Linking learning goals and educational resources through interactive concept map visualizations

Concept browsing interfaces can help educators and learners to locate and use learning resources that are aligned with recognized learning goals. The Strand Map Service enables users to navigate interactive visualizations of related learning goals and to request digital library resources aligned with learning goals. These interfaces are created using a programmatic Web service interface that dynamically generates interactive visual components. Preliminary findings suggest that these library interfaces appear to help users stay focused on the scientific content of their information discovery task, as opposed to focusing on the mechanics of searching.     

A lower bound for computing Oja depth

Let S={s₁,…,sn} be a set of points in the plane. The Oja depth of a query point θ with respect to S is the sum of the areas of all triangles (θ,si,sj). This depth may be computed in O(nlogn) time in the RAM model of computation. We show that a matching lower bound holds in the algebraic decision tree model. This bound also applies to the computation of the Oja gradient, the Oja sign test, and to the problem of computing the sum of pairwise distances among points on a line.     

The 802.11n MIMO-OFDM Standard for Wireless LAN and Beyond

An overview is given of the new IEEE 802.11n standard. This is the first wireless LAN standard based on MIMO-OFDM, a technique pioneered by Airgo Networks to give a significant performance increase in both range and rate relative to conventional wireless LAN. Performance results show that net user throughputs over 100 Mbps are achievable, which is about four times larger than the maximum achievable throughput using IEEE 802.11a/g. For the same throughput, MIMO-OFDM achieves a range that is about 3 times larger than non-MIMO systems. This significant improvement in range-rate performance makes MIMO-OFDM the ideal solution not only for wireless LAN, but also for home entertainment networks and 4G networks. Richard van Nee received the M.Sc. degree in Electrical Engineering from Twente University in Enschede, the Netherlands, in 1990. In May 1995, he received the PhD degree from Delft University of Technology. From 1995 to 2000, he worked for Lucent Technologies Bell Labs on wireless LAN transmission techniques. He was one of the original proposers of the CCK and OFDM modulation techniques which were adopted by the IEEE 802.11b and IEEE802.11a wireless LAN standards. In 2001, he cofounded Airgo Networks that developed the first MIMO-OFDM modem for wireless LAN and which techniques form the basis of the IEEE 802.11n standard. Together with Ramjee Prasad, he wrote a book on OFDM, entitled ‘OFDM for Mobile Multimedia Communications.’ In 2002 he received the Dutch Veder award for his contributions to standardization of wireless communications.     

探讨降低电磁干扰之道

电磁干扰是电子设备和系统设计当中不能回避的问题.电源是把电子设备和电源网络联系起来的部分,因此电源引起的电磁干扰值得认真关注.随着开关稳压器的广泛使用,它越来越多地存在于电子设备中.目前,减轻电磁干扰的方法很多,包括接地、屏蔽和滤波等方式,本文将着重介绍用多相同步和扩展频谱频率调制(SSFM)的方式来降低电磁干扰.     

Energy advantages of microprocessor platforms with on-chip configurable logic

System chips that incorporate configurable logic can reduce the energy consumed in executing software. The key is to use the configurable logic to execute performance-critical loops, producing average energy savings of 25% to 71% for embedded-system benchmarks.     

Effect of AlN and Al2O3 additions on the phase relationships and morphology of SiC Part I Compositions and properties

X-ray diffraction was utilized to follow the transformation from -SiC (3C) to the various -SiC polytypes in the presence of AlN and Al₂O₃ additives after hot pressing from 1700 to 2100°C. The 2H- and 6H-polytypes of -SiC were the predominate polytypes with additions of only AlN or Al₂O₃, respectively. The amount of 2H- and 6H-polytypes, and subsequently the microstructural morphology of the SiC materials, were found to be controlled by varying the amount of AlN and Al₂O₃. Improvements in fracture toughness to 9 MPa-m were achieved with flexural strengths ranging from 600 to 900 MPa. These results suggest that accurate control of the polytypic make-up of SiC-based materials, along with their mechanical properties, can be achieved through AlN and Al₂O₃ additions.     

Pathogenesis of oleic acid-induced lung injury in the rat: Distribution of oleic acid during injury and early endothelial cell changes

Oleic acid-induced lung injury, a well-described laboratory model for acute pulmonary injury in the rat and other species, causes morphologic and cellular changes similar to human adult respiratory distress syndrome (ARDS). Experiments were performed to test the hypothesis that the initial event of oleic acid lung injury is damage of the pulmonary vascular endothelium by oleic acid, with subsequent pulmonary damage and inflammation. Oleic acid levels were followed in the lung and other tissues by measuring accumulation of¹⁴C-oleic acid; the direct effects of oleic acid and other fatty acids on rat endothelial cells, alveolar type II cells, and hepatocytes in culture were determined. Lung tissue from treated rats was also examined by light and electron microscopy for evidence of endothelial cell damage. At 30 min after injury, oleic acid reached high concentrations in lung tissue as demonstrated by presence of radiolabel (3.24×10⁻⁶ moles per gram of tissue), with counts in the lung nearly an order of magnitude greater than in any other organ measured. Oleic acid was present in the lung mostly as free fatty acid (85%), and was also present in the alveolar fluid supernatans, rather than being cell-associated (1.7×10⁻⁷ moles vs. 1.1×10⁻⁸ moles at 30 min). Oleic acid was toxic to endothelial cells after one minute of exposure at concentrations of 5×10⁻⁴M and above. Electron microscopy showed endothelial cell changes as early as 10 min after induction of injuryin vivo, including the presence of endothelial cell blebbing. The results of these studies suggest that the initial event in oleic acid lung injury is damage to the pulmonary vascular endothelial cell.     

New words from old: A formalism for word-formation

Many languages make use of word-formation devices to allow speakers or writers to create new words when the existing vocabulary proves inadequate. In this paper we consider how these devices can be expressed formally, allowing them to be used in word- and sentence-generation, for dictionary expansion, and the like. The paper begins with some typical word-formation rules drawn mostly from French. Attention is drawn to some features of these rules which must be captured in any formal representation. The formal representation of a basic lexical transformation is presented in some detail, along with a number of examples. A computer implementation of the transformation system is described, together with a range of applications. A discussion of static and dynamic generation leads to the concept of an inverted transformation.Michael Levison is Professor and Head of the Department of Computing and Information Science at Queen's University at Kingston. His research interests currently centre on natural language generation and editing systems. He has written many articles on computer applications in literary and linguistic studies.Greg Lessard is an Associate Professor in the Department of French Studies at Queen's University. A linguist, his research interests include computational modelling of natural language performance (including second language learner French and linguistic humour) and computer-aided textual analysis (including repeated string and complex textual structures.)