Table of contents

We show for the first time that it is possible to separate a population of nanoparticles into two subpopulations solely on the basis of their dielectric properties. Using nanofabricated electrode arrays it has been shown that a solution of 93 nm diameter latex beads with a distribution of surface charge can be separated by the application of non-uniform AC electric fields (dielectrophoresis). The mixture separated into two populations, one experiencing positive dielectrophoresis and the other negative dielectrophoresis.

This review concerns the experimental and theoretical publications devoted to the important problem of the large piezoelectric anisotropy in -based polarized ferroelectric ceramics.

The dielectric properties of biaxially stretched polyethylene terephthalate (PET) films of thickness and 68% degree of crystallinity were investigated by means of dielectric relaxation spectroscopy in the frequency range Hz and the temperature range C. Differencial scanning calorimetry (DSC), in the range C, was employed to investigate the thermal properties of the PET samples. Besides measuring the relaxation associated with the glass transition and the secondary relaxation, special attention has been paid to the investigation of DC-conductivity-related effects. They give rise to high dielectric permittivity values and dielectric losses at low frequencies and high temperatures. The results are analysed within the complex permittivity formalism and discussed in terms of interfacial Maxwell - Wagner - Sillars polarization, the peak, conductivity relaxation, space-charge polarization, electrode polarization and DC conductivity. DC conductivity values determined from frequency plots of the AC conductivity follow the Vogel - Tamman - Fulcher equation at temperatures higher than the glass transition temperature, indicating that the charge-carrier transport mechanism is governed by the motion of the polymeric chains. On the basis of the temperature dependence of the DC conductivity PET is classified as a fragile system.

A scanning electron microscope (SEM) mirror-image method (MIM) is employed to investigate the charging behaviour of polarized polymethylmethacrylate (PMMA) under electron-beam irradiation. An ellipsoid is used to model the trapped charge distribution and a fitting method is employed to calculate the total amount of the trapped charge and its distribution parameters. The experimental results reveal that the charging ability decreases with increasing applied electric field, which polarizes the PMMA sample, whereas the trapped charge distribution is elongated along the direction of the applied electric field and increases with increasing applied electric field. The charges are believed to be trapped in some localization states, of activation energy and radius estimated to be about 19.6 meV and , respectively.

In this paper we develop an interpretation of magnetization data appropriate to materials where magnetization reversal occurs as a two-stage process: domain nucleation followed by domain wall motion, and apply it to films with perpendicular magnetic anisotropy. An interpretation of remanence curve data and time dependence data for a two-stage reversal system is proposed. The two principal remanence curves (IRM and DCD) yield data on the energy barrier distribution, while the delta-I plot which compares these two remanence curves offers a method of characterizing the relative importance of domain nucleation and domain wall motion. The interpretation is then applied to a series of magneto-optic thin films where the film thickness varies from 164 to 830 Å. All but the thickest film show magnetization reversal is controlled by both domain nucleation and domain wall motion. In the 830 Å film only domain wall motion appears important in controlling reversal.

In this paper we apply the interpretation of magnetization measurements developed in an associated paper to Tb/Fe multilayers for magneto-optic recording applications. Our results show that remanence curves and delta-I plots are able to determine the controlling mechanism for magnetization reversal in Tb/Fe multilayers. In the multilayer with the greatest Tb content this domain nucleation controlled magnetization reversal gave way to domain wall pinning controlled reversal for films with more than 6 bilayers. In the intermediate Tb content multilayers, domain wall pinning became important only after 20 bilayers, whereas for the lowest Tb content film reversal remained domain nucleation controlled throughout the series. The form of the time dependence of magnetization is connected to the magnetization reversal process. All the films that showed magnetization reversal dominated by domain nucleation also exhibited a nonlinear ln(t) time dependence whereas films showing domain wall pinning reversal exhibited a linear ln(t) time dependence. The form of the activation volume as a function of applied field is the same for all the films controlled by domain nucleation processes.

A strong quantum correlation between twin-beams at wavelength was observed. The intensity difference noise of twin-beams, which is generated by a semimonolithic OPO cavity pumped by a frequency-doubled and stabilized Nd:YAP laser, is about 80% (7 dB) below the short noise limit at the measurement frequency of 1.5 MHz. The threshold of the optical parametric oscillator is about 20 mW. The parametric dependence of the quantum correlation is experimentally investigated. The experimental results agree with the theory well.

The possibility of detecting and identifying targets immersed in the draught zone of a ship with a lidar is discussed in this paper. It is carried out by a polarimetric codification of optical signals. The sea surface roughness, in conjunction with wind direction, greatly disturbs light dispersion. Nevertheless, by using the Stokes - Mueller polarimetric formalism, a classification of immersed targets with various surfaces and covering properties can be laid down.

Finite-time thermodynamics with an ecological criterion is applied to an irreversible Carnot heat engine with finite thermal capacitance rates of the heat reservoirs and finite total conductance of the heat exchangers. The ecological function is defined as the power output minus the loss power or the product of the environmental temperature and the entropy production rate. The ecological function is optimized with respect to the cycle temperature ratio and the heat conductance ratio. It is shown that the ecological function is a useful and important criterion for the design of an irreversible Carnot heat engine, considering not only power output but also entropy generation and thermal efficiency. The optimum values of cycle temperature ratios and conductance ratios of irreversible Carnot heat engines are presented. Moreover, from the viewpoint of the ecological function, the thermal capacitance of the cold external fluid should be larger than that of the hot external fluid and the heat conductance of the hot-end heat exchanger should be smaller than that of the cold-end heat exchanger.

The drift velocity and the longitudinal diffusion coefficient of electrons in 0.206% and 1.98% ethane - argon mixtures and in pure ethane were measured in the E/N ranges 0.03 - 3 Td, 0.03 - 25 Td and 0.03 - 300 Td respectively. The measured swarm parameters in the mixtures were used to determine the essential vibrational excitation cross sections of the ethane molecule and those measured in pure ethane were used to derive the elastic momentum transfer cross section for the molecule in conjunction with the above derived vibrational cross sections. Consideration of realistic anisotropies of the electron scattering had little effect on electron swarm parameters.

A kinetic model for the ionization processes in high-temperature air in a strong electric field is developed. The model is used to study numerically the problem of the relaxation of the plasma properties in atmospheric-pressure air to a new steady state after an instantaneous change in the gas temperature between 300 and 1000 - 6000 K. Our simulation shows that the electrical properties of the plasma under the conditions of the leader being a long spark nearly follow the local value of the gas temperature. The reduced field E/N in the leader channel is found to decrease considerably as the gas temperature T increases from 1000 to 6000 K. The decrease in E/N is caused by the formation of NO molecules with low ionization energy at T < 4500 K and by associative ionization during collisions between O and N atoms, which becomes the dominant ionization mechanism at T > 4500 K. As a result, the value of E/N falls to 10 Td at T = 5000 K and to 1.5 Td at T = 6000 K for a current of 1 A and a channel radius of 0.1 cm. This agrees well with the experimental evidence showing that the leader bridges very long air gaps (about 200 m) at a moderate applied voltage (< 5 MV).

The two derivations of the equation of motion for the plasma armature - projectile system in a railgun are reviewed. Although they describe the same kinematical system, it is shown that they yield conflicting descriptions for the action - reaction forces over the plasma armature. The two inductances per unit length for the equations of motion are then given for the case in which the rail and current distributions are in the form of infinitesimally thin sheets and are shown to be different, although for a RAPID railgun this difference is not significant. Next, the lumped-parameter version of the railgun equation of motion is shown to be incapable of explaining anomalous effects occurring in the plasma armature, which have been observed in railgun firings, whereas no such problem arises with the MHD version. Finally, sufficient conditions under which the equations yield equivalent results are given, though these may not be realized in most railgun applications.

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The excitation of gas molecules in flue gas by electron impact is calculated with a Monte Carlo (MC) algorithm for electron dynamics in partially ionized gases. The MC algorithm is straightforward for any mixture of molecules for which cross sections are available. Electron drift is simulated in the first case for homogeneous electric fields and in the second case for secondary electrons which are produced by electron-beam irradiation. The electron energy distribution function, , the energy branching and the rate of excitation are calculated for standard gas mixtures of Ar - , and O. These fundamental process parameters are needed for the study of reactions to remove from flue gas. The calculated results indicate that the production of highly excited molecules in the high electric field of a streamer corona discharge has an efficiency similar to that of electron-beam irradiation.

General equations are derived whose solution gives the dependence of species concentrations of a closed gaseous system on time for a given dependence of temperature on time, on the assumption that either the dependence of pressure in on time or the dependence of volume of system on time is given. Some results from solving a previously proposed model are given for the case when is created by the products of dissociation and ionization and the temperature decreases exponentially from 10 000 K to 2500 K. Special attention is devoted to the relation between time-dependent composition and equilibrium composition.

This paper presents a general model allowing the prediction of the behaviour of given gap submitted to a given voltage. The only input data are the electrode geometry, the applied voltage waveform and the atmospheric pressure and temperature. The model also allows for various conditions for arrest or instability of the discharge. By assuming the discharge channel to be a long conductor and using a typical single LCR conductor line (L, C and R being respectively the line inductance, capacitance and resistance), we derive a predictive model for a positive discharge in long air gaps. This allows one to describe the evolution of the entire discharge, with the parameters L, C and R varying with time according to the channel characteristics and discharge geometry. The model allows us to determine the time histories of the current both during the leader and during the return stroke, the charge, the potential gradient in the leader channel, the power and energy injected into the gap and the channel's thermal radius. It also permits the simulation of an image converter working in streak or frame mode and the leader propagation velocities. Furthermore, it allows the trajectory of the discharge, which is obtained from a probability distribution, to be plotted in real time. Good agreement between computed and experimental results was obtained for various test configurations.

In the present paper, heat wave (LIMM) and pressure pulse (LIPP) measurements of the space-charge distributions in electron-beam irradiated Teflon FEP ( thick) are reported. The space-charge profiles obtained by the two methods are compared over the whole sample thickness. From the LIMM with the back surface heat sink, the space-charge distribution can be found from the surface of illumination up to at least half of the sample thickness. For the position of the bulk space charge, the heat wave and LIPP response results agree with each other to within . By using LIMM, an additional negative charge layer near the surface is found if the electron-beam irradiation is carried out through the metallized sample surface.

In electron-gas secondary neutral mass spectrometry (SNMS), a low-pressure plasma serves both as an ion source for sputter depth profiling the target and for post-ionizing the sputtered neutrals. In its high-frequency mode, a rectangular RF bias is applied to the target. We investigate by PIC/MC kinetic simulation the processes occurring in the vicinity of the substrate as a consequence of the voltage jumps: sheath expansion and contraction, as well as flux and energy of the ions impinging onto the substrate. In particular, we determine the enhancement of the ion current shortly after negatively charging the substrate; this enhancement is due to the acceleration of the large ion population in the expanding sheath. Our results indicate that already at a switch frequency of only 1 MHz the surface treatment by rectangularly shaped RF potentials is dominated by transient effects.

A component of neutral particles with hyper-thermal velocity has recently been observed in the flux from a new type of beam source for production of excited alkali atoms, the so called open diffusion source. The hyper-thermal component is probed with a time-of-flight technique and is found to consist of fast atoms with translational energies of several hundreds of electronvolts. They are formed in charge transfer reactions in the gas phase with cross sections of the order of 4000 - 8000 , which shows that highly electronically excited atoms are involved in the reaction.

We present a Hamiltonian treatment of gyrotrons and cyclotron auto-resonance masers for the cases of resonant particle evolution in a constant electromagnetic field and also for when the field evolves self-consistently with a single resonant particle. The former case relates to high-Q cyclotron resonance maser (CRM) oscillators operating close to saturation or to low-gain devices, whereas the latter describes the self-consistent CRM evolution both of the field and of electrons when the electron beam is perfectly pre-bunched. The particle phase spaces are described in detail for both cases.

A small megagauss generator which produces 110 T by fast semi-destructive capacitor discharge into a single-turn coil of 10 mm diameter is described. For spectroscopic applications the pulses are adequately resolved by 8 - 12 bit, 200 - 1000 MSa data recording systems. The technical implementation of the 60 kV discharge circuit with a total inductance of less than 26 nH, not including the field coil, is discussed in detail. The performance is characterized in terms of the oscillatory circuit parameters R, L and C with brief references to more fundamental studies on transient field phenomena. Safety features as well as the organization and handling of control units and data recording systems are explicitly described to demonstrate the applicability of the generator.