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111.
Computer simulations of the co-adsorption of water and methanoic acid at a range of surface features of calcite and fluorite minerals have shown that the relative adsorption energies for the two minerals are reversed when solvent effects are included in the calculations, a finding which is important in the search for effective surfactant reagents in flotation techniques, which are used extensively in the mining and pharmaceutical industries and in environmental remediation processes. 相似文献
112.
Organ MG Arvanitis EA Dixon CE Cooper JT 《Journal of the American Chemical Society》2002,124(7):1288-1294
It has been demonstrated that the same Pd catalyst can be used to effect allylic substitution or vinylic cross-coupling reactions selectively and interchangeably on polyfunctionalized olefin building blocks despite the differences in reaction mechanism. This was achieved by altering the pK(a) of the conjugate acid of the allylic leaving group while keeping the vinyl coupling partner constant. In the case of 2,3-dibromo-1-propene, Pd-catalyzed allylic ionization with malonate nucleophile proceeded selectively and quantitatively in the presence of the Suzuki reaction components necessary for cross-coupling. Conversely, the bromide of 2-bromo-1-(4-ethylphenoxy)-2-propene could be cross-coupled selectively without activation of the allylic phenoxy substituent. In both reactions, the same catalyst could then be used to complete the sequence, which typically involved heating as the trigger to promote the second, more reluctant reaction. Mechanistic considerations as well as synthetic applications demonstrating the value of this interchangeable catalyzed sequence are presented. 相似文献
113.
114.
W W Cooper 《The Journal of the Operational Research Society》1999,50(1):3-11
It is argued that movement toward the ‘control’ aspects of management should be effected to expand OR/MS activities beyond their present (almost exclusive) emphasis on ‘planning’ functions. This will involve increasing the amount of empirical-inferential approaches to research (based on ex-post data) as one way to help bring this about. Examples of such empirical-inferential research activities in OR/MS are supplied by reference to the early (founding) work of PMS Blackett and others on high-level policy problems during World War II. Extensions to the control function are evidenced in the work of Robert Fetter and others in the development of Diagnostic Related Groups on which the Prospective Payment Systems are based with large and important impacts on the health care delivery systems in the USA as well as other countries. Other examples covered include the use of OR concepts in the early ‘turnaround’ of Federal Express from failure to success. Other new methods will nevertheless be needed to extend and improve presently available OR/MS approaches. Some of these possibilities are illustrated with Data Envelopment Analysis. Ways to combine DEA with commonly used statistical methods are described to show how new and old methods may be combined to further enhance their power and range. Similar relations of DEA to other OR/MS approaches are now being studied, some of which are presently occurring with ‘fuzzy sets’ and ‘multiple objective programming.’ 相似文献
115.
T. H. Prettyman C. S. Cooper P. N. Luke P. A. Russo M. Amman D. J. Mercer 《Journal of Radioanalytical and Nuclear Chemistry》1998,233(1-2):257-264
A physics-based approach to gamma-ray response-function generation is presented in which the response of CdZnTe detectors
is modeled from first principles. Numerical modeling is used to generate response functions needed for spectrum analysis for
general detector configurations (e.g., electrode design, detector materials and geometry, and operating conditions). With
numerical modeling, requirements for calibration and characterization are significantly reduced. Elements of the physics-based
model, including gamma-ray transport, charge carrier drift and diffusion, and circuit response, are presented. Calculated
and experimental gamma-ray spectra are compared for a coplanar-grid CdZnTe detector. 相似文献
116.
Electron pair distribution functions are analyzed for a variety of SCF+CI wavefunctions, for a range of simple molecules. The statistical correlation between electrons of like spin introduced by the antisymmetry requirement on the many-electron wavefunction is contrasted with the manner in which unlike-spin electron correlation is introduced through the inclusion of configuration interaction. 相似文献
117.
118.
We observe the reaction dp → pspec (pπ?)p in a bubble chamber exposure at 25 GeV/c incident deuteron momentum. The (pπ?) system with invariant mass below 2.0 GeV is interpreted as neutron diffraction dissociation. The (pπ?) mass spectra show little if any direct evidence of N1 production. The decay angular distributions and the momentum transfer distributions of the (pπ?) system suggest a smooth increase in contributions from higher partial waves with increased mass or momentum transfer. A simple partial-wave analysis shows a P11 contribution below 1.3 GeV for small ?t′ and a dominant D13 contribution elsewhere. Both the P11 and D13 amplitudes peak far below the N1(1470) and N1(1520) resonances. We also find evidence for the charge-exchange reaction np → p(pπ?). In this process the (pπ?) system shows evidence for Δo(1236) and N1(1520) production. 相似文献
119.
120.
We review the properties of supersymmetric quantum mechanics for a class of models proposed by Witten. Using both Hamiltonian and path integral formulations, we give general conditions for which supersymmetry is broken (unbroken) by quantum fluctuations. The spectrum of states is discussed, and a virial theorem is derived for the energy. We also show that the euclidean path integral for supersymmetric quantum mechanics is equivalent to a classical stochastic process when the supersymmetry is unbroken (E0 = 0). By solving a Fokker-Planck equation for the classical probability distribution, we find Pc(y) is identical to |Ψ0(y)|2 in the quantum theory. 相似文献