Two-dimensional commensurate soliton structures

A phase diagram of pinned soliton structures in two dimensions has been found for a repulsive interactionU(x) between solitons withU(x)>0. The critical fugacity of the commensurate soliton structure is shown to be proportional toU(l), wherel is the period of this structure.     

Modification of chemically and physically obtained Fe3O4 magnetic nanoparticles with l-Lys for cell labeling

Russian Chemical Bulletin - Peculiar features of the modification of Fe3O4 magnetic nanoparticles (MNPs) obtained by co-precipitation from solutions of FeII and FeIII salts (10-nm MNPs) and by the...     

The hydrodechlorination of chlorobenzene in the vapor phase in the presence of metal-carbon nanocomposites based on nickel,palladium, and iron

Metal-carbon nanocomposites based on nickel, palladium, and iron and bimetallic palladium-nickel-carbon nanocomposites were for the first time used as catalysts of hydrodechlorination of chlorobenzene in the vapor phase in the atmosphere of hydrogen. Nickel and Pd-Ni nanoparticles completely coated by a carbon layer not only were stable to oxidation and agglomeration but also exhibited considerable activity in hydrodechlorination of chlorobenzene at temperatures much lower than those at which dechlorination on carbon carriers occurred. The dependence of catalytic properties (activity, selectivity, and stability) on temperature and nanocomposite composition was studied. Depending on the nature of the metal, the composition of bimetallic particles and temperature the selectivity could be changed, and the reaction could be directed toward the formation of benzene or cyclohexane. Carbon coating was stable under reaction conditions at least up to 350°C and did not hinder hydrodechlorination. Substrate adsorption likely occurred on the outside carbon surface of composite particles. The activity and structure of Ni@C composite remained almost unchanged after triple cycling over the temperature range from 50 to 350°C in a flow system.     

Catalytic effect of nanosized metal oxides in the Biginelli reaction

The effect of nanosized metal oxides on the regio- and stereoselectivity of the multicomponent Biginelli reaction and the reaction mechanism under conditions of heterogeneous catalysis were studied. It was found that the considerable activation of reagents occurred on the surface of metal nanooxides. The Biginelli reaction occurred by two mechanisms: a carbocationic mechanism took place along with the generally accepted mechanism (through the N-acyliminium ion). Nanosized metal oxides in the presence of chiral inductors increased the regio- and stereoselectivity of the Biginelli reaction.     

Rectangular lattice gas model with competing interactions and the two-dimensional ANNNI model in a field

A lattice gas model with short range competing interactions for adsorption on (110) surfaces of fcc crystals, in particular for O/Pd(110), as well as its Ising analog, the two-dimensional ANNNI model with antiferromagnetic axial nearest and next-nearest neighbour interactions in a field, are studied using the free fermion approximation and Monte Carlo techniques. The phase diagrams display different commensurate phases and incommensurate regions. Static and dynamic aspects of topological defects (walls and dislocations) characterising the incommensurate structures are investigated.     

Experimental determination of superheated liquid density by the optical fiber method

An experimental approach to determination of the density of liquid superheated with respect to the liquid-vapor equilibrium temperature, including the range of high degrees of superheating, is developed. The approach is based on application of an optical fiber method combined with a pure bubble chamber. Performance of the method for investigation of the refractive index and density for superheated liquids as functions of temperature and pressure is illustrated in experiments with n-hexane as a reference substance for thermophysical measurements. The relative density measurements are performed with a resolution up to 10^?4 at a characteristic time of 1 ms. For absolute measurements, the setup should be calibrated by the known data on the liquid density for the saturation line.     

Low-energy excitations of Yb As in a magnetic field

We discuss the effects of an applied magnetic field on the low-energy excitations in the low temperature phase of Yb₄As₃. We show also why the magnetic interaction of the Yb³⁺ ions is nearly of an isotropic Heisenberg spin-1/2 type. A small anisotropy due to an intrachain dipolar interaction leads to the opening of a gap when a magnetic field is applied. The model agrees with available experimental data. Simple experiments are suggested in order to further test the present theory. Received 3 February 1999     

Phase transitions in two-dimensional uniformly frustratedXY models. I. Antiferromagnetic model on a triangular lattice

A most popular model in the family of two-dimensional uniformly-frustratedXY models is the antiferromagnetic model on a triangular lattice [AFXY(t) model]. Its ground state is both continuously and twofold discretely degenerated. Different phase transitions possible in such systems are investigated. Relevant topological excitations are analyzed and a new class of such (vortices with a fractional number of circulation quanta) is discovered. Their role in determining the properties of the system proves itself essential. The characteristics of phase transitions related to breaking of discrete and continuous symmetries change. The phase diagram of the generalized AFXY(t) model is constructed. The results obtained are rederived in the representation of the Coulomb gas with half-integer charges, equivalent to the AFXY(t) model with the Berezinskii-Villain interaction.     

Effect of Annealing on Structural,Textural, Thermal,Magnetic, and Luminescence Properties of Calcium Fluoride Nanoparticles

Physics of the Solid State - Mesoporous nanocrystalline CaF2 powder was produced by pulsed electron beam evaporation (PEBE) in vacuum. The specific surface area (SSA) of CaF2 nanopowder (NP)...