Guarding a set of line segments in the plane

We consider the following problem: Given a finite set of straight line segments in the plane, find a set of points of minimum size, so that every segment contains at least one point in the set. This problem can be interpreted as looking for a minimum number of locations of policemen, guards, cameras or other sensors, that can observe a network of streets, corridors, tunnels, tubes, etc. We show that the problem is strongly NP-complete even for a set of segments with a cubic graph structure, but in P for tree structures.     

Parameterized complexity of coloring problems: Treewidth versus vertex cover

We compare the fixed parameter complexity of various variants of coloring problems (including List Coloring, Precoloring Extension, Equitable Coloring, L(p,1)-Labeling and Channel Assignment) when parameterized by treewidth and by vertex cover number. In most (but not all) cases we conclude that parametrization by the vertex cover number provides a significant drop in the complexity of the problems.     

逻辑函数的无冗余覆盖选择问题

逻辑函数的最小化算法可分为两大步骤：产生本源蕴涵项和在这些蕴涵项中选择一个最小覆盖。人说后者比前者更加困难,这的确是事实。我们这里提出一个无冗余和选择一个最小覆盖的算法。给定函数ｆ的一个本源覆盖Ｇ,首先将Ｇ分为三个子集：实质本源项子集Ｅ,完全冗余项子集Ｒ和相对冗余项子集Ｐ。然后在Ｐ中选择一个子集Ｐ＾＊,使Ｐ＾＊∪Ｅ为ｆ的一个近似最小覆盖。很明显,后一项任务比前者要复杂得多。所以,我们的讨论侧重于后     

谈插图在流行音乐CD封套设计中的应用

文章分析了插图在流行音乐CD封套设计中广泛应用的原因,对CD封套设计中的插图三个显著特点:时尚性、形式多元化、视觉艺术化进行了重点分析与讨论,证实插图在流行音乐CD封套设计中的优势所在,阐释了其美学价值和商业价值。     

Timestamping messages and events in a distributed system using synchronous communication

Determining order relationship between events of a distributed computation is a fundamental problem in distributed systems which has applications in many areas including debugging, visualization, checkpointing and recovery. Fidge/Mattern’s vector-clock mechanism captures the order relationship using a vector of size N in a system consisting of N processes. As a result, it incurs message and space overhead of N integers. Many distributed applications use synchronous messages for communication. It is therefore natural to ask whether it is possible to reduce the timestamping overhead for such applications. In this paper, we present a new approach for timestamping messages and events of a synchronously ordered computation, that is, when processes communicate using synchronous messages. Our approach depends on decomposing edges in the communication topology into mutually disjoint edge groups such that each edge group either forms a star or a triangle. We show that, to accurately capture the order relationship between synchronous messages, it is sufficient to use one component per edge group in the vector instead of one component per process. Timestamps for events are only slightly bigger than timestamps for messages. Many common communication topologies such as ring, grid and hypercube can be decomposed into edge groups, resulting in almost 50% improvement in both space and communication overheads. We prove that the problem of computing an optimal edge decomposition of a communication topology is NP-complete in general. We also present a heuristic algorithm for computing an edge decomposition whose size is within a factor of two of the optimal. We prove that, in the worst case, it is not possible to timestamp messages of a synchronously ordered computation using a vector containing fewer than components when N ≥ 2. Finally, we show that messages in a synchronously ordered computation can always be timestamped in an offline manner using a vector of size at most . An earlier version of this paper appeared in 2002 Proceedings of the IEEE International Conference on Distributed Computing Systems (ICDCS). The author V. K. Garg was supported in part by the NSF Grants ECS-9907213, CCR-9988225, an Engineering Foundation Fellowship. This work was done while the author C. Skawratananond was a Ph.D. student at the University of Texas at Austin.     

双锥平衡密封盖在装酸槽车上的应用

在装酸槽车上采用了“双锥平衡密封盖”，解决了汽车运输过程及贮罐贮存中酸雾对环境的污染问题，并实现了装卸过程中的压力自控，从而简化了操作，减少了浪费，取得了良好社会经济效益。     

高功率高透波材料的研究

本文叙述了以 TRR 树脂为基体，分别用 B 型石英玻璃纤维和 UHMWPE 纤维为增强材料，与 T 蜂窝复合制得高功率高透波材料的研究情况，两种蒙皮和 T 蜂窝在 9.375GHz 下的?和 ?分别为 2.79、3×10-4；2.13、4×10-4 和 1.14、9.43×10-4；夹层结构的插入损耗分别为 0.019－0.02dB 和 0.030－0.041dB。     

Age-related difference in perceptual responses and interface pressure requirements for driver seat design

Due to typical physiological changes with age, older individuals are likely to have different perceptual responses to and different needs for driver–seat interface design. To assess this, a study was conducted in which a total of 22 younger and older participants completed six short-term driving sessions. Three subjective ratings (comfort, discomfort and overall) were obtained, along with 36 driver–seat interface pressure measures, and were used to assess differences and similarities between the two age groups. For both age groups, localised comfort ratings were more effective at distinguishing between driver seats and workspaces. Older individuals appeared to be less sensitive to discomfort than younger individuals. Across age groups, two distinct processes were used in determining whole-body comfort and discomfort perceptions based on localised comfort/discomfort perceptions. Whole-body discomfort levels were largely affected by lower back discomfort in the younger group versus upper back discomfort in the older group. Four specific pressure measures at several body regions differed between the age groups, suggesting distinct contract pressure requirements and loading patterns among these groups.     

基于UG和Moldflow的遥控器后盖注塑模具设计

以UG为平台对遥控器后盖的注塑模具进行设计,通过Moldflow进行流动模拟分析,确定了浇注系统、冷却水道等的设计方案,并利用UG强大的CAM技术对模具零件（型腔/型芯）进行加工,生成加工轨迹.该设计提高了模具研发质量和生产效率,并对生产有借鉴意义.     

Supervised polarimetric SAR classification method based on Fisher linear discriminant

A supervised polarimetric SAR land cover classification method was proposed based on the Fisher linear discriminant.The feature parameters used in this classification method could be selected flexibly according to land covers to be classified.Polarimetric and texture feature parameters extracted from co-registered multifrequency and multi-temporal polarimetric SAR data could be combined together for classification use,without consideration of the dimension difference of each feature parameter and the joint probability density function of those parameters.Experimental result with AGRSAR L/C-band full polarimetric SAR data showed that a total classification accuracy of 94.33% was achieved by combining the polarimetric with texture feature parameters extracted from L/C dual band SAR data,demonstrating the effectiveness of this method.