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.     

Synthesis,Physicochemical Properties,and Structure of Heterocyclic β-Aminovinyl Ketones and Related Copper(II) Complex

Heterocyclic -aminovinyl ketones (HL) and the copper complex CuL₂ are synthesized and studied by IR and ¹H NMR spectroscopies. The crystal structure of one of the tautomeric HL molecules is determined by X-ray diffraction analysis. The crystals are triclinic: a = 9.261(6) Å, b = 9.448(6) Å, c = 11.310(5) Å, = 96.74(5)°, = 99.46(5)°, = 93.60(5)°, space group P . The compound has the form of a ketoamine tautomer. The structure contains intramolecular and intermolecular hydrogen bonds. The latter link the molecules into the center-symmetric dimers.     

Transesterification of Diethyl Carbonate with Methanol Catalyzed by Sodium Methoxide

Russian Journal of Organic Chemistry - The mechanism of sodium methoxide-catalyzed transesterification of diethyl carbonate with metha-nol to dimethyl carbonate has been studied by DFT quantum...     

Synthesis of monodisperse submicron spherical poly(methylmethacrylate) particles and the molecular dynamics simulation

The molecular-dynamics method has been used to determine the conformational states of poly(methyl methacrylate) chains in a medium composed of water and a monomer (methyl methacrylate). Experimentally detected spherical particles resulting from polymerization have been found to take the form of droplet-type aggregates containing several chains, with the water and monomer concentrations in the aggregates differing from those in the dispersion medium. It has been shown that the methyl methacrylate concentration in an initial reaction mixture of about 20% is optimal for the formation of spherical droplet-type aggregates. It has been experimentally established that spherical poly(methyl methacrylate) particles with a narrow size distribution are formed at a methyl methacrylate concentration of ≈23%.     

Azomethyne derivatives of 1,3-benzothiazine 1,1-dioxide

The Schiff's bases 2-alkyl-4-oxo-3,4-dihydro-2H-1,2-benzothiazine 1,1-dioxides have been synthesized for the first time, their structures in solution and in the crystalline state and their ability to form complexes have been investigated. The unusual condensation reaction of 1,2-benzothiazine 1,1-dioxide with ethyl orthoformate and 4-aminoantipyrine has been observed.     

Lattice vibrational spectra of nanocrystalline films of <Emphasis Type="Italic">para</Emphasis>-substituted benzene

We have obtained experimental low-frequency Raman spectra for para-dibromobenzene nanofilms of thickness ∼10 μm and ∼400 nm. With a decrease in the film thickness, the line frequencies are lowered, the linewidths increase, additional lines become more intense. We modeled the film structure by the molecular dynamics method and calculated the histograms of the lattice vibrational spectra by the Dean method. We found that as the film thickness decreases, the lattice parameters increase, the orientational disorder increases at its boundary. The structure of the studied film is similar to the structure of the para-dibromobenzene single crystal. In order to correctly interpret the lattice vibrational spectra, we need to take into account surface vibrations and the presence of vacancies in the structure. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 838–842, November–December, 2008.     

Behavior of Gallium Anodes in Carbonate Buffer Solutions

On the basis of a model put forward, experimental data on the electrochemical ionization of solid gallium in carbonate buffer media are analyzed. It is shown that the formation on the electrode of a matrix consisting of the hydrolysis products of gallium ions Ga(3+) is the initial anodic step. The charge transport in this matrix proceeds via an ejection mechanism. At pH > 10, this matrix transforms into a reaction layer, which supplies Ga(OH)₂CO₃ ^-complexes (at higher pH—Ga(OH)₄ ^-anions) to the electrolyte.