Permeability of Fractal Porous Media by Monte Carlo Simulations

The permeability of the fractal porous media is simulated by Monte Carlo technique in this work. Based oil the fractal character of pore size distribution in porous media, the probability models for pore diameter and for permeability are derived. Taking the bi-dispersed fractal porous media as examples, the permeability calculations are performed by the present Monte Carlo method. The results show that the present simulations present a good agreement compared with the existing fractal analytical solution in the general interested porosity range. The proposed simulation method may have the potential in prediction of other transport properties (such as thermal conductivity, dispersion conductivity and electrical conductivity) in fractal porous media, both saturated and unsaturated.

Transient Flows in Low Permeability Porous Media with Composite Start-Up Pressure Gradient

A new mathematical model for the transient flow in the composite low permeability is established. It is solved by FEM with different boundary conditions such as infinite, circular closed and constant pressure boundary conditions. The typical curves for transient wellbore pressure have been presented. It is shown that the pressure and pressure derivative curves with composite start-up pressure gradients have different slopes which are depended on the start-up pressure gradients and the mobility radios in different regions. The boundary effects are the same as the normal reservoirs without start-up pressure gradients. The study provides a new tool to analyze the transient pressure test data in the low permeability reservoir.

Deletion of yeast CWP genes enhances cell permeability to genotoxic agents

We have previously reported the development of a novel genotoxic testing system based on the transcriptional response of the yeast RNR3-lacZ reporter gene to DNA damage. This system appears to be more sensitive than other similar tests in microorganisms, and is comparable with the Ames test. In an effort to further enhance detection sensitivity, we examined the effects of altering major cell wall components on cell permeability and subsequent RNR3-lacZ sensitivity to genotoxic agents. Although inactivation of single CWP genes encoding cell wall mannoproteins had little effect, the simultaneous inactivation of both CWP1 and CWP2 had profound effects on the cell wall structure and permeability. Consequently, the RNR3-lacZ detection sensitivity is markedly enhanced, especially to high molecular weight compounds such as 4-nitroquinoline-N-oxide (> sevenfold) and phleomycin (> 13-fold). In contrast, deletion of genes encoding representative membrane components or membrane transporters had minor effects on cell permeability. We conclude that the yeast cell wall mannoproteins constitute the major barrier to environmental genotoxic agents and that their removal will significantly enhance the sensitivity of RNR-lacZ as well as other yeast-based genotoxic tests.

Microcystin-RR induced apoptosis in tobacco BY-2 suspension cells is mediated by reactive oxygen species and mitochondrial permeability transition pore status

When tobacco BY-2 cells were treated with 60 mu g/mL MC-RR for 5 d, time-dependent effects of MC-RR on the cells were observed. Morphological changes such as abnormal elongation, evident chromatin condensation and margination, fragmentation of nucleus and formation of apoptotic-like bodies suggest that 60 mu g/mL MC-RR induced rapid apoptosis in tobacco BY-2 cells. Moreover, there was a significant and rapid increase of ROS level before the loss of mitochondrial membrane potential (Delta Psi(m)) and the onset of cell apoptosis. Ascorbic acid (AsA), a major primary antioxidant, prevented the increase of ROS generation, blocked the decrease in Delta Psi(m) and subsequent cell apoptosis, indicating a critical role of ROS in serving as an important signaling molecule by causing a reduction of Delta Psi(m) and MC-RR-induced tobacco BY-2 cell apoptosis. In addition, a specific mitochondrial permeability transition pores (PTP) inhibitor, cyclosporin A (CsA), significantly blocked the MC-RR-induced ROS formation, loss of Delta Psi(m), as well as cell apoptosis when the cells were MC-RR stressed for 3 d, suggesting that PTP is involved in 60 mu g/mL MC-RR-induced tobacco cell apoptosis signalling process. Thus, we concluded that the mechanism of MC-RR-induced apoptosis signalling pathways in tobacco BY-2 cells involves not only the excess generation of ROS and oxidative stress, but also the opening of PTP inducing loss of mitochondrial membrane potential. (C) 2007 Published by Elsevier Ltd.

Structure and oxygen permeability of a dual-phase membrane

The dual-phase membrane of La0.15Sr0.85Ga0.3Fe0.7O3-delta-Ba0.5Sr0.5Fe0.2Co0.8O3-delta (LSGF-BSCF) was prepared successfully. This membrane was characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe micro-analyzer (EPMA). This membrane has a dense dual-phase structure: LSGF being the dense body of this membrane and BSCF as another phase running along the LSGF body. This structure is favorable for the oxygen permeation through the membrane. The oxygen permeation test shows that the oxygen permeation flux of LSGF-BSCF membrane (Jo(2) = 0.45 ml/min cm(2), at 915 degreesC) is much higher than that of LSGF membrane (Jo(2) = 0.05 ml/min cm(2)). Thickness dependence of oxygen permeation indicates that the oxygen permeation is controlled by the bulk diffusion. Compared to pure BSCF the dual-phase membrane of LSGF-BSCF is stable in reducing atmosphere. (C) 2003 Elsevier B.V. All rights reserved.

Gas permeability of a novel cellulose membrane

A novel cellulose membrane was prepared by using amine oxides as the solvent and its mechanical performance was measured. Steady-state permeation rates of carbon dioxide, hydrogen, methane, nitrogen, oxygen, argon and helium in the homogeneous dense cellulose membrane were measured in the temperature range of 298-353 K and under gas pressures up to 1 MPa. The effect of swelling on hydrophilic membrane permeability was studied in some detail on the cellulose membrane. The difference in gas permeability between the "dry" cellulose membrane and the "water-swollen" cellulose membrane was investigated, and the gas permeability between the cellulose membrane and the Cellophane was compared. In this paper, the separation performance Of CO2 over H-2 in a "water-swollen" cellulose membrane is reported for the first time and the separation factor Of CO2/H-2 can be up to 15. (C) 2002 Elsevier Science B.V. All rights reserved.

Synthesis and gas permeability of novel fluorinated poly(phenylene-co-naphthalimide)s

A new class of high-performance polymers [poly(phenylene-co-naphthalimide)s] was prepared through the Ni(0) catalytic coupling of N-(4-chloro-2-trifluromethylphenyl)-5-chloro-1,8-naphthalimide and 2,5-dichlorobenzophenone. The resulting copolymers exhibited high molecular weights (high inherent viscosities) and a combination of desirable properties such as good solubility in dipolar aprotic solvents, film-forming capability, and mechanical properties. The glass-transition temperatures of the copolymers ranged from 320 to 403 degrees C and increased as the content of the naphthalimide moiety increased. Tough polymer films, obtained via casting from N-methylpyrrolidone solutions, had tensile strengths of 64-107 MPa and tensile moduli of 3.4-4.7 GPa. The gas permeability coefficients of the copolymers were measured for H-2, CO2, O-2, CH4, and N-2. They showed oxygen permeability coefficients and permeability selectivity of oxygen to nitrogen (permeability coefficient for O-2/permeability coefficient for N-2) in the ranges of 1.39-4.31 and 4.92-5.38 barrer, respectively.

Gas permeability and permselectivity of polyimides prepared from phenylenediamines with methyl substitution at the ortho position

Polyimides were prepared from diamines: 2,4,6-trimethyl-1,3-phenylenediamine (3MPDA) and 2,3,4,5-tetramethyl-1,4-phenylenediamine (4MPDA). 1,4-Bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3'-4,4'-diphenylsulphone tetracarboxylic dianhydride (SO(2)PDA), 3,3',4,4'-diphenylsulphide tetracarboxylic dianhydride (SPDA), pyromellitic dianhydride (PMDA), and 2,2'-bis(3,4-dicarboxyphenyl)hexa-fluoroisopropane dianhydride (6FDA) were used as dianhydride. The gas permeabilities of H-2, O-2 and N-2 through the polyimides were measured at temperatures from 30 degrees C to 90 degrees C. The results show that as methyl and trifluoromethyl substitution groups densities increase from 7.73 x 10(-3) molcm(-3) to 13.50 x 10(-3)molcm(-3), the peameability of H-2 increases 10-fold at 60% loss of permselectivity of H-2/N-2 however, the permeability of O-2 increases 20-fold at 20% loss of permselectivity of O-2/N-2. For O-2/N-2 separation, PMDA-3MPDA has similar performance to 6FDA-3MPDA and 6FDA-4MPDA; all have higher permeabilities for O-2 than normal polyimides, and the P(O-2)/alpha(O-2/N-2) trade-off relationships lie on the upper bound line for polymers. (C) 1999 Society of Chemical Industry.

Effect of crosslinking distribution on gas permeability and permselectivity of crosslinked polyimides

Crosslinking modification of polyimide, prepared from 3,3'4,4'-benzophenone tetracarboxyl dianhydride (BTDA) and 2,3,5,6-tetramethyl-1,4-diphenylenediamine (4MPDA), was performed by two methods, putting the polyimide in ambient environment for 4 months, and under UV irradiation for 2 or 8 h. The gas permeation properties of the crosslinked polyimides were investigated. The crosslinked polyimides induced by UV irradiation, in which crosslinking occurs in the surface layer, are of much higher gas permselectivity of hydrogen to nitrogen than that induced by the ambient environment, in which crosslinking takes place in the whole matrix, but their gas permeabilities for hydrogen are similar. (C) 1999 Elsevier Science Ltd. All rights reserved.

Gas permeability and permselectivity of photochemically crosslinked copolyimides

A series of copolyimides were prepared from 2,4,6-trimethyl-1,3-phenylenediamines (3MPDA), 3,3',4,4'-benzophenone tetracarboxyl dianhydride (BTDA), and pyromellitic dianhydride (PMDA). Modification of the copolyimides by ultraviolet irradiation were carried out. Gas permeabilities of H-2, O-2, and N-2 through the copolyimides and photochemically crosslinked copolyimides were measured at temperatures from 30 to 90 degrees C. The relationships between gas permeabilities and temperature are in agreement with the Arrhenius equation. The structure of photochemically crosslinked copolyimides were characterized by Fourier transform infrared and gel measurement methods. Linear relationships between both log P and E-p and the volume fraction of PMDA-3MPDA exist. Photochemically crosslinking modification result in a decrease in gas permeability and an increase in E-p and alpha(H-2/N-2) for all the copolyimides. For H-2/N-2 separation, photochemically crosslinked copolyimides are of higher gas permeabilities and permselectivities simultaneously than normal polyimides. (C) 1999 John Wiley & Sons, Inc.