On the slow motion of a cylinder in a micropolar fluid

Slow steady 2-dimensional motion of an incompressible micropolar fluid in the unbounded region exterior to a cylinder of arbitrary cross section is considered. The possibility of a solution in the strict sense of the Stokes' approximation is examined. It is shown that the near and far boundary conditions can be satisfied simultaneously only when the drag on the cylinder is zero and the velocity and microrotation vectors satisfy an integral condition.     

On the nonuniformity of a capillary flow

It is established that the capillary rise of a liquid has an oscillatory character, in contrast to the commonly accepted opinion that a vertical capillary is filled at a monotonically varying velocity. The value of the tangential shear stress arising in an ascending liquid is evaluated for ethyl alcohol and distilled water.     

Measurements and modeling of the thermal properties of a calorimeter having a sapphire absorber

The response of a magnetic calorimeter with a sapphire crystal serving as an X-ray absorber has been studied as a function of temperature. Several different Au films were used to connect thermally the magnetic sensor to the absorber. The amplitude and time dependence of the signal resulting from the absorption of an X-ray were fit using an idealized model for the calorimeter. The values of the various parameters resulting from a fit of the data are internally consistent and provide a physical understanding of the processes determining the performance of the calorimeter. The fraction of the energy of the X-ray that is captured by the film without having first been down-converted to thermal phonons in the sapphire is found to depend on both the area and the thickness of the film. The rate at which the energy is transferred between thermal phonons in the sapphire and the electrons in the film is determined by the electron/phonon interaction in the gold. Also, an additional heat capacity was observed to be present in the sapphire, which, for want of a better means of characterization, is ascribed to the tunneling systems. The magnitude of this additional heat capacity and its thermal coupling to the lattice has been studied.     

Deformation of the Surface of a Conducting Liquid under the Action of a Pulse of a Strong Field

It has been shown that the development of the process of the so-called Frenkel–Tonks instability occurring in the case of application of an electric field to a plane surface of a conducting liquid is also determined by the size of the initial distortions of the surface.     

Algorithms for the Optimum Estimation of the Parameters of a Radio Signal in a Measurement Time of Less Than a Period and a Nonmultiple of a Period in Which the Result Is Tied to the Beginning of the Measurement Interval

Optimum estimates of the parameters of a noisy (white noise) sinusoidal radio signal of known frequency are considered, based on an investigation of the likelihood function, when the measurement time is less than a period and a nonmultiple of a period. Estimates are presented for the phase shift and the amplitude in the presence (absence) of a constant component and nonlinear distortions when the result is tied to the beginning of the measurement interval.     

The first-order phase transition as a result of the parametric action of a thermal field

The dynamics of an infinite chain of like particles linked both to each other and to a certain immobile base (a chain of bound oscillators) is considered. The chain of oscillators occurs in a variable and spatially inhomogeneous thermal electromagnetic field inducing significant fluctuations in the shape of potential of the interparticle interaction. It is shown that the field action renders the bound oscillators a parametric system pumped by the thermal field. An increase in the temperature (accompanied by an increase in the spectral density and frequency range of the thermal field) leads to an increase in the relaxation time of oscillators and eventually to their self-excitation. A condition of the corresponding first-order phase transition is obtained.     

Digital holographic profilometry of the inner surface of a pipe using a current-induced wavelength change of a laser diode

Phase-shifting digital holography is applied to the measurement of the surface profile of the inner surface of a pipe for the detection of a hole in its wall. For surface contouring of the inner wall, a two-wavelength method involving an injection-current-induced wavelength change of a laser diode is used. To illuminate and obtain information on the inner surface, a cone-shaped mirror is set inside the pipe and moved along in a longitudinal direction. The distribution of a calculated optical path length in an experimental alignment is used to compensate for the distortion due to the misalignment of the mirror in the pipe. Using the proposed method, two pieces of metal sheet pasted on the inner wall of the pipe and a hole in the wall are detected. This shows that the three-dimensional profile of a metal plate on the inner wall of a pipe can be measured using simple image processing.     

Stress behaviour in the vicinity of a crack approaching a bimaterial interface

The integral approach of Cook and Erdogan was used to obtain the asymptotic behaviour of a crack close to a bimaterial interface. It was found that, in addition to the square-root singularity which dominates the stresses in the vicinity of a conventional crack, there are two additional contributions to stress which should not be neglected. One contribution is due to an “image singularity” and the second is due to an O(1) term which can become very large for small tip to interface distances. It is shown how these features of the stress distribution can be used to advantage in the numerical calculation of stress intensity factors.     

A reexamination of the pressure at the tip of a fluid-filled crack

Previous studies of a fluid-filled crack in an elastic medium have been based on approximate global equations of continuity and motion, and on an assumption of pure radial flow in the crack. Such investigations have led to the existence of singularities in the fluid pressure at the crack tip and hence the conclusion that a crack cannot be completely filled with fluid. It is shown that this conclusion is a result of the approximate nature of the equations and is due to neglect of the transverse velocity component. It is shown too that the exact equations do not give rise to singular terms. Using these exact equations, and taking into account the 2-dimensional nature of the flow, an asymptotic solution near the crack tip is obtained resulting in a finite pressure.     

Modification of residual thermal stress in a metal-matrix composite with the use of a tailored interfacial region

A three-component cylinder model of a unidirectional composite is used to evaluate the importance of an interfacial region in the build-up of residual thermal stress. The components consist of the fibre, an interfacial region and the surrounding matrix. Four mismatch of thermal expansion terms are obtained from this analysis. Each is examined for its contribution to the residual stress state by comparing the coefficients of each mismatch term. The residual stress problem is seen as being influenced by more than the mismatch between the fibre and the matrix. When anisotropic fibre expansion exists in the specific metal-matrix composite, the interfacial region has a significant contribution to residual stress build-up. Further, an interfacial region with an elastic modulus of the order of the elastic modulus of the fibre has a larger effect on the residual stress than when it is of the order of that of the matrix. For an aluminium-matrix composite this large contribution is deleterious and a compliant interfacial region is preferred due to the present considerations.     

Model of the nonlinear operation of a laser with a gaussian mirror

Abstract

In this paper a semi-classical model of the nonlinear operation of a laser is extended to describe a laser with a Gaussian mirror. Modified nonlinear self-consistent equations including transverse and longitudinal field dependence, gain saturation, spatial hole burning and nonlinear dispersion effects are derived. With the help of an energy theorem an approximate solution for steady-state single mode operation is presented, which relates the small signal gain to the output power and the laser system characteristic parameters. The laser output power characteristics are presented for various cavity configurations, especially, revealing an influence of the Gaussian mirror parameter on the power efficiency of the laser.     

Tangential friction on the wall of a container with a spherical charge and fluid motion through the charge

Viscous tangential stress on the interior wall of a container with a spherical charge, that develops in filtration of an incompressible fluid through the charge is investigated. Based on an analysis of an experimental dependence of the dimensionless stress on the Reynolds number, two critical Reynolds numbers are determined: the first number corresponds to the beginning of an abrupt drop in the stress, and the second number, to its reaching a regime that is self-similar in velocity. Comparison with the theory permits interpretation of the effects of pseudoturbulence and turbulence, respectively. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 1, pp. 50–54, January–February, 1997.     

The Influence of a Surface Coating on the High-rate Fragmentation of a Ductile Material

A bifurcation analysis of a layered ductile structural element undergoing homogeneous, high-rate extension is presented. Formation of multiple strain localization sites provides a precursor to ductile fragmentation, and the objective of the analysis is to investigate the effect of an added surface layer on resistance of the structural element to fragmentation. The analysis shows that, in addition to dissipating plastic work, the outer layer can increase the total energy dissipation prior to fragmentation by increasing bifurcation strain. The analysis also shows that the strain hardening exponent of the outer layer plays an important role in increasing the bifurcation strain; higher values of hardening exponent result in higher bifurcation strain. Strength and density of the outer layer play a secondary role in increasing bifurcation strain. Once a material with a high hardening exponent is chosen for the outer material, its strength plays an important role in increasing the total dissipated energy. The analysis also reveals that, for certain combinations of strength and hardening exponent of the outer layer, the sandwich structure can dissipate more energy than a homogeneous core structure of the same total thickness and length. This is so even when the outer layer is weaker than the core. Energy dissipated per unit mass can be significantly improved by choosing a softer outer layer which displays high-strain hardening. Thus, the bifurcation analysis presented here provides a quantitative guideline for material selection in designing layered structures optimized for resistance to fragmentation.     

Analysis of the development of perturbations in a hypersonic boundary layer behind a wavy surface

The stability of a supersonic near-wall flow above a finely corrugated plate in the incident flow inside an aerodynamic tube with a Mach number of 6 has been studied experimentally. We obtained the perturbation growth coefficients that show that a wavy wall stabilizes the flow in the boundary layer with respect to the perturbations of the second mode, but it destabilizes the perturbations of the first mode. A bispectral analysis of perturbations is carried out. It is shown that with decreasing pulsation amplitudes of the second mode, nonlinear processes in the boundary layer behind the wavy surface become strongly suppressed: there is no harmonic resonance of the second mode, and nonlinear processes in the low-frequency region of the spectrum have an interaction amplitude that is an order of magnitude smaller and a much more limited frequency range. Due to the stabilizing effect of a wavy surface on perturbations of the second mode, the onset of a laminar-turbulent transition is generally delayed.     

On the motion of a spherical bubble deforming near a plane wall

Equations of motion are derived for an expanding spherical bubble in potential flow near a plane wall using the Lagrange-Thomson method and an extended Rayleigh dissipation function to account for the drag. This method is shown to yield the same acceleration of the bubble center as that obtained using the Lagally theorem. An extended Rayleigh-Plesset equation is derived to describe deformation in the vicinity of a plane wall, and expressions relating the drag force to the distance from the wall and the bubble growth rate are derived. The solution method for the velocity potential can also be applied to the case of non-spherical deformation.     

用于生物舱细胞培养的小型恒温箱的研制

介绍新研制的一台拟用于卫星搭载、生物舱细胞培养、使用温度范围为-20～80℃的小型中温恒温箱,其外箱尺寸为40cm×40cm×40cm,控温精度为37±0.5℃。为实现小空间的高效率与高精度的恒温效果,采用半导体制冷器件为系统提供冷、热量。此外,还对半导体制冷器件的性能影响因素进行分析,并详述了其安装过程。     

Finite element analysis of the motion of a gas-liquid interface in a forous medium

A numerical method is outlined for determining the movement of a gas-liquid interface in a porous medium following the withdrawal of gas from an underground reservoir. The governing equations for the flow of both gas and the underlying liquid are formulated in terms of the finite element process using the Galerkin approach. The method consists of an iterative technique in which solution of the basic equations is dependent on the location of the interface. Cubic isoparametric elements are employed to allow accurate modelling of the curved boundary and to provide a relatively large number of interface points for a small number of elements. Extensions of the method are indicated in the text.     

On the change in the modulus of elasticity with a decrease in the size of a nanocrystal

A model of nanocrystal in the form of a rectangular parallelepiped with a variable surface shape is used to show that, at high temperatures, modulus of elasticity B decreases with a decrease in size of the nanocrystal N, which is due to the increase in the surface pressure. However, at low temperatures, dependence B(N) is less pronounced and can even rise with a decrease in the nanocrystal size. This is because, at low temperatures, the increase in the surface pressure (which is larger than at high temperatures) leads to an increase in the modulus of elasticity for the entire nanocrystal. The more the nanocrystal shape deviates from the most energetically stable shape, the more pronounced the change in the dependence B(N) is.     

On the mechanism of microcrater formation on the surface of a target under the action of a high-power electron beam

The mechanism of microcrater formation under the action of an intense electron beam is theoretically studied for the clean surface of a flat solid target with small perturbations in the form of protrusions or cavities. It is shown that the formation of microcraters is related to the development of instabilities of the Rayleigh-Taylor and Richtmyer-Meshkov types and has a threshold character with respect to the energy deposited in the target. The laws of microcrater formation in the regimes of irradiation corresponding to typical experimental conditions are considered.     

Effects of a ferromagnetic metal stripe and a Schottky metal stripe on the electron transport in a nanostructure

In this paper, the spin-dependent electron transport in a two-dimensional electron gas (2DEG) modulated by a ferromagnetic (FM) metal stripe and a Schottky metal (SM) stripe is in detail studied. It is found that the position and the width of the SM stripe as well as the incident energy of electron play an important role on the spin polarization. It is also found that the spin polarization is obviously dependent on the electric-barrier height induced by an applied voltage to the SM stripe and such a device can be used as a voltage-tunable electron-spin filter.