Cluster perturbation theory for spin Hamiltonians

We extend cluster perturbation theory to quantum spin systems. As an application, we calculate the spectral function and the density of states of one-particle excitations of a chain of spin-1/2 particles with alternating exchange interaction.     

Autocatalytic gas-phase ethane dehydrogenation in a wall-less reactor

The thermal gas-phase pyrolysis of ethane was studied under conditions of the bulk heating of the reaction mixture with IR-laser radiation. The concentrations of ethane pyrolysis products as functions of reaction time were calculated in accordance with standard kinetic schemes; they showed that a classical radical chain mechanism corresponded to only highly dilute mixtures of ethane with an inert gas. As found by calculations, the experimental data on the kinetics of consumption of the initial substance and on the kinetics of buildup of pyrolysis products in undiluted mixtures of ethane and its conversion products were adequately described by an autocatalytic (with respect to ethylene) mechanism of ethane dehydrogenation. This mechanism involved the step of ethane interaction with ethylene to form methyl and propyl radicals.     

Random bond Potts model: The test of the replica symmetry breaking

The averaged spin-spin correlation function squared is calculated for the ferro-magnetic random bond Potts model in two dimensions. The technique being used is the renormalization group plus conformal field theory. The results are of the E-expansion type fixed point calculation, E being the deviation of the central charge (or the number of components) of the Potts model from the Ising model value. Calculations are done both for the replica symmetric and the replica symmetry broken fixed points. The results obtained allow for numerical simulation tests to decide between the two different criticalities of the random bond Potts model.     

Calculation of the Gibbs energy of mixing in crystals using Pitzer's model

Pitzer's model has been applied to the thermodynamic study at 25°C of a series of systems of the type MeX-MeX-H₂O, MeX-MeX-H₂O (where Me, Me=K, NH₄,Rb and Cs; X, X=Cl, Br and I), MeSO₄-MeSO₄-H₂O (where Me, Me=Mg, Ni, Zn and Co). The integral Gibbs energy of mixing G^mix and the excess Gibbs energy of mixing G^E(s) are calculated, and simplified correlation equations are proposed for their calculation. The results obtained are compared with experimental data from the literature and with values calculated using various theories. The rational activity coefficients of the mixed crystal components are estimated. The energy of phase transition of one structure into another has been estimated for the isodimorphous mixed crystals in the system MgSO₄–CoSO₄–H₂O.     

Dependence of the Bose-Condensate Population Fluctuations in a Gas of Interacting Particles on the System Size: Numerical Analysis

Radiophysics and Quantum Electronics - We consider the Bose-condensate population statistics for a gas of interacting particles confined into a three-dimensional cubic trap with different boundary...     

Study of interband cascade lasers with tunneling transition

Two-frequency lasing in a new class of heterolasers (interband cascade lasers with tunneling transition that separates two active regions of quantum wells located in a single waveguide) is realized and studied. The laser scheme weakens the competition between the quantum wells upon the simultaneous generation of the long-and short-wavelength modes.     

Radical Intermediates in the Decomposition of Substituted Coumarins

Summary. A series of coumarin derivatives containing substituents with an acidic CH₂ group in 3-position was decomposed on the surface of PbO₂. The radical intermediates were identified by EPR spectroscopy. Although the occurrence of several tautomeric forms is possible, the application of the spin trapping technique confirmed the formation of only one radical product, namely the C-radical resulting from the homolytic splitting of the C–H bond of the methylene group.     

Untersuchung von Obstkonserven

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