Design and tests of the z-coordinate drift chamber system for the opal central detector at LEP

A system of drift chambers has been designed to make high resolution measurements of the z-coordinates of charged tracks at the outer radius of the OPAL central detector at LEP. The unit module of this detector is a 25 cm drift length bidirectional cell with six sense wires in a thin 50 cm wide by 29 mm high drift slot. Tests indicate that the chamber has a wide and stable electric field operating range and its performance is unaffected by small misalignments between the drift electric field and an external magnetic field. The drift cell was found to have uniform acceptance up to its geometrical boundaries, and the z-resolution for beam tracks normal to the chamber was measured to be in the range of 40–175 μm.     

Method for the Calculation of the Electric Field near a Paraboloidal Metal Tip above a Conducting Plane

A theoretical method for the determination of an electric field near a paraboloidal metal (conducting) tip has been proposed. The accuracy of the proposed numerical solution has been analyzed. The dependence of the electric field strength at the tip vertex on the distance to the plane, which is applicable for predicting fields in various physical problems and engineering calculations, has been considered. The characteristic spatial distributions of the electric potential and field are presented.     

Voltage response and field reconstruction for a miniature fieldprobe in a spatially nonuniform electric field

A miniature E-field probe employing a 0.6-mm linear dipole antenna has been developed. The authors describe an analytical study of the probe's response to a spatially varying electric field. On the basis of the Nyquist sampling theorem, the spatial sampling frequency at which an electric field should be measured for good reconstruction is established. Using antenna theory, the voltage response of the probe is found in terms of the antenna's transmitting current and the measured electric field. This relationship is used to reconstruct the electric field from a set of discrete voltage responses. A method-of-moments program has been developed to determine numerically the voltage response of the antenna structure to a spatially varying electric field. Numerical results, which allow for the testing of certain theoretical findings important for analyzing measurement data, are presented. Although developed for only one-dimensional fields, the methodology can be applied to general three-dimensional fields     

Electronic Structure and Physical Characteristics of Dioxin Under External Electric Field

Dioxin is a highly toxic and caustic substance, which widely existed in the atmosphere, soil and water with tiny particles. Dioxin pollution has become a major problem that concerns the survival of mankind, which must be strictly controlled. The bond length, bond angle, energy, dipole moment, orbital energy level distribution of dioxin under the external field are investigated using DFT (density functional theory) on basis set level of B3LYP/6-31G (d, p). The results indicate that with the increase of the electric field, the length of one Carbon-Oxygen bond increases while another Carbon-Oxygen bond decreases. The energy gradually decreases with the electric field, while the change of the dipole moment has an opposite trend. In the infrared spectra, the vibration frequency decreases with the electric field increasing and shows an obvious red shift. Moreover, the ultraviolet-visible absorption spectra under different electric fields are analyzed with TD-DFT (time-dependent density functional theory) method. The wavelength of the strongest absorption peak increases and occurs red shift with the increase of the electric field. All the above results can provide reference for further research on the properties of dioxin under different external electric field.     

Optical response of a d-fiber antenna in a finite-element analysis intended for radio-over-fiber applications

An all-fiber antenna with a piezoelectric polymer-coated circular-core D fiber has been characterized by finite-element analysis. The response of the D-fiber antenna was determined over a wide frequency range from 1 to 500 MHz. The modeling predicts an electric-field-induced phase shift of 2.43 x 10(-5) rad/(V/m)/m at 5 MHz. At frequencies higher than 8 MHz the optical response is dominated by radial resonances of the D-fiber-coating composite. From the simulation results a minimum detectable electric field of 41-muV/m has been achieved with a 1-km length of coated D fiber. In addition, a D-fiber antenna network intended for microcellular communications has been analyzed by shot-noise-limited detection.     

Crack arrest model for a piezoelectric plate — A generalised Dugdale model

The constant search for new materials has provided impetus to research in piezoelectric materials. An anti-plane problem for a cracked unbounded two-dimensional poled piezoelectric plate has been investigated. The crack rims open on account of shear mechanical forces applied at the remote boundary and in-plane electric displacement field prescribed at the infinite boundary. Thus the crack yields both mechanically and electrically. Consequently, a plastic zone and a saturation zone protrude ahead of each tip of the crack. These developed zones are in turn closed by applying yield point shear stress at the rims of plastic zone and normal closing saturation limit displacement on the rims of saturation zones. Two cases are investigated when (i) the developed saturation zone length exceeds that of the developed plastic zone, and (ii) saturation zone length is smaller than that of the plastic zone. Fourier integral transform method is used in each case to obtain the length of plastic zone and saturation zone. Closed form analytic expressions are obtained in each case. Crack opening displacement and potential drop across the rims of the crack are also obtained. The effect of mechanical loads on crack closure in the presence of electric field is investigated and vice-versa. Also energy release rate expressions are obtained for both the cases.     

电场电炉合成碳化硅晶须的研究

给出了一种低成本合成高纯碳化硅晶须的新方法,采用电场催化技术,在较低的温度(120～1400℃)下合成了直径为100～200nm、长度为5～50μm的碳化硅晶须,研究结果表明,以炭黑和SiO₂微粉为原料在电场电炉中能够合成出高纯度、高含量的碳化硅晶须。     

The analysis of time-dependent creep in FGPM thick walled sphere under electro-magneto-thermo-mechanical loadings

Time-dependent creep response of a smart sphere made of functionally graded piezoelectric material (FGPM) is investigated. The vessel is subjected to an internal pressure, a uniform temperature field, an electric potential and a uniform magnetic field. Under such a loading condition initial elastic stresses are locked in the vessel at zero time. Due to high temperature, creep evolution causes stress redistribution in the sphere which is followed by electric potential redistribution across the thickness of the sphere. History of radial stresses is always reflected by history of electric potential which can be used for condition monitoring of the smart sphere. From the initial elastic stresses it has been found that imposing an electric potential decreases effective stresses. It has also been concluded from history of electric potential that electric potential redistribution is decreasing due to creep evolution and therefore this is followed by increasing effective stresses.     

The Temperature Effects on the Parabolic Quantum Dot Qubit in the Electric Field

The temperature effects on the parabolic quantum dot qubit in the electric field have been studied under the condition of electric-LO-phonon strong coupling using the variational method of Pekar type. The numerical results lead us to formulate the derivative relationships of the oscillation period of the electron in the superposition state of the ground state and the first-excited state with the electric field, the electron-LO-phonon coupling constant and the confinement length at different temperatures, respectively.     

Carrier depletion and exciton diffusion in a single ZnO nanowire

Carrier depletion and transport in a single ZnO nanowire Schottky device have been investigated at 5?K, using cathodoluminescence measurements. An exciton diffusion length of 200?nm has been determined along the nanowire axis. The depletion width is found to increase linearly with the reverse bias. The origin of this unusual dependence in semiconductor material is discussed in terms of charge location and dimensional effects on the screening of the junction electric field.     

Novel ring structure for minimisation of screening effect in carbon nanotube based field emitters

Carbon Nanotubes (CNTs) are promising candidates for cold cathodes because of their high aspect ratio and robustness. However, the major hindrance in cold cathode based applications is the screening effect, which reduces the effective field at the tip and thereby the current density. The emission current can be improved by minimising the screening effect. The adverse effect of screening can be addressed by either controlling the growth density or by optimising the patterns of CNT cathodes. Here, novel patterns have been used to increase edge length per unit area in planar vertically aligned CNT bundles. Our motive was to increase the number of effective emitters, since the CNT at the edges are less screened by the proximal CNTs. By varying geometry and spacing of solid CNT dot patterns and by introducing the square ring structures; we could successfully enhance the effective emitters at the edges. It has been observed that an enhancement of edge length from 0.032 per micron to 0.2 per micron increases the current density from 0.71mA/cm² to 16.2 mA/cm² at a field of 4.5 V/μm. CNTs in dotted structure with high value of edge length per unit area emit very high current density as compared to other dotted structures with low value of edge length per unit area Simulation studies confirms our argument that CNTs at the corners are the least screened and have the maximum local electric field.     

Alternating-Current Solenoid of Finite Length in a Medium with Hall Conductivity

The electric field of an alternating-current solenoid of finite length in conducting media is investigated. The first-order (Hall) effect of an externally applied, constant, axial magnetic field on the electric field is considered. The coil impedance and the electromotive force induced in a certain closed path are calculated numerically for small frequencies.     

The Local Electric Field in Photorefractive and Other Semi-insulating Materials

Abstract

Debye-Huckel theory is applied to determine the local electric field around a dipole in a photorefractive semi-insulating material. The dipole can be either induced, as in the presence of an electric field, or permanent. It is shown that when the Debye screening length is large, the local electric field E is given by E_M(? + 2)/3, where E _M is the macroscopic electric field. On the other hand, when the Debye screening length is small, the local electric field is equal to the macroscopic electric field.     

Effect of electric field on the vapor-phase growth of carbon nanostructures

A mathematical model of dc gas discharge plasma has been developed in order to determine the electric field strength at a substrate surface during plasmachemical deposition of carbon nanostructures. A numerical solution of the model equations has been obtained using the experimentally determined boundary conditions and model parameters. A comparison of the solution to experiment confirms the adequacy of the proposed mathematical model, which provides the electric field profiles and the electron and ion density distributions near the substrate surface. Estimations show that, for carbon nanostructures with a characteristic size of about 30 nm, the electric field strength at the surface is sufficiently high to provide for their directional growth along the field.     

The Electric Field Area in a Vacuum with Moving Charges

Technical Physics Letters - An exact analytical expression has been derived for the area of an electric field generated by charged particles moving at constant acceleration in vacuum. An...     

Optical fiber sensor for electric field and electric charge using low-coherence, Fabry-Perot interferometry

An optical fiber sensor for electric field and electric charge, based on the deflection of a small cantilever, has been developed. When the sensor head is placed in an electric field, induced charging produces deflection of the cantilever, which is measured using low-coherence, Fabry-Perot interferometry. The sensor has been used to measure the electric field in the vicinity of a Van de Graaff generator, in the range 135-650 V/cm. The measured deflections are in good agreement with the predictions of a simple model equating the electrostatic and mechanical forces acting on the cantilever.     

Interference of Three Electron Waves and Its Application to Direct Visualization of Electric Fields

We present a method for the interference of three electron waves and its application to direct visualization of pure-phase objects such as electromagnetic microfields. Using a transmission electron microscope equipped with a field-emission electron gun and two electron biprisms, an object wave and two reference waves at either side of the object wave are superposed to produce a new type of interference pattern. In this pattern, equal-phase lines of the object wave are directly displayed as intensity modulation of periodic interference fringes. An electric field around a latex particle, induced by electron-beam irradiation, has been observed. The electric charge of the particle is estimated, from an observed phase shift, to be 6.4 × 10⁻¹⁷C, which is equal to about 400 electrons. A change of the electric field around charged alumina particles at high temperatures has been observed dynamically.     

An approach for analysis of poled/depolarized piezoelectric materials with a crack

In this paper, the influence of dielectric medium inside a crack on crack growth, in an infinite poled or depolarized ceramic, has been studied by employing an electric boundary condition derived from the exact boundary conditions proposed by Sosa (1996). The effect of remanent polarization has also been examined. The results obtained show that electric displacement on crack surfaces is not always zero. Hence, for studying fracture problems of piezoelectric ceramics with cracks accurately, the exact boundary conditions should be implemented. In addition, the results indicate that the effect of remanent polarization is equivalent to that of a positive electric field and it cannot be neglected. It is also found that a positive electric field always has a tendency to open a crack, and a negative electric field tends to close a crack.     

Solid-state cooling line based on the electrocaloric effect

In this paper, the feasibility of using ferroelectric materials as a cooling device or solid-state refrigerator based on the electrocaloric effect has been considered. The electrocaloric responses of two different ferroelectric capacitors (PMN-25PT, PZN-4.5PT) are studied. In this study, the dynamics of temperature variation at the edges of a layered structure comprised of an electrocaloric material with heatconducting elements on its sides to an applied periodic electric field have been studied. Electrocaloric elements can generate directed heat flux as a thermal pump by alternative switching. A temperature reduction of 6° is obtained in an electric field of 1 KV/mm at a frequency of 1 Hz for PMN-25PT material after applying 80 cycles. It is shown that the type of applied electric pulses and ferroelectric material affect the results.     

The Change in Impedance of a Single-Turn Coil Due to a Flaw in a Coaxial Conducting Cylinder

The problem of detection and location of a small flaw inside a conducting cylinder using an eddy current coil coaxial with the cylinder has been addressed. The electric field at an arbitrary axial and radial position inside the conductor has been obtained from a previous solution of the boundary value problem. An expression for the change in complex impedance due to a small flaw located within a conducting body has been derived and is shown to be a function of the electric field at the position of the flaw. For the case of a degenerate point flaw, this expression is further simplified by using just the value of the electric field at the position of the centroid of the flaw. The overall impedance is shown to be a function of the ratio of the radii of the loop and cylinder and of the conductivity of the material. The expression for the change in complex impedance has been factored into two terms, one dependent on the axial location of the flaw, and the other on the depth of the flaw. The axial location of the flaw is seen to affect only the magnitude and phase of the change in impedance; whereas the depth of the flaw is seen to affect both the magnitude and phase of the change in impedance. Plots of the complex change in impedance as a function of the axial location and depth of the flaw have been provided to illustrate its functional dependence on these parameters.