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731.
John F. Olsen 《Journal of fluorine chemistry》1977,9(6):471-482
Ab-initio molecular orbital calculations using both minimal or STO-3G and extended or 4-31G basis sets have been applied to fluoroxytrifluormethane. Complete geometry optimizations using both basis sets have been applied to this molecule and the calculated structural parameters have been compared to the electron diffraction data. The extended basis set calculations are found to be in much better overall agreement with experiment although the minimal basis set does reproduce the angular parameters well, including the tilt angle. The barrier to the CF3 torsion has been computed and it compares favorably with the microwave spectral value.The electronic structure of CF3OF and some related molecules have been examined by partitioning the electrons according to the method of Mulliken. The highest occupied orbital in CF3OF is found to be largely an O-F π * orbital and the O-F bond is also found to be the least ionic and weakest bond in the molecule. The computed dipole moment of CF3OF agrees well with the experimental value. 相似文献
732.
We have measured the electrical resistance and magnetic susceptibility of the magnetic superconductor, YgCo7, at pressures up to 20 kbar and in magnetic fields up to 6T. We have found that pressure suppresses the magnetism resulting in a higher superconducting transition temperature and conclude that Y9Co7 is an itinerant ferromagnet, not a spin-glass. Pressure also sharpens the superconducting transition and increases the critical magnetic field, signifying that the long range ferromagnetic and superconducting order parameters co-exist but vary spatially. For pressures greater than 6 kbar, the magnetoresistance is always positive, further indicating the suppresion of magnetism by high pressure. 相似文献
733.
Carbon dioxide exhaled by the operators produces increased levels of this gas inside the trailers used for housing monitoring equipment for use in the field. These levels can be high enough to produce serious calibration errors in flame photometric detectors used for measuring ambient concentrations of gaseous sulphur products. Quantitative measurement of the carbon dioxide interference in the sulphur emission is reported, as well as a method of estimating the extent of quenching agent pollution. 相似文献
734.
735.
31P-magnetic resonance spectroscopy (MRS) has been shown to be a promising method for monitoring tumor response to radiation therapy. The purpose of the work reported here was to investigate whether the usefulness of 31P-MRS might be enhanced by measurement of spin-lattice relaxation times (T1s) in addition to resonance ratios. The work was based on the hypothesis that tumors having a high probability of being controlled locally would show shortened T1s during the treatment course due to reoxygenation and development of necrosis. BEX-t human melanoma xenografts, which show efficient reoxygenation and development of necrosis following single dose irradiation, were used as tumor models. Tumors were treated with single doses of 5.0 or 15.0 Gy and the T1s of the inorganic phosphate and nucleoside triphosphate β resonances were measured as a function of time after irradiation by using the superfast inversion recovery method. Fractional tumor water content was determined by drying excised tumors at 50°C until a constant weight was reached. The T1s in irradiated tumors were either longer than or not significantly different from those in unirradiated control tumors. The increase in the T1s following irradiation coincided in time with a radiation-induced increase in tumor water content, suggesting a causal relationship. The effects of reoxygenation and development of necrosis on T1s were probably overshadowed by the effects of tumor water content. Consequently, the usefulness of 31P-MRS in monitoring tumor response to radiation therapy might not be significantly enhanced by measurement of T1s. 相似文献
736.
T. Åkesson M. G. Albrow S. Almehed O. Benary H. Bøggild O. Botner H. Breuker V. Burkert A. A. Carter J. R. Carter W. E. Cleland S. Dagan E. Dahl-Jensen I. Dahl-Jensen G. Damgaard C. W. Fabjan S. Frankel U. Goerlach K. H. Hansen V. Hedberg G. Jarlskog N. Kjaer R. Kroeger K. Kulka D. Lissauer B. Lörstad A. Markou N. A. McCubbin U. Mjörnmark R. Møller W. Molzon B. S. Nielsen L. H. Olsen Y. Oren J. Schukraft K. Spang I. Stumer M. Sullivan J. A. Thompson H. H. Thodberg E. Vella J. Williamson W. J. Willis W. A. Zajc Axial Field Spectrometer Collaboration 《Zeitschrift fur Physik C Particles and Fields》1987,35(4):517-526
We have revised the additive quark model for inelastic hadronic cross sections with its implications to the average charged multiplicities. The correction to the additive quark model is on the level of 2 mb only if we take into account all possible quark-quark cross sections with respect to flavour. The quark-quark constitutent cross sections have been evaluated. We have attributed average charged multiplicities to the constituent quark cross sections and have found some regularities according to the flavour of the quarks. 相似文献
737.
Flows of fluids with single-integral memory functionals are considered. Evaluation of the stress at a material point involves the deformation history of that point, and a dominant computational cost in finite element approximation is the construction of streamlines. It is shown that the simple crossed-triangle macro-element is in many ways an ideal finite element for the difficult non-linear, non-self-adjoint problem. The question as to whether this element produces convergent velocity and pressure solutions is addressed in the light of its failure to satisfy the discrete LBB condition. The effect of the element's ill-disposed (‘spurious’) pressure modes is discussed, and a pressure smoothing scheme is given which gives good results in Newtonian and non-Newtonian flows at various Reynolds and Deborah numbers. As an example of the element's success in modelling such flows, the problem of pressure differences in flows over transverse slots is studied numerically. The results are compared with experimental observations of such flows. The effect of fluid memory on the relation between first normal-stress differences and pressure differences is investigated. 相似文献
738.
D. K. Olsen A. R. Barnett S. F. Biagi N. H. Merrill W. R. Phillips 《Nuclear Physics A》1974,220(3):541-568
The static quadrupole moments of the first excited Jπ = 2+ states in 20Ne and 22Ne and the reduced electric quadrupole transition probabilities of these states to the ground states were measured via projectile Coulomb excitation. The quadrupole moments were deduced from the shapes of γ-ray angular distributions. The results are: Q(20Ne, 2+) = −0.20±0.05 b and Q(22Ne, 2+) = −0.11±0.05 b. The transition strengths were deduced from yield measurements and by comparison with the yields of target γ-rays. The results are: B(E2; 0+ → 2+, 20Ne) = 0.037±0.003 e2 · b2 and B(E2; 0+ → 2+, 22Ne) = 0.025±0.002 e2· b2. The results for the transition strengths are consistent with the results of accurate timing methods and resolve discrepancies between previous experiments. The results for the quadrupole moments are consistent with earlier measurements, although the mean values we obtain are slightly lower. The experimental measurements are compared with theoretical predictions and a detailed discussion is given of corrections to this type of reorientation experiment. 相似文献
739.
A simple but versatile instrument with an electronic (non-servo) measuring circuit is described which is capable of making direct or differential measurements of the resistance or conductance of solutions over an absolute resistance range from 0-1 Omega to l MOmega, in six linear ranges. Linearity is better than 2% on all ranges, and reproducibility is better than 1 %. Drift is less than 1 % over 12 hr. Less than 0-01 % change in resistance can be measured in the differential modes, permitting more sensitive measurements than can be made in direct conductance measurements. Applications of the instrument for monitoring ion-exchange separations and conductometric titrations are illustrated. 相似文献
740.