945 resultados para Cr3 diffusion
Resumo:
Au-del des variables climatiques, dautres facteurs non climatiques sont considrer dans lanalyse de la vulnrabilit et de ladaptation au changement et variabilit climatiques. Cette mutation de paradigme place lagent humain au centre du processus dadaptation au changement climatique, notamment en ce qui concerne le rle des rseaux sociaux dans la transmission des nouvelles ides. Dans le domaine de lagriculture, le recours aux innovations est prn comme stratgie dadaptation. Llaboration et lappropriation de ces stratgies dadaptation peuvent tre considres comme des processus dinnovation qui dpendent autant du contexte social et culturel dun territoire, de sa dynamique, ainsi que de la stratgie elle-mme. Aussi, lappropriation et la diffusion dune innovation soprent partir dun processus dcisionnel lchelle de lexploitation agricole, qui son tour, demande une comprhension des multiples forces et facteurs externes et internes lexploitation et les multiples objectifs de lexploitant. Ainsi, la comprhension de lenvironnement dcisionnel de lexploitant agricole lchelle de la ferme est vitale, car elle est un pralable incontournable au succs et la durabilit de toute politique dadaptation de lagriculture. Or, dans un secteur comme lagriculture, il est reconnu que les rseaux sociaux par exemple, jouent un rle crucial dans ladaptation notamment, par le truchement de la diffusion des innovations. Aussi, lobjectif de cette recherche est danalyser comment les exploitants agricoles sapproprient et conoivent les stratgies dadaptation au changement et la variabilit climatiques dans une perspective de diffusion des innovations. Cette tude a t mene en Montrgie-Ouest, rgion du sud-ouest du Qubec, connue pour tre lune des plus importantes rgions agricoles du Qubec, en raison des facteurs climatiques et daphiques favorables. Cinquante-deux entrevues ont t conduites auprs de diffrents intervenants lagriculture aux niveaux local et rgional. Lapproche grounded theory est utilise pour analyser, et explorer les contours de lenvironnement dcisionnel des exploitants agricoles relativement lutilisation des innovations comme stratgie dadaptation. Les rsultats montrent que les innovations ne sont pas implicitement conues pour faire face aux changements et la variabilit climatiques mme si lvolution du climat influence leur mergence, la dcision dinnover tant largement dtermine par des considrations conomiques. Dautre part, ltude montre aussi une faiblesse du capital sociale au sein des exploitants agricoles lie linfluence prpondrante exerce par le secteur priv, principal fournisseur de matriels et intrants agricoles. Linfluence du secteur priv se traduit par la domination des considrations conomiques sur les proccupations cologiques et la tentation du profit court terme de la part des exploitants agricoles, ce qui pose la problmatique de la soutenabilit des interventions en matire dadaptation de lagriculture qubcoise. Ltude fait ressortir aussi la complmentarit entre les rseaux sociaux informels et les structures formelles de soutien ladaptation, de mme que la ncessit dtablir des partenariats. De plus, ltude place ladaptation de lagriculture qubcoise dans une perspective dadaptation prive dont la russite repose sur une socialisation des innovations, laquelle devrait conduire lmergence de processus institutionnels formels et informels. La mise en place de ce type de partenariat peut grandement contribuer amliorer le processus dadaptation lchelle locale.
Resumo:
La concentration locale des messagers chimiques secretes par les cellules peut etre mesuree afin de mieux comprendre les mecanismes moleculaires lies a diverses maladies, dont les metastases du cancer. De nouvelles techniques analytiques sont requises pour effectuer ces mesures locales de marqueurs biologiques a proximite des cellules. Ce memoire presentera le developpement dune nouvelle technique basee sur la reponse plasmonique sur des leviers AFM, permettant detudier les reactions chimiques et biologiques a la surface des leviers grace au phenomene de resonance des plasmons de surface (SPR), ainsi qua la diffusion Raman exaltee par effet de pointe (TERS). En effet, il est possible de localiser lamplification du signal Raman a la pointe dun levier AFM, tout comme le principe de la diffusion Raman exaltee par effet de surface (SERS) basee sur la diffusion de la lumiere par des nanoparticules metalliques, et permettant une large amplification du signal Raman. La surface du levier est recouverte dune nano-couche metallique dor, suivi par des reactions biologiques pour limmobilisation dun recepteur moleculaire, creant ainsi un biocapteur sur la pointe du levier. Une detection secondaire utilisant des nanoparticules dor conjuguees a un anticorps secondaire permet egalement une amplification du signal SPR et Raman lors de la detection dantigene. Ce memoire demontrera le developpement et la validation de la detection de limmunoglobuline G (IgG) sur la pointe du levier AFM.Dans des projets futurs, cette nouvelle technique dinstrumentation et dimagerie sera optimisee grace a la creation dun micro-detecteur proteique generalement adapte pour letude de la communication cellulaire. En integrant le signal SPR a la microscopie AFM, il sera alors possible de developper des biocapteurs SPR couples a une sonde a balayage, ce qui permettra deffectuer une analyse topographique et de lenvironnement chimique dechantillons cellulaires en temps reel, pour la mesure des messagers moleculaires secretes dans la matrice extracellulaire, lors de la communication cellulaire.
Resumo:
Introduction. Les programmes de vlos en libre-service (PVLS) reprsentent une innovation en transport actif. ce jour, la sensibilisation cette innovation en tant que prrequis laccessibilit na jamais t tudie. Objectif. Identifier les facteurs lis labsence de sensibilisation lexistence du PVLS Montral. Mthode. 7011 Montralais gs de 18 ans et plus ont t interrogs au cours de 3 sondages tlphoniques sur une priode couvrant deux saisons : avant la premire saison (n=2000), aprs la premire saison (n=2502) et aprs la deuxime saison (n=2509). Des analyses de rgression logistique ont t ralises sur 93,6 % (n=6562) de lchantillon pour examiner leffet du temps, de la proximit des stations de vlos et du niveau dducation sur labsence de sensibilisation lexistence du PVLS. Rsultats. Nous constatons que, aprs la premire saison dimplantation du PVLS, la probabilit dabsence de sensibilisation au PVLS est plus leve chez les individus dont le niveau dducation est faible que chez ceux dont le niveau dducation est lev (RC = 1,60; 95 % IC : 1,18; 2,19). Aussi, nous observons que, aprs la deuxime saison dimplantation, la probabilit dabsence de sensibilisation au PVLS est plus leve chez les individus dont le niveau dducation est faible et qui vivent dans un voisinage pourvu dun PVLS, que chez ceux dont le niveau dducation est lev et qui vivent dans un voisinage dpourvu dun PVLS (RC = 1,63, 95 % IC : 1,01; 2,64). Conclusion. Malgr laccessibilit au PVLS dans un voisinage, des ingalits sociales persistent.
Resumo:
Travail ralis l'EBSI, Universit de Montral, sous la direction de M. Yvon Lemay dans le cadre du cours SCI6850 Recherche individuelle, l'hiver 2015
Resumo:
On line isotope separation techniques (ISOL) for production of ion beams of short-lived radionuclides require fast separation of nuclear reaction products from irradiated target materials followed by a transfer into an ion source. As a first step in this transport chain the release of nuclear reaction products from refractory metals has been studied systematically and will be reviewed. High-energy protons (500 - 1000 MeV) produce a large number of radionuclides in irradiated materials via the nuclear reactions spallation, fission and fragmentation. Foils and powders of Re, W, Ta, Hf, Mo, Nb, Zr, Y, Ti and C were irradiated with protons (600 - 1000 MeV) at the Dubna synchrocyclotron, the CERN synchrocyclotron and at the CERN PS-booster to produce different nuclear reaction products. The main topic of the paper is the determination of diffusion coefficients of the nuclear reaction products in the target matrix, data evaluation and a systematic interpretation of the data. The influence of the ionic radius of the diffusing species and the lattice type of the host material used as matrix or target on the diffusion will be evaluated from these systematics. Special attention was directed to the release of group I, II and III-elements. Arrhenius plots lead to activation energies of the diffusion process.
Resumo:
A simple method based on laser beam deflection to study the variation of diffusion coefficient with concentration in a solution is presented. When a properly fanned out laser beam is passed through a rectangular cell filled with solution having concentration gradient, the emergent beam traces out a curved pattern on a screen. By taking measurements on the pattern at different concentrations, the variation of diffusion coefficient with concentration can be determined.
Resumo:
In the present study, radio frequency plasma polymerization technique is used to prepare thin films of polyaniline, polypyrrole, poly N-methyl pyrrole and polythiophene. The thermal characterization of these films is carried out using transverse probe beam deflection method. Electrical conductivity and band gaps are also determined. The effect of iodine doping on electrical conductivity and the rate of heat diffusion is explored.Bulk samples of poyaniline and polypyrrole in powder form are synthesized by chemical route. Open photoacoustic cell configuration is employed for the thermal characterization of these samples. The effect of acid doping on heat diffusion in these bulk samples of polyaniline is also investigated. The variation of electrical conductivity of doped polyaniline and polypyrrole with temperature is also studied for drawing conclusion on the nature of conduction in these samples. In order to improve the processability of polyaniline and polypyrrole, these polymers are incorporated into a host matrix of poly vinyl chloride. Measurements of thermal diffusivity and electrical conductivity of these samples are carried out to investigate the variation of these quantities as a function of the content of polyvinyl chloride.
Resumo:
In a recent paper [Phys. Rev. B 50, 3477 (1994)], P. Fratzl and O. Penrose present the results of the Monte Carlo simulation of the spinodal decomposition problem (phase separation) using the vacancy dynamics mechanism. They observe that the t1/3 growth regime is reached faster than when using the standard Kawasaki dynamics. In this Comment we provide a simple explanation for the phenomenon based on the role of interface diffusion, which they claim is irrelevant for the observed behavior.
Resumo:
A model has been developed for evaluating grain size distributions in primary crystallizations where the grain growth is diffusion controlled. The body of the model is grounded in a recently presented mean-field integration of the nucleation and growth kinetic equations, modified conveniently in order to take into account a radius-dependent growth rate, as occurs in diffusion-controlled growth. The classical diffusion theory is considered, and a modification of this is proposed to take into account interference of the diffusion profiles between neighbor grains. The potentiality of the mean-field model to give detailed information on the grain size distribution and transformed volume fraction for transformations driven by nucleation and either interface- or diffusion-controlled growth processes is demonstrated. The model is evaluated for the primary crystallization of an amorphous alloy, giving an excellent agreement with experimental data. Grain size distributions are computed, and their properties are discussed.
Resumo:
The study of simple chaotic maps for non-equilibrium processes in statistical physics has been one of the central themes in the theory of chaotic dynamical systems. Recently, many works have been carried out on deterministic diffusion in spatially extended one-dimensional maps This can be related to real physical systems such as Josephson junctions in the presence of microwave radiation and parametrically driven oscillators. Transport due to chaos is an important problem in Hamiltonian dynamics also. A recent approach is to evaluate the exact diffusion coefficient in terms of the periodic orbits of the system in the form of cycle expansions. But the fact is that the chaotic motion in such spatially extended maps has two complementary aspects- - diffusion and interrnittency. These are related to the time evolution of the probability density function which is approximately Gaussian by central limit theorem. It is noticed that the characteristic function method introduced by Fujisaka and his co-workers is a very powerful tool for analysing both these aspects of chaotic motion. The theory based on characteristic function actually provides a thermodynamic formalism for chaotic systems It can be applied to other types of chaos-induced diffusion also, such as the one arising in statistics of trajectory separation. It was noted that there is a close connection between cycle expansion technique and characteristic function method. It was found that this connection can be exploited to enhance the applicability of the cycle expansion technique. In this way, we found that cycle expansion can be used to analyse the probability density function in chaotic maps. In our research studies we have successfully applied the characteristic function method and cycle expansion technique for analysing some chaotic maps. We introduced in this connection, two classes of chaotic maps with variable shape by generalizing two types of maps well known in literature.
Resumo:
En aquest article es resumeixen els resultats publicats en un informe de l' ISS (Istituto Superiore di Sanit) del desembre de 2006, sobre un model matemtic desenvolupat per un grup de treball que inclou a investigadors de les Universitats de Trento, Pisa i Roma, i els Instituts Nacionals de Salut (Istituto Superiore di Sanit, ISS), per avaluar i mesurar l'impacte de la transmissi i el control de la pandmia de grip
Resumo:
In this paper we find that the diffusion pattern of mobile telephony in Colombia can be best characterised as following a Logistic curve. Although in recent years the rate of growth of mobile phone subscribers has started to slow down, we find evidence that there is still room for further expansion as the saturation level is expected to be reached in five years time. The estimated saturation level is consistent with some individuals possessing more than one mobile device.
Resumo:
Resumen tomado de la publicaci??n
Resumo:
The origin of the microscopic inhomogeneities in InxGa1-xAs layers grown on GaAs by molecular beam epitaxy is analyzed through the optical absorption spectra near the band gap. It is seen that, for relaxed thick layers of about 2.8m, composition inhomogeneities are responsible for the band edge smoothing into the whole compositional range (0.05<x<0.8). On the other hand, in thin enough layers strain inhomogeneities are dominant. This evolution in line with layer thickness is due to the atomic diffusion at the surface during growth, induced by the strain inhomogeneities that arise from stress relaxation. In consequence, the strain variations present in the layer are converted into composition variations during growth. This process is energetically favorable as it diminishes elastic energy. An additional support to this hypothesis is given by a clear proportionality between the magnitude of the composition variations and the mean strain
Resumo:
Diffusion tensor magnetic resonance imaging, which measures directional information of water diffusion in the brain, has emerged as a powerful tool for human brain studies. In this paper, we introduce a new Monte Carlo-based fiber tracking approach to estimate brain connectivity. One of the main characteristics of this approach is that all parameters of the algorithm are automatically determined at each point using the entropy of the eigenvalues of the diffusion tensor. Experimental results show the good performance of the proposed approach
