Design of fault-tolerant large-scale VOD servers: With emphasis onhigh-performance and low-cost

Recent technological advances in digital signal processing, data compression techniques, and high-speed communication networks have made Video-on-Demand (VOD) servers feasible. A challenging task in such systems is servicing multiple clients simultaneously while satisfying real-time requirements of continuous delivery of objects at specified rates. To accomplish these tasks and realize economies of scale associated with servicing a large user population, a VOD server requires a large disk subsystem. Although a single disk is fairly reliable, a large disk farm can have an unacceptably high probability of disk failure. Furthermore, due to real-time constraints, the reliability requirements of VOD systems are even more stringent than those of traditional information systems. Traditional RAID solutions are inadequate due to poor resource usage. Thus, in this paper, we present alternative schemes which provide a high degree of reliability at low disk storage, bandwidth, and memory costs for on-demand multimedia servers. Moreover, we discuss some of the main issues and trade-offs associated with providing fault tolerance in multidisk VOD systems. We would like to impress upon the reader that one of the main points of this paper is the exposition of trade-offs and issues associated with designing fault-tolerant VOD servers. It is not the case that one fault tolerance scheme is absolutely better than another, but rather that one must understand the trade-offs as well as one's system constraints and then choose a fault tolerance scheme accordingly     

改进遗传算法搜索性能的研究

本文针对改进遗传算法的搜索性能,提出了一种新的变异算子－自适应多位变异算子,它根据每一代的每一个体在当代中的优劣程度,自适应地控制其发生变异的位数。适应度差的个体变异的位数多,一方面使差的模式生存机会少,另一方面增加了种群的多样性,同时也扩大了搜索范围。我们用模式定理证明了该算子的有效性,并且我们作的仿真实验也同样表明该算子能大大改进遗传算法的搜索性能。     

Usability engineering for augmented reality: employing user-based studies to inform design

A major challenge, and thus opportunity, in the field of human-computer interaction and specifically usability engineering is designing effective user interfaces for emerging technologies that have no established design guidelines or interaction metaphors or introduce completely new ways for users to perceive and interact with technology and the world around them. Clearly, augmented reality is one such emerging technology. We propose a usability engineering approach that employs user-based studies to inform design, by iteratively inserting a series of user-based studies into a traditional usability engineering lifecycle to better inform initial user interface designs. We present an exemplar user-based study conducted to gain insight into how users perceive text in outdoor augmented reality settings and to derive implications for design in outdoor augmented reality. We also describe lessons learned from our experiences conducting user-based studies as part of the design process.     

Cross-Layer Optimization for State Update in Mobile Gaming

In a large-scale mobile gaming environment with limited wireless network bandwidth, efficient mechanisms for state update are crucial to allow graceful real-time interaction for a large number of players. By using the state updating threshold as a key parameter that bridges the resulting state distortion and the network traffic, we are able to study the fundamental traffic-distortion tradeoffs via both theoretical modeling and numerical analysis using real game traces. We consider a WiMAX link model, where the bandwidth allocation is driven by the underlying physical layer link quality as well as application layer gaming behaviors. Such a cross-layer optimization problem can be solved using standard convex programming techniques. By exploring the temporal locality of gaming behavior, we also propose a prediction method for on-line bandwidth adaptation. Using real data traces from a multiplayer driving game, TORCS, the proposed network-aware bandwidth allocation method (NABA) is able to achieve significant reduction in state distortion compared to two baselines: uniform and proportional policies.     

DALICA: Agent-Based Ambient Intelligence for Cultural-Heritage Scenarios

Villa Adriana is an enormous archaeological area where ancient artifacts and modern technology have found an unexpected equilibrium. The old artifacts are huge stone monuments; the modern technology includes PDAs and signals from the Galileo satellite combined with intelligent software agents. As part of the European CUSPIS project (Cultural Heritage Space Identification System, www. cuspis-project.info), we exploited intelligent agents for two ambient-intelligence scenarios applicable to Villa Adriana. One scenario involves cultural assets fruition-the possibility of accessing and enjoying cultural assets. This scenario concerns the dissemination of information about cultural assets; for example, users can visit a museum or archaeological site and receive on their mobile devices appropriate, personalized information about that place. The other scenario involves cultural assets monitoring, which concerns securely transporting cultural assets from the owner organization to a renter organization and back.     

Wavelet-based deconvolution

A fast computational algorithm for deconvolution of signals in the form of peaks with exponentially falling fronts in the presence of noise is proposed. The filter bank coefficients are constructed on the basis of new wavelets called quasi-wavelets, which are derived from the instrument’s pulse response (instrument function) or similar functions defined analytically. A regularization procedure is offered based on selecting the sampling interval of the observed signal and the smoothing parameter of the restoring filter. This method ensures separation of completely overlapping peaks (without any noticeable saddle between them). The systematic error of restoration with an exactly known instrument function is a few tenths of a percent at three-to fourfold noise suppression.     

A technique for measuring charges of relativistic nuclei in a nuclear emulsion on the PAVICOM automated facility

A technique for measuring the charges of relativistic nuclei in thick emulsion layers irradiated in a longitudinal direction is described. This technique has been implemented on the PAVICOM completely automated facility at the Lebedev Physical Institute. The calibration curves for relativistic nuclei with Z > 3 are presented. The advantages of this technique are demonstrated using charge measurements of ²⁸Si nuclear fragments as an example.     

Rhodium coated mirrors deposited by magnetron sputtering for fusion applications

Metallic mirrors will be essential components of all optical spectroscopy and imaging systems for ITER plasma diagnostics. Any change in the mirror performance, in particular, its reflectivity, due to erosion of the surface by charge exchange neutrals or deposition of impurities will influence the quality and reliability of the detected signals. Due to its high reflectivity in the visible wavelength range and its low sputtering yield, rhodium appears as an attractive material for first mirrors in ITER. However, the very high price of the raw material calls for using it in the form of a film deposited onto metallic substrates. The development of a reliable technique for the preparation of high reflectivity rhodium films is therefore of the highest importance. Rhodium layers with thicknesses of up to 2 microm were produced on different substrates of interest (Mo, stainless steel, Cu) by magnetron sputtering. Produced films exhibit a low roughness and crystallite size of about 10 nm with a dense columnar structure. No impurities were detected on the surface after deposition. Scratch tests demonstrate that adhesion properties increase with substrate hardness. Detailed optical characterizations of Rh-coated mirrors as well as results of erosion tests performed both under laboratory conditions and in the TEXTOR tokamak are presented in this paper.     

Fabrication of planar cobalt electrodes separated by a sub-10nm gap using high resolution electron beam lithography with negative PMMA

We present a fabrication process of cobalt nanoelectrodes compatible with spin-dependent transport measurements through a few or a single nano-object. It consists in etching a cobalt thin layer into pairs of planar nanoelectrodes separated by a nanometric gap using a negative Poly-MethylMethAcrylate (PMMA) mask patterned by high resolution electron beam lithography (HREBL). The irradiation parameters of 200keV HREBL on PMMA have been investigated using atomic force microscopy (AFM) to define accurately the PMMA transformation from positive to negative tone. The influence of the electron dose and the designed gap on the final gap between electrodes is presented. This complete study proves that PMMA can be used as a HREBL negative resist to fabricate nanoelectrodes separated by a controlled and reproducible gap ranging from 5nm to several tens of nanometers.