Volume 59, Issue 12

Neutron diffraction with isotopic H/D-substitution was used to study the network-modifying effect of water in a H 2 O-Na 2 O-2P 2 O 5 glass. The resolved fractions of P−O T and P−O B bonds and the O−O coordination number indicate similarity to the specifics of a metaphosphate structure. Thus, oxygen of H2O added ruptures a P−O−P bridge, increasing the number of terminal oxygens. The combined analysis of the first-neighbour peaks in the correlation functions of the hydrogenated and deuterated samples yields H−O distances of 0.101 and 0.157 nm and H−P distances of 0.223 and 0.250 nm. Such distances are well explained with the formation of O−H· · ·O hydrogen bridges. The corresponding O−O distances superpose with the edge lengths of the PO 4 tetrahedra. Significant fractions of short H−H distances typical of water molecules (0.155 nm) or clustering of hydrogen bridges are not detected. The Na−O coordination number of five is similar to that found for the NaPO 3 glass.

The linear attenuation coefficient (μ cm −1 ) of photon propogation and the thermal conductivity have been determined for some volcanic rocks, which are commonly used materials in building constructions especially as a cladding stone. The linear attenuation coefficient calculated using XCOM is compared with the measurement. Thermal conductivity has been extracted from P-Wave velocity measured using a Pundit apparatus. The relation between thermal conductivity and the attenuation coefficient are also investigated.

The instability of a stratified, viscoelastic (Walters B’ or Rivlin-Ericksen) magnetoplasma, including the effects of finite resistivity and suspended particles, is investigated using linear analysis. The horizontal applied magnetic field and the viscosity, as well as the viscoelasticity of the medium are assumed to be variable. The dispersion relation, which is obtained for the general case on employing boundary conditions appropriate to the case of two free boundaries, is then specialized for the two models. The hydromagnetic instability conditions are obtained and discussed analytically, and the results are numerically confirmed. The variation of the growth rate of the unstable modes with the different parameters has been evaluated analytically. All the physical parameters are found to have stabilizing as well as destabilizing effects on the considered system. For the Walters B’ viscoelastic model it was found that the kinematic viscoelasticity, fluid resistivity, and stratification parameter have a stabilizing effect, while the mass concentration (or relaxation frequency) of the suspended particles, kinematic viscosity, and Alfvén velocity have a destabilizing effect on the considered system. Also, for the case of the Rivlin-Ericksen viscoelastic model we found that the mass concentration of the suspended particles, Alfvén velocity, and kinematic viscosity have a stabilizing effect, while both the finite resistivity and stratification parameter have a destabilizing effect; the relaxation frequency of the suspended particles has no effect on the stability of the system. The case of a dusty plasma with infinite conductivity and presence (or absence) of a magnetic field is also considered. Its stability conditions are obtained, from which it is concluded that the presence of dust always reduces the growth rate of the unstable Rayleigh-Taylor perturbations. The limiting case of a viscid (and inviscid) finitely conducting dusty plasma is considered, and the stability conditions are discussed, from which we found that the magnetic field has a stabilizing effect in the absence of both viscosity and finite resistivity, the stability of the system ocurrs for values of the Alfvén velocity greater than a critical value. -PACS: 47.20.-k; 47.50+d; 47.65.+a.

Using an extended mapping approach, a new type of variable separation excitation with two arbitrary functions of the (2+1)-dimensional Broer-Kaup-Kupershmidt system (BKK) is derived. Based on this excitation, abundant propagating and non-propagating solitons, such as dromions, rings, peakons, compactons, etc. are found by selecting appropriate functions. - PACS: 05.45.Yv, 03.65.Ge

By introducing a set of ordinary differential equations which possess q-deformed hyperbolic function solutions, and a new ansatz, a method is developed for constructing a series of exact analytical solutions of some nonlinear evolution equations. The proposed method is more powerful than various tanh methods, the sec q -tanh q -method, generalized hyperbolic-function method, generalized Riccati equation expansion method, generalized projective Riccati equations method and other sophisticated methods. As an application of the method, an averaged dispersion-managed (DM) fiber system equation, which governs the dynamics of the core of the DM soliton, is chosen to illustrate the method. With the help of symbolic computation, rich new soliton solutions are obtained. From these solutions, some previously known solutions obtained by some authors can be recovered by means of some suitable choices of the arbitrary functions and arbitrary constants. Further, the soliton propagation and solitons interaction scenario are discussed and simulated by computer.

We present the experimental Compton profile of polycrystalline terbium, using 661.65 keV gamma-rays, emitted by 20 Ci 137 Cs. In the absence of band structure calculations, theoretical computations have been made using renormalised-free-atom (RFA) and free electron based profiles. It is seen that the RFA results with e − -e − correlation correction agree relatively better with the experiment. The data are interpreted in terms of spd-f hybridization in the valence state of terbium. From the RFA profile, we have also derived the cohesive energy of terbium, which is compared with other band structures and experimental investigations. - PACs Nos. 13.60.F, 71.15.Nc, 78.70. -g, 78.70.Ck

In this paper, two transformations are introduced to solve double sinh-Gordon equation and triple sinh-Gordon equation, respectively. It is shown that different transformations are required in order to obtain more kinds of solutions to different types of sinh-Gordon equations. - PACS: 03.65.Ge

The electron paramagnetic resonance (EPR) parameters g and the hyperfine structure constants A of Co 2+ in ZnX (X = S, Se, Te) and CdTe are studied, using the perturbation formulas of the EPR parameters for a 3d 7 ion in tetrahedra based on two mechanism models. In these formulas, both the contributions from the conventional crystal-field (CF) mechanism and those from the charge-transfer (CT) mechanism are taken into account. According to the investigations, the sign of the g-shift Δg CT from the CT mechanism is the same as Δg CF from the CF mechanism, whereas the contributions to the A value from the CF and CT mechanisms have opposite signs. Particularly, the contributions to the EPR parameters from the CT mechanism increase rapidly with increase of the spin-orbit coupling coefficient of the ligand and the covalency effect of the systems, i. e. S 2 − < Se 2 − < Te 2 −.

In this paper, the spin Hamiltonian parameters g factors g ∥ and g ⊥ of Yb 3+ and hyperfine structure constants A ∥ and A ⊥ of 171 Yb 3+ and 173 Yb 3+ in CaWO 4 crystal are calculated from the two-order perturbation formulae. In these formulae, the contributions of the covalence effects, the admixture between J =7/2 and J =5/2 states as well as the second-order perturbation are included. The needed crystal parameters are obtained from the superposition model and the local structure of the studied system. The calculated results are in reasonable agreement with the observed values. The results are discussed.

The gyromagnetic factors for Nd 3+ in scheelite-type ABO 4 compounds (A = Cd, Ca, Pb, Ba; B = Mo, W) are theoretically studied by the perturbation formulas of the anisotropic g factors g ∥ and g ⊥ for a 4f 3 ion in tetragonal symmetry. In these formulas, the contributions to the g factors due to the second-order perturbation terms and the admixtures of various energy levels are taken into account. The relevant crystal-field parameters are determined by the superposition model and the local geometrical relationship of the A 2+ sites occupied by the impurity Nd 3+ . The obtained g factors agree reasonably with the observed values. The discrepancies between theory and experiment are discussed.

Some new findings concerning the structural, optical, transport and magnetotransport properties of τ -(EDO-S,S-DMEDT-TTF) 2 (AuBr 2 ) 1+y and τ -(P-S,S-DMEDT-TTF) 2 (AuBr 2 ) 1+y (y ≈ 0.75) are reported. Some similarities and dissimilarities in the properties are discussed. The dissimilarities are more pronounced at low temperatures and high magnetic fields. The results are compared to those obtained of other conducting multilayered systems.

We propose and evaluate a structural model for mixed K-Ca nitrate melts and glasses, which invokes the presence of strongly bound Ca 2 (NO 3 ) 7 groups surrounded by K ions that can transport charge by relatively free jumps. To this purpose we first construct ionic models for the pure ANO 3 compounds (with A = alkali metal ion), by searching for suitable A +Z ·(NO 3 ) −Z interionic potentials in the space of interionic-law parameters with the help of known models for alkali chlorides. The available evidence mainly consists of infrared-active mode frequencies, and is compatible with two alternative types of interionic parameters. A choice between them is made on the basis of the fact that the NO 3 group has a flat triangular shape and can execute torsional oscillations giving rise to a low-frequency Raman-active mode in the melt. This interionic force model is then combined with a similar model for Ca(NO 3 ) 2 to evaluate the structural properties of a 3KNO 3 ·2Ca(NO 3 ) 2 unit, which is the constituent of the well-known glassformer CKN. We expect that the present model should be representative of other mixed alkali-divalent ion nitrate systems in the range of concentration where glass formation is observed.

By using the spin-orbit coupling mechanism and the empirical superposition model, the zero-field splittings D of Mn 2+ ions on both Mg 2+ sites in hexagonal 6H-RbMgF 3 crystal are calculated from the structural data of both Mg 2+ sites. The calculated results of both methods confirm the suggestion that Mn 2+ in 6H-RbMgF 3 occupies the Mg 2+ (I) site (which has D 3d site symmetry) and the zero-field splitting D of 6H-RbMgF 3 : Mn 2+ is explained reasonably.

A nonstatistical model for internal transition of collective vibrational energy to specific bonds in organic molecules is presented. The model is developed for molecules which contain a chain of identical biatomic dipoles, e.g. C-H groups. Resonant IR fields can induce collective vibrational excitations (excimols) in the dipole chain. The accumulated vibrational energy can be transmitted to particular bonds, which are not part of the chain but close enough for dipole-dipole interactions. Specific properties of such bonds enable a pile up of harvested excimol energy there, thus making dissociation of these bonds a likely exit channel. An analytical expression for the calculation of dissociation probabilities was derived and analysed. It is shown that the dissociation probability strongly depends on the position and orientation of the bond relative to the position and orientation of the dipoles in the chain. The consequences of the presented model were experimentally checked by comparing the fragmentation of the isomers Leucine and Isoleucine. - PACS: 30.00 - 34.10 - 36.40

MINDO-Forces SCF-molecular orbital calculations with complete geometry optimization have been performed on x-substituted phenylallyl cations, where x is H, OCH 3 , NH 2 , NO 2 , CN, F and CH 3 , in ortho, meta, or para positions. Optimized geometrical parameters, electron densities, heats of formation and stabilization energies were obtained. The substitutent effect on the geometrical parameters and the electron density are discussed by correlation analysis.

The enhancement of the molecular dipole moment under the influence of the crystal lattice relative to the value for the corresponding isolated molecule has been calculated for the three low-pressure polymorphs of glycine using the semiempirical MINDO/3 Hamiltonian. In these calculations the influence of the lattice on an arbitrarily chosen reference molecule has been included by modifying the diagonal elements of the H core matrix. Starting from a set of atomic charges calculated for the isolated molecule an initial crystal lattice had been set up and included into the calculation of new self-consistent (SCF) charges for the reference molecule. The resulting set of new SCF charges was then used to replace the lattice charges from the preceding run, and a new SCF calculation was performed. This iterative process was continued until the difference between the electronic energies and the sum of the absolute values of the differences between the atomic charges from two subsequent SCF calculations was lower than 10 −5 eV and 10 −5 e 0 , respectively. The results agree nicely with the experimental data obtained by other authors for α-glycine.

MINDO-Forces calculations with complete geometry optimization have been performed on α- substituted acetaldehydes XCH 2 CH=O and their enols (X = H, F, OH, CN, NH 2 , NO 2 , CH 3 , CF 3 , OCH 3 ). All substituents were found to decrease the stability of the acetaldehyde and mostly in the case of electron withdrawing capacity (e. g NO 2 and CF 3 ). This agrees with theoretical calculations, except in the case of F. The substituent effects on the stabilities in this study are compared with results obtained from our previous theoretical calculations on acetyl derivatives. Geometrical parameters, electron densities, and Gibbs free energies are reported.

MNDO calculations have been employed to study the effect of some substituents of the acetaldemine-vinylamine tautomeric system at the imine-carbon position of CH 3 CXNH, where X = H, F, CN, NH 2 , NO 2 , BH 2 , CH 3 and CF 3 . It is found that the substitutents F, NH 2 and NO 2 encourage the formation of the enamine tautomer. The substitutents CN, CH 3 , CF 3 and BH 2 encourage the formation of the imine tautomer. Isodesmic reactions, free energy change (ΔG), charge distribution and energy gap (E g ) between HOMO and LUMO were used to prove these findings. Resonance stabilization was a major factor in the determination of the most stable tautomer. These results were compared with previous work on the substitution at the σ -carbon position.

Computerized symbolic computation reflects the rapid expansion of computer sciences in various fields of science and engineering, while the studies on the liquid surfaces for rivers, oceans, aviation kerosene, liquid propellant for rockets, etc., are of current interest. In the presence of surface tension or sea ice, and with symbolic computation, the Hărăgus-Courcelle-Il’ichev model for surface liquid waves is hereby investigated. Several similarity reductions are presented, some of which are explicitly written out as exact analytic solutions having their rational expressions with respect to the dimensionless spatial variables of the model.