Determination of the electron density and electric field in the plasma of a low-pressure microwave electrode discharge in hydrogen from the measured spectral line intensities

The parameters of the plasma of a microwave electrode discharge in hydrogen at pressures of 1–8 torr and incident powers of 20–80 W are measured by the so-called “relative intensity” method. The method allows one to determine the electron density and electric field in plasma by measuring the relative intensities of the H_α, H_β, and 763.5-nm Ar line emission and calculating the electron-impact rate constants from the homogeneous Boltzmann equation. The measurements show that there are regions in the discharge where the electron density is higher (a bright electrode sheath) and lower (a spherical region) than the critical density for the frequency 2.45 GHz (n_cr～7×10¹⁰ cm^?3). Inside the spherical region, the electric field varies slightly over the radius and the electron density increases as the discharge boundary is approached. The observed discharge structure can be attributed to the presence of a self-sustained discharge zone (electrode sheath); a non-self-sustained discharge zone (spherical region); and a decaying plasma region, which is separated from the active discharge zone by an electric double layer.     

Dynamics of a relativistic electron beam in the vicinity of a spherical injecting body in space plasma

The dynamics of a relativistic electron beam in the vicinity of an injector in the form of a spherical conducting body in a space plasma is considered. An equation describing the radial evolution of a steady electron beam with a self-similar density profile in the electric field of the injector is formulated. A method for calculating the radial evolution of a relativistic electron beam in the vicinity of an injector is developed. The method is based on the numerical integration of a set of ordinary differential equations for the beam radius and field potential in the space charge region under the relevant boundary conditions at the injector surface. Results are presented from numerical simulations of the radial dynamics of an electron beam in the vicinity of a spherical screen system for neutralizing the electric charge carried away by the beam. The numerical results show that the electric field of the injector hastens the beam expansion.     

Diffusion-mediated localization on membrane surfaces.

Using the model of a cell membrane of a spherical surface in which membrane components may diffuse, the rate of localization due to trapping under diffusion control has been estimated by computing an analytical expression for the mean trapping time including the possibilities of a trapping probability less than 1 and/or the establishment of an equilibrium at the trap boundary.     

Calculation of the electric field in space plasma near a conducting sphere injecting an electron beam

The problem is considered of determining the electric field induced in the vicinity of a conducting spherical body that is at rest in a collisionless plasma and at the surface of which there is a prescribed sink of negative charge. The problem is solved for the general relativistic case under the assumption that the electron velocity in the neutralizing current is comparable with the speed of light. An integrodifferential equation is derived that describes the radial behavior of the electric field potential in the vicinity of the injector. A simplified method for determining the potential in the perturbed region is developed. The method implies that the problems of the potentials in a space charge region of radius R* (with a prescribed boundary potential ?*) adjacent the body and in the outer region r>R* are solved separately and then the solutions obtained are matched at boundary between these regions.     

Gel electrophoresis of micron-sized particles: a problem and a solution

The gel electrophoresis of spherical particles with a radius above 0.2 micron has not been reported yet. In the present study, video phase-contrast light microscopy is used to observe the motion of individual latex spheres, 0.52 micron in radius, during electrophoresis in 0.1% agarose gels. At 2 V/cm, the spheres initially migrate in the direction of the electrical field. However, each sphere eventually undergoes a cessation of all motion. Brownian motion is restored when the electrical potential gradient is reduced to zero. Arrest can be prevented by periodically inverting the direction of the electrical field. These observations are explained by electrical field-induced steric trapping of the spheres by gel fibers. Inversion of the electrical field should assist the application of agarose gel electrophoresis to micron-sized cellular organelles and cells.     

Swimming in circles: motion of bacteria near solid boundaries

Near a solid boundary, Escherichia coli swims in clockwise circular motion. We provide a hydrodynamic model for this behavior. We show that circular trajectories are natural consequences of force-free and torque-free swimming and the hydrodynamic interactions with the boundary, which also leads to a hydrodynamic trapping of the cells close to the surface. We compare the results of the model with experimental data and obtain reasonable agreement. In particular, the radius of curvature of the trajectory is observed to increase with the length of the bacterium body.     

Edge Effect on Density Estimates of a Radiotracked Population of Yellow-Necked Mice

ABSTRACT Density estimates for small-mammal populations from capture-mark-recapture (CMR) data have played an important role in many studies of theoretical and applied ecology. Defining effective trapping area (ETA) is one of the main issues affecting accuracy of density estimates. Our objective was to assess sensitivity of CMR density estimates to correctors based on movement parameters calculated from trapping and radiotelemetry data. From May to November 2005, we conducted monthly CMR trapping in a beech (Fagus sylvaticus) forest of the province of Trento, northern Italy. In conjunction with CMR, we radio-marked 32 yellow-necked mice (Apodemus flavicollis) captured from July to October and located them daily using radiotelemetry. We estimated population size (N) by model averaging with Program MARK. We calculated ETA using several definitions of the boundary strip, including full and half mean maximum distance moved (MMDM) from capture-recapture and telemetry data and mean radius of mean monthly home ranges. The boundary strip (W) increased with the amount of behavioral information embodied in the estimates. The largest W and lowest density values were based on radius of mean home ranges followed by MMDM calculated from telemetry data. The ETA based on movement distances increased more than proportionally when N decreased, suggesting that low population density combined with scarce resources results in rodents moving more in search of food, thus leading to overestimated ETA and underestimated density values. Although robust behavioral information would certainly improve density estimates, we suggest caution in relating ranging movements to capture probability and hence in using correctors based on movement distances to infer density values.     

Glow intensity profile in a spherically stratified gas discharge

The glow intensity profile in a spherically stratified gas discharge is measured. It is shown that the boundaries of striations are thin spherical glowing shells, whose thickness is proportional to the striation radius. Based on the analysis of the optical-emission characteristics of spherical striations, the spatial distribution of the electric field in the stratified discharge region is estimated.     

Electric breakdown of lipid vesicles

Theoretical expression for free energy F of spherical lipid vesicle containing through pore in the presence of diffusional potential difference is derived. It is assumed that the pore radius is small in comparison with vesicle size. According to estimation the variation of elastic energy of vesicle membrane with pore radius is small. Therefore electrical breakdown becomes reversible for reasonable region of r values. Conditions of equilibrium and dynamic modes of breakdown are analyzed. Random oscillation mode of intravesicular label discharge is shown for some region of vesicle parameters.     

Influence of mutual arrangement of the electric dipole and the spatial nonuniformity of brain electrical conductivity on the solution of the direct task of electroencephalography using the method of finite elements

The results of comparing the solutions of the direct task of electroencephalography on a spherical model and a spherical model with one nonuniformity are discussed. The nonuniformity was simulated by two parabolas situated on the same axis of symmetry and crossing the boundary of the gray and the white matter. The region between the larger and the smaller parabolas had the physical characteristics of the gray matter, and the region inside the smaller parabola had the characteristics of the cerebrospinal fluid. The task was to find a combination of parameters (distance between the dipole and the nonuniformity, angle of rotation of the dipole relative to the nonuniformity, sizes of the dipole and the nonuniformity, etc.) that provides the maximum effect of the difference of potentials on the outer surface of the scalp in the spherical model with one nonuniformity and the spherical model. The influence of the points of grounding on the value of the effect was analyzed (ground only at the right ear and ground at both ears). The data obtained show that a maximum difference of potentials is reached at the positions of dipoles close to tangential relative to the scalp surface.     

Improving the accuracy of a solid spherical source radius and depth estimation using the diffusion equation in fluorescence reflectance mode

Background  

Non-invasive planar fluorescence reflectance imaging (FRI) is used for accessing physiological and molecular processes in biological tissue. This method is efficiently used to detect superficial fluorescent inclusions. FRI is based on recording the spatial radiance distribution (SRD) at the surface of a sample. SRD provides information for measuring structural parameters of a fluorescent source (such as radius and depth). The aim of this article is to estimate the depth and radius of the source distribution from SRD, measured at the sample surface. For this reason, a theoretical expression for the SRD at the surface of a turbid sample arising from a spherical light source embedded in the sample, was derived using a steady-state solution of the diffusion equation with an appropriate boundary condition.     

The sieving of rod-shaped viruses during agarose gel electrophoresis. I. Comparison with the sieving of spheres

The sieving of rod-shaped viruses during agarose gel electrophoresis is quantitatively analyzed here with a previously proposed model [G. A. Griess et al. (1989) Biopolymers, 28, 1475-1484] that has one radius (PE) of the effective pore at each concentration of gel. By use of this model and an internal spherical size standard, a plot of electrophoretic mobility vs agarose percentage is converted to a plot of the radius of the effective sphere (effective radius) vs PE. Experimentally, when the concentration of the rod-shaped bacteriophage, fd, is progressively increased, eventually the electrophoretic mobility of fd becomes dependent on its concentration. The concentration of fd at which this occurs decreases as the agarose concentration decreases. After avoiding this dependence on the concentration of sample, the effective radius of rod-shaped particles, including bacteriophage fd, length variants of fd, and length variants of tobacco mosaic virus, is found to increase as PE increases until a plateau of approximately constant maximum effective radius is reached at PcE. In the region of this plateau, the effective sphere's measure that best approximates that of the rod is surface area. However, significant disagreement with the data exists for surface area; the maximum effective radius for fd varies as (length)0.69. For fd and its length variants, the value of 2.PcE/length increases from 0.21 to 0.86 as the length decreases from 2808 to 367 nm. The dependence of effective radius on PE and the proximity of 2.PcE to the length of the rod are explained by (a) random orientation of rods at PE values in the region of the plateau, and (b) increasingly preferential end-first orientation (reptation) of the rod as PE decreases below PcE. This hypothesis of reptation is supported by a significant dependence of electrophoretic mobility on electrical potential gradient for a PE below, but not above, PcE. The dependence of 2.PcE/length on length is not rigorously understood, but is qualitatively explained by flexibility of the rods. This apparent flexibility has thus far prevented determination of a rod's axial ratio from quantitation of sieving during agarose gel electrophoresis. The electrical potential dependence of electrophoretic mobility is determined here by a procedure of two-dimensional agarose gel electrophoresis. This procedure is also useful for detecting rod-shaped particles in heterogeneous mixtures of predominantly spherical particles.     

Analysis of vertical distributions and effective flight layers of insects: three-dimensional simulation of flying insects and catch at trap heights

The mean height and standard deviation (SD) of flight is estimated for over 100 insect species from their catches on several trap heights reported in the literature. The iterative equations for calculating mean height and SD are presented. The mean flight height for 95% of the studies varied from 0.17 to 5.40 m, and the SD from 0.12 to 3.83 m. The relationship between SD and mean flight height (X) was SD = 0.711X(-0.7849), n = 123, R(2) = 0.63. In addition, the vertical trap catches were fit to normal distributions and analyzed for skew and kurtosis. The SD was used to calculate an effective flight layer used in transforming the spherical effective attraction radius (EAR) of pheromone-baited traps into a circular EAR(c) for use in two-dimensional encounter rate models of mass trapping and mating disruption using semiochemicals. The EAR/EAR(c) also serves to reveal the attractive strength and efficacy of putative pheromone blends. To determine the reliability of mean flight height and SD calculations from field trapping data, simulations of flying insects in three dimensions (3D) were performed. The simulations used an algorithm that caused individuals to roam freely at random but such that the population distributed vertically according to a normal distribution of specified mean and SD. Within this 3D arena, spherical traps were placed at various heights to determine the effects on catch and SD. The results indicate that data from previous field studies, when analyzed by the iterative equations, should provide good estimates of the population mean height and SD of flight.     

Tubular Membrane Formation of Binary Giant Unilamellar Vesicles Composed of Cylinder and Inverse-Cone-Shaped Lipids

We have succeeded in controlling tubular membrane formations in binary giant unilamellar vesicles (GUVs) using a simple temperature changing between the homogeneous one-phase region and the two-phase coexistence region. The binary GUV is composed of inverse-cone (bulky hydrocarbon chains and a small headgroup) and cylinder-shaped lipids. When the temperature was set in the two-phase coexistence region, the binary GUV had a spherical shape with solidlike domains. By increasing the temperature to the homogeneous one-phase region, the excess area created by the chain melting of the lipid produced tubes inside the GUV. The tubes had a radius on the micrometer scale and were stable in the one-phase region. When we again decreased the temperature to the two-phase coexisting region, the tubes regressed and the GUVs recovered their phase-separated spherical shape. We infer that the tubular formation was based on the mechanical balance of the vesicle membrane (spontaneous tension) coupled with the asymmetric distribution of the inverse-cone-shaped lipids between the inner and outer leaflets of the vesicle (lipid sorting).     

Tubular Membrane Formation of Binary Giant Unilamellar Vesicles Composed of Cylinder and Inverse-Cone-Shaped Lipids

We have succeeded in controlling tubular membrane formations in binary giant unilamellar vesicles (GUVs) using a simple temperature changing between the homogeneous one-phase region and the two-phase coexistence region. The binary GUV is composed of inverse-cone (bulky hydrocarbon chains and a small headgroup) and cylinder-shaped lipids. When the temperature was set in the two-phase coexistence region, the binary GUV had a spherical shape with solidlike domains. By increasing the temperature to the homogeneous one-phase region, the excess area created by the chain melting of the lipid produced tubes inside the GUV. The tubes had a radius on the micrometer scale and were stable in the one-phase region. When we again decreased the temperature to the two-phase coexisting region, the tubes regressed and the GUVs recovered their phase-separated spherical shape. We infer that the tubular formation was based on the mechanical balance of the vesicle membrane (spontaneous tension) coupled with the asymmetric distribution of the inverse-cone-shaped lipids between the inner and outer leaflets of the vesicle (lipid sorting).     

Stability of the thin elastic shell model of the red blood cell

Fung and Tong have recently explained the sphering of red blood cells in hypotonic solution by showing that a thin-walled elastic membrane with the right extensional stiffness and surface tension distribution will swell into a sphere under internal pressure. In this report we investigate the stability of the spherical state of Fung and Tong's model by applying the static energy criterion, which requires a determination of the sign of the quadratic terms in the potential energy functional. It turns out that a spherical cell model with radius less than that of the equatorial radius of the original undeformed cell is indeed stable, if and only if the supposedly arbitrary elastic parameters in the model are restricted in their possble range of values.     

Radiation Inhibition of Amino Acid Uptake by Escherichia coli

The inhibition of macromolecular synthesis in Escherichia coli by ionizing radiation has been investigated. The survival of the ability to incorporate arginine, leucine, isoleucine, histidine, uracil, and glucose after various doses of gamma radiation, deuteron and alpha particle bombardment has been measured. All amino acids are incorporated by processes which show the same radiation sensitivity. The sensitivity of uracil corresponds to a volume which is roughly spherical, of radius about 160A, whereas the amino acids possess sensitive regions which are long and thin in character. The uptake of glucose is concerned with a smaller, roughly spherical unit. The possible identification of the radiation-sensitive targets with cellular constituents is discussed. The long thin character observed for amino acids suggests that the sensitive region affected by radiation is an unfolded form of a ribosome, or alternatively a long nucleic acid molecule. For uracil the sensitive region fits with a 70S ribosome, while for glucose a smaller particle would fit the data.     

Structure of a T = 1 aggregate of alfalfa mosaic virus coat protein seen at 4.5 A resolution

A T = 1 empty aggregate of alfalfa mosaic virus coat protein had been crystallized in a hexagonal unit cell and its orientation was determined with the rotation function. A single heavy-atom derivative has now been prepared and the position of the two Hg atoms per protein subunit were determined using a systematic Patterson search procedure, given the particle orientation. Phases, initially determined by single isomorphous replacement, were refined by six cycles of electron density averaging and solvent leveling to produce a 4.5 A resolution electron density map. The protein coat is confined between 95 and 58 A radius. The subunit boundary could be delineated easily. It has a central cavity reminiscent of the beta-barrel in other spherical plant viruses, but its topology could not be determined unambiguously. The spherical particle has large holes at the 5-fold axes, consistent with previous observations. The subunits have substantial interactions at the 2 and 3-fold axes. The structure of the elongated particles is discussed in relation to these results.