The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Massoud Kaviany - One of the best experts on this subject based on the ideXlab platform.
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effects of phonon pore scattering and pore randomness on Effective Conductivity of porous silicon
International Journal of Heat and Mass Transfer, 2000Co-Authors: Jae Dong Chung, Massoud KavianyAbstract:Abstract The observed low Effective thermal Conductivity of porous silicon makes for its convenient fabrication and integration as a thermal insulation layer in microelectronics. The observed average pore size is controlled by the etching process and ranges between 1 and 100 nm, which on the low end is much less than the bulk phonon mean-free path. This low Effective Conductivity, i.e., low Effective phonon mean-free path, can be explained with the inclusion of the effects of the phonon pore scattering and the pore randomness. The available two-dimensional porous silicon pore-network simulations are used along with the Boltzmann transport equation to determine the Effective Conductivity. It is shown that the hindering effect of the phonon pore scattering (due to reflection from the solid-pore interface) is significant for small pore size. Also, due to the dendritic structure of the pores, the hindering effect of the pore-network randomness is significant. The predictions are compared with the existing experiments and a good agreement is found.
Jae Dong Chung - One of the best experts on this subject based on the ideXlab platform.
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effects of phonon pore scattering and pore randomness on Effective Conductivity of porous silicon
International Journal of Heat and Mass Transfer, 2000Co-Authors: Jae Dong Chung, Massoud KavianyAbstract:Abstract The observed low Effective thermal Conductivity of porous silicon makes for its convenient fabrication and integration as a thermal insulation layer in microelectronics. The observed average pore size is controlled by the etching process and ranges between 1 and 100 nm, which on the low end is much less than the bulk phonon mean-free path. This low Effective Conductivity, i.e., low Effective phonon mean-free path, can be explained with the inclusion of the effects of the phonon pore scattering and the pore randomness. The available two-dimensional porous silicon pore-network simulations are used along with the Boltzmann transport equation to determine the Effective Conductivity. It is shown that the hindering effect of the phonon pore scattering (due to reflection from the solid-pore interface) is significant for small pore size. Also, due to the dendritic structure of the pores, the hindering effect of the pore-network randomness is significant. The predictions are compared with the existing experiments and a good agreement is found.
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Direct simulation of Effective Conductivity of porous silicon: Fourier treatments
KSME International Journal, 1999Co-Authors: Jae Dong ChungAbstract:The Effective thermal Conductivity of anisotropic porous-silicon layers is predicted using the simulated pore structure from a two-dimensional, diffusion-limited model along with the Fourier conduction. The low-dimensionality effect due to the phonon boundary scattering is included through an available modified solid Conductivity. It is shown that for the highly branched columnar structure, the Effective Conductivity across the layer is small and yet much larger than that along the layer. Good agreement is found with available experimental results. It is predicted that the combination of a small pore size and a high porosity leads to a very small Effective Conductivity. This makes porous-silicon layer an attractive insulator and readily integrable in silicon-based microstructures. In a following paper, the low-dimensionality effect is directly included in a Boltzmann treatment of phonon transport.
Damijan Miklavcic - One of the best experts on this subject based on the ideXlab platform.
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The Effective Conductivity and the Induced Transmembrane Potential in Dense Cell System Exposed to DC and AC Electric Fields
IEEE Transactions on Plasma Science, 2009Co-Authors: Mojca Pavlin, Damijan MiklavcicAbstract:Studying electric potential distribution on the cell membrane and electric Conductivity gives us an insight into the effects of the electric field on cells and tissues. Since cells are always surrounded by other cells, we studied how their interactions influence the induced transmembrane potential (TMP) and the Effective Conductivity in dense cell systems. We numerically and analytically studied the effect of cell organization on the induced TMP and the Effective Conductivity by organizing cells into simple-cubic, body-centered cubic, and face-centered infinite cubic lattices. We analyzed the general relation between the local quantities (electric field and the induced TMP) and the Effective properties such as Effective Conductivity. We demonstrated that the Effective Conductivity mainly depends on cell volume fraction, while the induced TMP is affected by cell volume fraction as well as cell ordering. We show that in contrast to some reported results, the phenomenological Effective medium theory (EMT) equations cannot be used to determine the local quantities (e.g., the induced TMP) in dense cell systems, whereas the Effective properties (e.g., Conductivity) can be readily analyzed with EMT equations. We further derive an analytical approximation for the induced TMP in dense cell system exposed to dc and ac electric fields, where dominant factors, which govern the local electric field and the induced TMP, are cell volume fraction and cell ordering. The presented theoretical analysis can be extended also to high frequencies or random distribution of cells.
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Effective Conductivity of a suspension of permeabilized cells a theoretical analysis
Biophysical Journal, 2003Co-Authors: Mojca Pavlin, Damijan MiklavcicAbstract:During the electroporation cell membrane undergoes structural changes, which increase the membrane Conductivity and consequently lead to a change in Effective Conductivity of a cell suspension. To correlate microscopic membrane changes to macroscopic changes in Conductivity of a suspension, we analyzed the Effective Conductivity theoretically, using two different approaches: numerically, using the finite elements method; and analytically, by using the equivalence principle. We derived the equation, which connects membrane Conductivity with Effective Conductivity of the cell suspension. The changes in Effective Conductivity were analyzed for different parameters: cell volume fraction, membrane and medium Conductivity, critical transmembrane potential, and cell orientation. In our analysis we used a tensor form of the Effective Conductivity, thus taking into account the anisotropic nature of the cell electropermeabilization and rotation of the cells. To determine the effect of cell rotation, as questioned by some authors, the difference between Conductivity of a cell suspension with normally distributed orientations and parallel orientation was also calculated, and determined to be <10%. The presented theory provides a theoretical basis for the analysis of measurements of the Effective Conductivity during electroporation.
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Effective Conductivity of a Suspension of Permeabilized Cells: A Theoretical Analysis
Biophysical Journal, 2003Co-Authors: Mojca Pavlin, Damijan MiklavcicAbstract:During the electroporation cell membrane undergoes structural changes, which increase the membrane Conductivity and consequently lead to a change in Effective Conductivity of a cell suspension. To correlate microscopic membrane changes to macroscopic changes in Conductivity of a suspension, we analyzed the Effective Conductivity theoretically, using two different approaches: numerically, using the finite elements method; and analytically, by using the equivalence principle. We derived the equation, which connects membrane Conductivity with Effective Conductivity of the cell suspension. The changes in Effective Conductivity were analyzed for different parameters: cell volume fraction, membrane and medium Conductivity, critical transmembrane potential, and cell orientation. In our analysis we used a tensor form of the Effective Conductivity, thus taking into account the anisotropic nature of the cell electropermeabilization and rotation of the cells. To determine the effect of cell rotation, as questioned by some authors, the difference between Conductivity of a cell suspension with normally distributed orientations and parallel orientation was also calculated, and determined to be
George W. Hanson - One of the best experts on this subject based on the ideXlab platform.
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Multiwall Carbon Nanotubes at RF-THz Frequencies: Scattering, Shielding, Effective Conductivity, and Power Dissipation
IEEE Transactions on Antennas and Propagation, 2011Co-Authors: Jay A. Berres, George W. HansonAbstract:Isolated, infinitely long multiwall carbon nanotubes (MWCNTs) interacting with electromagnetic waves in the microwave and far-infrared frequency regime are analyzed using a semi-classical approach. An expression for the bulk Effective Conductivity of MWCNTs is obtained, valid up to THz frequencies. The influence of the number of tube walls, the radius of the outermost tube wall, and the presence of a gold core on scattering and shielding is analyzed. Comparisons between metallic MWCNTs, metallic single wall carbon nanotubes (SWCNTs), and metal nanowires are provided.
D. Ziółkowski - One of the best experts on this subject based on the ideXlab platform.
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Axial thermal Effective Conductivity in packed-bed catalytic tubular reactors
Chemical Engineering Science, 1997Co-Authors: B. Legawiec, D. ZiółkowskiAbstract:Computer experiments have been performed in which the effects of the radial nonuniformities of the granular bed packed in tubular flow apparatus as well as those of the heat sources and sinks on the axial Effective thermal Conductivity of the system have been analysed. The computations have been compared to the experiments performed by Yagi et al. (1960, A.I.Ch.E.J. 6, 543546) on the axial thermal Effective Conductivity.