Comparison of Skidding Performance of Small Track-type Experimental Prototype Skidder and J-50 Skidding Tractor

In this paper, field experimental comparison is made between a small track-type experimental prototype skidder and a J-50 skidding tractor. Experimental data, including skidding productivity, soil compaction on skidding trails, and damage rate of the residual trees, are analyzed. The results indicate that with the condition of scattered skidding area and low skidding volume per cycle, small track-type experimental prototype skidder has advantage on working and a higher skidding productivity. It makes lower soil compaction to the skidding trails in the depth of 0-5 cm, 5-10 cm, and 10-15 cm. Under the same work conditions, the damage rate of the residual trees made by small track-type experimental prototype skidder is only 1/5 of those made by J-50 type skidding tractor. The damage rate is reduced by 80%.     

Stochastic structural model of rock and soil aggregates by continuum-based discrete element method

Ancient slope[1], debris-flow deposit[2] and rock-filling dam[3] are usually made of rock and soil aggregates (RSA). The RSA is a typical inhomogeneous and discontinuous medium, and its main characteristics include: (i) loose piling up by blocks or particles, (ii) mixing of different blocks with a range of shapes and sizes, (iii) stochastic distribu- tion of blocks in space, (4) fillings often in between blocks. The mechanical properties of these rock and soil aggregates are commonly obtaine…     

Analysis on the Logarithmic Model of Relationships

The logarithmic model is often used to describe the relationships between factors.It often gives good statistical characteristics.Yet,in the process of modeling of soil and water conservation,we find out that this“good”model cannot guarantee good result.In this paper we make an inquiry into the intrinsic reasons.It is shown that the logarithmic model has the property of enlarging or reducing model errors,and the disadvantages of the logarithmic model are analyzed.     

土壤样品的微波消解及其痕量铀的分析

对3个土壤样和2个放射性河床沉积物的国家标准物质进行了微波消解，又采用TOPO萃取和液体荧光法分析了样品中的铀含量，并将分析结果与国家标准方法GB11220．2-89的分析结果进行了比较。结果表明，微波消解法与国家标准方法一样，均不能实现土壤的全部消解，但与国家标准方法相比较，微波消解速度快，所需试剂量少，且易于实现定量控制，铀回收率高，分析精度高。对不溶物进行X射线能谱分析发现，其主要组成为铝、钛及过渡金属的氟化物或氧化物。同位素质谱分析表明，国家标准物质GBW08304中的^234U，^235U均比天然丰度低，另一个国家标准物质GBW08304a中铀的同位素分布与天然组成基本一致。     

基于神经元网络的燃油锅炉烟气氧含量的软

针对目前各种氧含量检测仪表在运行过程中的可靠性差、使用寿命短及价格昂贵等诸多不足，通过探寻锅炉运行中的其他参数与烟气氧含量的映射关系，建立ＢＰ神经元网络，提出了燃油锅炉烟气氧含量的软测量方法。结果表明，其精度完全达到了设计要求。     

交流电机软起动

介绍了用ＮＥ５５５控制固态继电器，实现交流电机软起动的装置，以及电流闭环控制设计。实验证明：该方案具有良好的软起动性能，且造价低。     

异步电机软起动装置的模糊控制器设计研究

介绍了DRQ系列异步电机软起动装置的硬件电路。在此基础上着重讨论了其模糊控制器的设计,探讨了模糊控制器量化因子和比例因子的选择与整定方法,使模糊控制与电流瞬时值采样相配合,达到了良好的控制效果。该方法电流波动小,无电流冲击与振荡现象。     

Analysis,simulation and verification of a bipolar current source power resonant inverter

A high‐frequency bipolar current source resonant inverter introduced in this paper has dramatic zero‐voltage‐switching (ZVS) characteristic. The analytic expressions of the resonant voltage and current are given. It indicates that the resonant waveform is composed of two parts, i.e. the oscillatory component and the stationary component. In special cases, the resonant waveform degenerates into the mono‐frequency component, as presents the graceful sinusoidal wave with very low total harmonic distortion (THD) value. Based on the closed‐form voltage and current, the component stresses on reactive elements are obtained. The impact of different component values and operating frequencies on ZVS feature is also discussed. It should be noted that the ZVS merit may be lost if the components are carelessly selected. The validity of the theoretical analysis has been proven with Pspice simulations and experimental results. Copyright © 2004 John Wiley Sons, Ltd.     

基于DSP非同步控制的新型软起动系统

提出了一种基于自关断器件拓扑结构主电路的新型软起动系统．该系统实现了触发脉冲的 非同步控制，而且能够消除定子电流的低次谐波。与晶闸管控制的软起动相比，新型软起动控制简单，节能效果突出。该系统采用DSP和单片机构成的双CPU结构，实现数据处理和系统监控的并行处理，提高系统的响应速度和可靠性。结果表明，该系统具有很好的可行性和广阔的应用前景。     

水与可持续发展

论述了水在可持续发展中的地位。当今存在的4大水问题，评估了未来的水形势，提出了解决水问题的途径。