A survey and taxonomy on virtual data center embedding

The Journal of Supercomputing - Data center network virtualization is being considered as a promising technology to provide a performance guarantee for cloud computing applications. One important...     

Experimental characterization and performance study of an ammonia–water–hydrogen refrigerator

We present in this paper an experimental study of a commercial diffusion-absorption refrigeration machine (DAR) operating on the Platen and Munters cycle. The temperatures at the inlet and outlet of every component of the machine, as well as the cabinet and ambient temperature are measured continuously. The tests are repeated for various electric power inputs to the refrigerator. The global heat transfer coefficient of the cabinet (UA)_cab is determined using both theoretical and experimental methods. This coefficient is found equal to 0.2 W/°C. The global heat transfer coefficient of the evaporator (UA)_evap is deduced using dynamic and steady state methods. This global heat transfer coefficient (UA)_evap is found equal to 0.3 W/°C. Finally the cooling capacity of the unit and the coefficient of performance are evaluated. The heating power supply to the generator necessary to ensure the desired state of this machine is found to be in the range of 35 W–45 W.     

Diffusion coefficient of hydrogen in a Pd-Ag membrane: Effect of hydrogen solubility

The permeabilities of hydrogen through a Pd₇₅-Ag₂₅ membrane have been measured at temperatures ranging from 423 to 573 K and under hydrogen pressure differences ranging from 69 to 256 kPa. From the available literature solubility data a neural network model has been developed in order to simulate the variation of the hydrogen content in the alloy as a function of pressure and temperature. Then, from steady state permeability measurements and calculated solubilities, the diffusion coefficients of hydrogen have been computed. At a given temperature, the diffusion coefficient has been found to decrease with the hydrogen content (0.1 ≤ n = H/M ≤ 0.37). A simple relation is then suggested to predict the variation of the diffusion coefficient on both temperature and hydrogen content. To account for the variation of the diffusion coefficient with n, the integration of Fick's law of diffusion has been performed numerically, resulting in non-linear profile of hydrogen content through the membrane under steady state permeation.     

A comparative study between three sensorless control strategies for PMSG in wind energy conversion system

This paper presents a comparative study of sliding mode, artificial neural network and model reference adaptive speed observers for a speed sensorless permanent magnet synchronous generator (PMSG) in wind energy conversion system (WECS). Wind velocity and position sensorless operating methods for wind generation system using observer are proposed only by measuring phase voltages and currents. Maximum wind energy extraction is achieved by running the wind turbine generator in variable-speed mode. In addition the three speed observers are compared to verify the robustness against parameter variations.     

The SemSPM approach: fine integration of WS-SecurityPolicy semantics to enhance matching security policies in SOA

The lack of semantics in WS-SecurityPolicy standard hampers the effectiveness of matching security policies. To resolve this problem, we present a semantic approach for matching Web service security policies. The approach consists in the transformation of WS-SP into an OWL-DL ontology and the definition of a set of rules which automatically generate semantic relations that can exist between the provider and requestor security requirements. We show how these relations lead to more correct and refined matching of security policies. We also describe the implementation details of our approach and its validation through a real-world use case.     

An EAP-EHash authentication method adapted to resource constrained terminals

In the era of mobile and wireless networks, the growing complexity of end devices and the accentuated tendency towards miniaturization of them raise new security challenges. Authentication is a crucial concern in resource constrained environments, and despite the great number of existing EAP methods, as explained in the article, we are still in need for EAP methods tightly adapted to wireless environments and satisfying heterogeneity of terminals and their limitations of resources. After a first comparative analysis of existing EAP methods, this article presents a new EAP-EHash method (EHash for encrypted hash) that is adapted to the highly vulnerable wireless environment by supporting mutual authentication and session key derivation and offering simplicity, rapidity, and easy-to-deploy features. This EAP-EHash was formally proven to satisfy the claimed security properties, thanks to the AVISPA tool. Implementation of it on an 802.11 testbed platform gave realistic authentication delays averaging 26 ms and thus proved that EAP-EHash is competitive to EAP-MD5 that is known to be the simplest of the EAP methods. Features of EAP-EHash include short execution delays and low bandwidth consumption, and as such, it appears attractive for wireless.     

Short arc duration laws and distributions at low current (<1 A)and voltage (14-42 VDC)

In the automobile industry, safety and comfort equipment require more and more switches which are operated over a wide range of electrical, mechanical and ambient conditions. In the low electrical power range, i.e., near minimum current and voltage, shorts and fluctuating arcing may occur. Using a testing apparatus capable of rapid measurements with high temporal resolution (0.2 ns) we have measured and analyzed arc durations on break in a pure resistive circuit near minimum arc current and voltage Ob exp(I//i_b)]. The lifetime and current intensity of the burst (t_b, i_b) are deduced for various contact materials. In addition, the histogram of arc duration fluctuations is well fitted by multiGaussian distributions centered around a multiple of the burst time. This confirms the burst mechanism and introduces the concept that arc duration values are discrete. On the other hand, the plot of arc occurrence in the first regime clarifies the significance of the minimum arc current (100%) and yields the current limit for arc appearance (0%). Finally, high voltages (14-28-42 V) and inductances (1 μH-10 mH) can produce long arc durations with the result that we may enter into the cathodic arc     

Transition from the anodic arc phase to the cathodic metallic arc phase in vacuum at low DC electrical level

Contact material transfer during arcing in relays has been described in several papers. Transfer from the anode to the cathode has been attributed to the anodic arc phase, and opposite transfer from the cathode to the anode has been attributed to the cathodic arc phase. In a previous paper we showed that the transition from the anodic to the cathodic arc occurs when a break arc becomes longer than a critical arc length, independently from electrical and mechanical parameters. In this paper, we completed our work by using the same breaking apparatus (14 VDC, 40 A) equipped with an arc length control device. We showed that the transition from the anodic to the cathodic arc occurs always at the same critical arc length, independently from the opening speed and the ambient pressure. Through measurements of material transfer in vacuum, we have shown that a cathodic arc in the metallic phase can occur, i.e., that material transfer direction is independent of metallic and gaseous phases. Finally, we showed that it was possible to distinguish the transition from the anodic to the cathodic arc by observing the evolution of the arc spots on the rivets.