Strong Electrostatic Field Research Articles

Modelling and simulation of electrostatic potential distribution in polyelectrolyte gels

The electrostatic potential energy distribution of polyelectrolyte gels has been modelled and simulated on the basis of Poisson-Boltzmann equation. The simulation was carried out with a three dimensional network model. The simulation reveals that there exist deep electrostatic potential wells at every crosslinking point and potential valleys around the polymer chains. The simulation results also indicated that a strong electrostatic field exists near the polymer chains especially around the crosslinking points. Various abnormal phenomena observed in the polymer gel, such as the presence of non-frozen water, higher electroconductivity at low temperature, electrocontractile behavior, etc., are considered to be associated with the presence of this strong electric field.

Influence of Electrostatic Field on Excess Conductivity of Thin YBaCuO Films

AbstractThe influence of a strong electrostatic field perpendicular to the electric current on the excess conductivity of YBa2Cu3O7−y thin films near Tco (R = 0) and also in those with weak links is investigated by modelling with an Arrhenius‐type law. One film with weak links is treated by Aslamazov‐Larkin formulas, too. It is shown that the excess or paraconductivity depends on the polarity and strength of the electric field and this dependence may be explained as a change of the dimension of fluctuation conductivity with the increase of the hole concentration.

Plasma-beam interaction in a wiggler.

The possibility of obtaining self-bunching of the beam, emission of coherent radiation and strong electrostatic fields in a plasma loaded free electron laser, is studied by means of a set of nonlinear self-consistent equations deduced from the Maxwell equations, the fluid plasma model, and the relativistic equations of motion for the electrons of the beam in the limit of plasma density much larger than the beam density.

Interpretation of the polarization infrared spectrum of CO2 monolayers adsorbed on ionic substrates

We interpret the polarization infrared spectrum of linear molecules adsorbed on ionic substrates on the basis of semi-classical interaction potentials. The frequency shifts and splittings and the intensities of the infrared signals are analyzed in terms of strong electrostatic surface fields with the additional influence of the lateral coupling between admolecules. Application to the CO2 monolayer adsorbed on clean NaCl and MgO(100) surfaces is discussed. A consistent quantitative comparison between calculated and measured peak intensities of the polarization spectrum requires the presence of two types of domains for the layer, oriented along the perpendicular step directions 〈100〉 and 〈010〉 with a relative weight 1:4. This corroborates the experimental assignment of the parallel and perpendicular polarized peaks associated with the bending and asymmetric stretching vibrational modes of the admolecule.

New experimental setup devoted to the Auger electron–ion coincidence spectroscopy

Taking advantage of the pulsed character of the synchrotron-radiation light, an original experimental setup combining an electron analyzer with a time-of-flight mass spectrometer without angular discrimination, operated with a strong pulsed electrostatic field, has been developed. This allows high counting rates for multiple coincidence measurements Auger electron photoion photoion coincidences. The focus is on the experimental setup; new results obtained with core exited N2O are shown and it is demonstrated how to get more insight into the relaxation dynamics by the selection of the excited state combined with the selection of the final state.

Clusters embedded in jellium: an effective method for the calculation of surface properties in strong electrostatic fields

We present a new method, clusters embedded in jellium, for the effective calculation of surface properties of metals in strong electrostatic fields. As examples we look at aluminum adsorption on an Al surface and at lithium adsorption on a Li surface.

Dc field-induced optical second harmonic generation from metal-electrolyte interfaces

Metal—electrolyte interfaces are associated with a strong (∼ 10 8 V m −1) electrostatic field. When such an interface is studied with second harmonic generation, this field can complicate the optical data by introducing a thrid-order electronic response of the metal. A theoretical framework is presented here for analyzing these dc field-affected second harmonic results for polycrystalline metal electrodes. The macroscopic features of the surface nonlinear polarization are analyzed. It is also shown explicitly that the dc field does not alter the characteristic polarization and angular dependencies of surface second harmonic generation.

The “back door” hypothesis for product clearance in acetylcholinesterase challenged by site-directed mutagenesis.

The active site of acetylcholinesterase is near the bottom of a long and narrow gorge. The dimensions of the gorge and the strong electrostatic field generated by the enzyme appear inconsistent with the enzyme's high turnover rate. Consequently, a "back door" mechanism involving movement of the reaction products through a transient opening near the active center was recently suggested. We investigated this hypothesis in human acetylcholinesterase by testing mutants at key residues (Glu-84, Trp-86, Asp-131, and Val-132) located near or along the putative back door channel. The turnover rates of all mutants tested, and in particular of V132K, where the channel is expected to be sealed by salt bridge Lys-132-Glu-452, are similar to that of the wild type enzyme. This indicates that the proposed back door is not a route for product clearance from the active site gorge of acetylcholinesterase and is probably of no functional relevance to its catalytic activity.

Electrostatic Effect on the Hydration Layer of Colloidal Silica Particles

The hydrodynamic radii of colloidal silica particles in the aqueous solutions were measured under various conditions of pH and salt concentration by means of the dynamic light scattering technique. In the salt free solutions the observed hydrodynamic radius increased by 1 nm from 13 nm at pH below 8 to 14 nm at pH above 9 according to the ionization of silanol groups. At pH above 9, the radius decreased from 14 nm in salt free solutions to 13 nm at the salt concentration of 10 -2 M. These results suggest that the strong electrostatic electric field makes the hydration layer on the surface of a silica particle thicker.

Electrostatic Properties of Two Porin Channels from Escherichia coli

The electrostatic interactions in the channels of OmpF and PhoE porins from Escherichia coli were analysed on the basis of a macroscopic multi-dielectric model of the protein-membrane complex derived from the respective porin X-ray structures. The membrane was represented as layers of distinct dielectric constants corresponding to the aliphatic core and the polar head groups of the lipids. The p K a values of the titratable groups and the electrostatic field in the region of the channel were calculated by the finite difference technique. In spite of the differences in sequences and charge constellations, the calculated electrostatic properties of the two porins are similar in several aspects: (1) unusual titration behaviour (p K a below 7) was found for some groups of the cluster of basic residues at the constriction of the pore; (2) a number of acidic groups buried between the internal loop and the barrel wall are stabilized in their protonated forms at neutral pH; (3) there is a strong transverse electrostatic field in the channel characterized by a screw-like form. The strength of the field is greatest at the region of the constriction zone. This would facilitate the diffusion of solutes with a large dipole moment such as free amino acids. Differences between the electrostatic fields of OmpF and PhoE are mainly confined to that end of the pore that faces the cell exterior in vivo. In OmpF the electrostatic potential is close to zero in this region of the channel, whereas a positive potential was found in PhoE. It was shown that the experimentally observed difference in ion selectivity of the two porins can largely be attributed to this distinct electrostatic property.

Behavior of Microscopic Liquid Droplets near A Strong Electrostatic Field: Droplet Electrospray

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTBehavior of Microscopic Liquid Droplets near A Strong Electrostatic Field: Droplet ElectrosprayD. B. Hager and N. J. DovichiCite this: Anal. Chem. 1994, 66, 9, 1593–1594Publication Date (Print):April 1, 1994Publication History Published online1 May 2002Published inissue 1 April 1994https://doi.org/10.1021/ac00081a040RIGHTS & PERMISSIONSArticle Views413Altmetric-Citations29LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (927 KB) Get e-Alerts Get e-Alerts

Open "Back Door" in a Molecular Dynamics Simulation of Acetylcholinesterase

The enzyme acetylcholinesterase generates a strong electrostatic field that can attract the cationic substrate acetylcholine to the active site. However, the long and narrow active site gorge seems inconsistent with the enzyme's high catalytic rate. A molecular dynamics simulation of acetylcholinesterase in water reveals the transient opening of a short channel, large enough to pass a water molecule, through a thin wall of the active site near tryptophan-84. This simulation suggests that substrate, products, or solvent could move through this "back door," in addition to the entrance revealed by the crystallographic structure. Electrostatic calculations show a strong field at the back door, oriented to attract the substrate and the reaction product choline and to repel the other reaction product, acetate. Analysis of the open back door conformation suggests a mutation that could seal the back door and thus test the hypothesis that thermal motion of this enzyme may open multiple routes of access to its active site.

Effects of Altervalent Cation Doping of TiO 2 on Kinetic Parameters of CO Hydrogenation and CO Oxidation on Supported Rh

The reactions of CO hydrogenation and CO oxidation over Rh are used to determine the influence of altervalent cation doping of a TiO 2 support on kinetic parameters. Rh crystallites are dispersed on TiO 2 doped with W 6+ cations at concentration levels up to 0.67 at%. It is shown that turnover frequencies of CO hydrogenation increase monotonically with increasing dopant content in the TiO 2 matrix, apparent activation energy is reduced, and selectivity shifts towards smaller-chain saturated hydrocarbons. Turnover frequencies of CO oxidation at low CO/O 2 ratios are shown to pass through a maximum with increasing W 6+ dopant content of TiO 2. A small activity enhancement is observed at higher CO pressures. The apparent activation energy is found to vary with W 6+ content. It is proposed that charge transferred from the doped semiconducting carrier to the metal crystallites alters the chemical potential of the crystallites and, therefore, the work function of surface metal atoms, while a strong electrostatic field is caused by the dipole developed at the metal-semiconductor interface. As a result, the mode of H 2 and CO adsorption is altered, as well as the intrinsic kinetic parameters of the reactions investigated.

Critical currents in oxygen-implanted YBa 2Cu 3O 7− σ thin films under magnetic and electrostatic fields

The strong negative electrostatic field applied to the surface of a high- T c superconducting YBa 2Cu 3O 7− σ thin film has been found to increase the transport critical current density ( J c) in the vicinity of T c. Ion implantation of oxygen increases J c but, after implantation, a decrease of the critical current under the influence of an electric field has been observed. The effect of the electric field on J c is explained by the modulation of superconducting properties of the polycrystalline film surface.

Excess conductivity and thermally activated dissipation studies under strong electrostatic field in YBa 2Cu 3O 7−δ thin films

Negative electrostatic field of 5 × 10 5 V cm -1 applied to the surface of YBa 2Cu 3O 7− δ thin film is found to decrease both the amplitude of fluctuation enhanced excess conductivity and the value of the pre-exponential factor in the Arrhenius law describing the dissipation near the zero-resistance state. Implantation with oxygen ions results in an increase of the activation energy U 0 and reduces the field-induced effects.

Seed cone evolution on positively charged Cu targets: Preliminary study by high-resolution electron microscopy

The electrostatic effect on the seed cone evolution at Ar+-bombarded Cu(111) surfaces was investigated by means of high-resolution transmission electron microscopy. A simultaneous supply of Mo seeds to the target biased at positive 100–150 V was found to induce an oriented growth of nanometer thick Mo layers on the cone slopes receiving high seed fluxes. In the seed layers thus grown, Mo atoms were so arranged that Mo〈100〉 was parallel with the ion-incidence direction, suggesting that depositing Mo atoms were forcibly stacked very close to one another along the ion beam, by a strong electrostatic field generated at the growth front of seed layer. Evidence is also presented that the seed layers were grown via a particle supply process of Kossel type.

Effect of Strong Electrostatic Fields on the Properties of Y1−xPrxBa2Cu3O7-Δ Ceramics

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High-intensity electrostatic-field exposure system for cultured biological cells.

We describe a new system for exposing cultured biological cells that have been plated on coverslips to strong electrostatic fields at magnitudes greater than 10(3) V/cm. Techniques are described that make use of mineral oil to render insignificant electrical conduction currents (total leakage current is less than 1.0 nA or less than 0.1 nA/coverslip), joule heating (less than 10(-6) W), or current-induced magnetic fields (less than 10(-13) T) in regions inhabited by cells. The mineral oil also eliminates a reduction in the strength of the applied field, which otherwise can occur from increased electrode-to-medium impedance at the site of application. Thus the applied field is reliably specified in the vicinity of a cell membrane. Control and electrostatic field chambers are housed in a grounded metal incubator. Cylindrical mu-metal shields can be used to reduce background magnetic fields in each chamber from 40 microT static and approximately 1 microT ac to, respectively, less than 3 microT static and approximately 100 nT ac. Contamination of cells by impurity atoms that may leach from electrodes was measured by atomic-absorption spectrophotometry and found to be negligible. Stray magnetic- and electric-field components within the incubator were measured, as were background fields around the laboratory.

High-field transport in semiconductors. I. Absence of the intra-collisional-field effect.

We show that the Levinson (Zh. Eksp. Teor. Fiz. 57, 660 (1969) [Sov. Phys.---JETP 30, 362 (1970)]) quantum transport equation reduces to the semiclassical Boltzmann equation in the limit of a strong homogeneous electrostatic field. To arrive at this conclusion we use a saddle-point approximation which has not been used in this field before. This approximation is exact in the high-field limit. We show that even for a relatively moderate field strength of 3\ifmmode\times\else\texttimes\fi{}${10}^{5}$ V/m in GaAs (even before the onset of the Gunn effect, when 90% of the electrons are still in the central valley) the saddle-point approximation can be used for a majority of the scattering events. The results in this paper are supported by numerical calculations based on realistic scattering mechanisms in GaAs.

Resonance-state calculation applying the Weyl-Titchmarsh theory: Application for the quantum-confined Stark effects on excitons in a GaAs-AlxGa1-xAs quantum well.

Strong electrostatic field effects on the resonance states of the quantum-confined electron, heavy hole, and light hole in a quantum well are investigated by a continuous-spectrum approach based on Weyl-Titchmarsh theory. The field-ionization mechanism by numerically calculated tunneling and radiative recombination lifetimes of various excitons in several resonance energy states is discussed. The crossover of the tunneling lifetime between the ground-state electron and the first-excited-state heavy hole occurs for fields of more than 100 kV/cm.