Results 1 - 10 of 1808
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[en] This paper examines the mechanisms of wet curing and subsequent drying at 23 °C and 40% RH influencing the curling of cement paste, plate-like beams. Both experimental and model results show that as the duration of the wet curing is increased, the member peak deflection also increases from one sided drying. Experiments suggest that the extended wet curing causes a pore structure refinement resulting in greater saturation and consequently greater shrinkage. A simplified 1-D, drying diffusion and shrinkage model is able to adequately predict experimentally measured peak curling deflections, and confirms the effect of saturation on curling. The results provide important insight into the volume stability of slabs and the potential negative impact of wet curing on slab curling.
[en] Highlights: • Precursor phase separation during crosslinking can create pores in ceramics. • Contents of hydrogen and vinyl bonds influence final porosity and pore size. • v-PDMS with vinyl bonds decreases pore size and narrows pore size distribution. • Excess hydrogen bonds from the base polymer with v-PDMS eliminates porosity.
[en] The malaria parasite Plasmodium falciparum requires the Plasmodium translocon of exported proteins (PTEX) to proliferate in human red blood cells. During the blood stages of malaria, several hundred parasite-encoded proteins are exported from the parasite into the cytosol of red blood cells. PTEX is the translocon for protein export and comprises 5 proteins: EXP2, PTEX150, PTEX88, Hsp101 and TRX2. Among them, EXP2 is thought to constitute the transmembrane pore, whereas the other components seem to play a role in unfolding the luggage proteins or providing a driving force. However, detailed functional and structural characterizations of PTEX proteins have not been performed. In this study, we expressed and characterized the membrane-associated component EXP2. Because expression of EXP2 is lethal to E. coli, EXP2 was expressed as a fusion protein with GST, and the recombinant EXP2 was obtained by protease digestion. The recombinant EXP2 formed pores in bilayer lipid membranes. The inner diameter of the pore was estimated to be approximately 3.5 nm based on electron microscopy images and channel currents. From this size and the molecular mass as determined by size exclusion chromatography and blue native polyacrylamide gel electrophoresis, we determined that the pore comprises approximately 10–12 EXP2 subunits. However, there is a possibility that the pore structure is different in the PTEX complex. These results provide important insights in the protein transport mechanism of PTEX, which will aid in developing new drugs targeting PTEX.
[en] Intensification of technological processes, limited by the square of the surface of an active element porous powder field, is possible at the expense of magnification of the square of the surface of the latter by its addition. Thus the overall dimensions of such skew field are preserved. The analytical dependence of the factor of magnification of the surface K on geometrical parameters of a powder article of the complex shape is obtained. The optimization of these parameters in view of technological limitations for the maximization of K is carried out. The technique of calculating of the intense - deformed state of the powder skew field of the complex geometrical shape in the isostatic pressing is developed. The basic correlation permitting to calculate strain and deformation fields when pressing are gained. The technique of dry isostatic pressing of the article of the complex shape and the corresponding deforming instrument are developed. (author)
[en] This paper shows the possibility of preparing nanoporous particle track etched membranes (nanoPTM) with perfectly smooth and cylindrical pores from polycarbonate film. Interest in the template use of these nanoPTM for the production of polymeric or metallic nanoscale materials is also emphasized
[en] The possibility of materials with organized porous structure, given size and pore allocation, deriving from wire is established by its regulated winding on mandrel, deformation in conditions of isostatic loading and consequent sintering (if necessary). To determine power characteristics of the pressing technological process, the calculating of workpiece (in the form of winding skew) tense-deformation state is made. Studying regularities of deformation field changing during the plastic strain in consideration of winding skew fields initial structure allowed to define structural characteristics of finished articles. The technology of producing permeable materials with organized porous structure is developed. (author)
[en] We present a laboratory system to evaluate radon flux and pore water radon via automated sediment equilibration experiments. The setup includes a measured mass of sediment and water inside a gas-tight reaction flask connected in a closed loop to a radon-in-air analyzer. Diffusive fluxes are determined either from the near-linear slope of the activity versus time over the first several hours or by running the experiment longer to estimate the equilibrium concentration via a curve fitting approach. By combining the equilibrium activity with relevant physical parameters, one can also estimate the pore water concentrations. (author)
[en] Various double-solvent systems, including EG–IPA, glycerol–IPA, EG–methanol and EG–ethanol etc., were used to fabricate nickel–cobalt sulfide (NCS). Their products showed different structure with granular-, hollow sphere-, honeycomb-, irregular sphere-like microstructures and so on. The electrochemical performances of these samples were investigated by CV and GCD measurements. The results indicate that at 1A/g, their specific capacitances are 912, 980, 1464, 1072, 1130, 1108, 1006 and 866 F/g, respectively, among which honeycomb-like structure has the best performance. The best sample also shows excellent charge–discharge performance, that is, it still retains more than 88% of the initial capacity after 2000 cycles. Furthermore, the formation mechanism of the pores in the honeycomb structure was studied in detail. Therefore, a special experiment was designed to reveal the cause of the pore formation. This study is of great significance for the design of transition metal compounds with excellent electrochemical properties.
[en] Porous materials with various pore sizes in the range of micropore (< 2 nm), mesopore (2-50 nm), and macropore (> 50 nm) are attractive due to their many emerging applications such as catalysts, separation systems, and low dielectric constant materials. The discovery of new M41S mesoporous silica families with pore sizes larger than 2 nm in diameter in 1992 extended the applications into much wider pore ranges, bringing in a new prosperous era in porous material research. The synthesis of these silica materials has been mainly accomplished through a self-assembly between surfactant molecules and inorganic species under various pH conditions. Recently, core-shell nanoparticles with a silica core and mesoporous shell under basic conditions were synthesized using the silica nanoparticles as a core, and a silica precursor (TEOS) and cationic surfactant (CTABr) as a material for the formation of the mesoporous shell. The resultant materials were very monodispersive in size and showed a narrow pore size distribution in the range of ca 2-3 nm in diameter, depending on the alkyl-chain length of the surfactants used. In this work, the mesoporous shell coated-fumed silicas (denoted as MS M-5s) were synthesized by using fumed silica instead of the silica nanoparticle as a core based on previous reports. Also, the structural properties of the MS M-5s such as the specific surface area and pore volume were easily controlled by varying the amount of the silica precursor and surfactant. The resultant materials exhibited a BET surface area of ca 279-446 m2/g and total pore volume of ca 0.64-0.74 cm3/g and showed a narrow pore size distribution (PSD) due to the removal of the organic surfactant molecules
[en] Porous coordination polymers (PCPs), which are microporous materials, have been given much attention from both scientific and commercial aspects regarding their application to gas storage, gas separation and catalytic reaction because of the regularity of their pore shape and pore size, accompanied with the functionality. Moreover, in recent years, flexible PCPs, which are structurally transformable depending upon external stimuli, have been attractive because they provide unique properties, dissimilar to those of zeolites. In this review, the chemistry and application of flexible crystalline PCPs are summarized and discussed. (topical review)