Heading towards an advanced signalling system for multimedia,multiparty services in broadband ISDN

Introduction of the broadband integrated services digital network (B-ISDN) will enable network users to make use of advanced multimedia, multiparty services. With this aim in view, RACE II project R2044, MAGIC, is investigating long-term signalling requirements, architecture and protocols for B-ISDN. New service concepts are being developed in MAGIC which will provide more flexibility when compared to narrowband ISDN (N-ISDN). The service requirements and other signalling requirements, such as the separation between call and associated connections at the network-node interface, are used to determine the distribution of functions over the network. The signalling protocols which are used to exchange the signalling information are subsequently developed. These signalling protocols are simulated to prove the performance and the feasibility of call handling concepts     

Thermal-Conductivity Characterization of Gas Diffusion Layer in Proton Exchange Membrane Fuel Cells and Electrolyzers Under Mechanical Loading

Accurate information on the temperature field and associated heat transfer rates is particularly important for proton exchange membrane fuel cells (PEMFC) and PEM electrolyzers. An important parameter in fuel cell and electrolyzer performance analysis is the effective thermal conductivity of the gas diffusion layer (GDL) which is a solid porous medium. Usually, this parameter is introduced in modeling and performance analysis without taking into account the dependence of the GDL thermal conductivity λ (in W · m⁻¹ · K⁻¹) on mechanical compression. Nevertheless, mechanical stresses arising in an operating system can change significantly the thermal conductivity and heat exchange. Metrology allowing the characterization of the GDL thermal conductivity as a function of the applied mechanical compression has been developed in this study using the transient hot-wire technique (THW). This method is the best for obtaining standard reference data in fluids, but it is rarely used for thermal-conductivity measurements in solids. The experiments provided with Quintech carbon cloth indicate a strong dependence (up to 300%) of the thermal conductivity λ on the applied mechanical load. The experiments have been provided in the pressure range 0 < p < 8 MPa which corresponds to stresses arising in fuel cells. All obtained experimental results have been fitted by the equation λ = 0.9log(12p + 17)(1 − 0.4e^−50p ) with 9% uncertainty. The obtained experimental dependence can be used for correct modeling of coupled thermo/electro-mechanical phenomena in fuel cells and electrolyzers. Special attention has been devoted to justification of the main hypotheses of the THW method and for estimation of the possible influence of the contact resistances. For this purpose, measurements with a different number of carbon cloth layers have been provided. The conducted experiments indicate the independence of the measured thermal conductivity on the number of GDL layers and, thus, justify the robustness of the developed method and apparatus for this type of application.     

An object-oriented analysis of a BISDN control system with a focus on the UNI protocol object

The control system of a BISDN network will undoubtedly be very complex to design, implement and maintain. Its complexity has led researchers to look for ways of breaking down the problem into smaller and manageable parts. This has motivated the use of an object-oriented approach to analyse and comprehend the BISDN control system. This paper thus presents an object-oriented analysis (OOA) of a BISDN control system. This analysis is based on a method introduced by Coad and Yourdon and comprises five steps. All five steps, namely identifying subjects, identifying objects, identifying structures, defining attributes, and defining operations, will be worked out in detail with an emphasis on the user network interface (UNI) signalling protocol object. Four subjects, nine objects, and three structures are identified in the problem space at hand. This structuring offers a framework to analyse in detail the three aspects, data, structure and dynamic behaviour, of the UNI signalling protocol. A parallel between this approach and the well known approach used by the International Telecommunication Union (ITU) for specifying signalling protocols and contained in Recommendation I.130 is drawn. The Coad and Yourdon OOA approach applied to a BISDN control system can be used for the analysis of different aspects of such systems. This paper focuses on the UNI signalling protocol object which leads to a complete specification. Any protocol resulting from such analysis can be claimed to be object-oriented protocol. This approach offers modularity and thus offers a way of structuring the problem space into identifiable objects and data. Full benefits of object orientation can be gained only in the consistent use of object orientation throughout all steps in the development process. The proposed approach allows one to create libraries of generic procedures which can be reused in specific implementations.     

Improving photovoltaic panel performance via an autonomous air cooling system – experimental and numerical simulations

ABSTRACT

The temperature rise of a PV panel during its functioning is known to induce losses of its performances. We propose to minimise these losses via a simple and autonomous air cooling system composed by a fan activated by the electricity produced by the panel. This fan blows ambient air on the rear face of the panel. Experimental measurements of the current intensity as well as voltage delivered by the panel and its front face temperature ensure the validation of the numerical code. Numerical and experimental results are in good agreement. As the main results of this autonomous cooling, when compared to the uncooled panel situation, the efficiency for harsh climatic condition increases of 29.52% while the panel temperature lowered of 39.29°C. Such results achieved with this quite simple autonomous cooling system on the improvement of the PV panel efficiency suggest interesting economic and commercial arguments.     

Static and Dynamic Tearing of Thin Steel Sheets

This paper presents the energy analysis of static mode III fracture of thin steel sheets. For dynamic tearing studies we used the Charpy test apparatus. Static tearing tests performed on three types of steel sheets indicate that the linear relationship of Mai and Cotterell is valid for specimens with a leg width W up to 30 mm. In the given range, the specific work of fracture _e is determined according to the Mai–Cotterell model. The _e kinetics is studied as a function of the sheet thickness B, radius of curvature , and loading rate V. The modified model includes a linear dependence of versus W. Moreover, we show that variation of the loading rate V from 1 to 300 mm/min has no effect on the specific work of fracture _e. A slight decrease in the dynamic fracture toughness J_0,d has been found.