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Slow Diffusion (slow + diffusion)
Selected AbstractsNitrate-Selective Solid Contact Electrodes with Poly(3-octylthiophene) and Poly(aniline) as Ion-to-Electron Transducers Buffered with Electron-Ion-Exchanging ResinELECTROANALYSIS, Issue 13-14 2006Galina Abstract The study of nitrate selective solid contact electrodes containing poly(3-octyl)thiophene and poly(aniline) demonstrated the advantage of buffering the transducing layer with electron-ion-exchanging resin. The buffering, in particular in the case of poly(aniline) doped with nitrate anions ensured significant improvement of the long-term stability and piece-to-piece reproducibility of the electrode potentials. It is shown that the redox species causes potential drift after a long time delay, probably because of slow diffusion in the membrane bulk. [source] Carrier-Mediated Transport of Toxic Heavy Metal Ions in Bulk Liquid MembranesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2004Lucia Brinchi Abstract Transport through a dichloromethane liquid membrane has been studied to investigate the ability of 1,1,7,7-tetraethyl-4-tetradecyldiethylenetriamine (TE14DT), previously tested for the transport of copper, to act as a carrier for toxic heavy metal ions such as Cd2+, Pb2+ and Hg2+. The carrier displayed a remarkable capability to extract all the metal ions from the source to the organic phases but only cadmium was efficiently transported across the membrane. The experimental conditions optimised for the transport of copper are inadequate for lead and mercury. In fact, the inefficacy of their transport could be due, as regards lead, to the slow diffusion of the complex through the membrane, while mercury remained in the organic phase because of the high stability of the mercury-carrier complex. Selectivity tests using binary mixtures of the metal ions showed TE14DT's capability to transport copper or cadmium also in the presence of lead in the source phase. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Role of the plasma membrane leaflets in drug uptake and multidrug resistanceFEBS JOURNAL, Issue 5 2010Hagar Katzir The present study aimed to investigate the role played by the leaflets of the plasma membrane in the uptake of drugs into cells and in their extrusion by P-glycoprotein and multidrug resistance-associated protein 1. Drug accumulation was monitored by fluorescence resonance energy transfer from trimethylammonium-diphenyl-hexatriene (TMA-DPH) located at the outer leaflet to a rhodamine analog. Uptake of dye into cells whose mitochondria had been inactivated was displayed as two phases of TMA-DPH fluorescence quenching. The initial phase comprised a rapid drop in fluorescence that was neither affected by cooling the cells on ice, nor by activity of mitochondria or ABC transporters. This phase reflects the association of dye with the outer leaflet of the plasma membrane. The subsequent phase of TMA-DPH fluorescence quenching occurred in drug-sensitive cell lines with a half-life in the range 20,40 s. The second phase of fluorescence quenching was abolished by incubation of the cells on ice and was transiently inhibited in cells with active mitochondria. Thus, the second phase of fluorescence quenching reflects the accumulation of dye in the cytoplasmic leaflet of the plasma membrane, presumably as a result of flip-flop of dye across the plasma membrane and slow diffusion from the inner leaflet into the cells. Whereas activity of P-glycoprotein prevented the second phase of fluorescence quenching, the activity of multidrug resistance-associated protein 1 had no effect on this phase. Thus, P-glycoprotein appears to pump rhodamines from the cytoplasmic leaflet either to the outer leaflet or to the outer medium. [source] Oscillatory zoning in garnet from the Willsboro Wollastonite Skarn, Adirondack Mts, New York: a record of shallow hydrothermal processes preserved in a granulite facies terraneJOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2003C. C. Clechenko Abstract Oscillatory zoning in low ,18O skarn garnet from the Willsboro wollastonite deposit, NE Adirondack Mts, NY, USA, preserves a record of the temporal evolution of mixing hydrothermal fluids from different sources. Garnet with oscillatory zoning are large (1,3 cm diameter) euhedral crystals that grew in formerly fluid filled cavities. They contain millimetre-scale oscillatory zoning of varying grossular,andradite composition (XAdr = 0.13,0.36). The ,18O values of the garnet zones vary from 0.80 to 6.26, VSMOW and correlate with XAdr. The shape, pattern and number of garnet zones varies from crystal to crystal, as does the magnitude of the correlated chemistry changes, suggesting fluid system variability, temporal and/or spatial, over the time of garnet growth. The zones of correlated Fe content and ,18O indicate that a high Fe3+/Al, high ,18O fluid mixed with a lower Fe3+/Al and ,18O fluid. The high ,18O, Fe enriched fluids were likely magmatic fluids expelled from crystallizing anorthosite. The low ,18O fluids were meteoric in origin. These are the first skarn garnet with oscillatory zoning reported from granulite facies rocks. Geochronologic, stable isotope, petrologic and field evidence indicates that the Adirondacks are a polymetamorphic terrane, where localized contact metamorphism around shallowly intruded anorthosite was followed by a regional granulite facies overprint. The growth of these garnet in equilibrium with meteoric and magmatic fluids indicates an origin in the shallow contact aureole of the anorthosite prior to regional metamorphism. The zoning was preserved due to the slow diffusion of oxygen and cations in the large garnet and protection from deformation and recrystallization in zones of low strain in thick, rigid, garnetite layers. The garnet provide new information about the hydrothermal system adjacent to the shallowly intruded massif anorthosite that predates regional metamorphism in this geologically complex, polymetamorphic terrane. [source] Protective organic-inorganic hybrid coatings on mild steel derived from Ti(OC4H9)4 -modified precursorsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 9 2004V. Nguyen Abstract Titania-poly(methyl methacrylate-co-butyl methacrylate-co-methacrylic acid) hybrids prepared by a sol-gel method were deposited by dip coating on mild steel. Transparent and defect free coatings with titania content ranging between 0 and 12.7 wt.% have been prepared. Barrier properties and dry adherence have been tested by electrochemical impedance spectroscopy (EIS) and the vertical pull-off test, respectively. The pull-off test results suggest that the titanium alkoxide precursor must intercede on the substrate/coating interphase during film formation to create specific adhesive bondings with the substrate. In this paper, two capacitance models are used to estimate the water uptake, one based on a uniform and one on a heterogeneous distribution of sorbed water. Water uptake determined from these two models is compared to the gravimetry results. It is suggested that a reliable determination of the actual water uptake in coatings from capacitance measurements require an extensive experimental work. The variations in the state of sorbed water with the specimen type or immersion time, the leaching of organics during immersion or the slow diffusion of ions are fundamental factors that must be considered when comparing the water uptake determined from gravimetry and capacitance models. [source] A Thermoreversible Polymer Mediates Controlled Release of Glial Cell Line-Derived Neurotrophic Factor to Enhance Kidney RegenerationARTIFICIAL ORGANS, Issue 8 2010Yousof Gheisari Abstract Previously, we reported that human mesenchymal stem cells (hMSCs) that were cultivated in growing embryos differentiated in an appropriate developmental milieu, thereby facilitating the development of a functional renal unit. However, this approach required transfection with an adenovirus that expressed glial cell line-derived neurotrophic factor (GDNF) to enhance the development of hMSC-derived renal tissue, and safety issues restrict the clinical use of such viral vectors. To circumvent this problem, we tested an artificial polymer as a means to diffuse GDNF. This GDNF-polymer, which exists in liquid form at 4°C but becomes a hydrogel upon heating to 37°C, was used as a thermoreversible switch, allowing the injection of hMSCs at low viscosity using a mouth pipette, with subsequent slow diffusion of GDNF as it solidified. The polymer, which was dissolved in a solution of GDNF at 4°C and then maintained at 37°C, acted as a diffuser of GDNF for more than 48 h. LacZ -transfected hMSCs and the GDNF-polymer (at 4°C) were placed in the nephrogenic sites of growing rat embryos that were maintained at 37°C. Forty-eight hours later, the resultant kidney anlagen were dissected out and allowed to continue developing for 6 days in vitro. Whole-organ X-Gal staining and fluorescence activated cell sorter analysis showed that the number of hMSC-derived cells was significantly increased in developed anlagen that have been generated from hMSCs plus GDNF-polymer compared with those from hMSCs plus GDNF-containing medium and was comparable to those from adenovirus-transfected hMSCs. These findings suggest that the GDNF-polymer can be used as a diffuser of GDNF for kidney organogenesis. [source] Revisiting glutaraldehyde cross-linking: the case of the Arg,Lys intermolecular doubletACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2010Michèle Salem In addition to the common use of glutaraldehyde to nonspecifically cross-link protein crystals through lysine residues disposed on the surface of the protein, the use of gentle vapour diffusion of glutaraldehyde offers a convenient way to limit polymerization and to allow slow diffusion throughout the crystal. In the case of trimeric barnase crystals, a specific cross-link was observed between an lysine side chain and an arginine side chain that were spatially disposed at the ideal distance on the protein surface in the three monomers. Here, the direct observation of a specific Lys,Arg cross-link site is reported and a mechanism is proposed for the reaction. [source] Analysing the factors influencing clean technology adoption: a study of the Spanish pulp and paper industryBUSINESS STRATEGY AND THE ENVIRONMENT, Issue 1 2005Pablo del Río González Technological change has a relevant role to play in the transition towards a sustainable industry. However, slow diffusion of clean technologies can be observed in OECD countries. The analysis of the determinants and barriers to clean technology adoption should be a main goal of economists and social scientists. This paper shows that three sets of interrelated factors prevent but also stimulate the widespread adoption and diffusion of clean technology: these are factors external and internal to the firm, conditions of the potential adopters and characteristics of the environmental technology. These factors are included in the so-called ,triangular model', which is further applied to the analysis of clean technology adoption in the pulp and paper industry in Spain. The empirical study shows that clean technology adoption decisions are the result of an interaction between these factors, often involving contradictory signals for the potential adopter. The paper closes with some public policy recommendations for the effective and efficient promotion of clean technology diffusion. Copyright © 2005 John Wiley & Sons, Ltd and ERP Environment. [source] Multiscale homogenization with bounded ratios and anomalous slow diffusionCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 1 2003Gérard Ben Arous We show that the effective diffusivity matrix D(Vn) for the heat operator ,t , (,/2 , ,Vn,) in a periodic potential Vn = ,Uk(x/Rk) obtained as a superposition of Hölder-continuous periodic potentials Uk (of period ,,d := ,d/,d, d , ,*, Uk(0) = 0) decays exponentially fast with the number of scales when the scale ratios Rk+1/Rk are bounded above and below. From this we deduce the anomalous slow behavior for a Brownian motion in a potential obtained as a superposition of an infinite number of scales, dyt = d,t , ,V,(yt)dt. © 2002 Wiley Periodicals, Inc. [source] | ||||||||||