On the absorption of a surface acoustic wave in a bulk superconductor in the presence of a supercurrent

Surface acoustic wave absorption in bulk superconductors in the current state at low temperatures is discussed. In this situation a group of quasiparticles are localized near the surface due to the inhomogeneous supercurrent distribution; the rest of the quasiparticles have infinite trajectories. It is shown that it is possible for the main contribution to the acoustic wave absorption to be due to this group, depending on the sonic frequency. If this frequency is large, the localized quasiparticles are the most important in the absorption. In this case the absorption coefficient can be larger than in the absence of the supercurrent. In addition, there is a dependence of the absorption on the angle between the directions of the acoustic wave propagation and of the supercurrent. In the case of lower acoustic frequency, the quasiparticles with infinite trajectories dominate in the absorption. In this situation the absorption coefficient is smaller than in the zero-current state, because of the Andreev reflection of a fraction of these quasiparticles. It is shown that by studying the absorption dependence on the direction and on the absolute value of the current it is possible to obtain information on the law of current decrease near the surface of the sample, on the angular dependence of the deformational potential tensor, etc.     

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.     

Development of a flow field structure in the vicinity of a circular cylinder in the presence of a laminar-turbulent transition

The Reynolds equations and the two-parameter differentialq-Ω model of turbulence are used to investigate a flow past a circular cylinder with an isothermal surface (temperature factorT _w0 = 0.5) at the Mach numberM _∞ = 5 in the range of Reynolds numbers Re = 10⁴-10⁸. It is demonstrated that the turbulization of flow leads to a shift of the separation point downstream, a reduction and stabilization of the separation zone length, a decrease in the maximum velocity in the separation zone, and an increase in the heat flux at the rear stagnation point compared with its value at the forward stagnation point.     

On a change in the sign of the entropy of vacancy formation in a crystal

The entropy of vacancy formation (s _v) in a crystal increases with the temperature and, at a certain critical temperature, changes its sign from negative to positive. Physical reasons for this change are considered and a condition under which s _v is positive is established. During the melting of metals, s _v is positive and the appearance of vacancies leads to disordering of the crystal, rendering it less stable and facilitating the formation of new vacancies.     

Stress intensity in the vicinity of a surface flaw in the linear part of a pipeline

Real sharp-edted surface and subsurface flaws detected in a gas pipeline body are modeled by surface semi-elliptical mathematical cracks (cuts) in a closed cylindrical shell. A relationship is proposed that relates the geometrical dimensions of the flaws to the crack aspect ratio. Based on the line spring model, the problem of stress state and boundary equilibrium conditions of a closed cylindrical shell with a surface semi-elliptical crack is reduced to a system of singular integral equations. An algorithm was developed for computational solution of the problem, and numerical analysis was made for the dependence of stress intensity factors on loading conditions and geometrical parameters of shell and crack. For a shell subjected to internal pressure and weakened by a surface longitudinal semi-elliptical crack, a closed approximation formula is proposed that interrelates pressure level, shell/crack dimensions, and material mechanical properties in boundary equilibrium conditions. The maximal error value is indicated for the results obtained using this formula. Lvov Polytechnic State University, Lvov, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 38–47, July–August, 1999.     

Spatial-Temporal Distributions of the Pressure in a Bed with a Well in Different Regimes of Production of a Fluid from the Well

Journal of Engineering Physics and Thermophysics - The problem on the nonstationary pressure field formed in a filter bed with a well in the regimes of start of a pump used in the production of a...     

Pseudosound Pressure Oscillations Caused By the Interaction of a Fluid Flow with the Obstacle in the Form of a Circular Cylinder in a Pipe

Journal of Engineering Physics and Thermophysics - A simulation of the vibroacoustic processes proceeding in a long pipe with an obstacle in the form of a circular cylinder, in which a fluid flows,...     

On the role of high-energy electrons in the formation of a plasma-beam discharge structure in a diode with a slit cathode

The spatial structure of visible emission from plasma of a transverse nanosecond pulsed electric discharge in a gas-filled diode with a hollow (slit) cathode has been experimentally studied. A relation is established between the regime of electron energy relaxation and the plasma-beam discharge structure formation. High values of the electron emission coefficient are observed in the experiment, which cannot be explained using the notion of electron emission from a cathode bombarded by fast heavy particles.     

聚醚砜四元制膜液体系的相图计算

以Ｆｌｏｒｙ－Ｈｕｇｇｉｎｓ理论为基础，对ＰＥＳ－ＰＧ－ＮＭＰ＿Ｈ２Ｏ＿）聚醚砜丙二醇－Ｎ－甲基－２－哟咯烷酮水）四元制液体系的相图进行了计算，利用三元相图考察Ｈ２Ｏ和ＰＧ对液－液相分离的影响，在三元的理论的基础上提出了低分子量添加剂的卤元改性Ｆｌｏｒｙ－Ｈｕｇｇｉｎｓ理论，并提出了一种获得四元相图的方法，利用四元相图能较争地描述四元体系，利用改性的四元理论，能了地理解该种体系的液－液相分离行为。     

Toward the problem of the resonances of a bubble radially pulsating in a liquid

Gas bubbles performing radial pulsations under the action of an acoustic field are analyzed. It is shown in detail that gas bubbles of constant mass may have only one resonance frequency.     

Variation of the contact angle in the quasistatic growth of a vapor bubble on a horizontal surface in a boiling liquid

The variation of the contact angle at the solid-liquid-vapor phase interface during the quasistatic growth of a bubble in the boiling of water is studied experimentally.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 4, pp. 566–570, April, 1986.     

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.     

Entropy losses in the flow of a dust-laden gas suspension in a nozzle

The unidimensional steady-state flow of a gas containing a system of solid particles in a nozzle is considered for the case in which the particles are characterized by a constant velocity lag; expressions are derived for the entropy losses in efficiency due to the friction between the gas and the particles and the irreversibility of interphase heat transfer.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 5, pp. 828–831, May, 1970.     

Plastic deformation in the vicinity of a crack and the criteria of fracture a review

Conclusions The existing solutions of problems concerning the determination of stresses and strains in bodies with cracks on the basis of the classical theory of plasticity are approximate and, in most cases, numerical. Solutions obtained by different authors for the same problem commonly differ among themselves and do not agree entirely with observations. In this connection it is necessary to work out optimal methods (programs) for solving such problems with more complete consideration of the actual conditions, in particular the three-dimensional character of the stress-strain state. It is also necessary to develop further the theoretical basis for setting up elastic-plastic problems, using current advancements in the physics of deformation and fracture of solids, because classical theories are not capable of describing the discrete mechanism of the phenomena. In this connection we may point to a method of solving elastic-plastic problems by modeling thin slip bands by surfaces of displacement discontinuity.Experimental investigations are very important, but at the present time they are conducted in sporadic and unsystematic fashion. There are as yet no full explanations of the causes leading to localized or diffuse plastic zones. Data on small plastic zones and their configuration in the thickness of the material are inadequate. We need direct investigations of plastic zones at cracks and of the formation of prefracture zones within them.The final and most important purpose of such investigations is the development of criteria of fracture in fairly plastic bodies with cracks. In this respect criteria of critical crack opening are distinguished. The actual ways of using these in practice, however, are not clearly defined, particularly in constructional design. An exception is found in those cases where the _k model is suitable, although the limits of its application have not yet been established. In this connection, further investigation is necessary, both of the _k model and of the creation of new models that take into account the variety of actual cases. Special attention should be given to precritical crack growth in prolonged loading (static or cyclic) and to the effect of surface-active media.Translated from Problemy Prochnosti, No. 2, pp. 3–18, February, 1973.     

Stratification of a cryogenic liquid in a reservoir in the case of circulation cooling

Based on the nature of changes over time in the vertical profile of temperatures within the volume of a reservoir, we have determined the magnitude of the circulation flow and the coefficient of convection in the circulation cooling of liquid hydrogen.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 60, No. 3, pp. 425–428, March, 1991.     

Experimental investigation of the dynamics of the phase transition boundary in the motion of a heated non-Newtonian fluid in a channel

The process of growth of the boundary crystallized phase in the motion of a heated non-Newtonian fluid in a channel with a cold wall has been studied experimentally. As the fluid, polypropylene with pseudoplastic properties was used. Experimental curves of the growth of the wall crystallized phase as a function of time were obtained for different values of the initial fluid melt temperature. The experimental value of the Nusselt number at the solid-liquid interface has been computed.     

Study of the drag of a throttle in the film boiling of a cryogenic liquid flowing in a horizontal pipe

A one-dimensional model is used to calculate the parameters of a two-phase flow and generalize test data on discharge coefficients.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.43, No.2, pp.186–190, August, 1982.     

On the influence of a martensitic transformation in the substrate on a hard coating

Cobalt was coated with TiC in a chemical vapour deposition process. The strain arising from the f.c.c.→h.c.p. transformation in cobalt imposes stresses in the coating. These stresses cause cracks in the coating perpendicular to the substrate-coating interface.The perpendicular cracks have a stress-concentrating effect on microvoids in the interface. A fracture mechanical estimation shows that the adherence of the coating under shear stress loading is markedly influenced by the cracks caused by the martensitic transformation.     

Evolution of linear waves in a liquid in the presence of a curtain of bubbles

We investigate certain features of the evolution of waves in an acoustically compressible liquid in passage through a curtain of bubbles between two parallel planes. We consider the problem of reflection from a plane solid wall separated from the liquid by a curtain of bubbles. Investigations showed that in relation to the duration of the pulse it is possible to select a curtain with corresponding parameters to moderate the effect of the wave on the wall. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 6, pp. 987–992, November–December, 1998.