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41.
42.
According to Stevenson's rule, there is a possibility that the chloromethyl and bromomethyl ions in the spectra of alkylhalides may not be formed from the molecular ion by processes described by electronic ground states alone. Since ion intensities at 75 eV are generally considered to be governed by appearance potentials, the operation of Stevenson's rule should influence correlations of intensity data according to the kinetic approach to mass spectra. Deviations from linearity were obtained in correlations of CH2Br+ intensities, but not in those of CH2CL+. Stevenson's rule is of help in explaining the deviations, but by its nature it is not absolute in predicting their occurrence with certainty. Consequently caution must be exercised in the interpretation of new data, particularly for aliphatic compounds. 相似文献
43.
Rules previously derived by Wolfe and Weare governing selective adsorption scattering intensities are investigated computationally via the attractive corrugated wall (ACW) model of Harvie and Weare. These rules, which correlate features of the scattering intensity with the form of the atom surface potential, correctly predict intensity features seen in the ACW calculation. 相似文献
44.
CM Thaker S Rayaprol Krushna Mavani DS Rana MS Sahasrabudhe SI Patil DG Kuberkar 《Pramana》2002,58(5-6):1035-1039
The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO3 perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good
example of these properties is (La1−2x
Pr
x
Ca
x
)MnO3 (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T
c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using
X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for
understanding the structural, transport and magnetic properties are discussed in detail. 相似文献
45.
The “relaxation” procedure introduced by Held and Karp for approximately solving a large linear programming problem related to the traveling-salesman problem is refined and studied experimentally on several classes of specially structured large-scale linear programming problems, and results on the use of the procedure for obtaining exact solutions are given. It is concluded that the method shows promise for large-scale linear programming 相似文献
46.
The buildup of a large long-lived electron-hole drop in stressed Ge is studied using its Alfvén wave resonances. This microwave method permits rapid time resolution of the formation process after a short intense (100 nsec, 7 W) laser excitation pulse. A delay of about 1 μsec is observed before the drop radius rapidly increases from zero to ~ 100 μm within the next μsec. This is consistent with the interpretation that the photo-produced electron-hole pairs are quickly accelerated to the strain-induced potential minimum which is well within the crystal. 相似文献
47.
48.
C.G. Cassapakis H.C. Bryant B.D. Dieterle C.P. Leavitt D.M. Wolfe B.E. Bonner J.E. Simmons C.W. Bjork P.J. Riley M.L. Evans G. Glass J.C. Hiebert M. Jain R.A. Kenefick L.C. Northcliffe D.W. Werren 《Physics letters. [Part B]》1976,63(1):35-38
The measured cross sections show a narrow high-energy peak (20–30 MeV/cFWHM) and a broad bump at lower momenta associated with pion production. Comparison is made to an intranuclear cascade calculation. 相似文献
49.
Philip Wolfe 《Mathematical Programming》1974,7(1):380-383
An algorithm is described for finding the minimum of any convex, not necessarily differentiable, functionf of several variables. The algorithm yields a sequence of points tending to the solution of the problem, if any; it requires the calculation off and one subgradient off at designated points. Its rate of convergence is estimated for convex and also for twice differentiable convex functions. It is an extension of the method of conjugate gradients, and terminates whenf is quadratic.
Editor's note. The communications of Wolfe and Lemarechal which follow — received almost simultaneously — display different points of view, but deal with the same problem and use similar techniques. They are preliminary versions of promising attacks on the problem of minimizing a convex, but not necessarily differentiable, function of many variables. MATHEMATICAL PROGRAMMING STUDY 3 entitledNondifferentiable optimization is to be devoted to this subject. 相似文献
50.
The amphoteric behavior of Sn, a commonly-used dopant in AsCl3GaH2 vapor epitaxy, is examined for Sn concentration from 5 × 1014 to 5 × 1017cm?3. The compensation ratio remains constant at 0.23 for low concentrations and begins to increase in the 1016cm?3 range. This behavior can be explained quantitatively with non-equilibrium impurity incorporation model which takes into account 3 × 1011 cm?2 surface states. 相似文献