Random arithmetic formulas can be reconstructed efficiently

Informally stated, we present here a randomized algorithm that given black-box access to the polynomial f computed by an unknown/hidden arithmetic formula ? reconstructs, on the average, an equivalent or smaller formula \({\hat{\phi}}\) in time polynomial in the size of its output \({\hat{\phi}}\) . Specifically, we consider arithmetic formulas wherein the underlying tree is a complete binary tree, the leaf nodes are labeled by affine forms (i.e., degree one polynomials) over the input variables and where the internal nodes consist of alternating layers of addition and multiplication gates. We call these alternating normal form (ANF) formulas. If a polynomial f can be computed by an arithmetic formula μ of size s, it can also be computed by an ANF formula ?, possibly of slightly larger size s ^O(1). Our algorithm gets as input black-box access to the output polynomial f (i.e., for any point x in the domain, it can query the black box and obtain f(x) in one step) of a random ANF formula ? of size s (wherein the coefficients of the affine forms in the leaf nodes of ? are chosen independently and uniformly at random from a large enough subset of the underlying field). With high probability (over the choice of coefficients in the leaf nodes), the algorithm efficiently (i.e., in time s ^O(1)) computes an ANF formula \({\hat{\phi}}\) of size s computing f. This then is the strongest model of arithmetic computation for which a reconstruction algorithm is presently known, albeit efficient in a distributional sense rather than in the worst case.     

利用仿真软件优化电磁场与电磁波教学

针对电磁场与电磁波课程理论公式复杂、相关概念模型抽象的特点,结合长期积累的教学经验,利用软件仿真将电磁场定理模型、分布特性可视化,简化推导计算过程,优化课程结构、节省课时的同时提高了教学效果。     

Microcellular foaming of PE/PP blends

Three different polyethylene/polypropylene (PE/PP) blends were microcellular foamed and their crystallinities and melt strengths were investigated. The relationship between crystallinity, melt strength, and cellular structure was studied. Experimental results showed that the three blends had similar variation patterns in respect of crystallinity, melt strength, and cellular structure, and these variation patterns were correlative for each blend. For all blends, the melt strength and PP melting point initially heightened and then lowered, the PP crystallinity first decreased, and then increased as the PE content increased. At PE content of 30%, the melt strength and PP melting point were highest and the PP crystallinity was least. The blend with lower PP crystallinity and higher melt strength had better cellular structure and broader microcellular foaming temperature range. So, three blends had best cellular structure at PE content of 30%. Furthermore, when compared with PE/homopolymer (hPP) blend, the PE/copolymer PP (cPP) blend had higher melt strength, better cellular structure, and wider microcellular foaming temperature range, so it was more suited to be microcellular foamed. Whereas LDPE/cPP blend had the broadest microcellular foaming temperature range because of its highest melt strength within three blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4149–4159, 2007     

甲烷磺酸电镀Sn-Pb合金添加剂研究

介绍了国内外磺酸型Sn-Pb合金电镀添加剂近十年的研究历程现况并根据各组分的化学结构及其在电镀中所体现出的性质将添加剂分为Sn^2 离子稳定剂、光亮剂及分散剂三类。最后列出了新研制的甲烷磺酸Sn-Pb合金电镀添加剂的主要性能及具体工艺配方。     

Synthesis and characterization of soluble aromatic azopolyamides containing sulfone and ether units

A series of new polyamides 3a–d containing aryl-azo, ether and sulfone groups in the main chain were synthesized from bis[4-(4-aminophenoxy)phenyl sulfone] 1 and several azo aromatic diacyl chlorides 2a–d by the low temperature solution polycondensation technique. FTIR spectroscopy, nuclear magnetic resonance (NMR) and elemental analyses confirmed the structure of these polymers. Owing to the aryl and amide groups in the main chain, these polymers exhibit photochromic properties as well as excellent thermal stabilities. The transition temperatures (T _g) are between 242 and 265 °C, and the char yields at 800 °C in nitrogen atmosphere were above 39%. Based on incorporation of flexible ether linkages and polar sulfone groups, the polyamides show desirable solubility in organic solvents such as DMAc, N,N-dimethylformamide (DMF), N-methyl-2-pyrroidinone (NMP) and dimethylsulfoxide (DMSO). And it is exemplified that polyamide containing 2 and 2′ substitutes performed better solubility. Funded by the National Natural Science Foundation of China (No. 50572081)     

基于Pro／E的VERICUT虚拟机床模型开发

虚拟机床建模是VERICUT中数控加工仿真的基础,以一个带升降台的3轴立式铣床为例,介绍VERICUT中虚拟机床模型在Pro／E系统中的创建、装配及输出过程,借以探讨二者的结合应用．该方法具有良好的通用性,可作为其它机床建模的参考．     

黄骅坳陷白水头断裂系统生长模式及其成因分析

在系统分析白水头断裂系统的断层组合、构造样式、主干断层及次级断层生长模式的基础之上,结合区域构造背景、伸展边界条件及断层间的相互作用,探讨了该断裂系统的形成机制.分析结果表明,区域构造背景下存在的伸展边界控制了整个白水头断裂系统总的构造格局.进一步证实了区内右旋走滑作用与伸展作用的相互耦合,致使次级断层沿走滑构造带出现转向或中断.断裂系统及系统内部断层间的运动学关系表明白水头断裂系统在古近纪是受两个构造动力控制,其一是地幔热作用引起岩石圈北西-南东向引张作用,其二是北北东向深断裂带的右旋剪切作用.     

基于网络消费者购买过程的网络营销策略分析

网络消费者是新的消费群体,与传统市场消费群体有着截然不同的特性。企业要想卓有成效地开展网络营销活动,获得来自虚拟世界的利益,就必须了解、分析和把握住网络消费者的消费过程,尽可能地为营销活动提供可靠的数据分析和营销依据。本文从网络消费者购买行为形成和实现的过程入手,对网络消费者购买过程的环节进行策略分析。     

大学生树立理性婚恋观的几点思考

于2005年9月1日正式实施的《普通高等学校学生管理规定》对于在校大学生能否结婚给出了明确、肯定的答案。详尽分析了在校大学生不宜结婚的主客观原因,提出应大力开展“爱情教育”和营造良好精神氛围以帮助大学生树立理性婚恋观。     

物探方法在隧道勘查中的应用探讨

通过对若干隧道的物探勘查表明,合理的运用高密度电法、地震折射波法和瞬态瑞雷波法以及声波测井法,可以有效的查明隧址区第四系覆盖层厚度、基岩垂向分带情况,推定断裂等构造破碎带的位置和产状,计算岩体波速、划分围岩级别,为隧址区的工程评价和隧址的合理选择提供科学依据。指出目前折射波法勘探存在的局限性,强调综合物探的合理性。提出采用高密度电阻率法、声波测井法和瞬态瑞雷波法的综合勘查方法进行隧道工程物探勘查,期望能为今后的隧道物探勘查提供指导。