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Transport Mechanisms (transport + mechanism)
Kinds of Transport Mechanisms Selected AbstractsTransport mechanism in the quantum well embedded with quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2009E. S. Kannan Abstract Electron transport in single and double quantum well system embedded with InAs quantum dots is investigated by carrying out magnetoresistance measurements at 1.2 K. At low carrier densities, the electrons are strongly localized due to disorder and undergo magnetic field induced insulator to quantum Hall liquid transitions characterized by temperature independent crossing points. At higher carrier densities no such magnetic field induced transition are observed. The potential induced by the electrons in the quantum dots were found to enhance the scattering between the edge states resulting in the substantial reduction of the width of the Hall plateau in the single quantum well system. In the double quantum well system, instead of plateaus abrupt increase in the Hall resistance is observed at integer filling factors. On sweeping the gate bias at fixed magnetic field, hysteresis effect was observed in the double quantum well system due to the charge trapping in the defect levels. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Transport mechanisms and performance simulation of a PEM fuel cellINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2008Geng-Po Ren Abstract A three-dimensional, gas,liquid two-phase flow and transport model has been developed and utilized to simulate the multi-dimensional, multi-phase flow and transport phenomena in both the anode and cathode sides in a proton exchange membrane (PEM) fuel cell and the cell performance with different influencing operational and geometric parameters. The simulations are presented with an emphasis on the physical insight and fundamental understanding afforded by the detailed distributions of velocity vector, oxygen concentration, water vapor concentration, liquid water concentration, water content in the PEM, net water flux per proton flux, local current density, and overpotential. Cell performances with different influencing factors are also presented and discussed. The comparison of the model prediction and experimental data shows a good agreement. Copyright © 2007 John Wiley & Sons, Ltd. [source] Vapor phase transport of unexploded ordnance compounds through soilsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2002Raghunathan Ravikrishna Abstract Unexploded ordnance(UXO) is a source of concern at several U.S. Department of Defense(DOD) sites. Localization of munitions and fate and transport of the explosive compounds from these munitions are a major issue of concern. A set of laboratory experiments were conducted in specially designed flux chambers to measure the evaporative flux of three explosive compounds (2,4-dinitrotoluene, 2,6-dinitrotoluene, and 1,3-dinitrobenzene) from three different soils. The effect of different soil moisture contents, the relative humidity of air contacting the soil surface, and soil temperature on the chemical fluxes were evaluated. A diffusion model was used to describe the chemical transport mechanism in the soil pore air. The soil-air partition constant was treated as a fit parameter in the model because of the uncertainty in the a priori estimation. The model predicts the qualitative trends of the experimental fluxes satisfactorily. Under extremely dry conditions, the flux decreased more rapidly than that predicted by the model. The fluxes from soils at 24°C were higher than those at 14°C, indicating a larger volatilization driving force at the higher temperature. [source] Li-Metal Symmetrical Cell Studies Using Ionic Organic Plastic Crystal Electrolyte,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Patrick C. Howlett A low current density preconditioning process, which produces an improved lithium transport mechanism is created by the action of charge flow through a plastic crystal electrolyte (figure). A reduction in cell polarisation at high applied current density is demonstrated which approaches the rates required for these electrolytes to be used in practical devices. [source] Advection of anchovy (Engraulis encrasicolus) larvae along the Catalan continental slope (NW Mediterranean)FISHERIES OCEANOGRAPHY, Issue 2 2007A. SABATÉS Abstract The Gulf of Lions is one of the main anchovy (Engraulis encrasicolus) spawning areas in the NW Mediterranean. During the spring, low-salinity surface water from the outflow of the Rhône is advected by the shelf-slope current along the continental slope off the Catalan coast. In June 2000, a Lagrangian experiment tracking these low-salinity surface waters was conducted to assess the importance of this transport mechanism for anchovy larvae and to determine the suitability of the tracked surface waters for survival of anchovy larvae. The experiment consisted of sampling the tracked water parcel for 10 days with three drifters launched at the core of the shelf-slope current where low-salinity surface waters were detected. The survey was completed by sampling the surrounding waters. Anchovy larvae from the spawning area in the Gulf of Lions were advected towards the south in the low-salinity waters. The size increase of anchovy larvae throughout the Lagrangian tracking closely followed the general growth rate calculated by otolith analysis (0.65 mm day,1). However, advection by the current was not the only mechanism of anchovy larval transport. A series of anticyclonic eddies, originated in the Gulf of Lions and advected southwards, seemed to play a complementary role in the transport of larvae from the spawning ground towards the nursery areas. These eddies not only contributed to larval transport but also prevented their dispersion. These transport and aggregation mechanisms may be important for anchovy populations along the Catalan coast and require further study. [source] Storage and mobility of black carbon in permafrost soils of the forest tundra ecotone in Northern SiberiaGLOBAL CHANGE BIOLOGY, Issue 6 2008GEORG GUGGENBERGER Abstract Boreal permafrost soils store large amounts of organic carbon (OC). Parts of this carbon (C) might be black carbon (BC) generated during vegetation fires. Rising temperature and permafrost degradation is expected to have different consequences for OC and BC, because BC is considered to be a refractory subfraction of soil organic matter. To get some insight into stocks, variability, and characteristics of BC in permafrost soils, we estimated the benzene polycarboxylic acid (BPCA) method-specific composition and storage of BC, i.e. BPCA-BC, in a 0.44 km2 -sized catchment at the forest tundra ecotone in northern Siberia. Furthermore, we assessed the BPCA-BC export with the stream draining the catchment. The catchment is composed of various landscape units with south-southwest (SSW) exposed mineral soils characterized by thick active layer or lacking permafrost, north-northeast (NNE) faced mineral soils with thin active layer, and permafrost-affected raised bogs in plateau positions showing in part thermokarst formation. There were indications of vegetation fires at all landscape units. BC was ubiquitous in the catchment soils and BPCA-BC amounted to 0.6,3.0% of OC. This corresponded to a BC storage of 22,3440 g m,2. The relative contribution of BPCA-BC to OC, as well as the absolute stocks of BPCA-BC were largest in the intact bogs with a shallow active layer followed by mineral soils of the NNE aspects. In both landscape units, a large proportion of BPCA-BC was stored within the permafrost. In contrast, mineral soils with thick active layer or lacking permafrost and organic soils subjected to thermokarst formation stored less BPCA-BC. Permafrost is, hence, not only a crucial factor in the storage of OC but also of BC. In the stream water BPCA-BC amounted on an average to 3.9% of OC, and a yearly export of 0.10 g BPCA-BC m,2 was calculated, most of it occurring during the period of snow melt with dominance of surface flow. This suggests that BC mobility in dissolved and colloidal phase is an important pathway of BC export from the catchment. Such a transport mechanism may explain the high BC concentrations found in sediments of the Arctic Ocean. [source] Detection of endogenous lithium in neuropsychiatric disorders,a model for biological transmutationHUMAN PSYCHOPHARMACOLOGY: CLINICAL AND EXPERIMENTAL, Issue 1 2002Ravi Kumar Kurup Abstract The human hypothalmus produces an endogenous membrane Na+ -K+ ATPase inhibitor, digoxin. A digoxin induced model of cellular/neuronal quantal state and perception has been described by the authors. Biological transmutation has been described in microbial systems in the quantal state. The study focuses on the plasma levels of digoxin, RBC membrane Na+ -K+ ATPase activity, plasma levels of magnesium and lithium in neuropsychiatric and systemic disorders. Inhibition of RBC membrane Na+ -K+ ATPase activity was observed in most cases along with an increase in the levels of serum digoxin and lithium and a decrease in the level of serum Mg++. The generation of endogenous lithium would obviously occur due to biological transmutation from magnesium. Digoxin and lithium together can produce added membrane Na+ -K+ ATPase inhibition. The role of membrane Na+ -K+ ATPase inhibition in the pathogenesis of neuropsychiatric and systemic disorders is discussed. The inhibition of membrane Na+ -K+ ATPase can contribute to an increase in intracellular calcium and a decrease in magnesium, which can result in a defective neurotransmitter transport mechanism, mitochondrial dysfunction and apoptosis, defective golgi body function and protein processing dysfunction, immune dysfunction and oncogenesis. Copyright © 2002 John Wiley & Sons, Ltd. [source] Uptake of Calcium by Mitochondria: Transport and Possible FunctionIUBMB LIFE, Issue 3-5 2001Thomas E. Gunter Abstract Vertebrate mitochondria contain a complex system for transport of Ca 2+ and related ions, consisting of two saturable modes of Ca 2+ influx and two separate, saturable mechanisms of Ca 2+ efflux. The characteristics of the mechanisms of Ca 2+ uptake, the uniporter and the RaM, are discussed here and suggestions are made about how the mechanisms may work together and separately to mediate the two physiological roles with which they are most commonly associated - control of the rate of cellular ATP production and induction of the permeability transition and apoptosis. It is argued that more subtlety of control of intramitochondrial free Ca 2+ concentration ([Ca 2+ ] m ) must be used by the uniporter and the RaM to fulfill their physiological roles than has been commonly recognized. This is because an increase in [Ca 2+ ] m is associated with both increased production of ATP which supports the continued life of the cell and with induction of the permeability transition and possibly apoptosis, which leads to cell death. The saturable mechanisms of mitochondrial Ca 2+ efflux and the Ca 2+ -induced mitochondrial permeability transition, which can transport Ca 2+ as well as other ions and molecules and is often considered as a Ca 2+ transport mechanism, are being reviewed separately. [source] Fat Migration in Chocolate: Diffusion or Capillary Flow in a Particulate Solid?,A Hypothesis PaperJOURNAL OF FOOD SCIENCE, Issue 7 2004J. M. Aguilera ABSTRACT: The exact mechanism of fat and oil migration in chocolate and chocolate coatings is still unknown. Nevertheless, the so-called "diffusion equation" derived from Fick's 2nd law has been extensively used to model the phenomenon, giving the impression that molecular diffusion is the single transport mechanism. We propose that chocolate may be microstructurally regarded as a particulate medium formed by an assembly of fat-coated particles (for example, cocoa solids, sugars crystals, and milk powder). Within this matrix the liquid fraction of cocoa fat (which increases with temperature) is likely to move under capillary forces through interparticle passages and connected pores. Based on available evidence (microstructure, kinetic data, temperature dependence of liquid fat fraction, and so on) we demonstrate that capillary forces may have an important role to play in bulk flow of liquid fat and oils. The Lucas-Washburn equation for capillary rise fits available data under most reported experimental conditions. Detailed microstructural analysis in actual products as well as data on key parameters (surface tension, contact angle, viscosity) is necessary to confirm this hypothesis. Bulk flow due to capillary effects, highly disregarded in structured foods, should be considered as a mass transfer mechanism in liquid-filled porous or particulate foods. [source] The position of an arginine residue influences substrate affinity and K+ coupling in the human glutamate transporter, EAAT1JOURNAL OF NEUROCHEMISTRY, Issue 2 2010Renae M. Ryan J. Neurochem. (2010) 114, 565,575. Abstract Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system and extracellular glutamate levels are controlled by a family of transporters known as excitatory amino acid transporters (EAATs). The EAATs transport glutamate and aspartate with similar micromolar affinities and this transport is coupled to the movement of Na+, K+, and H+. The crystal structure of a prokaryotic homologue of the EAATs, aspartate transporter from Pyrococcus horokoshii (GltPh), has yielded important insights into the architecture of this transporter family. GltPh is a Na+ -dependent transporter that has significantly higher affinity for aspartate over glutamate and is not coupled to H+ or K+. The highly conserved carboxy-terminal domains of the EAATs and GltPh contain the substrate and ion binding sites, however, there are a couple of striking differences in this region that we have investigated to better understand the transport mechanism. An arginine residue is in close proximity to the substrate binding site of both GltPh and the EAATs, but is located in transmembrane domain (TM) 8 in the EAATs and hairpin loop 1 (HP1) of GltPh. Here we report that the position of this arginine residue can explain some of the functional differences observed between the EAATs and GltPh. Moving the arginine residue from TM8 to HP1 in EAAT1 results in a transporter that has significantly increased affinity for both glutamate and aspartate and is K+ independent. Conversely, moving the arginine residue from HP1 to TM8 in GltPh results in a transporter that has reduced affinity for aspartate. [source] Species-specific interaction of HIV protease inhibitors with accumulation of cholyl-glycylamido-fluorescein (CGamF) in sandwich-cultured hepatocytesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2010Zhi-wei Ye Abstract Using sandwich-cultured hepatocytes from rat, dog, pig, and human, we investigated the species-specificity of interaction of HIV protease inhibitors (PI) with in vitro hepatic accumulation of the bile salt analogue cholyl-glycylamido-fluorescein (CGamF). Extracellular sodium depletion or coincubation with the OATP/Oatp inhibitors rifampicin and digoxin revealed that about 35% of active CGamF accumulation was mediated by Ntcp/NTCP in rat and human hepatocytes, while the contribution of this sodium-dependent transporter reached 50,60% in dog and pig hepatocytes. One or more sodium-independent transporters, likely belonging to the Oatp/OATP family, constitute a major transport mechanism for CGamF accumulation. Various HIV PI (0.5, 5, 25,µM) exhibited pronounced species differences in their interaction with active CGamF accumulation (1,µM), although some similarity was observed between the dog and human interaction profiles when HIV PI were tested at 0.5,µM. Atazanavir, indinavir, and darunavir were the most potent inhibitors of CGamF accumulation in human hepatocytes. Potent inhibition of CGamF accumulation by ritonavir in rat hepatocytes contrasted with a weak effect in human hepatocytes. Thorough characterization of in vitro disposition of probe substrates in preclinical species compared to human hepatocytes will ultimately support a better insight in species-specific mechanisms underlying drug interactions and drug-mediated toxicity. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 2886,2898, 2010 [source] Migration of mercury from dental amalgam through human teethJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2008Hugh H. Harris Exposure to mercury from dental amalgams, with possible negative health effects, has generally been considered to occur via either erosion or evaporation directly from the surface of fillings, followed by ingestion. The aim of this study was to determine the relative importance of the direct migration of mercury through the tooth as an alternative exposure pathway. X-ray fluorescence imaging has been used to determine quantitatively the spatial distribution of Hg, Ca, Zn and Cu in sections of human teeth that had been filled with amalgam for more than 20 years. X-ray absorption near-edge spectroscopy (XANES) was also employed to gain chemical information on the mercury present in the teeth. Hg (up to ,10,mg,g,1) and Zn (>100,mg,g,1) were detected in the teeth several millimetres from the location of the amalgams. At high resolution, Hg showed higher concentrations in dentinal tubules while Zn was generally evenly distributed. XANES showed that the chemical form of Hg that had migrated into the tooth had been altered from that present in the amalgam. The differing spatial distributions of Hg and Zn suggest distinct transport mechanisms for the two metals, presumably chemical for Zn and initially physical for Hg. Subsequent oxidation of Hg may lead to a loss of mobility or the development of a secondary transport mechanism. Most importantly the detection of Hg in areas of the tooth that once contained an active bloodstream and in calculus indicates that both exposure pathways should be considered as significant. [source] Solid-State Synthesis of Nanocrystalline BaTiO3: Reaction Kinetics and Powder PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2008Maria Teresa Buscaglia The formation of BaTiO3 nanoparticles by a solid-state reaction between nanocrystalline raw materials BaCO3 and TiO2 was studied as a function of temperature (400°,800°C), time (1,24 h), and titania particle size (15 and 30 nm). The reaction starts at 500°C and a high reaction rate is already observed at 600°C for the finest titania, with up to 90% conversion after 2 h. Two main reaction stages were observed at 600°,700°C. The first step is dominated by nucleation and growth of BaTiO3 at the TiO2,BaCO3 contact points and at the TiO2 surface. Surface diffusion of BaCO3 is, most likely, the prevailing mass transport mechanism responsible for the rapid formation of BaTiO3, even in the absence of a significant contribution from lattice diffusion. The second stage begins when the residual TiO2 cores are completely covered by the product phase. For longer times, the reaction can only proceed by the slower lattice diffusion, resulting in a strong decrease of the reaction rate. Single-phase BaTiO3 nanopowders with a specific surface area of 12,15 m2/g, an average particle size of 70,85 nm, a relative density of 96.5%,98.3%, and a tetragonality of 1.005 were obtained by calcination at 700°,800°C. Critical parameters in the preparation of ultrafine powders by solid-state reactions are the particle size of both raw materials, the absence of large hard agglomerates, and the homogeneity of the mixture. The use of fine raw materials and optimization of the reaction conditions make mechanical activation unnecessary. [source] The resonant structure of Jupiter's Trojan asteroids , I. Long-term stability and diffusionMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006P. Robutel ABSTRACT We study the global dynamics of the jovian Trojan asteroids by means of the frequency map analysis. We find and classify the main resonant structures that serve as skeleton of the phase space near the Lagrangian points. These resonances organize and control the long-term dynamics of the Trojans. Besides the secondary and secular resonances, that have already been found in other asteroid sets in mean motion resonance (e.g. main belt, Kuiper belt), we identify a new type of resonance that involves secular frequencies and the frequency of the great inequality, but not the libration frequency. Moreover, this new family of resonances plays an important role in the slow transport mechanism that drives Trojans from the inner stable region to eventual ejections. Finally, we relate this global view of the dynamics with the observed Trojans, identify the asteroids that are close to these resonances and study their long-term behaviour. [source] Intermolecular band dispersion in highly ordered monolayer and multilayer films of pentacene on Cu(110)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2008Hiroyuki Yamane Abstract We report the electronic structure and the charge transport mechanism of highly ordered films of pentacene on Cu(110) surface studied by angle-resolved ultraviolet photoemission spectroscopy using synchrotron radiation. For a flat-lying monolayer film, we observed the evidences of (i) formation of the interface states and (ii) two-dimensional intermolecular band dispersion of the resultant interface states, which may originate from the hybridization between the molecular orbi-tals and the wave function of the substrate. For an upright-standing multilayer film, we observed the two-dimensional intermolecular band dispersion, which originates from the intermolecular ,,, interaction. The observed effective masses of the hole for different azimuths demonstrate the presence of the anisotropy of the hole mobility in pentacene crystals also at higher temperatures. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electrical conductivity and optical properties of poly(3-thiophene boronic acid) organic semiconductorPOLYMER ENGINEERING & SCIENCE, Issue 4 2009Fahrettin Yakuphanoglu Electrical conductivity and optical properties of the poly(3-thiophene boronic acid) have been investigated. The room temperature electrical conductivity and activation energy of the poly(3-thiophene boronic acid) were 2.0 × 10,9 S/cm and 0.17 eV, respectively. In the semiconductor region of the polymer, the charge transport mechanism is taking place by the hopping process in the localized states. The direct optical band gap value of the poly(3-thiophene boronic acid) was found to be 1.92 eV via optical absorption method. The width of localized states for the polymer was determined to be 0.36 eV. The refractive index dispersion curve of the polymer obeys the single oscillator model. The refractive index dispersion parameter Eo/So for the poly(3-thiophene boronic acid) was determined to be 9.82 × 1012 eV m2. The optical dielectric constants of the polymer were determined. The real part of the dielectric constant of the polymer is higher than that of imaginary part of the dielectric constant. The imaginary part shows a peak corresponding to the absorption edge. It is evaluated that the electrical and optical results of the poly(3-thiophene boronic acid) indicate that it is an organic semiconductor with electrical and optical parameters. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Electromagnetic interference shielding by using conductive polypyrrole and metal compound coated on fabricsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 8 2002C. Y. Lee Abstract Electromagnetic interference (EMI) shielding materials of complex type of conductive polypyrrole (PPy) as an intrinsically conducting polymer and silver-palladium (AgPd) metal compound coated on woven or non-woven fabrics are synthesized. From dc conductivity and SEM photographs of PPy/fabric complexes, we discuss charge transport mechanism and the homogeneity of coating on the fabrics. The EMI shielding efficiency of PPy/fabric and AgPd/fabric complexes is in the range of 8,,,80 dB depending on the conductivity and the additional Ag vacuum evaporation. The highest EMI shielding efficiency of PPy/fabric complexes vacuum-evaporated by Ag is ,80 dB, indicating potential materials for military uses. We propose that PPy/fabrics are excellent RF and microwave absorber because of the relatively high absorbance and low reflectance of the materials. Copyright © 2002 John Wiley & Sons, Ltd. [source] Pilot-scale demonstration of in situ capping of PCB-containing sediments in the lower Grasse RiverREMEDIATION, Issue 1 2003James D. Quadrini A fish-consumption advisory is currently in effect in a seven-mile stretch of the Grasse River in Massena, New York, due to elevated levels of PCBs in fish tissue. One remedial approach that is being evaluated to reduce the PCB levels in fish from the river is in situ capping. An in-river pilot study was conducted in the summer of 2001 to assess the feasibility of capping PCB-containing sediments of the river. The study consisted of the construction of a subaqueous cap in a seven-acre portion of the river using various combinations of capping materials and placement techniques. Optimal results were achieved with a 1:1 sand/topsoil mix released from a clamshell bucket either just above or several feet below the water surface. A longer-term monitoring program of the capped area commenced in 2002. Results of this monitoring indicated: 1) the in-place cap has remained intact since installation; 2) no evidence of PCB migration into and through the cap; 3) groundwater advection through the cap is not an important PCB transport mechanism; and 4) macroinvertebrate colonization of the in-place cap is continuing. Additional follow-up monitoring in the spring of 2003 indicated that a significant portion of the cap and, in some cases, the underlying sediments had been disturbed in the period following the conclusion of the 2002 monitoring work. An analysis of river conditions in the spring of 2003 indicated that a significant ice jam had formed in the river directly over the capping pilot study area, and that the resulting increase in river velocities and turbulence in the area resulted in the movement of both cap materials and the underlying sediments. The pilot cap was not designed to address ice jam,related forces on the cap, as the occurrence of ice jams in this section of the river had not been known prior to the observations conducted in the spring of 2003. These findings will preclude implementation of the longer-term monitoring program that had been envisioned for the pilot study. The data collected immediately after cap construction in 2001 and through the first year of monitoring in 2002 serve as the basis for the conclusions presented in this article. It should be recognized that, based on the observation made in the spring of 2003, some of these conclusions are no longer valid for the pilot study area. The occurrence of ice jams in the lower Grasse River and their importance on sediments and PCBs within the system are currently under investigation. © 2003 Wiley Periodicals, Inc. [source] Nutritional, physiological, and histological responses in Atlantic salmon, Salmo salar L. fed diets with genetically modified maizeAQUACULTURE NUTRITION, Issue 3 2007G.-I. HEMRE Abstract The objective of this study was to evaluate whether standard fish meal diets prepared with increasing levels of genetically modified (GM; 150 and 300 g kg,1) maize (event MON810®) as a starch source, showed any nutritional or physiological adverse effects on Atlantic salmon, Salmo salar L. postsmolt. The diets with low or high inclusions of GM maize and its near-isogenic parental line (nongenetically modified; nGM maize), were balanced with Suprex maize (Reference) to obtain compositional equivalency of diet starch, sugars and all other nutrients. Total starch level in all diets was 160 g kg,1. After 82 days of feeding, fish growth was high in all groups, however fish fed the GM maize showed slight but significant lower feed intake, which was followed by slight but significant lower specific growth rate and final body weights, compared with fish fed nGM maize, none of the groups varied significantly from fish fed the Reference diet. There was no variation in feed conversion ratios (FCR), protein and lipid efficiency ratios (PER and LER), or protein- and lipid-productive values (PPV and LPV) in this study. No significant effect of maize type was detected on apparent digestibility coefficients (ADC) of dry matter, protein or lipid. Hematological analysis and plasma nutrients varied within normal ranges for Atlantic salmon in all diet groups, except for somewhat elevated aspartate aminotransferase (ASAT) values in all groups. Hepatosomatic index (HSI) with values ranging from 1.37 to 1.60, was significantly higher for the high GM maize group compared with the high nGM maize group but not when compared with the Reference diet group. Lowered spleen (SSI) and head-kidney somatic indices (H-KSI) were registered when fed GM compared with nGM maize, the Reference treatment was however, equal to both. Distal intestine somatic index (DISI) was significantly higher for GM maize-fed fish compared with nGM maize-fed fish, but not significantly different from the Reference diet group. Histological evaluation of the mid- and distal intestine, liver, spleen and head-kidney did not reveal any diet-related morphological changes. Maltase activities in the mid- and distal intestinal tissue homogenates were affected by diet, the fish fed high GM maize having higher activities compared with high nGM maize-fed fish. Leucine aminopeptidase (LAP) and alkaline phosphatase (AP) activities were not affected by diet. Sodium-dependent d -glucose uptake in brush border membrane vesicles (BBMV) isolated from pyloric caeca of fish fed high GM maize was significantly higher than that found in fish fed the analogous diet with high nGM maize. Based on the present findings, the conclusions made are: Atlantic salmon smolts fed GM maize (event MON810®), its near-isogenic parental line and suprex maize (Reference diet), all resulted in high growth rates, ADC and feed utilization. Health, when evaluated by means of mortality (low), normal ranges of blood and plasma parameters, except somewhat elevated ASAT values and minor variations in organ sizes, were considered good in all diet groups. The changes in the glucose transport mechanism and intestinal maltase enzyme activity in the gastrointestinal tract warrant further studies. [source] The problem of phase mixed shear Alfvén waves in the solar corona revisitedASTRONOMISCHE NACHRICHTEN, Issue 8 2008G. Mocanu Abstract The problem of phase mixing of shear Alfvén waves is revisited taking into account dissipative phenomena specific for the solar corona. In regions of space plasmas where the dynamics is controlled by the magnetic field, transport coefficients become anisotropic with transport mechanism having different behavior and magnitude depending on the orientation with respect to the ambient magnetic field. Taking into account realistic values for dissipative coefficients we obtain that the previous results derived in context of torsional Alfvén wave phase mixing are actually heavily underestimated so phase mixing cannot be used to explain the damping of torsional Alfvén waves and heating of open coronal structures. The presented results indicate that in order for phase mixing to still be a viable mechanism to explain heating or wave damping unrealistic assumptions have to be made. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Transport of Peptidomimetic Drugs by the Intestinal Di/tri-peptide Transporter, PepT1BASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 6 2002Birger Brodin The physiological function of the system is to transport small peptides resulting from digestion of dietary protein. Moreover, due to the broad substrate specificity of the system, it is also capable of transporting a number of orally administered peptidomimetic drugs. Absorbed peptides may be hydrolysed in the cells due to the high peptidase activity present in the cytosol. Peptidomimetic drugs may, if resistant to the cellular enzyme activity, pass the basolateral membrane via a basolateral peptide transport mechanism and enter the systemic circulation. As the number of new peptide and peptidomimetic drugs are rapidly increasing, the peptide transport system has gained increasing attention as a possible drug delivery system for small peptides and peptide-like compounds. In this paper we give an updated introduction to the transport system and discuss the substrate characteristics of the di/tri-peptide transporter system with special emphasis on chemically modified substrates and prodrugs. [source] Chloride ATPase pumps in nature: do they exist?BIOLOGICAL REVIEWS, Issue 2 2003GEORGE A. GERENCSER ABSTRACT Five widely documented mechanisms for chloride transport across biological membranes are known: anioncoupled antiport, Na+ and H+ -coupled symport, Cl, channels and an electrochemical coupling process. These transport processes for chloride are either secondarily active or are driven by the electrochemical gradient for chloride. Until recently, the evidence in favour of a primary active transport mechanism for chloride has been inconclusive despite numerous reports of cellular Cl, -stimulated ATPases coexisting, in the same tissue, with uphill ATP-dependent chloride transport. Cl, -stimulated ATPase activity is a ubiquitous property of practically all cells with the major location being of mitochondrial origin. It also appears that plasma membranes are sites of Cl, -stimulated ATPase pump activity. Recent studies of Cl, -stimulated ATPase activity and ATP-dependent chloride transport in the same plasma membrane system, including liposomes, strongly suggest a mediation by the ATPase in the net movement of chloride up its electrochemical gradient across the plasma membrane structure. Contemporary evidence points to the existence of Cl, -ATPase pumps; however, these primary active transporters exist as either P-, F- or V-type ATPase pumps depending upon the tissue under study. [source] Involvement of an influx transporter in the blood,brain barrier transport of naloxoneBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 4 2010Toyofumi Suzuki Abstract Naloxone, a potent and specific opioid antagonist, has been shown in previous studies to have an influx clearance across the rat blood,brain barrier (BBB) two times greater than the efflux clearance. The purpose of the present study was to characterize the influx transport of naloxone across the rat BBB using the brain uptake index (BUI) method. The initial uptake rate of [3H]naloxone exhibited saturability in a concentration-dependent manner (concentration range 0.5,µM to 15,mM) in the presence of unlabeled naloxone. These results indicate that both passive diffusion and a carrier-mediated transport mechanism are operating. The in vivo kinetic parameters were estimated as follows: the Michaelis constant, Kt, was 2.99±0.71,mM; the maximum uptake rate, Jmax, was 0.477±0.083,µmol/min/g brain; and the nonsaturable first-order rate constant, Kd, was 0.160±0.044,ml/min/g brain. The uptake of [3H]naloxone by the rat brain increased as the pH of the injected solution was increased from 5.5 to 8.5 and was strongly inhibited by cationic H1 -antagonists such as pyrilamine and diphenhydramine and cationic drugs such as lidocaine and propranolol. In contrast, the BBB transport of [3H]naloxone was not affected by any typical substrates for organic cation transport systems such as tetraethylammonium, ergothioneine or L -carnitine or substrates for organic anion transport systems such as p -aminohippuric acid, benzylpenicillin or pravastatin. The present results suggest that a pH-dependent and saturable influx transport system that is a selective transporter for cationic H1 -antagonists is involved in the BBB transport of naloxone in the rat. Copyright © 2010 John Wiley & Sons, Ltd. [source] Intracellular metabolite determination in the presence of extracellular abundance: Application to the penicillin biosynthesis pathway in Penicillium chrysogenum,BIOTECHNOLOGY & BIOENGINEERING, Issue 1 2010Rutger D. Douma Abstract Important steps in metabolic pathways are formed by the transport of substrates and products over the cell membrane. The study of in vivo transport kinetics requires accurate quantification of intra- and extracellular levels of the transported compounds. Especially in case of extracellular abundance, the proper determination of intracellular metabolite levels poses challenges. Efficient removal of extracellular substrates and products is therefore important not to overestimate the intracellular amounts. In this study we evaluated two different rapid sampling methods, one combined with cold filtration and the other with centrifugation, for their applicability to determine intracellular amounts of metabolites which are present in high concentrations in the extracellular medium. The filtration-based method combines fast sampling and immediate quenching of cellular metabolism in cold methanol, with rapid and effective removal of all compounds present outside the cells by means of direct filtration and subsequent filtration-based washing. In the centrifugation-based method, removal of the extracellular metabolites from the cells was achieved by means of multiple centrifugation and resuspension steps with the cold quenching solution. The cold filtration method was found to be highly superior to the centrifugation method to determine intracellular amounts of metabolites related to penicillin-G biosynthesis and allowed the quantification of compounds of which the extracellular amounts were 3,4 orders of magnitude higher than the intracellular amounts. Using this method for the first time allowed to measure the intracellular levels of the side chain precursor phenylacetic acid (PAA) and the product penicillin-G of the penicillin biosynthesis pathway, compounds of which the transport mechanism in Penicillium chrysogenum is still far from being sufficiently understood. Biotechnol. Bioeng. 2010;107: 105,115. © 2010 Wiley Periodicals, Inc. [source] Hydrogel-Perfluorocarbon Composite Scaffold Promotes Oxygen Transport to Immobilized CellsBIOTECHNOLOGY PROGRESS, Issue 2 2008Kyuongsik Chin Cell encapsulation provides cells a three-dimensional structure to mimic physiological conditions and improve cell signaling, proliferation, and tissue organization as compared to monolayer culture. Encapsulation devices often encounter poor mass transport, especially for oxygen, where critical dissolved levels must be met to ensure both cell survival and functionality. To enhance oxygen transport, we utilized perfluorocarbon (PFC) oxygen vectors, specifically perfluorooctyl bromide (PFOB) immobilized in an alginate matrix. Metabolic activity of HepG2 liver cells encapsulated in 1% alginate/10% PFOB composite system was 47,104% higher than alginate systems lacking PFOB. A cubic model was developed to understand the oxygen transport mechanism in the alginate/PFOB composite system. The theoretical flux enhancement in alginate systems containing 10% PFOB was 18% higher than in alginate-only systems. Oxygen uptake rates (OURs) of HepG2 cells were enhanced with 10% PFOB addition under both 20% and 5% O2 boundary conditions, by 8% and 15%, respectively. Model predictions were qualitatively and quantitatively verified with direct experimental OUR measurements using both a perfusion reactor and oxygen sensing plate, demonstrating a greater OUR enhancement under physiological O2 boundary conditions (i.e., 5% O2). Inclusion of PFCs in an encapsulation matrix is a useful strategy for overcoming oxygen limitations and ensuring cell viability and functionality both for large devices (>1 mm) and over extended time periods. Although our results specifically indicate positive enhancements in metabolic activity using the model HepG2 liver system encapsulated in alginate, PFCs could be useful for improving/stabilizing oxygen supply in a wide range of cell types and hydrogels. [source] Solvate-Supported Proton Transport in ZeolitesCHEMPHYSCHEM, Issue 4 2004Marion E. Franke Dr. Abstract Solvate-supported proton transport in zeolite H-ZSM-5 was studied by means of complex impedance spectroscopy. The zeolite shows enhanced proton mobility in the presence of NH3and H2O that depends on the concentration of the solvate molecule, temperature (298,773 K), and the SiO2/Al2O3ratio of the zeolite (30,1000). In general, proton conductivity in H-ZSM-5 is most effectively supported in the presence of NH3and H2O at high concentrations, low temperatures, and low SiO2/Al2O3ratios (,80). For the aluminum-rich samples desorption measurements reflect different transport mechanisms that depend on the respective temperature range. Up to about 393 K a Grotthus-like proton transport mechanism is assumed, whereas at higher temperatures (393,473 K) vehiclelike transport seems to dominate. The activation energies for NH4+and H3O+vehicle conductivity depend on the SiO2/Al2O3ratio, and the values are in the range of 49,59 and 39,49 kJ,mol,1, respectively, and thus significantly lower than those for "pure" proton conduction in solvate-free samples. [source] Microporous Niobia,Silica Membrane with Very Low CO2 PermeabilityCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 5 2008Vittorio Boffa Dr. Abstract A sol,gel-derived microporous ceramic membrane with an exceptionally low permeability for CO2 from gaseous streams was developed and characterized. The sols were prepared from a mixture of niobium and silicon alkoxide precursors by acid-catalyzed synthesis. Microporous films were formed by coating asymmetric ,-alumina disks with the polymeric sol (Si/Nb=3:1), followed by calcination at 500,°C. The membrane consists of a 150-nm-thick layer with a Si/Nb atomic ratio of about 1.5. The single-gas permeance of small gas molecules such as H2, CH4, N2, and SF6 decreases steadily with kinetic diameter. Hydrogen, helium, and carbon dioxide follow an activated transport mechanism through the membrane. The permeance of CO2 in this membrane is much lower than that in pure silica, and its behavior deviates strongly from the general trend observed with the other gases. This is attributed to a relatively strong interaction between CO2 and adsorption sites in the niobia,silica membrane. [source] Photoconduction and transport mechanisms in polycrystalline zincphthalocyanine thin filmsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2007S. Senthilarasu Abstract Zincphthalocyanine (ZnPc) thin films were prepared by the vacuum evaporation method under a pressure of 10 -6 mbar. The X-ray diffraction analysis of vacuum evaporated ZnPc films reveals that the structure of the films is polycrystalline in nature. The photoconduction properties have been studied in the wavelength range 400 ,800nm using suitable masks. The Photoconductivity of the films as a function of light intensity and applied voltage were studied and results were discussed in detail. The photoconduction was found to increase with higher light illumination and maximum at the band edge of the ZnPc thin film. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural, electrical and optical properties of Ge implanted GaSe single crystals grown by Bridgman techniqueCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2006H. Karaa Abstract Structural, optical and electrical properties of Ge implanted GaSe single crystal have been studied by means of X-Ray Diffraction (XRD), temperature dependent conductivity and photoconductivity (PC) measurements for different annealing temperatures. It was observed that upon implanting GaSe with Ge and applying annealing process, the resistivity is reduced from 2.1 × 109 to 6.5 × 105 ,-cm. From the temperature dependent conductivities, the activation energies have been found to be 4, 34, and 314 meV for as-grown, 36 and 472 meV for as-implanted and 39 and 647 meV for implanted and annealed GaSe single crystals at 500°C. Calculated activation energies from the conductivity measurements indicated that the transport mechanisms are dominated by thermal excitation at different temperature intervals in the implanted and unimplanted samples. By measuring photoconductivity (PC) measurement as a function of temperature and illumination intensity, the relation between photocurrent (IPC) and illumination intensity (,) was studied and it was observed that the relation obeys the power law, IPC ,,n with n between 1 and 2, which is indication of behaving as a supralinear character and existing continuous distribution of localized states in the band gap. As a result of transmission measurements, it was observed that there is almost no considerable change in optical band gap of samples with increasing annealing temperatures for as-grown GaSe; however, a slight shift of optical band gap toward higher energies for Ge-implanted sample was observed with increasing annealing temperatures. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Quasi-two-dimensional electrodeposition growth of Pb0.5Sn0.5 alloyCRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2006Bin Sun Abstract Electrodeposition of Pb0.5Sn0.5 alloy is carried out in a quasi-2D electrochemical cell. As the growth proceeds the morphologies of the deposits transit from cake-like to branched and finally to the compact morphology. We show that these morphological transitions arise from the changes in the transport mechanisms of the ions in the electrolyte cell. In addition, it is found that the current density on the growth interface can vary spontaneously due to the irregular shape of the deposit and the generation of hydrogen gas. It causes the formation of the complex microstructure with non-uniform composition. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||||||||||||||||||||||||||