2,223 research outputs found

    Transport in the metallic regime of Mn doped III-V Semiconductors

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    The standard model of Mn doping in GaAs is subjected to a coherent potential approximation (CPA) treatment. Transport coefficients are evaluated within the linear response Kubo formalism. Both normal (NHE) and anomalous contributions (AHE) to the Hall effect are examined. We use a simple model density of states to describe the undoped valence band. The CPA bandstructure evolves into a spin split band caused by the p‚ąídp-d exchange scattering with Mn dopants. This gives rise to a strong magnetoresistance, which decreases sharply with temperature. The temperature (TT) dependence of the resistance is due to spin disorder scattering (increasing with TT), CPA bandstructure renormalization and charged impurity scattering (decreasing with TT). The calculated transport coefficients are discussed in relation to experiment, with a view of assessing the overall trends and deciding whether the model describes the right physics. This does indeed appear to be case, bearing in mind that the hopping limit needs to be treated separately, as it cannot be described within the band CPA.Comment: submitted to Phys. Rev.

    Development and Implementation of an Isentropic Potential Vorticity Algorithm for use at Air Force Global Weather Center

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    This thesis presents and validates methods for calculating isentropic potential vorticity (IPV) and applies these methods in software programs planned for implementation at the Air Force Global Weather Center (AFGWC). The IPV programs will provide Air Force Weather forecasters additional tools to diagnose atmospheric kinematics and understand atmospheric dynamics. A FORTRAN program is recommended using mandatory-level isobaric data projected to be available on AFGWC computer systems, specifically, from the Navy Operational Global Atmosphere Prediction System and Medium Range Forecast models. Program development and analysis consists of three main steps: (1) data retrieval; (2) IPV calculations; and, (3) interpolation to an isentropic vertical coordinate system. This thesis recommends performing IPV calculations at constant pressure for comparison with other mandatory-level isobaric parameters, or in routine cross-sectional analysis. Additionally, a recommendation is made to calculate IPV at constant potential temperature from interpolated isentropic state variables instead of interpolating isobaric IPV fields. Applications of the developed programs include visualization of synoptic-scale motions an alternative method of locating the tropopause in cross-sectional analysis. This thesis is a significant effort to move toward operational use of isentropic analysis and the incorporation of IPV analysis into forecasting techniques at AFGWC

    Le Traitement des Eaux de Consommation : La Nécessité d'une Recherche en Chimie de l'Eau

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    L'objectif principal de cet article est de montrer que les travaux de recherche en chimie de l'eau sont absolument n√©cessaires √† la compr√©hension des ph√©nom√®nes r√©gissant la qualit√© des eaux de consommation produites et distribu√©es, ainsi qu'au d√©veloppement de technologies innovantes dans le domaine du traitement de ces eaux. Pour l'atteindre, il a √©t√© choisi de pr√©senter trois exemples des recherches men√©es √† l'Universit√© de Poitiers et √† l'√Čcole Polytechnique de Montr√©al¬†: deux exemples de recherche fondamentale, sur les mati√®res organiques naturelles et sur les m√©canismes d'oxydation par les radicaux hydroxyle et un exemple de la recherche d'application, sur l'√©volution de la qualit√© de l'eau lors de son traitement biologique par ozonation coupl√©e √† la filtration sur charbon actif en grains.The main purpose of this paper is to demonstrate that a better understanding of chemical reactions and a better technologies development for the drinking water treatment absolutly needs research in water chemistry. In order to reach this objective, two examples of recent fundamental research works in water chemistry and one example of research applied to drinking water treatment have been selected.The first one concerns a fundamental research on characterization and analysis of natural organic matter. Nowadays, the main analytical tools used for quantification of NOM are DOC (BDOC for the biodegradable fraction) and UV-absorbance. However, a better knowledge of NOM would be useful to predict water quality and determination of doses of some treatment chemicals, such as coagulants and oxidants. This paper presents some data about (i) NOM fractionning by XAD macroporous resins and relationship between UV-absorbance and 13C-NMR, and (ii) study of chlorination of the isolated fractions. Based on these results, one can suppose that aquatic NOM could be soon easily fractionnated and characterized by simples analytical tools. However, many research works are still necessary, particularly on the field of relationships between data of "heavy" analytical tools (13C-NMR, pyrolysis/GC/MS, etc.) and more simple others (UVA/DOC, BDOC, fluorescence etc.).The second paragraph of the paper relates oxidation mechanisms by hydroxyl radicals. In ozonation of drinking water, currently applied in the drinking water treatment, OH radicals production is a necessary consequence, considered as the main action of ozone by some authors. So, disinfection quality, bromate production, BDOC formation, pesticides removal will never be entirely understood as long as hydroxyl radicals participation in ozonation processes will not be really cleared up. To illustrate this purpose, the example of ozonation of a free aminoacid (glycine) by molecular ozone and by OH radicals is shown. Oxidation by "pure" OH radicals, produced by radiolysis, as compared to oxidation by molecular ozone, (at acidic pH in the presence of radical scavengers) shows that two mechanisms are really different. So, some works published some years ago, mixed up the two pathways. Such mechanisms on aminoacids oxidation should allow to understand some more descriptive data on water disinfection and pesticides oxidation.The third example concerns the changes of water quality during ozone/GAC treatment. It is well known that ozonation of naturel waters leads to an enhancement of water biodegradability, in terms of BDOC increase. So, if this BDOC is not removed in the plant, it can be the origin of bacteria regrowth in distribution system. The solutions are either to include, after ozonation step, a biological treatment step on activated carbon (BAC), or to increase chlorination doses applied in final disinfection. The effects of BAC treatment on BDOC and ozonation by-products removals, in the case of the drinking water treatment plant of Sainte-Rose (City of Laval, Quebec, Canada), are described. Finally, taking into account the cost of such a process, the last paragraph of this paper gives some recommandations for conception on BAC treatment.As for general conclusion, some new research topics in water chemistry for the drinking water treatment are enumerated and some ideas about organization and development of applied and fundamental researches in water chermistry for the drinking water treatment, are given

    Multi-scale analysis of compressible viscous and rotating fluids

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    We study a singular limit for the compressible Navier-Stokes system when the Mach and Rossby numbers are proportional to certain powers of a small parameter \ep. If the Rossby number dominates the Mach number, the limit problem is represented by the 2-D incompressible Navier-Stokes system describing the horizontal motion of vertical averages of the velocity field. If they are of the same order then the limit problem turns out to be a linear, 2-D equation with a unique radially symmetric solution. The effect of the centrifugal force is taken into account

    Approche pour l'identification des causes de la mauvaise décantation des solides biologiques

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    Les procédés d'épuration biologique à culture libre (boues activées) comprennent habituellement un décanteur qui permet de concentrer les solides biologiques en vue de leur recirculation en tête du réacteur biologique. Lorsque ce décanteur fonctionne mal on observe une perte de solides biologiques (SB), ce qui se traduit par une augmentation de la concentration des matières en suspension (MES) dans l'effluent du décanteur secondaire et par une baisse des performances du procédé d'épuration. Lorsque la concentration de MES dans l'effluent du décanteur secondaire est trop élevée on mesure l'indice de volume des boues (IVB). Un IVB faible indique que les solides biologiques ont de bonnes caractéristiques de décantation de sorte que la cause de la mauvaise efficacité du décanteur est d'ordre physique et peut être identifiée facilement. Lorsque l'IVB est élevé, la mauvaise décantation est alors causée par un désordre de l'écosystème qui se traduit le plus souvent par une croissance excessive d'organismes filamenteux. Les causes et les solutions d'un tel problème sont alors difficiles à identifier. Pour ce travail, les auteurs ont réalisé une importante revue bibliographique dont les résultats sont présentés sous la forme d'un cheminement critique (fig. 1). Dans cette figure, les cases numérotées de 1 à 48 sont liées par des énoncés logiques. Ainsi, en répondant à des questions simples, il est possible de cheminer dans la figure 1 et d'identifier les causes les plus probables du déséquilibre microbiologique ainsi que les solutions qui ont déjà été apportées avec succès. De plus les auteurs ont associé à chaque case une fiche technique (portant le même numéro que la case) sur laquelle sont présentées des explications et la liste des références consultées.Activated sludge is a microbiological aerated sewage treatment process which includes a secondary clarifier to separate the treated effluent from the biological solids. Part of the concentrated solids is recirculated to maintain an adequate concentration of mixed liquor suspended solids (MLSS) In the aerated basin. When the secondary clarifier malfunctions, some biological solids are lost to the effluent : the process efficiency drops and the concentration of suspended solids (SS) increases. When the SS in the effluent is too high the sludge volume index (SVI) must be measured. A low SVI means that the biological solids have good sedimentation characteristics : the problem is thon physical in nature and is easily identified. When the SVI is high, the problem is due to a disturbance of the microbiological ecosystem, which is at the origin of excessive filamentous organism growth. The origins and solutions of such a problem are much harder to find. To this end the authors proceeded with an important review of the literature, the results of which are summarized through a critical path, in figure 1. Files from 1 to 48 are linked by logical statements in such a way that by answering simple questions, one can proceed through the files and identify the must probable cause of the biological disturbance as well as the solution which has already proven successful. Furthermore, the authors have linked each file to a technical file which bears the same number and on which an explanation and references are found.Before proceeding with figure 1 to identify a problem in real life, one must obtain information, resulting from an analysis and observations, with regard to plant effluent, primary clarifier effluent and activated sludge characteristics, including the MLSS concentration. One must also know the chemical oxygen demand (COD), the soluble and total biochemical oxygen demand (BOD5), as well as the nitrogen and phosphorus concentrations in the plant influent. Furthermore, one must also be told of the presence of toxic material or industrial wastes in the sewage and of the fraction of pollution load which is in the form of particulates. Whether sudden changes in the quality of the plant influent have occurred is worth knowing. The concentration of oxygen or hydrogen sulfide in the primary clarifier is also important. One must also gather data related to the activated sludge treatment itself : type of reactor (completely mixed or plug flow), mixed liquor volatile suspended solids (MLVSS) concentration, dissolved oxygen concentration, rate of oxygen uptake and pH. Finally, the results of a microbiological analysis of the sludge are very useful.To illustrate the use of figure 1, let us say that we have the following data :a) Many filamentous microorganisms are present in the MLSS, in particular Microthrix parvicella, type 0092, and Thiothrix sp;b) The rate of dissolved oxygen uptake is 12 mg O2/g of SS - h;c) The rate of COD removal is 0,48 Kg/Kg of SS -d;d) There are no toxic substances in the plant influent;e) There are no abrupt changes in plant influent quality;f) The pHs of the plant influent and of the MLSS are 7,0 and 6,8 respectively;g) The ammonia nitrogen concentration of the plant influent is 1,2 mg/L (N);h) The phosphorus concentration of the plant influent is 4,4 mg/L (P);i) The total and soluble BOD5 concentrations of the plant influent are 400 and 80 mg/L respectively.With this information, we are ready to proceed through figure 1. From file one, one goes to file 2, since the rate of oxygen uptake is sufficient. Otherwise, we would have proceeded to file 32. The reactor being completely mixed, the next step is file 3, where it is said that, because of the low soluble BOD5 concentration one must go to file 9, where we find a fast of filamentous microarganisms which may be responsible for the disturbance. Since two of these microorganisms are effectively present in the mixed liquor suspended solids (MLSS), Microthrox parvicella and type 0092, we are invited to go to file 35, where it is stated that someone has already solved a similar problem by creating a modified contact zone to increase the substrats (organic matter) concentration around the microbiological flocs. The third filamentous microorganism is not identified in file 9. As a second possibility one may assume, in file 2. That the mixing is not complete, which is often the case. With the help of information and results of analyses already available, we proceed, through file 4, 14, 15 and 16, to file 20 where Thiothrixsp is included in the microorganisms listed. File 20 is linked to file 41, where it is said that the controlled addition of nitrogen in the plant influent has already been used to solve this type of problem.The critical path presented in this article is the result of an elaborate study. It may be used as a tool to identify the causes of bad biological flocs sedimentation in the secondary clarifier and select solutions that have already been used successfully

    Microvolume Protein Concentration Determination using the NanoDrop 2000c Spectrophotometer

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    Traditional spectrophotometry requires placing samples into cuvettes or capillaries. This is often impractical due to the limited sample volumes often used for protein analysis. The Thermo Scientific NanoDrop 2000c Spectrophotometer solves this issue with an innovative sample retention system that holds microvolume samples between two measurement surfaces using the surface tension properties of liquids, enabling the quantification of samples in volumes as low as 0.5-2 őľL. The elimination of cuvettes or capillaries allows real time changes in path length, which reduces the measurement time while greatly increasing the dynamic range of protein concentrations that can be measured. The need for dilutions is also eliminated, and preparations for sample quantification are relatively easy as the measurement surfaces can be simply wiped with laboratory wipe. This video article presents modifications to traditional protein concentration determination methods for quantification of microvolume amounts of protein using A280 absorbance readings or the BCA colorimetric assay

    Existence of global strong solutions to a beam-fluid interaction system

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    We study an unsteady non linear fluid-structure interaction problem which is a simplified model to describe blood flow through viscoleastic arteries. We consider a Newtonian incompressible two-dimensional flow described by the Navier-Stokes equations set in an unknown domain depending on the displacement of a structure, which itself satisfies a linear viscoelastic beam equation. The fluid and the structure are fully coupled via interface conditions prescribing the continuity of the velocities at the fluid-structure interface and the action-reaction principle. We prove that strong solutions to this problem are global-in-time. We obtain in particular that contact between the viscoleastic wall and the bottom of the fluid cavity does not occur in finite time. To our knowledge, this is the first occurrence of a no-contact result, but also of existence of strong solutions globally in time, in the frame of interactions between a viscous fluid and a deformable structure

    Adopting OER Across the University

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    In this presentation, four faculty members from across disciplines will present their experience adopting open educational resources and open pedagogical practices in their Fall 2019 courses. The presentation will share the benefits and challenges of OER, methods for overcoming challenges, student perceptions of OER, and highlights from each course
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