Static Phenomena Research Articles

A Reverse Conduction Static Induction Thyristor Model for Circuit Simulation

In a field of simulation concerning semiconductor power devices, there are process simulation, device simulation, circuit simulation. These simulations are selected for their purpose. In order to analyze static and dynamic phenomena of semiconductor power devices or passive devices, and to support the design of power conversion systems, many circuit simulation models of semiconductor power devices such as GTOs, IGBTs, Thyristors are fabricated.In this paper, a reverse coducting static induction thyristor model is proposed. The model is made up of SI thyristor model with two transistor analogue and diode model with SPICE internal diode, capacitance and resistance. For confirming the accuracy of this circuit model, some experiments are carried out. As a result, good agreement are shown between the measured and calculated results.

NMR methods for imaging of transport processes in micro-porous systems

Magnetic resonance imaging (MRI) allows non-destructive and non-invasive measurement and visualisation of both static and dynamic water phenomena. Flow and transport processes can either be measured by following the local intensity in time-controlled sequential images, by mapping the effect of contrast agents or labelled molecules, or by mapping the (proton) displacement in a well known time interval directly. By a proper choice of methods, a time window ranging from milliseconds to weeks (or even longer) can be covered. Combining transport measurements with relaxation time information allows the discrimination of transport processes in different environments or of different fluids, even within a single picture element within an image. Here we present an overview of the principles of NMR imaging techniques to visualise and unravel complex, heterogeneous transport processes in porous systems. Applications and limitations will be discussed, based on results obtained in model and artificial soil systems.

Static and dynamic properties of frictional phenomena in a one-dimensional system with randomness

Static and dynamic frictional phenomena at the interface with random impurities are investigated in a two-chain model with incommensurate structure. Static frictional force is caused by the impurity pinning and/or by the pinning due to the regular potential, which is responsible for the breaking of analyticity transition for impurity-free cases. It is confirmed that the static frictional force is always finite in the presence of impurities, in contrast to the impurity-free system. The nature of impurity pinning is discussed in connection with that in density waves. The kinetic frictional force of a steady sliding state is also investigated numerically. The relationship between the sliding velocity dependence of the kinetic frictional force and the strength of impurity potential is discussed.

Functional theory of extended Coulomb systems

A consistent formulation is presented for a functional theory of extended quantum many-particle systems with long-range Coulomb interactions, which extends the density-functional theory of Hohenberg and Kohn to encompass the theory of dielectrics formulated in terms of electric fields and polarization. We show that a complete description of insulators in the thermodynamic limit requires a functional of density and macroscopic polarization; nevertheless, for any insulator the state with zero macroscopic electric field can be considered a reference state that is a functional of the density alone. Dielectric phenomena involve the behavior of the material in the presence of macroscopic electric fields that induce changes of the macroscopic polarization from its equilibrium value in the reference state. In the thermodynamic limit there is strictly no ground state and constraints must be placed upon the electronic wave functions in order to have a well-defined energy functional; within these constrained subspaces the Hohenberg-Kohn theorems can be generalized in terms of the density and the change in the macroscopic polarization. The essential role of the polarization is shown by an explicit example of two potentials that lead to the same periodic density in a crystal, but different macroscopic electric fields and polarization. In themore » Kohn-Sham approach both the kinetic and the exchange-correlation energy are shown to depend upon the changes in polarization; this leads to generalized Kohn-Sham equations with a nonlocal operator. The effect can be traced to the polarization of the average exchange-correlation hole itself in the presence of macroscopic fields, which is essential for an exact description of static dielectric phenomena. {copyright} {ital 1997} {ital The American Physical Society}« less

Effects of strain-rate and ageing at 573 and 973 K on the mechanical (compressive) behaviour of 〈110〉 oriented (‘soft’) NiAl single crystals with and without microalloying additions of Ti, Zr, and Hf. II

The effects of impurity gettering on the mechanical behaviour of NiAl have received extensive attention recently. The present work was directed at static and dynamic strain ageing phenomena and strain-rate sensitivity minima, which are supposed to be related to the dislocation-impurity interactions, for 〈110〉 oriented NiAl single crystals with microalloying additions of Ti, Hf, and Zr as getters (0.1 at.%). The influence of ageing at 573 and at 973 K on compressive properties and microhardness was also investigated. The gettering effects were found to be less pronounced for NiAl + Ti and more pronounced for NiAl + Hf and NiAl + Zr, and the gettering effects lead to marked changes in the strength and ductility behaviour after ageing at 973 K as well as static strain-ageing at 573 K, and to strain-rate sensitivity. The observed effects are believed to be due to the formation of precipitates containing Ti, Hf, or Zr, their coarsening during ageing, and interactions of dislocations with either precipitates and/or solute atoms and interstitials.

Investigations on3He crystals using optical interferometry at mK temperatures

Our recent high-resolution interferometric investigations on4He solid/superfluid interfaces have revealed interesting static and dynamic phenomena in quantum crystals. In this work we have initiated studies of3He crystals and developed a new optical setup which combines two interferometric principles with different resolutions. Our setup allows determination of overall crystal shapes as well as high-resolution studies of facets down to millikelvin temperatures.

Equilibrium phase transitions in a porous medium.

Static critical phenomena of a three-dimensional Ising model confined in a porous medium made by spinodal decomposition have been studied using large-scale Monte Carlo simulations. We thus examine the influence of the geometry of Vycor-like materials on phase transitions. No surface interactions (preference of the Vycor-like material for one phase above the other) are taken into account. We find that the critical temperature depends on the average pore size D as ${\mathit{T}}_{\mathit{c}}$(D)=${\mathit{T}}_{\mathit{c}}$(\ensuremath{\infty})-c/D. The critical exponents are independent of pore size: we find \ensuremath{\nu}=0.8\ifmmode\pm\else\textpm\fi{}0.1, \ensuremath{\gamma}=1.4\ifmmode\pm\else\textpm\fi{}0.1, \ensuremath{\beta}=0.65\ifmmode\pm\else\textpm\fi{}0.13. No divergence is observed for the specific heat, indicating \ensuremath{\alpha}\ensuremath{\le}0. All data for all pore sizes can be collapsed well with the scaling function for the magnetic susceptibility \ensuremath{\chi}${\mathit{L}}^{\mathrm{\ensuremath{-}}\ensuremath{\gamma}/\ensuremath{\nu}}$=\ensuremath{\chi}\ifmmode \tilde{}\else \~{}\fi{}(${\mathit{tL}}^{1/\ensuremath{\nu}}$), where t=T/${\mathit{T}}_{\mathit{c}}$(D)-1. These critical phenomena are consistent with those computed for the randomly site-diluted Ising model. Experimental realizations of our numerical experiments are discussed. \textcopyright{} 1996 The American Physical Society.

COUPLED FINITE ELEMENT AND FOURIER TRANSFORM METHOD FOR TRANSIENT SCALAR FIELD PROBLEMS

ABSTRACT Transient electromagnetic field problems occur in the operation of electrical machinery and devices. Because of the complexity of the device geometry, it is customary to employ a numerical method to discretize the field region and combine it with a time stepping method. In this paper, an economical way of combining the finite element frequency domain solution with integral Fourier transform for evaluating the transient behavior, is described. Applications of this method to an L-R circuit and to a model for studying static electrification phenomena are presented.

Time-dependent critical spin fluctuations in magnetic salts

A short perspective of dynamic critical scattering is given, together with an orientation to modern theories of static and dynamic critical phenomena. The materials discussed are magnetic salts that are believed to spontaneously order through correlations induced by a Heisenberg exchange interaction between atomic spin moments.

Bifurcation and complex dynamics in fixed-bed catalytic reactors

Bifurcation theory and numerical continuation techniques are used to investigate the complex static and dynamic characteristics of a fixed-bed reactor modelled by a heterogeneous cell model. The model takes into account the thermal coupling between adjacent reactor cells due to radiation and conduction. A rich variety of interesting static phenomena is uncovered, including, multiplicity with a large number of steady states. A Hopf bifurcation point is identified from which a periodic branch emanates. The periodic branch terminates at a homoclinical infinite period (IP) bifurcation point. Wrong-way behaviour and sensitivity of the final steady-state profile to initial conditions are also observed.

A Topographic View of Supercooled Liquids and Glass Formation

Various static and dynamic phenomena displayed by glass-forming liquids, particularly those near the so-called "fragile" limit, emerge as manifestations of the multidimensional complex topography of the collective potential energy function. These include non-Arrhenius viscosity and relaxation times, bifurcation between the alpha- and beta-relaxation processes, and a breakdown of the Stokes-Einstein relation for self-diffusion. This multidimensional viewpoint also produces an extension of the venerable Lindemann melting criterion and provides a critical evaluation of the popular "ideal glass state" concept.

Bitter legacy: ideology and politics in the Arab world

Ideology has been described as the single most powerful force in modern Arab politics. In this analysis, Salem examines 20th-century nationalist, Marxist, and Islamic movements in the Arab world. He uses a multidisciplinary approach and a breadth of theoretical work from the fields of sociology, social psychology, and political science. He also draws on primary Arabic sources, examining the main works of Sati al-Husri, Michel Aflaq, Sayyid Qutb, and Antoun Saadeh. Salem argues that, throughout the 20th-century, ideology has served a crucial political function in integrating the masses into the modern state system and in legitimising new elites. This ideology was stimulated by the rapid pace of social, economic, political, and cultural change that began at the turn of the century and which caused considerable strain within the structure of the existing traditional belief systems. He not only analyses the rise of numerous movements including Arab nationalism, Marxism, and Islamic fundamentalism, but also Egyptian, Syrian, and Lebanese nationalism. Unlike many other studies that often treat ideologies as separate and static phenomena, the author places ideology in a comparative and dialectical framework. He approaches the work from a multidisciplinary perspective to study the movements and how their respective ideologies compete and reinforce one another. By considering religious and cultural variables and by examining a movements's roots, its appeal to different classes and generations, and how it fulfills people's psychological needs, the author provides a fuller understanding of the Arab society as a whole. Bitter Legacy aims to provide a panoramic review of modern Arab political thought and offers analytical tools for comprehending ideological change.

Relaxation phenomena in a system of interacting Stoner—Wohlfarth particles

The real ferromagnetic fine-particles system is simulated with an Interacting Stoner-Wohlfarth Particles System (ISWPS). The dynamic ISWPS model could describe both the static magnetization processes and relaxation phenomena. Results of the simulations are presented.

A PWL ladder circuit which exhibits hysteresis

AbstractA circuit model for static hysteresis is presented. the circuit has a ladder structure with linear capacitors and piece wise linear resistors. the model behaviour shows all basic characteristics of static hysteresis phenomena. the model is put into relation with others proposed in the literature. an analysis of the model properties and a detailed comparison with the static Preisach model are made.

Molecular interactions on surfaces

The potential energy surfaces describing interactions between molecules lie at the heart of much of chemical physics. Numerous spectroscopic and scattering techniques can provide a fairly direct measure of the interactions between gaseous species. Less detailed information is available for the lateral interactions between adsorbed molecules since these must be inferred from their impact upon static, kinetic, and dynamic surface phenomena. We have recently combined measurements of the coverage-dependent isothermal molecular desorption rate and adsorption isotherms with a quasiequilibrium analysis to make progress in understanding the general features of the lateral interaction potential between similar and different adsorbed molecules. Results from a variety of systems ranging from physisorption to weak chemisorption are presented which emphasize several dominant trends. Our results for physisorption systems are generally quantitatively consistent with a lateral potential described by a simple screened gas phase potential. For chemisorption systems, however, we often find evidence for a weak attractive well in the lateral potential with no counterpart in the gas phase potential. These weak attractions have a pronounced impact upon coverage-dependent static and kinetic phenomena.

Investigation on static electrification characteristics of transformer oil

In spite of extensive research and development (R and D) efforts for more than a decade, static electrification phenomena are still poorly understood, hence detailed investigations are necessary for an improved understanding for the cause of many failures of forced oil-cooled power transformers, which have been reported recently. Moreover, the methodologies for quantifying the static electrification of transformer oil are yet to be standardised. This paper details the investigations carried out on the charging tendency of paraffinic-based oil, employing laboratory methods, viz. mini static tester (MST) and spinning disc system (SDS), by varying influencing parameters, such as flow rate, temperature, moisture content, ageing, presence of copper, effect of additive, etc. In the case of MST, the flow rate was varied from 0.4 to 1.0 ml/s and, in the case of SDS, the rotational speed was varied from 250 to 2000 rpm. Further, the influ of 1,2,3 benzotriazole (BTA) as a charge suppressing agent, upto a concentration of 150 ppm, was also studied by both methods. The effect of copper, ageing, temperature and moisture content have also been studied on BTA-treated oils. It is also observed that both methods have ranked similarly the oils treated with different concentrations of BTA, at different humidity levels.

Hardening and strain-ageing by vacancies and their aggregates in FeAl

Abstract Yield stress and ageing discontinuities have been examined in a Fe-43% Al alloy after carefully ageing in an attempt to control the number of excess vacancies and the form of their annihilation aggregates. Vacancies, probably present as submicroscopic aggregates, can act as strengthening obstacles to subsequent dislocation movement. When the vacancies are present in the form of somewhat coarser aggregates or dislocation loops they may act both as dislocation obstacles and vacancy sources during subsequent deformation at intermediate temperatures. The strengthening obtained depends sensitively on the precise vacancy aggregate present. In addition, such vacancy aggregates can lead to significant dynamic dislocation locking and the appearance of both static and dynamic strain ageing phenomena.

Ising-Bloch transition in a nematic liquid crystal

We consider a nematic slab with homeotropic anchoring and investigate the effect of a magnetic field, H, parallel to the plates and an electric field, E, perpendicular to them (e a 0). The magnetic field is either fixed, or rotating at a frequency ω around an axis perpendicular to the plate. The main effect consists in an Ising-Bloch transition of the walls observed either in the (H 2 , E 2 ) or (H 2 , ω) parameter space. The latter case corresponds to the experimental observation recently made at Brandeis University [1]. Some of these results are understood within the framework of a Ginzburg-Landau model, directly derived from the Oseen-Zocher-Frank expression for nematic elasticity, which accounts for the main static and dynamic experimental phenomena observed. The spiral shaped textures obtained in the dynamic case probably represent one of the first simple physical analogs of the chemical and biological phenomena observed in excitable media

Magnetic resonance imaging of soil-water phenomena

2D and 3D images of static and dynamic water phenomena in packed clay soil columns were obtained by MRI. A spin-echo spin-warp Fourier imaging sequence, together with prefocused 90° selective pulse for 2D imaging, was selected. The images demonstrate the potential of using MRI for studies of static and dynamic water phenomena in soil with modest iron content and adequate water content.

Time-resolved photoluminescence in YBa2Cu3O6.4 and Bi2Sr2Ca1-zLuzCu2O8.

We report on the spectral investigation of the time-resolved photoluminescence in insulating ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.4}$ (YBCO) thin films and ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{1\mathrm{\ensuremath{-}}\mathit{z}}$${\mathrm{Lu}}_{\mathit{z}}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8}$ (BSCLCO) single crystals. The characteristic decay times of the photoexcited states in YBCO are two orders of magnitude longer than in BSCLCO, and have a different dependence upon the emission wavelength. These observations provide insight into the static photoinduced phenomena recently found in YBCO.