The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform
S S Zilitinkevich - One of the best experts on this subject based on the ideXlab platform.
-
turbulent Diffusion and turbulent Thermal Diffusion of aerosols in stratified atmospheric flows
Journal of Geophysical Research, 2009Co-Authors: Mikhail Sofiev, Viktoria Sofieva, T Elperin, N Kleeorin, I Rogachevskii, S S ZilitinkevichAbstract:[1] 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 nondiffusive 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 applied the theory of turbulent Thermal Diffusion to the Global Ozone Monitoring by Occultation of Stars (GOMOS) aerosol observations near the tropopause in order to explain the shape of aerosol vertical profiles with elevated concentrations located almost symmetrically with respect to temperature profile. We demonstrate that this theory is in good agreement with the observed profiles of aerosol concentration and temperature in the vicinity of the tropopause. 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 also derived a practically applicable formulation for dispersion of atmospheric trace species which takes into account the phenomenon of turbulent Thermal Diffusion. We evaluated the impact of turbulent Thermal Diffusion to the lower troposphere vertical profiles of aerosol concentration by means of numerical dispersion modeling and found a regular upward forcing of aerosols with coarse particles affected more strongly than fine aerosols.
-
turbulent Diffusion and turbulent Thermal Diffusion of aerosols in stratified atmospheric flows
arXiv: Atmospheric and Oceanic Physics, 2009Co-Authors: Mikhail Sofiev, Viktoria Sofieva, T Elperin, N Kleeorin, I Rogachevskii, S S ZilitinkevichAbstract: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.
Abbas Firoozabadi - One of the best experts on this subject based on the ideXlab platform.
-
new Thermal Diffusion coefficient measurements for hydrocarbon binary mixtures viscosity and composition dependency
Journal of Physical Chemistry B, 2008Co-Authors: Alana Leahydios, Lin Zhuo, Abbas FiroozabadiAbstract:New Thermal Diffusion coefficients of binary mixtures are measured for n-decane−n-alkanes and 1-methylnaphthalene−n-alkanes with 25 and 75 wt % at 25 °C and 1 atm using the thermogravitational column technique. The alkanes range from n-pentane to n-eicosane. The new results confirm the recently observed nonmonotonic behavior of Thermal Diffusion coefficients with molecular weight for binary mixtures of n-decane−n-alkanes at the compositions studied. In this work, the mobility and disparity effects on Thermal Diffusion coefficients are quantified for binary mixtures. We also show for the binary mixtures studied that the Thermal Diffusion coefficients and mixture viscosity, both nonequilibrium properties, are closely related.
-
Measurements of molecular and Thermal Diffusion coefficients in ternary mixtures
The Journal of chemical physics, 2005Co-Authors: Alana Leahy-dios, M. Mounir Bou-ali, Jean K. Platten, Abbas FiroozabadiAbstract:Thermal Diffusion coefficients in three ternary mixtures are measured in a thermogravitational column. One of the mixtures consists of one normal alkane and two aromatics (dodecane-isobutylbenzene-tetrahydronaphthalene), and the other two consist of two normal alkanes and one aromatic (octane-decane-1-methylnaphthalene). This is the first report of measured Thermal Diffusion coefficients (for all species) of a ternary nonelectrolyte mixture in literature. The results in ternary mixtures of octane-decane-1-methylnaphthalene show a sign change of the Thermal Diffusion coefficient for decane as the composition changes, despite the fact that the two normal alkanes are similar. In addition to Thermal Diffusion coefficients, molecular Diffusion coefficients are also measured for three binaries and one of the ternary mixtures. The open-end capillary-tube method was used in the measurement of molecular Diffusion coefficients. The molecular and Thermal Diffusion coefficients allow the estimation of Thermal Diffusion factors in binary and ternary mixtures. However, in the ternaries one also has to calculate phenomenological coefficients from the molecular Diffusion coefficients. A comparison of the binary and ternary Thermal Diffusion factors for the mixtures comprised of octane-decane-1-methylnaphthalene reveals a remarkable difference in the Thermal Diffusion behavior in binary and ternary mixtures.
-
Theoretical model of Thermal Diffusion factors in multicomponent mixtures
AIChE Journal, 2000Co-Authors: Abbas Firoozabadi, Kassem Ghorayeb, K.p. ShuklaAbstract:Unlike molecular Diffusion, neither measured Thermal Diffusion coefficients nor the theoretical framework exist for the estimation of Thermal Diffusion coefficients in nonideal multicomponent mixtures. This work derives a theoretical model for Thermal Diffusion coefficients in ideal and nonideal multicomponent mixtures, based on the thermodynamics of irreversible processes and the molecular kinetic approach incorporating explicit effects of nonequilibrium properties, such as the net heat of transport and molecular Diffusion coefficients, and of equilibrium properties of the mixture, which are determined by the Peng-Robinson equation of state. An interesting feature of this model is that in nonideal multicomponent mixtures Thermal Diffusion coefficients depend on molecular Diffusion coefficients, while in binary mixtures they do not. The model successfully describes Thermal Diffusion factors of binary mixtures for which experimental data are available, even those in extreme nonideal conditions and close to the critical point. Since experimental data on Thermal Diffusion factors in multicomponent hydrocarbon mixtures are not available, testing the model's accuracy was not possible. The model, however, successfully predicted spatial variation of composition in a ternary mixture of nC{sub 24}/nC{sub 16}/nC{sub 12}, providing an indirect verification. The six-component mixture of C{sub 1}/C{sub 3}/nC{sub 5}/nC{sub 10}/nC{sub 16}/C{sub 2} shows significant dependency of Thermal Diffusionmore » factors on the distance to the critical point. It also demonstrates for the first time that there is no need to adopt a sign convention for Thermal Diffusion coefficients in binary and higher mixtures. The thermodynamic stability analysis shows that when the Thermal Diffusion coefficient is positive, the component should go to the cold region in a binary mixture.« less
Dane Morgan - One of the best experts on this subject based on the ideXlab platform.
-
Thermal Diffusion boron doping of single crystal natural diamond
Journal of Applied Physics, 2016Co-Authors: Junghun Seo, Solomon Mikael, James Blanchard, Giri Venkataramanan, Weidong Zhou, Shaoqin Gong, Dane MorganAbstract: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 requires overcoming 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 doping in SCD without inducing graphitization transition or lattice damage can be readily realized with Thermal Diffusion at relatively low temperatures by using heavily doped Si nanomembranes as a unique dopant carrying medium. Atomistic simulations elucidate a vacancy exchange boron doping mechanism that occurs at the bonded interface between Si and diamond. 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 electronic devices. The novel doping mechanism may find its critical use in other wide bandgap semiconductors.
W Kohler - One of the best experts on this subject based on the ideXlab platform.
-
measurement of Diffusion and Thermal Diffusion in ternary fluid mixtures using a two color optical beam deflection technique
Journal of Chemical Physics, 2010Co-Authors: A Koniger, H Wunderlich, W KohlerAbstract:We have developed a highly sensitive two-color beam deflection setup to measure Diffusion and Thermal Diffusion in ternary fluid mixtures following a suggestion of Haugen and Firoozabadi [J. Phys. Chem. B 110, 17678 (2006)]. Simultaneous detection of two laser beams with different wavelengths makes it possible to determine the time dependent concentration profiles of all three components. By comparing the measured beam deflection signals to a numerical solution of the coupled heat and mass transport equations, the Diffusion matrix, the Thermal Diffusion, and the Soret coefficients are obtained by a numerical model combined with a nonlinear least-squares fitting routine. The results can be improved by additional Thermal Diffusion forced Rayleigh scattering experiments, which yield a contrast-weighted average Thermal Diffusion coefficient. The three Soret coefficients can be obtained independently from the stationary beam deflection amplitudes. Measurements have been performed on the symmetric (equal weight...
-
Thermal Diffusion of dilute polymer solutions the role of chain flexibility and the effective segment size
Macromolecules, 2009Co-Authors: D Stadelmaier, W KohlerAbstract:We have investigated the influence of the chain length and the size of the Kuhn segment on the Thermal Diffusion coefficient DT of dilute solutions of polymers in organic solvents. For oligomers and short polymer chains, DT increases with molar mass M and reaches a molar mass independent constant plateau value. A similar increase and plateau is observed for high polymers with increasing chain stiffness. For chains with Kuhn segments above 1 kg/mol, the plateau value is independent of the polymer and inversely proportional to the solvent viscosity. The Thermal Diffusion coefficient of such a polymer can be estimated to be DT ≈ 0.6 × 10−14 Pa m2 K−1 × η−1. No simple relation holds for short chains and flexible high polymers.
-
Thermal Diffusion of dilute polymer solutions the role of solvent viscosity
Journal of Chemical Physics, 2006Co-Authors: Marianne Hartung, J Rauch, W KohlerAbstract:We have performed measurements of the Thermal Diffusion coefficient DT in the dilute limit on polystyrene in cyclo-octane, cyclohexane, benzene, toluene, tetrahydrofuran, ethyl acetate, and methyl ethyl ketone and of poly(dimethyl-siloxane) in toluene. These data have been combined with literature data to test various theoretical predictions. The viscosity is identified as the dominating and only relevant solvent parameter. On the polymer side, the size or mass of an effective correlated segment determines the strength of the Soret effect. Large and heavy effective segments, as found in stiffer chains, lead to higher DT.We have performed measurements of the Thermal Diffusion coefficient DT in the dilute limit on polystyrene in cyclo-octane, cyclohexane, benzene, toluene, tetrahydrofuran, ethyl acetate, and methyl ethyl ketone and of poly(dimethyl-siloxane) in toluene. These data have been combined with literature data to test various theoretical predictions. The viscosity is identified as the dominating and only relevant solvent parameter. On the polymer side, the size or mass of an effective correlated segment determines the strength of the Soret effect. Large and heavy effective segments, as found in stiffer chains, lead to higher DT.
Peter R Herman - One of the best experts on this subject based on the ideXlab platform.
-
transition from Thermal Diffusion to heat accumulation in high repetition rate femtosecond laser writing of buried optical waveguides
Optics Express, 2008Co-Authors: Shane M Eaton, Haibin Zhang, Mi Li Ng, Jianzhao Li, Weijen Chen, Stephen Ho, Peter R HermanAbstract:A variable (0.2 to 5 MHz) repetition rate femtosecond laser was applied to delineate the role of Thermal Diffusion and heat accumulation effects in forming low-loss optical waveguides in borosilicate glass across a broad range of laser exposure conditions. For the first time, a smooth transition from Diffusion-only transport at 200-kHz repetition rate to strong heat accumulation effects at 0.5 to 2 MHz was observed and shown to drive significant variations in waveguide morphology, with rapidly increasing waveguide diameter that accurately followed a simple Thermal Diffusion model over all exposure variables tested. Amongst these strong Thermal trends, a common exposure window of 200-mW average power and ~15-mm/s scan speed was discovered across the range of 200-kHz to 2-MHz repetition rates for minimizing insertion loss despite a 10-fold drop in laser pulse energy. Waveguide morphology and Thermal modeling indicate that strong Thermal Diffusion effects at 200 kHz give way to a weak heat accumulation effect at ~1-µJ pulse energy for generating low loss waveguides, while stronger heat accumulation effects above 1-MHz repetition rate offered overall superior guiding. A comprehensive characterization of waveguide properties is presented for laser writing in the Thermal Diffusion and heat accumulation regimes. The waveguides are shown to be Thermally stable up to 800°C and can be written in a convenient 520-μm depth range with low spherical aberration.
-
transition from Thermal Diffusion to heat accumulation in high repetition rate femtosecond laser writing of buried optical waveguides
Optics Express, 2008Co-Authors: Shane M Eaton, Haibin Zhang, Weijen Chen, Peter R HermanAbstract:A variable (0.2 to 5 MHz) repetition rate femtosecond laser was applied to delineate the role of Thermal Diffusion and heat accumulation effects in forming low-loss optical waveguides in borosilicate glass across a broad range of laser exposure conditions. For the first time, a smooth transition from Diffusion-only transport at 200 kHz repetition rate to strong heat accumulation effects at 0.5 to 2 MHz was observed and shown to drive significant variations in waveguide morphology, with rapidly increasing waveguide diameter that accurately followed a simple Thermal Diffusion model over all exposure variables tested. Amongst these strong Thermal trends, a common exposure window of 200 mW average power and approximately 15-mm/s scan speed was discovered across the range of 200 kHz to 2 MHz repetition rates for minimizing insertion loss despite a 10-fold drop in laser pulse energy. Waveguide morphology and Thermal modeling indicate that strong Thermal Diffusion effects at 200 kHz give way to a weak heat accumulation effect at approximately 1 microJ pulse energy for generating low loss waveguides, while stronger heat accumulation effects above 1-MHz repetition rate offered overall superior guiding. A comprehensive characterization of waveguide properties is presented for laser writing in the Thermal Diffusion and heat accumulation regimes. The waveguides are shown to be Thermally stable up to 800 degrees C and can be written in a convenient 520 microm depth range with low spherical aberration.
