Influence of intermartensitic transitions on transport properties of Ni2.16Mn0.84Ga alloy

Magnetic, transport, and x-ray diffraction measurements of ferromagnetic shape memory alloy Ni$_{2.16}$Mn$_{0.84}$Ga revealed that this alloy undergoes an intermartensitic transition upon cooling, whereas no such a transition is observed upon subsequent heating. The difference in the modulation of the martensite forming upon cooling from the high-temperature austenitic state [5-layered (5M) martensite], and the martensite forming upon the intermartensitic transition [7-layered (7M) martensite] strongly affects the magnetic and transport properties of the alloy and results in a large thermal hysteresis of the resistivity $\rho$ and magnetization $M$. The intermartensitic transition has an especially marked influence on the transport properties, as is evident from a large difference in the resistivity of the 5M and 7M martensite, $(\rho_{\mathrm{5M}} - \rho_{\mathrm{7M}})/\rho _{\mathrm{5M}} \approx 15$, which is larger than the jump of resistivity at the martensitic transition from the cubic austenitic phase to the monoclinic 5M martensitic phase. We assume that this significant difference in $\rho$ between the martensitic phases is accounted for by nesting features of the Fermi surface. It is also suggested that the nesting hypothesis can explain the uncommon behavior of the resistivity at the martensitic transition, observed in stoichiometric and near-stoichiometric Ni-Mn-Ga alloys.Comment: 7 pages, 6 figures, REVTEX

Novel Scintillation Material - ZnO Transparent Ceramics

ZnO-based scintillation ceramics for application in HENPA LENPA analyzers have been investigated. The following ceramic samples have been prepared: undoped ones (ZnO), an excess of zinc in stoichiometry (ZnO:Zn), doped with gallium (ZnO:Ga) and lithium (ZnO:Li). Optical transmission, x-ray excited emission, scintillation decay and pulse height spectra were measured and analyzed. Ceramics have reasonable transparency in visible range (up to 60% for 0.4 mm thickness) and energy resolution (14.9% at 662 keV Cs137 gamma excitation). Undoped ZnO shows slow (1.6 {\mu}s) luminescence with maximum at 2.37 eV and light yield about 57% of CsI:Tl. ZnO:Ga ceramics show relatively low light yield with ultra fast decay time (1 ns). Lithium doped ceramics ZnO:Li have better decay time than undoped ZnO with fair light yield. ZnO:Li ceramics show good characteristics under alpha-particle excitation and can be applied for the neutral particle analyzers.Comment: 4 pages, 8 figures, research covered in this paper was presented at SCINT2011 conference as a poster, submitted for publication at IEEE Trans. Nucl. Sc

Strongly nonlinear dynamics of electrolytes in large ac voltages

We study the response of a model micro-electrochemical cell to a large ac voltage of frequency comparable to the inverse cell relaxation time. To bring out the basic physics, we consider the simplest possible model of a symmetric binary electrolyte confined between parallel-plate blocking electrodes, ignoring any transverse instability or fluid flow. We analyze the resulting one-dimensional problem by matched asymptotic expansions in the limit of thin double layers and extend previous work into the strongly nonlinear regime, which is characterized by two novel features - significant salt depletion in the electrolyte near the electrodes and, at very large voltage, the breakdown of the quasi-equilibrium structure of the double layers. The former leads to the prediction of "ac capacitive desalination", since there is a time-averaged transfer of salt from the bulk to the double layers, via oscillating diffusion layers. The latter is associated with transient diffusion limitation, which drives the formation and collapse of space-charge layers, even in the absence of any net Faradaic current through the cell. We also predict that steric effects of finite ion sizes (going beyond dilute solution theory) act to suppress the strongly nonlinear regime in the limit of concentrated electrolytes, ionic liquids and molten salts. Beyond the model problem, our reduced equations for thin double layers, based on uniformly valid matched asymptotic expansions, provide a useful mathematical framework to describe additional nonlinear responses to large ac voltages, such as Faradaic reactions, electro-osmotic instabilities, and induced-charge electrokinetic phenomena.Comment: 30 pages, 17 eps-figures, RevTe

Resonant Cyclotron Radiation Transfer Model Fits to Spectra from Gamma-Ray Burst GRB870303

We demonstrate that models of resonant cyclotron radiation transfer in a strong field (i.e. cyclotron scattering) can account for spectral lines seen at two epochs, denoted S1 and S2, in the Ginga data for GRB870303. Using a generalized version of the Monte Carlo code of Wang et al. (1988,1989b), we model line formation by injecting continuum photons into a static plane-parallel slab of electrons threaded by a strong neutron star magnetic field (~ 10^12 G) which may be oriented at an arbitrary angle relative to the slab normal. We examine two source geometries, which we denote "1-0" and "1-1," with the numbers representing the relative electron column densities above and below the continuum photon source plane. We compare azimuthally symmetric models, i.e. models in which the magnetic field is parallel to the slab normal, with models having more general magnetic field orientations. If the bursting source has a simple dipole field, these two model classes represent line formation at the magnetic pole, or elsewhere on the stellar surface. We find that the data of S1 and S2, considered individually, are consistent with both geometries, and with all magnetic field orientations, with the exception that the S1 data clearly favor line formation away from a polar cap in the 1-1 geometry, with the best-fit model placing the line-forming region at the magnetic equator. Within both geometries, fits to the combined (S1+S2) data marginally favor models which feature equatorial line formation, and in which the observer's orientation with respect to the slab changes between the two epochs. We interpret this change as being due to neutron star rotation, and we place limits on the rotation period.Comment: LaTeX2e (aastex.cls included); 45 pages text, 17 figures (on 21 pages); accepted by ApJ (to be published 1 Nov 1999, v. 525

Gamma Ray Bursts from the Evolved Galactic Nuclei

A new cosmological scenario for the origin of gamma ray bursts (GRBs) is proposed. In our scenario, a highly evolved central core in the dense galactic nucleus is formed containing a subsystem of compact stellar remnants (CSRs), such as neutron stars and black holes. Those subsystems result from the dynamical evolution of dense central stellar clusters in the galactic nuclei through merging of stars, thereby forming (as has been realized by many authors) the short-living massive stars and then CSRs. We estimate the rate of random CSR collisions in the evolved galactic nuclei by taking into account, similar to Quinlan & Shapiro (1987), the dissipative encounters of CSRs, mainly due to radiative losses of gravitational waves, which results in the formation of intermediate short-living binaries, with further coalescence of the companions to produce GRBs. We also consider how the possible presence of a central supermassive black hole, formed in a highly evolved galactic nucleus, influences the CSR binary formation. This scenario does not postulate ad hoc a required number of tight binary neutron stars in the galaxies. Instead, it gives, for the most realistic parameters of the evolved nuclei, the expected rate of GRBs consistent with the observed one, thereby explaining the GRB appearance in a natural way of the dynamical evolution of galactic nuclei. In addition, this scenario provides an opportunity for a cosmological GRB recurrence, previously considered to be a distinctive feature of GRBs of a local origin only. We also discuss some other observational tests of the proposed scenario.Comment: 25 pages, LATEX, uses aasms4.sty, accepted by Ap

Mechanisms of Manganese-Assisted Nonradiative Recombination in Cd(Mn)Se/Zn(Mn)Se Quantum Dots

Mechanisms of nonradiative recombination of electron-hole complexes in Cd(Mn)Se/Zn(Mn)Se quantum dots accompanied by interconfigurational excitations of Mn$^{2+}$ ions are analyzed within the framework of single electron model of deep {\it 3d}-levels in semiconductors. In addition to the mechanisms caused by Coulomb and exchange interactions, which are related because of the Pauli principle, another mechanism due to {\it sp-d} mixing is considered. It is shown that the Coulomb mechanism reduces to long-range dipole-dipole energy transfer from photoexcited quantum dots to Mn$^{2+}$ ions. The recombination due to the Coulomb mechanism is allowed for any states of Mn$^{2+}$ ions and {\it e-h} complexes. In contrast, short-range exchange and ${\it sp-d}$ recombinations are subject to spin selection rules, which are the result of strong {\it lh-hh} splitting of hole states in quantum dots. Estimates show that efficiency of the {\it sp-d} mechanism can considerably exceed that of the Coulomb mechanism. The phonon-assisted recombination and processes involving upper excited states of Mn$^{2+}$ ions are studied. The increase in PL intensity of an ensemble of quantum dots in a magnetic field perpendicular to the sample growth plane observed earlier is analyzed as a possible manifestation of the spin-dependent recombination.Comment: 14 pages, 2 figure

ПОРІВНЯЛЬНИЙ АНАЛІЗ КІРЛІАНОГРАФІЧНОГО СВІТІННЯ БІОЛОГІЧНОЇ ТКАНИНИ З БІОХІМІЧНИМИ ПРОЦЕСАМИ

Kirlian diagram samples Conducted. Achilles tendon dead people with various postmorbidnym period (from 5:0 until 22 days) and optoelectronics is part of the standard terms of the x-ray film developer. The results obtained were compared with biochemical indicators of the level of enzymes and content of degradation products of proteins, trace elements, derived from the investigated samples. For kirlianograficeskih studies used an experimental device, RIVERS 1, developed by Ukrainian Scientific Research Institute of mechanical engineering technologies (Dnepropetrovsk). For mathematical processing of results using Matlab program.The growing shortage of ATP causes the breach and termination of ion exchange, increases reactive oxygen generation, lipid peroxidation destroys cell membranes. The process of self digestion (autoliza) tissue tendons, as shown by the results of the experiments, had cyclical changes metabolism enzyme activity (ALT), carbohydrate (LDH), nucleotides, of total protein and micronutrients.Cравнивали кирлианографические изображения образцов и жидкой части ахиллова сухожилия разного по-стморбидного периода (от 5 часов до 22 суток) с показателями биохимических исследований в процессе аутолиза. Кирлианографию проводили на рентгеновской пленке. Использовали экспериментальный прибор «РЕК 1» (г. Днепропетровск). Процесс самопереваривания (аутолиза) тканей сухожилия, как показали результаты экспериментов, имел циклический характер изменения активности ферментов обмена аминокислот (АЛТ), углеводов (ЛДГ), нукле-отидов (мочевая кислота, мочевина), содержания общего белка и микроэлементов. Изменение площади засветки и фрактальности кирлиановских изображений также имело цикличный характер по давности аутолиза, что ображало характер энергетических изменений по содержанию взаимодействующих веществ.Порівняли кірліанографічне зображення зразків та рідини ахілового сухожилка різного постморбідного періоду (від 5 годин до 22 діб) із показниками біохімічних досліджень в процесі аутолізу. Кірліанографію проводили на рентгенівській плівці. Використовували експериментальний прилад «РЕК 1» (м. Дніпропетровськ). Процес саморуйнування тканин сухожилка, як показали результати експериментів, мав циклічний характер змінення активності ферментів обміну амінокислот (АЛТ), вуглеводів (ЛДГ), нуклеотидів (сечова кислота, сечовина), вмісту загального білка та мікроелементів. Зміни площі засвітки та фрактальності кірліанограм крапель біологічної речовини в процесі аутолізу також мали циклічність з часом, що віддзеркалювало характер енергетичних змін за вмістом речовин взаємодії