title: Single-vehicle data of highway traffic - a statistical analysis

abstract:
  In the present paper single-vehicle data of highway traffic are analyzed in
great detail. By using the single-vehicle data directly empirical time-headway
distributions and speed-distance relations can be established. Both quantities
yield relevant information about the microscopic states. Several fundamental
diagrams are also presented, which are based on time-averaged quantities and
compared with earlier empirical investigations. In the remaining part
time-series analyses of the averaged as well as the single-vehicle data are
carried out. The results will be used in order to propose objective criteria
for an identification of the different traffic states, e.g. synchronized
traffic.


title: Symmetric patterns of dislocations in Thomson's problem

abstract:
  Determination of the classical ground state arrangement of $N$ charges on the
surface of a sphere (Thomson's problem) is a challenging numerical task. For
special values of $N$ we have obtained using the ring removal method of Toomre,
low energy states in Thomson's problem which have icosahedral symmetry where
lines of dislocations run between the 12 disclinations which are induced by the
spherical geometry into the near triangular lattice which forms on a local
scale.


title: Exploring the fractional quantum Hall effect with electron tunneling

abstract:
  In this talk I present a summary of recent work on tunnel junctions of a
fractional quantum Hall fluid and an electron reservoir, a Fermi liquid. I
consider first the case of a single point contact. This is a an exactly
solvable problem from which much can be learned. I also discuss in some detail
how these solvable junction problems can be used to understand many aspects of
the recent electron tunneling experiments into edge states. I also give a
detailed picture of the unusual behavior of these junctions in their strong
coupling regime. A pedagogical introduction to the theories of edge states is
also included.


title:
The pseudogap in high-temperature superconductors: an experimental
  survey

abstract:
  We present an experimental review of the nature of the pseudogap in the
cuprate superconductors. Evidence from various experimental techniques points
to a common phenomenology. The pseudogap is seen in all high temperature
superconductors and there is general agreement on the temperature and doping
range where it exists. It is also becoming clear that the superconducting gap
emerges from the normal state pseudogap. The d-wave nature of the order
parameter holds for both the superconducting gap and the pseudogap. Although an
extensive body of evidence is reviewed, a consensus on the origin of the
pseudogap is as lacking as it is for the mechanism underlying high temperature
superconductivity.


title:
Effect of Thermal Phase Fluctuations on the Inductances of Josephson
  Junctions, Arrays of Junctions, and Superconducting Films

abstract:
  We calculate the factor by which thermal phase fluctuations, as distinct from
phase-slip fluctuations, increase the inductance, LJ, of a resistively-shunted
Josephson junction (JJ) above its mean-field value, L0. We find that quantum
mechanics suppresses fluctuations when T drops below a temperature, TQ =
h/kBGL0, where G is the shunt conductance. Examination of the calculated sheet
inductance, LA(T)/L0(T), of arrays of JJ's reveals that 2-D interconnections
halve fluctuation effects, while reducing phase-slip effects by a much larger
factor. Guided by these results, we calculate the sheet inductance,
LF(T)/L0(T), of 2-D films by treating each plasma oscillation mode as an
overdamped JJ. In disordered s-wave superconductors, quantum suppression is
important for LF(0)/LF(T) > 0.14, (or, T/TC0 < 0.94). In optimally doped YBCO
and BSCCO quantum suppression is important for l2(0)/l2(T) > 0.25, where l is
the penetration depth.


title:
Random Walks on Figure Eight:From Polymers Through Chaos to Gravity and
  Beyond

abstract:
  This paper is extended and broadly generalized version of earlier published
rapid communication, Phys.Rev.E, Vol.58, R 5213 (1998). It also elaborates on
some problems which were left unsolved or just mentioned in Physics Reports
Vol.298, 251 (1998). Applications of the obtained results include (but not
limited to) polymer physics, classical and quantum chaos, fractional Hall
effect, dynamics of textures in liquid crystals and 2+1 gravity. The paper
presents some self contained excerpts from mathematics(not discussed so far in
physics literature)to facilitate the uninterrupted reading of the manuscript.


title:
On the Relevance of Disorder for Dirac Fermions with Imaginary Vector
  Potential

abstract:
  We consider the effects of disorder in a Dirac-like Hamiltonian. In order to
use conformal perturbation theory, we argue that one should consider disorder
in an imaginary vector potential. This affects significantly the signs of the
lowest order $\beta$eta functions. We present evidence for the existence of two
distinct universality classes, depending on the relative strengths of the gauge
field verses impurity disorder strengths. In one class all disorder is driven
irrelevant by the gauge field disorder.


title: Magnetic-interference patterns in Josephson junctions with d+is symmetry

abstract:
  The magnetic interference pattern and the spontaneous flux in unconventional
Josephson junctions of superconductors with d+is symmetry are calculated for
different reduced junction lengths and the relative factor of the d and s wave
components. This is a time reversal broken symmetry state. We study the
stability of the fractional vortex and antivortex which are spontaneously
formed and examine their evolution as we change the length and the relative
factor of d and s wave components. The asymmetry in the field modulated
diffraction pattern exists for lengths as long as L=10\lambda_J.


title: Critical Behavior of Anisotropic Heisenberg Mixed-Spin Chains in a Field

abstract:
  We numerically investigate the critical behavior of the spin-(1,1/2)
Heisenberg ferrimagnet with anisotropic exchange coupling in a magnetic field.
A quantized magnetization plateau as a function of the field, appearing at a
third of the saturated magnetization, is stable over whole the
antiferromagnetic coupling region. The plateau vanishes in the ferromagnetic
coupling region via the Kosterlitz-Thouless transition. Comparing the quantum
and classical magnetization curves, we elucidate what are essential quantum
effects.


title: Stiff monatomic gold wires with a spinning zigzag geometry

abstract:
  Using first principles density functional calculations, gold monatomic wires
are found to exhibit a zigzag shape which remains under tension, becoming
linear just before breaking. At room temperature they are found to spin, what
explains the extremely long apparent interatomic distances shown by electron
microscopy.The zigzag structure is stable if the tension is relieved, the wire
holding its chainlike shape even as a free-standing cluster. This unexpected
metallic-wire stiffness stems from the transverse quantization in the wire, as
shown in a simple free electron model.


title:
Quasiclassical theory of superconductivity: a multiple interface
  geometry

abstract:
  The purpose of the paper is to suggest a new method which allows one to study
multiple coherent reflection/transmissions by partially transparent interfaces
(e.g. in multi-layer mesoscopic structures or grain boundaries in high-Tc's) in
the framework of the quasiclassical theory of superconductivity. It is argued
that typically the trajectory of the particle is a simply connected tree (no
loops) with knots, i.e. the points where interface scattering events occur and
ballistic pieces of the trajectory are mixed. A linear boundary condition for
the 2-component trajectory "wave function" which factorizes matrix (retarded)
Green's function, is formulated for an arbitrary interface, specular or
diffusive. To show the usage of the method, the current response to the vector
potential (the total superfluid density rho_s) of a SS' sandwich with the
different signs of the order parameter in S and S', is calculated. In this
model, a few percent of reflection by the SS' interface transforms the
paramagnetic response (rho_s < 0) created by the zero-energy Andreev bound
states near an ideal interface (see Fauchere et al. PRL, 82, 3336 (1999),
cond-mat/9901112), into the usual diamagnetic one (rho_s >0).


title:
Double-layer Heisenberg antiferromagnet at finite temperature: Brueckner
  Theory and Quantum Monte Carlo simulations

abstract:
  The double-layer Heisenberg antiferromagnet with intra- and inter-layer
couplings $J$ and $J_\perp$ exhibits a zero temperature quantum phase
transition between a quantum disordered dimer phase for $g>g_c$ and a Neel
phase with long range antiferromagnetic order for $g<g_c$, where $g=J_\perp/J$
and $g_c \approx 2.5$. We consider the behavior of the system at finite
temperature for $g \ge g_c$ using two different and complementary approaches;
an analytical Brueckner approximation and numerically exact quantum Monte Carlo
simulations. We calculate the temperature dependent spin excitation spectrum
(including the triplet gap), dynamic and static structure factors, the specific
heat, and the uniform magnetic susceptibility. The agreement between the
analytical and numerical approaches is excellent. For $T \to 0$ and $g \to
g_c$, our analytical results for the specific heat and the magnetic
susceptibility coincide with those previously obtained within the nonlinear
$\sigma$ model approach for $N\to \infty$. Our quantum Monte Carlo simulations
extend to significantly lower temperatures than previously, allowing us to
obtain accurate results for the asymptotic quantum critical behavior. We also
obtain an improved estimate for the critical coupling: $g_c = 2.525 \pm 0.002$.


title: Thermal Conductivity of Mg-doped CuGeO_3

abstract:
  The thermal conductivity $\kappa$ is measured in a series of Cu_1-xMg_xGeO_3
single crystals in magnetic fields up to 16 T. It has turned out that heat
transport by spin excitations is coherent for lightly doped samples, in which
the spin-Peierls (SP) transition exists, at temperatures well above the SP
transition temperature T_SP. Depression of this spin heat transport appears
below T^*, at which the spin gap locally opens. T^* is not modified with
Mg-doping and that T^* for each Mg-doped sample remains as high as T_SP of pure
CuGeO_3, in contrast to T_SP which is strongly suppressed with Mg-doping. The
spin-gap opening enhances phonon part of the heat transport because of reduced
scattering by the spin excitations, producing an unusual peak. This peak
diminishes when the spin gap is suppressed both in magnetic fields and with the
Mg-doping.


title: Efficiency of symmetric targeting for finite-T DMRG

abstract:
  Two targeting schemes have been known for the density matrix renormalization
group (DMRG) applied to non-Hermitian problems; one uses an asymmetric density
matrix and the other uses symmetric density matrix. We compare the numerical
efficiency of these two targeting schemes when they are used for the finite
temperature DMRG.


title: Physical Optimization of Quantum Error Correction Circuits

abstract:
  Quantum error correcting codes have been developed to protect a quantum
computer from decoherence due to a noisy environment. In this paper, we present
two methods for optimizing the physical implementation of such error correction
schemes. First, we discuss an optimal quantum circuit implementation of the
smallest error-correcting code (the three bit code). Quantum circuits are
physically implemented by serial pulses, i.e. by switching on and off external
parameters in the Hamiltonian one after another. In contrast to this, we
introduce a new parallel switching method that allows faster gate operation by
switching all external parameters simultaneously. These two methods are applied
to electron spins in coupled quantum dots subject to a Heisenberg coupling
H=J(t) S_1*S_2 which can generate the universal quantum gate
`square-root-of-swap'. Using parallel pulses, the encoding for three-bit
quantum error correction in a Heisenberg system can be accelerated by a factor
of about two. We point out that parallel switching has potential applications
for arbitrary quantum computer architectures.


title: Two electron view on metal-insulator transition in two dimensions

abstract:
  The model of two electrons with Coulomb interaction on a two-dimensional (2D)
disordered lattice is considered. It is shown that the interaction can give a
sharp transition to delocalized states in a way similar to the Anderson
transition in 3D. The localized phase appears when the ratio of the Coulomb
energy to the Fermi energy becomes larger than some critical value dependent on
the disorder. The relation to the experiments on metal-insulator transition in
2D is also discussed.


title: A Thought Construction of Working Perpetuum Mobile of the Second Kind

abstract:
  A previously published model of the isothermal Maxwell demon as one of models
of open quantum systems endowed with faculty of selforganization is
reconstructed here. It describes an open quantum system interacting with a
single thermodynamic bath but otherwise not aided from outside. Its activity is
given by the standard linear Liouville equation for the system and bath. Owing
to its selforganization property, the model then yields cyclic conversion of
heat from the bath into mechanical work without compensation. Hence, it
provides an explicit thought construction of perpetuum mobile of the second
kind, contradicting thus the Thomson formulation of the second law of
thermodynamics. No approximation is involved as a special scaling procedure is
used which makes the kinetic equations employed exact.


title:
Multiple Andreev reflections and enhanced shot noise in diffusive SNS
  junctions

abstract:
  We study the dc conductance and current fluctuations in diffusive voltage
biased SNS junctions with a tunnel barrier inside the mesoscopic normal region.
We find that at subgap voltages, eV<2Delta/n, the current associated with the
chain of n Andreev reflections is mapped onto the quasiparticle flow through a
structure of n+1 voltage biased barriers connected by diffusive conductors. As
a result, the current-voltage characteristic of a long SNINS structure obeys
Ohm's law, in spite of the complex multiparticle transport process. At the same
time, nonequilibrium heating of subgap electrons produces giant shot noise with
pronounced subharmonic gap structure which corresponds to stepwise growth of
the effective transferred charge. At eV\to 0, the shot noise approaches the
magnitude of the Johnson-Nyquist noise with the effective temperature
T^*=Delta/3, and the effective charge increases as (e/3)(1 + 2Delta/eV), with
the universal ``one third suppression'' factor. We analyse the role of
inelastic scattering and present a criterion of strong nonequilibrium.


title: Thermal Operators in Ising Percolation

abstract:
  We discuss a new cluster representation for the internal energy and the
specific heat of the d-dimensional Ising model, obtained by studying the
percolation mapping of an Ising model with an arbitrary set of
antiferromagnetic links. Such a representation relates the thermal operators to
the topological properties of the Fortuin-Kasteleyn clusters of Ising
percolation and is a powerful tool to get new exact relations on the
topological structure of FK clusters of the Ising model defined on an arbitrary
graph.


title:
Computational implementation of the Kubo formula for the static
  conductance: application to two-dimensional quantum dots

abstract:
  Kubo formula is used to get the d.c conductance of a statistical ensemble of
two-dimensional clusters of the square lattice in the presence of standard
diagonal disorder, a uniform magnetic field and random magnetic fluxes. Working
within a one-band tight-binding approach the calculation is quite general. The
shape of the cluster is rectangular with ideal leads attached to opposite
corners. Both geometrical characteristics and physical parameters can be easily
selected. The output is just the conductance of a system of given parameters or
a statistical ensemble of conductances measured for different disorder
realizations.


title:
Distribution of Avalanche Sizes in the Hysteretic Response of Random
  Field Ising Model on a Bethe Lattice at Zero Temperature

abstract:
  We consider the zero-temperature single-spin-flip dynamics of the
random-field Ising model on a Bethe lattice in the presence of an external
field h. We derive the exact self-consistent equations to determine the
distribution Prob(s) of avalanche sizes s, as the external field increases from
large negative to positive values. We solve these equations explicitly for a
rectangular distribution of the random fields for a linear chain and the Bethe
lattice of coordination number z=3, and show that in these cases, Prob(s)
decreases exponentially with s for large s for all h on the hysteresis loop. We
found that for z >3 and for small disorder, the magnetization shows a first
order discontinuity for several continuous and unimodel distributions of random
fields. The avalanche distribution Prob(s) varies as s^{-3/2} for large s near
the discontinuity.


title: On Anisotropic Transport in High Landau Levels

abstract:
  We would like to point out that: (i) according to the edge-bulk transport
models for the quantum Hall regime, the direction of low bulk conductance is
actually perpendicular to that expected naively; and (ii) the values of
experimental "high resistance" peaks correspond to value of bulk conductance
$\approx 1 e^{2}/h$.


title: Light Induced Melting of Colloidal Crystals in Two Dimensions

abstract:
  We demonstrate that particles confined to two dimensions (2d) and subjected
to a one-dimensional (1d) periodic potential exhibit a rich phase diagram, with
both ``locked floating solids'' and smectic phases. The resulting phases and
phase transitions are studied as a function of temperature and potential
strength. We find reentrant melting as a function of the potential strength.
Our results lead to universal predictions consistent with recent experiments on
2d colloids in the presence of a laser-induced 1d periodic potential.


title: A new hierarchy of avalanches observed in Bak-Sneppen evolution model

abstract:
  A new quantity, average fitness, is introduced in Bak-Sneppen evolution
model. Through this new quantity, a new hierarchy of avalanches is observed in
the evolution of Bak-Sneppen model. An exact gap equation, governing the
self-organization of the model, is presented. It is found that the
self-organized threshold of the new quantity can be exactly obtained. Two basic
exponents, avalanche distribution and avalanche dimension are given through
simulations of one- and two-dimensional Bak-Sneppen models. It is suggested
that this new quantity may be a good quantity in determining the emergence of
criticality.


title: Non-linear conductivity and quantum interference in disordered metals

abstract:
  We report on a novel non-linear electric field effect in the conductivity of
disordered conductors. We find that an electric field gives rise to dephasing
in the particle-hole channel, which depresses the interference effects due to
disorder and interaction and leads to a non-linear conductivity. This
non-linear effect introduces a field dependent temperature scale $T_E$ and
provides a microscopic mechanism for electric field scaling at the
metal-insulator transition. We also study the magnetic field dependence of the
non-linear conductivity and suggest possible ways to experimentally verify our
predictions. These effects offer a new probe to test the role of quantum
interference at the metal-insulator transition in disordered conductors.


title:
Quantum Statistical Mechanics of Nonrelativistic Membranes: Crumpling
  Transition at Finite Temperature

abstract:
  The effect of quantum fluctuations on a nearly flat, nonrelativistic
two-dimensional membrane with extrinsic curvature stiffness and tension is
investigated. The renormalization group analysis is carried out in first-order
perturbative theory. In contrast to thermal fluctuations, which soften the
membrane at large scales and turn it into a crumpled surface, quantum
fluctuations are found to {\em stiffen} the membrane, so that it exhibits a
Hausdorff dimension equal to two. The large-scale behavior of the membrane is
further studied at finite temperature, where a nontrivial fixed point is found,
signaling a crumpling transition.


title: Strong-Coupling Perturbation Theory of the Hubbard Model

abstract:
  The strong-coupling perturbation theory of the Hubbard model is presented and
carried out to order (t/U)^5 for the one-particle Green function in arbitrary
dimension. The spectral weight A(k,omega) is expressed as a Jacobi continued
fraction and compared with new Monte-Carlo data of the one-dimensional,
half-filled Hubbard model. Different regimes (insulator, conductor and
short-range antiferromagnet) are identified in the temperature--hopping
integral (T,t) plane. This work completes a first paper on the subject (Phys.
Rev. Lett. 80, 5389 (1998)) by providing details on diagrammatic rules and
higher-order results. In addition, the non half-filled case, infinite
resummations of diagrams and the double occupancy are discussed. Various tests
of the method are also presented.


title:
Coulomb Driven New Bound States at the Integer Quantum Hall States in
  GaAs/Al(0.3)Ga(0.7)As Single Heterojunctions

abstract:
  Coulomb driven, magneto-optically induced electron and hole bound states from
a series of heavily doped GaAs/Al(0.3)Ga(0.7)As single heterojunctions (SHJ)
are revealed in high magnetic fields. At low magnetic fields (nu > 2), the
photoluminescence spectra display Shubnikov de-Haas type oscillations
associated with the empty second subband transition. In the regime of the
Landau filling factor nu < 1 and 1 < nu <2, we found strong bound states due to
Mott type localizations. Since a SHJ has an open valence band structure, these
bound states are a unique property of the dynamic movement of the valence holes
in strong magnetic fields.


title: Quasicrystals in a Monodisperse System

abstract:
  We investigate the formation of a two-dimensional quasicrystal in a
monodisperse system, using molecular dynamics simulations of hard sphere
particles interacting via a two-dimensional square-well potential. We find that
more than one stable crystalline phase can form for certain values of the
square-well parameters. Quenching the liquid phase at a very low temperature,
we obtain an amorphous phase. By heating this amorphous phase, we obtain a
quasicrystalline structure with five-fold symmetry. From estimations of the
Helmholtz potentials of the stable crystalline phases and of the quasicrystal,
we conclude that the observed quasicrystal phase can be the stable phase in a
specific range of temperatures.


title: Valence band photoemission from the GaN(0001) surface

abstract:
  A detailed investigation by one-step photoemission calculations of the
GaN(0001)-(1x1) surface in comparison with recent experiments is presented in
order to clarify its structural properties and electronic structure. The
discussion of normal and off-normal spectra reveals through the identified
surface states clear fingerprints for the applicability of a surface model
proposed by Smith et al. Especially the predicted metallic bonds are confirmed.
In the context of direct transitions the calculated spectra allow to determine
the valence band width and to argue in favor of one of two theoretical bulk
band structures. Furthermore a commonly used experimental method to fix the
valence band maximum is critically tested.


title: First-Principles Calculations of Hyperfine Interactions in La_2CuO_4

abstract:
  We present the results of first-principles cluster calculations of the
electronic structure of La_2CuO_4. Several clusters containing up to nine
copper atoms embedded in a background potential were investigated.
Spin-polarized calculations were performed both at the Hartree-Fock level and
with density functional methods with generalized gradient corrections to the
local density approximation. The distinct results for the electronic structure
obtained with these two methods are discussed. The dependence of the
electric-field gradients at the Cu and the O sites on the cluster size is
studied and the results are compared to experiments. The magnetic hyperfine
coupling parameters are carefully examined. Special attention is given to a
quantitative determination of on-site and transferred hyperfine fields. We
provide a detailed analysis that compares the hyperfine fields obtained for
various cluster sizes with results from additional calculations of spin states
with different multiplicities. From this we conclude that hyperfine couplings
are mainly transferred from nearest neighbor Cu^{2+} ions and that
contributions from further distant neighbors are marginal. The mechanisms
giving rise to transfer of spin density are worked out. Assuming conventional
values for the spin-orbit coupling, the total calculated hyperfine interaction
parameters are compared to informations from experiments.


title: Auxiliary-field Monte Carlo for Quantum Spin and Boson Systems

abstract:
  We describe a new algorithm for the numerical simulation of quantum spin and
boson systems. The method is based on the Trotter decomposition in imaginary
time and a decoupling by auxiliary Ising spins. It can be applied, in
principle, to arbitrary (random) spin systems, however in general it suffers
from the ``minus-sign problem''. This problem is absent in the case of the
Ising model in a transverse field in arbitrary dimensions and geometries. We
show test results for the spin--1/2 XY model, the one--dimensional transverse
Ising model with disorder, and the phase transition induced by a transverse
field in the two-dimensional Ising model.


title:
Fluctuations, response and aging dynamics in a simple glass-forming
  liquid out of equilibrium

abstract:
  By means of molecular dynamics computer simulations we investigate the out of
equilibrium relaxation dynamics of a simple glass former, a binary
Lennard-Jones system, after a quench to low temperatures. We study both one
time quantities and two-times correlation functions. Two-times correlation
functions show a strong time and waiting time $t_w$ dependence. For large $t_w$
and times corresponding to the early $\beta$-relaxation regime the correlators
approach the Edwards-Anderson value by means of a power-law in time. at long
times $\tau$ the correlation functions can be expressed as $C_{\rm
AG}(h(t_w+\tau)/h(t_w))$ and compute the function $h(t)$. This function is
found to show a $t$-dependence which is a bit stronger than a logarithm and to
depend on the observable considered.
  Finally we discuss our measurements of the time dependent response function.
We find that at long times the correlation functions and the response are not
related by the usual fluctuation dissipation theorem but that this relation is
similar to the one found for spin glasses with one step replica symmetry
breaking.


title: Persistent current in a mesoscopic ring with diffuse surface scattering

abstract:
  The persistent current in a clean mesoscopic ring with ballistic electron
motion is calculated. The particle dynamics inside a ring is assumed to be
chaotic due to scattering at the surface irregularities of atomic size. This
allows one to use the so-called ``ballistic'' supersymmetric \sigma model for
calculation of the two-level correlation function in the presence of a nonzero
magnetic flux.


title:
Why is the bandwidth of sodium observed to be narrower in photoemission
  experiments?

abstract:
  The experimentally predicted narrowing in the bandwidth of sodium is
interpreted in terms of the non-local self-energy effect on quasi-particle
energies of the electron liquid. The calculated self-energy correction is a
monotonically increasing function of the wavenumber variable. The usual
analysis of photo-emission experiments assumes the final state energies on the
nearly-free-electron-like model and hence it incorrectly ascribes the non-local
self-energy correction to the final state energies to the occupied state
energies, thus leading to a seeming narrowing in the bandwidth.


title: Dynamics of Counterion Condensation

abstract:
  Using a generalization of the Poisson-Boltzmann equation, dynamics of
counterion condensation is studied. For a single charged plate in the presence
of counterions, it is shown that the approach to equilibrium is diffusive. In
the far from equilibrium case of a moving charged plate, a dynamical counterion
condensation transition occurs at a critical velocity. The complex dynamic
behavior of the counterion cloud is shown to lead to a novel nonlinear
force-velocity relation for the moving plate.


title:
Statistics of persistent events in the binomial random walk: Will the
  drunken sailor hit the sober man?

abstract:
  The statistics of persistent events, recently introduced in the context of
phase ordering dynamics, is investigated in the case of the 1D lattice random
walk in discrete time. We determine the survival probability of the random
walker in the presence of an obstacle moving ballistically with velocity v,
i.e., the probability that the walker remains up to time n on the left of the
obstacle. Three regimes are to be considered for the long-time behavior of this
probability, according to the sign of the difference between v and the drift
velocity V of the random walker. In one of these regimes (v>V), the survival
probability has a non-trivial limit at long times, which is discontinuous at
all rational values of v. An algebraic approach allows us to compute these
discontinuities, as well as several related quantities. The mathematical
structure underlying the solvability of this model combines elementary number
theory, algebraic functions, and algebraic curves defined over the rationals.


title: 1D Luttinger liquid & QED

abstract:
  Using its Conformal Field Theory description, the Luttinger liquid is coupled
to the quantum electromagnetic field. We compute the decoherence properties of
a superposition of two states obtained by creating the same elementary
excitation at different places in the system.


title: Granular Collapse as a Percolation Transition

abstract:
  Inelastic collapse is found in a two-dimensional system of inelastic hard
disks confined between two walls which act as an energy source. As the
coefficient of restitution is lowered, there is a transition between a state
containing small collapsed clusters and a state dominated by a large collapsed
cluster. The transition is analogous to that of a percolation transition. At
the transition the number of clusters n_s of size s scales as $n_s \sim
s^{-\tau}$ with $\tau \approx 2.7$.


title:
High-Temperature Series Analysis of the Free Energy and Susceptibility
  of the 2D Random-Bond Ising Model

abstract:
  We derive high-temperature series expansions for the free energy and
susceptibility of the two-dimensional random-bond Ising model with a symmetric
bimodal distribution of two positive coupling strengths J_1 and J_2 and study
the influence of the quenched, random bond-disorder on the critical behavior of
the model. By analysing the series expansions over a wide range of coupling
ratios J_2/J_1, covering the crossover from weak to strong disorder, we obtain
for the susceptibility with two different methods compelling evidence for a
singularity of the form $\chi \sim t^{-7/4} |\ln t|^{7/8}$, as predicted
theoretically by Shalaev, Shankar, and Ludwig. For the specific heat our
results are less convincing, but still compatible with the theoretically
predicted log-log singularity.


title: Quantum Return Probability for Substitution Potentials

abstract:
  We propose an effective exponent ruling the algebraic decay of the average
quantum return probability for discrete Schrodinger operators. We compute it
for some non-periodic substitution potentials with different degrees of
randomness, and do not find a complete qualitative agreement with the spectral
type of the substitution sequences themselves, i.e., more random the sequence
smaller such exponent.


title:
Comment on "Superconducting order parameter in partially substituted
  Bi2212 single crystals as measured by the tunneling effect"

abstract:
  In this Comment, we explain the reason for the discrepancy between two sets
of tunneling data obtained on Ni- and Zn-doped Bi2212 single crystals
(presented in H. Hancotte et al., Phys. Rev. B 55, R3410 (1997) and A.
Mourachkine, to be published in J. of Superconductivity, cond-mat/9902355).


title: Transport and Magnetism in Mesoscopic Superconductors

abstract:
  Superconductivity, discovered by Kamerlingh Onnes in 1911, continues to be a
fascinating subject of condensed matter physics today. Much interest has been
devoted to the study of the superconductivity induced in a metal which by
itself is not superconducting but is in electrical contact with a
superconductor. As the carriers of superconductivity, the Cooper pairs, diffuse
across the contact into the metal they remain correlated, although the pairing
mechanism is lifted; we call this the proximity effect. The observation of
these superconducting correlations has come within the reach of experiments in
the last decade. With state-of-the-art fabrication techniques mesoscopic
samples have been produced which are small and clean enough for the quantum
mechanical coherence of the electrons to be preserved over the sample size.
This theoretical thesis focuses on the variety of signatures of single-particle
physics that appear in the electrical transport and the magnetic screening
properties of these systems.
  We study the resonance structure in the finite voltage conductance and shot
noise of NS junctions. Mapping out the H-T phase diagram of a NS hybrid layer
we describe the diamagnetic screening including non-locality and impurities,
the magnetic breakdown of the Meissner expulsion, and discover a paramagnetic
instability towards spontaneous magnetic moments. We trace back the double
critical-current-flux periodicity in ballistic SNS junctions to non-locality.
Finally we exploit the Josephson relation of junctions with unconventional
superconductors for the implementation of a quantum computer.


title: Transport in finite incommensurate Peierls-Fr\"ohlich systems

abstract:
  We show that the conductance of a one-dimensional, finite charge-density-wave
(CDW) system of the incommensurate type is not renormalized at low temperatures
and depends solely on the leads. Within our formalism, we argue that a similar
behavior (perfect conductance) should occur for a wide class of one-dimensional
strongly correlated finite systems where interactions are current dependent.
The universal conductance is related to the presence of an (anomalous) chiral
symmetry. The fundamental role played by the finiteness of the sample and the
adiabaticity of the contacts to Fermi-liquid leads is evidenced.


title:
From ferromagnetism to spin-density wave: Magnetism in the two channel
  periodic Anderson model

abstract:
  The magnetic properties of the two-channel periodic Anderson model for
uranium ions, comprised of a quadrupolar and a magnetic doublet are
investigated through the crossover from the mixed-valent to the stable moment
regime using dynamical mean field theory. In the mixed-valent regime
ferromagnetism is found for low carrier concentration on a hyper-cubic lattice.
The Kondo regime is governed by band magnetism with small effective moments and
an ordering vector $\q$ close to the perfect nesting vector. In the stable
moment regime nearest neighbour anti-ferromagnetism dominates for less than
half band filling and a spin density wave transition for larger than half
filling. $T_m$ is governed by the renormalized RKKY energy scale $\mu_{eff}^2
<X_\sigma>^2 J^2\rho_0(\mu)$.


title: Transitions between metastable states in silica clusters

abstract:
  Relaxation phenomena in glasses can be related to jump processes between
different minima of the potential energy in the configuration space. These
transitions play a key role in the low temperature regime, giving rise to
tunneling systems responsible for the anomalous specific heat and thermal
conductivity in disordered solids with respect to crystals. By using a recently
developed numerical algorithm, we study the potential energy landscape of
silica clusters, taking as a starting point the location of first order saddle
points. This allows us to find a great number of adjacent minima. We analyze
the degree of cooperativity of these transitions and the connection of physical
properties with the topology of the configuration space. We also identify
two-level systems (pairs of minima constituting a tunneling system) and
calculate the quantum mechanical ground state splitting by means of the WKB
approximation.


title: Spin-orbit scattering in d-wave superconductors

abstract:
  When non-magnetic impurities are introduced in a d-wave superconductor, both
thermodynamic and spectral properties are strongly affected if the impurity
potential is close to the strong resonance limit. In addition to the scalar
impurity potential, the charge carriers are also spin-orbit coupled to the
impurities. Here it is shown that (i) close to the unitarity limit for the
impurity scattering, the spin-orbit contribution is of the same order of
magnitude than the scalar scattering and cannot be neglected, (ii) the
spin-orbit scattering is pair-breaking and (iii) induces a small id_xy
component to the off-diagonal part of the self-energy.


title: Hydrodynamic Excitations of Trapped Fermi Gases

abstract:
  We discuss collective excitations of a trapped dilute Fermi gas within a
hydrodynamic approximation. Analytical results are derived for both high- and
low-temperature limits and are applied to $^{40}$K and $^6$Li systems of
current experimental interest. We identify spectral signatures which can be
used to detect the onset of Fermi degeneracy. Also, we find an interesting
class of internal excitations with an unusual spectrum. Some of our results are
relevant to the case of trapped bosons as well. Our analysis suggests several
experiments which address fundamental problems of collective motion in quantum
fluids.


title:
Strongly Temperature Dependent Sliding Friction for a Superconducting
  Interface

abstract:
  A sudden drop in mechanical friction, between an adsorbed nitrogen monolayer
and a lead substrate, occurs when the lead passes through the superconducting
transition temperature. We attribute this effect to a sudden drop at the
superconducting transition temperature of the substrate Ohmic heating. The
Ohmic heating is due to the electronic screening current that results from the
sliding adsorbed film.


title: Composite Fermions and the Fractional Quantum Hall Effect

abstract:
  The mean field (MF) composite Fermion (CF) picture successfully predicts low
lying states of fractional quantum Hall systems. This success cannot be
attributed to a cancellation between Coulomb and Chern-Simons interactions
beyond the mean field and solely depends on the short range (SR) of the Coulomb
pseudopotential in the lowest Landau level (LL). The class of pseudopotentials
for which the MFCF picture can be applied is defined. The success or failure of
the MFCF picture in various systems (electrons in excited LL's, Laughlin
quasiparticles, charged magneto-excitons) is explained.


title: Dark states of dressed Bose-Einstein condensates

abstract:
  We combine the ideas of dressed Bose-Einstein condensates, where an
intracavity optical field allows one to design coupled, multicomponent
condensates, and of dark states of quantum systems, to generate a full quantum
entanglement between two matter waves and two optical waves. While the matter
waves are macroscopically populated, the two optical modes share a single
photon. As such, this system offers a way to influence the behaviour of a
macroscopic quantum system via a microscopic ``knob''.


title: Topological Phase Diagram of a Two-Subband Electron System

abstract:
  We present a phase diagram for a two-dimensional electron system with two
populated subbands. Using a gated GaAs/AlGaAs single quantum well, we have
mapped out the phases of various quantum Hall states in the density-magnetic
filed plane. The experimental phase diagram shows a very different topology
from the conventional Landau fan diagram. We find regions of negative
differential Hall resistance which are interpreted as preliminary evidence of
the long sought reentrant quantum Hall transitions. We discuss the origins of
the anomalous topology and the negative differential Hall resistance in terms
of the Landau level and subband mixing.


title:
Holon Pair Bose Condensation in High $T_c$ Cuprates; Symmetry Breaking
  and Supersymmetry Conditions

abstract:
  Using the t-J Hamiltonian of U(1) slave-boson symmetry, bose condensation is
discussed by showing the occurrence of symmetry breaking in the hole doped high
$T_c$ cuprates. The symmetry breaking is shown to take place with the d-wave
hole pairing, but not with the s-wave hole pairing. Based on a derived
supersymmetry Hamiltonian we find that there exists a possibility of
supersymmetry conditions in association with the pairing order parameters of
both spinon and holon.


title:
Ground State Property of an Alternating Spin Ladder Involving Two Kinds
  of Inter-Chain Interactions

abstract:
  The ground state property of the alternating spin ladder is studied in the
case that the system involves an antiferromagnetic intra-chain interaction as
well as two kinds of inter-chain interactions; one is between spins of the same
magnitude and the other is between spins with different magnitudes. The
calculation has been carried out by the exact diagonalization method. As a
consequence of the competition among interactions, the system is revealed to
show an interesting variety of phases in the ground state property. Its phase
diagram is exhibited in the parameter space of the system. We find that,
however small the total amount of the inter-chain interactions is, the
ferrimagnetic ground state becomes unstable in a certain region. In this case,
which of the ferrimagnetic and the singlet ground state to appear is determined
only by the ratio between the inter-chain interactions regardless of their
total amount. The nature of two phases appearing in the singlet region of the
phase diagram and the type of the phase transition between them are also
discussed. The results are ensured by comparing with those of obtained in other
models which are contained in our model as special limiting cases.


title: Application of exchange Monte Carlo method to ordering dynamics

abstract:
  We apply the exchange Monte Carlo method to the ordering dynamics of the
three-state Potts model with the conserved order parameter. Even for the deeply
quenched case to low temperatures, we have observed a rapid domain growth; we
have proved the efficiency of the exchange Monte Carlo method for the ordering
process. The late-stage growth law has been found to be $R(t) \sim t^{1/3}$ for
the case of conserved order parameter of three-component system.


title:
Effects of Orbital Degeneracy and Electron Correlation on Charge
  Dynamics in Perovskite Manganese Oxides

abstract:
  Taking the orbital degeneracy of $e_g$ conduction bands and the Coulomb
interaction into account in a double-exchange model, we investigate charge
dynamics of perovskite Mn oxides by the Lancz$\ddot{\rm o}$s diagonalization
method. In the metallic phase near the Mott insulator, it is found that the
optical conductivity for a spin-polarized two-dimensional system exhibits a
weight transfer to a broad and incoherent structure within the lower-Hubbard
band together with a suppressed Drude weight. It reproduces qualitative feature
of the experimental results. As an orbital effect, we find that an anomalous
charge correlation at quarter filling suppresses the coherent charge dynamics
and signals precursor to the charge ordering.


title:
Pairing in the Hubbard model: the Cu_{5}O_{4} Cluster versus the Cu-O
  plane

abstract:
  We study the Cu_{5}O_{4} cluster by exact diagonalization of a three-band
Hubbard model and show that bound electron or hole pairs are obtained at
appropriate fillings, and produce superconducting flux quantisation.
  The results extend earlier cluster studies and illustrate a canonical
transformation approach to pairing that we have developed recently for the full
plane. The quasiparticles that in the many-body problem behave like Cooper
pairs are W=0 pairs, that is, two-hole eigenstates of the Hubbard Hamiltonian
with vanishing on-site repulsion. The cluster allows W=0 pairs of d symmetry,
due to a spin fluctuation, and s symmetry, due to a charge fluctuation. Flux
quantisation is shown to be a manifestation of symmetry properties that hold
for clusters of arbitrary size.


title:
Dipolar interaction and incoherent quantum tunneling: a Monte Carlo
  study of magnetic relaxation

abstract:
  We study the magnetic relaxation of a system of localized spins interacting
through weak dipole interactions, at a temperature large with respect to the
ordering temperature but low with respect to the crystal field level splitting.
The relaxation results from quantum spin tunneling but is only allowed on sites
where the dipole field is very small. At low times, the magnetization decrease
is proportional to $\sqrt{t}$ as predicted by Prokofiev and Stamp, and at long
times the relaxation can be described as an extension of a relaxed zone. The
results can be directly compared with very recent experimental data on Fe_8
molecular clusters.


title:
The Hall effect in Zn-doped YBa_{2}Cu_{3}O_{7-\delta} revisited: Hall
  angle and the pseudogap

abstract:
  The temperature dependence of the Hall coefficient is measured with a high
accuracy in a series of Zn-doped YBCO_{6.78} crystals with the Zn concentration
from 0% to 1.3%. We found that the cotangent of the Hall angle, cot(\theta_H),
starts to deviate upward from the T^2 dependence below T_0 (which is roughly
130 K), regardless of the Zn concentration. We discuss that this deviation is
caused by the pseudogap; the direction of the deviation and its insensitivity
to the Zn doping suggest that the pseudogap affects cot(\theta_H) through a
change in the effective mass, rather than through a change in the Hall
scattering rate.


title: Tunneling singularities in the open Hubbard chain

abstract:
  We study singularities in the I-V characteristics for sequential tunneling
from resonant localized levels (e.g. a quantum dot) into a one dimensional
electron system described by a Hubbard model. Boundary conformal field theory
together with the exact solution of the Hubbard model subject to boundary
fields allows to compute the exponents describing the singularity arising when
the energy of the local level is tuned through the Fermi energy of the wire as
a function of electron density and magnetic field. For boundary potentials with
bound states a sequence of such singularities can be observed.


title: The superconducting order parameter and gauge dependence

abstract:
  The gauge dependence of the renormalization group functions of the
Ginzburg-Landau model is investigated. The analysis is done by means of the
Ward-Takahashi identities. After defining the superconducting order parameter,
it is shown that its exponent $\beta$ is in fact gauge independent. This
happens because in d=3 the Landau gauge is the only gauge having a physical
meaning, a property not shared by the four-dimensional model where any gauge
choice is possible. The analysis is done in both the context of the
$\epsilon$-expansion and in the fixed dimension approach. It is pointed out the
differences that arise in both of these approaches concerning the gauge
dependence.


title: Observation of breathers in Josephson ladders

abstract:
  We report on the observation of spatially-localized excitations in a ladder
of small Josephson junctions. The excitations are whirling states which persist
under a spatially-homogeneous force due to the bias current. These states of
the ladder are visualized using a low temperature scanning laser microscopy. We
also compute breather solutions with high accuracy in corresponding model
equations. The stability analysis of these solutions is used to interpret the
measured patterns in the I-V characteristics.


title: Infrared and Raman studies of the Verwey transition in magnetite

abstract:
  We present infrared and Raman measurements of magnetite (Fe_3O_4). This
material is known to undergo a metal-insulator and a structural transition
(Verwey transition) at T_V=120K. At temperatures below T_V, we observe a strong
gap-like suppression of the optical conductivity below 1000 cm^-1. The
structural aspect of the Verwey transition demonstrates itself by the
appearance of additional infrared- and Raman-active phonons. The frequencies of
the infrared-active phonons show no significant singularities at the transition
whereas their linewidths increase. The frequency and linewidth of the
Raman-active phonon at 670 cm^-1 changes abruptly at the transition. For T<T_V,
we observe fine structures in the infrared and Raman spectra which may indicate
strong anharmonicity of the system below the transition. Our estimate of the
effective mass of the carriers above the transition to be about 100 m, where m
is the free electron mass. Our measurements favor a polaronic mechanism of
conductivity and underline the importance of the electron-phonon interaction in
the mechanism of the Verwey transition.


title:
Thick surface flows of granular materials: The effect of the velocity
  profile on the avalanche amplitude

abstract:
  A few years ago, Bouchaud al. introduced a phenomenological model to describe
surface flows of granular materials [J. Phys. Fr. I, 4, 1383 (1994)]. According
to this model, one can distinguish between a static phase and a rolling phase
that are able to exchange grains through an erosion/accretion mechanism.
Boutreux et al. [Phys. Rev. E, 58, 4692 (1998)] proposed a modification of the
exchange term in order to describe thicker flows where saturation effects are
present. However, these approaches assumed that the downhill convection
velocity of the grains is constant inside the rolling phase, a hypothesis that
is not verified experimentally. In this article, we therefore modify the above
models by introducing a velocity profile in the flow, and study the physical
consequences of this modification in the simple situation of an avalanche in an
open cell. We present a complete analytical description of the avalanche in the
case of a linear velocity profile, and generalize the results for a power-law
dependency. We show, in particular, that the amplitude of the avalanche is
strongly affected by the velocity profile.


title: Strongly Enhanced Curie Temperature in Carbon-Doped Mn5Ge3 Films

abstract:
  The structural and magnetic properties of Mn5Ge3Cx films prepared at elevated
substrate temperatures TS are investigated. In particular, films with x >= 0.5
and TS = 680 K exhibit a strongly enhanced Curie temperature TC = 440 K
compared to Mn5Ge3 with TC = 304 K. Structural analysis of these films suggests
that the carbon is interstitially incorporated into the voids of Mn octahedra
of the hexagonal Mn5Si3-type structure giving rise to a lattice compression.
The enhanced ferromagnetic stability in connection with the lattice compression
is interpreted in terms of an Mn-Mn interaction mediated by C based on a change
in the electronic structure.


title:
Transverse ordering of an antiferromagnet in a field with oblique angle
  to the easy axis

abstract:
  Motivated by the recent experimental observations [Phys Rev B 57 R11051
(1998)] of transverse spin ordering in FeBr_2 induced by a magnetic field with
oblique angle to the easy axis of the system, we performed extensive Monte
Carlo simulations of a classical anisotropic Heisenberg model. We have
calculated the specific heat and the parallel and perpendicular components of
the magnetisation as well as the antiferromagnetic order parameter and studied
these quantities as a function of temperature. A tilted spin-flop phase is
obtained for certain parameter values. Many of the effects occuring in
connection with this phase agree qualitatively well with the experimental
facts.


title: Freezing of Polydisperse Hard Spheres

abstract:
  The fluid - crystal equilibria of polydisperse mixtures of hard spheres have
been studied by computer simulation of the solid phase and using an accurate
equation of state for the fluid. A new scheme has been developed to evaluate
the composition of crystalline phases in equilibrium with a given polydisperse
fluid. Some common assumptions in theoretical approaches and their results are
discussed on the light of the simulation results. Finally, no evidence of the
existence of a terminal polydispersity in the fluid phase is found for
polydisperse hard spheres, the disagreement of this finding with previous
molecular simulation results is explained in terms of the inherent limitations
of some ways of modeling the chemical potential as a function of the particle
size.


title:
Double Quantum Dots as Detectors of High-Frequency Quantum Noise in
  Mesoscopic Conductors

abstract:
  We propose a measurement set-up for detecting quantum noise over a wide
frequency range using inelastic transitions in a tunable two-level system as a
detector. The frequency-resolving detector consists of a double quantum dot
which is capacitively coupled to the leads of a nearby mesoscopic conductor.
The inelastic current through the double quantum dot is calculated in response
to equilibrium and non-equilibrium current fluctuations in the nearby
conductor, including vacuum fluctuations at very low temperatures. As a
specific example, the fluctuations across a quantum point contact are
discussed.


title: Simulation of Hard Particles in a Phase-Separating Binary Mixture

abstract:
  We simulate the motion of spherical particles in a phase-separating binary
mixture. By combining cell dynamical equations with Langevin dynamics for
particles, we show that the addition of hard particles significantly changes
both the speed and the morphology of the phase separation. At the late stage of
the spinodal decomposition process, particles significantly slow down the
domain growth, in qualitative agreement with earlier experimental data.


title:
Interplay between charge, orbital and magnetic order in
  Pr_{1-x}Ca_xMnO_3

abstract:
  We report resonant x-ray scattering studies of charge and orbital order in
Pr_{1-x}Ca_{x}MnO_3 with x=0.4 and 0.5. Below the ordering temperature, T_O=245
K, the charge and orbital order intensities follow the same temperature
dependence, including an increase at the antiferromagnetic ordering
temperature, T_N. High resolution measurements reveal, however, that long range
orbital order is never achieved. Rather, an orbital domain state is formed.
Above T_O, the charge order fluctuations are more highly correlated than the
orbital fluctuations. Similar phenomenology is observed in a magnetic field. We
conclude that the charge order drives the orbital order at the transition.


title: Nucleation of vortices by rapid thermal quench

abstract:
  We show that vortex nucleation in superfluid $^3$He by rapid thermal quench
in the presence of superflow is dominated by a transverse instability of the
moving normal-superfluid interface. Exact expressions for the instability
threshold as a function of supercurrent density and the front velocity are
found. The results are verified by numerical solution of the Ginzburg-Landau
equation.


title: Solitons in SO(5) Superconductivity

abstract:
  A model unifying superconductivity and antiferromagnetism using an underlying
approximate SO(5) symmetry has injected energy into the field of
high-temperature superconductivity. This model might lead to a variety of
interesting solitons. In this paper, the idea that superconducting vortices may
have antiferromagnetic cores is presented, along with the results of some
preliminary numerical work. An outlook for future work, including speculations
about other possible exotic solitons, is presented.


title:
Oscillation modes of two-dimensional nanostructures within the
  time-dependent local-spin-density approximation

abstract:
  We apply the time-dependent local-spin-density approximation as general
theory to describe ground states and spin-density oscillations in the linear
response regime of two-dimensional nanostructures of arbitrary shape. For this
purpose, a frequency analysis of the simulated real-time evolution is
performed. The effect on the response of the recently proposed spin-density
waves in the ground state of certain parabolic quantum dots is considered. They
lead to the prediction of a new class of excitations, soft spin-twist modes,
with energies well below that of the spin dipole oscillation.


title: Organized condensation of worm-like chains

abstract:
  We present results relevant to the equilibrium organization of DNA strands of
arbitrary length interacting with a spherical organizing center, suggestive of
DNA-histone complexation in nucleosomes. We obtain a rich phase diagram in
which a wrapping state is transformed into a complex multi-leafed, rosette
structure as the adhesion energy is reduced. The statistical mechanics of the
"melting" of a rosette can be mapped into an exactly soluble one-dimensional
many-body problem.

categories: cond-mat.soft cond-mat.dis-nn physics.bio-ph q-bio.BM


title:
Magnetic Field Induced Charged Exciton Studies in a
  GaAs/Al(0.3)Ga(0.7)As Single Heterojunction

abstract:
  The magnetophotoluminescence (MPL) behavior of a GaAs/Al(0.3)Ga(0.7)As single
heterojunction has been investigated to 60T. We observed negatively charged
singlet and triplet exciton states that are formed at high magnetic fields
beyond the nu=1 quantum Hall state. The variation of the charged exciton
binding energies are in good agreement with theoretical predictions. The MPL
transition intensities for these states showed intensity variations (maxima and
minima) at the nu=1/3 and 1/5 fractional quantum Hall (FQH) state as a
consequence of a large reduction of electron-hole screening at these filling
factors.


title: Self-avoiding polygons on the square lattice

abstract:
  We have developed an improved algorithm that allows us to enumerate the
number of self-avoiding polygons on the square lattice to perimeter length 90.
Analysis of the resulting series yields very accurate estimates of the
connective constant $\mu =2.63815852927(1)$ (biased) and the critical exponent
$\alpha = 0.5000005(10)$ (unbiased). The critical point is indistinguishable
from a root of the polynomial $581x^4 + 7x^2 - 13 =0.$ An asymptotic expansion
for the coefficients is given for all $n.$ There is strong evidence for the
absence of any non-analytic correction-to-scaling exponent.


title: Empirical Phase Diagram of Congested Traffic Flow

abstract:
  We present an empirical phase diagram of the congested traffic flow measured
on a highway section with one effective on-ramp. Through the analysis of local
density-flow relations and global spatial structure of the congested region,
four distinct congested traffic states are identified. These states appear at
different levels of the upstream flux and the on-ramp flux, thereby generating
a phase digram of the congested traffic flow. Observed traffic states are
discussed in connection with recent theoretical analyses.


title: Impurity spin relaxation in S=1/2 XX chains

abstract:
  Dynamic autocorrelations $<S_i^{\alpha}(t) S_i^{\alpha}>$ (\alpha=x,z) of an
isolated impurity spin in a S=1/2 XX chain are calculated. The impurity spin,
defined by a local change in the nearest-neighbor coupling, is either in the
bulk or at the boundary of the open-ended chain. The exact numerical
calculation of the correlations employs the Jordan-Wigner mapping from spin
operators to Fermi operators; effects of finite system size can be eliminated.
Two distinct temperature regimes are observed in the long-time asymptotic
behavior. At T=0 only power laws are present. At high T the x correlation
decays exponentially (except at short times) while the z correlation still
shows an asymptotic power law (different from the one at T=0) after an
intermediate exponential phase. The boundary impurity correlations follow power
laws at all T. The power laws for the z correlation and the boundary
correlations can be deduced from the impurity-induced changes in the properties
of the Jordan-Wigner fermion states.


title:
Phase diffusion and suppression of the supercurrent by
  quantum-mechanical fluctuations of the Josephson plasma

abstract:
  The RCSJ model of resistively and capacitively shunted Josephson junctions is
used to describe superconducting point contacts over a wide range of
resistances up to the metallic -- tunneling transition. Their small dynamic
capacitance of order $C = 0.1 $fF due to the point-contact geometry results in
a huge plasma frequency. The critical current is then strongly suppressed and
the contact resistance becomes finite because of quantum-mechanical zero-point
fluctuations of the Josephson plasma and the rather large escape rate out of
the zero-voltage state due to quantum tunneling. We test the predictions of the
RCSJ model on the classical superconductors lead, indium, aluminum, and
cadmium.


title:
Spin dynamics simulation of the three-dimensional XY model: Structure
  factor and transport properties

abstract:
  We present extensive Monte-Carlo spin dynamics simulations of the classical
XY model in three dimensions on a simple cubic lattice with periodic boundary
conditions. A recently developed efficient integration algorithm for the
equations of motion is used, which allows a substantial improvement of
statistics and large integration times. We find spin wave peaks in a wide range
around the critical point and spin diffusion for all temperatures. At the
critical point we find evidence for a violation of dynamic scaling in the sense
that independent components of the dynamic structure factor S(q,w) require
different dynamic exponents in order to obtain scaling. Below the critical
point we investigate the dispersion relation of the spin waves and the
linewidths of S(q,w) and find agreement with mode coupling theory. Apart from
strong spin wave peaks we observe additional peaks in S(q,w) which can be
attributed to two-spin wave interactions. The overall lineshapes are also
discussed and compared to mode coupling predictions. Finally, we present first
results for the transport coefficient D(q,w) of the out-of-plane magnetization
component at the critical point, which is related to the thermal conductivity
of He4 near the superfluid-normal transition.


title: Trapped $^{6}$Li : A high T_c superfluid ?

abstract:
  We consider the effect of the indirect interaction due to the exchange of
density fluctuations on the critical temperature of superfluid $^{6}$Li . We
obtain the strong coupling equation giving this critical temperature. This
equation is solved approximately by retaining the same set of diagrams as in
the paramagnon model. We show that, near the instability threshold, the
attractive interaction due to density fluctuations gives rise to a strong
increase in the critical temperature, providing a clear signature of the
existence of fluctuation induced interactions.


title:
Critical Behavior of the Conductivity of Si:P at the Metal-Insulator
  Transition under Uniaxial Stress

abstract:
  We report new measurements of the electrical conductivity sigma of the
canonical three-dimensional metal-insulator system Si:P under uniaxial stress
S. The zero-temperature extrapolation of sigma(S,T -> 0) ~\S - S_c\^mu shows an
unprecidentedly sharp onset of finite conductivity at S_c with an exponent mu =
1. The value of mu differs significantly from that of earlier stress-tuning
results. Our data show dynamical sigma(S,T) scaling on both metallic and
insulating sides, viz. sigma(S,T) = sigma_c(T) F(\S - S_cT^y) where sigma_c(T)
is the conductivity at the critical stress S_c. We find y = 1/znu = 0.34 where
nu is the correlation-length exponent and z the dynamic critical exponent.


title: Fractional-quantum-Hall edges at filling factor 1-1/m

abstract:
  We consider the edge of a two-dimensional electron system that is in the
quantum-Hall-effect regime at filling factor 1-1/m with m being an odd integer,
where microscopic theory explaining the occurrence of the quantum Hall effect
in the bulk predicts the existence of two counterpropagating edge-excitation
modes. These two modes are the classical edge-magnetoplasmon mode and a
slow-moving neutral mode. Assuming the electrons to be confined by a coplanar
neutralizing background of positive charges, and taking careful account of
long-range Coulomb interactions, we determine microscopically the velocity of
the neutral mode and the edge width. Our results are intended to guide
experimental efforts aimed at verifying the existence of the neutral mode,
which would provide a powerful confirmation of the current microscopic
understanding of quantum-Hall physics at the simplest hierarchical filling
Factors 1-1/m.


title: Capture of the Lamb: Diffusing Predators Seeking a Diffusing Prey

abstract:
  We study the capture of a diffusing "lamb" by diffusing "lions" in one
dimension. The capture dynamics is exactly soluble by probabilistic techniques
when the number of lions is very small, and is tractable by extreme statistics
considerations when the number of lions is very large. However, the exact
solution for the general case of three or more lions is still not known.


title:
Finite time and asymptotic behaviour of the maximal excursion of a
  random walk

abstract:
  We evaluate the limit distribution of the maximal excursion of a random walk
in any dimension for homogeneous environments and for self-similar supports
under the assumption of spherical symmetry. This distribution is obtained in
closed form and is an approximation of the exact distribution comparable to
that obtained by real space renormalization methods. Then we focus on the early
time behaviour of this quantity. The instantaneous diffusion exponent $\nu_n$
exhibits a systematic overshooting of the long time exponent. Exact results are
obtained in one dimension up to third order in $n^{-1/2}$. In two dimensions,
on a regular lattice and on the Sierpi\'nski gasket we find numerically that
the analytic scaling $\nu_n \simeq \nu+A n^{-\nu}$ holds.


title: A microscopic model for solidification

abstract:
  We present a novel picture of a non isothermal solidification process
starting from a molecular level, where the microscopic origin of the basic
mechanisms and of the instabilities characterizing the approach to equilibrium
is rendered more apparent than in existing approaches based on coarse grained
free energy functionals \`a la Landau.
  The system is composed by a lattice of Potts spins, which change their state
according to the stochastic dynamics proposed some time ago by Creutz. Such a
method is extended to include the presence of latent heat and thermal
conduction.
  Not only the model agrees with previous continuum treatments, but it allows
to introduce in a consistent fashion the microscopic stochastic fluctuations.
These play an important role in nucleating the growing solid phase in the melt.
The approach is also very satisfactory from the quantitative point of view
since the relevant growth regimes are fully characterized in terms of scaling
exponents.


title: Equilibrium sedimentation profiles of charged colloidal suspensions

abstract:
  We investigate the sedimentation equilibrium of a charge stabilized colloidal
suspension in the regime of low ionic strength. We analyze the asymptotic
behaviour of the density profiles on the basis of a simple Poisson--Boltzmann
theory and show that the effective mass we can deduce from the barometric law
corresponds to the actual mass of the colloidal particles, contrary to previous
studies.


title: Size Segregation of Granular Matter in Silo Discharges

abstract:
  We present an experimental study of segregation of granular matter in a
quasi-two dimensional silo emptying out of an orifice. Size separation is
observed when multi-sized particles are used with the larger particles found in
the center of the silo in the region of fastest flow. We use imaging to study
the flow inside the silo and quantitatively measure the concentration profiles
of bi-disperse beads as a function of position and time. The angle of the
surface is given by the angle of repose of the particles, and the flow occurs
in a few layers only near the top of this inclined surface. The flowing region
becomes deeper near the center of the silo and is confined to a parabolic
region centered at the orifice which is approximately described by the
kinematic model. The experimental evidence suggests that the segregation occurs
on the surface and not in the flow deep inside the silo where velocity
gradients also are present. We report the time development of the
concentrations of the bi-disperse particles as a function of size ratios, flow
rate, and the ratio of initial mixture. The qualitative aspects of the observed
phenomena may be explained by a void filling model of segregation.


title: In Situ Resistance Measurements of Strained Carbon Nanotubes

abstract:
  We investigate the response of multi-walled carbon nanotubes to mechanical
strain applied with an Atomic Force Microscope (AFM) probe. We find that in
some samples, changes in the contact resistance dominate the measured
resistance change. In others, strain large enough to fracture the tube can be
applied without a significant change in the contact resistance. In this case we
observe that enough force is applied to break the tube without any change in
resistance until the tube fails. We have also manipulated the ends of the
broken tube back in contact with each other, re-establishing a finite
resistance. We observe that in this broken configuration the resistance of the
sample is tunable to values 15-350 kW greater than prior to breaking.


title: Scaling of the distribution of fluctuations of financial market indices

abstract:
  We study the distribution of fluctuations over a time scale $\Delta t$ (i.e.,
the returns) of the S&P 500 index by analyzing three distinct databases.
Database (i) contains approximately 1 million records sampled at 1 min
intervals for the 13-year period 1984-1996, database (ii) contains 8686 daily
records for the 35-year period 1962-1996, and database (iii) contains 852
monthly records for the 71-year period 1926-1996. We compute the probability
distributions of returns over a time scale $\Delta t$, where $\Delta t$ varies
approximately over a factor of 10^4 - from 1 min up to more than 1 month. We
find that the distributions for $\Delta t \leq$ 4 days (1560 mins) are
consistent with a power-law asymptotic behavior, characterized by an exponent
$\alpha \approx 3$, well outside the stable L\'evy regime $0 < \alpha < 2$. To
test the robustness of the S&P result, we perform a parallel analysis on two
other financial market indices. Database (iv) contains 3560 daily records of
the NIKKEI index for the 14-year period 1984-97, and database (v) contains 4649
daily records of the Hang-Seng index for the 18-year period 1980-97. We find
estimates of $\alpha$ consistent with those describing the distribution of S&P
500 daily-returns. One possible reason for the scaling of these distributions
is the long persistence of the autocorrelation function of the volatility. For
time scales longer than $(\Delta t)_{\times} \approx 4$ days, our results are
consistent with slow convergence to Gaussian behavior.


title: Early Stages of Homopolymer Collapse

abstract:
  Interest in the protein folding problem has motivated a wide range of
theoretical and experimental studies of the kinetics of the collapse of
flexible homopolymers. In this Paper a phenomenological model is proposed for
the kinetics of the early stages of homopolymer collapse following a quench
from temperatures above to below the theta temperature. In the first stage,
nascent droplets of the dense phase are formed, with little effect on the
configurations of the bridges that join them. The droplets then grow by
accreting monomers from the bridges, thus causing the bridges to stretch.
During these two stages the overall dimensions of the chain decrease only
weakly. Further growth of the droplets is accomplished by the shortening of the
bridges, which causes the shrinking of the overall dimensions of the chain. The
characteristic times of the three stages respectively scale as the zeroth, 1/5
and 6/5 power of the the degree of polymerization of the chain.


title: Relativistic Quantum Thermodynamics of Ideal Gases in 2 Dimensions

abstract:
  In this work we study the behavior of relativistic ideal Bose and Fermi gases
in two space dimensions. Making use of polylogarithm functions we derive a
closed and unified expression for their densities. It is shown that both type
of gases are essentially inequivalent, and only in the non-relativistic limit
the spinless and equal mass Bose and Fermi gases are equivalent as known in the
literature.


title:
The Magnetic Origin of the Coherent Order Parameter in Hole-Doped
  Cuprates

abstract:
  The phase diagram for hole-doped cuprates is discussed. By examining some
recent inelastic neutron scattering data obtained on hole-doped cuprates we
conclude that the coherent gap in hole-doped cuprates has most likely the
magnetic origin and scales with Tc, on average, as 2Delta/kTc = 5.4.


title:
Hiking in the energy landscape in sequence space: a bumpy road to good
  folders

abstract:
  With the help of a simple 20 letters, lattice model of heteropolymers, we
investigate the energy landscape in the space of designed good-folder
sequences. Low-energy sequences form clusters, interconnected via neutral
networks, in the space of sequences. Residues which play a key role in the
foldability of the chain and in the stability of the native state are highly
conserved, even among the chains belonging to different clusters. If, according
to the interaction matrix, some strong attractive interactions are almost
degenerate (i.e. they can be realized by more than one type of aminoacid
contacts) sequence clusters group into a few super-clusters. Sequences
belonging to different super-clusters are dissimilar, displaying very small
($\approx 10%$) similarity, and residues in key-sites are, as a rule, not
conserved. Similar behavior is observed in the analysis of real protein
sequences.


title:
Optical spectra measured on cleaved surfaces of double-exchange
  ferromagnet La1-xSrxMnO3

abstract:
  Optical reflectivity spectra were measured on cleaved surfaces of
La1-xSrxMnO3 single crystals (x=0.175, T_C=283 K) over a temperature range
10-295 K. The optical conductivity $sigma(\omega)$ shows, keeping
single-component nature, incoherent-to-coherent crossover with increase of
electrical conductivity. The $\sigma(\omega)$ spectrum of low-temperature
ferromagnetic-metallic phase (10 K) exhibits a pronounced Drude-like component
with large spectral weight, contrary to the previous result. The present result
indicates that the optical spectrum of the manganites is sensitive to condition
of sample surfaces.


title:
Breakdown of a Magnetization Plateau due to Anisotropy in Heisenberg
  Mixed-Spin Chains

abstract:
  We discuss the critical behavior of the spin-(1,1/2) Heisenberg ferrimagnetic
chain in a magnetic field, whose magnetization curve exhibits a plateau at a
third of the full magnetization. A bond alternation stabilizes the massive
state, whereas an exchange anisotropy causes the breakdown of the plateau and
the onset of a gapless spin-fluid state, where the transition, lying in the XY
but ferromagnetic region, is of Kosterlitz-Thouless type. In order to elucidate
significant quantum effects, we investigate the model of classical version as
well.


title:
Broken-Symmetry Ground States of Halogen-Bridged Binuclear Metal
  Complexes

abstract:
  Based on a symmetry argument, we study ground states of what we call
MMX-chain compounds, which are the new class of halogen-bridged metal
complexes. Commensurate density-wave solutions of a relevant multi-band
Peierls-Hubbard model are systematically revealed within the Hartree-Fock
approximation. We numerically draw ground-state phase diagrams, where various
novel density-wave states appear.


title:
General theory of the modified Gutenberg-Richter law for large seismic
  moments

abstract:
  The Gutenberg-Richter power law distribution of earthquake sizes is one of
the most famous example illustrating self-similarity. It is well-known that the
Gutenberg-Richter distribution has to be modified for large seismic moments,
due to energy conservation and geometrical reasons. Several models have been
proposed, either in terms of a second power law with a larger b-value beyond a
cross-over magnitude, or based on a ``hard'' magnitude cut-off or a ``soft''
magnitude cut-off using an exponential taper. Since the large scale tectonic
deformation is dominated by the very largest earthquakes and since their impact
on loss of life and properties is huge, it is of great importance to constrain
as much as possible the shape of their distribution. We present a simple and
powerful probabilistic theoretical approach that shows that the Gamma
distribution is the best model, under the two hypothesis that the
Gutenberg-Richter power law distribution holds in absence of any condition
(condition of criticality) and that one or several constraints are imposed,
either based on conservation laws or on the nature of the observations
themselves. The selection of the Gamma distribution does not depend on the
specific nature of the constraint. We illustrate the approach with two
constraints, the existence of a finite moment release rate and the observation
of the size of a maximum earthquake in a finite catalog. Our predicted ``soft''
maximum magnitudes compare favorably with those obtained by Kagan [1997] for
the Flinn-Engdahl regionalization of subduction zones, collision zones and
mid-ocean ridges.


title: Renormalization of earthquake aftershocks

abstract:
  Together with the Gutenberg-Richter distribution of earthquake magnitudes,
Omori's law is the best established empirical characterization of earthquake
sequences and states that the number of smaller earthquakes per unit time
triggered by a main shock decays approximately as the inverse of the time
($1/t^p$, with $p \approx 1$) since the main shock. Based on these
observations, we explore the theoretical hypothesis in which each earthquake
can produce a series of aftershock independently of its size according to its
``local'' Omori's law with exponent $p=1+\theta$. In this scenario, an
aftershock of the main shock produces itself other aftershocks which themselves
produce aftershocks, and so on. The global observable Omori's law is found to
have two distinct power law regimes, the first one with exponent $p_-=1 -
\theta$ for time $t < t^* \sim \kappa^{-1/\theta}$, where $0<1-\kappa <1$
measures the fraction of triggered earthquakes per triggering earthquake, and
the second one with exponent $p_+=1 + \theta$ for larger times. The existence
of these two regimes rationalizes the observation of Kisslinger and Jones
[1991] that the Omori's exponent $p$ seems positively correlated to the surface
heat flow: a higher heat flow is a signature of a higher crustal temperature,
which leads to larger strain relaxation by creep, corresponding to fewer events
triggered per earthquake, i.e. to a larger $\kappa$, and thus to a smaller
$t^*$, leading to an effective measured exponent more heavily weighted toward
$p_+>1$.


title:
Stability Analysis of Optimal Velocity Model for Traffic and Granular
  Flow under Open Boundary Condition

abstract:
  We analyzed the stability of the uniform flow solution in the optimal
velocity model for traffic and granular flow under the open boundary condition.
It was demonstrated that, even within the linearly unstable region, there is a
parameter region where the uniform solution is stable against a localized
perturbation. We also found an oscillatory solution in the linearly unstable
region and its period is not commensurate with the periodicity of the car index
space. The oscillatory solution has some features in common with the
synchronized flow observed in real traffic.


title:
Theory of Unconventional Spin Density Wave: A Possible Mechanism of the
  Micromagnetism in U-based Heavy Fermion Compounds

abstract:
  We propose a novel spin density wave (SDW) state as a possible mechanism of
the anomalous antiferromagnetism, so-called the micromagnetism, in URu_2Si_2
below 17.5[K]. In this new SDW, the electron-hole pair amplitude changes its
sign in the momentum space as in the case of the unconventional
superconductivity. It is shown that this state can be realized in an extended
Hubbard model within the mean field theory. We also examine some characteristic
properties of this SDW to compare with the experimental results. All these
properties well explain the unsolved problem of the micromagnetism.


title: Reply to the Comment by Kiselev and Bouis

abstract:
  The possibility of the ferromagnetic state modifies the phase diagram in
Phys.Rev.Lett.81,3723(1998), as Kiselev and Bouis have pointed out. However,
the unconventional SDW that has been proposed in the letter above is still a
candidate for the curious magnetism in URu_2Si_2.


title: A pedagogical introduction to the replica method for fragile glasses

abstract:
  In this note I present a simplified version of the recent computation (Mezard
and Parisi 1998, 1999) of the properties of glasses in the low temperature
phase in the framework of the replica theory, using an extension of the tools
used in liquid theory. I will only consider here the case of the internal
energy at T=0, which can be studied in a simple way without introducing
replicas.


title: Structure and Dynamics of Liquid Iron under Earth's Core Conditions

abstract:
  First-principles molecular dynamics simulations based on density-functional
theory and the projector augmented wave (PAW) technique have been used to study
the structural and dynamical properties of liquid iron under Earth's core
conditions. As evidence for the accuracy of the techniques, we present PAW
results for a range of solid-state properties of low- and high-pressure iron,
and compare them with experimental values and the results of other
first-principles calculations. In the liquid-state simulations, we address
particular effort to the study of finite-size effects, Brillouin-zone sampling
and other sources of technical error. Results for the radial distribution
function, the diffusion coefficient and the shear viscosity are presented for a
wide range of thermodynamic states relevant to the Earth's core. Throughout
this range, liquid iron is a close-packed simple liquid with a diffusion
coefficient and viscosity similar to those of typical simple liquids under
ambient conditions.


title:
Defect formation in inhomogeneous 2-nd order phase transition: theory
  and experiment

abstract:
  The status quo in our understanding of defect formation during a rapid
transition into the broken symmetry state in condensed matter and cosmology is
discussed. An observation of vortex nucleation in neutron absorption
experiments in superfluid 3He-B is interpreted in terms of defect formation
during inhomogeneous cooling through T_c. Due to the temperature gradient in
the locally heated region the superfluid phase transition occurs as a
propagating front. The theoretical considerations of vortex formation at the
propagating front are based on work by Kibble-Volovik, Kopnin-Thuneberg, and
Aranson-Kopnin-Vinokur.


title:
Comment on "Theory of Unconventional Spin Density Wave: A Possible
  Mechanism of the Micromagnetism in U-based Heavy Fermion Compounds"

abstract:
  In the recent letter [1] by H. Ikeda and Y. Ohashi, a new, very attractive
idea is proposed for the explanation of the micromagnetism in U-based heavy
fermion compounds. For this sake a nontrivial spin density wave (d-SDW) is
introduced. Our goal is to claim, that in the model considered, the mean-field
analysis is incomplete: the ferromagnetic state missed by [1] overcomes d-SDW
in a large region of the phase diagram (Fig.1 in [1]).


title:
Spreading and shortest paths in systems with sparse long-range
  connections

abstract:
  Spreading according to simple rules (e.g. of fire or diseases), and
shortest-path distances are studied on d-dimensional systems with a small
density p per site of long-range connections (``Small-World'' lattices). The
volume V(t) covered by the spreading quantity on an infinite system is exactly
calculated in all dimensions. We find that V(t) grows initially as t^d/d for
t<< t^* = (2p \Gamma_d (d-1)!)^{-1/d} and later exponentially for $t>>t^*$,
generalizing a previous result in one dimension. Using the properties of V(t),
the average shortest-path distance \ell(r) can be calculated as a function of
Euclidean distance r. It is found that
  \ell(r) = r for r<r_c=(2p \Gamma_d (d-1)!)^{-1/d} log(2p \Gamma_d L^d), and
  \ell(r) = r_c for r>r_c.
  The characteristic length r_c, which governs the behavior of shortest-path
lengths, diverges with system size for all p>0. Therefore the mean separation s
\sim p^{-1/d} between shortcut-ends is not a relevant internal length-scale for
shortest-path lengths. We notice however that the globally averaged
shortest-path length, divided by L, is a function of L/s only.


title: Two-Dimensional Electron-Hole Systems in a Strong Magnetic Field

abstract:
  Two-dimensional systems containing Ne electrons and Nh holes (Ne>Nh) strongly
correlated through Coulomb interactions in the presence of a large magnetic
field are studied by exact numerical diagonalization. Low lying states are
found to contain neutral (X0) and negatively charged (X-) excitons and higher
charged exciton complexes (Xk-, a bound state of k neutral excitons and an
electron). Representing these states in terms of angular momenta and binding
energies of the different exciton complexes, and the pseudopotentials
describing their interactions with electrons and with one another, permits
numerical studies of systems that are too large to investigate in terms of
individual electrons and holes. Laughlin incompressible ground states of such a
multi-component plasma are found. A generalized composite Fermion picture based
on Laughlin type correlations is proposed. It is shown to correctly predict the
lowest band of angular momentum multiplets for different charge configurations
of the system for any value of the magnetic field.


title:
Depinning transition and thermal fluctuations in the random-field Ising
  model

abstract:
  We analyze the depinning transition of a driven interface in the 3d
random-field Ising model (RFIM) with quenched disorder by means of Monte Carlo
simulations. The interface initially built into the system is perpendicular to
the [111]-direction of a simple cubic lattice. We introduce an algorithm which
is capable of simulating such an interface independent of the considered
dimension and time scale. This algorithm is applied to the 3d-RFIM to study
both the depinning transition and the influence of thermal fluctuations on this
transition. It turns out that in the RFIM characteristics of the depinning
transition depend crucially on the existence of overhangs. Our analysis yields
critical exponents of the interface velocity, the correlation length, and the
thermal rounding of the transition. We find numerical evidence for a scaling
relation for these exponents and the dimension d of the system.


title:
Far-Infrared Spectroscopy in Spin-Peierls Compound CuGeO_3 under High
  Magnetic Fields

abstract:
  Polarized far-infrared (FIR) spectroscopic measurements and FIR
magneto-optical studies were performed on the inorganic spin-Peierls compound
CuGeO_3. An absorption line, which was found at 98 cm$^{-1}$ in the dimerized
phase (D phase), was assigned to a folded phonon mode of B$_{3u}$ symmetry. The
splitting of the folded mode into two components in the incommensurate phase
(IC phase) has been observed for the first time. A new broad absorption
centered at 63 cm$^{-1}$ was observed only in the ${\bf E}\parallel b$ axis
polarization, which was assigned to a magnetic excitation from singlet ground
state to a continuum state.


title:
The amorphous solid state: a locally stable thermodynamic phase of
  randomly constrained systems

abstract:
  The question of the local stability of the (replica-symmetric) amorphous
solid state is addressed for a class of systems undergoing a continuous liquid
to amorphous-solid phase transition driven by the effect of random constraints.
The Hessian matrix, associated with infinitesimal fluctuations around the
stationary point corresponding to the amorphous solid state, is obtained. The
eigenvalues of this Hessian matrix are all shown to be strictly positive near
the transition, except for one--the zero mode associated with the spontaneously
broken continuous translational symmetry of the system. Thus the local
stability of the amorphous solid state is established.


title: Nonequilibrium phase transition by directed Potts particles

abstract:
  We introduce an interface model with q-fold symmetry to study the
nonequilibrium phase transition (NPT) from an active to an inactive state at
the bottom layer. In the model, q different species of particles are deposited
or are evaporated according to a dynamic rule, which includes the interaction
between neighboring particles within the same layer. The NPT is classified
according to the number of species q. For q=1 and 2, the NPT is characterized
by directed percolation, and the directed Ising class, respectively. For $q \ge
3$, the NPT occurs at finite critical probability p_c, and appears to be
independent of q; the $q=\infty$ case is related to the Edwards-Wilkinson
interface dynamics.


title: Dynamics of ripple formation in sputter erosion: nonlinear phenomena

abstract:
  Many morphological features of sputter eroded surfaces are determined by the
balance between ion induced linear instability and surface diffusion. However,
the impact of the nonlinear terms on the morphology is less understood. We
demonstrate that while at short times ripple formation is described by the
linear theory, after a characteristic time the nonlinear terms determine the
surface morphology by either destroying the ripples, or generating a new
rotated ripple structure. We show that the morphological transitions induced by
the nonlinear effects can be detected by monitoring the surface width and the
erosion velocity.


title: Multifractality in Human Heartbeat Dynamics

abstract:
  Recent evidence suggests that physiological signals under healthy conditions
may have a fractal temporal structure. We investigate the possibility that time
series generated by certain physiological control systems may be members of a
special class of complex processes, termed multifractal, which require a large
number of exponents to characterize their scaling properties. We report on
evidence for multifractality in a biological dynamical system --- the healthy
human heartbeat. Further, we show that the multifractal character and nonlinear
properties of the healthy heart rate are encoded in the Fourier phases. We
uncover a loss of multifractality for a life-threatening condition, congestive
heart failure.


title:
A Search for Fluctuation-Dissipation Theorem Violations in Spin-Glasses
  from Susceptibility Data

abstract:
  We propose an indirect way of studying the fluctuation-dissipation relation
in spin-glasses that only uses available susceptibility data. It is based on a
dynamic extension of the Parisi-Toulouse approximation and a Curie-Weiss
treatment of the average magnetic couplings. We present the results of the
analysis of several sets of experimental data obtained from various samples.


title: Magnetic Field Induced Ordering in Quasi-One-Dimensional Quantum Magnets

abstract:
  Three-dimensional magnetic ordering transitions are studied theoretically in
strongly anisotropic quantum magnets. An external magnetic field can drive
quasi-one-dimensional subsystems with a spin gap into a gapless regime, thus
inducing long-range three-dimensional magnetic ordering due to weak residual
magnetic coupling between the subsystems. Compounds with higher spin degrees of
freedom, such as N-leg spin-1/2 ladders, are shown to have cascades of ordering
transitions. At high magnetic fields, zero-point fluctuations within the
quasi-1D subsystems are suppressed, causing quantum corrections to the ordering
temperature to be reduced.


title:
Relaxation Effects in the Transition Temperature of Superconducting
  HgBa2CuO4+delta

abstract:
  In previous studies on a number of under- and overdoped high temperature
superconductors, including YBa_{2}Cu_{3}O_{7-y} and Tl_{2}Ba_{2}CuO_{6+\delta},
the transition temperature T_c has been found to change with time in a manner
which depends on the sample's detailed temperature and pressure history. This
relaxation behavior in T_c is believed to originate from rearrangements within
the oxygen sublattice. In the present high-pressure studies on
HgBa_{2}CuO_{4+\delta} to 0.8 GPa we find clear evidence for weak relaxation
effects in strongly under- and overdoped samples ($T_c\simeq 40 - 50 K$) with
an activation energy $E_{A}(1 bar) \simeq 0.8 - 0.9 eV$. For overdoped
HgBa_{2}CuO_{4+\delta} E_{A} increases under pressure more rapidly than
previously observed for YBa_{2}Cu_{3}O_{6.41}, yielding an activation volume of
+11 \pm 5 cm^{3}; the dependence of T_c on pressure is markedly nonlinear, an
anomalous result for high-T_c superconductors in the present pressure range,
giving evidence for a change in the electronic and/or structural properties
near 0.4 GPa.


title:
Composite Fermion Picture for Multi-Component Plasmas in 2D
  Electron-Hole Systems in a Strong Magnetic Field

abstract:
  Low lying states of a 2D electron-hole system contain electrons and one or
more types of charged excitonic complexes. Binding energies and angular momenta
of these excitonic ions, and the pseudopotentials describing their interactions
with electrons and with one another are obtained from numerical studies of
small systems. Incompressible fluid ground states of such multi-component
plasmas are found in exact numerical diagonalizations. A generalized composite
Fermion (CF) picture involving Chern--Simons charges and fluxes of different
types is proposed and shown to predict the low lying states at any value of the
magnetic field.


title:
Composite Fermions and the Fractional Quantum Hall Effect: Essential
  Role of the Pseudopotential

abstract:
  The mean field (MF) composite Fermion (CF) picture successfully predicts the
band of low lying angular momentum multiplets of fractional quantum Hall
systems for any value of the magnetic field. This success cannot be attributed
to a cancellation between Coulomb and Chern--Simons interactions between
fluctuations beyond the mean field. It results instead from the short range
behavior of the Coulomb pseudopotential in the lowest Landau level (LL). The
class of pseudopotentials for which the MFCF picture is successful can be
defined, and used to explain the success or failure of the picture in different
cases (e.g. excited LL's, charged magneto-excitons, and Laughlin quasiparticles
in a CF hierarchy picture).


title:
Wavefunction-based correlated ab initio calculations on crystalline
  solids

abstract:
  We present a wavefunction-based approach to correlated ab initio calculations
on crystalline insulators of infinite extent. It uses the representation of the
occupied and the unoccupied (virtual) single-particle states of the infinite
solid in terms of Wannier functions. Electron correlation effects are evaluated
by considering virtual excitations from a small region in and around the
reference cell, keeping the electrons of the rest of the infinite crystal
frozen at the Hartree-Fock level. The method is applied to study the ground
state properties of the LiH crystal, and is shown to yield rapidly convergent
results.


title: A Monte Carlo Study of Equilibrium Polymers in a Shear Flow

abstract:
  We use an off-lattice microscopic model for solutions of equilibrium polymers
(EP) in a lamellar shear flow generated by means of a self-consistent external
field between parallel hard walls.
  The individual conformations of the chains are found to elongate in flow
direction and shrink perpendicular to it while the average polymer length
decreases with increasing shear rate.
  The Molecular Weight Distribution of the chain lengths retains largely its
exponential form in dense solutions whereas in dilute solutions it changes from
a power-exponential Schwartz distribution to a purely exponential one upon an
increase of the shear rate.


title:
Thermodynamical Properties of a Spin 1/2 Heisenberg Chain Coupled to
  Phonons

abstract:
  We performed a finite-temperature quantum Monte Carlo simulation of the
one-dimensional spin-1/2 Heisenberg model with nearest-neighbor interaction
coupled to Einstein phonons. Our method allows to treat easily up to 100
phonons per site and the results presented are practically free from truncation
errors. We studied in detail the magnetic susceptibility, the specific heat,
the phonon occupation, the dimerization, and the spin-correlation function for
various spin-phonon couplings and phonon frequencies. In particular we give
evidence for the transition from a gapless to a massive phase by studying the
finite-size behavior of the susceptibility. We also show that the dimerization
is proportional to $g^2/\Omega$ for $T<2J$.


title:
Topological Gauge Theory Of General Weitzenbock Manifolds Of
  Dislocations In Crystals

abstract:
  General Weitzenbock material manifolds of dislocations in crystals Are
proposed, the reference, idealized and deformation states of the bodies in
general case are generally described by the general manifolds, the topological
gauge field theory of dislocations is given in general case,true distributions
and evolution of dislocations in crystals are given by the formulas describing
dislocations in terms of the general manifolds,furthermore, their properties
are discussed.


title: Fragmented and Single Condensate Ground States of Spin-1 Bose Gas

abstract:
  We show that the ground state of a spin-1 Bose gas with an antiferro-
magnetic interaction is a fragmented condensate in uniform magnetic fields. The
number fluctuations in each spin component change rapidly from being enormous
(order $N$) to exceedingly small (order 1) as the magnetization of the system
increases. A fragmented condensate can be turned into a single condensate state
by magnetic field gradients. The conditions for existence and the method of
detecting fragmented states are presented.