Volume 60, Issue 7

We consider the blow-up of solutions as a function of time to the initial boundary value problem for the damped Boussinesq equation. Under some assumptions we prove that the solutions with vanishing initial energy blow up in finite time

In this paper, a new analytical formula has been derived for the two-center Coulomb integrals over Slater type orbitals using the Poisson equation. The obtained results from constructed computer program for the presented formula have been compared with the available literature and it is seen that the efficiency of the presented algorithm for a wide range of quantum numbers, orbital exponents and internuclear distances is satisfactory.

This paper treats the stability of two superposed gravitating streams rotating about the axis transverse to the horizontal magnetic field. The critical wave number for instability is found to be affected by rotation for propagation perpendicular to the axis about which the system rotates. The critical wave number for instability is not affected by rotation when waves propagate along the axis of rotation. The critical wave number is affected by both the magnetic field and the streaming velocity in both cases. Both the magnetic field and the rotation are stabilizing, while the streaming velocity is destabilizing.

We have developed a robust and efficient ultrasound liquid sprayer working at forty kilohertz. In the course of realizing the project of finding new ways in tobacco aromatization processes we met the problem of (approximate) analytical expressions of probability density functions for droplet sizes in various aerosols. This paper reports at what results we have arrived in that realm. Corresponding graphics of propability functions are presented.

This paper deals with the theoretical investigation of the effect of dust particles on the thermal convection in a ferromagnetic fluid subjected to a transverse uniform magnetic field. For a flat ferromagnetic fluid layer contained between two free boundaries, the exact solution is obtained, using a linear stability analysis. For the case of stationary convection, dust particles and non-buoyancy magnetization have always a destabilizing effect. The critical wavenumber and critical magnetic thermal Rayleigh number for the onset of instability are also determined numerically for sufficiently large values of the buoyancy magnetization parameter M 1 . The results are depicted graphically. It is observed that the critical magnetic thermal Rayleigh number is reduced because the heat capacity of the clean fluid is supplemented by that of the dust particles. The principle of exchange of stabilities is found to hold true for the ferromagnetic fluid heated from below in the absence of dust particles. The oscillatory modes are introduced by the dust particles. A sufficient condition for the non-existence of overstability is also obtained.

The effects of magnetic field strength on low-frequency surface ion plasma wave are investigated in semi-bounded magnetized dusty plasmas. The dispersion relation of the surface ion plasma wave is obtained by the plasma dielectric function with the specular reflection boundary condition. The results show that a transition from linear increase into the final level, i. e., the occurrence of a wave resonance. At a given frequency the phase velocity stays almost constant as long as the frequency remains below the respective resonance frequency.

The dielectric permittivity of the layered magnetic insulators [(CH 2 ) 3 (NH 3 ) 2 Cu 1 − x Cd x Cl 4 ] with x=0, 0.3, 0.6, and 1 has been studied in the temperature range 300 K- 470 K at different frequencies. Single crystal- and powder-measurements for x = 0 revealed a ferroelectric phase transition at (434± 2) K. The ferroelectric Cu crystal and the antiferroelectric Cd salt were found to form solid solutions in the range 0.3 < x < 0.6. The permittivity results of samples with x = 0.3 and 0.6 showed the broad permittivity-temperature plateau typical of dielectric relaxors. The two samples follow the relationship 1/ε −1/εm =(T −Tm)γ /C, with γ =1.75 and 1.71 and C =4.13·10 5 K and 1.19·10 5 K for x = 0.3 and x = 0.6 samples, respectively. Anomalous change in the temperature variation of the permittivity (δε' /δ T) for the x = 1 sample at T ~ 374 K is ascribed to a structural phase transition. Thermal analysis for the x = 0 sample reveals two phase changes at T 1 = 434.4 K and T 2 = 334.5 K. The T 1 transition confirms the ferroelectric transformation, and the transition at T 2 is related to an order-disorder phase change. -PACS #:81.05.-t, 77.22.-d

The isotropic Compton profile of europium, the most reactive lanthanide, has been measured at a resolution of 0.40 a.u. using 661.65 keV gamma-rays. In the absence of a band structure-based Compton profile, the experimental data are compared with renormalised-free-atom (RFA) and free electron models. It is seen that the RFA model with e−-e− correlation agrees better with the experiment than the free electron models. The first derivatives of the Compton profiles show the hybridization effects of s-, p-, d-, f-electrons. From our RFA data we have also computed the cohesive energy of europium. PACS: 13.60.F, 71.15.Nc, 78.70. -g, 78.70.Ck

X-Ray diffraction, using high-energy photons from a synchrotron, was used to extend the investigation of (ZnO) x (P 2 O 5 ) 1−x glasses to samples of ZnO content close to x = 0.8 which were obtained by roller-quenching. The isolated PO 4 tetrahedra are surrounded by ZnOn polyhedra, where Zn−O coordination numbers of ∼ 4.5 are determined. The small increase of NZnO from ∼ 4 at metaphosphate composition (x = 0.5) to ∼ 4.5 is not sufficient to explain the strong increase of the packing density beyond the minimum at x = 0.5. The medium-range order was analyzed on the basis of partial S PP (Q) and S ZnZn (Q) factors obtained from Reverse Monte Carlo simulations of glasses with 0 ≤ x ≤ 0.8. The positions of the first peaks in these factors, the number densities of P and Zn atoms and knowledge of definite P-P and Zn-Zn distances were used to check the applicability of simple models such as the dense packing of uniform P- and Zn-centered spherical environments for glasses with x=0.8 and 0.5, the packing of corrugated sheets for vitreous P 2 O 5 and the packing of phosphate chains for Zn metaphosphate glass.

Four types of heterojunctions were prepared: SnO 2 -As 2 (Se 0.9 Te 0.1 ) 3 , SnO 2 -(As 0.67 Sb 0.33 ) 2 Se 3 , n-GaAs-As 2 Se 3 and n-GaAs-As 2 S 3 . For all samples I-V characteristics and photosensitivity spectra were obtained. These heterostructures can be used for manufacturing rectifying devices and photoreceivers.

New Hofmann-type complexes in the form of M(4-Chpy) 2 Ni(CN) 4 [where 4-Chpy = 4-(3- cyclohexen-1-yl)pyridine and M = Ni, Co] were prepared in powder form, and their infrared spectra are reported in the range of 4000 - 400 cm −1 . The spectral findings suggest that these compounds are similar in structure to the Hofmann-type complexes, and their structure consists of polymeric layers |M-Ni(CN) 4 | ∞ with the 4-(3-cyclohexen-1-yl)pyridine molecule bound to the metal atom (M). PACS: 33.20.Ea, 33.20.Tp, 82.75-z

Cyclopentanone-tetracyanonickel complexes, given by the general formula of M(cyclopentanone) 2 Ni(CN) 4 (M = Ni, Cd and Co), were obtained for the first time. The similarities of the observed spectra with Hofmann-type complexes indicate that the obtained compounds are new examples of Hofmann-type complexes. - PACS: 33.20.Ea, 33.20.Tp

The defect structure for Cu 2+ in SrLaAlO 4 is theoretically investigated by the perturbation formulas of the spin Hamiltonian parameters (g factors g ‖ , g ⊥ and the hyperfine structure constants A ‖ and A ⊥ ) for a 3d 9 ion in tetragonally elongated octahedra. Based on these studies, the tetragonal center may be attributed to Cu 2+ occupying the host Al 3+ site, associated with one hole delocalized at the four oxygen ligands in planar coordination. Furthermore, the four Cu,O bonds (perpendicular to the four-fold axis) are found to suffer an outward stretch of about 0.06 Å due to (i) the local tenseness in this plane, arising from the size mismatching substitution of the smaller Al 3+ by the larger Cu 2+ and (ii) the weaker electrostatic attraction of the less charged Cu2+ acting upon the four oxygen ions containing the delocalized hole. The calculated spin Hamiltonian parameters agree well with the experimental data. The defect structure of this center is discussed.

The electron paramagnetic resonance (EPR) g factors g i (i = x,y, z) and the hyperfine structure constants A i for the rhombic Co 2+ center in magnesium acetate are theoretically studied from the perturbation formulas of these parameters for a 3d 7 ion under rhombic symmetry. In these formulas, the contributions from the admixture among different states, covalency effect and rhombic crystal-fields are taken into account. The related crystal-field parameters are determined from the superposition model and the local geometrical relationship of the impurity center. The calculated results show reasonable agreement with the observed values. In addition, the nuclear quadrupole interaction constant Q is analyzed, and its negative sign is verified theoretically.

The electron paramagnetic resonance spectra of γ -irradiated L-glutamine hydrochloride and N-carbamoyl- L-glutamic acid single crystals have been investigated at room temperature. Radiation damage centres are attributed to ĊH, ṄH 2 and CH 2 Ċ(NH 2 )COOH radicals.

The mean amplitudes of vibration of PH 3 BH 3 and PF 3 BH 3 were calculated from known spectroscopic and structural data between 0 and 1000 K and compared with those of related species. Bond peculiarities are also briefly discussed.