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51.
A classical result in Lorentzian geometry states that a strongly causal spacetime is globally hyperbolic if and only if the Lorentzian distance is finite valued for every metric choice in the conformal class. It is proved here that a non-total imprisoning spacetime is globally hyperbolic if and only if for every metric choice in the conformal class the Lorentzian distance is continuous. Moreover, it is proved that a non-total imprisoning spacetime is causally simple if and only if for every metric choice in the conformal class the Lorentzian distance is continuous wherever it vanishes. Finally, a strongly causal spacetime is causally continuous if and only if there is at least one metric in the conformal class such that the Lorentzian distance is continuous wherever it vanishes. 相似文献
52.
Non-equilibrium vibrational kinetics as recently developed for adlayers is applied to experimental data on H-atom recombination and abstraction at solid surfaces. This model allows one to fit vibrational and translational energy distribution functions of the excited diatoms leaving the surface. Eley–Rideal and Langmuir–Hinshelwood mechanisms involving vibrationally excited adatoms are presented together with a criterion for establishing their relative contribution to the total reaction rate. Analogies of this multilevel ‘hot atom' (HA) model with recently employed two and three levels HA kinetic schemes are presented and discussed. 相似文献
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van Well RM Marinelli L Altona C Erkelens K Siegal G van Raaij M Llamas-Saiz AL Kessler H Novellino E Lavecchia A van Boom JH Overhand M 《Journal of the American Chemical Society》2003,125(36):10822-10829
Sugar amino acids (SAAs) are useful building blocks for the design of peptidomimetics and peptide scaffolds. The three-dimensional structures of cyclic hybrid molecules containing the furanoid epsilon-SAA III and several amino acids were elucidated to study the preferred conformation of such an epsilon-SAA and its conformational influence on the backbone of cyclic peptides. NMR-based molecular dynamics simulations and empirical calculations of the cyclic tetramer 1, consisting of two copies of the SAA residue and two amino acids, revealed that it is conformationally restrained. The two SAA residues adopt different conformations. One of them forms an unusual turn, stabilized by an intraresidue nine-member hydrogen bond. The methylene functionalities of the other SAA residue are positioned in such a way that an intraresidue H bond is not possible. The X-ray crystal structure of 1 strongly resembles the solution conformation. Molecular dynamics calculations in combination with NMR analysis were also performed for compounds 2 and 3, which contain the RGD (Arg-Gly-Asp) consensus sequence and were previously shown to inhibit alpha(IIb)beta(3)-receptor-mediated platelet aggregation. The biologically most active compound 2 adopts a preferred conformation with the single SAA residue folded into the nine-member H bond-containing turn. Compound 3, containing an additional valine residue, as compared with compound 2, is conformational flexible. Our studies demonstrate that the furanoid epsilon-SAA III is able to introduce an unusual intraresidue hydrogen bond-stabilized beta-turn-like conformation in two of the three cyclic structures. 相似文献
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Ettore Bortolotti 《Monatshefte für Mathematik》1939,48(1):457-486
Mit 23 Figuren im Text. 相似文献
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[reaction: see text] A new, mild, and reversible method to convert primary amides to nitriles in good yields using PdCl2 in aqueous acetonitrile is described. 相似文献
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Francesco Chioccara Francesco Delia Gala Ettore Novellino Giuseppe Prota 《Journal of heterocyclic chemistry》1977,14(5):773-775
The reported synthesis of 3-phcnyl-2H-1,4-benzoxazin-2-one (II) via brominution of o-acel-amidophenyl phcnaeyl ether (Scheme) leads in lael to the 7-bromo-3-phenyl-2H-1,4-benzoxazin-2-ol (VIII). The structure of the other synthetic intermediates is also revised and a one-step synthesis of the lactone II is reported hy condensation of methyl phenylglyoxalale and o-amino-phenol. 相似文献