Oberbeck convection through vertical porous stratum

Natural convection through a vertical porous stratum is investigated both analytically and numerically. Analytical solutions are obtained using a perturbation method valid for small values of buoyancy parameterN and the numerical solutions are obtained using Runge-Kutta-Gill method. It is shown that analytical solutions are valid forN < 1 and several features of the effect of large values ofN are reported. The combined effects of increase in the values of temperature difference between the plates and the permeability parameter on velocity, temperature, mass flow rate and the rate of heat transfer are reported. It is shown that higher temperature difference is required to achieve the mass flow rate in a porous medium equivalent to that of viscous flow.     

Interaction of Antiseptic Compounds with Intercellular Lipids of Stratum Corneum

The interaction between three kinds of antiseptic compounds and components of intercellular lipids in the stratum corneum was characterized in terms of thermodynamics at pH 7.5 and 25°C, and the different mechanisms used to penetrate the stratum corneum were clarified. Anionic surfactants such as benzalkonium chloride and benzethonium chloride mainly bound to cholesterol (CH) and cholesterol sulfate with high affinity (10⁵–10⁶ M⁻¹) to extract endogenous CH from the stratum corneum and penetrated through the intercellular route. Chlorhexidine gluconate also bound to CH and accumulated in the stratum corneum without removing endogenous CH. An amphoteric surfactant of dodecyldiaminoethylglycine hydrochloride seemed to be incorporated into the lipid bilayer and bound to ceramide with its polar end close to the lipid polar heads by hydrophobic interaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Visualisation of liposomes prepared from skin and stratum corneum lipids by transmission electron microscopy

Transmission electron microscopy was used to visualize the liposomes prepared from total lipids extracted from mouse, human and porcine skin and stratum corneum. The total lipid composition was monitored by high precision thin layer chromatography coupled with a flame identification detector (HPTLC/FID, Iatroscan) and the fatty acid content of the samples was monitored by gas chromatography. The liposomes were prepared by the thin lipid film hydration method and they were visualized by transmission electron microscopy after negative staining using uranyl acetate. The structure of the vesicular structures present in the formulations largely depended on the lipid composition of the samples. The liposomes with high ceramide content were drop like vesicles with sharp tips, whereas the presence of excessive phospholipid content lead to bag like liposomes with two hemispheres divided by a membrane. Finally, the tendency of triacylglycerides to accumulate in the lipophylic region of the lipid bilayer, forms membranes with uneven thickness, resulting in structures with undulated membranes. A degree of fusion depending on the phospholipid content was also observed.     

The onset of penetrative double-diffusive convection

The onset of double-diffusive convection in a horizontal fluid layer is studied. The density is assumed to depend quadratically on the temperature and linearly on the solute concentration. Under the Boussinesq approximation, the linear stability of the conduction state is investigated with respect to the oscillatory and steady convection modes. For steady onset, the critical thermal Rayleigh number is found to be a double-valued function of the solutal Rayleigh number as long as the relative maximum of the density profile exists within the fluid layer. Driving mechanisms of the steady convections are discussed.     

Comparison of void fraction correlations for different flow patterns in horizontal and upward inclined pipes

A comparison of the performance of 68 void fraction correlations based on unbiased data set (2845 data points) covering wide range of parameters than previous assessments was made. A comprehensive literature search was undertaken for the available void fraction correlations and experimental void fraction data. After systematically refining the data, the performance of the correlations in correctly predicting the diverse data sets was evaluated. Comparisons between the correlations were made and appropriate recommendations drawn. The analysis showed that most of the correlations developed are very restricted in terms of handling a wide variety of data sets. Based on the observations made, an improved void fraction correlation which could acceptably handle all data sets regardless of flow patterns and inclination angles was suggested. It was shown that this correlation has the best predictive capability than all the correlations considered in this study.     

A general heat transfer correlation for non-boiling gas–liquid flow with different flow patterns in horizontal pipes

A general heat transfer correlation for non-boiling gas–liquid flow with different flow patterns in horizontal pipes is proposed. In order to overcome the effect of flow pattern on heat transfer, a flow pattern factor (effective wetted-perimeter) is developed and introduced into our proposed correlation. To verify the correlation, local heat transfer coefficients and flow parameters were measured for air–water flow in a pipe in the horizontal position with different flow patterns. The test section was a 27.9 mm ID stainless steel pipe with a length to diameter ratio of 100. A total of 114 data points were taken by carefully coordinating the liquid and gas superficial Reynolds number combinations. The heat transfer data were measured under a uniform wall heat flux boundary condition ranging from about 3000 W/m² to 10,600 W/m². The superficial Reynolds numbers ranged from about 820 to 26,000 for water and from about 560 to 48,000 for air. These experimental data including different flow patterns were successfully correlated by the proposed general two-phase heat transfer correlation with an overall mean deviation of 5.5%, a standard deviation of 11.7%, and a deviation range of −18.3% to 37.0%. Ninety three percent (93%) of the data were predicted within ±20% deviation.     

潞安矿区综放与分层开采岩层移动的相似材料模拟试验研究

本文根据相似理论,对潞安矿区综放与分层开采岩层与地表移动规律进行了相似材料模拟试验研究,获得了岩层与地表移动参数,对指导潞安矿区减小采动损害及保护煤柱留设具有实际应用价值。     

万州近水平地层区堆积层滑坡成因与变形破坏特征

近水平地层区堆积层滑坡作为一类典型的滑坡,有其特殊的成因与变形破坏特征。文章在研究万州近水平地层区堆积层滑坡的基础上,详细分析了其物质来源、结构成因、形成模式以及变形破坏特征。通过总结万州堆积层滑坡的滑体和滑床特征,得出了近水平地区堆积层滑坡的物质来源和结构成因为:崩塌堆积为主,冲、洪积为辅;形成模式为:后部陡壁形成,滑床形成,滑体底部物质形成,滑体土石混合体形成,滑体表层物质形成,滑动解体等6个阶段。变形破坏特征为:滑动多沿堆积层和基岩接触面滑动,同时也会沿软弱夹层发生滑动;滑体存在多层剪切带,并在不同位置的剪切带其变形速率和累计变形量差别较大,滑体存在着差异变形,对此文章结合实例进行了分析。     

循环荷载下土石混合体力学特性野外试验研究

土石混合体是一种物理、力学性质非常复杂的不连续介质。以云南某高速公路土石混合体边坡为例,分别对选取的3个试验点进行了单调加载、循环加载一次及多次循环加载试验,获取了其相应的剪切位移-剪切应力关系曲线,并对其曲线特征进行分析研究。通过对试样三维滑动面的形态分析,指出由于土石混合体三维滑动面的不规则性,利用传统的二维计算方法难以得到较为准确的强度参数。基于三维极限平衡理论,提出了土石混合体水平推剪试样强度参数的三维数据计算方法。并利用该方法得到了研究区土石混合体的相应的强度参数及残余强度参数。     

比奥固结有限元中参数正交敏感性分析

用邓肯-张模型求解比奥平面固结有限元涉及到的参数较多,本文通过正交试验研究参数共同随机变化对软土地基固结沉降的影响,发现其中的k、c、G、φ和F对整个固结沉降过程的影响是高度显著的; Pc在固结的初期影响是显著的;在其他参数变异较大时,Rf对固结沉降的影响相对较小,常渗透系数Kz在固结初期影响显著。本文结果对模型参数的取值、反演、随机分析以及固结沉降的估计具有参考价值。