Directional Self-Assembly of Zinc Oxide Micro- and Nanowires

Technical Physics Letters - Approaches to the directional self-assembly of zinc oxide micro- and nanowires with the aid of centrifugal forces have been developed in the framework of a sol-gel...     

Proton-conducting sorption-active cyclam-based layers on chemically modified PVC surfaces of cellulose fabric

At different concentrations of hydrochloric, sulfuric, and phosphoric acids, the conductivity of the following electrochemical cell was measured: anode-acid solution-in-air bridge-acid solution-cathode. Cellulose fabric, the fibers of which are encapsulated in polyvinyl chloride, the surface of which is chemically modified with porous layers of aggregates formed by acid molecules and salt groups of ethanol and acetate cyclams, served as the bridge. The range where the logarithmic conductivity is proportional to the acid concentration is found. In this range, the molar contents of acids and water in the layers are estimated, the presence of aggregates composed of acid hydrates and cyclam salt groups is determined, the structure of layer is studied, and the similarity between the H⁺ conductivity of the layers on fabric and the conductivity of membranes based on polymers involving the skeleton ammonia salt groups is followed. For the aggregate layers, the specific surface; the limiting volume of pores; and the adsorption capacities for water, alcohol, benzene, and hexane vapors are measured. The formation of aggregates is shown to produce an insubstantial effect on the adsorption characteristics of the surface. During migration of H⁺ ions in the fabric and on its surface, the following process was carried out in the electrochemical cell: adsorption of NH₃, formation of NH ₄ ⁺ ions, and transfer of NH ₄ ⁺ ions to the catholyte. The migration velocity of H⁺ ions is shown to correspond to the measured current in the circuit, and NH ₄ ⁺ ions formed are found to be accumulated in the catholyte.     

GaAs/AlAs resonant-tunneling diode for subharmonic mixers

A GaAs/AlAs resonant-tunneling diode is designed for use as part of a subharmonic mixer, and its prototypes are fabricated and characterized. Its current-voltage characteristics measured at room, liquid-nitrogen, or liquid-helium temperature provide evidence for its adequate performance over the entire temperature range. Its impedance is measured against frequency up to 40 GHz, on which basis an appropriate equivalent circuit is selected for the device, and its components are quantified. The operation of a subharmonic mixer incorporating the resonant-tunneling diode is simulated for a number of values of its quantum-well width. At liquid-helium temperature, adjusting the quantum-well width is predicted to make the appropriate local-oscillator power vary from 50 μW to 15 mW, while holding the conversion loss of a subharmonic mixer below 10 dB.     

An ultraviolet MSM photodetector with electrically tunable spectral sensitivity

Ultraviolet photodetectors based on interdigital Schottky-barrier contacts to a ZnCdS/GaP heterostructure, which have low dark currents, are fabricated and investigated. It is found that the characteristics of the spectral response of these detectors depend on the bias and the long-wavelength boundary of the response of a ZnCdS/GaP metal-semiconductor-metal (MSM) diode can be shifted from 355 nm to 440 nm as the bias varies from 40 to 80 V. It is found that, at the wavelength of the maximum photosensitivity (355 nm), the ampere-watt sensitivity of the detector is 0.1 A/W.     

Generalized equation for calculating rock cutting efficiency by pulsed water jets

One of the promising methods for rock cutting technology is the use of high-speed water jets.In order to improve the cutting capacity of water jets without increasing the hydraulic power of equipment,pulsed water jets are basically used to increase the rock cutting efficiency.However,there are no mature recommendations for selection of rational parameters,and the relationship between indicators of rock cutting efficiency and parameters of pulsed water jet is still not established.In this context,we aimed at developing a generalized equation for calculating rock cutting efficiency,in which all the major parameters in consideration of rock cutting process are included.Then,a calibration of the rational parameters of rock cutting by pulsed water jets was conducted.The results are likely helpful for increasing productivity and reducing energy consumption.     

Dynamics of the detonation-wave front in solid explosives

The important role of the shape of the front during detonation wave propagation in gas mixtures was substantiated by K. I. Shchelkin during construction of the theory of spinning detonation. Subsequently, a unique relationship between the curvature of the front and detonation wave parameters has been repeatedly confirmed in experiments, including for condensed high explosives (HEs). The existence of this relationship formed the basis of the theory of the dynamics of the detonation front which had been developed by the end of the 20th century. This paper presents the results of a study of detonation front propagation in cylindrical samples of a low-sensitivity HE of different diameters with one-point and plane-wave initiation. A unique relationship between the detonation velocity and the curvature of the detonation wave front has been found. Ordinary differential equations describing two-dimensional steady-state detonation front profiles for HE charges in the form of a plate, a cylinder, and a ring were derived assuming that the detonation velocity depends on the curvature of the front. It was taken into account that the boundary angle between the normal to the front and the HE edge is unique for each combination of HE and liner material. It was found that the same detonation front profile corresponds to several combinations of liner material and the determining size of the charge (plate thickness, radius of the cylinder or the inner radius of the ring). A comparison of experimental front profiles near the edges of HE charges for these combinations provides data on the dependence of detonation velocity on the curvature of the front at low velocities corresponding to shock-induced detonation regimes. Analysis of previously obtained data for detonating ring charges of low-sensitivity HEs shows that as the detonation velocity decreases, the total front curvature tends to a limit of about 0.05 mm⁻¹, i.e., of the order of the inverse critical diameter. The limit of the front curvature allows predicting the critical detonation diameter.     

Thermal Activation of Type X Zeolites in the Presence of Carbon Dioxide

It is found that the highest value of the separation factor of the nitrogen—oxygen mixture is observed for zeolite activated in the presence of 2 vol % CO₂ in nitrogen. It is shown on the basis of IR studies that the formation of bicarbonate structures is most characteristic for this sample.     

Use of Mathematical Simulation for Studying Wave Processes in Ultrasonic Diagnostics of Massif

The simulation results obtained can be helpful for determining the location and orientation of cracks (seams) traversed by a sounder. __________ Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 5, May 2005, pp. 46 – 48.     

Radiation-Induced Phase Transformations in Zirconium Alloys under Long-Term Irradiation

Variation of the phase composition and structure of zirconium alloys É125 and É635 under the action of irradiation is studied by the methods of microscopic x-ray energy dispersion analysis, radiographic analysis, and analytical transmission electron microscopy. Special features of phase transformations in the alloys under the action of long-term neutron irradiation at 290 – 315°C are analyzed.