用白色LED做背光照明需考虑的事项

在过去几年中,小型彩屏从稀有物品变成了便携式消费电子产品(如手机、PDA和数字照相机)的主流特性。把彩屏集成进小型便携式设备的挑战之一是需要白光作为背光。对于如手提电脑的大型显示屏,通常使用的冷阴极荧光灯(CCFL),但因在其尺寸方面的限制和设计复杂性,很难用于更小型的应用。而白色LED具有优异的光学特性,因此成为小型显示屏背光显示的首选解决方案。此外,白色LED也可以用作键盘的背光。将白色LED与光导相配合,可提供均匀的白色背光。白色LED方案面临的挑战设计师在集成白色LED时所面临的挑战在于有如下几方面。(1) LED具…     

Rainbow smelt population responses to species invasions and change in environmental condition

Invasive species can cause major disruptions in native food webs, yet the impact of species introductions and whether they will become invasive appears to be context-dependent. Rainbow smelt and alewife co-exist as invasive species in the Laurentian Great Lakes and as native species on the Atlantic coast of North America, but in Lake Champlain rainbow smelt is the dominant native forage fish and alewife are invasive. Alewife became abundant by 2007, providing an opportunity to explore the dynamics of these two species in a system where only one is invasive. We used data from a 28-year forage fish survey to compare demographics of rainbow smelt populations in three basins of Lake Champlain with different volumes, nutrient levels, and predator abundances. Rainbow smelt catch-per-unit-effort (CPUE) remained constant in the large, deep Main Lake before and after alewife invaded, but decreased in the two smaller basins. Declines were primarily a result of increased age-0 and age-1 mortality. Predation by top piscivores, system productivity, and competition for resources alone could not explain the patterns in CPUE across the basins. The mechanisms that allow alewife and rainbow smelt to co-exist could be related to system volume and oxythermal habitat availability, and may explain why the two species do not negatively affect each other in the Great Lakes. Summer hypoxia in the smaller basins could force individuals into smaller habitat volumes with higher densities of competitors and cannibalistic adult rainbow smelt. Habitat availability may mediate the impact of invasive alewife on native rainbow smelt.     

ANTARES: The HTR/VHTR project at Framatome ANP

Framatome ANP is developing a very high temperature reactor (VHTR), relying on its previous experience with high temperature reactor concepts, from its participation in the MODUL and the GT-MHR designs. While being a major actor in the nuclear reactor business with proven light water technology, AREVA wishes to be ready to meet the new challenges calling for small grid requirements, high temperature process heat and cogeneration. The Framatome ANP VHTR design for electricity production is based on an indirect cycle coupled to an “off-the-shelf” combined cycle gas turbine. Although direct cycle HTRs are being promoted for their high efficiency, preliminary evaluations show that the Framatome ANP design efficiency is on par with a direct cycle while avoiding power generation system (PGS) developments and keeping the PGS contamination free. Moreover, the nuclear heat source of the indirect cycle could also be used to meet the heat supplies from a standard design for multiple applications.     

Strengthening mechanism of load sharing of particulate reinforcements in a metal matrix composite

A 15 v% SiC particle reinforced Al-2618 matrix composite was selected to study strengthening mechanisms under different heat treatments to produce specimens in hard or soft matrices. The investigation showed that the conventional micro-mechanism models play a minor role in strengthening the composite by further addition of the SiC particles. A load sharing mechanism of the particulate reinforcements is suggested to explain the experimental yield strength increase. An analytical model based on Eshelby equivalent inclusion approach and Mori–Tanaka mean field extension was established by introducing numerical matrix and composite secant moduli to simulate the stress–strain curve of the composite. The same modeling work was also carried out by FEM analysis based on the unit cell model using a commercial ANSYS code. The modeling results by both models on evolution of the load carried by the SiC particles during straining provide strong evidences to back up the strengthening mechanism of the load sharing. However, the modeling work exposes that the load transfer mechanism plays a dominant role only for the composite with hard matrix and the reason for load transfer is mainly the mismatch strain between particulate reinforcement and matrix rather than commonly believed friction at their interfaces. Nevertheless, an experiment was used to estimate average stress level in the SiC particles by observation of the numbers of broken particles in the composite with different strains, which also offers a good support to the modeling work.     

Participatory practices at work

This article discusses workplace participatory practices: the reciprocal process of engaging in and learning through work. The reciprocity between the affordance of the workplace (its invitational qualities) and individuals' engagement in the workplace is proposed as a means of understanding how learning through work proceeds. How workplaces invite individuals or cohorts of individuals to participate in and learn through work can be understood in terms of how they are afforded opportunities to engage in activities and interactions that are central to the values and practices (i.e. continuity) of the work practice. These affordances are shaped by workplace norms, practices and affiliations (e.g. cliques, associations, occupational groupings, employment status) and are often characterised by contestation and inequitable distribution. Access to opportunities for practice, and therefore learning, is directed towards sustaining the work practice and/or the interests of particular individuals and groups. Nevertheless, how individuals engage in and learn from work is also shaped by their agencies, which are a product of their values, subjectivities and identities. These reciprocal processes of participation in workplaces are illuminated through an analysis of the micro-social processes that shape the participatory practices of three workers over a six-month period: a union worker, a grief counsellor and a school-based information technology consultant. The findings illuminate the bases for participation, performance and learning for each of the three workers.     

Suitability of VVC and HEVC for Video Telehealth Systems

Video compression in medical video streaming is one of the key technologies associated with mobile healthcare. Seamless delivery of medical video streams over a resource constrained network emphasizes the need of a video codec that requires minimum bitrates and maintains high perceptual quality. This paper presents a comparative study between High Efficiency Video Coding (HEVC) and its potential successor Versatile Video Coding (VVC) in the context of healthcare. A large-scale subjective experiment comprising of twenty-four non-expert participants is presented for eight different test conditions in Full High Definition (FHD) videos. The presented analysis highlights the impact of compression artefacts on the perceptual quality of HEVC and VVC processed videos. Our results and findings show that VVC clearly outperforms HEVC in terms of achieving higher compression, while maintaining high quality in FHD videos. VVC requires upto 40% less bitrate for encoding an FHD video at excellent perceptual quality. We have provided rate-quality curves for both encoders and a degree of overlap across both codecs in terms of perceptual quality. Overall, there is a 71% degree of overlap in terms of quality between VVC and HEVC compressed videos for eight different test conditions.     

Direct and real-time visualization of the disassembly of a single RecA-DNA-ATPgammaS complex using AFM imaging in fluid

RecA disassembly from circular double-stranded DNA (dsDNA) was studied by atomic force microscopy (AFM) imaging in fluid on a single molecule scale. The RecA/DNA complex was formed in the presence of ATPgammaS, and the disassembly was then initiated by buffer exchange to rinse off ATPgammaS. Performing AFM imaging in fluid allowed direct and real-time visualization of the disassembly of RecA from dsDNA in solution. It was found that RecA disassembly commenced from multiple sites both in deionized water and in buffer; the areas where RecA dissociated showed the appearance of "gaps" in the filamentous structure. RecA further disassembled either through the already existing "gaps" or by generation of new gaps. The disassembly was slower in buffer than in deionized water, suggesting that ions also contribute to the stabilization of the complex. RecA hexamers and monomers were observed in deionized water and in buffer, respectively, during the disassembly process.     

复杂性的增加迫使我们越来越注意可测性问题

1996年左右,我们对微处理器的未来进行了考虑,结论是如果我们参加传统的MHz竞赛的话--最终我们会撞上功率问题这堵墙。于是我们走上了一条不同的路。2001年,我们交付了第一款Power4器件,它使用了多核处理器。这种采用双核设计的芯片(一块芯片上有两个内核)由于实现了程序在两个     

Slow reception and under-citedness in climate change research: A case study of Charles David Keeling,discoverer of the risk of global warming

The Keeling curve has become a chemical landmark, whereas the papers by Charles David Keeling about the underlying carbon dioxide measurements are not cited as often as can be expected against the backdrop of his final approval. In this bibliometric study, we analyze Keeling’s papers as a case study for under-citedness of climate change publications. Three possible reasons for the under-citedness of Keeling’s papers are discussed: (1) The discourse on global cooling at the starting time of Keeling’s measurement program, (2) the underestimation of what is often seen as “routine science”, and (3) the amount of implicit/informal citations at the expense of explicit/formal (reference-based) citations. Those reasons may have contributed more or less to the slow reception and the under-citedness of Keeling’s seminal works.