Home About us Contact
|
Home About us Contact | ||
|
|
||
Temperature Experiments (temperature + experiment)
Selected AbstractsHydrogen ,leakage' during methanogenesis from methanol and methylamine: implications for anaerobic carbon degradation pathways in aquatic sedimentsENVIRONMENTAL MICROBIOLOGY, Issue 4 2007Niko Finke Summary The effect of variations in H2 concentrations on methanogenesis from the non-competitive substrates methanol and methylamine (used by methanogens but not by sulfate reducers) was investigated in methanogenic marine sediments. Imposed variations in sulfate concentration and temperature were used to drive systematic variations in pore water H2 concentrations. Specifically, increasing sulfate concentrations and decreasing temperatures both resulted in decreasing H2 concentrations. The ratio of CO2 and CH4 produced from 14C-labelled methylamine and methanol showed a direct correlation with the H2 concentration, independent of the treatment, with lower H2 concentrations resulting in a shift towards CO2. We conclude that this correlation is driven by production of H2 by methylotrophic methanogens, followed by loss to the environment with a magnitude dependent on the extracellular H2 concentrations maintained by hydrogenotrophic methanogens (in the case of the temperature experiment) or sulfate reducers (in the case of the sulfate experiment). Under sulfate-free conditions, the loss of reducing power as H2 flux out of the cell represents a loss of energy for the methylotrophic methanogens while, in the presence of sulfate, it results in a favourable free energy yield. Thus, hydrogen leakage might conceivably be beneficial for methanogens in marine sediments dominated by sulfate reduction. In low-sulfate systems such as methanogenic marine or freshwater sediments it is clearly detrimental , an adverse consequence of possessing a hydrogenase that is subject to externally imposed control by pore water H2 concentrations. H2 leakage in methanogens may explain the apparent exclusion of acetoclastic methanogenesis in sediments dominated by sulfate reduction. [source] High temperature experiments: a way to observe Raman scattering in luminescent samplesJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2007L. Raffaëlly Abstract Two methods to decrease the luminescence of a sample and to observe the Raman scattering are described: the change of the wavelength of excitation or the change of the temperature of the sample. The evolution of the luminescence intensity with temperature is explained by the use of an energy model with a metastable state and radiationless processes whose activation energy can be calculated. This method is applied with success to a Roman silicate glass: the Raman scattering initially hidden by the luminescence is then observed. Copyright © 2007 John Wiley & Sons, Ltd. [source] Optical and Mechanical Properties of Glasses and Glass,Ceramics Based on the Ge,Ga,Se SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008Mathieu Rozé In this paper, the mechanical and thermo-mechanical properties of glasses and glass,ceramics belonging to the Ge,Ga,Se system are studied. Pure glasses slightly transparent in the visible range up to 16 ,m have been synthesized. Glass,ceramics were made using an appropriate heat-treatment time and temperature from the 80GeSe2,20Ga2Se3 base glass in order to improve the mechanical properties. The optical and mechanical properties of glasses and glass,ceramics such as hardness and toughness were investigated. X-ray diffraction (XRD) versus temperature experiments were performed to understand the crystallization evolution as a function of heat-treatment time. GeGa4Se8 and GeSe2 crystalline phases have been determined with XRD. As a result, glass,ceramics with 40% density of crystals present a very low thermal expansion coefficient (11.8 × 10,6± 0.5 K,1) and an excellent infrared transmission in the 3,5 and 8,13 ,m regions. [source] High-temperature defect study of tellurium-enriched CdTe:InPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2006R. Grill Abstract The defect structure of donor-doped Te-rich CdTe is studied theoretically within quasi-chemical formalism and experimentally in heavily In-doped CdTe by in situ high temperature galvanomagnetic measurements in the temperature interval 900,200 °C. The experimental data are evaluated within defect model optimized to recent high temperature experiments and assuming doping-induced band gap renormalization. We show that a proper thermal treatment can be conveniently used for the optimization of room temperature electric properties and for a preparation of the semi-insulating detector grade material with a deep level doping below the limit 1013 cm,3 demanded in the detector industry. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Reduction of in-source collision-induced dissociation and thermolysis of sulopenem prodrugs for quantitative liquid chromatography/electrospray ionization mass spectrometric analysis by promoting sodium adduct formationRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2008Chad E. Wujcik Six chromatographically resolved sulopenem prodrugs were monitored for their potential to undergo both in-source collision-induced dissociation (CID) and thermolysis. Initial Q1 scans for each prodrug revealed the formation of intense [Prodrug2,+,H]+, [Prodrug2,+,Na]+, [Prodrug,+,Na]+, and [Sulopenem,+,Na]+ ions. Non-adduct-associated sulopenem ([Sulopenem,+,H]+) along with several additional lower mass ions were also observed. Product ion scans of [Prodrug3,+,Na]+ showed the retention of the sodium adduct in the collision cell continuing down to opening of the , -lactam ring. In-source CID and temperature experiments were conducted under chromatographic conditions while monitoring several of the latter ion transitions (i.e., adducts, dimers and degradants/fragments) for a given prodrug. The resulting ion profiles indicated the regions of greatest stability for temperature and declustering potential (DP) that provided the highest signal intensity for each prodrug and minimized in-source degradation. The heightened stability of adduct ions, relative to their appropriate counterpart (i.e., dimer to dimer adduct and prodrug to prodrug adduct ions), was observed under elevated temperature and DP conditions. The addition of 100,µM sodium to the mobile phase further enhanced the formation of these more stable adduct ions, yielding an optimal [Prodrug,+,Na]+ ion signal at temperatures from 400 to 600°C. A clinical liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay for sulopenem prodrug PF-04064900 in buffered whole blood was successfully validated using sodium-fortified mobile phase and the [PF-04064900,+,Na]+ ion for quantitation. A conservative five-fold increase in sensitivity from previously validated preclinical assays using the [PF-04064900,+,H]+ precursor ion was achieved. Copyright © 2008 John Wiley & Sons, Ltd. [source] 1H,NMR Spectroscopic Studies of the Conformational Isomers of PyrrolidinofullerenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2007Olena Lukoyanova Abstract Mixed bis-adduct derivatives of C60 containing a pyrrolidine and a malonate methano group were synthesized. Three regioisomers, the e,, the trans -2, and the trans -3, were isolated and characterized. In-depth NMR studies of these methano-pyrrolidinofullerenes showed that the nitrogen inversion on the pyrrolidine moiety is not a fast event in the 1H,NMR time scale as previously regarded. Solvent effects, variable temperature experiments, and protonation of the pyrrolidine nitrogen are addressed. [source] | ||||||||||