure of solvent accessibility/hydrogen bonding (and thus conformation) of solution-phase proteins and their complexes. The primary problem in such mass analyses is reliable and rapid assignment of mass spectral peaks to the correct charge state and degree of deuteration of each fragment peptide, in the presence of substantial overlap between isotopic distributions of target peptides, autolysis products, and other interferant species. Here, we show that at sufficiently high mass resolving power (m/Delta m(50%) > or = 100,000), it becomes possible to resolve enough of those overlaps so that automated data reduction becomes possible, based on the actual elemental composition of each peptide without the need to deconvolve isotopic distributions. We demonstrate automated, rapid, reliable assignment of peptide masses from H/D exchange experiments, based on electrospray ionization FT-ICR mass spectra from H/D exchange of solution-phase myoglobin. Combined with previously demonstrated automated data acquisition for such experiments, the present data reduction algorithm enhances automation (and thus expands generality and applicability) for high-resolution mass spectrometry-based analysis of H/D exchange of solution-phase proteins. PMID:20116280

Kazazic, Sasa; Zhang, Hui-Min; Schaub, Tanner M; Emmett, Mark R; Hendrickson, Christopher L; Blakney, Gregory T; Marshall, Alan G

2010-04-01

76

Automated Data Reduction for Hydrogen/Deuterium Exchange Experiments, Enabled by High-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry  

PubMed Central

Mass analysis of proteolytic fragment peptides following hydrogen/deuterium exchange offers a general measure of solvent accessibility/hydrogen bonding (and thus conformation) of solution-phase proteins and their complexes. The primary problem in such mass analyses is reliable and rapid assignment of mass spectral peaks to the correct charge state and degree of deuteration of each fragment peptide, in the presence of substantial overlap between isotopic distributions of target peptides, autolysis products, and other interferant species. Here, we show that at sufficiently high mass resolving power (m/?m50% ? 100,000), it becomes possible to resolve enough of those overlaps so that automated data reduction becomes possible, based on the actual elemental composition of each peptide without the need to deconvolve isotopic distributions. We demonstrate automated, rapid, reliable assignment of peptide masses from H/D exchange experiments, based on electrospray ionization FT-ICR mass spectra from H/D exchange of solution-phase myoglobin. Combined with previously demonstrated automated data acquisition for such experiments, the present data reduction algorithm enhances automation (and thus expands generality and applicability) for high-resolution mass spectrometry- based analysis of H/D exchange of solution-phase proteins. PMID:20116280

Kazazic, Sasa; Zhang, Hui-Min; Schaub, Tanner M.; Emmett, Mark R.; Hendrickson, Christopher L.; Blakney, Gregory T.; Marshall, Alan G.

2010-01-01

77

External reflection FTIR of peptide monolayer films in situ at the air/water interface: experimental design, spectra-structure correlations, and effects of hydrogen-deuterium exchange.  

PubMed Central

A Fourier transform infrared spectrometer has been interfaced with a surface balance and a new external reflection infrared sampling accessory, which permits the acquisition of spectra from protein monolayers in situ at the air/water interface. The accessory, a sample shuttle that permits the collection of spectra in alternating fashion from sample and background troughs, reduces interference from water vapor rotation-vibration bands in the amide I and amide II regions of protein spectra (1520-1690 cm-1) by nearly an order of magnitude. Residual interference from water vapor absorbance ranges from 50 to 200 microabsorbance units. The performance of the device is demonstrated through spectra of synthetic peptides designed to adopt alpha-helical, antiparallel beta-sheet, mixed beta-sheet/beta-turn, and unordered conformations at the air/water interface. The extent of exchange on the surface can be monitored from the relative intensities of the amide II and amide I modes. Hydrogen-deuterium exchange may lower the amide I frequency by as much as 11-12 cm-1 for helical secondary structures. This shifts the vibrational mode into a region normally associated with unordered structures and leads to uncertainties in the application of algorithms commonly used for determination of secondary structure from amide I contours of proteins in D2O solution. PMID:7919013

Flach, C R; Brauner, J W; Taylor, J W; Baldwin, R C; Mendelsohn, R

1994-01-01

78

Dissecting the binding mode of low affinity phage display peptide ligands to protein targets by hydrogen/deuterium exchange coupled to mass spectrometry.  

PubMed

Phage display (PD) is frequently used to discover peptides capable of binding to biological protein targets. The structural characterization of peptide-protein complexes is often challenging due to their low binding affinities and high structural flexibility. Here, we investigate the use of hydrogen/deuterium exchange mass spectrometry (HDX-MS) to characterize interactions of low affinity peptides with their cognate protein targets. The HDX-MS workflow was optimized to accurately detect low-affinity peptide-protein interactions by use of ion mobility, electron transfer dissociation, nonbinding control peptides, and statistical analysis of replicate data. We show that HDX-MS can identify regions in the two epigenetic regulator proteins KDM4C and KDM1A that are perturbed through weak interactions with PD-identified peptides. Two peptides cause reduced HDX on opposite sides of the active site of KDM4C, indicating distinct binding modes. In contrast, the perturbation site of another PD-selected peptide inhibiting the function of KDM1A maps to a GST-tag. Our results demonstrate that HDX-MS can validate and map weak peptide-protein interactions and pave the way for understanding and optimizing the binding of peptide scaffolds identified through PD and similar ligand discovery approaches. PMID:25325890

Leurs, Ulrike; Lohse, Brian; Ming, Shonoi; Cole, Philip A; Clausen, Rasmus P; Kristensen, Jesper L; Rand, Kasper D

2014-12-01

79

Sites involved in intra- and interdomain allostery associated with the activation of factor viia pinpointed by hydrogen-deuterium exchange and electron transfer dissociation mass spectrometry.  

PubMed

Factor VIIa (FVIIa) is a trypsin-like protease that plays an important role in initiating blood coagulation. Very limited structural information is available for the free, inactive form of FVIIa that circulates in the blood prior to vascular injury and the molecular details of its activity enhancement remain elusive. Here we have applied hydrogen/deuterium exchange mass spectrometry coupled to electron transfer dissociation to pinpoint individual residues in the heavy chain of FVIIa whose conformation and/or local interaction pattern changes when the enzyme transitions to the active form, as induced either by its cofactor tissue factor or a covalent active site inhibitor. Identified regulatory residues are situated at key sites across one continuous surface of the protease domain spanning the TF-binding helix across the activation pocket to the calcium binding site and are embedded in elements of secondary structure and at the base of flexible loops. Thus these residues are optimally positioned to mediate crosstalk between functional sites in FVIIa, particularly the cofactor binding site and the active site. Our results unambiguously show that the conformational allosteric activation signal extends to the EGF1 domain in the light chain of FVIIa, underscoring a remarkable intra- and interdomain allosteric regulation of this trypsin-like protease. PMID:25344622

Song, Hongjian; Olsen, Ole H; Persson, Egon; Rand, Kasper D

2014-12-19

80

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

81

Development and implementation of a FT-ICR mass spectrometer for the investigation of ion conformations of peptide sequence isomers containing basic amino acid residues by gas-phase hydrogen/deuterium exchange  

E-print Network

ions.24 Of the ion-molecule probes employed for structural determination, none have been as successful as hydrogen/deuterium (H/D) exchange. This isotope-labeling technique is based upon the exchange of labile hydrogens (i.e. amine, amide, and ?OH... on non-polar, aliphatic amino acids and peptides.39,43,44,45,46 In these systems, the most likely site for protonation is the N- terminal amine, with possible charge site solvation by amide carbonyl groups.47 Although understanding of gas-phase H...

Marini, Joseph Thomas

2004-09-30

82

beta-Lactamase binds to GroEL in a conformation highly protected against hydrogen/deuterium exchange.  

PubMed Central

Escherichia coli RTEM beta-lactamase reversibly forms a stable complex with GroEL, devoid of any enzymatic activity, at 48 degrees C. When beta-lactamase is diluted from this complex into denaturant solution, its unfolding rate is identical to that from the native state, while the unfolding rate from the molten globule state is too fast to be measured. Electrospray mass spectrometry shows that the rate of proton exchange in beta-lactamase in the complex at 48 degrees C is slower than in the absence of GroEL at the same temperature, and resembles the exchange of the native state at 25 degrees C. Similarly, the final number of protected deuterons is higher in the presence of GroEL than in its absence. We conclude that, for beta-lactamase, a state with significant native structure is bound to GroEL. Thus, different proteins are recognized by GroEL in very different states, ranging from totally unfolded to native-like, and this recognition may depend on which state can provide sufficient accessible hydrophobic amino acids in a suitably clustered arrangement. Reversible binding of native-like states with hydrophobic patches may be an important property of GroEL to protect the cell from aggregating protein after heat-shock. PMID:8901555

Gervasoni, P; Staudenmann, W; James, P; Gehrig, P; Plückthun, A

1996-01-01

83

Hydrogen\\/Deuterium Exchange Mass Spectrometry with Top-Down Electron Capture Dissociation for Characterizing Structural Transitions of a 17 kDa Protein  

Microsoft Academic Search

Amide H\\/D exchange (HDX) mass spectrometry (MS) is widely used for protein structural studies. Traditionally, this technique involves protein labeling in D(2)O, followed by acid quenching, proteolytic digestion, and analysis of peptide deuteration levels by HPLC\\/MS. There is great interest in the development of alternative HDX approaches involving the top-down fragmentation of electrosprayed protein ions, instead of relying on enzymatic

Jingxi Pan; Jun Han; Christoph H. Borchers; Lars Konermann

2009-01-01

84

Rapid identification of phase I and II metabolites of artemisinin antimalarials using LTQ-Orbitrap hybrid mass spectrometer in combination with online hydrogen/deuterium exchange technique.  

PubMed

Artemisinin drugs have become the first-line antimalarials in areas of multi-drug resistance. However, monotherapy with artemisinin drugs results in comparatively high recrudescence rates. Autoinduction of CYP-mediated metabolism, resulting in reduced exposure, has been supposed to be the underlying mechanism. To better understand the autoinduction of artemisinin drugs, we evaluated the biotransformation of artemisinin, also known as Qing-hao-su (QHS), and its active derivative dihydroartemisinin (DHA) in vitro and in vivo, using LTQ-Orbitrap hybrid mass spectrometer in conjunction with online hydrogen (H)/deuterium (D) exchange high-resolution (HR)-LC/MS (mass spectrometry) for rapid structural characterization. The LC separation was improved allowing the separation of QHS parent drugs and their metabolites from their diastereomers. Thirteen phase I metabolites of QHS have been identified in liver microsomal incubates, rat urine, bile and plasma, including six deoxyhydroxylated metabolites, five hydroxylated metabolites, one dihydroxylated metabolite and deoxyartemisinin. Twelve phase II metabolites of QHS were detected in rat bile, urine and plasma. DHA underwent similar metabolic pathways, and 13 phase I metabolites and 3 phase II metabolites were detected. Accurate mass data were obtained in both full-scan and MS/MS mode to support assignments of metabolite structures. Online H/D exchange LC-HR/MS experiments provided additional evidence in differentiating deoxydihydroxylated metabolites from mono-hydroxylated metabolites. The results showed that the main phase I metabolites of artemisinin drugs are hydroxylated and deoxyl products, and they will undergo subsequent phase II glucuronidation processes. This study also demonstrated the effectiveness of online H/D exchange LC-HR/MS(n) technique in rapid identification of drug metabolites. PMID:21766391

Liu, Tian; Du, Fuying; Wan, Yakun; Zhu, Fanping; Xing, Jie

2011-08-01

85

Isotopic effect study in the LHCD and LHH experiments in hydrogen/deuterium plasmas of the FT-2 tokamak  

SciTech Connect

Results of comparative experimental studies of the efficiency of lower hybrid current drive (LHCD) and lower hybrid heating (LHH) in the FT-2 tokamak in hydrogen and deuterium plasmas are presented. In the new comparative experimental runs in deuterium/hydrogen plasmas suppression of the LHCD and beginning of the interaction of LH waves with ions is controlled by the plasma density rise. Role of parametric instabilities in CD switch-off is considered. In order to analyze the experimentally observed effect of LHCD the GRILL3D and FRTC codes has been used.

Lashkul, S. I.; Altukhov, A. B.; Gusakov, E. Z.; Dyachenko, V. V.; Esipov, L. A.; Irzak, M. A.; Kantor, M. Yu.; Kouprienko, D. V.; Saveliev, A. N. [A. F. Ioffe Physical-Technical Institute, Politekhnicheskaya 26, 194021, St. Petersburg (Russian Federation); Shatalin, S. V. [St. Petersburg State Polytekhnical University, St. Petersburg (Russian Federation); Stepanov, A. Yu. [A.F. Ioffe Physical-Technical Institute, Politekhnicheskaya 26, 194021, St. Petersburg (Russian Federation)

2014-02-12

86

Hydrogen/deuterium exchange mass spectrometry with top-down electron capture dissociation for characterizing structural transitions of a 17 kDa protein.  

PubMed

Amide H/D exchange (HDX) mass spectrometry (MS) is widely used for protein structural studies. Traditionally, this technique involves protein labeling in D(2)O, followed by acid quenching, proteolytic digestion, and analysis of peptide deuteration levels by HPLC/MS. There is great interest in the development of alternative HDX approaches involving the top-down fragmentation of electrosprayed protein ions, instead of relying on enzymatic cleavage and solution-phase separations. A number of recent studies have demonstrated that electron capture dissociation (ECD) results in fragmentation of gaseous protein ions with little or no H/D scrambling. However, the successful application of this approach for in-depth protein conformational studies has not yet been demonstrated. The current work uses horse myoglobin as a model system for assessing the suitability of HDX-MS with top-down ECD for experiments of this kind. It is found that ECD can pinpoint the locations of protected amides with an average resolution of less than two residues for this 17 kDa protein. Native holo-myoglobin (hMb) shows considerable protection from exchange in all of its helices, whereas loops are extensively deuterated. Fraying is observable at some helix termini. Removal of the prosthetic heme group from hMb produces apo-myoglobin (aMb). Both hMb and aMb share virtually the same HDX protection pattern in helices A-E, whereas helix F is unfolded in aMb. In addition, destabilization is evident for some residues close to the beginning of helix G, the end of helix H, and the C-terminus of the protein. The structural changes reported herein are largely consistent with earlier NMR data for sperm whale myoglobin, although small differences between the two systems are evident. Our findings demonstrate that the level of structural information obtainable with top-down ECD for small to medium-sized proteins considerably surpasses that of traditional HDX-MS experiments, while at the same time greatly reducing undesired amide back exchange. PMID:19670873

Pan, Jingxi; Han, Jun; Borchers, Christoph H; Konermann, Lars

2009-09-01

87

Hydrogen-deuterium exchange of diborane in superacid solution through diboranonium (B sub 2 H sub 7 sup + ) and diboranium (B sub 2 H sub 5 sup + ) ions  

SciTech Connect

The slow proton/deuterium exchange of B{sub 2}H{sub 6} in the superacidic FSO{sub 3}D SbF{sub 5}/SO{sub 2}ClF medium at low temperature involving the corresponding isotopomeric diboranonium ions B{sub 2}H{sub 7}{sup +} is reported here. The structure of the B{sub 2}H{sub 7}{sup +} ion has also been probed by ab inito theoretical calculations. The H/D exchange is rationalized by the pathway that deuteriation occurs exclusively on an unbridged (terminal B-H) bond resulting in a B{sub 2}H{sub 6}D{sup +} ion which is expected to undergo polytopol (bond-to-bond) rearrangement scrambling all hydrogens and deuteriums followed by proton loss leading to the exchanged product. 18 references.

Olah, G.A.; Aniszfeld, R.; Surya Prakash, G.K.; Williams, R.E.; Lammertsma, K.; Guener, O.F.

1988-11-09

88

ETD in a Traveling Wave Ion Guide at Tuned Z-Spray Ion Source Conditions Allows for Site-Specific Hydrogen\\/Deuterium Exchange Measurements  

Microsoft Academic Search

The recent application of electron transfer dissociation (ETD) to measure the hydrogen exchange of proteins in solution at\\u000a single-residue resolution (HX-ETD) paves the way for mass spectrometry-based analyses of biomolecular structure at an unprecedented\\u000a level of detail. The approach requires that activation of polypeptide ions prior to ETD is minimal so as to prevent undesirable\\u000a gas-phase randomization of the deuterium

Kasper D. Rand; Steven D. Pringle; Michael Morris; John R. Engen; Jeffery M. Brown

89

Omegatron mass spectrometer in a hydrogen/deuterium detached plasma  

SciTech Connect

Diagnostics of the relative concentrations of the atomic and molecular ions were carried out in hydrogen/deuterium plasma with hydrogen/deuterium gas puff in the linear plasma device, TPD-SheetIV. An omegatron ion mass spectrometer is used for analyzing ion species.

Tonegawa, A.; Nishijima, T.; Ishioka, H.; Nakanowatari, A.; Kawamura, K. [Department of Physics, School of Science, Tokai University, Kitakaname 1117, Hiratsuka 259-1292 (Japan)

2008-03-12

90

Monitoring allostery in D 2 O: a necessary control in studies using hydrogen\\/deuterium exchange to characterize allosteric regulation  

Microsoft Academic Search

There is currently a renewed focus aimed at understanding allosteric mechanisms at atomic resolution. This current interest\\u000a seeks to understand how both changes in protein conformations and changes in protein dynamics contribute to relaying an allosteric\\u000a signal between two ligand binding sites on a protein (e.g., active and allosteric sites). Both nuclear magnetic resonance\\u000a (NMR), by monitoring protein dynamics directly,

Charulata B. Prasannan; Antonio Artigues; Aron W. Fenton

2011-01-01

91

Protonated hydronium dication, H/sub 4/O/sup 2 +/. Hydrogen-deuterium exchange of D/sub 2/H/sup 17/O/sup +/ in HF:SbF/sub 5/ and DH/sub 2//sup 17/O/sup +/ in DF:SbF/sub 5/ and theoretical calculations  

SciTech Connect

Isotopic hydronium ions D/sub 2/H/sup 17/O/sup +/ and DH/sub 2//sup 17/O/sup +/ in 1:1 (molar) HF:SbF/sub 5//SO/sub 2/ and DF:SbF/sub 2/SO/sub 2/ solutions, respectively, at -15/sup 0/C undergo slow hydrogen-deuterium exchange as monitored by /sup 17/O NMR spectroscopy. The rate of such exchange increases with the increase in the acidity of the fluoroantimonic acid medium (1:2 molar composition). The previously observed lack of exchange of isotopic hydronium ions in the somewhat weaker Magic Acid, FSO/sub 3/H:SbF/sub 5/, medium (H/sub 0/ approx. -21.5) suggests that in the stronger HF:SbF/sub 5/ medium (H/sub 0/ approx. -25 to -28), the exchange occurs through the intermediacy of protonated hydronium dication. Consequently, the structure and stability of protonated hydronium dication has been probed by ab initio theory. The T/sub d/ symmetry structure was found to be the minimum energy structure at the HF/6.31G* level. At the HF/6.31G* level this structure is thermodynamically unstable (dissociation preferred by 59.2 kcal/mol), it seems to have significant kinetic stability (deprotonation barrier 39.4 kcal/mol). 20 references, 1 table.

Olah, G.A.; Prakash, G.K.S.; Barzaghi, M.; Lammertsma, K.; von R. Schleyer, P.; Pople, J.A.

1986-03-05

92

Hot-carrier stress effects on gate-induced-drain leakage current in n-channel MOSFETs studied by hydrogen\\/deuterium isotope effect  

Microsoft Academic Search

The degradation of gate-induced-drain leakage (GIDL) current under hot-carrier stress (HCS) has been studied in n-channel MOSFETs that were annealed in hydrogen (H) or deuterium (D). It is found that the degradation of GIDL current (IGIDL) can be effectively suppressed by deuterium passivation of interface traps. By using the H\\/D isotope effect, the impacts of oxide charge trapping (?Nox) and

Kangguo Cheng; Joseph W. Lyding

2003-01-01

93

Nucleus polarizability contribution to the hydrogen-deuterium isotope shift  

E-print Network

The correction to the hydrogen-deuterium isotope shift due to the proton and deuteron polarizability is evaluated on the basis of modern experimental data on the structure functions of inelastic lepton-nucleus scattering. The numerical value of this contribution is equal 63\\pm 12 Hz.

R. N. Faustov; A. P. Martynenko

2001-08-10

94

Metabolite identification of artemether by data-dependent accurate mass spectrometric analysis using an LTQ-Orbitrap hybrid mass spectrometer in combination with the online hydrogen/deuterium exchange technique.  

PubMed

Artemether (ARM), the O-methyl ether prodrug of dihydroartemisinin (DHA), is a first-line antimalarial drug used in areas of multi-drug resistance. Artemisinin drugs can be metabolized extensively in vivo and this seems related to their autoinduction pharmacokinetics. In the present study, the metabolite identification of ARM was performed by the generic data-dependent accurate mass spectrometric analysis, using high-resolution (HR) liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) and tandem mass spectrometry (MS/MS) LTQ-Orbitrap hybrid mass spectrometer in conjunction with online hydrogen (H)/deuterium (D) exchange for rapid structural characterization. The LC separation was improved allowing the separation of ARM parent drugs and their metabolites from their diastereomers. A total of 77 phase I metabolites of ARM were identified in rat liver microsomal incubates and rat urine, including dihydroartemisinin and artemisinin. In rat bile, 12 phase II metabolites were found. Accurate mass data were obtained in both full scan and HR-MS/MS mode to support assignments of metabolite structures. Online H/D exchange LC/HR-ESI-MS experiments provided additional evidence in differentiating dihydroxylated deoxy-ARM from mono-hydroxylated ARM. The results showed the main phase I metabolites of artemether are hydroxylated, dehydro, demethylated and deoxy products, and they will undergo subsequent phase II glucuronidation processes. Most metabolites were reported for the first time. This study also demonstrated the effectiveness of high-resolution mass spectrometry in combination with an online H/D exchange LC/HR-MS(n) technique in rapid identification of drug metabolites. PMID:22006394

Liu, Tian; Du, Fuying; Zhu, Fanping; Xing, Jie

2011-11-15

95

Epitope mapping of a 95 kDa antigen in complex with antibody by solution-phase amide backbone hydrogen/deuterium exchange monitored by Fourier transform ion cyclotron resonance mass spectrometry.  

PubMed

The epitopes of a homohexameric food allergen protein, cashew Ana o 2, identified by two monoclonal antibodies, 2B5 and 1F5, were mapped by solution-phase amide backbone H/D exchange (HDX) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) and the results were compared to previous mapping by immunological and mutational analyses. Antibody 2B5 defines a conformational epitope, and 1F5 defines a linear epitope. Intact murine IgG antibodies were incubated with recombinant Ana o 2 (rAna o 2) to form antigen-monoclonal antibody (Ag-mAb) complexes. mAb-complexed and uncomplexed (free) rAna o 2 were then subjected to HDX. HDX instrumentation and automation were optimized to achieve high sequence coverage by protease XIII digestion. The regions protected from H/D exchange upon antibody binding overlap and thus confirm the previously identified epitope-bearing segments: the first extension of HDX monitored by mass spectrometry to a full-length antigen-antibody complex in solution. PMID:21861454

Zhang, Qian; Willison, LeAnna N; Tripathi, Pallavi; Sathe, Shridhar K; Roux, Kenneth H; Emmett, Mark R; Blakney, Greg T; Zhang, Hui-Min; Marshall, Alan G

2011-09-15

96

Excited state muon transfer in hydrogen/deuterium mixtures  

SciTech Connect

We report the first direct observation of excited state muon transfer in hydrogen/deuterium mixtures by direct measurement of {ital q}{sub 1{ital s}}, the probability that a {mu}{ital p} atom, which is initially formed in an excited state, reaches the 1{ital s} ground state. The dependence of {ital q}{sub 1{ital s}} on deuterium concentration {ital c}{sub {ital d}} was measured for two different densities at cryogenic temperatures using charge coupled devices to detect the muonic x rays. First results based on the analysis of the {ital K}{sub {alpha}} lines of the two isotopes are presented. {copyright} {ital 1996 The American Physical Society.}

Lauss, B.; Ackerbauer, P.; Breunlich, W.H.; Gartner, B.; Jeitler, M.; Kammel, P.; Marton, J.; Prymas, W.; Zmeskal, J. [Institute for Medium Energy Physics, Austrian Academy of Sciences, Boltzmanngasse 3, A-1090 Wien (Austria)] [Institute for Medium Energy Physics, Austrian Academy of Sciences, Boltzmanngasse 3, A-1090 Wien (Austria); Chatellard, D.; Egger, J.; Jeannet, E. [Institut de Physique de l`Universite, CH-2000 Neuchatel (Switzerland)] [Institut de Physique de l`Universite, CH-2000 Neuchatel (Switzerland); Daniel, H.; Kosak, A.; Hartmann, F.J. [Physik Department, TU Muenchen, D-85748 Garching (Germany)] [Physik Department, TU Muenchen, D-85748 Garching (Germany); Petitjean, C. [Paul Scherrer Institut, CH-5232 Villigen (Switzerland)] [Paul Scherrer Institut, CH-5232 Villigen (Switzerland)

1996-06-01

97

Radiative Correction to the Nuclear-Size Effect and Hydrogen-Deuterium Isotopic Shift  

E-print Network

The radiative correction to the nuclear charge radius contribution to the Lamb shift of order $\\alpha(Z\\alpha)^5m_r^3$ is calculated. In view of the recent high precision experimental data, this theoretical correction produces a significant contribution to the hydrogen-deuterium isotopic shift.

Michael I. Eides; Howard Grotch

1997-09-19

98

Folding Study of Venus Reveals a Strong Ion Dependence of Its Yellow Fluorescence under Mildly Acidic Conditions*S  

E-print Network

Folding Study of Venus Reveals a Strong Ion Dependence of Its Yellow Fluorescence under Mildly- cencethatisrelativelyinsensitivetochangesinpHandionconcen- trations. Here, we present a detailed study of the stability and fold- ing of Venus. By following hydrogen-deuterium exchange of 15 N-labeled Venus using NMR spectroscopy over 13 months, residue

Jackson, Sophie

99

Study Abroad & Exchange Students  

E-print Network

Study Abroad & Exchange Students Essential Guide 2011 #12;Study Abroad Office, The University of Western Australia CRICOS Provider Code: 00126G Page 2 CONTENTS THE STUDY ABROAD OFFICE ...................................................................................................................... 3 Study Abroad Office Staff

Petriu, Emil M.

100

Precision Measurement of the Hydrogen-Deuterium 1S-2S Isotope Shift  

NASA Astrophysics Data System (ADS)

Measuring the hydrogen-deuterium isotope shift via two-photon spectroscopy of the 1S-2S transition, we obtain 670 994 334 606(15) Hz. This is a 10-times improvement over the previous best measurement [A. Huber , Phys. Rev. Lett. 80, 468 (1998)PRLTAO0031-900710.1103/PhysRevLett.80.468] confirming its frequency value. A calculation of the difference of the mean square charge radii of deuterium and hydrogen results in ?r2?d-?r2?p=3.82007(65)fm2, a more than twofold improvement compared to the former value.

Parthey, Christian G.; Matveev, Arthur; Alnis, Janis; Pohl, Randolf; Udem, Thomas; Jentschura, Ulrich D.; Kolachevsky, Nikolai; Hänsch, Theodor W.

2010-06-01

101

The hydrogen/deuterium isotope effect of the host material on the lifetime of organic light-emitting diodes.  

PubMed

The hydrogen/deuterium primary kinetic isotope effect provides useful information about the degradation mechanism of OLED host materials. Thus, replacement of labile C-H bonds in the host with C-D bonds increases the device lifetime by a factor of five without loss of efficiency, and replacement with C-C bonds by a factor of 22.5. PMID:25325237

Tsuji, Hayato; Mitsui, Chikahiko; Nakamura, Eiichi

2014-12-01

102

The ground state properties of spin-aligned atomic hydrogen, deuterium, and tritium  

NASA Technical Reports Server (NTRS)

The internal energy, pressure, and compressibility of ground-state, spin-aligned atomic hydrogen, deuterium, and tritium are calculated assuming that all pair interactions occur via the atomic triplet (spin-aligned) potential. The conditions required to obtain atomic hydrogen and its isotopes in bulk are discussed; such a development would be of value in propulsion systems because of the light mass and energetic recombination of atomic hydrogen. Results show that atomic triplet hydrogen and deuterium remain gaseous at 0 K, and that tritium forms a liquid with a binding energy of approximately -0.75 K per atom at a molar volume of 130 cu cm per mole. The pair distribution function for these systems is calculated, and the predicted superfluid behavior of atomic triplet hydrogen and tritium is briefly discussed.

Etters, R. D.; Dugan, J. V., Jr.; Palmer, R. W.

1975-01-01

103

Hydrogen--Deuterium 1S--2S Isotope Shift and the Structure of the Deuteron A. Huber, Th. Udem, B. Gross, J. Reichert, M. Kourogi \\Lambda , K. Pachucki \\Lambda\\Lambda , M. Weitz, and T. W. Hansch  

E-print Network

Hydrogen--Deuterium 1S--2S Isotope Shift and the Structure of the Deuteron A. Huber, Th. Udem, B determined the hydrogen--deuterium isotope shift of the 1S--2S two--photon resonance with a 150 fold increase--based electron scattering experiments [2--4]. In 1993 optical spectroscopic measurements of the hydrogen

Pachucki, Krzysztof

104

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

2012-03-28

105

H/D Exchange Levels of Shape-Resolved Cytochrome c Conformers in the Gas Phase  

E-print Network

H/D Exchange Levels of Shape-Resolved Cytochrome c Conformers in the Gas Phase Stephen J. Valentine) in the gas phase are examined by simultaneous ion-mobility and hydrogen-deuterium exchange measurements with the idea that compact structures protect some hydrogens in the gas phase. Many sites that rapidly exchange

Clemmer, David E.

106

Neopentane and solid acids: direct hydron exchange before cracking.  

PubMed

The hydrogen/deuterium exchange reaction of 2,2-dimethylpropane (neopentane) over D(2)O-exchanged zeolites (MOR, FAU, BEA, MFI) using a batch recirculation reactor was studied by means of gas chromatography coupled with mass spectrometer. In the temperature range 473-573 K, H/D exchange proceeds without side reaction such as cracking at short contact times. Indeed the C-H bond has appeared favorably involved in the activation of neopentane compared to the less accessible C-C bond. The transition state allowing hydron exchange is most likely a carbonium species (pentacoordinated carbon) as in the case of the H/D exchange between methane and solid acid. The activation energies of the H/D exchange between neopentane and zeolites are the same for all zeolites indicating a common carbonium ion type transition state. On the basis of previous results in the case of the exchange between methane and liquid superacids, the deuterium exchange rates in neopentane were tentatively related to the acidity of the solids. However the order of activity MOR > MFI > BEA > FAU seems to be related to the size of the pores, which may suggest the involvement of a confinement effect in the zeolites cavities. Moreover we found that H/D exchange takes also place between neopentane and deuterated sulfated zirconia (SZ) emphasizing its strong acidity. PMID:16970460

Walspurger, Stéphane; Sun, Yinyong; Souna Sido, Abdelkarim Sani; Sommer, Jean

2006-09-21

107

Melbourne Global Mobility Exchange and Study Abroad  

E-print Network

Melbourne Global Mobility Exchange and Study Abroad Deadlines 2014 Semester 1, 2014 (March ­ June) Semester 2, 2014 (July ­ December) Exchange Students 1 November 2013 1 April 2014 Study Abroad Students 1 at the University of Melbourne. #12;Melbourne Global Mobility Exchange and Study Abroad English Language

Wu, Yih-Min

108

Determination of hydrogen/deuterium ratio with neutron measurements on MAST  

NASA Astrophysics Data System (ADS)

On MAST, compressional Alfvén eigenmodes can be destabilized by the presence of a sufficiently large population of energetic particles in the plasma. This dependence was studied in a series of very similar discharges in which increasing amounts of hydrogen were puffed into a deuterium plasma. A simple method to estimate the isotopic ratio nH/nD using neutron emission measurements is here described. The inferred isotopic ratio ranged from 0.0 to 0.6 and no experimental indication of changes in radial profile of nH/nD were observed. These findings are confirmed by TRANSP/NUBEAM simulations of the neutron emission.

Klimek, I.; Cecconello, M.; Sharapov, S. E.; Harrison, J.; Ericsson, G.

2014-11-01

109

Determination of hydrogen/deuterium ratio with neutron measurements on MAST  

SciTech Connect

On MAST, compressional Alfvén eigenmodes can be destabilized by the presence of a sufficiently large population of energetic particles in the plasma. This dependence was studied in a series of very similar discharges in which increasing amounts of hydrogen were puffed into a deuterium plasma. A simple method to estimate the isotopic ratio n{sub H}/n{sub D} using neutron emission measurements is here described. The inferred isotopic ratio ranged from 0.0 to 0.6 and no experimental indication of changes in radial profile of n{sub H}/n{sub D} were observed. These findings are confirmed by TRANSP/NUBEAM simulations of the neutron emission.

Klimek, I., E-mail: iwona.klimek@physics.uu.se; Cecconello, M.; Ericsson, G. [Department of Physics and Astronomy, Uppsala University, Uppsala (Sweden); Sharapov, S. E.; Harrison, J. [CCFE, Culham Science Centre, Abingdon (United Kingdom)

2014-11-15

110

Canadian Arctic Shelf Exchange Study  

NSDL National Science Digital Library

The Canadian Arctic Shelf Exchange Study (CASES) is an international effort under Canadian leadership to understand the biogeochemical and ecological consequences of sea ice variability and change on the Mackenzie Shelf. After an introduction to the program, this site lists the objectives of the program which covered the assessment of several potentials including the impact of increased UV radiation on biological productivity, the role of microheterotrophs and mesozooplankton in transforming particulate and dissolved matter on the shelf, the fluxes of particulate matter and carbon across the shelf to the deep basins, the distribution of riverine and airborne contaminants in the trophic web, and the potential impact of a reduction in ice habitat on birds and marine mammals. Objectives also included Physical and biological measurements that will be used to constrain and calibrate regional models of climate and ice dynamics in the western Canadian Arctic and biophysical models of the carbon flows on the Canadian Arctic shelf. The site offers links to descriptions of the scientific activities of both CASES 2002 and CASES 2003-2004, the Canadian Coast Guard Ship (CCGS) Amundsen, and the Schools On Board program, designed to interest Canadian high school students in Arctic studies. Most sections are enhanced by photographs and the site is also available in French.

111

The hydrogen exchange core and protein folding.  

PubMed Central

A database of hydrogen-deuterium exchange results has been compiled for proteins for which there are published rates of out-exchange in the native state, protection against exchange during folding, and out-exchange in partially folded forms. The question of whether the slow exchange core is the folding core (Woodward C, 1993, Trends Biochem Sci 18:359-360) is reexamined in a detailed comparison of the specific amide protons (NHs) and the elements of secondary structure on which they are located. For each pulsed exchange or competition experiment, probe NHs are shown explicitly; the large number and broad distribution of probe NHs support the validity of comparing out-exchange with pulsed-exchange/competition experiments. There is a strong tendency for the same elements of secondary structure to carry NHs most protected in the native state, NHs first protected during folding, and NHs most protected in partially folded species. There is not a one-to-one correspondence of individual NHs. Proteins for which there are published data for native state out-exchange and theta values are also reviewed. The elements of secondary structure containing the slowest exchanging NHs in native proteins tend to contain side chains with high theta values or be connected to a turn/loop with high theta values. A definition for a protein core is proposed, and the implications for protein folding are discussed. Apparently, during folding and in the native state, nonlocal interactions between core sequences are favored more than other possible nonlocal interactions. Other studies of partially folded bovine pancreatic trypsin inhibitor (Barbar E, Barany G, Woodward C, 1995, Biochemistry 34:11423-11434; Barber E, Hare M, Daragan V, Barany G, Woodward C, 1998, Biochemistry 37:7822-7833), suggest that developing cores have site-specific energy barriers between microstates, one disordered, and the other(s) more ordered. PMID:10452602

Li, R.; Woodward, C.

1999-01-01

112

Quantitative Assessment of Protein Structural Models by Comparison of H/D Exchange MS Data with Exchange Behavior Accurately Predicted by DXCOREX  

PubMed Central

Peptide amide hydrogen/deuterium exchange mass spectrometry (DXMS) data are often used to qualitatively support models for protein structure. We have developed and validated a method (DXCOREX) by which exchange data can be used to quantitatively assess the accuracy of 3-D models of protein structure. The method utilizes the COREX algorithm to predict a protein’s amide hydrogen exchange rates by reference to a hypothesized structure, and these values are used to generate a virtual data set (deuteron incorporation per peptide) that can be quantitatively compared to the deuteration level of the peptide probes measured by hydrogen exchange experimentation. The accuracy of DXCOREX was established in studies performed with thirteen proteins for which both high-resolution structures and experimental data were available. The DXCOREX-calculated and experimental data for each protein was highly correlated. We then employed correlation analysis of DXCOREX-calculated vs. DXMS experimental data to assess the accuracy of a recently proposed structural model for the catalytic domain of a Ca2+- independent phospholipase A2. The model’s calculated exchange behavior was highly correlated with the experimental exchange results available for the protein, supporting the accuracy of the proposed model. This method of analysis will substantially increase the precision with which experimental hydrogen exchange data can help decipher challenging questions regarding protein structure and dynamics. PMID:22012689

Liu, Tong; Pantazatos, Dennis; Li, Sheng; Hamuro, Yoshitomo; Hilser, Vincent J.; Woods, Virgil L.

2013-01-01

113

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

114

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

115

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 the…

Ahn, Song-ee

2011-01-01

116

Properties of the Dark and Signaling States of Photoactive Yellow Protein Probed by Solution Phase Hydrogen/Deuterium Exchange and Mass Spectrometry  

E-print Network

cytoplasmic protein originally isolated from the halophilic purple phototrophic bacterium, Halorhodospira, which is found in many sensory proteins from bacteria to human (7, 8). Although considerable effort hasProperties of the Dark and Signaling States of Photoactive Yellow Protein Probed by Solution Phase

Wysocki, Vicki H.

117

Fundamentals and applications of the hydrogen\\/deuterium isotope effect in improved hot-carrier reliability of MOS devices  

Microsoft Academic Search

The reliability due to hot-carrier effects poses increasing constraints on the downscaling of CMOS transistors. This thesis attempts to provide a thorough study on both fundamentals and applications of enhancing CMOS reliability by incorporation of deuterium at the oxide\\/silicon interface. The impacts of the high pressure deuterium process on device characteristics and reliability are first investigated. The effectiveness of the

Kangguo Cheng

2001-01-01

118

Comparative Studies on Micro Heat Exchanger Optimisation Tatsuya Okabe  

E-print Network

Comparative Studies on Micro Heat Exchanger Optimisation Tatsuya Okabe , Kwasi Foli ¡ , Markus- timisation of a micro heat exchanger (¤ HEX). The trend to- wards miniaturisation has led to the use of micro devices in industry and technology. Micro heat exchangers have very high heat transfer surface area

Coello, Carlos A. Coello

119

Periodicity of amide proton exchange rates in a coiled-coil leucine zipper peptide.  

PubMed

The two-stranded coiled-coil motif, which includes leucine zippers, is a simple protein structure that is well suited for studies of helix-helix interactions. The interaction between helices in a coiled coil involves packing of "knobs" into "holes", as predicted by Crick in 1953 and confirmed recently by X-ray crystallography for the GCN4 leucine zipper [O'Shea, E.K., Klemm, J.D., Kim, P.S., & Alber, T. (1991) Science 254, 539]. A striking periodicity, extending over six helical turns, is observed in the rates of hydrogen-deuterium exchange for amide protons in a peptide corresponding to the leucine zipper of GCN4. Protons at the hydrophobic interface show the most protection from exchange. The NMR chemical shifts of amide protons in the helices also show a pronounced periodicity which predicts a short H-bond followed by a long H-bond every seven residues. This variation was anticipated in 1953 by Pauling and is sufficient to give rise to a local left-handed superhelical twist characteristic of coiled coils. The amide protons that lie at the base of the "hole" in the "knobs-into-holes" packing show slow amide proton exchange rates and are predicted to have short H-bond lengths. These results suggest that tertiary interactions can lead to highly localized, but substantial, differences in stability and dynamics within a secondary structure element and emphasize the dominant nature of packing interactions in determining protein structure. PMID:1661141

Goodman, E M; Kim, P S

1991-12-17

120

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

2013-03-01

121

Superacid-promoted ionization of alkanes without carbonium ion formation: a density functional theory study.  

PubMed

The carbonium ion has been suggested to be the intermediate in superacid-promoted reactions (SbF(5)-HF) such as hydrogen-deuterium exchange and in the electrophilic C-H cleavage into hydrogen and the carbenium ion. In this study, the superacid-promoted C-H cleavage into hydrogen and the carbenium ion was studied using density functional theory (B3LYP and M062X) and ab initio methods (MP2 and CCSD). The calculations suggest that the superacid-promoted C-H cleavage proceeds via a concerted transition state leading to hydrogen (H(2)) and the carbenium ion without the formation of the elusive carbonium ion. The reactivity for the superacid-promoted C-H cleavage decreases upon going from isobutane (tertiary) > propane (secondary) > isobutane (primary) > propane (primary) > ethane > methane. PMID:22998332

Dinér, Peter

2012-10-11

122

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

123

Isotope effects of neodymium in different ligands exchange systems studied by ion exchange displacement chromatography.  

PubMed

The isotope effects of neodymium in Nd-glycolate ligand exchange system were studied by using ion exchange chromatography. The separation coefficients of neodymium isotopes, ?'s, were calculated from the observed isotopic ratios at the front and rear boundaries of the neodymium adsorption band. The values of separation coefficients of neodymium isotopes, ?'s, for the Nd-glycolate ligand exchange system were compared with those of Nd-malate and Nd-citrate, which indicated that the isotope effects of neodymium as studied by the three ligands takes the following direction Malate > Citrate > Glycolate. This order agrees with the number of available sites for complexation of each ligand. The values of the plate height, HETP of Nd in Nd-ligand exchange systems were also calculated. PMID:25685410

Ismail, Ibrahim; Fawzy, Ahmed S; Ahmad, Mohammad I; Aly, Hisham F; Nomura, Masao; Fujii, Yasuhiko

2013-03-01

124

EXCHANGE  

SciTech Connect

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

Boltz, J.C. (ed.)

1992-09-01

125

Proton translocation in cytochrome c oxidase: insights from proton exchange kinetics and vibrational spectroscopy.  

PubMed

Cytochrome c oxidase is the terminal enzyme in the electron transfer chain. It reduces oxygen to water and harnesses the released energy to translocate protons across the inner mitochondrial membrane. The mechanism by which the oxygen chemistry is coupled to proton translocation is not yet resolved owing to the difficulty of monitoring dynamic proton transfer events. Here we summarize several postulated mechanisms for proton translocation, which have been supported by a variety of vibrational spectroscopic studies. We recently proposed a proton translocation model involving proton accessibility to the regions near the propionate groups of the heme a and heme a3 redox centers of the enzyme based by hydrogen/deuterium (H/D) exchange Raman scattering studies (Egawa et al., PLoS ONE 2013). To advance our understanding of this model and to refine the proton accessibility to the hemes, the H/D exchange dependence of the heme propionate group vibrational modes on temperature and pH was measured. The H/D exchange detected at the propionate groups of heme a3 takes place within a few seconds under all conditions. In contrast, that detected at the heme a propionates occurs in the oxidized but not the reduced enzyme and the H/D exchange is pH-dependent with a pKa of ~8.0 (faster at high pH). Analysis of the thermodynamic parameters revealed that, as the pH is varied, entropy/enthalpy compensation held the free energy of activation in a narrow range. The redox dependence of the possible proton pathways to the heme groups is discussed. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems. PMID:25268561

Ishigami, Izumi; Hikita, Masahide; Egawa, Tsuyoshi; Yeh, Syun-Ru; Rousseau, Denis L

2015-01-01

126

Hydrogen Isotope Separation by Combined Electrolysis Catalytic Exchange Under Reduced Pressure  

SciTech Connect

At the National Institute for Fusion Science experimental studies on hydrogen isotope separation by a Combined Electrolysis Catalytic Exchange (CECE) process have been carried out in order to apply it to the system of water detritiation for D-D burning experiments of the Large Helical Device. As an improvement of the CECE process, we have developed a reduced-pressure method as a means of enhancing the separation factor. The feasibility of this method is examined through application to a CECE process using a prototype separation column. Hydrogen-deuterium isotope separation experiments are performed in the two cases where column pressures are 12 and 101 kPa, and the separation factors for hydrogen and deuterium are obtained as 6.8 and 5.6, respectively. It is confirmed that the present method is applicable and useful to the CECE process. The values of Height Equivalent to a Theoretical Plate (HETP) are estimated by analyses with the equilibrium stage model. The HETP values are 15 cm at 12 kPa and 13 cm at 101 kPa. The increase of superficial velocity with decreasing pressure may spoil the efficiency of the mass transfer.

Sugiyama, T. [National Institute for Fusion Science (Japan); Asakura, Y. [National Institute for Fusion Science (Japan); Uda, T. [National Institute for Fusion Science (Japan); Abe, Y. [Nagoya University (Japan); Shiozaki, T. [Nagoya University (Japan); Enokida, Y. [Nagoya University (Japan); Yamamoto, I. [Nagoya University (Japan)

2005-07-15

127

Interaction of arginine with protein during refolding process probed by amide H/D exchange mass spectrometry and isothermal titration calorimetry.  

PubMed

Arginine has been widely used as low molecular weight additive to promote protein refolding by suppressing aggregate formation. However, methods to investigate the role of arginine in protein refolding are often limited on protein's global conformational properties. Here, hydrogen/deuterium exchange mass spectrometry (HDX-MS) was used to study the effects of arginine on recombinant human granulocyte colony-stimulating factor (rhG-CSF) refolding at the scale of peptide mapping. It was found that deuteration levels of rhG-CSF refolded with arginine was higher than that without arginine during the whole refolding process, but they became almost the same when the refolding reached equilibrium. This phenomenon indicated that arginine could protect some amide deuterium atoms from being exchanged with hydrogen, but the protection diminished gradually along with refolding proceeding. Enzymatic digestion revealed six particular peptides of 16-47, 72-84, 84-93, 114-124, 145-153 and 154-162 were mainly responsible for the deuteration, and all of them dominantly located in protein's ?-helix domain. Furthermore, thermodynamics analysis by isothermal titration calorimetry provided direct evidence that arginine could only react with denatured and partially refolded rhG-CSF. Taking all of the results together, we suggest that arginine suppresses protein aggregation by a reversible combination. At the initial refolding stage, arginine could combine with the denatured protein mainly through hydrogen bonding. Subsequently, arginine is gradually excluded from protein with protein's native conformation recovering. PMID:25461798

Zhao, Dawei; Liu, Yongdong; Zhang, Guifeng; Zhang, Chun; Li, Xiunan; Wang, Qingqing; Shi, Hong; Su, Zhiguo

2015-01-01

128

A piloted simulation study of data link ATC message exchange  

NASA Technical Reports Server (NTRS)

Data link Air Traffic Control (ATC) and Air Traffic Service (ATS) message and data exchange offers the potential benefits of increased flight safety and efficiency by reducing communication errors and allowing more information to be transferred between aircraft and ground facilities. Digital communication also presents an opportunity to relieve the overloading of ATC radio frequencies which hampers message exchange during peak traffic hours in many busy terminal areas. A piloted simulation study to develop pilot factor guidelines and assess potential flight crew benefits and liabilities from using data link ATC message exchange was completed. The data link ATC message exchange concept, implemented on an existing navigation computer Control Display Unit (CDU) required maintaining a voice radio telephone link with an appropriate ATC facility. Flight crew comments, scanning behavior, and measurements of time spent in ATC communication activities for data link ATC message exchange were compared to similar measures for simulated conventional voice radio operations. The results show crew preference for the quieter flight deck environment and a perception of lower communication workload.

Waller, Marvin C.; Lohr, Gary W.

1989-01-01

129

Use of SAR in Regional Methane Exchange Studies  

NASA Technical Reports Server (NTRS)

Significant sources of uncertainty in global trace gas budgets are due to lack of knowledge concerning the areal and temporal extent of source and sink areas. Synthetic aperture radar (SAR) is particularly suited to studies of northern ecosystems because of its all-weather operating capability which enables the acquisition of seasonal data. As key controls on methane exchange, the ability to differentiate major vegetation communities, inundation, and leaf area index (LAI) with satellite and airborne SAR data would increase the accuracy and precision of regional and seasonal estimates of methane exchange. The utility of SAR data for monitoring key controls on methane emissions from Arctic and boreal ecosystems is examined.

Morrissey, L. A.; Livingston, G. P.; Durden, S. L.

1994-01-01

130

Heat Exchanger Design Studies for AN Lhc Inner Triplet Upgrade  

NASA Astrophysics Data System (ADS)

A luminosity upgrade of the CERN Large Hadron Collider (LHC) is planned to coincide with the expected end of life of the existing inner triplet quadrupole magnets. The upgraded inner triplet will have much larger heat loads to be removed from the magnets by the cryogenics system. A number of cryogenics design studies have been completed under the LHC Accelerator Research Program (LARP), including investigations of required heat exchanger characteristics to transfer this heat from the pressurized He II bath to the saturated He II system. This paper discusses heat exchangers both external to the magnet cold mass and internal to the magnet cold mass. A possible design for a heat exchanger external to the magnet cold mass is also presented.

Rabehl, R. J.; Huang, Y.

2008-03-01

131

HEAT EXCHANGER DESIGN STUDIES FOR AN LHC INNER TRIPLET UPGRADE  

SciTech Connect

A luminosity upgrade of the CERN Large Hadron Collider (LHC) is planned to coincide with the expected end of life of the existing inner triplet quadrupole magnets. The upgraded inner triplet will have much larger heat loads to be removed from the magnets by the cryogenics system. A number of cryogenics design studies have been completed under the LHC Accelerator Research Program (LARP), including investigations of required heat exchanger characteristics to transfer this heat from the pressurized He II bath to the saturated He II system. This paper discusses heat exchangers both external to the magnet cold mass and internal to the magnet cold mass. A possible design for a heat exchanger external to the magnet cold mass is also presented.

Rabehl, R. J.; Huang, Y. [Fermi National Accelerator Laboratory Batavia, Illinois, 60510 (United States)

2008-03-16

132

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...

133

Functional studies of split "Arabidopsis" Ca(2+)/H(+) exchangers  

Technology Transfer Automated Retrieval System (TEKTRAN)

In plants, high capacity tonoplast cation/H (+) antiport is mediated in part by a family of cation exchanger (CAX) transporters. Functional association between CAX1 and CAX3 has previously been shown. In this study, we further examine the interactions between CAX protein domains using nonfunctional ...

134

GAS COOLED, MOLTEN SALT HEAT EXCHANGER--DESIGN STUDY  

Microsoft Academic Search

BS> One of the major problems in the economic evaluation of the ; application of forced circulation, gas cooling to high temperature, molten salt ; power reactor systems is the definition of the required heat transfer equipment, ; its size and operating cost. A design study of the saltto-gas heat exchangers ; for such a gas-cooled system has recently been

MacPherson

1958-01-01

135

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

PubMed Central

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

2013-01-01

136

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

2013-01-01

137

Separation of organic ion exchange resins from sludge -- engineering study  

SciTech Connect

This engineering study evaluates the use of physical separation technologies to separate organic ion exchange resin from KE Basin sludge prior to nitric acid dissolution. This separation is necessitate to prevent nitration of the organics in the acid dissolver. The technologies under consideration are: screening, sedimentation, elutriation. The recommended approach is to first screen the Sludge and resin 300 microns then subject the 300 microns plus material to elutriation.

Duncan, J.B.

1998-08-25

138

Practical and economical implementation of online H/D exchange in LC-MS.  

PubMed

Structural elucidation is an integral part of drug discovery and development. In recent years, due to acceleration of the drug discovery and development process, there is a significant need for highly efficient methodologies for structural elucidation. In this work, we devised and standardized a simple and economical online hydrogen-deuterium exchange methodology, which can be used for structure elucidation purposes. Deuterium oxide (D2O) was infused as a postcolumn addition using the syringe pump at the time of elution of the analyte. The obtained hydrogen/deuterium (H/D) exchange spectrum of the unknown analyte was compared with the nonexchanged spectrum, and the extent of deuterium incorporation was delineated by using an algorithm to deconvolute partial H/D exchange, which confirmed the number of labile hydrogen(s) in the analyte. The procedure was standardized by optimizing flow rates of LC output, D2O infusion, sheath gas, and auxiliary gas using the model compound sulfasalazine. The robustness of the methodology was demonstrated by performing sensitivity analysis of various parameters such as concentrations of analyte, effect of matrices, concentrations of aqueous mobile phase, and types of LC modifiers. The optimized technique was also applied to chemically diverse analytes and tested on various mass spectrometers. Moreover, utility of the technique was demonstrated in the areas of impurity profiling and metabolite identification, taking pravastatin-lactone and N-oxide desloratidine, as examples. PMID:24117319

Shah, Ravi P; Garg, Amit; Putlur, Siva Prasad; Wagh, Santosh; Kumar, Vineet; Rao, Venugopala; Singh, Saranjit; Mandlekar, Sandhya; Desikan, Sridhar

2013-11-19

139

Study Abroad and Student Exchange Policy and Procedures Commencement Date: 1 July, 2005  

E-print Network

Study Abroad and Student Exchange Policy and Procedures Commencement Date: 1 July, 2005 Category, or seeking to be involved in, the Study Abroad and Student Exchange programs, and to those involved abroad participating in Study Abroad or Student Exchange programs at Curtin. International Student

140

Heat Exchanger Design Options and Tritium Transport Study for the VHTR System  

Microsoft Academic Search

This report presents the results of a study conducted to consider heat exchanger options and tritium transport in a very high temperature reactor (VHTR) system for the Next Generation Nuclear Plant Project. The heat exchanger options include types, arrangements, channel patterns in printed circuit heat exchangers (PCHE), coolant flow direction, and pipe configuration in shell-and-tube designs. Study considerations include: three

Chang H. Oh; Eung S. Kim

2008-01-01

141

Thermal stability and long term hydrogen/deuterium release from soft to hard amorphous carbon layers analyzed using in-situ Raman spectroscopy. Comparison with Tore Supra deposits  

E-print Network

The thermal stability of 200 nm thick plasma enhanced chemical vapor deposited a-C:H and a-C:D layers ranging from soft to hard layers has been studied and compared to that of deposits collected on the Tore Supra tokamak plasma facing components by means of in-situ Raman spectroscopy. Linear ramp heating and long term isotherms (from several minutes to 21 days) have been performed and correlations between spectrometric parameters have been found. The information obtained on the sp 2 clustering has been investigated by comparing the G band shift and the 514 nm photon absorption evolution due to the thermal treatment of the layer. The effects of isotopic substitution have also been investigated.

Pardanaud, C; Giacometti, G; Mellet, N; Pégourié, B; Roubin, P

2015-01-01

142

Written date: January 19, 2012 Preliminary study on the mechanical behaviour of heat exchanger pile  

E-print Network

Written date: January 19, 2012 Preliminary study on the mechanical behaviour of heat exchanger pile of Figures: 6 Abstract: The effects of temperature changes on the mechanical behaviour of heat exchanger cycles. 2 Key words: Model tests, heat exchanger pile, settlement, soil/structure interaction

Paris-Sud XI, Université de

143

Nonballistic heat conduction in an integrable random-exchange Ising chain studied with quantum master equations  

E-print Network

Nonballistic heat conduction in an integrable random-exchange Ising chain studied with quantum numerically investigate the heat conduction in a random-exchange Ising spin chain by using the quantum master equation. The chain is subject to a uniform transverse field h, while the exchange couplings Qn between

Li, Baowen

144

N:\\STUDY ABROAD\\Study Abroad OUT\\2013 ERASMUS AND INTERNATIONAL STUDENT EXCHANGE  

E-print Network

N:\\STUDY ABROAD\\Study Abroad OUT\\2013 ERASMUS AND INTERNATIONAL STUDENT EXCHANGE Internal programme during the academic year 2013/14 are required to submit this application form to the Study Abroad Team. You must first of all gain permission to study abroad from your Department/College (or

Mumby, Peter J.

145

Determinants of protein hydrogen exchange studied in equine cytochrome c.  

PubMed Central

The exchange of a large number of amide hydrogens in oxidized equine cytochrome c was measured by NMR and compared with structural parameters. Hydrogens known to exchange through local structural fluctuations and through larger unfolding reactions were separately considered. All hydrogens protected from exchange by factors greater than 10(3) are in defined H-bonds, and almost all H-bonded hydrogens including those at the protein surface were measured to exchange slowly. H-exchange rates do not correlate with H-bond strength (length) or crystallographic B factors. It appears that the transient structural fluctuation necessary to bring an exchangeable hydrogen into H-bonding contact with the H-exchange catalyst (OH(-)-ion) involves a fairly large separation of the H-bond donor and acceptor, several angstroms at least, and therefore depends on the relative resistance to distortion of immediately neighboring structure. Accordingly, H-exchange by way of local fluctuational pathways tends to be very slow for hydrogens that are neighbored by tightly anchored structure and for hydrogens that are well buried. The slowing of buried hydrogens may also reflect the need for additional motions that allow solvent access once the protecting H-bond is separated, although it is noteworthy that burial in a protein like cytochrome c does not exceed 4 angstroms. When local fluctuational pathways are very slow, exchange can become dominated by a different category of larger, cooperative, segmental unfolding reactions reaching up to global unfolding. PMID:9541406

Milne, J. S.; Mayne, L.; Roder, H.; Wand, A. J.; Englander, S. W.

1998-01-01

146

Investigation of the effect of intra-molecular interactions on the gas-phase conformation of peptides as probed by ion mobility-mass spectrometry, gas-phase hydrogen/deuterium exchange, and molecular mechanics  

E-print Network

of gly-gly-tyr are smaller than that of the protonated species, while the cesiated and doubly cesiated species are larger. Conversely, all of the alkali-adducted species of try-gly-gly have collision cross-sections that are larger than...

Sawyer, Holly Ann

2006-04-12

147

Simulation Studies on A Cross Flow Plate Fin Heat Exchanger  

Microsoft Academic Search

Compact heat exchangers which were initially developed for the aerospace industries in the 1940s have been considerably improved in the past few years. The main reasons for the good performance of compact heat exchangers are their special design which includes turbulent which in turn use high heat transfer coefficient and resists fouling, and maximum temperature driving force between the hot

M. Thirumarimurugan; T. Kannadasan; E. Ramasamy

148

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

149

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

150

Study of transient behavior of finned coil heat exchangers  

NASA Astrophysics Data System (ADS)

The status of research on the transient behavior of finned coil cross-flow heat exchangers using single phase fluids is reviewed. Applications with available analytical or numerical solutions are discussed. Investigation of water-to-air type cross-flow finned tube heat exchangers is examined through the use of simplified governing equations and an up-wind finite difference scheme. The degenerate case of zero air-side capacitance rate is compared with available exact solution. Generalization of the numerical model is discussed for application to multi-row multi-circuit heat exchangers.

Rooke, S. P.; Elissa, M. G.

1993-11-01

151

Study of transient behavior of finned coil heat exchangers  

NASA Technical Reports Server (NTRS)

The status of research on the transient behavior of finned coil cross-flow heat exchangers using single phase fluids is reviewed. Applications with available analytical or numerical solutions are discussed. Investigation of water-to-air type cross-flow finned tube heat exchangers is examined through the use of simplified governing equations and an up-wind finite difference scheme. The degenerate case of zero air-side capacitance rate is compared with available exact solution. Generalization of the numerical model is discussed for application to multi-row multi-circuit heat exchangers.

Rooke, S. P.; Elissa, M. G.

1993-01-01

152

Analytical Study on Thermal and Mechanical Design of Printed Circuit Heat Exchanger  

SciTech Connect

The analytical methodologies for the thermal design, mechanical design and cost estimation of printed circuit heat exchanger are presented in this study. In this study, three flow arrangements of parallel flow, countercurrent flow and crossflow are taken into account. For each flow arrangement, the analytical solution of temperature profile of heat exchanger is introduced. The size and cost of printed circuit heat exchangers for advanced small modular reactors, which employ various coolants such as sodium, molten salts, helium, and water, are also presented.

Su-Jong Yoon; Piyush Sabharwall; Eung-Soo Kim

2013-09-01

153

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

154

Experimental Studies on Coherent Synchrotron Radiation at an Emittance Exchange Beamline  

SciTech Connect

One of the goals of the Fermilab A0 photoinjector is to experimentally investigate 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.; /Fermilab

2012-04-01

155

An Efficient and Inexpensive Refrigerated LC System for H/D Exchange Mass Spectrometry  

NASA Astrophysics Data System (ADS)

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%.

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

2011-08-01

156

The combined effect of rain and wind on airwater gas exchange: A feasibility study  

E-print Network

The combined effect of rain and wind on air­water gas exchange: A feasibility study David T. Ho a to examine the combined effects of rain and wind on air­water 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

Ho, David

157

TG and DTA Study of the Thermal Dehydration of Metal-exchanged Zeolite4A Samples  

Microsoft Academic Search

Zeolite-4A is a hydrated aluminosilicate which becomes more hydrated when exchanged with transition metals. In this work,\\u000a the dehydration kinetics of cobalt, nickel and copper(II)-exchanged zeolite-4A were studied by means of TG and DTA over the\\u000a temperature range from 20 to 500C, and the numbers of water molecules in the metal-exchanged zeolite samples were calculated.\\u000a It was observed that, as

M. Afzal; G. Yasmeen; M. Saleem; P. K. Butt; A. K. Khattak; J. Afzal

2000-01-01

158

Polymerization of Benzene and Aniline on Cu(II)-Exchanged Hectorite Clay Films: A Scanning Force Microscope Study  

Microsoft Academic Search

The technique of scanning force microscopy (SFM) was used to study the nanometer-scale structure of Cu(II)-exchanged hectorite thin films. Supporting data were also obtained from Electron Spin Resonance (ESR) and X-ray diffraction (XRD) techniques. The surfaces studied included pure Cu(II)- exchanged hectorite, Cu(II)-exchanged hectorite exposed to benzene and Cu(II)-exchanged hectorite ex- posed to aniline. SFM images of the unexposed Cu(II)-exchanged

Michael P. Eastman; MICHAEL E. HAGERMAN; EDLIN D. BAIN; TIMOTHY L. PORTER

1996-01-01

159

Two-state vs. multistate protein unfolding studied by optical melting and hydrogen exchange  

E-print Network

Two-state vs. multistate protein unfolding studied by optical melting and hydrogen exchange LELAND MAYNE and S. WALTER ENGLANDER The Johnson Research Foundation, Department of Biochemistry and Biophysics energy parameters of cytochrome c determined by optical methods and by hydrogen exchange ~HX

Englander, S. Walter

160

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

161

Experimental studies of the transfer phenomena of tritium in an isotope exchange column for recovery tritium  

E-print Network

for hydrogen isotope's separation are very important for nuclear technology. One of the most important processes for tritium separation, is the catalyst isotope exchange water-hydrogen. The main problemExperimental studies of the transfer phenomena of tritium in an isotope exchange column

162

Content consumption and exchange among college students: a case study from India  

Microsoft Academic Search

This paper presents the results of our qualitative and exploratory study on content consumption and exchange among college students in the city of Bangalore in Karnataka, India. The purpose was to learn what specific content, like music or audio, video or movies, text, voice and pictures was consumed and exchanged among college students and also what influenced it. It was

Sarita Seshagiri

2009-01-01

163

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

E-print Network

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

Raschke, Tanya M.

164

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

165

Evaluating Humidity Recovery Efficiency of Currently Available Heat and Moisture Exchangers: A Respiratory System Model Study  

PubMed Central

OBJECTIVES: To evaluate and compare the efficiency of humidification in available heat and moisture exchanger models under conditions of varying tidal volume, respiratory rate, and flow rate. INTRODUCTION: Inspired gases are routinely preconditioned by heat and moisture exchangers to provide a heat and water content similar to that provided normally by the nose and upper airways. The absolute humidity of air retrieved from and returned to the ventilated patient is an important measurable outcome of the heat and moisture exchangers’ humidifying performance. METHODS: Eight different heat and moisture exchangers were studied using a respiratory system analog. The system included a heated chamber (acrylic glass, maintained at 37°C), a preserved swine lung, a hygrometer, circuitry and a ventilator. Humidity and temperature levels were measured using eight distinct interposed heat and moisture exchangers given different tidal volumes, respiratory frequencies and flow-rate conditions. Recovery of absolute humidity (%RAH) was calculated for each setting. RESULTS: Increasing tidal volumes led to a reduction in %RAH for all heat and moisture exchangers while no significant effect was demonstrated in the context of varying respiratory rate or inspiratory flow. CONCLUSIONS: Our data indicate that heat and moisture exchangers are more efficient when used with low tidal volume ventilation. The roles of flow and respiratory rate were of lesser importance, suggesting that their adjustment has a less significant effect on the performance of heat and moisture exchangers. PMID:19578664

Lucato, Jeanette Janaina Jaber; Adams, Alexander Bernard; Souza, Rogério; Torquato, Jamili Anbar; Carvalho, Carlos Roberto Ribeiro; Marini, John J

2009-01-01

166

An optical study of the exchange kinetics of membrane bound molecules.  

PubMed

The kinetics of molecular exchange between lipid bilayers are studied using a special fluorescence technique. Pyrene and pyrene decanoic acid are chosen as typical examples of an apolar and amphiphilic molecule. Their property of forming dimers in the excited state (excimer) is exploited. The time dependencies of monomer and excimer intensities after rapid mixing of vesicles doped with fluorescent probe with undoped ones are studied by stopped-flow technique. The transient curves reveal the information on the exchange kinetics. A theoretical analysis shows that the molecular exchange follows a first order kinetics. Surprisingly short half life-times tex for this exchange process are obtained (for dipalmitoyl phosphatidylcholine tex=3.3 s for T=23 degrees C, tex=0.5 s for T=68 degrees C). Multilamellar systems (onion like structure) show much slower exchange rates. The exchange rates are nearly equal for polar and unpolar molecules. Addition of cholesterol has a strong reducing effect on this rate. Charging of dipalmitoyl phosphatidylcholine vesicle surfaces by the addition of (a) EuCl3 to the aqueous phase and (b) dipalmitoyl phosphatidic acid to the lipid phase reduces the exchange rate by about an order of magnitude above the phase transition. In a separate experiment it is shown that the lipid exchange or fusion for two different lipids is a much slower process compared to the label exchange. In fact vesicles kept below the phase transition temperature Ttr for both lipids, do not fuse even after 70 h. Noticeable fusion occurs after 10 h when the mixture stays above Ttr. Experiment shows that the fusion of pure lipid vesicles is not very much affected by the presence of a charged lipid. Change in concentration of the monovalent ions in the aqueous solution by two orders of magnitude does not have an appreciable effect on the exchange rate of phospholipids. PMID:952921

Sengupta, P; Sackmann, E; Kühnle, W; Scholz, H P

1976-07-15

167

75 FR 77636 - Public Information Exchange on EPA Nanomaterial Case Studies  

Federal Register 2010, 2011, 2012, 2013, 2014

...comprehensive environmental assessment of nanomaterials. All interested public parties are...further case studies and workshops on nanomaterials. DATES: The Public Information Exchange...Workshops Engineered nanoscale materials (nanomaterials) have often been described as...

2010-12-13

168

STUDY OF INDUSTRIAL ION EXCHANGE SEPARATION OF RARE EARTH ELEMENTS BY EDTA COPPER METHOD. 3. MANUFACTURE OF ION EXCHANGE EQUIPMENT  

Microsoft Academic Search

Ion exchange equipment was manufactured for trial. The equipment has ; five ion exchange towers, and the total capacity is 100 liters of strong acid ; type ion exchange resin. The equipment purifies 2.2 kg of rare earth into an ; oxide. In the case of refining of 2.2 kg of cerium oxide, 79% in purity, 1.37 kg ; of

K. Nishigori; T. Ishiyama; T. Kuroda

1961-01-01

169

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

170

Two-Photon Exchange Effect Studied with Neural Networks  

E-print Network

An approach to the extraction of the two-photon exchange (TPE) correction from elastic $ep$ scattering data is presented. The cross section, polarization transfer (PT), and charge asymmetry data are considered. It is assumed that the TPE correction to the PT data is negligible. The form factors and TPE correcting term are given by one multidimensional function approximated by the feed forward neural network (NN). To find a model-independent approximation the Bayesian framework for the NNs is adapted. A large number of different parametrizations is considered. The most optimal model is indicated by the Bayesian algorithm. The obtained fit of the TPE correction behaves linearly in epsilon but it has a nontrivial Q2 dependence. A strong dependence of the TPE fit on the choice of parametrization is observed.

Krzysztof M. Graczyk

2011-08-30

171

Two-photon exchange effect studied with neural networks  

SciTech Connect

An approach to the extraction of the two-photon exchange (TPE) correction from elastic ep scattering data is presented. The cross-section, polarization transfer (PT), and charge asymmetry data are considered. It is assumed that the TPE correction to the PT data is negligible. The form factors and TPE correcting term are given by one multidimensional function approximated by the feedforward neural network (NN). To find a model-independent approximation, the Bayesian framework for the NNs is adapted. A large number of different parametrizations is considered. The most optimal model is indicated by the Bayesian algorithm. The obtained fit of the TPE correction behaves linearly in {epsilon} but it has a nontrivial Q{sup 2} dependence. A strong dependence of the TPE fit on the choice of parametrization is observed.

Graczyk, Krzysztof M. [Institute of Theoretical Physics, University of Wroclaw, pl. M. Borna 9, PL-50-204 Wroclaw (Poland)

2011-09-15

172

Study of thermal energy storage using fluidized bed heat exchangers  

NASA Technical Reports Server (NTRS)

The technical and economic feasibility of fluid bed heat exchangers (FBHX) for thermal energy storage (TES) in waste heat recovery applications is assessed by analysis of two selected conceptual systems, the rotary cement kiln and the electric arc furnace. It is shown that the inclusion of TES in the energy recovery system requires that the difference in off-peak and on-peak energy rates be large enough so that the value of the recovered energy exceeds the value of the stored energy by a wide enough margin to offset parasitic power and thermal losses. Escalation of on-peak energy rates due to fuel shortages could make the FBHX/TES applications economically attractive in the future.

Weast, T. E.; Shannon, L. J.; Ananth, K. P.

1980-01-01

173

FDM study of ion exchange diffusion equation in glass  

NASA Astrophysics Data System (ADS)

Ion-exchange technique in glass was developed to fabricate gradient refractive index optical devices. In this paper, the Finite Difference Method(FDM), which is used for the solution of ion-diffusion equation, is reported. This method transforms continual diffusion equation to separate difference equation. It unitizes the matrix of MATLAB program to solve the iteration process. The collation results under square boundary condition show that it gets a more accurate numerical solution. Compared to experiment data, the relative error is less than 0.2%. Furthermore, it has simply operation and kinds of output solutions. This method can provide better results for border-proliferation of the hexagonal and the channel devices too.

Zhou, Zigang; Yang, Yongjia; Wang, Qiang; Sun, Guangchun

2009-05-01

174

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. PMID:19674960

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

2009-01-01

175

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. 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.

2013-01-01

176

Characterization of the Unfolding of Ribonuclease A by a Pulsed Hydrogen Exchange Study: Evidence for Competing Pathways for Unfolding  

E-print Network

Characterization of the Unfolding of Ribonuclease A by a Pulsed Hydrogen Exchange Study: Evidence Sciences, Tata Institute of Fundamental Research, GKVK Campus, Bangalore 560 065, India ReceiVed July 16-state hydrogen exchange (HX), and pulse labeling by hydrogen exchange. First, native-state HX studies were used

177

Numerical Study on Crossflow Printed Circuit Heat Exchanger for Advanced Small Modular Reactors  

SciTech Connect

Various fluids such as water, gases (helium), molten salts (FLiNaK, FLiBe) and liquid metal (sodium) are used as a coolant of advanced small modular reactors (SMRs). The printed circuit heat exchanger (PCHE) has been adopted as the intermediate and/or secondary heat exchanger of SMR systems because this heat exchanger is compact and effective. The size and cost of PCHE can be changed by the coolant type of each SMR. In this study, the crossflow PCHE analysis code for advanced small modular reactor has been developed for the thermal design and cost estimation of the heat exchanger. The analytical solution of single pass, both unmixed fluids crossflow heat exchanger model was employed to calculate a two dimensional temperature profile of a crossflow PCHE. The analytical solution of crossflow heat exchanger was simply implemented by using built in function of the MATLAB program. The effect of fluid property uncertainty on the calculation results was evaluated. In addition, the effect of heat transfer correlations on the calculated temperature profile was analyzed by taking into account possible combinations of primary and secondary coolants in the SMR systems. Size and cost of heat exchanger were evaluated for the given temperature requirement of each SMR.

Su-Jong Yoon [Idaho National Laboratory (INL), Idaho Falls, ID (United States); Piyush Sabharwall [Idaho National Laboratory (INL), Idaho Falls, ID (United States); Eung-Soo Kim [Seoul National Univ., Seoul (Korea, Republic of)

2014-03-01

178

Study of exchange bias in NiCr2O4 nanoparticles  

NASA Astrophysics Data System (ADS)

We investigated exchange bias as a function of temperature in nanoparticles of ferrimagnetic normal spinel NiCr2O4. The studied bulk compound exhibits ferrimagnetic and canted antiferromagnetic ordering at 68 K and 30 K respectively. Sample characterization was carried out using X-Ray, Field Emission Scanning Electron Microscope (FE-SEM) and Transmission Electron Microscope (TEM) measurements. Magnetization measurements as a function of temperature has revealed interesting features. Magnetic isotherms of bulk and nanoparticle sample were also investigated at different temperatures. It was found that in nanoparticles, with decrease in temperature, exchange bias first increases, attains maximum value and then subsequently decreases. We argue that in nanoparticles, the higher exchange bias at 68 K is because of coexistence of ferrimagnetic and surface spin effect. However, the presence of glassy spin state may be the reason for decreasing exchange bias effect below Tc down to 5 K.

Singh, H.; Chakraborty, T.; Srikanth, K.; Chandra, R.; Mitra, C.; Kumar, U.

2014-09-01

179

T:\\Exchanges & Study Abroad\\Resource Room & MKTG\\Outreach\\Global Ambassadors 2009 -2010  

E-print Network

T:\\Exchanges & Study Abroad\\Resource Room & MKTG\\Outreach\\Global Ambassadors GLOBAL AMBASSADOR INTERNSHIP 2009 - 2010 2009 - 2010 The Study Abroad Center is pleased to announce the Global Ambassador Internship, which is designed to give Study Abroad Alumni the ability to practice and maintain skills learned

Lawrence, Rick L.

180

Field studies of leaf gas exchanges in oil palm tree (Elaeis guineensis Jacq.)  

E-print Network

Field studies of leaf gas exchanges in oil palm tree (Elaeis guineensis Jacq.) E. Dufrene B This study is part of a larger research pro- gram on climatic and biological factors affecting oil palm yield (A) in oil palm. Most of them have used young plants under laboratory conditions to study effects

Paris-Sud XI, Université de

181

Preliminary time-of-flight neutron diffraction studies of Escherichia coli ABC transport receptor phosphate-binding protein at the Protein Crystallography Station.  

PubMed

Inorganic phosphate is an essential molecule for all known life. Organisms have developed many mechanisms to ensure an adequate supply, even in low-phosphate conditions. In prokaryotes phosphate transport is instigated by the phosphate-binding protein (PBP), the initial receptor for the ATP-binding cassette (ABC) phosphate transporter. In the crystal structure of the PBP-phosphate complex, the phosphate is completely desolvated and sequestered in a deep cleft and is bound by 13 hydrogen bonds: 12 to protein NH and OH donor groups and one to a carboxylate acceptor group. The carboxylate plays a key recognition role by accepting a phosphate hydrogen. PBP phosphate affinity is relatively consistent across a broad pH range, indicating the capacity to bind monobasic (H2PO4-) and dibasic (HPO4(2-)) phosphate; however, the mechanism by which it might accommodate the second hydrogen of monobasic phosphate is unclear. To answer this question, neutron diffraction studies were initiated. Large single crystals with a volume of 8?mm3 were grown and subjected to hydrogen/deuterium exchange. A 2.5?Å resolution data set was collected on the Protein Crystallography Station at the Los Alamos Neutron Science Center. Initial refinement of the neutron data shows significant nuclear density, and refinement is ongoing. This is the first report of a neutron study from this superfamily. PMID:24915101

Sippel, K H; Bacik, J; Quiocho, F A; Fisher, S Z

2014-06-01

182

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. PMID:21619926

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

2011-01-01

183

A time-resolved study on the interaction of oppositely charged bicelles - implications on the charged lipid exchange kinetics.  

PubMed

Time-resolved small-angle X-ray scattering was applied to study charged lipid exchange between oppositely charged disc-shaped bicelles. The exchange of charged lipids gradually reduces the surface charge density and weakens the electrostatic attraction between the oppositely charged bicelles which form alternately stacked aggregates upon mixing. Initially, at a high surface charge density with almost no free water layer between the stacked bicelles, fast exchange kinetics dominate the exchange process. At a later stage with a lower surface charge density and a larger water gap between the stacked bicelles, slow exchange kinetics take over. The fast exchange kinetics are correlated with the close contact of the bicelles when there is almost no free water layer between the tightly bound bicelles with a charged lipid exchange time constant as short as 20-40 min. When the water gap becomes large enough to have a free water layer between the stacked bicelles, the fast lipid exchange kinetics are taken over by slow lipid exchange kinetics with time constants around 200-300 min, which are comparable to the typical time constant of lipid exchange between vesicles in aqueous solution. These two kinds of exchange mode fit well with the lipid exchange models of transient hemifusion for the fast mode and monomer exchange for the slow mode. PMID:25649711

Yang, Po-Wei; Lin, Tsang-Lang; Hu, Yuan; Jeng, U-Ser

2015-03-01

184

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

185

Computational Studies of Water Exchange around Aqueous Li+ with Polarizable Potential Models  

SciTech Connect

To enhance our understanding of the mechanism of water-exchange around the aqueous Li+, we carried out a systematic study on this system using molecular dynamics simulations with many-body 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 the 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. This work was funded by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences (BES), of the U.S. Department of Energy (DOE). Battelle operates Pacific Northwest National Laboratory for DOE. The calculations were carried out using computer resources provided by BES.

Dang, Liem X.; Annapureddy, Harsha V.

2013-08-28

186

Water transport study across commercial ion exchange membranes in the vanadium redox flow battery  

Microsoft Academic Search

The water transfer behaviour of Selemion CMV, AMV and DMV membranes (Asahi Glass, Japan) has been studied in the vanadium redox cell, as was the water transfer across Nafion 117 membrane (E.I. Du Pont, USA). The earlier water transport studies of a variety of commercial ion exchange membranes and non-ionic separators in the vanadium redox cell have shown that the

T. Mohammadi; S. C. Chieng; M. Skyllas Kazacos

1997-01-01

187

Quantitative Synthesis and Component Analysis of Single-Participant Studies on the Picture Exchange Communication System  

ERIC Educational Resources Information Center

The "Picture Exchange Communication System" (PECS) has emerged as the augmentative communication intervention of choice for individuals with autism spectrum disorder (ASD), with a supporting body of single-participant studies. This report describes a meta-analysis of 16 single-participant studies on PECS with percentage of nonoverlapping data…

Tincani, Matt; Devis, Kathryn

2011-01-01

188

Study of carbon dioxide condensation in chevron plate exchangers; heat transfer analysis  

Microsoft Academic Search

The experimental investigation of carbon dioxide condensation in brazed plate heat exchangers is the main objective of this study. The current level of concern for the environment is at an all time high, therefore, it is important to look into methods and resources that lead to a cleaner and healthier future for the planet. This study details one such effort

N. Hayes; Amir Jokar; Zahid H. Ayub

2011-01-01

189

A comparative study of personality, sexual arousal, and behavior exchange in biological and nonbiological incestuous fathers  

Microsoft Academic Search

The primary purpose of this study was to examine whether biological and nonbiological incestuous fathers differ on personality characteristics, sexual arousal patterns, and behavior exchange in intimate relationships. Secondarily, this study examined internal consistency and test-retest reliability for responses by child molesters to a set of commercially available 35mm stimulus slides used for the phallometric assessment of sexual arousal related

Terrence Vaccaro

1992-01-01

190

Heat Exchanger Design Options and Tritium Transport Study for the VHTR System  

SciTech Connect

This report presents the results of a study conducted to consider heat exchanger options and tritium transport in a very high temperature reactor (VHTR) system for the Next Generation Nuclear Plant Project. The heat exchanger options include types, arrangements, channel patterns in printed circuit heat exchangers (PCHE), coolant flow direction, and pipe configuration in shell-and-tube designs. Study considerations include: three types of heat exchanger designs (PCHE, shell-and-tube, and helical coil); single- and two-stage unit arrangements; counter-current and cross flow configurations; and straight pipes and U-tube designs in shell-and-tube type heat exchangers. Thermal designs and simple stress analyses were performed to estimate the heat exchanger options, and the Finite Element Method was applied for more detailed calculations, especially for PCHE designs. Results of the options study show that the PCHE design has the smallest volume and heat transfer area, resulting in the least tritium permeation and greatest cost savings. It is theoretically the most reliable mechanically, leading to a longer lifetime. The two-stage heat exchanger arrangement appears to be safer and more cost effective. The recommended separation temperature between first and second stages in a serial configuration is 800oC, at which the high temperature unit is about one-half the size of the total heat exchanger core volume. Based on simplified stress analyses, the high temperature unit will need to be replaced two or three times during the plant’s lifetime. Stress analysis results recommend the off-set channel pattern configuration for the PCHE because stress reduction was estimated at up to 50% in this configuration, resulting in a longer lifetime. The tritium transport study resulted in the development of a tritium behavior analysis code using the MATLAB Simulink code. In parallel, the THYTAN code, previously performed by Ohashi and Sherman (2007) on the Peach Bottom data, was revived and verified. The 600 MWt VHTR core input file developed in preparation for the transient tritium analysis of VHTR systems was replaced with the original steady-state inputs for future calculations. A Finite Element Method analysis was performed using COMSOL Multiphysics software to accurately predict tritium permeation through the PCHE type heat exchanger walls. This effort was able to estimate the effective thickness for tritium permeations and develop a correlation for general channel configurations, which found the effective thickness to be much shorter than the average channel distance because of dead spots on the channel side.

Chang H. Oh; Eung S. Kim

2008-09-01

191

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

PubMed Central

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 health care and the n-EPR in particular. Methods The study was conducted in three Dutch health care settings: acute care, diabetes care, and ambulatory mental health care. Two health care organisations were included per setting. Between January and June 2010, interviews were conducted with 17 stakeholders working in these organisations. Relevant themes were deduced by means of thematic qualitative analysis. Results Health care providers perceived electronic information exchange to promote the efficiency and quality of care. The problems they perceived in electronic information exchange mainly concerned the confidentiality and safety of information exchange and the reliability and quality of patient data. Many problems perceived by health care providers did not specifically apply to the n-EPR, but to electronic information exchange in general. Conclusions The implementation of the Dutch n-EPR has mainly followed a top-down approach, thereby neglecting the fact that the perceptions and preferences of its users (health care providers) need to be addressed in order to achieve successful implementation. The results of this study provide valuable suggestions about how to promote health care providers' willingness to adopt electronic information exchange, which can be useful for other countries currently implementing an n-EPR. Apart from providing information about the benefits and usefulness of electronic information exchange, efforts should be focused on minimising the problems as perceived by health care providers. The safety and confidentiality of electronic information exchange can be improved by developing tools to evaluate the legitimacy of access to electronic records, by increasing health care providers' awareness of the need to be careful when using patient data, and by measures to limit access to sensitive patient data. Improving health care providers' recording behaviour is important to improve the reliability and quality of electronically exchanged patient data. PMID:21982395

2011-01-01

192

Web-Based Exchange of Views Enhances "Global Studies"  

ERIC Educational Resources Information Center

Purpose: The aim of this article is to present the development-oriented Master's curriculum "Global Studies" (GS) at the University of Graz, Austria, as an example of interdisciplinary academic training with the purpose of fostering inter-"cultural" understanding. It aims to show that scientific disciplines can be understood as "cultures of…

Ahamer, Gilbert; Kumpfmuller, Karl A.; Hohenwarter, Michaela

2011-01-01

193

SuperLig Ion Exchange Resin Swelling and Buoyancy Study  

SciTech Connect

The objective of this study was to achieve a fundamental understanding of SuperLig resin swelling and shrinking characteristics, which lead to channeling and early breakthrough during loading cycles. The density of salt solution that causes resin floating was also determined to establish a limit for operation. Specific tests performed include (a) pH dependence, (b) ionic strength dependence and (c) buoyancy effect vs. simulant composition.

Hassan, N.M.

2000-07-27

194

Theoretical study of electron exchange in Mg2+–B collisions  

NASA Astrophysics Data System (ADS)

The electron capture of Mg2+ ions in collisions with boron atoms has been investigated using ab initio quantum chemical approaches. The potential energies of the electronic states implicated in the process together with the non adiabatic coupling matrix elements have been calculated by multi-reference configuration interaction methods. Total and partial cross sections for the charge transfer reaction are determined in the (1–600) keV impact energy range by means of semi-classical approaches. A detailed analysis of the electron capture mechanism taking into account radial and rotational interactions has been performed and compared to previous studies on collision systems involving the Mg2+ projectile ion.

Amami, M.; Zaidi, A.; Moussa, A.; Lahmar, S.; Bacchus-Montabonel, M.-C.

2015-03-01

195

A Study of 15N/14N Isotopic Exchange over Cobalt Molybdenum Nitrides  

PubMed Central

The 14N/15N isotopic exchange pathways over Co3Mo3N, a material of interest as an ammonia synthesis catalyst and for the development of nitrogen transfer reactions, have been investigated. Both the homomolecular and heterolytic exchange processes have been studied, and it has been shown that lattice nitrogen species are exchangeable. The exchange behavior was found to be a strong function of pretreatment with ca. 25% of lattice N atoms being exchanged after 40 min at 600 °C after N2 pretreatment at 700 °C compared to only 6% following similar Ar pretreatment. This observation, for which the potential contribution of adsorbed N species can be discounted, is significant in terms of the application of this material. In the case of the Co6Mo6N phase, regeneration to Co3Mo3N under 15N2 at 600 °C occurs concurrently with 14N15N formation. These observations demonstrate the reactivity of nitrogen in the Co–Mo–N system to be a strong function of pretreatment and worthy of further consideration. PMID:24265977

2013-01-01

196

Studies of Tropical/Mid-Latitude Exchange Using UARS Observations  

NASA Technical Reports Server (NTRS)

At the time this proposal was submitted, recent publications had suggested an important role for transport of midlatitude air into the tropical lower stratosphere. Most of these studies had employed data that gave only a time-averaged picture, making it difficult to determine the nature of the transport processes responsible for the observed behavior. We proposed to analyze observations of long-lived trace gases, such as nitric acid, methane, nitrous oxide, and chlorofluorocarbons, made from the Upper Atmosphere Research Satellite, to investigate the seasonal behavior of mixing between the midlatitudes and tropics. We planned to construct probability distributions of the concentrations of these species over small altitude ranges and to compare them to expectations based on modeled mean concentrations and knowledge of instrument precision. Differences from expectation were to be analyzed with respect to meteorological parameters to determine whether wave activity may have induced apparent mixing.

Avallone, Linnea

2001-01-01

197

Hydrogen exchange behavior of [U-15N]-labeled oxidized and reduced iso-1-cytochrome c.  

PubMed

Heteronuclear NMR spectroscopy was used to measure the hydrogen-deuterium exchange rates of backbone amide hydrogens in both oxidized and reduced [U-15N]iso-1-cytochrome c from the yeast Saccharomyces cerevisiae. The exchange data confirm previously reported data [Marmorino et al. (1993) Protein Sci. 2, 1966-1974], resolve several inconsistencies, and provide more thorough coverage of exchange rates throughout the cytochrome c protein in both oxidation states. Combining the data previously collected on unlabeled C102T with the current data collected on [U-15N]C102T, exchange rates for 53 protons in the oxidized state and 52 protons in the reduced state can now be reported. Most significantly, hydrogen exchange measurements on [U-15N]iso-1-cytochrome c allowed the observation of exchange behavior of the secondary structures, such as large loops, that are not extensively hydrogen-bonded. For the helices, the most slowly exchanging protons are found in the middle of the helix, with more rapidly exchanging protons at the helix ends. The observation for the Omega-loops in cytochrome c is just the opposite. In the loops, the ends contain the most slowly exchanging protons and the loop middles allow more rapid exchange. This is found to be true in cytochrome c loops, even though the loop ends are not attached to any regular secondary structures. Some of the exchange data are strikingly inconsistent with data collected on the C102S variant at a different pH, which suggests pH-dependent dynamic differences in the protein structure. This new hydrogen exchange data for loop residues could have implications for the substructure model of eukaryotic cytochrome c folding. Isotopic labeling of variant forms of cytochrome c can now be used to answer many questions about the structure and folding of this model protein. PMID:10194371

Baxter, S M; Fetrow, J S

1999-04-01

198

Semi-aerobic stabilized landfill leachate treatment by ion exchange resin: isotherm and kinetic study  

NASA Astrophysics Data System (ADS)

This study was carried out to investigate the treatability of ion exchange resin (Indion MB 6 SR) for the removal of chromium (VI), aluminium (III), zinc (II), copper (II), iron (II), and phosphate (PO4)3-, chemical oxygen demand (COD), ammonia nitrogen (NH3-N) and colour from semi-aerobic stabilized leachate by batch test. A range of ion exchange resin dosage was tested towards the removal efficiency of leachate parameters. It was observed that equilibrium data were best represented by the Langmuir model for metal ions and Freundlich was ideally fit for COD, NH3-N and colour. Intra particle diffusion model, pseudo first-order and pseudo second-order isotherm models were found ideally fit with correlation of the experimental data. The findings revealed that the models could describe the ion exchange kinetic behaviour efficiently, which further suggests comprehensive outlook for the future research in this field.

Zamri, Mohd Faiz Muaz Ahmad; Kamaruddin, Mohamad Anuar; Yusoff, Mohd Suffian; Aziz, Hamidi Abdul; Foo, Keng Yuen

2015-03-01

199

Sorption of SPADNS azo dye on polystyrene anion exchangers: equilibrium and kinetic studies.  

PubMed

The sorption of SPANDS from aqueous solution onto the macroporous polystyrene anion exchangers of weakly basic Amberlyst A-21 and strongly basic Amberlyst A-29 in a batch method was studied. The effect of initial dye concentration and phase contact time was considered to evaluate the sorption capacity of anion exchangers. Equilibrium data were attempted by various adsorption isotherms including the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models. A comparison of kinetic models applied to the adsorption rate constants and equilibrium sorption capacities was made for the Lagergren first-order, pseudo second-order and Morris-Weber intraparticle diffusion kinetic models. The results showed that the adsorption isotherm is in the good agreement with the Langmuir equation and that the adsorption kinetics of SPADNS on both anion exchangers can be best described by the pseudo second-order model. PMID:19660863

Greluk, Magdalena; Hubicki, Zbigniew

2009-12-15

200

Development of a Direct Contact Heat Exchanger, Phase 1 Study Report  

NASA Technical Reports Server (NTRS)

Electric power generation from geothermal brine requires, first, bringing the hot brine to the surface and then converting the heat to electric power. Binary conversion schemes were proposed, with the heat transfer between the brine and the working organic fluid taking place in a conventional tube and shell heat exchanger. If the brine is heavily laden with dissolved solids, however, solids buildup on the heat exchanger surfaces leads to a considerable degree of fouling and an accompanying drop in performance is experienced. A possible solution to this problem is the use of a direct contact exchanger with the secondary fluid power cycle. The proposed concept involves the formation of fluid sheets and bells as heat angles. Results of a study concerning the fluid mechanics of such surfaces are given.

Manvi, R.

1978-01-01

201

Study regarding the influence of the crimping angle on the performances of the heat exchangers  

NASA Astrophysics Data System (ADS)

The aim of this study is to determine the geometry of a plate for heat exchanger with high heat flow and low values for pressure losses. For this, in Solid Work software, were designed three plate geometries with different crimping angles for the flow channels. Was analyzed the influence of the crimping angle ? on the fluid distribution and heat transfer. Also, were compared the data resulted from Computational Fluid Dynamics numeric simulation with the experimental ones for the plate heat exchangers with gaskets. The analysis of the vortices and temperature field distribution was achieved with the aid of simulation software Fluent. In order to validate the numerical simulation's results experimental research were carried out on a heat exchangers stand

Irimie, O.; Bode, F.; Opruta, D.

2013-04-01

202

Chromosome instability and sister chromatid exchange (SCE) studies in patients with carcinoma of cervix uteri  

Microsoft Academic Search

Cytogenetic studies have been carried out using the G-banding technique in peripheral blood lymphocytes of 14 patients with carcinoma of the cervix uteri. Simultaneously, sister chromatid exchange (SCE) was also analyzed in the peripheral blood lymphocytes of these patients, along with those of 20 age-matched control subjects. The frequency of aberrant metaphases is significantly higher in patients with carcinoma of

Varinderpal S. Dhillon; Ranbir S. Kler; Ipninder K. Dhillon

1996-01-01

203

Application Instructions for BU United Kingdom Exchange and Study Abroad Programs  

E-print Network

Application Instructions for BU United Kingdom Exchange and Study Abroad Programs University. Complete the United Kingdom Program Preference Form. 2. Complete pages 1 and 2 (OAP 1) of the standard SUNY;Rev. 6/2013 United Kingdom Program Preference Form University of Nottingham University of Bath

Suzuki, Masatsugu

204

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

205

Multibody system model of a cargo airship to study the load exchange process  

Microsoft Academic Search

Projected cargo airships for the transport of large loads exceed the dimensions of existing aircrafts and gave rise to various technical problems. One important task in an airship mission is the loading and unloading of the heavy and spacious load from the payload bay of the airship. In order to study the dynamics of the load exchange process, mathematical models

Andreas Bockstedte; Edwin Kreuzer

2005-01-01

206

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

207

Experimental study of work exchange with a granular gas: the viewpoint of the Fluctuation Theorem.  

E-print Network

epl draft Experimental study of work exchange with a granular gas: the viewpoint of the Fluctuation of the fluctuations of energy flux between a granular gas and a small driven harmonic oscillator. The DC-motor driving forcing, between the motor and the gas are examined from the viewpoint of the Fluctuation Theorem

Boyer, Edmond

208

STUDY OF PROTON EXCHANGE MEMBRANE FUEL CELLS (PZT-PEMFCS) WITH NOZZLE AND DIFFUSER  

Microsoft Academic Search

Previous theoretical studies have shown that piezoelectric proton exchange membrane fuel cells (PZT-PEMFCs) might solve water flooding problems and increase cell performance. The innovative design of PZT-PEMFCs results in more oxygen being compressed into the catalyst layer. This enhances the electrochemical reaction and the current density, especially at a high PZT vibration frequency (64 Hz). In this investigation, a single,

Hsiao-Kang Ma; Shih-Han Huang; Ya-Ting Cheng; Chrung Guang Hou

2009-01-01

209

A STAGE-BASED STUDY OF DROUGHT RESPONSE IN CRYPTANTHA FLAVA (BORAGINACEAE): GAS EXCHANGE, WATER USE  

E-print Network

A STAGE-BASED STUDY OF DROUGHT RESPONSE IN CRYPTANTHA FLAVA (BORAGINACEAE): GAS EXCHANGE, WATER USE in the frequency of major droughts, yet we know little about the consequences of drought for the demography (Boraginaceae) to determine how plants of different developmental stages respond to drought through changes

Wait, D. Alexander

210

Hydrogen exchange mass spectrometry of bacteriorhodopsin reveals light-induced changes in the structural dynamics of a biomolecular machine.  

PubMed

Many proteins act as molecular machines that are fuelled by a nonthermal energy source. Examples include transmembrane pumps and stator-rotor complexes. These systems undergo cyclic motions (CMs) that are being driven along a well-defined conformational trajectory. Superimposed on these CMs are thermal fluctuations (TFs) that are coupled to stochastic motions of the solvent. Here we explore whether the TFs of a molecular machine are affected by the occurrence of CMs. Bacteriorhodopsin (BR) is a light-driven proton pump that serves as a model system in this study. The function of BR is based on a photocycle that involves trans/cis isomerization of a retinal chromophore, as well as motions of transmembrane helices. Hydrogen/deuterium exchange (HDX) mass spectrometry was used to monitor the TFs of BR, focusing on the monomeric form of the protein. Comparative HDX studies were conducted under illumination and in the dark. The HDX kinetics of BR are dramatically accelerated in the presence of light. The isotope exchange rates and the number of backbone amides involved in EX2 opening transitions increase roughly 2-fold upon illumination. In contrast, light/dark control experiments on retinal-free protein produced no discernible differences. It can be concluded that the extent of TFs in BR strongly depends on photon-driven CMs. The light-induced differences in HDX behavior are ascribed to protein destabilization. Specifically, the thermodynamic stability of the dark-adapted protein is estimated to be 5.5 kJ mol(-1) under the conditions of our work. This value represents the free energy difference between the folded state F and a significantly unfolded conformer U. Illumination reduces the stability of F by 2.2 kJ mol(-1). Mechanical agitation caused by isomerization of the chromophore is transferred to the surrounding protein scaffold, and subsequently, the energy dissipates into the solvent. Light-induced retinal motions therefore act analogously to an internal heat source that promotes the occurrence of TFs. Overall, our data highlight the potential of HDX methods for probing the structural dynamics of molecular machines under "engine on" and "engine off" conditions. PMID:22043856

Pan, Yan; Brown, Leonid; Konermann, Lars

2011-12-21

211

Advantages of chemical exchange-sensitive spin-lock (CESL) over chemical exchange saturation transfer (CEST) for hydroxyl- and amine-water proton exchange studies.  

PubMed

The chemical exchange (CE) rate of endogenous hydroxyl and amine protons with water is often comparable to the difference in their chemical shifts. These intermediate exchange processes have been imaged by the CE saturation transfer (CEST) approach with low-power and long-duration irradiation. However, the sensitivity is not optimal and, more importantly, the signal is contaminated by slow magnetization transfer processes. Here, the properties of CEST signals are compared with those of a CE-sensitive spin-lock (CESL) technique irradiating at the labile proton frequency. First, using a higher power and shorter irradiation in CE-MRI, we obtain: (i) an increased selectivity to faster CE rates via a higher sensitivity to faster CEs and a lower sensitivity to slower CEs and magnetization transfer processes; and (ii) a decreased in vivo asymmetric magnetization transfer contrast measured at ±15 ppm. The sensitivity gain of CESL over CEST is higher for a higher power and shorter irradiation. Unlike CESL, CEST signals oscillate at a very high power and short irradiation. Second, time-dependent CEST and CESL signals are well modeled by analytical solutions of CE-MRI with an asymmetric population approximation, which can be used for quantitative CE-MRI and validated by simulations of Bloch-McConnell equations and phantom experiments. Finally, the in vivo amine-water proton exchange contrast measured at 2.5 ppm with ?1 = 500 Hz is 18% higher in sensitivity for CESL than CEST at 9.4 T. Overall, CESL provides better exchange rate selectivity and sensitivity than CEST; therefore, CESL is more suitable for CE-MRI of intermediate exchange protons. PMID:25199631

Jin, Tao; Kim, Seong-Gi

2014-11-01

212

Unfolding and aggregation of monoclonal antibodies on cation exchange columns: Effects of resin type, load buffer, and protein stability.  

PubMed

The chromatographic behavior of a monoclonal antibody (mAb) that exhibits a pronounced two-peak elution behavior is studied for a range of strong cation exchange resins and with varying load buffer pH and composition. Six stationary phases are considered, including two tentacle-type resins (Fractogel EMD SO3-(M) and Eshmuno S), a resin with grafted polymeric surface extenders (Nuvia S), a resin with a bimodal pore size distribution (POROS HS 50), and two macroporous resins without polymer grafts (Source 30S and UNOsphere Rapid S). The two-peak elution behavior is very pronounced for the tentacle and polymer-grafted resins and for POROS HS 50, but is essentially absent for the two macroporous resins. The extent of this behavior decreases as the buffer pH and concentration increase and, consequently, mAb binding becomes weaker. Replacing sodium with arginine as the buffer counterion, which is expected to decrease the mAb binding strength, nearly completely eliminates the two-peak behavior, while replacing sodium with tetra-n-butylammonium hydroxide, which is expected to increase the mAb binding strength, dramatically exacerbate the effect. As shown by hydrogen-deuterium exchange mass spectrometry (HX-MS), the two-peak elution behavior is related to conformational changes that occur when the mAb binds. These changes result in increased solvent exposure of specific peptides in the Fc-region for either the Fractogel or the Nuvia resin. No significant conformational changes were seen by HX-MS when the mAb was bound to the UNOsphere resin or on the Fractogel resin when arginine was used in lieu of sodium as the load buffer counterion. Experiments with two additional mAbs on the Fractogel resin show that the two-peak elution behavior is dependent on the particular antibody. Circular dichroism suggests that the propensity of different mAbs to either precipitate directly or to form stabilizing intermolecular structures upon exposure to thermal stress can be related to their chromatographic behaviors. PMID:25739785

Guo, Jing; Carta, Giorgio

2015-04-01

213

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

214

Student exchange for nursing students: does it raise cultural awareness'? A descriptive, qualitative study.  

PubMed

With free movement for citizens within the European Union and with distant parts of our globe becoming more accessible, cultural awareness and cultural competence are becoming important skills for nurses. Internationalisation and raising awareness of other cultural contexts are essential elements in Swedish higher education, thus explaining the variety of student exchange programmes that are available. The aim of this study was to explore Swedish nursing students' perceptions of student exchange and their experiences. Data were collected through group interviews and then analysed following the principles of content analysis. Our analysis resulted in three categories: Preparing to go abroad, Reasons for going abroad and From expectation to experience. Cultural aspects and cultural awareness were emphasised as strong motivational factors, both personal and professional, behind participation in student exchange programmes. Information was also highlighted as a crucial means of reaching potential students as well as the power of knowledge through personal experience. This study highlights the importance of student exchange in expanding the individual student's personal and professional horizons. It also stresses the importance of including a transcultural nursing element in nursing curricula. PMID:24406034

Bohman, Doris M; Borglin, Gunilla

2014-05-01

215

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

216

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

217

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

218

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

2005-06-01

219

Hydrogen diffusion in bulk and nanoclusters of MgH2 and the role of catalysts on the basis of ab initio molecular dynamics  

NASA Astrophysics Data System (ADS)

We present ab initio molecular dynamics calculations based on density functional theory to study the hydrogen-deuterium exchange in bulk and nanoclusters of MgH2. Our calculations reveal the important role of catalysts to diffuse the hydrogen at low temperatures and increase the diffusion rate. We determine the diffusion constants, ?D? of deuterium, and show the single hydrogen-deuterium exchange in bulk and nanocluster of MgH2. Our calculated value of diffusion constant of deuterium in bulk MgH2 is in excellent agreement with the experimental value. Furthermore, we show the edge site importance of catalysts in the fast diffusion of hydrogen.

Ramzan, M.; Hussain, T.; Ahuja, R.

2009-06-01

220

Science and Technology Policies Information Exchange System (SPINES) Feasibility Study. Science Policy Studies and Documents No. 33(1).  

ERIC Educational Resources Information Center

A feasibility study was made to define, within the conceptual framework and in accordance with the recommendations of the UNISIST program, the managerial, technical, legal, and financial framework for the setting up of an International Science and Technology Policies Information Exchange System (SPINES). This report describes in some detail the…

Coblans, H.; And Others

221

Structural basis of sodium–potassium exchange of a human telomeric DNA quadruplex without topological conversion  

PubMed Central

Understanding the mechanism of Na+/K+-dependent spectral conversion of human telomeric G-quadruplex (G4) sequences has been limited not only because of the structural polymorphism but also the lack of sufficient structural information at different stages along the conversion process for one given oligonucleotide. In this work, we have determined the topology of the Na+ form of Tel23 G4, which is the same hybrid form as the K+ form of Tel23 G4 despite the distinct spectral patterns in their respective nuclear magnetic resonance (NMR) and circular dichroism spectra. The spectral difference, particularly the well-resolved imino proton NMR signals, allows us to monitor the structural conversion from Na+ form to K+ form during Na+/K+ exchange. Time-resolved NMR experiments of hydrogen–deuterium exchange and hybridization clearly exclude involvement of the global unfolding for the fast Na+/K+ spectral conversion. In addition, the K+ titration monitored by NMR reveals that the Na+/K+ exchange in Tel23 G4 is a two-step process. The addition of K+ significantly stabilizes the unfolding kinetics of Tel23 G4. These results offer a possible explanation of rapid spectral conversion of Na+/K+ exchange and insight into the mechanism of Na+/K+ structural conversion in human telomeric G4s. PMID:24476914

Wang, Zi-Fu; Li, Ming-Hao; Hsu, Shang-Te Danny; Chang, Ta-Chau

2014-01-01

222

been conducted to analyze the exchanger experimentally (Bose and Parker 1983; Bose et al. 1980, 1982). An analytical study of such heat exchangers, which uses a detailed mathematical model to describe their  

E-print Network

, 1982). An analytical study of such heat exchangers, which uses a detailed mathematical model-tube heat exchangers. Six 6-in (152-mm) wells were drilled at depths of 53, 60, 70, 80, 90, and 100 ft (16#12;been conducted to analyze the exchanger experimentally (Bose and Parker 1983; Bose et al. 1980

Oak Ridge National Laboratory

223

Numerical study of a round tube heat exchanger with louvered fins and delta winglets  

NASA Astrophysics Data System (ADS)

Louvered fin and round tube heat exchangers are widely used in air conditioning devices and heat pumps. In this study the effect of punching delta winglet vortex generators in the louvered fin surface is studied numerically. The delta winglets are located in a common-flow-down orientation behind each tube of the staggered tube layout. It is shown that the generated vortices significantly reduce the size of the tube wakes. Three important heat transfer enhancement mechanisms can be distinguished: a better flow mixing, boundary layer thinning and a delay in flow separation from the tube surface. The compound heat exchanger has a better thermal hydraulic performance then when only louvers or only delta winglets are used. Comparison to other enhanced fin designs clearly shows its potential, especially for low Reynolds number applications.

Huisseune, H.; T'Joen, C.; De Jaeger, P.; Ameel, B.; De Paepe, M.

2012-11-01

224

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

225

A hybrid-exchange density functional study of Ca-doped LaMnO3  

NASA Astrophysics Data System (ADS)

In this work, hybrid-exchange density functional theory calculations are carried out to determine the effects of A-site doping on the electronic and magnetic properties of the manganite series La1-xCaxMnO3. This study focuses on the nature of the ground state for an ordered Ca distribution. We show that the hybrid exchange functional, B3LYP, provides an accurate and consistent description of the electronic structure for LaMnO3 and La0.75Ca0.25MnO3. The magnetic ground states for the compositions studied are predicted correctly and comparisons have been made to available experimental data. This provides a basis for a first principles description of the magnetocaloric effect in La1-xCaxMnO3.

Korotana, R.; Mallia, G.; Gercsi, Z.; Harrison, N. M.

2013-05-01

226

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

227

Boron removal from aqueous solutions by ion-exchange resin: Column sorption–elution studies  

Microsoft Academic Search

A column sorption–elution study was carried out by using a strong base anion-exchange resin (Dowex 2×8) for the removal of boron from aqueous solutions. The breakthrough curve was obtained as a function of feed flow rate and the total and breakthrough capacity values of the resin were calculated. The boron on the resin was quantitatively eluted with 0.5M HCl solution

T. Ennil Köse; Ne?e Öztürk

2008-01-01

228

Boron Removal from Aqueous Solution by Ion-Exchange Resin: Column Sorption Elution Studies  

Microsoft Academic Search

A column sorption-elution study was carried out by using a strong base anion exchange resin (Dowex 2x8) for the removal of boron from aqueous solution. The breakthrough curve was obtained as a function of feed flow rate and capacity value of resin was calculated. The boron on the resin was quantitatively eluted with 0.5M HCl solution at different flow rates.

T. E. Bekta?; N. Öztiirk

2004-01-01

229

An anion-exchange chromatographic study on boron isotopic fractionation at 2 MPa at 293 K  

Microsoft Academic Search

To study boron isotopic fractionation at high pressure, column chromatography operated in the breakthrough manner was performed at 2.0MPa at 25.0°C. The fractionation factor (S) between boron adsorbed onto strongly basic anion-exchange resin and boron in solution was obtained as 1.013, which was smaller than the values at 0.1MPa (atmospheric pressure) found in literature. The pressure dependence of S was

Masaaki Musashi; Motoyuki Matsuo; Takao Oi; Masao Nomura

2006-01-01

230

Numerical and experimental studies of threedimensional plate-fin and tube heat exchangers  

Microsoft Academic Search

Fluid flow and heat transfer over a multi-row (1–6 rows) plate-fin and tube heat exchanger are studied numerically and experimentally. Fluid flow is incompressible, three-dimensional and laminar. The effects of different geometrical parameters such as tube arrangement, tube row numbers and fin pitch (8–12 fins per inch) are investigated in detail for the Reynolds number (based on the fin spacing

Wen-Jeng Chang

1996-01-01

231

Dynamic simulation of plate and frame heat exchanger undergoing food fouling: coconut milk fouling case study  

Microsoft Academic Search

The mathematical modelling and-simulation of plate heat exchangers with rapid fouling effects are presented. Crank-Nicolson's method and the ghost-node technique were used to solve the thermal model. Effects of fouling were added to the model through the overall heat-transfer coefficient correlation. A fourth order Runge-Kutta scheme was used to obtain the integral value of the fouling model. An experimental study

Phavanee Narataruksaa; Panya Triratana; Karn Pana-Suppamassadua; Peter J. Heggs; Suvit Tia

232

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

233

Hydrogen exchange methods to study protein folding Mallela M.G. Krishna,* Linh Hoang, Yan Lin, and S. Walter Englander  

E-print Network

Hydrogen exchange methods to study protein folding Mallela M.G. Krishna,* Linh Hoang, Yan Lin, and S. Walter Englander Johnson Research Foundation, Department of Biochemistry and Biophysics Available online 5 June 2004 Abstract The measurement of amino acid-resolved hydrogen exchange (HX) has

Englander, S. Walter

234

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

235

Mechanisms of Hydrogen Exchange of Methane with H-Zeolite Y: An ab Initio Embedded Cluster Study  

E-print Network

Mechanisms of Hydrogen Exchange of Methane with H-Zeolite Y: An ab Initio Embedded Cluster Study; In Final Form: April 21, 2000 We present ab initio embedded cluster studies on the mechanism of hydrogen

Truong, Thanh N.

236

Experimental study of the airside performance of tube row spacing in finned tube heat exchangers  

NASA Astrophysics Data System (ADS)

Almost all of the studies in dehumidifying coils are experimental studies. In this study, effect of tube regulation space on heat and mass transfer and friction factor for heat exchangers made from aluminum fins and cooper tubes are identified experimentally. External surface heat transfer coefficient, Colburn factor and friction factor was calculated by the help of the computer program by using experimental values done. After the diagrams investigated, with the decreasing of tube row spacing the external surface heat transfer in the dry surface and friction factor increased. If wet and dry surfaces are compared, Colburn and friction factor in wet surfaces is larger than Colburn and friction factor in dry surfaces.

Halici, Fethi; Taymaz, Imdat

2006-07-01

237

Charge-exchange erosion studies of accelerator grids in ion thrusters  

NASA Technical Reports Server (NTRS)

A particle simulation model is developed to study the charge-exchange grid erosion in ion thrusters for both ground-based and space-based operations. Because the neutral gas downstream from the accelerator grid is different for space and ground operation conditions, the charge-exchange erosion processes are also different. Based on an assumption of now electric potential hill downstream from the ion thruster, the calculations show that the accelerator grid erosion rate for space-based operating conditions should be significantly less than experimentally observed erosion rates from the ground-based tests conducted at NASA Lewis Research Center (LeRC) and NASA Jet Propulsion Laboratory (JPL). To resolve this erosion issue completely, we believe that it is necessary to accurately measure the entire electric potential field downstream from the thruster.

Peng, Xiaohang; Ruyten, Wilhelmus M.; Keefer, Dennis

1993-01-01

238

Optical study of electron-electron exchange interaction in CdTe/ZnTe quantum dots  

NASA Astrophysics Data System (ADS)

We present an experimental study of electron-electron exchange interaction in self-assembled CdTe/ZnTe quantum dots based on the photoluminescence measurements. The character and strength of this interaction are obtained by simultaneous observation of various recombination channels of a doubly negatively charged exciton X2-, including previously unrecognized emission lines related to the electron-singlet configuration in the final state. A typical value of the electron singlet-triplet splitting, which corresponds to the exchange integral of electron-electron interaction, has been determined as 20.4 meV with a spread of 1.4 meV across the wide population of quantum dots. We also evidence an unexpected decrease of energy difference between the singlet and triplet states under a magnetic field in Faraday geometry.

Kazimierczuk, T.; Smole?ski, T.; Kobak, J.; Goryca, M.; Pacuski, W.; Golnik, A.; Fronc, K.; K?opotowski, ?.; Wojnar, P.; Kossacki, P.

2013-05-01

239

Boron removal from aqueous solutions by ion-exchange resin: column sorption-elution studies.  

PubMed

A column sorption-elution study was carried out by using a strong base anion-exchange resin (Dowex 2 x 8) for the removal of boron from aqueous solutions. The breakthrough curve was obtained as a function of feed flow rate and the total and breakthrough capacity values of the resin were calculated. The boron on the resin was quantitatively eluted with 0.5M HCl solution at different flow rates. Three consecutive sorption-elution-washing-regeneration-washing cycles were applied to the resin in order to investigate the reusability of the ion-exchange resin. Total capacity values remained almost the same after three sorption-elution-regeneration cycles. The Thomas and the Yoon-Nelson models were applied to experimental data to predict the breakthrough curves and to determine the characteristic column parameters required for process design. The results proved that the models would describe the breakthrough curves well. PMID:17716813

Köse, T Ennil; Oztürk, Ne?e

2008-04-01

240

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. PMID:6426539

Baci?, G; Ratkovi?, S

1984-01-01

241

Study of a Market Model with Conservative Exchanges on Complex Networks  

E-print Network

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: Erd\\"{o}s-R\\'enyi 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 av...

Braunstein, L A; Iglesias, J R

2012-01-01

242

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

243

Study of junction flows in louvered fin round tube heat exchangers using the dye injection technique  

SciTech Connect

Detailed studies of junction flows in heat exchangers with an interrupted fin design are rare. However, understanding these flow structures is important for design and optimization purposes, because the thermal hydraulic performance of heat exchangers is strongly related to the flow behaviour. In this study flow visualization experiments were performed in six scaled-up models of a louvered fin round tube heat exchanger. The models have three tube rows in a staggered layout and differ only in their fin spacing and louver angle. A water tunnel was designed and built and the flow visualizations were carried out using dye injection. At low Reynolds numbers the streakline follows the tube contours, while at higher Reynolds numbers a horseshoe vortex is developed ahead of the tubes. The two resulting streamwise vortex legs are destroyed by the downstream louvers (i.e. downstream the turnaround louver), especially at higher Reynolds numbers, smaller fin pitches and larger louver angles. Increasing the fin spacing results in a larger and stronger horseshoe vortex. This illustrates that a reduction of the fin spacing results in a dissipation of vortical motion by mechanical blockage and skin friction. Furthermore it was observed that the vortex strength and number of vortices in the second tube row is larger than in the first tube row. This is due to the thicker boundary layer in the second tube row, and the flow deflection, which is typical for louvered fin heat exchangers. Visualizations at the tube-louver junction showed that in the transition part between the angled louver and the flat landing a vortex is present underneath the louver surface which propagates towards the angled louver. (author)

Huisseune, H.; Willockx, A.; De Paepe, M. [Department of Flow, Heat and Combustion Mechanics, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent (Belgium); T'Joen, C. [Department of Flow, Heat and Combustion Mechanics, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent (Belgium); Department Radiation, Radionuclides and Reactors, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); De Jaeger, P. [Department of Flow, Heat and Combustion Mechanics, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent (Belgium); NV Bekaert SA, Bekaertstraat 2, 8550 Zwevegem (Belgium)

2010-11-15

244

Numerical studies of an eccentric tube-in-tube helically coiled heat exchanger for IHEP-ADS helium purification system  

E-print Network

The tube-in-tube helically coiled (TTHC) heat exchanger is preferred in the purifier of IHEP-ADS helium purification system. The position of an internal tube is usually eccentric in a TTHC heat exchanger in practice, while most TTHC heat exchangers in the literature studied are concentric. In this paper, TTHC heat exchangers with different eccentricity ratios are numerically studied for turbulent flow and heat transfer characteristics under different flow rates. The fluid considered is helium at the pressure of 20Mpa, with temperature dependent thermo-physical properties for the inner tube and the annulus. The inner Nusselt number between the concentric and eccentric TTHC heat exchangers are compared, so is the annulus Nusselt number. The results show that with the eccentricity increasing, the annulus Nusselt number increases substantially. According to the numerical data, new empirical correlations of Nusselt number as a function of Reynolds number and eccentricity for the inner tube and the annulus are pres...

Zhang, Jianqin

2014-01-01

245

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

246

Health Information Exchange Implementation: Lessons Learned and Critical Success Factors From a Case Study  

PubMed Central

Background Much attention has been given to the proposition that the exchange of health information as an act, and health information exchange (HIE), as an entity, are critical components of a framework for health care change, yet little has been studied to understand the value proposition of implementing HIE with a statewide HIE. Such an organization facilitates the exchange of health information across disparate systems, thus following patients as they move across different care settings and encounters, whether or not they share an organizational affiliation. A sociotechnical systems approach and an interorganizational systems framework were used to examine implementation of a health system electronic medical record (EMR) system onto a statewide HIE, under a cooperative agreement with the Office of the National Coordinator for Health Information Technology, and its collaborating organizations. Objective The objective of the study was to focus on the implementation of a health system onto a statewide HIE; provide insight into the technical, organizational, and governance aspects of a large private health system and the Virginia statewide HIE (organizations with the shared goal of exchanging health information); and to understand the organizational motivations and value propositions apparent during HIE implementation. Methods We used a formative evaluation methodology to investigate the first implementation of a health system onto the statewide HIE. Qualitative methods (direct observation, 36 hours), informal information gathering, semistructured interviews (N=12), and document analysis were used to gather data between August 12, 2012 and June 24, 2013. Derived from sociotechnical concepts, a Blended Value Collaboration Enactment Framework guided the data gathering and analysis to understand organizational stakeholders’ perspectives across technical, organizational, and governance dimensions. Results Several challenges, successes, and lessons learned during the implementation of a health system to the statewide HIE were found. The most significant perceived success was accomplishing the implementation, although many interviewees also underscored the value of a project champion with decision-making power. In terms of lessons learned, social reasons were found to be very significant motivators for early implementation, frequently outweighing economic motivations. It was clear that understanding the guides early in the project would have mitigated some of the challenges that emerged, and early communication with the electronic health record vendor so that they have a solid understanding of the undertaking was critical. An HIE implementations evaluation framework was found to be useful for assessing challenges, motivations, value propositions for participating, and success factors to consider for future implementations. Conclusions This case study illuminates five critical success factors for implementation of a health system onto a statewide HIE. This study also reveals that organizations have varied motivations and value proposition perceptions for engaging in the exchange of health information, few of which, at the early stages, are economically driven. PMID:25599991

2014-01-01

247

Human recombinant [C22A] FK506-binding protein amide hydrogen exchange rates from mass spectrometry match and extend those from NMR.  

PubMed Central

Hydrogen/deuterium exchange behavior of human recombinant [C22A] FK506 binding protein (C22A FKBP) has been determined by protein fragmentation, combined with electrospray Fourier transform ion cyclotron resonance mass spectrometry (MS). After a specified period of H/D exchange in solution, C22A FKBP was digested by pepsin under slow exchange conditions (pH 2.4, 0 degree C), and then subjected to on-line HPLC/MS for deuterium analysis of each proteolytic peptide. The hydrogen exchange rate of each individual amide hydrogen was then determined independently by heteronuclear two-dimensional NMR on 15N-enriched C22A FKBP. A maximum entropy method (MEM) algorithm makes it possible to derive the distributions of hydrogen exchange rate constants from the MS-determined deuterium exchange-in curves in either the holoprotein or its proteolytic segments. The MEM-derived rate constant distributions of C22A FKBP and different segments of C22A FKBP are compared to the rate constants determined by NMR for individual amide protons. The rate constant distributions determined by both methods are consistent and complementary, thereby validating protein fragmentation/mass spectrometry as a reliable measure of hydrogen exchange in proteins. PMID:9336843

Zhang, Z.; Li, W.; Logan, T. M.; Li, M.; Marshall, A. G.

1997-01-01

248

Experimental Study on Heat Transfer of Plate Heat Exchanger and Application to Waste Heat Power Generation  

NASA Astrophysics Data System (ADS)

According to investigation on the steel plant, a large amount of low thermal energy is emitted directly to the environment without any utilization. It is apparent that energy cogeneration and energy conversion become a problem concerned by all countries. At present, the utilization of thermal energy stored in slag washing water is mainly confined to transformation to heating rather than electricity generation. The working mechanism of electricity generation using slag washing water and experimental study on heat transfer characteristics of plate heat exchanger are presented in this paper. The experimental results show the non-linear relationship between heat transfer coefficient of plate heat exchanger made by different materials and different flow velocity of clean water in the pipe. When the flow velocity is greater than 1 m/s, K retains a certain value while the resistance coefficient increases dramatically. By comparison of experimental data, it is found that the heat resistance outside plate heat exchanger is the main factor that influences performance of plate heat transfer.

Tang, X. Y.; Zhu, D. S.; Guo, C. Q.

2010-03-01

249

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

250

Quantifying tidally driven benthic oxygen exchange across permeable sediments: An aquatic eddy correlation study  

NASA Astrophysics Data System (ADS)

Continental shelves are predominately (˜70%) covered with permeable, sandy sediments. While identified as critical sites for intense oxygen, carbon, and nutrient turnover, constituent exchange across permeable sediments remains poorly quantified. The central North Sea largely consists of permeable sediments and has been identified as increasingly at risk for developing hypoxia. Therefore, we investigate the benthic O2 exchange across the permeable North Sea sediments using a combination of in situ microprofiles, a benthic chamber, and aquatic eddy correlation. Tidal bottom currents drive the variable sediment O2 penetration depth (from ˜3 to 8 mm) and the concurrent turbulence-driven 25-fold variation in the benthic sediment O2 uptake. The O2 flux and variability were reproduced using a simple 1-D model linking the benthic turbulence to the sediment pore water exchange. The high O2 flux variability results from deeper sediment O2 penetration depths and increased O2 storage during high velocities, which is then utilized during low-flow periods. The study reveals that the benthic hydrodynamics, sediment permeability, and pore water redox oscillations are all intimately linked and crucial parameters determining the oxygen availability. These parameters must all be considered when evaluating mineralization pathways of organic matter and nutrients in permeable sediments.

McGinnis, Daniel F.; Sommer, Stefan; Lorke, Andreas; Glud, Ronnie N.; Linke, Peter

2014-10-01

251

Nucleotide exchange in dimeric MCAK induces longitudinal and lateral stress at microtubule ends to support depolymerization  

PubMed Central

Summary Members of the kinesin-13 sub-family use their motor domains in an unconventional fashion to initiate microtubule depolymerization at microtubule (MT) ends, suggesting unique conformational transitions for lattice engagement, end adaptation or both. Using hydrogen/deuterium exchange and electron microscopy, we explored conformational changes in kinesin-13 MCAK in its dimeric form and when bound to a depolymerization intermediate. ATP hydrolysis relaxes the conformation of the free dimer, notably in the neck and N-terminal domain. Exchanging dimeric MCAK with ATP at the MT plus end induces outward curvature in ?/?-tubulin, accompanied by a restructuring of the MCAK neck and N-terminus, as it returns to a closed state. Re-establishing a closed dimer state imparts a lateral separation of paired tubulin dimers, which may assist in depolymerization. Thus, full-length ADP-MCAK transitions from an open diffusion-competent configuration to a closed state upon plus-end mediated nucleotide exchange, which is primarily mediated by conformational changes in the N-terminal domains of the dimer. PMID:25066134

Burns, Kyle M.; Wagenbach, Mike; Wordeman, Linda; Schriemer, David C.

2015-01-01

252

Immucillin-H binding to purine nucleoside phosphorylase reduces dynamic solvent exchange.  

PubMed Central

The rate and extent of hydrogen/deuterium (H/D) exchange into purine nucleoside phosphorylase (PNP) was monitored by electrospray ionization mass spectrometry (ESI-MS) to probe protein conformational and dynamic changes induced by a substrate analogue, products, and a transition state analogue. The genetic deficiency of PNP in humans is associated with severe T-cell immunodeficiency, while B-cell immunity remains functional. Inhibitors of PNP have been proposed for treatment of T-cell leukemia, to suppress the graft-vs.-host response, or to counter type IV autoimmune diseases without destroying humoral immunity. Calf spleen PNP is a homotrimer of polypeptide chains with 284 amino residues, molecular weight 31,541. Immucillin-H inhibits PNP with a Kd of 23 pM when only one of the three catalytic sites is occupied. Deuterium exchange occurs at 167 slow-exchange sites in 2 h when no catalytic site ligands are present. The substrate analogue and product prevented H/D exchange at 10 of the sites. Immucillin-H protected 32 protons from exchange at full saturation. When one of the three subunits of the homotrimer is filled with immucillin-H, and 27 protons are protected from exchange in all three subunits. Deuterium incorporation in peptides from residues 132-152 decreased in all complexes of PNP. The rate and/or extent of deuterium incorporation in peptides from residues 29-49, 50-70, 81-98, and 112-124 decreased only in the complex with the transition state analogue. The peptide-specific H/D exchange demonstrates that (1) the enzyme is most compact in the complex with immucillin-H, and (2) filling a single catalytic site of the trimer reduces H/D exchange in the same peptides in adjacent subunits. The peptides most highly influenced by the inhibitor surround the catalytic site, providing evidence for reduced protein dynamic motion caused by the transition state analogue. PMID:11045613

Wang, F.; Miles, R. W.; Kicska, G.; Nieves, E.; Schramm, V. L.; Angeletti, R. H.

2000-01-01

253

Magnetic switching dynamics due to ultrafast exchange scattering: A model study  

NASA Astrophysics Data System (ADS)

We study the heat-induced magnetization dynamics in a toy model of a ferrimagnetic alloy, which includes localized spins antiferromagnetically coupled to an itinerant carrier system with a Stoner gap. We determine the one-particle spin-density matrix including exchange scattering between localized and itinerant bands as well as scattering with phonons. While a transient ferromagneticlike state can always be achieved by a sufficiently strong excitation, this transient ferromagneticlike state only leads to magnetization switching for model parameters that also yield a compensation point in the equilibrium M (T ) curve.

Baral, Alexander; Schneider, Hans Christian

2015-03-01

254

Studies on PVA based nanocomposite Proton Exchange Membrane for Direct methanol fuel cell (DMFC) applications  

NASA Astrophysics Data System (ADS)

Different concentrations of Poly (vinyl alcohol)/Montmorillonite (PVA/MMT) based proton exchange membranes (PEMs) have been prepared by solution casting method. The structural and electrical properties of these composite membranes have been characterized by using X-ray diffraction (XRD), Fourier transform infrared spectroscopic (FTIR) and AC impedance spectroscopic methods. The conductivity of the PEMs has been estimated for the different concentration of MMT. Water/Methanol uptake measurement were also analyzed for the prepared PEMs and presented. The proton conductivity studies were carried out at room temperature with 100% of humidity.

Bahavan Palani, P.; Kannan, R.; Rajashabala, S.; Rajendran, S.; Velraj, G.

2015-02-01

255

An anion-exchange chromatographic study on boron isotopic fractionation at 2 MPa at 293 K.  

PubMed

To study boron isotopic fractionation at high pressure, column chromatography operated in the breakthrough manner was performed at 2.0 MPa at 25.0 degrees C. The fractionation factor (S) between boron adsorbed onto strongly basic anion-exchange resin and boron in solution was obtained as 1.013, which was smaller than the values at 0.1 MPa (atmospheric pressure) found in literature. The pressure dependence of S was discussed based on the polymerization of boron in the solution and resin phases and on the occurrence of the pressure dependent isotope effect relating to the molar volume changes of boron species upon isotope substitution. PMID:16890943

Musashi, Masaaki; Matsuo, Motoyuki; Oi, Takao; Nomura, Masao

2006-10-27

256

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

257

Exchange of unsaturated fatty acids between adipose tissue and atherosclerotic plaque studied with artificial neural networks.  

PubMed

The linoleic C18:2 (n-6) and linolenic C18:3 (n-3) are recognized as essential components of the diet. Free radical peroxidation of essential fatty acids (EFAs) present in lipoproteins produces oxidized low-density lipoproteins which play a critical role in the development of atherosclerosis. The accumulation of EFAs in the vascular wall and correlations between their content in the adipose tissue and atherosclerotic plaque have been confirmed. The present study was undertaken to determine the usefulness of a neural network for studying the exchange between tissues of linoleic, alpha-linolenic, and arachidonic acids-three fatty acids with a well-understood metabolism. Atheromatous plaques, adipose tissue, and serum were obtained from 31 patients who underwent surgery due to atherosclerotic stenosis of the abdominal aorta, iliac or femoral arteries. Fatty acids were extracted and separated as methyl esters using gas chromatography. Statistical analysis was done with STATISTICA neural networks package. Several correlations reported previously were corroborated and factors modifying the content of individual EFAs in adipose tissue and atherosclerotic plaque were revealed. Artificial neural networks (ANNs) were used to determine factors modifying the content of linoleic, alpha-linolenic, and arachidonic acids in human atheromatous plaques. The mechanism of exchange of some fatty acids between the adipose tissue, atheromatous plaque, and plasma is discussed. The results provide evidence for an effective mechanism of tissue uptake and turnover of linoleic acid. Reduced plasma levels of this acid are compensated by release from adipose tissue and atheromatous plaque. While alpha-linolenic acid is continuously taken up by the plaque, adipose tissue absorbs this acid to a certain level only. The dynamics of exchange of arachidonic acid between adipose tissue and atheromatous plaque reflects a minor role for adipose tissue in determining plaque content of this acid, suggesting that "de novo" synthesis is the chief source of arachidonic acid in plaques. PMID:14643180

Stachowska, E; Gutowska, I; Do?egowska, B; Chlubek, D; Bober, J; Ra?, M; Gutowski, P; Szumilowicz, H; Turowski, R

2004-01-01

258

Cultural implications of scientific exchanges by USA visitors to mainland China: a case study  

E-print Network

the developmental and theoretical interest centered on three aspects of the exchanges from visitors' perspectives: (I) why individual visitors were likely to engage actively in scientific exchanges with the PRC; (2) what types of inhibitors they were likely... to encounter during the process of scientific exchanges with the PRC; (3) what actions the host community, the PRC government and visitors' sponsors could take to remove the inhibitors to scientific exchanges so as to achieve optimal results from them. A...

Lu, Wei

1989-01-01

259

TASSEP -Interested in an exchange study visit to North America? College, through the School of Chemistry, is currently a member the Trans-Atlantic  

E-print Network

TASSEP -Interested in an exchange study visit to North America? College, through the School of Chemistry, is currently a member the Trans-Atlantic Science Student Exchange Programme (TASSEP). This well-established consortium arranges exchange study periods between students attending member Universities in North America

O'Mahony, Donal E.

260

Symmetry analysis in neutron diffraction studies of magnetic structures 4. Theoretical group analysis of exchange Hamiltonian  

Microsoft Academic Search

By analyzing the exchange Hamiltonian, we develop the technique of determining the magnetic structures liable to occur in a crystal. The technique rests on Bertaut's idea that the exchange matrix eigenfunction corresponds to some magnetic structure. A technically simple and efficient method of diagonalizing the exchange matrix is worked out using the devices of space group representation theory. A method

Yu. A. Izyumov; V. E. Naish; S. B. Petrov

1979-01-01

261

Remote sensing methods in studying the characteristics of water exchange through the straits between inland seas and ocean  

NASA Astrophysics Data System (ADS)

Study of processes of water exchange through the straits between the inland seas and ocean is an important task of modern oceanography. Examples of such water exchange can be observed in the Baltic Sea, Mediterranean Sea, Red Sea and others. In the Aral Sea there is a water exchange through the narrow strait - the channel between the eastern and western part of the sea. It is suggested that is very important to use the possibilities of remote sensing methods (acoustic and satellites) to observe the features of water exchange through the straits between inland seas and ocean. As an example, the results of the study of peculiarities of propagation of Mediterranean waters through the Strait of Gibraltar in the Gulf of Cadiz are presented. The results showed that the propagation of Mediterranean waters (including meddies) can be traced by acoustic and seismoacoustic profiling of the water column and satellites altimetry.

Sklyarov, Vladimir; Berezutsky, Alexandr

2010-05-01

262

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

SciTech Connect

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 of mainly sulfate and dissolved organic carbon. High-performance liquid chromatography analysis indicated the presence of oxalate, contributing to 10 to 20% of the organic carbon. The identity of the remainder is unknown. The presence of oxalate as a complexant is consistent with results from earlier work. Complexation studies with Cu{sup 2+} and Ni{sup 2+} showed the presence of two ligands: oxalate and ligand X. Although ligand X could not be identified, it could be characterized by its concentration ([X]{sub T} {approximately} 10{sup {minus}5} to 10{sup {minus}6} M), a deprotonation constant (pK{sub H} {approximately} 7.4 at I = 0.1 M), and a complexation constant for the NiX complex (log K{sub NiX}{approximately} 7.0 at I = 0.1 M). In the absence of irradiation, no evidence for the formation of ligands was found.

Loon, L.R. van; Hummel, W.

1999-12-01

263

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

264

Exchange interaction in hexagonal MnRhP from first-principles studies  

SciTech Connect

Electronic structure and magnetic properties for MnRhP have been studied from a first-principles density functional calculation. The calculated lattice constants, a?=?6.228 Å and c?=?3.571?Å, are in good agreement with the experimental values of a?=?6.223 Å and c?=?3.585?Å. The calculated moment of Mn is 3.1 ?{sub B}/atom, resulting in a total moment of 3.0 ?{sub B}/atom due to small moments induced at Rh and P sites. The magnetic moment of Mn decreases with unit cell size. The exchange interactions are dominated by positive Mn-Mn exchange coupling (J{sub Mn?Mn}), implying a stable ferromagnetic ordering in Mn sublattice. In particular, J{sub Mn?Mn} shows a maximum value (1.5 mRy) at the the optimized unit cell size. The structural distortion or unit cell size change will affect J{sub Mn?Mn}, which is intimately related to the magneto-elastic and magneto-caloric effect.

Liu, X. B., E-mail: liuxubo@uta.edu; Zhang, Qiming; Ping Liu, J., E-mail: pliu@uta.edu [Department of Physics, University of Texas at Arlington, Arlington, Texas 76019 (United States); Yue, M. [College of Material Science and Engineering, Beijing University of Technology, 100022 Beijing (China); Altounian, Z. [Centre for the Physics of Materials and Department of Physics, McGill University, Montreal, Quebec H3A 2T8 (Canada)

2014-05-07

265

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

NASA Technical Reports Server (NTRS)

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 was studied using spaced parallel plates. An internally air-cooled heat exchanger 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 aircooled heat exchangers to control temperature and minimize thermal nitrogen oxide emissions. Test conditions were 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 1.3x10 to the 5th power to 2.0x10 to the 5th power Pa. Propane fuel was used for all testing. Combustion efficiencies greater than 99.5 percent were measured. Nitrogen oxide emissions ranged from 1.7 to 3.3 g NO2/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

266

The effect of solvent on matrix-assisted laser desorption ionization mass spectrometry  

E-print Network

the abundance of protonated analyte ions and decreases the amount of cation adducts found in the mass spectrum. Thus, water stabilizes the interaction between the matrix and analyte in solution. In addition, a study using hydrogen/deuterium exchange using MALDI...

Campo, Karen Kay

1996-01-01

267

Performance enhancement study of mobile air conditioning system using microchannel heat exchangers  

Microsoft Academic Search

In the present paper, two retrofitted compact and high efficient microchannel heat exchangers were proposed. The new microchannel heat exchangers have advantages in compactness (17.2% and 15.1% volume reduction for evaporator and condenser, respectively), weight (2.8% and 14.9% lighter for evaporator and condenser, respectively), heat transfer characteristics compared with the currently used heat exchangers in mobile air conditioning (MAC) industry.

Zhaogang Qi; Yu Zhao; Jiangping Chen

2010-01-01

268

Emission control through Cu-exchanged X-zeolite catalysts: Experimental studies and theoretical modeling  

SciTech Connect

Catalysts based on X-zeolite have been developed by exchanging its Na{sup +} ion with Copper ions and its effectiveness in reducing NO{sub x} in an actual SI engine exhaust has been tested. Unlike noble metals, the doped X-zeolite catalysts, studied here, exhibit significant NO{sub x} reduction for a wide {lambda} range and exhibit a slow rate of decrease with increase in {lambda} ratio. Back pressure developed across the catalyst bed was found to be well-affordable and power loss due to back pressure is only minimal. During 30 hours of testing of the catalyst, no significant deactivation was observed. Additionally a mathematical model has been developed to predict the performance of the catalyst and to validate that against experimental results. Results predicted by the mathematical model agree well with the experimental results and absolute average deviation of experimental conversion efficiency is found to be less than 5% of the predicted value.

Bhattacharyya, S.; Das, R.K.

2000-01-01

269

Study on passive momentum exchange landing gear using two-dimensional analysis  

NASA Astrophysics Data System (ADS)

This paper discusses a landing response control system based on the momentum exchange principle for planetary exploration spacecraft. In the past, landing gear systems with cantilever designs that incorporate honeycomb materials to dissipate shock energy through plastic deformation have been used, but once tested before launch, the system cannot be used in a real mission. The sky crane system used for the Mars Science Laboratory by NASA can achieve a safe and precise landing, but it is highly complex. This paper introduces a momentum exchange impact damper (MEID) that absorbs the controlled object's momentum with extra masses called damper masses. The MEID is reusable, which makes it easy to ensure the landing gear's reliability. In this system, only passive elements such as springs are needed. A single-axis (SA) model has already been used to verify the effectiveness of MEIDs through simulations and experiments measuring the rebound height of the spacecraft. However, the SA model cannot address the rotational motion and tipping of the spacecraft. This paper presents a two-landing-gear-system (TLGS) model in which multiple MEIDs are equipped for two-dimensional analysis. Unlike in the authors' previous studies, in this study each MEID is launched when the corresponding landing gear lands and the MEIDs do not contain active actuators. This mechanism can be used to realize advanced control specifications, and it is simply compared with previous mechanisms including actuators, in which all of the MEIDs are launched simultaneously. If each MEID works when the corresponding gear lands, the rebound height of each gear can be minimized, and tipping can be prevented, as demonstrated by the results of our simulations.

Watanabe, Tsubasa; Hara, Susumu; Otsuki, Masatsugu

2014-12-01

270

Kafirin adsorption on ion-exchange resins: isotherm and kinetic studies.  

PubMed

Kafirin is a natural, hydrophobic and celiac safe prolamin protein obtained from sorghum seeds. Today kafirin is found to be useful in designing delayed delivery systems and coatings of pharmaceuticals and nutraceuticals where its purity is important and this can be obtained by adsorptive chromatography. This study is the first scientific insight into the isotherm and kinetic studies of kafirin adsorption on anion- and cation-exchange resins for practical applications in preparative scale chromatography. Adsorption isotherms of kafirin were determined for five anion- and two cation-exchange resins in batch systems. Isotherm parameters such as maximum binding capacity and dissociation constant were determined from Langmuir isotherm, and adsorptive capacity and affinity constant from Freundlich isotherm. Langmuir isotherm was found to fit the adsorption equilibrium data well. Batch uptake kinetics for kafirin adsorption on these resins was also carried out and critical parameters including the diffusion coefficient, film mass transfer coefficient, and Biot number for film-pore diffusion model were calculated. Both the isotherm and the kinetic parameters were considered for selection of appropriate resin for kafirin purification. UNOsphere Q (78.26 mg/ml) and Toyopearl SP-650M (57.4 mg/ml) were found to offer better kafirin binding capacities and interaction strength with excellent uptake kinetics under moderate operating conditions. With these adsorbents, film diffusion resistance was found to be major governing factor for adsorption (Bi<10 and ?<1). Based on designer objective function, UNOsphere Q was found be best adsorbent for binding of kafirin. The data presented is valuable for designing large scale preparative adsorptive chromatographic kafirin purification systems. PMID:25022481

Kumar, Prashant; Lau, Pei Wen; Kale, Sandeep; Johnson, Stuart; Pareek, Vishnu; Utikar, Ranjeet; Lali, Arvind

2014-08-22

271

Element exchange between minerals at hydrothermal conditions: A case study with spinel  

NASA Astrophysics Data System (ADS)

It is generally believed that the presence of a fluid phase enhances the reactivity of minerals and promotes exchange reactions between minerals that are physically separated from each other. Two end-member mechanisms can be considered for the bulk equilibration of the mineral with the fluid: volume diffusion and dissolution-precipitation. A key parameter, which may control the overall kinetic behavior, is the solubility of the relevant elements within the fluid (e.g., [1]). We investigated the reaction mechanism of a model system to identify the role of the various parameters, in particular those controlling the solubility. Two polished spinel crystals (hercynite with xFe=0.6 and synthetic Mg-spinel) react in the presence of H2O at 750 °C and 0.2 GPa in a welded-shut Au-capsule for 1-24 hrs. The crystals are physically separated by a tube of noble metal dividing the capsule into two connected chambers. The surface of the reacted crystals is analyzed using optical methods and SEM and the near surface chemistry is studied via RBS. From the latter we are able to extract Fe-concentration depth profiles. First results show an increasing surface concentration of Fe in Mg-spinel with time. The depth profiles for experiments up to 8 hours reveal a decrease of Fe-concentration within the first 100 nm from the surface towards the center of the Mg-spinel. The Fe depth profiles can be simulated with a simplified diffusion model, assuming a fixed surface concentration and their shapes indicate that the inter-diffusion coefficient in spinel is concentration dependent. Our derived Fe-Mg diffusion coefficient [D(Fe-Mg) ? 1x10-19 m2/s for pure MgAl2O4) and its compositional dependence is consistent with an independent experimental study using thin film diffusion couples that were annealed at dry conditions at 1 atm [2]. The observed kinetic behavior of the experimental system was simulated using the model of [1]. The model geometry is identical to the present experimental setup and for the mineral fluid interaction a pure exchange of elements is considered without any mass transfer. From the simulations we obtain constraints for the effective transport rate of Fe through the fluid, which is basically controlled by the diffusion coefficient in the fluid and the solubility of Fe. Our calculations suggest that the concentration of dissolved Fe is up to two orders of magnitude higher than predicted by theoretical solubility calculations. The reaction mechanism map reveals that the reaction is controlled by diffusion in both the solid and the fluid. These results highlight the importance of the concentration of dissolved species for the exchange process. The solubility of the mineral phases is an important factor controlling the development of compositional profiles and may even control the reaction mechanism. This study demonstrates that the following common wisdoms are wrong in the general case: (I) The presence of fluid enhances the rate of the overall exchange reaction. (II) The presence of H2O enhances diffusion in the solid phase. [1] Dohmen & Chakraborty (2003), AmMin, 88, pp. 1251-1270; [2] Vogt (2009), Msc-Thesis, Ruhr-Universität Bochum, p.78

Jonas, L.; Muller, T.; Dohmen, R.

2013-12-01

272

Plasma exchange and chlorambucil in polyneuropathy associated with monoclonal IgM gammopathy. IgM-associated Polyneuropathy Study Group.  

PubMed Central

The study compared chlorambucil alone with chlorambucil in combination with plasma exchange in patients with polyneuropathy associated with monoclonal IgM. Forty four patients were prospectively randomly assigned, in a comparative open trial, to receive either 0.1 mg/kg/day chlorambucil orally, for 12 months or chlorambucil associated with 15 courses of plasma exchange, during the first four months of treatment. They were evaluated by a neuropathy disability score and nerve conduction studies. No difference was found between the two treatment groups. The average neuropathy disability score improved by 2.1 points from baseline (21.0 to 18.9) in the chlorambucil group and by 1.8 points (20.4 to 18.6) in the chlorambucil + plasma exchange group (P = 0.70). The mean motor nerve conduction velocity decreased from 20.0 to 18.2 m/s in the chlorambucil group and increased from 20.5 to 22.5 m/s in the chlorambucil + plasma exchange group (P = 0.51). A slight improvement of the sensory component of the neuropathy disability score (from 10.5 to 8.3) was noted in both groups (P = 0.01). At the end of the study and according to self evaluation, 15 patients--eight from the chlorambucil group and seven from the chlorambucil + plasma exchange group--reported clinical improvement, whereas 15--eight from the chlorambucil group and seven from the chlorambucil + plasma exchange group--reported clinical worsening. Neuropathy remained stable in the others. Thus plasma exchange seemed to confer no additional benefit in the treatment of polyneuropathy associated with monoclonal IgM. PMID:7673949

Oksenhendler, E; Chevret, S; Léger, J M; Louboutin, J P; Bussel, A; Brouet, J C

1995-01-01

273

REMOVAL OF BORON FROM BALÇOVA-IZMIR GEOTHERMAL WATER BY ION EXCHANGE PROCESS: BATCH AND COLUMN STUDIES  

Microsoft Academic Search

In this study, the efficiency of boron removal from Balçova geothermal water provided by the Izmir Geothermal Energy Company, Turkey, has been investigated using boron selective ion exchange resins Diaion CRB 02 and Dowex (XUS 43594.00) by batch and column methods. The results of the column studies have been evaluated in terms of type of resin and feed flow rate,

I. Yilmaz Ipek; N. Kabay; M. Yuksel; Ö. Kirmizisakal; M. Bryjak

2008-01-01

274

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

275

A computational study of an HCCI engine with direct injection during gas exchange  

SciTech Connect

We present a new probability density function (PDF)-based computational model to simulate a homogeneous charge compression ignition (HCCI) engine with direct injection (DI) during gas exchange. This stochastic reactor model (SRM) accounts for the engine breathing process in addition to the closed-volume HCCI engine operation. A weighted-particle Monte Carlo method is used to solve the resulting PDF transport equation. While simulating the gas exchange, it is necessary to add a large number of stochastic particles to the ensemble due to the intake air and EGR streams as well as fuel injection, resulting in increased computational expense. Therefore, in this work we apply a down-sampling technique to reduce the number of stochastic particles, while conserving the statistical properties of the ensemble. In this method some of the most important statistical moments (e.g., concentration of the main chemical species and enthalpy) are conserved exactly, while other moments are conserved in a statistical sense. Detailed analysis demonstrates that the statistical error associated with the down-sampling algorithm is more sensitive to the number of particles than to the number of conserved species for the given operating conditions. For a full-cycle simulation this down-sampling procedure was observed to reduce the computational time by a factor of 8 as compared to the simulation without this strategy, while still maintaining the error within an acceptable limit. Following the detailed numerical investigation, the model, intended for volatile fuels only, is applied to simulate a two-stroke, naturally aspirated HCCI engine fueled with isooctane. The in-cylinder pressure and CO emissions predicted by the model agree reasonably well with the measured profiles. In addition, the new model is applied to estimate the influence of engine operating parameters such as the relative air-fuel ratio and early direct injection timing on HCCI combustion and emissions. The qualitative trends observed in the parametric variation study match well with experimental data in literature. (author)

Su, Haiyun; Vikhansky, Alexander; Mosbach, Sebastian; Kraft, Markus [Department of Chemical Engineering, University of Cambridge, Cambridge CB2 3RA (United Kingdom); Bhave, Amit [Reaction Engineering Solutions Ltd., 61 Canterbury Street, Cambridge CB4 3QG (United Kingdom); Kim, Kyoung-Oh; Kobayashi, Tatsuo [Higashifuji Technical Center, Toyota Motor Corporation, Mishuku 1200, Susono, Shizuoka 480-1193 (Japan); Mauss, Fabian [Division of Combustion Physics, Lund Institute of Technology, Box 118, S-22100 Lund (Sweden)

2006-10-15

276

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

277

Monte Carlo study of the double and super-exchange model with lattice distortion  

Microsoft Academic Search

In this work a magneto-elastic phase transition was obtained in a linear chain due to the interplay between magnetism and lattice distortion in a double and super-exchange model. It is considered a linear chain consisting of localized classical spins interacting with itinerant electrons. Due to the double exchange interaction, localized spins tend to align ferromagnetically. This ferromagnetic tendency is expected

J. R. Suárez; E. Vallejo; O. Navarro; M. Avignon

2009-01-01

278

Density Functional Theory Study of Transformations of Nitrogen Oxides Catalyzed by Cu-Exchanged Zeolites  

E-print Network

-Exchanged Zeolites W. F. Schneider* and K. C. Hass Ford Research Laboratory, MD 3083/SRL, Dearborn, Michigan 48121 density-functional-theory-based model of NO decomposition in Cu-exchanged zeolites (Schneider, W. F.; et al. J. Phys. Chem. B 1997, 101, 4353) is extended to consider more generally the Cu-zeolite catalyzed

Adams, James B

279

Theoretical and Experimental Studies of Energy Exchange from Jackrabbit Ears and Cylindrically Shaped Appendages  

PubMed Central

Convection properties of jackrabbit ears were examined in a wind tunnel and in the field in an attempt to study the possible thermal role of the large ears. This work was part of a study on energy exchange of appendages. Cylindrical copper models of various shapes, aluminum castings of domestic and jackrabbit ears, and an amputated jackrabbit ear were studied in a wind tunnel (a) to define the range for convective heat loss for appendages of various shapes, and (b) to study the effect on convection of model shape and orientation to the wind. Shape, i.e. length and closure, proved important. Orientation to the wind produced no consistent or significant variation in the convection coefficient. The convection coefficients from the ear castings fell within the range generated from the cylindrical models. The convection coefficients for the amputated rabbit ear fell partially within the range. Net thermal radiation loss at midday from the jackrabbit ears was found to be small. Convection from the ears, however, could account for the loss of over 100% of the animal's metabolic heat at an air temperature of 30°C. If air temperature exceeds body temperature, the animal must either store heat or resort to the evaporation of water. ImagesFIGURE 1FIGURE 2 PMID:5134209

Wathen, Patricia; Mitchell, John W.; Porter, Warren P.

1971-01-01

280

High-Temperature Study of Octahedral Cation Exchange in Olivine by Neutron Powder Diffraction  

NASA Astrophysics Data System (ADS)

Time-of-flight, neutron powder diffraction to 1000^circC provides precise octahedral site occupancies and intersite distribution coefficients for MnMgSiO_4 and MnFeSiO_4 olivines. Intersite exchange occurs in minutes down to 500^circC. Equilibrium distribution coefficients show that manganese ordering into the larger octahedral site decreases with increasing temperature. Exchange energies are 15.7 and 10.1 kilojoules per mole for magnesium-manganese and iron-manganese, respectively. Distribution coefficients deduced for FeMgSiO_4 olivine suggest an exchange energy of 4.8 kilojoules per mole. Intersite exchange energies are consistent with diffusion coefficients in the order iron > magnesium > manganese. Geothermometry based on magnesium-manganese and iron-manganese exchange may be possible only for samples equilibrated below 500^circC.

Henderson, C. M. B.; Knight, K. S.; Redfern, S. A. T.; Wood, B. J.

1996-03-01

281

Heat Exchanger/Humidifier Trade Study and Conceptual Design for the Constellation Space Suit Portable Life Support System Ventilation Subsystem  

NASA Technical Reports Server (NTRS)

As development of the Constellation Space Suit Element progresses, designing the most effective and efficient life support systems is critical. The baseline schematic analysis for the Portable Life Support System (PLSS) indicates that the ventilation loop will need some method of heat exchange and humidification prior to entering the helmet. A trade study was initiated to identify the challenges associated with conditioning the spacesuit breathing gas stream for temperature and water vapor control, to survey technological literature and resources on heat exchanger and humidifiers to provide solutions to the problems of conditioning the spacesuit breathing gas stream, and to propose potential candidate technologies to perform the heat exchanger and humidifier functions. This paper summarizes the results of this trade study and also describes the conceptual designs that NASA developed to address these issues.

Paul, Heather L.; Sompayrac, Robert; Conger, Bruce; Chamberlain, Mateo

2009-01-01

282

Heat Exchanger/Humidifier Trade Study and Conceptual Design for the Constellation Space Suit Portable Life Support System Ventilation Subsystem  

NASA Technical Reports Server (NTRS)

As development of the Constellation Space Suit Element progresses, designing the most effective and efficient life support systems is critical. The baseline schematic analysis for the Portable Life Support System (PLSS) indicates that the ventilation loop will need some method of heat exchange and humidification prior to entering the helmet. A trade study was initiated to identify the challenges associated with conditioning the spacesuit breathing gas stream for temperature and water vapor control, to survey technological literature and resources on heat exchanger and humidifiers to provide solutions to the problems of conditioning the spacesuit breathing gas stream, and to propose potential candidate technologies to perform the heat exchanger and humidifier functions. This paper summarizes the results of this trade study and also describes the conceptual designs that NASA developed to address these issues.

Paul, Heather L.; Conger, Bruce; Sompyrac, Robert; Chamberlain, Mateo

2008-01-01

283

High-resolution Studies of Charge Exchange in Supernova Remnants with Magellan, XMM-Newton, and Micro-X  

NASA Astrophysics Data System (ADS)

Charge exchange, the semi-resonant transfer of an electron from a neutral atom to an excited state in an energetic ion, can occur in plasmas where energetic ions are incident on a cold, at least partially neutral gas. Supernova remnants, especially in the immediate shock region, provide conditions conducive to charge exchange. The emission from post charge-exchange ions as the captured electron cascades down to the ground state, can shed light on the physical conditions of the shock and the immediate post-shock material, providing an important tool to understanding supernova explosions and their aftermath.I present a study of charge exchange in the galactic supernova remnant G296.1-0.5 in two bands: the optical and the X-ray. The optical study, performed using both imaging and spectroscopy from the IMACS instrument on the Magellan Baade Telescope at Las Companas Observatory, seeks to identify `Balmer-dominated shocks' in the remnant, which occur when charge exchange occurs between hot, post-shock protons and colder neutral hydrogen in the environment. The X-ray study probes line ratios in dispersed spectral data obtained with XMM-Newton RGS from an X-ray lobe in the NW of the remnant to hunt for signatures of charge exchange. The dispersed data are degraded by the extended nature of the source, blending many of the lines.We are working towards the future of spectroscopic studies in the X-ray for such extended sources with Micro-X: a sounding rocket-borne, high energy resolution X-ray telescope, utilizing an array of microcalorimeters to achieve high energy resolution for extended sources. I describe the design and commissioning of the payload and the steps toward launch, which is anticipated in the summer of 2015.

Heine, Sarah N.; Figueroa-Feliciano, Enectali; Castro, Daniel

2015-01-01

284

Enumeration of non-labile oxygen atoms in dissolved organic matter by use of ¹?O/ ¹?O exchange and Fourier transform ion-cyclotron resonance mass spectrometry.  

PubMed

We report a simple approach for enumeration of non-labile oxygen atoms in individual molecules of dissolved organic matter (DOM), using acid-catalyzed (16)O/(18)O exchange and ultrahigh-resolution Fourier-transform ion-cyclotron-resonance mass spectrometry (FTICR-MS). We found that by dissolving DOM in H2 (18)O at 95 °C for 20 days it is possible to replace all oxygen atoms of DOM molecules (excluding oxygen from ether groups) with (18)O. The number of exchanges in each molecule can be determined using high-resolution FTICR. Using the proposed method we identified the number of non-labile oxygen atoms in 231 molecules composing DOM. Also, using a previously developed hydrogen-deuterium (H/D)-exchange approach we identified the number of labile hydrogen atoms in 450 individual molecular formulas. In addition, we observed that several backbone hydrogen atoms can be exchanged for deuterium under acidic conditions. The method can be used for structural and chemical characterization of individual DOM molecules, comparing different DOM samples, and investigation of biological pathways of DOM in the environment. PMID:25216963

Kostyukevich, Yury; Kononikhin, Alexey; Zherebker, Alexander; Popov, Igor; Perminova, Irina; Nikolaev, Eugene

2014-10-01

285

Valence-bond study of the /H2, D2/ exchange reaction mechanism.  

NASA Technical Reports Server (NTRS)

The exchange reaction of H2 with D2 to form 2 HD is important in that it is fundamentally the simplest four-body exchange reaction and should therefore represent a model system on which various theories of reactions dynamics might be tested. A number of theoretical and experimental investigations carried out on this system are reviewed. It is concluded that a Y yields T yields Y mechanism for the (H2, D2) exchange is not a low energy pathway that would make theory compatible with the shock-tube experiments of Bauer and Ossa (1966) and of Burcat and Lifshits (1967).

Freihaut, B.; Raff, L. M.

1973-01-01

286

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

287

Speciation study of aluminium in beverages by Competitive Ligand Exchange-Adsorptive Stripping Voltammetry.  

PubMed

Competitive Ligand Exchange-Adsorptive Stripping Voltammetry (CLE-AdSV) was used for determining the speciation of aluminium in commonly consumed beverages (water, tea, infusion, coffee, orange juice, tomato juice, beer and red wine). Aluminium determination involves the adsorption of Al-complexes with the ligand cupferron onto a hanging mercury drop electrode. All samples were studied at pH 6.5 with an accumulation step at -0.60 V (all potential values in the paper are given versus the Ag/AgCl, [KCl]=3 M reference electrode) during 60 s, and a final cupferron concentration of 4 × 10(-4)M. These conditions were used to establish (i) the concentration of electro-labile aluminium, (ii) the range of ligand concentrations and (iii) the conditional stability constants of beverage samples using titration procedures. The results based on Ruzic plots were compared to computer simulation with Visual MINTEQ. This comparison suggests that labile monomeric Al-forms and soluble organic complexes of low molecular weight can be quantified by the CLE-AdSV procedure. Overall the relative uncertainties on the determination of the electro-active Al fraction and the complexing parameters, i.e., concentration and conditional stability constant of natural ligands in the samples, are less than 15%. Thanks to these results, information on Al bioavailability in beverages was collected and discussed. This study also illustrates the value of computer simulations when complex, time-consuming voltammetric techniques are applied. PMID:24720958

Magnier, A; Fekete, V; Van Loco, J; Bolle, F; Elskens, M

2014-05-01

288

Business School Exchanges InternationalExchangeProgram  

E-print Network

units on exchange so should keep a minimum of one semester's worth of elective study (24 credit points units per the exchange period, which is insufficient for a full semester study load of 24 credit points. Most partners cannot guarantee courses so you will not be assured of obtaining credit towards your

Viglas, Anastasios

289

Material Studies Related to the Use of NaK Heat Exchangers Coupled to Stirling Heater Heads  

NASA Technical Reports Server (NTRS)

NASA has been supporting design studies and technology development that could provide power to an outpost on the Moon, Mars, or an asteroid. Technology development efforts have included fabrication and evaluation of components used in a Stirling engine power conversion system. Destructive material evaluation was performed on a NaK shell heat exchanger that was developed by the NASA Glenn Research Center (GRC) and integrated with a commercial 1 kWe Stirling convertor from Sunpower Incorporated. The NaK Stirling test demonstrated Stirling convertor electrical power generation using a pumped liquid metal heat source under thermal conditions that represent the heat exchanger liquid metal loop in a Fission Power Systems (FPS) reactor. The convertors were operated for a total test time of 66 hr at a maximum temperature of 823 K. After the test was completed and NaK removed, the heat exchanger assembly was sectioned to evaluate any material interactions with the flowing liquid metal. Several dissimilar-metal braze joint options, crucial for the heat exchanger transfer path, were also investigated. A comprehensive investigation was completed and lessons learned for future heat exchanger development efforts are discussed.

Locci, Ivan E.; Bowman, Cheryl L.; Geng, Steven M.; Robbie, Malcolm G.

2011-01-01

290

Prediction of the outlet temperatures in triple concentric—tube heat exchangers in laminar flow regime: case study  

NASA Astrophysics Data System (ADS)

In this study there has been developed a numerical model of predicting outlet temperatures in a triple concentric-tube heat exchanger. For the model elaboration there have been used the equations of heat transfer and of fluid-dynamics, as well as a numerical algorithm to solve systems of non-linear equations. Based on experimental data, the obtained model has been practically tested to cool a petroleum product with water in a triple concentric-tube heat exchanger. The results obtained using the numerical simulation have been compared with the experimental data and data from literature in order to validate the proposed numerical model.

P?tr??cioiu, Cristian; R?dulescu, Sînziana

2015-01-01

291

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

2013-02-01

292

Pharmacodynamic Study of Polymerized Porcine Hemoglobin (pPolyHb) in a Rat Model of Exchange Transfusion  

PubMed Central

The objective of the present study is to evaluate the pharmacodynamic properties of polymerized porcine hemoglobin (pPolyHb) in an exchange transfusion model. Each of two groups of rats received a volume of pPolyHb or hetastarch that equalled 120–140% of estimated total blood volume (70 ml/kg) exchange transfusion. The results showed pPolyHb retained hemodynamic stability and exhibited superior volume expansion capability. Furthermore, pPolyHb effectively reverse anaerobic metabolism caused by a large amount of volume exchange. In comparison with hetastarch, pPolyHb increased blood oxygen content and tissue oxygenation. All these properties contribute to a higher effectiveness in sustaining the lives of rats in pPolyHb group. PMID:21381891

Zhu, Hongli; Dang, Xiaodong; Yan, Kunping; Dai, Penggao; Luo, Chao; Ma, Jun; Li, Yan; Chang, Thomas Ming Swi; Chen, Chao

2012-01-01

293

Experimental studies on pressure drop characteristics of cryogenic cross-counter flow coiled finned tube heat exchangers  

NASA Astrophysics Data System (ADS)

Cross-counter flow coiled finned tube heat exchangers used in medium capacity helium liquefiers/refrigerators were developed in our lab. These heat exchangers were developed using integrated low finned tubes. Experimental studies have been performed to know the pressure drop characteristics of tube side and shell side flow of these heat exchangers. All experiments were performed at room temperature in the Reynolds number range of 3000-30,000 for tube side and 25-155 for shell side. The results of present experiments indicate that available correlations for tube side can not be used for prediction of tube side pressure drop data due to complex surface formation at inner side of tube during formation of fins over the outer surface. Results also indicate that surface roughness effect becomes more pronounced as the value of di/ D m increases. New correlations based on present experimental data are proposed for predicting the friction factors for tube side and shell side.

Gupta, Prabhat Kumar; Kush, P. K.; Tiwari, Ashesh

2010-04-01

294

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...

295

Study of the Relationship between Leader-Member Exchange (LMX) and Individual Objective Performance within a University Learning Community  

ERIC Educational Resources Information Center

The study examined the relationship between leader-member exchange (LMX) and individual objective performance. While the LMX literature suggests a positive correlation between LMX and performance, a closer look at the research examined showed that the performance measurements were based on subjective measurements rather than objective…

Aikens, Shontarius D.

2012-01-01

296

Thermal hydraulic study on a high-temperature gas–gas heat exchanger with helically coiled tube bundles  

Microsoft Academic Search

An experimental study was carried out to investigate flow-induced vibration, heat transfer and pressure drop of helically coiled tubes of an intermediate heat exchanger (IHX) for the HTTR, using a full-size partial model and air as the fluid. The test model has 54 helically coiled tubes separated into three layer bundles, surrounding the center pipe. The vibration of the tube

Yoshiyuki Inagaki; Hiroshi Koiso; Hideki Takumi; Ikuo Ioka; Yoshiaki Miyamoto

1998-01-01

297

Study of suspending agents for gadolinium(III)-exchanged hectorite. An oral magnetic resonance imaging contrast agent  

Microsoft Academic Search

Clays modified with paramagnetic ions have been shown to be effective magnetic resonance imaging contrast agents. The efficacy in part relies on the suspension of the small clay particles in aqueous solution. In this study a series of macromolecules were eveluated as suspending agents for Gd(III) ion exchanged hectorite clay in water. The room temperature relaxivities for the Gd-hectorite clays

Jimin Shi

1996-01-01

298

Numerical Study on Characteristics of a Pre-Cooling He II Heat Exchanger  

NASA Astrophysics Data System (ADS)

A numerical analysis has been performed in order to investigate the heat transfer and pressure drop characteristics of a pre-cooling He II heat exchanger. The heat conduction in the pre-cooled helium path in the flow direction was taken into account. Temperature distribution and pressure drop in the heat exchanger have been calculated for various conditions. It was found that a long cooling path is required to pre-cool the helium below the ?-temperature, because of a large value of the He II heat conductivity function. This heat exchanger has an upper limit of mass flow rate. The efficiency of the heat exchanger decreases as the mass flow rate decreases under a small mass flow rate condition.

Ueno, Y.; Okamura, T.; Sato, A.

2004-06-01

299

A feasibility study of internal evaporative cooling for proton exchange membrane fuel cells  

E-print Network

An investigation was conducted to determine the feasibility of using the technique of ultrasonic nebulization of water into the anode gas stream for evaporative cooling of a Proton Exchange Membrane (PEM) fuel cell. The basic concept of this form...

Snyder, Loren E

2006-04-12

300

PROPOSITION DE SUJET DE THESE Fundamental study of oxygen exchange and diffusion in cathode  

E-print Network

materials for fuel cells G. Dezanneau, in collaboration with G. Geneste (CEA) Fuel cells are electrochemical factor for the cell efficiency. This efficiency is basically driven by the oxygen exchange and diffusion

Bezerianos, Anastasia

301

Magnetic nanoparticles : synthesis, characterization, applications and systematic study of exchanging biasing  

E-print Network

We systematically investigated the magnetic properties of colloidal cobalt nanoparticles after three extents of oxidation: The native sample has a thin (1.0 nm) CoO shell and exhibits no exchange biasing. The purposefully ...

Tracy, Joseph B. (Joseph Benjamin)

2005-01-01

302

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

303

Preliminary study of As-for-Sb exchange for device applications  

Microsoft Academic Search

The role of the growth conditions in the As-for-Sb exchange reaction is discussed in this paper. Superlattices formed by As exposure of Sb-stabilized GaSb surfaces were grown to compare the resulting anion exchange under different conditions. Statistical experimental design was used to systematically evaluate the effect of different growth conditions. The experiments were performed on GaSb [001] epi-ready substrates in

Tomas Sarmiento; Gary S. May

2003-01-01

304

Application of AVHRR vegetation index to study atmosphere-biosphere exchange of CO2  

NASA Technical Reports Server (NTRS)

The Advanced Very High Resolution Radiometer (AVHRR) satellite-borne sensor is presently used, together with field data, to determine the geographic distributions of the seasonal exchange of CO2 between the earth's atmosphere and the terrestrial biota. The exchange functions thus obtained are validated in virtue of the ability to reproduce the observed annual cycle of atmospheric CO2 in a three-dimensional tracer transport model. The AVHRR is carried by the TIROS-N series of polar-orbiting satellites.

Fung, I. Y.; Tucker, C. J.; Prentice, K. C.

1985-01-01

305

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

NASA Astrophysics Data System (ADS)

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.

Dragani?, I. N.; Seely, D. G.; McCammon, D.; Havener, C. C.

2011-06-01

306

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. PMID:21196287

Ferrazzano, Peter; Shi, Yejie; Manhas, Namratta; Wang, Yanping; Hutchinson, Beth; Chen, Xinzhi; Chanana, Vishal; Gerdts, Josiah; Meyerand, Mary Elizabeth; Sun, Dandan

2010-01-01

307

A comparison study of ionic polymer-metal composites (IPMCs) fabricated with Nafion and other ion exchange membranes  

NASA Astrophysics Data System (ADS)

Ionic polymer-metal composites (IPMCs) have been and still are one of the best candidates with great potential to be used as actuators and sensors particularly in bioengineering where the environmental conditions are in an aqueous medium. Each component of an IPMC is important. However, the ion exchange membrane should be more emphasized because it is where ions migrate when electrical stimulation is applied and eventually it produces deformation of the IPMC. So far, the most commonly used ion exchange membrane is Nafion and many studies have been conducted with it for IPMC applications. There are a number of other commercially available ion exchange membranes now, but only a few studies have been done on those membranes to be used in IPMC applications. In this study, four commercially available membranes, (1) Nafion N115 (DuPont), (2) CMI7000S (Membranes International Inc.), (3) F-14100 (fumatech), (4) GEFC-700 (Golden Energy Fuel Cell) were selected and fabricated in IPMCs and their potentials as actuators were examined by conducting various characterizations such as water uptake, ion exchange capacity, SEM, DSC, blocking force and bending displacement.

Park, Jiyeon; Palmre, Viljar; Kim, Kwang; Shin, Dongsuk; Kim, Daniel H.; Yim, Woosoon; Bae, Chulsung

2013-04-01

308

A droplet microchip with substance exchange capability for the developmental study of C. elegans.  

PubMed

The nematode Caenorhabditis elegans (C. elegans) has been widely used as a multicellular organism in developmental research due to its simplicity, short lifecycle, and its relevance to human genetics and biology. Droplet microfluidics is an attractive platform for the study of C. elegans in integrated mode with flexibility at the single animal resolution. However, it is still challenging to conduct the developmental study of worms within droplets initiating at the L1 larval stage, due to the small size, active movement, and the difficulty in achieving effective substance exchange within the droplets. Here, we present a multifunctional droplet microchip to address these issues and demonstrate the usefulness of this device for investigating post-embryonic development in individual C. elegans initiating at the larval L1 stage. The key components of this device consist of multiple functional units that enable parallel worm loading, droplet formation/trapping, and worm encapsulation in parallel. In particular, it exhibits superior functions in encapsulating and trapping individual larval L1 worms into droplets in a controlled way. Continuous food addition and expulsion of waste by mixing the static worm-in-droplet with moving medium plugs allows for the long-term culture of worms under a variety of conditions. We used this device to investigate the development processes of C. elegans in transgenic strains with deletion and overexpression of the hypoxia-inducible factor (HIF-1), a highly conserved transcript factor in regulating an organism's response to hypoxia. This microdevice may be a useful tool for the high throughput analysis of individual worms starting at the larval stage, and facilitates the study of developmental worms in response to multiple drugs or environmental toxins. PMID:25715864

Wen, Hui; Yu, Yue; Zhu, Guoli; Jiang, Lei; Qin, Jianhua

2015-03-31

309

Structure and properties of metal-exchanged zeolites studied using gradient-corrected and hybrid functionals. I. Structure and energetics  

NASA Astrophysics Data System (ADS)

The structural and energetic properties of purely siliceous, proton-, and Cu- and Co-exchanged chabazite have been studied using periodic density-functional (DFT) calculations with both conventional gradient-corrected exchange-correlation functionals and hybrid functionals mixing exact (i.e., Hartree-Fock) and DFT exchange. Spin-polarized and fixed-moment calculations have been performed to determine the equilibrium and excited spin-configurations of the metal-exchanged chabazites. For the purely siliceous chabazite, hybrid functionals predict a slightly more accurate cell volume and lattice geometry. For isolated Al/Si substitution sites, gradient-corrected functionals predict that the lattice distortion induced by the substitution preserves the local tetrahedral symmetry, whereas hybrid functionals lead to a distorted Al coordination with two short and two long Al-O bonds. Hybrid functionals yield a stronger cation-framework binding that conventional functionals in metal-exchanged zeolites, they favor shorter cation-oxygen bonds and eventually also a higher coordination of the cation. Both types of functionals predict the same spin in the ground-state. The structural optimization of the excited spin-states shows that the formation of a high-spin configuration leads to a strong lattice relaxation and a weaker cation-framework bonding. For both Cu- and Co-exchanged chabazite, the prediction of a preferred location of the cation in a six-membered ring of the zeolite agrees with experiment, but the energy differences between possible cation locations and the lattice distortion induced by the Al/Si substitution and the bonding of the cation depends quite significantly on the choice of the functional. All functionals predict similar energy differences for excited spin states. Spin-excitations are shown to be accompanied by significant changes in the cation coordination, which are more pronounced with hybrid functionals. The consequences of electronic spectra and chemical reactivity are analyzed in the following papers.

Göltl, Florian; Hafner, Jürgen

2012-02-01

310

High magnetic exchange coupling constants: a density functional theory based study of substituted Schlenk diradicals.  

PubMed

The Schlenk diradical has been known since 1915. After a detailed experimental work by Rajca, its magnetic nature has remained more or less unexplored. We have investigated by quantum chemical calculations the nature of magnetic coupling in 11 substituted Schlenk diradicals. Substitution has been considered at the fifth carbon atom of the meta-phenylene moiety. The UB3LYP method has been used to study 12 diradicals including the original one. The 6-311G(d,p) basis set has been employed for optimization of molecular geometry in both singlet and triplet states for each species. The singlet optimization has led to the optimization of the broken-symmetry structure for 10 species including the unsubstituted one. This development makes it possible to carry out further broken symmetry calculations in two ways. The triplet calculation has been done using 6-311++G(d,p) basis set and the optimized triplet geometry in both procedures. The broken symmetry calculations have used the optimized geometries of either the triplet states or the broken symmetry solutions. The first method leads to the prediction of electron paramagnetic resonance (EPR) compatible magnetic exchange coupling constant (J) in the range 517-617 cm(-1). A direct optimization of the broken symmetry geometry gives rise to a lower estimate of J, in the range of 411-525 cm(-1) and compatible with macroscopic Curie studies. The calculated J for the unsubstituted Schlenk diradical is 512 cm(-1) that can be compared with 455 cm(-1) estimated by Rajca. In both cases, introduction of groups with +M and +I effects (Ingold's notation) decreases the J value from that for the unsubstituted Schlenk diradical while -I and -M groups at the same position increases J. These trends have been explained in terms of Hammett constants, atomic spin densities, and dihedral angles. PMID:22889383

Latif, Iqbal A; Hansda, Shekhar; Datta, Sambhu N

2012-08-23

311

Factors Affecting Outcome in Acute Hypertriglyceridemic Pancreatitis Treated with Plasma Exchange: An Observational Cohort Study  

PubMed Central

Objectives The optimal therapy for hypertriglyceridemic acute pancreatitis, especially the role of plasma exchange (PE), is not entirely clear. The aim of our large, single-center, observational, cohort study was to analyze the factors affecting outcome in hypertriglyceridemic pancreatitis treated with PE. Methods We included 111 episodes of hypertriglyceridemic pancreatitis treated with PE, which occurred in 103 different patients. The Acute Physiology and Chronic Health Evaluation (APACHE) II score, triglycerides, delay to first PE, and PE treatment details were retrospectively obtained from the patients’ records. The main outcome measures were length of hospitalization and in-hospital mortality. Results The patients were 47±9 years old and the median APACHE II score at first PE was 4 (inter-quartile range (IQR) 2–7). There was a seasonal variation in the incidence of hypertriglyceridemic pancreatitis, and the recurrence rate was 1.6% per year. Triglycerides at presentation did not correlate with APACHE II or influence the outcome. The mean reduction in triglycerides during PE was 59% (from 44±31 to 18±15 mmol/l), which was twice the reduction observed during conservative treatment (27% daily). The median hospital stay was 16 days (IQR 10–24) and in-hospital mortality was 5%. The median delay to first PE was 35 hours (IQR 24–52), and there was no difference in mortality in the early and late PE groups (7% vs. 6%, p?=?0.79). The group with citrate anticoagulation during PE had a significantly lower mortality than the group with heparin anticoagulation (1% vs. 11%, p?=?0.04), and citrate was an independent predictor also in the multivariate model (p?=?0.049). Conclusions PE effectively reduced serum triglycerides faster than could be expected with conservative treatment. The delay in PE therapy did not influence survival. We found that citrate anticoagulation during PE was associated with reduced mortality, which should be confirmed in a randomized study. PMID:25047332

Gubensek, Jakob; Buturovic-Ponikvar, Jadranka; Romozi, Karmen; Ponikvar, Rafael

2014-01-01

312

Thermal Rates of Hydrogen Exchange of Methane with Zeolite: A Direct ab Initio Dynamics Study on the Importance of Quantum Tunneling Effects  

E-print Network

Thermal Rates of Hydrogen Exchange of Methane with Zeolite: A Direct ab Initio Dynamics Study ab initio dynamics study on the kinetics of the hydrogen exchange of methane with a zeolite model in cracking, isomerization, and alkylation of hydro- carbons. It has been established that such chemical

Truong, Thanh N.

313

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

314

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

315

A comparative study on the air-side performance of wavy fin-and-tube heat exchanger with punched delta winglets in staggered and in-line arrangements  

Microsoft Academic Search

The air-side heat transfer and fluid flow characteristics of wavy fin-and-tube heat exchanger with delta winglets are investigated numerically. The three-dimensional simulations are performed with renormalization-group (RNG) k?? model to lay the foundation for the design of the high-performance heat exchanger. The wavy fin-and-tube heat exchangers which have three-row round tubes in staggered or in-line arrangements are studied. The numerical

Liting Tian; Yaling He; Yubing Tao; Wenquan Tao

2009-01-01

316

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

317

Na+-H+ exchange at the apical membrane of Necturus gallbladder. Extracellular and intracellular pH studies.  

PubMed

The mechanism of luminal solution acidification was studied in Necturus gallbladder by measurement of mucosal solution and intracellular pH with glass electrodes. When the gallbladder was bathed by a Na-Ringer's solution it acidified the luminal side by a Na+-dependent, amiloride-inhibitable process. In the presence of ouabain, acidification was reduced but could be stimulated to a rate greater than that under control conditions by the imposition of an inwardly directed Na+ gradient. These results suggest that luminal acidification results from Na+-H+ exchange at the apical membrane and not by diffusion of metabolic CO2. Li+ can substitute for Na+ but K+, Rb+, Cs+, and tetramethylammonium (TMA+) cannot. The maximal rate of exchange was about five times greater for Na+ than for Li+. Intracellular pH (pHi) was measured with recessed-tip glass microelectrodes; with the tissue bathed in Na-Ringer's solution (pH 7.75), pHi was 7.51 +/- 0.04. After inhibition of Na+-H+ exchange by mucosal perfusion with amiloride (1 mM) or by complete Na+ replacement with TMA+, phi fell reversibly by 0.15 and 0.22 pH units, respectively. These results support the conclusion that Na+-H+ exchange at the apical membrane is the mechanism of luminal acidification and is involved in the maintenance of steady state pHi. PMID:7119733

Weinman, S A; Reuss, L

1982-08-01

318

STUDY OF INDUSTRIAL ION EXCHANGE SEPARATION OF RARE EARTH ELEMENTS BY EDTA COPPER METHOD. VII. MODELS OF INDUSTRIAL ION EXCHANGE TOWERS  

Microsoft Academic Search

Two new models of ion exchange towers were constructed: one hopper type, ; the other cylinder type\\/su Results of tests on the scale models indicate they can ; be scaled-up for industrial processes. (P.C.H.);

Nishigori

1961-01-01

319

Microcalorimetric study of adsorption and disassembling of virus-like particles on anion exchange chromatography media.  

PubMed

Chromatographic purification of virus-like particles (VLPs) is important to the development of modern vaccines. However, disassembly of the VLPs on the solid-liquid interface during chromatography process could be a serious problem. In this study, isothermal titration calorimetric (ITC) measurements, together with chromatography experiments, were performed on the adsorption and disassembling of multi-subunits hepatitis B virus surface antigen virus-like particles (HB-VLPs). Two gigaporous ion-exchange chromatography (IEC) media, DEAE-AP-280nm and DEAE-POROS, were used. The application of gigaporous media with high ligand density led to significantly increased irreversible disassembling of HB-VLPs and consequently low antigen activity recovery during IEC process. To elucidate the thermodynamic mechanism of the effect of ligand density on the adsorption and conformational change of VLPs, a thermodynamic model was proposed. With this model, one can obtain the intrinsic molar enthalpy changes related to the binding of VLPs and the accompanying conformational change on the liquid-solid interface during its adsorption. This model assumes that, when intact HB-VLPs interact with the IEC media, the total adsorbed proteins contain two states, the intact formation and the disassembled formation; accordingly, the apparent adsorption enthalpy, ?appH, which can be directly measured from ITC experiments, presents the sum of three terms: (1) the intrinsic molar enthalpy change associated to the binding of intact HB-VLPs (?bindHintact), (2) the intrinsic molar enthalpy change associated to the binding of HB-VLPs disassembled formation (?bindHdis), and (3) the enthalpy change accompanying the disassembling of HB-VLPs (?confHdis). The intrinsic binding of intact HB-VLPs and the disassembled HB-VLPs to both kinds of gigaporous media (each of which has three different ligand densities), were all observed to be entropically driven as indicated by positive values of ?bindHintact and ?bindHdis; while the nagative ?confHdis values suggested a spontenous enthalpy-driven process for the forming of HB-VLPs disassembled formation at all conditions studied. As ligand density increases, ?confHdis became more negative, which was in agreement with the findings from chromatography experiments, that higher ligand density leads to more serious disassembling of HB-VLPs. Results from thermodynamic studies provided us insight understanding on the mechanism of adsorption and conformational change of VLPs, as well as the effect of ligand densities on the structural stability of VLPs during IEC process. PMID:25744549

Yu, Mengran; Zhang, Songping; Zhang, Yan; Yang, Yanli; Ma, Guanghui; Su, Zhiguo

2015-04-01

320

Experimental study of the Fe-Mg exchange between garnet and biotite: Constraints on the mixing behavior and analysis of the cation-exchange mechanisms  

Microsoft Academic Search

New experimental data are presented for the Fe-Mg exchange between garnet and biotite in the temperature range 600-800 8C at 0.2 GPa. The Fe-Mg-Al mixing properties of biotite were evaluated and the garnet-biotite geothermometer was recalibrated. SEM ob- servations and comparative laser granulometry show that solution-precipitation largely controls the cation exchange mechanism, involving about 50% of the mineral volume. Mass

C. K. GESSMANN; B. SPIERING; M. RAITH

1997-01-01

321

"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

322

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

323

Monte Carlo study of a two-compartment exchange model of diffusion†  

PubMed Central

Multisite exchange models have been applied frequently to quantify measurements of transverse relaxation and diffusion in living tissues. Although the simplicity of such models is attractive, the precise relationship of the model parameters to tissue properties may be difficult to ascertain. Here, we investigate numerically a two-compartment exchange (Kärger) model as applied to diffusion in a system of randomly packed identical parallel cylinders with permeable walls, representing cells with permeable membranes, that may serve particularly as a model for axons in the white matter of the brain. By performing Monte Carlo simulations of restricted diffusion, we show that the Kärger model may provide a reasonable coarse-grained description of the diffusion-weighted signal in the long time limit, as long as the cell membranes are sufficiently impermeable, i.e. whenever the residence time in a cell is much longer than the time it takes to diffuse across it. For larger permeabilities, the exchange time obtained from fitting to the Kärger model overestimates the actual exchange time, leading to an underestimated value of cell membrane permeability. PMID:20882537

Fieremans, Els; Novikov, Dmitry S.; Jensen, Jens H.; Helpern, Joseph A.

2010-01-01

324

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

325

77 FR 48491 - Regulatory New Drug Review: Solutions for Study Data Exchange Standards; Notice of Meeting...  

Federal Register 2010, 2011, 2012, 2013, 2014

...HUMAN SERVICES Food and Drug Administration 21 CFR Chapter I [Docket No. FDA-2012-N-0780...and other members of the public on this topic and a set of premeeting questions discussed...to share with FDA concerning the general topic of data exchange standards? Dated:...

2012-08-14

326

Cerebral autoregulation and gas exchange studied using a human cardiopulmonary model  

E-print Network

developed a model of the human cardiopulmonary (CP) system, which included the whole body circulatory system Dynamical Systems Group, Rice University, Houston 77005; 2 Baylor College of Medicine, Houston 77005; 3, lung and peripheral tissue gas exchange, and the central nervous system control of arterial pressure

327

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

328

Study Abroad; Student and Academic Exchanges; Foreign Students in China; Chinese Students Abroad: Annotated Bibliography.  

ERIC Educational Resources Information Center

An annotated bibliography includes 66 items drawn from a wide variety of sources including scholarly journals, government reports, books, newspapers, and ERIC documents. While many of the cited works focus on educational exchange programs between China and Western nations since the Cultural Revolution, some of the sources deal with earlier…

Parker, Franklin

329

Study and development of a cryogenic heat exchanger for life support systems  

NASA Technical Reports Server (NTRS)

A prototype cryogenic heat exchanger for removal of waste heat from a spacecraft environmental control life support system was developed. The heat exchanger uses the heat sink capabilities of the cryogenic propellants and, hence, can operate over all mission phases from prelaunch to orbit, to post landing, with quiescent periods during orbit. A survey of candidate warm fluids resulted in the selection of E-2, a fluorocarbon compound, because of its low freezing point and high boiling point. The final design and testing of the heat exchanger was carried out, however, using Freon-21, which is similar to E-2 except for its low boiling point. This change was motivated by the desire for cost effectiveness of the experimental program. The transient performance of the heat exchanger was demonstrated by an analog simulation of the heat sink system. Under the realistic transient heat load conditions (20 sec ramp from minimum to maximum Freon-21 inlet temperature), the control system was able to maintain the warm fluid outlet temperature within + or - 3 F. For a 20-sec ramp from 0 F to -400 F in the hydrogen inlet temperature, at maximum heat load, the warm fluid outlet temperature was maintained within + or - 7 F.

Soliman, M. M.

1973-01-01

330

Chromosome Aberrations and Sister Chromatid Exchange Studies in Patients with Prostate Cancer: Possible Evidence of Chromosome Instability  

Microsoft Academic Search

Cytogenetic studies have been carried out using the G-banding technique in peripheral blood lymphocytes of 24 patients with prostate cancer. Of these, eight belong to stage B, six to stage C\\/e, three to C\\/sv, two to Do, and the remaining five to DI stage of carcinoma. Simultaneously, sister chromatid exchanges (SCEs) were also analyzed in the peripheral blood lymphocytes of

Varinderpal S Dhillon; Ipninder K Dhillon

1998-01-01

331

Experimental study on the heat transfer enhancement of MWNT-water nanofluid in a shell and tube heat exchanger  

Microsoft Academic Search

Heat transfer enhancement of multi-walled carbon natube(MWNT)\\/water nanofluid in a horizontal shell and tube heat exchanger has been studied experimentally. Carbon nanotubes were synthesized by the use of catalytic chemical vapor deposition (CCVD) method over Co–Mo\\/MgO nanocatalyst. Obtained MWNTs were purified using a three stage method. COOH functional groups were inserted for making the nanotubes hydrophilic and increasing the stability

R. Lotfi; A. M. Rashidi; A. Amrollahi

332

Study of Mesoscale Eddies in the Gulf of Lion and their role in the coastal-offshore exchanges  

Microsoft Academic Search

The main objective of LAgrangian Transport EXperiment (LATEX) project (2008-2011) is to study the influence of mesoscale structures on shelf-offshore exchanges in the Gulf of Lion (GoL). The LATEX strategy combines use of data from Lagrangian drifters, satellite images and hull-mounted ADCP data with numerical modeling. In this work, we simulate the mesoscale structures, occurring at the interface between the

Z. Y. Hu; A. M. Doglioli; A. A. Petrenko; R. Compbell; F. Diaz; I. Dekeyser

2010-01-01

333

A pilot study on phosphate and nitrate removal from secondary wastewater effluent using a selective ion exchange process.  

PubMed

A pilot study was conducted at a wastewater treatment plant (WWTP) in Easton, Pennsylvania, for the removal of varying concentrations of phosphate (HPO4(2-)) and nitrate NO3- using a newly developed ion exchange material referred to as Polymeric Ligand Exchanger (PLE). The PLE was prepared by immobilizing copper (II) ions onto a commercially available chelating resin, DOW-3N. The loaded copper ions act as ligand exchanger sites that selectively bind with target ligands such as phosphate and nitrate. This pilot study was the final experimental testing phase of the PLE toward the full process development for the selective removal of both phosphate and nitrate using secondary effluent from a fully operational WWTP. In order to establish the effectiveness of the PLE, a commercially available activated alumina (AA) was also tested for comparison. Effluent phosphorus and nitrate concentration of less than 0.1 mg l(-1) were achieved for up to 500 bed volumes; phosphorous was reduced from an average concentration of 4.0 mg l(-1) and nitrate from average concentration of 16.4 mg l(-1). In accord with prior laboratory observations, the pilot test results showed that the PLE could selectively remove phosphate from secondary municipal wastewater effluent under normal conditions (pH, ionic strength, dissolved organic carbon content). In addition, the pilot study provided new evidence that nitrate could be removed from secondary municipal wastewater effluent and concurrently with phosphate. The selective ion exchange process provides an alternative for concurrent removal of the eutrophic-enhancing nutrients, phosphate and nitrate. PMID:15242229

Kney, A D; Zhao, D

2004-05-01

334

Heat exchanges in fast, high-performance liquid chromatography. A complete thermodynamic study  

SciTech Connect

The successive physical transformations of the mobile phase that take place in very high pressure liquid chromatography were studied based on the formalism of classical thermodynamics. The eluent is initially under atmospheric pressure (P{sup 0}) and at ambient temperature (T{sub ext}). In a first step, it is compressed to a high pressure (P{sub max} of the order of 1 kbar) in the pump heads of the chromatograph. In a second step, the pressurized eluent is transferred to the inlet of the chromatographic column, along which, in a third step, it is decompressed to atmospheric pressure. Both the compression and the decompression of the fluid were considered to take place under conditions that can be either adiabatic or nonadiabatic and either reversible or irreversible. Applications of the first and second principles of thermodynamics allow the determination of the heat and energy exchanged between the eluent and the external surroundings during each transformation. Experimental data were acquired using acetonitrile as the mobile phase. The true state equation, {rho}(P, T), of liquid acetonitrile was used in the theoretical calculations. A series of four different flow rates (0.55, 0.85, 1.15, and 1.45 mL/min, corresponding to inlet pressures of 357.2, 559.5, 765.1, and 972.9 bar, respectively), were applied to a 2.1 x 100 mm column packed with 1.7-{micro}m bridged ethane-silicon hybrid particles. Thermocouples were used to measure the eluent temperature before and after its passage through the column. These data provide estimates of the variation of the internal energy of the eluent. The heat lost through the external wall of the column during the eluent decompression was estimated by measuring the surface temperature of the column tube under steady state. Both the compression and the decompression of acetonitrile were found to be nonadiabatic and irreversible transformations. The results showed that, during the eluent decompression, the heat released by the friction forces serves four different purposes: (1) it increases the eluent entropy at constant temperature (for 35%); (2) it increases the temperature of the eluent (for 5%); (3) it provides heat to the laboratory atmosphere (for 5%); and (4) it provides some work inside the column (for 5%). This quantitative heat balance description accounts well for the actual performance of the new, very high pressure liquid chromatographic technique.

Gritti, Fabrice [University of Tennessee, Knoxville (UTK); Guiochon, Georges A [ORNL

2008-01-01

335

ION EXCHANGE  

EPA Science Inventory

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

336

Science exchanges  

Microsoft Academic Search

Dwindling scientific and technical exchange between the United States and the Soviet Union and prospects for enhancing such exchanges were discussed at an August 2 hearing by the Foreign Affairs Committee of the U.S. House of Representatives. The committee also heard overviews on the United States' approach to international exchange of science and technology. The hearing was the first in

Barbara T. Richman

1983-01-01

337

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

338

Numerical study of a M-cycle cross-flow heat exchanger for indirect evaporative cooling  

Microsoft Academic Search

In this paper, numerical analyses of the thermal performance of an indirect evaporative air cooler incorporating a M-cycle cross-flow heat exchanger has been carried out. The numerical model was established from solving the coupled governing equations for heat and mass transfer between the product and working air, using the finite-element method. The model was developed using the EES (Engineering Equation

Changhong Zhan; Xudong Zhao; Stefan Smith; S. B. Riffat

2011-01-01

339

Thermal-hydraulic CFD study in louvered fin-and-flat-tube heat exchangers  

Microsoft Academic Search

Heat transfer performance prediction by CFD codes is of major interest. Usually air-side heat transfer characteristics of fin-and-tube heat exchangers are determined from limited experimental data. The ability of CFD code to predict flow patterns and thermal fields allows determining the heat transfer characteristics by performing ‘numerical experiments’. CFD calculations of a 1-row automotive condenser are compared to experimental results

Thomas Perrotin; Denis Clodic

2004-01-01

340

Experimental study of commercial size proton exchange membrane fuel cell performance  

Microsoft Academic Search

Commercial sized (16×16 cm2 active surface area) proton exchange membrane (PEM) fuel cells with serpentine flow chambers are fabricated. The GORE-TEX® PRIMEA 5621 was used with a 35-?m-thick PEM with an anode catalyst layer with 0.45mgcm?2 Pt and cathode catalyst layer with 0.6mgcm?2 Pt and Ru or GORE-TEX® PRIMEA 57 was used with an 18-?m-thick PEM with an anode catalyst

Wei-Mon Yan; Xiao-Dong Wang; Duu-Jong Lee; Xin-Xin Zhang; Yi-Fan Guo; Ay Su

2011-01-01

341

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

SciTech Connect

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

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

1999-06-01

342

Density-functional study of van der Waals forces on rare-gas diatomics: Hartree-Fock exchange  

NASA Astrophysics Data System (ADS)

A density-functional theory study of van der Waals forces on rare-gas diatomics is carried out. Hartree-Fock-Kohn-Sham formalism is used, that is, the exchange-correlation functional is expressed as the combination of Hartree-Fock exchange plus an approximation to the correlation energy functional. Spectroscopic constants (Re,?e, and De) and potential energy curves for the molecules He2, Ne2, Ar2, HeNe, HeAr, and NeAr are presented. Several approximations to the correlation functional are tested. The best results, in good agreement with reference experimental data, are obtained with the functional proposed by Wilson and Levy [L. C. Wilson and M. Levy, Phys. Rev. B 41, 12930 (1990)].

Pérez-Jordá, José M.; San-Fabián, Emilio; Pérez-Jiménez, Angel J.

1999-01-01

343

Thermodynamic study of the interaction between linear plasmid DNA and an anion exchange support under linear and overloaded conditions.  

PubMed

Anion-exchange chromatography has been successfully used in plasmid DNA (pDNA) purification. However, pDNA adsorption mechanism using this method is still not completely understood, and the prediction of the separation behavior is generally unreliable. Flow microcalorimetry (FMC) has proven its ability to provide an improved understanding of the driving forces and mechanisms involved in the adsorption process of biomolecules onto several chromatographic systems. Thus, using FMC, this study aims to understand the adsorption mechanism of linear pDNA (pVAX1-LacZ) onto the anion-exchange support Fast Flow (FF) Q-Sepharose. Static binding capacity studies have shown that the mechanism of pDNA adsorption onto Q-Sepharose follows a Langmuir isotherm. FMC experiments resulted in thermograms that comprised endothermic and exothermic heats. Endothermic heat major contributor was suggested to be the desolvation process. Exothermic heats were related to the interaction between pDNA and Q-Sepharose primary and secondary adsorption. Furthermore, FMC revealed that the overall adsorption process is exothermic, as expected for an anion-exchange interaction. Nevertheless, there are evidences of the presence of nonspecific effects, such as reorientation and electrostatic repulsive forces. PMID:25465014

Aguilar, P A; Twarda, A; Sousa, F; Dias-Cabral, A C

2014-11-01

344

The Benefits of Past and Current Regional Hydroclimate Projects to the Third Pole Environment (TPE) Water and Energy Exchanges Studies  

NASA Astrophysics Data System (ADS)

To improve understanding of the various processes at work on spatial and temporal scales from regional to global the Regional Hydroclimate Projects (RHP's) are established as part of the Global Energy and Water Exchanges (GEWEX)Project to link the regional observations and process understanding to the global scale. This is done through exchange of observations, data, modeling, transferability studies etc. In this presentation the series of RHP's that were underway over North and South America, Europe and Asia continuously from the early 1990's up to the present will be examined, the reasons they were established, how they evolved and how they are evolving or are likely to evolve in the future, with an emphasis on where they can and should benefit similar work proposed for the TPE. The results will be presented in the context of the World Climate Research Programme (WCRP) Grand Challenge related to the development of a water strategy that addresses the issue of past and future changes in Water, in general, and the GEWEX science question on global water resource systems, in particular. This material will address issues associated with how changes in land surface and hydrology influence past and future changes in water availability and security, how new observations lead to improvements in water management and how models become better in global and regional climate predictions and projections of precipitation and how these outcomes relate to the TPE Water and Energy Exchanges Studies.

Benedict, Sam; van Oevelen, Peter

2014-05-01

345

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

346

The current situation of the study on twisted tape inserts in pipe exchangers  

NASA Astrophysics Data System (ADS)

Heat transfer enhancement is used in many applications including heat exchangers, air conditioning, and refrigeration systems; hence many researchers have conducted experimental and numerical researches on heat transfer enhancement and have developed various techniques and methods. As a passive heat transfer technique, twisted tapes are widely used in various industries for their cost savings, lower maintenance requirements and the fact that they are easily set up. This paper introduces the principle of heat transfer enhancement of twisted tapes and reviews some of the experimental works done by researchers on this technique in recent years. The variously modified twisted tape inserts are widely researched and used to enhance heat transfer efficiency for heat exchangers. Twisted tapes perform better in low Re conditions and in square tubes. However, they could also cause higher pressure drops. Twisted tapes have great potential and profound implications if they can be used in traditional heat exchangers. Besides this, some correlations between the Nusselt number and friction factors are presented in this paper.

Man, Changzhong; Wang, Chong; Yao, Jinyu

2014-12-01

347

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

348

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

SciTech Connect

Chabazite, vermiculite, montmorillonite, hectorite, and kaolinite were used to remove Pb, through ion exchange, from 0.01 M aqueous Pb(NO[sub 3])[sub 2] solutions. These minerals contained 27 (Na-chabazite), 16, 9, 9, and 0.5 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[sub 3]). [sup 29]Si, [sup 27]Al, and [sup 23]Na magic angle spinning (MAS) nuclear magnetic resonance (NMR), [sup 23]Na double rotation (DOR) NMR, and [sup 23]Na 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 [minus]80 to [minus]100[degrees]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[sub 4] and AlO[sub 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 [minus]8 ppM peak on the [sup 23]Na MAS NMR spectrum. The behavior of the exchangeable cations in the interlayer sites was similar in all the clay minerals studied. 27 refs., 7 figs., 4 tabs.

Liang, J.J.; Sherriff, B.L. (Univ. of Manitoba, Winnipeg (Canada))

1993-08-01

349

Studies on synthetic inorganic ion exchangers-V: preparation, properties and ion-exchange behaviour of amorphous and crystalline thorium tungstate.  

PubMed

Amorphous and crystalline thorium tungstate have been prepared by mixing 0.1M thorium nitrate and 0.1M sodium tungstate under different conditions. The physico-chemical properties, chemical stability, composition, TGA, DTA, X-ray, infrared absorption and ion-exchange behaviour of thorium-tungstate are reported and discussed. Distribution coefficients of metal ions on thorium tungstate have been determined at pH 2-3 and 5.5-6.5. Selective ion-exchange separations of bismuth and mercury from other metal ions have been achieved on a column of thorium tungstate. PMID:18961820

De, A K; Chowdhury, K

1976-02-01

350

Study of Np(V) Sorption by Ionic Exchange on Na, K, Ca and Mg-Montmorillonite  

NASA Astrophysics Data System (ADS)

The transport behavior of actinides in soil and ground water are highly influenced by clay minerals due to their ubiquity in the environment, reactivity and colloidal properties. Neptunium(V) has been introduced in the environment as a result of nuclear weapons testing [e.g. 1, 2] and is a radionuclide of potential interest for safety assessment of high level radioactive waste disposal because its long half-life and high toxicity [3]. Surface complexation and ionic exchange have been identified as Np(V) sorption mechanisms onto montmorillonite. At pH below 5, Np(V) sorption is mainly attributed to ionic exchange. This study examines Np(V) ion exchange on Na, K, Ca and Mg forms of montmorillonite. Experiments were carried out using 237Np concentrations between 2 x 10-8 M and 5 x 10-6 M at three different ionic strengths 0.1, 0.01 and 0.001M. The pH was maintained at 4.5. Np(V) sorption to montmorillonite homoionized with monovalent cations (Na and K) demonstrated a markedly different behavior to that observed for montmorillonite homoionized with divalent cations (Ca and Mg). Np sorption to Na and K-montmorillonite was greater than Np sorption to Ca and Mg-montmorillonite. Isotherms with Na and K-montmorillonite showed a strong dependence on ionic strength: the percentage of Np adsorbed was near zero at 0.1M ionic strength, but increased to 30% at 0.001 M ionic strength. This suggests ionic exchange is the main Np adsorption mechanism under the experimental conditions investigated. Dependence on ionic strength was not observed in the Np sorption isotherms for Ca and Mg-montmorillonite indicating a low exchange capacity between Np and divalent cations. Modeling of the sorption experimental data will allow determination of the Na+?NpO2+ and K+?NpO2+ ionic exchange constants on montmorillonite. References: [1] A. R. Felmy; K. J. Cantrell; S. D. Conradson, Phys. Chem. Earth 2010, 35, 292-297 [2] D. K. Smith; D. L. Finnegan; S. M. Bowen, J. Environ. Radioact. 2003, 67, (1), 35-51 [3] N. Kozai; T. Ohnuki; S. Muraoka, J. Nucl. Sci. Technol. 1993, 30, (11), 1153-1159 This work was funded by U. S. DOE Office of Biological & Environmental Sciences, Subsurface Biogeochemistry Research Program, and performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Security, LLC under Contract DE-AC52-07NA27344. A. Benedicto was supported by a Spanish Ministry of Science and Innovation 'FPI' pre-doctoral contract in CIEMAT (Spain). LLNL-ABS-570160

Benedicto, A.; Begg, J.; Zhao, P.; Kersting, A. B.; Zavarin, M.

2012-12-01

351

Open inquiry-based learning experiences: a case study in the context of energy exchange by thermal radiation  

NASA Astrophysics Data System (ADS)

An open inquiry (OI)-based teaching/learning experience, regarding a scientific investigation of the process of energy exchange by thermal radiation, is presented. A sample of upper secondary school physics teachers carried out this experience at the University of Palermo, Italy, in the framework of ESTABLISH, a FP7 European Project aimed at promoting and developing inquiry-based science education. The teachers had the opportunity to personally experience an OI-based learning activity, with the aim of exploring the pedagogical potentialities of this teaching approach to promote both the understanding of difficult concepts and a deeper view of scientific practices. The teachers were firstly engaged in discussions concerning real-life problematic situations, and then stimulated to design and carry out their own laboratory activities, aimed at investigating the process of energy exchange by thermal radiation. A scientific study on the energy exchange between a powered resistor and its surrounding environment, during the heating and cooling processes, was designed and performed. Here we report the phases of this experiment by following the teachers' perspective. A structured interview conducted both before and after the OI experience allowed us to analyze and point out the teachers' feedback from a pedagogical point of view. The advantages and limits of an OI-based approach to promote the development of more student-centred inquiry-oriented teaching strategies are finally discussed.

Pizzolato, Nicola; Fazio, Claudio; Rosario Battaglia, Onofrio

2014-01-01

352

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. PMID:20455118

Wahrendorf, Morten; Ribet, Celine; Zins, Marie; Goldberg, Marcel; Siegrist, Johannes

2010-01-01

353

X-ray diffraction and absorption studies of ion exchanged glasses  

NASA Astrophysics Data System (ADS)

X-ray diffraction and absorption experiments were performed to determine the structure of commercial sodium silicate glasses before and after a silver-sodium ion exchange. EXAFS measurements at the Na and Ag K-edge display the transition of the sodium environment consisting of five oxygens analogously to that of disilicate glasses to the twofold coordination of silver similar to crystalline Ag 2O. The existence of Ag?Ag correlations could be deduced from both the curve-fitting analyses of Ag K-edge oscillations and the differential distribution function of diffraction data. The influence of silver incorporation on the silicate network structure has been shown.

Dubiel, M.; Schmitz, R.; Kolb, U.; Gutwerk, D.; Bertagnolli, H.

1995-02-01

354

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

PubMed Central

Small G-proteins of the superfamily Ras function as molecular switches, interacting with different cellular partners according to their activation state. G-protein activation involves the dissociation of bound GDP and its replacement by GTP, in an exchange reaction that is accelerated and regulated in the cell by guanine-nucleotide exchange factors (GEFs). Large conformational changes accompany the exchange reaction, and our understanding of the mechanism is correspondingly incomplete. However, much knowledge has been derived from structural studies of blocked or inactive mutant GEFs, which presumably closely represent intermediates in the exchange reaction and yet which are by design incompetent for carrying out the nucleotide exchange reaction. In this study we have used comparative modelling to recreate an exchange-competent form of a late, pre-GDP-ejection intermediate species in Arf1, a well-characterized small G-protein. We extensively characterized three distinct models of this intermediate using molecular dynamics simulations, allowing us to address ambiguities related to the mutant structural studies. We observed in particular the unfavorable nature of Mg associated forms of the complex and the establishment of closer Arf1-GEF contacts in its absence. The results of this study shed light on GEF-mediated activation of this small G protein and on predicting the fate of the Mg ion at a critical point in the exchange reaction. The structural models themselves furnish additional targets for interfacial inhibitor design, a promising direction for exploring potentially druggable targets with high biological specificity. PMID:20174625

Ben Hamida-Rebaï, Mériam; Robert, Charles H.

2010-01-01

355

Exchange integrals in magnetoelectric hexagonal ferrite (SrCo{sub 2}Ti{sub 2}Fe{sub 8}O{sub 19}): A density functional study  

SciTech Connect

The exchange integrals in magnetoelectric hexagonal ferrite SrCo{sub 2}Ti{sub 2}Fe{sub 8}O{sub 19} have been calculated by using density functional theory. To get 10 inter-sublattice and 3 intra-sublattice exchange integrals, the electronic structures and total energies of 20 spin arrangements have been calculated with General Gradient Approximation (GGA) + U method. The dependence of exchange integrals on U has been studied. The comparison between the exchange integrals in SrFe{sub 12}O{sub 19} and those in SrCo{sub 2}Ti{sub 2}Fe{sub 8}O{sub 19} shows that substitution of Co and Ti decreases the most interactions involving the 12?k sites. The investigation based on our exchange integrals indicates that magnetic interaction between R and S blocks reduces significantly in SrCo{sub 2}Ti{sub 2}Fe{sub 8}O{sub 19}.

Feng, Min [School of Physics, Nankai University, Tianjin 300071 (China); Shao, Bin [Department of Physics, Tsinghua University, Beijing 100084 (China); Lu, Yuan; Zuo, Xu, E-mail: xzuonku@gmail.com [College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071 (China)

2014-05-07

356

Theoretical studies of the nitrogen containing compounds adsorption behavior on Na(I)Y and rare earth exchanged RE(III)Y zeolites.  

PubMed

In this work, the adsorption behavior of nitrogen containing compounds including NH3, pyridine, quinoline, and carbazole on Na(I)Y and rare earth exchanged La(III)Y, Pr(III)Y, Nd(III)Y zeolites was investigated by density functional theory (DFT) calculations. The calculation results demonstrate that rare earth exchanged zeolites have stronger adsorption ability for nitrogen containing compounds than Na(I)Y. Rare earth exchanged zeolites exhibit strongest interaction with quinoline while weakest with carbazole. Nd(III)Y zeolites are found to have strongest adsorption to all the studied nitrogen containing compounds. The analysis of the electronic total charge density and electron orbital overlaps show that nitrogen containing compounds interact with zeolites by ?-electrons of the compounds and the exchanged metal atom. Mulliken charge population analysis also proves that adsorption energies are strongly dependent on the charge transfer between the nitrogen containing molecules and exchanged metal atom in the zeolites. PMID:25605601

Geng, Wei; Zhang, Haitao; Zhao, Xuefei; Zan, Wenyan; Gao, Xionghou; Yao, Xiaojun

2015-01-01

357

NMR-detected hydrogen exchange and molecular dynamics simulations provide structural insight into fibril formation of prion protein fragment 106–126  

PubMed Central

PrP106–126, a peptide corresponding to residues 107–127 of the human prion protein, induces neuronal cell death by apoptosis and causes proliferation and hypertrophy of glia, reproducing the main neuropathological features of prion-related transmissible spongiform encephalopathies, such as bovine spongiform encephalopathy and Creutzfeldt–Jakob disease. Although PrP106–126 has been shown to form amyloid-like fibrils in vitro, their structural properties have not been elucidated. Here, we investigate the conformational characteristics of a fibril-forming fragment of the mouse prion protein, MoPrP106–126, by using electron microscopy, CD spectroscopy, NMR-detected hydrogen–deuterium exchange measurements, and molecular dynamics simulations. The fibrils contain ?50% ?-sheet structure, and strong amide exchange protection is limited to the central portion of the peptide spanning the palindromic sequence VAGAAAAGAV. Molecular dynamics simulations indicate that MoPrP106–126 in water assumes a stable structure consisting of two four-stranded parallel ?-sheets that are tightly packed against each other by methyl–methyl interactions. Fibril formation involving polyalanine stacking is consistent with the experimental observations. PMID:14657385

Kuwata, Kazuo; Matumoto, Tomoharu; Cheng, Hong; Nagayama, Kuniaki; James, Thomas L.; Roder, Heinrich

2003-01-01

358

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

359

Higher Education Exchange, 2011  

ERIC Educational Resources Information Center

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

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

2011-01-01

360

A High-Resolution Modeling Study of the Bosphorus Strait Dynamics and Exchange Flows  

NASA Astrophysics Data System (ADS)

An all-time modelling challenge aims to establish a sound understanding of the high energy environment of the Turkish Straits System, relating to inter-basin water and material transports and their influence on the sensitive ecosystems of the adjacent seas. As a first step in this direction, well resolved, high level, physically representative predictive models of the Bosphorus Strait exchange flow hydrodynamics are developed, adequately representing its complex topography, hydraulic controls, dissipative hydraulic jumps, mixing and turbulence mechanisms, with the application of appropriate basin boundary and initial conditions and judiciously selected numerical and physical model options. Both the ROMS and MITgcm models are used and compared for performance. Idealized and real case model results successfully reproduce observed flow features. The unique maximal exchange regime of the Bosphorus Strait, with hydraulic controls are demonstrated, although frictional effects, especially of the highly irregular lateral boundaries, are found to be extremely important, associated with mixing and entrainment and nonlinear dynamics determining the two-way fluxes as a function of sea-level changes across the strait. The intercomparison of ROMS and MITgcm results are extremely satisfactory in the basic elements of the flow, except for some small differences.

Sözer, Adil; Sannino, Gianmaria; Özsoy, Emin

2013-04-01

361

Leach studies on cement-solidified ion exchange resins from decontamination processes at operating nuclear power stations  

SciTech Connect

The effects of varying pH and leachant compositions on the physical stability and leachability of radionuclides and chelating agents were determined for cement-solidified decontamination ion-exchange resin wastes collected from two operating commercial light water reactors. Small scale waste-form specimens were collected during waste solidifications performed at the Brunswick Steam Electric Plant Unit 1 and at the James A. FitzPatrick Nuclear Power Station. The collected specimens were leach tested, and their compressive strength was measured in accordance with the Nuclear Regulatory Commission's Technical Position on Waste Form'' (Revision 1), from the Low-Level Waste Management Branch. Leachates from these studies were analyzed for radionuclides, selected transition metals, and chelating agents to assess the leachability of these waste form constituents. Leachants used for the study were deionized water, simulated seawater, and groundwater compositions similar to those found at Barnwell, South Carolina and Hanford, Washington. Results of this study indicate that initial leachant pH does not affect leachate pH or releases from cement-solidified decontamination ion-exchange resin waste forms. However, differences in leachant composition and the presence of chelating agents may affect the releases of radionuclides and chelating agents. In addition, results from this study indicate that the cumulative releases of radionuclides and chelating agents observed for forms that disintegrated were similar to those for forms that maintained their general physical integrity.

McIsaac, C.V.; Akers, D.W.; McConnell, J.W.; Morcos, N.

1992-01-01

362

Leach studies on cement-solidified ion exchange resins from decontamination processes at operating nuclear power stations  

SciTech Connect

The effects of varying pH and leachant compositions on the physical stability and leachability of radionuclides and chelating agents were determined for cement-solidified decontamination ion-exchange resin wastes collected from two operating commercial light water reactors. Small scale waste-form specimens were collected during waste solidifications performed at the Brunswick Steam Electric Plant Unit 1 and at the James A. FitzPatrick Nuclear Power Station. The collected specimens were leach tested, and their compressive strength was measured in accordance with the Nuclear Regulatory Commission`s ``Technical Position on Waste Form`` (Revision 1), from the Low-Level Waste Management Branch. Leachates from these studies were analyzed for radionuclides, selected transition metals, and chelating agents to assess the leachability of these waste form constituents. Leachants used for the study were deionized water, simulated seawater, and groundwater compositions similar to those found at Barnwell, South Carolina and Hanford, Washington. Results of this study indicate that initial leachant pH does not affect leachate pH or releases from cement-solidified decontamination ion-exchange resin waste forms. However, differences in leachant composition and the presence of chelating agents may affect the releases of radionuclides and chelating agents. In addition, results from this study indicate that the cumulative releases of radionuclides and chelating agents observed for forms that disintegrated were similar to those for forms that maintained their general physical integrity.

McIsaac, C.V.; Akers, D.W.; McConnell, J.W.; Morcos, N.

1992-08-01

363

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

364

Studying the effects of interplay between anisotropy and exchange in molecular nanomagnets  

NASA Astrophysics Data System (ADS)

This dissertation presents work on several molecular nanomagnets using both theoretical and experimental approaches to understand the effects of the interplay between anisotropy and exchange in these systems. The molecular nanomagnets presented here can be classified into two different categories: single molecule magnets and antiferromagnetic wheels or grids. Magnetic anisotropy plays a significant role in these compounds and leads to bistability of the projections of the magnetic moment ('up' and 'down') at lower temperatures, separated by a barrier. The employment of electron paramagnetic resonance techniques allows the understanding of some basic issues in quantum physics. Results presented for two iron complexes show the importance of easy-axis anisotropy in determining whether a molecule can be treated as a single molecule magnet. The importance of transverse anisotropy can be understood from the results obtained for a mixed valent manganese compound. One may consider a giant spin instead of treating the individual spins of the magnetic centers while interpreting these results using the spin Hamiltonian. For a tetranuclear cobalt complex, however, this is no longer a valid approximation and one needs to consider the generalized spin Hamiltonian to interpret the results. An attempt is made to compare anisotropies in ferromagnetic and antiferromagnetic manganese based triangular units. Results from several theoretical techniques like the projection operator and exact diagonalization methods are then supported with results from experiments. This allows an understanding of the combined role of anisotropy and exchange in determining the barrier in these molecular magnets. Finally, results for an antiferromagnetic grid and a wheel are presented to demonstrate how high-frequency/high-field electron paramagnetic resonance can be a useful technique to observe quantum spin dynamics in this class of molecular nanomagnets.

Datta, Saiti

365

Study of complex heat exchange with account for phase transitions in secondary contour of the geothermal power plant  

Microsoft Academic Search

The numerical solution of complex heat exchange with account of phase transitions in secondary contour is obtained. Temperature, pressure and evaporation distributions along height of a heat exchanger and parametrical dependences of phase transitions boundaries on initial conditions are found.

A. B. Alkhasov; R. M. Aliyev; M. M. Ramazanov; G. M. Abasov

2000-01-01

366

Catalysts based on activated aluminum alloys. I. A study of copper-alumina catalysts by XPS and deuterium-hydrogen exchange  

SciTech Connect

Surface compositions and electron states of elements in copper-containing catalysts prepared by water treatment of copper-aluminum alloys activated by indium and gallium are studied by XPS. The copper contents in the surface layers of the catalysts is found to be less than that in the bulk. Fast isotopic H{sub 2}-D{sub 2} exchange at 70-200{degrees}C on reduced copper-containing samples and the absence of the exchange on copper-free samples indicate dissociative hydrogen adsorption on copper-containing active sites. The activation energy for the isotopic exchange is essentially dependent on the procedure of catalyst preparation.

Yakerson, V.I.; Subbotin, A.N.; Gudkov, B.S.; Tkachenko, O.P. [Zelinskii Institute of Organic Chemistry, Moscow (Russian Federation); Sarmurzina, R.G. [Institute Metallurgy, Alma-Ata (Kazakhstan)

1994-09-01

367

The Exchange Rate - A Shock-Absorber or Source of Shocks? A Study of Four Open Economies  

Microsoft Academic Search

The paper provides SVAR estimates for four open economies: the UK, Canada, Sweden and Denmark, making explicit a monetary policy reaction function and taking account of exchange rate targeting practices. The object of the analysis is to examine the idea that an independent money and exchange rate should allow for effective shock-absorption. A polar extreme would be that exchange markets

Michael J Artis; Michael Ehrmann

2000-01-01

368

Kitchen Appliance Upgrades Improve Water Efficiency at DOD Exchange Facilities: Best Management Practice Case Study #11: Commercial Kitchen Equipment (Brochure)  

SciTech Connect

The Exchange, formerly the Army and Air Force Exchange Service (AAFES), is a joint military activity and the U.S. Department of Defense?s (DOD) oldest and largest retailer. The Exchange is taking a leadership role in water efficiency improvements in their commercial kitchens by integrating water efficiency concepts into the organization?s overall sustainability plan and objectives.

Not Available

2011-09-01

369

Study of frost growth on heat exchangers used as outdoor coils in air source heat pump systems  

NASA Astrophysics Data System (ADS)

Scope and method of study. During winter heating operation, the outdoor coil of a heat pump acts as an evaporator and when the ambient temperature is near freezing, the moisture in the atmospheric air freezes on the coil surface. The frost growth affects the air flow and also adds resistance to heat transfer thus reducing the capacity and the efficiency of the heat pump. An experimental facility is designed and built to test a small scale heat exchanger working in frosting conditions. Tests are carried out using small scale fin-tube and microchannel heat exchanger over a range of glycol inlet temperatures, air velocities and ambient air RH. A semi-empirical frost model based on a scaling approach is developed and applied to both fin-tube heat and microchannel heat exchangers. The model is developed to handle non-uniformities in both refrigerant and air side. The frost model is integrated with a segment-by-segment heat exchanger calculation algorithm and is validated against experimental data. Frost growth model is also incorporated in a quasi-steady state system simulation algorithm. Findings and conclusions. From the experimental study it was observed that the temperature of the surface and air RH affected the rate of frost growth significantly while the air velocity did not have a great influence. It is demonstrated that a dry heat transfer correlation can be used during frost growth period by correctly accounting for frost thickness in the hydraulic diameter calculations. Ignoring the phenomenon of air redistribution was found to result in errors in the range of 20% to 50% in predicted frost thickness. Frost thickness predicted by the frost model is within 5% of the measured values for most of the cases. Frost mass accumulation predicted by the simple model is higher than the measured values due to a uniform thickness assumption in the model. An improved frost model based on 1-D finite volume discretization is also presented which improved the frost mass prediction to within 13% of measured values. The system simulation is validated against experimental results and found to match reasonable well. The discrepancy between simulation and experiments were due to the effects of system transience in the initial stages.

K P, Sankaranarayanan

2011-12-01

370

Modification of acid sites in ZSM-5 by ion-exchange: An in-situ FTIR study  

NASA Astrophysics Data System (ADS)

A study of the acid sites in Mn+-ZSM-5 zeolites (Mn+ = H+, Al3+, Ca2+, and Ba2+), synthesized by ion-exchange from the NH4+ form, has been carried out using X-ray diffraction, 27Al MAS NMR, and in-situ FTIR spectroscopy. X-ray diffraction data indicate that the crystalline structure of ZSM-5 is maintained on ion-exchange. 27Al MAS NMR spectroscopy confirms that Lewis acid sites in all of the Mn+-ZSM-5 zeolites are mainly located on the tetrahedral aluminum atoms in the zeolite framework. However, octahedral extra-framework aluminum is another source of Lewis acid sites in H+-ZSM-5 and Al3+-ZSM-5. Brønsted acid sites are identified as originating from the hydroxyl groups that bridge Al and Si atoms. The acid sites in Mn+-ZSM-5 have been characterized by in-situ FTIR spectroscopy with pyridine as the probe molecule. FTIR spectroscopy demonstrated that the number of accessible acid sites and ratio of Lewis to Brønsted acid sites in Mn+-ZSM-5 can be effectively modified by ion-exchange. The number of acid sites in Mn+-ZSM-5 increases in the same order as the acidity of cations with Ba2+ < Ca2+ < NH4+ < Al3+ < H+. Though the strength of both Lewis and Brønsted acid sites is virtually identical for all Mn+-ZSM-5 zeolites, the ratio of Brønsted to Lewis acid sites varies as a result of the loaded cation. In addition, modification of acid sites in Mn+-ZMS-5 by loading different cations is discussed in terms of the accessibility of the surface of the zeolite channels and the reactivity of the cations with Brønsted acid hydroxyls. We conclude that larger cations can effectively constrict the zeolite channels and impede the ability of pyridine to access acid sites on the surface of the channels.

Wu, Weiqiang; Weitz, Eric

2014-10-01

371

Influence of 8-Oxoguanosine on the Fine Structure of DNA Studied with Biasing-Potential Replica Exchange Simulations  

SciTech Connect

Chemical modification or radiation can cause DNA damage, which plays a crucial role for mutagenesis of DNA, carcinogenesis, and aging. DNA damage can also alter the fine structure of DNA that may serve as a recognition signal for DNA repair enzymes. A new, advanced sampling replica-exchange method has been developed to specifically enhance the sampling of conformational substates in duplex DNA during molecular dynamics (MD) simulations. The approach employs specific biasing potentials acting on pairs of pseudodihedral angles of the nucleic acid backbone that are added in the replica simulations to promote transitions of the most common substates of the DNA backbone. The sampled states can exchange with a reference simulation under the control of the original force field. The application to 7,8-dihydro-8oxo-guanosine, one of the most common oxidative damage in DNA indicated better convergence of sampled states during 10 ns simulations compared to 20 times longer standard MD simulations. It is well suited to study systematically the fine structure and dynamics of large nucleic acids under realistic conditions, including explicit solvent and ions. The biasing potential-replica exchange MD simulations indicated significant differences in the population of nucleic acid backbone substates in the case of 7,8-dihydro-8oxo-guanosine compared to a regular guanosine in the same sequence context. This concerns both the ratio of the B-DNA substates BI and BII associated with the backbone dihedral angles ? and z but also coupled changes in the backbone dihedral angles a and g. Such differences may play a crucial role in the initial recognition of damaged DNA by repair enzymes.

Kara, Mahmut; Zacharias, Martin W.

2013-03-05

372

A Comparison Study of CO2 Exchange Within the Sahelian/Sudanian Zone of Africa  

NASA Astrophysics Data System (ADS)

The paper summarizes some of the major findings from CO2 flux campaigns ranging from Hapex Sahel (Niger 1992) to the presently ongoing Sudan experiment. In total four sites are selected, all with sandy soils, low annual rainfall (250-500 mm), sparse vegetation with a maximum volumetric water holding capacity of approximately 15 %. At all sites the net carbon exchange is measured by eddy covariance technique while the two major components, i.e. the soil respiration and the net carbon assimilation are estimated by combining measurements and modeling. For the soil respiration it is found that the fist rainfall events prior to the proper rainy season generate significance CO2-busts form the wet soil. In general it is found that the soil is strongly controlled by temperature and soil moisture but also available soil carbon should play a significant role. Using the annual maximum leaf area index as a proxy for the available carbon content it is found that the modeling of the soil respiration can be significantly improved . Except for the early seson peaks the maximum respiration level is around 3-4 Ýmol m-2 s-1 during the growing season decreasing to 2 Ýmol m-2 s-1 during senescence and reaching values close to zero during the dry season. For the CO2 assimilation there are large diurnal fluctuations with downward directed fluxes reaching a maximum level of -20 Ýmol m-2 s-1 and upward directed nighttime fluxes typically around 5 Ýmol m-2 s-l. The photosynthetic CO2 uptake is modeled by use of a mechanistic model based on published values of the Rubisco capacity. The combined photosynthesis /soil respiration model is used for estimating seasonal carbon budgets and to estimate the environmental control of the CO2 exchange. Besides radiation and LAI, the CO2 assimilation is found to depend on soil moisture and temperature The sensitivity analysis shows that at low soil moisture the assimilation is determined by the water stress function whereas for soil moisture contents above 8 vol. % there is only little control on the assimilation. The temperature dependence confirms that there is an optimal temperature at around 36 oC and the assimilation rate decreases for both increasing and decreasing temperature. It is finally discussed how the extent of the Sahelian/Sudanian zone makes it necessary to combine the flux station data with earth observation technique when aiming at regional estimates.

Soegaard, H.; Ardoe, J.

2007-12-01

373

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.

1997-01-01

374

Studies of sorbent\\/ion-exchange materials for the removal of radioactive strontium from liquid radioactive waste and high hardness groundwaters  

Microsoft Academic Search

Different sorbents were studied in terms of their full-scale applicability for radioactive strontium removal in low-level liquid radioactive waste (LLRW) management. The following types of sorbent\\/ion-exchange materials were investigated: natural zeolite–clinoptilolite, modified natural clinoptilolite, synthetic zeolites, new synthetic crystalline materials selective to strontium, ion-exchange resins, and modified fiber sorbents. Simulated solutions for experimental tests were prepared according to the composition

Dmitry V Marinin; Garrett N Brown

2000-01-01

375

3-D Numerical study on the correlation between variable inclined fin angles and thermal behavior in plate fin-tube heat exchanger  

Microsoft Academic Search

In this study, the heat transfer enhancement and pressure drop values of seven different fin angles with plain fin-tube heat exchangers were investigated. The numerical simulation of the fin-tube heat exchanger was performed by using a three dimensional (3-D) numerical computation technique. Therefore, a CFD computer code, the FLUENT was used to solve the equation for the heat transfer and

Hac? Mehmet ?ahin; Ali R?za Dal; E?ref Baysal

2007-01-01

376

TRENTA Facility for Trade-Off Studies Between Combined Electrolysis Catalytic Exchange and Cryogenic Distillation Processes  

SciTech Connect

One of the most used methods for tritium recovery from different sources of tritiated water is based on the combination between Combined Electrolysis Catalytic Exchange (CECE) and Cryogenic Distillation (CD) processes. The development, i.e. configuration, design and performance testing of critical components, of a tritium recovery system based on the combination CECE-CD is essential for both JET and ITER. For JET, a Water Detritiation System (WDS) is not only needed to process tritiated water which has already been accumulated from operation, but also for the tritiated water which will be generated during decommissioning. For ITER, the WDS is one of the key systems to control the tritium content in the effluents streams, to recover as much tritium as possible and consequently to minimize the impact on the environment. A cryogenic distillation facility with the aim to investigate the trade-off between CECE-CD, to validate different components and mathematical modelling software is current under development at Tritium Laboratory Karlsruhe (TLK) as an extension of the existing CECE facility.

Cristescu, I. [Forschungszentrum Karlsruhe (Germany); Cristescu, I.R. [Forschungszentrum Karlsruhe (Germany); Doerr, L. [Forschungszentrum Karlsruhe (Germany); Glugla, M. [Forschungszentrum Karlsruhe (Germany); Hellriegel, G. [Forschungszentrum Karlsruhe (Germany); Schaefer, P. [Forschungszentrum Karlsruhe (Germany); Welte, S. [Forschungszentrum Karlsruhe (Germany); Kveton, O.; Murdoch, D

2005-07-15

377

The Experimental Study of Atmospheric Stirling Engines Using Pin-Fin Arrays' Heat Exchangers  

NASA Astrophysics Data System (ADS)

This paper reports experimental results on two kinds of atmospheric Stirling engines that were designed and manufactured using a pin-fin array heat exchanger for the heater and cooler (abbreviated to “pin-fin Stirling engine” hereafter). The first one is a large ? type pin-fin Stirling engine with a 1.7-liter displacement volume and power piston volume. The heater consists of an aluminum circular disk with a diameter of 270mm and with large-scale pin-fin arrays carved into the surface. The maximum output reached 91W at a temperature difference of 330K, which is 36% of the scheduled value and 68% of the Kolin's cubic power law. The maximum thermal efficiency was estimated 4.2%. The second engine is an ? type pin-fin Stirling engine. Glass syringes were used for the piston-cylinder system and the Ross-yoke mechanism was used for the crank mechanism. By changing temperature difference, the characteristic of output torque in the large range was measured with a precision torque detector.

Isshiki, Seita; Sato, Hidekazu; Konno, Shoji; Shiraishi, Hiroaki; Isshiki, Naotsugu; Fujii, Iwane; Mizui, Hiroyuki

378

Study and development of sulfated zirconia based proton exchange fuel cell membranes  

NASA Astrophysics Data System (ADS)

With the increasing consumption of energy, fuel cells are among the most promising alternatives to fossil fuels, provided some technical challenges are overcome. Proton exchange membrane fuel cells (PEMFCs) have been investigated and improvements have been made, but the problem with NafionRTM, the main membrane for PEMFCs, has not been solved. NafionRTM restricts the membranes from operating at higher temperatures, thus preventing them from working in small electronics. The problem is to develop a novel fuel cell membrane that performs comparably to NafionRTM in PEMFCs. The membranes were fabricated by applying sulfated zirconia, via template wetting, to porous alumina membranes. The fabricated membranes showed a proton conductivity of 0.016 S/cm in comparison to the proton conductivity of Nafion RTM (0.05 S/cm). Both formic acid and methanol had a lower crossover flux through the sulfated zirconia membranes (formic acid- 2.89x10 -7 mols/cm2s and methanol-1.78x10-9 mols/cm2s) than through NafionRTM (formic acid-2.03x10 -8 mols/cm2s methanol-2.42x10-6 mols/cm 2s), indicating that a sulfated zirconia PEMFC may serve as a replacement for NafionRTM.

Kemp, Brittany Wilson

379

47 CFR 54.305 - Sale or transfer of exchanges.  

Code of Federal Regulations, 2011 CFR

...existing rural incumbent local exchange carrier study area, the rural incumbent local exchange carrier shall...a binding agreement to buy or acquire exchanges...available to rural incumbent local exchange carriers that...1) For carriers that buy or acquire...

2011-10-01

380

47 CFR 54.305 - Sale or transfer of exchanges.  

Code of Federal Regulations, 2010 CFR

...existing rural incumbent local exchange carrier study area, the rural incumbent local exchange carrier shall...a binding agreement to buy or acquire exchanges...available to rural incumbent local exchange carriers that...1) For carriers that buy or acquire...

2010-10-01

381

47 CFR 54.305 - Sale or transfer of exchanges.  

Code of Federal Regulations, 2014 CFR

...existing rural incumbent local exchange carrier study area, the rural incumbent local exchange carrier shall...a binding agreement to buy or acquire exchanges...available to rural incumbent local exchange carriers that...1) For carriers that buy or acquire...

2014-10-01

382

47 CFR 54.305 - Sale or transfer of exchanges.  

Code of Federal Regulations, 2012 CFR

...existing rural incumbent local exchange carrier study area, the rural incumbent local exchange carrier shall...a binding agreement to buy or acquire exchanges...available to rural incumbent local exchange carriers that...1) For carriers that buy or acquire...

2012-10-01

383

47 CFR 54.305 - Sale or transfer of exchanges.  

Code of Federal Regulations, 2013 CFR

...existing rural incumbent local exchange carrier study area, the rural incumbent local exchange carrier shall...a binding agreement to buy or acquire exchanges...available to rural incumbent local exchange carriers that...1) For carriers that buy or acquire...

2013-10-01

384

87Rb spin diffusion in ferroelectric RbH2PO4 studied by two dimensional exchange NMR  

PubMed

We separate the contributions of spectral spin diffusion and chemical exchange in the 2D exchange NMR spectra of 87Rb in the pseudo-spin glass Rb1-x(ND4)xD2PO4 by studying the 87Rb spin diffusion in the isostructural compound RbH2PO4 at 85K, where the system is frozen in the ferroelectric phase state. The fact that the spin-diffusion time (TSD) of a particular point in the 2D spectrum depends essentially on its distance from the diagonal, allowed, even for the case of an unresolved 2D spectrum, to determine TSD as a function of the frequency separation Delta over two orders of magnitude. In accordance with existing theories, T-1SD(Delta) was found to be of Gaussian shape. However, we found huge discrepancies between the calculated and the experimentally determined second moments. This failure of the theory is not understood at present. Copyright 1999 Academic Press. PMID:10329220

Cereghetti; Kind

1999-05-01

385

Orientation and electronic structure of ion exchanged dye molecules on mica: An X-ray absorption study  

SciTech Connect

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 the authors have investigated the orientation and electronic structure of crystal violet (CV) and malachite green (MG) on muscovite mica, prepared by immersing the substrates for extended periods into aqueous solutions of the dyes of various concentrations. The K{sup +} ions of the mica surface are replaced by the organic cations via ion exchange. X-ray photoelectron spectroscopy reveals that only one amino group is involved in the interaction of CV and MG with the muscovite surface, i.e., certain resonance structures are abolished upon adsorption. With near edge X-ray absorption fine structure spectroscopy a significant tilt angle with respect to the surface was found for all investigated species. A flat orientation, as has often been proposed before, can effectively be ruled out. Hence, results are in marked contrast to the often quoted orientation and suggest that the specific surface areas determined with dyes may, in general, be overestimated.

Fischer, D.; Caseri, W.R.; Haehner, G. [ETH Zuerich (Switzerland)] [ETH Zuerich (Switzerland)

1998-02-15

386

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

387

A pilot evaluation study of the Picture Exchange Communication System (PECS) for children with autistic spectrum disorders.  

PubMed

A pilot study was conducted to evaluate the effects of training teachers of children with autistic spectrum disorders (ASDs) in the use of the Picture Exchange Communication System (PECS). Thirty-four children with ASDs (29 boys and 5 girls) were selected from eight specialist schools. Teaching staff attended a 2 day PECS workshop and received six half-day visits from PECS consultants. Data on the children's use of PECS, spontaneous communication, and adaptive behaviour were collected before the study and at set times following the workshop. Significant, rapid increases were recorded in the level of PECS attained by the children, in their PECS vocabulary, and in their frequency of PECS use over time. Improvements in children's general level of communication were slower to occur. The majority of participants showed improvements in their ability to use PECS. The results are discussed in relation to the methodological and practical difficulties that arose during the project. PMID:14516062

Magiati, Iliana; Howlin, Patricia

2003-09-01

388

A numerical study of synchronization in the process of biochemical substance exchange in a diffusively coupled ring of cells  

NASA Astrophysics Data System (ADS)

In this paper we numerically investigate a model of a diffusively coupled ring of cells. To model the dynamics of individual cells we propose a map with cell affinity, which is a generalization of the logistic map. First, the basic features of a one-cell system are studied in terms of the Lyapunov exponent, Kolmogorov complexity and Sample Entropy. Second, the notion of observational heterarchy, which is a perpetual negotiation process between different levels of the description of a phenomenon, is reviewed. After these preliminaries, we study how the active coupling induced by the consideration of the observational heterarchy modifies the synchronization property of the model with N=100 cells. It is shown numerically that the active coupling enhances synchronization of biochemical substance exchange in several different conditions of cell affinity.

Mihailovi?, Dragutin; Balaž, Igor; Arseni?, Ilija

2013-04-01

389

Corporate derivatives and foreign exchange risk management : A case study of non-financial firms of Pakistan  

Microsoft Academic Search

Purpose – The purpose of this paper is to identify the factors affecting firms' decision to use foreign exchange (FX) derivative instruments by using the data of 86 non-financial firms listed on Karachi Stock Exchange for the period 2004-2007. Design\\/methodology\\/approach – Required data were collected from annual reports of listed firms of Karachi Stock Exchange. Non-parametric test was used to

Talat Afza; Atia Alam

2011-01-01

390

Equilibrium Studies of Sodium-Ammonium, Potassium-Ammonium, and Calcium-Ammonium Exchanges on Clinoptilolite Zeolite  

Microsoft Academic Search

Forward and reverse ion-exchange isotherms for the binary sodium-ammonium, potassium-ammonium, and calcium-ammonium systems on clinoptilolite have been measured in aqueous solutions at a total concentration of 0.1 equiv\\/dm and at 298 K. Prior to exchange experiments it was attempted to prepare homoionic forms of the zeolite by exhaustive treatments with appropriate salt solutions of cations. With no binary exchanges, full

M. A. Jama; H. Yuecel

1989-01-01

391

Exploring Knowledge Exchange between Senior and Future Leaders: A Grounded-Theory Study  

ERIC Educational Resources Information Center

A grounded theory study examined senior leaders methods of knowledge sharing with junior leaders in a small commercial mortgage company. The study was designed to develop an emergent theory to explain the cultural elements that influenced the methods leaders used to transfer knowledge to junior people. The study identified a systemic value of…

Gonzaga, Stephanie Young

2009-01-01

392

Study of suspending agents for gadolinium(III)-exchanged hectorite. An oral magnetic resonance imaging contrast agent  

SciTech Connect

Clays modified with paramagnetic ions have been shown to be effective magnetic resonance imaging contrast agents. The efficacy in part relies on the suspension of the small clay particles in aqueous solution. In this study a series of macromolecules were eveluated as suspending agents for Gd(III) ion exchanged hectorite clay in water. The room temperature relaxivities for the Gd-hectorite clays were enhanced by the addition of poly(ethylene oxide), poly(ethylene glycol), cyclodextrins, and cholic acid to aqueous suspensions. Additionally, there was no evidence of free Gd(III) in solution in the presence of these suspending agents. In contrast the combination of alginic acid or poly(sodium 4-styrenesulfonate) with the clays resulted in release of the Gd(III) into solution. Xanthan gum, which is often used as an emulsifier and stabilizer in food products, forms a viscous suspension but also reacts with free Gd(III) ions. 25 refs., 10 figs., 2 tabs.

Balkus, K.J. Jr.; Shi, J. [Univ. of Texas, Richardson, TX (United States)] [Univ. of Texas, Richardson, TX (United States)

1996-12-25

393

Web-based documentation system with exchange of DICOM RT for multicenter clinical studies in particle therapy  

NASA Astrophysics Data System (ADS)

Conducting clinical studies is rather difficult because of the large variety of voluminous datasets, different documentation styles, and various information systems, especially in radiation oncology. In this paper, we describe our development of a web-based documentation system with first approaches of automatic statistical analyses for transnational and multicenter clinical studies in particle therapy. It is possible to have immediate access to all patient information and exchange, store, process, and visualize text data, all types of DICOM images, especially DICOM RT, and any other multimedia data. Accessing the documentation system and submitting clinical data is possible for internal and external users (e.g. referring physicians from abroad, who are seeking the new technique of particle therapy for their patients). Thereby, security and privacy protection is ensured with the encrypted https protocol, client certificates, and an application gateway. Furthermore, all data can be pseudonymized. Integrated into the existing hospital environment, patient data is imported via various interfaces over HL7-messages and DICOM. Several further features replace manual input wherever possible and ensure data quality and entirety. With a form generator, studies can be individually designed to fit specific needs. By including all treated patients (also non-study patients), we gain the possibility for overall large-scale, retrospective analyses. Having recently begun documentation of our first six clinical studies, it has become apparent that the benefits lie in the simplification of research work, better study analyses quality and ultimately, the improvement of treatment concepts by evaluating the effectiveness of particle therapy.

Kessel, Kerstin A.; Bougatf, Nina; Bohn, Christian; Engelmann, Uwe; Oetzel, Dieter; Bendl, Rolf; Debus, Jürgen; Combs, Stephanie E.

2012-02-01

394

Experimental study of a constrained vapor bubble fin heat exchanger in the absence of external natural convection.  

PubMed

In preparation for a microgravity flight experiment on the International Space Station, a constrained vapor bubble fin heat exchanger (CVB) was operated both in a vacuum chamber and in air on Earth to evaluate the effect of the absence of external natural convection. The long-term objective is a general study of a high heat flux, low capillary pressure system with small viscous effects due to the relatively large 3 x 3 x 40 mm dimensions. The current CVB can be viewed as a large-scale version of a micro heat pipe with a large Bond number in the Earth environment but a small Bond number in microgravity. The walls of the CVB are quartz, to allow for image analysis of naturally occurring interference fringes that give the pressure field for liquid flow. The research is synergistic in that the study requires a microgravity environment to obtain a low Bond number and the space program needs thermal control systems, like the CVB, with a large characteristic dimension. In the absence of natural convection, operation of the CVB may be dominated by external radiative losses from its quartz surface. Therefore, an understanding of radiation from the quartz cell is required. All radiative exchange with the surroundings occurs from the outer surface of the CVB when the temperature range renders the quartz walls of the CVB optically thick (lambda > 4 microns). However, for electromagnetic radiation where lambda < 2 microns, the walls are transparent. Experimental results obtained for a cell charged with pentane are compared with those obtained for a dry cell. A numerical model was developed that successfully simulated the behavior and performance of the device observed experimentally. PMID:15644365

Basu, Sumita; Plawsky, Joel L; Wayner, Peter C

2004-11-01

395

A new approach to measuring protein backbone protection with high spatial resolution using H/D exchange and electron capture dissociation  

PubMed Central

Inadequate spatial resolution remains one of the most serious limitations of hydrogen/deuterium exchange mass spectrometry (HDX MS), especially when applied to larger proteins (over 30 kDa). Supplementing proteolytic fragmentation of the protein in solution with ion dissociation in the gas phase has been used successfully by several groups to obtain near-residue level resolution. However, the restrictions imposed by the LC/MS/MS mode of operation on the data acquisition time frame makes it difficult in many cases to obtain signal-to-noise ratio adequate for reliable assignment of the backbone amide protection levels at individual residues. This restriction is lifted in the present work by eliminating the LC separation step from the workflow and taking advantage of the high resolving power and dynamic range of a Fourier transform ion cyclotron resonance mass spectrometer (FT ICR MS). A residue-level resolution is demonstrated for a peptic fragment of a 37 kDa recombinant protein (N-lobe of human serum transferrin) using electron-capture dissociation as an ion fragmentation tool. The absence of hydrogen scrambling in the gas phase prior to ion dissociation is verified using redundant HDX MS data generated by FT ICR MS. The backbone protection pattern generated by direct HDX MS/MS is in excellent agreement with the known crystal structure of the protein, but also provides information on conformational dynamics, which is not available from the static X-ray structure. PMID:23978257

Abzalimov, Rinat R.; Bobst, Cedric E.; Kaltashov, Igor A.

2013-01-01

396

A new approach to measuring protein backbone protection with high spatial resolution using H/D exchange and electron capture dissociation.  

PubMed

Inadequate spatial resolution remains one of the most serious limitations of hydrogen/deuterium exchange-mass spectrometry (HDX-MS), especially when applied to larger proteins (over 30 kDa). Supplementing proteolytic fragmentation of the protein in solution with ion dissociation in the gas phase has been used successfully by several groups to obtain near-residue level resolution. However, the restrictions imposed by the LC-MS/MS mode of operation on the data acquisition time frame makes it difficult in many cases to obtain a signal-to-noise ratio adequate for reliable assignment of the backbone amide protection levels at individual residues. This restriction is lifted in the present work by eliminating the LC separation step from the workflow and taking advantage of the high resolving power and dynamic range of a Fourier transform ion cyclotron resonance-mass spectrometer (FTICR-MS). A residue-level resolution is demonstrated for a peptic fragment of a 37 kDa recombinant protein (N-lobe of human serum transferrin), using electron-capture dissociation as an ion fragmentation tool. The absence of hydrogen scrambling in the gas phase prior to ion dissociation is verified using redundant HDX-MS data generated by FTICR-MS. The backbone protection pattern generated by direct HDX-MS/MS is in excellent agreement with the known crystal structure of the protein but also provides information on conformational dynamics, which is not available from the static X-ray structure. PMID:23978257

Abzalimov, Rinat R; Bobst, Cedric E; Kaltashov, Igor A

2013-10-01

397

Cross-cultural exchange: How students can frustrate the aims of study abroad programmes  

Microsoft Academic Search

Readily accepting that study abroad programmes may have as many differing forms and aims as there are participating institutions, and that by no means all programmes include academic content in their goals, I would nevertheless maintain:1.that a sociological perspective is as necessary as the hitherto predominantly psychological approach in obtaining a balanced assessment of study abroad programmes;2.that a social interactionist

Leslie R. Barnes

1982-01-01

398

GO GLOBAL WITH UAA! UAA offers study abroad and exchange programs in  

E-print Network

individuals with international experience, intercultural competence, the ability to understand situations from OF INTERNATIONAL & INTERCULTURAL AFFAIRS & YOU Excited about the possibility of studying abroad? We hope so! You & Intercultural Affairs are here to help you. Attend a Study Abroad 101 session and then sched- ule an individual

Pantaleone, Jim

399

Hydrogen-exchange labeling study of the allosteric R-state to T-state equilibrium in methemoglobin  

NASA Astrophysics Data System (ADS)

Hydrogen-exchange labeling methods can be used to identify functionally important changes at positions all through a protein structure, can monitor the effect at these positions of structure changes anywhere in the protein, and can quantify these effects in terms of change in structural-stabilization free energy. These methods were used to study effects at two widely separated positions in human methemoglobin (metHb). The results show that the observed changes in hydrogen-exchange behavior reflect changes in the global R-state to T-state equilibrium, and specifically that stabilizing salt links at the ?-chain N-terminus and the ?-chain C-terminus are reformed in the R-T transition. The strong allosteric effector, inositol hexaphosphate (IHP), switches R-state methemoglobin to the T-state, but achieves a T/R equilibrium constant of only ? 3 (at pH=6.5, 0°C). Addition of the weaker effector, bezafibrate (Bzf), promotes this transition by an additional 0.7 kcal (T/R shifts to ? 12). Bzf alone is insufficient to cause the transition, indicating that R/T is 10 or more in stripped metHb under these conditions. However, R/T is small enough, not more than 103, to be reversed by the differential (T versus R) binding energy of IHP. The R-T transition caused by IHP and Bzf acting together can be reversed by some covalent modifications that sever the stabilizing salt links at the chain termini and thus favor transition back to the R-state.

McKinnie, R. E.; Englander, J. J.; Englander, S. W.

1991-12-01

400

The exchange rate – A shock-absorber or source of shocks? A study of four open economies  

Microsoft Academic Search

The paper provides SVAR estimates for the UK, Canada, Sweden and Denmark, making explicit a monetary policy reaction function and taking account of exchange rate targeting practices. It examines the role of the exchange rate as shock-absorber as opposed to a source of its own, and destabilizing, shocks. We find that in all countries but the UK, real shocks are

Michael Artis; Michael Ehrmann

2006-01-01

401

Three-dimensional tracer model study of atmospheric CO2 - Response to seasonal exchanges with the terrestrial biosphere  

Microsoft Academic Search

A three-dimensional tracer transport model is used to investigate the annual cycle of atmospheric CO2 concentration produced by seasonal exchanges with the terrestrial biosphere. The tracer model uses winds generated by a global general circulation model to advect and convect CO2; no explicit diffusion coefficients are employed. A biospheric exchange function constructed from a map of net primary productivity, and

I. Fung; K. Prentice; E. Matthews; J. Lerner; G. Russell

1983-01-01

402

Polyacrylamide thorium (IV) phosphate as an important lead selective fibrous ion exchanger: synthesis, characterization and removal study.  

PubMed

The objective of the present research was to synthesize, characterize and to investigate the removal efficiency of lead (II) ion from synthetic lead solution by a hybrid fibrous ion exchanger. In the present study polyacrylamide thorium (IV) phosphate was synthesized by co-precipitation method and was characterized using SEM, XRD, FTIR and TGA-DSC. To know the practical applicability, a detailed removal study of lead ion was carried out. The removal of lead was 52.9% under neutral condition, and using 0.4 g of adsorbent in 100 mL of lead solution having initial concentration of 100 mg/L. Adsorption kinetic study revealed that the adsorption process followed first order kinetics. Adsorption data were fitted to linearly transformed Langmuir isotherm with R(2) (correlation coefficient)>0.99. Thermodynamic parameters were also calculated to study the effect of temperature on the removal process. In order to understand the adsorption type, equilibrium data were tested with Dubinin-Radushkevich isotherm. The percentage removal was found to increase gradually with increase in pH and 99% removal was achieved at pH 10. The process was rapid and equilibrium was established within first 30 min. PMID:18242841

Islam, Mahamudur; Patel, Rajkishore

2008-08-15

403

Study the adsorption of sulfates by high cross-linked polystyrene divinylbenzene anion-exchange resin  

NASA Astrophysics Data System (ADS)

In response to rising concerns about the effect of sulfate on water quality, human health, and agriculture, many jurisdictions around the world are imposing tighter regulations for sulfate discharge. This is driving the need for environmental compliance in industries like mining, metal processing, pulp and paper, sewage treatment, and chemical manufacturing. The sulfate removal from synthetic water by high cross-linked polystyrene divinylbenzene resin was studied at batch experiments in this study. The effect of pH, contact time, sulfates concentration, and adsorbent dose on the sulfate sequestration was investigated. The optimum conditions were studied on Saline water as a case study. The results showed that with increasing of the absorbent amount; contact time, and pH improve the efficiency of sulfate removal. The maximum sulfates uptake was obtained in pH and contact time 3.0 and 120 min, respectively. Also, with increasing initial concentration of sulfates in water, the efficiency of sulfate removal decreased. The obtained results in this study were matched with Freundlich isotherm and pseudo-second-order kinetic. The maximum adsorption capacity (Qm) and constant rate were found 0.318 (mg/g) and 0.21 (mg/g.min), respectively. This study also showed that in the optimum conditions, the sulfate removal efficiency from Saline water by 0.1 mg/L sulfates was 65.64 %. Eventually, high cross-linked polystyrene divinylbenzene resin is recommended as a suitable and low cost absorbent to sulfate removal from aqueous solutions.

Fathy, Mahmoud; Moghny, Th. Abdel; Awadallah, Ahmed E.; El-Bellihi, Abdel-Hameed A.-A.

2014-11-01

404

Equilibrium studies of sodium-ammonium potassium-ammonium, and calcium-ammonium exchanges on clinoptilolite zeolite  

SciTech Connect

Forward and reverse ion-exchange isotherms for the binary sodium-ammonium, potassium-ammonium, and calcium-ammonium systems on clinoptilolite have been measured in aqueous solutions at a total concentration of 0.1 equiv/dm{sup 3} and at 298 K. Prior to exchange experiments it was attempted to prepare homoionic forms of the zeolite by exhaustive treatments with appropriate salt solutions of cations. With no binary exchanges, full replacement of the cation by the ammonium ion is observed, which conflicts with some earlier work on clinoptilolite. Despite the observed partial exchange levels, clinoptilolite shows a very high preference for ammonium ion over sodium and calcium but not over potassium. Thermodynamic values for the exchanges were calculated and compared with data in the literature. Both the selectivity and thermodynamic affinity sequence, in agreement with previous work reported in the literature, are K{sup +} > NH{sub 4}{sup +} > Na{sup +} > Ca{sup 2+}.

Jama, M.A.; Yuecel, H. (Middle East Technical Univ., Ankara (Turkey))

1989-12-01

405

Attenuated total reflection infrared studies of oleate and trioctylphosphine oxide ligand adsorption and exchange reactions on CdS quantum dot films.  

PubMed

Ligand exchange reactions at the surface of oleate- and trioctylphosphine oxide (TOPO)-capped CdS quantum dots have been studied with attenuated total reflection infrared (ATR-IR) spectroscopy, using thin films deposited from organic solvent suspensions. The oleate and trioctylphosphine capping ligands were found to form highly ordered and densely packed monolayers on the CdS surface. Adsorbed oleate is coordinated to CdS in a chelating bidentate manner through the carboxylate functional group, while adsorbed trioctylphosphine oxide is coordinated though the P=O functional group and appears to have numerous adsorption environments on the CdS surface. Exposure of such films to aqueous solution was found to cause partial delamination of the films from the ATR prism interface which was reversible upon redrying. Ligand exchange reactions on the oleate- and trioctylphosphine-capped CdS films were studied in situ at room temperature by allowing the films to be exposed to dilute aqueous solutions of thiol-containing ligands. Oleate and trioctylphosphine oxide are both strongly adsorbed to the CdS surface, and ligand exchange with monothiol-containing ligands has been found to be highly dependent upon experimental conditions, in particular pH, where exchange is only observed at solution pH where the exchanging ligand is uncharged. This is attributed to the inability of a charged ligand to penetrate the hydrophobic polymethylene layer on the CdS surface. PMID:18312011

Young, Aidan G; Al-Salim, Najeh; Green, David P; McQuillan, A James

2008-04-15

406

Heat exchanger  

SciTech Connect

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

Drury, C.R.

1988-02-02

407

Toward a Checklist for Exchange and Interpretation of Data froma Toxicology Study  

EPA Science Inventory

With the advent of toxicogenomics came the need to share data across interdisciplinary teams and to deposit data associated with publications into public data repositories. Within a single institution, many variables associated with a study are standardized, for instance diet, an...

408

A Longitudinal Study of Teachers' Professional Development through an International Exchange  

ERIC Educational Resources Information Center

The Teachers' International Professional Development (TIPD) Programme was launched by the British Council in 2000 in response to a Government Green Paper on teacher training. This provides opportunities for teachers to participate in international study visits to gain first-hand experience of good practice. As part of this programme, eighteen…

Purves, Ross; Jackson, Anita; Shaughnessy, Julie

2005-01-01

409

GO GLOBAL WITH UAA! UAA offers study abroad and exchange programs in  

E-print Network

, international experience, proficiency in languages, intercultural competence, and the ability to understand OF INTERNATIONAL & INTERCULTURAL AFFAIRS & YOU Excited about the possibility of studying abroad? We hope so! You and Intercultural Affair's GoGlobal e-mail list. Go to our website or send your request to uaa

Pantaleone, Jim

410

Ion-Exchange Chromatographic Studies of Some Physiologically Important Organic Acids On Impregnated Papers  

Microsoft Academic Search

The chromatographic behaviour of 15 physiologically important organic acids has been studied on papers impregnated with hydrated stannic oxide. the mechanism of separation is discussed. Numerous bioanalytically important binary and ternary separations were achieved by using various aqeous, non-a queous and mixed solvent systems.

S. K. Dabral; K. P. Singh Muktawat; J. P. Rawat

1989-01-01

411

LAB STUDY ON REGENERATION OF SPENT DOWEX 21K 16-20 MESH ION EXCHANGE RESIN  

SciTech Connect

Currently the effort to remove chromate from groundwater in the 100K and 100H Areas uses DOWEX 21K 16-20. This report addresses the procedure and results of a laboratory study for regeneration of the spent resin by sodium hydroxide, sulfuric acid, or sodium sulfate to determine if onsite regeneration by the Effluent Treatment Facility is a feasible option.

DUNCAN, J.B.

2007-01-24

412

Social Studies Now. This Halloween, Exchange the Hysterical for the Historical.  

ERIC Educational Resources Information Center

A social studies wax museum can teach elementary students facts as they celebrate Halloween. A primary activity has students determine historic scenes to include in the wax museum, practice their poses, and put on a Halloween show. An intermediate activity has students research historic events, interpret information, create backdrops and props,…

Lindquist, Tarry

1996-01-01

413

The use of native cation-exchange chromatography to study aggregation and phase separation of monoclonal antibodies  

PubMed Central

This study introduces a novel analytical approach for studying aggregation and phase separation of monoclonal antibodies (mAbs). The approach is based on using analytical scale cation-exchange chromatography (CEX) for measuring the loss of soluble monomer in the case of individual and mixed protein solutions. Native CEX outperforms traditional size-exclusion chromatography in separating complex protein mixtures, offering an easy way to assess mAb aggregation propensity. Different IgG1 and IgG2 molecules were tested individually and in mixtures consisting of up to four protein molecules. Antibody aggregation was induced by four different stress factors: high temperature, low pH, addition of fatty acids, and rigorous agitation. The extent of aggregation was determined from the amount of monomeric protein remaining in solution after stress. Consequently, it was possible to address the role of specific mAb regions in antibody aggregation by co-incubating Fab and Fc fragments with their respective full-length molecules. Our results revealed that the relative contribution of Fab and Fc regions in mAb aggregation is strongly dependent on pH and the stress factor applied. In addition, the CEX-based approach was used to study reversible protein precipitation due to phase separation, which demonstrated its use for a broader range of protein–protein association phenomena. In all cases, the role of Fab and Fc was clearly dissected, providing important information for engineering more stable mAb-based therapeutics. PMID:20512972

Chen, Shuang; Lau, Hollis; Brodsky, Yan; Kleemann, Gerd R; Latypov, Ramil F

2010-01-01

414

A new metal exchanged zeolite for a present environmental problem. An in-situ XAS study  

NASA Astrophysics Data System (ADS)

The medium pore zeolite, TNU-9, is prepared and studied for the selective catalytic reduction (SCR) of NO using C3H8 as the reducing agent. The catalytic activity of TNU-9 zeolites for the SCR is comparable to other known highly active zeolites but with the advantage of TNU-9 of having almost the same catalytic performance in the presence of H2O during reaction. The nature and behaviour of Cu and Co active sites contained in the TNU-9 catalysts have been studied under operation conditions using X-ray Absorption Spectroscopy (XAS) to understand the key parameters controlling the performance of this reaction.1 It was found that the well dispersed Cu and Co centres need to be in a mixed valence state to obtain good catalytic results for the SCR and that the catalytic performance is related to the topology of the TNU-9 itself.

Alonso-Escobar, C.; Franch-Martí, C.; Palomares, A. E.; Rey, F.; Guilera, G.

2013-04-01

415

Atmosphere-ocean ozone exchange: A global modeling study of biogeochemical, atmospheric, and waterside turbulence dependencies  

Microsoft Academic Search

The significance of the removal of tropospheric ozone by the oceans, covering ?2\\/3 of the Earth's surface, has only been addressed in a few studies involving water tank, aircraft, and tower flux measurements. On the basis of results from these few observations of the ozone dry deposition velocity (VdO3), atmospheric chemistry models generally apply an empirical, constant ocean uptake rate

L. Ganzeveld; D. Helmig; C. W. Fairall; J. Hare; A. Pozzer

2009-01-01

416

Studies on a frustrated Heisenberg spin chain with alternating ferromagnetic and antiferromagnetic exchanges  

NASA Astrophysics Data System (ADS)

We study Heisenberg spin-1/2 and spin-1 chains with alternating ferromagnetic \\left(J_{1}^{F}\\right) and antiferromagnetic \\left(J_{1}^{A}\\right) nearest-neighbor interactions and a ferromagnetic next-nearest-neighbor interaction \\left(J_{2}^{F}\\right) . In this model frustration is present due to the non-zero J_{2}^{F} . The model with site spin s behaves like a Haldane spin chain, with site spin 2s in the limit of vanishing J_{2}^{F} and large J_{1}^{F}/J_{1}^{A} . We show that the exact ground state of the model can be found along a line in the parameter space. For fixed J_{1}^{F} , the phase diagram in the space of J_{1}^{A}-J_{2}^{F} is determined using numerical techniques complemented by analytical calculations. A number of quantities, including the structure factor, energy gap, entanglement entropy and zero temperature magnetization, are studied to understand the complete phase diagram. An interesting and potentially important feature of this model is that it can exhibit a macroscopic magnetization jump in the presence of a magnetic field; we study this using an effective Hamiltonian.

Sahoo, Shaon; Durga Prasad Goli, V. M. L.; Sen, Diptiman; Ramasesha, S.

2014-07-01

417

Experimental study of work exchange with a granular gas: the viewpoint of the Fluctuation Theorem  

E-print Network

This article reports on an experimental study of the fluctuations of energy flux between a granular gas and a small driven harmonic oscillator. The DC-motor driving this system is used simultaneously as actuator and probe. The statistics of work fluctuations at controlled forcing, between the motor and the gas are examined from the viewpoint of the Fluctuation Theorem. A characteristic energy $E_c$ of the granular gas, is obtained from this relation between the probabilities of an event and its reversal.

Antoine Naert

2011-12-09

418

Comprehensive Study of the Solubility, Thermochemistry, Ion Exchange, and Precipitation Kinetics of NO3 Cancrinite and NO33 Sodalite  

SciTech Connect

The precipitation of aluminosilicate phases from caustic nuclear wastes has proven to be problematic in a number of processes including radionuclide separations (cementation of columns by aluminosilicate phases), tank emptying (aluminosilicate tank heels), and condensation of wastes in evaporators (aluminosilicate precipitates in the evaporators, providing nucleation sites for growth of critical masses of radioactive actinide salts). In a collaboration between SNL and UCD, we have investigated why and how these phases form, and which conditions favor the formation of which phases. These studies have involved synthesis and characterization of aluminosilicate phases formed using a variety of synthesis techniques, kinetics of precipitation, structural investigations of aluminosilicate phases, thermodynamic calculations of aluminosilicate solubility, calorimetric studies of aluminosilicate precipitation, and a limited investigation of radionuclide partitioning and ion exchange processes (involving typical tank fluid chemistries and these materials). The predominant phases that are observed in the aluminosilicate precipitates from basic tanks wastes (i.e. Hanford, Savannah River Site ''SRS'' wastes) are the salt enclathrated zeolites: sodium nitrate, sodium carbonate and sodium hydroxide sodalite and cancrinite. These phases precipitate readily from the high ionic strength, highly basic solutions at ambient temperatures as well as at elevated temperatures, with or without the presence of an external Al and Si source (both are contained in the waste solutions), and upon interactions with reactive soil components such as clays.

Navrotsky, Alexandra; Liu, Qinyuan

2004-12-01

419

A QUANTUM MECHANICAL STUDY OF STRUCTURAL AND ELECTRONIC DILUTION EFFECTS IN PARAMAGNETIC CHEMICAL EXCHANGE SATURATION TRANSFER AGENTS  

PubMed Central

We present a computational study of the effect of chemical modifications of the meta and para substituents in the coordinating pendant arm of a modified 1,4,7,10-tetraazacyclododecane-N, N’, N?, N?-tetraamide (DOTAM) ligand on the Chemical Exchange Saturation Transfer (CEST) signal. Magnetic Resonance Imaging (MRI) is currently one of the most widely used techniques available. MRI has led to a new class of pharmaceuticals termed “imagining” or “contrast” agents. These agents usually work by incorporating lanthanide metals such as Gadolinium (Gd) and Europium (Eu). This allows the contrast agents to take advantage of the paramagnetic properties of the metals, which in turn enhances the signal detectable by MRI. The effect of simple electron-withdrawing (e.g., nitro) and electron-donating (e.g., methyl) substituents chemically attached to a modified chelate arm (pendant arm) is quantified by charge transfer interactions in the coordinated water-chelate system computed from quantum mechanics. This study attempts to reveal the origin of the substituent effect on the CEST signal and the electronic structure of the complex. We find that the extent of Charge Transfer (CT) depends on orbital orientations and overlaps. However, CT interactions occur simultaneously from all arms, which causes a dilution effect with respect to the pendant arm. PMID:25485283

Miller, Whelton A.; Moore, Preston B.

2014-01-01

420

Study of Mesoscale Eddies in the Gulf of Lion and their role in the coastal-offshore exchanges.  

NASA Astrophysics Data System (ADS)

The main objective of LAgrangian Transport EXperiment (LATEX) project (2008-2011) is to study the influence of mesoscale structures on shelf-offshore exchanges in the Gulf of Lion (GoL). The LATEX strategy combines use of data from Lagrangian drifters, satellite images and hull-mounted ADCP data with numerical modeling. In this work, we simulate the mesoscale structures, occurring at the interface between the continental slope and the coastal margin in the GoL, by using a realistic numerical model. Numerical studies show a clear influence of mesoscale eddies on matter and energies transfers between the coastal zone and open sea. The features of the eddies such as their size, position and behaviour issued from the numerical modeling help us set up the sampling strategy of the cruises. The in situ measurements allow us to validate the numerical results and furthermore, combined with the modeling results, to well understand the eddies's dynamics. A numerical Lagrangian diagnostic tool is applied to analyze the model outputs. Qualitative and quantitative simulations are made in order to evaluate the eddies' potential impact on the coastal-offshore transfer of matter and energy.

Hu, Z. Y.; Doglioli, A. M.; Petrenko, A. A.; Compbell, R.; Diaz, F.; Dekeyser, I.

2010-05-01

421

13-atom metallic clusters studied by density functional theory: Dependence on exchange-correlation approximations and pseudopotentials  

NASA Astrophysics Data System (ADS)

In this study, the 13-atom cluster structures of alkaline metals, alkaline-earth metals, boron group metals, carbon group metals, and 3d , 4d , and 5d transition metals in the periodic table are investigated by density functional theory with three kinds of exchange-correlation (XC) functionals: (i) local-density approximation (LDA); (ii) generalized gradient approximation (GGA) with Perdew-Wang 91; and (iii) generalized gradient approximation with Perdew-Burke-Ernzerhof. The dependence on pseudopotentials (PPs) with and without semicore electrons is also examined. The relative energies of five selected high-symmetry three-dimensional and four low-symmetry layer-type isomers for each element of interest are calculated and studied. Among the 44 metallic 13-atom clusters, our results show that the two GGA XC functionals have a great consistency; LDA and GGA results also reveal a great consistency, apart from the Cr, Mn, Fe, Co, Ni, and Rh 13-atom clusters, for which the results show a significant difference. Meanwhile, for most of the elements, the calculations with and without semicore PPs also produce consistent results, except for Cr, Mo, and V, which require a careful treatment of semicore states in the PPs.

Chou, J. P.; Chen, H. Y. T.; Hsing, C. R.; Chang, C. M.; Cheng, C.; Wei, C. M.

2009-10-01

422

The ESA SMOS+SOS Project: Oceanography using SMOS for innovative air-sea exchange studies  

NASA Astrophysics Data System (ADS)

We report on the work plan of the SMOS+Surface Ocean Salinity and Synergy (SMOS+SOS) project. SMOS+SOS is funded through the Support to Science Element (STSE) component of the European Space Agency's (ESA) Earth Observation Envelope Programme. The SMOS+SOS consortium consists of four organisations namely the National Oceanography Centre (UK), the LOCEAN/IFREMER/CATDS research team (France), the Met Office (UK) and Satellite Oceanographic Consultants Ltd (UK). The end of the SMOS+SOS project will be marked by a final open workshop most likely hosted by the UK Met Office in September/October 2014. The project is concerned with demonstrating the performance and scientific value of SMOS Sea Surface Salinity (SSS) products through a number of well-defined case studies. The case studies include: Amazon/Orinoco plumes (freshwater outflow); Agulhas and Gulf Stream (strong water mass boundary); Tropical Pacific/Atlantic (strong precipitation regime); sub-tropical North Atlantic (ie SPURS; strong evaporative regime); and Equatorial Pacific (equatorial upwelling). With SMOS measuring the SSS in the top cm of the ocean, validating SMOS against in situ salinity data taken typically at a few meters depth introduces assumptions about the vertical structure of salinity in the upper ocean. To address these issues, the project will examine and quantify discrepancies between SMOS and in situ surface salinity data at various depths in different regions characterised by strong precipitation or evaporation regimes. Equally, data editing and spatio-temporal averaging play a central role in determining the quality, errors and correlations in SMOS SSS data. The project will explore various processing and spatio-temporal averaging choices to define the SMOS SSS products that best address the needs of the oceanographic and data assimilation user community. One key aspect of this project is to determine how one can achieve useful accuracy/uncertainty in SSS without jeopardising SMOS's ability to capture rapidly-varying or small scale features such as rain cells or the mesoscale variability associated with river plumes and major western boundary currents. Finally, the study explores the ability of SMOS SSS to provide insights into new oceanographic processes when used in synergy with other data. Hence, synergy with Aquarius will be used to seek evidence of the possible impact of diurnal warming on the SMOS SSS data, and to explore differences in the salinity signatures of Tropical Instability Waves observed in the Pacific with SMOS and Aquarius.

Banks, Chris; Gommenginger, Christine; Boutin, Jacqueline; Reul, Nicolas; Martin, Matthew; Ash, Ellis; Reverdin, Gilles; Donlon, Craig

2013-04-01

423

Microtube strip heat exchanger  

NASA Astrophysics Data System (ADS)

Doty Scientific (DSI) believes their microtube-strip heat exchanger will contribute significantly to the following: (1) the closed Brayton cycles being pursued at MIT, NASA, and elsewhere; (2) reverse Brayton cycle cryocoolers, currently being investigated by NASA for space missions, being applied to MRI superconducting magnets; and (3) high-efficiency cryogenic gas separation schemes for CO2 removal from exhaust stacks. The goal of this current study is to show the potential for substantial progress in high-effectiveness, low-cost, gas-to-gas heat exchangers for diverse applications at temperatures from below 100 K to above 1000 K. To date, the highest effectiveness measured is about 98 percent and relative pressure drops below 0.1 percent with a specific conductance of about 45 W/kgK are reported. During the pre-award period DSI built and tested a 3-module heat exchanger bank using 103-tube microtube strip (MTS) modules. To add to their analytical capabilities, DSI has acquired computational fluid dynamics (CFD) software. This report describes the pre-award work and the status of the ten tasks of the current project, which are: analyze flow distribution and thermal stresses within individual modules; design a heat exchanger bank of ten modules with 400 microtube per module; obtain production quality tubestrip die and AISI 304 tubestrips; obtain production quality microtubing; construct revised MTS heat exchanger; construct dies and fixtures for prototype heat exchanger; construct 100 MTS modules; assemble 8 to 10 prototype MTS heat exchangers; test prototype MTS heat exchanger; and verify test through independent means.

Doty, F. D.

1990-12-01

424

Experimental and numerical study of a proton exchange membrane electrolyzer for hydrogen production  

NASA Astrophysics Data System (ADS)

Hydrogen as a fuel source has received attention from researchers globally due to its potential to replace fossil based fuels for energy production. Research is being performed on hydrogen production, storage and utilization methods to make its use economically feasible relative to current energy sources. The PEM electrolyzer is used to produce hydrogen and oxygen using water and electricity. Focus of our study is to provide a benchmark experiment and numerical model of a single cell electrolyzer that can assist in improving the current state of understanding of this system. Parametric analysis of an experimental cell was performed to understand the effect of operating parameters of electrolyzer on its performance. A CFD model was developed to model the physics of electrolyzer. The model was validated with the experiment; the information presented here can be used as a tool to improve the design from thermo-fluid aspects of the electrolyzer.

Deshmukh, Sachin S.

425

Talk, trust and time: a longitudinal study evaluating knowledge translation and exchange processes for research on violence against women  

PubMed Central

Background Violence against women (VAW) is a major public health problem. Translation of VAW research to policy and practice is an area that remains understudied, but provides the opportunity to examine knowledge translation and exchange (KTE) processes in a complex, multi-stakeholder context. In a series of studies including two randomized trials, the McMaster University VAW Research Program studied one key research gap: evidence about the effectiveness of screening women for exposure to intimate partner violence. This project developed and evaluated KTE strategies to share research findings with policymakers, health and community service providers, and women's advocates. Methods A longitudinal cross-sectional design, applying concurrent mixed data collection methods (surveys, interviews, and focus groups), was used to evaluate the utility of specific KTE strategies, including a series of workshops and a day-long Family Violence Knowledge Exchange Forum, on research sharing, uptake, and use. Results Participants valued the opportunity to meet with researchers, provide feedback on key messages, and make personal connections with other stakeholders. A number of factors specific to the knowledge itself, stakeholders' contexts, and the nature of the knowledge gap being addressed influenced the uptake, sharing, and use of the research. The types of knowledge use changed across time, and were specifically related to both the types of decisions being made, and to stage of decision making; most reported use was conceptual or symbolic, with few examples of instrumental use. Participants did report actively sharing the research findings with their own networks. Further examination of these second-order knowledge-sharing processes is required, including development of appropriate methods and measures for its assessment. Some participants reported that they would not use the research evidence in their decision making when it contradicted professional experiences, while others used it to support apparently contradictory positions. The online wiki-based 'community of interest' requested by participants was not used. Conclusions Mobilizing knowledge in the area of VAW practice and policy is complex and resource-intensive, and must acknowledge and respect the values of identified knowledge users, while balancing the objectivity of the research and researchers. This paper provides important lessons learned about these processes, including attending to the potential unintended consequences of knowledge sharing. PMID:21896170

2011-01-01

426

Measuring ligand exchange on the surface of gold nanoparticles: A study of competitive binding of ligands utilizing fluorescent resonance energy transfer  

NASA Astrophysics Data System (ADS)

This study was conducted to track ligand exchange on the surface of metallic nanoparticles in order obtain a better understanding of binding strength of various functional groups. This study develops groundwork for further understanding ligand exchange as nanoparticles transition from engineered to natural systems. A problem exists in knowing the fate of these particles if they are released into natural systems, by accident or with intent. To gain a better understanding of what may occur we look at the binding strength of different ligands. This is done to gain knowledge of the possibility of displacement of ligands occurring in the environment. In order to monitor the binding strength of different ligands a new characterization technique utilizing the phenomena of Fluorescent Resonance Energy Transfer (FRET) is employed. This technique utilizes the quenching properties of gold nanoparticles and fluorescent-labeled ligands to monitor competitive binding between two ligands. The use of fluorescence allows for a sensitive measurement (on the nanomole scale) of ligand exchange on the surface of gold nanoparticles. This study was conducted in three different parts. The first one was conducted to monitor the competitive binding between bound ligands and incoming mono-functional ligands. This was accomplished by tagging five different functional ligands with a fluorescein-dye. As the fluorescein-terminated ligands exchange on the surface of gold nanoparticles a change in fluorescence intensity is observed. The second study was conducted in the same manner as the first, however this study monitored the effect of bi-functional ligands verse mono-functional ligands as well to monitor concentration effects. The third study conducted was done using a two-dye system. In these studies both the incoming and bound ligand were tagged with a fluorescent-dye. This was done to monitor direct exchange of ligands.

D'Unger, Daniel W.

427

Law on Exchange InternationalExchangeProgram  

E-print Network

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

Viglas, Anastasios

428

Comparative studies of land-atmosphere energy exchange in high and low Arctic tundra ecosystems  

NASA Astrophysics Data System (ADS)

The energy balance of arctic terrestrial ecosystems is of crucial importance to understand future climate change in high northern latitudes. Despite a growing interest in the Arctic local measurements and observations of climate characteristics are still scarce. Therefore, we present first results of comparative short- and long-term eddy covariance and energy balance measurements of high and low Arctic terrestrial ecosystems in Greenland. The study area covers high Arctic tundra heath and fen ecosystems in Zackenberg (Northeast Greenland National Park, 74°30'N, 21°00'W) and low Arctic terrestrial ecosystems in the Kobbefjord area close to the city of Nuuk (West Greenland, 64°07'N, 51°21'W). By using a mobile eddy covariance and energy balance tower we collected data during late winter (April 2012), early summer (June/July 2012) and late summer (August 2012). Mobile eddy covariance and energy balance measurements during late winter in Zackenberg focus on the energy balance of undisturbed snow covered surfaces with variable snow depth and snow layer structure. Data collection on thin snow layers with disturbed surfaces and exposed vegetation also show the impact of Muskox cratering on the surface energy balance. Measurements during early summer in the Kobbefjord area were conducted on characteristic bare soils with scattered cushion plants, on grasslands with sedge vegetation and on shrub vegetation up to 100 cm in height. Late summer measurements of energy balance and eddy covariance in the Zackenberg valley focus on transect measurements of energy balance components and active layer thickness of adjacent high arctic fen and heath ecosystems. In addition to the short-term mobile measurements we use and analyse data sets from permanent stations monitoring eddy covariance and energy balance on heath and fen sites in both high and low Arctic environments. Long-term measurements provide continuous data since early April 2012 and in this study we compare our mobile measurements with this long-term energy balance data sets. First results of albedo characteristics during late winter show distinct differences among the measured snow surfaces. Albedo during summer varies considerably within and between the high and low Arctic tundra sites. Further results of energy flux partitioning and energy balance closure will be presented and discussed at the conference.

Stiegler, Christian; Lindroth, Anders; Lund, Magnus; Tamstorf, Mikkel P.

2013-04-01

429

Non-intrusive optical study of gas and its exchange in human maxillary sinuses  

NASA Astrophysics Data System (ADS)

We demonstrate a novel non-intrusive technique based on tunable diode laser absorption spectroscopy to investigate human maxillary sinuses in vivo. The technique relies on the fact that free gases have much sharper absorption features (typical a few GHz) than the surrounding tissue. Molecular oxygen was detected at 760 nm. Volunteers have been investigated by injecting near-infrared light fibre-optically in contact with the palate inside the mouth. The multiply scattered light was detected externally by a handheld probe on and around the cheek bone. A significant signal difference in oxygen imprint was observed when comparing volunteers with widely different anamnesis regarding maxillary sinus status. Control measurements through the hand and through the cheek below the cheekbone were also performed to investigate any possible oxygen offset in the setup. These provided a consistently non-detectable signal level. The passages between the nasal cavity and the maxillary sinuses were also non-intrusively optically studied, to the best of our knowledge for the first time. These measurements provide information on the channel conductivity which may prove useful in facial sinus diagnostics. The results suggest that a clinical trial together with an ear-nose-throat (ENT) clinic should be carried out to investigate the clinical use of the new technique.

Persson, L.; Andersson, M.; Svensson, T.; Cassel-Engquist, M.; Svanberg, K.; Svanberg, S.

2007-07-01

430

A comparative study of alginate beads and an ion-exchange resin for the removal of heavy metals from a metal plating effluent  

Microsoft Academic Search

The capacity of dry protonated calcium alginate beads to sorb metals from an industrial effluent was studied and compared with a commercial ion-exchange resin (Lewatit TP 207). Both sorbents decreased zinc, nickel, iron and calcium concentrations in the effluent, and released sodium during treatment. Alginate beads removed lower amounts of heavy metals than the resin, but exhibited faster uptake kinetics.