title: Two-Dimensional Wigner Crystal in Anisotropic Semiconductor

abstract:
  We investigate the effect of mass anisotropy on the Wigner crystallization
transition in a two-dimensional (2D) electron gas. The static and dynamical
properties of a 2D Wigner crystal have been calculated for arbitrary 2D Bravais
lattices in the presence of anisotropic mass, as may be obtainable in Si
MOSFETs with (110) surface. By studying the stability of all possible lattices,
we find significant change in the crystal structure and melting density of the
electron lattice with the lowest ground state energy.


title:
Reduction of critical temperatures in pure and thoriated UBe13 by
  columnar defects

abstract:
  We investigate the influence of columnar defects on the superconducting
transition temperatures of pure and thoriated UBe13. The defects cause all the
transitions to widen and to drop slightly in temperature. Quantitatively, the
single UBe13 transition resembles the lower transition in a sample with 3%
thorium more closely than the upper thoriated transition.


title: Mesoscopic Kondo Effect in an Aharonov-Bohm Ring

abstract:
  An interacting quantum dot inserted in a mesoscopic ring is investigated. A
variational ansatz is employed to describe the ground state of the system in
the presence of the Aharonov-Bohm flux. It is shown that, for even number of
electrons with the energy level spacing smaller than the Kondo temperature, the
persistent current has a value similar to that of a perfect ring with the same
radius. On the other hand, for a ring with odd number electrons, the persistent
current is found to be strongly suppressed compared to that of an ideal ring,
which implies the suppression of the Kondo-resonant transmission. Various
aspects of the Kondo-assisted persistent current are discussed.


title: Valence band excitations in V_2O_5

abstract:
  We present a joint theoretical and experimental investigation of the
electronic and optical properties of vanadium pentoxide. Electron energy-loss
spectroscopy in transmission was employed to measure the momentum-dependent
loss function. This in turn was used to derive the optical conductivity, which
is compared to the results of band structure calculations. A good qualitative
and quantitative agreement between the theoretical and the experimental optical
conductivity was observed. The experimentally observed anisotropy of the
optical properties of V_2O_5 could be understood in the light of an analysis of
the theoretical data involving the decomposition of the calculated optical
conductivity into contributions from transitions into selected energy regions
of the conduction band. In addition, based upon a tight binding fit to the band
structure, values are given for the effective V3d_xy-O2p hopping terms and are
compared to the corresponding values for alpha'-NaV_2O_5.


title:
Incommensurate Geometry of the Elastic Magnetic Peaks in Superconducting
  La1.88Sr0.12CuO4

abstract:
  We report magnetic neutron scattering measurements of incommensurate magnetic
order in a superconducting single crystal of La1.88Sr0.12CuO4. We find that the
incommensurate wavevectors which describe the static magnetism do not lie along
high-symmetry directions of the underlying CuO2 lattice. The positions of the
elastic magnetic peaks are consistent with those found in excess-oxygen doped
La2CuO4+y. This behavior differs from the precise magnetic order found in the
low temperature tetragonal La1.6-xNd0.4SrxCuO4 material for which stripes of
spin and charge have been observed. These observations have clear implications
for any stripe model proposed to describe the static magnetism in orthorhombic
La2CuO4-based superconductors.


title: Thermodynamics of Heat Shock Response

abstract:
  Production of heat shock proteins are induced when a living cell is exposed
to a rise in temperature. The heat shock response of protein DnaK synthesis in
E.coli for temperature shifts from temperature T to T plus 7 degrees,
respectively to T minus 7 degrees is measured as function of the initial
temperature T. We observe a reversed heat shock at low T. The magnitude of the
shock increases when one increase the distance to the temperature $T_0 \approx
23^o$, thereby mimicking the non monotous stability of proteins at low
temperature. Further we found that the variation of the heat shock with T
quantitatively follows the thermodynamic stability of proteins with
temperature. This suggest that stability related to hot as well as cold
unfolding of proteins is directly implemented in the biological control of
protein folding. We demonstrate that such an implementation is possible in a
minimalistic chemical network.


title:
Disorder-to-order transition in the magnetic and electronic properties
  of URh_2Ge_2

abstract:
  We present a study of annealing effects on the physical properties of
tetragonal single--crystalline URh_2Ge_2. This system, which in as-grown form
was recently established as the first metallic 3D random-bond heavy-fermion
spin glass, is transformed by an annealing treatment into a long-range
antiferromagnetically (AFM) ordered heavy-fermion compound. The transport
properties, which in the as-grown material were dominated by the structural
disorder, exhibit in the annealed material signs of typical metallic behavior
along the crystallographic a axis. From our study URh_2Ge_2 emerges as
exemplary material highlighting the role and relevance of structural disorder
for the properties of strongly correlated electron systems. We discuss the link
between the magnetic and electronic behavior and how they are affected by the
structural disorder.


title: Observation of domain wall resistivity in $\rm SrRuO_3$

abstract:
  $\rm SrRuO_3$ is an itinerant ferromagnet with $T_c \sim 150 \rm K$. When
$\rm SrRuO_3$ is cooled through $T_c$ in zero applied magnetic field, a stripe
domain structure appears whose orientation is uniquely determined by the large
uniaxial magnetocrystalline anisotropy. We find that the ferromagnetic domain
walls clearly enhance the resisitivity of $\rm SrRuO_3$ and that the
enhancement has different temperature dependence for currents parallel and
perpendicular to the domain walls. We discuss possible interpretations of our
results.


title: Nano-electronic Realizations of Quantum Bits

abstract:
  Quantum computers could perform certain tasks which no classical computer can
perform in acceptable times. Josephson junction circuits can serve as building
blocks of quantum computers. We discuss and compare two designs, which employ
charge or magnetic flux degrees of freedom to process quantum information. In
both cases, elementary single-qubit and two-qubit logic gates can be performed
by voltage or flux pulses. The coherence time is long enough to allow a series
of such operations. We also discuss the read-out, i.e., a quantum measurement
process. In the charge case it is accomplished by coupling a single-electron
transistor to the qubit.


title:
Chirally Stabilized Critical State in Marginally Coupled Spin and Doped
  Systems

abstract:
  We study a class of one-dimensional models consisting of a frustrated
(N+1)-leg spin ladder, its asymmetric doped version as a special example of a
Luttinger liquid in an active environment, and the N-channel Kondo-Heisenberg
model away from half-filling. It is shown that these models exhibit a critical
phase with generally a non-integer central charge and belong to the class of
chirally stabilized spin liquids recently introduced by Andrei, Douglas, and
Jerez [Phys. Rev. B 58, 7619 (1998)]. By allowing anisotropic interactions in
spin space, an exact solution in the N=2 case is found at a Toulouse point
which captures all universal properties of the models. At the critical point,
the massless degrees of freedom are described in terms of an effective S=1/2
Heisenberg spin chain and two critical Ising models. The Toulouse limit
solution enables us to discuss the spectral properties, the computation of the
spin-spin correlation functions as well as the estimation of the NMR relaxation
rate of the frustrated three-leg ladder. Finally, it is shown that the critical
point becomes unstable upon switching on some weak backscattering perturbations
in the frustrated three-leg ladder.


title: A Paradox in the Langevin Equation with Long-Time Noise Correlations

abstract:
  We solve the generalized Langevin equation driven by a stochastic force with
power-law autocorrelation function. A stationary Markov process has been
applied as a model of the noise. However, the resulting velocity variance does
not stabilizes but diminishes with time. It is shown that algebraic
distributions can induce such non-stationary affects. Results are compared to
those obtained with a deterministic random force. Consequences for the
diffusion process are also discussed.


title: CDW Ordering in Stripe Phase of Underdoped Cuprates

abstract:
  The in-plane resistivity and out-of-plane resistivity of non-superconducting
RBCO (R = Y, Tm) and Fe-doped Bi2212 single crystals are discussed. The
comparison of electrical transport properties of the cuprates and quasi-one
dimensional (1D) (TMTSF)2PF6 organic conductor suggests that RBCO and Bi2212
exhibit 1D transport properties, and the step rise at low temperatures in the
resistivities of the cuprates and quasi-1D organic conductor is due to
charge-density-wave ordering. We discuss also phonon-electron interactions in
cuprates at low temperatures.


title: Probing the spin polarization in ferromagnets

abstract:
  The emission of correlated electrons from an itinerant ferromagnet following
the impact of a polarized electron beam is analyzed in terms of irreducible
tensorial parameters that can be measured. Under favorable conditions,
specified in this work, these parameters are related to the spin polarization
in the ferromagnet. The formal results are illustrated by numerical studies of
the polarized electron pair emission from a Fe(110) surface and a novel
technique for the investigation of magnetic properties of ferromagnets is
suggested.


title:
Island nucleation in the presence of step edge barriers: Theory and
  applications

abstract:
  We develop a theory of nucleation on top of two-dimensional islands bordered
by steps with an additional energy barrier $\Delta E_S$ for descending atoms.
The theory is based on the concept of the residence time of an adatom on the
island,and yields an expression for the nucleation rate which becomes exact in
the limit of strong step edge barriers. This expression differs qualitatively
and quantitatively from that obtained using the conventional rate equation
approach to nucleation [J. Tersoff et al., Phys. Rev. Lett.72, 266 (1994)]. We
argue that rate equation theory fails because nucleation is dominated by the
rare instances when two atoms are present on the island simultaneously. The
theory is applied to two distinct problems: The onset of second layer
nucleation in submonolayer growth, and the distribution of the sizes of top
terraces of multilayer mounds under conditions of strong step edge barriers.
Application to homoepitaxial growth on Pt(111) yields the estimate $\Delta E_S
\geq 0.33$ eV for the additional energy barrier at CO-decorated steps.


title: Phase separation in disordered exclusion models

abstract:
  The effect of quenched disorder in the one-dimensional asymmetric exclusion
process is reviewed. Both particlewise and sitewise disorder generically
induces phase separation in a range of densities. In the particlewise case the
existence of stationary product measures in the homogeneous phase implies that
the critical density can be computed exactly, while for sitewise disorder only
bounds are available. The coarsening of phase-separated domains starting from a
homogeneous initial condition is addressed using scaling arguments and extremal
statistics considerations. Some of these results have been obtained previously
in the context of directed polymers subject to columnar disorder.


title: Spin Coulomb Drag

abstract:
  We introduce a distinctive feature of spin-polarized transport, the Spin
Coulomb Drag: there is an intrinsic source of friction for spin currents due to
the Coulomb interaction between spin ``up'' and spin ``down'' electrons. We
calculate the associated ``spin transrestistivity'' in a generalized random
phase approximation and discuss its dependence on temperature, frequency, and
electron density. We show that, in an appropriate range of parameters, such
resistivity is measurable and propose an experiment to measure it.


title: Ferromagnetic- and Superconducting-like Behavior of Graphite

abstract:
  We have identified ferromagnetic- and superconducting-like magnetization
hysteresis loops in highly oriented pyrolytic graphite samples below and above
room temperature. We also found that both behaviors are very sensitive to
low-temperature -- as compared to the sample synthesis temperature -- heat
treatment. The possible contribution of magnetic impurities and why these do
not appear to be the reason for the observed phenomena is discussed.


title: Two-scale analysis of the SU(N) Kondo Model

abstract:
  We show how to resolve coherent low-energy features embedded in a broad
high-energy background by use of a fully self-consistent calculation for
composite particle operators. The method generalizes the formulation of Roth,
which linearizes the dynamics of composite operators at any energy scale.
Self-consistent equations are derived and analyzed in the case of the
single-impurity SU(N) Kondo model.


title:
Nonlinear optical properties of a channel waveguide produced with
  crosslinkable ferroelectric liquid crystals

abstract:
  A binary mixture of ferroelectric liquid crystals (FLCs) was used for the
design of a channel waveguide. The FLCs possess two important functionalities:
a chromophore with a high hyperpolarizability $\beta$ and photoreactive groups.
The smectic liquid crystal is aligned in layers parallel to the glass plates in
a sandwich geometry. This alignment offers several advantages, such as that
moderate electric fields are sufficient to achieve a high degree of polar
order. The arrangement was then permanently fixed by photopolymerization which
yielded a polar network possessing a high thermal and mechanical stability
which did not show any sign of degradation within the monitored period of
several months. The linear and nonlinear optical properties have been measured
and all four independent components of the nonlinear susceptibility tensor
$\bar d$ have been determined. The off-resonant $d$-coefficients are remarkably
high and comparable to those of the best known inorganic materials. The
alignment led to an inherent channel waveguide for p-polarized light without
additional preparation steps. The photopolymerization did not induce scattering
sites in the waveguide and the normalized losses were less than 2 dB/cm. The
material offers a great potential for the design of nonlinear optical devices
such as frequency doublers of low power laser diodes.


title:
Phase-matched second-harmonic generation in a ferroelectric liquid
  crystal waveguide

abstract:
  True phase-matched second-harmonic generation in a waveguide of crosslinkable
ferroelectric liquid crystals is demonstrated. These materials allow the
formation of macroscopically polar structures whose order can be frozen by
photopolymerization. Homeotropic alignment was chosen which offers decisive
advantages compared to other geometries. All parameters contributing to the
conversion efficiency are maximized by deliberately controlling the
supramolecular arrangement. The system has the potential to achieve practical
level of performances as a frequency doubler for low power laser diodes.


title: Scale Dependent Dimension in the Forest Fire Model

abstract:
  The forest fire model is a reaction-diffusion model where energy, in the form
of trees, is injected uniformly, and burned (dissipated) locally. We show that
the spatial distribution of fires forms a novel geometric structure where the
fractal dimension varies continuously with the length scale. In the three
dimensional model, the dimensions varies from zero to three, proportional with
$log(l)$, as the length scale increases from $l \sim 1$ to a correlation length
$l=\xi$. Beyond the correlation length, which diverges with the growth rate $p$
as ${\xi} \propto p^{-2/3}$, the distribution becomes homogeneous. We suggest
that this picture applies to the ``intermediate range'' of turbulence where it
provides a natural interpretation of the extended scaling that has been
observed at small length scales. Unexpectedly, it might also be applicable to
the spatial distribution of luminous matter in the universe. In the
two-dimensional version, the dimension increases to D=1 at a length scale $l
\sim 1/p$, where there is a cross-over to homogeneity, i. e. a jump from D=1 to
D=2.


title:
Microwave Electrodynamics of the Antiferromagnetic Superconductor
  GdBa_2Cu_3O_{7-\delta}

abstract:
  The temperature dependence of the microwave surface impedance and
conductivity are used to study the pairing symmetry and properties of cuprate
superconductors. However, the superconducting properties can be hidden by the
effects of paramagnetism and antiferromagnetic long-range order in the
cuprates. To address this issue we have investigated the microwave
electrodynamics of GdBa_2Cu_3O_{7-\delta}, a rare-earth cuprate superconductor
which shows long-range ordered antiferromagnetism below T_N=2.2 K, the Neel
temperature of the Gd ion subsystem. We measured the temperature dependence of
the surface resistance and surface reactance of c-axis oriented epitaxial thin
films at 10.4, 14.7 and 17.9 GHz with the parallel plate resonator technique
down to 1.4 K. Both the resistance and the reactance data show an unusual
upturn at low temperature and the resistance presents a strong peak around T_N
mainly due to change in magnetic permeability.


title:
Fano Resonances in Electronic Transport through a Single Electron
  Transistor

abstract:
  We have observed asymmetric Fano resonances in the conductance of a single
electron transistor resulting from interference between a resonant and a
nonresonant path through the system. The resonant component shows all the
features typical of quantum dots, but the origin of the non-resonant path is
unclear. A unique feature of this experimental system, compared to others that
show Fano line shapes, is that changing the voltages on various gates allows
one to alter the interference between the two paths.


title: Quantum Kinetic Theory VI: The Growth of a Bose-Einstein Condensate

abstract:
  A detailed analysis of the growth of a BEC is given, based on quantum kinetic
theory, in which we take account of the evolution of the occupations of lower
trap levels, and of the full Bose-Einstein formula for the occupations of
higher trap levels, as well as the Bose stimulated direct transfer of atoms to
the condensate level introduced by Gardiner et al. We find good agreement with
experiment at higher temperatures, but at lower temperatures the experimentally
observed growth rate is somewhat more rapid. We also confirm the picture of the
``kinetic'' region of evolution, introduced by Kagan et al., for the time up to
the initiation of the condensate. The behavior after initiation essentially
follows our original growth equation, but with a substantially increased rate
coefficient.
  Our modelling of growth implicitly gives a model of the spatial shape of the
condensate vapor system as the condensate grows, and thus provides an
alternative to the present phenomenological fitting procedure, based on the sum
of a zero-chemical potential vapor and a Thomas-Fermi shaped condensate. Our
method may give substantially different results for condensate numbers and
temperatures obtained from phenomentological fits, and indicates the need for
more systematic investigation of the growth dynamics of the condensate from a
supersaturated vapor.


title:
Cooperativity and Spatial Correlations near the Glass Transition:
  Computer Simulation Results for Hard Spheres and Discs

abstract:
  We examine the dynamics of hard spheres and discs at high packing fractions
in two and three dimensions, modeling the simplest systems exhibiting a glass
transition. As it is well known, cooperativity and dynamic heterogeneity arise
as central features when approaching the glass transition from the liquid
phase, so an understanding of their underlying physics is of great interest.
Cooperativity implies a reduction of the effective degrees of freedom, and we
demonstrate a simple way of quantification in terms of the strength and the
length scale of dynamic correlations among different particles. These
correlations are obtained for different dynamical quantities $X_i(t)$ that are
constructed from single-particle displacements during some observation time
$t$. Of particular interest is the dependence on $t$. Interestingly, for
appropriately chosen $X_i(t)$ we obtain finite cooperativity in the limit $t
\to \infty$.


title: Meanfield treatment of Bragg scattering from a Bose-Einstein condensate

abstract:
  A unified semiclassical treatment of Bragg scattering from Bose-Einstein
condensates is presented. The formalism is based on the Gross-Pitaevskii
equation driven by classical light fields far detuned from atomic resonance. An
approximate analytic solution is obtained and provides quantitative
understanding of the atomic momentum state oscillations, as well as a simple
expression for the momentum linewidth of the scattering process. The validity
regime of the analytic solution is derived, and tested by three dimensional
cylindrically symmetric numerical simulations.


title:
Two-species percolation and Scaling theory of the metal-insulator
  transition in two dimensions

abstract:
  Recently, a simple non-interacting-electron model, combining local quantum
tunneling via quantum point contacts and global classical percolation, has been
introduced in order to describe the observed ``metal-insulator transition'' in
two dimensions [1]. Here, based upon that model, a two-species-percolation
scaling theory is introduced and compared to the experimental data. The two
species in this model are, on one hand, the ``metallic'' point contacts, whose
critical energy lies below the Fermi energy, and on the other hand, the
insulating quantum point contacts. It is shown that many features of the
experiments, such as the exponential dependence of the resistance on
temperature on the metallic side, the linear dependence of the exponent on
density, the $e^2/h$ scale of the critical resistance, the quenching of the
metallic phase by a parallel magnetic field and the non-monotonic dependence of
the critical density on a perpendicular magnetic field, can be naturally
explained by the model.
  Moreover, details such as the nonmonotonic dependence of the resistance on
temperature or the inflection point of the resistance vs. parallel magnetic are
also a natural consequence of the theory. The calculated parallel field
dependence of the critical density agrees excellently with experiments, and is
used to deduce an experimental value of the confining energy in the vertical
direction. It is also shown that the resistance on the ``metallic'' side can
decrease with decreasing temperature by an arbitrary factor in the degenerate
regime ($T\lesssim E_F$).


title:
Schrodinger equation approach to non-linear $\sigma$-models in the large
  N-limit

abstract:
  Non-linear d-dimensional vector $\sigma$-models are studied in the large
N-limit. It is found that a two-point correlation function obeys a standard
Schrodinger equation for a free quantum particle moving in the
$\delta$-function quantum well. The threshold problem for bound states in this
equation is shown to be equivalent to a critical behavior of these models above
and below the Curie point.
  The SU(N)- symmetric Ginzburg-Landau (GL) $\sigma$-model subject to a uniform
magnetic field H is considered in the large-N limit within the Schrodinger
equation approach. A upper critical magnetic field line $H_{c2}(T)$ of type-II
superconductors for an arbitrary external H is obtained without exploiting the
lowest Landau level (LLL) approximation. Both low-H perturbation expansion
terms and exponentially small corrections to the LLL approximation are
calculated.
  Correspondences between the one-particle quantum mechanics and critical
phenomena as well as some applications of the above method to other models of
statistical mechanics are also discussed.


title: An Exactly Solvable Two-Way Traffic Model With Ordered Sequential Update

abstract:
  Within the formalism of martix product ansatz, we study a two-species
asymmetric exclusion process with backward and forward site-ordered sequential
update. This model describes a two-way traffic flow with a dynamical impurity
and shows a phase transition between the free flow and the traffic jam. We
investigate characteristics of this jamming and examine similarities and
differences between our results and those with random sequential update.


title:
Breakdown of Dynamical Scale Invariance in the Coarsening of Fractal
  Clusters

abstract:
  We extend a previous analysis [PRL {\bf 80}, 4693 (1998)] of breakdown of
dynamical scale invariance in the coarsening of two-dimensional DLAs
(diffusion-limited aggregates) as described by the Cahn-Hilliard equation.
Existence of a second dynamical length scale, predicted earlier, is
established. Having measured the "solute mass" outside the cluster versus time,
we obtain a third dynamical exponent. An auxiliary problem of the dynamics of a
slender bar (that acquires a dumbbell shape) is considered. A simple scenario
of coarsening of fractal clusters with branching structure is suggested that
employs the dumbbell dynamics results. This scenario involves two dynamical
length scales: the characteristic width and length of the cluster branches. The
predicted dynamical exponents depend on the (presumably invariant) fractal
dimension of the cluster skeleton. In addition, a robust theoretical estimate
for the third dynamical exponent is obtained. Exponents found numerically are
in reasonable agreement with these predictions.


title:
Phonon-Coupled Electron Tunneling in Two and Three-Dimensional Tunneling
  Configurations

abstract:
  We treat a tunneling electron coupled to acoustical phonons through a
realistic electron phonon interaction: deformation potential and piezoelectric,
in two or three-dimensional tunneling configurations. Making use of slowness of
the phonon system compared to electron tunneling, and using a Green function
method for imaginary time, we are able to calculate the change in the
transition probability due to the coupling to phonons. It is shown using
standard renormalization procedure that, contrary to the one-dimensional case,
second order perturbation theory is sufficient in order to treat the
deformation potential coupling, which leads to a small correction to the
transmission coefficient prefactor. In the case of piezoelectric coupling,
which is found to be closely related to the piezoelectric polaron problem,
vertex corrections need to be considered. Summing leading logarithmic terms, we
show that the piezoelectric coupling leads to a significant change of the
transmission coefficient.


title: Magnetic properties of a two-electron quantum dot

abstract:
  The low-energy eigenstates of two interacting electrons in a square quantum
dot in a magnetic field are determined by numerical diagonalization. In the
strong correlation regime, the low-energy eigenstates show Aharonov-Bohm type
oscillations, which decrease in amplitude as the field increases. These
oscillations, including the decrease in amplitude, may be reproduced to good
accuracy by an extended Hubbard model in a basis of localized one-electron
Hartree states. The hopping matrix element, $t$, comprises the usual kinetic
energy term plus a term derived from the Coulomb interaction. The latter is
essential to get good agreement with exact results. The phase of $t$ gives rise
to the usual Peierls factor, related to the flux through a square defined by
the peaks of the Hartree wavefunctions. The magnitude of $t$ decreases slowly
with magnetic field as the Hartree functions become more localized, giving rise
to the decreasing amplitude of the Aharonov-Bohm oscillations.


title: Superconductivity in striped Hubbard Clusters

abstract:
  The CuO-planes of high-T_c superconductors were found to consist of geometric
stripes with alternating superconducting and antiferromagnetic areas. Here we
will investigate the repulsive Hubbard model of striped clusters as a possible
microscopic description of the superconducting elements. The focus of our
attention lies on the superconducting properties. We report in agreement with
the square Hubbard model a signal in the d-wave channel and investigate its
dependence on system size, cluster shape and interaction strength.


title:
Analysis of negative magnetoresistance. Statistics of closed paths. I.
  Theory

abstract:
  Statistics of closed paths in two-dimensional (2D) systems, which just
determines the interference quantum correction to conductivity and anomalous
magnetoconductance, has been studied by computer simulation of a particle
motion over the plane with randomly distributed scatterers. Both ballistic and
diffusion regimes have been considered. The results of simulation have been
analyzed in the framework of diffusion approximation. They are used for
calculation of the magnetic field dependence of magnetoconductance in the model
2D system. It is shown that the anomalous magnetoconductance can be in
principle described by the well known expression, obtained in the diffusion
approximation, but with the prefactor less than unity and phase breaking length
which differs from true value.


title:
Analysis of negative magnetoresistance. Statistics of closed paths. II.
  Experiment

abstract:
  It is shown that a new kind of information can be extracted from the Fourier
transform of negative magnetoresistance in 2D semiconductor structures. The
procedure proposed provides the information on the area distribution function
of closed paths and on the area dependence of the average length of closed
paths. Based on this line of attack the method of analysis of the negative
magnetoresistance is suggested. The method has been used to process the
experimental data on negative magnetoresistance in 2D structures with different
relations between the momentum and phase relaxation times. It is demonstrated
this fact leads to distinction in the area dependence of the average length of
closed paths.


title:
Solution of real-axis Eliashberg equations with different pair
  symmetries and tunneling density of states

abstract:
  The real-axis direct solution of the Eliashberg equations for the retarded
electron-boson interaction in the half-filling case and in the presence of
impurities is obtained for six different symmetries of the order parameter:
$s$, $s+\mathrm{i}d$, $s+d$, $d$, anisotropic-$s$ and extended-$s$. The
spectral function is assumed to contain an isotropic part
$\alpha_{is}^{2}F(\Omega) $ and an anisotropic one $\alpha_{an}^{2}F(\Omega)$
such that $\alpha_{is}^{2}F(\Omega)=g\cdot\alpha_{an}^{2}F(\Omega)$, where $g$
is a constant, and the Coulomb pseudopotential $\mu^{\ast}$ is set to zero for
simplicity. The density of states is calculated for each symmetry at $T= 2, 4,
40$ and 80 K. The resulting curves are compared to those obtained by analytical
continuation of the imaginary-axis solution of the Eliashberg equations and to
the experimental tunneling curves of optimally-doped Bi 2212 crystals.


title: s- and d-wave solution of Eliashberg equations with finite bandwidth

abstract:
  In this work, we discuss the results of the direct solution of the Eliashberg
equations with finite bandwidth, in the cases of s- and d-wave symmetry for the
pair wave function and in the presence of scattering from impurities. We show
that the reduction of the critical temperature $T_{\mathrm{c}}$ due to the
finite bandwidth depends on the value of the bandwidth itself, but is almost
independent of the symmetry of the order parameter. The same happens for the
shape of $Z(\omega)$ and $\Delta(\omega)$. Moreover, we discuss the effect of
the finite bandwidth on the shape of the quasiparticle density of states. The
results clearly indicate that the infinite bandwidth approximation leads to an
underestimation of the electron-boson coupling constant.


title:
ab-plane resistivity and possible charge stripe ordering in strongly
  underdoped La$_{2-x}$Sr$_{x}$CuO$_{4}$ single crystals

abstract:
  We have measured the ab-plane resistivity of La$_{2-x}$Sr$_x$CuO$_4$ single
crystals with small Sr content (x=0.052 $\div$ 0.075) between 4.2 and 300 K by
using the AC Van der Pauw technique. As recently suggested by Ichikawa et al.,
the deviation from the linearity of the $\rho_{\mathrm{ab}}(T)$ curve starting
at a temperature T$_{\mathrm{ch}}$ can be interpreted as due to a progressive
slowing down of the fluctuations of pre-formed charge stripes. An electronic
transition of the stripes to a more ordered phase could instead be responsible
for some very sharp anomalies present in the $\rho_{\mathrm{ab}}(T)$ of
superconducting samples just above $T_{\mathrm{c}}$.


title:
Resistivity and electron-phonon coupling in YNi$_2$B$_2$C single
  crystals

abstract:
  In this work, we present the results of precise measurements of the
resistivity of YNi$_2$B$_2$C single crystals with $T_{\rm c}$ = 15.5 K as a
function of the temperature, and analyze the experimental data in the framework
of the Bloch-Gr\"{u}neisen theory and electron-phonon coupling. The transport
electron-phonon spectral function that best fits the resistivity data is then
inserted in the real-axis Eliashberg equations, which are directly solved to
determine the normalized tunneling conductance both in s- and d-wave symmetry.


title:
3D-melting features of the irreversibility line in overdoped
  Bi$_2$Sr$_2$CuO$_6$ at ultra-low temperature and high magnetic field

abstract:
  We have measured the irreversible magnetization of an overdoped
Bi$_2$Sr$_2$CuO$_6$ single crystal up to B=28 T and down to T=60 mK, and
extracted the irreversibility line $B_{\rm irr}(T)$: the data can be
interpreted in the whole temperature range as a 3D-anisotropic vortex lattice
melting line with Lindemann number $c_{\rm L}=0.13$. We also briefly discuss
the applicability of alternative models such as 2D- and quantum melting, and
the connection with magnetoresistance experiments.


title: Singularity spectra of rough growing surfaces from wavelet analysis

abstract:
  We apply the wavelet transform modulus maxima (WTMM) method to the analysis
of simulated MBE-grown surfaces. In contrast to the structure function approach
commonly used in the literature, this new method permits an investigation of
the complete singularity spectrum. We focus on a kinetic Monte-Carlo model with
Arrhenius dynamics, which in particular takes into consideration the process of
thermally activated desorption of particles. We find a wide spectrum of Hoelder
exponents, which reflects the multiaffine surface morphology. Although our
choice of parameters yields small desorption rates (< 3 %), we observe a
dramatic change in the singularity spectrum, which is shifted towards smaller
Hoelder exponents. Our results offer a mathematical foundation of anomalous
scaling: We identify the global exponent alpha_g with the Hoelder exponent
which maximizes the singularity soectrum.


title:
A Monte Carlo analysis of the phase transitions in the 2D, $J_1-J_2$ XY
  model

abstract:
  We consider the 2D $J_1-J_2$ classical XY model on a square lattice. In the
frustrated phase corresponding to $J_2>J_1/2$, an Ising like order parameter
emerges by an ``order due to disorder'' effect. This leads to a discrete $Z_2$
symmetry plus the U(1) global one. Using a powerful algorithm we show that the
system undergoes two transitions at different but still very close
temperatures, one of Kosterlitz-Thouless (KT) type and another one which does
not belong to the expected Ising universality class. A new analysis of the KT
transition has been developed in order to avoid the use of the non-universal
helicity jump and to allow the computation of the exponents without a precise
determination of the critical temperature. Moreover, our huge number of data
enables us to exhibit the existence of large finite size effects explaining the
dispersed results found in the literature concerning the more studied
frustrated 2D, XY models.


title:
Quantum kinetic theory VII: The influence of vapor dynamics on
  condensate growth

abstract:
  We extend earlier models of the growth of a Bose-Einstein condensate to
include the full dynamical effects of the thermal cloud by numerically solving
a modified quantum Boltzmann equation. We determine the regime in which the
assumptions of the simple model are a reasonable approximation, and compare our
new results with those that were earlier compared with experimental data. We
find good agreement with our earlier modelling, except at higher condensate
fractions, for which a significant speedup is found. We also investigate the
effect of temperature on condensate growth, and find that this has a
surprisingly small effect.
  The discrepancy between theory and experiment remains, since the speedup
found in these computations does not occur in the parameter regime specified in
the the experiment.


title:
Correlation energy, pair-distribution functions and static structure
  factors of jellium

abstract:
  We discuss and clarify a simple and accurate interpolation scheme for the
spin-resolved electron static structure factor (and corresponding pair
correlation function) of the 3D unpolarized homogeneous electron gas which,
along with some analytic properties of the spin-resolved pair-correlation
functions, we have just published. We compare our results with the very recent
spin-resolved scheme by Schmidt et al., and focus our attention on the
spin-resolved correlation energies and the high-density limit of the
correlation functions.


title:
Quasiballistic correction to the density of states in three-dimensional
  metal

abstract:
  We study the exchange correction to the density of states in the
three-dimensional metal near the Fermi energy. In the ballistic limit, when the
distance to the Fermi level exceeds the inverse transport relaxation time
$1/\tau$, we find the correction linear in the distance from the Fermi level.
By a large parameter $\epsilon_{\rm F} \tau$ this ballistic correction exceeds
the diffusive correction obtained earlier.


title:
Fragilities of Liquids Predicted from the Random First Order Transition
  Theory of Glasses

abstract:
  A microscopically motivated theory of glassy dynamics based on an underlying
random first order transition is developed to explain the magnitude of free
energy barriers for glassy relaxation. A variety of empirical correlations
embodied in the concept of liquid "fragility" are shown to be quantitatively
explained by such a model. The near universality of a Lindemann ratio
characterizing the maximal amplitude of thermal vibrations within an amorphous
minimum explains the variation of fragility with a liquid's configurational
heat capacity density. Furthermore the numerical prefactor of this correlation
is well approximated by the microscopic calculation. The size of heterogeneous
reconfiguring regions in a viscous liquid is inferred and the correlation of
nonexponentiality of relaxation with fragility is qualitatively explained. Thus
the wide variety of kinetic behavior in liquids of quite disparate chemical
nature reflects quantitative rather than qualitative differences in their
energy landscapes.


title: Non-equilibrium tunneling into general quantum Hall edge states

abstract:
  In this paper we formulate the theory of tunneling into general Abelian
fractional quantum Hall edge states. In contrast to the simple Laughlin states,
a number of charge transfer processes must be accounted for. Nonetheless, it is
possible to identify a unique value corresponding to dissipationless transport
as the asymptotic large-$V$ conductance through a tunneling junction, and find
fixed points (CFT boundary conditions) corresponding to this value. The
symmetries of a given edge tunneling problem determine the appropriate boundary
condition, and the boundary condition determines the strong-coupling operator
content and current noise.


title:
Correlations near the vulcanization transition: A renormalization-group
  approach

abstract:
  Correlators describing the vulcanization transition are constructed and
explored via a renormalization group approach. This approach is based on a
minimal model that accounts for the thermal motion of constituents and the
quenched random constraints imposed on their motion by crosslinks. Critical
exponents associated with the correlators are obtained near six dimensions, and
found to equal those governing analogous entities in percolation theory. Some
expectations for how the vulcanization transition is realized in two
dimensions, developed with H. E. Castillo, are discussed.


title: Off-diagonal long-range order in one-dimensional many-body problem

abstract:
  We prove that there is off-diagonal long-range order in the symmetrised
version of the one-dimensional many-body problem presented by Jain and Khare
(Phys. Lett. A262 (1999)35). This model is related to the short-range Dyson
model employed to study intermediate statistics in systems like the Anderson
model in three dimensions at the metal-insulator transition point and
pseudointegrable billiards. To the best of our knowledge, this is the only
example showing quantum phases and possibility of Bose-Einstein condensation in
one-dimensional statistical mechanics.


title:
The Addition Spectrum of a Lateral Dot from Coulomb and Spin Blockade
  Spectroscopy

abstract:
  Transport measurements are presented on a class of electrostatically defined
lateral dots within a high mobility two dimensional electron gas (2DEG). The
new design allows Coulomb Blockade(CB) measurements to be performed on a single
lateral dot containing 0, 1 to over 50 electrons. The CB measurements are
enhanced by the spin polarized injection from and into 2DEG magnetic edge
states. This combines the measurement of charge with the measurement of spin
through spin blockade spectroscopy. The results of Coulomb and spin blockade
spectroscopy for first 45 electrons enable us to construct the addition
spectrum of a lateral device. We also demonstrate that a lateral dot containing
a single electron is an effective local probe of a 2DEG edge.


title:
Effect of a Domain Wall on the Conductance Quantization in a
  Ferromagnetic Nanowire

abstract:
  The effect of the domain wall (DW) on the conductance in a ballistic
ferromagnetic nanowire (FMNW) is revisited by exploiting a specific
perturbation theory which is effective for a thin DW; the thinness is often the
case in currently interested conductance measurements on FMNWs. Including the
Hund coupling between carrier spins and local spins in a DW, the conductance of
a FMNW in the presence of a very thin DW is calculated within the
Landauer-B\"{u}ttiker formalism. It is revealed that the conductance plateaus
are modified significantly, and the switching of the quantization unit from
$e^2/h$ to ``about $2e^2/h$'' is produced in a FMNW by the introduction of a
thin DW. This accounts well for recent observations in a FMNW.


title:
Application of Monte Carlo Method to Phase Separation Dynamics of
  Complex Systems

abstract:
  We report the application of the Monte Carlo simulation to phase separation
dynamics. First, we deal with the phase separation under shear flow. The
thermal effect on the phase separation is discussed, and the anisotropic growth
exponents in the late stage are estimated. Next, we study the effect of
surfactants on the three-component solvents. We obtain the mixture of
macrophase separation and microphase separation, and investigate the dynamics
of both phase separations.


title: Phonon mediated hole pairing in the 1D Hubbard model near half-filling

abstract:
  The Hamiltonian describing a system of strongly correlated electrons coupled
to dispersionless phonons was solved numerically for a ring of 8 atoms using
the density matrix renormalization group (DMRG) method. It was found that
electron correlation and electron-phonon coupling compete against each other,
and strong electron correlations suppress the charge-ordered insulating state.
This allows extended polarons to form in the strong electron-phonon coupling
regime. It is shown that in this regime two polarons may form a pair via phonon
mediated charge-fluctuation interaction. Based on the results we propose a
novel mechanism of hole pairing. This mechanism could be relevant to High-Tc
cuprates.


title: Simple Models of the Protein Folding Problem

abstract:
  The protein folding problem has attracted an increasing attention from
physicists. The problem has a flavor of statistical mechanics, but possesses
the most common feature of most biological problems -- the profound effects of
evolution. I will give an introduction to the problem, and then focus on some
recent work concerning the so-called ``designability principle''. The
designability of a structure is measured by the number of sequences that have
that structure as their unique ground state. Structures differ drastically in
terms of their designability; highly designable structures emerge with a number
of associated sequences much larger than the average. These highly designable
structures 1) possess ``proteinlike'' secondary structures and motifs, 2) are
thermodynamically more stable, and 3) fold faster than other structures. These
results suggest that protein structures are selected in nature because they are
readily designed and stable against mutations, and that such selection
simultaneously leads to thermodynamic stability and foldability. According to
this picture, a key to the protein folding problem is to understand the
emergence and the properties of the highly designable structures.


title:
Melting of Charge/Orbital Ordered States in Nd$_{1/2}$Sr$_{1/2}$MnO$_3$:
  Temperature and Magnetic Field Dependent Optical Studies

abstract:
  We investigated the temperature ($T=$ 15 $\sim $ 290 K) and the magnetic
field ($H=$ 0 $\sim $ 17 T) dependent optical conductivity spectra of a
charge/orbital ordered manganite, Nd$_{1/2}$Sr$_{1/2}$MnO$_3$. With variation
of $T$ and $H$, large spectral weight changes were observed up to 4.0 eV. These
spectral weight changes could be explained using the polaron picture.
Interestingly, our results suggested that some local ordered state might remain
above the charge ordering temperature, and that the charge/orbital melted state
at a high magnetic field (i.e. at $H=$ 17 T and $% T=$ 4.2 K) should be a three
dimensional ferromagnetic metal. We also investigated the first order phase
transition from the charge/orbital ordered state to ferromagnetic metallic
state using the $T$- and $H$% -dependent dielectric constants $\epsilon_1$. In
the charge/orbital ordered insulating state, $\epsilon_1$ was positive and
$d\epsilon_1/d\omega \approx 0$. With increasing $T$ and $H$, $\epsilon_1$ was
increased up to the insulator-metal phase boundaries. And then, $\epsilon_1$
abruptly changed into negative and $d\epsilon_1/d\omega >0$, which was
consistent with typical responses of a metal. Through the analysis of $%
\epsilon_1$ using an effective medium approximation, we found that the melting
of charge/orbital ordered states should occur through the percolation of
ferromagnetic metal domains.


title:
Resonant tunneling and the multichannel Kondo problem: the quantum
  Brownian motion description

abstract:
  We study mesoscopic resonant tunneling as well as multichannel Kondo problems
by mapping them to a first-quantized quantum mechanical model of a particle
moving in a multi-dimensional periodic potential with Ohmic dissipation. From a
renormalization group analysis, we obtain phase diagrams of the quantum
Brownian motion model with various lattice symmetries. For a symmorphic
lattice, there are two phases at T=0: a localized phase in which the particle
is trapped in a potential minimum, and a free phase in which the particle is
unaffected by the periodic potential. For a non-symmorphic lattice, however,
there may be an additional intermediate phase in which the particle is neither
localized nor completely free. The fixed point governing the intermediate phase
is shown to be identical to the well-known multichannel Kondo fixed point in
the Toulouse limit as well as the resonance fixed point of a quantum dot model
and a double-barrier Luttinger liquid model. The mapping allows us to compute
the fixed-poing mobility $\mu^*$ of the quantum Brownian motion model exactly,
using known conformal-field-theory results of the Kondo problem. From the
mobility, we find that the peak value of the conductance resonance of a
spin-1/2 quantum dot problem is given by $e^2/2h$. The scaling form of the
resonance line shape is predicted.


title:
Energy Spectrum of Spin Fluctuations in Superconducting La2-xSrxCuO4
  (0.10 < x < 0.25)

abstract:
  The energy spectrum of incommensurate spin fluctuations in superconducting
Sr-doped La2CuO4 has been studied by inelastic neutron scattering experiments.
An energy gap in the spin excitation spectrum is observed in the
superconducting state of optimally doped (x=0.15) and slightly overdoped
(x=0.18) samples. At temperatures well below Tc, the incommensurate peaks
diminish rapidly in intensity with decreasing energy below ~8meV and merge into
the background below ~3.5meV for x=0.15 and ~4.5meV for x=0.18. For both
samples, the energy spectrum of the q-integrated spin susceptibility, x"(w),
exhibits an enhancement around 7meV, which is caused by a broadening in the
momentum width of the incommensurate peaks. The gap-like structure in the
energy spectrum and the enhancement of x"(w) survive at Tc. On the other hand,
for both underdoped (x=0.10) and heavily overdoped (x=0.25) samples there is
neither a clear energy gap nor an enhancement of x"(w) below Tc.


title:
Toward Generalized Entropy Composition with Different q Indices and
  H-Theorem

abstract:
  An attempt is made to construct composable composite entropy with different
$q$ indices of subsystems and address the H-theorem problem of the composite
system. Though the H-theorem does not hold in general situations, it is shown
that some composite entropies do not decrease in time in near-equilibrium
states and factorized states with negligibly weak interaction between the
subsystems.


title:
Theory of vortex lattice effects on STM spectra in d-wave
  superconductors

abstract:
  Theory of scanning tunneling spectroscopy of low energy quasiparticle (QP)
states in vortex lattices of d-wave superconductors is developed taking account
of the effects caused by an extremely large extension of QP wavefunctions in
the nodal directions and the band structure in the QP spectrum. The oscillatory
structures in STM spectra, which correspond to van Hove singularities are
analysed. Theoretical calculations carried out for finite temperatures and
scattering rates are compared with recent experimental data for high
temperature cuprates.


title: La 7/8 Sr 1/8 MnO3: long period orbital order with hole stripes

abstract:
  The electronic structure of La 7/8 Sr 1/8 MnO 3 was studied by using the
rotation-invariant LSDA (Local Spin Density Approximation)+U formalism. We
found the specific kind of charge and orbital order for ferromagnetic
insulating solution in 2a*2b*4c supercell, where a, b, and c denote cubic
perovskite axes. The holes are distributed over 3-line stripes in every second
ac plane along a axis. The stabilization mechanism of the hole stripe is
attributed to the strong p-d hybridization.


title:
A simple model for the metal-insulator transition in a two-dimensional
  electron gas

abstract:
  We introduce an elementary model for the electrostatic self-consistent
potential in a two-dimensional electron gas. By considering the perpendicular
degree of freedom arising from the electron tunneling out of the system plane,
we predict a threshold carrier density above which this effect is relevant. The
predicted value agrees remarkably well with the onset for the insulator to
quasi-metallic transition recently observed in several experiments in SiO2-Si
and AlGaAs-GaAs heterojunctions.


title: Ergodicity of Random-Matrix Theories: The Unitary Case

abstract:
  We prove ergodicity of unitary random-matrix theories by showing that the
autocorrelation function with respect to energy or magnetic field strength of
any observable vanishes asymptotically. We do so using Efetov's supersymmetry
method, a polar decomposition of the saddle-point manifold, and an asymptotic
evaluation of the boundary terms generated in this fashion.


title: Fractons and high-$T_{c}$ superconductivity

abstract:
  We consider the concept of fractons in the context of high-$T_{c}$
superconductivity. These objects, which carry rational or irrational quantum
numbers, are classified into universal classes $h$ of particles or
quasiparticles which obey specific fractal distribution function. We show that
the relaxation time associated to Hall conductivity for the superconducting
cuprate systems came to out as $\tau_{H}\propto T^{-2}$. We also consider the
pairing of fractons as a mechanism to produce bosonic systems and therefore
superconducting states. For that an effective mass obtained from the propagator
of a charge-flux system is considered. In this way, some experimental results
of infrared studies of the cuprates for the effective mass,
$m^*=m_{e}(1+\lambda)$, compared with our effective mass expression,
$m_{eff}=m(1+s)$, show us that the dominant factor for interactions came from
the spin. Thus spin flutuactions as a mechanism of high-$T_{c}$
superconductivity and fractons as quasiparticles are related. An expression to
the low temperature specific heat of a quantum liquid of fractons is also
obtained.


title:
Quantum dynamics of charged and neutral magnetic solitons: Spin-charge
  separation in the one-dimensional Hubbard model

abstract:
  We demonstrate that the Configuration Interaction (CI) Approximation
recaptures essential features of the exact (Bethe Ansatz) solution to the 1D
Hubbard model. As such, it provides valuable route for describing effects which
go beyond mean-field theory for strongly correlated electron systems in higher
dimensions. The CI method systematically describes fluctuation and quantum
tunneling corrections to the Hartree-Fock Approximation (HFA). HFA predicts
that doping a half-filled Hubbard chain leads to the appearance of charged
spin-polarons or charged domain-wall solitons in the antiferromagnetic (AFM)
background. The CI method, on the other hand, describes the quantum dynamics of
these charged magnetic solitons and quantum tunneling effects between various
mean-field configurations. In this paper, we test the accuracy of the CI method
against the exact solution of the one-dimensional Hubbard model. We find
remarkable agreement between the energy of the mobile charged bosonic
domain-wall (as given by the CI method) and the exact energy of the doping hole
(as given by the Bethe Ansatz) for the entire $U/t$ range. The CI method also
leads to a clear demonstration of the spin-charge separation in 1D. Addition of
one doping hole to the half-filled antiferromagnetic chain results in the
appearance of two different carriers: a charged bosonic domain-wall (which
carries the charge but no spin) and a neutral spin-1/2 domain wall (which
carries the spin but no charge).


title: Viscoelastic Depinning of Driven Systems: Mean-Field Plastic Scallops

abstract:
  We have investigated the mean field dynamics of an overdamped viscoelastic
medium driven through quenched disorder. The model introduced incorporates
coexistence of pinned and sliding degrees of freedom and can exhibit continuous
elastic depinning or first order hysteretic depinning. Numerical simulations
indicate mean field instabilities that correspond to macroscopic stick-slip
events and lead to premature switching. The model is relevant for the dynamics
of driven vortex arrays in superconductors and other extended disordered
systems.

categories: cond-mat.dis-nn chao-dyn cond-mat.supr-con nlin.CD


title:
Charged surface in salty water with multivalent ions: Giant inversion of
  charge

abstract:
  Screening of a strongly charged macroion by oppositely charged colloidal
particles, micelles, or short polyelectrolytes is considered. Due to strong
lateral repulsion such multivalent counterions form a strongly correlated
liquid at the surface of the macroion. This liquid provides correlation induced
attraction of multivalent counterions to the macroion surface. As a result even
a moderate concentration of multivalent counterions in the solution inverts the
sign of the net macroion charge. We show that at high concentration of
monovalent salt the absolute value of inverted charge can be larger than the
bare one. This giant inversion of charge can be observed in electrophoresis.


title:
Correlation Functions of Multisite Interaction Spin-S models on the
  Bethe-like Lattices

abstract:
  Multisite interaction spin-S models in an external magnetic field are studied
recursively on the Bethe-like lattices. The transfer-matrix method is extended
to calculate exactly the two-spin correlation functions. The exact expressions
for the correlation length and magnetic susceptibility are derived for spin-1/2
models. The singularity of the correlation length with critical index $\nu =1$
and the proportionality of magnetic susceptibility to correlation length in the
second order phase transition region of spin-1/2 ferromagnetic models on the
Bethe-like lattices are established analytically.


title: Absence of the Vortex Solution in Gor'kov's Formalism

abstract:
  It is shown that the Abrikosov's vortex solution or its corresponding
two-particle pair potential is not the solution of the self-consistency
equation in Gor'kov's formalism. Since the self-consistency equation leads to a
superposition of different types of off-diagonal long-range order (ODLRO)
instead of one type of ODLRO only, it may not handle the vortex problem
appropriately. A possible resolution is suggested.


title: Brownian Particles far from Equilibrium

abstract:
  We study a model of Brownian particles which are pumped with energy by means
of a non-linear friction function, for which different types are discussed. A
suitable expression for a non-linear, velocity-dependent friction function is
derived by considering an internal energy depot of the Brownian particles. In
this case, the friction function describes the pumping of energy in the range
of small velocities, while in the range of large velocities the known limit of
dissipative friction is reached. In order to investigate the influence of
additional energy supply, we discuss the velocity distribution function for
different cases. Analytical solutions of the corresponding Fokker-Planck
equation in 2d are presented and compared with computer simulations. Different
to the case of passive Brownian motion, we find several new features of the
dynamics, such as the formation of limit cycles in the four-dimensional
phase-space, a large mean squared displacement which increases quadratically
with the energy supply, or non-equilibrium velocity distributions with
crater-like form. Further, we point to some generalizations and possible
applications of the model.


title:
On Dissipation Mechanism in the Intrinsic Josephson Effect in Layered
  Superconductors with d-wave Pairing

abstract:
  Conductivity mechanism in the regime of the intrinsic Josephson effect in
layered superconductors with singlet d-wave pairing is studied theoretically.
The cases of coherent and incoherent interlayer tunneling of electrons are
considered. The theory with coherent tunneling describes main qualitative
features of the effect observed in highly anisotropic high-T$_c$
superconductors at voltages smaller than the amplitude of the superconducting
gap, mechanism of the resistivity being related to excitations of the
quasiparticles via the d-wave gap. At voltages of the order of the gap
amplitude and larger, the I-V curves are better described by the incoherent
tunneling. Interaction of the Josephson junctions formed by the superconducting
layers due to charging effects is shown to be small.


title: Current carrying capacity of carbon nanotubes

abstract:
  The current carrying capacity of ballistic electrons in carbon nanotubes that
are coupled to ideal contacts is analyzed. At small applied voltages, where
electrons are injected only into crossing subbands, the differential
conductance is $4e^2/h$. At applied voltages larger than $\Delta E_{NC}/2e$
($\Delta E_{NC}$ is the energy level spacing of first non crossing subbands),
electrons are injected into non crossing subbands. The contribution of these
electrons to current is determined by the competing processes of Bragg
reflection and Zener type inter subband tunneling. In small diameter nanotubes,
Bragg reflection dominates, and the maximum differential conductance is
comparable to $4e^2/h$. Inter subband Zener tunneling can be non negligible as
the nanotube diameter increases because $\Delta E_{NC}$ is inversely
proportional to the diameter. As a result, with increasing nanotube diameter,
the differential conductance becomes larger than $4e^2/h$, though not
comparable to the large number of subbands into which electrons are injected
from the contacts. These results may be relevant to recent experiments in large
diameter multi-wall nanotubes that observed conductances larger than $4e^2/h$.


title:
Effects of microscopic strain distribution on Ga(1-x)In(x)As quantum
  wires grown by strain-induced lateral ordering

abstract:
  Band Structures and optical matrix elements of quantum wires(QWR's) made of
short-period superlattices(SPS) with strain-induced lateral ordering(SILO) are
investigated theoretically via an effective bond-orbital model(EBOM) combined
with a valence-force field(VFF) model. Valence-band anistropy, band mixing, and
effects due to local strain distribution at the atomistic level are all taken
into account. In particular, Ga(1-x)In(x)As QWR's grown by SILO process are
considered. A VFF model is used to find the equilibrium atomic positions in the
SILO QWR structure by minimizing the lattice energy. The strain tensor at each
atomic(In or GA) site is then obtained and included in the calculations of
electronic states and optical peroperties. It is found that different local
arrangement of atoms leads to very different strain distribution, which in term
alters the optical properties. In particular, we found that the optical
anisotropy can be reversed due to the change in shear strain caused by the
inter-change of atomic positions. Good agreement with the existing experimental
data on band gap and optical anisotropy can be obtained when a 2D alloy
structure with lateral composition modulation in the InAs/GaAs interface planes
of the SPS is used. Our studies revealed the possibility of "shear-strain
engineering" in SILO QWR light-emitting devices to achieve desired optical
anisotropy.


title:
Competition between ferromagnetic and charge-orbital ordered phases in
  Pr$_{1-x}$Ca$_{x}$MnO$_3$ for $x$=1/4, 3/8, and 1/2

abstract:
  Spin, charge, and orbital structures in models for doped manganites are
studied by a combination of analytic mean-field and numerical relaxation
techniques. At realistic values for the electron-phonon and antiferromagnetic
$t_{2g}$ spin couplings, a competition between a ferromagnetic (FM) phase and a
charge-orbital ordered (COO) insulating state is found for $x$=1/4, 3/8, and
1/2, as experimentally observed in Pr$_{1-x}$Ca$_{x}$MnO$_3$ for
$x$=0.3$\sim$0.5. The theoretical predictions for the spin-charge-orbital
ordering pattern are compared with experiments. The FM-COO energy difference is
surprisingly small for the densities studied, result compatible with the
presence of a robust colossal-magnetoresistive effect in
Pr$_{1-x}$Ca$_{x}$MnO$_3$ in a large density interval.


title: Stability of Bose-Einstein Condensates Confined in Traps

abstract:
  Bose-Einstein condensation has been realized in dilute atomic vapors. This
achievement has generated immerse interest in this field. Presented is a review
of recent theoretical research into the properties of trapped dilute-gas
Bose-Einstein condensates. Among them, stability of Bose-Einstein condensates
confined in traps is mainly discussed. Static properties of the ground state
are investigated by use of the variational method. The anlysis is extended to
the stability of two-component condensates. Time-development of the condensate
is well-described by the Gross-Pitaevskii equation which is known in nonlinear
physics as the nonlinear Schr\"odinger equation. For the case that the
inter-atomic potential is effectively attractive, a singularity of the solution
emerges in a finite time. This phenomenon which we call collapse explains the
upper bound for the number of atoms in such condensates under traps.


title:
Theory of Orbital Ordering, Fluctuation and Resonant X-ray Scattering in
  Manganites

abstract:
  A theory of resonant x-ray scattering in perovskite manganites is developed
by applying the group theory to the correlation functions of the pseudospin
operators for the orbital degree of freedom. It is shown that static and
dynamical informations of the orbital state are directly obtained from the
elastic, diffuse and inelastic scatterings due to the tensor character of the
scattering factor. We propose that the interaction and its anisotropy between
orbitals are directly identified by the intensity contour of the diffuse
scattering in the momentum space.


title: Nonequilibrium Quantum Evolution of Open Systems

abstract:
  We apply the Liouville-von Neumann (LvN) approach to open systems to describe
the nonequilibrium quantum evolution. The Liouville-von Neumann approach is a
unified method that can be applied to both time-independent (closed) and
time-dependent (open) systems and to both equilibrium and nonequilibrium
systems. We study the nonequilibrium quantum evolution of oscillator models for
open boson and fermion systems


title:
Algebraic Geometry Approach to the Bethe Equation for Hofstadter Type
  Models

abstract:
  We study the diagonalization problem of certain Hofstadter-type models
through the algebraic Bethe ansatz equation by the algebraic geometry method.
When the spectral variables lie on a rational curve, we obtain the complete and
explicit solutions for models with the rational magnetic flux, and discuss the
Bethe equation of their thermodynamic flux limit. The algebraic geometry
properties of the Bethe equation on high genus algebraic curves are
investigated in cooperation

categories: cond-mat hep-th math-ph math.AG math.MP nlin.SI


title:
Electron renormalization of sound interaction with two-level systems in
  superconducting metglasses

abstract:
  The crossing of temperature dependencies of sound velocity in the normal and
the superconducting state of metallic glasses indicates renormalization of the
intensity of sound interaction with two-level systems (TLS) caused by their
coupling with electrons. In this paper we have analyzed different approaches to
a quantitative description of renormalization using the results of
low-temperature ultrasonic investigation of ZrTiCuNiBe amorphous alloy. It is
shown that the adiabatic renormalization of the coherent tunneling amplitude
can explain only part of the whole effect observed in the experiment. There
exists another mechanism of renormalization affecting only nearly symmetric
TLS.


title:
Observation of Chaotic Dynamics in Dilute Sheared Aqueous Solutions of
  CTAT

abstract:
  The nonlinear flow behaviour of a viscoelastic gel formed due to entangled,
cylindrical micelles in aqueous solutions of the surfactant CTAT has been
studied. On subjecting the system to a step shear rate lying above a certain
value, the shear and normal stresses show interesting time dependent behaviour.
The analysis of the measured time series shows the existence of a finite
correlation dimension and a positive Lyapunov exponent, unambiguously implying
that the dynamics can be described by that of a dynamical system with a strange
attractor whose dimension increases with the increase in shear rate.


title:
Gap to Transition Temperature Ratio in Density Wave Ordering: a
  Dynamical Mean Field Study

abstract:
  We use the dynamical mean-field method to determine the origin of the large
ratio of the zero temperature gap to the transition temperature observed in
most charge density wave materials. The method is useful because it allows an
exact treatment of thermal fluctuations. We establish the relation of the
dynamical mean-field results to conventional diagrammatics and thereby
determine that in the physically relevant regime the origin of the large ratio
is a strong inelastic scattering.


title: Theory of Disordered Itinerant Ferromagnets I: Metallic Phase

abstract:
  A comprehensive theory for electronic transport in itinerant ferromagnets is
developed. We first show that the Q-field theory used previously to describe a
disordered Fermi liquid also has a saddle-point solution that describes a
ferromagnet in a disordered Stoner approximation. We calculate transport
coefficients and thermodynamic susceptibilities by expanding about the saddle
point to Gaussian order. At this level, the theory generalizes previous
RPA-type theories by including quenched disorder. We then study soft-mode
effects in the ferromagnetic state in a one-loop approximation. In
three-dimensions, we find that the spin waves induce a square-root frequency
dependence of the conductivity, but not of the density of states, that is
qualitatively the same as the usual weak-localization effect induced by the
diffusive soft modes. In contrast to the weak-localization anomaly, this effect
persists also at nonzero temperatures. In two-dimensions, however, the spin
waves do not lead to a logarithmic frequency dependence. This explains
experimental observations in thin ferromagnetic films, and it provides a basis
for the construction of a simple effective field theory for the transition from
a ferromagnetic metal to a ferromagnetic insulator.


title:
Theory of Disordered Itinerant Ferromagnets II: Metal-Insulator
  Transition

abstract:
  The theory for disordered itinerant ferromagnets developed in a previous
paper is used to construct a simple effective field theory that is capable of
describing the quantum phase transition from a ferromagnetic metal to a
ferromagnetic insulator. It is shown that this transition is in the same
universality class as the one from a paramagnetic metal to a paramagnetic
insulator in the presence of an external magnetic field, and that strong
corrections to scaling exist in this universality class. The experimental
consequences of these results are discussed.


title:
Wigner Crystal State for the Edge Electrons in the Quantum Hall Effect
  at Filling $\nu = 2$

abstract:
  The electronic excitations at the edges of a Hall bar not much wider than a
few magnetic lengths are studied theoretically at filling $\nu = 2$. Both
mean-field theory and Luttinger liquid theory techniques are employed for the
case of a null Zeeman energy splitting. The first calculation yields a stable
spin-density wave state along the bar, while the second one predicts dominant
Wigner-crystal correlations along the edges of the bar. We propose an
antiferromagnetic Wigner-crystal groundstate for the edge electrons that
reconciles the two results. A net Zeeman splitting is found to produce canting
of the antiferromagnetic order.


title: Systematic Study of Magnetic Interactions in Insulating Cuprates

abstract:
  The magnetic interactions in one-dimensional, two-dimensional (2D) and ladder
cuprates are evaluated systematically by using small Cu-O clusters. We find
that the superexchange interaction J between nearest neighbor Cu spins strongly
depends on Cu-O structure through the Madelung potential, and in 2D and ladder
cuprates there is a four-spin interaction Jcyc, with magnitude of 10% of J. We
show that Jcyc has a strong influence on the magnetic excitation in the
high-energy region of 2D cuprates.


title: Scenario of pseudogap in underdoped cuprate

abstract:
  So far, the theories of the cuprate pseudogap may be broadly divided into two
main schools of though. One is based upon the idea that view the pseudogap as
deriving from some of precursor superconductivity. Another assumes that
associate the pseudogap phenomena with magnetic pairing of some sort. Both the
scenario of superconducting fluctuation and the scenario of magnetic pairing of
some sort on the pseudogap in underdoped cuprate are based upon the idea that a
fluctuation of a certain type exists at temperatures higher than the usual
superconducting transition temperature and has an effect on the single particl
self-energy and just such a self-energy leads to the gap-like structure of the
spectral weight. In this paper we argue that although a fluctuation of a
certain type has an effect on the origin of the pseudogap, it is not the
crucial factor of the origin of the pseudogap in underdoped cuprate. We
analysis the scenario of the pseudogap in the underdoped cuprate based on the
model that can bring about the spin density wave (SDW) and find the new
dispersion characteristics of the high temperature cuprate superconductors
(excepting two different saddle points located at ($\pm\pi$, 0) and (0,
$\pm\pi$)) and suggest that the pseudogap formation might been due to the
unique interior of the underdoped cuprate.


title: Ground State Properties of an S=1/2 Distorted Diamond Chain

abstract:
  We investigate the ground state properties of an S=1/2 distorted diamond
chain described by the Hamiltonian ${\cal
H}=J_1\sum_\ell\bigl\{\bigl(\vecS_{3\ell-1}\cdot\vecS_{3\ell}
+\vecS_{3\ell}\cdot\vecS_{3\ell+1}\bigr)+J_2\vecS_{3\ell-2}\cdot\vecS_{3\ell-1}
+J_3\bigl(\vecS_{3\ell-2}\cdot\vecS_{3\ell}+\vecS_{3\ell}\cdot\vecS_{3\
ell+2}\bigr)-H S_{\ell}^z\bigr\}$ ($J_1,~J_2,~J_3\geq0$), which models well a
trimerized S=1/2 spin chain system
Cu$_3$Cl$_6$(H$_2$O)$_2$$\cdot$2H$_8$C$_4$SO$_2$. Using an exact
diagonalization method by means of the Lancz\"os technique, we determine the
ground state phase diagram in the H=0 case, composed of the dimerized, spin
fluid, and ferrimagnetic phases. Performing a degenerate perturbation
calculation, we analyze the phase boundary line between the latter two phases
in the $J_2,~J_3\llJ_1$ limit, the result of which is in good agreement with
the numerical result. We calculate, by the use of the density matrix
renormalization group method, the ground state magnetization curve for the case
(a) where $J_1=1.0$, $J_2=0.8$, and $J_3=0.5$, and the case (b) where
$J_1=1.0$, $J_2=0.8$, and $J_3=0.3$. We find that in the case (b) the
2/3-plateau appears in addition to the 1/3-plateau which also appears in the
case (a). The translational symmetry of the Hamiltonian $\cal H$ is
spontaneously broken in the 2/3-plateau state as well as in the dimerized
state.


title: Pathways in Two-State Protein Folding

abstract:
  The thermodynamics of proteins indicate that folding/unfolding takes place
either through stable intermediates or through a two-state process without
intermediates. The rather short folding times of the two-state process indicate
that folding is guided. We reconcile these two seemingly contradictory
observations quantitatively in a schematic model of protein folding. We propose
a new dynamical transition temperature which is lower than the thermodynamic
one, in qualitative agreement with in vivo measurement of protein stability
using E.coli. Finally we demonstrate that our framework is easily generalized
to encompass cold unfolding, and make predictions that relate the sharpness of
the cold and hot unfolding transitions.


title: Charge ordering and hopping in a triangular array of quantum dots

abstract:
  We demonstrate a mapping between the problem of charge ordering in a
triangular array of quantum dots and a frustrated Ising spin model. Charge
correlation in the low temperature state is characterized by an intrinsic
height field order parameter. Different ground states are possible in the
system, with a rich phase diagram. We show that electronic hopping transport is
sensitive to the properties of the ground state, and describe the singularities
of hopping conductivity at the freezing into an ordered state.


title: Irreversible phase transitions induced by an oscillatory input

abstract:
  A novel kind of irreversible phase transitions (IPT's) driven by an
oscillatory input parameter is studied by means of computer simulations. Second
order IPT's showing scale invariance in relevant dynamic critical properties
are found to belong to the universality class of directed percolation. In
contrast, the absence of universality is observed for first order IPT's.


title: Domain Structures of Smectic Films Formed by Bent-Shaped Molecules

abstract:
  We formulate a simple Landau type model describing macroscopic behaviour
recently discovered new smectic phases composed of achiral bent-shaped
molecules. Films of such smectics exhibit three types of ordering related to
dipole polarization, molecular tilt, and chirality. However due to specific
third order coupling of the order parameters these three types of
symmetry-breaking are not independent ones, and this fact leads to specific
domain structures really observed in experiments.


title: Analytical stripe phase solution for the Hubbard model

abstract:
  The self-consistent solution for the spin-charge solitonic superstructure in
quasi-one-dimensional electron system is obtained in the framework of the
Hubbard model as a function of a hole doping. Effects of interchain
interactions on the ground state are discussed. Results are used for the
interpretation of the observed stripe phases in doped antiferromagnets.


title:
A Consistent Picture for Resonance Neutron Peak and ARPES Spectra in
  High-Tc Superconductors

abstract:
  The spectra observed in ARPES measurements are examined together with the
resonance peak observed in neutron scatterings, based on the slave-boson
approach to $t-t^{\prime}-J$ model. We show that the peak/dip/hump features
arise from the scattering of electrons by collective spin excitations which, at
the same time, give rise to the neutron resonance mode. The doping dependences
and the dispersions of the peak/dip/hump positions are shown to be consistent
with experiments. Our results indicate that recently observed $\cos (6\theta)$
deviation from the pure d-wave also result from the renormalization by spin
fluctuations.


title: Fixed Number and Quantum Size Effects in Nanoscale Superconductors

abstract:
  In recent experiments on nanoscale Al particles, whose electron number was
fixed by charging effects, a ``negative gap'' was observed in particles with an
odd number of electrons. This observation has called into question the use of a
grand canonical ensemble in describing superconductivity in such ultrasmall
particles.
  We have studied the effects of fixed electron number and finite size in
nanoscale superconductors, by applying the canonical BCS theory for the
attractive Hubbard model. The ground state energy and the energy gap are
compared with the conventional and parity-projected grand canonical BCS
results, and in one dimension also with the exact solutions by the Bethe
ansatz. The crossover from the bulk to quantum limit is studied for various
regimes of electron density and coupling strength. The effects of boundary
conditions and different lattice structures are also examined.
  A ``negative gap'' for odd electron number emerges most naturally in the
canonical scheme. For even electron number, the gap is particularly large for
``magic numbers'' of electrons for a given system size or of atoms for a fixed
electron density. These features are in accordance with the exact solutions,
but are essentially missed in the grand canonical results.


title:
Photon-Assisted Quasiparticle Transport and Andreev Transport through an
  Interacting Quantum Dot

abstract:
  Resonant tunneling through a quantum dot coupled to superconducting
reservoirs in the presence of time-dependent external voltage has been studied.
A general formula of the current is derived based on the nonequilibrium Green's
function technique. Using this formula photon-assisted quasiparticle transport
has been investigated for the quantum dot connected to superconductors. In
addition, resonant Andreev transport through a strongly correlated quantum dot
connected to a normal metallic lead and a superconducting lead is studied.


title:
Finite temperature effects in Coulomb blockade quantum dots and
  signatures of spectral scrambling

abstract:
  The conductance in Coulomb blockade quantum dots exhibits sharp peaks whose
spacings fluctuate with the number of electrons. We derive the
temperature-dependence of these fluctuations in the statistical regime and
compare with recent experimental results. The scrambling due to Coulomb
interactions of the single-particle spectrum with the addition of an electron
to the dot is shown to affect the temperature-dependence of the peak spacing
fluctuations. Spectral scrambling also leads to saturation in the temperature
dependence of the peak-to-peak correlator, in agreement with recent
experimental results. The signatures of scrambling are derived using discrete
Gaussian processes, which generalize the Gaussian ensembles of random matrices
to systems that depend on a discrete parameter -- in this case, the number of
electrons in the dot.


title: Unconventional electronic Raman spectra of borocarbide superconductors

abstract:
  Borocarbide superconductors, which are thought to be conventional BCS-type
superconductors, are not so conventional in several electronic Raman
properties. Anisotropic gap-like features and finite scattering strength below
the gap were observed for the $R$Ni$_2$B$_2$C ($R$ = Lu, Y) systems in our
previous study. The effects of Co-doping on the 2$\Delta$ gap-like features and
the finite scattering strength below and above the gap are studied in $R$ = Lu
(B = B$^{11}$) system. In superconducting states, Co-doping strongly suppresses
the 2$\Delta$ peak in both B$_{2g}$ and B$_{1g}$ symmetries. Raman
cross-section calculation which includes inelastic scattering shows a
relatively good fit to the features above the 2$\Delta$ peak, while it does not
fully account for the features below the peak.


title:
Oxygen isotope effect on the in-plane penetration depth in underdoped
  La_{2-x}Sr_{x}CuO_{4} single crystals

abstract:
  We report measurements of the oxygen isotope effect (OIE) on the in-plane
penetration depth \lambda_{ab}(0) in underdoped La_{2-x}Sr_{x}CuO_{4} single
crystals. A highly sensitive magnetic torque sensor with a resolution of \Delta
\tau ~ 10^{-12} Nm was used for the magnetic measurements on microcrystals with
a mass of ~ 10 microg. The OIE on \lambda_{ab}^{-2}(0) is found to be -10(2)%
for x = 0.080 and -8(1)% for x = 0.086. It arises mainly from the oxygen mass
dependence of the in-plane effective mass m_{ab}*. The present results suggest
that lattice vibrations are important for the occurrence of high temperature
superconductivity.


title:
Order induced by dipolar interactions in a geometrically frustrated
  antiferromagnet

abstract:
  We study the classical Heisenberg model for spins on a pyrochlore lattice
interacting via long range dipole-dipole forces and nearest neighbor exchange.
Antiferromagnetic exchange alone is known not to induce ordering in this
system. We analyze low temperature order resulting from the combined
interactions, both by using a mean-field approach and by examining the energy
cost of fluctuations about an ordered state. We discuss behavior as a function
of the ratio of the dipolar and exchange interaction strengths and find two
types of ordered phase. We relate our results to the recent experimental work
and reproduce and extend the theoretical calculations on the pyrochlore
compound, Gd$_2$Ti$_2$O$_7$, by Raju \textit{et al.}, Phys. Rev. B {\bf 59},
14489 (1999).


title:
Spin correlations in nonlinear optical response: Light-induced Kondo
  effect

abstract:
  We study the role of spin correlations in nonlinear absorption due to optical
transitions from a deep impurity level to states above a Fermi sea. We
demonstrate that the Hubbard repulsion between two electrons occupying the
impurity state leads to a logarithmic divergence of the third-order nonlinear
optical susceptibility at the absorption threshold. This divergence is a
manifestation of the Kondo physics in the nonlinear optical response of Fermi
sea systems. Remarkably, the light-induced Kondo temperature, which governs the
shape of the Kondo-absorption spectrum, can be tuned by varying the intensity
and frequency of the pump optical field. We also show that, for off-resonant
pump excitation, the pump-probe spectrum exhibits a narrow peak below the
linear absorption onset.


title: Von Neumann Quantum Logic vs. Classical von Neumann Architecture?

abstract:
  The name of John von Neumann is common both in quantum mechanics and computer
science. Are they really two absolutely unconnected areas? Many works devoted
to quantum computations and communications are serious argument to suggest
about existence of such a relation, but it is impossible to touch the new and
active theme in a short review. In the paper are described the structures and
models of linear algebra and just due to their generality it is possible to use
universal description of very different areas as quantum mechanics and theory
of Bayesian image analysis, associative memory, neural networks, fuzzy logic.


title: Minimum Description Length and Compositionality

abstract:
  We present a non-vacuous definition of compositionality. It is based on the
idea of combining the minimum description length principle with the original
definition of compositionality (that is, that the meaning of the whole is a
function of the meaning of the parts).
  The new definition is intuitive and allows us to distinguish between
compositional and non-compositional semantics, and between idiomatic and
non-idiomatic expressions. It is not ad hoc, since it does not make any
references to non-intrinsic properties of meaning functions (like being a
polynomial). Moreover, it allows us to compare different meaning functions with
respect to how compositional they are. It bridges linguistic and corpus-based,
statistical approaches to natural language understanding.


title: Why C++ is not very fit for GUI programming

abstract:
  With no intent of starting a holy war, this paper lists several annoying C++
birthmarks that the author has come across developing GUI class libraries.
C++'s view of classes, instances and hierarchies appears tantalizingly close to
GUI concepts of controls, widgets, window classes and subwindows. OO models of
C++ and of a window system are however different. C++ was designed to be a
"static" language with a lexical name scoping, static type checking and
hierarchies defined at compile time. Screen objects on the other hand are
inherently dynamic; they usually live well beyond the procedure/block that
created them; the hierarchy of widgets is defined to a large extent by layout,
visibility and event flow. Many GUI fundamentals such as dynamic and geometric
hierarchies of windows and controls, broadcasting and percolation of events are
not supported directly by C++ syntax or execution semantics (or supported as
"exceptions" -- pun intended). Therefore these features have to be emulated in
C++ GUI code. This leads to duplication of a graphical toolkit or a window
manager functionality, code bloat, engaging in unsafe practices and forgoing of
many strong C++ features (like scoping rules and compile-time type checking).
This paper enumerates a few major C++/GUI sores and illustrates them on simple
examples.


title:
Multiplicative Algorithm for Orthgonal Groups and Independent Component
  Analysis

abstract:
  The multiplicative Newton-like method developed by the author et al. is
extended to the situation where the dynamics is restricted to the orthogonal
group. A general framework is constructed without specifying the cost function.
Though the restriction to the orthogonal groups makes the problem somewhat
complicated, an explicit expression for the amount of individual jumps is
obtained. This algorithm is exactly second-order-convergent. The global
instability inherent in the Newton method is remedied by a
Levenberg-Marquardt-type variation. The method thus constructed can readily be
applied to the independent component analysis. Its remarkable performance is
illustrated by a numerical simulation.


title: Effect of different packet sizes on RED performance

abstract:
  We consider the adaptation of random early detection (RED) as an active queue
management algorithm for TCP traffic in Internet gateways where different
maximum transfer units (MTUs) are used. We studied the two existing RED
variants and point out a weakness in both. The first variant where the drop
probability is independent from the packet size discriminates connections with
smaller MTUs. The second variant results in a very high Packet Loss Ratio
(PLR), and as a consequence low goodput, for connections with higher MTUs. We
show that fairness in terms of loss and goodput can be supplied through an
appropriate setting of the RED algorithm.


title: Compositionality, Synonymy, and the Systematic Representation of Meaning

abstract:
  In a recent issue of Linguistics and Philosophy Kasmi and Pelletier (1998)
(K&P), and Westerstahl (1998) criticize Zadrozny's (1994) argument that any
semantics can be represented compositionally. The argument is based upon
Zadrozny's theorem that every meaning function m can be encoded by a function
\mu such that (i) for any expression E of a specified language L, m(E) can be
recovered from \mu(E), and (ii) \mu is a homomorphism from the syntactic
structures of L to interpretations of L.
  In both cases, the primary motivation for the objections brought against
Zadrozny's argument is the view that his encoding of the original meaning
function does not properly reflect the synonymy relations posited for the
language.
  In this paper, we argue that these technical criticisms do not go through. In
particular, we prove that \mu properly encodes synonymy relations, i.e. if two
expressions are synonymous, then their compositional meanings are identical.
This corrects some misconceptions about the function \mu, e.g. Janssen (1997).
  We suggest that the reason that semanticists have been anxious to preserve
compositionality as a significant constraint on semantic theory is that it has
been mistakenly regarded as a condition that must be satisfied by any theory
that sustains a systematic connection between the meaning of an expression and
the meanings of its parts. Recent developments in formal and computational
semantics show that systematic theories of meanings need not be compositional.


title: RED behavior with different packet sizes

abstract:
  We consider the adaptation of random early detection (RED) as a buffer
management algorithm for TCP traffic in Internet gateways where different
maximum transfer units (MTUs) are used. We studied the two RED variants
described in [4] and point out a weakness in both. The first variant where drop
probability is independent from the packet size discriminates connections with
smaller MTUs. The second variant results in a very high packet loss ratio
(PLR), and as a consequence low goodput, for connections with higher MTUs. We
show that fairness in terms of loss and goodput can be supplied through an
appropriate setting of the RED algorithm.


title:
Predicting the expected behavior of agents that learn about agents: the
  CLRI framework

abstract:
  We describe a framework and equations used to model and predict the behavior
of multi-agent systems (MASs) with learning agents. A difference equation is
used for calculating the progression of an agent's error in its decision
function, thereby telling us how the agent is expected to fare in the MAS. The
equation relies on parameters which capture the agent's learning abilities,
such as its change rate, learning rate and retention rate, as well as relevant
aspects of the MAS such as the impact that agents have on each other. We
validate the framework with experimental results using reinforcement learning
agents in a market system, as well as with other experimental results gathered
from the AI literature. Finally, we use PAC-theory to show how to calculate
bounds on the values of the learning parameters.


title: Fractal Symbolic Analysis

abstract:
  Restructuring compilers use dependence analysis to prove that the meaning of
a program is not changed by a transformation. A well-known limitation of
dependence analysis is that it examines only the memory locations read and
written by a statement, and does not assume any particular interpretation for
the operations in that statement. Exploiting the semantics of these operations
enables a wider set of transformations to be used, and is critical for
optimizing important codes such as LU factorization with pivoting.
  Symbolic execution of programs enables the exploitation of such semantic
properties, but it is intractable for all but the simplest programs. In this
paper, we propose a new form of symbolic analysis for use in restructuring
compilers. Fractal symbolic analysis compares a program and its transformed
version by repeatedly simplifying these programs until symbolic analysis
becomes tractable, ensuring that equality of simplified programs is sufficient
to guarantee equality of the original programs. We present a prototype
implementation of fractal symbolic analysis, and show how it can be used to
optimize the cache performance of LU factorization with pivoting.


title: A Real World Implementation of Answer Extraction

abstract:
  In this paper we describe ExtrAns, an answer extraction system. Answer
extraction (AE) aims at retrieving those exact passages of a document that
directly answer a given user question. AE is more ambitious than information
retrieval and information extraction in that the retrieval results are phrases,
not entire documents, and in that the queries may be arbitrarily specific. It
is less ambitious than full-fledged question answering in that the answers are
not generated from a knowledge base but looked up in the text of documents. The
current version of ExtrAns is able to parse unedited Unix "man pages", and
derive the logical form of their sentences. User queries are also translated
into logical forms. A theorem prover then retrieves the relevant phrases, which
are presented through selective highlighting in their context.


title:
Agents of Choice: Tools that Facilitate Notice and Choice about Web Site
  Data Practices

abstract:
  A variety of tools have been introduced recently that are designed to help
people protect their privacy on the Internet. These tools perform many
different functions in-cluding encrypting and/or anonymizing communications,
preventing the use of persistent identifiers such as cookies, automatically
fetching and analyzing web site privacy policies, and displaying
privacy-related information to users. This paper discusses the set of privacy
tools that aim specifically at facilitating notice and choice about Web site
data practices. While these tools may also have components that perform other
functions such as encryption, or they may be able to work in conjunction with
other privacy tools, the primary pur-pose of these tools is to help make users
aware of web site privacy practices and to make it easier for users to make
informed choices about when to provide data to web sites. Examples of such
tools include the Platform for Privacy Preferences (P3P) and various
infomediary services.


title: Measures of Distributional Similarity

abstract:
  We study distributional similarity measures for the purpose of improving
probability estimation for unseen cooccurrences. Our contributions are
three-fold: an empirical comparison of a broad range of measures; a
classification of similarity functions based on the information that they
incorporate; and the introduction of a novel function that is superior at
evaluating potential proxy distributions.


title: Query Complexity: Worst-Case Quantum Versus Average-Case Classical

abstract:
  In this note we investigate the relationship between worst-case quantum query
complexity and average-case classical query complexity. Specifically, we show
that if a quantum computer can evaluate a total Boolean function f with bounded
error using T queries in the worst case, then a deterministic classical
computer can evaluate f using O(T^5) queries in the average case, under a
uniform distribution of inputs. If f is monotone, we show furthermore that only
O(T^3) queries are needed. Previously, Beals et al. (1998) showed that if a
quantum computer can evaluate f with bounded error using T queries in the worst
case, then a deterministic classical computer can evaluate f using O(T^6)
queries in the worst case, or O(T^4) if f is monotone. The optimal bound is
conjectured to be O(T^2), but improving on O(T^6) remains an open problem.
Relating worst-case quantum complexity to average-case classical complexity may
suggest new ways to reduce the polynomial gap in the ordinary worst-case versus
worst-case setting.


title: Nondeterministic Quantum Query and Quantum Communication Complexities

abstract:
  We study nondeterministic quantum algorithms for Boolean functions f. Such
algorithms have positive acceptance probability on input x iff f(x)=1. In the
setting of query complexity, we show that the nondeterministic quantum
complexity of a Boolean function is equal to its ``nondeterministic
polynomial'' degree. We also prove a quantum-vs-classical gap of 1 vs n for
nondeterministic query complexity for a total function. In the setting of
communication complexity, we show that the nondeterministic quantum complexity
of a two-party function is equal to the logarithm of the rank of a
nondeterministic version of the communication matrix. This implies that the
quantum communication complexities of the equality and disjointness functions
are n+1 if we do not allow any error probability. We also exhibit a total
function in which the nondeterministic quantum communication complexity is
exponentially smaller than its classical counterpart.