Positive Electric Potential Research Articles

Environmental TEM Study of Electron Beam Induced Electrochemistry of Pr0.64Ca0.36MnO3 Catalysts for Oxygen Evolution

Environmental transmission electron microscopy (ETEM) studies offer great potential for gathering atomic scale information on the electronic state of electrodes in contact with reactants. It also poses big challenges due to the impact of the high energy electron beam. In this article, we present an ETEM study of a Pr0.64Ca0.36MnO3 (PCMO) thin film electrocatalyst for water splitting and oxygen evolution in contact with water vapor. We show by means of off-axis electron holography and electrostatic modeling that the electron beam gives rise to a positive electric sample potential due to secondary electron emission. The value of the electric potential depends on the primary electron flux, the sample’s electric conductivity and grounding, and gas properties. We present evidence that two observed electrochemical reactions are driven by a beam induced electrostatic potential of the order of a volt. The first reaction is an anodic oxidation of oxygen depleted amorphous PCMO which results in recrystallization of the oxide. The second reaction is oxygen evolution which can be detected by the oxidation of a silane additive and formation of SiO2–y at catalytically active surfaces. The quantification of beam induced potentials is an important step for future controlled electrochemical experiments in an ETEM.

Influence of the temperature of positive ions on the sheath formation and parameter space region in magnetized electronegative plasmas

Abstract The parameter space regions and the sheath formation in an electronegative discharge in the presence of thermal positive ions and oblique magnetic field are investigated. It is assumed that the negative species are in thermal equilibrium and the positive ions have a finite temperature. Three regimes of uniform, multilayer stratified and pure stratified are found as functions of positive and negative ion temperature, electronegativity and the magnetic field. The influence of positive ion temperature in the presence of magnetic field on the profiles of the positive ion density, positive ion velocity and electric potential are investigated. The positive ion flux at the sheath edge as a function of magnetic field is obtained for different collisionality and positive and negative ion temperatures. Finally, the influence of the magnetic field, collision frequency and the positive ion temperature on the parameter space regions are discussed.

Remote energetic neutral atom imaging of electric potential over a lunar magnetic anomaly

AbstractThe formation of electric potential over lunar magnetized regions is essential for understanding fundamental lunar science, for understanding the lunar environment, and for planning human exploration on the Moon. A large positive electric potential was predicted and detected from single point measurements. Here, we demonstrate a remote imaging technique of electric potential mapping at the lunar surface, making use of a new concept involving hydrogen neutral atoms derived from solar wind. We apply the technique to a lunar magnetized region using an existing dataset of the neutral atom energy spectrometer SARA/CENA on Chandrayaan‐1. Electrostatic potential larger than +135 V inside the Gerasimovic anomaly is confirmed. This structure is found spreading all over the magnetized region. The widely spread electric potential can influence the local plasma and dust environment near the magnetic anomaly.

The effect of electric fields on bacterial attachment to conductive surfaces

Bacterial adhesion has been studied in various conditions. The bactericidal effect of strong electric voltages has been mainly tested within the context of preventing device-related infections in hospital environments. Little evidence is found in the literature on the mechanism of bacterial deposition as a function of an applied electric field. In this study, we assumed that an electric field, which was applied perpendicularly to the flow of a bacterial suspension, might impact the electrostatic energy barrier between the negatively charged bacterial cell and the positively charged electrode substrate. Experiments were carried out with a QCM-D electro-chemical module which allowed monitoring the adhered mass as well as the dissipation factor, while a bacterial suspension was passed through the module in a diffusion dominated flow regime and while an electric field was applied perpendicularly to the flow of the suspension. A Pseudomonas fluorescens strain was used in order to detect and estimate any bacterial adhesion on the electrode surface. While the results confirmed that a decrease of the recorded resonance frequency was in direct proportion to the amount of adhered bacteria (estimated by a visual control of the bacterial signal on the electrode sensor at the end of each experiment), the change in the resonance frequency as a function of the applied electric potential was rather counter-intuitive: with negative potential the rate of bacterial adhesion was faster and steadier than with a positive electric potential, when the bacterial rate of adhesion tended to level off. Moreover, analyses of the measured dissipation to the measured frequency shifts (ΔD/Δf) during the deposition experiment, which indicate the fluidic character of the adhered layer of bacteria, revealed that with negative electric potential the bacterial cells were rigidly connected, while with positive electric potentials the cells were rather loosely bound to the electrode. The measured data suggested that the applied electric potential might have an impact on the conformation of the surface appendages on the bacterial cell surface of P. fluorescens, causing a state of steric repulsion with an extended conformation induced by positive electric potentials, and a state of entangled conformations induced by negative potentials, which allowed the cells to overcome the electrostatic energy barrier.

In situ study of hydrogen silsesquioxane dissolution rate in salty and electrochemical developers

In order to better characterize the development of the electron-beam resist hydrogen silsesquioxane (HSQ), the authors used a quartz crystal microbalance (QCM) to study its rate of dissolution in situ. The authors determined the effect of both salt concentration and applied electric potential on the development rate of HSQ. The development rates were measured by spinning HSQ directly onto a quartz crystal resonator, and then developing in a QCM microfluidic module. In order to more directly observe the effect of electric potentials on the HSQ development rate, a film of HSQ was partially cross-linked in an O2 plasma asher and then developed in the QCM flow module with a salt-free NaOH solution. As the partially cross-linked HSQ slowly developed, electric potentials were applied and removed from the crystal allowing the observation of how the development rate increased upon the application of a positive electric potential. The increased development rate caused by both the addition of salt ions and a positive electric potential suggests that the rate may be limited by a build-up of negative charge on the HSQ.

Debye-scale solitary structures measured in a beam-plasma laboratory experiment

Abstract. Solitary electrostatic pulses have been observed in numerous places of the magnetosphere such as the vicinity of reconnection current sheets, shocks or auroral current systems, and are often thought to be generated by energetic electron beams. We present results of a series of experiments conducted at the UCLA large plasma device (LAPD) where a suprathermal electron beam was injected parallel to a static magnetic field. Micro-probes with tips smaller than a Debye length enabled the detection of solitary pulses with positive electric potential and half-widths 4–25 Debye lengths (λDe), over a set of experiments with various beam energies, plasma densities and magnetic field strengths. The shape, scales and amplitudes of the structures are similar to those observed in space, and consistent with electron holes. The dependance of these properties on the experimental parameters is shown. The velocities of the solitary structures (1–3 background electron thermal velocities) are found to be much lower than the beam velocities, suggesting an excitation mechanism driven by parallel currents associated to the electron beam.

Hydroxamic Acids Analogous Against Breast Cancer Cells: 2D‐QSAR and 3D‐QSAR Studies

AbstractThe cytotoxicity of 19 N‐aryl‐substituted hydroxamic acids has been tested in vitro towards human breast cancer MCF–7 cell lines by MTT assay. The IC50 values were found to be in the range from 61.94 to 337.54 μM. A total of 18 out of 19 molecules had higher inhibitory activities than hydroxyurea against MCF–7 cell. Five compounds with IC50 values in micromolar range were 3‐ to 5‐folds more potent than hydroxyurea (IC50=307.15 μM). By partial least squares (PLS) regression, 2D‐QSAR model reported herein provide interesting insight in understanding hydrophobic, electronic, and structural requirements of antitumor activity among these set of the compounds. The cross‐validated Q2cum values for optimal PLS model of hydroxamic acids is above 0.638 (remarkably higher 0.50), indicating good predictive abilities for log 1/IC50 values of hydroxamic acids (HAs). The k‐nearest neighbor molecular field analysis (kNN‐MFA) approach was used to generate three‐dimensional quantitative structure‐activity relationship (3D‐QSAR) models for these sets of molecules. Statistically stepwise variable selection k‐nearest neighbor molecular field analysis (SW‐kNN‐MFA) model is comparatively better as compared to the other two (i.e. simulated annealing k‐nearest neighbor molecular field analysis, SA‐kNN‐MFA, and genetic algorithm k‐nearest neighbor molecular field analysis, GA‐kNN‐MFA) with respect to both the internal (q2=0.7461) as well as external (pred_r2=0.6107) model validation and correctly predicts activity of ca. 74.61% and ca. 61.07% for the training and test set, respectively. It uses one steric and one electrostatic fields along with its 3k nearest neighbor (k=3) to evaluate the activity of new molecules. The developed SW‐kNN‐MFA model field plot indicated that the positive steric and electric potential are favorable for the increase in the activity and hence more bulky substituent at 5‐position of phenyl ring connected at amide group and less electronegative substituent at 3‐position of phenyl ring connected to carboxyl group are favourable for the increase in the potency of the molecules.

Vector interaction, charge neutrality, and multiple chiral critical-point structures

We investigate the combined effect of the repulsive vector interaction and the positive electric chemical potential on the chiral phase transition by considering neutral color superconductivity. The chiral condensate, diquark condensate, and quark number densities are solved in both two-flavor and two-plus-one-flavor Nambu-Jona-Lasinio models with the so called Kobayashi-Maskawa-'t Hooft term under the charge-neutrality constraint. We demonstrate that multiple chiral critical-point structures always exist in the Nambu-Jona-Lasinio model within the self-consistent mean-field approximation, and that the number of chiral critical points can vary from zero to four, which is dependent on the magnitudes of vector interaction and the diquark coupling. The difference between the dynamical chemical potentials induced by vector interaction for u and d quarks can effectively reduce the Fermi sphere disparity between the two flavors of diquark pairing. Thus the vector interaction works to significantly suppress the unstable region associated with chromomagnetic instability in the phase of neutral asymmetric homogeneous color superconductivity.

Charging of an electrically insulated metallic target by high-energy neutrals

The feasibility of acquiring a positive charge by an insulated metallic target exposed to a high-energy neutral flux is demonstrated. Reasoning from interaction mechanisms between neutrals and a metallic target, the energy characteristics of the backscattered electrons are determined. Conditions under which an electrically insulated metallic target placed in a vacuum, plasma, or air becomes positively charged are considered. The positive electric potential of the target is estimated.

Prediction of domain nucleation and growth during polarization switching in ferroelectric thin films

A three-dimensional constitutive model for polarization switching in ferroelectric ceramics is presented and implemented into a finite element code. The developed code is applied to investigate the nucleation and growth of domains in a ferroelectric thin film. Initially the thin film is completely poled upward and its bottom electrode is grounded. Then a point on the top surface of the film is subjected to a constant positive electric potential for a certain period of time, leading to a polarization switching downward. The distribution of electric field is not homogeneous within the film and so neither the distribution of polarization. It is found that initially the switched zone is of a dagger shape but after the switched zone penetrates the film thickness it changes to the shape of a reversed cup with the lower part wider that the upper part. It is also observed that the width of switched zone increases with the period and magnitude of applied potential. The predictions are qualitatively compared with experimental observations.

New Application of Carbon Nanotubes. Field Emission of Electrons and Field Evaporation of C20 from Carbon Nanotubes.

Electron emission from various types of nanotubes, e.g., multiwall nanotubes (MWNTs) with capped and open ends, and single-wall nanotubes (SWNTs), was investigated by field emission microscopy (FEM). Field emission patterns originating from the pentagons placed on a cap of a nanotube were observed for the capped MWNTs with clean surfaces. Emission current versus voltage characteristics revealed that open MWNTs possess the most excellent properties as field emitters among the nanotubes investigated. As an application of nanotube field emitters, field emission displays (FED) equipped with nanotube cathodes are now attracting considerable attention. Fabrication and performance of nanotube-based FED elements are also reviewed briefly. When a positive electric potential, being an opposite potential to the case of electron emission, was applied to nanotubes, carbon clusters were directly emitted from nanotubes through field evaporation. We found that C20+ were selectively emitted from both MWNTs and SWNTs under an extremely high field over 10 V/nm.

Ion trajectories in atom probe field ion microscopy and gas field ion sources

Trajectories of positive ions produced in a region close to a structured surface, modelled by spherical or spheroidal protrusions and kept at a positive electric potential with respect to a distant screen or detector are calculated. The results are discussed in comparison with similar practical situations produced by field ionization and field evaporation or desorption, such as those occurring in gas field ion sources, field ion microscopy and field desorption spectroscopy.

Electrochemically induced surface changes on microstructured Pt films on a Solid YSZ electrolyte

AbstractThin (500 Å) microstructured Pt films on single crystalline yttrium stabilized zirconia (YSZ) prepared by photolithography have been used to study the processes at the interface between the solid electrolyte and the Pt film when electrical potentials are applied. The experiments are performed under UHV conditions with a standard three‐electrode set‐up employing photoemission electron microscopy (PEEM) as spatially resolving method. Upon electrochemical “pumping” of oxygen by applying a positive electric potential to the Pt film we observe in PEEM a darkening of the Pt film reflecting a work function (WF) increase; a negative potential leads to a WF decrease. No time‐dependent spatial concentration profiles which would have been indicative of the slow diffusional spreading of a spillover species were observed.

Improved Physics Model for the Gasdynamic Mirror Fusion Propulsion System

The propulsion capability of the gasdynamic mirror (GDM) fusion propulsion device was examined in several previous publications without taking into account the electrostatic potential inherent to plasma cone nement in this system. This potential arises as a result of the initial rapid escape of the electrons through the mirrors because of the smallness of their mass. The remaining excess positive charge gives rise to a positive electric potential that slows down the electrons while speeding up the ions until equalization in their axial diffusion is achieved. In a thruster, the energy of the ions emerging from the magnetic nozzle will therefore be enhanced relative to their energy as they leave the mirror by an amount equal to that of the potential. In typical GDM parameters, this effect can translate into signie cant increases in the specie c impulse and thrust produced by the system. Nomenclature Ac = area of plasma core A0 = mirror area D = axial diffusion coefe cient E = electric e eld Ee = electron energy EL = escape energy e = electron charge erf = error function k = gradient scale length L = length of plasma <n l = coulomb logarithm m = particle mass N = particle density n = monoenergetic particle density R = plasma mirror ratio T = temperature V = plasma volume v = monoenergetic particle velocity vth = thermal velocity x = parameter, Eq. (26) z = charge number G = velocity-averaged particle e ux g = monenergetic e ux d = parameter, Eq. (25) m = mobility t = cone nement time y = collision frequency f = electrostatic potential

A novel antiporter activity catalyzing sodium and potassium transport from right-side-out vesicles of E. coli

Downhill sodium efflux from right-side-out E. coli membrane vesicles was found to be stimulated by negative electric potential, as has been reported earlier [Bassilana et al., Biochemistry 23 (1984) 1015–1022], and in agreement with the concept of electrogenic Na +/ nH + antiporters with n > 1. However, sodium efflux was much more accelerated by positive electric potential, indicating the operation of another sodium transport system. ΔpH (alkaline inside), created by a pH shift from 8.5 to 6.8 in the medium was found to drive sodium efflux against its concentration gradient, but only when the vesicles had been loaded with both Na + and K +. Efflux of K + against the concentration gradient was also observed under these conditions. When the vesicles were loaded separately with sodium tricine or potassium tricine, no K + efflux and insignificant Na + efflux were observed. We propose that there are at least two different mechanisms responsible for Na + efflux in E. coli vesicles. One is the Na +/ nH + antiporter previously described, and the other is a novel Na +,K +/ mH + antiporter.

Removal of the plasma contained in an atomic beam produced by electron beam heating

Removal of the plasma contained in a gadolinium atomic beam produced by electron beam heating was investigated. A positive or negative electric potential was applied to the plasma removal electrodes which were a pair of parallel electrodes put along the atomic beam. When a positive potential was applied to the plasma removal electrodes, the plasma could not be removed at high evaporation rates. On the other hand, the plasma could be removed by applying a high negative potential to both removal electrodes, even at high evaporation rates. The potentials applied to the electrodes required to remove the plasma were estimated using the model that a plasma at ground potential flows with the atomic beam; ions are extracted from the plasma by negatively biased removal electrodes. The estimated potentials required to remove the plasma agreed well with experimental values.

Effect of fluorochrome location in protein A on sensing efficiency of IgG

Fragment B of protein A conjugated with fluorescein at various lysine residues is prepared and separated by using a DEAE column in anion-exchange chromatography. The binding of IgG Fc to fragment B contributes to an additional positive electric potential around fragment B. The change in the local electrostatic environment and pH can then be specifically monitored by measuring the fluorescence intensity of fluorescein conjugated with fragment B before and after the introduction of IgG. The studies for the quantitative dependence of fluorescein location on the effectiveness of fluorescein for sensing the protein A-IgG reaction are presented and discussed.

負イオンを含む多成分プラズマ中の非線形イオン音波

Propagation of nonlinear ion-acoustic waves in a three-component plasma which consists of electrons and positive and negative ions have been investigated theoretically and experimentally. The Korteweg-de Vries (K-dV) equation is obtained by the reductive perturbation of the plasma taking the ion temperature into consideration. The dispersion term of the K-dV equation is positive for the concentration r of the negative ion considered here. On the other hand, the coefficient of the nonlinear term becomes negative at a critical concentration rc which depends on the mass ratio of the negative to positive ions and the temperature ratio of electrons to ions. Therefore, positive (electric potential), compressive (positive ion and electron density) solitons can exist when 0 rc. When r=rc, the nonlinear term in the K-dV equation disappear so that a higher-order term should be considered, which results in the modified K-dV equation. The modified K-dV equation has also soliton solutions which are irrespective of the sign, i.e., both positive and negative solitons coexist. The K-dV and the modified equations are obtained under the assumption that the amplitude is small. When the amplitude is large, original fluid equations are integrated numerically. The result is that when rc<r<rm, positive solitary waves exist if the amplitude is larger than a threshold. Experiments were carried out in a multi-dipole double-plasma device. The inner diameter of the device is 40cm and its total length is 90cm. The device is separated into a driver and a target section with an electrically floating mesh grid. The chamber was evacuated to 1×10-6Torr with a turbo-molecular pump. Argon and sulfur hexafluoride were introduced into the chamber under continuous pumping. Plasma parameters measured with a probe and a retarding energy analyzer were the electron density=108-109cm-3, the electron temperature=0.6-1eV and the ion temperature=0.05-0.1eV. Experimental results are compared with the theoretical results described above.

Hydrolysis of lecithin by phospholipase D at the surface of the mixed micelles

Hydrolysis of lecithin by phospholipase D at the surface of mixed micelles composed of L-α-dipalmitoyl phosphatidylcholine (DPPC) or dimyristoyl phosphatidylcholine (DMPC) and hepta-ethyleneglycol dodecylether (C 12E 7) and/or cetyltrimethylammonium chloride (CTAC) was investigated. The enzymatic reaction was analyzed by the decrease in fluorescence intensity of 8-anilino-1-naphthalenesulfonate (ANS) added to the solution. The rate constant, k, was determined from the gradient of the logarithm of the residual fraction of lecithin, α, against time, t. A break point was observed in the relation of ln α and t. The mole fraction of lecithin at the break point was independent of its initial value, X 0 PC, in mixed micelles. The rate constant decreased with increased positive electric potential at the surface of mixed micelles. On the basis of these results, the interaction between phospholipase D and mixed micelles at the interface, the difference in reactivity due to the variation of lecithin in mixed micelles, and the effect of positive electric potential at the surface of mixed micelles are discussed.

Address of the President Sir Andrew Huxley at the Anniversary Meeting, 30 November 1981

The Copley Medal is awarded to Dr P. D. Mitchell, F. R. S., in recognition of his formulation and development of the chemiosmotic hypothesis that energy released through the oxidation of food or the capture of photons is conserved in a gradient of protons before being used in the synthesis of adenosine triphosphate. It has long been known that the oxidation of food materials takes place in subcellular organelles known as mitochondria and that these oxidations are somehow coupled to the synthesis of adenosine triphosphate (ATP) from adenosine diphosphate and free phosphate ions, ATP being the ‘fuel’ for almost all the activities – synthetic, contractile, secretory etc. – of the cell. It was generally assumed that all the steps leading to ATP synthesis were straightforward chemical reactions, but despite prolonged effort by biochemists the intermediate chemical events were not identified. Mitchell proposed that a key step was the storage of energy from the oxidations in a physico-chemical rather than a purely chemical form and that the event directly driven by the oxidations was the movement of hydrogen ions across an insulating mitochondrial membrane to create both a positive electric potential and an excess concentration of hydrogen ions on one side of the membrane. The synthesis of ATP is then driven by hydrogen ions moving down this electrochemical gradient, through appropriate enzymes inserted in the membrane.