On the deterioration of ß″-alumina ceramics under electrolytic conditions

The degradation ofβ′'-alumina under electrolytic conditions was investigated at room temperature. With the use of an electrical-mechanical analogue, it was demonstrated that a large current concentration exists at the peripheries of blocked or unwetted areas. Thus, actual current densities at the sites of failure can be several times larger than the average current density. Implications regarding wetting ofβ′'-alumina by sodium are discussed. The concept of current focusing at the tips of sodium-filled cracks is demonstrated in a room temperature test.     

Theory of fluidized-bed electrical conduction

Mechanisms for the passage of electric current through a fluidized bed are discussed, and corresponding estimates for the effective electrical conductivity are given.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 11, pp. 889–900, November, 1978.     

Deformation-induced electric noise in steel under plasto-elastic alternating strain conditions

We have studied the relationship between mechanical stresses developed in steel under the conditions of cyclic plasto-elastic loading to a preset strain level and a noise component of the ac electric current induced by the alternating voltage applied to the sample. Both the mechanical and the electric noise characteristics are different in the steel samples not subjected to mechanical surface processing and in those with polished surfaces. It is shown that the stage of accumulation of the structural changes leading to fatigue fracture of a material can be determined by measuring the electric noise parameters of the samples.     

Conjugate problems of unsteady heat and mass conduction under varying external conditions

A closed system of algebraic and ordinary differential equations that enables one to simply and with a high degree of accuracy solve unsteady problems of heat conduction and diffusion extraction of a substance from solids of standard shapes - a plate, a cylinder, and a sphere - under varying external conditions is proposed. The method of solution is based on a unified universal dependence that describes with a high degree of accuracy the distribution of temperatures or concentrations of the substance in the above solids and on equations that determine variations in characteristics involved in this dependence with time and space as the solids move.     

Solubility limits of manganese in InSb under equilibrium and nonequilibrium synthesis conditions

We demonstrate that, in the case of InSb〈Mn〉 synthesis through quenching from the liquid state, a second phase in InSb precipitates at higher manganese concentrations than in the case of Czochralski growth. The observed concentration delay of second-phase precipitation can be accounted for in terms of both the complex, multistep formation of Lomer–Cottrell sessile dislocations, accompanying the crystallization of III–V compound semiconductors, and diffusion hindrances to dopant motion to dislocations, associated with the high quenching rate and the presence of other lattice defects.     

Self-organization of three-dimensional lead telluride nanoislands under conditions close to thermodynamic equilibrium

Three-dimensional lead telluride (PbTe) nanoislands were grown on (111)BaF₂ substrates by hotwall epitaxy (HWE) from vapor phase under conditions close to thermodynamic equilibrium and their surface morphology was studied by atomic force microscopy in various growth stages, including the initial stage of nucleation and the subsequent evolution of the size and shape of nanoislands. The distributions of island dimensions in the samples grown under various thermodynamic conditions were statistically analyzed. It is shown that the proposed HWE method ensures the formation of dense (∼8 × 10¹⁰ cm⁻²) self-organized arrays of PbTe quantum dots with parameters comparable with those of the quantum dots of the same material grown by molecular beam epitaxy according to the Volmer-Weber mechanism.     

Investigation of electrical conduction in polyvinyl formal

Current-voltage (I–V) characteristics of pure polyvinyl formal (PVF) were investigated at different fields, range 5–100 kV/cm, as a function of temperature, range 313–363 K. It was observed that while at low fields (up to 25 kV/cm), the conduction was Ohm’s law-dependent at high fields (beyond 25 kV/cm), the conduction was Poole-Frenkel (P-F) mechanism-dependent. An attempt was made to identify the nature of the current by comparing its observed dependence on temperature, electric field and electrode materials with their respective characteristic features of the existing theories of electrical conduction. The current showed a strong dependence on temperature. To identify the possible mechanism of conduction, current versus square root of field characteristics were drawn with aluminium, silver, copper and gold as upper electrodes and Al as the lower electrodes. The observed characteristic suggested that the charge carriers were generated by the field-assisted lowering of coulombic barriers at the traps, and were subsequently conducted through the bulk of the material by a hopping process between the localized states by a Jonscher-Ansari-modified P-F mechanism. The calculated value of the modified P-F barrier was ⋍ 1·94×10⁻¹⁹ J (1·21 eV).     

Evaluation of electrical conduction in iodine-doped polypyrrole

Electrical conductivity of polypyrrole has been measured after doping with different iodine concentrations. A thermally activated electrical conductivity was found which was pseudoohmic and increased with doping level. The results can also be fitted by log σ versusT ^−1/2 and log σ versusT ^−1/4 dependences, instead of the Arrhenius log σ versusT ⁻¹ dependence. From these results it was concluded that within the experimental scatter no significant distinction can be made between these different temperature dependence laws. Hence these data can only enable one to speculate about the true underlying transport model, rather than to draw decisive conclusions. Electrical conductivity results predicting the role of iodine dopant concentration on the conduction process of semiconducting polypyrrole are discussed.     

1/f noise of electrolytic capacitors as a reliability indicator

The electrical noise of capacitors and the relationship between typical imperfections in capacitors and their excess noise are described. It was assumed that a noisy capacitor is a poor-quality one. Investigations were aimed at the determination of a correlation between the inherent noise of capacitors and their reliability (time to failure) and also at the determination of an indicator to predict reliability. Investigations (noise measurements and reliability tests) were carried out on two samples of aluminium electrolytic capacitors. The method of reliability prediction for electrolytic capacitors based on their low-frequency noise is described. For reliability prediction the noise intensity G at a frequency of 2 Hz was used as a reliability indicator. It was found that the evaluated correlation coefficients between the noise parameter G and the time to failure, t, are statistically significant. It is concluded that it is possible to predict the lifetime of aluminium electrolytic capacitors on the basis of their 1/f noise. © 1998 John Wiley & Sons, Ltd.     

风雨条件下的水下噪声谱级预测

海洋表面的风、雨所产生的噪声是水下噪声场的重要组成部分。降水时雨致噪声可在比较宽的频带内决定噪声场的性质。在1~50kHz频段上,对已有的相关研究结果分析、综合,建立了一定风雨条件下的水下噪声谱级的经验预测算法。采用按频率线性分配大、小雨滴对噪声能量谱密度贡献的方法,在9~14kHz频段上对经验算法进行了修正。该修正经验算法不仅克服了经验算法在10kHz处经验预测值的跃变问题,而且通过两种算法预测值与某海域的实际观测数据的对比,表明修正经验算法比经验算法可以在更宽的频带内更加有效地预测一定风雨条件下的水下噪声谱级。     

Filtration in artificial porous media and natural sands under microgravity conditions

The goal of the present paper is to investigate experimentally and theoretically the capillary driven filtration in porous media with homogeneous and inhomogeneous porosity and permeability under microgravity conditions. The motivation having determined the choice of the environment was to study nonequilibrium phenomena in two-phase filtration in porous media. The paper contains the results illustrating the sensitivity of capillary forces to variations of porous media characteristics. The experimental results obtained for fluid imbibition into unsaturated artificial and natural porous media are compared. Theoretical and experimental results on determination of mixing fluxes in two-phase filtration are discussed.     

DC electrical conduction of zinc telluride thin films

Zinc telluride (ZnTe) thin films were deposited by thermal evaporation onto glass substrates kept at room temperature. X-ray diffraction studies showed that the films were polycrystalline and of cubic structure. The current-voltage (I-V) characteristics of the Au/ZnTe/Au thin film sandwich system at different temperatures were studied. The DC conduction was explained using the Schottky or Jonscher-Ansari modified Pool-Frenkel mechanism.     

Oxygen-ion diffusion and electrical conduction of LaMoFeO systems

Based on the novel oxygen ion conductor La₂Mo₂O₉, a series of Fe-doped samples of La₂Mo_2-xFe_xO_9-? (x = 0, 0.025, 0.05, 0.1) was prepared by conventional solid-state reaction method. The structure, phase transition, oxygen ion diffusion and electrical conductivity were studied with X-ray diffraction (XRD), differential scanning calorimeter (DSC), direct current (dc) resistivity, and dielectric relaxation (DR) measurements. One DR peak associated with the short-distance diffusion of oxygen vacancies was observed in both temperature and frequency spectra. The activation energy for oxygen ion diffusion in Fe-doped La₂Mo₂O₉ samples was smaller than that in un-doped samples. Fe doping can increase the ionic conductivity of La₂Mo_2-xFe_xO_9-? samples as well as the ionic transference number in the temperature range from 680°C to 400°C in comparison with the un-doped samples, although the electronic conductivity slightly increases. It is found that because of the small solubility of Fe₂O₃ in La₂Mo₂O₉ (<5%), Fe doping cannot suppress the phase transition that occurred around 570°C, but 2.5% K doping at La site at the same time (e.g. in sample La_1.95K_0.05Mo_1.95Fe_0.05O_9-?) can completely suppress this phase transition and increase conductivity at lower temperatures.     

Excess noise of an Er/Yb fiber superfluorescent radiation source

A study is made of the noise in the output intensity of a high-power superfluorescent fiber radiation source generating 20 mW in the 1.55 μm region of the spectrum. The source is constructed in an all-fiber technology from a quartz fiber activated with ytterbium and erbium. It is found that the spectral density of the noise in the frequency range 100–500 kHz is uniform and corresponds to the excess noise of “thermal” sources. It is shown that the noise in the output intensity of the source can be compensated (decreased by an order of magnitude) in a two-channel scheme of photodetection, where it approaches a level close to the photon shot noise. Pis’ma Zh. Tekh. Fiz. 23, 1–6 (December 12, 1997)     

A new theory of recording media noise

Previous investigations of the noise in particulate or grainy recording media have considered statistical variations in the processes by which the particles become magnetized. The theory of noise presented includes also statistical variations in the packing density of the particles. An extremely simple analysis shows that, when both of these phenomena are included properly, the noise power of recording media may always be expected to depend upon the magnetization, or signal level, and the particle packing factor. It is found that the recording media should always provide higher signal-to-noise ratios (SNRs) than was previously supposed. It is pointed out that the signal recovery or detection techniques employed today in magnetic storage devices cannot yield optimum SNRs or bit error rates. Some algebraic and/or conceptual errors in the published literature on noise are discussed.<>     

The evaluation of heat conduction via an electrical analog

The heat conduction through an object of arbitrary shape whose thermal conductivity is a known function of temperature can be calculated from the electrical resistance of an identically shaped object. This eliminates the need for tedious low temperature heat conduction measurements or computer calculations during design stages. Even in cases where an intermediate temperature heat shield is used (as on a mechanical dewer support) the electrical analog is applicable.