Propriétés physico-chimiques et thermodynamiques du système binaire hexamethylphotriamide + eau

Densities, dielectric constants, refractive indices, excess volumes enthalpies of mixing and excess free energies of hexamethylphosphotriamide (HMPT) + water mixtures are reported. The excess thermodynamic functions are negative and show their greatest deviation from ideality near 0,3 mole fraction of HMPT. These data indicate strong interaction between HMPT and water and suggest the existence of complexes of the type: HMPT – n H₂O.     

Potential and limits of water cooled divertor concepts based on monoblock design as possible candidates for a DEMO reactor

In this paper water-cooled divertor concepts based on tungsten monoblock design identified in previous studies as candidate for fusion power plant have been reviewed to assess their potential and limits as possible candidates for a DEMO concept deliverable in a short to medium term (“conservative baseline design”). The rationale and technology development assumptions that have led to their selection are revisited taking into account present factual information on reactor parameters, materials properties and manufacturing technologies.For that purpose, main parameters impacting the divertor design are identified and their relevance discussed. The state of the art knowledge on materials and relevant manufacturing techniques is reviewed. Particular attention is paid to material properties change after irradiation; phenomenon thresholds (if any) and possible operating ranges are identified (in terms of temperature and damage dose). The suitability of various proposed heat sink/structural and sacrificial layer materials, as proposed in the past, are re-assessed (e.g. with regard to the possibility of reducing peak heat flux and/or neutron radiation damages). As a result, potential and limits of various proposed concepts are highlighted, ranges in which they could operate (if any) defined and possible improvements are proposed.Identified missing point in materials database and/or manufacturing techniques knowledge that should be uppermost investigated in future R&D activities are reported.This work has been carried out in the frame of EFDA PPPT Work Programme activities.     

Etude comparative des techniques d’égalisation synchrone et fractionnée pour transmissions numériques par voie hertzienne

The paper presents a comparative study of synchronous and fractionally-spaced equalization techniques, in a multipath fading environment. The outage performance of 64-QAM and 256-qam 140 Mbit/s digital radio systems equipped with linear and decision feedback equalizers is evaluated. Results are given in terms of net fade margin improvement versus flat fade margin. They show that the 2 to 3 dB gain obtained for linear equalizers vanishes with non-linear equalizers.     

CATV in France: Present situation and future directions

Fibre-optic systems have been introduced in France initially in the subscriber loop (fibre to the home) for experimenting switched broadband services (Biarritz opened in 1984) and then, under the Plan Cǎble for CATV/multiservice networks (twelve cities or groups of cities, about 900,000 homes), and as CATV trunks and feeders in 40 other cities or groups of cities (another 4,500,000 homes). This unique experience with fibre in the subscriber loop, albeit slightly premature gives some assurance on the future economic feasibility of the fibre-to-the-home or fibre-to-the-office concepts under development. D2-MAC/packet with smart card access control has been selected as the standard for scrambling/enciphering audiovisual signals on cable and on satellite. The integration of the recent hybrid or fibre broadband TV networks and of their network management systems into the telecommunication networks is still being discussed.     

Updated band model parameters for H2O,CO2, CH4 and CO radiation at high temperature

Statistical narrow-band (SNB) model parameters for H₂O, CO₂, CH₄ and CO, and correlated-k (CK) parameters for H₂O and CO₂ are generated from line by line calculations and recently improved spectroscopic databases in wide temperature and spectral ranges. Results from the new parameters are compared to direct line by line calculations and to results from earlier model parameters [A. Soufiani, J. Taine, High temperature gas radiative property parameters of statistical narrow-band model for H₂O, CO₂ and CO and correlated-k (ck) model for H₂O and CO₂, Int. J. Heat Mass Transfer 40 (1997) 987–991] in terms of band averaged spectral transmissivities, Planck mean absorption coefficients, and total emissivities. The comparisons show first a good agreement between updated SNB, CK and LBL results. Significant improvements on earlier parameters are observed for H₂O and CO₂, especially at very high temperatures and path lengths. Model parameters and computer programs illustrating their implementation are provided as Supplementary data.     

Global approach test improvement using a neural network model identification to characterise solar combisystem performances

Solar CombiSystems (SCSs) are very efficient systems for reducing conventional energy consumption of building but their thermal performances are strongly dependent on the environment where they are installed (type of climate and thermal quality of the building). Currently it is impossible to predict the energy savings generated by a SCS as there is no standard test to characterise SCS performances.Currently, the Short Cycle System Performance Test (SCSPT), based on a 12 days test of the complete SCS on a semi-virtual test bench, is able to predict annual energy savings with a good accuracy, but the performance prediction is limited to only one environment (the building and the climate corresponding with the test).Based on the SCSPT procedure, this paper proposes an improvement of the method by identifying a global SCS model from the test data. Then, the identified model would be able to simulate the tested SCS in any environment and thus to characterise its performances.The proposed model to identify is a “grey box” model, mixing a “White Box” model composed of known physical equations and a “Black Box” model, which is an Artificial Neural Network (ANN). A complete process is developed to train and select a relevant global SCS model from such a test.This approach has been validated through numerical simulations of three detailed SCS models. Compared to those annual results, “Grey Box” SCS models trained from a twelve days sequence are able to predict energy consumption with a good accuracy for 27 different environments. An experimental application of this procedure has been used to characterise a real system.     

Evaluation of four numerical wind flow models for wind resource mapping

A wide range of numerical wind flow models are available to simulate atmospheric flows. For wind resource mapping, the traditional approach has been to rely on linear Jackson–Hunt type wind flow models. Mesoscale numerical weather prediction (NWP) models coupled to linear wind flow models have been in use since the end of the 1990s. In the last few years, computational fluid dynamics (CFD) methods, in particular Reynolds‐averaged Navier–Stokes (RANS) models, have entered the mainstream, whereas more advanced CFD models such as large‐eddy simulations (LES) have been explored in research but remain computationally intensive. The present study aims to evaluate the ability of four numerical models to predict the variation in mean wind speed across sites with a wide range of terrain complexities, surface characteristics and wind climates. The four are (1) Jackson–Hunt type model, (2) CFD/RANS model, (3) coupled NWP and mass‐consistent model and (4) coupled NWP and LES model. The wind flow model predictions are compared against high‐quality observations from a total of 26 meteorological masts in four project areas. The coupled NWP model and NWP‐LES model produced the lowest root mean square error (RMSE) as measured between the predicted and observed mean wind speeds. The RMSE for the linear Jackson‐Hunt type model was 29% greater than the coupled NWP models and for the RANS model 58% greater than the coupled NWP models. The key advantage of the coupled NWP models appears to be their ability to simulate the unsteadiness of the flow as well as phenomena due to atmospheric stability and other thermal effects. Copyright © 2012 John Wiley & Sons, Ltd.     

Dispersion and behavior of hydrogen during a leak in a prismatic cavity

Security is recognized as one of the most important problems facing the wider use of hydrogen and the increased risk of accidental release into the infrastructure. Prismatic cavity design can be represented one of the best solutions for this problem. For this reason, dispersion and accumulation of hydrogen in a prismatic cavity with natural ventilation are computationally investigated by the commercial software FLUENT.     

Investigation of aging mechanisms of high power Li-ion cells used for hybrid electric vehicles

High power lithium-ion batteries need to exhibit long service life to meet targets of automotive applications. This article describes the deep investigation of the so-called VL6P cells, high power lithium-ion cells mass produced by Johnson Controls - Saft (JC-S), in order to understand the root causes of their aging. Cells aged by calendar and cycle life are investigated here compared to fresh cells. Among the results of the different analyses, the most significant is that more active lithium is detected in negative electrode after aging. This tends to indicate that effect of aging is due to increase of positive electrode limitation. Results of this investigation will allow JC-S to continue to improve life of the lithium-ion cells.