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Pore Geometry (pore + geometry)
Selected AbstractsMonodisperse, Polymeric Nano- and Microsieves Produced with Interference HolographyADVANCED MATERIALS, Issue 17 2009An Maria Prenen Monodisperse microfiltration membranes are fabricated using interference lithography. The versatility of this technique to produce polymeric membranes optimized for flow and selectivity characteristics with a wide variety of pore geometries and dimensions is demonstrated. [source] Influence of the OMCs pore structures on the capacitive performances of supercapacitorASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009Gu-Zhen Nong Abstract In the present study, two mesoporous carbons OMC-KIT-6 and OMC-SBA-16 were nanocasted using mesoporous silica of KIT-6 and SBA-16 as templates and furfuryl alcohol as carbon precursor. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) characterizations confirmed that the resultant samples are mesoporous carbons, and the as-prepared OMC-KIT-6 has an Ia3d ordered structure, whereas OMC-SBA-16 belongs to Im3m space group. The surface area and the average pore size are (1658 m2 g,1 and 3.4 nm) for OMC-KIT-6 and (1638 m2 g,1 and 2.9 nm) for OMC-SBA-16, respectively. The results of cyclic voltammograms and galvanostatic charge-discharge tests show that these two mesoporous carbons have excellent capacitive performances. But the difference of capacitive behavior between OMC-KIT-6 and OMC-SBA-16 may be a result of the difference of pore geometries of these two carbons. In order to find out the function of mesopore in a supercapacitor, we compared the capacitive properties of mesoporous and microporous carbons; the experiment results indicated that these two kinds of carbon exhibit nearly ideal capacitive behavior at low scan rate. When the scan rate is enhanced up to 50 mV s,1 the performance of mesoporous carbon is more stable than microporous carbon. This outcome demonstrated that mesopore plays an important role in forming double layers in the electrode materials. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Perfectly Ordered, Free-Standing Nanowire Arrays With Controllable Geometry,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Adam Philip Robinson We demonstrate a novel focused ion beam (FIB) based technique for the production of substrate-supported, free-standing, perfectly ordered nanowire arrays with control over the pore geometry, pitch, diameter, and length. A FIB may be used to influence the site of pore formation in ultra-thin (<1 µm) oxide nanoporous templates adhered to substrates. Electrodeposition through the template results in the production of nanowire arrays with controlled, perfect ordering. [source] Effect of degree of fluid saturation on transport coefficients in disturbed soilsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2004A. Tuli Summary To improve the predictive capability of transport models in soils we need experimental data that improve their understanding of properties at the scale of pores, including the effect of degree of fluid saturation. All transport occurs in the same soil pore space, so that one may intuitively expect a link between the different transport coefficients and key geometrical characteristics of the pores such as tortuosity and connectivity, and pore-size distribution. To understand the combined effects of pore geometry and pore-size distribution better, we measured the effect of degree of water saturation on hydraulic conductivity and bulk soil electrical conductivity, and of degree of air saturation on air conductivity and gaseous diffusion for a fine sand and a sandy loam soil. To all measured data were fitted a general transport model that includes both pore geometry and pore-size distribution parameters. The results show that both pore geometry and pore-size distribution determine the functional relations between degree of saturation, hydraulic conductivity and air conductivity. The control of pore size on convective transport is more for soils with a wider pore-size distribution. However, the relative contribution of pore-size distribution is much larger for the unsaturated hydraulic conductivity than for gaseous phase transport. For the other transport coefficients, their saturation dependency could be described solely by the pore-geometry term. The contribution of the latter to transport was much larger for transport in the air phase than in the water phase, supporting the view that connectivity dominates gaseous transport. Although the relation between effective fluid saturation and all four relative transport coefficients for the sand could be described by a single functional relation, the presence of a universal relationship between fluid saturation and transport for all soils is doubtful. [source] Bioceramic Bone Graft Substitutes: Influence of Porosity and ChemistryINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2005Karin A. Hing Bioceramics have been considered for use as synthetic bone graft substitutes (BGSs) for over 30 years, throughout which there have been two primary areas of research: (i) optimization of the physical pore structure and (ii) formulation of an appropriate bioceramic chemistry. While it is well recognized that both the rate of integration and the final volume of regenerated bone are primarily dependent on the macroporosity, there still seems to be some dispute regarding the optimum "type" of porosity. The rate and quality of bone integration have, in turn, been related to a dependence on pore size, porosity volume fraction, and interconnection size and interconnection density, both as a function of structural permeability and mechano-transduction. Moreover, the role of strut microstructure and pore geometry have been considered with respect to their influence on entrapment and recruitment of growth factors (GFs) in addition to its influence on scaffold mechanics. Deconvoluting the relative affects of these parameters is complicated by the use of both resorbable and nonresorbable bioactive bioceramics, which are believed to mediate bioactivity in the osseous environment through two principal mechanisms: (i) directly through dissolution and release of ionic products in vivo, elevating local concentrations of soluble species that interact directly with local cells or influence cell behavior by their effect on local pH, (ii) indirectly through the influence that surface chemistry will have on protein adsorption, GF entrapment, and subsequent cell attachment and function. This article aims to review some of the recent developments in bioceramic BGSs, with a view to understanding how the various physiochemical parameters may be optimized to promote bone healing. [source] Simulation of the dynamics of depth filtration of non-Brownian particlesAICHE JOURNAL, Issue 4 2001V. N. Burganos A new simulator for flow of aqueous suspensions and deposition of non-Brownian particles in granular media can predict the pattern of deposition and concomitant reduction in permeability as functions of depth, time and system parameters. The porous structure of the granular medium represented as a 3-D network of constricted pores considers the converging,diverging character of flow within pores. Using Lagrangian-type simulation the particle deposition rate was calculated. Gravity and drag, as well as hydrodynamic and physicochemical interactions between suspended particles and pore walls, were considered in calculating 3-D particle trajectories. Deposit configurations were computed, and the evolution of the pore structure was simulated at discrete time steps. Changes in the pore geometry and nature of the collector surface affect flow and trajectory computations directly. Clusters of deposited particles were allowed to become reentrained if exposed to shear stress higher than a critical value. Reentrained clusters, which moved through downstream pores, might redeposit downstream at suitable sites and cause clogging of sufficiently narrow pores. Particle clusters clogging pores have a finite permeability, which significantly affects the system's transient behavior. Clogged pores act as collectors of solitary particles and of reentrained clusters, and substantially affect the transient behavior of the filter. The loss of permeability was monitored by calculating pore and network hydraulic conductance at each time step. Numerical results for the loss of permeability, temporal evolution of filter efficiency, and specific deposit profiles are based on suspension flow simulations in a typical granular porous medium. [source] A computational study of the porosity effects in silica monolithic columnsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10-11 2004Piotr Gzil Abstract We report on a theoretical study of the influence of the through-pore porosity on the main chromatographic performance parameters (reduced theoretical plate height, flow resistance, and separation impedance) of silica monoliths. To investigate this problem devoid of any structural uncertainties, computer-generated structural mimics of the pore geometry of silica monolithic columns have been studied. The band broadening in these synthetic monoliths was determined using a commercial Computational Fluid Dynamics (CFD) software package. Three widely differing external porosities (, = 0.38, , = 0.60, and , = 0.86) are considered and are compared on the basis of an identical intra-skeleton diffusivity (D s = 5×10,10m2/s), internal porosity (,int = 0.5), and for the same phase retention factor (k ´ = 1.25). Since the data are obtained for perfectly ordered structures, the calculated plate heights and separation impedances constitute the ultimate performance ever to be expected from a monolithic column. It is found that, if silica monoliths could be made perfectly homogeneous, domain size-based reduced plate heights as small as h min , 0.8 (roughly independent of the porosity) and separation impedances as small as Emin , 130 (, = 0.60) and Emin , 40 (, = 0.86) should be achievable with pure water as the working fluid. The data also show that, although the domain size is a much better reduction basis than the skeleton size, the former is still not capable of bringing the van Deemter curves of different porosity columns into perfect agreement in the C term dominated velocity range. It is found that, in this range, large porosity monoliths can be expected to yield smaller domain size-based reduced plate heights than small porosity monoliths. [source] Characterization of MOCVD grown GaN on porous SiC templatesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005F. Yun Abstract We have grown GaN layers by MOCVD on a set of nanoporous SiC templates with different porosity and morphology, produced by etching the anodized porous SiC starting material in a H2 environment at temperatures ,1500 °C, in an effort to attain improved films. The hydrogen etching serves to remove surface damage caused during mechanical polishing prior to anodization, remove the skin layer associated with anodization, tune the pore size, and consolidate pore geometry. Growth conditions favoring lateral overgrowth of GaN were employed on this set of samples to obtian GaN to a thickness of 2 µm. Atomically smooth surfaces were obtained for the epitaxial GaN layers. The GaN quality is highly dependent on the specifics of the porous templates used. An intensity increase of up to a factor of 30 was observed in the GaN excitonic peak compared to GaN grown on standard SiC substrate. The I-V data indicated significant reduction in the leakage current (in reverse bias) compared to GaN grown on standard SiC. The dependence of optical properties, crystalline quality, and surface morphology on the particulars of porous SiC templates is discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The relation between stomatal aperture and gas exchange under consideration of pore geometry and diffusional resistance in the mesophyllPLANT CELL & ENVIRONMENT, Issue 8 2009HARTMUT KAISER ABSTRACT The quantitative relation between stomatal aperture and gas exchange through the stomatal pore can be described by physical models derived from Fick's first law of diffusion. Such models, usually based on a simplified pore geometry, are used to calculate leaf conductance from stomatal pore dimensions or vice versa. In this study a combination of gas-exchange measurements and simultaneous microscopical observations of stomatal apertures was used to empirically determine this relationship. The results show a substantial deviation between measured stomatal conductance and that calculated from the simplified models. The main difference is a much steeper increase of conductance with aperture at small apertures. When the calculation was based on a realistic pore geometry derived from confocal laser scanning microscopy, a good fit to the experimentally found relationship could be obtained if additionally a significant contribution of a mesophyll diffusional resistance was taken into account. [source] About Darcy's law in non-Galilean frameINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2004C. Geindreau Abstract This paper is aimed towards investigating the filtration law of an incompressible viscous Newtonian fluid through a rigid non-inertial porous medium (e.g. a porous medium placed in a centrifuge basket). The filtration law is obtained by upscaling the flow equations at the pore scale. The upscaling technique is the homogenization method of multiple scale expansions which rigorously gives the macroscopic behaviour and the effective properties without any prerequisite on the form of the macroscopic equations. The derived filtration law is similar to Darcy's law, but the tensor of permeability presents the following remarkable properties: it depends upon the angular velocity of the porous matrix, it verifies Hall,Onsager's relationship and it is a non-symmetric tensor. We thus deduce that, under rotation, an isotropic porous medium leads to a non-isotropic effective permeability. In this paper, we present the results of numerical simulations of the flow through rotating porous media. This allows us to highlight the deviations of the flow due to Coriolis effects at both the microscopic scale (i.e. the pore scale), and the macroscopic scale (i.e. the sample scale). The above results confirm that for an isotropic medium, phenomenological laws already proposed in the literature fails at reproducing three-dimensional Coriolis effects in all types of pores geometry. We show that Coriolis effects may lead to significant variations of the permeability measured during centrifuge tests when the inverse Ekman number Ek,1 is ,,(1). These variations are estimated to be less than 5% if Ek,1<0.2, which is the case of classical geotechnical centrifuge tests. We finally conclude by showing that available experimental data from tests carried out in centrifuges are not sufficient to determining the effective tensor of permeability of rotating porous media. Copyright © 2004 John Wiley & Sons, Ltd. [source] | |||||||||||||