Study of 18-cm long single-sided AC-coupled silicon microstripdetectors

The SSC GEM silicon Central Tracker design incorporated 18-cm long single-sided AC-coupled silicon microstrip ladders. Compared to the 12-cm long ladders considered in the preliminary stages of the tracker design, the 18-cm long ladders have the advantage of reduced cost, channel count and overall power consumption, and led to a simplified tracker assembly. However, such long ships also present the challenge of maintaining satisfactory performance. The increased capacitance and series resistance contribute to lower signal-to-noise ratios, longer time walk, higher power consumption per channel and increased probability of crosstalk to neighboring channels. In this paper, an accurate method to calculate the geometric capacitance of the AC-coupled microstrips is presented and the calculated results are compared with measurements, SPICE simulations are performed to predict the noise, the extent of interstrip capacitive coupling and the dispersion of the detector signal due to the finite series resistance of the metal strips and the long length of the detector. The influence of the preamplifier current and the shaping time on the signal and noise levels is also presented. The study concludes that the 18-cm long ladders can successfully satisfy the performance goals of the GEM silicon Central Tracker     

Temperature distributions in air-conditioned rooms

This paper contributes to a better understanding of the parameters which influence the thermal comfort achievable in an air-conditioned room. First, simplified relationships were established to enable a study to be made of the temperature distribution using reduced scale models. A prototype and a 0·3 scale model were constructed. An experimental technique for measuring the air temperature at various points in the two rooms was then established. Experiments to test the validity of the similarity criteria were next carried out.A study was then made, for various supply conditions, of the temperature distribution in a room heated by blown hot air. In this way it was shown that the Archimedes number could be considered a characteristic number for the room air supply. The limit values required for good thermal comfort in a given room were established in this way.The differing results obtained should facilitate temperature distribution forecasting in air-conditioned rooms.     

Study of a new concept of photovoltaic–thermal hybrid collector

This work represents the second step of the development of a new concept of photovoltaic/thermal (PV/T) collector. This type of collector combines preheating of the air and the production of hot water in addition to the classical electrical function of the solar cells. The alternate positioning of the thermal solar collector section and the PV section permits the production of water at higher mean temperatures than most of existing hybrid collectors. These higher temperatures will allow the coupling of components such as solar cooling devices during the summer and obviously a direct domestic hot water (DHW) system without the need for additional auxiliary heating systems. In this paper, a simplified steady-state two-dimensional mathematical model of a PV/T bi-fluid (air and water) collector with a metal absorber is developed. Then, a parametric study (numerically and experimentally) is undertaken to determine the effect of various factors such as the water mass flow rate on the solar collector thermal performances. Finally, the results from an experimental test bench and the first simulation results obtained on full scale experiments are compared.     

Small signal gain of free electron lasers with nonuniform wigglers

The small-signal gain of free electron lasers is calculated by solving the single-electron equations of motion to second order in the laser field. Analytic results for free electron lasers with linearly varying wiggler resonant frequency show that the small signal gain of such lasers behaves differently from that of lasers with uniform wiggler resonant frequency and is significantly smaller.     

Hydrogen for oil refining via biomass indirect steam gasification: energy and environmental targets

The energy and CO₂ consequences of substitution of a fossil-fuel-based hydrogen production unit with a biomass-based process in a large European refinery are studied in this study. In the base case, the biomass-based process consists in atmospheric, steam–blown indirect gasification of air-dried woody biomass followed by necessary upgrading steps. The effect of gradually substituting the current refinery hydrogen production unit with this process on global energy and CO₂ targets is estimated first. Few process concepts are studied in further detail by looking at different degrees of heat integration with the remaining refinery units and possible polygeneration opportunities. The proposed process concepts are compared in terms of energy and exergy performances and potential reduction in refinery CO₂ emission also taking into account the effect of marginal electricity. Compared to the base case, an increase by up to 8 % points in energy efficiency and 9 % points in exergy efficiency can be obtained by exploiting process integration opportunities. According to energy efficiency, steam production appears the best way to use excess heat available in the process while electricity generation through a heat recovery steam cycle appears the best option according to exergy efficiency results. All investigated cases yield to significant reduction in CO₂ emissions at the refinery. It appears in particular that maximal emission reduction is obtained by producing extra steam to cover the demand of other refinery units if high efficiency marginal electricity scenarios are considered.     

Experimental and numerical study of a full scale ventilated enclosure: Comparison of four two equations closure turbulence models

Full-scale experimental and computational fluid dynamics (CFD) methods are used to investigate the velocity and temperature fields in a mechanically ventilated enclosure. Detailed airflow fields are measured in three cases of ventilation air temperature: an isothermal case, a hot case and a cold case. The ventilation system creates an axisymmetric jet which is developing near the ceiling. The experimental data are used to test four two equations turbulence models: a k–ε realizable model, a k–ε RNG model, a k–ω model and a k–ω SST model. It is found that, even if the models can predict reasonably the hot and isothermal cases global values of temperature and velocity, none of the models is reliable concerning the cold case. Moreover, a detailed analysis of the jet shows that none of the models is able to predict the exact experimental velocity and temperature fields.     

Electrical properties of new organic composites obtained by mechanochemical synthesis

We present new results on organic semiconductive and metallic composites obtained by direct solid-solid charge-transfer (CT) reaction. By this method, samples of arbitrarily large size are readily achievable. In the present study, we consider composites formed from the reaction between the following pairs of donors and acceptors: TTF and iodine, BEDT-TTF and TCNQ, BEDT-TTF and TCNE, BEDT-TTF and AuI as well as BEDT-TTF and AuI₃. Most of the composites show semiconducting properties only. Two of them, however, (BEDT-TTF)/(AuI) and (BEDT-TTF)₂/(AuI₃), exhibit a metallic behavior.     

Biomass-based hydrogen for oil refining: Integration and performances of two gasification concepts

In this work, two biomass-to-hydrogen concepts are designed and their integration with a large European refinery is investigated. One concept is based on indirect, atmospheric steam gasification while the second is based on pressurized direct oxygen-steam-blown gasification. The technologies chosen for gas cleaning, upgrading and hydrogen separation also differ in the two concepts. Heat integration and poly-generation opportunities are identified by means of process integration tools and four system configurations are identified. These are compared in terms of energy and exergy performances and potential for reduction of fossil CO₂ emissions at the refinery. It is found that the performance of the biomass-to-hydrogen concepts can be improved by up to 11% points in energy efficiency and 9% points in exergy efficiency. The design based on indirect gasification appears the most efficient according to both energy and exergy efficiencies. All configurations yield potential significant reductions of fossil CO₂ emissions at the refinery.     

Caractérisation thermique des parois en régime variable des températures. Mesure des facteurs de réponse

Résumé Cette étude présente une problématique expérimentale de détermination des caractéristiques thermophysiques des parois de batiments en régime variable des températures. Après avoir décrit les grandes orientations de recherche en matière de simulation numérique des batiments, les auteurs expliquent pourquoi, dans certains cas, on se trouve confronté obligatoirement à l'expérimentation pour accéder aux caractéristiques thermophysiques des parois. Ce problème posé, ils développent un schéma méthodologique expérimental qui leur permet, progressivement, d'atteindre la connaissance des facteurs de réponse des parois à forte hétérogénéité de constitution physique. Le montage expérimental est présenté avec des précisions sur ses différentes parties, le matériel et les techniques mises en œuvre pour remédier aux problèmes classiques de régulation de signaux ou de stabilité des ambiances thermiques. On montre, en particulier, comment les questions relatives aux coefficients d'échanges thermiques ont été réglées et les incertitudes sur la mesure qui y sont liées. Les facteurs de réponse sont mesurés pour trois parois de 1 m²: paroid de PVC (e=3 cm), paroid de platre (e=6 cm) et paroi de particules de bois pressées extrudée (e=3,4 cm). Les deux premières, considérées comme homogènes, ont permis de caler le modèle théorique. La troisième met en évidence la pertinence du montage par son hétérogénéité. Ces premières mesures sont alors présentées comme un support de discussion sur deux questions expérimentales importantes auxquelles les auteurs donnent une amorce de réponse: la qualité du signal impulsionnel (nécessité d'un signal pur?) et la nature des séries de facteurs de réponse mesurés (facteurs ambiance-ambiance ou surface-surface). Les auteurs terminent sur les perspectives de développement de telles mesures et la nécessité de passer à une échelle supérieure.

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Summary This study presents an experimental approach to the problem of determining the thermal and physical characteristics of building walls under variable temperature states. Having described the principal research approaches to numerical simulation of buildings, the authors explain why, in certain cases, there is a compulsory need for testing to define the thermal and physical characteristics of walls. Once this problem raised, they develop a methodical testing scheme with which it is progressively possible to identify the response factors of walls of pronounced heterogeneousness from the physical point de view. The test arrangement is presented with the essential details on the various parts, the equipment and techniques used to remedy classical problems of signal regulation or stability of thermal environments. Particular emphasis shows how questions concerning thermal exchange coefficients have been answered in spite of the uncertainty in the measurement involved. The response factors are measured for three walls of 1 m² surface area: a PVC wall 3 cm thick, a gypsum plaster wall 6 cm thick and an extruded compressed chipboard panel 3.4 cm thick. The theoretical model fit was based on the first two considered homogeneous. The heterogeneousness of the third underlines the relevance of the test arrangement. These preliminary measurements are then presented as a basis for discussion on two important experimental questions to which the authors give the beginning of an answer: the quality of the impulse signal (need for a pure signal) and the type of series of response factors measured (environment-environment or surface-surface). In closing the authors outline the development perspective of such measurements and the necessity for pursuing work on a larger scale.

     

Excitation nonlinearities in emission reabsorption laser-induced fluorescence techniques

The effects of the nonlinear behavior of fluorescent intensity with excitation intensity on emission reabsorption laser-induced fluorescence (ERLIF) are investigated. Excitation nonlinearities arise mainly as a consequence of the depletion of the ground-state population stemming from the finite lifetime of molecules in the excited state. These nonlinearities hinder proper suppression of the excitation intensity information in the fluorescence ratio, degrading measurement accuracy. A method for minimizing this effect is presented. This method is based on the approximation of the fluorescence intensity nonlinearities by a power law. Elevating the two-dimensional fluorescent intensity maps to the appropriate exponent allows for proper suppression of excitation intensity in the fluorescence ratio. An overview of the principles and constitutive equations behind ERLIF film-thickness measurements, along with a characterization of the fluorescence's nonlinear behavior, is presented. The power law approximation and processing scheme used to mitigate this behavior are introduced. Experimental proof of the validity of the approximation and processing scheme is provided.