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71.
T. C. Awes C. Barlag F. Berger M. A. Bloomer C. Blume D. Bock R. Bock E. -M. Bohne D. Bucher A. Claussen G. Clewing L. Dragon A. Eklund S. Garpman R. Glasow H. Gustafsson H. H. Gutbrod G. Hölker J. Idh P. Jacobs K. H. Kampert B. W. Kolb H. Löhner I. Lund F. E. Obenshain A. Oskarsson I. Otterlund T. Peitzmann F. Plasil A. M. Poskanzer M. Purschke B. Roters S. Saini R. Santo H. R. Schmidt S. P. Sørensen K. Steffens P. Steinhaeuser E. Stenlund D. Stüken G. R. Young 《Zeitschrift fur Physik C Particles and Fields》1995,65(2):207-213
Correlations between protons are studied in the target fragmentation region of reactions of protons and16O with C, Cu, Ag, Au and of32S with Al and Au at 200A GeV. The emitted protons were measured with the Plastic Ball detector in the WA80 experiment at the CERN SPS. The comparison of the correlation function with calculations, assuming a spherical, gaussian shaped source with a lifetime τ=0 fm/c, allows the extraction of radius parameters. The values are very close to those expected from the geometry of the target nuclei and increase with the target mass as αA Target 1/3 . Even in proton induced reactions the whole target nucleus is involved. The dependence of the radii on centrality, polar angleθ lab, and energy, and their relation to measured proton yields are presented. 相似文献
72.
Molecular dynamics simulations have been performed to gain insights into the catalytic mechanism of the hydrolysis of epoxides to vicinal diols by soluble epoxide hydrolase (sEH). The binding of a substrate, 1S,2S-trans-methylstyrene oxide, was studied in two conformations in the active site of the enzyme. It was found that only one is likely to be found in the active enzyme. In the preferred conformation the phenyl group of the substrate is pi-sandwiched between two aromatic residues, Tyr381 and His523, whereas the other conformation is pi-stacked with only one aromatic residue, Trp334. Two simulations were carried out to 1 ns for each conformation to evaluate the protonation state of active site residue His523. It was found that a protonated histidine is essential for keeping the active site from being disrupted. Long time scale, 4 ns, molecular dynamics simulation was done for the structure with the most likely combination of binding conformation and protonation state of His523. Near Attack Conformers (NACs) are present 5.3% of the time and nucleophilic attack on either epoxide carbon atom, approximately 75% on C(1) and approximately 25% on C(2), is found. A maximum of one hydrogen bond between the epoxide oxygen and either of the active site tyrosines, Tyr465 and Tyr381, is present, in agreement with experimental mutagenesis results that reveal a slight loss in activity if one tyrosine is mutated and essential loss of all activity upon double mutation of the two tyrosines in question. It was found that a hydrogen bond from Tyr465 to the substrate oxygen is essential for controlling the regioselectivity of the reaction. Furthermore, a relationship between the presence of this hydrogen bond and the separation of reactants was found. Two groups of amino acid segments were identified each as moving collectively. Furthermore, an overall anti-correlation was found between the movements of these two individually collectively moving groups, made up by parts of the cap-region, including the two tyrosines, and the site of the catalytic triad, respectively. This overall anti-correlated collective domain motion is, perhaps, involved in the conversion of E.NAC to E.TS. 相似文献
73.
A. Ríos A. Lynggaard-Jensen H. S. Jacobsen R. Whiteman H. Wacheux B. Karlberg A. B. Lindholm T. Stenstrøm H. Berridge A. Boenke 《Accreditation and quality assurance》1999,4(12):B512-B517
ETACS is the official acronym for the European project "European Testing and Assessment of Comparability of On-line Sensors/Analysers". This project has three main objectives to achieve the comparability of performance data for sensors and analysers in the environmental field. First, to develop a test protocol for validation and comparison of the performance of on-line sensors/analysers. The test protocol is intended to be generic, that is independent of the specific sensors/analysers and the specific parameters to be monitored. Second, the practical testing of this test protocol to assess its applicability and to develop the techniques used. Finally, to achieve widespread acceptance of the test protocol by producer/suppliers, users and relevant authorities to assist its early adoption as an agreed European standard. Laboratory tests for producing the test protocol have been carried out and completed to check the applicability of such a protocol. 相似文献
74.
Carbohydrates such as alditols (polyols or sugar alcohols), monosaccharides and disaccharides are separated as anions by anion-exchange chromatography with a sodium hydroxide eluent, MA1 CarboPac column and pulsed amperometric detection. We report a high-pH anion-exchange chromatographic-pulsed amperometric detection (HPAEC-PAD) method that determines all the polyols used as food additives in food products and the most commonly found mono- and disaccharides on a routine basis. The linearity, repeatability, internal reproducibility and accuracy are described. The applicability of the method has been demonstrated by the analysis of 46 relevant samples and by participation twice in the Food Analysis Performance Assessment Scheme (FAPAS) testing programme for food additives. 相似文献
75.
Christian K. Jørgensen 《Chemical physics letters》1982,89(6):455-458
Recent relativistic calculations on the uranyl ion suggest that the low wave numbers of the first electron transfer bands are due to a bonding 5f-like orbital containing the two loosest bound electrons. Comparison with UF6 makes it more likely that if indeed σu (and not πu) is the highest occupied MO, it is rather due to “pushing from below” by U 6p (like N 2s in N2). 相似文献
76.
Ab initio calculations on the thioborine molecule have been performed. Ionization potentials, force constants and geometry parameters are calculated in fair agreement with experimental values. A preliminary investigation of the sensitivity by nucleophilic attack has also been performed, indicating a rather strong tendency to undergo that type of reaction. 相似文献
77.
The electronic relaxation of ferric ions in Fe(NO3)3·9H2O and in frozen aqueous solutions has been investigated by use of Mössbauer spectroscopy. The application of an external magnetic field causes a pronounced increase of the spin—spin relaxation time, an effect which is contrary to that normally found in ferric compounds. An explanation is given based on a difference in the ionic state energies of the neighbouring ions induced by the applied magnetic field. 相似文献
78.
Mossin S Weihe H Sørensen HO Lima N Sessoli R 《Dalton transactions (Cambridge, England : 2003)》2004,(4):632-639
The synthesis, structure and magnetic properties of the one-dimensional chain compounds [Mn(cyclam)(SO4)]ClO4.H2O (1) and [Mn(cyclam)(HCOO)](CF3SO3)(ClO4) (2) are reported. Cyclam is the cyclic tetradentate ligand 1,4,7,11-tetraazacyclotetradecane. Both chain compounds exhibit antiferromagnetic interactions within the chains. A magnetic ordering phase transition at 5.5 K in (1) is investigated by magnetisation measurements along the three principal crystallographic axes of a single crystal and the results show unambiguously that the ferromagnetic ordering is only taking place along one crystallographic axis. The spin structure of the magnetic ordered phase and the magnitude of the ferromagnetic moment are correlated with the crystal structure and symmetry of the compound. 相似文献
79.
E. H. Mørkved 《Chemistry of Heterocyclic Compounds》2007,43(9):1197-1201
Syntheses and spectroscopic characteristics are reported for eight pyrazine-2,3-dicarbonitriles substituted with maleimide
residue in addition to phenyl, 2-thienyl, or 2-furyl substituent.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1409–1414, September, 2007. 相似文献
80.
Jørgen Sand 《BIT Numerical Mathematics》1985,25(2):391-398
We construct a polyhedral norm in which the fixed-step backward differentiation formulas of order one to three are contractive when applied to any differential equation of the formy=(t)y, (t) 0 (i.e. A0-contractive). The result also holds for non-uniform step-sequences if combined with certain restrictions on the stepwise order-selection. 相似文献