Deformation-Strength Relationships in Short-Term Tension of Heat-Resistant Materials

The analysis of 124 curves obtained in short-term tensile tests demonstrate that they can be described by varying strain hardening and softening characteristics. Different stress–strain curves can be produced at invariable yield strength and ultimate strength and interrelated proportional variations of the above characteristics. To determine some specific stress–strain curve, it is necessary to take account of yield strength and ultimate strength as well as strain corresponding to the latter. The relations between yield strength, ultimate strength and hardening and their practically complete absence between these parameters and softening were statistically established.     

Model of individual collisions for description of electron transport in matter

Distributions of electron characteristics are constructed with the use of data of elastic and nonelastic processes of interaction between electrons and matter. The data are taken from the National Nuclear Data Center, . These characteristics are used for developing the technique of modeling the electron transport in matter. The developed model does not use the well-known slowdown approximation and multiple scattering theories. The comparison of some moments of the distributions with the NIST data is carried out. The satisfactory fit of some results computed by using the developed model and MCNP results is obtained.     

A new approach to determination of the input impedance of a dipole antenna

In terms of the example of a tubular dipole, a new diffraction approach is developed for determining its input impedance. This approach makes it possible to avoid conventional a priori specification of the exciting electric field in the dipole’s gap. Two problems of diffraction of an E-polarized wave by the corresponding structures formed from metal tubes are solved. It is also shown that, when the widespread method involving specification of the form of the electric field in the dipole’s gap is applied, the quasi-electrostatic character of the field and the field singularities on the dipole’s edges should be taken into account. Then, the input impedance of the dipole can be calculated with a small error.     

Theory of short-pulse gain saturation in semiconductor laseramplifiers

Carrier heating and spectral hole burning are shown to have a strong influence on the amplification of ultrashort pulses using semiconductor laser amplifiers. Approximate analytical expressions for the effective saturation energy in different pulsewidth regimes are derived     

Mercury contamination in the vicinity of a derelict chlor-alkali plant Part II: contamination of the aquatic and terrestrial food chain and potential risks to the local population

This study investigated the environmental impact and level of risk associated with mercury (Hg) contamination near a derelict chlor-alkali plant in Pavlodar, Northern Kazakhstan. Several species of fish were sampled from the highly polluted Lake Balkyldak and the nearby river Irtysh, to assess the extent of Hg bioaccumulation in the aquatic food chain and potential human health risks. A small number of bovine tissue samples, water samples, soil and plant samples from a nearby village were also investigated in order to make a preliminary assessment of potential impacts on the terrestrial food chain. Mercury levels in fish caught from Lake Balkyldak ranged from 0.16 to 2.2 mg kg(-1) and the majority of fish exceeded current human health criteria for Hg. Interspecies comparisons indicated that Hg is accumulated in the order dace>carp>tench. Site-specific bioaccumulation factors (BAF) were calculated for THg, and were estimated for MeHg. Fish from the river Irtysh and floodplain oxbow lakes contained between 0.075 and 0.159 mg kg(-1) of Hg and can be regarded as uncontaminated. Soils were found to be impacted by past atmospheric emissions of Hg. Cattle grazing in the surroundings of the factory are exposed to Hg from contaminated soils, plants and surface water, but the consumption of contaminated fish from the lake appears to be the main route of exposure for humans.     

Theory of pulse-train amplification without patterning effects in quantum-dot semiconductor optical amplifiers

A theory for pulse amplification and saturation in quantum dot (QD) semiconductor optical amplifiers (SOAs) is developed. In particular, the maximum bit rate at which a data stream of pulses can be amplified without significant patterning effects is investigated. Simple expressions are derived that clearly show the dependence of the maximum bit rate on material and device parameters. A comparative analysis of QD, quantum well (QW), and bulk SOAs shows that QD SOAs may have superior properties; calculations predict patterning-free amplification up to bit rates of /spl sim/150-200 Gb/s with pulse output energies of /spl sim/0.2-0.4 pJ. The superiority of QD SOAs is based on: 1) the faster achievement of the regime of maximum gain in QD SOAs compared to QW and bulk SOAs and 2) the lower effective cross section of photon-carrier interaction in QDs.     

Methodological aspects of creep prediction for heat-resistant steels and alloys. Part 2. Prediction over wide ranges of temperatures and loading times

Evaluation of creep and long-term strength of metallic materials over wide temperature and stress ranges by calculation with equations on the basis of a limited body of initial data is proposed. The efficiency of evaluation can be greatly increased by systems analysis of known experimental data. __________ Translated from Problemy Prochnosti, No. 4, pp. 50–61, July–August, 2007.