These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Ab initio molecular dynamics study of the hydrogen-deuterium exchange in bulk lithiumborohydride (LiBH4)  

NASA Astrophysics Data System (ADS)

The hydrogen storage is still a challenge for mobile applications. The diffusion of hydrogen in solids is considered as a general model system but there is limited knowledge available for the dynamics of hydrogen in complex hydrides. In this letter, we present a systematic approach to study the hydrogen-deuterium exchange in bulk LiBH4 based on ab initio molecular dynamics. Our results predict the single hydrogen (deuterium) exchange in LiBH4, which supports the experimental results. The self-diffusion constant ?D? of deuterium in LiBH4 is around 1.42×10-8 m2 s-1.

Ramzan, M.; Ahuja, R.

2009-04-01

2

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

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

Hydrogen-deuterium exchange in structural biology  

NASA Astrophysics Data System (ADS)

The large difference in neutron scattering length of hydrogen and deuterium atoms provides a unique tool to study biological macromolecules. These molecules exist in an aqueous environment and have an atomic composition of about 50% hydrogen atoms with the rest being mainly carbon, oxygen and nitrogen. By simply changing the ratio of hydrogen to deuterium the contrast of a sample constituent can be changed without altering the chemical composition. The scattering difference between the hydrogen isotopes has now been used to study structural details of proteins, viruses, nucleic acid protein complexes and membranes. The use of small-angle scattering analysis from proteins in solution is a particularly good example of the power of this new technique. From the first experiments with myoglobin, hemoglobin and TMV solutions in 1968 at the HFBR in Brookhaven it became, however, soon evident that the flux was low and the detection system of a conventional spectrometer was inadequate to measure precisely small differences in the scattering pattern. Since these solution scattering patterns are circularly symmetrical, a development of multidetector systems was the first step to alleviate the need for better data. From an early five detector system [1] the development of linear and two-dimensional position sensitive detectors continues to this day [2-6]. Today, position sensitive area-detectors with an efficiency of 80% and 1.3 mm resolution with an active area of 50 cm × 50 cms are available. These detectors have a counting rate capability of 2 × 10 5 neutrons/s. Other instrumentation developments to facilitate the study of biomolecules include (1) cold moderators, (2) thin film multilayer monochromators [7-9], (3) neutron guides made either of multilayer supermirrors or coated with 58Ni [10,11], (4) various crystal and mirror focusing devices [12,13]. Some of these features have been incorporated in a small-angle neutron spectrometer at the High Flux Beam Reactor at the Brookhaven National Laboratory. This spectrometer has a unique combination of features such as a high resolution area-detector, adjustable wavelength bandwidth and automated sample changer.

Schoenborn, B. P.; Ramakrishnan, V.; Schneider, D.

1986-03-01

5

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

6

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

7

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

8

High-resolution mass spectrometry and hydrogen/deuterium exchange study of mitorubrin azaphilones and nitrogenized analogues.  

PubMed

Azaphilones represent numerous groups of wild fungal secondary metabolites that exhibit exceptional tendency to bind to nitrogen atoms in various molecules, especially those containing the amine group. Nitrogenized analogues of mitorubrin azaphilones, natural secondary metabolites of Hypoxylon fragiforme fungus, have been detected in the fungal methanol extract in very low concentrations. Positive electrospray ionization interfaced with high-resolution mass spectrometry was applied for confirmation of the elemental composition of protonated species. Collision-induced dissociation (CID) experiments have been performed, and fragmentation mechanisms have been proposed. Additional information regarding both secondary metabolite analogue families has been reached by application of gas-phase proton/deuterium (H/D) exchanges performed in the collision cell of a triple quadrupole mass spectrometer. An incomplete H/D exchange with one proton less than expected was observed for both protonated mitorubrin azaphilones and their nitrogenized analogues. By means of the density functional theory, an appropriate explanation of this behavior was provided, and it revealed some information concerning gas-phase H/D exchange mechanism and protonation sites. PMID:22899505

Svilar, Ljubica; Stankov-Jovanovic, Vesna; Lesage, Denis; Dossmann, Héloïse; Tabet, Jean-Claude

2012-08-01

9

Conformational dynamics of human FXR-LBD ligand interactions studied by hydrogen/deuterium exchange mass spectrometry: insights into the antagonism of the hypolipidemic agent Z-guggulsterone.  

PubMed

Farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily of transcription factors that plays a key role in the regulation of bile acids, lipid and glucose metabolisms. The regulative function of FXR is governed by conformational changes of the ligand binding domain (LBD) upon ligand binding. Although FXR is a highly researched potential therapeutic target, only a limited number of FXR-agonist complexes have been successfully crystallized and subsequently yielded high resolution structures. There is currently no structural information of any FXR-antagonist complexes publically available. We therefore explored the use of amide hydrogen/deuterium exchange (HDX) coupled with mass spectrometry for characterizing conformational changes in the FXR-LBD upon ligand binding. Ligand-specific deuterium incorporation profiles were obtained for three FXR ligand chemotypes: GW4064, a synthetic non-steroidal high affinity agonist; the bile acid chenodeoxycholic acid (CDCA), the endogenous low affinity agonist of FXR; and Z-guggulsterone (GG), an in vitro antagonist of the steroid chemotype. A comparison of the HDX profiles of their ligand-bound FXR-LBD complexes revealed a unique mode of interaction for GG. The conformational features of the FXR-LBD-antagonist interaction are discussed. PMID:24953769

Yang, Liping; Broderick, David; Jiang, Yuan; Hsu, Victor; Maier, Claudia S

2014-09-01

10

Functional visualization of viral molecular motor by hydrogen-deuterium exchange reveals transient states.  

PubMed

Molecular motors undergo cyclical conformational changes and convert chemical energy into mechanical work. The conformational dynamics of a viral packaging motor, the hexameric helicase P4 of dsRNA bacteriophage phi8, was visualized by hydrogen-deuterium exchange and high-resolution mass spectrometry. Concerted changes of exchange kinetics revealed a cooperative unit that dynamically links ATP-binding sites and the central RNA-binding channel. The cooperative unit is compatible with a structure-based model in which translocation is mediated by a swiveling helix. Deuterium labeling also revealed the transition state associated with RNA loading, which proceeds via opening of the hexameric ring. The loading mechanism is similar to that of other hexameric helicases. Hydrogen-deuterium exchange provides an important link between time-resolved spectroscopic observations and high-resolution structural snapshots of molecular machines. PMID:15834422

Lísal, Jirí; Lam, Tukiet T; Kainov, Denis E; Emmett, Mark R; Marshall, Alan G; Tuma, Roman

2005-05-01

11

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

PubMed

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

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

2014-12-11

12

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

13

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

14

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

PubMed Central

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

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

2014-01-01

15

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

PubMed Central

Probing the conformational changes of amyloid beta (A?) peptide aggregation is challenging owing to the vast heterogeneity of the resulting soluble aggregates. To investigate the formation of these aggregates in solution, we designed an MS-based biophysical approach and applied it to the formation of soluble aggregates of the A?42 peptide, the proposed causative agent in Alzheimer’s disease. The approach incorporates pulsed hydrogen–deuterium exchange coupled with MS analysis. The combined approach provides evidence for a self-catalyzed aggregation with a lag phase, as observed previously by fluorescence methods. Unlike those approaches, pulsed hydrogen–deuterium exchange does not require modified A?42 (e.g., labeling with a fluorophore). Furthermore, the approach reveals that the center region of A?42 is first to aggregate, followed by the C and N termini. We also found that the lag phase in the aggregation of soluble species is affected by temperature and Cu2+ ions. This MS approach has sufficient structural resolution to allow interrogation of A? aggregation in physiologically relevant environments. This platform should be generally useful for investigating the aggregation of other amyloid-forming proteins and neurotoxic soluble peptide aggregates. PMID:23959898

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

2013-01-01

16

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

17

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

18

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

NASA Astrophysics Data System (ADS)

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

Rajabi, Khadijeh

2015-01-01

19

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

20

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

PubMed Central

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

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

2013-01-01

21

Dynamics of the ?2-adrenergic G-protein coupled receptor revealed by hydrogen-deuterium exchange  

PubMed Central

To examine the molecular details of ligand activation of G-protein coupled receptor (GPCRs), emphasis has been placed on structure determination of these receptors with stabilizing ligands. Here we present the methodology for receptor dynamics characterization of the GPCR human ?2 adrenergic receptor bound to the inverse agonist carazolol using the technique of amide hydrogen/deuterium exchange coupled with mass spectrometry (HDX MS). The HDX MS profile of receptor bound to carazolol is consistent with thermal parameter observations in the crystal structure and provides additional information in highly dynamic regions of the receptor and chemical modifications demonstrating the highly complementary nature of the techniques. Following optimization of HDX experimental conditions for this membrane protein, better than 89% sequence coverage was obtained for the receptor. The methodology presented paves the way for future analysis of ?2AR bound to pharmacologically distinct ligands as well as analysis of other GPCR family members. PMID:20058880

Zhang, Xi; Chien, Ellen Y.T.; Chalmers, Michael J.; Pascal, Bruce D.; Gatchalian, Jovylyn; Stevens, Raymond C.; Griffin, Patrick R.

2010-01-01

22

Investigating the Interaction between the Neonatal Fc Receptor and Monoclonal Antibody Variants by Hydrogen/Deuterium Exchange Mass Spectrometry.  

PubMed

The recycling of immunoglobulins by the neonatal Fc receptor (FcRn) is of crucial importance in the maintenance of antibody levels in plasma and is responsible for the long half-lives of endogenous and recombinant monoclonal antibodies. From a therapeutic point of view there is great interest in understanding and modulating the IgG-FcRn interaction to optimize antibody pharmacokinetics and ultimately improve efficacy and safety. Here we studied the interaction between a full-length human IgG1 and human FcRn via hydrogen/deuterium exchange mass spectrometry and targeted electron transfer dissociation to map sites perturbed by binding on both partners of the IgG-FcRn complex. Several regions in the antibody Fc region and the FcRn were protected from exchange upon complex formation, in good agreement with previous crystallographic studies of FcRn in complex with the Fc fragment. Interestingly, we found that several regions in the IgG Fab region also showed reduced deuterium uptake. Our findings indicate the presence of hitherto unknown FcRn interaction sites in the Fab region or a possible conformational link between the IgG Fc and Fab regions upon FcRn binding. Further, we investigated the role of IgG glycosylation in the conformational response of the IgG-FcRn interaction. Removal of antibody glycans increased the flexibility of the FcRn binding site in the Fc region. Consequently, FcRn binding did not induce a similar conformational stabilization of deglycosylated IgG as observed for the wild-type glycosylated IgG. Our results provide new molecular insight into the IgG-FcRn interaction and illustrate the capability of hydrogen/deuterium exchange mass spectrometry to advance structural proteomics by providing detailed information on the conformation and dynamics of large protein complexes in solution. PMID:25378534

Jensen, Pernille Foged; Larraillet, Vincent; Schlothauer, Tilman; Kettenberger, Hubert; Hilger, Maximiliane; Rand, Kasper D

2015-01-01

23

Sub-Zero Temperature Chromatography for Reduced Back-Exchange and Improved Dynamic Range in Amide Hydrogen Deuterium Exchange Mass Spectrometry  

PubMed Central

Amide hydrogen/deuterium exchange is a commonly used technique for studying the dynamics of proteins and their interactions with other proteins or ligands. When coupled with liquid chromatography and mass spectrometry, hydrogen/deuterium exchange provides several unique advantages over other structural characterization techniques including very high sensitivity, the ability to analyze proteins in complex environments, and a large mass range. A fundamental limitation of the technique arises from the loss of deuterium label (back-exchange) during the course of the analysis. A method to limit loss of label during the separation stage of the analysis using sub-zero temperature reversed-phase chromatography is presented. The approach is facilitated by the use of buffer modifiers that prevent freezing. We evaluated ethylene glycol, dimethyl formamide, formamide, and methanol for their freezing point suppression capabilities, effects on peptide retention, and their compatibilities with electrospray ionization. Ethylene glycol was used extensively because of its good electrospray ionization compatibility; however formamide has potential to be a superior modifier if detrimental effects on ionization can be overcome. It is demonstrated using suitable buffer modifiers that separations can be performed at temperatures as low as ?30°C with negligible loss of deuterium label, even during long chromatographic separations. The reduction in back-exchange is shown to increase the dynamic range of HDX MS in terms of mixture complexity, and the magnitude with which changes in deuteration level can be quantified. PMID:23025328

Venable, John D.; Okach, Linda; Agarwalla, Sanjay; Brock, Ansgar

2012-01-01

24

Microsecond pulsed hydrogen/deuterium exchange of electrosprayed ubiquitin ions stored in a linear ion trap.  

PubMed

A pulse of D2O vapour on the order of microseconds is allowed to react with the +6 to +9 charge states of ubiquitin confined in a linear ion trap (LIT). Two envelopes of peaks are detected for the ions of ubiquitin, corresponding to the ions that exchange more quickly and more slowly. The deuterium uptake of the protonated sites on ubiquitin ions accounts for the ion population with the fast exchange. The hydrogen/deuterium exchange (HDX) kinetics of ubiquitin ions trapped in the LIT for 200 ms showed comparable structural transitions to those trapped for 300 ms. When ions are trapped for longer, i.e. up to 2000 ms, mainly the slow exchanging ion population is detected. In all experiments the +7 ions exchange the most, suggesting a short distance between the surface protonated sites and nearby charged sites, and concomitantly high accessibility of surface protonated sites towards D2O. The +6 ions are more compact than the +7 ions but have one fewer protonated site, therefore fewer surface availabilities for D2O attack. The data suggest that the +6 ions keep most of their solution-phase contacts intact while the hydrophobic core is slightly interrupted in the +7 ions, possibly due to the exposure of charged His68 that is normally buried in the hydrophobic pocket. The +8 and +9 ions have more protonated sites but are less compact than the +7 ions because of Coulombic repulsion, resulting in a larger distance between the protonated sites and the basic sites. The data indicate that the HDX mechanism of ions with the slower exchange corresponding to the second envelope of peaks is primarily governed via a relay mechanism. The results suggest that the pulsed HDX MS method is sampling a population of ubiquitin ions with a similar backbone fold to the solution. PMID:25553956

Rajabi, Khadijeh

2015-02-01

25

Amide hydrogen/deuterium exchange & MALDI-TOF mass spectrometry analysis of Pak2 activation.  

PubMed

Amide hydrogen/deuterium exchange (H/D exchange) coupled with mass spectrometry has been widely used to analyze the interface of protein-protein interactions, protein conformational changes, protein dynamics and protein-ligand interactions. H/D exchange on the backbone amide positions has been utilized to measure the deuteration rates of the micro-regions in a protein by mass spectrometry(1,2,3). The resolution of this method depends on pepsin digestion of the deuterated protein of interest into peptides that normally range from 3-20 residues. Although the resolution of H/D exchange measured by mass spectrometry is lower than the single residue resolution measured by the Heteronuclear Single Quantum Coherence (HSQC) method of NMR, the mass spectrometry measurement in H/D exchange is not restricted by the size of the protein(4). H/D exchange is carried out in an aqueous solution which maintains protein conformation. We provide a method that utilizes the MALDI-TOF for detection(2), instead of a HPLC/ESI (electrospray ionization)-MS system(5,6). The MALDI-TOF provides accurate mass intensity data for the peptides of the digested protein, in this case protein kinase Pak2 (also called ?-Pak). Proteolysis of Pak 2 is carried out in an offline pepsin digestion. This alternative method, when the user does not have access to a HPLC and pepsin column connected to mass spectrometry, or when the pepsin column on HPLC does not result in an optimal digestion map, for example, the heavily disulfide-bonded secreted Phospholipase A(2;) (sPLA(2;)). Utilizing this method, we successfully monitored changes in the deuteration level during activation of Pak2 by caspase 3 cleavage and autophosphorylation(7,8,9). PMID:22143461

Hsu, Yuan-Hao; Traugh, Jolinda A

2011-01-01

26

VIBRIO CHOLERAE TOXIN-COREGULATED PILUS STRUCTURE ANALYZED BY HYDROGEN/DEUTERIUM EXCHANGE MASS SPECTROMETRY  

PubMed Central

SUMMARY The bacterial pathogen Vibrio cholerae uses toxin-coregulated pili (TCP) to colonize the human intestine, causing the severe diarrheal disease cholera. TCP are long, thin, flexible homopolymers of the TcpA subunit that self-associate to hold cells together in microcolonies and serve as the receptor for the cholera toxin phage. To better understand TCP’s roles in pathogenesis, we characterized its structure using hydrogen/deuterium exchange mass spectrometry and computational modeling. We show that the pilin subunits are held together by tight-packing of the N-terminal ?-helices, but loose packing of the C-terminal globular domains leaves substantial gaps on the filament surface. These gaps expose a glycine-rich, amphipathic segment of the N-terminal ?-helix, contradicting the consensus view that this region is buried in the filament core. Our results explain extreme filament flexibility, suggest a molecular basis for pilus:pilus interactions, and reveal a previously unrecognized therapeutic target for V. cholerae and other enteric pathogens. PMID:18184591

Li, Juliana; Lim, Mindy S.; Li, Sheng; Brock, Melissa; Pique, Michael E.; Woods, Virgil L.; Craig, Lisa

2008-01-01

27

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

PubMed Central

Accumulating evidence suggests that solution-phase conformations of small globular proteins and large molecular protein assemblies can be preserved for milliseconds after electrospray ionization. Thus, the study of proteins in the gas-phase on this time-scale is highly desirable. Here we demonstrate that a travelling wave ion guide (TWIG) of a Synapt mass spectrometer offers a highly suitable environment for rapid and efficient gas-phase hydrogen/deuterium exchange (HDX). Gaseous ND3 was introduced into either the source TWIG or the TWIG located just after the ion mobility cell, such that ions underwent HDX as they passed through the ND3 on the way to the time-of-flight analyzer. The extent of deuterium labeling could be controlled by varying the quantity of ND3 or the speed of the travelling wave. The gas-phase HDX of model peptides corresponded to labeling of primarily fast exchanging sites due to the short labeling times (ranging from 0.1 to 10 ms). In addition to peptides, gas-phase HDX of ubiquitin, cytochrome c, lysozyme and apomyoglobin were examined. We conclude that HDX of protein ions in a TWIG is highly sensitive to protein conformation, enables the detection of conformers present on sub-milliseconds timescales and can readily be combined with ion mobility spectrometry. PMID:19921790

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

2009-01-01

28

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

PubMed Central

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

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

2014-01-01

29

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, Krisztián; Molnar, Kathleen S.; Coales, Stephen J.; Hamuro, Yoshitomo; Sfyroera, Georgia; Chen, Hui; Winters, Michael S.; Lambris, John D.

2008-01-01

30

Structural insights into glucan phosphatase dynamics using amide hydrogen-deuterium exchange mass spectrometry.  

PubMed

Laforin and starch excess 4 (SEX4) are founding members of a class of phosphatases that dephosphorylate phosphoglucans. Each protein contains a carbohydrate binding module (CBM) and a dual-specificity phosphatase (DSP) domain. The gene encoding laforin is mutated in a fatal neurodegenerative disease called Lafora disease (LD). In the absence of laforin function, insoluble glucans that are hyperphosphorylated and exhibit sparse branching accumulate. It is hypothesized that these accumulations trigger the neurodegeneration and premature death of LD patients. We recently demonstrated that laforin removes phosphate from phosphoglucans and hypothesized that this function inhibits insoluble glucan accumulation. Loss of SEX4 function in plants yields a similar cellular phenotype; an excess amount of insoluble, hyperphosphorylated glucans accumulates in cells. While multiple groups have shown that these phosphatases dephosphorylate phosphoglucans, there is no structure of a glucan phosphatase and little is known about the mechanism whereby they perform this action. We utilized hydrogen-deuterium exchange mass spectrometry (DXMS) and structural modeling to probe the conformational and structural dynamics of the glucan phosphatase SEX4. We found that the enzyme does not undergo a global conformational change upon glucan binding but instead undergoes minimal rearrangement upon binding. The CBM has improved protection from deuteration when bound to glucans, confirming its role in glucan binding. More interestingly, we identified structural components of the DSP that also have improved protection from deuteration upon glucan addition. To determine the position of these regions, we generated a homology model of the SEX4 DSP. The homology model shows that all of these regions are adjacent to the DSP active site. Therefore, our results suggest that these regions of the DSP participate in the presentation of the phosphoglucan to the active site and provide the first structural analysis and mode of action of this unique class of phosphatases. PMID:19754155

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

2009-10-20

31

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

PubMed Central

The native state of ?1-antitrypsin (?1AT), a member of the serine protease inhibitor (serpin) family, is considered a kinetically trapped folding intermediate that converts to a more stable form upon complex formation with a target protease. Although previous structural and mutational studies of ?1AT revealed the structural basis of the native strain and the kinetic trap, the mechanism of how the native molecule overcomes the kinetic barrier to reach the final stable conformation during complex formation remains unknown. We hypothesized that during complex formation, a substantial portion of the molecule undergoes unfolding, which we dubbed functional unfolding. Hydrogen-deuterium exchange coupled with ESI-MS was used to analyze this serpin in three forms: native, complexing, and complexed with bovine ?-trypsin. Comparing the deuterium content at the corresponding regions of these three samples, we probed the unfolding of ?1AT during complex formation. A substantial portion of the ?1AT molecule unfolded transiently during complex formation, including not only the regions expected from previous structural studies, such as the reactive site loop, helix F, and the following loop, but also regions not predicted previously, such as helix A, strand 6 of ?-sheet B, and the N terminus. Such unfolding of the native interactions may elevate the free energy level of the kinetically trapped native serpin sufficiently to cross the transition state during complex formation. In the current study, we provide evidence that protein unfolding has to accompany functional execution of the protein molecule. PMID:19136720

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

2009-01-01

32

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

33

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

34

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

35

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

PubMed

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

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

2015-02-01

36

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

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

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

PubMed

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

Keppel, Theodore R; Weis, David D

2014-12-01

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

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

NASA Astrophysics Data System (ADS)

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

Chipuk, Joseph E.; Brodbelt, Jennifer S.

2009-10-01

41

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

SciTech Connect

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

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

2009-04-22

42

Hexicon 2: automated processing of hydrogen-deuterium exchange mass spectrometry data with improved deuteration distribution estimation.  

PubMed

Hydrogen-deuterium exchange (HDX) experiments analyzed by mass spectrometry (MS) provide information about the dynamics and the solvent accessibility of protein backbone amide hydrogen atoms. Continuous improvement of MS instrumentation has contributed to the increasing popularity of this method; however, comprehensive automated data analysis is only beginning to mature. We present Hexicon 2, an automated pipeline for data analysis and visualization based on the previously published program Hexicon (Lou et al. 2010). Hexicon 2 employs the sensitive NITPICK peak detection algorithm of its predecessor in a divide-and-conquer strategy and adds new features, such as chromatogram alignment and improved peptide sequence assignment. The unique feature of deuteration distribution estimation was retained in Hexicon 2 and improved using an iterative deconvolution algorithm that is robust even to noisy data. In addition, Hexicon 2 provides a data browser that facilitates quality control and provides convenient access to common data visualization tasks. Analysis of a benchmark dataset demonstrates superior performance of Hexicon 2 compared with its predecessor in terms of deuteration centroid recovery and deuteration distribution estimation. Hexicon 2 greatly reduces data analysis time compared with manual analysis, whereas the increased number of peptides provides redundant coverage of the entire protein sequence. Hexicon 2 is a standalone application available free of charge under http://hx2.mpimf-heidelberg.mpg.de. PMID:24676893

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

2014-06-01

43

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

PubMed Central

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

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

2014-01-01

44

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

45

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

PubMed

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

McMahon, T B; Ohanessian, G

2015-01-28

46

Construct Optimization for Protein NMR Structure Analysis Using Amide Hydrogen / Deuterium Exchange Mass Spectrometry  

PubMed Central

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

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

2009-01-01

47

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

NASA Astrophysics Data System (ADS)

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

Sowole, Modupeola A.; Konermann, Lars

2013-07-01

48

Assessment of differences in the conformational flexibility of hepatitis B virus core-antigen and e-antigen by hydrogen deuterium exchange-mass spectrometry.  

PubMed

Hepatitis B virus core-antigen (capsid protein) and e-antigen (an immune regulator) have almost complete sequence identity, yet the dimeric proteins (termed Cp149d and Cp(-10)149d , respectively) adopt quite distinct quaternary structures. Here we use hydrogen deuterium exchange-mass spectrometry (HDX-MS) to study their structural properties. We detect many regions that differ substantially in their HDX dynamics. Significantly, whilst all regions in Cp(-10)149d exchange by EX2-type kinetics, a number of regions in Cp149d were shown to exhibit a mixture of EX2- and EX1-type kinetics, hinting at conformational heterogeneity in these regions. Comparison of the HDX of the free Cp149d with that in assembled capsids (Cp149c ) indicated increased resistance to exchange at the C-terminus where the inter-dimer contacts occur. Furthermore, evidence of mixed exchange kinetics were not observed in Cp149c , implying a reduction in flexibility upon capsid formation. Cp(-10)149d undergoes a drastic structural change when the intermolecular disulphide bridge is reduced, adopting a Cp149d -like structure, as evidenced by the detected HDX dynamics being more consistent with Cp149d in many, albeit not all, regions. These results demonstrate the highly dynamic nature of these similar proteins. To probe the effect of these structural differences on the resulting antigenicity, we investigated binding of the antibody fragment (Fab E1) that is known to bind a conformational epitope on the four-helix bundle. Whilst Fab E1 binds to Cp149c and Cp149d , it does not bind non-reduced and reduced Cp(-10)149d , despite unhindered access to the epitope. These results imply a remarkable sensitivity of this epitope to its structural context. PMID:24715628

Bereszczak, Jessica Z; Watts, Norman R; Wingfield, Paul T; Steven, Alasdair C; Heck, Albert J R

2014-07-01

49

Accessibility changes within diphtheria toxin T domain when in the functional molten globule state, as determined using hydrogen/deuterium exchange measurements.  

PubMed

The translocation domain (T domain) of diphtheria toxin adopts a partially folded state, the so-called molten globule state, to become functional at acidic pH. We compared, using hydrogen/deuterium exchange experiments associated with MS, the structures of the T domain in its soluble folded state at neutral pH and in its functional molten globule state at acidic pH. In the native state, the alpha-helices TH5 and TH8 are identified as the core of the domain. Based on the high-resolution structure of the T domain, we propose that TH8 is highly protected because it is buried within the native structure. According to the same structure, TH5 is partly accessible at the surface of the T domain. We propose that its high protection is caused by the formation of dimers. Within the molten globule state, high protection is still observed within the helical hairpin TH8-TH9, which is responsible for the insertion of the T domain into the membrane. In the absence of the lipid bilayer, this hydrophobic part of the domain self-assembles, leading to the formation of oligomers. Overall, hydrogen/deuterium-exchange measurements allow the analysis of interaction contacts within small oligomers made of partially folded proteins. Such information, together with crystal structure data, are particularly valuable for using to analyze the self-assembly of proteins. PMID:20050921

Man, Petr; Montagner, Caroline; Vitrac, Heidi; Kavan, Daniel; Pichard, Sylvain; Gillet, Daniel; Forest, Eric; Forge, Vincent

2010-02-01

50

PAS Domain Allostery and Light-Induced Conformational Changes in Photoactive Yellow Protein upon I2 Intermediate Formation, Probed with Enhanced Hydrogen/Deuterium Exchange Mass Spectrometry  

PubMed Central

Photoactive yellow protein (PYP) is a small bacterial photoreceptor that undergoes a light-activated reaction cycle. PYP is also the prototypical PAS (Per-Arnt-Sim) domain. PAS domains, found in diverse multi-domain proteins from bacteria to humans, mediate protein-protein interactions and function as sensors and signal transducers. Here, we investigate conformational and dynamic changes in solution in wild-type PYP upon formation of the long-lived putative signaling intermediate I2 with enhanced hydrogen/deuterium exchange mass spectrometry (DXMS). The DXMS results showed that the central ?-sheet remains stable but specific external protein segments become strongly deprotected. Light-induced disruption of the dark-state hydrogen-bonding network in I2 produces increased flexibility and opening of PAS core helices ?3 and ?4, releases the ?4-?5 hairpin, and propagates conformational changes to the central ?-sheet. Surprisingly, the first ~10 N-terminal residues, which are essential for fast dark state recovery from I2, become more protected. By combining the DXMS results with our crystallographic structures, which reveal detailed changes near the chromophore, but limited protein conformational change, we propose a mechanism for I2 state formation. This mechanism integrates the results from diverse biophysical studies of PYP, and links an allosteric T- to R-state conformational transition to three pathways for signal propagation within the PYP fold. Based upon the observed changes in PYP plus commonalities shared among PAS domain proteins, we further propose that PAS domains share this conformational mechanism, which explains the versatile signal transduction properties of the structurally conserved PYP/PAS module by framework-encoded allostery. PMID:16952373

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

2008-01-01

51

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

PubMed

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

Woofter, Ricky T; Maurer, Muriel C

2011-08-01

52

Understanding the conformational impact of chemical modifications on monoclonal antibodies with diverse sequence variation using hydrogen/deuterium exchange mass spectrometry and structural modeling.  

PubMed

Chemical modifications can potentially induce conformational changes near the modification site and thereby impact the safety and efficacy of protein therapeutics. Hydrogen/deuterium exchange mass spectrometry (HDX-MS) has emerged as a powerful analytical technique with high spatial resolution and sensitivity in detecting such local conformational changes. In this study, we utilized HDX-MS combined with structural modeling to examine the conformational impact on monoclonal antibodies (mAbs) caused by common chemical modifications including methionine (Met) oxidation, aspartic acid (Asp) isomerization, and asparagine (Asn) deamidation. Four mAbs with diverse sequences and glycosylation states were selected. The data suggested that the impact of Met oxidation was highly dependent on its location and glycosylation state. For mAbs with normal glycosylation in the Fc region, oxidation of the two conserved Met252 and Met428 (Kabat numbering) disrupted the interface interactions between the CH2 and CH3 domains, thus leading to a significant decrease in CH2 domain thermal stability as well as a slight increase in aggregation propensity. In contrast, Met oxidation in the variable region and CH3 domain had no detectable impact on mAb conformation. For aglycosylated mAb, Met oxidation could cause a more global conformational change to the whole CH2 domain, coincident with the larger decrease in thermal stability and significant increase in aggregation rate. Unlike Met oxidation, Asn deamidation and Asp isomerization mostly had very limited effects on mAb conformation, with the exception of succiminide intermediate formation which induced a measurable local conformational change to be more solvent protected. Structural modeling suggested that the succinimide intermediate was stabilized by adjacent aromatic amino acids through ring-ring stacking interactions. PMID:24597564

Zhang, Aming; Hu, Ping; MacGregor, Paul; Xue, Yu; Fan, Haihong; Suchecki, Peter; Olszewski, Leonard; Liu, Aston

2014-04-01

53

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

PubMed

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

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

2013-11-19

54

Gas-phase hydrogen/deuterium exchange of 5'- and 3'-mononucleotides in a quadrupole ion trap: exploring the role of conformation and system energy.  

PubMed

Gas-phase hydrogen/deuterium (H/D) exchange reactions for deprotonated 2'-deoxy-5'-monophosphate and 2'-deoxy-3'-monophosphate nucleotides with D(2)O were performed in a quadrupole ion trap mass spectrometer. To augment these experiments, molecular modeling was also conducted to identify likely deprotonation sites and potential gas-phase conformations of the anions. A majority of the 5'-monophosphates exchanged extensively with several of the compounds completely incorporating deuterium in place of their labile hydrogen atoms. In contrast, most of the 3'-monophosphate isomers exchanged relatively few hydrogen atoms, even though the rate of the first two exchanges was greater than observed for the 5'-monophosphates. Mononucleotides that failed to incorporate more than two deuterium atoms under default reaction conditions were often found to exchange more extensively when reactions were performed under higher energy conditions. Integration of the experimental and theoretical results supports the use of a relay exchange mechanism and suggests that the exchange behavior depends highly on the identity and orientation of the nucleobase and the position and flexibility of the deprotonated phosphate moiety. These observations also highlight the importance of the distance between the various participating groups in addition to their gas-phase acidity and basicity. PMID:17289398

Chipuk, Joseph E; Brodbelt, Jennifer S

2007-04-01

55

Nucleotide- and activator-dependent structural and dynamic changes of Arp2/3 complex monitored by hydrogen/deuterium exchange and mass spectrometry  

PubMed Central

Arp2/3 complex plays a central role in the de novo nucleation of filamentous actin as branches on existing filaments. To form a new actin filament the complex must bind ATP, protein activators (e.g. Wiskott-Aldrich syndrome proteins, WASp) and the side of an actin filament. Amide Hydrogen/Deuterium exchange (HDX) coupled with mass spectrometry (MS) was used to examine the structural and dynamic properties of the mammalian Arp2/3 complex in the presence of both ATP and the activating peptide segment from WASp. Changes in the rate of hydrogen exchange indicate that ATP binding causes conformational rearrangements of Arp2 and Arp3 that are transmitted allosterically to the ArpC1, ArpC2, ArpC4 and ArpC5 subunits. These data are consistent with the closure of nucleotide-binding cleft of Arp3 upon ATP binding, resulting in structural rearrangements that propagate throughout the complex. Binding of the VCA domain of WASp to ATP-Arp2/3 further modulates the rates of hydrogen exchange in these subunits, indicating that a global conformational reorganization is occurring. These effects may include the direct binding of activators to Arp3, Arp2 and ARPC1; alterations in the relative orientations of Arp2 and Arp3; and the long-range transmission of activator-dependent signals to segments proposed to be involved in binding the F-actin mother filament. PMID:19298826

Zencheck, Wendy D.; Xiao, Hui; Nolen, Bradley J.; Angeletti, Ruth; Pollard, Thomas D.; Almo, Steven C.

2010-01-01

56

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

PubMed

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

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

2014-12-19

57

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

58

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

59

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

SciTech Connect

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

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

2005-05-25

60

A comparative neutronic feasibility study for a hydrogen, deuterium and helium cold neutron sources situated in the center of a nuclear reactor core  

Microsoft Academic Search

A tool was developed to calculate the average cold neutron flux that could be generated for a spherically shaped cold neutron source situated in the center of a nuclear reactor core. The tool also estimates the subsequent nuclear heating of the cold source. The results were compared for three different cold source mediums; hydrogen, deuterium and helium. The tool utilizes

Malek Chatila

2003-01-01

61

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

SciTech Connect

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

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

2014-02-12

62

Fluoroketone inhibition of Ca(2+)-independent phospholipase A2 through binding pocket association defined by hydrogen/deuterium exchange and molecular dynamics.  

PubMed

The mechanism of inhibition of group VIA Ca(2+)-independent phospholipase A(2) (iPLA(2)) by fluoroketone (FK) ligands is examined by a combination of deuterium exchange mass spectrometry (DXMS) and molecular dynamics (MD). Models for iPLA(2) 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 iPLA(2) should greatly improve our ability to design new inhibitors with higher potency and selectivity. PMID:23256506

Hsu, Yuan-Hao; Bucher, Denis; Cao, Jian; Li, Sheng; Yang, Sheng-Wei; Kokotos, George; Woods, Virgil L; McCammon, J Andrew; Dennis, Edward A

2013-01-30

63

Probing lactate dehydrogenase activity in tumors by measuring hydrogen/deuterium exchange in hyperpolarized l-[1-(13)C,U-(2)H]lactate.  

PubMed

(13)C magnetic resonance spectroscopy and spectroscopic imaging measurements of hyperpolarized (13)C label exchange between exogenously administered [1-(13)C]pyruvate and endogenous lactate, catalyzed by lactate dehydrogenase (LDH), has proved to be a powerful approach for probing tissue metabolism in vivo. This experiment has clinical potential, particularly in oncology, where it could be used to assess tumor grade and response to treatment. A limitation of the method is that pyruvate must be administered in vivo at supra-physiological concentrations. This problem can be avoided by using hyperpolarized [1-(13)C]lactate, which can be used at physiological concentrations. However, sensitivity is limited in this case by the relatively small pyruvate pool size, which would result in only low levels of labeled pyruvate being observed even if there was complete label equilibration between the lactate and pyruvate pools. We demonstrate here a more sensitive method in which a doubly labeled lactate species can be used to measure LDH-catalyzed exchange in vivo. In this experiment exchange of the C2 deuterium label between injected hyperpolarized l-[1-(13)C,U-(2)H]lactate and endogenous unlabeled lactate is observed indirectly by monitoring phase modulation of the spin-coupled hyperpolarized (13)C signal in a heteronuclear (1)H/(13)C spin-echo experiment. PMID:22316419

Kennedy, Brett W C; Kettunen, Mikko I; Hu, De-En; Brindle, Kevin M

2012-03-14

64

Mapping of protein:protein contact surfaces by hydrogen/deuterium exchange, followed by on-line high-performance liquid chromatography-electrospray ionization Fourier-transform ion-cyclotron-resonance mass analysis.  

PubMed

For protein complexes too large, uncrystallizable/insoluble, or low concentration for conventional X-ray diffraction or nuclear magnetic resonance analysis, the contact surface(s) may be mapped by comparing H/2H exchange rate (and thus solvent accessibility) of backbone amide hydrogens in free vs. complexed protein(s). The protein is first exposed to 2H2O, allowed to exchange for each of several reaction periods, and then digested with pepsin. The extent and rate of H/2H exchange is determined by measuring the increase in mass with H/2H exchange period for each of the peptides. Here, we present an experimental protocol that combines rapid (to minimize back-exchange) HPLC front-end separation with ultrahigh-resolution mass analysis (needed to distinguish the isotopic distributions of dozens of peptides simultaneously). The method is used to study the assembled human immunodeficiency virus type capsid protein (CA) and its soluble form. PMID:12489858

Lam, TuKiet T; Lanman, Jason K; Emmett, Mark R; Hendrickson, Christopher L; Marshall, Alan G; Prevelige, Peter E

2002-12-20

65

Hydrogen-Exchange Mass Spectrometry for the Study of Intrinsic Disorder in Proteins  

PubMed Central

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

Balasubramaniam, Deepa; Komives, Elizabeth A.

2012-01-01

66

Theory of the hydrogen-deuterium isotope shift  

SciTech Connect

We present an overview of the contributions to the isotope shift of the 1[ital S]-2[ital S] transition between hydrogen and deuterium. We have calculated an additional contribution to the energy, due to the exchange of a virtual transverse photon between the electron and the deuteron. We also correct the previously evaluated finite-size and recoil contributions [F. Schmidt-Kaler [ital et] [ital al]., Phys. Rev. Lett. 70, 2261 (1993)]. Our result is 670 994 445(33) kHz, which is in disagreement with the experimental value of 670 994 337(22) KHz. This discrepancy is probably caused by an incorrect value for the deuteron radius.

Pachucki, K.; Weitz, M.; Haensch, T.W. (Max-Planck-Institut fuer Quantenoptik, Ludwig-Prandtl-Strasse 10, 85748 Garching (Germany))

1994-04-01

67

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

68

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

PubMed

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

Tsuji, Hayato; Mitsui, Chikahiko; Nakamura, Eiichi

2014-12-01

69

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

SciTech Connect

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

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

2010-01-01

70

Structural analyses of a constitutively active mutant of exchange protein directly activated by cAMP.  

PubMed

Exchange proteins directly activated by cAMP (EPACs) are important allosteric regulators of cAMP-mediated signal transduction pathways. To understand the molecular mechanism of EPAC activation, we have combined site-directed mutagenesis, X-ray crystallography, and peptide amide hydrogen/deuterium exchange mass spectrometry (DXMS) to probe the structural and conformational dynamics of EPAC2-F435G, a constitutively active EPAC2 mutant. Our study demonstrates that conformational dynamics plays a critical role in cAMP-induced EPAC activation. A glycine mutation at 435 position shifts the equilibrium of conformational dynamics towards the extended active conformation. PMID:23189173

White, Mark A; Li, Sheng; Tsalkova, Tamara; Mei, Fang C; Liu, Tong; Woods, Virgil L; Cheng, Xiaodong

2012-01-01

71

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

72

Use of pressure in reversed-phase liquid chromatography to study protein conformational changes by differential deuterium exchange.  

PubMed

The market of protein therapeutics is exploding, and characterization methods for proteins are being further developed to understand and explore conformational structures with regards to function and activity. There are several spectroscopic techniques that allow for analyzing protein secondary structure in solution. However, a majority of these techniques need to use purified protein, concentrated enough in the solution to produce a relevant spectrum. In this study, we describe a novel approach which uses ultrahigh pressure liquid chromatography (UHPLC) coupled with mass-spectrometry (MS) to explore compressibility of the secondary structure of proteins under increasing pressure detected by hydrogen-deuterium exchange (HDX). Several model proteins were used for these studies. The studies were conducted with UHPLC in isocratic mode at constant flow rate and temperature. The pressure was modified by a backpressure regulator up to about 1200 bar. It was found that the increase of retention factors upon pressure increase, at constant flow rate and temperature, was based on reduction of the proteins' molecular molar volume. The change in the proteins' molecular molar volume was caused by changes in protein folding, as was revealed by differential deuterium exchange. The degree of protein folding under certain UHPLC conditions can be controlled by pressure, at constant temperature and flow rate. By modifying pressure during UHPLC separation, it was possible to achieve changes in protein folding, which were manifested as changes in the number of labile protons exchanged to deuterons, or vice versa. Moreover, it was demonstrated with bovine insulin that a small difference in the number of protons exchanged to deuterons (based on protein folding under pressure) could be observed between batches obtained from different sources. The use of HDX during UHPLC separation allowed one to examine protein folding by pressure at constant flow rate and temperature in a mixture of sample solution with minimal amounts of sample used for analysis. PMID:25620238

Makarov, Alexey A; Schafer, Wes A; Helmy, Roy

2015-02-17

73

Hydrogen/deuterium fractionation factors of the aqueous ligand of cobalt in Co(H sub 2 O) sub 6 sup 2+ and Co(II)-substituted carbonic anhydrase  

SciTech Connect

The author has measured the hydrogen/deuterium fractionation factor for the rapidly exchanging aqueous ligands of cobalt in Co(H{sub 2}O){sub 6}{sup 2+} and in three Co(II)-substituted isozymes of carbonic anhydrase. The fractionation factor was determined from NMR relaxation rates at 300 MHz of the protons of water in mixed solutions of H{sub 2}O and D{sub 2}O containing these complexes. In each case, the paramagnetic contribution to 1/T{sub 2} was greater than to 1/T{sub 1}, consistent with a chemical shift mechanism affecting 1/T{sub 2}. The fractionation factors obtained from T{sub 2} were 0.73 {plus minus} 0.02 for Co(H{sub 2}O){sub 6}{sup 2+}, 0.72 {plus minus} 0.02 for Co(II)-substituted carbonic anhydrase I, 0.77 {plus minus} 0.01 for Co(II)-substituted carbonic anhydrase II, and 1.00 {plus minus} 0.07 for Co(Il)-substituted carbonic anhydrase III. He concluded that fractionation factors in these cases determined from T{sub 1} and T{sub 2} measured isotope preferences for different populations of ligand sites. Since T{sub 2} has a large contribution from a chemical shift mechanism, the fractionation factor determined from T{sub 2} has a large contribution of the fractionation of inner shell ligands. The fractionation factor of Co(H{sub 2}O){sub 6}{sup 2+} was used to interpret the solvent hydrogen isotope effects on the formation of complexes of cobalt with the bidentate ligands glycine, N,N-dimethylglycine, and acetylacetone. The contribution of the fractionation factor of the inner water shell in Co(H{sub 2}O){sub 6}{sup 2+} did not account completely for the measured isotope effect, and that the hydrogen/deuterium fractionation of outer shell water makes a large contribution to the isotope effect on the formation of these complexes.

Kassebaum, J.W.

1988-01-01

74

Applications of mass spectrometry to the study of protein aggregation.  

PubMed

Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles. Nowadays mass spectrometry-based approaches play a pivotal role in both detection and characterization of proteins. Here we describe two applications to study insoluble proteins: (a) hydrogen/deuterium exchange combined with mass spectrometry to analyze structural properties of amyloid fibrils and (b) the screening for inhibitors of the aggregation process by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. PMID:25447874

Bronsoms, Sílvia; Trejo, Sebastián A

2015-01-01

75

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.

76

A tripyrrolylmethane-based macrobicyclic triazacryptand: X-ray structure, size-selective anion binding, and fluoride-ion-mediated proton-deuterium exchange studies.  

PubMed

A new class of tripyrrolylmethane-based triazacryptand with bridgehead carbons and acyclic molecules were synthesized by the Mannich reaction of tripyrrolylmethane with primary or secondary amine hydrochloride and formaldehyde, respectively. The structure of the triazacryptand was determined by X-ray diffraction (XRD) method. The anion binding properties of both the bicyclic and acyclic receptors were studied by (1)H NMR titration method. The binding studies showed that both receptors exhibit very high affinity and bind strongly with the F(-) ion in DMSO-d(6). However, the binding constant of azacryptand with F(-) is much higher than that of the acyclic receptor. This is attributed to the preorganization of the azacryptand having a specific cavity size, and the strength and the number of hydrogen bonds formed by the F(-) ion. This is supported by the crystal structures of F(-), Cl(-), and Br(-) ion complexes of the bicyclic receptor and by DFT calculations. The X-ray structures showed that the azacryptand receptor forms an inclusion complex with only the F(-) ion; other anions bind in the clefts of the macrobicycle, thus supporting a size-selective anion binding behavior. The high affinity and the selectivity of the macrobicycle as a neutral receptor of the F(-) ion in the presence of other competitive anions in DMSO-d(6) were confirmed by (1)H NMR spectroscopy. Furthermore, the F(-)-ion-mediated hydrogen-deuterium exchanges were monitored by (19)F NMR spectroscopy, showing multiplets based on the formation of all possible deuterium-exchanged fluoride complexes in solution. PMID:23094950

Guchhait, Tapas; Mani, Ganesan; Schulzke, Carola; Anoop, Anakuthil

2012-11-01

77

Hydrogen/deuterium fractionation factors of the aqueous ligand of cobalt in Co(H sub 2 O) sub 6 sup 2+ and Co(II)-substituted carbonic anhydrase  

SciTech Connect

The authors have measured the hydrogen/deuterium fractionation factor for the rapidly exchanging, water ligands of cobalt in Co(H{sub 2}O){sub 6}{sup 2+} and in two Co(II)-substituted isozymes of carbonic anhydrase. The fractionation factor was determined from NMR relaxation rates at 300 MHz of the protons of water in mixed solutions of H{sub 2}O and D{sub 2}O containing these complexes. In each case, the paramagnetic contribution to 1/T{sub 2} was greater than to 1/T{sub 1}, consistent with a chemical shift mechanism affecting 1/T{sub 2}. The fractionation factors obtained from T{sub 1} for Co(H{sub 2}O){sub 6}{sup 2+} and for the isozymes of Co(II)-substituted carbonic anhydrase were close to the fractionation factor for bulk water which is unity. The fractionation factors obtained from T{sub 2} were 0.73 {plus minus}0.02 for Co(H{sub 2}O){sub 6}{sup 2+} and 0.72 {plus minus} 0./02 for Co(II)-substituted carbonic anhydrase I, with a value of 0.77 {plus minus} 0.01 for isozyme II. They concluded that fractionation factors in these cases determined from T{sub 1} and T{sub 2} measured isotope preferences for different populations of ligand sites. They suggest that since T{sub 2} has a large contribution from a chemical shift mechanism, the fractionation factor determined from T{sub 2} has a large contribution of the fractionation of inner-shell ligands. The fractionation factors determined from T{sub 1} are close to unity, the value of the fractionation factor of bulk water, and contain a large contribution of the fractionation of outer-shell water.

Kassebaum, J.W.; Silverman, D.N. (Univ. of Florida, Gainesville (USA))

1989-03-29

78

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

SciTech Connect

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

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

2010-03-22

79

Spatially resolved protein hydrogen exchange measured by subzero-cooled chip-based nanoelectrospray ionization tandem mass spectrometry.  

PubMed

Mass spectrometry has become a valuable method for studying structural dynamics of proteins in solution by measuring their backbone amide hydrogen/deuterium exchange (HDX) kinetics. In a typical exchange experiment one or more proteins are incubated in deuterated buffer at physiological conditions. After a given period of deuteration, the exchange reaction is quenched by acidification (pH 2.5) and cooling (0 °C) and the deuterated protein (or a digest thereof) is analyzed by mass spectrometry. The unavoidable loss of deuterium (back-exchange) that occurs under quench conditions is undesired as it leads to loss of information. Here we describe the successful application of a chip-based nanoelectrospray ionization mass spectrometry top-down fragmentation approach based on cooling to subzero temperature (-15 °C) which reduces the back-exchange at quench conditions to very low levels. For example, only 4% and 6% deuterium loss for fully deuterated ubiquitin and ?(2)-microglobulin were observed after 10 min of back-exchange. The practical value of our subzero-cooled setup for top-down fragmentation HDX analyses is demonstrated by electron-transfer dissociation of ubiquitin ions under carefully optimized mass spectrometric conditions where gas-phase hydrogen scrambling is negligible. Our results show that the known dynamic behavior of ubiquitin in solution is accurately reflected in the deuterium contents of the fragment ions. PMID:22536891

Amon, Sabine; Trelle, Morten B; Jensen, Ole N; Jørgensen, Thomas J D

2012-05-15

80

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

Microsoft Academic Search

The structure of an AKAP docked to the dimerization\\/docking (D\\/D) domain of the type II (RIIa) isoform of protein kinase A (PKA) has been well characterized, but there currently is no detailed structural information of an AKAP docked to the type I (RIa) isoform. Dual-specific AKAP2 (D- AKAP2) binds in the nanomolar range to both isoforms and provided us with

LORA L. BURNS-HAMURO; YOSHITOMO HAMURO; JACK S. KIM; PAUL SIGALA; ROSA FAYOS; DAVID D. STRANZ; PATRICIA A. JENNINGS; SUSAN S. TAYLOR; VIRGIL L. WOODS JR

2006-01-01

81

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

82

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

83

Erosion and redeposition behavior of selected NET-candidate materials under high-flux hydrogen, deuterium plasma bombardment in pisces  

NASA Astrophysics Data System (ADS)

Plasma erosion and redeposition behavior of selected candidate materials for plasma-facing components in the NET-machine have been investigated using the PISCES-A facility. Materials studied include SiC-impregnated graphite, 2D graphite weaves with and without CVD-SiC coatings, and isotropic graphite. These specimens were exposed to continuous hydrogen or deuterium plasmas under the following conditions: electron temperature range from 5 to 35 eV; plasma density range from 5 × 10 11 to 1 × 10 12 cm -3; flux range from 5 × 10 17 to 2 × 10 18 ions cm -2 s -1; fluence of the order from 10 21 to 10 22 ions/cm 2; bombarding energies of 50 and 100 eV; target temperature range from 300 to 1000°C. The erosion yield of SiC-impregnated graphite due to deuterium plasma bombardment is found to be a factor of 2 to 3 less than that of isotropic graphite materials. A further factor of 2-3 reduction in the erosion yield is observed in when redeposition associated with reionization of sputtered particle becomes significant. From post-bombardment surface analysis with AES, the surface composition in terms of the Si/C of SiC-impregnated graphite ratio is found to increase from 0.15 to 0.7 after hydrogen plasma bombardment to a fluence around 4 × 10 21 ions/cm 2 at 350 ° C. However, the final surface composition appears to remain unchanged up to 4 × 10 22 ions/cm 2, the highest fluence in the present study. Significant surface morphological modifications of SiC-impregnated graphite are observed after the high-fluence plasma exposure. Several structural problems such as coating-substrate adhesion have been pointed out for SiC-coated 2D graphite weave.

Franconi, E.; Hirooka, Y.; Conn, R. W.; Leung, W. K.; Labombard, B.; Nygren, R. E.

1989-04-01

84

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

PubMed

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

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

2013-03-01

85

Correlation study of the Athens Stock Exchange  

NASA Astrophysics Data System (ADS)

We study the year-after-year properties of three different portfolios traded in the Athens Stock Exchange (ASE) for the time period 1987-2004. We use the minimum spanning tree (MST) technique and the random matrix theory (RMT), which make it possible to examine at the same time the temporal evolution of the portfolios and of the market as a whole. The first four moments of the distribution of correlations and the normalized tree lengths of the MST show a similar behaviour for all three portfolios. However, by studying topological properties of the MST, such as the node degree k, we are able to identify changes to the MST associated to each portfolio that are due to a crisis in the market, like the one that happened during the period 1999-2001. We also see that, while the effect of the market to the information content of the correlation matrix for all three portfolios is almost the same, the market is affected differently by different economic sectors at different time periods.

Garas, Antonios; Argyrakis, Panos

2007-07-01

86

Experimental study of ocean-atmosphere exchanges  

SciTech Connect

The SOFIA/ASTEX and SEMAPHORE campaigns were performed over open ocean, near the Azores, to study the ocean-atmosphere exchanges at the local and meso-scales, with a particular insight to the spatial variability of fluxes and related processes. In both cases, the experimental strategy involved two research aircraft and an oceanographic vessel, as well as surface buoys. SOFIA/ASTEX was more particularly devoted to the study of boundary layer and cloud properties, including microphysical and radiative aspects, in the framework of the international campaign ASTEX. SEMAPHORE was aimed at the analysis of surface fluxes and interactions with the upper ocean at the mesoscale. It included an important network of ocean circulation and thermal properties, from ships, current meter moorings, current drifters, and drifting buoys. The thermal front associated with the Azores current is an important feature of the ocean circulation and was particularly investigated. The analysis of data from meteorological satellites is also an important aspect of the two campaigns.

Eymard, L.; Weill, A. [CETP, Velizy (France); Planton, S. [CNRM, Toulouse (France)] [and others

1994-12-31

87

Design study of plastic film heat exchanger  

NASA Astrophysics Data System (ADS)

This report presents the results of an effort to develop and design a unique thermoplastic film heat exchanger for use in an industrial heat pump evaporator system and other energy recovery applications. The concept for the exchanger is that of individual heat exchange elements formed by two adjoining and freely hanging plastic films. Liquid flows downward in a regulated fashion between the films due to the balance of hydrostatic and frictional forces. The fluid stream on the outside of film may be a free-falling liquid film, a condensing gas, or a noncondensing gas. The flow and structural principles are similar to those embodied in an earlier heat exchange system developed for use in waste water treatment systems (Sanderson). The design allows for high heat transfer rates while working within the thermal and structural limitations of thermoplastic materials. The potential of this new heat exchanger design lies in the relatively low cost of plastic film and the high inherent corrosion and fouling resistance. This report addresses the selection of materials, the potential heat transf er performance, the mechanical design and operation of a unit applied in a low pressure steam recovery system, and the expected selling price in comparison to conventional metallic shell and tube heat exchangers.

Guyer, E. C.; Brownell, D. L.

1986-02-01

88

Study Abroad and Exchange Fact Sheet 2013/14  

E-print Network

Study Abroad and Exchange Fact Sheet 2013/14 1 Contact Information Name of Institution University Courses Medicine Health Sciences Biological Sciences #12;Study Abroad and Exchange Fact Sheet 2013/14 2 Accumulation Transfer Scheme (CATS) points: 60 Modules vary and can be worth 10, 15 or 20 ECTS points Contact

Petriu, Emil M.

89

International Exchange as a Transformative Learning Experience: A Case Study  

ERIC Educational Resources Information Center

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

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

2012-01-01

90

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

PubMed Central

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

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

2012-01-01

91

EXCHANGE  

SciTech Connect

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

Boltz, J.C. (ed.)

1992-09-01

92

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

93

Acidic porous clay heterostructures: study of their cation exchange capacity  

Microsoft Academic Search

The cation exchange capacities (CECs) of two porous clay heterostructures (PCHs), derived from natural montmorillonite (PMH) and synthetic saponite (PSH), have been studied. Both materials are highly porous, with surface areas of 997 m2\\/g (PMH) and 1118 m2\\/g (PSH). In order to obtain exchangeable ammonium cations in the pore structures of the PCHs, different modifications are performed on calcined and

M Benjelloun; P Cool; T Linssen; E. F Vansant

2001-01-01

94

Cooperative Atmosphere-Surface Exchange Study-1999.  

NASA Astrophysics Data System (ADS)

Surface-station, radiosonde, and Doppler minisodar data from the Cooperative Atmosphere-Surface Exchange Study-1997 (CASES-97) field project, collected in a 60-km-wide array in the lower Walnut River watershed (terrain variation 150 m) southeast of Wichita, Kansas, are used to study the relationship of the change of the 2-m potential temperature 2m with station elevation ze, 2m/ze ,ze to the ambient wind and thermal stratification /z ,z during fair-weather nights. As in many previous studies, predawn 2m varies linearly with ze, and ,ze ,z over a depth h that represents the maximum elevation range of the stations. Departures from the linear 2m-elevation relationship (,ze line) are related to vegetation (cool for vegetation, warm for bare ground), local terrain (drainage flows from nearby hills, although a causal relationship is not established), and the formation of a cold pool at lower elevations on some days.The near-surface flow and its evolution are functions of the Froude number Fr = S/(Nh), where S is the mean wind speed from the surface to h, and N is the corresponding Brunt-Väisälä frequency. The near-surface wind is coupled to the ambient flow for Fr = 3.3, based on where the straight line relating ,ze to ln Fr intersects the ln Fr axis. Under these conditions, 2m is constant horizontally even though ,z > 0, suggesting that near-surface air moves up- and downslope dry adiabatically. However, 2m cools (or warms) everywhere at the same rate. The lowest Froude numbers are associated with drainage flows, while intermediate values characterize regimes with intermediate behavior. The evolution of 2m horizontal variability ? through the night is also a function of the predawn Froude number. For the nights with the lowest Fr, the ? maximum occurs in the last 1-3 h before sunrise. For nights with Fr 3.3 (,ze 0) and for intermediate values, ? peaks 2-3 h after sunset. The standard deviations relative to the ,ze line reach their lowest values in the last hours of darkness. Thus, it is not surprising that the relationships of ,ze to Fr and ,z based on data through the night show more scatter, and ,ze 0.5,z in contrast to the predawn relationship. However, ,ze

Moeng, Chin-Hoh; Poulos, Gregory S.; Lemone, Margaret A.

2003-10-01

95

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

Federal Register 2010, 2011, 2012, 2013

...Regulatory New Drug Review: Solutions for Study Data Exchange Standards; Notice of Meeting...Regulatory New Drug Review: Solutions for Study Data Exchange Standards'' the purpose...standards for the exchange of regulated study data. FDA also seeks input from...

2012-08-14

96

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

SciTech Connect

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

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

1980-09-01

97

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

PubMed

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

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

2015-01-01

98

Hydrogen Isotope Separation by Combined Electrolysis Catalytic Exchange Under Reduced Pressure  

SciTech Connect

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

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

2005-07-15

99

Exchange Bias Systems studied by High Resolution Quantitative Magnetic Force  

E-print Network

Exchange Bias Systems studied by High Resolution Quantitative Magnetic Force Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2 Introduction to Quantitative MFM 12 2.1 Magnetic Force Microscope study F/AF heterostructure-samples by VSM and quantitative, high resolution MFM. MFM works in magnetic

Amrhein, Valentin

100

Ligand exchange in quaternary alloyed nanocrystals--a spectroscopic study.  

PubMed

Exchange of initial, predominantly stearate ligands for pyridine in the first step and butylamine (BA) or 11-mercaptoundecanoic acid (MUA) in the second one was studied for alloyed quaternary Cu-In-Zn-S nanocrystals. The NMR results enabled us to demonstrate, for the first time, direct binding of the pyridine labile ligand to the nanocrystal surface as evidenced by paramagnetic shifts of the three signals attributed to its protons to 7.58, 7.95 and 8.75 ppm. XPS investigations indicated, in turn, a significant change in the composition of the nanocrystal surface upon the exchange of initial ligands for pyridine, which being enriched in indium in the 'as prepared' form became enriched in zinc after pyridine binding. This finding indicated that the first step of ligand exchange had to involve the removal of the surface layer enriched in indium with simultaneous exposure of a new, zinc-enriched layer. In the second ligand exchange step (replacement of pyridine with BA or MUA) the changes in the nanocrystal surface compositions were much less significant. The presence of zinc in the nanocrystal surface layer turned out necessary for effective binding of pyridine as shown by a comparative study of ligand exchange in Cu-In-Zn-S, Ag-In-Zn-S and CuInS2, carried out by complementary XPS and NMR investigations. PMID:25252174

Gabka, Grzegorz; Bujak, Piotr; Giedyk, Kamila; Kotwica, Kamil; Ostrowski, Andrzej; Malinowska, Karolina; Lisowski, Wojciech; Sobczak, Janusz W; Pron, Adam

2014-11-14

101

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

PubMed

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

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

2015-01-01

102

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

103

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

104

Study Abroad and Exchange Guide 2015 Never Stand Still  

E-print Network

Study Abroad and Exchange Guide 2015 Never Stand Still #12;A brighter future awaits 4 Your journey together to pursue their academic passions and to tackle some of the world's greatest challenges. Through you will be joining a talented and highly driven student community. I wish you well with your journey

Blennerhassett, Peter

105

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

106

Structure-resonance theory and the kinetics of the electrophilic deuterium-hydrogen exchange in benzenoid hydrocarbons  

SciTech Connect

Structure-resonance theory has recently been shown to correlate and to predict various physical and chemical properties of ..pi..-electron hydrocarbons. The major advantage of this theory is its simplicity. Its application requires only an enumeration of Kekule' structures, since it has been shown that an algorithm, logarithm of the Kekule' corrected structure count, gives an excellent approximation of the gound-state eigenvalues of the structure-function Hamiltonian matrix. The purpose of this contribution is to show that the structure-resonance theory can be used to correlate the rates of both the deuterium-hydrogen and hydrogen-deuterium exchange reactions of benzenoid hydrocarbons. Logarithms of the rates of deuterodeprotonation of nine alternant hydrocarbons and protodedeuteration of five hydrocarbons containing 17 and 12 different reaction sites, respectively, are correlated with the logarithms of the structure counts of the intermediate, ln SC/sub I/, and the reactant, ln SC/sub R/, and with their ratio, ln (SC/sub I//SC/sub R/). The quality of the correlations is very good. The results indicate that the differences in reactivities of benzenoid hydrocarbons in aromatic substitution reactions are due to differences in their resonance energies and that hyperconjugation does not play a significant role in the stabilization of the intermediates in the reaction studied.

Shawali, A.S. (Univ. of Cairo, Giza, Egypt); Parkanyi, C.; Herndon, W.C.

1982-01-01

107

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

108

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

PubMed

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

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

2012-07-01

109

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

Microsoft Academic Search

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

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

1998-01-01

110

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

E-print Network

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

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

2015-01-01

111

Vibrational and Rotational Energy Transfer: Relaxation of Hydrogen Fluoride and Deuterium Fluoride by Helium, Hydrogen, Deuterium, Hydrogen Fluoride, Deuterium Fluoride and Nitrogen  

NASA Astrophysics Data System (ADS)

The overtone vibration-laser double resonance technique provides a direct measure of the rates and mechanisms of rotational and vibrational energy transfer in the gas phase due to inelastic collisions of vibrationally excited HF or DF with a variety of collision partners. A laser pulse prepares HF (or DF) molecules in a single rotational level of an overtone vibration and a continuous HF (or DF) laser monitors the population in a pair of the intermediate rotational and vibrational levels. This work comprises two studies: one on vibrational energy transfer of DF ( upsilon = 3) relaxation in a DF gas sample and the other on rotational energy transfer of HF( upsilon = 2) with collision partners He, H_2, D_2, HF, DF and N_2. Rotational relaxation in the HF and DF systems is more rapid than vibrational relaxation allowing the study of the two processes independently of each other. We calculate the matrix of state-to-state rotational energy transfer rate constants for modeling the rotational energy transfer using energy based scaling laws due to the large number of parallel and sequential pathways for rotational relaxation. These scaling law models provide a fair representation of these data involving low J levels. The data demonstrate that each of the dissimilar collision partners are less efficient at rotationally relaxing HF(upsilon = 2) than HF itself. The average efficiencies for the rotational relaxation of HF(upsilon = 2) relative to self relaxation are 0.05: 0.3: 0.2: 0.4: 0.2 for He, H_2, D _2, DF, and N_2, respectively. The results show that, for H_2, D _2, and DF, multiquantum rotational energy transfer pathways are important while single quantum energy transfer dominates the relaxation of HF(upsilon = 2) by He and N_2. The experiments on DF vibrational energy transfer directly measure the bi-molecular rate constants for the self relaxation of DF(upsilon = 3) of k_3 = (17.0 +/- 1.8) times 10^ {-12} cm^3 molecules ^{-1} s^ {-1} and the fraction of DF(upsilon = 3) molecules relaxing by V-V energy transfer f_3(V-V) = (0.72 +/- 0.10). These results indicate the dominant influence of a near-resonant V-V mechanism, and comparison of this V-V branching fraction with the data available for HF( upsilon = 2) suggests that V-R energy transfer plays a significant role in the DF(upsilon = 3) V-T,R mechanism.

Muyskens, Mark Alan

112

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

113

ESCA study of rhodium(III)-exchanged zeolite catalysts  

SciTech Connect

Samples of both the often investigated rhodium(III)-zeolite Y and the seldom investigated rhodium(III)-zeolite A were prepared and studied by techniques of electron spectroscopy for chemical analysis (ESCA) both in the originally exchanged condition and after activation to the state in which they would be employed in a catalytic capacity. The ESCA data agree with previously reported ESR data which indicated that Rh(III) may be thermally reduced to Rh metal in the zeolite Y lattice, and that this reduction takes place under much milder conditions than comparable reduction of any other metal previously reported. Contrarily, the ESCA data indicated that Rh(III) was not reduced on the zeolite A, and this lack of reduction may be the explanation for the poor catalytic effect of Rh(III) supported on zeolite A. It is postulated that the metallic Rh produced by the activation of Rh(III)-exchanged zeolite Y and not the Rh(III) species is the true catalytic species in the so-called Rh(III)-zeolite catalysts. (BLM)

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

1980-09-01

114

Exchange Bias Studies in Core/Shell Structures Nanoparticles  

NASA Astrophysics Data System (ADS)

This study is focused on a comparison of magnetic properties of chemically synthesized core/shell structured iron/iron-oxide nanoparticles with different core sizes and comparable shell thickness. Particles were synthesized by high temperature decomposition of iron organometallic compounds. Thermomagnetic data revealed that particles are superparamagnetic at room temperature. The field cooled hysteresis loops showed interesting features of enhanced coercivity and horizontal and vertical shifts along directions of the cooling field, all strongly depend on temperature, indicative of an exchange-bias-like phenomenon. These effects were more pronounced in smaller core size nanoparticles with an exchange bias field of 4098 Oe. The spin-glass-like phase with high-field irreversibility in the iron oxide shells played the role of the fixed phase in the core/shell system and provided the pinning force to the reversible spins. The magnetic domains and higher contributions from the surface anisotropy in the hollow nanoparticles caused enormous magnetic frustration that is the origin of high field irreversibility and vertical shift of hysteresis loop in these particles.

Khurshid, Hafsa; Chandra, Sayan; Li, Wanfeng; Phan, Man-Huong; Hadjipanayis, George; Srikanth, Hariharan

2012-02-01

115

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

116

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

117

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

118

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

PubMed

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

Thomsen, N K; Poulsen, F M

1993-11-01

119

Study of hydraulic resistance and heat transfer in perforated-plate heat exchangers  

NASA Astrophysics Data System (ADS)

An experimental study is made of the hydraulic resistance and heat transfer in heat exchangers made of perforated plates with different internal geometries. Generalizing theoretical relations are obtained.

Shevyakova, S. A.; Orlov, V. K.

1983-07-01

120

Study of transient behavior of finned coil heat exchangers  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

121

Study Exchange in China Xi'an Jiaotong-Liverpool University  

E-print Network

Study Exchange in China Xi'an Jiaotong-Liverpool University International Student Recruitment and Support international@xjtlu.edu.cn #12;Study Exchange in China Xi'an Jiaotong-Liverpool University This presentation will cover the following: · Location of XJTLU and Suzhou, China · About XJTLU · Study options

Wong, Prudence W.H.

122

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

123

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

124

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

E-print Network

The combined effect of rain and wind on air­water gas exchange: A feasibility study David T. Ho a to examine the combined effects of rain and wind on air­water gas exchange. During this study, ASIL WRX I, a combination of 3 rain rates and 4 wind speeds were used, for a total of 12 different environmental conditions

Ho, David

125

Study of Multiferroic Manganites using Double-Exchange Models  

NASA Astrophysics Data System (ADS)

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

Dagotto, Elbio

2009-03-01

126

In ESI-source H/D exchange under atmospheric pressure for peptides and proteins of different molecular weights from 1 to 66?kDa: the role of the temperature of the desolvating capillary on H/D exchange.  

PubMed

Transition of proteins from the solution to the gas phase during electrospray ionization remains a challenging problem despite the large amount of attention it has received during the past few decades. One of the major questions relates to the extent to which proteins in the gas phase retain their condensed phase structures. We have used in-electrospray source hydrogen/deuterium exchange to determine the number of deuterium incorporations as a function of protein mass, charge state and temperature of the desolvating capillary where the reaction occurs. All experiments were performed on a Thermo LTQ FT Ultra equipped with a 7-T superconducting magnet. Ions were generated by an IonMax Electrospray ion source operated in the positive ESI mode. Deuterium exchange was performed by introducing a droplet of D2 O beneath the ESI capillary. We systematically investigated gas phase hydrogen/deuterium (H/D) exchange under atmospheric pressure for peptides and proteins of different molecular weights from 1 to 66?kDa. We observed that almost all proteins demonstrate similar exchange rates for all charge states and that these rates increase exponentially with the temperature of the desolvating capillary. We did not observe any clear correlation of the number of H/D exchanges with the value of the cross section for a corresponding charge state. We have demonstrated the possibility of performing in-ESI source H/D exchange of large proteins under atmospheric pressure. The simplicity of the experimental setup makes it a useful experimental technique that can be applied for the investigation of gas phase conformations of proteins. Copyright © 2015 John Wiley & Sons, Ltd. PMID:25601674

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

2015-01-01

127

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

PubMed Central

This study was done to better understand how lipases are activated at an interface. We investigated the conformational and solvation changes occurring during the adsorption of Humicola lanuginosa lipase (HLL) onto a hydrophobic surface using Fourier transform infrared-attenuated total reflection spectroscopy. The hydrophobic surfaces were obtained by coating silicon attenuated total reflection crystal with octadecyltrichlorosilane. Analysis of vibrational spectra was used to compare the conformation of HLL adsorbed at the aqueous-solid interface with its conformation in solution. X-ray crystallography has shown that HLL exists in two conformations, the closed and open forms. The conformational changes in HLL caused by adsorption onto the surface were compared with those occurring in three reference proteins, bovine serum albumin, lysozyme, and alpha-chymotrypsin. Adsorbed protein layers were prepared using proteins solutions of 0.005 to 0.5 mg/mL. The adsorptions of bovine serum albumin, lysozyme, and alpha-chymotrypsin to the hydrophobic support were accompanied by large unfoldings of ordered structures. In contrast, HLL underwent no secondary structure changes at first stage of adsorption, but there was a slight folding of beta-structures as the lipase monolayer became complete. Solvation studies using deuterated buffer showed an unusual hydrogen/deuterium exchange of the peptide CONH groups of the adsorbed HLL molecules. This exchange is consistent with the lipase being in the native open conformation at the water/hydrophobic interface. PMID:11964257

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

2002-01-01

128

Study of frost melting on a heat pump heat exchanger  

SciTech Connect

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

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

1990-01-01

129

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

E-print Network

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

Raschke, Tanya M.

130

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

Microsoft Academic Search

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

Sarita Seshagiri

2009-01-01

131

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

132

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

E-print Network

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

Englander, S. Walter

133

Study of the exchange energy of an inhomogeneous electron gas at a surface  

Microsoft Academic Search

In this work we have studied the exchange energy property of an inhomogeneous electron gas at a jellium surface. The nonlocal surface exchange energy is determined exactly for the accurate set of single-particle wave functions generated within the linear-potential approximation to the effective potential at a surface, and written in terms of a universal function of the field strength. It

C. Q. Ma; V. Sahni

1979-01-01

134

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

135

Study of Multiferroic Manganites using Double-Exchange Models  

Microsoft Academic Search

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

Elbio Dagotto

2009-01-01

136

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

E-print Network

CULTURAL IMPLICATIONS OI' SCIENTIFIC EXCHANGES BY USA VISITORS TO MAINLAND CHINA: A CASE STUDY A Thesis by Wei Lu Submitted to the Office of Graduate Studies of Texas ARM University in partial fulfillment of the requirements for the degree... of MASTER OF SCIENCE May 1989 Major Subject: Recreation and Resources Development CULTURAL IMPLICATIONS OF SCIENTIFIC EXCHANGES BY USA VISITORS TO MAINLAND CHINA: A CASE STUDY A Thesis by WEI LU Approved as to style and content by: Leslie M. Reid...

Lu, Wei

1989-01-01

137

Interaction between Plectranthus barbatus herbal tea components and acetylcholinesterase: binding and activity studies.  

PubMed

Plectranthus barbatus water extracts, have been used as herbal teas, for the treatment of various diseases. In a previous study it was demonstrated that antioxidant and anti-acetylcholinesterase active extract constituents and their metabolites were found in the plasma of rats after P. barbatus tea intraperitoneal administration. Consequently, a decrease in brain acetylcholinesterase activity occurred. The aim of the present research is to elucidate how P. barbatus extract components interact with acetylcholinesterase. The estimated thermodynamic parameters suggest that the main intermolecular interaction is hydrophobic association, although hydrogen bonds between flavonoids and the active gorge of the acetylcholinesterase molecule seem to occur and have a great impact on acetylcholinesterase inhibition. The hydroxyl positions in flavonoids seem to be of utmost importance for enzyme inhibition, as they interact with specific amino acid residues in the active gorge. FTIR analysis showed that the plant extract components do not interfere with the secondary structure of the enzyme, but decreases the rate of hydrogen-deuterium exchange, possibly by decreasing solvent accessibility in the acetylcholinesterase active gorge. The spectroscopic data complements docking studies of acetylcholinesterase inhibition by plant phenolic compounds, clarifying the dominant interactions between enzyme and inhibitor and the most important structural features of the inhibitor molecules. PMID:22801419

Falé, Pedro L V; Ascensão, Lia; Serralheiro, M Luisa; Haris, Parvez I

2012-11-01

138

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

139

Study of thermal energy storage using fluidized bed heat exchangers  

SciTech Connect

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

140

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

PubMed

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

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

2012-09-01

141

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

142

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

SciTech Connect

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

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

2014-03-01

143

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

144

Study of exchange bias in NiCr2O4 nanoparticles  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

145

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

NASA Astrophysics Data System (ADS)

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

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

146

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

147

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

148

Multiple modeling in the study of interaction of hemodynamics and gas exchange.  

PubMed

Circulation plays an important rule in gas exchange. Therefore, there is an interaction between circulation and gas exchange. To understand the dynamic effect of these two physiological systems, a computer simulation model of hemodynamics and gas exchange is established in this work. This model includes two physiological systems, namely the respiratory and circulatory systems. It consists of five parts: the model of gas transport, exchange and storage within the body, the multi-element nonlinear mathematical model of human circulatory system, an alveolar ventilation controller, a cardiac output controller, and a controller of breathing frequency. Model simulations provide results consistent with both dynamic and steady-state responses under hypoxia. Simulation results can reflect the interaction of hemodynamics and gas exchange. Using this model, the changes of pulmonary arterial pressure and right ventricular pressure in high altitude are studied. The optimal mode of breathing extra oxygen using nasal prongs or a facial mask is studied. This model may provide a useful tool to study reaction of hypoxia and the oxygen inhalation mode under hypoxia environments. PMID:11058694

Qiu, A; Bai, J

2001-01-01

149

A radiochemical study of the kinetics of ion exchange on hydrous titanium dioxide  

Microsoft Academic Search

This paper reports a radiochemical study of the kinetics of ion exchange of Na+ and Cs+ with H+ on hydrous titanium dioxide. The experimental conditions are set to favor the particle diffusion mechanism only, and this is confirmed by the Bt versus t plots. On the basis of these studies the various physical parameters such as the effective diffusion coefficients,

I. M. El-Naggar; M. A. El-Absy

1992-01-01

150

Simulation and experimental study of intermediate heat exchange in a sieve tray distillation column  

Microsoft Academic Search

The aim of this study was to combine a simulation study with an experimental in the investigation of intermediate heat exchange as a method to change the distribution of the driving forces in the column where the number of trays is kept constant. It was applied to a pilot plant sieve tray distillation column for a binary separation of ethanol

Ingela Niklasson Björn; Urban Grén; Fredrik Svensson

2002-01-01

151

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

152

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

PubMed Central

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

2013-01-01

153

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

154

Hydrogen isotope exchange experiments with Mt Mazama ash  

NASA Astrophysics Data System (ADS)

The 2H/H ratio in hydrous minerals and volcanic glass are routinely used as paleo proxies to infer ?2H value of meteoric waters and thus paleo-climate conditions. There is a widely held assumption that once environmental water is taken up by the ash to ~3-4 wt%, hydrogen isotopes preserve original hydrologic environmental conditions through time. We report a series of 2H -H aqueous exposure experiments of 7600BP Mt Mazama ash from the Crater Lake eruption. Native Mt. Mazama ash, ~69% SiO2 contains ~3.75% H2O with ?2H -145 %. Water exposure experiments for this ash were done at 70, 40 and 25°C, time from 0 to >7000 h, to evaluate rates of hydrogen uptake from deuterated waters (650 % to pure D2O). Measurements were performed on 1-2 mg of ash using TCEA-MAT253 GSMS. We also employ a KBr pellet technique with infrared spectroscopy to measure total water and molecular water peaks. In this fashion an estimation of the distribution of water vs. SiOH is possible. Time series experiments aided by infrared measurements demonstrate the following new results: 1) Depending on exposure time and temperature we observe 5 to >100 % 2H uptake in dried samples positively correlated with temperature. In as little as 48 hours approximately 5% ?2H increases are seen in samples incubated at 70 °C with 650 % water. At this rate the ash at 70 °C would take ~2.9 years to fully react with 2H. Other separate samples reacted with pure D2O develop a clear infrared signal at ~ 2600 cm-1 due to OD bond stretching. 2) Step heating experiments on native ash indicate the ?2H of the remaining water does not change until the ash is heated to past 200-220 °C. 3) A sample immersed in 650 % ?2H water for >300 days at 70 °C degassed and sampled at increasing temperature intervals as above shows an enrichment ranging from 250 % at no water lost to 20 % at .10 % water when compared to native ash. 4) Ash dried under vacuum at ~130 °C shows mostly (~80%) loss of molecular water accompanied by minor (~20%) hydroxyl loss. 5) Native ash dried to <3% water and ~-145% ?2H), and reacted with the 650 % prepared water evinces a much higher rate of 2H incorporation compared to rates with the native ash under all the same conditions. Given linearity of ?2H exchange through time and modeling the reaction as (pseudo) first order in concentration of deuterium yields the following isotopic half life values: for 70° C 1.43 years, for 40° C 4.1 years, and for 25 °C 12.1 years. An Arrhenius treatment yields an activation energy of 32-38 kjoules. 6) A second order kinetic treatment can be used to follow the reaction. A calculation using the reaction constant k at 25 °C assuming native ash exposed to -60 % ?2H water indicates it would take 2 years to rise from a starting value of -150 to approximately -100 % ?2H. Results of these experiments put quantitative limits on reliability of ?2H in ash in paleo-climate studies that are primarily controlled by the isotopic environments and temperatures. We hypothesize that hydrogen-deuterium exchange occurs in native ash exposed to isotopically labeled water. The effect is mediated through surface correlated water in addition to diffusion with both having a rate determining effect. There is nothing to suggest that deuterium-hydrogen exchange is selective for molecular or SiOH hydrogen in the ash.

Nolan, G. S.; Bindeman, I. N.; Palandri, J. L.

2011-12-01

155

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

156

Magnetization reversal studies of continuous and patterned exchange biased NiFe/FeMn thin films  

NASA Astrophysics Data System (ADS)

In this article we present a detailed investigation of the structural and magnetic properties of exchange biased NiFe (ferromagnet)/FeMn (antiferromagnet) thin films. The influence of the shape anisotropy on exchange bias and the magnetization reversal mechanism in a sample with patterned lines is compared with a continuous two-dimensional reference sample. Polarized neutron reflectivity (PNR) is employed to study the magnetization reversal by analyzing the spin-flip and non-spin-flip reflectivities. PNR measurements show that the magnetization reversal in the reference two-dimensional film and patterned lines is by domain wall motion rather than coherent rotation of magnetization.

Mohanty, J.; Vandezande, S.; Brems, S.; Van Bael, M. J.; Charlton, T.; Langridge, S.; Dalgliesh, R. M.; Temst, K.; Van Haesendonck, C.

2012-10-01

157

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

158

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

159

Study Exchange in China Xi'an Jiaotong-Liverpool University (XJTLU)  

E-print Network

Study Exchange in China Xi'an Jiaotong-Liverpool University (XJTLU) University of Liverpool Recruitment and Support Xi'an Jiaotong-Liverpool University international@xjtlu.edu.cn +86 (0)512 8816 1889 www.xjtlu.edu.cn www.facebook.com/XJTLU #12;Xi'an Jiaotong-Liverpool University is a Sino

Wong, Prudence W.H.

160

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

Microsoft Academic Search

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

Andreas Bockstedte; Edwin Kreuzer

2005-01-01

161

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

162

Modeling of temporal behavior of isotopic exchange between gaseous hydrogen and palladium hydride power  

SciTech Connect

A parametric rate-equation model is described which depicts the time dependent behavior of the isotopic exchange process occurring between the solid and gas phases in gaseous hydrogen (deuterium) flows through packed-powder palladium deuteride (hydride) beds. The exchange mechanism is assumed to be rate-limited by processes taking place on the surface of the powder. The fundamental kinetic parameter of the model is the isotopic exchange probability, p, which is the probability that an isotopic exchange event occurs during a collision of a gas phase atom with the surface. Isotope effects between the gas and solid phases are explicitly included in terms of the isotope separation factor, ..cap alpha... Results of the model are compared with recent experimental measurements of isotope exchange in the ..beta..-phase hydrogen/palladium system and, using a literature value of ..cap alpha.. = 2.4, a good description of the experimental data is obtained for p approx. 10/sup -7/. In view of the importance of the isotope effects in the hydrogen/palladium system and the range of ..cap alpha.. values reported for the ..beta..-phase in the literature, the sensitivity of the model results to a variation in the value of ..cap alpha.. is examined.

Melius, C F; Foltz, G W

1987-01-01

163

pH dependence of individual tryptophan N-1 hydrogen exchange rates in lysozyme and its chemically modified derivatives.  

PubMed

Nuclear magnetic resonance analyses have been made of the individual hydrogen-deuterium exchange rates of tryptophan indole N-1 hydrogens in native lysozyme and its chemically modified derivatives including lysozyme with an ester cross-linkage between Glu-35 and Trp-108, lysozyme with an internal amide cross-linking between the epsilon-amino group of Lys-13 and the alpha-carboxyl group of Leu-129, and lysozyme with the beta-aspartyl sequence at Asp-101. The pH dependence curves of the exchange rates for Trp-63 and Trp-108 are different from those expected for tryptophan. The pH dependence curve for Trp-108 exchange exhibits the effects from molecular aggregation at pH above 5 and from a transition between the two conformational fluctuations at around pH 4. The exchange rates for tryptophan residues in native lysozyme and modified derivatives are not correlated with the thermodynamic or kinetic parameters in protein denaturation, suggesting that the fluctuations responsible for the exchange are not global ones. The exchange rates for tryptophan residues remote from the modification site are perturbed. Such tryptophan residues are found to be involved in a small but distinct conformational change due to the modification. Therefore, the perturbations of the N-1 hydrogen exchange rates are related to the minor change in local conformation or in conformational strain induced by the chemical modification. PMID:3593697

Endo, T; Ueda, T; Yamada, H; Imoto, T

1987-04-01

164

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...

165

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

166

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

PubMed

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

Jin, Tao; Kim, Seong-Gi

2014-11-01

167

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

PubMed

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

Bohman, Doris M; Borglin, Gunilla

2014-05-01

168

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

SciTech Connect

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

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

2010-10-15

169

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

NASA Astrophysics Data System (ADS)

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

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

2004-01-01

170

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

Microsoft Academic Search

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

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

1981-01-01

171

Study of exchange bias behavior in Ni(Cr1-xFex)2O4  

NASA Astrophysics Data System (ADS)

Single phase samples of Ni(Cr1-xFex)2O4 were prepared by sol-gel method for x=0.0 to 0.1. Structural study at room temperature using X-ray diffraction shows that upon Fe substitution the crystal structure transforms from tetragonal cell with space group I41/amd to cubic cell with Fd 3 bar m space group. The ferrimagnetic transition temperature (TC) is found to increase from 73 K for x=0 to 187 K for x=0.1. Presence of large coercivity along with exchange bias phenomenon is observed as per M-H loop measurements. The origin of exchange bias is explained by considering the exchange anisotropy between the ferrimagnetic and the antiferromagnetic components. The temperature dependent behaviors of exchange bias field and the effective coercive field are found to be quite different, while the former one decreases exponentially but the latter one decreases in quadratic form with increase in temperature and both of them approach zero at TC.

Barman, Junmoni; Ravi, S.

2015-01-01

172

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

PubMed Central

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

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

2014-01-01

173

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

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

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

176

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

Microsoft Academic Search

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

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

2003-01-01

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

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

E-print Network

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

N. B. Ladygina; A. V. Shebeko

2004-04-15

179

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

180

Studies of the process of moisture exchange across a membrane using irreversible thermodynamics  

Microsoft Academic Search

On the basis of non-equilibrium thermodynamic theory, the coupling phenomena of heat and mass transfer during the process\\u000a of moisture exchange across a membrane were studied and the relevant physical and mathematical models were established. Formulae\\u000a for calculating the four characteristic parameters included in the non-equilibrium thermodynamic model were derived, and the\\u000a dependences of these parameters on the temperatures and

LiNing Wang; JingChun Min

2011-01-01

181

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

E-print Network

1 Perceived Reciprocity in Social Exchange and Health Functioning in Early Old Age: Prospective: Perceived Reciprocity in Social Exchange and Health Functioning in Early Old Age: Prospective Findings from in early old age. Methods: In the frame of the prospective French Gazel cohort study, data on reciprocity

Paris-Sud XI, Université de

182

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

183

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

E-print Network

Mechanisms of Hydrogen Exchange of Methane with H-Zeolite Y: An ab Initio Embedded Cluster Study exchange of methane with H-Zeolite Y. We found that inclusion of the Madelung field stabilizes with experimental observation. Introduction Zeolites are important technological materials due to their many

Truong, Thanh N.

184

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

E-print Network

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

Englander, S. Walter

185

Identification of the protein kinase A regulatory RIalpha-catalytic subunit interface by amide H/2H exchange and protein docking.  

PubMed

An important goal after structural genomics is to build up the structures of higher-order protein-protein complexes from structures of the individual subunits. Often structures of higher order complexes are difficult to obtain by crystallography. We have used an alternative approach in which the structures of the individual catalytic (C) subunit and RIalpha regulatory (R) subunit of PKA were first subjected to computational docking, and the top 100,000 solutions were subsequently filtered based on amide hydrogen/deuterium (H/2H) exchange interface protection data. The resulting set of filtered solutions forms an ensemble of structures in which, besides the inhibitor peptide binding site, a flat interface between the C-terminal lobe of the C-subunit and the A- and B-helices of RIalpha is uniquely identified. This holoenzyme structure satisfies all previous experimental data on the complex and allows prediction of new contacts between the two subunits. PMID:14583592

Anand, Ganesh S; Law, Dennis; Mandell, Jeffrey G; Snead, Aaron N; Tsigelny, Igor; Taylor, Susan S; Ten Eyck, Lynn F; Komives, Elizabeth A

2003-11-11

186

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

187

RBS-channeling, ERDA and XRD study of lithium tantalate modified by annealed proton exchange (APE)  

NASA Astrophysics Data System (ADS)

Lithium tantalate (LT) single crystals are very promising substrates for constructing highly sophisticated photonics devices. The used procedure for fabricating optical waveguides in them was annealed proton exchange (APE). Here we have used Rutherford backscattering spectrometry (RBS) - channeling analysis, X-ray diffraction (XRD) and elastic recoil detection analysis (ERDA) to study changes in the surface of the LT wafers caused by the APE treatment and to determine the concentration depth profiles of hydrogen atoms. The measurements were taken for both virgin (untreated) and APE:LT samples fabricated using various experimental conditions. We have found that the incorporation of hydrogen during the first step, i.e. the PE procedure (proton exchange), leads to modifications of the structure of the LT single crystal, which gradually relaxed towards the structure of the original LT during the post-proton-exchange annealing (A). This study also revealed a substantial dependence of sample behaviour on the crystallographic orientation of the pertinent substrate wafers (commonly used X-(<1 1 -2 0>) and Z-(<0 0 0 1>) cuts).

Macková, Anna; Salavcová, L.; Špirková, Jarmila; Groetzschel, R.; Eichhorn, F.

2006-08-01

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

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

E-print Network

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

Zhang, Jianqin

2014-01-01

190

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

PubMed Central

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

2014-01-01

191

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

192

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

193

Use of a moderated international Internet information exchange in the study of male reproduction.  

PubMed

It is clear that modern information technology is having a profound impact on the way researchers and clinicians exchange information. Use of the Internet is one example of how such change can be translated into scientific progress and improved patient care. Androlog, a moderated international information exchange, has proven to be very useful in the transfer of information pertaining to the study and treatment of male reproductive disorders. Allowing instantaneous dispersal of messages to members in 27 countries, this system has become a valuable source of scientific information, as well as an excellent forum for the discussion of a broad range of clinical and laboratory topics. Moderated-user groups such as Androlog are highly applicable to many other areas of urology. Establishment of such an information exchange requires only a modest investment in computer hardware and software and moderators who are willing to perform the necessary tasks of system administration and message review. Given the unique advantages provided by this method of communication, there is little doubt that systems such as Androlog will flourish in the future, providing a valuable tool in the advance of medical science. PMID:8693648

Meacham, R B; Niederberger, C S

1996-07-01

194

Nutrient exchange and release experiment and its simulation study in lake water-sediment interface.  

PubMed

The sediment distributed and insolated under lake was collected for experiments. The nutrient layer distribution conditions of sampled sediment and its physical and chemical characteristics were analyzed to simulate and assess the influence degree to lake water quality. Based on the dynamic water exchanging experiments the nutrient release process in sediment and influence mechanism to substance exchanging on water-sediment interface was studied, and the correlation between the changing content of total phosphors and total nitrogen in sediment and covered water were analyzed for setting up a simulation model. At the same time the influence degree is explained in detail. The experimental results indicated that even if clean water without nutrient contents was used for water exchangement so as to decrease pollution or prevent eutrophication, however owing to the vertical nutrient distribution in lake sediment, it will lead to the increasing release amount greatly especially when the organic nutrient contained in sediment turns into inorganic status because of isolation. Besides the release process of total phosphate (TP) and total nitrogen (TN) were modeled and each nutrient's exchanging equation at interface caused by covered water nutrient concentration changing was set up. According to the simulating prediction, TP and TN content of cover water will also sustain a steady higher level in a long period. The nutrient release amount of sediment is not only affected by the covered water concentration but also connects with accumulative time. The experiments provide the fundamental theoretical and practical basis for taking ecological restoration project. And research is helpful to prevent or restore lake eutrophication. PMID:17294663

Xue, Lian-Qing; Hao, Zhen-Chun

2006-01-01

195

Amplification of turbulent exchange over wide Arctic leads: Large-eddy simulation study  

NASA Astrophysics Data System (ADS)

Leads (narrow openings in the sea ice cover) are perhaps the most pronounced examples of heat islands naturally occurring on Earth. Large air-water temperature differences induce strong turbulent convection. In addition, large ice-water temperature differences induce more regular, breeze-like circulation at ice edges. Both the turbulent convection and the breeze result in intensive turbulent heat exchange between the ocean and the atmosphere. This study describes a series of turbulence-resolving experiments with the Large Eddy Simulation Nansen Center Improved Code (LESNIC). The numerical experiments quantify the turbulent heat exchange over leads of different widths. Contrary to the expected gradual decrease of the surface heat flux per unit area of open water, a strong amplification of the heat flux has been discovered for certain leads. This amplification results from a positive feedback between the horizontal entrainment of cool air in breeze and the turbulent heat exchange. Gradual reduction of the turbulent exchange for wider leads is thought to be due to development of self-organized structures in the convection. Pressure anomalies induced by the convective overturning could be comparable with the pressure anomalies due to the surface temperature difference. Their superposition limits the penetration of the cold breeze into the lead area. Without the horizontal entrainment, the near-surface temperature rises, reducing the average turbulent fluxes. In addition, the structures use the available kinetic energy to drive convective overturning. It also reduces the near-surface velocity and therefore fluxes. The maximum heat flux over open water was obtained for 2 km to 4 km leads. The maximum flux exceeds five-fold the flux in the homogeneous convection case. The revealed flux enhancement may have significant impact on the Arctic climate and more generally on the climate of urban areas and other heat islands. Therefore direct confirmation of the results from observational campaigns is urgently needed.

Esau, I. N.

2007-04-01

196

Experimental Study on Heat Transfer and Flow Characteristics of Air Cooling through Cross-flow Microchannel Heat Exchanger.  

E-print Network

??Air-side heat transfer and flow characteristics were studied through an air-to-deionized water cross-flow serpentine microchannel heat exchanger during air cooling. In the single phase, twenty… (more)

Dasgupta, Engr Sarbadaman

2011-01-01

197

Study of field ionization in the charge exchange injection for the IPNS upgrade  

SciTech Connect

The proposed I-MW neutron spallation source is a rapid-cycling synchrotron (RCS) with a design intensity of 1.04 {times} 10{sup 14} protons. A H- beam from the linac is injected into the synchrotron via the charge exchange process. Due to the high intensity of the beam, the minimization of beam loss is one of the primary concerns. In this paper, we study a possible beam loss associated with field ionization, which includes estimates of the charge fraction and level distribution of the excited hydrogen atoms after stripping, and an estimate of lifetime of the excited hydrogen atoms in the transverse magnetic field.

Chase, Yong-Chul, Cho, Yanglai

1995-07-01

198

Copper doping of silicate glasses by the ion-exchange technique: A photoluminescence spectroscopy study  

NASA Astrophysics Data System (ADS)

Copper-alkali ion exchange is used for doping superficial layers of different silicate glasses (commercial soda-lime and BK7) with copper ions. Spectroscopic and time-resolved photoluminescence properties of the obtained systems are studied in the range of 80-294 K. Analysis indicates the presence of Cu+ ions located in distorted octahedral sites, and a different position of the triplet electronic levels for the two glass matrices. The luminescence decay-time signal is simulated by a biexponential behavior, interpreted on the basis of a four-level scheme.

Borsella, E.; Dal Vecchio, A.; Garc?Ì?a, M. A.; Sada, C.; Gonella, F.; Polloni, R.; Quaranta, A.; van Wilderen, L. J. G. W.

2002-01-01

199

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

200

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

NASA Astrophysics Data System (ADS)

The Kuroshio edge exchange processes (KEEP) study is a multidisciplinary study on the internal cycling of material, especially carbon, within the East China Sea Shelf and the exchange of material between this Shelf and its adjoining Kuroshio. The project has been ongoing since 1989. The East China Sea Shelf is a net sink of atmospheric carbon dioxide. Rich supplies of nutrients, mostly from the upwelling of the Kuroshio Subsurface Water and, to a lesser extent, from the riverine discharges, notably from the Changjiang, sustain a high primary production (550 mg C m -2 d -1) on the Shelf and help the draw down of carbon dioxide. The sum of the demands for organic carbon for sustaining the observed bacterial production in the water column and the rate of sulfate reduction in the sediments of this Shelf appears to exceed its primary production. This suggests that a large fraction of the photosynthetically fixed carbon is recycled effectively within the Shelf. However, a comprehensive and definitive carbon budget for the Shelf cannot yet be constructed. Organic particles that survive oxidation within the Shelf and reach the Okinawa Trough are deposited in a belt along the upper northwestern slope of the Trough. A particle-rich mid-depth layer and the very high fluxes of sinking particles off the shelf break northeast of Taiwan suggest active cross shelf transport of particles from the Shelf to the Okinawa Trough. The cyclonic eddy at the shelf edge northeast of Taiwan is an important pathway for the exchange of dissolved and particulate materials between the Shelf and the Kuroshio. Nitrogen fixation may be a significant contributor of combined nitrogen to the oligotrophic Kuroshio Surface Water and the Taiwan Strait Warm Water so that it may support up to 25% of the new production in the Kuroshio Surface Water.

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

2000-03-01

201

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

E-print Network

glycosylation quanitification (chapter 4) and deamidation (chapter 5) was characterized in antibodies in solution. LC/ESI-MS was the method of choice for all studies. Hydrogen/deuterium exchange study showed that the method can be used to obtain region specific...

Sinha, Sandipan

2008-06-16

202

Multiple modeling in the study of interaction of hemodynamics and gas exchange  

Microsoft Academic Search

Circulation plays an important rule in gas exchange. Therefore, there is an interaction between circulation and gas exchange. To understand the dynamic effect of these two physiological systems, a computer simulation model of hemodynamics and gas exchange is established in this work. This model includes two physiological systems, namely the respiratory and circulatory systems. It consists of five parts: the

Anqi Qiu; Jing Bai

2001-01-01

203

A 1H n.m.r. study of isotope exchange catalysed by glycolytic enzymes in the human erythrocyte.  

PubMed Central

The exchange of hydrogen and deuterium atoms between the C-2 position of lactate and solvent was monitored in suspensions of human erythrocytes by using a non-invasive spin-echo p.m.r. method that permits continuous assessment of the rate and the extent of exchange. Exchange rates were measured in cells suspended in buffers made in 2H2O and 1H2O after the addition of L-[2-1H]lactate and L-[2-2H]lactate respectively. The rate of exchange is dependent on the activities of four glycolytic enzymes (fructose bisphosphate aldolase, triose phosphate isomerase, glyceraldehyde phosphate dehydrogenase and lactate dehydrogenase) and on the concentrations of their substrates. The dependence of the exchange on the following substrates was studied: (1) lactate, (2) the triose phosphates and fructose 1,6-bisphosphate and (3) pyruvate. Observation of the exchange in vitro, in a system produced by mixing the isolated enzymes, permits determination of the individual isotope-exchange equilibrium velocities of the enzymes. The dependence of the equilibrium velocity of human erythrocyte lactate dehydrogenase on NAD+ + NADH concentration was measured. Possible applications of these methods are discussed. PMID:7092833

Brindle, K M; Brown, F F; Campbell, I D; Foxall, D L; Simpson, R J

1982-01-01

204

Simulation of the CLAS12 dual hydrogen-deuterium target  

NASA Astrophysics Data System (ADS)

The primary mission of Jefferson Lab (Jlab) is to reveal the quark and gluon structure of nucleons and nuclei and to deepen our understanding of matter and quark confinement. This mission will be done using a 12-GeV electron beam incident on nuclear targets. One approved experiment E12-07-104 will measure the elastic scattering of electrons from deuterium to extract the neutron magnetic form factor (GM^n) using the CLAS12 detector. Calibrations will be done with a dual, co-linear target consisting of liquid hydrogen(LH2) and liquid deuterium (LD2) cells. The hydrogen target is used for calibration, and the deuterium one provides the data for the physics analysis. A CLAS12 simulation has been developed called gemc, where Geant4 is used to simulate the components of CLAS12. We have added the dual LH2-LD2 target to the gemc simulation. The targets parameters are stored in a mysql database and then read into the simulation at run time. Simulated particles start at a random point in the target volume and are propagated through the CLAS12 detector. We will present initial results showing the effect of target size and position on the distribution of hits in CLAS12.

Musalo, Christopher; Gilfoyle, Gerard

2011-10-01

205

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

206

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

SciTech Connect

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

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

1990-05-01

207

Exchange interaction in hexagonal MnRhP from first-principles studies  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

208

A study of silver-film ion-exchanged glass waveguides in phosphate glass  

NASA Astrophysics Data System (ADS)

In this work, properties of Ag thin-film ion exchange in Schott IOG-1 phosphate glass has been studied. Emphasis has been put on finding the proper diffusion parameters (self-diffusion coefficient for Ag + ions and the mobility ratio between the participating ions) at process temperatures of 90°C and 230°C. In order to extract the diffusion parameters a following procedure was utilized: An ion-exchanged slab waveguide was fabricated using the same process conditions as in the case of a two-dimensional waveguide fabrication. After slab waveguide fabrication, the effective refractive indices of the propagating modes were measured by prism coupling. Thereafter, a smooth refractive index profile was constructed by improved inverse Wentzel-Kramers-Brillouin method. This refractive index profile was compared with the Ag + ion concentration profile calculated from the diffusion equation by Crank-Nicolson method. The self-diffusion coefficient for Ag + ions and the ratio of the self-diffusion coefficients of Ag + and Na + ions were varied until convergence between the refractive index profile and the concentration profile was found. Using the diffusion parameters obtained from these experiments, two-dimensional waveguide mode profiles were calculated by finite difference method. These theoretically obtained mode profiles were compared with the measured mode profiles with different mask opening widths.

Yliniemi, Sanna; Albert, Jacques; Honkanen, Seppo

2007-02-01

209

Exchange interaction in hexagonal MnRhP from first-principles studies  

SciTech Connect

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

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

2014-05-07

210

A study of entropy rise across supersonic pressure exchange enhancing rotors  

NASA Astrophysics Data System (ADS)

Pressure exchange can be envisioned as a process where work is done by a fluid with high kinetic energy on another fluid with relatively low kinetic energy by utilizing the non-steady pressure forces at the fluid-fluid interface in the laboratory frame of reference. A novel supersonic ejector based on this process was conceptualized and offers non-dissipative flow induction, improved efficiency and environmental benefits. Entropy production in such devices holds the key to any efficiency improvements and therefore, entropy generation from flow structures such as oblique shocks under supersonic flow conditions was studied using schlieren photography. Oblique shocks emanating from the apexes of three cone-vane type of rotors (Truncated Ramp Vane, Ramp Vane and Double cone type) of different semi-cone vertex angles (20 deg., 10 deg., 25 deg. respectively), designed to produce pressure exchange were captured for upstream mach numbers (M=1.5, 1.75, 2) in air. Entropy rise across the oblique shocks was estimated from shock angle measurements and compared to a theoretical entropy rise. Analysis revealed that Double Cone Rotor produced three orders of magnitude higher entropy rise than the Ramp Vane Rotor. Furthermore, an increase in entropy rise (approximately 0.5 orders of magnitude) due a small angle of attack (2.5 deg.) was observed in the Ramp Vane Rotor.

Bulusu, Kartik; Garris, Charles

2010-11-01

211

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 BaseVised Manuscript ReceiVed: October 15, 2010 We have studied base strengths of nitrogen-substituted (nitrided in zeolites.8 A variety of studies have demonstrated the use of nitrogen-substituted zeolites as base

Auerbach, Scott M.

212

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

E-print Network

#12;been conducted to analyze the exchanger experimentally (Bose and Parker 1983; Bose et al. 1980, 1982). An analytical study of such heat exchangers, which uses a detailed mathematical model at the test site (Figure 1). The system was tested for seasonal performance over one cooling and one heating

Oak Ridge National Laboratory

213

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

PubMed

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

Wang, P; Wang, X G

2013-07-26

214

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

NASA Astrophysics Data System (ADS)

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 flowlengths and the boundary layers of the ambient air may be developing for a significant portion of the flowlength. These unique requirements of heat exchangers prompted an experimental study of compact heat exchangers made with relatively short rectangular fins that formed rectangular ducts. Compact heat exchangers made with rectangular fins were experimentally tested to determine the pressure drop of the air across the heat exchanger and the heat transfer to the air; the experiments were performed with air at Reynolds numbers between 100 and 1000. By placing the experimental apparatus in a chamber that was partially evacuated, experiments were also performed with air at a Reynolds number of approximately 250 at simulated elevated altitudes up to 83,000 feet. The results of the experiments performed at sea level and elevated altitudes compared very well. The results of the experiments that measured the pressure drop of the air determined the additional pressure drop caused by the developing boundary layers. An equation obtained from the data of the pressure drop measurements predicted the entrance length of the developing boundary layers. The Nusselt number of the air was calculated from the data of the heat transfer experiments. The Nusselt number significantly increased of the experiments performed with the boundary layers of the air developing for a significant portion of the rectangular duct. An equation was obtained that predicted the Nusselt number for compact heat exchangers with short flowlengths and with air at low Reynolds numbers. The equation that predicted the Nusselt number and the pressure drop data were used to design heat exchangers to operate at high altitudes.

Mathias, James Allen

215

SPURT: Studies of Stratosphere Troposphere Exchange based on a new concept for atmospheric measurement campaigns.  

NASA Astrophysics Data System (ADS)

SPURT (Spurenstofftransport in der Tropopausenregion) is a project in the German Atmospheric Research Programme AFO 2000. The aim of SPURT is to investigate stratosphere troposphere exchange based on airborne observations of trace gas distributions in the tropopause region. The platform used is a Learjet 35a modified for the use as a research aircraft and capable of flying at altitudes up to 14 km. The species measured include age tracers and long lived source gases, carbon monoxide , total reactive nitrogen, nitrogen oxide, ozone and water vapour, which are all measured with high precision and resolution. The measurement strategy is based on a new concept: we perform regular measurements campaigns, e.g. 4 times per year, each probing the UT/LS region above western Europe from high latitudes (north of 70°N) to subtropical latitudes (28° N). Rapid integration of the instruments enables to keep a single campaign period as short as 4-6 days. In summary, the SPURT strategy provides very frequent and flexible operations, with regard to time and observational area, employing sophisticated research payloads. Thus, climatological and process studies in regions of the atmosphere such as the UT/LS which can not be probed with sufficient resolution by satellites and other airborne programmes, become possible in a very cost effective way. The measurements are supported by meteorological forecasts and analysis and in addition the project includes a theoretical component involving several models. Selected results based on the first 6 SPURT campaigns will be presented. They include the investigation of the short-term, seasonal and latitudinal variability of the composition of the UT/LS and of the efficiency of exchange and mixing processes between the stratosphere and the troposphere. For future programmes, the SPURT concept could be consequently extended using modified payloads, e.g. by integrating instruments for studies on chemistry, aerosols and/or turbulence and mixing.

Engel, A.; Brunner, D.; Fischer, H.; Schiller, C.; Wirth, V.; Wernli, H.; Schmidt, U.

2003-04-01

216

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

NASA Astrophysics Data System (ADS)

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

Watanabe, Tsubasa; Hara, Susumu; Otsuki, Masatsugu

2014-12-01

217

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

218

An electrochemical quartz crystal microbalance study of a prospective alkaline anion exchange membrane material for fuel cells: anion exchange dynamics and membrane swelling.  

PubMed

A strategy has been devised to study the incorporation and exchange of anions in a candidate alkaline anion exchange membrane (AAEM) material for alkaline fuel cells using the electrochemical quartz crystal microbalance (EQCM) technique. It involves the electro-oxidation of methanol (CH3OH) under alkaline conditions to generate carbonate (CO3(2-)) and formate (HCOO(-)) ions at the electrode of a quartz crystal resonator coated with an AAEM film, while simultaneously monitoring changes in the frequency (?f) and the motional resistance (?R(m)) of the resonator. A decrease in ?f, indicating an apparent mass increase in the film, and a decrease in ?R(m), signifying a deswelling of the film, were observed during methanol oxidation. A series of additional QCM experiments, in which the effects of CH3OH, CO3(2-), and HCOO(-) were individually examined by changing the solution concentration of these species, confirmed the changes to be due to the incorporation of electrogenerated CO3(2-)/HCOO(-) into the film. Furthermore, the AAEM films were found to have finite anion uptake, validating the expected tolerance of the material to salt precipitation in the AAEM. The EQCM results obtained indicated that HCOO(-) and CO3(2-), in particular, interact strongly with the AAEM film and readily displace OH(-) from the film. Notwithstanding, the anion exchange between CO3(2-)/HCOO(-) and OH(-) was found to be reversible. It is also inferred that the film exhibits increased swelling in the OH(-) form versus the CO3(2-)/HCOO(-) form. Acoustic impedance analysis of the AAEM-film coated quartz resonators immersed in water showed that the hydrated AAEM material exhibits significant viscoelastic effects due to solvent plasticization. PMID:24588487

John, Jimmy; Hugar, Kristina M; Rivera-Meléndez, Johary; Kostalik, Henry A; Rus, Eric D; Wang, Hongsen; Coates, Geoffrey W; Abruña, Héctor D

2014-04-01

219

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

Microsoft Academic Search

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

Severin Hornung; Jürgen Glaser

2010-01-01

220

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

221

Density functional studies on Lewis acidity of alkaline earth metal exchanged faujasite zeolite  

Microsoft Academic Search

Lewis acidity of alkaline earth metal exchanged faujasite zeolite is investigated using density functional based reactivity descriptors with a 6T ring cluster which represents active site of the zeolite. We calculated global reactivity descriptors such as chemical hardness, chemical softness, electrophilicity index of the optimised cluster and local reactivity descriptors namely fukui function and relative electrophilicity of the exchanged cations

P. Mondal; K. K. Hazarika; A. Deka; R. C. Deka

2008-01-01

222

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

223

Kinetic and Mechanistic Studies of the Deuterium Exchange in Classical Keto-Enol Tautomeric Equilibrium Reactions  

ERIC Educational Resources Information Center

An extension of the classic keto-enol tautomerization of beta-dicarbonyl compounds into a kinetic analysis of deuterium exchange is presented. It is shown that acetylacetone and ethyl acetoacetate undergo nearly complete deuterium exchange of the alpha-methylene carbon when dissolved in methanol-d[subscript 4]. The extent of deuteration may be…

Nichols, Michael A.; Waner, Mark J.

2010-01-01

224

OSU Exchange and Departmental Study Abroad Program Coordinators Updated 2/11/14 TH  

E-print Network

,Copenhagen(TechnicalUniversityof DenmarkDTU) EXCHANGE CaineFrancis CollegeofEngineering,7377008,Caine.Francis@oregonstate.edu ITALY.Warnes@oregonstate.edu TAIWAN,Taipei(FuJenCatholicUniversity) LeslieRichards HumanDevelopment&FamilySciences,7371071, Leslie.Richards@oregonstate.edu TAIWAN,Taipei(NationalTaiwanUniversity) EXCHANGE TeppeiHayashi CaineFrancis International

Escher, Christine

225

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

226

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

227

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

228

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; Sørensen, Eva; Bracewell, Daniel G

2013-01-01

229

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

230

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

231

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

PubMed Central

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. PMID:23444051

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

2013-01-01

232

Organic matter exchange and cycling in mangrove ecosystems: Recent insights from stable isotope studies  

NASA Astrophysics Data System (ADS)

Mangrove ecosystems are highly productive tropical coastal ecosystems which have a potentially high impact on the carbon budget of the tropical and global coastal zone. The carbon dynamics in mangrove ecosystems has been the subject of numerous studies during the past decades, but we are still far from having an integrated view of the overall ecosystem functioning in terms of organic matter processing. The application of recent analytical techniques has produced a wealth of new information but has also indicated the gaps in our knowledge on organic matter cycling in these ecosystems. This paper provides an overview of our current understanding of organic matter dynamics in mangrove ecosystems, and reviews data based on stable isotope analyses, on (i) the delineation of carbon sources in different organic matter pools, (ii) utilization patterns of organic carbon by microbial and faunal communities, and (iii) organic matter exchange between mangroves and adjacent ecosystems. Although the use of stable isotopes has a number of limitations and has not always been able to unambiguously assess source contributions, it has been invaluable in refuting some long-standing paradwigms, and has shown that source characterization is crucial in order to better estimate organic matter budgets in these dynamic ecosystems. Future studies on process rates or flux measurements should therefore ideally be combined with a variety of chemical tracers to determine the source of the organic matter considered.

Bouillon, S.; Connolly, R. M.; Lee, S. Y.

2008-02-01

233

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

234

Equilibrium and kinetic ion exchange studies of Pb 2+, Cr 3+, Fe 3+ and Cu 2+ on natural clinoptilolite  

Microsoft Academic Search

In the present study ion exchange of Pb2+, Cu2+, Fe3+ and Cr3+ on natural clinoptilolite is examined at 27±1°C and initial concentration of 10meq\\/dm3. Equilibrium is favorable for Pb2+, unfavorable for Cu2+ and sigmoid for Cr3+ and Fe3+. Selectivity series deduced from equilibrium isotherms is Pb2+>Cr3+>Fe3+>Cu2+, while when maximum exchange levels (MELs) are considered, selectivity series is Pb2+>Cr3+?Cu2+?Fe3+. Cu2+ manifests

V. J. Inglezakis; M. D. Loizidou; H. P. Grigoropoulou

2002-01-01

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

2015-01-01

236

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

237

Use of Water Purified by Synthetic Resin Ion-Exchange Methods for the Study of Mineral Deficiencies in Plants  

Microsoft Academic Search

AN adequate supply of highly purified water is an essential requirement for the study of plant nutrition problems, particularly those relating to mineral deficiencies, when experiments are carried out on a large scale. Liebig, Vanselow and Chapman1 in California found that tap water purified by the synthetic resin ion-exchange principle was satisfactory for maintaining healthy growth in citrus and sweet

Eric J. Hewitt

1946-01-01

238

Experimental study of hydraulic and thermal behavior of an ice slurry in a shell and tube heat exchanger  

Microsoft Academic Search

Experiments were conducted in a shell and tube heat exchanger with an ethylene glycol ice slurry flowing in the tubes and hot water in the shell. Pressure loss in the tubes, inlet and outlet density for the ice slurry, in addition to inlet temperature, outlet temperature and mass flowrate for both fluids were measured. A transient study with a slurry

Simone Renaud-Boivin; Michel Poirier; Nicolas Galanis

239

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

240

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

241

ANION EXCHANGE METHOD FOR THE DETERMINATION OF PLUTONIUM IN WATER: SINGLE-LABORATORY EVALUATION AND INTERLABORATORY COLLABORATIVE STUDY  

EPA Science Inventory

This report gives the results of a single-laboratory evaluation and an interlaboratory collaborative study of a method for determining plutonium in water. The method was written for the analysis of 1-liter samples and involved coprecipitation, acid dissolution, anion exchange, el...

242

Orientation and Electronic Structure of Ion Exchanged Dye Molecules on Mica: An X-Ray Absorption Study  

Microsoft Academic Search

Dye molecules are frequently used to determine the specific surface area and the ion exchange capacity of high-surface-area materials such as mica. The organic molecules are often considered to be planar and to adsorb in a flat orientation. In the present study we have investigated the orientation and electronic structure of crystal violet (CV) and malachite green (MG) on muscovite

Dorothee Fischer; Walter R. Caseri; Georg Hähner

1998-01-01

243

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

SciTech Connect

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

Ueno, Y.; Okamura, T. [Tokyo Institute of Technology, Yokohama, Kanagawa, 226-8502 (Japan); Sato, A. [National Institute for Materials Science, Tsukuba, Ibaraki, 305-0047 (Japan)

2004-06-23

244

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

PubMed

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

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

2003-05-01

245

Empirical Study of Relations between Stock Returns and Exchange Rate Fluctuations in China  

NASA Astrophysics Data System (ADS)

The existing theories tell us that there exist interaction relations between stock prices and exchange rates. However, empirical research results don’t always support these theories. This paper uses quantile regression techniques to check whether the above theories hold in Chinese markets. We first eliminate the impact of the calendar effect and the time trends on stock market returns and exchange rate fluctuations using Gallant, Rossi, and Tachen’s method (1992) by combination with stepwise regression method, and then do quantile regression analysis according to the adjusted data. The empirical results are summarized as follows: the influences of exchange rate fluctuations to stock returns are negative at most quantiles of stock returns; the opposite influences are not significant at most quantiles of exchange rate fluctuations. Some explanations according to these results are given.

Chen, Jian-Bao; Wang, Deng-Ling; Cheng, Ting-Ting

246

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

E-print Network

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

Tracy, Joseph B. (Joseph Benjamin)

2005-01-01

247

Deep-Sea Research I 54 (2007) 269291 Experimental studies of rotating exchange flow  

E-print Network

limiting important heat and salt exchanges which in turn influence the global thermohaline circulation that in the ARTICLE IN PRESS www.elsevier.com/locate/dsri 0967-0637/$ - see front matter r 2006 Elsevier Ltd. All

Dalziel, Stuart

248

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

249

Simulating Forest Productivity and Surface-Atmosphere Carbon Exchange in the Boreas Study Region  

Microsoft Academic Search

Summary A process-based, general ecosystem model (BI- OME--BGC) was used to simulate daily gross primary produc- tion, maintenance and heterotrophic respiration, net primary production and net ecosystem carbon exchange of boreal as- pen, jack pine and black spruce stands. Model simulations of daily net carbon exchange of the ecosystem (NEE) explained 51.7% (SE = 1.32 g C m -2 day

JOHN S. KIMBALL; PETER E. THORNTON; MIKE A. WHITE; STEVEN W. RUNNING; H. A. Margolis; M. G. Ryan

1997-01-01

250

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

PubMed

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

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

2010-03-01

251

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

252

Thermogravimetric study of n -alkylammonium-intercalated montmorillonites of different cation exchange capacity  

Microsoft Academic Search

Three n-alkylammonium salts of varying alkyl chain length were ion exchanged with montmorillonites (MMT) of different cation exchange\\u000a capacity (CEC). The intercalated MMTs were characterized by thermogravimetry (TG), XRD, FTIR to acquire an insight into the\\u000a intergallery structural arrangement of the organic alkylammonium cations (AAC). The increment in the intergallery spacing\\u000a from XRD pattern was correlated with chain length and

Kausik Dana; Sankar Ghatak

2010-01-01

253

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

NASA Astrophysics Data System (ADS)

Accurate studies of low-energy charge exchange (CX) are critical to understanding underlying soft X-ray radiation processes in the interaction of highly charged ions from the solar wind with the neutral atoms and molecules in the heliosphere, cometary comas, planetary atmospheres, interstellar winds, etc.. Particularly important are the CX cross sections for bare, H-like, and He-like ions of C, N, O and Ne, which are the dominant charge states for these heavier elements in the solar wind. Absolute total cross sections for single electron capture by H-like ions of C, N, O and fully-stripped O ions from atomic hydrogen have been measured in an expanded range of relative collision energies (5 eV/u-20 keV/u) and compared to previous H-oven measurements. The present measurements are performed using a merged-beams technique with intense highly charged ion beams extracted from a 14.5 GHz ECR ion source installed on a high voltage platform at the Oak Ridge National Laboratory. For the collision energy range of 0.3 keV/u-3.3 keV/u, which corresponds to typical ion velocities in the solar wind, the new measurements are in good agreement with previous H-oven measurements. The experimental results are discussed in detail and compared with theoretical calculations where available.

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

2011-06-01

254

Experimental device and methods for studying milk deposit formation on heat exchange surfaces.  

PubMed

An experimental mini-heat-exchanger was developed in our laboratory.It can be inserted between the heating and holding sections of a pilot milk pasteurizer without modifying its temperature gradient. Representative soil samples from both heating and holding sections were obtained. Changes in soil composition according to running time were studied over a range of 1 min to 4 hours. Previously cleaned 0.4 mm thick stainless steel plates (304L) had to be cut into pieces before analysis. Different kinds of results were obtained. Scanning electron microscopy showed that the deposit was composed of two different types of soil. A dense deposit could be observed near the metal surface after only 1 min of treatment; the thickness of this deposit increased to 15 mum during the process. Over this layer, a spongy deposit only slightly bound to the former, could be observed Lightly fouled plates were analyzed by "in situ techniques" (X.P.S.)Thick deposits were embedded and sectioned for transmission electron microscopy and histochemical analyses.A microanalytical method was applied to deposits after removal and resulted in detection ranges exceeding 10 mg/cm(2). PMID:20568220

Tissier, J P; Lalande, M

1986-12-01

255

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

256

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

257

In Situ X-ray Diffraction Study of Cesium Exchange in Synthetic Umbite  

SciTech Connect

The exchange of Cs{sup +} into H{sub 1.22}K{sub 0.84}ZrSi{sub 3}O{sub 9} {center_dot} 2.16H{sub 2}O (umbite-(HK)) was followed in situ using time-resolved X-ray diffraction at the National Synchrotron Light Source. The umbite framework (space group P2{sub 1}/c with cell dimensions of a = 7.2814(3) {angstrom}, b = 10.4201(4) {angstrom}, c = 13.4529(7) {angstrom}, and {beta} = 90.53(1){sup o}) consists of wollastonite-like silicate chains linked by isolated zirconia octahedra. Within umbite-(HK) there are two unique ion exchange sites in the tunnels running parallel to the a-axis. Exchange Site 1 is marked by 8 member-ring (MR) windows in the bc-plane and contains K{sup +} cations. Exchange Site 2 is marked by a larger 8-MR channel parallel to [100], and contains H{sub 2}O molecules. The occupancy of the Cs{sup +} cations through these channels was modeled by Rietveld structure refinements of the diffraction data and demonstrated that there is a two-step exchange process. The incoming Cs{sup +} ions populated the larger 8-MR channel (Exchange Site 2) first and then migrated into the smaller 8-MR channel. During the exchange process a structural change occurs, transforming the exchanger from monoclinic P2{sub 1}/c to orthorhombic P2{sub 1}2{sub 1}2{sub 1}. This structural change occurs when Cs{sup +} occupancy in the small cavity becomes greater than 0.50. The final in situ ion exchange diffraction pattern was refined to yield umbite-(CsK) with the molecular formula H{sub 0.18}K{sub 0.45}Cs{sub 1.37}ZrSi{sub 3}O{sub 9} {center_dot} 0.98H{sub 2}O and possessing an orthorhombic unit cell with dimensions a = 10.6668(8) {angstrom}, b = 13.5821(11) {angstrom}, c = 7.3946(6) {angstrom}. Solid state {sup 133}Cs MAS NMR showed there is only a slight difference between the two cavities electronically. Valence bond sums for the completely occupied Exchange Site 1 demonstrate that Cs-O bonds of up to 3.8 {angstrom} contribute to the coordination of the Cs{sup +} cation.

C Fewox; A Clearfield; A Celestian

2011-12-31

258

Accessibility changes within diphtheria toxin T domain upon membrane penetration probed by hydrogen exchange and mass spectrometry.  

PubMed

The translocation domain of diphtheria toxin inserts in membrane and becomes functional when the pH inside endosomes is acid. At that stage, the domain is in a partially folded state; this prevents the use of high-resolution methods for the characterization of its functional structure. On that purpose, we report here the use of hydrogen/deuterium exchange experiments coupled to mass spectrometry. The conformation changes during the different steps of insertion into lipid bilayer are monitored with a resolution of few residues. Three parts of the translocation domain can be distinguished. With a high protection against exchange, the C-terminal hydrophobic helical hairpin is embedded in the membrane. Despite a lower protection, a significant effect in the presence of lipid vesicles shows that the N-terminal part is in interaction with the membrane interface. The sensitivity to the ionic strength indicates that electrostatic interactions are important for the binding. The middle part of the domain has an intermediate protection; this suggests that this part of the domain can be embedded within the membrane but remains quite dynamic. These results provide unprecedented insight into the structure reorganization of the protein to go from a soluble state to a membrane-inserted one. PMID:21986198

Man, Petr; Montagner, Caroline; Vitrac, Heidi; Kavan, Daniel; Pichard, Sylvain; Gillet, Daniel; Forest, Eric; Forge, Vincent

2011-11-18

259

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

E-print Network

TASSEP -Interested in an exchange study visit to North America? College, through the School-established consortium arranges exchange study periods between students attending member Universities in North America of Chemistry have carried out their Senior Sophister research projects (3 ­ 4 months) in North America under

O'Mahony, Donal E.

260

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

E-print Network

Thermal Rates of Hydrogen Exchange of Methane with Zeolite: A Direct ab Initio Dynamics Study ab initio dynamics study on the kinetics of the hydrogen exchange of methane with a zeolite model, particularly tunneling, were found to be significant even at the room temperature. Zeolites are important

Truong, Thanh N.

261

Plasma-exchange treatment for severe carbamazepine intoxication: a case study.  

PubMed

Acute poisoning is an important cause of morbidity and mortality during childhood. This manuscript reports the positive outcome of a pediatric case with a history of accidental carbamazepine intake treated using plasma exchange. A 3-year-old male presented with severe carbamazepine intoxication. He was comatose and had generalized tonic clonic seizure, ventricular tachycardia, and hypotension. Although he did not respond to classical therapies, we performed two sessions of plasma exchange. The patient recovered rapidly and was discharged from the hospital six days from the time of carbamazepine ingestion with no complication or neurologic impairment. Plasma exchange can be performed safely in very small children, and it might be the first line treatment, particularly for intoxication with drugs that have high plasma-protein-binding properties. PMID:24136443

Kozanoglu, Ilknur; Kahveci, Suat; Asma, Suheyl; Yeral, Mahmut; Noyan, Aytul; Boga, Can; Ozdogu, Hakan

2014-06-01

262

Studies of the reactivity of the ferrihydrite surface by iron isotopic exchange and Mossbauer spectroscopy  

USGS Publications Warehouse

A combination of chemical and spectroscopic techniques were employed to gain further insight into the structural nature of sites at the ferrihydrite surface. The kinetics of iron isotopic exchange demonstrated that there are at least two types of iron sites in ferrihydrite. One population of sites, referred to as labile sites, approached iron isotopic equilibrium within 24 hr in 59Fe-NTA solutions, while the second population of sites, referred to as non-labile, exhibited a much slower rate of isotopic exchange. Labile sites are more reactive (with respect to iron isotopic exchange) because they have fewer neighboring Fe octahedra and are therefore bound less strongly to the ferrihydrite structure. The labile population of sites probably is composed of end sites of the dioctahedral chain structure of 2-line ferrihydrite, which is a subset of the entire population population of surface sites. -from Authors

Rea, B.A.; Davis, J.A.; Waychunas, G.A.

1994-01-01

263

Numerical studies on flow and heat transfer in membrane helical-coil heat exchanger and membrane serpentine-tube heat exchanger  

Microsoft Academic Search

The flow and heat transfer characteristics of synthesis gas (syngas) in membrane helical-coil heat exchanger and membrane serpentine-tube heat exchanger under different operating pressures, inlet velocities and pitches are investigated numerically. The three-dimensional governing equations for mass, momentum and heat transfer are solved using a control volume finite difference method. The realizable k-? model is adopted to simulate the turbulent

Zhenxing Zhao; Xiangyu Wang; Defu Che; Zidong Cao

2011-01-01

264

Simple setup for gas-phase h/d exchange mass spectrometry coupled to electron transfer dissociation and ion mobility for analysis of polypeptide structure on a liquid chromatographic time scale.  

PubMed

Gas-phase hydrogen/deuterium exchange (HDX) is a fast and sensitive, yet unharnessed analytical approach for providing information on the structural properties of biomolecules, in a complementary manner to mass analysis. Here, we describe a simple setup for ND3-mediated millisecond gas-phase HDX inside a mass spectrometer immediately after ESI (gas-phase HDX-MS) and show utility for studying the primary and higher-order structure of peptides and proteins. HDX was achieved by passing N2-gas through a container filled with aqueous deuterated ammonia reagent (ND3/D2O) and admitting the saturated gas immediately upstream or downstream of the primary skimmer cone. The approach was implemented on three commercially available mass spectrometers and required no or minor fully reversible reconfiguration of gas-inlets of the ion source. Results from gas-phase HDX-MS of peptides using the aqueous ND3/D2O as HDX reagent indicate that labeling is facilitated exclusively through gaseous ND3, yielding similar results to the infusion of purified ND3-gas, while circumventing the complications associated with the use of hazardous purified gases. Comparison of the solution-phase- and gas-phase deuterium uptake of Leu-Enkephalin and Glu-Fibrinopeptide B, confirmed that this gas-phase HDX-MS approach allows for labeling of sites (heteroatom-bound non-amide hydrogens located on side-chains, N-terminus and C-terminus) not accessed by classical solution-phase HDX-MS. The simple setup is compatible with liquid chromatography and a chip-based automated nanoESI interface, allowing for online gas-phase HDX-MS analysis of peptides and proteins separated on a liquid chromatographic time scale at increased throughput. Furthermore, online gas-phase HDX-MS could be performed in tandem with ion mobility separation or electron transfer dissociation, thus enabling multiple orthogonal analyses of the structural properties of peptides and proteins in a single automated LC-MS workflow. PMID:25375223

Mistarz, Ulrik H; Brown, Jeffery M; Haselmann, Kim F; Rand, Kasper D

2014-12-01

265

Cerebral autoregulation and gas exchange studied using a human cardiopulmonary model  

E-print Network

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

266

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

267

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

E-print Network

's suggested using the hydrophobe catalysts. The catalyses of type platinum or palladium on the coal, silicagel for recovery tritium Anisia Bornea, Ion Cristescu, Marius Zamfirache, Carmen Varlam National Institute of R processes for tritium separation, is the catalyst isotope exchange water-hydrogen. The main problem

268

Feasibility and design studies for heat recovery from a refrigeration system with a canopus heat exchanger  

Microsoft Academic Search

This paper presents an investigation of the feasibility of heat recovery from the condenser of a vapour compression refrigeration (VCR) system through a Canopus heat exchanger (CHE) between the compressor and condenser components. The presence of the CHE makes it possible to recover the superheat of the discharged vapour and utilize it for increasing the temperature of the external fluid

S. C. Kaushik; M. Singh

1995-01-01

269

Study on metallic bipolar plate for proton exchange membrane fuel cell  

Microsoft Academic Search

Cost reduction is the most critical issue for ensuring the practical use of proton exchange membrane fuel cells (PEMFC). In current designs, the bipolar plate is the most expensive part in the repeating-parts of the PEMFC. To address this issue, bipolar plates made of several kinds of materials are being developed by various companies. Above all, a metallic bipolar plate

Toyoaki Matsuura; Megumi Kato; Michio Hori

2006-01-01

270

Study of multi-electron ionization and charge exchange in HIBF  

Microsoft Academic Search

Beam ion stripping on background gases or plasma in a Heavy Ion Beam Fusion (HIBF) chamber increases the charge state of the beam and the diameter of the focus, complicating the final focusing on the focusing target. To model beam transport in the chamber, it is necessary to know the beam charge-state evolution, including both ionization and charge exchange dynamics.

Linchun Wu

2007-01-01

271

RESIDENTIAL AIR EXCHANGE RATES FOR USE IN INDOOR AIR AND EXPOSURE MODELING STUDIES  

EPA Science Inventory

Data on air exchange rates are important inputs to indoor air quality models. ndoor air models, in turn, are incorporated into the structure of total human exposure models. ragmentary data on residential ventilation rates are available in various governmental reports, journal art...

272

Charge Exchange Studies for Solar System X-ray Emission Modeling  

NASA Astrophysics Data System (ADS)

As most of the gas in the Universe is not in thermal equilibrium, accurate modeling and interpretation of observations requires understanding of a variety of collisional processes. When ions and neutrals are present, charge exchange is one such process. While it can be important for the ionization balance, it can also affect ion emission spectra, such as in the case of the solar wind charge exchange (SWCX) mechanism. While charge exchange cross sections can be measured and/or calculated, the enhancements in the spectral line resolution and sensitivity from current X-ray observatories (Chandra, XMM-Newton, Suzaku), and planned missions (e.g., IXO and Astro-H) place severe demands on the collisional data. As a consequence, the construction of reliable charge exchange datasets for atmospheric and astrophysical modeling faces a number of challenges: i) Due to the quantity of required data at the quantum-state-resolved level, theory must provide the bulk of the results with experiment serving as benchmarks. ii) The accuracy of the scattering calculations is directly dependent on the reliability and availability of the quantum structure/chemical data. iii) Database construction requires consistent and appropriate funding which is typically lacking. We review these issues in the context of our on-going collaborative work on charge exchange calculations and measurements for SWCX modeling. Cross sections, diagnostic line ratios, and x-ray yields will be presented for collisions of C^5+, N^6+, O^6+, O^7+ with H and their role in X-ray emission from Earth's geocorona, the exosphere of Mars, Jupiter, comets, the heliosphere, and astrospheres will be discussed. This work was partially supported by NASA grants NNX09AV46G, NNG09WF24I, and NNH07ZDA001N.

Wu, Yong; Nolte, J.; Stancil, P.; Schultz, D.; Hui, Y.; Lieberman, H.; Buenker, R.; Shelton, R.; Draganic, I.; Havener, C.

2011-05-01

273

Structure and thermodynamics of amylin dimer studied by Hamiltonian-temperature replica exchange molecular dynamics simulations.  

PubMed

The loss of the insulin-producing ?-cells in the pancreatic islets of Langerhans, responsible for type-II diabetes, is associated with islet amyloid deposits. The main component of these deposits is the amyloid fibrils formed by the 37-residue human islet amyloid polypeptide (hIAPP also known as amylin). Although the fibrils are well characterized by cross ? structure, the structure of the transient oligomers formed in the early stage of aggregation remains elusive. In this study, we apply the Hamiltonian-temperature replica exchange molecular dynamics to characterize the structure and thermodynamics of a full-length hIAPP dimer in both the presence and the absence of the Cys2-Cys7 disulfide bond. We compare these results with those obtained on the monomeric and dimeric forms of rat IAPP (rIAPP) with a disulfide bridge which differ from the hIAPP by 6 amino acids in the C-terminal region, but it is unable to form fibrils. Using a coarse-grained protein force field (OPEP-the Optimized Potential for Efficient peptide structure Prediction) running for a total of 10-28 ?s per system studied, we show that sequences sample ?-helical structure in the N-terminal region but that the length of this secondary element is shorter and less stable for the chains without the disulfide bridge (residues 5-16 for hIAPP with the bridge vs 10-16 for hIAPP without the bridge). This ?-helix is known to be an important transient stage in the formation of oligomers. In the C-terminal, the amyloidogenic region of hIAPP, ?-strands are seen for residues 17-26 and 30-35. On the contrary, no significant ?-sheet content in the C-terminal is observed for either the monomeric or the dimeric rIAPP. These numerical results are fully consistent with recent experimental findings that the N-terminal residues are not part of the fibril by forming ?-helical structure but rather play a significant role in stabilizing the amyloidogenic region available for the fibrillation. PMID:21384830

Laghaei, Rozita; Mousseau, Normand; Wei, Guanghong

2011-03-31

274

Use of amide exchange mass spectrometry to study conformational changes within the endopolygalacturonase II-homogalacturonan-polygalacturonase inhibiting protein system  

Microsoft Academic Search

Amide exchange mass spectrometry (MS) was used to study the enzyme endopolygalacturonase II (EPG-II) from Aspergillus niger as it binds to an oligosaccharide substrate. A localized decrease in the level of deuterium incorporation in EPG-II of the EPG-II-oligosaccharide complex relative to that of the free EPG-II identified the location of substrate contact, which is in agreement with published site specific

Daniel King; Carl Bergmann; Ron Orlando; Jacques A. E. Benen; Harry C. M. Kester; Jaap Visser

2002-01-01

275

The Effectiveness of the Picture Exchange Communication System (PECS) for Children with Autism Spectrum Disorder (ASD): A South African Pilot Study  

ERIC Educational Resources Information Center

This study investigated the effects of introducing the Picture Exchange Communication System (PECS) on the frequency of requesting and commenting and the length of verbal utterances of two children with autism spectrum disorder (ASD) who presented with some spoken language, but limited use of language in communicative exchanges. A mixed research…

Travis, Julia; Geiger, Martha

2010-01-01

276

Escherichia coli acetate kinase mechanism studied by net initial rate, equilibrium, and independent isotopic exchange kinetics.  

PubMed

The equilibrium constant of the reaction catalyzed by acetate kinase (E.C. 2.7.2.1.) was determined: K = (MgADP) (acetylphosphate)/(MgATP)(acetate) = 6.7 +/- 1.3 X 10 (-4) (pH 7.4, 25 degrees). The respective free nucleotides uncomplexed to magnesium inhibit the net reaction in both directions: competitively with the respective magnesium nucleotide (MgATP or MgADP) and noncompetitively with the co-substrate (acetate or acetylphosphate). Excess free magnesium also inhibits the net reaction in both directions. The inhibition is not competitive with the phosphoryl donor (MgATP or acetylphosphate) but is competitive with respect to the phosphoryl acceptor (acetate or MgADP). A 50-fold increase in concentration of reactants at equilibrium in 0.1 M Tris/HCl, pH 7.4, at 25 degrees resulted in a rise to plateau levels of the acetate equilibrium acetylphosphate exchange rate (measured with [U-14C]acetate) and of the ATP equilibrium ADP exchange rate (measured with [U-14C]ADP and 10-fold higher than acetate equilibrium acetylphosphate), suggesting that there is no compulsory order of binding of magnesium nucleotide and co-substrate and that all chemical transformation steps cannot be much slower than the dissociation steps. The ATP equilibrium ADP exchange rate was independent of the presence or concentration of co-substrate, whereas the acetate equilibrium acetylphosphate exchange reaction occurred only in the presence of magnesium nucleotide, and the rate was directly related to the degree of saturation of enzyme with magnesium nucleotide. The independent ATP equilibrium ADP exchange, which presumably involves a phosphoenzyme intermediate, was progressively inhibited by increasingly elevated MgADP concentrations (when MgADP/MgATP greater than or equal 5), but increasing MgATP/MgADP was not inhibitory, suggesting that MgADP may bind to nonphosphorylated as well as phosphorylated enzyme, but that MgATP cannot bind to phosphorylated enzyme. While direct transfer of the phosphoryl group between nucleotide and co-substrate in a concerted mechanism has not been ruled out, an "activated ping pong" mechanism can also be proposed which is compatible with the isotopic exchange and initial net rate kinetic results. This mechanism includes a phosphoenzyme intermediate and requires enzyme-bount MgADP for phosphorylation of the enzyme by acetylphosphate. PMID:185218

Skarstedt, M T; Silverstein, E

1976-11-10

277

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

278

An NMR and computational study of a lithium amide and ethereal ligand exchange  

PubMed

The activation parameters for the exchange of an ethereal ligand in a chiral lithium amide was determined from full bandshape analysis of the dynamic NMR spectra. For diethyl ether, the activation parameters were deltaH++=11.0 kcalmol(-1) and deltaS++=12.0 cal K(-1)mol(-1). The exchange of the tetrahydrofuran ligand proceeds with a similar activation enthalpy deltaH++=11.2 kcalmol(-1); however, the entropy is close to zero. deltaS++=1.6 cal K(-1)mol(-1). The dissociation of the ethereal ligand was also modeled by means of semiempirical (PM3) and density functional (DFT) methods. The experimental 13C NMR chemical shifts for the carbons of uncoordinated and coordinated ethers were calculated with the GIAO-DFT (B3PW91/6-31G(d)) computational method. PMID:10993268

Hilmersson

2000-08-18

279

A study of inclusive Doubleomeron-Exchange in at GeV  

Microsoft Academic Search

.   We report measurements of the inclusive reaction, , in events where either or both the beam-like final-state baryons were detected in Roman-pot spectrometers and the central\\u000a system was detected in the UA2 calorimeter. A Double-omeron-Exchange (DPE) analysis of these data and single diffractive data from the same experiment demonstrates that, for central\\u000a masses of a few GeV, the extracted

S. Erhan; A. Kuzucu; M. Medinnis; N. Ozdes; P. E. Schlein; J. Zsembery

2002-01-01

280

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

SciTech Connect

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

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

1999-06-01

281

Interaction of strontium and europium with an aquatic fulvic acid studied by ultrafiltration and ion exchange techniques  

NASA Astrophysics Data System (ADS)

The complexation of an aquatic fulvic acid, FA, with Sr2+ and Eu3+ was studied using an ultrafiltration technique and an ion exchange distribution method. The total amount of bound metal (Sr2+ and Eu3+) was measured as a function of pH at low metal concentrations (trace levels) and constant FA concentration. In the Sr-FA system the bound metal fraction increased slightly with pH, and the values obtained from the two experimental techniques were comparable. For Eu-FA, according to the ultrafiltration data, the fraction of bound metal ion was relatively insensitive to pH changes, whereas values from the ion exchange measurements showed a strong and positive dependence on pH. The results are discussed in the light of possible intrinsic problems of the two methods.

Nordén, Maria; Ephraim, James; Allard, Bert

282

Results from the US/USSR exchange for heat load material studies of simulated tokamak disruptions  

NASA Astrophysics Data System (ADS)

This paper presents recent results from exchange I.2 of the US/USSR Exchange Program of Cooperation for Magnetic Confinement Fusion. Previous results from this exchange demonstrated much lower than expected ablation of graphites when the graphites were exposed to disruption like heat fluxes delivered by plasma gun sources. This lower than expected ablation has been accounted for by the 'vapor shielding' effect. Vapor shielding occurs when material is ablated from the surface of the graphite target early in the plasma pulse. This ablated material then shields the surface of the target from the rest of the incoming plasma pulse. Vapor shielding has been inferred from diagnostics and ablation data at all participating laboratories, and clear evidence of the effect has been found by laser interferometry at Kurchatov (Troitsk) in the 2MK-200 machine. Recent results from Kurchatov on the 2MK-200 and MKT experiments continue to indicate that the erosion of graphite exposed to disruption like heat fluxes is much lower than expected. Work from the University of New Mexico on the PLAIDS experiment confirms earlier important work conducted on the VIKA experiment at Efremov. This is particularly interesting in that PLAIDS and VIA have very similar plasma pulse characteristics.

Gahl, J. M.; Crawford, J. F.; McDonald, J. M.; McGrath, R. T.; Zakharov, A.

283

IMPACT OF SMALL COLUMN ION EXCHANGE STREAMS ON DWPF GLASS FORMULATION MELT RATE STUDIES  

SciTech Connect

This study was undertaken to evaluate the potential impacts of the Small Column Ion Exchange (SCIX) streams - particularly the addition of Monosodium Titanate (MST) and Crystalline Silicotitanate (CST) - on the melt rate of simulated feed for the Defense Waste Processing Facility (DWPF). Additional MST was added to account for contributions from the Salt Waste Processing Facility (SWPF). The Savannah River National Laboratory (SRNL) Melt Rate Furnace (MRF) was used to evaluate four melter feed compositions: two with simulated SCIX and SWPF material and two without. The Slurry-fed Melt Rate Furnace (SMRF) was then used to compare two different feeds: one with and one without bounding concentrations of simulated SCIX and SWPF material. Analyses of the melter feed materials confirmed that they met their targeted compositions. Four feeds were tested in triplicate in the MRF. The linear melt rates were determined by using X-ray computed tomography to measure the height of the glass formed along the bottom of the beakers. The addition of the SCIX and SWPF material reduced the average measured melt rate by about 10% in MRF testing, although there was significant scatter in the data. Two feeds were tested in the SMRF. It was noted that the ground CST alone (ground CST with liquid in a bucket) was extremely difficult to resuspend during preparation of the feed with material from SCIX and SWPF. This feed was also more difficult to pump than the material without MST and CST due to settling occurring in the melter feed line, although the yield stress of both feeds was high relative to the DWPF design basis. Steady state feeding conditions were maintained for about five hours for each feed. There was a reduction in the feed and pour rates of approximately 15% when CST and MST were added to the feed, although there was significant scatter in the data. Analysis of samples collected from the SMRF pour stream showed that the composition of the glass changed as expected when MST and CST were added to the feed. These reductions in melt rate are consistent with previous studies that showed a negative impact of increased TiO{sub 2} concentrations on the rate of melting. The impact of agitating the melt pool via bubbling was not studied as part of this work, but may be of interest for further testing. It is recommended that additional melt rate testing be performed should a potential reduction in melt rate of 10-15% be considered an issue of concern, or should the anticipated composition of the glass with the addition of material from salt waste processing be modified significantly from the current projections, either due to changes in sludge batch preparation or changes in the composition or volume of SCIX and SWPF material.

Fox, K.; Miller, D.; Koopman, D.

2011-04-26

284

Theoretical and computational studies of renewable energy materials: Room temperature ionic liquids and proton exchange membranes  

NASA Astrophysics Data System (ADS)

Two kinds of renewable energy materials, room temperature ionic liquids (RTILs) and proton exchange membranes (PEMs), especially Nafion, are studied by computational and theoretical approaches. The ultimate purpose of the present research is to design novel materials to meet the future energy demands. To elucidate the effect of alkyl side chain length and anion on the structure and dynamics of the mixtures, molecular dynamics (MD) simulations of three RTILs/water mixtures at various water mole fractions: 1-butyl-3-methylimidazolium (BMIM+)/BF4-, 1-octyl-3-methylimidazolium (OMIM+)/BF4-, and OMIM +/Cl- are performed. Replacing the BMIM + cation with OMIM+ results in stronger aggregation of the cations as well as a slower diffusion of the anions, and replacing the BF4- anion with Cl- alters the water distribution at low water mole fractions and slows diffusion of the mixtures. Potential experimental manifestations of these behaviors in both cases are provided. Proton solvation properties and transport mechanisms are studied in hydrated Nafion, by using the self-consistent multistate empirical valence bond (SCI-MS-EVB) method. It is found that by stabilizing a more Zundel-like (H5O 2+) structure in the first solvation shells, the solvation of excess protons, as well as the proton hydration structure are both influenced by the sulfonate groups. Hydrate proton-related hydrogen bond networks are observed to be more stable than those with water alone. In order to characterize the nature of the proton transport (PT), diffusive motion, Arrhenius activation energies, and transport pathways are calculated and analyzed. Analysis of diffusive motion suggests that (1) a proton-hopping mechanism dominates the proton transport for the studied water loading levels and (2) there is an obvious degree of anti-correlation between the proton hopping and the vehicular transport. The activation energy drops rapidly with an increasing water content when the water loading level is smaller than ˜ 10 H2O/SO 3-, which is consistent with experimental observations. The sulfonate groups are also found to have influence on the proton hopping directions. The temperature and water content effects on the PT pathways are also investigated. The morphological effects on proton solvation and transport in hydrated Nafion are investigated, by using the SCI-MS-EVB method. Two of the most significant morphological models of Nafion, the lamellar model and the cylinder model, are selected. The two models exhibit distinct PT patterns, which result in different proton diffusion rates. In both models, the interaction between protons and the sulfonate groups are proven to be the key to determining PT behavior. The proton solvation structure change as a function of the distance between protons and sulfonate groups has been analyzed. It is found that the increase of water cylinder radius or water layer height leads to the presence of more protons around the sulfonate groups. Furthermore, at a lower hydration level, the increased amount of protons around the sulfonate groups consists of more Zundel-like structures, which is influenced by the distinct morphological structures of Nafion.

Feng, Shulu

2011-12-01

285

A Single Disulfide Bond Disruption in the ?3 Integrin Subunit Promotes Thiol/Disulfide Exchange, a Molecular Dynamics Study  

PubMed Central

The integrins are a family of membrane receptors that attach a cell to its surrounding and play a crucial function in cell signaling. The combination of internal and external stimuli alters a folded non-active state of these proteins to an extended active configuration. The ?3 subunit of the platelet ?IIb?3 integrin is made of well-structured domains rich in disulfide bonds. During the activation process some of the disulfides are re-shuffled by a mechanism requiring partial reduction of some of these bonds; any disruption in this mechanism can lead to inherent blood clotting diseases. In the present study we employed Molecular Dynamics simulations for tracing the sequence of structural fluctuations initiated by a single cysteine mutation in the ?3 subunit of the receptor. These simulations showed that in-silico protein mutants exhibit major conformational deformations leading to possible disulfide exchange reactions. We suggest that any mutation that prevents Cys560 from reacting with one of the Cys567–Cys581 bonded pair, thus disrupting its ability to participate in a disulfide exchange reaction, will damage the activation mechanism of the integrin. This suggestion is in full agreement with previously published experiments. Furthermore, we suggest that rearrangement of disulfide bonds could be a part of a natural cascade of thiol/disulfide exchange reactions in the ?IIb?3 integrin, which are essential for the native activation process. PMID:23527123

Levin, Lihie; Zelzion, Ehud; Nachliel, Esther; Gutman, Menachem; Tsfadia, Yossi; Einav, Yulia

2013-01-01

286

Exchange splitting of surface and bulk electronic states in excited magnetic states of Gd: First-principles study  

NASA Astrophysics Data System (ADS)

Recent pump-probe experiments provide time evolution of the bulk and surface electronic states in Gd excited by the laser pulse. These experiments are in close connection with earlier spectroscopic experiments probing temperature dependence of the exchange splitting of the electronic states. We report first-principles study of the electronic states in excited Gd modeled by the noncollinearity of the 4 f spin moments. In agreement with experiments we obtain a strong difference in the properties of the bulk and surface electronic states. To reveal the origin of this behavior we apply the concept of spin mixing to characterize the electronic states of the excited system. The surface states remain weakly spin mixed with respect to the local atomic spin axis of the surface layer that explains the persistence of the exchange splitting in highly excited Gd. On the other hand, a smaller part of the surface state localized in the second layer becomes strongly spin mixed leading to decreased value of the exchange splitting. In contrast to the surface states the bulk states are strongly spin mixed and average the influence of the atomic spin-up and spin-down potentials. This leads to the properties of the bulk states that are usually associated with the Stoner model. The good agreement between calculational results and the results of the pump-probe experiment support the assumption of ultrafast disordering of the 4 f moments after laser irradiation.

Sandratskii, L. M.

2014-11-01

287

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

288

Droplet infiltration and OM composition of intact soil structural surfaces for studying mass exchange  

NASA Astrophysics Data System (ADS)

During rapid percolation through macropores with local nonequilibrium conditions water and solute mass exchange with the porous matrix and sorption of reactive components is both taken place at the surface of preferential flow paths. Aggregate surfaces can be coated by illuviated clayey particles and biopores covered by plant residues or earthworm casts. By controlling wettability and sorption properties, the organic matter (OM) of surface coatings may also affect the transport properties of structured soils. Composition of OM in wall coatings was found spatially distributed at the mm-scale; thus, it remained unclear if water absorption by the soil matrix (i.e., mass exchange) was affected by locally-distributed OM. For samples with intact aggregate surfaces and biopore walls taken at clay-illuvial subsoil horizon of Luvisols developed from Loess and glacial till, the mm-scale spatial distribution of OM composition was measured using diffuse reflectance infrared spectroscopy (DRIFT). Spectra were analysed with respect to alkyl and carboxyl functional groups in OM to obtain an estimate for its potential wettability. The infiltration dynamic of water droplets was evaluated using contact angle measurements and droplet penetration time. The potential wettability of OM differed for coatings and burrow walls and was generally lower for the Loess-derived than for the till-derived samples. The droplet infiltration times were significantly lower only for the Loess Luvisol samples. The results suggest that mass exchange between flow path and matrix can be affected by OM composition of structural surfaces among other factors such as texture, moisture, and chemical status (pH).

Leue, Martin, ,, Dr.; Gerke, PD Horst H., ,, Dr.; Godow, Sophie Ch.; Ellerbrock, PD Ruth H., ,, Dr.

2014-05-01

289

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

SciTech Connect

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

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

2014-05-07

290

Hole spin polarization in the exchange field of the dilute magnetic (Ga,Mn)As semiconductor studied by means of polarized hot-electron photoluminescence spectroscopy  

NASA Astrophysics Data System (ADS)

We have studied the hole spin polarization in the exchange field of ferromagnetic (Ga,Mn)As by means of polarized hot-electron photoluminescence (HPL). We found that the holes contribute to the HPL spectrum in two very different states. Most of the holes are strongly localized on Mn acceptors whose spin polarization under circularly polarized excitation is not sensitive to the exchange field arising in the ferromagnetic state below the Curie point. In contrast, the spin polarization of weakly localized or delocalized holes strongly decreases below the Curie temperature. This effect is explained by the hole spin orientation in the exchange field. The spin splitting of the weakly localized or delocalized holes in the mean exchange field is estimated ??6meV (equivalent to the built-in exchange field ?90T ).

Sapega, V. F.; Sablina, N. I.; Panaiotti, I. E.; Averkiev, N. S.; Ploog, K. H.

2009-07-01

291

Higher Education Exchange, 2004  

ERIC Educational Resources Information Center

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

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

2004-01-01

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

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

294

A flash-photolysis electron spin resonance study of radicals formed from carboxylic acids; exchange effects in spin-polarized radicals  

NASA Astrophysics Data System (ADS)

The time-integration spectroscopy (TIS) technique has been applied to the study of transient radicals created by flash photolysis of solutions of benzene-1,2,4,5-tetracarboxylic acid (pyromellitic acid), benzene-1,2,-dicarboxylic acid (phthalic acid) and benzene-1,4-dicarboxylic acid (terephthalic acid). In these systems electron transfer, proton transfer and rotational isomerism all affect the spin-polarized spectra observed. The exchange processes are analysed theoretically, in the case of proton exchange for the first time in the polarized situation, and it is shown that the two different exchange processes can be simply differentiated in the time-dependent TIS spectra.

McLauchlan, K. A.; Ritchie, A. J. D.

295

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

296

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

NASA Astrophysics Data System (ADS)

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

K P, Sankaranarayanan

2011-12-01

297

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

SciTech Connect

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

Kara, Mahmut; Zacharias, Martin W.

2013-03-05

298

Study of electron—molecule collision via finite-element method and R-matrix propagation technique: Exact exchange  

NASA Astrophysics Data System (ADS)

We have applied the finite-element method to electron—molecule collision with the exchange effect implemented rigorously. All the calculations are done in the body-frame within the fixed-nuclei approximation, where the exact treatment of exchange as a nonlocal effect results in a set of coupled integro-differential equations. The method is applied to e- H2 and e- N2 scatterings and the cross sections obtained are in very good agreement with the corresponding results we have generated from the linear-algebraic approach. This confirms the significant difference observed between our results generated by linear-algebraic method and the previously published e- N2 cross sections (M. A. Morrison and B. C. Saha, Phys. Rev. A36, 3682, 1987). Our studies show that the finite-element method is clearly superior to the linear-algebraic approach in both memory usage and CPU time especially for large systems such as e- N2. The system coefficient matrix obtained from the finite-element method is often sparse and smaller in size by a factor of 12 to 16, compared to the linear-algebraic technique. Moreover, the CPU time required to obtain stable results with the finite-element method is significantly smaller than the linear-algebraic approach for one incident electron energy. The usage of computer resources in the finite-element method can even be reduced much further when (1) scattering calculations involving multiple electron energies are preformed in one computer run and (2) exchange, which is a short range effect, is approximated by a sparse matrix.

Abdolsalami, Farzan; Abdolsalami, Mehran; Perez, Lennard; Gomez, Pedro; Silva, Mark

1995-10-01

299

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

300

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

NASA Astrophysics Data System (ADS)

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 to understand this role. Using information on canopy structure such as the vertical canopy density area (CAD), we seek similarity forms of universal functions to describe turbulent parameters. These general forms will allow a more general description of the exchange properties, such as variances and covariances, for a wide variety of forests within the canopy layer (CL). Introducing a dimensionless height, zc' = f(CAD), a normalized cumulative canopy area density, we find that turbulent parameters profiles are bounded by two curves when zc ' is used, which represent sparse (mainly conifers) and dense canopies (mostly deciduous). Using zc' to determine the displacement height (d) provides a better agreement of wind profiles above the canopy among several forest types. Presence of the canopy alters the shape of the spectra and cospectra. An attenuation of the spectra in a frequency band (0.4 < f ' < 2, where f' is the dimensionless frequency) in w spectrum is observed when the canopy is foliated, but it is absent when the canopy is leafless. The observed spectra in the roughness sub layer are more peaked than those observed over flat surfaces. As the measurement height is higher, away from to the canopy top, the normalized heat flux cospectra start to be broader than the normalized momentum flux, going asymptotically to the cospectral shapes over flat surfaces. At high wind speed, the cospectra of the turbulent parameters shift to high frequencies, affecting the proper period of the Reynolds' averaging that has to be chosen. Therefore, during low wind speed days, longer the Reynods' averaging should be used to sample the slow moving eddy. The 4-30 minute oscillations can contribute about 17% of the noontime period fluxes. Accounting the contribution from these oscillations we are able to improve the energy budget closure.

Sakai, Ricardo Kendi

301

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

Microsoft Academic Search

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

Dmitry V Marinin; Garrett N Brown

2000-01-01

302

Crude Oil Imports, Oil Price Volatility and Exchange Rate Adjustments: An Empirical Study Based on Monthly Data from 1995 to 2010  

Microsoft Academic Search

\\u000a Based on high frequency monthly data from 1995 to 2010, this study has employed VAR model to analyze the relationship between\\u000a the international crude oil prices, exchange rate and China’s crude oil imports. The Empirical results show that China’s crude\\u000a oil imports has a rather stable long term relationship with the international crude oil price adjustment and the RMB exchange

Chen Zhang

303

In vitro studies using ion exchange resins as potential phosphate binders for renal failure patients.  

PubMed

The uptake of phosphate [expressed as phosphorus (P)] by the anion exchange resins, Dowex 1-X8, Dowex SBR, and Bio-Rex 5, aluminum hydroxide, and sucralfate tablets was evaluated. The maximum uptake capacities (in mg P per gram of "wet" resin or solid) were 56, 49, and 84 mg for Dowex SBR, Dowex 1-X8, and Bio-Rex 5 resins, respectively, and 164-168 mg for aluminum hydroxide and sucralfate. At a concentration of P considered to approximate that encountered in the stomach (0.3 mg/ml), Bio-Rex 5 resin, aluminum hydroxide, and sucralfate bound similar amounts of P. Physiologic concentrations of bicarbonate or chloride and simulated gastric or intestinal fluids caused small changes in P uptake by Bio-Rex 5 resin. The resins bound large quantities of taurocholic (TA) and glycocholic (GA) acids. However, when Bio-Rex 5 was converted to the taurocholate form, it bound the same amount of P as the original chloride-form resin, and the binding of TA was prevented. PMID:3841765

Burt, H M; Cameron, E C; Leung, M; Erber, H; Price, J D

304

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

305

Three Dimensional Computational Study on Proton Exchange Membrane Fuel Cell by Operation Conditions  

NASA Astrophysics Data System (ADS)

A single-phase, fully three-dimensional simulation model for a proton exchange membrane(PEM) fuel cell was used to examine the interdigitated flow field with electrochemical reaction and ion, electron, and water transport(electro-osmotic drag flux and back diffusion flux) through the polymer membrane. The numerical results showed that the fuel cell with an interdigitated flow field resulted in better performance than a fuel cell with a conventional flow field due to its strong convective transport across gas diffusion layer(GDL). However, the pressure drop in an interdigitated flow field is much greater than in conventional flow field. To investigate the effect of relative humidity on the performance of a PEM fuel cell, the humidification condition was set to 100% at the anode flow field and was changed by 0-100% at the cathode flow field. Maximum power density was obtained for a 70% humidified condition at the cathode where the oxygen concentration is moderately high while maintaining high ion conductivity at the polymer membrane.

Lee, Pil Hyong; Park, Bong Il; Hwang, Sang Soon

306

Density functional study of hydrogen in amorphous silicon  

NASA Astrophysics Data System (ADS)

Hydrogenated amorphous silicon is a relatively new material with device applications including photovoltaics. Intrinsic and light-induced electronic defects reduce the efficiency of a-Si:H solar cells. Although hydrogen is implicated in these defects, microscopic understanding of the structure and energetics of hydrogen in a-Si:H has been limited. The current limits are in part due to the lack of reliable theoretical calculations. Here we apply density functional methods to study H in a-Si:H. First, we develop a new atomistic model for a-Si:H. Then, using molecular dynamics simulations, we compare several currently available atomistic models. Finally, we calculate the properties of hydrogen in these models, including the geometric environments, the energetics, the electronic structure and the vibrational properties. Our most important conclusions are presented below. Our calculations are consistent with the following microscopic picture for long range diffusion of H in a-Si:H. Clustered Si-H bonds constitute the dominant trapping species. Upon the dissociation of 2 H atoms, a Si-Si bond forms leaving a nominally 4-fold coordinated weak bond complex. The 2 H atoms move away separately along Si-Si bond center sites until trapped at another weak bond complex. The calculated activation energy is found in agreement with established experimental results. Also, our calculations are successfully applied to observations of H evolution, hydrogen-deuterium exchange and long range diffusion in p-type amorphous silicon. Our calculations clarify the role of H during electronic defect formation. We calculate the energetics for H to move from a variety of Si-H bonds to the bulk chemical potential. For isolated Si-H bonds (i.e. in micro-cavities without any bond reconstruction) the energetics are not consistent with observations. However, if the remaining Si reconstructs with a nearby silicon creating a 5-fold coordinated defect then the energetics are in agreement with observations. Therefore, our results indicate that the dangling bond model for intrinsic defects in amorphous silicon should be revisited.

Tuttle, Blair R.

307

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

308

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

309

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

310

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

311

First-principles studies of interlayer exchange coupling in (Ga, Mn)As-based diluted magnetic semiconductor multilayers  

NASA Astrophysics Data System (ADS)

Interlayer exchange coupling (IEC) in a series model diluted magnetic semiconductor multilayers consisting of two magnetic (Ga, Mn)As layers separated by nondoped or Be-doped GaAs nonmagnetic spacers is studied by first-principles calculations. For the GaAs spacers without Be doping, the IEC is always ferromagnetic and is well described by the Ruderman-Kittle-Kasuya-Yoshida interaction based on a two-band model for a gaped system. For the Be-doped GaAs spacers, the IEC is found to be tunable and the antiferromagnetic IEC is achieved via Be-doping in the interfaces between the (Ga, Mn)As layers and the spacers.

Luo, M.; Tang, Z.; Zheng, J.; Zhu, Z. Q.; Chu, J. H.

2010-09-01

312

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

313

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

314

Interannual variability in carbon dioxide exchanges at a boreal wetland in the BOREAS northern study area  

Microsoft Academic Search

Climatological measurements, including carbon dioxide flux density, were made from April to September in 1994 and from April to November in 1996 at a fen wetland near Thompson, Manitoba, Canada, as part of the Boreal Ecosystem-Atmosphere Study (BOREAS). For both years, the study period was warmer and drier than the 24-year climate normals. The period of CO2 uptake was similar

David W. Joiner; Peter M. Lafleur; J. Harry McCaughey; Paul A. Bartlett

1999-01-01

315

Raman spectroscopic study of the aging and nitration of actinide processing anion-exchange resins in concentrated nitric acid  

SciTech Connect

Degradation of two types of anion exchange resins, Dowex 11 and Reillex HPQ, from the action of concentrated nitric acid (4 to 12 M) and radiolysis [from depleted uranium as UO{sub 2}{sup 2+} nitrate species and {sup 239}Pu as Pu(IV) nitrate species] was followed as a function of time with Raman vibrational spectroscopy. Elevated temperatures ({approx}50 degree sign C) were used in the absence of actinide metal loading to simulate longer exposures of the resin to a HNO{sub 3} process stream and waste storage conditions. In the absence of actinide loading, only minor changes in the Dowex resin at acid concentrations {<=}10 M were observed, while at 12 M acid concentration, the emergence of a Raman peak at 1345 cm-1 indicates the addition of nitro functional groups to the resin. Similar studies with the Reillex resin show it to be more resistant to nitric acid attack at all acid concentrations. Incorporation of weakly radioactive depleted uranium as the UO{sub 2}{sup 2+} nitrate species to the ion-exchange sites of Dowex 11 under differing nitric acid concentrations (6 to 12 M) at room temperature showed no Raman evidence of resin degradation or nitration, even after several hundred days of contact. In contrast, Raman spectra for Dowex 11 in the presence of {sup 239}Pu as Pu(IV) nitrate species reveal numerous changes indicating resin alterations, including a new mode at 1345 cm-1 consistent with a Pu(IV)-nitrate catalyzed addition of nitro groups to the resin backbone. (c) 2000 Society for Applied Spectroscopy.

Buscher, C. T. [Chemical Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Chemical Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Donohoe, R. J. [Chemical Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Chemical Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Mecklenburg, S. L. [Nuclear Materials Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Nuclear Materials Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Berg, J. M. [Nuclear Materials Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States) [Nuclear Materials Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); the Glen T. Seaborg Institute for Transactinium Science, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Tait, C. D. [Chemical Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States) [Chemical Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Huchton, K. M. [Nuclear Materials Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Nuclear Materials Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Morris, D. E. [Chemical Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States) [Chemical Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1999-08-01

316

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

317

A Microcalorimetric Study of the Heat Effects of Sorption of Imino Acids on KU-2 × 8 H-Sulfocation Exchanger  

NASA Astrophysics Data System (ADS)

The thermokinetic characteristics of sorption of proline and hydroxyproline on H-sulfocation exchanger were determined. The absorption of dipolar imino acid ions by the cation exchanger was found to be an exothermic process accompanied by a decrease in the enthalpy component of sorption. The enthalpy character of sorption was to a greater extent characteristic of hydroxyproline.

Kotova, D. L.; Davydova, E. G.; Krysanova, T. A.; Astapov, A. V.

2008-04-01

318

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

NASA Astrophysics Data System (ADS)

In response to rising concerns about the effect of sulfate on water quality, human health, and agriculture, many jurisdictions around the world are imposing tighter regulations for sulfate discharge. This is driving the need for environmental compliance in industries like mining, metal processing, pulp and paper, sewage treatment, and chemical manufacturing. The sulfate removal from synthetic water by high cross-linked polystyrene divinylbenzene resin was studied at batch experiments in this study. The effect of pH, contact time, sulfates concentration, and adsorbent dose on the sulfate sequestration was investigated. The optimum conditions were studied on Saline water as a case study. The results showed that with increasing of the absorbent amount; contact time, and pH improve the efficiency of sulfate removal. The maximum sulfates uptake was obtained in pH and contact time 3.0 and 120 min, respectively. Also, with increasing initial concentration of sulfates in water, the efficiency of sulfate removal decreased. The obtained results in this study were matched with Freundlich isotherm and pseudo-second-order kinetic. The maximum adsorption capacity (Qm) and constant rate were found 0.318 (mg/g) and 0.21 (mg/g.min), respectively. This study also showed that in the optimum conditions, the sulfate removal efficiency from Saline water by 0.1 mg/L sulfates was 65.64 %. Eventually, high cross-linked polystyrene divinylbenzene resin is recommended as a suitable and low cost absorbent to sulfate removal from aqueous solutions.

Fathy, Mahmoud; Moghny, Th. Abdel; Awadallah, Ahmed E.; El-Bellihi, Abdel-Hameed A.-A.

2014-11-01

319

Numerical study of heat transfer in two-row heat exchangers having extended fin surfaces  

SciTech Connect

This paper reports on a three-dimensional study of air through two-row cylinder tubes. The analysis is intended to present a comparison of numerical and experimental data to validate the laminar flow postulation. The current study explores the influence of four perforated fin surfaces on the pressure drop and heat transfer rate. To gain further insight into the three-dimensional vortical flow structure, the authors conduct a topological study of the velocity field. Examination of the surface flow topology and the flow patterns at cross-flow plumes sheds some light on the complex interaction of the cylinder tube with the mainstream flow. This study clearly reveals a saddle point in front of the first row of cylinder tubes. Also clearly revealed by the computed solutions is a flow reversal found in the wake of the tube. The character of the critical-point-induced flow is also addressed. This study shows that the addition of perforated fins is not without deficiency. There is, in fact, a trade-off between the benefit of having an improved heat transfer and the penalty of having an increased pressure drop.

Sheui, T.W.H.; Tsai, S.F.; Chiang, T.P. [National Taiwan Univ., Taipei (Taiwan, Province of China). Dept. of Naval Architecture and Ocean Engineering

1999-05-28

320

Slow Chemical Exchange in an Eight-Coordinated Bicentered Ruthenium Complex Studied by One-Dimensional Methods. Data Fitting and Error Analysis  

NASA Astrophysics Data System (ADS)

Threefold carbonyl rotation in Ru 2(CO) 6(? 2- PPh 2)(? 2- ? 1:? 2- C?C - i- Pr) provides an excellent system for studying slow chemical exchange. One-dimensional relaxation-type experiments, in which spin-lattice relaxation and exchange compete, are performed to see if the threefold rotation is concerted, or a series of pairwise exchanges. Crucial to this study are the error estimates of the parameters; thus, methods for data fitting and error analysis are presented. The conclusions are that the process is concerted, and the barrier is approximately 46 kJ/mol. As an appendix, a discussion of the principle of detailed balance in complex systems, such as the present, is given. This solves the standard kinetic problem of what is the equilibrium state which results from a general kinetic scheme.

Bain, Alex D.; Cramer, J. A.

321

Simulation study of a proton exchange membrane (PEM) fuel cell system with autothermal reforming  

Microsoft Academic Search

This paper presents the results of a study for a 100kW net electrical power PEM fuel cell system. The major system components are an autothermal reformer, high and low temperature shift reactors, a preferential oxidation reactor, a PEM fuel cell, a combustor and an expander. Intensive heat integration within the PEM fuel cell system has been necessary to achieve acceptable

Atilla Ersoz; Hayati Olgun; Sibel Ozdogan

2006-01-01

322

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

323

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...

324

Social Studies Now. This Halloween, Exchange the Hysterical for the Historical.  

ERIC Educational Resources Information Center

A social studies wax museum can teach elementary students facts as they celebrate Halloween. A primary activity has students determine historic scenes to include in the wax museum, practice their poses, and put on a Halloween show. An intermediate activity has students research historic events, interpret information, create backdrops and props,…

Lindquist, Tarry

1996-01-01

325

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

326

The use of native cation-exchange chromatography to study aggregation and phase separation of monoclonal antibodies  

PubMed Central

This study introduces a novel analytical approach for studying aggregation and phase separation of monoclonal antibodies (mAbs). The approach is based on using analytical scale cation-exchange chromatography (CEX) for measuring the loss of soluble monomer in the case of individual and mixed protein solutions. Native CEX outperforms traditional size-exclusion chromatography in separating complex protein mixtures, offering an easy way to assess mAb aggregation propensity. Different IgG1 and IgG2 molecules were tested individually and in mixtures consisting of up to four protein molecules. Antibody aggregation was induced by four different stress factors: high temperature, low pH, addition of fatty acids, and rigorous agitation. The extent of aggregation was determined from the amount of monomeric protein remaining in solution after stress. Consequently, it was possible to address the role of specific mAb regions in antibody aggregation by co-incubating Fab and Fc fragments with their respective full-length molecules. Our results revealed that the relative contribution of Fab and Fc regions in mAb aggregation is strongly dependent on pH and the stress factor applied. In addition, the CEX-based approach was used to study reversible protein precipitation due to phase separation, which demonstrated its use for a broader range of protein–protein association phenomena. In all cases, the role of Fab and Fc was clearly dissected, providing important information for engineering more stable mAb-based therapeutics. PMID:20512972

Chen, Shuang; Lau, Hollis; Brodsky, Yan; Kleemann, Gerd R; Latypov, Ramil F

2010-01-01

327

Study on the occurrence of spontaneously established perpendicular exchange bias in Co49Pt51/IrMn bilayers  

NASA Astrophysics Data System (ADS)

In this study, perpendicular exchange bias (PEB) effect in the as-grown Co49Pt51/IrMn bilayers was demonstrated at room temperature using single-layered Co49Pt51 alloy thin film as ferromagnetic (FM) layer. Several unusual features were observed in this system, viz.,: (i) the PEB was spontaneously established without any external magnetic field treatments, (ii) single-shifted loops were obtained rather than double-shifted ones, and (iii) the spontaneous PEB effect was accompanied by a reduction in perpendicular coercivity, Hc? from 1024 to 632 Oe. The results of x-ray diffraction revealed the formation of IrMn (111) texture. Training effect studies indicate that the PEB effect is stable in this system with less than 5% variation in PEB value within 15 repetitive scans. Significant reduction in the PEB effect was found for the CoPt/IrMn films either grown or subjected to post-annealing under external magnetic field (Hind). The thickness dependence of PEB effect with respect to the FM and antiferromagnetic layers were also investigated and a largest PEB value of 533 Oe was obtained for the sample grown with 3-nm thick CoPt and 10-nm thick IrMn layers. The results of present study thus establish an opportunity to realize PEB effect in the absence of external field during fabrication.

Tsai, C. Y.; Hsu, Jen-Hwa; Saravanan, P.; Lin, K. F.

2014-05-01

328

A proton-deuterium exchange study of three types of Desulfovibrio hydrogenases  

Microsoft Academic Search

Summary Hydrogenases are among the main enzymes involved in bacterial anaerobic corrosion of metals. The study of their mode of action is important for a full comprehension of this phenomenon. The three types ofDesulfovibrio hydrogenases [(Fe), (NiFe), (NiFeSe)] present different patterns in the pH dependence of their activity. The periplasmic enzyme fromDesulfovibrio salexigens and the cytoplasmic enzyme fromDesulfovibrio baculatus both

Guy D. Fauque; Yves M. Berlier; Melvin H. Czechowski; Bernard Dirnon; Paul A. Lespinat; Jean LeGall

1987-01-01

329

First laboratory study of air-sea gas exchange at hurricane wind speeds  

NASA Astrophysics Data System (ADS)

In a pilot study conducted in October and November 2011, air-sea gas transfer velocities of the two sparingly soluble trace gases hexafluorobenzene and 1,4-difluorobenzene were measured in the unique high-speed wind-wave tank at Kyoto University, Japan. This air-sea interaction facility is capable of producing hurricane strength wind speeds of up to u10 =67 m s-1. This constitutes the first lab study of gas transfer at such high wind speeds. The measured transfer velocities k600 spanned two orders of magnitude, lying between 11 cm h-1 and 1180 cm h-1 with the latter being the highest ever measured wind-induced gas transfer velocity. The measured gas transfer velocities are in agreement with the only available data set at hurricane wind speeds (McNeil and D'Asaro, 2007). The disproportionately large increase of the transfer velocities found at highest wind speeds indicates a new regime of air-sea gas transfer, which is characterized by strong wave breaking, enhanced turbulence and bubble cloud entrainment.

Krall, K. E.; Jähne, B.

2014-04-01

330

Radioisotopic studies of the binding, exchange, and distribution of 5-hydroxytryptamine synthesized from its radioactivity precursor  

PubMed Central

1. The synthesis, distribution, storage, and subsequent metabolism of 5-hydroxytryptamine (5-HT) produced in mice from the administration of its radioactive precursor, 5-hydroxytryptophan, has been investigated to form the basis for a similar study to be conducted by radioautography. 2. Intravenous injection of the radioactive material was found to be essential for significant uptake of radioactivity by tissue. The duration of the period during which radioactive material was available for uptake by the tissue was 2 hr. 3. The relative distribution of radioactivity in individual organs was studied and the radioactive compounds present in each were identified and quantitatively assayed. No unrelated routes of metabolism of the labelled material were found and radioautographic results may be interpreted in terms of the metabolic picture which emerged. 4. Radioactive 5-HT was bound in tissues in preference to both its precursor, and metabolite, 5-hydroxytryptamine-O-glucuronide, and the radioactive 5-HT produced in vivo after the injection of labelled 5-hydroxytryptophan probably entered and labelled the endogenous 5-HT pool. 5. Fixatives prepared with buffer solutions made hypertonic by the addition of sucrose could rapidly and effectively halt the movement of radioactive 5-HT out of tissues and prevent its subsequent extraction during histological processing. 6. It is concluded that localization of sites concerned with 5-HT metabolism by means of radioautography is feasible and the 5-HT so localized will probably reflect the physiological compartmentalization of the amine. PMID:5298336

Gershon, M. D.; Ross, L. L.

1966-01-01

331

A kinetic study of copper ion exchange by Kelex 100 at a heptane-water interface  

SciTech Connect

A study of the kinetics of Cu{sup 2+} extraction by 7-(4-ethyl-1-methyloctyl)8-hydroxyquinoline (Kelex 100) has been undertaken in a static transfer cell, where the total concentration of the Cu{sup 2+}-Kelex 100 complex in the organic phase is monitored in situ as the reaction proceeds using attenuated total internal reflectance spectroscopy. The temporal characteristics of the extraction of Cu{sup 2+} from water into heptane could be accounted for using a simple one-dimensional diffusion model coupled with a reaction-limited interaction between Cu{sup 2+} and Kelex 100. Rate constants for the reaction of Kelex 100 and Cu{sup 2+} at a model interface were obtained from stopped flow experiments using a neutral micelle (C{sub 12}E{sub 8}) system. These rate constants were used to model the reaction between Cu{sup 2+} and Kelex 100 at the heptane-water interface.

McCulloch, J.K.; Perera, J.M.; Kelly, E.D.; White, L.R.; Stevens, G.W.; Grieser, F. [Univ. of Melbourne, Parkville, Victoria (Australia)] [Univ. of Melbourne, Parkville, Victoria (Australia)

1996-12-25

332

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

333

Effect of therapeutic hypothermia on gas exchange and respiratory mechanics: a retrospective cohort study.  

PubMed

Targeted temperature management (TTM) may improve respiratory mechanics and lung inflammation in acute respiratory distress syndrome (ARDS) based on animal and limited human studies. We aimed to assess the pulmonary effects of TTM in patients with respiratory failure following cardiac arrest. Retrospective review of consecutive cardiac arrest cases occurring out of hospital or within 24 hours of hospital admission (2002-2012). Those receiving TTM (n=44) were compared with those who did not (n=42), but required mechanical ventilation (MV) for at least 4 days following the arrest. There were no between-group differences in age, gender, body mass index, APACHE II, or fluid balance during the study period. The TTM group had lower ejection fraction, Glasgow Coma Score, and more frequent use of paralytics. Matched data analyses (change at day 4 compared with baseline of the individual subject) showed favorable, but not statistically significant trends in respiratory mechanics endpoints (airway pressure, compliance, tidal volume, and PaO2/FiO2) in the TTM group. The PaCO2 decreased significantly more in the TTM group, as compared with controls (-12 vs. -5 mmHg, p=0.02). For clinical outcomes, the TTM group consistently, although not significantly, did better in survival (59% vs. 43%) and hospital length of stay (12 vs. 15 days). The MV duration and Cerebral Performance Category score on discharge were significantly lower in the TTM group (7.3 vs. 10.7 days, p=0.04 and 3.2 vs. 4, p=0.01). This small retrospective cohort suggests that the effect of TTM ranges from equivalent to favorable, compared with controls, for the specific respiratory and clinical outcomes in patients with respiratory failure following cardiac arrest. PMID:24840620

Karnatovskaia, Lioudmila V; Festic, Emir; Freeman, William D; Lee, Augustine S

2014-06-01

334

Fast exhaust channel optical absorption method and apparatus to study the gas exchange in large diesel engines  

NASA Astrophysics Data System (ADS)

An optical absorption spectroscopic method and apparatus with shorter than 1 ms response time have been used to study the gas exchange processes in realistic conditions for a single cylinder of a large diesel engine. The method is based on measuring the differential line-of-sight optical uv absorption of the exhaust-gas-contained SO2 as a function of time in the exhaust port area just after the exhaust valves. The optical absorption by SO2 is determined from light transmission measurements at 280 and 340 nm performed through optical probes installed into the exhaust channel wall. The method has been applied to a continuously fired, large, medium speed production-line-type diesel engine with 990 kW rated power. The test engine was operated with standard light fuel oil (MDO Termoshell) and with light fuel oil treated with a sulfur additive {Di-Tert-Butyldisulfid [(CH3)3C]2S2}. The latter was to improve the optical absorption signals without increasing the fouling of the exhaust channel optical probes as in the case of heavier fuel oil qualities. In the reported case of a four-stroke diesel engine measurement results show that the method can provide time-resolved information of the SO2 density in the exhaust channel and thus give information on the single-cylinder gas exchange. During the inlet and exhaust valve overlap period the moment of fresh air entering into the measurement volume can be detected. If independent exhaust gas temperature and pressure data are available, the absorption measurements can readily be used for determining the burnt gas fraction in the exhaust channel. In this work the possibility of using the optical absorption measurement to determine the instaneous exhaust gas temperature was studied. Based on known fuel properties and conventional averaged SO2 measurements from the exhaust channel a known concentration of SO2 was assumed in the exhaust gas after the exhaust valves opening and before the inlet and exhaust valves overlap period. Together with an exhaust gas pressure measurement the optical absorption signal was used to determine the instaneous exhaust gas temperature. Due to the minimal modifications needed by the engine for optical access, and continuously fired operation with relevant power levels and realistic fuel qualities, this measurement method, with some further development, can be useful to obtain time-resolved data from the exhaust channel of real production-line-type diesel engines.

Vattulainen, J.; Hernberg, R.; Hattar, C.; Gros, S.

1998-01-01

335

Law on Exchange InternationalExchangeProgram  

E-print Network

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

Viglas, Anastasios

336

Coordination of Cd 2+ ions in the internal pore system of zeolite-X: A combined EXAFS and isotopic exchange study  

NASA Astrophysics Data System (ADS)

The effect of prolonged contact time (up to 130 days) on the immobilization of Cd by sorption to calcium exchanged zeolite-X (CaX), under environmentally relevant conditions, was studied using both isotopic exchange and extended X-ray absorption fine structure spectroscopy (EXAFS). Sorption and isotopic exchange measurements revealed time-dependent Cd sorption and indicated the movement of Cd 2+ ions into less accessible sites due to ageing. EXAFS suggested progressive fixation of Cd in the double six-ring ( D6R) unit of the CaX structure. Proportional allocation of the apparent Cd-Si bond distance to two 'end-members', across all contact times, indicated that the bond distance for labile Cd was 3.41 Å and for non-labile (or fixed) Cd was 3.47 Å.

Ahmed, I. A. M.; Young, S. D.; Mosselmans, J. F. W.; Crout, N. M. J.; Bailey, E. H.

2009-03-01

337

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

338

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

339

Numerical study of the role of shielding and exchange effects and of correlation and relativistic corrections in the Dirac-Fock approximation  

Microsoft Academic Search

The purpose of this work is to provide a quantitative underpinning to the qualitative understanding of the various physical effects which play a role in the spectra of many-electron atoms. Shielding and exchange contributions are studied, as functions of the principal quantum number n, the orbital angular momentum l, and the nuclear charge Z, for neutral alkali-metal atoms in the

S. S. Liaw; G. Feldman; T. Fulton

1988-01-01

340

Photoexcitation and ionization in carbon dioxide - Theoretical studies in the separated-channel static-exchange approximation  

NASA Technical Reports Server (NTRS)

Vertical-electronic static-exchange photoexcitation and ionization cross sections are reported which provide a first approximation to the complete dipole spectrum of CO2. Separated-channel static-exchange calculations of vertical-electronic transition energies and oscillator strengths, and Stieltjes-Chebyshev moment methods were used in the development. Detailed comparisons were made of the static-exchange excitation and ionization spectra with photoabsorption, electron-impact excitation, and quantum-defect estimates of discrete transition energies and intensities, and with partial-channel photoionization cross sections obtained from fluorescence measurements and from tunable-source and (e, 2e) photoelectron spectroscopy. Results show that the separate-channel static-exchange approximation is generally satisfactory in CO2.

Padial, N.; Csanak, G.; Mckoy, B. V.; Langhoff, P. W.

1981-01-01

341

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

342

Mechanisms of hydrogen exchange in proteins from nuclear magnetic resonance studies of individual tryptophan indole NH hydrogens in lysozyme.  

PubMed

The individual rates of solvent exchange of the six tryptophan indole NH hydrogens of lysozyme in 2H2O have been measured over a wide range of temperatures by using 1H NMR. Two distinct mechanisms for exchange have been identified, one characterized by a high activation energy and the other by a much lower activation energy. The high-energy process has been shown to be associated directly with the cooperative thermal unfolding of the protein and is the dominant mechanism for exchange of the most slowly exchanging hydrogen even 15 degrees C below the denaturation temperature. Rate constants and activation for the folding and unfolding reactions were obtained from the experimental exchange rates. At low temperatures, a lower activation energy mechanism is dominant for all hydrogens, and this can be associated with local fluctuations in the protein structure which allows access of solvent. The relative exchange rates and activation energies can only qualitatively be related to the different environments of the residues in the crystal structure. There is provisional evidence that a mechanism intermediate between these two extremes may be significant for some hydrogens under restricted conditions. PMID:7074052

Wedin, R E; Delepierre, M; Dobson, C M; Poulsen, F M

1982-03-01

343

Analytical and experimental study of fluid friction and heat transfer in low Reynolds number flow heat exchangers  

NASA Astrophysics Data System (ADS)

Analysis of fluid friction and heat transfer in low Reynolds number flow heat exchangers is undertaken. Three configurations typically utilized in compact heat exchangers are examined. These are: the plain non- circular duct of constant cross-sectional area, the offset or interrupted strip fin, and the turbulator strip. Analytical models for each of these geometries are developed by combining asymptotic solutions using simple non-linear superposition. Models for predicting the friction factor-Reynolds number product, f Re, and Nusselt number, Nu, in non-circular ducts for hydrodynamically fully developed flow (HFDF), hydrodynamically developing flow (HDF), thermally fully developed flow (TFDF), thermally developing flow (TDF), and simultaneously developing flow (SDF) are developed. Thermal and hydrodynamic entrance models are developed by combining the asymptotic solutions for small and large values of the dimensionless duct length. Through the use of a novel characteristic length, the square root of the cross-sectional flow area, scatter in the dimensionless data for fully developed laminar flows is considerably reduced. Most numerical and analytical data are predicted within +/-10% for HFDF and TFDF, +/-12% for HDF and TDF, and +/-15% for SDF for most non-circular ducts. Simple analytic models for predicting the Fanning friction factor, f, and Colburn j factor of two common enhancement devices, the offset strip fin and the turbulator strip are developed from fundamental solutions of fluid dynamics and heat transfer. Models for the offset strip fin are valid over the full range of Reynolds numbers for rectangular and other non-circular sub-channel cross- sections. Model predictions for the offset strip fin agree with published experimental data within +/-20%. Models for the turbulator strip are valid over the full Reynolds number range for both straight and curved turbulator profiles. Model predictions for the turbulator strip agree with new experimental data to within +/-20%. Finally, a detailed experimental study of the thermal and hydraulic characteristics of turbulator strips is undertaken. Simple design correlations are presented along with a performance evaluations of each device using the constant mass flow rate and constant pumping power criteria.

Muzychka, Yuri Stephan

1999-11-01

344

Kinetic study of the removal of dimethyl phthalate from an aqueous solution using an anion exchange resin.  

PubMed

Phthalate acid esters are becoming an important class of pollutants in wastewaters. This study addresses the kinetics of removal of dimethyl phthalate (DMP) using the anion exchange resin D201-OH from an aqueous solution. The effects of various factors on the removal rate and efficiency were investigated. An overall initial removal rate (OIRR) law and a pseudo first-order kinetic (PFOK) model were also developed. The internal diffusion of DMP within the resin phase of D201-OH is the rate-controlling step. Optimization of the particle size and pore structure of the resin D201-OH, the DMP concentration, and the reaction temperature can improve the DMP removal rate. The hydrolysis reaction of DMP catalyzed by D201-OH indicates an overall reaction order of 1.76, a value that is between the first order and the second order. The apparent activation energy of the reaction is 34.6 kJ/mol, which is below the homogeneous alkaline hydrolysis activation energy of 44.3 kJ/mol. The OIRR law can quantify the initial removal rate under different conditions. The results also show that the theoretical DMP removal efficiency predicted by the PFOK model agrees well with the experimentally determined values. Our research provides valuable insights into the primary parameters influencing the kinetic process, which enables a focused improvement in the removal or hydrolysis rate for similar processes. PMID:24510529

Xu, Zhengwen; Cheng, Ling; Shi, Jing; Lu, Jiangang; Zhang, Weiming; Zhao, Yunlong; Li, Fengying; Chen, Mindong

2014-05-01

345

Study of operating conditions and cell design on the performance of alkaline anion exchange membrane based direct methanol fuel cells  

NASA Astrophysics Data System (ADS)

Direct methanol fuel cells using an alkaline anion exchange membrane (AAEM) were prepared, studied, and optimized. The effects of fuel composition and electrode materials were investigated. Membrane electrode assemblies fabricated with Tokuyama® AAEM and commercial noble metal catalysts achieved peak power densities between 25 and 168 mW cm-2 depending on the operating temperature, fuel composition, and electrode materials used. Good electrode wettability at the anode was found to be very important for achieving high power densities. The performance of the best AAEM cells was comparable to Nafion®-based cells under similar conditions. Factors limiting the performance of AAEM MEAs were found to be different from those of Nafion® MEAs. Improved electrode kinetics for methanol oxidation in alkaline electrolyte at Pt-Ru are apparent at low current densities. At high current densities, rapid CO2 production converts the hydroxide anions, necessary for methanol oxidation, to bicarbonate and carbonate: consequently, the membrane and interfacial conductivity are drastically reduced. These phenomena necessitate the use of aqueous potassium hydroxide and wettable electrode materials for efficient hydroxide supply to the anode. However, aqueous hydroxide is not needed at the cathode. Compared to AAEM-based fuel cells, methanol fuel cells based on proton-conducting Nafion® retain better performance at high current densities by providing the benefit of carbon dioxide rejection.

Prakash, G. K. Surya; Krause, Frederick C.; Viva, Federico A.; Narayanan, S. R.; Olah, George A.

2011-10-01

346

Microcalorimetric study of thermal unfolding of lysozyme in water/glycerol mixtures: An analysis by solvent exchange model  

NASA Astrophysics Data System (ADS)

Folded protein stabilization or destabilization induced by cosolvent in mixed aqueous solutions has been studied by differential scanning microcalorimetry and related to difference in preferential solvation of native and denatured states. In particular, the thermal denaturation of a model system formed by lysozyme dissolved in water in the presence of the stabilizing cosolvent glycerol has been considered. Transition temperatures and enthalpies, heat capacity, and standard free energy changes have been determined when applying a two-state denaturation model to microcalorimetric data. Thermodynamic parameters show an unexpected, not linear, trend as a function of solvent composition; in particular, the lysozyme thermodynamic stability shows a maximum centered at water molar fraction of about 0.6. Using a thermodynamic hydration model based on the exchange equilibrium between glycerol and water molecules from the protein solvation layer to the bulk, the contribution of protein-solvent interactions to the unfolding free energy and the changes of this contribution with solvent composition have been derived. The preferential solvation data indicate that lysozyme unfolding involves an increase in the solvation surface, with a small reduction of the protein-preferential hydration. Moreover, the derived changes in the excess solvation numbers at denaturation show that only few solvent molecules are responsible for the variation of lysozyme stability in relation to the solvent composition.

Spinozzi, Francesco; Ortore, Maria Grazia; Sinibaldi, Raffaele; Mariani, Paolo; Esposito, Alessandro; Cinelli, Stefania; Onori, Giuseppe

2008-07-01

347

[Studies on siderophore exchange properties between staphylococci and various species of gram-positive and gram-negative bacteria].  

PubMed

The ability of iron utilizing by means of staphylococcal siderophores by bacteria belonging to genera: Acinetobacter, Corynebacterium, Curtobacterium, Clavibacter, Bacillus and Mycobacterium was investigated. The staphylococcal donor strains (18 species) used in these experiments were characterized by the ability to utilize siderophores produced by various strains belonging to aforenamed genera. The utilization of staphylococcal siderophores was studied on agar media in which minimally effective concentrations of ethylenediaminedi-ortho-hydroxyphenylacetic acid (EDDA) were used to inhibit indicator strains. Test colonies (staphylococcal) were applied to the surface of the media to determine whether the indicator organisms could obtain the required iron for growth by utilizing chelators from the test colony. The growth inhibition by EDDA of most strains from the Acinetobacter rods and from the coryneform-organisms (plant pathogen) genera, and strains from the species: B. subtilis, M. phlei, M. smegmatis, M. fortuitum was reversed by staphylococcal siderophores. None of the staphylococcal strains investigated, had the ability to exchange siderophores with strains from the species: C. pseudodiphtheriticum, Corynebacterium ANF group, B. megaterium, M. vaccae, M. chitae and M. parafortuitum. PMID:10803251

Szarapi?ska-Kwaszewska, J; Mikucki, J

1999-01-01

348

Remarks on the study of the X(3872) from Effective Field Theory with Pion-Exchange Interaction  

E-print Network

In a recent paper Phys.Rev.Lett. 111, 042002 (2013) (arXiv:1304.0846), the charmonium state X(3872) is studied in the framework of an effective field theory. In that work it is claimed that (i) the one-pion exchange (OPE) alone provides sufficient binding to produce the X as a shallow bound state at the $D^0\\bar{D}^{*0}$ threshold, (ii) short-range dynamics (described by a contact interaction) provides only moderate corrections to the OPE, and (iii) the X-pole disappears as the pion mass is increased slightly and therefore the X should not be seen on the lattice, away from the pion physical mass point, if it were a molecular state. In this paper we demonstrate that the results of Phys.Rev.Lett. 111, 042002 (2013) (arXiv:1304.0846) suffer from technical as well as conceptual problems and therefore do not support the conclusions drawn by the authors.

Baru, V; Filin, A A; Guo, Feng-Kun; Hammer, H -W; Hanhart, C; Meißner, Ulf-G; Nefediev, A V

2015-01-01

349

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

350

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

351

Job Exchange  

NSDL National Science Digital Library

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

1998-01-01

352

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. PMID:25360096

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

2014-01-01

353

A new ion exchange behavior of protonated titanate nanotubes after deprotonation and the study on their morphology and optical properties  

NASA Astrophysics Data System (ADS)

After the deprotonation of protonated titanate nanotubes (H2Ti3O7), we observed a novel ion exchange behavior on them. In the past literatures, protonated titanate nanotubes prepared via hydrothermal method have been reported with a poor exchangeability which may due to the chemical bonding of interlayer protons to nearby oxygen atoms. However, in this experiment under alkali environment (pH > 10), protonated titanate nanotubes exhibited a vast ion exchange capacity toward [Co(NH3)6]2+. This interesting phenomenon is contrary to the past reports which found protonated titanate nanotubes hardly could be ionexchanged by objective cations. This paper proves the deprotonation process on H2Ti3O7 nanotubes sufficiently facilitates the diffusion of metal complex cations into protonated titanate nanotubes and significantly changes their ion exchange capacity. As a consequence of cabalt intercalting via ion exchange, the tube wall of H2Ti3O7 nanotubes is observed to get loosened. Additionally, the exciton concentrations corresponding to the nanotube surface states are discussed in the paper.

Zhang, Huibin; Cao, Lixin; Liu, Wei; Su, Ge

2012-10-01

354

High-productivity membrane adsorbers: Polymer surface-modification studies for ion-exchange and affinity bioseparations  

NASA Astrophysics Data System (ADS)

This dissertation centers on the surface-modification of macroporous membranes to make them selective adsorbers for different proteins, and the analysis of the performance of these membranes relative to existing technology. The common approach used in these studies, which is using membrane technology for chromatographic applications and using atom transfer radical polymerization (ATRP) as a surface modification technique, will be introduced and supported by a brief review in Chapter 1. The specific approaches to address the unique challenges and motivations of each study system are given in the introduction sections of the respective dissertation chapters. Chapter 2 describes my work to develop cation-exchange membranes. I discuss the polymer growth kinetics and characterization of the membrane surface. I also present an analysis of productivity, which measures the mass of protein that can bind to the stationary phase per volume of stationary phase adsorbing material per time. Surprisingly and despite its importance, this performance measure was not described in previous literature. Because of the significantly shorter residence time necessary for binding to occur, the productivity of these cation-exchange membrane adsorbers (300 mg/mL/min) is nearly two orders of magnitude higher than the productivity of a commercial resin product (4 mg/mL/min). My work studying membrane adsorbers for affinity separations was built on the productivity potential of this approach, as articulated in the conclusion of Chapter 2. Chapter 3 focuses on the chemical formulation work to incorporate glycoligands into the backbone of polymer tentacles grown from the surface of the same membrane stationary phase. Emphasis is given to characterizing and testing the working formulation for ligand incorporation, and details about how I arrived at this formulation are given in Appendix B. The plant protein, or lectin, Concanavalin A (conA) was used as the target protein. The carbohydrate affinity membrane adsorbers were found to have a static binding capacity for con A (6.0 mg/mL) that is nearly the same as the typical dextran-based separation media used in practice. Binding under dynamic conditions was tested using flow rates of 0.1-1.0 mL/min. No bound lectin was observed for the higher flow rate. The first Damkohler number was used to assess whether adsorption kinetics or mass transport contributed the limitation to conA binding. Analyses indicate that this system is not limited by the accessibility of the binding sites, but by the inherently low rate of adsorption of conA onto the glycopolymer. The research described in Chapter 4 focuses on reaction chemistry experiments to incorporate a phosphonate-based polymer in the membrane platform to develop a new class of affinity adsorbers that function based on their affinity for Arginine (Arg) amino acid residues. The hypothesis was that benzyl phosphonate-containing functional polymers would form strong complexes with Arg-rich proteins as a result of multivalent binding. Introducing a new class of affinity membranes for purification of Arg-rich and Arg-tagged proteins may have an impact similar to the introduction of immobilized metal ion affinity chromatography (IMAC), which would be a significant achievement. Using Arg-tags would overcome some of the associated drawbacks of using metal ions in IMAC. Additionally, some cell penetrating peptides are said to be Arg-rich, and this would be a convenient feature to exploit for their isolation and purification. Lysozyme was used as a model Arg-rich protein. The affinity membranes show a static binding capacity of 3 mg/mL. (Abstract shortened by UMI.)

Chenette, Heather C. S.

355

Ion-Exchange Procedure Developed for Isolation of Element 106 (Seaborgium) and Study of Its Chemistry in H2SO4 and H2SO4\\/HF Solutions, with W as Imitator  

Microsoft Academic Search

Ion-exchange behavior of W, Hf, Sr (homologs of elements 106, 104, and 102, respectively), U (pseudohomolog of element 106), Cm, and Eu in H2SO4 and H2SO4\\/HF solutions was studied. The static and dynamic ion-exchange properties of these elements were determined as influenced by the solution composition and the nature of the ion exchanger. The best conditions were found for separating

L. I. Guseva; G. S. Tikhomirova

2002-01-01

356

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

357

Heat exchanger  

DOEpatents

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

Brackenbury, Phillip J. (Richland, WA)

1986-01-01

358

Heat exchanger  

DOEpatents

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

Brackenbury, P.J.

1983-12-08

359

Studies in reduction-roast leaching ion exchange of copper converter slag from an Indian copper complex, Ghatshila  

SciTech Connect

Large quantities of converter and anode slags are generated in different unit operations for the production of copper in I.C.C. Ghatshila. The converter slag contains about 2.75% copper, 0.9% nickel, 52.0% iron, and 0.6% cobalt and cannot be rejected due to its economic importance. X-ray diffraction (XRD) studies revealed the presence of copper in elemental, oxide, and silicate phases and iron in silicate (Feyalite) and oxide (Fe{sub 2}O{sub 3}) phases. From the earlier work on leaching by an acetic acid lixiviant up to 55% copper could be extracted at 250 mL of acetic acid/100 g of slag, 125 C temperature, and 35 atm of oxygen pressure. Low copper recovery was attributed to the presence of copper silicate and sulfide phases which could not be detected by XRD. Therefore, reduction roasting by noncoking coal was done to increase the copper recovery. A coal sample from Talchar which contained 30% fixed carbon, 40% volatile, and 30% ash was used for reduction roasting. Maximum percent extraction of copper and nickel (97% Cu and 20% Ni) could be achieved at the temperature of 720 C for 90 min of roasting with 20% reductant. The acetic acid requirement was 130 mL/100 g of reduced pellets, while leaching at the oxygen pressure of 35 atm for 120 min at 120 C. Iron dissolution was minimum (max 1%) in all the experiments. The ion-exchange technique was employed to separate copper from acetate solution. Zeolite resin was found to be suitable for the separation of copper from leach liquor. About 92% copper was recovered by geolite. 2.5 N H{sub 2}SO{sub 4} was found to be most effective for the stripping of the copper from resin.

Bodas, M.G.; Mathur, S.B. [National Metallurgical Lab., Jamshedpur (India). Non-Ferrous Process Div.] [National Metallurgical Lab., Jamshedpur (India). Non-Ferrous Process Div.

1997-12-01

360

Ion exchange phenomena  

SciTech Connect

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

Bourg, I.C.; Sposito, G.

2011-05-01

361

Antisymmetric and Anisotropic Exchange as Studied by EPR in a Molecular Composite [NH3-(CH2)2-NH3]CuCl4  

NASA Astrophysics Data System (ADS)

The monoclinic crystal structure of [NH3-(CH2)2-NH3]CuCl4 consists of two-dimensional (b, c) layers of square planar (CuCl4)2 - entities, separated from each other by [NH3-(CH2)2-NH3]2+ alkylene chain sheets. Electron Paramagnetic Resonance (EPR) data have been obtained in single crystals of 2C2CuCl4 when rotated around a*, b and c -axes, at X-band. Only one EPR exchange-collapsed line was observed for the two magnetically inequivalent copper ions in the lattice. The angular variation of its position and peak-to-peak linewidth were measured in three perpendicular planes. A careful analysis of experimental data permits to obtain the principal values of the g-factor g = 2.053, g = 2.274. The contributions to the linewidths were analyzed in terms of the antisymmetric exchange (d) and the anisotropic exchange (D) and yielded |dx/dy| = 0.92 and |(d2x + 2.2D2)1/2/dy| = 0.65. Lineshape studies show that the exchange between the two inequivalent copper ions is anisotropic.

Bissey, J.-Cl.; Filloleau, N.; Beziade, P.; Chanh, Nguyen-Ba; Zouari, R.; Daoud, A.

1997-06-01

362

Ion Exchange Membrane Processes  

SciTech Connect

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

Wallace, R.M.

2002-10-30

363

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

364

Hydra: software for tailored processing of H/D exchange data from MS or tandem MS analyses  

PubMed Central

Background Hydrogen/deuterium exchange mass spectrometry (H/DX-MS) experiments implemented to characterize protein interaction and protein folding generate large quantities of data. Organizing, processing and visualizing data requires an automated solution, particularly when accommodating new tandem mass spectrometry modes for H/DX measurement. We sought to develop software that offers flexibility in defining workflows so as to support exploratory treatments of H/DX-MS data, with a particular focus on the analysis of very large protein systems and the mining of tandem mass spectrometry data. Results We present a software package ("Hydra") that supports both traditional and exploratory treatments of H/DX-MS data. Hydra's software architecture tolerates flexible data analysis procedures by allowing the addition of new algorithms without significant change to the underlying code base. Convenient user interfaces ease the organization of raw data files and input of peptide data. After executing a user-defined workflow, extracted deuterium incorporation values can be visualized in tabular and graphical formats. Hydra also automates the extraction and visualization of deuterium distribution values. Manual validation and assessment of results is aided by an interface that aligns extracted ion chromatograms and mass spectra, while providing a means of rapidly reprocessing the data following manual adjustment. A unique feature of Hydra is the automated processing of tandem mass spectrometry data, demonstrated on a large test data set in which 40,000 deuterium incorporation values were extracted from replicate analysis of approximately 1000 fragment ions in one hour using a typical PC. Conclusion The customizable workflows and user-friendly interfaces of Hydra removes a significant bottleneck in processing and visualizing H/DX-MS data and helps the researcher spend more time executing new experiments and interpreting results. This increased efficiency will encourage the analysis of larger protein systems. The ability to accommodate the tandem MS dimension supports alternative data collection and analysis strategies, as well as higher resolution localization of deuteration where permitted by the fragmentation mechanism. PMID:19473537

Slysz, Gordon W; Baker, Charles AH; Bozsa, Benjamin M; Dang, Anthony; Percy, Andrew J; Bennett, Melissa; Schriemer, David C

2009-01-01

365

Amide hydrogen exchange in HIV-1 subtype B and C proteases - insights into reduced drug susceptibility and dimer stability.  

PubMed

Since its identification, HIV has continued to have a detrimental impact on the lives of millions of people throughout the world. The protease of HIV is a major target in antiviral treatment. The South African HIV-1 subtype C (C-SA) protease displays weaker binding affinity for some clinically approved protease inhibitors in comparison with the HIV-1 subtype B protease. The heavy HIV burden in sub-Saharan Africa, where subtype C HIV-1 predominates, makes this disparity a topic of great interest. In light of this, the enzyme activity and affinity of protease inhibitors for the subtype B and C-SA proteases were determined. The relative vitality, indicating the selective advantage of polymorphisms, of the C-SA protease relative to the subtype B protease in the presence of ritonavir and darunavir was four- and tenfold greater, respectively. Dynamic differences that contribute to the reduced drug susceptibility of the C-SA protease were investigated by performing hydrogen-deuterium exchange/mass spectrometry (HDX/MS) on unbound subtype B and C-SA proteases. The reduced propensity to form the E35-R57 salt bridge, and alterations in the hydrophobic core of the C-SA protease, are proposed to affect the anchoring of the flexible flaps, resulting in an increased proportion of the fully open flap conformation. HDX/MS data suggested that the N-terminus of both proteases is less stable than the C-terminus of the proteases, thus explaining the increased efficacy of dimerization inhibitors targeted toward the C-terminus of HIV proteases. As far as we are aware, this is the first report on assessment of HIV protease dynamics using HDX/MS. PMID:25283307

Naicker, Previn; Stoychev, Stoyan; Dirr, Heini W; Sayed, Yasien

2014-12-01

366

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

367

A COMPARATIVE STUDY OF EXCHANGE RATE REGIMES AND MACRO-INSTABILITIES IN THE TWIN ECONOMIES OF SINGAPORE AND HONG KONG  

Microsoft Academic Search

Based on a small, open-economy IS-LM prototype model, this paper examines the sources of macroeconomic instabilities in Hong Kong and Singapore operating under two different currency board arrangements. The empirical findings suggest that in general, both external and internal factors contribute to the macroeconomic volatilities observed in the two economies. There is evidence of a tradeoff between exchange rate and

YUE MA; Y. Y. KUEH; RAYMOND C. W. NG

2007-01-01

368

Flax Pond ecosystem study: exchanges of carbon in water between a salt marsh and Long Island Sound  

Microsoft Academic Search

Flax Pond, a tidal marsh on the north shore of Long Island, New York, was used to examine the exchanges of carbon in its various forms between a salt marsh and the coastal waters. The marsh removed fine particulate carbon from the tidal water throughout the year; it tended to be a small source of C as total COâ and

G. M. Woodwell; D. E. Whitney; C. A. S. Hall; R. A. Houghton

1977-01-01

369

Flax Pond ecosystem study: Exchanges of phosphorus between a salt marsh and the coastal waters of Long Island Sound  

Microsoft Academic Search

The exchanges of phosphorus between the Flax Pond, a tidal Spartina alterniflora marsh on the north shore of Long Island (USA) and Long Island Sound were measured over 18 months. Phosphate was exported from the marsh from May through December and imported during the remainder of the year. Organic phosphorus appears to be accumulated in all seasons, but the yearly

G. M. Woodwell; D. E. Whitney

1977-01-01

370

PASSIVE EXCHANGES DURING WATER VAPOUR ABSORPTION IN MEALWORMS (TENEBRIO MOLITOR): A NEW APPROACH TO STUDYING THE PHENOMENON  

Microsoft Academic Search

SUMMARY The weights of single mealworms were continuously recorded at 20 °C during exposure to periods of constant humidity and to abrupt changes in atmospheric vapour pressure. Two exchange stages were recognized in each animal. Weight changes were either limited to slow losses, suggesting transpiration through the external cuticle, or showed more rapid humidity- dependent gains as well as losses.

JOHN MACHIN

371

Heat transfer and pressure drop studies on a PCM-heat exchanger module for free cooling applications  

Microsoft Academic Search

Free cooling\\/Night ventilation is the process of storing the cool energy available in the night time ambient air in a storage device. During the day time the cool energy is retrieved from the storage device in order to cool the building using mechanical ventilation system. The modular heat exchanger developed in this work is a shell and tube type with

V. Antony Aroul Raj; R. Velraj

2011-01-01

372

An analytical study of heat exchanger effectiveness and thermal performance in a solar energy storage system with PCM  

Microsoft Academic Search

Solar thermal energy storage systems can be categorized based on materials that store either as sensible heat or as latent heat of fusion. For convenience, the latter are designated as phase change materials (PCM). It is a fairly well accepted fact that PCM storage devices usually require less storage volume. In a recent paper, heat exchanger effectiveness for PCM storage

J. C. Y. Wang; C. C. K. Kwok; S. Lin; G. H. Vatistas

1984-01-01

373

The effect of the exchangeable metallic cation on the colloid properties of laponite treated with acridine orangea spectrophotometric study  

Microsoft Academic Search

The adsorption of the cationic dye acridine orange (AO) by different monoionic laponites leads to changes in the colloid properties of this synthetic mineral in aqueous solutions. The organic cation is adsorbed by the mechanism of cation exchange. Small amounts of adsorbed dye keep the clay in a peptized state with all metallic cations. Greater amounts of AO result in

D. Garfinkel-Shweky; S. Yariv

1995-01-01

374

Kinetics of oxygen exchange between bisulfite ion and water as studied by oxygen-17 nuclear magnetic resonance spectroscopy  

SciTech Connect

The nuclear magnetic relaxation times of oxygen-17 have been measured in aqueous sodium bisulfite solutions in the pH range from 2.5 to 5 as a function of temperature, pH, and S(IV) concentration, at an ionic strength of 1.0 m. The rate law for oxygen exchange between bisulfite ion and water was obtained from an analysis of the data, and is consistent with oxygen exchange occurring via the reaction SO/sub 2/ + H/sub 2/O right reversible H/sup +/ + SHO/sub 3//sup -/. The value of k/sub -1/ is in agreement with relaxation measurements. Direct spectroscopic evidence was found for the existence of two isomers of bisulfite ion: one with the proton bonded to the sulfur (HSO/sub 3//sup -/) and the other with the proton bonded to an oxygen (SO/sub 3/H/sup -/). (The symbol SHO/sub 3//sup -/ in the above chemical equation refers to both isomeric forms of bisulfite ion.) The relative amounts of the two isomers were determined as a function of temperature, and the rate and mechanism of oxygen exchange between the two was investigated. One of the two isomers, presumably SO/sub 3/H/sup -/, exchanges oxygens with water much more rapidly than does the other. A two-pulse sequence was developed which greatly diminished the solvent peak in the NMR spectrum.

Horner, D.A.

1984-08-01

375

Adsorption of Nitrogen Monoxide and Carbon Monoxide on Copper-Exchanged ZSM-5: A Cluster and Embedded Cluster Study  

E-print Network

Adsorption of Nitrogen Monoxide and Carbon Monoxide on Copper-Exchanged ZSM-5: A Cluster symmetrically to two framework oxygen atoms, and the other bonds asymmetrically to three framework oxygen atoms, in which a Cu cation is in fixed- coordination with water ligands (Cu+[H2O]n),26-28 to more realistic ones

Truong, Thanh N.

376

Analysis of one-dimensional pure-exchange NMR experiments for studying dynamics with broad distributions of correlation times  

NASA Astrophysics Data System (ADS)

One-dimensional (1D) exchange NMR experiments can elucidate the geometry, time scale, memory, and heterogeneity of slow molecular motions (1 ms-1 s) in solids. The one-dimensional version of pure-exchange (PUREX) solid-state exchange NMR, which is applied to static samples and uses the chemical shift anisotropy as a probe for molecular motion, is particularly promising and convenient in applications where site resolution is not a problem, i.e., in systems with few chemical sites. In this work, some important aspects of the 1D PUREX experiment applied to systems with complex molecular motions are analyzed. The influence of intermediate-regime (10 ?s-1 ms) motions and of the distribution of reorientation angles on the pure-exchange intensity are discussed, together with a simple method for estimating the activation energy of motions occurring with a single correlation time. In addition, it is demonstrated that detailed information on the motional geometry can be obtained from 1D PUREX spectral line shapes. Experiments on a molecular crystal, dimethyl sulfone, confirm the analysis quantitatively. In two amorphous polymers, atactic polypropylene (aPP) and polyisobutylene (PIB), which differ only by one methyl group in the repeat unit, the height of the normalized exchange intensity clearly reveals a striking difference in the width of the distribution of correlation times slightly above the glass transition. The aPP shows the broad distribution and Williams-Landel-Ferry temperature dependence of correlation times typical of polymers and other "fragile" glass formers. In contrast, the dynamics in PIB occur essentially with a single correlation time and exhibits Arrhenius behavior, which is more typical of "strong" glass formers; this is somewhat surprising given the weak intermolecular forces in PIB.

deAzevedo, E. R.; Tozoni, J. R.; Schmidt-Rohr, K.; Bonagamba, T. J.

2005-04-01

377

Analysis of one-dimensional pure-exchange NMR experiments for studying dynamics with broad distributions of correlation times.  

PubMed

One-dimensional (1D) exchange NMR experiments can elucidate the geometry, time scale, memory, and heterogeneity of slow molecular motions (1 ms-1 s) in solids. The one-dimensional version of pure-exchange (PUREX) solid-state exchange NMR, which is applied to static samples and uses the chemical shift anisotropy as a probe for molecular motion, is particularly promising and convenient in applications where site resolution is not a problem, i.e., in systems with few chemical sites. In this work, some important aspects of the 1D PUREX experiment applied to systems with complex molecular motions are analyzed. The influence of intermediate-regime (10 micros-1 ms) motions and of the distribution of reorientation angles on the pure-exchange intensity are discussed, together with a simple method for estimating the activation energy of motions occurring with a single correlation time. In addition, it is demonstrated that detailed information on the motional geometry can be obtained from 1D PUREX spectral line shapes. Experiments on a molecular crystal, dimethyl sulfone, confirm the analysis quantitatively. In two amorphous polymers, atactic polypropylene (aPP) and polyisobutylene (PIB), which differ only by one methyl group in the repeat unit, the height of the normalized exchange intensity clearly reveals a striking difference in the width of the distribution of correlation times slightly above the glass transition. The aPP shows the broad distribution and Williams-Landel-Ferry temperature dependence of correlation times typical of polymers and other "fragile" glass formers. In contrast, the dynamics in PIB occur essentially with a single correlation time and exhibits Arrhenius behavior, which is more typical of "strong" glass formers; this is somewhat surprising given the weak intermolecular forces in PIB. PMID:15945644

deAzevedo, E R; Tozoni, J R; Schmidt-Rohr, K; Bonagamba, T J

2005-04-15

378

Segmented heat exchanger  

DOEpatents

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

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

2010-12-14

379

Growth of calcium phosphate on ion-exchange resins pre-saturated with calcium or hydrogenphosphate ions: an SEM\\/EDX and XPS study  

Microsoft Academic Search

Calcium phosphate formed on the surfaces of ion-exchange resins pre-saturated with either Ca2+ or HPO42- ions has been studied using a combination of scanning electron microscopy (SEM)\\/energy dispersive X-ray (EDX) analysis and X-ray photoelectron spectroscopy (XPS). Calcium phosphate was formed at a temperature of 36.5°C via two methods. On Ca2+ or HPO42--saturated resins, 1.5xSBF (simulated body fluid) solution was used

M. R. Mucalo; M. Toriyama; Y. Yokogawa; T. Suzuki; Y. Kawamoto; F. Nagata; K. Nishizawa

1995-01-01

380

Structure-dynamic determinants governing a mode of regulatory response and propagation of allosteric signal in splice variants of Na+/Ca2+ exchange (NCX) proteins.  

PubMed

The Ca2+-dependent allosteric regulation of Na+/Ca2+ exchanger (NCX) proteins represents Ca2+ interaction with the cytosolic domains, CBD1 (calcium-binding domain 1) and CBD2, which is associated either with activation, inhibition or no response to regulatory Ca2+ in a given splice variant. CBD1 contains a high affinity Ca2+-sensor (which is highly conserved among splice variants), whereas primary information upon Ca2+ binding to CBD1 is modified by alternative splicing of CBD2, yielding the diverse regulatory responses to Ca2+. To resolve the structure-dynamic determinants of splicing-dependent regulation, we tested two-domain tandem (CBD12) constructs possessing either positive, negative or no response to Ca2+ using hydrogen-deuterium exchange MS (HDX-MS), SAXS, equilibrium 45Ca2+ binding and stopped-flow kinetics. Taken together with previously resolved crystallographic structures of CBD12, the data revealed that Ca2+ binding to CBD1 rigidifies the main-chain flexibility of CBD2 (but not of CBD1), whereas CBD2 stabilizes the apo-CBD1. Strikingly, the extent and strength of Ca2+-dependent rigidification of CBD2 is splice-variant dependent, where the main-chain rigidification spans from the Ca2+-binding sites of CBD1, through a helix of CBD2 (positioned at the domains' interface) up to the tip of CBD2 [>50 Å (1 Å=0.1 nm)] or alternatively, it stops at the CBD2 helix in the splice variant exhibiting an inhibitory response to regulatory Ca2+. These results provide a structure-dynamic basis by which alternative splicing diversifies the regulatory responses to Ca2+ as well as controls the extent and strength of allosteric signal propagation over long distance. PMID:25387769

Giladi, Moshe; Lee, Su Youn; Hiller, Reuben; Chung, Ka Young; Khananshvili, Daniel

2015-02-01

381

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.

382

Dynamics of ligand exchange mechanism at Cu(II) in water: An ab initio quantum mechanical charge field molecular dynamics study with extended quantum mechanical region  

SciTech Connect

Ab initio quantum mechanical charge field molecular dynamics (QMCF-MD) were successfully applied to Cu(II) embedded in water to elucidate structure and to understand dynamics of ligand exchange mechanism. From the simulation studies, it was found that using an extended large quantum mechanical region including two shells of hydration is required for a better description of the dynamics of exchanging water molecules. The structural features characterized by radial distribution function, angular distribution function and other analytical parameters were consistent with experimental data. The major outcome of this study was the dynamics of exchange mechanism and reactions in the first hydration shell that could not be studied so far. The dynamical data such as mean residence time of the first shell water molecules and other relevant data from the simulations are close to the results determined experimentally. Another major characteristic of hydrated Cu(II) is the Jahn-Teller distortion which was also successfully reproduced, leading to the final conclusion that the dominating aqua complex is a 6-coordinated species. The ab initio QMCF-MD formalism proved again its capabilities of unraveling even ambiguous properties of hydrated species that are far difficult to explore by any conventional quantum mechanics/molecular mechanics (QM/MM) approach or experiment.

Moin, Syed Tarique; Hofer, Thomas S.; Weiss, Alexander K. H.; Rode, Bernd M. [Theoretical Chemistry Division, Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innrain 80-82, A-6020 Innsbruck (Austria)

2013-07-07

383

Comparison of intravenous immunoglobulin and plasma exchange in treatment of mechanically ventilated children with Guillain Barré syndrome: a randomized study  

PubMed Central

Introduction Respiratory failure is a life threatening complication of Guillain Barré syndrome (GBS). There is no consensus on the specific treatment for this subset of children with GBS. Methods This was a prospective randomized study to compare the outcome of intravenous immunoglobulin (IVIG) and plasma exchange (PE) treatment in children with GBS requiring mechanical ventilation. Forty-one children with GBS requiring endotracheal mechanical ventilation (MV) within 14 days from disease onset were included. The ages of the children ranged from 49 to 143 months. Randomly, 20 children received a five-day course of IVIG (0.4 g/kg/day) and 21 children received a five-day course of one volume PE daily. Lumbar puncture (LP) was performed in 36 patients (18 in each group). Results Both groups had comparable age (p = 0.764), weight (p = 0.764), duration of illness prior to MV (p = 0.854), preceding diarrhea (p = 0.751), cranial nerve involvement (p = 0.756), muscle power using Medical Research Council (MRC) sum score (p = 0.266) and cerebrospinal fluid (CSF) protein (p = 0.606). Children in the PE group had a shorter period of MV (median 11 days, IQR 11.0 to 13.0) compared to IVIG group (median 13 days, IQR 11.3 to 14.5) with p = 0.037. Those in the PE group had a tendency for a shorter Pediatric Intensive Care Unit (PICU) stay (p = 0.094). A total of 20/21 (95.2%) and 18/20 (90%) children in the PE and IVIG groups respectively could walk unaided within four weeks after PICU discharge (p = 0.606). There was a negative correlation between CSF protein and duration of mechanical ventilation in the PE group (p = 0.037), but not in the IVIG group (p = 0.132). Conclusions In children with GBS requiring MV, PE is superior to IVIG regarding the duration of MV but not PICU stay or the short term neurological outcome. The negative correlation between CSF protein values and duration of MV in PE group requires further evaluation of its clinical usefulness. Trial Registration Clinicaltrials.gov Identifier NCT01306578 PMID:21745374

2011-01-01

384

Present day pacemakers for pulse generator exchange: is 3.5 V a sufficient nominal setting for the pulse amplitude? Thera Pacemaker Study Group.  

PubMed

Projected pacemaker longevity is calculated according to the nominal setting, which is 3.5 V for pulse amplitude in most present day pacemakers. The aim of this study was to test whether the nominal ventricular output setting of 3.5 V and 0.4 ms provides a 100% safety margin if these pacemakers are connected to implanted ventricular pacing leads. The study included 24 patients undergoing pulse generator exchange. The new pacemaker was either a Thera DR (n = 21) or Thera SR (n = 3) device. Ventricular pacing leads were implanted 70 +/- 38 months previously. Intraoperative measurements included pacing threshold at 0.5-ms pulse duration, impedance, and R wave amplitude. To achieve a 100% safety margin with 3.5 V, the cut-off pacing threshold is 1.7 V. At discharge it was assessed whether ventricular pulse amplitude remained at < or = 3.5 V or was programmed to > 3.5 V. At pulse generator exchange, pacing threshold was 1.2 +/- 0.5 V, including four patients with pacing thresholds > 1.7 V. Impedance was 587 +/- 189 omega and R wave amplitude was 12.8 +/- 4.8 mV. At discharge, ventricular pulse amplitude remained at the nominal setting in 13 patients, including 2 patients with high pacing thresholds at pacemaker exchange, and was programmed to < 3.5 V in 7 patients. Ventricular pulse amplitude was programmed to > 3.5 V in four patients. Two of these patients had high pacing thresholds (> 1.7 V/0.5 ms) at pulse generator exchange; the other two patients were programmed to > 3.5 V, although 3.5 V already provided a 100% safety margin. After pulse generator exchange, 92% of the patients could be paced with a 3.5-V pulse amplitude. Pacemakers were programmed in four patients > 3.5 V, but in only two of them to obtain a sufficient safety margin. High pacing thresholds at pulse generator exchange did not generally predict high pacing thresholds at discharge. PMID:8945049

Schuchert, A; Van Langen, H; Michels, K; Meinertz, T

1996-11-01

385

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

386

Antiferromagnetic order and phase transitions in GdS as studied with X-ray resonance-exchange scattering  

Microsoft Academic Search

:   We report on X-ray resonance exchange and neutron scattering of metallic GdS. At the LII and L III absorption edges of Gd, resonance enhancements of more than two orders of magnitude over the non-resonant magnetic scattering\\u000a are observed. Polarisation analysis proves that these enhancements are due to dipolar transitions from the 2p to the 5d states. The branching ratio

Th. Brückel; D. Hupfeld; J. Strempfer; W. Caliebe; K. Mattenberger; A. Stunault; N. Bernhoeft; G. J. McIntyre

2001-01-01

387

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

388

Flax pond ecosystem study: exchanges of CO/sub 2/ between a salt marsh and the atmosphere  

SciTech Connect

Profiles of CO/sub 2/ concentration, windspeed, and temperature were used in the aerodynamic flux technique to calculate the CO/sub 2/ exchange between a Long Island salt marsh and the atmosphere. Uptake of CO/sub 2/ by the marsh during hours of sunlight and release during the night occurred during all times of the year. The rates of CO/sub 2/ exchange were highest during midsummer, 2.3 g CO/sub 2/.m/sup -2/.h/sup -1/ averaged over the daylight hours of July, and 1.3 g CO/sub 2/.m/sup -2/.h/sup -1/ for both uptake and release. The net 24-h exchange rates followed Spartina growth and senescence during the summer and fall, and photosynthesis of benthic algae during late winter and spring. There was a net uptake of Co/sub 2/ over 24 h by the marsh during all seasons except autumn. The net annual flow of carbon was from the atmosphere to Flax Pond (approx. = 300 g C.m/sup -2/.yr/sup -1/ averaged over the entire marsh ecosystem). This flux was larger than the net exchange of carbon between the marsh and either uplands, sediments, or coastal waters. The net uptake of CO/sub 2/ during summer was less than the net productivity of the vascular plants, indicating that some of the CO/sub 2/ assimilated by the plants came from heterotrophic respiration within the marsh. Nevertheless, respiration by the plants was by far the largest source of CO/sub 2/ from the marsh surface. Nighttime respiration of the ecosystem released a total of approx. = 510 g C.m/sup -2/.yr/sup -1/ to the atmosphere.

Houghton, R.A.; Woodwell, G.M.

1980-12-01

389

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

Microsoft Academic Search

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

Scott A. Wood; Anthony E. Williams-Jones

1993-01-01

390

Silver structure environments in ion-exchanged silicate glasses studied by X-ray absorption fine structure.  

PubMed

X-ray absorption fine structure (XAFS) technique was used to analyze structural geometry of Ag atoms introduced into soda-lime silicate glass and soda aluminosilicate glass by ion-exchange method. The results show that Ag+ ion in soda aluminosilicate glass takes a coordination number of 1.6 with a Ag-O distance of 2.20 A when the ion-exchange ratio x is smaller than 0.47 and of 2.28 A when x is larger than 0.47. The introduced Ag+ ions are stabilized at the non-bridge oxygen (NBO) sites when x is lower than 0.47. The Na+ ions in AlO4 (O4 represents the bridging oxygen) sites are exchanged by Ag+ ions after all Na+ in NBO sites are replaced. The disorder of Ag-O coordination increases gradually with increasing x from 0.24 to 0.47 in soda aluminosilicate glass and increases dramatically when x is larger than 0.47. Ag+ ions takes a coordination number of 1.6 in the ion-exchanged soda-lime silicate glass and of 1.3 after subsequently thermal treatment with the same Ag-O distance of 2.14 A. Debye-Waller factor (DWF) of Ag-O coordination in soda aluminosilicate glass is higher than that in soda-lime silicate glass. Small Ag cluster has a reduced interatomic distance and a larger DWF. Ag nanoparticle in sample Ag-7 is in a state of tensile stress. PMID:19441594

Yang, X C; Li, W J; Dubiel, M; Huang, W H; Yano, T

2009-02-01

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

A Density Functional Theory Study of the Magnetic Exchange Coupling in Dinuclear Manganese(II) Inverse Crown Structures  

NASA Astrophysics Data System (ADS)

The magnetic exchange coupling constants between two Mn(II) centers for a set of five inverse crown structures have been investigated by means of a methodology based on broken-symmetry unrestricted density functional theory. These novel and highly unstable compounds present superexchange interactions between two Mn centers, each one with S = 5/2 through anionic "guests" such as oxygen, benzene, or hydrides or through the cationic ring formed by amide ligands and alkali metals (Na, Li). Magnetic exchange couplings calculated at B3LYP/6-31G(d,p) level yield strong antiferromagnetic couplings for compounds linked via an oxygen atom or hydride and very small antiferromagnetic couplings for those linked via a benzene molecule, deprotonated in either 1,4- or 1,3- positions. Analysis of the magnetic orbitals and spin polarization maps provide an understanding of the exchange mechanism between the Mn centers. The dependence of J with respect to 10 different density functional theory potentials employed and the basis set has been analyzed.

Vélez, Ederley; Alberola, Antonio; Polo, Víctor

2009-10-01

393

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

394

Magnetization dynamics in an exchange-coupled NiFe/CoFe bilayer studied by x-ray detected ferromagnetic resonance  

NASA Astrophysics Data System (ADS)

Exchange-coupled hard and soft magnetic layers find extensive use in data storage applications, for which their dynamical response has great importance. With bulk techniques, such as ferromagnetic resonance (FMR), it is difficult to access the behaviour and precise influence of each individual layer. By contrast, the synchrotron radiation-based technique of x-ray detected ferromagnetic resonance (XFMR) allows element-specific and phase-resolved FMR measurements in the frequency range 0.5–11 GHz. Here, we report the study of the magnetization dynamics of an exchange-coupled Ni0.81Fe0.19 (43.5 nm)/Co0.5Fe0.5 (30 nm) bilayer system using magnetometry and vector network analyser FMR, combined with XFMR at the Ni and Co L2 x-ray absorption edges. The epitaxially grown bilayer exhibits two principal resonances denoted as the acoustic and optical modes. FMR experiments show that the Kittel curves of the two layers cannot be taken in isolation, but that their modelling needs to account for an interlayer exchange coupling. The angular dependence of FMR indicates a collective effect for the modes of the magnetically hard CoFe and soft NiFe layer. The XFMR precessional scans show that the acoustic mode is dominated by the Ni signal with the Co and Ni magnetization precessing in phase, whereas the optical mode is dominated by the Co signal with the Co and Ni magnetization precessing in anti-phase. The response of the Co signal at the Ni resonance, and vice versa, show induced changes in both amplitude and phase, which can be ascribed to the interface exchange coupling. An interesting aspect of phase-resolved XFMR is the ability to distinguish between static and dynamic exchange coupling. The element-specific precessional scans of the NiFe/CoFe bilayer clearly have the signature of static exchange coupling, in which the effective field in one layer is aligned along the magnetization direction of the other layer.

Stenning, G. B. G.; Shelford, L. R.; Cavill, S. A.; Hoffmann, F.; Haertinger, M.; Hesjedal, T.; Woltersdorf, G.; Bowden, G. J.; Gregory, S. A.; Back, C. H.; de Groot, P. A. J.; van der Laan, G.

2015-01-01

395

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

396

Experimental Study and Modeling of the Stream-Subsurface Exchange of p,p'-DDE in the Presence of Naturally Occurring Fine Particles  

NASA Astrophysics Data System (ADS)

The stream-subsurface exchange process plays a significant role in the fate and transport of contaminants in streams due to the increased interactions between contaminants and bed sediments. The presence of suspended sediments such as naturally occurring fine particles is known to introduce large reactive surface areas which allow them to sorb contaminants and modify the contaminant behavior in natural streams. In this study, experiments were conducted in a recirculating flume to investigate the stream-subsurface exchange of p,p'-DDE in the presence of kaolinite colloids and natural river sediments. p,p'-DDE was analyzed using a gas chromatography with an electron capture detector combined with a solid-phase microextraction (SPME) technique. A process-based multi-phase exchange model considering kinetic sorption/desorption of DDE to both the bed sediments and suspended particles was applied to interpret the experimental results. The model input parameters were obtained using independent small-scale batch experiments. Results presented here will contribute to the mechanistic understanding of the complex transport processes in natural streams and to the development of reliable, predictive models for the assessment of contaminated streams.

Camarena, C.; Otero, D.; Ren, J.; Burton, A.; Packman, A.

2007-12-01

397

Escherichia coli Single-Stranded DNA-Binding Protein: NanoESI-MS Studies of Salt-Modulated Subunit Exchange and DNA Binding Transactions  

NASA Astrophysics Data System (ADS)

Single-stranded DNA-binding proteins (SSBs) are ubiquitous oligomeric proteins that bind with very high affinity to single-stranded DNA and have a variety of essential roles in DNA metabolism. Nanoelectrospray ionization mass spectrometry (nanoESI-MS) was used to monitor subunit exchange in full-length and truncated forms of the homotetrameric SSB from Escherichia coli. Subunit exchange in the native protein was found to occur slowly over a period of hours, but was significantly more rapid in a truncated variant of SSB from which the eight C-terminal residues were deleted. This effect is proposed to result from C-terminus mediated stabilization of the SSB tetramer, in which the C-termini interact with the DNA-binding cores of adjacent subunits. NanoESI-MS was also used to examine DNA binding to the SSB tetramer. Binding of single-stranded oligonucleotides [one molecule of (dT)70, one molecule of (dT)35, or two molecules of (dT)35] was found to prevent SSB subunit exchange. Transfer of SSB tetramers between discrete oligonucleotides was also observed and is consistent with predictions from solution-phase studies, suggesting that SSB-DNA complexes can be reliably analyzed by ESI mass spectrometry.

Mason, Claire E.; Jergic, Slobodan; Lo, Allen T. Y.; Wang, Yao; Dixon, Nicholas E.; Beck, Jennifer L.

2013-02-01

398

23Na magnetization-transfer NMR studies of concentration and temperature dependence of ionophore-induced equilibrium exchange of Na + across prototypical cell membranes  

NASA Astrophysics Data System (ADS)

The 23Na magnetization-transfer NMR methods described in a recent communication (D. C. Shungu and R. W. Briggs, J. Magn. Reson.77, 491, 1988) are applied here to the monensin-mediated cation transport system to establish the range of rate constants which can be accurately measured by this technique, to determine the order of the transport "reaction" with respect to the ionophore, and to obtain the activation parameters for the transport process. A wide range of exchange rates is induced by increasing the concentration of the ionophore, and by carrying out the measurements at several temperatures. Analysis of the derived data indicates that, at low monensin concentrations, the transmembrane exchange "reaction" follows first-order reaction kinetics with respect to the ionophore, but becomes zero-order at high ionophore concentrations. The temperature dependence of the exchange rate constants has allowed the determination of the transport activation energy, enthalpy, and entropy of 10.6 kcal/mol, 10.0 kcal/mol, and -15.9 cal/mol deg, respectively. These results, together with previous data on this transport system, are used to give a coherent and consistent description of carrier-mediated transmembrane cation transport. Finally, applicability of the 23Na magnetization-transfer NMR technique to study the kinetics of the sodium "pump" is discussed in the light of the present findings.

Shungu, Dikoma C.; Buster, Douglas C.; Briggs, Richard W.

399

/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

400

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

401

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

402

Diffusion by atomic place exchange in ultrathin iron films on Ag(100): an ion scattering spectroscopy study  

NASA Astrophysics Data System (ADS)

The surface composition of ultrathin (0-10 ML) iron films deposited on a well defined Ag(100) substrate at 140 K has been investigated by ion scattering spectroscopy. The data unambiguously show the occurrence of intermixing. The concentration of Ag at the surface decreases rather rapidly with the film thickness but it is still relevant (˜ 10%) even in the case of the thickest layer. The data are interpreted in terms of an atomic place exchange between silver and incident iron atoms at the surface of the growing film.

Canepa, M.; Magnano, E.; Campora, Andrea; Cantini, P.; Salvietti, M.; Mattera, L.

1996-05-01

403

Study of coupled heat and water transfer in proton exchange membrane fuel cells by the way of internal measurements  

NASA Astrophysics Data System (ADS)

Measurements of electrode temperatures within a proton exchange membrane fuel cell were performed using platinum wires. A temperature difference of 7°C between the electrodes and the bipolar plates was observed for a cell operating at a current density of 1.5 A.cm-2. These measurements show a strong non-uniformity of the temperature profile through membrane electrode assembly (MEA) that future phenomenological models must take into account. In addition, the simultaneous measurements of heat and water flux through the MEA leads to the conclusion that produced water crosses the diffusion layer in vapor phase. A very simple heat transfer model is proposed.

Thomas, A.; Maranzana, G.; Didierjean, S.; Dillet, J.; Lottin, O.

2012-11-01

404

An experimental study of the effect of Ca upon garnet-clinopyroxene Fe-Mg exchange equilibria  

Microsoft Academic Search

A series of basaltic compositions and compositions within the simple system CaO-MgO-FeO-Al2O3-SiO2 have been crystallized to garnetclinopyroxene bearing mineral assemblages in the range 24–30 kb pressure, 750°–1,300° C temperature. Microprobe analyses of coexisting garnet and clinopyroxene show that KD(Fe2+\\/MgG+\\/Fe2+\\/MgCpx) for the Fe-Mg exchange reaction between coexisting garnet and clinopyroxene is obviously dependent upon the Ca-content and apparently independent of the

D. J. Ellis; D. H. Green

1979-01-01

405

Structure and properties of metal-exchanged zeolites studied using gradient-corrected and hybrid functionals. III. Energetics and vibrational spectroscopy of adsorbates  

NASA Astrophysics Data System (ADS)

The influence of the exchange-correlation functional (semilocal gradient corrected or hybrid functional) on density-functional studies of the adsorption of CO and NO in Cu- and Co-exchanged chabazite has been investigated, extending the studies of the structural and electronic properties of these materials [F. Göltl and J. Hafner, J. Chem. Phys. 136, 064501 (2012), 10.1063/1.3676408; F. Göltl and J. Hafner, J. Chem. Phys. 136, 064502 (2012), 10.1063/1.3676409] and including for comparison carbonyls and nitrosyls of Cu and Co. Hybrid functionals predict much lower adsorption energies than conventional semilocal functionals, in better agreement with experiment as far as data are available for comparison. The calculated adsorption energies show a strong linear correlation with the stability of the cation sites. For Cu(I)-chabazite the calculated adsorption energies span almost the interval between the adsorption energies calculated for pure neutral and positively charged Cu-carbonyls and nitrosyls. For divalent Cu(II) and Co(II) the adsorption energies at cations in chabazite are much lower than the metal-molecule binding energies in the free carbonyls or nitrosyls, especially for the most stable cation location in a six-membered ring of the chabazite structure. For the stretching modes of adsorbed CO only hybrid functionals reproduce the blueshift of the frequency reported for all Cu(I)- and Co(II)-zeolites. For Cu(II)-chabazite both types of functionals predict a blueshift, the larger value calculated with hybrid functionals being in better agreement with observation. For NO adsorbed on Cu(I)-chabazite all functionals produce a redshift, the smaller value derived with hybrid functionals being in better agreement with experiment. For NO adsorbed in Cu(II)- and Co(II)-chabazite gradient-corrected functionals produce the best agreement with experiment for cations located in a six-membered ring. Semilocal functionals tend to underestimate the frequencies, while hybrid functionals tend to overestimate. The decisive factors determining the influence of the functionals are the larger HOMO-LUMO gap and the larger bandgap of the zeolite host, as well as the larger exchange-splitting of the cation eigenstates predicted with hybrid functionals. For Co(II)-chabazite the tendency to overestimate the exchange-splitting and to stabilize a high-spin state lead to better results with semilocal functionals. Finally, a comprehensive discussion of the influence of the exchange-correlation functional on the physico-chemical properties of these complex systems, based all three papers of this series is presented.

Göltl, Florian; Hafner, Jürgen

2012-02-01

406

Photoluminescence studies of silver-exchanged cadmium selenide crystals. Modification of a chemical sensor for aniline derivatives by heterojunction formation  

NASA Astrophysics Data System (ADS)

Single-crystal n-CdSe surfaces have been modified by an exchange reaction with aqueous Ag(+) that converts part of the surface to Ag2Se and releases Cd2(+) to solution. Formation of Ag2Se is established by x ray powder diffraction. The ESCA and Auger spectroscopy are consistent with the formation of Ag2Se islands having thicknesses of 0 to 500 A, depending on reaction conditions. Steady-state photoluminescence (PL) experiments show that Ag(+)-exchanged CdSe (CdSe/Ag(+)) can be superior to CdSe as an aniline sensor: ring-substituted aniline derivatives in toluene solution cause enhancements of the CdSe band edge PL in CdSe/Ag(+) samples relative to a toluene ambient, with the effect about twice as large as for unexchanged CdSe. The variations in PL intensity of CdSe/Ag(+) are well fit by a dead-layer model, allowing estimation of the adduct-induced change in depletion width.

Leung, Larry K.; Komplin, Norma J.; Ellis, Arthur B.; Tabatabaie, Ned

1991-05-01

407

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

SciTech Connect

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 through SB17), MST additions, CST additions to Tank 40 or to a sludge batch preparation tank (Tank 42 or Tank 51, referred to generically as Tank 51 in this report), streams from the Salt Waste Processing Facility (SWPF), and two canister production rates. A wide array of potential glass frit compositions was used to support this assessment. The sludge and frit combinations were evaluated using the predictive models in the current DWPF Product Composition Control System (PCCS). The results were evaluated based on the number of frit compositions available for a particular sludge composition scenario. A large number of candidate frit compositions (e.g., several dozen to several hundred) is typically a good indicator of a sludge composition for which there is flexibility in forming an acceptable waste glass and meeting canister production rate commitments. The MST and CST streams will significantly increase the concentrations of certain components in glass, such as Nb{sub 2}O{sub 5}, TiO{sub 2}, and ZrO{sub 2}, to levels much higher than have been previously processed at DWPF. Therefore, several important assumptions, described in detail in the report, had to be made in performing the evaluations. The results of the paper studies, which must be applied carefully given the assumptions made concerning the impact of higher Ti, Zr, and Nb concentrations on model validity, provided several observations: (1) There was difficulty in identifying a reasonable number of candidate frits (and in some cases an inability to identify any candidate frits) when a waste loading of 40% is targeted for Sludge Batches 8, 16, and 17, regardless of the addition of SCIX or SWPF streams. This indicates that the blending strategy for these sludge batches should be reevaluated by Savannah River Remediation (SRR). (2) In general, candidate frits were available to accommodate CST additions to either Tank 40 or Tank 51. A larger number of candidate frits were typically available for the sludge batches when CST is added to Tank 51 rather than Tank 40, meaning that more compositional flexibility would be available for frit selection and DWPF operation. Note however that for SB8 and SB17, no candidate frits were available to accommodate CST going to Tank 40 with and without SWPF streams. The addition of SWPF streams generally improves the number of candidate frits available for processing of a given sludge batch. (3) The change in production rate from 40 Sludge Receipt and Adjustment Tank (SRAT) batches per year (i.e., the current production rate) to 75 SRAT batches per year, without SWPF streams included, had varied results in terms of the number of candidate frits available for processing of a given sludge batch. Therefore, this variable is not of much concern in terms of incorporating the SCIX streams. Note that the evaluation at 75 SRAT batches per year (approximately equivalent to 325 canisters per year) is more conservative in terms of the impact of SCIX streams as compared to a production rate of 400 canisters per year. Overall, the outcome of this paper study shows no major issues with the ability to identify an acceptable glass processing window when CST from the SCIX process is transferred to either Tank 40 or Tank 51. The assumptions used and the model limitations identified in this report must be addressed through further experimental studies, which are currently being performed. As changes occur to the planned additions of MST and CST, or to the sludge batch preparation strategy, additional evaluations will be performed to determine the potential impacts. As stated above, the issues with Sludge Batches 8, 16, and 17 should be further evaluated by SRR. A

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

2010-06-29

408

The incidence of ventilator-associated pneumonia using the PneuX System with or without elective endotracheal tube exchange: A pilot study  

PubMed Central

Background The PneuX System is a novel endotracheal tube and tracheal seal monitor, which has been designed to minimise the aspiration of oropharyngeal secretions. We aimed to determine the incidence of ventilator-associated pneumonia (VAP) in patients who were intubated with the PneuX System and to establish whether intermittent subglottic secretion drainage could be performed reliably and safely using the PneuX System. Findings In this retrospective observational study, data was collected from 53 sequential patients. Nine (17%) patients were initially intubated with the PneuX System and 44 (83%) patients underwent elective exchange to the PneuX System. There were no episodes of VAP while the PneuX System was in situ. On an intention to treat basis, the incidence VAP was 1.8%. There were no complications from, or failure of, subglottic secretion drainage during the study. Conclusions Our study demonstrates that a low incidence of VAP is possible using the PneuX System. Our study also demonstrates that elective exchange and intermittent subglottic secretion drainage can be performed reliably and safely using the PneuX System. PMID:21450078

2011-01-01

409

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

SciTech Connect

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

Clark, J.L.

1980-01-01

410

Study of a silicate glass doped with Cd-S-Se nanocrystals and optical waveguides formed with Cs-K ion exchange  

NASA Astrophysics Data System (ADS)

Zinc-boron-silicate glass doped with cadmium sulfide-selenide was synthesized, and arising and growth of Cd-S-Se microcrystals in the glass matrix under annealing was studied. The annealing dependant shift of absorption edge of the glass samples was demonstrated. Transmission electron microscopy proved that quantum confinement effect was an origin of the shifts. Growth of the microcrystals was followed by increase of their dispersion. Also the growth led to transformation of structure of the microcrystals from cubical to hexagonal. Cesium-potassium ion exchange in the SDG was applied to optical waveguides formation. Differences of the alkaline ion profiles in the glass samples annealed differently were observed.

Lipovskii, Andrey A.; Nikonorov, Nikolai V.; Kharchenko, Mikhail V.; Sitnikova, A. A.

1994-10-01

411

Spectroscopic studies of micelle-enhanced ligand exchange of gallium (III)/4-(2-pyridylazo) resorcinol complex by calf thymus DNA  

NASA Astrophysics Data System (ADS)

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of gallium (III) with 4-(2-pyridylazo) resorcinol (PAR) under varying conditions has been studied spectrophotometrically. At pH 6.0, CTAB (0.05% w/v) markedly enhanced the absorption intensity of gallium (III)-PAR complex. Furthermore, the introduction of CTAB provided unique selectivity for the ligand exchange of Ga(III)-PAR by calf thymus dsDNA over calf thymus ssDNA. This phenomenon offers a novel spectrophotometric sensing strategy for direct detection of dsDNA.

Romeika, Jennifer M.; Spurgeon, Charina L.; Yan, Fei

2014-01-01

412

Woven heat exchanger  

DOEpatents

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

Piscitella, Roger R. (Idaho Falls, ID)

1987-01-01

413

Application of Advanced Very High Resolution Radiometer vegetation index to study atmosphere-biosphere exchange of CO2  

NASA Technical Reports Server (NTRS)

Normalized difference vegetation indices derived from radiances measured by the Advanced Very High Resolution Radiometer were used to prescribe the phasing of terrestrial photosynthesis. The satellite data were combined with field data on soil respiration and a global map of net primary productivity to obtain the seasonal exchange of CO2 between the atmosphere and the terrestrial biosphere. The monthly fluxes of CO2 thus obtained were employed as source/sink functions in a global three-dimensional atmospheric tracer transport model to simulate the annual oscillations of CO2 in the atmosphere. The results demonstrate that satellite data of high spatial and temporal resolution can be used to provide quantitative information about seasonal and longer-term variations of photosynthetic activity on a global scale.

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

1987-01-01

414

Strong cation exchange chiral stationary phase--a comparative study in high-performance liquid chromatography and subcritical fluid chromatography.  

PubMed

The performance of a strong cation exchange-type (SCX) chiral stationary phase (CSP) was evaluated with subcritical fluid chromatography (subFC) and high performance liquid chromatography (HPLC). The chromatographic conditions in subFC were optimized by changing the amount of polar organic modifier, concentration of a basic additive in the modifier, system pressure and temperature. In this way the concentration of in situ formed transient ionic species could be varied. The gradual change of the concentration of the transient buffer, i.e. gradient elution conditions in subFC, was found beneficial for separation of a mixture of racemic compounds. The strength and amount of the in situ formed buffer was estimated on the basis of comparative experiments in subSFC and HPLC. PMID:24028932

Wolrab, Denise; Macíková, Pavla; Boras, Mario; Kohout, Michal; Lindner, Wolfgang

2013-11-22

415

Carbon X-ray absorption spectra of fluoroethenes and acetone: a study at the coupled cluster, density functional, and static-exchange levels of theory.  

PubMed

Near carbon K-edge X-ray absorption fine structure spectra of a series of fluorine-substituted ethenes and acetone have been studied using coupled cluster and density functional theory (DFT) polarization propagator methods, as well as the static-exchange (STEX) approach. With the complex polarization propagator (CPP) implemented in coupled cluster theory, relaxation effects following the excitation of core electrons are accounted for in terms of electron correlation, enabling a systematic convergence of these effects with respect to electron excitations in the cluster operator. Coupled cluster results have been used as benchmarks for the assessment of propagator methods in DFT as well as the state-specific static-exchange approach. Calculations on ethene and 1,1-difluoroethene illustrate the possibility of using nonrelativistic coupled cluster singles and doubles (CCSD) with additional effects of electron correlation and relativity added as scalar shifts in energetics. It has been demonstrated that CPP spectra obtained with coupled cluster singles and approximate doubles (CC2), CCSD, and DFT (with a Coulomb attenuated exchange-correlation functional) yield excellent predictions of chemical shifts for vinylfluoride, 1,1-difluoroethene, trifluoroethene, as well as good spectral features for acetone in the case of CCSD and DFT. Following this, CPP-DFT is considered to be a viable option for the calculation of X-ray absorption spectra of larger ?-conjugated systems, and CC2 is deemed applicable for chemical shifts but not for studies of fine structure features. The CCSD method as well as the more approximate CC2 method are shown to yield spectral features relating to ??-resonances in good agreement with experiment, not only for the aforementioned molecules but also for ethene, cis-1,2-difluoroethene, and tetrafluoroethene. The STEX approach is shown to underestimate ??-peak separations due to spectral compressions, a characteristic which is inherent to this method. PMID:23556727

Fransson, Thomas; Coriani, Sonia; Christiansen, Ove; Norman, Patrick

2013-03-28

416

NH3-TPD-MS study of Ce effect on the surface of Mn- or Fe-exchanged zeolites for selective catalytic reduction of NOx by ammonia  

NASA Astrophysics Data System (ADS)

The selective catalytic reduction (SCR) of NOx with NH3 is considered to be a promising technique for the efficient reduction of highly detrimental NOx emitted from diesel engine vehicles to N2. This study was focused on a series of catalysts with ZSM-5 as support, prepared by Mn- or Fe-exchange followed by wet impregnation of Ce, or Fe or Mn. These catalysts were characterized by temperature-programmed desorption coupled with a mass spectrometer using ammonia (NH3-TPD-MS). Specifically, NH3-TPD-MS was used as a means of identifying the various strengths of acid sites and their relative abundance in an attempt to explain the effect of the catalyst surface acid sites on DeNOx activity. Acid sites with adsorption energies ranging from 47.0 to 75.6 kJ/mol were detected for all of the catalysts. For the same concentration of exchanged metal it was found that the DeNOx activity depends strongly on the type of metal. Furthermore, the acid site strength and distribution depend on the active metal and correlate with the observed DeNOx catalyst activity. Additionally, SEM metal mapping images confirmed the presence of well dispersed active metal on the surface of all catalysts. The catalysts with bimetallic active phase were stable and demonstrated high NOx conversion over a broad temperature range. Impregnation of metal-exchanged zeolites with Ce enhanced the low temperature NOx conversion. Observed differences of activity between the various catalysts of this study may be due to the formation of new ammonia activation sites. The ammonia desorption profile during the elevation of temperature was correlated to the DeNOx activity.

Stanciulescu, M.; Bulsink, P.; Caravaggio, G.; Nossova, L.; Burich, R.