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Double Layer (double + layer)
Kinds of Double Layer Terms modified by Double Layer Selected AbstractsHigh-Density Carrier Accumulation in ZnO Field-Effect Transistors Gated by Electric Double Layers of Ionic LiquidsADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Hongtao Yuan Abstract Very recently, electric-field-induced superconductivity in an insulator was realized by tuning charge carrier to a high density level (1,×,1014 cm,2). To increase the maximum attainable carrier density for electrostatic tuning of electronic states in semiconductor field-effect transistors is a hot issue but a big challenge. Here, ultrahigh density carrier accumulation is reported, in particular at low temperature, in a ZnO field-effect transistor gated by electric double layers of ionic liquid (IL). This transistor, called an electric double layer transistor (EDLT), is found to exhibit very high transconductance and an ultrahigh carrier density in a fast, reversible, and reproducible manner. The room temperature capacitance of EDLTs is found to be as large as 34,µF cm,2, deduced from Hall-effect measurements, and is mainly responsible for the carrier density modulation in a very wide range. Importantly, the IL dielectric, with a supercooling property, is found to have charge-accumulation capability even at low temperatures, reaching an ultrahigh carrier density of 8×1014 cm,2 at 220,K and maintaining a density of 5.5×1014 cm,2 at 1.8,K. This high carrier density of EDLTs is of great importance not only in practical device applications but also in fundamental research; for example, in the search for novel electronic phenomena, such as superconductivity, in oxide systems. [source] Nonlinear Smoluchowski velocity for electroosmosis of Power-law fluids over a surface with arbitrary zeta potentialsELECTROPHORESIS, Issue 5 2010Cunlu Zhao Abstract Electroosmotic flow of Power-law fluids over a surface with arbitrary zeta potentials is analyzed. The governing equations including the nonlinear Poisson,Boltzmann equation, the Cauchy momentum equation and the continuity equation are solved to seek exact solutions for the electroosmotic velocity, shear stress, and dynamic viscosity distributions inside the electric double layer. Specifically, an expression for the general Smoluchowski velocity is obtained for electroosmosis of Power-law fluids in a fashion similar to the classic Smoluchowski velocity for Newtonian fluids. The existing Smoluchowski slip velocities under two special cases, (i) for Newtonian fluids with arbitrary zeta potentials and (ii) for Power-law fluids with small zeta potentials, can be recovered from our derived formula. It is interesting to note that the general Smoluchowski velocity for non-Newtonian Power-law fluids is a nonlinear function of the electric field strength and surface zeta potentials; this is due to the coupling electrostatics and non-Newtonian fluid behavior, which is different from its counterpart for Newtonian fluids. This general Smoluchowski velocity is of practical significance in determining the flow rates in microfluidic devices involving non-Newtonian Power-law fluids. [source] Electrophoresis of a charge-regulated toroid normal to a large diskELECTROPHORESIS, Issue 2 2008Jyh-Ping Hsu Abstract The electrophoresis of a charge-regulated toroid (doughnut-shaped entity) normal to a large disk is investigated under the conditions of low surface potential and weak applied electric field. The system considered is capable of modeling the electrophoretic behavior of various types of biocolloids such as bacterial DNA, plasmid DNA, and anabaenopsis near a perfectly conducting planar wall. The influences of the size of the toroid, the separation distance between the toroid and the disk, the charged conditions on the surfaces of the toroid and the disk, and the thickness of electric double layer on the electrophoretic mobility of the toroid are discussed. The results of numerical simulation reveal that under typical conditions the electrophoretic behavior of the toroid can be different from that of an integrated entity. For instance, if the surface of the toroid carries both acidic and basic functional groups, its mobility may have a local maximum as the thickness of double layer varies. We show that the electrophoretic behavior of the toroid is different, both qualitatively and quantitatively, from that of the corresponding integrated particle (particle without hole). [source] A model incorporating the diffuse double layer to predict the electrical conductivity of bulk soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2007M. A. Mojid Summary A model has been developed to predict the electrical conductivity of bulk soil. The total soil-water content is divided into free water and water in the diffuse double layer (DDL) around clay particles. These two fractions of soil water conduct electrical current through the soil and are assumed to act in parallel with the soil solid. The volume of water in the DDL is evaluated from the surface area of the clay and the thickness of the DDL. The surface area of the clay is estimated from its cation exchange capacity (CEC) and surface charge density. A transmission coefficient correcting for the effect of the tortuous flow path of current through the soil, and a proportionality constant relating the electrical conductivity of water in the DDL to that of free water, are included in the model. The transmission coefficient is a function of the contents of water and clay and has been modelled in terms of these factors. The values of the proportionality constant and those relating to the transmission coefficient were optimized for five different soils. The electrical conductivities of the five soils estimated by the model compare well with the measured values, which, however, deviate systematically from predictions by the three-component model of Rhoades et al. [source] The Effects of Moisture in Low-Voltage Organic Field-Effect Transistors Gated with a Hydrous Solid ElectrolyteADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Nikolai Kaihovirta Abstract The concept of using ion conducting membranes (50,150 ,m thick) for gating low-voltage (1 V) organic field-effect transistors (OFETs) is attractive due to its low-cost and large-area manufacturing capabilities. Furthermore, the membranes can be tailor-made to be ion conducting in any desired way or pattern. For the electrolyte gated OFETs in general, the key to low-voltage operation is the electrolyte "insulator" (the membrane) that provides a high effective capacitance due to ionic polarization within the insulator. Hydrous ion conducting membranes are easy to process and readily available. However, the role of the water in combination with the polymeric semiconductor has not yet been fully clarified. In this work electrical and optical techniques are utilized to carefully monitor the electrolyte/semiconductor interface in an ion conducting membrane based OFET. The main findings are that 1) moisture plays a major part in the transistor operation and careful control of both the ambient atmosphere and the potential differences between the electrodes are required for stable and consistent device behavior, 2) the obtained maximum effective capacitance (5 ,F cm,2) of the membrane suggests that the electric double layer is distributed over a broad region within the polyelectrolyte, and 3) electromodulation spectroscopy combined with current,voltage characteristics provide a method to determine the threshold gate voltage from an electrostatic field-effect doping to a region of (irreversible) electrochemical perturbation of the polymeric semiconductor. [source] Chitosan Hydrogel-Capped Porous SiO2 as a pH Responsive Nano-Valve for Triggered Release of InsulinADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Jianmin Wu Abstract A pH responsive, chitosan-based hydrogel film is used to cap the pores of a porous SiO2 layer. The porous SiO2 layer is prepared by thermal oxidation of an electrochemically etched Si wafer, and the hydrogel film is prepared by reaction of chitosan with glycidoxypropyltrimethoxysilane (GPTMS). Optical reflectivity spectroscopy and scanning electron microscopy (SEM) confirm that the bio-polymer only partially infiltrates the porous SiO2 film, generating a double layer structure. The optical reflectivity spectrum displays Fabry,Pérot interference fringes characteristic of a double layer, which is characterized using reflective interferometric Fourier transform spectroscopy (RIFTS). Monitoring the position of the RIFTS peak corresponding to the hydrogel layer allows direct, real-time observation of the reversible volume phase transition of the hydrogel upon cycling of pH in the range 6.0,7.4. The swelling ratio and response time are controlled by the relative amount of GPTMS in the hydrogel. The pH-dependent volume phase transition can be used to release insulin trapped in the porous SiO2 layer underneath the hydrogel film. At pH 7.4, the gel in the top layer effectively blocks insulin release, while at pH 6.0 insulin penetrates the swollen hydrogel layer, resulting in a steady release into solution. [source] Coupled lattice-Boltzmann and finite-difference simulation of electroosmosis in microfluidic channelsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2004Dzmitry Hlushkou Abstract In this article we are concerned with an extension of the lattice-Boltzmann method for the numerical simulation of three-dimensional electroosmotic flow problems in porous media. Our description is evaluated using simple geometries as those encountered in open-channel microfluidic devices. In particular, we consider electroosmosis in straight cylindrical capillaries with a (non)uniform zeta-potential distribution for ratios of the capillary inner radius to the thickness of the electrical double layer from 10 to 100. The general case of heterogeneous zeta-potential distributions at the surface of a capillary requires solution of the following coupled equations in three dimensions: Navier,Stokes equation for liquid flow, Poisson equation for electrical potential distribution, and the Nernst,Planck equation for distribution of ionic species. The hydrodynamic problem has been treated with high efficiency by code parallelization through the lattice-Boltzmann method. For validation velocity fields were simulated in several microcapillary systems and good agreement with results predicted either theoretically or obtained by alternative numerical methods could be established. Results are also discussed with respect to the use of a slip boundary condition for the velocity field at the surface. Copyright © 2004 John Wiley & Sons, Ltd. [source] Charge and Mass Transfer Across the Metal/Solution InterfaceISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2008Eliezer Gileadi Electrode reactions are characterized by charge transfer across the interface. The charge can be carried by electrons or by ions. It is shown here that when both mass and charge cross the interface, the charge must be carried by the ionic species, not by the electrons, as a result of the very large difference in the time scale for electron and ion transfer. A prime example of charge transfer by ions is metal deposition. It is proposed that ion transfer occurs by migration of the ions across the interface, under the influence of the high electrostatic field in the double layer. The rate constants observed for metal deposition are comparable to those for outer-sphere charge transfer. These unexpectedly high rate constants for metal deposition are explained by a model in which removal of the solvation shell and reduction of the effective charge on the metal ion occur in many small steps, and a make-before-break mechanism exists, which lowers the total Gibbs energy of the system as it moves along the reaction coordinate from the initial to the final state. [source] Long-range and short-range mechanisms of hydrophobic attraction and hydrophilic repulsion in specific and aspecific interactionsJOURNAL OF MOLECULAR RECOGNITION, Issue 4 2003Carel Jan van Oss Abstract Among the three different non-covalent forces acting in aqueous media, i.e. Lifshitz,van der Waals (LW), Lewis acid,base (AB) and electrical double layer (EL) forces, the AB forces or electron,acceptor/electron,donor interactions are quantitatively by far the predominant ones. A subset of the AB forces acting in water causes the hydrophobic effect, which is the attraction caused by the hydrogen-bonding (AB) free energy of cohesion between the water molecules which surround all apolar as well as polar molecules and particles when they are immersed in water. As the polar energy of cohesion among water molecules is an innate property of water, the hydrophobic attraction (due to the hydrophobic effect) is unavoidably always present in aqueous media and has a value of ,Ghydrophobic,=,,102,mJ/m2, at 20,°C, being equal to the AB free energy of cohesion between the water molecules at that temperature. The strong underlying hydrophobic attraction due to this effect can, however, be surmounted by very hydrophilic molecules and particles that attract water molecules more strongly than the free energy of attraction of these molecules or particles for one another, plus the hydrogen-bonding free energy of cohesion between the water molecules, thus resulting in a net non-electrical double layer repulsion. Each of the three non-covalent forces, LW, AB or EL, any of which can be independently attractive or repulsive, decays, dependent on the circumstances, as a function of distance according to different rules. These rules, following an extended DLVO (XDLVO) approach, are given, as well as the measurement methods for the LW, AB and EL surface thermodynamic properties, determined at ,contact'. The implications of the resulting hydrophobic attractive and hydrophilic repulsive free energies, as a function of distance, are discussed with respect to specific and aspecific interactions in biological systems. The discussion furnishes a description of the manner by which shorter-range specific attractions can surmount the usually much stronger long-range aspecific repulsion, and ends with examples of in vitro and in vivo effects of hydrophilization of biopolymers, particles or surfaces by linkage with polyethylene oxide (PEO; also called polyethylene glycol, PEG). Copyright © 2003 John Wiley & Sons, Ltd. [source] Formation Mechanism of Hydrous Zirconia Particles Produced by the Hydrolysis of ZrOCl2 Solutions: III, Kinetics Study for the Nucleation and Crystal-Growth Processes of Primary ParticlesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2001Koji Matsui The formation rate and primary particle size of monoclinic, hydrous zirconia particles produced by the hydrolysis of various ZrOCl2 solutions (with and without the addition of HCl, NH4OH, NaCl, CaCl2, or AlCl3) were measured to clarify the effects of the H+ and Cl, ion concentrations on the nucleation and crystal-growth processes of primary particles of hydrous zirconia. Chemical-kinetic analyses, to which Avrami,Erofeev's equation was applied, and XRD measurements revealed that both the rate constant and the primary particle size of the hydrous zirconia decreased as the concentrations of H+ and/or Cl, ions produced by hydrolysis increased. The nucleation rate per unit of ZrOCl2 concentration and the crystal-growth rate of the primary particles of the hydrous zirconia were determined by analyzing the relationships between the rate constant and primary particle size. The nucleation rate per unit of ZrOCl2 concentration revealed almost no change and remained constant as the H+ and/or Cl, ion concentrations increased, except in the case of a slight increase for ZrOCl2 solutions with added HCl. The crystal-growth rate decreased as the H+ and/or Cl, ion concentration increased. The present kinetic analyses revealed that the decrease in rate constant with increasing H+ and/or Cl, ion concentrations resulted from the decrease in the crystal-growth rate. The decreasing tendency of the crystal-growth rate was attributed to interference with crystal growth by the Cl, ions attracted onto the particle surface through the formation of an electric double layer. The formation mechanisms for the primary particles of hydrous zirconia were determined based on the present experimental results. [source] Interaction of Phytochemical-Quercetin with the Other Antioxidant, Ascorbic Acid and their Protective Effect in Tilapia after Ultraviolet IrradiationJOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 5 2009Gustavo A. Rodriguez-Montes De Oca Semi-purified, casein-gelatin-based diets were prepared and supplemented with quercetin (Q) and/ or ascorbic acid (AA): control diet C,Q,(100 mg/kg AA), diet C ,Q+ (100 mg/kg AA + quercetin 10 g/kg), diet C +Q, (1000 mg/kg AA), and diet C +Q+ (1000 mg/kg AA + quercetin 10 g/kg). These diets were fed to tilapia for 19 wk and then fish were divided into controls and ultraviolet (UV) treatments. Fish were exposed to UV radiation. Control groups were protected with a MYLAR® polyester film and plexiglass. At week 20, the same fish were re-exposed to UV radiation. Control groups of fish were protected by a double layer of MYLAR® and the UV groups were exposed with no protection. Before UV exposure, 24 h after, and 7 d after the second treatment, fish liver and skin were dissected for Q and AA analyses. The proportion of oxidized ascorbate was significantly increased in fish from treatments C ,Q, and C ,Q+ . Q concentrations in fish after exposures were negligible in skin, whereas liver concentrations were significantly different among control (34 ± 10 ,g/g) and UV-irradiated fish (11 ± 6 ,g/g), respectively. The interaction between these two dietary antioxidants may change after chronic UV irradiation. [source] Multistep filling of porous silicon with conductive polymer by electropolymerizationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009Kazuhiro Fukami Abstract The filling of porous silicon with polypyrrole by electropolymerization was investigated. The filling with polypyrrole proceeded preferentially along the porous silicon wall, leading to the formation of tubular structures. By repeating the porosification, the pore filling and the additional porosification, through-tubes of polypyrrole were formed in macropores. The technique to form through-tube was also applied to medium-sized pores. A double layer with polypyrrole was produced by the repetition of porosification and pore filling twice. The immobilization of glucose oxidase was performed by electropolymerization in an aqueous solution containing glucose oxidase and pyrrole. Glucose oxidase was immobilized physically in the polypyrrole film. In the double layer, the sensitivity of glucose oxidase was measured by electrochemical oxidation of hydrogen peroxide, which was produced by the enzymatic reaction of glucose oxidase to gluconolactone. When glucose oxidase was immobilized in the upper layer, glucose was detected sensitively. On the other hand, when glucose oxidase was immobilized in the lower layer, the sensing current showed a slow and a low response. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Small molecule detection by reflective interferometric Fourier transform spectroscopy (RIFTS)PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009Claudia Pacholski Abstract A new method for the compensation of matrix effects in biosensing experiments referred to as reflective interferometric Fourier transform spectroscopy (RIFTS) has been developed recently [1]. It employs a porous silicon sensor comprised of two porous silicon layers stacked one on top of the other. The structure has a complicated reflectivity spectrum that can be resolved by FFT analysis leading to three distinctive peaks which are assigned to the layers in the porous silicon structur. If the double layer is appropriately designed, the bottom layer can act as a reference channel. In this paper the specific sensing of small molecules using RIFTS is demonstrated for the first time. Ac-L-Lys-D-Ala-D-Ala has been immobilized to the sensor surface representing the capture probe and vancomycin was used as target analyte. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dielectric properties of Li doped Li-Nb-O thin filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007G. Perentzis Abstract Lithium niobate LiNbO3 was prepared as a thin film layered structure deposited on stainless steel substrate using e-gun evaporation. The Li doping was provided for by the formation of Li-Nb-O/Li/LiNb-O sandwich structure and annealing at about 250 °C. AC impedance spectroscopy measurements were performed on the samples at temperatures from the interval between 28 and 165 °C and in a frequency range of 10,3 to 106 Hz. Using the values Z , and Z , at different frequencies, the dielectric parameters , parts of the complex permittivity ,, and ,, and loss tangent tan , were calculated. The results prove validity of the proposed equivalent circuit containing parallel RC elements connected in series where the first RC element represents the bulk of material and the second RC element belongs to the double layer at the metal interface. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Flux growth and structure of two compounds with the EuIn2P2 structure type, AIn2P2 (A = Ca and Sr), and a new structure type, BaIn2P2ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009Japheth F. Rauscher Single crystals of the new Zintl phases AIn2P2 [A = Ca (calcium indium phosphide), Sr (strontium indium phosphide) and Ba (barium indium phosphide)] have been synthesized from a reactive indium flux. CaIn2P2 and SrIn2P2 are isostructural with EuIn2P2 and crystallize in the space group P63/mmc. The alkaline earth cations A are located at a site with m symmetry; In and P are located at sites with 3m symmetry. The structure type consists of layers of A2+ cations separated by [In2P2]2, anions that contain [In2P6] eclipsed ethane-like units that are further connected by shared P atoms. This yields a double layer of six-membered rings in which the In,In bonds are parallel to the c axis and to one another. BaIn2P2 crystallizes in a new structure type in the space group P21/m with Z = 4, with all atoms residing on sites of mirror symmetry. The structure contains layers of Ba2+ cations separated by [In2P2]2, layers of staggered [In2P6] units that form a mixture of four-, five- and six-membered rings. As a consequence of this more complicated layered structure, both the steric and electronic requirements of the large Ba2+ cation are met. [source] Drag enhancement of aqueous electrolyte solutions in turbulent pipe flowASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2007E. Benard Abstract Experimental measurements have indicated that drag enhancement occurs when aqueous electrolyte solutions are flowing in the turbulent regime. The primary electroviscous effect due to the distortion by the shear field of the electrical double layer surrounding the ions in solution is invoked to explain the drag enhancement. Calculations using the Booth model for symmetrical one-to-one electrolytes enabled the increased viscosity in the turbulent regime to be calculated. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Voltammetric Manifestation of the Ultraslow Dynamics at the Interface between Water and an Ionic Liquid,CHEMPHYSCHEM, Issue 13 2010Prof. Takashi Kakiuchi Abstract The ultraslow relaxation (on the order of minutes) of the electrical double-layer structure, related to a change in the phase-boundary potential across the interface between water (W) and the ionic liquid (IL) trioctylmethylammonium bis(nonafluorobutanesufonyl)amide ([TOMA+][C4C4N,]) (Y. Yasui et al., J. Phys. Chem. B. 2009, 113, 3273), appears to be invisible in the transfer of tetrapropylammonium ions across the [TOMA+][C4C4N,]|W interface, provided that the charging current, which shows an unusual dependence on the voltage scan rate, is subtracted to obtain the faradaic current. This counterintuitive observation can be explained by the differences in the timescales of the fast and slow components of the relaxation dynamics of the electrical double layer on the IL side (ms and min). In contrast, the effect of the slow dynamics becomes surfaced in ion-transfer voltammetry when the ion is surface-active. The transfer of pentadecafluorooctanoate across the [TOMA+][C4C4N,]|W interface is irreversible, which is attributable to the self-inhibition of pentadecafluorooctanoate ions transferred to the IL phase. This process is likely to be affected by the ultraslow structural change of the IL side of the interface. [source] Linear Expression of the Mathematical Relationship between Electroosmotic Mobility and Buffer ConcentrationCHINESE JOURNAL OF CHEMISTRY, Issue 1 2006Xu Xu Abstract It was believed that electroosmotic mobility ,eo is inversely proportional to the square root of the ionic strength I. But the linear relationship for regression analysis was expressed differently in different papers. The paper studied the linear expression of the mathematical relationship between ,eo and c (background buffer concentration) by mathematical transform and real experimental data. ,eo values of fused silica capillary were determined in four buffer systems. Their experimental conditions were controlled carefully for decreasing temperature difference ,T and pH difference ,pH in 50 µm ID capillary, in which no double layer overlap existed. The linear relationship between the reciprocal of electroosmotic mobility and the square root of concentration (or ionic strength) was derived by mathematical method. The regression analysis of experimental data was shown to well correspond to the relationship. The constants in regression equation could be well defined and the calculated results were acceptable. [source] Study on the Radius of an Electrical Spherical Micelle: Functional Theoretical ApproachCHINESE JOURNAL OF CHEMISTRY, Issue 4 2004Zheng-Wu Wang Abstract For the purpose of eliminating restriction, the Poisson-Boltzmann (PB) equation, which represents the potential of the electrical double layer of spherical micelles, can be solved analytically only under the lower potential condition, a kind of iterative method in functional analysis theory has been used. The radius of the spherical particle can be obtained from the diagram of the second iterative solution of the potential versus the distance from the center of the particle. The influences of the concentration of the ions, the charge number of ions, the aggregation number of the particle, the dielectric constant of solvent and the temperature of system on the radius also have been studied. [source] High Power Density Electric Double Layer Capacitor with Improved Activated CarbonCHINESE JOURNAL OF CHEMISTRY, Issue 2 2003Yang Hui Abstract The improvement on commercial activated carbon (AC) through the reactivation under steam in the presence of NiCl2 catalyst leads to the increases of both energy and power densities of electric double layer (dl) capacitors. When AC was treated at 875 °C for 1 h, its discharge specific capacitance increases up to 53.67 F· g,1, an increase of about 25% compared to the as-received AC. Moreover, a significant increase in high rate capability of electric dl capacitor was found after the improvements. Surprisingly, both the treated and untreated AC samples showed similar specific surface area and pore size distribution, but some changes in the surface groups and their concentrations after reactivation were verified by X-photoelectron spectra. Thus, it is reasonable to conclude that the decrease in the surface concentration of the carbonyl-containing species for the improved AC results in an increase of accessibility of the pores to the organic electrolyte ion, causing the enhancements of both the specific capacitance and high rate capability. [source] Development and fine structure of the yolk nucleus of previtellogenic oocytes in the medaka Oryzias latipesDEVELOPMENT GROWTH & DIFFERENTIATION, Issue 6 2000Hirokuni Kobayashi The development and fine structure of yolk nuclei in the cytoplasm of previtellogenic oocytes were examined by electron microscopy during several stages of oogenesis in the medaka, Oryzias latipes. Shortly after oogenesis starts, oocytes 20,30 ,m in diameter have much electron-dense (basophilic) cytoplasm, within which a continuous or discontinuous, irregular ring-shaped lower electron-dense area of flocculent appearance (LF) begins to emerge around the nucleus. The yolk nucleus is first recognized within an LF area as a few fragments of dense granular thread measuring 20,25 nm in width. The threads consist of two rows of very dense granules resembling ribosomes or ribonucleoprotein (RNP)-like particles in size and electron density. These thread-like fragments gradually increase in number and length until they assemble into a compact, spherical mass of complicated networks. Analysis of serial sections suggests that the yolk nucleus is a complicated mass of numerous, small deformed vacuoles composed of a single lamella with double layers of ribosomes or RNP-like granules, rather than a mass of granular threads. When oocytes develop to greater than 100 ,m in diameter, the yolk nucleus begins to fragment before dispersing throughout the surrounding cytoplasm, concomitantly with the disappearance of LF areas. At this stage of oogenesis, a restricted region of the granulosa cell layer adjacent to the yolk nucleus becomes somewhat columnar in morphology, fixing the vegetal pole region of the oocyte. [source] Decreasing effective nanofluidic filter size by modulating electrical double layers: Separation enhancement in microfabricated nanofluidic filtersELECTROPHORESIS, Issue 23 2008Hansen Bow Abstract Conventional methods for separating biomolecules are based on steric interactions between the biomolecules and randomly oriented gel fibers. The recently developed artificial molecular sieves also rely on steric interactions for separation. In this work, we present an experimental investigation of a method that can be used in these sieves to increase separation selectivity and resolution. This method exploits the electrostatic repulsion between the charged molecules and the charged nanofluidic structure. Although this method has been mentioned in the previous work, it has not been examined in detail. We characterize this method by comparing the selectivity with that achieved in devices with different dimensions. The results of this study are relevant to the optimization of chip-based gel-free biomolecule separation and analysis. [source] High-Density Carrier Accumulation in ZnO Field-Effect Transistors Gated by Electric Double Layers of Ionic LiquidsADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Hongtao Yuan Abstract Very recently, electric-field-induced superconductivity in an insulator was realized by tuning charge carrier to a high density level (1,×,1014 cm,2). To increase the maximum attainable carrier density for electrostatic tuning of electronic states in semiconductor field-effect transistors is a hot issue but a big challenge. Here, ultrahigh density carrier accumulation is reported, in particular at low temperature, in a ZnO field-effect transistor gated by electric double layers of ionic liquid (IL). This transistor, called an electric double layer transistor (EDLT), is found to exhibit very high transconductance and an ultrahigh carrier density in a fast, reversible, and reproducible manner. The room temperature capacitance of EDLTs is found to be as large as 34,µF cm,2, deduced from Hall-effect measurements, and is mainly responsible for the carrier density modulation in a very wide range. Importantly, the IL dielectric, with a supercooling property, is found to have charge-accumulation capability even at low temperatures, reaching an ultrahigh carrier density of 8×1014 cm,2 at 220,K and maintaining a density of 5.5×1014 cm,2 at 1.8,K. This high carrier density of EDLTs is of great importance not only in practical device applications but also in fundamental research; for example, in the search for novel electronic phenomena, such as superconductivity, in oxide systems. [source] Sorption of tannic acid on zirconium pillared clayJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 1 2002P Vinod Abstract Zirconium pillared clay (PILC) was prepared using montmorillonite as the base clay. Adsorption of tannic acid (tannin) was studied by a batch equilibrium technique, as a function of adsorbate concentration, temperature, pH, agitation speed, particle size of the adsorbent and ionic strength. The process of uptake is governed by diffusion controlled first-order reversible rate kinetics. The higher uptake for the pH range 4.0,6.0 was attributed to external hydrogen bonding between phenolic-OH groups of tannin molecules and the hydrogen bonding sites on the clay. The removal of tannin by adsorption was found to be >99.0% depending on the initial concentration in the pH range of 4.0,6.0. The process involves both film and pore diffusion to different extents. The effects of solute concentration, temperature, agitation speed and particle size on the diffusion rate were investigated. Tannin uptake was found to increase with ionic strength due to the compression of diffuse double layers. The applicability of Langmuir and Freundlich isotherm models has been tested. The maximum adsorption capacity of PILC was found to be 45.8,µmol,g,1 of clay and the affinity constant is 2.9,×,10,2,dm3,µmol,1 at 30,°C. Thermodynamic parameters such as ,G,°,,H,° and ,S,° were calculated to predict the nature of adsorption. The isosteric enthalpies of adsorption were also determined and found to decrease with increasing surface coverage. Regeneration with hot water (60,°C) has been investigated for several cycles with a view to recovering the adsorbed tannin and also restoring the sorbent to its original state. Copyright © 2001 Society of Chemical Industry [source] Emulsifying properties of gum kondagogu (Cochlospermum gossypium), a natural biopolymerJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 8 2009Ganga Modi Naidu Vegi Abstract BACKGROUND: Natural polymers are widely used as emulsifying agents in the food and pharmaceutical industries because of their low cost, biocompatibility and non-toxic nature. In the present study, emulsifying properties of the novel natural biopolymer gum kondagogu (GKG) were investigated. GKG solutions of different concentrations (0.1,0.6% w/v) were prepared in water and emulsified with liquid paraffin oil (40% v/v) in a high-speed homogeniser. Flow properties of the emulsions were measured using a rheometer. Emulsion stability and droplet size distribution were determined by visual observation, photomicrography and laser-scattering particle size distribution analysis. RESULTS: The emulsions prepared with GKG showed pseudoplastic behaviour. The size of oil droplets and the viscosity of emulsions at concentrations of 0.4,0.6% w/v showed little change over time (up to 30 days), indicating that the emulsions were stable. Measurements of the zeta potential of emulsions adjusted to different pH, with and without added electrolyte, showed that the stabilisation of emulsions with GKG was due to mutual repulsion between electrical double layers of particles and adsorption of macromolecules on oil droplets. CONCLUSION: The results of this experimental investigation show that GKG is a good emulsifying agent even at low concentrations, with many potential applications in the food and pharmaceutical industries. Copyright © 2009 Society of Chemical Industry [source] Mesoporous GaAs double layers for layer transfer processesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2009Enrique Garralaga Rojas Abstract Mesoporous GaAs double layers with different porosities and thicknesses up to 7,µm are formed on highly doped p-type 4,inch GaAs substrates by means of electrochemical etching in highly concentrated hydrofluoric acid electrolytes. Small ,111, oriented pyramids form at the interface between porous layer and substrate if etching current densities below 7.5,mA,cm,2 are applied. Porous double layers with different porosities are obtained by varying simultaneously the etching current density and the electrolyte concentration. The porosity of the porous GaAs layers decreases nearly linearly from 69 to 53% with electrolyte concentrations increasing from 30 to 50,wt.%, respectively. The etching process increases the mean roughness of the porous layer surface from 0.15 to 0.24,nm. [source] Spin-wave spectra and magnetization of ferro,ferrimagnetic double layersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2008Wei Jiang Abstract The spin-wave spectra and magnetization of the ferro,ferrimagnetic double layers are studied by using a linear spin-wave approximation and retarded Green's-function method. We obtain the four branches of the spin-wave spectra. Two energy gaps are found to exist in the energy band. The effects of the interlayer exchange coupling, the intralayer exchange coupling and the spin quantum numbers on the spin-wave spectra and the energy gaps are discussed. The minimum (maximum) value point on the spin-wave spectra and energy gaps correspond to a system that has a high symmetrical magnetic structure and the balance of quantum competitions among the exchange couplings and the spin quantum numbers of the system. There is a crossover between sublattice magnetizations in ferromagnetic layer that is affected by quantum fluctuations, thermal fluctuations and frustration of spins. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hydrogen-bonding controls the solid-state and enantiomeric comformations of the amino alcohol ligand 2-[(2-hydroxyethyl)amino]cyclohexanolACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010Alvaro S. de Sousa The crystal structure of the title compound, C8H17NO2, consists of (R,R) and (S,S) enantiomeric pairs packed in adjacent double layers which are characterized by centrosymmetric hydrogen-bonded dimers, generated via N,H...O and O,H...O interactions, respectively. Intermolecular interactions, related to acceptor and donor molecule chirality, link the achiral double layers into tubular columns, which consist of a staggered hydrophilic inner core surrounded by a hydrophobic cycloalkyl outer surface and extend in the [011] direction. [source] Conformational isomers of the [(5-methyl-2-pyridinio)aminomethylene]diphosphonate dianion and [(5-methyl-2-pyridyl)aminomethylene]diphosphonate trianion in salts with 4-aminopyridine and ammoniaACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2009Ewa Matczak-Jon The crystal structures of two salts, products of the reactions between [(5-methyl-2-pyridyl)aminomethylene]bis(phosphonic acid) and 4-aminopyridine or ammonia, namely bis(4-aminopyridinium) hydrogen [(5-methyl-2-pyridinio)aminomethylene]diphosphonate 2.4-hydrate, 2C5H7N2+·C7H10N2O6P22,·2.4H2O, (I), and triammonium hydrogen [(5-methyl-2-pyridyl)aminomethylene]diphosphonate monohydrate, 3NH4+·C7H9N2O6P23,·H2O, (II), have been determined. In (I), the Z configuration of the ring N,C and amino N,H bonds of the bisphosphonate dianion with respect to the Cring,Namino bond is consistent with that of the parent zwitterion. Removing the H atom from the pyridyl N atom results in the opposite E configuration of the bisphosphonate trianion in (II). Compound (I) exhibits a three-dimensional hydrogen-bonded network, in which 4-aminopyridinium cations and water molecules are joined to ribbons composed of anionic dimers linked by O,H...O and N,H...O hydrogen bonds. The supramolecular motif resulting from a combination of these three interactions is a common phenomenon in crystals of all of the Z -isomeric zwitterions of 4- and 5-substituted (2-pyridylaminomethylene)bis(phosphonic acid)s studied to date. In (II), ammonium cations and water molecules are linked to chains of trianions, resulting in the formation of double layers. [source] Two-dimensional hydrogen-bonded networks in 1-(diaminomethylene)thiouron-1-ium nitrate and bis[1-(diaminomethylene)thiouron-1-ium] phosphonate monohydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Jan Janczak Crystals of the title compounds, C2H7N4S+·NO3,, (I), and 2C2H7N4S+·HPO32,·H2O, (II), are built up from 1-(diaminomethylene)thiouron-1-ium cations and nitrate anions in (I), and from phosphonate anions and water molecules in (II). In both crystals, the cations and anions are linked together via N,H...O hydrogen bonds. The 1-(diaminomethylene)thiouron-1-ium cations exhibit a twisted conformation. Both arms of the cations are planar and are turned in opposite directions around the C,N bond involving the central N atom. Hydrogen-bonding interactions join oppositely charged units into layers in the nitrate salt and into double layers in the phosphonate monohydrate salt. In addition, the structures are stabilized by ,,, interactions between the delocalized , bonds of the cations. The significance of this study lies in the illustration of the differences between the supramolecular aggregations in the nitrate and phosphonate salts of a small organic molecule. The different geometries of the counter-ions and their different potential for hydrogen-bond formation results in markedly different hydrogen-bond arrangements. [source] | ||||||||||||||||||||||||||||||||||