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41.
Elemental fluroine was found to substitute, in a regio and stereospecific way, tertiary unactivated hydrogens in alkanes - the most unreactive family of organic compounds. 相似文献
42.
Shlomo Moran Yehoshua Perl 《Journal of Algorithms in Cognition, Informatics and Logic》1981,2(1):22-30
In many optimization problems a solution is a subset of optimum number of elements satisfying some desired property. An element is redundant if it does not belong to any solution of the problem. An element is essential if it belongs to every solution of the problem. We consider the complexity of indentifying redundant and essential elements in a sample of NP-Hard optimization problems. It is shown that these identification problems are also NP-Hard. The proofs are based on an analysis of the original reductions of Cook [The complexity of theorem proving procedures, in “Proceedings, Third Annual Assoc. Comput. Mach. Symposium on Theory of Computing”, pp. 151–158, Assoc. Comput. Mach., New York 1971] and Karp [Reducibility among combinational problems, in “Complexity of Computer Computations” (R. E. Miller and J. W. Thatcher, Eds.), pp. 85–104, Plenum, New York 1972]. 相似文献
43.
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45.
Oscar H Ibarra Shlomo Moran Roger Hui 《Journal of Algorithms in Cognition, Informatics and Logic》1982,3(1):45-56
We show that any m × n matrix A, over any field, can be written as a product, LSP, of three matrices, where L is a lower triangular matrix with l's on the main diagonal, S is an m × n matrix which reduces to an upper triangular matrix with nonzero diagonal elements when the zero rows are deleted, and P is an n × n permutation matrix. Moreover, L, S, and P can be found in O(mα?1n) time, where the complexity of matrix multiplication is O(mα). We use the LSP decomposition to construct fast algorithms for some important matrix problems. In particular, we develop O(mα?1n) algorithms for the following problems, where A is any m × n matrix: (1) Determine if the system of equations (where is a column vector) has a solution, and if so, find one such solution. (2) Find a generalized inverse, , of A (i.e., ). (3) Find simultaneously a maximal independent set of rows and a maximal independent set of columns of A. 相似文献
46.
Specific direct mono fluorinations on various sites of the steroidal skeleton of bile acids were achieved by introduction of electronegative groups at selected points. 相似文献
47.
The maximized overlap population, defined as Σμ≠νPμνSμν, and a related quantity, Σμ,νPμνS2μν are computed for a series of configurations. The extremum of both approximate molecular geometries, the latter with an accuracy suitable for predictive value. The maximum overlap orbitals predict dipole and quadrupole moments that give reasonable agreement with experimental values. 相似文献
48.
The relation between Coulomb displacement energies,ΔE c , andΔr=r n -r p , the difference between the rms radii of neutrons and protons in nuclei, is investigated within the energy density formalism (EDF). The variational equation, obtained by minimizing the Coulomb plus symmetry energies, is solved assuming the symmetry interaction is a simple functional of the local nuclear matter density. Varying parameters of the model, rather unique relation betweenΔE c andΔr is obtained (within ±50 keV).ΔE c isindependent ofr ex, the rms radius of the excess neutrons distribution. Using the experimental values ofr p and adjusting the model to reproduce the recent data onΔr (Δr∽~0.05 fm for48Ca and208Pb), which are significantly smaller than those obtained from current Hartree-Fock calculations, the calculatedΔE c agree with the experimental results. Using the value ofΔr~0.05 fm and the experimental values ofr ex, a small compression (<0.02 fm) of the proton core in the analogue state relative to its parent state emerges, thus contributing an additional electrostatic term to the Coulomb displacement energy. The size of this relative core-compression effect depends on the values assumed forΔr andr ex, it increases with the decreasing ofΔr and the increasing ofr ex. IfΔr~0.05 fm the effect is large enough to remove the long standing Coulomb energy anomaly. The main result of the present work is the correlation betweenΔE c andΔr, suggesting that the difficulties of current Hartree-Fock calculations in reproducing isotope shifts ofr p , the small value ofr n ?r p and the values ofΔE c may all be different manifestations of some missing residualp n effective interaction. 相似文献
49.
Shlomo Carmi 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1969,20(4):487-500
Zusammenfassung Die Energiemethode wird zur Untersuchung der Stabilität einer beliebigen Kanalströmung angewandt. Es wird eine auf Eigenwertabschätzungen basierte qualitative Beschreibung der Fläche (, ) gegeben, welche die Schranke für den Instabilitätsbereich in Abhängigkeit von Längs- bzw. Querwellenzahl der Störungen darstellt. Eine allgemeine untere Grenze für die minimalisierende Querwellenzahl und den zugehörigen Eigenwert (0, ) wird angegeben. Das Problem der Energiestabilität wird dann für eine Klasse von Geschwindigkeitsprofilen mit Wendepunkt gelöst. Die durch numerische Integration erhaltenen Ergebnisse werden mit den Ergebnissen der linearen Stabilitätstheorie verglichen. 相似文献
50.
A procedure is presented which allows the application of linear response theory and the random phase approximation to an open shell. The procedure is applied to Ca isotopes. The general features of giant multipole resonances are found to vary smoothly with the mass. The resonances exhibit more structure in the open 1f shell nuclei. While the energy-weighted dipole sum is practically constant in all isotopes, the isoscalar quadrupole and octupole energy weighted sums increase continuously by ~ 30 % from 40Ca to 48Ca. 相似文献