具有高功率密度的三相AC-DC 48V电源

在电力系统的电源质量国际标准规定中,电网连接设备的线电流谐波要低于门限值;因此,要求AC-DC变流器运行时要具有高功率因数和低线电流失真。本文实现了一种用于电源系统的三相AC-DC48V电力电子变流器,并进行了相关的实验测试与讨论。在电源设计上的主要限制条件是要求功率密度达到每立方分米9000W,同时供电线路中不用中性线。     

Weak quantifier elimination for the full linear theory of the integers

We describe a weak quantifier elimination procedure for the full linear theory of the integers. This theory is a generalization of Presburger arithmetic, where the coefficients are arbitrary polynomials in non-quantified variables. The notion of weak quantifier elimination refers to the fact that the result possibly contains bounded quantifiers. For fixed choices of parameters these bounded quantifiers can be expanded into disjunctions or conjunctions. We furthermore give a corresponding extended quantifier elimination procedure, which delivers besides quantifier-free equivalents also sample values for quantified variables. Our methods are efficiently implemented within the computer logic system redlog, which is part of reduce. Various examples demonstrate the applicability of our methods. These examples include problems currently discussed in practical computer science.     

4号花园 穴居透光

你是否曾化身为一只昆虫,钻进大地的皮肤下？这个花园是一次穿越洞穴的旅程,参观者会匆匆穿过某种动物的庇护所或是将其据为己有。它有几个寓意：进入一个混有泥土和树枝的地下巢穴体会鼹鼠或蚯蚓的生活;也可以根据安排的活动环节走完这个洞穴,或呆在地下,头顶花梗,仔细观察动物留下的痕迹和它们的＂居住＂环境,以及各种生态系统。