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Desenvolvimento de método para separação química de Gálio-67 pela técnica de difusão térmica; Development of method to chemical separation of gallium-67 by thermal diffusion technique

Martins, Patricia de Andrade
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 10/09/2012 PT
Relevância na Pesquisa
66.09%
Radioisótopos de gálio são estudados e avaliados para aplicações médicas desde 1949. Nos últimos 50 anos 67Ga tem sido amplamente utilizado no diagnóstico de diversas patologias, incluindo lesões inflamatórias crônicas e agudas, bacterianas ou estéreis e diversos tipos de tumores. No Brasil 30% das clinicas que prestam serviços de Medicina Nuclear utilizam o Citrato de 67Ga com uma demanda de distribuição no IPEN-CNEN/SP de 37 GBq (1 Ci) por semana. O 67Ga apresenta meia-vida física de 3,26 dias (78 horas) e decai 100% por captura eletrônica para o 67Zn estável. Seu decaimento inclui a emissão de raios γ com energias de 93,3 keV (37%), 184,6 keV (20,4%), 300,2 keV (16,6%) e 888 keV (26%). No IPEN o 67Ga era produzido a partir da reação 68Zn(p, 2n)67Ga. Após a irradiação, o alvo era totalmente dissolvido em HCl concentrado e a solução percolada em resina catiônica DOWEX 50W-X8, 200-400 mesh, condicionada em HCl 10 mol L-1. Zinco, níquel e cobre eram eluídos em HCl 10 mol L-1 e o 67Ga em HCl 3,5 mol L-1. O produto final era obtido na forma de citrato de 67Ga. Este trabalho apresenta um método inédito, rápido, direto e eficiente de separação química e obtenção de 67GaCl3 a partir da difusão térmica (aquecimento do alvo) aliada à extração em ácido acético concentrado. A purificação foi realizada por cromatografia de troca iônica. Realizou-se a eletrodeposição do zinco natural em placas de cobre niquelado como substrato e os depósitos de zinco obtidos foram aderentes ao substrato...

Estudo computacional da difusão térmica em proteínas termoestáveis; Computational study of thermal diffusion in thermostable proteins

Muniz, Heloisa dos Santos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 19/02/2013 PT
Relevância na Pesquisa
56.35%
Mecanismos de difusão de energia vibracional em biomoléculas têm sido relacionadas a função, alosterismo e sinalização intramolecular. Neste trabalho nós utilizamos uma metodologia computacional para analisar o fluxo de energia em proteínas. Simulações de Dinâmica Molecular são utilizadas para o estudo de difusão térmica, provendo artifícios que não são possíveis experimentalmente: a proteína é esfriada a baixas temperaturas e apenas um resíduo é aquecido através do acoplamento de um banho térmico. Consequentemente, o calor flui do aminoácido aquecido para a proteína, revelando os caminhos da difusão da energia vibracional. Pelo fato de que proteínas termoestáveis possam ter particulares mecanismos de relaxação, distribuição e dissipação da energia vibracional, elas são sistemas interessantes para serem utilizadas por este método. Um padrão de difusão de calor de uma proteína termofílica pode ser identificado e comparado com outro de uma proteína homóloga mesofílica. Aqui estudamos um conjunto de proteínas em particular, as pertencentes à família 11 de Xilanases. O mapa de difusão térmica obtido da proteína no vácuo mostrou diferenças entre xilanases mesofílica e termofílica, e termofílica e hipertermofílica: qualquer que seja o resíduo aquecido...

Dinâmica molecular e redes complexas no estudo da difusão térmica em xilanases da família 11; Molecular dynamics and complex networks in the study of thermal diffusion in family 11 xylanases

Censoni, Luciano Borges
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 25/07/2013 PT
Relevância na Pesquisa
66.2%
Proteínas tipicamente são capazes de manter a sua conformação funcional somente dentro de um intervalo limitado de temperaturas. A despeito do maquinário sofisticado de manutenção da homeostase celular, é sabido que uma variedade de fenômenos moleculares são capazes de induzir desequilíbrios localizados de energia vibracional, e que a eficiência com que cada proteína dissipa estas perturbações pode estar relacionada com a sua tolerância a altas temperaturas. No entanto, a transferência de energia térmica entre diferentes segmentos de uma cadeia proteica é difícil de caracterizar experimentalmente. Uma alternativa teórica para a investigação destes mecanismos é o emprego de simulações de Dinâmica Molecular, particularmente associadas à técnica de Difusão Térmica Anisotrópica (ATD). Aqui, verificamos a possibilidade de empregar conceitos da teoria de Redes Complexas para construir modelos para estruturas de proteínas, e por meio destes identificar resíduos com capacidade significativa de dissipar perturbações térmicas. Investigamos os diversos protocolos de construção de modelos de rede para proteínas encontrados na literatura, e utilizamos dados experimentais representativos da base SCOP para calcular com rigor os parâmetros numéricos necessários. Produzimos uma definição precisa para o conceito de contato entre resíduos de aminoácidos...

Thermal diffusion in solids : an overview

Morgado, M. Fátima; Pinheiro, J. D. R. S.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //1985 ENG
Relevância na Pesquisa
46.27%
Thermal diffusion in liquids and gases has been the focus of a number of studies and is considered, at present, a reasonably wellknown topic. In solids though, the phenomena is far less understood namely in what regards the effects of thermal gradients upon the integrity and characteristics of materials. Furthermore it is not clear whether or not thermal diffusion can be used as a purificating method for solids. Yet, many current techniques such as the laser, used in metal working and other solids, induce strong thermal gradients being, therefore, potential cause for the occurrence of thermal diffusion. In this work, a survey and discussion of theoretical and experimental studies of thermal diffusion in solids is undertaken.

Viscosity, Thermal Conductivity and Thermal Diffusion Ratio of the Alkali Metal Vapours.

Fialho, Paulo; Ramires, Maria de Lurdes V.; Fareleira, João M.N.A.; Nieto de Castro, Carlos A.
Fonte: Technomic Publishing Company Publicador: Technomic Publishing Company
Tipo: Parte de Livro
Publicado em //1994 ENG
Relevância na Pesquisa
56.11%
Copyright © 1994 by Technomic Publishing Company, Inc.; Proceedings of the Twenty-Second International Conference on Thermal Condutivity. Tempe, Arizona, November 7-10, 1993.; The Subcommittee of Transport Properties of IUP AC started in 1982 a project with the objective of correlating and predicting the transport properties of the alkali metal vapours, in the temperature and pressure zones that are useful to the scientific and industrial uses. In a recent paper [1] the authors suggested a new approach to assess the available experimental data, based in the kinetic theory of gas mixtures, which is a modification of the method developed by Vargaftik and Yargin[2]. In the present communication, we present the surfaces for the viscosity and thermal conductivity, and thermal diffusion ratio which have been developed for lithium, sodium and potassium with average uncertainties of 1%, 0.5% and 0.5%, respectively, for temperature ranges 800-2000 K (lithium) and 700-1500 K (sodium and potassium). . For rubidium and cesium, the available data does not allow a similar development of the corresponding surfaces. It is interesting to note that no clear evidence for the presence of dimers was found for cesium within experimental uncertainty.

Detection of single-molecule interactions using correlated thermal diffusion

Mehta, A. D.; Finer, J. T.; Spudich, J. A.
Fonte: The National Academy of Sciences of the USA Publicador: The National Academy of Sciences of the USA
Tipo: Artigo de Revista Científica
Publicado em 22/07/1997 EN
Relevância na Pesquisa
46.18%
Observation of discrete, single-molecule binding events allows one to bypass assumptions required to infer single-molecule properties from studies of ensembles of molecules. Optically trapped beads and glass microneedles have been applied to detect single-molecule binding events, but it remains difficult to identify signs of binding events given the large displacements induced by thermal forces. Here, we exploit thermal diffusion by using correlation between motion of optically trapped beads attached to both ends of a single actin filament to track binding events of individual myosin molecules. We use correlated diffusion to measure the stiffness of a single myosin molecule and estimate its thermal fluctuation in a poststroke state as comparable in amplitude to the measured stroke distance. The use of correlated diffusion to measure kinetics of single-molecule interactions and the stiffness of the interacting moieties should be applicable to any pair of interacting molecules, and not limited to biological motors.

Design of a thermal diffusion sensor for noninvasive assessment of skin surface perfusion and endothelial dysfunction

Li, Vivian V. (Vivian Victoria)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 121 p.
ENG
Relevância na Pesquisa
46.2%
The skin microcirculation performs a range of vital functions, such as maintaining nutritional perfusion to the tissues and overall thermoregulation. Not only does impairment to the skin blood supply lead to tissue necrosis and other disease complications, increasing evidence shows that dysfunctional vasoreactivity in the skin microcirculation is associated with multiple disease states, including hypertension, diabetes mellitus, hypercholesterolemia, peripheral vascular disease, and coronary artery disease, and it is one of the earliest indicators of systemic endothelial dysfunction, the precursor to atherosclerotic disease. Endothelial dysfunction is functionally characterized by abnormal vasomotor response to either a pharmacological or flow-mediated stimulus and can be demonstrated in the skin by measuring reperfusion following a period of ischemia, a phenomenon known as post-occlusive reactive hyperemia (PORH). In my research, I have reviewed the literature regarding endothelial dysfunction and its association with a wide range of cardiovascular risk factors. I have also described the mechanisms thought to link endothelial function in the central vascular beds (i.e. coronary) to that of peripheral conduit vessels and the microcirculation. The knowledge thus gathered confirmed that the microcirculation of the skin is an appropriate site for endothelial function assessment. The ultimate goal of my thesis is to design a noninvasive sensor that is capable of obtaining a quantitative measure of skin perfusion...

An Efficient Method of Modeling Material Properties Using a Thermal Diffusion Analogy: An Example Based on Craniofacial Bone

Davis, Julian L.; Dumont, Elizabeth R.; Strait, David S.; Grosse, Ian R.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 11/02/2011 EN
Relevância na Pesquisa
46.13%
The ability to incorporate detailed geometry into finite element models has allowed researchers to investigate the influence of morphology on performance aspects of skeletal components. This advance has also allowed researchers to explore the effect of different material models, ranging from simple (e.g., isotropic) to complex (e.g., orthotropic), on the response of bone. However, bone's complicated geometry makes it difficult to incorporate complex material models into finite element models of bone. This difficulty is due to variation in the spatial orientation of material properties throughout bone. Our analysis addresses this problem by taking full advantage of a finite element program's ability to solve thermal-structural problems. Using a linear relationship between temperature and modulus, we seeded specific nodes of the finite element model with temperatures. We then used thermal diffusion to propagate the modulus throughout the finite element model. Finally, we solved for the mechanical response of the finite element model to the applied loads and constraints. We found that using the thermal diffusion analogy to control the modulus of bone throughout its structure provides a simple and effective method of spatially varying modulus. Results compare favorably against both experimental data and results from an FE model that incorporated a complex (orthotropic) material model. This method presented will allow researchers the ability to easily incorporate more material property data into their finite element models in an effort to improve the model's accuracy.

Importance of thermal diffusion in the gravo-magnetic limit cycle

Owen, James E.; Armitage, Philip J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/09/2014
Relevância na Pesquisa
46.22%
We consider the role of thermal diffusion due to turbulence and radiation on accretion bursts that occur in protoplanetary discs which contain dead zones. Using 1D viscous disc models we show that diffusive radial transport of heat is important during the gravo-magnetic limit cycle, and can strongly modify the duration and frequency of accretion outbursts. When the Prandtl number is large - such that turbulent diffusion of heat is unimportant - radial radiative diffusion reduces the burst duration compared to models with no diffusive transport of heat. When the Prandtl number is small ($\lesssim 25$) we find that turbulent diffusion dominates the radial transport of heat, reducing the burst duration to $\lesssim 10^3$ years as well as increasing the burst frequency. Furthermore, inclusion of radial transport of heat extends the range of infall rates under which the disc undergoes accretion bursts from $10^{-8}$ to $10^{-6}$ M$_\odot$ yr$^{-1}$ with no diffusion, to $10^{-8}$ to $\gtrsim10^{-4}$ M$_\odot$ yr$^{-1}$ with radiative and strong turbulent diffusion. The relative roles of radiative and turbulent thermal diffusion are likely to vary during an accretion burst, but simple estimates suggest that the expected Prandtl numbers are of the order of 10 in protoplanetary discs...

Turbulent thermal diffusion in a multi-fan turbulence generator with the imposed mean temperature gradient

Eidelman, A.; Elperin, T.; Kleeorin, N.; Rogachevskii, I.; Sapir-Katiraie, I.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/02/2006
Relevância na Pesquisa
46.29%
We studied experimentally the effect of turbulent thermal diffusion in a multi-fan turbulence generator which produces a nearly homogeneous and isotropic flow with a small mean velocity. Using Particle Image Velocimetry and Image Processing techniques we showed that in a turbulent flow with an imposed mean vertical temperature gradient (stably stratified flow) particles accumulate in the regions with the mean temperature minimum. These experiments detected the effect of turbulent thermal diffusion in a multi-fan turbulence generator for relatively high Reynolds numbers. The experimental results are in compliance with the results of the previous experimental studies of turbulent thermal diffusion in oscillating grids turbulence (Buchholz et al. 2004; Eidelman et al. 2004). We demonstrated that turbulent thermal diffusion is an universal phenomenon. It occurs independently of the method of turbulence generation, and the qualitative behavior of particle spatial distribution in these very different turbulent flows is similar. Competition between turbulent fluxes caused by turbulent thermal diffusion and turbulent diffusion determines the formation of particle inhomogeneities.; Comment: 9 pages, 9 figure, REVTEX4, Experiments in Fluids...

Einstein's random walk and thermal diffusion

Kim, Yong-Jung
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/07/2013
Relevância na Pesquisa
46.27%
Thermal diffusion has been studied for over 150 years. Despite of the long history and the increasing importance of the phenomenon, the physics of thermal diffusion remains poorly understood. In this paper Ludwig's thermal diffusion is explained using Einstein's random walk. The only new structure added is the spatial heterogeneity of the random walk to reflect the temperature gradient of thermal diffusion. Hence, the walk length and the walk speed are location dependent functions in this paper. Then, a mathematical understanding of such a random walk gives the foundation of the thermal diffusion as clearly as the original homogeneous case of Einstein.; Comment: 11 pages, 2 figures

Thermal Diffusion Doping of Single Crystal Diamond

Seo, Jung-Hun; Mikael, Solomon; Mi, Hongyi; Venkataramanan, Giri; Blanchard, James P.; Zhou, Weidong; Gong, Shaoqin; Ma, Zhenqiang
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.13%
With the best overall electronic and thermal properties, single-crystal diamond (SCD) is the extreme wide bandgap material that is expected to revolutionize power electronics and radio-frequency electronics in the future. However, turning SCD into useful semiconductors faces doping challenges, as conventional substitutional doping techniques, such as thermal diffusion and ion-implantation, are not easily applicable to SCD. Here we report a simple and easily accessible doping strategy demonstrating that electrically activated, substitutional boron doping in natural SCD without any phase transitions or lattice damage which can be readily realized with thermal diffusion at relatively low temperature. For the boron doping, we employ a unique dopant carrying medium: heavily doped Si nanomembranes. We further demonstrate selectively doped high-voltage diodes and half-wave rectifier circuits using such doped SCD. Our new doping strategy has established a reachable path toward using SCDs for future high-voltage power conversion systems and for other novel diamond-based electronics.; Comment: This paper has been withdrawn by the author due to a crucial sign error in equation 1

Turbulent thermal diffusion of aerosols in geophysics and laboratory experiments

Eidelman, A.; Elperin, T.; Kleeorin, N.; Krein, A.; Rogachevskii, I.; Buchholz, J.; Gruenefeld, G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/11/2004
Relevância na Pesquisa
46.18%
We discuss a new phenomenon of turbulent thermal diffusion associated with turbulent transport of aerosols in the atmosphere and in laboratory experiments. The essence of this phenomenon is the appearance of a nondiffusive mean flux of particles in the direction of the mean heat flux, which results in the formation of large-scale inhomogeneities in the spatial distribution of aerosols that accumulate in regions of minimum mean temperature of the surrounding fluid. This effect of turbulent thermal diffusion was detected experimentally. In experiments turbulence was generated by two oscillating grids in two directions of the imposed vertical mean temperature gradient. We used Particle Image Velocimetry to determine the turbulent velocity field, and an Image Processing Technique based on an analysis of the intensity of Mie scattering to determine the spatial distribution of aerosols. Analysis of the intensity of laser light Mie scattering by aerosols showed that aerosols accumulate in the vicinity of the minimum mean temperature due to the effect of turbulent thermal diffusion. Geophysical applications of the obtained results are discussed.; Comment: 9 pages, 6 figures, revtex4

Turbulent Diffusion and Turbulent Thermal Diffusion of Aerosols in Stratified Atmospheric Flows

Sofiev, M.; Sofieva, V.; Elperin, T.; Kleeorin, N.; Rogachevskii, I.; Zilitinkevich, S. S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/08/2009
Relevância na Pesquisa
46.29%
The paper analyzes the phenomenon of turbulent thermal diffusion in the Earth atmosphere, its relation to the turbulent diffusion and its potential impact on aerosol distribution. This phenomenon was predicted theoretically more than 10 years ago and detected recently in the laboratory experiments. This effect causes a non-diffusive flux of aerosols in the direction of the heat flux and results in formation of long-living aerosol layers in the vicinity of temperature inversions. We demonstrated that the theory of turbulent thermal diffusion explains the GOMOS aerosol observations near the tropopause (i.e., the observed shape of aerosol vertical profiles with elevated concentrations located almost symmetrically with respect to temperature profile). In combination with the derived expression for the dependence of the turbulent thermal diffusion ratio on the turbulent diffusion, these measurements yield an independent method for determining the coefficient of turbulent diffusion at the tropopause. We evaluated the impact of turbulent thermal diffusion to the lower-troposphere vertical profiles of aerosol concentration by means of numerical dispersion modelling, and found a regular upward forcing of aerosols with coarse particles affected stronger than fine aerosols.; Comment: 19 pages...

Diffusion transport coefficients for granular binary mixtures at low density. Thermal diffusion segregation

Garzó, Vicente; Murray, J. Aaron; Reyes, Francisco Vega
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.2%
The mass flux of a low-density granular binary mixture obtained previously by solving the Boltzmann equation by means of the Chapman-Enskog method is considered further. As in the elastic case, the associated transport coefficients $D$, $D_p$ and $D'$ are given in terms of the solutions of a set of coupled linear integral equations which are approximately solved by considering the first and second Sonine approximations. The diffusion coefficients are explicitly obtained as functions of the coefficients of restitution and the parameters of the mixture (masses, diameters and concentration) and their expressions hold for an arbitrary number of dimensions. In order to check the accuracy of the second Sonine correction for highly inelastic collisions, the Boltzmann equation is also numerically solved by means of the direct simulation Monte Carlo (DSMC) method to determine the mutual diffusion coefficient $D$ in some special situations (self-diffusion problem and tracer limit). The comparison with DSMC results reveals that the second Sonine approximation to $D$ improves the predictions made from the first Sonine approximation. We also study the granular segregation driven by a uni-directional thermal gradient. The segregation criterion is obtained from the so-called thermal diffusion factor $\Lambda$...

Thermal diffusion segregation in granular binary mixtures described by the Enskog equation

Garzó, Vicente
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.2%
Diffusion induced by a thermal gradient in a granular binary mixture is analyzed in the context of the (inelastic) Enskog equation. Although the Enskog equation neglects velocity correlations among particles which are about to collide, it retains spatial correlations arising from volume exclusion effects and thus it is expected to apply to moderate densities. In the steady state with gradients only along a given direction, a segregation criterion is obtained from the thermal diffusion factor $\Lambda$ measuring the amount of segregation parallel to the thermal gradient. As expected, the sign of the factor $\Lambda$ provides a criterion for the transition between the Brazil-nut effect (BNE) and the reverse Brazil-nut effect (RBNE) by varying the parameters of the mixture (masses, sizes, concentration, solid volume fraction, and coefficients of restitution). The form of the phase diagrams for the BNE/RBNE transition is illustrated in detail for several systems, with special emphasis on the significant role played by the inelasticity of collisions. In particular, an effect already found in dilute gases (segregation in a binary mixture of identical masses and sizes {\em but} different coefficients of restitution) is extended to dense systems. A comparison with recent computer simulation results shows a good qualitative agreement at the level of the thermal diffusion factor. The present analysis generalizes to arbitrary concentration previous theoretical results derived in the tracer limit case.; Comment: 7 figures...

Thermal diffusion in the IGM of clusters of galaxies

Shtykovskiy, P.; Gilfanov, M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/09/2009
Relevância na Pesquisa
46.16%
We revisit the phenomenon of elements diffusion in the intergalactic medium (IGM) in clusters of galaxies. The diffusion is driven by gravity, concentration and temperature gradients. The latter cause thermal diffusion, which has been so far ignored in IGM studies. We consider the full problem based on the Burgers' equations and demonstrate that the temperature gradients present in clusters of galaxies may successfully compete with gravity, evacuating metals from cooler regions. Under the combined action of gravity and temperature gradients, complicated metallicity profiles with several peaks and depressions may be formed. For a typical cool core cluster, the thermal diffusion may significantly reduce and even reverse the gravitational sedimentation of metals, resulting in the depression in their abundance in the core. This may have implications for diagnostics of the low temperature plasma in the centers of clusters of galaxies.; Comment: 10 pages, 8 figures; accepted to MNRAS

The Entropy Rate of Thermal Diffusion

Haller Jr, John L.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.14%
The thermal diffusion of a free particle is a random process and generates entropy at a rate equal to twice the particle temperature in natural units of information per second. The rate is calculated using a Gaussian process with a variance as a combination of quantum and classical diffusion. The solution to the diffusion of a free particle is derived from the equation for kinetic energy and its associated imaginary diffusion constant and a real diffusion constant representing classical diffusion. We find the entropy of the initial state is one natural unit, which is the same amount of entropy the process generates after the de-coherence time, hbar over twice the temperature.; Comment: Six pages with equations and a figure

Thermal diffusion by Brownian motion induced fluid stress

Kreft, Jennifer; Chen, Yeng-Long
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/02/2007
Relevância na Pesquisa
46.18%
The Ludwig-Soret effect, the migration of a species due to a temperature gradient, has been extensively studied without a complete picture of its cause emerging. Here we investigate the dynamics of DNA and spherical particles sub jected to a thermal gradient using a combination of Brownian dynamics and the lattice Boltzmann method. We observe that the DNA molecules will migrate to colder regions of the channel, an observation also made in the experiments of Duhr, et al[1]. In fact, the thermal diffusion coefficient found agrees quantitatively with the experimental value. We also observe that the thermal diffusion coefficient decreases as the radius of the studied spherical particles increases. Furthermore, we observe that the thermal fluctuations-fluid momentum flux coupling induces a gradient in the stress which leads to thermal migration in both systems.; Comment: 6 pages, 5 figues

Thermal diffusion effect on a three-dimensional mhd free convection with mass transfer flow from a porous vertical plate

Ahmed,N.; Sarmah,H. K.; Kalita,D.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2011 EN
Relevância na Pesquisa
66.18%
A systematic analysis to study the effect of thermal diffusion on a three dimensional free convective flow with mass transfer of an incompressible viscous electrically conducting fluid past a porous vertical plate with transverse sinusoidal suction velocity is presented. Due to this type of suction velocity at the plate the flow becomes three-dimensional one. A magnetic field of uniform strength is assumed to be applied normal to the plate directed into the fluid region. The magnetic Reynolds number is considered to be small so that the induced magnetic field can be neglected. An analytical solution of the problem is obtained. The expressions for the velocity field, fluid temperature, species concentration, fluid pressure, skin-friction, Nusselt number and Sherwood number and current density are obtained in non-dimensional forms. The effects of Hartmann number, Soret number, Reynolds number and Prandtl number on the velocity field, temperature and concentration distributions, skin friction at the plate and on the amplitudes of the first order skin-friction, the first order Nusselt number and the first order Sherwood number at the plate are discussed graphically. It is seen that the thermal diffusion and applied magnetic field have significant effects on the flow and on the heat and mass transfer characteristics.