Metal-glass contacts in high electric fields

In the presence of high electric fields, the region adjacent to a metallic anode of an ionic conducting glass quickly becomes depleted of mobile ionic carriers. At the cathode, however, electrons are injected into the glass from the metal electrode and cause the effective conductivity of this region to increase.     

Negative electron diffusivity in high electric fields

The prediction that the electron diffusivity may be negative in high electric fields under some conditions has been examined starting from the Boltzmann equation and assuming a Maxwellian distribution function. It is found that the diffusion constant is positive for predominant acoustic phonon, polar optical phonon or impurity atom scattering. But the constant may be negative when effects of nonparabolicity are important and energy relaxation is limited by non-polar optical phonon scattering but the momentum relaxation is dominated by impurity atom scattering. Calculations with the parameter values of InSb, silicon and germanium show that only in materials like germanium at low temperatures of about 27 K the diffusion constant may be negative for impurity concentrations of 10¹⁷–10¹⁸ cm^?3.     

Photoconductivity in ZnSe under high electric fields

High voltage photoconductive switches utilizing polycrystalline ZnSe mere investigated. Experiments have been performed on polycrystalline ZnSe switches in a longitudinal geometry. Electrodes of perforated metal films, a transparent liquid electrolyte, plasma, and ultraviolet-light-generated carriers were used. High-bias fields of up to 100 kV/cm and current densities over 100 kA/cm² can be applied to the polycrystalline ZnSe switches. Nonlinear effects were observed at high fields with near band edge illumination. Applications of these effects are discussed     

Prediction of magnetically induced electric fields in biologicaltissue

There are many potential medical applications in which it is desirable to noninvasively induce electric fields. One such application that serves as the backdrop of this work is that of stimulating neurons in the brain. The magnetic fields necessary must be quite high in magnitude, and fluctuate rapidly in time to induce the internal electric fields necessary for stimulation. Attention is focused on the calculation of the induced electric fields commensurate with rapidly changing magnetic fields in biological tissue. The problem is not a true eddy current problem in that the magnetic fields induced do not influence the source fields. Two techniques are introduced for numerically predicting the fields, each employing a different gauge for the potentials used to represent the electric field. The first method employs a current vector potential (analogous to A in classical magnetic field theory where DEL x A = B) and is best suited to two-dimensional (2-D) models. The second represents the electric field as the sum of a vector plus the gradient of a scalar field; because the vector can be determined quickly using Biot Savart (which for circular coils degenerates to an efficient evaluation employing elliptic integrals), the numerical model is a scalar problem even in the most complicated three dimensional geometry. These two models are solved for the case of a circular current carrying coil near a conducting body with sharp corners.     

Three-dimensional computer model of electric fields in internaldefibrillation

The automatic internal defibrillator delivers a low-energy shock directly to the heart. Optimal strategies for these shock deliveries are determined by studying a three-dimensional computer model of the electric fields produced by initial defibillation electrodes. A finite-element analysis technique is used to calculate energy and current density distributions in three commonly used electrode configurations: (1) patch-patch (PP), (2) catheter-patch (CP), and (3) catheter-catheter (CC). analysis of these simulations indicates that : (1) the PP and CP configurations are more effective at channeling energy to the myocardium than the CC configuration; (2) small electrodes and the edges of the electrodes give rise to high local current densities which might cause damage to the myocardium: (3) energy delivered to the myocardium is not significantly altered for different electrode placements tested; (4) electrode size influences current density distribution, especially near the electrodes; and (5) energy distribution is sensitive to the relative conductances of the myocardial tissue and blood     

Filling of dislocation levels in strong electric fields

The dependence of the filling factor for occupation of the energy levels of an edge dislocation by electrons on the external electric field is investigated theoretically. An analytical relation is derived for the filling factor. It is established that the dislocation filling factor decreases as the electric field is increased. Fiz. Tekh. Poluprovodn. 32, 36–37 (January 1998)     

A survey of electric and magnetic fields among VDT operators inoffices

The ambient electric and magnetic fields as well as the electromagnetic fields associated with video display terminals (VDTs) at 150 offices are measured. The aim of the study is to determine the general level of the various electromagnetic parameters in offices and establish a technical base for a case referent study of skin symptoms among VDT workers. The median value of the 50-Hz background field in the 150 offices is 0.07 μT. Seven of the offices have background levels higher than 0.5 μT, which is high enough to cause distortion of the picture on the screen. The dominant source for electric fields in the ELF range is electric equipment in the office, not the VDTs. The equivalent surface potential is less than 0.5 kV for 63% of the measured VDTs. The computer monitor is a major source of magnetic fields in the offices. The median value of the magnetic field in the ELF range in front of the VDT is 0.21 μT, and in the VLF range it is 0.03 μT     

A monolithic conditioner for thermocouple signals

The authors discusses a monolithic signal conditioner for direct thermocouple input which provides gain, common-mode signal rejection, and cold-junction compensation. It provides 50 to 1 ambient temperature rejection and a nominal 10 mV//spl deg/C output range. It operates on as little as 800 /spl mu/W, provides a thermocouple fault alarm and has provision for use as a set-point feedback controller as well as for signal measurements. The circuit is fabricated on a standard linear IC process and uses laser-wafer-trimmed thin-film resistors to achieve 1/spl deg/C temperature calibration.     

Weak electric fields affect plant development

High-strength electric currents and fields can alter plant physiology by the production of heat within the plant tissue and by the ionization of air molecules at the plant tips. It has been suggested that weak low-frequency electric and magnetic filelds may alter germination and early plant development [4], [5], but the question has not been resolved. Our aim was to determine the possible existence of weak electric-field effects on sunflower germination and to calculate the electric-field threshold inside the seed for any such effects. We found that an applied electric field of 5 kV/m, 60 Hz, produced an internal electric field of 7.5 ×10-4 V/m in a seed in moist soil and resulted in a statistically significant decrease of about 5 percent in germination rate. No effect was found for an applied field of 1 kV/m (1.5 ×10-4 V/m inside the seed). These results established for the first time that electric fields can affect plants by a nonthermal mechanism other than air ionization.     

Leakage at low electric fields in thin oxides

Leakage currents at high electric fields in silicon dioxide films are known to be dominated by tunnelling from the conduction band of the silicon into the oxide conduction band. Little work has been reported on conduction at low electric fields and the effects of aging on this low-level mechanism. We report on the results of experiments indicating that low-field conduction in SiO2 may be of a Poole-Frenkel nature (i.e. a hopping mechanism).     

A simple method for calculating electric and magnetic fields inGTEM cell

A method based on coordinate transformation is presented to calculate the electric and magnetic field distributions in gigahertz TEM cells (GTEM cells). Here quasi-static approximations are employed, therefore the results are valid once operational frequencies well below the cutoff frequency of the cell. The method is illustrated by calculating the fields in a typical test structure. The results indicated here are useful in radiated emission and susceptibility studies     

Electrical conductivity of n-InSb films in strong electric fields

The effect of a strong electric field on the electrical conductivity of n-InSb films grown on oxidized silicon substrates was considered. It is established that the electrical conductivity increases with increasing charge-carrier density. The activation energy of charge carriers is estimated from experimental data.     

A cellular preconcentrator utilizing dielectrophoresis generated by curvy electrodes in stepping electric fields

Concentrating rare cells, such as circulating tumor cells (CTC), circulating fetal cells, and stem cells, is an important technique in biological and clinical studies. The main purpose of the present study was to design a dielectrophoretic microdevice for achieving an effective preconcentration of cells. Interdigitated, curvy electrodes were designed to generate the stepping electric field by switching the electric field to an adjacent electrode pair via relays. The positive dielectrophoretic cells were not only conveyed in the direction of the stepping electric field but were also concentrated at the last pair of electrodes as the high-electric-field region between the adjacent electrodes was gradually decreased in the direction of the stepping electric field. Numerical simulations of the electric field and the particle trajectory were performed to demonstrate the concept of the proposed design. The overall circuit system generating the stepping electric field for cellular pre-concentration was constructed on a printed circuit board (PCB) and the microdevice was assembled with the PCB. The pre-concentration of HeLa cells, which are a human cervical carcinoma cell line, was successfully achieved and took about 340 s in the preliminary experiment when the peak-to-peak voltage of 10 V and a frequency of 1 MHz were applied.     

Electromagnetic complex source pulsed beam fields

Vector electromagnetic pulsed beam fields are constructed by using current dipoles located at complex coordinate points. As in the scalar case, the direction, collimation, and directivity of the field are determined essentially by the imaginary displacement of the source coordinate. The vector fields also depend on the polarization of the dipole with respect to the beam axis. The properties of the field for two special cases in which the dipole is directed either along or transverse to the beam axis are examined analytically and numerically. The general polarization case is thereby considered as a superposition of these two special cases. As expected, the strongest radiation is achieved when the dipole is directed transverse to the beam axis     

A note on the mixed potential representation of electric fields inlayered media

A mixed potential formulation is given for electrical fields in layered environments. Contributions to the field from charges are identified explicitly through a scalar Green's function for layered media. The outcome is a computationally expedient Sommerfeld integral representation     

Second-order model of membrane electric field induced by alternating external electric fields

With biological cells exposed to ac electric fields below 100 kHz, external field is amplified in the cell membrane by a factor of several thousands (low-frequency plateau), while above 100 kHz, this amplification gradually decreases with frequency. Below 10 MHz, this situation is well described by the established first-order theory which treats the cytoplasm and the external medium as pure conductors. At higher frequencies, capacitive properties of the cytoplasm and the external medium become increasingly important and thus must be accounted for. This leads to a broader, second-order model, which is treated in detail in this paper. Unlike the first-order model, this model shows that above 10 MHz, the membrane field amplification stops decreasing and levels off again in the range of tens (high-frequency plateau). Existence of the high-frequency plateau could have an important impact on present theories of high-frequency electric fields effects on cells and their membranes.     

On the error exponent of trellis source coding

In this paper, we develop a single-letter lower bound on the error exponent for the problem of trellis source coding. We demonstrate that for the case of a binary source with the Hamming distortion measure, and for rates close to the rate-distortion curve, this bound is superior to Marton's block-coding exponent, for the same computational complexity.     

Summary of electric vehicle energy source technologies

The many requirements that electric vehicles impose on energy sources are presented. The capabilities and potential problem areas of various electrochemical energy sources being considered for vehicle propulsion are reviewed, and their state of technology development is compared to expected vehicular performance requirements.     

TDOA声源定位中阵列阵型对误差的影响

在麦克风阵列声源定位中,不同阵列阵型及声源频率高低均对定位结果产生影响,探讨上述不同变量对定位结果产生误差的定量分析。使用到达时间差测量(TDOA)算法,运用16个麦克风分别组成十字型、同心圆、方型、L型、Y型阵列,探讨不同形状的麦克风阵列在不同频率声源下所产生的定位误差,并在Matlab上进行仿真分析,尝试得到较为准确的声源定位结果,提出一种误差最小的用于麦克风阵列声源定位的同心圆阵列阵型。