Φ90mm圆盘延伸机前卡钢分析

探讨了造成Φ90mm圆盘延伸机前卡钢的原因,分析了轧件轧制过程中的第一、第二次咬入的受力情况,提出了预防前卡钢的措施。该措施实施后,基本消除了前卡钢现象。     

An algorithm for the three-dimensional packing problem with asymptotic performance analysis

The three-dimensional packing problem can be stated as follows. Given a list of boxes, each with a given length, width, and height, the problem is to pack these boxes into a rectangular box of fixed-size bottom and unbounded height, so that the height of this packing is minimized. The boxes have to be packed orthogonally and oriented in all three dimensions. We present an approximation algorithm for this problem and show that its asymptotic performance bound is between 2.5 and 2.67. This result answers a question raised by Li and Cheng [5] about the existence of an algorithm for this problem with an asymptotic performance bound less than 2.89. This research was partially supported by FAPESP (proc. 93/0603-1) and by CNPq/ProTeM-CC, project ProComb (proc. 680065/94-6).     

无源软开关电路拓扑的研究

提出一个研究无源软开关电路的新技术方法;其特征是对基本的单管隔离型PWM DC/DC变换器进行类比分析,由此直接导出可行的缓冲能量再生复位电路.该新方法能使DC/DC PWM硬开关变换器转变为软开关变换器.以新型Boost无源软开关变换器为例,进行了电路理论分析与中功率样机的实验测试;结果表明此新变换器具有较宽的软开关工作范围、较低的电应力、较小的缓冲元件量值等特点.由此认为,这种研究方法推导简单、物理意义清晰,还能深入地研究无源软开关的新电路拓扑.     

气控盘式辅助刹车在车载钻机中的应用分析

在对比分析了传统辅助水刹车与气控盘式辅助刹车的特性后,重点对气控盘式辅助刹车进行了数学分析,得到了该辅助刹车的制动扭矩取决于施加的气体压力,与钻具质量无关,冷却液的流量应同钻柱质量保持正比关系,可精确控制下钻速度并易于实现自动送钻功能。得出了气控盘式辅助刹车更适用于车载钻机的结论。     

三峡蓄水初期水库近坝区水环境特性分析

通过现场观测和数值模拟的方法，对三峡水库近坝区在蓄水初期的水流和水环境特性进行了 分析。对蓄水初期的溶解氧、BOD、COD和NH3-N、Cu等水质参数进行了观测，将蓄水初期水质资料与蓄水之前的结果进行了对比，分析了近坝区水环境变化趋势。采用大涡模拟紊流模型，考虑水体表面的热交换，对三峡近坝区的流动和水温分布特性进行了模拟。研究结果表明，三峡水库蓄水初期近坝区水流特性明显改变，主要表现为水深增加、流速变缓，部分地段有回流区出现。水质指标变化不明显，坝前断面溶解氧浓度、悬浮物浓度有所降低，和悬浮物密切相关的污染物总磷、重金属也随之降低；蓄水初期139m水位时坝前水域尚没有出现温度分层现象。     

Three-dimensional stability analysis of the dam foundation at Baise

It is usually difficult to determine the actual safety factors of rock masses in an ordinary two-dimensional stability analysis if the safety factors of the different cross sections in the rock mass vary significantly. In addition to the actual slope, arch dam abutment, and the actual foundation of a high building, another example is that the different cross sections of the foundation in the monolith of a gravity dam vary significantly, just like the condition at the overflow dam in the Baise project. A three-dimensional stability analysis method based on the upper-bound theorem was employed to solve this problem. The parameters used in the analysis were obtained from geomechanics tests, as well as continuity simulations of the randomly distributed joints. Two failure patterns against sliding are analyzed. One pattern is the foundation slide along deep-seated planes which were determined by calculations. The other pattern is the foundation slide along the planes across the bottom of the high steps in the foundation pit. The results indicate that a special overflow dam monolith can be considered to be safe in case of considering the three dimensional effect. However, a key wall with a depth of 5m must be constructed at the upper side of this monolith in order to ensure the safety of the foundation. Translated from Chinese Journal of Rock Mechanics and Engineering, 2006, 25(3): 533–538 [译自: 岩土力学与工程学报]     

陕西省引红济石调水工程1#支洞塌方原因分析及对策

塌方是隧洞施工过程中经常遇到的难题,本文针对引红济石工程1#支洞在施工过程中出现的两次塌方原因进行分析,总结出隧洞施工过程中避免塌方的主要方法和策略,具有普遍的借鉴意义。     

A rule-based approach for robust clump splitting

This paper presents a robust rule-based approach for the splitting of binary clumps that are formed by objects of diverse shapes and sizes. First, the deepest boundary pixels, i.e., the concavity pixels in a clump, are detected using a fast and accurate scheme. Next, concavity-based rules are applied to generate the candidate split lines that join pairs of concavity pixels. A figure of merit is used to determine the best split line from the set of candidate lines. Experimental results show that the proposed approach is robust and accurate.     

Stability of large-scale coal-fired MHD channels

Stability of large-scale coal-fired MHD channels is studied by (1) linearized stability analysis, and (2) time-dependent 1-D analysis. The channel length is 15 m with 600 electrode pairs, and the output power ranges from 220.6 MW through 258.7 MW. Linearized stability analyses show that the Faraday channels operated with fixed loading resistance are stable, whereas the two waves of u and u–a (u, a: gas and sound velocity) become unstable in the Faraday channel with fixed loading factor. Two waves of u and u–a are unstable in the diagonal channel with fixed loading current and the u + a wave becomes unstable in the diagonal channel with fixed electrode current. Time-dependent one-dimensional analyses indicate that the Faraday channels with fixed load resistance are smooth without growth of fluctuation. The diagonal channels with fixed electrode current are smooth with no fluctuation, though the linear theory indicates that the u + a wave is unstable. The diagonal channel with fixed load current suffers large disturbance along the latter half of the channel, being consistent with the linearized analysis which indicates that the u - a and u waves are unstable.     

The use of the stable isotope 44Ca in studies of calcium incorporation into dentin

The incorporation into rat incisor dentin of two calcium isotopes, the stable ⁴⁴Ca and the radioactive ⁴⁵Ca, was studied using secondary ion mass spectrometry (SIMS) stepscanning and imaging, and autoradiography, respectively. The results demonstrated a time-dependent incorporation of the calcium isotopes into the mineral phase of dentin. With the SIMS step-scanning, detecting ⁴⁴Ca, the ion yield was high in the odontoblasts 2 min after intravenous injection. After 10 min a marked increase in signal intensity was found at the dentin mineralization front. This result was consistent with those obtained by ⁴⁵Ca autoradiography; a peak of incorporation occurred 10 min after injection of the isotope. Likewise, localization of ⁴⁴Ca to the mineralization front could be demonstrated 10 min after injection by SIMS imaging. In images obtained at earlier intervals, no such increase in ion yield could be detected. The results show that the nonradioactive, stable isotope ⁴⁴Ca can be used as a marker for biomineralization in a similar way to radioactive ⁴⁵Ca.