The shortest He–He distance! r(He–He)=1.265 Å. The electronic interaction between confined pairs of He atoms in the C20H20 dodecahedrane cage is analyzed (see figure). A key observation about bonding that emerges uniquely from endohedral complexes is that a short internuclear separation does not necessarily imply the existence of a chemical bond.
Results obtained with an “electronic tongue” device based on an array of ion-selective field transistors integrated into a
flow-injection system are presented. The component concentrations in mineral waters from Spanish manufacturers are analyzed.
Processing of analytical signals by the partial least squares method improves the accuracy of component determination in mineral
waters of close compositions. A single chip integrates sensors sensitive to pH, K+, Na+, Ca2+, and Cl− ions. Mineral waters are classified and the concentrations of the main components are calculated with an error not exceeding
10%. 相似文献
Limited diffraction ultrasonic transducers are devices that have a large depth of acoustic field without important effects of diffraction, which make them optimal in applications of medical images, among others. This report details how this special type of piezoelectric device was designed by means of a simple technology using three electrodes in the form of concentric rings in both faces of a ferroelectric ceramic disk, which were used to apply a profile of non-homogeneous polarization. Once designed, the radiation fields emitted by these resonators were characterized experimentally by electro-acoustic and acousto-optic techniques and were compared with those emitted by conventional devices. As shown in the experimental characterizations, ultrasonic transducers with optimal properties for use in medical applications such as good collimation of the ultrasound beam, high lateral resolution, as well as little effects of diffraction were obtained. 相似文献
Disordered geometrical boundaries such as rough surfaces induce important modifications to the mode spectrum of the electromagnetic quantum vacuum. In analogy to Anderson localization of waves induced by a random potential, here we show that the Casimir-Polder interaction between a cold atomic sample and a rough surface also produces localization phenomena. These effects, that represent a macroscopic manifestation of disorder in quantum vacuum, should be observable with Bose-Einstein condensates expanding in proximity of rough surfaces. 相似文献
The parameters used to characterize the acoustic behaviour of fibrous absorbent materials are usually the complex characteristic impedance and the complex wavenumber, which permit the calculation of the airflow resistance and vice versa. Different methods have been satisfactorily used by other authors in order to perform this characterization on the basis of a macroscopic modelling of the behaviour of these materials. In this paper, the suitability of this approach for predicting the acoustic response of absorbent materials to impulsive excitations is evaluated. The constant term of the airflow resistance equation for absorbent materials with different densities is quantified by means of a modified version of the impulse method. These values are then incorporated into one-dimensional acoustic calculations in order to predict the response of absorbing materials to pressure pulse excitation. The very good concordance observed between calculated and measured reflection and transmission coefficients shows the suitability of the proposed procedure for the characterization of absorbent materials. 相似文献
We report the crystallographic parameters of LaMnO3 obtained from X-ray diffraction data and electronic properties predictions using the density functional theory (DFT). LaMnO3 was prepared by the citrate precursor method (CPM). The initial solution was 0.1 M of each cation and the citrate nitrate relation was one. The solution was dried at 373 K; the yielded foam was annealed at 873 K and then was characterized by X-ray diffraction. Diffraction peaks show that the space group is R-3c (#167) with a=b =5.523 Å and c=13.324 Å (rhombohedrally distorted perovskite). Structural results of the Rietveld method have a matching of 97% with that obtained from the Structure Prediction Diagnostic Software. DFT calculation reveals a half-metallic character and its magnetic moment is about 2.0 μB. 相似文献
The title compounds, poly[bis(2,2′‐bipyridine)bis(μ3‐hydrogen phosphato)nitratodi‐μ2‐oxo‐dicopper(II)vanadium dihydrate], [Cu2(VO2)(HPO4)2(NO3)(C10H8N2)2]·2H2O, (I), and poly[bis(2,2′‐bipyridine)bis(μ3‐hydrogen phosphato)nitratodi‐μ2‐oxo‐dicopper(II)vanadium phosphoric acid solvate], [Cu2(VO2)(HPO4)2(NO3)(C10H8N2)2]·H3PO4, (II), were obtained by similar hydrothermal methods but under different crystallization conditions. The trinuclear entity which serves as the basic unit in both structures presents two independent CuII ions immersed in similar square‐pyramidal N2O3 environments plus an octahedral VO6 core and is organized into a one‐dimensional polymer, which is essentially identical in the two structures. The compounds are stabilized by different solvates, viz. two crystallization water molecules in (I) and a phosphoric acid molecule in (II), which provide the main structural differences through the diversity of interchain interactions in which they serve as bridges. 相似文献
The first two crystal structures of enamines derived from 1‐n‐alkyl‐3‐methyl‐5‐pyrazolones, namely 1‐(n‐hexyl)‐3‐methyl‐4‐[1‐(phenylamino)propylidene]‐2‐pyrazolin‐5‐one, C19H27N3O, (I), and N,N′‐bis{1‐[1‐(n‐hexyl)‐3‐methyl‐5‐oxo‐2‐pyrazolin‐4‐ylidene]ethyl}hexane‐1,6‐diamine, C30H52N6O2, (II), are reported. The molecule of (II) lies about an inversion centre. Both (I) and (II) are stabilized by intramolecular N—H⋯O hydrogen bonding. This confirms previous results based on spectroscopic evidence alone. 相似文献
Dynamical networks are characterized by 1) their topology (structure of the graph of interactions among the elements of a network); 2) the interactions between the elements of the network; 3) the intrinsic (local) dynamics of the elements of the network. A general approach to studying the commulative effect of all these three factors on the evolution of networks of a very general type has been developed in [1]. Besides, in this paper there were obtained sufficient conditions for a global stability (generalized strong synchronization) of networks with an arbitrary topology and the dynamics which is a composition (action of one after another) of a local dynamics of the elements of a network and of the interactions between these elements. Here we extend the results of [1] on global stability (generalized strong synchronization) to the case of a general dynamics in discrete time dynamical networks and to general dynamical networks with continuous time. 相似文献