Electric Field

This paper presents a method of calculating the possible striking points of lightning and their probabilities. The calculations are based on a dynamic electromagnetic model. This model is based on the Wave-Pair concept which is presented as an analytical model for calculating the electric field strengths at a desired observation point. Based on that model the electric field strength values are calculated at certain chosen points. When those fields exceed critical field strength, an up going discharge starts from each point. When one of these up going discharges meets the down going Leader the path is made for the Return Stroke. This method is compared with the Rolling Sphere Method, and the comparison yield evidence that the proposed model is more accurate results. A study case of calculating the probability of lightning stroke to a complex of buildings and installations is also given.

In this work an optimized version of the field-mill sensor structure for atmospheric electric field measurements was presented. Both the mechanical structure and the electronic front-end, acquisition and control system are optimized in order to reduce the power consumption and to enhance the instrument metrological performance in term of sensitivity and frequency band. A solar power operated system was realized and tested. The developed system is also equipped with a GPS receiver, allowing data synchronization. This feature enables the implementation of a distributed measurement system for the monitoring of the atmospheric electric field.

We show that the shape of electroluminescence transients in organic semiconductors can be conveniently used to obtain the diffusion constant D of injected charge carriers, enabling the study of generalized Einstein relationship under nonequilibrium conditions as a function of the electric field. The appearance of peak at the onset of transient is shown to be the signature of diffusive regime of transport. We demonstrate it for two representative materials, Alq 3 and polymer poly [2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene], with the focus on the role of hot carriers in transport and their diffusivity.

Ion mobility spectrometry has become the most successful and widely used technology for the detection of trace levels of nitro-organic explosives on handbags and carry on-luggage in airports throughout the US. The low detection limits are provided by the efficient ionization process, namely, atmospheric pressure chemical ionization (APCI) reactions in negative polarity. An additional level of confidence in a measurement is imparted by characterization of ions for mobilities in weak electric fields of a drift tube at ambient pressure. Findings from over 30 years of investigations into IMS response to these explosives have been collected and assessed to allow a comprehensive view of the APCI reactions characteristic of nitro-organic explosives. Also, the drift tube conditions needed to obtain particular mobility spectra have been summarized. During the past decade, improvements have occurred in IMS on the understanding of reagent gas chemistries, the influence of temperature on ion stability, and sampling methods. In addition, commercial instruments have been refined to provide fast and reliable measurements for on-site detection of explosives. The gas phase ion chemistry of most explosives is mediated by the fragile CONO(2) bonds or the acidity of protons. Thus, M(-) or M.Cl(-) species are found with only a few explosives and loss of NO(2), NO(3) and proton abstraction reactions are common and complicating pathways. However, once ions are formed, they appear to have stabilities on time scales equal to or longer than ion drift times from 5-20 ms. As such, peak shapes in IMS are suitable for high selectivity and sensitivity.

We analyze the pair production of charged particles in two-dimensional Anti-de Sitter space (AdS_2) with a constant, uniform electric field. We compute the production rate both at a semi-classical level, viewing Schwinger pair production as a tunneling event, and at the full quantum level, by extracting the imaginary part of the one-loop amplitude. In contrast to the usual Schwinger pair production in flat space, pair production in AdS_2 requires a sufficiently large electric field E^2> M^2+1/4 in order to overcome the confining effect of the AdS geometry -- put in another way, the presence of an electric field E raises the Breitenlohner-Freedman bound to M^2 > -1/4 + E^2. For E greater than this threshold, the vacuum is unstable to production of charged pairs in the bulk. We expect our results to be helpful in constructing supersymmetric AdS_2 X S^2 perturbative string vacua, which enter in the near-horizon limit of extremal charged black holes. Although the generalized Breit...

One of the important phenomena which is important in equipment when they are under high voltage stress is Partial discharge (PD). Partial discharge measurement is commonly used to evaluate the performance of the insulation in high voltage system. Modeling of the discharge in insulation can give a better understanding of this important phenomenon. A cavity within a dielectric material is a highly stressed area and the ideal place for starting partial discharge and breakdown. The applied voltage is one of the important factors that PD activity is influenced by that. Previous studies have considered the behavior of PD activity in a spherical cavity at 50Hz of sinusoidal applied voltage. However, still not so much work on the simulation of the PD activity in the cavity under different condition. Also, there is little data are available on the effect of parameters on the PD activity. This paper describes the behavior of PD activity as a function of applied voltage in a cylindrical cavity within a homogeneous dielectric. COMSOL and MATLAB software were used to carry out the simulation based on the finite element method (FEM). The number of PDs per cycle changed with different applied voltage so the highest number of PD at 20kV and the lowest value at 8kV. The maximum PD magnitude is raised from 1200pC at 8kV to 2400pC at 20kV applied voltage. The number of PD is most prevalent for sinusoidal followed by triangular waveform and then sawtooth. Comparison of the simulation results and experimental results are in good agreement. The result can help the researcher to understand more about the characteristics and behavior of partial discharge. Which may help the insulation diagnostic testing or condition monitoring.

The classical Yang-Mills equation of motion is numerically investigated in the Lorentz gauge for a SU(2) gauge group. The color-electric field of two point-like charges is studied in the "empty" vacuum and in a state with an instanton present. The major effect for a fixed orientation of the instanton is that the color-electric field lines are expelled or attracted from the instanton region depending on the orientation of the instanton. If over the orientations of the instanton is averaged, this effect drops out. In this case of a random instanton orientation, we find that the external color-electric field is expelled from the instanton core. The origin of this effect is discussed.

The Boltzmann equation for transport in semiconductors is projected onto spherical harmonics in such a way that the resultant balance equations for the coefficients of the distribution function times the generalized density of states can be discretized over energy and real space by box integration. This ensures exact current continuity for the discrete equations. Spurious oscillations of the distribution function are successfully suppressed by stabilization based on a maximum entropy dissipation principle avoiding the H-transformation. The derived formulation can be used on arbitrary grids as long as box integration is possible. The new approach works not only with analytical bands but also with full-band structures in the case of holes. Results are presented for holes in bulk silicon based on a full band structure and electrons in a Si NPN BJT. For the first time the convergence of the spherical harmonics expansion is shown for a device and it is found that the quasiballistic transport in nanoscale devices requires an expansion of considerably higher order than the usual first one. The stability of the discretization is demonstrated for a range of grid spacings in the real space and bias points which produce huge gradients in the electron density and electric field. It is shown that the resultant large linear system of equations can be solved memory efficiently by the numerically robust package ILUPACK.

Silicon thin films grown near the boundary between the amorphous/microcrystalline growth offer superior properties for industrial applications. Series of silicon samples, in which crossing of this transition region was achieved by changing a single technological parameter (dilution of silane in hydrogen, deposition temperature, sample thickness) were used to test our model of transport, connecting the macroscopically observed transport properties and the crystallinity, hydrogen content, grain size and grain boundaries. Microscopic study by AFM led to the formulation of the geometrical model of growth of mixed phase Si. The demand for research of microcrystalline or polycrystalline silicon prepared at low substrate temperatures is stimulated by the use of cheap plastic substrates. In addition to a direct deposition an alternative technology, such as metal-induced crystallization supported by the electric field is discussed. Possible future application of thin silicon films, for example in a "nanolithography", is also shown. *

Drift wave maps, area preserving maps that describe the motion of charged particles in drift waves, are derived. The maps allow the integration of particle orbits on the long time scale needed to describe transport. Calculations using the drift wave maps show that dramatic improvement in the particle confinement, in the presence of a given level and spectrum of EϫB turbulence, can occur for q(r) profiles with reversed shear. A similar reduction in the transport, i.e., one that is independent of the turbulence, is observed in the presence of an equilibrium radial electric field with shear. The transport reduction, caused by the combined effects of radial electric field shear and both monotonic and reversed shear magnetic q profiles, is also investigated.

In modeling of release of a dust particle from a plasma-facing wall it is usually assumed that electron velocity distribution is Maxwellian. However, the absorption of fast electrons by the conducting wall can lead to truncation of fast component of reflecting electrons from the wall. In this work we study the effect of truncation of electron velocity distribution on the release condition of a conducting spherical dust particle from the plasma-facing wall. The truncation increases the electric field at the wall surface compared to that calculated in absence of the truncation. The stronger electric field makes the dust particle hard released when the gravitational force is directed from the wall and applied wall potential is shallower than the floating one.

This study is concerned with the anisotropy of the electron drift velocity in germanium crystals at high electric "elds and low temperature, and its in#uence on the charge collection process in n-type, high-purity germanium (HPGe) detectors of closed-end, coaxial geometry. The electron trajectories inside HPGe detectors are simulated using a phenomenological model to calculate the dependence of the drift velocity on the angle between the electric "eld and the crystal orientation. The resulting induced currents and pulse shapes for a given detector geometry and preampli"er bandwidth are compared to experiment. Experimentally, the dependence of the pulse shapes on the conductivity anisotropy in closed-end HPGe detectors was observed. The experimental data on pulse shapes were obtained by sampling preampli-"er signals of an encapsulated, hexaconical EUROBALL detector, which was irradiated by collimated Na and Am sources. The crystal orientation was measured by neutron re#ection. Qualitative agreement between the simulated and experimental pulse shapes was found. A variation in the charge collection time of up to 50 ns was observed for di!erent drift directions of the carriers relative to the crystal orientation. Furthermore, a de#ection of the trajectories from a straight radial drift direction of about 203 was predicted by the simulations. These two main e!ects of charge carrier drift velocity anisotropy in coaxial Ge detectors are expected to play an important role in the development of -ray tracking detectors.

The idea behind the methods described in the remaining part of this book is to speed up antigen-antobody precipitation in an electric field. This permits fast assays and assays in which diffusion can be kept to a minimum, giving a high resolving power. This can be done by running antigens through a gel with antibodies under circumstances in which the net migration of 0 40 80 120 160 200 240 280 320 360 FIG. 8.1. Development of human serum albumin immunoprecipitates. Human serum was submitted to rocket immunoelectrophoresis against rabbit anti-human albumin. The plate was photographed at various times after start of the electrophoresis, indicated on the figure in minutes. The electrical field strength was 3 V/crn. The buffer was Tris-barbital, pH 8.6, the ionic strength was 0.02.

The distribution of electric field for the alignment and attachment of carbon nanotubes (CNTs) was simulated. To be attached at the desired place, the aligned and attracted CNTs should be stayed in the desired area called the stable region or the quasi-stable region for an instant where the change of electric field is minimized. Since the conical electrode has the very narrow sized quasi-stable region, few CNTs can be attached. The rectangular electrodes have a wide stable region, so lots of CNTs can be attached. The results indicate that the round electrode which has a proper sized quasi-stable region is more effective for aligning and attaching a single CNT than the conical or rectangular shaped electrodes.

The low-latitude boundary layer (LBL) and its separation from the cusp have previously been identified using observations of particle precipitation at magnetosheath energies. Using $3-3 satellite observations, we have determined that these identifications can also be made from energetic particle observations on polar-orbiting satellites. It is found that the equatorward boundary of the LBL is identifiable as an approximately discontinuous decrease in 33-keV electron fluxes from low to high latitudes. Both the energetic ion and electron fluxes decrease discontinuously at the boundary between the LBL and the cusp or polar cap. A distinct LBL is nearly always identifiable in energetic particle measurements in the 10-14 MLT region when counting rates are statistically significant. The identifications obtained using the energetic particle measurements have been compared to those obtained using criteria developed by Newell and Meng (1988, 1989) for magnetosheath energy particle precipitation. In this way, we have evaluated the accuracy of both techniques and used the energetic particle measurements to supplement the identifications obtained using the Newell and Meng criteria. We propose that the Newell and Meng threshold on ion energy flux can be reduced by a factor of 6. This modification provides identification of the LBL for lower ion intensity levels than has previously [_een thought possible. Source, acceleration, and scattering processes have also been studied within _nd in the vicinity of the LBL. Observed trapped pitch angle distn'butions of energetic electrons imply that the LBL is at least partially on closed field lines. Strong scattering of energetic protons is found within and equatorward of the LBL and thus must occur at least partially along closed field lines. Field-aligned electron acceleration by parallel electric fields can be discerned within and poleward of the LBL, but a more detailed analysis is necessary for a statistical study. Conical ion acceleration was seen relatively frequently within the LBL and about half as often poleward of the LBL. Neither acceleration process could be identified anywhere equatorward of the LBL.

A typical 1 /f noise is excited in a GaAs filament with the Hooge's noise parameter of about aH = 2 x The noise level increases in proportion to the square of the terminal voltage, and decreases approximately in inverse proportion to the total number of carriers within the device. A transition from the typical 1 lfnoise characteristics to the diffusion noise characteristics of MESFET's was observed when the electric field was increased above 1 kV/cm. The noise parameters were also investigated as a function of the device width between 2 and 200 pm. Deep levels within the n-GaAs active layer and the high electric field are the main factors of the nonideal l/fcharacteristics.

Using the ladder operator technique, a construction of the supersymmetric Hamiltonian is proposed. We show that the accidental degeneracies associated with the Coulomb and isotropic oscillator problems may be attributed to the existence of a supersymmetry of the Hamiltonians.

Abstrat-Mammalian cells can be cultured and therefore studied in vitro. Normally, the cells' morphology and other static properties are observed with the aid of a light microscope. A method is described here that allows observation of the dynamical aspects of cultured cells. Mammalian fibroblasts are cultured in polystyrene dishes that contain evaporated gold electrodes. As the cells attach to the electrodes, their presence and their motion is directly reflected in the -measured impedance.

We propose an equivalent circuit representation of the photogenerated charge separation and propagation in dye sensitized polycrystalline semiconductor in contact with a redox electrolyte. The suggested equivalent circuit for this type of photocell is based on an electrical transmission-line, and uses distributed photodiode model for the semiconductor-redox electrolyte interface. It was found that for small signal conditions, diodes can be replaced by equivalent elements, each consisting of a resistor and a capacitor connected in series. The equivalent circuit also provides for Beer-Lambert characteristics of light absorption. The simulation of the transmission line equivalent circuit, subjected to short pulse illumination, allows us to reproduce the experimentally found difference between the photocurrent responses of the photocell to illumination from the electrolyte side, and its response to illumination through the semitransparent back electrode, to which the polycrystalline sem...

A set of heavily doped Al0.48In0.52As samples grown by molecular beam epitaxy on InP (Fe) substrates was investigated using the photoreflectance (PR) technique. The spectra at 300 K are characterized by a transition in the vicinity of the InP energy gap, followed by strongly damped Franz-Keldysh oscillations (FKOs) which do not appear when the spectra are obtained at 77 K. The builtin electric field estimated from FKOs shows a small doping dependence but is substantially affected by the inclusion of a thin layer of AlxGayIn1-x-yAs (x≡0.22) at the interface between InP (Fe) and AlInAs:Si. In order to explain these results, a model based on the discontinuity of the energy bands in the InP/AlInAs and InP/AlGaInAs/AlInAs systems and also on the matching of the Fermi levels between the different materials is suggested.

We demonstrate feedback control optimization for the Stark deceleration and trapping of neutral polar molecules using evolutionary strategies. In a Stark-decelerator beamline, pulsed electric fields are used to decelerate OH radicals and subsequently store them in an electrostatic trap. The efficiency of the deceleration and trapping process is determined by the exact timings of the applied electric field pulses. Automated optimization of these timings yields an increase of 40 % of the number of trapped OH radicals.

An isoparametric 3D electromechanical hexahedral finite element integrating a 3D phenomenological ferroelectric and ferroelastic constitutive law for domain switching effects is proposed. The model presents two internal variables which are the ferroelectric polarization (related to the electric field) and the ferroelastic strain (related to the mechanical stress). An implicit integration technique of the constitutive equations based on the return-mapping algorithm is developed. The mechanical strain tensor and the electric field vector are expressed in a curvilinear coordinate system in order to handle the transverse isotropy behavior of ferroelectric ceramics. The hexahedral finite element is implemented into the commercial finite element code Abaqus Ò via the subroutine user element. Some linear (piezoelectric) and non linear (ferroelectric and ferroelastic) benchmarks are considered as validation tests.

Finite-amplitude bifurcation diagrams of axisymmetric liquid bridges anchored between two plane parallel electrodes subjected to a potential difference and in the presence of an axial gravity field are found by solving simultaneously the Laplace equation for the electric potential and the Young-Laplace equation for the interface by means of the Galerkinlfinite element method. Results show the strong stabilizing effect of the electric field, which plays a role somewhat similar to the inverse of the slenderness. It is also shown that the electric field may determine whether the breaking of the liquid bridge leads to two equal or unequal drops. Finally, the sensitivity of liquid bridges to an axial gravity in the presence of the electric field is studied.

Numerical computation of the electric field strength and ionic space charge density in electrode systems consisting of ionizing wire and non-ionizing cylinder, connected to the same DC high-voltage supply and facing a grounded plate, is a difficult problem, which is of interest to several electrostatic processes applications. In a previous study a simple numerical method has been proposed to calculate the spatial distributions of electric field and ionic space charge in a case of a continuum and uniform corona discharge originating at the surface of the wire. The aim of the present paper is to improve the physical model of the corona discharge in this particular electrode configuration, by assuming a more realistic law of charge injection on the wire circumference. The computations were carried out for an ionizing wire of radius r ¼ 0.1 mm, located at different distances h from a metallic tubular support of radius R ¼ 13.4 mm.The initial conditions of the corona discharge took into account the non-uniformity of the charge injection around the ionizing wire electrode. The computational results were compared with those obtained under the assumption of uniform corona discharge. The comparison pointed out that neither the non-uniformity of the electric field nor that of the charge injection can be neglected. They depend on the geometry of the electrode system and affect the distribution of the electric field and of the space charge density in the inter-electrode gap.

The first satellite observations of the total field-aligned component of the quasi-dc Poynting flux are presented for two passes over the polar region, one in the noon sector and one in the afternoon. The energy input due to electron precipitation is also presented. In the noon pass the downward Poynting flux in the auroral oval was comparable to the kinetic energy input rate. The peak electromagnetic energy input rate of 6 ergs/(cm 2 s) equaled the peak particle input while the integrated electromagnetic value along the trajectory was 60% that of the particles. In the afternoon pass the peak electromagnetic energy input was also about 6 ergs/(cm 2 s), but the peak particle energy was 6 times this value. The average electromagnetic input was 10% of the particle input for the pass. In this study we can measure the Poynting flux only over a limited range of scale sizes; thus the contribution to the total energy budget in the polar cap cannot be determined. Both passes show small regions characterized by upward Poyntiag flux suggesting a neutral wind dynamo. There is also evidence during part of the noontime pass that the external generator acted in opposition to an existing wind field since the Poynting flux was greater than the estimate of Joule heating from the electric field measurement alone (i.e., from •pE2). In the course of deriving Poynting's theorem for the geophysical case we also present a proof that ground magnetometer systems respond primarily to the Hall current which does not depend upon geometric cancellation between the field generated by Pedersen and field-aligned currents.

Steeply-dipping mineralized bodies present a particular problem for audio-magnetotelluric (AMT) exploration. Such targets have little observable effect on currents flowing perpendicular to their dominant strike, thus TM-mode AMT data are not useful for target detection or delineation. The TE-mode and vertical-field transfer function data do detect such targets, and appropriately-designed surveys can define their geometries. The anomalous responses due to such targets are greater in the magnetic fields than in the electric fields. Conducting overburden suppresses the high frequency response, moving the anomaly maxima to lower and lower frequency with increasing overburden conductance. For optimal resolution of target geometries, all five AMT components must be measured at each and every site.

An EMC experimental kit is developed to illustrate the fundamental mechanisms of radiated emissions from printed circuit boards. The kit is then expanded to cover and demonstrate some of the EMC design techniques such as shielding and filtering that are useful for reducing radiated emissions. In this paper, the experimental kit and the experiment configurations are described. Representative results are given in order to show the PCB layout effect on the differential and common mode radiated emissions. Moreover, the need for integral application of shielding and filtering is emphasized as the outcome of the experiments.

Using a block model of 1532 cubical cells, temperature distributions are calculated for the lowest 21 cm of the human leg for electric fields recommended in the ANSI RF safety guideline. The thermal model uses inhomogeneous volume-averaged tissue properties: blood-flow rate, metabolism, thermal conductivity, specific heat, etc. The SAR's are obtained using the impedance method. A modified method of finite difference technique is used to solve the 3-D heat conduction equation for the thermal model. Numerical results are obtained for RF currents at 3 and 40 MHz projected for the E fields recommended by the ANSI Standard (614 and 61.4 V/m, respectively) and also for power densities one-tenth of that level. Temperatures as high as 41.6" are obtained for some internal cells for the higher Efields while relatively moderate temperatures on the order of 37°C are obtained for the lower E fields. Some of the calculated results for the surface temperature have been compared and found to be in good agreement with the experimental data for initial rates of heating.

A new model describing laser noise in terms of non-Markovian stochastic phase jumps has been recently introduced. In this letter an exact expression for the correlation function for the electric field is obtained. This expression, valid for all possible values of the parameters of the stochastic process, reduces to the previously reported approximations. A procedure is described for the inverse problem of determining the stochastic parameters from measured data for real lasers.

Vertebrates have evolved electrosensory receptors that detect electrical stimuli on the surface of the skin and transmit them somatotopically to the brain. In chondrichthyans, the electrosensory system is composed of a cephalic network of ampullary organs, known as the ampullae of Lorenzini, that can detect extremely weak electric fields during hunting and navigation. Each ampullary organ consists of a gel-filled epidermal pit containing sensory hair cells, and synaptic connections with primary afferent neurons at the base of the pit that facilitate detection of voltage gradients over large regions of the body. The developmental origin of electroreceptors and the mechanisms that determine their spatial arrangement in the vertebrate head are not well understood. We have analyzed electroreceptor development in the lesser spotted catshark (Scyliorhinus canicula) and

The horizontal electric field both at points above and below ground in the vicinity of lightning return strokes were evaluated by numerical solution of Sommerfeld's integrals. Results are presented for ground conductivities in the range of 0.01 and 0.0001 S/m. The results are compared with the following approximate procedures used in the literature to calculate horizontal electric fields: (a) the surface impedance approximation, (b) the quasi static approximation frequently used in lightning protection standards and (c) Cooray's simplified formula for the computation of underground electric field. Based on this comparison the distance range in which these approximations are valid is obtained. The results obtained show that: (1) The surface impedance approximation can generate correct horizontal electric field when the distance to the point of observation is larger than about 50 m, 100 m, and 500 m for ground conductivities of 0.01, 0.001 and 0.0001 S/m respectively.

Consider a conducting disk surrounded by a thin dielectric layer submitted to an electric field at the pulsation ω. The conductivity of the layer grows like ω 1−γ , γ ∈ [0, 1], when the pulsation ω tends to infinity. Using a pseudodifferential approach on the torus, we build an equivalent boundary condition with the help of an appropriate factorization of Helmholtz operator in the layer. This generalized impedance condition approximates the thin membrane in the high frequency limit for small thickness of the layer. L 2 -error estimates are given and we illustrate our results with numerical simulations. This work extends, in the circular geometry, previous works of Lafitte and Lebeau [7], [8], in which γ identically equals zero.

The purpose of this study was to examine the feasibility of using irreversible electroporation (IRE) as a non-chemical method for eliminating microorganisms of liquid drugs. The studied drug was a topical ophthalmic medication, a pharmaceutical field in which the problem of microbial contamination has not yet been adequately solved, especially in the case of eye drops prescribed for chronic use. Commercially available Hylo-Comod® preservative-free eye drop solution was subjected to contamination with Escherichia coli bacteria (106 colony forming units/mL). Electroporation parameters for bacterial control were investigated by comparing the effects of electrical fields of 5.4, 7.2, and 10 kV/cm, delivered as 100-µs square pulses at 1 Hz in sequences of 10 pulses, 20 pulses, or 20 pulses delivered as four sets of five pulses with 1-min intervals between each set. Microorganism survival after treatment was determined by pour plate counting. Effects of the treatment parameters on temperature and pH were recorded. Bacterial survival was lowest (0.14% ± 0.03%) after application of 20 pulses delivered as four separate sets. With that application mode, the solution remained at pH 7.5 and the temperature rose to 35.6° ± 0.2°C. Because IRE can be efficiently delivered under conditions that avoid the potentially deleterious effects of electrical pulses on temperature and pH, it appears to be a feasible method for bacterial control of drugs in solution. The principles established in this study can be applied to any drug in solution and optimized individually according to the solution's composition.

The differentiation and proliferation of neural stem/progenitor cells (NPCs) depend on various in vivo environmental factors or cues, which may include an endogenous electrical field (EF), as observed during nervous system development and repair. In this study, we investigate the morphologic, phenotypic, and mitotic alterations of adult hippocampal NPCs that occur when exposed to two EFs of estimated endogenous strengths. NPCs treated with a 437 mV/mm direct current (DC) EF aligned perpendicularly to the EF vector and had a greater tendency to differentiate into neurons, but not into oligodendrocytes or astrocytes, compared to controls. Furthermore, NPC process growth was promoted perpendicularly and inhibited anodally in the 437 mV/mm DC EF. Yet fewer cells were observed in the DC EF, which in part was due to a decrease in cell viability. The other EF applied was a 46 mV/mm alternating current (AC) EF. However, the 46 mV/mm AC EF showed no major differences in alignment or differentiation, compared to control conditions. For both EF treatments, the percent of mitotic cells during the last 14 h of the experiment were statistically similar to controls. Reported here, to our knowledge, is the first evidence of adult NPC differentiation affected in an EF in vitro. Further investigation and application of EFs on stem cells is warranted to elucidate the utility of EFs to control phenotypic behavior. With progress, the use of EFs may be engineered to control differentiation and target the growth of transplanted cells in a stem cell-based therapy to treat nervous system disorders.

The application of a nonuniform ac electric field to an electrolyte using coplanar microelectrodes results in steady fluid flow. The flow has its origin in the interaction of the tangential component of the nonuniform field with the induced charge in the electrical double layer on the electrode surfaces. Termed ac electro-osmosis, the flow has been studied experimentally and theoretically using linear analysis. This paper presents experimental observations of the fluid flow profile obtained by superimposing images of particle movement in a plane normal to the electrode surface. These experimental streamlines demonstrate that the fluid flow is driven at the surface of the electrodes. Experimental measurements of the impedance of the electrical double layer on the electrodes are also presented. The potential drop across the double layer at the surface of the electrodes is calculated numerically using a linear double layer model, and also using the impedance of the double layer obtained from experimental data. The ac electro-osmotic flow at the surface of the electrodes is then calculated using the Helmholtz-Smoluchowski formula. The bulk fluid flow driven by this surface velocity is numerically calculated as a function of frequency and good agreement is found between the numerical and experimental streamlines.

An integral equation analysis is proposed to determine the phase constant of an arbitrarily shaped dielectric waveguide. The main feature of this approach is the use of Green's scalar identity in which only simple contour integrals have to be evaluated. Different scalar Green's functions are considered to satisfy the boundary conditions for the electric and magnetic fields in each region. This approach is combined with the boundary element technique with linear elements for the computation. The case of the rectangular dielectric image waveguide is first discussed, and numerical results are found to be consistent with other theories and experiments. Also, the cases of hollow rectangular and semicircular image waveguides are analyzed and numerical results are presented.

The application of a DC electric field down gradient to the contaminated zone in the subsurface can create an electrokinetic barrier. The electrical potential gradient causes the movement of ions which in turn imposes a viscous drag on the pore water. In clayey soils, this viscous drag can generate a high enough pore water pressure capable of counteracting the ground water gradient. This phenomenon can be used effectively as a barrier to prevent contaminant migration. A finite element model was developed to simulate the contaminant migration in soil under coupled hydraulic, electrical and chemical gradients. The model is also capable of predicting the associated changes in the soil like the pore water pressure, pH and voltage gradient as a function of time and distance from the electrode. This model was validated using the w experimental data presented by Yeung Yeung, A.T., 1990. Electro-kinetic barrier to contaminant x transport through compacted clay. PhD Thesis, University of California, Berkeley, 260 pp. . The results indicate very good agreement between the experimental and simulated results. The model predications show that when the anode is placed down gradient of the cathode, the cation migration could be completely arrested. However, the anions were found to move faster in the direction of the ground water flow and reduce the effectiveness of the barrier. This could be avoided by carefully designing the placement of the electrodes. If the contaminant of interest is either a cation or an anion, a simple double row of anode and cathode electrode arrangement could serve as an effective barrier. On the other hand, if the contaminant includes both anions and cations, then a triple-row configuration of electrodes need to be implemented. The model ) Corresponding author. 0169-7722r00r$ -see front matter q 2000 Elsevier Science B.V. All rights reserved.

and the calculations of Glendenning et al. (5), (GWM:neutrons) predict lower pressures. The uncertainty in the pressure due to the asymmetry term widens the range of possible EOSs that may be consistent with the experimental data. For this purpose, it is important to obtain experimental constraints on the asymmetry term (39-41) (see SOM text) and to complement them with improved constraints on the EOS of symmetric nuclear matter. We have analyzed the flow of matter in nuclear collisions to determine the pressures attained at densities ranging from two to five times the saturation density of nuclear matter. We obtained constraints on the EOS of symmetric nuclear matter that rule out very repulsive EOSs from relativistic mean field theory and very soft EOSs with a strong phase transition at densities Ͻ 3 0 , but not a softening of the EOS due to a transformation to quark matter at higher densities. Investigations of the asymmetry term of the EOS are important to complement our constraints on the symmetric nuclear matter EOS. Both measurements relevant to the asymmetry term and improved constraints on the EOS for symmetric matter appear feasible; they can provide the experimental basis for constraining the properties of dense neutron-rich matter and dense astrophysical objects such as neutron stars. Plasmas are an attractive medium for the next generation of particle accelerators because they can support electric fields greater than several hundred gigavolts per meter. These accelerating fields are generated by relativistic plasma waves-space-charge oscillations-that can be excited when a highintensity laser propagates through a plasma. Large currents of background electrons can then be trapped and subsequently accelerated by these relativistic waves. In the forced laser wake field regime, where the laser pulse length is of the order of the plasma wavelength, we show that a gain in maximum electron energy of up to 200 megaelectronvolts can be achieved, along with an improvement in the quality of the ultrashort electron beam.

The multi-walled carbon nanotube (MWCNT) dispersed polymethylmethacrylate (PMMA) composite membranes have been prepared for hydrogen gas permeation application. Composite membranes are characterized by Raman spectroscopy, optical microscopy, X-ray diffraction, electrical measurements and gas permeability measurements. The effect of electric field alignment of MWCNT in PMMA matrix on gas permeation has been studied for hydrogen gas. The permeability measurements indicated that the electrically aligned MWCNT in PMMA has shown almost 2 times higher permeability for hydrogen gas as compare to randomly dispersed MWCNT in PMMA. The enhancement in permeability is explained on the basis of well aligned easy channel provided by MWCNT in electrically aligned sample. The effect of thickness of membrane on the gas permeability also studied and thickness of about 30 m found to be optimum thickness for fast hydrogen gas permeates.

A novel low-loss planar dielectric waveguide is proposed. It is based on a high-permittivity dielectric slab parallel to a metal ground. The guiding channel is limited at the sides by a number of air holes which are lowering the effective permittivity. A mode with the electric field primarily parallel to the ground plane is used, similar to the E11x mode of an insulated image guide. A rather thick gap layer between the ground and the high-permittivity slab makes this mode to show the highest effective permittivity. The paper discusses the mode dispersion behaviour and presents measured characteristics of a power divider circuit operating at a frequency of about 8 GHz. Low leakage of about 14% is observed at the discontinuities forming the power divider. Using a compact dipole antenna structure, excitation efficiency of more than 90% is obtained.

We report numerical results on the repton model of Rubinstein [Phys. Rev. Lett. 59, 1946 (1987)] as adapted by Duke [Phys. Rev. Lett. 62, 2877 (1989)] as a model for the gel electrophoresis of DNA. We describe an efficient algorithm with which we have simulated chains of N reptons with N several hundred in some instances. The diffusion coefficient D

We present new numerical and analytic solutions of the two-dimensional Fokker-Planck equation supplemented by a parallel quasilinear diffusion term. The results show a large enhancement of the perpendicular temperature of both the electrons resonant with the applied RF fields and the more energetic electrons in the tail. Both the RF generated current and power dissipated are substantially increased by the perpendicular energy broadening in the resonant region. In the presence of a small DC electric field the RF current generated is very much enhanced, much more than in a simple additive fashion. In addition we present a relativistic formulation of the two-dimensional Fokker-Planck quasilinear equation. From conservation equations, based upon this formulation, we derive the characteristics of RF current drive with energetic electrons. These show how the RF driven current and its figure of merit (I/Pd) increase with the energy of the current-carrying electrons, and that their perpendicular, random momentum must also increase. The results are relevant to recent experiments of lower-hybrid current drive on Alcator C and PLT in which the applied RF spectra are resonant with very energetic electrons, and in which large perpendicular temperatures of the energetic electrons have been observed. It is pointed out that substantial improvements in the figure of merit, (I/P), of present experiments may be achieved by current drive with fast-waves in the lower-hybrid frequency range. The ultimate limitation in this type of current drive is likely to be the confinement of the very energetic electrons.

We present a parametric experimental study of convective electrokinetic instability (EKI) in an isotropically etched, cross-shaped microchannel using quantitative epifluorescence imaging. The base state is a three-inlet, one-outlet electrokinetic focusing flow configuration where the centre sample stream and sheath flows have mismatched ionic conductivities. Electrokinetic flows with conductivity gradients become unstable when the electroviscous stretching and folding of conductivity interfaces grows faster than the dissipative effect of molecular diffusion. Scalar images, critical applied fields required for instability, and temporal and spatial scalar energy are presented for flows with a wide range of applied d.c. electric field and centre-tosheath conductivity ratios. These parameters impose variations of the electric Rayleigh number across four orders of magnitude. We introduce a scaling for charge density in the bulk fluid as a function of local maximum conductivity gradients in the flow. This scaling shows that the flow becomes unstable at a critical electric Rayleigh number (Ra e, = 205) and applies to a wide range of applied field and centre-tosheath conductivity ratios. This work is relevant to on-chip electrokinetic flows with conductivity gradients such as field amplified sample stacking, flow at the intersections of multi-dimensional assays, electrokinetic control and separation of sample streams with poorly specified chemistry, and low-Reynolds number micromixing.

Several electrostatic technologies, such as separation of granular mixtures, flocking, printing, or biological cell manipulation, are based on the accurate control of conductive particle motion in insulating gases or liquids by means of relatively high dc electric fields. This paper aimed at characterizing the behavior of such particles by numerical modeling of two aspects: 1) particle motion under the action of electric field forces and 2) insulation breakdown triggered by mobile particles. The equations of particle motion were written by taking into account both gravitational and drag forces, as well as the rebound at particle impact with the electrodes. If the particles move in ionized air, their charge varies in time. In that case, the equation of particle charge should be added to the mathematical model. The output data of the programs for numerical simulation of particle behavior are in good agreement with the available experimental results. Particle movements were shown to be influenced by the intensity of the electric field, by the density of the space charge, by size and mass density of the particles, as well as by their coefficient of restitution at impact with the electrodes. The conclusions regarding the behavior of conductive particles in insulating fluids are useful for the development of improved electrostatic separation technologies; they are of particular interest to all manufacturers of high-voltage equipment.