Effect of electron tunneling on the crystallization of nanostructured metal sols

Regularities of the self-organization of bimodal ensembles of nanoparticles into crystalline structures in metal lyosols are studied by the Brownian dynamics method. Differences in the thicknesses of adsorption layers, van der Waals, elastic, and electrostatic interactions, and random and dissipative forces, as well as variations in interparticle electrostatic interactions due to electron tunneling are taken into account in the model. Pair potentials for polydisperse ensembles of particles are analyzed and the correlation between the pattern of potential curves and the type of forming structures is revealed. The possibility of the selective coagulation of particles with different sizes by virtue of dissimilar charging at the moment of their approach is demonstrated. The kinetics of this process is investigated. Specific features of the crystallization of bimodal sols are discussed using real gold organosols as examples.     

Search for two-neutrino 2<Emphasis Type="Italic">K</Emphasis> capture in <Superscript>124</Superscript>Xe: the method and preliminary results

The technique used in the experiment in the search for the process of 2K2ν-capture in ¹²⁴Xe using large high-pressure proportional counters is briefly described. The measurements with a xenon sample enriched to 21% (or ~57 g) of the ¹²⁴Xe isotope carried out for 3340 hours yielded a zero signal. The resultant upper limit on the ¹²⁴Xe half-life with respect to the 2ν-mode of the nuclear capture of two K-shell electrons amounts to T_1/2>4.6 10²¹ yr at the 90% confidence level.     

Eigenoscillations of three- and two-element flexible systems

Eigenfrequencies and eigenmodes of composite mechanical systems consisting of a thin-walled cylindrical shell and elastic beams [beam–shell–beam (BSB), beam–beam–beam (BBB), etc. systems] are described by using semi-analytical methods. The methods are less universal comparing with the Finite Element Method, but they are very accurate and CPU-efficient, and they could have advantages in studying multicomponent structures. A comparative analysis of eigenfrequencies and eigenmodes of the considered composite systems versus characteristic geometric dimensions is presented.     

Conversions of ethanol in thermolysis of dyes adsorbed on a silica surface

Using thermal desorption measurements with mass spectrometric analysis of the gas phase, we have studied the characteristics of the interaction of ethanol molecules with the silica surface under conditions when some of the adsorption centers are occupied by molecules of a heteroaromatic dye. The characteristics of the thermal conversions of ethanol on the surface are described in terms of ideas concerning the nature of the active centers on a surface of dispersed silicon dioxide. We observed occurrence of the reaction of ethoxylation of the surface with an increase in temperature. The interaction between the ethanol molecules and the dye molecules occurs with formation of a complex in an excited state upon UV irradiation, which stimulates adsorption of the solvent in strongly bound forms with decomposition of the complex in the surface layer.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 1, pp. 87–91, January–February, 1992.     

Sol-Gel Porous Glass as Holographic Medium

Experiments on hologram recording in porous structure obtained by the sol-gel technology were performed. It was shown that holograms with a diffraction efficiency close to 100% can be obtained with the exposure of about 0.1 J/cm. A pronounced birefringence was observed in dry samples, but it diminished upon immersion in liquids. To explain this effect, a theoretical model was developed. it was shown that even a low asymmetry in pore structure leads to a pronounced birefringence.     

X-ray diffraction investigation of the structure of propolis films

The structure of films of a biological organic material (propolis) on inorganic substrates is investigated for the first time. It is established that, despite the complex chemical composition (involving more than 300 different components), the propolis films prepared from an alcohol solution on amorphous glass substrates and on semiconductor substrates with a small number of dangling bonds have a crystal structure.     

$\mathcal{H}$-Matrix approximation for the operator exponential with applications

Summary. We develop a data-sparse and accurate approximation to parabolic solution operators in the case of a rather general elliptic part given by a strongly P-positive operator [4]. In the preceding papers [12]–[17], a class of matrices (-matrices) has been analysed which are data-sparse and allow an approximate matrix arithmetic with almost linear complexity. In particular, the matrix-vector/matrix-matrix product with such matrices as well as the computation of the inverse have linear-logarithmic cost. In the present paper, we apply the -matrix techniques to approximate the exponent of an elliptic operator. Starting with the Dunford-Cauchy representation for the operator exponent, we then discretise the integral by the exponentially convergent quadrature rule involving a short sum of resolvents. The latter are approximated by the -matrices. Our algorithm inherits a two-level parallelism with respect to both the computation of resolvents and the treatment of different time values. In the case of smooth data (coefficients, boundaries), we prove the linear-logarithmic complexity of the method. Received June 22, 2000 / Revised version received June 6, 2001 / Published online October 17, 2001     

An algorithmic representation of fractional powers of positive operators

We are concerned with a new representation of fractional powers of operators by a series using exclusively contractive operators or operators with uniformly bounded powers. This representation is suitable for the construction of efficient approximations for which the error estimates are given and the convergence is investigated. The rate of convergence turns out to be exponential for bounded operators and polynomial for unbounded operators