Incidence of aflatoxins, ochratoxin A and zearalenone in tunisian foods

A total of 209 samples of different groups of foods widely consumed by the Tunisian population were collected during 2004–2005 years. Samples were analyzed for contamination with aflatoxins, ochratoxin A and zearalenone, using competitive enzyme-linked immunosorbent assay (ELISA). The predominant mycotoxin was ochratoxin A with a mean level of 3.5 ± 5.3 ng g⁻¹ in 59.8% of studied samples. Furthermore, Aflatoxins were detected in all analyzed commodities with a contamination frequency of 50.5%. In addition, aflatoxin B1 was found in 37% of the samples. The zearalenone was detected around 15% with a mean level of 10.4 ± 11.8 ng g⁻¹. Species, dried fruits and sorghum were the most contaminated samples by aflatoxin and ochratoxin mycotoxins, whereas Rice was the least contaminated commodity. The most frequent mycotoxins co-occurrence included aflatoxins and ochratoxin A, which have been detected in 33.8% of analyzed samples. Furthermore, the simultaneous contamination by aflatoxins, ochratoxin A and zearalenone was observed in 7.2% of studied samples.     

Thermal degradation kinetics of insulating/conducting epoxy/Zn composites under nonisothermal conditions

This article deals with the nonisothermal degradation kinetics of insulating and conducting epoxy/Zn composites. A comparison of thermal degradation data obtained from epoxy/Zn composites revealed that the addition of zinc content in epoxy significantly increases its degradation rate. However, the zinc content activates the degradation until its melting point (419.5°C) and then it starts stabilizing the matrix due to its higher specific heat in molten state. Kinetics of the phenomena fairly explains this behavior in terms of the comparison of general kinetic equations for epoxy/Zn composites. It is to notice that both the values of effective activation energy and reaction model (Šestâk Berggren/SB‐m, n) for insulator/conductor composite pair have been found almost the same emphasizing upon negligible polymer–metal interactions in both cases. These mechanistic clues derived from comparative kinetic study have been found in good agreement with the results obtained through morphological analysis of samples by scanning electron microscopy and X‐ray diffraction techniques. POLYM. COMPOS., 34:2049–2060, 2013. © 2013 Society of Plastics Engineers     

Electrical conductivity of urea–formaldehyde–cellulose composites loaded with copper

This work is concerned with the preparation and characterization of composite materials prepared by compression molding of mixtures of copper powder and a commercial grade thermosetting resin of urea–formaldehyde filled with α‐cellulose in powder form. The electrical conductivity of the composites is <10⁻¹² S/cm, unless the metal content reaches the percolation threshold of 24.0 vol %, beyond which the conductivity increases markedly by as much as 11 orders of magnitude, indicating an insulator–conductor phase transition. The homogeneity of these composites was checked by the morphologies of the constituents (filler and matrix) and the composites characterized by optical microscopy. The density of the composites was measured and compared with values calculated assuming different void levels within the samples to discuss the porosity effect. Finally, the obtained results on electrical conductivity have been well interpreted with the statistical percolation theory. The deduced critical parameters, such as the threshold of percolation, V_f*, the critical exponent, t, and the packing density coefficient, F, were in good accord with earlier studies. In addition, the hardness of samples remained almost constant with the increase of metal concentration. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Electrical resistivity of polymeric matrix loaded with nickel and cobalt powders

This paper reports on the electrical properties of various polymers (epoxy resin, silicone, polyurethane) filled with metal particles (Cobalt and Nickel). The results of this study give evidence of the expected non-conducting to conducting transition as the conducting filler volume fraction V _f is increased. The location of threshold is found to depend on the features and the properties of composite's constituents: the type, the viscosity and the surface tension of the matrix as well as the nature, the size, the shape, the geometry and the surface energy of the conducting particles and the composite porosity. The morphology of the filler particles and their dispersion in the matrix have been investigated by Optical and Scanning Electron Microscopies (SEM) and density measurements. The obtained results have been explained on the basis of the statistical percolation theory.     

Vibro-acoustic analysis of micro-perforated sandwich structure used in space craft industry

In satellite telecommunications lightweight parabolic reflectors are made with multilayered composite material. During launcher lift-off and the first stage of the flight, vibro-acoustic excitations due to the thrust system and aerodynamic forces are the most critical. The random acoustic load applied to the antenna structure becomes very important and can damage the structure and its equipments. To reduce the acoustic loads, micro-perforated thin shell structures are used in order to reduce the acoustic load applied. CAD and numerical software tools are needed to design and optimise such structures. The computation of the acoustic load induced by a diffuse field on a micro-perforated structure is not classical. The aim of this study is to develop a numerical local impedance model to represent the effect of the perforation to be used within vibro-acoustic software.     

A comparative study of three different sensorless vector control strategies for a Flywheel Energy Storage System

The aim of this paper is to ensure the sensorless control of an inertial storage system associated to an isolated Hybrid Energy Production Unit (HEPU). The Flywheel Energy Storage System (FESS) is used as energy buffers in order to store or retrieve energy into a stand-alone load. A comparative study of three different techniques based on a sensorless vector-controlled induction motor (IM) driving a flywheel are presented. First, a speed estimation algorithm based on model reference adaptive system (MRAS) theory is proposed. Then, a model reference adaptive speed observers is introduced in this paper with an accurate stability study. This observer strategy is then ameliorated with a new reduced adaptive speed observer. The observer parameters are adapted during flux weakening in order to obtain close tracking of the flywheel speed. The accuracy of the presented models is confirmed by simulation results.     

Aflatoxin determination in commonly consumed foods in Tunisia

BACKGROUND: To investigate natural aflatoxin occurrence, a total of 180 samples of different foods widely consumed in Tunisia were analysed by an in‐house‐validated high‐performance liquid chromatography method including affinity column clean‐up and post‐column bromination techniques. RESULTS: The method used appeared to be rapid, selective and reproducible, and its performances were established. Detection limits were 0.05 ng g^?1 for aflatoxin B1 and 0.025 ng g^?1 for aflatoxins B2, G1 and G2. Aflatoxins were detected in all investigated commodities except rice, with an overall contamination frequency of 34.4% and concentrations ranging from 0.1 to 40.6 ng g^?1. Aflatoxin B1 was found in all contaminated samples. Sorghum, spices and nuts were most contaminated. CONCLUSION: This study has provided an effective analytical method for the reliable determination of aflatoxins in food samples. Over one‐third of the samples investigated were contaminated with aflatoxins. Sorghum, spices and nuts were most contaminated, whereas rice showed no contamination. Copyright © 2010 Society of Chemical Industry     

Evaluating the effects of herbal essences from spearmint and wild thyme on the quality of camel's milk

The aim of this study was to improve the sensory and physicochemical properties of camel's milk using two essential oils (EOs), spearmint (Mentha spicata) and wild thyme (Zataria multiflora). Total bacterial counts in the flavoured milks were lower than those of the plain milk, and microbial population was the lowest in the milk containing spearmint EO during 5 days of storage. Considering the sensory evaluations, milks treated with the above EOs received higher scores compared with those of untreated milk. The highest scores were given to the milk containing spearmint EO at 0.09 mL L^?1. No significant differences were observed in the mean particle sizes of the samples after 5 days of storage. The addition of EOs from camel's milk resulted in higher organoleptic properties and shelf life, and, in turn, it can improve the consumption rate of camel's milk.     

LAD-CBM; new data processing tool for diagnosis and prognosis in condition-based maintenance

This paper investigates the application of a data mining technique called Logical Analysis of Data (LAD) to condition-based maintenance. The existing classification techniques are mainly based on statistical analysis and modeling approaches. This paper presents a classification technique based on combinatory and Boolean theory. It is shown that LAD is particularly suitable for detecting the state of equipment because of its new way of pre-processing noisy and missing data. A numerical example and an application are presented.