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     

Validation of Solids Suspension Viscosity Measurements Using Computational Fluid Dynamics

Accurately measuring the viscosity of a solids suspension requires uniform suspension of the solids in the viscometer cup. In a cup‐and‐impeller viscometer system, solids may settle when the impeller speed is too low, causing viscosity measurements to appear lower than that of a well‐suspended slurry. Pre‐mixing of a solids suspension is typically performed to achieve steady state prior to measurements. Data here shows that the measured viscosity values differ depending on the pre‐mixing speed, indicating that the solids are not properly suspended at all speeds. A commonly used cup‐and‐vane impeller system can be thought of as a mixing tank that should operate above the uniform‐suspension speed (USS), although determining the USS experimentally is rather subjective. Computational fluid dynamics (CFD) is employed here to determine the USS of a pretreated corn stover (PCS) solids suspension and to confirm the experimentally measured USS.     

换了时空 一起怀旧

这座庭院,是律师Richard J.Urowsky在纽约曼哈顿西村的一座私人花园。在翻修过住宅后,在毗邻街道和住宅后面的两块空地上,Richard便萌生了修建两座花园的想法,使其成为一处舒适的室外场所。     

Sex- and site-dependent variations in the thickness and mechanical properties of human skin in vivo

A new method for the in vivo characterization of the physical properties of skin is presented. This comprises an ultrasound device to measure the vertical displacement of the surface of the skin, as well as its thickness and that of the hypodermis under suction. In combination with this, a mathematical model is used to calculate the following skin parameters: Young's modulus, the initial stress and an index of non-elasticity. These parameters were evaluated from the volar forearm and the forehead of 30 male and 30 females, of similar ages (28 +/- 6-years-old). The sensitivity of the testing procedure, allowing the characterization of the mechanical parameters of the skin, easily differentiated these two sites, and in some cases, differences between women and men were demonstrated. The main results showed for both sexes that the thickness (P = 0.0001), Young's modulus (P = 0.0001), and the index of non-elasticity (P = 0.0001) were greater for the forehead than for the ventral forearm, but that the initial stress was lower (P = 0.0001). The results show that the skin is thicker, stiffer and less tense and elastic on the forehead than on the ventral forearm, suggesting structural differences between these two sites (collagen fibre network, elastic fibres, epidermis, stratum corneum, microvascularization, actinic damage, presence of sebaceous glands, etc.). It is hoped that this device will be useful for the evaluation of certain skin disorders (scleroderma, Ehlers-Danlos syndrome, cutis laxa, oedema, etc.) and their therapy, as well as being a useful tool in skin ageing and cosmetic product assessment.     

Prototyping synchronous group applications

Cooperative team-based activities are changing the nature of work. Current frameworks provide the necessary base communication and coordination tools but require application designers to handle low-level details such as defining a communication protocol. They also provide limited support for prototyping such applications and experimenting with alternative designs. We introduce a sharing style called strong sharing. Its implementation in Object World insulates application designer from low-level communication details. CoSARA, a system built on Object World, lets application designers prototype synchronous group applications by graphically specifying the multiuser interactions. After we describe strong sharing, we describe Object World and how it facilitates building synchronous group applications. Then we describe the CoSARA design methodology for prototyping synchronous group applications and show how we used it to build a multiuser block diagram editor     

Definition of encapsulation barrier requirements: A method applied to organic solar cells

To reach sufficient lifetime for commercial applications, organic solar cells (OPV) require encapsulation with a low permeability barrier material toward atmosphere oxidizing agents, specifically water. Moreover, barrier materials should have the same driving aspects as organic devices like transparency, flexibility and low cost processing techniques such as coating or lamination. The generally admitted value of 10^?6 g m^?2 day^?1 for water vapor transmission rate (WVTR) derived from OLED technology should not be considered as an applicable golden rule and some recent studies demonstrate that OPV cells can be protected with medium barrier materials with a WVTR of around 10^?3 g?m^?2 day^?1. This improved stability is mainly related to the development of new cell architectures. However, a global barrier requirement cannot be defined, but has to be on one hand established in direct relationship between intrinsic stability of the device and on the other hand on the targeted lifetime and operating conditions. In this study, we applied a method to define rapidly the barrier requirement of two OPV cell types named classical and inverted structures. This method combines barrier measurements of encapsulating materials with accelerated lifetime experiments of encapsulated cells and enables to establish the barrier levels necessary to ensure the protection of a given device depending on the intrinsic stability and targeted lifetime.     

Predicting unit performance by assessing transformational and transactional leadership.

How do leadership ratings collected from units operating under stable conditions predict subsequent performance of those units operating under high stress and uncertainty? To examine this question, the authors calculated the predictive relationships for the transformational and transactional leadership of 72 light infantry rifle platoon leaders for ratings of unit potency, cohesion, and performance for U.S. Army platoons participating in combat simulation exercises. Both transformational and transactional contingent reward leadership ratings of platoon leaders and sergeants positively predicted unit performance. The relationship of platoon leadership to performance was partially mediated through the unit's level of potency and cohesion. Implications, limitations, and future directions for leadership research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An ultrasonic array-based system for real-time inspection of carbon-epoxy composite plates

A real-time ultrasonic imager operating at a frequency of 3.5 MHz to test composites in immersion has been developed. It is based on linear array transducers and provides either B-scan or transmission images of composite plates of a few centimeters thickness. The electronic scanning has a pitch of 1.25 mm and an amplitude of 80 mm, and the electronic focusing as well as the acoustic lens on the arrays are set to work at a depth of 40 mm in water. Tests made on composite and plastic plates of 5 to 17 mm thickness show that the system allows the detection of different types of defects and that the interpretation of the ultrasonic signals can be performed on line.