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The scattering behaviors of nitrogen molecules reflected at a platinum surface are studied by the molecular dynamics method for the gas-surface interaction. The platinum surface is assumed to physically adsorb xenon molecules. Distributions of molecular velocities after reflection are obtained for the impinging molecules with specified velocities within a small range. The scattering distribution shows a bimodal behavior consisting of diffuse reflection and a distribution shifting to the velocity distribution of the impinging molecules. Comparison between the present scattering distribution and the Cercignani-Lampis-Lord scattering kernel shows large differences. A simple scattering kernel using a bimodal distribution is proposed assuming mutual independence of distributions in each velocity component and is compared favorably to the present scattering distribution. In addition, the scattering kernel of the rotational energy of the molecule is discussed. [ABSTRACT FROM AUTHOR]

The Couette flow and a thermal problem of a rarefied nitrogen gas between two platinum walls are considered to investigate the characteristics of the reflected gas molecule at a solid surface. The analysis is based on the molecular dynamics (MD) method for the gas-wall interaction together with the direct simulation Monte-Carlo (DSMC) method for the motion of gas molecules. The accommodation coefficients of momentum, translational, and rotational energies of the molecule are obtained. The velocity and rotational energy distributions of the molecule at the wall surface are also obtained. It is found that the Maxwell-type distribution function consisting of specular and diffuse reflections well describes the distribution function of the reflected molecules if the accommodation coefficient involved is chosen properly. It is also found that the flow and temperature fields subject to the Maxwell-type reflection conditions decomposed into each direction of the space coordinates result in good agreements with those of the DSMC combined with the MD calculation. [ABSTRACT FROM AUTHOR]

Mesenchymal tumors of the appendix are very rare. Mesenteric fibromatosis is the most common diagnosis in the case of isolated proliferative fibroblastic lesion found in this region. However, the differential diagnosis between fibromatosis and well-differentiated fibrosarcoma (Grade I) can be difficult in some borderline cases. A rare case of proliferative fibroblastic lesion involving the appendix and mesoappendix is presented, and its origin, diagnosis and differential diagnosis are discussed. [ABSTRACT FROM AUTHOR]

A theoretical study is made of thermophoresis of a solid sphere in a rarefied gas in which a uniform temperature gradient and a uniform velocity at infinity exist. The analysis is carried out on the basis of the linearized Bhatnager-Gross-Krook (BGK) equation, from which simultaneous integral equations for the density, flow velocity, and temperature are derived. These equations are solved numerically over a wide range of Knudsen numbers covering the area from the slip flow to the nearly free molecular flow. A formula for the variation of the thermophoretic force acting on the sphere versus the Knudsen number is obtained for any value of thermal conductivity of the sphere when there is no imposed flow at infinity. The thermophoretic velocity of a suspended sphere in a gas is also calculated. The flow patterns as well as the distributions of temperature are shown. [ABSTRACT FROM AUTHOR]

The flow of a rarefied gas past a circular cylinder at low Mach numbers is studied on the basis of the linearized Bhatnager–Gross–Krook model equation. The flow field is divided into two regions: the kinetic region adjacent to the cylinder and the near continuum region outside it. The Oseen–Stokes equation is treated in the near continuum region. In the kinetic region, the simultaneous integral equations for the flow velocity, density, and temperature are derived from the model equation. These equations are solved numerically by matching with the Oseen–Stokes solution. The distributions of the flow velocity are obtained for a wide range of the Knudsen numbers. The drag on the cylinder is also calculated and is favorably compared with the previous formulas valid for small and large Knudsen numbers. [ABSTRACT FROM AUTHOR]

The objective of this study was to clarify the etiology of acute cholecystitis and the role of bacteria in the bile in this condition. We evaluated 52 patients with acute cholecystitis; 46 had cholesterol stones and 6 had no claculi. In the presence of cystic duct obstruction, circulatory disturbance occurs gradually, but circulatory disturbance alone cannot cause severe inflammation unless a bacterial infection is present. If there is no obstruction, rapid circulatory disturbance produces necrotic changes of the gallbladder wall, which are implicated in a fulminant course. In both instances, bacterial infection may play an important role in fulminant cholecystitis. Bacteria implicated in acute cholecystitis are usually present in the bile before the onset of this disease. [ABSTRACT FROM AUTHOR]