Stress-strain relations in elastoplastic solids with Dugdale-type cracks

Mechanical behavior of a two-dimensional elastoplastic solid with rectilinear cracks is investigated. Plastic strip model is used to reduce plasticity problem to the equivalent linear elasticity formulation. Two realizations of the mixed mode plastic strip model are considered: in-line plastic strips as proposed by Becker and Gross [Int. J. Fract. 37 (1988) 163], and inclined plastic strips of Panasyuk and Savruk [Appl. Mech. Rev. 47 (1994) 151]. The effective mechanical response predictions are based on the procedure presented in Kachanov et al., [Appl. Mech. Rev. 47 (1994) 151]. Stress-strain relations are obtained for parallel and randomly oriented non-interacting cracks. Results are compared with known elastic solutions.     

Experience with Construction of Underground Sections of Buildings by the “From Top Down” Scheme

Experience gained with the method of installing the underground section of a building from the top down is described in an example of the construction of specific projects in Moscow, design, construction and monitoring problems are exposed, advantages and disadvantages of this method are indicated, and observational data are cited for the settlements of existing buildings located within the zone of influence of new construction.     

A study of thermal processes in high-power InGaN/GaN flip-chip LEDs by IR thermal imaging microscopy

Results of an experimental study of temperature fields generated in high-power AlGaInN heterostructure flip-chip light-emitting diodes (LEDs) via their self-heating at high working currents are presented. The method of IR thermal imaging microscopy employed in the study enables a direct measurement of the temperature distribution over the p-n junction area with a high resolution of ∼3 μm at an absolute measurement error of ∼2 K. It is shown that large temperature gradients may arise in high-power LEDs at high excitation levels as a result of current crowding. This effect should be taken into account when designing lightemitting chips and estimating the admissible operation modes. The method of IR thermal imaging microscopy can also reveal microscopic defects giving rise to current leakage channels and impairing device reliability.     

Heat transfer to near-critical helium in horizontal channels

Experimental results on heat transfer and pressure losses during a forced motion of helium of near-critical state parameters in a horizontal channel are reported. A method of calculation of temperature and pressure distributions along the channel is proposed.     

Studying the free convection in closed axisymmetric spaces

We have developed an analytical method of calculating the heat-transfer coefficients, the boundary-layer thicknesses, and the temperature and velocity distributions in the boundary layer for the quasisteady free convection in closed axisymmetric spaces for a given heat-flux density at the boundary. We have derived experimental relationships for the heat-transfer coefficient in the case of free convection in a sphere.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 16, No. 6, pp. 977–983, June, 1969.     

Calculation of the thermodynamic parameters of helium in a centrifugal force field

The design of cooling systems for a cryoalternator's superconducting field windings must be based on the knowledge of the distribution of the thermodynamic parameters (primarily temperature) of the helium in both its liquid and gaseous phases in centrifugal force fields. This paper proposes a set of ordinary differential equations describing the distributions. By numerically solving the set, the effects of the angular velocity of rotation, filling factor and temperature (pressure) at the axis of rotation upon the pressure, temperature and density distributions in helium in rotating vessels have been studied. Formulee for the approximation of the distributions have been obtained, which are applicable to rotation axis temperatures from 3 to 4.6 K (corresponding to saturation pressures 0.24 × 10⁵ to 1.4 × 10⁵ Pa), angular velocities of rotation from 50 to 300 rad s^?1 and filling factors from 0.1 to 0.9.     

Vapour phase motion in cryogenic systems containing superheated and subcooled liquids

The development of vent pipelines, and venting storage tanks for cryogenic liquids requires the knowledge of the law of motion as well as regularities of vapour content variation in the liquid and heat dissipation by the vapour phase. This is a theoretical study of the effect of superheating (subcooling) of the liquid, relative acceleration and reduced pressure upon the size and velocity of noninteracting vapour bubbles, moving in the liquid, and upon their resistance and heat transfer coefficients.     

Calculation of the helium thermodynamic state in rotating cryostats

The present paper contains basic essential data for the design of rotating cryostats. The effect of the filling factor, angular velocity of rotation, reduced temperature at the axis of rotation and the method of helium supply to a rotating cryostat on temperature, pressure and density distribution is discussed. The maximum sub-cooling and distance from the axis of rotation at which the critical pressure is reached is studied theoretically. For vapour phase quasi-saturation there is a good agreement between the calculated data on temperature distribution and the experimental results available.     

Diversity of Properties of Device Structures Based on Group-III Nitrides,Related to Modification of the Fractal-Percolation System

A fractal-percolation system that includes extended defects and random fluctuations in the alloy composition is formed during the growth of device structures based on Group-III nitrides. It is established that the specific features of this system are determined not only by the growth conditions. It is shown that the diversity of the electrical and optical properties of InGaN/GaN LEDs (light-emitting diodes) emitting at wavelengths of 450–460 and 519–530 nm, as well as that of the electrical properties of AlGaN/GaN HEMT (high-electron-mobility transistor) structures, is due to modification of the properties of the fractal-percolation system both during the growth process and under the action of the injection current and irradiation. The influence exerted by these specific features on the service life of light-emitting devices and on the reliability of AlGaN/GaN HEMT structures is discussed.