The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Otakar Quadrat - One of the best experts on this subject based on the ideXlab platform.
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electrical conductivity of carbon fibres polyester resin composites in the Percolation threshold region
European Polymer Journal, 2002Co-Authors: Jarmila Vilcakova, Petr Saha, Otakar QuadratAbstract:Abstract The electrical conductivity of composites of a polyester resin filled with short carbon fibres has been investigated with a special attention to the properties in the Percolation threshold region. A very low Percolation threshold (0.7–0.8 vol% of the filler) was confirmed. In contrast to S-shaped curves calculated according to the Percolation theory of composites of globular particles, the experimental conductivity vs. fibre content dependence, after a steep increase in the Percolation region, increased almost linearly. This atypical behaviour was explained by a different mechanism of formation of fibrous and globular conducting structures above the Percolation threshold. An increase in scatter of conductivity values observed at Percolation threshold as a consequence of great fluctuation of fibre arrangement manifested itself also in the conductivity–temperature dependences.
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Electrical conductivity of carbon fibres/polyester resin composites in the Percolation threshold region
European Polymer Journal, 2002Co-Authors: Jarmila Vilcakova, Petr Saha, Otakar QuadratAbstract:Abstract The electrical conductivity of composites of a polyester resin filled with short carbon fibres has been investigated with a special attention to the properties in the Percolation threshold region. A very low Percolation threshold (0.7–0.8 vol% of the filler) was confirmed. In contrast to S-shaped curves calculated according to the Percolation theory of composites of globular particles, the experimental conductivity vs. fibre content dependence, after a steep increase in the Percolation region, increased almost linearly. This atypical behaviour was explained by a different mechanism of formation of fibrous and globular conducting structures above the Percolation threshold. An increase in scatter of conductivity values observed at Percolation threshold as a consequence of great fluctuation of fibre arrangement manifested itself also in the conductivity–temperature dependences.
Jarmila Vilcakova - One of the best experts on this subject based on the ideXlab platform.
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electrical conductivity of carbon fibres polyester resin composites in the Percolation threshold region
European Polymer Journal, 2002Co-Authors: Jarmila Vilcakova, Petr Saha, Otakar QuadratAbstract:Abstract The electrical conductivity of composites of a polyester resin filled with short carbon fibres has been investigated with a special attention to the properties in the Percolation threshold region. A very low Percolation threshold (0.7–0.8 vol% of the filler) was confirmed. In contrast to S-shaped curves calculated according to the Percolation theory of composites of globular particles, the experimental conductivity vs. fibre content dependence, after a steep increase in the Percolation region, increased almost linearly. This atypical behaviour was explained by a different mechanism of formation of fibrous and globular conducting structures above the Percolation threshold. An increase in scatter of conductivity values observed at Percolation threshold as a consequence of great fluctuation of fibre arrangement manifested itself also in the conductivity–temperature dependences.
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Electrical conductivity of carbon fibres/polyester resin composites in the Percolation threshold region
European Polymer Journal, 2002Co-Authors: Jarmila Vilcakova, Petr Saha, Otakar QuadratAbstract:Abstract The electrical conductivity of composites of a polyester resin filled with short carbon fibres has been investigated with a special attention to the properties in the Percolation threshold region. A very low Percolation threshold (0.7–0.8 vol% of the filler) was confirmed. In contrast to S-shaped curves calculated according to the Percolation theory of composites of globular particles, the experimental conductivity vs. fibre content dependence, after a steep increase in the Percolation region, increased almost linearly. This atypical behaviour was explained by a different mechanism of formation of fibrous and globular conducting structures above the Percolation threshold. An increase in scatter of conductivity values observed at Percolation threshold as a consequence of great fluctuation of fibre arrangement manifested itself also in the conductivity–temperature dependences.
James L. Wright - One of the best experts on this subject based on the ideXlab platform.
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Percolative Transport and Cluster Diffusion Near and Below the Percolation Threshold of a Porous Polymeric Matrix
Pharmaceutical Research, 2006Co-Authors: Jayne E. Hastedt, James L. WrightAbstract:Purpose The purpose of this research was to develop a quantitative mass transport model to describe the release of a drug from a porous inert matrix dosage form near and below the Percolation threshold for the system. Methods Cumulative release profiles were generated for a series of tablets composed of a binary mixture of varying amounts of non-conducting (poly(vinyl stearate)) and conducting (benzoic acid) components. The porous microstructure was analyzed using re-constructed three-dimensional images of leached microtomed tablet sections. Poly(vinyl stearate) was characterized for transport properties, molecular weight and thermal properties. Results Based on Percolation theory, the binary matrix was determined to have a Percolation threshold of 0.09 ± 0.02. Transport, which could not be explained by “classical” Percolation theory or surface diffusion alone, was observed below the Percolation threshold for the system. Conclusions A model describing transport near and below the Percolation threshold in matrices composed of two phases, polymer and drug, was developed. The Percolation model developed accounts for diffusion within the porous structure and through the inert, insoluble polymeric amorphous regions of the matrix. The low Percolation threshold and subsequently high coordination was concluded to be due to the biphasic classical porous and nonclassical polymeric diffusional transport mechanisms associated with the system studied.
Luis G. Gorostiza - One of the best experts on this subject based on the ideXlab platform.
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Percolation in an ultrametric space
Electronic Journal of Probability, 2013Co-Authors: Donald A. Dawson, Luis G. GorostizaAbstract:We study Percolation in the hierarchical lattice of order N where the probability of connection between two points separated by distance k is of the form c k / N k ( 1+δ) , δ>-1. Since the distance is an ultrametric , there are significant differences with Percolation in the Euclidean lattice. We consider three regimes: δ 1 , where it does not occur and δ=1 which is the critical case corresponding to the phase transition. In the critical case we use an approach in the spirit of the renormalization group method of statistical physics, and connectivity results of Erdős-Renyi random graphs play a key role. We find sufficient conditions on c k such that Percolation occurs, or that it does not occur. An intermediate situation called pre-Percolation, which is necessary for Percolation, is also considered. In the cases of Percolation we prove uniqueness of the constructed Percolation clusters. In a previous paper we studied Percolation in the N→∞ limit (mean field Percolation), which provided a simplification that allowed finding a necessary and sufficient condition for Percolation. For fixed N there are open questions, in particular regarding the behaviour at the critical values of parameters in the definition of c k . Those questions suggest the need to study ultrametric random graphs .
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Percolation in an ultrametric space
arXiv: Probability, 2010Co-Authors: Donald A. Dawson, Luis G. GorostizaAbstract:We study Percolation on the hierarchical lattice of order $N$ where the probability of connection between two points separated by distance $k$ is of the form $c_k/N^{k(1+\delta)},\; \delta >-1$. Since the distance is an ultrametric, there are significant differences with Percolation on the Euclidean lattice. There are two non-critical regimes: $\delta 1$, where it does not occur. In the critical case, $\delta =1$, we use an approach in the spirit of the renormalization group method of statistical physics and connectivity results of Erd\H{o}s-Renyi random graphs play a key role. We find sufficient conditions on $c_k$ such that Percolation occurs, or that it does not occur. An intermediate situation called pre-Percolation is also considered. In the cases of Percolation we prove uniqueness of the constructed Percolation clusters. In a previous paper \cite{DG1} we studied Percolation in the $N\to\infty$ limit (mean field Percolation) which provided a simplification that allowed finding a necessary and sufficient condition for Percolation. For fixed $N$ there are open questions, in particular regarding the existence of a critical value of a parameter in the definition of $c_k$, and if it exists, what would be the behaviour at the critical point.
Isidoro Caraballo - One of the best experts on this subject based on the ideXlab platform.
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Estimation of the Percolation thresholds in dextromethorphan hydrobromide matrices
European Journal of Pharmaceutical Sciences, 2001Co-Authors: Luz Maria Melgoza, Antonio M. Rabasco, Horacio Sandoval, Isidoro CaraballoAbstract:Abstract Percolation theory is a multidisciplinary theory that studies chaotic systems. It has been applied in the pharmaceutical field since 1987. Knowledge of the Percolation threshold — one of the most important concepts in Percolation theory — results in a clear improvement of the solid dosage form design. The Percolation threshold is the concentration showing the maximum probability to obtain, for the first time, a percolating cluster of a substance. In this work, the Percolation thresholds of dextromethorphan·HBr/Eudragit® RS-PM inert matrices were estimated. The drug Percolation threshold was estimated as 0.3691±0.0541 (P=0.05) of the total porosity (ranging between 23 and 36% w/w of drug). The SEM micrographs of the matrices are consistent with the estimated Percolation range. In agreement with previous reports, different Percolation thresholds were found for the matrix forming excipient Eudragit® RS-PM. The site Percolation threshold (based on the release properties) ranged between 10 and 20% v/v of the excipient, the site-bond Percolation threshold (estimated from the mechanical properties) between 29.5 and 34% v/v of the excipient and the swelling Percolation threshold between 34.3 and 46.9% v/v of the excipient. These Percolation ranges are in agreement with those found previously for Eudragit® RS-PM matrices containing naltrexone·HCl and morphine·HCl.