Angular selectivity of liquid crystal composite gratings

Angular selectivity of volume phase transmission gratings formed in a liquid crystal composite for s-and p-polarized light is investigated in the absence of external electric field.     

Towards a Mobile Code Management Environment for Complex,Real-Time,Distributed Systems

We present a novel mobile code management environment,currently under design and development. Our design employs anopen architecture, suitable for ``plug-and-play' with COTS andother groups' tools. While we have studied new algorithms, costand objective functions, and other fundamental issues, the maincontribution of this experimental research work is in the environmentitself. It should be noted that networked platforms, such asthe World Wide Web, are inherently not suitable for traditional,predictable real-time applications. Thus, real-time concernsnecessarily need to be blended with others concerns, and thetarget applications, making use of our environment, will toobe a blend of partially hard real-time and partially (or mostly)soft-real- time ones. The prototype environment will thereforesupport performance-based analysis and management focusing notonly on predictability but also on compilation, efficiency, safetyand other tradeoffs. We have selected the Java language and itsbytecode format as a representation for mobile code as well asa language for our implementation.     

Investigation into the formation of phases with a Ba<Subscript>2</Subscript>Ti<Subscript>9</Subscript>O<Subscript>20</Subscript>-type structure in the BaO-TiO<Subscript>2</Subscript> and BaO-SrO-TiO<Subscript>2</Subscript> systems

The mechanism of formation of barium titanate Ba₂Ti₉O₂₀ in the BaO-TiO₂ and BaO-SrO-TiO₂ systems is investigated using initial mixtures prepared by three methods, namely, mechanical grinding of the initial reactants, coprecipitation from aqueous solutions of salts, and the sol-gel technique. It is established that, irrespective of the preparation procedure, the formation of Ba₂Ti₉O₂₀ proceeds through the formation of the intermediate phases BaTi₄O₉ and BaTi₅O₁₁. The nature of the intermediate phases is determined by the homogeneity and dispersion of the initial mixture, as well as by the stability of the intermediate phase. The most optimum conditions for the synthesis of Ba₂Ti₉O₂₀ are provided by the formation of BaTi₅O₁₁ as an intermediate phase upon heat treatment of the coprecipitation products in the nanocrystalline state. The metastability and structural defects in the BaTi₅O₁₁ intermediate phase encourage a decrease in the temperature of the final heat treatment by 100–150°C in the course of the preparation of Ba₂Ti₉O₂₀ single-phase ceramics.     

Analysis of the “tailored” contact surface region in a shock tube

A simple method is presented for the computation of the initial parameters of the gas, the working time, and the optimal relationship between the lengths of the high-pressure chamber and the low-pressure channel of a shock tube in the tailored contact surface region which permits a substantial increase in the working time.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 3, pp. 537–542, September, 1976.     

Statistical kinetics of thermally activated fracture

The kinetics of thermofluctuational development of a single crack is approximated by a homogeneous Markov process. Considering an ensemble of non-interacting cracks, we calculate the distribution functions of the dimensions of the crack and of the longevity of identical samples under isothermal creep conditions due to the randomness of thermal fluctuations and of structural inhomogeneities of the samples. The connection between these distributions is discussed. The results are confirmed by available experimental data. It is shown that the scattering of usually observed in experiments reflects the thermally activated nature of the fracture process.

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Résumé En utilisant un processus de chaîne homogène de Markov, on obtient une approximation du développement d'une fissure simple sous des fluctuations thermiques. En considérant un ensemble de fissures sans interactions, on calcule les fonctions de distribution des dimensions de la fissure ainsi que la durée de vie d'éprouvettes identiques, sous des conditions de fluage isotherme dont le caractère aléatoire est dû à des fluctuations thermiques et à l'hétérogénéité structurale des éprouvettes. On discute la relation qui existe entre ces fonctions et on trouve une vérification des résultats de l'analyse dans les données expérimentales disponibles.On montre que la dispersion de la durée de vie que l'on observe au cours d'essais est le reflet de la nature thermoactive du processus de rupture.

     

Phase equilibria in the system LaMnO3 + δ-SrMnO3-LaFeO3-SrFeO3 − d

We have revealed the formation of a continuous series of orthorhombic LaMn_{1 ? y} Fe_yO₃ solid solutions (0<y<1); La_{1 ? x} Sr_xFeO₃ solid solutions in the composition range 0 < x ≤ 0.8, with an orthorhombic structure at 0 < x ≤ 0.6 and a cubic structure at 0.6 < x ≤ 0.8; and a tetragonal SrMn_{1 ? y} Fe_yO₃ phase in the range 0.6 ≤ y ≤ 1. The composition stability limits of the perovskite phase La_{1 ? x} Sr_xMn_{1 ? y} Fe_yO₃ have been determined, and the 1100°C isotherm of the La₂O₃-SrO-Mn₃O₄-Fe₂O₃ system in air has been constructed.     

Corrosion-resistant analogue of Hadfield steel

The concept of alloying austenitic steels with carbon + nitrogen is used for the development of a corrosion-resistant austenitic CrMn steel having an impact wear resistance close to that of the Hadfield steel. A higher stabilization of the austenitic phase by C + N, as compared to carbon or nitrogen alone, is substantiated by ab initio calculation of the electron structure, measurements of the concentration of free electrons and calculations of the phase equilibrium. Based on these results, the compositions (mass%) Cr18Mn18C0.34N0.61 and Cr18Mn18C0.49N0.58 were melted and tested along with Hadfield steel Mn12C1.2. Mechanical tests have shown that, as compared to the Hadfield steel, the experimental steels possess a higher strength, plasticity, hardness and the same resistance to impact wear. TEM studies of the surface layer after impact treatment revealed a mixture of the amorphous phase, nanocrystals and fine-twinned austenite. At the same time, using Mössbauer spectroscopy of conversion electrons, the ferromagnetic ordering was found in the surface layer of up to 10 μm in depth, which is the sign of the strain-induced martensitic phase. The hypothesis of a transition from the low-spin to the high-spin state of the iron atoms within the thin twins in austenite was proposed in order to interpret the discrepancy between TEM and Mössbauer studies. Potentiodynamic measurements and immersion tests show that the CrMnCN steels possess a significantly higher pitting potential and resistance to general corrosion in comparison with Hadfield steel.     

Parabolic flight experiments with PK-4

PK-4 is an experiment designed to investigate complex plasmas (low-temperature plasmas containing microparticles, e.g. dust grains) in a combined dc/rf discharge under microgravity conditions on board of the International Space Station. Within the 35th and 36th ESA parabolic flight campaigns first experiments under microgravity conditions in a specially designed experiment set-up have been performed. The particle flow inside the tube, the appearance of dust waves, and lane formation in interpenetrating particle clouds have been observed.     

Nanoscale Magnetic Behavior of C60 Thin Films in Earth Magnetic Field under Polarization Light Influences

Magnetic behavior of C₆₀ thin films in the Earth's magnetic field under polarization light influence is presented. Transformation of magnetic field for two fullerene thin films of different thickness is investigated. Two proton magnetometers were used for these measurements. Samples of 30 nm and 250 nm thickness illustrate a significant change of magnetic field intensity under the influence of polarization light, in range from 3.4 to 12.9 nT, for 200 measurement data per sample.