bluuebunny/crossref_metadata_2025 huggingface dataset:
SUPERCONDUCTIVITY IN 2+1 DIMENSIONS VIA KOSTERLITZ-THOULESS MECHANISM: LARGE N AND FINITE TEMPERATURE ANALYSES
Authors: MACKENZIE R. , PANIGRAHI P.K. , SAKHI S.
Published: November 2004

We analyze a (2+1)-dimensional model with charged, relativistic fermions interacting through a four-fermi term. Taking advantage of its large N renormalizability, the various phases of this model are studied at finite temperature and beyond the leading order in 1/N. Although the vacuum expectation value (VEV) of a charged order parameter is zero at any nonzero temperature, the model nevertheless exhibits a rich phase structure in the strong coupling regime, because of the nonvanishing VEV of a neutral order parameter and due to the nontrivial dynamics of the vortex excitations on the plane. These include a confined vortex phase which is superconducting at low temperatures, an intermediate temperature phase with deconfined vortices, and a high temperature phase, where the neutral order parameter vanishes. The manifestation of superconductivity at low temperatures and its disappearance above a critical temperature is explicitly shown to be due to the vortex confinement/deconfinement mechanism of Kosterlitz and Thouless. The ground state does not break parity or time reversal symmetries and the ratio of the energy gap to Tc is bigger than the conventional BCS value, for N≲22.
AN EXAMPLE OF q-DEFORMED FIELD THEORY
Authors: BARDEK V. , DOREŠIĆ M. , MELJANAC S.
Published: November 2004

The nonrelativistic Chern–Simons theory with the single-valued anyonic field is proposed as an example of q-deformed field theory. The corresponding q-deformed algebra interpolating between bosons and fermions, both in position and momentum space, is analyzed. A possible generalization to a space with an arbitrary dimension is suggested.
LAUGHLIN'S WAVE FUNCTIONS, COULOMB GASES AND EXPANSIONS OF THE DISCRIMINANT
Authors: DI FRANCESCO P. , GAUDIN M. , ITZYKSON C. , LESAGE F.
Published: November 2004

In the context of the fractional quantum Hall effect, we investigate Laughlin's ansatz for the ground state wave function at fractional filling of the lowest Landau level. Interpreting its normalization in terms of a one-component plasma, we find the effect of an additional quadrupolar field on the free energy, and derive estimates for the thermo dynamically equivalent spherical plasma. In the second part of the paper, we present various methods for expanding the wave function in terms of Slater determinants, and obtain sum rules for the coefficients. We also address the apparently simpler question of counting the number of such Slater states using the theory of integral polytopes.
MODULAR GROUPS FOR TWISTED NARAIN MODELS
Authors: ERLER JENS , SPALIŃSKI MICHAŁ
Published: November 2004

We demonstrate how to find modular discrete symmetry groups for ZN orbifolds. The Z7 orbifold is treated in detail as a nontrivial example of a (2, 2) orbifold model. We give the generators of the modular group for this case which, surprisingly, does not contain SL (2; Z)3 as had been speculated. The treatment models with discrete Wilson lines are also discussed. We consider examples which demonstrate that discrete Wilson lines affect the modular group in a nontrivial manner. In particular, we show that it is possible for a Wilson line to break SL (2, Z).
MATRIX ELEMENTS OF Uq[su(2)k] VERTEX OPERATORS VIA BOSONIZATION
Authors: BOUGOURZI A. H. , WESTON ROBERT A.
Published: November 2004

We construct bosonized vertex operators (VO's) and conjugate vertex operators (CVO's) of Uq[ su (2)k] for arbitrary level k and representation j ≤ k/2. Both are obtained directly as two solutions of the defining condition of vertex operators — namely that they intertwine Uq[ su (2)k] modules. We construct the screening charge and present a formula for the n-point function. Specializing to j = 1/2 we construct all VO's and CVO's explicitly. The existence of the CVO allows us to place the calculation of the two-point function on the same footing as k = 1; that is, it is obtained without screening currents and involves only a single integral from the CVO. This integral is evaluated and the resulting function is shown to obey the q-KZ equation and to reduce simply to both the expected k = 1 and q = 1 limits.
CHEN INTEGRALS, GENERALIZED LOOPS AND LOOP CALCULUS
Authors: TAVARES J.N.
Published: November 2004

We use Chen iterated line integrals to construct a topological algebra [Formula: see text] of separating functions on the group of loopsLℳp. [Formula: see text] has a Hopf algebra structure which allows the construction of a group structure on its spectrum. We call this topological group the group of generalized loops [Formula: see text] Then we develop a loop calculus, based on the end point and area derivative operators, providing a rigorous mathematical treatment of the early heuristic ideas of Gambini, Trias and also Mandelstam, Makeenko and Migdal. Finally, we define a natural action of the “pointed” diffeomorphism group Diff p(ℳ) on [Formula: see text], and consider a variational derivative which allows the construction of homotopy invariants. This formalism is useful for constructing a mathematical theory of loop representation of gauge theories and quantum gravity.
ORBIFOLD COMPACTIFICATIONS WITH CONTINUOUS WILSON LINES
Authors: MOHAUPT THOMAS
Published: November 2004

We identify the untwisted moduli of heterotic orbifold compactifications for the case where the gauge twist is realized by a rotation. The Wilson lines are found to have both continuous and discrete parts. For the case of the standard Z3 orbifold we classify all possibilities of breaking the gauge group E(6) ⊗ SU (3) by nine of the eighteen Wilson moduli and by additional discrete Wilson lines.
FERMIONS FROM PHOTONS: BOSONIZATION OF QED IN 2+1 DIMENSIONS
Authors: KOVNER A. , KURZEPA P.S.
Published: November 2004

We perform the complete bosonization of (2+1)-dimensional QED with one fermionic flavor in the Hamiltonian formalism. The Fermi operators are explicitly constructed in terms of the vector potential and the electric field. We carefully specify the regularization procedure involved in the definition of these operators, and calculate the fermionic bilinears and the energy-momentum tensor. The algebra of bilinears exhibits the Schwinger terms which also appear in perturbation theory. The bosonic Hamiltonian is a local, polynomial functional of Ai and Ei, and we check explicitly the Lorentz invariance of the resulting bosonic theory. Our construction is conceptually very similar to Mandelstam’s construction in 1+1 dimensions, and is dissimilar from the recent bosonization attempts in 2+1 dimensions, which hinge crucially on the presence of a Chern-Simons term.
A SPECIAL REPRESENTATION OF A QUANTUM ACTION FUNCTIONAL
Authors: GOLFAND YU. A.
Published: November 2004

A special representation of a quantum action functional is considered in detail for a case of trilinear classical interaction (this case is presented without proof in Ref. 7) as well as for a general case. All steps of the consideration are well grounded mathematically. Nontrivial mathematics becomes necessary for developing an adequate calculation technique. Some features of the representation (the manifest symmetry with respect to permutation of particles is the most important among them) enable one to construct consistent methods of calculation and to get approximate but nonperturbative solutions. It is probable that the method can compete with lattice calculations in the course of subsequent elaboration and basing on a computer.
EVALUATION OF OBSERVABLES IN THE GAUSSIAN N=∞ KAZAKOV-MIGDAL MODEL
Authors: DOBROLIUBOV M.I. , SEMENOFF G.W. , WEISS N. , MOROZOV A.
Published: November 2004

In this paper, we examine the properties of observables in the Kazakov-Migdal model. We present explicit formulae for the leading asymptotics of adjoint Wilson loops as well as some other observables for the model with a Gaussian potential. We discuss the phase transition in the large N limit of the D=1 model. One of the appendices is devoted to discussion of the N=∞ Itzykson-Zuber integrals for arbitrary eigenvalue densities.
INTERESTING FEATURES OF PARTICLES PRODUCED IN 4.5 A GeV/c28Si-EMULSION INTERACTIONS
Authors: NASR MUSTAFA ABDUSALAM , KHUSHNOOD H.
Published: November 2004

Results on some interesting features of secondary particles produced in collisions of 4.5 A GeV/c 28Si with emulsion nuclei are discussed. Mean multiplicities of grey, black, shower and heavily ionizing particles obtained in this study are compared with their corresponding values obtained for different projectile nuclei. The variations of D(Ns) and  with  and D(Nc) and  with  are also investigated. Finally, integral Nc distribution is plotted and fitted with a best-fitting analytical expression.
A THREE-DIMENSIONAL GAUGE THEORY COUPLED TO FERMIONIC SCALARS AND VECTORS
Authors: McKEON D.G.C.
Published: November 2004

By involving the group indices of an SU(2) gauge theory in three Euclidean dimensions in the Lorentz transformation, one finds that the gauge field can be decomposed into a scalar, vector and tensor field which mix under a gauge transformation. It is shown how this gauge field can be coupled to an O(3) spinor field whose transformation properties allow one to decompose it into a fermionic scalar and a fermionic vector field. Radiative corrections must be done in a way that respects the dimensionality of the theory; it is demonstrated how operator regularization can be used to this end by computing the temperature dependence of the η function arising from spinors.
FERMI QUANTIZATION OF TENSOR SYSTEMS
Authors: REIFLER FRANK , MORRIS RANDALL
Published: November 2004

In this paper we characterize classical tensor systems which admit Fermi quantization as those having unitary Lie Poisson brackets. Examples include Euler’s tensor equation for a rigid body and Dirac’s equation in tensor form, for which we give a new derivation which is simple and direct.
NEW SERIES OF 3D LATTICE INTEGRABLE MODELS
Authors: MANGAZEEV V.V. , SERGEEV S.M. , STROGANOV YU. G.
Published: November 2004

In this paper we present a new series of three-dimensional integrable lattice models with N colors. The case N=2 generalizes the elliptic model of Ref. 8. The weight functions of the models satisfy modified tetrahedron equations with N states and give a commuting family of two-layer transfer matrices. The dependence on the spectral parameters corresponds to the static limit of the modified tetrahedron equations, and weights are parametrized in terms of elliptic functions. The models contain two free parameters: elliptic modulus and additional parameter η. Also, we briefly discuss symmetry properties of weight functions of the models.
QUANTUM HADRODYNAMICS IN TWO DIMENSIONS
Authors: RAJEEV S.G.
Published: November 2004

A nonlocal and nonlinear theory of hadrons, equivalent to the color singlet sector of two-dimensional QCD, is constructed. The phase space of this theory is an infinite-dimensional Grassmannian. The baryon number of QCD corresponds to a topological invariant (“virtual rank”) of the Grassmannian. It is shown that the hadron theory has topological solitons corresponding to the baryons of QCD. [Formula: see text] plays the role of ħ in this theory; Nc must be an integer for topological reasons. We also describe the quantization of a toy model with a finite-dimensional Grassmannian as the phase space. In an appendix, we show that the usual Hartree-Fock theory of atomic and condensed matter physics has a natural formulation in terms of infinite-dimensional Grassmannians.
QUANTUM-DEFORMED CANONICAL TRANSFORMATIONS, W∞ ALGEBRAS AND UNITARY TRANSFORMATIONS
Authors: GOZZI E. , REUTER M.
Published: November 2004

We investigate the algebraic properties of the quantum counterpart of the classical canonical transformations using the symbol calculus approach to quantum mechanics. In this framework we construct a set of pseudodifferential operators which act on the symbols of operators, i.e. on functions defined over phase space. They act as operatorial left and right multiplication and form a W∞×W∞ algebra which contracts to its diagonal subalgebra in the classical limit. We also describe the Gel’fand-Naimark-Segal (GNS) construction in this language and show that the GNS representation space (a doubled Hilbert space) is closely related to the algebra of functions over phase space equipped with the star product of the symbol calculus.
REVERSIBLE, METASTABLE, ULTRAFAST PHOTOINDUCED ELECTRON TRANSFER FROM SEMICONDUCTING POLYMERS TO BUCKMINSTERFULLERENE AND IN THE CORRESPONDING DONOR/ACCEPTOR HETEROJUNCTIONS
Authors: SARICIFTCI N. S. , HEBGER A. J.
Published: November 2004

The results of comprehensive studies of photoinduced electron transfer from semiconducting (conjugated) polymers to buckminsterfullerene are reviewed. Steady state and femtosecond time-resolved photoinduced absorption (photoexcitation spectroscopy), steady state and picosecond time-resolved photoluminescence, steady state and picosecond photoconductivity, and steady state light-induced electron spin resonance measurements are summarized as experimental evidence which demonstrates ultrafast, long lived photoinduced electron transfer. Comparative studies with different semiconducting polymers as donors demonstrate that in degenerate ground state polymers, soliton excitations form before the electron transfer can occur; thereby inhibiting charge transfer and charge separation. In non-degenerate ground state systems, photoinduced electron transfer occurs in less than 10−12 s , quenching the photoluminescence as well as the intersystem crossing into the triplet manifold. The importance of electron–phonon coupling and structural relaxation following photoexcitation in these quasi-one-dimensional semiconducting polymers is proposed as a principal contribution to the stabilization of the charge separated state. Utilizing thin films of the semiconducting polymer (donor) and buckminsterfullerene (acceptor) to form a heterojunction interface, we have fabricated bilayers which functioned as photodiodes and as photovoltaic cells. The results are discussed in terms of opportunities for solar energy conversion, for photodiode detector devices, and for a variety of other applications which use photoinduced charge separation.
LINE TENSION AT WETTING
Authors: INDEKEU J. O.
Published: November 2004

A review is presented of recent theoretical advances on a fundamental problem in statistical mechanics that concerns the three-phase contact line ℒ and its tension τ near a wetting phase transition. In addition to answering the intriguing question whether or not ℒ and τ vanish at wetting, recent work has also revealed that τ displays universal singular behavior, reflecting critical phenomena associated with the wetting transition. Three factors are crucial for determining the fate of ℒ and τ at wetting: the order of the wetting transition, the range of the intermolecular forces, and the upper critical dimension du, above which mean-field theory holds and below which fluctuations dominate. For most systems studied experimentally, du < 3, so that the mean-field predictions should be correct in d = 3. In the thermal fluctuation regime, for d < du, hyperscaling predicts the value 2(d – 2)/(d – 1) for the critical exponent of τ(θ), in the limit that the contact angle θ approaches 0.
DYNAMICS OF THE EDGE EXCITATIONS IN THE FQH EFFECTS
Authors: WEN XIAO-GANG
Published: November 2004

We review the dynamical theory of the edge excitations in the FQH effects.
EXTREME TYPE II SUPERCONDUCTORS: UNIVERSAL PROPERTIES AND TRENDS
Authors: SCHNEIDER T. , KELLER H.
Published: November 2004

We review and analyze experiment results of the specific heat, the muon–spin rotation (μSR) relaxation rate and the fluctuation contributions to the magnetization and dc conductivity of extreme type II superconductors from the point of view of critical phenomena. Our estimates of critical exponents and amplitudes, the measured scaling behavior, the consistencies with the universal relations between the critical amplitudes and the decrease of the transition temperature (T c ) with decreasing thickness, which corresponds to a dimensional crossover from 3d and 2d xy critical behavior, provide considerable evidence for a three-dimensional xy critical point. The estimated volume of the critical correlation length amplitudes turns out to be comparable to that in super-fluid Helium and is several orders of magnitude smaller than in BCS superconductors. Moreover, motivated by the Uemura plot, which relates the measured T c to the zero temperature μSR relaxation rate, and by the hyperuniversal relation between T c and critical amplitudes of the London penetration depth and phase correlation length, we propose a simple "universal" scaling ansatz, where the plot of the rescaled transition temperature versus rescaled μSR relaxation rate should fall on a single parabola. Our analysis of the μSR data reveals excellent agreement with this scaling ansatz for a large class of cuprate and Chevrel-phase superconductors. The resulting dependence of T c on the zero-temperature "condensate density" is then used to explore universal trends in the pressure (α) and isotope (β) coefficients. In good agreement with experiment we find that α and β fall into common T c -α and T c -β regions, respectively, forming two branches, one for systems with positive and the other for compounds with negative pressure or isotope coefficient. The two branches merge at the maximum T c where the coefficients vanish and the magnitude of the coefficients increases with decreasing T c . The "universal" scaling ansatz also implies that the critical amplitudes of the penetration depth and phase correlation length are related to the zero temperature condensate density. This quantity is also related to the hole concentration. Finally we discuss the temperature dependence of the penetration depth. μSR measurements indicate that for various cuprates the temperature dependence for 0 < T < T c appears to be bounded by the two-fluid model and the dilute charged Bose gas behaviors, respectively. Consistent with the dependence of T c on the zero temperature condensate density, compounds with high T c 's turn out to be closer to two-fluid behavior, while compounds with decreasing T c and in turn with lower condensate density clearly reveal the crossover to the dilute gas limit. These trends combined with T → 0 point uniquely to Bose condensation of interacting and weakly charged pairs as the mechanism that drives the transition.
CONDUCTANCE FLUCTUATIONS IN A TWO-DIMENSIONAL ELECTRON GAS IN THE TUNNELING AND HOPPING REGIMES
Authors: POPOVIĆ DRAGANA , WASHBURN S. , FOWLER A.B.
Published: November 2004

We report results of low temperature conductance measurements made on a wide two-dimensional electron gas as a function of sample length L and temperature, in a regime where conduction proceeds via tunneling or hopping through channels of localized states. We extend our recent study of the behavior of the ensemble averaged logarithm of conductance  and focus on fluctuations of conductance as a function of the chemical potential μ, which occur on at least three characteristic gate voltage scales VC. A detailed study of VC and variance vs. L and T for those three types of fluctuations reveals a complex behavior, probably caused by several competing effects. Our results suggest that both disorder and electron-electron interactions have to be taken into account to describe the properties of our samples.
ABOUT THE CROSSOVER PHENOMENON FOR VRH-CONDUCTIVITY
Authors: Shlimak I.S. , Lea M.J.
Published: November 2004

In a number of recent publications observations of the phenomenon of crossover from the Efros-Shklovskii (ES)-law to the Mott-law in VRH-conductivity were reported. In some experiments, deviations were observed from a straight line in a lnR vs T−1/2 plot to lower resistance values with increasing temperature. However, deviations to higher resistance with increasing temperature should be observed. In other experiments deviations from the “T−1/2 law” to higher resistances with decreasing temperature were observed. This effect was considered as a transition to a simple activation process, “T−1 law”, caused by the appearance of a hard gap at the Fermi level. In the present work an alternative explanation is given, based on the idea that the temperature range showing the “T−1/2 behaviour” actually corresponds to the crossover regime, while the real ES-regime is only reached in the low-temperature limit.
MULTIFRACTAL ANALYSIS OF BROADLY-DISTRIBUTED OBSERVABLES AT CRITICALITY
Authors: JANSSEN MARTIN
Published: November 2004

The multifractal analysis of disorder-induced localization-delocalization transitions is reviewed. Scaling properties of this transition are generic for multi parameter coherent systems which show broadly-distributed observables at criticality. The multifractal analysis of local measures is extended to more general observables including scaling variables such as the conductance in the localization problem. The relation of multifractal dimensions to critical exponents such as the order parameter exponent β and the correlation length exponent ν is investigated, We discuss a number of scaling relations between spectra of critical exponents, showing that all of the critical exponents necessary to characterize the critical phenomenon can be obtained within the generalized multifractal analysis. Furthermore we show how bounds for the correlation length exponent ν are obtained by the typical order parameter exponent α0 and make contact between the multifractal analysis and the finite size scaling approach in 2-d by relying on conformal mapping arguments.
HIGH TEMPERATURE EFFECTS IN THE HUBBARD MODEL
Authors: FABIAN J.
Published: November 2004

In this paper we investigate the Hubbard model at high temperatures. For this reason a simple algebraic method based on the Γ-representation of an original Hamiltonian is developed. The results thus obtained does imply no paradoxes as it is when doing some approximations starting from Lieb’s and Wu’s solutions. It is shown that a periodic behavior of observables can be predicted from high temperature perturbation theory. This periodicity is based on the Aharonov-Bohm-like effects on a lattice with the dimension d>1. An explicit formula for the periodic part of magnetization is given for d=2.
TRANSPORT COEFFICIENTS FOR RIGID STAR-LIKE POLYMERS
Authors: STRATING P. , WIEGEL F.W.
Published: November 2004

In this paper, we calculate the rotational and translational diffusion coefficient for a star-like molecule and the shear viscosity for a dilute suspension of these molecules, starting from the Debye-Brinkman equation. For this type of molecules, the calculations can be done exactly, providing reliable insight into draining effects. We also derive simple approximate formulas for the transport coefficients valid in the relevant parameter regime.
THE LINEAR RESPONSE APPROACH TO THE FOKKER-PLANCK EQUATION I: THEORY
Authors: BIANUCCI MARCO , MANNELLA RICCARDO , GRIGOLINI PAOLO , WEST BRUCE J.
Published: November 2004

We show that a Brownian motion can be derived for a particle coupled to a bath with a finite number of chaotic degrees of freedom, using no thermodynamics assumptions. We point out that although diffusion is easily derived in terms of the unperturbed bath via the central limit theorem, friction is obtained only when the coupling between particle of interest and bath is considered. The only assumption made is that the bath should respond linearly (in statistical sense) to a weak external perturbation. We prove that the calculation of the friction can be traced back to the bath susceptibility.
THE LINEAR RESPONSE APPROACH TO THE FOKKER-PLANCK EQUATION II: A NONLINEAR STOCHASTIC BOOSTER
Authors: BIANUCCI MARCO , MANNELLA RICCARDO , GRIGOLINI PAOLO , WEST BRUCE J.
Published: November 2004

It has been pointed out in I1 that the friction resulting from the interaction between a Brownian particle and a nonlinear bath cannot in general be evaluated by a second-order perturbation treatment with the conventional Liouville or Liouville-like approach. It has also been shown that a convenient way of proceeding is to express the dynamics of the bath within a master equation approach, which makes it possible to apply a linear response treatment (LRT) also in the case of a nonlinear bath. We check the internal consistency of this theory using as a bath for the velocity w of the Brownian particle a doorway variable ξ, which executes random jumps among some discrete values. In this specific condition the explicit expression for the master equation driving the motion of the bath is easily derived. It is also relatively easy to check the predictions of the theory with computer calculations. The internal consistency of the theory is proved and the agreement with the numerical calculation is shown to be remarkably good in the parameter region where the LRT approach is expected to hold.
THE QUADRATIC TIME-DEPENDENT HAMILTONIAN: EVOLUTION OPERATOR, SQUEEZING REGIONS IN PHASE SPACE AND TRAJECTORIES
Authors: MIZRAHI S.S. , MOUSSA M.H.Y. , BASEIA B.
Published: November 2004

We consider the most general Time-Dependent (TD) quadratic Hamiltonian written in terms of the bosonic operators a and a+, which may represent either a charged particle subjected to a harmonic motion, immersed in a TD uniform magnetic field, or a single mode photon field going through a squeezing medium. We solve the TD Schrödinger equation by a method that uses, sequentially, a TD unitary transformation and the diagonalization of a TD invariant, and we verify that the exact solution is a complete set of TD states. We also obtain the evolution operator which is essential to express operators in the Heisenberg picture. The variances of the quadratures are calculated and a phase space of parameters introduced, in which we identify squeezing regions. The results for some special cases are presented and as an illustrative example the parametric oscillator is revisited and the trajectories in phase space drawn.
EDGE ASYMPTOTICS OF PLANAR ELECTRON DENSITIES
Authors: DUNNE GERALD V.
Published: November 2004

The N→∞ limit of the edges of finite planar electron densities is discussed for higher Landau levels. For full filling, the particle number is correlated with the magnetic flux, and hence with the boundary location, making the N→∞ limit more subtle at the edges than in the bulk. In the nth Landau level, the density exhibits n distinct steps at the edge, in both circular and rectangular samples. The boundary characteristics for individual Landau levels, and for successively filled Landau levels, are computed in an asymptotic expansion.
ATOMIC STABILIZATION IN THE PRESENCE OF INTENSE LASER PULSES
Authors: SU Q. , SANPERA A. , ROSO-FRANCO L.
Published: November 2004

The nonperturbative response of atomic systems under strong laser radiation has been an important area of research both experimentally and theoretically. In a typical experiment, a very high power laser (operating at an intensity of the order of 1013 W/cm 2 or higher, delivering 1 µm wavelength light pulses with duration from a few pico-seconds down to a few hundred femto-seconds) is focused down to a tight spot in space filled with dilute gas where ionization occurs. These experiments have been successful in studying the single-atom strong-field physics where the predictions of ionization based on low-field perturbation theory are invalid. Various theories have been used to explain new effects associated with different intensity regions. In this review we intend to summarize the steps for arriving at a new theoretical prediction of atoms in laser pulses of intensity 1016 W/cm 2 or stronger. The prediction that atoms tend to stabilize in laser pulses strong enough to produce full ionization is rather counter-intuitive. The phenomenon of atomic stabilization will be introduced through space-time integration of Schrödinger equation. A more quantitative account of the associated effects during a stabilization will be analyzed through a simplified one-dimensional long-range potential. To further understand the features of stabilization, a one-dimensional short-range potential is also employed. We will mention some possible experimental consequences of stabilization.
SQUEEZING AND DISPLACEMENT OF THE PHONON BATH ENVIRONMENT IN A SUPERCONDUCTING TUNNEL JUNCTION
Authors: EXTREMERA A.
Published: November 2004

The effects of a phonon bath environment on the dynamics of a superconducting tunnel junction are investigated. In the Ohmic case, the coupling dependence of the renormalized tunneling splitting is obtained. At weak damping, the shape of the double well is manifested in the coupling representation. Special attention is devoted to squeezing Hamiltonians, a useful tool in the determination of critical parameters related to coherent oscillations.
A CONDUCTION MODEL OF THE ELECTRORHEOLOGICAL EFFECT
Authors: ATTEN P. , FOULC J.-N. , FELICI N.
Published: November 2004

A conduction model is proposed to explain the electrorheological effect under D.C. or low frequency A.C. fields. An approximate analysis taking into account the bulk conduction of the solid and the nonlinear conduction properties of the liquid is confirmed by experiments on large scale spheres. A good agreement between measurements and predictions is also obtained when air replaces the liquid. Finally the predictions are extended to the case of surface conduction of the solid spheres.
INFLUENCE OF PARTICLE SIZE ON THE DYNAMIC STRENGTH OF ELECTRORHEOLOGICAL FLUIDS
Authors: SHIH YUNG-HUI , CONRAD HANS
Published: November 2004

The electrical properties, rheology and structure of model ER fluids consisting of glass beads in silicone oil were investigated as a function of electric field E (0–4 kV/mm ), particle size D (6–100 µ m ) and shear rate [Formula: see text]. The conductivity of the suspensions was 3 orders of magnitude greater than that of the host oil at E ⋝ 1 kV/mm ; their low-voltage d.c. permittivity was about 1.35 times larger. The flow stress of the suspensions was given by [Formula: see text] where τE is the polarization component and τ vis the viscous component. The linear dependence of τE on E was attributed to dipole saturation. The observed opposing effects of D and [Formula: see text] on τE were concluded to result from their respective influence on the strength of the columnar structure normally produced by the electric field and its fragmentation during shear. The constant C1 was in agreement with the Einstein equation for the effect of volume fraction of particles on the viscosity of suspensions. The parameter C2/D was concluded to reflect either the effect of particle surface area on viscosity or a polydispersion effect. The present results did not correlate with the Mason number as normally formulated, but did when it was appropriately modified.
THE EFFECT OF SOLID FRACTION CONCENTRATION ON THE TIME DOMAIN PERFORMANCE OF AN ER FLUID IN THE SHEAR MODE
Authors: BULLOUGH W. A. , MAKIN J. , FIROOZIAN R. , JOHNSON A. R. , HOSSEINI-SIANAKI A.
Published: November 2004

Some aspects of electro-stress and electro-hydraulic time delay in an electro-rheological fluid are examined for their dependence on the volume fraction of solid in the mixture. Early results show that the density matching of the solid and liquid phases of an ERF brings little improvement in the serviceability of a suspension. Subsequent testing is based on non density matched mixtures which are examined over a range of 0 ≤ shear rate ≤ 19000 s −1, 15 ≤ temperature ° C ≤ 50 and 20 ≤ % volume fraction of solid ≤ 40. The effect of prolonged operation on the durability of the fluid is also reported. The results are used to provide pointers towards fluid selection, a control strategy and to help in the determination of operating parameters in order to optimise clutch performance. Testing took place on a concentric clutch (Couette) type apparatus which had an electrode separation of 0.5 mm.
INFLUENCE OF DIMENSIONALITY AND SURFACE ORDERING ON PHASE TRANSITIONS: STUDIES OF FREELY-SUSPENDED LIQUID-CRYSTAL FILMS
Authors: BAHR CHRISTIAN
Published: November 2004

Freely-suspended films of smectic liquid crystals can be regarded as membranes consisting of a stack of an integral number of molecular (smectic) layers with the layer planes being parallel to the two free surfaces. Because of their variable thickness (between thousands and only two layers) and the large variety of phase transitions between different smectic phases, freely-suspended films are excellent systems to study the influence of the dimensional cross-over from three to two dimensions on phase transitions. Further, because the free surface of a liquid crystal has a strong ordering effect (contrary to solids which exhibit generally surface-induced disorder), freely-suspended films are well-suited for the study of the effect of enhanced surface order on phase transitions. A review of the corresponding experimental work is given.
QUASI-PARTICLES IN THE CHIRAL POTTS MODEL
Authors: KEDEM RINAT , McCOY BARRY M.
Published: November 2004

We study the quasi-particle spectrum of the integrable three-state chiral Potts chain in the massive phase by combining a numerical study of the zeros of associated transfer matrix eigenvalues with the exact results of the ferromagnetic three-state Potts chain and the three-state superintegrable chiral Potts model. We find that the spectrum is described in terms of quasi-particles with momenta restricted only to segments of the Brillouin zone 0≤P≤2π where the boundaries of the segments depend on the chiral angles of the model.
GAUGE FIELD IMPROVEMENT, FORM-SCALAR DUALITY, CONFORMAL INVARIANCE AND QUASI-LOCALITY
Authors: DESER S. , SCHWIMMER A.
Published: November 2004

The problem of maintaining scale and conformal invariance in Maxwell and general N form gauge theories away from their critical dimension dc=2(N+1) is analyzed. We first exhibit the underlying group-theoretical clash between locality, gauge, Lorentz and conformal invariance requirements. “Improved"-traceless-stress tensors are then constructed; each violates one of the above criteria. However, when d=N+2, there is a duality equivalence between N-form models and massless scalars in d=N+2. Here we show that N-form conformal invariance is not lost, by constructing a quasilocal gauge invariant improved stress tensor. The correlators of the scalar theory are then reproduced, including the latter’s trace anomaly. This resolves the old conformal invariance “paradox” between the dual partners.
SCHWINGER-BOSON STUDIES OF THE SINGLE HOLE MOTION IN A 2D QUANTUM ANTIFERROMAGNET
Authors: WU C.Q. , SU Z.B. , YU L.
Published: November 2004

Within the Schwinger-boson approach for the t-J model, the single hole problem in a two-dimensional quantum antiferromagnet is studied by using the quantum Bogoliubovde Gennes formalism which treats the distortion of the spin background and quantum spin fluctuations on an equal footing. Several self-trapped localized hole states are found in the distorted spin-background as in the case of an anisotropic Heisenberg model. These localized hole states survive at finite temperatures when the antiferromagnetic order becomes short-ranged. The energy separation between the two lowest states is reduced by considering the spin-background distortion, but it remains finite.
A MEAN FIELD STUDY OF THE PHASE TRANSITIONS IN A CLASS OF SYSTEMS WITH COMPLEX ORDER PARAMETERS
Authors: BLAGOEVA EVGENIA J.
Published: November 2004

A generalized Landau free energy for a complex order parameter expanded up to sixth-order is investigated using group theoretical arguments and the mean-field approximation. Results for the phase transitions that occur are presented. The phase diagram for all allowed values of the expansion coefficients is constructed with an emphasis placed on the influence of the anisotropy in the order parameter space. The results can be used in discussions of unconventional superconductors and modulated structural and magnetic orderings.
LIMIT CYCLING IN AN OBSERVER-BASED CONTROLLED SYSTEM WITH FRICTION: NUMERICAL ANALYSIS AND EXPERIMENTAL VALIDATION
Authors: PUTRA DEVI , NIJMEIJER HENK
Published: November 2004

This paper investigates limit cycling behavior of observer-based controlled mechanical systems with friction compensation. The limit cycling is induced by the interaction between friction and friction compensation, which is based on the estimated velocity. The limit cycling phenomenon, which is experimentally observed in a rotating arm manipulator, is analyzed through computational bifurcation analysis. The computed bifurcation diagram confirms that the limit cycles can be eliminated by enlarging observer gains and controller gains at the cost of a steady state error. The numerical results match well with laboratory experiments.
SINGLE-INPUT MULTI-OUTPUT STATE-FEEDBACK CHAOTIFICATION OF GENERAL DISCRETE SYSTEMS
Authors: ZHANG HUAIZHOU , CHEN GUANRONG
Published: November 2004

This Letter improves the Chen–Lai chaotification algorithm for discrete-time systems from multiple-input to single-input state feedback, while preserving its mathematical rigor.
STABILITY ANALYSIS FOR DELAYED CELLULAR NEURAL NETWORKS BASED ON LINEAR MATRIX INEQUALITY APPROACH
Authors: LIAO XIAOFENG , WONG KWOK-WO , YANG SHIZHONG
Published: November 2004

Some sufficient conditions for the asymptotic stability of cellular neural networks with time delay are derived using the Lyapunov–Krasovskii stability theory for functional differential equations as well as the linear matrix inequality (LMI) approach. The analysis shows how some well-known results can be refined and generalized in a straightforward manner. Moreover, the stability criteria obtained are delay-independent. They are less conservative and restrictive than those reported so far in the literature, and provide a more general set of criteria for determining the stability of delayed cellular neural networks.
CHEN'S ATTRACTOR EXISTS
Authors: ZHOU TIANSHOU , TANG YUN , CHEN GUANRONG
Published: November 2004

By applying the undetermined coefficient method, this paper finds homoclinic and heteroclinic orbits in the Chen system. It analytically demonstrates that the Chen system has one heteroclinic orbit of Ši'lnikov type that connects two nontrivial singular points. The Ši'lnikov criterion guarantees that the Chen system has Smale horseshoes and the horseshoe chaos. In addition, there also exists one homoclinic orbit joined to the origin. The uniform convergence of the series expansions of these two types of orbits are proved in this paper. It is shown that the heteroclinic and homoclinic orbits together determine the geometric structure of Chen's attractor.
ALGORITHM FOR EXACT LONG TIME CHAOTIC SERIES AND ITS APPLICATION TO CRYPTOSYSTEMS
Authors: KAWAMOTO SHUNJI , HORIUCHI TAKESHI
Published: November 2004

It is said that the numerical generation of exact chaotic time series by iterating, for example, the logistic map, will be impossible, because chaos has a high dependency on initial values. In this letter, an algorithm to generate them without the accumulation of inevitable round-off errors caused by the iteration is proposed, where rational numbers are introduced. Also, it is shown that the period of the chaotic time series depends on the rational numbers including large prime numbers, which are fundamentally related to the Mersenne and the Fermat prime ones. Since the time series are numerically regenerated by the proposed algorithm in an usual computer environment, it could be applied to cryptosystems which do not need the synchronization, and have a large key-space by using large prime numbers.
EXPERIMENTAL REALIZATION OF CONTROLLING CHAOS IN THE PERIODICALLY SWITCHED NONLINEAR CIRCUIT
Authors: KOUSAKA TAKUJI , YASUHARA YOSIHITO , UETA TETSUSHI , KAWAKAMI HIROSHI
Published: November 2004

This letter presents an experimental confirmation of controlling the chaotic behavior of a target unstable periodic orbit when the periodically switched nonlinear circuit has a chaotic attractor. The pole assignment for the corresponding discrete system derived from such a nonautonomous system via Poincaré mapping works effectively, and the control unit is easily realized by the window comparator, sample-hold circuits, and so on.
CHAOTIC ANALYSIS OF A TIME SERIES COMPOSED OF SEISMIC EVENTS RECORDED IN JAPAN
Authors: PAVLOS G.P. , KARAKATSANIS L. , LATOUSSAKIS J.B. , DIALETIS D. , PAPAIOANNOU G.
Published: November 2004

A chaotic analysis approach was applied to an earthquake time series recorded in the Japanese area in order to test the assumption that the earthquake process could be the manifestation of a chaotic low dimensional process. For the study of the seismicity we have used a time series consisting of time differences between two consecutive seismic events with magnitudes greater than 2.6. The results of our study show that the underlying mechanism, as expressed by the time series, can be described by low dimensional chaotic dynamics. The power spectrum of the time series shows a power law profile with two slopes, α=1.4 in the low frequency and α=0.05 in the high frequency regions, while the slopes of the correlation integrals show an apparent plateau at the scaling region, which saturates at the value D≈3.2. The largest Lyapunov exponent was found to be ≈0.9. The positive value of the largest Lyapunov exponent reveals strong sensitivity to initial conditions of the supposed earthquake dynamics.
NONINVERTIBLE TWO-DIMENSIONAL MAPS ARISING IN RADIOPHYSICS
Authors: MAISTRENKO VLADIMIR , MAISTRENKO YURI , SUSHKO IRINA
Published: November 2004

We study a two-parameter family of noninvertible maps modeling a generator which consists of two identical nonlinear amplifiers and two delay circuits. The ratio of the delays determines the dimension of the map and our attention is mainly on the two-dimensional case. The mechanism of transition to chaos appears to be one-dimensional and is realized through a period-doubling cascade. To get a more complete description we suggest the use of so-called triangular maps. Phase portraits are constructed for some types of model triangular maps. Also we get one- and two-dimensional bifurcation diagrams for the maps considered and attractor basins in the case of multistability using computer simulation.
CHAOS OF TRAVELING WAVES IN A DISCRETE CHAIN OF DIFFUSIVELY COUPLED MAPS
Authors: AFRAIMOVICH V.S. , NEKORKIN V.I.
Published: November 2004

An infinite set of stationary traveling waves are found in a discrete analog of the nonlinear diffusion Huxley equation. Their profiles are determined by the trajectories of Bernoulli scheme containing two symbols. It is proved that these waves are stable with respect to perturbations moving with the same speed. Thus it is shown that chaos of traveling waves is realized in this system.
EXPERIMENTAL CONTROL OF CHAOS IN CHUA’S CIRCUIT VIA TUNNELS
Authors: ITOH MAKOTO , MURAKAMI HIROYUKI , CHUA LEON O.
Published: November 2004

In this letter, we propose a new experimental method for converting a chaotic attractor in Chua’s circuit to a periodic orbit. A tunnel mechanism is used to achieve this conversion. Using this method, we were able to demonstrate experimentally that periodic orbits of very high periods (e.g., greater than 30) can be robustly stabilized.
APPROACHING NONLINEAR DYNAMICS BY STUDYING THE MOTION OF A PENDULUM III: PREDICTABILITY AND CONTROL OF CHAOTIC MOTION
Authors: HÜBINGER B. , DOERNER R. , HENG H. , MARTIENSSEN W.
Published: November 2004

We apply the concepts of predictability and control of chaotic motion to the driven damped pendulum. A physical measure of predictability is defined and determined from experimental data as well as from the equations of motion. The results are presented in predictability portraits which constitute an intrinsic pattern of zones of varying predictability. The origin of these patterns is related to the unstable periodic orbits and their invariant manifolds within the attractor. In order to control the chaotic motion of the pendulum we implement an extension of the OGY feedback control method, which we call “local control method.” With this control scheme any motion of the pendulum which is a solution of the systems equations of motion can be stabilized. We apply the control formalism in order to stabilize experimentally unstable periodic orbits as well as arbitrarily chosen chaotic trajectories.
SYSTEM IDENTIFICATION AND MODEL-BASED CONTROL OF A CHAOTIC SYSTEM
Authors: QAMMAR HELEN K. , MOSSAYEBI FARAMARZ
Published: November 2004

In this paper the control of a hyper2chaotic system is considered to show the role of system identification techniques in developing a model for effective control of highly complex systems. An indirect adaptive control scheme is considered and it is shown that simple prediction models which cannot possibly represent the dynamics of the chaotic system lead to stable control. Furthermore, it is shown that higher dimensional prediction models which more closely represent the chaotic process dynamics lead to controlled systems with sparse and disjoint basins of attraction for the desired steady state solution. The use of highly nonlinear models also results in a complex pattern of convergence to the desired state.
CLASSICAL DYNAMICS OF RYDBERG ELECTRONS IN CROSSED FIELDS: THE STRUCTURE OF PHASE SPACE AND CHAOS-ORDER ALTERNATIONS
Authors: MILCZEWSKI JAN VON , DIERCKSEN G.H.F. , UZER T.
Published: November 2004

Highly excited Rydberg atoms are atomic-scale laboratories where the quantum mechanics of chaotic systems can be tested. The symmetry breaking introduced into the Coulomb potential by crossed electric and magnetic fields leads to very interesting nonlinear dynamics, but is also a source of great complexity. In this article, we analyse the phase space and dynamics of a highly excited electron in the combined Coulomb, electric, and magnetic fields by bringing out the classical structures that support the complexity of the motion.
CHAOS IN COOPERATION: CONTINUOUS-VALUED PRISONER’S DILEMMAS IN INFINITE-VALUED LOGIC
Authors: MAR GARY , DENIS PAUL ST.
Published: November 2004

The Prisoner’s Dilemma (PD) has become a paradigm of the evolution of cooperation. The PD can be generalized to the continuous-valued case in which players are allowed to choose intermediate levels of cooperation. When continuous-valued PDs are played in the spatial context of cellular automata, generous strategies are favored.

Continuous-valued PDs are naturally represented in infinite-valued logic. The infinite-valued logic allows us to prove that cooperative interactions between continuous-valued strategies are paradigmatically chaotic. Escape-time diagrams using a given level of mutual cooperation as a threshold produce fractal images. The sensitive dependence of chaotic dynamical systems models a practical unpredictability within the PD (even though only deterministic nonstochastic strategies are involved) that is characteristic of many real life choice situations.
CHAOS AND CANARDS IN THE VAN DER POL EQUATION WITH PERIODIC FORCING
Authors: ITOH MAKOTO , MURAKAMI HIROYUKI
Published: November 2004

Chaotic attractors in the van der Pol equation with periodic forcing are studied. Computer results are given, and the range of the parameter corresponding to the chaotic attractor is discussed. Moreover, its piecewise linear version is studied. The experimental results display the large difference between the dynamics of the van der Pol equation with periodic forcing and its piecewise linear version.
COMPARISON OF DATA FROM BÉNARD-MARANGONI CONVECTION IN A SQUARE CONTAINER WITH A MODEL BASED ON SYMMETRY ARGUMENTS
Authors: MINDLIN G.B. , ONDARÇUHU T. , MANCINI H.L. , PÉREZ GARCÍA C. , GARCIMARTÍN A.
Published: November 2004

We report the results of a Bénard-Marangoni convection experiment. The container has a square symmetry and a small aspect ratio (i.e. the quotient between a typical horizontal length and the fluid depth). Based on a few dynamical considerations and the symmetries of the problem we improve on a previously proposed model, building a new one which successfully predicts the existence and parameter space location of qualitatively new solutions.