Closing the gap: Improved bounds on optimal POMDP solutions

POMDP algorithms have made significant progress in recent years by allowing practitioners to find good solutions to increasingly large problems. Most approaches (including point-based and policy iteration techniques) operate by refining a lower bound of the optimal value function. Several approaches (e.g., HSVI2, SARSOP, grid-based approaches and online forward search) also refine an upper bound. However, approximating the optimal value function by an upper bound is computationally expensive and therefore tightness is often sacrificed to improve efficiency (e.g., sawtooth approximation). In this paper, we describe a new approach to efficiently compute tighter bounds by i) conducting a prioritized breadth first search over the reachable beliefs, ii) propagating upper bound improvements with an augmented POMDP and iii) using exact linear programming (instead of the sawtooth approximation) for upper bound interpolation. As a result, we can represent the bounds more compactly and significantly reduce the gap between upper and lower bounds on several benchmark problems. Copyright © 2011, Association for the Advancement of Artificial Intelligence. All rights reserved.

复合垂直流人工湿地在奥林匹克森林公园龙型水系的应用

介绍了北京奥林匹克森林公园人工湿地系统的设计,跟踪调查了复合垂直流人工湿地在龙型水系水质改善中的功能和效果。复合垂直流人工湿地系统占地面积为41 500 m2,处理水量为2 600 m3/d的污水处理厂尾水(再生水)和20 000 m3/d的主湖循环水。一年多的运行表明,该系统与其他生态工程的协同作用有效地改善了公园内的龙型水系水质,特别是在奥运期间,在保证了奥运主湖水质良好的同时,为运动员和观众提供了优美的休息环境,取得了良好的生态、环境、经济和文化等综合效益。

鲫鱼肝脏AChE的提取及有机磷农药对AChE的抑制效应研究

本研究利用淡水鲫鱼肝脏为主要原材料提取乙酰胆碱酯酶(acetylcholinesterase,AChE),并设计正交试验确定了鲫鱼肝脏中乙酰胆碱酯酶的最佳提取条件:通过酶抑制法衡量敌敌畏、辛硫磷、三唑磷、乐果等四种不同种类有机磷农药对粗酶液的抑制作用;将鱼肝和鱼脑中乙酰胆碱酯酶活性及蛋白含量的进行对比研究。研究结果表明:提取液pH值、提取液种类以及原料与提取液的质量体积比对酶液的活性影响显著;被测四种有机磷农药中,敌敌畏对AChE活性抑制作用最强。鱼脑的AChE比酶活是肝脏的AChE比酶活的3～7倍。

淡水水体麻痹性贝毒污染的现状

麻痹性贝毒是一类水溶性的神经毒素,造成神经细胞电压敏感性钠离子通道(VSSC)高亲和力障碍,与细胞膜离子结合后引起细胞膜内外正常离子的流动失衡,造成膜电位反常,使人瘫痪。麻痹性贝毒的污染及其产毒藻已成为一个受人关注的公共健康问题。综述麻痹性贝毒的理化性质和毒性特点、淡水水体麻痹性贝毒污染及其5种淡水产毒蓝藻,并对淡水中PSP防治工作提出建议。

中国淡水甲藻两个新记录属

我国此前关于光薄甲藻GlenodiniumgymnodiniumPenard在西藏那错湖的记录是基于错误的鉴定,作者在相差显微镜下对标本进行了重新检查,发现此甲藻的细胞壁由多数甲片构成,甲片大小相似,多为六角形,应属于网甲藻属WoloszynskiaThompson的微小网甲藻W.tenuissima(Lauterborn)Thompson。中型四角甲藻TetradiniumintermediumGeitler采于武汉的一小池塘,附着于一鞘藻属Oedogonium植物的丝状体上,属于甲藻门中的不运动种类,

200 v superjunction N-type lateral insulated-gate bipolar transistor with improved latch-up characteristics

This paper evaluates the technique used to improve the latching characteristics of the 200 V n-type superjunction (SJ) lateral insulated-gate bipolar transistor (LIGBT) on a partial silicon-on-insulator. SJ IGBT devices are more prone to latch-up than standard IGBTs due to the presence of a strong pnp transistor with the p layer serving as an effective collector of holes. The initial SJ LIGBT design latches at about 23 V with a gate voltage of 5 V with a forward voltage drop (VON) of 2 V at 300 Acm2. The latch-up current density is 1100 Acm2. The latest SJ LIGBT design shows an increase in latch-up voltage close to 100 V without a significant penalty in VON. The latest design shows a latch-up current density of 1195 A cm2. The enhanced robustness against static latch-up leads to a better forward bias safe operating area. © 1963-2012 IEEE.

Composite electrospun gelatin fiber-alginate gel scaffolds for mechanically robust tissue engineered cornea.

A severe shortage of good quality donor cornea is now an international crisis in public health. Alternatives for donor tissue need to be urgently developed to meet the increasing demand for corneal transplantation. Hydrogels have been widely used as scaffolds for corneal tissue regeneration due to their large water content, similar to that of native tissue. However, these hydrogel scaffolds lack the fibrous structure that functions as a load-bearing component in the native tissue, resulting in poor mechanical performance. This work shows that mechanical properties of compliant hydrogels can be substantially enhanced with electrospun nanofiber reinforcement. Electrospun gelatin nanofibers were infiltrated with alginate hydrogels, yielding transparent fiber-reinforced hydrogels. Without prior crosslinking, electrospun gelatin nanofibers improved the tensile elastic modulus of the hydrogels from 78±19 kPa to 450±100 kPa. Stiffer hydrogels, with elastic modulus of 820±210 kPa, were obtained by crosslinking the gelatin fibers with carbodiimide hydrochloride in ethanol before the infiltration process, but at the expense of transparency. The developed fiber-reinforced hydrogels show great promise as mechanically robust scaffolds for corneal tissue engineering applications.