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31.
The ν = 0 and 1 rotational spectrum of BrO in the state has been observed in selected regions between 60 and 400 GHz. The precision of previously measured parameters and the quality of the fit has been improved. In addition, the centrifugal distortion constant, D02, the effective Λ-doubling constant, qeff, the perpendicular quadrupole coupling constant, eqQ2, and a linear combination of the magnetic hyperfine constant, b, and nuclear spin-rotation constant, Crs, have been measured for the first time. The values of ωe and ωexe derived from the mechanical constants are in good agreement with very recent optical data. 相似文献
32.
A simple relaxation of the Ge-GaAs (110) interface is studied theoretically using self-consistent pseudopotentials. The relaxation is one in which the distance between the Ge and GaAs atomic planes at the interface is increased by 20%. Band edge discontinuities are found to be insensitive to this type of relaxation in spite of large distortions of the electronic charge density. 相似文献
33.
34.
Kasinathan D Kunes J Lazicki A Rosner H Yoo CS Scalettar RT Pickett WE 《Physical review letters》2006,96(4):047004
The highest superconducting temperature Tc observed in any elemental metal (Li with Tc approximately 18-20 K at pressure 35-48 GPa) is shown to arise from increasingly strong electron-phonon coupling concentrated along intersections of Kohn anomaly surfaces with the evolving Fermi surface. First-principles linear response calculations of the phonon spectrum and spectral function alpha2F(omega) reveal very strong Q- and phonon-polarization dependence of coupling strength, resulting in values of in the observed range. The sharp momentum dependence of the coupling even for the simple Li Fermi surface indicates more generally that a fine Q mesh is required for precise evaluation of lamda. 相似文献
35.
Zachary N. Pickett William A. Howard Christopher R. Graves 《Journal of chemical crystallography》2008,38(9):717-721
Abstract Two substituted pyridinium chloride salts, namely 4-chloro-2,6-bis(hydroxymethyl)pyridinium chloride (triclinic, P-1, a = 6.0651(8) ?, b = 8.4393(8) ?, c = 8.6554(9) ?, α = 78.845(1)°, β = 83.156(1)°, γ = 89.047(1)°; V = 431.55(8) ?3; Z = 2) and 4-dimethylamino-2,6-bis(hydroxymethyl)pyridinium chloride hemihydrate (orthorhombic, Aba2, a = 17.2179(14) ?, b = 17.6332(15) ?, c = 7.2068(6) ?; V = 2188.0(3) ?3; Z = 4), have been structurally characterized. Hydrogen bonding and van der Waals contacts are evident in both structures.
Furthermore, the 4-dimethylamino derivative features a trigonal planar dimethylamino group with some π interaction between
the nitrogen atom and the pyridine ring.
Graphical Abstract Two compounds, namely 4-chloro-2,6-bis(hydroxymethyl)pyridinium chloride and 4-dimethylamino-2,6-bis(hydroxymethyl)pyridinium chloride hemihydrate, have been spectroscopically and structurally characterized. 相似文献
36.
Wang X Li Z Zeng X Luo Q Evans DJ Pickett CJ Liu X 《Chemical communications (Cambridge, England)》2008,(30):3555-3557
Infrared data for mono-iron complexes possessing two cis-CO together with M?ssbauer data for the enzyme and a model complex support the assignment that the iron centre of the cluster-free hydrogenase Hmd is low-spin Fe(II). 相似文献
37.
Nomeir AA Pramanik BN Heimark L Bennett F Veals J Bartner P Hilbert M Saksena A McNamara P Girijavallabhan V Ganguly AK Lovey R Pike R Wang H Liu YT Kumari P Korfmacher W Lin CC Cacciapuoti A Loebenberg D Hare R Miller G Pickett C 《Journal of mass spectrometry : JMS》2008,43(4):509-517
Posaconazole (SCH 56592) is a novel triazole antifungal drug that is marketed in Europe and the United States under the trade name 'Noxafil' for prophylaxis against invasive fungal infections. SCH 56592 was discovered as a possible active metabolite of SCH 51048, an earlier lead. Initial studies have shown that serum concentrations determined by a microbiological assay were higher than those determined by HPLC from animals dosed with SCH 51048. Subsequently, several animals species were dosed with (3)H-SCH 51048 and the serum was analyzed for total radioactivity, SCH 51048 concentration and antifungal activity. The antifungal activity was higher than that expected based on SCH 51048 serum concentrations, confirming the presence of active metabolite(s). Metabolite profiling of serum samples at selected time intervals pinpointed the peak that was suspected to be the active metabolite. Consequently, (3)H-SCH 51048 was administered to a large group of mice, the serum was harvested and the metabolite was isolated by extraction and semipreparative HPLC. LC-MS/MS analysis suggested that the active metabolite is a secondary alcohol with the hydroxyl group in the aliphatic side chain of SCH 51048. All corresponding monohydroxylated diastereomeric mixtures were synthesized and characterized. The HPLC retention time and LC-MS/MS spectra of the diastereomeric secondary alcohols of SCH 51048 were similar to those of the isolated active metabolite. Finally, all corresponding individual monohydroxylated diasteriomers were synthesized and evaluated for in vitro and in vivo antifungal potencies, as well as pharmacokinetics. SCH 56592 emerged as the candidate with the best overall profile. 相似文献
38.
Ibrahim SK Liu X Tard C Pickett CJ 《Chemical communications (Cambridge, England)》2007,(15):1535-1537
We report the assembly of the first electropolymeric materials incorporating catalytic diiron subsites related to those of the iron-only hydrogenases. 相似文献
39.
Effective exposure temperatures (Teff) in Arizona were calculated from hourly or 10-min parsed irradiation data along with ambient, black panel, and sample temperatures. The Teff represents a constant temperature that creates the same amount of photodegradation as the naturally varying temperature and provides a benchmark temperature for making lifetime predictions from accelerated laboratory exposures. The annual ambient and black panel Teff at a Wittmann, Arizona site were 30 °C and 42 °C, respectively, assuming that the photodegradation has an activation energy (Ea) of 21 kJ/mol (5 kcal/mol). Teff was only weakly dependent on Ea over the range of 10-40 kJ/mol (3-10 kcal/mol). Samples exposed as van sunroofs were found to have Teff that were offset from the black panel temperatures by a constant amount for the entire year. Thus, measurements of sample and black panel need to be made for only a few weeks to determine the offset and give the annual sample Teff if the annual black panel Teff is known. Light-colored samples probably are better compared with the ambient temperatures. Sample temperatures in xenon arc exposures usually are higher than the outdoor Teff, so Arrhenius temperature corrections need to be carried out to relate accelerated to outdoor exposures. Temperatures in xenon arc exposure tests often correspond more closely to maximum temperatures that samples might encounter for only a few hours per year. 相似文献
40.
Superconductivity of MgB2: covalent bonds driven metallic 总被引:3,自引:0,他引:3
A series of calculations on MgB2 and related isoelectronic systems indicates that the layer of Mg2+ ions lowers the nonbonding B pi ( p(z)) bands relative to the bonding sigma ( sp(x)p(y)) bands compared to graphite, causing sigma-->pi charge transfer and sigma band doping of 0.13 holes/cell. Because of their two dimensionality the sigma bands contribute strongly to the Fermi level density of states. Calculated deformation potentials of gamma point phonons identify the B bond stretching modes as dominating the electron-phonon coupling. Superconductivity driven by sigma band holes is consistent with the report of destruction of superconductivity by doping with Al. 相似文献