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281.
Antonio Guerrero Jacobo Gmez-Lara Jorge Cervantes 《Journal of organometallic chemistry》1992,430(3):273-286
Mass spectral fragmentation of a series of transition metal substituted disilanes, LMSiMe2SiMe2ML, LM = (η5-C5H5)Fe(CO)2- (Fp), (η5-C5H5)Fe(η5-C5H4)- (Fc), RFe(CO)2(η5-C5H4), are reported. They exhibit significant distinctions depending on the nature of LM. Direct cleavage of the Si---Si bond occurs in the order Fc å Fp å RFe(CO)2(η5-C5H4) owing to the capacity of the LM fragment to stabilize positive charge. For complexes containing a direct Fe---Si bond, i.e. Fp-SiMe2SiMe2ML, disilene complexed ions are observed, and those complexes containing both an Fp group and a (η5-C5H4-SiMe2SiMe2) group exhibit significant formation of (C5H4=Si=SiMe2) complexed ions. Little disproportionation is observed for any of the complexes studied, in contrast to organodisilanes. 相似文献
282.
From the aerial parts of Salvia aspera one new tri-nordammarane named amblyol (1) was isolated besides amblyone (2). An X-ray analysis was performed on compound 1. In addition, three known neoclerodane diterpenoids were also isolated. The structures of these compounds were established by spectral and chemical methods. The presence of dammarane triterpenoids in a Mexican Salvia is described for the first time. 相似文献
283.
The problems arising when quantizing systems with periodic boundary conditions are analysed, in an algebraic (group-) quantization scheme, and the failure of the Ehrenfest theorem is clarified in terms of the already defined notion ofgood (andbad) operators. The analysis of constrained Heisenberg-Weyl groups according to this quantization scheme reveals the possibility for quantum operators without classical analogue and for new quantum (fractional) numbers extending those allowed for Chern classes in traditional Geometric Quantization. This study is illustrated with the examples of the free particle on the circumference and the charged particle in a homogeneous magnetic field on the torus, both examples featuring anomalous operators, non-equivalent quantization and the latter, fractional quantum numbers. These provide the rationale behind flux quantization in superconducting rings and Fractional Quantum Hall Effect, respectively.Work partially supported by the DGICYT. 相似文献
284.
Blanca R. Manzano Félix A. Jalón Gustavo Espino Ana Guerrero Rosa M. Claramunt Consuelo Escolástico José Elguero M. Aránzazu Heras 《Polyhedron》2007
A novel ruthenium bisbipyridine complex, [Ru(bpy)2(hpzb)](PF6)2 (1) (hpzb = hexakis(pyrazol-1-yl)benzene) was obtained in the reaction between [Ru(bpy)2Cl2], the tritopic ligand hpzb and NH4PF6. A high selectivity has been found in the reaction and when the hpzb ligand was made to react with more than one ruthenium fragment, it coordinated selectively only to the first metallic fragment, and it was not possible to introduce two or three ruthenium centres. A similar complex with a deuterated bipyridine has also been obtained. The reaction with the methylated ligand hexakis(3,5-dimethylpyrazol-1-yl)benzene does not take place. A complete assignment of all the proton and carbon NMR signals of 1 was carried out. The orientation of the free pyrazolyl groups is also discussed. The redox properties and the anticancer activity of complex 1 have been studied. 相似文献
285.
In this paper, we analyze how to update incomplete Cholesky preconditioners to solve least squares problems using iterative methods when the set of linear relations is updated with some new information, a new variable is added or, contrarily, some information or variable is removed from the set. Our proposed method computes a low-rank update of the preconditioner using a bordering method which is inexpensive compared with the cost of computing a new preconditioner. Moreover, the numerical experiments presented show that this strategy gives, in many cases, a better preconditioner than other choices, including the computation of a new preconditioner from scratch or reusing an existing one. 相似文献
286.
Dr. Susana Ibáñez Dr. Antonio Guerrero Dr. Macarena Poyatos Prof. Eduardo Peris 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(29):10566-10575
A rational synthetic procedure for the preparation of a series of pyrene‐based neutral and dicationic bis‐azole compounds is reported. The method allows the tailored design of pyrene‐based azoles with different substituents at the nitrogen atoms of the heterocycles, for which the relative conformation of the resulting bis‐azoles can be easily controlled. The bis‐azoliums were used for the preparation of the related diplatinum complexes by reaction with [{Pt(ppy)(μ‐Cl)2}2] (ppy=2‐phenylpyridinate). The X‐ray molecular structure of one of the resulting compounds, a diplatinum(II) bis(N‐heterocyclic carbene) complex, is described. Studies on the photophysical properties of all new species are described. The emission of the bis‐azole‐based compounds seems to be independent of their substitution patterns, which basically indicates that physical properties such as solubility, melting point, and viscosity can be fine‐tuned while maintaining the luminescence properties. Finally, the energies associated with the HOMO and LUMO levels suggest that this family provides versatility to match the energy levels of a wide range of host materials, which is important for the preparation of organic light‐emitting devices. 相似文献
287.
The effect of high-pressure treatments on the gelation of egg yolk dispersions was studied by using differential scanning
calorimetry (DSC) and small amplitude oscillatory shear (SAOS). The influence of pressure of processing and pH were analysed.
The DSC results suggest a progressive decrease in thermal denaturation enthalpy as pressure level increases related to protein
denaturation. SAOS was used to evaluate the effect of different pressure levels on the linear viscoelastic behaviour of egg
yolk dispersions. An increase in the pressure level produces a dramatic change in the linear viscoelastic behaviour undergoing
a sol–gel transition. High hydrostatic pressure (HHP) processing was also analysed as a function of pH and solids content.
The results obtained confirm that the impact of high pressure on aggregation and network formation can be modulated by pH.
HHP processing of egg yolk systems is highly affected by protein concentration particularly when it is compared to heat processing. 相似文献
288.
We study transitivity conditions on the norm of JB
*-triples, C
*-algebras, JB-algebras, and their preduals. We show that, for the predual X of a JBW
*-triple, each one of the following conditions i) and ii) implies that X is a Hilbert space. i) The closed unit ball of X has some extreme point and the norm of X is convex transitive. ii) The set of all extreme points of the closed unit ball of X is non rare in the unit sphere of X. These results are applied to obtain partial affirmative answers to the open problem whether every JB
*-triple with transitive norm is a Hilbert space. We extend to arbitrary C
*-algebras previously known characterizations of transitivity [20] and convex transitivity [36] of the norm on commutative
C
*-algebras. Moreover, we prove that the Calkin algebra has convex transitive norm. We also prove that, if X is a JB-algebra, and if either the norm of X is convex transitive or X has a predual with convex transitive norm, then X is associative. As a consequence, a JB-algebra with almost transitive norm is isomorphic to the field of real numbers.
Received: 9 June 1999 / Revised version: 20 February 2000 相似文献
289.
E. Oset J. A. Oller J. R. Pel ez A. Ramos H. C. Chiang F. Guerrero S. Hirenzaki T. S. H. Lee E. Marco J. C. Nacher Y. Okumura A. Parre o H. Toki M. Vicente-Vacas 《Nuclear Physics A》2000,670(1-4):111-118
We report on recent progress on the chiral unitary approach, analogous to the effective range expansion in Quantum Mechanics, which is shown to have a much larger convergence radius than ordinary chiral perturbation theory, allowing one to reproduce data for meson meson interaction up to 1.2 GeV. Applications to physical processes so far unsuited for a standard chiral perturbative approach are presented. Results for the extension of these ideas to the meson baryon sector are discussed, together with applications to kaons in a nuclear medium and K− atoms. 相似文献