NVT Monte Carlo simulations are first used to describe the distribution of Na cations in Faujasite for several Si/Al ratios. These calculations were performed by combining two different sets of potential parameters combined with both T-atoms and explicit Si,Al models. Grand Canonical Monte Carlo simulations are then employed to investigate the influence of water adsorption on the distribution of cations in the case of a Faujasite sample with 56 cations (NaY56). These simulations data are compared to available experimental data and the influence of the choice of the forcefield for describing the cation/zeolite interaction on these results is discussed. 相似文献
Ac conductivity and dielectric losses are measured on a sodium aluminosilicate glass using various experimental conditions. Data obtained using metallic contacts and insulating barriers are compared. The influences of the thermal environment, i.e. iso versus non-isothermal, and of the application of a constant dc electric field, i.e. BIAS, are also investigated. It is thus shown that the use of non-isothermal conditions and insulating barriers is a convenient tool for extracting and hence for analyzing the bulk intrinsic polarization response of the sample. The analysis of this response with a simple model based on distribution of energy barriers gives some insights into the glass structure which turns out to be rather homogeneous. 相似文献
The negative charge originating from deprotonation of the methyl group is distributed over the 2‐picolyl ring. Bonding properties derived from the electron density distribution support the enamide character of picolyllithium (PicLi; the picture shows the deformation density of [2‐PicLi?PicH]2), but electrophilic attack occurs at the deprotonated C atom. This reactivity is rationalized by the electrostatic potential, which guides electrophiles towards the nucleophilic C atom.
The pqs quorum sensing communication system of Pseudomonas aeruginosa controls virulence factor production and is involved in biofilm formation, therefore playing an important role for pathogenicity. In order to attenuate P. aeruginosa pathogenicity, we followed a ligand-based drug design approach and synthesized a series of compounds targeting PqsR, the receptor of the pqs system. In vitro evaluation using a reporter gene assay in Escherichia coli led to the discovery of the first competitive PqsR antagonists, which are highly potent (K(d,app) of compound 20: 7 nM). These antagonists are able to reduce the production of the virulence factor pyocyanin in P. aeruginosa. Our finding offers insights into the ligand-receptor interaction of PqsR and provides a promising starting point for further drug design. 相似文献
Nuclear proteins obtained from human brain tumor cell lines by differential salt extraction were subjected to high-resolution two-dimensional electrophoresis. Several hundred spots were detectable in the low salt (0.4 M NaCl) extract using silver staining. These patterns exhibited remarkable differences between the different cell lines we analyzed. A less complex pattern occurred when nuclei were subsequently treated with high salt (2.5 M NaCl/5 M urea). We compared the electropherograms from various human glioblastoma cell lines and found them very similar and even a high degree of similarity occurs between glioblastomas and other human tumor cell lines. Beside these more general observations we detected several proteins at least enriched in human glioblastomas which were totally absent in low grade astrocytomas and nonglial tumors. They could be separated from the bulk of nonspecific proteins by simple modifications of the isoelectric focusing conditions. From these results we conclude that nuclear proteins obtained by sequential salt extraction and separated by two-dimensional techniques may provide tumor specific proteins suitable for antibody production. 相似文献
The effect of pre-stress on the propagation and reflection ofplane waves in an incompressible isotropic elastic half-spacehas been examined recently by the authors (Ogden & Sotiropoulos,1997). In the present paper the corresponding analysis for compressiblematerials is detailed. In the two-dimensional context consideredfor incompressible materials the (homogeneous) plane waves werenecessarily shear waves. By contrast, in the compressible contextpure shear waves can propagate only in specific directions inthe considered principal plane and, in a general direction,a quasi-shear wave may be accompanied by a quasi-longitudinalwave, as is the case in the anisotropic linear theory. The dependenceof the (in-plane) slowness section on the pre-stress (and finitedeformation) and on the choice of constitutive law is elucidated.This information is used to determine the reflection coefficientsfor reflection of either a (quasi-) shear wave or a (quasi-)longitudinal wave from the boundary of the half-space and tocharacterize the different cases which arise depending on thegeometry of the slowness section. The theoretical results are illustrated by numerical calculationsfor the range of possible types of behaviour with referenceforms of strain-energy function and different states of finitedeformation and to the question of stability of the half-space. 相似文献
Invisibility devices exploit ambiguities in the inverse scattering problem of light in media. Scattering also serves as an important general tool to infer information about the structure of matter. We elucidate the nature of scattering ambiguities that arise in central potentials. We show that scattering is a tomographic projection: The integrated scattering angle is a projection of a scattering function onto the impact parameter. This function depends on the potential but may be multivalued, allowing for ambiguities where several potentials share the same scattering data. In addition, multivalued scattering angles also lead to ambiguities. We apply our theory to show that it is, in principle, possible to construct an invisibility device without infinite phase velocity of light. 相似文献