The min-dist location selection and facility replacement queries

We propose and study a new type of location optimization problem, the min-dist location selection problem: given a set of clients and a set of existing facilities, we select a location from a given set of potential locations for establishing a new facility, so that the average distance between a client and her nearest facility is minimized. The problem has a wide range of applications in urban development simulation, massively multiplayer online games, and decision support systems. We also investigate a variant of the problem, where we consider replacing (instead of adding) a facility while achieving the same optimization goal. We call this variant the min-dist facility replacement problem. We explore two common approaches to location optimization problems and present methods based on those approaches for solving the min-dist location selection problem. However, those methods either need to maintain an extra index or fall short in efficiency. To address their drawbacks, we propose a novel method (named MND), which has very close performance to the fastest method but does not need an extra index. We then utilize the key idea behind MND to approach the min-dist facility replacement problem, which results in two algorithms names MSND and RID. We provide a detailed comparative cost analysis and conduct extensive experiments on the various algorithms. The results show that MND and RID outperform their competitors by orders of magnitude.     

基于移动平台的校园资讯系统设计与实现

为了让高校师生可以快捷方便地获取到校园各类资讯,摆脱时间和空间的限制,设计了一种基于移动平台的校园资讯系统。该系统在PC平台上采用Asp.Net和SQL Server 2005技术,基于B/S的三层网络结构设计,在移动平台上基于C/S模式设计并开发了一个具备相应功能的Android手机客户端应用[1]。该系统具有查询课程、查询教室、查询考试安排、学生交友、发布商品、查询商品等基本功能。该移动平台系统界面友好,操作方便,资讯丰富,极大地方便了高校师生的学习、工作和生活。     

RIAIL:大规模图上的可达性查询索引方法

图被广泛用来建模在社交网络、语义网、计算生物学和软件分析中的应用.可达性查询是图数据上的一种基础查询.当前,针对图上的可达性查询已经提出了一些索引算法,但是它们不能灵活地扩展到大的图数据.因此,提出了一种索引方法RIAIL(reachability index augmented by interval labeling).RIAIL将结点的标记信息表示成四元组.前两个元素是区间标记,编码生成树的可达性信息,后两个元素编码非树边的可达性信息.RIAIL查询时只需索引且索引创建代价小.最后,通过大量真实和人工生成数据集上的实验说明,RIAIL能够高效地处理可达性查询,并且可以简单地扩展到大的图数据.     

到达数据中时空异常聚簇发现

在时空数据中有一类表示用户在某一时间到达某一地点的数据——到达数据,到达数据可以是社交网站的签到数据、轨迹数据中的停留点及公共交通中乘客抵达的位置数据,这些数据的聚簇可以反映用户的聚集行为.基于到达数据,提出一类新的时空数据查询——时空异常聚簇发现.将到达数据进行周期性划分,通过时空聚类算法对一个时间段的数据进行聚类,比较不同时间段内聚簇的差异度,发现具有最大簇异常度的前k个簇.通过该查询发现的时空异常聚簇可以应用于城市安全管理、基于位置的服务和交通调度等方面.定义了异常簇查询模型,提出了针对任意形状聚簇的簇差异度度量,将异常簇查询转化为二分图最大匹配问题,对二分图构建与匹配进行了优化并提出了高效的查询算法.利用真实数据集进行了充分实验,验证了查询结果的实际意义,评估了所提出的各查询算法在不同参数设置下的查询效率.     

Swelling behavior of poly(sodium acrylate)/kaoline superabsorbent composite

Using partly neutralized acrylic acid as monomer, kaoline ultrafine powder as filler and N,N′‐(dimethyl)acrylamide as crosslink agent, poly(sodium acrylate)/kaoline superabsorbent composite was synthesized by aqueous solution polymerization method. Using the superabsorbent composite as collagen, a hydrogel was prepared. The influence of the neutralization degree of superabsorbent collagen, the compositions, the concentration, and the pH value of exterior solution on the swelling behavior of the hydrogel was investigated. It was found that the swelling capability of the hydrogel depended on the groups on the collagen. The swelling capability of the hydrogel relied on the ionic intensity, molecular polarity, molecular volume, as well as the concentration of exterior solution. When the pH value of exterior solution was equal to seven, the hydrogel has a maximum swelling value of 800 times. POLYM. ENG. SCI. 46:324–328, 2006. © 2006 Society of Plastics Engineers     

Dynamic mechanical,rheological, and morphological studies of polyacrylate-graft-poly (vinyl chloride) suspension resin

A series of polyacrylate-graft-poly (vinyl chloride) (ACR-g-PVC) resins were prepared through suspension graft copolymerization. Three kinds of polyacrylate latices were grafted by vinyl chloride using suspension polymerization method at 57 ± 0.1°C, respectively. The dynamic mechanical and rheological properties and the morphology of the resulting ACR-g-PVC resins were investigated. Poly (butyl acrylate)-graft-poly (vinyl chloride) (PBA-g-PVC) resin exhibited better toughness, and the optimized content of PBA in ACR-g-PVC resin was 6–8 wt%. The melt viscosity of ACR-g-PVC resin was much lower than that of pure PVC. The nature of the fracture surfaces of ACR-g-PVC material indicated that it has good toughness. The impact strength of the PBA-g-PVC material was greatly improved compared with that of pure PVC. The Young's modulus of the ACR-g-PVC material containing less than 15 wt% of PBA was comparable to that of pure PVC according to their dynamic mechanical analysis curves. For all of the ACR-g-PVC resins, there were two individual relaxations in the low-temperature range. One was β transition of PVC, and the other was α transition of ACR. The glass transition temperature of PVC in the ACR-g-PVC resin shifted to lower temperature when the content of the PBA was above 50 wt%. POLYM. ENG. SCI., 47:996–1003, 2007. © 2007 Society of Plastics Engineers     

用玻璃球负载纳米级SO4^2-／TiO2固体超强酸催化合成乙酸正丁酯

用玻璃球负载纳米级SO42-/TiO2固体超强酸催化合成乙酸正丁酯,对催化剂的制备条件和乙酸正丁酯的合成条件进行了研究。在最佳反应条件下,乙酸的转化率为99.3%,催化剂重复使用8次后乙酸的转化率仍高达92.3%。该催化剂选择性好,未发现有副产物生成,看来具有较好的应用前景。     

Research on the friction and wear mechanism of Poly(vinyl alcohol)/hydroxylapatite composite hydrogel

Poly(vinyl alcohol)/Hydroxylapatite (PVA/HA) composite hydrogel was prepared with poly(vinyl alcohol) and hydroxylapatite as raw materials, using the method of repeated freezing and thawing. The morphologies of PVA/HA composite hydrogel were observed by means of high-accuracy 3D profiler and scanning electron microscope (SEM). The compressive elastic modulus and the stress relaxation characteristics of PVA/HA composite hydrogel were measured using the flat-head cylinder indenter. The friction and wear tests between PVA/HA composite hydrogel and bovine knee articular cartilage were performed on the micro-tribometer. The worn morphologies of PVA/HA composite hydrogel were observed with environmental scanning electron microscope (ESEM). The results showed that PVA/HA composite hydrogel has the cross-link network microstructure which is similar to that of the natural bovine knee articular cartilages. With the increase of freezing-thawing cycles and the HA content, the degree of cross-link and the crystallization of PVA/HA composite hydrogel both increase, the elastic modulus increases evidently, the rate of stress relaxation is improved and the value of balance stress decreases. The friction coefficient decreases with the increase of the freezing-thawing cycles and the HA content. The more the freezing-thawing cycles are, the earlier the friction coefficient reaches the stable balance value. The friction deformation depth between PVA/HA composite hydrogel and bovine knee articular cartilage is inversely proportional to freezing-thawing cycles and the HA content. The main wear mechanisms of PVA/HA composite hydrogel are plastic flowing and adhesive flaking. The wear severity degree decreases with the increase of freezing-thawing cycles and the HA content. Supported by Key Program of the National Natural Science Foundation of China (Grant No. 50535050), Program for New Century Excellent Talents in University (Grant No. NCET-06-0479) and Natural Science Foundation of Jiangsu Province (Grant No. BK2005403)     

有机浆料发泡法制备多孔羟基磷灰石

本文以湿法合成的羟基磷灰石粉体为原料,采用树脂、异氰酸与水发泡工艺制备多孔生物陶瓷材料。采用浆料发泡法制得的生物陶瓷材料具有三维无序孔和二维直通孔复合结构,其总气孔率可达70%～85%;宏观孔径主要分布在0.3～0.6mm之间,微观孔径主要分布在1～3μm之间,抗压强度可达0.85MPa。通过控制烧结温度,可以调节生物陶瓷材料中羟基磷灰石(HAP)和β-磷酸三钙(β-TCP)的成分配比,从而使之满足多孔生物陶瓷材料生物相容性和生物降解性的要求。     

基于嵌入式多串口扩展的出租车智能导航终端设计与实现

目前,ARM处理器在嵌入式系统中得到了广泛的应用,但其通常只有3个及以下的串口,难以满足需要多串口设备的系统需求;分析研究基于ARM处理器的智能车载导航终端的多串口扩展问题,提出采用具有单串口扩展为5串口功能的串口扩展芯片GM8125,实现嵌入式系统的多串口扩展需求,并在串口通信中采用分层设计的方法,提高系统的稳定性和运行效率;该出租车智能移动导航终端系统经过实际调试与运行,能够实现预定功能且效果良好,能够应用到新型的智能交通调度系统中。