Negative Charge Layer Research Articles

Auroral hot-ion dynamo model with finite gyroradii

Discrete auroras have (1) narrow size s≲30km in at least one dimension (e.g., north-south) and (2) often rapid variation of forms, especially where the size is extremely small, s⩽1km. These points mesh with spatial and temporal features observed at several Earth radii in earthward flows (bursts) of hot plasma along high-latitude geomagnetic field lines. The flows (include PSBL) usually have some filamentary structure with transverse widths of a few local gyroradii of the hot protons (kT∼1–30keV), i.e., widths that encompass auroral-arc size when scaled by magnetic field-line separation. At these widths, modest density gradients (δn∼0.01–0.1cm−3) lead to charge separation by differential mirroring of hot protons and electrons and large perpendicular electric fields. Thermal escape of ionspheric electrons into positive charge layer builds up magnetic field-aligned potential difference that accelerates hot electrons from negative charge layer into the ionosphere within auroral arc thickness. As a corollary, the model delineates a mechanism for charge-driven plasma instabilities.

Membrane biophysics

Membrane biophysics

Titanium dioxide nanoparticles-coated column for capillary electrochromatographic separation of oligopeptides

A novel column made through the condensation reaction of TiO2 nanoparticles (TiO2 NPs) with silanol groups of the fused-silica capillary is described. EOF measurements under various buffer constitutions were used to monitor the completion of reactions. The results indicated that the EOF was dependent on the interactions between buffers and the bonded TiO2 NPs. With formate/Tris buffer, EOF reversal at pH below 5 and cathodic EOF at pH above 5 were indicated. The pI of the bonded TiO2 NPs was found at approximately ph 5. Only cathodic EOF was illustrated by substituting the mobile phase with either glutamate or phosphate buffer. It was elucidated that both glutamate and phosphate buffer yield a negative charge layer on the surface of TiO2 NPs attributable to the formation of a titanium complex. The CEC performance of the column was tested with angiotensin-type oligopeptides. Some parameters that would affect the retention behavior were investigated. The interactions between the bonded phases and the analytes were explicated by epitomized acid-base functional groups of the oligopepetides and the speciation of the surface oxide in different pH ranges. The average separation efficiencies of 3.1 x 10(4) plates/m is readily achieved with a column of 70 cm (50 cm) x 50 mum ID under an applied voltage of 15 kV, phosphate buffer (pH 6.0, 40 mM), and UV detection at 214 nm.

Effect of current density on electron beam induced charging in sapphire and yttria-stabilized zirconia

This article presents a study performed with a dedicated scanning electron microscope on the electrical property evolution of surfaces of (0001)-oriented sapphire (Al2O3) and (100)-oriented yttria-stabilized zirconia (YSZ) single crystals, during a 1.1 keV electron irradiation at room temperature. The type of charges trapped on the irradiated areas and the charging kinetics are determined by measuring the total secondary electron emission yield σ during the injection process, by means of two complementary detectors. At low current density (<7×106 pA cm−2) where positive charging is observed in both materials, charges trapped in Al2O3 are stable, whereas they are unstable in YSZ. This leads to two different charging kinetics. As charging is progressing in Al2O3, σ varies from its initial intrinsic value 7.5 down to a steady value σ=1 which corresponds to the self-regulated regime. Under the same conditions, σ varies in YSZ from 2.35 down to a steady value above 1 (σ=1.1 in the experiment presented). At high current density (above 7×106 and 6×109 pA cm−2, respectively, for Al2O3 and YSZ), the regulation of the charge regime is controlled by the formation of a negative charge layer due to the reduction of the secondary electron emission by the elastic interaction of incident electrons with secondaries. The difference in the charging kinetics of the two materials is attributed to the difference in conductivities. The higher conductivity of YSZ is responsible for the slower charging kinetics in YSZ, the less pronounced current density effect, and the vanishing of positive charges when irradiation stops.

Proteinuria: the diagnostic strategy based on determination of various urinary proteins

Basal glomerular membrane represents mechanical and electrical barrier for passing of the plasma proteins. Mechanical barrier is composed of cylindrical pores and filtration fissure, and negative layer charge in exterior and interior side of basal glomerular membrane, made of heparan sulphate and sialoglycoprotein, provides certain electrical barrier. Diagnostic strategy based on different serum and urine proteins enables the differentiation of various types of proteinuria. Depending on etiology of proteinuria it can be prerenal, renal and postrenal. By analyzing albumin, alpha1-microglobulin, immunoglobulin G and alpha2-macroglobulin, together with total protein in urine, it is possible to detect and differentiate causes of prerenal, renal (glomerular, tubular, glomerulo-tubular) and postrenal proteinuria. The adequate and early differentiation of proteinuria type is of an immense diagnostic and therapeutic importance.

Horizontal structure of the electric field in the stratiform region of an Oklahoma mesoscale convective system

This analysis combines vertical electric field components Ez observed by two research aircraft flying horizontally at two levels, with vertical soundings of thermodynamic parameters and Ez made by five balloons, to produce a quasi‐three‐dimensional view of the space charge distribution in the trailing stratiform cloud region behind a mesoscale convective system (MCS) that developed in central Oklahoma late in the afternoon of 2 June 1991. The balloons were launched serially at one‐hour intervals from two sites separated by 80 km along a north‐south line as the MCS moved eastward, yielding two east‐west time‐height cross‐sections of the Ez structure within the quasi‐steady state trailing stratiform region behind the MCS. The balloon measurements are consistent with a vertical stack of five rearward‐ and downward‐sloping horizontal sheets of charge of alternating polarity, beginning at the bottom with a negative charge layer below the 0°C level and a positive layer near the 0°C level. This structure persisted for more than 2 hours. The two aircraft flew back and forth along a north‐south line through the balloon launch sites during the balloon launch period. Aircraft measurements demonstrated that the vertical electric field (Ez) at constant altitude varied in the north‐south direction. The peak magnitudes of Ez deduced from the airborne instrument systems agreed with the magnitudes deduced from the balloon measurements at the aircraft altitudes of 4.5 km and 5.8 km AGL. Rapid reversals in polarity of Ez with peak magnitude >50 kV m−1 observed by the aircraft at 4.5 km, just above the 0°C level, confirms the thin concentrated positive charge layer observed there by balloons and suggests that this charge layer is undulating above and below 4.5 km altitude, at least in the north‐south direction. Microphysically, this layer contained large aggregates and pockets of low cloud liquid water concentration. At the 5.8 km level, the polarity of Ez was always positive but the magnitude varied from zero to 25 kV m−1. Aircraft‐observed Ez at both altitudes varied on horizontal scales of ∼10 km or greater at both levels, suggesting that the charge density derived using the one‐dimensional infinite‐layer Gauss's law approximation applied to the balloon soundings of Ez is valid in this study. These observations show that layers of charge can persist for hours as they advect rearward in a storm‐relative sense, possibly due to continuing in situ charge separation, and/or due to weak dispersion, slow recombination and slow settling of charge attached to low mobility low terminal velocity ice hydrometeors.

Novel Na-3-Mica: Alkaline Earth Cation Exchange and Immobilization

The cation-exchange capacities for the alkaline earth metals Ba, Mg, and Ca, and their immobilization in the interlayers of a novel swelling fluorine mica (Na-3-mica) with a high-layer-charge density were studied. The mica was fully exchanged or saturated with Ba, Mg, and Ca ions and the cation-exchange capacities were determined to be 246, 338, and 322 meq (100 g)−1, respectively, on anhydrous basis of mica. The chemical analyses of the saturated micas indicated that about three exchangeable interlayer sodium ions per unit cell existed in the mica as a result of the total negative layer charge due to both Mg vacancies in octahedral sheets and Al substitution in tetrahedral Si sheets of the silicate. The Ba, Mg, and Ca leachabilities of the saturated micas were investigated in 0.5 M NaCl background solutions at room temperature and these were compared to the Sr leachability of the Sr-saturated mica. The degree of the cation immobilization in the interlayers increased in the order of Ca<Sr<Ba<Mg. This could be explained by the interlayer spacings and structures of the saturated micas.

A physical model of anode spot formation in a high-current vacuum arc

Physical and mathematical models are suggested for the description of anode heating and anode spot formation. An increase in the vacuum discharge current is accompanied by the crisis of cathode ion flow which leads, at a certain (critical) value of current, to the impossibility for the ions to reach the anode. It is known that, in this case, a layer of negative space charge with positive anode drop is formed, as well as an electron beam. The magnitude of anode drop depends on the thickness of the space charge layer and on the form of the electric circuit. A nonlinear dependence of the space charge layer thickness on the discharge current density is obtained. The presence of such a dependence makes it possible to solve the electric circuit in view of nonlinear unsteady-state resistance and capacitance of the layer and to calculate the voltage across the layer, the current density and the power density on the anode, as well as to calculate the anode surface temperature. The results of calculations of the time required for anode spot formation and of the time dependence of voltage across the space charge layer agree with the experimental data.

Parallel electric fields in the upward current region of the aurora: Numerical solutions

Direct observations of the parallel electric field by the Fast Auroral Snapshot satellite and the Polar satellite suggest that the ionospheric boundary of the auroral cavity is consistent with an oblique double layer that carries a substantial fraction (roughly 5% to 50%) of the auroral potential. A numerical solution to the Vlasov–Poisson equations of a planar, oblique double layer reproduces many of the properties of the observed electric fields, electron distributions, and ion distributions. The solutions indicate that the electron and ion distributions that emerge from the ionospheric side dominate the structure of the double layer. The ionospheric electron distribution includes scattered and reflected (mirrored) primaries, auroral secondaries, photoelectrons, and a cold population. A large fraction of the ionospheric electrons is reflected by the parallel electric field whereas the ionospheric ions are strongly accelerated. The steep density gradient between the ionosphere and the auroral cavity results in a highly asymmetric double layer, with a strong, localized positive charge layer on the ionospheric side and a moderate, extended negative charge layer on the auroral cavity side. This structure results in an asymmetric electric field, a feature also seen in the observations. The electric field observations, however, do not always support a planar double layer since the parallel and perpendicular signals are not always well correlated. Fully two-dimensional solutions are needed to better reproduce the observed features.

Thermal and acoustic pulse studies of space-charge profiles in electron-irradiated fluoroethylene propylene

We report complementary studies of space-charge distributions in electron-beam irradiated fluoroethylene propylene (FEP) (thicknesses of 13 and 26 µm) using the thermal pulse (TP) method and the laser-induced pressure-pulse (LIPP) method. The distributions obtained by the two methods are compared to show the strengths of both methods, the high near-surface resolution of the TP method (better than 100 nm) and the nearly constant resolution versus depth of the LIPP method (1-2 µm). In addition to the expected implanted negative charge at a depth governed by the electron energy, a negative near-surface charge layer was found close to the metal/FEP interface if the electron beam entered the dielectric through that interface. This finding provides new insights into the charging of dielectrics using electron beams.

Vanadyl Phosphate and Its Intercalation Reactions. A Review

The structure of the layered αI-VOPO4, VOPO4·2H2O, and their intercalation reactions are discussed. These reactions are divided into two groups. The first includes intercalation reactions of molecular guests which proceed as acid-base processes between the host layered lattice (Lewis acid) and a donor atom of the guest (base). Interaction of water molecules, alcohols, amines, carboxylic acids and their derivatives, heterocyclic N- and S-donors, and complex compounds with vanadyl phosphates is discussed. Vanadyl phosphate, in particular vanadyl phosphate dihydrate can also undergo the second type of the reactions which involves the reduction of a fraction of vanadium(V) atoms to vanadium(IV) with concomitant intercalation of alkylammonium, hydronium or mono- and divalent metal cations to counterbalance the induced negative layer charge. A review with 76 references.

Influence of the layer charge density of smectites on the interaction with methylene blue

Six Na-saturated smectites were isolated from bentonites of various deposits. Their H-forms were prepared using H–OH–H resins. The interaction of methylene blue (MB) (0.05 mmol g-1) with Na-saturated untreated and H-autotransformed clay samples was investigated by the VIS spectroscopy of their dispersions. The spectra provided information about the formation of protonated dye cations, dimers, and higher agglomerates on the clay surface. The amounts of various dye forms were compared with the distributions of negative layer charge of the used clays, obtained by the alkylammonium method. Formation of MB dimers and higher agglomerates reflected sensitively the layer charge density of the smectites. MB cations formed predominantly higher agglomerates at the surface of those smectites with high charge density. Suppressed dye agglomeration was observed for the samples of lower layer charge density and was caused by greater distances between the adsorbed MB cations. Due to the high sensitivity of MB agglomeration on the layer charge and the simplicity of the method, MB–clay interaction can potentially be utilized for the layer charge characterization of smectites.

A comparison of space-charge distributions in electron-beam irradiated FEP obtained by using heat-wave and pressure-pulse techniques

In the present paper, heat wave (LIMM) and pressure pulse (LIPP) measurements of the space-charge distributions in electron-beam irradiated Teflon FEP ( thick) are reported. The space-charge profiles obtained by the two methods are compared over the whole sample thickness. From the LIMM with the back surface heat sink, the space-charge distribution can be found from the surface of illumination up to at least half of the sample thickness. For the position of the bulk space charge, the heat wave and LIPP response results agree with each other to within . By using LIMM, an additional negative charge layer near the surface is found if the electron-beam irradiation is carried out through the metallized sample surface.

Slightly negative surface potential and charging model of insulator in the negative-ion implantation

In the negative-ion implantation into insulators, a slightly negative surface potential was obtained from the energy analysis of emitted electrons. Since emitted electrons offer an information of the surface potential, the surface potential was evaluated as an energy shift of the peak in the electron-energy distribution from the peak energy for a SiO 2 (40 nm)/Si without charging effect. From the obtained results of surface potentials of many kinds of insulators during C − implantation as a function of the ion energy from 5 keV to 35 keV, it was found that the surface potential had a slightly negative value in a range from −2 to −12 V, and that the negative surface potential had a linear dependence on the ion velocity. This negative surface potential of insulators could not be explained by the charging model adopted for isolated electrodes. Therefore, taking account of the true electron-emission yield more than unity and of a quite low mobility in insulators, we have proposed a charging model of an electric double layer formed as a negative-charge layer at the surface and a positive-charge layer below the surface. The relationship between the surface potential and the true electron-emission yield, or the surface barrier are discussed.

Structure of alkyl ammonium solutions in vermiculite clays

Swelling vermiculite clays are ideal systems in which to study confined aqueous and organic fluids. The clay platelets themselves are well characterised and carry a negative charge of around 0.1–0.2 C m–2. To balance this negative layer charge a variety of interlayer counterions can be exchanged into the clay pores. These counterions draw polar solvents, such as water, into the interlayer region, thereby forcing the clay platelets apart. We report on neutron diffraction studies of the hydration of vermiculites containing alkyl ammonium counterions. Owing to the subtle balance between hydrophobic and hydrophilic hydration these particular ions induce a fascinating variety of clay swelling behaviour. When the counterions are methyl or ethyl ammonium, vermiculites will only absorb a maximum of two layers of water. However, increasing the hydrophobic chain length can induce macroscopic colloidal swelling: in dilute aqueous solutions propyl and butyl ammonium vermiculties expand to form 1D colloidal gels, with layer spacings of up to 1000 A. Surprisingly perhaps, this macroscopic swelling is not observed with slightly longer chain alkyl ammonium counterions, such as pentyl or hexyl. We find that the layer spacing in the macroscopically swollen gels is inversely proportional to the root of the salt concentration in the solution, and that there is a temperature-induced phase transition, in which the gels collapse at high temperatures. In both methyl and butyl ammonium vermiculite the counterions are only loosely bound to the clay platelets, and do not behave as surfactants. In the absence of any strong interlayer structuring we therefore attribute the macroscopic swelling of propyl and butyl ammonium vermiculites to the ability of the hydrophobic chains to weaken the clay–counterions–clay Coulombic attraction, without forming a water repellent micelle-like interlayer region.

Confirmation of Aluminum Distribution in Thermally Grown Oxide of Silicon Wafers

The concentration depth profile of aluminum (Al) in the thermally-grown silicon (Si) dioxide ( SiO2) is investigated in detail using high resolution inductively coupled plasma mass spectroscopy. A conceptual model is proposed where the Al segregated at the very top of the SiO2 creates a negative charge layer by forming an (AlOSi)- network, and a small amount of Al residing in the SiO2–Si interface gives some possibilities of forming interface traps. This interpretation is based on the results reported here and on previous results obtained from ac surface photovoltage measurements.

Aluminium coordination and structural disorder in halloysite and kaolinite by 27Al NMR spectroscopy

AbstractIt has been suggested that interlayer water in halloysite is due to the presence of hydrated cations that balance the negative layer charge produced by Al for Si substitution. To find evidence of 4-coordinate Al (Al(IV)), we investigated six halloysites and two kaolinites using ‘high-field’ and ‘medium-field’ solid-state 27Al MAS NMR spectroscopy. We found Al(IV) in both kaolinite and five halloysite samples, but the contents are all &lt;1% and provide no basis for distinguishing between kaolinite and halloysite. Therefore, the presence of interlayer water in halloysite cannot be attributed to Al for Si substitution. There are, however, signals, tentatively assigned to A1(V), present in the kaolinite spectra but not in the halloysite spectra. The shapes of the low-frequency ‘tails’ of Al(VI) signals in medium-field NMR vary from sample to sample. We interpret this variation in terms of a ‘crystallinity index’. Disorder in kaolinite appears to be primarily the result of Al-vacancy displacements in the octahedral sheet. The NMR crystallinity indices correlate with those from IRS and DTA but not with those from XRD.

Horizontal Distribution of Electrical and Meteorological Conditions across the Stratiform Region of a Mesoscale Convective System

Five soundings of the electric field and thermodynamic properties were made in a mesoscale convective system (MCS) that occurred in Oklahoma and Texas on 2–3 June 1991. Airborne Doppler radar data were obtained from three passes through the stratiform echo. From these electrical, kinematical, and reflectivity measurements, a conceptual model of the electrical structure of an MCS is developed. Low-level reflectivity data from the storm's mature and dissipating stages show typical MCS characteristics. The leading convective region is convex forward, and the back edge of the stratiform echo is notched inward. The maximum areal extent of the low-level echo is about 250 km × 550 km, and the radar bright band is intense (reflectivity 45–50 dBZ) through an area of at least 50 km × 100 km. The reflectivity above the bright band is horizontally stratified with decreasing intensity and echo-top height toward the rear of the system. Analyses of the velocity data reveal a convective-line-relative flow structure of front-to-rear flow and mesoscale ascent aloft, and weak rear inflow and descent below about 5 km. The electric field soundings are similar over a period of 3 h and a horizontal scale of 100 km across the stratiform region, suggesting that the charge structure is nearly steady state and the charge regions are horizontally extensive and layered. The basic charge structure consists of four layers: a 1–3-km-deep region of positive charge (density ρ ≈ +0.2 nC m−3) between 6 and 10 km, negative charge (ρ ≈ −1.0–2.5 nC m−3) between 5 and 6 km, positive charge (ρ ≈ +1.0–3.0 nC m−3) near 0°C, and negative charge (ρ ≈ −0.5 nC m−3) near cloud base. The upper positive and densest negative charge layers could result from advection of charge from the convective region. The negative charge layer may be augmented by noninductive collisional charging in the stratiform region. The positive charge near 0°C is probably caused by one or more in situ charging mechanisms. The negative charge near cloud base is likely the result of screening layer formation. In addition to the basic four charge layers, positive charge is found below the cloud in each sounding, and in the two soundings closest to the convection (70–100 km distant) there is a low-density negative charge region near echo top.

Far-Infrared Study of the Interlayer Torsional-Vibrational Mode of Mixed-Layer Illite/Smectites

AbstractInvestigation of mixed-layer illite/smectites with far-infrared (FIR) spectroscopy indicates the presence of torsional mode absorption bands associated with interlayer fixed-K sites. By contrast, hydrated montmorillonitic interlayer cation sites are transparent in the far IR. The presence or absence of bands for interlayer cation sites appears to be related to both the magnitude and site of negative layer charge within the 2:1 layer structure. The bimodal nature of illite/smectite spectra leads to the suggestion that two different fixed-K environments occur within illite/smectite structures. These two environments are controlled by the composition of the octahedral sheet. The torsional modes at 112 and 89 cm-1 represent fixed-K sites influenced, respectively, by an Al-rich, high-charge dioctahedral layer and a heterogeneous Al-Fe-Mg-bearing, low-charge layer. A general trend of increasing absorption of the 112 cm-1 band, relative to the 89 cm-1 band, is observed in a typical diagenetic illite/smectite sequence of Miocene shales from the Gulf of Mexico sedimentary basin. The absorbance strength of both torsional bands is also seen to increase with increasing degree of illitization and the amount of fixed potassium in the illite/smectite. These observations are consistent with the concept of shales undergoing illitization during burial diagenesis by both the collapse of high-charge smectite layers to form illite layers (i.e., transformation) and the formation of new high-charge (-0.9) illite layers at the expense of smectite layers (i.e., dissolution/ neoformation).

Direct observation of space charge evolution in e-irradiated Kapton films

The pressure wave propagation method was applied to analyze in a vacuum the evolution of the space charge in electron-irradiated Kapton H films. The 125 mu m thick films were irradiated in a vacuum chamber with a monoenergetic electron beam in the 10 to 50 keV energy range. The method allows direct observation of the depth of penetration of electrons and first results on Kapton are presented. The space charge generated in the irradiated and nonirradiated regions was observed during and after the irradiation process. The space charge is influenced by electric field-assisted detrapping of incident electrons and their interaction with the lattice as they drift. Interfacial effects are indicated by the buildup of a negative charge layer at the metal-polymer interface.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>