Electrical contact resistance between stainless steel bipolar plate and carbon felt in PEFC: A comprehensive study

Bipolar plate represents a key component of Proton Exchange Membrane Fuel Cell (PEFC) with several essential functions, among them the electric connection of elementary cells. Usually made of graphite, this component is studied worldwide in order to develop a commercially viable alternative: different ways have been being investigated, and to date, despite corrosion issues, stainless steel (SS) appears as a good candidate material, but its Electrical Contact Resistance (ECR) can reach unacceptable values when exposed to PEFC environment. This paper offers a comprehensive study of the parameters acting on ECR when using uncoated SS in PEFC: roughness, which influences the surface contact area with carbon baking, bulk composition of the alloy, which influences only partly the nature of passive films, and the composition and structure of passive films, strongly modified by surface treatments and ageing conditions.     

The effect of a scattering layer on the edge output of a luminescent solar concentrator

The effect of adding white scattering layers to the bottom side of luminescent solar concentrator waveguides is evaluated. It is determined that adding a rear scatterer separated from the waveguide by an air gap results in a large increase of energy output from the waveguides, and this enhancement persists over long (>30 cm) distances, although the magnitude of the enhancement decreases with distance. An attached scatterer resulted in the greatest improvement of light output for short (∼6 cm) distances, but actually reduced edge emissions over longer distances. We provide estimates for the relative contribution of dye-emitted light and scattered light to the total waveguide emission, as well as distinguishing between the contributions of direct and indirect scattering of light to the total output as a function of dye content of the waveguides.     

A hierarchical approach for planning a multisensor multizone search for a moving target

This paper deals with a well-known problem in the general area of search theory: optimize the search resources sharing so as to maximize the probability of detection of a (moving) target. However, the problem we consider here considerably differs from the classical one. First, there is a bilevel search planning and we have to consider jointly discrete and continuous optimization problems. To this perspective original methods are proposed within a common framework. Furthermore, this framework is sufficiently general and versatile so as to be easily and successfully extended to the difficult problem of the multizone multisensor search planning for a Markovian target.     

RFID behavior study in enclosed marine container for real time temperature tracking

The performance of radio waves in open environments has been studied for years. In contrast, the behavior of Radio Frequency Identification (RFID) inside metal enclosed areas is not yet understood. This research project focuses on the 3-D mapping of RFID signal strength inside a 12 m refrigerated marine container instrumented with three different types of radio frequency (RF) emitters: 915 MHz reader; 2.45 GHz reader and 433 MHz RF transmitter. The main goal is to find a frequency/configuration that would allow real time reading of the temperature in a shipment of perishable products using RFID. Only one frequency and one antenna were used at a time. The RF transmitter antenna was mounted at two different places inside the container; at the top of the front wall (facing back) and on the ceiling in the middle of the container (facing down). The signal strength was acquired by a spectrum analyzer and its antenna was mounted on a small electric cart inside the container. The cart was programmed to move along the length of the container and stop repeatedly, allowing three automated measures per position. All data were analyzed in terms of power level and attenuation. The maps showed that the RFID antenna positioned at the front of the container delivered slightly better results than the one in the middle of the ceiling. The results showed a significantly higher performance at the 433 MHz level. This article was presented at Food Processing Automation Conference, American Society of Agricultural and Biological Engineering (ASABE), Providence, RI, June 28–29 2008.     

A Functional Programming Framework for Latency Insensitive Protocol Validation

Latency insensitive protocols (LIPs) have been proposed as a viable means to connect synchronous IP blocks via long interconnects in a system-on-chip. The reason why one needs to implement LIPs on long interconnects stems from the fact that with increasing clock frequencies, the signal delay on some interconnects exceeds the clock period. Correctness of a system composed of synchronous blocks communicating via LIPs is established by showing latency equivalence between a completely synchronous composition of the blocks, and the LIP based composition. A design flow based on a synchronous composition specification, and stepwise refinement to LIP composition can be easily conceived, and a proof obligation to show latency equivalence between the synchronous specification and the refinement needs to be discharged. In this work, we propose a functional programming based framework for modeling and simulating LIP, and implement the semantics of various refinement steps in the programming model, so we can validate the LIP model against the original system within this functional programming framework. Such validation becomes easier due to the inherent denotational model of functional languages. We specifically use Standard ML to model the original system implementation as well as its latency insensitive version and compare the two by creating a model that contains both, giving them the same inputs and checking their outputs to be latency equivalent.     

Réflexion libre à travers ľATM paragraphs on ATM

Fifteen years after its first tentative steps in the laboratory, ATM seems to have reached the thankless age of confrontation with the reality of operational networks while others would say the age of potential to fulfil and promises to keep. The following article does not pretend to be an in-depth technical analysis of a particular aspect or development of ATM but rather the thoughts of a witness to a number of past, present and future issues. The objective is much more to stimulate thought on ATM than to provide definitive answers to often difficult questions.     

Arachidonic acid autoxidation in an aqueous media effect of α-tocopherol,cysteine and nucleic acids

The autoxidation of arachidonic acid dispersed in aqueous media was evaluated simultaneously with and without different agents, e.g., α-tocopherol at different concentrations, cysteine, DNA and RNA. The autoxidation rate of arachidonic acid was evaluated by quantitative gas liquid chromatography (GLC) determination of the unoxidized acid and by spectrophotometric measurement of conjugated dienes. α-Tocopherol exhibited a prooxidant activity at concentrations of 1.25 × 10⁻⁴ M and 1.25 × 10⁻⁵ M and a weak antioxidant activity at a concentration of 1.25 × 10⁻⁶ M. Cysteine showed antioxidant activity and greatly reduced the prooxidant activity of α-tocopherol. DNA and RNA had no effect in either case. α-Tocopherol oxidation was followed by high pressure liquid chromatography (HPLC). The prooxidant effect was accompanied by a rapid oxidation of α-tocopherol, except in the presence of cysteine, which prevented the oxidation of α-tocopherol.     

ATM: A contribution to the debate on broadband ISDN

The definition of broadband ISDN recently became a major topic of research and predevelopments. Fast packet technologies are widely recognized as the basis for BISDN. Even if international consensus has appeared far more quickly than could have been expected a few years ago, a lot of issues remain open. This paper is a contribution to discussions on some important topics relating to the definition of asynchronous transfer mode.     

Application du concept d'echelles multiples a l'ecoulement dans une turbomachine axiale

An asymptotic theory to the flow in an axial compressor is presented with the aim of devising a coupling process between the so-called meridian through flow and the flow around cascades. The small parameter ? is the inverse of the (supposed ? 1) number of blades per row and/or number of stages. As a matter of fact, the cascade flow is treated as a small perturbation of the through flow and has to be computed, locally, as the two dimensional unsteady flow around an array of couples of cascades alternately fixed and in motion. The array is constructed by developing on a plane the section of the compressor by a circular cylinder, and continuing by periodicity, the couple of cascades, so obtained, at each location. The coupling between through flow and cascade flow is part of the analysis. It occurs by the way that the equations of through flow are obtained through an averaging process, completed on a domain of periodicity of the array of cascades, while the through flow appears, locally, as an unperturbed flow for the linearized problem defining the cascade flow. The tridimensional nature of the complete flow is built in by the coupling itself, as is visualized by the occurence of source terms in each of the two sets of equations describing through flow and cascade flow. This paper is aimed at giving a preliminary answer to the question of how to devise an, as rational as possible, way of inscribing the familiar scheme of cascade flow within the computation of a mean through flow. The main output is that the concept of cascade flow should be revisited and reassessed as one of unsteady flow around an array of cascades.