边坡坡度对路堤风吹雪影响研究

路堤边坡坡度是影响风吹雪区域路堤积雪的重要因素,利用现场模型试验以及流场数值模拟的方法,研究边坡坡度对路堤积雪影响规律,分析积雪形成机理。结果表明:路堤周围积雪范围与流场风速减弱区域存在较好的对应关系,但并非定量对应,用流场中风速减弱区域简单地定量判断积雪范围的方法误差较大;迎风边坡坡度的改变对路堤周围积雪分布影响较大,较缓的迎风边坡坡度将有效地减小路堤周围积雪量和积雪范围,路面更不易形成积雪,可以减小风雪流对路堤工程的危害;背风边坡坡度的改变对路堤周围积雪影响较小,路堤设计时可作为次要因素考虑;根据试验和模拟结果得出路面不易积雪的临界边坡坡度在40°和45°之间,保守起见,建议工程应用中取40°为路面不易积雪的临界边坡坡度。     

Comparison of snow drifting measurements at an alpine ridge crest

Experiments at Weissfluhjoch, Davos, Switzerland, compared mass flux measured by rocket-shaped snowdrift gages (modified Mellor traps), with gages made of porous filter fabric, and with several electronic systems. A new method of electronic analysis gave results similar to the mass flux measured by mechanical traps. The experiments also reexamined the vertical profile of drift flux in the vicinity of the ridge crest, confirming the flux maximum at about 1 m height above the ridge crest, and adding details near the surface. Profiles measured at a secondary change in the windward ridge face, within a few meters of the crest, showed only a slight maximum, supporting the view that the drift flux maximum develops near the crest.     

A wind tunnel study of the aerodynamic roughness associated with drifting snow

Characteristics of wind profiles observed with drifting snow in a cold wind tunnel are similar to those observed in the field. The aerodynamic roughness increases with wind velocity during drifting.Equations are developed to describe the relationship among various characteristics of the trajectories of saltating snow particles, as measured from photographs and cinefilm. The momentum flux by saltating particles is estimated from measurements of mass flux, and it is shown that the apparent change in surface roughness is caused by the particles in the lowest layers of saltation. The observed effect of surface hardness on the roughness change can be explained by the proposed equation for momentum flux.     

Some features of formation of the structural strength of ceramic materials

On the basis of preliminary investigations of the characteristics of the crack-propagation resistance of various types of ceramic and cermet materials, we give a general evaluation of their potentialities in the context of the influence of the structural-metallurgical factor and the micromechanisms of fracture on the serviceability of the materials. We propose to evaluate the mechanical efficiency of ceramic materials by comparing their diagrams of structural strength at room and service temperatures. We found certain advantages of cermets in ensuring crack resistance under short- and long-term loading. We propose a classification of dominant and secondary micromechanisms of stress relaxation that manifest themselves in the process of crack growth in ceramics and cermets. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 2, pp. 7–17, March–April, 1998.     

The shear strength index of alpine snow

A shear frame (area 0.025 m²) was used to measure an index of the shear strength of alpine snow. Shear indices were stratified according to snow crystal morphology, and then were correlated with measurements of snow density, temperature, and crystal size. The correlations of shear index with density were significant for all crystal morphologies except for the melt-refreeze morphology. Shear indices correlated erratically with snow temperatures and crystal size.Shear strength was also measured with a large rotary vane (0.5 m diameter). A comparison of rotary vane indices, shear frame indices, and slab avalanche measurements suggests that shear indices decrease with increasing sample size.     

Dry deposition and desorption of toxic gases to and from snow surfaces

A model describing toxic gas deposition to and desorption from a snow surface is presented. The model is based on the assumption that the deposition is caused by an adsorption of the toxic gas to small amounts of liquid water, which exist in the snow at temperatures equal to or below 0°C. It includes molecular diffusion in the snow, partition between gas and solution by use of Henry's law, drainage flow in melting snow and decomposition of agent. The interface to the atmosphere is defined by the flux to and from the surface with help of the aerodynamic resistance and the resistance in the viscous sub-layer. Deposition velocities to snow for some air pollutants are reviewed. The model is compared with sarin experiments in a test chamber, which verifies two main features of the model—primarily decreasing deposition with time and decreasing deposition with decreasing temperature. The model shows that the accumulation of sarin in the top layer of snow could be high enough to give lethal or severe injuries to people if the snow was used as drinking water. However, there is a tendency of the model to give too low deposition (too high surface resistance). Possible reasons for this observation are discussed.     

Some features of magnetron sputtering

In a low pressure sputtering system of the magnetron type for depositing thin solid films, two different discharge modes occur: a positive space-charge-dominated mode and a negative space-charge-dominated mode. The positive space-charge-dominated mode predominates in a weak magnetic field of some few hundred gauss and is widely used for sputtering, although the current density is non-uniform at the cathode surface. The negative space-charge-dominated mode predominates in a strong magnetic field of more than several hundred gauss and is also used for sputtering since the mode shows uniform current distribution at the cathode surface.In the magnetron sputtering system the working pressure is so low that the scattering of sputtered atoms by gas molecules can be neglected. Thus energetic sputtered atoms impinge on the substrates during film growth. This causes some phenomena which are rarely observed in a conventional diode sputtering system, e.g. an abnormal surface texture and an unusual crystalline structure are found in the resultant sputtered films. There is evidence that thin films of compounds normally only formed at high temperature can be synthesized at lower substrate temperatures.     

Some features of the thermal stratification of liquids during natural convection in cylindrical cavities with annular ribs

The effect of annular ribs on the temperature of the free surface of a liquid during natural convection in a heated vertical cylindrical cavity has been investigated. A method is proposed for calculating the limiting value of this temperature.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 5, pp. 759–763, November, 1988.     

自然材料微结构的几种特征

自然材料微结构是仿生机械结构设计的灵感来源.利用激光扫描共聚焦显微镜分析了鸭子下层绒毛、水稻叶毛、松针维管束鞘、水稻侧根和松针的微结构;用扫描电镜分析了黄瓜外表皮、仙人掌表皮组织、水稻叶脉、蚊子复眼、仙人掌组织、鹌鹑蛋蛋壳、水稻根和贝壳的微结构．结合前人对其它自然材料微结构的研究,总结了自然材料的结构特征,典型微结构特征有分形结构、分级结构、多尺度结构、多孔结构、梯度结构和整合结构;并且讨论了典型生物微结构原型在仿生结构设计方面的应用．分析了自然材料微结构特征的一般性特征,即对称性和自相似性．     

Specific features of the strength of carbon whiskers

The strength of filamentary crystals (whiskers) of graphitelike materials, which are characterized by a layered structure and significantly anisotropic mechanical behavior, is briefly analyzed. Model thin rods (with micro-or nanoscale dimensions) of such materials exhibit certain specific features in the statistical tensile strength behavior, which are related to competition between the normal separation and mutual sliding of the adjacent graphene layers.     

Disciplinary variables that affect the shape of Bradford's bibliograph

The influence of various factors upon the shape of Bradford's bibliograph was assessed through an examination of 16 bibliographies, of which ten were comprehensive. We obtained a curvature score for each bibliograph plotted in a standard landscape format so as to permit comparison; we found that the amount of concave up curvature (convexity): (a) is negatively correlated with a bibliography's overall publication density; (b) depends on the status (technical vs. nontechnical) of the disciplinary source of a bibliography, with technical disciplines showing less convexity; and (c) is complexly affected by the historical changes in the discipline. Findings are discussed in the context of questions about the graphical formulation of Bradford's Law.     

Some features of the critical point

A characteristic relation is derived for the critical point. Some features of the critical point are brought out by an examination of the entire condensate-state region of a substance.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 4, pp. 732–734, April, 1972.     

Some specific features of crack propagation

A theoretical study was made of brittle crack propagation under the influence of oscillations excited in a solid by the fracture process itself and propagated faster than the crack. It was shown that oscillations of a specific kind (transverse guiding waves) are excited during the process of fracture.     

Some features of the magnetorheological effect

The Theological properties of magnetorheological suspensions (MRS) are investigated in a wide concentration range of particles of the disperse ferromagnetic phase in the presence of a magnetic field. It is shown that, along with an increase in the concentration of ferromagnetic particles, the range of control of the viscous stress increment in an MRS can be broadened by changing the size and shape of the ferromagnetic particles, introducing nonmagnetic particles into the dispersion medium as well as by heating the medium to the Curie temperature. Academic Scientific Complex “A. V. Luikov Heat and Mass Transfer of the Academy of Sciences of Belarus,” Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 5, pp. 771–775, September-October, 1997.