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Search Results: 1 - 10 of 60 matches for " Djamila Hourlier "
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Size-dependent catalytic and melting properties of platinum-palladium nanoparticles
Guisbiers Grégory,Abudukelimu Gulmira,Hourlier Djamila
Nanoscale Research Letters , 2011,
Abstract: While nanocatalysis is a very active field, there have been very few studies in the size/shape-dependent catalytic properties of transition metals from a thermodynamical approach. Transition metal nanoparticles are very attractive due their high surface to volume ratio and their high surface energy. In particular, in this paper we focus on the Pt-Pd catalyst which is an important system in catalysis. The melting temperature, melting enthalpy, and catalytic activation energy were found to decrease with size. The face centered cubic crystal structure of platinum and palladium has been considered in the model. The shape stability has been discussed. The phase diagram of different polyhedral shapes has been plotted and the surface segregation has been considered. The model predicts a nanoparticle core rich in Pt surrounded by a layer enriched in Pd. The Pd segregation at the surface strongly modifies the catalytic activation energy compared to the non-segregated nanoparticle. The predictions were compared with the available experimental data in the literature. PACS 65.80-g; 82.60.Qr; 64.75.Jk
Polarization-dependent light extinction in ensembles of polydisperse, vertical semiconductor nanowires: A Mie scattering effective medium
Grzegorz Grzela,Djamila Hourlier,Jaime Gómez Rivas
Physics , 2013, DOI: 10.1103/PhysRevB.86.045305
Abstract: We present an experimental and theoretical study of the angle- and polarization-dependent light extinction in random arrays of polydisperse semiconductor nanowires epitaxially grown on substrates. The specular reflectance is described by averaging the scattering properties of individual nanowires obtained from Lorenz-Mie theory over the diameter distribution. The complex effective refractive index describing the propagation and attenuation of the coherent beam scattered in forward direction is determined in the independent scattering approximation and used to calculate the angle- and polarization-dependent reflectance. Our measurements demonstrate the highly anisotropic scattering in ensembles of aligned nanowires.
Antimicrobial activity of autochthonous lactic acid bacteria isolated from Algerian traditional fermented milk “Ra b”
M Abdelbasset, K Djamila
African Journal of Biotechnology , 2008,
Abstract: Twenty samples of traditional fermented milk “Raib” were collected in eastern Algeria from individual household. They were evaluated for the presence of autochthonous bacteriocin-producing lactic acid bacteria. From 13 of these samples 52 strains of lactic acid bacteria were isolated, and shown to exhibit inhibitory activity against the indicator strain Listeria monocytogenes. Five of these inhibitor-producing isolates were selected for further study on the basis of their relatively wide antimicrobial spectrum. The inhibitory spectra of activity of the selected strains were evaluated against a range of Gram-positive and Gram-negative test organisms. Listeria monocytogenes and Staphylococcus aureus were the most sensitive indicator tested. All the antimicrobial compounds produced by the selected lactic acid bacteria were fully or partially inactivated by some of the proteolytic enzymes, but were unaffected by catalase which indicates their proteinaceous nature. The compounds were heat stable up to 120°C for 20 min, and were active from pH 3.0 to 10.0. Highest bacteriocin activity was recorded under acidic conditions and activity decreased with increasing alkalinity.
Study of the Kinetics Adsorption of Organic Pollutants on Modified Cellulosic Polymer Using Ultraviolet-Visible Spectroscopy
Djamila Ghemati,Djamel Aliouche
Journal of Spectroscopy , 2013, DOI: 10.1155/2013/639717
Abstract: We report a study on the formation of the complex acrylamidomethylated-β-cyclodextrin, then on the grafting on cellulosic polymer. The grafting is initiated by ceric ions Ce(IV) and confirmed by infrared spectroscopy analysis (FTIR). Scanning electron microscopy (SEM) analysis was carried out to evaluate properties of structure and surface of grafted polymers. The experiments of the study of adsorption of balance of phenol and hydroquinone and a reactive dye, acid dyes, and cationic dyes using ultraviolet-visible microscopy were made in aqueous solutions for 24 hours at different pH. Our results indicate formation of a permanent chemical bond between β-cyclodextrin and polymers material. The cellulosic polymers can effectively be modified without significant change in the structural properties. Then, the results of organic pollutants adsorption in aqueous medium show the aptitude of the polymer modified to fix the phenol derivatives and synthetics dyes and used in the processing industrial liquid waste. The differences in adsorption capacities may be due to the effect of dye structure. The negative value of free energy change indicated the spontaneous nature of adsorption. 1. Introduction Phenol is an aromatic organic compound, is toxic by ingestion, inhalation or by contact, and destroys aquatic microorganisms. It has a characteristic pungent odor and a contact giving an intense burning. Phenol and its derivatives are present in discharges from several industrial sectors such as oil refineries, chemical plants, or processes for treating wood. It is mainly used in organic synthesis; it is the raw material for production of bisphenol A, caprolactam, alkyl phenols, salicylic acid, and diphenyl ethers of chlorophenols. For these reasons, phenol and its derivatives are among the most common pollutants in industrial wastewater. However, even at very low concentrations, phenol gives the water an unpleasant taste and smell, which is why it is necessary to develop and implement effective methods of treatment of phenolic wastewater. Phenol and its compounds are usually removed by adsorption or biological treatment [1]. Color is the first contaminant to be recognized in wastewater and the presence of very small amounts of dyes in water is highly visible and undesirable. Neglecting this aesthetic problem, the greatest environmental concern with dyes is their absorption and reflection of sunlight entering the water, which interferes with the growth of bacteria, limiting it to levels insufficient to biologically degrade impurities in the water. It is evident,
Décomposition monomorphe des structures relationnelles et profil de classes héréditaires
Djamila Oudrar,Maurice Pouzet
Mathematics , 2014,
Abstract: We present a structural approach of some results about jumps in the behavior of the profile (alias generating function) of hereditary classes of finite structures. We start with the following notion due to N.Thi\'ery and the second author. A \emph{monomorphic decomposition} of a relational structure $R$ is a partition of its domain $V(R)$ into a family of sets $(V_x)_{x\in X}$ such that the restrictions of $R$ to two finite subsets $A$ and $A'$ of $V(R)$ are isomorphic provided that the traces $A\cap V_x$ and $A'\cap V_x$ have the same size for each $x\in X$. Let $\mathscr S_\mu $ be the class of relational structures of signature $\mu$ which do not have a finite monomorphic decomposition. We show that if a hereditary subclass $\mathscr D$ of $\mathscr S_\mu $ is made of ordered relational structures then it contains a finite subset $\mathfrak A$ such that every member of $\mathscr D$ embeds some member of $\mathfrak A$. Furthermore, for each $R\in \mathfrak A$ the profile of the age $\mathcal A(R)$ of $R$ (made of finite substructures of $R$) is at least exponential. We deduce that if the profile of a hereditary class of finite ordered structures is not bounded by a polynomial then it is at least exponential. This result is a part of classification obtained by Balogh, Bollob\'as and Morris (2006) for ordered graphs. {\it To cite this article: Djamila Oudrar, Maurice Pouzet, C. R. Acad. Sci. Paris, Ser. I.}
Profile and hereditary classes of ordered relational structures
Djamila Oudrar,Maurice Pouzet
Mathematics , 2014,
Abstract: Let $\mathfrak{C}$ be a class of finite combinatorial structures. The \textit{profile} of $\mathfrak{C}$ is the function $\varphi_{\mathfrak{C}}$ which counts, for every integer $n$, the number $\varphi_{\mathfrak{C}}(n)$ of members of $\mathfrak{C}$ defined on $n$ elements, isomorphic structures been identified. The \textit{generating function of} $\mathfrak{C}$ is $\mathcal {H}_{\mathfrak{C}}(x):=\sum_{n\geqq 0}\varphi_{\mathfrak{C}}(n)x^{n}$. Many results about the behavior of the function $\varphi_{\mathfrak{C}}$ have been obtained. Albert and Atkinson have shown that the generating series of several classes of permutations are algebraic. In this paper, we show how their results extend to classes of ordered binary relational structures; putting emphasis on the notion of hereditary well quasi order, we discuss some of their questions and answer one.
A Metapopulation Model for Chikungunya Including Populations Mobility on a Large-Scale Network
Djamila Moulay,Yoann Pigné
Computer Science , 2012, DOI: 10.1016/j.jtbi.2012.11.008
Abstract: In this work we study the influence of populations mobility on the spread of a vector-borne disease. We focus on the chikungunya epidemic event that occurred in 2005-2006 on the R\'eunion Island, Indian Ocean, France, and validate our models with real epidemic data from the event. We propose a metapopulation model to represent both a high-resolution patch model of the island with realistic population densities and also mobility models for humans (based on real-motion data) and mosquitoes. In this metapopulation network, two models are coupled: one for the dynamics of the mosquito population and one for the transmission of the disease. A high-resolution numerical model is created out from real geographical, demographical and mobility data. The Island is modeled with an 18 000-nodes metapopulation network. Numerical results show the impact of the geographical environment and populations' mobility on the spread of the disease. The model is finally validated against real epidemic data from the R\'eunion event.
Effect of Humidity on Thermal Comfort in the Humid Tropics  [PDF]
Harimi Djamila, Sivakumar Kumaresan, Chi-Ming Chu
Journal of Building Construction and Planning Research (JBCPR) , 2014, DOI: 10.4236/jbcpr.2014.22010
Abstract: This paper presents the main findings of the effect of indoor humidity on occupants’ thermal comfort in the humid tropics of Malaysia. An extensive field investigation was carried out in Kota Kinabalu city and the surrounding areas, located in East Malaysia. A total of 890 individuals were asked to complete a questionnaire. Measured indoor climates were also recorded. The survey was designed as cross sectional data collection. The present investigation found that the occupants were thermally comfortable at wide relative humidity range. The mean relative humidity corresponding to the optimum comfort temperature was close to 73%. Regression models failed to predict accurately the effect of relative humidity on occupants’ thermal perceptions. In addition, a quadratic regression model was developed for the prediction of the mean indoor relative humidity based on indoor temperature. The suggested regression model can be used for an approximate prediction of indoor relative humidity when required.
Research and Filtering Informations from Internet with Agents
Sid Ahmed Rahal,Djamila Mokeddem
Information Technology Journal , 2007,
Abstract: This research presents a conceptual framework of multiagent system destined to information-rich environment such as the Internet. The system has three types of agents: Interface Agent, Execution agent and Information Agents. We particularly describe the Interface Agent Filter-Agent that interact with the user receiving user specifications and delivering results according to user preferences (user profile). Filter-Agent is an information filter for Internet news groups using a neural prediction model to score articles based on relevance. The filtering process uses the technique called the backward propagation of errors to adjust the connection weights of a neural network with three layers. The elements of network input vector are not simply the occurrences of terms in documents, but we use the TFIDF formula. The user can construct his profile in a particular domain, providing a keywords set and selecting a sample of documents which he evaluates with feedback values. The trained network uses the article profile to predict expected usefulness as represented by the feedback value. Documents are sorted in descending order of the output value computed.
Catalytic Reduction of Benzaldehyde Under Hydrogen Flow over Nickel-Containing Mesoporous Silica Catalysts  [PDF]
Adel Saadi, Kahina Lanasri, Khaldoun Bachari, Djamila Halliche, Chérifa Rabia
Open Journal of Physical Chemistry (OJPC) , 2012, DOI: 10.4236/ojpc.2012.21010
Abstract: The hydrogenation of benzaldehyde over a series of nickel-containing mesoporous silicas with different nickel contents was studied at atmospheric pressure in the range temperature of 393 - 513 K under H2 ?ow. These materials (noted Nin-HMS with n = Si/Ni = 50, 25, 15) have been prepared at room temperature using a route based on hydrogen bonding and self-assembly between neutral primary amine micelles (S0) and neutral inorganic precursors (I0). They were characterized by their chemical analysis, BET surface area, XRD, FT-IR, and SEM microscopy. The obtained products were benzylalcohol, toluene, benzene with yields depending on the nickel content (Si/Ni ratio) and reaction temperature. The products of benzaldehyde hydrogenation (benzylalcohol, and toluene) and hydrogenolysis (benzene) were preferentially formed at low/middle and high reaction temperature respectively. The mesoporous Ni-containing materials were very active hydrogenation catalysts with almost 90% selectivity to benzylalcohol product and showed excellent stability. A mechanism in which the reaction could be initiated by a benzaldehyde reduction over Nin-HMS materials under hydrogen flow with formation of reaction products is proposed.
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