About the equivalent radiative temperature for clear skies

The cold sky radiation constitutes a heat sink mainly used for passive cooling systems. The usefulness of this resource is commonly expressed in terms of the equivalent sky temperature T_c, whose accurate determination still remains as an interesting problem. Increasing the number and the diversity of the observations is necessary. An inexpensive pyrradiometer, made for that purpose, is described here. In addition, analysis of five years of observations with the Carpentras pyrradiometer (National Meteorology) lead us to propose a formulation for T_c which points out the influence of the boundary layer.     

Application of UVP within Porous Beds

Standard measurement devices do not normally provide detailed information about flows in porous media because either they are too intrusive (e.g., hot/film wire anemometers) or because the solid phase impedes their physical access to the flow as in the case of laser Doppler anemometers or particle image velocimetry (PIV). In this study, a Metflow ultrasonic velocity profiler (UVP) is used to measure instantaneous velocity fields within porous media composed of plastic balls packed in a cubic pattern. Simple considerations of the ultrasound beam properties and propagation, plus a comparison with measurements performed by a PIV system, demonstrate that UVP devices are suitable for such a purpose.     

Severe and early alteration of action potential during acute cardiac rejection in rats

INTRODUCTION: Alteration of cardiac action potential and its adaptation to heart rate could contribute to cardiac dysfunction and arrhythmias during acute cardiac rejection. METHODS AND RESULTS: Heterotopic heart transplantation was performed in allogeneic and syngeneic rats in which the action potentials of right and left ventricles were measured at 1, 2.5, 3.3, and 5.7 Hz successively using standard microelectrode techniques and compared with nontransplanted hearts. For each frequency, we measured action potential amplitude, action potential duration, transmembrane resting potential, and Vmax. In the right ventricle, at 1 Hz in the presence of rejection (n = 40), a significant increase was observed in action potential duration at 20%, 50%, and 70% repolarization (82.5%, 75.6%, and 70.8%, respectively) and in action potential amplitude (+17.9 mV), and the resting potential was decreased (-5.3 mV). A lack of adaptation of action potential duration to the driving frequency was observed in the rejecting heart group in contrast to controls (n = 20) and nonrejecting hearts (n = 13). Similar results were observed in the left ventricle and surprisingly in the native hearts (n = 11) of recipients with allografted rejecting hearts in the abdominal position. CONCLUSION: Action potential and its adaptation to the driving frequency is considerably altered during acute rejection. A humoral factor could contribute to cardiac dysfunction.     

Concrete damage evolution analysis by backscattered ultrasonic waves

In the case of in situ non-destructive evaluation of concrete, the one side access and the lack of knowledge of structure depth often increase the difficulties to control the material. The backscattered ultrasonic waves' exploitation can be a solution. Scatterers present in the medium return information resulting from interaction with the incident wave. We study the modelling of the backscattered waves and their experimental measurement. The signal model is adapted to simulate the concrete damage incidence on the ultrasonic waves. The limits of its exploitation are deduced. Experimentally, concrete specimens were examined for five states of thermal damage. According to the model the backscattered waves' attenuation evolves with the damage. The sensitiveness of an ultrasonic indicator to microstructural evolutions is analysed.     

Comparaison de la fiabilité opérationnelle des modules optiques équipant les systémes à 34 Mbit/s de France télécom

The purpose of the joint research programme conducted by the CNET and Alcatel CIT on various France Telecom 34 Mbit/s multimode optical links (0.85 and 1.3 μm) is to assess their behaviour versus time, compare their operational reliability and the different types of optoelectronic components used. Traceability on the entire product life cycle was performed using a micro-computer data base. Data was recorded from the begin-ning (January 1985) until the end of the first quarter of 1990. Analysis of the results obtained has taken into account the influence of storage and the failure analyses carried out on rejected components. The results obtained on 0.85 μm optical transmit modules have been used to elaborate a modelling procedure for reliability predictions.     

The advantages of directly identifying continuous-time transfer function models in practical applications

The direct identification and estimation of continuous-time models from sampled data is now mature. This paper does not present any new methodology, nor does it compare the performance of existing methods. Its main aim is to discuss the advantages of direct, continuous-time model identification with the help of illustrative examples that are all based on real data from practical applications. Although the specific method of statistical parameter estimation is relatively unimportant in this regard, the latest and most sophisticated time domain identification algorithm that is freely available to the reader is used in these examples in order to ensure that the results reflect the best performance that can be achieved at this time by time-domain identification.     

Determinants of e-consumer productivity in product retrieval on a commercial website: An experimental approach

This article investigates what determines e-consumer productivity, in the specific case of product retrieval, on a commercial website. With a 2 × 2 × 2 factorial design on 292 participants, an online experiment reveals that productivity in product retrieval (measured in terms of effectiveness, efficiency, and time) relates to website design (e.g., abstraction level of labels, animation), user characteristics (e.g., Internet experience, product category familiarity, cognitive absorption), and situational characteristics (e.g., task nature). The results also confirm interactive effects among the type of strategy used, the nature of the task, and the website design. These findings have notable implications for both research and practice.