Null Energy Condition Violation and Classical Stability in the Bianchi I Metric

The stability of isotropic cosmological solutions in the Bianchi I model is considered. We prove that the stability of isotropic solutions in the Bianchi I metric for a positive Hubble parameter follows from their stability in the Friedmann-Robertson-Walker metric. This result is applied to models inspired by string field theory, which violate the null energy condition. Examples of stable isotropic solutions are presented. We also consider the k-essence model and analyse the stability of solutions of the form $\Phi(t)=t$.Comment: 27 pages, references added, accepted for publication in Phys. Rev.

Generalized stacking fault energetics and dislocation properties: compact vs. spread unit dislocation structures in TiAl and CuAu

We present a general scheme for analyzing the structure and mobility of dislocations based on solutions of the Peierls-Nabarro model with a two component displacement field and restoring forces determined from the ab-initio generalized stacking fault energetics (ie., the so-called $\gamma$-surface). The approach is used to investigate dislocations in L1$_{0}$ TiAl and CuAu; predicted differences in the unit dislocation properties are explicitly related with features of the $\gamma$-surface geometry. A unified description of compact, spread and split dislocation cores is provided with an important characteristic "dissociation path" revealed by this highly tractable scheme.Comment: 7 two columns pages, 2 eps figures. Phys. Rev. B. accepted November 199

Bosons in a Lattice: Exciton-Phonon Condensate in Cu2O

We explore a nonlinear field model to describe the interplay between the ability of excitons to be Bose-condensed and their interaction with other modes of a crystal. We apply our consideration to the long-living para-excitons in Cu2O. Taking into account the exciton-phonon interaction and introducing a coherent phonon part of the moving condensate, we derive the dynamic equations for the exciton-phonon condensate. These equations can support localized solutions, and we discuss the conditions for the moving inhomogeneous condensate to appear in the crystal. We calculate the condensate wave function and energy, and a collective excitation spectrum in the semiclassical approximation; the inside-excitations were found to follow the asymptotic behavior of the macroscopic wave function exactly. The stability conditions of the moving condensate are analyzed by use of Landau arguments, and Landau critical parameters appear in the theory. Finally, we apply our model to describe the recently observed interference and strong nonlinear interaction between two coherent exciton-phonon packets in Cu2O.Comment: 34 pages, LaTeX, four figures (.ps) are incorporated by epsf. Submitted to Phys. Rev.

Non-minimally Coupled Cosmological Models with the Higgs-like Potentials and Negative Cosmological Constant

We study dynamics of non-minimally coupled scalar field cosmological models with Higgs-like potentials and a negative cosmological constant. In these models the inflationary stage of the Universe evolution changes into a quasi-cyclic stage of the Universe evolution with oscillation behaviour of the Hubble parameter from positive to negative values. Depending on the initial conditions the Hubble parameter can perform either one or several cycles before to become negative forever.Comment: 22 pages, 6 figures, v4:Section 2 expanded, references added, accepted for publication in Class. Quant. Gra

Stable Exact Solutions in Cosmological Models with Two Scalar Fields

The stability of isotropic cosmological solutions for two-field models in the Bianchi I metric is considered. We prove that the sufficient conditions for the Lyapunov stability in the Friedmann-Robertson-Walker metric provide the stability with respect to anisotropic perturbations in the Bianchi I metric and with respect to the cold dark matter energy density fluctuations. Sufficient conditions for the Lyapunov stability of the isotropic fixed points of the system of the Einstein equations have been found. We use the superpotential method to construct stable kink-type solutions and obtain sufficient conditions on the superpotential for the Lyapunov stability of the corresponding exact solutions. We analyze the stability of isotropic kink-type solutions for string field theory inspired cosmological models.Comment: 23 pages, v3:typos corrected, references adde

СТРУКТУРА И МАГНИТНЫЕ СВОЙСТВА ПОРОШКА ГЕКСАФЕРРИТА СТРОНЦИЯ ПОСЛЕ ИЗМЕЛЬЧЕНИЯ В ВОДЕ И ТОЛУОЛЕ С ПОСЛЕДУЮЩИМ ОТЖИГОМ

oai:oai.mateltech.elpub.ru:article/107Structural changes of strontium hexaferrite powders after milling in water and toluene and after subsequent annealing were studied using X-ray diffraction, Scanning Electron Microscopy and Laser diffraction. Also magnetic properties changes were studied. The coarse-grain powder milling leads to an abrupt decrease of its particles size and the average crystallite size as well as an increase of SrFe12O19 phase lattice microstrains. Saturation magnetization and remanence decrease after milling in both media. At the same time coercive force of milled powders changes insignificantly with increasing milling time. The subsequent annealing allowed us to increase the magnetic properties of the powder. The annealed powders are characterized by the following magnetic properties: µ0Нci = 0,42¸0,49 T, µ 0Ir = 0,23¸0,24 T, (BH)max = 8-9,6 kJ/m3.Методами рентгеноструктурного анализа, растровой электронной микроскопии и лазерной дифракции исследованы структурные изменения в порошке гексаферрита стронция при измельчении в воде и толуоле, а также при последующем отжиге. Кроме того, изучено изменение магнитных свойств порошка. Установлено, что измельчение крупнозернистого порошка гексаферрита стронция приводит к значительному уменьшению размера частиц порошка, снижению размера областей когерентного рассеяния и увеличению микродеформации решетки фазы SrFe12O19. Обнаружено, что остаточная намагниченность и намагниченность насыщения при измельчении в обеих средах уменьшаются, а коэрцитивная сила меняется мало с увеличением продолжительности измельчения. В результате последующего отжига магнитные свойства порошка гексаферрита стронция резко увеличиваются, что обусловлено формированием нанокристаллической структуры. Для отожженных порошков характерны следующие свойства: µ0Нci = 0,42 µ 0,49 Тл, μоIr = 0,23 µ 0,24 Тл, (BH)max = 8,0 µ 9,6 МДж/м3. Показано, что магнитные свойства отожженных порошков зависят от среды и длительности процесса измельчения

Prospects in Analytical Atomic Spectrometry

Tendencies in five main branches of atomic spectrometry (absorption, emission, mass, fluorescence and ionization spectrometry) are considered. The first three techniques are the most widespread and universal, with the best sensitivity attributed to atomic mass spectrometry. In the direct elemental analysis of solid samples, the leading roles are now conquered by laser-induced breakdown and laser ablation mass spectrometry, and the related techniques with transfer of the laser ablation products into inductively-coupled plasma. Advances in design of diode lasers and optical parametric oscillators promote developments in fluorescence and ionization spectrometry and also in absorption techniques where uses of optical cavities for increased effective absorption pathlength are expected to expand. Prospects for analytical instrumentation are seen in higher productivity, portability, miniaturization, incorporation of advanced software, automated sample preparation and transition to the multifunctional modular architecture. Steady progress and growth in applications of plasma- and laser-based methods are observed. An interest towards the absolute (standardless) analysis has revived, particularly in the emission spectrometry.Comment: Proofread copy with an added full reference list of 279 citations. A pdf version of the final published review may be requested from Alexander Bol'shakov <[email protected]

Experimental study of 4-aminobenzoilgidrazid succinic acid antidiabetic activity

In experiments on intact rats and rats with steroid diabetes was studied the effects of prolonged introduction of 4-aminobenzoilgidrazid of succinic acid. It is shown that this substance potentiates the hypoglycemic effect of insulin, increases glucose tolerance and reduces the hyperglycemic effect of adrenaline