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261.
A. de la Maza O. López M. Cócera L. Coderch J. L. Parra J. Guinea 《Colloid and polymer science》1999,277(12):1200-1204
The capacity of the glycoprotein (GP) excreted by Pseudoalteromonas antarctica NF3 to protect phosphatidylcholine (PC) liposomes against the action of Triton X-100 was studied in detail. Increasing amounts
of GP assembled with liposomes resulted in a linear increase in the effective surfactant-to-PC molar ratios needed to produce
the same alterations in liposomes and in a linear fall in the surfactant partitioning between the bilayer and the aqueous
phase. Thus, the higher the proportion of GP assembled with liposomes the lower the surfactant ability to alter the permeability
of vesicles and the lower its affinity with these bilayer structures. In addition, increasing GP proportions resulted in a
progressive increase in the free surfactant concentration (S
W) for the same surfactant–liposome interaction step. The fact that S
W was always lower than the surfactant critical micelle concentration indicates that the interaction was mainly ruled by the
action of surfactant monomers, regardless of the amount of GP assembled.
Received: 4 May 1999 Accepted in revised form: 6 July 1999 相似文献
262.
Four surfactants, sodium cholate(SC), n-dodecyl-β-D-maltopyranoside(DDM), lauryldimethylamine oxide(LDAO) and Triton X-100(TX), which are generally used in photosynthetic pigment-protein complexes preparation, were studied on their interaction with photosynthetic membrane from Rhodobacter sphaeroides 2.4.1 by electrochromic absorption band-shift of endogenous carotenoids and by vesicle size measurements as well. The surfactant critical micelle concentration(cmc) was found to be negatively correlated with the capability of enhancing the permeability of photosynthetic membranes to proton, and more elaborated model of surfactants interacting with membranes was obtained. The electrochromic absorption band-shift measurement might develop into a useful tool to evaluate the effects of surfactants on various membranes. 相似文献
263.
K. Jalaiah K. Vijaya Babu K. Rajasekhar Babu V. Venkat Kumar R.V. Krishnaiah 《Chinese Journal of Physics (Taipei)》2018,56(5):2039-2051
The zirconium and copper co-substituted Ni0.75Zn0.25ZrxCuxFe2-2xO4 (where x?=?0.05, 0.1, 0.15, 0.2) ferrites have been prepared by sol-gel auto-combustion method. The XRD patterns provide the evidence of single phase cubic spinel structure. The theoretical and experimental lattice parameters have resemblance with increase dopant concentration. The sintered density and porosity show the opposite trend with dopant concentration. The FT-IR spectrum of prepared samples reveal cubic spinel with () space group. The wave numbers of tetrahedral and octahedral sites show agnate trend. The dielectric constant and loss factors decreased with increasing dopant concentration. The saturation magnetization and net magnetic moment have the identical trend with increasing dopant concentration. The coercive field is decreased with increasing dopant concentration. The Y–K angles are increased with increasing dopant concentration. The Q-factor in prepared samples, exhibit narrower frequency bands with increasing frequency. 相似文献
264.
An analysis of the radial flow in the heterogeneous porous media based on fractal and constructal tree networks 总被引:1,自引:0,他引:1
In this paper, an analysis of the radial flow in the heterogeneous porous media based on fractal and constructal tree networks is presented. A dual-domain model is applied to simulate the heterogeneous porous media embedded with a constructal tree network based on the fractal distribution of pore space and tortuosity nature of flow paths. The analytical expressions for seepage velocity, pressure drop, local and global permeability of the network and binary system are derived, and the transport properties for the optimal branching structure are discussed. Notable is that the global permeability (Kn) of the network and the volume fraction (fn) occupied by the network exhibit linear scaling law with the fractal dimension (Dp) of channel diameter bylogKn∼0.46Dp and logfn∼1.03Dp, respectively. Our analytical results are in good agreement with the available numerical results for steady-state soil vapor extraction and indicate that the fractal dimension for pore space has significant effect on the permeable properties of the media. The proposed dual-domain model may capture the characteristics of heterogeneous porous media and help understanding the transport mechanisms of the radial flow in the media. 相似文献
265.
K. Suga Y. Matsumura Y. Ashitaka S. Tominaga M. Kaneda 《International Journal of Heat and Fluid Flow》2010,31(6):974-984
In order to understand the effects of the wall permeability on turbulence near a porous wall, flow field measurements are carried out for turbulent flows in a channel with a porous bottom wall by a two-component particle image velocimetry (PIV) system. The porous media used are three kinds of foamed ceramics which have almost the same porosity (0.8) but different permeability. It is confirmed that the flow becomes more turbulent over the porous wall and tends to be turbulent even at the bulk Reynolds number of Reb=1300 in the most permeable wall case tested. Corresponding to laminar to turbulent transition, the magnitude of the slip velocity on the porous wall is found to increase drastically in a narrow range of the Reynolds number. To discuss the effects of the wall roughness and the wall permeability, detailed discussions are made of zero-plane displacement and equivalent wall roughness for porous media. The results clearly indicate that the turbulence is induced by not only the wall roughness but the wall permeability. The measurements have also revealed that as Reb or the wall permeability increases, the wall normal fluctuating velocity near the porous wall is enhanced due to the effects of the wall permeability. This leads to the increase of the turbulent shear stress resulting in higher friction factors of turbulence over porous walls. 相似文献
266.
黏性土渗透性温度效应实验研究 总被引:5,自引:0,他引:5
由于全球气候变暖、城市热岛效应加剧和核废料地质处置等原因,温度对黏性土工程性质的影响日益受到关注。本文在实验的基础上,采用直接测量法,对南京下蜀土、淤泥质土以及混合土3种试样,进行了5°~45°温度下的变水头渗透实验,分析了温度对黏性土渗透性的影响。实验结果表明:温度对3种试样的渗透性均有较大影响。温度越高,渗透性越大; 试样的密度越大,渗透系数随温度变化率越低; 在3种试样中,混合土的渗透系数高于淤泥质土和下蜀土的对应值,而淤泥质土的渗透系数又略大于下蜀土。最后对黏性土渗透性的温度效应机理进行了分析,认为水的动力黏滞性,黏粒的双电层厚度以及土的微结构三方面因素的共同作用引起了黏性土渗透性的温度效应。
黏性土,渗透系数,温度效应,机理 相似文献
黏性土,渗透系数,温度效应,机理 相似文献
267.
Although there are a number of mathematical modeling studies for carbon dioxide (CO2) injection into aquifer formations, experimental studies are limited and most studies focus on injection into sandstone reservoirs
as opposed to carbonate ones. This study presents the results of computerized tomography (CT) monitored laboratory experiments
to analyze permeability and porosity changes as well as to characterize relevant chemical reactions associated with injection
and storage of CO2 in carbonate formations. CT monitored experiments are designed to model fast near well bore flow and slow reservoir flows.
Highly heterogeneous cores drilled from a carbonate aquifer formation located in South East Turkey were used during the experiments.
Porosity changes along the core plugs and the corresponding permeability changes are reported for different CO2 injection rates and different salt concentrations of formation water. It was observed that either a permeability increase
or a permeability reduction can be obtained. The trend of change in rock properties is very case dependent because it is related
to distribution of pores, brine composition and thermodynamic conditions. As the salt concentration decreases, porosity and
the permeability decreases are less pronounced. Calcite deposition is mainly influenced by orientation, with horizontal flow
resulting in larger calcite deposition compared to vertical flow. 相似文献
268.
In the porous media literature, unidirectional fibrous systems are broadly categorized as ordered or disordered. The former
class, easily tractable for analysis purposes but limited in its relation to reality, involves square, hexagonal and various
staggered arrays. The latter class involves everything else. While the dimensionless hydraulic permeability of ordered fibrous
media is known to be a deterministic function of their porosity ϕ, the parameters affecting the permeability of disordered
fiber arrays are not very well understood. The objective of this study is to computationally investigate flow across many
unidirectional arrays of randomly placed fibers and derive a correlation between K and some measure of their microstructure. In the process, we explain the wide scatter in permeability values observed computationally
as well as experimentally. This task is achieved using a parallel implementation of the Boundary Element Method (BEM). Over
600 simulations are carried out in two-dimensional geometries consisting of 576 fiber cross-sections placed within a square
unit cell by a Monte Carlo procedure. The porosity varies from 0.45 to 0.90. The computed permeabilities are compared with
earlier theoretical results and experimental data. Analysis of the computational results reveals that the permeability of
disordered arrays with ϕ < 0.7 is reduced as the non-uniformity of the fiber distribution increases. This reduction can be
substantial at low porosities. The key finding of this study is a direct correlation between K and the mean nearest inter-fiber spacing , the latter depending on the microstructure of the fibrous medium. 相似文献
269.
Open-cell metal foams are often used in heat exchangers and absorption equipment because they exhibit large specific surface
area and present tortuous coolant flow paths. However, published research works on the characteristics of fluid flow in metal
foams are relatively scarce, especially for the flow oscillation condition. The present experimental investigation attempts
to uncover the behavior of steady and oscillating flows through metal foams with a tetrakaidecahedron structure. In the experiments,
steady flow was supplied by an auto-balance compressor and flow oscillation was provided by an oscillating flow generator.
The pressure drop and velocity were measured by the differential pressure transducer and hot-wire sensor, respectively. The
friction factor of steady flow in metal foam channel was analyzed through the permeability and inertia coefficient of the
porous medium. The results show that flow resistance in the metal foams increases with increasing form coefficient and decreasing
permeability. The empirical equation obtained by the present study indicates that the maximum friction factor of oscillating
flow through the tested aluminum foams with specific structure is governed by the hydraulic ligament diameter-based kinetic
Reynolds number and the dimensionless flow amplitude. 相似文献
270.
The permeability coefficient is a key factor that reflects the nutrient release capability of polymer-coated fertilizers. To investigate the permeability coefficient of polyethylene (PE) controlled-release film and to determine the difference between the controlled-release film and a dense membrane, we designed a film permeation device to measure the permeability coefficient of a PE controlled-release film coating for urea, and a mathematical model was used to check the accuracy of these measurements. By measuring the permeation coefficient of a dense, PE membrane, the compactness of the PE controlled-release film was analyzed, and the nutrient release pathway of PE-coated fertilizer was discussed. Research indicated that urea was constantly released through PE controlled-release film and the permeability coefficient remained constant. The permeability coefficient for PE controlled-release film coating on urea with 1–4 months release time was in the range of 7.17–18.7E-15 m2/s with 2.6 times difference between the maximum and minimum. The permeability coefficient decreased as the release time increased, conforming to the inversely proportional relationship between permeation amount and time in the nutrient release model. It is investigated that the measured values are close to the theoretical values and can be used in model calculation. The urea permeability coefficient of PE dense membrane was 7.11E-18 m2/s, which is 1000–2600 times smaller than that of the PE controlled-release film. The contribution of permeability of polymer material itself is negligible. It can be concluded that PE controlled-release film is not a dense membrane but porous and that nutrient release is mainly determined by pore configuration of the film. 相似文献