Adjacent Pores Research Articles

Control of ionic selectivity by a pore helix residue in the Kv1.2 channel

Interaction between the selectivity filter and the adjacent pore helix of voltage-gated K(+) (Kv) channels controls pore stability during K(+) conduction. Kv channels, having their selectivity filter destabilized during depolarization, are said to undergo C-type inactivation. We examined the functionality of a residue at the pore helix of the Kv1.2 channel (V370), which reportedly affects C-type inactivation. A mutation into glycine (V370G) caused a shift in reversal potential from around -72 to -9 mV. The permeability ratios (P(Na)/P(K)) of the wild type and V370G mutant are 0.04 and 0.76, respectively. In the wild-type, P(Rb)/P(K), P(Cs)/P(K) and P(Li)/P(K) are 0.78, 0.10 and 0.05, respectively. Kv1.2 V370G channels had enhanced permeability to Rb(+) and Cs(+) (P(Rb)/P(K) and P(Cs)/P(K) are 1.63 and 1.18, respectively); however, Li(+) permeability was not significantly augmented (P(Li)/P(K) is 0.13). Therefore, in addition to its known effect on pore stability, V370 of Kv1.2 is also crucial in controlling ion selectivity.

Influence of pores on the thermal insulation behavior of thermal barrier coatings prepared by atmospheric plasma spray

The defects in materials play very important role on the effective thermal conductivity. Especially, the spatial and geometrical characteristics of pores are significant factors for the thermal insulation behavior of thermal barrier coatings (TBCs). In this paper, finite element method was employed to simulate the thermal transfer behavior of TBCs with different spatial and geometrical characteristic of pores. The simulation results indicate that the thermal insulation effect of TBCs would be enhanced when the pore size, pore volume fraction and pore layers which are perpendicular to the thickness direction increase and the space between the adjacent pores decreases. It is predicted that the effective thermal conductivity is different at different directions for the atmospheric plasma spray (APS) TBCs. A novel method, Computational Micromechanics Method (CMM), was utilized to depict the thermal transferring behavior of actual coatings. At the same time, model with different kinds of defects were established, and the effective thermal conductivity as the function of defect orientation angle, defect volume fraction and defect shape coefficient was discussed in detail. The simulation results will help us to further understand the heat transfer process across highly porous structures and will provide us a powerful guide to design coating with high thermal insulation property.

Enhanced rate capability of multi-layered ordered porous nickel phosphide film as anode for lithium ion batteries

Porous nickel phosphide films are fabricated by electrodeposition through self-assembled polystyrene sphere multi-layers as template. After the removal of the template, well-ordered and close-packed spherical pores are left in the films. The thin walls of the adjacent pores make up a three-dimensional network nanostructure in the triple-layer porous Ni 3P film. The as-prepared triple-layer porous film delivers significantly enhanced rate capability over the single- and double-layer ones. After 50 cycles, the capacity of the triple-layer Ni 3P porous film still sustains 557 mAh g −1 and 243 mAh g −1 at a charge–discharge rate of 0.2 C and 5 C (1 C = 388 mA g −1), respectively. According to the analysis of electrochemical impedance spectrum (EIS), the improved electrochemical performance of the triple-layer film can be attributed to the fast migration of Li + through surface-passivating layer and the facilitated charge transfer into Ni 3P three-dimensional network nanostructure.

Effect of Membrane Structural Characteristics on Mass Transfer in a Membrane Absorption Process

Carbon dioxide is absorbed by de-ionized water or NaOH aqueous solution in the unsteady-state membrane absorption process. A theoretical model has been developed to describe the mass transfer behavior in the liquid phase, in which the effects of membrane structural characteristics are investigated. The concentration profiles in the liquid phase are calculated as a function of time. When the membrane porosity is relatively high or the pore size is relatively small, the solute concentration profile near the membrane surface can get homogeneous instantly due to the short distance between adjacent pores. In this case, the existence of the porous membrane has less effect on the mass transfer process. However, when the membrane porosity is relatively low or the pore size is relatively large, the distance between the adjacent pores is large, so the concentration profile near the membrane surface is hard to get homogeneous during the absorption process. Therefore, the concentration profile can be influenced significantly by the membrane structural characteristics, which means that the membrane structure has a significant effect on the mass transfer in liquid phase. Moreover, the chemical reaction in the liquid phase makes it difficult for the concentration profile near the membrane surface to get homogeneous. The disturbance in the liquid phase caused by the gas flow and pressure fluctuation is also taken into account in the model, and the model results agree well with the experimental data.

Hierarchical Carbon Foams with Independently Tunable Mesopore and Macropore Size Distributions

Hierarchical carbon foams with independently tunable mesopore and macropore size distributions were formed in a high internal phase emulsion (HIPE) template. The HIPE consists of an internal oil phase that controls the macropore dimensions and an aqueous resorcinol-formaldehyde precursor solution external phase that directs the mesopore size distribution. Once the emulsion is formed, the precursor solution is cured, fluid elements are extracted from the monolith via solvent exchange, and then the sample is pyrolyzed to create a hierarchical open-cell foam consisting of macropores with mesoporous carbon xerogel walls. Both mesopore and macropore size distributions may be independently tuned by changing the synthesis parameters. These samples have a peak in the mesopore size distribution that may be tuned to between 5 and 8 nm and macropore average diameters that may be tuned to between 0.7 and 2.1 microm. Furthermore, the 0.7 and 2.1 microm average diameter macropores have 0.18 and 0.53 microm diameter macropore windows between adjacent pores, respectively. Pore volumes up to 5.26 cm(3)/g and electrical conductivities as high as 0.34 S/cm are observed after 1200 degrees C carbonization of the framework. These foams may have potential applications as 3-D current collectors in batteries and as fuel cell catalyst supports.

Interfacial energy effects and the evolution of pore size distributions during quartz precipitation in sandstone

Pore size is usually thought to control the rate of crystal growth in porous geological media by determining the ratio of mineral surface area to fluid volume. However, theory suggests that in micron-scale to nanometer scale pores, interfacial energy (surface energy) effects can also become important. Interfacial energy typically increases the solubility of very small crystals growing in tiny pores, and when the fluid is close to equilibrium – as is often the case in geological systems – mineral precipitation could occur in relatively large pores, while in very small adjacent pores crystal growth might be suppressed. Such a mechanism would effectively restrict the reactive surface area of the porous medium, thereby reducing the bulk reaction rate. We investigated the pore size distributions in naturally cemented sandstone adjacent to an isolated stylolite and found that quartz precipitation was inhibited in pores smaller than 10 μm in diameter. Furthermore, we demonstrate that kinetic formulations which assume constant solubility cannot reproduce the observed pore size patterns in mineralized samples; by contrast, excellent fits with the data are obtained when interfacial energy effects are taken into account. Reaction rates in geological media determined in field studies can be orders of magnitude lower than those measured in laboratory experiments, and we propose that reduced reaction rates in porous media with micron and submicron-scale porosity could account for much of the apparent paradox.

Role of the porous structure of the bioceramic scaffolds in bone tissue engineering

AbstractThe porous structure of biomaterials plays a critical role in improving the efficiency of biomaterials in tissue engineering. Here we fabricate successfully porous bioceramics with accurately controlled pore parameters, and investigate the effect of pore parameters on the mechanical property, the cell seeding proliferation and the vascularization of the scaffolds. This study shows that the porosity play an important role on the mechanical property of the scaffolds, which is affected not only by the macropores size, but also by the interconnections of the scaffolds. Larger pores are beneficial for cell growth in scaffolds. In contrast, the interconnections do not affect cell growth much. The interconnections appear to limit the number of blood vessels penatrating through adjacent pores, and both the pores size and interconnections can determine the size of blood vessels. The results may be referenced on the selective design of porous structure of biomaterials to meet the specificity of biological application.

Effect of the Microstructure on the Fatigue Strength of Highly Densified Sintered Steel

We have already reported that die wall lubricated warm compaction followed by high temperature sintering enabled the high sintered density above 7.7 Mg/m3 and the excellent tensile strength of 2200 MPa.In order to improve the mechanical property of highly densified sintered steel, we have tried to control the microstructure by the combination of fine and coarse powders of different chemistry, and production of composite structure of ductile martensite as a matrix and hard martensite in the sinter-neck regions proved to be an effective method to increase the tensile strength.In this paper, the effect of the microstructure on the rotating bending fatigue strength of the highly densified sintered steel was investigated. In case of bright quenching and tempering, the endurance limit of the composite structure was 580 MPa which was the same as the single-phase structure. The crack origin was the large residual pore which consisted of some adjacent residual pores. In case of carburized quenching and tempering, the endurance limit of the composite structure was 615 MPa less than the fatigue strength of wrought steel at 107 cycles, and the crack origin was the grain boundary near the specimen surface.

3D metallo-dielectric structures combining electrochemical and electroplating techniques

Three-dimensional (3D) periodic nickel micro-structures with a periodicity of 4 μm and high number of structural periods were fabricated by electrodeposition. Macroporous silicon, consisting of periodic arrays of sine-wave modulated pores, was used as a deposition template. It was prepared by electrochemical etching of silicon and subsequent pore widening by multiple oxidation/oxide-removal steps. The pore widening allows to open windows between adjacent pores obtaining a 3D network of interconnected voids embedded in silicon. This structure is then void-free filled with nickel in the electroplating process. The combination of electrochemical etching and electroplating techniques opens a route for the fabrication of large-scale 3D-periodic metallic micro-structures.

Improved Interpretation of Nuclear Magnetic Resonance T1 and T2 Distributions for Permeability Prediction: Simulation of Diffusion Coupling for a Fractal Cluster of Pores

NMR relaxometry is a powerful tool for inferring porosity and permeability data. In practice, measured magnetization decay curves are inverted for relaxation time distributions. Subsequently, one presumes a linear relationship between the pore radius distribution and the T1 and T2 distribution, for longitudinal and transverse magnetization, respectively. The fundamental equations used are based on a pore model, in which pores are assumed to be isolated from each other with respect to the NMR process and have smooth walls. The present study is based on a geometrical pore space model with connected pores and structured pore walls. The physical processes of surface relaxation, irreversible dephasing of magnetic spins and diffusive proton exchange between pores, are described by a system of differential equations. The solution yields a set of exponential functions representing the relaxation time distribution. We describe the difference between the distributions obtained for diffusion coupling and for isolated pores. With diffusion coupling on, the spectral width of the T1 distribution is strongly reduced, which indicates that the influence of large and small radii according to the T1-pore radius relationship is mixed to some extent. For a fractal pore space structure, where large pores are surrounded by adjacent minor pores, the T1 distribution does not resolve these substructures. Nevertheless, permeability values calculated from the logarithmic mean relaxation time T1,LM are quite the same for diffusion coupling and for isolated pores. The T2 distribution for diffusion coupling is little constricted and gives a better resolution of the pore wall structures than the corresponding T1 distribution. The permeability values from T2 distributions agree with the values from longitudinal magnetization, provided that we use a corrected relaxation time T2,corr, accounting for the dependence of the surface relaxivity ρ2 on pore radius. The study shows that radius distributions calculated from a T1 and from a T2 distribution differ from one another and both present an altered image of the true pore radius distribution. In practice, this has no serious influence on estimating permeability of medium- to high-permeability sandstones with the currently applied methods. The presented methodology of calculating the NMR response of pore space models with diffusion coupling may facilitate understanding porosity-permeability relationships of different rock types such as carbonate rocks with micro-porosity.

Flow of oil–water emulsions through a constricted capillary

The flow of oil-in-water emulsions through quartz micro-capillary tubes was analyzed experimentally. The capillaries were used as models of connecting pore-throats between adjacent pore body pairs in high-permeability media. Pressure drop between the inlet and outlet ends of the capillary was recorded as a function of time, for several values of the volumetric flow rate. Several distinct emulsions were prepared using synthetic oils in deionized water, stabilized by a surfactant (Triton X-100). Two oils of different viscosity values were used to prepare the emulsions, while two distinct drop size distributions were obtained by varying the mixing procedure. The average oil drop size varied from smaller to larger than the neck radius. The results are presented in terms of the extra-pressure drop due to the presence of the dispersed phase, i.e. the difference between the measured pressure drop and the one necessary to drive the continuous phase alone at the same flow rate. For emulsions with drops smaller than the capillary throat diameter, the extra-pressure drop does not vary with capillary number and it is a function of the viscosity ratio, dispersed phase concentration and drop size distribution. For emulsions with drops larger than the constriction, the large oil drops may partially block the capillary, leading to a high extra pressure difference at low capillary numbers. Changes in the local fluid mobility by means of pore-throat blockage may help to explain the additional oil recovery observed in laboratory experiments and the sparse data on field trials.

Estimate of maximum pore size in keyhole laser welding of carbon steel

Porosity is easily formed in welded joints during high power laser welding due to keyhole instability. Large pores have detrimental effects on the fatigue resistance of a component and cause many failures in welded parts. This paper is aimed at predicting the maximum pore dimension in long laser welded joints, starting from the sampling of large pores in shorter joints. Two sampling strategies and, consequently, two estimating techniques, both belonging to the statistics of extremes, were explored. The first approach, extreme value type, is used to estimate the size of the maximum pore in each of a series of steel samples. In each sample, the larger single pore or two large pores which are very close are the measured maximum pore. The second approach, threshold value type, is used to estimate the size of pores larger than a critical threshold in a single sample of steel. Both approaches lead to good estimates of the largest pore distribution in short laser welded joints. However, the first one is more adequate to describe the largest pore distribution, because it allows the synergetic effect of two adjacent pores to be considered. In particular, the Gumbel distribution adequately fits the experimental data even in the case of welded joints 10 times longer than the investigated bead length.

On the Nature of hERG Inactivation using KcsA, Shaker and Kv1.2 as Structural and Functional Models

In K+ channels, C-type inactivation locks the selectivity filter in a non-conductive state. The prokaryotic proton-gated potassium channel KcsA undergoes a time dependent inactivation process. The interaction between Glu71 and Asp80 is one of the key driving forces that promote filter instability and inactivation. This interaction promotes a compression of the selectivity filter parallel to the permeation pathway, which biases it towards the inactivated conformation. Since KcsA represents a structural model for the pore domain of K+ channels, it is obvious that a detailed understanding of the molecular basis of inactivation is not limited to this prokaryotic channel, but offers new directions into how inactivation gating might proceed in other K+ channels. Here, using patch clamp experiments, EPR spectroscopy, functional assays, molecular dynamics, and X-ray crystallography we show that interactions involving residues Trp67, Tyr78, and Asp80 in KcsA, conserved in most potassium channels, also constitute critical contacts between the selectivity filter and its adjacent pore helix which determines the rate and extent of C-type inactivation in Shaker, Kv1.2, and hERG. Substitution of a tryptophan or tyrosine at the pore helix to phenylalanine in these channels decreases the rate and extent of inactivation, pointing this position as key modulator of gating. Furthermore, by substituting equivalent amino acids critical for hERG inactivation in KcsA we were able to create a non-conducting KcsA mutant with normal pH activated lower gate. These results suggest commonalities in inactivation gating mechanism of eukaryotic channels, and provide evidence that the hydrogen bond network and Van der Waals interactions between the pore helix, selectivity filter, and external vestibule serve as the basis for C-type inactivation in the K+ channel family.

Mobilization of Entrapped Organic Fluids by Elastic Waves and Vibrations

Summary The organic fluids entrapped in pore constrictions by capillary forces can be mobilized by the application of elastic-wave vibrations because of the nudging effect, which allows quantitative description. The model used for such calculations is a single-pore channel with converging/diverging geometry, in which the organic phase is entrapped as a continuous blob occupying several adjacent pores. The ganglion is released from the constriction when the wave-acceleration amplitude exceeds a threshold value that scales with the frequency as A/f = a constant. This means that the wave intensity is the only required criterion for the release. In an ensemble of ganglia, the percentage of them mobilized and, therefore, the flow rate increases with the amplitude and decreases with frequency. The vibrations are inefficient for mobilization if the frequency is sufficiently high. The typical vibratory amplitudes required to produce noticeable increases in the average flow rates are on the order of 10 m/s2 and much higher at the frequencies in excess of approximately 10 Hz. These estimates provide guidelines for the possible applications of elastic-wave stimulation of organic-fluid flow in porous environments.

Prediction of convective transport within unsaturated concrete utilizing pore size distribution data

The durability of concrete structures is often compromised by physical and chemical interaction with the external environment that leads to ongoing maintenance and, in the worst cases, can lead to reduced structural integrity and consequent asset replacement. Concrete is a porous material and most field-exposed concrete is partially saturated with water. Where the concrete is unsaturated and there is no external water pressure acting on a concrete surface, the primary mechanisms of transport into concrete are convective-diffusion ingress (i.e. uptake of water and water-borne agents due to capillary attraction). This paper assesses capillarity and outlines a predictive model of the uptake of water by concrete based on analysis of the pore size distribution. It is acknowledged that concrete has a multitude of internal pores with a broad range of lengths and cross-sectional shapes, surface roughness, tortuosities, random meeting and divergence with adjacent pores, microcracks and fractures, and variable pore-water chemical composition, however the prediction model shows reasonable agreement with water sorptivity test data.

Nanostructures and luminescence properties of porous ZnO thin films prepared by sol–gel process

ZnO thin films containing nano-sized pores were synthesized on solid substrates through a sol–gel process by accommodating cetyl-trimethyl-ammonium bromide (CTAB) as an organic template in the precursor solution. By X-ray diffraction the resultant ZnO films were found to possess ordered pore arrays forming lamellar structure with the spacing between two adjacent pores being ∼3.0 nm. Photoluminescence measurements indicated that the surfactants effectively passivated the surface defects of the ZnO films responsible for the green emission. Al doping was found to improve not only the lamellar structure of the pore arrays but also the near-band-gap emission intensity while the suppression effect of CTAB on the green emission remained undisturbed. With a proper control of doping level, the optical property as well as the structural integrity can be tailored to augment the potential of ZnO films for the optoelectronics and sensor applications.

Computed Tomography Study of Fibre Reinforced Autoclaved Aerated Concrete

Abstract A preferential orientation of fibres is induced by the production process of fibre reinforced autoclaved aerated concrete. For a better understanding of the development of the fibre arrangement during the foaming process of the concrete, digital radiography was used to study the evolution of orientation in situ. The strength and the deformation behaviour of this building material are largely influenced by the fibre orientation. Therefore information on the fibre orientation is highly desirable. Computed tomography measurements allow for the non destructive investigation of the material. The contrast between fibres and concrete matrix is sufficiently high, even for glass fibres. Two different ways to study the fibre orientation are compared. The results correlate with the strength and the deformation behaviour of the samples. A high resolution study of the fibre environment shows that the fibres align the adjacent pores.

The formation mechanism of titania nanotube arrays in hydrofluoric acid electrolyte

Self-organized and highly ordered titania nanotube arrays (TNAs) were prepared through electrochemical anodic oxidization on a titanium foil in 0.5 wt.% hydrofluoric acid (HF) electrolyte. The current density and morphology images during the formation process of TNAs were studied. Results show that the formation of TNAs includes the following processes. Initially, dense oxide of titania was rapidly formed on the titanium surface, followed by small pore formation. The adjacent small pores were then integrated and become larger pores. At the same time, small tubes were transformed. These small tubes were further integrated into larger tubes until the primary tube formation. Finally, the tubular structure was gradually optimized and eventually developed into the highly ordered TNAs. A model was proposed to explain the formation mechanism of TNAs fabricated on a titanium foil in HF acid electrolyte.

Microstructure evolution in dry–wet cast polysulfone membranes by cryo-SEM: A hypothesis on macrovoid formation

Time-sectioning cryogenic scanning electron microscopy (cryo-SEM) was introduced in an earlier publication as a technique to directly visualize wet microstructures. In this work, the evolution of an asymmetric membrane microstructure of dry–wet cast (phase inversion) polysulfone solution coatings is methodically captured using cryo-SEM. The images show that the as-deposited, homogeneous coating (predecessor of the membrane) partially phase separates into a dispersion of droplets during the brief initial drying step, and then, on immersion in a coagulant, skins at the free surface and undergoes complete phase separation below, first by nucleation and growth, rapidly followed by partial coalescence into bicontinuous, open-celled structures. The phase-separated region is two-tiered consisting of an intermediate fine-scaled layer lying above a thicker and coarser layer. The membranes also display disproportionately large voids called macrovoids. Cryo-micrographs suggest that macrovoids in phase-separating coatings form due to a unique network instability triggered by successive tensile ruptures of the gelled polymer-rich network. In this wet cast process, a hypothesis is developed showing how (i) build-up of compressive pressure in pores and tensile stress in the network from overall swelling and local syneresis, (ii) vertical rupture (normal to substrate), (iii) stress localization, (iv) post-rupture relaxation and (v) plausible horizontal ruptures may cause this network instability and drive convective flows from adjacent pores into the growing void. Mathematical analysis of stress development and supporting cryo-micrographs of a dry cast process are also included in appendices.

Palynological and Revisional Studies of Thalictrum L. in Korea

The pollen and revisional study aimed for an elucidation of taxonomic delimitation and relationship of Thalictrum taxa in Korea, especially among the morphologically confused taxa. Pollen grains of 63 populations of 17 taxa were investigated by light and scanning electron microscopy. Although pollen morphology was not useful for the species classification, it revealed a tendency in which Sects. Physocarpum, Erythrandra and Tripterium having broad filaments and round-tipped anthers possess closer distance between adjacent pores, less echinus number per unit area, smaller pollen, and higher echinus, on the contrary to Sects. Omalophysa, Camptonotum and Thalictrum having filiform filaments and acute-acuminate- or more or less round-tipped anthers. The palynological result did not support several section system by Tamura (1992) but one section system by Lecoyer (1885). If a infrasectional system is needed, it was suggested that the system dividing the section into two (Clauiformes and Filiformes sensu Lecoyer) would be natural on the basis of stamen and pollen characteristics. Revisional study found out that 17 taxa(16 species) of Thalictrum are distributed in Korean including T. filimentosum which presence in Korea was not confirmed.