Retardation Of Diffusion Research Articles

Dynamics of water in binary and ternary solutions of DNA and porphyrins

The dynamics of heavy water (at 20°C) in solutions with polyanionic DNA chains and ternary systems containing DNA and negatively charged tetraphenylporphyrins has been investigated using neutron resonance spin echo in the time range t = 1−1000 ps. The diffusion dynamics has been observed in the momentum transfer range q = 1.3−1.8 A−1, and the relaxation rates in single-component, binary, and ternary systems are close to each other. Apart from the relaxation, the vibrational mode in the solutions has been revealed at the momentum transfer q = 1.9 A−1. The introduction of porphyrins into the solution (one molecule per ten DNA base pairs) has resulted in a retardation of diffusion and a considerable increase (by 5–10%) in the frequency of translational vibrations of water molecules due to the interaction with porphyrin molecules.

Diffusion of Ti, V and Nb in Ni<sub>3</sub>Al at Elevated Temperatures

Interdiffusion coefficients of Al replacing elements in Ni-Al-X (X=Ti, V and Nb) were estimated by a series of experiments using diffusion couples of Al rich pseudo-binary systems at three different temperatures of 1423, 1473 and 1523K. In order to obtain interdiffusion coefficients of the pseudo-binary systems, the experimental data was analyzed by the Sauer and Freise method, and also impurity diffusion coefficients of Ti, V and Nb in Ni3Al were estimated by applying the Darken-Manning equation. The magnitude of interdiffusion coefficient decreased in order of V, Ti and Nb at all three temperatures. Impurity diffusion coefficients were described by the expressions: , , . The activation enthalpies obtained from the experimental data confirmed the retardation of Ti, V and Nb diffusion in Ni3Al by the anti-site diffusion mechanism. These results are consistent with our previous work on diffusion of Re and Ru in Ni3Al .

Impact of oxygen on the diffusion of silicon in germanium: density functional theory calculations

In the present study, density functional theory calculations have been used to predict the binding energies of clusters formed between lattice vacancies, silicon and oxygen atoms (SixOyVz) and the energy barriers associated with the migration of silicon in germanium in the presence of oxygen. It is predicted that SixOyVz clusters are stable. The results are discussed in view of recent experimental studies (Silvestri et al Semicond. Sci. Technol. 21, 758 (2006)), which suggest that the association of oxygen with silicon and vacancies leads to a retardation of silicon diffusion in germanium.

Improvement in Thermal Stability of Nickel Silicides Using NiNx Films

A nickel nitride film is proposed as a Ni source for silicidation to improve the thermal stability of a nickel silicide (NiSi) layer. The stability of the film was investigated for temperatures above . The nitrogen content in the film could be controlled by varying the flow ratio during deposition. When the film was annealed, the formation temperature of the NiSi layer was higher than that of layers formed from the pure Ni film due to the retardation of Ni diffusion into the Si substrate by an amorphous Si–N layer at the nickel nitride/Si interface. After an additional annealing above , the sheet resistances of the NiSi layers formed from the film remained low, while the of those formed from the pure Ni film increased sharply. Apparently, the suppression of the agglomeration of the NiSi layer by the utilization of the film can improve its thermal stability.

In vitro studies on the hypoglycemic potential of Ficus racemosa stem bark

Medicinal plants have been reported to play an important role in modulating glycemic responses and have preventive and therapeutic implications. Several mechanisms have been proposed for the antidiabetic effect of medicinal plants such as inhibition of carbohydrate-metabolizing enzymes, manipulation of glucose transporters, beta-cell regeneration and enhancing insulin-releasing activity. The present investigation evaluated the possible mechanism of action through which Ficus racemosa stem bark (Moraceae) exerts its hypoglycemic effect using suitable in vitro techniques. Ficus racemosa bark (FRB) exhibited significantly higher (P < or = 0.01) glucose-binding capacity than wheat bran (WB) and acarbose (ACB) consequently showed significantly higher (P < or = 0.01) retardation of glucose diffusion compared to WB and ACB. In case of amylolysis kinetics the liberation of glucose was greatly inhibited by FRB, as reflected by a significantly lower (P < or = 0.01) glucose diffusion rate in the system containing FRB compared to the control and acarbose. Furthermore, FRB significantly increased (P < or = 0.01) the rate of glucose transport across the yeast cell membrane and also in isolated rat hemi-diaphragm. The findings indicate F. racemosa bark to possess strong hypoglycemic effect and hence can be utilized as an adjunct in the management of diabetes mellitus.

Moisture Effects on the 1/F Noise Of Mos Devices

We have exposed MOS gate and field oxide transistors to moisture treatments with all pins grounded for up to three weeks. Irradiated field oxide structures showed a significant decrease in low frequency noise with moisture treatment, due to the passivation of Si dangling bonds at or near the Si/SiO2 interface. With moisture exposure, pMOS gate oxide transistors showed significant increases in pre-irradiation 1/f noise and post-irradiation oxide- and interface-trap charge densities. The 1/f noise of nMOS gate oxide transistors shows much less sensitivity to moisture exposure than pMOS transistors, before and after irradiation. We attribute these differences in sensitivities to moisture treatment to the enhancement of water diffusion in SiO2 by B atoms in the oxides that overlie the source/drain junctions of the pMOS transistors, in contrast to the retardation of moisture diffusion by P atoms in the corresponding regions of the nMOS devices.

Impact of Carbon on the Diffusion of Donor Atoms in Germanium

We report experiments on the diffusion of n-type dopants in isotopically controlled Ge multilayer structures doped with carbon. The diffusion profiles reveal a strong aggregation of the dopants within the carbon-doped layers and a retarded penetration depth compared to dopant diffusion in high purity natural Ge. Dopant aggregation and diffusion retardation is strongest for Sb and similar for P and As. Successful modeling of the simultaneous self- and dopant diffusion is performed on the basis of the vacancy mechanism and additional reactions that take into account the formation of carbon-vacancy-dopant and dopant-vacancy complexes. The stability of these complexes is confirmed by density functional theory calculations. The overall consistency between experimental and theoretical results supports the stabilization of donor-vacancy complexes in Ge by the presence of carbon and the dopant deactivation via the formation of dopant-vacancy complexes. These results help to develop concepts to suppress the enhanced diffusion of n-type dopants and the donor deactivation in Ge. Both issues hamper the formation of ultra shallow donor profiles with high active dopant concentrations that are required for the fabrication of Ge-based n-type metal oxide semiconductor field effect transistors.

Interpretation of the enhancement of field‐scale effective matrix diffusion coefficient in a single fracture using a semi‐analytical power series solution

AbstractA power series solution for convergent radial transport in a single fracture (PCRTSF) is developed. Transport processes considered in PCRTSF include advection and hydrodynamic dispersion in the fracture, molecular diffusion in the matrix, diffusive mass exchange across the fracture‐matrix interface, and mixing effects in the injection and the extraction boreholes. An analytical solution in terms of a power series in Laplace domain is developed first, which is then numerically inverted by de‐Hoog et al.'s algorithm. Four dimensionless parameters determine the behaviour of a breakthrough curve (BTC) calculated by PCRTSF, which are, in the order of decreasing sensitivity, the matrix diffusion factor, two mixing factors, and the Peclet number. The first parameter is lumped from matrix porosity, effective matrix diffusion coefficient, fracture aperture, and retardation factors. Its value increases as the matrix diffusion effect becomes significant. A non‐zero matrix diffusion factor results in a − 3/2 slope of the tail of a log–log BTC, a common property for tracer diffusion into an infinite matrix. Both mixing factors have equal effects on BTC characteristics. However, the Peclet number has virtually no effect on BTC tail. PCRTSF is applied to re‐analyse two published test results that were obtained from convergent radial tracer tests in a discrete, horizontal fracture in Silurian dolomite. PCRTSF is able to fit the field BTCs better than the original channel model does if a large matrix diffusion coefficient is used. Noticeably, the ratio of field‐scale to lab‐scale matrix diffusion coefficients can be as large as 378. This enhancement of the field‐scale matrix diffusion coefficient may be ascribed to the presence of a degraded zone at the fracture‐matrix interface because of karstic effects, or to flow channeling as a result of aperture heterogeneity. Copyright © 2009 John Wiley &amp; Sons, Ltd.

高レベル放射性廃棄物地層処分における緩衝材の核種移行抑制機能

Among the properties for controlling radionuclide migration of bentonite, used as a buffer material composing engineered barriers for the geological disposal of high-level radioactive waste, studies on the water penetration, swelling, chemical buffering and nuclide migration retardation properties were reviewed. For water penetration properties, the effects of bentonite dry density, silica sand mixture, temperature and salinity are approximately clear, and a model, applicable for various dry densities, silica sand contents and montmorillonite contents also has been developed. For swelling properties, the effects of bentonite dry density, silica sand mixture, salinity, interlayer cation, montmorillonite content and saturation degree are approximately clear, and a thermodynamic model, applicable for various dry densities, silica sand contents, salinities and montmorillonite contents has been developed. For chemical buffering properties, although data acquisition by a batch method and studies to directly measure pH and chemical component of the porewater of compacted bentonite have been conducted, data acquisition in compacted system and geochemical analysis have just started. Finding accumulation and data acquisition for various conditions such as high pH and saline groundwater are still needed. For nuclide migration retardation properties, the effects of bentonite dry density, salinity, silica sand mixture, montmorillonite content, particle size, interlayer cation, the charge of diffusion species and temperature on diffusion have been comprehensively studied. Data on the effect of interlayer cation on diffusion coefficient and activation energy and data on diffusion coefficient and activation energy for effective diffusion coefficient are however still insufficient. Inconsistency between batch sorption and retardation in diffusion should be additionally considered together with data setting method for safety assessment analysis.After the year 2000, studies for saline groundwater conditions have been powerfully conducted, and it is understood that saline groundwater conditions affect all properties described above. Continuing these studies, studies on the long-term behaviour considered the effect of alteration are necessary.

Interaction of Lipopolysaccharide and Phospholipid in Mixed Membranes: Solid-State 31P-NMR Spectroscopic and Microscopic Investigations

Lipopolysaccharide (LPS), which constitutes the outermost layer of Gram-negative bacterial cells as a typical component essential for their life, induces the first line defense system of innate immunity of higher animals. To understand the basic mode of interaction between bacterial LPS and phospholipid cell membranes, distribution patterns were studied by various physical methods of deep rough mutant LPS (ReLPS) of Escherichia coli incorporated in phospholipid bilayers as simple models of cell membranes. Solid-state 31P-NMR spectroscopic analysis suggested that a substantial part of ReLPS is incorporated into 1,2-dimyristoyl- sn-glycero-3-phosphocholine lipid bilayers when multilamellar vesicles were prepared from mixtures of these. In egg L- α-phosphatidylcholine (egg-PC)-rich membranes, ReLPS undergoes micellization. In phosphatidylethanolamine-rich membranes, however, micellization was not observed. We studied by microscopic techniques the location of ReLPS in membranes of ReLPS/egg-PC (1:10 M/M) and ReLPS/egg-PC/1-palmitoyl-2-oleoyl- sn-glycero-3-phosphoglycerol (POPG) (1:9:1 M/M/M). The influence of ReLPS on the physicochemical properties of the membranes was studied as well. Microscopic images of both giant unilamellar vesicles and supported planar lipid bilayers showed that LPS was uniformly incorporated in the egg-PC lipid bilayers. In the egg-PC/POPG (9:1 M/M) lipid bilayers, however, ReLPS is only partially incorporated and becomes a part of the membrane in a form of aggregates (or as mixed aggregates with the lipids) on the bilayer surface. The lipid lateral diffusion coefficient measurements at various molar ratios of ReLPS/egg-PC/POPG indicated that the incorporated ReLPS reduces the diffusion coefficients of the phospholipids in the membrane. The retardation of diffusion became more significant with increasing POPG concentrations in the membrane at high ReLPS/phospholipid ratios. This work demonstrated that the phospholipid composition has critical influence on the distribution of added ReLPS in the respective lipid membranes and also on the morphology and physicochemical property of the resulting membranes. A putative major factor causing these phenomena is reasoned to be the miscibility between ReLPS and individual phospholipid compositions.

Diffusion and defect reactions between donors, C, and vacancies in Ge. I. Experimental results

The diffusion of self-atoms and $n$-type dopants such as phosphorus, arsenic, and antimony in germanium was studied by means of isotopically controlled multilayer structures doped with carbon. The diffusion profiles reveal an aggregation of the dopants within the carbon-doped layers and a retarded penetration depth compared to dopant diffusion in high-purity natural Ge. Dopant aggregation and diffusion retardation are strongest for Sb and similar for P and As. In addition, the shape of the dopant profiles changes for dopant concentrations in the range of ${10}^{20}\text{ }{\text{cm}}^{\ensuremath{-}3}$ mainly due to the formation of dopant-vacancy complexes, which is more significant at high concentrations. Accurate modeling of the simultaneous self-diffusion and dopant diffusion is achieved on the basis of the vacancy mechanism and additional reactions that take into account the formation of neutral carbon-vacancy-dopant and neutral dopant-vacancy complexes. The stability of these complexes is compared to theoretical calculations published recently and to additional calculations presented in Part II. The overall consistency between the experimental and theoretical results supports the stabilization of donor-vacancy complexes in Ge by the presence of carbon and the dopant deactivation via the formation of dopant-vacancy and carbon-vacancy-dopant complexes.

Protein-Protein Interaction on Lysozyme Crystallization Revealed by Rotational Diffusion Analysis

Intermolecular interactions between protein molecules diffusing in various environments underlie many biological processes as well as control protein crystallization, which is a crucial step in x-ray protein structure determinations. Protein interactions were investigated through protein rotational diffusion analysis. First, it was confirmed that tetragonal lysozyme crystals containing fluorescein-tagged lysozyme were successfully formed with the same morphology as that of native protein. Using this nondisruptive fluorescent tracer system, we characterized the effects of sodium chloride and ammonium sulfate concentrations on lysozyme-lysozyme interactions by steady-state and time-resolved fluorescence anisotropy measurements and the introduction of a novel interaction parameter, k rot. The results suggested that the specific attractive interaction, which was reflected in the retardation of the protein rotational diffusion, was induced depending on the salt type and its concentration. The change in the attractive interactions also correlated with the crystallization/precipitation behavior of lysozyme. Moreover, we discuss the validity of our rotational diffusion analysis through comparison with the osmotic second virial coefficient, B 22, previously reported for lysozyme and those estimated from k rot.

Metal Transport Parameters of a Gneiss Saprolitic Silty Soil for Liner Design

Diffusion coefficients and retardation factors of two metal cations ( Cd2+ and Pb2+ ) were measured for a compacted Brazilian saprolitic soil derived from gneiss, aiming to assess its geoenvironmental performance as a liner for waste disposal sites. This soil occurs extensively all over the country in very thick layers, but has not been used in liners because of its hydraulic conductivity, higher than 10−9 m∕s when compacted at optimum water content of standard Proctor energy, but which can be reduced by means of appropriate compaction techniques or additives. Batch, column, and diffusion tests were carried out with monospecies synthetic solutions at pH 1, 3, and 5.5. Measured diffusion coefficients varied between 0.5 and 4× 10−10 m2 ∕s . Retardation factors show that cadmium, a very mobile cation, is not adsorbed at pH 1 but is significantly retained at pH 3 and pH 5.5, whereas lead is retained at all tested pH values though slightly at pH 1. Estimated retardation factors from batch tests were 1.3–2.3 ti...

On the origin of nitrogen-induced retardation of boron diffusion in amorphous silica

The effect of N incorporation on B diffusion in amorphous SiO2 is presented based on spin-polarized density functional theory calculations. Our results show that N incorporation leads to the decrease of O vacancy concentration, which is largely responsible for the retarded B diffusion by reducing diffusion mediators such as E′ and S centers. We also determine the ground state structure of the BN complex, along with possible formation routes. The direct BN bonding interaction appears to only slightly increase the activation energy of B diffusion.

Methylation pattern analysis using high‐throughput microarray of solid‐phase hyperbranched rolling circle amplification products

Monitoring the methylation pattern of a single tumor cell might be important in understanding the mechanism of tumor initiation and progression. In this study, we developed a method based on molecular cloning microarray strategy for analyzing methylation patterns of a single DNA fragment from a group of tumor cells. In the method, a microarray of single monoclones of bisulfate-treated PCR products was fabricated by two-primer hyperbranched rolling circle amplification (HRCA) in polyacrylamide gel, in which a library of the bisulfate-treated PCR products with different methylated status from tumor cells were ligated to circle molecules to form HRCA templates, and one of the HRCA primers was modified with acrylamide on its 5'-end. Due to the diffusion retardation of HRCA products in a polyacrylamide matrix, the HRCA products are localized near their respective templates, and formed to a microarray of monoclones. After the nonimmobilized strands were removed, three pairs of probes were used to detect different CpG sites of each clone simultaneously by hybridization. We successfully analyzed the methylation patterns of P16 gene for three cases of stomach tumor tissues. This method could provide a significant tool in detecting the distribution of cells with different methylation patterns in one tumor tissue.

Role of the ammonium group in the diffusion of quaternary ammonium compounds in Streptococcus mutans biofilms

Cetylpyridinium chloride (CPC), a quaternary ammonium compound, was shown to interact irreversibly with Streptococcus mutans biofilms, leading to a slow diffusion compared with poly(ethylene glycol) (PEG) molecules of similar size. The objective of this work is to determine if the retardation of CPC diffusion and its strong binding to biofilms is caused by interactions between the ammonium group of CPC and the exopolysaccharide (EPS) matrix. First, we characterized the diffusion of two analogues of CPC in S. mutans biofilms: dodecylpyridinium chloride (DPC), carrying a shorter alkyl chain than CPC, and tetramethylene bispyridinium chloride (TMBPC), a compound carrying two positively charged ammonium groups. Second, we cultured biofilms with different densities of EPS and examined the impact of this density on the transport properties of CPC. The diffusion of these compounds was probed using infrared spectroscopy with attenuated total reflectance sampling. The diffusion of CPC, DPC and TMBPC in S. mutans biofilm is slower than that of PEG10k. In addition, TMBPC and DPC, as PEG10k, could be readily washed out from the biofilms while CPC association was practically irreversible. The penetration of CPC through the EPS matrix was found to be not significantly affected by the increased EPS density, whereas the penetration of PEG with a molar mass of 10k was considerably reduced. These results suggest that the interactions between the quaternary ammonium groups and the EPS matrices are not the prime contribution of the strong CPC binding, and the alkyl chain length plays a role in this association, likely through hydrophobic interactions.

Sorption and diffusion of HTO and cesium in crushed granite compacted to different lengths

In this study, batch and through-diffusion experiments have been performed in order to determine the distribution coefficients (Kd), apparent diffusion coefficients (Da) and retardation factor (Rf), respectively. Both apparent and effective diffusion coefficient (Da and De) of Cs were obtained by accumulative concentration method developed by Crank (1975). In addition, a non-reactive radionuclide, HTO, was initially conducted in through-diffusion experiment for assessing the ability of radionuclide retardation. The distribution coefficients (Kd) obtained by batch tests in 14 days under aerobic and anaerobic systems were 2.06 and 3.52 ml/g. Moreover, it is found in through-diffusion test that Rf = 4.12 and 4.40 and Kd = 0.97 and 1.06 of Cs did not have an obvious discrepancy in a length/diameter/ (L/D) ratio of 0.44 and 1.78. However, Rf and Kd revealed a larger difference in an L/D ratio closing to 1 due to the geometric change of one-dimension diffusive hypothesis. Therefore, it demonstrates that Rf and Kd obtained by through-diffusion experiments only could be achieved at a lower or larger L/D ratio and would be reliable for long-term performance assessment.

Enamel diffusion modulated by Er:YAG laser: (Part 2). Organic matrix

Organic matrix (OM) has been hypothesized as a key player in the laser-induced retardation of enamel diffusion (LRED). Therefore, this study was aimed to quantify the contribution of OM in LRED. Four groups of enamel sections (n=10) were assigned to 'normal', 'laser treated', 'OM extracted' and 'laser+OM extraction' groups for measurement of diffusion coefficient (DC) using fluorescence recovery after photobleaching (FRAP) and fluorophores transport study (FTS). Er:YAG laser treatment and OM extraction were performed on respective groups. Sections were characterized with stereomicroscopy and polarized light microscopy. Treatment effects were statistically assessed with a factorial ANOVA. DC measured by FRAP and FTS coupled with confocal microscopy revealed the significant effect of OM (p=0.001) and laser treatment (p<0.01). After OM extraction, the laser effect on diffusion decreased about 34-75%, confirming the significant role of OM in LRED. Both FRAP and FTS may be promising tools to quantify enamel DC.

Characterisation of Fiber Obtained from Pumpkin (cucumis moschata duch.) Mesocarp Through Enzymatic Treatment

Cell wall-enriched pumpkin ( Cucumis moschata Duch.) powder was submitted to enzymatic hydrolysis by cellulase or hemicellulase in order to evaluate the performance of these cell wall-degrading enzymes on that substrate. Different enzyme-substrate ratios were evaluated and the effect exerted by the buffer on cell wall polysaccharides. Cellulase produced the release of pectin macromolecules which include homogalacturonans side chains, the rhamnogalacturonan I core and rhamnogalacturonan II, in conjunction with xylogalacturonans. The content of galacturonic acid in product obtained ranged from 545 to 781 g/kg of fiber. Hemicellulases produced intense pectin hydrolysis leading to fiber-fractions with galacturonic acid contents ranging from 390 to 444 g/kg of fiber and enriched in glucose polymers as the enzyme proportion increased. Few rhamnogalacturonan-I was present.The acidic citrate buffer (pH 5.2) used for allowing enzyme activity could per se remove noncovalent cross-links like ionic bonds. As a consequence, pectin-in-extensin entanglements, pectins joined by Ca2+-bridges through the homogalacturonan side chains, and some pectins that are originally soluble in cold water due to little or no binding to the cell wall, could be removed by this citrate buffer. Enzymatic hydrolysis as well as buffer extraction produced fiber-products with an important thickening effect of aqueous systems. This effect was smaller as the ratio enzyme-substrate was increased and, in general, the fiber fractions isolated produced an in vitro glucose diffusion retardation.

Role of segregating impurities in grain-boundary diffusion

The impact of segregating impurities on grain-boundary diffusion is investigated using a kinetic Monte Carlo simulation of boundary transport on a lattice that is appropriate for both slab and pipe geometries. More specifically, the grain-boundary diffusivity is determined as a function of impurity concentration using an analog of the experimental sectioning method. The retardation of diffusion that results from segregation is interpreted in terms of site-blocking models that reflect the local free volume available to a diffusing tracer. Finally, the results of this investigation are interpreted in the context of experimental determinations of grain-boundary diffusivity in doped ceramic oxides.