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1.
A new three-dimensional magic angle spinning (MAS) experiment is proposed, based on a combination of the two-dimensional rotor-synchronized MAS experiment of Spiess and co-workers and a new chemical shift anisotropy amplification method. The new experiment is demonstrated on a macroscopically ordered sample of ultra-high molecular weight poly(ethylene). 相似文献
2.
Shao L Crockford C Geen H Grasso G Titman JJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,167(1):75-86
A new NMR experiment which allows a measurement of the chemical shift anisotropy (CSA) tensor under magic angle spinning (MAS) is described. This correlates a fast MAS spectrum in the omega2 dimension with a sideband pattern in omega1 in which the intensities mimic those for a sample spinning at a fraction of the rate omega r/N, and these sidebands result from an amplification by a factor N of the modulation caused by the CSA. Standard methods can be used to extract the principal tensor components from the omega1 sideband patterns, and the nature of the experiment is such that the use of a large number of t1 increments can be avoided without compromising the resolution of different chemical sites. The new experiment is useful for accurately measuring narrow shift anisotropies. 相似文献
3.
The reaction of tetracyclone with the cyclo-octatetraene-dimethyl acetylenedicarboxylate adduct at . 110° produces, in addition to the [4+2] Π cycloadduct (49%), 1,2,3,8-tetraphenylcyclo-octatraene (11%), together with the diketone (5%). In a similar reaction with the esterified cyclo-octatetraene-maleic anhydride adduct , the major product (82%) is accompanied by the cyclohexa-1,3-diene and the dihydrosemibullvalene derivative . Thermolysis of at . 145° leads to the cyclobutene ., which on catalytic hydrogonation followed by decarbonylation at 180°–190° gives 2,3,4,5-tetraphenylcyclo-octa-1,3,5-triene . Attempted thermal conversion of into a dihydrosemibullvalene failed. 相似文献
4.
R Nirmala V Sankaranarayanan K Sethupathi AV Morozkin T Geethakumary Y Hariharan 《Pramana》2002,58(5-6):1101-1104
New R
2Ti3Ge4 (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac
magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize
in the parent, Sm5Ge4-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series.
The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales
with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays
a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects. 相似文献
5.
F. Cassidy R.W. Moore G. Wootton K.H. Baggaley G.R. Geen L.J.A. Jennings A.W.R. Tyrrell 《Tetrahedron letters》1981,22(3):253-256
Synthetic routes for the preparation of 12-azaprostacyclin analogues are described. 相似文献
6.
R. E. Van Geen 《Rheologica Acta》1973,12(3):468-478
Résumé Des mesures fines de l'effet photoélastique présenté par des matériaux soumis à une sollicitation sinuoïdale en régime établi, montrent un comportement inhabituel, et présentant une forte dépendance chromatique. En outre, la biréfringence peut être déphaséeen avance sur la sollicitation. Une analyse macrorhéologique, basée sur les fonctions de transfert, et l'adoption d'un modèle microrhéologique distinguant une composante hyperélastique et une composante entropique, fournissent une explication.
Summary Precise measurements on the photoelastic effect exhibited by materials harmonically loaded, show an unusual behaviour, with a strong chromatic dependance. The phase shift of the birefringence to the stress may also be positive, negative or zero. The use of transfer functions, at the macrorheological scale, and the assumption of a microrheological model with a hyperelastic and an entropic component, may explain the phenomenon.相似文献
7.
We report on the role of cross-relaxation in the decay of the 1D2 level of trivalent Pr in YPO4 in crystals with Pr concentrations of 0.1%, 1%, 2%, and 5%. We have found that the 1D2 level decay is purely radiative in the low-doped system. As the Pr concentration is increased, the 1D2 luminescence is quenched due to a cross-relaxation energy transfer between two Pr ions. The temporal behavior of the 1D2 luminescence following pulsed excitation has been monitored in each sample at temperatures between 30 K and 300 K, and all decay curves were fit to the Yokota–Tanimoto model. The decay times decrease as temperature increases, due to an increase in both the radiative rate and the energy transfer rate with temperature. There is little evidence of diffusion at any temperature, even in the more concentrated samples. We have also fit the decay curves using the LumiTrans computer simulation. A comparison of the fits to the decay curves of the two methods is presented. 相似文献
8.
Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta0.33V0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV2. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase. 相似文献
9.
10.
Cysteine oxidation, either biologically reversible or irreversible, is the main posttranslational modification associated with redox signaling and oxidative stress. Maleimide‐polyethylene glycol (m‐PEG) has been used to detect reversibly oxidized proteins by reacting to the reduced cysteine residues leading to mobility shift in immunoblots; a method called PEG‐switch. With PEG‐switch, both reduced and oxidized proteins can be observed on the same immunoblot simultaneously, providing a simple quantitative measurement for protein thiol modifications. In this report, we optimized the assay conditions and exploited the applications of PEG‐switch in quantitation of the extent of protein thiol oxidation in cells in response to H2O2 and insulin. In addition, we have proposed a redox scoring system for measuring the redox status of any given protein from the m‐PEG immunoblot. Our results provided quantitative data showing that two cysteine residues of protein tyrosine phosphatase 1B are prone to oxidation following insulin treatment in cultured HeLa cells. 相似文献