半金属摩擦材料与灰铸铁滑动摩擦表面层特性的分析研究

半金属摩擦材料具有摩擦系数稳定、耐磨性好、对环境污染小和对偶件表面损伤小等优点，但其在摩擦热和界面应力等因素作用下，表层会发生弹性变形、塑性变形、元素扩散、组分转移和摩擦化学反应等现象。因此，利用扫描电子显微镜、Ｘ射线能量色散谱和差热－热重分析，对铜纤维增强的半金属摩擦材料与灰铸铁滑动摩擦表面层的特性作了分析研究，考察了表面层特性对摩擦磨损行为的影响。结果表明，在给定的试验条件下，半金属摩擦材料摩擦表面形成了富铁贫铜表面层，其所含有机组分的摩擦热分解深度约为０．３５ｍｍ，含铜量为１５％—２０％（ｗｔ）的材料之磨损性能较好，还能在偶件灰铸铁摩擦表面形成比较均匀连续的铜转移膜，龟裂脱落是偶件磨损的重要机制。研究结果可以作为研制和应用半金属摩擦材料的科学依据。

Analysis of Aquifer Characteristics and Groundwater Quality in Southwest Punjab, India

A study was conducted in eight districts, viz., Faridkot, Moga, Ferozepur, Muktsar, Bathinda, Mansa, Barnala and Sangrur in south-western part of the Punjab, India to characterize aquifer strata by preparing a fence diagram depicting sub-surface strata and distribution of groundwater quality. The sub-surface lithology drilled upto a depth of 60 m reveal the presence of top most layer of impervious strata comprising of clay upto the depth of 2 m to 5 m which impedes the percolation of surface runoff into the soil leading to surface flooding and water logging even in areas having saturated zone beyond the depth of 5 m. Thick pervious strata of 45 m to 50 m thickness is encountered in central and south-sentral part of the study area comprising of Bathinda, Muktsar and Mansa districts which at certain places are separated by one or two thin layers of impervious or semi-pervious strata comprising of clay and sand occasionally associated with ＂kankar＂ of thickness ranging between 2 m to 5 m. The northern, western and eastern parts, however, exhibit three to four layered pervious zones ranging in thickness from 5 m to 25 m separated by thin layers of impervious and semi pervious strata. The groundwater quality in about 6% of the study area in eight districts is fit, 18% is marginal and 76% is unfit for irrigation purpose.

Mechanical Characteristics of Chemically Degraded Surface Layers of Wood

The aim of this research was to find out whether the effect of chemical corrosion changes mechanical characteristics of surface layers of wooden construction elements. Degradation of the surface layers of wood was caused by chemical reactions of the basic substances of wood mass with compounds contained in antifire coatings. Fire retardants containing corrosive substances were often and repeatedly used in the Czech Republic on many wooden building constructions. This process of chemical corrosion is in practise called as ＂surface defibering of wood＂. This contribution presents standard and special experimental methods used for measuring the selected mechanical characteristics （compression strength, tension strength, bending strength, hardness and impact resistance） in the damaged surface layer of wooden construction elements. The material for experimental measuring was a construction element removed from a historical roof （ca 150 years old）. Mechanical characteristics of the surface layer of the defibered element were compared with the values measured in the deeper subsurface layer of non-damaged wood. The results of the experiments proved loss of cohesive strength and decrease of mechanical characteristics of wood only in a thin surface layer.

Influence of advection on the characteristics of turbulence over uneven surface in the oasis and the Gobi Desert

Utilizing experimental data of the atmospheric surface layer in the Gobi Oasis of Jinta in a comparative study, we demonstrate that under the condition of unstable stratification, the normalization variances of temperature in the oasis and Gobi Desert meetφs （z∧）= φθ（Z/∧） =αθ（-Z/ ∧）-1/3 while normalization variances of both humidity and CO2 in the oasis meet φ（Z/∧）= αs （1 - βs z /∧）-1/3 ; the normalization variance of temperature in the oasis is large due to disturbance by advection, whereas variance of CO2 in the Gobi Desert has certain degree of deviation relative to Monin-Obukhov （M-O） scaling, and humidity variance completely deviates from variance M-O scaling. The above result indicates that under the condition of advection, hu-midity variance meets the relation δ2 sm=D2 δ2SA ＋ δ2SB and it is determined by relative magnitude of scalar variance of ad- midity variance meets the relation δsm = D2δsA ＋ δsB vection transport. Our study reveals that, if the scalar variance of humidity or CO2 transported by advection is much larger than local scalar variance, observation value of scalar variance will deviate from M-O scaling; when scalar variance of advection transport is close to or less than local scalar variance, the observation value of scalar variance approximately meets M-O scal- ing.

Relationship of atmospheric boundary layer depth with thermodynamic processes at the land surface in arid regions of China

The atmospheric boundary layer （ABL） is an important physical characteristic of the Earth＇s atmosphere. Compared with the typical ABL, the ABL in arid regions has distinct features and is formed by particular mechanisms. In this paper, the depth of the diurnal and nocturnal ABLs and their related thermodynamic features of land surface processes, including net radiation, the ground-air temperature difference and sensible heat flux, under typical summer and winter conditions are discussed on the basis of comprehensive observations of the ABL and thermodynamic processes at the land surface carried out in the extreme arid zone of Dunhuang. The relationships of the ABL depth in the development and maintenance stages with these thermodynamic features are also investigated. The results show that the depth of the ABL is closely correlated with the thermodynamic features in both development and maintenance stages and more energy is consumed in the development stage. Further analysis indicates that wind velocity also affects ABL development, especially the development of a stable boundary layer in winter. Taken together, the analysis results indicate that extremely strong thermodynamic processes at the land surface are the main driving factor for the formation of a deep ABL in an arid region.