bluuebunny/crossref_metadata_2025 huggingface dataset:
SUMMARY TALK: HIROOMI UMEZAWA, HIS PHYSICS AND RESEARCH
Authors: KAMEFUCHI SUSUMU
Published: October 2004

After giving a brief biographical sketch of H. Umezawa, I shall discuss his physics and research attitude by studying his list of publications. In so doing I first make a statistical analysis and then a global observation. The basic method invoked in the latter consists in my 3-stage theory of understanding, and on this basis I examine the implications of two incidents Umezawa experienced in Europe as well as the present status of his physics.
GAP PROBABILITY OF A ONE-DIMENSIONAL GAS MODEL
Authors: CHEN Y. , MANNING S.M.
Published: October 2004

We investigate the gap formation probability of the effective one-dimensional gas model recently proposed for the energy level statistics for disordered solids at the mobility edge. It is found that in order to get the correct form for the gap probability of this model, the thermodynamic limit must be taken very carefully.
DYNAMICAL BEHAVIOR OF APERIODIC INTERGROWTH CRYSTALS
Authors: SCHMICKER D. , VAN SMAALEN SANDER
Published: October 2004

An overview is given of the current knowledge pertaining to the sliding mode in incommensurate intergrowth compounds. It is found that both theoretical understanding and experimental information is wanting. Responsible for the latter is the lack of high-quality, very pure crystals of incommensurate intergrowth compounds, thus destroying the sliding mode by the effect of pinning. A phenomenological description is presented of the sliding mode in the long wavelength limit, using an extension of the theory of elasticity. The six by six elastic tensor is extended to a nine by nine elastic tensor describing the elastic waves in (3+1)-dimensional aperiodic crystals. The equations of motion are solved and symmetry restrictions on the components of this elastic tensor are given for all superspace groups. Experimental information as obtained by Brillouin scattering, inelastic neutron scattering and X-ray diffraction is discussed against the background of the present theoretical knowledge. Particular attention is given to pinning, to damping and the existence of propagating and overdamped regimes, and to the polarization of the sliding mode.
A CLASS OF COLLECTIVE EXCITATIONS OF THE HUBBARD MODEL: η EXCITATION OF THE NEGATIVE-U MODEL
Authors: DEMLER EUGENE , ZHANG SHOU-CHENG , BULUT NEJAT , SCALAPINO DOUGLAS J.
Published: October 2004

In this series of papers we present a detailed study of the particle-particle collective excitations of the Hubbard model, and their contribution to the density and spin excitation spectrum. In the first paper, we shall investigate the singlet particle-particle pair with momentum (π, π), the η particle, of the negative-U Hubbard model. We review three previously obtained theorems about the η particle and develop a self-consistent linear response theory which takes into account its contribution to the density excitation spectrum in the superconducting state. We show that this self-consistent theory agrees with the exact theorems as well as the results of numerical Monte Carlo simulations.
A FUNCTIONAL INTEGRATION METHOD FOR QUANTUM SPIN SYSTEMS AND ONE-DIMENSIONAL LOCALIZATION
Authors: KOLOKOLOV I.V.
Published: October 2004

A number of problems in statistical physics can be reformulated in terms of a two-state system evolving in a random field. The corresponding evolution operator can be written in the form of time-ordered operator exponential. Functional formalism allows us to rewrite the latter as a product of usual matrix exponentials using a nonlinear change of functional integration variables. In this review I present this formalism applied to two physical systems the quantum Heisenberg magnet and one-dimensional quantum mechanics in a spatially random potential. First, I derive a representation of the partition function of a quantum Heisenberg ferromagnet as a functional integral over number valued fields (a real one and a complex one) free of constraints. The fields of integration as functions of time obey initial conditions instead of the usual periodic boundary conditions. This is a manifestation of the finite-dimensionality of the space of spin states. In the subsequent sections I study the one-dimensional localization problem. The change of functional integration variables gives simultaneously explicit expressions for the averaging weight and for the Green function of the stationary Schrödinger equation. It allows to compute density correlators of arbitrary orders. The generalization to the case of different energy correlators (Berezinskii-Gor’kov equations) is considered too. In the present review such technical points as regularizations of functional integrals and transformations are discussed in more details than in the original papers.
(2+1)-DIMENSIONAL QUANTUM GRAVITY AND THE 3D-ISING MODEL
Authors: MARTELLINI MAURIZIO , RASETTI MARIO
Published: October 2004

We show that (2+1)-dimensional Euclidean quantum gravity is equivalent, under mild topological assumptions, to a Gaussian fermionic system. Furthermore we argue that the corresponding (2+1)-dimensional Euclidean quantum gravity partition function may be related to the partition function of the reduced 3D-lattice Ising model for finite lattices.
NEW DEVELOPMENTS AND CLASSICAL THEORIES OF TURBULENCE
Authors: LEVICH E.
Published: October 2004

In this paper we review certain classical and modern concepts pertinent for the theory of developed turbulent flows. We begin by introducing basic facts concerning the properties of the Navier-Stokes equation with the emphasis on invariant properties of the vorticity field. Then we discuss classical semiempirical approaches to developed turbulence which for a long time have constituted a basis for engineering solutions of turbulent flows problems. We do it for two examples, homogeneous isotropic turbulence and flat channel turbulent flow.

Next we discuss the insufficiency of classical semi-empirical approaches. We show that intermittency is an intrinsic feature of all turbulent flows and hence it should be accounted for in any reasonable theoretical approach to turbulence. We argue that intermittency in physical space is in one to one correspondence with certain phase coherence of turbulence in an appropriate dual space, e.g. Fourier space for the case of homogeneous isotropic turbulence.

In the same time the phase coherence has its origin in invariant topological properties of vortex lines in inviscid flows, modified by the presence of small molecular viscosity. This viewpoint is expounded again using the examples of homogeneous isotropic turbulence and channel flow turbulence.

Finally we briefly discuss the significance of phase coherence and intermittency in turbulence for the fundamental engineering challenge of turbulence control.
THE DYNAMICS OF DIRAC FERMIONS ON SINGULAR SURFACES
Authors: MARTELLINI M. , SEDRAKYAN A. , SPREAFICO M.
Published: October 2004

The determinant of induced Dirac action for fermions living on a two-dimensional surface immersed with Whitney singularities into 3D Euclidean space is calculated exactly in Weyl invariant regularization.
A FIELD THEORETICAL APPROACH FOR STRINGS AND INTERFACES OF ISING-LIKE MODELS AT d>1
Authors: MARTELLINI M. , SPREAFICO M. , YOSHIDA K.
Published: October 2004

Starting from a generalized version of David-Distler-Kawai treatment of 2d-induced quantum gravity, we impose a series of “physical” boundary conditions to obtain an unique field theoretical Lagrangian describing random surface models and strings at given dimensions d>1. Our theory reproduces the critical exponents obtained by numerical simulations on d-dimensional Ising-like models for lower d-values. One observes, at appropriate dimensions d, the transition to the so-called branched polymer phase.
AN APPROACH FOR THERMODYNAMIC REASONING
Authors: WANG LIQIU
Published: October 2004

Re-examination of classical thermodynamics exposes some problems. The introduction of a new reasoning approach leads to a new branch of classical thermodynamics — structural thermodynamics. An inequality principle of thermodynamic state variables decouples structure of a process set with its working medium. The introduction of optimization into thermodynamic analyses changes the attitude of classical thermodynamics from observing/describing systems to controlling/optimizing the systems. To illustrate the approach, structural thermodynamic analyses are performed for reversible heat engines and a class of irreversible heat engines. This leads to and extends the classical Carnot theory.
COUPLED STATES IN ELECTRON–PHONON SYSTEM, SUPERCONDUCTIVITY AND HIGH Tc SUPERCONDUCTIVITY OF CRYSTALS
Authors: YAREMKO A. M. , MOZDOR E. V. , KRUCHININ S. P.
Published: October 2004

The new theoretical approach is proposed for studying the coupled states responsible for superconductivity in crystal without using the idea of electron pairing. From our approach it follows that BCS electron-pairing postulates are only approximate. It is shown that superconductivity (SC) coupled states can be created by pairs of electrons with nonzero full momentum and spin (k1 + k2 ≠ 0, s + s' ≠ 0). The model numerical calculations have shown that dependence of SC gap (energy of coupled states) on temperature is nonexponential and depends on the momenta of electrons in pair.
IRREVERSIBILITY IN CLASSICAL MECHANICS AS A CONSEQUENCE OF POINCARÉ GROUP
Authors: PAVLOTSKY I. P. , STRIANESE M.
Published: October 2004

In the post-Galilean approximation of Poincaré Group (i.e. in the approximation in which the corrections of order O (c−2), c denoting the light velocity, to the Galilei group are taken in account) the Lagrangians are singular on a submanifold of the phase space. It is a local singularity, which differs from the ones considered by Dirac. The dynamical properties are essentially peculiar on the studied singular surfaces.1–4 In particular, on some submanifolds of the singular manifold the velocities are not determined uniquely: in each point of the submanifold we get the infinite set of components of velocity. It means the loss of the reversibility of the motion in a sense that transformation of the phase space, corresponding to Lagrangian, has not a property of a group. It is shown, that if the values of the derivates of the molecular potentials are large enough the irreversibility of motion takes place. As consequence we obtain the relaxation to the equilibrium. This property does not exist if the Lagrangian is invariant with respect to Galilei Group.
GINZBURG–LANDAU THEORY OF A d-WAVE SUPERCONDUCTOR WITH MASS ANISOTROPY — PAIRING SYMMETRY AND VORTEX STRUCTURES
Authors: XU JI-HAI , REN YONG , TING C. S.
Published: October 2004

YBa 2 Cu 3 O 7 (YBCO) exhibits a large anisotropy between the a (or y) and b (or x) axes in the CuO2 planes. This anisotropy can be modeled by introducing an anisotropic mass parameter λ = mx /my. Assuming a d-wave pairing interaction together with a repulsive on-site Coulomb interaction, we developed a Ginzburg–Landau theory for a d-wave superconductor with mass anisotropy in the presence of a magnetic field. We show that the order parameter always has s + d symmetry. The vortex structures for λ = 1 and λ > 1 have been numerically studied. For high T c cuprates with tetragonal structure (λ = 1), the vortex shows a four-fold symmetry and the vortex lattice may have oblique or triangular structure depending on the strength of the applied magnetic field, temperature, and the other parameters. For YBCO we choose λ = 2, the single vortex has an elliptic shape, and the vortex lattice always shows an oblique structure. All these results are in good agreement with experimental measurements.
ANISOTROPIC VORTEX DYNAMICS AND PHASE DIAGRAM OF YBa2Cu3O7 SINGLE CRYSTALS WITH CANTED COLUMNAR DEFECTS
Authors: REED D. S. , YEH N.-C. , JIANG W. , KRIPLANI U. , KONCZYKOWSKI M. , HOLTZBERG F.
Published: October 2004

The anisotropic vortex dynamics and phase diagram are determined for a YBa 2 Cu 3 O 7 single crystal with columnar defects oriented at ±7.5° relative to the crystalline c-axis. A second-order splayed-glass to vortex-liquid transition is manifested for magnetic fields nearly parallel to the columns via the critical scaling of vortex AC and DC transport properties. In contrast, for magnetic fields aligned close to the ab-plane, an XY-like vortex-glass transition prevails. For magnetic fields at intermediate angles, there is no evidence of any vortex phase transition, and the vortex dynamics is described in terms of the thermally activated flux flow model.
ANALYSIS OF THE TWO-DIMENSIONAL NEGATIVE-U HUBBARD MODEL BY COMPOSITE OPERATOR METHOD
Authors: DI MATTEO T. , MANCINI F. , MARRA S. , MATSUMOTO H.
Published: October 2004

The two-dimensional negative-U Hubbard model is studied by means of the composite operator approach. In a generalized mean-field approximation we calculate different quantities, as the chemical potential, the double occupancy, the static uniform spin magnetic susceptibility and the density of states for various values of the particle density, attractive on-site interaction and temperature. Comparison with the results obtained by numerical analysis on finite size lattices shows a good agreement.
PHASE SPACE REPRESENTATION FOR OPEN QUANTUM SYSTEMS WITHIN THE LINDBLAD THEORY
Authors: ISAR A. , SANDULESCU A. , SCHEID W.
Published: October 2004

The Lindblad master equation for an open quantum system with a Hamiltonian containing an arbitrary potential is written as an equation for the Wigner distribution function in the phase space representation. The time derivative of this function is given by a sum of three parts: the classical one, the quantum corrections and the contribution due to the opening of the system. In the particular case of a harmonic oscillator, quantum corrections do not exist.
PATH-INTEGRAL APPROACH FOR ELECTRON–PHONON INTERACTION EFFECTS IN HARMONIC QUANTUM DOTS
Authors: MUKHOPADHYAY SOMA , CHATTERJEE ASHOK
Published: October 2004

We use the Feynman–Haken path-integral formalism to obtain the polaronic correction to the ground state energy of an electron in a polar semiconductor quantum dot with parabolic confinement in both two and three dimensions. We perform calculations for the entire range of the electron–phonon coupling parameter and for arbitrary confinement length. We apply our results to several semiconductor quantum dots and show that the polaronic effect in some of these dots can be considerably large if the dot sizes are made smaller than a few nanometers.
MAGNETORHEOLOGICAL FINISHING
Authors: KORDONSKI W.I. , JACOBS S.D.
Published: October 2004

The technology of finishing for optics, ceramics, and semiconductors is one of the most promising uses of the magnetorheological effect. It perfectly coupled with computer control, allowing in quantity production the unique accuracy and quality of a polished surface to be achieved. The polishing process may appear as follows. A part rotating on the spindle is brought into contact with an magnetorheological polishing (MRP) fluid which is set in motion by the moving wall. In the region where the part and the MRP fluid are brought into contact, the applied magnetic field creates the conditions necessary for the material removal from the part surface. The material removal takes place in a certain region contacting the surface of the part which can be called the polishing spot or zone. The polishing process comes to the program-simulated movement of the polishing spot over the part surface. The mechanism of the material removal in the contact zone is considered as a process governed by the particularities of the Bingham flow in the contact zone. The problem like the hydrodynamic theory of lubrication is treated for plastic film. As this takes place the shear stresses distribution in the film is obtained from the experimental measurements of the pressure distribution in the contact spot. Reasonable correlation between calculated and experimental magnitudes of the material removal rate for glass polishing lends support to the validity of the approach.
THE CONDUCTION MODEL OF ELECTRORHEOLOGICAL EFFECT REVISITED
Authors: BOISSY C. , ATTEN P. , FOULC J.-N.
Published: October 2004

The conduction model for DC fields predicting the attraction force between slightly conducting spheres in contact is examined in the light of a refined picture of the conduction processes in the liquid phase. Taking into account the saturation of current density in the liquid and the injection of ions occurring at the solid/liquid interfaces, new expressions of the attraction force F between spheres in contact are derived. Predictions are compared with measurements performed using two half spheres of centimetre size immersed in a mineral oil. The case of injection occurring at the solid/liquid interfaces is also considered.
Surface Feedback for Virtual Environment Systems Using Electrorheological Fluids
Authors: Taylor P.M. , Hosseini-Sianaki A. , Varley C.J.
Published: October 2004

A tactile array system, when incorporated in an information system, provides a means of conveying tactile data to the user. Such arrays have many applications including simulators for training purposes and Braille systems for the blind. The use of ER fluids in these systems would provide an inexpensive alternative to the existing technologies because of the simple and flexible designs. An experimental study has been conducted which involves a simple 5×5 array of tactels, each tactel being independently energised in order to configure a variety of shapes. A series of tests are carried out on two different types of ER fluids under a range of electric fields and sensor speeds. The results show that for the given tactel spacing, the programmed shapes are easily detected for all conditions and are directly comparable to similar tests undertaken on a solid shape.
THE ROTARY ELECTRORHEOLOGICAL EFFECT
Authors: HALSEY THOMAS C. , ANDERSON ROBERT A. , MARTIN JAMES E.
Published: October 2004

The viscous response of electrorheological fluids is usually manipulated through the use of DC or uniaxial AC electric fields. The result is that fibrillated structures parallel to the field form in a quiescent fluid; the distortion of such structures in a flow determines the enhanced viscous response, at least at low and moderate flow rates. We have conducted preliminary studies of electrorheological response in a different field configuration-a rotating electric field. With respect to the uniaxial AC case, there are two new developments in this type of field. The structures formed are disk-like, in the plane of the rotating field. Furthermore, the structures rotate either with or against the field, depending on the dielectric or conductivity contrast with the surrounding fluid.
HIGH SPEED JOURNAL BEARINGS LUBRICATED WITH ELECTRO-RHEOLOGICAL FLUIDS: AN EXPERIMENTAL INVESTIGATION
Authors: NIKOLAKOPOULOS P.G. , PAPADOPOULOS C.A.
Published: October 2004

It is well known that the imposition of an electric field on an Electro-Rheological (ER) fluid alters the viscosity and as a consequence the f flow properties of the f fluid. If such a fluid is used to lubricate a journal bearing system, it is expected that the imposition of an electric field between the rotor and the stator will cause the alteration of the dynamic properties of the journal bearing. For the present, it has been proved that this is valid only for low speeds and high radial clearances of Couette type viscometers. In this paper an experiment in a high speeds (16000 to 65000 s −1) journal bearing with small radial clearance is presented. The experiment performed has showed the phenomenon and has proved that the ER FLUID at high shear rates under constant temperature, follows the Bingham model in realistic bearings. Properties such as wall shear stress, dynamic yield stress relative viscosity are experimentally determined as functions of the electric field, for different particle concentrations and the shear strain rate under constant or free to vary temperature (due to operating conditions, angular velocity, friction). Concluding the ER fluids can be used to create “smart” journal bearings. Vibration controllers can be constructed to control the stability of the ER fluid lubricated bearings.
RHEOLOGICAL SYNERGISTIC EFFECTS OF ELECTRIC AND MAGNETIC FIELDS IN IRON PARTICLE SUSPENSION
Authors: KOYAMA KIYOHITO
Published: October 2004

The effects of electric field and/or magnetic field on the rheological property of iron suspension were studied by use of parallel-plate rheometers developed for electro-magnetorheological (EMR) measurements. The EMR effect, which is defined as an increase in the shear stress under combined fields, was dependent on the strength and direction of the fields. In particular, significant synergism was found in the EMR effect when the electric and magnetic fields were applied in parallel. Observation of the suspensions solidified in parallel field and crossed field conditions revealed different structures of aggregated particles for these combined fields. The parallel field induced many chains along the field, while the crossed field induced a network structure. It is concluded that the synergistic EMR effect in parallel field is due to the increase in the number of particle chains bridging the plates.
A COMPARISON OF THE PERFORMANCE OF ER FLUIDS IN SQUEEZE
Authors: Sproston J L , Wahed A K El , Williams E W , Stanway R
Published: October 2004

This paper is concerned with an experimental and theoretical study of the characteristics of two ER fluids and their application to vibration control when used in squeeze flow.

It is seen that when the fluids are sandwiched between two electrodes, the lower one oscillating and the upper one fixed, displacement control of the lower electrode can be achieved by control of the applied field. Of particular interest is the dependence of the force transmitted across the fluids on oscillation frequency and applied field. A time-dependent theoretical model is seen to satisfactorily predict the device performance when allowance is made for a non-linear dependence of the post-yield shear stress on shear rate.
A GENERALISED PRESENTATION OF VALVE AND CLUTCH DATA FOR AN ER FLUID, AND PRACTICAL PERFORMANCE PREDICTION METHODOLOGY
Authors: PEEL D J , STANWAY R , BULLOUGH W A
Published: October 2004

In previous papers a technique for comparing the performance of a particular electrorheological (ER) fluid in different situations was derived from steady, laminar, shear and flow mode experimental data and static cell tests. By plotting non-dimensional Hedström Number (He) and Friction Coefficient (Cf) against Reynolds Number (Re) via use of the Bingham plastic constitutive equation, one continuous and overlapping relationship was shown for constant field excitation over a range of operating conditions and geometries. In the present work the same treatment is extended to a different fluid, of higher solid volume fraction and different constituents, which was tested on different instruments at a different uniform temperature, so as to attest the generality of the technique. In doing this the methodology of converting low shear rate Couette viscometer data to practical flow valve performance predictions is illustrated.
Transfer Function Identification of an Electro-Rheological Actuator
Authors: Brookfield D.J. , Dlodlo Z.B.
Published: October 2004

A fluid clutch utilising an Electro-Rheological (ER) suspension provides a controlled torque coupling between input and output through the control of the applied electric field. If the input is driven at constant speed the device can be considered as an ER torque actuator and thus be used to drive robot links or other mechanisms requiring precise positioning. Such an ER torque actuator can replace a DC servo-motor in robotic applications with the benefits of low time constant and smooth output torque unaffected by cogging (i.e. variation in torque of a DC motor as the magnetic reluctance of the armature-stator path changes with rotation).

Although the ER actuator has many benefits, it suffers from a non-linear and time varying relationship between input voltage and output torque. These undesirable characteristics can be mitigated by providing a local closed loop controller around the system. The design of such a controller requires a knowledge of the relationship between the applied voltage and output torque; i.e. the transfer function of the actuator. This transfer function has been determined by observing the response of an ER torque actuator in the frequency domain. It is shown that a linear transfer function model reasonable represents the actuator behaviour, that the actuator is a stable second order system and that the time constant of the clutch studied is sufficiently short to hold considerable promise for robotic applications. Furthermore, the maximum torque capability is shown to be sufficient for many medium scale industrial robots.
THE EFFECT OF SCALE FACTOR ON THE PERFORMANCE OF ELECTRO-RHEOLOGICAL FLUID DAMPERS
Authors: Gordaninejad F. , Bindu R.
Published: October 2004

Theoretical and experimental scale analyses are conducted to investigate the effects of length of the damper and electric field strength on the damping and stiffness coefficients of electrorheological fluid (ERF) dampers. It is demonstrated that by employing the results obtained from smaller size prototypes, the energy absorbing capacity of larger dampers can be estimated.
PERFORMANCE ANALYSIS OF AN ENGINE MOUNT FEATURING ER FLUIDS AND PIEZOACTUATORS
Authors: CHOI S.H. , CHOI Y.T. , CHOI S.B. , CHEONG C.C.
Published: October 2004

Conventional rubber mounts and various types of passive or semi-active hydraulic engine mounts for a passenger vehicle have their own functional aims on the limited frequency band in the broad engine operating frequency range. In order to achieve high system performance over all frequency ranges of the engine operation, a new type of engine mount featuring electro-rheological(ER) fluids and piezoactuators is proposed in this study. A mathematical model of the proposed engine mount is derived using the bond graph method which is inherently adequate to model the interconnected hydromechanical system. In the low frequency domain, the ER fluid is activated upon imposing an electric field for vibration isolation while the piezoactuator is activated in the high frequency domain. A neuro-control algorithm is utilized to determine control electric field for the ER fluid, and H∞ control technique is adopted for the piezoactuator Comparative works between the proposed and single-actuating(ER fluid only or piezoactuator only) engine mounts are undertaken by evaluating force transmissibility over a wide operating frequency range.
Elastohydrodynamic Performance of Unexcited Electro-Rheological Fluids
Authors: Dwyer-Joyce R.S. , Bullough W.A. , Lingard S.
Published: October 2004

Exploratory test results are presented for a series of mixtures of unexcited electrorheological (ER) fluids under elastohydrodynamic lubrication (ehl) conditions. These were obtained from direct observation of film formation in an optical interferometric apparatus. Results are presented as photographs of the fluid film and plots of film thickness versus speed for a range of ER fluid solid fractions. Adequate film formation is limited by the tendency of the solid particles to evade the contact region. At very low contact speeds particles enter the chl contact and generate a fluid film. At higher speeds the particulates do not become entrained in the contact; the film formation is then determined by the viscosity of the base fluid.
ELECTRORHEOLOGICAL EFFECT OF LIQUID CRYSTALLINE POLYMERS
Authors: INOUE AKIO , MANIWA SYUNJI , IDE YOICHIROH , ODA HIROJI
Published: October 2004

A series of side chain liquid crystalline polymers (LCPs) containing different spacer length and various terminal structures has been prepared and their electrorheological (ER) effect has been investigated. Although the LCP itself showed small ER effect, a mixture of the LCP with a plain polydimethylsiloxane (PDMS) oil was found to show a large increase in shear stress upon application of an electric field. The shear stresses under DC 2 kV/mm of an electric field were 14 to 4 times those without the application of an electric field over the temperature range of 30 to 160 °C for a 2:1 mixture (by weight) of a LCP containing an oxyethylene spacer and a mesogen based on 4-cyanophenyl benzoate with PDMS. Two mechanisms responsible for the generation of the ER effect was suggested from the investigation using phenyl-substituted PDMS and an analysis by DSC: oriented LC network induction, and phase separation between the LC base polymer and PDMS.
THE DEVELOPMENT OF ELECTRORHEOLOGICAL FLUIDS FOR AN AUTOMOTIVE SEMI-ACTIVE SUSPENSION SYSTEM
Authors: WEYENBERG THOMAS R. , PIALET JOSEPH W. , PETEK NICHOLAS K.
Published: October 2004

The feasibility of electrorheological (ER) dampers for an automotive semi-active suspension was evaluated in a three phase program. In the first phase, ER fluid performance targets were derived. The desired ride and handling attributes of the suspension system were translated into damper specifications, which were then translated into the ER fluid performance targets. The damper specifications included dynamic range, bandwidth, power draw, and packaging. The ER fluid performance parameters then included zero-field viscosity, ER stress, response time, and power density. In the second phase, the dampers and the ER fluid were developed to meet the performance targets. Trade-offs were made between damper design and fluid formulation to achieve the desired damper dynamic range and power draw. A state-diagram approach using screen test data was used to select candidate ER fluids. In the third phase of the program, a prototype semi-active suspension system using fast, continuously variable ER dampers was installed on a demonstration vehicle. Heave, pitch, and roll motions of the vehicle were controlled by applying voltages independently to the four dampers as determined by a modified sky-hook algorithm. The system was designed to respond in less than 10 ms with an average power requirement less than 40 W for normal road surfaces and handling. Laboratory data from a pressure driven flow screen test and a damper test are presented that document the ER fluid performance specification and selection process. Vehicle performance data are presented that demonstrate the features of ER technology for the semi-active suspension application. Remaining issues for commercialization of ER fluids are discussed.
POLARIZATION OF SURFACE IONS ON A SPHERICAL PARTICLE IN AN ELECTRIC FIELD
Authors: Hu Yue , Kumar Vidya , Blackmon Kristen E.
Published: October 2004

Polarization of surface ions on a spherical colloidal particle in a transient electric field is simulated using a random walk method. Total polarization increases as ion density increases but saturates when the Coulomb repulsive forces between the ions become dominant. The time constant of polarization is shorter for larger ion densities, and non-linear relations between polarization and the electric field strength are also seen.
CHARACTERISATION OF THE COMPLEX SHEAR MODULUS PROPERTIES OF ELECTRO-RHEOLOGICAL FLUIDS BY THE DIRECT STIFFNESS AND MASTER CURVE TECHNIQUES
Authors: Oyadiji S O
Published: October 2004

The direct stiffness technique was employed to characterise the complex modulus properties of a silicone oil-based electrorheological fluid over a frequency range from 30Hz to 300Hz and a temperature range from 0°C to 60ºC. The ER fluid device utilised was a set of concentric cylinders possessing a radial gap of 3mm between adjacent cylinders. Electric field strengths of between 0kV/mm and 2kV/mm were applied across the ER fluid. The results show that the shear modulus of the ER fluid decreased monotonically as the temperature was increased from 0ºC to 60ºC. Overall, the shear modulus decreased by a factor of up to 20. On the other hand, the shear loss factor increased from a low value of about 0.05 at 0ºC to a high value of about 1.0 at 60ºC. Conversely, as the electric field strength was increased from 0kV/mm to 2kV/mm, the shear modulus increased whereas the loss factor decreased. At all temperatures and electric field strengths of these investigations, both the shear modulus and loss factor increased in value as the excitation frequency was increased. The sets of measured temperature- and frequency-dependent data were converted, using the master curve technique, to master curves of shear modulus and loss factor which vary with frequency over several decades at a constant reference temperature and for varying levels of the electric field strength.
FIELD-INDUCED LABYRINTHINE PATTERNS IN FERROFLUID EMULSIONS
Authors: FLORES GEORGE A. , IVEY MARK L. , LIU JING , MOHEBI M. , JAMASBI N.
Published: October 2004

A ferrofluid emulsion goes through gas — solid phase transition when an external magnetic field is applied. The solid structures are observed as either column, bent-wall, or labyrinthine patterns. The appearance of these different patterns depend upon the rate of the field applied, thickness of the sample cell along the field direction, and the volume fraction of the emulsion droplets used. Using optical microscopy, formed patterns are recorded and analyzed in which a “phase” diagram of the structural transition from column to bent-wall is measured.
CONDUCTIVITY AND FORCE BETWEEN PARTICLES IN A MODEL ELECTRORHEOLOGICAL FLUID II: INTERACTION FORCE
Authors: WU C.W. , CHEN Y. , TANG X. , CONRAD H.
Published: October 2004

The interaction force between humidified glass spheres forming a single-row chain in silicone oil was determined in shear as a function of the number of particles in the chain, the electric field and the shear strain (separation of the particles). The measured values of the interaction force vs the average distance of separation of the particles and the electric field exponent were in accord with the conductivity model for ER response. With increase in shear strain the separation of the particles soon became localized and one or both of the particles next to the gap began oscillating back-and-forth leading ultimately to rupture of the chain with increased shear.
BOUNDARY EFFECTS AT ERF SPREADING IN ELECTRIC FIELD
Authors: KOROBKO E.V. , GORODKIN R.G. , MELNICHENKO V.V. , ZHOU L.W.
Published: October 2004

Results of the experimental investigation of the electrorheological fluid flow with a free boundary, in particular, drop spreading over a substrate in an electric field are reported. Residual thixotropic effects and a change in the drop shape have been revealed. A dependence of the characteristic parameters of the drop (its height, radius and wetting angle) on an electric field intensity and observation time have been established.
THE ANOMALOUS DISPERSION AND RHEOLOGICAL RESPONSE OF ER MATERIALS
Authors: Filisko Frank E. , Schubring Adam
Published: October 2004

A large low frequency dielectric dispersion, termed anomalous because it’s source is not clear, is observed in all ER active materials. It follows a classical Arrhenius behavior and as such, characteristc frequencies can be obtained for various temperatures. However it has not been directly associated with the rheological behavior of ER materials. In this study, rheological response times were obtained for an ER material by recording the response to a step increase in field. The response times of 41 msec. obtained dielectrically and 30 msec. obtained rheologically strongly indicate that the anomalous dispersion is associated with the mechanical ER phenomenon.
SU(2) FUSION HIERARCHIES OF DILUTE MODELS
Authors: ZHOU YU-KUI
Published: October 2004

The dilute AL models have been studied by analyzing their adjacency conditions, face weights and transfer matrices. The new results including two su(2) fusion rules and Bethe ansatz solutions of the fused transfer matrices are presented. Some relevant physics aspects such as the finite-size corrections to transfer matrices are also discussed.
RELATION BETWEEN MICROSCOPIC AND MACROSCOPIC CHARACTERISTICS OF STATISTICAL SYSTEMS
Authors: COLEMAN A.J. , YUKALOV V.I.
Published: October 2004

Order parameters of physical systems and order indices of their density matrices are, respectively, macroscopic and microscopic characterisics of a statistical system. We claim that there are situations in which the index provides more information than the parameter. This is proved by the exhibition of an exactly solvable model of a Bose system with mid-range order for which the order parameter is zero but for which an order index changes continuously as the Hamiltonian is varied.
THE ATTRACTOR BASIN OF NEURAL NETWORK WITH CORRELATED INTERACTIONS
Authors: TAN Z. , SCHÜLKE L.
Published: October 2004

The attractor basin is studied when correlations (symmetries) in the interaction are imposed for diluted Gardner-Derrida neural network. A clear relation between the attractor basin and the symmetry is obtained in a small range of symmetry parameter. The size of the attractor basin is smaller than that in the case without imposed correlations. For special values of the symmetry parameter the model leads to results obtained in the model with no correlations.
ANOMALOUS RELAXATION IN FRACTAL AND DISORDERED STRUCTURES
Authors: FUJIWARA S. , YONEZAWA F.
Published: October 2004

For the purpose of clarifying the mechanisms of the anomalous relaxation, we carry out the Monte Carlo simulations of random walks in fractal and disordered structures. From our calculations of the relaxation functions and the complex susceptibilities, we find that the anomalous relaxation is of the Cole-Cole type in fractal structures while it is of the stretched-exponential type in non-fractal disordered structures. A most interesting aspect indicated by the results of our work is that the concept of “fractal”, originally introduced from purely mathematical point of view, is shown to play an important role in understanding some properties of realistic physical systems.
QUANTUM TRANSPORT IN MESOSCOPIC RINGS WITH STUBS
Authors: CHO SAM YOUNG , CHOI TAESEUNG , RYU CHANG-MO
Published: October 2004

Quantum transport in the open-system mesoscopic rings with stubs in the absence of magnetic field is investigated by using the one-dimensional quantum waveguide theory. It is shown that discretely localized states due to the presence of stubs play an important role in the electron transport. The behavior of transmission probability shows the asymmetric Fano resonance, which arises from the interaction between the continuum states and the discrete states. Amplification of the persistent currents by the localized states due to the stub is clearly shown. Negative currents are also noticed.
ELECTRONIC CONDUCTANCE OF A T-SHAPED WAVEGUIDE IN LOCAL MAGNETIC FIELD
Authors: GU B.Y. , SHI J.R.
Published: October 2004

A theoretical study of the electronic conductance of an electron waveguide with a T-stub in local magnetic field is presented. The conductance as a function of Fermi energy and magnetoconductance of a T-stub with various dimensions are calculated. It is found that at low incident electron energies the conductance is hardly changed with the magnetic field. At high energies the magnetic field shifts the resonant peaks and enhances the transmission on the average. Oscillatory structures of the magnetoconductance present for a T-stub with larger area while smooth curves exist for a stub with smaller area. Intuitive interpretations are given in terms of magnetic induced quasibound states and antiresonant reflections. The possibility of a magnetically controlled mesoscopic device is discussed.
AHARONOV-BOHM EFFECT IN THE PRESENCE OF EVANESCENT MODES
Authors: GUPTA B.C. , DEO P. SINGHA , JAYANNAVAR A.M.
Published: October 2004

It is known that differential magnetoconductance of a normal metal loop connected to reservoirs by ideal wires is always negative when an electron travels as an evanescent modes in the loop. This is in contrast to the fact that the magnetoconductance for propagating modes is very sensitive to small changes in geometric details and the Fermi energy and moreover it can be positive as well as negative. Here we explore the role of impurities in the leads in determining the magnetoconductance of the loop. We find that the change in magnetoconductance is negative and can be made large provided the impurities do not create resonant states in the systems. This theoretical finding may play a useful role in quantum switch operations.
THE STUDIES ON MULTIPLE METASTABLE STATES IN MAGNETIC MULTILAYER
Authors: XIE NING , ZHOU LEI , JIN SHENGYU , TAO RUIBAO
Published: October 2004

Using a classical approach, the magnetic configuration of ground state has been studied for the ferromagnetic multilayer system with easy axis anisotropy. The existence of multiple metastable states are obviously shown, and a multi-step transition is presented in the magnetic loop of hysteresis. A bilayer system is discussed analytically, and the numerical calculations are carried out for some complicated multilayer systems.
MBE FABRICATION OF GaAs/AlGaAs LOW-DIMENSIONAL STRUCTURES ON IN SITU PATTERNED GaAs SUBSTRATES
Authors: ISHIKAWA TOMONORI , LÓPEZ MÁXIMO
Published: October 2004

We have developed a novel processing technique, conducted entirely under an ultra-high vacuum environment, to pattern GaAs substrates on which GaAs/AlGaAs low-dimensional structures are subsequently regrown. In this technique, called in situ electron-beam (EB) lithography, a thin surface-oxide-layer is selectively formed by EB-stimulated oxidation under a controlled oxygen atmosphere. This is used as a mask material to define patterned mesas by Cl 2 gas etching. Subsequently, the initial mesa size is reduced by the regrowth of a GaAs buffer layer; finally, low-dimensional structures, such as quantum-wire or -box structures, are formed on the top of the mesas by the growth of a quantum well. This in situ technique is advantageous for the fabrication of arbitrarily designed low-dimensional structures with high quality.
STUDY ON A TOY MODEL OF STRONGLY CORRELATED ELECTRONS
Authors: NOGUEIRA FLAVIO S. , ANDA ENRIQUE V.
Published: October 2004

A toy model of strongly correlated fermions is studied using Green function and functional integration methods. The model exhibits a metal-insulator transition as the interaction is varied. In the case of unrestricted hopping an equivalence of the model with the Hubbard model with infinite range hopping is established. The generalization to the case with N components is made.
GUTZWILLER APPROXIMATION IN DEGENERATE HUBBARD MODELS
Authors: LU JIAN PING
Published: October 2004

The details of the Generalized-Gutzwiller-Approximation in degenerate Hubbard models are presented. It is found that the metal-insulator transition occurs at a finite correlation Uc when the average number of electrons per lattice site is an integer. A derivation is given for the general expression of Uc(x, N) which reproduces all previously known Gutzwiller solutions, including that of the boson Hubbard model. The Uc depends sensitively on both the band degeneracy N and the filling x. Effects of the lattice structure on the metal-insulator transition and the effective mass are discussed.
ON THE PATH INTEGRAL APPROACH TO THE TUNNELING TIME
Authors: MARTIN THIERRY
Published: October 2004

The path integral formulation of the traversal time in tunneling utilizes a restricted Feynman amplitude. We present a derivation based on the Fisher Lee formula to compute the average time and the integrated distribution for arbitrary potentials. The (complex) tunneling time can be expressed as a derivative with respect to a potential which surrounds the region over which the particle is “detected”, and a correspondence with other tunneling time scales which depend on energy derivatives of the transmission coefficient is found. A semiclassical treatment confirms that there are two time scales associated with this measurement procedure. The imaginary component is related to the multiple instanton bounces in the inverted potential. The issue of positive times is found to depend crucially on the behavior of the transmission coefficient for asymptotic limits of the measurement potential. The calculation of higher moments of the distribution allows to define a positive barrier interaction time, without appealing to any regularization procedure.
COMBINED HRTEM AND PEELS ANALYSIS OF NANOPOROUS AMORPHOUS CARBON
Authors: PENG J.L. , FAN X.D. , BURSILL L.A.
Published: October 2004

Both the mass density (1.37 kgm/m 3) and sp3/sp2+sp3 bonding fraction (0.15) were determined for an unusual nanoporous amorphous carbon consisting of curved single graphitic sheets. A combination of High-Resolution Transmission Electron Microscopy (HRTEM) and Parallel Electron Energy Loss Spectroscopy (PEELS) was used. The values of these two parameters provide important constraints for the determination of the structure of this relatively low density variety of nanoporous carbon. The results are relevant also in the search for negatively-curved Schwarzite-related carbon structures. New data are also presented for Highly-Oriented Pyrollytic Graphite (HOPG), Chemically Vapour Deposited (CVD) diamond, C60, Glassy Carbon (GC) and Evaporated Amorphous Carbon (EAC); these are compared with the results for NAC. Kramers-Kronig Analysis (KKA) of the low-loss PEELS data shows that the band gaps of both NAC and EAC are collapsed relative to that of CVD diamond.
SIZE IDENTIFICATION OF UNDERWATER OBJECTS FROM BACKSCATTERING SIGNALS OF ARBITRARY LOOKING ANGLES
Authors: LI W. , LIU G. R. , ZHANG X. M.
Published: October 2004

The inverse problem of determining the size, shape and orientation of a submerged object using the scattered field data is studied. Based on the physical optics approximate, the profile function of the object is found directly proportional to its ramp response that is the second integral of the impulse response. Through analyzing the feature of the ramp response in different computed frequency ranges, it is found that the low-frequency data are essential to the shape of the underwater object while the high-frequency data are very important to the size of the object. Therefore, when employing the high-frequency data to compute the ramp response, the edge of the object can only be highlighted in the illuminated region at certain aspect. Based on this finding, a new method is developed to estimate the size of underwater objects. The present method uses different frequency ranges to determine different parameters of the underwater objects so as to achieve the best accuracy. A number of examples are presented to demonstrate the effectiveness of the present method in using the ramp response technique to identify the size of both rigid and elastic bodies.
FINITE ELEMENT MODELING OF ACOUSTICS USING HIGHER ORDER ELEMENTS PART I: NONUNIFORM DUCT PROPAGATION
Authors: LISTERUD EIVIND , EVERSMAN WALTER
Published: October 2004

Cubic serendipity elements have been implemented into a nonuniform duct model of acoustic propagation in a moving medium. This model uses a convective potential formulation derived from the inviscid linearized mass and momentum equations. The model requires post-processing to calculate acoustic pressure. These elements outperform the quadratic serendipity elements in terms of computational efficiency based on visual observations and error norm analysis of acoustic pressure. CPU time reduction of up to 40% has been observed without sacrificing accuracy. Any penalty in numerical accuracy incurred by using serendipity elements rather than Lagrangian elements is far outweighed by the gains in dimensionality. The computational gains for calculation of acoustic potential are considerably less. Analytical expressions for the modal and convective effects on the propagating wavelength have been formulated and compared to numerical results. Preliminary assessment of alternative finite element approaches to model the convective potential formulation has been conducted. Stabilization and wave approximation methods have been implemented to solve simple one-dimensional problems.