Parametric excitation of surface waves at the boundary between a magnetized plasma and a metal

A study is made of the parametric excitation of potential surface waves propagating in a planar plasma-metal waveguide structure in a magnetic field perpendicular to the plasma-metal boundary. An external, spatially uniform, alternating electric field at the second harmonic of the excited wave is used as the source of parametric excitation. A set of equations is derived that describes the excitation of surface waves due to the onset of decay instability. Expressions for the growth rates in the linear stage of instability are obtained, and the threshold amplitudes of the external electric field above which the parametric instability can occur are found. Analytic expressions for the saturation amplitudes are derived with allowance for the self-interaction of each of the excited waves and the interaction between them. The effect of the plasma parameters and the strength of the external magnetic field on the saturation amplitude, growth rates, and the threshold amplitudes of the pump electric field are analyzed.     

Membrane electropermeabilization effects of frequency and membrane surface order on liposome leakage

Liposomes containing fluorescence marker were exposed to an alternating electric field of 80 V peak to peak square electric waves at different frequencies 0.01, 1, and 100 kHz to perturb the liposome permeation. The efflux of fluorescence dye after application of the electric field was measured by recording the fluorescence emission due to the complex formation reaction between the fluorescence dye and calcium ions in the bulk medium solution. Two independent sets of experiments were conducted: 1) calcium ions were present during electropulsation; and 2) they were added after electric field application. Two parameters, fluorescence emission intensity and increment of temperature of the solution in the chamber, were studied. The effect of membrane surface order on the fluorescence dye leakage from the liposomes was studied by addition of urea at threshold concentration before the liposomes sealed. The data demonstrate the existence of frequency dependency window at 1 kHz. Furthermore, the data were interpreted according to the theory of interactions of electromagnetic fields with highly polarized and deformed materials such as liposome particles. The urea caused an enhancement of the fluorescence dye leakage at frequency of 100 kHz. This effect could be explained as a decrease of the membrane binding rigidity due to the disordering effect of urea on the membrane lipid surface. Our conclusion is that the frequency and the membrane surface order are additional parameters that influence the processes of membrane electropermeabilization.     

Microbial denitrification by immobilized bacteria Pseudomonas denitrificans stimulated by constant electric field

A comparative study of microbial reduction of nitrate ions by immobilized Pseudomonas denitrificans cells in the presence and in the absence of a constant electric field was carried out. The experiments were carried out in a continuous stirred tank reactor at a broad range of dilution rates. The cathode potential was maintained constant around the standard potential value of the nitrate/nitrite redox couple. The residual outlet concentrations of nitrate, when the electric field was applied, were much lower than those obtained without the electric field, all other conditions being equal. It was demonstrated that the electric field had a significant effect on the nitrate reduction rate allowing the use of much higher inlet flow rates compared to the flow rate in the absence of an electric field.     

Microbial activities and foliar uptake of nitrogen in the epiphytic bromeliad Vriesea gigantea

In contrast to terrestrial plants, epiphytic tank bromeliads take up nutrients mainly over their tank leaf surface. The form in which nutrients are available in the tanks is determined by the source and the complex interplay between tank microbes, which transform them and the epiphytes that take them up. To elucidate the importance of different nitrogenous compounds for the nitrogen (N) nutrition of Vriesea gigantea from the Atlantic Rainforest, Brazil, N transformation processes in tank water as well as foliar uptake rates were estimated by 15N labelling techniques. Microorganisms actively transformed N compounds in the tank. Specifically, organic N compounds were rapidly mineralized to NH4+, while nitrification was negligible. Plants took up both organic and inorganic N forms, with a clear preference for NH4+. NH4+ comprised the largest and, because of fast mineralization rates, the most constant dissolved N pool in the tank water. Excretion of ureases by the plants together with an unusual uptake kinetic for urea also suggests that urea may be potentially important as an N source.     

The effect of psychoemotional load on ventricular repolarization reflected in integral body surface potential maps

The aim of the present study was to investigate the reflection of psychoemotional stress in the body surface potential distribution as documented by isointegral maps of cardiac activation and recovery. In 72 young men (18.3+/- 7.3 y.) with no cardiovascular history body surface potential maps (BSPMs) at rest and during the test of mental arithmetic were recorded. The digitalized data for each point of the QRS, STT and QRST integral maps, for each subject in both situations, were processed and evaluated by methods of univariate as well as spatial mathematical and statistical modeling. The results showed during MA a significant decrease of repolarization integral values over the sternum and right precordium, which contributed to analogically localized decrements also in the QRST BSM. The decrease occurred in more than 2/3 of lead points. The most pronounced changes were observed in the right precordial area, where potentials decreased in more than in 70 % of subjects. In conclusion, the discriminative power of the difference STT and QRST integral maps was strong enough to distinguish the mental arithmetic induced changes in the superficial cardiac electric field. These adrenergic transient alterations in ventricular recovery may be of importance in subjects at risk for ventricular arrhythmias.     

Experimental Measurement of Monovalent Cation Adsorption onto Bacillus subtilis Cells

Typically, the effects of ionic strength on metal adsorption to geosorbents are accounted for by models of the surface electric field, assuming a planar surface. However, bacterial cell walls are not two-dimensional surfaces. Furthermore, electric field model parameters for complex systems are difficult to determine and apply. We propose an alternative approach to electric field models of ionic strength effects by explicitly accounting for monovalent cation adsorption onto specific bacterial binding sites. We calculate stability constants for monovalent metal-bacterial surface complexes, and use them to determine the magnitude of correction needed for a previously determined stability constant for a Cd-bacterial surface complex.     

Effect of Geometric Parameters on the Performance of P-Type Junctionless Lateral Gate Transistors

This paper examines the impact of two important geometrical parameters, namely the thickness and source/drain extensions on the performance of low doped p-type double lateral gate junctionless transistors (DGJLTs). The three dimensional Technology Computer-Aided Design simulation is implemented to calculate the characteristics of the devices with different thickness and source/drain extension and based on that, the parameters such as threshold voltage, transconductance and resistance in saturation region are analyzed. In addition, simulation results provide a physical explanation for the variation of device characteristics given by the variation of geometric parameters, mainly based on investigation of the electric field components and the carries density variation. It is shown that, the variation of the carrier density is the main factor which affects the characteristics of the device when the device''s thickness is varied. However, the electric field is mainly responsible for variation of the characteristics when the source/drain extension is changed.     

A data-driven model of the generation of human EEG based on a spatially distributed stochastic wave equation

We discuss a model for the dynamics of the primary current density vector field within the grey matter of human brain. The model is based on a linear damped wave equation, driven by a stochastic term. By employing a realistically shaped average brain model and an estimate of the matrix which maps the primary currents distributed over grey matter to the electric potentials at the surface of the head, the model can be put into relation with recordings of the electroencephalogram (EEG). Through this step it becomes possible to employ EEG recordings for the purpose of estimating the primary current density vector field, i.e. finding a solution of the inverse problem of EEG generation. As a technique for inferring the unobserved high-dimensional primary current density field from EEG data of much lower dimension, a linear state space modelling approach is suggested, based on a generalisation of Kalman filtering, in combination with maximum-likelihood parameter estimation. The resulting algorithm for estimating dynamical solutions of the EEG inverse problem is applied to the task of localising the source of an epileptic spike from a clinical EEG data set; for comparison, we apply to the same task also a non-dynamical standard algorithm.     

Electroporation of the photosynthetic membrane: A study by intrinsic and external optical probes

The study examines the relationship between electric field-induced conductivity and permeability changes in a biological membrane (electroporation) and the amplitude-duration parameters of the externally applied electric field. These reversible changes were characterized in giant photosynthetic membrane vesicles by means of the calibrated response of an intrinsic voltage-sensitive optical probe (electrophotoluminescence) and by the uptake studies of dextran-FITC fluorescent probes of different molecular weights. We quantitatively monitored electric field-induced conductivity changes by translating the electrophotoluminescence changes into conductivity changes. This was carried out by measuring the attenuation of the electrophotoluminescent signal after the addition of known amounts of gramicidin. The results demonstrate that electroporation involves the reversible formation of discrete holes in the membrane having radii <5.8 nm. The total area of the electric field-induced holes was 0.075% of the total surface of the vesicle. The formation of the electropores was affected differently by the electric field strength than by its duration. Increase in electric field strength caused increase in the total area of the vesicle that undergoes electroporation. Increase in the duration of the electric field increases the area of single electropores. Each of the two electric parameters can be rate limiting for the dynamics of electropore formation. These results are in accordance with the model of electroporation based on electric field-induced expansion of transient aqueous holes.     

Self-consistent model of a pulsed air discharge excited by surface waves

A complete self-consistent electrodynamic model of a pulsed gas discharge excited by surface waves is developed. The model allows one to calculate both the initial phase of the discharge front propagation and the parameters of the produced plasma. The spatiotemporal evolution of the electromagnetic field and plasma parameters at the discharge front is investigated for the first time. It is shown that discharge propagation is mainly governed by a breakdown wave in an inhomogeneous electric field at the leading edge of the ionization front. It is found that the effect of the electric field enhancement in the plasma resonance region significantly affects the velocity of the breakdown wave. The results of calculations agree well with experimental data.     

Transient electric birefringence of colloidal particles immersed in shear flow. Part II. The initial response under the action of a rectangular electric pulse and the behavior at a low alternating electric field

The time-dependent rotational diffusion equation for rigid macromolecules in solution has been approximately solved for two cases in order to extend the electric birefringence technique to streaming-electric birefringence. One is for the initial period through the application of a rectangular electric pulse to the solution immersed in a low shear flow. The purpose of this is expansion of the distribution function into a function series made by the product of the powers of reduced time (= Thetat) and hydrodynamic field alpha (= G Theta , G: velocity gradient, Theta: rotary diffusion constant) and a surface harmonic P(i)(j)cos jphi. The solution for the build-up process at arbitrary electric field strength is found, but is limited to low hydrodynamic fields. The other is for the response when an alternating electric field is applied to the solution in a shear flow. Here, instead of reduced time, the maximum electric field E(0) is chosen as a parameter for the expansion. The expressions for the intensity of the transmitted light through crossed Nicols are derived in two optical systems where the polarizer is set at an angle of 45 degrees and 0 degrees to the direction of the electric field. The results in the former case show that we can determine four parameters, the ratio of velocity gradient to rotary diffusion constant, the axial ratio of a particle, the anisotropy of electric polarizability, and the optical anisotropy factor, from four values observed in two optical systems, namely, two light intensities before applying an electric field and two initial slopes of the build-up after applying an electric field. On the other hand, when a low alternating electric field with extremely high frequency is applied, the build-up of the light intensity in the former case is the same as that of electric birefringence for pure induced dipole orientation. The build-up for the latter optical system is the same as the expression for pure induced dipole orientation of Eq. (38) shown in a previous work.     

The nature of sources of bioelectric and biomagnetic fields.

The goal of this paper is to examine the origins and relative importance of primary and secondary sources of electric and magnetic fields for excitable tissue. It is shown that for axonal and cardiac tissue a comparison of the relative field strength from both primary and secondary sources shows only the latter to be significant. Even if the divergence and curl of the primary source were independent (and hence were both needed to define the primary source), because the secondary sources all arise from the divergence of the primary source the magnetic field reflects the same source component as the electric field. As a consequence magnetic and electric fields arising from active tissue are strongly linked.     

Confinement and manipulation of actin filaments by electric fields

When an AC electric field was applied across a small gap between two metal electrodes elevated above a surface, rhodamine-phalloidin-labeled actin filaments were attracted to the gap and became suspended between the two electrodes. The variance of each filament's horizontal, lateral displacement was measured as a function of electric field intensity and position along the filament. markedly decreased as the electric field intensity increased. Hypothesizing that the electric field induces tension in the filament, we estimated the tension using a linear, Brownian dynamic model. Our experimental method provides a novel means for trapping and manipulating biological filaments and for probing the surface conductance and mechanical properties of single polymers.     

Surface structure of ionic liquids under an external electric field

Abstract

Surface structure and properties play an important role in many applications of ionic liquids (ILs). ILs can form unique surface structures that are very different from the bulk. In imidazolium-based ILs, for example, polar groups form ordered layer structure, while cationic alkyl chains are bundled together and point out from the surface. In many applications, ILs work under an external electric field. However, the effect of external electric field on the surface structure of ILs is still not clear. Here by using coarse-grained molecular dynamics simulation, we found that an electric field as strong as 1 V/nm is required to alter the surface structure of 1-dodecyl-3-methylimidazolium nitrate. Under a strong external electric field, layered structure disappears, and instead a sparser, more homogeneous and less orientationally ordered surface develops.     

Problems of structural and functional identification of biological tissues

Theoretical methods for identification of topological and functional parameters of biological tissues (e.g., myocardium) are considered. Unknown topological parameters include the network dimension and connectivity, while unknown functional parameters include the resistivity of the cellular membrane and cytoplasm. The cell size (length and diameter), the input resistance of the tissue, and the fundamental electric potential field formed by a “point” current source (intracellular microelectrode) are treated as experimentally known parameters.     

Polyethylene glycol and electric field treatment of plant protoplasts: characterization of some membrane properties

Petiolar protoplasts of a dihaploid line of winter oilseed rape Brassica napus L. ssp. oleifera were exposed to fusogenic polyethylene glycol (PEG) and electric field treatments. The surface properties and stability of membrane components of the treated protoplasts were investigated by contact angle measurements in aqueous two-phase systems and differential scanning calorimetry, respectively. The leakage of intracellular components was estimated with respect to amino acids, proteins and DNA. Both fusogenic treatments resulted in the same apparent changes in membrane surface hydrophobicity and the same destabilization of membrane components. However, the PEG-treated protoplasts were more leaky than both the control and the electric field-treated protoplasts. The results indicate that the molecular mechanisms of PEG- and electrical field-induced fusion are similar. However, the effects of the latter appear to be less harmful presumably because the parameters for electric field treatment are more easily controlled.     

Plasmonic Enhancement of Fluorescence and Raman Scattering by Metal Nanotips

We report modifications to the optical properties of fluorophores in the vicinity of noble metal nanotips. The fluorescence from small clusters of quantum dots has been imaged using an apertureless scanning near-field optical microscope. When a sharp gold tip is brought close to the sample surface, a strong distance-dependent enhancement of the quantum dot fluorescence is observed, leading to a simultaneous increase in optical resolution. These results are consistent with simulations of the electric field and fluorescence enhancement near plasmonic nanostructures. Highly ordered periodic arrays of silver nanotips have been fabricated by nanosphere lithography. Using fluorescence lifetime imaging microscopy, we have created high-resolution spatial maps of the lifetime components of vicinal fluorophores; these show an order of magnitude increase in decay rate from a localized volume around the nanotips, resulting in a commensurate enhancement in the fluorescence emission intensity. Spatial maps of the Raman scattering signal from molecules on the nanotips shows an enhancement of more than five orders of magnitude.     

Bioelectrorheological model of the cell. 1. Analysis of stresses and deformations

An electrorheological model of a cell in alternating electric field is proposed. The model relates changes in the spherical cell's shape to the field conditions, electric parameters of cytoplasm, cell membrane and external medium, and to the rheological parameters of the membrane. Stresses were determined using Maxwell's stress tensor for isotropic media. Shear stresses in the cell membrane were analyzed. Predictions of the model for variations of shear stress in cellular membranes subjected to an external periodic electric field are presented and related to the conditions prevailing in electrobiological research.