Search

The lifetime of a photovoltaic module operating in natural environment may never be known. It is useful to look for mathematical laws that are reliable in predicting the approximate warranty and performance times of these instruments before they fail. Literature is rich of many laws (parametric, semi-parametric or non-parametric) that have a high efficiency in all scientific branches. Parametric laws are used more than others in the branches of electronics. In this paper, we examined the validity of some reliability laws (15 models) to simulate the degradation of the maximum electrical power of crystalline silicon photovoltaic modules and to estimate their lifetimes when exposed to Saharan environments (especially the Sahara of Adrar in the South West of Algeria and the desert of California in the United States of America) where the climate is generally warm and dry during half a year. A genetic algorithm (a method of artificial intelligence) has been used here to calculate the parameters of each tested model. The modified Weibul model is the most adequate one compared to the other parametric models tested. In this study, the average lifespan of photovoltaic modules in the desert of California has been estimated to approximately 30 years (29 years for Adrar) for which the electrical energy supplied reaches 46% of its initial value. The prediction results must be taken into consideration for any construction study of a solar station in desert environments. [ABSTRACT FROM AUTHOR]

The aim of this work is to evaluate the chemical composition and biological activities of essential oils obtained from aerial parts of six wild Algerian Mentha species ( M. aquatica , M. arvensis , M. x piperita , M. pulegium , M. rotundifolia and M. x villosa) , collected from the National Park of El-Kala. Chemical composition was analyzed by GC‐MS, the DPPH, β-carotene bleaching and ion chelating assays were carried to assess the antioxidant activity, the Ellman method were used to determine the inhibition of acetylcholinesterase. Essential oil yields and compositions varied among species. The highest yield of oils (1.8%) recorded for M. pulegium . 27 compounds were identified with the predominance of oxygenated monoterpenes such as menthofurane (73.38%), rotundifolone (65.99%), pulegone (59.12%), α menthol (49.89%), menthone (20.84%), neomenthol (20.76%), 1.8-cineole (18.16%). M. aquatica and M. arvensis exhibited the strongest DPPH radical scavenging activity (IC 50 = 0.69 ± 0.06 mg/ml and 0.76 ± 0.20 mg/ml, respectively) and the highest capacity to prevent β -carotene bleaching (IC 50 = 0.16 ± 0.02 mg/ml and 0.22 ± 0.01 mg/ml, respectively). The uppermost ferrous ion chelating activity was observed for M. aquatica , M. arvensis and M. villosa (1.72 < IC 50 < 1.73 mg/ml). Whereas essential oil of M. arvensis was found to be the most efficient (IC 50 = 27.5 μg/ml) against acetylcholinesterase. Consequently, essential oils of Mentha species could be exploited for their pharmacological application in order to prevent induced diseases relied to oxidative stress. [ABSTRACT FROM AUTHOR]

Abstract: Rosmarinus officinalis is the most used medicinal species in the Mediterranean region. It includes several botanical varieties and forms. Quantitative and genetic markers were used to assess the genetic diversity and genetic differentiation between eight natural Tunisian populations belonging to two allopatric varieties R. officinalis var. typicus Batt. and R. officinalis var. troglodytorum Maire endemic to Tunisia. The systematical position of the former has been recently questioned. The genetic differentiation among populations and varieties was assessed using flower traits (corolla length, pollen grain size, fertility and viability, style and stamen length), essential oil compounds, allozymes and RAPDs. The four sets of markers allowed similar patterns of high genetic differentiation among populations. PCAs performed on single or combined traits provided a good distinction among the two varieties with a high heterogeneity among var. typicus populations according to the bioclimate. The high differentiation among varieties arises from genetic drift and low level of gene flow among them due to habitat fragmentation. The recognition of both varieties should be maintained in the treatment of Tunisian R. officinalis. Conservation and improvement strategies should be made appropriately according to the variety and the bioclimate. [Copyright &y& Elsevier]

Sixteen Tunisian natural populations of Hypericum humifusum from different bioclimates (sub-humid, upper semi-arid and lower semi-arid) were assessed for their genetic diversity using nine isozymes. For all populations and all enzymes, 11 polymorphic loci were detected. The allelic frequencies varied according to the populations. A high genetic diversity and an excess of heterozygosity were observed within populations (Ap = 2.02; P% = 64.29; Ho = 0.321). The outbreeding mating system and the high number of individuals in the starting populations may contribute to this high variation. A relatively high level of differentiation (FST = 0.142) and a restricted gene flow among populations (Nm =1.34) were revealed. The lower semi-arid populations showed the highest differentiation (FST = 0.205). The relationship between FST and geographic distance matrices was not significant, indicating that the genetic structure among populations is more closely linked to habitat fragmentation and probably to founder events. Nei's unbiased genetic distances among pairs of populations were low (0.012-0.119). The unweighted pair group method with arithmetic averaging algorithm cluster based on these distances showed four sub-clusters. Population groupings had no evident relationship with bioclimates or geographic regions. The substantial differentiation between populations and their high genetic similarity suggest their recent divergence as a result of habitat fragmentation. Most of the total variation was found within populations, thus ex-situ conservation should be based on sampling seeds within, rather than among, populations. Populations harbouring rare alleles and a high genetic diversity level should be collected first. [ABSTRACT FROM AUTHOR]

Abstract: Nineteen Tunisian carob populations from different sites were studied to assess their genetic variation based on pods and kernels measures. The mean of the main descriptive morphological values of pods were weight (16.39g), length (168.9mm), width (20.5mm), lateral thickness (8.3mm), central thickness (5.8mm), number of viable kernels (12.26), number of aborted kernels (1.38), kernels weight (0.2g), kernel length (9.1mm), kernel width (6.9mm), kernel thickness (4.1mm) and kernel yield (17.2%). Most of the parameters measured showed significant differences (P <0.05 to P <0.001) that indicates a high genetic diversity; type and geographical origin of trees being taken as the source of variation. The relationship among these characters was analysed by principal component analysis (PCA) resulting in the separation of these populations classed in three grouped and three ungrouped populations. [Copyright &y& Elsevier]

Abstract: Staphylococcus aureus is the leading cause of nosocomial infections. Almost as soon as penicillin was introduced, penicillin-resistant strains of S. aureus began to appear. This resistance was due to the production of inducible, narrow spectrum β-lactamase, efficient at hydrolysing penicillins. In our days, conventional methods are time consuming and still remain the predominant approaches for detection and identification of bacteria and resistance patterns. Thus, there is an important clinical need for rapid detection of bacteria directly from patient samples. Rapid methods based on physical or electrochemical technologies can contribute significantly. In this paper, we use cyclic voltammetry and impedance spectroscopy technique to study the electric properties of the immobilized penicillin G for biosensor application. The penicillin G can be immobilized by simple adsorption on gold electrode via sulfur group. Fourier transform infra-red spectroscopy and atomic force microscopy has been used to study the molecular structure and the distribution of the penicillin G on the electrode. The selective detection of the two strains S. aureus bacteria (one resistance and the other sensitive) can be observed by quartz crystal microbalance technique. [Copyright &y& Elsevier]

The essential oil of 12 Tunisian natural populations of Myrtus communis L. (Myrtacea), prospected in three bioclimatic stages (humid inferior, sub-humid and semi-arid superior) were analyzed. Oil was extracted by n-hexane from crushed leaves and analysed by GC and GC-MS. Twenty-four components, representing approximately 79.10% of the oil, were identified. The major constituents were α-pinene (19.20%) and 1,8-cineole (15.96%). The other important constituents were linalool (7.66%), α-terpineol (7.51%) and limonene (5.75%). The percentage of all components varied within and among populations according to their bioclimatic appurtenance. α-Pinene, camphene and 1,8-cineole were the main compounds to differentiate the populations according to the bioclimate. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]