The Lille establishment

Abstract

Until about 1910, pictorial and professional photographers produced strikingly different work and interacted very little with one another. Most pictorialists strove to create atmospheric, mysterious and emotionally charged images that often resembled other works of art. They hand-crafted photographs that were sofdy focused, low in tonalities and printed in such exotic processes as gum-bichromate, platinum or photogravure. Motivated by pure self-expression, pictorialists made every effort to prove that their pictures were fine art, looking down on utilitarian photographs as crass and soulless.     

Characterization of Dual Corona-Electrostatic Electrodes for Electrostatic Processes Applications

The dual corona-electrostatic electrodes consist of one or several ionizing elements (wires, needles, and blades) attached to a metallic support. This paper analyzes the characteristic features of a particular type of such electrodes and formulates recommendations on their design and utilization. The experiments focused on several models of dual corona-electrostatic electrodes, the ionizing element being the edge of a thin metallic blade. The tested devices had similar cylindrical metallic supports but blades of different sizes. Thus, it was possible to investigate the influence of electrode geometry on corona onset voltage and spark-over threshold in configurations that are specific to industrial electrostatic processes. Most of the experiments were performed by using roll-type electrostatic separators. A special experimental setup was employed for the study of the distribution of corona current density at the surface of a plate collecting electrode. For the model having the blade edge closer to the metallic support, the corona onset voltage was higher, and the corona discharge affected a smaller area at the surface of the collector. These experiments are discussed in relation with the results of the numerical analysis of the electric field generated by the different electrode configurations. At a given voltage and distance between the ionizing element and the collector, the presence of the cylindrical support diminishes the electric field at the edge of the blade and distorts the field lines. These effects were exploited in the design of the electrode system of an electrostatic separator for the recycling industry.     

Assessment of the method used to construct clearness index maps for the new European Solar Radiation Atlas (ESRA)

We present an assessment of the methods used to construct maps for a new solar radiation atlas for Europe. For this atlas, station data and satellite-derived data are used in an interpolation/merging process to derive maps of the long-term monthly global radiation that cover an area ranging from 30° W to 70° E and from 25° to 75° N. Our focus is on the discussion of the accuracy of the method applied: a co-kriging technique. Special emphasis is put on a discussion as to whether the use of satellite-derived radiation maps with a low spatial resolution brings benefits.     

Experimental modeling of high-voltage corona discharge using design of experiments

Many studies, both experimental and numerical, were devoted to the electric current of corona discharge and some mathematical models were proposed to express it. As it depends on several parameters, it is difficult to find a theoretical or an experimental formula, which considers all the factors. So we opted for the methodology of experimental designs, also called Tagushi’s methodology, which represents a powerful tool generally employed when the process has many factors to consider. The objective of this paper is to model current using this experimental methodology. The factors considered were geometrical factors (interelectrode interval, surface of the grounded plane electrode, curvature radius of the point electrode), climatic factors (temperature and relative humidity), and applied high voltage. Results of experiments made it possible to obtain mathematical models and to analyse the interactions between all factors.     

Numerical Modeling of Conductive Particle Trajectories in Roll-Type Corona-Electrostatic Separators

Several attempts have already been made to simulate particle trajectories in roll-type electrostatic separators. However, the predictive value of the results is limited by an excessive number of simplifying assumptions regarding the electric field distribution, as well as particle charging and discharging mechanisms. The present work is aimed at improving the existing models by taking into account: (1) the non-uniformity of the electric field in the active zone of the separator and (2) the effect of spark discharges occurring between the electrodes. Based on previous observations, the conductive particles were assumed to lift-off when no longer exposed to corona discharge. The numerical simulations were performed for particles of various sizes. The electric field was computed in each point of the trajectory using a finite element program. It was found that: (1) some of the smaller particles impact the static electrode and are deviated to the middling compartment of the collector and (2) field annealing which accompanies spark discharges significantly affects the trajectories of conductive particles. The results of this study could guide the design of new electrostatic separation applications.     

<Emphasis Type="Italic">SetExp</Emphasis>: a method of transformation of timed automata into finite state automata

Real-time discrete event systems are discrete event systems with timing constraints, and can be modeled by timed automata. The latter are convenient for modeling real-time discrete event systems. However, due to their infinite state space, timed automata are not suitable for studying real-time discrete event systems. On the other hand, finite state automata, as the name suggests, are convenient for modeling and studying non-real time discrete event systems. To take into account the advantages of finite state automata, an approach for studying real-time discrete event systems is to transform, by abstraction, the timed automata modeling them into finite state automata which describe the same behaviors. Then, studies are performed on the finite state automata model by adapting methods designed for non real-time discrete event systems. In this paper, we present a method for transforming timed automata into special finite state automata called Set-Exp automata. The method, called SetExp, models the passing of time as real events in two types: Set events which correspond to resets with programming of clocks, and Exp events which correspond to the expiration of clocks. These events allow to express the timing constraints as events order constraints. SetExp limits the state space explosion problem in comparison to other transformation methods of timed automata, notably when the magnitude of the constants used to express the timing constraints are high. Moreover, SetExp is suitable, for example, in supervisory control and conformance testing of real-time discrete event systems.     

Monthly means of daily solar irradiation over Egypt estimated from satellite database and various empirical formulae

Monthly means of daily solar irradiation retrieved from the HelioClim-3 version 3 database (HC3v3), elaborated from Meteosat satellite images, were tested at 14 Egyptian stations along with the model of Yang, Koike, and Ye (YKY) and 10 empirical models (EMs) for the period 2004 to 2009. YKY and EMs were fitted to measurements from the period 1980 to 1989. Overall, HC3v3 exhibits a bias of 0.4 MJ m^?2 (i.e. 2% of the mean of the observations – similar to the best EMs). The root mean square error (RMSE) was 1.8 MJ m^?2 (9%) for HC3v3, which is lower than for most EMs. Coefficients of determination (R²) were greater than 0.9 for most models. The regression line between estimates and observations exhibits a slope of 1.01 and an intercept of 0.09 MJ m^?2 for HC3v3, reflecting a better performance than other models. HC3v3 shows remarkably constant performance as a function of irradiation or cloudiness compared with EMs and YKY. In general, HC3v3 is preferred to EMs when estimating monthly means of daily solar irradiation in Egypt. It is suggested that more effort is needed towards the validation and promotion of HC3v3 before researchers and practitioners use it rather than EMs.     

Experimental Study of the Corona Discharge in a Modified Coaxial Wire-Cylinder Electrostatic Precipitator

Coaxial wire-cylinder electrode arrangements are widely used for the electrostatic precipitation of dust particles contained in flue gases. The aim of this paper was to evaluate a new design, which was expected to increase the particle collection efficiency. The collector electrode of the several models under study consisted of a cylinder with alternate small- and large-diameter sections. In a first set of experiments, the current–voltage characteristics of each model were compared with those obtained for a standard wire-cylinder electrode arrangement, at both polarities of the high-voltage supply, and for three values of the inlet airflow rate, namely, 0, 4.5, and 6 $hbox{dm}^{3}/hbox{min}$, with the corresponding air velocities in the large-diameter sections being 0, 6.0, and 8.0 cm/s. A second set of experiments showed that the current density distribution inside the models depends on the geometry of the electrode system but is roughly the same at 4.5 and 6 $hbox{dm}^{3}/hbox{min}$. The particle collection efficiency of the different models was evaluated in a third set of experiments, performed with 2-g samples of starch powder, under various operating conditions. Data analysis revealed that the modified precipitators have higher efficiency than the standard model. As expected, for a given geometry of the electrode arrangement, the efficiency was found be lower at higher inlet airflow rates. These findings could serve in the design of new industrial electrostatic precipitators.