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1.
Ludger Hannibal 《International Journal of Theoretical Physics》1991,30(11):1431-1444
A discussion of the 1950s and 1960s on the existence of an explicit covariant canonical formalism is renewed. A new point of view is introduced where Hamilton's principle, based on the existence of a Hamiltonian, is postulated independently from the Lagrange formalism. The Hamiltonian is determined by transformation properties and dimensional considerations. The variation of the action without constraints leads to an explicit covariant canonical formalism and correct equations of motion. The introduction of the charge as a fifth momentum gives rise to a reformulation of classical relativistic point mechanics as a five-dimensionalU(1) gauge theory with a theoretically invisible extra dimension. A generalization to other gauge groups is given. The inversion of the proper time is introduced as a new particle-antiparticle symmetry that allows one to show that in the five-dimensional classical theory all particles have positive energy. 相似文献
2.
Modelling financial and insurance time series with Lévy processes or with exponential Lévy processes is a relevant actual practice and an active area of research. It allows qualitatively and quantitatively good adaptation to the empirical statistical properties of asset returns. Due to model incompleteness it is a problem of considerable interest to determine the dependence of option prices in these models on the choice of pricing measures and to establish nontrivial price bounds. In this paper we review and extend ordering results of stochastic and convex type for this class of models. We also extend the ordering results to processes with independent increments (PII) and present several examples and applications as to α-stable processes, NIG-processes, GH-distributions, and others. Criteria are given for the Lévy measures which imply corresponding comparison results for European type options in (exponential) Lévy models. 相似文献
3.
Bulk properties and free interfaces of mixtures of charged platelike colloids and salt are studied within the density-functional theory. The particles are modeled by hard cuboids with their edges constrained to be parallel to the Cartesian axes corresponding to the Zwanzig model. The charges of the particles are concentrated in their center. The density functional is derived by functional integration of an extension of the Debye-Hückel pair distribution function with respect to the interaction potential. For sufficiently small macroion charges, the bulk phase diagrams exhibit one isotropic and one nematic phase separated by a first-order phase transition. With increasing platelet charge, the isotropic and nematic binodals are shifted to higher densities. The Donnan potential between the coexisting isotropic and nematic phases is inferred from bulk structure calculations. Nonmonotonic density and nematic order parameter profiles are found at a free interface interpolating between the coexisting isotropic and nematic bulk phases. Moreover, electrically charged layers form at the free interface leading to monotonically varying electrostatic potential profiles. Both the widths of the free interfaces and the bulk correlation lengths are approximately given by the Debye length. For fixed salt density, the interfacial tension decreases upon increasing the macroion charge. 相似文献
4.
The title compounds were prepared by reaction of CaSb2, SrSb2, or BaSb3 with the transition metals and antimony in sealed silica tubes. They crystallize with the cubic LaFe4P12-structure, which was refined from single-crystal X-ray data of CaFe4Sb12, SrRu4Sb12, and BaRu4Sb12 to residuals of R = 0.014, 0.016, and 0.014, respectively. The thermal parameters of the alkaline earth ions increase with decreasing ionic size. The Sb? Sb distances are greater in the iron compound than they are in the two ruthenium compounds. This is rationalized to be due to a larger portion of electrons in antibonding Sb? Sb states in the iron compound. 相似文献
5.
Matthias Freytag Frank T. Edelmann Ludger Ernst Peter G. Jones Reinhard Schmutzler 《无机化学与普通化学杂志》2004,630(3):377-383
The reaction of the symmetric diphosphene 2, 4, 6‐(CF3)3‐C6H2‐P=P‐C6H2‐2, 4, 6‐(CF3)3 4 with Ru3(CO)12 led to the 50‐electron Ru3P2 nido‐cluster Ru3(CO)9[μ‐P‐C6H2‐2, 4, 6‐(CF3)3]2 5 , which in solution at room temperature displays hindered rotation of the aromatic rings about the C(aryl)—P bonds. The structure of 5 was determined by X‐ray crystal structure analysis; its Ru3P2 centre forms a distorted square pyramid with one ruthenium atom at the apex. One of the two C6H2(CF3)3 groups is also appreciably distorted. Temperature‐dependent 19F NMR studies of the [A3M3X]2 spin system (A = M = CF3, X = 31P) of 5 indicated a rotational barrier ΔG≠ of 82.3 kJ mol‐1 at 141 °C. The same Ru3P2 core was obtained by the reaction of the unsymmetric diphosphene Mes*‐P=P‐Mes 11 with Ru3(CO)12; hindered rotation about the C(aryl)—P bonds was also observed, in this case. 相似文献
6.
Chromium-Reformatsky and chromium-homoaldol reactions run under neutral and mild reaction conditions. They are highly chemoselective, tolerant towards most common functional groups, and are not prone to retroaldol reactions. Initial studies directed to transfer these homogeneous chromium-mediated solution-phase reactions to solid phase are presented. The main objective was to develop a methodology to aid a combinatorial iterative strategy to polyols (polyketides) on solid phase. A general reactivity problem was observed with polystyrene based resins compared to the solution-phase reactions, independent if the electrophilic (aldehyde) or nucleophilic (bromide) end of the polyol chain was supported to the resin. A complicated penetration, or loss of the polar solvent environment after penetration into the resin, might be responsible for the reduced reactivity. Application of either a soluble polystyrene resin or a polystyrene resin with a polar polyethylene glycol tether resulted in improved yields. 相似文献
7.
Gerhard Holxe Titus A. Jenny Petr Nesvadba Albert Gossauer Ludger Ernst Walter Keller Christoph Kratky 《Helvetica chimica acta》1991,74(6):1287-1295
On treatment with H2SO4/MeOH, epimerization of hexamethyl cis-5,6-dihydroxycobyrinate c,8-lactam ( 3 ) takes place quantitatively at C(6), yielding the corresponding trans-diol 4 . The corresponding lactone 7 , whose structure has been established by X-ray analysis, is obtained from xanthocorrinoids 5 and 6 under similar conditions. 相似文献
8.
9.
Burghard Grüning Gerhard Holze Albert Gossauer Ludger Ernst 《Helvetica chimica acta》1985,68(6):1771-1781
The transformation of the c-acetic-acid chain of hexamethyl Coα, Coβ-dicyanocobyrinate into an ethyl group (→ 2 ) as well as the synthesis of the pentadecaalkyl-cobalticorrin 6d from commercial cyanocobalamin are described. On reaction of 2 or 6d with O2 in the presence of ascorbic acid, migration of the CH3 group at C(5) to the vicinal position C(6) takes place concomitantly with the introduction of a carbonyl group at C(5). 相似文献
10.
Antonio L. Braga Helmoz R. Appelt Claudio C. Silveira Ludger A. Wessjohann Paulo H. Schneider 《Tetrahedron》2002,58(52):10413-10416
The enantioselective alkynylation reaction of aldehydes with alkynes and diethylzinc, catalyzed by chiral disulfide–oxazolidine ligands, provides a simple, practical and inexpensive method to access chiral propargylic alcohols in good yields and satisfactory ee's. 相似文献