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1

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

2

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

PubMed

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

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

2012-12-01

3

Using Hydrogen/Deuterium Exchange Mass Spectrometry to Study Conformational Changes in Granulocyte Colony Stimulating Factor upon PEGylation  

PubMed Central

PEGylation is the covalent attachment of polyethylene glycol to proteins, and it can be used to alter immunogenicity, circulating half life and other properties of therapeutic proteins. To determine the impact of PEGylation on protein conformation, we applied hydrogen/deuterium exchange mass spectrometry (HDX MS) to analyze Granulocyte Colony Stimulating Factor (G-CSF) upon PEGylation as a model system. The combined use of HDX automation technology and data analysis software allowed reproducible and robust measurements of the deuterium incorporation levels for peptic peptides of both PEGylated and non-PEGylated G-CSF. The results indicated that significant differences in deuterium incorporation were induced by PEGylation of G-CSF, although the overall changes observed were quite small. PEGylation did not result in gross conformational rearrangement of G-CSF. The data complexity often encountered in HDX MS measurements was greatly reduced though a data processing and presentation format designed to facilitate the comparison process. This study demonstrates the practical utility of HDX MS for comparability studies, process monitoring and protein therapeutic characterization in the biopharmaceutical industry. PMID:22227798

Wei, Hui; Ahn, Joomi; Yu, Ying Qing; Tymiak, Adrienne; Engen, John R.; Chen, Guodong

2012-01-01

4

Using hydrogen/deuterium exchange mass spectrometry to study conformational changes in granulocyte colony stimulating factor upon PEGylation.  

PubMed

PEGylation is the covalent attachment of polyethylene glycol to proteins, and it can be used to alter immunogenicity, circulating half life and other properties of therapeutic proteins. To determine the impact of PEGylation on protein conformation, we applied hydrogen/deuterium exchange mass spectrometry (HDX MS) to analyze granulocyte colony stimulating factor (G-CSF) upon PEGylation as a model system. The combined use of HDX automation technology and data analysis software allowed reproducible and robust measurements of the deuterium incorporation levels for peptic peptides of both PEGylated and non-PEGylated G-CSF. The results indicated that significant differences in deuterium incorporation were induced by PEGylation of G-CSF, although the overall changes observed were quite small. PEGylation did not result in gross conformational rearrangement of G-CSF. The data complexity often encountered in HDX MS measurements was greatly reduced through a data processing and presentation format designed to facilitate the comparison process. This study demonstrates the practical utility of HDX MS for comparability studies, process monitoring, and protein therapeutic characterization in the biopharmaceutical industry. PMID:22227798

Wei, Hui; Ahn, Joomi; Yu, Ying Qing; Tymiak, Adrienne; Engen, John R; Chen, Guodong

2012-03-01

5

Using Hydrogen/Deuterium Exchange Mass Spectrometry to Study Conformational Changes in Granulocyte Colony Stimulating Factor upon PEGylation  

NASA Astrophysics Data System (ADS)

PEGylation is the covalent attachment of polyethylene glycol to proteins, and it can be used to alter immunogenicity, circulating half life and other properties of therapeutic proteins. To determine the impact of PEGylation on protein conformation, we applied hydrogen/deuterium exchange mass spectrometry (HDX MS) to analyze granulocyte colony stimulating factor (G-CSF) upon PEGylation as a model system. The combined use of HDX automation technology and data analysis software allowed reproducible and robust measurements of the deuterium incorporation levels for peptic peptides of both PEGylated and non-PEGylated G-CSF. The results indicated that significant differences in deuterium incorporation were induced by PEGylation of G-CSF, although the overall changes observed were quite small. PEGylation did not result in gross conformational rearrangement of G-CSF. The data complexity often encountered in HDX MS measurements was greatly reduced through a data processing and presentation format designed to facilitate the comparison process. This study demonstrates the practical utility of HDX MS for comparability studies, process monitoring, and protein therapeutic characterization in the biopharmaceutical industry.

Wei, Hui; Ahn, Joomi; Yu, Ying Qing; Tymiak, Adrienne; Engen, John R.; Chen, Guodong

2012-03-01

6

Difference in fibril core stability between two tau four-repeat domain proteins: a hydrogen-deuterium exchange coupled to mass spectrometry study.  

PubMed

One of the signatures of Alzheimer's disease and tauopathies is fibrillization of the microtubule-associated protein tau. The purpose of this study was to compare the high-resolution structure of fibrils formed by two different tau four-repeat domain constructs, tau4RD and tauK18, using hydrogen-deuterium exchange coupled to mass spectrometry as a tool. While the two fibrils are found to be constructed on similar structural principles, the tauK18 fibril has a slightly more stable core. This difference in fibril core stability appears to be reflective of the mechanistic differences in the aggregation pathways of the two proteins. PMID:24256615

Ramachandran, Gayathri; Udgaonkar, Jayant B

2013-12-10

7

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

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

Dynamics of hydrogen-deuterium exchange in Chlamydomonas centrin.  

PubMed

Chlamydomonas reinhardtii centrin is a 169-amino acid residue calcium binding protein belonging to the EF-hand protein superfamily. Centrin is associated with the microtubule organizing center (MTOC) in all eukaryotes, and in Chlamydomonas, centrin is a component of the flagellar basal body apparatus. Recombinant full-length centrin, calmodulin, and terminal domain fragments [Ccen-N (residues 1-94) and Ccen-C (residues 99-169)] were used to examine hydrogen-deuterium (H --> D) exchange dynamics using combined attenuated total reflectance (ATR) Fourier transform-infrared (FT-IR) spectroscopy, curve fit, and two-dimensional correlation analysis. Analysis of the Ccen-N and Ccen-C fragments allowed separation of domain specific solvent exchange events and together with analysis of the full-length proteins provides novel insight into domain accessibility to the aqueous environment and the internal dynamics of the protein. PMID:15709753

Ortiz, Mildred; Sanoguet, Zuleika; Hu, Haitao; Chazin, Walter J; McMurray, Cynthia T; McMurray, Cynthia; Salisbury, Jeffrey L; Pastrana-Rios, Belinda

2005-02-22

10

A Hydrogen-Deuterium Exchange Study on Nickel-based Binary-Ternary Amorphous and Crystalline Membranes  

NASA Astrophysics Data System (ADS)

Hydrogen is a major role player in current global sustainable energy scenario. Research around the world is carried out to harness hydrogen from all possible sources. One of these sources is water gas shift reaction after the coal gasification process. Sustainable infrastructure can be viable in countries like USA and Australia, making this process viable. Various methods are used to harness this hydrogen from the water gas. One of these methods is the use of inorganic membranes based on Pd, Ag, Ni, Zr and other transition metals. Pd addition to the membranes makes the membranes more expensive for commercial use. Various bulk properties like hydrogen permeation and absorption are studied on Pd and Pd-based alloys. Alternate alloys based on Ni, V, Ta etc are being studied to substitute the use of Pd making this technology more cost efficient. A current balance in research in this area is fund to exist by coating the non-precious metal membranes with Pd to improve the surface interaction with hydrogen. The nature of membranes used for hydrogen separation is important aspect for the overall performance. Crystalline materials provide better bulk properties, however, are not durable under high temperature and hydrogen pressure. In this research, non-Pd coated Ni-based amorphous membranes were made by melt spin technique, which have been studied for their surface properties. Gas phase H2-D2 exchange reaction has been carried out on the membrane surface. This provides a measure of catalytic activity of the above mentioned membranes. More studies included the crystallographic phase change determination, bulk hydrogen solubility measurements, surface conduction measurements and surface morphological studies. During this research, it has been observed that crystalline materials provide more surface activity for hydrogen than their amorphous counterparts. Ni64Zr36 alloy has been shown to exhibit similar kinetic rates as metallic Ni. Also, microkinetic analysis was performed to determine the heat of hydrogen absorption and desorption on the alloy surface. Electrochemical Impedance Spectroscopy was conducted on the membranes to determine the surface resistance and it was found that Ni64Zr36 as-spun ribbon displayed highest resistance while Ni60Ta20Zr20 showed lowest resistance. Absorption studies on Ni60V 40 binary alloy and Ni60V20Zr20 ternary alloy indicated that the addition of Zr to these non-coated alloys increased the hydrogen solubility in the bulk. SEM and TEM analyses showed the presence of possible nano crystalline phases in Ni64Zr36 membrane. XRD and SEM studies conducted on post treated samples showed the possible phase segregation of Ni and ZrO2. Ni60Nb40 did not show any phase transformations after hydrogen heat treated unlike its ternary composition, Ni60Nb20Zr20. It is noteworthy to mention that bubbles were observed during SEM on Ni 64Zr36 post-treated sample on the surface due to possible hydrogen trapping and subsequent release of hydrogen gas.

Adibhatla, Anasuya

11

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

12

Quantifying hydrogen-deuterium exchange of meteoritic dicarboxylic acids during aqueous extraction  

NASA Astrophysics Data System (ADS)

Hydrogen isotope ratios of organic compounds in carbonaceous chondrites provide critical information about their origins and evolutionary history. However, because many of these compounds are obtained by aqueous extraction, the degree of hydrogen-deuterium (H/D) exchange that occurs during the process needs to be quantitatively evaluated. This study uses compound- specific hydrogen isotopic analysis to quantify the H/D exchange during aqueous extraction. Three common meteoritic dicarboxylic acids (succinic, glutaric, and 2-methyl glutaric acids) were refluxed under conditions simulating the extraction process. Changes in D values of the dicarboxylic acids were measured following the reflux experiments. A pseudo-first order rate law was used to model the H/D exchange rates which were then used to calculate the isotope exchange resulting from aqueous extraction. The degree of H/D exchange varies as a result of differences in molecular structure, the alkalinity of the extraction solution and presence/absence of meteorite powder. However, our model indicates that succinic, glutaric, and 2-methyl glutaric acids with a D of 1800 would experience isotope changes of 38, 10, and 6, respectively during the extraction process. Therefore, the overall change in D values of the dicarboxylic acids during the aqueous extraction process is negligible. We also demonstrate that H/D exchange occurs on the chiral -carbon in 2-methyl glutaric acid. The results suggest that the racemic mixture of 2-methyl glutaric acid in the Tagish Lake meteorite could result from post-synthesis aqueous alteration. The approach employed in this study can also be used to quantify H/D exchange for other important meteoritic compounds such as amino acids.

Fuller, M.; Huang, Y.

2003-03-01

13

Analysis of overlapped and noisy hydrogen/deuterium exchange mass spectra.  

PubMed

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. PMID:24018862

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

2013-12-01

14

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

15

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

16

Hydrogen/deuterium exchange of cross-linkable ?-amino acid derivatives in deuterated triflic acid.  

PubMed

In this paper we report here a hydrogen/deuterium exchange (H/D exchange) of cross-linkable ?-amino acid derivatives with deuterated trifluoromethanesulfonic acid (TfOD). H/D exchange with TfOD was easily applied to o-catechol containing phenylalanine (DOPA) within an hour. A partial H/D exchange was observed for trifluoromethyldiazirinyl (TFMD) phenylalanine derivatives. N-Acetyl-protected natural aromatic ?-amino acids (Tyr and Trp) were more effective in H/D exchange than unprotected ones. The N-acetylated TFMD phenylalanine derivative afforded slightly higher H/D exchange than unprotected derivatives. An effective post-deuteration method for cross-linkable ?-amino acid derivatives will be useful for the analysis of biological functions of bioactive peptides and proteins by mass spectrometry. PMID:25229846

Wang, Lei; Murai, Yuta; Yoshida, Takuma; Okamoto, Masashi; Masuda, Katsuyoshi; Sakihama, Yasuko; Hashidoko, Yasuyuki; Hatanaka, Yasumaru; Hashimoto, Makoto

2014-07-01

17

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

2014-01-01

18

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

19

Nepenthesin from Monkey Cups for Hydrogen/Deuterium Exchange Mass Spectrometry*  

PubMed Central

Studies of protein dynamics, structure and interactions using hydrogen/deuterium exchange mass spectrometry (HDX-MS) have sharply increased over the past 5–10 years. The predominant technology requires fast digestion at pH 2–3 to retain deuterium label. Pepsin is used almost exclusively, but it provides relatively low efficiency under the constraints of the experiment, and a selectivity profile that renders poor coverage of intrinsically disordered regions. In this study we present nepenthesin-containing secretions of the pitcher plant Nepenthes, commonly called monkey cups, for use in HDX-MS. We show that nepenthesin is at least 1400-fold more efficient than pepsin under HDX-competent conditions, with a selectivity profile that mimics pepsin in part, but also includes efficient cleavage C-terminal to “forbidden” residues K, R, H, and P. High efficiency permits a solution-based analysis with no detectable autolysis, avoiding the complication of immobilized enzyme reactors. Relaxed selectivity promotes high coverage of disordered regions and the ability to “tune” the mass map for regions of interest. Nepenthesin-enriched secretions were applied to an analysis of protein complexes in the nonhomologous end-joining DNA repair pathway. The analysis of XRCC4 binding to the BRCT domains of Ligase IV points to secondary interactions between the disordered C-terminal tail of XRCC4 and remote regions of the BRCT domains, which could only be identified with a nepenthesin-based workflow. HDX data suggest that stalk-binding to XRCC4 primes a BRCT conformation in these remote regions to support tail interaction, an event which may be phosphoregulated. We conclude that nepenthesin is an effective alternative to pepsin for all HDX-MS applications, and especially for the analysis of structural transitions among intrinsically disordered proteins and their binding partners. PMID:23197791

Rey, Martial; Yang, Menglin; Burns, Kyle M.; Yu, Yaping; Lees-Miller, Susan P.; Schriemer, David C.

2013-01-01

20

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

21

Improved Sequence Resolution by Global Analysis of Overlapped Peptides in Hydrogen/Deuterium Exchange Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Management of the enormous amount of data produced during solution-phase hydrogen/deuterium exchange monitored by mass spectrometry has stimulated software analysis development. The proteolysis step of the experiment generates multiple peptide fragments, most of which overlap. Prior automated data reduction algorithms extract the deuteration level for individual peptides, but do not exploit the additional information arising from fragment overlap. Here, we describe an algorithm that determines discrete rate constant values to each of the amide hydrogens in overlapped fragments. By considering all of the overlapped peptide segments simultaneously, sequence resolution can be improved significantly, sometimes to the individual amino acid level. We have validated the method with simulated deuterium uptake data for seven overlapped fragments of a poly-Ala nonapeptide, and then applied it to extract rate constant values for the first 29 N-terminal amino acids of C22A FK506-binding protein.

Fajer, Piotr G.; Bou-Assaf, George M.; Marshall, Alan G.

2012-07-01

22

Structural changes of ultrasonicated bovine serum albumin revealed by hydrogen-deuterium exchange and mass spectrometry.  

PubMed

The structural changes of bovine serum albumin (BSA) under high-intensity ultrasonication were investigated by fluorescence spectroscopy and mass spectrometry. Evidence for the ultrasonication-induced conformational changes of BSA was provided by the intensity changes and maximum-wavelength shift in fluorescence spectrometry. Matrix-assisted laser desorption-ionization time-of-flight mass spectroscopy (MALDI-TOF MS) revealed the increased intensity of the peak at the charge state +5 and a newly emerged peak at charge state +6, indicating that the protein became unfolded after ultrasonication. Prevalent unfolding of BSA after ultrasonication was revealed by hydrogen-deuterium exchange coupled with mass spectrometry (HDX-MS). Increased intensity and duration of ultrasonication further promoted the unfolding of the protein. The unfolding induced by ultrasonication goes through an intermediate state similar to that induced by a low concentration of denaturant. PMID:25224638

Zhang, Qiuting; Tu, Zongcai; Wang, Hui; Huang, Xiaoqin; Sha, Xiaomei; Xiao, Hui

2014-11-01

23

SAIDE: A Semi-Automated Interface for Hydrogen/Deuterium Exchange Mass Spectrometry  

PubMed Central

Deuterium/hydrogen exchange in combination with mass spectrometry (DH MS) is a sensitive technique for detection of changes in protein conformation and dynamics. Since temperature, pH and timing control are the key elements for reliable and efficient measurement of hydrogen/deuterium content in proteins and peptides, we have developed a small, semiautomatic interface for deuterium exchange that interfaces the HPLC pumps with a mass spectrometer. This interface is relatively inexpensive to build, and provides efficient temperature and timing control in all stages of enzyme digestion, HPLC separation and mass analysis of the resulting peptides. We have tested this system with a series of standard tryptic peptides reconstituted in a solvent containing increasing concentration of deuterium. Our results demonstrate the use of this interface results in minimal loss of deuterium due to back exchange during HPLC desalting and separation. For peptides reconstituted in a buffer containing 100% deuterium, and assuming that all amide linkages have exchanged hydrogen with deuterium, the maximum loss of deuterium content is only 17% of the label, indicating the loss of only one deuterium molecule per peptide.

Villar, Maria T.; Miller, Danny E.; Fenton, Aron W.; Artigues, Antonio

2011-01-01

24

Protein Conformation in Amorphous Solids by FTIR and by Hydrogen/Deuterium Exchange with Mass Spectrometry  

PubMed Central

Solid-state hydrogen/deuterium exchange (ssHDX) with electrospray ionization mass spectrometry (ESI-MS) and Fourier transform infrared (FTIR) spectroscopy were used to assess protein conformation in amorphous solids. Myoglobin, lysozyme, ?-lactoglobulin, ribonuclease A, E-cadherin 5, and concanavalin A were co-lyophilized with carbohydrates (trehalose, raffinose, and dextran 5000), linear polymers (polyvinyl alcohol and polyvinyl pyrrolidone) or guanidine hydrochloride (negative control). For ssHDX, samples were exposed to D2O vapor at 33% relative humidity and room temperature, and then reconstituted at low temperature (4°C) and pH 2.5 and analyzed by ESI-MS. Peptic digestion of selected proteins was used to provide region-specific information on exchange. FTIR spectra were acquired using attenuated total reflectance. FTIR and ssHDX of intact proteins showed preservation of structure by raffinose and trehalose, as indicated by FTIR band intensity and protection from exchange. ssHDX of peptic digests further indicated that these protective effects were not exerted uniformly along the protein sequence but were observed primarily in ?-helical regions, a level of structural resolution not afforded by FTIR. The results thus demonstrate the utility of HDX with ESI-MS for analyzing protein conformation in amorphous solid samples. PMID:18835903

Sinha, Sandipan; Li, Yunsong; Williams, Todd D.; Topp, Elizabeth M.

2008-01-01

25

Structural Insights into Fibrinogen Dynamics Using Amide Hydrogen/Deuterium Exchange Mass Spectrometry  

PubMed Central

We determined the amide hydrogen/deuterium exchange profile of native human fibrinogen under physiologic conditions. After optimization of the quench and proteolysis conditions, more than 1,200 peptides were identified by mass spectrometry, spanning more than 90% of the constituent A?, B?, and ? chain amino acid sequences. The compact central and distal globular regions of fibrinogen were well protected from deuterium exchange, with the exception of the unfolded amino-terminal segments of the A? and B? chains extending from the central region, and the short ? chain “tail” extending from each distal globular region. The triple-helical coiled-coil regions, which bridge the central region to each distal region, were also well protected with the exception of a moderately fast-exchanging area in the middle of each coiled coil adjacent to the ? chain carbohydrate attachment site. These dynamic regions appear to provide flexibility to the fibrinogen molecule. The ? chain “out loop” contained within each coiled-coil also exchanged rapidly. The ?C domain (A? 392–610) exchanged rapidly, with the exception of a short segment sandwiched between a conserved disulfide linkage in the N-terminal ?C subdomain. This latter finding is consistent with a mostly disordered structure for the ?C domain in native fibrinogen. Analysis of the dysfibrinogen B? 235 Pro/Leu, which exhibits abnormal fibrin structure, revealed enhanced deuterium exchange surrounding the Pro/Leu substitution site as well as in the vicinity of the high affinity calcium binding site and the A knob polymerization pocket within the ?C domain. The implication of these changes with respect to fibrin structure is discussed. PMID:23875785

Marsh, James J.; Guan, Henry S.; Li, Sheng; Chiles, Peter G.; Tran, Danny; Morris, Timothy A.

2013-01-01

26

Methods for the Analysis of High Precision Differential Hydrogen Deuterium Exchange Data.  

PubMed

Hydrogen/deuterium exchange (HDX) mass spectrometry has been widely applied to the characterization of protein dynamics. More recently, differential HDX has been shown to be effective for the characterization of ligand binding. Previously we have described a fully automated HDX system for use as a ligand screening platform. Here we describe and validate the required data analysis workflow to facilitate the use of HDX as a robust approach for ligand screening. Following acquisition of HDX data at a single on-exchange time point (n ? 3), one way analysis of variance in conjunction with the Tukey multiple comparison procedure is used to establish the significance of any measured difference. Analysis results are graphed with respect to a single peptide, ligand or group of ligands, or displayed as an overview within a heat map. For the heat map display, only ?%D values with a Tukey-adjusted P value less than 0.05 are colored. Hierarchical clustering is used to bin compounds with highly similar HDX signatures. The workflow is evaluated with a small data set showing the ligand binding domain (LDB) of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR?) screened against 10 functionally selective ligands. More significantly, data for the vitamin D receptor (VDR) in complex with 87 ligands are presented. To highlight the robustness and precision of our automated HDX platform we analyzed the data from 4191 replicate HDX measurements acquired over an eight month timeframe. Ninety six percent of these measurements were within 10 percent of the mean value. Work has begun to integrate these analysis and graphing components within our HDX software suite. PMID:21528013

Chalmers, Michael J; Pascal, Bruce D; Willis, Scooter; Zhang, Jun; Iturria, Stephen J; Dodge, Jeffery A; Griffin, Patrick R

2011-04-30

27

Dynamic Structural Changes During Complement C3 Activation Analyzed by Hydrogen/Deuterium Exchange Mass Spectrometry  

PubMed Central

Proteolytic cleavage of component C3 to C3b is a central step in the activation of complement. Whereas C3 is largely biologically inactive, C3b is directly involved in various complement activities. While the recently described crystal structures of C3 and C3b provide a molecular basis of complement activation, they do not reflect the dynamic changes that occur in solution. In addition, the available C3b structures diverge in some important aspects. Here we have utilized hydrogen/deuterium exchange coupled with mass spectrometry (HDX-MS) to investigate relative changes in the solution-phase structures of C3 and C3b. By combining two forms of mass spectrometry we could maximize the primary sequence coverage of C3b and demonstrate the feasibility of this method for large plasma proteins. While the majority of the 82 peptides that could be followed over time showed only minor alterations in HDX, we observed clear changes in solvent accessibility for 16 peptides, primarily in the ?-chain (?’NT, MG6-8, CUB, TED, C345C domains). Most of these peptides could be directly linked to the structural transitions visible in the crystal structures and revealed additional information about the probability of the structural variants of C3b. In addition, a discontinuous cluster of seven peptides in the MG3, MG6, LNK and ?’NT domains showed a decreased accessibility after activation to C3b. Although no gross conformational changes are detected in the crystal structure, this area may reflect a structurally flexible region in solution that contributes to C3 activation and function. PMID:18456336

Schuster, Michael C.; Ricklin, Daniel; Papp, Krisztian; Molnar, Kathleen S.; Coales, Stephen J.; Hamuro, Yoshitomo; Sfyroera, Georgia; Chen, Hui; Winters, Michael S.; Lambris, John D.

2008-01-01

28

Platform Dependencies in Bottom-up Hydrogen/Deuterium Exchange Mass Spectrometry*  

PubMed Central

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

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

2013-01-01

29

Measuring the hydrogen/deuterium exchange of proteins at high spatial resolution by mass spectrometry: overcoming gas-phase hydrogen/deuterium scrambling.  

PubMed

Conspectus Proteins are dynamic molecules that exhibit conformational flexibility to function properly. Well-known examples of this are allosteric regulation of protein activity and ligand-induced conformational changes in protein receptors. Detailed knowledge of the conformational properties of proteins is therefore pertinent to both basic and applied research, including drug development, since the majority of drugs target protein receptors and a growing number of drugs introduced to the market are therapeutic peptides or proteins. X-ray crystallography provides a static picture at atomic resolution of the lowest-energy structure of the native ensemble. There is a growing need for sensitive analytical tools to explore all of the significant molecular structures in the conformational landscape of proteins. Hydrogen/deuterium exchange monitored by mass spectrometry (HDX-MS) has recently emerged as a powerful method for characterizing protein conformational dynamics. The basis of this method is the fact that backbone amides in stable hydrogen-bonded structures (e.g., ?-helices and ?-sheets) are protected against exchange with the aqueous solvent. All protein structures are dynamic, however, and eventually all of the protecting hydrogen bonds will transiently break as the protein-according to thermodynamic principles-cycles through partially unfolded states that correspond to excited free energy levels. As a result, all of the backbone amides will eventually become temporarily solvent-exposed and exchange-competent over time. Consequently, a folded protein in D2O will gradually incorporate deuterium into its backbone amides, and the kinetics of the process can be readily monitored by mass spectrometry. The deuterium uptake kinetics for the intact protein (global exchange kinetics) represents the sum of the exchange kinetics for the individual backbone amides. Local exchange kinetics is typically achieved by using pepsin digestion under quench conditions (i.e., under cold acidic conditions where the amide hydrogen exchange rate is slowed by many orders of magnitude). The ability to localize the individual deuterated residues (the spatial resolution) is determined by the size (typically ?7-15 residues) and the number of peptic peptides. These peptides provide a relatively coarse-grained picture of the protein dynamics. A fundamental understanding of the relationship between protein function/dysfunction and conformational dynamics requires in many cases higher resolution and ultimately single-residue resolution. In this Account, we summarize our efforts to achieve single-residue deuterium levels in proteins by electron-based or laser-induced gas-phase fragmentation methods. A crucial analytical requirement for this approach is that the pattern of deuterium labeling from solution is retained in the gas-phase fragment ions. It is therefore essential to control and minimize any occurrence of gas-phase randomization of the solution deuterium label (H/D scrambling) during the MS experiment. For this purpose, we have developed model peptide probes to accurately measure the onset and extent of H/D scrambling. Our analytical procedures to control the occurrence of H/D scrambling are detailed along with the physical parameters that induce it during MS analysis. In light of the growing use of gas-phase dissociation experiments to measure the HDX of proteins in order to obtain a detailed characterization and understanding of the dynamic conformations and interactions of proteins at the molecular level, we discuss the perspectives and challenges of future high-resolution HDX-MS methodology. PMID:25171396

Rand, Kasper D; Zehl, Martin; Jørgensen, Thomas J D

2014-10-21

30

Influence of domain interactions on conformational mobility of the progesterone receptor detected by hydrogen/deuterium exchange mass spectrometry.  

PubMed

Structural and functional details of the N-terminal activation function 1 (AF1) of most nuclear receptors are poorly understood due to the highly dynamic intrinsically disordered nature of this domain. A hydrogen/deuterium exchange (HDX) mass-spectrometry-based investigation of TATA box-binding protein (TBP) interaction with various domains of progesterone receptor (PR) demonstrate that agonist-bound PR interaction with TBP via AF1 impacts the mobility of the C-terminal AF2. Results from HDX and other biophysical studies involving agonist- and antagonist-bound full-length PR and isolated PR domains reveal the molecular mechanism underlying synergistic transcriptional activation mediated by AF1 and AF2, dominance of PR-B isoform over PR-A, and the necessity of AF2 for full AF1-mediated transcriptional activity. These results provide a comprehensive picture elaborating the underlying mechanism of PR-TBP interactions as a model for studying nuclear receptor (NR)-transcription factor functional interactions. PMID:24909783

Goswami, Devrishi; Callaway, Celetta; Pascal, Bruce D; Kumar, Raj; Edwards, Dean P; Griffin, Patrick R

2014-07-01

31

Characterization of stress-exposed granulocyte colony stimulating factor using ELISA and hydrogen/deuterium exchange mass spectrometry.  

PubMed

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. PMID:25070584

Tsuchida, Daisuke; Yamazaki, Katsuyoshi; Akashi, Satoko

2014-10-01

32

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

33

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

34

Hydrogen-Deuterium Exchange and Mass Spectrometry Reveal the pH-Dependent Conformational Changes of Diphtheria Toxin T Domain.  

PubMed

The translocation (T) domain of diphtheria toxin plays a critical role in moving the catalytic domain across the endosomal membrane. Translocation/insertion is triggered by a decrease in pH in the endosome where conformational changes of T domain occur through several kinetic intermediates to yield a final trans-membrane form. High-resolution structural studies are only applicable to the static T-domain structure at physiological pH, and studies of the T-domain translocation pathway are hindered by the simultaneous presence of multiple conformations. Here, we report the application of hydrogen-deuterium exchange mass spectrometry (HDX-MS) for the study of the pH-dependent conformational changes of the T domain in solution. Effects of pH on intrinsic HDX rates were deconvolved by converting the on-exchange times at low pH into times under our "standard condition" (pH 7.5). pH-Dependent HDX kinetic analysis of T domain clearly reveals the conformational transition from the native state (W-state) to a membrane-competent state (W(+)-state). The initial transition occurs at pH 6 and includes the destabilization of N-terminal helices accompanied by the separation between N- and C-terminal segments. The structural rearrangements accompanying the formation of the membrane-competent state expose a hydrophobic hairpin (TH8-9) to solvent, prepare it to insert into the membrane. At pH 5.5, the transition is complete, and the protein further unfolds, resulting in the exposure of its C-terminal hydrophobic TH8-9, leading to subsequent aggregation in the absence of membranes. This solution-based study complements high resolution crystal structures and provides a detailed understanding of the pH-dependent structural rearrangement and acid-induced oligomerization of T domain. PMID:25290210

Li, Jing; Rodnin, Mykola V; Ladokhin, Alexey S; Gross, Michael L

2014-11-01

35

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

36

An On-Line, High-Pressure Digestion System for Protein Characterization by Hydrogen/Deuterium Exchange and Mass Spectrometry  

PubMed Central

The rapid and complete digestion of proteins is important when protein characterization by hydrogen deuterium exchange (HDX) is coupled with mass spectrometry. We developed a single-pump, on-line, high pressure digestion system that relies on UPLC technology to aid in the digestion of proteins. Two model proteins, A?1–42 and NBSA, were used to demonstrate the efficacy of the high pressure system. Both model proteins readily aggregate and are difficult to digest under normal conditions. Our high pressure system successfully digests these proteins into small, overlapping peptides. The extra information afforded by overlapping peptides allows us to pinpoint HDX protection to protein segments smaller than the digested peptide. The calculated average segment length (ASL) for both model proteins decreased by 2-fold for high pressure digestion compared to digestion at ambient pressure. PMID:20095571

Jones, Lisa M.; Zhang, Hao; Vidavsky, Ilan; Gross, Michael L.

2010-01-01

37

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

38

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

SAWYER Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY December 2004 Major Subject: Chemistry 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 A Dissertation by HOLLY ANN SAWYER Submitted to Texas A...

Sawyer, Holly Ann

2006-04-12

39

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

40

Mass spectrometric approaches using electrospray ionization charge states and hydrogen-deuterium exchange for determining protein structures and their conformational changes.  

PubMed

Electrospray ionization (ESI) mass spectrometry (MS) is a powerful analytical tool for elucidating structural details of proteins in solution especially when coupled with amide hydrogen/deuterium (H/D) exchange analysis. ESI charge-state distributions and the envelopes of charges they form from proteins can provide an abundance of information on solution conformations that is not readily available through other biophysical techniques such as near ultraviolet circular dichroism (CD) and tryptophan fluorescence. The most compelling reason for the use of ESI-MS over nuclear magnetic resonance (NMR) for measuring H/D after exchange is that larger proteins and lesser amounts of samples can be studied. In addition, MS can provide structural details on transient or folding intermediates that may not be accessible by CD, fluorescence, and NMR because these techniques measure the average properties of large populations of proteins in solution. Correlations between measured H/D and calculated parameters that are often available from crystallographic data can be used to extend the range of structural details obtained on proteins. Molecular dynamics and energy minimization by simulation techniques such as assisted model building with energy refinement (AMBER) force field can be very useful in providing structural models of proteins that rationalize the experimental H/D exchange results. Charge-state envelopes and H/D exchange information from ESI-MS data used complementarily with NMR and CD data provides the most powerful approach available to understanding the structures and dynamics of proteins in solution. PMID:14623985

Yan, Xuguang; Watson, Jeffrey; Ho, P Shing; Deinzer, Max L

2004-01-01

41

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

42

Structural stability and internal motions of Escherichia coli ribonuclease HI: 15N relaxation and hydrogen-deuterium exchange analyses.  

PubMed

The relationship between the structural stability and the internal motions of proteins was investigated through measurements of 15N relaxation and hydrogen-deuterium exchange rates of ribonuclease HI from Escherichia coli and its thermostable quintuple mutant (Gly23-->Ala, His62-->Pro, Val74-->Leu, Lys95-->Gly, and Asp134-->His), which has a higher melting temperature by 20.2 degreesC. For most of the residues, the generalized order parameters (S2) obtained from 15N relaxation analyses as well as the localized hydrogen-bond-breaking motions (local breathing) observed as fast H-D exchange rates were largely unaffected by the mutations, indicating no global mutational effect on the internal motions. Several local mutational effects were observed for residues close to the mutation sites as follows. The S2 value significantly increased for Lys96 and Val98, which indicated that motions on the pico- to nanosecond time-scale became restricted within a protruding region including the Lys95-->Gly mutation site. In contrast, slight decreases in S2, and drastic increases in the chemical exchange motion on the micro- to millisecond time-scale (Deltaex), were observed for residues located in the joining region between the protrusion and the major domain of the protein. These changes may be caused by the elimination of the bulky Lys95 side-chain at the center of the protrusion. Deltaex observed for residues in alpha-helix I of the wild-type protein was reduced for the mutant, probably because a cavity in the hydrophobic core is filled by the Val74-->Leu mutation. The local breathing at position 134 was restricted by the Asp134-->His mutation, probably because the reduction of the negative charge repulsion contributes to the stability of the native major conformation relative to the breathing conformations around position 134. PMID:9533889

Yamasaki, K; Akasako-Furukawa, A; Kanaya, S

1998-04-01

43

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

PubMed Central

SNARE proteins mediate fusion of intracellular eukaryotic membranes and their ?-helical transmembrane domains are known to contribute to lipid bilayer mixing. Synthetic transmembrane domain peptides were previously shown to mimic the function of SNARE proteins in that they trigger liposome fusion in a sequence-specific fashion. Here, we performed a detailed investigation of the conformational dynamics of the transmembrane helices of the presynaptic SNAREs synaptobrevin II and syntaxin 1a. To this end, we recorded deuterium/hydrogen-exchange kinetics in isotropic solution as well as in the membrane-embedded state. In solution, the exchange kinetics of each peptide can be described by three different classes of amide deuteriums that exchange with different rate constants. These are likely to originate from exchange at different domains of the helices. Interestingly, the rate constants of each class vary with the TMD sequence. Thus, the exchange rate is position-specific and sequence-specific. Further, the rate constants correlate with the previously determined membrane fusogenicities. In membranes, exchange is retarded and a significant proportion of amide hydrogens are protected from exchange. We conclude that the conformational dynamics of SNARE TMD helices is mechanistically linked to their ability to drive lipid mixing. PMID:18456822

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

2008-01-01

44

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

45

Fourier transform mass spectrometry to monitor hyaluronan-protein interactions: use of hydrogen/deuterium amide exchange  

PubMed Central

The use of Fourier transform mass spectrometry (FTMS) to monitor noncovalent complex formation in the gas phase under native conditions between the Link module from human tumor necrosis factor stimulated gene-6 (Link_TSG6) and hyaluronan (HA) oligosaccharides is reported. In particular, a titration experiment with increasing concentrations of octasaccharide (HA8) to protein produced a noncovalent complex with 1:1 stoichiometry when the oligosaccharide was in molar excess. However, in the presence of a molar excess of tetrasaccharide (HA4) nearly all proteins and oligosaccharides were observed in their unbound charge states. These results are consistent with solution-phase properties for this interaction in which HA8, but not HA4, supports high affinity Link_TSG6 binding. Hydrogen/deuterium amide exchange mass spectrometry (H/D-EX MS) was also utilized to investigate the level of global deuterium incorporation, over time, for Link_TSG6 in both the absence and presence of HA8. After dilution into quenching conditions, deuterium incorporation reached limiting asymptotic values of 37 and 26 deuterons for the free and bound protein at 240 and 480 min, respectively, indicating that the oligosaccharide interferes with amide exchange on binding. To detect sequence-specific deuterium incorporation, pepsin digestion of Link_TSG6 in both the absence and presence of HA8 was performed. A level of deuterium incorporation of 10–30% was observed for peptides analyzed in free Link_TSG6. Interestingly, HA8 blocked some sites of proteolysis in Link_TSG6 compared to the free protein. Molecular modeling indicated that amino acids proximal to the ligand correlated with regions of the protein that were resistant to enzymatic digestion. Of the peptides that could be analyzed by H/D-EX MS in the presence of the ligand, a 30–60% reduction in deuterium incorporation, relative to the free protein, was observed, even for those sequences not directly involved in HA binding. These results support the utility of FTMS as a method for the characterization of protein–carbohydrate interactions. PMID:17154353

Seyfried, Nicholas T.; Atwood, James A.; Yongye, Austin; Almond, Andrew; Day, Anthony J.; Orlando, Ron; Woods, Robert J.

2014-01-01

46

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

47

Unfolding and aggregation of a glycosylated monoclonal antibody on a cation exchange column. Part II. Protein structure effects by hydrogen deuterium exchange mass spectrometry.  

PubMed

Hydrogen-deuterium exchange mass spectrometry (HX-MS) with proteolytic fragmentation is used to determine patterns of unfolding, as measured by increased solvent exposure, with peptide-level resolution for a glycosylated monoclonal antibody both when eluted from a tentacle-type cation exchange column (Fractogel EMD SO3-) and while bound to the resin. Two peaks are obtained when the bound protein is eluted with either a NaCl gradient or with two NaCl steps at increasing concentration. The first, early eluting peak contains only monomeric species whose structure is consistent with the native monomer. The second, late eluting peak contains a mixture of monomeric and aggregated species. The monomeric species in this mixture is also found to have a structure consistent with that of the native mAb, showing no evidence of increased solvent exposure. The aggregated species show instead significant unfolding in areas of the protein structure contained within the Fc region. The same peptides that exhibit the greatest level of solvent exposure in the aggregated species are also found in the fraction of protein that elutes from the resin only at high salt concentration, indicating that the aggregates are formed when the strongly-bound unfolded intermediate is desorbed at high salt. There is no evidence that the unfolded intermediate, formed while the protein is bound on the resin, is present in any of the eluted fractions indicating that, upon desorption from the resin, the intermediate either quickly refolds or forms aggregates which end-up co-eluting with the refolded protein at high salt concentrations. PMID:25011681

Guo, Jing; Carta, Giorgio

2014-08-22

48

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

PubMed

We utilized gas phase hydrogen/deuterium (H/D) exchange reactions and ab initio calculations to investigate the complexation between a model peptide (Arg-Gly-Asp[triple bond]RGD) with various alkali metal ions. The peptide conformation is drastically altered upon alkali metal ion complexation. The associated conformational changes depend on both the number and type of complexing alkali metal ions. Sodium has a smaller ionic diameter and prefers a multidentate interaction that involves all three amino acids of the peptide. Conversely, potassium and cesium form different types of complexes with the RGD. The [RGD + 2Cs - H]+ species exhibit the slowest H/D exchange reactivity (reaction rate constant of approximately 6 x 10(-13) cm3molecule(-1)s(-1) for the fastest exchanging labile hydrogen with ND3). The reaction rate constant of the protonated RGD is two orders of magnitude faster than that of the [RGD + 2Cs - H]+. Addition of the first cesium to the RGD reduces the H/D exchange reaction rate constant (i.e., D0) by a factor of seven whereas sodium reduces this value by a factor of thirty. Conversely, addition of the second alkali metal ions has the opposite effect; the rate of D0 disappearance for all [RGD + 2Met - H]+ species (Met[triple bond]Na, K, and Cs) decreases with the alkali metal ion size. PMID:11766754

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

2001-12-01

49

Identification of Pharmacological Chaperones for Gaucher Disease and Characterization of Their Effects on ?-Glucocerebrosidase by Hydrogen/Deuterium Exchange Mass Spectrometry  

PubMed Central

Point mutations in ?-glucocerebrosidase (GCase) can result in a deficiency of both GCase activity and protein in lysosomes thereby causing Gaucher Disease (GD). Enzyme inhibitors such as isofagomine, acting as pharmacological chaperones (PCs), increase these levels by binding and stabilizing the native form of the enzyme in the endoplasmic reticulum (ER), and allow increased lysosomal transport of the enzyme. A high-throughput screen of the 50 000-compound Maybridge library identified two, non-carbohydrate-based inhibitory molecules, a 2,4-diamino-5-substituted quinazoline (IC50 5 ?M) and a 5-substituted pyridinyl-2-furamide (IC50 8 ?M). They raised the levels of functional GCase 1.5–2.5-fold in N370S or F213I GD fibroblasts. Immunofluorescence confirmed that treated GD fibroblasts had decreased levels of GCase in their ER and increased levels in lysosomes. Changes in protein dynamics, monitored by hydrogen/deuterium-exchange mass spectrometry, identified a domain III active-site loop (residues 243–249) as being significantly stabilized upon binding of isofagomine or either of these two new compounds; this suggests a common mechanism for PC enhancement of intracellular transport. PMID:18972510

Tropak, Michael B.; Kornhaber, Gregory J.; Rigat, Brigitte A.; Maegawa, Gustavo H.; Buttner, Justin D.; Blanchard, Jan E.; Murphy, Cecilia; Tuske, Steven J.; Coales, Stephen J.; Hamuro, Yoshitomo; Brown, Eric D.

2010-01-01

50

Hydrogen/deuterium exchange mass spectrometry reveals specific changes in the local flexibility of plasminogen activator inhibitor 1 upon binding to the somatomedin B domain of vitronectin.  

PubMed

The native fold of plasminogen activator inhibitor 1 (PAI-1) represents an active metastable conformation that spontaneously converts to an inactive latent form. Binding of the somatomedin B domain (SMB) of the endogenous cofactor vitronectin to PAI-1 delays the transition to the latent state and increases the thermal stability of the protein dramatically. We have used hydrogen/deuterium exchange mass spectrometry to assess the inherent structural flexibility of PAI-1 and to monitor the changes induced by SMB binding. Our data show that the PAI-1 core consisting of ?-sheet B is rather protected against exchange with the solvent, while the remainder of the molecule is more dynamic. SMB binding causes a pronounced and widespread stabilization of PAI-1 that is not confined to the binding interface with SMB. We further explored the local structural flexibility in a mutationally stabilized PAI-1 variant (14-1B) as well as the effect of stabilizing antibody Mab-1 on wild-type PAI-1. The three modes of stabilizing PAI-1 (SMB, Mab-1, and the mutations in 14-1B) all cause a delayed latency transition, and this effect was accompanied by unique signatures on the flexibility of PAI-1. Reduced flexibility in the region around helices B, C, and I was seen in all three cases, which suggests an involvement of this region in mediating structural flexibility necessary for the latency transition. These data therefore add considerable depth to our current understanding of the local structural flexibility in PAI-1 and provide novel indications of regions that may affect the functional stability of PAI-1. PMID:22957734

Trelle, Morten Beck; Hirschberg, Daniel; Jansson, Anna; Ploug, Michael; Roepstorff, Peter; Andreasen, Peter A; Jørgensen, Thomas J D

2012-10-16

51

Predicting protein aggregation during storage in lyophilized solids using solid state amide hydrogen/deuterium exchange with mass spectrometric analysis (ssHDX-MS).  

PubMed

Solid state amide hydrogen/deuterium exchange with mass spectrometric analysis (ssHDX-MS) was used to assess the conformation of myoglobin (Mb) in lyophilized formulations, and the results correlated with the extent of aggregation during storage. Mb was colyophilized with sucrose (1:1 or 1:8 w/w), mannitol (1:1 w/w), or NaCl (1:1 w/w) or in the absence of excipients. Immediately after lyophilization, samples of each formulation were analyzed by ssHDX-MS and Fourier transform infrared spectroscopy (FTIR) to assess Mb conformation, and by dynamic light scattering (DLS) and size exclusion chromatography (SEC) to determine the extent of aggregation. The remaining samples were then placed on stability at 25 °C and 60% RH or 40 °C and 75% RH for up to 1 year, withdrawn at intervals, and analyzed for aggregate content by SEC and DLS. In ssHDX-MS of samples immediately after lyophilization (t = 0), Mb was less deuterated in solids containing sucrose (1:1 and 1:8 w/w) than in those containing mannitol (1:1 w/w), NaCl (1:1 w/w), or Mb alone. Deuterium uptake kinetics and peptide mass envelopes also indicated greater Mb structural perturbation in mannitol, NaCl, or Mb-alone samples at t = 0. The extent of deuterium incorporation and kinetic parameters related to rapidly and slowly exchanging amide pools (Nfast, Nslow), measured at t = 0, were highly correlated with the extent of aggregation on storage as measured by SEC. In contrast, the extent of aggregation was weakly correlated with FTIR band intensity and peak position measured at t = 0. The results support the use of ssHDX-MS as a formulation screening tool in developing lyophilized protein drug products. PMID:24816133

Moorthy, Balakrishnan S; Schultz, Steven G; Kim, Sherry G; Topp, Elizabeth M

2014-06-01

52

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

53

Is the pre-Tg DSC endotherm observed with solid state proteins associated with the protein internal dynamics? Investigation of bovine serum albumin by solid state hydrogen/deuterium exchange.  

PubMed

DSC thermograms of solid state pure proteins often show a distinct endotherm at a temperature far below the glass transition temperature of the system (Tg). We hypothesized this endotherm represents enthalpy recovery associated with an internal mobility transition of the protein molecule. Although the existence of an internal transition has been postulated, whether this endotherm is associated with such a transition has not previously been discussed. The purpose of this study was to investigate the origin of the pre-Tg endotherm in lyophilized bovine serum albumin (BSA). Due to strong glass behavior, the system Tg was determined by extrapolating Tg data of disaccharide/BSA formulations to zero saccharide. A small pre-Tg endotherm around 40-60 °C was observed in amorphous BSA equilibrated at 11%RH. The apparent activation energy suggested the endotherm was "?-mobility"-related. A solid state hydrogen/deuterium exchange study using FTIR was conducted over a temperature range spanning the endotherm. We found a fast phase, followed by essentially a plateau level which is highly temperature dependent in the 40-60 °C range, suggesting enhanced internal protein motion as the system passes through the temperature range of the endotherm. These results suggest the pre-Tg endotherm is associated with a protein internal mobility transition. PMID:23669417

Mizuno, Masayasu; Pikal, Michael J

2013-10-01

54

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

PubMed Central

HXMS (hydrogen/deuterium exchange mass spectrometry) of the glucocorticoid receptor ligand-binding domain (GR LBD) complexed with the agonist dexamethasone and the antagonist RU-486 is described. Variations in the rates of exchange were observed in regions consistent with the published crystal structures of GR LBD complexed with RU-486 when compared with the GR dexamethasone complex. We also report the HXMS results for agonist-bound GR LBD with the coactivator transcriptional intermediary factor 2 (TIF2) and anatagonist-bound GR LBD with nuclear receptor corepressor (NCoR). Alterations in exchange rates observed for agonist-bound GR LBD with TIF2 present were consistent with the published crystal structural contacts for the complex. Alterations in exchange rates observed for antagonist-bound GR LBD with NCoR were a subset of those observed with TIF2 binding, suggesting a common or overlapping binding site for coactivator and corepressor. PMID:16600964

Frego, Lee; Davidson, Walter

2006-01-01

55

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

E-print Network

changes. Allosterically sensitive amide hydrogens located at near amino acid resolution help to confirm­4). For relatively small proteins, HX can be measured at an amino acid resolved level by NMR methods. For larger An automated high-throughput, high-resolution deuterium ex- change HPLC-MS method (DXMS) was used to extend

Englander, S. Walter

56

Fluoroketone Inhibition of Ca2+-Independent Phospholipase A2 through Binding Pocket Association Defined by Hydrogen/Deuterium Exchange and Molecular Dynamics  

PubMed Central

The mechanism of inhibition of group VIA Ca2+-independent phospholipase A2 (iPLA2) by fluoroketone (FK) ligands is examined by a combination of deuterium exchange mass spectrometry (DXMS) and molecular dynamics (MD). Models for iPLA2 were built by homology with the known structure of patatin and equilibrated by extensive MD simulations. Empty pockets were identified during the simulations and studied for their ability to accommodate FK inhibitors. Ligand docking techniques showed that the potent inhibitor 1,1,1,3-tetrafluoro-7-phenylheptan-2-one (PHFK) forms favorable interactions inside an active-site pocket, where it blocks the entrance of phospholipid substrates. The polar fluoroketone headgroup is stabilized by hydrogen bonds with residues Gly486, Gly487, and Ser519. The nonpolar aliphatic chain and aromatic group are stabilized by hydrophobic contacts with Met544, Val548, Phe549, Leu560, and Ala640. The binding mode is supported by DXMS experiments showing an important decrease of deuteration in the contact regions in the presence of the inhibitor. The discovery of the precise binding mode of FK ligands to the iPLA2 should greatly improve our ability to design new inhibitors with higher potency and selectivity. PMID:23256506

2012-01-01

57

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

NASA Astrophysics Data System (ADS)

The recent application of electron transfer dissociation (ETD) to measure the hydrogen exchange of proteins in solution at single-residue resolution (HX-ETD) paves the way for mass spectrometry-based analyses of biomolecular structure at an unprecedented level of detail. The approach requires that activation of polypeptide ions prior to ETD is minimal so as to prevent undesirable gas-phase randomization of the deuterium label from solution (i.e., hydrogen scrambling). Here we explore the use of ETD in a traveling wave ion guide of a quadrupole-time-of-flight (Q-TOF) mass spectrometer with a "Z-spray" type ion source, to measure the deuterium content of individual residues in peptides. We systematically identify key parameters of the Z-spray ion source that contribute to collisional activation and define conditions that allow ETD experiments to be performed in the traveling wave ion guide without gas-phase hydrogen scrambling. We show that ETD and supplemental collisional activation in a subsequent traveling wave ion guide allows for improved extraction of residue-specific deuterium contents in peptides with low charge. Our results demonstrate the feasibility, and illustrate the advantages of performing HX-ETD experiments on a high-resolution Q-TOF instrument equipped with traveling wave ion guides. Determination of parameters of the Z-spray ion source that contribute to ion heating are similarly pertinent to a growing number of MS applications that also rely on an energetically gentle transfer of ions into the gas-phase, such as the analysis of biomolecular structure by native mass spectrometry in combination with gas-phase ion-ion/ion-neutral reactions or ion mobility spectrometry.

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

2011-10-01

58

ETD in a traveling wave ion guide at tuned Z-spray ion source conditions allows for site-specific hydrogen/deuterium exchange measurements.  

PubMed

The recent application of electron transfer dissociation (ETD) to measure the hydrogen exchange of proteins in solution at single-residue resolution (HX-ETD) paves the way for mass spectrometry-based analyses of biomolecular structure at an unprecedented level of detail. The approach requires that activation of polypeptide ions prior to ETD is minimal so as to prevent undesirable gas-phase randomization of the deuterium label from solution (i.e., hydrogen scrambling). Here we explore the use of ETD in a traveling wave ion guide of a quadrupole-time-of-flight (Q-TOF) mass spectrometer with a "Z-spray" type ion source, to measure the deuterium content of individual residues in peptides. We systematically identify key parameters of the Z-spray ion source that contribute to collisional activation and define conditions that allow ETD experiments to be performed in the traveling wave ion guide without gas-phase hydrogen scrambling. We show that ETD and supplemental collisional activation in a subsequent traveling wave ion guide allows for improved extraction of residue-specific deuterium contents in peptides with low charge. Our results demonstrate the feasibility, and illustrate the advantages of performing HX-ETD experiments on a high-resolution Q-TOF instrument equipped with traveling wave ion guides. Determination of parameters of the Z-spray ion source that contribute to ion heating are similarly pertinent to a growing number of MS applications that also rely on an energetically gentle transfer of ions into the gas-phase, such as the analysis of biomolecular structure by native mass spectrometry in combination with gas-phase ion-ion/ion-neutral reactions or ion mobility spectrometry. PMID:21952892

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

2011-10-01

59

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

representation of an Ion Mobility-o-TOF MS............................ 6 3 Partial mass spectra of protonated GlyGlyHis reacted with deuterated methanol. Reaction times ranging from 1 ? 120 seconds.......................... 10 4 Temporal plot for gas...-phase H/D exchange of protonated GlyGlyHis with deuterated methanol at ~1.4 E-7 torr .......................................................... 11 5 Schematic representation of a typical cubic cell......................................... 16 6...

Marini, Joseph Thomas

2004-09-30

60

Phonon localization by mass disorder in dense hydrogen-deuterium binary alloy.  

PubMed

Using a combination of the Raman spectroscopy and density functional theory calculations on dense hydrogen-deuterium mixtures of various concentrations, we demonstrate that, at 300 K and above 200 GPa, they transform into phase IV, forming a disordered binary alloy with six highly localized intramolecular vibrational (vibrons) and four delocalized low-frequency (<1200??cm^{-1}) modes. Hydrogen-deuterium mixtures are unique in showing a purely mass-induced localization effect in the quantum solid: chemical bonding is isotope-independent while the mass varies by a factor of 2. PMID:25379921

Howie, Ross T; Magd?u, Ioan B; Goncharov, Alexander F; Ackland, Graeme J; Gregoryanz, Eugene

2014-10-24

61

Phonon Localization by Mass Disorder in Dense Hydrogen-Deuterium Binary Alloy  

NASA Astrophysics Data System (ADS)

Using a combination of the Raman spectroscopy and density functional theory calculations on dense hydrogen-deuterium mixtures of various concentrations, we demonstrate that, at 300 K and above 200 GPa, they transform into phase IV, forming a disordered binary alloy with six highly localized intramolecular vibrational (vibrons) and four delocalized low-frequency (<1200 cm-1) modes. Hydrogen-deuterium mixtures are unique in showing a purely mass-induced localization effect in the quantum solid: chemical bonding is isotope-independent while the mass varies by a factor of 2.

Howie, Ross T.; Magd?u, Ioan B.; Goncharov, Alexander F.; Ackland, Graeme J.; Gregoryanz, Eugene

2014-10-01

62

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

63

Diffusion of hydrogen, deuterium, and tritium in niobium  

SciTech Connect

The diffusion of hydrogen in niobium was investigated over the temperature range 148 to 500 degrees Kelvin, using measurements of the elastic after effect caused by long range diffusion (the Gorsky Effect). Relaxation curves for pure annealed niobium were generally not of the single exponential form expected from the Gorsky Effect theory, but were described well by a sum of two exponential curves with different amplitudes and relaxation times. The effects of oxygen and nitrogen interstitials on the diffusion were studied and were not in agreement with conventional trapping models. Deuterium and tritium diffusion in niobium were also studied, and a non-classical isotope effect was observed. Hydrogen diffusion coefficients in several Nb-Ta alloys were measured, and the diffusivity in all these alloys exhibited a non-Arrhenius temperature dependence. Experimental results were compared to several models for diffusion and trapping. A model is presented which can account for the form of the relaxation curves observed in pure, annealed niobium.

Matusiewicz, Gerald Robert

1981-01-01

64

Longitudinal Lelectroproduction of Charged Pions on Hydrogen, Deuterium, and Helium 3  

SciTech Connect

Conventional pictures of nuclear interactions, in which the pion mediates the long/medium range part of the nuclear force, predict an enhancement of the virtual pion cloud in nuclei relative to that in the free nucleon. Jefferson Lab Experiment E91003 measured charged pion electroproduction from Hydrogen, Deuterium, and Helium-3. The longitudinal cross section, which in the limit of pole dominance can be viewed as the quasifree knockout of a virtual pion, was extracted via a Rosenbluth separation. The longitudinal cross sections from Deuterium and Helium-3 were compared to Hydrogen to look for signatures of the nuclear pions.

David Gaskell

2001-05-01

65

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

66

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

PubMed

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

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

2013-03-21

67

Ab initio molecular dynamics study of the hydrogen diffusion in sodium and lithium hydrides  

NASA Astrophysics Data System (ADS)

Light weight complex metal hydrides, sodium hydride (NaH), and lithium hydride (LiH) are the last step materials during hydrogen release process of alanates and borates, which are promising candidates for hydrogen storage. We report ab initio molecular dynamics (MD) calculations based on density functional theory to study the hydrogen-deuterium exchange in NaH and LiH. We predict the single hydrogen-deuterium exchange in NaH and LiH and calculate the self-diffusion constants, ?D?NaH?1.46×10-9 m2 s-1 of deuterium in NaH at 420 K and ?D?LiH?1.49×10-9 m2 s-1 of deuterium in LiH at 550 K, which are in good agreement with the experimental values.

Ramzan, M.; Ahuja, R.

2009-07-01

68

Irreversible thermal denaturation of cytochrome c studied by electrospray mass spectrometry  

Microsoft Academic Search

This work uses electrospray ionization mass spectrometry (ESI-MS) in conjunction with hydrogen\\/deuterium exchange (HDX) and\\u000a optical spectroscopy for characterizing the solution-phase properties of cytochrome c (cyt c) after heat exposure. Previous work demonstrated that heating results in irreversible denaturation for a subpopulation of\\u000a proteins in the sample. However, that study did not investigate the physical reasons underlying this interesting effect.

Jiangjiang Liu; Lars Konermann

2009-01-01

69

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

NASA Astrophysics Data System (ADS)

The performance of a high-density polarized hydrogen/deuterium gas target internal to a medium-energy electron storage ring is presented. Compared to our previous electron scattering experiments with tensor-polarized deuterium at NIKHEF (Zhou et al., Nucl. Instr. and Meth. A 378 (1996) 40; Ferro-Luzzi et al., Phys. Rev. Lett. 77 (1996) 2630; Van den Brand et al., Phys. Rev. Lett. 78 (1997) 1235; Bouwhuis et al., Phys. Rev. Lett. 82 (1999) 687; Zhou et al., Phys. Rev. Lett. 82 (1999) 687) the target figure of merit, ( polarization) 2× luminosity, was improved by more than an order of magnitude. The target density was increased by upgrading the flux of nuclear-polarized atoms injected into the storage cell and by using a longer (60 cm) and colder (˜70 K) storage cell. A maximal target thickness of 1.2 (1.1)±0.1×10 14 nuclei/ cm2 was achieved with deuterium (hydrogen). With typical beam currents of 110 mA, this corresponds to a luminosity of about 8.4 (7.8)±0.8×10 31e- nuclei cm -2 s-1. By reducing the molecular background and using a stronger target guide field, a higher polarization was achieved. The target was used in combination with a 720 MeV polarized electron beam stored in the AmPS ring (NIKHEF) to measure spin observables in electron-proton and electron-deuteron scattering. Scattered electrons were detected in a large acceptance magnetic spectrometer. Ejected hadrons were detected in a single time-of-flight scintillator array. The product of beam and target vector polarization, PePt, was determined from the known spin-correlation parameters of e' p quasi-elastic (or elastic) scattering. With the deuterium (hydrogen) target, values up to PePt=0.49±0.03 (0.32±0.03) were obtained with an electron beam polarization of Pe=0.62±0.04 (0.56±0.03) as measured with a Compton backscattering polarimeter (Passchier et al., Nucl. Instr. and Meth. A 414 (1998) 4988). From this, we deduce a cell-averaged target polarization of Pt=0.78±0.07 (0.58±0.07), including the dilution by unpolarized molecules.

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

2001-12-01

70

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

71

A critical compilation of experimental data on spectral lines and energy levels of hydrogen, deuterium, and tritium  

SciTech Connect

For more than 50 years, Charlotte Moore's compilation of atomic energy levels and its subsequent revisions have been the standard source of reference data for the spectra of hydrogen and its isotopes. In those publications, theoretical data based on quantum-electrodynamic calculations have been given. This reflects the fact that the theory of the hydrogen spectrum has been perfected to an extent far exceeding the capabilities of the best measurements. However, rapid advances in the techniques of laser spectroscopy and optical frequency metrology have recently put experiments on a par with theory in terms of precision. This calls for construction of new comprehensive data sets for H, D, and T that summarize the latest experimental work and can be directly compared with the modern theoretical reference data. The present work compiles several tens of recent measurements of the hydrogen, deuterium, and tritium fine and hyperfine structure intervals and presents sets of energy levels and Ritz wavelengths derived from those measurements. Data exist for the fine structure of energy levels of hydrogen and deuterium up to principal quantum number n = 12. For higher lying levels, there are many observed lines with unresolved fine structure. From those observations, level centers (centers of the fine structure) are derived by a least-squares optimization, and Ritz wavelengths of series with upper levels up to n = 40 are obtained. For tritium, the n = 2 and 3 energy level intervals are derived from experimental observations.

Kramida, A.E., E-mail: Alexander.kramida@nist.go [Atomic Physics Division, National Institute of Standards and Technology, 100 Bureau Dr., MS 8422, Gaithersburg, MD 20899 (United States)

2010-11-15

72

Epitope mapping of a monoclonal antibody against human thrombin by H/D-exchange mass spectrometry  

E-print Network

Epitope mapping of a monoclonal antibody against human thrombin by H/D-exchange mass spectrometry human thrombin has been determined by hydrogen/ deuterium exchange coupled to MALDI mass spectrometry. The antibody epitope was identified as the surface of thrombin that retained deuterium in the presence

Komives, Elizabeth A.

73

Determination of hydrogen/deuterium ratio with neutron measurements on MASTa)  

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

74

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.

75

Protein Dynamics in Phosphorylation-Mediated Allostery Probed by Amide Exchange Mass Spectrometry  

NASA Astrophysics Data System (ADS)

A major goal of molecular biology is to correlate molecular structure with function. Since most enzymes and biological catalysts are proteins, the focus for correlating 'form' with 'function' has been entirely on protein macromolecular structure. It is obvious that any understanding of protein function must come through an understanding protein dynamics. Furthermore, all of the regulatory reactions are through changes in dynamics brought about by post-translational modifications, the most important of which is phosphorylation. This review highlights the important role of covalent phosphorylation and noncovalent phosphates in regulating allosteric effects and function through a study of protein dynamics. Mass spectrometry is a relatively new and increasingly important tool for describing protein dynamics. All examples described in this review have been studied by amide hydrogen/deuterium exchange mass spectrometry.

Ghosh, Madhubrata; Anand, Ganesh S.

2013-11-01

76

Type 1 and Type 2 scenarios in hydrogen exchange mass spectrometry studies on protein-ligand complexes.  

PubMed

Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) is a widely used technique for probing protein structure and dynamics. Exposure to D2O induces the deuteration of backbone N-H groups via a process that involves transient excursions to partially unfolded protein conformers. The resulting mass shifts can be probed by MS, usually in combination with proteolytic digestion and/or electron-based fragmentation. Studies on protein-ligand complexes represent a particularly important HDX/MS application. The prevailing view is that ligand binding should reduce deuteration rates, and it is often expected that this reduction will be most pronounced in the vicinity of the interaction site. Many protein-ligand systems do indeed behave in a fashion that is consistent with this paradigm. In this review we point out that the opposite effect may be encountered as well. Also, mixed scenarios are possible where ligand binding induces elevated HDX rates in some protein regions, whereas rates in other segments are reduced. We present a framework that links ligand-induced changes in HDX kinetics to alterations in the occupancy of excited protein conformers. Spontaneous ligand binding will always lower the free energy of the ground state. In contrast, the corresponding free energy shifts of excited states are largely unpredictable, giving rise to a range of possible HDX responses. "Type 1" scenarios, characterized by a reduction of HDX rates are just as feasible as "Type 2" behavior where deuteration is accelerated. Even "Type 0" phenomena may be encountered, where HDX rates are unaffected by the presence of ligand. Type 0/1/2 scenarios can coexist in the same protein (these terms are not to be confused with the EX1/EX2 expressions which refer to a different aspect of protein HDX). Allosteric effects and ligand-induced protein-protein contacts can affect the outcome of protein-ligand binding studies as well. In summary, comparative HDX measurements conducted in the presence and in the absence ligand provide a detailed fingerprint of biomolecular interactions. However, protein-ligand interactions can elicit a wide range of responses, and the interpretation of binding site mapping experiments may not always be straightforward. PMID:25319399

Konermann, Lars; Rodriguez, Antony D; Sowole, Modupeola A

2014-10-27

77

Use of H/D isotope effects to gather information about hydrogen bonding and hydrogen exchange rates  

NASA Astrophysics Data System (ADS)

Polar side-chains in proteins play important roles in forming and maintaining three-dimensional structures, and thus participate in various biological functions. Until recently, most protein NMR studies have focused on the non-exchangeable protons of amino acid residues. The exchangeable protons attached to polar groups, such as hydroxyl (OH), sulfhydryl (SH), and amino (NH2) groups, have mostly been ignored, because in many cases these hydrogen atoms exchange too quickly with water protons, making NMR observations impractical. However, in certain environments, such as deep within the hydrophobic interior of a protein, or in a strong hydrogen bond to other polar groups or interacting ligands, the protons attached to polar groups may exhibit slow hydrogen exchange rates and thus become NMR accessible. To explore the structural and biological implications of the interactions involving polar side-chains, we have developed versatile NMR methods to detect such cases by observing the line shapes of 13C NMR signals near the polar groups, which are affected by deuterium-proton isotope shifts in a mixture of H2O and D2O. These methods allow the detection of polar side-chains with slow hydrogen-deuterium exchange rates, and therefore provide opportunities to retrieve information about the polar side-chains, which might otherwise be overlooked by conventional NMR experiments. Future prospects of applications using deuterium-proton isotope shifts to retrieve missing structural and dynamic information of proteins are discussed.

Takeda, Mitsuhiro; Miyanoiri, Yohei; Terauchi, Tsutomu; Yang, Chun-Jiun; Kainosho, Masatsune

2014-04-01

78

Parameter dependence of the radial electric field in the edge pedestal of hydrogen, deuterium and helium plasmas  

NASA Astrophysics Data System (ADS)

The characteristics of the edge radial electric field (Er) are studied in deuterium, hydrogen and helium plasmas at ASDEX Upgrade. The minimum of the Er well is analyzed as a function of pedestal parameters and the best correlation is found between the depth of the Er well and the ion pressure at the pedestal top. This result is consistent with Er being balanced by the main ion pressure gradient term. Studying the radial position of the Er minimum reveals that the Er well moves closer to the last closed flux surface the deeper the Er well is. This suggests that for deeper Er wells the distance between the steepest gradients in the ion temperature and ion density profile is reduced. The width of the Er well shows no significant variations despite changing the ion temperature, magnetic field and plasma particle species. At AUG, the Er well is on average 1.2 cm wide. A multi-machine comparison supports a machine size scaling of Er and indicates that the Er shear layer covers the outer 2% of the plasma minor radius independent of the size of the machine. Based on this scaling, the width of the Er well in ITER is estimated to ?4 cm.

Viezzer, E.; Pütterich, T.; McDermott, R. M.; Conway, G. D.; Cavedon, M.; Dunne, M. G.; Dux, R.; Wolfrum, E.; the ASDEX Upgrade Team

2014-07-01

79

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

80

Preliminary design study of heat pipe heat exchangers  

Microsoft Academic Search

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

K. T. Feldman; D. C. Lu

1976-01-01

81

Columnar studies with selective ion exchange  

SciTech Connect

Secondary recovery of oil using water or steam injection to pressurize the strata has highlighted the water softening process using acidic cation exchangers which are regenerated with brine followed by a polishing weakly acidic cation exchanger. Development of a program to produce bries with low hardness suitable for secondary oil recovery is described. Results of laboratory tests with various resins for softening brines are presented. Calculations for a typical plant using Ionac SR-1 to soften a 25% brine are included. (BLM)

McGarvey, F.X.; Gottlieb, M.C.

1981-12-01

82

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

PubMed Central

The use of mass spectrometry to study protein-ligand interactions is expanding into more complex systems including protein-DNA interactions. The excess amount of a model DNA, or more typically an oligodeoxynucleotide (ODN), needed to study such interactions in an amide H/D exchange experiment, for example, causes serious signal suppression in the protein analysis. We describe here a modification of the traditional H/D exchange protocol whereby we utilize a strong anion exchange column to remove rapidly the ODN from solution before MS analysis. We showed the successful incorporation of such a column in a study of two protein-ODN systems: (1) the DNA-binding domain of human telomeric repeat binding factor 2 with a telomeric oligodeoxynucleotide and (2) thrombin with the thrombin-binding aptamer. The approach gave no appreciable difference in back-exchange compared to a method in which no SAX is used. PMID:18417359

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

2008-01-01

83

Mechanism of Ligand Exchange Studied Using Transition Path Sampling  

E-print Network

Mechanism of Ligand Exchange Studied Using Transition Path Sampling Preston T. Snee, Jennifer@socrates.berkeley.edu Abstract: The mechanism of intermolecular ligand exchange has been studied using transition path sampling that there are multiple steps in the reaction mechanism. The first involves partial dissociation of the coordinated

Harris, Charles B.

84

Xenon NMR studies of dynamics and exchange in zeolites  

SciTech Connect

We have found, despite earlier reports to the contrary, that for many microporous solids with one-dimensional channels (ZSM-12, ALPO-5, VPI-5, SSZ-24) the chemical shift has an anisotropic component. For ALPO-11, a detailed model has been developed which accounts for the loading-dependent chemical shift in terms of intraparticle exchange of statistical distributions of xenon atoms with 0, 1 or 2 nearest neighbors. A similar model can be applied to ZSM-12 up to moderate loadings. At higher loading levels 2D exchange methods show that interparticle exchange occurs as well. The same approach was used to study interparticle exchange in X and Y zeolite mixtures, exchange amongst zeolite clusters of up to 8 xenon atoms in the supercages of AgA zeolite, and main channel - side pocket exchange in mordenite. The parameters derived are directly relevant to the understanding of sorption and diffusion processes in zeolites.

Moudrakovski, I.L.; Ratcliffe, C.I.; Ripmeester, J.A. [Steacie Institute for Molecular Sciences, Ottawa, Ontario (Canada)

1996-10-01

85

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

86

Comparative studies on micro heat exchanger optimisation  

Microsoft Academic Search

Although many methods for dealing with multi-objective optimisation (MOO) problems are avail- able (Deb01) and successful applications have been re- ported (Coe01), the comparison between MOO meth- ods applied to real-world problem was rarely car- ried out. This paper reports the comparison between MOO methods applied to a real-world problem, namely, the optimisation of a micro heat exchanger ( HEX).

Tatsuya Okabe; Kwasi Foli; Markus Olhofer; Yaochu Jin; Bernhard Sendhoff

2003-01-01

87

Exchange Bias Systems studied by High Resolution Quantitative Magnetic Force  

E-print Network

Exchange Bias Systems studied by High Resolution Quantitative Magnetic Force Microscopy;Abstract It is generally believed that exchange bias (EB) implies the presence of pinned uncompen- sated domains to areas of proportionally higher pin-UCS aligned antiparallel to F-moments. This confirms our

Amrhein, Valentin

88

Preliminary joint neutron and X-ray crystallographic study of human carbonic anhydrase II  

PubMed Central

Carbonic anhydrases catalyze the interconversion of CO2 to HCO3 ?, with a subsequent proton-transfer (PT) step. PT proceeds via a proposed hydrogen-bonded water network in the active-site cavity that is stabilized by several hydrophilic residues. A joint X-ray and neutron crystallographic study has been initiated to determine the specific water network and the protonation states of the hydrophilic residues that coordinate it in human carbonic anhydrase II. Time-of-flight neutron crystallographic data have been collected from a large (?1.2?mm3) hydrogen/deuterium-exchanged crystal to 2.4?Å resolution and X-­ray crystallographic data have been collected from a similar but smaller crystal to 1.5?Å resolution. Obtaining good-quality neutron data will contribute to the understanding of the catalytic mechanisms that utilize water networks for PT in protein environments. PMID:19407386

Fisher, S. Z.; Kovalevsky, A. Y.; Domsic, J. F.; Mustyakimov, M.; Silverman, D. N.; McKenna, R.; Langan, Paul

2009-01-01

89

Studies of spin-exchange optical pumping  

NASA Astrophysics Data System (ADS)

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

Chann, Bien

90

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

PubMed Central

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

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

2010-01-01

91

Plasma exchange in Canada. The Canadian Apheresis Study Group.  

PubMed Central

Since 1982 the Canadian Apheresis Study Group (CASG) has collected data on plasma exchange activities in Canada. In 1987, 5907 such procedures were carried out on 700 patients for more than 22 different diseases; this represented an increase of 28% over the figure for 1982. A shift in activity has occurred over the years; originally hematologic disorders accounted for most of the procedures; however, in 1987, 60% of the exchanges were done to treat neurologic disorders, mainly myasthenia gravis and acute and chronic Guillain-Barré syndrome. Several prospective randomized clinical trials have recently been completed by the CASG in the hope of determining the optimal application of plasma exchange. These studies, currently under review, include 168 patients with multiple sclerosis, 100 with thrombotic thrombocytopenic purpura and 43 with rapidly progressive glomerulonephritis. Reactions occur in 12% of cases; they are usually minor and are limited to circumoral paresthesia, mild hypertension or hypotension and hives. PMID:2178759

Rock, G A; Tricklebank, G W; Kasaboski, C A

1990-01-01

92

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

93

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

94

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

95

Monte Carlo Study of Ferromagnetic Transition in Double Exchange Systems  

E-print Network

Monte Carlo Study of Ferromagnetic Transition in Double Exchange Systems Yukitoshi Motome and Nobuo to treat these fluc- tuations is the Monte Carlo (MC) method. In the MC calculations in a finite size Research), 2-1 Hirosawa, Wako, Saitama 351-0198; E-mail: motome@riken.go.jp the present DE system, since

Katsumoto, Shingo

96

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

97

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

98

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

PubMed

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

Harris, Stephen A; Anstey, Peter R

2009-12-01

99

H/D Exchange Centroid Monitoring is Insufficient to Show Differences in the Behavior of Protein States  

PubMed Central

Differential hydrogen/deuterium exchange (H/DX) coupled with mass spectrometry (H/DX-MS) offers a rapid and sensitive characterization of changes in protein following perturbations induced by changes in folding, ligand binding, oligomerization, and modification. The characterization of H/DX rates in software tools and automated data processing often relies on the centroid mass calculation, and, thereby, the deuterium distribution in the mass spectra is neglected. Here we present an example demonstrating the clear limitation of using only a centroid approach to characterize the H/DX rate, in which the change in protein is not reflected as the difference in deuterium uptake based on centroid calculation. PMID:23397137

Zhang, Jun; Ramachandran, Pradeep; Kumar, Rajiv

2013-01-01

100

Chemical and Physical Characterization of Therapeutic Proteins in Solution and Amorphous Solids  

E-print Network

The chemical and physical stability of proteins in solution and solids was addressed in this dissertation. Protein-excipient interactions in lyophilized solids were studied by hydrogen/deuterium exchange with mass spectrometry ...

Sinha, Sandipan

2008-06-16

101

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

Federal Register 2010, 2011, 2012, 2013

...No. FDA-2012-N-0780] Regulatory New Drug Review: Solutions for Study Data Exchange Standards; Notice of Meeting; Request...announced a meeting entitled ``Regulatory New Drug Review: Solutions for Study Data Exchange Standards.'' The document was...

2012-09-17

102

A Role for Altimeter Radars in Gas Exchange Studies  

NASA Astrophysics Data System (ADS)

Accurate estimates of air-sea transfer rates of radiatively active gases are needed for studies of regional and global gas cycling and for climate change studies. However, estimates using traditional wind speed - gas transfer velocity parameterizations vary by a factor of 2- 3, contributing significantly to error budgets in global modeling of gas exchange and the carbon cycle. A decade of research has shown the utility of sea surface roughness, represented by the mean square surface slope (mss) due to gravity-capillary scale waves, as a proxy for gas exchange. Normalized backscatter of altimeter radars can be used in scattering models to estimate mss by combining coordinated ship-based measurements of mss with satellite overflights. These coordinated field experiments over the last decade have begun to provide the data necessary to calibrate mss estimates from altimeter radars. Now we have developed this technique into an alternative approach for assessing global gas transfer velocity fields remotely. This paper will trace the evolution of this concept from key laboratory and in situ observations to remote sensing observations and construction of a decade-long time series from the TOPEX and Jason-1 data streams.

Frew, N. M.; Glover, D. M.; McCue, S. J.

2006-07-01

103

Information exchange networks for chronic illness care in primary care practices: an observational study  

Microsoft Academic Search

BACKGROUND: Information exchange networks for chronic illness care may influence the uptake of innovations in patient care. Valid and feasible methods are needed to document and analyse information exchange networks in healthcare settings. This observational study aimed to examine the usefulness of methods to study information exchange networks in primary care practices, related to chronic heart failure, diabetes and chronic

Michel Wensing; Jan van Lieshout; Jan Koetsenruijter; David Reeves

2010-01-01

104

Thermal Performance Study of a Prototype Multiport Heat Exchanger  

NASA Astrophysics Data System (ADS)

Great efforts have been made to investigate the thermal performance and fluid flow behaviour in Minichannel Heat Exchangers (MICHX), however, the examination of air side in a multiport serpentine slab heat exchanger is rare. In the current investigation, experiments were conducted on air heating via a prototype multiport MICHX. Hot DI-water at different mass flow rates and a constant inlet temperature of 70°C was passed through the channels. The water side Reynolds numbers were varied from 255 to 411. The airside Reynolds numbers were calculated based on the free mean stream velocity and varied from 1750 to 5250, while, the air inlet temperatures were in the range of 22.5°C to 34.5°C. The effects of dimensional parameters, such as Reynolds number, Nusselt number, Prandtl number, Brinkman number, and Dean number on the heat transfer performance were investigated. The effect of the serpentine on the enhancement of DI water thermal performance behaviour was studied. Heat transfer correlations were established and compared to the results in the open literature.

Fotowat, Shahram

105

A study on the simulation and experiment of a microchannel counter-flow heat exchanger  

Microsoft Academic Search

Numerical simulations and experimental tests were carried out to study the fluid flow and heat transfer characteristics for a rectangular-shaped microchannel heat exchanger. Moreover, influences of gravity to heat transfer and pressure drop behaviors of the microchannel heat exchanger were presented by variation of the physical inclinations of the microchannel heat exchanger system used for experiments. For experimental results, a

Thanhtrung Dang; Jyh-tong Teng; Jiann-cherng Chu

2010-01-01

106

Social network analysis: An approach and technique for the study of information exchange  

Microsoft Academic Search

Social network analysis is an approach and set of techniques used to study the exchange of resources among actors (i.e., individuals, groups, or organizations). One such resource is information. Regular patterns of information exchange reveal themselves as social networks, with actors as nodes in the network and information exchange relationships as connectors between nodes. Just as roads structure the flow

Caroline Haythornthwaite

1996-01-01

107

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

108

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

109

A Numerical Study on Flow and Heat Transfer Analysis of Various Heat Exchangers  

Microsoft Academic Search

This paper describes numerical methodologies of the flow and heat transfer analysis in heat exchangers of various types. Heat\\u000a exchangers considered in the present study include a louver fin radiator for a vehicle, a shell and tube heat exchanger for\\u000a HVAC and plate heat exchangers with patterns of herringbone and of dimple used in waste heat recovery. For the analysis

Myungsung Lee; Chan-Shik Won; Nahmkeon Hur

110

Ion temperatures in HIP-1 and SUMMA from charge-exchange neutral optical emission spectra  

NASA Technical Reports Server (NTRS)

Ion temperatures were obtained from observations of the H sub alpha, D sub alpha, and He 587.6 nm lines emitted from hydrogen, deuterium, and helium plasmas in the SUMMA and HIP-1 mirror devices at Lewis Research Center. Steady state discharges were formed by applying a radially inward dc electric field between cylindrical or annular anodes and hollow cathodes located at the peaks of the mirrors. The ion temperatures were found from the Doppler broadening of the charge-exchange components of spectral lines. A statistical method was developed for obtaining scaling relations of ion temperature as a function of current, voltage, and magnetic flux density. Derivations are given that take into account triangular monochromator slit functions, loss cones, and superimposed charge-exchange processes. In addition, the Doppler broadening was found to be sensitive to the influence of drift on charge-exchange cross section. The effects of finite ion-cyclotron radius, cascading, and delayed emission are reviewed.

Patch, R. W.; Lauver, M. R.

1976-01-01

111

Modelling real exchange rate behaviour: a cross-country study  

Microsoft Academic Search

The paper examines the behaviour of bilateral real exchange rates between Germany and fourteen major economies for the period January 1972 to December 1994. Time series techniques are used to consider a number of hypotheses including whether the real exchange rate is mean reverting; whether deviations follow a stable time series process; whether the underlying process can be modelled adequately

Ashok Parikh; Geoffrey Williams

1998-01-01

112

Approximate exchange perturbation study of intermolecular interactions in molecular complexes  

Microsoft Academic Search

In an attempt to rationalize and improve an approximate exchange perturbation scheme related to the model of Murrell et al., more accurate approximations are introduced eliminating the use of empirical parameters. The total interaction energy was evaluated as the sum of additive electrostatic, exchange, charge transfer, and dispersion contributions. It is proven that the assumption of intramolecular ZDO approximation is

W. Andrzej Sokalski; Henryk Chojnacki

1978-01-01

113

Parametric performance studies on fluidized-bed heat exchangers  

NASA Astrophysics Data System (ADS)

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

Stoeffler, R. C.

1982-01-01

114

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

115

XAFS Studies of Silver Environments in Ion-Exchanged Glasses  

SciTech Connect

The X-ray absorption fine structure (XAFS) technique was used to analyze the structural geometry of Ag atoms introduced into soda-lime silicate glass and soda aluminosilicate glass by ion-exchange methods. The results show that Ag+ ions in aluminosilicate glass are coordinated by about two oxygens and the nearest-neighbor Ag-O distance increases when the Ag+-for-Na+ ion-exchange ratio is larger than 0.47. When the exchange ratio is low, the introduced Ag+ ions are stabilized at the non-bridge oxygen (NBO) site with a Ag-O distance of 2.20 A, and the Na+ ions in the AlO4 site are exchanged by Ag+ ions after full replacement of the NBO sites with a Ag-O distance of 2.28 A. The disorder of Ag-O coordination increases with increasing ion-exchange ratio in aluminosilicate glass where Ag+ ions are coordinated by NBO and bridge oxygen (BO)

Yang, X. C. [College of Materials Science and Engineering, Tongji University, Shanghai 200092 (China); Dubiel, M. [Department of Physics, Martin Luther University of Halle, D-06108 Halle (Germany)

2007-02-02

116

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

PubMed

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

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

2011-08-01

117

HDXFinder: Automated Analysis and Data Reporting of Deuterium/Hydrogen Exchange Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Hydrogen/deuterium exchange in combination with mass spectrometry (H/D MS) is a sensitive technique for detection of changes in protein conformation and dynamics. However, wide application of H/D MS has been hindered, in part, by the lack of computational tools necessary for efficient analysis of the large data sets associated with this technique. We report a novel web-based application for automatic analysis of H/D MS experimental data. This application relies on the high resolution of mass spectrometers to extract all isotopic envelopes before correlating these envelopes with individual peptides. Although a fully automatic analysis is possible, a variety of graphical tools are included to aid in the verification of correlations and rankings of the isotopic peptide envelopes. As a demonstration, the rate constants for H/D exchange of peptides from rabbit muscle pyruvate kinase are mapped onto the structure of this protein.

Miller, Danny E.; Prasannan, Charulata B.; Villar, Maria T.; Fenton, Aron W.; Artigues, Antonio

2012-02-01

118

HDXFinder: automated analysis and data reporting of deuterium/hydrogen exchange mass spectrometry.  

PubMed

Hydrogen/deuterium exchange in combination with mass spectrometry (H/D MS) is a sensitive technique for detection of changes in protein conformation and dynamics. However, wide application of H/D MS has been hindered, in part, by the lack of computational tools necessary for efficient analysis of the large data sets associated with this technique. We report a novel web-based application for automatic analysis of H/D MS experimental data. This application relies on the high resolution of mass spectrometers to extract all isotopic envelopes before correlating these envelopes with individual peptides. Although a fully automatic analysis is possible, a variety of graphical tools are included to aid in the verification of correlations and rankings of the isotopic peptide envelopes. As a demonstration, the rate constants for H/D exchange of peptides from rabbit muscle pyruvate kinase are mapped onto the structure of this protein. PMID:22083588

Miller, Danny E; Prasannan, Charulata B; Villar, Maria T; Fenton, Aron W; Artigues, Antonio

2012-02-01

119

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

120

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

121

Parametric performance studies on fluidized-bed heat exchangers  

NASA Astrophysics Data System (ADS)

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

Stoffler, R. C.

1981-10-01

122

NAO influence on net sea ice production and exchanges in the Arctic region: a numerical study  

E-print Network

NAO influence on net sea ice production and exchanges in the Arctic region: a numerical study Aixue The variability of net sea ice production and sea ice exchange between the Arctic and its adjacent seas are studied, using a coupled sea ice-ocean general circulation model. The wind driven divergence (or ice flux

Hu, Aixue

123

Experimental study of several types of ground heat exchanger using a steel pile foundation  

Microsoft Academic Search

An experimental study of several types of ground heat exchangers (GHEs) installed in a steel pile foundation, including double-tube, U-tube, and multi-tube GHEs, was carried out at Saga University. Water flows through the heat exchangers and exchanges heat to or from the ground. The performance of GHEs was investigated under actual operation in the cooling mode with flow rates of

Jalaluddin; Akio Miyara; Koutaro Tsubaki; Shuntaro Inoue; Kentaro Yoshida

2011-01-01

124

Information Exchange Procedures. Outcomes Study Procedures. Technical Report No. 66.  

ERIC Educational Resources Information Center

The Information Exchange Procedures (IEP) developed by the National Center for Higher Education Management Systems (NCHEMS) are a set of standard definitions and procedures for collecting information about disciplines and student degree programs, outcomes of instructional programs, and general institutional characteristics. A fundamental purpose…

Byers, Maureen

125

Positional isotope exchange studies on enzyme using NMR spectroscopy  

SciTech Connect

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

Matsunaga, T.O.

1987-01-01

126

Experimental Study of Reputation Mechanisms in an Exchange Economy  

Microsoft Academic Search

We experimentally evaluate reputation mechanisms in an exchange market in which participants have the option of not fulfilling their con- tracts. These mechanisms vary in the information they provide on past behavior. Participants can choose who they trade with, allowing endoge- nous response to low reputation through ostracizing or price discriminat- ing behaviors. The participants responded strategically to the provided

Kay-Yut Chen; Nathan Wozny

127

NMR studies of proton exchange kinetics in aqueous formaldehyde solutions.  

PubMed

Aqueous solutions of formaldehyde, formalin, are commonly used for tissue fixation and preservation. Treatment with formalin is known to shorten the tissue transverse relaxation time T2. Part of this shortening is due to the effect of formalin on the water T2. In the present work we show that the shortening of water T2 is a result of proton exchange between water and the major constituent of aqueous solutions of formaldehyde, methylene glycol. We report the observation of the signal of the hydroxyl protons of methylene glycol at 2ppm to high frequency of the water signal that can be seen at low temperatures and at pH range of 6.0±1.5 and, at conditions where it cannot be observed by the single pulse experiment, it can be detected indirectly through the water signal by the chemical exchange saturation transfer (CEST) experiment. The above finding made it possible to obtain the exchange rate between the hydroxyl protons of the methylene glycol and water in aqueous formaldehyde solutions, either using the dispersion of the spin-lattice relaxation rate in the rotating frame (1/T1?) or, at the slow exchange regime, from the line width hydroxyl protons of methylene glycol. The exchange rate was ?10(4)s(-1) at pH 7.4 and 37°C, the activation energy, 50.2kJ/mol and its pH dependence at 1.1°C was fitted to: k (s(-1))=520+6.5×10(7)[H(+)]+3.0×10(9)[OH(-)]. PMID:24632100

Rivlin, Michal; Eliav, Uzi; Navon, Gil

2014-05-01

128

NMR studies of proton exchange kinetics in aqueous formaldehyde solutions  

NASA Astrophysics Data System (ADS)

Aqueous solutions of formaldehyde, formalin, are commonly used for tissue fixation and preservation. Treatment with formalin is known to shorten the tissue transverse relaxation time T2. Part of this shortening is due to the effect of formalin on the water T2. In the present work we show that the shortening of water T2 is a result of proton exchange between water and the major constituent of aqueous solutions of formaldehyde, methylene glycol. We report the observation of the signal of the hydroxyl protons of methylene glycol at 2 ppm to high frequency of the water signal that can be seen at low temperatures and at pH range of 6.0 ± 1.5 and, at conditions where it cannot be observed by the single pulse experiment, it can be detected indirectly through the water signal by the chemical exchange saturation transfer (CEST) experiment. The above finding made it possible to obtain the exchange rate between the hydroxyl protons of the methylene glycol and water in aqueous formaldehyde solutions, either using the dispersion of the spin-lattice relaxation rate in the rotating frame (1/T1?) or, at the slow exchange regime, from the line width hydroxyl protons of methylene glycol. The exchange rate was ?104 s-1 at pH 7.4 and 37 °C, the activation energy, 50.2 kJ/mol and its pH dependence at 1.1 °C was fitted to: k (s-1) = 520 + 6.5 × 107[H+] + 3.0 × 109[OH-].

Rivlin, Michal; Eliav, Uzi; Navon, Gil

2014-05-01

129

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

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

130

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

SciTech Connect

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

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

2010-11-04

131

Tailoring exchange interactions in engineered nanostructures: an ab initio study.  

PubMed

We present a novel approach to spin manipulation in atomic-scale nanostructures. Our ab initio calculations clearly demonstrate that it is possible to tune magnetic properties of subnanometer structures by adjusting the geometry of the system. By the example of two surface-based systems we demonstrate the following. (i) The magnetic moment of a single adatom coupled to a buried magnetic Co layer can be stabilized in either a ferromagnetic or an antiferromagnetic configuration depending on the spacer thickness. It is found that a buried Co layer has a profound effect on the exchange interaction between two magnetic impurities on the surface. (ii) The exchange interaction between magnetic adatoms can be manipulated by introducing artificial nonmagnetic Cu chains to link them. PMID:18764280

Brovko, O O; Ignatiev, P A; Stepanyuk, V S; Bruno, P

2008-07-18

132

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

133

Cost-effectiveness study of heat pipe heat exchangers  

Microsoft Academic Search

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

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

1977-01-01

134

Ion exchange studies on zinc-rich waste liquors  

Microsoft Academic Search

This paper reports on the use of ion exchange resins for the recovery of zinc, in a relatively pure form, from a zinc-rich industrial waste liquor and from model zinc-rich solutions. Lewatit OC-1026 resin was found to have good zinc selectivity, whilst the chelating resins Purolite S-930, Metalfix Chelamine and Metalfix Chelosolve showed greater selectivity for the major contaminant ions,

C Simpson; S. H Laurie

1999-01-01

135

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

Microsoft Academic Search

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

Y. H. Yau; M. Ahmadzadehtalatapeh

2011-01-01

136

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

137

Blowing snow studies in the Canadian Arctic Shelf Exchange Study, 2003-04  

Microsoft Academic Search

Between mid January and early May 2004, during the Canadian Arctic Shelf Exchange Study 2003-04 expedition, we conducted a field project in which we deployed blowing-snow particle counters, visibility sensors, a FlowCapt device, snow bags, an electric field meter and other instruments related to the observation of drifting and blowing snow on first-year ice in Franklin Bay, Northwest Territories, Canada.

S. A. Savelyev; M. Gordon; J. Hanesiak; T. Papakyriakou; P. A. Taylor

2006-01-01

138

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, Rogerio; Torquato, Jamili Anbar; Carvalho, Carlos Roberto Ribeiro; Marini, John J

2009-01-01

139

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

140

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

141

ATP-induced dimerization of the F0F1 ? subunit from Bacillus PS3: a hydrogen exchange-mass spectrometry study.  

PubMed

F0F1 ATP synthase harnesses a transmembrane electrochemical gradient for the production of ATP. When operated in reverse, this multiprotein complex catalyzes ATP hydrolysis. In bacteria, the ? subunit is involved in regulating this ATPase activity. Also, ? is essential for coupling ATP hydrolysis (or synthesis) to proton translocation. The ? subunit consists of a ? sandwich and two C-terminal helices, ?1 and ?2. The protein can switch from a compact fold to an alternate conformation where ?1 and ?2 are separated, resulting in an extended structure. ? from the thermophile Bacillus PS3 (T?) binds ATP with high affinity such that this protein may function as an intracellular ATP level sensor. ATP binding to isolated T? triggers a major conformational transition. Earlier data were interpreted in terms of an ATP + T?extended ? ATP·T?compact transition that may mimic aspects of the regulatory switching within F0F1 (Yagi et al. (2007) Proc. Natl. Acad. Sci. U.S.A., 104, 11233–11238). In this work, we employ complementary biophysical techniques for examining the ATP-induced conformational switching of isolated T?. CD spectroscopy confirmed the occurrence of a large-scale conformational transition upon ATP binding, consistent with the formation of stable helical structure. Hydrogen/deuterium exchange (HDX) mass spectrometry revealed that this transition is accompanied by a pronounced stabilization in the vicinity of the ATP-binding pocket. Surprisingly, dramatic stabilization is also seen in the ?8??9 region, which is remote from the site of ATP interaction. Analytical ultracentrifugation uncovered a previously unrecognized feature of T?: a high propensity to undergo dimerization in the presence of ATP. Comparison with existing crystallography data strongly suggests that the unexpected ?8??9 HDX protection is due to newly formed protein–protein contacts. Hence, ATP binding to isolated T? proceeds according to 2ATP + 2T?extended ? (ATP·T?compact)2. Implications of this dimerization propensity for the possible role of T? as an antibiotic target are discussed. PMID:24870150

Rodriguez, Antony D; Dunn, Stanley D; Konermann, Lars

2014-06-24

142

Ion exchange study of some new biphenol–thiourea–formaldehyde terpolymer resins  

Microsoft Academic Search

Terpolymer resins, synthesized by reacting 2,2?-dihydroxybiphenyl with thiourea and formaldehyde in presence of HCl as catalyst, proved to be selective chelating ion-exchange resins for certain metal ions. Chelating ion-exchange properties of these terpolymer were studied for Fe3+, Cu2+, Ni2+, Co2+, Zn2+, Cd2+ and Pb2+ ions. A batch equilibrium method has been employed in the study of the selectivity of metal

Manjusha M. Jadhao; Mukesh Thite; L. J. Paliwal; N. S. Bhave

2012-01-01

143

Studies on decontamination of spent ion exchange resin used for plutonium purification in PUREX stream  

Microsoft Academic Search

This paper deals with the studies on decontaminations of spent ion exchange resin used for purification of plutonium in PUREX\\u000a process stream. Studies were carried out to optimize the chemical procedure for removal of plutonium and fission products\\u000a activities form spent Ion Exchange resin. Different metal complexing reagents were tested for leaching out of radionuclides\\u000a entrapped in irradiated spent ion

K. K. Gupta; Suman Kumar Singh; G. A. Inamdar; A. Madhusudan; S. C. Tripathi

2009-01-01

144

Ribonuclease Sa conformational stability studied by NMR-monitored hydrogen exchange.  

PubMed

The conformational stability of ribonuclease Sa (RNase Sa) has been measured at the per-residue level by NMR-monitored hydrogen exchange at pH* 5.5 and 30 degrees C. In these conditions, the exchange mechanism was found to be EXII. The conformational stability calculated from the slowest exchanging amide groups was found to be 8.8 kcal/mol, in close agreement with values determined by spectroscopic methods. RNase Sa is curiously rich in acidic residues (pI = 3.5) with most basic residues being concentrated in the active-site cleft. The effects of dissolved salts on the stability of RNase Sa was studied by thermal denaturation experiments in NaCl and GdmCl and by comparing hydrogen exchange rates in 0.25 M NaCl to water. The protein was found to be stabilized by salt, with the magnitude of the stabilization being influenced by the solvent exposure and local charge environment at individual amide groups. Amide hydrogen exchange was also measured in 0.25, 0.50, 0.75, and 1.00 M GdmCl to characterize the unfolding events that permit exchange. In contrast to other microbial ribonucleases studied to date, the most protected, globally exchanging amides in RNase Sa lie not chiefly in the central beta strands but in the 3/10 helix and an exterior beta strand. These structural elements are near the Cys7-Cys96 disulfide bond. PMID:15909979

Laurents, Douglas V; Scholtz, J Martin; Rico, Manuel; Pace, C Nick; Bruix, Marta

2005-05-31

145

Phosphorylation- and Nucleotide-Binding-Induced Changes to the Stability and Hydrogen Exchange Patterns of JNK1?1 Provide Insight into Its Mechanisms of Activation.  

PubMed

Many studies have characterized how changes to the stability and internal motions of a protein during activation can contribute to their catalytic function, even when structural changes cannot be observed. Here, unfolding studies and hydrogen-deuterium exchange (HX) mass spectrometry were used to investigate the changes to the stability and conformation/conformational dynamics of JNK1?1 induced by phosphorylative activation. Equivalent studies were also employed to determine the effects of nucleotide binding on both inactive and active JNK1?1 using the ATP analogue, 5'-adenylyl-imidodiphosphate (AMP-PNP). JNK1?1 phosphorylation alters HX in regions involved in catalysis and substrate binding, changes that can be ascribed to functional modifications in either structure and/or backbone flexibility. Increased HX in the hinge between the N- and C-terminal domains implied that it acquires enhanced flexibility upon phosphorylation that may be a prerequisite for interdomain closure. In combination with the finding that nucleotide binding destabilizes the kinase, the patterns of solvent protection by AMP-PNP were consistent with a novel mode of nucleotide binding to the C-terminal domain of a destabilized and open domain conformation of inactive JNK1?1. Solvent protection by AMP-PNP of both N- and C-terminal domains in active JNK1?1 revealed that the domains close around nucleotide upon phosphorylation, concomitantly stabilizing the kinase. This suggests that phosphorylation activates JNK1?1 in part by increasing hinge flexibility to facilitate interdomain closure and the creation of a functional active site. By uncovering the complex interplay that occurs between nucleotide binding and phosphorylation, we present new insight into the unique mechanisms by which JNK1?1 is regulated. PMID:25178256

Owen, Gavin R; Stoychev, Stoyan; Achilonu, Ikechukwu; Dirr, Heini W

2014-10-23

146

Condensing heat exchanger microbial growth and control study-phase 2  

SciTech Connect

The Space Station Temperature and Humidity Control Condensing Heat Exchangers will be utilized to collect and remove atmospheric water vapor generated by the metabolic and hygienic activity of crew members. The porous hydrophillic coating within the heat exchangers will always be wet. Cabin air will continuously flow through the heat exchangers during system operation which makes them a potential site for microbial colonization. This paper summarizes the findings form an ongoing study which evaluates biofilm formation on wet hydrophilic coated panels compared to panels to which microbial control measures have have been applied. The control measures evaluated are an antimicrobial agent within the coating and periodic drying.

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

1993-12-31

147

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

148

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

Microsoft Academic Search

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.

Minsung Kim; Young-Jin Baik; Seong-Ryong Park; Ho-Sang Ra; Hyug Lim

2010-01-01

149

Coming to Canada to Study: Factors that Influence Student's Decisions to Participate in International Exchange  

ERIC Educational Resources Information Center

Increasing numbers of students are participating in study abroad programs. Outcomes associated with these programs have been studied extensively, but relatively little is known about what motivates and influences students to participate. This study investigated factors that motivate and influence students to study on exchange and explored how…

Massey, Jennifer; Burrow, Jeff

2012-01-01

150

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

151

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

152

Information Exchange Procedures Cost Study Procedures Manual. Technical Report No. 65.  

ERIC Educational Resources Information Center

This document provides the definitions and procedures for the costing portion of the NCHEMS Information Exchange Procedures (IEP). Also included is an overview of the eight steps and more detailed activities to be performed by institutions using related computer software to conduct the IEP cost study. The IEP cost study implementation steps are:…

Johnson, Richard S.; Huff, Robert A.

153

The Value of the Voting Right: A Study of the Milan Stock Exchange Experience  

Microsoft Academic Search

I study the large premium (82 percent) attributed to voting shares on the Milan Stock Exchange. The premium varies according to the ownership structure and the concentration of the voting rights, and it can be rationalized in the presence of enormous private benefits of control. A case study seems to indicate that in Italy private benefits of control can easily

Luigi Zingales

1994-01-01

154

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

155

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

156

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

157

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. Copyright © 2014 John Wiley & Sons, Ltd. PMID:25199631

Jin, Tao; Kim, Seong-Gi

2014-11-01

158

An STM study of molecular exchange processes in organic thin film growth.  

PubMed

The growth of a fullerene derivative (PCBM) on top of a layer of a tetrathiafulvalene (TTF) derivative previously deposited on Au(111) has been studied by scanning tunneling microscopy (STM). The results show that the preferential interaction with the gold substrate induces the exchange of PCBM molecules with the exTTF monolayer, expelling exTTF molecules to the outer surface. This exchange process is forbidden when the thickness of the exTTF layer increases above the monolayer, and the larger surface energy of PCBM leads to the growth of 3D islands. PMID:25035072

Gallego, José M; Ecija, David; Martín, Nazario; Otero, Roberto; Miranda, Rodolfo

2014-09-01

159

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

160

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

NASA Astrophysics Data System (ADS)

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

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

161

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

162

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

163

Initial rate and isotope exchange studies of rat skeletal muscle hexokinase  

Microsoft Academic Search

The kinetic mechanism of rat skeletal muscle hexokinase (hexokinase II) was investigated in light of a proposal by Cornish-Bowden and his co-workers. The authors investigated the mechanism of action of hexokinase II by studying initial rate kinetics in the nonphysiological direction and by isotope exchange at chemical equilibrium. The former experiments were carried out in the absence of inhibitors and

N. J. Ganson; H. J. Fromm

1985-01-01

164

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

165

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

166

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

SciTech Connect

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

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

2011-12-31

167

Exchange-Rate Regimes: \\  

Microsoft Academic Search

Traditionally the IMF's Annual Report on Exchange Arrangements and Exchange Restrictions has been the main source of information about the exchange-rate policies pursued by member countries. The classification contained therein has been used to document the evolution of exchange rate regimes over time as well as to study the relationship between economic performance and the choice of exchange rate system.

Hans Genberg; Alexander K. Swoboda

2004-01-01

168

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

169

Conceptual study of in-tank cesium removal using an inorganic ion exchange material  

SciTech Connect

Presently, the Hanford Site contains approximately 230,000 m{sup 3} of mixed waste stored in 177 underground tanks. Approximately 55,000 m{sup 3} of this waste is sludge, 90,000 m{sup 3} is salt cake, and 80,000 m{sup 3} is supernate. Although the pretreatment and final disposal requirements for the waste have not been entirely defined, it is likely that some supernatant pretreatment will be required to remove {sup 137}Cs and possibly {sup 90}Sr and the transuranic components. The objective of this study was to estimate the number of HLW glass canisters resulting from the use of inorganic ion exchanger materials as in-tank pretreatment technology. The variables in the study were: number of contacts between waste and ion exchange material; ion exchange material; and decontamination requirement. This conceptual study investigates a generic in-tank Cs removal flowsheet using crystalline silico-titanates and IE-96 zeolites, and the impact of each ion exchanger on the number of glass canisters produced. In determining glass formulation, data based on current reference technology was used. Sample calculations from the worksheets and summaries of final calculated results are included at the end of this report.

Goheen, R.S.; Kurath, D.E.

1996-04-01

170

PILOT STUDY ON INTERNATIONAL EXCHANGE ON DIOXINS AND RELATED COMPOUNDS: INTERNATIONAL EXCHANGE OF RESEARCH AND TECHNOLOGY INFORMATION ON DIOXINS AND RELATED COMPOUNDS  

EPA Science Inventory

The Pilot Study on International Information Exchange on Dioxins and Related Compounds was initiated in 1985 to apply the cooperative efforts of numerous nations to address the problems associated with CDDs, CDFs, and related compounds. he Pilot Study conducted activities to exam...

171

A transaction level study of the effects of central bank intervention on exchange rates  

Microsoft Academic Search

We study the effects of sterilised intervention operations executed on behalf of the Swiss National Bank (SNB) using tick-by-tick transactions data between 1986 and 1995. We extend the preliminary analysis of [Economic Journal 109 (1999) 662] by matching these data with indicative intra-day exchange rate quotes and news-wire reports of central bank activity. Using an event study approach we find

Richard Payne; Paolo Vitale

2003-01-01

172

Diode laser absorption spectroscopy for studies of gas exchange in fruits  

NASA Astrophysics Data System (ADS)

Gas exchange in fruits, in particular oxygen transport in apples, was studied non-intrusively using wavelength modulation diode laser absorption spectroscopy at about 761 nm, applied to the strongly scattering intact fruit structure. The applicability of the technique was demonstrated by studies of the influence of the skin to regulate the internal oxygen balance and of cling film in modifying it by observing the response of the signal from the internal oxygen gas to a transient change in the ambient gas concentration. Applications within controlled atmosphere fruit storage and modified atmosphere packaging are discussed. The results suggest that the technique could be applied to studies of a large number of problems concerning gas exchange in foods and in food packaging.

Persson, L.; Gao, H.; Sjöholm, M.; Svanberg, S.

2006-07-01

173

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

PubMed Central

Doubly-protonated bradykinin (RPPGFSPFR) and an angiotensin III analogue (RVYIFPF) were subjected to hydrogen/deuterium (H/D) exchange with CD3OD in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. A bimodal distribution of deuterium incorporation was present for bradykinin after H/D exchange for 90 s at a CD3OD pressure of 4 × 10?7 Torr, indicating the existence of at least two distinct populations. Bradykinin ion populations corresponding to 0–2 and 5–11 deuteriums (i.e., D0, D1, D2, D5, D6, D7, D8, D9, D10, and D11) were each monoisotopically selected and fragmented via sustained off-resonance irradiation (SORI) collision-induced dissociation (CID). The D0–D2 ion populations, which correspond to the slower exchanging population, consistently require lower SORI amplitude to achieve a similar precursor ion survival yield as the faster-reacting (D5–D11) populations. These results demonstrate that conformation/protonation motif has an effect on fragmentation efficiency for bradykinin. Also, the partitioning of the deuterium atoms into fragment ions suggests that the C-terminal arginine residue exchanges more rapidly than the N-terminal arginine. Total deuterium incorporation in the b1/y8 and b2/y7 ion pairs matches very closely the theoretical values for all ion populations studied, indicating that the ions of a complementary pair are likely formed during the same fragmentation event, or that no scrambling occurs upon SORI. Deuterium incorporation into the y1/a8 pseudo-ion pair does not closely match the expected theoretical values. The other peptide, doubly-protonated RVYIFPF, has a trimodal distribution of deuterium incorporation upon H/D exchange with CD3OD at a pressure of 1 × 10?7 Torr for 600 s, indicating at least three distinct ion populations. After 90 s of H/D exchange where at least two distinct populations are detected, the D0–D7 ion populations were monoisotopically selected and fragmented via SORI-CID over a range of SORI amplitudes. The precursor ion survival yield as a function of SORI amplitude falls into two distinct behaviors corresponding to slower- and faster-reacting ion populations. The slower-reacting population requires larger SORI amplitudes to achieve the same precursor ion survival yield as the faster exchanging population. Total deuterium incorporation into the y2/b5 ion pairs matches closely the theoretical values over all ion populations and SORI amplitudes studied. This result indicates the y2 and b5 ions are likely formed by the same mechanism over the SORI amplitudes studied. PMID:18802500

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

2008-01-01

174

Parametric Sensivity Study of Operating and Design Variables in Wellbore Heat Exchangers  

SciTech Connect

This report documents the results of an extensive sensitivity study conducted by the Idaho National Engineering and Environmental Laboratory. This study investigated the effects of various operating and design parameters on wellbore heat exchanger performance to determine conditions for optimal thermal energy extraction and evaluate the potential for using a wellbore heat exchanger model for power generation. Variables studied included operational parameters such as circulation rates, wellbore geometries and working fluid properties, and regional properties including basal heat flux and formation rock type. Energy extraction is strongly affected by fluid residence time, heat transfer contact area, and formation thermal properties. Water appears to be the most appropriate working fluid. Aside from minimal tubing insulation, tubing properties are second order effects. On the basis of the sensitivity study, a best case model was simulated and the results compared against existing low-temperature power generation plants. Even assuming ideal work conversion to electric power, a wellbore heat exchange model cannot generate 200 kW (682.4e+3 BTU/h) at the onset of pseudosteady state. Using realistic conversion efficiency, the method is unlikely to generate 50 kW (170.6e+3 BTU/h).

G. Michael Shook; Gopi Nalla; Gregory L. Mines; K. Kit Bloomfield

2004-05-01

175

Parametric Sensitivity Study of Operating and Design Variables in Wellbore Heat Exchangers  

SciTech Connect

This report documents the results of an extensive sensitivity study conducted by the Idaho National Engineering and Environmental Laboratory. This study investigated the effects of various operating and design parameters on wellbore heat exchanger performance to determine conditions for optimal thermal energy extraction and evaluate the potential for using a wellbore heat exchanger model for power generation. Variables studied included operational parameters such as circulation rates, wellbore geometries and working fluid properties, and regional properties including basal heat flux and formation rock type. Energy extraction is strongly affected by fluid residence time, heat transfer contact area, and formation thermal properties. Water appears to be the most appropriate working fluid. Aside from minimal tubing insulation, tubing properties are second order effects. On the basis of the sensitivity study, a best case model was simulated and the results compared against existing low-temperature power generation plants. Even assuming ideal work conversion to electric power, a wellbore heat exchange model cannot generate 200 kW (682.4e+3 BTU/h) at the onset of pseudosteady state. Using realistic conversion efficiency, the method is unlikely to generate 50 kW (170.6e+3 BTU/h).

Nalla, G.; Shook, G.M.; Mines, G.L.; Bloomfield, K.K.

2004-05-01

176

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

177

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

178

Density functional study of NO decomposition with Cu-exchanged zeolites  

Microsoft Academic Search

Cu ions exchanged into zeolites like ZSM-5 show high catalytic activity for the decomposition of environmentally harmful NO to harmless Nsb2 and Osb2. The present work is an attempt to study this phenomenon using a first-principles quantum mechanics-based density functional method. A small cluster model is proposed and used to examine the properties of zeolite-bound Cu ions, and their interactions

Ramamurthy Ramprasad

1997-01-01

179

Study on removing zinc from nickel electrolyte by ion-exchange  

Microsoft Academic Search

In the process of nickel production by diaphragm electrolysis, the quality of the product has been tremendously affected by\\u000a the content of zinc in the nickel electrolyte. Removing zinc from nickel electrolyte by ion-exchange is studied in the paper.\\u000a Resin D201 is selected as the resin for zinc removing. Effects of the operative parameters, such as temperature, pH value\\u000a and

Gui-qing Zhang; Qi-xiu Zhang; Lian-sheng Xiao; Bo-fan Gong

2000-01-01

180

Preliminary experimental study of a bio-inspired, phase-change particle capillary heat exchanger  

Microsoft Academic Search

In this study a new cooling concept using encapsulated phase-change particles flowing with water in a parallel-plate mini-channel is presented. This novel concept is inspired by the gas exchange process in alveolar capillaries, where red blood cells (RBCs) flow with blood plasma, yielding very high gas transfer efficiency. Another important characteristic of alveolar capillary blood flow, which is related to

Fatemeh Hassanipour; José L. Lage

2010-01-01

181

Comparative study of key exchange and authentication methods in application, transport and network level security mechanisms  

NASA Astrophysics Data System (ADS)

The key-exchange and authentication are two crucial elements of any network security mechanism. IPsec, SSL/TLS, PGP and S/MIME are well-known security approaches in providing security service to network, transport and application layers; these protocols use different methods (based on their requirements) to establish keying materials and authenticates key-negotiation and participated parties. This paper studies and compares the authenticated key negotiation methods in mentioned protocols.

Fathirad, Iraj; Devlin, John; Jiang, Frank

2012-09-01

182

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

183

STUDY OF FROST GROWTH ON HEAT EXCHANGERS USED AS OUTDOOR COILS IN AIR SOURCE HEAT PUMP SYSTEMS  

E-print Network

STUDY OF FROST GROWTH ON HEAT EXCHANGERS USED AS OUTDOOR COILS IN AIR SOURCE HEAT PUMP SYSTEMS OF FROST GROWTH ON HEAT EXCHANGERS USED AS OUTDOOR COILS IN AIR SOURCE HEAT PUMP SYSTEMS Dissertation of Frost Growth . . . . . . . . . . . . . . . . . . . . . 7 2.2 Frost Growth on Simple Geometries

184

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

Microsoft Academic Search

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

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

2004-01-01

185

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

186

Water-to-water heat transfer in tube–tube heat exchanger: Experimental and analytical study  

Microsoft Academic Search

Tube–tube heat exchanger (TTHE) is a low cost, vented double wall heat exchanger which increases reliability by avoiding mixing of fluids exchanging heat. It can be potentially used for heat recovery from engine cooling circuit, oil cooling, desuperheating in refrigeration and air conditioning, dairy, and pharmaceutical industry, chemical industry, refinery, etc. These tube–tube heat exchangers are successfully demonstrated for superheat

Milind V. Rane; Madhukar S. Tandale

2005-01-01

187

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

188

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

189

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

190

Experimental study of the Kirchhoff-Law-Johnson-Noise secure key exchange  

NASA Astrophysics Data System (ADS)

The Kirchhoff-Law-Johnson-Noise (KLJN) secure key distribution system provides a way of exchanging secure keys by using classical physics (electricity and thermodynamics). Several theoretical studies have addressed the performance and applicability of the communication protocol, and they have indicated that it is protected against all known types of attacks. However, until now, there have been very few real physical implementations and experimental tests of the protocol. With our work, we continue filling this gap. Details of implementing a KLJN based system are presented using a dedicated hardware and an off-the-shelf solution as well. Furthermore, the results of experimental tests and analysis of the performance will be presented.

Mingesz, Robert

2014-09-01

191

The exchange processes in o-vanillin salicyloylhydrazone as studied by two-dimensional NMR  

NASA Astrophysics Data System (ADS)

Multidimensional NMR studies of o-vanillin salicyloylhydrazone at various temperatures have been undertaken in deuterated dimethyl sulfoxide and its cryoprotective mixture in H 2O and D 2O, acetone and acetonitrile. The molecule is found to exist in two conformers in dimethyl sulfoxide and the cryoprotective mixture. The exchange between the two conformers has been detected from the two-dimensional experiments — information which is not easily obtainable from the normal one-dimensional spectra. Results in the different solvents are interpreted in terms of solvent—solute interactions.

Agarwala, B. V.; Puri, V.; Naganagowda, G. A.; Khetrapal, C. L.

1994-11-01

192

Equilibrium and kinetic studies on the adsorption of acidic dye by the gel anion exchanger.  

PubMed

In the present study, the gel anion exchanger Purolite A-850 of N(+)(CH(3))(3) functional groups was used in order to remove the acidic dye (Acid Blue 29) from aqueous solutions. Batch experiments were conducted to study the effect of phase contact time (1-180 min), initial concentration of dye (100-500 mg/L), solution pH (1-8), anion exchanger dosage (0.25-1.0 g) as well as temperature (20-40 degrees C). The contact time necessary to reach equilibrium was 40 min with the exception for the solution of the initial concentration 500 mg/L. The amounts of Acid Blue 29 adsorbed at equilibrium using the strongly basic anion exchanger were equal to 9.97, 19.97, 29.96 and 49.90 mg/g for the dye solutions of the initial concentrations 100, 200, 300 and 500 mg/L, respectively. The equilibrium sorption capacity slightly increased when the temperature of dye solution increased from 20 to 40 degrees C. The experimental data were analyzed by the Langmuir, Freundlich and Temkin models of adsorption. The adsorption isotherm data were fitted well to the Langmuir isotherm and the monolayer adsorption capacity was found to be 83.303 mg/g at 20 degrees C. The value of R(L) was equal to 0.00054 (favourable). The kinetic data obtained at different concentrations were modeled using the pseudo-first order, pseudo-second order and intraparticle diffusion equations. The experimental data were well described by the pseudo-second order kinetic model. PMID:19692176

Wawrzkiewicz, Monika; Hubicki, Zbigniew

2009-12-30

193

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

SciTech Connect

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

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

2011-03-01

194

An Empirical Study of Liquidity and Information Effects of Order Flow on Exchange Rates  

Microsoft Academic Search

We propose a simple structural model of exchange rate determination which draws from the analytical framework recently proposed by Bacchetta and van Wincoop (2003) and allows us to disentangle the liquidity and information effects of order flow on exchange rates. We estimate this model employing an innovative transaction data-set that covers all direct foreign exchange transactions completed in the USD\\/EUR

Francis Breedon; Paolo Vitale

2005-01-01

195

Temperature-Dependent Halogen-Exchange Activity Studies of Zeolite-Derived Aluminum Trifluoride  

SciTech Connect

A high-surface-area (190 m{sup 2}/g) amorphous aluminum trifluoride material ('plasma-AlF{sub 3}') was synthesized by plasma decomposition of zeolite, and its structural and reactivity properties were investigated. High-resolution transmission electron microscopy of plasma-AlF{sub 3} indicates morphological features on the nanometer-scale, whereas temperature-programmed X-ray diffraction is used to determine the phase-transition temperatures of plasma-AlF{sub 3} to {beta}- and {alpha}-AlF{sub 3}. Halogen-exchange reactivity is studied by temperature-programmed reaction (TPR) techniques using the dismutation of CCl{sub 2}F{sub 2} as a model reaction. Plasma-AlF{sub 3} is found to possess an unexpected low-temperature (>315 C) activity not observed with the well-known halogen-exchange catalyst {beta}-AlF{sub 3}. Supporting TPR studies on aluminum trifluoride hydrates are performed to correlate this new activity with an amorphous AlF{sub 3} structure, and a simple Lewis acid model is presented to explain the reactivity data.

Hajime,E.; Delattre, J.; Stacy, A.

2007-01-01

196

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

197

Stratosphere-troposphere exchange associated with a cut-off anticyclone: a case study  

NASA Astrophysics Data System (ADS)

We study stratosphere-troposphere exchange (STE) in Northern Hemisphere winter associated with a cut-off anticyclone. This study is inspired by observations of water vapor laminae in the lowermost stratosphere, which were linked to filamentation at flanks of cut-off anticyclone. A case study approach is adopted. The event we investigate occurred in February 2004 over the Northern Atlantic. Calculations of cross-tropopause fluxes (CTF) done by semi-Lagrangian method demonstrate that intensive two-way STE occurred at the flanks of the anticyclone. Attention is given to attribution of these fluxes to physical processes. Calculations of turbulence index suggest a link between turbulence and STE. The CTF calculated using assimilated winds from ECMWF model are compared with those calculated using ECMWF forecast winds in order to assess the impact of dynamical inconsistencies between analysis wind fields on STE estimations.

Karpechko, A. Y.; Lukyanov, A.

2006-12-01

198

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

Microsoft Academic Search

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

Y. H. Yau

2007-01-01

199

Study of the structure of an electrolyte in the ion-exchange resin phase by the nuclear magnetic resonance method  

Microsoft Academic Search

The structure of the electrolyte HF in the ion-exchange-res in phase was studied by the nuclear rnagnetic resonance method. A difference was noted between the concentration dependence of the chemical displacement of the absorbed electrolyte for cation and anion exchangers; this leads to the conclusion that the structure of the electrolyte differs in the respective phases, i.e., confirms the earlier

P. M. Borodin; M. K. Nikitin; E. N. Sventitskii

1965-01-01

200

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

201

Theoretical study of acetonitrile-exchange reactions on hexasolvated divalent cations in the first transition series elements  

NASA Astrophysics Data System (ADS)

Penta-, hexa-, and heptaacetonitrile complexes of divalent cations of the first transition series are studied by ab initio molecular orbital calculations. The factors that determine the structural stability and the reaction mechanism of solvent-exchange reactions are discussed. All the penta- and hexaacetonitrile species are at local minima, whereas the geometrical stability of the heptacoordinated species depends on the 3d electron configurations. The structural stability of heptaacetonitrile species is intermediate between those of hydrogen cyanide complexes and hydrates. Acetonitrile exchange reactions have more dissociative character than hydrogen cyanide exchange reactions because the inductive effect of the methyl group in CH3CN destabilizes the heptacoordinated structures. The successive binding energies show that associative mechanisms are favorable for acetonitrile exchange with earlier members of the first transition series, whereas dissociative mechanisms become favorable for later members.

Wasada, Hiroaki; Wasada-Tsutsui, Yuko; Hashimoto, Tomohiro; Funahashi, Shigenobu

202

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

203

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

E-print Network

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... differences and interpersonal relation problem. Actions to remove inhibitors to optimal scientific exchanges were: for host community removing the guests' protective environmental bubble, education in the customs of guests, language training for hosts...

Lu, Wei

2012-06-07

204

Conformational changes of ubiquitin during electrospray ionization as determined by in-ESI source H/D exchange combined with high-resolution MS and ECD fragmentation.  

PubMed

In the paper, we have demonstrated the possibility of performing hydrogen/deuterium (H/D) exchange of proteins in the region of gas-phase ion formation in an electrospray ion source by saturating the electrospray ionization source with vapors of a deuterating agent (D2 O or MeOD). In this region, charged droplets are shrinking and the protein ions transfer into the gas phase. As a model protein, we have used ubiquitin whose ion mobility spectrometry and gas-phase H/D exchange in the vacuum part of a mass spectrometer demonstrated the presence of gas-phase conformers with different cross sections and H/D exchange rates. In our experiments, we observed monomodal deuterium distributions for all solvents, charge states, desolvating capillary temperature and types of deuterating agent. Also, we found that the number of H/D exchanges increases with an increasing desolvating capillary temperature and decreasing charge state. We observed that solution composition (49?:?50?:?1 H2 O?:?MeOH?:?formic acid or 99?:?1 H2 O?:?formic acid) influences the charge-state distribution but did not change the degree of H/D exchange for the same charge state. Electron-capture dissociation fragmentation shows that higher charge states contain a segment that is protected from access by the deuterating agent. Copyright © 2014 John Wiley & Sons, Ltd. PMID:25303388

Kostyukevich, Yury; Kononikhin, Alexey; Popov, Igor; Nikolaev, Eugene

2014-10-01

205

Heat transfer and flow studies of the liquid droplet heat exchanger  

NASA Technical Reports Server (NTRS)

This paper describes a lightweight, highly effective liquid droplet heat exchanger (LDHX) concept for thermal management in space. Heat is transferred by direct contact between fine droplets (100 to 300 micron diameter) of a low vapor pressure liquid and an inert working gas. Complete separation of the droplet and gas media in the microgravity environment is accomplished by configuring the LDHX as a vortex chamber. A quasi-one-dimensional, two-phase heat transfer model of the LDHX is developed and used to investigate the potential use of the LDHX for both heating and cooling the working gas in a 100-k W(e) Braytoan cycle. Experimental studies on a small scale LDHX chamber, using air and water as the two media, show excellent agreement with the theoretical model.

Bruckner, A. P.; Shariatmadar, A.

1987-01-01

206

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

207

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

208

Water Sorption and Vapor-Phase Deuterium Exchange Studies on Methemoglobin CC, SC, SS, AS, and AA  

PubMed Central

Five hemoglobins whose genetic relationship to one another involves one set of alleles, hemoglobins CC, SC, SS, AS, and AA, were studied in the Met form. Two different investigations were conducted at 28°C on these methemoglobins within a McBain gravimetric sorption system: sorption of H2O vapor and vapor-phase deuterium-hydrogen exchange. For each of the five samples there was close agreement between the per cent hydration of polar sites as determined from sorption studies and the maximum per cent of labile hydrogens that were exchanged during the vapor-phase deuterium exchange study. Both studies measured a slight increase in the number of polar sites accessible to H2O or D2O vapor for those samples in which the substituent in the sixth position from the N-terminus of the two ?-chains had a positively charged side chain and a slight decrease for those in which the substituent had a negatively charged side chain. The in-exchange of deuterium for hydrogen occurred at a faster observed rate than the out-exchange of hydrogen for deuterium. PMID:5030563

Killion, Philip J.; Cameron, Bruce F.

1972-01-01

209

Muon spin relaxation study of exchange coupling in dilute AgMn alloys  

SciTech Connect

We have observed for the first time conduction-electron mediated muon-impurity coupling, and deduced the strength of the conduction electron-Mn exchange coupling. Our results are marginally consistent with a wave-vector dependent exchange model. 16 refs.

Heffner, R.H.; Cooke, D.W.; Hutson, R.L.; Schillaci, M.E.; Dodds, S.A.; Gist, G.A.; MacLaughlin, D.E.

1985-01-01

210

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

Microsoft Academic Search

Using the external heat exchanger in large-scale CFB boilers can control combustion and heat transfer separately, make the adjustments of bed temperature and steam temperature convenient. The state of gas-solid two phase flow in the external heat exchanger is bubbling fluidized bed, but differs from the regular one as there is a directional flow in it. Consequently, the temperature distribution

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

2010-01-01

211

An experimental study of a cross-flow type plate heat exchanger for dehumidification\\/cooling  

Microsoft Academic Search

The thermal and dehumidification behaviour of a standard cross-flow type plate heat exchanger, intended for use as a dehumidifier\\/cooler, has been investigated both experimentally and numerically. Three sets of experiments have been carried out where air is blown into the primary and secondary sides of the exchanger, while water and liquid desiccant were being sprayed in a counter flow arrangement.

W. Y Saman; S Alizadeh

2002-01-01

212

Magnetic force microscope study of antiferromagnet-ferromagnet exchange coupled films  

NASA Astrophysics Data System (ADS)

Magnetic microstructure in micron and submicron size elements made of bilayer antiferromagnet-ferromagnet (AFM/FM) (AFM: NiMn, PtMn, and IrMn; FM: NiFe and CoFe) exchange coupled polycrystalline films have been studied using a magnetic force microscope. AFM/FM elements with various thickness of FM layer (50-500 A) have been examined and compared with nonexchange biased FM elements of the same size, shape, and thickness. Micromagnetic structures observed in AFM/FM elements with thick (>200 A) FM layer indicated that, in addition to unidirectional anisotropy, the AFM layer induces uniaxial anisotropy in a FM layer. Bilayers with a NiMn or PtMn AFM layer exhibited higher induced uniaxial anisotropy than ones with IrMn. In the elements with a thin (<100 A) FM layer and NiMn or PtMn as an AFM layer, a local switching of the magnetization direction under an external applied field has been observed. The size of the "switched" areas depends on the material and thickness of the FM and AFM layers. No local switching, just slight rippling of magnetization in the FM, was observed in the samples with an IrMn AFM layer. The results can be explained using either the model of thermally activated switching of AFM grains or the model of induced uniaxial anisotropy at the AFM/FM interface suggesting local variations of induced uniaxial anisotropy. In both models, the in-plane exchange in the FM layer has to be taken into account.

Pokhil, Taras; Song, Dian; Linville, Eric

2002-05-01

213

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

214

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

215

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

216

DFT Study of Nitrogen-Substituted FAU: Effects of Ion Exchange and Aluminum Content on Base Strength  

E-print Network

DFT Study of Nitrogen-Substituted FAU: Effects of Ion Exchange and Aluminum Content on Base catalysts.9,10 However, there has been no systematic study of base strength versus aluminum content ambiguously identified.6,9,10,12-19 By combining 29 Si solid-state NMR and quantum calculations of chemical

Auerbach, Scott M.

217

Fouling of an anion exchange chromatography operation in a monoclonal antibody process: Visualization and kinetic studies  

PubMed Central

Fouling of chromatographic resins over their operational lifetimes can be a significant problem for commercial bioseparations. In this article, scanning electron microscopy (SEM), batch uptake experiments, confocal laser scanning microscopy (CLSM) and small-scale column studies were applied to characterize a case study where fouling had been observed during process development. The fouling was found to occur on an anion exchange (AEX) polishing step following a protein A affinity capture step in a process for the purification of a monoclonal antibody. Fouled resin samples analyzed by SEM and batch uptake experiments indicated that after successive batch cycles, significant blockage of the pores at the resin surface occurred, thereby decreasing the protein uptake rate. Further studies were performed using CLSM to allow temporal and spatial measurements of protein adsorption within the resin, for clean, partially fouled and extensively fouled resin samples. These samples were packed within a miniaturized flowcell and challenged with fluorescently labeled albumin that enabled in situ measurements. The results indicated that the foulant has a significant impact on the kinetics of adsorption, severely decreasing the protein uptake rate, but only results in a minimal decrease in saturation capacity. The impact of the foulant on the kinetics of adsorption was further investigated by loading BSA onto fouled resin over an extended range of flow rates. By decreasing the flow rate during BSA loading, the capacity of the resin was recovered. These data support the hypothesis that the foulant is located on the particle surface, only penetrating the particle to a limited degree. The increased understanding into the nature of the fouling can help in the continued process development of this industrial example. Scanning electron microscopy (SEM), batch uptake experiments, confocal laser scanning microscopy (CLSM) and small-scale column experiments were applied to characterize a case study where fouling had been observed on an anion exchange chromatography in a monoclonal antibody process. The results suggest the foulant is located on the particle surface, resulting in a minimal decrease in saturation capacity, but having a significant impact on the kinetics of adsorption, severely decreasing protein uptake rate. PMID:23483524

Close, Edward J; Salm, Jeffrey R; Iskra, Timothy; S?rensen, Eva; Bracewell, Daniel G

2013-01-01

218

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

219

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

220

First principle study of selective catalytic nitrogen oxide reduction over copper-exchanged zeolites  

NASA Astrophysics Data System (ADS)

Cu-ZXM5 is as promising catalyst candidate for mobile source (auto truck) NOX emission control. The present work studies this phenomenon from different perspectives. Firstly, a methodology is developed to validate the proposed NO decomposition mechanism with a kinetic Reactor model. The Reactor model involves a plug flow reactor that simulates forty-two elementary reactions. The simulation operates at moderate temperatures (300-1000 K) and the results are compared with micro-reactor experimental results. Secondly, gas phase reaction of NO with NH3 in the thermal deNOX process is studied to reveal origins of ammonia's selectivity for NO over O2. The gas phase study does electronic comparison of the competing reactions of NH3 radical with NO and O2 respectively. NH3 selectivity lies in strongly bound H2NNO adduct that readily rearranges and decompose to N2 and H2O. The pronounced discrimination of NH3 against reaction with O2 is explored through comparison of the electronic structures of the H2NNO and H2NOO radical adducts and provides insight into the selectivity of NH3 in the surface reactions. Thirdly, thermal chemistry of selective catalytic reduction (SCR) of NOX with ammonia over Cu-exchanged zeolites is investigated with density functional theory (DFT). The catalytic reaction pathways are mapped out and compared with those in the gas phase reactions, which reveals that the major activation barriers are lowered in the catalytic reactions.

Sun, Donghai

221

Advantages of the gas-exchange approach to microbiological studies. Memorandum report 1983-1985  

SciTech Connect

Studies of the effects of various chemical or physical stimuli on the growth rates of microorganisms generally involve some measure of biomass. In the case of algae, one might measure the cell number, the chlorophyll concentration, the fluorescence, or the wet weight of the culture as a function of time. Each such measurement requires a sampling of the culture which could be a disturbing factor in the system being measured. Another disadvantage of these traditional measurements is that the times required for significant change to take place in the culture might be hours or days; furthermore, growth rate measurements calculated from the data must be based on the assumption that during the time between measurements the growth rate was constant. This report describes another approach to the problem. It consists simply of monitoring the O/sub 2/ or CO/sub 2/ concentration of an air stream passing through the system (the gas exchange method), and it has several distinct advantages: 1) there is no need to take samples of the culture, 2) each measurement is a rate measurement and indicates the performance of the culture at that very moment, and 3) transitory changes in growth rates are readily detected. Examples are given of studies made previously with this method at NRL. Also the possible value of these methods in a study of the corrosion susceptibility of alloys is described.

Hannan, P.J.; Jones, D.S.

1986-04-03

222

Improving DNA data exchange: Validation studies on a single 6 dye STR kit with 24 loci.  

PubMed

The idea of developing a new multiplex STR amplification system was conceived in 2011 as an effective way to implement the new European standard set (ESS) of 12 STR markers adopted by The Council of the European Union in 2009 while maintaining an effective compatibility and information exchange with the historical DNA profiles contained in the Spanish national DNA database (around 200,000 DNA profiles) mainly based on the 13 CODIS core STR loci plus D19S433 and D2S1338 markers. With this goal in mind we proposed to test and validate a single STR amplification system for simultaneous analysis of 21 STR markers covering both CODIS and ESS core STR loci plus three additional markers (D19S433, D2S1338, and SE33) also contained in commonly used STR kits and national DNA databases. In 2012, we started the first beta-testing with a 6-dye STR kit prototype containing 24 loci (now known as the GlobalFiler™ PCR Amplification Kit) developed by Life Technologies in response to the CODIS Core Loci Working Group's recommendation to expand the CODIS Core Loci. This prototype included our proposal of 21 autosomal STR markers and two Y-chromosome markers (DYS391 and Y-indel) and maximizes concordance with established databases and previously analyzed samples by maintaining primer sequences of previous Identifiler(®)/NGM SElect™ kits for the 21 STR markers except for TPOX. This paper describes the validation studies conducted with the first commercial available 6-dye STR kit for casework using a 3500 genetic analyzer for fragment detection that included the analysis of the following parameters and aspects: analytical threshold, sensitivity & stochastic threshold, heterozygous balance, stutter threshold, precision and accuracy, repeatability and reproducibility, genotype concordance, DNA mixtures, species specificity, and stability studies with case type samples. The studies demonstrated that the GlobalFiler™ system provided equivalent overall performance to previous forensic STR PCR kits, but with enhanced discrimination power for a better match efficiency that would reduce the chance of adventitious matches during DNA data exchange among national DNA databases. PMID:25082138

Martín, Pablo; de Simón, Lourdes Fernández; Luque, Gracia; Farfán, María José; Alonso, Antonio

2014-11-01

223

Enumeration of non-labile oxygen atoms in dissolved organic matter by use of (16)O/ (18)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

224

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

PubMed Central

Objective: Improving the process of evidence-based practice in primary health care requires an understanding of information exchange among colleagues. This study explored how clinically oriented research knowledge flows through multidisciplinary primary health care teams (PHCTs) and influences clinical decisions. Methods: This was an exploratory mixed-methods study with members of six PHCTs in Ontario, Canada. Quantitative data were collected using a questionnaire and analyzed with social network analysis (SNA) using UCINet. Qualitative data were collected using semi-structured interviews and analyzed with content analysis procedures using NVivo8. Results: It was found that obtaining research knowledge was perceived to be a shared responsibility among team members, whereas its application in patient care was seen as the responsibility of the team leader, usually the senior physician. PHCT members acknowledged the need for resources for information access, synthesis, interpretation, or management. Conclusion: Information sharing in interdisciplinary teams is a complex and multifaceted process. Specific interventions need to be improved such as formalizing modes of communication, better organizing knowledge-sharing activities, and improving the active use of allied health professionals. Despite movement toward team-based models, senior physicians are often gatekeepers of uptake of new evidence and changes in practice. PMID:23646028

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

2013-01-01

225

Multidimensional Separations of Ubiquitin Conformers in the Gas Phase: Relating Ion Cross Sections to H/D Exchange Measurements  

PubMed Central

Investigating gas-phase structures of protein ions can lead to an improved understanding of intramolecular forces that play an important role in protein folding. Both hydrogen/deuterium (H/D) exchange and ion mobility spectrometry provide insight into the structures and stabilities of different gas-phase conformers, but how best to relate the results from these two methods has been hotly debated. Here, high-field asymmetric waveform ion mobility spectrometry (FAIMS) is combined with Fourier-transform ion cyclotron resonance mass spectrometry (FT/ICR MS) and is used to directly relate ubiquitin ion cross sections and H/D exchange extents. Multiple conformers can be identified using both methods. For the 9+ charge state of ubiquitin, two conformers (or unresolved populations of conformers) that have cross sections differing by 10% are resolved by FAIMS, but only one conformer is apparent using H/D exchange at short times. For the 12+ charge state, two conformers (or conformer populations) have cross sections differing by <1%, yet H/D exchange of these conformers differ significantly (6 versus 25 exchanges). These and other results show that ubiquitin ion collisional cross sections and H/D exchange distributions are not strongly correlated and that factors other than surface accessibility appear to play a significant role in determining rates and extents of H/D exchange. Conformers that are not resolved by one method could be resolved by the other, indicating that these two methods are highly complementary and that more conformations can be resolved with this combination of methods than by either method alone. PMID:16023362

Robinson, Errol W.; Williams, Evan R.

2009-01-01

226

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

PubMed Central

Introduction In 2008, one of the oldest fixed site needle exchanges in a large urban city in Canada was closed due to community pressure. This service had been in existence for over 20 years. Case Description This case study focuses on the consequences of the switch to mobile needle exchange services immediately after the closure and examines the impact of the closure on changes in risk behavior related to drug use, needle distribution and access to services The context surrounding the closure was also examined. Discussion and Evaluation After the closure of the fixed site exchange, access to needle exchange services decreased as evidenced by the sharp decline in numbers of clients reached, and the numbers of needles distributed and collected monthly. Reports related to needle reuse and selling of syringes suggest changes in risk behaviors. Thousands of needles remain unaccounted for in the community. To date, a new fixed site has not been found. Conclusion Closing the fixed site needle exchange had an adverse effect on already vulnerable clients and reduced access to comprehensive harm reduction services. While official public policy supports a fixed site, politicization of the issue has meant a significant setback for harm reduction with reduced potential to meet public health targets related to reducing the spread of blood borne diseases. This situation is unacceptable from a public health perspective. PMID:20500870

2010-01-01

227

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

228

Exchange transfusion with fluorocarbon for studying synaptically evoked optical signal in rat cortex.  

PubMed

Optical imaging of intrinsic signal is a powerful technique for studying the functional organization of the brain [T. Bonhoeffer, D. S. Kim, D. Malonek, D. Shoham, A. Grinvald, Optical imaging of the layout of functional domains in area 17 and across the area 17/18 border in cat visual cortex, Eur. J. Neurosci. 7 (1995) 1973-1988; M. Hubener, D. Shoham, A. Grinvald, T. Bonhoeffer, Spatial relationships among three columnar systems in cat area 17, J. Neurosci. 17 (1997) 9270-9284; D. Malonek, A. Grinvald, Interactions between electrical activity and cortical microcirculation revealed by imaging spectroscopy: implications for functional brain mapping, Science 272 (1996) 551-554; A. Shmuel, A. Grinvald, Functional organization for direction of motion and its relationship to orientation maps in cat area 18, J. Neurosci. 16 (1996) 6945-6964] [1] [10] [14] [22]. Three components of intrinsic optical signal can be distinguished. Two of these components can be attributed either to changes in blood volume or to changes in oxygen consumption [R.D. Frostig, E.E. Lieke, D.Y. Ts'o, A. Grinvald, Cortical functional architecture and local coupling between neuronal activity and the microcirculation revealed by in vivo high resolution optical imaging of intrinsic signals, Proc. Natl. Acad. Sci. U. S. A. 87 (1990) 6082-6086] [7]. The origin of the third component is not yet clear but the component seems to be based on scattered light [H.U. Dodt, G. D'Arcangelo, E. Pestel, W. Zieglgansberger, The spread of excitation in neocortical columns visualized with infrared-dark field videomicroscopy, NeuroReport 7 (1996) 1553-1558; K. Holthoff, O.W. Witte, Intrinsic optical signals in rat neocortical slices measured with near-infrared dark-field microscopy reveal changes in extracellular space, J. Neurosci. 16 (1996) 2740-2749; B.A. MacVicar, D. Hochman, Imaging of synaptically evoked intrinsic optical signals in hippocampal slices, J. Neurosci. 11 (1991) 1458-1469; L. Trachsel, H.U. Dodt, W. Zieglgansberger, The intrinsic optical signal evoked by chiasm stimulation in the rat suprachiasmatic nuclei exhibits GABAergic day-night variation, Eur. J. Neurosci. 8 (1996) 319-328] [3] [9] [13] [24]. A spectral fitting method with three components is used for the analysis of intrinsic optical signal [M. Nemoto, Y. Nomura, C. Sato, M. Tamura, K. Houkin, I. Koyanagi, H. Abe, Analysis of optical signals evoked by peripheral nerve stimulation in rat somatosensory cortex: dynamic changes in hemoglobin concentration and oxygenation, J. Cereb. Blood Flow Metab. 19 (1999) 246-259] [17]. In order to validate the analysis, we need the knowledge on contribution of signal resulted from hemoglobin to total intrinsic optical signal. The exchange transfusion with fluorocarbon has the advantage that can change the spectral contribution of hemoglobin [M. Ferrari, M.A. Williams, D.A. Wilson, N.V. Thakor, R.J. Traystman, D.F. Hanley, Cat brain cytochrome-c oxidase redox changes induced by hypoxia after blood-fluorocarbon exchange transfusion, Am. J. Physiol. 269 (1995) H417-H424; A.L. Sylvia, C.A. Piantadosi, O(2) dependence of in vivo brain cytochrome redox responses and energy metabolism in bloodless rats, J. Cereb. Blood Flow Metab. 8 (1988) 163-172] [6] [23]. Here we describe a new method of the reduction of hemoglobin signal from somatosensory evoked optical intrinsic signal in rat cortex by the combination of exchange transfusion with fluorocarbon and imaging system of thinned skull cranial window. The method allows for the study of the synaptically evoked changes in light scattering as well as fluorescence of calcium indicator or voltage-sensitive dye without absorption of hemoglobin. PMID:10719260

Nomura, Y; Fujii, F; Sato, C; Nemoto, M; Tamura, M

2000-02-01

229

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

230

Studying the aerodynamic parameters characterizing motion of gas suspension in a countercurrent cyclone heat exchanger  

Microsoft Academic Search

The physical pattern of flow in a countercurrent cyclone heat exchanger obtained from experiments carried out on a small-scale model of it is presented. Self-oscillation behavior of a toroidal vortex occurring in the apparatus was experimentally observed. A possibility of reducing the quantity of large particles of solid materials 0.07-0.15 mm in size entrained from a countercurrent cyclone heat exchanger

P. A. Kovgan; M. G. Abuov

2009-01-01

231

Studying the aerodynamic parameters characterizing motion of gas suspension in a countercurrent cyclone heat exchanger  

Microsoft Academic Search

The physical pattern of flow in a countercurrent cyclone heat exchanger obtained from experiments carried out on a small-scale\\u000a model of it is presented. Self-oscillation behavior of a toroidal vortex occurring in the apparatus was experimentally observed.\\u000a A possibility of reducing the quantity of large particles of solid materials 0.07–0.15 mm in size entrained from a countercurrent\\u000a cyclone heat exchanger

P. A. Kovgan; M. G. Abuov

2009-01-01

232

An experimental study on the thermal performance of ground heat exchanger  

SciTech Connect

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

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

2007-08-15

233

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

Microsoft Academic Search

\\u000a Using the external heat exchanger in large-scale CFB boilers can control combustion and heat transfer separately, make the\\u000a adjustments of bed temperature and steam temperature convenient. The state of gas-solid two phase flow in the external heat\\u000a exchanger is bubbling fluidized bed, but differs from the regular one as there is a directional flow in it. Consequently,\\u000a the temperature distribution

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

234

Experimental study on helium-air exchange flow through small openings with vertical partition  

Microsoft Academic Search

The helium-air exchange flow may occur at the rupture accident of a standpipe in a high temperature engineering test reactor.\\u000a A test vessel with three types of small opening is used for experiments. An estimation method of mass increment is applied\\u000a to measure the exchange flow rate. Flow measurements are made with the single opening and partitioned, opening, for opening

Tae-il Kang

1998-01-01

235

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

2014-07-01

236

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

SciTech Connect

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

Gober, J.R.

1988-01-01

237

F- and H-Area Seepage Basins Water Treatment System Process Optimization and Alternative Chemistry Ion Exchange/Sorbent Material Screening Clearwell Overflow Study  

SciTech Connect

This study investigated alternative ion exchange/sorbent materials and polishing chemistries designed to remove specific radionuclides not removed during the neutralization/precipitation/clarification process.

Serkiz, S.M.

2000-08-30

238

Basic study of radiative and convective heat exchange in a room with floor heating  

SciTech Connect

Radiative heat exchange is a dominant factor in a room with a heated floor. Convective heat exchange is also important because it is increased by air circulation caused by natural convection. Surface temperatures inside the room increase when surfaces receive radiative heat flux originating from the heated floor. Since convective heat exchange takes place between the room air and the inside surfaces, it directly affects the room air temperature. Although radiative heat exchange does not influence room air temperature directly, it decreases the temperature difference between inside surfaces. These behaviors determine the wall surface temperatures and the amount of heat flux between the room air and the inside surfaces. This paper presents several basic characteristics of heat transfer on inside surfaces and temperature and velocity distribution in a room with a heated floor. Basic experiments and numerical analysis on radiative and convective heat transfer were carried out. The following conclusions were obtained: (1) a floor heating experiment produces approximately uniform air temperature except near windows where cold drafts lower the air temperature; (2) numerical analysis qualitatively predicts this kind of room air temperature distribution within 1.8 F (1 C); (3) convective heat exchange constitutes approximately half of the total heat exchange based on numerical analysis.

Hanibuchi, Haruo [Sekisui House Ltd., Kizu, Kyoto (Japan); Hokoi, Shuichi [Kyoto Univ., Sakyo, Kyoto (Japan). Dept. of Architecture and Environmental Design

1998-10-01

239

Study on the Heat-flow Controlable Heat Exchanger (first report)  

NASA Astrophysics Data System (ADS)

Heat generating devices and heat recovery systems are desired to control the heat flow and the temperature, contrary to the prior thermo-siphon uncontrolable heat flow. Then, authors have developed a heat flow controlable heat exchanger having a bubble pump mechanism without movable par t. The heat exchanger is consisted of evaporator, condenser, vapor passage pipe, liquid return pipe with a reverse-U type pipe, and heater located on the reverse pipe. Further the system encloses evaporating liquid and is possible to control heat flow between the evaporator to the condenser by adjusting the heater power. This paper presents experimental results on the system. The following results are obtained. (1) The heat exchanger can control heat flow between the evaporator to the condenser by adjusting the heater input which is smaller about 1/20 the above heat flow. (2) The complex heat flow controlable heat exchanger system is possible to control the output temperature by changing its operating heat exchanger number. (3) This heat exchanger is useful to the heat recovery at the room, the temperature control at the space, and the system joining heat storage system.

Hamano, Masayoshi; Yanadori, Michio; Kawano, Tomohiro

240

The effects of configurations on the performance of microchannel counter-flow heat exchangers–An experimental study  

Microsoft Academic Search

The influences of configurations on the performance of microchannel heat exchangers were studied experimentally. The parameters associated with geometrical configuration consist of substrate thickness, cross-sectional area, and inlet\\/outlet locations. In order to evaluate the effects of these parameters, two categories of fluid flow conditions (varying the inlet temperature of hot side and varying the mass flow rate of cold side)

Thanhtrung Dang; Jyh-tong Teng

2011-01-01

241

Out-of-hours GPs and palliative care-a qualitative study exploring information exchange and communication issues  

Microsoft Academic Search

BACKGROUND: Out-of-hours general practitioners (GPs) cover the community over a significant proportion of a given week, and palliative care patients are seen as a priority. Little is known about how well these GPs feel supported in their line of work and whether communication exchanges work well for the proportion of their patients who have palliative care needs. For this study,

Mark Taubert; Annmarie Nelson

2010-01-01

242

A Pilot Evaluation Study of the Picture Exchange Communication System (PECS) for Children with Autistic Spectrum Disorders  

Microsoft Academic Search

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.

Iliana Magiati; Patricia Howlin

2003-01-01

243

COMPETITIVE INTELLIGENCE COMPARISON BASED ON THE TYPES OF INDUSTRY. CASE STUDY: LISTED COMPANIES IN TEHRAN STOCK EXCHANGE (TSE)  

Microsoft Academic Search

The purpose of this study is to compare competitive intelligence based on the types of industry. In order to do this, the listed companies in Tehran Stock Exchange (TSE) during a five year period (2004-2008) have been selected. These companies’ products are grouped into five industrial categories; that are, food & drink, tile & ceramic, petrochemical, automobile & parts manufacturing,

Mortazavi Mahdy; Javadi Pour Far Mahnoosh

2011-01-01

244

A Longitudinal Study of the Moderating Role of Extraversion: Leader-Member Exchange, Performance, and Turnover during New Executive Development  

ERIC Educational Resources Information Center

Identifying factors that help or hinder new executives in "getting up to speed" quickly and remaining with an organization is vital to maximizing the effectiveness of executive development. The current study extends past research by examining extraversion as a moderator of relationships between leader-member exchange (LMX) and performance,…

Bauer, Talya N.; Erdogan, Berrin; Liden, Robert C.; Wayne, Sandy J.

2006-01-01

245

PAPER STUDY EVALUATIONS OF THE INTRODUCTION OF SMALL COLUMN ION EXCHANGE WASTE STREAMS TO THE DEFENSE WASTE PROCESSING FACILITY  

Microsoft Academic Search

The objective of this paper study is to provide guidance on the impact of Monosodium Titanate (MST) and Crystalline Silicotitanate (CST) streams from the Small Column Ion Exchange (SCIX) process on the Defense Waste Processing Facility (DWPF) flowsheet and glass waste form. A series of waste processing scenarios was evaluated, including projected compositions of Sludge Batches 8 through 17 (SB8

K. Fox; T. Edwards; M. Stone; D. Koopman

2010-01-01

246

Low Mass MS/MS Fragments of Protonated Amino Acids Used for Distinction of Their 13C- Isotopomers in Metabolic Studies  

NASA Astrophysics Data System (ADS)

Glu, Gln, Pro, and Ala are the main amino acids involved in ammonia detoxification in mosquitoes. In order to develop a tandem mass spectrometry method (MS2) to monitor each carbon of the above isotopically-labeled 13C-amino acids for metabolic studies, the compositions and origins of atoms in fragments of the protonated amino acid should be first elucidated. Thus, various electrospray (ESI)-based MS2 tools were employed to study the fragmentation of these unlabeled and isotopically-labeled amino acids and better understand their dissociation pathways. A broad range of fragments, including previously-undescribed low m/z fragments was revealed. The formulae of the fragments (from m/z 130 down to m/z 27) were confirmed by their accurate masses. The structures and conformations of the larger fragments of Glu were also explored by ion mobility mass spectrometry (IM-MS) and gas-phase hydrogen/deuterium exchange (HDX) experiments. It was found that some low m/z fragments ( m/z 27-30) are common to Glu, Gln, Pro, and Ala. The origins of carbons in these small fragments are discussed and additional collision induced dissociation (CID) MS2 fragmentation pathways are proposed for them. It was also found that small fragments (? m/z 84) of protonated, methylated Glu, and methylated Gln are the same as those of the underivatized Glu and Gln. Taken together, the new approach of utilizing low m/z fragments can be applied to distinguish, identify, and quantify 13C-amino acids labeled at various positions, either in the backbone or side chain.

Ma, Xin; Dagan, Shai; Somogyi, Árpád; Wysocki, Vicki H.; Scaraffia, Patricia Y.

2013-04-01

247

Scalable properties of metal clusters: A comparative study of modern exchange-correlation functionals  

NASA Astrophysics Data System (ADS)

The performance of eight generalized gradient approximation exchange-correlation (xc) functionals is assessed by a series of scalar relativistic all-electron calculations on octahedral palladium model clusters Pdn with n = 13, 19, 38, 55, 79, 147 and the analogous clusters Aun (for n up through 79). For these model systems, we determined the cohesive energies and average bond lengths of the optimized octahedral structures. We extrapolate these values to the bulk limits and compare with the corresponding experimental values. While the well-established functionals BP, PBE, and PW91 are the most accurate at predicting energies, the more recent forms PBEsol, VMTsol, and VT{84}sol significantly improve the accuracy of geometries. The observed trends are largely similar for both Pd and Au. In the same spirit, we also studied the scalability of the ionization potentials and electron affinities of the Pd clusters, and extrapolated those quantities to estimates of the work function. Overall, the xc functionals can be classified into four distinct groups according to the accuracy of the computed parameters. These results allow a judicious selection of xc approximations for treating transition metal clusters.

Koitz, Ralph; Soini, Thomas M.; Genest, Alexander; Trickey, S. B.; Rösch, Notker

2012-07-01

248

Electrical transport studies in the topological insulator Bi2Se3 with exchange induced ferromagnetism  

NASA Astrophysics Data System (ADS)

The proximity-induced ferromagnetic order in topological insulator (TI)/ferromagnetic insulator (FI) heterostructures induces ferromagnetism in TI, which breaks local time reversal symmetry that can lead to many exotic properties, such as image magnetic monopole, topological magneto-electric effects, etc.[1] We achieved this novel ferromagnetic order in a TI Bi2Se3 through Bi2Se3/EuS bi-layer structures. Electric transport studies show a dramatic suppression of the weak anti-localization (WAL) effect in Bi2Se3/EuS compared to controlled Bi2Se3 samples. In contrast to the case of surface doping a TI with magnetic atoms (i.e. Fe), here the WAL cannot be quenched even with a full coverage EuS capping layer, which points that its origin can be the opening of a surface gap rather than a reduction of the magnetic scattering length. The results are analyzed with a theoretical model providing a value for the induced surface exchange gap. Other experimental results, such as the anomalous Hall effect that support the proximity induced ferromagnetism in Bi2Se3 will be discussed.[4pt] [1] Qi, X.-L. & Zhang, S.-C., Rev Mod Phys 83, 1057-1110, (2011).

Wei, Peng; Katmis, Ferhat; Assaf, Badih; Heiman, Donald; Moodera, Jagadeesh

2013-03-01

249

Green function studies of the interlayer exchange coupling in magnetic multilayers  

NASA Astrophysics Data System (ADS)

The Interlayer Exchange Coupling (IEC) of magnetic multilayers has been one of the most studied problems in condensed matter physics for the last decade. It is found that for a multilayer structure in which magnetic layers are separated by a spacer, the magnetic moments of each layer orient themselves parallel, antiparallel or even perpendicular to each other, depending on the thickness of the spacer. This variable interlayer coupling of the magnetizations is oscillatory and usually multiperiodic. Its determination has posed interesting challenges, because often calculated results differ from the experimental ones. From the application standpoint, multilayer structures are used in the new generation of recording heads. In the first part of the present work, we used the Reflection Amplitude Approximation (RAA) to calculate the coupling in the prototypical system of an Fe/Cr trilayer. We were able to identify the origin of the long period oscillation in the coupling, and obtain a coupling strength that was among the best theoretical predictions. In the second part, we used a more accurate method that employed the so called Analytical Green Function (AGF). The results of this approach offered a good checkpoint of RAA, and they were in good agreement with the experimental findings in Fe/Cr and Co/Cu systems. We then calculated the intrinsic biquadratic coupling and compared it to the extrinsic one, obtained from the thickness fluctuation model. We also studied the effect that the finite thickness of the magnetic layers may have on the coupling, in particular in the appearance of Fano resonances. Finally, we studied how the coupling changes when roughness, alloying of the spacer, or strain are present. In all cases, the results were in very good agreement with experiment, showing that the AGF method is a very accurate, and yet very efficient method, for the determination of the IEC.

Tsetseris, Leonidas

250

First-principles study of the magnetic stability and the exchange couplings of LaMn2O5  

NASA Astrophysics Data System (ADS)

Using first principles calculations, the electronic and magnetic properties of the multiferroic LaMn2O5 have been studied. In particular, we have studied the magnetic stability of this material not only in ab-plane but also along c direction. Beside this, the exchange couplings between manganese ions have been calculated using Heisenberg model by including only the nearest neighbour interactions. It is shown that the stable magnetic order of LaMn2O5 is of antiferromagnetic type, which is in good agreement with the experiments. In order to show the effect of the temperature on the properties of our compound we have carried out this study using two crystal structures: the higher symmetric one (space group Pbam) that reported experimentally at T(98.8 k) and the lower symmetric one (space group Pmc21) that obtained from the relaxation, in our calculations, at T = 0 K starting from the stable magnetic order.This structure deformation at T = 0 can be related to the exchange coupling striction. The density of states show an insulating behavior in the antiferromagnetic state of LaMn2O5 at Fermi level and there is a small band gap, confirming the experimental fact that LaMn2O5 is an insulator. We have found that the nature of the mechanism of these magnetic exchange coupling is an indirect super-exchange.

El Hallani, F.; Naji, S.; Ez-Zahraouy, H.; Benyoussef, A.

2013-10-01

251

Freezing in residential air-to-air heat exchangers: an experimental study  

SciTech Connect

Mechanical ventilation of residences, with heat recovery in air-to-air heat exchangers, is an increasingly common practice. When this technique of ventilation is used in cold climates, however, freezing can occur in the air-to-air heat exchanger and substantially reduce its performance. A laboratory investigation was conducted to determine the indoor and outdoor environmental conditions that lead to freezing, the impact of freezing on performance, and the effect on performance of a common freeze protection strategy based on periodic defrosts. In experiments with three different models of air-to-air heat exchangers, the temperature of the inlet cold airstream at which freezing was initiated ranged from -3/sup 0/C to -12/sup 0/C and varied with the humidity of the inlet warm airstream. Freezing caused the temperature efficiency of a cross-flow heat exchanger to decrease at a rate that ranged from 1.5 to 13.2 percentage points per hour. Small rates of decrease in efficiency (0.6 to 2.0 percentage points per hour) resulted from freezing in a counterflow exchanger. The rate of decrease in efficiency depended on the airstream temperatures and humidities, and the duration of the period of freezing. The amount of time required to defrost the heat exchanger's core was 6 to 26% of the total operating time. The average temperature efficiency for freeze-defrost cycles ranged from 48 to 64 percent in tests of the cross-flow exchanger and 70 to 82 percent in tests of the counterflow exchanger. When the frequency and duration of defrosts were nearly optimal, approximately a ten to fifteen percentage point decrease in average temperature efficiency was attributed to the freezing and required defrosts. The results suggested that the rate of performance deteriorations due to freezing can be reduced by avoiding small airflow passages that can easily be plugged with ice and by designing the exchanger so that condensed water does not drain toward the cold regions of the core.

Fisk, W.J.; Archer, K.M.; Chant, R.E.; Hekmat, D.; Offermann, F.J.; Pedersen, B.S.

1983-09-01

252

A study of exchange bias in BiFeO3 core/NiFe2O4 shell nanoparticles  

NASA Astrophysics Data System (ADS)

We have carried out magnetization measurements on BiFeO3 core/NiFe2O4 shell nanoparticles, and searched for the exchange bias phenomenon in this system. The core-shell nature of these nanoparticles has been established from the transmission electron microscopy images. The neutron diffraction study establishes that the core is G-type antiferromagnetic, while the shell is ferrimagnetic in nature. The search for an exchange bias phenomenon in the core-shell system shows a shift of the field-cooled (FC) hysteresis loops, at 5 K, along the magnetic field axis. The present investigation shows an unusual shift of the zero field-cooled (ZFC) hysteresis loop along the magnetic field axis as well. An enhancement of the remanent magnetization along with a decrease in the coercivity is also observed in the FC case, as compared to the corresponding values in the ZFC case, which is not found commonly in any conventional exchange-biased system. All these features indicate the presence of an interface exchange coupling between core and shell of the studied nanoparticles.

Yusuf, S. M.; Manna, P. K.; Shirolkar, Mandar M.; Kulkarni, S. K.; Tewari, R.; Dey, G. K.

2013-05-01

253

Ion exchange equilibrium between ion exchange membrane and electrolyte solutions  

Microsoft Academic Search

The ion exchange equilibrium between an ion exchange membrane and solutions of different electrolytes was studied. The matrix of the ion exchange membrane used consists of a vinyl polychloride network reinforced by a polyester screen; with quaternary and tertiary ammonium as functional groups. The data, provided by manufacturer, were completed by the experimental determinations of humidity percentage and ion exchange

Ch. Hannachi; S. Bouguecha; B. Hamrouni; M. Dhahbi

2008-01-01

254

Parametric performance studies on fluidized-bed heat exchangers. Task 1: Fouling characteristics  

NASA Astrophysics Data System (ADS)

Analyses and experiments are being performed to investigate the heat transfer performance of single and multistage shallow fluidized beds for application to the recovery of heat from sources such as waste heat, and coal combustion or coal gasification. Tests were conducted to investigate the effects of liquid condensate fouling on fluidized bed heat exchanger performance. Liquid condensates used in these tests were water and glycerol (which is more viscous than water). The tests showed that fluidized bed heat exchanger performance is degraded by condensation within the bed and the degradation is caused by bed particles adhering to the heat exchanger surface, not by particle agglomeration. Liquid condensate did not continuously build up within the bed. After a period of dry out, heat transfer equal to that obtained prior to condensation was again obtained.

Stoeffler, R. C.

1982-09-01

255

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

256

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

NASA Astrophysics Data System (ADS)

The pion double charge exchange reactions, 209Bi(?+, ?-xn)209-xAt, have been studied by radiochemical techniques for incident pion energies of 100, 180, and 300 MeV. Cross sections for the chemically separated At isotopes A=205-209 were determined by alpha-particle and gamma-ray spectroscopy. The contribution of secondary processes, such as 209Bi(?+, 3,4He)X followed by 209Bi(4He, xn)213-xAt and 209Bi(3He, xn)212-xAt, which mimic the double charge exchange process, was evaluated through a study of the 209Bi(?-, X)At reactions, since double charge exchange channels cannot contribute to At production in such ?- interactions. Such secondary reactions were further characterized through target thickness studies employing 100-300 MeV ?- beams. An upper limit of the cross sections for 209At production via elastic or inelastic double charge exchange below particle emission thresholds was determined to be 6 ?b-a result which is roughly consistent with independent spectrometer measurements. Double charge exchange processes in which 8-50 MeV of excitation energy remains in 209At (to be later dissipated by neutron evaporation) are found to be much more probable as evidenced by the 209Bi(?+, ?-xn)209-xAt, x=2-4 excitation functions which are seen to be strongly and inversely dependent on the incident pion energy. NUCLEAR REACTIONS 209Bi(?+, ?-xn)209-xAt, E?+=100-300 MeV; 209Bi(?-, X)207-211At, E?-=100-300 MeV; measured ?(E), deduced secondary contributions; alpha particle and ?-ray spectroscopy, Si and Ge(Li) detectors, high purity targets, carrier-free radiochemistry.

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

1983-03-01

257

The role of exchange and emotion on commitment: A study of teachers.  

PubMed

Recent experimental work in social exchange offers keen insight into factors that enhance commitment to individuals, groups, and relationships. In this article we explore the relevance of this work to school settings. Specifically, we use structural equation modeling and data from the 2004 Schools and Staffing Survey (SASS) to test whether the commitment-enhancing processes laid out in Lawler's affect theory of social exchange might reduce teacher turnover, an issue plaguing school districts across the country. Our results support such a model and demonstrate the importance of interdependence for fostering commitment among teachers, with interaction, affect, and cohesion as intervening factors. PMID:23017968

Price, Heather E; Collett, Jessica L

2012-11-01

258

Corrosion study of heat exchanger tubes in pressurized water cooled nuclear reactors by conversion electron Mössbauer spectroscopy  

Microsoft Academic Search

57Fe-conversion electron Mössbauer spectroscopy (CEMS) — a sensitive tool to analyze the phase composition of corrosion products\\u000a on the surface of stainless steel — was applied to study real specimens from the Paks Nuclear Power Plant, Hungary. The primary\\u000a circuit side of the heat exchanger tubes was studied on selected samples cut out from the steam generators during regular\\u000a maintenance.

Z. Homonnay; P. Á. Szilágyi; E. Kuzmann; K. Varga; Z. Németh; A. Szabó; K. Radó; J. Schunk; P. Tilky; G. Patek

2007-01-01

259

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

260

The model and empirical estimation of the optimal flexibility of RMB exchange-rate regime: A study based on the price-stabilization  

Microsoft Academic Search

Under the Mundell-Fleming-Dornbusch (M-F-D) framework, the paper develops a stochastic model to study the optimal choice of\\u000a RMB exchange rate regime based on two objectives, namely the exchange rate stabilization and price stabilization. The paper\\u000a finds that different policy objectives will lead to different optimal choices of RMB exchange-rate regime. If the central\\u000a bank aims to stabilize the price level,

Xiaohui Liu; Conglai Fan

2010-01-01

261

A comparative study of adsorption of perfluorooctane sulfonate (PFOS) onto granular activated carbon, ion-exchange polymers and non-ion-exchange polymers.  

PubMed

Perfluorooctane sulfonate (PFOS) is the latest chemical categorized as persistent organic pollutants (POPs). PFOS appears in the environmental water and tap water in ng L(-1) level. The process of adsorption has been identified as an effective technique to eliminate PFOS in water. Three non-ion-exchange polymers (DowV493, DowL493 and AmbXAD4), two ion-exchange polymers (DowMarathonA and AmbIRA400) and one granular activated carbon (GAC) (Filtersorb400) were tested with regard to their sorption kinetics and isotherms at low PFOS concentrations (100-1000 ng L(-1) equilibrium concentrations). The sorption capacities at 1 microg L(-1) equilibrium concentration decreased in the following order: ion-exchange polymers>non-ion-exchange polymers > GAC, but at further low equilibrium concentration (100 ng L(-1)) non-ion-exchange polymers showed higher adsorption capacity than other adsorbents. In the case of sorption kinetics, GAC and ion-exchange polymers reached the equilibrium concentration within 4 h and AmbXAD4 within 10 h. DowV493 and DowL493 took more than 80 h to reach equilibrium concentration. AmbIRA400 was identified as the best filter material to eliminate PFOS at equilibrium concentration > 1000 ng L(-1). Considering both adsorption isotherms and adsorption kinetics, AmbXAD4 and DowMarathonA were recommended to eliminate PFOS at ng L(-1) equilibrium concentration. PMID:20546842

Senevirathna, S T M L D; Tanaka, S; Fujii, S; Kunacheva, C; Harada, H; Shivakoti, B R; Okamoto, R

2010-07-01

262

Heat transfer and flow studies of the liquid droplet heat exchanger  

Microsoft Academic Search

This paper describes a lightweight, highly effective liquid droplet heat exchanger (LDHX) concept for thermal management in space. Heat is transferred by direct contact between fine droplets (100 to 300 micron diameter) of a low vapor pressure liquid and an inert working gas. Complete separation of the droplet and gas media in the microgravity environment is accomplished by configuring the

A. P. Bruckner; A. Shariatmadar

1987-01-01

263

Numerical study of heat transfer enhancement of counter nanofluids flow in rectangular microchannel heat exchanger  

Microsoft Academic Search

The performance of a counter-flow rectangular shaped microchannel heat exchanger (MCHE) using nanofluids was modeled. The 3D steady, laminar developing flow and conjugate heat transfer in aluminum MCHE using finite volume method was solved. The effects of nanofluid types, Re number and nanoparticle concentration on the thermal, and flow fields were examined. It is found that the MCHE performance is

H. A. Mohammed; G. Bhaskaran; N. H. Shuaib; R. Saidur

2011-01-01

264

Study of protonation and deuterium exchange of carbazoles in trifluoroacetic acid-1,2-dichloroethane  

Microsoft Academic Search

The protonation of the aromatic ring of 9-methylcarbazole under the influence of trifluoroacetic acid in 1,2-dichloroethane was established by spectrophotometry. Deuterium exchange between 9-methylcarbazole and deuterotrifluorotrifluoroacetic acid was evaluated quantitatively by means of mass spectrometry and the PMR spectra. Highly deuterated carbazole and 9-methylcarbazole were obtained for the first time.

E. E. Sirotkina; N. V. Moskalev; I. G. Shabotkin; V. D. Ogorodnikov; É. B. Khayut

1985-01-01

265

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

266

Sensible heat exchange at the Antarctic snow surface: a study with automatic weather stations  

Microsoft Academic Search

Data of four automatic weather stations (AWSs) are used to calculate the turbulent exchange of sensible heat at the Antarctic snow surface for a 4 year period (1998-2001). The AWSs are situated on the ice shelf, in the coastal\\/inland katabatic wind zone and on the interior plateau in Dronning Maud Land, East Antarctica. Sensible heat flux (SHF) is calculated using

Michiel van den Broeke; Dirk van As; Carleen Reijmer; Roderik van de Wal

2005-01-01

267

Studies on a high-temperature regenerative heat exchanger for closed-cycle MHD power generation  

Microsoft Academic Search

This paper reports on a numerical heat- transfer analysis in the combustion chamber of a pebble bed regenerative heat exchanger carried out for the heating period. A radiative zone method coupled with chemical and two-dimensional fluid dynamic calculations is employed in the analysis, and the results agree well with the measured data. The analysis also shows that higher temperature can

Y. Kim; Y. Shinagawa; K. Yoshikawa; S. Shioda

1990-01-01

268

Comparative study of rotating regenerators and heat-pipe heat exchangers  

Microsoft Academic Search

A heat wheel was purchased and installed for air to air heat recovery on a Terylene fiber drying and setting oven at ICI Wilton. At the same time a heat pipe heat exchanger was prepared at IRD and tested under controlled conditions. The heat wheel was then replaced by the heat pipe unit. During this procedure measurements were made regularly

D. B. A. MacMichael; D. A. Reay; E. L. Foster

1980-01-01

269

Optimization of baffl ec onfigurations to prevent aeroacoustic instabilities in heat exchangers: a preliminary study  

Microsoft Academic Search

It is well known that gas heat exchangers are prone to aeroacoustic instabilities, which often lead to severe noise levels, structural vibrations and fatigue. These are unacceptable, as they threaten the component integrity and expose the plant workers to excessive noise levels. Such phenomenon is due to a cooperative interplay between the Karman vortices generated by the cross-flow and the

Miguel Moreira; José Antunes; Martins Paulino; Heitor Pina

270

"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

271

A measurement study determining the effect of Internet eXchange points on popular webservers  

Microsoft Academic Search

Internet exchange points (IXPs) are an upcoming and essential component of the Internet infrastructure exhibiting numerous effects on various aspects of Internet topology and packet routing. While IXPs have been shown to play a major role in the evolution of the Internet topology, there has been little prior work in determining their effect on packet routing across the Internet. This

Mohammad Zubair Ahmad; Ratan Guha

2010-01-01

272

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

273

Effects of River Discharge on Hyporheic Exchange Flows in Large Gravel-Bed Rivers: An Empirical Study  

NASA Astrophysics Data System (ADS)

Current in situ understanding of exchange flows in riverbeds, and the ecological implications, has been largely derived from research in small streams. Comparatively little research has been conducted in large rivers, making it difficult to "scale-up" (spatially and temporally) our knowledge from small streams to understand observations and develop predictive models for large rivers. The studies conducted on small streams typically encompass too few sites, over too small of a longitudinal scale, with discrete sampling events (versus continuous sampling), resulting in an understanding of processes that is not directly transferrable to the study of much larger rivers. In addition, very few of these studies evaluate the effects of variable river discharge on riverbed exchange flows. We studied exchange flows between the river and riverbed at 14 sites distributed throughout 160km of the Snake River in Hells Canyon, Idaho, USA. Interactions between river water and pore water within the riverbed were quantified through the use of self-contained temperature and water level data loggers suspended inside of piezometers. The data were recorded at 20 min intervals over a period of 200 days when the mean daily discharge was 218-605 m3 s-1, with hourly stage changes as large as 1.5 m. The effects of discharge on vertical exchange between the river and riverbed were evaluated through measured hydraulic and temperature gradients, and the application of a numerical model. The vertical hydraulic gradients (VHG) between the river and the riverbed suggested the potential for predominantly small magnitude vertical exchange. The VHG also showed little relationship to changes in river discharge at most sites. Despite the relatively small VHG at most sites, the results from the numerical modeling suggested that there was significant vertical hydrologic exchange during all time periods. Our observations confirm the presence, and quantify the relative importance, of both advective and diffusive riverbed transport processes. The combined results of temperature monitoring and numerical modeling indicated that only two sites were significantly affected by short-term (hourly to daily) large magnitude changes in discharge. Although the two sites exhibited acute flux reversals between river water and hyporheic water resulting from short-term large magnitude changes in discharge, these flux reversals had minimal effect on mean daily riverbed temperatures.

Hanrahan, T. P.

2004-12-01

274

The effect of a Heat and Moisture Exchanger (Provox ® HME) on pulmonary protection after total laryngectomy: a randomized controlled study  

Microsoft Academic Search

The goal of this randomized controlled study was to investigate the effect of Heat and Moisture Exchanger use on pulmonary\\u000a symptoms and quality of life aspects in laryngectomized patients. Eighty laryngectomized patients were included and randomized\\u000a into an HME and Control group. The effect of the HME was evaluated by means of Tally Sheets and Structured Questionnaires.\\u000a The results showed

Stanis?aw Bie?; S?awomir Ok?a; Corina J. van As-Brooks; Annemieke H. Ackerstaff

2010-01-01

275

Study on the exergy loss of the horizontal concentric micro-fin tube heat exchanger  

Microsoft Academic Search

Experimental and theoretical investigations on the entropy generation, exergy loss of a horizontal concentric micro-fin tube heat exchanger are presented. The experiments setup are designed and constructed for the measured data by using hot water and cold water as working fluids. The micro-fin tube is fabricated from the copper tube with an inner diameter of 8.92mm. The experiments are performed

Paisarn Naphon

2011-01-01

276

Numerical study of heat transfer enhancement of counter nanofluids flow in rectangular microchannel heat exchanger  

Microsoft Academic Search

This paper reports a numerical analysis of the performance of a counter-flow rectangular shaped microchannel heat exchanger (MCHE) using nanofluids as the working fluids. Finite volume method was used to solve the three-dimensional steady, laminar developing flow and conjugate heat transfer in aluminum MCHE. The nanofluids used were Ag, Al2O3, CuO, SiO2, and TiO2 and the performance was compared with

H. A. Mohammed; G. Bhaskaran; N. H. Shuaib; R. Saidur

2011-01-01

277

A Comparison Study of Numerical Simulations in a Borehole Heat Exchanger Field  

Microsoft Academic Search

Borehole heat exchanger (BHE) field with heat-pump was installed at the building of the Korea Earthquake Research Center in Korea Institute of Geoscience and Mineral (KIGAM). It consists of 28 BHEs equipped with a double U-tube and three monitoring wells. Two BHEs are equipped with optical fiber that measures temperature of the U-tube. A borehole televiewer survey was conducted in

S. Kim; G. Bae; K. Lee; B. Shim; Y. Song

2007-01-01

278

Observational study of turbulent exchange between the surface and canopy layer over several forest types  

Microsoft Academic Search

Several field projects have been organized (e.g., AMERIFLUX, and EUROFLUX) to quantify the role of the terrestrial ecosystems as a sink of CO2 and source of H2O(v) and other trace gases that can be important in global climate change. As forests are a porous boundary, the understanding of turbulent exchange from the canopy layer to the atmosphere is a step

Ricardo Kendi Sakai

2000-01-01

279

An experimental and modelling study of a photovoltaic\\/proton-exchange membrane electrolyser system  

Microsoft Academic Search

An experimental model of a photovoltaic (PV) module-proton exchange membrane (PEM) electrolyser system has been built. A model has been developed for each device separately based on the experimental results. Output current–voltage (I–V) characteristics of the PV module are modelled in respect to different irradiance and temperature conditions by experimental tests. Similarly, input I–V characteristic and hydrogen formation characteristic of

Ozcan Atlam

2009-01-01

280

Motivation for International Exchange.  

ERIC Educational Resources Information Center

An objective analysis of students' initial motivation for studying overseas was attempted by surveying students before they embarked on their exchange programs. Eighty-eight students who were planning to study in France, Great Britain, Germany, and the People's Republic of China were surveyed. The exchange program was sponsored by the University…

Brewer, Elizabeth

281

Hydrophilic and antimicrobial Ag-exchanged zeolite a coatings: A year-long durability study and preliminary evidence for their general microbiocidal efficacy  

E-print Network

of silver content, and high antimicrobial activity to Escherichia Coli after submersion in double deHydrophilic and antimicrobial Ag-exchanged zeolite a coatings: A year-long durability study Antimicrobial Micro-gravity a b s t r a c t Silver exchanged zeolite A (Ag­ZA) coatings have been proposed

Chen, Wilfred

282

Atom exchange between aqueous Fe(II) and goethite: an Fe isotope tracer study.  

PubMed

The reaction of aqueous Fe(II) with Fe(III) oxides is a complex process, comprising sorption, electron transfer, and in some cases, reductive dissolution and transformation to secondary minerals. To better understand the dynamics of these reactions, we measured the extent and rate of Fe isotope exchange between aqueous Fe(II) and goethite using a 57Fe isotope tracer approach. We observed near-complete exchange of Fe atoms between the aqueous phase and goethite nanorods over a 30-day time period. Despite direct isotopic evidence for extensive mixing between the aqueous and goethite Fe, no phase transformation was observed, nor did the size or shape of the goethite rods change appreciably. High-resolution transmission electron microscopy images, however, appear to indicate that some recrystallization of the goethite particles may have occurred. Near-complete exchange of Fe between aqueous Fe(II) and goethite, coupled with negligible change in the goethite mineralogy and morphology, suggests a mechanism of coupled growth (via sorption and electron transfer) and dissolution at separate crystallographic goethite sites. We propose that sorption and dissolution sites are linked via conduction through the bulk crystal, as was recently demonstrated for hematite. Extensive mixing between aqueous Fe(II) and goethite, a relatively stable iron oxide, has significant implications for heavy metal sequestration and release (e.g., arsenic and uranium), as well as reduction of soil and groundwater contaminants. PMID:19320165

Handler, Robert M; Beard, Brian L; Johnson, Clark M; Scherer, Michelle M

2009-02-15

283

A Good Learning Opportunity, but Is It for Me? A Study of Swedish Students' Attitudes towards Exchange Studies in Higher Education  

ERIC Educational Resources Information Center

This article describes students' involvement and interest in exchange programmes in Swedish higher education. Law and Engineering bachelor's programmes were chosen to exemplify an over-represented and under-represented group respectively in terms of international mobility in this context. The study combines interview and survey data. The…

Ahn, Song-ee

2014-01-01

284

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

285

Ion exchange and dehydration experimental studies of clinoptilolite: Implications to zeolite dating  

SciTech Connect

Variable effects were noted on the argon (Ar) and potassium (K) contents of clinoptilolite fractions used in ion-exchange and dehydration experiments. The K contents of clinoptilolite fractions were differently affected during cation exchange with Ca-, Cs-, K-, and Na-chloride solutions. Ar was generally less affected during these experiments, except for a Na-clinoptitolite fraction exchanged for five days. Loss of Ar during organic heavy-liquid treatment and cleaning using acetone and deionized water does occur, as indicated by comparing the amounts of radiogenic Ar of treated and untreated fractions. Moreover, a regular decrease in radiogenic Ar contents was noted in clinoptilolite fractions during dehydration experiments at different temperatures for 16 hours. Comparable losses do not occur from saturated samples that were heated in 100 C for more than five months. Water appears to play a vital role in stabilizing the clinoptilolite framework structure and in the retention of Ar. The radiogenic Ar depletion pattern noted in clinoptilolite fractions dehydrated in unsaturated environment at different temperatures is similar to variations in the amount of radiogenic Ar observed in clinoptilolite samples from the unsaturated zone of an altered tuff. These results can be used to evaluate the extent of zeolitic water (and hence Ar) retention in unsaturated geologic settings. The utility of alkali zeolites (e.g., phillipsite, clinoptilolite, and mordenite) from low-temperature, open-hydrologic alteration as potential dateable minerals was evaluated using the K/Ar method as part of the Yucca Mountain Site Characterization Project, which is evaluating Yucca Mountain, Nevada, as a potential high-level radioactive waste repository site.

WoldeGabriel, G.

1995-02-01

286

Transient homodimer interactions studied using the electron self-exchange reaction.  

PubMed

Transient homodimer protein interactions have been investigated by analyzing the influence of ionic strength (NaCl) on the electron self-exchange (the bimolecular reaction whereby the two oxidation states of a redox protein interconvert) rate constant (k(ese)) of four plastocyanins. The k(ese) values for the plastocyanins from spinach, Dryopteris crassirhizoma (a fern), and the green alga Ulva pertusa, which possess acidic patches of varying size and locations, increase 190-, 29-, and 21-fold, respectively, at elevated ionic strength (I = 2.03 M). In contrast, the k(ese) for the almost neutral cyanobacterial plastocyanin from Anabaena variabilis exhibits very little dependence on ionic strength. The temperature dependence of the k(ese) for spinach plastocyanin (I = 0.28 M) provides evidence for poor packing at the homodimer interface. Representative structures of the transient homodimers involved in electron self-exchange, which are consistent with fits of the ionic strength dependence of k(ese) to van Leeuwen theory, have been obtained from protein modeling and docking simulations. The Coulombic energy of the docked homodimers follows the order spinach > D. crassirhizoma > U. pertusa > A. variabilis, which matches that of the overall influence of ionic strength on k(ese). Analysis of the homodimer structures indicates that poor packing and high planarity are features of the interface that favor transient interactions. The physiologically relevant Mg2+ ion has a much more pronounced influence on the k(ese) of spinach plastocyanin, which along with the known properties of the thylakoid lumen suggests a biological role for electron self-exchange. PMID:15743773

Sato, Katsuko; Crowley, Peter B; Dennison, Christopher

2005-05-13

287

Gas exchange function through the middle ear mucosa in piglets: comparative study of normal and inflamed ears.  

PubMed

The gas exchange function through the middle ear (ME) mucosa was investigated by comparing normal and inflamed ears in an animal model. Piglets were examined (n = 15) because their tympanic bulla closely resembles the human mastoid air cell system. Four untreated ears served as controls. Eleven ears were injected with glycerin into the tympanic bulla to induce inflammation and were studied as inflamed ears. Two respiratory conditions, spontaneous respiration and hyperventilation by a ventilator, were alternated repeatedly. ME pressure was measured intermittently by a tympanometer and blood gas was measured simultaneously. In all four normal ears, both ME pressure and carbon dioxide (CO2) partial pressure in the blood decreased in parallel following alternation of the respiratory conditions from spontaneous respiration to hyperventilation, while both pressure levels increased in parallel when respiration was changed from hyperventilation to spontaneous respiration. This result indicates that there is a gas exchange between the ME and the blood through the mucosa. However, ME pressure change in inflamed ears was limited, though the change in CO2 partial pressure in the blood was the same as that in normal ears. There was a significant difference in the degree of ME pressure change occurring in normal ears compared to that in inflamed ears, suggesting that inflammation of the mucosa reduced gas exchange function in the ME. PMID:10219389

Yamamoto, Y

1999-01-01

288

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

289

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

290

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

291

Higher Education Exchange, 2005  

ERIC Educational Resources Information Center

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

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

2005-01-01

292

Higher Education Exchange, 2008  

ERIC Educational Resources Information Center

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

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

2008-01-01

293

Higher Education Exchange, 2007  

ERIC Educational Resources Information Center

"Higher Education Exchange" publishes case studies, analyses, news, and ideas about efforts within higher education to develop more democratic societies. Contributors to this issue of the "Higher Education Exchange" discuss the concept of growing public scholars; each contribution incorporates a student component. Articles include: (1) "Foreword"…

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

2007-01-01

294

Higher Education Exchange, 2010  

ERIC Educational Resources Information Center

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

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

2010-01-01

295

Transfer-of-saturation NMR studies of protein-ligand complexes. Three-site exchange  

NASA Astrophysics Data System (ADS)

Equilibrium and transient saturation transfer effects were calculated for a three-site exchange system involving a ligand binding to a protein to form a complex which can exist in two states. The calculations show that, in an experiment in which the change in intensity of a resonance of the free ligand on saturating the corresponding resonance from one of the states of the complex is monitored, substantial effects can be seen even when the form of the complex being saturated represents less than 0.1% of the total complex at equilibrium. The implications of this finding for experiments in which the saturation transfer effect is used to locate resonances of bound ligands are discussed. The time course of the change in intensity of the resonance of the free ligand on irradiation of the resonance of one of the states of the complex consists of two exponential phases, which offers a method for distinguishing two-site and three-site exchange, but it is shown that this will not be reliable in practice, since there are many circumstances under which the two phases will not be resolvable.

Clore, G. M.; Roberts, G. C. K.; Gronenborn, A.; Birdsall, B.; Feeney, J.

296

Double-exchange model study of multiferroic RMnO3 perovskites  

SciTech Connect

In this proceeding, recent theoretical investigations by the authors on the multiferroic RMnO3 perovskites are briefly reviewed at first. Using the double-exchange model, the realistic spiral spin order in undoped manganites such as TbMnO3 and DyMnO3 is well reproduced by incorporating a weak nextnearest neighbor superexchange ( 10% of nearest neighbor superexchange) and moderate Jahn-Teller distortion. The phase transitions from the A-type antiferromagnet (as in LaMnO3), to the spiral phase (as in TbMnO3), and finally to the E-type antiferromagnet (as in HoMnO3), with decreasing size of the R ions, were also explained. Moreover, new results of phase diagram of the three-dimensional lattice are also included. The ferromagnetic tendency recently discovered in the LaMnO3 and TbMnO3 thin films is explained by considering the substrate stress. Finally, the relationship between our double-exchange model and a previously used J1-J2-J3 model is further discussed from the perspective of spin wave excitations.

Dong, Shuai [ORNL; Yu, Rong [ORNL; Yunoki, Seiji [RIKEN, Japan; Liu, J.-M. [Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing; Dagotto, Elbio R [ORNL

2009-01-01

297

Double-exchange model study of multiferroic RMnO3 perovskites  

NASA Astrophysics Data System (ADS)

In this proceeding, recent theoretical investigations by the authors on the multiferroic RMnO3 perovskites are briefly reviewed at first. Using the double-exchange model, the realistic spiral spin order in undoped manganites such as TbMnO3 and DyMnO3 is well reproduced by incorporating a weak next-nearest neighbor superexchange (~10% of nearest neighbor superexchange) and moderate Jahn-Teller distortion. The phase transitions from the A-type antiferromagnet (as in LaMnO3), to the spiral phase (as in TbMnO3), and finally to the E-type antiferromagnet (as in HoMnO3), with decreasing size of the R ions, were also explained. Moreover, new results of phase diagram of the three-dimensional lattice are also included. The ferromagnetic tendency recently discovered in the LaMnO3 and TbMnO3 thin films is explained by considering the substrate stress. Finally, the relationship between our double-exchange model and a previously used J1-J2-J3 model is further discussed from the perspective of spin wave excitations.

Dong, S.; Yu, R.; Yunoki, S.; Liu, J.-M.; Dagotto, E.

2009-10-01

298

Enhancing the quality of H/D exchange measurements with mass spectrometry detection in disulfide-rich proteins using electron capture dissociation.  

PubMed

Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) has become a potent technique to probe higher-order structures, dynamics, and interactions of proteins. While the range of proteins amenable to interrogation by HDX MS continues to expand at an accelerating pace, there are still a few classes of proteins whose analysis with this technique remains challenging. Disulfide-rich proteins constitute one of such groups: since the reduction of thiol-thiol bonds must be carried out under suboptimal conditions (to minimize the back-exchange), it frequently results in incomplete dissociation of disulfide bridges prior to MS analysis, leading to a loss of signal, inadequate sequence coverage, and a dramatic increase in the difficulty of data analysis. In this work, the dissociation of disulfide-linked peptide dimers produced by peptic digestion of the 80 kDa glycoprotein transferrin in the course of HDX MS experiments is carried out using electron capture dissociation (ECD). ECD results in efficient cleavage of the thiol-thiol bonds in the gas phase on the fast LC time scale and allows the deuterium content of the monomeric constituents of the peptide dimers to be measured individually. The measurements appear to be unaffected by hydrogen scrambling, even when high collisional energies are utilized. This technique will benefit HDX MS measurements for any protein that contains one or more disulfides and the potential gain in sequence coverage and spatial resolution would increase with disulfide bond number. PMID:24820935

Bobst, Cedric E; Kaltashov, Igor A

2014-06-01

299

Experimental Background Studies in the Two Photon Exchange (TPE) Experiment at Jefferson Lab  

SciTech Connect

This work is based on the improvement of an existing simulation for the two photon exchange (TPE) experiment at Jefferson Lab developed within the GEANT4 framework. This experiment will determine the ratio of the positron-proton elastic scattering cross section and the electron-proton elastic scattering cross section with high precision. To accomplish this measurement requires the use of a variety of devices and complex arrangements, creating background particles that manage to reach the detector system (CLAS). A number of test runs have identified the sources of background in the detector guided by previous simulations. Even so, the remaining background can be reduced considerably by the microscopic identification and locating of the background sources performed by our new simulation.

Pena, Cristian; Brooks, W. K.; Hakobyan, Hayk [Universidad Tecnica Federico Santa Maria, Valparaiso (Chile)

2010-08-04

300

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

301

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

302

AN EXPERIMENTAL STUDY AND NUMERICAL SIMULATION OF TWO-PHASE FLOW OF CRYOGENIC FLUIDS THROUGH MICROCHANNEL HEAT EXCHANGER  

Microsoft Academic Search

The design, fabrication, testing and analysis of a microchannel heat exchanger, a key component for a microminiature Joule-Thomson Cryogenic Refrigerator is described. Results show that the heat exchanger can be fabricated efficiently and economically with the existing manufacturing technology. The heat exchanger was tested to be mechanically robust and durable under high pressure operating condition. \\

W. W. Yuen; I. C. Hsu

303

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

304

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

305

A Study on a Performance of Water-Spray-Type Ice Thermal Energy Storage Vessel with Vertical Heat Exchanger Plates  

NASA Astrophysics Data System (ADS)

A system with a water-embedded-trpe ice storage vessel is widely used because of its simple structure and compactness. However, the water-embedded-type ice storage vessel has a disadvantage, that is, the solidification rate is very small. The use of falling water film seems to be one of promising ways for solving this disadvantage. We have found in a previous study that the use of the falling water film is very effective, especially for high initial water temperatures. In the present study, we eexamined the performance of a faling-water-film-type ice thermal energy storage vessel with pratical size, having vertical heat exchanger plates. The ice making performance coefficient, ?, increases with time, and it becomes am aximum value of 2.5, after that, it decreases gradually. In order to make ice efficiently, it is necessary to set a flow rate of refrigerant properly and to adjust a difference between the evaporating temperature of refrigerant and the freezing point of water so that the refrigerant evaporates in the heat exchanger plates overall.

Yoshimura, Kenji; Sasaguchi, Kengo; Fukuda, Toshihito; Koyama, Shigeru

306

Studies of cation exchange for the isolation and concentration of trace level components of complex aqueous mixtures  

SciTech Connect

Trace level organic bases are concentrated from aqueous solution by cation exchange on a column of sulfonated macroreticular XAD-4 resin. Washing of the column with organic solvents removes neutrals and acids. Ammonia gas is introduced into the column prior to elution of the basic-organics with either methanol or ether containing ammonia. After solvent evaporation, the concentrated sample is analyzed by gas chromatography. Recoveries of over 85% are found with at least one of the eluents for over 50 bases tested at levels <1 ppM. Improved recoveries and reproducibility are seen over a simple ether extraction procedure. Samples of river water, shale oil process water, and supernatant from an agricultural chemical disposal pit are analyzed. Porous, bifunctional chelating resins are prepared by base-catalyzed polymerization of a phenol and iminodiacetic acid with an aldehyde. These resins are used to concentrae trace levels of cesium-137 and strontium-90 from simulated nuclear waste. Various phenols, aldehydes, and templates are tested. Several experimental parameters are examined to determine their effect on resin affinity. Reaction temperature is found to have a significant effect on resin affinity. Attempts to determine the structure of these resins are made using various analytical techniques, most notably photoacoustic spectroscopy. The affinity of these resins for other metals is examined, and they are found to sorb Cu/sup 2 +/, Fe/sup 2 +/, and Pb/sup 2 +/ effectively. Preliminary studies of functionalized poly(styrene-divinylbenzene)s, coated exchangers, and liquid ion exchangers as possible approaches to nuclear waste decontamination are performed. 26 references, 26 figures, 25 tables.

Kaczvinsky, J.R. Jr.

1984-12-01

307

Full-dimensional quantum dynamics study of exchange processes for the D + H2O and D + HOD reactions  

NASA Astrophysics Data System (ADS)

The exchange processes of D + H2O and D + HOD reactions are studied using initial state-selected time-dependent wave packet approach in full dimension. The total reaction probabilities for different partial waves, together with the integral cross sections, are obtained both by the centrifugal sudden (CS) approximation and exact coupled-channel (CC) calculations, for the H2O(HOD) reactant initially in the ground rovibrational state. In the CC calculations, small resonance peaks in the reaction probabilities and quick diminishing of the resonance peaks with the increase of total angular momenta J do not lead to clear step-like features just above the threshold in the cross sections for the title reactions, which are different in other isotopically substituted reactions where the hydrogen atom was included as the reactant instead of the deuterium atom [B. Fu, Y. Zhou, and D. H. Zhang, Chem. Sci. 3, 270 (2012); B. Fu and D. H. Zhang, J. Phys. Chem. A 116, 820 (2012)]. It is interesting that the shape resonance-induced features resulting from the reaction tunneling are significantly diminished accordingly in the reactions of the deuterium atom and H2O or HOD, owing to the weaker tunneling capability of the reagent deuterium atom in the title reactions than the reagent hydrogen atom in other reactions. In the CS calculations, the resonance peaks persist in many partial waves but cannot survive the partial-wave summations. The cross sections for the D' + H2O --> D'OH + H and D' + HOD --> D'OD + H reactions are substantially larger than those for the D' + HOD --> HOD' + D reaction, indicating that the D'/H exchange reactions are much more favored than the D'/D exchange.

Fu, Bina; Zhang, Dong H.

2012-05-01

308

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

309

Activation of small alkanes in Ga-exchanged zeolites: A quantum chemical study of ethane dehydrogenation  

SciTech Connect

Quantum chemical calculations on the mechanism of ethane dehydrogenation catalyzed by Ga-exchanged zeolites have been undertaken. Two forms of gallium, adsorbed dihydride gallium ion GaH{sub 2}+Z{sup {minus}} and adsorbed gallyl ion [Ga=O]{sup +}Z{sup {minus}}, were considered. It was found that GaH{sub 2}{sup +}Z{sup {minus}} is the likely active catalyst. On the contrary, [Ga=O]{sup +}Z{sup {minus}} cannot be a working catalyst in nonoxidative conditions, because regeneration of this form is very difficult. Activation of ethane by GaH{sub 2}{sup +}Z{sup {minus}} occurs via an alkyl mechanism and the gallium atom acts as an acceptor of the ethyl group. The carbenium activation of ethane, with gallium abstracting a hydride ion, is much (ca. 51 kcal/mol) more difficult. The catalytic cycle for the alkyl activation consists of three elementary steps: (1) rupture of the ethane C-H bond; (2) formation of dihydrogen from the Bronsted proton and hydrogen bound to Ga; and (3) formation of ethene from the ethyl group bound to Ga. The best estimates (MP2/6--311++G(2df,p)//B3LYP/6--31G*) for the activation energies of these three steps are 36.9, ca. 0, and 57.9 kcal/mol, respectively.

Frash, M.V.; Santen, R.A. van

2000-03-23

310

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

311

X-ray spectroscopic study of charge exchange phenomena in plasma-wall interaction  

NASA Astrophysics Data System (ADS)

Jets of energetic ions launched at laser-burnt-through foils represent an efficient tool for investigation of plasma interaction with solid surfaces (plasma-wall interaction, PWI) and for description of transient phenomena occurring close to the walls. Highly charged ions approaching the secondary target interpenetrate the near surface layer, collide with the counter-propagating matter and capture a large number of electrons. This results in a creation of atoms in highly excited Rydberg states or hollow ions with multiple inner vacancies; plasma jet and target ions may also undergo charge exchange (CE) processes. We report PWI experiments with Al/Si(PMMA) and Al/C targets irradiated at normal or oblique laser incidence. The distinct dip structures observed in red wings of Al Ly? self-emission is interpreted in terms of CE between C6+ and Al12+ in the near-wall zone. The spectroscopic identification of CE phenomena is supported by results of analytical and numerical calculations.

Renner, O.; Krouský, E.; Šmíd, M.; Liska, R.; Váchal, P.; Khattak, F. Y.; Dalimier, E.; Oks, E.

2013-11-01

312

The effect of a Heat and Moisture Exchanger (Provox HME) on pulmonary protection after total laryngectomy: a randomized controlled study.  

PubMed

The goal of this randomized controlled study was to investigate the effect of Heat and Moisture Exchanger use on pulmonary symptoms and quality of life aspects in laryngectomized patients. Eighty laryngectomized patients were included and randomized into an HME and Control group. The effect of the HME was evaluated by means of Tally Sheets and Structured Questionnaires. The results showed a significant decrease in the frequency of coughing, forced expectoration, and stoma cleaning in the HME group. There were trends for the prosthetic speakers to report more fluent speech with the HME and for the HME group to report fewer sleeping problems. In conclusion, this study, performed in Poland, confirms the results of previous studies performed in other countries, showing that pulmonary symptoms decrease significantly with HME use and that related aspects such as speech and sleeping tend to improve, regardless of country or climate. PMID:19562362

Bie?, Stanis?aw; Ok?a, S?awomir; van As-Brooks, Corina J; Ackerstaff, Annemieke H

2010-03-01

313

Exchangeable equilibria  

E-print Network

The main contribution of this thesis is a new solution concept for symmetric games (of complete information in strategic form), the exchangeable equilibrium. This is an intermediate notion between symmetric Nash and symmetric ...

Stein, Noah D. (Noah Daniel)

2011-01-01

314

The empirical study of a four-row heat pipe heat exchanger to predict the year-round energy recovery in the tropics  

Microsoft Academic Search

The effect of heat pipe heat exchanger on the heat recovery was studied in the tropics. The performance of the heat exchanger was monitored during the one week of operation (168 h) to find out the performance characteristic curves. Three coil face velocities namely, 2, 2.2 and 2.5 m\\/s were tested and the temperature of return air was controlled at

YH Yau; M Ahmadzadehtalatapeh

2011-01-01

315

Comparison study of global and local approaches describing critical phenomena on the Polish stock exchange market  

NASA Astrophysics Data System (ADS)

We confront global and local methods to analyze the financial crash-like events on the Polish financial market from the critical phenomena point of view. These methods are based on the analysis of log-periodicity and the local fractal properties of financial time series in the vicinity of phase transitions (crashes). The whole history (1991-2008) of Warsaw Stock Exchange Index (WIG) describing the largest developing financial market in Europe, is analyzed in a daily time horizon. We find that crash-like events on the Polish financial market are described better by the log-divergent price model decorated with log-periodic behavior than the corresponding power-law-divergent price model. Predictions coming from log-periodicity scenario are verified for all main crashes that took place in WIG history. It is argued that crash predictions within log-periodicity model strongly depend on the amount of data taken to make a fit and therefore are likely to contain huge inaccuracies. Turning to local fractal description, we calculate the so-called local (time dependent) Hurst exponent H for the WIG time series and we find the dependence between the behavior of the local fractal properties of the WIG time series and the crashes appearance on the financial market. The latter method seems to work better than the global approach - both for developing as for developed markets. The current situation on the market, particularly related to the Fed intervention in September’07 and the situation on the market immediately after this intervention is also analyzed from the fractional Brownian motion point of view.

Czarnecki, ?ukasz; Grech, Dariusz; Pamu?a, Grzegorz

2008-12-01

316

Effects of surface temperature contrast on land-atmosphere exchange: A case study from Monsoon 90  

NASA Astrophysics Data System (ADS)

Atmospheric boundary layer (ABL) simulations over remotely sensed boundary conditions using a large eddy simulation (LES) code are employed here to explore the dynamical coupling of heterogeneous land surfaces and the ABL. The LES was recently extended to incorporate remotely observed surface states, and the ability to account for the soil and vegetation (i.e., two sources) contributions to the mass and energy exchanges [Albertson et al., 2001]. In this effort we explore the impacts of changes in the magnitude of surface variability (i.e., spatial contrasts). We focus our simulations and analysis with rescaled surface temperature fields to explore a wider range of contrasts (i.e., spatial variance). We demonstrate that the increase in temperature contrast has negligible effect on regionally averaged fluxes. However, the strength of coupling (or feedback) between spatial fields of land surface and surface layer temperature (z ˜ 10 m) increases with increasing temperature contrast. This dampens increases in the spatial variance in the sensible heat flux relative to increases in the spatial variance in surface temperature, suggesting the feedbacks act to limit the spatial variability in the flux. We also use the LES to explore the errors induced in spatially distributed heat flux predictions from using spatially uniform atmospheric variables in a related two-source energy-balance radiometric surface temperature scheme. The use of spatially uniform atmospheric variables is commonly employed when computing surface fluxes from remotely sensed land surface data. This leads to significant differences in the spatial distribution of land surface fluxes when compared to LES derived fluxes. This was particularly evident in the overestimated Bowen ratio (?), primarily for locations with relatively low vegetation cover.

Kustas, William P.; Albertson, John D.

2003-06-01

317

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

318

Feasibility and kinetics study on the direct bio-regeneration of perchlorate laden anion-exchange resin.  

PubMed

Anion exchange is one of the most promising treatment technologies for the removal of low levels of perchlorate. The spent anion-exchange resins, however, need to be disposed of or regenerated because they contain high contents of perchlorate. This study investigated the feasibility and kinetics of a direct bio-regeneration method. The method accomplished resin regeneration and biological perchlorate destruction concurrently, by directly contacting the spent resin with the perchlorate-reducing bacteria (PRB). The results indicated that the method was effective in regeneration of perchlorate and nitrate loaded resin and the resin could be repeatedly regenerated with the method. The regenerated resin was effective, stable, and durable in the filtration treatment of perchlorate in well water from the Saddle River area, NJ. Moreover, the method was also effective in regeneration of the spent A-530E resin, which had high perchlorate affinity and was yet very difficult for regeneration with the conventional brine desorption technique. Besides, the results further suggested that the perchlorate and nitrate desorption from the loaded resin coupling with their subsequent biological reduction could be the direct bio-regeneration mechanism. No biofilm was formed on the regenerated resin surface according to a scanning electron microscopy (SEM) analysis. PMID:18786692

Wang, Chao; Lippincott, Lee; Meng, Xiaoguang

2008-11-01

319

Comparative study on performance of a zigzag printed circuit heat exchanger with various channel shapes and configurations  

NASA Astrophysics Data System (ADS)

Comparative study has been performed with various channel cross-sectional shapes and channel configurations of a zigzag printed circuit heat exchanger (PCHE), which has been considered as a heat exchanging device for the gas turbine based generation systems. Three-dimensional Reynolds-averaged Navier-Stokes equations and heat transfer equations are solved to analyze conjugate heat transfer in the zigzag channels. The shear stress transport model with a low Reynolds number wall treatment is used as a turbulence closure. The global Nusselt number, Colburn j-factor, effectiveness, and friction factor are used to estimate the thermal-hydraulic performance of the PCHE. Four different shapes of channel cross section (semicircular, rectangular, trapezoidal, and circular) and four different channel configurations are tested to determine their effects on thermal-hydraulic performance. The rectangular channel shows the best thermal performance but the worst hydraulic performance, while the circular channel shows the worst thermal performance. The Colburn j-factor and friction factor are found to be inversely proportional to the Reynolds number in cold channels, while the effectiveness and global Nusselt number are proportional to the Reynolds number.

Lee, Sang-Moon; Kim, Kwang-Yong

2013-07-01

320

Salt-Zeolite Ion Exchange Equilibrium Studies for Complete Set of Fission Products in Molten LiCl-KCl  

SciTech Connect

This paper presents results on LiCl-KCl based molten salts/zeolite-A contact experiments and the associated equilibrium ion exchange model. Experiments examine the contact behaviors of various ternary salts (LiCl-KCl-YCl3, LiCl-KCl-LaCl3, and LiCl-KCl-PrCl3) and quaternary salts (LiCl-KCl-CsCl-NdCl3 and LiCl-KCl-CsCl-SrCl2) with the zeolite-A. The developed equilibrium model assumes that there are ion exchange and occlusion sites, both of which are in equilibrium with the molten salt phase. A systematic approach in estimating total occlusion capacity of the zeolite-A is developed. The parameters of the model, including the total occlusion capacity of the zeolite-A, were determined from fitting experimental data collected via multiple independent studies including the ones reported in this paper. Experiments involving ternary salts were used for estimating the parameters of the model, while those involving quaternary salts were used to validate the model.

Tae-Sic Yoo; Steven M. Frank; Michael F. Simpson; Paula A. Hahn; Terry J. Battisti; Supathorn Phongikaroon

2010-09-01

321

Slow Dynamics at the Glass Transition in Semicrystalline Polymers Studied by Pure-Exchange ^13C NMR  

NASA Astrophysics Data System (ADS)

The dynamics in the amorphous regions of semicrystalline polymers exert important influences on mechanical properties but have been difficult to characterize. New solid-state nuclear magnetic resonance (NMR) techniques, PUREX (pure-exchange) and CODEX (centerband-only detection of exchange), enable studies of the molecular motions near the glass transition (T_g) in the amorphous regions of semicrystalline polymers. This is achieved by selectively suppressing the dominant signals of the static segments in the crystallites. We have applied both techniques to analyze the geometry and time scale of the slow motions around Tg in isotactic poly(1-butene) (iPB1), in polypropylenes (iPP, sPP, aPP), and in fully amorphous polyisobutylene (PIB) for reference. The apparent activation energies for iPB1, sPP, and PIB were found to be 90, 125, and 115 kJ/mol, respectively. In iPB1, indications of slow motions in two distinct regions were observed.

Bonagamba, Tito J.; Deazevedo, Eduardo R.; Becker-Guedes, Fabio; Schmidt-Rohr, Klaus

2001-03-01

322

The Canopy Horizontal Array Turbulence Study (CHATS): Influence of canopy density and atmospheric stability on turbulent exchange  

NASA Astrophysics Data System (ADS)

Understanding the micrometeorology within and above forest canopies is of great interest for many environmental applications such as weather and climate forecasting as well as for vegetation-atmosphere scalar exchanges. Within a canopy, both the ground and the vegetation can act as scalar sources/sinks, where the distribution of canopy sources/sinks depends on the amount and state of the canopy foliage. For deciduous trees, the foliage evolves across a seasonal cycle from bare limbs in winter (no photosynthesis and an open canopy) to rapid growth in spring (increasing photosynthesis and canopy density), to maturity in summer (more constant photosynthesis and canopy density), to senescence and leaf-drop in fall (decreasing photosynthesis and canopy density). Thus a broad spectrum of different conditions occurs through the year, thereby imposing height and seasonal dependence on dynamical and scalar fluxes. The Canopy Horizontal Array Turbulence Study (CHATS) took place in 2007 focusing on a 10 m tall deciduous walnut orchard in Dixon, California (USA). High spatial resolution micrometeorological measurements were deployed aiming to establish the influence of seasonality (prior to, and follwing leaf-out) on canopy exchange. This talk will discuss the sensitivity of velocity, temperature and humidity fields within and above the deciduous walnut orchard at CHATS to the canopy evolution and atmospheric stability.

Patton, E. G.

2011-12-01

323

Effect of Taiwan mutation (D7H) on structures of amyloid-? peptides: replica exchange molecular dynamics study.  

PubMed

Recent experiments have shown that the Taiwan mutation (D7H) slows the fibril formation of amyloid peptides A?40 and A?42. Motivated by this finding, we have studied the influence of D7H mutation on structures of A? peptide monomers using the replica exchange molecular dynamics simulations with OPLS force field and implicit water model. Our study reveals that the mechanism behind modulation of aggregation rates is associated with decrease of ?-content and dynamics of the salt bridge D23-K28. Estimating the bending free energy of this salt bridge, we have found that, in agreement with the experiments, the fibril formation rate of both peptides A?40 and A?42 is reduced about two times by mutation. PMID:25010208

Truong, Phan Minh; Viet, Man Hoang; Nguyen, Phuong H; Hu, Chin-Kun; Li, Mai Suan

2014-07-31

324

New selective anion-exchange resins for nitrate removal from contaminated drinking water and studies on analytical anion-exchange chromatography  

SciTech Connect

Phosphonium resins and ammonium resins of composition resin-R{sub 3}P{sup +}A{sup {minus}} where R is varied from methyl to pentyl were evaluated for nitrate/sulfate selectivity, capacity and nitrate decontamination of drinking water. Phosphonium resins were found to be more nitrate selective and have higher capacities than ammonium resins. A mixed bed process, where nitrate removal and water softening is accomplished in a single column, was also evaluated. A small piece of silver wire, coated with an insoluble silver salt, works well as a selective potentiometric detector for halide ions in ion chromatography. A silver-silver chloride electrode was found to be a selective and reproducible detector for chloride, bromide, iodide, thiocyanate and thiosulfate anions separated by ion chromatography. Calibration curves were non-linear and had slopes ranging from 40 to 60 mV/log concentrations. A working range of 0.05 to 2 mM was used. Two methods for the determination of aluminum by anion chromatography are presented. In the first method, a standard excess of fluoride ion is added to the sample. Evidence is given for the formation of a strong complex of neutral aluminum trifluoride which elutes very quickly from an anion exchange column. The excess fluoride is retained and can be determined. The aluminum concentration can then be related to the difference in fluoride peak height between the sample and standard. In a second method, Al(III) is determined directly by anion chromatography when sodium phthalate is used as an eluent. It was found that Al(III)-phthalate complexes thus formed would show some retention on an anion exchange column. The method is uniquely insensitive to the presence of many foreign cations. Al(III) was successfully determined, by this method, in a 40-fold molar excess of iron(III).

Lockridge, J.E.

1989-01-01

325

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

326

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

327

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

328

Experimental study of xurographic microchannel single-pass single-phase counterflow heat exchanger.  

E-print Network

??Xurography is a relatively inexpensive rapid prototyping microfabrication method used to manufacture microfluidic devices. An experimental study of water flow in rectangular xurographic microchannel counterflow… (more)

Alshareef, Sultan M.

2012-01-01

329

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

330

Chronopotentiometric study of ceramic cation-exchange membranes based on zirconium phosphate in contact with nickel sulfate solutions  

Microsoft Academic Search

In this article, the innovative cation-exchange membranes obtained from ceramic materials are presented. Different microporous ceramic supports were obtained from an initial mixture of alumina and kaolin, to which a varying content of starch was added in order to obtain supports with different pore size distributions. The deposition of zirconium phosphate into the porous supports generates membranes with cation-exchange properties.

M. C. Martí-Calatayud; M. García-Gabaldón; V. Pérez-Herranz; S. Sales; S. Mestre

2012-01-01

331

Theoretical and experimental studies of rectangular duct heat exchangers to be used in a high-altitude subsonic aircraft  

Microsoft Academic Search

A unique need exists for heat exchangers that operate efficiently at an altitude of 85,000 feet. The application involves transferring heat to the low pressure ambient air at a low velocity that is in the laminar flow regime. Because it is desired that low pressure ambient air experience a small decrease in pressure, heat exchangers were examined with relatively short

James Allen Mathias

2001-01-01

332

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

333

Two-Band Fluctuation Exchange Study on Superconductivity of ?'-(BEDT-TTF)2ICl2 under High Pressure  

NASA Astrophysics Data System (ADS)

We study the pressure dependence of the superconducting transition temperature of an organic superconductor ?'-(BEDT-TTF)2ICl2 by applying the fluctuation exchange method to the Hubbard model on the original two-band lattice at 3/4 filling rather than the single-band model in the strong dimerization limit. Our study is motivated by the fact that hopping parameters evaluated from a first-principles study suggest that the dimerization of the BEDT-TTF molecules is not very strong particularly high pressures. Solving the linearized Eliashberg’s equation, a dxy-wavelike superconducting state with realistic values of Tc is obtained in a pressure regime somewhat higher than the actual experimental result. These results are similar to those obtained within the single-band model in the previous study by Kino et al. We conclude that the resemblance to the dimer limit is due to a combination of a good Fermi surface nesting, a large density of states near the Fermi level, and a moderate dimerization, which cooperatively enhance electron correlation effects and also the superconducting Tc.

Nakano, Tsuguhito; Kuroki, Kazuhiko

2006-03-01

334

Predicting Daily Stock Returns: A Lengthy Study of the Hong Kong and Tokyo Stock Exchanges  

Microsoft Academic Search

If stock markets are efficient then it should not be possible to predict stock returns, i.e., no explanatory variable in a stock market regression model should be statistically significant. In this study, we find results indicating that daily effects exist in stock market returns. These daily or calendar effects previously shown to exist by others clearly indicate the purpose of

Jeffrey E. Jarrett

2008-01-01

335

Heat exchanger fouling: A model study of the scaleup of laboratory data  

Microsoft Academic Search

Fouling of heat transfer equipment is a complex industrial problem. Many experiments have been carried out on a small scale to study the problem, but few models which can be used industrially have been developed. One problem may be that multiple mechanisms, often found in fouling, make scaleup very difficult. A series of possible scaleup strategies are tested using a

P. J. Fryer

1995-01-01

336

Teacher burnout : a flickering flame : an empirical study among teachers from a social exchange perspective  

Microsoft Academic Search

In this thesis, burnout has been studied among Dutch teachers using the theoretical frame of equity theory. Burnout is a metaphor that describes a particular syndrome which is typically found in human service professions, such as teaching, and is assumed to be linked to the emotional strain of working frequently and intensively with other people. Although burnout among teachers has

Joan Ellen van Horn

2002-01-01

337

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

338

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...

339

Prospects for HERMES-spin structure studies at HERA  

SciTech Connect

HERMES (HERA Measurement of Spin), is a second generation experiment to study the spin structure of the nucleon by using polarized internal gas targets in the HERA 35-GeV electron storage ring. Scattered electrons and coincident hadrons will be detected in an open geometry spectrometer which will include particle identification. Measurements are planned for each of the inclusive structure functions, g{sub 1},(x), g{sub 2}(x), b{sub 1}(x) and A(x), as well as the study of semi-inclusive pion and kaon asymmetries. Targets of hydrogen, deuterium and {sup 3}He will be studied. The accuracy of data for the inclusive structure functions will equal or exceed that of current experiments. The semi-inclusive asymmetries will provide a unique and sensitive probe of the flavor dependence of quark helicity distributions and properties of the quark sea. Monte Carlo simulations of HERMES data for experiment asymmetries and polarized structure functions are discussed.

Jackson, H.E. [Argonne National Lab., IL (United States). Physics Div.

1994-12-31

340

Biotic controls on CO 2 and CH 4 exchange in wetlands – a closed environment study  

Microsoft Academic Search

Wetlands are significant sources of the important greenhouse gas CH4. Here we explore the use of an experimental system developed for the determination of continuous fluxes of CO2 and CH4 in closed ecosystem monoliths including the capture of 14CO2 and 14CH4 following pulse labelling with 14CO2. We show that, in the ecosystem studied, ebullition (bubble emission) may account for 18

Torben R. Christensen; Nicolai Panikov; Mihail Mastepanov; Anna Joabsson; Angela Stewart; Mats Öquist; Martin Sommerkorn; Sebastian Reynaud; Bo Svensson

2003-01-01

341

Studies on a frustrated Heisenberg spin chain with alternating ferromagnetic and antiferromagnetic exchanges.  

PubMed

We study Heisenberg spin-1/2 and spin-1 chains with alternating ferromagnetic (J(F)(1)) and antiferromagnetic (J(A)(1)) nearest-neighbor interactions and a ferromagnetic next-nearest-neighbor interaction (J(F)(2)). In this model frustration is present due to the non-zero J(F)(2). The model with site spin s behaves like a Haldane spin chain, with site spin 2s in the limit of vanishing J(F)(2)and large J(F)(1)/J(A)(1). We show that the exact ground state of the model can be found along a line in the parameter space. For fixed J(F)(1), the phase diagram in the space of J(A)(1)-J(F)(2) 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. PMID:24935169

Sahoo, Shaon; Durga Prasad Goli, V M L; Sen, Diptiman; Ramasesha, S

2014-07-01

342

Decomposition Pathways of Tetraalkylammonium Hydroxides: Experimental and DFT Studies and Their Implications for Alkaline Exchange Fuel Cell Membranes  

SciTech Connect

The mechanism of the thermal decomposition of a series of alkyl trimethyl ammonium hydroxides ([RMe{sub 3}N][OH], R = Et, n-Pr, i-Bu, PhCH{sub 2}, Me{sub 3}CCH{sub 2}) was studied using TGA, evolved gas analysis and NMR spectroscopy due to the importance of these and related ions in anion exchange fuel cell membranes. Isotopic labeling with deuterium showed that deprotonation of the methyl groups of the ammonium ions by deuteroxide establishes a rapid equilibrium between the tetraalkyl ammonium ions and the nitrogen ylide species and water that scrambles the deuterium with the proton on the methyl groups. The products of the thermal decomposition when R = Et, n-Pr, i-Bu are predominately olefins arising from Hoffmann elimination, while the neopentyl substituted ammonium ion gives only neopentyl trimethyl amine and methanol, the products of S{sub N}2 attack of hydroxide on the methyl groups. DFT studies of these reactions confirm the relative activation barriers that are observed in the experimental decomposition studies.

Pivovar, B. S.; Edson, J. B.; Macomber, C. S.; Long, H.; Boncella, J. M.

2012-01-01

343

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

344

Parametric study of graphite foam fins and application in heat exchangers  

NASA Astrophysics Data System (ADS)

This thesis focuses on the simulation and experimental studies of finned graphite foam extended surfaces to test their heat transfer characteristics and potential applications in condensers. Different fin designs were developed to conduct a parametric study on the thermal effectiveness with respect to thickness, spacing and fin offset angle. Each fin design was computationally simulated to estimate the heat transfer under specific conditions. The simulations showed that this optimal fin configuration could conduct more than 297% the amount of thermal energy as compared to straight aluminum fins. Graphite foam fins were then implemented into a simulation of the condenser system. The condenser was simulated with six different orientations of baffles to examine the incoming vapor and resulting two-phase flow patterns. The simulations showed that using both horizontal and vertical baffling provided the configuration with the highest heat transfer and minimized the bypass regions where the vapor would circumvent the graphite foam. This baffle configuration increased the amount of vapor flow through the inner graphite fins and cold water pipes, which gave this configuration the highest heat transfer. The results from experimental tests using the condenser system confirmed that using three baffles will increase performance consistent with the simulation results. The experimental data showed that the condenser using graphite foam had five times the heat transfer compared to the condenser using only aluminum fins. Incorporating baffles into the condenser using graphite foam enabled this system to conduct nearly ten times more heat transfer than the condenser system which only had aluminum fins without baffles. The results from this research indicate that graphite foam is a far superior material heat transfer enhancement material for heat transfer compared to aluminum used as an extended surface. The longitudinal and horizontal baffles incorporated into the condenser system greatly enhanced the heat transfer because of the increased interaction with the porous graphite foam fins.

Collins, Michael

345

Experimental study of the impact of large-scale wind farms on land-atmosphere exchanges  

NASA Astrophysics Data System (ADS)

Large-scale wind farms, covering a significant portion of the land and ocean surface, may affect the transport of momentum, heat, mass and moisture between the atmosphere and the land locally and globally. To understand the wind-farm-atmosphere interaction, we conducted wind-tunnel experiments to study the surface scalar (heat) flux using model wind farms, consisting of more than ten rows of wind turbines—having typical streamwise and spanwise spacings of five and four rotor diameters—in a neutral boundary layer with a heated surface. The spatial distribution of the surface heat flux was mapped with an array of surface heat flux sensors within the quasi-developed regime of the wind-farm flow. Although the overall surface heat flux change produced by the wind farms was found to be small, with a net reduction of 4% for a staggered wind farm and nearly zero change for an aligned wind farm, the highly heterogeneous spatial distribution of the surface heat flux, dependent on the wind-farm layout, was significant. The difference between the minimum and maximum surface heat fluxes could be up to 12% and 7% in aligned and staggered wind farms, respectively. This finding is important for planning intensive agriculture practice and optimizing farm land use strategy regarding wind energy project development. The well-controlled wind-tunnel experiments presented in this study also provide a first comprehensive dataset on turbulent flow and scalar transport in wind farms, which can be further used to develop and validate new parameterizations of surface scalar fluxes in numerical models.

Zhang, Wei; Markfort, Corey D.; Porté-Agel, Fernando

2013-03-01

346

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

347

A Comprehensive Study of the Solubility, Thermochemistry, Ion Exchange and Precipitation Kinetics of NO3 Cancrinite and No3 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. This report focuses on the portion of the work performed at UC Davis by Professor Navrotsky's group.

Jove-Colon, Carlos; Navrotsky, Alexandra

2004-12-31

348

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

349

Mössbauer Studies on Exchange Interactions in CoFe2O4  

NASA Astrophysics Data System (ADS)

Two polycrystalline samples of CoFe2O4 were prepared by slow cooling and quenching and studied using Mössbauer spectroscopy and X-ray diffraction. The crystals were found to have a cubic spinel structure with the lattice constants of the slowly cooled sample being a0=8.381 Å and the quenched sample being a0=8.391 Å. The temperature dependence of the magnetic hyperfine field in 57Fe nuclei at the tetrahedral (A) and octahedral (B) sites was analyzed based on the Néel theory of ferrimagnetism. For the slowly cooled sample, the intersublattice A-B superexchange interaction and intrasublattice A-A superexchange interaction were antiferromagnetic with a strength of JA--B=-25.0kB and JA--A=-18.9kB, respectively, while the intrasublattice B--B superexchange interaction was ferromagnetic with a strength of JB--B=3.9kB. In the quenched sample, however, their strengths were JA--B=-22.6kB, JA--A=-17.6kB, and JB--B=3.9kB, respectively.

Kim, Sam Jin; Lee, Seung Wha; Kim, Chul Sung

2001-08-01

350

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

351

Numerical Study of Convective Heat Transfer in Flat Tube Heat Exchangers Operating in Self-Sustained Oscillatory Flow Regimes  

E-print Network

Laminar, two-dimensional, constant-property numerical simulations of flat tube heat exchanger devices operating in flow regimes in which self-sustained oscillations occur were performed. The unsteady flow regimes were transition flow regimes...

Fullerton, Tracy

2012-02-14

352

High-resolution studies of charge exchange in supernova remnants with Magellan, XMM-Newton, and Micro-X  

E-print Network

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. ...

Heine, Sarah Nicole Trowbridge

2014-01-01

353

Numerical study on air-side performance of an integrated fin and micro-channel heat exchanger  

Microsoft Academic Search

A new type of aluminum heat exchanger with integrated fin and micro-channel has been proposed. The air-side heat transfer and flow characteristics of the integrated fin and micro-channel heat exchanger are systematically analyzed by a 3D numerical simulation. The effect of flow depth, fin height, fin pitch and fin thickness at different Reynolds number is evaluated by calculating Colburn factor

Jiong Li; Shuangfeng Wang; Wang Cai; Weijun Zhang

2010-01-01

354

Plasma-exchange therapy in chronic inflammatory demyelinating polyneuropathy: A double-blind, sham-controlled, cross-over study  

Microsoft Academic Search

Summary Eighteen patients with definite, untreated chronic inflam- matory demyelinating polyradiculoneuropathy (CIDP) of chronic progressive (nine patients) or relapsing course (nine patients) were randomizedprospectively to receive 10plasma- exchange (PE) or sham plasma-exchange (SPE) treatments over 4 weeks in a double-blind trial. After a wash-out period of 5 weeks or when they returned to baseline scores, patients were crossed over to

A. F. Hahn; C. F. Bolton; N. Pillay; C. Chalk; T. Benstead; V. Bril; K. Shumak; M. K. Vandervoort; T. E. Feasby

1996-01-01

355

Ab-initio study of exchange constants and electronic structure in diluted magnetic group-IV semiconductors  

NASA Astrophysics Data System (ADS)

Exchange-constants have been evaluated from first-principles in Mn-doped Ge, mainly focusing on the effects of the impurity concentration and of the arrangement of Mn-atoms in the semiconducting matrix. As expected, the Mn-concentration strongly affects the magnitude of the exchange constants (especially between Mn as first-nearest-neighbors (NNs) in the cation position). Interestingly, the arrangement of Mn atoms is found to be relevant for the behavior of the second-NN exchange-constant along the [110]-bonding direction, which shows either a strongly ferromagnetic or a marked antiferromagnetic behavior, depending on whether the interaction is mediated by a Ge or by an Mn atom, respectively. This suggests that, at least for rather high values of the doping concentration (~10%), a detailed knowledge of the Mn positions in the host is required for a careful prediction of the exchange constants and, therefore, of the ordering Curie temperature in Mn-doped Ge. The analysis of the impurity- and host-induced effects on the exchange constants is carried out by comparing (i) Mn- and Cr-doped Ge and (ii) Mn-doped Ge and GaAs. Our findings regarding the global weak antiferromagnetism for CrGe confirm that ferromagnetism in diluted magnetic semiconductors requires the presence of holes, whereas Ge and GaAs appear rather similar as for the exchange constants, both showing strong environmental effects.

Picozzi, Silvia; Ležai?, Marjana

2008-05-01

356

CLOSED-LOOP TREATMENT OF ELECTROLYTIC AND ELECTROLESS NICKEL RINSE WATER BY POINT-OF-USE ION EXCHANGE: A CASE STUDY.  

EPA Science Inventory

Closed-Loop Treatment of Electrolytic and Electroless Nickel Rinse Water by Point-Of-Use Ion Exchange: A Case Study. Dave Szlag1, Joe Leonhardt2, Albert Foster1, Mike Goss1 and Paul Bolger1. 1 U.S. EPA, National Risk Management Research Laboratory, 26 W. M. L. King D...

357

Application of a heat pipe heat exchanger to dehumidification enhancement in a HVAC system for tropical climates—a baseline performance characteristics study  

Microsoft Academic Search

In Malaysia, humidity control is a common problem in built environments in tropical hot and humid climates as it is an important aspect of the maintenance of comfortable and healthy conditions within a controlled airspace. An 8-row thermosyphon-based heat pipe heat exchanger (HPHX) for tropical building HVAC systems was studied experimentally. This research was an investigation into how the sensible

Yat H. Yau

2007-01-01

358

An experimental study on the heat transfer characteristics of a heat pipe heat exchanger with latent heat storage. Part II: Simultaneous charging\\/discharging modes  

Microsoft Academic Search

In this part of the paper, the performance of the simultaneous charging\\/discharging operation modes of the heat pipe heat exchanger with latent heat storage is experimentally studied. The experimental results show that the device may operate under either the fluid to fluid heat transfer with charging heat to the phase change material (PCM) or the fluid to fluid heat transfer

Zhongliang Liu; Zengyi Wang; Chongfang Ma

2006-01-01

359

Variational quantum Monte Carlo study of two-dimensional Wigner crystals: Exchange, correlation, and magnetic-field effects  

NASA Astrophysics Data System (ADS)

The two-dimensional Wigner crystals are studied with the variational quantum Monte Carlo method. The close relationship between the ground-state wave function and the collective excitations in the system is illustrated, and used to guide the construction of the ground-state wave function of the strongly correlated solid. Exchange, correlation, and magnetic-field effects all give rise to distinct physical phenomena. In the absence of any external magnetic field, interesting spin orderings are observed in the ground state of the electron crystal in various two-dimensional lattices. In particular, two-dimensional bipartite lattices are shown not to lead necessarily to an antiferromagnetic ground state. In the quantum Hall effect regime, a strong magnetic field introduces energy and length scales. The magnetic field quenches the kinetic energy and poses constraints on how the electrons may correlate with each other. Care is taken to ensure the appropriate translational properties of the wave function when the system is in a uniform magnetic field. We have examined the exchange, intra-Landau-level correlation as well as Landau-level-mixing effects with various variational wave functions. We also determine their dependences on the experimental parameters such as the carrier effective mass at a modulation-doped semiconductor heterojunction. Our results, when combined with some recent calculations for the energy of the fractional quantum Hall liquid including Landau-level-mixing, show quantitatively that in going from n doping to p doping in GaAs/AlxGa1-xAs heterojunction systems, the crossover filling factor from the fractional quantum Hall liquid to the Wigner crystal changes from filling factor ?~1/5 to ?~1/3. This lends strong support to the claim that the observed reentrant insulating phases around ?=1/5 for n-doped and around ?=1/3 for p-doped high-mobility samples are primarily caused by electron-electron interaction effects. We discuss the possible implications of our theoretical results for some recent experiments carried out in the quantum Hall regime in search of the electron solid.

Zhu, Xuejun; Louie, Steven G.

1995-08-01

360

A modeling study of water and salt exchange for a micro-tidal, stratified northern Gulf of Mexico estuary  

NASA Astrophysics Data System (ADS)

A three-dimensional hydrodynamic model is applied to the Mobile Bay system to study water and salt exchange with the northern Gulf of Mexico via Main Pass (MP) and eastern Mississippi Sound via Pass-aux-Herons (PaH). On average, more water leaves the Bay through MP than through PaH, and the Bay gains salt through MP and loses about the same amount through PaH. However, the volume discharge rate Qf and salt transport rate FS vary greatly in response to wind and river discharge with the range of variation 1-2 orders of magnitude larger than the corresponding mean. Stratification plays a key role for salt transport through MP. During periods of large river discharge, the landward shear dispersive transport FE peaking during equatorial tides and the landward tidal oscillatory transport FT peaking during tropic tides, respectively, balance the seaward advective transport QfS0. During periods of relatively weak stratification, FS at MP is almost entirely determined by QfS0 and its variability is well correlated with north-south (along-estuary) wind, associated with the barotropic (water level) adjustment. At the shallow, weakly stratified PaH, FS is almost identical to QfS0, and Qf is well correlated with east-west wind, with the correlation becoming stronger during the dry period.

Kim, Choong-Ki; Park, Kyeong

2012-08-01

361

Flow maldistribution in heat exchangers  

Microsoft Academic Search

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

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

1999-01-01

362

A patient-specific study of type-B aortic dissection: evaluation of true-false lumen blood exchange  

PubMed Central

Background Aortic dissection is a severe pathological condition in which blood penetrates between layers of the aortic wall and creates a duplicate channel – the false lumen. This considerable change on the aortic morphology alters hemodynamic features dramatically and, in the case of rupture, induces markedly high rates of morbidity and mortality. Methods In this study, we establish a patient-specific computational model and simulate the pulsatile blood flow within the dissected aorta. The k-? SST turbulence model is employed to represent the flow and finite volume method is applied for numerical solutions. Our emphasis is on flow exchange between true and false lumen during the cardiac cycle and on quantifying the flow across specific passages. Loading distributions including pressure and wall shear stress have also been investigated and results of direct simulations are compared with solutions employing appropriate turbulence models. Results Our results indicate that (i) high velocities occur at the periphery of the entries; (ii) for the case studied, approximately 40% of the blood flow passes the false lumen during a heartbeat cycle; (iii) higher pressures are found at the outer wall of the dissection, which may induce further dilation of the pseudo-lumen; (iv) highest wall shear stresses occur around the entries, perhaps indicating the vulnerability of this region to further splitting; and (v) laminar simulations with adequately fine mesh resolutions, especially refined near the walls, can capture similar flow patterns to the (coarser mesh) turbulent results, although the absolute magnitudes computed are in general smaller. Conclusions The patient-specific model of aortic dissection provides detailed flow information of blood transport within the true and false lumen and quantifies the loading distributions over the aorta and dissection walls. This contributes to evaluating potential thrombotic behavior in the false lumen and is pivotal in guiding endovascular intervention. Moreover, as a computational study, mesh requirements to successfully evaluate the hemodynamic parameters have been proposed. PMID:23829346

2013-01-01

363

Feature- and Face-Exchange illusions: new insights and applications for the study of the binding problem  

PubMed Central

The binding problem is a longstanding issue in vision science: i.e., how are humans able to maintain a relatively stable representation of objects and features even though the visual system processes many aspects of the world separately and in parallel? We previously investigated this issue with a variant of the bounce-pass paradigm, which consists of two rectangular bars moving in opposite directions; if the bars are identical and never overlap, the motion could equally be interpreted as bouncing or passing. Although bars of different colors should be seen as passing each other (since the colors provide more information about the bars' paths), we found “Feature Exchange”: observers reported the paradoxical perception that the bars appear to bounce off of each other and exchange colors. Here we extend our previous findings with three demonstrations. “Peripheral Feature-Exchange” consists of two colored bars that physically bounce (they continually meet in the middle of the monitor and return to the sides). When viewed in the periphery, the bars appear to stream past each other even though this percept relies on the exchange of features and contradicts the information provided by the color of the bars. In “Face-Exchange” two different faces physically pass each other. When fixating centrally, observers typically report the perception of bouncing faces that swap features, indicating that the Feature Exchange effect can occur even with complex objects. In “Face-Go-Round,” one face repeatedly moves from left to right on the top of the monitor, and the other from right to left at the bottom of the monitor. Observers typically perceive the faces moving in a circle—a percept that contradicts information provided by the identity of the faces. We suggest that Feature Exchange and the paradigms used to elicit it can be useful for the investigation of the binding problem as well as other contemporary issues of interest to vision science.

Shapiro, Arthur G.; Caplovitz, Gideon P.; Dixon, Erica L.

2014-01-01

364

The voltage-sensitive Na+/H+ exchange in sea urchin spermatozoa flagellar membrane vesicles studied with an entrapped pH probe.  

PubMed

Flagellar plasma membrane vesicles were isolated from sea urchin sperm using osmotic lysis. A membrane impermeant fluorescence pH indicator, pyranine, was incorporated into the vesicles as they resealed after lysis and was used to measure the intravesicular pH (pHi). Addition of Na+ rapidly alkalinized the pHi of vesicles prepared with an internal acidic pH gradient. The pHi increase showed ionic selectivity in the order of Na+ greater than Li+ much greater than K+ approximately equal to Cs+ approximately equal to O. Complete removal of monovalent anions such as Cl- and HCO3- did not affect the exchange, thus ruling out the participation of an anion carrier in the process. The optimal operation of the exchanger, however, required the presence of a transmembrane potential, which could be generated by the diffusion potential of either K+, a naturally permeant ion, or Cs+ which was artificially made permeant by the ionophore valinomycin. Depolarization inhibited the exchange in both the forward and the reverse directions, which is consistent with the voltage-gated electroneutral exchange mechanism proposed previously for this exchanger (Lee, H. C. J. Biol. Chem. (1984) 259, 15315-15319). The voltage sensitivity of the Na+/H+ exchanger was found to be modulated by the presence of Mg2+. A model involving the screening of the internal surface potential was proposed to account for the Mg2+ effect. The vesicle preparation used in this study allows complete control of the internal contents and represents a major simplification of the system as compared with the intact sperm and the isolated flagella used previously. PMID:2993289

Lee, H C

1985-09-01

365

Plasma exchange or immunoadsorption in patients with rapidly progressive crescentic glomerulonephritis. A Swedish multi-center study.  

PubMed

A therapeutic removal of antibodies may be achieved by immunoadsorption (IA) or by plasma exchange (PE). The aim of this prospective randomised study was to compare the efficacy of these different techniques with regard to treatment of patients with rapidly progressive glomerulonephritis (RPG) having at least 50% crescents. Forty-four patients with a RPG were included for treatment either by IA or PE (with albumin as substitution for removed plasma). All patients were additionally treated with immunosuppression. A median of 6 sessions of PEs were performed in 23 patients compared with 6 IAs in 21 patients. Goodpasture's syndrome (GP) was present in 6 patients (PE 3, IA 3). All of them started and ended in dialysis, two died. Among the remaining 38 patients (26 men, 12 women) 87% had antibodies to ANCA. Creatinine clearance for PE versus IA were at a median at start 17.1 and 19.8 ml/min, and at 6 months 49 and 49 ml/min, respectively. At 6 months 7 of 10 patients did not need dialysis (remaining: IA 0/5 and PE 2/5, n.s.). The extent of improvement did not differ between the groups. Three patients died during the observation period of 6 months (IA 2; PE 1, on HD). Although no difference was found between the IA or the PE group this study shows that the protocol used was associated with an improved renal function in most patients (except for Goodpasture's syndrome) whereas 70% of them could leave the dialysis program. PMID:10212042

Stegmayr, B G; Almroth, G; Berlin, G; Fehrman, I; Kurkus, J; Norda, R; Olander, R; Sterner, G; Thysell, H; Wikström, B; Wirén, J E

1999-02-01

366

Agriculture on Exchange InternationalExchangeProgram  

E-print Network

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

Viglas, Anastasios

367

A density functional theory study of 3d-4f exchange interactions in Cr-Nd codoped GaN  

NASA Astrophysics Data System (ADS)

The density functional theory based calculations of Cr, Nd and Cr/Nd co-doped wurtzite GaN generated using GGA and TB-mBJ exchange correlation functionals are being reported. All the structures were geometrically optimized and fully relaxed. The dopants introduced new energy levels in the forbidden energy gap, whose hybridization and interaction are discussed in detail to explain electronic and ferromagnetic properties of the materials. The 3d-3d interaction seems to be responsible for double exchange interaction in Cr:GaN whereas spin polarization caused by 4f-5d-CB interaction causes ferromagnetism in Nd:GaN. A model is proposed to explain the ferromagnetic ordering and 3d-4f exchange interactions in new codoped system Cr/Nd:GaN according to which 4f-5d-CB-3d interaction via 4f-5d, 4f-2p and 2p-3d coupling plays role.

Majid, Abdul; Dar, Amna

2014-11-01

368

STUDIES OF X-RAY PRODUCTION FOLLOWING CHARGE EXCHANGE RECOMBINATION BETWEEN HIGHLY CHARGED IONS AND NEUTRAL ATOMS AND MOLECULES  

SciTech Connect

We have used microcalorimeters built by the NASA/Goddard Space Flight Center and the Lawrence Livermore National Laboratory Electron Beam Ion Trap to measure X-ray emission produced by charge exchange reactions between highly charged ions colliding with neutral helium, hydrogen, and nitrogen gas. Our measurements show the spectral dependence on neutral species and also show the distinct differences between spectra produced by charge exchange reactions and those produced by direct impact excitation. These results are part of an ongoing experimental investigation at the LLNL EBIT facility of charge exchange spectral signatures and can be used to interpret X-ray spectra produced by a variety of laboratory and celestial sources including cometary and planetary atmospheres, the Earth's magnetosheath, the heliosphere, and tokamaks.

Brown, G V; Beiersdorfer, P; Chen, H; Clementson, J; Frankel, M; Gu, M F; Kelley, R L; Kilbourne, C A; Porter, F S; Thorn, D B; Wargelin, B J

2008-08-28

369

IEL Policy Exchange  

NSDL National Science Digital Library

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

370

Salt-Zeolite Ion Exchange Equilibrium Studies for Complete Set of Fission Products in Molten LiCl-KCl  

Microsoft Academic Search

This paper presents results on LiCl-KCl based molten salts\\/zeolite-A contact experiments and the associated equilibrium ion exchange model. Experiments examine the contact behaviors of various ternary salts (LiCl-KCl-YCl3, LiCl-KCl-LaCl3, and LiCl-KCl-PrCl3) and quaternary salts (LiCl-KCl-CsCl-NdCl3 and LiCl-KCl-CsCl-SrCl2) with the zeolite-A. The developed equilibrium model assumes that there are ion exchange and occlusion sites, both of which are in equilibrium with

Tae-Sic Yoo; Steven M. Frank; Michael F. Simpson; Paula A. Hahn; Terry J. Battisti; Supathorn Phongikaroon

2010-01-01

371

Study of plate-fin heat exchanger and cold plate for the active thermal control system of Space Station  

NASA Technical Reports Server (NTRS)

Plate-fin heat exchangers will be employed in the Active Thermal Control System of Space Station Freedom. During ground testing of prototypic heat exchangers, certain anomalous behaviors have been observed. Diagnosis has been conducted to determine the cause of the observed behaviors, including a scrutiny of temperature, pressure, and flow rate test data, and verification calculations based on such data and more data collected during the ambient and thermal/vacuum tests participated by the author. The test data of a plate-fin cold plate have been also analyzed. Recommendation was made with regard to further tests providing more useful information of the cold plate performance.

Chyu, MING-C.

1992-01-01

372

Interpersonal Exchange in Isolation.  

National Technical Information Service (NTIS)

The study explored interpersonal exchange in isolated and non-isolated groups. Nine dyads formed at different levels on need achievement, need dominance, need affiliation and dogmatism worked out lived in a small room for ten days, with no outside contact...

I. Altman, W. W. Haythorn

1965-01-01

373

Increasing NDVI values in northern Alaska: studies that mix shrub density, spectral and CO2 exchange measurements  

NASA Astrophysics Data System (ADS)

Delineating the mechanisms and consequences of changes in tundra landscapes is central to predicting the functional ecology of Alaska in the 21st Century. Evidence has been mounting during the last decade that shrub communities are expanding in the Arctic and Normalized Difference Vegetation Index (NDVI) values which measure surface greenness are rising. Several studies have suggested that NDVI increases are being driven by increases in shrub abundance. While it is clear that NDVI has increased across vegetation types, it is not clear that NDVI values are increasing in moist acidic tundra (MAT), the most extensive vegetation type in arctic Alaska and the one most likely to be changed by global warming. The MAT is important to large mammal herbivores such as caribou which provide subsistence for indigenous people. The focus of this research was to determine what rising NDVI values actually mean in the MAT. The degree to which tundra community composition affects NDVI is still very poorly understood. In order to clarify the role of shrub encroachment per se as opposed to other functional groups in driving increases in NDVI, we measured functional group composition in moist acidic tundra in conjunction with hand-held measures of NDVI and direct CO2 exchange measurements to explicitly link spectral properties, shrub, graminoid and bryophyte density and trace gas feedbacks to atmospheric chemistry. Point frame data shows a shrub coverage of Betula nana (Dwarf Birch) and Salix pulchra (Diamond Leaf Willow) combined of 5% to 35% in MAT. Our results seem to indicate that high shrub density (>30%) corresponds to peak season NDVI values greater than .75 whereas low shrub density correspond to values below .65 (R2=.66). Furthermore, NDVI is closely correlated with canopy leaf area and greater leaf area is associated with higher rates of gross and net ecosystem CO2 uptake.

Anderson-Smith, A.; Lewis, A.; Sullivan, P.; Welker, J. M.

2010-12-01

374

Textile Exchange  

NSDL National Science Digital Library

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

375

Segmented heat exchanger  

SciTech Connect

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

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

2010-12-14

376

Implementation Team Responsiveness and User Evaluation of Customer Relationship Management: A Quasi-Experimental Design Study of Social Exchange Theory  

Microsoft Academic Search

Customer Relationship Management (CRM) systems require extensive configuration during which users come into extensive contact with the technical imple- mentation team. Previous research examining other Enterprise Resource Planning (ERP) modules has shown that user perception of the responsiveness of such teams, as an indicator of a possible social exchange, is significantly associated with an in- creased favorable assessment of the

David Gefen; Catherine M. Ridings

2002-01-01

377

Linguistic and Cultural Exchange and Appropriation: A Survey Study in a Multi-Ethnic Neighbourhood in The Netherlands.  

ERIC Educational Resources Information Center

Investigated the interplay between languages and cultures in the multilingual and multicultural neighborhood of Lombok/Transvaal in Utrecht in The Netherlands. Results confirm that because Turkish, Moroccan, and Surinamese immigrants differ with respect to immigration history, level of education, and Dutch proficiency, processes of exchange and…

Jongenburger, Willy; Aarssen, Jeroen

2001-01-01

378

Knowledge Exchange between Universities and the Creative Industries in the UK: A Case Study of Current Practice  

ERIC Educational Resources Information Center

The importance to the economy of knowledge exchange between universities and industry has long been recognized, and in the UK a number of initiatives are in place to support such activities. These initiatives have helped to stimulate engagement between universities and the creative industries, a sector of increasing importance to the UK economy.…

Ferguson, Morag

2014-01-01

379

The Role of Learned Societies in Knowledge Exchange and Dissemination: The Case of the Regional Studies Association, 1965-2005  

ERIC Educational Resources Information Center

This paper discusses the role of learned societies in knowledge exchange and dissemination. It attempts to "map" the organisations that are considered to reside under the term and discusses how they have developed through history. In doing so, it seeks to highlight that whilst several types of organisations inhabit the landscape of learned…

Hopkins, James

2011-01-01

380

Native American-Native Siberian Cultural Exchange: Ancient Tribal Connections Come to Light in Monument Valley Study Program.  

ERIC Educational Resources Information Center

Describes the 1995-97 student exchange program between the Navajo Nation in San Juan School District, Utah, and the Khanty-Mansisk region of Siberia. Similarities were found in language, string games, folk tales, sweat lodges, clan traditions, traditional arts and crafts, and stories of ancient meetings between the two peoples and use of the…

Hubbard, Pat

1998-01-01

381

Micromagnetic study of exchange spring media with a rough interface on an example of FePt films  

NASA Astrophysics Data System (ADS)

In this paper exchange spring media with a rough interface between magnetically hard and soft materials are considered. As an example a nanostructure of FePt L10/A1 films is analysed. The observed features, such as inclusions of L10 phase in A1 matrix, were transferred into finite element numerical models. Also, the distribution of the hard phase along the thickness of the medium was analysed. It was found to fit linear, logistic and quadratic functions in the interface region. Micromagnetic simulations show that the position and size of obstacles significantly alter the switching field of the media. Moreover, the minimal switching field of Hsw = 0.9 T was observed for a quadratic L10 distribution in an 18 nm thick interface region. The numerical results agree well with an analytical formula of the pinning field of exchange spring media, which is derived for the general case of spatially varying magnetization, anisotropy and exchange constant. It is emphasized that the applicability of the numerical methods described here is not limited to FePt L10/A1 films but could be interesting also for other exchange spring media, such as CoPt L10/A1 or FePt(L10)/FeAu(L10).

Dymerska, Barbara; Lee, Jehyun; Fidler, Josef; Suess, Dieter

2012-12-01

382

STUDIES ON THE SEPARATION OF THE RARE EARTHS FROM THORIUM IN SULPHATE SOLUTIONS, USING CATION EXCHANGE RESINS  

Microsoft Academic Search

An ion exchange method for the sepration of the rare earth elements from ; thorium has been investigated. The method is based on the difference in the ; extent of complexing of the metal ions by sulfate ions in aqueous solution. ; Variables investigated were: sulfate concentration, nature of the counter-ion ( ; i.e,, the cation whose sulfate salt supplies

D. C. Lewis; J. C. Ingles

1958-01-01

383

A Study of Learners' Perceptions of Online Intercultural Exchange through Web 2.0 Technologies  

ERIC Educational Resources Information Center

This paper reports a Spanish-American telecollaborative project through which students used "Twitter," blogs and podcasts for intercultural exchange over the course of one semester. The paper outlines the methodology for the project including pedagogical objectives, task design, selection of web tools and implementation. Using…

Lee, Lina; Markey, Alfred

2014-01-01

384

Perceived Reciprocity in Social Exchange and Health Functioning in Early Old Age: Prospective Findings from the GAZEL-Study  

E-print Network

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 health and well-being quite substantially. The socio-emotional dimension of interpersonal exchange lies

Paris-Sud XI, Université de

385

Media Effects and the Active Elite AudienceA Study of Communications in the London Stock Exchange  

Microsoft Academic Search

This article explores the impact of communications on investor behaviour and trading patterns in the London Stock Exchange (LSE). The significance of the work is two-fold. First, for many observers, the wild trading patterns that regularly occur in stock markets suggest the presence of ‘strong’ media effects in action; a finding in conflict with mainstream audience research. Second, the audience

Aeron Davis

2005-01-01

386

Improved method and case study of thermal response test for borehole heat exchangers of ground source heat pump system  

Microsoft Academic Search

Thermal response test (TRT) is crucial for the determination of the ground thermal conductivity and the evaluation of the thermal performance of borehole heat exchangers (BHEs) of ground source heat pump (GSHP) system. This paper presented a novel constant heating-temperature method (CHTM) for TRT. Further, a type of improved TRT equipment was developed and the mathematical model to deal with

Huajun Wang; Chengying Qi; Hongpu Du; Jihao Gu

2010-01-01

387

Conformational dynamics of a membrane transport protein probed by H/D exchange and covalent labeling: the glycerol facilitator.  

PubMed

Glycerol facilitator (GF) is a tetrameric membrane protein responsible for the selective permeation of glycerol and water. Each of the four GF subunits forms a transmembrane channel. Every subunit consists of six helices that completely span the lipid bilayer, as well as two half-helices (TM7 and TM3). X-ray crystallography has revealed that the selectivity of GF is due to its unique amphipathic channel interior. To explore the structural dynamics of GF, we employ hydrogen/deuterium exchange (HDX) and oxidative labeling with mass spectrometry (MS). HDX-MS reveals that transmembrane helices are generally more protected than extramembrane segments, consistent with data previously obtained for other membrane proteins. Interestingly, TM7 does not follow this trend. Instead, this half-helix undergoes rapid deuteration, indicative of a highly dynamic local structure. The oxidative labeling behavior of most GF residues is consistent with the static crystal structure. However, the side chains of C134 and M237 undergo labeling although they should be inaccessible according to the X-ray structure. In agreement with our HDX-MS data, this observation attests to the fact that TM7 is only marginally stable. We propose that the highly mobile nature of TM7 aids in the efficient diffusion of guest molecules through the channel ("molecular lubrication"). In the absence of such dynamics, host-guest molecular recognition would favor semipermanent binding of molecules inside the channel, thereby impeding transport. The current work highlights the complementary nature of HDX, covalent labeling, and X-ray crystallography for the characterization of membrane proteins. PMID:22227391

Pan, Yan; Piyadasa, Hadeesha; O'Neil, Joe D; Konermann, Lars

2012-02-24

388

Exchange Rate Regimes: Does What Countries Say Matter?  

Microsoft Academic Search

Traditionally, the IMF's Annual Report on Exchange Arrangements and Exchange Restrictions has been the main source of information about the exchange rate policies pursued by member countries. The classification contained therein has been used to document the evolution of exchange rate regimes over time as well as to study the relationship between economic performance and the choice of exchange rate

Hans Genberg; Alexander K. Swoboda

2005-01-01

389

Molecular exchange dynamics in partially filled microscale and nanoscale pores of silica glasses studied by field-cycling nuclear magnetic resonance relaxometry  

NASA Astrophysics Data System (ADS)

Nuclear magnetic spin-lattice relaxation experiments have been performed in partially filled porous glasses with wetting and nonwetting fluids. The frequency dependence of the spin-lattice relaxation rate in Vycor (4 nm pores) and VitraPOR #5 (1 ?m pores) silica glasses was studied as a function of the filling degree with the aid of field-cycling NMR relaxometry. The species of primary interest were water (``polar'') and cyclohexane (``nonpolar''). Spin-lattice relaxation was examined in the frequency range from 1 kHz to 400 MHz with the aid of a field-cycling NMR relaxometer and an ordinary 400 MHz NMR spectrometer. Three different mobility states of the fluid molecules are distinguished: The adsorbed state at the pore walls, the bulklike liquid phase, and the vapor phase. The adsorbate spin-lattice relaxation rate is dominated by the ``reorientation mediated by translational displacements'' (RMTD) mechanism taking place at the adsorbate/matrix interface at frequencies low enough to neglect rotational diffusion of the molecules. The experimental data are analyzed in terms of molecular exchange between the different mobility states. Judged from the dependence of the spin-lattice relaxation rates on the filling degree, limits for slow and fast exchange (relative to the RMTD time scale) can be distinguished and identified. It is concluded that water always shows the features of slow exchange irrespective of the investigated pore sizes and filling degrees. This is in contrast to cyclohexane which is subject to slow exchange in micrometer pores, whereas fast exchange occurs in nanoscopic pores. The latter case implies that the vapor phase contributes to molecular dynamics in this case at low filling degrees while it is negligible otherwise.

Mattea, C.; Kimmich, R.; Ardelean, I.; Wonorahardjo, S.; Farrher, G.

2004-12-01

390

Automated red blood cell exchange as an adjunctive treatment for severe Plasmodium falciparum malaria at the Vienna General Hospital in Austria: a retrospective cohort study  

PubMed Central

Background Severe falciparum malaria is associated with considerable rates of mortality, despite the administration of appropriate anti-malarial treatment. Since overall survival is associated with total parasite biomass, blood exchange transfusion has been proposed as a potential method to rapidly reduce peripheral parasitaemia. However, current evidence suggests that this treatment modality may not improve outcome. Automated red blood cell exchange (also referred to as “erythrocytapheresis”) has been advocated as an alternative method to rapidly remove parasites from circulating blood without affecting patients’ volume and electrolyte status. However, only limited evidence from case reports and case series is available for this adjunctive treatment. This retrospective cohort study describes the use of automated red blood cell exchange for the treatment of severe malaria at the Medical University of Vienna. Methods Epidemiologic data for imported malaria cases in Austria are reported and data of patients treated for malaria at the General Hospital/Medical University of Vienna were extracted from electronic hospital records. Results Between 2000 and 2010, 146 patients were hospitalized at the Medical University of Vienna due to malaria and 16 of those were classified as severe malaria cases. Eleven patients of this cohort were potentially eligible for an adjunctive treatment with automated red blood cell exchange. Five patients eventually underwent this procedure within a period of seven hours (range: 3–19 hours) after hospital admission. Six patients did not undergo this adjunctive treatment following the decision of the treating physician. The procedure was well tolerated in all cases and rapid reduction in parasite counts was achieved without occurrence of haemodynamic complications. One patient died within seven days, whereas four patients survived without any sequelae. Discussion and conclusion Automated red blood cell exchange was a safe and efficient procedure to rapidly clear peripheral parasitaemia. Whether the fast reduction in parasite biomass may ultimately improve patient survival remains however unclear. Randomized controlled trials are needed to conclusively appreciate the value of this adjunctive treatment. PMID:22564543

2012-01-01

391

Educator Exchange Resource Guide.  

ERIC Educational Resources Information Center

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

Garza, Cris; Rodriguez, Victor

392

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

Microsoft Academic Search

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 Hâ-Dâ exchange at 70-200°C on reduced copper-containing samples and the absence of

V. I. Yakerson; A. N. Subbotin; B. S. Gudkov; O. P. Tkachenko; R. G. Sarmurzina

1994-01-01

393

Kinetics study and thermodynamic behavior for removing cesium, cobalt and nickel ions from aqueous solution using nano-zirconium vanadate ion exchanger  

Microsoft Academic Search

The goal of this batch-test kinetic study is to evaluate the effectiveness of the different prepared nano-zirconium vanadate ion exchangers for removing cesium, cobalt and nickel from aqueous solution. The prepared samples are characterized using X-ray diffraction, Scanning Electron Microscope and Specific surface area. Analysis of the respective rate data in accordance with three kinetic models is applied. It is

M. M. Abd El-Latif; M. F. Elkady

2011-01-01

394

PHYSICAL REVIEW B 84, 224437 (2011) Ab initio study of the intrinsic exchange bias at the SrRuO3/SrMnO3 interface  

E-print Network

PHYSICAL REVIEW B 84, 224437 (2011) Ab initio study of the intrinsic exchange bias at the SrRuO3/Sr, and it is only active in heterostructures involving multiferroics. Using the SrRuO3/SrMnO3 superlattice). An example is provided by the (111) surface of G-type AFM materials. In these cases, a large EB would

Tennessee, University of

395

Study of Ram-air Heat Exchangers for Reducing Turbine Cooling-air Temperature of a Supersonic Aircraft Turbojet Engine  

NASA Technical Reports Server (NTRS)

The sizes and weights of the cores of heat exchangers were determined analytically for possible application for reducing turbine cooling-air temperatures of an engine designed for a Mach number of 2.5 and an altitude The sizes and weights of the cores of heat exchangers were determined analytically for possible application for reducing turbine cooling-air temperatures of an engine designed for a Mach number of 2.5 and an altitude of 70,000 feet. A compressor-bleed-air weight flow of 2.7 pounds per second was assumed for the coolant; ram air was considered as the other fluid. Pressure drops and inlet states of both fluids were prescribed, and ranges of compressor-bleed-air temperature reductions and of the ratio of compressor-bleed to ram-air weight flows were considered.

Diaguila, Anthony J; Livingood, John N B; Eckert, Ernst R G

1956-01-01

396

Experimental study of turbulent flow heat transfer and pressure drop in plate heat exchanger with chevron plates  

Microsoft Academic Search

Experimental heat transfer and isothermal pressure drop data for single-phase water flows in a plate heat exchanger (PHE) with chevron plates are presented. In a single-pass U-type counterflow PHE, three different chevron plate arrangements are considered: two symmetric plate arrangements with β = 30 deg\\/30 deg and 60 deg\\/60 deg, and one mixed-plate arrangement with β = 30 deg\\/60 deg.

A. Muley; R. M. Manglik

1999-01-01

397

Effect of Natural Ion Exchanger Chabazite for Remediation of Lead Toxicity : An Experimental Study in Teleost Fish Heteropneustes fossilis  

Microsoft Academic Search

Zeolites are synthetic and naturally occurring sodium\\/calcium aluminosilicate minerals having unique adsorption, cation-exchange, dehydration-rehydration, and catalytic properties. They are used for the removal of ammonia, phosphates and heavy metals, and also as dietary supplement in animal diets in pet litters and as ammonia filters in kidney-dialysis unit. In the present investigation, toxicity of lead nitrate with reference to protein contents

Meeta Mishra; Subodh Kumar Jain

398

Comparison of classic laryngeal mask airway with Ambu laryngeal mask for tracheal tube exchange: A prospective randomized controlled study  

PubMed Central

Background and Aim: Exchanging endotracheal tube (ETT) with classic laryngeal mask airway™ (CLMA™) prior to emergence from anaesthesia is a safe technique to prevent the coughing and haemodynamic changes during extubation. We had compared CLMA™ and AMBU laryngeal mask™ (ALM™) during ETT/laryngeal mask (LM) for haemodynamic changes and other parameters. Methods: A total of 100 American Society of Anesthesiologist Grade I and II adult female patients undergoing elective laparoscopic cholecystectomy under general anaesthesia were selected and randomly divided into two groups of 50 patients each. In Group I, CLMA™ and in Group II, ALM™ was placed prior to tracheal extubation. Haemodynamic parameters were recorded during ETT/LM exchange. Glottic view was seen through the LM using flexible fibrescope. Coughing/bucking during removal of LM, ease of placement and post-operative sore throat for both groups were graded and recorded. Statistical Analysis: Data within the groups was analysed using paired t-test while between the groups was analysed using unpaired t-test. Chi-square test was used to analyse grades of glottic view, coughing, and post-operative sore throat. Results: In Group I, there was a significant rise in systolic blood pressure and heart rate in contrast to insignificant rise in Group II. Glottis view was significantly better in Group II. Incidence of coughing, ease of placement and post-operative sore throat was identical between both groups. Conclusion: ALM™ is superior to CLMA™ for exchange of ETT before extubation due to greater haemodynamic stability during exchange phase and is better positioned. PMID:23983284

Jain, Shruti; Khan, Rashid M; Ahmed, Syed M; Singh, Manpreet

2013-01-01

399

Sorption Behavior of In(III) Ions onto Cation-Exchange Carboxylic Resin in Aqueous Solutions: Batch and Column Studies  

Microsoft Academic Search

Indium and its compounds have numerous industrial applications in the manufacture of liquid crystal displays and semiconductors. They are considered hazardous substances. This article reports the research into the recovery of In(III) from aqueous solution by sorption. Cation-exchange carboxylic resin (D155 resin) was used as a sorbent for indium(III) ions extraction in this research. The factors of parameters, such as

Chunhua Xiong; Xiaoxiang Han; Caiping Yao

2010-01-01

400

Gradient chromatofocusing. versatile pH gradient separation of proteins in ion-exchange HPLC: characterization studies.  

PubMed

A new chromatofocusing technique called gradient chromatofocusing is characterized. Gradient chromatofocusing generates linear pH gradients on anion-exchange columns with inexpensive low molecular mass buffer components via HPLC gradient mixing. Gradient chromatofocusing results are compared with that of conventional chromatofocusing in the chromatography of several proteins on a Mono P column, including beta-lactoglobulin A and B, ovalbumin, BSA, and conalbumin. Gradient chromatofocusing shows superior performance, with resolution increases greater than 3-fold being realized for the entire protein mixture and up to 25-fold for a particular protein pair. This performance superiority arises from inherent advantages in the gradient chromatofocusing technique in optimizing conditions pertinent to separation, including buffer concentration and pH gradient slope. These resolution gains arise from both increases in separation factor and decreases in peak width achieved with the pH gradient chromatofocusing technique through the manipulation of buffer concentration and the pH gradient profile. Gradient chromatofocusing is also compared with conventional NaCl gradient ion-exchange chromatography using the same Mono P column, demonstrating 3-fold resolution gains, resulting from a 3-fold decrease in peak width. The present work demonstrates the significantly improved performance that gradient chromatofocusing has in protein separations compared to other ion-exchange chromatographic techniques. Mechanisms for the various effects are discussed. PMID:12433100

Shan, Lian; Anderson, David J

2002-11-01

401

Parametric performance studies on fluidized-bed heat exchangers. Quarterly technical progress report, 28 July-30 September 1981  

SciTech Connect

Analyses and experiments will be performed in this program to investigate the performance of single- and multi-stage shallow fluidized beds for possible application to the recovery of heat from sources such as waste heat, and coal combustion or coal gasification. This work is an extension of work done previously under Contracts EC-77-C-03-1433 and DE-AC03-79ET11348. In this program, tests will be conducted to (1) investigate the effects of fouling due to liquid condensate in the gas stream on fluidized bed heat exchanger performance, (2) investigate the performance of fluidized beds which are staged using baffle plates, and (3) investigate the effects of different heat exchanger surface geometries. During the quarter ending 30 September 1981, work progressed in selecting the conditions for that portion of the program involving fouling by a liquid condensate. Modifications were made to the Fluidized Bed Heat Exchanger Facility for the fouling experiments and plans were developed for preliminary tests in those investigations.

Not Available

1981-10-29

402

Study on the influence of isotope exchange of hydrogen with deuterium on the vibrational spectrum of lysozyme by inelastic neutron scattering  

SciTech Connect

The influence of isotope exchange of hydrogen with deuterium on the lysozyme dynamics was studied by incoherent inelastic neutron scattering. The generalized vibrational densities of states G({omega}) were constructed from experimental results for protonated and deuterated protein samples at 200, 280, and 311 K. The major isotope effect was observed in G({omega}) in the frequency region higher than 100 cm{sup -1}. At all temperatures, both the Debye mode and the region of G({omega}), whose spectral dimension corresponds to the fracton mode, are observed in the low-frequency region of the densities of states of both protonated and deuterated lysozyme. The influence of the hydrogen isotope exchange on the low-frequency region of G({omega}) is insignificant.

Svanidze, A. V., E-mail: svanidze@mail.ioffe.ru; Lushnikov, S. G. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation); Sashin, I. L. [Joint Institute for Nuclear Research (Russian Federation); Gvasaliya, S. N. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)

2007-09-15

403

Observations of Volatile Organic Compounds (VOC) from the Remote North Atlantic: Preliminary Results from the High-Wind Gas-Exchange Study (HiWinGS)  

NASA Astrophysics Data System (ADS)

Marine biogenic volatile organic compounds (BVOCs) can play a controlling role in setting the oxidative capacity of the marine boundary layer, secondary organic aerosol production rates and the chemistry of the upper ocean. Models suggest a wide range of significance for these reactive trace gases driven largely by local biophysical controls. This variability remains poorly constrained by observations, particularly from open-ocean regions. Here, we report preliminary BVOC mixing ratios and direct flux measurements from the High-Wind Gas Exchange Study (HiWinGS). This research cruise targeted regions of enhanced trace gas exchange, driven by elevated biological activity and strong surface winds in the remote North Atlantic during Fall of 2013. A custom-built chemical-ionization time-of-flight mass spectrometer was deployed to capture full mass spectra at high resolution (10 Hz) with demonstrated sensitivity (>10^2 Hz/pptv) to a wide range of BVOC species such as dimethylsulfide, isoprene, monoterpenes and alkylamines.

Kim, M.; Bertram, T. H.

2013-12-01

404

An XML model of an enhanced data dictionary to facilitate the exchange of pre-existing clinical research data in international studies.  

PubMed

Pre-existing clinical research data sets exchanged in international epidemiology research often lack the elements needed to assess their suitability for use in multi-region meta-analyses or other clinical studies. While the missing information is generally known to local investigators, it is not contained in the files exchanged between sites. Instead, such content must be solicited by the study coordinating center though a series of lengthy phone and electronic communications: an informal process whose reproducibility and accuracy decays over time. This report describes a set of supplemental information needed to assess whether clinical research data from diverse research sites are truly comparable, and what metadata ("data about the data") should be preserved when a data set is archived for future use. We propose a structured Extensible Markup Language (XML) model that captures this information. The authors hope this model will be a first step towards preserving the metadata associated with clinical research data sets, thereby improving the quality of international data exchange, data archiving, and merged-data research using data collected in many different countries, languages and care settings. PMID:17911757

Duda, Stephany N; Cushman, Clint; Masys, Daniel R

2007-01-01

405

Psychology on Exchange InternationalExchangeProgram  

E-print Network

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

Viglas, Anastasios

406

Corrosive resistant heat exchanger  

DOEpatents

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

Richlen, Scott L. (Annandale, VA)

1989-01-01

407

Kinetics of Hg(II) Exchange between Organic Ligands, Goethite, and Natural Organic Matter Studied with an Enriched Stable Isotope Approach.  

PubMed

The mobility and bioavailability of toxic Hg(II) in the environment strongly depends on its interactions with natural organic matter (NOM) and mineral surfaces. Using an enriched stable isotope approach, we investigated the exchange of Hg(II) between dissolved species (inorganically complexed or cysteine-, EDTA-, or NOM-bound) and solid-bound Hg(II) (carboxyl-/thiol-resin or goethite) over 30 days under constant conditions (pH, Hg and ligand concentrations). The Hg(II)-exchange was initially fast, followed by a slower phase, and depended on the properties of the dissolved ligands and sorbents. The results were described by a kinetic model allowing the simultaneous determination of adsorption and desorption rate coefficients. The time scales required to reach equilibrium with the carboxyl-resin varied greatly from 1.2 days for Hg(OH)2 to 16 days for Hg(II)-cysteine complexes and approximately 250 days for EDTA-bound Hg(II). Other experiments could not be described by an equilibrium model, suggesting that a significant fraction of total-bound Hg was present in a non-exchangeable form (thiol-resin and NOM: 53-58%; goethite: 22-29%). Based on the slow and incomplete exchange of Hg(II) described in this study, we suggest that kinetic effects must be considered to a greater extent in the assessment of the fate of Hg in the environment and the design of experimental studies, for example, for stability constant determination or metal isotope fractionation during sorption. PMID:25280234

Jiskra, Martin; Saile, Damian; Wiederhold, Jan G; Bourdon, Bernard; Björn, Erik; Kretzschmar, Ruben

2014-11-18

408

Preliminary studies on the heat exchanger option for S-CO{sub 2} power conversion cycle coupled to water cooled SMR  

SciTech Connect

For more than a half century, the steam Rankine cycle had been the major power conversion cycle for a nuclear power plant. However, as the interest on the next generation reactors grows, a variety of alternative power conversion systems have been studied. Among them, the S-CO{sub 2} cycle (Supercritical carbon dioxide Brayton cycle) is considered as a promising candidate due to several benefits such as 1) Relatively high thermal efficiency at relatively low turbine inlet temperature, 2) High efficiency with simple lay-out 3) Compactness of turbo-machineries. 4) Compactness of total cycle combined with PCHE (Printed Circuit Heat Exchanger). According to the conventional classification of heat exchangers (HE), there are three kind of HE, 1) Tubular HEs, 2) Plate-type HEs, 3) Extended surface HEs. So far, the researcher has mostly assumed PCHE type HE for the S-CO{sub 2} cycle due to its compactness with reasonably low pressure drop. However, PCHE is currently one of the most expensive components in the cycle, which can have a negative effect on the economics of the cycle. Therefore, an alternative for the HE should be seriously investigated. By comparing the operating condition (pressure and temperature) there are three kind of HE in the S-CO{sub 2} cycle, 1) IHX (Intermediate Heat exchanger) 2) Recuperator and 3) Pre-cooler. In each heat exchanger, hot side and cold side coolants are different, i.e. reactor coolant to S-CO{sub 2} (IHX), S-CO{sub 2} to S-CO{sub 2}(Recuperator), S-CO{sub 2} to water (Pre-cooler). By considering all the attributes mentioned above, all existing types of heat exchangers are compared to find a possible alternative to PCHE. The comparing factors are 1) Size(volume), 2) Cost. Plate fin type HEs are considered to be the most competitive heat exchanger regarding the size and the cost after some improvements on the design limit are made. (authors)

Ahn, Y.; Lee, J. [Dept. of Nuclear and Quantum Engineering, Korea Advanced Inst. of Science and Technology, 373-1 Guseong-dong Yuseong-gu, Daejeon, 305-701 (Korea, Republic of); Lee, J. I. [Dept. of Nuclear and Quantum Engineering, Korea Advanced Inst. of Science and Technology, 373-1 Guseong-dong Yuseong-gu, Daejeon, 305-701 (Korea, Republic of); Dept. of Nuclear Engineering, Khalifa Univ. of Science, Technology and Research (KUSTAR), P.O.Box 127788, Abu Dhabi (United Arab Emirates)

2012-07-01

409

Foreign exchange risk exposure: Survey and suggestions  

Microsoft Academic Search

Assessing the sensitivity of firm value to exchange rate changes has been one of the most challenging issues in international financial management over the last two decades. This paper reviews the rapidly growing exchange exposure literature, with particular reference to recent developments. The studies reviewed focus on two primary areas of inquiry: the theoretical foundations of exchange risk exposure and

Aline Muller; Willem F. C. Verschoor

2006-01-01

410

Trust and Transitions in Modes of Exchange  

ERIC Educational Resources Information Center

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

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

2010-01-01

411

Moral Reasoning and the Marital Exchange Relationship  

Microsoft Academic Search

Social psychologists have increasingly taken a social exchange view of the satisfaction or adjustment of partners in intimate relationships. After an initial focus on the applicability of exchange principles to intimate relationships, the emphasis has begun to shift to variations in exchange orientation. Based upon questionnaire responses from 194 young, married American subjects, this study examined the effect of moral

Gary L. Hansen

1991-01-01

412

Chemical exchange program analysis.  

SciTech Connect

As part of its EMS, Sandia performs an annual environmental aspects/impacts analysis. The purpose of this analysis is to identify the environmental aspects associated with Sandia's activities, products, and services and the potential environmental impacts associated with those aspects. Division and environmental programs established objectives and targets based on the environmental aspects associated with their operations. In 2007 the most significant aspect identified was Hazardous Materials (Use and Storage). The objective for Hazardous Materials (Use and Storage) was to improve chemical handling, storage, and on-site movement of hazardous materials. One of the targets supporting this objective was to develop an effective chemical exchange program, making a business case for it in FY07, and fully implementing a comprehensive chemical exchange program in FY08. A Chemical Exchange Program (CEP) team was formed to implement this target. The team consists of representatives from the Chemical Information System (CIS), Pollution Prevention (P2), the HWMF, Procurement and the Environmental Management System (EMS). The CEP Team performed benchmarking and conducted a life-cycle analysis of the current management of chemicals at SNL/NM and compared it to Chemical Exchange alternatives. Those alternatives are as follows: (1) Revive the 'Virtual' Chemical Exchange Program; (2) Re-implement a 'Physical' Chemical Exchange Program using a Chemical Information System; and (3) Transition to a Chemical Management Services System. The analysis and benchmarking study shows that the present management of chemicals at SNL/NM is significantly disjointed and a life-cycle or 'Cradle-to-Grave' approach to chemical management is needed. This approach must consider the purchasing and maintenance costs as well as the cost of ultimate disposal of the chemicals and materials. A chemical exchange is needed as a mechanism to re-apply chemicals on site. This will not only reduce the quantity of unneeded chemicals and the amount spent on new purchases, but will also avoid disposal costs. If SNL/NM were to realize a 5 percent reduction in chemical inventory and a 10 percent reduction in disposal of unused chemicals the total savings would be $189, 200 per year.

Waffelaert, Pascale

2007-09-01

413

Composite ion exchange materials  

SciTech Connect

Composite ion exchange materials can be formed by sorbing ion exchange polymers on inert, high surface area substrates. In general, the flux of ions and molecules through these composites, as measured electrochemically, increases as the ratio of the surface area of the substrate increases relative to the volume of the ion exchanger. This suggests that fields and gradients established at the interface between the ion exchanger and substrate are important in determining the transport characteristics of the composites. Here, the authors will focus on composites formed with a cation exchange polymer, Nafion, and two different types of microbeads: polystyrene microspheres and polystyrene coated magnetic microbeads. For the polystyrene microbeads, scanning electron micrographs suggest the beads cluster in a self-similar manner, independent of the bead diameter. Flux of Ru(NH3)63+ through the composites was studied as a function of bead fraction, bead radii, and fixed surface area with mixed bead sizes. Flux was well modeled by surface diffusion along a fractal interface. Magnetic composites were formed with columns of magnetic microbeads normal to the electrode surface. Flux of Ru(NH3)63+ through these composites increased exponentially with bead fraction. For electrolyses, the difference in the molar magnetic susceptibility of the products and reactants, Dcm, tends to be non-zero. For seven redox reactions, the ratio of the flux through the magnetic composites to the flux through a Nafion film increases monotonically with {vert_bar}Dcm{vert_bar}, with enhancements as large as thirty-fold. For reversible species, the electrolysis potential through the magnetic composites is 35 mV positive of that for the Nafion films.

Amarasinghe, S.; Zook, L.; Leddy, J. [Univ. of Iowa, Iowa City, IA (United States)

1994-12-31

414

Ion-exchange mechanism of layered transition-metal oxides: case study of LiNi(0.5)Mn(0.5)O?.  

PubMed

An ion-exchange process can be an effective route to synthesize new quasi-equilibrium phases with a desired crystal structure. Important layered-type battery materials, such as LiMnO2 and LiNi(0.5)Mn(0.5)O2, can be obtained through this method from a sodium-containing parent structure, and they often show electrochemical properties remarkably distinct from those of their solid-state synthesized equivalents. However, while ion exchange is generally believed to occur via a simple topotactic reaction, the detailed phase transformation mechanism during the process is not yet fully understood. For the case of layered LiNi(0.5)Mn(0.5)O2, we show through ex situ X-ray diffraction (XRD) that the ion-exchange process consists of several sequential phase transformations. By a study of the intermediate phase, it is shown that the residual sodium ions in the final structure may greatly affect the electrochemical (de)lithiation mechanism. PMID:25033369

Gwon, Hyeokjo; Kim, Sung-Wook; Park, Young-Uk; Hong, Jihyun; Ceder, Gerbrand; Jeon, Seokwoo; Kang, Kisuk

2014-08-01

415

Organophosphorus Ligands in Studies of Metal Complexes. Investigations of Ligand Exchange and Multielement Trace Analysis using Dithiophosphinic Ligands  

Microsoft Academic Search

On mixing organic solutions of [Et2PS2]M\\/n and [Prop2PS2]M\\/n [M=Pd(II), Pt(II), Rh(III), lr(III), Cr(III)] an equilibrium is obtained containing statistical amounts of the corresponding mixed ligand complexes as can be shown by 31P{H}-NMR, HPLC and FD-MS. With Pt(II)- and Pd(II)-chelates the kinetics of ligand exchange was determined by HPLC. Mixed complexes ML2L? and MLL?2 were isolated from the equilibrium solutions in

W. Kuchen; E. Lehnert; Peter Panster; Peter Kleinschmit

1987-01-01

416

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

SciTech Connect

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

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

1988-02-23

417

Ion-exchange studies on poly-o-anisidine Sn(IV) phosphate nano composite and its application as Cd(II) ion-selective membrane electrode  

Microsoft Academic Search

An organic-inorganic composite, poly-o-anisidine Sn(IV) phosphate, was chemically synthesized by mixing ortho-anisidine into\\u000a gels of Sn(IV) phosphate with different mixing volume ratios. Studies on the effect of eluant concentration, elution behavior\\u000a and separation of metal ions were carried out to understand the ion-exchange capabilities. Due to Cd(II) selective nature\\u000a of composite, revealed by distribution studies, Cd(II) ion selective membrane electrode

Asif Ali Khan; Anish Khan

2010-01-01

418

Fully correlated study of {sub {lambda}}{sub {lambda}}{sup 6}He hypernucleus including {lambda}N space-exchange correlations  

SciTech Connect

We present a fully correlated study of the six-body {sub {lambda}}{sub {lambda}}{sup 6}He hypernucleus. The wave function involves all relevant dynamic correlations as well as the space-exchange correlation (SEC). Calculations for energy breakdown, {lambda}{lambda}-separation energy, nuclear core polarization, and point proton radius have been performed. The baryon density profiles have also been calculated. Effect of SEC on all these physical observables is found to be significant. The findings suggest that a study ignoring SEC would be deficient.

Usmani, A. A.; Hasan, Z. [Department of Physics, Aligarh Muslim University, Aligarh 202 002 (India)

2006-09-15

419

A Monte Carlo study of the magnetization reversal in DyFe2/YFe2 exchange-coupled superlattices  

NASA Astrophysics Data System (ADS)

Monte Carlo simulations are used to perform an atomic scale modeling of the magnetic properties of epitaxial exchange-coupled DyFe2/YFe2 superlattices. These samples, extremely well-researched experimentally, are constituted by a hard ferrimagnet DyFe2 and a soft ferrimagnet YFe2 antiferromagnetically coupled. Depending on the layers' thickness and on the temperature, the field dependence of the magnetization depth profile is complex going from a unique giant ferromagnetic block to exchange spring behavior when the soft YFe2 layers reverse for positive bias fields. In some particular conditions of temperature and layers' thicknesses, it can even be easier to reverse the hard thin DyFe2 layers for positive fields, while the soft thick YFe2 layers keep their magnetization along the field. In this work, we reproduce by Monte Carlo simulations hysteresis loops for the net and compound-specific magnetizations at different temperatures, and assess the quality of the results by a direct comparison to experimental hysteresis loops.

Djedai, S.; Talbot, E.; Berche, P. E.

2014-11-01

420

The effect of hydrogen/deuterium introduction on photoluminescence of 3C-SiC crystals  

SciTech Connect

The effect of the incorporation and annealing of deuterium in 3C-SiC on its photoluminescence is reported. A 3C-SiC crystal has been implanted with 100 kev deuterium and subsequently annealed at temperatures between 1015 C and 1220 C for 1 to 5 minutes. SIMS depth profiles indicate hydrogen is strongly trapped by defects generated through ion bombardment, but a gradual damage repairing occurs during annealing. Photoluminescence was measured with 488 nm Ar laser excitation for sample temperatures from 89 K to 400 K. The PL peak wavelength of 540 nm at room temperature has shifted to 538 nm at 89 K. The peak PL intensity decreases with measurement temperature while its full width at half maximum (FWHM) exhibits an increasing trend. PL data were taken at five annealing stages. The post-implantation peak PL intensity and its integrated area increase initially with annealing temperature and time. After the final annealing at 1218 C for 2 minute, PL intensity and its integrated area exhibit a decrease in level.

Lee, B.K.; Steckl, A.J. [Univ. of Cincinnati, OH (United States). Nanoelectronics Lab.; Zavada, J.M. [Army Research Office, Research Triangle Park, NC (United States); Wilson, R.G. [Hughes Research Labs., Malibu, CA (United States)

1998-12-31

421

A primary hydrogen-deuterium isotope effect observed at the single-molecule level  

Microsoft Academic Search

The covalent chemistry of reactants tethered within a single protein pore can be monitored by observing the time-dependence of ionic current flow through the pore, which responds to bond making and breaking in individual reactant molecules. Here we use this `nanoreactor' approach to examine the reaction of a quinone with a thiol to form a substituted hydroquinone by reductive 1,4-Michael

Siran Lu; Wen-Wu Li; Dvir Rotem; Ellina Mikhailova; Hagan Bayley

2010-01-01

422

Measurements of kinetic isotope effects and hydrogen\\/deuterium distributions over methane oxidative coupling catalysts  

Microsoft Academic Search

The kinetic isotope effect for CHâ compared to that for CDâ has been measured for the oxidative coupling reaction of methane over Li\\/MgO, SrCOâ, and SmâOâ catalysts in a flow reactor. Each catalyst gave results consistent with C-H bond breaking being the slow step. For temperatures between 680-780 C over Li\\/MgO, k{sub H}\\/k{sub D} decreased slightly with temperature. The isotope

P. F. Nelson; C. A. Lukey; N. W. Cant

1989-01-01

423

Structure Dynamics Guided Enzyme Improvement of ENDO-BETA-1, 4-XYLANASE I  

E-print Network

Enzyme structure dynamics has recently been revealed to be essential for structure-function relationship. Among various structure dynamics analysis platforms, hydrogen deuterium exchange mass spectrometry stands as an efficient and high...

Uzuner, Ugur

2013-06-06

424