Comparison between three years of daily global radiation measurements in three Tunisian sites against assessments from METEOSAT Wefax images

GISTEL is a satellitary methodology based on a simple physical model with two components. It is used to estimate global solar irradiance from METEOSAT data. The treated images in the present sequel are of Wefax type of the ‘visible channel’ of METEOSAT.Our method has been applied in Tunisia. The estimated daily solar global radiation is compared to the measured values performed in three meteorological stations in the North of Tunisia during three successive years. The obtained results have shown that the accuracy level of our method is acceptable for energy applications. Our results show the convenience of GISTEL method to METEOSAT-Wefax images. In general, the relative error does not exceed 20% of the global irradiation. The recorded errors between estimated and measured values are, in some cases, linked to the model's parameters. They may also arise from the geographical situation of the site, the satellitary data or from the earth-based solar irradiation.     

Use of HR Meteosat images for the mapping of global solar irradiation in Tunisia: preliminary results and comparison with Wefax images

The evaluation of the incident solar energy on a given site becomes at the present time, one of the needs of the users and the manufacturers of energetic solar systems. For this purpose, we have developed, in collaboration with the Energy Climate Laboratory of Avignon University (France), an assessment method (GISTEL) of solar irradiation using Meteosat satellite images.We have shown in previous papers (Ben Djemaâ A, Delorme C. Solar Energy 48(5) 1992 325; Chaâbane M, Ben Djemaâ A, Kossentini A. Solar Energy 57(6) 1996 449) the simplicity and efficiency of the GISTEL method to estimate global solar irradiation and its convenience compared with B2 and Wefax images.Herein we describe briefly our method and present the preliminary results obtained from a series of high resolution (HR) Meteosat images. The results are compared with values obtained at eight Tunisian meteorological stations and are then compared with the results obtained using Wefax images. A statistical study of the errors between estimated and measured values is presented and analysed.We also show the efficiency of the map-form of solar energy data for Tunisian territory and its potential for future studies. For Tunisia and African countries, these images present the best means for solar studies since they cover the quasi-totality of the African continent with a good temporal and spatial resolution.     

Improvement of rheological properties of Algeria crude oil by addition of extra-light crude oil and a surfactant agent

Abstract

Effect of surfactant and extra-light crude oil addition on the rheological behaviors of an Algeria crude oil in order to improving its flowability were studied at low temperature. These rheological properties include steady flow behavior, yield stress and viscoelastic behavior. An AR-2000 rheometer was employed in all of the rheological examination tests. Results show that Toluene and extra-light crude oil addition causes a strong reduction in viscosity, the yield stress and can effectively increase of crude oil transport capacity. The toluene addition gets its best flow capacity and lowest viscosity at 6%. The extra-light crude oil addition obtains its best flow capacity and lowest viscosity at 50%. The viscoelasticity character of the crude oil has indicate a significantly influence by the addition of Toluene and extra-light crude oil.     

Rheological behavior of Algerian crude oil: effect of temperature and refined product

Abstract

The rheological behavior and its variation with temperature and refined product concentration of a crude oil sample coming from a quagmire of the separation station of Tin Fouye Tabankort oilfield/southern Algeria were investigated experimentally. The experiments were carried out at various temperatures (20, 30 and 50?°C) over the shear rate range of 0 to 700?s^?1 by using a controlled stress rheometer (AR 2000, TA Instrument). The results showed that the crude oil exhibit non-Newtonian of shear thinning behavior at low shear rate and Newtonian behavior at high shear rate and was adequately described by Casson and Herschel–Bulkley models. The rheological measurements through the steady flow test and viscoelastic behavior, including the storage modulus (G′), loss modulus (G″), and complex modulus (G*), has indicated that the rheological properties of the crude oil were greatly influenced by the temperature and the additive concentration.     

Electrical properties of ITO/benzylated cyclodextrins (β-CDs (Bz))/Al diode structures

Abstract

Investigations of the electrical characteristics of benzylated cyclodextrins (β-CDs (Bz)) diodes are reported. We present current–voltage characteristics and impedance spectroscopy measurements performed on partially benzylated cyclodextrins β-CDs (Bz) thin films in sandwich structures ITO/b-CDs (Bz)/Al. The static electrical characterizations show a space charge limited conduction (SCLC) and a conductivity with power low frequency behavior characteristic of a hopping transport in disordered materials. The impedance spectra can be discussed in terms of an equivalent circuit model designed as a parallel resistor R_p and capacitor C_p network in series with resistor R_s. We extract numerical values of these parameters by fitting experimental data. Their evolution with bias voltages has shown that the SCLC mechanism is characterized by an exponential trap distribution. We estimated from the capacitance voltage characteristic an acceptor concentration of about 10¹¹ cm^?3 due to trap states.     

Modeling and control of photovoltaic and fuel cell based alternative power systems

Photovoltaic (PV) systems and fuel cells (FCs) represent interesting solutions as being alternative power sources with high performance and low emission. This work presents a modeling and control study of two power generators; photovoltaic array and fuel cell based systems. An MPPT approach to optimize the PV system performances is proposed. The PV system consists of a PV array connected to a DC-DC buck converter and a resistive load. A maximum power point tracker controller is required to extract the maximum generated power. Based on Incremental Conductance (INC) principle, the idea of the proposed control is to use a Fuzzy Logic Controller (FLC) that allows the choice of the duty cycle step size which is used to be fixed in conventional MPPT algorithms. The variable step is computed according to the value of the PV power-voltage characteristic slope. The second working system comprises a controlled DC-DC converter fed by a proton exchange membrane fuel cell (PEMFC) and supplies a DC bus. The mathematical model of the PEMFC system is given. The converter duty cycle is adjusted in order to regulate the DC bus voltage. Obtained simulation results validate the control algorithms for both of studied power systems.     

Nanostructural, optical and electrical properties of vacuum evaporated films of an azo-calix[4]arene derivative

The nanomorphology, optical and electrical properties of vacuum-deposited azo-calix[4]arene thin films have been investigated. The nanostructured films exhibit absorption spectra with a resolved electronic structure in the UV-vis and a blue photoluminescence emission at about 430 nm independent of the excitation wavelength. The current-voltage (I-V) characteristics of ITO/azo-calix[4]arene/Au devices have been studied. The I-V dependence follows a power law, I ∝ V^m, which is typical of a space-charge-limited current. Moreover, from the I-V measurements, we have estimated the effective hole mobility of ∼7.5 × 10⁻⁶ cm²/V s in the vacuum-deposited azo-calix[4]arene thin films. Using impedance spectroscopy over a broad frequency range, i.e. 100 Hz to 10 MHz, it is found that the ac behavior of an ITO/azo-calix[4]arene/Au device shows several features, described by the simple RC circuit representing an undepleted bulk region. Values of the electrical circuit parameters deduced from fitting experimental data to the model have given a dielectric relaxation time in the millisecond range.     

Optical and electrical properties of novel peripherally tetra and mono -quinoleinoxy substituted metallophtalocyanines

Two new Zinc phtalocyanine, ZnPcR₁ and ZnPcR₄, with peripheral mono and tetra quinoleinoxy substituents of the phtalocyanine ring, were characterized to investigate their optical and electrical properties. The modification of the chemical structure allows the elongation of the π-conjugation, leading to an enhanced solubility as well as a broadening of the ZnPcR₁ and ZnPcR₄ absorption spectra. The UV–Visible absorption spectra show a typical behavior of phtalocyanine for the two π-conjugated systems with an optical band gap of 1.70 and 1.74 eV for ZnPcR₁ and ZnPcR₄ respectively and the Photoluminescence study exhibits a green emission for both compounds. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels were estimated using cyclic voltammetry analysis and the calculated electrochemical gap was found to be equal to the optical one. Current–voltage characteristics and impedance spectroscopy measurements performed on sandwich structures ITO/phtalocyanine derivatives/Al are used to elucidate the conduction mechanisms. The static electrical characterizations showed a space charge limited conduction with exponential trap distribution at high applied bias voltage. The impedance spectra were discussed in terms of an equivalent circuit model designed as a parallel resistor R_p and capacitor C_p network in series with a resistor R_s. The evolution of the electrical parameters deduced from fitting of the experimental data is discussed. The conduction mechanism revealed by I–V characteristics is in agreement with the impedance spectroscopy results.     

Semi-heterarchical control of FMS: From theory to application

This paper presents both a model and a real implementation of a semi-heterarchical control system for flexible manufacturing systems (FMS). After presenting the concepts of heterarchical and semi-heterarchical control, a product-based control structure, composed of a dynamic allocation process (DAP) and a dynamic routing process (DRP), is proposed. Though the associated control processes (DAP and DRP) are hierarchically dependant, each is managed heterarchically, with no supervisor. The dynamic allocation algorithms are presented, and our highly distributed approach to routing control is then explained in detail. A real distributed application of the active entities and the control architecture was implemented in the AIP-PRIMECA pole at the University of Valenciennes, and this implementation is described in detail. A mixed-integer linear model of the FMS was used to compute lower bounds. The flexibility and robustness of our approach are highlighted through several real experiments.     

On the SAR change detection review and optimal decision

Change detection is the process of identifying differences in the state of an object or scene after the occurence of an event. In this paper, we will present several similarity measures for automatic synthetic aperture radar (SAR) change detection, which can be classified into two families: the first regroups the measures based on pixel radiometry and the second collects the detectors based on local statistics. This article details a judicious method for SAR image change detection using Dezert–Smarandache Theory (DSmT). On the one hand, a Rayleigh distribution function is used to characterize globally the radar texture data, which allows mass assignment through the Kullback–Leibler distance. On the other hand, local pixel measurements are introduced through the Rayleigh Distribution Ratio indicator to refine the mass attribution and take into account the context information. Finally, DSmT is carried out by comparing the modelling results between temporal images. This technique has been applied on both simulated and real data and allows very satisfactory change detection results.