Showing papers by "Tunis University published in 2001"

The gene encoding alsin, a protein with three guanine-nucleotide exchange factor domains, is mutated in a form of recessive amyotrophic lateral sclerosis.

Abstract: Amyotrophic lateral sclerosis (ALS) and primary lateral sclerosis (PLS) are neurodegenerative conditions that affect large motor neurons of the central nervous system. We have identified a familial juvenile PLS (JPLS) locus overlapping the previously identified ALS2 locus on chromosome 2q33. We report two deletion mutations in a new gene that are found both in individuals with ALS2 and those with JPLS, indicating that these conditions have a common genetic origin. The predicted sequence of the protein (alsin) may indicate a mechanism for motor-neuron degeneration, as it may include several cell-signaling motifs with known functions, including three associated with guanine-nucleotide exchange factors for GTPases (GEFs).

The Introduced Green Alga Caulerpa Taxifolia Continues to Spread in the Mediterranean

Abstract: The tropical green alga Caulerpa taxifolia in the Mediterranean has spread steadily since its introduction in 1984. At the end of 2000, approximately 131 km2 of benthos had been colonized in 103 independent areas along 191 km of coastline in six countries (Spain, France, Monaco, Italy, Croatia and Tunisia). Large regions neighboring the invaded areas appear favorable to further colonization, and there is thus no reason to believe that spreading will slow down in the years to come.

The CR Yamabe conjecture the case $n=1$

Abstract: Let (M,θ) be a compact CR manifold of dimension 2n+1 with a contact form θ, and L=(2+2/n)Δ b +R its associated CR conformal laplacien. The CR Yamabe conjecture states that there is a contact form &θtilde; on M conformal to θ which has a constant Webster curvature. This problem is equivalent to the existence of a function u such that¶\(\)¶D. Jerison and J.M. Lee solved the CR Yamabe problem in the case where n≥2 and (M,θ) is not locally CR equivalent to the sphere S 2n+1 of C n . In a join work with R. Yacoub, the CR Yamabe problem was solved for the case where (M,θ) is locally CR equivalent to the sphere S 2n+1 for all n. In the present paper, we study the case n=1, left by D. Jerison and J.M. Lee, which completes the resolution of the CR Yamabe conjecture for all dimensions.

Infrared absorption in S i / S i 1 − x Ge x / Si quantum wells

Abstract: The infrared intersubband optical transitions in SiGe/Si quantum wells is theoretically examined. We have used the $8\ifmmode\times\else\texttimes\fi{}8,$ $12\ifmmode\times\else\texttimes\fi{}12,$ and $14\ifmmode\times\else\texttimes\fi{}14$ $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ Hamiltonians taking into account both the p-like first conduction band and the s-like second conduction band to calculate wave functions and energy dispersion of the valence band of ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}}_{0.8}{\mathrm{Ge}}_{0.2}/\mathrm{Si}$ quantum wells. We discuss intersubband absorption in the valence band and we show that the p-p interaction favors intersubband transitions for an optical polarization parallel to the layer plane $(x$ polarization). For z polarization, both s-p and p-p interactions play the same footing role in intervalence band transitions.

Luttinger-like parameter calculations

Abstract: We have calculated the Luttinger-like parameters, used in the $8\ifmmode\times\else\texttimes\fi{}8$ Hamiltonian describing both conduction and valence bands, via a second-order perturbation theory that allows one to make the L\"owdin renormalization valid for a set of nondegenerate energy levels. We show that the formulas given in the paper by Pidgeon and Brown [Phys. Rev. 146, 575 (1966)] are the correct ones, contrary to what is claimed in recent papers. This leads to strong discrepancies when the spin-orbit splitting is not much smaller than the band gap. For example, the ratio between the Luttinger-like parameters ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\gamma}}}_{1},$ calculated in the two cases, is of the order of 1.5 in GaAs, 3 in InAs, and 16 in InSb. The accuracy of the equations used by Pidgeon and Brown is also discussed.

Asymptotically self-similar global solutions of a general semilinear heat equation

Abstract: We consider the general nonlinear heat equation $\partial_t u = \Delta u +a|u|^{p_1-1}u+g(u), u(0)=\varphi,$ on $(0,\infty)\times I\!\!R^n ,$ where $a\in I\!\!R, p_1>1+(2/n)$ and g satisfies certain growth conditions. We prove the existence of global solutions for small initial data with respect to a norm which is related to the structure of the equation. We also prove that some of those global solutions are asymptotic for large time to self-similar solutions of the single power nonlinear heat equation, i.e. with $g\equiv 0.$

Energy-band structure of GaAs and Si: A sps * k.p method

Abstract: A twenty-band $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ Hamiltonian taking into account the spin-orbit coupling is used to describe the valence band and the first two conduction bands all over the Brillouin zone. The basis functions are ${\mathrm{sp}}^{3}{s}^{*}$-like functions used in linear combination of atomic orbitals. To get the right dispersion up to the Brillouin zone edge, the influence of other bands $(d$ bands) is mimicked via Luttinger-like parameters in the valence band and in the conduction band. The method is applied to GaAs and Si. A satisfying agreement is obtained near the band extrema as well in the direct gap semiconductor (GaAs) as in the indirect gap semiconductor (Si). In particular, while the $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ Hamiltonian parameters are adjusted to get the longitudinal mass 0.92 of the silicon conduction band, the transverse mass, which results from the calculation without further adjustment, is equal to 0.19 which is the experimental value.

Blowup rates for nonlinear heat equations with gradient terms and for parabolic inequalities

Abstract: Consider the nonlinear heat equation (E): ut − ∆u = |u| u + b|∇u| . We prove that for a large class of radial, positive, nonglobal solutions of (E), one has the blowup estimates C1(T − t) −1/(p−1) ≤ ‖u(t)‖∞ ≤ C2(T − t) . Also, as an application of our method, we obtain the same upper estimate if u only satisfies the nonlinear parabolic inequality ut − uxx ≥ u . More general inequalities of the form ut − uxx ≥ f(u) with, for instance, f(u) = (1 + u) log (1 + u) are also treated. Our results show that for solutions of the parabolic inequality, one has essentially the same estimates as for solutions of the ordinary differential inequality v̇ ≥ f(v).

Genotypic variability for tolerance to salinity of N2-fixing common bean (Phaseolus vulgaris)

Abstract: Le haricot (Phaseolus vulgaris L.) est souvent soumis dans le sol a diverses contraintes environnementales. L'une des ces contraintes est la salinite qui represente une limitation majeure du rendement des legumineuses a graines, particulierement quand la croissance des plantes depend de la fixation symbiotique de l'azote. Pour confirmer la variabilite de la reponse a une salinite moderee et identifier les criteres morphologiques et physiologiques associes a la tolerance, 9 lignees de haricot (BAT477, Coco blanc, DOR585, ABA16, NAG310, Flamingo, BRB17, Candide et Striker) sont inoculees avec une souche efficiente Rhizobium tropici CIAT899, et cultivees sur sable sterile sous serre vitree en absence ou en presence de 25 mM NaCl. Une variation genotypique dans la tolerance au sel a ete observee : ABA16 et BRB17 sont les lignees les plus sensibles alors que BAT477 et Flamingo sont les plus tolerantes. Les parametres estimes relatifs a la croissance et a la fixation symbiotique de l'azote montrent que (i) certaines lignees exprimant une croissance vigoureuse en milieu temoin sont severement affectees par le traitement salin, (ii) la relative tolerance au sel d'autres lignees repose particulierement sur leur aptitude a maintenir une importante surface foliaire et a developper un systeme nodulaire abondant et efficace.

A study of Gm allotypes and immunoglobulin heavy gamma IGHG genes in Berbers, Arabs and sub-Saharan Africans from Jerba Island, Tunisia

Abstract: The Gm polymorphism of human IgG immunoglobulins was investigated in three different ethnic groups--Arabs, Berbers and 'dark-skinned people'--on Jerba Island, Tunisia. The genetic relationships among these groups and several populations from North Africa, sub-Saharan Africa, west Asia and Europe were analysed by principal coordinate analysis, Fst significance testing, and analysis of molecular variance based on haplotype frequencies. The results revealed a non-significant genetic differentiation between Arabs and Berbers from Jerba. However, the Jerbian population of sub-Saharan African origin was close to Ethiopians. Gene flow among the three Jerbian populations, as well as an East African origin of the dark-skinned individuals, is proposed to account for the observed genetic pattern. However, the genetic diversity observed among the different Tunisian populations did not show any significant correlation with either geographic or linguistic differentiation. A preliminary analysis of the restriction fragment length polymorphism of the IGHG genes in Arabs and Berbers from Jerba confirmed the close genetic relationship between the two populations. However, it also indicated a lower level of genetic diversity in the Berbers, which may be explained by more rapid genetic drift due to longer isolation on the island.

Case Study of Water Table Evaporation at Ichkeul Marshes (Tunisia)

Abstract: The method of Gardner was used to estimate the evaporation rate from bare soils under high water table conditions, at Ichkeul marshes, of northern Tunisia. For this purpose, water content, soil-water suction, and water table depth were measured at three sites. Other common approaches that provide estimates of water table evaporation such as the Averianov and Coudrain-Ribstein et al. empirical formulas and the approach used by the U.S. Geological Survey's groundwater flow model MODFLOW were also evaluated. Next, a 2D groundwater simulation model, using the Gardner equations for computing evaporation rate, was developed to quantify the aquifer budget and groundwater losses via evaporation at the total area of the marshes. The model was calibrated in a steady-state condition. The results indicated significant groundwater losses by water table evaporation. The sensitivity of the groundwater model to the Averianov and MODFLOW approaches was analyzed. The best results (piezometric head and the area distribution...

Some observations on the age and growth of thin-lipped grey mullet, Liza ramada Risso, 1826 (Pisces, Mugilidae) in three North African wetland lakes: Merja Zerga (Morocco), Garâat Ichkeul (Tunisia) and Edku Lake (Egypt)

Abstract: Age and growth characteristics of the thin-lipped Grey Mullet (Liza ramada) were investigated in three North African wetland lakes: Merja Zerga (Morocco), Garâat Ichkeul (Tunisia) and Edku Lake (Egypt). Age structure of the mullet populations was very similar in all three study lakes. Small differences in growth were indicated, especially for the Moroccan population, where growth tended to be slower than for the other two populations. The fastest growth was observed in the Edku population while the best condition was observed in the Ichkeul population. Compared with some European populations, the sampled North African populations have faster growth and better condition factors.

Hedysarum phylogeny mediated by RFLP analysis of nuclear ribosomal DNA – RFLP and Hedysarum phylogeny

Abstract: The RFLP technique has been employed to investigate phylogenetic relationships between species of the Hedysarum genus Homologous DNA probes were used to generate patterns from a set of the Mediterranean group The degree of band sharing was used to estimate genetic distances between species and to draw phylogenetic trees These are in good agreement with phylogeny based on morphological and isozyme markers, but contain novel insights The results are discussed in the context of current work in molecular biosystematics in Hedysarum complex Attempts made in this approach to access the extent of variability at the DNA level occurring with the domestication process have been investigated With the availability of the tested probes, it has been assumed that the genetic structure is not affected by the domestication process

A comparative study of hysteresis and PWM control techniques applied to an injection-current-based three-phase rectifier

Abstract: In this paper, two control laws based respectively on hysteresis and pulse-width-modulation (PWM) techniques are applied on a unity-power-factor current-injection-based three-phase rectifier. A theoretical analysis is carried out in order to evaluate the performance of each technique, in terms of the line current ripple and the switching frequency. The control detuning problem, which contributes mainly to the line current distortion, is also considered. In order to highlight the comparative study, numerical simulation is accomplished using the Power System Blockset tool of Matlab/Simulink.

The Short– and Long–run Performance of New Listings in Tunisia

Abstract: This study examines abnormal stock market returns of new listings on the Tunisian Stock Exchange. Substantial positive abnormal returns are found on the first listing day and this finding is similar to that obtained in other countries. Subsequent performance is poor and investors who bought shares at the close of trading on the first day would have lost about 22% against the Tunis Stock Exchange index over a three–year period. The possible causes of this are investigated. Among the factors found in the literature that possibly affect the level of long–term performance, only the state of the IPO market, the initial return, the delay in reaching the ‘first market price’ and the size of the firms have significant coefficients. This result is supportive of the traditional fad’s interpretation of long–term underperformance.

Asymptotic self-similar behavior of solutions for a semilinear parabolic system

Abstract: This paper studies the global existence and the asymptotic self-similar behavior of solutions of the semilinear parabolic system ∂tu=Δu+a1|u|p1-1u+b1|v|q1-1v, ∂tv=Δv+a2|v|p2-1v+b2|u|q2-1u, on (0,∞)×ℝn, where a1, bi∈ℝ and pi, qi>1. Let p=min{p1,p2, q1(1+q2)/(1+q1), q2(1+q1)/(1+q2)}. Under the condition p>1+2/n we prove the existence of globally decaying mild solutions with small initial data. Some of them are asymptotic, for large time, to self-similar solutions of appropriate asymptotic systems having each one a self-similar structure. All possible asymptotic self-similar behaviors are discussed in terms of exponents pi, qi, the space dimension n and the asymptotic spatial profile of the related initial data.

Putting Robust Statistical Methods into Practice: Poverty Analysis in Tunisia

Abstract: Poverty analysis often results in the computation of poverty indexes based on so-called poverty lines which can be region speci…c poverty lines. The poverty lines are made of two components, namely the amount of income to satisfy the food and the non food needs. For both components, one needs to estimate quantities such as local prices or the consummers’ average basket, and this is often done through a parametric model. The resulting estimates depend on the data at hand and on the type of estimators that are used. Classical estimators (and testing procedures) such as the maximum likelihood estimator (MLE) or the least squares (LS) estimator are extremely sensitive to model deviations such as contamination in the data and hence are said not robust. The resulting analysis can therefore give a picture whicjavascript:void(0);h is far from reality. Therefore a robust statistical approach to the estimation of the poverty lines is very important especially because these lines will serve to compute poverty indices. The main purpose of this paper is therefore to show how robust statistical procedure can be used in poverty analysis and the di¤erent picture on poverty comparisons they can give to the Tunisian case.

Contribution of blotting techniques to the study of rapeseeds (Brassica napus L.) lipases.

Abstract: A recent advance in the study of plant lipases involving immunological techniques is presented. In an attempt to characterize lipases of cotyledons from germinating rapeseed seedlings and to investigate an eventual cross-reactivity with animal lipases, we have prepared anti-porcine pancreatic lipase antibodies raised in rabbit. It is shown by enzyme-linked immunosorbent assay and dot-blotting that these antibodies react with lipases in the rapeseed crude extract and in the different cellular fractions obtained by differential centrifugation. Preincubation of the antiserum with the rapeseed crude extract affects the amount of antibodies binding to the porcine pancreatic lipase. We demonstrate immunochemical cross-reactivity between rapeseed and porcine pancreatic lipase. Using the immunoblotting procedure, it is found that antibodies bind specifically to a single polypeptide with a molecular mass of about 55 kDa. Rapeseed lipase activity decreased after immunoprecipitation suggesting that antibodies were bound to some catalytic site residues. We conclude from the data obtained in this study that the two different lipase species present close similarities in amino acid sequence and antigen characteristics.*

Thinking and writing in EFL: cutting off Medusa's Head

Abstract: This research examines university students' writing problems and strategies; it also tries to investigate the way learner difficulties and strategies are perceived by students and teachers. Two questionnaires were conducted to find out both students' and teachers' assessment of these difficulties and strategies, and a corpus of 25 exam copies was examined, errors were classified, their sources analysed and strategies defined. This study aims to point out the major difficulties that our EFL learners encountered in writing and to find out some of the reasons that could explain them. It also tries to see whether there were any discrepancies between the students' and teachers' assessment of writing difficulties and strategies and the students' 'real' problems and strategy use, at least, as they were displayed in their exam copies. One of the major goals is also to identify and define Tunisian learners' writing strategies and see whether they match those of ESL and EFL learners in the literature. The research is based on the following hypotheses: a) Students have difficulties in expressing their thoughts and ideas in the EFL because they generate them in the L1 and then try to translate them in the FL. b)Students' problems are mainly conceptual; i.e, they result fom a lack of understanding of the new concepts introduced in the course and course materials. The results showed that the learners' difficulties were mainly grammatical and organizational and that, just like other learners, our students made use of metacognitive, cognitive, social and affective strategies when handling their linguistic tasks.

Stability and swelling behaviour of a concentrated sponge phase

Abstract: Using small angle X-ray scattering technique, we study the remarkable stability of the sponge phase domain which extends continuously from the brine rich corner to the concentrated side of the phase diagram of a cationic surfactant+alcohol+brine system. The scattering data show the persistence of the elementary bilayer structure, over a very wide range of dilution, while a swelling behaviour is observed independent of sensitive changes of salinity and temperature. We discuss this swelling behaviour on the basis of three different dilution laws which were proposed for a symmetric sponge phase.

The Mahalla: The Origins of Beylical Sovereignty in Ottoman Tunisia during the Early Modern Period

Abstract: (2001). The mahalla: the origins of Beylical sovereignty in Ottoman Tunisia during the early modern period. The Journal of North African Studies: Vol. 6, No. 1, pp. 105-116.

Écoulements transitoires dans les conduites déformables avec dégazage de l'air dissous

Abstract: Un modele mathematique permettant d'etudier le phenomene de degazage de l'air dissous dans les ecoulements transitoires en conduites deformables est presente. Le degazage se produit lorsque la pression devient inferieure a la pression de saturation exprimee par la loi de Henry. Dans ces conditions, la quantite de gaz degagee est proportionnelle a la difference entre les pressions de saturation et ambiante. L'air se degage sous forme de petites bulles qui evoluent selon la loi isotherme. Dans la zone de degazage, la fraction massique en gaz libre est utilisee pour exprimer la masse volumique du fluide a l'aide d'une moyenne ponderee des masses volumiques des deux phases du melange : liquide et gazeuse. L'influence de la deformation radiale des parois de la conduite sur l'evolution du regime transitoire est representee par une relation entre la pression du fluide et la section de la conduite. La formulation mathematique aboutit a un systeme de deux equations aux derivees partielles non lineaires de type hyperbolique dont la resolution est conduite par une methode des differences finies conservatives

About Conditional Belief Function Independence

Abstract: In this paper, we study different concepts of conditional belief functions independence in the context of the transferable belief model. We especially clarify the relationships between the concepts of conditional non-interactivity, irrelevance and doxastic independence. Conditional non-interactivity is defined by the 'mathematical' property useful for computation considerations and corresponds to decomposionality of the belief functions. Conditional irrelevance is defined by a 'common sense' property based on conditioning. Conditional doxastic independence is defined by a particular form of irrelevance, the one preserved under Dempster's rule of combination.

Opérateurs de transmutation et théorème de Paley–Wiener associés à un opérateur aux dérivées et différences sur R

Abstract: Resume Nous considerons un operateur aux derivees et differences singulier Λ sur la droite reelle. Nous construisons une paire de transformations integrales qui transmutent Λ en l'operateur d / d x . En utilisant les proprietes de ces operateurs de transmutation, on definit une nouvelle analyse harmonique sur R correspondant a l'operateur Λ .

Nucleotide sequence comparison of the 3' terminal region of the genome of pepper vein mottle virus isolates from Tunisia and Ivory Coast.

Abstract: Three Tunisian PVMV isolates identified in pepper and tomato fields and one isolate from Ivory Coast were submitted to biological and molecular analysis Phenotypically, Tunisian isolates induced mild symptoms while the Ivory Coast one is more aggressive on tobacco As no PVMV sequence data are available, detailed sequence comparisons of coat protein gene (CP) were made No nucleotide or amino acid changes in this region could be related to the pathogenicity of the isolates analysed With the aim to increase our molecular understanding of the biological properties, we have sequenced the 3'-non translated region (3'NTR) Results suggest that this region of the RNA genome may be involved in the modulation of disease symptoms

Preuves de la non-stratification du Trias dans le Turonien de la Koudiat Sidii (Nord-Ouest de la Tunisie)

Abstract: The cartographic and biostratigraphic datings carried out at Koudiat Sidii do not confirm the interbedding of the Triassic rocks within the Turonian sediments. Interrelationships between cartographic, drill holes and gravimetric dating show that the Triassic rocks form the core of a large anticline, flanked by Cretaceous and Neogene outcrops. Of this structure, in large parts collapsed and buried under a thick Quaternary deposit, we only see the western flank, formed by dolomitic breccia of Triassic rocks supporting a set that spreads from Upper Cenomanian to Upper Senonian. The occurrence of Triassic debris flow reworked in the Turonian allows us to interpret the Triassic material as a diapiric extrusion, which reached the surface during the Turonian times, in the tectonic corner of ancient faults trending north–south and NE–SW. During the Tertiary tightening phases, oriented NW–SE, the induced folded structures are strongly controlled by these tectonic directions. Particularly, the meridian fold corresponds to the torsion of J. Hout NE–SW fold in the neighbourhood of the north–south palaeofaults.