A characterization of span program size and improved lower bounds for monotone span programs

We give a characterization of span program size by a combinatorial-algebraic measure. The measure we consider is a generalization of a measure on covers which has been used to prove lower bounds on formula size and has also been studied with respect to communication complexity.?In the monotone case our new methods yield lower bounds for the monotone span program complexity of explicit Boolean functions in n variables over arbitrary fields, improving the previous lower bounds on monotone span program size. Our characterization of span program size implies that any matrix with superpolynomial separation between its rank and cover number can be used to obtain superpolynomial lower bounds on monotone span program size. We also identify a property of bipartite graphs that is suficient for constructing Boolean functions with large monotone span program complexity. Received: September 30, 2000.     

电信管理网TMN开发探讨

本文论述了TMN产生的背景以及TMN的体系结构 ,并根据HiTMN的开发实践讨论了TMN发展的若干重要问题。     

Towards optimal simulations of formulas by bounded-width programs

We show that, over an arbitrary ring, for any fixed >0, all balanced algebraic formulas of sizes are computed by algebraic straight-line programs that employ a constant number of registers and have lengthO (s ¹⁺). In particular, in the special case where the ring isGF(2), we obtain a technique for simulating balanced Boolean formulas of sizes by bounded-width branching programs of lengthO(s ¹⁺), for any fixed >0. This is an asymptotic improvement in efficiency over previous simulations in both the Boolean and algebraic settings.     

Numerical stability of symmetric solitary-wave-like waves of a two-layer fluid—Forced modified KdV equation

Forced internal waves at the interface of a two-layer incompressible fluid in a two-dimensional domain with rigid horizontal boundaries are studied. The lower boundary is assumed to have a small obstruction. We derive a time-dependent forced modified KdV equation when the KdV theory fails and study the stabilities of four types of symmetric time-independent solitary-wave-like solutions numerically.     

基于DSP低Q值感应加热电源的研究

为了增加感应加热电源的炉壁厚度及提高输出功率,本文提出了一种新型低Q值感应加热电源,采用Buck斩波电路来调节电源的输出功率,通过改变Buck电路的占空比D来改变C2两端的电压值,从而调整逆变器的输入电压,使电源的输出功率恒定;控制系统采用TI公司的TMS320F28335作为控制芯片,控制功率开关管的导通与关断,使电源能够恒定功率输出,并且实现自动变频功能,提高感应加热电源的工作稳定性.实验结果表明,当感应线圈直径不变时,炉胎的炉壁越厚,内径越小,感应线圈与被加热金属的互感系数越小,系统的无功能量增加;低Q值感应加热电源可以把其内部更多的无功能量转换成有功能量,并且炉壁越厚,输出功率越大.该研究提高了电源的输出功率,解决了传统感应加热电源无法加厚炉壁的缺点.     

DCS安全级仪控平台的分析研究

美国西屋公司的AP1000核电站,采用了数字化仪控系统,实现方式为Common Q＋Ovation。这种集成的仪控系统设计,减少了接口和软件平台的数量,提供了优化的结构和性能。Common Q平台属1E级,AP1000核电站的保护与安全监测系统（PMS）就是在这一平台上实现的。本文对西屋公司的仪控平台Common Q进行评述,并结合目前国内外DCS产品性能特点进行对比性分析,研究Common Q平台的优点及不足。     

465Q系列连杆珩磨工艺分析

由于各种汽车发动机连杆小头孔的尺寸、材料及表面要求存在差别,在珩磨加工时要根据具体型号发动机连杆进行珩磨工艺参数的选择.文中介绍连杆孔珩磨工艺参数的选择方法,确定465Q系列连杆小头孔的珩磨工艺参数,并针对珩磨加工出现的问题进行分析,找出影响工件质量的主要因素,对计算出的参数进行了修订.生产实践证明,连杆小头孔珩磨工艺参数选择得当可提高加工精度、降低成本、提高加工效率、延长零件的使用寿命.     

建筑用Q235钢在高温（火灾）条件下的力学性能研究

对建筑常用的Q235钢在火灾情况下的力学性能分析，获得了Q235钢在高温下的屈服强度、极限强度、弹性模量、伸长率等力学性能指标的变化规律，并在恒温加载和恒载加温两种试验下对Q235钢进行强度对比。     

基于IBR实现VLAN之间通信应用研究

通过实例介绍如何使用IRB协议来实现VLAN之间的相互访问,着重分析了IRB的配置和它们之间的通信原理,在实际应用中实现了新老设备之间的互连,不但优化了配置而且节省了成本,该方法具有一定的应用参考价值。     

80 t UHP DC EAF-LF-CC工艺生产Q390B低合金高强度钢的实践

杭钢用80 t UHP DC电弧炉-钢包炉(LF)-200 mm×200 mm连铸及700×1/650×3轧机轧制,生产直径75 mm的Q390B低合金高强度圆钢.LF精炼时控制(%)0.16～0.19C,1.35～1.52Mn,0.03～0.05V,≤0.025S,≤0.025P,喂CaSi线并全程吹氩,连铸采用长水口保护浇注.检验结果表明,钢材具有良好的表面质量、低倍组织,夹杂物≤2.0级,钢的σs 380～465 MPa,σb 545～625 MPa,δ 22.0%～28.5%,AK 98～210 J.