Propagation of detonation in fuel–air mixtures in flat channels

The wide scatter of the values of the measured detonation cell size in fuel + air mixtures restricts the applicability of this parameter in the estimation of the geometric limits of detonation propagation, including in rectangular channels whose height is much larger than their width. The critical channel height for the propagation of detonation has been experimentally determined for hydrogen + air, propane + air, and ethylene + air mixtures. In order to reveal the specific features of the propagation and decay of detonation in a narrow channel, numerical simulation has been carried out for a hydrogen + air mixture with account taken of the cellular structure of the detonation wave.     

Ammonium and caesium carbonate peroxosolvates: supramolecular networks formed by hydrogen bonds

Diammonium carbonate hydrogen peroxide monosolvate, 2NH₄⁺·CO₃²⁻·H₂O₂, (I), and dicaesium carbonate hydrogen peroxide trisolvate, 2Cs⁺·CO₃²⁻·3H₂O₂, (II), were crystallized from 98% hydrogen peroxide. In (I), the carbonate anions and peroxide solvent molecules are arranged on twofold axes. The peroxide molecules act as donors in only two hydrogen bonds with carbonate groups, forming chains along the a and c axes. In the structure of (II), there are three independent Cs⁺ ions, two of them residing on twofold axes, as are two of the four peroxide molecules, one of which is disordered. Both structures comprise complicated three‐dimensional hydrogen‐bonded networks.     

The magnetic field effect in the presence of the electric field on fluorescence of a methylene-linked compound of pyrene and n,n-dimethylaniline doped in a polymer film

Recent experimental data by Mizoguchi and Ohta are analyzed under the assumption of fast equilibrium between the locally excited (LE), radical-ion-pair (RIP), and exciplex states. In the absence of the equilibrium, no magnetic field effect on the LE fluorescence would be observed. Owing to the equilibrium, the relative electric-field-induced changes of the quantum yields of the LE and exciplex emissions as functions of the magnetic field are linearly connected to each other. The electric field shifts the equilibrium from the LE state toward the RIP state. Predictions are made for the magnetic field effect on the fluorescence kinetics.     

Study of weighted Monte Carlo algorithms with branching

Various weighted algorithms for numerical statistical simulation are formulated and studied. The trajectory of an algorithm branches when the current weighting factor exceeds unity. As a result, the weight of an individual branch does not exceed unity and the variance of the estimate for the computed functional is finite. The unbiasedness and finiteness of the variance of estimates are analyzed using the recurrence “partial“ averaging method formulated in this study. The estimation of the particle reproduction factor and solutions to the Helmholtz equation are considered as applications. The comparative complexity of the algorithms is examined using a test problem. The variances of weighted algorithms with branching as applied to integral equations with power nonlinearity are analyzed.     

Vacuum solutions in the Neveu-Schwarz field theory of a fermionic string and the zero-curvature representation in graded spaces

We demonstrate that vacuum solutions in the Neveu-Schwarz field theory of a fermionic string incorporating the GSO(−) sector are naturally related to the zero-curvature representation in a graded space of special form. We use the same representation to describe the equivalence of the cubic and nonpolynomial theories with the GSO(−) sector also taken into account. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 159, No. 1, pp. 131–141, April, 2009.     

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