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41.
42.
A numerical model of the negative DC corona plasma along a thin wire in dry air is presented. The electron number density and electric field are determined from solution of the one-dimensional coupled continuity equations of charge carriers and Maxwell's equation. The electron kinetic energy distribution is determined from the spatially homogeneous Boltzmann equation. A parametric study is conducted to examine the effects of linear current density (0.1–100 A per cm of wire length), wire radius (10–1000 m), and air temperature (293–800 K) on the distribution of electrons and the Townsend second ionization coefficient. The results are compared to those previously determined for the positive corona discharge. In the negative corona, energetic electrons are present beyond the ionization boundary and the number of electrons is an order of magnitude greater than in the positive corona. The number of electrons increases with increasing gas temperature. The electron energy distribution does not depend on discharge polarity. 相似文献
43.
44.
W. Davidson 《General Relativity and Gravitation》1992,24(2):179-185
Non-stationary cylindrically symmetric one-parameter solutions to Einstein's equations are given for a perfect fluid. There is a time singularity (t=0) at which the pressurep and density are equal to + throughout the radial coordinate range 0 r < , but the solutions are well behaved fort > 0,p and decreasing steadily to zero asr increases through the range 0r<, or as t increases through the range 0<t<. The motion is irrotational with shear, expansion and acceleration. The family of solutions, of Petrov type I, are generally spatially inhomogeneous, of class B(ii), having two spacelike Killing vectors which are mutually orthogonal and hypersurface orthogonal, associated with an orthogonally transitive groupG
2. The particular members for which there are equations of statep=/3 andp= are specially considered. 相似文献
45.
Sabatino Nacson Alex. G. Harrison William R. Davidson 《Journal of mass spectrometry : JMS》1986,21(6):317-319
The collision-induced dissociation (CID) mass spectra of protonated cocaine and protonated heroin have been measured using a triple quadrupole mass spectrometer at 50 eV ion/neutral collision energy for protonated molecules prepared by different protonating agents. The CID mass spectra of protonated cocaine using H+(H2O)n, H+(NH3)n and H+((CH3)2NH)n as protonating agents are essentially identical and it is concluded that, regardless of the initial site of protonation, the fragmentation reactions occurring on collisional activation are identical. By contrast, protonated heorin prepared with H+(H2O)n and H+(NH3)n as protonating agents show substantial differences. That formed by reaction of H+(H2O)n shows a much more abundant peak corresponding to loss of CH3CO2H. From a comparison with model compounds, and from a consideration of the three-dimensional structure of heroin, it is concluded that with H+(H2O)n as protonating agent significant protonation occurs at the acetate group attached to the alicyclic ring, leading to acetic acid loss on collisional activation, but that reaction of H+(NH3)n leads to protonation at the nitrogen function. The proton attached to nitrogen cannot interact with the acetate group and, consequently, the probability of loss of acetic acid on collislional activation is greatly reduced. 相似文献
46.
α-Oxo-carboxylic acids undergo photo-oxidative decarboxylation from both C-1 and C-2 positions, and reaction does not involve singlet oxygen: a mechanism involving an electron transfer reaction is postulated. 相似文献
47.
Lam WH Gaspar PP Hrovat DA Trieber DA Davidson ER Borden WT 《Journal of the American Chemical Society》2005,127(27):9886-9894
CASSCF, CASPT2, CCSD(T), and (U)B3LYP electronic structure calculations have been performed in order to investigate the thermal fragmentation of P-phenylphosphirane (1) to phenylphosphinidene (PhP) and ethylene. The calculations show that generation of triplet PhP via a stepwise pathway is 21 kcal mol(-1) less endothermic and has a 12 kcal mol(-1) lower barrier height than concerted fragmentation of 1 to give singlet PhP. The formation of singlet PhP via a concerted pathway is predicted to be stereospecific, whereas formation of triplet PhP is predicted to occur with complete loss of stereochemistry. However, calculations on fragmentation of anti-cis-2,3-dimethyl-P-mesitylphosphirane (cis-1Me) to triplet mesitylphosphinidene (MesP) indicate that this reaction should be more stereospecific, in agreement with the experimental results of Li and Gaspar. Nevertheless, with a predicted free energy of activation of 42 kcal mol(-1), the formation of MesP from cis-1Me is not likely to have occurred in an uncatalyzed reaction at the temperatures at which this phosphirane has been pyrolyzed. 相似文献
48.
D. W. Davidson Y. P. Handa C. I. Ratcliffe J. A. Ripmeester J. S. Tse J. R. Dahn 《Molecular Crystals and Liquid Crystals》2013,570(1-2):141-149
Low-temperature neutron and X-ray diffraction studies show the gas hydrates of oxygen and nitrogen to be structure II (Fd3m), as recently found also for the hydrates of the small argon and krypton molecules. New lattice parameters of three structure I and 14 structure II hydrates from powder X-ray diffraction at 170 K are reported. The thermal expansion coefficient of tetrahydrofuran hydrate was determined from X-ray diffraction at some 50 temperatures between 18 and 263 K and found to be three times as great as for ice near 100 K and 30% higher near 250 K. Lattice parameters qf 40 type II clathrate hydrates are compared at 0°C and found to lie within 0.10 Å of 17.30 Å. 相似文献
49.
Michelle Galgoci Janel E. Davidson Clinton K. Harrington Dennis L. Hasha Christian T. Goralski 《合成通讯》2013,43(17):2477-2483
A simple method for the preparation of the title compounds via the reaction of dimethyl 2-ethenylcyclopropane-1,1-dicarboxylate with 6M ammonia in methanol is described. 相似文献
50.