Dynamics of Adsorbate Islands with Nanoscale Resolution

Surface catalytic processes produce, under certain conditions, small clusters of adsorbed atoms or groups, called islands which, after they have been formed, move as individual entities. Here we consider the catalytic reduction of NO with hydrogen on platinum. (i) Using video field ion microscopy, we observe the dynamic motion of small hydroxyl islands on the Pt(001) plane; despite changes in their morphology, the islands dimensions are confined to values corresponding to 10 to 30 Pt atoms suggesting cooperative effects to be in operation. (ii) We construct an automaton (or lattice Monte-Carlo) model on the basis of a set of elementary processes governing the microscopic dynamics. The agreement between the simulation results and the experimental observations suggests a possible mechanism for the formation and dynamics of hydroxyl islands.     

Photochromic LC copolymers containing azobenzene and crown‐ether groups

An approach for the creation of a novel family of multifunctional crown‐ether‐containing comb‐shaped copolyacrylates consisting of chromophoric (azobenzene), ionophoric (crown‐ether), and mesogenic groups in the same macromolecule was developed. Phase behavior of the copolymers was studied, and correlation between their molecular structure and thermal properties was established. The increase of crown‐ether‐containing groups' concentration up to 26 mol % leads to disruption of nematic order and formation of amorphous phase. Influence of copolymers complexation with potassium perchlorate on mesomorphic properties of such systems was investigated. It was shown that complexation leads to decrease in mesophase thermostability due to the significant reducing of the side group anisometry by perchlorate counter ion. The comparative investigations of photooptical properties and photoorientation processes of copolymers and their complexes were also performed. An essential difference in kinetics of photooptical behavior was revealed; the bulky crown‐ether substituents decrease rotational mobility and prevent photoorientation process of azobenzene fragments diminishing photoinduced orientation and order parameter. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6532–6541, 2008     

Electrodeposition of Tin-Antomony-Copper Alloy from Sulfate Electrolytes with Organic Additives

The process of electrodeposition of a tin-antimony-copper alloy from a sulfate electrolyte with organic additives was studied.     

Pure gauge configurations and tachyon solutions for cubic fermionic string field theory equations of motion

Special perturbative pure gauge solutions parameterized by a pair of wedge states are parts of the nontrivial (not purely gauge) tachyon solutions of the cubic fermionic string field theory describing the non-BPS brane true vacuum. We demonstrate explicitly that for the large parameter of the perturbation expansion, these pure gauge configurations are no longer solutions of the equations of motion. We show that this problem is solved by adding an extra term that is just the term needed for the first Sen conjecture to hold.     

Imperfection of the nanostructure, phase transitions, 55Mn NMR, and magnetoresistive properties of La 0.73+ Ca 0.3 ? x2+ Sr x2+ MnO3 ± δ ceramics

Magnetoresistive ceramic samples La_0.7Ca_{0.3 − x} Sr _x MnO_{3 ± δ} sintered at temperatures of 1150 and 1350°C are investigated using X-ray diffraction, microscopic, resistance, and magnetic (χ, ⁵⁵Mn NMR) measurements. The specific features of the influence of the composition on the type and parameters of the perovskite structure, its imperfection, the porous crystallite structure, the metal-semiconductor and ferromagnetic-paramagnetic phase transitions, the ⁵⁵Mn NMR spectra, and the magnetoresistance effect are established. The magnetic phase diagram is constructed. The conclusions are drawn regarding the nonuniformity of the distribution of ions and vacancies around manganese involved in the high-frequency electron-hole exchange (Mn³⁺ ai Mn⁴⁺) and the nanostructured separation of the perovskite structure containing anion and cation vacancies, with the concentrations and magnetoresistance effect decreasing and the lattice parameters and phase transition temperatures increasing as calcium is replaced by strontium. Original Russian Text ? A.V. Pashchenko, A.A. Shemyakov, V.P. Pashchenko, V.A. Turchenko, V.K. Prokopenko, Yu.F. Revenko, Yu.V. Medvedev, B.M. éfros, G.G. Levchenko, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 6, pp. 1127–1136.     

Influence of Nonlocal Effects on Kinetic Parameters of Heterogeneous Charge Transfer Reactions

The influence of the spatial dispersion of the solvent and of the effect of the electrical field penetration into a metal on the free energy of the solvent reorganization and the activation free energy for heterogeneous charge transfer reactions is studied. The calculations are based on the exactly solved model of a sharp metal/electrolyte interface, the model of a Born sphere for the ion, and the three-mode approximation for the dielectric function of the solvent. In the sharp-interface model, in the case of a mirror reflection, a relationship for the dielectric tensor of a heterogeneous system comprising two contacting media with a plane interface is obtained, along with an expression for the potential created by a point charge. This expression formally coincides with the expression derived earlier by Vorotyntsev and Kornyshev, but it contains true bulk dielectric functions of contacting media. In the model of the Born sphere for the ion and the three-mode approximation for the dielectric function of the solvent, an expression for the potential of image forces, which determines the dependence of the solvent reorganization energy on the distance from the reacting ion to the electrode, is obtained. It is shown that both the reorganization energy and the activation free energy decrease with decreasing distance from the ion to the electrode. The calculation results are compared with estimates of the reorganization energy obtained from experimental data for the reaction Fe³⁺/Fe²⁺ and the reaction of the hydronium ion discharge.     

Space-time evolution of the hadronic source in peripheral to central Pb+Pb collisions

Two-particle correlations of negative pions as a function of charged particle multiplicity are studied in Pb+Pb collisions at GeV per nucleon using the NA44 experiment at the CERN Super Proton Synchrotron(SPS). We find that the source size parameters increase with the charged particle multiplicity. However the slope of the source size parameters plotted as a function of charged multiplicity is slightly larger at high multiplicity than at low multiplicity. The value of is independent of charged multiplicity. For Pb+Pb collisions, is larger than and for all multiplicity intervals, whereas these three radius parameters were approximately equal in S+Nucleus collisions. The ratios () and () for Pb+Pb data show almost no dependence on charged multiplicity. The duration of pion emission is constant at 3.81.1 fm/c as a function of the charged multiplicity in Pb+Pb collisions. Effective volume (V) is also calculated as V=, assuming a cylindrically shaped source. We found, within the limited statistics, the effective volume rapidly increases at high multiplicity. Received: 17 July 2000 / Revised version: 3 November 2000 / Published online: 8 December 2000     

In-water gas combustion for thrust production

The paper presents the results of experimental study for hydrodynamic processes occurring during combustion of a stoichiometric mixture propane-oxygen in combustion chambers with different configurations and submerged into water. The pulses of force acting upon a thrust wall were measured for different geometries: cylindrical, conic, hemispherical, including the case of gas combustion near a flat thrust wall. After a single charge of stoichiometric mixture propane-oxygen is burnt near the thrust wall, the process of cyclic generation of force pulses develops. The first pulse is generated due to pressure growth during gas combustion, and the following pulses are the result of hydrodynamic pulsations of the gaseous cavity. Experiments demonstrated that efficient generation of thrust occurs if all bubble pulsations are used during combustion of a single gas combustion. In the series of experiments, the specific impulse on the thrust wall was in the range 10⁴–10⁵ s (10⁵–10⁶ m/s) with account for positive and negative components of impulse.