Methods for measuring amplitudes of signals from Cherenkov counters

Measurements of the pulse heights in the T0 start trigger detector of the ALICE experiment are necessary both for time-amplitude offline correction of start signal T0 used in the time-of-flight TOF detector and for monitoring the state of the Cherenkov counters in the detector. A high amplitude resolution is not required for these tasks; what is needed is fast encoding and interfacing with the data readout system in which only time channels are available. Therefore, amplitudes are measured in the detector by pulse-height-to-time conversion using two independent methods, one of which involves quasi-logarithmic charge-to-time converter (QTC) and the other employs two—leading-edge (LED) and constant-fraction (CFD)—timing discriminators. The main characteristics of both methods and results of calibrations of the appropriate devices using a pulsed laser are presented.     

Interface states and capacitance-voltage characteristics of n-SnO2:Ni/p-Si heterostructures under gas-adsorption conditions

The n-SnO₂:Ni/p-Si heterostructures were synthesized with a mean size of 6–8 nm of crystallites in the tin dioxide layer. The capacitance-voltage characteristics of these structures were measured in dry air and under adsorption of NO₂ and C₂H₅OH molecules. The variation of a reference-signal frequency within 0.5–20 kHz made it possible to separate out the contribution of heterointerface states to the structure capacitance. Adsorption of NO₂ molecules was shown to reduce the density of the heterointerface states, while adsorption of ethanol molecules resulted in its increase.     

Variation of the adsorption properties of porous silicon in the course of natural and high-temperature aging

The photo-and thermostimulated adsorption-desorption processes on the surface of porous silicon (por-Si) were studied in the course of natural and high-temperature degradation of the samples. The results of IR absorption, luminescence, and Auger electron spectroscopy measurements indicate that an active stage in the sample morphology variation under the natural aging conditions lasts for a prolonged time (exceeding 74 days) upon the por-Si layer formation and is accompanied by redistribution of the adsorbed molecules. The surface properties vary so as to favor the adsorption of oxygen, carbon, and, probably, OH groups. The high-temperature (1149 K) treatment of the por-Si surface in acetone vapor favors the formation of a carbonized layer possessing a characteristic photoluminescence spectrum with a maximum intensity at 458 nm. The IR spectra indicate the presence of a silicon carbide phase, identified as the cubic β-SiC, with a characteristic absorption at 800–833 cm⁻¹. A strong shift of the high-frequency wing of the IR absorption spectrum is explained by the carbon substitution for one oxygen in the O-Si-O groups.     

Effect of heat treatment on the structural and phase transformations and mechanical properties of TiNi alloy subjected to severe plastic deformation by torsion

Effect of annealing on the structural and phase transformations and mechanical properties of large-size samples of the Ti_49.4Ni_50.6 alloy preliminary subjected to severe plastic deformation by torsion under a high pressure (HPT) is studied. The study was performed by transmission and scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, and measurements of mechanical properties. The annealing was found to result in the nanocrystallization of initial samples amorphized by HPT. In this alloy, the high-strength uniform nanostructured state is formed the size of nanocrystalline grains of which and the mechanical properties depend on the temperature and time of annealing.     

Thermometry of microwave discharge in powder mixtures by the thermal radiation spectrum

The temperature is determined in pulsed microwave discharges in powder mixtures at atmospheric pressure. The effect of microwave radiation of gyrotron (wavelength of 4 mm, power up to 200 kW, pulse duration of 1 to 10 ms) on a finely divided medium causes the emergence of plasma in a gas medium between solid particles; the thresholds (with respect to power) of generation of plasma in powder mixtures are hundreds of times lower than those in gas. The method of determining the discharge temperature consists in recording the radiation in a wide spectral range (200 to 850 nm) and comparing the obtained spectrum with the Planck spectrum in the Wien region. In the case of similarity of two spectra, the discharge temperature is determined as a parameter of the spectrum under observation. In so doing, no data on the emissivity of discharge are required for determining the temperature. It is demonstrated that microwave-discharge plasma in powders is characterized by a temperature of 2000–3000 K.     

An estimate of the limit state of power transformers and autotransformers

The main indicators of the limit technical state of transformers and autotransformers, for which their further use is impermissible or inadvisable, are considered. The main elements of a power transformer which determine its limit state are the windings and the cores. Important indicators for estimating the technical state of the windings is the wear of the coil insulation, the degree of mechanical fastening of the windings and, in particular, the absence of dangerous deformations. Wear of the coil insulation is estimated from the degree of polymerization and the short-circuit resistance. The cores of the transformer become damaged fairly rapidly during operation. Normalized values of the above indicators are given as well as experience in using them in the Russian Federation and the Ukraine to estimate the limit state of transformers and autotransformers. The amount of inspection in order to reach conclusions on the technical state of a transformer and temporary measures until they are replaced are indicated. __________ Translated from élektricheskie Stantsii, No. 1, pp. 44–49, 2008.     

Features of the long-term photo emf relaxation in a heteroepitaxial ZnSe-GaAs structure

The spectral characteristics and transverse distribution of the photo emf were studied in a heteroepitaxial ZnSe-GaAs structure obtained by MBE on a zinc-stabilized GaAs(100) substrate surface. The spectral measurements revealed unusual manifestations of the long-term photo emf relaxation, whereby the amplitude of the spectral characteristic of the photo emf depends on the direction of wavelength variation of the exciting monochromatic light. Dependence of the amplitude and sign (phase) of the photo emf on the intensity of light absorbed in the sample can be explained by time variation of the effective lifetime of the electron-hole pairs and by a difference in the lifetime values between various layers of the structure. Resistivity gradients at the heterostructure interface exhibit a layer character.     

The possibilities of acoustic emission testing of rails during exploitation

The possibilities of acoustic emission testing of rails on a bridge are considered. The stress-strain state of a rail under conditions of train loading is analyzed. The problems of minimization of levels of mechanical and electromagnetic noises are considered. The results of field acoustic emission tests and their analysis are presented.