Evaluating the effects of frame of reference on spatial collaboration using desktop collaborative virtual environments

Spatial collaboration is an everyday activity in which people work together to solve a spatial problem. For example, a group of people will often arrange furniture together or exchange directions with one another. Collaborative virtual environments using desktop PCs are particularly useful for spatial activities when the participants are distributed. This work investigates ways to enhance distributed, collaborative spatial activities. This paper explores how different frames of reference affect spatial collaboration. Specifically, it reports on an experiment that examines different combinations of exocentric and egocentric frames of reference with two users. Tasks involve manipulating an object, where one participant knows the objective (director) and the other performs the interactions (actor). It discusses the advantages and disadvantages of the different combinations for a spatial collaboration task. Findings from this study demonstrate that frames of reference affect collaboration in a variety of ways and simple exocentric-egocentric combinations do not always provide the most usable solution.     

移动WiMAX的发展现状

基于IEEE 802.16-2004及ETSI HiperMAN空中接口标准的WiMAX,正在被证明是一个高性价比的替代有线和DSL服务的固定无线技术.150多次的WiMAX试验及在五大洲的部署,清楚地证明了世界范围内对WiMAX作为固定无线服务技术的接受程度.     

A 3D unsplit-advection volume tracking algorithm with planarity-preserving interface reconstruction

A new volume tracking method is introduced for tracking interfaces in three-dimensional (3D) geometries partitioned with orthogonal hexahedra. The method approximates interface geometries as piecewise planar, and advects volumes in a single unsplit step using fully multidimensional fluxes that have their definition based in backward-trajectory remapping. By using multidimensional unsplit advection, the expense of high-order interface reconstruction is incurred only once per timestep. Simple departures from strict backward-trajectory remapping remove any need for consideration of volume computations involving shapes consisting of non-planar ruled surfaces. Second-order accuracy of the method is demonstrated even for vigorous 3D deformations.     

Transfer formalisms

We discuss some different ideas about the sort of formalism appropriate for translation (more specifically, transfer) that have been explored within Eurotra. The intention is not to evaluate these different ideas, but to outline the issues of general interest and relevance that they raise. Section 1 describes some common assumptions, section 2 describes the different ways they have been interpreted, and section 3 considers some further implications.     

白光LED驱动方案

本文介绍了驱动白光LED的方案和典型应用电路。     

Storage and Feeding Losses of Large Round Bales

Alfalfa was harvested in large round bales or small square bales and storage and feeding losses were determined for different storage methods. Large bales were stored 1) in a barn; 2) outside in single rows and uncovered; 3) outside in two-high stacks and covered; and 4) outside in three-high stacks and covered. These bales were fed to dairy heifers with small square bales for comparison. Dry matter storage losses were 2% for large bales stored inside, 6% for large bales stored outside covered, and 15% for large bales stored outside uncovered. Feeding losses of large bales were 12% for stored inside, 25% for stored outside uncovered, and 13 to 15% for stored outside covered. Total losses for large round bales were 40% (stored outside uncovered), 20% (stored outside covered) and 15% (stored inside). Intake and gains were greatest for small bales (2.35 kg/100 kg body weight and .77 kg/d, respectively) and least for large bales (2.11 kg/100 kg body weight and .54 kg/d) stored outside uncovered.Rain penetrated 10 to 25 cm into uncovered bales stored outside. The resulting weathered hay, about 40% of the original bale dry weight, deteriorated. Heifers rummaged through this unpalatable material, and large feeding losses resulted. Storage and feeding losses of large round bales stored outside are economically important enough to warrant protection of bales.     

Littman光栅外腔可调谐Yb3+双包层光纤激光器

本文对LD泵浦的光栅外腔可调谐双包层Yb3 光纤激光器进行了实验研究．采用Littman外腔结构，研究了Yb3 光纤激光器的调谐特性．输出激光调谐范围42nm，谱线宽度0．08nm，最大输出功率达到了460mW，斜率效率约30％．并对其输出光功率随波长的变化进行了观测和分析．     

Developing habitat associations for fishes in Lake Winnipeg by linking large scale bathymetric and substrate data with fish telemetry detections

Understanding relationships between freshwater fishes and habitat is critical for effective fisheries and habitat management. Habitat suitability indices (HSI) are commonly used to describe fish–habitat associations in rivers and other freshwater ecosystems. When applied to large lakes however, standard sampling procedures are inadequate because of larger sampling areas and an increased risk of fish collection bias through one-time observations. Here, we use lake bathymetry, substrate, and multiple fish telemetry detections collected from a systematically deployed receiver grid to develop HSI for four fish species (lake sturgeon, freshwater drum, common carp, and walleye) in Lake Winnipeg. Seasonal variations in habitat use based on water depth and substrate were observed in three of four species. Lake sturgeon remained in shallow locations with predominantly gravel substrate near the mouth of the Winnipeg River regardless of season. Freshwater drum persisted over fine substrate in both summer and winter but had a broader depth range in the summer compared to winter. Common carp shifted from mid-range depths and silt substrate in the summer to shallow depths and gravel substrate in the winter. Walleye showed an unchanging association to fine substrate but expanded from primarily mid-range depths in the summer to include shallower depths in the winter. These findings show how multiple telemetry detections per fish can be combined with hydroacoustic data to provide informative habitat associations for fishes in a large lacustrine ecosystem.     

The application of coherent optics to the study of adhesive joints. I. Speckle photography

A new technique of coherent optics, speckle photography, has been applied to the study of the behavior of adhesive joints under shear stress. This technique allows the determination of the in-plane motion by a point-by-point analysis with a sensitivity of about 3 μm. This property has been used to measure the interfacial displacement of model glass-glass joints bonded by different types of adhesive when submitted to shear. The experimental results permit direct verification of Volkersen's theory as well as the determination of the actual shear modull of the thin adhesive layer. The simplicity of use and interpretation of the technique of speckle photography should lead to significant application of this method in the future for the study of adhesive joints.     

Transparent,methacrylate-based polymer networks with controlled crosslinker ductility

A series of transparent methacrylate-based crosslinked polymer networks are prepared in which the crosslinker length is controlled as a means to investigate the effects of network ductility on mechanical and ballistic properties. In each network the optical clarity of pure poly(methyl methacrylate) (PMMA) is retained, as well as a low value of haze. Both the glass transition temperature (T_g) and the tensile modulus of the networks are highly tunable, with network values both above and well below that of pure PMMA or the pure crosslinker network. The ballistic performance is likewise affected, with performance values of up to 400% greater than neat PMMA. We examine the effects of the crosslinker molecular weight on the impact performance, finding that, in these systems, the molecular weight between crosslinks is not a driving factor for the impact performance, and this may broadly translate to polymer networks in general. We find that improvements in ballistic performance can be realized at low molecular weight between crosslinks, provided the crosslinking agent is of sufficient ductility.