Gallium(III) adsorption on carbonates and oxides: X-ray absorption fine structure spectroscopy study and surface complexation modeling

Adsorption of Ga on calcite, magnesite, amorphous silica, and manganese oxide as a function of pH and gallium concentration in solution was studied using a batch adsorption technique. Adsorbed complexes of Ga on calcite, magnesite, and delta-MnO2 were further characterized using XAFS spectroscopy. At high surface loadings from supersaturated solutions, Ga is likely to form a polymeric network at the surface (edge- and corner-sharing octahedra). At low surface loadings, Ga presents as isolated octahedra, probably attached to the Me-O sites on the surface, and coordinated by water molecules and hydroxide groups at 1.90-1.94 A. At pH>6, Ga therefore changes its coordination from 4 to 6 when adsorbing from solution (Ga(OH)(-)4(aq)) onto metal surface sites (MeOGa(OH)n(H2O)2-n(5-n), Me = Ca, Mg, or Mn, and n=1 and 2 for carbonate minerals and MnO2, respectively). Because the EXAFS is not capable of seeing hydrogen atoms, the protonation of surface complexes was determined by fitting the experimental pH-dependent Ga adsorption edge. A surface complexation model which assumes the constant capacitance of the electric double layer (CCM) and postulates the formation of positively charged, neutral and negatively charged surface complexes for carbonates, manganese oxide and silica, respectively, was used to describe the dependence of adsorption equilibria on aqueous solution composition in a wide range of pH and Ga concentration.     

Magnetic properties of two-dimensional and layered systems

We consider two-dimensional magnetic systems and compare our results with experimental data on (C₂H₅NH₃)₂CuCl₄.     

Current in narrow channels of anisotropic superconductors

We argue that, in channels cut out of anisotropic single crystal superconductors and narrow on the scale of London penetration depth, the persistent current must cause the transverse phase difference provided the current does not point in any of the principal crystal directions. The difference is proportional to the current value and depends on the anisotropy parameter, on the current direction relative to the crystal, and on the transverse channel dimension. An idea on how to measure the transverse phase is proposed.     

Conservation laws in the quantum version ofN-positional Potts model

A quantum analogue of theN-positional Potts model is constructed. The system is shown to possess an infinite set of involutory conservation laws in the phase transition point.     

The calculation of the steady-state distribution dispersion in lasers with due regard of atomic correlations

For a laser model with a single mode on two-level atoms the steady-state dispersion of the quasiprobability distribution in the lowest orders in the adiabatic parameter and the ratio of the atom-field coupling constant to the atomic relaxation constant is calculated, with inclusion of the contribution of atomic correlations. A critical comparison with results of other authors is performed.     

Non-linear magnetization dynamics of ferromagnetic insulators at parallel pumping

The non-linear dynamic equation for weakly anisotropic ferromagnetic insulators at parallel pumping in the region of frequencies less than that of the parametric resonance is derived. This equation is used for solving some non-linear problems. The process of the non-linear relaxation of magnetization is considered. The non-linear loss in energy in ferromagnets is studied in the low-frequency region ωτ_∥ ? 1, where τ_∥ is the time relaxation of magnetization connected with the dipole-dipole interaction. In the frequency region ωτ_∥ ? 1 a new type of instability is found. If the amplitude of the variable magnetic field $\text{H(t) =}\text{H}\text{+ h}\text{cos}\text{ωτ}$ satisfies the condition $\text{h}\text{H}\text{? Z}{}_{\mathrm{<mtext>c</mtext>}}\text{≈ 2}$, then the ferromagnet is characterized by the stationary homogeneous value of magnetization. In the amplitude region $\text{h/}\text{H > Z}{}_{\mathrm{<mtext>c</mtext>}}$, this state is unstable and the magnetization starts rotating. At the threshold of instability the magnetic state changes abruptly. The loss in energy in the stability region is found.     

Hall effect for neutral atoms

It is shown that polarizable neutral systems can drift in crossed magnetic and electric fields. The drift velocity is perpendicular to both fields, but, contrary to the drift velocity of a charged particle, it exists only if the fields vary in space or time. We develop an adiabatic theory of this phenomenon and analyze conditions for its experimental observation. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 652–657 (25 April 1996) Deceased. Published in English in the original Russian journal. Edited by Steve Torstveit.     

Quantum fluctuations in the vicinity of an instanton in the SU(N) group

A general form of the quadratic Lagrangian in the presence of a self-dual classical field has been obtained. The calculation of the amplitude of the vacuum-vacuum transition in the SU(N) group has been reduced to calculation of similar amplitudes in the SU(2) group for scalar particles with different isospins. The value of the amplitude for one instanton has been obtained.