Distribution of sand dunes and sand shifts along the southern fringe of the Mu Us Desert since the Ming Dynasty

This article takes the two segments of the Ming Great Walls, Dabian and Erbian, and their associated barracks and forts as geographical references. Based on a detailed scrutiny of historical records of the Ming and Qing dynasties, and on field surveys, the southern boundaries of the sand dunes and sand shifts of the Mu Us Desert in the Ming and Qing dynasties are carefully reconstructed. A comparison of the southern boundaries of the sand dunes and sand shifts of the Mu Us Desert in Ming and Qing with the modern boundary revealed in remote sensing imagery clearly shows that the southern boundary of dunes and shifts in the Mu us Desert has expanded only in a few areas and on a small scale. In the area to the south of Changle Fort, along the direction of annually prevailing winds, sand drifts have penetrated through the Jialu River valley into the loess region and have formed a sand strip of 32 km long and 3 km wide. To the east of Qingping Fort, sand drifts penetrated toward the eastern loess region through the Luhe River valley and have formed another sand strip of 8 km long and 2 km wide. Generally speaking, though the intensity of human activity has been increasing in this area since the Ming Dynasty, the Mu Us Desert has not significantly expanded toward the southeast or southwest. The sand-loess boundary in the southern fringe of the Mu Us Desert has been almost unchanged since the Ming Dynasty.     

A novel method to improve the performance of heatexchanger——Temperaturefields coordination of fluids

The methods to enhance the heat transfer in heat exchanger may be classified into two levels: one is to improve the heat transfer coefficient; the other is to upgrade the whole arrangement of the heat exchangers. For the second level, the performance of heat exchanger can be upgraded by increasing the coordination degree between the temperature fields of cold and hot fluids. When the temperature distributions are similar to each other, the temperature difference field (TDF) is more uniform, which means that the temperature fields are more coordinated with each other. For the cross-flow heat exchanger, rearrangement of the heat exchange surface area should improve the heat transfer effectiveness, which is even equal to that of the counter-flow heat exchanger when the surface area is reassigned optimally. For the multi-stream heat exchanger, the thermal performance is also dependent on the uniformity of the TDF, and the parallel-flow arrangement may achieve higher heat exchange effectiveness than the counter-flow arrangement, which indicates that the performance of heat exchanger depends on the coordination degree of temperature fields instead of the flow arrangement.     

高校图书馆数据库建设浅议

文章阐述了高校图书馆建立数据库的意义及优势,数据库建设中的标准化问题以及在建库中 需解决的问题和应采取的措施。     

几种植物对生活污水的处理效果研究

选取蛇泡草，红辣蓼，鹅不食草和田边菊作为人工湿地的栽培物，并对它们处理污水的效果进行研究，结果表明，不同的植物对生活污水的处理效果有所不同，红辣蓼对NH^ 4-N的去除率最高，24－48h之间的平均值为24．5％，蛇泡草对TP的去除率最高，24－48h之间的平均值为17．0％，所有受试植物对污水的处理效果均在40－48h之间达到顶峰。     

试论声乐教学中的情感问题

声乐教育中的情感问题始终是歌唱艺术中的最重要问题。要真正达到声情并茂,只有用心去体会,用多层次的“情”与一定的审美技能相互结合,才能达到完美境界。     

关于强纯整半群

本文在研究匀称带及其对应半格的匀称性中，提出了强纯整半群的概念，证明了强纯整半群不必是逆半群，因此这是比逆半群宽的一类纯整半群。文中又定义了基本强纯整半群，得到了基本强纯整半群同构于Hall半群WB的满幂纯整半群，最后证明了若带B匀称，则B所对应的半格也是匀称的。     

微波辐射条件下4-烷氧基苯乙酸的合成

作者采用常压微波辐射的方法，以4－烷氧基苯乙酮为原料，合成了一系列4－烷氧基苯乙酸。该法反应速度快，收率高，设备简单，对于徽皮在有机合成中的应用以及苯乙酮类化合物的Willgerodt反应的研究均具有一定价值。     

基于订单生产的多品种装配流水线的平衡

就订单生产条件下的多品种装配流水生产线的平衡问题展开讨论 ,进而建立以优化人力成本为目标多品种装配流水线的人力成本模型 ,最后通过运用混合遗传算法进行流水线的平衡 ,并根据实验数据进行验证     

γMn基合金反铁磁畸变与高阻尼孪晶的形成

根据反铁磁序引起的点阵畸变与磁长程序参量之间的关系，计算了γMn-Cu合金顺磁→反铁磁转变引起的点阵畸变，并将计算值与实验数据进行了比较，通过γMn-Fe基合金高阻尼特性测定，验证了反铁磁序与孪晶高阻尼的关系在其他锰基合金中同样存在的推测，讨论了γMn基合金高阻尼行为的物理本质，结果表明，γMn-Cu和γMn-Fe合金顺磁→反铁磁转变引起的四方畸变均可触发微孪晶的形成，且在一定条件下可能诱发马氏体相变。     

汞在北京大气中细颗粒物上的分布

为了解汞在北京大气中细颗粒上的分布 ,用 AN- 2 0 0型安德森冲击式分级采样器于 1 997年 1 1月 3 0日～ 1 998年 2月 8日 (采暖期 ) ,在北京 3个采样点同步采取不同粒径 (4.7～ 1 0 ,1 .1～4.7和 0 .43～ 1 .1 μm)的颗粒物 ,测定了其上汞的质量浓度 .影响大气中颗粒态汞的因素较多 ,释放源是其中之一 .3个采样点中最大颗粒物态汞浓度并未在工业区出现 ,表明北京市大气中颗粒态汞的环境行为复杂 ,可能具有广域扩散性 .3个采样点颗粒物态总汞质量分数为 (0 .98～ 2 .90 )× 1 0 -6,表明北京市大气中存在一定的汞污染